AU766430B2

AU766430B2 - Electrical wire insulation

Info

Publication number: AU766430B2
Application number: AU61019/99A
Authority: AU
Inventors: Giles Henry Rodway
Original assignee: Tyco Electronics UK Ltd
Current assignee: Tyco Electronics UK Ltd
Priority date: 1998-09-17
Filing date: 1999-09-17
Publication date: 2003-10-16
Anticipated expiration: 2019-09-17
Also published as: KR20010079751A; EP1116243B1; IL141338A0; ZA200101181B; CZ299046B6; AU6101999A; HUP0103585A2; KR100638181B1; DE69930532T2; CN1331160C; JP2002525819A; RO121928B1; NO20011307D0; NO324458B1; CA2340386A1; RU2231147C2; IL141338A; BR9913843A; GB9820214D0; TR200100761T2

Abstract

An electrical wire or cable having insulation comprising (i) at least a first layer of a polyolefin-based formulation, of which at least 20 %, preferably at least 40 %, more preferably at least 60 % or very preferably at least 80 % of the weight of the polymeric portion of the said formulation consists of a carbonyl-containing polymer (homopolymer or copolymer or terpolymer), of which polymer the or at least one constituent monomer is a carboxylic acid ester, preferably an acrylate or acetate, especially an alkyl acrylate (preferably methyl acrylate, ethyl acrylate, propyl acrylate or butyl acrylate), the said monomer itself constituting at least 5 %, preferably at least 9 %, more preferably at least 15 % by weight of the said co-, or ter- polymer when used, and the remainder or the majority of the remainder of the said co-, or ter- polymer preferably being derived from olefinic monomer, preferably ethylene; in contact with (ii) at least a second layer of another material formulation, containing at least 10 %, more preferably at least 50 %, very preferably at least 90 %, especially 100 %, by weight of the second layer, of polyvinylidine fluoride (PVDF), or especially preferably a copolymer based on VDF with a partially or fully fluorinated co-monomer, most preferably a copolymer of VDF and hexafluoropropylene (HFP); wherein the said layers (i) and (ii) whilst in contact with each other have been subjected to cross-linking reaction, preferably by radiation, more preferably ionising radiation, sufficient to prevent delamination of the two layers during a 1 hour acetone immersion test at 23 DEG C, or to increase the peel bond strength between the said layers to at least 5N according to the ASTM B1876-95 method described below preferably increasing the bond strength by at least 50 %, more preferably by at least 100 %, especially by at least 500 % or 1000 %, compared to that between the uncrosslinked layers.

Description

WO 00/17889 PCT/GB99/03116 1 ELECTRICAL WIRE INSULATION This invention relates to insulation for electrical wire or cable (hereinafter "wire") in which a strong bond is achieved at an interface between a layer of polyolefin-based material and a layer of polyvinylidene fluoride-based material. The invention is especially useful in multi-layer insulation of electrical wires, making it possible to achieve highperformance bonding between layers of such materials while retaining an acceptable balance in the complex relationships of other wire performance requirements, which are specialised and different from the criteria for other kinds of article such as mouldings or packaging films.

The following abbreviations will be used hereinafter: PJ Primary jacket; pro-rad crosslinking promoter; TMPTM trimethylolpropanetrimethacrylate; ASTM American Society for Testing and Materials; PVDF polyvinylidene fluoride; VDF vinylidene fluoride; HFP hexafluoropropylene; HDPE high density polyethylene; EEA ethylene/ethyl acrylate; EMA ethylene/methyl acrylate; EVA ethylene/vinyl acetate; EA ethyl acrylate; MA methyl acrylate; VA vinyl acetate.

Dual wall wire insulation comprising a polyolefin inner layer (core) and polyvinylidene fluoride (PVDF) outer layer (primary jacket or PJ) has been commercially available for over 30 years, and is available from several different manufacturers. These products all have negligible adhesion between the inner (polyolefin) and outer (PVDF) layers, which are consequently easily separable. It has been necessary to accept certain disadvantages arising from this lack of bonding, which limits the robustness of the construction. For example, the outer insulation layer can crack and peel off the inner layer if subjected to mechanical stress, exposure to certain fluids, contact with sharp objects, or impact.

