Microporous polyolefin membrane and method of production thereof

摘要

A microporous polyolefin membrane formed from a polyolefin composition, said composition having a weight-average molecular weight/number-average molecular weight ratio of 10-300 and comprising 1 weight % or more of an ultra-high molecular weight polyolefin having a weight-average molecular weight of 7 x 10<5>, said microporous membrane having a thickness of 0.1-25 mu m, a porosity of 35-95%, an average pore diameter of 0.001-0.2 mu m and a breaking strength of 0.2 kg or more per 15 mm width is produced by (a) preparing a solution comprising 10-50 weight % of the polyolefin composition and 50-90 weight % of a solvent; (b) extruding the solution through a die; (c) cooling the extruded solution to form a gel-like mass; (d) stretching the gel-like mass at a temperature equal to or lower than the melting point of the polyolefin composition plus 10 DEG C; and (e) removing any remaining solvent.