JP2001300273A - Ceramic filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic filter having a high strength and comprising respective constituent members in which cracks are hardly formed. SOLUTION: The ceramic filter comprises a substrate 2 of a porous body having single or a large number of through holes in parallel, a filtration membrane 3 formed on the surface of the substrate 2 and having the average fine pore diameter smaller than that of the substrate 2, and a seal member 5 for covering at least the end part of the substrate 2 and the filtration membrane 3 in the periphery of the end part of the substrate 2. The seal member 5 is made of a material having a thermal expansion coefficient smaller by a degree within a prescribed range than that of the substrate or that of the filtration membrane 3 and different from those of substrate and the filtration membrane 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic filter in which a filtration membrane having a smaller average pore diameter than a substrate is formed on the surface of a substrate made of a porous ceramic body, and more particularly, to a filter having high strength and high filter strength. The present invention relates to a ceramic filter in which cracks are unlikely to occur in the constituent members of (1).

[0002]

2. Description of the Related Art A ceramic filter is a filter using a ceramic porous body, and has physical strength, durability,
Because of its excellent corrosion resistance and the like, it is used for removing suspended substances, bacteria, dust, and the like in liquids and gases in a wide range of fields such as water treatment and exhaust gas treatment, or pharmaceutical and food fields.

In a ceramic filter, a porous ceramic body may be used as it is as a filter medium.
In order to improve both filtration performance and fluid permeation amount (that is, processing capacity), a ceramic porous body is used as a substrate (support).
It is common to form a filtration membrane made of ceramic on the surface. For example, the average pore size of the filtration membrane is 0.01
While the filter is configured to be as small as about 1.0 μm to ensure filtration performance, the average pore diameter of the base is configured to be large to about 1 to several hundreds μm to reduce the flow resistance inside the base and increase the fluid permeation (that is, (Processing capacity) is being improved.

[0004] Furthermore, as the ceramic filter, one obtained by processing a base material into various shapes according to the purpose of filtration is used, and the base material is formed in a tubular shape having a single through-hole or a plurality of parallel through-holes. Honeycomb-shaped (including monolith-shaped) has been widely used. A filter in which a filter membrane is formed on the surface of a tube-shaped or honeycomb-shaped substrate, for example, an inner peripheral surface of a through-hole, is housed in a housing, and the outer peripheral surface side of the substrate and the end surface of the substrate where the through-hole is opened. With a structure that is air-tightly isolated by an O-ring or the like, it is used as a cross-flow type filter.

According to the cross-flow type filter, the fluid to be treated, such as a gas or a liquid, is supplied into the through-hole from one end face side of the base material, so that the fluid permeates through the filtration membrane on the inner peripheral surface of the through-hole. While the filtered fluid is collected from the outer peripheral surface side of the substrate, the unfiltered fluid to be processed can be collected from the other end surface side of the substrate.

However, as shown in FIG. 1B, simply by isolating the vicinity of the end face of the base material 12 with the O-ring 14, the fluid to be treated is formed from the end face of the base material 12 where the filtration membrane 13 is not formed. Because it invades the inside of the material 12
The intended filtration cannot be performed, and the already filtered filtration fluid is contaminated.

Therefore, as shown in FIG. 1A, at least the base material 2 is formed by a sealing material 5 made of ceramic or the like.
There has been proposed a membrane separation device in which a filtration membrane 3 is coated at the end and near the end of the substrate 2 (Japanese Patent Application Laid-Open No. 61-8106).
Such a structure can prevent the fluid to be treated from intruding from the end face of the base material 2, and since the fluid to be treated always passes through the filtration membrane 3, the intended filtration can be performed, and the already filtered fluid can be obtained. This is useful in that contamination of the filtered fluid can also be prevented.

[0008]

By the way, in a ceramic filter composed of a plurality of members such as a base material, a filtration membrane, and a sealing material, as in the above-described membrane separation device, each component is made to be a physical filter adapted to its function. In many cases, it is required to use different materials in order to obtain materials having proper and chemical characteristics or in view of cost. However, in such a case, if the thermal expansion coefficients of the respective components are extremely different from each other, a tensile stress and a compressive stress are generated mutually, so that cracks are generated in the respective components or the mechanical strength of the filter is developed. There was a problem that it was not possible.

