Porous resin film and process for producing the same.

摘要

A process for producing a porous resin film containing a polyolefin resin as a main component, comprising melting a mixture of (A) 100 parts by weight of a polyolefin resin, (B) 0 to 50 parts by weight of a polyester-polyether type thermoplastic elastomer, and (C) a thermoplastic polyester resin having an instrinsic viscosity of not more than 0.5, the amount of the component (C) being from 25 to 90 part by weight per 100 parts of the total amount of the component (A) and the component (B), by heating the mixture at a temperature of not less than the melting temperature of the component (C); kneading the mixture at a shear rate of not less than 200/sec. while cooling the mixture to a temperature of not more than the crystallization temperature of the component (C) and not less than the melting temperature of the component (A); subjecting the mixture to film-forming at a temperature of less than the melting temperature of the component (C) and not less than the melting temperature of the component (A) and cooling the resultant rapidly to obtain a non-stretched film; and stretching the non-stretched film in at least one direction. The porous film obtained by the process has an excellent water proof and an excellent water vapor permeability.