Abrasion and flexural fatigue resistance of the insulation, as well as resistance to wrinkling on bending (which can cause difficulties in sealing the wire or inserting it into grommets or connectors) are also detrimentally affected by having two readily separable insulation layers. It has not been thought possible to bond layers of two such dissimilar classes of 2 material as polyolefins and PVDFs on a wire at commercially acceptable cost and manufacturing efficiency. Moreover, available bonding techniques could unacceptably affect the wire performance characteristics. The conventional approach to the bonding of polyolefins and PVDF is to employ a tie layer material US patent 5,589,028), but these tend to be expensive, and when used on wire may compromise other properties, e.g. heat ageing, and add complexity to the manufacturing process in forming the extra layer. They may also be of limited effectiveness in terms of the bond strength developed.

It has now been discovered, according to the present invention, that the dissimilar insulation materials of a polyolefin-based core and a polyvinylidene fluoride-based PJ can be bonded together to a significant level of adhesion on an electrical wire or cable; that this bonding tends to reduce or eliminate the aforementioned robustness problems on a wire; and that this bonding can be achieved, contrary to expectation, without unacceptable effects on crack propagation resistance, cost, or on the general balance of wire performance characteristics.

In the wire or cable insulation according to the present invention, significant bond strength is unexpectedly achieved by a combination of a selected formulation of a polyolefin-based layer, in contact with a polyvinylidene fluoride-based layer, and a cross-linking reaction, preferably effected by the application of radiation, especially coo• ionising radiation.

The invention accordingly provides an electrical wire or cable having insulation comprising at least a first layer of a polyolefin-based material comprising at least 20%, by weight (of the whole material composition) of a carbonyl-containing polymer (homopolymer or copolymer or terpolymer), of which polymer the or at least one constituent monomer is a carboxylic acid ester, the said monomer itself constituting at S 30 least 5% by weight of the said co-, or ter- polymer when used and the remainder of the 3 said co-, or ter- polymer when used and the remainder of the said co-, or ter- polymer being derived from olefinic monomer; in contact with (ii) at least a second layer of a material containing at least 10%, by weight based on the whole material composition, of polyvinylidene fluoride (PVDF), or of a copolymer based on VDF with a partially or fully fluorinated co-monomer; wherein the said layers and (ii) whilst in contact with each other have been subjected to cross-linking reaction sufficient to increase the peel bond strength between the said layers to at least According to another aspect of the invention, we provide an electrical wire or cable having insulation comprising at least a first layer of a polyolefin-based formulation, of which at least 40% of the weight of the polymeric portion of the said formulation consists of a carbonylcontaining polymer (homopolymer or copolymer or terpolymer), of which polymer the or at least one constituent monomer is a carboxylic acid ester, the said monomer itself constituting at least 5% by weight of the said co-, or ter- polymer when used, and the 2 0 remainder or the majority of the remainder of the said co-, or ter- polymer being derived from olefinic monomer, in contact with (ii) at least a second layer of another material formulation, containing at least by weight of the second layer, of polyvinylidine fluoride (PVDF), or a copolymer based 25 on VDF with a partially or fully fluorinated co-monomer; wherein the said layers and (ii) whilst in contact with each other have been subjected *oo* •to cross-linking reaction, sufficient to prevent delamination of the two layers during a 1 hour acetone immersion test at 23 0 C, or to increase the peel bond strength between the 30 said layers to at least 5N according to the ASTM B 1876-95 method described below, increasing the bond strength by at least 50% compared to that between the uncrosslinked layers.

4 Preferably, the respective layers have been brought into contact with each other at a temperature above the melting or softening point of the polymeric material in at least one of the layers, thus tending to maximise the intimacy of their interfacial contact and so possibly encouraging the formation of adhesion-promoting interfacial cross-links in the subsequent cross-linking reaction.

The polvolefin-based layer in addition to the polymeric portion of the formulation, for which the requirements are stipulated above, may contain whatever else is required in the way of additives such as anti-oxidants, pigments, fillers, flame retardants, etc, as known per se, to give the required mechanical, thermal, electrical etc. properties to the polymer.

The polyvinylidene fluoride-based layer (ii) also may contain other additives as known per se to give it required properties in addition to bonding.

