Thermally conductive silicone composition

Abstract

The present disclosure relates to thermally conductive silicone compositions selected from non-curing thermally conductive silicone greases and curable thermally conductive silicone rubber compositions which, in each case, contain high levels (e.g., greater than 65 wt. %) of thermally conductive fillers but which thermal conductivity is further increased without increasing the specific gravity (i.e., density) resulting from the introduction of a greater quantity of thermally conductive fillers. The present disclosure also extends to methods for achieving the above and to uses for such materials.

Description

[0001] THERMALLY CONDUCTIVE SILICONE COMPOSITION

[0002] The present disclosure relates to thermally conductive silicone compositions selected from non-curing thermally conductive silicone greases and curable thermally conductive silicone rubber compositions which, in each case, contain high levels (e.g., greater than 65 wt. %) of thermally conductive fillers but which thermal conductivity is further increased without increasing the specific gravity (i.e., density) resulting from the introduction of a greater quantity of thermally conductive fillers. The present disclosure also extends to methods for achieving the above and to uses for such materials.

[0003] The properties of thermally conductive silicone compositions make them desirable for a variety of end use applications requiring heat transfer, for example they have been used as non-structural components in electronics, serving as thermal interface materials, pottants or encapsulants.

[0004] Non-curing thermally conductive silicone greases (alternatively referred to as thermal silicone greases, thermal silicone pastes, thermal silicone interface materials, thermal silicone gels and / or silicone heat sink compounds / pastes are thermally (but typically not electrically) conductive silicone compositions used as an interface to improve heat coupling between components of an article and / or as a means of filling insulation gaps, i.e., to increase thermal conductance across adjacent, often jointed surfaces to drain away waste heat generated by frictional and / or electrical resistance.

[0005] Hydrosilylation (addition) curable silicone rubber compositions and peroxide curable silicone rubber compositions which in each case generate cured silicone-based products may, for example, be used to coat and when cured encapsulate solid state electonic devices such as time transistors and integrated circuits and the circuit boards on which these devices are often mounted to protect them from contact with moisture, corrosive materials and other impurities present in the environment in which these devices operate. However, while such curable compositions and the resulting cured silicone-based products effectively protect solid state devices from materials that can adversely affect their operation, they typically do not possess the thermal conductivity required to dissipate the large amounts of heat generated during their operation.

[0006] One method for increasing heat dissipation is to increase the thermal conductivity of the materials used to coat or encapsulate the solid-state devices by the provision of hydrosilylation (addition) curable thermally conductive silicone rubber compositions or peroxide curable thermally conductive silicone rubber compositions involves the introduction of thermally conductive fillers (sometimes referred to as heat conductive fillers) to the compositions and resulting encapsulating material.

[0007] However, such thermally conductive silicone compositions suffer from a variety of problems not least because of the high levels of such fillers required in order to generate high thermal conductivities of e.g., at least 1.0 W / mK (measured in accordance with ISO 22007-2 - hot disk method). Such high thermal conductivities are achieved by increasing the amount of thermally conductive fillers in the respective compositions, but the presence of such fillers in amounts of say greater than 65 or 80 weight % (wt. %) of tire composition generally results in the un-cured compositions or pre -cured materials having significantly increased viscosities causing impaired handling characteristics and additionally, in the lattercase, upon cure, result in cured silicone-based products with poor physical properties as the vast majority of thermally conductive fillers are not reinforcing.

[0008] Whilst such silicone compositions may be acceptable for some applications, industry is increasingly demanding compositions which have the desired high levels of thermal conductivity without necessarily such high content of thermally conductive fillers.

[0009] Solutions have been identified, for example, the high viscosity of pre-cured compositions due to the level of thermally conductive filler present can be avoided by dilution of the compositions with non-reactive silicones or organic solvents, but this has been found to result in compatibility problems with the diluents bleeding out of the subsequently cured silicone-based products with time and furthermore, such products historically have not satisfied the physical property demands of the industry.

[0010] However, fabricators are now seeking to streamline their production processes by utilizing multi-purpose materials in place of multi-component assemblies. Traditional thermally conductive (TC) silicones cannot be used as structural components such as an extruded hose, gasket, or preformed article. As such, there is a growing need for TC silicones with mechanical toughness, and in forms that can be fabricated by extrusion, molding, or calendaring.

[0011] With the rise of electric vehicles and hybrid vehicles, thermally conductive elastomers are needed and poised for growth especially in tire mobility and transportation market. These newer vehicles require enhanced thermal management and need a structural elastomer with thermally conductive properties.

[0012] In general, the target is high thermal conductivities, and to achieve this target, high loadings of thermally conductive fillers are needed. Which leads to tire following trade-offs;

[0013] 1) High density conductive fillers add weight to the end article.

[0014] 2) Increased formulation costs,

[0015] 3) High conductive (e.g., not reinforcing) filler loadings are detrimental to mechanical properties (for example, but not limited to, 70% or more).

[0016] 4) High filler loading leads to abrasion of tooling.

[0017] These challenges are well known in the field.

[0018] There is provided herein a thermally conductive silicone composition, which comprises the following components:

[0019] a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof;

[0020] b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition;

[0021] and

[0022] c) preformed silicone elastomeric particulates having an average particle size of 1 mm or less, in an amount of from 0.5 to 30 wt. % of the composition;which composition is a non-curing thermally conductive silicone grease unless additionally comprising components (d) and (e) when component (a) comprises an average of at least two unsaturated groups per molecule, or component (f)

[0023] wherein components (d) and (e) are:

[0024] 5 (d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; and

[0025] (e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and

[0026] (f) an organic peroxide curing agent (sometimes referred to as a free-radical initiator).

[0027] 10 There is also provided a method for making a thermally conductive silicone composition, which comprises mixing the following components:

[0028] a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof;

[0029] 15 b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the thermally conductive filler composition; and

[0030] c) preformed silicone elastomeric particulates having an average particle size of 1 mm or less, in an amount of from 0.5 to 30 wt. % of the composition

[0031] d) to form a non-curing thermally conductive silicone grease unless; or additionally adding components (d) 20 and (e) when component (a) comprises an average of at least two unsaturated groups per molecule, or component (f)

[0032] wherein components (d) and (e) are:

[0033] (d) an organosilicon compound having an average of at least two Si-H groups per molecule or at least three Si-H groups per molecule; and

[0034] 25 e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and

[0035] f) is an organic peroxide curing agent;

[0036] to form a curable thermally conductive silicone rubber composition and curing said curable thermally conductive silicone rubber composition.

