Porous PTFE Materials and Articles Produced Therefrom

• US 20080053892A1
• Filed: 10/31/2007
• Published: 03/06/2008
• Est. Priority Date: 07/18/2005
• Status: Abandoned Application

• Current Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Original Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Inventors: Bacino, John, Hobson, Alex, Strid, Jason
• Application Number:
  US11/931,890
• Publication Number:
  US 20080053892A1
• Time in Patent Office: Days
• US Class Current: 210/483
• CPC Class Codes: B01D 2325/0283 Pore size
• CPC Class Codes: B01D 2325/20 Specific permeability or cut-off range
• CPC Class Codes: B01D 2325/24 Mechanical properties, e.g. strength
• CPC Class Codes: B01D 2325/43 Specific optical properties
• CPC Class Codes: B01D 39/1692 Other shaped material, e.g. perforated or porous sheets
• CPC Class Codes: B01D 67/0027 by stretching
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/12 Composite membranes; Ultra-thin membranes
• CPC Class Codes: B01D 71/36 Polytetrafluoroethene
• CPC Class Codes: B32B 2264/0257 Polyolefin particles, e.g. polyethylene or polypropylene homopolymers or ethylene-propylene copolymers
• CPC Class Codes: B32B 2307/414 Translucent
• CPC Class Codes: B32B 2307/54 Yield strength; Tensile strength
• CPC Class Codes: B32B 2307/72 Density
• CPC Class Codes: B32B 2307/724 Permeability to gases, adsorption
• CPC Class Codes: B32B 2307/726 Permeability to liquids, absorption
• CPC Class Codes: B32B 2307/732 Dimensional properties
• CPC Class Codes: B32B 27/12 next to a fibrous or filamentary layer
• CPC Class Codes: B32B 27/322 comprising halogenated polyolefins, e.g. PTFE
• CPC Class Codes: B32B 3/02 characterised by features of form at particular places, e.g. in edge regions non-uniform thickness B32B3/263
• CPC Class Codes: B32B 3/26 characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids foam layer B32B5/18; layer of synthetic resin characterised by fillers that create voids or cavities B32B27/205; characterised by an apertured layer
• CPC Class Codes: B32B 5/022 : Non-woven fabric
• CPC Class Codes: B32B 5/024 : Woven fabric
• CPC Class Codes: B32B 5/026 : Knitted fabric
• CPC Class Codes: B32B 5/16 : characterised by features of a layer formed of particles, e.g. chips, powder or granules layer formed of natural mineral particles B32B19/00; layer being formed of wood fibres, chips or particles B32B21/02
• CPC Class Codes: B32B 5/245 : another layer next to it being a foam layer
• CPC Class Codes: B32B 7/05 : the layers not being connected over the whole surface, e.g. discontinuous connection or patterned connection using interposed adhesives or bonding materials applied in spaced arrangements B32B7/14
• CPC Class Codes: B32B 7/12 : using interposed adhesives or interposed materials with bonding properties
• CPC Class Codes: Y10T 428/249954 : With chemically effective material or specified gas other than air, N, or carbon dioxide in void-containing component
• CPC Class Codes: Y10T 428/269 : including synthetic resin or polymer layer or component
• CPC Class Codes: Y10T 442/2139 : Coating or impregnation specified as porous or permeable to a specific substance [e.g., water vapor, air, etc.]

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.

Claims

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 m²/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 m²/g.

24. The article of claim 21, wherein the PTFE membrane surface area is at least 23 m²/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<sup>−

3</sup> (bubble point)+1.3 and a surface area of at least 17 m²/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<sup>−

3</sup> (bubble point)+1.6.

41. The article of claim 39 in the form of a filter cartridge.