Silicone rubber composition

Abstract

The present disclosure relates to curable silicone rubber compositions which are fire-resistant and ceramifiable upon cure, as well as fire-resistant, ceramifiable silicone rubber elastomers made upon the cure of said compositions and their applications and uses.

Description

[0001] SILICONE RUBBER COMPOSITION

[0002] The present disclosure relates to curable silicone rubber compositions which are fire-resistant and ceramifiable upon cure, as well as fire-resistant, ceramifiable silicone rubber elastomers made upon the cure of said compositions and their applications and uses.

[0003] Silicone rubber compositions which are formed by high temperature vulcanization (HTV) curable reactions are typically prepared by initially making a silicone rubber base composition by mixing polydiorganosiloxane polymers containing usually but not always at least two unsaturated groups selected from alkenyl groups, alkynyl groups or a mixture thereof per molecule with reinforcing silica fillers, and / or other reinforcing and non-reinforcing inorganic or resinous siloxane fillers.

[0004] HTV curable silicone rubber compositions are typically curable by hydrosilylation or by free radical initiation using e.g., peroxides Such compositions often incorporate very high viscosity organopolysiloxane polymers, i.e., organopolysiloxane polymers having a viscosity of at least one million mPa.s, often several million mPa.s, at 25°C. Such polymers are referred to in the industry as organopolysiloxane polymer gums, siloxane gums or silicone gums and the like (hereafter referred to as silicone gum(s)) because of their very high viscosity and high molecular weight. Because of the difficulty in measuring tire viscosity of such highly viscous fluids, silicone gums, tend to be defined by way of their Williams plasticity values in accordance with ASTM D926-08 as opposed to by viscosity. Reinforcing silica fillers, when used, are naturally hydrophilic which renders them difficult to inter-mix with tire polydiorganosiloxane polymer(s) and as such said fillers are usually either pre -treated with a treating agent to render them hydrophobic, or alternatively are provided in a hydrophilic form. In tire latter case a hydrophobic treating agent is usually (but not always) provided to treat the silica in situ during the silicone rubber base mixing process, i.e., incorporation and dispersion of silica in polymer is undertaken in the presence of a treating agent.

[0005] The product of this mixing step is typically referred to as a silicone rubber base. This may be provided in a form suitable for mixing with other ingredients as discussed below. Alternatively, it may be in the form of a concentrate (often referred to by the industry as a "masterbatch” (MB)) which is typically diluted with further polydiorganosiloxane polymer(s) before use. Once the silicone rubber base has been prepared, the other ingredients in the composition may be introduced and mixed into the silicone rubber base to form a final composition and which can then be cured.

[0006] Whilst silicone elastomers are well known for providing excellent heat resistance at elevated temperatures, e.g., up to 250°C or even higher, regrettably they do not have as good a level of fire resistance which is desired for some of the applications for which they are utilised unless provided with fire-resistant additives. In some applications the silicone rubber composition is provided with one or more ceramifiable fillers in an amount of from 25 wt. % or more of tire composition. These may include, but are not limited to, glass powder, alumina, wollastonite and / or mica. Wollastonite, for example, is a calcium metasilicate, comprising about 48.3 wt. % calcium oxide and subject to impurities tire remainder is substantially silicon dioxide. When a cured silicone rubber material is filled with a sufficient amount of ceramifiable filler(s), such as the above, upon burning the ceramifiable filler will form a solid char which, it has been proposed, can be used to surround and encase for the sake of example, cables and wires and the like in a fire situation. However, most of these materials are not fire-resistant and as such do not prevent fire.

[0007] High consistency rubbers (HCRs) exposed to fires can form problematic levels of volatile organic compounds (VOCs) that evaporate and ignite in air / oxygen atmospheres in the presence of a spark and / or fire. HCRs, without additive systems, are hardly self-extinguishing under vertical fire test conditions and regularly bum under vertical test conditions, sometimes even completely up to the clamp gripper. For electrical supply insulation applications, cable applications and busbar coating applications such as high voltage insulation, 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 VO performance of the HCR elastomer is highly favorable, if not mandatory, at a sample / coating thickness of 3 mm or less 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.

[0008] Several fire-resistant additives have been proposed to be used in silicone elastomeric materials to enhance their fire-resistant properties. Examples of fire-resistant additives proposed for use in peroxide cured silicone rubber elastomers to provide improved fire resistance include platinum materials such as platinum and platinum materials as described in US3514424A and US3635874A. Combinations of such platinum materials in combination with other additives including combinations with for example titanium dioxide, carbon black, group (II) metal oxides, rare earth metal oxides, rare earth metal hydroxides, benzotriazole, and / or an aromatic acid selected from the group consisting of mononuclear aromatic acids and halogenated mononuclear aromatic acids are known.

[0009] There remains an ongoing need for the development of improved ceramifiable silicone rubber elastomers with improved fire-resistant properties, especially in view of ever increasingly complex environmental, health and safety requirements.

[0010] There is provided herein a curable fire-resistant and ceramifiable silicone rubber composition comprising: (a) at least one organopolysiloxane polymer(s), optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule which organopolysiloxane polymer(s) (a) have a Williams plasticity value of at least 50mm / 100 in accordance with ASTM D926-08;

[0011] (b) optionally one or more reinforcing silica fillers, selected from fumed silica, colloidal silica and precipitated silica;

[0012] (c) ceramifiable filler consisting or comprising of wollastonite, which is present in an amount of from 25 to 60 wt. % of the composition;

[0013] (d) an organic peroxide curing agent.

[0014] (e) a fire -resistance additive comprising (i) platinum metal or a platinum metal compound comprising at least 3.0 ppm platinum metal content by weight with respect to the weight of the composition herein; and optionally one or both of (ii) one or more fillers selected from quartz, fumed silica, precipitated silica, hydromagnesite, huntite, calcium carbonate, mica, kaolin, aluminum hydroxide (ATH), magnesium hydroxide (MDH), talc, wollastonite, and montmorillonite; and

[0015] (iii) cerium hydroxide, cerium oxide, hydrous cerium oxide or a mixture comprising two or more thereof;

[0016] and

[0017] (f) one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or a mixture thereof, in an amount of from 0.1 to 3.0 wt. % of the composition.

[0018] A fire-resistant and ceramifiable silicone rubber elastomer which is tire cured product of tire above a curable fire-resistant and ceramifiable silicone rubber composition.

[0019] A method of making a fire-resistant, ceramifiable silicone rubber elastomer from a curable fire-resistant and ceramifiable silicone rubber composition as hereinbefore described; by tire following steps:

[0020] (A) when component (b) is present, preparing a silicone rubber base composition by mixing component (a) with component (b) and optionally some or all of component (c);

[0021] (B) Introducing components (d), (e) and (f) and all remaining component (c) into tire silicone base composition of step (A) when component (b) is present, or into component (a) when component (b) is not present, in any suitable order and mixing to prepare a curable fire-resistant and ceramifiable silicone rubber composition; and

[0022] (C) curing the curable fire-resistant and ceramifiable silicone rubber composition at a temperature of between 90 and 400°C.

[0023] A fire-resistant, ceramifiable silicone rubber elastomer which is the product of the above method.

[0024] Use of one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or a mixture thereof, (f) in an amount of from 0.1 to 3.0 wt. % of a curable ceramifiable silicone rubber composition; to enhance the fire -resistance properties of said curable ceramifiable silicone rubber composition, which curable ceramifiable silicone rubber composition otherwise comprises:

[0025] (a) at least one organopolysiloxane polymer, optionally comprising one or more alkenyl and / or alkynyl groups per molecule which organopolysiloxane polymer (a) has a Williams plasticity value of at least 50mm / 100 in accordance with ASTM D926-08;

[0026] (b) optionally one or more reinforcing silica fillers, selected from fumed silica, colloidal silica and precipitated silica;

[0027] (c) ceramifiable filler consisting or comprising of wollastonite, which is present in an amount of from 25 to 60 wt. % of tire curable ceramifiable silicone rubber composition;

[0028] (d) an organic peroxide curing agent; and

[0029] (e) a fire -resistance additive comprising: ( i ) platinum metal or a platinum metal compound comprising at least 3.0 ppm platinum metal content by weight with respect to the weight of the composition herein; and optionally one or both of

[0030] (ii) one or more fillers selected from quartz, fumed silica, precipitated silica, hydromagnesite, huntite, calcium carbonate, mica, kaolin, aluminum hydroxide (ATH), magnesium hydroxide (MDH), talc, wollastonite, and montmorillonite; and

[0031] (iii) cerium hydroxide, cerium oxide, hydrous cerium oxide or a mixture comprising two or more thereof.

[0032] It has been surprisingly found that the addition of a small amount (0.1 to 3.0 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition) of component (f) a tetra-alkoxy titanate significantly improves the fire resistance properties of the resulting elastomer when the composition is cured, to the extent that the resulting fire-resistant and ceramifiable silicone rubber elastomer which is the cured product of tire above composition and / or product of the above process gives a UL94 VO performance at a sample / coating thickness of about 2 mm when tested in accordance with standard test UL94 (the Underwriters Laboratories of US (UL) standard test UL94 (The Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing). Often when only standard fire-resistant additives were provided in the composition such curable and ceramifiable compositions could not achieve a UL94 VO performance.

