Patent Publication Number: US-9406417-B2

Title: Methods of manufacturing wire, multi-layer wire pre-products and wires

Description:
This application is a divisional of U.S. patent application Ser. No. 13/085,253, filed Apr. 12, 2011, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure refers to exemplary methods for manufacturing wires, as well as to exemplary multi-layer wire pre-products and exemplary wires. 
     BACKGROUND 
     The term “wire” as used herein refers to a conductive core, wherein the conductive core is enveloped by at least one insulative layer. The term “wire” as used herein also encompasses cables, or groups of two or more insulated conductive cores. 
     Wires have been ubiquitous since at least the Industrial Age for all types of electrical applications. These applications include, without limitation, commercial and residential power supply, appliances, computers and personal electronics of all shapes and sizes, vehicles of all types, including fossil fuel-powered and electrically-powered automobiles and recreational vehicles. 
     Historically, wires were manufactured by a simple heat-curing method. The historical heat-curing method involved feeding a conductive core into an extruder wherein at least one insulative layer was extruded about the conductive core. To form insulative layers using such methods, all starting materials, including cross-linkable polymers and their associated curing agents, were combined in an extruder prior to extrusion. Then, the starting materials were extruded about the conductive core at temperatures ranging from about 80° C. to about 110° C. depending upon the particular materials. Next, the extruded wire pre-product was heat cured at temperatures ranging from about 135° C. to about 155° C. for a length of time to cause sufficient cross-linking in the insulative layer or layers to confer onto the insulative layer or layers the desired properties, including physical, mechanical and/or electrical properties. 
     Such historical heat-curing methods were efficient and relatively inexpensive. For example, by adding all of the starting materials to the extruder at roughly the same time, manufacturers may have realized a gain in manufacturing efficiency. That is, manufacturers could avoid slowing manufacturing line speeds and could avoid purchasing additional equipment to manage the addition of separate materials at separate times. 
     However, historical heat-curing methods faced numerous challenges. For example, manufacturers sought to avoid premature cross-linking during extrusion, also known as scorching. Significant scorching could damage extrusion equipment and generate wire that would not meet technical specifications, including physical, mechanical and/or electrical specifications. Accordingly, manufacturers were left to experiment with polymer and curing agent combinations to minimize scorching. 
     Eventually, technical demands on wire became more sophisticated, and wire produced by historical heat-curing methods failed to satisfy a variety of technical specifications. This occurred in many industries. By way of non-limiting example, in the automotive industry, certain original equipment manufacturers (OEMs) require wire to withstand scrape abrasion such that when a conductive core of a wire has a cross-sectional area of 0.22 mm 2  or less, the insulation on the wire remains intact following 150 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. Wire manufactured by historical heat-curing methods does not satisfy this standard. 
     To meet the growing technical demands on wire, manufacturers increasingly turned away from historical heat-curing methods and toward radiation or electron beam (e-beam) manufacturing methods. Indeed, e-beam manufacturing methods remain in use today. 
     E-beam manufacturing methods typically involve feeding a conductive core into an extruder where at least one insulative layer is extruded about the conductive core. To form an insulative layer, all starting materials for the layer are added to the extruder. Then, the starting materials are extruded about the conductive core. Next, the extruded wire pre-product is collected on a spool before being exposed to radiation. Radiation initiates curing, so curing agents are not typically used in e-beam manufacturing methods. 
     E-beam manufacturing methods have advantages over historical heat-curing methods. As non-limiting examples, the cross-linking reaction in e-beam manufacturing methods is faster and more uniform, especially for thin wall wires. The e-beam manufacturing methods produce wire that satisfies more challenging technical specifications. As a non-limiting example, e-beam manufacturing methods are more effective at preparing abrasion-resistant wires and ultra thin wall wires with a temperature class rating of Class D (150° C.) or higher. 
     E-beam manufacturing methods, however, also involve numerous challenges. The equipment is expensive and there are attendant safety procedures and precautions whenever radiation is used in a manufacturing method. These safety efforts can add to expenses and slow manufacturing line speeds. Additionally, e-beam manufacturing methods may be more difficult to use with thick wall wires. This may be because, at commercially acceptable manufacturing line speeds, there is a potential for incomplete penetration of electron beams through a dense polymeric insulative layer or layers. Incomplete penetration can lead to incomplete curing, which in turn can cause wire to fail technical specifications. For example, the insulation of the wires may swell or crack. 
     Additionally, using e-beam manufacturing methods to form very flexible wire presents challenges. This may be because, to spool extruded wire that is not yet cured (that is, extruded wire pre-product), the insulative layer or layers must be sufficiently hard to avoid becoming misshapen or deformed. Generally, this requires the extruded wire pre-product to have a hardness of about 80 Shore A or higher. After curing, the cross-linked polymer in the wire causes the wire to be substantially harder than the extruded wire pre-product. As a result, wire made by e-beam manufacturing methods can fail to achieve flexibility-related mechanical properties desired for certain industrial applications. By way of non-limiting example, it may be useful to produce a flexible wire having a tensile stress at yield of less than 9 MPa and a tensile modulus at 200 MPa. Wire produced by e-beam manufacturing methods would not be expected to exhibit such mechanical properties. 
