U.S. patent application number 10/332511 was filed with the patent office on 2004-11-25 for alumina-silica-based fiber, ceramic fiber, ceramic fiber complex, retaining seal material, production method thereof, and alumina fiber complex production method.
Invention is credited to Doushita, Masakage, Takahashi, Hidetomo, Tanahashi, Kazutomo.
Application Number | 20040234428 10/332511 |
Document ID | / |
Family ID | 19001526 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040234428 |
Kind Code |
A1 |
Tanahashi, Kazutomo ; et
al. |
November 25, 2004 |
Alumina-silica-based fiber, ceramic fiber, ceramic fiber complex,
retaining seal material, production method thereof, and alumina
fiber complex production method
Abstract
An object of the present invention is to provide a manufacturing
method by which alumina-silica based fibers excellent in mechanical
strength can be readily and securely obtained, and the present
invention obtains precursor fibers as a material by using an
alumina-silica based fiber spinning stock solution for use in an
inorganic salt method. Next, the precursor fibers are heated under
an environment which makes it difficult to carry out an oxidizing
reaction on the carbon component contained in the precursor fibers.
Thus, the precursor fibers are sintered to obtain alumina-silica
based fibers.
Inventors: |
Tanahashi, Kazutomo;
(Ogaki-shi, JP) ; Doushita, Masakage; (Ogaki-shi,
JP) ; Takahashi, Hidetomo; (Ogaki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
19001526 |
Appl. No.: |
10/332511 |
Filed: |
January 26, 2004 |
PCT Filed: |
May 27, 2002 |
PCT NO: |
PCT/JP02/05124 |
Current U.S.
Class: |
422/180 ;
428/397; 502/439; 502/527.24 |
Current CPC
Class: |
F01N 3/2864 20130101;
F01N 3/2853 20130101; D01D 5/253 20130101; B82Y 30/00 20130101;
D01F 9/10 20130101; F01N 2350/04 20130101; C04B 2235/3418 20130101;
C04B 2235/80 20130101; F01N 2330/14 20130101; C04B 2235/6567
20130101; C04B 2235/96 20130101; C04B 2235/3218 20130101; C04B
2235/658 20130101; Y10T 428/2973 20150115; C04B 35/62245 20130101;
D01D 5/04 20130101; C04B 35/80 20130101; C04B 2235/5284 20130101;
F01N 2330/06 20130101; C04B 35/634 20130101; C04B 2235/422
20130101; C04B 35/117 20130101; C04B 2235/5264 20130101; C04B
2235/526 20130101; C04B 2235/656 20130101; C04B 2235/9661
20130101 |
Class at
Publication: |
422/180 ;
428/397; 502/439; 502/527.24 |
International
Class: |
F01N 003/28 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2001 |
JP |
2001-157701 |
Claims
1. An alumina-silica based fiber which presents a blackish
color.
2. An alumina-silica based fiber which presents a blackish color
derived from a carbon component.
3. An alumina-silica based fiber which has a residual carbon
content of 1% by weight or more, presents a blackish color derived
from its residual carbon component, and has a fiber tensile
strength of 1.2 GPa or more, a fiber bending strength of 1.0 GPa or
more and a fracture toughness of 0.8 MN/m.sup.3/2 or more.
4. A manufacturing method of alumina-silica based fibers,
comprising: a spinning step of obtaining precursor fibers by using
a spinning stock solution of the alumina-silica based fibers for an
inorganic salt method as a material; and a firing step of heating
said precursor fibers under an environment which makes it difficult
to carry out an oxidizing reaction on the carbon component
contained in said precursor fibers, thereby sintering said
precursor fibers.
5. The manufacturing method of alumina-silica based fibers
according to claim 4, wherein said precursor fiber is heated at a
temperature of 1000 to 1300.degree. C. under a nitrogen
atmosphere.
6. The manufacturing method of alumina-silica based fibers
according to claim 4 or 5, wherein the carbon component contained
in said precursor fiber is derived from an organic polymer added to
said spinning stock solution of the alumina-silica based fiber as a
fiber-drawing property applying agent.
7. A holding seal material which has the alumina-silica based
fibers, according to any of claims 1 to 3, aggregated into a mat
shape as a constituent element, and is placed in a gap between a
ceramic body capable of allowing a fluid to flow through the inside
thereof and a metal shell covering the outer circumference of the
ceramic body.
8. The holding seal material according to claim 7, wherein said
ceramic body includes a catalyst carrier, and said holding seal
material is used as a holding seal material for a catalyst
converter.
9. A holding seal material which has a fiber aggregation of
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to flow through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein a crystallization rate in a portion on a first face side is
different from that in a portion on a second face side.
10. A holding seal material which has a fiber aggregation of
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to flow through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein a crystallization rate is gradually increased from a first
face side toward a second face side.
11. The holding seal material according to claim 10, comprising a
sheet of fiber aggregation, wherein the crystallization rate of the
fiber aggregation is gradually increased from the first face side
toward the second face side.
12. The holding seal material according to any of claims 9 to 11,
wherein the difference between the crystallization rates in the
portion on the first face side and that in the portion on the
second face side is 3% by weight or more.
13. The holding seal material according to any of claims 9 to 11,
wherein the crystallization rate in the portion on the first face
side is 0 to 1% by weight, and the crystallization rate in the
portion on the second face side is 1 to 10% by weight.
14. The holding seal material according to any of claims 9 to 13,
wherein said ceramic body includes a catalyst carrier, and said
holding seal material is used as a holding seal material for a
catalyst converter.
15. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein a crystallization rate
is made different depending on portions.
16. The holding seal material according to claim 15, wherein said
ceramic body includes a catalyst carrier, and said holding seal
material is used as a holding seal material for a catalyst
converter.
17. A manufacturing method of the holding seal material according
to any of claims 9 to 14, comprising: a spinning step of obtaining
precursor fibers by using a spinning stock solution of ceramic
fibers as material; a laminating step of laminating said precursor
fibers to form a mat-shaped fiber aggregation; and a firing step of
sintering said fiber aggregation so as to provide a difference
between a firing temperature on a first face side and that on a
second face side.
18. The manufacturing method of a holding seal material according
to claim 17, wherein the difference between said firing
temperatures is set to 100.degree. C. or more.
19. The manufacturing method of a holding seal material according
to claim 17, wherein the firing temperature on the first face side
is set to 800 to 1100.degree. C., and the firing temperature on the
second face side is set to 1100 to 1400.degree. C.
20. A catalyst converter comprising: a catalyst carrier; a
cylinder-shaped metal shell covering the outer circumference of the
catalyst carrier; and a holding seal material placed in a gap
between these elements, and having alumina-silica based fibers
aggregated into a mat shape as a constituent element, wherein said
holding seal material is placed in said gap in such a state that a
first face side having a relatively small crystallization rate is
made in contact with said metal shell, and a second face side
having a relatively large crystallization rate is made in contact
with said catalyst carrier.
21. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein said alumina-silica
based fiber has a non-circular shape in its cross-section.
22. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein said alumina-silica
based fiber has a deformed shape in its cross-section.
23. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein said alumina-silica
based fiber has a flat shape in its cross-section.
24. The holding seal material according to any of claims 21 to 23,
wherein said alumina-silica based fiber has a substantially
elliptical or cocoon shape in its cross-section.
25. The holding seal material according to claim 21 or 22, wherein
said alumina-silica based fiber is a hollow fiber.
26. The holding seal material according to any of claims 21 to 25,
wherein said ceramic body includes a catalyst carrier, and said
holding seal material is used as a holding seal material for a
catalyst converter.
27. A manufacturing method of alumina-silica based fibers used in
the holding seal material according to any of claims 21 to 26,
comprising: a spinning step of obtaining precursor fibers by
discharging a spinning stock solution containing a solution of
aluminum salt water, silica sol and an organic polymer through a
nozzle; and a firing step of heating and sintering said precursor
fibers, wherein dried hot air is blown to said precursor fibers
immediately after having been discharged from the discharging
section of said nozzle having a non-circular shape in its
cross-section.
28. The manufacturing method of alumina-silica based fibers
according to claim 27, wherein said dried hot air is blown in a
forward direction with respect to the discharging direction of said
precursor fiber.
29. The manufacturing method of alumina-silica based fibers
according to claim 27 or 28, wherein a water-soluble plasticizer is
preliminarily added to said spinning stock solution.
30. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein the dispersion of fiber
diameter in said alumina-silica based fiber is within .+-.3
.mu.m.
31. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein the dispersion of fiber
length in said alumina-silica based fiber is within .+-.4 mm.
32. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein the dispersion of fiber
diameter in said alumina-silica based fiber is within .+-.3 .mu.m,
and the dispersion of fiber length in said alumina-silica based
fiber is within .+-.4 mm.
33. The holding seal material according to any of claims 30 to 32,
wherein the content of shots is 3% by weight or less.
34. A holding seal material which has alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein the average fiber
diameter of said alumina-silica based fiber is 5 to 15 .mu.m, the
dispersion of fiber diameter therein is within .+-.3 .mu.m, the
average fiber length thereof is 5 to 20 mm, the dispersion of fiber
length therein is within .+-.4 mm, and no shots are contained
therein.
35. The holding seal material according to any of claims 30 to 34,
wherein said ceramic body includes a catalyst carrier, and said
holding seal material is used as a holding seal material for a
catalyst converter.
36. A manufacturing method of the holding seal material according
to any of claims 30 to 35, comprising: a spinning step of obtaining
long precursor fibers by continuously discharging a spinning stock
solution containing a solution of aluminum salt water, silica sol
and an organic polymer through a nozzle; a cutting step of chopping
said long fibers into a predetermined length to obtain short
fibers; a molding step of allowing said short fibers to aggregate
three-dimensionally, thereby forming into a mat-shaped fiber
aggregation; and a firing step of heating and sintering said
mat-shaped fiber aggregation.
37. A holding seal material which has ceramic fibers aggregated
into a mat shape as a constituent element, and is placed in a gap
between a ceramic body capable of allowing a fluid to flow through
the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein said ceramic fibers are
partially bonded to each other by a ceramic adhesive.
38. The holding seal material according to claim 37, wherein said
ceramic adhesive comprises a substance which constitutes said
ceramic fiber.
39. The holding seal material according to claim 37, wherein said
ceramic fibers are alumina-silica based fibers, and said ceramic
adhesive has alumina as a main component.
40. The holding seal material according to any of claims 37 to 39,
wherein 1 to 8% by weight of said ceramic adhesive is contained
therein.
41. The holding seal material according to any of claims 37 to 40,
wherein said ceramic body includes a catalyst carrier, and said
holding seal material is used as a holding seal material for a
catalyst converter.
42. A manufacturing method of the holding seal material according
to any of claims 37 to 41, comprising: a spinning step of obtaining
precursor fibers by using a spinning stock solution of ceramic
fibers as a material; a firing step of heating and sintering said
precursor fibers; a molding step of allowing thus obtained ceramic
fibers to aggregate three-dimensionally, thereby forming into a
mat-shaped aggregation; and bonding step of bonding the ceramic
fibers forming said aggregation by using a ceramic adhesive.
43. The manufacturing method of a holding seal material according
to claim 42, wherein in said bonding step, after the material
solution of said ceramic adhesive has been supplied between the
ceramic fibers forming said aggregation, said aggregation is heated
to sinter specific components in said material solution so as to be
formed into ceramics.
44. The manufacturing method of a holding seal material according
to claim 42, wherein in said bonding step, after said aggregation
has been impregnated with a water-soluble metal solution, which is
said material solution, having a low viscosity, said aggregation is
dried and heated so that the metal component in said solution is
sintered to be formed into ceramics.
45. The manufacturing method of a holding seal material according
to claim 44, wherein said water-soluble metal solution is supplied
by an amount of 1 to 10% by weight of said aggregation.
46. The manufacturing method of a holding seal material according
to any of claims 43 to 45, wherein said spinning stock solution of
the ceramic fibers is a spinning stock solution of alumina-silica
based fibers prepared by using an inorganic salt method, and said
water-soluble metal solution is a water solution containing
aluminum ions.
47. A manufacturing method of the holding seal material according
to any of claims 37 to 41, comprising: a spinning step of obtaining
precursor fibers by using a spinning stock solution of ceramic
fibers as a material; a molding step of allowing said precusor
fibers to aggregate three-dimensionally, thereby forming into a
mat-shaped aggregation; a liquid substance supplying step of
allowing a liquid substance capable of being a ceramic adhesive
later to adhere to portions at which said precursor fibers forming
said aggregation are overlapped adjacent to each other; and a
firing step of heating said aggregation to sinter said precursor
fibers and said liquid substance.
48. The manufacturing method of a holding seal material according
to claim 47, wherein in said liquid substance supplying step, the
aggregation including said precursor fibers of alumina-silica based
fibers is put in a highly moistened environment with high
moisture.
49. The manufacturing method of a holding seal material according
to claim 47, wherein in said liquid substance supplying step, a
non-aqueous liquid substance containing an inorganic element
contained in said alumina-silica based fiber is atomized and
supplied to the aggregation including the precursor fibers of the
alumina-silica based fibers.
50. The manufacturing method of a holding seal material according
to any of claims 47 to 49, wherein a cutting step of chopping the
long fibers of said precursor fibers into a predetermined length to
obtain short fibers is carried out between said spinning step and
said molding step.
51. A ceramic fiber aggregation wherein three-dimensionally
aggregated ceramic fibers are partially bonded to each other by a
ceramic adhesive.
52. A ceramic fiber aggregation comprising ceramic fibers having a
branched structure.
53. A ceramic fiber having a branched structure.
54. A manufacturing method of an alumina fiber aggregation,
comprising: a spinning step of obtaining a continuous long-fiber
precursor by using an alumina fiber stock solution used in an
inorganic salt method as a material; a chopping step of cutting
said continuous long-fiber precursor into short-fiber precursors; a
mat preparing step of preparing a mat-shaped short fiber precursor
by using thus obtained said short-fiber precursor; and a firing
step of firing said mat-shaped short fiber precursor to manufacture
an alumina fiber aggregation.
Description
TECHNICAL FIELD
[0001] The present invention relates to an alumina-silica based
fiber, a ceramic fiber, a ceramic fiber aggregation, a holding seal
material and manufacturing methods thereof, as well as a
manufacturing method of alumina fiber aggregation.
BACKGROUND ART
[0002] Recently, there has been a problem that particulates
contained in exhausted gas discharged from combustion engines of
vehicles such as buses, trucks, construction machines and the like
affect the environment and the human body.
[0003] There have been various ceramic filters which allow the
exhausted gas to pass through porous ceramic, thereby capturing the
particulates in the exhausted gas and purifying the exhausted
gas.
[0004] As one example of such ceramic filters, there is used a
honeycomb filter 30 in which a plurality of porous ceramic members
40 shown in FIG. 16 are bound by means of an adhesive layer 34 to
constitute a column-shaped ceramic block 35, and a seal material
layer 33 is formed around the column-shaped ceramic block 35.
Moreover, as shown in FIG. 17, this porous ceramic member 40 is
provided with a number of through holes 42 aligned in the
longitudinal direction so that each partition wall 43 separating
the through holes 42 from each other functions as a filter.
[0005] In other words, as shown in FIG. 17(b) , with respect to
each of the through holes 42 formed in the porous ceramic member
40, either of the ends on the inlet side or outlet side of the
exhaust gas is sealed by a filling material 41 so that the exhaust
gas, flown into a through hole 42, is always allowed to flow out
through another through hole 42 after having passed through this
partition wall 43 that separates through holes 42; thus, when the
exhaust gas passes through the partition wall 43, particulates
thereof are captured by the partition wall 43 so that the exhaust
gas is purified.
[0006] Moreover, a seal material layer 33 is formed on the outer
circumferential portion so that one portion thereof is formed to
prevent the exhaust gas from leaking from the through holes 42
exposed to the outside of the porous ceramic member 40.
[0007] With respect to a non-oxide-based ceramic material
constituting the porous ceramic member 40 of this type, silicon
carbide, which is excellent in heat resistance, and easily
subjected to a recovering process and the like, is used in various
vehicles such as large-size vehicles and vehicles having diesel
engines.
[0008] Further, in addition to the above-mentioned particulates,
the above-mentioned exhaust gas contains CO, NOx, HC, etc., and in
order to remove these substances from the exhaust gas, an exhaust
gas purifying catalyst converter, which has virtually the same
shape as the above-mentioned honey comb filter 30 with a catalyst
such as platinum deposited therein, has been proposed.
[0009] Moreover, in recent years, studies have been conducted on
the next generation clean power sources which do not use petroleum
as the power source, and among these, for example, fuel cells have
been considered to be a very prospective power source.
[0010] The fuel cells, which utilize electricity that is obtained
when hydrogen and oxygen react with each other to form water as a
power source, have an arrangement in which oxygen is directly taken
from the air while methanol, gasoline and the like are modified and
utilized to provide hydrogen, and upon modifying these methanol,
gasoline and the like, an exhaust gas purifying catalyst converter,
which has virtually the same shape as the above-mentioned honeycomb
filter 30 with a copper-based catalyst deposited therein, has been
utilized.
[0011] Generally, these honeycomb filter 30, an exhaust gas
purifying catalyst converter, a catalyst converter for a fuel cell
and the like are placed inside a cylinder-shaped metal shell, and
used, and in this case, there is a gap between the honeycomb filter
30, the exhaust gas purifying catalyst-converter or the catalyst
converter for a fuel cell and the above-mentioned metal shell, and
in order to fill the gap, a holding seal materials 50 shown in FIG.
18 is interpolated therein.
[0012] As shown in FIG. 18, the holding seal material 50 is
provided with a convex fitting section 52 placed on one of the
shorter sides of a base material portion 51 having a virtually
rectangular shape, and a concave fitting section 53 placed on the
other shorter side.
[0013] The convex fitting section 52 and the concave fitting
section 53 are just fitted to each other when the holding seal
material 50 is wound around the outer circumference of the
honeycomb filter 30; thus, it is possible to prevent the holding
seal material 50 from deviation.
[0014] Conventionally, the holding seal material of this type has
been formed through the following first through fourth methods.
[0015] In other words, in the first method for manufacturing the
above-mentioned holding seal material, first, a starting material
containing an alumina source and a silica source is heated to
approximately 2000.degree. C., and subjected to a spinning process
in a fused state, and then quickly cooled down to obtain ceramic
fibers that has virtually the same alumina content and silica
content. Then, a material is produced by aggregating the
above-mentioned ceramic fibers into a mat shape. This material is
stamped out by using a metal mold to manufacture holding seal
materials.
[0016] In the second method for manufacturing the above-mentioned
holding seal material, first, a spinning stock solution containing
an alumina source and a silica source is prepared, and by
discharging this solution through a nozzle, a precursor fiber
having a true round shape in its cross-section is continuously
obtained. Next, the long fiber of the precursor fiber obtained
through the above-mentioned spinning process is sintered, and the
resulting alumina-silica based fiber is then chopped into short
fibers having a predetermined length. Next, the short fibers thus
obtained are put into a mold to form a fiber aggregation having a
mat shape. This fiber aggregation is stamped out by using a metal
mold to manufacture holding seal materials.
[0017] Moreover, in the third method for manufacturing the
above-mentioned holding seal material, a spinning stock solution,
preliminarily prepared for use in an inorganic salt method, is
supplied to a centrifugal nozzle, and the spinning stock solution
is blown out of the nozzle by a centrifugal force exerted on the
centrifugal nozzle to form precursor fibers. Next, the resulting
precursor fibers are aggregated into a mat shape, and this
mat-shaped aggregation is stamped out by using a metal mold to
manufacture holding seal materials.
[0018] In the fourth method for manufacturing the above-mentioned
holding seal material, first, an alumina fiber stock solution
(alumina-silica fiber stock solution) is subjected to a spinning
process to form a continuous long-fiber precursor, and an alumina
long fiber is manufactured by sintering this continuous long-fiber
precursor.
[0019] Next, after this alumina long fiber has been cut into
alumina short fibers, these alumina short fibers are collected,
untied, and laminated, and this is then pressed to form an alumina
fiber aggregation having a mat shape.
[0020] Then, this mat-shaped aggregation is stamped out into a
predetermined shape to manufacture holding seal materials.
[0021] The holding seal material, thus manufactured, is wound on
the outer circumferential face of the above-mentioned honeycomb
filter, the exhaust gas purifying catalyst converter or the
catalyst converter for a fuel cell, and this is then housed in a
metal shell; and in such a housed state, since the holding seal
material is compressed in the thickness direction so that a
repulsive force (face pressure) resisting against the compressing
force is exerted in the holding seal material. The repulsive force
thus exerted makes it possible to hold elements, such as the
honeycomb filter, the exhaust gas purifying catalyst converter and
the catalyst converter for a fuel cell, inside the above-mentioned
metal shell.
[0022] In the case where the honeycomb filter, the exhaust gas
purifying catalyst converter, the catalyst converter for a fuel
cell, etc. are housed inside the above-mentioned metal shell
through a press-fitting method, a metal cylinder member having an
O-letter shape in its cross-section is used, and when these are
housed inside thereof by using a canning method, a clam shell,
which is formed by dividing a metal cylinder member having an
O-letter shape in its cross-section into a plurality of pieces
along the axis-line direction thereof, is used. Moreover, in
addition to this method, a metal shell, which uses a tightening
method in which welding, bonding and bolt-fastening processes are
carried out by using a metal cylinder-shaped member having a
C-letter shape or a U-letter shape in its cross-section, is also
utilized.
[0023] However, with respect to the holding seal material
manufactured through the first method, since this member is
subjected to vibration and high temperatures of such as exhaust
gas, when it is used, the face pressure is gradually lowered as
time elapses, resulting in degradation in the holding property and
sealing property of the catalyst carrier in a comparatively early
period of time.
[0024] Moreover, with respect to the holding seal material
manufactured by the first method, properties for securely holding
the honeycomb filter, the exhaust gas purifying catalyst converter,
the catalyst converter for a fuel cell, etc. for a long period of
time are required; however, the conventional ceramic fibers,
manufactured through the above-mentioned fusing method, has a very
low level of crystallization rate (mullite rate), that is, less
than 1% by weight, in addition to its high level of amorphous
components. For this reason, when the resulting fibers are
subjected to high temperatures for a long time, thermal shrinkage
occurs as crystallization advances, resulting in brittleness in the
fibers. Therefore, the holding seal material, manufactured by using
these fibers, fails to provide a sufficiently high initial face
pressure, and causes high degradation with time in the face
pressure during the application.
[0025] In order to solve these problems, a method for increasing
the crystallization rate of the ceramic fibers to approximately 10%
by weight has been proposed; however, in this case, hardening of
the fibers causes degradation in the elasticity and flexibility of
the holding seal material and the subsequent degradation in the
sealing property.
[0026] Moreover, with respect to the holding seal material
manufactured by the second method, properties for securely holding
the honeycomb filter, the exhaust gas purifying catalyst converter,
the catalyst converter for a fuel cell, etc. for a long period of
time are required; however, the alumina-silica based fiber having a
round shape in its cross-section, manufactured in the second
method, tends to lose its flexibility to become brittle, and is
easily broken, when exposed to high temperatures for a long time.
Therefore, the holding seal material manufactured by these fibers
is susceptible to degradation with time in the face pressure.
[0027] Furthermore, with respect to the holding seal material
manufactured by the third method, when the formation of ceramic
fibers is carried out by using the blowing method, the basis weight
(weight per unit area) of the mat-shaped aggregation comes to have
a higher positional dependence.
[0028] In other words, the degree of aggregation in fibers is not
constant with the result that when the position at which the
mat-shaped aggregation is stamped out differs, the face pressure
value of the resulting holding seal material tends to differ.
Consequently, it has not been possible to obtain a holding seal
material having excellent stability in quality.
[0029] Here, in the alumina fiber aggregation formed by the
above-mentioned fourth method, alumina short fibers, used for the
alumina fiber aggregation, fail to have sufficiently high
mechanical strength, and have comparatively great dispersions, with
the result that the initial face pressure of the alumina fiber
aggregation becomes insufficient, and the degradation with time in
the face pressure of the above-mentioned alumina fiber aggregation
is comparatively large; therefore, there have been demands for
improvements.
[0030] Here, "the initial face pressure" refers to a face pressure
of an alumina fiber aggregation in a state where neither load nor
heat is applied thereto.
[0031] The present invention has been devised to solve the
above-mentioned problems, and an object of a first group of the
present invention is to provide a holding seal material which has a
high initial face pressure, and is less susceptible to degradation
with time in the face pressure, to provide an alumina-silica based
fiber excellent in mechanical strength and suitable for obtaining
the above-mentioned holding seal material and a manufacturing
method thereof, and also to provide a manufacturing method of
alumina-silica based fibers capable of securely obtaining the
above-mentioned alumina-silica based fiber excellent in mechanical
strength easily.
[0032] Moreover, an object of a second group of the present
invention is to provide a holding seal material which has a high
initial face pressure, and is less susceptible to degradation with
time in the face pressure, with excellent sealing properties, and a
catalyst converter, and also to provide a manufacturing method of a
holding seal material which is suitable for obtaining the
above-mentioned holding seal material.
[0033] Furthermore, an object of a third group of the present
invention is to provide a holding seal material which is less
susceptible to degradation with time in the face pressure, and also
to provide a manufacturing method of alumina-silica based fibers
that are used for the above-mentioned holding seal material.
[0034] Furthermore, an object of a fourth group of the present
invention is to provide a holding seal material excellent in
quality stability, and also to provide a manufacturing method of a
holding seal material which is suitable for obtaining the
above-mentioned holding seal material.
[0035] Furthermore, an object of a fifth group of the present
invention is to provide a holding seal material which is less
susceptible to degradation with time in face pressure, and also to
provide a manufacturing method of a holding seal material which is
suitable for the above-mentioned holding seal material, a ceramic
fiber aggregation and ceramic fibers thereof.
[0036] Furthermore, an object of a sixth group of the present
invention is to provide a manufacturing method of an alumina fiber
aggregation which has alumina short fibers having high strength
with small dispersions so that it provides a sufficiently high
initial face pressure, and is less susceptible to degradation with
time.
SUMMARY OF THE INVENTION
[0037] The present inventors studied hard so as to solve the
problems for the above-mentioned first group of the present
invention, and after a number of processes of trial and error,
fortunately, made it possible to produce alumina-silica based
fibers excellent in mechanical strength. The alumina-silica based
fibers thus produced generally have a blackish color, and have
characteristics that are clearly different from those of white,
transparent alumina-silica based fibers that have been generally
known. The present inventors further studied hard so as to find the
cause of generation of the color which is different from the color
of the generally-known fibers. As a result, they found that as the
residual carbon content in the fibers increased, the fibers came to
have a blackish color, and that the presence of the residual carbon
content improved the mechanical strength. Thus, based upon these
findings, the present inventors further studied hard, and finally
arrived at the following first group of the present invention.
[0038] That is, the invention of claim 1 according to the first
group of the present invention summarizes an alumina-silica based
fiber which presents a blackish color.
[0039] The invention of claim 2 according to the first group of the
present invention summarizes an alumina-silica based fiber which
presents a blackish color derived from a carbon component.
[0040] The invention of claim 3 according to the first group of the
present invention summarizes an alumina-silica based fiber which
has a residual carbon content of 1% by weight or more, presents a
blackish color derived from its residual carbon component, and has
a fiber tensile strength of 1.2 GPa or more, a fiber bending
strength of 1.0 GPa or more and a fracture toughness of 0.8
MN/m.sup.3/2 or more.
[0041] The invention of claim 4 according to the first group of the
present invention summarizes a manufacturing method of
alumina-silica based fibers, including: a spinning step of
obtaining precursor fibers by using a spinning stock solution of
the alumina-silica based fibers for an inorganic salt method as a
material; and a firing step of heating the above-mentioned
precursor fibers under an environment which makes it difficult to
carry out an oxidizing reaction on the carbon component contained
in the above-mentioned precursor fibers, thereby sintering the
above-mentioned precursor fibers.
[0042] The invention of claim 5 according to the first group of the
present invention summarizes the invention of claim 4, wherein the
above-mentioned precursor fiber is heated at a temperature of 1000
to 1300.degree. C. under a nitrogen atmosphere.
[0043] The invention of claim 6 according to the first group of the
present invention summarizes the invention of claim 4 or claim 5,
wherein the carbon component contained in the above-mentioned
precursor fiber is derived from an organic polymer added to the
above-mentioned spinning stock solution of the alumina-silica based
fiber as a fiber-drawing property applying agent.
[0044] The invention of claim 7 according to the first group of the
present invention summarizes a holding seal material which has
alumina-silica based fibers, according to any of claims 1 to 3,
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body.
[0045] The invention of claim 8 according to the first group of the
present invention summarizes the invention of claim 7, wherein the
above-mentioned ceramic body includes a catalyst carrier, and the
above-mentioned holding seal material is used as a holding seal
material for a catalyst converter.
[0046] In order to solve the problem for the second group of the
present invention, the invention of claim 9 according to the second
group of the present invention summarizes a holding seal material
which has a fiber aggregation of alumina-silica based fibers
aggregated into a mat shape as a constituent element, and is placed
in a gap between a ceramic body capable of allowing a fluid to flow
through the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein a crystallization rate
in a portion on a first face side is different from that in a
portion on a second face side.
[0047] The invention of claim 10 according to the second group of
the present invention summarizes a holding seal material which has
a fiber aggregation of alumina-silica based fibers aggregated into
a mat shape as a constituent element, and is placed in a gap
between a ceramic body capable of allowing a fluid to flow through
the inside thereof and a metal shell covering the outer
circumference of the ceramic body, wherein a crystallization rate
is gradually increased from a first face side toward a second face
side.
[0048] The invention of claim 11 according to the second group of
the present invention summarizes the invention of claim 10,
including a sheet of fiber aggregation, wherein the crystallization
rate of the fiber aggregation is gradually increased from the first
face side toward the second face side.
[0049] The invention of claim 12 according to the second group of
the present invention summarizes the invention of any of claims 9
to 11, wherein the difference between the crystallization rates in
the portion on the first face side and that in the portion on the
second face side is 3% by weight or more.
[0050] The invention of claim 13 according to the second group of
the present invention summarizes the invention of any of claims 9
to 11, wherein the crystallization rate in the portion on the first
face side is 0 to 1% by weight, and the crystallization rate in the
portion on the second face side is 1 to 10% by weight.
[0051] The invention of claim 14 according to the second group of
the present invention summarizes the invention of any of claims 9
to 13, wherein the above-mentioned ceramic body includes a catalyst
carrier, and the above-mentioned holding seal material is used as a
holding seal material for a catalyst converter.
