Process for preparing a foamed perfluorocarbon dielectric coaxial cable

Abstract

An improved foamable dielectric composition comprising a melt extrudable perfluorocarbon resin containing therein (i) a polytetrafluoroethylene (PTFE) nucleating agent and (ii) a volatile blowing agent, preferably a lower fluorocarbon blowing agent having only one or two carbon atoms; a process for forming such a composition; and, products produced therewith. More specifically, a foamed melt extrudable fluorinated ethylene-propylene (FEP) polymer containing therein a PTFE nucleating agent and blown to a foamed structure by means of a volatile fluid--e.g., a lower fluorocarbon such as fluoromethane or, preferably, fluoroethane, a process for forming such a foamed compostion; and, products produced therewith such as jacketed electrical conductors and/or coaxial cables wherein at least one conductor is bonded to such a foamed melt extrudable resin. The foamed dielectric melt extrudable resin is characterized by its thermal stability, fire resistance, small closed cell structure, low density, and low insulating loss characteristics. In a preferred embodiment, the melt extrudable foamed resin comprises a perfluorocarbon polymer having a closed cellular structure with cells ranging from 10 to 40 mils., a density at least as low as 1.0 g./cc., and an insulation loss of less than 1.8 db/100 ft. at 1000 MHz.