JPH0238502A - Metal powder composition for injection molding and manufacture of metal sintered member - Google Patents

Abstract

PURPOSE:To obtain complicate-shaped high density metal sintered member by using a composition blending binder, which uses polystyrene, polybutyl methacrylate and ethylene vinyl acetate copolymer as essential components, to metal powder. CONSTITUTION:The organic binder is blended at 5-15pts.wt. to 100pts.wt. of the metal powder to prepare the metal powder composition for injection molding. The organic binder is used with 5-30wt.% polystyrene, 5-35% polybutyl methacrylate and 5-25% ethylene vinyl acetate copolymer as the essential components. This composition is heated and kneaded to make pellet, and the injection molding is executed. After removing the binder by heating the molded material, the sintering is executed. By this method, high density metal sintered member having complicate-shape is industrially manufactured.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a metal powder composition for injection molding and a method for producing a metal sintered member using the same. "Prior Art" Generally, the field of ceramics. Then, by adding plasticity to a mixture of raw material powder and an organic binder, and obtaining a green molded body using an injection molding method, the binder is removed and the green molded body is fired, thereby creating products with complex shapes that cannot be molded by press molding etc. It is well known that it can be mass-produced with good dimensional accuracy.

On the other hand, metal sintered parts have long been manufactured using the so-called powder metallurgy method, in which raw material powder is mixed with a small amount of organic matter, molded using a press molding method, and then sintered. In order to mass-produce members with complex shapes, attempts have been made to adapt the injection molding method used for producing the above-mentioned ceramic products to the production of metal sintered members.

``Problem to be solved by the invention'' In the production of metal sintered parts using the injection molding method, the average particle size of the raw material powder for ceramics is as fine as 3 gm or less;・The raw material powder used for metal sintered parts often has a higher specific gravity than general ceramic powder, such as alumina. ・General ceramic powder, such as oxide-based powder such as alumina. Compared to ceramics, it has poor wettability with binders, so even if you try to manufacture it under the same conditions as when manufacturing ceramic products, you will experience poor injection moldability, insufficient strength of the green molded product, and deformation when removing the binder. Not only is it difficult to manufacture good sintered members such as ceramics, but the current situation is that even green molded bodies in the previous process cannot be manufactured satisfactorily.

The present invention has been made in view of the above-mentioned circumstances, and is an injection molding method that enables industrial production of high-density sintered metal members with complex shapes and high mass productivity. An object of the present invention is to provide a metal powder composition for use in metal powder compositions and a method for producing a metal sintered member.

"Means and Effects for Solving the Problems" The present invention provides a metal powder composition for injection molding in which 5 to 15 parts by weight of an organic binder is blended with 100 parts by weight of metal powder, wherein the organic binder is polystyrene. A metal powder composition for injection molding, characterized in that it contains as essential components 5 to 30% by weight of polybutyl methacrylate, 5 to 35% by weight of polybutyl methacrylate, and 5 to 25% by weight of ethylene vinyl acetate copolymer, and its use. This is a method for manufacturing sintered metal parts.

(Requirements constituting the means) The organic binder used in the present invention contains as an essential component a thermoplastic resin consisting of polystyrene, polybutyl methacrylate, and ethylene-vinyl acetate copolymer.

Polystyrene, polybutyl methacrylate, and ethylene vinyl acetate copolymer are all known commercially available products.
The blending ratios are such that the organic binder contains 5 to 30% by weight of polystyrene, 5 to 35% by weight of polybutyl methacrylate, and 5 to 25% by weight of ethylene vinyl acetate copolymer. It is something that

Regarding the action and blending ratio of each thermoplastic resin in the organic binder, polystyrene has an excellent binder effect on powders, strongly bonds particles together, and is itself a thermoplastic resin with very good injection moldability. A plastic resin that imparts strength to green molded bodies, is particularly effective in preventing damage to thin parts, and also provides excellent shape retention to green molded bodies, making the molded bodies easier to handle. However, if the amount is less than 5% by weight, the above effects cannot be obtained, and if it exceeds 30% by weight, the fluidity of the mixture decreases and the injection moldability is impaired. Polybutyl methacrylate, like polystyrene, is a thermoplastic resin that exhibits an excellent binder effect on powder and is very effective in imparting strength to green molded products. Polystyrene and ethylene-vinyl acetate copolymers do not substantially start thermal decomposition unless it is above 300°C, whereas polybutyl methacrylate undergoes thermal decomposition at 220 to 240°C, so in a system in which these three components coexist, The thermal decomposition temperature range of the binder is expanded, and when removing the binder by thermal decomposition, the thermal decomposition of the binder does not occur suddenly but proceeds gradually, making it very effective in preventing blisters, cracks, deformation, etc. of molded objects. However, if the amount is less than 5% by weight, the above effect cannot be obtained, and if it exceeds 35% by weight, the fluidity of the mixture decreases, injection moldability is impaired, and release from the mold becomes difficult. becomes worse.

