U.S. patent application number 09/153115 was filed with the patent office on 2001-05-31 for monolithic ceramic filter.
This patent application is currently assigned to HIROSHI YORITA. Invention is credited to KAMEI, YUJI, TAGUCHI, HISATOMI, YORITA, HIROSHI.
Application Number | 20010002008 09/153115 |
Document ID | / |
Family ID | 26521508 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010002008 |
Kind Code |
A1 |
YORITA, HIROSHI ; et
al. |
May 31, 2001 |
MONOLITHIC CERAMIC FILTER
Abstract
A monolithic ceramic filter having a portion of the partition
wall of a honeycomb structure exposed with its end face on an outer
wall surface of the structure and increased in thickness as
compared to the remaining portion of the partition wall to form a
flow resistance relaxing portion is disclosed. The monolithic
ceramic filter may also have a groove-shaped recess which is
separated via a partition from a liquid supply passage of a
honeycomb structure and is in communication with the outside of the
structure. The flow resistance of the filtrate within the partition
walls may be diminished to enable efficient filtration. The filter
is produced simply by extrusion molding. There is no necessity of
forming holes for discharging the filtrate in some cases.
Inventors: |
YORITA, HIROSHI; (TOYOAKE,
JP) ; TAGUCHI, HISATOMI; (AICHI-GUN, JP) ;
KAMEI, YUJI; (NAGOYA, JP) |
Correspondence
Address: |
Barry E Bretschneider ESQ
Morrison & Foerster LLP
2000 Pennsylvania Avenue NW
Washington
DC
20006-1888
US
|
Assignee: |
HIROSHI YORITA
|
Family ID: |
26521508 |
Appl. No.: |
09/153115 |
Filed: |
September 15, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09153115 |
Sep 15, 1998 |
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08855034 |
May 13, 1997 |
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5855781 |
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08855034 |
May 13, 1997 |
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08094904 |
Jul 22, 1993 |
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Current U.S.
Class: |
210/496 ;
210/510.1 |
Current CPC
Class: |
Y10S 55/30 20130101;
B01D 2201/46 20130101; B01D 63/061 20130101; B01D 63/066 20130101;
B01D 29/31 20130101 |
Class at
Publication: |
210/496 ;
210/510.1 |
International
Class: |
B01D 039/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 1992 |
JP |
4-216575 |
Sep 12, 1992 |
JP |
4-274807 |
Jul 23, 1992 |
JP |
4-216575 |
Sep 21, 1992 |
JP |
4-274807 |
Jul 23, 1992 |
JP |
4-216575 |
Sep 21, 1992 |
JP |
4-274807 |
Claims
What is claimed is:
1. A monolithic ceramic filter comprising a honeycomb structure,
wherein a portion of partition wall of the honeycomb structure
extends from the inside of the honeycomb structure to an outer wall
surface of the honeycomb structure and has an increased thickness
as compared to the remaining portion of the partition wall to
constitute a flow resistance relaxing portion.
2. The ceramic filter as defined in claim 1, wherein said flow
resistance relaxing portion has at least one filtrate discharge
conduit opening extending to an outer wall surface of the honeycomb
structure within the increased thickness of the flow resistance
relaxing portion.
3. The ceramic filter as defined in claim 1, wherein the flow
resistance relaxing portion extends over the entire axial length of
the honeycomb structure.
4. The ceramic filter as defined in claim 3, wherein the flow
resistance relaxing portion comprises a plurality of wall portions
of increased thickness which extends from one side to the other
side thereof.
5. The ceramic filter as defined in claim 3, wherein the flow
resistance relaxing portion comprises a plurality of wall portions
of increased thickness which extend parallel to each other.
6. The ceramic filter as defined in claim 2, wherein the filtrate
discharge conduit opening comprises bores extending transverse of
the honeycomb structure.
7. The ceramic filter as defined in claim 6, wherein the said bores
are disposed parallel to each other.
8. The ceramic filter as defined in claim 1 or 2, wherein the flow
resistance relaxing portion has a thickness 2 to 5 times of the
partition wall of the honeycomb structure.
