Polytetrafluoroethylene molded articles coated with fused fluoropolymer resin

Abstract

The present invention relates to a molded article of polytetrafluoroethylene or modified polytetrafluoroethylene having a fluoropolymer resin coating, the coating comprising a heat-flowable tetrafluoroethylene copolymer wherein the surface of the coated article has a reduced roughness compared to the molded article prior to coating. The coating for the molded article is preferably a fused powder, most preferably formed by electrostatically applying a fluoropolymer powder resin to the molded PTFE article. In a preferred embodiment, the fluoropolymer powder resin comprises a mixture of heat-flowable tetrafluoroethylene copolymer powder and a polytetrafluoroethylene that has a temperature of crystallization of at least 305° C. and a heat of crystallization of at least 50 J/g. The surfaces of the articles are smoother than the original articles so that they resist adhesion of chemical contaminants and have applicability for chemical containers and transport pipes in the rigorously clean environment of the semiconductor industry.

1 . A process for forming a smooth surface on a molded article of polytetrafluoroethylene or modified polytetrafluoroethylene by coating said article with a heat-flowable fluoropolymer powder resin and heating the coated article to form a fused fluoropolymer resin coating, wherein the surface of the coated article has a reduced roughness compared to the molded article prior to coating.  
     
     
         2 . The process of  claim 1  wherein said heat-flowable fluoropolymer resin comprises a tetrafluoroethylene copolymer.  
     
     
         3 . The process of  claim 1  wherein said fluoropolymer resin coating comprises a copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether) (PFA).  
     
     
         4 . The process of  claim 1  wherein said fluoropolymer resin coating comprises a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP).  
     
     
         6 . The process of  claim 1  wherein said fluoropolymer resin coating comprises a mixture of heat-flowable tetrafluoroethylene copolymer and a polytetrafluoroethylene that has a temperature of crystallization of at least 305° C. and a heat of crystallization of at least 50 J/g.  
     
     
         7 . The process of  claim 1  wherein said coating is formed by electrostatically applying said fluoropolymer powder resin to said molded PTFE article.  
     
     
         8 . The process of  claim 1  wherein the surface of the coated article has a roughness that is reduced by at least 25% as compared to the molded article prior to coating.  
     
     
         9 . The process of  claim 1  wherein the surface of the coated article has a roughness that is reduced by at least 50% as compared to the molded article prior to coating.  
     
     
         10 . The process of  claim 1  wherein the surface of the coated article has a roughness that is reduced by at least 75% compared to the molded article prior to coating.  
     
     
         11 . The process of  claim 1  wherein the coated surface has a center line average roughness (R a ) of less than 1.5 micrometers.  
     
     
         12 . The process of  claim 1  wherein the coated surface has a center line average roughness (R a ) of less than 1.0 micrometer.  
     
     
         13 . The process of  claim 1  wherein the coated surface has a center line average roughness (R a ) of less than 0.5 micrometer.  
     
     
         14 . The process of  claim 1  wherein the thickness of the fused fluoropolymer resin coating is 100 μm or less.