To produce the subject film, excellent in affinity for aqueous solution systems, having a high liquid retention ratio and retaining properties and a low gas permeation coefficient and useful as a separator for cells or batteries by carrying out the graft copolymerization of a specific amount of an acrylic monomer with a polyethylene microporous film according to the ionizing radiation treatment.
This hydrophilic polyethylene microporous film is obtained by preparing a solution comprising 10-50wt.% polyethylene, containing ≥1wt.% component having ≥7×105 weight-average molecular weight, a ratio of weight-average molecular weight/number-average molecular weight of 100-300 and 50-90wt.% solvent, extruding the resultant solution through a die, cooling the extruded solution, forming a gelatinous molding, drawing the formed molding at a temperature below (the melting point of the polyester +10°C), then removing the residual solvent, producing a polyethylene microporous film having 30-95% porosity and 0.005-1μm average through-hole diameter and carrying out the graft copolymerization of 5-30wt.% acrylic monomer with the microporous surface and film surface according to the ionizing radiation treatment. The resultant film has ≤1×10-10ml.cm/cm2.sec.cmHg gas permeation coefficient and ≤10kΩcm resistivity.
MIYASAKA KENJI
IZUMI YUZO