[0033] The curable fire-resistant and ceramifiable silicone rubber composition as hereinbefore described comprises the following components:

[0034] Component (a)

[0035] Component (a) is at least one organopolysiloxane polymer optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule which organopolysiloxane polymer (a) has a Williams plasticity value of at least 50mm / 100 in accordance with ASTM D926-08.

[0036] It will be appreciated that given the fact that the curable fire-resistant and ceramifiable silicone rubber compositions described herein are cured by a free radical process, no unsaturated groups are essential in component (a) for cure to take place. However, in a preferred embodiment component (a) comprises one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule; alternatively, an average of two or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule.

[0037] Each organopolysiloxane polymer of component (a) comprises multiple siloxy units, of formula (I):

[0038] R’aSiO(4-a) / 2 (I)

[0039] The subscript “a” is 0, 1, 2 or 3.

[0040] Siloxy units may be described by a shorthand (abbreviated) nomenclature, namely - " M," " D," " T," and " Q", when R’ is (other than the unsaturated groups) independently selected from an aliphatic hydrocarbyl group, a substituted aliphatic hydrocarbyl group, an aromatic group or a substituted aromatic group, as further described below. The M unit corresponds to a siloxy unit where a = 3, that is R SiOi / :: 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 / 2The organopolysiloxane polymer of component (a) is substantially linear but may contain a proportion of branching due to the presence of T units (as previously described) within the molecule, hence the average value of a in structure (I) is about 2.

[0041] The unsaturated groups of component (a) may be positioned either terminally or pendently on the organopolysiloxane polymer, or in both locations. The unsaturated groups of component (a) may be alkenyl groups or alkynyl groups as described above. Each alkenyl group, when present, may comprise for example from 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. When present the alkenyl groups may be exemplified by, but not limited to, vinyl, allyl, methallyl, isopropenyl, propenyl, and hexenyl and cyclohexenyl groups. Each alkynyl group, when present, may also 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. Examples of alkynyl groups may be exemplified by, but not limited to, ethynyl, propynyl, and butynyl groups. Preferred examples of die unsaturated groups of component (a) include vinyl, propenyl, isopropenyl, butenyl, allyl, and 5-hexenyl.

[0042] In formula (I), each R’, other than die unsaturated groups described above, is independently selected from an aliphatic hydrocarbyl group, a substituted aliphatic hydrocarbyl group, an aromatic group or a substituted aromatic group. Each aliphatic hydrocarbyl group may be exemplified by, but not limited to, alkyl groups having from 1 to 20 carbons per group, alternatively 1 to 15 carbons per group, alternatively 1 to 12 carbons per group, alternatively 1 to 10 carbons per group, alternatively 1 to 6 carbons per group or cycloalkyl groups such as cyclohexyl. Specific examples of alkyl groups may include methyl, ethyl, propyl, pentyl, octyl, undecyl, and octadecyl groups, alternatively methyl and ethyl groups. Substituted aliphatic hydrocarbyl group are preferably non-halogenated substituted alkyl groups.

[0043] The aliphatic non-halogenated organyl groups are exemplified by, but not limited to alkyl groups as described above with a substituted group such as oxygen containing groups such as polyoxyalkylene groups, carbonyl groups, alkoxy groups and hydroxyl groups. Further organyl groups may include boron containing groups. Examples of aromatic groups or substituted aromatic groups are phenyl groups and substituted phenyl groups with substituted groups as described above.

[0044] Component (a) may, for example, 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) with optionally each polymer containing at least one, alternatively an average of at least two unsaturated groups, typically alkenyl groups as described above. They may for example be trialkyl terminated, alkenyldialkyl terminated alkynyldialkyl terminated or may be terminated with any other suitable terminal group combination providing each polymer has a Williams plasticity of at least 50mm / 100 measured in accordance with ASTM D926-08. Other alternatives include

[0045] 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 di alkylalkenyl 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. In each case component (a) has a Williams plasticity of at least 50mm / 100 measured in accordance with ASTM D926-08. As previously indicated organopolysiloxane polymers of this magnitude are generally referred to in tire industry as organopolysiloxane polymer gums, siloxane gums or silicone gums (hereafter referred to as a silicone gum) because of their very high viscosity (at least 1,000,000 mPa. s at 25°C, often many millions mPa. s at 25 °C) and high molecular weight. Because of tire difficulty in measuring tire viscosity of such highly viscous fluids silicone gums, tend to be defined by way of their Williams plasticity values as opposed to viscosity. Component (a) is a silicone gum and has a Williams plasticity of at least 50 mm / 100 measured in accordance with ASTM D926-08, alternatively 75 mm / 100 measured in accordance with ASTM D926-08, alternatively 100mm / 100 measured in accordance with ASTM D926-08, alternatively at least 125mm / 100 measured in accordance with ASTM D926-08, alternatively at least 140mm / 100 measured in accordance with ASTM D926-08. Typically, silicone gums have a Williams plasticity of from about 100mm / 100 to 450mm / 100 measured in accordance with ASTM D926-08.

[0046] The number average molecular weight (Mn) and weight average molecular weight (Mw) of such polymers are typically determined by gel permeation chromatography using polystyrene standards. If where shown or required, the present disclosure the number average molecular weight and weight average molecular weight values of the silicone gums used as component (a) herein were determined using a Waters 2695 Separations Module equipped with a vacuum degasser, and a Waters 2414 refractive index detector (Waters Corporation of MA, USA). The analyses were performed using certified grade toluene flowing at 1.0 mL / min as the eluent. Data collection and analyses were performed using Waters Empower GPC software.

[0047] The degree of polymerization of the polymer was approximately the number average molecular weight of the polymer divided by 74 (the molecular weight of one component (I) depicted above).

[0048] Typically, the alkenyl and / or alkynyl content, e.g., vinyl content of the polymer is from 0.01 to 3 wt. % for each organopolysiloxane polymer containing at least two silicon-bonded alkenyl groups per molecule of component (a), alternatively from 0.01 to 2.5 wt. % of component (a), alternatively from 0.01 to 2.0 wt. %, alternatively from 0.01 to 1.5 wt. % of component (a) of the or each organopolysiloxane polymer containing at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl or alkynyl groups per molecule of component (a). The alkenyl / alkynyl content of component (a) is determined using quantitative infra-red analysis in accordance with ASTM El 68- 16.

[0049] Component (a) may be present in the curable fire-resistant and ceramifiable silicone rubber composition in an amount of from 25 wt. % to about 70 wt. % of the composition, alternatively from 30 to 60 wt. % of the composition, alternatively from 30 to 55 wt. % of the composition, alternatively from 30 to 50 wt. % of the composition. Typically, component (a) is present in an amount which is the difference between 100 wt. % and the cumulative wt. % of the other components / ingredients of the composition.

[0050] Component (b) (Optional)

[0051] Component (b) is optional in the current curable fire-resistant and ceramifiable silicone rubber composition and is one or more reinforcing silica fillers, selected from fumed silica, colloidal silica and precipitated silica alternatively is fumed silica. Preferably said reinforcing silica fillers are in a finely divided form. In one embodiment component (b) is an essential component in the

[0052] composition. Precipitated silica, fumed silica and / or colloidal silica, particularly fumed silica are preferred when present because of their relatively high surface area, which is typically at least 50 m2 / g (Brunauer-Emmett-Teller (BET) method in accordance with ISO 9277:2010); alternatively, having surface areas of from 50 to 450 m2 / g (BET method in accordance with ISO 9277: 2010), alternatively having surface areas 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.

[0053] The reinforcing silica filler(s) of component (b) are naturally hydrophilic and are treated with one or more treating agents to render them hydrophobic. These surface modified reinforcing fillers of component (b) do not clump and can be homogeneously incorporated into organopolysiloxane polymer (a), described below, as the surface treatment makes the fillers easily wetted by organopolysiloxane polymer (a).

[0054] When present, component (b) is present in an amount of up to 25 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition, alternatively from 1.0 to 25 wt. % of the composition, alternatively of from 5.0 to 25 wt. % of the composition, alternatively of from 10.0 to 20 wt. % of the composition.

[0055] The reinforcing silica fillers when used are naturally hydrophilic which renders them difficult to intermix with the polydiorganosiloxane polymer(s) and as such said fillers are usually either pre-treated with a treating agent to render them hydrophobic, or alternatively are provided in a hydrophilic form. In the latter case a hydrophobic treating agent is usually (but not always) provided to treat the silica in situ during the silicone rubber base mixing process, i.e., incorporation and dispersion of silica in polymer is undertaken in the presence of a treating agent. The product of this mixing step is a silicone rubber base composition. This may be provided in a form suitable for mixing with other ingredients as discussed below. Alternatively, it may be in the form of a concentrate (often referred to by the industry as a “masterbatch” (MB)) which is typically diluted with further polydiorganosiloxane polymer(s) before use. A variety of treating agents may be utilised to render the filler hydrophobic. The treating agents reacts with OH-groups on the silica filler surface resulting in a reduced number of free OH-groups on the silica and as such rendering the silica surface increasingly hydrophobic.

