Liquid silicone rubber composition

Abstract

The present disclosure relates to hydrosilylation (addition) curable liquid silicone rubber compositions, to silicone elastomeric materials with improved fire retardancy which are produced by curing said hydrosilylation (addition) curable liquid silicone rubber compositions and to a method for preparing said silicone elastomeric materials.

Description

[0001] LIQUID SILICONE RUBBER COMPOSITION The present disclosure relates to hydrosilylation (addition) curable liquid silicone rubber compositions, to silicone elastomeric materials with improved fire retardancy which are produced by curing said hydrosilylation (addition) curable liquid silicone rubber compositions and to a method for preparing said silicone elastomeric materials. Hydrosilylation curable liquid silicone rubber compositions containing: (i) organopolysiloxane polymers having unsaturated (alkenyl and / or alkynyl) groups and a viscosity up to about 750,000mPa.s at 25oC; (ii) compounds containing silicon-bonded hydrogen atoms; and (iii) a hydrosilylation catalyst are known in the art and are used to prepare silicone elastomeric materials with a broad spectrum of physical properties including electrical insulation, resistance and stability to heat, freeze resistance, abrasion resistance, and long-term flexibility. This unique combination of properties renders elastomers made from liquid silicone rubber suitable for utilisation in a wide range of electrical and / or insulative applications, such as in or for electrical connectors, commonly used to create closed electrical circuits in automotive, residential, and infrastructural settings. For example, liquid silicone rubbers (LSRs) have been broadly utilized as seals in or for electrical connectors due to their excellent balance of mechanical properties, chemical and thermal stabilities and ease of processing. They may be used to mate rigid thermoplastic housing components forming a tight connection that provides both electrical and environmental isolation to connector junctions. These may be used in automotive vehicles which are becoming increasingly dependent on electrical and electronical systems for the full operation thereof, even more so since the introduction of electric and hybrid vehicles. Hence, electrical failures can lead to devices such as radio, light, ventilation etc. malfunctioning or breaking down. Many of the electrical connectors used for such devices rely on the aforementioned silicone rubber materials to prevent electrical failings and they need to be able to avoid failure in e.g., vehicles at increasing engine temperatures. Whilst silicone elastomers are well known for providing excellent heat resistance at elevated temperatures, e.g., up to 250oC or even higher, regrettably they do not have as good a level of flame retardancy as is desired for some of the applications for which they are utilised unless provided with flame-retardant additives. For the avoidance of doubt by flame-retardant additives we mean additives introduced into liquid silicone rubber compositions which when cured to silicone elastomers provide elastomeric products with the ability to slow down the burning process and promote self-extinguishment when a flame source is removed. Furthermore, it is to be understood that while the addition of flame-retardant additives into liquid silicone rubber compositions provide a degree of protection against fire hazards for the resulting silicone elastomers after the composition has been cured, their performance is generally lower than that of inherently flame-resistant materials. When exposed to flames or intense heat, flame-retardant materials may initially resist ignition, but they can eventually catch fire if the exposure is sustained. Liquid Silicon rubbers exposed to flames can form problematic levels of volatile organic compounds (VOCs) that evaporate and ignite in air / oxygen atmospheres in presence of a spark and / or flame (fire triangle). Whilst LSRs, without additive systems, perform surprisingly well under horizontal burning test conditions, they perform far less well under vertical test conditions and noticeably burn, sometimes even completely up to the clamp gripper under such testing (Burn [%] 100). For electrical supply insulation applications such as high voltage insulation, LSRs are tested for tracking and erosion resistance performance, which gives an indication of the thermal degradation of materials by electric arcing of the liquid silicone rubber elastomeric material which provides an important indicator of the service lifetime of silicone rubber materials as well the flammability thereof in accordance with e.g., UL94. UL94 is an Underwriters Laboratories of US (UL) standard test UL94 (The Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing) a UL94 V0 performance of the elastomer is highly favourable, if not mandatory, at a sample / coating thickness of 3 mm due to original equipment manufacturers (OEM) requirements. UL 94 has been harmonized with other standards i.e., IEC 60695-11-10, IEC 60695- 11-20, ISO9772 and ISO9773. It has been found that whilst commercial liquid silicone rubber elastomers give excellent long term tracking and erosion resistance performance, flammability results are often between V-1 and V-0; where V-1 indicates: “burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed”; and V-0 indicates: “burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed. Whereas for e.g., busbars, cable and wire coating and potentially for future seals in electric powered (EV) vehicles a UL94 V0 performance of the Liquid silicone rubber elastomer is increasingly desired at a sample thickness of 3 mm. Several flame retardancy additives have been proposed for use in silicone elastomeric materials to enhance their flame-resistant properties. Examples of flame-retardant additives proposed for use in peroxide cured silicone rubber elastomers to provide improved flame retardancy include platinum materials such as platinum and platinum materials as described in US3514424A and US3635874A. Combinations of such aforementioned platinum materials in combination with other additives including combinations such as titanium dioxide, carbon black, Group II metal oxides, rare earth metal oxides and rare earth metal hydroxides, and an aromatic acid selected from the group consisting of mononuclear aromatic acids and halogenated mononuclear aromatic acids. In contrast elastomers made from liquid silicone rubber compositions have tended to rely on inorganic compounds such as aluminum trihydroxide (ATH), magnesium dihydroxide (MDH), titanium dioxide, iron oxide and cerium silanolate have been used as flame retardant additives. However, there remains an ongoing need for the development of further fire-retardant silicone rubber elastomers especially in view of the ever increasingly complex environmental, health and safety requirements. There is provided herein a two-part hydrosilylation curable silicone rubber composition, which comprises the following components: a) one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule and having a viscosity in a range of from 1000 mPa.s to 750,000 mPa.s at 25oC; b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule; c) a silica reinforcing filler which is optionally hydrophobically treated; d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; e) a flame-retardant additive comprising one or more phenolic antioxidants selected from an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, tannic acid, 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzenealkyl 3-(3,5-di-tert-butyl-4- hydroxyphenyl)propanoate wherein the alkyl group contains from 1 to 20 carbons and 2,2'- Methylene-bis(6-tert-butyl-p-cresol); and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii), where: f)(i) is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, in an amount 0.05 to 2.0 wt. % of the composition; and f)(ii) is a component selected from cyanuric acid, urea, biuret, N,N′-Bis(trimethylsilyl)urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition; wherein the two parts are Part (A) and Part (B) wherein Part (A) comprises a proportion of components (a) and (c) and all of component (d) and Part (B) comprises the remainder of components (a) and (c) and all of component (b). The total wt. % of the composition (i.e., Part (A) + Part (B)) is 100 wt. %. There is also provided a silicone elastomeric material which is the cured product of the above hydrosilylation curable silicone rubber composition, which silicone elastomeric material has a UL94 with a V-0 performance at a sample thickness of 3 mm. There is also provided a process for making a silicone elastomeric material comprising the steps of preparing a Part (A) composition comprising: a proportion of component (a) one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule and having a viscosity in a range of from 1000 mPa.s to 750,000 mPa.s at 25oC; a proportion of component (c) a silica reinforcing filler which is optionally hydrophobically treated; and the whole of component (d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; preparing a Part (B) composition comprising: the remainder of component (a) the remainder of component (c); and the whole of component d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and comprising component (e) in Part (A), Part (B) or both Part (A) and Part (B) and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii) in Part (A), Part (B) or both Part (A) and Part (B); wherein e) is a flame-retardant additive comprising one or more phenolic antioxidants selected from an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, tannic acid, 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene alkyl 3-(3,5-di-tert- butyl-4-hydroxyphenyl)propanoate wherein the alkyl group contains from 1 to 20 carbons and 2,2'-Methylene-bis(6-tert-butyl-p-cresol); and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii), where: f)(i) is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, in an amount 0.05 to 2.0 wt. % of the composition; and f)(ii) is a component selected from cyanuric acid, urea, biuret, N,N′-Bis(trimethylsilyl)urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition; mixing the Part (A) and Part (B) compositions together and curing at a temperature of from 80oC to 200oC. There is also provided a silicone elastomeric material obtained or obtainable from the process above. There is also provided the use of a combination of components (e) and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii) wherein e) is a flame-retardant additive comprising one or more phenolic antioxidants selected from an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, tannic acid, 1,3,5- Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, alkyl 3-(3,5-di-tert-butyl-4- hydroxyphenyl)propanoate wherein the alkyl group contains from 1 to 20 carbons and 2,2'- Methylene-bis(6-tert-butyl-p-cresol); and: f)(i) is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, in an amount 0.05 to 2.0 wt. % of the composition; and