WO2002001580A1

WO2002001580A1 - High-conductivity carbon-fiber cable with protected core

Info

Publication number: WO2002001580A1
Application number: PCT/US2000/024246
Authority: WO
Inventors: Joseph Casella
Original assignee: Joseph Casella
Priority date: 1999-09-02
Filing date: 2000-09-05
Publication date: 2002-01-03
Also published as: AU7109800A

Abstract

An electrically conductive cable assembly includes an electrically conductive core having carbon fiber filaments, a fiberglass braid surrounding the core and a conductive, acrylic latex layer surrounding the braid. A protective silicone rubber layer may be added to surround the conductive, acrylic latex layer. Furthermore, for specific applications, a shield may be provided around the protective jacket. An additional silicone jacket may be provided around the shield.

Description

HIGH-CONDUCTIVITY CARBON-FIBER CABLE WITH PROTECTED CORE

BACKGROUND OF THE INVENTION

The instant invention relates generally to electrical conductors, and more

specifically relates to an electrically conducting cable assembly. Even more specifically

the instant invention relates to an electrically conducting cable assembly with a carbon-fiber

core. Carbon fiber may be used as the core of an electrical cable, as taught by U.S. Patent

No. 4,369,423, incorporated by reference herein. Because of its brittleness, it requires

special handling during the manufacturing process to avoid fraying and breakage of the

carbon-fiber filaments. Also, steps must be taken to maintain the integrity of the core

when the cable is used. A significant problem encountered in the past uses of carbon-fiber

as a core is the "paint-brush" effect, where the ends of the cores in finished cables spread

out, making connection to the cable problematic, both with respect to mechanical and

electrical considerations.

SUMMARY OF THE INVENTION

By coating the carbon fiber core with a conductive acrylic latex, the physical

integrity of the core is preserved and the conductivity of the cable is enhanced.

The instant invention is directed to an electrically conductive cable assembly which

includes an electrically conductive core, a braid surrounding the core and a conductive,

acrylic latex layer surrounding the braid. It is preferable that the core comprises carbon

fiber filaments and may be fabricated from PAN-type or pitch-base carbon fibers. The braid is preferably a fiberglass braid and a protective jacket of silicon rubber may be

provided around the conductive, acrylic latex layer.

Additional layers may be added when appropriate. For example, another fiberglass

braid layer may be added to surround the protective jacket. Furthermore an additional

outer jacket may be added surrounding the fiberglass braid layer.

The fiberglass braid layer which surrounds the carbon fiber core holds all of the

filaments together in a single bundle while covering a minimal surface area of the core.

The conductive, acrylic latex layer surrounds the braid/core layers, such that the

conductive latex contacts the carbon fiber filaments in the core, as well as the braid. The

above structure enhances the flexibility of the cable assembly. Furthermore, the use of the

conductive, acrylic latex helps to improve the conductivity and reduce the resistance of the

cable assembly. Furthermore, the constitution of the core itself, preferably made of PAN-

type or pitch-type carbon fibers enhances the conductivity of the cable assembly and thus

reduces the resistance and line losses along the length of the cable. Thus, in accordance

with the instant invention, an improved carbon-fiber cable is obtained which has

flexibility, tensile strength, with improved conductivity and less resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an illustration of a carbon-fiber cable as used for an ignition cable,

showing the layers surrounding the core;

Fig. 2 is an illustration of a variation of the carbon-fiber cable of Fig. 1, as used

for an ignition cable; Fig. 3 is an illustration of a carbon-fiber cable as used for a microphone wire or

audio cable;

Fig. 4 is an illustration of a carbon-fiber cable as used for a coaxial cable; and

Fig. 5 is an illustration of a carbon-fiber cable used for digital transmission of

information.

DETAILED DESCRIPTION OF THE INVENTION

A cable 10, illustrated in Fig. 1, comprises four components: a carbon-fiber core

20, a braid 30, a conductive latex coating 40, and, optionally, a protective jacket 50. The

carbon-fiber core 20 may be fabricated from polyacrylonitrile (PAN-type) or other types

(e.g. pitch-base) of carbon fibers (or combinations thereof) combined in a serving process.

Generally, a PAN-type of carbon-fiber is more flexible than a pitch-base of carbon fiber

and therefore is more preferable. The core 20 may comprise any user-determined number

of individual filaments that will achieve the desired performance. For example, to obtain

a core of 24,000 filaments, one may take two sheaves of ends of 12,000 each. One may

construct a core with an even larger number of filaments (e.g. , 36,000 or 48,000, etc.) as

demanded by the application. Generally, carbon-fiber is sold in sheaves of 3000, 6000,

12000. It is convenient to provide bundles having multiple sheaves (for example, several

sheaves of 12,000 filaments) to obtain a desired total number of filaments.

