ZA200101181B

ZA200101181B - Electrical wire insulation.

Info

Publication number: ZA200101181B
Application number: ZA200101181A
Authority: ZA
Inventors: Giles Henry Rodway
Original assignee: Tyco Electronics Ltd Uk
Priority date: 1998-09-17
Filing date: 2001-02-12
Publication date: 2002-05-13
Also published as: EP1116243A1; AU766430B2; HUP0103585A2; NO324458B1; CN1318200A; CN1331160C; JP2002525819A; ID29877A; RO121928B1; IL141338A0; CA2340386C; TR200100761T2; AU6101999A; CA2340386A1; DE69930532D1; PL192515B1; EP1116243B1; PL346214A1; RU2231147C2; CZ2001482A3

Description

( * . ® v wo 00/17889 PCT/GB99/03116

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 Jayer 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 high- performance 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 (e.g. US patent 5,589,028), but these tend to be expensive, and when used on wire may compromise other properties, €.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 10 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 ionising radiation.

The invention accordingly provides an electrical wire having insulation comprising: (i) at least a first layer of a polyolefin-based material comprising, of which at least 20%, : preferably at least 40%, more preferably at least 60% or at least 80%, by weight (of the whole material composition) of a carbonyl-containing polymer (homopolymer or : copolymer or terpolymer) having a non-aromatic backbone, 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 of the said co-, or ter- polymer preferably being derived from olefinic monomer, preferably ethylene. in contact with;

Ta , . 7 @ y wooonrsss ; PCT/GB99/03116 (ii) at least a second layer of a material containing at least 10%, more preferably at Jeast 50%, or at least 90%, by weight of polyvinylidine fluoride (PVDF), or especially preferably 2 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 increase the peel bond strength between the sald layers 10 at least SN, 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.

According to another aspect of the invention, we provide an electrical wire 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 of 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 the acetone immersion test e described below, or to increase the peel bond strength between the said layers to at Jeast

SN 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.

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 mterfacial contact and so possibly encouraging the formation of adhesion-promoting interfacial cross-links in the subsequent cross-linking reaction.

The polvolefin-based layer (i) 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 polvvinvlidene fluoride-based laver (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; - 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. 10 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.

EN . oo WO 00/17889 : PCT/GB99/03116

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, 2 significant bond could be one ’ for which the peel force exceeds 5N, and a strong bond one of peel force greater than 10N. A convenient method for gauging the bond strength between the said layers, (i) and (ii), when they have been fabricated onto a wire, is to place a sample wire, of total length 60mm, into acetone (e.g. Fisher Scientific UK, AR certified grade acetone), to a depth of acetone equivalent to 70% of the length of sample wire, at 23 (+/- 3)°C, 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 1t occurs, the above-mentioned extension of the PJ typically results in a PJ «be 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

MICToscope.

Methods of fabricating the wire may include any process which causes intimate contact between the above-mentioned layers: (i) and (ii). Examples include coating of one 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 (i) is preferably the inner layer and the PVDF-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.

CT/GB99/03116 i WO 00/17889 6 PCT/GB99/03116 ® )

The insulation on the wire 1s 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 Jeast 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°C '

Pressing time: 2 minute preheat, 1 minute at pressure

Pressing pressure: 20-40 Tons over a 300mm by 300mm metal plate

Le @. WO 00/17889 PCT/GB99/03116

Cooling conditions: 2 minutes between water cooled, 300mm by 300mm, metal plates, at a pressure as above 1]

; e

Example of Effect of Radiation Dose on Bond strength developed between appropriate polvolefin and PVDF-based materials

Material 1 Material 2 Dose(Mrad) Peel

N)

EVA copolymer of 25wt% VA | VDF/HFP copolymer 0 0.5 content of 10wt1% HFP content +7.5wt% additives

EEA copolymer of 15wt% EA | VDF/HFP copolymer 1 : ro

EEA copolymer of 15wt% EA | VDF/HFP copolymer 24 go I

EEA copolymer of 15wt% EA | VDF/HFP copolymer 20 52

Ea i I

Ethylene/acrylic ester/maleic | VDF/HFP copolymer <5 anhydride terpolymer of 19wt% | of 10wt% HFP content acrylic ester content

