| abstract |
Provided is a polyolefin multilayer microporous film that has a low air permeability value, maintains high porosity and mechanical strength even when formed into a thin film, possesses exceptional impedance characteristics, and has exceptional cell characteristics when used as a cell separator. A polyolefin multilayer microporous film including at least a first microporous layer and a second microporous layer, wherein the polyolefin multilayer microporous film is characterized in that the first microporous layer comprises a first polyolefin resin that contains polypropylene, the second microporous layer comprises a second polyolefin resin that contains an ultrahigh-molecular-weight polyethylene, and the following requirements (I) and (II) are satisfied. (I) The film thickness is 25 μm or less, and the film thickness (μm) and the porosity (%) satisfy the following relationship. Porosity (%)/film thickness (μm) ≥ 3.0 ...(Formula) (II) The air permeability calculated for a thickness of 16 µm is 100 sec/100 cm 3 to 300 sec/100 cm 3 . |