MICROPOROUS POLYOLEFIN MEMBRANE, ITS PRODUCTION METHOD, BATTERY SEPARATOR, AND BATTERY

摘要

A multi-layer, microporous polyolefin membrane comprising first microporous layers constituting at least both surface layers and at least one second microporous layer disposed between both surface layers; said first microporous layer being made of a first polyolefin comprising (i) polypropylene, or (ii) a mixture of 50% or more by mass of polypropylene and a polyethylene resin; said second microporous layer being made of a second polyolefin comprising (i) a mixture of 7% or less by mass of ultra-high-molecular-weight polyethylene having weight-average molecular weight of 1 x 10 6 or more and the other polyethylene than said ultra-high-molecular-weight polyethylene, (ii) the other polyethylene than said ultra-high-molecular-weight polyethylene, or (iii) a mixture of 50% or less by mass of polypropylene and said mixture (i) or said polyethylene (ii); said second microporous layer having a larger average pore diameter than that of said first microporous layer; and the total thickness of said first microporous layers being 15-60% per 100% of the total thickness of said first and second microporous layers.