Patent ID: 8354461

Claim:
A foamable composition for extruded foam insulation on a conductor, said insulation containing cells of uniform size concentrated towards the center of said insulation, whereby said insulation has a skin on its interior and exterior surfaces, said composition comprising: a) a partially-crystalline melt-processible fluorinated tetrafluoroethylene/hexafluoropropylene copolymer being substantially free of alkali metal ion, having less than about 20 unstable end groups per 10 6 carbon atoms, and having a melt flow rate of from about 25 to 35 g/10 min, and b) a foam nucleating package providing said 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 tetrafluoroethylene/hexafluoropropylene copolymer and said foam nucleating package, the extrusion of said foam insulation exceeding 500 ft/min, and wherein said foam nucleating package comprises i) boron nitride, ii) calcium tetraborate, 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 sulfur or phosphorus; M is 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.