The core 20 is covered with a braid 30, applied as a woven wrap with preferably

4-5 wraps per inch, thus covering a minimal amount of surface area of the core. The braid should be sufficiently wrapped around the core to properly hold all the filaments in the

fiber bundle in place before the next fabricating step described below. Furthermore, the

braid helps to keep the fibers together at the end for termination purposes. The braid 30

can be of fiberglass or some other heat-resistant material that can be wrapped around the

core 20.

The braid- wrapped core 20 is then immersed in a bath of conductive, acrylic latex

sizing which contacts and bonds with the core 20 through the braid 30. The sizing may

comprise 75 % latex and 25 % carbon black, but other percentages may be employed to vary

the conductivity or the binding and/or strengthening effect of the latex. A radio of 75 %

latex and 25 % carbon black is found to provide the necessary performance and still be cost

effective. After immersion, the cable 10 is passed through an oven to dry the latex. To

insure uniformity of the latex layer 40, the latex can be applied in several stages, perhaps

in 10 mil coatings each and then dried in an oven. One may employ a multi-station

bath/oven that provides for multiple coatings and dryings. The heating temperatures of the

oven may range from approximately 260 °F - 800°F.

The conductive latex layer 40 provides enhanced conductivity, improved pull

strength, and protection for the core 20. As to the last item, the latex layer 40 holds the

fibers together during manufacture to minimize filament breakage and keeps the filaments

at the ends of the cables together to avoid the "paint brush" effect. Once the core/fiberglass/latex combination is dry, it may be covered with a

protective jacket 50, such as clear silicone rubber or some other suitable material. The

jacket 50 can be applied as an extrusion onto the latex-covered assembly to a desired final,

finished diameter (e.g., 5mm - 8mm, although other diameters may be used if desired).

For automotive ignition cable applications, one may preferably use silicone having a high

durometer (e.g. , shore A of 65-85), high tensile strength (1400 psi), and a high tear B (90

ppi or greater).

Fig. 2 illustrates the variations of the electrically conductive cable assembly of Fig.

1. While the cable assembly of Figs. 1 and 2 are specifically directed ignition cables, they

may also be used for other purposes. Furthermore, in Fig. 2, elements which are the same

or similar to those in Fig. 1 will use the same reference numeral. As in Fig. 1, the cable

assembly of Fig. 2 has a carbon-fiber core 20 wrapped with a fiberglass braid 30, and

further covered by conductive latex coating 40. For example, the cable assembly of Fig.

2 has a core which may have from 6,000 to 48,000 filaments, depending on the application

for its use. The larger the current or voltage, the greater the number of strands used. In

the cable assembly of Fig. 2, jacket 50 may consist of a 3mm thick layer of black (or any

other appropriate color) EPDM type of rubber. Alternatively, jacket 50 may comprise a

ferrite impregnated silicon for improve protection against electromagnetic interference

(EMI) and radio frequency interference (RFI) noise. Layer 60 surrounding jacket 50 may comprise a fiberglass braid. The fiberglass

braid for layer 60 provides for additional pull strength or tensile strength for the cable

assembly. Alternatively, layer 60 may be a high temperature teflon for extreme protection

from loss of current through the outer jacket, in a high voltage application. For example,

when the ignition cable of Fig. 2 is used with an internal combustion engine of extremely

high horsepower (for example 5,000 horsepower), the extreme temperature and high

voltages may easily be accommodated. Furthermore, an outer jacket 70 of silicon rubber

is formed around layer 60.

Fig. 3 illustrates a cable assembly in accordance with the instant invention which

is adapted for use as a microphone wire or an audio cable. The finished size of outer

jacket 70 is preferred to have a diameter from 8mm to 10mm, although other sizes may be

used when appropriate. For a microphone wire, the cable assembly of Fig. 3 illustrates

a core 20 having from 6,000 to 24,000 carbon-fiber filaments or strands. A braided layer,

preferably a fiberglass braided layer, is wrapped around the bundle of carbon-fiber

filaments. Additionally, a conductive latex layer is formed around the braid/core

assembly, such that the conductive latex coating contacts the braid and the carbon-fibers

themselves. Jacket 50 surrounds the conductive latex coating 40 and is provided of silicon

rubber. The jacket 50 may be black silicon rubber or any other appropriate color. When

used as an audio cable, it would be desirable to have a larger core. For example, it may

be desirable to have a core of 48,000 to 96,000 filaments. With the trend today toward

large audio cables, the additional filaments, when compared with the lower frequency use as a microphone wire, may be desirable. When used as a microphone wire or audio cable,

a finished size may range from 2mm to 4mm, however, any appropriate size may used.

