Patent ID: 8597775

Claim:
A microporous polyolefin multilayer film comprising an inner layer made of a resin mixture containing polypropylene of 50-90 wt % having a melting temperature of 160° C. or higher and polyethylene of 10-50 wt % having a melting temperature of 125° C. to 135° C. and a surface layer formed on both surfaces of the inner layer, made of a resin mixture containing polyethylene of 95% or more having a melting temperature of 125° C. or higher, wherein a thickness of the film is 9-50 μm, a puncture strength is 0.15N/μm or more, a permeability is 1.5×10 −5 Darcy or more, a multiplication of the puncture strength and the permeability is 0.4×10 −5 Darcy·N/μm or more, a shrinkage in a transverse direction at 120° C. for 1 hour is 15% or less, and a melt fracture temperature of 160° C. or higher.