[0052] The invention of claim 15 according to the second group of
the present invention summarizes a holding seal material which has
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to flow through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein a crystallization rate is made different depending on
portions.
[0053] The invention of claim 16 according to the second group of
the present invention summarizes the invention of claim 15, wherein
the above-mentioned ceramic body includes a catalyst carrier, and
the above-mentioned holding seal material is used as a holding seal
material for a catalyst converter.
[0054] The invention of claim 17 according to the second group of
the present invention summarizes a manufacturing method of a
holding seal material of any of claims 9 to 14, including: a
spinning step of obtaining precursor fibers by using a spinning
stock solution of ceramic fibers as material; a laminating step of
laminating the above-mentioned precursor fibers to form a
mat-shaped fiber aggregation; and a firing step of sintering the
above-mentioned fiber aggregation so as to provide a difference
between a firing temperature on a first face side and that on a
second face side.
[0055] The invention of claim 18 according to the second group of
the present invention summarizes the invention of claim 17, wherein
the difference between the above-mentioned firing temperatures is
set to 100.degree. C. or more.
[0056] The invention of claim 19 according to the second group of
the present invention summarizes the invention of claim 17, wherein
the firing temperature on the first face side is set to 800 to
1100.degree. C., and the firing temperature on the second face side
is set to 1100 to 1400.degree. C.
[0057] The invention of claim 20 according to the second group of
the present invention summarizes a catalyst converter comprising: a
catalyst carrier; a cylinder-shaped metal shell covering the outer
circumference of the catalyst carrier; and a holding seal material
placed in a gap between these elements, and having alumina-silica
based fibers aggregated into a mat shape as a constituent element,
wherein the above-mentioned holding seal material is placed in the
above-mentioned gap in such a state that a first face side having a
relatively small crystallization rate is made in contact with the
above-mentioned metal shell, and a second face side having a
relatively large crystallization rate is made in contact with the
above-mentioned catalyst carrier.
[0058] In order to solve the problem for the third group of the
present invention, the invention of claim 21 according to the third
group of the present invention summarizes a holding seal material
which has alumina-silica based fibers aggregated into a mat shape
as a constituent element, and is placed in a gap between a ceramic
body capable of allowing a fluid to flow through the inside thereof
and a metal shell covering the outer circumference of the ceramic
body, wherein the above-mentioned alumina-silica based fiber has a
non-circular shape in its cross-section.
[0059] The invention of claim 22 according to the third group of
the present invention summarizes a holding seal material which has
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to f low through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein the above-mentioned alumina-silica based fiber has a
deformed shape in its cross-section.
[0060] The invention of claim 23 according to the third group of
the present invention summarizes a holding seal material which has
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to flow through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein the above-mentioned alumina-silica based fiber has a flat
shape in its cross-section.
[0061] The invention of claim 24 according to the third group of
the present invention summarizes the invention of any of claims 21
to 23, wherein the above-mentioned alumina-silica based fiber has a
substantially elliptical or cocoon shape in its cross-section.
[0062] The invention of claim 25 according to the third group of
the present invention, summarizes the invention of claim 21 or 22,
wherein the above-mentioned alumina-silica based fiber is a hollow
fiber.
[0063] The invention of claim 26 according to the third group of
the present invention, summarizes the invention of any of claims 21
to 25, wherein the above-mentioned ceramic body includes a catalyst
carrier, and the above-mentioned holding seal material is used as a
holding seal material for a catalyst converter.
[0064] The invention of claim 27 according to the third group of
the present invention summarizes a manufacturing method of
alumina-silica based fibers used in a holding seal material of any
of claims 21 to 26, including: a spinning step of obtaining
precursor fibers by discharging a spinning stock solution
containing a solution of aluminum salt water, silica sol and an
organic polymer through a nozzle; and a firing step of heating and
sintering the above-mentioned precursor fibers, wherein dried hot
air is blown to the above-mentioned precursor fibers immediately
after having been discharged from the discharging section of the
above-mentioned nozzle having a non-circular shape in its
cross-section.
[0065] The invention of claim 28 according to the third group of
the present invention summarizes the invention of claim 27, wherein
the above-mentioned dried hot air is blown in a forward direction
with respect to the discharging direction of the above-mentioned
precursor fiber.
[0066] The invention of claim 29 according to the third group of
the present invention summarizes the invention of claim 27 or claim
28, wherein a water-soluble plasticizer is preliminarily added to
the above-mentioned spinning stock solution.
[0067] Moreover, in order to solve the problem for the fourth group
of the present invention, the invention of claim 30 according to
the fourth group of the present invention summarizes a holding seal
material which has alumina-silica based fibers aggregated into a
mat shape as a constituent element, and is placed in a gap between
a ceramic body capable of allowing a fluid to flow through the
inside thereof and a metal shell covering the outer circumference
of the ceramic body, wherein the dispersion of fiber diameter in
the above-mentioned alumina-silica based fiber is within .+-.3
.mu.m.
[0068] The invention of claim 31 according to the fourth group of
the present invention summarizes a holding seal material which has
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to flow through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein the dispersion of fiber length in the above-mentioned
alumina-silica based fiber is within .+-.4 mm.
[0069] The invention of claim 32 according to the fourth group of
the present invention summarizes a holding seal material which has
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to flow through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein the dispersion of fiber diameter in the above-mentioned
alumina-silica based fiber is within .+-.3 .mu.m, and the
dispersion of fiber length in the above-mentioned alumina-silica
based fiber is within .+-.4 mm.
[0070] The invention of claim 33 according to the fourth group of
the present invention summarizes the invention of any of claims 30
to 32, wherein the content of shots is 3% by weight or less.
[0071] The invention of claim 34 according to the fourth group of
the present invention summarizes a holding seal material which has
alumina-silica based fibers aggregated into a mat shape as a
constituent element, and is placed in a gap between a ceramic body
capable of allowing a fluid to flow through the inside thereof and
a metal shell covering the outer circumference of the ceramic body,
wherein the average fiber diameter of the above-mentioned
alumina-silica based fiber is 5 to 15 .mu.m, the dispersion of
fiber diameter therein is within .+-.3 .mu.m, the average fiber
length thereof is 5 to 20 mm, the dispersion of fiber length
therein is within .+-.4 mm, and no shots are contained therein.
[0072] The invention of claim 35 according to the fourth group of
the present invention summarizes the invention of any of claims 30
to 34, wherein the above-mentioned ceramic body includes a catalyst
carrier, and the above-mentioned holding seal material is used as a
holding seal material for a catalyst converter.
[0073] The invention of claim 36 according to the fourth group of
the present invention summarizes a manufacturing method of a
holding seal material of any of claims 30 to 35, including: a
spinning step of obtaining long precursor fibers by continuously
discharging a spinning stock solution containing a solution of
aluminum salt water, silica sol and an organic polymer through a
nozzle; a cutting step of chopping the above-mentioned long fibers
into a predetermined length to obtain short fibers; a molding step
of allowing the above-mentioned short fibers to aggregate
three-dimensionally, thereby forming into a mat-shaped fiber
aggregation; and a firing step of heating and sintering the
above-mentioned mat-shaped fiber aggregation.
[0074] Moreover, the inventors of the present invention studied
hard to solve problems for the fifth group of the present
invention.
[0075] As a result, it has been found that when an external load is
applied for a long time in a manner so as to compress the fiber
aggregation, the ceramic fibers constituting the fiber aggregation
tend to slide on one another to cause dispersions, resulting in
degradation in the face pressure of the fiber aggregation.
Therefore, the inventors of the present application have attempted
to solve the problems of sliding and dispersions among the fibers
by applying any means to obtain better results, and take portions
at which fibers are adjacent to each other with overlapped parts
into consideration. Thus, they have further studied energetically
to improve such portions, and finally have reached the following
fifth group of the present invention.
[0076] The invention of claim 37 according to the fifth group of
the present invention summarizes a holding seal material which has
ceramic fibers aggregated into a mat shape as a constituent
element, and is placed in a gap between a ceramic body capable of
allowing a fluid to flow through the inside thereof and a metal
shell covering the outer circumference of the ceramic body, wherein
the ceramic fibers are partially bonded to each other by a ceramic
adhesive.
[0077] The invention of claim 38 according to the fifth group of
the present invention summarizes the invention of claim 37, wherein
the above-mentioned ceramic comprises a substance which constitutes
the above-mentioned ceramic fiber.
[0078] The invention of claim 39 according to the fifth group of
the present invention summarizes to the invention of claim 37,
wherein the above-mentioned ceramic fibers are alumina-silica based
fibers, and the above-mentioned ceramic adhesive has alumina as a
main component.
[0079] The invention of claim 40 according to the fifth group of
the present invention summarizes to the invention of any of claims
37 to 39, wherein 1 to 8% by weight of the above-mentioned ceramic
adhesive is contained therein.
[0080] The invention of claim 41 according to the fifth group of
the present invention summarizes to the invention of any of claims
37 to 40, wherein the above-mentioned ceramic body includes a
catalyst carrier, and the above-mentioned holding seal material is
used as a holding seal material for a catalyst converter.
[0081] The invention of claim 42 according to the fifth group of
the present invention summarizes a manufacturing method of a
holding seal material according to any of claims 37 to 41,
including: a spinning step of obtaining precursor fibers by using a
spinning stock solution of ceramic fibers as a material; a firing
step of heating and sintering the above-mentioned precursor fibers;
a molding step of allowing thus obtained ceramic fibers to
aggregate three-dimensionally, thereby forming into a mat-shaped
aggregation; and bonding step of bonding the ceramic fibers forming
the above-mentioned aggregation by using a ceramic adhesive.
[0082] The invention of claim 43 according to the fifth group of
the present invention summarizes the invention of claim 42, wherein
in the above-mentioned bonding step, after the material solution of
the above-mentioned ceramic adhesive has been supplied between the
ceramic fibers forming the above-mentioned aggregation, the
above-mentioned aggregation is heated to sinter specific components
in the above-mentioned material solution so as to be formed into
ceramics.
[0083] The invention of claim 44 according to the fifth group of
the present invention summarizes the invention of claim 42, wherein
in the above-mentioned bonding step, after the above-mentioned
aggregation has been impregnated with a water-soluble metal
solution, which is the above-mentioned material solution, having a
low viscosity, the above-mentioned aggregation is dried and heated
so that the metal component in the above-mentioned solution is
sintered to be formed into ceramics.
[0084] The invention of claim 45 according to the fifth group of
the present invention summarizes the invention of claim 44, wherein
the above-mentioned water-soluble metal solution is supplied by an
amount of 1 to 10% by weight of the above-mentioned
aggregation.
[0085] The invention of claim 46 according to the fifth group of
the present invention summarizes the invention of any of claims 43
to 45, wherein the above-mentioned spinning stock solution of the
ceramic fibers is a spinning stock solution of alumina-silica based
fibers prepared by using an inorganic salt method, and the
above-mentioned water-soluble metal solution is a water solution
containing aluminum ions.
[0086] The invention of claim 47 according to the fifth group of
the present invention summarizes a manufacturing method of a
holding seal material of any of claims 37 to 41, including: a
spinning step of obtaining precursor fibers by using a spinning
stock solution of ceramic fibers as a material; a molding step of
allowing the above-mentioned precusor fibers to aggregate
three-dimensionally, thereby forming into a mat-shaped aggregation;
a liquid substance supplying step of allowing a liquid substance
capable of being a ceramic adhesive later to adhere to portions at
which the above-mentioned precursor fibers forming the
above-mentioned aggregation are overlapped adjacent to each other;
and a firing step of heating the above-mentioned aggregation to
sinter the above-mentioned precursor fibers and the above-mentioned
liquid substance.
[0087] The invention of claim 48 according to the fifth group of
the present invention summarizes the invention of claim 47, wherein
in the above-mentioned liquid substance supplying step, the
aggregation including the above-mentioned precursor fibers of
alumina-silica based fibers is put in a highly moistened
environment with high moisture.
[0088] The invention of claim 49 according to the fifth group of
the present invention summarizes the invention of claim 47, wherein
in the above-mentioned liquid substance supplying step, a
non-aqueous liquid substance containing an inorganic element
contained in the above-mentioned alumina-silica based fiber is
atomized and supplied to the aggregation including the precursor
fibers of the alumina-silica based fibers.
[0089] The invention of claim 50 according to the fifth group of
the present invention summarizes the invention of any of claims 47
to 49, wherein a cutting step of chopping the long fibers of the
above-mentioned precursor fibers into a predetermined length to
obtain short fibers is carried out between the above-mentioned
spinning step and the above-mentioned molding step.
[0090] The invention of claim 51 according to the fifth group of
the present invention summarizes a ceramic fiber aggregation
wherein three-dimensionally aggregated ceramic fibers are partially
bonded to each other by a ceramic adhesive.
[0091] The invention of claim 52 according to the fifth group of
the present invention summarizes a ceramic fiber aggregation
comprising ceramic fibers having a branched structure.
[0092] The invention of claim 53 according to the fifth group of
the present invention summarizes a ceramic fiber having a branched
structure.
[0093] Moreover, in order to solve the problem for the sixth group
of the present invention, the invention of claim 54 according to
the sixth group of the present invention summarizes a manufacturing
method of an alumina fiber aggregation, including: a spinning step
of obtaining a continuous long-fiber precursor by using an alumina
fiber stock solution used in an inorganic salt method as a
material; a chopping step of cutting the above-mentioned continuous
long-fiber precursor into short-fiber precursors; a mat preparing
step of preparing a mat-shaped short fiber precursor by using thus
obtained short-fiber precursor; and a firing step of firing the
above-mentioned mat-shaped short fiber precursor to manufacture an
alumina fiber aggregation.
[0094] The following description will be given of "operations" of
the first group of the present invention.
[0095] In accordance with the inventions of claims 1, 2 and 3 of
the first group of the present invention, since black colored
alumina-silica based fibers are generally excellent in the
mechanical strength, the application of these fibers makes it
possible to achieve a holding seal material that has a high initial
face pressure, and is less susceptible to degradation with time in
the face pressure.
[0096] Here, when the fiber tensile strength, fiber bending
strength and fracture toughness are the above-mentioned values or
more, it is possible to achieve alumina-silica based fibers that
have very high resistance against tension and bending, and are
flexible and unbreakable. Therefore, it becomes possible to improve
the initial face pressure, and also to securely prevent degradation
with time in the face pressure. Moreover, the alumina-silica based
fibers that are black colored, contain carbon components in the
fibers thereof, and since the crystallization is allowed to
progress in the entire alumina-silica based fibers, it becomes
possible to achieve the excellent mechanical strength such as
tensile strength.
[0097] In accordance with the invention of claim 4 of the first
group of the present invention, it is possible to sinter the
precursor fibers without causing oxidation in the carbon components
in the precursor fibers. For this reason, it is possible to allow
much carbon components to remain in the fibers, and consequently to
securely obtain fibers that are excellent in the mechanical
strength easily.
[0098] Here, since most of the carbon components in the precursor
fibers are normally burnt to disappear before the firing
temperature has been attained, the carbon components seldom remain
in the alumina-silica based fibers obtained through the firing
step. However, in the case where the precursor fibers are heated
under an environment that hardly allows oxidizing reaction of the
carbon components to progress, it is considered that carbon is
allowed to remain in the fibers to be assembled into the ceramic
skeleton to a certain degree.
[0099] In accordance with the invention of claim 5 in the first
group of the present invention, an inexpensive nitrogen atmosphere
is utilized as an inert atmosphere in which the firing step is
carried out; therefore, it becomes possible to cut manufacturing
costs. Moreover, since the firing temperature is set in the
above-mentioned preferable range, it is possible to obtain
alumina-silica based fibers having high strength stably.
[0100] When the heating temperature of the precursor fibers is less
than 1000.degree. C., the sintering step of the precursor fibers
tends to become insufficient, and in such a case, even when the
residual carbon content is sufficient, it becomes difficult to
stably obtain alumina-silica based fibers having high strength. In
contrast, even when the heating temperature of the precursor fibers
is set so as to exceed 1300.degree. C., this fails to especially
increase the strength of the alumina-silica based fibers, resulting
in deterioration in economical efficiency instead of
improvements.
[0101] In accordance with the invention of claim 6 according to the
first group of the present invention, the above-mentioned organic
polymer not only serves as a string-drawing-property applying
agent, but also functions as carbon sources that add carbon to the
precursor fibers so as to allow the alumina-silica based fibers to
have appropriate strength. Therefore, it is not necessary to
especially add carbon sources to the spinning stock solution in a
separated manner, thereby making it possible to eliminate the
necessity of greatly modifying the composition of the spinning
stock solution. Thus, it is possible to preliminarily avoid
imbalance in the stock solution composition, and consequently to
prevent degradation in the basic physical properties in the
alumina-silica based fibers. Moreover, since no carbon source needs
to be added, it becomes possible to reduce the manufacturing costs.
Furthermore, since the above-mentioned organic polymer is easily
dispersed in the spinning stock solution evenly, the carbon sources
are evenly dispersed in the precursor fibers. Consequently, the
resulting alumina-silica based fibers are allowed to have an even
residual carbon content, and tend to have less irregularity in the
mechanical strength.
[0102] In this case, since the organic polymer of this type is
burned to disappear normally at a temperature of approximately 500
to 600.degree. C., nothing is left in the alumina-silica based
fibers obtained through the firing step. However, it is considered
that, when the precursor fibers are heated under an environment
that hardly allows the oxidizing reaction of carbon contents to
progress, carbon constituting the organic polymer is allowed to
remain in the fibers, and assembled into the ceramic skeleton to a
certain degree.
[0103] In accordance with the invention of claim 7 according to the
first group of the present invention, since the alumina-silica
based fibers having excellent mechanical strength are used as the
constituent elements, it becomes possible to provide a holding seal
material that has a high initial face pressure, tends to have less
degradation with time in the face pressure.
[0104] In accordance with the invention of claim 8 according to the
first group of the present invention, since the alumina-silica
based fibers having excellent mechanical strength are used as the
constituent elements with the ceramic body being composed of a
catalyst carrier, and since the holding seal material is used as a
catalyst converter-use holding seal material, it becomes possible
to provide a catalyst-converter-use holding seal material that has
a high initial face pressure, and is less susceptible to
degradation with time in the face pressure.
[0105] In other words, in accordance with the invention of claim 8
of the first group of the present invention, the holding seal
material of claim 7 is provided as a catalyst-converter-use holding
seal material that includes alumina-silica based fibers as its
constituent elements, and is placed in a gap between the catalyst
carrier and the metal shell that covers the outer circumference of
the catalyst carrier.
[0106] The following description will be given of "operations" of
the second group of the present invention.
[0107] In accordance with the invention of claim 9 according to the
second group of the present invention, the crystallization rate on
the portion on the first face side is made different from the
crystallization rate on the portion on the second face side. With
this arrangement, the portion on the face side that has a
relatively high crystallization rate, and is excellent in the heat
resistance is placed on a high-temperature side, and the portion on
the face side that has a relatively low crystallization rate, and
is excellent in the elasticity and flexibility is placed on a
low-temperature side. Therefore, the fibers are made less
susceptible to brittleness on the high-temperature side, and on the
low-temperature side, it becomes possible to avoid the occurrence
of a gap to the other members. Thus, it becomes possible to achieve
a holding seal material that is excellent in the sealing property,
in addition to the advantages that it has high initial face
pressure, and is less susceptible to degradation with time in the
face pressure.
[0108] In accordance with the invention of claim 10 according to
the second group of the present invention, since the
crystallization rate is gradually increased from the first face
side toward the second face side, the portion on the second face
side that is excellent in the heat resistance can be placed on a
high-temperature side, and the portion on the first face side that
is excellent in the elasticity and flexibility can be placed on a
low-temperature side. Therefore, the fibers are made less
susceptible to brittleness on the high-temperature side, and on the
low-temperature side, it becomes possible to avoid the occurrence
of a gap to the other members. Thus, it becomes possible to achieve
a holding seal material that is excellent in the sealing property,
in addition to the advantages that it has high initial face
pressure, and is less susceptible to degradation with time in the
face pressure.
[0109] In accordance with the invention of claim 11 according to
the second group of the present invention, different from a
structure constituted by a plurality of sheets of fiber
aggregations that have mutually different crystallization rates, it
is possible to eliminate the necessity of the jobs for mutually
superposing the fiber aggregations so as to be bonded to one
another, and consequently to reduce the number of processes upon
manufacturing the device. Moreover, since it is possible to provide
a thinner structure in comparison with the laminated structure of a
plurality of sheets, the resulting structure is comparatively
easily placed in a narrow gap. Moreover, in comparison with the
laminated structure of a plurality of sheets in which fluids might
pass through the interface between the fiber aggregations, since no
interface exists in such a single sheet structure of the third
invention of the second group of the present invention, it is not
necessary to take the passage of fluid into consideration. Thus, it
is possible to provide a structure that is excellent in the sealing
property.
[0110] In accordance with the invention of claim 12 according to
the second group of the present invention, since the difference
between the crystallization rate of the portion on the first face
side and the crystallization rate of the portion on the second face
side is set to 3% by weight or more so that it becomes possible to
securely improve the face pressure characteristics and the sealing
property.
[0111] When the difference between the crystallization rate of the
portion on the first face side and the crystallization rate of the
portion on the second face side is less than 3% by weight, the
difference between the crystallization rates of the two sides
becomes too small, it may not be able to provide the target
characteristics.
[0112] In accordance with the invention of claim 13 according to
the second group of the present invention, the crystallization rate
of the portion on the first face side and the crystallization rate
of the portion on the second face side are respectively set in the
above-mentioned desired ranges so that it becomes possible to
securely improve the face pressure characteristics and the sealing
property. In the case where the crystallization rate of the portion
on the first face side exceeds 1% by weight or in the case where
the crystallization rate of the portion on the second face side
becomes less than 1% by weight, the difference between the
crystallization rates of the two sides becomes too small, failing
to provide the target characteristics. In contrast, when the
crystallization rate on the second face side exceeds 10% by weight,
the heat resistance on the corresponding portion may be
degradated.
[0113] In accordance with the invention of claim 14 according to
the second group of the present invention, since the ceramic body
is composed of a catalyst carrier, and since the holding seal
material is used as a catalyst converter-use holding seal material,
it becomes possible to provide a catalyst-converter-use holding
seal material that is also excellent in the sealing property in
addition to the advantages that it has high initial face pressure,
and is less susceptible to degradation with time in the face
pressure.
[0114] In other words, in accordance with the invention of claim 14
according to the second group of the present invention, the holding
seal material of any one of claims 9 to 13 is provided as a
catalyst converter-use holding seal material that uses
alumina-silica based fibers as its constituent elements, and is
placed in a gap between the catalyst carrier and the metal shell
covering the outer circumference of the catalyst carrier.
[0115] In accordance with the invention of claim 15 according to
the second group of the present invention, the crystallization rate
is not even, and set to be different depending on portions. With
this arrangement, the portion that has a relatively high
crystallization rate, and is excellent in the heat resistance is
placed on a high-temperature side, and the portion that has a
relatively low crystallization rate, and is excellent in the
elasticity and flexibility is placed on a low-temperature side.
Therefore, the fibers are made less susceptible to brittleness on
the high-temperature side, and on the low-temperature side, it
becomes possible to avoid the occurrence of a gap to the other
members. Thus, it becomes possible to achieve a holding seal
material that has an excellent sealing property, in addition to the
advantages that it has high initial face pressure, and is less
susceptible to degradation with time in the face pressure.
[0116] In accordance with the invention of claim 16 according to
the second group of the present invention, since the ceramic body
comprises a catalyst carrier, and since the holding seal material
is used as a catalyst converter-use holding seal material, it
becomes possible to obtain a catalyst-converter-use holding seal
material that has an excellent sealing property in addition to the
advantages that it has high initial face pressure, and is less
susceptible to degradation with time in the face pressure.
[0117] In other words, in accordance with the invention of claim 16
of the second group of the present invention, the holding seal
material of claim 15 is provided as a catalyst-converter-use
holding seal material that includes alumina-silica based fibers as
its constituent elements, and is placed in a gap between the
catalyst carrier and the metal shell that covers the outer
circumference of the catalyst carrier.
[0118] In accordance with the invention of claim 17 according to
the second group of the present invention, a mat-shaped fiber
aggregation is sintered in a manner in which a gap is provided
between the firing temperature on the first face side and the
firing temperature on the second face side so that it is possible
to securely form a holding seal material having different
crystallization rates on the respective sides comparatively easily.
Moreover, this manufacturing method is also suitable for the
manufacturing process of the holding seal material in which the
crystallization rate is gradually increased from the first face
side toward the second face side in a sheet of fiber aggregation.
Moreover, a conventional firing device is commonly applied to this
manufacturing method without the necessity of utilizing a special
firing device. Thus, it becomes possible to avoid an increase in
the facility costs.
[0119] In accordance with the invention of claim 18 according to
the second group of the present invention, the difference between
the firing temperatures is set to 100.degree. C. or more so that
the first face side and the second face side are made different
from each other in the easiness in firing with a difference in the
crystallization rates being formed between the both faces. Thus, it
becomes possible to more securely form a holding seal material
having different crystallization rates on the respective sides.
[0120] In accordance with the invention of claim 19 according to
the second group of the present invention, the firing temperature
on the first face side is set to a temperature lower than that on
the second face side; therefore, upon firing, it is possible to
provide a holding seal material in which the crystallization rate
gradually increases from the first face side toward the second face
side.
[0121] When the firing temperature on the first face side is less
than 800.degree. C., the firing reaction does not progress
sufficiently, failing to provide mechanical strength that is
required. When the firing temperature on the first face side
exceeds 1100.degree. C. or when the firing temperature on the
second face side is less than 1100.degree. C., the difference
between the crystallization rates of the two sides becomes too
small, failing to obtain the target characteristics. When the
firing temperature on the second face side exceeds 1400.degree. C.,
the crystallization progresses excessively, may cause degradation
in the mechanical strength and heat resistance.
[0122] The operations of the invention of claim 20 according to the
second group of the present invention are described as follows.
Normally, when a catalyst converter is used, the catalyst carrier,
which is directly exposed to a high-temperature fluid, comes to
have a higher temperature, while the metal shell does not have a
temperature as high as the catalyst carrier. Therefore, the
high-temperature resistance is especially required on the face side
that is made in contact with the catalyst carrier. By taking this
fact into consideration, the above-mentioned invention allows the
second face side that has a comparatively greater crystallization
rate, that is, the face side that is excellent in the heat
resistance, to contact the catalyst carrier. Further, the first
face side that has a comparatively smaller crystallization rate,
that is, the face side that is excellent in the elasticity and
flexibility although it is inferior in the heat resistance, is made
in contact with the metal shell. Consequently, the fibers on the
portion that is made in contact with the catalyst carrier are less
susceptible to brittleness, and make it possible to form a holding
seal material that has a high initial face pressure, and is less
susceptible to degradation with time in the face pressure.
Moreover, since an elastic force is exerted on the portion in
contact with the metal shell, this structure makes it possible to
reduce the occurrence of a gap to the metal shell, and consequently
to provide a holding seal material that is excellent in the sealing
property.
[0123] As described above, it is possible to achieve a catalyst
converter that is excellent in the holding property in the catalyst
carrier, and less susceptible to leakage of fluid with high process
efficiency.
[0124] The following description will be given of "operations" of
the third group of the present invention.
[0125] In accordance with the invention of claim 21 according to
the third group of the present invention, the fiber having a
non-circular shape in its cross-section becomes more flexible than
the fiber having a circular shape in its cross-section. In other
words, the non-circular shape of the above-mentioned fiber provides
a characteristic in which it is bent in a specific direction
comparatively easily.
[0126] Further, this characteristic makes the fiber less
susceptible to breaking, and also makes it possible to maintain the
repulsive force for a long time. Here, in the present
specification, "the cross-section of a fiber" refers to a
cross-section formed when a fiber is cut perpendicularly to the
extending direction of the fiber.
[0127] In accordance with the invention of claim 22 according to
the third group of the present invention, the fiber having a
deformed shape in its cross-section becomes more flexible than the
fiber having a circular shape in its cross-section. In other words,
the deformed shape of the above-mentioned fiber provides a
characteristic in which it is bent in a specific direction
comparatively easily. Consequently, this characteristic makes the
fiber less susceptible to breaking, and also makes it possible to
maintain the repulsive force for a long time.
[0128] In accordance with the invention of claim 23 according to
the third group of the present invention, the fiber having a flat
shape in its cross-section becomes more flexible than the fiber
having a circular shape in its cross-section. In other words, the
flat shape of the above-mentioned fiber provides a characteristic
in which it is bent in a specific direction comparatively easily.
Consequently, this characteristic makes the fiber less susceptible
to breaking, and also makes it possible to maintain the repulsive
force for a long time.
[0129] In accordance with the invention of claim 24 according to
the third group of the present invention, when the holding seal
material is formed by using fibers, each having a virtually
elliptical or cocoon shape in its cross-section, the fibers are
easily engaged with each other, making the fibers less susceptible
to sliding and deviation with each other. Therefore, it becomes
possible to reduce degradation in the face pressure.
[0130] In accordance with the invention of claim 25 according to
the third group of the present invention, the hollow fiber having a
space inside thereof is excellent in its heat-insulating property
in comparison with a fiber without a space inside thereof.
Therefore, when the fibers of this type are used in a holding seal
material, it is possible to reduce the quantity of heat that is
released from the ceramic body to the metal shell, and consequently
to carry out a catalyst reaction effectively. Moreover, in the
hollow fiber, sound and vibration are absorbed and damped by the
space inside the fiber. Therefore, when the fibers of this type are
used in a holding seal material, it is possible to provide
excellent noise-insulation and vibration-insulation properties.
[0131] In accordance with the invention of claim 26 according to
the third group of the present invention, since the ceramic body
comprises a catalyst carrier, and since the holding seal material
is used as a catalyst converter-use holding seal material, it is
possible to obtain a catalyst-converter-use holding seal material
that is able to maintain the repulsive force for a long time.
[0132] In other words, in accordance with the invention of claim 26
according to the third group of the present invention, the holding
seal material of the present invention of the third group is
provided as a catalyst-converter-use holding seal material that has
alumina-silica based fibers as its constituent elements and is
placed in a gap between the catalyst carrier and the metal shell
covering the outer circumference of the catalyst carrier.
