(11) EP 0 450 789 A1


(43) Date of publication:
09.10.1991 Bulletin 1991/41

(21) Application number: 91302305.7

(22) Date of filing: 18.03.1991
(51) International Patent Classification (IPC)5H01B 7/36
(84) Designated Contracting States:

(30) Priority: 26.03.1990 US 498889

(71) Applicant: AT&T Corp.
New York, NY 10013-2412 (US)

(72) Inventors:
  • Bleich, Larry Lynn
    Omaha, Nebraska 68144 (US)
  • Lueddecke, Donald E.
    St. Charles, Missouri 63303 (US)
  • Mottine, John Joseph, Jr.
    Omaha, Nebraska 68118 (US)
  • Zerbs, Stephen T.
    Gretna, Nebraska 68028 (US)

(74) Representative: Johnston, Kenneth Graham et al
AT&T (UK) LTD. AT&T Intellectual Property Division 5 Mornington Road
Woodford Green Essex, IG8 OTU
Woodford Green Essex, IG8 OTU (GB)

(56) References cited: : 

    (54) Surface colored insulated conductor

    (57) An insulated conductor (20) comprises a centrally disposed transmission medium (22) and enclosing plastic insulation material (21). The plastic insulation material is at least substantially non-porous. A colorant material (23) covers the surface of the plastic insulation material. The resulting colored insulated conductor has electrical properties which are greatly improved over those for a conductor which has been insulated with a plastic material having a colorant dispersed throughout.


    Technical Field

    [0001] This invention relates to a surface colored insulated conductor.

    Background of the Invention

    [0002] A plastic insulated metallic conductor for communications use, for example, generally is made by extruding plastic insulation about a moving metallic wire. One of the most popular materials for insulation has been polyvinyl chloride (PVC). For identification purposes during use of the insulated wire, the insulation extrudate generally includes a colorant which is distributed throughout the insulating plastic material. Colorant materials used for such purpose generally are metallic based pigment materials such as titanium dioxide, for example, which result in an increased number of electrical defects such as faults, for example, in the final product due to improper pigment dispersion.

    [0003] It would be far simpler if all the manufactured wire could be made with a neutral insulation material such as a clear plastic, for example, and then colored subsequently. The changeover of colors in a marking apparatus, positioned after an extruder along a manufacturing line, is far less costly than changeover in the extruder and results in improved quality and performance.

    [0004] The application of a colorant material to the surface of a moving insulated conductor has been accomplished as described in U.S. patent 4,877,645. Relative motion is caused to occur between an insulated conductor and a source of a colorant material in a direction along a longitudinal axis of the insulated conductor. Colorant material is directed in spray patterns toward the insulated conductor in such a manner that substantially all the surface area of the insulated conductor covered therewith. A first plurality of the spray patterns is such that each spray thereof occupies only an area of a plane and is at a predetermined angle to the axis of the insulated conductor with the first plurality being disposed between a colorant supply head and a takeup. A second plurality of spray patterns may be disposed between the colorant supply head and a payoff. Each of the second plurality of spray patterns is fully conical. The first and the second pluralities of the spray patterns are arranged and spaced along the longitudinal axis of the insulated conductor.

    [0005] Further of importance is the need to stabilize the moving insulated conductor against undulatory movement. Otherwise, the resulting coloring could be non-uniform. Also, undesired undulations could cause the moving colored insulated conductor to engage undesirably guides or other equipment. Control over undesired undulatory movement also is provided by the hereinbefore-identified, U.S. patent.

    [0006] Of importance with respoect to colored insulation are electrical properties of cable which include such conductors. One electrical property is capacitance. Capacitance is an effect somewhat similar to the magnetic field known to exist around a current-carrying conductor. The capacitive effect results from electrostatic charges on adjacent surfaces, such as metallic conductros in a pair or pairs within a shield.

    [0007] The value of capacitance varies in relation to the charged surfaces, their geometry or shape and the characteristics of the material between them. The basic unit of measurement for capacitance is the Farad (F) although most normal values are expressed in micro-Farads (uF), equal to millionths of a Farad, or pico-Farads (pF), which are trillionths of a Farad.

    [0008] Electronic conductors and cables by nature develop capacitive effects whenever current is flowing. These effects are major concerns because capacitive losses by means of charges leaving the surfaces of the conductors accumulate along the length of the cable. Although it is impossible to eliminate capacitance, certain factors can be adjusted to achieve an acceptable level.