9. A monolithic ceramic filter comprising a honeycomb structure
which comprises communication voids separated from cells of the
honeycomb structure of the filter cell partition walls, said voids
communicating with the lateral outside of said honeycomb structure
over the entire length of the honeycomb structure and extending
over the entire axial length thereof.
10. The ceramic filter as defined in claim 9, wherein said
communication voids are each a groove-shaped recess extending from
the outer peripheral wall of said honeycomb structure toward the
inside.
11. The ceramic filter as defined in claims 9, wherein the
honeycomb structure has such a shape as to permit production
thereof by extrusion molding.
12. The ceramic filter as defined in claim 9 which comprises an end
frame surrounding the honeycomb structure fitted on at least one
end thereof.
13. The ceramic filter as defined in claim 12 wherein said end
frame has protrusions engaged in said communication voids to close
the same at an end of the honeycomb structure.
14. The ceramic filter as defined in claim 11, wherein said
communication voids extend from the inside of the honeycomb
structure except central part of the honeycomb structure in the
transverse direction thereof.
15. The ceramic filter as defined in claim 11, where in said
communication voids extend from the outer peripheral wall toward
the inside ending at an intermediate position.
16. The ceramic filter as defined in claim 15, wherein said
communication voids extend alternately from one side of the outer
peripheral wall and from the opposite side thereof as viewed in the
cross section of the honeycomb structure.
17. The ceramic filter as defined in claim 1, 2, 9 or 12, wherein
the honeycomb structure is formed of a porous ceramic material and
has a filtration membrane on a surface facing each cell of the
honeycomb structure.
18. The ceramic filter as defined in claim 17, wherein an
intermediate porous layer is disposed between the honeycomb
structure and the filter membrane.
19. The ceramic filter as defined in claim 17, wherein said filter
membrane is a porous ceramic having a smaller pore size than that
of honeycomb structure.
20. The ceramic filter as defined in claim 9, wherein said
honeycomb structure further comrises a flow resistance relaxing
portion which is formed of a thickened portion of the cell
partition wall, said thickened portion extending from the inside of
the honeycomb structure to an outer wall thereof.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a monolithic ceramic filter which
has a honeycomb structure capable of achieving a high filtration
area and a low filtration resistance and which may be employed for
microfiltration, ultrafiltration and reverse osmosis.
BACKGROUND
[0002] Heretofore, a number of researches have been conducted for
achieving a compact ceramic filter with a high filtration area, and
proposals have been made of monolithic ceramic filters having a
honeycomb structure.
[0003] With the monolithic ceramic filters, the filtrate produced
on filtration by a filtration membrane formed on the surface of the
supply liquid passages flows within the partition walls towards an
outer wall of the filter before being discharged out of the filter
at the outer wall of the filter. Thus the flow volume of the
filtrate within the partition wall becomes larger as the outer wall
is approached.
[0004] With the conventional ceramic filters, having the honeycomb
structure, the partition wall has a constant wall thickness.
Consequently, the flow rate of the filtrate within the partition
wall is increased significantly at a region close to the outer
wall, so that the flow resistance to the filtrate is increased
significantly to limit the speed of filtration. Consequently, a
ceramic filter having a larger filtration area has been difficult
to be put into practice on the industrial scale.
[0005] As solutions to this problem, crossflow ceramic filters
having filtrate conduits as disclosed in JP Patent KOHYO
Publication (National laying-open of PCT international application)
Nos. 01-501534 (WO 88/07398) or 03-500386 (WO 90/03831), have been
proposed.
SUMMARY OF THE DISCLOSURE
Problem to be Solved by the Invention
[0006] However, the above-mentioned ceramic filters having the
filtrate conduits is complicated in structure and in need of highly
complex manufacture techniques. For instance, these ceramic filters
require either additional complicated processing and machining on a
monolith honeycomb structure, or complicated work for assembling a
number of honeycomb members (slabs), in order to produce flow out
channels of the filtrate.
Objects of the Invention
[0007] It is an object of the present invention to provide a
ceramic filter of a high filtration area which is free of the
above-mentioned problems and with which it becomes possible to
inhibit increase in the flow resistance to the filtrate within the
partition wall without limitation imposed on the filtration
speed.
