JPH04160078A - Production of ceramic porous body - Google Patents

Abstract

PURPOSE:To obtain a high strength ceramic porous body having two or more kinds of different open pores at high porosity by filling a slurry prepd. by blending ceramic powder with a curable resin and an emulsion contg. a liq. org. substance as a pore forming material into the voids in a molded body of resin granules and carrying out firing. CONSTITUTION:A slurry prepd. by blending ceramic powder of 1mum particle diameter such as alumina powder with 1-35wt.%, preferably 5-25wt.% curable resin such as epoxy resin basing on the amt. of the ceramic powder and an emulsion of <=10mum average particle diameter contg. 100-300vol.% liq. org. substance basing on the amt. of the ceramic powder is filled into the voids in a molded body of spherical resin granules which burn out in a firing process to form large pores, e.g. foamed polystyrene granules. The molded body is then dried by heating, dewaxed and fired to obtain a ceramic porous body useful as an exhaust gas filter, a catalyst carrier, a bioreactor, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a ceramic porous body having two or more types of communicating pores with different pore sizes, which is suitable for exhaust gas filters, catalyst carriers, bioreactors, and the like.

(Prior art) Ceramic porous bodies with different pore sizes have large pores that act as passages for mass transfer, and fine pores that provide an environment favorable for chemical or biological reactions. , useful in bioreactors, etc.

Conventionally, methods for manufacturing porous ceramic bodies with relatively large pores with low pressure loss include methods in which urethane foam is impregnated with ceramic slurry, dried and heat treated to burn out the urethane foam and sinter the ceramics, and ceramic powder. A method is known in which a mixture of a combustible substance and a combustible substance is formed and fired. Furthermore, in order to create fine pores with an extremely large specific surface area, a method is known in which a ceramic raw material having a particle size composition is formed and sintered.

However, by combining these methods, it is possible to produce a ceramic porous body having fine pores of 10 μm or less in the skeleton of a ceramic porous body with a relatively large pore size of 100 μm or more, but due to the manufacturing method, the pores in the skeleton are It is difficult to control because it is determined by the air gap between
The problem is that the strength of the resulting porous ceramic body is low.

Therefore, there is a strong desire for a ceramic porous body that has two or more controlled communicating pores with different diameters, high porosity, and high strength.

(Problem M to be solved by the invention) The present inventor has completed the present invention as a result of intensive research in view of the problems of the existing ceramic porous bodies mentioned above. The object of the present invention is to provide a method for producing a ceramic porous body having two or more different types of communicating pores, high porosity, and high strength.

(Means for solving the problem) The above-mentioned object is to fill the voids of a resin particle molded body formed by bonding spherical resin particles with a slurry of a ceramic raw material containing ceramic powder and a curable resin to form communicating holes. This is achieved by a method for manufacturing a porous ceramic body characterized in that an emulsion of a liquid organic substance is blended as a pore-forming material into the ceramic raw material.

The spherical resin particles applied to the present invention are burned out in the firing process and function to shape the large pores of the product of the present invention. Specifically, for example, polystyrene, polyethylene,
polypropylene, nylon, polyester, acrylic,
Examples include organic resin particles such as phenol, epoxy, ethylene-vinyl acetate copolymer, styrene-butadiene block polymer, urethane and wax, and their foams, but among these, these are inexpensive and easy to remove. Styrofoam is suitable.

These spherical resin particles must be in contact with each other in order to form continuous pores. The molded body in which the resin particles are bonded to each other can be produced by, for example, filling a container with resin particles and compressing the resin particles, filling the container with resin particles whose surface is coated with adhesive and molding the container, or filling the container with resin particles and molding the resin particles. It can be produced by selecting and applying an appropriate method from known methods, such as a method in which particles are filled, a resin solvent is injected for a short period of time, the resin particles are adhered to each other, and then the solvent is removed.

The slurry in the present invention contains ceramic powder, a curable resin that increases the strength of the green body through a curing action, a liquid organic substance in an emulsion state, and a dispersion medium.

Examples of the ceramic powder used in the present invention include oxides such as alumina, zirconia, zircon, cordierite, mullite, titania, silica, aluminum titanate, and magnesia, silicon nitride, aluminum nitride,
Examples include non-oxide powders such as silicon carbide and sialon.

Furthermore, for the purpose of producing silicon nitride, aluminum nitride, and silicon carbide by reaction sintering, metal silicon powder, metal aluminum powder, #2 raw powder, etc. may be used, and ceramic powder applicable to the present invention. is not limited to these, and the type and amount of ceramic powder can be selected as appropriate depending on the application, such as heat resistance, thermal shock resistance, corrosion resistance, acid resistance, oxidation resistance, etc. . The particle size of the ceramic powder is preferably 10 μm or less, more preferably 2 μm or less, and most preferably lam or less in terms of ease of sintering and slurry storage stability.