[0056] Typically, the one or more silica fillers (b) is or are surface treated with a suitable low molecular weight organosilicon compounds disclosed in the art applicable to prevent creping of organosiloxane compositions during processing. For example, organosilanes, polydiorganosiloxanes, or organosilazanes e.g., hexaalkyl disilazane, short chain siloxane diols or fatty acids or fatty acid esters such as stearates may be used to render the filler(s) hydrophobic and therefore easier to handle and obtain a homogeneous mixture with the other ingredients.

[0057] Optionally additional hydrophobing agents may be utilised, for example, organosilanes, or organosilazanes e.g., hexaalkyl disilazane and short chain methyl vinyl siloxane diols. Specific examples include, but are not restricted to, silanol terminated trifluoropropylmethylsiloxane, silanol terminated vinyl methyl (ViMe) 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 methyltrimethoxy silane, dimethyldimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, chlorotrimethyl silane, dichlorodimethyl silane, trichloromethyl silane.

[0058] In one embodiment, the heating agent may be selected from silanol terminated vinyl methyl (ViMe) siloxane, hexaorganodisiloxanes, such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes, such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane and; hydroxyldimethyl terminated polydimethylmethylvinyl siloxane, octamethyl cyclo tetrasiloxane, and silanes including but not limited to, methyltriethoxysilane, dimethyldiethoxysilane and / or vinyltriethoxysilane. A small amount of water can be added together with the silica treating agent(s) as processing aid.

[0059] Component (c)

[0060] Component (c) is a ceramifiable filler consisting or comprising of wollastonite, Other suitable ceramifiable fillers which may be present in a mixture with wollastonite include but are not limited to glass powder, alumina and silicate fillers for example, mica, kaolin, sepiolite and diopside and the like. Wollastonite, for example, is a calcium metasilicate, comprising about 48.3 wt. % calcium oxide and subject to impurities the remainder is substantially silicon dioxide. It can have a wide range of particle sizes e.g., from 0.1 to about 300pm but for the present application has an average particle size of from 0.1 to 200 pm, alternatively 0.1 to 100 pm, alternatively 0.1 to 50 pm alternatively 0.1 to 25 pm using a laser diffraction particle analyzer from Microtrac Retsch GmbH. It typically has an acicular morphology, that is a needle-like shape with an aspect ratio (length-to-diameter) of 3: 1 or greater; alternatively, an aspect ratio of greater than 5: 1, alternatively an aspect ratio of greater than 10: 1, alternatively an aspect ratio of greater than 15: 1 in each case measured using scanning electron microscopy (SEM). In one embodiment as described herein the wollastonite has a BET surface area (ISO 9277: 2010) of from about 0.5 to 25 m2 / g, alternatively 0.5 to 10 m2 / g. Suitable commercially available grades of wollastonite are those sold under the NYAD™ trademark supplied by NYCO Minerals, Inc., Willsboro N. Y. such as NYAD™ 400 and NYAD™ 1250.

[0061] Component (c) is present in an amount of from 25 to 60 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition, alternatively from 30 to 60 wt. % of the composition alternatively from 30 to 55 wt. % of the composition. When a mixture preferably at least half of the mixture is wollastonite.

[0062] Component (d)

[0063] Component (d) of the curable fire-resistant and ceramifiable silicone rubber composition is an organic peroxide curing agent (sometimes referred to as a free-radical initiator). Examples include any of the well-known commercial peroxides used to cure high temperature vulcanisable (HTV) compositions. Suitable organic peroxides which may be used as free radical initiators include but are not limited to substituted or unsubstituted dialkyl-, alkylaroyl-, diaroyl-peroxides, e.g., benzoyl peroxide and 2,4-dichlorobenzoyl peroxide, ditertiarybutyl peroxide, dicumyl peroxide, t- butyl cumyl peroxide, bis(t-butylperoxyisopropyl) benzene, bis(t-butylperoxy)-2,5-dimethyl hexyne, Di-(4-methylbenzoyl)-peroxide, 2,4-dimethyl-2,5-di(t- butylperoxy) hexane, di-t-butyl peroxide and 2,5-bis(tert-butyl peroxy)-2,5-dimethylhexane, 2,2-bis(t-butylperoxy)-p- diisopropylbenzene, l,l,bis(t-butylperoxy)-3,3,5-trimethylcyclohexane and p -chlorobenzoyl peroxide. Mixtures of the above may also be used.

[0064] The amount of the organic peroxides used is determined by the nature of the curing process, the organic peroxide used, and the composition used. Typically, the amount of peroxide catalyst utilised in a curable fire-resistant and ceramifiable silicone rubber composition as described herein is from 0.2 to 3 wt. %, alternatively 0.2 to 2 wt. % in each case based on the weight of the curable fire-resistant and ceramifiable silicone rubber composition.

[0065] Component (e)

[0066] (i)Component (e) is a fire-resistance additive comprising platinum metal or a platinum metal compound comprising at least 3.0 ppm platinum metal content by weight with respect to the weight of the composition herein, which in a preferred alternative is introduced in in an organopolysiloxane polymer, optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule,; and optionally one or both of

[0067] (ii) one or more fillers selected from quartz, fumed silica, precipitated silica, hydromagnesite, huntite, calcium carbonate, mica, kaolin, aluminum hydroxide (ATH), magnesium hydroxide (MDH), talc, wollastonite, and montmorillonite; and

[0068] (iii) cerium hydroxide, cerium oxide, hydrous cerium oxide or a mixture comprising two or more thereof. Components(e)(i), (e)(ii) and (e)(iii) of component (e) may be introduced into the composition as individual ingredient, in individual masterbatches, or in the form of a single masterbatch.

[0069] In one embodiment component (e) is provided in the form of a masterbatch comprising component (e)(i) and optionally one or both of components (e)(ii) and (e)(iii).

[0070] When in the form of a masterbatch component (e) also comprises at least one organopolysiloxane polymer. The at least one organopolysiloxane polymer may form part of a silicone rubber base together with a filler such as component (b), component (c) or a mixture of components (b) and (c). Preferably when a silicone rubber base is used for the masterbatch it comprises at least one organopolysiloxane polymer with a filler such as component (b). In one embodiment the at least one organopolysiloxane polymer may be component (a) as defined above.

[0071] Compound (e)(i)

[0072] The platinum metal compound of (e)(i) may for example be platinum compounds often used to catalyse hydrosilylation reactions, 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, tire platinum-olefin complexes of the formulae (PtC12.(olefin)2 and H(PtC13.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 compounds 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 compounds with phosphorus, sulfur, and amine ligands can be used as well, e.g., (Ph3P)2PtCl2; and complexes of platinum with vinylsiloxanes, such as sym-divinyltetramethyldisiloxane.

[0073] Hence, specific examples of suitable platinum-based compounds of component (e) include:

[0074] (i) complexes of chloroplatinic acid with organosiloxanes containing ethylenically unsaturated hydrocarbon groups are described in US 3,419,593;

[0075] (ii) chloroplatinic acid, either in hexahydrate form or anhydrous form;

[0076] (iii) a platinum-containing compound which is obtained by a method comprising reacting chloroplatinic acid with an aliphatically unsaturated organosilicon compound, such as divinyltetramethyldisiloxane;

[0077] (iv) alkene -platinum-silyl complexes as described in US Pat. No. 6,605,734 such as (COD)Pt(SiMeC12)2 where “COD” is 1,5 -cyclooctadiene; and / or (v) Karstedt’s catalyst is a Pt2(divinyl tetramethyl disiloxane)3complex typically containing from 30 to 50 wt. % platinum metal in the complex.

[0078] It is typically introduced into a silicone rubber composition in a 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. 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.

[0079] In one preferred embodiment component (e)(i) 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.

[0080] The amount of platinum metal present is at least 3.0 ppm by weight with respect to the weight of the composition herein which in a preferred embodiment is introduced into the composition in an organopolysiloxane polymer optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule; generally from 3.0 ppm to 10,000 ppm of platinum-group metal, per million parts (ppm), based on the weight of die curable fire-resistant and ceramifiable silicone rubber composition; alternatively, between 3.0 and 5000 ppm; alternatively, between 3.0 and 3,000 ppm, and alternatively between 3.0and 1,000 ppm. In specific embodiments, the platinum metal content may range from 3.0 to 1,000 ppm, alternatively 3.0 to 750 ppm, alternatively 3.0 to 500 ppm by weight with respect to the weight of the composition herein which as previously indicated in a preferred embodiment is introduced into the composition in an organopolysiloxane polymer optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule; based on the weight of tire composition. The ranges may relate solely to the platinum content within the component (e)(i) or to the component (e)(i) altogether (including its ligands) as specified, but typically these ranges relate solely to the platinum content within the component (e)(i).

[0081] The platinum compound 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 platinum or platinum compound is provided e.g., in a polymer or solvent, the amount of component (e)(i) present will be within the range of from 0.001 to 3.0 wt. % of the composition, alternatively from 0.001 to 2.5 wt. % of the composition, alternatively 0.01 to 2.0 wt. %, of the composition.

[0082] In a preferred embodiment component (e) is component (e)(i).