[0037] 30 There is also provided a method of increasing thermal conductivity of a thermally conductive silicone composition selected from a non-curing thermally conductive silicone grease or a curable thermally conductive silicone rubber composition in each case comprising thermally conductive fillers in an amount of from 65 to 95 wt. % of the composition without introducing additional thermally conductive fillers by

[0038] 35 Introducing a component (c) comprising preformed silicone elastomeric particulates having an average particle size of 1 mm or less, in an amount of from 0.5 to 30 wt. % of a composition otherwise comprisingthe following components:

[0039] a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof;

[0040] b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition; to form a non-curing thermally conductive silicone grease unless; or additionally adding components (d) and (e) when component (a) comprises an average of at least two unsaturated groups per molecule, or component (f)

[0041] wherein components (d) and (e) are:

[0042] d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; and

[0043] e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and

[0044] f) is an organic peroxide curing agent;

[0045] to form a curable thermally conductive silicone rubber composition and curing said curable thermally conductive silicone rubber composition.

[0046] There is also provided a use of of a component (c) comprising preformed silicone elastomeric particulates having an average particle size of 1 nun or less, in an amount of from 0.5 to 30 wt. % to increase thermal conductivity of a thermally conductive silicone composition selected from a noncuring thermally conductive silicone grease or a hydrosilylation (addition) curable thermally conductive silicone robber composition otherwise comprising the following components:

[0047] a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof 8;

[0048] b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition; to form a non-curing thermally conductive silicone grease unless; or additionally adding components (d) and (e) when component (a) comprises an average of at least two unsaturated groups per molecule, or component (f)

[0049] wherein components (d) and (e) are:

[0050] d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; and

[0051] e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and

[0052] f) is an organic peroxide curing agent;

[0053] to form a curable thermally conductive silicone rubber composition.

[0054] The total weight % (wt. %) of each of tire above compositions is 100 wt. %.There is also provided a composite article having a heat dissipating surface in contact with a non-curing thermally conductive silicone grease as hereinbefore described or a silicone rubber material which is the cured product of the curable thermally conductive silicone rubber composition hereinbefore described. In one embodiment, when the above composition is an uncurable thermally conductive silicone grease, in one embodiment said uncurable thermally conductive silicone grease does not contain component (e) or component (f).

[0055] The thermal conductivity of a composition is increased by adding more and more thermally conductive fillers but unfortunately this directly correlates to the material’s specific gravity otherwise known as its relative density, a dimensionless ratio value which herein is the ratio of:

[0056] density of the thermally conductive silicone composition : density of water at 4°C

[0057] The density of water at 4°C is 1kg per litre. In a preferred embodiment the above compositions have a minimum bulk thermal conductivity at least 1.0 W / mK (Watts per meter Kelvin) (measured in accordance with ISO 22007-2 - hot disk method).

[0058] Herein we have found a means of increasing thermal conductivity without increasing the specific gravity of the thermally conductive silicone composition to any significant extent by breaking tire prior art understanding that to increase thermal conductivity one must introduce a greater quantity of thermally conductive fillers, irrespective of tire amount of thermally conductive fillers already present in a composition. While it is believed a significant amount of thermally conductive fillers say at least 65 wt. % will always be required to make a thermally conductive silicone composition suitably thermally conductive, the addition of further conductive fillers can be limited by excluding tire volume of tire composition into which the thermally conductive fillers can migrate during mixing or later use by introducing component (c) to provide non-conductive silicone domains into the non-curing thermally conductive silicone grease or curable thermally conductive silicone rubber composition and in the latter case the resulting elastomer matrix thereof.

[0059] The resulting composition) s) is / are therefore designed to preferably provide either a non-curing thermally conductive silicone grease or a curable thermally conductive silicone rubber composition with a thermal conductivity of e.g., at least 1.0 W / mK (measured in accordance with ISO 22007-2 - hot disk method). There follow details of the components present in the composition described herein.

[0060] Component (a)

[0061] Component (a) of the thermally conductive silicone composition is one or more organopolysil oxane polymers which may, but do not necessarily, comprise an average of at least two unsaturated groups per molecule, alternatively at least two unsaturated groups per molecule which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof.

[0062] It will be appreciated that given the thermally conductive silicone compositions described herein may be non-curing thermally conductive silicone greases or curable thermally conductive silicone rubber compositions when they are the former no unsaturated groups are essential in component (a). However, when the thermally conductive silicone composition described herein is a curable thermally conductivesilicone rubber composition component (a) comprises an average of at least one unsaturated group per molecule selected from alkenyl groups, alkynyl groups or a mixture thereof per molecule; alternatively an average of at least two or more unsaturated groups per molecule selected from alkenyl groups, alkynyl groups or a mixture thereof per molecule.

[0063] Each organopolysiloxane polymer of component (a) comprises multiple siloxy units, of formula (I):

[0064] R’aSiO(4-a) / 2 (I)

[0065] The subscript “a” is 0, 1 , 2 or 3.

[0066] 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’sSiOia; the D unit corresponds to a siloxy unit where a = 2, namely R’jSiChc; the T unit corresponds to a siloxy unit where a = 1, namely R’iSiOa / 2', the Q unit corresponds to a siloxy unit where a = 0, namely SiChn. The 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 subscript a in structure (I) is about 2.

[0067] When present, i.e., when tire thermally conductive silicone composition is a curable thermally conductive silicone rubber composition and optionally when the thermally conductive silicone composition described herein is a non-curing thermally conductive silicone grease, tire unsaturated groups of component (a) may be positioned either terminally or pendently on the organopolysiloxane polymer, or in both locations. When present, 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 the unsaturated groups of component (a) include vinyl, propenyl, isopropenyl, butenyl, allyl, and 5-hexenyl. In formula (I), each R’, other than the 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. Substitutedaliphatic hydrocarbyl groups may be non-halogenated substituted alkyl groups or halogenated substituted alkyl groups like 3, 3, 3 -trifluoropropyl and nonatluorohexyl groups.

