WO2001018824A1

WO2001018824A1 - Dual layer system suitable for use as electrical insulation for wires and other conductors

Info

Publication number: WO2001018824A1
Application number: PCT/US2000/040778
Authority: WO
Inventors: Young Joon Kim; Anthony E. Listro; Francis A. Gnatek
Original assignee: Judd Wire, Inc.
Priority date: 1999-09-07
Filing date: 2000-08-30
Publication date: 2001-03-15
Also published as: AU1105801A

Abstract

A dual layer system suitable for use as an outer covering or jacket for providing electrical insulation to wires or other conductors is provided. The dual layer system demonstrates a balance of physical properties including greatly improved wire-to-wire abrasion resistance.

Description

DUAL LAYER SYSTEM SUITABLE FOR USE AS ELECTRICAL INSULATION FOR WIRES AND OTHER CONDUCTORS

1. Field of the Invention.

The present invention generally relates to an electrically insulating dual layer system that employs melt-processed, cross-linked fluorocarbon polymers and that is suitable for use as an outer covering or jacket for wires or other conductors.

2. Background of the Invention.

It is known to use cross-linked polymeric compositions as electrical insulation on wires or other conductors. In fact, insulated wires coated with a layer of a chemical or radiation cross-linked fluorocarbon polymer (e.g., ethylene tetrafluoroethylene copolymers "ETFE copolymers") are extensively used for the wiring in aircraft. Boeing Specification Number BMS 13-48 (dated July 29, 1996) sets various standards for insulated wires that are coated with a layer of a radiation cross-linked ETFE copolymer. Insulated wires coated with a layer of a radiation cross-linked ETFE copolymer, however, have been observed to have a material disadvantage. In particular, when the outer surfaces of such insulated wires become damaged, subsequent flexing of the wires causes the damage (i.e., split) to extend or propagate at a relatively fast rate through the coating thereby ultimately exposing the wire. Such a tendency is problematic especially in aircraft applications where the consequences of insulation failure can be catastrophic.

U.S. Patent No. 5,059,483 to Lunk et al., discloses and claims an insulated electrical conductor that serves to address the above-referenced deficiency of ETFE copolymer coated wires. In particular, Lunk et al. teach that its insulated electrical conductor demonstrates an increased resistance to notch propagation. Such an increase is attributed to the use of a dual layer coating employing ETFE copolymers having a melting point of at least 200 °C, where an inner ETFE layer has little or no cross-linking. However, as will be readily appreciated by those skilled in the art, minimizing the level of cross-linking in an inner ETFE layer in a dual layer coating constitutes an arduous task. It is therefore an object of the present invention to provide a dual layer system suitable for use as an outer covering or jacket for providing electrical insulation to wires or other conductors that does not require minimization of cross-linking levels in any layer.

It is a further object of the present invention to provide an insulated conductor that demonstrates a balance of physical properties.

SUMMARY OF THE INVENTION

The present invention therefore relates to a dual layer system suitable for use as an outer covering or jacket for providing electrical insulation to wires or other conductors, wherein the dual layer system is comprised of: a) an inner electrically insulating layer that comprises a first melt- processed, cross-linked fluorocarbon polymer composition wherein the polymer has a melting point of <200°C; and b) an outer electrically insulating layer that comprises a second melt processed, cross-linked fluorocarbon polymer composition wherein the polymer has a melting point of ≥200°C. The present invention also relates to an insulated conductor that demonstrates a balance of physical properties and that comprises a metal conductor or wire having the above-identified dual layer system releasably adhered thereto.

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

DETAILED DESCRIPTION OF THE INVENTION

Although the present inventive dual layer system or jacket will be described herein in reference to insulated wires or other conductors, it is not so limited. This dual layer system can be utilized in any application where a balance of physical properties is desired. For example, the inventive dual layer system can be used to prepare electrically insulating containers for sensitive high temperature instruments and scratch resistant films for solar collectors.