Furthermore, ethylene vinyl acetate copolymer also shows an excellent binder effect on powder, increasing the strength of green molded products,
Adds elasticity to the molded body. Also.

A substance that not only increases the fluidity of the mixture and makes injection molding easier, but also maintains the shape of the molded product while the functional components are thermally decomposed and removed during binder removal treatment by thermal decomposition. However, if the amount is less than 5%, the above effect cannot be obtained, and if it exceeds 25%, the blistering phenomenon of the molded product becomes noticeable when removing the binder by thermal decomposition, making it difficult to remove the binder. bring about.

In addition, the organic interlayer of the present invention contains additives such as wax, plastic valve], lubricant, etc. as necessary.

These components have the effect of imparting plasticity to the mixture, improving fluidity, increasing wettability with powder, and making the monomer mixture uniform.

Waxes include paraffin wax and microcrystalline wax; plasticizers include dioctyl phthalate and cyptyl phthalate-1; lubricants include stearic acid and metal salts of stearate; and they are usually used for ceramic injection. Any material used for molding can be used.

In addition, these components are preferably used within the normal usage range, and the amounts used are not particularly limited here;
Needless to say, if used beyond common sense, the strength of the green molded product will drop significantly, and when depintering is performed by thermal decomposition, significant deformation will occur.

Next, examples of the metal powder used in the present invention include stainless steel powder, carbonyl iron powder, and the like.

The particle size (average particle size) of these particles is preferably 1 to 50 m. When the average particle size becomes smaller than 1 gm, the specific surface area of the powder increases relatively, and even if the amount of binder used is increased, it is often difficult to obtain a mixture with flow characteristics suitable for injection molding. Also, although injection molding is possible,
It is difficult to perform the subsequent binder removal step smoothly, and the molded product after binder removal becomes brittle and difficult to handle. On the other hand, in the case of coarse powder exceeding 50 pLm,
The strength of the green molded body and the heated molded body after depaintering is significantly reduced.

The metal powder composition for injection molding according to the present invention is one in which 5 to 15 parts by weight of the organic pinter is blended with 100 parts by weight of the metal powder.

If the amount of organic painter used is less than 5 parts by weight, the mixture as an injection molding material will lack fluidity and it will be difficult to mold it into the desired shape, while if it exceeds 15 parts by weight, the molded product will be The density does not decrease, shrinkage increases during firing, and dimensional accuracy is reduced, and when removing the binder by thermal decomposition, a large amount of gas is generated.
becomes extremely difficult.

A metal sintered member using the metal powder composition for injection molding according to the present invention is produced as follows.

First, the metal powder that is the composition of the present invention and the organic binder are sufficiently heated and kneaded using a kneader such as a pressure kneader to uniformly disperse the metal powder in the organic binder, and then crushed into an appropriate shape, for example, coarsely pulverized. It is made into pellets or pellets and used as an injection molding material.

Next, this material is injection molded using a known device and method commonly used in blast molding to form a molded product of a desired shape.

Thereafter, the organic binder is removed from the molded body by a method such as thermal decomposition, and the molded body is fired at an appropriate temperature and atmosphere to obtain a metal sintered member having a desired shape.

In injection molding of metal powder, it is very important to find the combination, blending ratio, and amount of organic binder that is suitable for the metal powder used.Thermoplastic resin, which is an essential component, is especially important, and its type, If the blending amount is incorrect, not only will it not be possible to uniformly disperse the metal powder in the organic binder, but also injection molding will be defective due to lack of fluidity of the molding material, and the green molded product will have a significant lack of strength, resulting in difficulty in ejecting it from the mold and waiting for the next process. This may cause damage during transportation or storage, or cracks, blisters, deformation, etc. may occur in the molded product when the binder is removed. Furthermore, if the thermal stability of the organic binder is poor, the organic binder will deteriorate within the cylinder during injection molding, resulting in poor injection.