[0083] Component (e)(ii)

[0084] When present, component (e)(ii) is a suitable reinforcing filler or non-reinforcing filler selected from quartz, fumed silica, precipitated silica, hydromagnesite, huntite, calcium carbonate, mica, kaolin, aluminum hydroxide (ATH), magnesium hydroxide (MDH), talc, wollastonite, and montmorillonite. In each case fumed silica, precipitated silica, wollastonite are as previously described. Hydromagnesite, (Mg5(CO3)4(OH)2.4H2O) is sometimes referred to as light magnesium carbonate. When present component (e)(ii) is present in component (e) in an amount of from 30 to 70 wt. % of component (e) and is preferably quartz, fumed silica, precipitated silica or wollastonite. When component (c) and component (e)(ii) are the same filler the amount of said filler present will be the amount present (in wt. %) in component (c) + the amount present ( in wt. %) in component (e)(ii). Hence, were both component (c) & component (e)(ii) wollastonite, the total amount of wollastonite can be greater than 70 wt. % of the composition. When component (e)(ii) is present preferably it is present in combination with (e)(i) or is present in combination with (e)(i) and (e)(iii).

[0085] Component (e)(iii)

[0086] When present, component (e)(iii) is cerium hydroxide, cerium oxide, hydrous cerium oxide or a mixture comprising two or more thereof; alternatively, component (e)(iii) is cerium hydroxide. When present component (e)(iii) may be introduced as a masterbatch. The masterbatch may for example be a 1: 1 ratio by weight of component (e)(iii), typically cerium hydroxide, in a silicone polymer. Any suitable silicone polymer may be used e.g., component (a) herein or a hydroxy-dimethylsiloxy-end-capped

[0087] poly dimethylsiloxane having a Williams plasticity of 40 mm / 100 to 160mm / 100 measured in accordance with ASTM D926-08.

[0088] Hence, in one embodiment component (e) is a fire -resistance additive comprising a masterbatch which comprises from about 0.5 to 10 wt. % of a masterbatch comprising component (e)(i) in a siloxane polymer with (e)(i) having a platinum metal content of at least 3.0 ppm by weight with respect to the weight of the composition herein which in a preferred embodiment is introduced into tire composition in an organopolysiloxane polymer optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof in the curable fire-resistant and ceramifiable silicone rubber composition, together with 30 to 70 wt. % of component (e) being component (e)(ii), preferably quartz, fumed silica, precipitated silica or wollastonite, and optionally 2 to 10 wt. % of cerium hydroxide which masterbatch also comprises at least one organopolysiloxane polymer and wherein said component (e) is present in an amount of from 0.5 to 8.5 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition.

[0089] Component (f)

[0090] Component (f) is one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or a mixture thereof, alternatively one or more tetra-alkoxy titanate(s), in an amount of from 0.1 to 2.5 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition. For the avoidance of doubt, such tetra-alkoxy titanates are sometimes respectively referred to as tetra-alkoxy titanium or as tetra-alkyl titanates and likewise tetra-alkoxy zirconate equivalents can also be alternatively named.

[0091] Any suitable tetra-alkoxy titanates and / or tetra-alkoxy zirconates which act as condensation catalysts may be utilised. The tetra-alkoxy titanates and tetra-alkoxy zirconates may comprise compounds according to the general formula

[0092] M[OR7]4 Where M is titanium or zirconium and each R7may be the same or different and represents a monovalent, primary, secondary or tertiary aliphatic hydrocarbon group which may be linear or branched containing from 1 to 10 carbon atoms.

[0093] Typically, each R7may be the same or different and include but are not restricted to methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, tertiary amyl (C (C2H5) (CH3)2). pentyl or hexyl groups and branched secondary alkyl groups such as 2,4-dimethyl-3-pentyl groups. In some embodiments one or more R7groups may contain partial unsaturation. In one embodiment all the R7are the same alkyl group. Examples include the following tetra-alkoxy titanates and their zirconate equivalents:

[0094] Ti (OCH2CH(CH3)2)4tetraisobutyltitanate or tetraisobutoxy titanium (TiBT),

[0095] Ti[OC(CH3)3]4tetra tertiary butyl titanate or tetra tertiarybutoxy titanium (TtBT)

[0096] Ti (C (C2H5) (CH3)2)4- tetrateriary amyl titanate

[0097] Ti(OCH2CH2CH2CH3)4tetra n-butyl titanate or tetra n-butoxy titanium (TnBT)

[0098] And other suitable tetra-alkoxy titanate catalysts such as Tyzor™ 9000 commercially available from Dorf Ketal Speciality Catalysts, LLC which has has the formula

[0099] Ti [isopropoxy] a’ [t-butoxy]b’

[0100] where die total number of [isopropoxy] + [tertiary butoxy] groups per Ti atom] (a’ + b’) is 4 and wherein, on average drere are about 10% [isopropoxy] and 90% [t-butoxy] groups.

[0101] For the avoidance of doubt, die one or more tetra-alkoxy titanate(s), one or more teta-alkoxy zirconate(s) or a mixture thereof of component (f) are not partially or completely chelated.

[0102] Said one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or mixtures thereof (component (f)) herein are present in the curable fire-resistant and ceramifiable silicone rubber composition in an amount of from 0.1 to 3.0 wt. % of the composition, alternatively 0.2 to 2.5 wt. % of die composition, alternatively from 0.2 to 2.0 wt.% of the composition.

[0103] Additional optional components

[0104] Additional optional components may be present in the curable fire-resistant and ceramifiable silicone rubber composition as hereinbefore described depending on the intended final use thereof. Examples of such optional components include a magnesium compound selected from magnesium oxide, magnesium hydroxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof; pot life extenders, non-reinforcing fillers, lubricants, metal deactivators, smoke reducing additives, pigments and / or colouring agents, heat stabilizers, compression set additives, plasticizers and mixtures thereof. Magnesium compound

[0105] The optional magnesium compound when present is selected from magnesium oxide, magnesium hydroxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof, with magnesium oxide, particularly preferred.

[0106] 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).

[0107] The optional magnesium compound, preferably magnesium oxide, when present, is / are present in the curable fire-resistant and ceramifiable silicone rubber composition in an amount of from 0.05 to 3.0 wt. % of the composition, alternatively from 0.5 to 2.5 wt. % of the composition, alternatively from 0.75 to 2.5 wt. % of the composition alternatively from 1.0 to 22.25 wt. % of the composition.

[0108] Pot life extenders, such as triazole, may be used, but are not considered necessary herein in the scope of the present disclosure. The curable fire-resistant and ceramifiable silicone rubber composition may thus be free of pot life extender.

[0109] Non-reinforcing Fillers

[0110] When present, optional non-reinforcing fillers may include but are not limited to crushed quartz, diatomaceous earths, barium sulphate, iron oxide, titanium dioxide, carbon black, talc, wollastonite precipitated calcium carbonate and ground calcium carbonate. 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, aluminium trihydroxide, graphite, zirconium oxide, copper carbonate, e.g., malachite, nickel carbonate, e.g., zarachite, barium carbonate, e.g., witlierite and / or strontium carbonate e.g., strontianite.

[0111] Aluminium 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 Ca3Al2Si3O12. Aluminosilicates comprise ground silicate minerals, such as but not limited to, sillimanite; Al2SiO5; mullite; 3Al2O3.2SiO2; kyanite; and Al2SiO5.

[0112] The ring silicates group comprises silicate minerals, such as but not limited to, cordierite and Al3(Mg,Fe)2[Si4Al2O18]. The chain silicates group comprises ground silicate minerals, such as but not limited to, wollastonite and Ca[SiO3].

[0113] The sheet silicates group comprises silicate minerals, such as but not limited to, mica;

[0114] K2Al14[Si6Al2O20](OH)4; pyrophyllite; Al4[Si8O20](OH)4, talc; Mg6[Si8O20](OH)4; serpentine for example, asbestos; Kaolinite; Al4[Si4O10](OH)8; and vermiculite. The optional non-reinforcing filler, when present, is present in an amount up to 20 wt.% of the curable fire-resistant and ceramifiable silicone rubber composition.

[0115] Such non-reinforcing fillers may be hydrophobically treated as described above with respect to optional reinforcing fillers (b) and ceramifiable fillers (c).

[0116] Lubricants Examples of lubricants include tetrafluoroethylene, resin powder, fluorinated graphite, talc, boron nitride, fluorine oil, silicone oil, molybdenum disulfide, and mixtures or derivatives thereof. When present in the curable fire-resistant and ceramifiable silicone rubber curable composition, said lubricants are typically present in an amount of from 0.1 to 5% by weight of the composition.

[0117] Optional Pigments / Colorants

[0118] The curable fire-resistant and ceramifiable 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.

[0119] Suitable white pigments and / or colorants include titanium dioxide, zinc oxide, lead oxide, zinc sulfide, lithopone, zirconium oxide, and antimony oxide.

[0120] 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 aluminium, copper, copper oxide, bronze, stainless steel, nickel, zinc, and brass.

[0121] Suitable organic non-white pigments and / or colorants include monoarylide yellow, diarylide yellow, benzimidazolone yellow, heterocyclic yellow, 5-[(2,3-dihydro-6-methyl-2-oxo-1H-benzimidazol-5-yl)azo]barbituric acid, 3,3'-[(2,5-dimethyl-p-phenylene)bis[imino(1-acetyl-2-oxoethylene)azo]]bis[4-chloro-N-(5-chloro-o-tolyl)benzamide, 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, P-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 diketop yrrolo pyrrole pigments.

