POLYETHYLENE MICROPOROUS MEMBRANE, PROCESS FOR PRODUCTION THEREOF, AND BATTERY SEPARATOR

摘要

A polyethylene microporous membrane which comprises a polyethylene resin containing 1% by mass or more of an ultra-high molecular weight polyethylene having a mass average molecular weight of 7 x 105 or higher and having the ratio of the number average molecular weight to the mass average molecular weight of 5 to 300, and which comprises (a) a coarsely structured layer whic h is formed on at least one surface and has an average pore size of exceeding 0.04 .mu.m and (b) a densely structured layer having an average pore size of 0.04 .mu.m or less, wherein the area ratio of the densely structured layer t o the coarsely structured layer on the cross-section surface of the membrane i s 0.1 to 0.8.