Patent ID: 8778525

Claim:
A multi-layer, microporous polyethylene membrane having a three-layer structure comprising a first microporous layer constituting two surface layers and a second microporous layer sandwiched between the two surface layers, wherein the first microporous layer being made of a polyethylene resin, which is a mixture of ultra-high-molecular-weight polyethylene having a mass-average molecular weight of 1×10 6 to 15 ×10 6 and high-density polyethylene, and the second microporous layer being made of a mixture of the polyethylene resin and a heat-resistant resin other than polypropylene, the heat-resistant resin having a melting point or a glass transition temperature of 180° C. to 260° C. and being dispersed in the form of fine particles in the polyethylene resin, and the second microporous layer having pores containing fine particles of the heat-resistant resin as nuclei from which the cleavage of polyethylene resin fibrils starts.