JPH04201434A - Preparation of molded item made of polyimide resin - Google Patents

Abstract

PURPOSE:To get rid of occurrence of cracks on the side face of a molded item even if a high pressure is applied by coating the inner wall of a mold with a fluorinated resin when a molded item is prepd. by performing compression molding of a polyimide resin or a polyimide resin compd. consisting of a polyimide resin and a filler in a mold and thereafter calcining it. CONSTITUTION:As a polyimide resin, a compd. having mainly a polyimide structure of formula is used. Various fillers can be incorporated in the polyimide resin for providing moldability, dimensional stability, low water absorption properties, etc. As the type for molding, a polyimide resin powder is compressed in a mold wherein the inner wall is coated with a fluorinated resin to mold a compressed powder and then, it is calcined by heating. The pressure for molding the compressed powder is pref. 2,000-5,000kg/cm<2> and the calcining temp. is pref. 370-430 deg.C. The method for coating the inner wall of the mold with the fluororesin is not specifically restricted and e.g. a method wherein a commercially available 'Teflon' coating agent is applied by coating or by spraying can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a polyimide resin molded product that has high strength and does not cause cracks on the side surfaces of the molded product.

(Conventional technology) Polyimide resin is a resin with extremely excellent heat resistance, but
Its softening point is so high that normal melt molding is impossible.

Therefore, conventionally, to mold polyimide resin, a mold is filled with polyimide resin powder or a resin compound with an inorganic filler added thereto, and a pressurizing device such as a hydraulic press, pneumatic press, or mechanical press is used to mold the polyimide resin. A green compact is formed by applying pressure using a
A compression firing molding method is used in which a polyimide resin molded product is obtained by heating and firing at a high temperature of about 0°C.

[Problem to be solved by the invention]

In order to obtain a high-strength molded product by compressing and firing polyimide resin, it is necessary to apply a pressure of approximately 2000 to 5000 kg/cn. The higher the pressure, the stronger the molded product can be obtained, but above a certain pressure When pressurized to a certain degree, cracks occur on the surface of the green compact, especially on the sides, which has the disadvantage that it loses its commercial value.

This crank does not occur if the compression pressure is lowered, but if the pressure is low, there is a problem in that the strength of the molded product decreases.

In addition, as a means to prevent the occurrence of cranking, methods of spray coating boron nitride, silicone, graphite, etc. on the mold are known, but no satisfactory results could be obtained with any of these methods.

An object of the present invention is to provide a method for producing a molded product that does not cause cracks on the side surface of the molded product even when high pressure is applied when polyimide resin or a blend of polyimide resin and filler is compressed and fired.

[Means to solve the problem]

In order to solve the problems of the prior art described above, the present invention takes the following measures.

That is, the method for producing a polyimide resin molded article of the present invention involves compression molding a polyimide resin composition or a polyimide resin compound consisting of a polyimide resin and a filler in a mold, and then firing it to produce a molded article. , is characterized in that a fluororesin is applied to the inner wall of the mold.

The polyimide resin used in the present invention mainly has the following polyimide structure.

The second polyimide resin is usually made by reacting pyromellitic anhydride and diaminodiphenyl ether.
A copolymer in which part of the acid component or diamine component is replaced with another acid or diamine component, or a resin mixture partially mixed with a polyimide resin having another molecular structure can also be used, but resins with the above polyimide structure can also be used. is optimal.

As the fluororesin used in the present invention, polytetrafluoroethylene resin or a copolymer thereof can be used, but polytetrafluoroethylene is most suitable.

The method of applying the fluororesin to the inner wall of the mold is not particularly limited, but for example, a method of painting or spraying a commercially available "Teflon" coating agent can be adopted.

On the other hand, various fillers can be added to the polyimide resin of the present invention for the purpose of imparting moldability, dimensional stability, low water absorption, etc.

Preferred fillers include glass fibers, carbon fibers, fibrous materials such as inorganic whiskers, talc, silica, alumina, kaolin, wollastenite, glass peas, and ceramic powder. It is preferably 10 to 60% by weight based on the total amount.

Furthermore, as the amount of filler added increases, cracks tend to occur in the molded product, but if the amount is 60% by weight or less, this can be prevented by applying the fluororesin to the mold.

In the molding method of the present invention, polyimide resin powder is compressed in a mold whose inner wall is coated with fluororesin to form a green compact, which is then heated and sintered. It is preferably 2000 to 5000 kg/cm2, and the firing temperature is preferably 370 to 430°C.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Using a mold with an inner diameter of 30φ and a height of 150III11, 3
A cylindrical polyimide resin green compact of 0φ×10 mm was molded.

As the polyimide resin, aromatic polyimide polymerized from pyromellitic anhydride and diaminodiphenyl ether was used. The compacting pressure of the green compact was 5 ton/cn+''.

When the inner surface of the mold was coated with Teflon (manufactured by DuPont), no cracks occurred on the side of the compact, but when the inner surface of the mold was chrome plated, cracks were not formed on the side of the compact. occured.

Example 2 The polyimide resin used in Example 1 was molded using the mold used in Example 1 while changing the molding pressure. The results are shown in Table 1. When the inner surface of the mold was chrome plated, no cracking occurred on the side surface of the green compact only when the molding pressure was 1 ton/c+a2 or less, but when the mold was coated with Teflon, No cracks were generated when a pressure of 5 ton/cm was applied.

Table 1 Example 3 In place of the "Teflon" coating in Example 1, Neoflon manufactured by Daikin Industries, Ltd. was used. As in Example 1, cracks occurred in the chrome plating, but no cracks occurred in the "Neoflon" coated product.

[Effects of the Invention] Since the present invention is a method for producing a polyimide resin molded product by applying a fluororesin to the inner surface of a mold and compression molding, cracks do not occur on the surface of the molded product, especially on the side surfaces.

Agent: Patent Attorney Nobuo Kogawa -

Claims (1)

[Claims] A polyimide resin or a polyimide resin compound consisting of a polyimide resin and a filler is compression molded in a mold, and then
A method for producing a polyimide resin molded article, which comprises applying a fluororesin to the inner wall of the mold when producing the molded article by firing.