Ethylene/acrylic ester/maleic | VDF/HFP copolymer 20 21 anhydride terpolymer of 19wt% | of 10wt% HFP content acrylic ester content

Example of Effect of Percentage Comonomer in Ethviene Copolymer Material on bond strength 10 appropriate PVDFE-based material after electron beam crosslinking

EMA copolymer with 9wt% MA | VDF/HFP copolymer 20 4 content of 10wt% HFP content - +7.5wt% additives

EMA copolymer with 28wt% MA | Same as above 20 45

Ee a

SUBSTITUTE SHEET (RULE 26}

oT (TY WO 00/17889 . PCT/GB99/03116

Example of Effect of percentage Copolymer in a polvolefin polvmer blend on bond strength with appropriate PVDF-based material after electron beam crosslinking

Material 1 | Material 2 Dose(Mrad) Peel force |. } (N) 100% HDPE VDF/HFP copolymer 20 of 10wt% HFIP content +7.5wt% additives 20% HDPE + 80% EEA] Same as above 20 70 copolymer of 15wt% EA content ee TY

Example of Effect of PVDF-based material type on bond strength with appropriate polyolefin based material after electron beam crosslinking

Va [wens [bev [ew

EVA copolymer with 25wt% VA | PVDF homopolymer 15 4

As above VDF/HFP copolymer 15 17.5 pd

Example of Effect of the addition of Pro-rad in Olefinic Material on bond strength with appropriate PVDF-based material after electron beam crosslinking

ER LC LR hs li) 20% HDPE + 80% EEA VDF/HFP copolymer 20 70 copolymer of 15wt% EA content of 10wt% HFP content +7.5wt% additives 19% HDPE + 77%EEA | Same as above 20 >130 . copolymer of 15wt% EA content + 4% TMPTM pro-rad ! Examples of Wire Construction

An electrical wire in which the insulation consists of two polymeric layers bonded together according to the present invention was made as follows:

SUBSTITUTE SHEET (RULE 26)

cw, e

The inner layer of insulation (i.e. nearer to the wire conductor) was a polyolefin-based material, consisting predominantly of (a) an EEA copolymer containing 15wt% EA and (b) 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 20Mrads.

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 Jayer 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 10 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 20 .

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 oo @ wo oon7sss PCT/GBY9/03116 relevant to harsh handling and end-use environments. The following results were obtained. : : :

J v

Example of scrape abrasion resistance improvement

Method: Equipment=conventional type wire scrape abrader, wire: size 0.75mm’ (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 10cm, at 55 cycles/minute

Wire No. of scrape cycles to abrade through PJ at 40°C

A > 800

Wire No. of scrape cycles to abrade through PJ at 5°C ae | mmm ew

Example of cold impact resistance improvement

Method: wire size 6mm’(conductor cross sectional area), impact weight 800g, drop height 275mm onto anvil, anvil area impacting on wire of dimensions 7mm Xx 2mm widening to 3.4mm via 45° taper each side, ambient temperature 5°C. Visual detection of insulation crack propagation.

Wire Result of cold impact test

Ei oom peo pom ora

Severe cracks in PJ, >5 mm in length, propagate away from site

I Ri I

Example of solvent resistance improvement >

Method: wire size 0.75mm?, length of wire 60mm,acetone immersion length 75% of wire length, immersion time 1hour, temperature 23°C

Wire Result of acetone immersion test

Type

A No separation/delamination of core and PJ, no cracking of either oo insulation layer observed

PJ wrinkled very severely along immersed length, cracking ) spontaneously in two places, and exposing 2-3mm of core

Claims

= i Claims

1. An electrical wire or cable having insulation comprising (1) 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; 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 (i) 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 SN.

2. An electrical wire or cable according to claim 1, wherein the carboxylic acid ester is an acrylate or acetate.

3. An electrical wire or cable according to either of claims 1 or 2, wherein the carboxylic acid ester is an alkyl acrylate.

4. An electrical wire or cable according to claim 3, wherein the alkyl acrylate is methyl acrylate, ethyl acrylate, propyl acrylate or butyl acrylate.

5. An electrical wire or cable according to any one of claims 1 to 4, wherein the remainder of the said co-, or ter- polymer is derived from olefinic monomer.