[0008] Other objectives will become apparent from the entire
dislosure.
[0009] According to the First Aspect of the present invention, the
above object may be achieved by a monolithic ceramic filter,
characterized in that a portion of partition wall of a honeycomb
structure of the filter has its end face exposed on an otter wall
surface of the honeycomb structure and has an increased thickness
as compared to the remaining portion of the partition wall to
constitute a flow resistance relaxing portion. It is most
advantageous that this monolithic ceramic filter can be produced
simply by the extrusion technology.
[0010] According to the Second Aspect of the present invention,
additional to the First Aspect, the flow resistance relaxing
portion (i.e., thick wall portion) has a filtrate discharging
conduit opening reaching an outer wall surface of the honeycomb
structure. According to the Second Aspect the production is also
simple and easy since the filtrate discharging conduit openings can
be produced within the thick wall portion additional to the First
Aspect.
[0011] With such flow resistance relaxing portion, the flow
resistance offered to the filtrate may be prevented from being
increased.
[0012] Besides, with the above-mentioned filtrate discharging
conduit opening, the flow resistance imposed to the filtrate may be
additionally prevented from being increased.
[0013] According to the Third Aspect of the present invention, the
above object may be achieved by a monolithic ceramic filter defined
as follows:
[0014] A monolithic ceramic filter comprising communication voids
separated from cells of a honeycomb structure of the filter by cell
partition walls, with the voids being in communication with the
lateral outside of the honeycomb structure and continuously
extending axially through the honeycomb structure.
[0015] According to the Fourth Aspect of the present invention,
based on the monolithic ceramic filter by the Third Aspect, an end
frame is fitted on the end of said ceramic filter, preferably on
both the ends.
[0016] Preferably, the communication voids are groove-shaped
recesses formed in the outer peripheral wall of the honeycomb
structure.
[0017] Preferably, the ceramic filters are of such a shape as to
permit production thereof by extrusion molding, which simplifies
the production significantly.
[0018] Preferably, the end frames are each provided with
protrusions engaged in the communication voids or the groove-shaped
recesses to close the communication voids at the ends of the
honeycomb structure.
[0019] The communication voids may extend from the inside of the
honeycomb structure except the central part of the honeycomb
structure in the transverse direction thereof. The communication
voids may extend from the outer peripheral wall toward the inside
ending at an intermediate position. Also the communication voids
may extend alternately from one side of the outer peripheral wall
and from the opposite side thereof as viewed in the cross section
of the honeycomb structure. This arrangement is possible
particularly in the case where the honeycomb structure has a
square-shaped cross section.
[0020] Further arrangement of the communication voids
(groove-shaped recesses) or the flow resistance relaxing portions
are exemplified in FIGS. 8 to 9.
Concept Underlying the Invention
[0021] Although the honeycomb type filter is effective as a ceramic
filter having a high filtration area, the filtration speed is
limited due to the significantly increased flow resistance
presented to the filtrate, with the consequence that it is
difficult to utilize the honeycomb ceramic filter of a high
filtration area on an industrial scale. The present invention
provides a monolithic ceramic filter having a high filtration area
in which limitations on the filtration speed are resolved by
preventing increase in the flow resistance imposed on the
filtrate.
[0022] The flow resistance offered to the filtrate within the
partition wall (pressure loss .DELTA.P) is represented by
Kozeny-Carmen's formula 1 Q A = 3 P L ( 1 - ) 2 S 2 ( 1 )
[0023] Since 2 D = 4 ( 1 - ) S ( 2 )
[0024] the following formula (3) 3 Q A = D 2 P 16 L ( 3 )
[0025] holds. In the above formulas (1) to (3), Q denotes the flow
volume, A the cross-sectional area, .epsilon. the pore ratio,
.DELTA.P pressure loss, .kappa. a constant, L a distance, .mu. the
viscosity, S the surface area and D the pore diameter.
[0026] The above formula demonstrates that the flow resistance to
the filtrate may be diminished such as by increasing the
cross-sectional area A, increasing the pore diameter D, decreasing
the distance L or by increasing the pore ratio .epsilon.. The
present invention has been accomplished on the basis of the above
finding.
