Porous film, process for producing the same, and use of the same

摘要

A porous film comprising a composition of 10 to 90% by weight of polypropylene and 10 to 90% by weight of polyethylene having an Mw/Mn ratio, as determined by high-temperature gel-permeation chromatography, of 10 or less is disclosed. The porous film has a high tensile modulus, a satisfactory appearance, and a uniform thickness. A battery separator comprising the porous film performs a shut-down function (an increase in resistance) in case of a temperature rise due to an abnormal current.