Paste extruded insulator with air channels

Abstract

The invention provides an insulated wire having a conductor and an insulator of paste extruded PTFE fine powder around the conductor. The paste extruded insulator has at least one closed continuous longitudinal air channel spaced apart from the conductor. The invention further provides a process for forming an insulator around a conductor by paste extruding lubricated PTFE fine powder in an extrusion device comprising a die, mandrel, and at least one channel-forming member. The die and mandrel form a converging chamber leading to an extrusion orifice and the channel-forming member is positioned in the orifice. The mandrel has a central bore for supplying the conductor. Lubricated PTFE fine powder is forced through the chamber and out of the exit of the orifice as a lubricated green extrudate around the conductor forming an insulator with at least one closed longitudinal air channel spaced apart from the conductor.

Description

FIELD OF THE INVENTION [0001] This invention relates to an insulated wire and a method for manufacturing it by paste extruding an insulator of polytetrafluoroethylene. BACKGROUND OF THE INVENTION [0002] Polytetrafluoroethylene (PTFE) fine powder has been used for many years as a wire insulator. However, despite the desirable properties of high molecular weight PTFE, namely low dielectric constant and low dissipation factor, other polymers have been used in forming insulation for wires, especially in large diameter, high frequency coaxial transmission cable because of the processing limitations of PTFE. [0003] Polytetrafluoroethylene (PTFE) fine powder is a type of PTFE that is made by aqueous dispersion polymerization, followed by coagulation of the dispersion and drying of the resultant coagulated solids to obtain the fine powder. Because the PTFE fine powder does not flow in the melt condition sufficiently to enable melt processing, the powder has been fabricated into articles and...

AI Technical Summary

Benefits of technology

[0013]FIG. 2 is an enlarged perspective view of one embodiment of a mandrel tip employed in the extrusion device of FIG. 1.

[0014]FIG. 3 is a partial perspective view of an insulator formed using the mandrel tip illustrated in FIG. 2.

[0015]FIG. 4 is an enlarged perspective view of a second embodiment of a mandrel tip for use in the extrusion device of FIG. 1.

[0016]FIG. 5 is a partial perspective view of an insulator formed using the mandrel tip illustrated in FIG. 4.

[0017]FIG. 6 is a partial perspective cut away view of a coaxial cable with insulated wire having an insulator and longitudinal air channels made according to this invention.

Problems solved by technology

However, despite the desirable properties of high molecular weight PTFE, namely low dielectric constant and low dissipation factor, other polymers have been used in forming insulation for wires, especially in large diameter, high frequency coaxial transmission cable because of the processing limitations of PTFE.

Nonetheless, PTFE has been difficult to form into large diameter insulators for wire because of difficulties in drying the green extrudate to remove the lubricant from thick structures of paste extruded PTFE fine powder.

Large diameter PTFE insulators have also been expensive because of the quantity of PTFE fine powder required.

Another significant requirement for high frequency communication cable is noncombustibility that fluoropolymers can provide but structures of polyethylene, polypropylene or polyvinyl chloride cannot.

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