The curable resin used in the present invention is present in a slurry containing ceramic powder and an emulsion of a liquid organic substance, and is used to increase the strength of the green body through its curing action. As the curable resin, a crosslinking reaction type resin that forms a three-dimensional network bond is preferable, and examples thereof include soluble or dispersible resins such as epoxy, phenol, urea, and melamine. Among these, epoxy resins that cause a crosslinking reaction in an alkaline region where a deflocculant acts effectively are particularly preferred.

In the present invention, the amount of the curable resin added is preferably kept to the minimum necessary amount within the scope of achieving the purpose of the present invention. In other words, the curable resin is burned and removed during the manufacturing process of the ceramic sintered body, and the final product is does not remain, and excessive addition is economically disadvantageous. Furthermore, if the amount of curable resin added increases, cracks tend to occur frequently during the degreasing process, so from this point of view as well, it is better not to add too much.The content of curable resin is preferably 1 to 10% relative to the inorganic powder. The emulsion of the liquid organic substance in the present invention, which is 35% by weight, more preferably 5 to 25% by weight, acts as a pore-forming agent and plays an important role in forming a ceramic porous body having fine continuous pores. be.

Examples of liquid organic substances include liquid paraffin, liquid isopropylene, and other polymer compounds that are liquid at room temperature. Further examples include, but are not limited to, liquid materials in which high-molecular polymers such as styrene, methacrylate, and azirylate are dissolved in organic solvents, and materials that are liquid at room temperature to form communicating pores may be used. is preferred.

The continuous pores in the ceramic porous body are caused by the dispersion state of the emulsion being destroyed before or during the curing of the curable resin, and the dispersed particles of the liquid resin changing from a free state to a connected state, and the continuous organic phase is formed during the firing process. It is formed by being removed by incineration.

Emulsions can be produced by selecting an appropriate method from known methods.9 For example, a method in which a dispersion medium containing an emulsifier is stirred with a high-speed shear mixing device such as a homomixer and a liquid organic substance is sequentially added dropwise, an emulsifier and a liquid organic substance A common method is a forced emulsification method, typified by a method in which a dispersion medium is sequentially added dropwise to a mixture of the above while stirring the mixture using a high-speed shear mixing vMW. The emulsifier used may be an anionic, cationic, or nonionic emulsifier, but anionic and nonionic emulsifiers excluding alkali metal salts are preferred in order to improve the dispersion stability of the ceramic powder and avoid residual metal impurities. Although the content is an important factor determining the porosity of the final product,
If the content is too low, the resulting pores will not be continuous pores but closed pores. - On the other hand, if the content is too large, the strength of the resulting ceramic body will be reduced. The content of the liquid organic substance in the emulsion is preferably 20 to 400% by volume, more preferably 100 to 300% by volume based on the ceramic powder. The particle size of the emulsion is an important factor determining the pore size of the final product. Considering the storage stability of the emulsion, the average particle diameter is 50 μm or less, preferably 10 μm or less. The particle size of the emulsion can be appropriately controlled by the type and amount of the emulsifier used and the shear rate.

In the present invention, water is usually used as a dispersion medium for the slurry.

The slurry in the present invention is a mixed phase mainly composed of the ceramic powder, a hardening resin that increases the strength of the green body through hardening action, and a liquid organic substance in an emulsion state. A deflocculant for effectively and stably dispersing powder in a dispersion medium.
In order to make the workability of the slurry suitable, viscosity adjusting agents, drying speed adjusting agents, etc. may be included as appropriate.

The slurry can be prepared according to a conventional method. For example, first, ceramic powder is uniformly mixed in a dispersion solvent using a ball mill, attritor, etc., and then the resulting ceramic powder dispersion is mixed with a liquid resin emulsion and a hardening mold. It can be prepared according to a conventional method such as adding a resin and mixing uniformly. The solid content concentration of the slurry is preferably 20 to 60% by volume, and the viscosity is preferably 100 to 2000 cps, more preferably 500 to 1000 cps, from the viewpoint of separation by sedimentation of ceramic powder and ease of handling.

The slurry prepared as described above is filled into the voids of a spherical resin molded container prepared in advance. Filling can be done by any suitable method such as simple pouring, pressurized injection, reduced pressure injection, vibration injection, etc. If the hardening resin is left to stand at room temperature or cured by heat treatment, a handleable green body is created. can get. The dispersion solvent is then removed from the green body by air drying or heat drying. Subsequently, in a degreasing step, spherical resin particles, liquid organic matter, and curable resin are removed, followed by firing. Degreasing is preferably carried out by raising the temperature at a relatively slow rate of temperature e.g. It is preferable to do this, and it is usually carried out in an air atmosphere, but it is preferable to select an atmosphere such as a II gas atmosphere depending on the mM of the ceramic raw material powder.

