POLYESTER FILM, PROCESS FOR PRODUCING THE SAME AND USE THEREOF

摘要

A polyester film produced by melt extrusion of a polyester containing dicarboxylic acid units and diol units, 1 to 80 mol% of the diol units consisting of diol units having a cycloacetal skeleton, which polyester film exhibits an in-plane retardation of <= 20 nm at a wavelength of 550 nm. This polyester film is an optically isotropic polyester film easily produced through extrusion molding and thus excelling in economic efficiency. This polyester film is useful in the manufacturing of optical products and optical members, such as a retardation film, a protective film for polarizing plate, a light diffusion sheet, a lens sheet, an antireflective film and an optical information recording medium.