| abstract |
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 extruding a melt-blend of a polyethylene resin containing 7% or less by mass of ultra-high-molecular-weight polyethylene having a weight-average molecular weight of 1 x 106 or more, and a membrane-forming solvent, stretching a gel-like sheet obtained by cooling an extrudate, washing it, stretching the resultant microporous membrane to 1.1-1.8 fold in at least one direction, and heat-setting it at a temperature in a range of the stretching temperature of the microporous membrane plus or minus 5 degrees centigrade. |