[0133] In accordance with the invention of claim 27 according to
the third group of the present invention, a spinning stock solution
is discharged through a nozzle having a non-circular shape in its
cross-section. Immediately after discharged from the discharging
section of the nozzle, the precursor fiber has a cross-sectional
shape to which the cross-sectional shape of the discharging section
is reflected in a certain degree. However, as time has elapsed
since the discharge, the cross-sectional shape thereof tends to
have a roundness (in other words, is subjected to the Barus'
effect) due to the influence of a surface tension exerted on the
precursor fiber so that the cross-section of the precursor fiber
has a circular shape. Therefore, dry hot air is blown thereto in a
state immediately after the discharge so that the precursor fiber
is dried and solidified by being removed its moisture in the
precursor fiber. Consequently, it is possible to maintain a desired
cross-sectional shape given by the discharging section of the
nozzle, and consequently to obtain a fiber having a section of a
non-circular shape comparatively easily.
[0134] In accordance with the invention of claim 28 according to
the third group of the present invention, the dry hot air is blown
to the precursor fiber in a forward direction with respect to the
discharging direction thereof so that the fiber is dried and
solidified, and also extended simultaneously. Moreover, by carrying
out the extending process in this manner, it becomes possible to
control the fiber diameter and shape comparatively easily.
[0135] In accordance with the invention of claim 29 according to
the third group of the present invention, a water-soluble
plasticizer is preliminarily added to the spinning stock solution
so that the elastic modulus of the spinning stock solution becomes
smaller with the Barus' effect being reduced. Therefore, the
discharge behavior of the spinning stock solution at the time of
the spinning process is stabilized. Consequently, the fiber becomes
less susceptible to thread breakage even when it is extended with a
strong tension, and the fiber cross-sectional shape becomes less
susceptible to have roundness due to elastic deformation. Moreover,
the above-mentioned plasticizer has a water-soluble property so
that it is dispersed in the spinning stock solution evenly. Thus,
it becomes possible to reduce the Barus' ratio to a virtually fixed
value, and consequently to obtain a fiber having the target fiber
diameter and cross-sectional shape comparatively easily.
[0136] The following description will be given of "operations" of
the fourth group of the present invention.
[0137] In accordance with the invention of claim 30 according to
the fourth group of the present invention, in the case where a
holding seal material constituted by alumina-silica based fibers
each having a fiber diameter with the dispersions thereof being set
within .+-.3 .mu.m, it becomes possible to accumulate the fibers
evenly, and consequently to reduce the positional dependence of the
basis weight. Therefore, it becomes possible to reduce dispersions
in the face pressure value, and consequently to provide stable
quality.
[0138] In accordance with the invention of claim 31 according to
the fourth group of the present invention, in the case where a
holding seal material constituted by alumina-silica based fibers
each having a fiber length with the dispersions thereof being set
within .+-.4 mm, it becomes possible to accumulate the fibers
evenly, and consequently to reduce the positional dependence of the
basis weight. Therefore, it becomes possible to reduce dispersions
in the face pressure value, and consequently to provide stable
quality.
[0139] In accordance with the invention of claim 32 according to
the fourth group of the present invention, the synergistic effect
obtained by reducing both of the fiber-diameter dispersion and the
fiber-length dispersion makes it possible to further reduce the
positional dependence of the basis weight, and consequently to
further reduce the dispersions in the face pressure value.
[0140] In accordance with the invention of claim 33 according to
the fourth group of the present invention, the content of shot
(non-fiber material) in the holding seal material is set to 3% by
weight or less so that it becomes possible to further reduce the
positional dependence of the basis weight, and consequently to
further reduce the dispersions in the face pressure value.
[0141] In accordance with the invention of claim 34 according to
the fourth group of the present invention, it becomes possible to
extremely reduce the positional dependence of the basis weight, and
consequently to further reduce the dispersions in the face pressure
value, and it also becomes possible to improve the face pressure
and sealing property.
[0142] The average fiber diameter of less than 5 .mu.m makes it
difficult to provide a sufficient face pressure due to a reduction
in the strength of the fiber, and also causes a problem in which
the fibers tend to be inhaled by the respiratory organs. In the
case of the average fiber diameter exceeding 15 .mu.m, when the
fibers are formed into a mat-shaped fiber aggregation, its aeration
resistance is reduced, resulting in degradation in the sealing
property. In addition to this adverse effect, there might be
degradation in the breaking strength. This adverse effect is
considered to be caused by an increase in small scratches generated
by an increase in the fiber surface area.
[0143] The case where the average fiber length being less than 5 mm
causes a problem in which the fibers tend to be inhaled by the
respiratory organs. Moreover, this fiber no longer substantially
exhibits characteristics as the fiber, and when the fibers are
formed into a mat-shaped fiber aggregation, the fibers are not
allowed to entangle with one another preferably, making it
difficult to obtain a sufficient face pressure. The average fiber
length exceeding 20 mm makes the fibers entangled with one another
too strongly, with the result that the fibers tend to be
accumulated unevenly when the fibers are formed into a mat-shaped
aggregation. In other words, the positional dependence of the basis
weight becomes higher, causing an adverse effect to the reduction
in the dispersions in the face pressure value.
[0144] When the content of the shot is high, the positional
dependence of the basis weight becomes higher, causing an adverse
effect to the reduction in the dispersions in the face pressure
value.
[0145] In accordance with the invention of claim 35 according to
the fourth group of the present invention, since the ceramic body
is composed of a catalyst carrier, and since the holding seal
material is used as a catalyst converter-use holding seal material,
it becomes possible to reduce the dispersions in the face pressure
value, and also to provide a catalyst-converter-use holding seal
material with stable quality.
[0146] In other words, in accordance with the invention of claim 35
according to the fourth group of the present invention, the holding
seal material of the fourth group of the present invention forms a
catalyst-converter-use holding seal material that includes
alumina-silica based fibers as its constituent elements, and is
placed in a gap between the catalyst carrier and the metal shell
that covers the outer circumference of the catalyst carrier.
[0147] In accordance with the invention of claim 36 according to
the fourth group of the present invention, since the spinning
process is carried out by using an inorganic salt method, it is
possible to control the fiber diameter in a narrow range by
properly setting the shape and size of the discharging section.
Thus, it becomes possible to reduce dispersions in the fiber
diameter. Moreover, this method chops long fibers to obtain short
fibers; therefore, different from a method in which fibers are
obtained through a blowing process, it is possible to control the
fiber length in a narrow range. Thus, it becomes possible to reduce
dispersions in the fiber length. In addition to these effects, it
is also possible to avoid the generation of shot. Consequently,
this manufacturing method makes it possible to obtain the
above-mentioned holding seal material securely with ease.
[0148] The following description will be given of "operations" of
the fifth group of the present invention.
[0149] In accordance with the invention of claim 37 according to
the fifth group of the present invention, it is possible to provide
a structure wherein, so to speak, a cross-linking bridge is placed
between portions at which ceramic fibers are adjacent to each other
with overlapped parts, and consequently to make the respective
fibers less susceptible to sliding and deviation. Therefore, even
when an external compressing load has been imposed on the holding
seal material for a long time, the member is less susceptible to
reduction in the face pressure. Moreover, in the holding seal
material of the present invention, the fibers are partially bonded
to each other so that the voids inside the holding seal material
are not entirely filled, thereby making it possible to maintain
physical characteristics (elasticity, heat insulating property and
the like) originally required for the holding seal material.
Moreover, since a ceramic adhesive that is excellent in heat
resistance is used, the bonded portions are less susceptible to
reduction in the strength even if the holding seal material is
subjected to a high temperature when it is used.
[0150] In accordance with the invention of claim 38 according to
the fifth group of the present invention, since the ceramic
adhesive is made of a substance constituting the ceramic fibers, it
has a high affinity for the fibers, and allows the bonded portions
to have high strength.
[0151] Therefore, it becomes possible to securely prevent
degradation with time in the face pressure.
[0152] In accordance with the invention of claim 39 according to
the fifth group of the present invention, since alumina-silica
based fibers containing a minute amount of amorphous component are
used, it is possible to improve the heat resistance of the fibers
itself, and consequently to reduce the degradation with time in the
face pressure at high temperatures. Since the ceramic adhesive
mainly composed of alumina has a very high affinity for
alumina-silica based fibers, it is possible to further provide
higher strength to the bonded portions.
[0153] In accordance with the invention of claim 40 according to
the fifth group of the present invention, by setting the content of
the ceramic adhesive in the above-mentioned desired range, it is
possible to provide high strength to the bonded portions while
maintaining desired physical properties in the holding seal
material.
[0154] When the above-mentioned content is less than 1% by weight,
the fibers might not be bonded to one another with high strength.
In contrast, in the case where the above-mentioned content exceeds
8% by weight, although the problem with the bonding strength is
solved, the voids inside the holding seal material tend to be
filled, failing to provide desired physical properties as the
holding seal material.
[0155] In accordance with the invention of claim 41 according to
the fifth group of the present invention, since the ceramic body is
composed of a catalyst carrier, and since the holding seal material
is used as a catalyst converter-use holding seal material, it is
possible to provide a catalyst converter-use holding seal material
which is less susceptible to degradation with time in the face
pressure even when an external load is imposed thereon for a long
time, and is also less susceptible to reduction in the strength of
the bonded portions even when it is subjected to a high
temperature.
[0156] In other words, in accordance with the invention of claim 41
according to the fifth group of the present invention, the holding
seal material of the fifth group of the present invention forms a
catalyst-converter-use holding seal material that includes
alumina-silica based fibers as its constituent elements, and is
placed in a gap between the catalyst carrier and the metal shell
that covers the outer circumference of the catalyst carrier.
[0157] In accordance with the invention of claim 42 according to
the fifth group of the present invention, since the firing step and
the bonding process of the precursor fibers are carried out
separately, it becomes possible to securely obtain ceramic fibers
having a desired shape in comparison with a case in which both of
the processes are carried out simultaneously, and it is also
possible to securely bond the fibers having the above-mentioned
desired shape. Therefore, it becomes possible to securely produce a
holding seal material that is less susceptible to degradation with
time in the face pressure with ease.
[0158] In accordance with the invention of claim 43 according to
the fifth group of the present invention, since a surface tension
is exerted on a material solution of the liquid-state ceramic
adhesive, the material solution is allowed to securely adhere to
portions at which the fibers are adjacent to each other with
overlapped parts, when this is supplied to the aggregation. By
heating this in this state, the specific component in the material
solution adhered to the corresponding portions is formed into
ceramics, thereby providing a cross-linking structure between the
fibers.
[0159] In accordance with the invention of claim 44 according to
the fifth group of the present invention, a surface tension is
exerted on a water-soluble metal solution with low viscosity;
therefore, when the aggregation is impregnated with this solution,
the solution is allowed to securely adhere to portions at which the
fibers are adjacent to each other with overlapped parts. Here, the
impregnation method makes it possible to securely inject the
solution to the inside of the aggregation evenly. In this state,
the aggregation is first dried to remove moisture to a certain
degree, and then heated so that the metal component in the solution
adhered to the corresponding portions is oxidized to form ceramics,
thereby providing a cross-linking structure between the fibers.
[0160] In accordance with the invention of claim 45 in accordance
with the fifth group of the present invention, the quantity of
supply of the water-soluble metal solution is set in the
aforementioned preferable range so that it becomes possible to
increase the strength of the bonded portions while maintaining
desired physical properties of the holding seal material.
[0161] The quantity of supply of less than 1% by weight causes an
insufficient quantity of the solution to adhere to the portions at
which the fibers are adjacent to each other with overlapped parts,
sometimes failing to mutually bond the fibers strongly.
[0162] In contrast, the quantity of supply exceeding 10% by weight
causes the voids inside the holding seal material to be easily
filled with the excessive solution, sometimes impairing desired
physical properties in the holding seal material.
[0163] In accordance with the invention of claim 46 according to
the fifth group of the present invention, it is possible to form a
cross-linking structure made from alumina having a high affinity
for the fibers between the alumina-silica based fibers. Therefore,
it is possible to increase the strength of the bonded portions, and
consequently to securely prevent degradation with time in the face
pressure. Moreover, the fibers obtained through the inorganic salt
method have a crystal structure so that the resulting advantage is
to provide higher strength at high temperatures, in comparison with
amorphous fibers obtained through a fusing method.
[0164] Consequently, it is possible to obtain a holding seal
material that is less susceptible to degradation in the face
pressure at high temperatures.
[0165] In accordance with the invention of claim 47 according to
the fifth group of the present invention, the precursor fibers are
formed into ceramics through a firing step to provide
alumina-silica based fibers. In this case, portions at which the
fibers are adjacent to each other with overlapped parts are bonded
through a liquid-state substance (that is, ceramic adhesive) that
has been formed into ceramics. In this manner, in the eleventh
invention of the fifth group of the present invention, since the
firing step and bonding process of the precursor fibers are carried
out simultaneously, it is possible to reduce the number of heating
steps in comparison with a case in which these processes are
carried out separately. Thus, it is possible to reduce the
manufacturing costs. Consequently, it becomes possible to
manufacture a holding seal material that is less susceptible to
degradation with time in the face pressure effectively at low
costs.
[0166] In accordance with the invention of claim 48 according to
the fifth group of the present invention, when the aggregation is
put under a high humidity environment with high moisture, water
vapor, which has entered the inside of the aggregation, is
condensed to moisture. The moisture is allowed to selectively
adhere to adjacent overlapped portions of the fibers through a
surface tension exerted thereon. Since the precursor fibers of the
alumina-silica based fibers are water-soluble so that the adjacent
overlapped portions are dissolved to a certain degree due to the
adhesion of the moisture. Then, since a liquid-state substance,
generated by such dissolution, has virtually the same composition
as the alumina-silica based fibers, this is actually allowed to
form a ceramic adhesive later. In other words, in accordance with
the above-mentioned present invention, the liquid-state substance,
which will forma ceramic adhesive later, is securely allowed to
adhere to the adjacent overlapped parts. Moreover, since the
liquid-state substance basically has virtually the same composition
as the alumina-silica based fibers, it has a high affinity for the
above-mentioned precursor fibers, and makes it possible to securely
bond the fibers mutually with high strength. Consequently, it
becomes possible to securely prevent degradation with time in the
face pressure.
[0167] In accordance with the invention of claim 49 according to
the fifth group of the present invention, a non-aqueous
liquid-state substance is atomized and supplied so that the
liquid-state substance is securely injected to the inside of the
aggregation, and allowed to selectively adhere to the adjacent
overlapped portions between the fibers through a function of
surface tension. In other words, in accordance with the
above-mentioned present invention, it is possible to allow the
liquid-state substance which will form a ceramic adhesive later to
securely adhere to the adjacent overlapped parts. Moreover, the
above-mentioned liquid-state substance is a non-aqueous substance;
therefore, even when this adheres to the precursor fibers of the
alumina-silica based fibers having a water-soluble property, this
does not dissolve the fibers. Therefore, it is possible to avoid a
possibility that the precursor fibers are dissolved too much with
the result that the strength of the fibers is lowered, and it is
not necessary to precisely set conditions for preventing the
over-dissolving. Consequently, it is possible to manufacture a
holding seal material comparatively easily. Moreover, since the
above-mentioned liquid-state substance contains inorganic elements
contained in the alumina-silica based fibers so that it exerts a
high affinity for the precursor fibers, and makes it possible to
securely bond the fibers mutually with high strength. Therefore, it
becomes possible to securely prevent degradation with time in the
face pressure.
[0168] In accordance with the invention of claim 50 according to
the fifth group of the present invention, the following operations
are obtained. Since the precursor fibers are un-sintered and
comparatively soft, these are not susceptible to cracks and the
like in a cutting portion even when an impact is exerted thereon
during a cutting process. Therefore, the alumina-silica based
fibers, obtained by sintering these, are excellent in mechanical
strength with stable end shapes. Thus, it becomes possible to
improve the initial face pressure. In contrast, in the case where
the precursor fibers are subjected to a cutting process after
having been sintered, the impact at the time of the cutting process
tends to cause cracks in the cutting portion of the alumina-silica
based fibers. This is because, in general, when precursor fibers
are sintered to form ceramics, the fibers become brittle although
they become hard. Consequently, not only the alumina-silica based
fibers come to have unstable end shapes, but also the mechanical
strength of the fibers is lowered.
[0169] In accordance with the invention of claim 51 according to
the fifth group of the present invention, the ceramic fibers, which
are aggregated three-dimensionally, are partially bonded to one
another by a ceramic adhesive so that this structure is less
susceptible to sliding and deviation among the mutual fibers, and
also less susceptible to reduction in the face pressure. Moreover,
since the fibers are partially bonded to one another in the
above-mentioned ceramic fiber aggregation, the voids inside thereof
are not entirely filled, with sufficient elasticity and
heat-insulating property being maintained. Moreover, since the
ceramic adhesive that is excellent in heat resistance is used, this
structure is less susceptible to reduction in the strength in the
bonded portions even when it is subjected to a high
temperature.
[0170] In accordance with the invention of claim 52 according to
the fifth group of the present invention, since this arrangement
contains ceramic fibers having a branching structure, it makes the
fibers less susceptible to sliding and deviation with each other in
comparison with an arrangement having no branching structure.
[0171] In accordance with the invention of claim 53 according to
the fifth group of the present invention, when comparison is made
between an arrangement which contains the ceramic fibers having a
branching structure and an arrangement which contain the ceramic
fibers having no branching structure, the former is less
susceptible to sliding and deviation among the fibers in comparison
with the latter, when these are aggregated three-dimensionally.
Thus, the former arrangement makes it possible to provide a fiber
aggregation that is less susceptible to degradation in the face
pressure.
[0172] The following description will be given of "operations" of
the sixth group of the present invention.
[0173] The sixth group of the present invention has an arrangement
in which a firing step is carried out after a spinning process, a
chopping process and a mat-forming process have been executed;
therefore, the cut face of the short fiber precursor is free from
the generation of chips, burs and micro-cracks, and this is then
subjected to the firing step so that it is possible to manufacture
alumina short fibers that are excellent in the mechanical strength,
and consequently to provide an alumina fiber aggregation that has a
sufficiently high initial face pressure, and is less susceptible to
degradation with time in the face pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0174] FIG. 1 is a perspective view showing a holding seal material
in an embodiment of the present invention.
[0175] FIG. 2 is a perspective view for describing manufacturing
processes of a catalyst converter in the above-mentioned
embodiment.
[0176] FIG. 3 is a cross-sectional view showing the catalyst
converter of the above-mentioned embodiment.
[0177] FIG. 4 is a cross-sectional view showing a catalyst
converter of another embodiment.
[0178] FIG. 5 is a schematic view for describing a firing step of a
mat-shaped fiber aggregation in embodiments according to a second
group of the present invention.
[0179] FIG. 6 is a graph showing degradation with time of face
pressure in examples and comparative examples according to the
second group of the present invention.
[0180] FIG. 7 is a cross-sectional view showing a catalyst
converter of another example according to the second group of the
present invention.
[0181] FIG. 8 is a schematic view showing a spinning device of an
embodiment according to a third group of the present invention.
[0182] FIG. 9 is a schematic view showing a nozzle metal mouth
shape and the cross-section of a fiber obtained through the nozzle
in the examples and comparative examples according to the third
group of the present invention.
[0183] FIG. 10 is an SEM photograph showing a cross-section of an
alumina-silica based fiber 6 of example 5 according to the third
group of the present invention.
[0184] FIG. 11 is an SEM photograph showing a cross-section of an
alumina-silica based fiber 6 of example 7 according to the third
group of the present invention.
[0185] FIG. 12 is an enlarged cross-sectional view of a main part
of a ceramic fiber of an embodiment according to a fifth group of
the present invention.
[0186] FIG. 13 is a graph showing the results of comparison tests
carried out on examples and comparative examples according to the
fifth group of the present invention.
[0187] FIG. 14 is an SEM photograph showing ceramic fibers forming
a holding seal material according to the fifth group of the present
invention.
[0188] FIG. 15 (a) is an SEM photograph showing a cut face of an
alumina short fiber which is used in an alumina fiber aggregation
manufactured through a manufacturing method of alumina fiber
aggregation according to a sixth group of the present invention,
and FIG. 15(b) is an SEM photograph showing a cut face of an
alumina short fiber which is used in an alumina fiber aggregation
manufactured through a conventional method.
[0189] FIG. 16 is a perspective view schematically showing one
example of a honeycomb filter.
[0190] FIG. 17(a) is a perspective view schematically showing one
example of a porous ceramic member forming the honeycomb filter
shown in FIG. 16, and FIG. 17(b) is a cross-sectional view taken
along line A-A thereof.
[0191] FIG. 18 is a plan view schematically showing one example of
a holding seal material.
EXPLANATION OF SYMBOLS
[0192] 1 catalyst converter
[0193] 2 catalyst carrier
[0194] 3 metal shell
[0195] 4 holding seal material
[0196] 6 alumina-silica based fiber
[0197] 6A precursor fiber
[0198] 7 ceramic adhesive
[0199] 17 flow path
[0200] 18 spinning stock solution
[0201] 19 nozzle
[0202] 19a metal mouth serving as nozzle discharging section
[0203] 20 catalyst carrier
[0204] 30 honeycomb filter
[0205] 33 seal material layer
[0206] 34 bonding layer
[0207] 35 ceramic block
[0208] 40 porous ceramic member
[0209] 41 filler
[0210] 42 through hole
[0211] 43 partition wall
[0212] 50 holding seal material
[0213] 51 base material portion
[0214] 52 convex fitting section
[0215] 53 concave fitting section
[0216] A1 extending direction
[0217] M1 fiber aggregation
[0218] S1 first face side
[0219] S2 second face side
DETAILED DISCLOSURE OF THE INVENTION
[0220] First, the following description will be given of
embodiments according to a first group of the present
invention.
[0221] Referring to FIGS. 1 to 3, the following description will be
given of a catalyst converter used for an automobile exhaust gas
purifying device according to one embodiment of the first group of
the present invention in detail.
[0222] This catalyst converter 1 according to the embodiment of the
first group of the present invention, shown in FIG. 3, is placed in
the middle of an exhaust pipe of an engine in a chassis of an
automobile. Since the distance from the engine to the catalyst
converter 1 is relatively short, exhaust gas having a high
temperature of approximately 700 to 900.degree. C. is supplied to
the catalyst converter 1. In the case where the engine is a
lean-burn engine, exhaust gas having a higher temperature of
approximately 900 to 1000.degree. C. is supplied to the catalyst
converter 1.
[0223] As shown in FIG. 3, the catalyst converter 1 of the
embodiment according to the first group of the present invention is
basically constituted by a catalyst carrier 2, a metal shell 3
covering the outer circumference of the catalyst carrier 2, and a
holding seal material 4 which is placed in a gap between the two
members 2 and 3.
[0224] The catalyst carrier 2 is made from a ceramic material which
is typically represented by cordierite and the like. The catalyst
carrier 2 is a column-shaped member having a circular shape in its
cross-section.
[0225] Moreover, the cross-sectional shape of the catalyst carrier
2 is not limited to a complete round shape, and may have, for
example, an elliptical shape or an elongated circular shape. In
this case, the cross-sectional shape of the metal shell 3 may be
changed to an elliptical shape or an elongated circular shape
correspondingly.
[0226] Moreover, the catalyst carrier 2 is preferably a honeycomb
structural body having a number of cells 5 that extend in the axis
direction. A noble metal based catalyst such as platinum and
rhodium, which can purify exhaust gas components, is carried on the
cell walls. Here, with respect to the catalyst carrier 2, in
addition to the above-mentioned cordierite carrier, for example, a
honeycomb porous sintered body and the like made of, for example,
silicon carbide, silicon nitride and the like, may be used.
[0227] Moreover, with respect to the catalyst carrier 2, in
addition to the cordierite carrier molded into a honeycomb shape
shown in the embodiment, a honeycomb porous sintered body made of,
for example, silicon carbide, silicon nitride and the like, may be
used.
[0228] In FIG. 3, the catalyst carrier 2 has a structure in which
either the inlet side or the outlet side of each cell 5 is sealed
with a sealing member; however, as shown in FIG. 4, a catalyst
carrier 20 having a structure in which neither the inlet side nor
the outlet side of each cell 5 is sealed with a sealing member may
be used.
[0229] Here, in the following, description will be given of the
catalyst converter 1 shown in FIG. 3.
[0230] With respect to the metal shell 3, in the case where, for
example, a press-fitting scheme is adopted upon assembling, a metal
cylinder member having an O-letter shape in its cross-section is
used. Here, with respect to a metal material forming the cylinder
member, metal, which is excellent in heat resistance and impact
resistance, (for example, steel products and the like, such as
stainless steel) , is preferably selected. In the case where a
so-called canning scheme is adopted instead of the press-fitting
scheme, members formed by dividing the above-mentioned metal
cylinder member having the O-letter shape in its cross-section into
a plurality of pieces along the axis direction (that is, clam
shells) are used.
[0231] In addition to this arrangement, in the case where a
wrap-tightening scheme is adopted upon assembling, for example, a
metal cylinder member having a C-letter shape or a U-letter shape
in its cross-section, that is, a metal cylinder member having a
slit (opening section) extending along the so-called axis direction
at only one portion, is used. In this case, upon assembling the
catalyst carrier 2, a structure in which the holding seal material
4 is secured to the catalyst carrier 2 is housed inside the metal
shell 3, and in this state, the metal shell 3 is wrapped and
tightened, and the opening ends thereof is then joined (by welding,
bonding, bolt-fastening and the like) Joining works such as
welding, bonding and bolt-fastening are carried out in the same
manner, also in the case where the canning scheme is adopted.
[0232] As shown in FIG. 1, the holding seal material 4 is a
mat-shaped member having an elongated shape, and a convex fitting
section 11 is placed on its one end, and a concave fitting section
12 is placed on the other end. As shown in FIG. 2, upon wrapping
onto the catalyst carrier 2, the convex fitting section 11 is just
engaged with the concave fitting section 12.
[0233] Moreover, the shape of the holding seal material 4 may be
desirably modified. For example, by omitting the concave and convex
fitting sections 11, 12, a simpler shape may be used.
[0234] The holding seal material 4 of the embodiment according to
the first group of the present invention is constituted by ceramic
fibers aggregated into a mat shape (that is, a fiber aggregation)
serving as a main element. With respect to the above-mentioned
ceramic fibers, in the embodiment according to the first group of
the present invention, alumina-silica based fibers 6 are used. In
this case, alumina-silica based fibers 6 in which the mullite
crystal content is set in a range of 0% by weight or more to 10% by
weight or less are preferably used. Such a chemical composition
makes it possible to reduce the amorphous component, and
consequently to provide excellent heat resistance; thus, it becomes
possible to provide a high repulsive force upon application of a
compressive load. Therefore, even when these fibers are subjected
to a high temperature while being placed in the gap, it is possible
to make them less susceptible to reduction in the face
pressure.
[0235] The quantity of alumina in the alumina-silica based fibers 6
is preferably set in a range of 40 to 100% by weight, and the
quantity of silica is preferably set in a range of 0 to 60% by
weight.
[0236] Moreover, the lower limit of the average fiber diameter of
the alumina-silica based fibers 6 is set to approximately 3 .mu.m,
and the upper limit thereof is set to approximately 25 .mu.m, more
preferably, the lower limit of the average fiber diameter thereof
is set to approximately 5 .mu.m, and the upper limit thereof is set
to approximately 15 .mu.m. This is because, when the average fiber
diameter is too small, the fibers tend to cause a problem in which
the fibers are inhaled by the respiratory organs. The lower limit
of the average fiber length of the alumina-silica based fibers 6 is
set to approximately 0.1 mm, and the upper limit thereof is set to
approximately 100 mm, and more preferably, the lower limit of the
average fiber length thereof is set to approximately 2 mm, and the
upper limit thereof is set to approximately 50 mm.
[0237] Different from normal alumina-silica based fibers that have
a transparent whitish color, the alumina-silica based fibers 6 of
the embodiment according to the first group of the present
invention are characterized by a blackish color.
[0238] The alumina-silica based fibers 6 having "the blackish
color" include those having not only a black color (pitch-black)
but also a grayish black color.
[0239] Here, the alumina-silica based fibers 6 are preferably set
to have a brightness of N8 or less which is specified in JIS Z
8721.
[0240] In this case, N of the brightness refers to a symbol
determined as follows. By setting an optimal brightness of black to
0 while setting an optimal brightness of white to 10, the
respective colors between the brightness of black and the
brightness of white are divided into 10 in brightness, and
indicated by symbols of N0 to N10, so as to allow the sense of
brightness of colors in the same symbol to be represented by the
same rate.
[0241] In the actual measurements, each color is compared with
color notes corresponding to N0 to N10. In this case, the first
digit below the decimal point is set to 0 or 5.
[0242] The blackish color in which the alumina-silica based fibers
6 are colored is derived from carbon components contained in a
spinning stock solution.
[0243] The lower limit of the quantity of residual carbon
components in the alumina-silica based fibers 6 is set to 1% by
weight or more, preferably, the lower limit thereof is set to 1% by
weight with the upper limit being set to 20% by weight, and more
preferably, the lower limit thereof is set to 5% by weight with the
upper limit being set to 10% by weight. The quantity of residual
carbon components of less than 1% by weight tends to fail to
improve the mechanical strength sufficiently. In contrast, an
excessive quantity of residual carbon components tends to cause
degradation in the basic physical properties (for example, heat
resistance and the like) of the alumina-silica based fibers 6.
[0244] The quantity of carbon components can be calculated with
respect to the reference sample during the manufacturing process,
or by using a laser Raman spectrometer or based upon the intensity
ratio, etc. of X-rays, the quantity of carbon components can be
calculated.
[0245] The fiber tensile strength of the alumina-silica based
fibers 6 is preferably set to 1.2 GPa or more, more preferably
1.5GPa or more. The fiber bending strength thereof is preferably
set to 1.0 GPa or more, more preferably 1.5 GPa or more. The
breaking strength is set to 0.8 MN/m.sup.3/2 or more, more
preferably 1.3 MN/m.sup.3/2 or more. This is because increasing the
values of the fiber tensile strength, fiber bending strength and
breaking strength makes it possible to provide alumina-silica based
fibers 6 that can resist tension and bending sufficiently, and are
flexible and less susceptible to fracturing.
[0246] Additionally, the alumina-silica based fibers 6 of the
embodiment according to the first group of the present invention
contain carbon components in the fibers so that it is considered
that crystallization is allowed to progress in the entire
alumina-silica based fibers 6, thereby increasing the tensile
strength.
[0247] In addition to a complete round shape, the cross-sectional
shape of the alumina-silica based fibers 6 may be set to a deformed
cross-sectional shape (such as an elliptical shape, an elongated
circular shape and a generally-triangular shape).