Fig. 4 illustrates the use of the electrically conductive cable assembly as a coaxial

cable. As with the previous embodiments, a core 20 is wrapped with fiberglass braid 30

and surrounded by a conductive layer 40 of conductive, acrylic latex. A jacket 50

surrounds conductive layer 40 and may preferably be formed of EPDM rubber. An outer

conductive layer 65 (or sleeve) is formed around jacket 50. Outer conductive layer 65 is

formed of woven carbon-fiber, and more specifically of a herringbone weave. Thus, in

a coaxial cable in accordance with the instant invention, core 20, which may be preferably

formed of 6,000 to 12,000 carbon-fiber filaments, functions as the inner conductor. The

outer conductor (or sleeve) 55 operates, in conjunction with the inner conductor, as a wave

guide.

Fig. 5 illustrates the electrically conductive cable assembly adapted for use as a

digital transmission signal cable. In the signal cable of Fig. 5, a core 20 of woven carbon-

fiber filaments or strands is wrapped with fiberglass braid 30, which is in turn covered with

a coating of conductive latex 40. In an application for transmitting digital signals, it is

anticipated that 24,000 or more filaments would be appropriate, although any number may

be used. Jacket 50, surrounding fiberglass braid 40 and is preferably formed of a layer of

EPDM type rubber. A layer 60, preferably of teflon coating, is provided to cover jacket 0. Furthermore, an outer jacket 70, preferably of silicone rubber, is added to layer 60

provide a cover and insulation for it.

Claims

WHAT IS CLAIMED IS:

1. An electrical conductive cable assembly, comprising:

an electrically conductive core;

a braid surrounding said core; and

a conductive, acrylic latex layer surrounding said braid.

2. The electrical conductive assembly as set forth in claim 1 , wherein said core

comprises carbon fiber filaments.

3. The electrical conductive assembly as set forth in claim 2, wherein said

carbon fiber filaments are selected from a group consisting of PAN-type and pitch-base

type carbon fibers.

4. The electrical conductive assembly as set forth in claim 1 , wherein the braid

is a fiberglass braid.

5. The electrical conductive assembly as set forth in claim 3 , wherein said braid

is a fiberglass braid.

6. The electrical conductive assembly as set forth in claim 1 , further comprising

a protective jacket surrounding said conductive, acrylic latex layer.

7. The electrical conductive assembly as set forth in claim 6, wherein said

protective jacket is silicone rubber.

8. The electrical conductive assembly as set forth in claim 6, wherein said

protective jacket is made of EPDM rubber.

9. The electrical conductive assembly as set forth in claim 6, wherein said

protective jacket is a ferrite impregnate silicon shield.

10. The electrical conductive assembly as set forth in 8 or 9, further comprising

a second layer of fiberglass braid surrounding said protective jacket.

11. The electrical conductive assembly as set forth in either claim 8 or 9, further

comprising a second layer of high temperature teflon surrounding said protective jacket.

12. The electrical conductive assembly as set forth in claim 10, further

comprising an outer jacket of silicon rubber surrounding said second layer.

13. A method of fabricating an electrically conductive cable assembly,

comprising the steps of:

covering a core of carbon fibers with a fiberglass braid; covering said carbon-fiber core and fiberglass braid with a coating of conductive,

acrylic latex, such that said conductive, acrylic latex coating contacts said core; and

covering said core, fiberglass braid and latex coating with a protective jacket

selected from a group consisting of ferrite impregnated silicone and EPDM rubber.

14. The method of claim 13 wherein said latex covering step includes immersing

said core and braid into a bath of conductive, acrylic latex, such that said acrylic latex

bonds with said core through said braid.

15. The method of claim 14, further comprising forming an outer layer around

said jacket, wherein said outer layer is selected from a group consisting of fiberglass braid

and high temperature teflon.

16. The method of claim 15, further comprising forming an outer jacket around

said outer layer.

17. An electrically conductive coaxial cable assembly, comprising:

an electrically conductive core of carbon fiber filaments;

a braid surrounding said core;

a conductive, acrylic latex layer surrounding said braid and in contact with said

core;

an insulating jacket surrounding said latex layer; an outer conductor surrounding said insulating jacket; and

an outer jacket surrounding said outer conductor.

18. The electrically conductive coaxial cable assembly of claim 17, wherein said

braid is a fiberglass braid.

19. The electrically conductive coaxial cable assembly of claim 18, wherein said

outer conductor is woven carbon fiber.

20. The electrically conductive coaxial cable assembly of claim 19, wherein said

woven carbon fiber is a herringbone weave.

21. An electrically conductive cable assembly, comprising:

an electrically conductive core of carbon fiber filaments;

a fiberglass braid surrounding said core;

a conductive acrylic latex layer surrounding said braid and in contact with said core;

an insulating jacket surrounding said latex layer;

a teflon coating surrounding said insulating jacket; and

an outer jacket surrounding said teflon coating.