BIAXIALLY ORIENTED POLYESTER FILM

摘要

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film which is reduced in the dimensional change caused by a use environment when formed into a magnetic recording medium or an environmental change during preservation and can be formed into an excellent high density magnetic recording medium reduced in error rate. SOLUTION: The biaxially oriented polyester film has laminated constitution including an A-layer and a B-layer and wherein the coefficient of humidity expansion in the width direction thereof is 3-6 ppm/%RH. The A-layer contains polyester with a glass transition temperature of below 150°C and 1-10 mass% of non-crystalline thermoplastic resin (P) with a glass transition temperature of 220-280°C and the B-layer contains polyester with a glass transition temperature of below 150°C. The surface roughness RaA of the A-layer is 0.3-10 nm, the undulation index of the B-layer is 1-10 and the surface roughness RaB of the B-layer is larger than the surface roughness RaB of the B-layer. COPYRIGHT: (C)2011,JPO&INPIT