f)(ii) is a component selected from cyanuric acid, urea, biuret, N,N′-Bis(trimethylsilyl)urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition; as a flame-retardant additive in a silicone elastomeric material which is the cured product of a hydrosilylation curable silicone rubber composition, which otherwise comprises the following components: a) one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule and having a viscosity in a range of from 1000 mPa.s to 750,000 mPa.s at 25oC; b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule; c) a silica reinforcing filler which is optionally hydrophobically treated; d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof. As previously indicated the total wt. % of the composition is 100 wt. %. The components of the composition are hereafter described in further detail. Component (a) Component (a) of the composition is one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule and having a viscosity in a range of from 1000 mPa.s to 750,000 mPa.s at 25oC. Component (a) is a polyorganosiloxane, such as a polydiorganosiloxane having at least two unsaturated groups per molecule, which unsaturated groups are each independently selected from an alkenyl group and an alkynyl group. Alternatively, component (a) has at least three unsaturated groups per molecule. The unsaturated groups of component (a) may be terminal, pendent, or in both locations. Alkenyl groups may have 2 to 30, alternatively 2 to 24, alternatively 2 to 20, alternatively 2 to 12, alternatively 2 to 10, and alternatively 2 to 6 carbon atoms. Possible alkenyl groups are exemplified by, but not limited to, vinyl, allyl, methallyl, propenyl, and hexenyl and cyclohexenyl groups. Alkynyl groups may have 2 to 30, alternatively 2 to 24, alternatively 2 to 20, alternatively 2 to 12, alternatively 2 to 10, and alternatively 2 to 6 carbon atoms. Alkynyl groups may be exemplified by, but not limited to, ethynyl, propynyl, and butynyl groups. Component (a) has multiple units of the formula (I): R’aSiO(4-a) / 2(I) in which each R’ is independently selected from an aliphatic hydrocarbyl, or aliphatic non- halogenated organyl group (that is any aliphatic organic substituent group, regardless of functional type, having one free valence at a carbon atom). Saturated aliphatic hydrocarbyls are exemplified by, but not limited to alkyl groups such as methyl, ethyl, propyl, pentyl, octyl, undecyl, and octadecyl and cycloalkyl groups such as cyclohexyl. Unsaturated aliphatic hydrocarbyls are exemplified by, but not limited to the alkenyl groups and alkynyl groups described above. The aliphatic non-halogenated organyl groups are exemplified by, but not limited to, suitable nitrogen containing groups such as amido groups, imido groups; oxygen containing groups such as polyoxyalkylene groups, carbonyl groups, alkoxy groups and hydroxyl groups. The subscript “a” is 0, 1, 2 or 3, typically in this instance a is mainly 2 but may contain some units where a is 1 or 3. Siloxy units may be described by a shorthand (abbreviated) nomenclature, namely - "M," "D," "T," and "Q", when R’ is as described above, alternatively an alkyl group, typically a methyl group The M unit corresponds to a siloxy unit where a = 3, that is R’3SiO1 / 2; the D unit corresponds to a siloxy unit where a = 2, namely R’2SiO2 / 2; the T unit corresponds to a siloxy unit where a = 1, namely R’1SiO3 / 2; the Q unit corresponds to a siloxy unit where a = 0, namely SiO4 / 2. The polyorganosiloxane, such as a polydiorganosiloxane of component (a), is substantially linear but may contain a proportion of branching due to the presence of T units (as previously described) or very occasionally Q groups (as previously described) within the molecule, hence the average value of subscript a in structure comprising multiple units of formula (I) is about 2. Examples of typical R’ groups on component (a) the one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule, include mainly alkyl groups, especially methyl and ethyl, alternatively methyl groups but may also include aryl groups and / or fluoroalkyl groups such as trifluoropropyl or perfluoroalkyl groups in addition to the required at least two unsaturated groups selected from alkenyl and / or alkynyl groups, typically alkenyl groups The groups may be in pendent position (on a D or T siloxy unit) or may be terminal (on an M siloxy unit). Hence, the polymer chain of component (a) may be selected from polydimethylsiloxanes, alkylmethylpolysiloxanes, alkylarylpolysiloxanes or copolymers thereof (where reference to alkyl means any suitable alkyl group, alternatively an alkyl group having two or more carbons) providing each component (a) polymer comprises at least two alkenyl and or alkynyl groups, typically at least two alkenyl groups. Such polymer chains may have any suitable terminal groups, for example, they may be trialkyl terminated, alkenyldialkyl terminated alkynyldialkyl terminated or may be terminated with any other suitable terminal group combination providing each polymer contains at least two unsaturated groups selected from alkenyl and alkynyl groups per molecule. In one embodiment the terminal groups of such a polymer don’t comprise any silanol terminal groups. Hence component (a) may, for the sake of example, be: a dialkylalkenyl terminated polydimethylsiloxane, e.g., dimethylvinyl terminated polydimethylsiloxane; a dialkylalkenyl terminated dimethylmethylphenylsiloxane, e.g., dimethylvinyl terminated dimethylmethylphenylsiloxane; a trialkyl terminated dimethylmethylvinyl polysiloxane; a dialkylvinyl terminated dimethylmethylvinyl polysiloxane copolymer; a dialkylvinyl terminated methylphenylpolysiloxane, a dialkylalkenyl terminated methylvinylmethylphenylsiloxane; a dialkylalkenyl terminated methylvinyldiphenylsiloxane; a dialkylalkenyl terminated methylvinyl methylphenyl dimethylsiloxane; a trimethyl terminated methylvinyl methylphenylsiloxane; a trimethyl terminated methylvinyl diphenylsiloxane; or a trimethyl terminated methylvinyl methylphenyl dimethylsiloxane. Component a) has a viscosity of from 1000 mPa.s to 750,000 mPa.s at 25oC, alternatively 2,500 mPa.s to 500,000 mPa.s at 25oC, alternatively 2,500 mPa.s to 400,000 mPa.s at 25oC, alternatively 2,500 mPa.s to 300,000 mPa.s at 25oC, alternatively 2,500 mPa.s to 250,000 mPa.s at 25oC, alternatively 2,500 mPa.s to 100,000 mPa.s at 25oC, alternatively 5000 mPa.s to 75,000 mPa.s at 25oC, 10,000 mPa.s to 60,000 mPa.s at 25oC and is preferably present in an amount of from 25 to 60 wt. % of the composition, alternatively in an amount of from 30 to 60 wt. % of the composition, alternatively in an amount of from 35 to 55 wt. % of the composition. Viscosity may be measured at 25 °C using either a BrookfieldTMrotational viscometer with spindle LV-4 for viscosities over 15,000mPa.s (Spindle LV-4 designed for viscosities in the range between 1,000-2,000,000 mPa.s) at an appropriate rpm and using a BrookfieldTMrotational viscometer with a cone plate arrangement with cone CP-52 for viscosities up to 15, 000mPa.s at 25°C and an appropriate rpm. Component (b) Component (b) functions as a cross-linker and is provided in the form of an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule. Component (b) normally contains three or more silicon-bonded hydrogen atoms so that the hydrogen atoms can react with the unsaturated alkenyl and / or alkynyl groups of component (a) to form a network structure therewith and thereby cure the composition. Some or all of Component (b) may alternatively have two silicon bonded hydrogen atoms per molecule when polymer (a) has greater than two unsaturated groups per molecule. The molecular configuration of the organosilicon compound having at least two, alternatively at least three Si-H groups per molecule (b) is not specifically restricted. It may be a polyorganosiloxane which can have a straight chain, be branched (a straight chain with some branching through the presence of T groups), cyclic or be a silicone resin based. While the molecular weight of component (b) is not specifically restricted, the viscosity is typically from 5 to 50,000 mPa.s at 25ºC using the test methodology as described for component (a). Silicon-bonded organic groups used in component (b) may be exemplified by alkyl groups such as methyl, ethyl, propyl, n-butyl, t-butyl, pentyl, hexyl; aryl groups such as phenyl tolyl, xylyl, or similar aryl groups; 3-chloropropyl, 3,3,3-trifluoropropyl, or similar halogenated alkyl group, preferred alkyl groups having from 1 to 6 carbons, especially methyl ethyl or propyl groups or phenyl groups. Preferably the silicon-bonded organic groups used in component (b) are alkyl groups, alternatively methyl, ethyl or propyl groups. Examples of the organosilicon compound having at least two, alternatively at least three Si-H groups per molecule (b) include but are not limited to: (a’) trimethylsiloxy-terminated methylhydrogenpolysiloxane, (b’) trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxane, (c’) dimethylhydrogensiloxy-terminated dimethylsiloxane-methylhydrogensiloxane copolymers, (d’) dimethylsiloxane-methylhydrogensiloxane cyclic copolymers, (e’) copolymers and / or silicon resins consisting of (CH3)2HSiO1 / 2 units, (CH3)3SiO1 / 2 units and SiO4 / 2 units, (f’) copolymers and / or silicone resins consisting of (CH3)2HSiO1 / 2 units and SiO4 / 2 units, (g’) Methylhydrogensiloxane cyclic homopolymers having between 3 and 10 silicon atoms per molecule; alternatively, component (b), the cross-linker, may be a filler, e.g., silica treated with one of the above, and mixtures thereof. In one embodiment component (b) is selected from a methylhydrogenpolysiloxane capped at both molecular terminals with trimethylsiloxy groups; a copolymer of a methylhydrogensiloxane and a dimethylsiloxane capped at both molecular terminals with trimethylsiloxy groups; dimethylsiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups; a copolymer of a methylhydrogensiloxane and a dimethylsiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups. The cross-linker (b) is generally present in the hydrosilylation curable silicone rubber composition such that the molar ratio of the total number of the silicon-bonded hydrogen atoms in component (b) to the total number of alkenyl and / or alkynyl groups in component (a) is from 0.5 : 1.0 to 10.0 : 1.0. When this ratio is less than 0.5:1, a well-cured composition will not be obtained. When the ratio exceeds 10:1, there is a tendency for the hardness of the cured composition to increase when heated. Preferably component (b) is in an amount such that the molar ratio of silicon-bonded hydrogen atoms of component (b) to alkenyl / alkynyl groups, alternatively alkenyl groups of component (a) ranges from 0.7 : 1.0 to 5.0 : 1.0, alternatively from 0.9 : 1.0 to 2.5 : 1.0, and further alternatively from 0.9 : 1.0 to 2.0 : 1.0. The silicon-bonded hydrogen (Si-H) content of component (b) is determined using quantitative infra-red analysis in accordance with ASTM E168. In the present instance the silicon-bonded hydrogen to