JPH0597537A - Production of ceramic porous material - Google Patents

Abstract

PURPOSE:To obtain a ceramic porous material having an excellent porosity, an excellent strength, etc., by charging the slurry of a ceramic raw material mixed with starch in the space of a resin particle molded product obtained by binding spherical resin particles, and subsequently heating the charged slurry. CONSTITUTION:Spherical resin particles such as foamed styrene resin particles or polyethylene particles are charged in a container and press-bonded by a compression method, etc., to form a resin particle molded product. Separately, a slurry containing ceramic powder (e.g. alumina powder), starch powder (e.g. corn starch powder) and a curable resin (e.g. an epoxy resin) is produced. The slurry is charged in the space of the resin particle molded product. The charged slurry is heated at a temperature above the gelatinization temperature of the starch powder to form a green molded product, which is dried and subsequently subjected to a resin-removing process in which the spherical resin particles, starch powder and curable resin are burnt off, followed by calcining the remained molded product to provide the objective ceramic porous product having communicated pores.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an exhaust gas filter, a catalyst carrier, a bioreactor, etc. having different diameters.
The present invention relates to a method for producing a ceramic porous body having more than one type of continuous ventilation holes.

[0002]

2. Description of the Related Art In a ceramic porous body having different pore diameters, the air holes serve as passages for mass transfer, and the fine pores provide an environment advantageous for chemical reactions or biological reactions.
For example, it is useful for an exhaust gas filter carrying a catalyst, a bioreactor and the like. Conventionally, as a method for producing a ceramic porous body having relatively large continuous pores of 100 μm or more, a method of impregnating urethane foam with a ceramic slurry, drying and firing to burn away the urethane foam to sinter the ceramic, ceramic powder A method of molding and firing a mixture of a body and a combustible substance is known. On the other hand, as a method for producing a ceramic porous body having a small pore size of 20 μm or less, (a)
A method of adjusting the particle size distribution of the ceramic raw material powder to leave pores in the particle gaps after firing, (b) firing at a low temperature or in a short time, and without intentionally completing the sintering,
There are known a method of leaving pores in the interstices between particles, a method of incorporating (c) an organic emulsion into a ceramics slurry, and solidifying the ceramics slurry, followed by firing to form pores in the organic particles.

Various methods for producing a ceramic porous body having both air holes and small pores have been proposed by combining the method for producing a porous ceramic body having large pores and the method for producing a porous ceramic body having small pores. There is. Among these proposals, in particular, a ceramic porous body (Japanese Patent Application No. 2-283080) produced by combining the method for producing air holes described above and the method for producing small pores to which the organic emulsion described in (c) is applied is Although excellent in strength, it has the following drawbacks. That is, since the emulsion contains many bubbles during production, when used as a pore-forming agent, it is difficult to control the porosity because pores other than the pores formed by the emulsion particles are generated in the skeleton of the porous body. .. Further, the emulsion is difficult to control the particle size due to the manufacturing method, and it is difficult to control the pore size.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have completed the present invention as a result of earnest researches in view of the above-mentioned problems of the existing methods for producing a porous ceramic body, The purpose of the invention is to provide a method for producing a continuous ceramics porous body having both high porosity, high strength, and fine pores with strictly controlled fine pores.

[0005]

The above object is to fill a void of a resin particle compact formed by binding spherical resin particles with a slurry of a ceramic raw material containing a ceramic powder and a curable resin, and to form a continuous vent hole. When manufacturing a ceramics porous body having the above, at least one or more kinds of starch powders are blended in the ceramics raw material, and heated at a temperature not lower than the minimum gelatinization temperature of the blended starch powders to form a green body. This is achieved by the method for producing a porous ceramic body.

The spherical resin particles applied to the present invention are burned off in the firing step to form the air holes of the product of the present invention. Specifically, for example, organic resin particles such as polystyrene, polyethylene, polypropylene, nylon, polyester, acrylic, phenol, epoxy, ethylene-vinyl acetate copolymer, styrene-butadiene block polymer, urethane and wax, and foaming thereof. Examples of the body include styrene foam, which is inexpensive and easy to remove. These spherical resin particles are required to be in contact with each other in order to form continuous air holes. The method for producing a molded body in which the resin particles are bound to each other is, for example, a method of appropriately filling the container with resin particles and compressing the same, or a method of appropriately filling and molding resin particles with an adhesive applied to the surface of the container, An appropriate method may be selected and used from known methods such as a method of appropriately filling the container with the resin particles, injecting the resin solvent for a short time to cause the resin particles to adhere to each other and then removing the solvent.

The slurry in the present invention contains a ceramic powder, at least one or more kinds of starch powder, a curable resin which enhances the green body strength by the curing action, and a dispersion medium.