[0248] The lower limit of the thickness of the holding seal
material 4 in the state prior to the assembling process is
preferably set to approximately 1.1 times greater than a gap
between the catalyst carrier 2 and the metal shell 3, more
preferably approximately 1.5 times greater than the gap. Moreover,
the upper limit of the thickness of the holding seal material 4 is
preferably set to approximately 4.0 times greater than a gap
between the catalyst carrier 2 and the metal shell 3, more
preferably approximately 3.0 times greater than the gap. The
above-mentioned thickness of less than 1.1 times fails to provide a
high carrier holding property, resulting in the possibility of
deviation and backlash of the catalyst carrier 2 with respect to
the metal shell 3. Since this case of course fails to provide a
high sealing property, leakage of exhaust gas tends to occur from
the gap portion, failing to achieve a high pollution-preventive
property. Moreover, the thickness exceeding 4.0 times makes it
difficult to install the catalyst carrier 2 in the metal shell 3
especially when the fitting-in scheme is adopted. Therefore, this
case tends to fail to improve the assembling property.
[0249] The lower limit of GBD (bulk density) of the holding seal
material 4 after the assembling process is preferably set to 0.10
g/cm.sup.3, and the upper limit thereof is preferably set to 0.30
g/cm.sup.3; moreover, the lower limit of the above-mentioned GBD is
more preferably set to 0.10 g/cm.sup.3, and the upper limit thereof
is more preferably set to 0.25 g/cm.sup.3. When the value of GBD is
extremely small, it sometimes becomes difficult to achieve a
sufficiently high initial face pressure. In contrast, when the
value of GBD is extremely great, the quantity of alumina-silica
based fibers 6 to be used as a material increases, and tends to
cause high costs.
[0250] The initial face pressure of the holding seal material 4 in
the assembled state is set to 50 kPa or more, more preferably 70
kPa or more. This is because, when the value of the initial face
pressure is high, it is possible to maintain a preferable holding
property of the catalyst carrier 2, even in the event of
degradation with time in the face pressure.
[0251] Here, the holding seal material 4 may be subjected to a
needle punching process, a resin impregnation process and the like,
if necessary. The application of these processes makes it possible
to compress the holding seal material 4 in the thickness direction
and consequently to make it thinner.
[0252] Next, description will be given of the sequence of processes
for manufacturing a catalyst converter 1 according to the first
group of the present invention.
[0253] First, an aluminum salt solution, silica sol and an organic
polymer are mixed to form a spinning stock solution. In other
words, the spinning stock solution is prepared through an inorganic
salt method. The aluminum salt solution, which forms a source of
alumina, also serves as a component for applying viscosity to the
spinning stock solution.
[0254] Here, with respect to such an aqueous solution, an aqueous
solution of basic aluminum salt is preferably selected. The silica
sol, which serves as a silica source, also serves as a component
for giving high strength to the fibers. The organic polymer, which
is a component serving as a fiber-drawing property applying agent
to the spinning stock solution, is also a component that serves as
a carbon source for giving preferable mechanical strength to the
alumina-silica based fibers 6 in the embodiment according to the
first group of the present invention. With respect to the organic
polymer, a straight chain polymer containing carbon, such as PVA
(polyvinyl alcohol) , may be used. Here, with respect to the
component serving as a carbon source, not limited to the straight
chain polymer, any component having a comparatively low molecular
weight without a chain structure (which is not a polymer) may be
selected as long as it contains carbon.
[0255] Next, by condensing under vacuum the resulting spinning
stock solution, the spinning stock solution is prepared so as to
have a concentration, temperature and viscosity suitable for the
spinning process. In this case, the spinning stock solution, which
had a concentration of approximately 20% by weight, is preferably
condensed to approximately 30 to 40% by weight. Moreover, the
viscosity thereof is preferably set to 10 to 2000 Poise.
[0256] Further, when the spinning stock solution thus prepared is
discharged into air through a nozzle of a spinning device, a
precursor fiber, which has a cross-sectional shape that is
analogous to the nozzle metal mouth shape, is continuously
obtained. The precursor fiber, thus subjected to the spinning
process, is successively wound up while being extended. In this
case, for example, a dry-type pressurizing spinning method is
preferably adopted.
[0257] Moreover, carbon components contained in the precursor
fibers thus obtained need not be derived from the organic polymer
added thereto as the fiber-drawing property applying agent, and may
be derived from a carbon source applied thereto separately. In this
case, not limited to only the organic substance such as an organic
polymer, for example, an inorganic substance such as carbon may be
used.
[0258] Next, the precursor fiber is sintered through a firing step
to be formed into ceramics (crystallized) so that the precursor
fiber is hardened to obtain an alumina-silica based fiber 6.
[0259] In the firing step, it is necessary to heat the precursor
fiber under an environment which makes it difficult to carry out an
oxidizing reaction on the carbon component (that is, the
above-mentioned organic polymer) contained in the precursor fiber.
More specifically, in the embodiment according to the first group
of the present invention, the heating step is carried out in a
nitrogen atmosphere that is a typical inert atmosphere.
[0260] Here, the environment that makes it difficult to carry out
an oxidizing reaction on the carbon component is not necessarily
limited to an inert atmosphere, and includes, for example, an
atmosphere having a reduced pressure. When the firing step is
carried out in a reduced-pressure atmosphere, it is possible to
suppress the progress of the oxidizing reaction in comparison with
a case in which the firing step is carried out in a normal-pressure
atmosphere.
[0261] Moreover, the firing step may be carried out in an inert
atmosphere other than nitrogen, such as argon, or may be carried
out in a reduced-pressure inert atmosphere.
[0262] Upon carrying out a heating step in a nitrogen atmosphere,
the lower limit of the temperature is set to 1000.degree. C., more
preferably 1050.degree. C., and the upper limit of the temperature
is set to 1300.degree. C., more preferably 1250.degree. C.
[0263] The heating temperature of less than 1000.degree. C. tends
to cause an insufficient sintering step of the precursor fiber,
resulting in difficulty in stably providing an alumina-silica based
fiber 6 having high strength. In contrast, even when the heating
temperature is set so as to exceed 1300.degree. C., the
alumina-silica based fiber 6 is not allowed to have high strength
especially, and causes degradation in economical efficiency.
[0264] In other words, in the manufacturing method of
alumina-silica based fibers according to the first group of the
present invention, the heating step may be carried out on the
precursor fibers in an inert atmosphere and/or under a
reduced-pressure, in a firing step. In accordance with the
manufacturing method of alumina-silica based fibers according to
the first group of the present invention, it is possible to stably
provide alumina-silica based fibers having excellent mechanical
strength.
[0265] Successively, the long fibers of the alumina-silica based
fibers 6 obtained from the above-mentioned respective steps are
chopped into a predetermined length to form shorter fibers in a
certain extent. Thereafter, the short fibers are collected, untied
and laminated, or a fiber-dispersed solution, obtained by
dispersing the short fibers in water, is poured into a mold, and
pressed and dried so that a mat-shaped fiber aggregation is
obtained. Further, this fiber aggregation is punched out into a
predetermined shape to form a holding seal material 4 having a
blackish color.
[0266] Then, the holding seal material 4 is impregnated with an
organic binder, if necessary, and the resulting holding seal
material 4 may then be compressed and molded in the thickness
direction. With respect to the organic binder used in this case,
polyvinyl alcohol, acrylic resin and the like may be used, in
addition to latex and the like such as acrylic rubber and nitrile
rubber and the like.
[0267] Moreover, the holding seal material 4 is wrapped around the
outer circumferential face of the catalyst carrier 2 and secured by
the organic tape 13. Thereafter, this is subjected to a
press-fitting, canning or wrap-tightening step to complete a
desired catalyst converter 1.
[0268] Consequently, in accordance with the embodiment according to
the first group of the present invention, the following effects can
be obtained.
[0269] The alumina-silica based fibers 6, used in the holding seal
material 4, have a blackish color derived from carbon components,
and is excellent in mechanical strength such as the fiber tensile
strength, fiber bending strength and fracture toughness. Therefore,
the application of these fibers makes it possible to achieve a
holding seal material 4 which has a high initial face pressure, and
is less susceptible to degradation with time in the face pressure.
Consequently, it becomes possible to obtain a catalyst converter 1
which is excellent in the holding property of the catalyst carrier
2 and sealing property.
[0270] In the case where the catalyst converter 1 is constituted by
using the blackish alumina-silica based fibers 6, even if a
substance having a blackish color such as soot has adhered to the
holding seal material 4, a change in the external appearance of the
holding seal material 4 is hardly noticeable. In other words, since
the holding seal material 4 originally has a blackish color, no
major change occurs in color before and after the application. This
point is advantageous in that any impression of "deteriorated" or
"stained" is not given to the user.
[0271] In accordance with the manufacturing method of the
embodiment according to the first group of the present invention,
the firing step for sintering the precursor fibers is executed by
carrying out a heating step under an environment which makes it
difficult to carry out an oxidizing reaction on the carbon
component contained in the precursor fibers. Therefore, it is
possible to allow much carbon components to remain in the
alumina-silica based fibers 6, and consequently to securely provide
alumina-silica based fibers 6 that are excellent in mechanical
strength with ease.
[0272] In accordance with the manufacturing method of the
embodiment according to the first group of the present invention,
an inexpensive nitrogen atmosphere is used as the inert atmosphere
in which the firing step is carried out. For this reason, it is
possible to reduce manufacturing costs of the holding seal material
4. Moreover, since the heating step is carried out by setting the
firing temperature within the above-mentioned preferable range, it
becomes possible to stably obtain alumina-silica based fibers 6
with high strength.
[0273] In accordance with the manufacturing method of the
embodiment according to the first group of the present invention,
the carbon component contained in the precursor fibers is derived
from the organic polymer that has been added to the spinning stock
solution as a fiber-drawing property applying agent. Therefore, it
is not necessary to especially add carbon sources to the spinning
stock solution in a separated manner, thereby making it possible to
eliminate the necessity of greatly modifying the composition of the
spinning stock solution. Thus, it is possible to preliminarily
avoid imbalance in the stock solution composition, and consequently
to prevent degradation in the basic physical properties in the
alumina-silica based fibers 6. Moreover, since no carbon source
needs to be added, it becomes possible to reduce the manufacturing
costs. Furthermore, since the above-mentioned organic polymer is
easily dispersed in the spinning stock solution evenly, the carbon
sources are evenly dispersed in the precursor fibers. Consequently,
the resulting alumina-silica based fibers 6 are allowed to have an
even residual carbon content, and less susceptible to irregularity
in the mechanical strength.
[0274] Moreover, the embodiment according to the first group of the
present invention has exemplified a case where the holding seal
material 4 according to the first group of the present invention is
applied to a catalyst converter 1 used for an exhaust gas purifying
device; however, the holding seal material 4 according to the first
group of the present invention may of course be applied to devices
other than the catalyst converter 1 used for an exhaust gas
purifying device, such as a diesel particulate filter (DPF) , a
catalyst converter used for a fuel cell modifier and the like.
[0275] The following description will be given of an embodiment
according to a second group of the present invention.
[0276] Referring to FIGS. 1 to 6, the following description will be
given of a catalyst converter used for an automobile exhaust gas
purifying device in accordance with one embodiment of the second
group of the present invention in detail.
[0277] This catalyst converter 1 according to the embodiment of the
second group of the present invention, shown in FIG. 3, is
substantially the same as the catalyst converter according to the
first group of the present invention, and formed from a catalyst
carrier 2, a metal shell 3 covering the outer circumference of the
catalyst carrier 2, and a holding seal material 4 which is placed
in a gap between the two members 2 and 3.
[0278] Moreover, in the same manner as a catalyst converter 1 of
another example shown in FIG. 7, this converter may have a
structure in which: the holding seal material 4 is constituted by a
plurality of sheets (two in this case) of fiber aggregations M1
having mutually different crystallization rates, and these fiber
aggregations M1 may be superposed and bonded to each other. In this
case, the fiber aggregation M1 having a smaller crystallization
rate needs to be made in contact with the metal shell 3, and the
fiber aggregation M1 having a greater crystallization rate needs to
be made in contact with the catalyst carrier 2.
[0279] Here, with respect to the catalyst carrier 2 and the metal
shell 3, the same members that have been explained in the catalyst
converter according to the first group of the present invention may
be used; therefore, the description thereof is omitted.
[0280] Moreover, not limited to a complete round shape, the
cross-sectional shape of the catalyst carrier 2 may be set to, for
example, an elliptical shape or an elongated circular shape. In
such a case, the cross-sectional shape of the metal shell 3 may be
modified to an elliptical shape or an elongated circular shape in a
corresponding manner.
[0281] Moreover, with respect to the catalyst carrier 2, in
addition to a cordierite carrier molded into a honeycomb shape
shown in the embodiment, for example, a honeycomb porous sintered
body of, for example, silicon carbide or silicon nitride and the
like, may be used.
[0282] Furthermore, as shown in the catalyst carrier 20 shown in
FIG. 4, those having no sealing member may be used.
[0283] As shown in FIG. 1, the holding seal material 4 is a
mat-shaped member having an elongated shape, and a convex fitting
section 11 is placed on its one end, and a concave fitting section
12 is placed on the other end. As shown in FIG. 2, upon wrapping
onto the catalyst carrier 2, the convex fitting section 11 is just
engaged by the concave fitting section 12.
[0284] Moreover, the shape of the holding seal material 4 may be
desirably modified. For example, by omitting the recessed and
convex fitting sections 11, 12, a simpler shape may be used.
[0285] The holding seal material 4 in accordance with the
embodiment according to the second group of the present invention
is constituted by ceramic fibers aggregated into a mat shape (that
is, a fiber aggregation M1) serving as a main element. With respect
to the above-mentioned ceramic fibers, in the embodiment according
to the second group of the present invention, alumina-silica based
fibers 6 are used.
[0286] In the holding seal material 4 of the embodiment according
to the second group of the present invention, the mullite
crystallization rate is not even, but different depending on
portions thereof. In other words, in one sheet of fiber aggregation
M1, the crystallization rate on the first face side S1 portion and
the crystallization rate on the second face side S2 portion are
different from each other, and more specifically, the
crystallization rate is allowed to gradually increase from the
first face side S1 toward the second face side S2.
[0287] Here, the first face side S1 in the holding seal material 4
is a face side that is subjected to a firing step at a
comparatively low temperature, and is placed in a manner so as to
contact the metal shell 3 side on which heat resistance is not
required so much. Therefore, the first face side S1 may be regarded
as a low-temperature firing face or a shell-side contact face. The
second face side S2 is a face side that is subjected to a firing
step at a comparatively high temperature, and is placed in a manner
so as to contact the catalyst carrier 2 side on which heat
resistance is required. Therefore, the second face side S2 may be
regarded as a high-temperature firing face or a bearing-member side
contact face.
[0288] In this case, the difference between the crystallization
rate of the surface layer portion of the first face side S1 and the
crystallization rate of the surface layer portion of the second
face side S2 is preferably set to 3% by weight or more. More
specifically, the crystallization rate of the surface layer portion
of the first face side S1 is preferably set to 0 to 1% by weight,
and the crystallization rate of the surface layer portion of the
second face side S2 is preferably set to 1 to 10% by weight.
[0289] In the case where the crystallization rate of the surface
layer portion on the first face side S1 exceeds 1% by weight and in
the case where the crystallization rate of the surface layer
portion on the second face side S2 is less than 1% by weight, the
difference between the crystallization rates of the two sides
becomes too small, failing to obtain target characteristics. In the
case where the crystallization rate of the surface layer portion on
the second face side S2 exceeds 10% by weight, the heat resistance
of the corresponding portion might be lowered. Additionally, it is
preferable to set the crystallization rate of the surface layer
portion on the first face side S1 to 0% by weight, that is, it is
preferable to form the corresponding portion by using an amorphous
material.
[0290] Here, the above-mentioned crystallization rate is measured
based upon peaks of mullite by using X-ray diffraction; and
supposing that the material having no peak is set to 0% by weight
in crystallization rate, a peak measured by 100% mullite is set to
100% by weight in crystallization rate, and the corresponding
crystallization rate can be measured from a ratio between the value
at 100% by weight and a sampled value.
[0291] Moreover, the above-mentioned crystallization rate may be
obtained by calculating the weight ratio from the difference
between dissolving rates of mullite and silica in an HF
solution.
[0292] With respect to the quantity of alumina, the quantity of
silica in the alumina-silica based fibers 6, the average fiber
diameter of the alumina-silica based fibers 6 and the average fiber
length, these factors are preferably set in the same manner as
those explained in the catalyst converter according to the first
group of the present invention; therefore, the description thereof
is omitted.
[0293] With respect to the alumina-silica based fibers 6 located on
the second face side S2, it is preferable to set the fiber tensile
strength to 1.0 GPa or more, the fiber bending strength to 0.8 GPa
or more, and the elastic modulus to 9.5.times.10.sup.10 N/m.sup.2
or more, respectively. With respect to the alumina-silica based
fibers 6 located on the first face side S1, it is preferable to set
the fiber tensile strength to 2.0 GPa or more, the fiber bending
strength to 1.5 GPa or more, and the elastic modulus to
11.0.times.10.sup.10 N m.sup.2 or more, respectively. The reason
for this is because, as the fiber tensile strength, the fiber
bending strength and the like are increased, the alumina-silica
based fibers 6 come to have very strong resistance to tensile and
bending.
[0294] The cross-sectional shape of the alumina-silica based fibers
6, the thickness of the holding seal material 4 prior to the
assembling process, the GBD (bulk density) of the holding seal
material 4 after the assembling process and the initial face
pressure of the holding seal material 4 in the assembled state of
the embodiment according to the second group of the present
invention are preferably set in the same manner as those described
in the catalyst converter according to the first group of the
present invention; therefore, the description thereof is
omitted.
[0295] Here, such a holding seal material 4 may be subjected to a
needle punching process, a resin impregnation process, etc., if
necessary. By applying these processes, it becomes possible to
compress the holding seal material 4 in the thickness direction,
and consequently to make it thinner in the thickness direction.
[0296] The following description will be given of a sequence of
processes for manufacturing a catalyst converter 1 according to the
second group of the present invention.
[0297] First, a spinning stock solution is prepared in the same
manner as the method explained in the manufacturing method of the
catalyst converter according to the first group of the present
invention so that long fibers of the precursor fibers are
produced.
[0298] Successively, the long fibers of the precursor fibers are
chopped into a predetermined length to form shorter fibers in a
certain extent. Thereafter, the short fibers are collected, untied
and laminated, or a fiber-dispersed solution, obtained by
dispersing the short fibers in water, is poured into a mold, and
pressed and dried so that a mat-shaped fiber aggregation M1 is
obtained.
[0299] Following the above-mentioned laminating process, the fiber
aggregation M1 is subjected to a firing step so that the precursor
fibers are sintered, and formed into ceramics (crystallized). Thus,
the precursor fibers are hardened to form alumina-silica based
fibers 6. FIG. 5 shows an electric furnace 21 that is used as a
firing device in the embodiment according to the second group of
the present invention.
[0300] Here, the firing step may be carried out by using a firing
device other than the exemplified electric furnace 21.
[0301] The above-mentioned electric furnace 21 is a device for
continuously heating and sintering an object to be fired while it
is being transported in the horizontal direction. A net conveyor
belt 23 serving as a transporting means is housed in a main body 22
constituting the electric furnace 21. A mat-shaped fiber
aggregation M1 that is an object to be fired is placed on the net
conveyor belt 23. An upper-side electric heater 24 serving as a
first heating means is placed above the net conveyor belt 23 with a
gap therefrom, and a lower-side electric heater 25 serving as a
second heating means is placed below the net conveyer belt 23 with
a gap therefrom. These electric heaters 24, 25 are connected to a
power supply through a temperature-control means, which is not
shown. In this device, these two kinds of electric heaters 24 and
25 are individually temperature-controlled.
[0302] In the firing step, after a preliminary heating step
(preliminary process) has been carried out on the above-mentioned
fiber aggregation M1 in the electric furnace 21 that is maintained
in an atmospheric pressure that is a normal pressure, a main
heating step (firing step) is carried out in the electric furnace
21 that is maintained also in an atmospheric pressure that is a
normal pressure.
[0303] In this case, the temperature settings of these two kinds of
electric heaters 24, 25 are changed so as to provide a temperature
difference to a certain degree. In other words, the fiber
aggregation M1 is sintered with a difference being set between the
firing temperature on the first face side S1 and the firing
temperature on the second face side S2. Here, in the embodiment
according to the second group of the present invention, the set
temperature of the electric heater 24 on the upper side is higher
than the set temperature of the electric heater 25 on the lower
side.
[0304] In this case, the difference between the set temperatures at
the time of the firing step is preferably set to 100.degree. C. or
more, especially 200.degree. C. or more. The above-mentioned
temperature difference of less than 100.degree. C. fails to provide
a sufficient difference in the easiness of sintering between the
first face side S1 and the second face side S2, making it difficult
to provide a difference in the crystallization rates.
[0305] Moreover, the firing temperature of the first face side S1
is preferably set in a range of 800 to 1100.degree. C., and the
firing temperature of the second face side S2 is preferably set in
a range of 110.0 to 1400.degree. C.
[0306] The firing temperature on the first face side S1 of less
than 800.degree. C. fails to allow the sintering reaction to
progress sufficiently, failing to obtain the required mechanical
strength. When the firing temperature on the first face side S1
exceeds 1100.degree. C., or when the firing temperature on the
second face side S2 is less than 1100.degree. C., the difference in
the crystallization rate between the two sides becomes too small,
failing to provide target characteristics.
[0307] The firing temperature exceeding 1400.degree. C. on the
second face side S2 makes the crystallization to progress too
quickly, resulting in degradation in the mechanical strength and
heat resistance.
[0308] Moreover, the firing time (more specifically, the time
during which the maximum heating temperature is maintained) is
preferably set in a range of 10 to 60 minutes. If the firing time
is too short, the sintering reaction might not progress
sufficiently even when the temperature is set to be sufficiently
high. Consequently, it becomes impossible to obtain mechanical
strength required. If the firing time is too long, the production
efficiency is lowered, and the crystallization might progress too
quickly, resulting in degradation in the mechanical strength and
heat resistance.
[0309] In the succeeding punch-out process, the mat-shaped fiber
aggregation M1 that has been subjected to the firing step is
punched out into a predetermined shape to form a holding seal
material 4.
[0310] Then, after the holding seal material 4 has been impregnated
with an organic binder, if necessary, the holding seal material 4
may be further compressed, and molded in the thickness direction.
With respect to the organic binder used in this case, polyvinyl
alcohol, acrylic resin and the like may be used, in addition to
latex and the like such as acrylic rubber and nitrile rubber and
the like.
[0311] Further, the holding seal material 4 is wrapped around the
outer circumferential face of the catalyst carrier 2 and secured by
the organic tape 13. Thereafter, this is subjected to a
press-fitting, canning or wrap-tightening process to complete a
desired catalyst converter 1.
[0312] Here, the exemplified holding seal material 4 has a
structure, that is to say, in which its crystallization rate
differs along the thickness direction. In contrast, the holding
seal material in which its crystallization rate differs in the
length direction, or the holding seal material in which its
crystallization rate differs in the width direction, may be
provided. For example, when the latter holding seal material is
wrapped around the catalyst carrier 2, the catalyst carrier 2 is
allowed to have different crystallization rates between its one end
and the other end. In other words, the one end is allowed to have
excellent heat resistance, while the other end is allowed to have
excellent elasticity and flexibility. Therefore, when the end
portion on the side having a greater crystallization rate and
excellent heat resistance is placed so as to face the exhaust gas
flow-in side, it becomes possible to achieve a catalyst converter 1
having excellent resistance and wind erosion resistance.
[0313] Consequently, in accordance with the embodiment according to
the second group of the present invention, the following effects
can be obtained.
[0314] Normally, when the catalyst converter 1 is used, the
catalyst carrier 2, which is directly exposed to high-temperature
exhaust gas, comes to have a high temperature, while the
temperature of the metal shell 3 does not become so high as the
temperature of the catalyst carrier 2. Therefore, the face side
that is made in contact with the catalyst carrier 2 requires
especially high temperature resistance. By taking these facts into
consideration, the embodiment according to the second group of the
present invention has an arrangement in which the second face side
S2 having a relatively higher crystallization rate, that is, the
face side having excellent heat resistance, is made in contact with
the catalyst carrier 2. In contrast, the first face side S1 having
a relatively lower crystallization rate, that is, the face side
that is excellent in elasticity and flexibility although it is
inferior in heat resistance, is allowed to contact the metal shell
3. Therefore, the fibers at the portion contacting the catalyst
carrier 2 are less susceptible to brittleness, making it possible
to provide a holding seal material 4 which has a high initial face
pressure, and is less susceptible to degradation with time in the
face pressure. Moreover, since an elastic force is exerted at the
portion contacting the metal shell 3, it is possible to reduce the
occurrence of a gap with the metal shell 3, and consequently to
provide a holding seal material 4 that is excellent in the sealing
property.
[0315] As described above, it is possible to achieve a catalyst
converter 1 that is excellent in the holding property of the
catalyst carrier 2, and less susceptible to exhaust gas leakage,
and has good process efficiency.
[0316] The holding seal material 4 according to the second group of
the present invention comprises a sheet of fiber aggregation M1,
and the crystallization rate is gradually increased from the first
face side S1 toward the second face side S2 of the fiber
aggregation M1. Therefore, different from a structure constituted
by a plurality of fiber aggregations M1 having different
crystallization rates, it becomes possible to eliminate the
necessity of jobs for mutually superposing the fiber aggregations
M1 and for bonding these to each other, and consequently to reduce
the number of manufacturing processes. Thus, it becomes possible to
provide a holding seal material 4 that is easily manufactured.
[0317] Moreover, since it is possible to make the structure thinner
in comparison with a superposed structure having a plurality of
sheets, it becomes possible to place the structure in a narrow gap
comparatively with ease. Thus, it is possible to easily carry out
not only a wrap-tightening process, but also a fitting-in process
at the time of the canning operation.
[0318] Furthermore, in the superposed structure having a plurality
of sheets, exhaust gas might pass through the interface between the
fiber aggregations M1. In contrast, since this holding seal
material 4 has a single-sheet structure that is free from the
interface, it is not necessary to take the passage of exhaust gas
into consideration. Thus, it becomes possible to provide a device
having an excellent sealing property.
[0319] In this holding seal material 4, the crystallization rate of
the portion on the first face side S1 and the crystallization rate
of the portion on the second face side S2 are set in the
above-mentioned desirable range. Therefore, it is possible to
securely improve the face pressure characteristic and sealing
property, and to achieve a catalyst converter 1 having high
performances.
[0320] In a manufacturing method of the embodiment according to the
second group of the present invention, the firing step is carried
out with a gap being provided between the firing temperature of the
first face side S1 and the firing temperature of the second face
side S2 of the mat-shaped fiber aggregation M1. Therefore, it is
possible to securely manufacture a holding seal material 4 having
different crystallization rates on its surface and rear surface
comparatively with ease. Moreover, such a manufacturing method is
extremely suited for providing a holding seal material 4 having an
arrangement in which the crystallization rate is gradually
increased from the first face side S1 toward the second face side
S2 in a single sheet of fiber aggregation M1. Furthermore, a
conventional firing device is commonly applied to this
manufacturing method without the necessity of applying a special
firing device. Thus, it becomes possible to avoid an increase in
the facility costs.
[0321] In the embodiment according to the second group of the
present invention, the firing step is carried out with the firing
temperatures on the first face side S1 and the second face side S2
being set within the above-mentioned preferable range. Therefore,
it becomes possible to securely manufacture the holding seal
material 4 of the embodiment according to the second group of the
present invention in which the crystallization rate gradually
increases from the first face side S1 toward the second face side
S2.
[0322] Furthermore, the holding seal material according to the
second group of the present invention is provided as a holding seal
material that includes alumina-silica based fibers aggregated into
a mat shape as its constituent elements, and is placed in a gap
between the catalyst carrier and the metal shell that covers the
outer circumference of the catalyst carrier, and this holding seal
material may be provided as a catalyst-converter-use holding seal
material that is characterized by a structure in which the
first-face-side portion is made from an amorphous material and the
second-face-side portion is made from a crystal material.
[0323] With this arrangement, it becomes possible to achieve a
holding seal material for catalyst-converter-use that has an
excellent sealing property in addition to the advantages that it
has high initial face pressure, and is less susceptible to
degradation with time in the face pressure.
[0324] Here, the embodiment according to the second group of the
present invention has exemplified a case in which the holding seal
material 4 is applied to a catalyst converter 1 used for an
exhaust-gas-purifying device. However, the holding seal material 4
according to the second group of the present invention may of
course be applied to devices other than the catalyst converter 1
used for an exhaust-gas-purifying device, such as a diesel
particulate filter (DPF) and a catalyst converter used for a fuel
cell modifier.
[0325] The following description will be given of an embodiment
according to a third group of the present invention.
[0326] Referring to FIGS. 1 to 3, as well as FIGS. 8 and 9, the
following description will be given of a catalyst converter used
for an automobile exhaust gas purifying device in accordance with
one embodiment according to the third group of the present
invention in detail.
[0327] This catalyst converter 1 in accordance with the embodiment
of the third group of the present invention, shown in FIG. 3, is
virtually the same as the catalyst converter according to the first
group of the present invention, and constituted by a catalyst
carrier 2, a metal shell 3 covering the outer circumference of the
catalyst carrier 2, and a holding seal material 4 that is placed in
a gap between the two members 2 and 3.
[0328] Here, with respect to the catalyst carrier 2 and the metal
shell 3, the same members that have been explained in the catalyst
converter according to the first group of the present invention may
be used; therefore, the description thereof is omitted.
[0329] Moreover, not limited to a complete round shape, the
cross-sectional shape of the catalyst carrier 2 may be set to, for
example, an elliptical shape or an elongated circular shape.
[0330] Moreover, with respect to the catalyst carrier 2, in
addition to a cordierite carrier molded into a honeycomb shape
shown in the embodiment, for example, a honeycomb porous sintered
body of, for example, silicon carbide or silicon nitride and the
like, may be used.
[0331] Furthermore, as shown in the catalyst carrier 20 shown in
FIG. 4, those having no sealing member may be used.
[0332] As shown in FIG. 1, the holding seal material 4 is a
mat-shaped member having an elongated shape, and a convex fitting
section 11 is placed on its one end, and a concave fitting section
12 is placed on the other end. As shown in FIG. 2, upon wrapping
onto the catalyst carrier 2, the convex fitting section 11 is just
engaged by the concave fitting section 12.
