BIAXIALLY ORIENTED POLYESTER FILM AND PRODUCTION THEREOF

摘要

PURPOSE:To obtain the title film excellent in strength and workability by producing this film so that the breaking strength in the width direction and F5 value satisfy the specified conditions in a biaxially oriented film wherein F5 value in the longitudinal direction is regulated to >= 15 kg/mm<2>. CONSTITUTION:In a film wherein F5 value in the longitudinal direction is regulated to >= 15 kg/mm<2>, it is necessary that the value of TsTD/F5TD calculated from the breaking strength measured in the width direction and F5 value is regulated to <= 2.20. When this value is regulated to >= 2.20, lug rise of the film is caused in the case of performing slitting of the biaxially oriented film. When slitting is performed after a magnetic layer is coated, drop out is caused by the cause due to shaving powder of the film. Polyester is melted and extruded and the unoriented film molded into a sheet is successively oriented to 2.5 - 5.0 times at 80 - 130 deg. in the order of the lateral direction and the longitudinal direction and thereby a biaxially oriented film is produced. Then this film is reoriented to 1.05 - 2.0 times at 100 - 180 deg. in the longitudinal direction and heated at 160 - 240 deg. and fixed. The F5 value in the longitudinal direction is regulated to 15 kg/mm<2> and the value of TsTD/F5TD calculated from the breaking strength in the width direction and F5 value is regulated to <= 2.20.