Advantages of achieving a strong bond in accordance with this invention include: abrasion resistance of surface layer, and the insulation as a whole can increase if it (the surface layer) is bonded to a substrate material; 20 improved resistance to peel, especially if one of the layers is damaged/perforated; improved resistance to blistering of the two layers, if heat is applied; improved resistance to delamination/creasing/wrinkling between the two layers, e.g.

due to mechanical stress or chemical exposure e.g to solvents.

achievement of reduced wire bend wrinkling and improvement in the above characteristics, while maintaining adequate cut-through and notch propagation resistance, the latter being unexpected since strongly adherent layers would normally be expected fairly easily to transmit a cut or notch in the outer layer through to the inner layer.

The bond strength described in this application can be measured in terms of peel strength between bonded strips of the two materials in question. A standard method which can be used for such a test is ASTM 1876-95 By this definition, a significant bond could be one for which the peel force exceeds 5N, and a strong bond one of peel S"force greater that 1ION. A convenient method for gauging the bond strength between the said layers, and when they have been fabricated onto a wire, is to place a sample wire, of total length 60mm, into acetone Fisher scientific UK, AR certified grade acetone), to a depth of acetone equivalent to 70% of the length of sample wire, at 23 5 for a period of 1 hour. Wires with negligible bonding of the insulation layers experience an extension of the PVDF PJ, along the axis of the wire, that is independent of any extension of the polyolefin core, and/or wrinkling of the PJ such that it delaminates from the core in places. When it occurs, the above-mentioned extension of the PJ typically results in a PJ "tube" extending for 1mm or more beyond the cut end of the core in the sample wire, following the above test. Wires with significantly bonded insulation layers experience an extension of the core and PJ, together, without separation, beyond the cut edge of the conductor, along the axis of the wire and/ or wrinkling of the core and PJ layers together, without delamination. Any such wrinkling of the core and PJ together can be distinguished from wrinkling of the PJ only by examining a cross-section of the wrinkles under a microscope.

Preferably, the carboxylic acid ester is an acrylate or acetate, more preferably an alkyl acrylate.

Preferably, the olefinic monomer in layer is ethylene.

Preferably, in layer at least 80% of the weight of the polymeric portion consists of the carbonyl-containing polymer.

Preferably, in layer the carboxylic acid ester constitutes at least 15% by weight of the said co or ter- polymer when used.

Preferably, layer (ii) contains at least 90%, more preferably 100%, by weight of the second layer, of PVDF or a copolymer based on VDF with a partially or fully fluorinated co-monomer.

Methods of fabricating the wire may include any process which causes intimate contact between the above-mentioned layers and Examples include coating of one S" 30 material onto a pre-formed layer of the other, dual or multi-walled extrusion to form insulation layers respectively containing one or other of the aforementioned two classes of material. The olefin-based material is preferably the inner layer and the PVDF- 5a based layer (ii) preferably the outer layer on the wire. The layers made from the two different materials could be coextruded, tandem extruded, multipass extruded, or coated by other means. Known wire insulation processes such as tube draw-down extrusion may be used, to form one or more of the layers, but pressure extrusion as known per se is preferred for optimum adhesion of the second and any subsequent insulation layers to be applied to a pre-formed underlying layer.

i' ••go* WO 00/17889 PCT/GB99/03116 6 The insulation on the wire is exposed to a cross-linking reaction, which may involve chemical reagents such as peroxides, but preferably is effected by radiation, especially from a source of ionising radiation capable of causing the formation of free radicals and thus, cross-links, in the polymers, some of which should preferably be formed in the region of the interface between the two materials. Penetration of the radiation into the material at least as far as the interface is therefore desirable, although not necessarily essential if ion or radical mobility, for example, enables molecular reactions to continue at or near the interface after the radiation process. The radiation source could, for example, be a radio-isotope, or an X-ray source, or possibly a non-ionising radical-generating source, for example a UV source, but is preferably an electron beam, more preferably one providing a beam dose greater than 2 Mrads, preferably at least 5 Mrads, more preferably at least 10 Mrads, very preferably at least 15Mrads, into the material.

It has been found that enhancements to the interfacial bond strength may be obtained by using certain additives. Additives preferably include a cross-linking promoter ("pro-rad") in the polyolefin-based material and/or in the PVDF-based material. Known cross-linking materials may be used, preferably methacrylate/acrylate based ones, and, very preferably, those of the type trimethylolpropanetrimethacrylate (TMPTM), in the polyolefin material and/or in the PVDF-based material.