The base material mainly has a particle size of 5 to 200.
It is composed of an aggregate of about μm and a sintering aid having a particle size of less than 5 μm, which is an additive for strengthening the bond between the aggregates, but the aggregate and the sintering aid are different materials. Often.
Therefore, when the coefficients of thermal expansion are extremely different between the constituent materials of the base material as in the case of the constituent members of the filter, tensile stress and compressive stress are generated mutually, and the strength of the filter is reduced. was there.

In order to solve these problems, a method may be conceived in which each constituent member of the filter or the constituent material of the substrate is made of a material having a thermal expansion coefficient as close as possible. However, as a result of the study by the present inventors, it has been found that these situations cannot be prevented by merely making the thermal expansion coefficients between the constituent members or between the constituent materials of the base material close to each other.

The present invention has been made in view of such problems of the related art, and an object of the present invention is to make each constituent member of a filter or a constituent material of a base material different from each other. High strength, and
An object of the present invention is to provide a ceramic filter in which cracks do not easily occur in each component of the filter.

[0012]

Means for Solving the Problems As a result of intensive studies on the problems of the above-mentioned prior arts by the present inventors, a predetermined thermal expansion coefficient difference is provided between the constituent members of the filter or between the constituent materials of the base material. The present inventors have found that the above problems can be solved by generating an internal stress during the present invention, and completed the present invention.

[0013] That is, according to the present invention, a base material made of a porous body having a single or a plurality of parallel through holes, and an average pore diameter formed on the surface of the base material as compared with the base material Is a ceramic filter comprising: a filtration membrane having a small diameter, and a sealing material covering at least the base membrane end portion and the filtration membrane in the vicinity of the base membrane end portion, wherein the sealing material is 0 to 4 × 10 ^{− 6}
A ceramic filter characterized by being formed of a material different from the base material and having a small coefficient of thermal expansion in the range of / ° C. (hereinafter referred to as “first invention”).

[0014] In the first invention, the sealing material is filtered.
0-3 × 10 for over membrane ^-6Thermal expansion coefficient within the range of
It is preferable to use a small material composed of a material different from that of the filtration membrane.
More preferably, the sintering aid contained in the base material is replaced with the bone constituting the base material.
0-3 × 10 for wood^-6Low coefficient of thermal expansion within the range of / ° C
Furthermore, it is more preferable to use a material that is different from the aggregate.
Good.

Further, according to the present invention, a base material formed of a porous body having a single or a plurality of parallel through holes, and an average pore diameter formed on the surface of the base material as compared with the base material Is small, and a sealing material that covers at least the substrate membrane and the filtration membrane in the vicinity of the substrate membrane, wherein the sealing material is 0 to 3 × 10
There is provided a ceramic filter having a small coefficient of thermal expansion in the range of ^-6 / ° C. and made of a material different from that of the filtration membrane (hereinafter referred to as “second invention”).

In the second invention, the sintering aid contained in the base material is added to the aggregate constituting the base material by 0 to 3 × 10 ^−6.
It is preferable to use a material having a small coefficient of thermal expansion in the range of / ° C and different from the aggregate.

Further, according to the present invention, a base material composed of a porous body having a single or a plurality of parallel through holes, and an average pore diameter formed on the surface of the base material as compared with the base material A small filtration membrane, and a sealing material that covers the filtration membrane at least in the vicinity of the base end and the base end, and a sintering aid contained in the base, There is provided a ceramic filter characterized by having a small coefficient of thermal expansion within a range of 0 to 3 × 10 ⁻⁶ / ° C. with respect to the constituent aggregate and made of a material different from the aggregate (hereinafter referred to as “third filter”). Invention ").)

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Structure of Filter The ceramic filter of the present invention comprises at least a base material, a filtration membrane, and a sealing material as constituent members.

Substrate The “substrate” in the present invention is a member having a function as a support for a filtration membrane, and is a porous ceramic body mainly composed of an aggregate and a sintering aid. . As the shape of the substrate, either a tube shape having a single through hole or a honeycomb shape (including a monolith shape) having a large number of parallel through holes is used.

