Foamed FEP-FLUROCARBON resin offers better insulation foamed resin. Coaxial cables can be made with larger dia conductors, without changing OD, if foam replaces unfoamed insulation. These cables, insulated with foamed FEP, have the same 400 F continuous-service temperature associated with unfoamed FEP. Other advantages include less resin cost per unit length of cable, lower weight, better flexibility and lower attenuation.
The preferred technique for foaming FEP resin consists of extruding resin that has been 1) impregnated with a blowing agent and 2) contains a nucleating agent. The gas-laden resin usually contains, by weight, less than 1% blowing agent and 1% nucleating agent.
The dissolved gas expands within the molten resin as it leaves the extruder die. Extrusion techniques involving thermal decomposition of a chemical blowing agent mixed with a resin are not used. Commercially available blowing agents of this type decompose and release gas at temperature below those needed to incorporate them in FEP resin.
The foaming agents used, dichlorodifluoromethane or chlorodifluoromethan, are intimately dissolved in the resin at room temperature for 4 days to obtain equilibrium absorption while the FEP is still in cube form. Pressure used in lower than the total pressure available from a cylinder of the gas.
A finely divided nucleating agent is incorporated in the resin to control the size of cells formed. Nucleating agents such as boron nitride or silicon dioxide are the most efficient.
Fluoropolymers & Compounds ,Fluorine Products, and Composite Films are available.