[0027] According to the First Aspect of the present invention, as
shown in FIGS. 1 to 3, the cross-sectional area A is increased by
having a thick wall portion (12), increased in thickness, of a
partition wall connecting to an outer wall (13) so as to serve as a
filtrate passage (flow resistance relaxing portion), whereas
according to the Second Aspect, the distance L is decreased by the
filtrate discharging conduit opening (14) connecting to the outer
wall surface.
[0028] According to the Third Aspect of the present invention, by
providing communication voids separated from the cells of the
honeycomb structure by means of partition walls (cell partition
walls) for communication with the outside of the honeycomb
structure, the flow distance L which is traversed by the filtrate
resulting from filtration through the filtration membrane before
the filtrate is discharged out of an outer wall of the filter after
flowing through the inside of the partition walls is diminished. In
this manner, a monolithic ceramic filter is realized in which the
flow resistance presented to the filtrate is suppressed to a
smaller value and in which limitation imposed on the filtration
speed has been significantly eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a side elevational view showing a supporting
member of a honeycomb structure according to Example 1 of the
present invention.
[0030] FIG. 2 is a side elevational view showing a supporting
member of a honeycomb structure according to Example 2 of the
present invention.
[0031] FIG. 3 is a cross-sectional view taken along line A-A' of
FIG. 2.
[0032] FIG. 4 is a perspective view of a supporting member of a
honeycomb structure according to a Comparative Example.
[0033] FIG. 5 is a perspective view showing a supporting member of
a honeycomb structure according to Example 3 of the present
invention.
[0034] FIG. 6 is a perspective view showing the ceramic filter of
Example 3 of the present invention, when fitted with end
frames.
[0035] FIG. 7 is a perspective view showing a honeycomb supporting
member according to a modified embodiment.
[0036] FIGS. 8 and 9 show further arrangements of flow resistance
relaxing portions or communication voids as viewed in the cross
section of the honeycomb structure.
PREFERRED EMBODIMENTS
[0037] Throughout all the Aspects, the shape which permits
production of the filter by extrusion molding may be exemplified by
a shape such that a number of thick wall portions or voids are
formed uninterruptedly from one to the other end face of the
honeycomb structure in the same direction as the direction of
extrusion of the open cells of the honeycomb structure.
[0038] As regards the Second Aspect, the discharging conduit
openings could be formed axially of the honeycomb structure within
the thick wall portions, which allows advantageous extrusion
molding. However, this arrangement would require additional
measures at both the ends for separating the filtrate from the
in-and out flow fluids. Throughout the First to Fourth Aspects, the
filtrate can be discharged laterally out of the outer peripheral
wall, and the separating conduits for the filtrate at both the
honeycomb ends is either dispensed of or significantly
simplified.
[0039] With the monolithic ceramic filter according to the First
Aspect of the present invention, a part of the partition wall of
the honeycomb structure is thickened and designed as a flow
resistance relaxing portion. For instance, the thickened walls can
be arranged at an interval of certain number of cells. A simplest
example is a parallel arrangement as shown in FIG. 1. In FIG. 1
additional thick walls may be disposed across (e.g., vertically)
the holizontal thick walls.
[0040] The flow resistance relaxing portion comprises a portion of
partition wall of the honeycomb structure, which portion has a
thickness larger than that of the remaining portion of the
partition wall and has its end face exposed in the outer (lateral)
wall surface of the honeycomb structure. Preferably, the partition
wall of the flow resistance relaxing portion has a thickness two to
five times that of the remaining portion of the partition wall.
[0041] It is noted that, if the thickness is less than the doubled,
the effects of the flow resistance relaxing portion would be
lowered, whereas, if the thickness is more than five times, the
filtration area is decreased to lower the entire filtration
capacity of the filter.
[0042] It is preferred that the honeycomb structure comprises a
supporting member or substrate of the honeycomb structure, formed
of porous ceramics having a mean pore diameter preferably in a
range of from 1 .mu.m to 100 .mu.m, more preferably in a range of 5
.mu.m to 20 .mu.m, and a filtration membrane (1) (, preferably of
porous ceramics) with a mean pore diameter in a range of from 5 nm
to 5 .mu.m, formed on the above-mentioned supporting member. The
filtration membrane may be of any suitable material other than
ceramics as a filtration membrane.
