Low bake temperature fluoropolymer coatings

1. A fluoropolymer coating comprising high temperature resistant polymer binder, low melting tetrafluoroethylene/hexafluoropropylene copolymer having a melting point of below 255° C. by the method of ASTM D 4591, and low molecular weight polytetrafluoroethylene having a heat of crystallization of at least about 50 J/g, wherein said high temperature resistant polymer binder comprises at least one member selected from the group consisting of polysulfones, polyethersulfones, polyimides, polyamide imides, polyamic acid salts and polyphenylene sulfide.

2. The fluoropolymer coating of claim 1 wherein said low melting tetrafluoroethylene/hexafluoropropylene copolymer has a melting point of about 250° C. or below by the method of ASTM D 4591.

3. The fluoropolymer coating of claim 1 wherein said low melting tetrafluoroethylene/hexafluoropropylene copolymer has a melting point of about 240° C. or below by the method of ASTM D 4591.

4. The fluoropolymer coating of claim 1 wherein said tetrafluoroethylene/hexafluoropropylene copolymer has a melting point that falls in the range of from about 40° C. below the melting point of said polymer binder to about 25° C. above the melting point of the polymer binder.

5. The fluoropolymer coating of claim 1 wherein said low melting tetrafluoroethylene/hexafluoropropylene copolymer has a melt flow rate of about 20 to about 60 by ASTM D 1238, measured at a temperature of 297° C. and a load of 2,060 g.

6. The fluoropolymer coating of claim 1 containing from about 25 to about 50 weight percent of said polymer binder from about 50 to about 75 weight percent of said tetrafluoroethylene/hexafluoropropylene copolymer and said polytetrafluoroethylene, said weight percents based on the combined dry weights of said polymer binder, said tetrafluoroethylene/hexafluoropropylene copolymer and said polytetrafluoroethylene.

7. The fluoropolymer coating of claim 1 wherein the fluoropolymer comprises from about 20 to about 60 weight percent of said tetrafluoroethylene/hexafluoropropylene copolymer and from about 40 to about 80 weight percent of said polytetrafluoroethylene, said weight percents based on the combined dry weights of said tetrafluoroethylene/hexafluoropropylene copolymer and said polytetrafluoroethylene.

8. A composition for forming a fluoropolymer coating comprising solvent, high temperature resistant polymer binder, low melting tetrafluoroethylene/hexafluoropropylene copolymer having a melting point of below 255° C. by the method of ASTM D 4591, and low molecular weight polytetrafluoroethylene having a heat of crystallization of at least about 50 J/g, wherein said high temperature resistant polymer binder comprises at least one member selected from the group consisting of polysulfones, polyethersulfones, polyimides, polyamide imides, polyamic acid salts and polyphenylene sulfide.

9. The composition of claim 8 further comprising surfactant.

10. A process for forming a fluoropolymer coating on a substrate, comprising:

i) applying to the surface of the substrate a coating composition comprising solvent, high temperature resistant polymer binder, low melting tetrafluoroethylene/hexafluoropropylene copolymer having a melting point of below 255° C. by the method of ASTM D 4591, and low molecular weight polytetrafluoroethylene having a heat of crystallization of at least about 50 J/g, wherein said high temperature resistant polymer binder comprises at least one member selected from the group consisting of polysulfones, polyethersulfones, polyimides, polyamide imides, polyamic acid salts and polyphenylene sulfide,

ii) removing said solvent from the coating composition on said substrate, and

iii) heating the coating composition of said substrate at a temperature sufficient to melt said polymer binder and said tetrafluoroethylene/hexafluoropropylene copolymer, and,

iv) cooling said coating composition to a temperature below the melting points of said polymer binder and said tetrafluoroethylene/hexafluoropropylene copolymer to form said fluoropolymer coating on said substrate.

11. The process of claim 10 wherein said substrate comprises nitinol.

12. An coated substrate having a coating composition comprising high temperature resistant polymer binder, low melting tetrafluoroethylene/hexafluoropropylene copolymer having a melting point of below 255° C. by the method of ASTM D 4591, and low molecular weight polytetrafluoroethylene having a heat of crystallization of at least about 50 J/g, wherein said high temperature resistant polymer binder comprises at least one member selected from the group consisting of polysulfones, polyethersulfones, polyimides, polyamide imides, polyamic acid salts and polyphenylene sulfide.

13. The coated substrate of claim 12 wherein said substrate comprises nitinol.

14. The coated substrate of claim 12 wherein the dry film thickness of said coating is from about 0.1 to about 0.4 mils.

15. The coated substrate of claim 12 wherein said coating has a static coefficient of friction of about 0.2 or less and a kinetic coefficient of friction of about 0.17 or less, said coefficients of friction measured by the method of ASTM 1894.