Coating electrically conductive wire with polyolefin
AssigneeComm/Scope Company
InventorsFrederic Nash Wilkenloh, Paul Alan Wilson, Steve Allen Fox
Life of this patent
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Abstract
Disclosed is a coaxial cable having greatly improved mechanical and electrical properties derived from a foamed dielectric having a dielectric constant in the range of 1.32 to 1.1, such cable being provided by a novel method of coating a center conductor of the cable with a dielectric with an extruded cellular polyolefin base composition which has been rendered cellular by the direct injection of a blowing agent in a liquid form into the polymer during an extrusion process. Also disclosed is an apparatus and a method of continuous wire electropolishing and pre-coating.
Claims9
A method of covering an electrically conductive wire with a polyolefin comprising:
- (a) mixing a polyolefin with a nucleating agent to form a mixture;
- (b) pressurizing above atmospheric pressure and heating said mixture to a temperature below that of the decomposition temperature of said nucleating agent sufficient to render said polyolefin molten;
- (c) injecting into said pressurized molten polyolefin and nucleating agent mixture a physical blowing agent in a liquid state selected from the group comprising dichlorotetrafluoroethane, trichlorotrifluorethane and mixtures of trichlorofluoromethane and dichlorodifluoromethane and mixing under pressure the blowing agent in its liquid state with said pressurized and heated mixture of polyolefin and nucleating agent, said liquid blowing agent being convertible to a gas upon exposure to atmospheric pressure;
- (d) cooling the mixture described in step (c) above to a predetermined temperature below that achieved in step (b) but above the solidification temperature of said mixture;
- (e) coating the thus cooled mixture of step (d) onto a coating of unfoamed polyolefin on a wire and adhesively bonding it thereto;
- (f) exposing the coated wire of step (e) to atmospheric pressure and temperatures below that achieved by step (d) for autogenously converting said blowing agent into a gas to expand said polyolefin by creating a multiplicity of cells wherein said gas is entrapped thereat, and solidifying the thusly expanded mixture.
A method of covering an electrically conductive wire with a polyolefin comprising:
- (a) providing first and second extruders each having access and outlet ports, the outlet port of said first extruder being in communication with the access port of said second extruder and said second extruder having a die in communication with its outlet port, adapted for the simultaneous passage there through of molten plastic material and an inner conductor in the form of a wire;
- (b) providing a mixture of polyolefin and a nucleating agent;
- (c) pressurizing and heating said mixture in said first extruder between 1,000 and 4,000 psig and 325.degree. to 400.degree. respectively so as to melt the polyolefin but not to thermally decompose the nucleating agent;
- (d) injecting into said heated and pressurized mixture in said first extruder a physical blowing agent in a liquid state selected from the group consisting of dichlorotetrafluoroethane, trichlorotrifluoroethane and mixtures of trichlorofluoromethane and dichlorodifluoromethane;
- (e) transferring under pressure the mixture of polyolefin, nucleating agent and liquid physical blowing agent created by step (d) to said second extruder;
- (f) cooling the mixture in the secondary extruder to a temerature below 250.degree. F. and maintaining pressure on it within the range of 2,500 to 1,000 psig;
- (g) passing a wire coated with an unfoamed polyolefin through the die of said second extruder and simultaneously coating the cooled mixture of step (f) on to said coated wire and adhesively bonding it thereto;
- (h) exposing the coated wire of step (g) to atmospheric pressure and temperatures below that achieved by step (f) for autogenously converting said liquid blowing agent into a gas to expand the polyolefin by creating a multiplicity of cells wherein the gas is entrapped thereat, and then solidifying the thusly expanded mixture.
Dependencies are inferred from the claim text.