     Accordingly, there is a need for improved manufacturing methods and wires. Efficient and cost effective methods are desired that can produce wires that meet can meet increasingly demanding technical specifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the claims are not limited to the illustrated examples, an appreciation of various aspects is best gained through a discussion of various examples thereof. Referring now to the drawings, illustrative examples are shown in detail. Although the drawings represent the exemplary illustrations, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an embodiment. Further, the specific examples described herein are not intended to be exhaustive or otherwise limiting or restricting to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings, as follows: 
         FIG. 1  illustrates an exemplary method of manufacturing wire. 
         FIG. 2  illustrates an exemplary method of manufacturing wire. 
         FIG. 3  shows a cross-section of an exemplary multi-layer wire pre-product. 
         FIG. 4  shows a cross-section of an exemplary multi-layer wire pre-product. 
         FIG. 5  graphically depicts cure completion testing results of exemplary wire. 
         FIG. 6  graphically depicts scrape abrasion testing results of exemplary wire. 
         FIG. 7  graphically depicts scrape abrasion testing results of exemplary wire. 
     
    
    
     DETAILED DESCRIPTION 
     Reference in the specification to “an exemplary illustration”, an “example” or similar language means that a particular feature, structure, or characteristic described in connection with the exemplary approach is included in at least one illustration. The appearances of the phrase “in an illustration” or similar type language in various places in the specification are not necessarily all referring to the same illustration or example. 
     Referring to  FIGS. 1 and 3 , an exemplary process for manufacturing wires is depicted, as is an exemplary multi-layer wire pre-product  25 . Generally, a conductive core  15  is fed into an extruder  20 . Monomers, oligomers or polymers to form a cross-linkable receptor polymer  22  are added to a hopper of the extruder  20 . No curing agent is added. Separately, monomers, oligomers or polymers to form a donor polymer  23  are added to a different hopper of the extruder  20 . Curing agent to be associated with the donor polymer  23  is included in the hopper with the donor polymer  23  and any other starting materials. The receptor polymer  22  is then co-extruded with the donor polymer  23 , the donor polymer  23  being associated with a curing agent. A multi-layer wire pre-product  25  is generated from the co-extrusion process. The multi-layer wire pre-product  25  includes the donor polymer  23  disposed about the receptor polymer  22 , which is in turn disposed about the conductive core  15 . The term “about” as used herein means circumferentially enveloping, but not necessarily in direct contact. The multi-layer wire pre-product  25  is heat cured at heat curing station  35  to generate resultant wire  40 . Unexpectedly, the resultant wire  40  has properties thought to be achievable only through e-beam manufacturing methods. 
     The exemplary process depicted in  FIG. 1  is not generally limited by the materials selected for use as conductive cores  15 . Also, except for melt temperatures, the exemplary process is similarly not limited by the particular cross-linking polymer selected for use as a receptor polymer  22  or by the polymer selected for use as a donor polymer  23 . 
     Conductive Cores 
     “Conductive core”, as used herein, refers to at least one material such as a metal or a metalloid having conductive or semi-conductive properties for use in a wire. A wide range of conductive cores  15  may be suitable for use with the methods and wires disclosed herein. That is, the conductive core  15  may have a range of chemical compositions, so long as the conductive core  15  conducts electricity sufficiently for the application. Suitable conductive cores  15 , for example, may include a metal comprising at least one of copper, nickel silver, beryllium, phosphor bronze, nickel, aluminum, or steel. Additionally, metals may be plated with another metal-containing material. For example, tin-plating, silver-plating, gold-plating, or nickel-plating may be suitable for use with the methods and wires disclosed herein. Exemplary conductive materials may also include copper-clad aluminum and copper-clad steel. 
     In applications where the conductive core  15  is semi-conductive, conductive core  15  may include a range of suitable semi-conductive materials. Such materials may include, with out limitation, silicon, graphite, germanium, antimony and gallium arsenide phosphide. 
     Conductive cores  15  may be configured in any of a wide range of arrangements. For example, the conductive core  15  may be solid (i.e., comprise a single strand of metal), or the conductive core  15  may be stranded. When the conductive core  15  is stranded, any number of strands may be used. For example, the number of strands can equal or exceed 6, 19, 37, 50, 154, 494, 741 or 1140 strands. The strands may all be of the same chemical composition, or different strands may have different chemical compositions. A wide range of configurations of strands may be suitable for the use with the methods and wires disclosed herein. For example, the strands say be woven or non-woven. Additionally, the conductive core  15  may comprise layers of strands upon one another. The configuration of adjacent layers of strands can be the same as or different from one another, whether woven or non-woven. 
