Polyolefin composition, its production method, and a battery separator made therefrom

Abstract

The invention relates to a polyolefin composition. The polyolefin composition can be in the form of a multi-layer, microporous polyolefin membrane comprising a first microporous layer containing 7% or less by mass of ultra-high-molecular-weight polyethylene having a weight-average molecular weight of 1×10 6 or more, and having a structure in which a pore size distribution curve obtained by mercury intrusion porosimetry has at least two peaks, and a second microporous layer containing 8% or more by mass of the ultra-high-molecular-weight polyethylene.

1 . A method for forming a polyolefin, comprising,
 (1) combining a first polyolefin composition and a first membrane-forming solvent to prepare a first polyolefin solution, wherein the first polyolefin is produced by combining resins of   (a) a first polyethylene having an Mw that is less than 1×10 6 ;   (b) the first polyethylene and a second polyethylene having a Mw of at least 1×10 6 , wherein the second polyethylene is present in an amount that does not exceed 7% by mass based on the combined mass of the first and second polyethylene;   (c) the first polyethylene and a first polypropylene, wherein the amount of the polypropylene ranges does not exceed 25% by mass based on the combined mass of the first polyethylene and the first polypropylene; or   (d) the first polyethylene, the second polyethylene, and the first polypropylene, wherein the first polypropylene is present in an amount that does not exceed 25% by mass based on the combined mass of the first polyethylene, the second polyethylene, and the first polypropylene, and wherein the second polyethylene is present in an amount that does not exceed 7% by mass based on the combined mass of the first and second polyethylene; and   (2) combining a second polyolefin composition and a second membrane-forming solvent to prepare a second polyolefin solution, wherein the second polyolefin composition is produced by combining resins of   (a) a fourth polyethylene having an Mw of at least 1×10 6 ;   (b) a third polyethylene having an Mw that is less than 1×10 6  and the fourth polyethylene, wherein the fourth polyethylene is present in an amount of at least 8% by mass based on the combined mass of the third and fourth polyethylene;   (c) the fourth polyethylene and a second polypropylene wherein the second polypropylene is present in an amount that does not exceed 25% by mass based on the combined mass of the fourth polyethylene and the second polypropylene; or   (d) the third polyethylene, the fourth polyethylene, and the second polypropylene, wherein second polypropylene is present in an amount that does not exceed 25% by mass based on the combined mass of the third polyethylene, the fourth polyethylene, and the second polypropylene, and the fourth polyethylene is present in an amount of at least 8% by mass based on the combined mass of the third and fourth polyethylene.   
     
     
         2 . The method of  claim 1 , further comprising;
 (3) extruding at least a portion of the first polyolefin solution through a first die and co-extruding at least a portion of the second polyolefin solution through a second die in order to form a multi-layer extrudate,   (4) cooling the multi-layer extrudate to form a multi-layer, gel-like sheet,   (5) removing the first and second membrane-forming solvents from the multi-layer, gel-like sheet to form a solvent-removed gel-like sheet, and   (6) drying the solvent-removed gel-like sheet in order to form the multi-layer, microporous polyolefin membrane.   
     
     
         3 . The method of  claim 1 , further comprising;
 (3) extruding at least a portion of the first polyolefin solution through a first die to make a first extrudate and extruding at least a portion of the second polyolefin solution through a second die to make a second extrudate, and then laminating the first and second extrudates to make a multi-layer extrudate,   (4) cooling the multi-layer extrudate to form a multi-layer, gel-like sheet,   (5) removing the first and second membrane-forming solvents from the multi-layer, gel-like sheet to form a solvent-removed gel-like sheet, and   (6) drying the solvent-removed gel-like sheet in order to form the multi-layer, microporous polyolefin membrane.   
     
     
         4 . The method of  claim 1 , further comprising
 (3) extruding at least a portion of the first polyolefin solution through a first die to make a first extrudate,   (4) extruding at least a portion of the second polyolefin solution through a second die to make a second extrudate,   (5) cooling first and second extrudates to form at least one first gel-like sheet and at least one second gel-like sheet,   (6) laminating the first and second gel-like sheets to form a multi-layer, gel-like sheet,   (7) removing the first and second membrane-forming solvents from the multi-layer, gel-like sheet to form a solvent-removed gel-like sheet, and   (8) drying the solvent-removed gel-like sheet in order to form the multi-layer, microporous polyolefin membrane.   
     
     
         5 . The method of  claim 1 , further comprising:
 (3) extruding at least a portion of the first polyolefin solution through a first die to make a first extrudate,   (4) extruding at least a portion of the second polyolefin solution through at least a second die to make a second extrudate,   (5) cooling first and second extrudates to form at least one first gel-like sheet and at least one second gel-like sheet,   (6) removing the first and second membrane-forming solvents from the first and second gel-like sheets,   (7) drying the solvent-removed first and second gel-like sheets to form at least one first microporous polyolefin membrane and at least one second microporous polyolefin membrane, and   (8) laminating the first and second microporous polyolefin membranes in order to form the multi-layer, microporous polyolefin membrane.