JPH0571536B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an injection molding binder that can significantly shorten the degreasing process in the process of obtaining a sintered body using inorganic powder as a raw material.

[Conventional technology]

(Background) Conventional inorganic powder injection molding binders include, for example, wax-based binders and resin-based binders. (Problems with the prior art) However, such conventional wax-based or resin-based binders have the following drawbacks: (1) With wax-based binders, the degreasing process can be shortened, making it difficult to mold large molded objects. (2) Resin-based binder The molded product has sufficient strength and is easy to handle, but blisters and cracks tend to occur during degreasing, so it is difficult to obtain a good product unless the degreasing is done gradually over a long period of time, and it is also difficult to obtain large molded products. There was a problem that both injection moldability and degreasability could not be satisfied.

[Problem to be solved by the invention]

Therefore, an object of the present invention is to provide a binder for inorganic powder injection molding that satisfies both moldability and degreasability.

[Means to solve the problem]

(Principle) Therefore, as a result of considering ways to solve both of the above problems, the present inventor found that (1) as a measure to improve injection moldability, the melting point range of the binder is blunted to improve fluidity. (2) In order to prevent blisters and cracks from occurring during the degreasing process, the polymer chains are not simply broken randomly at the decomposition temperature, but are broken gradually from the ends. It was found that it is desirable to select a resin that can be cut in a specific manner. Therefore, as a result of intensive research based on this knowledge, we have arrived at the following invention. (Summary) That is, the present invention provides (a) a polyhydroxy compound having an average molecular weight of 1000 or more obtained by addition-polymerizing an alkylene oxide to an organic compound having two or more active hydrogen groups, and a polyhydric carboxylic acid or its anhydride or lower alkyl An inorganic powder injection molding binder characterized by containing a high molecular weight compound having an average molecular weight of 20,000 or more obtained by reacting with an ester, and (b) a resin acid or a wax. Below, we will explain the main items related to the outbreak. (High molecular weight compound) Examples of organic compounds having two or more active hydrogen groups used in the production of the binder of the present invention include ethylene glycol, propylene glycol, glycerin, polyethylene glycol, polypropylene glycol, ethanolamines, ethyleneamines, etc. can be mentioned. Examples of the alkylene oxide to be added to the above organic compound having two or more active hydrogen groups to form a polyhydroxy compound include ethylene oxide, propylene oxide, butylene oxide, etc., but ethylene oxide alone or other Preferably, ethylene oxide is added to alkylene oxide. The resulting polyhydroxy compound must have a molecular weight of 1000 or more. Examples of the polyhydric carboxylic acid, anhydride thereof, or lower alkyl ester thereof to be combined with the above polyhydroxy compound include sebacic acid,
Examples include phthalic acid, isophthalic acid, terephthalic acid, alkyl esters thereof such as dimethyl ester and diethyl ester, and acid anhydrides such as phthalic anhydride and pyromellitic acid. The high molecular weight compound obtained by the esterification reaction of a polyhydroxy compound and a polyhydric carboxylic acid, its anhydride or its lower alkyl ester should have a molecular weight of 20,000 or more for the purpose. Incidentally,
This polycondensation reaction product mainly has ether bonds as a bonding mode, and because of its hydrophilic nature, it has excellent compatibility with inorganic powders, and when decomposed by heat, it retains its shape well, so it can be used as a binder for injection molding. It can be said that it is suitable for (Fatty acid or wax) Examples of the fatty acid include myristic acid, palmitic acid, stearic acid, behenic acid, etc., and examples of the wax include ordinary paraffin wax and ester wax. At this time, a plasticizer such as a phthalate ester may be used in combination, if necessary. (Binder) The binder of the present invention is used as a binder for injection molding as a composition obtained by melting and mixing a high molecular weight compound, a fatty acid or wax, and additives that may be added as desired using a kneader or the like. be. The blending ratio of the high molecular weight compound and fatty acid or wax is high molecular weight compound/fatty acid or wax = 50/50 to 98/2, preferably 70/30.
~95/5. The amount of the binder of the present invention to be blended with the inorganic powder is 7 to 30 parts by weight per 100 parts of the inorganic powder. (How to use) To use the binder according to the present invention, after kneading it with an inorganic powder in a kneader etc., molding it in an injection molding machine, heating the obtained molded product at a low temperature, degreasing,
The desired sintered body is produced by firing. The inorganic powders used here are mainly raw material powders of new ceramics, such as aluminum oxide, zirconium oxide, silicon oxide, titanium oxide, titanate, PZT, ferrite, silicon nitride, aluminum nitride, silicon carbide, This includes single substances such as tungsten carbide or mixtures thereof, but also includes iron powder, stainless steel powder, aluminum powder, precious metal powder, and intermetallic compounds.

