| 摘要 |
PROBLEM TO BE SOLVED: To provide a production method of a polyolefin microporous film which is excellent in curling resistance when used as a separator for a lithium ion secondary battery.SOLUTION: A production method of a polyolefin microporous film includes: (a) an extrusion step to melt, knead, and extrude a resin composition including a polyolefin resin and a pore forming material; (b) a sheet molding step to mold the obtained extruded product into a sheet-like shape; (c) a primary stretching step to stretch the obtained sheet-like molded article at least once and at least in one direction; (d) an extraction step to extract the pore forming material from the obtained stretched sheet; and (e) a secondary stretching step to stretch the obtained sheet at least in one direction, in which the secondary stretching step in the (e) step consists of stretching stages with two or more stages, and the strain rates in a stretching stage of the second or later stretching stage is larger than the strain rate in the previous stage.SELECTED DRAWING: None |
