GB2035333A - Flame retardant insulating compositions - Google Patents

Abstract

The invention concerns a novel cladded elongate substrate such as a jacketed cable, the cladding being flame retarded and comprising a vinyl acetate/alkene copolymer composition incorporating a halogen-free inorganic flame retardant. The composition is characterised by a high content of vinyl acetate and/or the presence of a polyalkene or alkene/alkene copolymer blended with the vinyl acetate/alkene copolymer.

Description

SPECIFICATION Improvements in or relating to flame retardant compositions The present invention relates to flame retardant compositions and more specifically to cladding for elongate substrates, e.g. electrical insulation for a wire or cable, formed from such compositions.

Accordingly, the present invention provides 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 vinyl acetate/alkene copolymer as sole polymer or as one component of a polymer blend, and incorporates an effective amount of a halogen-free inorganic flame retardant, with the provisos that: i) the vinyl acetate/alkene copolymer has a vinyl acetate content of greater than 55 weight per cent, or ii) the vinyl acetate/alkene copolymer is blended with a polyalkene or alkene/alkene copolymer and the blend contains less than 66 weight per cent vinyl acetate/alkene copolymer, or iii) when the vinyl acetate/alkene copolymer is blended with a polyalkene or alkene/alkene copolymer and the blend contains at least 66 weight per cent vinyl acetate/alkene copolymer, then the vinyl acetate/alkene copolymer has a vinyl acetate content of greater than 40 weight per cent.

The alkene component of the vinyl acetate alkene copolymer and the polyalkene, when present, preferably comprises a C2-C6 alkene, particularly an a-unsaturated alkene such as ethylene, 1-propylene and 1-butene and particularly ethylene. Alkene/alkene copolymers which may be employed in the compositions of the invention are preferably C2-CG.alkene/C2-C12 alkene copolymers, particularly ethylene copolymers with C3-C12 alkenes, especiaMy-a-unsaturated C3-C12 alkenes such as n-propyl-l-ene, n-but-l-ene, n-pent-l-ene and n-hex-l-ene. Particularly preferred ethylene copolymers contain greater than 50 weight per cent, for example greater than 60 weight per cent, more preferably greater than 70 weight per cent, for example greater than 85 weight per cent, ethylene.Of particular interest are the so-called linear low density ethylene copolymers having a density yin the range 0.910 to 0.940 gm/cm3 at 25"C described in UK Patent Application No. 7,911,916 and Canadian Patent No. 873,828, the disclosures of which are incorporated herein by reference.

In the case where the vinyl acetate/alkene copolymer is employed in the polymeric composition in the absence of a polyalkene or alkene/alkene copolymer blend component, then 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.

In the case where the vinyl acetate/alkene copolymer is employed in the polymeric composition in the presence of a polyalkene or alkene/alkene copolymer blend component, then preferably the vinyl acetate content of the vinyl acetate/alkene copolymer is at least 30 weight per cent, more preferably greater than 40 weight per cent, for example in the range 45 to 98 weight per cent, particularly greater than 55 weight per cent, e.g. up to 95 weight per cent, especially 65 to 95 weight per cent, e.g. 65 to 90 weight per cent and more especially 65 to 85 weight per cent, for example 70 to 80 weight per cent.Additionally or alternatively, the weight ratio of vinyl acetate/alkene copolymer to the polyalkene or alkene/alkene copolymer blend component is preferably in the range 1: 0.2 to 4, more preferably 1: 0.2 to 1.5, or for certain applications 1: 1.5 to 4.0 or even 1: 2.5 to 4.0.