     The conductive core  15  may have a cross-sectional area of a wide range of sizes. For example, cross-sectional areas of conductive core  15  may be as small as about 0.13, 0.22, or 0.35 mm 2 . Additionally, cross-sectional areas of conductive core  15  may be as large as or larger than about 1, 2, 3, 4, 5 or 6 mm 2 . 
     The conductive core  15  may have any set of properties desired for a particular application. For example, with respect to electrical properties, the conductive resistance of a conductive core  15  can be as low as about 0.1 mOhm/m at 20° C. or as high as about 130 mOhm/m at 20° C. In other words, properties such as electrical properties of conductive cores  15  do not limit the methods and wires disclosed herein. 
     Cross-Linkable Receptor Polymers 
     “Cross-linkable receptor polymers”, as used herein, refers to polymers having a chemical structure such that the polymers are capable of cross-linking upon curing, the receptor polymers being substantially free of curing agent. “Substantially free”, as used herein, encompasses the complete absence of curing agents, but also allows for incidental and/or trace amounts of curing agents to be detectable in the receptor polymer  22  using standard chemical analytical methods. Such incidental and/or trace amounts of curing agents should not comprise more than about 0.2% or more than about 1% by weight of the receptor polymer. 
     A wide range of cross-linkable polymers or cross-linkable polymer combinations may be suitable for use as a receptor polymer  22  so long as the receptor polymer  22  has a melt temperature higher than an extrusion temperature and higher than a melt temperature for a donor polymer  23 . “Melt temperature”, as used herein, refers to the temperature range when a polymer transitions from a crystalline or semi-crystalline phase to a viscous amorphous phase. “Extrusion temperature”, as used herein, refers to the temperature at which resins in the extruder  20  exit the extruder  20  through a nozzle. 
     The difference in melt temperature between the receptor polymer  22  and the donor polymer  23  should be large enough to avoid scorching and small enough to generate a sufficient state of cure to confer desired properties upon the insulation of wire  40 . The difference in melt temperature between the receptor polymer  22  and the donor polymer  23  may be at least about 5° C., at least about 10° C. at least about 20° C., or least about 40° C. The difference in melt temperature between the receptor polymer  22  and the donor polymer  23  may be greater or lower, depending upon the materials used for the receptor polymer  22  and the donor polymer  23  and the intended use of the wire  40 . 
     To avoid scorching, melt temperatures for suitable receptor polymers  22  should be higher than the extrusion temperature. Exemplary melt temperatures for suitable receptor polymers  22  may be, on the low end, as low as or lower than about 125° C., about 135° C. or about 150° C. Exemplary melt temperatures for suitable receptor polymers  22  on the high end may be as high as or higher than about 200° C., about 250° C. or about 300° C. The range of suitable melt temperatures for receptor polymers  22  may vary depending upon the materials used for the receptor polymer  22  and the donor polymer  23  and the intended use of the wire  40 . 
     Suitable cross-linkable receptor polymers  22  may include one or more of substituted or unsubstituted cross-linkable polyolefins such as polyethylene (including by way of non-limiting example, one or more of ultra high molecular weight polyethylene (UHMWPE) or high density polyethylene (HDPE)). Additional suitable receptor polymers  22  may include polyvinyl chloride (PVC), ethylene vinyl acetate (EVA) and cross-linking fluoropolymers. Suitable commercially available receptor polymers  22  may include PETROTHENE® HDPE from Lyondell, MARLEX® HDPE from Chevron Phillips Chemical Co., TEFLON® and TEFZEL® fluoropolymers from Dupont, or KYNAR® and KYNAR FLEX® fluoropolymers from Arkema. 
     Donor Polymers 
     “Donor Polymers”, as used herein, refers to polymers having curing agent associated therewith to eventually migrate from the donor polymer  23  to the receptor polymer  22 . A wide range of polymer or polymer combinations may be suitable for use as a donor polymer  23  so long as the donor polymer  23  has a melt temperature lower than the receptor polymer  22 , as described above. Additionally, the donor polymer  23  may have a melt temperature at or below the extrusion temperature. To avoid premature migration of curing agent and scorching, melt temperatures for suitable donor polymers  22  should not be too far below the extrusion temperature. Exemplary melt temperatures for suitable donor polymers  23  may be, on the low end, as low as or lower than about 55° C., about 70° C. or about 80° C. Exemplary melt temperatures for suitable donor polymers  23  on the high end may be as high as or higher than about 100° C., about 115° C. or about 125° C. The range of suitable melt temperatures may vary depending upon the materials used for the receptor polymer  22  and the donor polymer  23  and the intended use of the wire  40 . 
