Polyethylene microporous membrane, method for manufacturing the same, and separator including microporous membrane

A method for manufacturing a polyethylene microporous membrane, the method comprising:

• (a) melting and kneading a mixture including a polyethylene resin having a weight average molecular weight of 1×105 g/mol to 10×105 g/mol and a diluent through an extruder to prepare a melt;
• (b) extruding the melt to mold it into a sheet form;
• (c) sequentially biaxially stretching the sheet in the machine direction and in the transverse direction to mold it into a film;
• (d) extracting the diluent from the stretched film and drying the film;
• and
• (e) heat treating the dried film at a temperature at which 20% to 50% of crystals of the dried film melt,
• wherein the temperature at which 20% to 50% of crystals of the dried film melt in (e) is 133° C. to 145° C.,
• wherein in (c), a stretch ratio in the machine direction (SRMD) is 4.0 times or more, a stretch ratio in the transverse direction (SRTD) is 5.3 times or more, and a ratio (SRMD/SRTD) between the stretch ratio in the machine direction and the stretch ratio in the transverse direction is 0.5 to 0.75.