GB2044777A - Flame-retarded polymer compositions - Google Patents

Abstract

Flame retarded polymeric compositions comprise a vinyl ester copolymer at least some of the ester groupings of the copolymer containing at least 3 carbon atoms. Preferred flame-retarding additives are inorganic materials such as hydrated alumina and zinc borate. The compositions exhibit low flammability whilst permitting a notable balance of physical properties.

Description

SPECIFICATION Improvements in or relating to polymeric compositions The present invention relates to flame retardant polymeric compositions.

In many commercial applications of polymers, non-flammability requirements are becoming increasingly more stringent particularly in relation to the electrical insulation field, e.g. wire and cable jackets and wire harnessing, and in the construction industry, e.g. panelling and cladding materials and also in relation to dimensionally recoverable, especially heat recoverable, articles.

As a result, a large number of flame retardants have been developed for use in the polymeric materials normally employed in such industries. It is generally acknowledged, however, that even in the rare event that sufficient flame retardancy can be imparted to such polymeric materials, this is at the expense of other properties. For example, high levels of organo-halogen or organo-phosphorous flame retardants are often unacceptable in view of corrosive and/or toxic gas liberation under pyrolysis conditions. As regards inorganic flame retardants, many polymer materials cannot substain the high loadings necessary for satisfactory flame retardancy without considerable detriment to the physical properties thereof, e.g. tensile strength or elongation at break.

It has now been found that a certain class of polymers not employed hitherto in applications where flammability problems arise, permit an extraordinary level of flame retardancy when employed in association with flame retardants and enable the stringent flammability requirements to be met whilst exhibiting a satisfactory balance of physical properties. Such flame retardancy is indicated in standard flammability tests, e.g. ASTMD-2863 even at temperatures as high as 300"C or higher.

Accordingly, the present invention provides a flame retarded polymeric composition which comprises a non-cross-linked or cross-linked unsubstituted or substituted vinyl ester copolymer, at least some of the ester grouping of the polymer containing at least 3 carbon atoms, incorporating an effective amount of a flame retardant and with the proviso that when the composition is non-cross-linked any copolymer of vinyl proprionate with ethylene contains greater than 20 mole % vinyl propionate.

The term "copolymer" as employed herein is employed in a broad sense to mean any polymer containing at least two different monomeric species and including terpolymers and the like.

Many of the vinyl ester copolymers within the scope of the present invention are not commercially available. They may be produced in manner known per se e.g. from commercially available vinyl ester copolymers by ester interchange as described for example in US Patent 2,558,547 and 2,558,548.

The vinyl ester monomers of interest in the copolymers employed in the invention are those of formula I,

wherein R1, R2 and R3 are each, independently, hydrogen or a C,-C20 substituted or unsubstituted hydrocarbon e.g. C,-C6 alkyl, and R4 is a C2-C20 substituted or unsubstituted hydrocarbon, especially where R,, R2 and R3 are each, independently, hydrogen or C,-C6 alkyl, and one or R1, R2 and R3 may also signify phenyl or benzyl, and R4 is a C2-C20 alkyl, alkenyl, alkoxyalkyl or alkoxyalkenyl, aryl or aralkyl, e.g. phenyl, naphthyl or benzyl, or C,-C4 alkyl alkoxyphenyl or benzyl, and particularly when R4 is C3-C,7, more preferably C6-C,5 alkyl, or phenyl or benzyl.

Examples of vinyl esters monomers of interest in the copolymers employed in the invention are vinyl propionate, vinyl hexanoate, vinyl versatate, vinyl stearate, vinyl laurate, vinyl methoxyacetate, vinyl trimethylacetate, vinyl isobutyrate, vinyl tert. pentoate, vinyl lactate, vinyl caprylate, vinyl perlargonate, vinyl myristate, vinyl oleate, vinyl linoleate, vinyl benzoate, vinyl (C,-C4) alkoxy benzoate, vinyl octylphthalate, vinyl P-phenyl butyrate, vinyl ss-naphthoate, vinyl ethyl phthalate and vinyl phenyl acetate. Other vinyl ester monomers of interest are described in UK Patent No. 1,539,664 the disclosure of which is incorporated herein by reference.