[0333] The holding seal material 4 in accordance with the
embodiment according to the third group of the present invention is
constituted by ceramic fibers aggregated into a mat shape (that is,
a fiber aggregation) serving as a main element. With respect to the
above-mentioned ceramic fibers, in the embodiment according to the
third group of the present invention, alumina-silica based fibers 6
are used. In this case, the alumina-silica based fibers 6, which
have a mullite crystal content in a range of 0% by weight or more
to 10% by weight or less, are preferably used. The fibers having
such a chemical composition make it possible to provide excellent
heat resistance and a high repulsive force upon application of a
compressing load, because the amorphous component thereof becomes
smaller. Therefore, even when it is subjected to a high temperature
while being placed in the gap, the possibility of reduction in the
face pressure to be generated is comparatively lowered.
[0334] The chemical composition of the alumina-silica based fibers
6 is preferably set so that alumina is in a range of 68 to 83% by
weight and silica is in a range of 32 to 17% by weight, and
specifically, Al.sub.2O.sub.3:SiO.sub.2=72:28 is more
preferred.
[0335] If alumina is less than 68% by weight, or if silica exceeds
32% by weight, it might be difficult to improve the heat resistance
and the repulsive force upon application of a compressing load
sufficiently. In the case where alumina exceeds 83% by weight, or
in the case where silica is less than 17% by weight also, it might
be difficult to improve the heat resistance and the repulsive force
upon application of a compressing load sufficiently.
[0336] With respect to the average fiber diameter and the average
fiber length of the alumina-silica based fibers 6, these are
preferably set in the same manner as explained in the catalyst
converter according to the first group of the present invention;
therefore, the description thereof is omitted.
[0337] Moreover, the tensile strength of each of the alumina-silica
based fibers 6 is preferably set to 0.1 GPa or more, more
preferably 0.5 GPa or more.
[0338] Here, the alumina-silica based fibers 6 of the embodiment
according to the third group of the present invention needs to have
a non-circular shape in the cross-section thereof, that is, a
deformed shape in the cross-section thereof. Some examples of the
fibers having a deformed cross-sectional shape are shown on the
right-side column of a table in FIG. 9. A fiber having a virtually
elliptical cross-section (fiber having an elliptical cross-section)
is shown on the first row in the right-side column as one example
of the fiber having a flat cross-sectional shape. A fiber having a
cross-section with a virtually cocoon-shape (fiber having a
cocoon-shaped cross-section) is shown on the second row in the
right-side column as one example of the fiber having a flat
cross-sectional shape. Moreover, a hollow fiber having an empty
space inside thereof is shown on the third row in the right-side
column.
[0339] Moreover, not limited to the exemplified elliptical shape
and cocoon shape, the cross-sectional shape of the
alumina-silica-based fibers 6 may be set to, for example, an
elongated circular shape, a triangular shape or a rectangular
shape.
[0340] Furthermore, not limited to the exemplified hollow shape,
the cross-sectional shape of the alumina-silica based fibers 6 may
be set to, for example, a shape having two or more spaces inside
thereof and the like.
[0341] In the catalyst converter according to the third group of
the present invention, the thickness of the holding seal material 4
prior to the assembling process, the GBD (bulk density) of the
holding seal material 4 after the assembling process and the
initial face pressure of the holding seal material 4 in the
assembled state are preferably set in the same manner as those
described in the catalyst converter according to the first group of
the present invention; therefore, the description thereof is
omitted.
[0342] Here, the holding seal material 4 may be subjected to a
needle punching process, a resin impregnation process, etc., if
necessary. By applying these processes, it becomes possible to
compress the holding seal material 4 in the thickness direction,
and consequently to make it thinner in the thickness direction.
[0343] The following description will be given of a sequence of
processes for manufacturing a catalyst converter 1 according to the
third group of the present invention.
[0344] First, a spinning stock solution 18 is prepared by mixing an
aluminum salt aqueous solution, silica sol and an organic polymer.
In other words, the spinning stock solution 18 is prepared by using
an inorganic salt method. The aluminum salt aqueous solution, which
serves as an alumina source, also serves as a component giving
viscosity to the spinning stock solution 18. With respect to such
an aqueous solution, an aqueous solution of basic aluminum salt is
preferably selected. The silica sol, which serves as a silica
source, also serves as a component for giving high strength to the
fibers. The organic polymer is a component for giving a
fiber-drawing property to the spinning stock solution 18.
[0345] In the embodiment according to the third group of the
present invention, a water soluble plasticizer is preferably
further added to the spinning stock solution 18 as a Barus'-ratio
reducing agent at the time of nozzle-discharging. The lower limit
of the amount of addition of the above-mentioned plasticizer is
preferably set to 0.1% by weight with the upper limit thereof being
preferably set to 10% by weight, and particularly, the lower limit
thereof is more preferably set to 0.1% by weight with the upper
limit being set to 3% by weight.
[0346] When the above-mentioned amount of addition is less than
0.1% by weight, the elastic modulus is not lowered sufficiently
with the result that the expected Barus' ratio reducing effect by
the addition of the plasticizer might not be obtained. In contrast,
the amount of addition exceeding 10% by weight tends to cause
adverse effects on the physical properties of the alumina-silica
based fibers 6 as the ratio of non-ceramic components in the
spinning stock solution 18 increases.
[0347] Moreover, the Barus' ratio may be reduced by using a method
other than the method of adding a water-soluble substance to the
spinning stock solution 18.
[0348] With respect to the above-mentioned plasticizer, a
water-soluble organic substance is preferably selected, and more
specifically, glycol ethers with high viscosity may be preferably
selected. The organic substances of this type make it possible to
securely reduce the elastic modulus of the spinning stock solution
18 even by a small amount of addition. Moreover, glycol ethers are
completely burned to disappear by heat that is applied up to the
end of the sintering step carried out after the spinning
process.
[0349] Here, examples of glycol ethers that can be used as the
plasticizer include: tetraethylene glycol monobutyl ether
(3,6,9,12-tetraoxahexa decanol) , triethylene glycol monobutyl
ether (3,6,9-trioxatridecanol), diethylene glycol monobutyl ether
(2-(2-butoxyethoxy) ethanol), propylene glycol monobutyl ether,
ethylene glycol monobutyl ether, propylene glycol monomethyl ether
(1-methoxy-2-propanol) , a mixture of propylene glycol monomethyl
ether acetate and acetic acid and the like. Besides the
above-mentioned glycol ethers, for example, a viscous organic
substance such as polyethylene glycol and glycerin and the like may
be used as the plasticizer. Moreover, only one kind. of these
organic substances listed here may be added to the spinning stock
solution 18; however, two kinds or more of these may be combined
and added thereto.
[0350] Next, the resulting spinning stock solution 18 is condensed
under vacuum so as to provide a spinning stock solution 18 that has
been adjusted to have a density, temperature and viscosity suited
for the spinning process. Here, the spinning stock solution 18,
which has been set to a concentration of approximately 20% by
weight, is condensed and preferably set to approximately 30 to 40%
by weight. Moreover, the viscosity is preferably set to 10 to 1500
Poise.
[0351] Moreover, the spinning stock solution 18 thus prepared is
discharged into the air through a nozzle 19 of a spinning device 20
shown in FIG. 8 so that a precursor fiber 6A, which has a
cross-sectional shape that is approximated by the cross-sectional
shape of a metal mouth 19a serving as a nozzle discharging section,
is continuously obtained. More specifically, the precursor fiber
6A, which has a fiber with an elliptical cross-section as shown on
the first row in the right-side column, is produced by using a
metal mouth 19a having a rectangular cross-section shown on the
first row in the right-side column. The precursor fiber 6A having a
cocoon cross-sectional shape shown on the second row in the
right-side column is produced by using a metal mouth 19a having a
virtually dumbbell shaped cross-section shown on the second row in
the left-side column of the table in FIG. 9. The precursor fiber 6A
having a hollow cross-sectional shape shown on the third row in the
right-side column is produced by using a metal mouth 19a having a
virtually C-letter shape shown on the third row on the left-side
column of the table in FIG. 9.
[0352] Here, in the case of the fiber having an elliptical
cross-sectional shape as shown on the first row on the right side
of the table in FIG. 9, the degree of oblateness (ratio of a minor
axis and a major axis) is preferably set in a range of 1:1.1 to
1:3. The fiber having a degree of oblateness exceeding 1:3 might
cause a reduction in the initial face thickness.
[0353] Then, the precursor fiber 6A, thus spun out through the
metal mouth 19a, is successively taken up while being extended. In
this case, for example, a dry-type pressurizing spinning method may
be preferably used.
[0354] Preferably, dry hot air is blown to the precursor fiber 6A
immediately after it has been discharged from the metal mouth 19a.
In this case, it is preferable to blow dry hot air, and more
preferable to blow hot air having a temperature of normal
temperature or more. With this arrangement, it becomes possible to
dry the precursor fiber 6A quickly with high efficiency.
[0355] In the case of the spinning device 20 shown in FIG. 8, a
flow path 17 through which dried hot air is allowed to flow is
formed in the nozzle 19. A dry air discharge port, which opens
downward (in the same direction as the nozzle 19) at a position
just next to the metal mouth 19a of the nozzle 19, is formed on one
end of the flow path 17. The other end of the flow path 17 is
connected to an air source through a pipe which is not shown, not
shown. Therefore, when pressurized air, which has been heated and
dried, is supplied, dried hot air is discharged in a forward
direction with respect to the discharging direction (in other
words, extending direction A1: downward direction in FIG. 8) of the
precursor fiber 6A. As a result, the precursor fiber 6A,
immediately after discharged, is dried by hot air. The temperature
of the dried hot air is preferably set to 30 to 100.degree. C., and
the wind speed is preferably set to 1 to 50 m/s.
[0356] Next, the precursor fiber 6A is sintered through a firing
step to be formed into ceramics (crystallized) so that the
precursor fiber 6A is hardened to obtain an alumina-silica based
fiber 6. Here, the plasticizer is completely burned to disappear by
heat at this time, and hardly remains in the alumina-silica based
fibers 6.
[0357] In the above-mentioned firing step, it is preferable to set
the firing condition so as to make the mullite crystal content in
the resulting alumina-silica based fibers 6 having 10% by weight or
less. For example, the firing temperature in the firing step is
preferably set in a range of 1000 to 1300.degree. C. The firing
temperature of less than 1000.degree. C. fails to completely dry
and sinter the precursor fibers 6A, with the result that it becomes
difficult to securely provide excellent heat resistance and a high
repulsive force at the time of application of a compressing load to
the holding seal material 4. In contrast, in the case of a firing
temperature exceeding 1300.degree. C., the mullite crystallization
in the alumina-silica based fiber 6 is allowed to easily progress.
For this reason, it becomes difficult to reduce the mullite crystal
content to 10% by weight or less, and consequently, it may not be
able to securely provide excellent heat resistance and a high
repulsive force at the time of application of a compressing load to
the holding seal material 4.
[0358] Successively, the long fibers of the alumina-silica based
fiber 6 that have been obtained through the above-mentioned
respective processes are chopped into a predetermined length to
form shorter fibers in a certain extent. Thereafter, the short
fibers are collected, untied and laminated, or a fiber-dispersed
solution, obtained by dispersing the short fibers in water, is
poured into a mold, and pressed and dried so that a mat-shaped
fiber aggregation is obtained. Further, this fiber aggregation is
punched out into a predetermined shape to form a holding seal
material 4.
[0359] Thereafter, the holding seal material 4 is impregnated with
an organic binder, if necessary, and the resulting holding seal
material 4 may then be compressed and molded in the thickness
direction. With respect to the organic binder used in this case,
polyvinyl alcohol, acrylic resin and the like may be used, in
addition to latex and the like such as acrylic rubber and nitrile
rubber and the like.
[0360] Moreover, the holding seal material 4, obtained by punching
out the above-mentioned fiber aggregation into a predetermined
shape, is wrapped around the outer circumferential face of the
catalyst carrier 2 and secured by the organic tape 13. Thereafter,
this is subjected to a press-fitting, canning or wrap-tightening
process to complete a desired catalyst converter 1.
[0361] Consequently, in accordance with the embodiment according to
the third group of the present invention, the following effects can
be obtained.
[0362] The holding seal material 4 of the embodiment according to
the third group of the present invention is constituted by
alumina-silica based fibers 6 having a cross-section that is not a
circular shape, but a deformed shape. The fibers of this type
become more flexible in comparison with fibers having a circular
cross-sectional shape. In other words, since the alumina-silica
based fiber 6 has a non-circular shape, it has such a
characteristic that it is bent in a specific direction
comparatively easily. This characteristic makes the alumina-silica
based fibers 6 less susceptible to breaking, and allows them to
maintain the repulsive force for a long time. Thus, in case of the
holding seal material 4 manufactured by using such alumina-silica
based fibers 6, it becomes possible to reduce the possibility of
degradation with time in the face pressure. Therefore, it is
possible to achieve a catalyst converter 1 which is excellent in
the holding property of the catalyst carrier 2 and the sealing
property against exhaust gas.
[0363] Moreover, in the case of the holding seal material 4 using
fibers having an elliptical cross-sectional shape and fibers having
a cocoon-shaped cross-section, the alumina-silica based fibers 6
are easily engaged with one another, so that the alumina-silica
based fibers 6 are less susceptible to sliding and deviation.
[0364] Therefore, it becomes possible to reduce degradation in the
face pressure.
[0365] Moreover, the hollow fibers are excellent in heat-insulating
property in comparison with those having no space inside thereof.
Therefore, the holding seal material 4 using such fibers makes it
possible to reduce the quantity of heat that is released from the
catalyst carrier 2 to the metal shell 3, and consequently to carry
out a catalyst reaction with high efficiency. Furthermore, the
hollow fibers make it possible to absorb and attenuate sound and
vibration by the spaces inside the fibers. Therefore, the
application of the holding seal material 4 using these makes it
possible to achieve a catalyst converter 1 that is excellent in
noise insulating and vibration insulating properties.
[0366] In accordance with the manufacturing method of the
embodiment according to the third group of the present invention, a
spinning stock solution 18 is discharged through the metal mouth
19a of a nozzle 19 having a non-circular shape in its
cross-section. Immediately after discharged from the metal mouth
19a, the precursor fiber 6A has a cross-sectional shape to which
the cross-sectional shape of the metal mouth 19a is reflected in a
certain degree. However, as time has elapsed since the discharge,
the cross-sectional shape thereof tends to have a roundness (in
other words, is subjected to the Barus' effect) due to the
influence of a surface tension exerted on the precursor fiber 6A so
that the cross-section of the precursor fiber 6A comes to have a
circle-wise shape. Therefore, in the embodiment according to the
third group of the present invention, dry hot air is blown thereto
in a state immediately after the discharge so that the precursor
fiber 6A is dried and solidified by being removed its moisture in
the precursor fiber 6A. Consequently, it becomes possible to
maintain a desired cross-sectional shape given by the metal mouth
19a, and consequently to obtain an alumina-silica based fiber 6
having a non-circular sectional shape comparatively easily. In
other words, this manufacturing method is a desirable method to
obtain the above-mentioned holding seal material 4.
[0367] In accordance with the manufacturing method of the
embodiment according to the third group of the present invention,
the dry hot air is blown in a forward direction with respect to the
discharging direction of the precursor fiber 6A so that the fiber
6A is dried and solidified, and also extended simultaneously.
Moreover, by carrying out the extending process in this manner, it
becomes possible to control the fiber diameter and shape
comparatively easily. Therefore, it is possible to manufacture
desired alumina-silica based fibers 6 easily as well as
effectively.
[0368] In accordance with the manufacturing method of the
embodiment according to the third group of the present invention, a
water-soluble plasticizer is preliminarily added to the spinning
stock solution 18 so that the elastic modulus of the spinning stock
solution 18 becomes smaller with the Barus' effect being reduced.
Therefore, the discharge behavior of the spinning stock solution 18
at the time of the spinning process is stabilized. Consequently,
the precursor fiber 6A becomes less susceptible to thread breakage
even when it is extended with a strong tension, and the fiber
cross-sectional shape becomes less susceptible to roundness due to
elastic deformation. Moreover, the above-mentioned plasticizer has
a water-soluble property so that it is dispersed in the spinning
stock solution 18 evenly. Thus, it becomes possible to reduce the
Barus' ratio to a virtually fixed value, and consequently to obtain
a fiber having the target fiber diameter and cross-sectional shape
comparatively easily. Therefore, it becomes possible to manufacture
desired alumina-silica based fibers 6 easily as well as
effectively.
[0369] Moreover, the third group of the present invention may
include a ceramic-fiber-use spinning device that is used for
forming the ceramic fibers according to the holding seal material
of the third group of the present invention, that is, a
ceramic-fiber-use spinning device which includes a nozzle having a
metal mouth having a non-circular cross-sectional shape, and a flow
path through which dry hot air is supplied, with a hot-air
discharging port being formed in the vicinity of the metal mouth,
and which is arranged so as to blow dry hot air through the
above-mentioned hot-air discharging port in a forward direction
with respect to the discharging direction of the ceramic precursor
fibers.
[0370] Here, the embodiment according to the third group of the
present invention has exemplified a case in which the holding seal
material 4 according to the third group of the present invention is
applied to a catalyst converter 1 used for an exhaust-gas-purifying
device. However, the holding seal material 4 according to the third
group of the present invention may of course be applied to devices
other than the catalyst converter 1 used for an
exhaust-gas-purifying device, such as a diesel particulate filter
(DPF) and a catalyst converter used for a fuel cell modifier.
[0371] The following description will be given of an embodiment
according to a fourth group of the present invention.
[0372] Referring to FIGS. 1 to 3, the following description will be
given of a catalyst converter used for an automobile exhaust gas
purifying device in accordance with an embodiment according to the
fourth group of the present invention in detail.
[0373] The catalyst converter 1 in accordance with the embodiment
of the fourth group of the present invention, shown in FIG. 3, is
virtually the same as the catalyst converter according to the first
group of the present invention, and constituted by a catalyst
carrier 2, a metal shell 3 covering the outer circumference of the
catalyst carrier 2, and a holding seal material 4 that is placed in
a gap between the two members 2 and 3.
[0374] Here, with respect to the catalyst carrier 2 and the metal
shell 3, the same members that have been explained in the catalyst
converter according to the first group of the present invention may
be used; therefore, the description thereof is omitted.
[0375] Moreover, with respect to the catalyst carrier 2, in
addition to a cordierite carrier molded into a honeycomb shape
shown in the embodiment, for example, a honeycomb porous sintered
body and the like of, for example, silicon carbide or silicon
nitride and the like, may be used.
[0376] Furthermore, as shown in the catalyst carrier 20 shown in
FIG. 4, those having no sealing member may be used.
[0377] As shown in FIG. 1, the holding seal material 4 is a
mat-shaped member having an elongated shape, and a convex fitting
section 11 is placed on its one end, and a concave fitting section
12 is placed on the other end. As shown in FIG. 2, upon wrapping
onto the catalyst carrier 2, the convex fitting section 11 is just
engaged by the concave fitting section 12.
[0378] The holding seal material 4 in accordance with the
embodiment according to the fourth group of the present invention
is constituted by ceramic fibers aggregated into a mat shape (that
is, a fiber aggregation) serving as a main element. With respect to
the above-mentioned ceramic fibers, in the embodiment according to
the fourth group of the present invention, alumina-silica based
fibers 6 are used. In this case, the alumina-silica based fibers 6,
which have a mullite crystal content in a range of 0% by weight or
more to 10% by weight or less, are preferably used. The fibers
having such a chemical composition make it possible to provide
excellent heat resistance and a high repulsive force upon
application of a compressing load, because the amorphous component
thereof becomes smaller. Therefore, even when it is subjected to a
high temperature while being placed in the gap, the possibility of
reduction in the face pressure to be generated is lowered.
[0379] The lower limit of a permissible range of alumina content in
the alumina-silica based fibers 6 is set to 50% by weight with the
upper limit being set to 100% by weight, and the lower limit of a
permissible range of silica content is set to 0% by weight with the
upper limit being set to 50% by weight. Here, with respect to the
alumina content, the lower limit is preferably set to 68% by weight
with the upper limit being preferably set to 83% by weight, and
with respect to the silica content, the lower limit is preferably
set to 32% by weight with the upper limit being preferably set to
17% by weight; more specifically, the contents are more preferably
set as Al.sub.2O.sub.3:SiO.sub.2=72:28.
[0380] If alumina is less than 68% by weight, or if silica exceeds
32% by weight, it might be difficult to improve the heat resistance
and the repulsive force upon application of a compressing load
sufficiently. If alumina exceeds 83% by weight, or if silica is
less than 17% by weight also, it might be difficult to improve the
heat resistance and the repulsive force upon application of a
compressing load sufficiently.
[0381] The lower limit of the average fiber diameter of the
alumina-silica based fibers 6 is preferably set to 5 .mu.m, with
the upper limit being set to 15 .mu.m, and the dispersion in the
fiber diameter is preferably limited to a range within .+-.3 .mu.m.
Further, the lower limit of the average fiber diameter is more
preferably set to 7 .mu.m, with the upper limit being set to 12
.mu.m, and the dispersion in the fiber diameter is more preferably
limited to a range within .+-.2 .mu.m.
[0382] The average fiber diameter of less than 5 .mu.m makes it
difficult to provide a sufficient face pressure due to a reduction
in the strength of the fiber itself, and also causes a problem in
which the fibers tend to be inhaled by the respiratory organs. In
the case of the average fiber diameter exceeding 15 .mu.m, when the
fibers are formed into a mat-shaped fiber aggregation, its aeration
resistance is reduced, resulting in degradation in the sealing
property. In addition to this adverse effect, there might be
degradation in the breaking strength. This adverse effect is
considered to be caused by an increase in small scratches generated
by an increase in the fiber surface area. Additionally, in the case
where the dispersion in the fiber diameter exceeds .+-.3 .mu.m, the
fibers tend to be accumulated unevenly, with the result that the
positional dependence of the basis weight becomes higher.
[0383] The lower limit of the average fiber length of the
alumina-silica based fibers 6 is preferably set to 5 mm, with the
upper limit being set to 20 mm, and the dispersion in the fiber
length is preferably limited to a range within .+-.4 mm. Further,
the lower limit of the average fiber length is more preferably set
to 8 mm, with the upper limit being set to 13 mm, and the
dispersion in the fiber diameter is more preferably limited to a
range within .+-.2 .mu.m.
[0384] The average fiber length of less than 5mm causes a problem
in which the fibers tend to be inhaled by the respiratory organs.
Moreover, this fiber no longer exhibits characteristics as the
fiber, and when the fibers are formed into a mat-shaped fiber
aggregation, the fibers are not allowed to entangle with one
another preferably, making it difficult to obtain a sufficient face
pressure. The average fiber length exceeding 20 mm makes the fibers
entangled with one another too strongly, with the result that the
fibers tend to be accumulated unevenly when the fibers are formed
into a mat-shaped aggregation. In other words, the positional
dependence of the basis weight becomes higher, causing an adverse
effect to the reduction in the dispersions in the face pressure
value. Moreover, in the case where the dispersion in the fiber
length exceeds .+-.4 mm also, the fibers tend to be accumulated
unevenly, causing the positional dependence of the basis weight to
become higher.
[0385] The content of shot in the holding seal material 4 is
preferably set to 3% by weight or less, more preferably 0% by
weight, that is, no shot contained at all.
[0386] When shot is contained, the positional dependence of the
basis weight becomes higher, causing an adverse effect to inhibit
the reduction in the dispersions in the face pressure value.
[0387] Moreover, the tensile strength of each of the alumina-silica
based fibers 6 is preferably set to 0.1 GPa or more, more
preferably 0.5GPa or more. In addition to a complete round shape,
the cross-sectional shape of each the alumina-silica based fibers 6
may be set to a deformed cross-sectional shape (for example, an
elliptical shape, an elongated circular shape, or a virtually
triangular shape).
[0388] In the catalyst converter according to the fourth group of
the present invention, the thickness of the holding seal material 4
prior to the assembling process, the GBD (bulk density) of the
holding seal material 4 after the assembling process and the
initial face pressure of the holding seal material 4 in the
assembled state are preferably set in the same manner as those
described in the catalyst converter according to the first group of
the present invention; therefore, the description thereof is
omitted.
[0389] Here, such a holding seal material 4 may be subjected to a
needle punching process, a resin impregnation process, etc., if
necessary. By applying these processes, it becomes possible to
compress the holding seal material 4 in the thickness direction,
and consequently to make it thinner.
[0390] The following description will be given of a sequence of
processes for manufacturing a catalyst converter 1 according to the
fourth group of the present invention.
[0391] First, a spinning stock solution is prepared by mixing an
aluminum salt aqueous solution, silica sol and an organic polymer.
In other words, the spinning stock solution is prepared by using an
inorganic salt method. The aluminum salt aqueous solution, which
serves as an alumina source, also serves as a component giving
viscosity to the spinning stock solution.
[0392] With respect to such an aqueous solution, an aqueous
solution of basic aluminum salt is preferably selected. The silica
sol, which serves as a silica source, also serves as a component
for giving high strength to the fibers. The organic polymer is a
component for giving a fiber-drawing property to the spinning stock
solution.
[0393] An antifoamer, etc. may be added to the spinning stock
solution. Here, by altering the ratio of the aluminum salt and
silica sol, it becomes possible to control the chemical composition
of the alumina-silica based fibers 6 to a certain extent.
[0394] Moreover, not limited to those exemplified here, the
composition of the spinning stock solution may be desirably changed
as long as it does not cause great degradation in the spinning
property and physical properties of the fibers.
[0395] Next, the resulting spinning stock solution is condensed
under vacuum to prepare a spinning stock solution that has been
prepared to have a density, temperature, viscosity and the like
suitable for the spinning. In this case, the spinning stock
solution, which has had approximately a concentration of 20% by
weight, is preferably condensed to have 30 to 40% by weight.
Moreover, the viscosity is preferably set to 10 to 2000 Poise.
[0396] Moreover, the spinning stock solution thus prepared is
continuously discharged into the air through a nozzle of a spinning
device, and taken up while the resulting precursor fiber being
extended. In this case, for example, a dry-type pressurizing
spinning method may be preferably used.
[0397] Incidentally, by properly setting the cross-sectional shape
and size of the nozzle discharging port, with the discharging,
extending and taken-up conditions being set to fixed states, it
bocomes possible to control the fiber diameter in a narrow range.
This arrangement makes it possible to reduce dispersions in the
fiber diameter.
[0398] Successively, the long fibers of the precursor fibers,
obtained through the above-mentioned processes, are chopped to a
length set to approximately 0.5 to 10 mm so as to form short
fibers. The advantages of such a short-fiber-spinning method are to
make the dispersion of the fiber length smaller by controlling the
fiber length in a narrow range, and to preliminarily avoid the
occurrence of shot. In other words, the length of the resulting
short fibers is basically dependent on the mechanical precision of
the cutting device with very small width of dispersions.
[0399] Further, with respect to the cutting device, for example, a
guillotine cutter or other mechanical cutting devices may be used
to cut the long fibers.
[0400] Thereafter, the short fibers are collected, untied and
laminated, or a fiber-dispersed solution, obtained by dispersing
the short fibers in water, is poured into a mold, and pressed and
dried so that a mat-shaped fiber aggregation is obtained.
[0401] Next, the mat-shaped fiber aggregation is sintered through a
firing step to be formed into ceramics (crystallized) so that the
precursor fiber is hardened to obtain an alumina-silica based fiber
6.
[0402] In the above-mentioned firing step, it is preferable to set
the firing condition so as to make the mullite crystal content in
the resulting alumina-silica based fibers 6 at 10% by weight or
less. For example, the firing temperature in the firing step is
preferably set in a range of 1000 to 1300.degree. C. The firing
temperature of less than 1000.degree. C. fails to completely dry
and sinter the precursor fibers, with the result that it becomes
difficult to securely provide excellent heat resistance and a high
repulsive force at the time of application of a compressing load to
the holding seal material 4. In contrast, in the case of a firing
temperature exceeding 1300.degree. C., the mullite crystallization
in the alumina-silica based fiber 6 is allowed to easily progress.
For this reason, it becomes difficult to reduce the mullite crystal
content to 10% by weight or less, and consequently, it may not be
able to securely provide excellent heat resistance and a high
repulsive force at the time of application of a compressing load to
the holding seal material 4.
[0403] Here, instead of the above-mentioned method in which the
long fibers of the precursor fibers are chopped into short fibers,
and then fired, the firing step may be preliminarily carried out
before the chopping process of the long fibers into short
fibers.
[0404] Further, the fiber aggregation is punched out into a
predetermined shape to form a holding seal material 4. Then, after
the holding seal material 4 has been impregnated with an organic
binder, if necessary, the holding seal material 4 may be further
compressed, and molded in the thickness direction. With respect to
the organic binder used in this case, polyvinyl alcohol, acrylic
resin and the like may be used, in addition to latex and the like
such as acrylic rubber and nitrile rubber and the like.
[0405] Moreover, the holding seal material 4 is wrapped around the
outer circumferential face of the catalyst carrier 2 and secured by
the organic tape 13. Thereafter, this is subjected to a
press-fitting, canning or wrap-tightening process to complete a
desired catalyst converter 1.
[0406] Consequently, in accordance with the embodiment according to
the fourth group of the present invention, the following effects
can be obtained.
[0407] In the holding seal material 4 of the embodiment according
to the fourth group of the present invention, the dispersion in the
fiber diameter of the alumina-silica based fibers 6 is reduced
within a range of .+-.3 .mu.m with the dispersion in the fiber
length thereof being reduced within a range of .+-.4 mm, and the
content of shot is set to 3% by weight or less. Therefore, with
these synergistic effects, it is possible to extremely reduce the
positional dependence of the basis weight, and also to reduce
dispersions in the face pressure effectively. Thus, it becomes
possible to achieve a holding seal material 4 that is stable in
quality.
[0408] In accordance with the holding seal material 4 according to
the fourth group of the present invention, in addition to the
effect that reduces the dispersion in the face pressure, it is also
possible to improve the face pressure value; therefore, it becomes
possible to reduce the quantity of the alumina-silica based fibers
6 required for manufacturing a sheet of holding seal material 4.
Thus, it becomes possible to reduce the costs of the holding seal
material 4.