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 polymeric 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 dimethyl-dichlorosilane, methyl trichlorosilane, vinyl trichlornsilane, y-methacryloxypropyl-trimethyoxysilane, N, N-bis (ss-hydroxyethyl)-y-amine-propyl- triethoxy silane, vinyl propyl-trimethoxysilane, y-methacryloxpropyl-trimethoxy silane, y-mercaptopropyltrimethoxy silane, vinyl trimethoxy silane, y-glycidoxy propyl trimethoxysilane, B-(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, isopropyl-triisostearoyl 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 Awl203. 3H2O, ammonium or sodium dawsonite, hydrated'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 m2g, desirably at least 1 m2/g, e.g. 1 to 80m2/g, 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 retardantis preferably used in an amount by weight of from 10 to 400 parts thereof per 100 parts of the polymeric 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 theflame retardant the compositions of the present invention may comprise additional additives, for example fillers, stabilisers such as ultra-violet 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 may be 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-butylperoxy)-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 co-curing 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 an 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 substate, 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 may be 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, the disclosures of which are incorporated herein by reference. 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. Preferred blend thermoplastic polymers for heat-recoverable applications are the thermoplastic polyalkenes and alkene/alkene copolymers herelnbefore disclosed.

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, the disclosure of which is incorporated herein by reference.

One aspect of the present invention of particular interest concerns electrical insulation where extremely stringent nonflammability 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.

Afurther aspect of the present invention or 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 carrying 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. Further, when compared to analogous compositions having no polyalkene or alkene/alkene copolymer blend component and the same level of vinyl acetate content, claddings formed from compositions including a polyalkene or alkene/alkene blend component are also found to possess a substantial improvement in their inertness to chemical solvents particularly to oils, their flame retardancy and often their smoke emission under rigorous flammability conditions.

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

Example 1 Constituent Function Parts vinyl acetate/ethylene polymeric base material 100 copolymer having a 70% vinyl acetate content (available from Wacker Chemie GmbH under the trade name VAE 711) titanate treated alumina flame retardant pre- 150 trihydrate* treated with coupling agent carbon black (available pigment, U.V. screen 2 from Cabot Corp. under the trade name Vulcan 9) polymerised 1,2-di antioxidant 2 hydro-2,2,4-trimethylquinoline (available from R.T.Vandervilt Inc under the trade name Agerite Resin D) 1:1 dispersion of poly thermal stabiliser 4 carbodiimide (available from Bayer AG under the trade name Rhenogran P-50) in an ethylene/ vinyl acetate copolymer containing 17% vinyl acetate (available from Bayer AG under the trade name Levapren) triallyl cyanurate prorad 4 dibasic lead phosphite acid scavenger 1 *Hydral 705 (trade name - available from Alcoa Corp.) coated with 1.5% titanium di(dioctylpyrophosphate) oxyacetate (available from Kenrich Petrochemical Inc. under the trade name Ken-React 138S).

The constituents of the above mentioned composition were rnixed in a laboratory Banbury mixer in accordance with the following sequence.

The Banbury mixer was charged with polymer, antioxidant, thermal stabiliser and acid scavenger and mixed for 1 minute. The carbon black was then added and over a period of 4 minutes the flame retardant was added in small portions. At the end of this period, the prorad was added and mixing continued for 1 minute.

The mix was then removed and milled on a cold mill and then pelletised. The pellets were compression moulded into plaques at 190"C and irradiated with an electron beam at a radiation dosage of 12 Mrads. The level offlammability of the plaque was established by measuring the limiting oxygen index (LOI) in accordance with ASTMD 2863. A result of 50.0 was obtained Example2 Constituent Parts vinyl acetate/ethylene 100 copolymer silane treated alumina 150 trihydrate vulcan 9 2 1:1 dispersion of poly 2 carbodiimide (Rhenogran P.50) in an ethylene/ vinyl acetate copolymer containing 17% vinyl acetate (Levapren) agerite resin D 2 triallyl cyanurate 1 dibasic lead phosphite 1 *Copolymers comprising 18,25,40,60 and 70% vinyl acetates were employed.

In analogous manner to Example 1 a series of plaques were made up employing a series of compositions (see above) differing only in the vinyl acetate content of the copolymer constituent.

