METALLIC MOLD FOR MOLDING SYNTHETIC RESIN.

摘要

Maintenance of tight adhesion between the metal of the metallic mold for molding synthetic resin and polyimide ten times different from said metal in thermal expansion coefficient has hitherto been considered difficult when the metallic mold metal and the polyimide in close contact therewith are subjected to injection molding involving severe heating/cooling cycle repeated several tens of thousands of times. The most important advantage of injection molding using a mold resides in the possibility of obtaining a product in a complicated shape through a single process of molding, and there is a demand for molding a mirror- finish-surface product while maintaining such advantage as described above without extension of cooling time in the metallic mold and with improvement in reproducibility of the surface of the metallic mold. This invention provides a metallic mold to satisfy the demand required for a molded product and to ensure durability required for a mold. Concretely, a metallic mold for molding synthetic resin according to this invention is characterized in that: a polyimide layer is formed on the wall surface forming a mold cavity of the main metallic mold composed of such kind of metal as having thermal conductivity of 0.05 cal/cm.sec. DEG C or higher at room temperature; said polyimide layer measures 0.02 to 2 mm in thickness, has thermal conductivity of 0.002 cal/cm.sec. DEG C or under, and has as high a resistance to heat as 200 DEG C of glass transition temperature; and said polyimide is formed by heating a precursory solution of straight chain type high molecular polyimide spread over the metallic mold wall surface and has a breaking elongation of 10 % or larger as well as adhesion strength to the mold wall surface amounting to 500 g/10 mm width or above.