JP2728838B2 - Method for producing porous sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous sintered body, and more particularly, to a ceramic having continuous ventilation holes suitable for a molten metal filter, an exhaust gas filter, a catalyst carrier, a lightweight refractory, and the like. The present invention relates to a method for manufacturing a porous sintered body.

[0002]

2. Description of the Related Art Porous ceramic sintered bodies having continuous vents are useful for filters for molten metal, exhaust gas filters, catalyst carriers, lightweight refractories, etc., and many of them have already been put to practical use. Methods for producing these ceramic porous bodies include impregnating urethane foam with a ceramic slurry, drying and heat treating to burn off the urethane foam and sinter the ceramics, molding a mixture of ceramic powder and a combustible substance and firing the mixture. There are known methods.

[0003] Of these methods, the method of impregnating urethane foam with a ceramic slurry is an effective method for obtaining a porous ceramic body having a high porosity, but the trace of the urethane foam incinerated and removed at the center of the skeleton of the ceramic sintered body. There is a disadvantage that the voids remain and the strength is reduced. In order to overcome this drawback, a method of using flammable particulates such as styrene foam as a pore-forming material (for example, see JP-A-63-2658)
No. 80) has been proposed. According to this method, it is possible to produce a ceramic porous sintered body having high strength, high porosity, and open pores. In this method, as a method of removing combustible particulate matter, a method of burning out during the firing step. There is a method of dissolving and removing the ceramic green body with an organic solvent before drying.

However, in the method (1), since the combustible particulate matter remains without being removed during the drying step prior to the firing step, drying shrinkage of the skeleton portion of the green body is hindered. Cracks occur Therefore, there is a disadvantage that the strength of the final product is reduced. In the method (1), since an organic solvent is used, there is a danger in the operation thereof, and further, the exhaust gas treatment and the waste liquid treatment are complicated.

[0005]

SUMMARY OF THE INVENTION The present inventor has conducted intensive studies in view of the various problems of the conventional method for producing a porous ceramic sintered body, and as a result, completed the present invention. An object of the present invention is to provide a method for producing a ceramic porous sintered body having high air efficiency and continuous air holes.

[0006]

Means for Solving the Problems In a method for producing a porous sintered body by filling a slurry containing a curable resin and an inorganic powder into the voids of spherical particles of a synthetic resin foam, the following (A) and (4) This is achieved by a method for producing a porous sintered body having continuous air holes, which comprises the step (B).

(A) Spherical particles of a synthetic resin foam are
A step of applying a hydrocarbon solvent having an initial boiling point of 150 ° C. or higher and an aromatic solvent content of 20% by volume or less. (B) a step of treating the green body filled with the slurry containing the curable resin and the inorganic powder in a high-humidity atmosphere at 50 ° C. or higher.

In the present invention, spherical particles of a synthetic resin foam such as styrene foam (hereinafter referred to as spherical particles of the foam)
Are filled with a ceramic slurry in the voids of the resin particle molded body formed. Next, the spherical particles of the foam are softened and shrunk by a heat treatment. However, since the spherical particles of the foam are treated in a high humidity atmosphere, evaporation of water in the ceramic slurry portion, that is, the skeleton portion of the ceramic is suppressed. Therefore, the skeleton of the ceramics does not practically undergo drying shrinkage.

Only after the shrinkage of the spherical particles of the foam is completed, the skeleton is dried. A dry shrinkage-free crack in the skeleton portion due to the restraint of the molded product of the spherical particles of the foam as seen in the conventional method does not occur, and a dry body that is uniform and free from cracks can be obtained. The petroleum hydrocarbon solvent pre-applied to the spherical particles of the foam plays an important role in making the softening and shrinking of the spherical particles of the foam easier.

In the present invention, the spherical particles of the foam serve to form pores of the ceramic porous body. In the case of polystyrene foam spherical particles, the spherical particles of the foam can be produced by generally treating beads containing a foaming gas such as butane in the particles in steam at 100 to 140 ° C. for 3 to 10 minutes. Particle size is 0.5-10m
Up to m can be appropriately controlled by the type of beads and foaming conditions.

The hydrocarbon-based solvent used in the present invention functions to easily soften and shrink the foam spherical particles forming the pores at a relatively low temperature which can be realized by an ordinary heating device, as described above. Things. The hydrocarbon-based solvent is obtained as a mixture of paraffin-based, naphthenic-based and aromatic-based hydrocarbons, but the effect on the softening / shrinking action of the spherical particles of the foam differs significantly depending on the composition ratio and the distillation temperature range.

