| 摘要 |
A method for producing a highly permeable microporous polyolefin membrane comprising 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 3 x 10<5> and less than 1 x 10<6> 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 3 x 10<5> and less than 1 x 10<6> 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 drat ratio of 3-50 in a molten state, cooling the stretched extrudate to solidify to a gel-like sheet, removing a residual solvent from the gel-like sheet and drying the resultant sheet, and heat-setting the sheet at a temperature of 80 DEG C or higher and its melting point or lower. In the production method of the present invention, a viscous solution of a polyolefin or its composition is uniaxially stretched before it is cooled to solidify to a gel-like sheet. Uniaxial stretching of a viscous polyolefin solution allows micropores to have a large average diameter, thereby not only improving the permeability of the microporous polyolefin membrane, but also accelerating the production speed of membranes, leading to higher productivity. <IMAGE> |