The physical properties, water and oil resistance properties were measured and are set out in Table 1. TABLE 1 Effect of% VA on Properties %VA 18 25 40 60 60 70 Elvax 460 Elvax 360 Vyna. EY 902-30 VAE 631 VAE 651 VAE 711 (Dupont Co) (Dupont Co) (USI Chemicals Co) (------Wacker Chemie GmbH------) T.S. @ 23 C (MPa) 14.2 15.7 9.4 10.9 10.0 13.1 Eb @ 23 C (%) 120 170 240 160 150 150 (per BS703 part A2) T.S. @ 150 C (MPa) 2.55 2.75 1.76 2.01 1.82 1.74 Eb @ 150 C (%) 1.85 130 155 65 70 60 M100 @ 150 C (MPa) 1.35 2.17 0.97 - - (Per BS7282) % Weight gain +53 +37 - +12 +6 +3 ASTM No. 2, 24 hrs @ 100 C 48 hrs @ 50 C +1.2 +1.6 - +5.2 +6.1 +4.6 48 hrs @ 90 C + 8.9 +9.2 +19 +11 +14 +10 (Per ASTDM 570-77 except that sample disc 25mm diam.

and 1.5mm thickness is employed) The results show no significant negative effect on physical properties of increase in vinyl acetate content of the copolymer only and, in the case of oil resistance, a substantial increase is observed.

The flammability values were also measured (LOI) and graphically set out in the accompanying figure. As a control, the LOI values of otherwise identical compositions except for the absence of the flame retardant were also measured and shown on the figure.

The graph clearly shows a dramatic increase in non-flammability as the vinyl acetate content of the copolymer increases with LOI values of greater than 40 being recorded when the vinyl acetate content of the polymer exceeds 55 weight per cent.

Examples 3 to 14 The relevant compositions set out in Table 2 below which shows the parts (approximated to the nearest whole number) of the various constituents, were uniformly blended on a two roll laboratory mill heated to a temperature of 120 to 1 40"C, compression moulded into plaques at 1900C and then irradiated under atmospheric conditions with a 5.8 MEV electron beam at the radiation dosages indicated. Samples were subjected to the Test Methods set out below.

Examples 15to20 The relevant compositions set out in Table 2 were blended in analogous manner to that described in the preceding Examples, the two roll laboratory mill being cooled to prevent sticking and plaques produced therefrom for comparison purposes in the following tests.

TABLE 2 Example No. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 DYNH 3 (trade name) low density polyethylene ex Union Carbide 0 0 0 0 30 24 20 16 0 17 14 0 0 0 0 0 0 0 Sclair 11-D-1 (trade name) low density polyethylene ex Dupont 35 28 27.5 22 0 0 0 0 17 0 0 14 0 0 0 0 0 0 Vynathene EY-907 (trade name) 60% weight vinyl acetateethylene copolymer ex USI 15 12 0 0 20 16 0 0 33 33 26 26 0 0 0 0 0 0 Vynathene EY-902 (trade name) 40% weight vinyl acetateethylene copolymer ex USI 0 0 22.5 18 0 0 30 24 0 0 0 0 0 0 40 50 0 0 Elvax 360 (trade name) 75% weight ethylene-vinyl acetate copolymer ex Dupont 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40 50 Elvax 460 (trade name) 82% weight ethylene-vinyl acetate copolymer ex Dupont 0 0 0 0 0 0 0 0 0 0 0 0 40 50 0 0 0 0 Alumina Trihydrate (silane coated) Hydral 705 (trade name)-available from Alcoa Corp. coated with 1.5% vinyltrimethyoxyethoxysilane 50 60 50 60 50 60 50 60 50 50 60 60 60 50 60 60 60 50 Radiation dosage (Mrads) 6 6 6 6 12 12 12 12 6 12 12 6 12 12 12 12 12 12 Test Methods The plaques produced in accordance with the preceding Example were subjected to the following tests.

Water resistance measured ASTM-D-570-77 except that as % water uptake sample disc 25mm in diameter and 1.5mm in thickness is employed.

Oil resistance measured ASTM-D-570-77 except that as % oil uptake sample disc 25mum in diameter and 1.5mm in thickness is employed Tensile strength BS 903 part A2 Elongation BS 903 part A2 Flammability measured as ASTM-D-2863 limiting oxygen index.

Smoke emission measured in an Aminco NBS smoke chamber, in accordance with the Aminco-NBS smoke density chamber catalogue No. J4-5800B, J4-5800BE, instruction 1410 published Nov. 1975 by American Instrument Co. 8030 Georgia Ave.

Silver Spring, Maryland 20910.

