Porous PTFE Materials and Articles Produced Therefrom
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.