| 摘要 |
PURPOSE: To obtain a polyolefin finely porous membrane having high piercing strength and hardly tears and useful for a battery separator, etc., by extruding a solution containing ultrahigh molecular weight polyolefin, etc., from a die and stretching under a specific condition. CONSTITUTION: A solution composed of (A) 10-50wt.% polyolefin having 10-300 a ratio of weight-average molecular weight/number-average molecular weight and containing >=1wt.% high-molecular weight polyolefin such as PE having >=7×10<5> weight-average molecular weight and (B) 50-90wt.% a solvent such as nonane is extruded from a die, cooled to form a gel-like molded material and the gel-like molded material is stretched at a ratio of a longitudinal draw ratioλm to a lateral draw ratioλt:(λm/λt) of 0.5-3, preferably 1-3 at (crystal dispersion temperature)-(melting point +10 deg.C) andλm andλt>=2, preferably 3-30 to obtain the objective polyolefin finely porous membrane. Preferably, a face draw ratio is >=10.
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