alkenyl (vinyl) and / or alkynyl ratio is important when relying on a hydrosilylation cure process. Generally, this is determined by calculating the total weight % of alkenyl groups in the composition, e.g., vinyl [V] and the total weight % of silicon bonded hydrogen [H] in the composition and given the molecular weight of hydrogen is 1 and of vinyl is 27 the molar ratio of silicon bonded hydrogen to vinyl is 27[H] / [V]. Typically, dependent on the number of unsaturated groups in component (a) as well as the number of Si-H groups in component (b), component (b) will be present in an amount of from 0.1 to 10 wt. % of the hydrosilylation curable silicone rubber composition, alternatively 0.1 to 7.5wt. % of the hydrosilylation curable silicone rubber composition, alternatively 0.5 to 7.5wt. %, further alternatively from 0.5% to 5 wt. % of the hydrosilylation curable silicone rubber composition Component (c) Component (c) is a silica reinforcing filler which is optionally hydrophobically treated; The reinforcing fillers of component (c) may be exemplified by fumed silica and / or a precipitated silica and / or a colloidal silica. In one alternative, the fumed silica, precipitated silica and / or colloidal silica are provided in a finely divided form. Precipitated silica, fumed silica and / or colloidal silicas are particularly preferred because of their relatively high surface area, especially when provided in a finely divided form, which is typically at least 50 m² / g (BET method in accordance with ISO 9277: 2010). Fillers having surface areas of from 50 to 450 m² / g (BET method in accordance with ISO 9277: 2010), alternatively of from 50 to 300 m² / g (BET method in accordance with ISO 9277: 2010), are typically used. All these types of silica are commercially available. When silica reinforcing filler (c) is naturally hydrophilic (e.g., untreated silica fillers), it is typically treated with a treating agent to render it hydrophobic. These surface modified silica reinforcing fillers (c) do not clump and can be homogeneously incorporated into polydiorganosiloxane polymer (a), described below, as the surface treatment makes the fillers easily wetted by component (a). Typically, silica reinforcing filler (c) may be surface treated with any low molecular weight organosilicon compounds disclosed in the art applicable to prevent creping of liquid silicone rubber (LSR) compositions during processing. For example, organosilanes, polydiorganosiloxanes, or organosilazanes e.g., hexaalkyl disilazane, short chain siloxane diols may be used to render the silica reinforcing filler (c) (s) hydrophobic and therefore easier to handle and obtain a homogeneous mixture with the other ingredients. These may include but are not restricted to, silanol terminated trifluoropropylmethylsiloxane, silanol terminated vinyl methyl (ViMe) siloxane, silanol terminated methyl phenyl (MePh) siloxane, liquid hydroxyl dimethyl-terminated polydiorganosiloxane containing an average from 2 to 20 repeating units of diorganosiloxane in each molecule, hydroxyl dimethyl terminated Phenylmethyl Siloxane, hexaorganodisiloxanes, such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes, such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane and tetramethyldi(trifluoropropyl)disilazane; hydroxyldimethyl terminated polydimethylmethylvinyl siloxane, octamethyl cyclotetrasiloxane, and silanes including but not limited to methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, chlorotrimethyl silane, dichlorodimethyl silane, trichloromethyl silane. A small amount of water can be added together with the silica treating agent(s) as processing aid. In one embodiment, the treating agent may be selected from silanol terminated vinyl methyl (ViMe) siloxane, liquid hydroxyldimethyl-terminated polydiorganosiloxane containing an average from 2 to 20 repeating units of diorganosiloxane in each molecule, hexamethyldisiloxane, divinyltetramethyldisiloxane; hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane and hydroxyldimethyl terminated polydimethylmethylvinyl siloxane, octamethyl cyclotetrasiloxane, and methyltriethoxysilane, dimethyldiethoxysilane and / or vinyltriethoxysilane. A small amount of water can be added together with the silica treating agent(s) as processing aid. The surface treatment of untreated silica reinforcing filler (c) may be undertaken prior to introduction in the composition or in situ (i.e., in the presence of at least a portion of the other ingredients of the composition herein by blending these ingredients together at room temperature or above until the filler is completely treated. Typically, untreated silica reinforcing filler (c) is treated in situ with a treating agent in the presence of component (a) which results in the preparation of a silicone rubber base material which can subsequently be mixed with other ingredients. Silica reinforcing filler (c) is optionally present in an amount of up to 40 wt. % of the composition, alternatively from 1.0 to 40wt. % of the composition, alternatively of from 5.0 to 35wt. % of the composition, alternatively of from 10.0 to 35wt. % of the composition. Component (d) Component (d) of the composition is a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof. These are usually selected from catalysts of the platinum group of metals (platinum, ruthenium, osmium, rhodium, iridium and palladium), or a compound of one or more of such metals. Alternatively, platinum and rhodium compounds are preferred due to the high activity level of these catalysts in hydrosilylation reactions, with platinum compounds most preferred. In a hydrosilylation (or addition) reaction a hydrosilylation catalyst such as component (d) herein catalyses the reaction between an unsaturated group, usually an alkenyl group e.g., vinyl with Si-H groups. The catalyst (d) can be a platinum group metal, a platinum group metal deposited on a carrier, such as activated carbon, metal oxides, such as aluminum oxide or silicon dioxide, silica gel or powdered charcoal, or a compound or complex of a platinum group metal. Preferably the platinum group metal is platinum. Examples of preferred hydrosilylation catalysts (d) are platinum based catalysts, for example, platinum black, platinum oxide (Adams catalyst), platinum on various solid supports, chloroplatinic acids, e.g., hexachloroplatinic acid (Pt oxidation state IV) (Speier catalyst), chloroplatinic acid in solutions of alcohols e.g., isooctanol or amyl alcohol (Lamoreaux catalyst), and complexes of chloroplatinic acid with ethylenically unsaturated compounds such as olefins and organosiloxanes containing ethylenically unsaturated silicon-bonded hydrocarbon groups, e.g., tetra-vinyl-tetramethylcyclotetrasiloxane- platinum complex (Ashby catalyst). Soluble platinum compounds that can be used include, for example, the platinum-olefin complexes of the formulae (PtCl2.(olefin)2 and H(PtCl3.olefin), preference being given in this context to the use of alkenes having 2 to 8 carbon atoms, such as ethylene, propylene, isomers of butene and of octene, or cycloalkanes having 5 to 7 carbon atoms, such as cyclopentene, cyclohexene, and cycloheptene. Other soluble platinum catalysts are, for the sake of example a platinum-cyclopropane complex of the formula (PtCl2C3H6)2, the reaction products of hexachloroplatinic acid with alcohols, ethers, and aldehydes or mixtures thereof, or the reaction product of hexachloroplatinic acid and / or its conversion products with vinyl-containing siloxanes such as methylvinylcyclotetrasiloxane in the presence of sodium bicarbonate in ethanolic solution –. Platinum catalysts with phosphorus and amine ligands can be used as well, e.g., (Ph3P)2PtCl2; and complexes of platinum with vinylsiloxanes, such as sym- divinyltetramethyldisiloxane. Hence, specific examples of suitable platinum-based catalysts include: (i) complexes of chloroplatinic acid with organosiloxanes containing ethylenically unsaturated hydrocarbon groups are described in US 3,419,593; (ii) chloroplatinic acid, either in hexahydrate form or anhydrous form; (iii) a platinum-containing catalyst which is obtained by a method comprising reacting chloroplatinic acid with an aliphatically unsaturated organosilicon compound, such as divinyltetramethyldisiloxane; (iv) alkene-platinum-silyl complexes as described in US Pat. No.6,605,734 such as (COD)Pt(SiMeCl2)2where “COD” is 1,5-cyclooctadiene; and / or (v) Karstedt’s catalyst is Pt2(divinyl tetramethyl disiloxane)3 complex typically containing from 30 to 50 wt. % platinum metal in the complex. It is typically introduced into a silicone rubber composition in premix with a vinyl siloxane polymer. The combination being from about from 0.25 to 2.0 wt. % of the catalyst complex in 99.75 wt. % to 98 wt. % of the vinyl siloxane polymer which usually has a viscosity of from about 200 to 750 mPa.s using the test methodology as described for component (a). Solvents such as toluene and the like organic solvents have been used historically as alternatives but the use of vinyl siloxane polymers by far the preferred choice. These are described in US3,715,334 and US3,814,730. In one preferred embodiment component (d) may be selected from co-ordination compounds of platinum. In one embodiment hexachloroplatinic acid and its conversion products with vinyl-containing siloxanes, Karstedt's catalysts and Speier catalysts are preferred. Component (d) is typically present in a quantity of platinum atom that provides from 0.1 to 500ppm (parts per million) with respect to the weight of the reactive ingredients, components (a) and (b). The catalyst may be added as a single species or as a mixture of two or more different species. Typically, dependent on the form / concentration in which the catalyst is provided the amount of catalyst present will be within the range of from 0.05–1.5 wt. % of the composition, alternatively from 0.05–1.0 wt. %, alternatively from 0.1–1.0 wt. %, alternatively 0.1 to 0.5 wt. %, of the composition, wherein the platinum catalyst is provided in a masterbatch of polymer such as (a) described above. Component (e) Component (e) is a flame-retardant additive comprising: comprising one or more phenolic antioxidants selected from an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, tannic acid, 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate wherein the alkyl group contains from 1 to 20 carbons and 2,2'-Methylene-bis(6-tert-butyl-p-cresol). The flame-retardant additive of component (d) comprises one or more phenolic antioxidants elected from the group of an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, alternatively 1 to 18 carbons, alternatively 1 to 16 carbons e.g., stearyl 3,4,5- trihydroxybenzoate and dodecyl 3,4,5-trihydroxybenzoate, the latter of which is often referred to as dodecyl gallate (antioxidant 2 in the following examples) of the structure: phenolic antioxidants tannic acid ((1,2,3,4,6-pentakis[3,4-dihydroxy-5-[(3,4,5-trihydroxybenzoyl)oxy]benzoate]beta-D- glucopyranose) (antioxidant 5 in the following examples) of the structure

