WO1990007779A1

WO1990007779A1 - Miniature electric cable

Info

Publication number: WO1990007779A1
Application number: PCT/US1989/004580
Authority: WO
Inventors: Edwin R. Peterson
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-30
Filing date: 1989-10-12
Publication date: 1990-07-12
Anticipated expiration: 1991-06-30
Also published as: AU4488889A

Abstract

A plurality of conductors (12) in parallel side-by-side relation is contained in an extruded insulating coating (22), each conductor (12) comprising a pair of tinsel conductor ribbons (18, 20) spirally wrapped in opposite directions about a multi-filament tensile core (14) strand of unbonded multi-filaments (16).

Description

TITLE OF INVENTION:

MINIATURE ELECTRIC CABLE

D E S C R I P T I O N

BACKGROUND OF THE INVENTION

Technical Field. This invention relates to a small size electric cable primarily for telephone, data and other signal transmission where cable tensile strength and flexibility are the major concerns.

Background Art. In the electronics field there is a general class of flexible cables known as tinsel cables. Tinsel cables are used in applications where great flexi¬ bility for the cable is required. Generally they are. constructed by spiral wrapping a tinsel foil of conductive material, usually copper, around a tensile filament or element, usually nylon or polyester. The wire is then coated with a thermoplastic insulating material. The required number of independent wires are then arranged in a flat parallel ribbon and jacketed with a second plastic material, to form a multi-wire, flexible, cable, which can be subjected to repeated flexure without fatiguing the tinsel, conductive, metal foil. The primary structural member able to withstand tensile stress in these prior art flexible cables is the plastic jacket. However, at the dimensional sizes taught by the present invention, there is insufficient plastic material in the plastic jacket to be of any use as a structural member able to withstand even moderate tensile stress. Two problems exist in the current technology, namely that the tensile filaments are not particularly strong, and secondly, repeated flexure of the cable oftentimes results in localized elongation of the tensile filaments and slippage of the spiral wrapped conductive material, thus resulting in a decrease in current carrying capacity eventually resulting in a break in conductivity.

The tensile filaments taught by the prior art are usually nylon, polyester or other polymer material. These tensile filaments are subject to elongation factors of 10% at strain forces of a mere 4 grams/denier (35 cN/Tex) and will break at force levels of approximately 8 grams/denier (70 cN/Tex) . These forces can be easily incurred with miniature cables merely by inadvertently tugging on the cable or, in a localized fashion, merely by folding and crimping the cable.

As a result the present technology has developed to include double spiral wraps of conductive material in order to compensate for the slippage of tinsel foil around the elongated or broken tensile filaments.

An attempt to provide such a cable is disclosed in Harayama, United States Patent No. 4,567,321. However, even the Harayama disclosure teaches the use of a nylon fiber, polyamide resin or porous, expanded, sintered PTFE as a tensile member around which are spiraled conductive tinsel foils. The cable taught by Harayama will work in applications requiring great flexibility, but not in applications requiring both great flexibility and tensile strength. An example of an application requiring great flexi¬ bility and significant tensile strength is described in applicant's United states Patent 4,646,987 in connection with a take-up reel for a telephone handpiece electric cord, where the reel is supported by the cord itself.

Although the reel in said patent is relatively small compared to other available take-up reels for electric cords, it is desired to provide a cord or cable which will allow the reel to be even smaller and less intrusive in the use of the telephone, yet still retain the required tensile strength, such an improvement could have applica¬ tion to many fields of use. Accordingly, it is an object of this invention to provide a miniature electric cable that is flat so that it coils up compactly, of great flexibility, and of high tensile strength in order to withstand the normal tugs and pulls of regular use.

DISCLOSURE OF INVENTION

The present cord, which may also be referred to as a cable, contains one or more flexible tensile elements of an aramid fiber from the family of aromatic polyamides. Each such tensile element in the cable is wrapped, covered or coated with a conductive material such as spiralled copper foil in one or more layers, wrapped in one or more directions or layered or interwoven mechani¬ cally. This conductor takes relatively little stress in tension or flexure while the tension elements bear the major loads.

A plurality of such conductor tensile elements, in many cases called tensile wire, may then be combined into a flat cord or ribbon cable by an outer covering. The covering may be applied by one or more methods such as extrusion, lamination, molding, dip, spray or other pre- coating or weaving. The covering provides high tempera- ture resistance, a fire retardant, wear resistance, elec¬ trical insulation between elements and to the exterior, mechanical support and geometric separation of plural conductors and stability.

The present preferred embodiment, although developed for telephone handset use, also has wide application for data and other signal transmission.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a greatly enlarged cross section view of the cable.

Fig. 2 is a schematic view in side elevation illu¬ strating the method of manufacture of one of the conduc¬ tors in the cable. Fig. 3 is a cross section view of one of the conduc¬ tors in Fig. l.