Vinyl ester copolymers of interest include mixed vinyl ester copolymers, e.g. copolymers of vinyl esters containing at least 3 ester carbon atoms with vinyl acetate or higher vinyl esters, as well as copolymers with comonomers other than vinyl esters. Other such comonomers include unsaturated hydro-carbons such as olefins, e.g. ethylene, propylene and C4-C,2 a-unsaturated olefins, e.g. but-1-ene and oct-1-ene, styrene, unsubstituted or substituted esters other than vinyl esters, e.g. C4-C,2 (meth)acrylates, and other vinyl monomers, e.g. vinyl chloride.

When copolymers with comonomers other than vinyl esters containing at least 3 ester carbon atoms are employed, then preferably the vinyl ester monomer(s) is present in at least 5 mole %, preferably at least 10 mole %, e.g. 20-95 mole %, more preferably at least 30 mole %, e.g.

40-95 mole %.

Furthermore. the vinyl ester copolymer may be employed as a blend system containing other polymers. Blend polymers of interest are those which are preferably compatible either alone or in association with compatibilising agents, with the vinyl ester polymer and which do not render the compositions unsuitable for the purpose for which they are intended.Such polymers include thermoplastic and elastomeric polymers, examples of which are polyesters including block copolymers of the type available from Dupont under the trade name Hytrel and described in Polymer Engineering and Science 14, volume 12, pages 849-852, 1974, "Segmented Polyether Ester copolymers-a new generation of high performance elastomers", polyolefins, e.g. branched low density polyethylene, linear low density polyethylene (e.g. as described in Canadian Patent 873,828 and UK Patent Application 7,911,916) and linear high density polyethylene, silicone resins and elastomers, (meth)acrylate homo- ar copolymers, e.g. terpolymers of ethylene, methyl acrylate and a cure-site carboxyl-containing monomers such as the terpolymer commercially available from Dupont under the trade name "Vamac" and analogous polymers described in UK Patent 1,548,232, ethylene/vinyl acetate copolymers, EPDM (a linear terpolymer based on ethylene propylene diene monomer), SBR (styrene/butadiene rubber) and block copolymers of styrene with butadiene or isoprene.

When blends are employed, then preferably the vinyl ester polymer is present in the blend in at least 20 wt /Q, e.g. 30-99 wt %, more preferably at least 40 wt % e.g. 50-99 wt %.

It may be desirable that the compositions of the invention include a coupling agent to improve the compatibility of the flame retardant with the polymer and thereby to improve the physical properties of the compositions, particularly when flame retardant inorganic fillers are employed.

Preferred coupling agents include organo silicon and titanium derivatives such as silanes and titanates although in some cases processing aids such as stearic acid and stearates, aluminium soaps such as aluminium diisopropoxy diversatate or polyoxo carhoxylates such as polyoxo aluminium stearate may be particularly useful.

As examples of silanes may be mentioned dimethyl-dichlorosilane, methyl trichlorosilane, vinyl trichlorosilane, y-methacryloxypropyl-trimethoxysilane, N, N-bis(fl-hydroxyethyl)-y-amino-propyl-tri- ethoxy silane, y-methacryloxyprnpyl-tnmethoxy silane, y-mercaptopropyl-trimethQxy silane, vinyl trimethoxy silane, y-glycidoxy propyl trimethoxysilane and vinyl trimethoxyethoxysilane. Further appropriate silanes are exemplified in UK Patent No. 1,284,Q82.

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 and titanium di-(dioctyl pyrophosphate).

Additional suitable titanium compounds are described in S.J. Monte S-G. Sugerman, J.

Elastomers a 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 Kenrich Petrochem Inc.

Examples of aluminium soaps and polyoxo aluminium carboxylates are listed in UK Patent No.

825,878.

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

Flame retardants such as organo-halogen, organo phosphorus or boron compounds or flame retardant inoganic fillers may be employed. The preferred flame retardants are however the halogen- and phosphorus-free compounds, particularly inorganic fillers such as metallic oxides, e.g. antimony trioxide, stannic oxide and molybdenum trioxide, and fillers that release water on heating. Of specific interest are the inorganic fillers that release water on heating, particularly hydrated aluminium oxides such as Awl203. 3H2O, ammonium or sodium dawsonite, hydrated magnesia, hydrated calcium carbonate and hydrated calcium silicate, especially alumina trihydrates.

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, for example by treatment with one of the above mentioned coupling agents or, in the case of hydrated inorganic flame retardants such as alumina trihydrate, with a processing aid such as stearic acid or stearates e.g. calcium stearate.

