Patent ID: 7332531

Claim:
A microporous high density polyethylene film prepared from a composition, comprising: 20-50 wt % high density polyethylene with a weight average molecular weight of 2×10 5 -5×10 5 (component I), containing 5 wt % or less molecule with a molecular weight of 1×10 4 or less; and 80-50 wt % diluent (component II), wherein, tensile strengths are 1,100 kg/cm 2 or more in transverse and machine directions respectively, a puncture strength is 0.22 N/μm or more, a gas permeability (Darcy's permeability constant) is 1.3×10 −5 Darcy or more, and shrinkages are 5% or less in transverse and machine directions, respectively, by heat setting the film at a temperature range where 10-30 wt % of a crystalline portion of the film is molten.