Porous air permeable polytetrafluoroethylene composites with improved mechanical and thermal properties

• US 9,862,859 B2
• Filed: 09/10/2015
• Issued: 01/09/2018
• Est. Priority Date: 09/12/2014
• Status: Active Grant

• Current Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Original Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Inventors: Dutta, Anit, Nachbar, Leslie S.
• Primary Examiner(s): Vo, Hai
• Application Number:
  US14/850,434
• Publication Number:
  US 20160075915A1
• Time in Patent Office: 852 Days
• CPC Class Codes: B01D 2325/22 Thermal or heat-resistance properties
• CPC Class Codes: B01D 2325/24 Mechanical properties, e.g. strength
• CPC Class Codes: B01D 67/0088 Physical treatment with compounds, e.g. swelling, coating or impregnation
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 71/36 Polytetrafluoroethene
• CPC Class Codes: B01D 71/54 Polyureas; Polyurethanes
• CPC Class Codes: B01D 71/641 Polyamide-imides
• CPC Class Codes: B01D 71/643 Polyether-imides
• CPC Class Codes: B29C 55/005 characterised by the choice of materials
• CPC Class Codes: B32B 2255/102 synthetic resin or rubber layer being a foamed layer
• CPC Class Codes: B32B 2255/26 Polymeric coating
• CPC Class Codes: B32B 2266/025 Polyolefin
• CPC Class Codes: B32B 2266/06 Open cell foam
• CPC Class Codes: B32B 2307/724 Permeability to gases, adsorption
• CPC Class Codes: B32B 27/322 comprising halogenated polyolefins, e.g. PTFE
• CPC Class Codes: B32B 5/20 foamed in situ
• CPC Class Codes: B32B 5/32 at least two layers being foamed and next to each other
• CPC Class Codes: C08J 2475/04 Polyurethanes
• CPC Class Codes: C08J 2479/08 Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
• CPC Class Codes: C08J 5/2293 After-treatment of fluorine-containing membranes
• CPC Class Codes: C08J 7/0427 : with only one layer of a composition containing a polymer binder with more layers C08J7/042
• CPC Class Codes: C08J 7/046 : Forming abrasion-resistant coatings; Forming surface-hardening coatings
• CPC Class Codes: C08J 7/056 : Forming hydrophilic coatings
• CPC Class Codes: C09D 127/16 : Homopolymers or copolymers of vinylidene fluoride
• CPC Class Codes: C09D 127/18 : Homopolymers or copolymers of tetrafluoroethene
• CPC Class Codes: C09D 127/20 : Homopolymers or copolymers of hexafluoropropene
• CPC Class Codes: C09D 175/04 : Polyurethanes
• CPC Class Codes: C09D 179/08 : Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors

Abstract

Porous air permeable expanded PTFE composite with enhanced mechanical and thermal properties are described. The node and fibril microstructure of expanded PTFE is coated on and within the node and fibril microstructure with a suitably chosen polymer to impart property enhancement while maintaining porosity. The coating polymer content of the composite is maintained between 3 and 25 weight percent of the composite and the areal mass of the composite is less than 75 gm/m². Exemplary enhancement to properties may include, among others, Average Tensile Strength (ATS) (in MPa)×Z strength (in MPa) of 50 MPa² or greater, preferably 100 MPa² or greater, with air flow less than 500 Gurley seconds. Coating polymers with appropriate temperature resistance provides composites which further exhibit shrinkage of less than 10% at temperatures up to 300° C. with air flow of less than 500 Gurley seconds.

Claims

1. An article comprising:

a porous, air-permeable composite comprising

an expanded polytetrafluoroethylene (ePTFE) substrate having a microstructure comprising nodes, fibrils, and pores, said nodes being interconnected by said fibrils and said pores being a void space between said nodes and fibrils; and

at least one polyimide coating, wherein said polyimide coating conforms to surfaces of said nodes and fibrils throughout a thickness of said ePTFE substrate without occluding said pores of said ePTFE substrate, and wherein said polyimide coating comprises a polyimide content from 0.5 to 5 percent by weight,

wherein said composite exhibits a Gurley air flow of less than 500 seconds and a product of average tensile strength (ATS)×

Z Strength of at least 100 MPa².

