| abstract |
A process for producing a relatively thick microporous ultra-high-molecular-weight polyolefin membrane, comprising the steps of: (a) preparing a solution of an ultra-high-molecular-weight polyolefin having a weight-average molecular weight of 5 x 10⁵ or more; (b) extruding said solution from a die while rapidly cooling it in advance to its gelation temperature or below, thereby forming a gel-like sheet; (c) removing at least 10 wt % of said solvent from said gel- like sheet so that said gel-like sheet contains 10 to 90 wt % of said ultra-high-molecular-weight polyolefin; (d) stretching said gel-like sheet at a temperature equal to or lower than that which is 10°C above the melting point of said ultra-high-molecular-weight polyolefin; and (e) removing the residual solvent from the stretched product. |