Patent ID: 8486521

Claim:
A microporous polyethylene film prepared from a mixture comprising 20-50 wt % polyethylene having a weight average molecular weight from 2.0×10 5 to 4.5×10 5 as the sole polyethylene used to prepare the film and 80-50 wt % diluent, the microporous polyethylene film having a film thickness of 5-40 μm, a porosity of 35-55%, a permeability from 2.5×10 −5 to 10.0×10 −5 Darcy, a puncture strength of at least 0.10 N/μm at 90° C., a puncture angle of at least 30° at 90° C., and a permeability from 2.0×10 −5 to 8.0×10 −5 Darcy after shrinking freely at 120° C. for 1 hour.