Multi-Layer Ignition Wire

Attention is directed to commonly assigned copending U.S. patent application Ser. No. 889,158, entitled "Ignition Wire", filed by the same inventors on July 25, 1986, now abandoned and continuation-in-part application Ser. No. 938,104, entitled "Ignition Wire", filed Dec. 4, 1986.

The field of art to which this invention pertains is insulated electrical conductors, and specifically ignition wire.

In the electrical conductor art, in addition to electrical insulating properties, consideration is also given to physical properties provided by particular insulation material, and depending on the particular use such insulated wires are to be put, the physical property requirements can be quite demanding.

In the automotive area, for example with ignition wire, the physical requirements for the wire are particularly severe. In addition to insulating ability, the wire must be capable of extreme heat aging and oil resistance as well.

And of course, while extreme physical properties are obtainable, in view of the significant amounts of wire used for this purpose in the automotive industry, manufacturing costs can be a significant consideration.

Accordingly, there is a constant search in this art for insulating materials for automotive ignition wire which have the requisite combination of insulating properties, physical properties, and reasonable costs to produce.

The present invention is directed to a multilayer electrically conducting ignitionwire of simplified construction having an improved jacketing material as the outermost layer. The wire comprises a glass fiber core coated with an adhesion layer, which is overcoated with a layer of thermally stable radio frequency suppessing insulating polymer. On top of the insulating polymer is helically wound a layer of electrically conducting wire. The electrically conducting wire is overcoated with a semiconducting polymer layer containing release agent. Over top of the semiconducting polymer layer is applied improved jacketing material comprising a blend of ethylene propylene-diene monomer with ethylene vinyl acetate, stabilized with a mixture of phenolic antioxidant and a metal salt antioxidant.

Another aspect of the invention is an improved ignition wire with the similar jacketing material, and semiconducting polymer layers as recited above. However, in place of the helically wrapped wire, radio frequency suppressing insulating polymer layer, adhesion layer, and glass fiber bundle is used a conductor element comprising a graphite impregnated glass fiber bundle wrapped in a glass fiber braid layer.

The foregoing, and other features and advantages of the present invention will become more apparent from the following description and accompanying drawings.

FIG. 1 shows a jacketed wire of simplified construction according to the present invention utilizing a helically wound linear wire for condctivity.

FIG. 2 shows a jacketed wire according to the present invention utilizing graphite impregnated glass as a conducting element.

In FIG. 1, the glass fiber bundle 1 is of the type conventionally used in this art and typically comprises sixteen strands per bundle of Johathan Temple glass fiber ECG 150/4/16 (sixteen strands per bundle represents a typical OEM construction although fewer strands maybe used, e.g. twelve strands per bundle for a typical after-market construction). The primary purpose of the bundle is to provide a strength member base for the subsequently helically wrapped wire conductor 4 in FIG. 1.

Over this glass fiber bundle is applied a (dip coated) layer of adhesive 2 to improve the adhesion between the glass fiber bundle and the subsequently applied radio frequency suppressing insulating polymer layer 3. This adhesive is any conventional adhesion promoter such as Chemlok.TM. adhesive available from Hughson Chemicals. As stated, over this adhesive layer is provided a radio frequency suppressing insulating polymer which provide insulation between the glass fiber and the subsequently helically wrapped wire conductor 4. This polymer material is commercially available ethylene-propylene-diene monomer type material and contain conventional manetic particles such as iron oxide to provide the radio frequency suppressing function. The mateial typically contains about 20% by weight of the particles.

Upon the insulating polymer layer is next helically wrapped a wire conductor. This wires typically a high resistance metal such as commecially available nickel alloys (e.g. ESO 6015 available from Vereinigie Deutsche Metallwerke, A.G.). The number of turns per inch and the wire diameter size is dependent upon the resistance requirements of the particular wire, but typically 43 gauge (American Wire Gaue) wire is used with 120 turns per inch.

The next layer comprises a semiconducting polymer layer 5. This layer also contains release agents. The polymer is typically a thermoplastic polymer (such as silicone or acrylic polymer) for example commercially available from Acheson Colloids Company uner the product designation ED580. The polymer contain conducting particles (for example carbon particles) and release agents (for example carbon particles or DuPont Teflon.RTM. particles) to provide the release characteristics and semiconducting function. There should be sufficient release agents present to allow the subsequently applied layers to strip cleanly and sufficient semiconducting particles to reduce or eliminate an excessive voltage gradients which may occur due to imperfections (burrs, spikes, etc.) in the conducto itself.

The final layer is the polymer jacket layer 6. This layer comprises a mixture of ethylene-propylene-diene monomer wth ethylene vinyl acetate (EVA) copolymer and a mixture of a phenolic antioxidant and a metal salt antioxidant. The ethylene-proylene-diene monomer typically comprises 68% ethylene and 32% propylene with a small amount of nonconjugated diene termonomer for cross-linking. This material is commerically available from Uniroyal as Royalene.TM. 512. The ethylene vinyl acetate copolymer tyically contains 40% by weight vinyl acetate and an be obtained from E.I. DuPont denemours as Elvax.TM. 40. The EPDM provides electrically insulating properties, particularly low specific inductive capacity, high dielectric breakage votage, and low dissipation factor, etc. The ethylene vinyl acetate provdes physical properties such as high oil resistance. The ethylene vinyl acetate typically has a melt index of 48-66 (ASTM D1238). The EPDM is typically high viscosity, the diene component providing a cross-linking function and the ethylene component providing crystallinity, the overall blend being workable and typically having a viscosity of 60 Mooney (ML 1+4) at 125.degree. C. The amount of vinyl acetate used can be less than the 40% with a sacrifice in some of the physial properties, such as oil resistance.

