POLYETHYLENE MICROPOROUS MEMBRANE, PROCESS FOR PRODUCTION THEREOF, AND BATTERY SEPARATOR

摘要

A microporous polyethylene membrane made of a polyethylene resin comprising 15% or less by mass of ultra-high-molecular-weight polyethylene having a mass-average molecular weight of 1 x 10 6 or more, which is constituted by a dense-structure layer having an average pore diameter of 0.01 to 0.05 µm, and a coarse-structure layer formed on at least one surface and having an average pore diameter 1.2-fold to 5.0-fold of that of the dense-structure layer, has a high electrolytic solution absorption speed with thickness and air permeability little changing when compressed. Such a microporous polyethylene membrane is produced by extruding a melt blend of the above polyethylene resin and a membrane-forming solvent through a die, cooling the resultant extrudate with a temperature distribution in a thickness direction to provide a gel-like sheet, stretching the gel-like sheet at a temperature from the crystal dispersion temperature of the polyethylene resin + 10°C to the crystal dispersion temperature + 30°C, removing the membrane-forming solvent, and stretching the membrane again to 1.05-fold to 1.45-fold.