U.S. patent application number 09/789075 was filed with the patent office on 2001-11-29 for method of making multilayer sheets for firestops or mounting mats.
Invention is credited to Howorth, Gary F., Langer, Roger L., Sanocki, Stephen M..
Application Number | 20010046456 09/789075 |
Document ID | / |
Family ID | 27121784 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046456 |
Kind Code |
A1 |
Langer, Roger L. ; et
al. |
November 29, 2001 |
Method of making multilayer sheets for firestops or mounting
mats
Abstract
A multilayer intumescent mat or sheet is useful for mounting a
pollution control device or as a firestop. In one aspect, the
multilayer intumescent sheet of the invention comprises a
non-moldable flexible non-intumescent layer and a non-moldable
flexible intumescent layer comprising an intumescent material
wherein the layers form a single sheet without the use of auxiliary
bonding means. The mat desirably includes a significant proportion
of inorganic fiber containing shot, and small proportions of
shot-free inorganic fiber and intumescent material. In another
aspect, the multilayer intumescent sheet of the invention comprises
a first non-moldable intumescent layer comprising a first
intumescent material and a second non-moldable intumescent layer
comprising a second intumescent material, the first and second
intumescent materials being different, wherein the layers form a
single sheet without the use of auxiliary bonding means. The
invention also provides a pollution control device comprising a
multilayer sheet of the invention disposed between a monolith and a
housing.
Inventors: |
Langer, Roger L.; (Hudson,
WI) ; Sanocki, Stephen M.; (Stillwater, MO) ;
Howorth, Gary F.; (St. Paul, MN) |
Correspondence
Address: |
Harold C. Knecht III
Office of Intellectual Property Counsel
3M Innovative Properties Company
P O Box 33427
St. Paul
MN
55133-3427
US
|
Family ID: |
27121784 |
Appl. No.: |
09/789075 |
Filed: |
February 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09789075 |
Feb 20, 2001 |
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08990961 |
Dec 15, 1997 |
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6224835 |
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08990961 |
Dec 15, 1997 |
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08796827 |
Feb 6, 1997 |
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6051193 |
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Current U.S.
Class: |
422/179 ;
422/180; 422/221 |
Current CPC
Class: |
B32B 27/04 20130101;
Y02T 10/20 20130101; B32B 25/02 20130101; F01N 3/2864 20130101;
F01N 3/0211 20130101; B01D 53/88 20130101; D21H 13/46 20130101;
D21H 13/38 20130101; F01N 3/2857 20130101; B01D 53/94 20130101;
Y02T 10/12 20130101 |
Class at
Publication: |
422/179 ;
422/180; 422/221 |
International
Class: |
F01N 003/28 |
Claims
What is claimed is:
1. A pollution control device comprising: a metal housing having a
peripheral wall; a pollution control monolith disposed within the
metal housing and defining a circumferential gap between the
pollution control monolith and the peripheral wall; and a mounting
mat disposed between the pollution control monolith and the
peripheral wall within the circumferential gap for positioning the
pollution control monolith and supporting the pollution control
monolith with reduced mechanical and thermal shock, the mounting
mat comprising: an inner layer of non-intumescent material toward
the pollution control monolith, the inner layer comprising, by dry
weight percent: from more than 0 to 50% shot-free inorganic fiber;
from 40 to 98% inorganic fiber with shot; and binder; an outer
layer toward the peripheral wall, the outer layer comprising, by
dry weight percent: from 20 to 65% intumescent particles; and
binder; wherein the mounting mat is compressed between the
circumferential wall and the pollution control monolith to exert a
mounting pressure on the pollution control monolith.
2. The pollution control device of claim 1, wherein the outer layer
further comprises, by dry weight percent: from more than 0 to 40%
of shot-free inorganic fiber; and from 10 to 78% of the inorganic
fiber with shot.
3. The pollution control device of claim 2, wherein the shot-free
inorganic fiber of the outer layer is of the same type as the
shot-free inorganic fiber of the inner layer, and wherein the
inorganic fiber with shot of the outer layer is of the same type as
the inorganic fiber with shot of the inner layer.
4. The pollution control device of claim 2, wherein the relative
proportions of shot-free inorganic fiber to inorganic fiber with
shot are the same for the inner layer and the outer layer.
5. The pollution control device of claim 1, wherein the inner layer
and the outer layers form a single sheet without the use of
auxiliary bonding means.
6. The pollution control device of claim 1 as a catalytic
converter, wherein the inner layer has a thickness t.sub.i, the
intumescent particles have an initial intumescing temperature
T.sub.int, and the outer layer has a thickness t.sub.o which is
within the formula:t.sub.o(t.sub.o+t.sub.i)(T.sub.int-25.degree.
C.)/475.degree. C.
7. The pollution control device of claim 1, wherein the inner layer
has a thickness t.sub.i, the intumescent particles have an initial
intumescing temperature T.sub.int, the pollution control device has
a temperature of the monolith which causes substantial gap increase
T.sub.g, and the outer layer has a thickness t.sub.o which is
within the formula:0.8(t.sub.o+t.s- ub.i)(T.sub.int-25.degree.
C.)/(T.sub.g-25.degree. C.)
t.sub.o1.2(t.sub.o+t.sub.i)(T.sub.int-25.degree.
C.)/(T.sub.g-25.degree. C.).
8. The pollution control device of claim 1, wherein the thickness
of the inner layer plus the thickness of the outer layer is from
greater than 100% to 400% of the circumferential gap.
9. The pollution control device of claim 1, having a first cycle
maximum of less than about 100%.
10. The pollution control device of claim 1, having a second cycle
minimum of less than about 90%.
11. The pollution control device of claim 1, having a maximum
mounting pressure of less than about 500 kPa.
12. The pollution control device of claim 1, having a minimum
mounting pressure of greater than about 15 kPa.
13. The pollution control device of claim 1 wherein the particles
are unexpanded vermiculite.
14. The pollution control device of claim 1, wherein the inorganic
fiber with shot is about 50% silica, 50% alumina fiber.
15. The pollution control device of claim 1, where the shot-free
inorganic fiber is high alumina fiber.
16. A pollution control device comprising: a metal housing having a
peripheral wall; a pollution control monolith disposed within the
metal housing and defining a circumferential gap between the
pollution control monolith and the peripheral wall, the pollution
control device having a temperature of the monolith which causes
substantial gap increase T.sub.g; and a mounting mat compressed
between the pollution control monolith and the peripheral wall
within the circumferential gap and exerting a mounting pressure on
the pollution control monolith for positioning the pollution
control monolith and supporting the pollution control monolith with
reduced mechanical and thermal shock, the mounting mat comprising:
an inner layer of non-intumescent material toward the pollution
control monolith, the inner layer having a thickness t.sub.i; an
outer layer toward the peripheral wall, the outer layer comprising,
by dry weight percent: from about 20 to 65% intumescent particles
having an initial intumescing temperature T.sub.int; and binder;
the outer layer having a thickness t.sub.o which is within the
formula:0.8(t.sub.o+t.sub.- i)(T.sub.int-25.degree.
C.)/(T.sub.g-25.degree. C.)
t.sub.o1.2(t.sub.o+t.sub.i)(T.sub.int-25.degree.
C.)/(T.sub.g-25.degree. C.)
17. The pollution control device of claim 16, wherein the inner
layer and the outer layers form a single sheet without the use of
auxiliary bonding means.
18. A pollution control device comprising: a metal housing having a
peripheral wall; a pollution control monolith disposed within the
metal housing and defining a circumferential gap between the
pollution control monolith and the peripheral wall; and a mounting
mat compressed between the pollution control monolith and the
peripheral wall within the circumferential gap for positioning the
pollution control monolith and supporting the pollution control
monolith with reduced mechanical and thermal shock, the mounting
mat comprising, by dry weight percent. from greater than 0 to less
than about 30% intumescent particles; and binder; the mounting mat
having a first cycle maximum of less than about 100%, and having a
second cycle minimum of less than about 90%.
19. The pollution control device of claim 18 wherein the mounting
mat further comprises, by dry weight percent: from about 40 to 98%
inorganic fiber with shot.
20. The pollution control device of claim 18, wherein the mounting
mat has a first cycle maximum of about 0%.
21. A pollution control device comprising: a metal housing having a
peripheral wall; a pollution control monolith disposed within the
metal housing and defining a circumferential gap between the
pollution control monolith and the peripheral wall; and a mounting
mat compressed between the pollution control monolith and the
peripheral wall within the circumferential gap for positioning the
pollution control monolith and supporting the pollution control
monolith with reduced mechanical and thermal shock, the mounting
mat comprising, by dry weight percent: from greater than 0 to less
than about 30% intumescent particles; from about 40 to 98%
inorganic fiber with shot; and binder; the intumescent particles
being non-homogeneously positioned in the mounting mat away from
the pollution control monolith and toward the peripheral wall.
22. A method of forming a pollution control device comprising:
providing an aqueous slurry; separating the aqueous slurry into a
first portion and a second portion; adding intumescent material to
the second portion; drying a first layer out of the first portion
and a second layer out of the second portion, the first layer and
the second layer forming a mounting mat; compressing the mounting
mat into a gap between a monolith and a metal housing such that the
first layer is toward the monolith and the second layer is toward
the metal housing so as to position and support the monolith with
reduced mechanical and thermal shock.
23. The method of claim 22, further comprising heating the monolith
to a temperature sufficient to cause the intumescent material to
expand.
24. The method of claim 22, wherein the aqueous slurry comprises,
by dry weight percent, from 40 to 98% inorganic fiber with
shot.
25. The method of claim 22, wherein the second layer comprises, by
dry weight percent, from 20 to 65% intumescent material and the
mounting mat comprises, by dry weight percent, from greater than 0
to less than about 30% intumescent material.
26. The method of claim 22, further comprising the steps of:
depositing the first portion onto a permeable substrate; partially
removing water from the first portion to form the first layer; and
depositing the second portion onto the first layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This is a continuation in part of application Ser. No.
08/796,827, filed Feb. 6, 1997 and entitled "MULTILAYER INTUMESCENT
SHEET".
FIELD OF THE INVENTION
[0002] This invention relates to flexible intumescent sheets useful
as firestops or as mounting mats for catalytic converters and
diesel particulate filters or traps and particularly to such
devices containing flexible multilayer intumescent sheets that have
at least two layers with differing intumescent properties.
BACKGROUND OF THE INVENTION
[0003] Pollution control devices are employed on motor vehicles to
control atmospheric pollution. Such devices include catalytic
converters and diesel particulate filters or traps. Catalytic
converters typically contain a ceramic monolithic structure which
supports the catalyst. The monolithic structure may also be made of
metal. Diesel particulate filters or traps are wall flow filters
which have honeycombed monolithic structures typically made from
porous crystalline ceramic materials.
[0004] Each of these devices has a metal housing (typically
stainless steel) which holds a monolithic structure made of ceramic
or metal such as steel. The monolithic structures have walls with a
catalyst thereon. The catalyst oxidizes carbon monoxide and
hydrocarbons, and reduces the oxides of nitrogen in engine exhaust
gases to control atmospheric pollution.
[0005] Ceramic monoliths are often described by their wall
thickness and the number of openings or cells per square inch
(cpsi). In the early 1970s, monoliths with a wall thickness of 12
mils and a cell density of 300 cpsi were common ("12/300
monoliths"). As emission laws become more stringent, wall
thicknesses have decreased as a way of increasing geometric surface
area, decreasing heat capacity and decreasing pressure drop of the
monolith. The standard has progressed to 6/400 monoliths.
[0006] With their thin walls, ceramic monolithic structures are
fragile and susceptible to vibration or shock damage and breakage.
The damaging forces may come from rough handling or dropping during
engine assembly, from engine vibration or from travel over rough
roads. The monoliths are also subject to damage due to high thermal
shock, such as from contact with road spray.
