| 摘要 |
PURPOSE:To obtain a film whose thermal shrinkage factors of both a lateral and longitudinal directions are low, by a method wherein stretching of the lateral direction is begun from a specific temperature and then the same is performed while raising a temperature up to the necessary maximum temperature at a specific speed. CONSTITUTION:An unstretched sheet is produced by melting and extruding polyester resin. Then the unstretched sheet is stretched in a longitudinal direction. It is preferable to set a temperature 90-120 deg.C at this time. Then the same is heated at the temperature of 90 deg.C or higher and the same is stretched in a lateral direction while performing a temperature rise up to the necessary maximum temperature at a speed not exceeding 10 deg.C/second after that. It is preferable that a temperature rising speed in this instance is 5 deg.C/second or lower. Then a relaxation process is performed at need. Relaxation of 0.5-6% is performed in a lateral direction at the necessary maximum temperature or lower, to begin with, as the relaxation process. Then the relaxation of 0.1-1.0% is performed in a longitudinal direction at 80 deg.C-120 deg.C. Isotropy in thermal expansivity of an end part of a polyester film can be improved and thermal shrinkage factors of both a lateral and longitudinal directions can be reduced. |