[0068] 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.

[0069] 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 an average of at least two unsaturated groups, alternatively at least two, 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. Other alternatives include

[0070] 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.

[0071] Preferably component (a) has a zero-shear viscosity of at least lOmPa.s at 25°C, alternatively at least 50 mPa.s at 25°C. Unless otherwise indicated viscosity measurements provided are zero-shear viscosity (t]0) values, obtained by extrapolating to zero the value taken at low shear rates (or simply taking an average of values) in the limit where the viscosity-shear rate curve is rate-independent, which is a test-method independent value provided a suitable, properly operating rheometer is used. For example, the zero-shear viscosity of a substance at 25 °C may be obtained by using commercial rheometers such as an Anton-Parr MCR-301 rheometer or a TA Instruments AR-2000 rheometer equipped with cone-and-plate fixtures of suitable diameter to generate adequate torque signal at a series of low shear rates, such as 0.01 s’1, 0.1 s’1and 1.0 s’1while not exceeding the torque limits of the transducer. Alternatively, the viscosity of component (a) may be measured at 25°C in accordance with the ASTM D4287 Cone and Plate Method using a Brookfield DV-III Ultra Rheometer.

[0072] The viscosity of component (a) may in some instances be very high e.g., at least 1,000,000 mPa.s at 25°C up to many millions of mPa.s at 25°C. In such circumstances, because of tire difficulty in measuring the viscosity of such highly viscous fluids, often referred to as silicone gums, it is usually preferred toprovide a Williams plasticity value rather than a viscosity measurement. These are obtained in accordance with ASTM D926-08. In this instance when component (a) is a very viscous material of at least l,000,000mPa.s at 25°C and has a Williams plasticity of at least 50mm / 100 measured in accordance with ASTM D926-08, component (a) will be described by its Williams plasticity measured in accordance with ASTM D926-08. When component (a) is a silicone gum it has a Williams plasticity of at least 50mm / 100 measured 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. Typically, silicone gums have a Williams plasticity of from about 75mm / 100 to 450mm / 100 measured in accordance with ASTM D926-08.

[0073] 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 tire number average molecular weight and weight average molecular weight values of tire 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.

[0074] 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).

[0075] 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 an average of 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 0.001 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 groups, 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 E168.

[0076] Component (a) may be present in the thermally conductive silicone composition in an amount of from 4 wt. % to about 19 to 20 wt. % of the composition, alternatively from 5 to about 19 or 20 wt. % of the composition, alternatively from 5 to 17.5 wt. % of the composition, alternatively from 7.5 to 17.5 wt. % of the composition. Typically, component (a) is present in an amount which is the difference between 100 wt. % and tire cumulative wt. % of the other components / ingredients of tire thermally conductive silicone composition.Component (b)

[0077] Component (b) of the thermally conductive silicone composition is at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition.

[0078] Any suitable thermally conductive fillers may be utilised as component (b). Examples include: metals e.g., bismuth, lead, tin, antimony, indium, cadmium, zinc, silver, copper, nickel, aluminum, iron and silicon metal;

[0079] alloys e.g., alloys of one or more of bismuth, lead, tin, antimony, indium, cadmium, zinc, silver, aluminum, iron and / or silicon; for example, Fe-Si alloy, Fe-Al alloy, Fe-Si-Al alloy, Fe-Si-Cr alloy, Fe-Ni alloy, Fe-Ni-Co alloy, Fe-Ni-Mo alloy, Fe -Co alloy, Fe-Si-Al-Cr alloys, Fe-Si-B alloy and Fe-Si-Co-B alloy;

[0080] ferrites, Mn-Zn ferrite, Mn-Mg-Zn ferrite, Mg-Cu-Zn ferrite, Ni-Zn ferrite, and a Ni-Cu-Zn ferrite and Cu-Zn ferrite;

[0081] Metal oxides such as, aluminium oxide (alumina), zinc oxide, silicon oxide, magnesium oxide, beryllium oxide, chromium oxide and titanium oxide;

[0082] metal hydroxides such as magnesium hydroxide, aluminum hydroxide, barium hydroxide and calcium hydroxide;

[0083] metal nitrides, such as boron nitride, aluminum nitride and silicon nitride;

[0084] metal carbides such as silicon carbide, include boron carbide and titanium carbide; and

[0085] metal silicides such as magnesium silicide, titanium silicide, silicide, zirconium, tantalum silicide, niobium silicide, chromium silicide, and a tungsten silicide and molybdenum silicide. Appropriate forms of carbon may also be utilised, such as for tire sake of example graphite, carbon nanotubes, graphene and carbon fullerenes.

[0086] The thermally conductive filler may be a mixture of two or more of tire above. In some embodiments, combinations of metallic and inorganic fillers, may be used, for example a combination of aluminium and aluminium oxide fillers; a combination of aluminium and zinc oxide fillers; or a combination of aluminium, aluminium oxide, and zinc oxide fillers.

[0087] Of the above, aluminium oxide, aluminum hydroxide, aluminium nitride, boron nitride, aluminium and zinc oxide and mixtures thereof are preferred.

[0088] The shape of the thermally conductive filler particulates is not specifically restricted, e.g., they may be powders and / or fibres, however, rounded or spherical particulates may prevent viscosity increase to an undesirable level upon high loading of the thermally conductive filler in the composition and as such are preferred. The volume median particle diameter and D50 particle size distribution of the thermally conductive filler will depend on various factors including the type of thermally conductive filler selected and the exact amount added to the curable composition, as well as the bond line thickness of tire device in which tire cured silicone -based product of the composition will be used. In some particular instances, tire thermally conductive filler may have a volume median particle diameter ranging from 0.1-100 micrometres (pm) measured by laser diffraction particle size analysis, alternatively 0.1 micrometre to 80micrometres, alternatively 0.1 micrometre to 50 micrometres. The thermally conductive silicone compositions as described herein comprise from 65 wt. % to 95 wt. %, alternatively from 70 wt. % to 95 wt. %, alternatively from 75 wt. % to 95 wt. %, alternatively 75 wt. % to 90 wt.% thermally conductive filler (b).

