| 摘要 |
PROBLEM TO BE SOLVED: To simplify a longitudinally orienting step and to suppress damage of a film surface and contamination of a roll by cooling to solidify melted polyester in a sheet-like state, then uniaxially orienting by a specific draw rate at a first stage and then orienting it in a direction perpendicular to the orienting direction. SOLUTION: After melted polyester is cooled to be solidified in a sheet-like state, it is oriented 4.5 times or more in one direction in an orienting zone of a first stage, and then oriented in a lateral direction. After biaxially orienting, it is heat treated. In this case, the polyester sheet is preferably initially oriented at a temperature of glass transition temperature (Tg1) of the film immediately before the orienting to 30 deg.C higher than the Tg1. And, it is preferable to use plasticizing material to upgrade its stretchability. As the material, gas at the ambient temperature and ordinary pressure or water vaporized at 100C or higher in a heat treating step and evaporating out of the film is used. |