[0043] The honeycomb structure may also comprise an intermediate
layer formed between the supporting member of the honeycomb
structure and the filtration membrane. This optional intermediate
layer has a mean pore diameter intermediate between the mean pore
diameter of the supporting member and that of the filtration
membrane. However, the supporting member for the honeycomb
structure devoid of the filtration membrane also suffices,
depending on the desired filtration accuracy.
[0044] The following is a typical method or producing the
supporting member for the honeycomb structure.
[0045] The ceramic starting material having a suitable particle
diameter is mixed with an organic binder and water, and the
resulting mixture is kneaded and extruded to a body having plastic
moldability. Sintering aid such as clay, glass etc. may also be
added as inorganic binders, if need be. The body is further
extrusion molded by an extrusion molding machine having a
predetermined die lip. The molded product is dried and sintered to
complete a supporting member, that is, a honeycomb skelton (First
and Third Aspect).
[0046] According to the Second Aspect filtrate discharging conduit
openings (14) which open in the outer peripheral surface,
preferably after drying, are formed at a predetermined pitch. The
conduit openings (14) are disposed, preferably at right angles to
the honeycomb axis for a better distribution and ease in
manufacture.
[0047] According to the Third Aspect, a green molded product is
extrusion molded by an extrusion molding machine having a
corresponding die lip. Otherwise as in the First Aspect, to produce
a supporting member of a honeycomb structure having groove-shaped
peripheral recesses (15) on the outer periphery (FIGS. 5 and
7).
[0048] The porous ceramics may be of any material such as alumina,
silica, zirconia, mullite, spinel, cordierite, carbon, silicon
carbide, silicon nitride or the like.
[0049] On the surface of a raw fluid supply passage (11) of a
supporting member having a honeycomb structure shown in FIGS. 1, 3
or FIGS. 5, 7, a filtration membrane formed of porous ceramics
having a mean pore size of 5 nm to 5 .mu.m is formed to produce a
ceramic filter. The following is a typical method for producing
such filtration membrane.
[0050] To a ceramic starting material in the form of powders or
colloidal solution, having a suitable particle size, a solvent such
as water, an organic binder, deflocculating agent, a pH adjustment
agent, etc. are added and mixed together to produce a slip. This
slip is coated on the surfaces of raw fluid supply passages (11) of
a supporting member having a honeycomb structure. The resulting
product is dried and sintered to produce a filtration membrane. The
materials of the filtration membrane embrace alumina, zirconia,
titania etc.
[0051] According to the Fourth Aspect, the ceramic filter, produced
in this matter, is fitted on its both ends with end frames (16). As
shown in FIG. 6, each end frame (16) preferably comprises a rim
portion (16a) and a plurality of protrusions 16b arranged for
stopping up the groove-shaped recesses of the ceramic filter at the
honeycomb ends. The end frame (16) is formed of stainless steel,
ceramics, resins or the like and sealed or fused by an organic or
inorganic adhesive or glasses. By mounting the end frame (16) in
this manner, it becomes possible to prevent a raw fluid from being
mixed into a filtrate, as well as to facilitate setting of the
ceramic filter on a housing, not shown. The frames can also serve
to strengthen the ceramic honeycomb structure.
[0052] The ceramic filter may also be used under such a condition
in which both ends of the groove-shaped recesses are sealed with an
organic material, such as epoxy resin, or with an inorganic
material, such as cement or glass sealing paste, thus without using
the end frames. In addition, the ceramic filter may be used under
such a condition in which end frame devoid of protrusions are
affixed to the filter having both ends of the grooved recesses
thereof sealed as described above.
[0053] Although the cross-sectional profile of each supply fluid
passage (cell) is square in FIGS. 1 to 3, and FIGS. 5 to 7, it may
also be other shapes of polygon such as triangle, hexagon etc.
circle and others. Besides although the supply fluid passages
(cells) are arranged in a pattern of square meshes at the honeycomb
ends and assume an outer profile of circular or square shape, they
may also be arranged in any other patterns, such as patterns of
hexagons, concentric circles, etc. in which the thick wall portions
and grooved recesses may be arranged radially.