The results are set out in Table 3 below and clearly demonstrate interalia the improved oil resistance of the blends (Examples 3 to 14) when compared to the copolymer in the absence of blend polyethylene component (Examples 15 to 20), having the same ethylene and vinyl acetate content as the blend, as well as improved flame retardancy and in the majority of cases lower smoke emission.

TABLE 3 Example No. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 % Water Uptake @ 90 C 24h 6.0 6.2 6.5 5.8 6.7 5.2 7.7 5.0 9.0 7.3 9.7 7.4 7.3 6.8 8.0 15.4 5.6 7.6 48h 8.1 7.4 8.4 7.1 8.8 8.4 10.8 7.5 13.4 11.4 14.5 11.8 7.8 8.6 12.5 18.2 8.0 10.3 % Oil Uptake @ 100 C ASTM NO. 2 (Mineral Oil) 15 14 32 22 20 15 47 25 13 13 27 21 69 100 54 42 42 66 Synthetic lubricating Oil British Spec. D. Eng.R.D. 15 13 37 23 22 12 37 34 33 29 9.7 7.4 42 60 80 77 39 56 2487 Tensile Strength (MPa) 11.6 11.8 11.8 11.8 10.8 10.5 13.1 7.5 12.1 11.2 11.1 9.9 13.3 12.0 12.0 13.5 14.5 16.3 Elongation (%) 130 100 145 60 . 74 18 110 25 230 102 168 47 40 85 200 240 70 146 Oxygen Index (%O2) 26.0 31.5 27.0 32.5 23.5 33.5 25.5 28.5 29.0 30.0 33.0 30.0 28.0 25.0 34.0 27.0 27.5 24.0 T16 (min) Flaming Mode 9.5 10 8 11 8 9 7.3 7.3 8.5 9 8.5 8.5 7 6 10.5 1.5 9 4 Example 21 A heat-shrinkable tape was produced from the following formulation:: Constitutent *Sclair 11 D1 17 Vinyl acetate/ethylene 33 copolymer containing 60% vinyl acetate Al203.3H20 coated with 50 1.5% of vinyl trime thoxyethoxy silane *Sclair 11 Dl is the Trade Name for a linear low density ethylene/butene copolymer commercially available from Dupont.

The constituents were compounded on a twin roll mill at 120 to 140"C, cooled and pelletised. The pellets so produced were fed to a conventional extruder fitted with a tape die, maiptained at 1400C and extruded into tape 100mm wide and 1.5mm thick. The resulting tape was subsequently irradiated with high energy electrons to a total dose of 6 Mrads.

After irradiation, the tape was heated to 1 500C, expanded lengthwise to 50% of its original length and allowed to cool in this expanded condition. Thereafter the tape was coated with a thin layer (0.5mm) of a hot-melt adhesive of composition in accordance with W. German Offenlengungshrift 2,723,116, Example 3, formulation "0".The physical properties of the tape prior to coating were as follows: Tensile Strength (23"C) 12.0 MPa Elongation at break (23"C) 266 % LOI (23 C) 29 Tensile Strength (150"C) 2.0MPa Elongation at break (150"C) 105 % 100% Tangent Modulus (150"C) 1.2 MPa The heat-shrinkable adhesive coated tape so produced was employed to seal the joint of a 150mm diameter metal air conditioning duct by pre-heating the duct in the region of the joint, wrapping the tape around the duct over the joint region so that sequential turns of the tape partially overlap and heating the tape with a conventional propane gas torch, so causing the tape to shrink tightly around the joint and causing the adhesive to melt and form a strong adhesive bond between the cladding so formed and the duct substrate.

In a modification, the pelletised material is extruded in the form of a sleeve, which is then rendered radially heat-recoverable and coated with adhesive in analogous manner to that described above. The sleeve so produced is then located about the duct joint and recovered by the application of heat.