The polymer used in the first fluorocarbon polymer composition of the inventive dual layer system is a melt-processable, crystalline fluorocarbon polymer or mixture of such polymers that has/have a melting point of less than 200 °C and preferably, from about 140° to about 170°C. As is well known to those skilled in the art, melting of crystalline polymers occurs over a temperature range. The term "melting point", as used herein, means crystalline melting point T_m or the temperature of disappearance of the last traces of crystallinity in the polymer or in the major polymeric component of a mixture of crystalline polymers. The term "fluorocarbon polymer", as used herein, means a polymer or mixture of polymers containing more than 40 % by weight, preferably more than 62 % by weight, fluorine.

In a preferred embodiment, the polymer used in the first fluorocarbon polymer composition of the present invention is a copolymer of ethylene and tetrafluoroethylene and optionally one or more copolymerizable comonomers ("ETFE copolymers") that demonstrates a tensile strength of < 40 megapascals (MPa) (ASTM D

638), a % elongation at break of > 200% (ASTM D 638), and a flexural modulus of < 1 ,200 MPa (ASTM D 790). In a more preferred embodiment, the polymer is an ETFE copolymer that comprises 25 to 40 mole % of units derived from ethylene, 45 to 55 mole % of units derived from tetrafluoroethylene and up to 20 mole % of units derived from one or more other comonomers. Contemplated comonomers include, but are not limited to, hexafluoropropylene (HFP), hexafluoroisobutene (HFIB), perfluorobutylethylene (PFBE), vinylidene fluoride (VDF) and vinylfiuoride (VF). Chlorofluorohydrocarbons such as monofluorotrifluoroethylene can also be used as a component of the fluorocarbon polymers of the present invention. In yet a more preferred embodiment, the polymer is an ETFE copolymer that comprises ethylene, tetrafluoroethylene and hexafluoropropylene. Such copolymers are described in EP 0 677 538 Al (CA 2,147,045 Al), which is incorporated herein by reference. In a most preferred embodiment, the polymer is an ETFE copolymer that comprises approximately 37 mole % of ethylene, approximately 50 mole % of tetrafluoroethylene and approximately 12 mole % of hexafluoropropylene. Such copolymers are available from Dyneon LLC, Oakdale, MN under the trade designation HTE E- 14660.

The present invention evolved in part from the surprising discovery that fluorocarbon polymers having a melting point of <200°C may be effectively employed with moderate cross-linking as an inner layer in a dual layer system suitable for use as an outer coating or jacket for providing electrical insulation to wires or other electrical conductors without adversely impacting upon the system's resistance to notch propagation.

The first fluorocarbon polymer composition preferably contains (as extruded) from about 0 to about 4 % by weight of a cross-linking agent. The first fluorocarbon polymer composition of the present invention generally has less cross-linking than the second fluorocarbon polymer composition.

The polymer used in the second fluorocarbon polymer composition of the inventive dual layer system is a melt-processable, crystalline fluorocarbon polymer or mixture of such polymers that is/are compatible with the polymer or mixture of polymers used in the first fluorocarbon polymer composition and that has/have a melting point of at least 200 °C, and preferably, from about 260 to about 270 °C.

In a preferred embodiment, the polymer used in the second fluorocarbon polymer composition of the present invention is an ETFE copolymer. In a more preferred embodiment, the polymer is an ETFE copolymer that comprises 35 to 60 mole % (preferably 40 to 50 mole %) of units derived from ethylene, 35 to 60 mole % (preferably 50 to 55 mole %) of units derived from tetrafluoroethylene and up to 10 mole %

(preferably 2 mole %) of units derived from one or more fluorinated comonomers (e.g., HFP, HFIB, PFBE, VDF and VF). Such copolymers are available from E.I. DuPont de Nemours and Company ("duPont"), Wilmington, DE under the trade designation TEFZEL 200 and from Daikin America, Inc., Orangeburg, NY, under the trade designation NEOFLON EP-541.

