| abstract |
Disclosed is a method of producing a microporous polyolefin membrane having a thickness of 5-200 µm, a relatively large pore size (e. g., 0.1-0.5 µm) and a high permeability (e.g., 5-170 sec/100cc). The membrane is suitable for use in water treatment, microfiltration, etc. The method comprises dissolving a polyolefin composition in a solvent to prepare a solution, extruding the solution through a die lip into a form of gel-like sheet, rapidly cooling the gel-like sheet, removing a residual solvent from the cooled sheet by a washing solvent, and drying the resultant sheet to remove the washing solvent. The polyolefin composition is a mixture of (A) an ultra high molecular weight polyolefin having a weight average molecular weight of 5 × 10 5 or more and (B) a polyolefin having a weight average molecular weight less than 5 × 10 5, and a (B) / (A) weight ratio of 0.2 to 20. |