Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Utilizing diverse solid particles
Patent
1997-05-09
1998-02-17
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Utilizing diverse solid particles
264126, 264127, B29C 4302
Patent
active
057188556
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of molding an aromatic polyimide resin having excellent quality.
TECHNICAL BACKGROUND
Moldings of an aromatic polyimide resin have excellent varous properties such as friction resistance, chemical resistance, radiation resistance and the like in addition to excellent heat resistance, and are widely used as mechanism parts such as sliding member, or used in the fields of automobiles, office instruments, electric and electronic parts, aerospace, atomic energy, general industrial machines, and the like.
In general, moldings of aromatic polyimide resin are molded by forming a powder impact (green product) by compression molding, and then sintering the same in an inert atmosphere such as nitrogen in a non-pressure state. Thus the method of producing a molding of a non-fusible polyimide resin is the same molding method as in ceramics and powder metallurgy, and it is known that when molding, a fluorine resin is added for the purpose of improving molding workability, such as reducing friction resistance at molding or relaxing internal stress of the molding. Further, the thus-obtained molding of polyimide resin having a fluorine resin added thereto is, as a result of effects at molding as mentioned above, a homogeneous product having a small density distribution, and an excellent molding which does not cause lamination on appearance can be obtained. It is also known that a fluorine resin is added for the purpose of improving sliding properties of the molding of polyimide resin, However, if the molding of such a polyimide resin containing a fluorine resin is sintered in an inert atmosphere, there is the problem on the quality. Specifically, if the molding of a polyimide resin having a fluorine resin or the like added thereto is sintered at high temperature, there are the problems that hue on appearance of the molding changes, thereby causing color shade, and the like. On the other hand, if the sintering temperature is lowered, there is no problem on color shade and the like, but the problem arises that strength of the molding is not sufficient.
Accordingly, the object of the present invention is to solve the problem in the sintering step in the case of molding an aromatic polyimide resin by adding a fluorine resin thereto, and is to provide a molding method which can obtain an aromatic polyimide resin molding having excellent quality.
DISCLOSURE OF THE INVENTION
As a result of extensive investigations in view of the above problems, the present inventors have reached to complete the present invention. That is, the present invention relates to a method of molding an aromatic polyimide resin, characterized in that in the step of compression molding a powder of an aromatic polyimide resin composition comprising an aromatic polyimide resin and a fluorine resin added thereto, followed by sintering, the resulting molding is sintered in a mixed gas atmosphere of oxygen and inert gas, or sintered in an inert gas atmosphere, and then heat treated in a mixed gas atmosphere of oxygen and inert gas.
It is preferred that the mixed gas of oxygen and inert gas has the oxygen gas concentration of 0.1 to 20%. Further, it is preferred that the above-mentioned sintering temperature and heat treatment temperature are in the range of 360.degree. to 480.degree. C.
A method of producing an aromatic polyimide resin powder used in the present invention is not particularly limited, and for example, the following methods can be employed: a method of obtaining an aromatic polyimide powder by heating a polyamic acid solution in the presence of a tertiary amine, as described in Japanese Patent Publication Sho 39-30060 or Japanese Laid-Open Patent Application Hei 4-142332; a method of producing a polyimide powder, characterized in that a uniform solution having a low rotational viscosity prepared by dissolving almost equimolar amounts of a biphenyltetracarboxylic acid component and an aromatic diamine component in an amide type solvent in which a polyimide produced does not dissolve
REFERENCES:
patent: 4302413 (1981-11-01), Howe et al.
patent: 4948869 (1990-08-01), Ogoe et al.
patent: 5069848 (1991-12-01), Saruwatari et al.
patent: 5316711 (1994-05-01), Thorne
Akahori Kiyokazu
Iwamoto Kazunari
Kaneka Corporation
Theisen Mary Lynn
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