Extrusion of a Foamable Fluoropolymer

Abstract

A process for making an extruded foamable composition is disclosed where the foamable composition includes a partially-crystalline melt processable perfluoropolymer and a foam nucleating package. The process makes a foamed product having uniform foam cell size at high speeds without loss of product quality.

1 . An extrusion process comprising:
 a) extruding a foamable composition comprising foamed cells wherein 90% of the foamed cells are 50 micrometers in diameter or less, and said foamable composition comprises:
 i) a partially-crystalline melt-processible perfluoropolymer, and 
 ii) a foam nucleating agent ranging from 0.1-10 wt % of the combined weight of said perfluoropolymer and said foam nucleating agent. 
   
     
     
         2 . The process according to  claim 1 , wherein said foam nucleating agent has a foam nucleating effective amount of at least one thermally stable compound which is selected from the group consisting of sulfonic and phosphonic acids and salts thereof. 
     
     
         3 . The process according to  claim 1 , wherein said foamable composition is extruded at a speed of greater than 500 ft/m in (150 m/min). 
     
     
         4 . The process according to  claim 1 , wherein said perfluoropolymer has a melt flow rate of from about 25 to 35 g/10 min. 
     
     
         5 . The process according to  claim 1 , wherein said perfluoropolymer is made by polymerizing monomers selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and perfluoro(alkyl vinyl ether). 
     
     
         6 . The process according to  claim 1 , wherein said perfluoropolymer is substantially free of metal ions. 
     
     
         7 . The process according to  claim 1 , wherein said perfluoropolymer is polymerized and isolated without the use of metal-ion containing reagents. 
     
     
         8 . The process according to  claim 1 , wherein said foamed insulation has a tensile strength of at least 2000 psi and an elongation of at least 200%. 
     
     
         9 . The process according to  claim 1 , wherein said perfluoropolymer comprises from about 0.5 to 10 by weight of at least one perfluoro(alkyl vinyl ether). 
     
     
         10 . The process according to  claim 1 , wherein said extruded foamable composition has a capacitance coefficient of variation (COV) of no greater than 1%. 
     
     
         11 . The A process according to  claim 1 , further comprising providing a self-skinning foamable composition. 
     
     
         12 . The process according to  claim 12 , wherein said foamable composition has a void content of 10-50%. 
     
     
         13 . The process according to  claim 1 , wherein said foamable composition has a spark resistance of less than 1 spark per 1000 feet (300 m) when tested at 1.5 kV. 
     
     
         14 . The process according to  claim 1 , further comprising creating a foamed covering for a substrate. 
     
     
         15 . The process according to  claim 1 , further comprising creating a foamed device. 
     
     
         16 . The process according to  claim 15 , wherein said foamed device comprises a tube or a sheet. 
     
     
         17 . An extrusion foaming process comprising extruding a foamable composition comprising:
 a) a partially-crystalline melt-processible perfluoropolymer, wherein said perfluoropolymer is fluorinated in the melt and   b) a foam nucleating package comprising
 i) boron nitride, 
 ii) a synergistic amount of at least one inorganic salt that is thermally stable at the fluoropolymer extrusion temperature, and consists of a metal cation and a polyatomic anion, and satisfies the relationship
   0.36×[14-pKa]−0.52≧[ r −0.2  q] 2>0.11×[14−pKa]−0.28 
 
   
       where
 R=crystal ionic radius of the cation, in Angstroms 
 Q=valence of the cation 
 pKa=−log of Ka for the following reaction
   HA −(n−1) <=>H + +A −n    
 
 where A is the salt anion, H is hydrogen, and n=absolute value of the valence of the anion; and
 iii) a foam nucleating agent of the formula
   [Z(CF 2 ) x (CF 2 CFX) p (R′) y (CH 2 ) z RO 3 ] n M 
 
 
 
       wherein:
 Z is selected from CCl 3 , CCl 2 H, H, F, Cl or Br; 
 each X, independently, is selected from H, F or Cl; 
 R is selected from sulfur or phosphorus; M is selected from H or a metallic, ammonium, substituted ammonium or quaternary ammonium cation; 
 x is an integer and is 0 to 10; 
 p is an integer and is 0 to 6; 
 y is 0 or 1; 
 z is an integer and is 0 to 10; 
 x+y+z+p is a positive integer or, if x+y+z+p is 0, Z is CCl 3  or CCl 2 H; 
 n is the valence of M; and 
 R′ is selected from 
 a C 5-6  perfluorinated alicyclic ring diradical; 
 a C 1-16  perfluorinated aliphatic polyether diradical with repeat units selected from [CF 2 O], [CF 2 CF 2 O], and [CF 2 CF(CF 3 )O]; and 
 a substituted or unsubstituted aromatic diradical, in which case, Z is H; 
 and said foam nucleating package ranges from 0.1-5 wt % of the combined weight of said perfluoropolymer and said foam nucleating package. 
 
     
     
         18 . The process according to  claim 17 , wherein said perfluoropolymer is made by polymerizing monomers selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and perfluoro(alkyl vinyl ether). 
     
     
         19 . The process according to  claim 17 , wherein said perfluoropolymer is made by polymerizing monomers selected from the group consisting of tetrafluoroethylene and perfluoro(alkyl vinyl ether). 
     
     
         20 . The process according to  claim 16 , wherein said at least one inorganic salt of the foam nucleating package comprises calcium tetraborate. 
     
     
         21 . The process according to  claim 16 , wherein said foam nucleating agent of the foam nucleating package comprises Zonyl® BAS. 
     
     
         22 . The process according to  claim 16 , wherein said foam nucleating package comprises 91.1±0.5 weight percent boron nitride, 2.5±0.2 weight percent calcium tetraborate, and 6.4±0.2 weight percent Zonyl® BAS of the total weight percent of the foam nucleating package.