| abstract |
(57) [Abstract] (with correction) [PROBLEMS] A porous film having excellent pore closing properties, excellent high-temperature piercing strength near the closing temperature, and excellent membrane rupture resistance, and a high-capacity battery using the same. Provide a separator. SOLUTION: A polyolefin porous film having the following characteristics. 1) intrinsic viscosity [η] is 2.5 dl / g or more, 2) Mw / Mn is 10 or less, 3) film thickness is 10 to 100 μm m, 4) Air permeability is 50 to 1500 sec / 100 ml, 5) The porosity is 30 to 80%, 6) The piercing strength (25 ° C.) ≧ 12 g / μm, 7) Puncture strength (135 ° C.) ≧ 9 g / μ m. This film further has a closure temperature of 140 ° C. or less, a rupture resistance time of 2 minutes or more, and 105 ° C. Has at least one of the requirements that the heat shrinkage ratio is less than 6% in the above, is extremely useful as a battery separator film, especially a high capacity battery separator film. |