[0089] In one embodiment said thermally conductive filler(s) may have a volume median particle diameter D(v,0.5) of between 0.1-100 micrometres (pm).

[0090] The volume median particle diameter D(v,0.5) is the particle diameter value for a D50 particle size distribution (or median particle size distribution) where 50% of the distribution is above said value and 50% is below said value. The thermally conductive filler (b) may be a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one property such as particle shape, volume median particle diameter, particle size distribution, and type of filler. The volume median particle diameter D(v,0.5) values herein were taken from supplier datasheets and / or were measured by laser diffraction particle size analysis using a Malvern Mastersizer 2000 with Hydro 2000MU dispersion unit. The parameters relied upon were refractive index (R.I.) of particle: 1.78 / 0.1; dispersant: water (1.33); obscuration: -10%; inner stirring speed: 3000rpm.

[0091] Samples were prepared before analysis by mixing 0.5g fillers + 25ml water, shaking the mixture and introducing the resulting mixture into the Hydro2000MU dispersion unit with 2min inner sonication. Component (c)

[0092] Component (c) are preformed silicone elastomeric particulates having an average particle size of 1 mm or less, in an amount of from 0.5 to 30 wt. % of tire composition, alternatively in an amount of from 0.5 to 25 wt. % of the composition, alternatively in an amount of from 0.5 to 20 wt. % of tire composition, alternatively in an amount of from 0.5 to 15 wt. % of tire composition. The preformed silicone elastomeric particulates (c) may be made from new compositions or are physically recycled and / or reclaimed silicone elastomeric particulates (c). In one embodiment the preformed silicone elastomeric particulates (c) are physically recycled and / or reclaimed silicone elastomeric particulates (c).

[0093] The terms recycling and reclaiming as used herein are intended to define the function of recovering and converting waste materials into new materials and usable products.

[0094] The average particle size of particulates provided is given irrespective to their method of preparation. For example, in the case of physically recycled and / or reclaimed silicone elastomeric particulates (c) it is the average particle size of particulates subsequent to physically recycling and / or reclaiming the source of the silicone elastomer particulates (c). The use of recycled / reclaimed silicone elastomer particulates (c) provides a more sustainable thermally conductive silicone composition selected from non-curing thermally conductive silicone grease or curable thermally conductive silicone rubber composition offering a lower carbon footprint to tire user by enabling replacement of a proportion of for example at least 2 wt. %, alternatively at least 5 wt. %, alternatively at least 10 wt. % new silicone compositions, with mechanically recycled cured silicone elastomer particulates, from a variety of sources, sufficiently compatible with thermally conductive silicone compositions which provide useful elastomeric propertiesthereto. Hence, this solution provides both the benefit of reducing the carbon footprint associated with producing new compositions as well as providing a High value alternative to incineration or landfilling as an end-of-life option for the silicone elastomers used in the preparation of the preformed silicone elastomeric particulates.

[0095] The Preformed silicone elastomeric particulates (c) may be made as new particulates or may be derived from a recycling / reclaiming process derived from any suitable source such as post-industrial or postconsumer waste mainly obtained from condensation cured (RTV) silicone elastomers formerly used as adhesives, refrigerant spacers, potting agents coatings and sealants such as weatherproofing sealants and coatings and / or tire sealants or silicone rubber elastomers prepared from hydrosilylation curable compositions, peroxide free-radical cure compositions or UV cure compositions using photoinitiators or photo-catalysts, which elastomers may have been used in applications such as airbag coatings, gaskets and seals adhesives, coatings, foams, molded rubber articles, hoses and tubing like medical tubing, encapsulants and potting agents or the like. The original elastomer and the resulting physically recycled and / or reclaimed silicone rubber particulates may be dense or have inclusions or voids, as in foams. However, silicone elastomers made from any suitable cure system may be utilised as the source of preformed silicone elastomeric particulates.

[0096] Newly made particulate used as preprepared silicone elastomeric particulates herein may be made from condensation cured (RTV) silicone elastomer compositions or prepared from hydrosilylation curable compositions, peroxide free-radical cure compositions or UV cure compositions using photoinitiators or photo-catalysts or polymers having thiol-ene or acrylic groups which can be UV activated. These may all be obtained via their usual curing process into slabs / lumps or the like and then are physically (e.g., mechanically) ground, attrited or otherwise reduced in size into discrete particulates using a grinding device as described elsewhere herein or wherein the curable silicone composition may be cured into particulates by spraying using a spraying device such as a spray drier; or by dispersed and curing tire compositions in an aqueous surfactant solution. The latter are often preferred due to their ability to form spherical cured silicone particulates.

[0097] When the preformed silicone elastomeric particulates are the result of physical recycling or reclaiming, physical recycling methods are utilised to transform silicone elastomers into powders, granules, crumbs, or pellets (referred to collectively herein as “particulates”). The source of the silicone elastomers may be from, for example, post-industrial scrap or waste rubber, pre-consumer scrap or waste rubber, or postconsumer scrap or waste rubber. For the avoidance of doubt and for the sake of this disclosure physically ( mechanically) recycled / reclaimed particulates have their original crosslinked structure preserved, whereas chemically recycled materials do not.

[0098] When tire origin of the cured silicone rubber elastomeric particulates is unknown a priori, the cured rubber from which it originates or the physically recycled or reclaimed particulates can be characterized by a variety of known methods to ascertain the composition including spectroscopic techniques includinginfrared techniques such as Fourier transform infrared (FTIR) spectroscopy, attenuated total reflectance infrared spectroscopy ( ATR-IR), infrared microscopy, Raman spectroscopy, Raman microscopy, solid state nuclear magnetic resonance (NMR) spectroscopy; chemical derivatization and titration techniques; chemical digestion followed by chromatography such as gas chromatography (GC), gas chromatographymass spectrometry (GC-MS), liquid chromatography (LC), or by a variety of known elemental or ion analysis techniques such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), x-ray fluorescence (XRF), and neutron activation analysis (NAA).

