HEAT-SHRINKABLE POLYESTER FILM AND PROCESS FOR PRODUCTION THEREOF

摘要

In the heat-shrinkable polyester film of the present invention, the main shrinkage direction is the longitudinal direction. In addition, the hot-water heat shrinkage ratios in the longitudinal direction and the width direction when the film is treated in hot water at 90°C for 10 seconds, the refractive indexes in the longitudinal direction and the width direction and the natural shrinkage ratio after aging at 40°C and 65% RH for 700 hours or more are each controlled in predetermined ranges. The heat-shrinkable polyester film of the present invention is manufactured by stretching an unstretched film at a ratio of 2.5 times or more and 6.0 times or less in the width direction at a temperature of Tg + 5°C or more and Tg + 40°C or less, passing the film in an intermediate zone that does not execute an active heating operation, heat-treating the film at a temperature of 100°C or more and 170°C or less over a period of 1.0 second or more and 10.0 seconds or less, cooling the film to a surface temperature of 30°C or more and 70°C or less, stretching the film at a ratio of 2.0 times or more and 7 times or less in the longitudinal direction at a temperature of Tg + 5°C or more and Tg + 80°C or less, and subsequently cooling the film at a cooling rate of 30°C/second or more and 70°C/second or less to a surface temperature of the film of 45°C or more and 75°C or less.