| 摘要 |
PROBLEM TO BE SOLVED: To provide a composite film having a function interrupting permeability at a low temperature and attain improvement of a permeating function and mechanical strength, by laminating a specific polyolefine fine porous film, glass fiber cloth and non woven fabric. SOLUTION: In polyolefine of 5×10<5> or more weight average molecular weight, as necessary when a temperature rises in a battery inside by short-circuit an electrode, a substance of 5 to 30wt.% giving a shut down function at a low temperature is added to obtain polyolefine (composition), it is fused, kneaded, after extrusion molding, extracted and drawn, so as to obtain a polyolefine fine porous film of 100 to 200sec/100cc air permeability, 0.001 to 0.5μm average through hole size, 500kg/cm<2> or more rupture strength, 30 to 95% porosity and 5 to 50μm thickness. This polyolefine fine porous film and glass fiber cloth or nonwoven fabric of 10μm or less fiber size, 25 to 100μm thickness and 10 to 100g/cm<2> metake (weight/unit area) are laminated, to be integrally formed at 5 to 100kg/cm<2> roll pressure by heating at 50 to 120 deg.C.
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