WETTABLE FLUOROPOLYMER FIBER MATERIAL

Abstract

A wettable, dispersion spun fluoropolymer fiber prepared from non-melt-processible fluoropolymer particles.

Claims

1. A composition of matter comprising a viscous material and a fluoropolymer fiber material including between about 15% and about 25% by weight of a cellulosic matrix polymer.

2. The composition of claim 1 wherein the fluoropolymer fiber material includes dispersion spun fluoropolymer fibers prepared from a spin mix including an aqueous dispersion of insoluble fluoropolymer particles and an aqueous solution containing the cellulosic matrix polymer wherein the cellulosic matrix polymer is coagulated about the fluoropolymer particles to form the fluoropolymer fibers.

3. The composition of claim 1 wherein the cellulosic matrix polymer is selected from the group consisting of methylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose and carboxymethylcellulose.

4. The composition of claim 1 wherein the fluoropolymer fiber material is uniformly and substantially wetted by the viscous material.

5. The composition of claim 1 wherein the viscous material is a thermoset resin.

6. The composition of claim 5 wherein the thermoset resin is selected from the group consisting of epoxy, polyester, phenolic, vinyl ester, polyurethane, silicone, polyamide and polyamide-imide.

7. A prepreg comprising the composition of claim 5.

8. The composition of claim 1 wherein the viscous material is an aqueous solution.

9. The composition of claim 1 wherein the viscous material is a polymer solution.

10. The composition of claim 1 including about 10% to about 20% by weight of the fluoropolymer fiber material.

11. A wet-laid nonwoven material prepared from the composition of claim 1.

12. The composition of claim 2 including about 10% to about 20% by weight of the fluoropolymer fiber material wherein the fluoropolymer fiber material is substantially wetted by the viscous material.

13. The composition of claim 1 wherein the composition is a colloidal suspension.

14. A method of making a composition of matter comprising: forming a mixture by combining fluoropolymer particles with a matrix polymer solution containing a matrix polymer, forming a fluoropolymer fiber by extruding the mixture into a coagulation bath, the fluoropolymer fiber including at least about 15% by weight of the matrix polymer, and combining the fluoropolymer fiber with a viscous material.

15. The method of claim 14 wherein the fluoropolymer fiber is substantially wetted by the viscous material.

16. The method of claim 14 wherein the viscous material is a thermoset resin.

17. The method of claim 14 wherein the matrix polymer is a cellulosic polymer.

18. The method of claim 14 wherein the fluoropolymer fiber is un-sintered.

19. The method of claim 14 comprising forming a self-lubricating bearing from the composition of matter.

20. The method of claim 14 comprising forming a coating from the composition of matter.

21. The method of claim 14 comprising forming a woven material from the fluoropolymer fiber prior to combining the fluoropolymer fiber with the viscous material, the woven material including about 100% by weight of the fluoropolymer fiber.

22. The method of claim 21 wherein, when the viscous material is an adhesive, adhering the woven material to a metal substrate.

23. The method of claim 15 wherein the viscous material is a thermoset resin, the matrix polymer is a cellulosic polymer and the fluoropolymer fiber is un-sintered.

24. A mixture comprising: a first material prepared from a matrix spun fluoropolymer yarn, the fluoropolymer yarn including about 15% to about 25% by weight of a cellulosic matrix polymer, and a second material selected from the group consisting of a thermoset resin, an adhesive, an elastomer resin and a thermoplastic resin, wherein the first material is substantially wetted by the second material.

25. The mixture of claim 24 wherein the first material is uniformly dispersed in the second material.

26. The mixture of claim 24 wherein the mixture is a colloidal suspension.

27. The mixture of claim 24 wherein the second material is a thermoset resin.

28. The mixture of claim 24 wherein the first material is not etched and the mixture is free of surfactant.

29. The mixture of claim 24 including about 0.5% to about 40% by weight of the first material.

30. The mixture of claim 24 including about 10% to about 20% by weight of the first material.

31. The mixture of claim 24 wherein the fluoropolymer yam includes 18% to 21% by weight of the cellulosic polymer.

32. A wet-laid nonwoven material prepared from the mixture of claim 1.

33. The mixture of claim 24 wherein the first material is a woven material including about 100% by weight of the fluoropolymer yam and the second material is the adhesive.

34. A method of making a composition of matter comprising: forming a mixture by mixing a dispersion of insoluble fluoropolymer particles with a solution of a soluble matrix polymer, extruding the mixture into a coagulation solution in which the matrix polymer becomes insoluble thereby forming a fluoropolymer fiber including the fluoropolymer particles and the insoluble matrix polymer, drying the fluoropolymer fiber, and thereafter, combining the fluoropolymer fiber with a first material whereby the fluoropolymer fiber is substantially wetted by the first material.

35. The method of claim 34 wherein the fluoropolymer fiber is an intact, un-sintered fluoropolymer fiber.

36. The method of claim 34 wherein the fluoropolymer fiber includes about 15% to about 25% by weight of the insoluble matrix polymer.

37. The method of claim 34 wherein the matrix polymer is a cellulosic matrix polymer.

38. The method according to claim 34 wherein the composition is a colloidal suspension.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention is directed to a readily dispersible, dispersion spun fluoropolymer fiber and mixtures formed therefrom. Generally, the fluoropolymer fiber is prepared by forming an aqueous dispersion of fluoropolymer particles, mixing the dispersion with an aqueous matrix polymer solution containing a matrix polymer, extruding the mixture into a coagulation bath and forming a fiber structure. The fiber structure is then heated to dry the fiber structure but without decomposing the matrix polymer. The resulting fiber includes about 15% to about 25% by weight of the matrix polymer. When mixed with a viscous material such a thermoset, elastomeric or thermoplastic resin, the fiber is uniformly and substantially wetted by the second material.