[0099] When the preformed silicone elastomeric particulates are physically recycled or reclaimed silicone elastomeric particulates, any suitable physical recycling method including mechanical reclaiming, thermo-mechanical reclaiming, cryo-mechanical reclaiming, and wet / solution grinding can be utilised to obtain the particulates. Examples of methods which may be utilised to generate tire particulates include, for the sake of example, cryomilling (at liquid nitrogen temperatures), using milling equipment known in tire art such as ball mills, pin mills, and the like, tornado milling (which can be done at either ambient or cryogenic temperatures in the solid state) and wet jet milling (e.g., wet jet) where the rubber is pulverized by an intense water stream.

[0100] The preformed silicone elastomeric particulates preferably have an average particle size of 1 mm or less. Smaller particle sizes are preferable to minimize stress-concentrating defects in the new article, but satisfactory performance has been achieved even for relatively large 1 mm sized milled preformed silicone elastomeric particulates. Alternatively, tire average particle size of tire preformed silicone elastomeric particulates was 600pm or less, alternatively the average particle size of the preformed silicone elastomeric particulates was 500pm or less, alternatively the average particle size of the preformed silicone elastomeric particulates was 400pm or less, alternatively the average particle size of the preformed silicone elastomeric particulates was 300pm or less, alternatively the average particle size of tire preformed silicone elastomeric particulates was 200pm or less. Particulates of an acceptable size may be obtained by mechanical screening through a sized mesh. Smaller particulates are obtained by filtering through increasingly small meshes.

[0101] In one embodiment the aforementioned silicone elastomeric particulates are physically recycled and / or reclaimed silicone elastomeric particulates (c).

[0102] If the silicone elastomer to be made into physically recycled or reclaimed particulates is adhered to another material in prior use, they are preferably separated or delaminated. For example, in the case of wanting to recycle airbag articles the first step is to recover the silicone elastomer by delaminating same from the textile / fabric support. After which the resulting coating may be broken down into particulates using one of the physical (mechanical) processes listed above. However, it is to be understood that delamination or separation of silicone materials from certain substrates or articles may be imperfect and can lead to some residual minority fraction of adventitious non-silicone contaminants in the resulting physically recycled and / or reclaimed silicone elastomeric particulates (c)., such as small fragments offabric or plastic substrates that may be present in quantities less than 10 wt. % of a particulate mixture, preferably 5 wt. % or less, with less being desirable.

[0103] Physical recycling and / or reclamation using one or more of the different methods described above offers:

[0104] 1) the advantage of being able to reuse inorganic fillers,

[0105] 2) the ability to incorporate contaminated feedstocks from deployed silicone elastomers, and the ability to tolerate residual Si-H from hydrosilylation cured silicone elastomers without needing to undergo the depolymerization, neutralization, filtration, and stripping steps associated with chemical recycling processes.

[0106] In one example, cured silicone rubber samples were shredded with a paper shredder or cut with scissors until they were of a predetermined size e.g., less than 2cm particle size before being fed to a mill such as a Mikro™ UMP-B mill commercially available from Hosokawa Micron Corporation. The shredded / cut rubber samples can be mixed with dry ice (which may be crushed to a powder using mortar and pestle) in an approximately 1 : 1 weight ratio in order to reduce tire temperature of the rubber and help stiffen it for milling. The rubber / dry ice mixture can then be fed into a suitable mill using a knife blade rotor rotating at an rpm of > 10,000. The rubber can then be allowed to leave the milling chamber through a stainless-steel screen when the rubber is cut finer than the hole size of tire screen, e.g., a 2-3 mm diameter round holes could be used for a first pass. The rubber milled in tire first pass can then undergo a second pass with dry ice again as before and fed through the Mikro™ UMP-B mill for a second pass this time using a 1mm slotted screen.

[0107] If desired for more accurate particle size measurements samples can be measured using laser diffraction with e.g., a Beckman Coulter™ LS 13320 Particle Size Analyzer with the Tornado (dry) module commercially available from Beckman Coulter Inc., relying on the Beckman Coulter™ software to deconvolute the diffraction signal to a particle size distribution determined using Fraunhofer diffraction model. It will be appreciated that Utilization of waste silicone rubber particulates into the composition makes the end product more sustainable.

[0108] When the thermally conductive silicone composition as hereinbefore described is a hydrosilylation (addition) curable thermally conductive silicone rubber composition, the hydrosilylation (addition) curable thermally conductive silicone rubber composition additionally comprises components (d) and (e) as described below:

[0109] Component (d)

[0110] Component (d) of the hydrosilylation (addition) curable thermally conductive silicone rubber composition functions as a cross-linker and is provided in the form of an organosilicon compound having an average of least two or an average of at least three Si-H groups per molecule. Component (d) normally contains three or more silicon-bonded hydrogen atoms so that tire hydrogen atoms can react with the unsaturated alkenyl and / or alkynyl groups of polymer (a), required when the thermally conductive silicone composition is a hydrosilylation (addition) curable thermally conductive silicone rubber composition, to form a network structure therewith and thereby cure the composition. Some or allof Component (d) may alternatively have two silicon bonded hydrogen atoms per molecule when polymer (a) has greater than two unsaturated groups per molecule.

[0111] The molecular configuration of the organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule (d) is not specifically restricted, and it can be a straight chain, branched (a straight chain with some branching through the presence of T groups), cyclic or silicone resin based.

[0112] While the molecular weight of component (d) is not specifically restricted, the viscosity is typically from 5 to 50,000 mPa.s at 25°C relying on either a Brookfield DV-III Ultra Programmable Rheometer for viscosities greater than or equal to 50,000 mPa.s, and a Brookfield DV 3T Rheometer for viscosities less than 50,000 mPa.s, in order to obtain a good miscibility with polymer (a). However, in the case of very low viscosities e.g., less than lOOmPa.s at 25°C, they may be measured using a glass capillary viscometer in accordance with ASTM D-445.

[0113] Silicon-bonded organic groups used in component (d) 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 tire silicon-bonded organic groups used in component (d) are alkyl groups, alternatively methyl, ethyl or propyl groups.