The hydrocarbon solvent used in the present invention has an initial boiling point of 150 ° C. or higher and an aromatic solvent content of 20% by volume or less. If the initial boiling point is less than 150 ° C., the effect of softening and shrinking the spherical particles of the foam is excessive, and the shrinking of the expanded spherical particles occurs before the heating step in a high humidity atmosphere, and the obtained porous sintered body The pore size cannot be strictly controlled. Similarly, when the content of the aromatic solvent exceeds 20% by volume, the effect of softening and shrinking the spherical particles of the foam is excessive, and the pore diameter of the obtained porous sintered body cannot be strictly controlled.

In the present invention, the method of applying a hydrocarbon solvent to the spherical particles of the foam is, for example, when the spherical particles of the foam are styrene foam spheres, a petroleum hydrocarbon solvent is used as the hydrocarbon solvent in a closed container. How to give vibration
There are a method of dropping a petroleum-based hydrocarbon solvent while stirring the styrofoam sphere with a stirrer, a method of injecting a petroleum-based hydrocarbon into a preformed styrofoam sphere molded body, and thereafter removing excess solvent. The addition amount of the petroleum hydrocarbon solvent is preferably such that the surface of the expanded polystyrene sphere is further covered.

In the present invention, a method for producing a molded resin particle formed by binding the spherical particles of the foam is, for example, a method of filling the spherical particles of the foam into an appropriate container and compressing the same, and a method of forming the pre-foamed foam. In a suitable container, steam of 100 ° C. or higher is injected into the container to fuse the spherical particles of the foam. The slurry in the present invention is prepared using an inorganic powder, a curable resin for increasing the strength of the green body by a curing action, and a dispersion medium.

Examples of the inorganic powder include oxides such as alumina, zirconia, zircon, cordierite, mullite, titania, silica, aluminum titanate, and magnesia; and non-oxidized materials such as silicon nitride, aluminum nitride, silicon carbide, and sialon. Substance powder. Further, 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 given, but are not limited thereto. The type and amount of the inorganic powder can be appropriately selected according to the intended use, such as heat resistance, thermal shock resistance, corrosion resistance, acid resistance, and oxidation resistance. The particle diameter of the inorganic powder is 10 μm or less, preferably 2 μm or less, and most preferably 1 μm or less in view of sinterability and slurry stability.

The curable resin used in the present invention is:
The hardening action increases the strength of the green body. As the curable resin, a cross-linkable resin capable of forming a three-dimensional network is preferable, and examples thereof include soluble or dispersed resins such as epoxy, phenol, urea, and melamine. Among these, an epoxy resin in which a cross-linking reaction occurs particularly in an alkaline region where a peptizer effectively acts is preferable.

In the present invention, the amount of the curable resin to be added is preferably kept to the minimum necessary within the range for achieving the object of the present invention. That is, the curable resin is burned and removed in the production process of the ceramic sintered body and does not remain in the final product, and excessive addition is economically disadvantageous. Further, when the addition amount of the curable resin is increased, the generation of cracks in the degreasing step tends to be promoted, and from this point too, excessive addition should be avoided. The content of the curable resin is preferably from 1 to 35% by weight, more preferably from 5 to 25% by weight, based on the inorganic powder.

In the present invention, examples of the dispersion medium of the slurry include water, methyl alcohol, ethyl alcohol, toluene, xylene, acetone, methyl ethyl ketone, and kerosene. Usually, water is most preferred as the dispersion medium because of its easy handling. However, in the case of non-oxide ceramics having poor water resistance, a non-aqueous solvent is preferably used.

The slurry in the present invention is a mixed phase mainly composed of the above-mentioned inorganic powder and a curable resin which enhances the green body strength by a curing action.
A deflocculant for effectively and stably dispersing the inorganic powder in the dispersion medium, a viscosity adjusting agent for improving the workability of the slurry, and a drying speed adjusting agent can be appropriately contained. Preparation of the slurry is performed according to a conventional method. For example, first, an inorganic powder and a curable resin are mixed in a dispersion solvent by a ball mill, an attritor, or the like.

The slurry prepared as described above is filled in the voids of a preformed styrene foam resin molded article container. Examples of the filling method include a simple pouring method, a pressure injection method, a reduced pressure injection method, and a vibration injection method. A handleable green body obtained by curing the curable resin by standing at room temperature or by heat treatment is obtained. Next, the green body is taken out of the container, and the foamed styrene balls treated in a high humidity atmosphere of 50 ° C. or more are softened and shrunk within 30 minutes to 3 hours. Next, the dispersion solvent is removed by air drying or heat drying. Next, in a degreasing step, the curable resin is incinerated and removed, and subsequently baked. Degreasing is performed at a relatively slow temperature rising rate, for example, 500 ° C to 60 ° C at 10 to 200 ° C / hr.
It is preferable to carry out the process by raising the temperature to 0 ° C. to decompose and burn off the contained organic matter. Firing at 1200 ° C ~
It is preferable to carry out the treatment at 1800 ° C., which is usually carried out in an air atmosphere.