     Donor polymers  23  may be cross-linkable, but need not be cross-linkable. Suitable donor polymers  23  may include one or more of substituted or unsubstituted cross-linkable polyolefins such as polyethylene (including by way of non-limiting example, one or more of linear low-density polyethylene (LLDPE) or low-density polyethylene (LDPE)). Suitable donor polymers may also include ethylene-propylene copolymers (EPM), ethylene-propylene-diene (EPDM) elastomers, ethylene vinyl acetate (EVA) or ethylene-vinyl acetate copolymer (EVM). Suitable commercially available donor polymers  23  may include ELVAX® EVA from Dupont, LEVAPRENE® EVM from LANXESS, PETROTHENE® LDPE from Lyondell, BOREALIS® LDPE from Borealis AG, ROYALENE® EPDM from Lion Copolymer, NEOPRENE® synthetic rubber from Dupont, NORDEL IP® hydrocarbon rubber from The Dow Chemical Co., ENGAGE® polyolefin from The Dow Chemical Co., TAFMER® alpha-olefin copolymer from Mitsui Chemical, and TYRIN® chlorinated polyethylene resin from The Dow Chemical Co. 
     Donor polymers  23  must be associated with at least one curing agent. A wide range of curing agents may be used. For example, curing agents may include one or more peroxides. Exemplary peroxides may include diacyl peroxide, dalkyl peroxide, hydroperoxides, ketone peroxide, organic peroxide, peroxy(di)carbonate, peroxyester, and peroxyketal. Curing agents may also include, sulfur, amines, and diamines, or any combination thereof. Suitable commercially available curing agents may include DI-CUP®, LUPEROX LP®, LUPEROX 101®, LUPEROX 224®, VUL-CUP R® and VUL-CUP 40KE® peroxides from Arkema, VAROX DCP®, VAROX VC-R®, VAROX DBPH peroxides from Vanderbilt Co. Inc. 
     Coagents may optionally be included with one or more curing agents. A range of coagent may be used. Coagents may include, for example, one or more of di- or tri-functional acrylate or methacrylate, vinyl butadiene, vinyl butadiene-styrene copolymers. Coagents may optionally be included with the starting materials for the receptor polymer  22  or the donor polymer  23  or both. 
     The amount of curing agent associated with the donor polymer  23  should be enough so that sufficient curing agent migrates from the donor polymer  23  to the receptor polymer  22  during heat curing to cause sufficient cross-linking to confer the desired properties onto wire  40 . Too little curing agent may lead to insufficient cross-linking, thereby generating wires that fail to satisfy technical specifications. Exemplary problems associated with insufficient curing or cross-linking may include swelling or cracking of wire insulation during manufacture or use. 
     By way of non-limiting example, for wires to be used in the automotive industry, too little curing agent may cause a wire  40  to fail one or more of the tests set forth in International Organization for Standardization (ISO) 6722 for road vehicles 60V and 600V single-core cables, which is incorporated by reference herein in its entirety. Among other tests, the ISO standards delineate a pressure test at high temperature, abrasion tests, heat aging tests, and tests for resistance to chemicals. 
     For the pressure test described in Section 7.1 of ISO 6722, wire samples are subjected to a load that is calculated as a function of the cross-sectional area of the conductive core of the wire (the outside diameter of the wire less the nominal thickness of the insulation in the wire), and heated for 4 hours in an oven. The temperature of the oven depends on the class of the wire being tested. For example, Class A rated wire would be heated to 85±2° C., whereas Class B rated wire would be heated to 100±2° C. The wire samples are then immersed in a salt water bath for 10 seconds, then subjected to 1 kV for 1 minute. If breakdown of the wire samples does not occur, then the wire samples pass the test. 
     There are two exemplary resistance-to-abrasion tests delineated in ISO 6722, a needle test (Section 9.3) and a sandpaper test (Section 9.2). For the needle test, a needle having a diameter of about 0.45± 0.01 mm may be selected to make abrasions of about 15.5±0.1 mm in length at a frequency of about 55±5 cycles per minute. An applied force of 7 N±0.mm 2  is exerted upon the sample wires. Suppliers and OEMs supplement the ISO standard by agreeing how many cycles of abrasion scrapes a wire having a conductive core of a particular cross-sectional area must endure while the insulation of the wire remains intact. For example, OEMs may require a supplier to manufacture a wire having a conductive core with a cross-sectional area of 1.5 mm 2  or greater, and require that the insulation of such a wire remain intact following at least 1500 cycles of abrasions. Similarly, OEMs may require a supplier to manufacture a wire having a conductive core with a cross-sectional area of about 0.22 mm 2  or less, and require that the insulation of such a wire remain intact following at least 150 cycles of abrasion scrapes. Other specifications are contemplated, such as wires having a conductive core with a cross-sectional area of about 0.35 mm 2  or about 0.5 mm 2 , which are common wire sizes. For such wires, technical specifications may require insulation to withstand at least 200 or 300 cycles of abrasion scrapes, respectively. 
