| 摘要 |
PURPOSE: To provide a base film superior in the deep drawability, flatness, heat resistance or the like by specifying the average refractive index, the surface orientation and the heat of fusion of a biaxial orientation polyester film having a specific composition. CONSTITUTION: A film is made of polyester comprising 1-50 mol.% of an isophthalic acid unit as a dicarboxylic acid component. An average refractive index of the film is below 1.598, the surface orientation of the film is 0.050-0.140, and the heat of fusion is below 8 cal/G. An isophthalic acid copolymer mainly composed of polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, terephthalic acid and 1,4-cyclohexanedimethanol is preferably used as polyester to be used. By adding the isophthalic acid unit in the copolymer, the formability of the film can be improved without impairing the heat resistance not so much. |