[0002] I ,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4- hydroxybenzyl) benzene or is alternatively known as 3,3',3'',5,5',5''-hexa-tert-butyl-α,α',α''- (mesitylene-2,4,6-triyl)tri-p-cresol) (antioxidant 1 in the following examples) and which has the structure: from the IrganoxTMrange including and an alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate wherein the alkyl group has 1 to 20 carbons, alternatively 1 – 18 carbons, an example being IrganoxTM1076 sold by BASF which is named octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate (antioxidant 6 in the following examples) and has the following structure:

[0003] Other sterically hindered phenolic antioxidants which may be used herein include for the sake of example the following: Methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate (antioxidant 3 in the following examples) which has the structure: cresol) or 2,2 -Methylene-bis(6-tert-butyl-4-methylphenol) which has the structure: (e) may be present in the composition in an amount of from 0.001 to 4wt. % of the composition, alternatively of from 0.01 to 3.5wt. % of the composition, alternatively 0.01 to 3wt. % of the composition, alternatively 0.025 to 2.5 wt. % of the composition, alternatively 0.025 to 2.0 wt. % of the composition. Component (f) Component (f) is optional and comprises (f)(i) and (f)(ii) wherein: f)(i) is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, in an amount 0.05 to 2.0 wt. % of the composition; and f)(ii) is a component selected from cyanuric acid, urea, biuret, N,N′-Bis(trimethylsilyl)urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition. Component (f)(i), when present, is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide; and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, with magnesium oxide, magnesium carbonates and magnesium hydroxycarbonates particularly preferred. The magnesium carbonates and magnesium hydrogen carbonates may be selected from magnesite (MgCO3), barringtonite (MgCO3.2H2O), nesquihonite (MgCO3.3H2O), lansfordite (MgCO3.5H2O); pokrovskite (Mg2(CO3)(OH)2.0.5H2O), artinite (Mg2(CO3)(OH)2.3H2O), hydromagnesite (Mg5(CO3)4(OH)2.4H2O) which is sometimes referred to as light magnesium carbonate, dypingite (Mg5(CO3)4(OH)2.5H2O) which is sometimes referred to as heavy magnesium carbonate, giorgiosite (Mg5(CO3)4(OH)2.5-6H2O) and shelkovite (Mg7(CO3)5(OH)4.24H2O). Component (f)(i) is present in the composition in an amount of from 0.05 to 2.0 wt. % of the composition, alternatively from 0.1 to 1.5 wt. % of the composition, alternatively from 0.1 to 1.25 wt. % of the composition alternatively from 0.15 to 1.25 wt. % of the composition. Component (f)(ii) (f)(ii), when present, is selected from cyanuric acid, urea, biuret, N,N′- urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition; For the avoidance of doubt: Cyanuric acid exists in a tautomeric equilibrium of 1,3,5-triazine-2,4,6-triol, (structure 1 below) and its tri-keto tautomer 1,3,5-Triazinane-2,4,6-trione (structure 2 below). It is to be understood that reference to cyanuric acid herein is to be considered to cover both tautomers. H2N-C(=O) – N(H)-C(=O)-NH2 It has several alternative names such as 2-imidodicarbonic diamide and carbamylurea but will be referred to herein as biuret. Furthermore, urea has the structure O urea has the structure composition herein in an amount of from 0.005 to 0.2 wt. % of the composition and in each case is widely commercially available. Optional Additives Such hydrosilylation curable silicone rubber compositions may also comprise one or more optional additives depending on the intended use. Examples include cure inhibitors, pigments / colorants Non-reinforcing fillers, Silicone resins, which may or may not comprise active groups such as alkenyl groups; mold releasing agents, adhesion promoters, compression set additives electrically conductive fillers, thermally conductive fillers, pot life extenders, lubricants, heat stabilisers, metal deactivators, UV light stabilizers, bactericides, wetting agents and the like. Cure Inhibitors Cure inhibitors are used, when required, to prevent or delay the addition-reaction curing process especially during storage. The optional addition-reaction inhibitors of platinum-based catalysts are well known in the art and include hydrazines, triazoles, phosphines, mercaptans, organic nitrogen compounds, acetylenic alcohols, silylated acetylenic alcohols, maleates, fumarates, ethylenically or aromatically unsaturated amides, ethylenically unsaturated isocyanates, olefinic siloxanes, unsaturated hydrocarbon monoesters and diesters, conjugated ene-ynes, hydroperoxides, nitriles, and diaziridines. Alkenyl-substituted siloxanes as described in US3989667 may be used, of which cyclic methylvinylsiloxanes are preferred. One class of known hydrosilylation reaction inhibitors are the acetylenic compounds disclosed in US3445420. Acetylenic alcohols such as 2-methyl-3-butyn-2-ol constitute a preferred class of inhibitors that will suppress the activity of a platinum-containing catalyst at 25 ºC. Compositions containing these inhibitors typically require heating at temperature of 70 ºC or above to cure at a practical rate. Examples of acetylenic alcohols and their derivatives include 1-ethynyl-1-cyclohexanol (ETCH), 2- methyl-3-butyn-2-ol, 3-butyn-1-ol, 3-butyn-2-ol, propargyl alcohol, 1-phenyl-2-propyn-1-ol, 3,5- dimethyl-1-hexyn-3-ol, 1-ethynylcyclopentanol, 3-methyl-1-penten-4-yn-3-ol, and mixtures thereof. Derivatives of acetylenic alcohol may include those compounds having at least one silicon atom. When present, inhibitor concentrations as low as 1 mole of inhibitor per mole of the metal of catalyst will in some instances impart satisfactory storage stability and cure rate. In other instances, inhibitor concentrations of up to 500 moles of inhibitor per mole of the metal of catalyst are required. The optimum concentration for a given inhibitor in a given composition is readily determined by routine experimentation. Dependent on the concentration and form in which the inhibitor selected is provided / available commercially, when present in the composition, the inhibitor is typically present in an amount of from 0.0125 to 10% by weight of the composition. In one embodiment the inhibitor when present is selected from 1-ethynyl-1-cyclohexanol (ETCH) and / or 2-methyl-3-butyn-2-ol and is present in an amount of greater than zero to 0.1 % by weight of the composition. Non-Reinforcing Fillers Non-reinforcing fillers may include crushed quartz, diatomaceous earths, barium sulphate, iron oxide, titanium dioxide and carbon black, talc, wollastonite. Other fillers which might be used alone or in addition to the above include aluminite, calcium sulphate (anhydrite), gypsum, calcium sulphate, clays such as kaolin, magnesium hydroxide e.g., brucite, graphite, copper carbonate, e.g., malachite, nickel carbonate, e.g., zarachite, barium carbonate, e.g., witherite and / or strontium carbonate e.g., strontianite. Other fillers may include, aluminum oxide, silicates from the group consisting of olivine group; garnet group; aluminosilicates; ring silicates; chain silicates; and sheet silicates. The olivine group comprises silicate minerals, such as but not limited to, forsterite and Mg2SiO4. The garnet group comprises ground silicate minerals, such as but not limited to, pyrope; Mg3Al2Si3O12; grossular; and Ca2Al2Si3O12. Aluminosilicates comprise ground silicate minerals, such as but not limited to, sillimanite; Al2SiO5; mullite; 3Al2O3.2SiO2; kyanite; and Al2SiO5. Ring silicates may be utilized as non-reinforcing fillers, these include silicate minerals, such as but not limited to, cordierite and Al3(Mg,Fe)2[Si4AlO18]. The chain silicates group comprises ground silicate minerals, such as but not limited to, wollastonite and Ca[SiO3]. Sheet silicates may alternatively or additionally be used as non-reinforcing fillers where appropriate group comprises silicate minerals, such as but not limited to, mica; K2AI14[Si6Al2O20](OH)4; pyrophyllite; Al4[Si8O20](OH)4; talc; Mg6[Si8O20](OH)4; serpentine for example, asbestos; Kaolinite; Al4[Si4O10](OH)8; and vermiculite. Low viscosity Polymers Silicone polymers having the same description as component (a) may be incorporated into the composition. Typically, they may have a viscosity of 100 to 750mPa.s at 25oC measured using a BrookfieldTMrotational viscometer with a cone plate arrangement with cone CP-52 at 12rpm. Silicone Resins Optional silicone resins may comprise silicone resins containing unsaturated groups selected from alkenyl groups, alkynyl groups or a mixture of alkenyl groups and alkynyl groups, selected from T silicone resins (silsesquioxanes), DT silicone resins, MQ silicone resins, MDT silicone resins, MTQ silicone resins, QDT silicone resins or mixtures thereof. MQ resins are particularly preferred. Such resins using the MDTQ notation described previously comprise Q type (SiO4 / 2) siloxane units T type (R21SiO3 / 2) siloxane units; D type (R21SiO3 / 2) siloxane units and R2₃SiO1 / 2(M) siloxane units as indicated. These resins can be classified into two broad categories: silsesquioxanes and silicates. Silsesquioxanes, or T resins, are predominantly comprised of T units and can be synthesized by the hydrolysis and condensation of alkoxysilanes, chlorosilanes, or mixtures thereof. Silicates, or MQ resins, are predominantly comprised of M and Q units and can be synthesized through the hydrolysis and condensation of alkoxysilanes and chlorosilanes. Alternatively, MQ resins can be synthesized through the polymerization of aqueous alkali silicates in the presence of acid followed by reaction with triorgano alkoxysilanes, triorgano chlorosilanes, hexaorganodisiloxanes or mixtures thereof. Preferably, when present the silicone resins are one or more MQ resins. Typically, the MQ resins when present, comprise SiO4 / 2 (Q) siloxane units and R2₃SiO1 / 2 (M) siloxane units wherein each R2may be the same or different and denotes a monovalent group selected from hydrocarbon groups, having from 1 to 20 carbon atoms and, alternatively from 1 to 12 carbon atoms. Examples of suitable R2groups include alkyl groups, such as methyl, ethyl, propyl, pentyl, octyl, undecyl and octadecyl; cycloaliphatic groups, such as cyclohexyl; alkenyl groups, having from 2 to 12 carbons, such as vinyl, propenyl, butenyl, pentenyl, hexenyl, and the like; alkynyl groups selected from ethynyl, propynyl, butynyl, pentynyl or hexynyl and the like; aryl groups such as phenyl, tolyl, xylyl, benzyl, alpha-methyl styryl and 2-phenylethyl; alternatively R2groups are vinyl, methyl, ethyl or phenyl groups, e.g., examples of preferred R2₃SiO1 / 2(M) siloxane units include Me₃SiO1 / 2, PhMe₂SiO1 / 2, ViMe₂SiO1 / 2and Ph₂MeSiO1 / 2,where Me hereinafter denotes methyl, Vi is vinyl and Ph hereinafter denotes phenyl. T silicone resins may alternatively be referred to as silsesquioxanes. The silicone resin (f), when present, is typically delivered in a hydrocarbon or silicone solvent, free from solvent the silicone resin is typically a solid but in one embodiment herein the silicone resin is delivered in a silicone solvent such as a non-functional polydimethylsiloxane or a polydimethylsiloxane comprising two or more alkenyl groups per molecule, such as for example component (a) herein. For example, any suitable MQ resin may be utilized if required. The molar ratio of M siloxane units to Q siloxane units has a value of from 0.5:1 to 1.2:1, alternatively 0.6:1 to 1.1:1, alternatively 0.8:1 to 1.1:1, alternatively 0.9:1 to 1.1:1. In one embodiment MQ resin (e) includes a resinous portion wherein the M units are bonded to SiO4 / 2 siloxane units (i.e., Q units) and each of Q units is bonded to at least one other SiO4 / 2 siloxane unit. The molar ratio of M units to Q units is from 0.3 : 1 to 1.2 : 1, alternatively 0.4:1 to 1.1:1, alternatively 0.5:1 to 1:1, alternatively 0.6:1 to 0.9:1. Such an MQ resin may have a number-average molecular weight (Mn) of from 2000 to 50,000g / mol, alternatively from 3,000 to 30,000 g / mol. In one embodiment, when present, the silicone resin may be mixed with component (a) as herein described and the silicone resin may be an alkenyl-containing silicone resin that comprises Q units (SiO4 / 2) and M units with vinyldialkylsiloxy M units e.g., vinyldimethylsiloxy M units and trialkylsiloxy M units e.g., trimethylsiloxy M units. Typically, the alkyl groups have from 1 to 12, alternatively 1 to 6 carbons, alternatively are methyl or ethyl groups., wherein the alkenyl group is present in the range from 0.5 wt. % to 3.5 wt. % of the resin with the resin comprising from 40 to 80 wt. % of the mixture. Optional Pigments / Colorants The hydrosilylation curable flame-retardant silicone rubber composition as described herein may further comprise one or more pigments and / or colorants which may be added if desired. The pigments and / or colorants may be coloured, white, black, metal effect, and luminescent e.g. fluorescent and phosphorescent. Suitable white pigments and / or colorants include titanium dioxide, zinc oxide, lead oxide, zinc sulfide, lithophone, zirconium oxide, and antimony oxide. Suitable non-white inorganic pigments and / or colorants include, but are not limited to, iron oxide pigments such as goethite, lepidocrocite, hematite, maghemite, and magnetite black iron oxide, yellow iron oxide, brown iron oxide, and red iron oxide; blue iron pigments; chromium oxide pigments; cadmium pigments such as cadmium yellow, cadmium red, and cadmium cinnabar; bismuth pigments such as bismuth vanadate and bismuth vanadate molybdate; mixed metal oxide pigments such as cobalt titanate green; chromate and molybdate pigments such as chromium yellow, molybdate red, and molybdate orange; ultramarine pigments; cobalt oxide pigments; nickel antimony titanates; lead chrome; carbon black; lampblack, and metal effect pigments such as aluminum, copper, copper oxide, bronze, stainless steel, nickel, zinc, and brass. Suitable organic non-white pigments and / or colorants include phthalocyanine pigments, e.g. phthalocyanine blue and phthalocyanine green; monoarylide yellow, diarylide yellow, benzimidazolone yellow, heterocyclic yellow, DAN orange, quinacridone pigments, e.g. quinacridone magenta and quinacridone violet; organic reds, including metallized azo reds and nonmetallized azo reds and other azo pigments, monoazo pigments, diazo pigments, azo pigment lakes, β-naphthol pigments, naphthol AS pigments, benzimidazolone pigments, diazo condensation pigment, isoindolinone, and isoindoline pigments, polycyclic pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, and diketopyrrolo pyrrole pigments. The pigments and / or colorants, when present, are present in the range of from 2 wt. %, alternatively from 3 wt. %, alternatively from 5 wt. % of the composition to 15 wt. % of the composition, alternatively to 10 wt. % of the composition. Mold release agent Any suitable mold release agent may be utilised. It may, for example, be a hydroxydimethyl terminated polydimethylsiloxane having viscosity of approximately 21 mPa.s at 25oC measured using a BrookfieldTMrotational viscometer with spindle LV-2 at 12rpm. Compression Set additives Any suitable compression set additives may be included in the composition. These may include, for example, 2-Hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide which is sold commercially as ADK STABTMCDA-1 from Adeka Corporation and 1-N',12-N'-bis(2- hydroxybenzoyl)dodecanedihydrazide which is sold commercially as ADK STABTMCDA-6 from Adeka Corporation. Lubricants Any suitable lubricants may be used. Examples of suitable lubricants silicone containing oils such as trimethylsilyl terminated phenylmethylsiloxane dimethylsiloxane copolymers having a viscosity of from 100mPa.s to 200mPa.s at 25oC using the viscosity test methodology as described for component (a) and mixtures or derivatives thereof. The hydrosilylation curable silicone rubber compositions described above are usually stored before use in two or more parts. In the case of a two-part composition, the two parts are usually referred to as part (A) and part (B): Part (A) typically contains the catalyst (d) in addition to polyorganosiloxane (a) and silica reinforcing filler (c), and Part (B) usually contains cross-linker component (b), and when present optional inhibitor as well as the remaining polyorganosiloxane (a) and the remaining silica reinforcing filler (c). It is important for the catalyst (d) to be stored separately from cross-linker (b) to prevent premature cure during storage. Components (e) and when present (f)(i) and (f)(ii) may be stored in either part (A) or part (B) or in both parts providing they do not negatively affect the storage of any of the essential ingredients present in the respective part, including each other of said components (e) and (f). Alternatively, components (e) and (f)(i) when present are stored in the Part (B) composition and component (f)(ii) is stored in the Part (A) composition. Alternatively, if desired components (e) and if present (f)(i) and / or (f)(ii) may be added into the remaining composition i.e., to the combination of the part (A) and part (B) compositions during or after the part (A) composition and the part (B) compositions are mixed together prior to use. Any optional additives, other than the inhibitor described above, may be incorporated into either part (A) or part (B) or in both parts providing they do not negatively affect the storage of any of the essential ingredients present in the respective part. The compositions can be designed to be mixed in any suitable ratio e.g., part (A) : part (B) may be mixed together in ratios of from 10:1 to 1:10, alternatively from 5:1 to 1:5, alternatively from 2:1 to 1:2, but most preferred is a ratio of 1:1. Ingredients / components in each of Part (A) and / or Part (B) may be mixed together individually in their respective part or may be introduced into the composition in pre-prepared in combinations for, e.g., ease of mixing the final composition. For Example, components (a) and (c) are often mixed together to form an LSR polymer base or masterbatch prior to introduction of other ingredients. These may then be mixed with the other ingredients of the Part being made directly or may be used to make pre-prepared concentrates commonly referred to in the industry as masterbatches. In this instance, for ease of mixing ingredients, one or more masterbatches may be utilized to successfully mix the ingredients to form Part (A) and / or Part (B) compositions. For example, a “fumed silica” masterbatch may be prepared. This is effectively an LSR silicone rubber base with the silica reinforcing filler (c) treated in situ. Parts A and B of the composition may be prepared by combining all of their respective components at ambient temperature. Any mixing techniques and devices described in the prior art can be used for this purpose. The particular device to be used will be determined by the viscosities of components and the final composition. A suitable mixer may include but are not limited to kneader mixer, a static mixer in a liquid injection molding machine, a Z-blade mixer, a planetary mixer, a two-roll mill (open mill), a three-roll mill, a HaakeTMRheomix OS Lab mixer, a screw extruder or a twin-screw extruder or the like. Speed mixers as sold by e.g., Hauschild and as DC 150.1 FV, DAC 400 FVZ or DAC 600 FVZ, may alternatively be used. Cooling of components during mixing may be desirable to avoid premature curing of the composition. Prior to use the respective Part (A) and Part (B) compositions are mixed together in the desired ratio, typically a weight ratio. Curing of the hydrosilylation curable silicone rubber composition on the substrate can, for example, take place in a mold to form a molded part, by injection molding, using e.g., a Liquid injection molding system (LIMS) press moulding, extrusion moulding, transfer moulding, press vulcanization, or calendaring. In the case of a process for the manufacture of a two-part silicone rubber composition as hereinbefore described the process may comprise the steps: (i) preparation of a silicone base composition comprising components (a) polymer and (c) silica reinforcing filler, (ii) dividing the resulting base into two parts, part (A) and part (B) and introducing the catalyst (d) into part (A) and the cross-linker (b) and inhibitor (if present) in the part (B) composition. (iii) Introducing the other components any other optional additives into either or both part (A) and part (B); and (iv) Storing the part (A) and part (B) compositions separately. In an alternative process component (e) is not introduced into either component (A) or component (B) when separate but is introduced as part of the mixing process when the part (A) and part (B) compositions are mixed together prior to use e.g., during mixing prior to injection molding. Typically, the part (A) and part (B) compositions are thoroughly mixed in the required weight ratio as described above, immediately before use in order to avoid premature cure. The curing stage cure is then undertaken. If / when component (e), and when present (f)(i) and / or (f)(ii) is / are introduced during the mixing process together with part (A) and part (B) typically the weight ratio of part (A) and part (B) will remain the