Examples of the ceramic powder used in the present invention include oxides such as alumina, zirconia, zircon, spinel, cordierite, mullite, titania, silica, aluminum titanate, calcia, magnesia and LAS, and silicon nitride. Aluminum nitride, silicon carbide,
Non-oxide powder such as sialon can be used. Furthermore, for the purpose of producing silicon nitride, aluminum nitride, and silicon carbide by reaction sintering, metal silicon powder, metal aluminum powder, carbon powder, and the like can be mentioned, but the invention is not limited to these, and the object of the present invention is Various ceramic raw materials can be used as long as they do not interfere with the above. The type and blending amount of the ceramic powder can be appropriately selected according to its application such as heat resistance, thermal shock resistance, corrosion resistance, and oxidation resistance.
The particle size of the ceramic powder is preferably 10 μm or less, more preferably 5 μm or less, and most preferably 2 μm or less in view of easy sinterability and storage stability of the slurry.

The starch powder used in the present invention has a function of functioning as a binder by gelatinization to solidify the green body and, at the same time, a function of forming fine open pores as a pore forming agent.

As the starch powder, those which are generally used can be used as they are, and particularly preferable ones are those which are separated and extracted from plants and include sugars, proteins, celluloses, fats and other contaminants. The product was purified by removing the substance. For example, one or more grains that have been separated and extracted and purified from grains such as rice, wheat and corn, beans, potatoes such as potatoes, taro and tapioca, and fruits such as bananas are used. Further, the particle diameters are different from each other, and those having rice, wheat or the like as a mother are relatively fine grains, and those having potatoes or fruits as a mother are relatively coarse grains. Among these starch powders, corn, rice, wheat and potato starch powders having a uniform particle size are particularly suitable for use in the present invention.
The content of starch powder is an important factor that determines the state of pore formation in the fine pores of the final product. If the starch powder is too small, the pores obtained will be closed pores instead of continuous pores. On the other hand, if the content is too large, the strength of the obtained ceramic body becomes small. The content of the starch powder is 10 to 50 parts by weight, preferably 20 to 40 parts by weight, based on the ceramic powder.

In the present invention, one type of starch powder may be used, but it is preferable to use a mixture of two or more types. That is, as described below, the slurry is heat-treated after casting, but when all the starch powders corresponding to the content necessary to form the continuous air holes are gelatinized, the drying speed of the green body becomes significantly slower and cracks occur. In order to obtain a green body free from this, drying treatment at low temperature for a long time is required, which causes a problem unsuitable for industrial production. Therefore, two or more types of starch are blended, heat treatment is performed at an intermediate temperature of the gelatinization temperature of these starches, and the starch below the heat treatment temperature is gelatinized to form a binder,
It is preferable that starch exceeding the heat treatment temperature is not gelatinized and is simply used as a pore forming agent.

The curable resin used in the present invention is
In the slurry containing the ceramic powder and the starch powder, it is supplementarily added in order to increase the strength of the green powder due to the gelatinizing action of the starch powder to a handleable strength. As the curable resin, a cross-linking reaction type resin that bonds three-dimensionally is preferable, for example,
Examples thereof include soluble or dispersed resins such as epoxy, phenol, urea and melamine. Of these, an epoxy resin in which a crosslinking reaction occurs particularly in an alkaline region where the peptizer effectively acts is preferable.

In the present invention, the amount of the curable resin added should be kept to the minimum necessary within the range in which the object of the present invention is achieved. That is, the curable resin is burned and removed in the manufacturing process of the ceramics sintered body and does not remain in the final product, and excessive addition is economically disadvantageous. Further, when the amount of the curable resin added is increased, the occurrence of cracks in the degreasing process tends to be promoted. From this point as well, it is preferable to avoid excessive addition. The content of the curable resin is preferably 0.5 to 15% by weight, more preferably 1 to 10% with respect to the ceramic powder.
% By weight.

In the present invention, it is advisable to use water as the dispersion medium of the slurry from the viewpoint of control and handling of the manufacturing process.

The slurry in the present invention is a mixed phase containing, as a main component, the above-mentioned ceramic powder, starch powder as a binder and pore-forming agent, and a curable resin which enhances the green body strength by the curing action. A foaming agent, a peptizing agent for effectively and stably dispersing the ceramic powder in the dispersion medium, a viscosity adjusting agent for making the workability of the slurry suitable, a drying speed adjusting agent and the like can be appropriately contained.

The slurry is prepared by a conventional method.
For example, first, the ceramic powder is uniformly mixed in a dispersion solvent in advance with a ball mill, an attritor, or the like. It can be produced by adding starch powder and a curable resin to the dispersant of the obtained ceramic powder and uniformly mixing them. The solid content concentration of the slurry is preferably 20 to 60% by volume, and its viscosity is preferably 100 to 2000 cps from the standpoint of separation and handling workability of the ceramic powder,
More preferably, it is 500 to 1000 cps.

The slurry prepared as described above is filled in the voids of the spherical resin molded body container prepared in advance. Examples of the filling method include a simple pouring method, a pressure injection method, a reduced pressure injection method, and a vibration injection method.

In the present invention, after the slurry is filled into a desired shape, heat treatment is performed at a gelatinization temperature of at least one starch or higher to produce a green body. That is, when the starch powder is heated above the gelatinization temperature, the outer shell of the starch powder is destroyed, and the starch powder exhibits a function as a pasty binder and also a pore forming agent. Further, when gelatinized powder at a heating temperature or higher is present, gelatinization does not occur and remains in granular form, which serves as a granular pore-forming agent.