[0114] Examples of die organosilicon compound having an average of at least two or an average of at least diree Si-H groups per molecule (d) include but are not limited to:

[0115] (a’) trimethylsiloxy-terminated methylhydrogenpolysiloxane,

[0116] (b’) trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxane,

[0117] (c’) dimethylhydrogensiloxy-terminated dimetiiylsiloxane-methylhydrogensiloxane copolymers, (d’) dimethylsiloxane-methylhydrogensiloxane cyclic copolymers,

[0118] (e’) copolymers and / or silicon resins consisting of (CHshHSiOi / z units, (CHs SiOie units and SiO4 / 2 units,

[0119] (f’) copolymers and / or silicone resins consisting of (CH ihHSiOi / j units and SiO4 / 2 units,

[0120] (g’) Methylhydrogensiloxane cyclic homopolymers having between 3 and 10 silicon atoms per molecule;

[0121] (h ’) an Si-H terminated methylhydrosiloxane-phenylmethylsiloxane co-polymer having a zero-shear viscosity of from 50 to 300 cSt and 30 to 75 mol % of phenylmethylsiloxane units.

[0122] alternatively, component (c), the cross-linker, may be a filler, e.g., silica treated with one of the above, and mixtures thereof

[0123] In one embodiment the Component (d) 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 amethylhydrogensiloxane and a dimethylsiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups.

[0124] The cross-linker (d) is generally present in the hydrosilylation (addition) curable thermally conductive silicone rubber composition such that the molar ratio of the total number of the silicon-bonded hydrogen atoms in component (d) to the total number of alkenyl and / or alkynyl groups in polymer (a) and in component (d) is from 0.5:1 to 20:1. When this ratio is less than 0.5:1, a well-cured composition will not be obtained. When the ratio exceeds 20:1 , there is a tendency for the hardness of the cured composition to increase when heated. Preferably in an amount such that the molar ratio of silicon-bonded hydrogen atoms of component (d) to alkenyl groups and / or alkynyl groups, alternatively alkenyl groups of component (a) and component (d) ranges from 0.7 : 1.0 to 5.0 : 1.0, preferably from 0.9 : 1.0 to 2.5 : 1.0, and most preferably from 0.9 : 1.0 to 2.0 : 1.0.

[0125] The silicon-bonded hydrogen (Si-H) content of component (d) is determined using quantitative infra-red analysis in accordance with ASTM E168. In the present instance the silicon-bonded hydrogen to alkenyl (typically vinyl) and / or alkynyl ratio is important when relying on a hydrosilylation cure process.

[0126] Generally, this is determined by calculating tire total weight % of alkenyl groups in the composition, e.g., vinyl [V] and the total weight % of silicon bonded hydrogen [H] in tire composition and given tire molecular weight of hydrogen is 1 and of vinyl is 27 tire molar ratio of silicon bonded hydrogen to vinyl is 27[H] / [V].

[0127] Typically, dependent on the number of unsaturated groups in component (a) as well as tire number of Sill groups in component (d), component (d) will be present in an amount of from 0.1 to 10 wt. % of the thermally conductive silicone rubber composition, alternatively 0.1 to 7.5wt. % of the thermally conductive silicone composition, alternatively 0.5 to 7.5wt. %, further alternatively from 0.5% to 5 wt. % of tire thermally conductive silicone rubber composition.

[0128] Component (e)

[0129] Component (e) of the thermally conductive silicone composition as hereinbefore described when in the form of a hydrosilylation (addition) curable thermally conductive silicone rubber 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 (e) herein catalyses the reaction between an unsaturated group, usually an alkenyl group e.g., vinyl with Si-H groups.

[0130] The hydrosilylation catalyst of component (e) 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 of component (e) 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 (PtC12.(olefin)2and H / PtCla. 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 tire sake of example a platinum-cyclopropane complex of the formula (PtCECsHe , tire 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, sulfur, and amine ligands can be used as well, e.g., ( PhiPHPtCI2; and complexes of platinum with vinylsiloxanes, such as sym-divinyltetramethyldisiloxane.

[0131] Hence, specific examples of suitable platinum-based catalysts of component (e) include

[0132] (i) complexes of chloroplatinic acid with organosiloxanes containing ethylenically unsaturated hydrocarbon groups are described in US 3,419,593;

[0133] (ii) chloroplatinic acid, either in hexahydrate form or anhydrous form;

[0134] (iii) a platinum-containing catalyst which is obtained by a method comprising reacting chloroplatinic acid with an aliphatically unsaturated organosilicon compound, such as divinyltetramethyldisiloxane;

[0135] (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;

[0136] (v) In some embodiments, the catalyst component (e) may be encapsulated, microencapsulated, or absorbed in a carrier or shell such as a wax, thermoplastic resin, organosilicon resin or siliceous matrix to promote stability below a certain trigger such as heat or shear, e.g., via a latent heat cure approach, in which die encapsulate melts / softens under heat; and / or

[0137] (vi) Karstedt’s catalyst is a Pt2(divinyl tetramethyl disiloxane) ! complex typically containing from 30 to 50 wt. % platinum metal in die complex. 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 die 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 die 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 (e) 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.

[0138] The catalytic amount of the hydrosilylation catalyst is generally between 0.01 ppm, and 10,000 parts by¬ weight of platinum-group metal, per million parts (ppm), based on the weight of the composition; alternatively, between 0.01 and 5000ppm; alternatively, between 0.01 and 3,000 ppm, and alternatively between 0.01 and 1 ,000 ppm. In specific embodiments, the catalytic amount of the catalyst may range from 0.01 to 1,000 ppm, alternatively 0.01 to 750 ppm, alternatively 0.01 to 500 ppm and alternatively 0.01 to 100 ppm of metal based on the weight of the composition. The ranges may relate solely to the metal content within the catalyst or to the catalyst altogether (including its ligands) as specified, but typically these ranges relate solely to the metal content within die catalyst. Tire catalyst may be added as a single species or as a mixture of two or more different species. Typically, dependent on tire form / concentration in which the catalyst is provided e.g., in a polymer or solvent, the amount of component (e)present will be within the range of from 0.001 to 3.0 wt. % of the composition, alternatively from 0.001 to 1.5 wt. % of the composition, alternatively from 0.01-1.5 wt. %, alternatively 0.01 to 1.0 wt. %, of the thermally conductive silicone composition as hereinbefore described when in tire form of a hydrosilylation (addition) curable thermal ly conductive silicone rubber composition.