     For the ISO 6722 sandpaper test, 150 J garnet sandpaper is applied to sample wires at a rate of 100±75 mm/min with an applied force of at least 0.63 N. Depending upon the cross-sectional area of the conductive core, an additional mass of a pre-selected magniuude is added to the apparatus to apply additional force on the sample wires. The sandpaper is drawn across the wire until at least some of the conductive core is exposed. The length of the sandpaper required to expose the conductive core is recorded as the measure of resistance to sandpaper abrasion. The ISO 6722 standard increases the length of sandpaper required to pass the test with the cross-sectional area of the conductive core of the sample wires. For example, a 60V thin wall wire for smaller gauge wires would require testing with an additional mass of 100 g, and the length of the sandpaper making the abrasion on the sample wire without exposing the conductive core would be 200 mm in length for a conductive core having a cross-sectional area of 0.13 mm 2 , 224 mm in length for a conductive core having a cross-sectional area of 0.22 mm 2 , and 250 mm in length for a conductive core having a cross-sectional area of 0.35 mm 2 . By comparison, a 60V thin wall wire for larger gauge wires would require testing with an additional mass of 200 g, and the length of sandpaper making the abrasion on the sample wire without exposing the conductive core would be 300 mm in length for a conductive core having a cross-sectional area of 0.5 mm 2 , 450 mm in length for a conductive core having a cross-sectional area of 1.5 mm 2 , and 500 mm in length for a conductive core having a cross-sectional area of 2.0 mm 2 . 
     Heat aging tests are described in Section 10 of ISO 6722. For example, for long term aging, sample wires are placed in an oven for 3000 hours. The temperature depends upon the class rating of the sample wires. For example, class C wire is heated at 125±2° C. and class D wire is heated at 150±2° C. This simulates aging. After simulated aging, the sample wires are cooled at room temperature for at least about 16 hours, then the wires are wound into a winding. If any of the conductive core is exposed in the winding (that is, if the insulation cracks), then the sample wire fails the test. If not, the sample wire is immersed in a salt water bath for 10 minutes, then subjected to 1 kV for 1 minute. If breakdown of the sample wires does not occur, then the sample wires pass the test. 
     Resistance-to-chemicals tests are described in Section 11 of ISO 6722. For example, for resistance to hot water, closely wound sample wires of a specified length are immersed in a salt water bath at 185±5° C. for 7 days, which completes one cycle. After five cycles, the sample wires are cooled, visually inspected, then subjected to 1 kV for 1 minute. If there is no cracking on the insulation, the sample wires pass the visual inspection. If breakdown of the sample wires does not occur, then the sample wires pass the test. 
     Unexpectedly, wires  40  manufactured by the methods disclosed herein passed the battery of tests disclosed in ISO 6722 with cross-linked insulation of the wires  40  having a state of cure as low as 50%. Generally, to pass a battery of tests such as those described above and detailed in ISO 6722, sufficient curing agent should be associated with the donor polymer  23  to ensure a state of cure of at least about 50% of the receptor polymer  22  collectively with any and all other insulative cross-linkable polymers in the wire  40 . There may be instances where technical specifications can be satisfied with an even lower state of cure. Additionally, there may be instances where a state of cure of at least about 75% is desired to satisfy particular technical specifications. On the low end, curing agents may comprise about 0.25% by weight of the polymer or polymers comprising the receptor polymer  22  together with any other cross-linkable polymers in the wire  40 , but weigh percentages may be about 0.5%, about 1.0%, 2.0% or about 3.5% of the total cross-linkable starting materials. Depending upon the particular application for the wire  40  and technical specifications placed upon the wire  40  to be manufactured, less or more curing agent may be added than the specific ranges exemplified herein. 
     Optional Materials 
     Except for the issues specific to curing agents as described herein, a wide range of additional ingredients may be placed in the extruder  20  to be extruded with the receptor polymer  22  or the donor polymer  23 . Such ingredients may include, by way of non-limiting example, monomers, oligomers or polymers to form one or more thermoplastic polymer insulative layers, fire retardants, processing aids, antioxidants, thermal stabilizers, elastomers, reinforcing fillers, antiozonants, accelerants, vulcanization agents, crack inhibitors, metal oxides and pigments. 
     Multi-Layer Wire Pre-Product 
     In multi-layer wire pre-product  25 , receptor polymers  22  and donor polymers  23  may be disposed in any layer configuration so long as the receptor polymer  22  is between the conductive core  15  and the donor polymer  23 . The receptor polymer  22  and the donor polymer  23  need not be in direct contact with one another or with the conductive core  15 . 
     Referring to  FIGS. 3 and 4 , exemplary configurations of insulative layers comprising receptor polymers  22  and donor polymers  23  are depicted. In  FIG. 3 , an exemplary multi-layer pre-product  25  is shown. Receptor polymer  22  is in direct contact with conductive core  15 , and donor polymer  23  is in direct contact with the receptor polymer  22 . In  FIG. 4 , an exemplary multi-layer pre-product  25 ′ is shown. Insulative layer  26  is disposed between the conductive core  15  and the receptor polymer  22 , and insulative layer  27  is disposed between the receptor polymer  22  and the donor polymer  23 . Insulative layers  26  and  27  may be the same or different, and may comprise any of a wide range of polymer or polymers, whether or not cross-linking. Additional polymer layers may optionally be disposed over at least a portion of the donor polymer  23  as well. 
