| abstract |
PROBLEM TO BE SOLVED: To provide a high shrinkage rate, high strength, a high-speed shutdown function when heat is generated, to balance the shrinkage rate and the piercing strength, and to have excellent battery characteristics when used as a battery separator. To provide highly safe polyolefin microporous membranes. SOLUTION: This is a microporous polyolefin membrane comprising an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more (A) or a composition containing an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more (B). Rate is 35-9 A microporous polyolefin membrane having a heat shrinkage of more than 3% but not more than 15% and a puncture strength of 400 to 650 g / 25 μm. |