[0122] The pigments and / or colorants, when present, are present in the range of from 0.1 wt. %, alternatively from 0.5 wt. %, alternatively from 1 wt. % of the composition to 15 wt. % of the composition, alternatively to 10 wt. % of the composition.

[0123] Heat stabilizers may include metal compounds such as red iron oxide, yellow iron oxide, ferric hydroxide, cerium oxide, cerium hydroxide, lanthanum oxide, copper phthalocyanine, fumed titanium dioxide, iron naphthenate, cerium naphthenate, cerium dimethylpolysilanolate and acetylacetone salts of a metal chosen from copper, zinc, aluminum, iron, cerium, zirconium, titanium and the like. Other examples of heat stabilizers may include suitable antioxidants or metal scavengers such as salicyloylaminotriazole. The amount of heat stabilizer when present in the curable fire-resistant and ceramifiable silicone rubber composition may range from 0.01 to 2.5 % weight of the composition. Compression set additives may include l,2-bis(3,5-di-tert-butyl-4-hydroxylhydrocinnamoyl)hydrazine, 2-Hydroxy-N-lH-l,2,4-triazol-3-ylbenzamide, and N’ 1, N’12-Bis(2-hydroxybenzoyl)dodecanedihydrazide.

[0124] One or more plasticizer(s), one or more extender(s) or a mixture thereof

[0125] The curable fire-resistant and ceramifiable silicone rubber composition as described above may also include one or more plasticizer(s), one or more extender) s) or a mixture thereof.

[0126] These may be in the form of silicone or organic fluids which are unreactive with organopolysiloxane polymer(s) (a). If present the plasticizer or extender content will be present in an amount of from 0.5 to 30 wt. % of the composition, alternatively from 0.5 to 10 wt. % of the composition.

[0127] Examples of non-reactive silicone fluids useful as plasticizers include polydiorganosiloxanes such as polydimethylsiloxane having terminal triorganosiloxy groups wherein the organic substituents are, for example, methyl, vinyl or phenyl or combinations of these groups. Such polydimethylsiloxanes can for example have a viscosity of from about 5 to about 100,000 mPa.s at 25°C (measured as described above). Hence, in one alternative, the present disclosure thus provides a curable fire-resistant and ceramifiable silicone rubber composition, which comprises:

[0128] a) at least one organopolysiloxane polymer, optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule which organopolysiloxane polymer (a) has a Williams plasticity value of at least 50mm / 100 in accordance with ASTM D926-08, alternatively at least 75mm / 100 measured in accordance with ASTM D926-08, alternatively at least 100mm / 100 measured in accordance with ASTM D926-08, alternatively at least 125mm / 100 measured in accordance with ASTM D926-08, alternatively at least 140mm / 100 measured in accordance with ASTM D926-08, with a maximum Williams plasticity of from about 300mm / 100 to 450mm / 100 measured in accordance with ASTM D926-08, in the composition in an amount of from 25 wt. % to about 70 wt. % of the composition, alternatively from 30 to 60 wt. % of the composition, alternatively from 30 to 55 wt. % of the composition, alternatively from 30 to 50 wt. % of the composition.

[0129] b) optionally one or more reinforcing silica fillers, selected from fumed silica, colloidal silica and precipitated silica, alternatively, when present fumed silica, colloidal silicas and / or a precipitated silica having a BET surface area of at least 50 m2 / g (ISO 9277: 2010); alternatively, having surface areas of from 50 to 450 m2 / g (ISO 9277: 2010), alternatively having surface areas of from 50 to 300 m2 / g (BET method in accordance with ISO 9277: 2010). When present, they are typically used in an amount of up to 25 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition, alternatively from 1.0 to 25 wt. % of the composition, alternatively of from 5.0 to 25 wt. % of the composition, alternatively of from 5.0 to 20 wt. % of the composition.

[0130] c) ceramifiable filler consisting or comprising of wollastonite, which is present in an amount of from 25 to 60 wt. % of the composition; when a wollastonite is present in a mixture, other suitable ceramifiable fillers which may be present include but are not limited to glass powder, alumina and silicate fillers for example, mica, kaolin, sepiolite and diopside and the like; component (c) is present in an amount of from 25 to 60 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition; alternatively, from 30 to 60 wt. % of the composition alternatively from 30 to 55 wt. % of the composition and when a mixture preferably at least half of component (c) is wollastonite;

[0131] (d) an organic peroxide curing agent, typically, the in an amount from 0.2 to 3 wt. %, alternatively 0.2 to 2 wt. % in each case based on the weight of the curable fire-resistant and ceramifiable silicone rubber composition.

[0132] (e) a fire -resistance additive comprising:

[0133] (i) platinum metal or a platinum metal compound comprising at least 3.0 ppm platinum metal content by weight with respect to the weight of the composition herein which in a preferred embodiment is introduced into the composition in an organopolysiloxane polymer optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule; and optionally one or both of

[0134] (ii) one or more fillers selected from quartz, fumed silica, precipitated silica, hydromagnesite, huntite, calcium carbonate, mica, kaolin, aluminum hydroxide (ATH), magnesium hydroxide (MDH), talc, wollastonite, and montmorillonite;

[0135] (iii) cerium hydroxide, cerium oxide, hydrous cerium oxide or a mixture comprising two or more thereof;

[0136] component (e) may be in the form of a masterbatch comprising component (e)(i) and optionally one or both of components (e)(ii) and (e)(iii), which masterbatch also comprises at least one organopolysiloxane polymer, which may if desired be the same as component (a); and

[0137] (f) one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or mixtures thereof, in an amount of from 0.1 to 3.0 wt. % of the composition, alternatively 0.2 to 2.5 wt. % of the composition, alternatively from 0.2 to 2.0 wt.% of the composition. The one or more tetra-alkoxy titanate(s) and one or more tetra-alkoxy zirconate(s) may comprise compounds according to the general formula M[OR7]4

[0138] Where M is titanium or zirconium and each R7may be tire same or different and represents a monovalent, primary, secondary or tertiary aliphatic hydrocarbon group which may be linear or branched containing from 3 to 10 carbon atoms.

[0139] The total wt. % of any combination of the components in the above composition is 100 wt. %. The composition may also contain one or more of the above optional additives in amounts indicated again providing the total wt. % of tire composition is 100 wt. %.

[0140] Given component (a) is a silicone gum, generally the curable fire-resistant and ceramifiable silicone rubber composition is prepared by combining all of components together. In such a case the preparation of the elastomer resulting from the cure of the curable fire-resistant and ceramifiable silicone rubber composition comprises the steps of

[0141] (A) when component (b) is present, preparing a silicone rubber base composition by mixing component (a) with component (b) and optionally some or all of component (c);

[0142] (B) Introducing components (d), (e) and (f) and all remaining component (c) into the silicone base composition of step (A) when component (b) is present, or into component (a) when component (b) is not present, in any suitable order and mixing to prepare a curable fire-resistant and ceramifiable silicone rubber composition; and

[0143] (C) curing tire curable fire-resistant and ceramifiable silicone rubber composition at a temperature of between 90 and 400°C, alternatively 90 to 300°C, alternatively 90 to 250°C.

[0144] When components (b) and some or all of component (c) are present in step (A) they can be added in any order or simultaneously into the gum and mixed to form tire silicone rubber base. If desired or required a hydrophobing agent is introduced during step (A) in tire event component (B) is to be treated in situ. In step (B), when component (b) is present, once the silicone rubber base has been prepared dre remaining components (d), (e), (f) and all remaining component (c) as well as any optional additives to be incorporated are added into the silicone rubber base product of step (A) above in any suitable order. Typically, the organic peroxide (d) is introduced last to avoid tire commencement of cure prior to tire thorough mixing into tire silicone rubber base of all other components.

[0145] Alternatively, in step (B) when component (b) is not present, the components (c), (d), (e), (f) as well as any optional additives to be incorporated are added into component (a) in airy suitable order. Again typically, the organic peroxide (d) is introduced last to avoid the commencement of cure prior to the thorough mixing into the silicone rubber base of all other components; and

[0146] Often, especially when component (a) is a silicone gum, ingredients such as (d), (e) and (f) are added into the component (a) or the silicone rubber base in the forms of masterbatches or concentrates to simplify the dispersion therein.

[0147] One reason a silicone rubber base is prepared first when component (b) is present is to enable optional component (b) and any component (c) present to be treated in-situ with a hydrophobing treating agent before the remaining ingredients are introduced into the mixture in any suitable order. However, when component (b) is not present component (c) may be introduced directly into component (a) without hydrophobic treatment if preferred but hydrophobing treating agent may be utilised if desired to treat component (c).

[0148] Any mixing techniques and devices described in die prior art can be used for this purpose. The particular device to be used will be determined by die viscosities of components and the final curable coating composition. Suitable mixers include but are not limited to paddle type mixers e.g., planetary mixers and kneader type mixers or using a two-roll mill. However, when component (a) is a gum mixing is preferably undertaken, as previously indicated using a kneader mixer. Cooling of components during mixing may be desirable to avoid premature curing of the composition.