    [0009] Another electrical property of importance in cable design is mutual capacitance. The mutual capacitance of an insulated conductor pair, much like series resistance, depends on the conductor diameter and interaxial spacing. Additionally, it is a function of the relative dielectric constant of the insulating system which separates the conductors. This insulating system typically includes insulation applied to the conductors and material, if any, which is disposed between the insulation and the conductor and which for many cables is air. The relative dielectric constant is the ratio of the mutual capacitance of the pair to the value it would have if all the insulation were replaced with air, which has a dielectric constant of 1.0.

    [0010] A standard value for mutual capacitance of 0.083 micro-Farads per mile is used in the design of most modern cables. Lower capacitance values require higher manufacturing costs, whereas higher values cause increased attenuation. Some lower capacitance cables are produced, but only in limited amounts for special requirements.

    [0011] It is known that the inclusion of colorant pigments in the composition of the insulation compromises the electrical properties of the insulated conductor discussed hereinbefore. Conductor insulation which has a pigment throughout affects adversely electrical properties such as capacitance. As mentioned hereinabove, achieving lower capacitance values results in higher manufacturing costs whereas higher values cause increased attenuation.

    [0012] What is sought after is an insulated conductor having a color identification system which does not affect adversely the electrical properties of the insulated metallic conductor. What is needed an what is not provided in the prior art is an insulated conductor which has a uniform color and which has enhanced electrical properties.

    Summary of the Invention

    [0013] The foregoing problems of the prior art have been overcome by the insulated metallic conductor of this invention. An identifiable transmission medium includes a transmission medium, and a layer of a plastic insulating material which encloses the transmission medium. The plastic insulating material of the invention comprises a composition which is non-porous or at least substantially non-porous. A surface layer of a colorant material encloses the layer of plastic material and facilitates identification of the transmission medium. Because of the non-porous insulation, the colorant material is prevented from infiltrating the insulation and remains disposed adjacent to an outer surface thereof. As a result, the electrical characteristics of a metallic conductor which is insulated and provided with a surface colorant are enhanced from those of prior art insulated conductors.

    [0014] In a preferred embodiment, a metallic conductor is insulated with an ethylene chlorotrifluoroethylene fluoropolymer plastic material. An ink composition of matter comprising about 15 to 40 percent by weight of solids and about 60 to 85 percent by weight of a solvent system is applied as a surface colorant to the fluoropolymer plastic insulation.

    Brief Description of the Drawing

    [0015] FIG. 1 is a cross sectional view of a metallic conductor, for example, which has been enclosed with plastic insulation material and provided with a surface colorant; and

    [0016] FIG. 2 is an overall schematic view of a manufacturing line for coloring plastic insulation on a moving conductor wire.

    Detailed Description

    [0017] Referring now to FIG. 1, there is shown a surface coated plastic insulated conductor wire 20. The insulated conductor comprises a metallic conductor 22 and insulation cover 21, which comprises a non-porous or at least a substantially non-porous plastic material, and a surface colorant layer 23.

    [0018] As shown in FIG. 2, a metallic conductor 22 is moved along a manufacturing line from a supply reel 24 and advanced through a drawing apparaturs 25 wherein the diameter of the wire is reduced. Thereafter, it is annealed in an annealer 26, then cooled and reheated to a desired temperature after which is it moved into and through an extruder 28.

    [0019] In the extruder 28, a plastic insulating material is applied to the moving wire to enclose it. Desirably, the insulating material is a clear or neutral color plastic material which is characterized as being non-porous or which is at least substantially non-porous. Such a material is a fluoropolymer, for example. The details of the structure of the drawing apparatus, annealer and extruder are all well known in the art and do not require elaboration herein. Afterwards, the plastic insulated wire is moved through a cooling trough 31 by a capstan 33 and onto a takeup 35. A conventional marking device 32 may be used to apply a band marking to the insulation.

    [0020] Between the extruder 28 and the takeup 35, a colorant material is applied to the plastic insulated wire. The location along the manufacturing line where it is applied depends on the kind of plastic material comprising the extrudate. If the extrudate is PVC, the colorant may be applied after the insulated wire is advanced out of the cooling trough 31, or before it enters the cooling trough. However, PVC exhibits porosity and even after it has been cooled, the colorant material will penetrate the insulation through the pores and move closer to the metallic conductor.

    [0021] On the other hand, if the extrudate comprises an insulating material which is non-porous, or another insulating material which is at least substantially non-porous, the colorant material may be applied at a location between the extruder 28 and the cooling trough 31. Further, when a fluoropolymer plastic insulation is used, the colorant material does not infiltrate the insulation and is maintained about the outer surface of the insulation. As a result, the colorant material is spaced a distance equal to the thickness of the insulation from the metallic conductor 22.

