METHOD FOR PRODUCING POLYOLEFIN MICROPOROUS FILM, BATTERY SEPARATOR AND NONAQUEOUS ELECTROLYTE SECONDARY BATTERY

摘要

PROBLEM TO BE SOLVED: To provide a polyolefin microporous film having good cycle characteristics and excellent in electrolyte injection property and a battery separator obtained by the production method and to provide a nonaqueous electrolyte secondary battery having the battery separator.SOLUTION: There is provided a method for producing a polyolefin microporous film which comprises: a step 1 of kneading a polyolefin resin and a plasticizer to form a kneaded product; a step 2 of processing the kneaded product into a sheet-like molded product; a step 3 of rolling the sheet-like molded product to obtain a rolled product; and a step 4 of stretching the rolled product, where in the step 3, the film thickness maintenance rate, defined as the film thickness maintenance rate=(the film thickness after stretching/the film thickness before stretching)×100, is 35% or more and 90% or less.