Experimental results: All results quoted in the tables below were obtained by testing pressed plaques of the two materials prepared by the usual polymer handling techniques, well known per se. The plaques were pressed together to bond them face-to-face and the bonded assembly was irradiated as indicated. Plaques were used for these demonstration experiments rather than wires, due to the relative ease of measuring bond strength on plaques. Conditions for these experiments were as follows: Plaque dimensions: 150mm by 150mm by 0.85mm Pressing temperature: 200 0

C

Pressing time: 2 minute preheat, 1 minute at pressure Pressing pressure: 20-40 Tons over a 300mm by 300mm metal plate WO 00/17889 PCT/GB9903116 Cooling conditions: 2 minutes between water cooled, 300mm by 300mm, metal plates, at a pressure as above 590 PCT...

1" PGTIGB 9 9 /l S-0'SG8 0 2 NOVEMBER 1999 Example of Effect of Radiation Dose on Bond strength developed between aDDroT)flate ~olvolefin and PVDF-based materials Material 1 Material 2 Dose(Mrad) Peel force

(N)

EVA copolymer of 25wt% VA VDF/HFP copolymer 0 content of lOwt% HF? content additives Same as above Same as above 15 EEA copolymer of l5wt% EA VDF/}JFP copolymer 0 1 content of lOwt% HF? content EEA copolymer of 15wt% EA. VDF/HFP .copolymer 8 24 content of lOwt% HIF? content EEA copolymer of 15wt% EA VDF/HFP copolymer 20 52 content of lOwt% HF? content Ethylene/acrylic ester/maleic. VDF/HFP copolymer 0 anhydride terpolymer of l9wt% of lowt% HF? content acrylic ester content Ethylene/acrylic ester/maleic VDF/HFP copolymer 20 21 anhydride terpolymer of 19wt% of lOwt% HF? content acrylic ester content Example of Effect of Percentage Comonomer in Ethylene, Copolymer Material o bond strength to propriate, ?VDF-based material after electron beam crosslinking Material 1 Material 2 Dose(Mrad) Peel (N) EMA copolymer with 9wt% MA VDF/KFP copolymer 20 4 content of lOwt% HF? content +7.Swt% additives EMA copolymer with 28wt% MA Same as above 20 content SUBSTITUTE SHEET (RULE 26) ;X A(590 PCT...

G~991O31 1~f PCTI'GlpB 9 k~ 0 2 §f9 ExapleofEffctof erentgeCo~olvmer in a Dolvolefmn Dolvmer blend on bond strength with appropriate PVDF-based material after electron beam crosslinkinr Material 1 Material 2 Dose(Mrad) Peel force

(N)

100% HDPE VDF/HFP copolymer 20 -0 of lOwt% BT? content additives HDPE 80% EEA Same as above 20 copolymer of 15wt% EA content ExaMle of Effect of PVDF-based material =ye on bond strength with apropriate polvolefin based material after electron beam crosslinking Material 1 Material 2 Dose(Mrad) Peel (N) EVA copolymer with 25wt% VA PVDF homopolymer 15 4 content As above VDF/HFP copolymer 15 17.5 1 of lOwt% HFP content Example of Effect of the addition-of Pro-rad in Olefinic Material on bond strengt with approriate PVDF-based material after electron beam crosslinking Material 1 Material 2 Dose(Mrad) Peel (N) HDPE 80% EEA VDF/HFP copolymer 20 copolymer of l~wt% EA content of lOwt% HFP content additives 19% HDPE 77%EEA Same as above 20 130 copolymer of 15wt% EA content 4% TMPTM pro-rad ExaMnles of Wire Construction An electrical wire in which the insulation consists of two polymeric layers according to the present invention was made as follows: bonded together SUBSTIlLTT 7 r7- WO 00/17889 PCT/GB99/03116 The inner layer of insulation nearer to the wire conductor) was a polyolefin-based material, consisting predominantly of an EEA copolymer containing 15wt% EA and HDPE in a weight ratio of approximately 8:2 copolymer:HDPE, with usual other additives present in smaller proportions including crosslinking promoters, stabilisers, antioxidants, pigments and process aids at a total level of 24wt%. This layer was pressure extruded onto the metallic conductor.