[0054] Further possible arrangements of the flow resistance
relaxing portions (12) or communication voids (15) are illustrated
in FIGS. 8 and 9, each for the square cells (11). FIG. 8 represents
a round profile of outer wall 13, while FIG. 9 a square profile
thereof. Although not illustrated, concentric arrangement of cells
(11) is possible in which the flow resistance relaxing portions
(12) or the communication voids (15) may be disposed radially. As
is apparent from these Figures, a combination of the flow
resistance relaxing portion(s) (12') and the communication void(s)
(15) is also possible. The former (12') is shown in FIG. 9 in an
intersecting fashion. Such combination would serve to strengthen
the honeycomb structure provided with the communication voids
(15).
EXAMPLES
Example 1 (First Aspect)
[0055] To 100 parts by weight of alumina, having a mean particle
size of 40 .mu.m, 8 parts by weight of glass powders having a mean
particle size of 5 .mu.m as an inorganic binder, and 7 parts by
weight of methyl cellulose as an organic binder, and a
predetermined amount of water, were added and kneaded to form a
plastic body for extrusion. Using an extrusion molding machine,
having a die lip which will produce a cross-sectional shape as
shown in FIG. 1, the body for extrusion was extrusion-molded and
dried to a sufficiently dried supporting member. The resulting
supporting member was sintered in a sintering furnace at
1250.degree. C. to produce a supporting member having a honeycomb
structure shown in FIG. 1. The supporting member had a diameter and
a length of 150 mm and 1000 mm, respectively, a mean pore size of
10 .mu.m, a thickness of partition wall of 2 mm, a thickness of a
portion of the partition wall connecting to an outer wall thickened
so as to be used as a filtrate passage (flow resistance relaxing
portion) (12) of 8 mm, and a size of the supply liquid passage of
the size of a side equal to 4 mm of a square.
[0056] 100 parts by weight of fine alumina powders having a mean
particle size of 0.6 .mu.m, 75 parts by weight of water and 40
parts by weight of an organic binder (a water-soluble acrylic resin
having a solid content of 30%) were charged into a container of a
synthetic material and stirred and mixed with alumina pebbles for
24 hours in a ball mill to produce a slip for forming a filtration
membrane. This slip for forming the filtration membrane was
adsorbed to the surface of supply liquid passages of the supporting
member of the honeycomb structure to form a (green) filtration
membrane. The supporting member with the (green) filtration
membrane thereon was then dried and sintered at 1250.degree. C. The
filtration membrane thus produced had a mean pore size of 0.2
.mu.m.
[0057] The ceramic filter thus produced had a pure water
transmission flow velocity at a differential pressure of 1
kg/cm.sup.2 equal to 2.5 m.sup.3/m.sup.2 hr.
Example 2 (Second Aspect)
[0058] As shown in FIGS. 2 and 3, a ceramic filter was produced in
the same way as in Example 1, except that a plurality of conduit
openings (through-holes) (14) for discharging the filtrate were
formed transverse to the honeycomb structure in the flow resistance
relaxing portions (12) of the supporting member of the honeycomb
structure to reach the outer wall surface of the supporting member
throughout the flow resistance relaxing portion. The conduit
openings (14) for discharging the filtrate were 4 mm in diameter,
while the distance between neighboring through-holes in the flow
resistance relaxing portion was 10 cm in a parallel
arrangement.
[0059] The ceramic filter thus produced had a pure water
transmission flow velocity at a differential pressure of 1
kg/cm.sup.2-equal to 2.7 m.sup.3/m.sup.2 hr.
[0060] Note, however, the conduit openings for discharging need not
be a through-hole, but can open only with one ends thereof, while
in this case alternate arrangement of openings to right and left
(or up and down) surfaces of the outer wall is preferred.
