MICROPOROUS MEMBRANE, BATTERY SEPARATOR AND METHOD FOR PRODUCING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a cleavage resistant battery separator which is a thin microporous shutdown separator and has sufficient strength so that the hole may not open with easiness. SOLUTION: A microporous membrane comprises at least 80 wt.% of a polymer selected from the group consisting of polypropylene, polyethylene and their copolymer and has at least about 50 kgf/cm2 of lateral resistance to cleavage. The microporous membrane is prepared by processes comprising a process of extruding a film precursor by a tubular film method at a blow-up ratio of at least about 1.5, a process for annealing the above film precursor and a process for drawing the annealed film precursor to form the microporous membrane. The multilayer shutdown separator is made of the above microporous membrane.