The flame retardant is preferably used in an amount by weight of from 1 0 to 400 parts per 100 parts of polymers, most preferably from 5Q to 200 parts per 100 parts of polymer. Notable results have been obtained using an amount of from 80 to 1 50 parts by weight of flame retardant per 100 parts of polymer.

Apart from the flame retardant, the compositions of the present invention may comprise additional additives, for example fillters, stabilisers such as ultra-violet stabilisers, antioxidants, acid acceptors and anti-hydrolysis stabilisers, foaming agents and colourants and processing aids such as plasticizers.

It is preferred that the compositions contain less than 5 weight per cent halogen or phosphorus in the composition as a whole and more preferably less than 2 weight per cent halogen or phosphorus and particularly contain no halogen or phosphorus.

For most purposes it is preferred that the compositions of the invention are substantially crosslinked.

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 nonpolymeric 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%.

The compositions of the invention are produced in conventional manner, for example by blending together the components of the composition in a Ban bury mixer.

They may then be processed into shaped articles, for example by extrusion or moulding, and when desired simultaneously or subsequently cross-linked. Shaped articles so produced also form part of the present invention.

The polymeric components of the composition may be cross-linked either 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, 2,5-bis(t-butylperoxy)-2,5-dimethylhexyne-3, and a,a-bis, (t-butyl peroxy)-d i-isopropyl benzene. Other examples of appropriate cross-linking agents are disclosed in C.S. Sheppard and V.R. Kamath, Polymer Engineering and Science 19, No. 9, 597-606, 1979, "The Selection and Use of Free Radical Initiators", the disclosure of which is incorporated herein by reference.In a typical chemically cross-linkable composition there will be about 0.5 to 5 weight percent of cross-linking agent 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 tetra-methacrylate.

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 2to 80 Mrads, preferably 2 to 50 Mrads, e.g. 2 to 20 Mrads and particularly 4 to 1 2 Mrads are in general appropriate.

For the purposes of promoting cross-linking during irradiation, preferably 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 compositions of the invention in non-cross-linked form incorporating an effective amount of a cross-linking agent or prorad also form part of the present invention. In such form, the compositions may also be employed as adhesives.

The compositions of the invention are particularly suitable for electrical insulation use where flammability requirements are stringent, for example in confined areas such as in aircraft, ships, mines or underground railways.

The production of electrical insulation material may be achieved by conventional techniques, for example by extrusion of the non-cross-linked composition, as an insulator onto an electrical apparatus such as a copper conductor as a primary insulation or a bundle or primary insulated copper wires as a cable jacket and, preferably, simultaneously or subsequently cross-linking the applied insulation. Alternatively, the material may be extruded and cross-linked separately and then employed as an insulating filler in cable construction.

The compositions of the present invention are also suitable for use as cladding and panelling materials, and as fire blocks, e.g. for cable feed-throughs, partidularly in the passenger transit industry e.g. in aircraft, trains and ships, for oil rigs and in the construction industry. For such use the materials may be employed in any desired shape produced for example by thermoforming.

The compositions of the present invention are also particularly suitable in cross-linked form for the production of dimensionally recoverable articles, that is to say, articles, the dimensional configuration of which may be made substantially to change when subjected to an appropriate treatment. Of particular interest are heat recoverable articles, the dimensional configuration of which may be made substantially to change when subjected to heat treatment. Heat-recoverable articles may be produced by deforming a dimensionally heat-stable configuration to a heatunstable configuration, in which case the article tends to assume the original heat-stable configuration on the application of heat alone.As is made clear in US Patent No. 2,027,962, however, the original dimensionally heat-stable configuration may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form. Alternatively a preformed dimensionally heat-stable article may be deformed to a dimensionally heat-unstable form in a separate stage. In the production of dimensionally recoverable articles, the composition may be cross-linked at any stage in the production process that will accomplish the desired dimensional recoverability, subsequent to the shaping of the dimensionally unstable configuration.One manner of producing a heatrecoverable article comprises shaping the pre-cross-linked composition into the desired heat stable form, subsequently cross-linking the composition, heating the article to a temperature above the crystalline melting point or for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed shape of the article is retained. In use, since the deformed state of the article is heat unstable, application of heat will cause the article to assume its original heat stable shape.Such dimensionally recoverable articles may be employed for covering and/or sealing splices and terminations in electrical conductors, for environmentally sealing damaged regions or joints in utility supply systems, e.g. gas or water pipes, district heating systems, ventilation and heating ducts and conduits or pipes carrying domestic or industrial effluent.

