JPH0331660B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) 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 produce ceramic molded bodies, and among them, press molding is generally widely used. For example, ceramic molded bodies are 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 resulting 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 conventional example is as described in "Binder for Ceramics Molding" (Management Development Center Publishing Department). (Problems to be solved by the invention) However, in the conventional method as described above, water-soluble PVA is used as a binder, so when the aqueous slurry is granulated and dried, a PVA layer is formed on the surface of the granules due to migration. After 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 spherical granules because cavities occurred at the scattered locations. 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. In addition, the press pressure transmission ability was extremely poor, and the density and strength of the ceramic molded bodies varied widely, making it difficult to efficiently obtain a good product. Furthermore, when a PVA layer is formed on the surface of the granules due to migration, the granules become extremely hard and difficult to crush, requiring a large amount of press pressure during molding, leading to problems such as shortening the life of the mold. Ta. Therefore, an object of the present invention is to provide a method for stably and efficiently manufacturing ceramic molded bodies with high density and strength at low press pressure. (Means for Solving the Problems) As a result of intensive research to achieve the above object, the present inventors have developed 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 vinyl product is used as a binder, a binder layer will not be formed on the surface of the granules, and therefore spherical granules can be easily and stably obtained, and the obtained granules are easily crushed. The inventors have discovered that the following objectives can be achieved, and have arrived at the present invention. That is, the present invention provides (A) ceramic raw material 100
parts by weight, and (B) a partially saponified product of polyvinyl acetate with an average degree of polymerization of 50 to 2000 and an average saponification degree of 2 to 85 mol%.
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 0.2 to 10 parts by weight. Ceramic raw materials used in the present invention include, but are not necessarily limited to, oxide-based materials such as alumina, zirconia, and ferrite, and non-oxide-based materials 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
2000, with an average degree of saponification of 2 to 85 mol%.
The average degree of polymerization of partially saponified polyvinyl acetate is 50
If it is less than 2,000, the strength of the ceramic molded product obtained will be weak, while if it exceeds 2,000, the granules will be hard and difficult to crush, so a large press pressure will be required during molding. In addition, if the average saponification degree is less than 2 mol%, it will be difficult to uniformly disperse the binder in the slurry, while if it exceeds 85 mol%, it will become water-soluble and will have no clouding point below 100°C and will dry out. Since precipitation does not occur even if the temperature rises in the step, a binder layer is formed on the granule surface due to migration, making it difficult to obtain spherical, especially true spherical granules. Partially saponified polyvinyl acetate is not limited to unmodified products, but may be modified with alkyl vinyl ether, hydroxy vinyl ether, allyl acetate, amide, vinyl silane, etc., as long as the effects of the present invention are not impaired. It may be hot. Furthermore, it may be a mixture of two or more types having different average degrees of polymerization and average degrees of saponification. The present invention involves press-molding granules made of a ceramic raw material and a partially saponified product of polyvinyl acetate as described above, and such granules can be prepared, for example, as follows.
First, 100 parts by weight of ceramic raw materials and powder of partially saponified polyvinyl acetate having an average degree of polymerization of 50 to 2000, preferably 100 to 1000, and an average degree of saponification of 2 to 85 mol%, preferably 10 to 65 mol% are mixed. Mixing 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight, with water,
An aqueous slurry may be obtained by kneading with a mixer such as a ball mill or a kneader, and the obtained aqueous slurry may be granulated and dried using a spray dryer. The amount of water is not particularly limited, but from the viewpoint of slurry stability, drying speed, or drying heat amount, it is
