JPH11322440A - Formation of ceramic powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid production of dry cracks even when a formed body has high water content and the body is large in size with large thickness and to largely decrease the drying period by forming a ceramic powder in a wet method into a body and drying the body while preventing vaporization of water from the side faces. SOLUTION: In the forming method of a ceramic powder, after a ceramic powder is compacted in a wet method, the compacted body is dried. In this method, the side faces of the compacted body are covered with a water impermeable film. In order to cover the side faces of the compacted body with a water impermeable film, a water impermeable film is only adhered or wrapped around the required part. As for the film material, any material which does not permeate water can be used, and for example, wrapping films for foods and vinyl tapes can be used. As for the ceramic powder, not only oxides such as alumina and zirconia but a nonoxide material such as silicon nitride and silicon carbide can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming ceramic powder, and more particularly to a method for forming ceramic powder with emphasis on drying.

[0002]

2. Description of the Related Art Conventionally, a molded article formed by wet molding contains a large amount of moisture immediately after molding, and therefore, when it is dried, it is rapidly dried and a dry crack is generated. For this reason, the compact was placed in an apparatus such as a thermo-hygrostat, and the temperature and humidity of the drying atmosphere were controlled to control the drying speed and dry.

[0003]

However, in this drying, when the moisture in the molded article becomes high in moisture content, or when the molded article becomes thick or large in size or size, dry cracks are likely to occur. Therefore, it was necessary to further reduce the drying speed and dry. Therefore, there is a problem that the period required for drying is significantly increased.

[0004] The present invention has been made in view of the problems of the above-described method for forming ceramic powder, and has as its object to dry a molded product having high water content or a thick or large molded product. It is an object of the present invention to provide a method for forming a ceramic powder which can be dried without any problem without increasing the time required for the ceramic powder.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object. As a result, if drying is performed while preventing moisture from evaporating from the side surface of the molded body, the drying period is not extended. The present inventors have also found that a molded article free of dry cracks can be obtained, and have completed the present invention.

That is, the present invention relates to a method for forming a ceramic powder, comprising drying the formed body after wet-forming the ceramic powder, wherein the drying method covers the side surface of the formed body with an impermeable film. The present invention provides a method for forming a ceramic powder, characterized in that the method is a drying method. This will be described in more detail below.

As described above, as a method for molding ceramic powder, a method for drying a ceramic powder is a method in which a molded body is dried by covering the side surface with a water-impermeable film. Drying of the molded body
As shown in FIGS. 2, 4 and 6, by covering the side surface of the molded body with an impermeable film to prevent evaporation of moisture from the side surface and drying, no cracks due to drying are generated.

[0008] The reason is that it is considered that dry cracks occur when a portion having different drying shrinkage is formed in a molded product, stress is concentrated on the portion, and a crack is generated. It is thought that when the product becomes a thick product or a large product, a portion having a different drying shrinkage tends to be formed, and cracks are more likely to occur. In the drying shrinkage, since the molded body is a three-dimensional body, the shrinkage direction is also three-dimensional, and the drying proceeds in a complicated manner, and a portion having a different drying shrinkage is easily formed. By preventing the evaporation of water from the side part, the direction of drying shrinkage becomes two-dimensional of the upper and lower surfaces, the complexity of drying is reduced, and as a result, it is difficult to form parts with different drying shrinkage, shortening the drying period. Even so, it seems that dry cracks are unlikely to occur.

In order to cover the side surface of the molded body with the water-impermeable film, for example, it is only necessary to stick or wind the water-impermeable film on the portion. As the material of the film, anything may be used as long as water does not pass through,
For example, food packaging wrap or vinyl tape may be used.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The molding method of the present invention will be described in more detail. First, as a ceramic powder, not only oxides such as alumina and zirconia but also non-oxides such as silicon nitride, sialon and silicon carbide may be used. Prepare these powders. An appropriate sintering aid may be appropriately added to these powders.

[0011] Wet molding is performed using the prepared powder. The wet molding includes casting, extrusion, injection molding, self-curing molding using a self-curing ceramic slurry, and the present invention can be applied to any molding method. In particular, among these, especially in a molded article having a high water content or a molded article having a large thickness or a large size, the effect of the present invention is particularly large because the drying shrinkage becomes larger. A water-impermeable film such as a vinyl tape is attached to or wound on the side surface of the obtained molded body, placed in a thermo-hygrostat, dried at a predetermined temperature and humidity. The dried molded body is degreased by a conventional method, and sintered in a predetermined atmosphere, firing temperature and firing time to obtain a ceramic product.