The second fluorocarbon polymer composition preferably contains (as extruded) from about 4 to about 16 % by weight of a cross-linking agent. Where the second fluorocarbon polymer composition contains a greater amount of cross-linking agent, it is submitted that some degree of migration of the cross-linking agent from the second fluorocarbon polymer composition to the first fluorocarbon polymer composition may occur when the outer and inner layers of the dual layer system are first contacted (i.e., upon extrusion). As will be readily apparent to those skilled in the art, the degree of migration will depend, in part, upon the length of time in which the layers are in contact prior to being subjected to a cross-linking step. Preferred cross-linking agents are radiation cross-linking agents that contain multiple carbon-carbon double bonds. In a preferred embodiment, cross-linking agents containing at least two allyl groups and more preferably, three or four allyl groups, are employed. Particularly preferred cross-linking agents are triallyl isocyanurate (TAIC), triallylcyanurate (TAC) and trimethallylisocyanurate (TMAIC). In addition to the above component(s), the first and second fluorocarbon polymer compositions may advantageously contain other additives such as pigments (e.g., titanium oxide), lubricants (e.g., PTFE powder), antioxidants, stabilizers, flame retardants (e.g., antimony oxide), fibers, mineral fibers, dyes, plasticizers and the like. However, some such additives may have an adverse effect on the insulating and/or physical properties of the inventive dual layer system.

It is noted that titanium oxide pigments have been identified by the present inventors as having a slight adverse effect on wire-to-wire abrasion resistance. This pigment is used to impart "laser marking" to the dual layer system, a technique that is becoming more popular among aerospace wire and cable users. It is further noted that PTFE powder has been identified by the present inventors as having a beneficial effect on wire-to- wire abrasion resistance if radiation levels used for cross-linking are kept below 25 Mrads.

In a preferred embodiment, the dual layer system of the present invention is prepared from: 1) an inner layer that comprises a first fluorocarbon polymer composition comprising: a. from about 97.0 to about 100 % by wt. of a copolymer comprising approximately 37 mole % of units derived from ethylene, approximately 50 mole % of units derived from tetrafluoroethylene and approximately 12 mole % of units derived from hexafluoropropylene, wherein the copolymer has a melting point of <200°C, and b. up to about 3.0 % by wt. of a triallyl isocyanurate cross- linking agent, wherein the sum of components a and b total 100 % by wt., and 2) an outer layer that comprises a second fluorocarbon polymer composition comprising: a. from about 86.0 to about 90.0 % by wt. of a copolymer comprising 35 to 60 mole % of units derived from ethylene, 35 to 60 mole % of units derived from tetrafluoroethylene and 0 to 10 mole % of units derived from a third monomer selected from the group consisting of HFP, HFIB, PFBE, VDF, VF and the like, wherein the copolymer has a melting point of >200°C, b. from about 8 to about 10 % by wt. of a triallyl isocyanurate cross-linking agent, c. up to about 3 % by wt. of a titanium oxide pigment, d. up to about 3 % by wt. of an antimony oxide flame retardant, and e. up to about 0.5 % by wt. of a polytetrafluoroethylene lubricant, wherein the sum of components a through e total 100 % by wt. The present inventive dual layer system is suitable for use as an outer covering or jacket for providing electrical insulation to stranded or solid metal wires or other electrical conductors.

The components of each respective layer may be blended together by any conventional process until a uniform mix is obtained. In a preferred embodiment, a twin- screw extruder is used for compounding. The inner and outer layers are preferably formed by melt-extrusion, particularly by either sequential or co-extrusion, depending upon the particular application. The layers formed by the first and second fluorocarbon polymer compositions are then cross-linked using known techniques which include chemical and radiation cross-linking methods. In a preferred embodiment, the layers are subjected to an irradiation step to effect cross-linking in each layer. In a preferred embodiment, the dosage of ionizing radiation (e.g., accelerated electrons or gamma rays) employed in the irradiation step is below 30 megarads (Mrads), more preferably, between 5 and 25 Mrads and, most preferably, between 15 and 25 Mrads. It is theorized that, at higher irradiation levels (e.g., ≥ 25 MRads), cross-linking occurs even in the absence of a cross-linking agent. The irradiation step is preferably carried out at ambient temperature. Self heating during irradiation may raise the temperature of the layers as high as 100°C.

The insulated conductor of the present invention comprises a metal conductor or wire having the inventive dual layer system releasably adhered thereto.

In a preferred embodiment, the outer layer of the dual layer system has a thickness of from 0.10 to 0.65 millimeters (mm), while the inner layer has a thickness of from 0.05 to 0.40 mm.