     Insulative layers, including the donor polymer  23  and the receptor polymer  22 , may have any of a wide range of dimensions, individually or collectively. For example, with respect to the collective thickness of the insulative layers, at least thick wall, thin wall, ultra thin wall, and ultra ultra thin wall wires  40  may be manufactured according to the methods disclosed herein. Exemplary thicknesses of collective insulative layers may range From about 0.16 mm to about 1.28 mm. The thickness ratio of donor polymer  23  to receptor polymer  22  may vary. If the receptor polymer  22  is more expensive, it may be advantageous to use just enough receptor polymer  22  to satisfy technical specifications for the particular wire  40  being manufactured. Exemplary thickness ratios (by volume) of receptor polymer  22  to donor polymer  23  may be about 1:1, about 1:1.5, about 1:2 or about 1:5. The low end of this range may have more direct application to smaller gauge wires such as automotive ignition wires, and the high end of this range may have more direct application to larger gauge wires, for example, battery wires. Depending upon the technical specifications for resultant wire  40 , thickness ratios may be lower or higher than the specific ranges exemplified herein. 
     Insulative layers, including the layers comprising donor polymer  23  and the receptor polymer  22 , may have a wide range of properties, including electrical properties, individually or collectively. For example, an average dielectric constant for the collective insulative layers made using the methods disclosed herein may be as lower as or lower than about 1.2, and the dielectric constant may be as high as or higher than about 7. 
     Insulative layers other than the layers comprising donor polymer  23  and the receptor polymer  22  may comprise a broad range of materials. For example, it is contemplated that tapes, separators, foils, shields and braids made from a broad cross-section of materials may be included as insulative layers. Such insulative layers may reside between the conductive core  15  and the layer comprising receptor polymer  22 , between the receptor polymer  22  and the donor polymer  23 , and/or outside the donor polymer  23 . 
     Manufacturing Methods 
     A wide range of manufacturing methods may be used to create a multi-layer wire pre-product  25  and ultimately resultant wire  40 . Referring to  FIG. 1 , co-extrusion is shown as an exemplary manufacturing method to create a multi-layer wire pre-product  25  comprising an insulative layer including a receptor polymer  22  and comprising an insulative layer including a donor polymer  23 . A conductive core  15  is fed into an extruder  20 . Monomers, oligomers or polymers to form a cross-linkable receptor polymer  22  are added to a hopper of the extruder  20 . No curing agent is added. Separately, monomers, oligomers or polymers to form a donor polymer  23  are added to a different hopper of the extruder  20 . In this example, curing agent to be associated with the donor polymer  23  is included in the hopper with the starting materials to form the donor polymer  23  and any other starting materials. A receptor polymer  22  is co-extruded with a donor polymer  23 , the donor polymer  23  being associated with a curing agent by being extruded with the curing agent. A multi-layer wire pre-product  25  is generated from the co-extrusion process where a donor polymer  23  is disposed about the receptor polymer  22 , which is in turn disposed about the conductive core  15 . 
     Referring to  FIG. 2 , serial extrusion, also referred to as tandem extrusion, is shown as an exemplary manufacturing method to create a multi-layer wire pre-product  25 . Two extruders are used, extruder  20  and extruder  21 . Extruder  20  accepts a feed of conductive core  15 , and accepts starting materials into a hopper to extrude, at least, a receptor polymer  22  about the conductive core  15 . No curing agent is added. The product of extruder  20  is fed to extruder  21 . In the example of  FIG. 2 , the starting materials to form donor polymer  23  are added to the hopper with a curing agent to be associated with the donor polymer  23  by being processed in the extruder  20  together with donor polymer  23 . A multi-layer wire pre-product  25  is generated from the serial extrusion where a donor polymer  23  is disposed about the receptor polymer  22 , which is in turn disposed about the conductive core  15 . 
     Additional manufacturing methods are contemplated to generate the multi-layer wire pre-product  25 . For example, a receptor polymer  22  may be extruded about a conductive core  15  in a completely separate process from the extrusion of a donor polymer  23 , and the layers are brought together manually or by other methods, including manual labor, prior to heat curing. 
     If a receptor polymer  22  is extruded in a separate process from the extrusion of the donor polymer  23 , then the extrusion temperature for the receptor polymer  22 , substantially free of curing agent, is not limited to those temperatures below a cure temperature for a particular cross-linkable polymer and curing agent combination. Extrusion temperatures below the cure temperatures may still be used, but higher extrusion temperatures may be useful for, for example, increasing manufacturing line speeds. By way of non-limiting example, extrusion temperatures for a receptor polymer  22  can be as high or higher than about 125° C., about 200° C., or about 300° C. 
     If receptor polymer  22  and donor polymer  23  are co-extruded, times and temperatures for extrusion should be set to minimize migration of curing agents from the donor polymer  23  to the receptor polymer  22  during extrusion to avoid scorching. The temperature may depend upon the materials selected for the donor polymer  23  and the receptor polymer  22 . Typical extrusion temperatures are less than about 125° C., less than about 100° C., or less than about 80° C. The time of extrusion should maximize line speed without sacrificing the desired properties in resultant wire  40  below technical specifications. 