The aggregate is a main component of the base material and is composed of ceramic particles having an average particle size of about 5 to 200 μm. By forming and sintering the clay containing the aggregate, a porous body having pores according to the particle size of the aggregate, that is, a base material is formed. The material of the aggregate may be appropriately selected so as to be suitable for the purpose of filtration, and for example, alumina, mullite, cordierite, silicon carbide, ceramic waste and the like can be used.

The sintering aid is an additive for strengthening the bond between aggregates, and is made of ceramic particles having an average particle size of less than 5 μm. By incorporating the kneaded material together with the aggregate, the bond between the aggregates is strengthened, and a strong porous body is formed. The material of the sintering aid is not particularly limited, but for example, alumina, silica, zirconia, titania, glass frit, feldspar, cordierite, and the like can be used. Normally, the joint strength between aggregates is secured,
In order to prevent the pores of the porous body from being blocked, about 10 to 35% by mass is contained with respect to the total mass of the aggregate and the sintering aid.

Filtration membrane The "filtration membrane" in the present invention is a thin film-shaped ceramic porous body having an average pore diameter smaller than that of a substrate, and is formed by forming at least one layer, and in some cases two or more layers. Make multiple layers.
Usually, the “filtration membrane” refers to a member for securing the filtration function of the filter, but the “filtration membrane” in the present invention includes an intermediate layer (a plurality of layers) Of these, layers other than the uppermost layer) are also included.

The filtration membrane is formed by forming a slurry containing ceramic particles of about 0.1 to 5 μm having an average particle size smaller than that of the aggregate constituting the base material on the surface of the base material and then sintering the slurry. Is formed. The “surface of the substrate” forming the filtration membrane includes, in some cases, the outer peripheral surface of the substrate in addition to the inner peripheral surface of the through-hole of the substrate. The material of the ceramic particles may be the same as the aggregate constituting the base material.

Sealing material The term "sealing material" as used in the present invention is a member for preventing the fluid to be treated from entering the inside of the base material from the end face of the base material. It is necessary to cover the filtration membrane in the vicinity of the part and the end of the substrate.

As the sealing material, for example, borosilicate glass,
It can be formed by applying a glaze made of a glassy substance (glass frit or the like) such as feldspar glass so as to cover the base end and the filtration membrane near the base end, and then sintering. . However, the filter is not particularly limited to glaze as long as it has a pore diameter equal to or smaller than that of the filtration membrane, and in some cases, the filtration membrane can be used as a sealing material.

(2) Embodiment of the present invention The present invention relates to a ceramic filter as described above.
A predetermined thermal expansion coefficient difference is given between the constituent members of the filter or between the constituent materials of the base material, and intrinsic stress is generated between them. The ceramic filter of the present invention has high strength and does not easily cause cracks in each component of the filter, even when the components of the filter or the components of the substrate are made of different materials. Hereinafter, the ceramic filter of the present invention will be described in detail.

First Invention In the first invention, a sealing material is applied to a substrate at 0 to 4 × 10 ^-6.
It is made of a material having a small coefficient of thermal expansion in the range of / ° C and different from the base material. By giving a thermal expansion coefficient difference within the above range between the sealing material and the base material, a compressive stress is generated on the sealing material side and a tensile stress is generated on the base material side, so that the occurrence of cracks in each component of the filter is prevented. You.

When the coefficient of thermal expansion of the sealing material is smaller than the above range with respect to the coefficient of thermal expansion of the base material, an excessive compressive stress is applied to the sealing material, so that a zigzag shape as shown in FIG. On the other hand, when the crack is generated and the crack is larger than the above range, a tensile stress is applied to the sealing material, so that a linear crack as shown in FIG. 4 is generated. It should be noted that even when the thermal expansion coefficient of the sealing material is extremely close to the thermal expansion coefficient of the base material, if the thermal expansion coefficient is slightly higher than the thermal expansion coefficient of the base material, cracks in the sealing material cannot be prevented. .

Second invention According to the second invention, the same idea as in the first invention is used, and the sealing material has a small coefficient of thermal expansion within a range of 0 to 3 × 10 ⁻⁶ / ° C. with respect to the filtration membrane. It is made of a material different from the filtration membrane.

If the coefficient of thermal expansion of the sealing material is smaller than the above range with respect to the coefficient of thermal expansion of the filtration membrane, excessive compressive stress is applied to the sealing material. Since stress is applied, cracks occur in the sealing material. Further, even when the thermal expansion coefficient of the sealing material is extremely close to the thermal expansion coefficient of the filtration membrane, if the thermal expansion coefficient is slightly higher than the thermal expansion coefficient of the filtration membrane, cracks in the sealing material cannot be prevented. The same is true.