The inventive insulated conductor demonstrates a balance of physical properties. In a more preferred embodiment, the inventive conductor demonstrates greatly improved wire-to-wire abrasion resistance. In particular, the inventive conductor satisfies commercial and/or military aircraft insulated wire or conductor specifications set for original elongation or elongation at break, notch sensitivity, accelerated aging or shrinkage resistance, crosslink proof or high temperature cut-through resistance, dry arc resistance, wet arc resistance, and wire-to-wire abrasion resistance.

The above-referenced properties have been measured in accordance with the test procedures detailed in Boeing Specification Support Standard BSS 7324 entitled

"Procedure for Testing Electrical Wire and Cable" dated December 2, 1998 ("Boeing BSS 7324"), which is incorporated herein by reference. In a preferred embodiment, the insulated conductor of the present invention demonstrates an elongation at break (expressed as a percentage of the original length) ranging from about 50 to about 150 %, a wire-to-wire abrasion resistance ranging from about 1,500,000 to about 35,000,000 cycles to failure and satisfies the "pass" criteria dictated in Boeing Specification Number BMS 13-48 (dated July 29, 1996) and Military Specification No. MIL-W-22759E (dated December 31, 1990) for notch sensitivity, accelerated aging, crosslink proof, dry arc resistance and wet arc resistance. The invention is now described with reference to the following examples which are for the purpose of illustration only and are not intended to imply any limitation on the scope of the invention.

SPECIFIC EMBODIMENTS COMPONENTS USED ETFE(I)_{Tπ 2}oo°c ^: copolymer comprising 40 to 50 mole % of ethylene; 50 to 55 mole % of tetrafluoroethylene; and 0 to 10 mole % of a fluorinated termonomer, marketed under the trade designation TEFZEL 200 by E.I. duPont de Nemours and Company ("duPont"), Wilmington, DE.

ETFE(II)_Tmj2oo°c^{: a} copolymer comprising 40 to 50 mole % of ethylene; 50 to 55 mole % of tetrafluoroethylene; and 0 to 10 mole % of a fluorinated termonomer, marketed under the trade designation NEOFLON EP-541 by Daikin America, Inc.,

Orangeburg, NY.

ETFE_Tm<20o=_c: a copolymer comprising approximately 37 mole % of ethylene; approximately 50 mole % of tetrafluoroethylene; and approximately 12 mole % hexafluoropropylene, marketed under the trade designation HTE E- 14660 by Dyneon LLC, Oakdale, MN.

TAIC: a triallyl isocyanurate cross-linking agent marketed under the trade designation TAIC® triallyl isocyanurate by Nippon Kasei Chemical Co., Ltd., Tokyo, Japan.

TITANIUM OXIDE: TiO₂ pigment in powder form (>96 % in purity) marketed under the trade designation TiPure by duPont.

ANTIMONY OXIDE: Sb,O₃ flame retardant in powder form ( ≥ 99.0 % in purity) marketed under the trade designation Antimony Oxide TMS by Anzon Inc., Philadelphia, PA.

PTFE POWDER: polytetrafluoroethylene lubricant in powder form (≥ 99 % purity) marketed under the trade designation ZONYL MP1200 by duPont.

SAMPLE PREPARATION AND TEST METHODS The components used to prepare the inner layers of the inventive dual layer system were compounded using a Leistritz Micro 270 twin-screw-extruder with vacuum venting under the following conditions: barrel temperature: linearly increased from 220°C (heating zone 4) to

255 °C (heating zone 8) with heating zones 1 through 3 maintained at 50 °C; screw speed: 71 rpm; in- and out-put rate: 7 to 8 kg/hr; and power draw: 2.0 to 2.5 kW.

The compounded material was then pelletized and the pellets dried at 80 ° C for 4 hours. The dried pellets were then melt-blended at approximately 280°C and then extruded over a 20 AWG, 19 strand, silver plated copper conductor to a thickness of 0.076 ± 0.006mm using a ³/" O.D., 25: 1 L/D ratio, single-screw Brabender extruder, Model No. PL 2200 under the following conditions: barrel temperature: linearly increased from 200 °C (heating zone l) to 280 °C (heating zone 4) with heating zones 1 through 3 maintained at 50 °C; screw speed: 6 rpm; in- and out-put rate: 1.5 to 1.7 kg hr; power draw: 0.8 to 1.5 kW; and line speed: 233 ft/min.

