Expanded ptfe filament with round cross section

Abstract

Fine expanded PTFE fiber with round cross section and smooth outer surface are obtained by twisting flat stretched filaments above the optimum limit for these fibers and subsequently further stretching with heat treatment. These filaments can be used for fabrics, among other applications, and they present the following properties: low shrinkage, low elongation under tension and high tensile strength. The invention also suggest a process of manufacturing said fiber, comprising the steps of twisting said expanded PTFE filament in excess to the optimum for the fiber, and stretching the twisted fiber under heat treatment until the fiber returns to its optimum twist and is fixed.

1 . A twisted fiber of expanded polytetrafluoroethylene wherein the fiber has a round cross section with smooth outer surface without grooves.  
     
     
         2 . A fiber according to  claim 1 , wherein said cross section presents a diameter ranging from 33 to 410 μm.  
     
     
         3 . A fiber according to  claim 1 , wherein it presents a filament number of about 18 to 1818 dtex.  
     
     
         4 . A fiber according to  claim 1 , wherein it presents a density of about 1.0 to 2.1 g/cm3.  
     
     
         5 . A fiber according to  claim 4 , wherein said density is of about 1.3 to 2.0 g/cm3.  
     
     
         6 . A fiber according to  claim 1 , it presents a tensile strength from 440 to 1800 MPa.  
     
     
         7 . A fiber according to  claim 1 , wherein its matrix tensile strength ranges from 650 to 2600 MPa.8. A fiber according to  claim 1 , wherein it presents an elongation at maximum stress of about 0.5% to 4.5%.  
     
     
         9 . A fiber according to claim  8 , wherein said elongation at maximum stress is of 1.0 to 3.0%.  
     
     
         10 . A fiber according to  claim 1 , wherein its shrinkage is of about 0.1 to 2.0%.  
     
     
         11 . A fiber according to  claim 10 , wherein said shrinkage is of 0.1 to 1.1%.  
     
     
         12 . A process for producing a fiber of expanded polytetrafluoroethylene (PTFE), said process comprising: 
 a) twisting said expanded PTFE fiber to the optimum twisting for the fiber,    b) submitting the fiber to heat treatment until it is fixed,    whereby the fiber retains a round cross section with a smooth outer surface.    
     
     
         13 . A process for producing a fiber of expanded polytetrafluoroethylene (PTFE); said process comprising: 
 a) twisting said expanded PTFE filament in excess to the optimum for the fiber;    b) stretching the twisted fiber under heat treatment until the fiber returns to its optimum twist and is fixed, whereby the fiber retains a round cross section with a smooth outer surface.    
     
     
         14 . A process according to  claim 13  wherein said expanded PTFE filament is twisted between 300 and 2000 twists per meter (TPM).  
     
     
         15 . A process according to  claim 13  or  14  wherein the stretching results in a stretching ratio of the fiber after twisting between 1.1 and 20.0.  
     
     
         16 . A process according to  claim 15  wherein said stretching ratio of the fiber is between 1.2 and 8.0.  
     
     
         17 . A process according to any of  claims 13  to  16  wherein the temperature of the heat treatment during the stretching is between 300 and 500° C.  
     
     
         18 . A fiber obtained according to the process of  claim 13  wherein the fiber has between 300 and 2000 twists per meter (TPM).  
     
     
         19 . A fiber according to  claim 18  wherein said filament has, a tensile strength between 440 and 1800 MPa, an elongation at maximum stress between 0.5% and 4.5%, a diameter between 33 and 410 μm, a filament number between 18 and 1818 dtex, and a density between 1.0 and 2.1 g/cm3.  
     
     
         20 . A fiber according to  claim 18  wherein said fiber is a monofilament.  
     
     
         21 . A fiber according to  claim 18  further comprising at least one pigment.  
     
     
         22 . A fiber according to  claim 18  further comprising at least one filler.