6. An electrical wire or cable according to claim 5, wherein the olefinic monomer is ethylene. AMENDED SHEET 10.05.2002 x 2

7. An electrical wire or cable having insulation comprising (1) at least a first layer of a polyolefin-based formulation, of which at least 20% 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, the said monomer itself constituting at least 5%, by weight of the said co-, or ter- polymer when used, in contact with (ii) at least a second layer of another material formulation, containing at least 10% by weight of the second layer, of polyvinylidine fluoride (PVDF); wherein the said layers (i) and (ii) whilst in contact with each other have been subjected to cross-linking reaction, sufficient to prevent delamination of the two layers during a 1 hour acetone immersion test at 23°C, or to increase the peel bond strength between the said layers to at least SN according to the ASTM B1876-95 method.

8. An electrical wire or cable according to claim 7, wherein at least 40% of the weight of the polymeric portion of the said polyolefin-based formulation consists of a carbonyl-containing polymer.

9. An electrical wire or cable according to either of claims 7 or 8, wherein at least 60% of the weight of the polymeric portion of the said polyolefin-based formulation consists of a carbonyl-containing polymer.

10. An electrical wire or cable according to any one of claims 7 to 9, wherein at least 80% of the weight of the polymeric portion of the said polyolefin-based formulation consists of a carbonyl-containing polymer.

11. An electrical wire or cable according to any one of claims 7 to 10, wherein the carboxylic acid ester is an acrylate or acetate. AMENDED SHEET 10.05.2002

. .

12. An electrical wire or cable according to any one of claims 7 to 11, wherein the carboxylic acid ester is an alkyl acrylate.

13. An electrical wire or cable according to claim 12, wherein the alkyl acrylate is methyl acrylate, ethyl acrylate, propyl acrylate or butyl acrylate.

14. An electrical wire or cable according to any one of claims 7 to 13, wherein the said monomer itself constitutes at least 9% by weight of the said co-, or ter- polymer when used.

15. An electrical wire or cable according to any one of claims 7 to 14, wherein the said monomer itself constitutes at least 15% by weight of the said co-, or ter- polymer when used.

16. An electrical wire or cable according to any one of claim 7 to 15, wherein the remainder or the majority of the remainder of the said co-, or ter- polymer is derived from olefinic monomer.

17. An electrical wire or cable according to claim 16, wherein the olefinic monomer is ethylene.

18. An electrical wire or cable according to any one of claims 7 to 17, wherein the second layer of the other material formulation contains at least 50%, by weight of the second layer, of polyvinylidine fluoride (PVDF).

19. An electrical wire or cable according to any one of claims 7 to 18, wherein the second layer of the other material formulation contains at least 90%, by weight of the second layer, of polyvinylidine fluoride (PVDF). AMENDED SHEET 10.05.2002

Pi 1

20. An electrical wire or cable according to any one of claims 7 to 19, wherein the second layer of the other material formulation contains 100%, by weight of the second layer, of polyvinylidine fluoride (PVDF).

21. An electrical wire or cable according to any one of claims 7 to 17, wherein the second layer of the other material formulation contains at least 50%, by weight of the second layer, of a copolymer based on VDF with a partially or fully fluorinated co- monomer.

22. An electrical wire or cable according to any one of claims 7 to 17, and 21 wherein the second layer of the other material formulation contains at least 90%, by weight of the second layer, of a copolymer based on VDF with a partially or fully fluorinated CO-monomer.

23. An electrical wire or cable according to any one of claims 7 to 17, and 22 wherein the second layer of the other material formulation contains 100%, by weight of the second layer, of a copolymer based on VDF with a partially or fully fluorinated co- monomer.

24. An electrical wire or cable according to any one of claims 21 to 23, wherein the copolymer and co-monomer are a copolymer of VDF and hexafluoropropylene (HEP).

25. An electrical wire or cable according to any one of claims 7 to 24, wherein the cross-linking reaction is by radiation.

26. An electrical wire or cable according to claim 25, wherein the radiation is ionising radiation.

27. An electrical wire or cable according to any one of claims 7 to 26, wherein the cross-linking reaction increases the bond-strength by at least 50% compared to that between the uncrosslinked layers. AMENDED SHEET 10.05.2002

I's [4

28. An electrical wire or cable according to any one of claims 7 to 27, wherein the cross-linking reaction increases the bond-strength by at least 100% compared to that between the uncrosslinked layers.

