BIAXIALLY ORIENTED POLYESTER FILM FOR MEMBRANE SWITCH

摘要

A biaxially oriented polyester film for a membrane switch, which is made from a polyester containing at least 80 mol% of ethylene-2,6-naphthalene dicarboxylate recurring units and which has an endothermic peak with an endothermic energy of at least 0.4 mJ/mg at a temperature of 110 to 160 DEG C. This film is produced by subjecting a biaxially oriented polyester film produced from the above polyester in accordance with a method known per se to the following steps in the order named: (1) the step of heating the film under no strain at a temperature of 150 to 180 DEG C for 1 to 5 hours; and (2) the step of heating the film in an unrolled or rolled state at a temperature of 80 to 122 DEG C for 5 to 200 hours.