BIAXIALLY STRETCHED POLYESTER FILM AND METHOD FOR MANUFACTURING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film having excellent dimensional stability and high rigidity and suitable as the base of a high density magnetic recording tape especially hard to generate a dimensional change under a use environment. SOLUTION: The biaxially stretched polyester film comprises a polyester and a polyimide and is characterized in that a melting point (Tm) and a minute heat absorption peak temperature (Tmeta) due to a differential scanning calorimeter is Tmeta=(Tm-60 deg.C)-(Tm-100 deg.C) and at least one of a ratio R1 M(=IMD/I55 ) of the Raman peak intensity (IMD) in the longitudinal direction of the film and the Raman peak intensity (I55 ) in the direction of 55 deg. with respect to the surface of the film at 1780 cm<-1> in a laser Raman scattering method and a ratio R1 T(=ITD/I55 ) of the Raman peak intensity (ITD) in the width direction of the film and the Raman peak intensity (I55 ) in the direction of 55 deg. with respect to the surface of the film is 2.5-20.