As described above, in the present invention, both the starch powder having a gelatinization temperature lower than the heat treatment temperature and the curable resin serve as binders. The total content of the starch powder below the gelatinization temperature and the curable resin is
It is preferable to select the blending amount of the starch powder and the heat treatment temperature so as to be 10 to 30 weight. By heat treatment, the starch powder is gelatinized, and the curable resin is also cured to obtain a handleable green body. Then, the green body is subjected to air-drying or heat-drying to remove the dispersion solvent. Next, in the degreasing step, the spherical resin particles, the starch powder, and the curable resin are incinerated and removed, and subsequently, firing is performed. Degreasing is performed at a relatively slow temperature rising rate, for example, 500 at 10 to 200 ° C / hr.
It is preferable to carry out by raising the temperature from ℃ to 600 ℃, decompose and gasify and remove the contained organic matter. The firing is preferably performed at 1200 ° C. to 1800 ° C., and is usually performed in an atmospheric atmosphere, but a nitrogen gas atmosphere or the like may be appropriately selected depending on the type of ceramic raw material powder.

[0020]

The ceramic porous body of the present invention has two or more kinds of continuous air holes having different diameters, and has a high porosity and high strength. As a result, the air hole diameter portion has a feature that the pressure loss is low and a large flow rate can be obtained, so that it plays a role of facilitating mass transfer. On the other hand, since the fine pore size has a large specific surface area, it is chemically extremely active, and has catalyst-supporting ability and bioreactivity, and it does not cause problems such as breakage during use, so it is suitable for exhaust gas filters and bioreactors. Is.

[0021]

Example First, styrofoam classified to a particle size of 1 mm was vibratingly filled into a polypropylene female container having a size of 50 × 100 × 100 mm, and then compressed to a size of 40 × 100 × 100 mm by a male mold having an injection port at the center. Then, the styrofoam molded body was prepared by fixing. The volume occupied by the styrofoam was 70% and the voids were 30%.

Then, 0.5 as a ceramic material powder
Aluminum oxide containing 0.8% by weight of average particle size containing magnesia in weight% was prepared, water and a deflocculant were added at the compounding ratio shown in Table 1, and mixed and dispersed in a ball mill for 24 hours to obtain a ceramic powder slurry. Got

Next, various starch powders shown in Table 1 were prepared as a binder and a pore-forming agent, and a water-soluble epoxy was prepared as a curable resin, which was mixed with a ceramic powder dispersion to have a viscosity of 75.
A 0 cps slurry was made. Here, as the water-soluble epoxy, Denacol EX-320 manufactured by Nagase Chemical Industries,
Kao Poise 532A was used as a peptizer. The blending amount of the water-soluble epoxy shown in Table 1 is the total amount with the triethylenetetramine added as a curing agent.

The slurry was injected from the upper injection port of the Styrofoam molded body prepared in advance, heat-treated at a predetermined temperature for 10 hours, and the green body was demolded and dried. Baking is performed at 0.5 ° C./min up to 400 ° C. in an air atmosphere electric furnace, and thereafter 1
The temperature was raised at a rate of 0 ° C./min, and the temperature was maintained at 1500 ° C. for 2 hours, and then cooled. In addition, Table 1 shows a comparison of comparative examples produced by using an emulsion of liquid paraffin produced by a forced emulsification method instead of starch powder. The physical properties of the obtained ceramic porous body were evaluated by the following methods.

[A] Handling property of green body When the green body was taken out from the casting container, those that could be released from the mold without damage were evaluated as ◯, and those that were damaged during the mold removal were evaluated as x.

[B] Pore size 1) Atmosphere part The ceramic porous body was cut, and the diameter of the granular porosity was measured by an optical microscope. 2) Fine pores Porous ceramics were crushed and the pore size distribution of the open pores was measured by mercury porosimetry.

[C] Porosity of fine pores Simultaneously with the measurement of [B] -2), the porosity of pores forming open pores was measured by mercury porosimetry.

[D] Bending Strength A porous ceramic body was cut into a sample piece of 5 × 10 × 70 mm, and the span was 60 mm and the crosshead speed was 0.5.
A three-point bending strength test was conducted at mm / min. The bending strength was defined as the average of the ten measured values.

[0029]

[Table 1]

As is clear from Table 1, fine pores are not formed in the one containing no starch powder (Exp. No.
1). In addition, the handling property of the green body is poor unless it is treated at a temperature higher than the gelatinization temperature of at least one starch (E
xp. No2). If a liquid organic emulsion is used instead of starch, the pore diameter of the fine pores cannot be strictly controlled (Exp.
No. 8 has two peaks in the fine pore size distribution).

Claims (1)

[Claims] 1. When manufacturing a ceramic porous body having continuous ventilation holes by filling a void of a resin particle molded body formed by binding spherical resin particles with a slurry of a ceramic raw material containing a ceramic powder and a curable resin. Mixing at least one starch powder in the ceramic raw material,
A method for producing a porous ceramic body, which comprises heating a blended starch powder at a temperature not lower than the minimum gelatinization temperature to form a green body.