| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a porous film which has a more uniform thickness and also a high strength and nevertheless, a high porosity and an outstanding air permeability, compared to a conventional porous film. SOLUTION: This method for manufacturing a porous film comprises at least the steps of melting and kneading a polyolefin resin and a composition containing a solvent, then cooling the extrusion into sheet-like moldings after an extruding process and treating the sheet-like moldings by rolling, followed by stretching and solvent removing processes. In this method, the rolling process is performed by sequentially carrying out a heating/pressurizing step and a cooling/pressurizing step. This method is characterized in that the rolling factor T obtained by calculation in formula (1) which represents the build-up amount of a pressurizing force in the heating and pressurizing step and the cooling and pressurizing step, is 1,000 or more per 100 mm of the width of the sheet-like moldings immediately before rolling. Rolling factor T [N.h] = pressurizing force N×pressurizing time [h] (1) (wherein, the pressurizing force is a force to act on an object to be rolled in a compression direction and the pressurizing time is time over which the pressurizing force works).
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