By molding the ceramic powder by the above-described method, even if the molded product has a high water content, or has a large thickness or a large size, a molded product which does not cause dry cracks without extending the drying period can be obtained. Obtainable.

[0013]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention and Comparative Examples.

Example 1 (1) Molding of Ceramic Powder 100 parts by weight of alumina powder having a purity of 99.5% and an average particle diameter of 0.6 μm, 5.5 parts by weight of an acrylic binder, and polycarbonate After adding 0.5 part by weight of an acid dispersant and 32 parts by weight of water and mixing them for 12 hours with a pot mill,
A slurry was prepared by vacuum degassing. After the obtained slurry was poured into a gypsum mold from which a molded body having the size shown in FIG. 1 was obtained, the molded body was released. The side part of the obtained molded body (FIG. 2)
Is covered with a food packaging wrap and placed in a constant temperature / humidity bath at 40 ° C.-80% RH for drying.

(2) Evaluation The weight of the molded article during drying was checked, and the period up to the end of drying was examined. As a result, the drying was completed in 10 days. The obtained molded body was visually observed to check for cracks. As a result, no crack was observed. In addition, this compact
It was degreased at a temperature of 00 ° C., sintered at a temperature of 1600 ° C. for 3 hours in the air, and the obtained sintered body was visually observed for cracks. As a result, no crack was observed.

(Example 2) After the slurry obtained in Example 1 was poured into a gypsum mold from which a molded body having the size shown in FIG. 3 was obtained, the molded body was demolded. A side surface portion (shaded portion in FIG. 4) of the obtained molded body was covered with a vinyl tape wound thereon, and it was placed in a constant temperature / humidity bath at 40 ° C.-80% RH and dried.

(2) Evaluation Evaluation was performed in the same manner as in Example 1. As a result, drying was completed in 10 days, no crack was observed in the obtained molded body, and no crack was observed in the obtained sintered body.

(Example 3) The slurry obtained in Example 1 was poured into a gypsum mold from which a molded body having the size shown in FIG. 5 was obtained, and the molded body was released. A food packaging wrap is attached and covered on the side surface (shaded portion in FIG. 6) of the obtained molded body,
It was put in a constant temperature and humidity chamber of 40 ° C.-80% RH and dried.

(2) Evaluation Evaluation was performed in the same manner as in Example 1. As a result, drying was similarly completed in 10 days, and no crack was observed in the obtained molded body, and no crack was observed in the obtained sintered body.

(Comparative Examples 1-2) For comparison, Comparative Example 1
Then, the molded body was molded in the same manner as in Example 1 except that the side portion of the molded body was not covered with the food packaging wrap, and the molded body was placed in a constant temperature and humidity chamber at 30 ° C. and 80% RH. Dry,
The obtained molded body was evaluated in the same manner as in Example 1. As a result, the drying was completed by the same drying for 10 days as in Example 1, but cracks were observed in the molded body. On the other hand, in Comparative Example 2,
Evaluation was made in the same manner as in Comparative Example 1 except that the dried product of Comparative Example 1 was placed in a constant temperature / humidity bath at 20 ° C.-95% RH and dried. As a result, no cracks were found in the molded product, but two
It took five days. This indicates that even a molded article having a high water content and a large thickness or a large thickness can be dried without a problem in a shorter period of time than in the prior art as seen in Examples 1 to 3.

[0021]

As described above, according to the molding method of the present invention, even if the molded body contains high moisture and the size of the molded body is thick and large, the drying period can be greatly reduced. The molding method can be shortened. As a result, production efficiency can be greatly improved, and ceramics can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a view showing the shape and size of a molded article.

FIG. 2 is a view showing a side surface portion of the molded body of FIG. 1;

FIG. 3 is a view showing the shape and size of a molded body.

FIG. 4 is a view showing a side surface portion of the molded body of FIG. 3;

FIG. 5 is a view showing the shape and size of a molded body.

FIG. 6 is a view showing a side surface portion of the molded body of FIG. 5;

Claims (1)

[Claims] 1. After the ceramic powder is molded by a wet method,
A method for forming a ceramic powder, comprising drying the formed body by covering a side surface portion of the formed body with a water-impermeable film. .