same, e.g., if part (A) and part (B) are mixed in a 1 : 1 weight ratio there might be for example 49.5 wt. % of each of part (A) and part (B) and 1 wt. % of component (e), (f) or the mixture thereof mixed together before curing e.g., by molding. The silicone elastomer compositions and methods herein may be utilised in a wide variety of applications, for example, in a wide range of electrical and / or insulative applications. In one embodiment there is also provided herein the use of flame-retardant silicone rubber material being the cured product of the hydrosilylation curable flame-retardant silicone rubber composition described above as a means of electrical insulation on a part of an electrical power supply means, for example as a means of electrical insulation of an electrical power insulator selected from a suspension insulator, a tension insulator, a post insulator a railway insulator a hollow core insulator and / or as insulation for an electrical power cable, a busbar or a surge arrestor. There is also provided herein an electrical power cable comprising: o an electrically conductive core; o one or more layers of insulation around said core and o an outer sheath made from the flame-retardant silicone rubber being the cured product of the above composition. The outer sheath of such electric cables e.g., may be used for example high voltage power cable in electrical vehicles and high-speed trains, in high heat resistant rubber for turbo charger hoses but are mainly intended for electrical power supply. The outer sheath may be applied by any suitable method, for example by extrusion. Furthermore, the composition herein may be used in or for the manufacture of automotive parts, cable accessories; electrical and electronic parts; packaging parts; construction parts; household parts; and gasket sealants. EXAMPLES All viscosities were measured at 25oC unless otherwise indicated. Viscosities of individual components in the following examples were measured using a BrookfieldTMrotational viscometer with spindle LV-4 for viscosities over 15,000mPa.s (Spindle LV-4 designed for viscosities in the range between 1,000-2,000,000 mPa.s) at an appropriate rpm and using a BrookfieldTMrotational viscometer with a cone plate arrangement with cone CP-52 for viscosities up to 15, 000mPa.s at an appropriate rpm unless otherwise indicated. Table 1: 2-part liquid silicone rubber elastomer compositions (Elas.1 and 2) Elas.1 Part A Elas.1 Part B Elas.2 Part A Elas.2 Part B Resin masterbatch 1 40.73 33.03 40.93 32.39 Polymer 1: polymer 1 is a vinyldimethyl terminated polydimethylsiloxane having a viscosity of 53,000mPa.s at 25oC measured using a BrookfieldTMrotational viscometer with spindle LV-4 at 6rpm, Resin masterbatch 1: is a blend of a Resin 1 in polymer 2 in a 33.5 : 66.5 weight ratio; Resin 1: is a vinyldimethyl and trimethylated MQ resin having a vinyl content of 1.95 wt. % Polymer 2: was a Vinyldimethylsiloxy-endcapped polydimethylsiloxane having a viscosity of about 2100 mPa.s CP-52 cone plate and a vinyl content of 0.26 wt. %) Silica 1 is fumed silica filler having a surface area of approximately 400 m2 / g. The silica is hydrophobized and contains vinyl functionalization; Resin masterbatch 2: was a blend of 64.6 wt. % polymer 1 and 34.4 wt. % of Resin 1 Cross-linker 1: is a dimethyl methylhydrogen siloxane methylsilsesquioxane mixture having a capillary viscosity of 15 mm2 / s (cSt) measured in accordance with ASTM D-445 and a hydrogen content as Si-H of 0.811 wt.%. Karstedt’s catalyst was supplied in a premix of 1.27 wt.% of Pt2(divinyl tetramethyl disiloxane)3 diluted in 98.73 of polymer 3; Polymer 3: polymer 3 is a vinyl terminal poly(dimethylsiloxane-co-methylvinylsiloxane) having a viscosity of 450 mPa.s at 25°C using a BrookfieldTMrotational viscometer with a cone plate arrangement with cone CP-52 at 12rpm, Inhibitor was 1-ethynyl-1-cyclohexanol (ETCH) Colour paste: was a colorant additive used to colour elastomer 2 composition. The colour paste contained about 35 wt. % titanium dioxide (TiO2). A series of comparative examples omitting any component (e) (C.1 to C.5) were prepared using elastomer compositions 1 and 2 depicted in Table 1 and the compositions prepared are depicted in Table 2. Table 2: Comparative compositions C.1 to C.5 prepared using Elas.1 and 2 depicted in Table 1 with cyanuric acid and hydromagnesite (wt. %) C.1 C.2 C.3 C.4 C.5 Elas 1 Part A 5000 5 0 e co po e s o eac co pos o epc e a e a o e were weighed and homogenized in a Hauschild dental highspeed mixer. In use the respective. Part (A) and part (B) compositions for each Elas. were prepared separately and then mixed together in a 1 : 1 weight ratio. Test plates for 3mm UL94 V0 tests were prepared and the compositions thereon were cured at 135°C for 10 minutes. The resulting test plates with cured silicone elastomeric material thereon were then stored in accordance with the UL94 requirements for 48hours (h) at room temperature and50% relative humidity. Subsequent to the required storage period each sample was evaluated for flame retardant behavior via the flammability test according to the International Electrotechnical Commission (IEC) 6069511-10 test i.e. the UL 94 test utilised for vertical burning. Individual test specimens having been cut to dimensions of 13 mm x125 mm x 3 mm. The t1, t2 and t3 results in accordance with IEC 6069511-10 for each elastomer prepared are provided in Table 3. Table 3: The t1, t2 and t3 results in accordance with IEC 6069511-10 for comparative compositions C.1 to C.5 as well as the t2 + t3 values. C.1 C.2 C.3 C.4 C.5 t1 [s] 4.4 6.2 4.6 9.0 8.0 t1 is the “Afterflame time” after a first flame application in accordance with the test method; t2, is the Afterflame time after the second flame application, t2 in accordance with the test method; and t3 is the afterglow time after said second flame application in accordance with the test method; Wherein an “afterflame” is defined as a flame which persists after the ignition source has been removed. The afterflame Time is the length of time during which an afterflame persists under the test conditions. Afterglow is the persistence of glowing combustion after both removal of the ignition source and the cessation of any flaming and the afterglow Time is the length of time during which an afterglow persists under test conditions. The only difference between C.1 and C.2 was that C.2 contained the colour paste comprising TiO2. It was found that the presence of the TiO2 resulted in only slightly higher value for t1 in C.2, but clear reduction in t2. The addition of cyanuric acid appears to have greatly reduced the value of t3 in C.2 but moved t2 again to higher times. It was found that C4 and C5: while holding t1 on slightly increased time scale, cyanuric acid and magnesium carbonate together balanced negative impact of TiO2present in the colour paste. It appeared that the presence of a larger amount of hydromagnesite in C.5 than C. 4 demonstrated a noteworthy reduction in t2 time but no effect on t1 flame period and consequently the combined t1+t2 times resulted in a V-1 rating. A series of examples (Ex.1 to Ex.4) in accordance with this disclosure were prepared and the composition prepared are depicted in Table 4. Table 4: Examples Ex.1 to Ex.4 prepared using Elas.1 depicted in Table 1 with an assortment of antioxidants (wt. %) Ex.1 Ex.2 Ex.3 Ex.4 Elas.1 Part A 50.00 50.00 50.00 50.00 (1,3,5-Trimethyl-2,4,6- tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene) Antioxidant 2 was dodecyl 3,4,5-trihydroxybenzoate; Antioxidant 3 was Methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate; and Antioxidant 4 was 2,2 -Methylene-bis(6-tert-butyl-4-methylphenol). The Ex.1 to Ex.4 compositions in Table 4 were prepared in a similar fashion as above and cured. Subsequently they were tested in accordance with IEC 6069511-10 and the t1, t2 and t3 results in accordance with IEC 6069511-10 for each elastomer prepared are provided in Table 5 below and are also compared to comparative C.1. Table 5: The t1, t2 and t3 results in accordance with IEC 6069511-10 for Ex.1 to Ex.4 and for C. 1 as well as the t2 + t3 values. C.1 Ex.1 Ex.2 Ex.3 Ex.4 It was found from the results of Table 5 that the elastomers of Ex 1, 2, 3 and 4 show clear reductions in both t2 and t3 times and consequently reduced t2 + t3 times. This resulted in less formation of volatiles during the first afterflame time, as well as reduced glowing, when the Ex 1, 2, 3 and 4 elastomers contained Antioxidant 1, 2, 3, and 4 respectively. Combined [t1 + t2] afterflame times ended with most examples having a combined value of about 10 seconds i.e., approximately in the range of V-1. A further series of examples (Ex.5 to 9) in accordance with this disclosure were prepared and the compositions prepared are depicted in Table 6. Table 6: Compositions of Ex.5 to Ex.9 (wt. %) Ex.5 Ex.6 Ex.7 Ex.8 Ex.9 Elas.1 Part A 50.00 , . The Ex.5. to Ex.9 compositions in Table 6 were prepared in a similar fashion as above and cured. Subsequently they were tested in accordance with IEC 6069511-10 and the t1, t2 and t3 results in accordance with IEC 6069511-10 for each elastomer prepared are provided in Table 7 below and are compared with previously prepared results C.1 and C.2. Table 7: The t1, t2 and t3 results in accordance with IEC 6069511-10 for Ex.5 - 9 as well as the t2 + t3 values compared with C.1 and C.2. C.1 C.2 Ex.5 Ex.6 Ex.7 Ex.8 Ex.9 It can be seen that when comparing Ex.5 to C.1 a clear improvement in respect to t2, t3 and consequently t2 + t3 with magnesium oxide and antioxidant 2. Again, a comparison of Ex.6 and Ex.7 with C2 (containing TiO2) clear improvements can be seen with Antioxidant 1in combination with cyanuric acid. A further series of examples (Ex.10 to 12) in accordance with this disclosure were prepared and the compositions prepared are depicted in Table 8. Table 8: Compositions of Ex.10 to Ex.12 (wt. %) Ex.10 Ex.11 Ex.12 Elas.2 Part A 49.95 49.95 49.95 r fashion as above and cured. Subsequently they were tested in accordance with IEC 6069511-10 and the t1, t2 and t3 results in accordance with IEC 6069511-10 for each elastomer prepared are provided in Table 9 below. Table 9: The t1, t2 and t3 results in accordance with IEC 6069511-10 for Ex.10 -12 as well as the t2 + t3 values. Ex.10 Ex.11 Ex.12 Ex.10 – 12 demonstrate clear V0 flame retardant performance for 3mm thickness with cyanuric acid incorporated showing best t2 / t3 impact. The inclusion of urea additives gave minimal loss in t2 / 3. A further series of examples Ex.13 to 18 in accordance with this disclosure were prepared and the compositions prepared are depicted in Table 10 below.

