GB2107720A - Improvements in or relating to cladded substrate - Google Patents

Abstract

An elongate substrate, for example a wire or cable or a pipe or duct, is provided over at least part of its length with a flame retarded cladding formed from a polymeric composition which comprises a crosslinked blend of a vinyl acetate/alkene copolymer, preferably a vinyl acetate/ethylene copolymer, having a vinyl acetate content of greater than 55 weight per cent, with a thermoplastic elastomeric polyester or a styrene/butadiene rubber, and incorporates an effective amount of a halogen- free inorganic flame retardant, e.g. alumina trihydrate.

Description

SPECIFICATION Improvements in or relating to cladded substrates The present invention relates to cladding for elongate substrates, e.g. electrical insulation for a wire or cable.

Accordingly, the present invention provides an elongate substrate provided, over at least a part thereof, with a frame retarded cladding, said cladding being formed from a polymeric composition which comprises a substantially crosslinked blend of a vinyl acetate/alkene copolymer that has a vinyl acetate/alkene copolymer that has a vinyl acetate content of greater than 55 weight percent with a thermoplastic elastomeric polyester or a styrene/butadiene rubber, and incorporates an effective amount of a halogen-free inorganic frame retardant.

The alkene component of the vinyl acetate alkene copolymer preferably comprises a C2-C6 alkene, particularly an a-unsaturated alkene such as ethylene, 1-propylene and 1-butene and particularly ethylene.

Preferably the vinyl acetate content of the vinyl acetate/alkene copolymer is up to 95 weight per cent, more preferably 60 to 95 weight per cent, e.g. 60 to 75 per cent, particularly 65 to 95 weight per cent, more particularly 65 to 90 weight per cent, e.g. 65 to 75 per cent, and especially 65 to 85 weight per cent, for example 70 to 80 weight per cent.

Additionally or alternatively, it is preferred that the overall amount of vinyl acetate in the blend is at least 30 weight per cent, particularly greater than 40 weight per cent, e.g. in the range 65 to 75 weight per cent.

Under most circumstances, it may be desirable that the polymeric composition include a coupling agent to improve the compatibility of the flame retardant with the polymer component(s) of the composition, e.g. to improve the physical properties of the composition. Preferred coupling agents include organo-silicon and titanium derivatives such as silanes and titanates.

As examples of silanes may be mentioned dimethyldichlorosilane, methyl trichlorosilane, vinyl trichlorosilane, y-methacryloxypropyl-trimethoxysilane, N,N-bis (ss-hydroxyethyl)-y-amine-propyl-triethoxy silage, vinyl propyl-trimethoxysilane, y-methacryloxpropyl-trimethoxy silane, y-merca ptopropyl-trimethoxy silane, vinyl trimethoxy silane, y-glycidoxy propyl trimethoxysilane, ss-(3,4-epoxy-cyclohexyl) ethyl trimethyl silane and vinyl trimethoxyethoxysilane. Further appropriate silanes are exemplified in UK Patent No.

1,284,082.

As examples of titanates and other organo-titanium derivatives useful as coupling agents may be mentioned tetraisooctyl titanate, isopropyl diisostearyl methacryl titanate, isopropyltriisostearoyl titanate, isopropyl-triacryl titanate, titanium di-(dioctyl pyrophosphate) and especially the so-called hybrid titanates such as isopropyl dimethacryl isostearoyl titanate. Additional suitable titanium compounds are described in S.J. Monte & G. Sugerman, J. Elastomers & Plastics Volume 8 (1976) pages 30-49, and in Bulletins KR 0376-4 and 0278-7 "Ken-React Titanate Coupling Agents for Filled Polymers" published by Ken rich Petrochem Inc, the disclosures of which are incorporated herein by reference.

The weight ratio of coupling agent, when employed, to fire retardant preferably lies in the range 0.005 to 0.1:1 respectively, more preferably 0.01 to 0.05 1 respectively.

The preferred flame retardants are those that release water on heating, particularly hydrated aluminium oxides of the formula Al203.xH2O wherein x lies in the range 0.5 to 3 especially Al2O3. 3H20, ammonium or sodium dawsonite, hydrate magnesia and hydrated calcium silicate, especially a-alumina trihydrates. Flame retardants such as alumina trihydrate preferably have a specific surface area of at least 0.1 m2/g, desirably at least 1 m21g, e.g. 1 to 80m21g, especially 3 to 20m2/g, as measured by the Brunauer, Emmett and Teller (BET) nitrogen absorption method.

The particle size of the flame retardant is preferably less than 5 microns, and most preferably less than 2 microns. Alternatively or additionally, it may be advantageous to employ a flame retardant comprising a blend of different particle sizes, for example to reduce the melt viscosity of the composition. If desired the flame retardant may be chemically treated, to improve its compatibility with the polymeric material, with one of the above mentioned coupling agents or, in the case of certain flame retardants such as alumina trihydrate, with processing aids such as stearic acid or stearates, e.g. calcium stearate.

