High melt spinning of fluoropolymer fibers

Abstract

The processes and apparatus of the present invention concerns melt spinning high viscosity fluoropolymers into single filaments or multi-filament yarns at high spinning speeds, the melt spinning being carried out at a temperature which is at least 90° C. greater than the melting point of the polymer or in the case of perfluoropolymer, at a temperature of at least 450° C., and the yarns produced by the process, wherein the filaments exhibit a greater axial orientation in the center of the filament than at the surface.

What is claimed is:  
     
         1 . A process for melt spinning a composition comprising a highly fluorinated thermoplastic polymer, comprising the steps of: 
 melting a composition comprising a highly fluorinated thermoplastic polymer to form a molten fluoropolymer composition;    conveying said molten fluoropolymer composition under pressure to an extrusion die of an apparatus for melt spinning; and    extruding the molten fluoropolymer composition through the extrusion die to form filaments, said die being at a temperature of at least 450° C., at a shear rate of at least 100 sec −1 , at a spinning speed of at least 500 m/min.    
     
     
         2 . The process of  claim 1  further comprising shielding the filaments.  
     
     
         3 . The process of  claim 1  further comprising exposing the molten fluoropolymer composition to an intermediate temperature ranging between the melting temperature of said composition and a temperature less than the temperature of the extrusion die prior to extruding said composition through the extrusion die.  
     
     
         4 . The process of  claim 1  wherein the highly fluorinated polymer has a melt flow rate of 1 to 50 g/10 minutes at 372° C.  
     
     
         5 . The process of  claim 1  wherein the fluorinated polymer is a copolymer of tetrafluoroethylene and a perfluoroolefin.  
     
     
         6 . The process of  claim 5  wherein the fluorinated polymer is a copolymer of tetrafluoroethylene and hexafluoropropylene.  
     
     
         7 . The process of  claim 5  wherein the fluorinated polymer is a copolymer of tetrafluoroethylene and a perfluoroalkylvinyl ether.  
     
     
         8 . The process of  claim 7  wherein the perfluoroalkyl vinyl ether is perfluoromethylvinyl ether, perfluoroethylvinyl ether, or perfluoropropylvinyl ether.  
     
     
         9 . The process of  claim 1  wherein the temperature of the die is at least 500° C.  
     
     
         10 . The process of  claim 1  wherein the extrusion die is thermally isolated from other areas of the apparatus that may contain the fluoropolymer composition.  
     
     
         11 . The process of  claim 1  wherein the spinning speed is at least 1000 m/min.  
     
     
         12 . The process of  claim 1  wherein the shear rate is at least 500 sec −1 .  
     
     
         13 . The process of  claim 1  further comprising drawing the fibers.  
     
     
         14 . The process of  claim 1  further comprising a relaxation stage.  
     
     
         15 . A process for melt spinning a composition comprising polytetrafluoroethylene homopolymer, comprising the steps of: melting a composition comprising polytetrafluoroethylene homopolymer to form a molten polytetrafluoroethylene composition; conveying said molten polytetrafluoroethylene composition under pressure to an extrusion die of an apparatus for melt spinning; and extruding the molten polytetrafluoroethylene composition through the extrusion die to form molten filaments.  
     
     
         16 . The process of  claim 15  wherein the temperature of the extrusion die is at least 450° C.  
     
     
         17 . The process of  claim 15  wherein the spinning speed is at least 50 mpm.  
     
     
         18 . The process of  claim 17  wherein the spinning speed is at least 200 mpm.  
     
     
         19 . The process of  claim 18  wherein the spinning speed is at least 500 mpm.  
     
     
         20 . The process of  claim 15  further comprising shielding the filaments.  
     
     
         21 . An apparatus for melt-spinning fibers, comprising: 
 a spinneret assembly comprising: 
 means for filtering;  
 a spinneret;  
 an elongated transfer line, said transfer line being disposed between said filtration means and said spinneret;  
 means for heating said elongated transfer line;  
 means for heating said spinneret; and  
   an elongated annealer disposed beneath said spinneret assembly.    
     
     
         22 . The apparatus of  claim 21  wherein the elongated annealer comprises an inner tube disposed within an outer tube, said inner tube and said outer tube separated from each other by an annular space.  
     
     
         23 . The apparatus of  claim 22  further comprising a mesh tube disposed adjacent the inner wall of said inner tube extending at least partially down the length of said inner tube.  
     
     
         24 . The apparatus of  claim 22  further comprising at least one perforated plate disposed within said annular space, extending radially with respect to the circumference of said outer tube, and attached to the outer wall of said inner tube or the inner wall of said outer tube, or to both tubes.  
     
     
         25 . The apparatus of  claim 24  further comprising a screen placed on or in close proximity to the at least one perforated plate.  
     
     
         26 . The apparatus of  claim 21  wherein the elongated annealer further comprises means for measuring or controlling air flow rate.  
     
     
         27 . The apparatus of  claim 21  wherein the spinneret is removable.  
     
     
         28 . The apparatus of  claim 21  wherein the transfer line is removable.  
     
     
         29 . The apparatus of  claim 21  wherein said means for heating the spinneret is a conduction heater, a convection heater or an induction heater.  
     
     
         30 . The apparatus of  claim 21  wherein the spinneret has a plurality of extrusion holes all of which are arranged in one circle.  
     
     
         31 . The apparatus of  claim 21  further comprising means for accumulating the spun filaments.  
     
     
         32 . Oriented monofilament or multifilament yarn of highly fluorinated thermoplastic polymer wherein the orientation of the filaments are greater in the core of the filaments than at the surface of the filaments.  
     
     
         33 . The yarn of  claim 32  having a tenacity of at least 2 g/d .  
     
     
         34 . The yarn of  claim 33  having an elongation of at least 15%.  
     
     
         35 . The yarn of  claim 32  wherein said polymer is ethylene/tetrafluoroethylene copolymer  
     
     
         36 . Sewing thread containing the yarn of  claim 32 .  
     
     
         37 . Dental floss containing the yarn of  claim 32 .  
     
     
         38 . Fishing line containing the yarn of  claim 32 .  
     
     
         39 . Staple fiber of the yarn of  claim 32 .  
     
     
         40 . The yarn of  claim 32  containing colorant  
     
     
         41 . Process for making monofilament or multifilament yarn of highly fluorinated thermoplastic polymer comprising melt spinning said polymer at a temperature above the melting point of said polymer which is effective to produce said yarn wherein the filaments thereof are oriented greater in the core of said filaments than at the surface thereof.  
     
     
         42 . The process of  claim 41  wherein said melt spinning is carried out at a temperature of at least 90° C. greater than the melting point of said polymer.  
     
     
         43 . The process of  claim 42  wherein said yarn is produced at a speed of at least 500 m/min.  
     
     
         44 . Oriented monofilament or multifilament yarn of ethylene/tetrafluoroethylene copolymer having a tenacity of at least 2 g/d and elongation of at least 15%.