JPH11302302A - Starch for gel cast molding and molding using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject starch dispersible into cold water, being gelatinized by heating, capable of lessening a foamy defect remaining after drying and baking of a molded starch than a conventional one by adjusting its average particle diameter to a specific value or smaller. SOLUTION: This starch is dispersible into cold water, is gelatinized by heating and has <=3 μm, preferably <=1 μm average particle diameter. Such a starch is obtained, for example, by a method for classifying only fine starch by a cyclone so as to make the average particle diameter <=3 μm. In a method for molding powder into a fixed shape, comprising dispersing the powder into water to give a slurry, casting the slurry into a forming mold and hardening the molded material, this starch is added to the slurry and used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to ceramics,
The present invention relates to starch used by adding a metal or the like to a slurry when forming the metal by so-called gel cast molding, and gel cast molding using the starch.

[0002]

[Prior art] As a molding method of ceramics and metals,
Conventionally, various methods such as press molding, injection molding, and casting are known. As one of such molding methods, a molding method called gel cast molding (gel casting method) has recently attracted attention. . This molding method is a method in which powder such as ceramics is dispersed in a gas-dispersible liquid such as water to form a slurry, which is poured into a mold and cured to form the powder into a predetermined shape. There is an advantage that a molded article having a complicated shape can be produced relatively easily.

In gel cast molding, agar and gelatin are widely used as additives for hardening a slurry, and a curable resin such as an epoxy resin is used as in the molding method described in Japanese Patent Publication No. 7-22931. May be added to utilize its self-hardening. However, since the agar, gelatin and resin have high viscosity in water, there is a problem that it is difficult to prepare a slurry having high concentration and high fluidity.

Therefore, as an additive for hardening a slurry in gel cast molding, for example, Japanese Patent Application Laid-Open
As disclosed in Japanese Patent No. 45574, a method using starch has been devised. The starch referred to here is a starch (so-called beta starch) which does not dissolve in cold water but exhibits viscosity by being dissolved, decomposed, and swelled by heating. Since this starch does not dissolve in cold water but only disperses, a slurry having no viscosity and high fluidity can be produced.

[0005]

The starch used for gel casting is separated from potatoes and cereals.
It is obtained by purification, and its particle size is determined by the type of raw material, and generally has an average particle size of 50-100 μm in potato.
m, 20 to 50 μm for sweet potato, 5 to corn
It is 20 μm, the finest in rice, about 4 to 10 μm, and there is no finer starch.

In the gel cast molding using these starches, starch is mixed with powders such as ceramics in cold water to form a slurry, which is poured into a mold and heated to gel to obtain a molded body. Can be
After drying and firing this molded body, a bubble-like defect remains in the portion where the starch was present. And, in the gel cast molding using the above-mentioned conventional starch, because the particle diameter of the starch is too large, the remaining defects also become large, and as a result,
There is a problem that only low-density, low-strength and low-reliability products can be obtained.

The present invention has been made in view of such a conventional situation, and an object of the present invention is to provide a starch used for gel cast molding, which has air bubbles remaining after drying and firing of a molded article. It is an object of the present invention to provide a starch having a small average particle diameter capable of reducing the shape defect, and a molding method using the same.

[0008]

According to the present invention, there is provided starch which is dispersed in cold water and gelled by heating, wherein the starch has an average particle diameter of 3 μm or less.

Further, according to the present invention, in a molding method for molding a powder into a predetermined shape by pouring a slurry in which the powder is dispersed in water into a molding die and curing the slurry, the slurry contains cold water. A molding method characterized by adding starch which is dispersed and gelled by heating and having an average particle diameter of 3 μm or less is provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the starch of the present invention is a starch that is dispersed in cold water and gels by heating, and has an average particle size of 3 μm or less, preferably 1 μm or less. When gel cast molding is performed using such a fine starch, after drying and firing of the obtained molded body (cured body), it is possible to reduce bubbles-like defects remaining in the portion where the starch granules existed. As a result, a product having higher density, higher strength and higher reliability than before can be obtained.