~100 parts by weight is preferred. 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, and petriol, wax, and stearic acid. Alternatively, a lubricant such as a salt thereof may be added. When forming granules from an aqueous slurry, a binder layer is not formed on the granule surface due to migration, and spherical granules without depressions, particularly preferably true spherical granules, can be easily and stably obtained because: Perhaps the partially saponified product of polyvinyl acetate as a binder is emulsified and dispersed in the aqueous slurry, or even if it is dissolved, it has a cloud point below 100°C, so it precipitates as the temperature rises during the drying stage. This is thought to be because the degree of freedom 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), 2 parts by weight of partially saponified polyvinyl acetate with an average degree of polymerization of 180 and an average degree of saponification of 35 mol%, and 55 parts by weight of water were kneaded in a ball mill for 24 hours. An aqueous slurry was obtained. The viscosity of this slurry was 420 cps at 30°C. When this slurry was then spray-dried using a spray dryer, perfectly spherical granules without a binder layer on the surface could be obtained. These granules had good fluidity, and when molded under a press pressure of 600 kg/cm ² , the granules were completely crushed. The obtained alumina molded body had a density of 2.263 g/cm ³ and a strength of 20.9 Kg/cm ² . Examples 2 to 10 Ceramic molded bodies were prepared in the same manner as in Example 1 using various ceramic raw materials shown in Table 1 and partially saponified polyvinyl acetate in the proportions shown in Table 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 begin to move is less than 30 degrees. ×: The angle when the granules start moving is 30 degrees or more. Ease of crushing of granules ◎: When the press pressure is less than 500 kg/cm ² , the shape of the granules cannot be determined. ○: The shape of the granules cannot be determined at a press pressure of 500 to 600 Kg/cm ² . Δ: The shape of the granules cannot be distinguished when the press pressure is 600 to 800 Kg/cm ² . ×: The shape of the granules cannot be distinguished at 800 kg/
A press pressure of cm ² or more is required. Comparative Example 1 After kneading 100 parts by weight of alumina (average particle size 0.6μ) with 75 parts by weight of water in a ball mill for 22 hours, 10 parts by weight of a 20% aqueous solution of PVA with an average degree of polymerization of 600 and an average degree of saponification of 88 mol% was added. In addition, the mixture was further kneaded for 2 hours to obtain an aqueous slurry. The viscosity of this slurry is 560 cps at 30℃
It was hot. When this slurry was then spray-dried using a spray dryer, a binder layer was completely formed on the surface, resulting in granules with very many depressions. The granules were hard, and when molded under a press pressure of 600 kg/cm ² , the boundaries of the granules remained intact. In addition, the density of the obtained alumina molded body was 2.197 g/
cm ³ , the strength was low at 10.2 Kg/cm ² . Comparative Example 2 100 parts by weight of alumina (average particle size 0.6μ), 2 parts by weight of partially saponified polyvinyl acetate with an average degree of polymerization of 180 and an average degree of saponification of 1 mol%, and 55 parts by weight of water were mixed in a ball mill for 24 hours. The mixture was kneaded to form an aqueous slurry. Although the viscosity of this slurry was 320 cps at 30°C, 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.
Furthermore, it was very difficult to mold these granules. Comparative Example 3 Instead of a partially saponified polyvinyl acetate with an average degree of polymerization of 180 and an average degree of saponification of 35 mol%,
A ceramic molded body was prepared in the same manner as in Example 1 except that a partially saponified polyvinyl acetate having a saponification degree of 85 mol % and an average degree of saponification of 85 mol % was used. The results are shown in Table 1. Comparative Example 4 Instead of a partially saponified polyvinyl acetate with an average degree of polymerization of 180 and an average degree of saponification of 35 mol%,
30. A ceramic molded body was prepared in the same manner as in Example 1 except that a partially saponified polyvinyl acetate having an average degree of saponification of 60 mol% was used. The results are shown in Table 1. Comparative Example 5 The same procedure was carried out except that a partially saponified polyvinyl acetate having an average degree of polymerization of 2500 and an average degree of saponification of 65 mol% was used instead of a portion of polyvinyl acetate having an average degree of polymerization of 180 and an average degree of saponification of 35 mol%. A ceramic molded body was produced in the same manner as in Example 1. The results are shown in Table 1.

【table】

[Table] (Effects of the Invention) According to the present invention, it is possible to efficiently obtain granules with good fluidity that have no binder layer on the surface, do not have depressions, and are spherical, preferably true spheres. Therefore, uneven supply of granules to the mold does not occur, and the product yield can be significantly improved. Furthermore, 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, and it is very effective industrially.

Claims (1)

[Claims] 1. An aqueous slurry containing (A) 100 parts by weight of ceramic raw materials and (B) 0.2 to 10 parts by weight of partially saponified polyvinyl acetate having an average degree of polymerization of 50 to 2000 and an average degree of saponification of 2 to 85 mol% is prepared. A method for producing a ceramic molded body, which comprises press-molding granules obtained by drying the granules.