[0007] The ceramic monoliths have a coefficient of thermal
expansion generally an order of magnitude less than the metal
housing which contains them. For instance, the gap between the
peripheral wall of the metal housing and the monolith may start at
about 4 mm, and may increase a total of about 0.33 mm as the engine
heats the catalytic converter monolithic element from 25.degree. C.
to a maximum operating temperature of about 900.degree. C. At the
same time, the metallic housing increases from a temperature of
about 25.degree. C. to about 530 C. Even though the metallic
housing undergoes a smaller temperature change, the higher
coefficiential thermal expansion of the metallic housing causes the
housing to expand to a larger peripheral size faster than the
expansion of the monolithic element. Such thermal cycling typically
occurs hundreds or thousands of times during the life of the
vehicle.
[0008] To avoid damage to the ceramic monoliths from road shock and
vibrations, to compensate for the thermal expansion difference, and
to prevent exhaust gases from passing between the monoliths and the
metal housings (thereby bypassing the catalyst), mounting mats or
mounting paste materials are disposed between the ceramic monoliths
and the metal housings. The process of placing the monolith within
the housing is also called canning and includes such steps as
wrapping a sheet of mat material around the monolith, inserting the
wrapped monolith into the housing, pressing the housing closed, and
welding flanges along the lateral edges of the housing. The paste
may be injected into the gap between the monolith and the metal
housing, perhaps as a step in the canning process.
[0009] Typically, the paste or sheet mounting materials include
inorganic binders, inorganic fibers, intumescent materials, organic
binders, fillers and other adjuvants. The materials may be used as
sheets, mats, or pastes. Known mat materials, pastes, and
intumescent sheet materials used for mounting a monolith in a
housing are described in, for example, U.S. Pat No. 3,916,057
(Hatch et al.), U.S. Pat No. 4,305,992 (Langer et al.), U.S. Pat
No. 4,385,135 (Langer et al.), U.S. Pat No. 5,254,410 (Langer et
al.), U.S. Pat No. 5,242,871 (Hashimoto et al.), U.S. Pat No.
3,001,571 (Hatch), U.S. Pat No. 5,385,873 (MacNeil), U.S. Pat No.
5,207,989 (MacNeil), and GB 1,522,646 (Wood). With any of these
materials, the mounting material should remain very resilient at a
full range of operating temperatures over a prolonged period of
use.
[0010] To continually improve emission standards, it has been
desired to move the catalytic converter closer to the engine and
thereby increase the temperature of the exhaust gasses traveling
through the catalytic converter. The hotter catalytic converter and
exhaust gasses therein increase the efficiency of the reactions
which remove pollution from the exhaust gasses. As hotter catalytic
converter temperatures are used, the mounting materials must be
able to withstand the severe temperatures. In addition, the thermal
transmission properties of the mounting material become more
important toward protecting closely mounted engine components from
the hot exhaust temperatures. Decreasing the converter skin
temperature is important in preventing heat damage in the engine
compartment and radiation into the passenger compartment.
[0011] It has also been desired to continually decrease wall
thicknesses of the ceramic monolithic structure to enhance the
catalytic converter operation. Extremely thin wall monoliths, such
as 4/400, 4/600, 4/900, 3/600, 3/900 and 2/900 monoliths, have been
developed or are expected to be developed in the not too distant
future. The monoliths with extremely thin walls are even more
delicate and susceptible to breakage. Typical intumescent mounting
structures provide compression pressures which increase during use
of the catalytic converter to a pressure above the initial mounting
pressure. Increasing compression pressures during use of the
catalytic converter also reduce the ability of support mats or
pastes to sufficiently insulate the monolith from vibration damage
or mechanical shock. Because of these various problems, published
reports have advised against using intumescent mounting mats for
extremely thin wall monoliths mounted close to the engine. See for
example Umehara et al., "Design Development of High Temperature
Manifold Converter Using Thin Wall Ceramic Substrate", SAE paper
no. 971030, pg. 123-129, 1997.
[0012] The exposed edges of the mounting materials are subject to
erosion from the pulsating hot exhaust gases, particularly as the
mounting materials are thermally cycled numerous times. Under
severe conditions, over a period of time, the mounting materials
can erode and portions of the materials can be blown out. In time,
a sufficient amount of the mounting materials can be blown out and
the mounting materials can fail to provide the needed protection to
the monolith.
[0013] Solutions to the erosion problem include the use of a
stainless steel wire screen (see e.g., U.S. Pat. No. 5,008,086
(Merry)) and braided or rope-like ceramic (i.e., glass, crystalline
ceramic, or glass-ceramic) fiber braiding or metal wire material
(see, e.g., U.S. Pat. No. 4,156,333 (Close et al.)), and edge
protectants formed from compositions having glass particles (see,
e.g., EP 639701 A1 (Howorth et al.), EP 639702 A1 (Howorth et al.),
and EP 639700 A1 (Stroom et al.)) to protect the edge of the
intumescent mat from erosion by exhaust gases. These solutions
employ the use of state of the art mounting materials as the
primary support for the monolith.
[0014] Known bonded multilayer mounting mats are typically made by
first separately forming the layers and then bonding the layers
together using an adhesive or a film or other means such as, for
example, stitches or staples. Typically, adhesively or film bonded
multilayer mounting mats contain higher levels of organic material
which produces undesirable smoke and odor when used in a catalytic
converter. To prevent such smoke and odor, the mounting mats would
have to be preheated before installation to burn off the organic
bonding materials. The adhesive or film bonding layer also affects
the thermal properties of the mat. Additionally, such mounting mats
are more expensive to manufacture due to the cost of bonding the
layers together and the cost of the adhesive or film used. Some
disadvantages of mechanically bonded or attached multilayered
mounting mats include the expense of added steps and materials and
the mat may be weakened at the point of mechanical attachment such
as where stitches or staples perforate the mat. Other multilayer
mounting mats are comprised of separate layers that must be
individually mounted within the catalytic converter housing.
[0015] A disadvantage of a single layer mat or sheet containing
expandable graphite or a mixture of expandable graphite and
unexpanded vermiculite is that typically such single sheet
constructions having a homogeneous or uniform composition
throughout the sheet require relatively high amounts of expandable
graphite for the desired low temperature expansion which increases
the cost of the mat.
[0016] A need thus exists for a mounting system which is
sufficiently resilient and compressible to accommodate the changing
gap between the monolith and the metal housing over a wide range of
operating temperatures and a large number of thermal cycles. While
the state of the art mounting materials have their own utilities
and advantages, there remains an ongoing need to improve mounting
materials for use in pollution control devices. Additionally, one
of the primary concerns in forming the mounting mat is balancing
between the cost of the materials and performance attributes. It is
desirable to provide such a high quality mounting system at the
lowest possible cost.
SUMMARY OF THE INVENTION
[0017] The invention provides a multilayer intumescent mat or sheet
that is useful as a mounting for a catalytic converter element or a
diesel particulate filter or as a firestop. In one aspect, the
layer adjacent the ceramic monolith contains a mixture of
inexpensive shot-containing inorganic fiber material and more
expensive, shot-free inorganic fiber material. The layer adjacent
the metal housing contains an intumescent material. In another
aspect of the invention, the layer adjacent the metal housing is
thin enough and the intumescent material has a high enough
intumescing temperature that the intumescent material does not
begin to expand until the gap between the ceramic monolith and the
metal housing begins to expand.
[0018] Some of the advantages of the present invention include, for
example, that the flexible multilayer sheet: is made without
adhesives or other auxiliary bonding means; can be formulated so to
expand or intumesce over specific temperature ranges using
relatively less intumescent material; can be made using a
continuous process; is easier to handle and requires less labor to
install than mats made from two or more individually bonded sheets;
and requires less organic materials than adhesively bonded or
laminated sheets because an adhesive is not required.
[0019] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed. Additional features and advantages of the
invention will be set forth in and will be apparent from the
following description and examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective view of a catalytic converter
incorporating a preferred embodiment of the present invention and
shown in disassembled relation.
[0021] FIG. 2 is a longitudinal central section through a diesel
particulate filter incorporating a preferred embodiment of the
present invention.
[0022] FIG. 3 is a plot of gap change vs. heating/time interval for
the real condition fixture test of Table 2.
[0023] FIG. 4 is a temperature vs. radial location vs. heating/time
interval graph for the real condition fixture test of Table 2.
[0024] FIG. 5 is real condition fixture test results of a prior art
intumescent mounting mat.
[0025] FIG. 6 is real condition fixture test results of the
mounting mat of Example 10.
[0026] FIG. 7 is real condition fixture test results of the
mounting mat of Example 11.
[0027] FIG. 8 is real condition fixture test results of the
mounting mat of Example 12.
[0028] FIG. 9 is real condition fixture test results of the
mounting mat of Example 13.
[0029] FIG. 10 is real condition fixture test results of the
mounting mat of Example 14.
[0030] FIG. 11 is the temperature vs. radial location vs. time
graph of FIG. 4 overlaid with an intumescent temperature range of
Example 13.
[0031] FIG. 12 is real condition fixture test results of an
additional comparative example.
[0032] While the above-identified drawing figures set forth
preferred or desired embodiments, other embodiments of the present
invention are also contemplated, some of which are noted in the
discussion. In all cases, this disclosure presents the illustrated
embodiments of the present invention by way of representation and
not limitation. Numerous other minor modifications and embodiments
can be devised by those skilled in the art which fall within the
scope and spirit of the principles of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] In general terms, the flexible multilayer sheet of the
present invention is substantially inorganic and comprises at least
two non-moldable flexible layers wherein at least one of the layers
comprises an intumescent material. The two layers desirably form a
single resilient sheet without auxiliary bonding means, such as by
coforming one layer on top of the other in a single wet laid
sheet.
[0034] One of the unique features of the intumescent sheets of the
present invention is that the sheets, taken as a whole and
particularly in cross-section, have a non-homogeneous composition.
This feature results from forming a single sheet from at least two
adjacent layers wherein each adjacent layer has a homogeneous, but
distinct composition. The desired sheets include a non-intumescent
layer containing ceramic fibers, and an intumescent layer
containing either unexpanded vermiculite, unexpanded treated
vermiculite, or a mixture of both. In another preferred embodiment,
a first intumescent layer contains intumescent graphite and a
second intumescent layer contains either unexpanded vermiculite,
unexpanded treated vermiculite, or a mixture of both. In another
preferred embodiment, a first intumescent layer contains a mixture
of expandable graphite and unexpanded vermiculite and a second
intumescent layer contains either unexpanded vermiculite,
unexpanded treated vermiculite, or a mixture of both.
[0035] In one aspect, the multilayer intumescent sheet of the
invention comprises at least one non-moldable flexible
non-intumescent layer and at least one non-moldable flexible
intumescent layer comprising an intumescent material wherein the
layers form a single sheet without the use of auxiliary bonding
means. In another aspect, the multilayer intumescent sheet of the
invention provides at least (a) a first non-moldable intumescent
layer comprising a first intumescent material and (b) a second
non-moldable intumescent layer comprising a second intumescent
material, the first and second intumescent materials being
different, wherein the layers form a single sheet without the use
of auxiliary bonding means.
[0036] In another aspect, the invention provides a catalytic
converter or a diesel particulate filter or pollution control
device using a multilayer sheet of the invention. A pollution
control device of the invention comprises a housing, a monolithic
structure or element(s), and a multilayer intumescent sheet
comprising (a) at least one non-moldable flexible non-intumescent
layer; and (b) at least one non-moldable flexible intumescent layer
comprising an intumescent material, said layers forming a single
sheet without the use of auxiliary bonding means, said multilayer
sheet being disposed between the structure and the housing to hold
the structure in place.
[0037] In yet another aspect, the invention provides a pollution
control device of the invention comprising a housing, a monolithic
structure or element(s), and a multilayer intumescent sheet
comprising at least (a) a first non-moldable flexible intumescent
layer comprising a first intumescent material; and (b) a second
non-moldable flexible intumescent layer comprising a second
intumescent material, the first and second intumescent materials
being different, said layers forming a single sheet without the use
of auxiliary bonding means, said multilayer sheet being disposed
between the structure and the housing to hold the structure in
place.
[0038] In another aspect, the invention provides a flexible
multilayer intumescent sheet useful as a firestop comprising at
least (a) a non-moldable flexible non-intumescent layer comprising
endothermic filler; and (b) a non-moldable flexible intumescent
layer comprising an intumescent material, said layers forming a
single sheet without the use of auxiliary bonding means.
