JPH01160878A - Production of precursor of ceramic porous article - Google Patents

Abstract

PURPOSE:To efficiently obtain a high-quality and stable ceramic porous article precursor, by packing a mixed liquid of ceramic material powder with two or more kind of starch powder having different gelatinization temperatures and water into a mold frame and heat-heating the mixed liquid at specific temperature. CONSTITUTION:A ceramic material powder is blended with two or more kind of starch powders having different gelatinization temperature to give an uniform, viscous and slurry-like dope, which is then packed into a mold frame. Then, the dope is heat-treated at temperature which is not lower than gelatinization temperature of a starch powder having lowest gelatinization temperature among the above-mentioned starch powder and is not higher than gelatinization temperature of a starch powder having highest gelatinization temperature among the above-mentioned starch powder to solidify the dope and removed from the mold to provide the aimed porous article precursor. In the precursor, starch powder having lower gelatinization temperature than the above- mentioned treating temperature is gelatinized at the above-mentioned temperature, uniformly permeated between particles of ceramic material powder and acted as a binder for bonding the particles. The starch powder having higher gelatinization powder than the above-mentioned treating temperature maintains the shape in swelled state without gelatinizing and works as a pore-forming agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a porous ceramic precursor used for filter media, catalyst carriers, and the like.

[Conventional technology]

In general, ceramic porous bodies are made using powdered materials such as Kibushi clay, Mimitome clay, feldspar, and silica stone, either alone or in combination.
It is obtained by adding water to make a slurry, filling a mold with this slurry, shaping it, and then firing it at a temperature higher than the sintering temperature of the powdered raw material. However, the above-mentioned porous ceramic material forms pores between the particles of the raw material, and there are limits to both the porosity and the pore diameter of the pores, and it is difficult to satisfy the requirements for ventilation and liquid permeability as a filter material. It's not something you can do. Therefore, as a manufacturing method for ceramic porous bodies whose porosity and pore diameter can be freely adjusted, purified ceramic material powder is mixed with a resin binder, a pore-forming agent, and water, and this is formed using a mold, etc. There is a method of degreasing and firing by raising the temperature. However, in this method, papermaking sludge, plant-based materials such as cellulose, or spherical particles such as polystyrene are used as the pore-forming agent, and resins such as epoxy, urethane, and polyvinyl alcohol are used as the binder. There is a problem in that it is difficult to completely burn out and remove these in the degreasing process, and in doing so, harmful exhaust gas is generated. In addition, the mechanical strength is weak because the bonding state between the particles of the ceramic material powder in the manufactured porous ceramic body is weak, and especially in the case of a large porous ceramic body, there is a problem that cracks and cracks are easily generated. There is. In order to solve these problems, the inventors have already disclosed in Japanese Patent Application No. 60-229100 a method of using starch as a pore-forming agent and binder. Starch consists of circular or elliptical particles each having independent cells, and the particle structure is composed of an outer shell and internal components contained within the outer shell. This starch is insoluble in water at temperatures below approximately 50°C, exhibits a swollen state at temperatures of 50 to 70°C, and exhibits a swelling state at temperatures of approximately 70°C.
The outer shell is destroyed and becomes gelatinized. The above method utilizes these properties of starch. That is, starch is mixed with ceramic material powder and water to form a slurry, and this is filled into a mold while maintaining the temperature below the gelatinization temperature of the starch so that the starch acts as a pore-forming agent. Preform. In this state, the molded product is extremely soft, and those with a simple shape can be released from the mold with careful work, while those with a complex shape must be heated to a temperature above the gelatinization temperature of starch. By heat-treating, the outer shell of the starch particles is destroyed and acts as a glue-like binder, solidifying the whole to form a stable molded product. In this state, the molded product is relatively stable and has a certain degree of strength, so even if it has a complicated shape, it can be easily released from the mold. Then, the obtained molded product is further dried as necessary to obtain a precursor.

[Problems to be Solved by the Invention] However, in the above method, the pre-formed pre-solidified body has low strength and easily loses its shape. For shaped objects, it is necessary to carry out the molding together, which results in poor thermal efficiency and requires a long time. and,
At that time, the inside of the presolidified material is difficult to dry because heat is not easily transmitted, and the processing steps to obtain the precursor include presolidification at a temperature below the gelatinization temperature of starch, and a temperature above the gelatinization temperature of starch. In addition to heat treatment performed at high temperatures, drying may also be performed after mold release, which poses a problem in that the work becomes complicated. Another problem is that during the heat treatment, a large temperature difference occurs between the inside and outside of the pre-solidified body, making it easier for cracks to occur. Furthermore, the starch used as a pore-forming agent has the functions of both a binder and a pore-forming agent, so both functions are somewhat unstable. If the heat treatment conditions are not strictly controlled, patchy or non-uniform pores will be formed, resulting in poor aesthetics and poor quality.