[0004] Table 10: Compositions of Ex.13 to Ex.18 (wt. %) Ex.13 Ex.14 Ex.15 Ex.16 Ex.17 Ex.18 Elas.2 Part A 50.00 50.00 49.975 49.95 49.95 49.975 Antioxidant 5 was tannic acid; and Antioxidant 6 was IrganoxTM1076 (Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate) The Ex.13 to Ex.18 compositions in Table 10 were prepared in a similar fashion as above and cured. Subsequently they were tested in accordance with IEC 6069511-10 and the t1, t2 and t3 results in accordance with IEC 6069511-10 for each elastomer prepared are provided in Table 11 below. Table 11: The t1, t2 and t3 results in accordance with IEC 6069511-10 for Ex.13 - 18 as well as the t2 + t3 values. Ex.13 Ex.14 Ex.15 Ex.16 Ex.17 Ex.18 Ex.13 and 14 (having TiO2) both test result in V0; MgO tends to support good t1 times while magnesium carbonate loses on t1 but shows good impact on t2 / t3. Ex 15 to 18: Addition of cyanuric acid can be seen to balancing t1 versus t2 / t3 (in the presence of TiO2). A further series of compositions were prepared using alternative 2-part liquid silicone rubber elastomer compositions (Elas.3, 4 and 5) as depicted in Table 12 as the standard starting compositions: Table 12: 2-part liquid silicone rubber elastomer compositions (Elas.3, 4 and 5) Elas.3 Elas.3 Elas.4 Elas.4 Elas.5 Elas.5 Part A Part B Part A Part B Part A Part B , , d and: Masterbatch 1: Masterbatch 1 contains: 70.8 parts by weight of Polymer 1 (described above), and 22.4 parts by weight of a fumed silica filler having a surface area of approximately 300m2 / g. The silica is hydrophobized and contains no vinyl functionalization; Masterbatch 2: Masterbatch 2 contains: 66.6 parts by weight of a Polymer 1 (described above), and 25.8 parts by weight of a fumed silica filler having a surface area of approximately 300m2 / g. The silica is hydrophobized and has a vinyl functionalization of approximately 0.178 mmol / g. The parts by weight values given above are not percentage values and therefore do not need to add to one hundred. Cross-linker 2: Cross-linker 2 was a trimethyl terminated polymethylhydrogen dimethylsiloxane having a viscosity of 30mPa.s at 25oC using a BrookfieldTMrotational viscometer with a cone plate arrangement with cone CP-52 at 12rpm. Mold release Agent: The mold release agent was a hydroxydimethyl terminated polydimethylsiloxane having viscosity of approximately 21 mPa.s at 25oC measured using a BrookfieldTMrotational viscometer with spindle LV-2 at 12rpm. Cyclotetrasiloxane: The cyclotetrasiloxane was tetravinyl-tetramethyl-cyclotetrasiloxane. Phenylmethyl siloxane copolymer: the phenylmethyl siloxane copolymer was Trimethylsilyl terminated phenylmethylsiloxane dimethylsiloxane copolymer having a viscosity of 125 mPa.s at 25°C using a BrookfieldTMrotational viscometer with a cone plate arrangement with cone CP-52 at 12rpm. CDA 6: was dodecanedioyl-di-(N′-salicyloyl)hydrazine, a synonym for which is 1-N',12-N'-bis(2- hydroxybenzoyl)dodecanedihydrazide, which is sold commercially as ADK STABTMCDA-6 from Adeka Corporation. In use the respective. Part (A) and part (B) compositions for each Elas. were prepared separately and then mixed together in a 1 : 1 weight ratio. The above part A and part B compositions of Elas.3, part A and part B compositions of Elas.4 and part A and part B compositions of Elas.5 were utilised to make the samples tested in Table 13 below. Table 13: Compositions using Elas.3, 4 and 5 and assorted additives (wt. %) C.6 Ex.19 C.7 Ex.20 C.8 Ex.21 Ex.22 Elas 3 Part A 5000 49975 5 In the above Table Antioxidants 1 and 5 are as previously defined. The compositions prepared in accordance with the compositions of Table 13 were prepared in a similar fashion as above and cured. Subsequently they were tested in accordance with IEC 60695 11-10 and the t1, t2 and t3 results in accordance with IEC 6069511-10 for each elastomer prepared are provided in Table 14 below. Table 14: The t1, t2 and t3 results in accordance with IEC 6069511-10 for the compositions in Table 13 as well as the t2 + t3 values. C.6 Ex.19 C.7 Ex.20 C.8 Ex.21 Ex.22 t1 [s] 4.8 0 7.0 7.0 9.0 7.4 7.2 nt in the results for Ex.19 in each of t1, t2, and t3 and consequently also t2 + t3. Whilst C.7 and Ex.20 had not dissimilar t1 results it can be seen that Ex.20 had comparatively better t2 and t3 results and consequently t2 + t3 results. Comparative C.8 demonstrates a high t1 value indicating a higher flammable content than other elastomers tested and certainly when compared to Ex.21 and Ex.22, Ex.21 and Ex.22 gave much improved t1, t2, t3 and consequently t2 + t3 results. A series of physical property tests were undertaken to assess the effect of using component (e) the antioxidants as hereinbefore described and the results comparing comparative C.2 and Ex.8 are provided below in Table 15. Table 15: Physical property comparison of C.2 and Ex.8 C.2 Ex.8 Shore A hardness was measured in accordance with ASTM D 2240 Tensile strength and elongation at break results were measured in accordance with ASTM D412 Tear strength was measured in accordance with ASTM D624 utilising Die B. It will be seen that the addition of the antioxidants of component (e) herein did not have a significant effect on the physical properties of the elastomers produced using the compositions herein. The tensile strength and elongation results are slightly reduced for Ex.8, but the hardness and tear strength results were pretty much unaffected.

