To provide polyolefin fine porous membranes excellent in permeation performance and mechanical strengths, reduced in bends or the like at the time of molding and excellent in retention volume of an electrolyte.
A desired polyolefin fine porous membrane is made of a polyolefin composition comprising 70-95 wt.% polyethylene having a weight average molecular weight of 5×105 or more or polyethylene composition thereof and 5-30 wt.% polypropylene having a weight average molecular weight of 1×104 or more. In this instance, the thickness variation within an adjoining area of 1 mm2 in every area direction in the surface of the membrane is rendered ±1 μm or more to cause microscopic recesses and projections on the surface of the polyolefin fine porous membrane and as a result, the moldability, the permeability and retention of an electrolyte are improved.
FUNAOKA HIDEHIKO
KAIMAI NORIMITSU
KONO KOICHI
Next Patent: ILLUMINANT AND METHOD FOR INDICATING PASSAGEWAY