SOLVENT STRETCH PROCESS FOR PREPARING MICROPOROUS FILMS FROM PRECURSOR FILMS OF CONTROLLED CRYSTALLINE STRUCTURE

摘要

Microporous films having improved morphological structure are prepared by the "solvent stretch" method from an olefinic precursor film having a controlled crystalline structure. The crystalline structure of the precursor film is controlled by preparing said film from an olefinic crystalline homopolymer characterized as having a melt index of about 3 to 20 in the absence of a nucleating agent and a molecular weight distribution ratio of about 3.8 to about 13. In another embodiment the crystalline structure of the precursor film is controlled by incorporating a nucleating agent into the crystalline polymer resin from which the precursor film is prepared which thereby permits a reduction in the melt index of the polymer to about 0.3.