The flame retardant is preferably used in an amount by weight of from 10 to 400 parts thereof per 100 parts of the polymer component(s), most preferably from 50 to 200 parts per 100 parts of the polymeric component(s). Notable results have been obtained using an amount of from 80 to 150 parts by weight of the flame retardant per 100 parts of the polymeric component.

Apart from the flame retardant the compositions of the present invention may comprise additional additives, for example fillers, stabilisers such as ultraviolet stabilisers antioxidants, acid acceptors and anti-hydrolysis stabilisers, foaming agents and colourants, processing aids such as plasticizers, or additional polymers. If additional additives are employed, then it is preferred that the compositions contain less than 5 weight per cent halogen in the composition as a whole and more preferably less than 2 weight per cent halogen and particularly contain no halogen.

The polymeric compositions may be produced in conventional manner, for example by blending the components thereof in a Banbury mixer. They may then be processed into cladding form, for example by extrusion or moulding, depending on the nature of the cladding and substrate, and simultaneously or subsequently cross-linked.

The polymeric composition maybe cross-linked, for example by the incorporation of a cross-linking agent or by exposure to high energy radiation. Suitable cross-linking agents are free radical initiators such as peroxides for example, dicumyl peroxide, 2,5-bis (t-butyl peroxy)-2,5-dimethylhexane and a,a-bis (t butyl-peroxy)-di-isopropylbenzene. In a typical chemically cross-linkable composition there will be about 0.5 to 5 weight per cent of peroxide based on the weight of the polymeric blend. The cross-linking agent may be employed alone or in association with a cocuring agent such as a poly-functional vinyl or allyl compound, e.g. triallyl cyanurate, triallyl isocyanurate or pentaerithritol tetramethacrylate.

Radiation cross-linking may be effected by exposure to high energy irradiation such as electron beam or y-rays. Radiation dosages in the range 2 to 80 Mrads, preferably 2 to 50 Mrads, e.g. 2 to 20 Mrads and particularly 4 to 12 Mrads are in general appropriate. For the purposes of promoting cross-linking during irradiation, preferably from 0.2 to 5 weight per cent of a prorad such as a poly-functional vinyl or allyl compound, for example, triallyl cyanurate, triallyl isocyanurate or pentaerithritol tetramethacrylate are incorporated into the composition prior to irradiation.

The degree of cross-linking of the compositions may be expressed in terms of the gel content (ANSI/ASTM D2765-68) of the cross-linked polymeric composition, i.e. excluding non-polymeric additives that may be present. Preferably the gel content of the cross-linked composition is at least 10%, more preferably at least 20%, e.g. at least 30% more preferably at least 40%.

When it is desired to apply the cladding as a sheath over the length of substrate, it may be convenient to extrude the polymeric composition, prior to cross-linking thereof, directly onto the substrate with simultaneous or subsequent cross-linking.

Alternatively, and particularly when the cladding is intended only to envelop a section of the length of the substrate, it may be convenient to produce the cladding prior to the application thereof to the substrate, for example as a tape or sheet to be wrapped around the substrate or as a sleeve within which the substrate is inserted. When the cladding is produced prior to the application thereof to the substrate, then it is preferred that it is produced in dimensionally recoverable form, that is to say, in a form such that the dimensional configuration thereof may be made substantially to change when subjected to appropriate treatment, especially heat-recoverable form, the dimensional configuration of which maybe made substantially to change when subjected to heat.The cladding may be rendered heat-recoverable by deformation of the heat-stable configuration thereof in cross-linked form at an appropriate elevated temperature, e.g. at a temperature above the crystalline melting point or softening point of the polymeric composition with subsequent cooling whilst in the deformed configuration, in manner known perse, for example as described in US Patents 2,027,962, 3,086,242 and 3,957,372. For heat-shrinkable applications it is preferable that the polymeric composition of the cladding comprises a blend of the vinyl acetate/alkene copolymer with at least one thermoplastic polymer. The weight ratio of vinyl acetate/alkene copolymer to thermoplastic polymer may for example be in the range 1; 0.2 to 4 e.g. 1: 0.2 to 1.5, particularly 1: 0.2 to 0.55.

In addition and under certain circumstances, it may be desirable to coat at least a part of the surface of the cladding which is to contact the substrate with a sealant or adhesive, e.g. a hot-melt, heat activatable, pressure sensitive or contact adhesive or a mastic, particularly with a hot-melt adhesive such as disclosed in W. German Offenlegungschrift 2,723,116.

One aspect of the present invention of particular interest concerns electrical insulation where extremely stringent non-flammability requirements exist. Examples of the application of the present invention to electrical insulation are primary and secondary wire insulation, cable jackets and wire and cable harness conduits, where the cladding is applied over the length of the substrate, and wire and cable splice covers and terminations in tape, sheet or sleeve form, and cable and harness break-outs in the form of tapes or moulded components e.g. udders (often referred to as boots) where the cladding is applied only to a section of the length of the wire, cable or harness system.