(Effects of the Invention) The porous ceramic body of the present invention has two or more types of communicating pores of different diameters and has a high porosity. The atmospheric pore diameter part has the advantage of low pressure loss and large flow rate, and facilitates mass transfer. On the other hand, since the micropores have a large specific surface area, they are extremely chemically active and have excellent catalyst supporting ability and biological reactivity. f The ceramic porous body of the present invention having both of these features is particularly suitable for exhaust gas filters, bioreactors, and the like.

Example I First, Styrofoam classified to a particle size of 3 mm was placed in a 50×1
After vibrating and filling a polypropylene female container with dimensions of 00 x 100 mm, a male container with an injection port in the center was used to fill the container.
A polystyrene foam molded body was prepared by compressing and fixing it to a size of 0x100x100 mm. Here, the occupied volume of the styrene foam was 70%, and the void area was 30%.

A dispersion of ceramic powder and an emulsion of a liquid organic substance having the pure composition shown below were prepared.

Ceramic aluminum oxide 80% by weight Water 19% deflocculant 1% emulsion liquid paraffin 45% water 50% emulsifier 5% by weight Ceramic powder dispersion is prepared in a ball mill in the specified amount. The mixture was mixed and dispersed for 24 hours. Aluminum oxide is 0.
A particle containing 5% by weight of magnesium and having an average particle diameter of 2 μm was used, and on the peptizing side, Boise 530 manufactured by Kao was used. The emulsion of the liquid organic substance was obtained by sequentially adding the liquid organic substance dropwise at a rate of 20 cc/min while stirring water at 70° C. to which an emulsifier had been added in advance at a rate of 3000 cps using a homomixer. The emulsifier used was a mixture of Kao's nonionic Emulsifying Rule Emulgen 220, Emulken 9-0, and Tween 20 in a weight ratio of 1:1:1.

The average particle size of the liquid resin was 15μ.

A slurry was prepared by mixing the obtained ceramic powder dispersion, liquid organic substance emulsion, and resin shown in Table 1 at a solid content ratio of 63:23:14. Here, Denacol EX-421 manufactured by Nagase Chemical Industries, Ltd. was used as the water-soluble epoxy. As the amount of epoxy resin, the total amount of water-soluble epoxy and water-soluble amine was calculated by converting the solid content. Further, in the system using melamine and phenol, para-toluenesulfonic acid was added to the slurry to adjust the pH to 2 to 2.5.

The slurry prepared as described above was injected from the upper injection port of the styrofoam molded body prepared in advance, and heated at 80°C for 12 hours.
After curing by heat treatment for several hours, the green body was removed from the mold and dried. Firing is performed using an atmospheric electric furnace at 0.5°C up to 400°C.
After that, the temperature was raised at a rate of 10° C./min, held at 1500° C. for 1 hour, and then cooled.

The appearance of the green body was evaluated based on the following criteria.

O: No cracks and sufficient strength for handling Δ: No cracks but some difficulty in handling ×: Cracks have occurred and handling is difficult The appearance evaluation of fired products is based on the following criteria. I did it.

O: Firing was completed without any cracks Δ: Some cracks were generated As shown in Table 1, a satisfactory ceramic body could not be manufactured using polyvinyl alcohol, which does not have hardening properties, and a ceramic body was produced using a thermosetting resin as a binder. It can be seen that it is possible to manufacture

Example 2 A second example was carried out in the same manner as in Example 1, except that a solid epoxy resin and a water-soluble amine were used as the curable resin, and the types of nonionic and anionic emulsifiers were appropriately selected when preparing the emulsion of the liquid organic substance. Emulsions of various organic substances were prepared as shown in the table, and porous ceramic bodies were manufactured. Results Here, the micropore opening efficiency was measured by mercury intrusion method, and the closed porosity was calculated from the apparent density of the ceramic body and the true specific gravity of the ceramic. The atmospheric porosity is
It was calculated from the weight of the ceramic body, the open porosity and the closed porosity of the micropores.

It is clear from Table 2 that continuous pores can be formed by using a liquid organic emulsion.

Example 3 Ceramic bodies were produced in the same manner as in Example 1 except that the amount of liquid organic matter was changed as shown in Table 3 below. However, the firing temperature was 1650°C, and the bending strength was determined by cutting the prepared ceramic porous body into 10 x 30 x 80 mm, and measuring span 6 in accordance with the JTS standard (R1601).
0mm, crosshead speed 0.5mm/m
This is a value measured by conducting a three-point bending test at in.

As is clear from Table 3, if the liquid organic substance is too small, it becomes difficult for the micropores to become continuous pores, and if it is too large, the strength tends to decrease.

Claims (1)

[Claims] When manufacturing a ceramic porous body having communicating pores by filling the voids of a resin particle molded body formed by bonding spherical resin particles with a slurry of a ceramic raw material containing ceramic powder and a curable resin, in the ceramic raw material A method for producing a porous ceramic body, characterized in that an emulsion of a liquid organic substance is blended as a pore-forming material.