[0409] In accordance with the manufacturing method of the
embodiment according to the fourth group of the present invention,
since the spinning process is carried out by using an inorganic
salt method, it is possible to control the fiber diameter in a
narrow range, and consequently to reduce dispersions in the fiber
diameter. Moreover, this method chops long fibers to obtain short
fibers; therefore, different from a method in which fibers are
obtained through a blowing process, it is possible to control the
fiber length in a narrow range. Thus, it becomes possible to reduce
dispersions in the fiber length. In addition to these effects, it
is also possible to avoid the generation of shot. Consequently,
this manufacturing method makes it possible to obtain the
above-mentioned holding seal material 4 securely with ease.
[0410] As clearly described above, the manufacturing method of the
embodiment according to the fourth group of the present invention
makes it possible to provide a desirable method to obtain the
above-mentioned holding seal material 4.
[0411] The manufacturing method of the holding seal material
according to the fourth group of the present invention may include
a method for firing the produced ceramic short fibers as one of the
inventions of the fourth group; that is, a ceramic short fiber
producing method which includes a spinning process in which a
spinning stock solution containing an aluminum salt aqueous
solution, silica sol and an organic polymer is continuously
discharged from a nozzle to obtain a long fiber of a precursor
fiber, a cutting process for chopping the above-mentioned long
fiber into a predetermined length to obtain short fibers, and a
firing step for heating and sintering the above-mentioned short
fibers. This method relates to a manufacturing method of ceramic
short fibers which can reduce dispersions in the fiber length and
fiber diameter.
[0412] Moreover, the embodiment according to the fourth group of
the present invention has exemplified a case in which the holding
seal material 4 according to the fourth group of the present
invention is applied to a catalyst converter 1 used for an
exhaust-gas-purifying device; however, the holding seal material 4
according to the fourth group of the present invention may of
course be applied to devices other than the catalyst converter 1
used for an exhaust-gas-purifying device, such as a diesel
particulate filter (DPF) , a catalyst converter and the like used
for a fuel cell modifier.
[0413] The following description will be given of embodiments
according to a fifth group of the present invention.
[0414] [First Embodiment]
[0415] Referring to FIGS. 1 to 3, as well as FIG. 12, the following
description will be given of a catalyst converter used for an
automobile exhaust gas purifying device in accordance with the
first embodiment according to the fifth group of the present
invention in detail.
[0416] This catalyst converter 1 in accordance with the embodiment
of the fifth group of the present invention, shown in FIG. 3, is
virtually the same as the catalyst converter according to the first
group of the present invention, and constituted by a catalyst
carrier 2, a metal shell 3 covering the outer circumference of the
catalyst carrier 2, and a holding seal material 4 that is placed in
a gap between the two members 2 and 3.
[0417] Here, with respect to the catalyst carrier 2 and the metal
shell 3, the same members that have been explained in the catalyst
converter according to the first group of the present invention may
be used; therefore, the description thereof is omitted.
[0418] Moreover, with respect to the catalyst carrier 2, in
addition to a cordierite carrier molded into a honeycomb shape
shown in the embodiment, for example, a honeycomb porous sintered
body of, for example, silicon carbide or silicon nitride and the
like, may be used.
[0419] Furthermore, as shown in the catalyst carrier 20 shown in
FIG. 4, those having no sealing member may be used.
[0420] As shown in FIG. 1, the holding seal material 4 is a
mat-shaped member having an elongated shape, and a convex fitting
section 11 is placed on its one end, and a concave fitting section
12 is placed on the other end. As shown in FIG. 2, upon wrapping
onto the catalyst carrier 2, the convex fitting section 11 is just
engaged by the concave fitting section 12.
[0421] The holding seal material 4 in accordance with the
embodiment according to the fifth group of the present invention is
constituted by ceramic fibers aggregated into a mat shape (that is,
a fiber aggregation) serving as a main element. With respect to the
above-mentioned ceramic fibers, in the embodiment according to the
fifth group of the present invention, alumina-silica based fibers 6
are used. In this case, the alumina-silica based fibers 6, which
have a mullite crystal content in a range of 0% by weight or more
to 10% by weight or less, are preferably used. The fibers having
such a chemical composition make it possible to provide excellent
heat resistance and a high repulsive force upon application of a
compressing load, because the amorphous component thereof becomes
smaller. Therefore, even when it is subjected to a high temperature
while being placed in the gap, the possibility of reduction in the
face pressure to be generated is comparatively lowered.
[0422] The chemical composition of the alumina-silica based fibers
6 is preferably set so that alumina is in a range of 68 to 83% by
weight and silica is in a range of 32 to 17% by weight, more
specifically, Al.sub.2O.sub.3:SiO.sub.2=72:28.
[0423] If alumina is less than 68% by weight, or if silica exceeds
32% by weight, it might be difficult to improve the heat resistance
and the repulsive force upon application of a compressing load
sufficiently. In the case where alumina exceeds 83% by weight, or
in the case where silica is less than 17% by weight also, it might
be difficult to sufficiently improve the heat resistance and the
repulsive force upon application of a compressing load.
[0424] As schematically shown in FIG. 12, in the case of the
alumina-silica based fibers 6 constituting this holding seal
material 4, the fibers are partially bonded to each other by a
ceramic adhesive 7. Thus, it is possible to provide a structure
wherein, so to speak, a cross-linking bridge is placed between
portions at which ceramic fibers are adjacent to each other with
overlapped parts. In other words, the holding seal material 4 is
constituted by the alumina-silica based fibers 6 having a branched
structure.
[0425] Here, there are voids inside the holding seal material
4.
[0426] Moreover, instead of the exemplified alumina-silica based
fibers 6, for example, other ceramic fibers such as crystalline
alumina fibers and silica fibers and the like may be used to form
the holding seal material 4.
[0427] The ceramic adhesive 7 preferably comprises a substance that
constitutes the ceramic fibers. The above-mentioned ceramic
adhesive 7 of this characteristics has a high affinity to the
fibers, and allows the bonded portions to have high strength; thus,
it becomes possible to securely prevent degradation with time in
the face pressure. For this reason, in the embodiment according to
the fifth group of the present invention, the ceramic adhesive 7
mainly composed of alumina is adopted.
[0428] Moreover, with respect to the ceramic adhesive 7, a
substance that does not constitute the ceramic fibers may be
adopted. For example, in the case where the alumina-silica based
fibers 6 are selected, a ceramic adhesive 7 made of zirconia,
titania, yttria, ceria, calcia, or magnesia and the like may be
used.
[0429] The lower limit of the content of the ceramic adhesive 7 is
preferably set to 1% by weight with the upper limit thereof being
set to 8% by weight, and the lower limit thereof is more preferably
set to 3% by weight with the upper limit being set to 7% by
weight.
[0430] When the above-mentioned content is less than 1% by weight,
the fibers might not be bonded to one another with high strength.
In contrast, in the case where the above-mentioned content exceeds
8% by weight, although the problem with the bonding strength is
solved, the voids inside the holding seal material 4 tend to be
filled, failing to provide desired physical properties, that is,
elasticity and heat-insulating property, to the holding seal
material 4.
[0431] With respect to the average fiber diameter and average fiber
length of the alumina-silica based fibers 6, these factors are
preferably set in the same manner as those explained in the
catalyst converter according to the first group of the present
invention; therefore, the description thereof is omitted.
[0432] Moreover, the tensile strength (relative strength) of each
fiber of the alumina-silica based fibers 6 is preferably set to 0.1
GPa or more, more preferably 0.5 GPa or more. In addition to a
complete round shape shown in FIG. 12, the cross-sectional shape of
the alumina-silica based fibers 6 may be set to a deformed
cross-sectional shape (such as an elliptical shape, an elongated
circular shape and a generally-triangular shape).
[0433] With respect to the catalyst converter according to the
fifth group of the present invention, the thickness of the holding
seal material 4 prior to the assembling process, the GBD (bulk
density) of the holding seal material 4 after the assembling
process and the initial face pressure of the holding seal material
4 in the assembled state are preferably set in the same manner as
those described in the catalyst converter according to the first
group of the present invention; therefore, the description thereof
is omitted.
[0434] Here, the holding seal material 4 may be subjected to a
needle punching process, a resin impregnation process and the like,
if necessary. The application of these processes makes it possible
to compress the holding seal material 4 in the thickness direction
and consequently to make it thinner.
[0435] Next, an explanation will be given on the sequence of
processes for manufacturing a catalyst converter 1 according to the
fifth group of the present invention.
[0436] First, a spinning stock solution is prepared in the same
manner as explained in the catalyst converter manufacturing method
according to the fourth group of the present invention, and long
fibers of precursor fibers are formed.
[0437] Then, the precursor fibers are formed into ceramics
(crystallized) by carrying out a first firing step to harden the
precursor fibers; thus, alumina-silica based fibers 6 are
obtained.
[0438] In the above-mentioned firing step, it is preferable to set
the firing condition so as to make the mullite crystal content in
the resulting alumina-silica based fibers 6 having 10% by weight or
less. For example, the firing temperature in the firing step is
preferably set in a range of 1000 to 1300.degree. C. The firing
temperature of less than 1000.degree. C. fails to completely dry
and sinter the precursor fibers, with the result that it may not be
able to securely provide excellent heat resistance and a high
repulsive force at the time of application of a compressing load to
the holding seal material 4. In contrast, in the case of a firing
temperature exceeding 1300.degree. C., the mullite crystallization
in the alumina-silica based fiber 6 is allowed to easily progress.
For this reason, it becomes difficult to reduce the mullite crystal
content to 10% by weight or less, and consequently, it becomes
difficult to securely provide excellent heat resistance and a high
repulsive force at the time of application of a compressing load to
the holding seal material 4.
[0439] Successively, the long fibers of the alumina-silica based
fibers 6, obtained through the above-mentioned processes, are
chopped to a predetermined length by using, for example, guillotine
cutter, to form shorter fibers in a certain extent. Thereafter, the
short fibers are collected, untied and laminated, or a
fiber-dispersed solution, obtained by dispersing the short fibers
in water, is poured into a mold, and pressed and dried so that a
mat-shaped fiber aggregation is obtained. Further, this fiber
aggregation is punched out into a predetermined shape to form a
holding seal material 4.
[0440] After the above-mentioned molding process, a bonding process
is carried out so that the above-mentioned short fibers
constituting a fiber aggregation are mutually bonded by a ceramic
adhesive 7. More specifically, the following processes are carried
out.
[0441] First, a material solution of the ceramic adhesive 7 is
prepared, and supplied between short fibers that constitute the
aggregation. In other words, in the first step of the bonding
processes, a liquid-state substance supplying process in which a
liquid-state substance is supplied between the short fibers
constituting the aggregation so that the liquid-state substance
that is formed into a ceramic adhesive 7 later is allowed to adhere
to portions at which the precursor fibers constituting the
above-mentioned aggregation are adjacent to each other with
overlapped parts, is carried out. In this case, with respect to the
above-mentioned material solution, for example, a water-soluble
metal solution such as a water solution of aluminum chloride is
preferably used. Here, a water solution of aluminum salt other than
chlorides, that is, a water solution other than a water solution of
aluminum chloride containing aluminum ions, may be used.
Additionally, a water solution containing metal cations other than
aluminum ions, such as a water solution of zirconium chloride, a
water solution of titanium chloride and a water solution of
chromium chloride and the like may be selected.
[0442] Here, in place of a basic water solution of aluminum
chloride, for example, the spinning stock solution of the
alumina-silica based fibers may be commonly used so as to carry out
the bonding process. In this case as well, the ceramic adhesive 7
made from the fiber-constituting substance may be prepared.
[0443] The above-mentioned water-soluble metal solution is
preferably set to have a low viscosity, more specifically,
approximately, 0.1 to 10 centipoise. The water-soluble metal
solution having a low viscosity easily has a surface tension
exerted thereon, with the result that it is possible to provide a
better adhesive property to portions in which short fibers are
adjacent with each other with overlapped parts. Moreover, when the
viscosity is too high, it becomes difficult to allow the solution
to securely enter the inside of the fiber aggregation evenly.
[0444] The lower limit of the quantity of supply of the
water-soluble metal solution in the fiber aggregation is set to 1%
by weight, with the upper limit thereof being set to 10% by weight,
and more preferably, the lower limit thereof is set to 2% by weight
with the upper limit thereof being set to approximately 8% by
weight. The quantity of supply of less than 1% by weight causes an
insufficient quantity of the solution to adhere to the portions at
which the fibers are adjacent to each other with overlapped parts,
sometimes failing to mutually bond the fibers strongly. In
contrast, the quantity of supply exceeding 10% by weight causes the
voids inside the holding seal material 4 to be easily filled with
the excessive solution, sometimes impairing desired physical
properties in the holding seal material 4.
[0445] Examples of the method for supplying a material solution to
the fiber aggregation include a method in which the fiber
aggregation is immersed into a solution so that the inside thereof
is impregnated with the solution, a method in which a solution in a
mist state is supplied into the fiber aggregation by using a spray
atomizing process, a method in which a solution is dipped and
supplied into the fiber aggregation and the like. Among these, the
impregnation method is preferably used. The impregnation method
makes it possible to allow the material solution to securely enter
the inside of the fiber aggregation evenly.
[0446] After the impregnation process, it is preferable to heat and
dry the fiber aggregation. The heating and drying processes make it
possible to remove excessive moisture in the material solution to a
certain degree, and consequently to carry out a firing step in the
next process in a stable manner.
[0447] Next, the dried fiber aggregation is again fired at a high
temperature, and the metal component in the material solution,
adhered to the mutual adjacent portions of the short fibers, is
sintered and formed into ceramics; thus, a cross-linking bridge
made from the ceramic adhesive 7 is formed at the corresponding
portion so that the short fibers are bonded to each other.
[0448] Thereafter, the holding seal material 4 is impregnated with
an organic binder, if necessary, and the holding seal material 4
maybe compressed and molded in a thickness direction. In this case,
with respect to the organic binder, polyvinyl alcohol, acrylic
resin and the like may be used, in addition to latexes such as
acrylic rubber, nitrile rubber and the like.
[0449] Then, the holding seal material 4, obtained by punching out
the above-mentioned fiber aggregation into a predetermined shape,
is wound around the outer circumferential face of the catalyst
carrier 2 and secured by the organic tape 13. Thereafter, this is
subjected to a press-fitting, canning or wrap-tightening process to
complete a desired catalyst converter 1.
[0450] Therefore, in accordance with the first embodiment according
to the fifth group of the present invention, the following effects
can be obtained.
[0451] In accordance with the first embodiment according to the
fifth group of the present invention, the holding seal material 4
makes it possible to provide a structure wherein, so to speak, a
cross-linking bridge is placed between portions at which ceramic
fibers are adjacent to each other with overlapped parts by using
the ceramic adhesive 7, and consequently to make the respective
fibers less susceptible to sliding and deviation.
[0452] Therefore, even when an external load is imposed thereon in
a manner so as to compress the holding seal material 4 for a long
time, this structure is less susceptible to degradation in the face
pressure. Moreover, in this holding seal material 4, since the
short fibers are partially bonded to each other so that the voids
inside the holding seal material 4 are not completely filled.
Therefore, physical properties (elasticity, heat-insulating
property, and the like) , inherently required for the holding seal
material 4, are maintained. Moreover, the ceramic adhesive 7, which
is used as the crosslinking bridge, is excellent in heat
resistance. Therefore, even when the holding seal material 4 is
subjected to a high temperature of approximately 1000.degree. C.
during use, the bonding portions are less susceptible to
degradation in strength, and this advantage also makes it possible
to prevent a reduction in the face pressure.
[0453] In accordance with the first embodiment according to the
fifth group of the present invention, the alumina-silica based
fibers 6 are selected, and the ceramic adhesive 7 mainly composed
of alumina is also selected. In other words, the ceramic adhesive 7
comprises a substance constituting the alumina-silica based fibers
6. For this reason, this adhesive provides very high affinity for
the corresponding fibers, and consequently increases the strength
of the bonded portions. Therefore, this combination makes it
possible to securely prevent degradation with time in the face
pressure. Further, the application of the alumina-silica based
fibers 6 having excellent heat resistance makes it possible to
reduce degradation with time in the face pressure at high
temperatures.
[0454] In the first embodiment according to the fifth group of the
present invention, the content of the ceramic adhesive 7 is set in
the above-mentioned preferable range. Therefore, it becomes
possible to provide high strength in the bonded portions while
maintaining desired properties in the holding seal material 4.
[0455] In accordance with the first embodiment according to the
fifth group of the present invention, upon manufacturing the
holding seal material 4, the firing step and bonding process of the
precursor fibers are carried out in a separated manner. More
specifically, the bonding process is carried out after the firing
step of the precursor fibers. For this reason, it is possible to
securely provide alumina-silica based fibers 6 having a better
shape in comparison with a case in which both of the processes are
carried out simultaneously so that the above-mentioned
alumina-silica based fibers 6 having a desired shape are securely
bonded to each other. Therefore, it becomes possible to securely
manufacture a holding seal material 4 that is less susceptible to
degradation with time in the face pressure easily.
[0456] [Second Embodiment]
[0457] The following description will be given of a second
embodiment according to the fifth group of the present invention.
Here, explanations will be mainly given on points that are
different from the first embodiment according to the fifth group of
the present invention, and those same parts are indicated by the
same reference numerals, and the description thereof is
omitted.
[0458] In this case, a holding seal material 4 having the
above-mentioned structure is manufactured in the following
sequence. First, a spinning process is carried out in the same
manner as the first embodiment according to the fifth group of the
present invention to provide long fibers of precursor fibers by
using a spinning stock solution of the alumina-silica based fibers
6 as a material. Next, a cutting process is carried out so that the
long fibers are chopped by a guillotine cutter to form shorter
fibers in a certain extent. Then, a molding process is carried out
in such a manner that the short fibers are collected, untied and
laminated; or a fiber-dispersed solution, obtained by dispersing
the short fibers in water, is poured into a mold, and pressed and
dried, so that a mat-shaped fiber aggregation is obtained. Next, a
liquid-state substance supplying process is carried out in such a
manner that the liquid-state substance, which forms ceramic
adhesive 7 later, is allowed to adhere to portions at which the
precursor fibers constituting the fiber aggregation are adjacent to
each other with overlapped parts. Next, in a sintering step, the
fiber aggregation is heated so that the precursor fibers and the
liquid-state substance are simultaneously sintered. Lastly, the
fiber aggregation is subjected to a punching process and the like
to provide a holding seal material 4.
[0459] In other words, in contrast to the first embodiment
according to the fifth group of the present invention in which the
liquid-state-substance supplying process is carried out in a stage
after the firing step (after the fibers have been formed into
ceramics), the second embodiment according to the fifth group of
the present invention carries out this process in a stage prior to
the firing step (in a state of un-sintered precursor fibers), which
forms a great difference from the first embodiment.
[0460] With respect to the specific example of the liquid-state
substance supplying process, the following two methods are
listed.
[0461] In the first method, a fiber aggregation, made from
precursor fibers of the alumina-silica based fibers 6, is placed
under a highly moistened environment with high moisture so that the
liquid-state substance is supplied thereto. In this case, vapor,
existing under the highly moistened environment, is allowed to
securely enter the inside of the fiber aggregation, and then
condensed into moisture. Moreover, the moisture is allowed to
selectively adhere to the adjacent overlapped parts of the fibers
by a function of surface tension. Here, the precursor fibers of the
alumina-silica based fibers 6 are water-soluble. For this reason,
the adhesion of moisture causes the surface of the precursor fibers
at the adjacent overlapped parts to be dissolved to a certain
extent. Since the liquid-state substance, generated by such
dissolution, has virtually the same composition as the
alumina-silica based fibers 6, it is actually allowed to form a
ceramic adhesive 7 later. Therefore, when a firing step is carried
out at a temperature in a range of 1000 to 1300.degree. C., the
precursor fibers and the liquid-state substance are simultaneously
sintered to form ceramics, with the result that a cross-linking
bridge made from the ceramic adhesive 7 is formed between the
alumina-silica based fibers 6. Here, in this method, the conditions
(for example, the quantity of vapor, processing temperature,
processing time, etc.) need to be set to a level that does not
cause over-dissolution of the precursor fibers. Therefore, in the
case where moisture is directly supplied through an atomizing
process and the like, it is necessary to take over-dissolution into
consideration.
[0462] The second method is characterized in that a non-aqueous
liquid-state substance containing the same inorganic element
contained in the alumina-silica based fibers 6 is sprayed onto the
fiber aggregation composed of the precursor fibers of the
alumina-silica based fibers 6 so that the corresponding substance
is supplied thereto. In this case, the sprayed non-aqueous
liquid-state substance is allowed to securely enter the inside of
the fiber aggregation, and also to selectively adhere to the
adjacent overlapped portions between the fibers through a function
of surface tension. With respect to the non-aqueous liquid-state
substance, for example, commercially available non-aqueous silicone
oils and the like are listed. Since the silicon oil contains
silicon (Si) that is an inorganic element contained in the
alumina-silica based fibers 6, this is allowed to actually form the
ceramic adhesive 7 later.
[0463] Therefore, when a firing step is carried out at a
temperature of 1000 to 1300.degree. C., the precursor fibers and
the non-aqueous liquid-state substance are simultaneously sintered
to form ceramics, with the result that a cross-linking bridge made
from the ceramic adhesive 7 is formed between the alumina-silica
based fibers 6. In this case, the ceramic adhesive 7 is an oxide of
silicon (silica: SiO.sub.2) . Here, in addition to the non-aqueous
silicone oil, for example, a material, formed by dissolving, for
example, TEOS (ethyl silicate) in oil, may be used.
[0464] In accordance with the second embodiment according to the
fifth group of the present invention, the following effects can be
obtained.
[0465] In the manufacturing method of the second embodiment
according to the fifth group of the present invention, the firing
step and bonding process of the precursor fibers are carried out
simultaneously; therefore, in comparison with the manufacturing
method of the first embodiment according to the fifth group of the
present invention in which these processes are carried out
simultaneously, it is possible to reduce the number of heating
steps. Thus, it becomes possible to reduce thermal energy to be
applied thereto, and consequently to reduce the manufacturing
costs. Therefore, it becomes possible to manufacture a holding seal
material 4 that is less susceptible to degradation with time in the
face pressure efficiently at low costs.
[0466] In the case where the first method is adopted, the
liquid-state substance to be formed into the ceramic adhesive 7
later is allowed to securely adhere to the adjacent overlapped
portions. Moreover, basically, the above-mentioned liquid-state
substance, which is a fiber-dissolved substance, has virtually the
same composition as the alumina-silica based fibers 6.
[0467] For this reason, the above-mentioned liquid-state substance
has a high affinity for the precursor fibers, and makes it possible
to securely bond the fibers to each other with high strength.
Therefore, it is possible to securely prevent degradation with time
in the face pressure.
[0468] The application of the second method also allows the
liquid-state substance that forms the ceramic adhesive 7 later to
securely adhere to portions at which the fibers are adjacent to
each other with overlapped parts. Further, in this case, a
non-aqueous liquid-state substance is used. For this reason, even
when this adheres to the precursor fibers of the alumina-silica
based fibers 6 having a water-soluble property, the precursor
fibers are not dissolved. Therefore, it is not necessary to worry
about degradation in the strength of the alumina-silica based
fibers 6 itself due to too much dissolution of the precursor
fibers, and it is not particularly necessary to set specific
conditions carefully for preventing over-dissolution. Consequently,
it is possible to manufacture a holding seal material 4
comparatively easily. Moreover, since the above-mentioned
liquid-state substance contains the inorganic element contained in
the alumina-silica based fibers 6, it has a high affinity for the
precursor fibers so that the fibers are securely bonded to each
other with high strength. Thus, it becomes possible to securely
prevent degradation with time in the face pressure.
[0469] In the manufacturing method of the second embodiment
according to the fifth group of the present invention, a cutting
process is carried out between the spinning process and the molding
process so that the long fibers of the precursor fibers are
mechanically cut into a predetermined length so as to obtain short
fibers. In other words, the manufacturing method of the second
embodiment according to the fifth group of the present invention is
different from the manufacturing method of the first embodiment
according to the fifth group of the present invention which carries
out a cutting process after the firing step in that the cutting
process is carried out prior to the firing step.
[0470] In the case where the cutting process is carried out after
the sintering step of the precursor fibers as in the case of the
manufacturing method of the first embodiment according to the fifth
group of the present invention, the alumina-silica based fibers 6
tend to have cracks and splinters on the cut portion of the
alumina-silica based fibers 6 due to an impact at the time of the
cutting process. This is because, in general, when precursor fibers
are sintered to form ceramics, the fibers become brittle although
they become hard. Consequently, the alumina-silica based fibers 6
come to have unstable end shapes, and the mechanical strength of
the fibers is lowered.
[0471] In contrast, since the precursor fibers are un-sintered and
comparatively soft, they are less susceptible to cracks and the
like on the cut portion even when they are subjected to a
mechanical impact at the time of the cutting process. Therefore,
the alumina-silica based fibers 6, obtained by sintering these,
have stable end shapes, and are excellent in mechanical strength.
Consequently, in accordance with the second embodiment according to
the fifth group of the present invention, it is possible to improve
the initial face pressure. The resulting property for preventing
the generation of cracks and the like is considered to give effects
also on prevention of degradation with time in the face pressure to
a certain degree.
[0472] Moreover, in accordance with the manufacturing method of the
second embodiment according to the fifth group of the present
invention, since the cutting subject is each of the precursor
fibers that are not so hard, the blades of a guillotine cutter
serving as a mechanical cutting device are less susceptible to
damages and abrasion. Therefore, it becomes possible to eliminate
the necessity of frequently exchanging deteriorated blades, and
consequently to prevent an increase in the running costs. Moreover,
since it is not necessary to make the blades so hard,
generally-used blades can be applied; thus, it becomes possible to
prevent an increase in the facility costs.
[0473] Additionally, in the case where the second method is adopted
in the second embodiment according to the fifth group of the
present invention, a method which can replace the atomizing method
upon supplying the non-aqueous liquid-state substance, for example,
a dipping method, may be adopted. It is of course possible to
vaporize and supply the non-aqueous liquid-state substance.
[0474] Moreover, in the manufacturing method of the holding seal
material according to the fifth group of the present invention, the
water solution containing aluminum ions may be supplied as a basic
water solution of aluminum chloride or as the above-mentioned
spinning stock solution of the alumina-silica based fibers.
[0475] Furthermore, in the manufacturing method of the holding seal
material according to the fifth group of the present invention, the
water-soluble metal solution may be prepared as a water solution
containing at least one material selected from the group consisting
of aluminum chloride, zirconium chloride, titanium chloride and
chromium chloride.
[0476] Here, the embodiment according to the fifth group of the
present invention has exemplified a case in which the holding seal
material 4 according to the fifth group of the present invention is
applied to a catalyst converter used for an exhaust-gas-purifying
device; however, the holding seal material 4 according to the fifth
group of the present invention may of course be applied to devices
other than the catalyst converter 1 used for an
exhaust-gas-purifying device, such as a diesel particulate filter
(DPF) and a catalyst converter used for a fuel cell modifier.
[0477] The following description will be given of an embodiment
according to a sixth group of the present invention.
[0478] The manufacturing method of an alumina fiber aggregation
according to the sixth group of the present invention comprises: a
spinning step of obtaining a continuous long-fiber precursor by
using an alumina fiber stock solution used in an inorganic salt
method as a material; a chopping step of cutting the continuous
long-fiber precursor into short-fiber precursors; a mat preparing
step of preparing a mat-shaped short fiber precursor by using thus
obtained said short-fiber precursor; and a firing step of firing
the mat-shaped short fiber precursor to manufacture an alumina
fiber aggregation.
[0479] In the manufacturing method of an alumina fiber aggregation
according to the sixth group of the present invention, the firing
step is carried out after the spinning process, the chopping
process and the mat-forming process so that it becomes possible to
sufficiently increase the mechanical strength of the alumina short
fibers that are used in the alumina fiber aggregation to be
manufactured, and also to manufacture an alumina fiber aggregation
that has a high initial face pressure, and is less susceptible to
degradation with time in the face pressure.
[0480] The reason for this is explained as follows.
[0481] In other words, in the case where alumina short fibers to be
used in an alumina fiber aggregation are manufactured by using a
conventional method, a continuous long fiber precursor, obtained by
carrying out a spinning process on an alumina-fiber stock solution,
is fired to form an alumina long fiber, and this alumina long fiber
is then cut by using a mechanical means such as a cutter to provide
the alumina short fibers; however, the alumina short fibers thus
manufactured tend to have burs on the cut face thereof (see FIG.
15(b)).
[0482] Here, FIG. 15(a) shows an SEM photograph of a
cross-sectional face of one of the alumina short fibers used in an
alumina fiber aggregation that has been manufactured by a
manufacturing method of an alumina fiber aggregation of the present
invention, and FIG. 15(b) shows an SEM photograph of a
cross-sectional face of one of the alumina short fibers used in an
alumina fiber aggregation that has been manufactured by a
conventional method.
[0483] Upon cutting an alumina long fiber, one portion of the
alumina long fiber tends to chip in the vicinity of the cut face,
before the above-mentioned cutter or the like has completely cut
the alumina long fiber, and resulting chips adhere to the cut face
to cause burs on the cut face of the alumina short fiber, as shown
in FIG. 15(b).
[0484] When the alumina long fiber is cut by a mechanical means
such as a cutter, a great shearing stress is exerted on the cut
face. However, since the above-mentioned alumina long fiber is made
of hard, brittle ceramics having a certain degree of strength, and
the shearing stress, exerted on the cut face, causes chips on one
portion of the alumina long fiber, and it is considered that the
chips adhere to the cut face, with the result that burs, shown in
FIG. 15(b), are generated.
[0485] Moreover, a number of alumina short fibers to be used in an
alumina fiber aggregation are entangled with one another in a
complex manner; and when burs are generated on the cut face of each
alumina short fiber, the burs cause damages to other alumina short
fibers when they are entangled with one another in a complex
manner.
[0486] When the above-mentioned alumina short fiber is observed in
detail, there are portions on which micro-cracks are generated due
to the above-mentioned chips and burs, and there are other portions
on which micro-cracks are generated due to forces that are imposed
on the fiber at the time of the cutting process.
[0487] Therefore, these chips, burs, micro-cracks and the like
cause a failure to provide sufficient mechanical strength in the
alumina short fibers, and make the dispersions greater.
[0488] Here, the degradation with time in the initial face pressure
and the face pressure of the alumina fiber aggregation is caused
depending on the mechanical strength of the alumina short fibers
used in the alumina fiber aggregation, and when each alumina short
fiber has excellent mechanical strength, the initial face pressure
of the alumina fiber aggregation is maintained sufficiently high
with the degradation with time in the face pressure being
reduced.
