| 摘要 |
<p>A microporous membrane having a structure in which its pore size distribution curve obtained by mercury intrusion porosimetry has at least two peaks, which is produced by extruding a combination of a diluent or solvent and a polyolefin resin composition comprising (a) from about 74 to about 99 % of a first polyethylene resin having a weight average molecular weight of from about 2.5 x 10 5 to about 5 x 10 5 and a molecular weight distribution of from about 5 to about 100, (b) from about 1 to about 5 % of a second polyethylene resin having a weight average molecular weight of from about 5 x 10 5 to about 1 x 10 6 and a molecular weight distribution of from about 5 to about 100, and (c) from 0 to about 25 % of a polypropylene resin having a weight average molecular weight of from about 3 x 10 5 to about 1.5 x 10 6 , a molecular weight distribution of from about 1 to about 100, and a heat of fusion of 80 J/g or higher, percentages based on the mass of the polyolefin composition; cooling the extrudate to form a high polyolefin content cooled extrudate; stretching the cooled extrudate in at least one direction at a high stretching temperature to form a stretched sheet; removing at least a portion of the diluent or solvent from the stretched sheet to form a membrane; stretching the membrane to a high magnification in at least one direction to form a stretched membrane; and heat-setting the stretched membrane to form the microporous membrane.</p> |