    [0022] In one embodiment of this invention, the plastic material of the insulation is a flouropolymer plastic material and more specifically an ethylene cholorotrifluoroethylene (ECTFE) fluoropolymer plastic material which is available commercially from the Ausimont Company under the tradename "Halar" plastic material.

    [0023] A colorant material application apparatus 40 is included in the manufacturing line and is effective to apply a colorant material to substantially the entire surface area of the moving insulated conductor. Advantageously, the application apparatus 40 is a non-contact device.

    [0024] It has been relatively easy to coat polyvinyl chloride materials with inks, commonly used inks being compatible with polyvinyl chloride resins. However, it was found to be relatively difficult to provide an ink which adhered suitably to the fluoropolymer insulation. Inks used to coat polyvinyl chloride insulation were easily removed from fluoropolymer insulation as the inked insulated conductors were routed over sheaves and other equipment on an insulating line.

    [0025] The surface colorant layer 23 of the colored, insulated transmission medium of this invention overcomes those problems. Preferably, the colorant material is a solvent based ink. For application to the ECTFE fluoropolymer plastic material, the ink comprises about 15 to 40 percent by weight of solids and about 60 to 85 percent by weight of a solvent system. More specifically, for application to an ECTFE fluoropolymer plastic insulation material, the ink composition comprises about 7 to 20 percent by weight of a vinyl resin, preferably of vinyl chloride vinyl acetate copolymers. Of the vinyl resin in the preferred embodiment for coloring ECTFE, about 5 to 15 percent by weight comprises a vinyl resin designated VYNS-3 vinyl resin and available from the Union Carbide Company. The VYNS-3 resin has a relatively high molecular weight and imparts toughness to the composition of the ink. The vinyl resin of the ink for application to ECTFE includes about 2 to 8 percent by weight of a vinyl resin designated VAGH which also is available from the Union Carbide Company. VAGH vinyl resin is a hydroxyl modified vinyl resin and provides compatibility with and adhesion to the ECTFE insulation.

    [0026] Also included in the ink is about 0.2 to 2.0 percent by weight of a plasticizer. It has been found that a suitable plasticizer is one designated Santicizer 546 and marketed by Monsanto. The plasticizer is used to provide flexibility for the ink composition as well as to help with solvent release. It is well known that vinyls have a tendency to retain solvents. The plasticizer is effective to hold open the vinyl resin to allow the solvent to escape.

    [0027] Further included in the ink composition is a wax constituent in the amount of about 1 to 5 percent by weight. A suitable wax is Fluo-HT wax which is a fluorocarbon type wax available commercially from Micropowder wax of Scarsdale, New York. A portion of the wax constituent remains on the surface of the insulated conductor and allows the insulated conductor to be moved slidably across surfaces such as sheaves and guides, which otherwise might abrade the insulation ink covering.

    [0028] A pigment is included in the ink composition in the amount of about 5 to 20 percent by weight. Suitable pigments include, for example, organics and inorganics such as, for example, titanium dioxide.

    [0029] A feature of the ink composition of the surface colored insulation of this invention is that the VYNS resin is pigmented. The VYNS resin is difficult to work because of its relatively high molecular weight and yet it is important that the pigment is dispersed suitably in the VYNS resin. VYNS resin has a molecular weight of 35000 which appears to be the highest molecular weight of any polyvinyl chloride known to be manufactured. The next highest molecular weight polyvinyl chloride is VAGH which has a molecular weight of 23000.

    [0030] The ink composition also includes a solvent system designed by matching hydrogen bonding coefficients and solubility parameters of the resin component and the solvent system. This insures suitable release of the components of the solvent system from the resin to facilitate rapid drying and is most important to the success of the colorant system. It is important that the solvent system is such that the ink is capable of drying in about one tenth to one-sixth of a second. Included in the solvent system is about 40 to 70 percent by weight of the solvent system of methyl ethyl ketone, which is a most active solvent. The methyl ethyl ketone is used to cause the composition to go into solution. Also included in the solvent system is about 30 to 60 percent by weight of the solvent system of toluene and 0 to 5 percent by weight of the solvent system of xylene. Toluene is a fast evaporating solvent which is not particularly compatible with vinyl resin. The more compatible a solvent is with a resin, the more the resin endeavors to hold onto the solvent. The toluene with its low compatibility with vinyl resins is included to help in the removal of the solvent. Where there is high humidity, moisture from the ambient condenses into the ink. The xylene constituent is included to avoid blushing. Xylene is a slow solvent which is included so that the ink coating does not close and trap in the solvent. Otherwise the ink coating could be removed from the insulated conductor as it is wound on a reel.