"Example" Example 1 1.96 parts of polystyrene was added to 1 part by weight of JIS-304 stainless steel powder having an average particle size of 7.41 Lm.
parts by weight, polybutyl methacrylate]・2.52 parts by weight,
1.12 parts by weight of ethylene-hinyl acetate copolymer, 4.4 parts of paraffin wax having a melting point of 58°C as a wax
After heating and kneading 1 part by weight of dibutyl phthalate as a plasticizer at 150°C for 1 hour using a pressurizer, the mixed material is made into a pellet of about 3 x 3 x 4 mm and used as an injection molding material.

The molding temperature is 120-160°C, the injection pressure is 500-
Bolts specified in JIS B-1176 with a height of 50 mm and a maximum wall thickness of 5 mm are formed under the conditions of 1000 kg/cm2.

The temperature of the obtained molded product was raised from room temperature to 120°C over 3 hours in a N2 atmosphere, and after 120°C, the temperature was increased to 5 to 15°C, and the same temperature was maintained for 2 hours to thermally decompose and remove the organic binder. After that, vacuum baking was performed at a temperature of 1350°C for 1 hour.

The obtained sintered body was a good sintered body with a theoretical density ratio of 95% and no defects such as cracks.

Example 2 1.82 parts by weight of polystyrene, 2.08 parts by weight of polybutyl methacrylate, 1-3 parts by weight of ethylene-vinyl acetate copolymer per 100 parts by weight of carbonyl iron powder having an average particle size of 14 ILm. After heating and kneading 3.8 parts by weight of paraffin wax having a melting point of 69°C as a wax and 1 part of stearic acid as a lubricant at 150°C for 1 hour using a pressurized knee gun, bolts were screwed in the same manner as in Example 1. Shape and remove binder. This was heated to 1200°C in a reducing atmosphere.
It was sintered at a temperature of 1 hour.

The obtained sintered body was a good sintered body without defects and had a theoretical density ratio of 90%.

Example 3: 1.55 parts by weight of polystyrene, 3.15 parts by weight of polybutyl methacrylate, and 1.6 parts by weight of ethylene-vinyl acetate copolymer for 100 parts by weight of JIS Fist 316 stainless steel powder having an average particle size of 32ILm. The heating, molding, depaining, and sintering were carried out in the same manner as in Example 1, except that 5.2 parts by weight of microcrystalline wax with a melting point of 84° C. was used as the wax and 1 part by weight of dibutyl phthalate was used as the plasticizer.

The obtained sintered body was a good sintered body with a theoretical density ratio of 86% and no defects such as cracks.

Comparative example.

For 100 parts of the metal powder used in Example 1, 1.74 parts by weight of polybutyl methacrylate, 4.06 parts by weight of ethylene vinyl acetate copolymer, and 4.0 parts by weight of polyethylene wax.
2 parts by weight and 1 part by weight of steric acid in a pressurized knee gun for 14 hours.
Example 1 by heating and kneading at 0°C for 1 hour and molding temperature at 130°C.
Form a bolt similar to.

This was heated in a N2 atmosphere from room temperature to 120°C in 3 hours, and after 120°C, the temperature was increased to 45°C at a heating rate of 3°C/hour.
The temperature was raised to 0° C. and the binder was removed by holding at the same temperature for 2 hours, but during the degreasing process, significant blistering occurred and the binder could not be removed satisfactorily.

"Effects of the Invention" By using the metal powder composition for injection molding obtained according to the present invention, sintered metal parts with complex shapes and high density can be manufactured industrially by injection molding method, unlike conventional methods. This can greatly contribute to the technical field.

Patent applicant Daiichi Kogyo Seiyaku Co., Ltd.

Claims (2)

[Claims] (1) In a metal powder composition for injection molding in which 5 to 15 parts by weight of an organic binder is blended to 100 parts by weight of metal powder, the organic binders include 5 to 30 parts by weight of polystyrene and 5 to 35 parts by weight of polybutyl methacrylate. A metal powder composition for injection molding, characterized in that it contains 5 to 25% by weight of ethylene-vinyl acetate copolymer as an essential component. (2) A method for producing a metal sintered member, which comprises using the metal powder composition for injection molding according to claim 1.