[0021]

The ceramic porous sintered body of the present invention comprises:
It has high porosity and high strength, and is suitable for molten metal filters, exhaust gas filters, lightweight refractories, catalyst carriers, and the like. Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 First, 500 cc of styrene foam spheres classified to a particle diameter of 3 mm were placed in a 2 l beaker and stirred while stirring.
10cc of a petroleum hydrocarbon solvent manufactured by Shell Chemical Co., Ltd.
Was dropped, and a petroleum hydrocarbon solvent was applied to the surface of the expanded polystyrene sphere. Then, these are 50 × 100 × 100 m
After vibration-filling into a female female container made of m-size polypropylene, 40 × 100 × 1 in a male type having an inlet at the center.
It was compressed to a size of 00 mm and fixed to prepare a foamed polystyrene sphere.

Subsequently, a slurry having a pure composition shown below was mixed and dispersed for 24 hours using an alumina ball mill. Slurry composition Aluminum oxide 77% by weight Water-soluble epoxy resin 8% by weight Water 14% by weight Peptizer 1% by weight Aluminum oxide containing 0.5% by weight of magnesia and having an average particle size of 2 μm is used. Used was Denaseol EX-421 manufactured by Nagase Kasei Kogyo Co., Ltd.
Kao's Poise 530 was used as the peptizer. As the amount of the water-soluble epoxy resin, the total amount of the water-soluble epoxy and the water-soluble amine was converted into a solid content.

The slurry prepared as described above is injected from an upper injection port of a styrene foam molded article prepared in advance,
Heat treatment was performed at 40 ° C. for 12 hours, and after curing of the curable resin, the green body was released. Then, at 70 ° C and 100% humidity,
The foam was treated for 8 hours to soften and shrink the styrene foam balls. Next, the substrate was treated at 90 ° C. and a humidity of 70% for 96 hours, dried first, and then completely dried at 100 ° C.

The firing is performed in an air atmosphere electric furnace at 400 ° C.
After that, the temperature was raised at a rate of 0.5 ° C./min thereafter, at a rate of 10 ° C./min, kept at 1500 ° C. for 1 hour, and then cooled.

[Table 1]

The evaluation of the solubility of the petroleum hydrocarbon solvent in the expanded polystyrene spheres was performed according to the following criteria. ：: Not dissolved at room temperature △: Slightly dissolved and particle size of styrofoam spheres changed ×: Completely dissolved and unusable The appearance of a green body was evaluated according to the following criteria. ：: Styrofoam spheres were sufficiently softened and shrunk and no cracks were observed. ×: Styrofoam was not softened and shrunk and remained, and cracks were observed around them.

The appearance of the fired body was evaluated according to the following criteria. ：: Baking was possible without generation of cracks △: Some cracks were generated ×: Cracks were generated

Here, the bending strength was determined by cutting a prepared ceramic porous body into 10 × 30 × 80 mm and performing a three-point bending test at a span of 60 mm and a crosshead speed of 0.5 mm / min in accordance with JIS (R1601). Was. From Table 1, it can be seen that the strength of the ceramic porous body to which no petroleum hydrocarbon is applied is small, and that many fine cracks are generated by microstructure observation. A petroleum solvent having a high content of an aromatic solvent dissolves styrene foam at room temperature and cannot be used. The content of the aromatic solvent is 20% by volume or less, preferably 1% by volume or less, and the initial boiling point is 15% by volume.
It turns out that it is 0 degreeC or more.

Example 2 Using an expanded polystyrene ball having a particle diameter of 1 mm, an inorganic powder in which 80% by weight of aluminum oxide having an average particle diameter of 0.5 μm and 20% by weight of zirconia having an average particle diameter of 0.3 μm were mixed. Various ceramics bodies were produced in the same manner as in Example 1 except that the humidity in the step of dissolving and removing styrofoam with petroleum hydrocarbons was 95% and the treatment temperature was appropriately changed. The petroleum hydrocarbon used here is DOSB manufactured by Shell Chemical. Table 2 shows the results.

[0030]

[Table 2]

Claims (1)

(57) [Claims] 1. A method for producing a porous sintered body by filling a slurry containing a curable resin and an inorganic powder into voids of spherical particles of a synthetic resin foam, comprising the following steps (A) and (B): A method for producing a porous sintered body having continuous pores, characterized by comprising: (A) The initial boiling point of the spherical particles of the synthetic resin foam is 15 in advance.
A step of applying a hydrocarbon solvent having an aromatic solvent content of 20% by volume or less at 0 ° C. or more. (B) a step of treating the green body filled with the slurry containing the curable resin and the inorganic powder in a high-humidity atmosphere at 50 ° C. or higher.