[0039] In another aspect, the invention provides a process for
making a multilayer intumescent sheet comprising the steps of (a)
providing a first slurry and a second slurry, said first and second
slurries comprising inorganic materials and at least one of the
slurries contains an intumescent material; (b) depositing the first
slurry onto a permeable substrate; (c) partially dewatering said
first slurry to form a first layer; (d) depositing the second
slurry onto said first layer; and (e) dewatering said second slurry
to form a second layer, said layers forming a single sheet without
auxiliary bonding means, wherein said process is a continuous
process.
[0040] Generally, each of the homogeneous layers of the multilayer
sheets of the invention can comprise from 0.3 to 99.7 dry weight
percent of the entire multilayer sheet. Desirably, each of the
layers comprise from 1.5 to 98.5 dry weight percent, more
desirably, from 8 to 92 dry weight percent, and even more desirably
from 15 to 85 dry weight percent of the sheet. In one embodiment,
the inner layer comprises at least 50 dry weight percent of the
sheet, and more desirably about 60 to 85 percent of the dry weight
percent of the sheet. The dry weight percents can be calculated
from the individual slurry compositions.
[0041] The sheets of the present invention are useful, for example,
for mounting catalytic converters and diesel particulate filters,
and as fire protection sheets or stops in buildings. Of course, the
composition, thickness, and width of each of the layers may be
varied to fit any contemplated end use.
[0042] Generally, the multilayer intumescent sheets of the
invention have a thickness of at least 0.1 mm, desirably of at
least 0.5 mm, and more desirably of at least 1 mm. Typical
thicknesses of multilayer intumescent sheets of the invention for
use in pollution control devices range from about 2 to about 11
mm.
[0043] Prior to being heated during use in a pollution control
device, the intumescent sheets of the present invention are
flexible and resilient and can be handled and flexed and wrapped
around a monolith without breaking or undesirable cracking.
[0044] The multilayer sheets of the present invention also
contemplate sheets comprising three or more non-moldable flexible
layers which form a single sheet without auxiliary bonding means
wherein at least one of the layers comprises an intumescent
material.
[0045] As used herein, the phrase "without auxiliary bonding means"
means without the use of bonding means such as resins, adhesives,
adhesive tapes, stitches, staples, and other externally used
bonding means.
[0046] As used herein, "layer" means a thickness of material having
a homogeneous composition that is separately formed by first
depositing and then at least partially dewatering a dilute slurry
having a homogeneous composition. Each of the layers of the
multilayer sheets of the invention may have the same or different
widths and thicknesses.
[0047] As used herein, "non-moldable layer" means a layer that is
made from compositions of materials containing 10 percent or less
by weight solids that are wet laid using papermaking
techniques.
[0048] As used herein, "intumescent material" means a material that
expands, foams, or swells when exposed to a sufficient amount of
thermal energy.
[0049] As used herein, "intumescent layer" means a layer of the
sheet that contains an intumescent material.
[0050] As used herein, "non-intumescent layer" means a layer of the
sheet that does not contain an intumescent material.
[0051] The non-moldable flexible intumescent layers of the present
invention include compositions of materials that can be wet laid
into flexible and resilient sheets. Generally, the non-moldable
flexible intumescent layers of the invention comprise, by dry
weight percent of the layer, from about 5 to about 85 percent
intumescent material, and less than 20 percent organic binder.
[0052] The non-moldable flexible intumescent layer desirably
comprises, on a dry weight basis of the layer, from about 5 to
about 85 percent intumescent material, from about 0.5 to about 15
percent organic binder, and from about 10 to about 65 percent
inorganic fibers, and more desirably comprises from about 5 to
about 70 percent intumescent material, from about 0.5 to about 9
percent organic binder, and from about 30 to about 45 percent
inorganic fibers. The non-moldable flexible intumescent layers of
the invention may also contain one or more inorganic fillers,
inorganic binders, organic fibers, and mixtures thereof
[0053] Another non-moldable flexible intumescent layer desirably
comprises, by dry weight percent, about 20 percent to about 65
percent unexpanded vermiculite flakes or ore, about 10 percent to
about 65 percent inorganic fibers, about 0.5 percent to about 20
percent organic binders, and up to 40 percent inorganic
fillers.
[0054] Another non-moldable flexible intumescent layer desirably
comprises, by dry weight percent, about 20 percent to about 90
percent expandable graphite, about 10 percent to about 65 percent
inorganic fibers, about 0.5 percent to about 20 percent organic
binders, and up to 40 percent inorganic fillers.
[0055] Another non-moldable flexible intumescent layer desirably
comprises, by dry weight percent, about 20 percent to about 90
percent expandable sodium silicate, about 10 percent to about 65
percent inorganic fiber, about 0.5 percent to about 20 percent
organic binders, and up to 40 percent inorganic filler.
[0056] Another non-moldable flexible intumescent layer desirably
comprises, by dry weight percent, about 20 percent to about 90
percent of a mixture of expandable graphite and either treated or
untreated unexpanded vermiculite, wherein the expandable graphite
is from about 5 to about 95 dry weight percent of the intumescent
mixture and said unexpanded vermiculite is from about 95 to about 5
dry weight percent of the intumescent mixture, about 10 percent to
about 50 percent inorganic fibers, about 0.5 percent to about 20
percent organic binders, and up to 40 percent inorganic
fillers.
[0057] The choice of the intumescent materials can vary depending
on the desired end use. For example, for higher temperatures, that
is, above about 500 C., unexpanded vermiculite materials are
suitable since they start to expand at a temperature range of from
about 300.degree. C. to about 340.degree. C. to fill the expanding
gap between an expanding metal housing and a monolith in a
catalytic converter. For lower temperature use, that is,
temperatures below about 500.degree. C., such as in diesel
monoliths or particulate filters, expandable graphite or a mixture
of expandable graphite and unexpanded vermiculite materials may be
desired since expandable graphite starts to expand or intumesce at
about 210.degree. C. Treated vermiculites are also useful and
expand at a temperature of about 290.degree. C.
[0058] Useful intumescent materials include, but are not limited
to, unexpanded vermiculite ore, treated unexpanded vermiculite ore,
partially dehydrated vermiculite ore, expandable graphite, mixtures
of expandable graphite with treated or untreated unexpanded
vermiculite ore, processed expandable sodium silicate, for example
EXPANTROL.TM. insoluble sodium silicate, commercially available
from Minnesota Mining and Manufacturing Company, St. Paul, Minn.,
and mixtures thereof For purposes of the present application, it is
intended that each of the above-listed examples of intumescent
materials are considered to be different and distinguishable from
one another. Desired intumescent materials include unexpanded
vermiculite ore, treated unexpanded vermiculite ore, expandable
graphite, and mixtures thereof An example of a desirable
commercially available expandable graphite material is GRAFOIL.TM.
Grade 338-5O expandable graphite flake, from UCAR Carbon Co., Inc.,
Cleveland, Ohio.
[0059] Treated unexpanded vermiculite flakes or ore includes
unexpanded vermiculite treated by processes such as by being ion
exchanged with ion exchange salts such as ammonium dihydrogen
phosphate, ammonium nitrate, ammonium chloride, potassium chloride,
or other suitable compounds as is known in the art.
[0060] The amount and type of intumescent material incorporated
into the mounting mat contributes significantly to the cost of the
product. Untreated intumescent materials, such as unexpanded
vermiculite, are generally less expensive than treated intumescent
materials, but may provide different intumescing temperatures and
amounts and rates of expansion. In one aspect, the present
invention desirably produces significant intumescent expansion with
a low proportion of intumescent material, such as from greater than
0 to less than about 30% intumescent particles by dry weight
percent of the total mat. A well-timed and significant intumescent
expansion is achieved by non-homogeneously positioning the
intumescent particles in the outer layer or toward the outside of
the mat.
[0061] Suitable organic binder materials include aqueous polymer
emulsions, solvent based polymer solutions, and polymers or polymer
resins (100 percent solids). Aqueous polymer emulsions are organic
binder polymers and elastomers in the latex form, for example,
natural rubber lattices, styrene-butadiene lattices,
butadiene-acrylonitrile lattices, ethylene vinyl acetate lattices,
and lattices of acrylate and methacrylate polymers and copolymers.
Polymers and polymer resins include natural rubber,
styrene-butadiene rubber, and other elastomeric polymer resins.
Acrylic latex and polyvinyl acetate organic binders are
preferred.
[0062] Examples of desirable commercially available organic binders
include RHOPLEX.RTM. HA-8 (a 45.5 percent by weight solids aqueous
acrylic emulsion) from Rohm & Haas, Philadelphia, Pa. and
AIRFLEX.RTM. 600BP (a 55 percent solids aqueous polyvinyl acetate
emulsion) from Air Products, Allentown, Pa.
[0063] Useful inorganic fibers include for example, fiberglass,
ceramic fibers, non-oxide inorganic fibers, such as graphite fibers
or boron fibers, and mixtures thereof Useful ceramic fibers include
aliminoborosilicate fibers, aluminosilicate fibers, alumina fibers,
and- mixtures thereof
[0064] Examples of desirable aluminoborosilicate fibers include
those commercially available under the trade designations "NEXTEL"
312 and "NEXTEL" 440 from Minnesota Mining and Manufacturing
Company, St. Paul, Minn. Examples of desirable aluminosilicate
fibers include those available under the trade designations
"FIBERFRAX" 7000M from Unifrax Corp., Niagara Falls, N.Y.,
"CERAFIBER" from Thermal Ceramics, Augusta, Ga.; and "SNSC Type
1260 D1" from Nippon Steel Chemical Company, Tokyo, Japan. An
example of a desirable commercially available alumina fiber is
SAFFIL.TM. fibers which are polycrystalline alumina fibers
available from ICI Chemicals and Polymers, Widnes Chesire, UK.
[0065] Examples of other suitable inorganic fibers include: quartz
fibers, commercially available, for example, under the trade
designation "ASTROQUARTZ" from J. P. Stevens. Inc., Slater, N.C.;
glass fibers, such as magnesium aluminosilicate glass fibers, for
example, those commercially available under the trade designation
"S2-GLASS" from Owens-Corning Fiberglass Corp., Granville, Ohio;
silicon carbide fibers, for example, those commercially available
under the trade designations "NICALON" from Nippon Carbon, Tokyo,
Japan, or Dow Corning, Midland, Mich., and "TYRANNO" from Textron
Specialty Materials, Lowell, Mass.; silicon nitride fibers, for
example, those available from Toren Energy International Corp., New
York, N.Y.; small diameter metal fibers, such as BEKI-SHELD.RTM. GR
90/C2/4 stainless steel fibers, which are commercially available
from Beckaert, Zweregan, Belgium and micrometal fibers under the
trade designation "RIBTEC" from Ribbon Technology Corp., Gahanna,
Ohio, and mixtures thereof Useful commercially available carbon
(graphite) fibers (non-intumescent) include those under the trade
designation "IM7" from Hercules Advanced Material Systems, Magna,
Utah.
[0066] The non-moldable flexible intumescent layers of the present
invention may also contain one or more filler materials. Filler
materials may be present in the flexible intumescent layer at dry
weight levels of up to about 90 percent, desirably at levels of up
to about 60 percent, and more desirably at levels of up to 40
percent.
[0067] Suitable fillers and non-intumescent particles include for
example, glass particles, hollow glass spheres, inert filler
materials such as calcium carbonate, reinforcing and/or light
weight filler materials such as mica, perlite, expanded
vermiculite, processed expanded vermiculite platelets, delaminated
vermiculite, endothermic filler materials such as aluminum
trihydrate, magnesium phosphate hexahydrate, zinc borate, and
magnesium hydroxide, and mixtures thereof
[0068] The non-moldable flexible intumescent layers of the
invention may also contain up to about 90 percent, desirably
contain up to about 30 percent, and more desirably contain up to
about 15 percent, by dry weight of the layer, inorganic binder.
Useful inorganic binders include clay materials such as bentonite,
and colloidal silicas, and mixtures thereof
[0069] The non-moldable flexible intumescent layers of the
invention may also contain up to about 90 percent, desirably
contain up to about 10 percent, and more desirably contain up to
about 3 percent, by dry weight, of organic fiber. Useful organic
fibers include aramid fibers such as KEVLAR.RTM. polyamide fibers,
thermo bonding fibers, for example Hoeschst Celanese HC-106
bicomponent fibers, and rayon fibers, polyolefin fibers, and
mixtures thereof.
