| 摘要 |
PURPOSE:To enable the decrease in the anisotropy of the coefft. of linear expansion and the coefft. of moisture expansion in the plane of a film by forming the film in such a way that the double refractive index is of a specified value or below and that the rate of the change in the size in the plane of the film after treatment under the condition of a specific temp. and humidity is of a specified value or below. CONSTITUTION:A biaxially stretched polyester film having the small anisotropy of the refractive index in the plane of the film is subjected to a suitable post treatment, by which the film having the small reversible and non-reversible anisotropy in the plane of the film is obtd. More specifically, the double refractive index (DELTAn) of the film is regulated to <=5X10<-3> and the rate of the change in the size in the plane of the film after the treatment for 72hr at 53 deg.C and 90% humidity is regulated to <=0.03%. The polyester here refers to polyester contg. >=80wt% ethylene terephthalate unit and the remaining <=20wt% may be copolymer polyester or other polymer. A stabilizer such as phosphoric acid, phosphorous acid or their ester, etc., an additive such as titanium dioxide, fine granular silica, kaolin or the like, a lubricant, etc. may be incorporated in the polyester. |
