METHOD OF PRODUCING HIGHLY PERMEABLE MICROPOROUS POLYOLEFIN MEMBRANE

摘要

A process for preparing a highly permeable microporous polyolefin film, characterized by extruding, at a draft ratio ranging from 3 to 50, a polyolefin solution comprising 5 to 40 % by weight of either a polyolefin having a weight-average molecular weight ranging from 3x105 to less than 1x106 and a weight-average molecular weight/number-average molecular weight ranging from 5 to 300 or a polyolefin composition having as a whole a weight-average molecular weight ranging from 3x105 to less than 1x106 and a weight-average molecular weight/number-average molecular weight ranging from 5 to 300 and 95 to 60 % by weight of a solvent, melt stretching the extrudate monoaxially, cooling and solidifying the stretched extrudate to form a gel, removing the residual solvent from the gel followed by drying, and heat setting the dried gel at a temperature ranging from 80 ~C to the melting point thereof. Monoaxially stretching the viscous polyolefin solution in a molten state serves not only to increase the average pore diameter of the micropores to thereby improve the permeability of the microporous polyolefin film, but also to increase the rate of film preparation to thereby improve the productivity drastically.