| 摘要 |
A heat-shrinkable polyester film which causes the main shrinkage in the lengthwise direction and which is controlled in such a way that the lengthwise and widthwise heat shrinkage factors observed when treated in warm water of 90°C for 10 seconds, the lengthwise and widthwise refraction indexes, and the natural shrinkage factor observed after the aging at 40°C and 65%RH for 700 hours fall within prescribed ranges respectively. The heat-shrinkable polyester film can be produced by stretching an unstretched film at a temperature ranging from the Tg plus 5°C to the Tg plus 40°C at a draw ratio of 2.5 to 6.0 in the widthwise direction, passing the resulting film through an intermediate zone not accompanied with positive heating, heat-treating the film at 100 to 170°C for 1.0 to 10.0 seconds, cooling the film to lower the surface temperature of the film to a temperature of 30 to 70°C, stretching the film at a temperature ranging from the Tg plus 5°C to the Tg plus 80°C at a draw ratio of 2.0 to 7 in the lengthwise direction, and then cooling the film at a cooling rate of 30 to 70°C/sec to lower the surface temperature of the film to a temperature of 45 to 75°C. |
