Process for preparing a foamed perfluorocarbon dielectric coaxial cable

• US 4,304,713 A
• Filed: 02/29/1980
• Issued: 12/08/1981
• Est. Priority Date: 02/29/1980
• Status: Expired due to Term

• Current Assignee: Andrew Corporation (CommScope Holding Company, Inc.)
• Original Assignee: Andrew Corporation (CommScope Holding Company, Inc.)
• Inventors: Perelman, Robert D.
• Primary Examiner(s): Anderson, Philip
• Application Number:
  US06/125,859
• Time in Patent Office: 648 Days
• Field of Search: 264/53, 264/DIG. 13, 264/45.9, 264/174, 264/DIG. 5, 521/98, 29/458, 29/828
• US Class Current: 264/45.9
• CPC Class Codes: C08J 2327/12 containing fluorine atoms
• CPC Class Codes: C08J 2427/00 Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
• CPC Class Codes: C08J 9/0061 characterized by the use of several polymeric components
• CPC Class Codes: C08J 9/14 organic
• CPC Class Codes: C08J 9/144 containing carbon, halogen and hydrogen only
• CPC Class Codes: H01B 11/1839 of cellular structure
• CPC Class Codes: H01B 13/142 of cellular material
• CPC Class Codes: Y10S 264/05 Use of one or more blowing agents together
• CPC Class Codes: Y10S 264/13 Cell size and distribution control while molding a foam
• CPC Class Codes: Y10T 29/49123 Co-axial cable
• CPC Class Codes: Y10T 29/49885 with coating before or during assembling

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.

Claims

1. A process for preparing the core for a foam dielectric coaxial cable, said process comprising the steps of:

(a) forming a mixture of a melt extrudable fluorinated ethylene-propylene polymer and a polytetrafluoroethylene nucleating agent;

(b) heating the polymer and nucleating agent mixture to the molten state;

(c) extruding the molten mixture through an extrusion die while feeding a continuous conductor axially through the extrusion die so as to form a layer of foam dielectric surrounding and in intimate contact with the continuous conductor along the entire length and about the entire periphery thereof;

(d) dissolving or injecting a volatile liquid blowing agent in the melt extrudable polymer at a point in the process prior to exit of the moisture from the extrusion die; and

,

(e) recovering the foamed articles exiting from the extrusion die.

2. The process of claim 1 wherein the fluorinated ethylene-propylene polymer is a copolymer of tetrafluoroethylene and hexafluoropropylene.

3. The process of claim 1 wherein the volatile liquid blowing agent is a fluorocarbon.

4. The process of claim 1 wherein the fluorocarbon blowing agent is a lower fluorocarbon having from 1 to 2 carbon atoms.

5. The process of claim 4 wherein the lower fluorocarbon is a fluoroethane represented by the formula:

##STR5##

6. The process of claim 1 wherein the fluorocarbon blowing agent is 1,2-dichloro-1,1,2,2-tetrafluoroethane.

7. The process of claim 1 wherein on the order of 0.5 parts by weight of polytetrafluoroethylene are contained within on the order of 100 parts by weight of the fluorinated ethylene-propylene polymer.

8. The process of claim 1 wherein the average particle size of the polytetrafluoroethylene is less than 200 microns.