Patent ID: 7976987

Claim:
A separator for a nonaqueous secondary battery comprising a polyolefin microporous membrane at least one surface of which is laminated with a heat resistant porous layer containing a heat resistant resin, the heat resistant porous layer containing an inorganic filler containing a metallic hydroxide that undergoes dehydration reaction at a temperature of 200 to 400° C., wherein the inorganic filler satisfies the following items (a) and (b): (a) 0.1≦d50≦1 (μm) (b) 0<α≦2 wherein d50 represents an average particle diameter (μm) of weight accumulation of 50% by weight calculated from a smaller particle side in a particle size distribution by laser diffraction, and α represents homogeneity of the inorganic filler and is expressed by α=(d90−d10)/d50, wherein d90 represents an average particle diameter (μm) of weight accumulation of 90% by weight calculated from a smaller particle side in a particle size distribution by laser diffraction, and d10 represents an average particle diameter (μm) of weight accumulation of 10% by weight calculated from a smaller particle side in a particle size distribution by laser diffraction.