| 摘要 |
PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film improved in productivity by reducing the rupture of a film at the time of lateral stretching and the loss of edge parts not becoming a product and further in quality such as thickness uniformity or irregularity of physical properties in the lateral direction of the film and to provide a method for producing this film at a high speed. SOLUTION: The producing method is constituted so that molten polyester is injected to a rotary cooling body from a cap and quenched to mold a non- stretched sheet which is, in turn, successively stretched longitudinally and laterally to be thermally fixed. In this case, the film after stretched in the longitudinal direction is laterally stretched by grasping the lateral end parts where the refractive index in the lateral direction of the film is more than that of -0.04 or more of the flat central part in the lateral direction of the film, that is, 1.54-1.6. The biaxially stretched film thus obtained is reduced in thickness fluctuations in the longitudinal direction and has specific characteristics by FFT analysis. |
