JPS61122152A - Ceramic composition for injection molding - 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 (Field of Industrial Application) The present invention relates to a ceramic composition for injection molding, and more particularly to a ceramic composition for injection molding into a product of a desired shape prior to sintering ceramic powder. The present invention relates to a suitable ceramic composition for injection molding.

(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 product is heated to a temperature higher than 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 with high strength can be obtained.

Generally, it is known that when the ceramic powder is fine and has a large specific surface area, high-strength sintered crystals can be obtained.
There is a tendency to Therefore, there are problems in that flow marks, weld lines, and internal defects often appear on injection molded products.

On the other hand, when degreasing injection molded products, depending on the type of organic material and degreasing conditions, the molded product may become deformed or swell, cracks may occur in the molded product, or even the surface of the molded product may peel off. This results in a poor yield of molded products.

Acrylic resin (Japanese Unexamined Patent Publication No. 58-99171) is an organic material used for injection molding of ceramic powder.
, combination of ethylene-vinyl acetate copolymer, paraffin and higher fatty acid diester (JP-A-58-135173
Publication No.) etc. are known.

(Problems to be Solved by the Invention) Ceramic compositions containing an acrylic resin as an organic material have very good lipophilicity in molded products, but do not have sufficient fluidity during injection molding.

Ceramic compositions containing ethylene-vinyl acetate copolymer, paraffin, and higher fatty acid diester as organic materials have good fluidity during injection molding, but may cause cracks and blisters in the molded product during degreasing. Problems such as deformation of the product are likely to occur, and in order to obtain a good degreased molded product, it is necessary to heat the product at a very low temperature increase rate for a long time.

(Means for Solving the Problems) The present inventor has proposed a method that has good fluidity and dimensional stability during injection molding, and also prevents swelling or deformation of the molded product when degreasing the injection molded product. As a result of research aimed at developing an injection molding composition that does not cause cracks in molded products, it was discovered that the above objective could be achieved by using a specific amount of a specific compound as an organic material, and the present invention. completed.

According to the present invention, the ceramic powder is composed of 45 to 65% by volume and the organic material is 55 to 35% by volume, and the organic material has a composition of 5 to 50% by weight of ethylene-vinyl acetate copolymer and 20 to 70% by weight of acrylic resin. %, 10-40% by weight wax, and 3-18% by weight plasticizer.

Specific examples of the ceramic powder in the present invention include powders of silicon nitride, silicon carbide, alumina, zirconia, sialon, and metallic silicon. The particle size of these powders (
Centrifugal sedimentation method), it is usually sufficient if the particle size is 10μ or less. but,
In the present invention, the particle size is 1μ or less or the specific surface area (
The best effect is achieved when using a powder with a BET method of 9 rr (/g or more). If necessary, the ceramic powder may be pretreated with a sintering aid or other aids to improve its physical properties. It may be blended.

As the ethylene-vinyl acetate copolymer, it is preferable to use one having a vinyl acetate content of 5 to 40% by weight.

If the vinyl acetate content is too low, the molding shrinkage rate during injection molding will increase, resulting in poor dimensional stability of the molded product. If the vinyl acetate content is too high, the shape retention during injection molding will be poor (and the strength of the injection molded product will be reduced).The ratio of ethylene-vinyl acetate copolymer in the organic material is 5 to 50%.
% by weight, preferably 15-40% by weight, more preferably 25-35% by weight. If the proportion is more than 50% by weight, bulges and cranks are likely to occur in the injection molded product during degreasing. If the above ratio is less than 5% by weight, the molded product will be distorted or cracked when it is taken out after injection molding.

Specific examples of acrylic resins include ethyl acrylate,
Examples include polymers and copolymers of acrylic esters such as propyl acrylate and butyl acrylate, and methacrylic esters such as butyl methacrylate. The number average molecular weight of acrylic resin is 10,000 to 170,000, especially 50,000 to 170,000.
It is preferably 150,000. If the number average molecular weight is less than 50,000, the strength of the injection molded product will not be sufficient, and the rate of decomposition gas generation during the gas degreasing process will increase, causing blistering and cracking of the molded product. If the number average molecular weight is greater than 170,000, fluidity during injection molding will be extremely reduced. The proportion of acrylic resin in the organic material is 20-70% by weight, preferably 22-55% by weight. If this ratio is less than 20iif%, the injection molded product is likely to bulge or crack during degreasing, and if the ratio is more than 70M%, the molded product may crack or stick to the mold during injection molding.

Waxes include mineral-based montan wax, petroleum-based paraffin wax, microcrystal wax,
Polyolefin-based synthetic waxes, modified waxes thereof, and the like may be used.

The proportion of wax in the organic material is from 10 to 40% by weight, preferably from 15 to 35% by weight. If the proportion is less than 1°N%, it is not possible to improve the fluidity during injection molding,
If the proportion is more than 40% by weight, the molded product tends to stick to the mold during injection molding.

Examples of plasticizers include phthalate esters such as diethyl phthalate, dibutyl phthalate, dioctyl phthalate. The proportion of plasticizer in organic material is 3-1
8% by weight, preferably 7-12% by weight. If the proportion of plasticizer is less than 3% by weight, the effect as a plasticizer will not appear, and 183! If it exceeds ffi%, it causes swelling during degreasing of injection molded products.