     Depending upon the particular method of manufacturing multi-layer wire pre-product  25  selected, different extruders  20  may be selected. Single hopper and dual hopper extruders may be used. New and used exemplary extruders  20  are commercially available from many sources, including but not limited to Davis Standard or Progressive Machinery, Inc. 
     Referring to  FIGS. 1 and 2 , after the multi-layer wire pre-product  25  has been formed, it is heat cured at curing station  35 , which may comprise a steam cure station. As the multi-layer pre-product  25  is run through the heat curing station  35 , the donor polymer  23  begins to melt. Then, curing agent in the donor polymer  23  migrates from the donor polymer  23 , through any intermittent layers, and into the receptor polymer  22 . The cross-linking reaction commences in, at least, the receptor polymer  22 . The cross-linking of any other cross-linkable polymers also occurs during curing. Collectively, the insulative layers about the conductive core  15  are the insulation of resultant wire  40 . The state of cure of the insulation of resultant wire  40  will depend, in part, on the time and temperature of cure. 
     Again, faster line speeds are generally more commercially desirable than slower line speeds, so high cure temperatures and short cure times may be used so long as the time and temperature for cure permit sufficient cross-linking so that insulation of the resultant wire  40  may satisfy technical specifications. Typical cure times may range anywhere from about 20 seconds or 30 seconds to about 2 minutes to about 5 minutes to about 10 minutes. Typical cure temperatures may be as low as about 130° C. or about 140° C., and may be as high as about 170° C., about 180° C. or about 200° C. The technical specifications for the resultant wire  40  drive the cure times and the cure temperatures. Thus, it is contemplated that both cure times and cure temperatures may be higher or lower than the exemplary ranges disclosed herein. 
     A wide range of equipment and methods of heat curing may be used. Such equipment may include Davis Standard steam tube cure equipment. It is contemplated that the heat curing need not be applied heat from an external source. That is, the heat that initiates curing may be generated from an exothermic reaction in the materials. Any commercially reasonable manufacturing line speed can be selected for use herein. Typical manufacturing line speeds may be from about 300 m/min to about 1250 m/min Unexpectedly, when manufacturing line speeds were as high as about 900 m/min or higher, and the degree of cross-linking in the insulative layer including the receptor polymer  22  was less than 75%, the resultant wires  40  made by the methods disclosed herein were exceptionally resistant to scrape abrasion and passed the tests set forth in ISO 6722 set forth above. 
     Example 1 
     Copper wire was fed to a Davis Standard extruder, and PETROTHENE® HDPE was added to the hopper. The wire feed had a cross sectional area of about 0.5 mm 2 . The HDPE was extruded at 200±5° C. for 120 minutes and collected for use as a receptor polymer for wire samples to be prepared. A first sample of PETROTHENE® LDPE comprising 0.5 wt % of VULCUP R® curing agent was extruded for use as a low concentration donor polymer. A second sample of PETROTHENE® LDPE comprising 1.5 wt % of VULCUP R® curing agent was extruded for use as a high concentration donor polymer. The receptor polymer was inserted into the low concentration donor polymer and cured at 200±5° C. for about 1.5 minutes. Three cured samples were collected and tested for state of cure by ASTM D2765 solvent extraction. In each instance, a state of cure of greater than 50% was achieved. Additional receptor polymer samples were inserted into high concentration donor polymer cured at 200±5° C. for about 1.5 min. Three cured wire samples were collected and tested for state of cure by ASTM D2765 solvent extraction. In each instance, a state of cure of about 70% was achieved. The results are graphically depicted in  FIG. 5 . 
     Example 2 
     A cured wire with a low concentration donor polymer produced in Example 1 was tested for scrape abrasion. Similarly, a cured wire with a high concentration donor polymer produced in Example 1 was tested for scrape abrasion. The collective insulative layers of the cured wire made with the low concentration donor polymer remained in tact following over 700 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. The collective insulative layers of the cured wire made with the low concentration donor polymer remained in tact following over 600 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. Unexpectedly, both heat-cured samples exceeded a technical requirement that the insulative layer or layers above a conductive core remain in tact following at over 600 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. The results are graphically depicted in  FIG. 6 . 
     Example 3 
     Copper wire was fed to a Davis Standard extruder, and PETROTHENE® HDPE was added to the hopper. The wire feed had a cross sectional area of about 0.35 mm 2 . The HDPE was extruded at 200±5° C. for 60 minutes and collected for use as a receptor polymer for wire samples to be prepared. BOREALIS® Polyethylene LDPE comprising 1.5 wt % of VULCUP R® curing agent was extruded for use as a low concentration donor polymer at 100° C. for 20 min. The extruded HDPE was inserted into the extruded LDPE prior to steam cure. Cure temperatures were set to 200±5° C. In one trial, line speeds were set at about 98 m/min. In a second trial, line speeds were set at about 457 m/min. In the first trial, the state of cure was determined to be greater than 73%, and the scrape abrasion resistance was determined to be greater than 250 needle scrapes. In the second trial, the state of cure was determined to be greater than 60%, and the scrape abrasion resistance was determined to be greater than 250 needle scrapes. Unexpectedly, across the range of line speeds, the cured wire exceed the technical requirements of an ability to withstand 200 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. 