The outer layer of insulation consisted predominantly of a PVDF/HFP copolymer containing 10wt% HFP, which in this example contains a crosslinking promoter, and other known additives such as pigments, plasticisers, stabilisers, antioxidants and process aids in usual proportions totalling 7.5wt%.. This outer layer was pressure extruded in a separate operation onto the pre-formed inner layer. This coated wire product was then passed through an electron beam, and received a radiation dose of In a second example a wire was made as above, in which the crosslinking promoter in the inner layer was 4% TMPTM, and the the outer layer of insulation was comprised solely of the PVDF/HFP copolymer containing 10wt% HFP. This coated wire product was then passed through an electron beam, and received a radiation dose of 20 Mrads. This wire was subjected to the acetone immersion test, confirming that the insulation layers were significantly bonded together.

In a third example, a wire of the same construction as the second example was made by tandem pressure extrusion of the inner and outer insulation layers. This coated wire product was then passed through an electron beam, and received a radiation dose of Mrads. This wire was subjected to the acetone immersion test, confirming that the insulation layers were significantly bonded together.

Demonstration of Improved performance of wires constructed as in the second example above, relative to current commercially available wire.

A wire of the above construction and manufacturing process (designated wire A) was compared with a market leading commercially available polyolefin/PVDF dual-walled wire (designated wire B) of the same dimensions, over a range of tests for wire robustness WO 00/17889 PCT/GB99/03 116 relevant to harsh handling and end-use environments.

obtained.

The following results were WO 00/17889 PCT/GB99/03116 12 Example of scrape abrasion resistance improvement Method: Equipment =conventional type wire scrape abrader, wire size 0.75mm2(conductor cross sectional area), blade type flat, width 3.5mm held perpendicular to wire, with 0.05mm radiused edges each side, applied load 1.8kg, stroke length at 55 cycles/minute Wire No. of scrape cycles to abrade through PJ at Type A 800 B 272 Wire No. of scrape cycles to abrade through PJ at 5 C Type A 1350 B 212 Example of cold impact resistance improvement Method: wire size 6mm2(conductor cross sectional area), impact weight 800g, drop height 275mm onto anvil, anvil area impacting on wire of dimensions 7mm x 2mm widening to 3.4mm via 450 taper each side, ambient temperature 5 0 C. Visual detection of insulation crack propagation.

Wire Result of cold impact test Type A No cracks in PJ propagate away from site of anvil impact B Severe cracks in PJ, 5 mm in length, propagate away from site of anvil impact. PJ starts to peel off core Example of solvent resistance improvement Method: wire size 0.75mm 2 length of wire 60mm,acetone immersion length 75% of wire length, immersion time 1hour, temperature 23 0

C

Wire IResult of acetone immersion test

I

13 A No separation/delamination of core and PJ, no cracking of either insulation layer observed B PJ wrinkled very severely along immersed length, cracking spontaneously in two places, and exposing 2-3mm of core In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that a reference herein to a prior art publication does not constitute an admission that the publication forms a part of the common general knowledge in the art in Australia, or any other country.

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SS S S 55

Claims

1. An electrical wire or cable having insulation comprising at least a first layer of a polyolefin-based material comprising at least 20%, by weight (of the whole material composition) of a carbonyl-containing polymer (homopolymer or copolymer or terpolymer), of which polymer the or at least one constituent monomer is a carboxylic acid ester, the said monomer itself constituting at least 5% by weight of the said co-, or ter- polymer when used and the remainder of the said co-, or ter- polymer being derived from olefinic monomer; in contact with (ii) at least a second layer of a material containing at least 10%, by weight based on the whole material composition, of polyvinylidene fluoride (PVDF), or of a copolymer based on VDF with a partially or fully fluorinated co-monomer; wherein the said layers and (ii) whilst in contact with each other have been subjected to cross-linking reaction sufficient to increase the peel bond strength between the said layers to at least

2. An electrical wire or cable having insulation comprising 20 at least at first layer of a polyolefin-based formulation, of which at least 40% of the weight of the polymeric portion of the said formulation consists of a carbonyl- containing polymer (homopolymer or copolymer or terpolymer), of which polymer the or at least one constituent monomer is a carbocylic acid ester, the said monomer itself constituting at least 5% by weight of the said co-, or ter- polymer when used, and the remainder or the majority of the remainder of the said co-, or ter- polymer being derived from olefinic monomer, in contact with (ii) at least a second layer of another material formulation, containing at least i: by weight of the second layer, of polyvinylidene fluoride (PVDF), or a copolymer based 30 on VDF with a partially or fully fluorinated co-monomer; wherein the said layers and (ii) whilst in contact with each other have been subjected Sto cross-linking reaction, sufficient to prevent delamination of the two layers during a 1 .hour acetone immersion test at 23 0 C, or to increase the peel bond strength between the said layers to at least 5N according to the ASTM B 1876-95 method herein before described increasing the bond strength by at least 50% compared to that between the uncrosslinked layers. 15

3. A wire or cable according to claim 1, wherein the said layers and (ii) whilst in contact with each other have been subjected to the cross-linking reaction, sufficient to prevent delamination of the two layers during a 1 hour acetone immersion test at 23 0 C.