The blending ratio of ceramic powder and organic material is 45-65% by volume of ceramic powder and 35-55% by volume of organic material.
It is. If the blending ratio of the organic material is smaller than the above-mentioned lower limit, the fluidity of the composition will deteriorate, and if the blending ratio is larger than the above-mentioned upper limit, it will be difficult to blend the organic material into the ceramic powder.
No difference was observed in the gag effect either.

The compositions of the invention can contain lubricants in addition to organic materials. As the lubricant, stearic acid, zinc stearate, etc. may be used. The blending amount of the lubricant is preferably 15% by volume or less based on the total amount of the ceramic powder and the organic material.

There are no particular restrictions on the method of blending the organic material into the ceramic powder. For example, using a pressure kneader,
A method can be adopted in which ceramic powder is gradually added into the organic material heated to ~150<0>C. The resulting mixture is cooled and then pulverized using a pulverizer to obtain a ceramic injection molding composition. The ceramic injection molding composition of the present invention can be molded into a desired shape using a common plastic injection molding machine.

There are no particular restrictions on the degreasing method for removing organic materials from injection molded products, and for example, a method of raising the temperature from room temperature to about 450° C. using a hot air circulating electric furnace can be adopted. The heating rate is 50°C/hour from room temperature to 80°C, and 3 to 40°C between 80 and 450"C. There are no particular restrictions on the atmosphere during degreasing, and an air atmosphere may be used. A gas atmosphere may be used.

(Effects of the Invention) As can be seen from the results of the examples, the ceramic composition for injection molding of the present invention has good fluidity during injection molding, so it can produce molded products with good dimensional stability at low injection pressure. Furthermore, it has the excellent feature that when degreasing an injection molded product, the molded product does not swell or deform, and no cracks occur in the molded product.

(Example) Examples are shown below.

Example 1 Ethylene-vinyl acetate copolymer (manufactured by Mitsui Polychemicals,
Evaflex 210) 30% by weight, acrylic resin (Sanyo Chemical, CB-1) 40% by weight, blended wax (
An organic material consisting of 20% by weight of D793 (manufactured by Middle East Yushi) and 10% by weight of dibutyl phthalate was prepared.

54 parts by volume of silicon nitride powder (manufactured by Ube Industries, average particle size 0°2μ, specific surface area 10n?/g) containing 5-fold N-silicon mixture of ittria and alumina were added to 46 parts by volume of the above organic material, and a pressure kneader was added. The mixture was kneaded at 140° C. and 2 atm for 30 minutes. A paste was made into 5 to 6 pieces of granules. The granules are injected at a cylinder temperature of 140℃ and an injection pressure of 800kg/c.
Ra, mold temperature 4 o'c flat plate (60 x 80 mm x 4
(Tomo) was formed. The molded product had no cranks, no weld lines, and no flow marks. This flat plate was placed in a hot-air one-shield circular electric furnace and heated from room temperature to 80°C at 50"c/hour in an air atmosphere for 80 to 400"
Degreasing was carried out by raising the temperature between C and C at a rate of 4°C/hour. No blistering, cranking or surface peeling was observed in the degreased molded product.

Example 2 Implemented except that the blending ratios of ethylene-vinyl acetate copolymer, acrylic resin, compounded wax, and dibutyl phthalate-1 were changed to 29% by weight, 50% by weight, 10% by weight, and 11% by weight, respectively. Organic material was prepared as in Example 1.

Silicon nitride powder containing 5% by weight of ittria and alumina (manufactured by Nippon Denko, average particle size 1° 5μ) 54
37 parts by volume of the above organic material and 9 parts by volume of stearic acid were kneaded using a pressure kneader at 140°C and 2 atm for 30 minutes. The kneaded material was made into granules of 5 to 6H. 5 of the kneaded material
It was made into 6 pieces of granules. The granules were heated to a nozzle temperature of 140°C.
Injection molding was carried out into a square bar (127 x 12.7 x 6.4 mm) at an injection pressure of 1000 kg/cni 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 coated molded product.

Comparative Example 1 Example except that the compounded wax was not used and the proportions of the ethylene-vinyl acetate copolymer, acrylic resin, and dibutyl phthalate were changed to 28% by weight, 62% by weight, and 10% by weight, respectively. Granules were obtained in the same manner as in 2. An attempt was made to injection mold this granular material in the same manner as in Example 2, but the fluidity during injection molding was poor.
A square bar with the desired shape could not be obtained unless the injection pressure was 1200 kg/cut.

This molded article was degreased in the same manner as in Example 1. Many small racks were observed in the degreased molded product.

Claims (1)

[Claims] Ceramic powder 45-65% by volume and organic material 55-3
The composition of the organic material is 5% to 50% by weight of ethylene-vinyl acetate copolymer, and 20% to 50% by weight of acrylic resin.
70% by weight, wax 10-40% by weight and plasticizer 3-
Ceramic composition for injection molding which is 18% by weight.