[0489] However, as described earlier, in the conventional alumina
fiber aggregation, the mechanical strength of the alumina short
fibers used in the alumina fiber aggregation is not sufficiently
high with high dispersions thereof; therefore, it is not possible
to obtain sufficiently high initial face pressure in the alumina
fiber aggregation, and it is considered that the degradation with
time in the face pressure becomes comparatively greater.
[0490] In the manufacturing method of the alumina fiber aggregation
according to the sixth group of the present invention, the
continuous long fiber precursor obtained from the spinning process
is cut by a cutter or the like without being subjected to a firing
step so that a short fiber precursor is formed. In other words,
since the above-mentioned continuous long fiber precursor is only
subjected to an extending process after having been subjected to a
spinning process, it is soft, and even when the continuous long
fiber precursor is cut by a cutter or the like, no chips are
generated in the vicinity of the cut face due to a shearing stress
exerted on the cut face (see FIG. 15(a)). Moreover, the cut face is
less susceptible to micro-cracks.
[0491] Therefore, the alumina short fibers to be used in the
alumina fiber aggregation which is manufactured later are allowed
to have sufficiently high mechanical strength with smaller
dispersions thereof, in comparison with those alumina short fibers
to be used in alumina fiber aggregation manufactured in a
conventional method. For this reason, the alumina fiber
aggregation, manufactured through the manufacturing method of the
alumina fiber aggregation in the present invention, is allowed to
have a high initial face pressure, and less susceptible to
degradation with time.
[0492] The following description will be given of the manufacturing
method of an alumina fiber aggregation according to the sixth group
of the present invention in detail.
[0493] In the manufacturing method of an alumina fiber aggregation
according to the sixth group of the present invention, first, a
spinning process is carried out to obtain a continuous long fiber
precursor by using an alumina-fiber stock solution to be used in an
inorganic salt method as a material.
[0494] In the spinning process, first, the above-mentioned
alumina-fiber stock solution to be used in the inorganic salt
method is prepared.
[0495] The above-mentioned alumina-fiber stock solution is prepared
by using the inorganic salt method. More specifically, it is
preferably prepared by mixing silica sol in a water solution of
aluminum salt, since this method makes it possible to provide
alumina fibers having high strength.
[0496] With respect to the above-mentioned water solution of
aluminum salt, for example, a water solution of basic aluminum salt
may be selected. Here, the aluminum salt water solution serving as
an alumina source is a component used for applying viscosity to the
above-mentioned alumina-fiber stock solution.
[0497] Here, in this alumina-fiber stock solution, the ratio of
mixing of the aluminum salt water solution and silica sol is
preferably set to 40 to 100% by weight of alumina and 0 to 60% by
weight of silica in terms of alumina and silica equivalent
amount.
[0498] Moreover, an organic polymer may be added to such alumina
fiber stock solution, if necessary. Thus, it becomes possible to
apply a fiber-drawing property to the alumina-fiber stock
solution.
[0499] With respect to the organic polymer, a straight-chain
polymer containing carbon, such as PVA (polyvinyl alcohol) and the
like, maybe used; however, in addition to this, any compound having
a comparatively low molecular weight without a straight-chain
structure (which is not a polymer) maybe selected as long as it
contains carbon.
[0500] Next, by condensing under vacuum the resulting spinning
stock solution, the alumina-fiber stock solution is prepared so as
to have a concentration, temperature and viscosity suitable for the
spinning process. In this case, the alumina-fiber stock solution,
which has been normally set to approximately a concentration of 20%
by weight, is preferably condensed to approximately 30 to 40% by
weight. Moreover, the viscosity of the alumina-fiber stock solution
after concentration under vacuum is preferably set to 1 to 200
Pa.multidot.s (10 to 2000 P)
[0501] Further, by discharging the alumina-fiber stock solution
thus prepared into a high-speed gas flow through a nozzle of a
spinning device by using a dry-type pressurizing spinning method
and the like, a material fiber, which has a cross-sectional shape
that is analogous to the nozzle metal mouth shape, is continuously
obtained. The material fiber, thus subjected to the spinning
process, is successively wound up while being extended so that a
continuous long-fiber precursor is obtained.
[0502] With respect to the shape of the opening of the nozzle, it
is not particularly limited, and any desired shape, such as a
complete round shape, a triangular shape, a Y-letter shape and a
star shape, may be selected.
[0503] Moreover, the above-mentioned material fiber in the state of
being spun out is preferably extended approximately 100 to 200
times to be formed into a continuous long-fiber precursor. Thus,
this is set to a range in which an alumina fiber having preferable
strength can be manufactured. In the case where the cross-sectional
shape of the continuous long-fiber precursor is set to a complete
round shape, the lower limit of the average fiber diameter is
preferably set to 3 .mu.m with the upper limit being set to 25
.mu.m, and the lower limit of the average fiber diameter is more
preferably set to 5 .mu.m with the upper limit being set to 15
.mu.m.
[0504] Furthermore, it is preferable to carry out a crimping
process for applying a crimp to the above-mentioned continuous
long-fiber precursor. This arrangement allows the alumina short
fibers to be preferably entangled with one another, when the
alumina short fibers are formed into a mat shape in the succeeding
mat-forming process.
[0505] Next, a chopping process is carried out so as to cut the
above-mentioned continuous long-fiber precursor into a short fiber
precursor.
[0506] In this chopping process, the above-mentioned continuous
long-fiber precursor is cut in a manner so as to preferably set its
lower limit to 0.1 mm, more preferably 2 mm, with its upper limit
being set to 100 mm, more preferably 50 mm.
[0507] More specifically, a plurality of the continuous long-fiber
precursors are aligned side by side, and cut by a rectangular
cutter or the like, and in this case, the cutting process is
preferably carried out so that the cut faces become flat. If the
cut face of each short fiber precursor has an aspire shape, the cut
face of the alumina short fiber to be formed later also has an
aspire shape, and if these short fiber precursor and alumina short
fibers are inhaled, serious damages might be caused in the human
body.
[0508] Next, a mat-forming process is carried out so that a
mat-shaped short-fiber precursor is produced by using the resulting
short-fiber precursor.
[0509] In this mat-forming process, after the resulting precursor
short fibers have been collected, untied and laminated, these are
pressed to form a mat-shaped short-fiber precursor.
[0510] In this mat-shaped short-fiber precursor, the
above-mentioned short-fiber precursor is in an entangled state to a
certain degree.
[0511] Not particularly limited, the shape of the above-mentioned
mat-shaped short-fiber precursor is normally set to a rectangular
shape.
[0512] Moreover, the size thereof is appropriately determined in
accordance with the purpose of use of the alumina fiber
aggregation.
[0513] Next, this mat-shaped short-fiber precursor is preferably
subjected to a needle punch process. In this needle punch process,
by sticking a needle into the above-mentioned mat-shaped
short-fiber precursor, the upper and lower short-fiber precursors
are preferably entangled so that it is possible to provide a
mat-shaped short-fiber precursor having high bulkiness and
elasticity.
[0514] Then, the above-mentioned mat-shaped short-fiber precursor
is fired in a firing step to manufacture an alumina fiber
aggregation, thereby completing the manufacturing method of the
alumina fiber aggregation according to the sixth group of the
present invention.
[0515] In this firing step, first, the above-mentioned mat-shaped
short-fiber precursor is preferably heated (pre-processing) under
conditions of 400 to 600.degree. C. for 10 to 60 minutes in an
oxygen-containing atmosphere. This process is applied so as to fire
and eliminate organic components contained in the short fiber
precursor used in the mat-shaped short-fiber precursor.
[0516] Next, the mat-shaped short-fiber precursor, which has been
subjected to the above-mentioned pre-processing, is heated to a
temperature in the atmosphere, with the lower limit being set to
1000.degree. C., preferably, 1050.degree. C., and the upper limit
being set to 1300.degree. C., preferably, 1250.degree. C. so that
the short-fiber precursor is sintered. The heating temperature of
less than 1000.degree. C. tends to make the sintering step of the
short fiber precursor insufficient, making it difficult to obtain
an alumina fiber aggregation with high strength. In contrast, the
heating temperature exceeding 1300.degree. C. fails to provide high
strength of the alumina fiber aggregation, resulting in
disadvantages in the productivity and economical efficiency.
[0517] In this firing step, the short fiber precursor used in the
mat-shaped short-fiber precursor is sintered to be formed into
alumina short fibers, and the above-mentioned precursor short
fibers are entangled in a complex manner through the
above-mentioned needle punch process and the like, and then these
entangled precursor short fibers are fired so as to be mutually
bonded. Thus, the manufactured alumina fiber aggregation is allowed
to have excellent mechanical strength.
[0518] Moreover, the mat-shaped short-fiber precursor, fired in the
above-mentioned conditions, has its organic components fired and
eliminated so that its volume is reduced.
[0519] Normally, the above-mentioned alumina short fibers are
mainly composed of alumina and silica, and the alumina short fibers
are preferably set to have a mullite crystal content of 0 to 10% by
weight or less. Since the alumina short fiber shaving such a
chemical composition has a small amorphous component so that it has
excellent heat resistance and high repulsive force upon application
of compressing load. Therefore, in the case where the alumina fiber
aggregation according to the sixth group of the present invention
is used as a holding seal material such as a honeycomb filter 10 as
described in the prior art section, even when this is subjected to
a high temperature in a state placed in a gap between the metal
shell and the honeycomb filter 10, it is possible to reduce the
possibility of reduction in the face pressure to be generated.
[0520] Moreover, the fiber tensile strength of the above-mentioned
alumina short fiber is preferably set to 1.2 GPa or more, more
preferably 1.5 Gpa or more. Further, the fiber bending strength of
the alumina short fibers is preferably set to 1.0 GPa or more, more
preferably 1.5 GPa or more. Moreover, the fracture toughness value
of the alumina short fibers is preferably set to 0.8 MN/m.sup.3/2
or more, more preferably 1.3 MN /m.sup.3/2 or more. This is because
as the fiber tensile strength, the fiber bending strength and the
fracture toughness value increase, the alumina short fibers become
very strong against the tension and bending, thereby forming
flexible alumina short fibers that are less susceptible to
damage.
[0521] Thereafter, the above-mentioned alumina fiber aggregation is
formed into a holding seal material having virtually the same shape
as the holding seal material 30 shown in FIG. 18 by a punching
process and the like.
[0522] The size of the holding seal material is properly determined
in accordance with the purpose of use, and when used as a holding
seal material to be wound around the outer circumference of the
honeycomb filter 10, for example, shown in FIG. 16, the thickness
of the holding seal material is set to approximately 1.1 to 4 times
the gap between the outer diameter of the honeycomb filter 10 and
the inner diameter of the metal shell housing the honeycomb filter
10, more preferably approximately 1.5 to 3 times the gap.
[0523] The thickness of the holding seal material of less than 1.1
times the above-mentioned gap fails to provide a high holding
property in the honeycomb filter 10 when the honeycomb filter 10 is
housed in the metal shell, resulting in the possibility of
deviation and backlash of the honeycomb filter 10 against the metal
shell. Since this case of course fails to provide a high sealing
property, leakage of exhaust gas tends to occur from the gap
portion, causing an insufficient purifying property for exhaust
gas. In contrast, if the thickness of the holding seal material
exceeding four times the above-mentioned gap, it becomes difficult
to place the honeycomb filter 10 in the metal shell, in particular,
when a press-fitting system is adopted so as to place the honeycomb
filter 10 in the metal shell.
[0524] Moreover, after the holding seal material has been housed in
the metal shell, the lower limit of the bulk density thereof is
preferably set to 0.1 g/cm.sup.3, with the upper limit thereof
being set to 0.3 g/cm.sup.3, and the lower limit of the bulk
density of the holding seal material is more preferably set to 0.1
g/cm.sup.3, with the upper limit being set to 0.25 g/cm.sup.3. The
bulk density of less than 0.1 g/cm.sup.3fails to provide a
sufficiently high initial face pressure of the holding seal
material; in contrast, the bulk density exceeding 0.3 g/cm.sup.3
increases the quantity of alumina short fibers to be used as a
material, resulting in high manufacturing costs.
[0525] Furthermore, the aforementioned holding seal material may be
subjected to the needle punching process, if necessary, and after
the holding seal material has been subjected to an impregnation
process in an organic binder, this may be further compressed and
molded in the thickness direction of the holding seal material. The
application of these processes makes it possible to compress the
holding seal material in the thickness direction and consequently
to make it thinner.
[0526] With respect to the above-mentioned organic binder, PVA and
acrylic resins may be used, in addition to latexes and the like
such as acrylic rubber and nitrile rubber and the like.
[0527] As described above, in the manufacturing method of the
alumina fiber aggregation according to the sixth group of the
present invention, the alumina-fiber stock solution is subjected to
a spinning process, and extended to form a continuous long-fiber
precursor, and the resulting continuous long-fiber precursor is
then cut to form short-fiber precursors; then, these are formed
into a mat precursor so that an alumina fiber aggregation is
manufactured by sintering this mat precursor.
[0528] In accordance with the manufacturing method of the alumina
fiber aggregation according to the sixth group of the present
invention, the cut surface of the above-mentioned short-fiber
precursor is free from the generation of chips, burs and
micro-cracks, and this is then subjected to a sintering step so
that it is possible to manufacture alumina short fibers that are
excellent in the mechanical strength.
[0529] In other words, since the alumina short fibers to be used in
the alumina fiber aggregation are allowed to have excellent
mechanical strength, it becomes possible to provide an alumina
fiber aggregation that has a sufficiently high initial face
pressure, and is less susceptible to degradation with time in the
face pressure.
[0530] The following description will be given of more specific
examples of the above-mentioned embodiments, and comparative
examples thereof; however, the present invention is not intended to
be limited by these examples.
BEST MODE FOR CARRYING OUT THE PRESENT INVENTION
[0531] The following description will be given of examples and
comparative examples according to the first group of the present
invention.
EXAMPLE 1
[0532] In example 1, first, a basic water solution of aluminum
chloride (23.5% by weight) , silica sol (20% by weight, silica
particle size 15 nm) and polyvinyl alcohol (10% by weight) that is
a fiber-drawing property applying agent were mixed to prepare a
spinning stock solution. Next, the resulting spinning stock
solution was condensed under vacuum at 50.degree. C. by using an
evaporator to prepare a spinning stock solution having a
concentration of 38% by weight with a viscosity of 1500 Poise.
[0533] After preparation, the spinning stock solution was
continuously discharged into the air through a nozzle (having a
complete round shape in its cross-section) of the spinning device,
and the precursor fibers thus formed were wound up while being
extended.
[0534] Next, after the above-mentioned precursor fibers had been
subjected to a heating step (pre-processing) at 250.degree. C. for
30 minutes in an electric furnace that is maintained at normal
pressure in a nitrogen atmosphere, these were sintered at
1250.degree. C. for 10 minutes in an electric furnace that is
maintained at normal pressure in a nitrogen atmosphere in the same
manner.
[0535] As a result, a complete-round-shaped alumina-silica based
fiber 6 which had an alumina-silica weight ratio of 72:28, an
average-fiber-size of 10.5 .mu.m and a quantity of residual carbon
of 5% by weight (see Table 1) was obtained. When the mechanical
strengths of this alumina-silica based fiber 6 were measured by
publicly known methods, the fiber tensile strength was 2.0 GPa, the
fiber bending strength was 1.8 GPa, and the fracture toughness was
1.5 MN/m.sup.3/2. In other words, the alumina-silica based fibers 6
of embodiment 1 had excellent mechanical strengths.
[0536] When the resulting alumina-silica based fibers 6 were
visually observed, the diameter and cross-sectional shape thereof
were evenly set and could be referred to have excellent stability
in quality. Moreover, the alumina-silica based fiber 6 had a black
color (so-called carbon black color) , which was a novel feature
that had not been provided.
[0537] Next, the long fiber of the alumina-silica based fiber 6 was
chopped into a length of 5 mm to provide short fibers. Thereafter,
these short fibers were dispersed in water, and the resulting fiber
dispersion solution was poured into a mold, and pressed and dried
so that a mat-shaped fiber aggregation was obtained. Then, samples
were formed from this fiber aggregation, and with respect to the
face pressure, measuring tests were carried out in the following
manner.
[0538] First, the fiber aggregation was punched out to a square
shape with 25 mm in each side to prepare a face-pressure
measuring-use sample, and this was sandwiched by special jigs, and
adjusted to have a bulk density (GBD) of 0.30 g/cm.sup.3. The
face-pressure measuring-use sample in this state was held in the
atmosphere at 1000.degree. C., and the face pressure was measured 1
hour later, 10 hours later, and 100 hours later. Here, the face
pressure which had been measured without heating in a
non-sandwiched state was defined as "initial face pressure", and
the face pressure 100 hours later was defined as "face pressure
after endurance tests". Moreover, the expression, (face pressure
after endurance tests/initial face pressure).times.100(%) was
calculated, and defined as the degradation with time rate of face
pressure. Table 1 shows the results of these tests.
[0539] In accordance with the results of the tests, in the sample
of example 1, both of the initial face pressure and the face
pressure after endurance tests exceeded 100 kPa, and the
degradation with time rate of face pressure was maintained within
50%, which was a comparatively low level. Here, when the sample
obtained 100 hours later was observed, it was found that the
properties of the alumina-silica based fiber 6 were not
particularly changed, and still had a black color. The quantity of
residual carbon was also maintained at 5% by weight.
[0540] Moreover, after the above-mentioned mat-shaped fiber
aggregation had been punched out to a predetermined shape, and
actually formed into a holding seal material 4, this was wound
around a catalyst carrier 2, and the resulting member 2 was
press-fitted into a metal shell 3.
[0541] With respect to the catalyst carrier 2, a cordierite
monolith having an outer diameter of 130 mm.phi. and a length of
100 mm was used. With respect to the metal shell 3, a cylinder
member, which was made of SUS304 having an O-letter shape in its
cross-section with 1.5 mm in thickness and 140 mm.phi. in inner
diameter, was used. A catalyst converter 1, assembled in this
manner, was actually loaded into a gasoline engine of 3 liters, and
this was subjected to a continuous driving test. As a result, upon
traveling, neither noise nor backlash of the catalyst carrier 2 was
generated so that it was confirmed that the initial face pressure
was improved, with the degradation with time in the face pressure
being securely prevented. Moreover, it was possible to provide an
excellent anti-wind erosion property.
EXAMPLES 2, 3
[0542] In examples 2, 3, alumina-silica based fibers 6 were
respectively prepared basically in the same sequence as example 1
except that the firing temperature and the firing time were changed
as shown in Table 1. As a result, it was possible to obtain
alumina-silica based fibers 6 that were excellent in mechanical
strengths.
[0543] Moreover, when face-pressure measuring-use samples were
formed, and the initial face pressure, the face pressure after
endurance tests and the degradation with time rate of face pressure
were measured on these, preferable results were obtained in the
same manner as example 1 (see Table 1).
[0544] Of course, no changes were observed with respect to the
color and quantity of residual carbon.
[0545] Furthermore, a holding seal material 4 was formed so as to
prepare a catalyst converter 1, and a continuous driving test was
carried out by loading this. As a result, upon traveling, neither
noise nor backlash of the catalyst carrier 2 was generated so that
it was confirmed that the initial face pressure was improved, with
the degradation with time in the face pressure being securely
prevented.
COMPARATIVE EXAMPLE 1
[0546] In comparative example 1, a spinning process was carried out
by using as pinning stock solution having the same composition as
example 1 so that precursor fibers were formed. Next, after the
above-mentioned precursor fibers had been subjected to a heating
step (pre-processing) at 250.degree. C. for 30 minutes in an
electric furnace that is maintained at normal pressure in an active
atmosphere containing oxygen (the atmosphere) , these were sintered
at 1250.degree. C. for 10 minutes in an electric furnace that is
maintained at normal pressure in the same active atmosphere (the
atmosphere) in the same manner.
[0547] As a result, a complete-round-shaped alumina-silica based
fiber 6 with a transparent white color, which had an alumina-silica
weight ratio of 72:28, an average-fiber-diameter of 10.2 .mu.m and
a quantity of residual carbon of 0% by weight (see Table 1), was
obtained. The mechanical strengths of this alumina-silica based
fiber 6 were shown in Table 1, which indicated approximately half
of the values of examples 1 to 3. In other words, the
alumina-silica based fiber 6 of comparative example 1 was clearly
inferior to those obtained in examples 1 to 3.
[0548] Moreover, face-pressure measuring-use samples were prepared
so that the initial face pressure, the face pressure after
endurance tests and the degradation with time rate of face pressure
were measured, and it was confirmed that these values were clearly
inferior to those of examples 1 to 3 (see Table 1).
1TABLE 1 Comparative Example 1 Example 2 Example 3 Example 1 Firing
atmosphere Nitrogen Nitrogen Nitrogen Atmosphere Firing temperature
1250.degree. C. 1290.degree. C. 1150.degree. C. 1250.degree. C.
Firing time 10 minutes 5 minutes 20 minutes 10 minutes Color of
fiber Black (5) Black (6) Black (8) White (9) (Brightness) Quantity
of residual 3% by weight 5% by weight 1% by weight 0% by weight
carbon Average fiber diameter 10.5 .mu.m 10.5 .mu.m 10.5 .mu.m 10.2
.mu.m Fiber tensile strength 2.0 Gpa 1.8 Gpa 2.3 Gpa 1.1 Gpa Fiber
bending strength 1.8 Gpa 1.6 Gpa 2.0 Gpa 0.9 Gpa Fracture toughness
1.5 MN/m.sup.3/2 1.6 MN/m.sup.3/2 1.5 MN/m.sup.3/2 0.7 MN/m.sup.3/2
Bulk density 0.10 g/cm.sup.3 0.10 g/cm.sup.3 0.10 g/cm.sup.3 0.10
g/cm.sup.3 Initial face pressure 185 kPa 180 kPa 192 kPa 144 kPa
Face pressure after 107 kPa 105 kPa 105 kPa 35 kPa endurance tests
Degradation with time 42.2% 41.7% 45.3% 75.7% rate of face
pressure
[0549] Next, the following description will be given of examples
and comparative examples according to the second group of the
present invention.
EXAMPLE 4
[0550] In example 4, first, long fibers of precursor fibers were
prepared in the same manner as example 1.
[0551] Next, the long fiber of precursor fiber was chopped to a
length of 5 mm so that short fibers were prepared. Thereafter,
these short fibers were dispersed in water, and the resulting fiber
dispersion solution was poured into a mold, and pressed and dried
so that a mat-shaped fiber aggregation M1 was obtained.
[0552] In a firing step following the above-mentioned laminating
process, after the above-mentioned fiber aggregation M1 had been
subjected to a heating step (pre-processing) at 250.degree. C. for
30 minutes in an electric furnace 21 that is maintained at normal
pressure in the atmosphere, these were sintered in the electric
furnace 21 that is maintained at normal pressure in the atmosphere
in the same manner.
[0553] In example 4, the temperature of an upper electric heater 24
was set higher so that the surface temperature on the first face
side S1 was set to 1250.degree. C. at the firing time, while the
temperature of a lower electric heater 25 was set lower so that the
surface temperature on the second face side S2 was set to
1000.degree. C. In other words, a firing temperature difference of
250.degree. C. was prepared. The firing time was set to 30
minutes.
[0554] The alumina-silica based fibers 6 on the surface layer
portion of the first face side S1 and the surface layer portion of
the second face side S2 of the fiber aggregation M1 thus obtained
were respectively sampled, and these fibers were examined with
respect to several points. Table 2 shows the test results.
[0555] With respect to the crystallization rate of the
alumina-silica based fibers 6, the rate on the surface layer
portion of the first face side S1 was clearly smaller than that on
the surface layer portion of the second face side S2.
[0556] In contrast, with respect to the fiber tensile strength,
fiber bending strength, elastic modulus and extension rate of the
alumina-silica based fibers 6, those factors on the surface layer
portion of the first face side S1 were clearly greater than those
on the surface layer portion of the second face side S2.
[0557] Here, the weight ratio of alumina-silica was 72:28, the
average fiber diameter was 10.5 .mu.m, and the cross-sectional
shape of the fiber had a complete round shape.
[0558] The mat-shaped fiber aggregation M1 was punched out to a
square shape with 25 mm in each side to prepare a face-pressure
measuring-use sample, and this was sandwiched by special jigs, and
adjusted to have a bulk density (GBD) of 0.30 g/cm.sup.3. The
face-pressure measuring-use sample in this state was held in the
atmosphere at 1000.degree. C., and the face pressure was measured 1
hour later, 10 hours later, and 100 hours later, respectively.
Here, the face pressure which had been obtained 1 hour later was
defined as "initial face pressure", and the face pressure 100 hours
later was defined as "face pressure after endurance tests".
Moreover, the expression, (face pressure after endurance
tests/initial face pressure).times.100(%) was calculated, and
defined as the degradation with time rate of face pressure. The
results of these tests are shown in a graph of FIG. 6.
[0559] In accordance with the results of the tests, in the sample
of example 4, both of the initial face pressure and the face
pressure after endurance tests exceeded 100 kPa, and the
degradation with time rate of face pressure was maintained at a
comparatively low level.
[0560] A catalyst converter 1 was assembled in the same as example
1 by using the mat-shaped fiber aggregation M1, and this was loaded
into a gasoline engine of 3 liters, and subjected to a continuous
driving test. As a result, upon traveling, neither noise nor
backlash of the catalyst carrier 2 was generated so that it was
confirmed that the initial face pressure was improved, with the
degradation with time in the face pressure being securely
prevented. Moreover, no leakage of exhaust gas was found so that an
excellent sealing property was obtained together with an excellent
anti-wind erosion property.
[0561] COMPARATIVE EXAMPLE 2
[0562] In comparative example 2, a firing step was carried out at
1250.degree. C. for 30 minutes in an even manner without setting
any difference in the firing temperature. Except for this point, a
fiber aggregation M1 was formed basically under the same conditions
as the examples.
[0563] In comparative example 2, the physical properties of the
alumina-silica based fiber 6 (the crystallization rate, the fiber
tensile strength, fiber bending strength, elastic modulus and
extension rate) were virtually the same as those of the
alumina-silica based fibers 6 located on the surface layer portion
on the second face side S2 of the example. In other words, there
was no specific difference in the crystallization rate, etc.
depending on portions.
[0564] Moreover, face-pressure measuring-use samples were prepared
in the same manner as the examples, and measurements were carried
out on these with respect to the initial face pressure, face
pressure after endurance tests and degradation with time rate of
face pressure. As shown in a graph of FIG. 6, the samples of
comparative example 2 were clearly inferior to those of example
4.
2TABLE 2 First face side Second face side Firing temperature
1000.degree. C. 1250.degree. C. Firing time 30 minutes 30 minutes
Crystallization 0.0% by weight 8.3% by weight rate Fiber tensile
2.3 GPa 1.1 Gpa strength Fiber bending 2.0 GPa 0.9 GPa strength
Elastic modulus 11.3 .times. 10.sup.10 N/m.sup.2 9.8 .times.
10.sup.10 N/m.sup.2 Extension rate 2.3% 1.0%
[0565] The following description will be given of examples and
comparative examples according to the third group of the present
invention.
EXAMPLE 5
[0566] In example 5, face-pressure-evaluation-use samples of a
holding seal material 4 were formed in the following manner.
[0567] First, a basic water solution of aluminum chloride (23.5% by
weight) , silica sol (20% by weight, silica particle size 15 nm) ,
polyvinyl alcohol (10% by weight) and tetraethylene glycol
monobutylether (1% by weight) were mixed to prepare a spinning
stock solution 18. Next, the resulting spinning stock solution 18
was condensed under vacuum at 50.degree. C. by using an evaporator
to prepare a spinning stock solution 18 having a concentration of
38% by weight with a viscosity of 1000 Poise.
[0568] After preparation, the spinning stock solution 18 was
supplied to a spinning device 20 of FIG. 8. The shape of a metal
mouth 19a of the nozzle 19 was set to a rectangular shape (longer
side: 500 .mu.m, shorter side: 50 .mu.m) , as shown on the 1.sup.st
row in the left column of the table of FIG. 9. During the spinning
process, dry hot air of 10 m/s at 50.degree. C. was continuously
discharged from a dry-air discharging port.
[0569] Thus, the spinning stock solution 18 was continuously
discharged into the air through the metal mouth 19a so that a
precursor fiber 6A was formed, and the precursor fiber 6A thus
formed was wound up while being extended. At this time, dry hot air
was blown to the precursor fibers 6 in the forward direction of the
discharging direction thereof so that the drying process and
extending process were carried out simultaneously.
[0570] Next, after the above-mentioned precursor fibers 6A had been
subjected to a heating step (pre-processing) at 250.degree. C. for
30 minutes in an electric furnace that is maintained in the air
atmosphere, these were sintered at 1200.degree. C. for 10 minutes
in an electric furnace in the same manner.
[0571] As a result, as shown on the 1.sup.st row in the right
column of the table of FIG. 9 and FIG. 10, an alumina-silica based
fiber 6 (average major axis: 15 .mu.m, average minor axis: 10
.mu.m) which had an elliptical cross-section according to example
5, was obtained. This alumina-silica based fiber 6 had a mullite
crystal content of approximately 8% by weight and an alumina-silica
weight ratio of 72:28. Here, hardly any organic substances were
contained in the components of the alumina-silica based fiber 6.
Moreover, FIG. 10 shows an SEM photograph that indicates a
cross-section of the alumina-silica based fiber 6 according to
example 5.
[0572] Next, the long fiber of the alumina-silica based fiber 6 was
chopped into a length of 5 mm to provide short fibers. Thereafter,
these short fibers were dispersed in water, and the resulting fiber
dispersion solution was poured into a mold, and pressed and dried
so that a mat-shaped fiber aggregation having a thickness of 20 mm
was obtained. This was then punched out to a square shape with 25
mm in each side to prepare a face-pressure evaluation sample of
example 5.
[0573] In the face-pressure evaluation test, the above-mentioned
sample was compressed to a thickness of 3 mm by using a compressing
jig, and this process was repeated five times. In this case, the
face pressure value at the time of the first compression and the
face pressure value at the time of the fifth compression were
measured, and based upon the results of the measurements, the rate
of residual face pressure (%), which forms an index of the degree
of degradation with time in face pressure, was found. The result of
this was 95.0% as shown in Table 3.
