| 摘要 |
PURPOSE:To improve a heat resistance and a solvent resistance, and to reduce an optical distortion, i.e., double refraction by combining polyester films having special photoelastic constant, glass transition temperature, haze value, double refraction index in a surface. CONSTITUTION:A polyester film made at least of an A layer and a B layer in which photoelastic constant of polyester of the A layer is 1.6X10-<3>mm<2>/kgf or less and glass transition temperature of polyester of the B layer is 75 deg.C or higher, has 5% or less of a haze value at the time of dipping in solvent, 2.5 x 10<-4> or less of double refraction in an entire layer, and a front layer of at least one side of the film is the A layer. For example, as the A layer polyester, polybutylene terephthalate having 18 of relative viscosity is used. In the polyester of the B layer, terephthalic acid is used as dicarboxylic acid, and polyester having 20 of relative viscosity and containing 50mol% of ethylene glycol and 50mol% of bis(4-hydroxyethoxyphenyl)sulfone is used as dihydroxy compound. |