Third Invention The third invention is directed to a method wherein the sintering aid contained in the base material has a thermal expansion coefficient of 0 to 3 × 10 ^-6 / ° C. with respect to the aggregate constituting the base material. It is made of a small, different material from the aggregate. The first and second inventions focus on the difference in thermal expansion coefficient between the constituent members of the filter, while the third invention focuses on the difference in thermal expansion coefficient between the constituent materials of the base material. is there.

Specifically, when the coefficient of thermal expansion of the sintering aid is smaller than the above range with respect to the coefficient of thermal expansion of the aggregate, compressive stress is applied to the sintering aid. Since a tensile stress is applied to the sintering aid, the strength of the base material decreases in any case.

Calculation of Thermal Expansion Coefficient Difference The thermal expansion coefficient difference in the first and second inventions is calculated based on the linear thermal expansion amount ΔL ₁ of each evaluation sample of the substrate, the filtration membrane, and the sealing material.
ΔL ₃ is measured, and is calculated from the linear thermal expansion coefficients K _{1 to} K _{3 of} the respective components defined by the following equations (1) to (3). K ₁ = (ΔL ₁ / ΔT ₁ ) / L (1) K ₂ = (ΔL ₂ / ΔT ₁ ) / L (2) K ₃ = (ΔL ₃ / ΔT ₁ ) / L (3) (however, , K ₁ : coefficient of thermal expansion of the sealing material (× 10 ⁻⁶ /
° C), K ₂ : coefficient of thermal expansion of substrate (× 10 ^-6 / ° C), K ₃ :
Thermal expansion coefficient of filter membrane (× 10 ⁻⁶ / ° C.), ΔL ₁ : linear thermal expansion of sealing material sample between Ts ₁ and Tt ₁ (unit:
mm), ΔL ₂ : linear thermal expansion of the substrate sample between Ts ₁ and Tt ₁ (unit: mm), ΔL ₃ : linear thermal expansion of the filtration membrane sample between Ts ₁ and Tt ₁ (unit: mm), L:
Length of each evaluation sample at room temperature (unit: mm))

Specifically, as an evaluation sample, a single sintered body of a base material, a filtration membrane, and a sealing material was cut into a cross section of 3 mm × 4 m
m and a length L of 20 mm (measured at room temperature) were processed into a rectangular column, and the linear heat of each evaluation sample at a temperature difference ΔT ₁ between the reference temperature Ts ₁ and the transition temperature Tt ₁ of the sealing material. The expansion amounts ΔL _{1 to} ΔL ₃ are detected by a differential transformer using a high-precision two-sample thermal analyzer-TMA standard type (trade name: manufactured by Rigaku Denki Co., Ltd.) using a differential transformer. Measurement.

The “reference temperature Ts ₁ ” is generally set to a temperature at which a change in the coefficient of linear thermal expansion of the evaluation sample is small. Therefore, in consideration of the fact that the evaluation sample of the present invention is a ceramic, 40 ° C. is specified in any of the above formulas (1) to (3).

The “transition temperature Tt _{1 of the} sealing material”
Is defined as a temperature at which the linear thermal expansion rapidly rises when the sealing material sample changes from a glassy state to a supercooled liquid in the above-described linear thermal expansion measurement. 2 (b) is an example of a case where there is a crystal transition as cristobalite, although linear thermal expansion amount at a temperature range lower than the transition temperature Tt ₁ indicates a bending convex, as in this case provision can do. The “softening point of the sealing material” described later refers to a temperature at which the amount of linear thermal expansion of the sealing material sample shows a maximum value and starts to shrink as shown in FIG.

