Porous PTFE Materials and Articles Produced Therefrom

Abstract

Novel porous PTFE membranes are described possessing a unique combination of high strength, low flow resistance, and small pore size. Additionally, unique constructions with superior filtration and venting properties incorporating porous PTFE membranes are described.

1 . A method of forming a porous PTFE membrane comprising: 
 forming an extruded lubricated tape of PTFE polymer by a paste forming process;    stretching the extruded lubricated tape transversely at a ratio of at least 3:1, and drying the stretched tape to remove lubricant;    longitudinally expanding the resulting tape at a temperature above 327° C.; 
 then transversely expanding the tape at a temperature above 327° C.  
   
   
   
       2 . The method of  claim 1 , wherein said transverse expansion is carried out at a transverse expansion ratio of at least 20:1.  
   
   
       3 . The method of  claim 1 , wherein said transverse expansion is carried out at a transverse expansion ratio of at least 30:1.  
   
   
       4 . The method of  claim 1 , wherein the ratio of transverse expansion to longitudinal expansion is at least 1.  
   
   
       5 . The method of  claim 1 , wherein the ratio of transverse expansion to longitudinal expansion is at least 2.  
   
   
       6 . A method of forming a porous PTFE membrane comprising: 
 forming an extruded lubricated tape of PTFE polymer by a paste forming process;    stretching the extruded lubricated tape transversely, and drying the stretched tape to remove lubricant;    longitudinally expanding the resulting tape at a temperature above 327° C.;    then transversely expanding the tape at an expansion ratio of 20:1 or greater,    wherein the transverse expansion/longitudinal expansion ratio is greater than 2.    
   
   
       7 . The method of  claim 6 , wherein said extruded lubricated tape is stretched transversely at a ratio of at least 3:1.  
   
   
       8 . The method of  claim 6 , wherein said transverse expansion ratio is at least 30:1.  
   
   
       9 . The method of  claim 6 , wherein the transverse expansion/longitudinal expansion ratio is greater than 3.  
   
   
       10 . The method of  claim 6 , wherein the longitudinal expansion is at a temperature above 340° C.  
   
   
       11 . A method of forming a porous PTFE membrane comprising: 
 forming an extruded lubricated tape of PTFE polymer by a paste forming process;    stretching the extruded lubricated tape transversely, and drying the stretched tape to remove lubricant;    longitudinally expanding the resulting tape at a temperature above 327° C.;    then transversely expanding the tape at an expansion ratio of 20:1 or greater.    
   
   
       12 . The method of  claim 11 , wherein said extruded lubricated tape is stretched transversely at a ratio of at least 3:1.  
   
   
       13 . The method of  claim 11 , wherein said transverse expansion ratio is at least 30:1.  
   
   
       14 . The method of  claim 11 , wherein the longitudinal expansion is at a temperature above 340° C.  
   
   
       15 . A method of forming a porous PTFE membrane comprising: 
 forming an extruded lubricated tape of PTFE polymer by a paste forming process;    stretching the extruded lubricated tape transversely, and drying the stretched tape to remove lubricant;    longitudinally expanding the resulting tape;    then transversely expanding the tape at an expansion ratio of 20:1 or greater.    
   
   
       16 . The method of  claim 15 , wherein said extruded lubricated tape is stretched transversely at a ratio of at least 3:1.  
   
   
       17 . The method of  claim 15 , wherein said transverse expansion ratio is at least 30:1.  
   
   
       18 . The method of  claim 15 , wherein the longitudinal expansion is at a temperature above 340° C.  
   
   
       19 . The method of  claim 15 , wherein the transverse expansion is at a temperature above 360° C.  
   
   
       20 . The method of  claim 18 , wherein the transverse expansion is at a temperature above 360° C.  
   
   
       21 . An article comprising an expanded PTFE membrane having a membrane surface area of at least 17 m 2 /g.  
   
   
       22 . The article of  claim 21 , wherein said PTFE membrane has a light transmission through the membrane of greater than 50%.  
   
   
       23 . The article of  claim 21 , wherein the PTFE membrane surface area is at least 20 m 2 /g.  
   
   
       24 . The article of  claim 21 , wherein the PTFE membrane surface area is at least 23 m 2 /g.  
   
   
       25 . An article comprising an expanded PTFE membrane having a light transmission through the membrane of at least 50% and a porosity of at least 50%.  
   
   
       26 . The article of  claim 25 , wherein the expanded PTFE membrane has a light transmission through the membrane of at least 85% and a porosity of at least 75%.  
   
   
       27 . An article comprising an expanded PTFE membrane having a water entry pressure versus Gurley equal to or above the line defined by the equation WEP=3(Gurley)+2500.  
   
   
       28 . The article of  claim 27 , wherein the expanded PTFE membrane has a water entry pressure equal to or above the line defined by the equation WEP=3(Gurley)+2900.  
   
   
       29 . The article of  claim 27 , further comprising at least one additional layer selected from the group consisting of non-woven, scrim and fabric.  
   
   
       30 . The article of  claim 27 , further comprising at least one additional layer on each side of the PTFE membrane.  
   
   
       31 . The article of  claim 30 , wherein said at least one additional layer comprises at least one porous membrane.  
   
   
       32 . The article of  claim 31 , wherein said at least one additional layer comprises ePTFE.  
   
   
       33 . The article of  claim 27  in the form of a filter.  
   
   
       34 . The article of  claim 27  in the form of a vent.  
   
   
       35 . The article of  claim 27  in the form of a filter cartridge.  
   
   
       36 . An article comprising expanded PTFE membrane which is instantly wettable with water, said membrane having a water flux rate versus bubble point equal to or above the line defined by the equation log (water flux rate)=−0.01 (bubble point)+1.3.  
   
   
       37 . The article of  claim 36 , having a water flux rate versus bubble point equal to or above the line defined by the equation log (water flux rate)=−0.01 (bubble point)+2.48.  
   
   
       38 . The article of  claim 36  in the form of a filter cartridge.  
   
   
       39 . An article comprising an expanded PTFE membrane having a water flux rate versus bubble point equal to or above the line defined by the equation log (water flux rate)=−3.5×10 −3  (bubble point)+1.3 and a surface area of at least 17 m 2 /g.  
   
   
       40 . The article of  claim 39 , wherein the water flux rate versus bubble point is equal to or above the line defined by the equation log (water flux rate)=−3.5×10 −3  (bubble point)+1.6.  
   
   
       41 . The article of  claim 39  in the form of a filter cartridge.