| 摘要 |
A microporous polyolefin 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 (1) extruding a melt-blend of (a) (i) a polyethylene resin containing 7% or less by mass of ultra-high-molecular-weight polyethylene having a weight-average molecular weight of 1×106 or more, or (ii) a mixture of 75% by mass or more of said polyethylene resin and 25% or less by mass of polypropylene, and (b) a membrane-forming solvent, (2) stretching a gel-like sheet obtained by cooling an extrudate, (3) washing it, (4) stretching the resultant microporous membrane to 1.1-1.8 fold in at least one direction, and (5) heat-setting it at a temperature in a range of the stretching temperature of the microporous membrane plus or minus 5 degrees centigrade.
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