| 摘要 |
PURPOSE:To contrive to improve the flat slipperiness of the title film by a method wherein the stretching measure of film is specified. CONSTITUTION:Unstretched film consists of polyester resin containing 0.001- 1wt% of finely divided particles originated from catalyst residue and/or inert mineral particles as insoluble matters is polyester. Firstly, said unstretched film is stretched longitudinally in a single stage or multi-stages at the stretching temperature ranging from the glass transition point of the film Tg to the melting point of the film Tm minus 100 deg.C so as to realize the states that the mean value of double refractive index n after the film being longitudinally stretched lies in 0.35-0.048, the maximum and minimum values of double refractive index n of the longitudinally stretched film are respectively 0.055 or less and 0.030 or more and at the same time its mean refractive index lies from 1.5770 or more to 1.5850 or less. Secondly, the film is laterally stretched at the stretching temperature of Tm minus 80 deg.C or less with the lateral draw ratio of 3.5 or more. Thirdly, the film is stretched longitudinally again at the stretching temperature of Tg plus 10 deg.C-Tm minus 80 deg.C. Finally, the film is thermoset, if necessary. Thus, a film with little unevenness in thickness and high flat slipperiness is obtained. |