The thermal expansion coefficient difference in the third invention is also the first.
In the same manner as in the second invention, the linear thermal expansion amounts ΔL _{4 to} ΔL ₅ of the evaluation sample composed of a single sintered body of the sintering aid and the aggregate were measured, and were determined by the following equations (4) and (5). It is calculated from the specified linear thermal expansion coefficients K ₄ and K _{5 of the} constituent materials. K ₄ = (ΔL ₄ / ΔT ₂ ) / L (4) K ₅ = (ΔL ₅ / ΔT ₂ ) / L (5) (where K ₄ is the linear thermal expansion coefficient of the sintering aid (× 10) ^-6 /
° C), K ₅ : coefficient of linear thermal expansion of the aggregate (× 10 ^-6 / ° C), Δ
L ₄ : linear thermal expansion of sintering aid sample between Ts ₂ and Tt ₂ (unit: mm), ΔL ₅ : linear thermal expansion of aggregate sample between Ts ₂ and Tt ₂ (unit: mm) ), L: length of each evaluation sample at room temperature (unit: mm))

The “reference temperature Ts ₂ ” is set to 40 ° C. in each of the above equations (4) and (5). The “transition temperature Tt ₂ of the sintering aid” is the temperature at which the linear thermal expansion rapidly rises due to the transition of the sintering aid sample from the glassy state to the supercooled liquid in the above thermal expansion measurement. Stipulate. However, when the above transition temperature does not exist in the temperature range below the firing temperature of the substrate, Tt ₂ is 65.
The linear thermal expansion coefficient is calculated assuming that the temperature is 0 ° C.

Manufacturing Method The filter of the present invention can be used as a component (sealant, base material, filtration membrane) or base material of a filter having a predetermined difference in thermal expansion coefficient based on the thermal expansion coefficient measured in advance by the above method. Except for selecting the material of the constituent materials of the material (sintering aid, aggregate), it is possible to manufacture according to a conventionally known method of manufacturing a ceramic filter.

For example, first, in addition to the aggregate and the sintering aid, a dispersion medium, an organic binder, a surfactant, a plasticizer, and the like are added as necessary, and the kneaded clay is extruded and formed. The substrate is dried and fired to produce a substrate, and then the ceramic particles are dispersed in a dispersion medium such as water, and a film is formed by adding an organic binder, a pH adjuster, a surfactant, and the like as necessary. The slurry is formed into a film on the inner peripheral surface of the through hole of the base material, dried and baked to form a filtration membrane, and further, a glaze made of a glassy material as a sealing material is applied to the end of the base material, and then dried. A filter can be obtained by a firing method.

[0041]

EXAMPLES Hereinafter, the filter of the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

The substrates used in Examples 1 to 3 were produced as follows. As an aggregate constituting the base material, an alumina abrasive (alumina purity: 95% by mass, referred to as “alumina” in the table) sieved so as to have an average particle size of 30 to 100 μm, or mullite porcelain ( Mullite purity: 95% by mass, and described as "mullite" in the table).

In the above aggregate, feldspar glass having an average particle size of 0.5 to 5 μm (denoted as “feldspar” in the table) and cordierite-containing glass (denoted as “cordierite” in the table) as a sintering aid. ) Or borate glass (referred to as "boric acid" in the table), water was added as a dispersion medium, and methylcellulose was added as an organic binder, and the kneaded clay was extruded to obtain an extruded body. . The extruded product was dried and fired to obtain a tube-shaped substrate having an outer diameter (Lo) of 30 mmφ, an inner diameter (Li) of 22 mmφ, and a length of 250 mm. The average pore diameter of the substrate measured by the mercury intrusion method was 5 to 20 μm.

In the first embodiment, in order to cover the end portion and the vicinity of the end portion of the base material described above, in the second embodiment,
Any one of feldspathic glass, cordierite-containing glass, or borate glass having an average particle size of 0.5 to 5 μm so as to cover the end portion of the base material and the filtration membrane near the base end portion is a sealing material. And then baked at a temperature 150 ° C. higher than the softening temperature of the sealing material. After the baking, the presence or absence of cracks was evaluated by immersing in a dye aqueous solution, washing with water, and visually observing the surface of the sealing material.

Example 1 In Example 1, various sealing materials and base materials were used, and the effect of giving various thermal expansion coefficient differences between the sealing material and the base material was evaluated. The results are shown in Table 1 and FIGS.

[0046]

[Table 1]

As is clear from Table 1, no crack was generated in any of the seal materials when a difference in thermal expansion coefficient was given between the seal material and the substrate within the range specified in the present invention ( Examples 1-1 to 1-5).