The components used to prepare the outer layer of the inventive dual layer system were compounded using a Leistritz Micro 270 twin-screw-extruder with vacuum venting under the following conditions: barrel temperature: linearly increased from 220 °C (heating zone l) to

270 °C (heating zone 4) with heating zones 1 through 3 maintained at 50 °C; screw speed: 70 to 170 rpm; in- and out-put rate: 4.5 to 5.5 kg/hr; and power draw: 2.5 to 3.6 kW.

The compounded material was then pelletized and the pellets dried at 80 °C for 4 hours. The dried pellets were then melt-blended at approximately 280°C and then extruded over the conductors coated with the inner layer to a thickness of 0.127 ± 0.007 mm using a %" O.D., 25:1 L/D ratio, single-screw Brabender extruder, Model No. PL 2200 under the following conditions: barrel temperature: linearly increased from 200 °C (heating zone 1) to

280 °C (heating zone 4) with heating zones 1 through 3 maintained at 50 °C; screw speed: 14 to 21 rpm; in- and out-put rate: 1.0 to 2.0 kg/hr; power draw: 2.0 to 3.5 kW; and line speed: 72 to 155 ft/min.

The composition of each layer is set forth in Table 1 hereinbelow.

The inner and outer layers of the dual layer system were cross-linked by irradiating the coated wire samples at dosage levels of 5, 10, 15, 20 and 25 Mrads using a Nishin Electron Beam, Model No. 500Kv.

The cross-linked coated wire samples were then subjected to the test procedures identified below. The subject test procedures are fully described in the Boeing Specification Support Standard BSS 7324 entitled "Procedure for Testing Electrical Wire and Cable" dated December 2, 1998 ("Boeing BSS 7324"), which is incorporated herein by reference.

Original elongation (%): Boeing BSS 7324 (ASTM D3032), paragraph no. 7.14, pp. 46-47;

Notch Sensitivity (P,F): Boeing BSS 7324, paragraph no. 7.37a, (Procedure I), pp. 83-84;

Accelerated aging or Boeing BSS 7324, shrinkage resistance (P,F): paragraph no. 7.1a, pp. 12-14;

Crosslink proof or high Boeing BSS 7324, temperature cut-through paragraph no. 7.40b (Procedure II), p. 87; resistance (P,F):

Dry arc resistance (P,F): Boeing BSS 7324, paragraph no. 7.4.5, pp. 23-26;

Wet arc resistance (P,F): Boeing BSS 7324, paragraph nos. 7.4.6 and 7.4.7 , pp. 26-29; and

Wire-to-wire abrasion resistance (cycles to failure): Boeing BSS 7324, paragraph no. 7.57, p. 108.

WORKING EXAMPLES AND TEST RESULTS Examples 1 to 9 and Control C-l In Examples 1 to 9 and Control C-l, wires coated with dual layer systems having identical outer layers and inner layers comprised of varying amounts of a low- melting ETFE copolymer or a conventional ETFE copolymer and cross-linking agent were prepared and tested and the results tabulated in Table 1. Control C-l employed the conventional ETFE in both the inner and outer layers. The amounts of the components used are parts by weight and are calculated to add up to 100 parts by weight total.

TABLE 1 SUMMARY OF EXAMPLES 1 TO 9 AND C-l

Working Examples 1 to 9 illustrate the balance of properties that can be obtained within the framework of the present invention. In particular, Examples 1 to 4 demonstrate that at irradiation or beam dosage levels of 10 and 15 Mrads, a good balance between % original elongation and wire-to-wire abrasion resistance can be achieved. The properties demonstrated by these Examples are comparable to those obtained for Control C-l .

Examples 1 , 5 and 8 demonstrate that a reduction in beam dosage or cure levels generally results in an increase in % elongation and a corresponding decrease in wire-to-wire abrasion resistance.

Examples 10 to 15 and Control C-2 In Examples 10 to 15 and Control C-2, wires coated with dual layer systems and irradiated at elevated beam dosage levels were prepared and tested and the results tabulated in Table 2. The amounts of the components used are parts by weight and are calculated to add up to 100 parts by weight total.