Such articles may be in tape, sheet, sleeve or moulded form. In addition and under certain circumstances, it may be desirable to coat at least a part of the surface of the heat-recoverable article with a sealant or adhesive, e.g. a hot-melt, heat-activatable, pressure sensitive or contact adhesive ar a mastic, particularly with a hot-melt adhesive such as disclosed in W. German Offenlegungschrift, 2,723,11 6, the disclosure of which is incorporated herein by reference.

For heat-recoverable applications it is preferable that the composition comprises a blend of the vinyl ester copolymer with at least one thermoplastic polymer. The weight ratio of vinyl ester 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 ta Q.55. Preferred blend thermoplastic polymers for heat-recoverable applications are thermoplastic alkene homo and copolymers. Polyalkene homo polymers are preferably derived from a C2-C6 alkene, particularly an a-unsaturated alkene such as ethylene, 1-propylene and 1-butene and particularly ethylene.Polyalkene copolymers are preferably C2-C6 alkene/C2-C,2 alkene copolymers, particularly ethylene copolymers with C3-C,2 alkenes, espe cially a-unsaturated C3-C,2 alkenes such as n propyl-1-ene, nbut-1-ene, rrpent-l-ene and rxhex- 1-ene and alkene vinyl ester e.g. ethylene/vinyl acetate copolymers. 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 in 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.

The invention is illustrated by the accompanying examples wherein unless otherwise indicated parts and percentages are by weight and temperatures are expressed in "C.

Examples 1-9 The relevant compositions set out in the examples below were compounded on a 2 roll laboratory mill heated to a temperature of 120-140"C, moulded at 190"C into test plaques and irradiated on a 5.8 MeV electron beam to a total dose of 6 Mrads. Flammability (Limiting Oxygen Index-LOl) was measured following the ASTM-D-2863 method; in addition Limiting Oxygen Indices and Critical Temperature Indices were obtained following the method of A.F.

Routley (ERA Symposium "Flammability and Smoke Testing Materials", London 1974) and described in detail by J.P. Redfern (Technical Information Sheet No. 24 "Critical Oxygen Index in Temperature Studies" available from Stanton Redcroft, a Division of L. Oerting Ltd).

Example 1 The composition prepared from equal weights of a copolymer of vinyl versatate" (25%) and vinyl acetate (75%) (hereinafter referred to as VV/VA), and alumina trihydrate (ALTH) exhibited the following oxygen index values for the given test temperatures. The alumina trihydrate is known as Hydral 705 (Trade Name-available from Alcoa Corporation) and was silane coated with 1.5% vinyl trimethoxyethoxysilane.

Temperature 'C LOI 23 58.5 300 25.0 340 19.5 370 16.0 ("Vinyl versatate is the vinyl ester of versatic acid, a mixture of C9, Cl, acids available from Shell Ltd).

By extrapolation of these results the critical temperature index (CTI) (the temperature at which LOI equals 20.8%) was found to be 335 C.

Example 2 A composition analogous to that of example 1 was prepared except that the percentage of VV/VA in this example was 40%. The following flammability was obtained.

Temperature C LOI 23 90.5 300 29.5 340 23.5 370 20.0 CTl = 360 A composition containing VV/VA, silane coated alumina trihydrate and Hytrel 4056 (a polyester resin available from Dupont) was prepared. The weight ratio of the components was 36, 60 and 4% respectively. It exhibited a limiting oxygen index of 78.0 at 23 C.

Example 4 A composition similar to that in example 3 was prepared. The weight ratio of the components was VV/VA-32%, Hytrel 4058-8% and Silane treated ALTH-60%. It exhibited a limiting oxygen index of 73.0 at 23 C.

Example 5 A composition similar to that of example 4 was prepared with the following components; VV/VA-28%, Hytrel 405612% and Silane treated ALTH-60%. It exhibited a limiting oxygen index of 70.0 at 23 C.

Example 6 A composition containing 50% VV/VA and 50% hydrated magnesia was prepared in analagous manner to example 1. It exhibited a limiting oxygen index of 31.5 at 23 C.