This invention was made in view of these circumstances, and it is possible to reduce the number of processing steps and perform efficient work, has good thermal efficiency, does not cause cracks due to temperature differences, and has a high quality and stable precursor. The object of the present invention is to provide a method for manufacturing a ceramic molded body precursor that can be obtained.

[Means for solving problems]

In order to achieve the above object, the method for producing a ceramic molded body precursor of the present invention involves mixing a ceramic material powder and two or more types of starch powders having different gelatinization temperatures in water to form a uniform viscous slurry. After filling this into a mold, gelatinize the starch powder whose gelatinization temperature is higher than or equal to the gelatinization temperature of the starch powder with the lowest temperature among the starch powders and whose gelatinization temperature is the highest temperature. It takes a structure in which it is heat treated at a temperature below that temperature and then hardened and demolded.

[Function] That is, in the method of the present invention, as in the conventional example, ceramic material powder, starch, and water are mixed to form a slurry, which is preformed at a temperature below the gelatinization temperature of starch, and then molded into a mold. Instead of obtaining a stable molded body by heat treatment at a temperature higher than the gelatinization temperature of whole starch, two or more types of starch powders with different gelatinization temperatures are mixed with ceramic material powder and water, and this is mixed into a mold. A stable pre-solidified product is obtained by filling the starch into a starch, followed by heat treatment at a temperature approximately midway between the gelatinization temperatures of the two or more types of starch. In this pre-solidified product, the starch powder whose gelatinization temperature is lower than the above-mentioned treatment temperature is gelatinized at the above-mentioned temperature and uniformly penetrates between the particles of the ceramic material powder, and acts as a binder to bind the particles, and also acts as a binder to bind the particles. Starch powder whose gelatinization temperature is higher than the processing temperature maintains its shape in a swollen state without gelatinization and acts as a pore-forming agent. Therefore, due to the binder effect of the gelatinized starch, the pre-solidified material has
It is in a stable state with a certain degree of mechanical strength, and even if it is released from the mold in that state, it will not crack or break. Therefore, unlike the conventional example, there is no need to perform heat treatment multiple times in which the entire mold is further heat treated after pre-solidification, and one heat treatment in a released state is sufficient. Therefore, processing can be carried out with good thermal efficiency, and defects such as cracks caused by a large temperature difference between the inside and outside of the pre-solidified material during drying can be prevented. Since the precursor thus obtained is in a relatively strong bond, it can be processed by cutting, grinding, lathing, etc.

In the next step, this precursor is placed in a furnace and heated to the combustion temperature of starch to burn out the starch (degreasing process), and then heated to the sintering temperature of ceramic material powder and fired. A ceramic porous body can be obtained by completing the above steps.

The ceramic material powder mentioned above is wood tablet clay.

In addition to being able to use powders that are raw materials for ceramics, such as porcelain clay, feldspar, silica, kaolin, and montmorillonite cordierite, alone or in combination, it is possible to obtain powders that provide high structural strength or have low chemical composition impurities. For the purpose of
Aluminum oxide.

New ceramic material powders such as silicate, aluminum silicate, magnesia, zirconium oxide, zirconium silicate, titanium oxide, silicon carbide, silicon nitride, and iron oxide can be used alone or in combination of two or more. Moreover, it can be used by appropriately mixing it with the above raw material powder for ceramics.

As the starch powder, commercially available starch powders can be used as they are, and particularly preferred starch powders are those separated and extracted from plants, and saccharides.

It is purified by removing proteins, cellulose, fats, and other impurities. For example, rice.

Grains such as wheat and corn, beans, potatoes, taro,
It is isolated, extracted and purified from sweet potato necks such as tapioca and fruits such as bananas. These gelatinization temperatures differ depending on the parent plant; for example, one whose parent plant is potato is 70 to 72°C, and one whose parent plant is rice is 71°C.
~73°C9 Wheat-based products are 76-78°C9
Those made from corn have a temperature of 80 to 82°C. The particle size also differs, with those made from rice, wheat, etc. having relatively fine grains, and those made from potatoes.

Those whose parent bodies are fruits are relatively coarse-grained. In this invention, these are used in appropriate combination.

As described above, the method of the present invention is to fill a mold with a slurry in which a ceramic material powder that does not itself contain a binder component is mixed with two or more kinds of starch powders and water having different gelatinization temperatures, and A stable pre-solidified product is obtained by heat-treating the starch at a temperature approximately halfway between the high and low gelatinization temperatures of the starches above, and gelatinizing the starch powder with a low gelatinization temperature to act as a binder. At the same time, starch powder with a high gelatinization temperature is made to act as a pore-forming agent. In its production, 5 to 15 parts by weight of starch powder with a low gelatinization temperature for the binder and 10 to 15 parts by weight of starch powder with a high gelatinization temperature for the pore forming agent are added to 100 parts by weight of the ceramic material powder.
It is preferable to set the amount to 40 parts by weight. That is,
If the starch powder for the binder is less than 5 parts by weight, it will have little effect as a binder (if it exceeds 15 parts by weight, the strength of the ceramic porous body will be weakened. This is because the pores formed tend to become closed cells and it is difficult to form a continuous pore structure suitable for a filter medium.On the other hand, if the amount exceeds 40 parts by weight, the ceramic porous body becomes structurally weak.