Example 22 Aformulation comprising 40% by weight of a vinyl acetate/ethylene copolymer, containing 60% copolymerised vinyl acetate was compounded with 60% by weight of alumina trihydrate in an internal mixer of the Ban bury type, at a temperature of about 1 25"C. After compounding the material on a twin roll mill, the material was removed as a strip, cooled and diced into pellets and lightly talced to prevent biocking of the pellets. The material was then extruded as a cable jacket qnto a multi-conductor cable of O.D. 22.5mm to provide a jacket having a wall thickness of 1.25mm, using a 31/2 inch extruder,25: LID ratio screw, at temperatures along the barrel of 60, 80, 120, 120, 130"C and an extruded die temperature profile of 150,140, 120"C. The jacketed cable was then irradiated with high energy electrons to a total dosq of 5 Mrads. The jacketed material was found to have the following physical properties.

23"C Tensile Strength 4.4MPa Elongation at break 275% 1500C Tensile Strength 1.Q7 MPa 100% secant modulus 0.88 MPa Elongation at break 142% Limiting Oxygen Index Temperature LOI 23 C 54.5 1500C 43.0 275 C 27.0 300 C 26.0 Examples 23 and 24 The procedure of Example 22 was repeated employing formulations comprising 40% of a vinyl acetate (60%)/ethylene (40%) copolymer and 60% of alumina trihydrate treated with 5% of isopropyl, triisostearoyl titanate (Example 23) or isopropyl dimethacryl isostearoyl titanate (Example 24).

The physical and electrical properties of the cable jacket so produced are set out below.

Example 23 Tensile Strength (23 C) 6.6 MPa Elongation at break (23 C) 900 % Impact Brittleness (perASTM-D-746) -17 C Ae (capacitance difference 1-14 days per BS-6899 at 1000 H3) 40 % E (capacitance at 14 days per BS-6899 at 1000 H3) 18 Example 24, Tensile Strength (23 C) 9.7 MPa Elongation at break (23 C) 850 % Impact Brittleness (perASTM-D-746) -22 C Ae (1-14 days per BS-6899 at 1000 H3) 22 % E (at 14 days per BS-6899 at 1000 H3) 6.5 Examples25, and 27 The procedure of Example 22 was repeated employing 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.

The elastomers employed in the various examples were as follows: Example 25: EPDM - a linearterpolymer based on ethylene propylenediene monomer.

Example 26: Hytrel - tradename for a thermoplastic elastomeric polyester derived from dimethyl terephthalate, a polyglycol and a short chain diol, commercially available from Dupont.

Example 27: Styrene/butadiene rubber.

In Examples 25 and 27 the compounding temperature on the Banbury mixer was 130"C. In Example 26, the compounding temperature on the Banbury mixer was 1800C and the temperatures along the extruder barrel were 75, 90, 125, 140 and 165"C. In each case, after compounding, the material was removed as a hide which was cut into narrow strips and fed to the extruder. The jacketed materials were found to have the following physical properties.

Example Example Example 25 26 27 Tensile Strength @ 23"C (MPa) 14.0 11.5 14.7 Elongation at break @ 23"C (%) 195 240 174 Impact Brittleness (perASTM-D-746)"C -30 -32 -42 LOI @ 23"C 37.6 38.8 33.2 LOI @250 C 22.6 25.1 20.4

Claims (35)

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 cross-linked vinyl acetate/alkene copolymer as sole polymer or as one component of a polymer blend, and incorporates an effective amount of a halogen-free inorganic flame retardant, with the provisos that: i) the vinyl acetate/alkene copolymer has a vinyl acetate content of greater than 55 weight per cent, or ii) the vinyl acetate/alkene copolymer is blended with a polyalkene or alkene/alkene copolymer and the blend contains less than 66 weight per cent vinyl acetate/alkene copolymer, or iii) when the vinyl acetate/alkene copolymer is blended with a polyalkene or alkene/alkene copolymer and the blend contains at least 66 weight per cent vinyl acetate alkene copolymer, then the vinyl acetate/aikene copolymer has a vinyl acetate content of greater than 40 weight per cent.

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 preceeding claims wherein the cladding is located about the substrate by dimensional recovery thereof.

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

8. A cladded substrate according to any one of the preceeding claims wherein the vinyl acetate/atkene 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 preceeding claims wherein the vinyl acetate/alkene copolymer is a vinyl acetate/ethylene copolymer.

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

12. A cladded substrate according to any one of the preceeding claims wherein the vinyl acetate/alkene copolymer is present and a blend with at least one further polymer.