Example 7 A composition containing 50% VV/VA 25% hydrated magnesia and 25% ALTH was prepared in analagous manner to example 1. It exhibited a limiting oxygen index of 38.5 at 23 C.

Example 8 A composition containing 50% VV/VA, 33% ALTH and 17% Firebrake (Trade Name-zinc borate available from U.S. Borax Corp.) was prepared. It exhibited a limiting oxygen index of 41.0 at 23 C.

Example 9 As a comparison, a sample of VV/VA alone was prepared and tested. It exhibited a limiting oxygen index of 20.5 at 23 C.

Examples 10 to 53 In analogous manner to that described above the compositions set out in the accompanying Tables I, II and 111 were prepared and subjected to limiting oxygen index testing. In the tables, the following abbreviations are employed.

VV/VA' . . a 25% vinyl versatate (vide supra) 75% vinyl acetate copolymer VV/VA2. . a 78% vinyl versatate/22% vinyl acetate copolymer VL/VA... a 50% vinyl laurate/50% vinyl acetate copolymer LLDPE... a linear low density polyethylene available from Dupont under the trade name Sclair 11 -D- 1 BLDPE' . . a branched low density polyethylene commercially available from Union Carbide Corporation under the trade name DYNH-3 Silicone Elastomer..a commercially available polydimethylsiloxane rubber containing 25% reinforcing silica filler Silicone Resin ... a thermoplastic mono-organo polysiloxane produced in accordance with the process described in Example 3 of French Patent Application No. 7,822,138 by hydrolysing 166.4 moles of phenyltrichlorosiloxane and 93.7 moles of methyltrichlorosilane and end capping with 9.2 moles of trimethylchlorosilane.The resulting resin has a TMA softening point of 119 EPDM...a linear terpolymer based on ethylene propylene diene monomer commercially available from Exxon Corp. under the trade name Vistalon 3704 Al2QS 3H2O silane coated... alumina trihydrate coated with 1.5% thereof of trimethoxye thoxysilane VA/VV/E... an 85% vinyl acetate/10% vinyl versatate 5% ethylene terpolymer VA/E. . . a 60% vinyl acetate/40% ethylene copolymer Hytrel..trade name for a thermoplastic elastomeric polyester derived from dimethyl terephthalate, a polyglycol and a short chain diol, commercially available from Dupont-Grade 4056 VA/VPA/E1. . a 19 m-ole % vinyl acetate/14 mole % vinyl phenyl acetate/67 mole % ethylene terpolymer VA/VPA/E2. . a 4 mole % vinyl acetate/7.3 mole % vinyl phenyl acetate/88.7 mole % ethylene terpolymer VA/VP/E. . a 25 mole % vinyl acetate/8 mole % vinyl palmitate/67 mole % ethylene terpolymer VA/VS/E1 .. a 3 mole % vinyl acetate/15 mole % vinyl stearate/82 mole % ethylene terpolymer VA/VS/E2... a 2.7 mole % vinyl acetate/8.6 mole % vinyl stearate/88.7 mole % ethyleneterpolymer VA/VB/E... a 2.7 mole % vinyl acetate/8.6 mole % vinyl benzoate/88.7 mole % ethylene terpolymer VA/VH/E1...a 4.7 mole % vinyl acetate/6.6 mole % vinyl hexanoate/88.7 mole % ethylene terpolymer VA/VL/E. . a 1.9 mole %. vinyl acetate/9.4 mole % vinyl laurate/88.7 mole % ethylene terpolymer VPA/E,... an 18 mole % vinyl phenyl acetate/82 mole % ethylene copolymer TABLE I EXAMPLE NO.

CONSTITUENTS 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 VV/VA1 74.5 74.5 74.5 75 75 75 75 74.5 36 32 28 20 VV/VA2 40 VL/VA 75 70 65 30 30 LLDPE 15 15 15 BLDPE1 10 10 SILICONE ELASTOMER 10 SILICONE RESIN 4 8 12 20 EPDM 5 10 Al2O3 3H2O 60 60 60 60 Al2O3 3H2O SILANE COATED 37 37 37 74.5 60 210 210 210 117 190 Al2O3 . H2O 74.5 37 37 Mg(OH)2 70.0 37 37 Ca(OH)2 74.5 37 ELECTRON BEAM DOSE Mrads 6 6 6 6 7.5 7.5 7.5 7.5 6 6 6 6 12 12 12 12 6 6 LOI @ 23 31.6 25.6 22.1 29.6 32.0 30.0 28.5 34.0 69 93 94 94 33 65.5 61.5 63.5 61.5 71.1 TABLE II EXAMPLE NO.