There are no particular restrictions on the amount of water used, but
It is important that the amount is sufficient to completely disperse the starch powder and to obtain an overall uniform slurry.

The ceramic porous body thus obtained has a continuous pore structure with a three-dimensional network structure, and a porosity of approximately 50 to 80% by volume, and the pore size can be adjusted by the particle size of the starch powder used. can.

-When starch powder is used for S, the average pore diameter is 120μ
The upper limit is approximately m, and in order to obtain more pores, a starch lump that has been processed and gelatinized and then hardened is crushed and classified.

Next, examples will be described.

[Example] - First, as a ceramic material powder, high-purity aluminum oxide with a purity of 99.7% and an average particle size of 10 μm was prepared. Next, as a starch powder for a binder, potato starch (gelatinization temperature, 70.5°C), wheat starch (gelatinization temperature, 78°C) was prepared as a starch powder for a pore-forming agent,
They were blended in the following proportions.

Aluminum oxide 3500g Potato starch 250g Wheat starch 1000g Water 3580g Thoroughly knead the raw materials in this combination to form a slurry-like viscous stock solution.
The formwork made of vinyl chloride resin (inner diameter 7
It is a cylindrical piece with a diameter of 5 mm and a depth of 320 mm, with a diameter of 30 mm in the center.
20 pieces (having a core of mm) were each filled.

This was pre-solidified by heat treatment at a temperature of 75°C for 16 hours, and then taken out from the mold to obtain a cylindrical pre-solidified body.

Next, this pre-solidified material is placed in a dryer set at a temperature of 70"C and held for 5 days to obtain a precursor, which is then further placed in an oxidizing gas furnace to reach a final temperature of 1600°C. Degreasing and firing were performed by raising the temperature to .As a result,
The numbers of non-defective products and defective products in each process were as follows.

(Margins below) Good product Cracks Cracks After mold release 17 1 0 2 After drying
16 0 0 1 After degreasing and firing 1
4 0 1 1 The ceramic porous body obtained in the above example had a porosity of 68% and an average pore diameter of 3 to 12μ.
m, it could be satisfactorily used as a general filtration filter, and was homogeneous with no uneven pores.

[Comparative example]

A ceramic porous body was produced in the same manner as in the above example except that 1250 g of wheat starch alone was used as the starch powder and the pre-solidification temperature was 80°C. The results were as follows.

Good product Crack Cracks Cracked after mold release 13 5 1 1 After drying
12 0 1 0 After degreasing and firing 1
1 0 0 1 [Effects of the Invention] As described above, the method of the present invention produces a slurry in which a ceramic material powder that does not itself contain a binder component, two or more types of starch powders having different gelatinization temperatures, and water are mixed. By filling the mold into a mold and pre-solidifying it at a temperature intermediate between the gelatinization temperatures of two or more types of starch powder, the one with a lower gelatinization temperature among the starch powders is gelatinized and acts as a binder, making it stable. In addition to obtaining a pre-solidified product, starch powder having a high gelatinization temperature is made to act as a pore-forming agent. Therefore, unlike the conventional example, there is no need to perform three-step heat treatment, and the precursor can be obtained by heat treatment within the mold and drying after release from the mold.

In this way, since drying after pre-solidification is performed after release from the mold, it is possible to carry out processing with good thermal efficiency, and it is possible to avoid defects such as cracks due to large temperature differences between the inside and outside of the pre-solidified product during drying. It can be prevented. In addition, since the starch used is divided into two types, one for the binder and the other for the pore-forming agent, its action stability is excellent, and evenly distributed pores can be formed, making it possible to obtain a high-quality ceramic porous body. become able to.

Claims (2)

[Claims] (1) Ceramic material powder and two or more types of starch powder with different gelatinization temperatures are mixed with water to form a uniform viscous slurry stock solution, which is filled into a mold, and then the above starch powder is mixed with water. A porous ceramic characterized by being hardened and demolded by heat treatment at a temperature that is higher than the gelatinization temperature of the starch powder with the lowest gelatinization temperature and lower than the gelatinization temperature of the starch powder with the highest gelatinization temperature. Method for producing body precursor. (2) The method for producing a ceramic porous body precursor according to claim 1, wherein at least one of the starch powders is a processed starch.