Methods of making thick, highly oriented, opaque, low-density, microporous polyolefin films and the films made thereby

摘要

A method of making a polyolefin film in accordance with this invention includes the steps of: blending a propylene block copolymer with a beta nucleating agent; extruding a film layer from the blend and providing a total area draw ratio in excess of 20, where at least one part of the stretching occurs at <120° C., for forming the film with a density no greater than 0.40 g/cm<3 >and a thickness greater than 160 gauge. The film also constitutes a part of this invention