| 摘要 |
PURPOSE: To provide a porous film which has practically sufficient mechanical strengths and excellent ion penetrability. CONSTITUTION: This porous film having fine pores, comprising a thermoplastic resin, is characterized in that the fine pores are formed from a three-dimensional net tissue comprising trunk fibrils extended in one direction of the film and branch fibrils connecting the trunk fibrils to each other, that the formation density of the branch fibrils is larger than the formation density of the trunk fibrils, and that an average fine pore diameter d (μm) determined by a bubble point method (ASTM F316-86) and an average fine pore diameter r (μm) determined by a mercury press-in method (JIS-K1150) satisfy the expression: 1.20<=2r/d<=1.70. |