On the other hand, when the coefficient of thermal expansion of the sealing material is smaller than the coefficient of thermal expansion of the base material beyond the scope of the present invention,
As shown in FIG. 3, zigzag cracks are generated in the sealing material due to the compressive stress (Comparative Example 1-1). On the contrary, when the cracks are larger than the scope of the present invention, the cracks caused by the tensile stress in the sealing material. Occurred (Comparative Examples 1-2 to 1-5). The crack in this case was a linear crack as shown in FIG. 4 (Comparative Example 1-3). Further, when the thermal expansion coefficient of the sealing material was very close to the thermal expansion coefficient of the base material or was slightly smaller than the thermal expansion coefficient of the base material, cracking of the sealing material could not be prevented (Comparative Example 1). -2).

Example 2 In Example 2, various sealing materials and filtration membranes were used, and the effect of giving various thermal expansion coefficient differences between the sealing materials and the filtration membranes was evaluated.

In Example 2, alumina having an average particle size of 1 to 3 μm was used as ceramic particles constituting the filtration membrane.
Using either mullite or cordierite, a slurry prepared by adding water as a dispersion medium and carboxymethylcellulose as an organic binder to the ceramic particles is produced on the inner peripheral surface of the above-described base material by a conventionally known method. After the film is dried and fired, the average thickness is 150 μm.
m of filtration membrane was formed. The average pore size of the filtration membrane measured by the air flow method described in ASTM F316 is 0.8.
１1 μm.

In Example 2, the presence or absence of cracks was evaluated by visually observing the surface of the sealing material on both the upper surface of the filtration membrane and the upper surface of the substrate. Table 2 shows the results.

[0052]

[Table 2]

As is apparent from Table 2, when a difference in thermal expansion coefficient between the sealing material and the filtration membrane, or between the sealing material and the substrate within the range specified in the present invention, is given, the upper surface of the filtration membrane and the upper surface of the substrate In both cases, no cracks occurred in the sealing material (Example 2-
1-2-5).

On the other hand, when the coefficient of thermal expansion of the sealing material is smaller than the coefficient of thermal expansion of the filtration membrane beyond the range of the present invention, zigzag cracks are generated in the sealing material due to compressive stress (Comparative Example 2). 1) Conversely, when the sealing material was larger than the range of the present invention, linear cracks occurred in the sealing material due to tensile stress (Comparative Examples 2-2 to 2-5). Also,
When the coefficient of thermal expansion of the sealing material was very close to the coefficient of thermal expansion of the filtration membrane or was slightly smaller than the coefficient of thermal expansion of the filtration membrane, cracking of the sealing material could not be prevented (Comparative Example 2-2). ).

Example 3 In Example 3, various aggregates and sintering aids were used, and the effect of giving various thermal expansion coefficient differences between the aggregate and the sintering aid was evaluated.

In the third embodiment, first, a water-impermeable rubber tube having one end sealed and the other end connected to a hydraulic pump is inserted into the through-hole of the base material manufactured by the above-described method. . Then, the rubber tube is expanded in the through hole by gradually applying a water pressure by a water pressure pump, and a pressure gauge indication value P when the base material is broken is measured. When the base material is broken, the rubber tube is broken, and the pressure gauge indication value returns to 0 instantaneously.
The internal pressure breaking strength D was calculated from the following equation (6), and the strength of the substrate (that is, the filter) was evaluated. In the base material of this embodiment, the outer diameter Lo is 30 mm and the inner diameter Li is 22 mm, so that the internal pressure breaking strength D is a value obtained by multiplying the pressure gauge indication value P by about 3.3. D = P × (Lo ² + Li ² ) / (Lo ² −Li ² ) (6) (however, D: internal pressure breaking strength (MPa), P: pressure gauge indicated value (MPa), Lo: base material outer diameter (Mm), Li: substrate inner diameter (mm))

In this example, the filter was evaluated as having high strength when the indicated pressure gauge value P when the substrate was broken was 2 MPa or more. Generally, a ceramic filter performs filtration at an internal pressure of about 0.2 MPa. In order to prevent breakage due to a sudden change in filtration pressure (for example, a water hammer phenomenon), a 10-fold safety factor is required. That is, it is preferable to have the pressure gauge indicating value P which is 10 times or more of the normal operation internal pressure of 0.2 MPa. Table 3 shows the results.