[0149] When component (b) is present, the preparation of the silicone rubber base (i.e., Step (A)) may be achieved by mixing together component (a) with components (b) and some or all of component (c) together with the optional treating agent at a temperature in the range of from 80°C to 250°C, alternatively from 90 °C to 220 °C, alternatively 120 °C to 200 °C for a period of from 30 minutes to 2 hours, alternatively 40 minutes to 2 hours, alternatively of from 45 minutes to 90 minutes, to ensure the reinforcing silica filler is in-situ treated by the optional treating agent and thoroughly mixed into component (a). The resulting silicone rubber base may then be cooled to approximately room temperature (23°C to 25°C).

[0150] In step (C), curing the curable fire-resistant and ceramifiable silicone rubber composition takes place at a temperature of from 90 and 400°C, alternatively 90 to 300°C, alternatively 90 to 250°C dependent on the means of cure for example a temperature of up to 400°C might be used for extrusion applications especially with high line speeds whilst temperatures of 300°C or 250°C being suitable for molding applications. Typically, cure may take place in any suitable manner. For example, the composition may be introduced into a mold and is then press cured for a suitable period of time, or be processed by injection moulding, encapsulation moulding, press moulding, dispenser moulding, profile extrusion, extrusion, transfer moulding, press vulcanization, centrifugal casting, calendaring, bead application or blow moulding. Dependent on the cure method selected the composition may be cured for a suitable period of time, e.g., from 5 s seconds to an hour, alternatively from 10 seconds to 50 minutes, alternatively from 20 seconds to 40 minutes or as otherwise desired or required.

[0151] As and when required, samples may be additionally post-cured by heating to a temperature of from 100°C to 250°C for up to 24 hours.

[0152] It is known that unfortunately standard peroxide cured silicone elastomers, when exposed to flames generate unwanted levels of volatile organic compounds (VOCs). Such VOCs evaporate out of the body of the elastomer and ignite in an air / oxygen atmosphere in the presence of a spark in accordance with the fire triangle definition of the three elements a fire needs to ignite).

[0153] A number of ceramifiable silicone elastomers have been proposed and are used to insulate electric power distribution articles for example in Automotive electric vehicle (EV) applications, and / or as insulating coatings for wires, cables and busbars (metallic strips / bars housed inside e.g., switchgear and panelboards for local high current power distribution and also used to connect high voltage equipment at electrical substations with low-voltage equipment in e.g., battery -banks). However, such silicone elastomeric materials are not fire resistant because their mode of operation relies upon the formation of a protective char around tire insulated article to protect it in a fire situation after the silicone elastomer has burnt. Hence, they cannot be considered self-extingui shing under standard test UL94. In the vertical test they are held at the top of the sample and a fire is commenced at the bottom of the sample and the burn height is the % of the distance between top and bottom to burn. Hence, a bum height (%) of 0% implies no bum, A burn height of 100% means buming / glowing up to clamps. Upon testing the bum height under vertical test conditions (flammability test according to IEC 60695 11-10 which is equivalent to the UL 94 -vertical burning testing) is often 100%, pr thereabouts i.e. it bums completely up to the clamp gripper (Bum height (%) 100).

[0154] When a standard silicone rubber bums the char structure is quite fragile and flaky. Thus, if a cable is covered with a standard silicone rubber the resulting char may flake away or crack during burning, exposing new polymer surfaces for pyrolysis as well as the cable core material. If the char structure remains hard, there is a possibility that flame spread will be decreased. The use of component (c) the ceramifiable filler(s) described herein result in a hard char being formed. However, without the presence of component (f) herein compositions cannot be considered fire-resistant.

[0155] It has been unexpectedly and surprisingly identified in tire present disclosure that addition of component (f) herein, one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or mixtures thereof, in an amount of from 0.1 to 3.0 wt. % of the composition changes a curable ceramifiable silicone rubber composition containing a ceramifiable filler consisting of or comprising wollastonite from completely failing flammability test to a perfectly flame -resistant UL94 VO-rated material and consequently being able to be considered a curable fire-resistant and ceramifiable silicone rubber composition.

[0156] Hence, it has been found that the inclusion of component (f) results in a fire-resistant elastomer which can be used in ceramifiable compositions for electrical equipment for example busbars as described elsewhere, particularly busbars used in the protection in electric vehicle (EV) batteries assemblies. It is believed that tire disclosure herein solves a major issue for the industry by being able to provide a coating that is both ceramifiable in case of extreme heat / flame but also flame-resistant / self-extinguishable to prevent further propagation of a fire to e.g., other parts of an EV battery assembly.

[0157] This enables such compositions and the cured silicone rubber materials resulting therefrom in the auto and cable markets as fire-resistant rubber materials, for e.g., use in electrical insulation but also in the manufacture of automotive parts, e.g., as a protective layer in an E-battery; cable accessories; electrical and electronic parts; packaging parts; construction parts; household parts; and gasket sealants. The cable accessories may be electrical connectors, electrical terminations and wire seals. Hence, such elastomers may be 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.

[0158] There is also provided herein an electrical power cable comprising:

[0159] an electrically conductive core;

[0160] one or more layers of insulation around said core one of which being made from tire fire- resistant silicone rubber being the cured product of tire above composition described herein. The fire-resistant silicone rubber layer of such electric cables e.g., may be used for example as 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 and may be applied by any suitable method, for example by extrusion.

[0161] 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.

[0162] Examples

[0163] A series of examples and comparative examples now follow. In the following examples all BET surface area values provided were measured in accordance with ISO 9277: 2010. All Plasticity values provided were Williams plasticity results measured in accordance with ASTM D926-08, Vinyl content, silanol content and silicon bonded hydrogen content were all measured using quantitative infra-red analysis in accordance with ASTM E168-16. Capillary viscosity measurements were undertaken using a glass capillary viscometer in accordance with ASTM D-445. Other viscosity measurements were made at 25 °C using the equipment and / or method specified.

[0164] A first series of examples and comparative examples were prepared using the compositions depicted in Table la.

[0165] Table la: Compositions of C. 1, C. 2, Ex. 1 and Ex. 2 (wt. %)

[0166] C. 1 C. 2 Ex. 1 Ex. 2

[0167] Silicone rubber base 1 94.5 72.5 73.5 71.5

[0168] Silicone rubber base 2 20.0 20.0 20.0

[0169] Peroxide 1 1.5 1.5 1.5 1.5

[0170] tetra-alkoxy titanate 1 1.0 1.0

[0171] FR Masterbatch 1 4.0 4.0 4.0 4.0

[0172] Additive 1 2.0 2.0

[0173]

[0174] In the above:

[0175] Silicone rubber base 1 was a blend of 50 wt. % wollastonite 1 (NYAD™ 1250 commercially available from Imerys S. A.) in masterbatch 1.

[0176] Masterbatch 1 was 28.9 wt. % fumed silica which was vinyl-silicone surface-treated having a BET surface area of 190 m² / g (silica 1) and 71.1 wt. % of a vinyldimethyl-siloxy end-capped polydimethylsiloxane having a Williams plasticity of 150 mm / 100 (polymer 1).

[0177] Silicone rubber base 2 was 12.1 wt. % of fumed silica which was vinyl-silicone surface-treated having a BET surface area of 230 m² / g (silica 2) with 65.7 wt. % of Polymer 1; 21.2 wt. % of a vinyldimethyl-siloxy end-capped poly-vinylmethyl-dimethyl-siloxane copolymer having a Williams plasticity of 153 mm / 100 and a vinyl content of about 682 ppm (polymer 2), and 1.0 wt. % of a vinyldimethyl-siloxy endcapped poly-vinylmethyl-dimethyl-siloxane copolymer having a viscosity of 8000 mPa.s at 25°C measured with a Brookfield™ RVF rheometer using spindle 3 at 2 revolutions per minute (rpm) which had a vinyl content of 7.7% (polymer 3).

[0178] Peroxide 1 was a paste of 50 wt. % Bis-(2,4-Dichlorobenzoyl)-peroxide in silicone oil commercially available as Noviper™ DB 50 from Novichem Sp.

[0179] Tetra-alkoxy titanate 1 was Tetra isobutyl titanate (otherwise known as ttrakis-isobutyl-orthotinate). FR Masterbatch 1 was 49.65 wt. % of Wollastonite 1, 37.20 wt. % of Polymer 1, 7.45 wt. % of a Karstedt Catalyst Premix, 0.7 wt. % of a hydroxy-dimethylsiloxy-end-capped polydimethylsiloxane having a capillary viscosity of 41.5 cSt at 25°C and a silanol content of 4.0 % (polymer 4) and 5.0 wt. % of Masterbatch 2.

[0180] The Karstedt Catalyst Premix, consisted of 1.27 wt. % of Pt₂(divinyl tetramethyl disiloxane)₃ complex diluted in 98.73 wt. % of a vinyl terminal poly(dimethylsiloxane-co-methylvinylsiloxane) having a viscosity of 450 mPa.s at 25°C using a Brookfield™ rotational viscometer with a cone plate arrangement using cone CP-52 at 12rpm (polymer 10).

[0181] Masterbatch 2, was a mixture of 50 wt. % of cerium hydroxide in 50 wt. % of a hydroxy-dimethylsiloxy-end-capped polydimethylsiloxane having a Williams plasticity of 50 mm / 100 (polymer 5).

