HEAT-RESISTANT MICROPOROUS FILM

A heat resistant microporous membrane containing a thermoplastic resin having a crystalline melting point of 140-300 DEG C and having a layer structure formed in the direction of membrane thickness, said layer structure containing 5-100% of a layer defined by the following (A) and 95-0% of a layer defined by the following (B): (A) a layer in which the micropores are intra-spherulitic voids, and (B) a layer in which the micropores are intra-spherulitic voids and inter-spherulitic voids.