Fig. 4 is a schematic view illustrating the extrusion process in making the cable.

BEST MODE FOR CARRYING OUT INVENTION

Referring first to Fig. 1, electric cable 10 contains four parallel spaced apart conductors 12 each on a tensile core 14. In the present embodiment each tensile core 14 comprises a plurality of separate unbonded filaments 16, and the conductor 12 comprises a first flat tinsel ribbon of conductive material 18 spiral wound in one direction on core 14 and a second flat tinsel ribbon of conductive material 20 spiral wound in the opposite direction on top of the ribbon 18, as shown in Fig. 2. Core 14 of this tinsel wire is fabricated of a plural¬ ity of separate unbonded filaments 16 of an aramid fiber from the family of aromatic polyamides. In the preferred embodiment this is preferably "KEVLAR" which is a regi¬ stered trademark of the DuPont Corporation. The aramid fibers are much less susceptible to elongation, suffering approximately 1% elongation at 4 grams/denier (35 cN/Tex) and have a much higher resistance to breakage, at 22 grams/denier (194.2 cN/Tex) , which is almost three times stronger than that found in a tinsel wire using conven¬ tional nylon tensile filaments.

In the preferred embodiment each of tensile cores 14 in four wire strip 10 has a cross sectional area of 7.74 square millimeters. The tinsel ribbons 18 and 20 are 1% cadmium and 99% copper and are .051 mm thick and .508 mm wide. The preferred extruded insulating coating 22 is a polyvinylidene fluoride having a maximum thickness of .508 mm and a maximum width of 4.06 mm. With the centers of the four parallel conductors 12 are spaced apart from each other 1.02 mm. In this configuration each of the con¬ ductors 12 have a tensile strength of 40 N to 44.5 N, for a combined cable strength of 160 N to 178 N. This com- pares to a standard cable using a nylon tensile core of comparable size, would have a tensile strength of only between 53 N to 67 N.

Fig. 4 illustrates the extrusion process to produce the four-conductor cable 10 in Fig. 1. The four conduc- tors 12 on their tensile strands 14 are fed in parallel spaced relation through molten thermoplastic material 22 in an extrusion die 24.

The tinsel wire conductor 12 is very flexible because the copper bands can slide over each other allowing the conductor to flex freely in any direction without fatigu¬ ing the metal. And because of the low elongation factor of the aramid fiber tensile core 14, the wire is more resistent to loss of conductivity by slippage of the tinsel coils 18 and 20 even when the cable is folded over and crimped.

The foregoing dimensions are stated by way of example and do not limit the scope of the invention.

While there is shown and described the present pre¬ ferred embodiment of the invention, it is to be distinctly understood that this invention is not limited thereto but may be variously embodied to practice within the scope of the following claims.

Claims

Claim 1. An electric cable characterized by an aramid fiber tensile element having a multi-filament strand of unbonded filaments, an electric conductor surrounding said strand, and a thermoplastic insulating coating of flat configuration extruded on said tensile element and conduc¬ tor.

Claim 2. The electric cable of Claim 1 which is further characterized by a multi, unbraided, filaments of. aramid fiber.

Claim 3. The electric cables of Claim 2 wherein the electric conductor is further characterized by a spiral wrapping of a flat tinsel ribbon of electrically con- ductive material.

Claim 4. The electric cables of Claim 1 wherein the electric conductor is further characterized by a spiral wrapping of a flat tinsel ribbon of electrically con¬ ductive material.

Claim 5. The electric cable of Claims 1 or 2 which is further characterized by: a spiral wrapping of a flat tinsel ribbon of electric¬ ally conductive material; and a second flat tinsel ribbon of electrically conductive material overlying said first ribbon and wrapped in the opposite spiral direction.

Claim 6. The electric cable of Claims 3 or 4 which is further characterized by a second flat tinsel ribbon of electrically conductive material overlying said first ribbon and wrapped in the opposite spiral direction.

Claim 7. The electric cable of Claims 1, 2, 3 or 4 wherein the thermal plastic insulating coating is further characterized as polyvinylidene fluoride.

Claim 8. The electric cable of Claims 3 or 4 which is further characterized by: a second flat tinsel ribbon of electrically conductive material overlying said first ribbon and wrapped in the opposite spiral direction; and said thermal plastic insulating coating is a poly¬ vinylidene fluoride material.

Claim 9. The electric cable of Claims 1, 2, 3 or 4 is further characterized as having a plurality of said ten- sile elements with spiral tinsel wrappings in parallel side-by-side relation contained within said insulating coating.

Claim 10. The electric cable of Claims 3 or 4 is further characterized by: a second flat tinsel ribbon of electrically conductive material overlying said first ribbon and wrapped in the opposite spiral direction; said thermal plastic insulating coating is a poly¬ vinylidene fluoride material; and a plurality of said tensile elements with spiral tinsel wrappings in parallel side-by-side relation con- tained within said insulating coating.