TABLE 2 SUMMARY OF EXAMPLES 10 TO 15 AND C-2

10

*>

15

20

Working Example 10 and Control C-2 demonstrate comparable physical properties while Working Examples 14 and 15 demonstrate the greatly improved wire-to- wire abrasion resistance that can be achieved by the insulated conductors of the present invention. It is noted that Examples 14 and 15 also demonstrate a slight decrease in % original elongation or elongation at break. The values obtained, however, are still well within acceptable limits.

In addition to the above, it is observed that the presence of PTFE POWDER in the outer layer of the dual layer system of the present invention serves to increase wire-to- wire abrasion resistance when beam dosage levels of ≤ 25 Mrads are employed. Moreover, it is observed that the presence of TITANIUM OXIDE in the outer layer might adversely impact upon the wire-to-wire abrasion resistance of the inventive system. When comparing Working Examples 10 and 12, it appears that the presence of PTFE POWDER in the outer layer contributes to an increase in wire-to-wire abrasion resistance while a comparison of Working Examples 12 and 14 appears to suggest that the presence of TITANIUM OXIDE might have contributed to a decrease in the wire-to- wire abrasion resistance. Dry arc and wet arc resistance failures in Working Example 13 appear to be due to the tendency of PTFE POWDER to degrade at higher beam dosage levels.

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

We claim:

Claims

1. A dual layer system suitable for use as an outer covering or jacket for providing electrical insulation to wires or other conductors, which comprises: an inner electrically insulating layer that comprises a first melt-processed, cross-linked fluorocarbon polymer composition wherein said polymer has a melting point of

< 200° C; and an outer electrically insulating layer that comprises a second melt-processed, cross-linked fluorocarbon polymer composition wherein said polymer has a melting point of ≥ 200° C.

2. The dual layer system of Claim 1, wherein said polymer of said first melt- processed, cross-linked fluorocarbon polymer composition is a crystalline fluorocarbon polymer or mixture of such polymers.

3. The dual layer system of Claim 2, wherein said polymer is a copolymer of ethylene, tetrafluoroethylene and, optionally, one or more copolymerizable comonomers.

4. The dual layer system of Claim 3, wherein said copolymer comprises from about 25 to about 40 mole % of units derived from ethylene, from about 45 to about 55 mole % of units derived from tetrafluoroethylene and up to about 20 mole % of units derived from one or more fluorinated comonomers, wherein said comonomers are selected from the group consisting of hexafluoropropylene, hexafluoroisobutene, perfluorobutylethylene, vinylidene fluoride, vinyl fluoride, and mixtures thereof.

5. The dual layer system of Claim 4, wherein said fluorinated comonomer is hexafluoropropylene.

6. The dual layer system of Claim 1 , wherein said polymer of said second melt- processed, cross-linked fluorocarbon polymer composition is a crystalline fluorocarbon polymer or mixture of such polymers.

7. The dual layer system of Claim 6, wherein said polymer is a copolymer of ethylene, tetrafluoroethylene and, optionally, one or more copolymerizable comonomers.

8. The dual layer system of Claim 7, wherein said copolymer comprises from about 35 to about 60 mole % of units derived from ethylene, from about 35 to about 60 mole % of units derived from tetrafluoroethylene and up to about 10 mole % of units derived from one or more fluorinated comonomers, wherein said comonomers are selected from the group consisting of hexafluoropropylene, hexafluoroisobutene, perfluorobutylethylene, vinylidene fluoride, vinyl fluoride, and mixtures thereof.

9. The dual layer system of Claim 1, wherein said system demonstrates an elongation at break ranging from about 50 to about 150% and a wire-to-wire abrasion resistance ranging from about 1,500,000 to about 35,000,000 cycles to failure.

10. The dual layer system of Claim 1 , wherein said second melt-processed, cross- linked fluorocarbon polymer composition further comprises a polytetrafluoroethylene lubricant and wherein each layer of said dual layer system has been cross-linked using radiation dosage levels of < 25 Mrads.