[0070] Other suitable examples of intumescent sheet materials
having compositions suitable for use as a non-moldable flexible
intumescent layer of the invention include those described in U.S.
Pat. No. 3,916,057 (Hatch et al.), U.S. Pat. No. 4,305,992 (Langer
et al.), U.S. Pat. No. 4,385,135 (Langer et al.), U.S. Pat. No.
5,254,410 (Langer et al.), U.S. Pat. No. 4,865,818 (Merry et al.),
U.S. Pat. No. 5,151,253 (Merry et al.), U.S. Pat. No. 5,290,522
(Rogers et al.), and U.S. Pat. No. 5,523,059 (Langer), each of
which are hereby incorporated by reference.
[0071] The multilayer flexible sheet of the present invention may
also include at least one non-moldable flexible non-intumescent
layer. Generally, the non-moldable flexible non-intumescent layers
may contain at least one of inorganic fibers, organic binder,
filler materials, organic fiber or may contain any combination
thereof. Useful non-intumescent layers include combinations of
inorganic fiber and organic binder, and organic binder and organic
fiber.
[0072] A suitable non-moldable flexible non-intumescent layer
comprises, by dry weight percent, about 10 percent to about 99.5
percent inorganic fibers, about 0.5 percent to about 20 percent
organic binders, and up to 90 percent fillers. A desirable flexible
non-intumescent layer comprises, by dry weight percent, from about
20 to about 99.5 percent inorganic fibers, about 0.5 to 20 percent
organic binder and up to 60 percent fillers. The non-moldable
flexible non-intumescent layer of the invention may also contain
one or more organic fibers, inorganic binders, and mixtures
thereof.
[0073] Inorganic fibers useful in the non-moldable flexible
non-intumescent layers of the present invention include those
described above and particularly aluminosilicate fibers,
commercially available under the trademarks "FIBERFRAX" 7000M from
Unifrax Co., Niagara Falls, N.Y.; "CERAFIBER" from Thermal
Ceramics, Augusta, Ga.; polycrystalline alumina fibers commercially
available as SAFFIL.TM. fibers from ICI Chemicals and Polymers,
Widnes Chesire, UK; and others such as glass fibers,
zirconia-silica fibers, crystalline alumina whiskers, and
microfiberglass, available from Schuller International Co., Denver,
Colo.; high temperature fiberglass such as under the trade
designation of "S-2 GLASS" HT from Owens-Corning, and mixtures
thereof.
[0074] Generally speaking, inorganic fibers containing a
substantial amount of shot are less expensive than shot-free
inorganic fibers. However, as discussed in U.S. Pat. No. 4,929,429,
incorporated herein by reference, shot-free inorganic fibers
generally provide more resilient mats which better maintain holding
forces at all temperatures including a return to room temperature.
The type of inorganic fibers used also affect the cost. Generally
speaking, alumina/silica inorganic fibers, such as about 50%
alumina, 50% silica fibers, are relatively inexpensive.
[0075] In one aspect the present invention includes a mixture of
shot-free inorganic fiber and inorganic fiber with shot. This
mixture is desirably used in both the non-intumescent layer and the
intumescent layer. In so using the mixture, the shot-free inorganic
fiber of the outer layer is of the same type as the shot-free
inorganic fiber of the inner layer, and the inorganic fiber with
shot of the outer layer is of the same type as the inorganic fiber
with shot of the inner layer. Also, the relative proportions of
shot-free inorganic fiber to inorganic fiber with shot are the same
for both the inner layer and the outer layer. This is believed to
result in more consistent thermal conductivity and specific heats
throughout both layers.
[0076] The mixture may include, by dry weight percent, at least
about 40% inorganic fiber with shot, up to about 98% inorganic
fiber with shot. The shot content may be greater than about 10%,
more desirably greater than about 25%, and most desirably about 50%
of the inorganic bulk content, such as a 50% fiber, 50% shot bulk.
The inorganic fiber may be alumina/silica fibers, such as about 50%
alumina, 50% silica fibers.
[0077] The mixture may include more than 0% shot-free inorganic
fiber, up to about 50% shot-free inorganic fiber. The present
invention desirably includes from more than 0% to about 30%
shot-free inorganic fiber, by dry weight percent of the layer. The
present invention even more desirably uses a mix of about 25%
shot-free inorganic fiber, 75% inorganic fiber with shot as a dry
weight percent of the inorganic fiber content. The present
invention desirably uses a high alumina fiber for the shot-free
inorganic fiber, such as an about 96% alumina fiber. Higher ranges
of shot-free inorganic fiber may also be used, but the present
invention produces beneficial results even though small portions of
shot-free inorganic fiber are used.
[0078] Organic binders useful in the non-moldable flexible
non-intumescent layers of the present invention include those
described above and particularly natural rubber lattices, poly
vinylacetate, styrene-butadiene lattices, butadiene acrylonitrile
lattices, and lattices of acrylate and methacrylate polymers and
copolymers.
[0079] Fillers useful in the non-moldable flexible non-intumescent
layers of the present invention include those described above and
particularly expanded vermiculite, delaminated vermiculite, hollow
glass microspheres, perlite, and others such as alumina trihydrate,
magnesium phosphate hexahydrate, calcium carbonate, and mixtures
thereof. Filler materials may be present in the flexible
non-intumescent layer at dry weight levels of up to about 90
percent, desirably at levels of up to about 60 percent, and more
desirably at levels of up to 40 percent.
[0080] Inorganic binders useful in the non-moldable flexible
non-intumescent layers of the present invention include those
described above for the non-moldable flexible intumescent layers
and particularly bentonite and other clays. Inorganic binders may
be present in the non-moldable flexible layers at levels up to
about 90 percent, desirably up to about 30 percent, and more
desirably, up to about 15 percent by dry weight of the layer.
[0081] Organic fibers useful in the non-moldable flexible
non-intumescent layers of the present invention include those
described above for the non-moldable flexible intumescent layers.
Organic fibers may be present in the non-moldable flexible layers
of the invention at levels up to about 90 percent, desirably up to
about 10 percent, and more desirably, up to 3 percent by dry weight
percent of the layer.
[0082] Other additives or process aides that may be included in any
one of the layers of the invention include defoaming agents,
surfactants, dispersants, wetting agents, salts to aid
precipitation, fungicides, and bactericides. Generally, these types
of additives are included in one or more of the layers in amounts
of less than about 5 dry weight percent.
[0083] Desirably, the multilayer sheets of the invention are made
by making at least two dilute (desirably, not over 5 percent solids
by weight) aqueous slurries containing the desired materials,
depositing the first slurry onto a permeable substrate, such as a
screen or a "wire" of a papermachine, partially dewatering the
first slurry by gravity and/or vacuum to form a base or "lower"
layer, depositing the second slurry onto the partially dewatered
lower layer, partially dewatering the second or top layer, and then
pressing to density both layers with, for example, pressure rollers
and then fully drying the sheet with heated rollers, to form the
finished sheet. It is to be understood that either or any of the
layers of the sheet of the present invention may be formed first as
the lower layer of the sheet. However, the layer having the
greatest thickness when dry (such as the inner non-intumescent
layer) is desirably the layer that is formed first.
[0084] The steps of depositing and then dewatering a slurry onto a
partially dewatered layer provides a partial intermingling of the
components of both slurries. This intermingling permanently and
effectively bonds the layers together to form a one-piece sheet
where the layers may not be cleanly separated. The intermingling of
the layer components may be practically invisible to the eye or may
be to such an extent so as to form a visible boundary or gradient
layer between the two layers. In either case, the layers are
permanently bound to one another and form a single sheet with each
layer being a portion of the whole sheet. Depositing a second layer
slurry onto a first layer slurry as the first layer slurry is being
dewatered results in a high amount of intermingling between the
layers. Depositing a second layer slurry onto a partially dewatered
and first-formed layer provides two distinct, but bound layers with
little visible intermingling. The former is generally accomplished
by depositing and then dewatering both slurries in close sequence
using vacuum dewatering on an inclined wire section of a wire
former. The latter is generally accomplished by depositing and
vacuum forming the lower layer on the inclined section of a wire
former and then depositing and dewatering the top layer by
sufficient vacuum (through the lower layer) on a planar or flat
portion of a wire former. The top layer should be dewatered at a
sufficient rate so as to prevent undesirable settling out of the
intumescent or other higher density filler materials. A sufficient
dewatering rate will provide layers having homogeneous compositions
outside of the "intermingled" or "gradient" layer.
[0085] Generally, when making the slurries, the higher density
materials such as the intumescent materials and higher density
fillers (if used) are added to the slurries in a smaller volume
mixing vessel at a constant rate just prior to the depositing step.
The slurries containing the fillers and intumescent materials are
agitated sufficiently so to prevent these particles from settling
out in the mixing tank prior to forming the individual layers. Such
slurries should be partially dewatered almost immediately after
being deposited on the wire so to prevent undesirable settling of
the higher density particles. Vacuum dewatering of the slurries is
desirable.
[0086] After the partially dewatered multilayered sheet is formed,
the sheet is dried to form an end-use product. Useful drying means
include wet pressing the sheet material through compression or
pressure rollers followed by passing the sheet material through
heated rollers and forced hot air drying as is known in the
art.
[0087] The multilayer sheets of the invention may be made using
fourdrinier machines having both an inclined and a flat wire
section and a second headbox in addition to the headbox ordinarily
furnished with such machines. The multilayer sheets of the
invention may also be made on any commercially available inclined
wire former designed to make multi-ply sheets, for example, a
DOUMAT.TM. DELTAFORMER.TM. from Sandy Hill Corp., Hudson Falls,
N.Y. A desirable fourdrinier machine has both an inclined screen
area and a subsequent flat or horizontal screened area where the
"second" layer may be deposited from a second headbox onto the
lower layer and then dewatered using vacuum.
[0088] Additionally, the multilayer sheets of the invention can
further include edge protection materials. Suitable materials
include a stainless steel wire screen wrapped around the edges as
described in U.S. Pat. No. 5,008,086 (Merry), incorporated herein
by reference, and braided or rope-like ceramic (that is, glass,
crystalline ceramic, or glass-ceramic) fiber braiding or metal wire
material as described in U.S. Pat. No. 4,156,533 (Close et al.),
incorporated herein by reference. Edge protectants can also be
formed from compositions having glass particles as described in EP
639 701 A1 (Howorth et al.), EP 639 702 A1 (Howorth et al.), and EP
639 700 A1 (Stroom et al.), all of which are incorporated herein by
reference.
[0089] In another aspect, the invention provides a pollution
control device, for example, a catalytic converter or a diesel
particulate filter, using a multilayer sheet of the invention. FIG.
1 shows a catalytic converter 10 similar to that disclosed in U.S.
Pat. No. 4,865,818 to Merry et al. but incorporating a preferred
embodiment of the present invention. The catalytic converter 10
contains a catalyst which is typically coated onto a monolithic
structure 20 mounted in the converter 10. The monolithic structure
20 is typically ceramic, although metal monoliths have been used.
The catalyst oxidizes carbon monoxide and hydrocarbons, and reduces
the oxides of nitrogen in automobile exhaust gas to control
atmospheric pollution.
[0090] The catalytic converter 10 includes a metal housing 11 which
holds within it the monolithic structure 20. The housing 11 has
inlet and outlet ends 12 and 13, respectively.
[0091] The monolithic structure 20 generally has very thin walls to
provide a large amount of surface area so it is fragile and
susceptible to breakage. The monolithic structure 20 also has a
coefficient of thermal expansion generally an order of magnitude
less than the metal (usually stainless steel) housing 11 in which
it is contained. In order to avoid damage to the monolith 20 from
shock and vibration, to compensate for the thermal expansion
difference, and to prevent exhaust gasses from passing between the
monolith 20 and the metal housing 11, an intumescent sheet material
mat 30 according to the present invention is disposed between the
monolithic structure 20 and the metal housing 11. The sheet
material 30 may have a first end 31 and a second end 32.
