Process for the preparation of heat resistant polyester film

摘要

A polyester film having excellent heat resistance and insulation property is produced by the inventive process which comprises: melt-extruding a polyester resin into a sheet, extending the sheet to shape it into a film and treating the film thermally to heat-set, wherein the polyester resin has an intrinsic viscosity of 0.7 to 0.75 dl/g and other portions which satisfy formula (1) and the thermal treatment is carried out so that formula (2) is satisfied: [COOH]/[IV]<50 (1) 1.0<S/D<1.2 (2) wherein: [COOH] represents the content (meq/106) of terminal carboxyl groups in the polyester resin; [IV] represents the intrinsic viscosity (dl/g) of the polyester resin; S represents the X-ray crystal size ( ANGSTROM ) of the heat-set polyester film; and D represents the degree of crystallinity (%) of the heat-set polyester film.