13. A cladded substrate according to Claim 12 wherein the vinyl acetate/alkene copolymer is present as a blend with a thermoplastic polymer.

14. A cladded substrate according to either of Claims 13 or 14 wherein the vinyl acetate/alkene copolymer is present as a blend with a polyalkene or an alkene/alkene copolymer.

15. A cladded substrate according to ciaim 14 wherein the vinyl acetate/alkene copolymer is present as a blend with a polyethylene or an ethylene/C3-C12 alkene copolymer.

16. A cladded substrate according to Claim 15 wherein the vinyl acetate/alkene copolymer is present as a blend with a linear ethylene/C3-C12 alkene copolymer having a density in the range 0.910 to 0.940 gm/cm3 at 25"C.

17. A cladded substrate according to any one of claims 12 to 16 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.

18. A cladded substrate according to Claim 17 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.

19. A cladded substrate according to any one of Claims 12 to 18 wherein the overall amount of vinyl acetate in the blend is at least 30 weight per cent.

20. A cladded substrate according to any one of the preceeding claims wherein the polymeric composition of the cladding incorporates a coupling agent.

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

22. A flame retarded polymeric composition which comprises a substantially cross-linked blond of vinyl acetate/alkene copolymer with a polyalkene or an alkene/alkene copolymer and incorporates an effective amount of a halogen-free inorganic flame retardant, and when the blend comprises at least 66 weight per cent vinyl acetate/alkene copolymer, this copolymer has a vinyl acetate content of greater than 40 weight per cent.

23. A composition according to Claim 22 wherein the blend component is a polyethylene or an ethylene/C3-C12 alkene copolymer.

24. A composition according to Claim 23 wherein the blend component is a ethylene/C3-Cr2 alkene copolymer having a density in the range 0.910 to 0.940 gm/cm3 at 25"C.

25. A composition according to any one of claims 22 to 24 wherein the weight ratio of vinyl acetate/alkene copolymer to polyalkene or alkene/alkene copolymer in the blend is in the range 1: 0.2 to 4.

26. A composition according to Claim 25 wherein the weight ratio of vinyl acetate/alkene copolymer to polyalkene or alkene/alkene copolymer in the blend is in the range 1 : 0.2 to 1.5

27. A composition according to any one of Claims 22 to 26 wherein the overall amount of vinyl acetate in the blend is at least 30 weight per cent.

28. A composition according to Claim 22 substantially as described herein with specific reference to Examples 3 to 14.

29. Heat-recoverable flame retarded cladding formed from a polymeric composition which comprises a substantially cross-linked blend of a vinyl acetate/alkene copolymer with a thermoplastic polymer and incorporates an effective amount of a halogen-free inorganic flame retardant, with the provisos that:: (i) the vinyl acetate/alkene copolymer has a vinyl acetate content of greater than 55 weight per cent, or (ii) the vinyl acetate/alkene copolymer is blended with a polyethylene or thermoplastic alkene/alkene copolymer and the blend contains less than 66 weight per cent vinyl acetate/alkene copolymer, or (iii) when the vinyl acetate/alkene copolymer is blended with a polyalkene or thermoplastic alkene/alkene copolymer and the blend contains at least 66 weight per cent vinyl acetate/alkene copolymer, then the vinyl acetate/alkene copolymer has a vinyl acetate content of greater than 40 weight per cent,

30. A heat-recoverable flame retarded cladding according to Claim 29 wherein the polymeric composition is as defined in any one of Claims 22 to 28.

31. A heat-recoverable flame retarded cladding according to either of claims 29 or 30 wherein the weight ratio of vinyl acetate/alkene copolymer to thermoplastic polymer is in the range 1: 0.2 to 0.55.

32. A heat-recoverable flame retarded cladding according to Claim 29 substantially as described herein with specific reference to Example 16.

33. Aflame retarded cladding as defined in any one of Claims 1 to 32 wherein at leastpartofone surface thereof is coated with sealant or adhesive.

34. Aflame retarded cladding according to Claim 33 wherein the coating is a hot-melt adhesive.

35. Aflame retarded cladding according to Claim 33 substantially as described herein with specific reference to Example 16.