[0182] Additive 1 was “32.4 wt. % of magnesium oxide, 31.8 wt. % of Masterbatch 3, 31.8 wt. % of a vinyl terminal poly(dimethylsiloxane-co-methylvinylsiloxane) having a Williams plasticity of 155 mm / 100, and a vinyl content of 650 ppm (polymer 6); and 4% of Masterbatch 4.

[0183] Masterbatch 3, was 23.4 wt. % of Silica 2 in 76.6 wt. % of Polymer 2.

[0184] Masterbatch 4, was 16.7 wt. % of untreated silica 2, and 33.33 wt. % of Polymer 6, and 50 wt. % of a hydroxy-dimethylsiloxy-end-capped poly dimethylsiloxane having a capillary viscosity of 41.5 cSt at 25°C and a silanol group content of 4.0 wt. % (quantitative infra-red analysis in accordance with ASTM E168-16) (Polymer?).

[0185] The two bases were first mixed together in a Werner & Pfleiderer Z-Blade Mixer after which the remaining ingredients were introduced into the resulting mixed base by mixing the ingredients together first in the Z-Blade Mixer and finally on a two roll mill and then 2mm standard test sheets were prepared for flammability tests in accordance with IEC 60695-11-101 UL94 VX conditions: whilst relying on BS EN 60695-11-10 / IEC 60695-11 -10 method B - fire testing.

[0186] The comparatives and examples were prepared by press curing at 135°C for 10 min. Once cured individual test specimens were cut to dimensions of 13 mm xl25 mm x 2 mm.

[0187] Once cured each comparative example and example were evaluated for flame retardant behavior via flammability test according to IEC 60695 11-10 (equivalent to UL 94 - vertical burning). The average values for the required five samples for each cured product under analysis are provided in Table lb. Table lb: UL94 Testing for Flammability of Plastic Materials for C. 1, C. 2, Ex. 1 and Ex. 2

[0188] C. 1 C. 2 Ex. 1 Ex. 2

[0189] tl (seconds (s)) 5 3 0 0

[0190] t2 (s) 8 63 5 0

[0191] t2 + t3 (s) 25 79 7 0

[0192] Bum height (%) 0 30 0 0

[0193] UL94 V(X) VI Fail VO VO

[0194]

[0195] In the above:

[0196] tl is tire “Afterflame time” after a first flame application in accordance with tire test method;

[0197] t2, is the Afterflame time after the second flame application, t2 in accordance with tire test method; and

[0198] t3 is tire afterglow time after said second flame application in accordance with tire test method;

[0199] 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.

[0200] Bum height (%) is the % of the sample to have burned in the vertical burn test in accordance with IEC 60695 11-10 (equivalent to UL 94 - vertical burning) in which in the vertical test samples are held at the top of the sample by a clamp or the like and a fire is commenced at the bottom of the sample and the burn height is the % of the distance between top and bottom to bum. Hence, as previously indicated, a bum height (%) of 0% implies no bum, A burn height of 100% means burning / glowing up to clamps. The bum height (%) was measured using a ruler and measuring the original length of the sample before testing and measuring tire remaining silicone length after the test was completed.

[0201] It will be appreciated therefore that for C. 1, for example, the total cumulative time for the tl + t2 values is effectively (5 x 5 = 25) + (5 x 8 = 40) = 65 seconds. This value fails the test for V0 accreditation which requires the cumulative value for five test samples to be a maximum of 50 seconds.

[0202] A further set of comparative examples and Examples were prepared using the compositions identified in Table 2a below. Table 2a: Compositions of C. 3 to C. 5, Ex. 3 and Ex. 4 (wt. %)

[0203] C. 3 C.4 C. 5 Ex. 3 Ex. 4

[0204] Silicone rubber base 1 97.5 75.5 72,5 71.5 97.4

[0205] Silicone rubber base 2 20.0 20.0 20.0

[0206] Peroxide 1 1.5 1.5 1.5 1.5 1.5

[0207] tetra-alkoxy titanate 1 1.0

[0208] tetra-alkoxy titanate 2 1.0 1.0 0.5

[0209] FR Masterbatch 1 4.0 4.0

[0210] Additive 1 2.0 2.0 2.0

[0211] Karstedt Catalyst Premix 0.1

[0212] Polymer 4 0.5

[0213]

[0214] In the above all ingredients are as previously described apart from tetra-alkoxy titanate 2 which was Tetra-n-butyl-titanate.

[0215] Once prepared C. 3 to C. 5 and Ex. 3 were also assessed in accordance with UL94 Testing for Flammability of Plastic Materials and the results are provided in Table 2b.

[0216] Table 2b: UL94 Testing for Flammability of Plastic Materials for C. 3 to C. 5, Ex. 3 & Ex. 4

[0217] C. 3 C.4 C.5 Ex. 3 Ex. 4

[0218] tl (s) 240 120 3 0 8

[0219] t2 (s) 63 6 0

[0220] t2 + 13 (s) 79 16 0

[0221] Bum height (%) 100 100 30 0 0

[0222] UL94 V(X) Fail Fail Fail VO VO

[0223]

[0224] It will be seen that all the comparative examples were deemed to fail UL94 and that each of these comparative examples either had no tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) present or no FR 1 flame retardant masterbatch present. Given the results for Ex. 3 as well as those of Ex. 1 and Ex. 2 above, a surprising synergistic effect is apparent when the two are combined in the same composition, in each case resulting in a UL 94 VO grading. It is also seen that in Ex. 4 the addition of a small amount of Platinum (e)(i), in the absence of components (e)(ii) and (e)(iii) when in combination with tetra-alkoxy titanate 2 also achieved UL94 VO.

[0225] A further set of comparatives and examples C. 6, C. 7, Ex. 5 & Ex. 6 were prepared in the same manner as described above, using the compositions provided in Table 3a below. Table 3a: Compositions of C. 6, C. 7, Ex. 4 & Ex. 5 (wt. %)

[0226] C.6 Ex. 5 Ex. 6 C. 7

[0227] Silicone rubber base 1 68.5 67.5 69.5

[0228] Silicone rubber base 2 20.0 20.0 20.0 20.0

[0229] Silicone rubber base 3 69.5

[0230] Peroxide 1 1.5 1.5 1.5 1.5

[0231] tetra-alkoxy titanate 1 1.0 1.0 1.0

[0232] Additive 1 2.0 2.0

[0233] Platinum masterbatch 8.0 8.0 8.0 8.0

[0234]

[0235] In the above, all ingredients are as described except for Silicone rubber base 3 and the platinum masterbatch.

[0236] Silicone rubber base 3 which was 38.60 wt. % of surface -treated silica 2, 35.10 wt. % of Polymer 1, and 26.30 wt. % of Polymer 2 and therefore did not contain wollastonite.

[0237] The platinum masterbatch was 74.3 wt. % of silicone rubber base 3, 22.2 wt. % of the Karstedt Catalyst Premix and 3.5 wt. % of untreated silica 2.

[0238] Again, the examples were prepared and cured in the same manner as before and were then assessed in accordance with UL94 Testing for Flammability of Plastic Materials and the results are provided in Table 3b.

[0239] Table 3b: UL94 Testing for Flammability of Plastic Materials for C. 6, C. 7, Ex. 5 & Ex. 6

[0240] C.6 Ex. 5 Ex. 6 C. 7

[0241] tl (s) 170 2 0 136

[0242] t2 (s) 1 8

[0243] t2 + 13 (s) 1 16

[0244] Bum height (%) 100 0 0 100

[0245] UL94 V(X) Fail VO VO Fail

[0246]

[0247] Again, it will be seen that the comparatives failed UL94. C. 7 did not contain wollastonite indicating that component (c) appears to be essential especially given tire poor tl result which resulted in t2 and t3 values not being taken. Ex. 5 and 6, however, both successfully gained a VO grading.

[0248] A further set of comparative examples and examples were prepared from the compositions depicted in Table 4a. All three compositions contained a variety of additives. Table 4a: Compositions of C. 8, Ex. 7 & Ex. 8 (wt. %)

[0249] C. 8 Ex. 7 Ex. 8

[0250] Silicone rubber base 1 55.87 55.23 54.86

[0251] Silicone rubber base 4 31.40 31.09 31.46

[0252] Peroxide 1 1.5 1.49 1.49

[0253] tetra-alkoxy titanate 1 1.0

[0254] tetra-alkoxy titanate 2 1.0

[0255] FR Masterbatch 1 6.11 6.11 6.11

[0256] Additive 1 0.57 0.57 0.56

[0257] Additive 2 3.5 3.47 3.48

[0258] Compounding aid 1 0.26 0.26 0.26

[0259] Pigment 1 0.53 0.52 0.52

[0260] Pigment 2 0.26 0.26 0.26

[0261]

[0262] In the above:

[0263] Silicone rubber base 4 was 29.20 wt. % vinyl-silicone surface-treated Silica 2, 67.90 wt. % of Polymer 1, 1.00 wt. % of Polymer 3, and 1.90 wt. % of, a vinyldimethyl-siloxy end-capped poly-vinylmethyl-dimethyl-siloxane copolymer having a Williams plasticity of 140 mm / 100 and a vinyl content of about 3750 ppm, (polymer 8).

