POLYOLEFIN MICROPOROUS FILM AND METHOD FOR PREPARING THE SAME

It is an object of the present invention to provide a microporous polyolefin membrane, high in pin puncture strength, adequate in pore diameter and high in porosity, comprising (A) an ultra-high-molecular-weight polyolefin having a weight-average molecular weight of 5 × 10 or more, or (B) a composition containing an ultra-high-molecular-weight polyolefin having a weight-average molecular weight of 5 × 10 or more, and having a porosity of 30 to 95%, bubble point exceeding 980 KPa and pin puncture strength of 4,900 mN/25 µm or more.