Patent ID: 6676871
Filing Date: 2004-01-13
Classification: B29C,B29K,B32B,C08J

Abstract:
A process for producing a microporous film having a high isotropic tendency, that is permeable to gases but impermeable to aqueous liquids, said film comprising at least one layer, comprising the following successive steps:(a) forming a mixture comprising a polyolefin matrix which comprises at least one polymer and at least one mineral and/or organic filler; (b) extruding a web comprising at least one layer of said mixture by melt flow; (c) prestretching the web upon contact with a drive roll; (d) cooling and solidifying the prestretched web by contact with said drive roll, wherein said cooling of the prestretched web is partial and limited to a temperature within the range permitting further stretching of said web; and (e) further stretching the solidified web, at a temperature suitable for forming a microporous film, wherein said further stretching is achieved by pulling said web at the moment when tangential separation from said drive roll occurs, said roll acting as a forwarding roll for said further stretching operation.