[0139] When the thermally conductive silicone composition as hereinbefore described is a peroxide curable thermally conductive silicone rubber composition, the curable thermally conductive silicone rubber composition additionally comprises component (f) (but not component (e)) as described below:

[0140] Component (f)

[0141] Component (f) of the curable thermally conductive 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 vulcanizable (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, 1,1 ,bis(t-butyl peroxy) -3,3,5 -trimethylcyclohexane and p-chlorobenzoyl peroxide. Mixtures of the above may also be used.

[0142] The amount of the organic peroxides (f) 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 thermally conductive 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 tire composition.

[0143] When an organic peroxide curing agent (sometimes referred to as a free-radical initiator) is present, it is not essential for component (a) to comprise an average of at least two unsaturated groups per molecule,such groups are optional because of the free-radical cure process which does not require the presence of alkenyl e.g.. vinyl groups.

[0144] The thermally conductive silicone compositions selected from non-curing thermally conductive silicone greases or curable thermally conductive silicone rubber compositions or the cured silicone-based products resulting from the latter comprising at from 65 to 95 wt.% thermally conductive filler (b) described herein will have a thermal conductivity of at least 1.OW / mK, measured in accordance with ISO 22007-2 - hot disk method.

[0145] The thermal conductivity of the cured silicone -based products will depend on the thermally conductive filler(s) utilised. In the case of less conductive thermally conductive fillers (b) such as aluminium oxide and aluminium hydroxide when present in an amount of 65 to 95 wt. % of the composition thermal conductivity of the product will be typically still beat least 1. OW / mK and (ISO 22007-2 - hot disk method).

[0146] It has been found that rather than by the traditional route of further increasing tire thermal conductivity of tire thermally conductive silicone compositions selected from non-curing thermally conductive silicone greases or curable thermally conductive silicone rubber compositions or the cured silicone-based products resulting therefrom, tire addition of component (c) the preformed silicone elastomeric particulates in air amount of from 0.5 to 30 wt. % causes tire thermal conductivity to be increased without increasing the specific gravity thereof by effectively reducing tire volume of tire thermally conductive silicone compositions sor tire cured silicone -based products resulting therefrom, in which tire conductive filler can be situated, i.e., concentrating the thermally conductive filler content.

[0147] One advantage herein when using such fillers in combination with the compositions herein result in said cured silicone -based products having satisfactory physical properties such as tensile strength and elongation at break.

[0148] Optional additives when the thermally conductive silicone compositions are selected from noncuring thermally conductive silicone greases or curable thermally conductive silicone rubber compositions

[0149] The thermally conductive silicone compositions irrespective of whether they are non-curing thermally conductive silicone greases or curable thermally conductive silicone rubber compositions may include one or more of the following additional optional additives, rheology modifiers, reinforcing fillers, semireinforcing fillers, treating agents for rendering fillers hydrophobic, pigments and / or coloring agents, mold release agents, adhesion promoters, cure modifiers, anti-oxidants, heat stabilizers, metal deactivators Acid scavengers, green strength modifiers, species for oil bleed / lubricationand flame retardants.

[0150] Optional Reinforcing and semi-reinforcing fillers

[0151] Whilst not preferred given the requirement herein for high thermal conductivity, one optional additive in tire thermally conductive silicone compositions as described herein is at least one silica or calcium carbonate reinforcing or semi -reinforcing filler / s).When present, the silica reinforcing fillers maybe exemplified by precipitated silica, fumed silica and / or colloidal silicas. Preferably the silica reinforcing fillers are finely divided. The calcium carbonate is preferably precipitated calcium carbonate. Precipitated silica, fumed silica and / or colloidal silicas are particularly preferred because of their relatively high surface area, which is typically at least 50 m2 / g (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 97 . 2010), are typically used. All these types of silica are commercially available.

[0152] The silica reinforcing filler(s) are naturally hydrophilic and therefore may be treated with a treating agent to render them hydrophobic.

[0153] Filler treating agents

[0154] In the present composition any of tire above fillers may be surface treated with a suitable low molecular weight organosilicon compounds which can be used to render fillers hydrophobic. The fillers may be either component (b), the reinforcing and / or semi -reinforcing fillers described above or both component (b) and the reinforcing and / or semi-reinforcing fillers. Examples of suitable treating agents include organosilanes, polydiorganosiloxanes, or organosilazanes e.g., hexaalkyl disilazane and short chain siloxane diols. Specific examples include, but are not restricted to, silanol terminated trifluoropropyhnetliylsiloxane, silanol terminated vinyl methyl (ViMe) siloxane, silanol terminated methyl phenyl (MePh) siloxane, liquid hydroxyldimethyl-terminated polydiorganosiloxane containing an average from 2 to 20 repeating units of diorganosiloxane in each molecule, hydroxyldimethyl 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, decyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, chlorotrimethyl silane, dichlorodimethyl silane, and trichloromethyl silane.

[0155] 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, hexaorganodisiloxanes, such as hexamethyldi siloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes, such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane and; hydroxyldimethyl terminated polydimethylmethylvinyl siloxane, octamethyl cyclotetrasiloxane, and silanes including but not limited to methyltriethoxysilane, dimethyldiethoxysilane and / or vinyltriethoxysilane. A small amount of water can be added together with tire silica treating agent(s) as processing aid.

[0156] The surface treatment of the untreated fillers may be undertaken prior to introduction in the composition or in situ, i.e., in tire presence of at least a portion of the other components of the composition herein by blending these components together at room temperature or above until tire filler is completely treated.When both reinforcing filler and thermally conductive filler (component (b)) are present they may be treated simultaneously. If separate filler treating agents are being used for the reinforcing filler and component (b) respectively they will need to be treated separately or sequentially.

[0157] Typically, any untreated reinforcing filler is preferably treated in situ with a treating agent in the presence of organopolysiloxane polymers (a) which results in the preparation of a silicone rubber base material which can subsequently be mixed with other components.

[0158] Optional Pigments / Colorants

[0159] The 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.

[0160] Suitable white pigments and / or colorants include but are not limited to titanium dioxide, zinc oxide, lead oxide, zinc sulfide, lithopone, zirconium oxide, and antimony oxide.