[0058]

[Table 3]

As is clear from Table 3, when a difference in thermal expansion coefficient was given between the aggregate and the sintering aid within the range specified in the present invention, the pressure gauge indicated value P was 2 MPa in each case. As described above, the filter had high strength (Examples 3-1 to 3-3).
-5).

On the other hand, when the thermal expansion coefficient of the sintering aid is smaller than the thermal expansion coefficient of the aggregate beyond the range of the present invention (Comparative Example 3-1), and conversely, when the thermal expansion coefficient is larger than the range of the present invention. In any of Comparative Examples 2-2 to 3-3, the pressure gauge indication value P was less than 2 MPa, and the filter strength was reduced.
Also, when the coefficient of thermal expansion of the sintering aid was very close to or slightly smaller than the coefficient of thermal expansion of the aggregate, the strength of the filter decreased (Comparative Example 3-2). Further, when the coefficient of thermal expansion of the sintering aid was equal to the coefficient of thermal expansion of the aggregate, the pressure gauge indicated value P was 2 MPa or more, but was the lowest in the examples (Example 3-5).

[0061]

The present invention provides a predetermined difference in the coefficient of thermal expansion between the constituent members of the filter (sealant, base material, filtration membrane) or the constituent materials of the base material (sintering aid, aggregate), Since the intrinsic stress is generated between them, the tensile stress and the compressive stress generated between the constituent members of the filter and between the constituent materials of the base material can be reduced. Therefore, according to the present invention, there is provided a ceramic filter which has high strength and is less likely to crack in each component of the filter even when the components of the filter or the components of the substrate are made of different materials. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a filter loaded in a housing, where (a) is a filter provided with a sealing material,
(B) shows a filter without a sealing material.

FIGS. 2A and 2B are graphs showing a thermal expansion curve of a sealing material, wherein FIG. 2A shows a normal case, and FIG.

FIG. 3 is a photograph showing a surface texture of a ceramic material (sealant) in which a crack is generated by a compressive stress.

FIG. 4 is a photograph showing a surface texture of a ceramic material (seal material) in which a crack is generated by a tensile stress.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Housing, 2 ... Base material, 3 ... Filtration membrane, 4 ... O-ring, 5 ... Sealing material, 11 ... Housing, 12 ... Base material, 1
3 ... filtration membrane, 14 ... O-ring.

Claims (5)

[Claims] 1. A base material comprising a porous body having a single or a plurality of parallel through holes, a filtration membrane formed on the surface of the base material and having a smaller average pore diameter than the base material, A ceramic filter comprising at least a base material end and a sealing material covering a filtration membrane near the base material end, wherein the sealing material is in a range of 0 to 4 × 10 ⁻⁶ / ° C. with respect to the base material. A ceramic filter characterized by having a small coefficient of thermal expansion and made of a material different from a base material. 2. A base material comprising a porous body having a single or a plurality of parallel through holes, and a filtration membrane formed on the surface of the base material and having a smaller average pore diameter than the base material, A ceramic filter having at least a base material end and a sealing material covering a filtration membrane near the base material end, wherein the sealing material is in a range of 0 to 3 × 10 ⁻⁶ / ° C. with respect to the filtration membrane. A ceramic filter characterized by having a small thermal expansion coefficient and made of a material different from that of a filtration membrane. 3. A base material comprising a porous body having a single or a plurality of parallel through holes, and a filtration membrane formed on the surface of the base material and having a smaller average pore diameter than the base material, A sealing material covering at least a base end and a filtration membrane in the vicinity of the base end, and a sintering aid contained in the base material with respect to the aggregate constituting the base material. A ceramic filter characterized by having a small coefficient of thermal expansion within a range of 0 to 3 × 10 ⁻⁶ / ° C. and made of a material different from an aggregate. 4. A sealing material is provided in an amount of 0 to 3 × 10
^2. The ceramic filter according to claim 1, wherein the ceramic filter is made of a material having a small coefficient of thermal expansion within a range of ^-6 / .degree. 5. A material different from the aggregate, which has a small thermal expansion coefficient within a range of 0 to 3 × 10 ⁻⁶ / ° C. with respect to the aggregate constituting the substrate, using a sintering aid contained in the substrate. The ceramic filter according to claim 1, wherein the ceramic filter comprises: