| abstract |
A nonaqueous secondary battery separator is provided that is excellent in heat resistance, shutdown characteristics, membrane resistance and handling property. The present invention is a polyolefin microporous membrane used for a nonaqueous secondary battery separator containing the polyolefin microporous membrane at least one surface of which is coated and integrated with a heat resistant porous layer, characterized in that the membrane has (A) a thickness of 5 to 20 µm, (B) a porosity of 35 to 50%, (C) an air permeability per unit thickness (JIS P8117) of 10 to 30 sec/100 cc·µm and a total air permeability of the membrane (JIS P8117) of 400 sec/100 cc or less, and (D) Y/X of 1 × 10 -3 to 1 × 10 -2 ohm·cm 2 / (sec/100 cc), wherein the air permeability (JIS P8117) is represented by X sec/100 cc, and the membrane resistance upon impregnating the polyolefin microporous membrane with an electrolytic solution is represented by Y ohm·cm 2 . |