JPS62182150A - Manufacture of ceramic formed body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method of manufacturing a ceramic molded body by press molding.

(Prior Art) Conventionally, various methods have been employed to manufacture ceramic molded bodies, and among them, press molding is the most common and widely used method. For example, a ceramic molded body is manufactured by preparing an aqueous slurry from ceramic raw materials, a binder, and water, spray-drying this with a spray dryer to obtain granules, and press-molding the obtained granules. Generally, water-soluble polyvinyl alcohol (hereinafter abbreviated as PVA) is used. The shape and performance of the granules obtained by granulating and drying the aqueous slurry have a great influence on the workability in the pressing process, and influence the performance and product yield of the ceramic molded body. The above-mentioned conventional technology is as described in "Binder for Ceramic Molding" (Management Development Center Publishing Department).

(Problems to be solved by the invention) However, in the conventional method as described above, water-soluble PV
Since A is used as a binder, when the aqueous slurry is granulated and dried, P is deposited on the granule surface due to migration.
After the VA layer was formed and such a PVA layer was formed, water was scattered from one place in this layer and drying was completed. the result.

It was very difficult to stably obtain single spherical granules because cavities occurred from the scattered areas.

Here, when the granulated granules cave in and lose their spherical shape, the fluidity of the granules deteriorates, resulting in a problem that stable supply of the granules to the mold during press molding becomes impossible. Furthermore, there were problems in that the ability to transmit press pressure was extremely poor, the density and strength of the ceramic molded bodies varied widely, and it was difficult to efficiently obtain a good product.

moreover.

When a PVA layer is formed on the granule surface due to migration, the granule becomes very hard and difficult to crush.
There was a problem in that large press pressure was required during molding, which shortened the life of the mold. Therefore, one object of the present invention is to provide a method for stably and efficiently producing a ceramic molded body having high density and strength at low press pressure.

(Means for Solving the Problems) As a result of extensive research in order to achieve the above object, the present inventors have developed a polyacetic acid with an average degree of polymerization of 50 to 2000° and an average degree of saponification of 2 to 85 mol%. If a partially saponified product of vinyl chloride is used as a binder, a single layer of binder will not be formed on the surface of the granules, and therefore spherical granules can be obtained easily and stably. The inventors have discovered that the above objects can be achieved and have arrived at the present invention.

That is, the present invention comprises (A) 100 parts by weight of a ceramic raw material, and (B) an average degree of polymerization of 50 to 2,000. Partially saponified polyvinyl acetate with an average saponification degree of 2 to 85 mol% 0.
The gist of the present invention is a method for producing a ceramic molded body, which comprises press-molding granules obtained by granulating and drying an aqueous slurry containing 2 to 10 parts by weight.

Ceramic raw materials used in the present invention include:

Examples include, but are not limited to, oxide A such as alumina, zirconia, and ferrite, and non-oxides such as silicon carbide.

The partially saponified polyvinyl acetate used as a binder in the present invention has an average degree of polymerization of 50 to 2,000. It has an average saponification degree of 2 to 85 mol%. If the average degree of polymerization of the partially saponified polyvinyl acetate product is less than 50, the strength of the resulting ceramic molded body will be low;
If it exceeds 00, the granules are hard (hard to crush, so large press pressure is required during molding.If the average degree of saponification is less than 2 mol%, it will be difficult to uniformly disperse the binder in the slurry, On the other hand, if it exceeds 85 mol%, it will become water-soluble and will not have a cloud point below 100°C, and will not precipitate even if the temperature rises in the drying stage, so a single layer of binder will be formed on the surface of the granules due to migration, resulting in two-spherical, especially true It becomes difficult to obtain spherical granules.

The partially saponified product of polyvinyl acetate is not limited to unmodified products, but may be used within the range that does not impair the effects of the present invention.
For example, alkyl vinyl ether.

Hydroxy vinyl ether, allyl acetate, amide.

It may also be a material modified with vinyl silane or the like.

In addition, two types of materials with different average degrees of polymerization and average saponification degrees, etc.
It may be a mixture of more than one species.

In the present invention, granules made of a ceramic raw material and a partially saponified product of polyvinyl acetate as described above are press-molded, and such granules can be prepared, for example, as follows.

First, 100 parts by weight of ceramic raw materials and an average polymerization degree of 5
0~2000. Preferably 100-1000. A powder of a partially saponified polyvinyl acetate having an average saponification degree of 2 to 85 mol%, preferably 10 to 65 mol%, is mixed with 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and water. They may be mixed and kneaded using a mixer such as a ball mill or a kneader to obtain an aqueous slurry, and the resulting aqueous slurry may be granulated and dried using a spray dryer. The amount of water is not particularly limited.

From the viewpoint of slurry stability, drying speed, or drying heat amount, 15 to 100 parts by weight is preferable. Partially saponified polyvinyl acetate may be emulsified and dispersed in advance to form a solution. In addition, the granules used in the present invention may optionally contain dispersants such as ammonium polycarboxylate, polyacrylic acid oligomers or ammonium salts thereof, plasticizers such as glycerin, glycols, petriol, and wax.

A lubricant such as stearic acid or a salt thereof may be added.

