| 摘要 |
A process of producing porous films having a high porosity and excellent air permeability, even though they have a small film thickness and a high strength, and a process of producing battery separators. The process of producing porous films includes the steps of melt kneading a composition comprising a polyolefin resin, a thermoplastic elastomer and a solvent; extruding and cooling the melt kneaded material into a sheet molding; rolling the sheet molding; and stretching and desolvating the rolled sheet molding, wherein the rolling is carried out under a condition such that the sheet molding after rolling has an elastic recovery rate as calculated by the following equation (1) of 20% or lower: Elastic recovery rate (r) (%)=100x(t-t0)/t0 (1) wherein t0 represents a minimum clearance of a sheet rolling section in the rolling; and t represents a sheet thickness in the elastic recovery state after pressure release.
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