[Effect]

The binder obtained according to the present invention is a high molecular weight compound mainly composed of ether bonds, and the kneaded product blended with inorganic powder has a small change in viscosity due to temperature, so the molding conditions are relatively relaxed. Also,
In the degreasing process for injection molded products, organic matter decomposes while maintaining the shape, so shape retention is good and even relatively large molded products can be degreased in a short time. In addition, since the coexisting components fatty acids and wax have excellent lubricity, they facilitate release from the mold.
Moreover, it does not adversely affect degreasing.

【Example】

Hereinafter, details of the implementation of the invention will be described with reference to Examples, but the examples are of course for illustration only and are not intended to limit or limit the idea of the invention. Example 1 In an autoclave, 4.5 kg of ethylene oxide was gradually blown into 500 g of polypropylene glycol (weight average molecular weight: 2000) in an alkaline catalyst to complete the reaction. 75 g of dimethyl terephthalate was added to this, and ester condensation polymerization was performed at 200° C. and 0.05 Torr to obtain a high molecular weight compound with a weight average molecular weight of 130,000. Obtained 1.2Kg of high molecular weight compound and stearic acid
Put 0.2Kg into a 3-capacity pressure kneader and heat at 110℃.
Partially stabilized zirconia TZ− after melting with
Gradually add 3YS (product of Tosoh Corporation) to a kneaded mass of 9.3
Got Kg. This kneaded material was formed into pellets and put into the hopper of an injection molding machine (manufactured by Japan Steel Works, mold clamping force: 28 tons), and injection molded into a 25 mm square cube at a cylinder temperature of 105°C. The obtained molded body was heated in the atmosphere for 48 hours in a fat furnace.
After final degreasing at 500°C, the fired body was fired at 1500°C in a firing furnace and was free of defects. Comparative Example 1 The type of binder in Example 1 was changed to polyethylene and stearic acid, and the cylinder temperature was changed.
A molded body was obtained by changing the temperature to 180°C. Even though the temperature was gradually increased to degrease the molded product over 96 hours in the degreasing process, cracks and blisters occurred in the molded product. Example 2 5 In an autoclave, 4.7 kg of ethylene oxide was added to 235 g of polytetramethylene glycol (weight average molecular weight 1200), and then 45 g of pyromellitic anhydride was added and kneaded to obtain a polymer with a weight average molecular weight of 200,000. 1.0Kg of molecular weight compound was collected and put into a pressure kneader together with 0.1Kg of solid paraffin (melting point 61℃) and 0.1Kg of dioctyl phthalate, and after melting at 115℃, 13Kg of stainless steel powder (average particle size 12.6μm) was gradually added. A kneaded product was obtained. This kneaded product was injection molded under the same conditions as in Example 1 to obtain a 25 mm square cube. The obtained molded body was degreased and then fired in a vacuum to obtain a fired body completely free of defects.

【Effect of the invention】

As explained above, the present invention can provide a binder for inorganic powder injection molding that satisfies both moldability and degreasing properties, and by using the obtained binder, it is possible to manufacture new ceramics and metal sintered bodies. It can contribute to the development of industry.

Claims (1)

[Claims] 1 (a) A polyhydroxy compound with an average molecular weight of 1000 or more obtained by addition polymerizing an alkylene oxide to an organic compound having two or more active hydrogen groups, and a polyhydric carboxylic acid or its anhydride or lower alkyl ester. 1. A binder for inorganic powder injection molding, comprising a high molecular weight compound having an average molecular weight of 20,000 or more obtained by reacting the following: and (b) a fatty acid or wax. 2. The binder according to claim 1, wherein the alkylene oxide is ethylene oxide.