11. A dual layer system suitable for use as an outer covering or jacket for providing electrical insulation to wires or other conductors, which is prepared from: 1) an inner electrically insulating layer that comprises a first melt- processable, cross-linkable fluorocarbon polymer composition that comprises:

(a) from about 97.0 to about 100% by wt. of a copolymer comprising from about 25 to about 40 mole % of units derived from ethylene, from about 45 to about 55 mole % of units derived from tetrafluoroethylene and up to about 20 mole % of units derived from one or more fluorinated comonomers, wherein said comonomers are selected from the group consisting of hexafluoropropylene,hexafluoroisobutene,perfluorobutylethylene,vinylidene fluoride, vinyl fluoride, and mixtures thereof, and wherein said copolymer has a melting point of < 200° C; and

(b) up to about 3.0% by wt. of a cross-linking agent, wherein the sum of components (a) and (b) total 100% by wt., and

2) an outer electrically insulating layer that comprises a second melt- processable, cross-linkable fluorocarbon polymer composition that comprises: (a) from about 86.0 to about 90.0% by wt. of a copolymer comprising from about 35 to about 60 mole % of units derived from ethylene, from about 35 to about 60 mole % of units derived from tetrafluoroethylene and up to about 10 mole % of one or more copolymerizable fluorinated comonomers, wherein said comonomers are selected from the group consisting of hexafluoropropyleneJτexafluoroisobutene,perfluorobutylethylene,vinylidene fluoride, vinyl fluoride, and mixtures thereof, and wherein said copolymer has a melting point of ≥ 200° C; and (b) from about 8 to about 10% by wt. of a cross-linking agent, wherein the sum of components (a) and (b) total 100% by wt.

12. The dual layer system of Claim 11, wherein said cross-linking agent of said inner layer and of said outer layer is selected from the group consisting of triallylisocyanurate, triallylcyanurate, trimethallylisocyanurate, and mixtures thereof.

13. The dual layer system of Claim 11, wherein said second melt-processable, cross-linkable fluorocarbon polymer composition further comprises a polytetrafluoroethylene lubricant.

14. An insulated conductor comprising a wire having an insulating coating releasably adhered thereto, wherein said insulating coating is a dual layer system which comprises: an inner electrically insulating layer that comprises a first melt-processed, cross-linked fluorocarbon polymer composition wherein said polymer has a melting point of

15. The insulated conductor of claim 14, wherein said polymer of said first melt- processed, cross-linked fluorocarbon polymer composition is a crystalline fluorocarbon polymer or mixture of such polymers.

16. The insulated conductor of claim 15 , wherein said polymer is a copolymer of ethylene, tetrafluoroethylene and, optionally, one or more copolymerizable comonomers.

17. The insulated conductor of claim 16, wherein said copolymer comprises from about 25 to about 40 mole % of units derived from ethylene, from about 45 to about 55 mole % of units derived from tetrafluoroethylene and up to about 20 mole % of units derived from one or more fluorinated comonomers, wherein said comonomers are selected from the group consisting of hexafluoropropylene, hexafluoroisobutene, perfluorobutylethylene, vinylidene fluoride, vinyl fluoride, and mixtures thereof.

18. The insulated conductor of claim 17, wherein said fluorinated comonomer is hexafluoropropylene.

19. The insulatedconductorof claim 14, wherein said polymer of said second melt- processed, cross-linked fluorocarbon polymer composition is a crystalline fluorocarbon polymer or mixture of such polymers.

20. The insulated conductor of claim 19, wherein said polymer is a copolymer of ethylene, tetrafluoroethylene and, optionally, one or more copolymerizable comonomers.

21. The insulated conductor of Claim 20, wherein said copolymer comprises from about 35 to about 60 mole % of units derived from ethylene, from about 35 to about 60 mole % of units derived from tetrafluoroethylene and up to about 10 mole % of units derived from one or more fluorinated comonomers, wherein said comonomers are selected from the group consisting of hexafluoropropylene, hexafluoroisobutene, perfluorobutylethylene, vinylidene fluoride, vinyl fluoride, and mixtures thereof.

22. The insulated conductor of Claim 14, wherein said dual layer system demonstrates an elongation at break ranging from about 50 to about 150% and a wire-to- wire abrasion resistance ranging from about 1,500,000 to about 35,000,000 cycles to failure.

23. The insulated conductor of Claim 14, wherein said second melt-processed, cross-linked fluorocarbon polymer composition further comprises a polytetrafluoroethylene lubricant and wherein each layer of said dual layer system has been cross-linked using radiation dosage levels of < 25 Mrads.