Polyolefin microporous membrane and preparation method thereof

The invention relates to a polyolefin microporous membrane and a preparation method thereof. The polyolefin microporous membrane is composed of a modified superhigh molecular weight polyolefin master grain and high-density polyolefin, wherein the modified superhigh molecular weight polyolefin master grain is composed of the following components by weight percent: 40-70% of superhigh molecular weight polyethylene resins, 10-25% of modified resins, 15-25% of additives and 5-10% of lubricants. The quantity of crystal points of the polyolefin microporous membrane provided by the invention is reduced; the tensile strength is high; the homogeneity of product property is excellent; the method is simple in process; and the prepared polyolefin microporous membrane product has a suitable pore size,excellent ventilating property, a low-temperature disconnecting function and excellent mechanical property.