| 摘要 |
PURPOSE:To improve heat resistance, strength, continuity in film making and a draw ratio of a longitudinal direction, by a method wherein the subject film is made into a polyester film wherein at least specific ratio of an acid ingredient and glicol ingredient are constituted respectively of terephthalic acid and 1,4- cyclohexanedimethanol, and density, a birefringent index and Young's modulus of a longitudinal direction of the film are limited. CONSTITUTION:At least 80 mol% of an acid ingredient of a film is constituted of terephthalic acid, preferably at least 90 mol%, preferably further at least 95 mol%. Then at least 90 mol% in a glycol ingredient is constituted of 1,4- cyclohexanedimethanol, preferably at least 95 mol%, preferably further at least 97 mol%. Density of the film is made so as to fall within a range of 1.220-1.250 g/cm<2>, preferably a range of 1.224-1.240 g/cm<2>. A birefringence index (DELTAn) and Young's modulus of a longitudinal direction of the film are made so as to fall respectively within range of 0.010-0.040 and 310-370 kg/mm<2>. |
