JPH0369858B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ceramic composition for injection molding;
More specifically, the present invention relates to a ceramic composition for injection molding suitable for injection molding a product in a desired shape prior to sintering ceramic powder.

(Prior Art) As a method for molding ceramic powder into a product of a desired shape, a method has been developed in which ceramic powder and an organic material are mixed, the resulting mixture is heated and fluidized, and injection molded. The injection molded article is then heated above the decomposition temperature of the organic material to decompose and remove the contained organic material. This process is called degreasing. By subjecting the degreased molded product to main firing, a sintered molded product having high strength can be obtained.

Generally, it is known that when ceramic powder is fine and has a large specific surface area, a sintered product with high strength can be obtained. Liquidity tends to decrease. Therefore, there are problems in that it is not possible to obtain a blend of ceramic powder and organic material with a large content of ceramic powder, and that injection molded products often have flow marks, weld lines, and internal defects. be.

On the other hand, when degreasing an injection molded product, depending on the type of organic material, the amount of organic material filled into the ceramic, or the degreasing conditions, the molded product may become deformed or swell, cracks may occur in the molded product, or even molding may occur. The surface of the product may peel off, resulting in a poor yield of molded products.

Acrylic resin (Japanese Unexamined Patent Publication No. 58-99171) is known as an organic material used for injection molding of ceramic powder. Additionally, there is a method of blending a silane-based coupling agent or a titanium-based coupling agent with an organic material (Japanese Patent Publication No. 59-41949), and a method of blending a surfactant (Japanese Patent Application Laid-open No. 59-35058).
is publicly known.

(Problems to be Solved by the Invention) Generally, when ceramic powder and organic material are mixed, it is not only extremely difficult to fill the ceramic powder to a high level, but also uniformly, due to poor wettability between the ceramic powder and the organic material. It is also difficult to disperse the When a molded article is obtained using such a non-uniform injection molding composition, there is a drawback that many cracks and pores are generated during the degreasing and sintering steps.

It has been proposed to improve the wettability with ceramic powder by adding silane coupling agents, titanium coupling agents, or surfactants to organic materials, but no significant effect has been found, especially for materials with large specific surface areas. Almost no effect is observed on ceramic powder.

(Means for Solving the Problems) The present inventor has discovered that even if a high proportion of ceramic powder is blended into an organic material, it can be easily kneaded, has good fluidity and dimensional stability during injection molding, and Research was conducted with the aim of developing a ceramic composition for injection molding that does not swell or deform and does not cause cracks in the molded product when degreasing the molded product. As a result, the inventors discovered that the above object could be achieved by using an organic material and an aluminum chelate compound in combination, and completed the present invention.

According to the invention, 45-65% by volume of ceramic powder, 25-65% by volume of organic material selected from resins and waxes.
55% by volume, and aluminum chelate compound 0.1
An injection moldable ceramic composition is provided comprising ˜10% by volume.

Specific examples of the ceramic powder in the present invention include powders of silicon nitride, silicon carbide, alumina, zirconia, sialon, cordierite, and silicon metal. The particle size of these powders (centrifugal sedimentation method) should normally be 10 μm or less. However, in the present invention, the best effect is achieved when powders with a particle size of less than 1 micron or a specific surface area (BET method) of more than 9 m ² /g are used. If necessary, a sintering aid or other aids for improving physical properties may be mixed in advance with the ceramic powder.

Specific examples of the resin include acrylic resin, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyethylene, polypropylene, and polystyrene. Examples of acrylic resins include polymers and copolymers of acrylic esters such as ethyl acrylate, propyl acrylate, and butyl acrylate, and methacrylic esters such as butyl methacrylate.

As the wax, mineral-based montan wax, petroleum-based paraffin wax, microcrystalline wax, polyolefin-based synthetic wax, wax modified from these waxes, etc. can be used.

The resin and wax can be used alone or in combination.

The amount of organic material used is 25-55% by volume, preferably
It is 30-50% by volume. If the amount of organic material used is too small, fluidity cannot be imparted to the ceramic powder, and if the amount used is too large, the molded product is likely to swell or crack during degreasing.

Specific examples of aluminum chelate compounds include alkyl acetoacetate aluminum diisopropylate, aluminum tris(acetylacetonate), and aluminum monoacetylacetonate bis(ethylacetoacetate).

The amount of aluminum chelate compound used is 0.1~
10% by volume, preferably 1-6% by volume. The aluminum chelate compound improves the wettability between the ceramic powder and the organic material. If the amount used is less than the above range, it is not only difficult to knead a compound containing a high degree of ceramic powder, but even if it can be kneaded, it will not exhibit moldable fluidity. Even if the amount of the aluminum chelate compound used exceeds the above range, the kneading properties of the compound with a high content of ceramic powder will not be further improved, and some cavities caused by the aluminum chelate compound will be formed during degreasing of injection molded products. This causes swelling and swelling.

The composition of the present invention may contain a lubricant or a plasticizer in addition to the above-mentioned components. As the lubricant, stearic acid, zinc stearate, etc. may be used. The amount of lubricant to be blended is preferably 15% by volume or less based on the composition. Examples of plasticizers include phthalate esters such as diethyl phthalate, dibutyl phthalate, dioctyl phthalate. The amount of plasticizer used is preferably 10% by volume or less based on the composition. If the amount of plasticizer used is greater than the above amount, it will cause blistering during degreasing of the injection molded product.

There are no particular restrictions on the method of mixing the ceramic powder, organic material, and aluminum chelate compound; for example, using a pressure kneader,
A method of gradually adding ceramic powder and an aluminum chelate compound into an organic material heated to 150°C. After mixing an organic solvent solution of an aluminum chelate compound and ceramic powder, the organic solvent is evaporated and removed, and then pressurized together with the organic material. A method such as kneading with a kneader can be adopted. Specific examples of the organic solvent include n-hexane, butanol, benzene, toluene, xylene, and ethyl acetate.