29. An electrical wire or cable according to any one of claims 7 to 28, wherein the cross-linking reaction increases the bond-strength by at least 500% or 1000% compared to that between the uncrosslinked layers.

30. A wire or cable according to any one of claims 1 to 6, wherein the said layers (i) and (ii) whilst in contact with each other have been subjected to cross-linking reaction, sufficient to prevent delamination of the two layers during a 1 hour acetone immersion test at 23°C.

31. A wire or cable according to claim 30, wherein the cross-linking reaction is by radiation.

32. A wire or cable according to claim 31, wherein the radiation is ionising radiation.

33. A wire or cable according to any preceding claim, wherein the cross-linking reaction has increased the bond strength by at least 50%, compared to that between the uncrosslinked layers.

34. A wire or cable according to claim 33, wherein the bond strength is increased by at least 100% compared to that between the uncrosslinked layers.

35. A wire or cable according to either of claims 33 or 34, wherein the bond strength is increased by 500% or 1000% compared to that between the uncrosslinked layers.

36. 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 AMENDED SHEET 10.05.2002 and at a temperature above the melting or softening point of the polymeric material in at least one of the layers.

37. A wire or cable according to any preceding claim, wherein the polyvinylidene fluoride-based layer comprises a copolymer of VDF and hexafluoropropylene (HFP), that copolymer constituting a majority by weight of the material in that layer.

38. A wire or cable according to claim 37, wherein the copolymer constitutes substantially all of the material by weight in that layer.

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

40. A wire or cable according to claim 39, wherein the hexafluoropropylene (HFP) content is 8 -12 wt%.

41. A wire or cable according to either of claims 39 or 40, wherein the hexafluoropropylene (HFP) content is 9 -11 wt%.

42. 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.

43. 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.

44. A wire or cable according to claim 43, wherein the said outer layer has been pressure-extruded onto the said inner layer.

45. A wire or cable according to any preceding claim, wherein the cross-linking reaction has been effected by radiation. AMENDED SHEET 10.05.2002

46. A wire or cable according to claim 45, wherein the radiation is ionising radiation.

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

48. A wire or cable according to any preceding claim, which contains at least one cross-linking promoter in the material of either or both of the said layers (i) and (ii).

49. A wire or cable according to claim 48, wherein the cross-linking promoter has been added only to the material of the said layer (1).

50. A wire or cable according to any preceding claim, which contains at least one cross-linking promoter in the material of either or both of the said layers (i) and (ii), wherein the cross-linking promoter is a multifunctional acrylate or methacrylate ester.

51. A wire or cable according to claim 50, wherein the cross-linking promoter is trimethylolpropane-trimethacrylate (TMPTM).

52. A wire or cable according to either of claims 50 or 51, wherein the cross-linking promoter has been added only to the material of the said layer (i).

53. A wire or cable according to any of the preceding claims, wherein the polyvinylidene-based layer (ii) is substantially transparent.

54. A wire or cable according to claim 52, wherein the polyvinylidene-based layer (ii) contains substantially only PVDF or the said VDF copolymer.

55. 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 (i) and (ii) AMENDED SHEET 10.05.2002 in contact with each other, and subjecting the said layers while in contact with each other to the said cross-linking reaction.

56. A method according to claim 55, wherein the respective layers are brought into contact with each other (a) prior to cross-linking of either layer and (b) at a temperature above the melting or softening point of the polymeric material in at least one of the layers.

57. A method according to either of claims 55 or 56, wherein layer (i) is pressure- extruded onto the conductor and/or layer (ii) is pressure-extruded over layer (i).

58. A method according to any one of claims 55 to 57, wherein layers (i) 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.

59. An electrical wire or cable according to claim 1, substantially as herein described with reference to any one of the illustrative examples.

60. An electrical wire or cable according to claim 7, substantially as herein described with reference to any one of the illustrative examples.

61. A method according to claim 55, substantially as herein described with reference to any one of the illustrative examples. AMENDED SHEET 10.05.2002