[0574] After this fiber aggregation had been punched out to a
predetermined shape and formed into a holding seal material 4, this
was wound around a catalyst carrier 2, and the resulting member 2
was press-fitted into a metal shell 3. With respect to the catalyst
carrier 2, a cordierite monolith having an outer diameter of 130
mm.phi. and a length of 100mm was used. With respect to the metal
shell 3, a cylinder member, which was made of SUS304 having an
O-letter shape in its cross-section with 1.5 mm in thickness and
140 mm.phi. in inner diameter, was used. A catalyst converter 1,
assembled in this manner, was actually loaded into a gasoline
engine of 3 liters, and this was subjected to a continuous driving
test. As a result, upon traveling, neither noise nor backlash of
the catalyst carrier 2 was generated even after a lapse of
considerably long time so that it was confirmed that the degree of
degradation with time in the face pressure was reduced.
EXAMPLE 6
[0575] In example 6, the same sequence as example 5 was basically
carried out except that the shape of the metal mouth 19a was
changed. As a result, an alumina-silica based fiber 6 (average
major axis: 30 .mu.m, average minor axis: 10 .mu.m) which had an
elliptical cross-section according to example 6, was obtained. This
alumina-silica based fiber 6 had a mullite crystal content of
approximately 8% by weight and an alumina-silica weight ratio of
72:28. Here, hardly any organic substances were contained in the
components of the alumina-silica based fiber 6.
[0576] Next, the mat-shaped fiber aggregation was punched out to a
square shape with 25 mm in each side to prepare a face-pressure
evaluation sample of example 6, and this was subjected to a
face-pressure evaluation test in the same manner as example 1. As a
result, in Example 6, the residual rate of 94.0% was obtained (see
FIG. 3).
[0577] Moreover, a holding seal material 4 was prepared, and a
catalyst converter 1 was assembled, and this was then actually
loaded into a gasoline engine of 3 liters, and subjected to a
continuous driving test. As a result, upon traveling, neither noise
nor backlash of the catalyst carrier 2 was generated even after a
lapse of considerably long time so that it was confirmed that the
degree of degradation with time in the face pressure was
reduced.
EXAMPLE 7
[0578] In example 7, the same sequence as example 5 was basically
carried out except that the shape of the metal mouth 19a was formed
into a virtually dumbbell shape having a size as shown on the
second row in the left column of the table of FIG. 9. As a result,
as shown on the second row in the right column of FIG. 9 and FIG.
11, an alumina-silica based fiber 6 (average width: 20 .mu.m,
average center thickness: 5 .mu.m, average edge portion thickness:
10 .mu.m) which had a cocoon shaped cross-section or a virtually
peanut-shaped cross-section according to example 7was obtained.
This alumina-silica based fiber 6 had a mullite crystal content of
approximately 8% by weight and an alumina-silica weight ratio of
72:28. Here, hardly any organic substances were contained in the
components of the alumina-silica based fiber 6. Furthur, FIG. 11 is
an SEM photograph that shows a cross-section of the alumina-silica
based fiber according to example 7.
[0579] Next, the mat-shaped fiber aggregation was punched out to a
square shape with 25 mm in each side to prep area face-pressure
evaluation sample of example 2, and this was subjected to a
face-pressure evaluation test in the same manner as example 5. As a
result, in example 7, the residual rate of 89.9% was obtained (see
FIG. 3).
[0580] Moreover, a holding seal material 4 was prepared, and a
catalyst converter 1 was assembled, and this was then actually
loaded into a gasoline engine of 3 liters, and subjected to a
continuous driving test. As a result, upon traveling, neither noise
nor backlash of the catalyst carrier 2 was generated even after a
lapse of considerably long time so that it was confirmed that the
degree of degradation with time in the face pressure was
reduced.
EXAMPLE 8
[0581] In example 8, the same sequence as example 5 was basically
carried out except that the shape of the metal mouth 19a was formed
into a virtually C-letter shape having a size as shown on the third
row in the left column of the table of FIG. 9. As a result, as
shown on the third row in the right column of FIG. 9, an
alumina-silica based fiber 6 having a hollow cross-sectional shape
(outer diameter: 20 .mu.m, inner diameter: 10 .mu.m) according to
example 8 was obtained. This alumina-silica based fiber 6 had a
mullite crystal content of approximately 8% by weight and an
alumina-silica weight ratio of 72:28. Here, hardly any organic
substances were contained in the components of the alumina-silica
based fiber 6.
[0582] Next, the mat-shaped fiber aggregation was punched out to a
square shape with 25 mm in each side to prepare a face-pressure
evaluation sample of example 8, and this was subjected to a
face-pressure evaluation test in the same manner as example 1. As a
result, in example 8, the residual rate of 94.6% was obtained (see
FIG. 3).
[0583] Moreover, a holding seal material 4 was prepared, and a
catalyst converter 1 was assembled, and this was then actually
loaded into a gasoline engine of 3 liters, and subjected to a
continuous driving test. As a result, upon traveling, neither noise
nor backlash of the catalyst carrier 2 was generated even after a
lapse of considerably long time so that it was confirmed that the
degree of degradation with time in the face pressure was
reduced.
TEST EXAMPLE 1
[0584] In test example 8, the same sequence as example 5 was
basically carried out except that the shape of the metal mouth 19a
was changed. As a result, an alumina-silica based fiber 6 having an
elliptical cross-sectional shape (average major axis: 35 .mu.m,
average minor axis: 10 .mu.m) according to test example 1 was
obtained. This alumina-silica based fiber 6 had a mullite crystal
content of approximately 8% by weight and an alumina-silica weight
ratio of 72:28. Here, hardly any organic substances were contained
in the components of the alumina-silica based fiber 6.
[0585] Next, the mat-shaped fiber aggregation was punched out to a
square shape with 25 mm in each side to prepare a face-pressure
evaluation sample of test example 1, and this was subjected to a
face-pressure evaluation test in the same manner as example 1. As a
result, in test example 1, the residual rate of 92.0% was obtained
(see FIG. 3).
[0586] However, it was found that its initial face pressure was
lower in comparison with the respective examples.
COMPARATIVE EXAMPLE 3
[0587] In comparative example 3, the same sequence as example 5 was
basically carried out except that the shape of the metal mouth 19a
was formed into a complete round shape having a diameter of 0.2 mm
as shown on the fourth row in the left column of the table of FIG.
9. As a result, as shown on the fourth row in the right column of
FIG. 9, an alumina-silica based fiber 6 having a complete round
cross-sectional shape (outer diameter: 10 .mu.m) according to
comparative example 3 was obtained. This alumina-silica based fiber
6 having a complete round cross-sectional shape of comparative
example 3 had a mullite crystal content of approximately 8% by
weight and an alumina-silica weight ratio of 72:28. Here, hardly
any organic substances were contained in the components of the
alumina-silica based fiber 6.
[0588] Next, the mat-shaped fiber aggregation was punched out to a
square shape with 25 mm in each side to prepare a face-pressure
evaluation sample of comparative example 3, and this was subjected
to a face-pressure evaluation test in the same manner as example 5.
As a result, in comparative example 3, the residual rate was 85.0%,
which was clearly inferior to the respective examples (see FIG.
3).
[0589] Therefore, it was found that the degree of degradation with
time in face pressure would be greater in comparison with the
respective examples.
3TABLE 3 Face Fiber pressure Face pressure sectional value in value
in Residual shape the first time the fifth time rate Example 5
Elliptical shape 202 kPa 192 kPa 95.0% Example 6 Elliptical shape
200 kPa 188 kPa 94.0% Example 7 Cocoon shape 208 kPa 187 kPa 89.9%
Example 8 Hollow shape 205 kPa 194 kPa 94.6% Comparative Complete
213 kPa 181 kPa 85.0% Example 3 round shape
[0590] The following description will be given of examples and
comparative examples according to the fourth group of the present
invention.
EXAMPLE 9
[0591] In example 9, face-pressure-evaluation-use samples of a
holding seal material 4 were formed in the following manner.
[0592] First, a basic water solution of aluminum chloride (23.5% by
weight) , silica sol (20% by weight, silica particle size 15 nm),
polyvinyl alcohol (10% by weight) and an antifoamer (n-octanol)
were mixed to prepare a spinning stock solution. Next, the
resulting spinning stock solution was condensed under vacuum at
50.degree. C. by using an evaporator to prepare a spinning stock
solution having a concentration of 38% by weight with a viscosity
of 1000 to 2000 Poise.
[0593] The spinning stock solution, thus prepared, was continuously
discharged into the air through the nozzle of a spinning device,
and the precursor fiber thus formed was wound up while being
extended.
[0594] At this time, in order to control the fiber diameter, the
following conditions were set. In other words, the diameter of the
nozzle discharging port was set to 0.1 to 0.2 mm, the length was
set to 0.3 to 2.0 mm, and the discharging rate was set to 1.5 to
2.0 cm/s; thus, the spinning stock solution was discharged. After
the precursor fiber derived from the spinning stock solution had
been extended at a rate 100 to 200 times the above-mentioned
discharging rate, the fiber was wound around a winder having a
diameter of approximately 12 cm. A cylinder having a length of 2 to
4 m was placed between the nozzle discharging port and the winder,
and the precursor fiber was allowed to pass through the cylinder.
The upper half of the inside of the cylinder was set to a
temperature of 35 to 40.degree. C., and the lower half of the
inside of the cylinder was set to a temperature of 25 to 30.degree.
C.
[0595] Successively, the long fiber of the precursor fiber was
chopped to a length of 10 mm by using a guillotine cutter so that
short fibers were prepared. Thereafter, these short fibers
(approximately 1.0 g) were dispersed in water, and the resulting
fiber dispersion solution was poured into a mold, and pressed and
dried so that a mat-shaped fiber aggregation having a square shape
with 25 mm in the longitudinal and lateral sides was obtained.
[0596] Next, after the above-mentioned mat-shaped fiber aggregation
had been subjected to a heating step (pre-processing) at
250.degree. C. for 30 minutes in an electric furnace that is
maintained in the air atmosphere, this was sintered at 1250.degree.
C. for 10 minutes in an electric furnace in the same manner.
[0597] As a result, a sample of the holding seal material 4, made
from the complete-round-shaped alumina-silica based fiber 6 that
had a mullite crystal content of approximately 8% by weight and an
alumina-silica weight ratio of 72:28, was obtained.
[0598] Alumina-silica based fibers 6 were taken from a plurality of
portions of the sample of example 9 thus obtained, and the average
fiber diameter (.mu.m) and the minimum, maximum and average fiber
length (mm) thereof as well as the minimum value, maximum value and
shot content (%) were examined. Table 4 shows the results of the
measurements. In accordance with these values, in example 9,
dispersions in the fiber diameter and dispersions in the fiber
length were extremely small so that it was confirmed that these
values are maintained within the above-mentioned preferable ranges.
Moreover, no shot was contained in the sample.
[0599] Next, a plurality of samples having a square shape with 25
mm in each side were punched out from a large one sheet of
mat-shaped fiber aggregation, and the basis weight was examined
from each of these based upon the area and weight thereof, and the
face pressure thereof was measured by using an autograph. Table 4
also shows the results of these. Here, the measured face pressure
values were based upon the data obtained when GBD was set to 0.30
g/cm.sup.3. These values showed that in example 9, dispersions in
the basis weight and dispersions in the face pressure were small,
indicating stability in quality. Moreover, it was also found that
the average face pressure value became higher.
COMPARATIVE EXAMPLE 4
[0600] In comparative example 4, the same spinning stock solution
as example 9 was condensed under vacuum at 50.degree. C. by using
an evaporator to prepare a spinning stock solution having a
concentration of 38% by weight with a viscosity of 10 to 100
Poise.
[0601] With respect to the spinning device, a disc-shaped
centrifugal nozzle, which has a diameter of 50 to 100 mm with
discharging holes of 0.2 to 0.8 mm being placed at 16 positions
with equal intervals, was used. Then, by using a centrifugal force
exerted when this nozzle was rotated at the number of revolutions
of 1000 to 2000 rpm, the spinning stock solution was discharged,
and formed into fibers. Moreover, the resulting precursor fibers
were blown by air in 0.5 to 1.0 kPa at 30.degree. C., collected,
and laminated to form a mat-shaped fiber aggregation. This was
molded into a square shape with 25 mm in the longitudinal and
lateral sides, and subjected to the same pre-processing and firing
step in the same conditions as example 9 to be formed into
ceramics.
[0602] Alumina-silica based fibers 6 were taken from a plurality of
portions of the sample of comparative example obtained by such a
blowing method, and the average fiber diameter (.mu.m) and the
minimum, maximum and average fiber length (mm) thereof as well as
the minimum value, maximum value and shot content (%) were
examined. Table 4 shows the results of the measurements. In
accordance with these values, with respect to comparative example
4, it was confirmed that dispersions in the fiber diameter and
dispersions in the fiber length became considerably greater in
comparison with the examples. Moreover, the shots of 3% by weight
or more were contained in the sample.
[0603] Next, a plurality of samples having a square shape with 25
mm in each side were punched out from a large one sheet of
mat-shaped fiber aggregation, and the basis weight was examined
from each of these based upon the area and weight thereof, and the
face pressure thereof was measured by using an autograph. Table 1
also shows the results of these. Here, the face pressure measured
values were based upon the data obtained when GBD was set to 0.30
g/cm.sup.3. These values showed that in comparative example 4,
dispersions in the basis weight and dispersions in the face
pressure were greater in comparison with example 9, indicating
instability in quality. Moreover, it was also found that the
average face pressure value was considerably lower than that of
example 9.
4TABLE 4 Comparative Example 8 Example 4 Average fiber diameter 7.1
.mu.m 6.8 .mu.m Lower limit value of fiber 4.8 .mu.m 1.1 .mu.m
diameter (-2.3 .mu.m) (-5.7 .mu.m) Upper limit value of fiber 9.2
.mu.m 22.3 .mu.m diameter (+2.1 .mu.m) (+15.5 .mu.m) Average fiber
length 10 mm 26 mm Lower limit value of fiber 9 mm 2 mm length (-1
mm) (-24 mm) Upper limit value of fiber 11 mm 60 mm length (+1 mm)
(+34 mm) Shot content 0.0% by weight 3.8% by weight Average basis
weight 1152 g/m.sup.2 1147 g/m.sup.2 Lower limit value of basis
1093 g/m.sup.2 1012 g/m.sup.2 weight (-59 g/m.sup.2) (-135
g/m.sup.2) Upper limit value of basis 1183 g/m.sup.2 1251 g/m.sup.2
weight (+31 g/m.sup.2) (+104 g/m.sup.2) Average face pressure 212
kPa 154 kPa Lower limit value of face 201 kPa 123 kPa pressure (-11
kPa) (-31 kPa) Upper limit value of face 218 kPa 178 kPa pressure
(+6 kPa) (+24 kPa) *Values inside parentheses indicate a difference
from the average value.
[0604] The following description will be given of examples and
comparative examples according to the fifth group of the present
invention.
EXAMPLE 10
[0605] In example 10, samples for face pressure evaluation of a
holding seal material 4 were formed in the following manner.
[0606] First, a basic water solution of aluminum chloride (23.5% by
weight) , silica sol (20% by weight, silica particle size 15 nm),
polyvinyl alcohol (10% by weight) and an antifoamer (n-octanol)
were mixed to prepare a spinning stock solution. Next, the
resulting spinning stock solution was condensed under vacuum at
50.degree. C. by using an evaporator to prepare a spinning stock
solution having a concentration of 38% by weight with a viscosity
of 1000 Poise.
[0607] The spinning stock solution, thus prepared, was continuously
discharged into the air through a nozzle of a spinning device, and
the precursor fiber thus formed was wound up while being
extended.
[0608] After the above-mentioned precursor fiber had been subjected
to a heating step (pre-processing) at 250.degree. C. for 30 minutes
in an electric furnace that is maintained in the air atmosphere,
this was sintered at 1250.degree. C. for 10 minutes in an electric
furnace in the same manner.
[0609] As a result, complete-round-shaped alumina-silica based
fibers 6 having an average fiber diameter of 9 .mu.m, which had a
mullite crystal content of approximately 8% by weight and an
alumina-silica weight ratio of 72:28, were obtained.
[0610] Successively, the long fiber of the precursor fiber 6 was
chopped to a length of 5 mm by using a guillotine cutter so that
short fibers were prepared. Thereafter, these short fibers
(approximately 1.0 g) were dispersed in water, and the resulting
fiber dispersion solution was poured into a mold, and pressed and
dried so that a mat-shaped fiber aggregation having a square shape
with 25 mm in the longitudinal and lateral sides was obtained.
[0611] Then, after this fiber aggregation had been impregnated with
a 5% by weight low-viscosity water solution (1 Centipoise) of
aluminum chloride for approximately 1 to 60 seconds, the resulting
fiber aggregation was heated and dried at 100.degree. C. for 10
minutes or more. Further, the dried fiber aggregation was sintered
at a temperature of 1200.degree. C. or more for 10 minutes so that
a cross-linking bridge formed by a ceramic adhesive 7 mainly made
from alumina was formed at adjacent portions of the short fibers.
FIG. 14 shows an SEM photograph that indicates alumina-silica based
fibers 6 of the present example 10 which were bonded to each other
by the ceramic adhesive 7.
[0612] This fiber aggregation was used as a
face-pressure-evaluation sample, and the sample was housed inside
compressing jig of an autograph. Then, a pressing force was applied
to the sample in the thickness direction, and when this had been
pressed to 3 mm in thickness, the face pressure (MPa) was measured
1 hour later, 10 hours later and 100 hours later. The results are
shown in a graph of FIG. 13.
COMPARATIVE EXAMPLE 5
[0613] In comparative example 5, a face-pressure-evaluation sample
was prepared basically in the same manner as example 10, except
that no bonding process was carried out. Then,
face-pressure-evaluation tests were carried out in the same manner
as example 10 by using an autograph. The results are shown in a
graph of FIG. 13.
[0614] (Results of Tests)
[0615] In accordance with the graphs in FIG. 13, with respect to
the initial face pressure, example 10 had a higher value than
comparative example 5. Further, with respect to the degree of
degradation in face pressure after a lapse of 100 hours, example 10
was clearly smaller than comparative example 5.
[0616] Moreover, in example 10, after the above-mentioned fiber
aggregation had been punched out to a predetermined shape and
formed into a holding seal material 4, this was wound around a
catalyst carrier 2, and the resulting member 2 was press-fitted
into a metal shell 3. With respect to the catalyst carrier 2, a
cordierite monolith having an outer diameter of 130 mm.phi. and a
length of 100 mm was used. With respect to the metal shell 3, a
cylinder member, which was made of SUS304 having an O-letter shape
in its cross-section with 1.5 mm in thickness and 140 mm.phi. in
inner diameter, was used. A catalyst converter 1, assembled in this
manner, was actually loaded into a gasoline engine of 3 liters, and
this was subjected to a continuous driving test. As a result, upon
traveling, neither noise nor backlash of the catalyst carrier 2 was
generated.
[0617] Here, tests were carried out, in which the alumina-silica
based fibers 6 obtained from the manufacturing method of the second
embodiment according to the fifth group of the present invention
and the alumina-silica based fibers 6 obtained from the
manufacturing method of the first embodiment according to the fifth
group of the present invention were compared with each other, with
respect to the fiber diameter and mechanical strength thereof. The
specific testing method thereof is shown below.
[0618] In the former case, 10 fibers were arbitrarily sampled from
the short fibers cut to a predetermined length, and these were
sintered to form alumina-silica based fibers 6. Then, the average
value of the fiber diameter and the standard deviation of the 10
alumina-silica based fibers 6 were examined. As a result, the
average value was 7.1 .mu.m and the standard deviation was 0.74
.mu.m. Moreover, 10 alumina-silica based fibers 6 were subjected to
a publicly known tensile strength test so that the average value
and the standard deviation of the absolute strength were examined.
As a result, the average value was 6.19 gf, and the standard
deviation was 1.88 gf. Furthermore, the average value and the
standard deviation of the relative strength were examined from the
data of the above-mentioned tensile strength test. As a result, the
average value was 1.40 GPa, and the standard deviation was 0.45
GPa.
[0619] In the latter case, a long fiber of the sintered
alumina-silica based fiber 6 was cut to a predetermined length to
obtain short fibers, and 10 fibers were arbitrarily sampled from
these. Then, the average value of the fiber diameter and the
standard deviation of the 10 alumina-silica based fibers 6 were
examined. As a result, the average value was 7.2 .mu.m and the
standard deviation was 0.52 .mu.m. Moreover, 10 alumina-silica
based fibers 6 were subjected to a publicly known tensile strength
test so that the average value and the standard deviation of the
absolute strength were examined. As a result, the average value was
4.86 gf, and the standard deviation was 2.16 gf. Furthermore, the
average value and the standard deviation of the relative strength
were examined from the data of the above-mentioned tensile strength
test. As a result, the average value was 1.22 GPa, and the standard
deviation was 0.61 GPa.
[0620] The above-mentioned results show that the alumina-silica
based fibers 6 of the second embodiment according to the fifth
group of the present invention are not only excellent in mechanical
strength, but also smaller in mechanical dispersions, in comparison
with the example of the first embodiment according to the fifth
group of the present invention. Therefore, the application of the
alumina-silica based fibers 6 obtained as described above makes it
possible to provide a holding seal material 4 having even
quality.
[0621] The following description will be given of examples and
comparative examples according to the sixth group of the present
invention.
EXAMPLE 11
[0622] First, a basic water solution of aluminum chloride (23.5% by
weight) , silica sol (20% by weight, silica particle size 15 nm)
and polyvinyl alcohol (10% by weight) that serves as a
fiber-drawing property applying agent were mixed to prepare a
spinning stock solution. Next, the resulting spinning stock
solution condensed under vacuum at 50.degree. C. by using an
evaporator to prepare a spinning stock solution having a
concentration of 38% by weight with a viscosity of 150
Pa.multidot.s (1500 P) The alumina fiber spinning stock solution,
thus prepared, was continuously discharged into the air through a
nozzle (having a complete round cross-sectional shape) of a
spinning device, and wound up while being extended so that a
continuous long fiber precursor was formed.
[0623] Next, the continuous long precursor fiber was cut to a
length of 7.5 mm by using a rectangular-shaped cutter so that short
fibers were prepared, and after having been untied, collected and
laminated, these short fibers were pressed so that a mat-shaped
fiber aggregation was obtained.
[0624] Next, after the above-mentioned mat-shaped fiber aggregation
had been subjected to a heating step (pre-processing) at
500.degree. C. for 30 minutes in an electric furnace that is
maintained at normal pressure in the air so that organic components
were burnt and eliminated, this was sintered at 1250.degree. C. for
10 minutes in an electric furnace that was maintained at normal
pressure in the atmosphere to prepare an alumina fiber
aggregation.
[0625] The above-mentioned alumina fiber aggregation had an
alumina-silica weight ratio of 72:28, was obtained, and the average
fiber diameter of the alumina short fibers was 7.3 .mu.m with a
complete round cross-sectional shape.
COMPARATIVE EXAMPLE 6
[0626] After a continuous long-fiber precursor had been prepared in
the same manner as example 11, the continuous long-fiber precursor
was subjected to a sintering step in the same firing conditions as
example 11 so that an alumina long fiber was prepared. The average
fiber diameter of the alumina long fiber was 7.2 .mu.m.
[0627] Next, the continuous long precursor fiber was cut to a
length of 5 mm by using a rectangular-shaped cutter so that alumina
short fibers were prepared, and after having been untied, collected
and laminated, these short fibers were pressed so that a mat-shaped
fiber aggregation was obtained.
[0628] The respective physical properties of the alumina fiber
aggregations in accordance with example 11 and comparative example
6 were evaluated by using the following methods, and the results
are shown in the following Table 5.
[0629] (1) Strength of Alumina Short Fibers
[0630] The tensile strength of the alumina short fibers used in
each of the alumina fiber aggregations in example 11 and
comparative example 6 was measured by a tensile tester. The
measurements were carried out on ten alumina short fibers that had
been arbitrarily sampled, and the average value was determined as
the strength of each of the alumina short fibers according to
example 11 and comparative example 6, and the dispersions thereof
were evaluated based upon the standard deviation.
[0631] (2) Measurements on Face Pressure
[0632] Each of the fiber aggregations according to example 11 and
comparative example 6 was punched out to a square shape with 25 mm
in each side to prep area face-pressure measuring-use sample, and
the face pressure of the face-pressure measuring-use sample in a
non-sandwiched state without a heating step was measured as
"initial face pressure", and the above-mentioned face-pressure
measuring-use sample was sandwiched by special jigs, and adjusted
to have a bulk density of 0.30 g/cm.sup.3 , and then held in the
atmosphere at 1000.degree. C.; thus, the face pressure measured 100
hours later was defined as "face pressure after endurance
tests".
[0633] Moreover, the expression, [100-(face pressure after
endurance tests/initial face pressure).times.100] (%),was
calculated to find the degradation with time rate of face
pressure.
[0634] (3) Observation on Cut Face
[0635] States of the cut face of the alumina short fibers according
to example 11 and comparative example 6 were observed by using a
scanning electron microscope (SEM) so as to examine any chips,
burs, micro-cracks and the like.
5 TABLE 5 Strength of Average fiber diameter alumina short fiber
(.mu.m) Average strength (N) Dispersion Example 10 7.3 6.3 .times.
10.sup.-4 1.88 Comparative Example 6 7.2 5.0 .times. 10.sup.-4 2.16
Face pressure (kPa) Face pressure after Degradation with Initial
face pressure endurance tests time test (%) Example 10 145 102 29.7
Comparative Example 6 140 91 35 Presence or absence of chips, burs
and micro-cracks Example 10 Absence Comparative Example 6
Presence
[0636] As clearly shown by the results in Table 5, the average
fiber strength of the alumina short fibers according to example 11
was 6.3.times.10.sup.-4 N with its standard deviation being set to
1.88, while the average fiber strength of the alumina short fibers
according to comparative example 6 was 5.0.times.10.sup.-4 N with
its standard deviation being set to 2.16. The alumina short fibers
according to example 11 was superior to the alumina short fibers
according to comparative example 6 in the average strength and
dispersion thereof.
[0637] The initial face pressure of the face-pressure measuring-use
sample according to example 11 was 145 kPa with the face pressure
after endurance tests being set to 102 kPa, while the initial face
pressure of the face-pressure measuring-use sample according to
comparative example 6 was 140 kPa with the face pressure after
endurance tests being set to 91 kPa; thus, in both of the face
pressures, the sample according to example 11 had better
results.
[0638] Moreover, with respect to the degradation with time rate of
the face-pressure measuring-use sample also, the sample according
to example 11 had better results.
[0639] Furthermore, none of chips, burs and micro-cracks were found
on the cut face of the alumina short fiber according to example 11;
however, a number of chips, burs and micro-cracks were observed on
the cut face of the alumina short fiber according to comparative
example 6.
Industrial Applicability
[0640] As described above in detail, in accordance with the
inventions of claims 1 to 3 according to the first group of the
present invention, since it is possible to achieve excellent
mechanical strength, it becomes possible to provide alumina-silica
based fibers that are suitable for obtaining a holding seal
material which has a high initial face pressure, and is less
susceptible to degradation with time in the face pressure.
[0641] In accordance with the invention of claim 4 according to the
first group of the present invention, it is possible to provide a
manufacturing method which can securely provide alumina-silica
based fibers that are excellent in mechanical strength easily.
[0642] In accordance with the invention of claim 5 according to the
first group of the present invention, it is possible to obtain the
above-mentioned fibers at low costs in a stable manner.
[0643] In accordance with the invention of claim 6 according to the
first group of the present invention, it is possible to maintain
basic physical properties of the fibers while reducing costs.
[0644] In accordance with the invention of claim 7 according to the
first group of the present invention, it is possible to provide a
holding seal material which has a high initial face pressure, and
is less susceptible to degradation with time in the face
pressure.
[0645] In accordance with the invention of claim 8 according to the
first group of the present invention, it is possible to provide a
catalyst-converter-use holding seal material which has a high
initial face pressure, and is less susceptible to degradation with
time in the face pressure.
[0646] In accordance with the invention of claims 9 to 16 according
to the second group of the present invention, it is possible to
provide a holding seal material which has a high initial face
pressure, is less susceptible to degradation with time in the face
pressure, and is also excellent in the sealing property.
[0647] In accordance with the invention of claims 17 to 19
according to the second group of the present invention, it is
possible to provide a manufacturing method that is suitable for
obtaining a holding seal material according to the second group of
the present invention.
[0648] In accordance with the invention of claim 20 according to
the second group of the present invention, it is possible to
provide a catalyst converter which has a high initial face
pressure, is less susceptible to degradation with time in the face
pressure, and is also excellent in the sealing property.
[0649] In accordance with the inventions of claims 21 to 26
according to the third group of the present invention, it is
possible to provide a holding seal material that is less
susceptible to degradation with time in the face pressure.
[0650] In accordance with the invention of claims 27 to 29
according to the third group of the present invention, it is
possible to provide a manufacturing method that is suitable for
obtaining a holding seal material according to the third group of
the present invention.
[0651] In accordance with the invention of claims 30 to 35
according to the fourth group of the present invention, it is
possible to provide a holding seal material that is excellent in
quality stability.
[0652] In accordance with the invention of claims 36 according to
the fourth group of the present invention, it is possible to
provide a manufacturing method that is suitable for obtaining a
holding seal material according to the fourth group of the present
invention.
[0653] In accordance with the inventions of claims 37 to 41
according to the fifth group of the present invention, it is
possible to provide a holding seal material that is less
susceptible to degradation with time in the face pressure.
[0654] In accordance with the invention of claims 42 to 50
according to the fifth group of the present invention, it is
possible to provide a manufacturing method that is suitable for
obtaining a holding seal material according to the fifth group of
the present invention.
[0655] In accordance with the invention of claims 51 and 52
according to the fifth group of the present invention, it is
possible to provide a ceramic fiber aggregation that is suitable
for the above-mentioned excellent holding seal material, etc.
according to the fifth group of the present invention.
[0656] In accordance with the invention of claim 53 according to
the fifth group of the present invention, it is possible to provide
a ceramic fiber aggregation that is suitable for the
above-mentioned excellent holding seal material, etc. according to
the fifth group of the present invention.
[0657] In accordance with a manufacturing method of an alumina
fiber aggregation according to the sixth group of the present
invention, it is possible to make the strength of alumina short
fibers used in the alumina fiber aggregation superior, and also to
reduce the dispersions thereof. Therefore, it is possible to
manufacture an alumina fiber aggregation which has a high initial
face pressure, and is less susceptible to the degradation with
time.
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