CONSTITUENTS 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 VV/VA1 10 108 96 84 108 96 84 VL/VA 30 30 70 60 45 50 50 VA/VV/E 180 160 VA/E 30 45 25 15 HYTREL 12 24 36 LLDPE 15 15 15 SILICONE ELASTOMER 20 10 12 24 36 EPDM 5 Al2O3 3H2O 180 180 180 180 180 180 Al2O3 . 3H2O 157 155 210 210 210 210 210 180 240 SILANE COATED ELECTRON BEAM 6 6 12 12 12 12 12 8 8 8 8 8 8 12 12 DOSE Mrads LOI @ 23 97.0 99.7 70.0 72.5 60.5 76.5 87.5 99.7 81.5 88.7 77.9 72.9 68.5 31.0 42.5 TABLE III EXAMPLE NO.

CONSTITUENTS 43 44 45 46 47 48 49 50 51 52 53 VA/VPA/E1 40 30 VA/VPA/E2 40 VA/VP/E 40 30 VA/VS/E1 40 VA/VS/E2 40 VA/VB/E 40 VA/VH/E 40 VA/VL/E 40 VPA/E 40 Al2O3 . 3H2O 60 60 70 60 70 60 60 60 60 60 60 ELECTRON BEAM DOSE Mrads 12 12 12 12 12 12 12 12 12 12 12 LOI @ 23 35.0 29.0 49.0 34.5 49.5 25.5 28.5 29.0 26.6 28.1 27.0 In the preceeding Examples where LOI values in the range 25 to 35 are obtained, these are accompanied by a notable balance of physical properties as measured for example by tensile strength (MPa) and elongation at break (%) at 23"C (per BS903 part A2). Such properties render such materials suitable for heat-recoverable applications or for processing by thermoforming techniques into, e.g. cladding and panneling.In the preceeding Examples where higher LOI values are obtained, e.g. greater than 35, and depending on the particular application it is desired to alter the balance of physical properties, this may be achieved by changing the filler level and/or by blending with an appropriate polymer whilst still permitting high LOI values to be achieved.

Examples 54 to 57 In analogous manner to that described above, the compositions set out in Table IV were prepared and subjected to limiting oxygen index and physical property testing. In the tables, the following abbreviations are employed. Other abbreviations are as previously defined in Examples 10 to 53.

VA/VH/E2... a 28 mole % vinyl acetate/5 mole % vinyl hexanoate/67 mole % ethylene terpolymer VA/VS/E3... a 27 mole % vinyl acetate/6 mole % vinyl stearate/67 mole % ethylene terpolymer VA/VH... a 78 mole % vinyl hexanoate/22 mole % vinyl acetate copolymer.

TABLE IV CONSTITUENTS 54 55 56 57 VA/VH/E2 32 40 VA/VS/E3 40 VA/VH 24 Awl203 . 3H2O 68 60 60 60 Silane Coated Silicone Elastomer 16 Electron Beam Dose 12 12 1 2 12 (M rads) LOI @ 23"C 54.5 38.0 36.2 60.2 Tensile Strength (MPa) 11.1 - 6.36 @ 23"C (per BS703 part A2) % Elongation at break 63 - 86 @ 23 (per BS703 part A2) Example 58 Example 1 is repeated employing each of the following copolymers instead of VVE/VA viz.

(a) Vinyl laurate (40%)/Vinyl acetate (60%) (b) Vinyl stearate (40%)/Vinyl acetate (60%) (c) Vinyl versatate (40%)/Vinyl acetate (60%) (d) Vinyl benzoate (40%)/Vinyl acetate (60%) (e) Vinyl propionate (40%)/Vinyl acetate (60%) (f) Vinyl versatate (40%)/Vinyl propionate (60%) (g) Vinyl stearate (40%)/Vinyl propionate (60%) (h) Vinyl benzoate (40%)/Vinyl propionate (60%) (i) Ethylene (59%)/Vinyl acetate (7%)/Vinyl phenyl acetate (34%) (j) Ethylene (56%)/Vinyl acetate (11 %)/Vinyl laurate (33%) (k) Ethylene (69%)/Vinyl acetate (13%)/Vinyl propionate (18%) In each case, substantial flame retardancy is observed.