[0092] The housing 11, which is also referred to as a can or a
casing, can be made from suitable materials known in the art for
such use and is typically made of metal. Desirably, the housing II
is made of stainless steel.
[0093] Suitable catalytic converter elements 20, also referred to
as monoliths, are known in the art and include those made of metal
or ceramic. The monoliths or elements 20 are used to support the
catalyst materials for the converter 10. A useful catalytic
converter element is disclosed, for example, in U.S. Pat. No. RE
27,747 (Johnson), incorporated by reference.
[0094] Ceramic catalytic converter elements are commercially
available, for example, from Corning Inc., Corning, N.Y., and NGK
Insulator Ltd., Nagoya, Japan. For example, a honeycomb ceramic
catalyst support is marketed under the trade designation "CELCOR"
by Corning Inc. and "HONEYCERAM" by NGK Insulator Ltd. Metal
catalytic converter elements are commercially available from Behr
GmbH and Co., Germany.
[0095] The monolith 20 of the present invention may particularly be
an extremely thin walled ceramic element. As used in this
application, an "extremely thin walled" monolith is one having a
wall thickness of less than 6 mils (less than 0.15 mm). The
extremely thin wall monolith 20 may even more desirably be one
having a wall thickness of 4 mils or less (0.10 mm or less), such
as for example a 4/400, 4/600, 4/900, 3/600, 3/900 or 2/900
monolith.
[0096] For additional details regarding catalytic monoliths see,
for example, "Advanced Ceramic Substrate: Catalytic Performance
Improvement by High Geometric Surface Area and Low Heat Capacity,"
Umehara et al., Paper No. 971029, SAE Technical Paper Series, 1997;
"Systems Approach to Packaging Design for Automotive Catalytic
Converters," Stroom et al., Paper No. 900500, SAE Technical Paper
Series, 1990; "Thin Wall Ceramics as Monolithic Catalyst Supports,"
Howitt, Paper 800082, SAE Technical Paper Series, 1980; and "Flow
Effects in Monolithic Honeycomb Automotive Catalytic Converters,"
Howitt et al., Paper No. 740244, SAE Technical Paper Series,
1974.
[0097] The catalyst materials coated onto the catalytic converter
elements include those known in the art (for example, metals such
as ruthenium, osmium, rhodium, iridium, nickel, palladium, and
platinum, and metal oxides such as vanadium pentoxide and titanium
dioxide). For further details regarding catalytic coatings see, for
example, U.S. Pat. No. 3,441,381 (Keith et al.).
[0098] FIG. 2 shows a diesel particulate filter 40 similar to that
disclosed in U.S. Pat. No. 5,174,969 to Fischer et al. but
incorporating a preferred embodiment of the present invention. The
diesel particulate filter or trap 40 is a wall flow filter which
has a honeycombed monolithic structure 42 comprising a bundle of
tubes. A catalyst is typically coated onto the monolithic structure
42 mounted in the diesel particulate filter 40. The catalyst
oxidizes carbon monoxide and hydrocarbons, and reduces the oxides
of nitrogen in diesel engine exhaust gas to control atmospheric
pollution.
[0099] The diesel particulate filter 40 includes a metal housing 44
which holds within it the monolithic structure 42. The housing 44
has inlet and outlet ends 46 and 48, respectively. The monolithic
structure 42 generally has very thin walls to provide a large
amount of surface area so it is fragile and susceptible to
breakage. The monolithic structure 42 also has a coefficient of
thermal expansion generally an order of magnitude less than the
metal (usually stainless steel) housing 44 in which it is
contained. In order to avoid damage to the monolith 42 from shock
and vibration, to compensate for the thermal expansion difference,
and to prevent exhaust gasses from passing between the monolith 42
and the metal housing 44, an intumescent sheet material mat 50
according to the present invention is disposed between the
monolithic structure 42 and the metal housing 44.
[0100] Useful monolithic type diesel particulate filter elements 42
are typically wall flow filters comprised of honeycombed, porous,
crystalline ceramic (for example, cordierite) material. Alternate
cells of the honeycombed structure are typically plugged such that
exhaust gas enters in one cell and is forced through the porous
wall of one cell and exits the structure through another cell. The
size of the diesel particulate filter element 42 depends on the
particular application needs. Useful diesel particulate filter
elements are commercially available, for example, from Corning
Inc., Corning, N.Y., and NGK Insulator Ltd., Nagoya, Japan. Useful
diesel particulate filter elements are discussed in "Cellular
Ceramic Diesel Particulate Filter," Howitt et al., Paper No.
810114, SAE Technical Paper Series, 1981.
[0101] In use, the multilayer sheet 30, 50 of the invention is
disposed between the monolith 20, 42 and the housing 11, 44 in
similar fashion for either a catalytic converter 10 or for a diesel
particulate filter 40. This may be done by wrapping the monolith
20, 42 with the multilayer sheet 30, 50 of the invention, inserting
the wrapped monolith into the housing 11, 44, and sealing the
housing 11, 44. The intumescent multilayer sheet 30, 50 holds the
monolith 20, 42 in place within the housing 11, 44 and seals the
gap between the monolith 20, 42 and the housing 11, 44 to prevent
exhaust gases from bypassing the monolith 20, 42.
[0102] The multilayer sheet 30, 50 is significantly compressed
between the monolith 20, 42 and the housing 11, 44. For instance,
the thickness of the multilayer sheet is generally from greater
than 100% to about 400% of the circumferential gap. The compression
of the multilayer sheet 30, 50 provides an initial mounting
pressure which is desirably between about 20 and 500 kPa. The
compression also increases the density of the multilayer sheet to a
desirable mount density of about 0.3 to 0.6 g/cc, more desirably to
a mount density of about 0.4 to 0.5 g/cc, and most desirably to a
mount density of about 0.45 g/cc.
[0103] The mats 30, 50 are multilayer sheets comprising (a) at
least one non-moldable flexible layer that may be non-intumescent
or intumescent; and (b) at least one non-moldable flexible
intumescent layer comprising an intumescent material, said layers
desirably forming a single sheet without the use of auxiliary
bonding means.
[0104] An example of a multilayer sheet 30 suitable for use in a
catalytic converter 10 comprises a non-moldable flexible
non-intumescent layer comprising ceramic fiber and organic binder,
and a non-moldable flexible intumescent layer comprising unexpanded
vermiculite, ceramic fiber, and organic binder.
[0105] An example of a multilayer sheet 50 suitable for use in a
diesel particulate filter 40 comprises a first non-moldable
flexible intumescent layer comprising ceramic fiber, unexpanded
vermiculite, and organic binder, and a second non-moldable flexible
intumescent layer comprising ceramic fiber, expandable graphite,
and organic binder.
[0106] The orientation of the multilayer sheet between the housing
and the monolith is dependent on the compositions of the layers of
the sheet. For example, the intumescent layer of a sheet of the
invention containing an intumescent material such as expandable
graphite would advantageously be placed adjacent to a diesel
monolith. This is because diesel particulate filters are typically
heated to temperatures below about 500.degree. C. and expandable
graphite starts to expand at a temperature of about 210.degree.
C.
[0107] During use of the pollution control device, the mounting mat
should remain resilient at all operating temperatures, for a large
number of thermal cycles. In one aspect, the present invention
provides a maximum mounting pressure of less than about 500 kPa,
and a minimum mounting pressure of greater than about 15 kPa. It
may also be desirable for the minimum mounting pressure being
provided to be greater than about 20 kPa. In another aspect, the
present invention provides a low level of erosion, such as an
initial erosion rate of less than about 0.1 g/hour, and more
desirably an initial erosion rate of less than about 0.05 g/hour,
and most desirably an initial erosion rate of about 0.01 g/hour or
less.
[0108] In another aspect, the invention provides a multilayer sheet
material useful as a firestop for limiting the spread of fire
through openings in the walls, floors, and ceilings of
structures.
[0109] An example of a multilayer intumescent sheet useful as a
firestop comprises a first non-moldable flexible intumescent layer
comprising unexpanded vermiculite, organic binder and alumina
trihydrate, and a second non-moldable flexible intumescent layer
comprising expandable graphite, organic binder, and aluminum
trihydrate wherein said layers form a single sheet without the use
of auxiliary bonding means.
[0110] An example of a desirable multilayer sheet material for use
as a firestop comprises a non-moldable flexible layer comprising
alumina trihydrate as described in U.S. Pat. No. 4,600,634,
incorporated by reference herein, and a non-moldable flexible
intumescent layer comprising an intumescent material, wherein said
layers form a single sheet without the use of auxiliary bonding
means.
[0111] In use, a multilayer sheet of the invention useful as a
firestop is desirably oriented such that the layer containing the
intumescent material faces toward the side most likely to get
hot.
[0112] The present invention also contemplates intumescent sheets
having three or more layers wherein at least one layer comprises an
intumescent material and wherein adjacent layers are desirably
comprised of different compositions.
Real Condition Fixture Test (RCFT)
[0113] The RCFT is a test which models actual conditions found in a
catalytic converter (automotive or diesel) with a monolith (metal
or ceramic), or in a diesel particulate trap during normal use, and
measures the pressure exerted by the mounting material under those
modeled normal use conditions.
[0114] Two 50.8 mm by 50.8 mm heated stainless steel platens,
controlled independently, are heated to different temperatures to
simulate the metal housing and monolith temperatures, respectively.
Simultaneously, the space or gap between the platens increased by a
value calculated from the temperature and the thermal expansion
coefficients of a typical catalytic converter of the type
specified. The temperatures of the platen and the gap are presented
in Tables 1 and 2 below. The pressure force exerted by the mounting
material is measured by a Sintech ID computer-controlled load frame
with an Extensometer available from MTS Systems Corp., Research
Triangle Park, N.C.
1TABLE 1 Monolith Shell Gap Change Temperature (C) Temperature (C)
(cm) 25 25 0.0000 63 30 0.0001 100 35 0.0003 150 40 0.0003 200 55
0.0012 200 120 0.0068 200 (soak) 120 0.0068 150 90 0.0046 100 60
0.0024 63 42 0.012 25 25 0.000
[0115] The above Table 1 conditions model a 12.7 cm. diameter
ceramic monolith with a 409 stainless steel shell and is
representative of the conditions found in a diesel catalytic
converter with a ceramic monolith.
2TABLE 2 Monolith Shell Time Temperature Temperature Gap Change
Interval (C) (C) (cm) a 25 25 0.0003 b 100 25 0.0003 c 150 30
0.0003 d 200 35 0.0003 e 250 38 0.0003 f 300 40 0.0003 g 350 45
0.0003 h 400 50 0.0003 i 450 60 0.0003 j 500 70 0.0003 k 550 85
0.0013 l 600 100 0.0025 m 650 125 0.0038 n 700 150 0.0051 o 750 185
0.0076 p 800 220 00102 q 850 325 0.0165 r 900 430 0.0229 s 900 480
0.0267 t 900 530 0.0305 u 900 (soak) 530 0.0305 v 850 502 0.0292 w
800 474 0.0279 x 750 445 0.0254 y 700 416 0.0229 z 650 387 0.0216
aa 600 358 0.0203 bb 550 329 0.0191 cc 500 300 0.0178 dd 450 275
0.0165 ee 400 250 0.0152 ff 350 215 0.0127 gg 300 180 0.0102 hh 250
1155 0.0089 ii 200 130 0.0076 jj 150 95 0.0051 kk 100 60 0.0025 ll
50 50 0.0003
[0116] The above Table 2 conditions model a ceramic monolith with a
stainless steel shell and an initial 4 mm gap and is representative
of the conditions found in an automotive catalytic converter during
a full heating and cooling cycle. For instance, the Table 2
conditions model a cycle such as driving the automobile over a
substantial distance to allow the engine to fully warm up, and the
turning the engine off and allowing the engine to fully cool back
to ambient conditions. Such a thermal cycle will typically occur
hundreds or thousands of times during the life of the vehicle.
[0117] FIGS. 3 and 4 are graphical representations of the above
Table 2 real condition fixture test. A detailed understanding of
how the thermal conditions exist in an actual catalytic converter
is useful toward understanding how the mounting mats of the present
invention show improved results over prior art mounting mats.
