Fluoropolymer blending process

Abstract

Aqueous dispersions on non-melt flowable PTFE and melt-fabricable perfluoropolymer are mixed together, followed by recovery of the resultant mixture of the dispersed particles of each of these polymers, and melt mixing of the resultant mixture of particles to obtain a blend in which the PTFE particles form the disperse phase and the perfluoropolymer forms the continuous phase, the melt mixing producing advantageous melt viscosities and the blend exhibiting advantageous physical properties even at high PTFE contents of about 30 wt %.

1 . Process for melt fabricating perfluoropolymer, comprising forming a mixture of submicrometer-size particles of non-melt-flowable polytetrafluoroethylene and melt-fabricable perfluoropolymer, melt blending said mixture to form a dispersion of said particles of non-melt flowable polytetrafluoroethylene in a continuous phase of said melt-fabricable perfluoropolymer, and molding the resultant melt blend into an article.  
   
   
       2 . The process of  claim 1  wherein said melt blending and molding is done by extrusion or injection molding.  
   
   
       3 . The process of  claim 1  wherein said article is pellets for subsequent molding into a final article.  
   
   
       4 . The process of  claim 1  wherein said article is a final article.  
   
   
       5 . The process of  claim 1  wherein said non-melt flowable polytetrafluoroethylene constitutes at least about 0.1 wt % of the combined weight of said non-melt-flowable polytetrafluoroethylene and said melt-fabricable perfluoropolymer.  
   
   
       6 . The process of  claim 1  wherein said non-melt flowable polytetrafluoroethylene constitutes at about 4 to 40 wt % of the combined weight of said non-melt-flowable polytetrafluoroethylene and said melt-fabricable perfluoropolymer.  
   
   
       7 . The process of  claim 1  wherein said mixture of submicrometer-size particles of non-melt-flowable polytetrafluoroethylene and melt-fabricable perfluoropolymer is formed by mixing together an aqueous dispersion of submicrometer-size particles comprising non-melt flowable polytetrafluoroethylene and an aqueous dispersion of submicrometer-size particles comprising melt-fabricable perfluoropolymer and separating the resultant mixture of said submicrometer-size particles from the resultant mixture of said aqueous dispersions.  
   
   
       8 . The process of  claim 1  wherein said submicrometer-size particles of non-melt flowable polytetrafluoroethylene are core/shell particles, said polytetrafluoroethylene being present in said core and at least a portion of said perfluoropolymer being present in said shell.  
   
   
       9 . The process of  claim 1  wherein all of said melt-fabricable perfluoropolymer in said melt mixture comes from said submicrometer-size particles thereof.  
   
   
       10 . The process of  claim 7  wherein said separating is done by co-coagulating said mixed-together aqueous dispersions and drying the resultant mixture of submicrometer-size particles.  
   
   
       11 . The process of  claim 1  wherein said melt blending is carried out in a single screw extruder.  
   
   
       12 . The process of  claim 1  wherein the mixture of submicrometer-size particles of non-melt-flowable polytetrafluoroethylene and melt-fabricable perfluoropolymer is characterized by a reduction in melt viscosity upon increasing shear rate from about 10 s −1  to about 100 s −1  that is at least 10% greater than the reduction in melt viscosity at the same shear rates for the melt-fabricable perfluoropolymer by itself, as determined by the capillary rheometer method.  
   
   
       13 . The process of  claim 12  wherein said reduction in melt viscosity is obtained when said particles of non-melt flowable polytetrafluoroethylene constitute at least 4 wt % of the combined weight of said particles of said non-melt-flowable polytetrafluoroethylene and said melt-fabricable perfluoropolymer.  
   
   
       14 . The process of  claim 1  wherein the mixture of submicrometer-size particles of non-melt-flowable polytetrafluoroethylene and melt-fabricable perfluoropolymer is characterized by an elongation of at least 200% when said particles of non-melt flowable polytetrafluoroethylene constitute at least 4 wt % of the combined weight of said particles of non-melt-flowable polytetrafluoroethylene and said melt-fabricable perfluoropolymer.  
   
   
       15 . The process of  claim 1  wherein the tensile strength of said mixture is as least as great as that of said melt-fabricable perfluoropolymer by itself.  
   
   
       16 . Process for melt fabricating perfluoropolymer, comprising forming a mixture of submicrometer-size particles of non-melt-flowable polytetrafluoroethylene and melt-fabricable perfluoropolymer, melt blending said mixture, and molding the resultant melt blend into an article, said mixture of submicrometer-size particles of non-melt-flowable polytetrafluoroethylene and melt-fabricable perfluoropolymer being characterized by either elongation at break of at least 75% and/or viscosity reduction of at least 10% when shear is increased from about 10 s −1  to 100 s −1 , both with respect to the elongation and viscosity reduction of the perfluoropolymer by itself, at a composition at which said polytetrafluoroethylene constitutes at least 4 wt % of the combined weight of said polytetrafluoroethylene and said perfluoropolymer.  
   
   
       17 . Molded article obtained by the process of  claim 16.