Example 59 To exemplify the ability of the polymer systems of the invention to accept high loadings of inorganic fillers, a VA/VL copolymer (vide supra) was loaded with 80% of silane coated alumina trihydrate (vide supra) and cross-linked in analogous manner to that described in Example 1. The resulting material exhibited the following LOI values at different temperatures whilst possessing an acceptable balance of physical properties.

TEMPERATURE LOl 23D 100 250" 100 300" 88 410 45 Examples 60-65 Heat-shrinkable tapes were produced from the formulations set out in Table V. In the table the following abbreviations are employed. Other abbreviations are as defined in the preceeding Examples.

IBLDPE2. . a branched low density polyethylene available under the trade name PN220 from BXL Limited EVA . an ethylene/vinyl acetate copolymer 18% vinyl acetate Al203 . 3H2O stearic acid, . alumina trihydrate available under the trade name Hydral 705 from Alcoa Corp. and coated with 2% stearic acid The constituents of each formulation were compounded on a twin roll mill at 120 to 140 C.

cooled and pelletised. The pellets so produced were fed to a conventional extruded filler with a tape die, maintained at 140 C and extruded into a tape 6 mm wide and 2 mm thick. The resulting tape was subsequently irradiated with high energy electrons to a total dosage of 8 Mrads. After irradiation, the tape was heated to 140 C, expanded length wise to double its original length and allowed to cool in this expanded condition. Thereafter the tape was coated with a thin layer (0.5 mm) of a hot-melt adhesive of composition in accordance with W. German Offenlegungschrift 2,723,116, Example 3, formulation "0". The physical properties and LOI of the resulting tapes are set out in Table V.

The heat-shrinkable adhesive coated tapes so produced were employed to seal the joints of 150 mm diameter metal air conditioning ducts by preheating the duct in the region of the joint, wrapping each tape around the duct over the joint region so that sequential turns of each tape partially overlap and heating each tape with a conventional propane gas torch to a temperature of 145"C, so causing the adhesive to melt and each tape to shrink tightly around the joint and form a strong adhesive band between each tape and duct.

TABLE V EXAMPLE NO.

CONSTITUENTS 60 61 62 63 64 65 VL/VA 20 30 60 90 BLDPE2 10 10 30 VAE 20 10 60 30 EVA 40 40 40 VA/VH/E2 120 120 Al203 . 3H2O 50 50 160 160 160 160 Stearic Acid Coated % Elongation at 320 340 400 400 518 366 break @ 23"C @ 150 C 400 400 400 7400 400 350 Tensile strength 3.2 2.3 6.4 4.1 8.3 5.8 (MPa) @ 23"C @ 150 C 0.9 0.6 0.9 0.8 1.7 1.5 100% Tangent 0.4 0.2 0.50 0.35 0.85 0.8 Modulus @ 150 C (MPa) LOI 29.5 29.5 30.5 31.5 26.0 27.0 EXAMPLE 66 CONSTITUENTS PARTS BY WEIGHT LLDPE 50 VAE 50 VL/VA 50 Awl203 . 3H20 150 Silane Coated The above formulation was compounded in an internal mixer of the Banbury type, at a temperature of about 1 25do. After compounding, the material was processed into a strip on a twin roll mill, cooled diced into pellets, and lightly talced to prevent blocking of the pellets. The material was then 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 1.2 mm, using a 3 > inch extruder, 25.1 L/D ratio screw, at barrel temperatures of 60, 80, 110, 1 20 and 1 30to and an extruded die temperature temperature profile of 150, 140 and 1 20do. The jacketed cable was then irradiated with high energy electrons to a total dose of 8 Mrads. The jacketed material was found to have the following properties.

% Elongation @ 23do... 100 Tensile Strength (MPa) @ ....... 8 LOI @ 23DC. . . 31.5 CTI. . 250do

Claims (31)

1. A flame retarded polymeric composition which comprises a non-cross-linked or crosslinked unsubstituted or substituted vinyl ester copolymer, at least some of the ester groupings of the polymer containing at least 3 carbon atoms, incorporating an effective amount of a flame retardant and with the proviso that when the composition is non-cross-linked, any copolymer of vinyl propionate with ethylene contains greater than 20 mole % vinyl propionate.