[0118] The relationship between the gap filled by the mounting
material and the operating temperature of the ceramic monolith at
any particular time is a complex, non-linear phenomenon. As shown
in FIG. 3, the gap change during a full thermal running cycle can
be characterized into three basic portions. During initial low
temperature heating (i.e., from time/heating interval "a" to
time/heating interval "j ", during initial running of the engine),
the gap has a no change portion 60. During high temperature heating
(i.e., from time/heating interval "k" to time/heating interval "u",
as the engine approaches steady state thermal operating
conditions), the gap undergoes a high increase portion 62. The high
gap increase portion 62 begins at a temperature T.sub.g, the lowest
temperature of the monolith 20 at which a substantial increase in
gap size is observed. During cool down (i.e., from time/heating
interval "v" to an ambient temperature, after the engine is shut
off and the engine allowed to cool), the gap undergoes a steady
decline portion 64. It is recognized that if the engine is run for
less than a full thermal cycle, or restarted before the engine has
fully cooled, then the various portions 60, 62, 64 will be
intermingled.
[0119] The relationship between gap change and ceramic monolith
temperature is further explained with reference to FIG. 4. The
monolith surface temperatures and housing surface temperatures for
selected time/heating intervals are based on measurements taken
during an actual engine heating and cooling of a catalytic
converter. The temperature verses radial location in the mounting
mat as a function of time during the heating/cooling cycle of the
engine is modeled based on several assumptions.
[0120] The location of the monolithic wall 20 moves radially
outward as a function of temperature according to its coefficient
of thermal expansion 68, which determines the slope of line 68. Due
to the relatively low coefficient of the thermal expansion 68 of
the monolith 20, the radial location of the edge of the monolith 20
changes very little during its heating cycle from 25 C. to 900 C.
The location of the housing wall 11 also moves radially outward
outward as a function of temperature, but at a significantly
greater slope due to its higher coefficient of thermal expansion
70. Due to its relatively larger coefficient of expansion 70, the
radial location of the peripheral wall 11 changes significantly
during its heating cycle from 25 C. to 530 C.
[0121] A temperature differential 72 is believed to exist at least
during the heating cycle due to thermal contact resistance at the
interface between the monolith 20 and the mounting mat 30.
Similarly, at least during the heating cycle, a temperature
differential 74 is believed to exist due to thermal contact
resistance between the mounting mat 30 and the peripheral wall of
the housing 11. Thermal contact resistances also exist during
steady state (time/heating interval "u") and cooling (time/heating
intervals "v" to "ll"), but are believed to result in significantly
smaller temperature differentials. The magnitude of the thermal
contact resistances and resultant temperature differentials 72, 74
is not known and will vary from system to system based on the
molecular interaction between the material of the mounting mat 30
and materials of the ceramic monolithic 20 and housing 11. The
temperature differentials 72, 74 are believed to be fairly small
relative to the overall temperature drop from the monolith 20 to
the housing 11.
[0122] For simplicity, temperature distributions through the
mounting mat 30 are modeled as linearly decreasing. It is
recognized that the radial nature of the heat transfer in most
catalytic converter systems will provide a curvature to each of the
temperature distribution lines, but the magnitude of the curvature
is quite small because the radius of the mat 30 is quite small
relative to its thickness. Additionally, the heat transfer is
transient, which will also affect the amount of curvature of the
temperature profiles through the mat 30. The temperature
distribution shown in FIG. 4 is based on a constant value for the
coefficient of thermal conduction through the mounting mat 30,
without any interfaces in the mat 30. While the noted assumptions
change based on the particular circumstances of each mounting mat,
the temperature distribution profile shown in FIG. 4 is sufficient
for explanatory purposes of the present invention.
[0123] As the ceramic monolith 20 is initially heated, a time
dependent thermal gradient sets up across the mounting mat 30.
During the typical heating cycle of the monolith 20 from 25.degree.
C. (ambient) to 500.degree. C. (i.e., from time interval "a" to
time interval "j", T.sub.m=475.degree. C.), the housing 11 only
increases in temperature a relatively small amount, from 25.degree.
C. to 70.degree. C. ( T.sub.h=45.degree. C.). Much of the initial
heat from the monolith 20 is not directly transmitted to the
housing 11, but rather is absorbed in increasing the temperature of
the mounting mat 30 as a function of the mounting mat's specific
heat. Additionally, the conduction of heat through the mounting mat
30 does not occur instantaneously, but rather takes time as a
function of the coefficient of thermal conduction through the
mounting mat 30. These factors create a thermal "lag" of heating
from the monolith 20 to the housing 11.
[0124] The coefficient of thermal expansion 70 of the metal housing
11 is about 10 times the coefficient of thermal expansion of the
ceramic monolith 20. During the heating/time interval "a" to "j",
the difference between T.sub.m and T.sub.h is equally offset by the
difference in coefficients of thermal expansion 68, 70, and the gap
remains substantially constant.
[0125] During high temperature heating as the engine approaches
steady state thermal operating conditions, the thermal "lag"
extends out or catches up to considerably raise the temperature of
the housing 11. During heating of the monolith 20 from 550.degree.
C. to 900.degree. C. (i.e., from time interval "k" to time interval
"u", T.sub.m=350.degree. C.), the housing 11 increases in
temperature a relatively large amount, from 85.degree. C. to
530.degree. C. (T.sub.h=445.degree. C.). The higher coefficient of
thermal expansion 70 of the metal housing 11 combines with the
greater temperature change, and the gap increases considerably.
[0126] During cooling, there is no source of heat for the monolith
20, and the temperature profile is due to the time necessary to
dissipate the thermal energy stored in the catalytic converter.
Thermal "lag" effects are seen equally at both the inside and the
outside of the mounting mat 30, and the temperature gradient across
the mounting mat 30 has a significantly shallower slope. During
cooling of the monolith 20 from 900.degree. C. to 50.degree. C.
(i.e., from time interval "u" to time interval "ll",
T.sub.m=850.degree. C.), the housing 11 decreases in temperature
commensurately, from 530.degree. C. to 50.degree. C.
(T.sub.h=480.degree. C.). The higher coefficient of thermal
expansion 70 of the metal more than offsets the smaller temperature
change, and the gap decreases slowly.
[0127] The ideal mounting mat will have expansion properties which
mirror the change in gap size at the various thermal temperatures
reached for the ceramic monolithic and the peripheral wall.
Additionally, the mounting mat will have resiliency properties
which remain substantially constant regardless of thermal cycling
and any compression cycling. Heating and thermal cycling of the mat
should not cause brittleness nor decrease erosion resistance. It is
desired to produce a mounting mat which is low in cost, while
maintaining a substantially constant holding force at all gap
changes. The present invention allows the thermal expansion
properties of the intumescent materials to be better utilized
relative to the change in the gap.
Thickness Measurement
[0128] The thickness of the flexible non-moldable sheets is
measured by placing a 21/2 inch (6.35 centimeter) diameter
deadweight exerting 0.7 psi (4.8 kPa) upon the sheet and measuring
the compressed thickness. As used herein, the "thickness" of the
sheets or layers is determined by this measurement, even though the
sheets are compressed with substantially greater forces in
installation between the ceramic monolithic 20 and the peripheral
wall of the metal housing 11. Comparisons between the thickness of
the outer layer and the thickness of the inner layer can be made at
any circumferential location on the mat 30, 50.
[0129] The thickness measurement is also taken prior to the first
and subsequent heating cycles which cause expansion of the
unexpended vermiculite or other intumescent material. As will be
further explained, the compressive force (and hence the
uncompressed thickness of the mat 30, 50) can change based on the
compression and heating history of the mat 30, 50.
Cold Erosion Test
[0130] This test is an accelerated test conducted under conditions
that are more severe than actual conditions in a catalytic
converter provides comparative data as to the erosion resistance of
a mat mounting material.
[0131] A test sample is cut into a square measuring 2.54 cm by 2.54
cm, weighed, and mounted between two high temperature Inconel 601
steel plates using spacers to obtain a mount density of
0.700+/-0.005 g/cm.sup.3. The test assembly is then heated for two
hours at 800.degree. C. and cooled to room temperature. The cooled
test assembly is then positioned 3.8 mm in front of an air jet
oscillating back and forth over the edge of the mat at 20 cycles
per minute. The test is discontinued after 0.2 grams of material is
lost or after 24 hours, whichever occurs first. The air jet
impinges on the mat at a velocity of 305 meters per second. The
erosion rate is determined by the weight loss divided by the time
of the test and is reported in grams/hour (g/hr).
EXAMPLES
[0132] The examples described below were made on a fourdrinier
papermaking machine having an inclined wire section and a
subsequent flat wire section. The inclined wire section was
inclined at an angle of 23 degrees from horizontal. A first headbox
was mounted on the inclined wire section. A second headbox was
mounted either on the inclined wire section in the slurry pond of
the first headbox or on the flat wire section. The headboxes
provide a slurry pond zone wherein the flow rate of the slurry onto
the moving wire can be controlled. Vacuum sources or boxes were
placed below and slightly in front of each headbox for dewatering
the slurries when they were deposited onto the wire section. To
prevent undesirable settling out of relatively dense filler and
intumescent particles during the deposition of the slurries onto
the wire, the vacuum boxes were placed in close proximity to the
headboxes such that dewatering of the slurries coincided with the
deposition of the slurries on the wire. The fourdrinier machine was
connected via a conveyer belt to a conventional wet pressing roll
and a series of conventional steam-heated drying rolls and finally
to a conventional winding roll. Conventional pumps were used to
pump the slurries to each of the headboxes and the pump rates were
controlled using flow controllers.
Examples 1-5
[0133] One-hundred pounds (45.4 kg) of ceramic fibers
(FIBERFRAX.TM. 7000M, available from Unifrax Co., Niagara Falls,
N.Y.) were slushed in 960 gallons (3,634 L) of water in a Mordon
Slush-Maker for one minute. The fiber slush was transferred to a
2000 gallon (7,520 L) chest and diluted with an additional 140
gallons (526 L) of water. Thirty-nine pounds (17.7 kg) of 45.5
percent solids latex (RHOPLEX.RTM. HA-8, available from ROHM &
HAAS, Philadelphia, Pa.) was added while mixing. Eleven pounds (5.0
kg) of aluminum sulfate (50 percent solids) was then added to
coagulate the latex. This latex-fiber slurry is hereafter referred
to as formula "A".
[0134] A second slurry was prepared by slushing 100 pounds (45.4
kg) of ceramic fibers (FIBERFRAX.TM. 7000M) in 960 gallons (3,634
L) of water and mixing for one minute. Forty-three pounds (19.5 kg)
of expanded vermiculite (ZONOLITE.RTM. #5, available from W. R.
Grace Co., Cambridge, Mass.) were added to the slushed fibers and
mixed until dispersed. The fiber-expanded vermiculite slurry was
pumped to a 1500 gallon (5,678 L) chest and diluted with an
additional 140 gallons (526 L) of water. Thirty-nine pounds (17.7
kg) of latex (RHOPLEX.RTM. HA-8, 45.5 percent solids) was added
while mixing and 11 pounds (5.0 kg) of alum (50 percent solids) was
added to coagulate the latex. This slurry is hereafter referred to
as formula "B".
[0135] The formula A and B slurries were metered to separate 50
gallon (189 L) mixing tanks where unexpanded vermiculite having a
mesh size of between 20 and 50 mesh, referred to as "V" below, and
expandable graphite (GRAFOIL.RTM. Grade 338-50 expandable graphite
flake, available from UCAR Carbon Co., Inc., Cleveland, Ohio),
referred to as "G" below, were metered and mixed into the "A"
and/or "B" slurries at a sufficient rate to maintain a
substantially constant concentration. The slurries containing the
intumescent materials were under continuous agitation using a
3-bladed propeller rotating at sufficient speed to keep the
intumescent material suspended within the slurry. The slurries and
particles were metered at variable rates and directed to either the
top or bottom layer headboxes to make multi-layer sheets having the
desired dry weight compositions and thicknesses. The slurry
contained in the bottom layer headbox was kept under continuous
agitation using a horizontal rotating mixing roll. Both headboxes
were mounted on the inclined section of the wire as described
above. The wire speed was maintained at about 2 feet/min (0.61
m/min) and the A and B slurries were pumped to the respective
headboxes at a rate of about 5 gal/min (18.9 L/min) to achieve the
desired layer basis weight and thickness. Sufficient vacuum was
applied to the slurries to obtain formed and dewatered layers. The
dewatered multilayer sheets were then wet pressed through rollers,
dried using drying rollers, and then wound on a winding stand to
form a continuous roll. The total sheet thickness, sheet and layer
basis weights, and dry weight percentages of V and G in each layer
of Examples 1-5 are shown in Table 3 below.