[0015] By fluoropolymer fiber it is meant a fiber prepared from polymers such as polytetrafluoroethylene, and polymers generally known as fluorinated olefinic polymers, for example, copolymers of tetrafluoroethylene and hexafluoropropene, copolymers of tetrafluoroethylene and perfluoroalkyl-vinyl esters such as perfluoropropyl-vinyl ether and perfluoroethyl-vinyl ether, fluorinated olefinic terpolymers including those of the above-listed monomers and other tetrafluoroethylene based copolymers. For the purposes of this invention, the preferred fluoropolymer fiber is a polytetrafluoroethylene fiber.

[0016] By substantially wetted it is meant that the viscous material remains in contact with at least at least 90% or about 100% of the surface of the fluoropolymer fiber material two minutes after mechanically mixing the fluoropolymer fiber material with the viscous material. Alternatively, substantially wetted means that the viscous material exhibits a contact angle with the fluoropolymer fiber material of less than 90°, less than 60°, less than 45°, less than 30° or less than 15°.

[0017] The fluoropolymer fiber of the present invention is dispersion spun by mixing a dispersion of insoluble fluoropolymer particles with a solution of a soluble matrix polymer and coagulating the mixture into filaments by extruding the mixture into a coagulation solution in which the matrix polymer becomes insoluble. One method which is commonly used to dispersion spin fluoropolymers includes spinning the polymer from a mixture of an aqueous dispersion of the polymer particles and viscose, where cellulose xanthate is the soluble form of the matrix polymer, as taught for example in U.S. Pat. Nos. 3,655,853; 3,114,672 and 2,772,444. However, the use of viscose suffers from some serious disadvantages. For example, when the fluoropolymer particles and viscose mixture is extruded into a coagulation solution for making the matrix polymer insoluble, the acidic coagulation solution converts the xanthate into unstable xantheic acid groups, which spontaneously lose CS2, an extremely toxic and volatile compound. Preferably, the fluoropolymer fiber of the present invention is prepared using a more environmentally friendly method than those methods utilizing viscose. One such method is described in U.S. Pat. Nos. 5,820,984; 5,762,846, and 5,723,081, which patents are incorporated herein in their entireties by reference. In general, this method employs a cellulosic ether polymer such as methylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose or carboxymethylcellulose as the soluble matrix polymer, in place of viscose. For the purposes of this invention, the preferred method of making the fluoropolymer fiber is by dispersion spinning where the matrix polymer is a cellulosic ether polymer.

[0018] Following extrusion of the mixture into the coagulation solution, the filaments are washed in near neutral pH water to remove substantially all ions and impurities such as additives and/or dispersants that are present in the initial fluoropolymer dispersion. The resulting fluoropolymer fiber is then partially dried by passing the fiber over a series of heating rolls operating at a temperature that is less than the sintering temperature of the fibers or about 100° F. to about 400° F. Thereafter, the partially dried fluoropolymer filament fiber may be passed directly from the series of heated rolls to a series of drawing rolls operating at ambient temperature. After drawing, the fluoropolymer filament fiber is further dried, wound and stored.

[0019] The fluoropolymer fiber material prepared according to the foregoing process includes between about 15% and about 25% by weight of the cellulosic matrix polymer. The presence of the cellulosic matrix polymer in the disclosed amounts improves the hydrophilicity of the fluoropolymer fiber and makes it readily dispersible in and substantially wettable by liquids.

[0020] Depending on the anticipated use of the fluoropolymer fiber material, the fluoropolymer fiber can be made into floc or staple using any number of means known in the art. Preferably, the fluoropolymer fiber is cut into floc or staple by a guillotine cutter, which is characterized by a to-and-fro movement of a cutting blade. Following cutting, the fluoropolymer fibers preferably have lengths ranging between 127 microns and 115,000 microns.

[0021] When the processed fluoropolymer fiber material of the present invention is mixed with a resin and molded into a part, the properties imparted to the part by including the fiber material are enhanced or improved over the properties imparted by the prior art or conventional fluoropolymer fibers, including for example, increasing the resistance of the part to chemicals, oxidation, moisture, weathering, ozone or ultraviolet radiation and increasing the hydrophilicity or wettability of the part. Thus, the processed fluoropolymer fiber can be used to impart these improved properties in electrical components, chemical processing equipment and in coatings for cooking utensils, pipes, bearings, bushings, fabrics, filters and gaskets. Specific applications are described, for example, in U.S. Pat. No. 6,695,734 (rubber belts); U.S. Pat. No. 6,506,491 (friction applications such as bearings, bushings and seals); U.S. Pat. No. 6,299,939 (diaphragms for use in an electrolytic cells); U.S. Pat. No. 6,180,574 (self-lubricating bearings and coatings), U.S. Pat. No. 5,527,569 (filter media for forming filter cloth, filter bags and filter cartridges) and U.S. Patent Application Publication No. 20060057925 (prepregs and nonwoven materials for low friction bearing surfaces).

[0022] As will be apparent to one skilled in the art, various modifications can be made within the scope of the aforesaid description. Such modifications being within the ability of one skilled in the art form a part of the present invention and are embraced by the claims below.