Comparative Example 1
[0061] As shown in FIG. 4, a ceramic filter was produced in the
same way as in Example 1, except that the portion of the partition
wall connecting to the outer wall which was thickened so as to be
used as a filtrate passage (flow resistance relaxing portion) (12)
was not formed in the supporting member having the honeycomb
structure. The ceramic filter thus produced had a pure water
transmission flow velocity at a differential pressure of 1
kg/cm.sup.2 equal to 1.9 m.sup.3/m.sup.2 hr.
Examples 3 (Third and Fourth Aspects)
[0062] Using a die lip having a corresponding cross-section, a
supporting member of a honeycomb structure as shown in FIG. 5
having a cross section with the groove-shaped peripheral recess 15
formed in the outer peripheral wall was produced otherwise in the
same manner as in Example 1.
[0063] The supporting member had a mean pore size of 10 .mu.m, a
diameter and a length of 150 mm and 1000 mm, respectively, a
thickness of a partition wall of 2 mm, a width of the groove-shaped
peripheral straight recess of 4 mm and a size of each side of a
square of a liquid supply passage (cell) of 4 mm.
[0064] Subsequently, a slip was prepared as in Example 1. This slip
for forming the filtration membrane was adsorbed to the surface of
supply liquid passages of the supporting member of the honeycomb
structure to form a (green) filtration membrane. The supporting
member with the (green) filtration membrane thereon was then dried
and sintered at 1250.degree. C. The filtration membrane thus
produced had a mean pore size of 0.2 .mu.m.
[0065] The ceramic filter, produced in this manner, was fitted with
end frames as shown in FIG. 6, and the pure water filtration flow
rate at a differential pressure of 1 kg/cm.sup.2 was measured and
found to be 2.9m.sup.3/m.sup.2h.
Comparative Example 2
[0066] As shown in FIG. 4, a ceramic filter was produced in the
same way as in Example 3 except not forming peripheral
groove-shaped recesses in the supporting member of the honeycomb
structure and not fitting the end frames on the ends of the
supporting member. Namely, the same filter as Comparative Example 3
and the result is the same.
Meritorious Effect of the Invention
[0067] The monolithic ceramic filter according to the present
invention, generally, is of the honeycomb structure capable of
being produced by extrusion molding and hence is compact and easy
in the industrial mass production, and may be increased in its
filtration area. In addition, according to the First Aspect, by
designing a part of the partition wall of the honeycomb structure
as the flow resistance relaxing portion comprising a part of the
partition wall of the honeycomb structure which is exposed with its
end face on the outer wall surface of the honeycomb structure and
which is larger in thickness than the remaining portion of the
partition wall, the flow resistance presented to the filtrate
within the partition wall is decreased, as shown by pure water
transmission flow velocity data given in the above Examples, with
the result that the filtration may be carried out efficiently.
Besides, with the monolithic ceramic filter according to the First
Aspect of the present invention, the complicated production process
of stopping up both ends of the filtrate discharging passages
(cells) or the supply liquid passages may be eliminated to enable
less costly manufacture.
[0068] According to the Second Aspect, thick wall portion which
constitutes the flow resistance relaxing portion has conduit
openings for discharging the filtrate, and thus a still improved
filtration rate is achieved, additional to the First Aspect.
[0069] The monolithic ceramic filter according to the Third Aspect
of the present invention is compact in size and simple in the
structure, and have an increased filtration area. In addition,
since the filter includes communication voids separated from the
cells of the honeycomb structure via cell partition walls and
communicating with the outside of the honeycomb structure, the flow
resistance presented to the filtrate within the partition walls
(cell walls) is diminished, as shown by pure water filtration flow
rate data of the illustrative Example, thus enabling the filtration
to be performed efficiently. Besides, the monolithic ceramic filter
of such a shape as to permit production thereof by extrusion
molding, according to the Third Aspect, can be produced at low
costs because there is no necessity of boring openings for
discharging the filtrate in the honeycomb structure.
[0070] According to the Fourth Aspect, the unit according to the
Third Aspect can be assembled into a filter casing without
difficulty and with an improved strength.
[0071] It should be noted that modifications apparent in the art
can be made within the gist and concept of the invention as
disclosed herein, without departing from the scope as claimed by
the appended claims.
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