| 摘要 |
PURPOSE: To efficiently obtain a biaxially stretched film high in mechanical strength by setting the main axis of molecular orientation to the longitudinal direction of a film and setting the specific resistance of the film at a time of melting to a specific value. CONSTITUTION: In a case film, the main axis of molecular orientation is set to the longitudinal direction of the film and the specific resistance of the film at a time of melting is set to below 5×10<8>Ω.cm. As polyester, polyethylene terephthalate or polyethylene-2,6-naphthalate is especially pref. from a viewpoint of mechanical strength, heat resistance, chemical resistance, durability or general-purpose properties. The melt specific resistance of polyester is determined based on the kind, present state and quantity of the metal contained in polyester and becomes lower as the quantity of a non-deactivated molten metal is larger and the amt. of precipitated internal particles is smaller. Polyester is pref. cast while draft is applied to a film within a temp. range wherein the temp. of polyester at the time of the emission from a flat die is below the completion temp of the endothermic peak at the time of melting and equal to or higher than temp. falling crystallization start temp. |
