| 摘要 |
PROBLEM TO BE SOLVED: 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. SOLUTION: A desired polyolefin fine porous membrane is made of a polyolefin composition comprising 70-95 wt.% polyethylene having a weight average molecular weight of 5×10<5> or more or polyethylene composition thereof and 5-30 wt.% polypropylene having a weight average molecular weight of 1×10<4> or more. In this instance, the thickness variation within an adjoining area of 1 mm<2> in every area direction in the surface of the membrane is rendered±1μm 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.
|
