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Abstract

A method for preparing a microporous polyolefin shaped article which includes the steps of (1) melt blending a polyolefin with an additive which is miscible with the polymer at the melt temperature of the blend but which phase separates on cooling to form a solution; (2) forming a shaped article from the solution; (3) cooling the shaped article by use of a patterned chill roll to provide areas on the surface of the article where the polymer mixture does not contact the chill roll; and (4) (a) removing at least a substantial portion of the compatible liquid; or (b) stretching the article in at least one direction sufficient to permanently attenuate the article and effect orientation of the polymer; or (c) a combination of (a) and (b) to form a microporous polyolefin shaped article. The article is of substantially uniform thickness and has a patterned surface. The patterned surface provides substantially skinless areas having high microporosity and skinned areas or reduced porosity.

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First Claim