[0264] Additive 2 was “40.00 wt. % of a commercially available titanium dioxide sold under the trade name AEROXIDE™ TiO₂ P 25 by Evonik AG; in 40.00 wt. % of silicone Rubber Base 5, and 20.00 wt. % of a trimethylsiloxy-end-capped poly(dimethylsiloxane) having a viscosity of 60.000 cSt determined using a Brookfield™ HBT rheometer Spindle CP-52 at 25°C and 10 rpm (polymer 9).

[0265] Wherein silicone rubber base 5 is a mixture of 29.20 wt. % of vinyl-surface treated Silica 2, 57.50 wt. % of Polymer 1, and 13.30 wt. % of Polymer 2.

[0266] Compounding aid 1 was 16.66 wt. % of untreated Silica 1 in 33.33 wt. % of Polymer 6, and 50 wt. % of Polymer 7.

[0267] Pigment 1 was an orange pigment in the form of a mixture of 30 wt. % 5-[(2,3-dihydro-6-methyl-2-oxo-lH-benzimidazol-5-yl)azo]barbituric acid, in 70 wt. % of a vinyl terminal poly(dimetliylsiloxane-co-methylvinylsiloxane.

[0268] Pigment 2 was a yellow pigment in tire form of a mixture of 30 wt. % of 3,3'-[(2,5-dimethyl-p-phenylene)bis[imino(l-acetyl-2-oxoethylene)azo]]bis[4-chloro-N-(5-chloro-o-tolyl)benzamide], in 70 wt. % of a vinyl terminal poly(dimethylsiloxane-co-methylvinylsiloxane) having a Williams plasticity of 270 mm / 100.

[0269] These were prepared and cured as described above and then underwent UL94 assessment. Table 4b: UL94 Testing for Flammability of Plastic Materials for C. 8, Ex. 7 & Ex. 8

[0270] C. 8 Ex. 7 Ex. 8

[0271] tl (s) 170 0 0

[0272] t2 (s) 6 1

[0273] t2 + 13 (s) 9 1

[0274] Bum height (%) 100 0 0

[0275] UL94 V(X) Fail VO VO

[0276]

[0277] It can be seen that comparative C. 8 completely failed UL 94 testing, however tire addition of two different tetra-alkoxy titanates in both Ex. 7 and Ex. 8 gave much improved results with both graded UL 94 VO.

Claims

1. WHAT IS CLAIMED IS:

1. A curable fire-resistant and ceramifiable silicone rubber composition comprising:3.(a) at least one organopolysiloxane polymer(s), optionally comprising one or more unsaturated groups per molecule selected from alkenyl, alkynyl groups or a mixture thereof per molecule which organopolysiloxane polymer(s) (a) have a Williams plasticity value of at least 50mm / 100 in accordance with ASTM D926-08;4.(b) optionally one or more reinforcing silica fillers, selected from fumed silica, colloidal silica and precipitated silica;5.(c) ceramifiable filler consisting or comprising of wollastonite, which is present in an amount of from 25 to 60 wt. % of the composition;6.(d) an organic peroxide curing agent.7.(e) a fire -resistance additive comprising8.(i) platinum metal or a platinum metal compound comprising at least 3.0 ppm platinum metal content by weight with respect to tire weight of the composition herein; and optionally one or both of9.(ii) one or more fillers selected from quartz, fumed silica, precipitated silica, hydromagnesite, huntite, calcium carbonate, mica, kaolin, aluminum hydroxide (ATH), magnesium hydroxide (MDH), talc, wollastonite, and montmorillonite; and10.(iii) cerium hydroxide, cerium oxide, hydrous cerium oxide or a mixture comprising two or more thereof;11.and12.(f) one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or a mixture thereof, in an amount of from 0.1 to 3.0 wt. % of the composition.

2. A curable fire-resistant and ceramifiable silicone rubber composition in accordance with claim 1 wherein component (a) has a Williams plasticity of greater than lOOmm / 100.

3. A curable fire-resistant and ceramifiable silicone rubber composition in accordance with claim 1 or 2 wherein component (e) is a masterbatch comprising component (e)(i) and optionally one or both of components (e)(ii) and (e)(iii), which masterbatch also comprises at least one organopolysiloxane polymer.

4. A curable fire-resistant and ceramifiable silicone rubber composition in accordance with claim 3 wherein component (e) is a fire -resistance additive comprising a masterbatch comprising comprises from about 0.5 to 10 wt. % of a masterbatch comprising component (e)(i) in a siloxane polymer with (e)(i) having a platinum metal content of at least 3.0 ppm by weight with respect to the weight of the composition herein;in the curable fire-resistant and ceramifiable silicone rubbercomposition, 30 to 70 wt. % of component (e)(ii), preferably quartz, fumed silica, precipitated silica or wollastonite, and optionally 2 to 10 wt. % of cerium hydroxide which masterbatch also comprises at least one organopolysiloxane polymer and wherein said component (e) is present in an amount of from 0.5 to 8.5 wt. % of the curable fire-resistant and ceramifiable silicone rubber composition.

5. A curable fire-resistant and ceramifiable silicone rubber composition in accordance with any one of claims 1 to 4 wherein component (f) is a tetra-alkoxy titanate, tetra-alkoxy zirconate of the one or more may comprise compounds having the structure17.M[OR7]418.Where M is titanium or zirconium and each R7is selected from n-propyl, isopropyl, n-butyl, tertiary butyl, isobutyl tertiary amyl (C (C2H5) (CH₃)₂). Pentyl, hexyl or 2,4-dimethyl-3-pentyl.

6. A curable fire-resistant and ceramifiable silicone rubber composition in accordance with claim 5 wherein each R7is selected from n-butyl, tertiary butyl, isobutyl, tertiary amyl (C (C2H5) (CH₃)₂, n-pentyl, n-hexyl or 2, 4 -dime thy 1-3 -pentyl groups.

7. A curable fire-resistant and ceramifiable silicone rubber composition in accordance with any one of claim 1 to 6 which additionally comprises a magnesium compound selected from magnesium oxide, a magnesium carbonate, a magnesium hydrogen carbonate; or a mixture thereof.

8. A curable fire-resistant and ceramifiable silicone rubber composition in accordance with any one of claim 1 to 7 which additionally comprises one or more of the following pot life extenders, lubricants, metal deactivators, smoke reducing additives, pigments and / or colouring agents, heat stabilizers, compression set additives, plasticizers and mixtures thereof.

9. A fire-resistant and ceramifiable silicone rubber elastomer which is the cured product of the curable fire-resistant and ceramifiable silicone rubber composition in accordance with any one of claims 1 to 8.

10. A method of making a fire-resistant, ceramifiable silicone rubber elastomer from a curable fire-resistant and ceramifiable silicone rubber composition in accordance with any one of claims 1 to 8; by the following steps:24.(A) when component (b) is present, preparing a silicone rubber base composition by mixing component (a) with component (b) and optionally some or all of component (c);25.(B) Introducing components (d), (e) and (f) and all remaining component (c) into the silicone base composition of step (A) when component (b) is present, or into component (a) when component (b) is not present, in any suitable order and mixing to prepare a curable fire-resistant and ceramifiable silicone rubber composition; and26.(C) curing the curable fire-resistant and ceramifiable silicone rubber composition at a temperature of between 100 and 400°C.

11. A fire-resistant, ceramifiable silicone rubber elastomer which is the product obtained from the method of claim 10.

12. A fire-resistant and ceramifiable silicone rubber elastomer in accordance with claim 9 or 11 which has a UL94 V0 performance.

13. Use of one or more tetra-alkoxy titanate(s), one or more tetra-alkoxy zirconate(s) or a mixture thereof, (f) in an amount of from 0.1 to 3.0 wt. % of a curable ceramifiable silicone rubber composition; to enhance the fire-resistance properties of said composition,30.which curable ceramifiable silicone rubber composition otherwise comprises:31.(a) at least one organopolysiloxane polymer, optionally comprising one or more alkenyl and / or alkynyl groups per molecule which organopolysiloxane polymer (a) has a Williams plasticity value of at least 50mm / 100 in accordance with ASTM D926-08;32.(b) optionally one or more reinforcing silica fillers, selected from fumed silica, colloidal silica and precipitated silica;33.(c) ceramifiable filler consisting or comprising of wollastonite, which is present in an amount of from 25 to 60 wt. % of the composition;34.(d) an organic peroxide curing agent; and35.(e) a fire -resistance additive comprising36.(i) platinum metal or a platinum metal compound comprising at least 3.0 ppm platinum metal content by weight with respect to the weight of the composition herein; and optionally one or both of37.(ii) one or more fillers selected from quartz, fumed silica, precipitated silica, hydromagnesite, huntite, calcium carbonate, mica, kaolin, aluminum hydroxide (ATH), magnesium hydroxide (MDH), talc, wollastonite, and montmorillonite; and38.(iii) cerium hydroxide, cerium oxide, hydrous cerium oxide or a mixture comprising two or more thereof.

14. Use in accordance with claim 13 wherein component (e) is a masterbatch comprising component (e)(i) and optionally one or both of components (e)(ii) and (e) (iii), which masterbatch also comprises at least one organopolysiloxane polymer.

15. An electrical power cable comprising an electrically conductive core and one or more layers of insulation around the core, one of which is made of a fire-resistant, ceramifiable silicone rubber elastomer which is the cured product of the curable fire-resistant and ceramifiable silicone rubber composition in accordance with any one of claims 1 to 8.

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