2. A copolymer according to Claim 1 wherein the vinyl ester copolymer includes vinyl ester monomeric units of formula I,

wherein R1, R2 and R3 are each, independently, hydrogen or a C,-C20 substituted or unsubstituted hydrocarbon and R4 is a C2-C20 substituted or unsubstituted hydrocarbon.

3. A composition according to Claim 2 wherein R1, R2, R3 of formula I are each, independently, hydrogen or C1-C6 alkyl.

4. A composition according to Claim 3 wherein R1, R2 and R3 of formula I are each hydrogen.

5. A composition according to any one of Claims 2 to 4 wherein R4 of formula I is C2-C20 alkyl, alkenyl, alkoxyalkyl or alkoxyalkenyl, aryl, aralkyl, or aryl or aralkyl substituted by C1-C4 alkyl or alkoxy.

6. A composition according to Claim 5 wherein R4 of formula I is C2-C20 alkyl, alkenyl, alkoxyalkyl or alkoxyalkenyl, phenyl, naphthyl, benzyl, or phenyl, naphthyl or benzyl substituted by C1-C4 alkyl or alkoxy.

7. A composition according to Claim 6 wherein R4 of formula I is C3-C17 alkyl, phenyl or benzyl.

8. A composition according to any one of the preceding claims wherein the vinyl ester polymer is a copolymer of a vinyl ester as defined with a different ester and/or an unsaturated hydrocarbon.

9. A composition according to Claim 8 wherein the vinyl ester polymer is a copolymer of a vinyl ester as defined with a different vinyl ester, the ester grouping of which contains at least 2 carbon atoms, a C2-C,2 olefin and/or a C4-C,2 (meth)acrylate.

1 0. A composition according to Claim 9 wherein the vinyl ester polymer is a copolymer of a vinyl ester as defined with vinyl acetate and/or ethylene.

11. A composition according to any one of the preceding claims wherein the vinyl ester copolymer contains at least 5 mole % of a vinyl ester monomer containing at least 3 ester carbon atoms.

12. A composition according to Claim 11 wherein the vinyl ester copolymer contains 10 to 95 mole % of a vinyl ester monomer containing at least 3 ester carbon atoms.

1 3. A composition according to any one of the preceding claims wherein the composition comprises a blend of the vinyl ester copolymer with at least one other polymer.

14. A composition according to Claim 1 3 wherein the blend polymer comprises a polyethylene, polyester, a silicone resin or elastomer, a (meth)acrylate homo- or copolymer, an ethylene/vinyl acetate copolymer, an EPDM or an SBR.

1 5. A composition according to either of Claims 1 3 or 14 containing at least 20 weight % vinyl ester copolymer in the blend.

1 6. A composition according to any one of the preceding claims in substantially cross-linked form.

1 7. A composition according to Claim 1 6 having a gel content in accordance with ANSI/ASTM D2765-68 of at least 10%.

1 8. A composition according to any of the preceding claims wherein the flame retardant is an inorganic flame retardant.

1 9. A composition according to Claim 1 8 wherein the inorganic flame retardant is hydrated.

20. A composition according to Claim 1 9 wherein the hydrated inorganic flame retardant comprises alumina trihydrate.

21. A composition according to any one of the preceding claims incorporating 10 to 400 parts of flame retardant per 100 parts of polymer(s).

22. A composition according to any one of the preceding claims incorporating less than 5 weight per cent halogen or phosphorus.

23. A composition according to Claim 1 substantially as described herein with reference to Examples 1 to 66.

24. Flame retarded electrical insulation comprising a composition as defined in any one of the preceding claims.

25. A wire or cable provided with electrical insulation according to Claim 24.

26. A flame retarded wire or cable according to Claim 25 substantially as described herein with reference to Example 66.

27. A flame retarded heat-recoverable article comprising a composition as defined in any one of Claims 1 to 23 in cross-linked and heat-recoverable form.

28. An article according to Claim 27 in the form of an extruded tape, sheet or sleeve or a hollow moulded part.

29. An article according to either of Claims 27 or 28 incorporating a thermoplastic polymer.

30. An article according to Claim 29 wherein the thermoplastic polymer is an ethylene homo- or copolymer.

31. A heat-recoverable article according to Claim 27 substantially as described herein with reference to Examples 60 to 65.