| 摘要 |
PCT No. PCT/JP98/04241 Sec. 371 Date Jun. 23, 1999 Sec. 102(e) Date Jun. 23, 1999 PCT Filed Sep. 21, 1998 PCT Pub. No. WO99/21914 PCT Pub. Date May 6, 1999A method for producing a highly permeable microporous polyolefin membrane including the steps of preparing a polyolefin solution containing 5-40 weight % of a polyolefin or a polyolefin composition and 95-60 weight % of a solvent, the polyolefin having a weight-average molecular weight of not less than 3x105 and less than 1x106 and a weight-average molecular weight/number-average molecular weight of 5-300, and the polyolefin composition having a weight-average molecular weight of not less than 3x105 and less than 1x106 and a weight-average molecular weight/number-average molecular weight of 5-300 as a whole, extruding the polyolefin solution, stretching the extrudate uniaxially at a draft ratio of 3-50 in a molten state, cooling the stretched extrudate to solidify to a gel-like sheet, removing residual solvent, drying the resultant sheet, and heat-setting at a temperature of 80 DEG C. or higher and its melting point or lower. A polyolefin or its composition is uniaxially stretched before it is cooled to a gel-like sheet. Uniaxial stretching of a viscous polyolefin solution allows micropores to have a large average diameter, thereby improving permeability of the microporous polyolefin membrane and accelerating production.
|