4. A wire or cable according to any preceding claim, wherein the cross-linking reaction has increased the bond strength by at least 500% or 1000%, compared to that between the uncrosslinked layers. A wire or cable according to any preceding claim, wherein the respective layers have been brought into contact with each other prior to cross-linking of either layer and at a temperature above the melting or softening point of the polymeric material in at least one of the layers.

6. A wire or cable according to any preceding claim, wherein the polyvinylidene fluoride-based layer comprises a copolymer of VDF and hexafluoropropylene (HFP).

7. A wire or cable according to claim 6, wherein the copolymer of VDF and hexafluoropropylene (HFP), has HFP content 8-12wt%. 20 8. A wire or cable according to any preceding claim, wherein the polyolefin- based layer comprises a mixture of polyethylene and the said carbonyl-containing polymer.

9. A wire or cable according to any preceding claim, comprising an inner layer of the said polyolefin-based material and an outer layer of the said polyvinylidene fluoride-based material. A wire or cable according to claim 9, wherein the said outer layer has been S pressure-extruded onto the said inner layer. d

11. A wire or cable according to any preceding claim, wherein the cross-linking reaction has been effected by ionising radiation.

12. A wire or cable according to any preceding claim, comprising multiple alternating layers of the materials constituting the said layers and (ii).

13. A wire or cable according to any preceding claim, which contains at least one 16 crosslinking promoter in the material of either or both of the said layers and (ii).

14. A wire or cable according to claim 13, the cross-linking promoter having been added only to the material of the said layer A wire or cable according to claim 13 or 14, wherein the crosslinking promoter is a multifunctional acrylate or methacrylate ester.

16. A wire or cable according to claim 15, wherein the crosslinking promoter is trimethylolpropanetrimethacrylate (TMPTM).

17. A wire or cable according to any one of the preceding claims, wherein the carboxylic acid ester is an acrylate or acetate.

18. A wire or cable according to claim 17, wherein the carboxylic acid ester is an alkyl acrylate.

19. A wire or cable according to any one of the preceding claims, wherein the olefinic monomer in layer is ethylene.

20. A wire or cable according to any one of the preceding claims, wherein, in layer at least 80% of the weight of the polymeric portion consists of the carbonyl- containing polymer. S25

21. A wire or cable according to any one of the preceding claims, wherein, in layer the carboxylic acid ester constitutes at least 15% by weight of the said co- or ter- polymer when used.

22. A wire or cable according to any one of the preceding claims, wherein layer (ii) contains at least 90% by weight of the second layer, of PVDF or a copolymer based on VDF with a partially or fully fluorinated co-monomer.

23. A wire or cable according to any one of the preceding claims, wherein layer (ii) 35 contains at least 100% by weight of the second layer, of PVDF or a copolymer based on VDF with a partially or fully fluorinated co-monomer. 17

24. A wire or cable according to any of the preceding claims, wherein the polyvinylidene-based layer (ii) is substantially transparent. A wire or cable according to claim 24, wherein the polyvinylidene-based layer (ii) contains substantially only PVDF or the said VDF co-polymer.

26. A method of making a wire or cable according to any of the preceding claims, comprising the steps of providing on an electrical conductor the said layers and (ii) in contact with each other, and subjecting the said layers while in contact with each other to the said cross-linking reaction.

27. A method according to claim 26, wherein the respective layers are brought into contact with each other prior to cross-linking of either layer and at a temperature above the melting or softening point of the polymeric material in at least one of the layers.

28. A method according to claim 26 or 27, wherein layer is pressure extruded onto the conductor and/or layer (ii) is pressure extruded over layer

29. A method according to claim 26, 27 or 28 wherein layers and (ii) are co- extruded or tandem extruded onto the wire in a single pass of the conductor from an extrusion process pay-out device to an extrusion process take-up device. A wire or cable substantially as herein described with reference to the 9 25 examples.

31. A method substantially as herein described with reference to the examples.