Microporous material and a method of making same

Abstract

A method for producing a microporous material comprising the steps of: providing an ultrahigh molecular weight polyethylene (UHMWPE); providing a filler; providing a processing plasticizer; adding the filler to the UHMWPE in a mixture being in the range of from about 1:9 to about 15:1 filler to UHMWPE by weight; adding the processing plasticizer to the mixture; extruding the mixture to form a sheet from the mixture; calendering the sheet; extracting the processing plasticizer from the sheet to produce a matrix comprising UHMWPE and the filler distributed throughout the matrix; stretching the microporous material in at least one direction to a stretch ratio of at least about 1.5 to produce a stretched microporous matrix; and subsequently calendering the stretched microporous matrix to produce a microporous material which exhibits improved physical and dimensional stability properties over the stretched microporous matrix.

What is claimed is: 
     
         1 . A method for producing a microporous material comprising the steps of:
 mixing ultra high molecular weight polyethylene (UHMWPE), filler and processing plasticizer together to form a mixture, having a weight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight;   wherein the filler constitutes from about 5 percent to about 95 percent by weight of the microporous material;   extruding said mixture to form a sheet;   calendering said sheet;   extracting all or part of said processing plasticizer from said sheet to produce a matrix comprising UHMWPE and said particulate filler, the filler being distributed throughout said matrix, to produce a microporous matrix sheet;   stretching said microporous matrix sheet in at least one stretching direction to a stretch ratio of at least about 1.5 to produce a stretched microporous matrix sheet; and   calendering said stretched microporous matrix sheet.   
     
     
         2 . The method of  claim 1 , wherein the filler constitutes from about 45 percent to about 95 percent by weight of the microporous material. 
     
     
         3 . The method of  claim 1 , wherein the filler constitutes from about 55 percent to about 80 percent by weight of the microporous material. 
     
     
         4 . The method of  claim 1 , wherein the filler constitutes from about 61.1 percent by weight of the microporous material. 
     
     
         5 . The method of  claim 1 , wherein the filler is selected from silica, precipitated silica, silica gel, or fumed silica. 
     
     
         6 . The method of  claim 1 , wherein the filler is silica. 
     
     
         7 . The method of  claim 1 , wherein the ratio of filler to processing plasticizer is 1:15 to 3:1 by weight. 
     
     
         8 . The method of  claim 1 , wherein the ratio of filler to UHMWPE is about 2.6. 
     
     
         9 . The method of  claim 1  where said microporous matrix sheet is stretched in at least one direction to a stretch ratio from about 1.5 to 15. 
     
     
         10 . The method of  claim 1  where said UHMWPE is mixed with a high density (HD) polyethylene to produce a polyolefin mixture, where said polyolefin mixture has at least 50% UHMWPE by weight of said polyolefin mixture; where said filler to said polyolefin mixture is in a range of from 1:9 to 15:1 filler to polyolefin mixture by weight and where said matrix comprises UHMWPE and HD polyethylene and said particulate filler distributed throughout said matrix. 
     
     
         11 . A method for producing a microporous material comprising the steps of:
 mixing ultra high molecular weight polyethylene (UHMWPE), filler and processing plasticizer together to form a mixture, having a weight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight;   wherein the filler constitutes from about 5 percent to about 95 percent by weight of the microporous material;   extruding said mixture to form a sheet;   calendering said sheet;   extracting all or part of said processing plasticizer from said sheet to produce a matrix comprising UHMWPE and said particulate filler, the filler being distributed throughout said matrix, to produce a microporous matrix sheet;   stretching said microporous matrix sheet in at least one stretching direction to a stretch ratio of at least about 1.5 to produce a stretched microporous matrix sheet; and   calendering said stretched microporous matrix sheet;   wherein said microporous matrix sheet having a thickness of no greater than 53.3 microns and a tensile strength in the machine direction of at least 72.9 N/mm 2 .   
     
     
         12 . The method of  claim 11 , wherein the filler constitutes from about 45 percent to about 95 percent by weight of the microporous material. 
     
     
         13 . The method of  claim 11 , wherein the filler constitutes from about 55 percent to about 80 percent by weight of the microporous material. 
     
     
         14 . The method of  claim 11 , wherein the filler constitutes from about 61.1 percent by weight of the microporous material. 
     
     
         15 . The method of  claim 11 , wherein the filler is selected from silica, precipitated silica, silica gel, or fumed silica. 
     
     
         16 . The method of  claim 11 , wherein the filler is silica. 
     
     
         17 . The method of  claim 11 , wherein the ratio of filler to processing plasticizer is 1:15 to 3:1 by weight. 
     
     
         18 . The method of  claim 11 , wherein the ratio of filler to UHMWPE is about 2.6. 
     
     
         19 . The method of  claim 11  where said microporous matrix sheet is stretched in at least one direction to a stretch ratio from about 1.5 to 15. 
     
     
         20 . The method of  claim 11  where said UHMWPE is mixed with a high density (HD) polyethylene to produce a polyolefin mixture, where said polyolefin mixture has at least 50% UHMWPE by weight of said polyolefin mixture; where said filler to said polyolefin mixture is in a range of from 1:9 to 15:1 filler to polyolefin mixture by weight and where said matrix comprises UHMWPE and HD polyethylene and said particulate filler distributed throughout said matrix. 
     
     
         21 . The method of  claim 1 , wherein the filler includes carbon material. 
     
     
         22 . The method of  claim 21 , wherein the carbon material is at least one of carbon black, activated carbons, and carbon fibers. 
     
     
         23 . The method of  claim 11 , wherein the filler includes carbon material. 
     
     
         24 . The method of  claim 23 , wherein the carbon material is at least one of carbon black, activated carbons, and carbon fibers. 
     
     
         25 . A microporous material produced by the method of  claim 1 . 
     
     
         26 . A battery separator comprising the microporous material of  claim 25 . 
     
     
         27 . A microporous material produced by the method of  claim 11 . 
     
     
         28 . A battery separator comprising the microporous material of  claim 27 . 
     
     
         29 . A microporous material produced by the method of  claim 21 . 
     
     
         30 . A battery separator comprising the microporous material of  claim 29 . 
     
     
         31 . A microporous material produced by the method of  claim 23 . 
     
     
         32 . A battery separator comprising the microporous material of  claim 31 .