| 摘要 |
A microporous membrane having excellent properties which is produced by extruding a combination of a diluent or solvent and a polyolefin resin composition comprising (a) from about 40 to about 60% of a first polyethylene resin having a weight average molecular weight of from about 2.5x105 to about 4x105 and a molecular weight distribution of from about 5 to about 100, (b) from about 20 to about 40% of a first polypropylene resin having a weight average molecular weight of from about 0.8x106 to about 1.5x106, a molecular weight distribution of from about 1 to about 100 and a heat of fusion of 80 J/g or higher, (c) from about 10 to about 30% of a second polypropylene resin having a weight average molecular weight of from about 4x105 to about 7x105, a molecular weight distribution of from about 5 to about 100 and a heat of fusion of 80 J/g or higher, and (d) from about 0 to about 10% of a second polyethylene resin having a weight average molecular weight of from about 1x106 to about 5x106 and a molecular weight distribution of from about 5 to about 100, 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; optionally stretching the membrane to a high magnification in at least one direction to form a stretched membrane; and heat-setting the membrane product to form the microporous membrane.
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