Patent ID: 9647253
Date: 2017-05-09
CPC Classifications: B01D,B29C,B29K,B29L,H01M,Y02E

Claim:
1. A method of producing a microporous membrane comprising: (a) stretching a multi-layer extrudate in at least one of a machine direction (MD) or traverse direction (TD), the extrudate comprising at least first and second layers, the first layer comprising a first polyolefin and at least a first diluent, and the second layer comprising a second polyolefin and at least a second diluent, the second polyolefin comprising polypropylene in an amount in the range of from 25.0 wt. % to 35.0 wt. % based on the weight of the second polyolefin, the polypropylene having an Mw>0.9×10 (b) removing at least a portion of the first and second diluents from the stretched extrudate to produce a dried membrane having a first length along MD and a first width along TD; (c) stretching the membrane in MD from the first length to a second length larger than the first length by a first magnification factor in the range of from about 1.1 to about 1.5 followed by stretching the membrane in TD from the first width to a second width that is larger than the first width by a second magnification factor in the range of from about 1.1 to about 1.3, wherein the TD dry stretching magnification factor is less than the MD dry stretching magnification factor; and then (d) reducing the second width to a third width, the third width being in the range of from the first width to about 1.1 times larger than the first width, such that the membrane has a TD 105° C. heat shrinkage of 0.5% or less, a 130° C. heat shrinkage of 8.0% or less in at least one planar direction, and a TD maximum shrinkage in a molten state of 11.0% or less.