    [0031] An ink composition has been described for use with an ECTFE fluoropolymer insulation. For other non-porous or substantially non-porous materials, other ink systems may be appropriate.

    [0032] The apparatus 40 for applying the surface colorant ink may be that disclosed in U.S. Patent 4,877,645. The apparatus may include a manifold head 42 which is connected to a source fo supply (not shown) of colorant material. The head has an annular shape to allow the plastic insulated conductor to be advanced therethrough. Extending from one side of the manifold head are a plurality of tubular support members 44-44 which are connected through the manifold head to the source of supply. Attached to each tubular member is a nozzle 46 which has an entry port that communicates with the passageway through its associated tubular member.

    [0033] Each nozzle is one which is adapted to provide a particular spray pattern of the colorant. Preferably the nozzle emits colorant material therefrom in a single plane or sheet.

    [0034] Also, each nozzle is positioned to emit its spray in a plane which is at a particular angle to the path of travel of the plastic insulated wire. The angle is such that the spray has a component parallel to the path of travel of the insulated conductor but in a direction opposite to the direction of movement of the insulated conductor. Because of the direction of the spray pattern, the velocity components tend to provide a smoothing action on the ink and thereby prevent excessive buildup. The result is a surface having a substantially uniform coating thereon.

    [0035] In addition to the predetermined angle at which the nozzles are disposed, there are other factors about their positions which are important. First, the nozzles are staggered along the path of travel of the plastic insulated conductor. The staggered arrangement prevents interference among the spray patterns. Secondly, the nozzles are generally equiangularly spaced about the periphery of the plastic insulated conductor. Thirdly, each of the nozzles is spaced a desired distance, i.e., about one half inch, from the path of travel of the insulated conductor. It has been found that as the distance increases beyond one half inch, less coverage of the plastic insulation with the ink is experienced. Movement of the nozzles toward or away from the insulated conductor may be accomplished with the arrangement shown in the hereinbefore-identified. U.S. Patent 4,877,645.

    [0036] The nozzles also are advantageous from another standpoint. Important to the uniform coating of the plastic insulation is improved stability against undesired undulations as the insulated conductor is advanced through the applicator apparatus. It has been found that because of the spray patterns emitted from the nozzles, the plastic insulated conductor is substantially free of any undulations from its desired path.

    [0037] It should be observed from the drawings that the nozzles 46-46 are disposed between the manifold head and the takeup. It has been found that the coloring operation is enhanced by disposing a second plurality of spray nozzles 48-48 between the manifold head 42 and the extruder 28. Unlike the first plurality of nozzles, each of the second plurality of nozzles provides a solid cone-shaped spray pattern of the colorant material. Each nozzle of the second plurality provides a uniform spray of medium to large size droplets.

    [0038] Surprisingly, it has been found that the electrical properties of the surface colored insulated conductor of this invention are enhanced significantly over those of one in which the colorant is dispersed throughout the insulation (dispersed colorant). Electrical tests performed on 24 gauge ECTFE plastic insulated, surface colored metallic conductors included mutual capacitance, capacitance unbalance, high voltage breakdown in cable and insulate fault level. The ECTFE insulation was provided with an ink colorant as described hereinabove. Mutual capacitance values for surface colored and insulated conductors having a colorant dispersed throughout the insulation are shown in Table I as measured in micro-Farads per mile.

    [0039] The consistency of the mutual capacitance for surface colored conductors improved as is seen by the smaller standard deviation. Also, maximum mutual capacitance decreased and the average mutual capacitance was slightly higher.

    [0040] As can be seen in Table II, capacitance unbalance-to-ground as measured over a two month period improved in all categories. Again, only four pair cables were reviewed. The units were pico-Farads per 1.000 feet.

    [0041] In high voltage breakdown data, two, three and four pair cables were examined. The defects per thousand linear feet (TLF) for insulated cable conductors having colorant dispersed throughout the insulation were 0.00749. The surface colored conductors in a cable had 0.00223 high voltage breakdown defects per TLF. This data shows a defect rate that is reduced by factor of 3.35 by using the surface colored conductors.

