Polyolefin microporous membrane

Abstract

The purpose of this invention is to provide a polyolefin microporous membrane that exhibits excellent membrane resistance and battery life when used as a battery separator, excellent permeability and foreign matter capture ability when used as a filter material, and excellent moisture permeability, waterproofness, and softness when used in clothing applications. The present invention relates to a polyolefin microporous membrane that satisfies either (i) or (ii) below: (i) when the arithmetic mean height of the surface with the larger arithmetic mean height is set as Sa1 and the arithmetic mean height of the other surface is set as Sa2, Sa1 / Sa2 is 1.10 or more, both Sa1 and Sa2 are 0.30 μm or more, and the bubble point pore size is 100 nm or more and 4000 nm or less; or (ii) when the height of the protruding valleys of the surface with the larger protruding valley height is set as Svk1 and the height of the protruding valleys of the other surface is set as Svk2, Svk1-Svk2 is 0.30 or more, both Svk1 and Svk2 are 1.00 μm or more, and the thickness-converted Gore-Krei permeability is 0.01 to 1.00 [s / 100 cm3 / μm].