BIAXIALLY ORIENTED POLYESTER FILM AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film which comprises polyethylene naphthalenedicarboxylate as a main component and has excellent curl resistance in a process for thermally treating the film and when used at high temperature, and to provide a method for producing the same. SOLUTION: This biaxially oriented polyester film comprising polyethylene naphthalenedicarboxylate as a main component is characterized in that a refractive index difference between both the sides of the film in a direction vertical to the main orientation direction is 0.005 to 0.020 as absolute values, and the side having a larger refractive index in the direction vertical to the main orientation direction is a curl inside at a thermal treatment at 180°C. COPYRIGHT: (C)2007,JPO&INPIT