Foamable Fluoropolymer Composition

Abstract

The present invention discloses a foamable composition. The foamable composition includes a partially-crystalline melt processible perfluoropolymer and a foam nucleating package. The foamable composition has a uniform foam cell size where the foam cell size of at least 90% of the foamed cells is 50 micrometers or less. The foam nucleating package ranges from 0.1 to 10 wt % of the combined weight of the perfluoropolymer and the foam nucleating package.

1 . A foamable composition comprising:
 a) a partially-crystalline melt-processible perfluoropolymer and   b) a foam nucleating package comprising a uniform foam cell size wherein the foam cell size of 90% of the foamed cells is 50 micrometers or less, and said foam nucleating package ranges from 0.1-10 wt % of the combined weight of said perfluoropolymer and said foam nucleating package.   
     
     
         2 . The composition according to  claim 1 , wherein said foam nucleating package comprises a foam nucleating agent having 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 composition according to  claim 1 , wherein said perfluoropolymer has a melt flow rate of from about 25 to 35 g/10 min. 
     
     
         4 . The composition 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). 
     
     
         5 . The composition according to  claim 4 , wherein said perfluoropolymer is fluorinated in the melt. 
     
     
         6 . The composition according to  claim 4 , wherein said hexafluoropropylene ranges from 3 to 20 weight percent of the perfluoropolymer. 
     
     
         7 . The composition according to  claim 1 , wherein said perfluoropolymer is substantially free of metal ions. 
     
     
         8 . The composition according to  claim 1 , wherein said perfluoropolymer is polymerized and isolated without the use of metal ion containing reagents. 
     
     
         9 . The composition 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 composition according to  claim 9 , wherein said perfluoro(alkyl vinyl ether) is perfluoro(ethyl vinyl ether). 
     
     
         11 . The composition according to  claim 9 , wherein said perfluoro(alkyl vinyl ether) is perfluoro(propyl vinyl ether). 
     
     
         12 . The composition according to  claim 9 , wherein said perfluoro(alkyl vinyl ether) is perfluoro(methyl vinyl ether). 
     
     
         13 . The composition according to  claim 1 , comprising a tensile strength of at least 2000 psi (13.8 MPa) and an elongation of at least 200%. 
     
     
         14 . The composition according to  claim 1 , comprising a capacitance coefficient of variation (COV) of no greater than 1%. 
     
     
         15 . The composition according to  claim 1 , comprising a foamable composition having a void content of 10-50%. 
     
     
         16 . The composition according to  claim 1 , wherein said composition is self-skinning. 
     
     
         17 . The composition according to  claim 1 , wherein said foamable composition has a spark resistance of less than one spark per 1000 feet (300 m) when tested at 1.5 kV. 
     
     
         18 . 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, Z is H, and said foam nucleating package ranges from 0.1-10 wt % of the combined weight of said perfluoropolymer and said foam nucleating package.   
     
     
         19 . The composition according to  claim 18 , wherein said perfluoropolymer is made by polymerizing monomers selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and perfluoro(alkyl vinyl ether). 
     
     
         20 . The composition according to  claim 18 , wherein said perfluoropolymer is made by polymerizing monomers selected from the group consisting of tetrafluoroethylene and perfluoro(alkyl vinyl ether). 
     
     
         21 . The composition according to  claim 18 , wherein said at least one inorganic salt of the foam nucleating package comprises calcium tetraborate. 
     
     
         22 . The composition according to  claim 18 , wherein said foam nucleating agent of the foam nucleating package comprises Zonyl® BAS. 
     
     
         23 . The composition according to  claim 21 , wherein said foam nucleating agent of the foam nucleating package comprises Zonyl® BAS. 
     
     
         24 . The composition according to  claim 22 , 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.