Example 6
[0136] Seventy-five pounds (34.1 kg.) of ceramic fibers
(FIBERFRAX.TM. 7000M) were slushed in 400 gallons (1514 L) of water
in a Mordon Slush-Maker for 90 seconds then transferred to a 2000
gallon (7570 L) chest. Another 75 pounds (34.1 kg) of ceramic
fibers (FIBERFRAX.TM. 7000M) were slushed as described above and
added to the 2000 gallon (7570 L) chest and the combined batches
were diluted with 250 gallons (946 L) of rinse water. Twenty-two
pounds (10 kg.) of latex (AIRFLEX.TM. 600BP, 55 percent solids),
3.3 pounds (1.5 kg.) liquid sodium aluminate (NALCO.TM. 2372, from
Nalco Chemical, Naperville, Ill.), and 3.1 ounces (0.09 liters) of
defoamer (FOAMASTER.TM. III, from Henkel Co., Edison, N.J.) were
then added to the chest while mixing. After 2 to 3 minutes, the pH
of the mixture was measured at 5.6. Then, 23 pounds (10.4 kg) of
aluminum sulfate (50 percent solids) was diluted with and
equivalent volume of water and slowly added to the chest while
mixing to form a slurry. This slurry is hereafter referred to as
formula "C".
[0137] Two-hundred gallons (757 L) of formula "C" slurry was then
pumped into a 1500 gallon (5678 L) chest and diluted with an
additional 200 gallons (757 L) of water. Fifty gallons (189 L) of
this slurry was drained from the chest. The resultant slurry is
hereafter referred to as formula "D." Fifty pounds (22.7 kg) of
expandable graphite (G) (GRAFOIL.TM. Grade 338-50 expandable
graphite flake) was added to the formula "D" slurry while mixing.
At this time, 3.4 ounces (0.1 L) of red dye (GRAPHTOL.TM. Red
pigment dispersion, from Sandoz Colors and Chemicals East Hanover,
N.J.) was added to the formula "C" slurry in the 2000 gallon (7570
L) chest containing base stock. Continuous mixing in addition to
recirculation of the slurries by pumping from a bottom outlet
through a 2 inch (5.1 centimeter) hose was maintained at a rate
sufficient to keep all solids suspended in both chests.
[0138] Formula "C" slurry was then metered and delivered to a mix
tank of 50 gallon (189 L) capacity at a rate sufficient to maintain
the desired base web basis weight. Unexpanded vermiculite (V) was
added to the mixing tank at a rate sufficient to maintain the
desired proportion of vermiculite in the bottom layer of the sheet.
These proportions were obtained by first measuring the basis weight
of the layer formed without vermiculite and then adjusting the
formula "C" slurry flow to the mix tank before metering unexpanded
vermiculite into the mix tank, and then adjusting the rate of
addition of the unexpanded vermiculite to obtain the desired basis
weight of the resulting bottom layer.
[0139] The formula "C"+V slurry from the mix tank was fed by
gravity to the first headbox mounted on the inclined wire section
of the above described fourdriner machine to form a 12 inch (30.5
cm) wide layer at a wire speed of 26.4 inches (67.1 cm) per minute.
The formula "D"+G slurry was delivered to the second headbox
mounted on the flat wire section of the fourdrinier machine.
Sufficient vacuum was maintained through the lower layer at the
point where the formula "D"+G slurry was delivered so to partially
dewater the slurry to form a non-moldable flexible layer having
about 70 percent expandable graphite by weight. Example 6 is
described in Table 3 below.
3TABLE 3 BASIS WEIGHT.sup.2 THICKNESS.sup.3 EXAMPLE LAYER
FORMULA.sup.1 (g/m.sup.2) (mm) 1 Top B + 10% V 752 Bottom A 1152
(1904) 2 Top B + 10% V 752 Bottom A + 54% V 2477 (3229) 3 Top A
1108 Bottom A + 54% V 2477 (3229) 4 Top A + 61% G 900 Bottom A +
54% V 2477 (3377) 5 Top A + 61% G 1290 Bottom A + 54% V 2477 (3767)
6 Top D + 70% G 560 Bottom C + 37% V 2390 (2950) (6.1) .sup.1V =
unexpanded vermiculite; G = expandable graphite; (%) = percent by
dry weight in the layer. .sup.2The total basis weight of both
layers is shown in parentheses. .sup.3The total thickness of both
layers is shown in parentheses.
[0140] All of the above multilayer sheets were flexible and
resilient and the layers were bonded together such that the layers
could not be cleanly separated at the boundary between the layers.
Each of the multilayer sheet examples could be handled without
breaking or undesirable cracking. The above examples also
demonstrate that such flexible and resilient multilayer sheets may
be made using a continuous process that is less expensive and more
efficient when compared with a process wherein multiple layers are
bonded together using an adhesive or other auxiliary bonding
means.
Example 7
[0141] Example 6 described above and Comparative Example 1,
described below, were tested and compared for holding strength
under the Real Condition Fixture Test (RCFT) described above. The
temperatures used in the RCFT are representative of those found in
a diesel catalytic converter. Comparative Example 1 (C1) was a 4070
gram per square meter (nominal) single layer, low temperature
intumescent ceramic fiber sheet containing unexpanded vermiculite,
commercially available under the trademark "INTERAM" TYPE 200 from
Minnesota Mining and Manufacturing Company, St. Paul, Minn. The
starting mount densities for Example 6 and C1 were 0.9 and 1.0
grams per cubic centimeter respectively.
[0142] The results of the RCFT for Example 6 and C1 are shown in
Table 4 below. The results of the test show that the multilayer
sheet of the invention provides higher pressures or holding force
over the temperature range than the sheet of Comparative Example
1.
4TABLE 4 Monolith Shell Gap Example 6 Comparative 1 Temperature
Temperature Change Pressure (C1) (C) (C) (cm) (kPa) Pressure (kPa)
25 25 0.0000 291.5 215.6 63 30 0.0001 231.2 162.1 100 35 0.0003
228.0 160.9 150 40 0.0003 223.1 152.5 200 55 0.0012 155.8 94.3 200
120 0.0068 101.1 57.8 200 (soak) 120 0.0068 117.2 47.8 150 90
0.0046 115.5 49.9 100 60 0.0024 130.1 57.9 63 42 0.0012 140.4 65.4
25 25 0.0000 146.2 76.1
Example 8
[0143] A multilayer sheet containing a mixture of unexpanded
vermiculite and expandable graphite in the top layer and unexpanded
vermiculite in the bottom layer was made as described above for
Examples 1-5. Example 8 is described below in Table 5.
5TABLE 5 BASIS WEIGHT.sup.2 THICKNESS.sup.3 EXAMPLE LAYER
FORMULA.sup.1 (g/m.sup.2) (mm) 8 Top A + 33% V + 526 Bottom 22%G
2733 A + 55% V (3259) (5.3) .sup.1V = unexpanded vermiculite; G =
expandable graphite; (%) = percent by dry weight in the layer.
.sup.2The total basis weight of both layers is shown in
parentheses. .sup.3The total thickness of both layers is shown in
parentheses.
[0144] The multilayer intumescent sheet of Example 8 was flexible
and could be handled without breaking or undesirable cracking. The
multilayer sheet of Example 8 also could not be cleanly separated
at the boundary between the layers.
Example 9
[0145] Example 8 described above and Comparative Example 2,
described below, were tested and compared for holding strength
under a RCFT using the temperature profile described above for an
automotive catalytic converter. Comparative Example (C2) was a 3100
gram per square meter (nominal) single layer, intumescent ceramic
fiber sheet containing unexpanded treated vermiculite and is
commercially available under the trademark "INTERAM" TYPE 100 from
Minnesota Mining and Manufacturing Company, St. Paul, Minn. The
starting mount density for Example 8 and C2 was 1.0 grams per cubic
centimeter.
[0146] The results of the RCFT for Example 8 and C2 are shown in
Table 6 below. The results of the test show that the intumescent
multilayer sheet of Example 8 provides higher pressures or holding
force over the temperature range and provides a lower pressure drop
at low temperatures (25-400.degree. C.) than the intumescent sheet
of Comparative Example 2.
6TABLE 6 Monolith Shell Gap Example 8 Comparative 2 Temperature
Temperature Change Pressure (C2) (C) (C) (cm) (kPa) Pressure (kPa)
25 25 0.0003 310 183 100 25 0.0003 259 101 150 30 0.0003 251 93 200
35 0.0003 226 80 250 38 0.0003 220 70 300 40 0.0003 246 65 350 45
0.0003 330 80 400 50 0.0003 434 123 450 60 0.0003 370 142 500 70
0.0003 380 184 550 85 0.0013 393 227 600 100 0.0025 448 282 650 125
0.0038 540 357 700 150 0.0051 640 442 750 185 0.0076 713 526 800
220 0.0102 787 626 850 325 0.0165 1021 853 900 430 0.0229 1251 1022
900 480 0.0267 1184 983 900 530 0.0305 1152 959 900 (soak) 530
0.0305 944 869 850 502 0.0292 914 804 800 474 0.0279 869 800 750
445 0.0254 903 829 700 416 0.0229 940 904 650 387 0.0216 889 808
600 358 0.0203 830 770 550 329 0.0191 788 737 500 300 0.0178 682
635 450 275 0.0165 640 619 400 250 0.0152 529 475 350 215 0.0127
418 432 300 180 0.0102 289 306 250 155 0.0089 162 173 200 130
0.0076 76 96 150 95 0.0051 56 83 100 60 0.0025 68 83 50 50 0.0003
88 108
[0147] The holding pressure has a first cycle minimum (at
heating/time interval "f") which can be numerically characterized
as a percentage increase of the initial holding force:
(183-65)/183=64%
[0148] The holding pressure has a substantial increasing portion
from heating/time interval "f" to heating/time interval "r",
associated with the first heating of the unexpanded vermiculite
material to a temperature above its intumescing temperature
T.sub.int of about 300 to 340.degree. C. The holding pressure has a
first cycle maximum (at heating/time interval "r") which can be
numerically characterized as a percentage increase of the initial
holding force:
(1022-183)/183=458%
[0149] This first cycle maximum reflects that full expansion of the
intumescent material during the first cycle is substantially
complete at heating/time interval "r", when the housing is at
430.degree. C. The holding pressure drops (i.e., has a first cycle
loss) to a post-cycle ambient hold force 80. The first cycle loss
is approximately 41%. The first cycle loss is due to the ongoing
effects of the high compression/heating history of the mat
material.
[0150] Additional RCFT results of Comparative Example 2 are further
shown in FIG. 5. This RCFT was run on a second, different "INTERAM"
TYPE 100 mat from Minnesota Mining and Manufacturing Company, St.
Paul, Minn., and due to slight differences in mount density provide
slightly higher mount pressures (i.e., about 300 kPa rather than
183 kPa) than those given in Table 6. The first cycle minimum 76 is
about 60%, the first cycle maximum 78 is about 305%, and the first
cycle loss can be numerically characterized as a percentage
decrease of the initial holding force:
(300-146)/300=51%
[0151] FIG. 5 also shows subsequent thermal/compression cycles of
the CE2 mounting mat. The holding pressure has a subsequent cycle
minimum 82 which can be numerically characterized as a percentage
decrease of the initial holding force:
(300-90)/300=70%
[0152] The subsequent cycle minimum point 82 can also be used to
determine a second cycle loss, numerically characterized as a
percentage decrease of the post-cycle ambient hold force 80:
(145-90)/145=38%
[0153] The ideal mounting mat would reduce each of the first cycle
minimum 76, the first cycle maximum 78, the first cycle loss, the
subsequent cycle minimum 82 and the second cycle loss to as close
to zero percent (i.e., as close to constant pressure) as
possible.
