POLYIMIDE FILM AND ITS PRODUCTION

摘要

PURPOSE:To obtain a polyimide film improved in heat resistance, mechanical properties and dimensional stability by forming a polyimide having specified repeating units into a film, stretching this film by heating, and heat-setting it under tension. CONSTITUTION:A polyamic acid obtained by polymerizing pyromellitic dianhydride with 4,4'-bis(3-aminophenoxy)biphenyl is imidized to obtain a polyimide having repeating units of the formula. This polyimide is melt-extruded to obtain an unstretched film. This film is stretched in one direction or two rectangular directions at 230-320 deg.C at a draw ratio of 1.5-10 and heat-set under tension at a temperature from 250 deg.C to the melting point to obtain the title film having a density (at 23 deg.C) of 1.335-1.390g/cm<3> and a refractive index (at 23 deg.C) along the direction of thickness of 1.605-1.680.