Polyetrafluoroethylene compositions

• US 5,708,044 A
• Filed: 01/10/1996
• Issued: 01/13/1998
• Est. Priority Date: 09/02/1994
• Status: Expired due to Term

• Current Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Original Assignee: W. L. Gore & Associates (W.L. Gore & Associates)
• Inventors: Branca, Phillip A.
• Primary Examiner(s): COONEY, JOHN M
• Application Number:
  US08/584,576
• Time in Patent Office: 734 Days
• Field of Search: 264/127, 264/154, 264/288.8, 521/54, 521/59, 521/134, 521/145
• US Class Current: 521/145
• CPC Class Codes: B29C 55/005 characterised by the choice of materials
• CPC Class Codes: B29K 2027/18 PTFE, i.e. polytetrafluorethene , e.g. ePTFE, i.e. expanded polytetrafluorethene
• CPC Class Codes: B29K 2105/0088 Blends of polymers
• CPC Class Codes: C08L 2205/02 containing two or more polymers of the same C08L -group
• CPC Class Codes: C08L 2666/04 Macromolecular compounds according to groups C08L7/00 - C08L49/00, or C08L55/00 - C08L57/00; Derivatives thereof
• CPC Class Codes: C08L 27/18 Homopolymers or copolymers or tetrafluoroethene

Abstract

In the present invention a blend of resin composition and blending technique is optimized to provide a desired balance of node size and fibril length with the additional property of thermal stability in the resulting stretched material.

The stretched blend can be described as a polytetrafluoroethylene porous material having a microstructure of nodes interconnected by fibrils in which the material comprises a blend of two different polytetrafluoroethylenes, one polytetrafluoroethylene being a homopolymer of tetrafluoroethylene and the other polytetrafluoroethylene being a modified polymer of tetrafluoroethylene.

Claims

1. A stretched porous polytetrafluoroethylene having a microstructure of nodes interconnected by fibrils in which the material comprises a mixture of two different polymers, one polymer being polytetrafluoroethylene homopolymer and the other polymer being a non-resilient modified polytetrafluoroethylene polymer in which the polymer contains units of a comonomer in an amount insufficient to cause the polymer to become melt-processible.

2. A material of claim 1 in which the weight ratio of the polytetrafluoroethylene homopolymer to the modified polytetrafluoroethylene polymer is between 90/10 and 10/90.

3. A material of claim 1 in which the weight ratio of the polytetrafluoroethylene homopolymer to the modified polytetrafluoroethylene polymer is between 50/50 and 20/80.

4. The material of claims 1, 2, or 3 in the form of a tape filament, film, rod, or tube.

5. A material of claim 1 in which the homopolymer is present predominantly in the fibrils, and the modified polytetrafluoroethylene is present predominantly in the nodes.

6. A material of claim 1 in which the relaxation time of the materials is greater than 200 seconds.

7. A material of claim 1 in which the average fibril length is greater than 100 μ

m.

8. A material of claim 1 in which the coarseness factor is greater than 0.60 (g/cc)/psi.

9. Process for preparing a porous polytetrafluoroethylene material which comprises the steps in sequence of:

(a) forming an aqueous dispersion of a polytetrafluoroethylene homopolymer and a non-resilient modified polytetrafluoroethylene polymer in which the modified polymer contains units of a comonomer in an amount insufficient to cause the polymer to become melt-processible;

(b) coagulating the solids from the dispersion;

(c) lubricating and paste extruding the coagulated material; and

(d) stretching the material.

10. The process of claim 9 wherein the stretched mixture is then heat-treated.