Examples 10-16
[0154] Fourteen pounds (6.3 kg) of 50% silica, 50% alumina bulk
containing about 50% fibers, 50% shot (KAOWOOL.RTM. HA Bulk,
available from Thermal Ceramics, Augusta, Ga.) and 4.2 pounds (1.9
kg) of 96% alumina fibers containing substantially no shot
(SAFFIL.RTM. LDM, available from ICI Chemicals and Polymers, Widnes
Chesire, UK) were slushed in 400 gallons (1514 L) of water in a
Mordon Slush-Maker for 65 seconds. The fiber slush was transferred
to a 1500 gallon (5679 L) chest and diluted with an additional 300
gallons (1136 L) of rinse water. Six pounds (2.7 kg) of acrylic
ethyl vinyl acetate latex binder (55% solids AIRFLEX.RTM. 600 BP,
available from Air Products, Allentown, Pa.) was added while
mixing. Six pounds (2.7 kg) of aqueous aluminum sulfate solution
known as papermaker's alum (50 percent solids) was then added to
coagulate the latex. Two-thirds ounces (20 ml) of a defoaming agent
(FOAMASTER.RTM. III, available from Henkel Corp., Edison N.J.) and
seven pounds (3.2 kg) of a 0.1% liquid polyacrylamide flocculant
(NALCO.RTM. 7530, available from Nalco Chemical Co. of Naperville,
Ill.) were also added. This latex-fiber slurry is hereafter
referred to as formula "E".
[0155] The formula "E" slurry was separated into two separate
portions, with about 80% of the slurry in one portion and about 20%
of the slurry in the second portion. An amount of unexpanded
vermiculite having a mesh size of between 18 and 50 mesh (available
from Cometals, Inc.) was metered and mixed into the 20% portion of
the "E" slurry at a rate to maintain a substantially constant
concentration. The "E" slurry containing the intumescent material
was under continuous agitation to keep the intumescent material
suspended within the slurry.
[0156] The 80% portion of the "E" slurry was directed to the bottom
layer headbox, and the 20% portion of the "E" slurry containing the
intumescent particles was directed to the top layer headbox to make
multi-layer sheets having the desired dry weight compositions. The
wire speed was maintained at about 1.7 feet/min (0.52 m/min) and
the slurry portions were pumped to the respective headboxes at a
total rate of about 16 gal/min (61 L/min) to achieve the desired
layer basis weight and thickness. Sufficient vacuum was applied to
the slurries to obtain formed and dewatered layers. The dewatered
multilayer sheets were then wet pressed through rollers, dried
using drying rollers, and then wound on a winding stand to form a
continuous roll. The dry weight percentages of intumescent
particles in each layer and overall, layer and total sheet
thickness, and layer and sheet basis weights of Examples 10-14 are
shown in Table 7 below.
7TABLE 7 INTUMESCENT BASIS PARTICLE WEIGHT THICKNESS EXAMPLE LAYER
CONTENT (g/m.sup.2) (mm) 10 Top 0% 265 1.4 Bottom 0% 1100 5.8
Overall 0% 1365 7.2 11 Top 31% 384 1.3 Bottom 0% 1100 5.6 Overall
8% 1365 6.9 12 Top 45% 480 1.1 Bottom 0% 1100 5.5 Overall 13.6%
1580 6.6 13 Top 50% 525 0.9 Bottom 0% 1100 5.4 Overall 16% 1625 6.3
14 Top 63% 720 1.1 Bottom 0% 1100 5.2 Overall 25% 1820 6.3
[0157] The RCFT results of Examples 10-14 are shown in FIGS. 6-10.
For each of these samples, the RCFT was run for multiple
thermal/compression cycles. The test results for subsequent cycles
are strikingly different than the test results for each first
cycle. While the gap change occurs substantially equally regardless
of previous thermal/compression cycling, the pressure force exerted
by the mat changes significantly. That is, the previous thermal and
compression history of each mat significantly affects the amount of
holding pressure in subsequent heating cycles.
[0158] Several interrelated effects are believed to contribute to
the significant change produced by prior thermal and compression
history of each mat. The amount of intumescent expansion is
significantly different for unexpanded vermiculite versus
previously expanded vermiculite. While unexpanded vermiculite
undergoes significant expansion the first time it is heated to its
intumescent temperature T.sub.int, the intumescent expansion
properties are significantly reduced for subsequent thermal
cycling. High compression forces are believed to have a significant
affect on the fiber matrix within the mat. High compression forces
within the mat, particularly when combined with high temperature,
can cause microscopic fiber damage, shrinkage and/or compression
setting which causes the fiber matrix to be less resilient and
assert less mounting force subsequent to the high mounting
pressure/temperature. Compression and high temperature cycling
effects on the fiber matrix can also change the erosion resistance
properties of the mat and thermal conductivity of the mat.
[0159] The first cycle minimum 76, the first cycle maximum 78, the
first cycle loss, the subsequent cycle minimum 82 and the second
cycle loss for each of Examples 10-14 as compared to Comparative
Example 2 are reported below in Table 8.
8TABLE 8 FIRST FIRST FIRST SUBSEQUENT SECOND CYCLE CYCLE CYCLE
CYCLE CYCLE EXAMPLE MINIMUM MAXIMUM LOSS MINIMUM LOSS CE-2 (FIG. 5)
60% 305% 52% 70% 38% 10 (FIG. 6) 98% 0% 50% 99% 99% 11 (FIG. 7) 67%
0% 48% 91% 84% 12 (FIG. 8) 62% 2% 52% 81% 63% 13 (FIG. 9) 63% 2%
54% 75% 45% 14 (FIG. 10) 87% 69% 68% 78% 32%
[0160] The ideal mounting mat would reduce each of the first cycle
minimum 76, the first cycle maximum 78, the first cycle loss, the
subsequent cycle minimum 82 and the second cycle loss to as close
to zero percent (i.e., at as constant a mounting pressure) as
possible. As contrasted to Comparative Example 2 which also
includes an intumescent material, the present invention desirably
reduces the first cycle maximum 78 to a value less than about 100%,
more desirably to a value less than about 50%, and even more
desirably to a value less than about 10%. As contrasted to Example
10 which contains the same fiber mix but without the intumescent
layer, the present invention desirably reduces the first cycle
minimum 76 to a value less than about 90%, and even more desirably
to a value less than about 75%. As contrasted to Example 10, the
present invention desirably reduces the subsequent cycle minimum 82
to a value less than about 95%, more desirably to a value of about
90% or less, and more desirably to a value of about 75% or less.
Also as contrasted to Example 10, the present invention desirably
reduces the second cycle loss to a value less than about 95%, more
desirably to a value less than about 85%, and even more desirably
to a value of about 45% or less. These excellent results are
achieved with minimal material costs, including only a small amount
of intumescent material and a small amount of shot-free, high
alumina fiber.
[0161] The excellent results of the present invention can be
further explained with reference to FIG. 11. FIG. 11 includes an
"intumescent zone" 84 of Example 13 superimposed onto the
temperature-radial location-time/heating interval graph of FIG. 3.
The "intumescent zone" 84 is defined by the intumescing temperature
of the intumescent material and by the radial location of the
intumescent material in the mat 30. The intumescent material of
Example 13 is unexpanded vermiculite, with an intumescing
temperature T.sub.int of about 300 to 340.degree. C. Other
intumescent materials will have different intumescing temperatures,
and may intumescent at a narrower or broader temperature range. The
intumescent material of Example 13 is only located in the outer
about 15-40% of the thickness of the mat 30 (after the mat 30 is
compressed between the monolith 20 and the housing 11).
[0162] It is believed that the transmission of heat throughout the
mat of the present invention remains fairly continuous. That is,
because the mat is coformed, and perhaps also because the mat has
the same inorganic fiber mix throughout the mat, heat is
transmitted through the mat without setting up a thermal contact
resistance (i.e., a point of temperature discontinuity) between the
two layers of the mat. Accordingly, the assumption of linear
temperature distributions through the mat remains fairly
accurate.
[0163] The first temperature line to hit the intumescent zone 84
occurs after heating/time interval "j", at about heating/time
interval "l". This coincides with the start of the high increase
portion 62 of the gap. As the temperature lines move through the
intumescent zone (i.e., until about heating/time interval "q") the
intumescent material expands. The expansion of the intumescent
material increases the mounting pressure during this important
stage of the RCFT curve (FIG. 9), just when the gap is increasing
most.
[0164] With the small proportion of intumescent material used and
properly located within the mat, only limited expansion of the mat
occurs, such that the first cycle maximum 78 is quite low.
Resilience reduction of the fiber matrix due to high compression
forces at high temperatures is minimized. Accordingly, subsequent
cycles maintain maximum resiliency and holding force provided by
the fiber matrix.
[0165] To obtain the most desired benefits of the present
invention, the ratio between the outer layer thickness t.sub.o and
inner layer thickness ti should be such that the temperature curve
does not hit the intumescent zone 84 until the gap hits the high
increase portion 62. With a gap that begins a high increase portion
at a monolith temperature of 500.degree. C. (475.degree. C. over
ambient), this can be mathematically stated as:
t.sub.o (t.sub.o+t.sub.i)(T.sub.int-25.degree. C.)/475.degree.
C.
[0166] Recognizing that the transient effects of heat transfer, the
radial nature of the system and any differences in thermal
conductivity between the two layers will affect the linearity of
the thermal gradients through the mounting mat, the edge of the
intumescent zone 84 may be varied within about 10 to 20% while
still substantially retaining the benefits of the present
invention. The temperature of the monolith T.sub.g which starts the
high gap increase portion 62 can also be different from 500.degree.
C. if the size of the gap or the thermal conductivity is
significantly altered. That is:
0.8(t.sub.o+t.sub.i)(T.sub.int-25.degree. C.)/(T.sub.g-25.degree.
C.) t.sub.o1.2(t.sub.o+t.sub.i)(T.sub.in-25.degree.
C.)/(T.sub.g-25.degree. C.)
[0167] FIG. 12 shows a single cycle RCFT on a single layer
non-intumescent mat similar to Example 10 but containing no
shot-free high alumina inorganic fiber. Instead, all of the
inorganic fiber material was provided by an about 50% alumina 50%
silica bulk containing about 50% fibers and about 50% shot. As can
be seen by comparison to Examples 10-14 shown in FIGS. 6-10, this
mat provides poor results, including a first cycle minimum of 100%,
a first cycle loss of 68%, a subsequent cycle minimum of 100% and a
second cycle loss of 100%. The combination of shot-free inorganic
fiber and inorganic fiber containing shot of each of Examples 10-14
provide much better results.
[0168] Cold erosion tests were run on Examples 10, 11 and on two
additional examples 15 and 16. The parameters and results of the
cold erosion test are given below in Table 9.
9TABLE 9 TOTAL MAT MOUNT EROSION INTUMESCENT DENSITY DENSITY RATE
EXAMPLE CONTENT (g/cc) (g/cc) (g/hour) 10 0% .175 0.4 0.001 11 8%
.205 0.4 0.001 15 27% .239 0.4 0.011 16 29% .276 0.4 0.076
[0169] As shown by this data, the present invention provides
excellent erosion rate results, such as less that about 0.1 g/hour,
and more desirably about 0.01 g/hour or less, and most desirably
about 0.001 g/hour or less, provided the vermiculite particle
content in the outer layer is not too high. The erosion rate varies
significantly based on the mount density, and higher mount
densities can be used for high vermiculite content mats or mats
with high vermiculite content layers.
Equivalents
[0170] It will be apparent to those skilled in the art that various
modifications and variations can be made in the articles and method
of the present invention without departing from the spirit or scope
of the invention. For example, the thicknesses of each the various
layers discussed herein are substantially constant throughout the
layer. It is recognized that mats could be constructed within the
present invention but not having an areally uniform construction,
such as having side edges which are thicker or provide different
thermal properties than the center of the mat. It should be
understood that this invention is not intended to be unduly limited
by the illustrative embodiments and examples set forth herein and
that such examples and embodiments are presented by way of example
only with the scope of the invention to be limited only by the
claims set forth herein as follows.
* * * * *