The resulting mixture is cooled and then pulverized using a pulverizer to obtain a composition for ceramic injection molding. The ceramic injection molding composition of the present invention can be molded into a desired shape using a conventional plastic injection molding machine.

There are no particular restrictions on the degreasing method for removing organic materials and aluminum chelate compounds from injection molded products, and for example, a method of raising the temperature from room temperature to about 450° C. using a hot air circulation electric furnace can be adopted. The heating rate is 50 from room temperature to 80℃.
The rate is preferably 3 to 6°C/hour between 80 and 450°C. There is no particular restriction on the atmosphere during degreasing, and it may be an air atmosphere or an inert gas atmosphere.

(Effects of the Invention) As can be seen from the results of the Examples, the ceramic composition for injection molding of the present invention allows a compound containing a high proportion of ceramic powder to be kneaded in a short period of time. Furthermore, since the ceramic composition for injection molding of the present invention has good fluidity during injection molding, it is possible to obtain molded products with good dimensional stability at low injection pressure. It has the excellent characteristics that the molded product does not swell or deform, and no cracks occur in the molded product.

(Example) Examples are shown below. In the following, "%" indicates "capacity %" unless otherwise specified.

Example 1 Silicon nitride powder containing 5% by weight of ittria and alumina (manufactured by Ube Industries, average particle size
0.15μ, specific surface area 13m ² /g) 55%, ethylene-vinyl acetate copolymer (Mitsui Polychemicals, Evaflex 210) 11%, acrylic resin (Sanyo Chemicals, CB-1) 13.5%, compounded wax ( Chukyo Yushi Co., Ltd., D-793) 6.5%, dibutyl phthalate 3.5%,
A formulation was prepared consisting of 8% stearic acid and 2.5% aluminum chelate compound (alkylacetoacetate aluminum diisopropylate: Prene Act AL-M, manufactured by Kawaken Fine Chemicals).

The above compound was mixed in a pressure kneader at 140℃ and 2 atm.
Kneaded for 20 minutes. The kneaded material was made into particles of 5 to 6 mm. Granules, cylinder temperature 140℃, injection pressure
^Flat plate (60mm x 80mm x
4 mm) was molded. The molded product had no cracks, no weld lines, and no flow marks. This flat plate was placed in a hot air circulation electric furnace and heated from room temperature to 80°C at a rate of 50°C/hour in an air atmosphere.
Degreasing was carried out by increasing the temperature between 80 and 400°C at a rate of 4°C/hour.
No blistering, cracking, or surface peeling was observed in the degreased molded product.

Example 2 Silicon nitride powder containing 5% by weight of ittria and alumina (manufactured by Nippon Denko, average particle size
1.5μ) 60%, ethylene-vinyl acetate copolymer 9.5
%, acrylic resin (Sanyo Chemical, CB-1)
17.5%, dibutyl phthalate 3%, stearic acid 8% and aluminum chelate compound (alkyl acetoacetate aluminum diisopropylate: manufactured by Kawaken Fine Chemical, Prene Act AL)
-M) A formulation consisting of 3% was prepared.

This mixture was mixed in a pressure kneader at 140℃ and 2 atm.
Kneaded for 30 minutes. Make the kneaded material into granules of 5 to 6 mm,
A square bar (127 x 12.7 x 6.4 mm) was injection molded at a nozzle temperature of 160°C, an injection pressure of 1000 Kg/cm ² and a mold temperature of 35°C.

This molded article was degreased in the same manner as in Example 1. No blistering, cracking, or surface peeling was observed in the degreased molded product.

Example 3 Silicon nitride powder containing 5% by weight of ittria and alumina (manufactured by Ube Industries, average particle size
0.15μ, specific surface area 13m ² /g) 55%, polystyrene (Asahi Kasei, Styron 470) 20%, atactic polypropylene (Chitsuso Petrochemicals, Vistac L) 10%, polyethylene (Ube Industries, J-
3524), 4% stearic acid, 4% dibutyl phthalate, and 3% aluminum chelate compound (alkyl acetoacetate aluminum diisopropylate: Kawaken Fine Chemical Co., Ltd., Prene Act AL-M), Granules were obtained in the same manner as in Example 1. The granules were heated at a cylinder temperature of 160℃ and an injection pressure of 1000℃.
Kg/cm ² , flat plate (60×80×4mm) at mold temperature 160℃
It was molded into.

This molded product was placed in a hot air circulation electric furnace and heated from room temperature to 80℃ for 50 minutes in a nitrogen gas atmosphere.
Degreasing was carried out by increasing the temperature between 80 and 500°C at a rate of 4°C/hour. No blisters, cracks, or cavities were observed in the degreased molded product.

Comparative Example 1 Silicon nitride powder containing 5% by weight of ittria and alumina (manufactured by Nippon Denko, average particle size
1.5μ) 60%, ethylene-vinyl acetate copolymer 10.3
%, acrylic resin (Sanyo Chemical, CB-1)
A formulation consisting of 18.9% dibutyl phthalate, 3.2% dibutyl phthalate and 7.6% stearic acid was prepared.

This formulation was kneaded as in Example 2. However, in the obtained kneaded product, the ceramic powder and the organic material did not get wet and did not become dry and sticky. Further, even when the kneading temperature was set to 160°C, a good kneaded product could not be obtained.

Claims (1)

[Claims] 1. A ceramic composition for injection molding comprising 45-65% by volume of ceramic powder, 25-55% by volume of an organic material selected from resins and waxes, and 0.1-10% by volume of an aluminum chelate compound.