| 摘要 |
PURPOSE:To manufacture a film of superior uniform thickness and dimension stability by specifying stretching magnification of a polyester film in the amorphous state and vertical stretching in a manner that birefringence rate is in the specified range, and then stretching by specified magnification in the lateral direction. CONSTITUTION:A PET polymer film in the amorphous state is preheated sufficiently to 100 deg.C or over normally, and then first stretching is carried out by 1.2-4.0 times stretching magnification in which DELTAn is 1.0X10<-3>-2.5X10<-2>. Then, stretching magnification is adjusted in the range of 1.0-3.5 times so that birefringence rate is in the range of 3.0X10<-2>-8.0X10<-2> without being cooled to the glass transition temperature or under, and second stretching is carried out in single or multiorientation. Then, third stretching is carried out at the film temperature less than that of second stretching and in the range of 95-250.DELTAn-130-250.DELTAn deg.C so that the final vertical stretching magnification is in the range of 4-9 times, while being stretched by 3.2 times or more in the lateral direction. DELTAn represents birefringence rate after the film is stretched in the vertical direction and before being stretched in the lateral direction. |