To produce a satisfactory blend of physical and electrical properties the EPDM and EVA polymers are typically used in about equal proportions. Natually one skilled in this art may vary from this ratio with concurrent decrease in either insulating or physical properties. The composition is typically mixed so as to have a vicosity of between 10 and 20 inch pounds at 380.degree. F. usig a Monsanto Rheometer with 3.degree. arc at 900 cycles per minutes. This provides a composition suitable for extrusion application.

As stated above, the equal amounts (based on parts by weight) provides processability, oil resistance, heat resistance, and insulating properties suitable for commercial applications.

As the antioxidant any phenolic antioxidant and metal salt mixture can be used with a hindered alkylated phenol and zinc mercaptotolylimidazol being preferred (e.g. Ciba Geigy's Irganox 1035 and RT Vanderbuilt Vanox ZMTI or Mobay's ZMB-2 respectively).

Typicaly these materials are used at about 3.5% by weight based on total weight of the jacket material. The order of mixing of the components of the jacket material is not critical. Typically the materials are mixed in a size 11 Farrel mixer to about 75% loading capacity. The materials are mixed for about 10 minutes at room temperature and extruded typically at about 190.degree. F. to about 200.degree. F.

FIG. 2 is similar to FIG. 1 insofar as the outermost two layers in FIG. 2 (numbered 12 and 13) are similar to the outermost two layers in FIG. 1 (numbered 5 and 6). The conductor 10 in FIG. 2 is a glass fiber bundle impregnated with carbon particles, for example as is available from Johathan Temple (as a 60 end 150/1/0 roving carbon impregnated glass). This Material is particularly appropriate for use in those enviroments where less demanding voltage and temperature requirements are needed.

The glass braid 11 applied to the graphite impregnated glass is typically a mixture of interwoven cotton thread and glass used in equal amounts, as is conventionaly used in this art.

The article of the type disclosed in FIG. 1 is typically made by dip coating the adhesive out of a conventional solvent or water based solution using a conventional dip coating tower oven operation. The semiconducting layer, and the jacket material are extruded using commercially available extrusion equipment such as a John Royal extruder. The semiconducting polymer layer applied to the coied conductor is similarly dipped coated as described above.

A Johathan Temple ECG 150/4/16 strand glass fiber bundle was dip coated with a layer of Chemlok 234 b adhesive. The adhesive was dried in a tower oven. Over the adhesive layer was extruded a layer of radio frequency insulating polymer comprising ethylene-proylene-diene monomer containing 20% by weight of 0.4 micron diameter iron oxide partices. The coated conductor was next overwrapped using a conventional wire winder with 43 gauge nickel alloy wire (Alloy C) spaced at 120 turns per inch. This was overcoated using a dip coating process and tower oven drying with semiconducting polymer layer of thermoplastic polymer containing carbon black and Teflon particles. This is typically applied out of solution at about 12% solids by weight. Finally, the jacket material (ethylene vinyl acetate containng 40% by weight vinyl acetate stabilized with 3.5% of a mixture of hindered alkylated phenol and zinc mercaptotolylimidazole at a ratio of 1:2) is exruded over the semiconducting polymer layer using a John Royal 4.5 inch, 20/1 (length/diameter) extruder. The jacketed conuctor was then cured in a continuous vulcanization tube havin a cure time in a 300 foot long tube of about 1.5 minutes at 250 psig steam pressure. The glass fiber bundle has a diameter of 52 mils and a layer approximately 1 mil thick of adhesive was coated on the glass fiber bundle. The amount of RF insulating polymer applied to the adhesive layer increased the diameter of the wire to 75 mils. The coil wrap increased this diameter to 79 mils, with about 1 mil thick semiconducting polymer subsequently applied. The extruded polymer jacket resulted in a wire with a 315 mil diameter.

The method of Example I was repeated except that in place of the glass fiber bundle, adhesive layer, RF insulating polymer layer, and helically wrapped conductor layer a graphite impregnated glass overbraided with a glass fiber containing braid material was used. The graphite impregnated glass used was obtained from Johathan Temple as 60N/10/1/0 carbon impregnated glass roving. The braid used to wrap the grahite impregnated glass was four cariers of 60-2-2 cotton thread and four carriers of 150/1/0-3glass using a Wardwell braider for the operation. The graphite impegnated glass had a diameter of 75 mils after wrapping with the glass fiber braid. Approximately 1 mil thick coating was applied to the glass fiber braid and from that point on the diameter of the layered product paralleled that in Example I.

The jacket material useful in Example I and Example II above has been made with the following composition.

The above composition is strained and screened to remove impurities and then mixed with a peroxide curing agent (Vulcup.TM. R, Hercules) at 2 parts by weight (0.93%) and various pigments added for color at 3 parts by weight (1.394%).

Various fillers, processing aids, coagents, curing agents, etc. can be added to the jacket material to aid in processing and curing. This includes such things as paraffin wax, polyethylene, vinylsilanes, peroxides, fillers such as talc and hydrated alumina, etc.

In addition to lower cost than conventional silicone jacket material used in this enviroment, the polymer jacket according to the present invention has at least a 275.degree. F. SAE J557 rating and in fact the material shown in FIG. 1 has a 400.degree. F. rating. Furthermore, the material has excellent electrical insulating properties, heat resistance, oil resistance, and abrasion resistance. Use of fewer layers than constructions conventionally used in this art with no significant loss of critical physical or electrical properties positively effects both the effects both the efficiency and costs of manufacture.

Although this invention has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.