    [0042] The number of faults, i.e. that is, high voltage breakdowns while a conductor was being insulated was collected. Data was compared between prior art insulated conductors and surface colored insulated conductors. The faults per reel for non-top coated wire was 5.375. Each reel held approximately 33,400 feet of insulated conductor. The surface colored product exhibited 3.38 faults per reel. The fault level decreased by a factor of 1.59.

    [0043] In the industry, it had been thought that lower capacitance values require higher manufacturing costs, while higher values result in increased attenuation. Unexpectedly for surface colored insulated conductors of this invention, capacitance values were improved by being lower while manufacturing costs decreased.

    [0044] At voice frequencies, the attenuation is a function of frequency, series resistance and mutual capacitance. An assumption can be made that because frequency and resistance remain constant, and mutual capacitance decreases, then the attenuation of the surface colored ECTFE is also better than ECTFE insulated conductors in which a colorant is dispersed throughout the insulation.

    [0045] The dielectric constant varies with the color of insulation with insulated conductors in which the colorant is dispersed throughout the insulation. This is because the various pigments used have different characteristics. Example pigments are carbon black, iron oxide, titanium dioxide and chromium oxide. By surface coloring the insulation, the pigment variability is substantially removed from the conductor's insulation, thereby providing consistent dielectric constants for all colors of insulated conductors. It is believed that the dielectric constant of the virgin plastic is lower and consquently better than the dielectric constant of the material with color in it. For these reasons, electrical properties and consequently transmission rates are significantly improved in the surface colored conductor (FIG. 1) versus the insulated conductor having a colorant dispersed throughout the insulation.

    [0046] The electric field is most intense at the conductor surface and radiates outward, and is less intense the further away from the conductor. The further away the impurities of the colorant are moved from the conductor, the better the transmission rate. In addition, the thinner the layer of the surface colorant, the lower the effect of the colorant on the transmission signal.

    [0047] Each of two 24 gauge metallic conductors was insulated with an ECTFE plastic insulation. In one example, the insulation had a thickness of 0.005 to 0.007 inch with color chips being dispersed throughout the plastic insulation. In the other example, the ECTFE insulation had a thickness of 0.005 to 0.007 inch and was surface colored with a 0.0001 to 0.0005 inch thick composition of matter. In the latter example, about 98 to 99% of the plastic material had a homogenous dielectric property with 1 to 2% of the covering being the ink spaced from the metallic conductor and having a different dielectric constant. As a result, in the latter mentioned example, the surface colorant had a negligible effect on the transmission properties of the conductor.

    [0048] It is to be understood that the above-described arrangements are simply illustrative of the invention. Other arrangements may be devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.


    1. An identifiable transmission medium, which comprises: a transmission medium; and a layer of a plastic material which encloses said transmission medium, said transmission medium being characterized in that
       said plastic material of said layer comprising a composition of matter which is at least substantially non-porous; and said transmission medium being further characterized by
       a surface layer of a colorant material which encloses said layer of plastic material, which facilitates identification of said transmission medium and which is confined substantially to an outer surface of said layer of plastic material.
    2. The transmission medium of claim 1, wherein said insulation material is a fluoropolymer plastic material.
    3. The transmission medium of claim 2, wherein said colorant material of said surface layer comprises an ink.
    4. The transmission medium of claim 3, wherein said surface layer has a thickness in the range of about 0.0002 to 0.0005 cm.
    5. The transmission medium of claim 3, wherein said ink of said surface layer is a composition of matter which includes about 15 to 40 percent weight of solids and about 60 to 85 percent by weight of solvent system.
    6. The transmission medium of claim 5, wherein said ink is a composition of matter comprising about 7 to 20 percent by weight of a vinyl resin, about 0.2 to 2.0 percent by weight of a plasticizer, about 1.0 to 5.0 percent by weight of a wax and about 5 to 20 percent by weight of a pigment, about 40 to 70 percent by weight of the solvent system of a methyl ethyl ketone solvent, about 30 to 60 percent by weight of the solvent system of toluene and about 0 to 5 percent by weight of the solvent system of xylene.
    7. The transmission medium of claim 6, wherein said vinyl resin comprises about 5 to 15 percent by weight of a relatively high molecular weight vinyl resin.
    8. The transmission medium of claim 7, wherein said relatively high molecular weight vinyl resin has a molecular weight of 35000.
    9. The transmission medium of claim 7, wherein the hydrogen bonding coefficients and solubility parameters of the resin component and of the solvent system are matched to insure suitable release of components of the solvent system to facilitate drying.
    10. A cable which is suitable for communication transmission, said cable including a plurality of said transmission medium of claim 1.


    Search report