Biaxially oriented porous membranes, composites, and methods of manufacture and use

Abstract

At least a selected microporous membrane is made by a dry-stretch process and has substantially round shaped pores and a ratio of machine direction tensile strength to transverse direction tensile strength in the range of 0.5 to 6.0. The method of making the foregoing microporous membrane may include the steps of: extruding a polymer into a nonporous precursor, and biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction including a simultaneous controlled machine direction relax. At least selected embodiments of the invention may be directed to biaxially oriented porous membranes, composites including biaxially oriented porous membranes, biaxially oriented microporous membranes, biaxially oriented macroporous membranes, battery separators, filtration media, humidity control media, flat sheet membranes, liquid retention media, and the like, related methods, methods of manufacture, methods of use, and the like.

1 . A porous membrane comprising:
 at least one layer of porous polymer film made by a dry-stretch process including the steps of:   extruding a polymer into at least a single layer nonporous precursor, and   biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction stretching including a simultaneous controlled machine direction relax,   and having substantially round shaped pores, a porosity of about 40% to 90%, a ratio of machine direction tensile strength to transverse direction tensile strength in the range of about 0.5 to 5.0, a Gurley of less than about 100, a mean flow pore diameter of at least about 0.04 microns, an Aquapore size of at least about 0.07 microns, and a hydro-head pressure greater than about 140 psi.   
     
     
         2 . The membrane according to  claim 1 , wherein the machine direction stretching of said biaxially stretching includes the step of transverse direction stretching with simultaneous machine direction stretching, and wherein said biaxially stretching further includes the step of transverse direction relax. 
     
     
         3 . The membrane according to  claim 2 , wherein said biaxially stretching of said nonporous precursor further includes an additional step of machine direction stretching. 
     
     
         4 . The membrane according to  claim 1 , wherein said dry-stretch process further includes the step of:
 machine direction stretching to form a porous intermediate prior to said biaxial stretching.   
     
     
         5 . The membrane according to  claim 1 , wherein said biaxially stretching of said nonporous precursor includes the machine direction stretching, an additional transverse direction stretching with simultaneous machine direction stretching, and a transverse direction relax. 
     
     
         6 . The membrane according to  claim 1 , wherein said dry-stretch process includes the steps of:
 machine direction stretching followed by said biaxial stretching including said transverse direction stretching with simultaneous controlled machine direction relax, a second transverse direction stretching with simultaneous machine direction stretching, followed by transverse direction relax.   
     
     
         7 . The membrane according to  claim 1 , with said porous polymer film further having a thickness of at least about 8 microns, a transverse direction tensile strength of at least about 300 kgf/cm2, a standard deviation of mean flow pore diameter of less than about 0.025, a water intrusion pressure of at least about 80 psi, and a WVTR of at least about 8,000 g/m 2 -day. 
     
     
         8 . The membrane according to  claim 1 , with said porous polymer film further having a transverse direction shrinkage of less than about 1.0% at 90° C. 
     
     
         9 . The membrane according to  claim 1 , with said porous polymer film further having a transverse direction shrinkage of less than about 1.5% at 105° C. 
     
     
         10 . The membrane according to  claim 1 , with said porous polymer film further having a transverse direction shrinkage of less than about 3.0% at 120° C. 
     
     
         11 . The membrane according to  claim 1 , with said porous polymer film further having a thickness in a range of about 8 microns to 80 microns. 
     
     
         12 . The membrane according to  claim 1 , wherein said nonporous precursor is one of a blown film and a slot die film. 
     
     
         13 . The membrane according to  claim 1 , wherein said nonporous precursor is a single layer precursor formed by at least one of single layer extrusion and multilayer extrusion. 
     
     
         14 . The membrane according to  claim 1 , wherein said nonporous precursor is a multilayer precursor formed by at least one of coextrusion and lamination. 
     
     
         15 . The membrane according to  claim 1 , wherein said porous polymer film comprises one of polypropylene, polyethylene, blends thereof, and combinations thereof. 
     
     
         16 . The membrane according to  claim 1 , wherein said precursor is one of a single layer precursor and a multilayer precursor. 
     
     
         17 . The membrane according to  claim 1 , wherein said membrane further includes at least one nonwoven, woven, or knit layer bonded to at least one side of said porous polymer film. 
     
     
         18 . The membrane according to  claim 1 , wherein said membrane has substantially round shaped pores, a porosity of about 40% to 90%, a ratio of machine direction tensile strength to transverse direction tensile strength in the range of about 0.5 to 5.0, a Gurley of less than about 100, a mean flow pore diameter of at least about 0.04 microns, an Aquapore size of at least about 0.07 microns, and a hydro-head pressure greater than about 140 psi. 
     
     
         19 . The membrane according to  claim 1  wherein said polymer being selected from the group consisting of polyolefins, fluorocarbons, polyamides, polyesters, polyacetals (or polyoxymethylenes), polysulfides, polyphenyl sulfide, polyvinyl alcohols, co-polymers thereof, blends thereof, and combinations thereof. 
     
     
         20 . The membrane according to  claim 1  with said porous polymer film further having a porosity of about 65% to 90%, a ratio of machine direction tensile strength to transverse direction tensile strength in the range of about 1.0 to 5.0, a Gurley of less than about 20, a mean flow pore diameter of at least about 0.05 microns, an Aquapore size of at least about 0.08 microns, and a hydro-head pressure greater than about 145 psi. 
     
     
         21 . The membrane according to  claim 1 , wherein said substantially round shaped pores have at least one of an aspect ratio in the range of about 0.75 to 1.25 and a sphericity factor in the range of about 0.25 to 8.0. 
     
     
         22 . At least one of a filtration membrane, a humidity control membrane, a gas and/or liquid separation membrane, a selective passage of humidity and blockage of liquid water membrane, and a multi-layered membrane structure comprising the membrane of  claim 1 . 
     
     
         23 . The membrane according to  claim 1 , wherein said biaxially stretching step of said dry-stretch process includes the simultaneous biaxial stretching of a plurality of separate, superimposed, layers or plies of nonporous precursor, wherein none of the plies are bonded together during the stretching process. 
     
     
         24 . The membrane according to  claim 1 , wherein said biaxially stretching step of said dry-stretch process includes the simultaneous biaxial stretching of a plurality of bonded, superimposed, layers or plies of nonporous precursor, wherein all of the plies are bonded together during the stretching process. 
     
     
         25 . A battery separator comprising:
 at least one layer of porous polymer film made by a dry-stretch process including the steps of:   extruding a polymer into at least a single layer nonporous precursor, and   biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction stretching including a simultaneous controlled machine direction relax,   and having substantially round shaped pores, a porosity of about 40% to 70%, a ratio of machine direction tensile strength to transverse direction tensile strength in the range of about 0.5 to 5.0, a Gurley of less than about 300, a mean flow pore diameter of at least about 0.01 microns, and an Aquapore size of at least about 0.04 microns.   
     
     
         26 . The battery separator according to  claim 25 , wherein said substantially round shaped pores have at least one of an aspect ratio in the range of about 0.75 to 1.25 and a sphericity factor in the range of about 0.25 to 8.0.