A further aspect of the present invention of particular interest concerns the sealing or mechanical or environmental protection of pipes or ducts or at least sections thereof, e.g. joints or damaged regions, e.g. in utility supply systems such as gas or water pipes, district heating pipes, ventilation and heating ducts, and conduits or pipes carying domestic or industrial effluent. One important example of such application is in the jointing of air conditioning or ventilation ducts where the cladding may be employed in the form of a tape or sheet to be wrapped around the joint or a sleeve encompassing the joint, especially in heat-recoverable form.

In the above mentioned uses, the claddings in accordance with the invention are characterised by notably low flammability and low smoke and corrosive gas emission under rigorous flammability conditions. Such low flammability characteristics have been found to be directly attributable to the overall level of vinyl acetate in the copolymer of the composition.

The invention is illustrated by the accompanying Examples, wherein parts and percentages are by weight.

Examples I and2 Formulations comprising 24% of a vinyl acetate (60%)/ethylene copolymer, 16% of an elastomer (see below) and 60 of alumina trihydrate treated with 1.5% of the weight of alumina trihydrate of vinyl trimethoxyethoxy silane were compounded in an internal mixer of the Ban bury type at a temperature of 1800C for Example 1 and 1300C for Example 2. After compounding the material on a twin roll mill, the material was removed as a hide which was cut into narrow strips and fed into a 3 1/2 inch extruder, 25:1 UD ratio screw.The material was extruded as a cable jacket onto a multi-conductor cable of O.D. 22.5 mm to provide a jacket having a wall thickness of 1.25 mm at temperatures along the barrel of 75,90, 125,140 and 165 C for Example 1 and 60,80, 120, 120, 130'C for Example 2, and an extruded die temperature profile of 150, 140, 1 20"C. The jacketed cable was then irradiated with high energy electrons to a total dose of 5 Mrads.

The elastomers employed in the examples were as follows: Example 1: Hytrel (RTM)-tradename for a thermoplastic elastomeric polyester derived from a dimethyl terephthalate, a polyglycol and a short chain diol, commercially available for du Pont.

Example 2: Styrene/butadiene rubber.

The jacketed materials were found to have the following physical properties: Example Example 1 2 Tensile Strength @ 23"C 11.5 14.7 (MPa) Elongation at break @ 23 C (%) 240 174 Impact Brittleness (perASTM-D-746)"C -32 -42 LOI @ 23 C 38.8 33.2 LOI @ 250"C 25.1 20.4

Claims (17)

1. An elongate substrate provided, over at least a part thereof, with a flame retarded cladding, said cladding being formed from a polymeric composition which comprises a substantially crosslinked blend of a vinyl acetate/alkene copolymer that has a vinyl acetate content of greater than 55 weight percent with a thermoplastic elastomeric polyester or a styrene.butadiene rubber, and incorporates an effective amount of a halogen-free inorganic flame retardant.

2. A cladded substrate according to Claim 1, wherein the cladding comprises electrical insulation.

3. A cladded substrate according to Claim 2, wherein the substrate comprises a wire, cable or electrical harness.

4. A cladded substrate according to Claim 1, wherein the cladding provides a seal or mechanical or environmental protection.

5. A cladded substrate according to Claim 4, wherein the substrate comprises a pipe or duct.

6. A cladded substrate according to any one of the preceding claims, wherein the cladding is located about the substrate by dimensional recovery thereof.

7. A cladded substrate according to any one of the preceding claims, wherein a sealant or adhesive is interposed between the substrate and cladding.

8. A cladded substrate according to any one of the preceding claims, wherein the vinyl acetate/alkene copolymer of the cladding has a vinyl acetate content in the range of 60 to 95 weight per cent.

9. A cladded substrate according to Claim 8, wherein the vinyl acetate/alkene copolymer of the cladding has a vinyl acetate content in the range 65 to 85 weight per cent.

10. A cladded substrate according to any one of the preceding claims, wherein the vinyl acetate/alkene copolymer is a vinyl acetate ethylene copolymer.

11. A cladded substrate according to any one of the preceding claims, wherein the halogen-free inorganic flame retardant is alumina trihydrate.

12. A cladded substrate according to any one of the preceding claims, wherein the weight ratio of vinyl acetate/alkene copolymer to the other polymer(s) of the blend is in the range 1: 0.2 to 4.

13. A cladded substrate according to Claim 12, wherein the weight ratio of vinyl acetate/alkene copolymer to the other polymer(s) of the blend is in the range 1: 0.2 to 1.5

14. A cladded substrate according to any one of the preceding claims, wherein the overall amount of vinyl acetate in the blend is at least 30 weight per cent.

15. A cladded substrate according to any one of the preceding claims wherein the polymeric composition ofthe cladding incorporates a coupling agent.

16. A cladded substrate as claimed in any one of the preceding claims, wherein the blend contains a styrene.butadiene rubber.

17. A cladded substrate according to Claim 1, substantially as described herein with specific reference to the Examples.