When forming granules from an aqueous slurry, a single layer of binder is not formed on the granule surface due to migration, and the reason why spherical granules without depressions, particularly preferably pearl granules, can be easily and stably obtained is probably due to the binder. Even if the partially saponified product of polyvinyl acetate is emulsified and dispersed in the aqueous slurry or dissolved,
This is thought to be because the binder has a cloud point below 0° C., so it precipitates as the temperature rises during the drying stage, and the flexibility of the binder is lost and migration does not occur.

(Examples) Hereinafter, the present invention will be explained in more detail by giving examples.

Example 1 100 parts by weight of alumina (average particle size 0.6μ) was added with an average degree of polymerization of 180. 2 parts by weight of a partially saponified polyvinyl acetate having an average saponification degree of 35 mol % and 55 parts by weight of water were kneaded in a ball mill for 24 hours to obtain an aqueous slurry. The viscosity of this slurry was 420 cps at 30°C. When this slurry was then spray-dried using a spray dryer, it was possible to obtain granules that were perfectly spherical and had no binder layer on the surface. The granules had good fluidity (when molded at a press pressure of 600 kg/-, the granules were completely crushed. The density of the obtained alumina molded body was 2263 g/cJ, and the strength was 20
．． It was 9 kg/cj.

Examples 2 to 10 Various ceramic raw materials shown in Table 1 and partially saponified products of polyvinyl acetate were used in the proportions shown in Table 1.

A ceramic molded body was produced in the same manner as in Example 1. The results are shown in Table 1.

Here, the fluidity of the granules was evaluated by placing the granules on cardboard and tilting the paper, and measuring the angle at which the granules started to move.

Furthermore, the crushability of the granules was evaluated by the press pressure required to make the shape of the granules indistinguishable on the surface of the molded product when press-molded. The evaluation criteria are as follows.

evaluation Granule fluidity ○: The angle when the granules start moving is less than 30 degrees.

×: The angle when the granules start moving is 30 degrees or more.

Ease of crushing of granules◎If the nibless pressure is less than 500 kg/cnT, the shape of the granules cannot be determined.

When the O-nibble pressure is 500 to 600 kg/c, the shape of the granules cannot be determined.

△When the nibless pressure is 600 to 800 kg/crA, the shape of the granules cannot be determined.

×: It takes 800 kg for the shape of the granules to become indiscernible.
A press pressure of ca1 or higher is required.

Comparative Example 1 After kneading 100 parts by weight of alumina (average particle size 0.6μ) and 75 parts by weight of water in a ball mill for 22 hours, the average degree of polymerization was 6.
00. 10 parts by weight of a 20% aqueous solution of PVA having an average degree of saponification of 88 mol % was added, and the mixture was further kneaded for 2 hours to obtain an aqueous slurry. The viscosity of this slurry was 560 cps at 30°C. This slurry was then spray-dried using a spray dryer.

A single layer of binder was completely formed on the surface, resulting in granules with many depressions. This granule is hard <, 600 kg/ci
When molded with a press pressure of □, the boundaries of the granules remained completely. In addition, the density of the obtained alumina molded body was 2197
In terms of g/cJ, the strength was 10.2 kg/a (which was also low).

Comparative Example 2 Alumina (average particle size: 0.6 μm), 100-layer small size, average degree of polymerization: 180. 2 parts by weight of partially saponified polyvinyl acetate having an average degree of saponification of 1 mol % and 55 parts by weight of water were kneaded in a ball mill for 24 hours to obtain an aqueous slurry. This slurry had a viscosity of 320 cps at 30°C, but a large amount of undispersed binder remained. When this slurry was then spray-dried using a spray dryer, the shape of the granules was poor and a large amount of fine powder was generated. Also, it was very difficult to mold these granules.

Comparative Example 3 Average degree of polymerization 180. Instead of a partially saponified polyvinyl acetate with an average saponification degree of 35 mol%, an average polymerization degree of 180. A ceramic molded body was produced in the same manner as in Example 1 except that a partially saponified polyvinyl acetate having an average degree of saponification of 85 mol% was used. The results are shown in Table 1.

Comparative Example 4 Average degree of polymerization 180. Instead of a partially saponified polyvinyl acetate having an average saponification degree of 35 mol%, an average degree of polymerization of 30. A ceramic molded body was produced in the same manner as in Example 1 except that a partially saponified polyvinyl acetate having an average saponification degree of 60 mol% was used. The results are shown in Table 1.

Comparative Example 5 Average degree of polymerization 180. In place of the polyvinyl acetate portion with an average saponification degree of 35 mol%, an average polymerization degree of 2500. A ceramic molded body was produced in the same manner as in Example 1 except that a partially saponified polyvinyl acetate having an average saponification degree of 65 mol% was used. The results are shown in Table 1.

(Effect of the invention) According to the present invention, there is no binder layer on one surface.

It is possible to efficiently obtain granules with good fluidity that are free from depression and are spherical, preferably true spherical.

Therefore, uneven supply of granules to the mold does not occur, and the yield of products can be significantly improved. Also.

Since the granules are easily crushed, a high-density and high-strength ceramic molded body can be obtained even when molded at low press pressure.

Therefore, the life of the mold is extended.

It is industrially very effective.

Claims (1)

[Claims] (1) (A) 100 parts by weight of ceramic raw materials; (B) average degree of polymerization 50 to 2000, average degree of saponification 2 to 8
5 mol% polyvinyl acetate partially saponified product 0.2-10
1. A method for producing a ceramic molded body, comprising press-molding granules obtained by granulating and drying an aqueous slurry containing parts by weight.