     Example 4 
     Copper wire was fed to a Davis Standard extruder, and PETROTHENE® HDPE was added to the hopper. The wire feed had a cross sectional area of about 0.5 mm 2 . The HDPE was extruded at 200±5° C. for 60 minutes and collected for use as a receptor polymer for wire samples to be prepared. BOREALIS® Polyethylene LDPE comprising 1.5 wt % of VULCUP R® curing agent was extruded for use as a low concentration donor polymer at 100±5° C. for 20 minutes. The extruded HDPE was inserted into the extruded LDPE prior to steam cure. Cure temperatures were set to 200±5° C. In one trial, line speeds were set at about 98 m/min. In a second trial, line speeds were set at about 457 m/min. In the first trial, the state of cure was determined to be greater than 65%, and the scrape abrasion resistance was determined to be greater than 700 needle scrapes. In the second trial, the state of cure was determined to be greater than 53%, and the scrape abrasion resistance was determined to be greater than 700 needle scrapes. Unexpectedly, across the range of line speeds, the cured wire exceed the technical requirements of an ability to withstand 300 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. 
     Example 5 
     Copper wire was fed to a Davis Standard extruder, and PETROTHENE® HDPE was added to the hopper. The wire feed had a cross sectional area of about 1.0 mm 2 . The HDPE was extruded at 200±5° C. for 60 minutes and collected for use as a receptor polymer for wire samples to be prepared. BOREALIS® Polyethylene LDPE comprising 1.5 wt % of VULCUP R® curing agent was extruded for use as a low concentration donor polymer at 100±5° C. for 20 minutes. The extruded HDPE was inserted into the extruded LDPE prior to steam cure. Cure temperatures were set to 200±5° C. In one trial, line speeds were set at about 98 m/min. In a second trial, line speeds were set at about 457 m/min. In the first trial, the state of cure was determined to be greater than 64%, and the scrape abrasion resistance was determined to be greater than 800 needle scrapes. In the second trial, the state of cure was determined to be greater than 62%, and the scrape abrasion resistance was determined to be greater than 800 needle scrapes. Unexpectedly, across the range of line speeds, the cured wire exceed the technical requirements of an ability to withstand 500 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. 
     Example 6 
     Copper wire was fed to a Davis Standard extruder, and PETROTHENE® HDPE was added to the hopper. The wire feed had a cross sectional area of about 1.5 mm 2 . The HDPE was extruded at 200±5° C. for 60 minutes and collected for use as a receptor polymer for wire samples to be prepared. BOREALIS® Polyethylene LDPE comprising 1.5 wt % of VULCUP R® curing agent was extruded for use as a low concentration donor polymer at 100±5° C. for 20 minutes. The extruded HDPE was inserted into the extruded LDPE prior to steam cure. Cure temperatures were set to 200±5° C. In one trial, line speeds were set at about 98 m/min. In a second trial, line speeds were set at about 457 m/min. In the first trial, the state of cure was determined to be greater than 66%, and the scrape abrasion resistance was determined to be greater than 3000 needle scrapes. In the second trial, the state of cure was determined to be greater than 60%, and the scrape abrasion resistance was determined to be greater than 3000 needles scrapes. Unexpectedly, across the range of line speeds, the cured wire exceed the technical requirements of an ability to withstand 1500 cycles of abrasion scrapes with a needle having a diameter of 0.45±0.01 mm. 
     Example 7 
     Copper wire was fed to a Davis Standard extruder. The wire feed had a cross sectional area of about 1.5 mm 2 . PETROTHENE® HDPE was added to the hopper and was extruded at 200° C. for 60 minutes then collected for use as a receptor polymer. BOREALIS® Polyethylene LDPE containing 1.5% by weight of VULCUP R® curing agent was extruded at 100±5° C. for 20 minutes and collected for use as a low concentration donor polymer. The extruded HDPE was inserted into the extruded LDPE prior to steam cure. Cure temperatures were set to 200±5° C. Each of the samples was tested or scrape abrasion with a needle having a diameter of 0.45±0.01 mm. The tests were run at 38° C., 43° C., 49° C. and 54° C. Unexpectedly, the collective insulative layers comprising both the donor and the receptor polymer remained in tact after more than 3400 scrapes. Also unexpectedly, the performance remained substantially constant over the tested temperature range. The results are graphically depicted in  FIG. 7 . 
     With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claimed invention. 
     Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation and is limited only by the following claims. 
     All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary in made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.