The fine starch having an average particle diameter of 3 μm or less does not generally exist and needs to be prepared by a special method. A typical production method is, for example, a method of classifying only fine starch with a cyclone so that the average particle diameter is 3 μm or less.

[0012] By the way, if the starch is simply made finer, a method of pulverization may be considered. However, the starch refined by the pulverization does not disperse in cold water but exhibits a property of absorbing water and increasing viscosity. Not suitable for This is because it is considered that molecules constituting starch do not gel due to their chemical structure, but to gel due to a change in molecular arrangement and physical structure. Therefore, when pulverized, this physical structure is destroyed, and water is absorbed and thickened in cold water. Conversely, it is a particle in which the molecules constituting the starch are arranged in a structure that is insoluble in cold water, and has an average particle diameter of 3 μm.
Artificially produced starch, particles of less than or equal to m, can also be used for gel cast molding as the starch of the present invention.

[0013] The molding method of the present invention is the same as the conventional method except that starch, which is dispersed in cold water and gelled by heating and has an average particle size of 3 µm or less, preferably 1 µm or less, is used. It is the same as the gel cast molding. That is, the starch is added to a slurry in which a powder of ceramics, metal, or the like is dispersed in water, and the resultant is poured into a mold. Then, by heating and curing (gelling), a molded body (cured body) in which the powder is molded into a predetermined shape is obtained. Since the molded body obtained by this molding method has few defects remaining after drying and firing as described above, the finally obtained product has high density, high strength and high reliability compared to the conventional one. .

The types of powders of ceramics, metals, etc. to which the molding method of the present invention is applied are not particularly limited. For example, as ceramic powder,
Powders such as alumina, silicon nitride, silicon carbide, zirconia, and sialon can be used. Also, if necessary, a dispersant,
Those to which additives such as an antifoaming agent and a surfactant are added, and those to which various auxiliaries are added in order to improve the characteristics of the sintered body of the powder can be used.

[0015]

EXAMPLES Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Examples and Comparative Examples) Seven types of starch as shown in Table 1 below were used, and alumina (average particle diameter of 0.1%) was used.
5 μm) 60 vol%, water and dispersant 35 vol%, starch 5
vol% was mixed with a stirrer to obtain a slurry. After the obtained slurry was defoamed, it was poured into a 500 cc polyethylene container and capped. This was placed in a hot water bath at 70 ° C. and left for 6 hours to harden the slurry. After the thus obtained cured product was taken out of the polyethylene container, the moisture was dried and fired at 1600 ° C. in a firing furnace. The density of the obtained sintered body was determined by an underwater Archimedes method. Further, a bending test piece was cut out from the sintered body and the bending strength was measured (the measuring method was in accordance with JIS R1610). The results are as shown in Table 1. In Examples 1 and 2 using fine starch having an average particle diameter of 3 μm or less, final results were smaller than Comparative Examples using a conventional starch having a large average particle diameter. The density and strength of the obtained sintered body were high.

[0017]

[Table 1]

[0018]

As described above, when gel casting is performed using the starch of the present invention, after the obtained molded body is dried and calcined, the bubble-like particles remaining in the portion where the starch particles are present are obtained. Defects can be reduced. And
As a result, it is possible to obtain a product having higher density, higher strength and higher reliability than before.

Claims (3)

[Claims] 1. A starch which is dispersed in cold water and gels by heating, wherein the starch has an average particle size of 3 μm or less. 2. A molding method for molding a powder into a predetermined shape by pouring a slurry in which the powder is dispersed in water into a molding die and curing the slurry, dispersing the powder into cold water, and heating the gel by heating. Molding method, wherein starch having an average particle diameter of 3 μm or less is added. 3. The molding method according to claim 2, wherein the average particle size of the starch is 1 μm or less.