2. The article of claim 1, wherein said composite has a strength in the z-direction of at least 0.4 MPa.

3. The article of claim 1, wherein said composite exhibits a Gurley air flow of 100 seconds or less.

4. The article of claim 1, wherein said article further comprises at least one filler.

5. The article of claim 1, wherein said composite comprises at least two ePTFE layers.

6. The article of claim 1, wherein said composite has an areal mass of 75 gm/m² or less.

7. The article of claim 1, wherein said composite has a Z strength of at least 0.4 MPa at room temperature.

8. An article comprising:

a porous, air-permeable composite comprising

an expanded polytetrafluoroethylene (ePTFE) substrate having a microstructure comprising nodes, fibrils, and pores, said nodes being interconnected by said fibrils and said pores being a void space between said nodes and fibrils; and

at least one polyimide coating, wherein said polyimide coating conforms to surfaces of said nodes and fibrils throughout a thickness of said ePTFE substrate without occluding said pores of said ePTFE substrate, and wherein said polyimide coating comprises a polyimide content from 0.5 to 5 percent by weight,

wherein said composite exhibits a Gurley air flow of less than 500 seconds, a mass per area of 75 gm/m² or less, and a shrinkage of less than 10% in at least one direction when measured at a temperature of 200°

C.

9. The article of claim 8, wherein composite exhibits a Gurley air flow of 100 seconds or less.

10. The article of claim 8, wherein said ePTFE substrate further comprises at least one filler within its microstructure.

11. The article of claim 8, wherein said composite comprises at least two ePTFE layers.

12. An article comprising:

a porous, air-permeable composite comprising

an expanded polytetrafluoroethylene (ePTFE) substrate having a microstrueture comprising nodes, fibrils, and pores, said nodes being interconnected by said fibrils and said pores being a void space between said nodes and fibrils; and

at least one polyimide coating wherein said polyimide coating conforms to surfaces of said nodes and fibrils throughout a thickness of said ePTFE substrate without occluding said pores of said ePTFE substrate, and wherein said polyimide coating comprises a polyimide content from 0.5 to 5 percent by weight,

wherein said composite exhibits a Gurley air flow of less than 500 seconds, a mass per area of 75 gm/m² or less, and a shrinkage of less than 10% in at least one direction when measured at a temperature of 300°

C.

13. The article of claim 12, wherein said composite article exhibits a Gurley air flow of 100 seconds or less.

14. The article of claim 12, wherein said ePTFE substrate further comprises at least one filler within its microstructure.

15. The article of claim 12, wherein said composite comprises at least two ePTFE layers.

16. An article comprising:

a porous, air-permeable composite comprising

an expanded polytetrafluoroethylene (ePTFE) substrate having a microstructure comprising nodes, fibrils, and pores, said nodes being interconnected by said fibrils and said pores being a void space between said nodes and fibrils; and

at least one polyimide coating, wherein said polyimide coating conforms to surfaces of said nodes and fibrils throughout a thickness of said ePTFE substrate without occluding said pores of said ePTFE substrate, and wherein said polyimide coating comprises a polyimide content from 0.5 to 5 percent by weight,

wherein said composite exhibits a Gurley air flow of less than 500 seconds and shrinkage of less than 10% in at least one direction when measured at a temperature of 300°

C.

17. An article comprising;

a porous, air-permeable composite comprising

an expanded polytetrafluoroethylene (ePTFE) substrate having a microstructure comprising nodes, fibrils, and pores, said nodes being interconnected by said fibrils and said pores being a void space between said nodes and fibrils; and

at least one polyimide coating, wherein said polyimide coating conforms to surfaces of said nodes and fibrils throughout a thickness of said ePTFE substrate without occluding said pores of said ePTFE substrate, and wherein said polyimide coating comprises a polyimide content from 0.5 to 5 percent by weight,

wherein said composite exhibits a Gurley air flow of less than 500 seconds, a mass per area of less than 75 gm/m², a Z-strength of at least 0.4 MPa at room temperature and, a shrinkage of less than 10% in at least one direction when measured at a temperature of 300°

C.