Claims

WHAT IS CLAIMED IS:

1. A two-part hydrosilylation curable silicone rubber composition, which comprises the following components: a) one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule and having a viscosity in a range of from 1000 mPa.s to 750,000 mPa.s at 25oC; b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule; c) a silica reinforcing filler which is optionally hydrophobically treated; d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; e) a flame-retardant additive comprising one or more phenolic antioxidants selected from an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, tannic acid, 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzenealkyl 3-(3,5-di-tert-butyl-4- hydroxyphenyl)propanoate wherein the alkyl group contains from 1 to 20 carbons and 2,2'- Methylene-bis(6-tert-butyl-p-cresol); and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii), where: f)(i) is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, in an amount 0.05 to 2.0 wt. % of the composition; and f)(ii) is a component selected from cyanuric acid, urea, biuret, N,N′-Bis(trimethylsilyl)urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition; wherein the two parts are Part (A) and Part (B) wherein Part (A) comprises a proportion of components (a) and (c) and all of component (d) and Part (B) comprises the remainder of components (a) and (c) and all of component (b).

2. A two-part hydrosilylation curable silicone rubber composition in accordance with claim 1 wherein flame-retardant additive (e) is selected from a dodecyl 3,4,5-trihydroxybenzoate; tannic acid; 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene a methyl 3-(3,5-di-tert- butyl-4-hydroxyphenyl)propanoate; and 2,2'-Methylene-bis(6-tert-butyl-p-cresol).

3. A two-part hydrosilylation curable silicone rubber composition in accordance with claim 1 which comprises component (f)(i), component (f)(ii) or both component (f)(i) and component (f)(ii).

4. A two-part hydrosilylation curable silicone rubber composition in accordance with claim 1 wherein component (f)(i) is a magnesium carbonate, a magnesium hydroxy carbonate or a mixture thereof is selected from MgCO3, MgCO3.2H2O, MgCO3.3H2O, MgCO3.5H2O,Mg2(CO3)(OH)2.0.5H2O, Mg2(CO3)(OH)2.3H2O, Mg5(CO3)4(OH)2.4H2O, Mg5(CO3)4(OH)2.5H2O, Mg5(CO3)4(OH)2.5-6H2O and Mg7(CO3)5(OH)4.24H2O.

5. A two-part hydrosilylation curable silicone rubber composition in accordance with claim 1 wherein component (f)(ii) is urea.

6. A two-part hydrosilylation curable silicone rubber composition in accordance with any preceding claim which additionally comprises one or more additives selected from cure inhibitors, pigments / colorants, Non-reinforcing fillers, Silicone resins; mold releasing agents, adhesion promoters, compression set additives, electrically conductive fillers, thermally conductive fillers, pot life extenders, lubricants, heat stabilisers, metal deactivators, UV light stabilizers, bactericides and wetting agents.

7. A silicone elastomeric material which is the cured product of the hydrosilylation curable silicone rubber composition in accordance with preceding claim, which silicone elastomeric material has a UL94 V-0 performance at a sample thickness of 3 mm measured in accordance with IEC 6069511-10.

8. A process for making a silicone elastomeric material in accordance with claim 7 comprising the steps of preparing a Part (A) composition comprising: a proportion of component (a) one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule and having a viscosity in a range of from 1000 mPa.s to 750,000 mPa.s at 25oC; a proportion of component (c) a silica reinforcing filler which is optionally hydrophobically treated; and the whole of component (d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; preparing a Part (B) composition comprising: the remainder of component (a) the remainder of component (c); and the whole of component d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and comprising component (e) in Part (A), Part (B) or both Part (A) and Part (B) and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii) in Part (A), Part (B) or both Part (A) and Part (B); wherein e) is a flame-retardant additive comprising one or more phenolic antioxidants selected from an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, tannic acid, 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene alkyl 3-(3,5-di-tert- butyl-4-hydroxyphenyl)propanoate wherein the alkyl group contains from 1 to 20 carbonsand 2,2'-Methylene-bis(6-tert-butyl-p-cresol); and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii), where: f)(i) is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, in an amount 0.05 to 2.0 wt. % of the composition; and f)(ii) is a component selected from cyanuric acid, urea, biuret, N,N′-Bis(trimethylsilyl)urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition; mixing the Part (A) and Part (B) compositions together and curing at a temperature of from 80oC to 200oC.

9. A process for making a silicone elastomeric material in accordance with claim 8 which comprises in the part (A) composition, the Part (B) composition, or both, a component (f)(i), a component (f)(ii) or both component (f)(i) and component (f)(ii).

10. A process for making a silicone elastomeric material in accordance with claim 8 or 9 wherein component (f)(i) is a magnesium carbonate, a magnesium hydroxy carbonate or a mixture thereof selected from MgCO3, MgCO3.2H2O, MgCO3.3H2O, MgCO3.5H2O, Mg2(CO3)(OH)2.0.5H2O, Mg2(CO3)(OH)2.3H2O, Mg5(CO3)4(OH)2.4H2O, Mg5(CO3)4(OH)2.5H2O, Mg5(CO3)4(OH)2.5-6H2O and Mg7(CO3)5(OH)4.24H2O.

11. A process for making a silicone elastomeric material in accordance with claim 8 or 9 two- part hydrosilylation curable silicone rubber composition in accordance with claim 1 wherein component (f)(ii) is urea.

12. A silicone elastomeric material obtained or obtainable from the process of claims 8, 9, 10 or 11.

13. Use of a component (e) and optionally component (f)(i), (f)(ii) or both (f)(i) and (f)(ii) wherein e) is a flame-retardant additive comprising one or more phenolic antioxidants selected from an alkyl 3,4,5-trihydroxybenzoate wherein the alkyl group contains from 1 to 20 carbons, tannic acid, 1,3,5- Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, alkyl 3-(3,5-di-tert-butyl-4- hydroxyphenyl)propanoate wherein the alkyl group contains from 1 to 20 carbons and 2,2'- Methylene-bis(6-tert-butyl-p-cresol); and: f)(i) is one or more inorganic oxides selected from titanium dioxide, zirconium oxide, aluminum oxide, zinc oxide and / or a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, in an amount 0.05 to 2.0 wt. % of the composition; andf)(ii) is a component selected from cyanuric acid, urea, biuret, N,N′-Bis(trimethylsilyl)urea or a mixture thereof in an amount of from 0.005 to 0.2 wt. % of the composition; as a flame-retardant additive in a silicone elastomeric material whichcured product of a hydrosilylation curable silicone rubber composition, which otherwise comprises the following components: a) one or more polyorganosiloxanes containing at least two unsaturated groups, selected from alkenyl groups and alkynyl groups, per molecule and having a viscosity in a range of from 1000 mPa.s to 750,000 mPa.s at 25oC; b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule; c) a silica reinforcing filler which is optionally hydrophobically treated; d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof.

14. Use of flame-retardant silicone rubber being the cured product of the two-part hydrosilylation curable silicone rubber composition in accordance with any one of claims 1 to 6, as a means of electrical insulation.

15. Use of flame-retardant silicone rubber in accordance with claim 14, as a means of electrical insulation of an electrical power insulator selected from a suspension insulator, a tension insulator, a post insulator a railway insulator a hollow core insulator and / or as insulation for an electrical power cable, a busbar or a surge arrestor.

Images