| abstract |
A method of producing a microporous polyolefin membranenhaving a relatively large pore size and a high permeability, thenmembrane being suitable for use in water treatment, microfiltration,netc. The method comprises dissolving a polyolefin composition in ansolvent to prepare a solution, extruding the solution through a die lipninto a form of gel-like sheet, rapidly cooling the gel-like sheet,nremoving a residual solvent in the cooled sheet by a washing solventnand drying the resultant sheet to remove the washing solvent. Thenpolyolefin composition is a mixture of (A) an ultra high molecularnweight polyolefin having a weight average molecular weight of 5 xn10 5 or more and (B) a polyolefin having a weight average molecularnweight less than 5 x 10 5 , and a weight ratio of (B)/(A) is 0.2 to 20. |