| 摘要 |
PURPOSE:To obtain the titled film which is superior in flat and easily sliding properties, by a method wherein a difference between a shrinkage factor in a longitudinal direction and that in a widthward direction at a nonreversible process under specific terms satisfies a specific expression, in the film wherein R to be obtained through polarized light and fluorescent strength of a polyester film is shown by a specific expression. CONSTITUTION:A polyester raw material containing particles is dried by a conventional device, melted and extruded through an extruding machine and unoriented polyester sheet is molded by cooling and curing. The same is oriented in a longitudinal direction and after orientation further in the longitudinal direction the same is oriented in a crosswise direction in the next place, reoriented longitudinally so that 0.95<=R(45 deg.)<=1.05 is given again in the longitudinal direction and then fixed thermally according to necessity. Then calendering treatment is applied to said film for 72hr under terms of the temperature of 53 deg.C and the humidity of 90% and a target film whose difference between a shrinkage factor alphaMD in the longitudinal direction and that alphaTD in a widthward direction at a nonreversible process is shown by an expression is obtained. EFFECT:The titled sheet is superior in anisotropy within the surface, the anisotropy within the surface of a dimensional variation at a nonreversible process and flat and easily sliding properties. |