[0161] 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.

[0162] Suitable organic non-white pigments and / or colorants include phthalocyanine pigments,

[0163] 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, |3-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, qui noph thal one pigments, and diketopyrrolo pyrrole pigments.

[0164] Flame Retardants

[0165] Examples of flame retardants include but are not limited to, aluminium hydroxide, magnesium hydroxide, chlorinated paraffins, hexabromocyclododecane, triphenyl phosphate, dimethyl methylphosphonate, tris(2,3-dibromopropyl) phosphate (brominated tris), and mixtures or derivatives thereof.

[0166] Further Additional optional components when the thermally conductive silicone composition is a curable thermally conductive silicone rubber compositionWhen the thermally conductive silicone compositions are curable thermally conductive silicone robber compositions, they may further additionally include compression set additives and when the curable thermally conductive silicone rubber compositions are hydrosilylation (addition) curable they may additionally include cure inhibitors.

[0167] Optional Compression Set Additives

[0168] Whilst compression set is not usually deemed a critical performance for non-curing thermally conductive silicone greases, the cured product of the curable thermally conductive silicone rubber compositions usually shows very high compression set due to high loading of thermally conductive filler(s) in the compositions to achieve thermal conductivity. Whilst this may not be as significant given less thermally conductive filler is required in the present disclosure than would have been the case historically because herein the thermal conductivity is increased without further increasing the specific gravity thereof by effectively reducing the volume of the thermally conductive silicone compositions in which the thermally conductive fillers can be present, if desired the inclusion of certain compression set additives in the composition may have a significant improving effect on compression set. The compression set is measured herein in accordance with ASTM D395 and is the permanent deformation remaining after removal of a force that was applied to it. The term is often a property of interest when using elastomers. Compression set occurs when a material is compressed to a specific deformation, for a specified time, at a specific temperature. Compression set testing measur es the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As a robber material is compressed over time, it loses its ability to return to its original thickness. This loss of resiliency (memory) may reduce the capability of an elastomeric gasket, seal or cushioning pad to perform over a long period of time. The compression set additive use herein may be selected from, for example, Dodecanedioic acid, bis[2-(2-hydroxy benzoyl)hydrazide], diphenyl sulfide, salicyloylaminotriazole, l,2-di[-(3,5-di-tert-butyl-4-hydroxyp-henyl)propionyl]hydrazine, copper(II) phthalocyanine and mixtures thereof, such as Dodecanedioic acid, bis[2-(2-hydroxy benzoyl)hydrazide] and copper (II) phthalocyanine. The compression set additive, when present is added to the composition in an amount of from 0.01-5 wt. % of the composition, alternatively from 0.01-2 wt. % of the composition.

[0169] Optional hydrosilylation reaction cure inhibitors

[0170] When the thermally conductive silicone composition is a hydrosilylation (addition) curable thermally conductive silicone robber composition, said composition may also comprise one or more optional hydrosilylation reaction inhibitors. Hydrosilylation reaction inhibitors are used, when required, to prevent or delay the hydrosilylation reaction inhibitors curing process especially during storage. The optional hydrosilylation 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 anddiesters, conjugated ene-ynes, hydroperoxides, nitriles, and diaziridines. Alkenyl-substituted siloxanes as described in US3989667 may be used, of which cyclic methylvinylsiloxanes are preferred.

[0171] 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 °C. Compositions containing these inhibitors typically require heating at temperature of 70 °C or above to cure at a practical rate.

[0172] Examples of acetylenic alcohols and their derivatives include 1-ethynyl-l -cyclohexanol (ETCH), 2-methyl-3-butyn-2-ol, 3-butyn-l-ol, 3-butyn-2-ol, propargyl alcohol, l-phenyl-2-propyn-l-ol, 3,5-dimethyl-l-hexyn-3-ol, 1-ethynylcyc lopentanol, 3-methyl-l-penten-4-yn-3-ol, and mixtures thereof. Derivatives of acetylenic alcohol may include those compounds having at least one silicon atom.

[0173] When present, hydrosilylation reaction inhibitor concentrations may be as low as 1 mole of hydrosilylation reaction inhibitor per mole of the metal of catalyst (e) will, in some instances, still impart satisfactory storage stability and cure rate. In other instances, hydrosilylation reaction inhibitor concentrations of up to 500 moles of inhibitor per mole of the metal of catalyst are required. The optimum concentration for a given hydrosilylation reaction inhibitor in a given composition is readily determined by routine experimentation. Dependent on the concentration and form in which the hydrosilylation reaction inhibitor selected is provided / available commercially, when present in the composition, the inhibitor is typically present in an amount of from 0.0125 to lOwt. % of the composition.

[0174] In one embodiment tire inhibitor, when present, is selected from 1-ethynyl-l -cyclohexanol (ETCH) and / or 2-methyl-3-butyn-2-ol and is present in an amount of greater than zero to 0.1 wt. % of the composition.

[0175] Hence, in one alternative, tire present disclosure provides a thermally conductive silicone composition in the form of a non-curing thermally conductive silicone grease which comprises:

[0176] a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof; and which is present in the composition in an amount of from 4 wt. % to about 19 or 20 wt. % of the composition, alternatively from 5 to about 19 or 20 wt. % of the composition, alternatively from 5 to 17.5 wt. % of the composition, alternatively from 7.5 to 17.5 wt. % of the composition, alternatively the difference between 1 OOwt. % and the cumulative amount of all other ingredients present in the composition;

[0177] b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition, alternatively from 65 wt. % to 90 wt.%, in one embodiment the thermally conductive filler has a volume median particle diameter of between 0.1-100 micrometres (pm) measured by laser diffraction particle size analysis;

[0178] c) preformed silicone elastomeric particulates, which may be made from new compositions or are physically recycled and / or reclaimed silicone elastomeric particulates (c), preferably have anaverage particle size of 1 mm or less and are present in an amount of from 0.5 to 30 wt. % of the composition.

[0179] Such a non-curing thermally conductive silicone grease may comprise one or more additional additives selected from reinforcing fillers, semi-reinforcing fillers, treating agents for rendering fillers hydrophobic, pigments and / or coloring agents and flame retardants. The total wt. % of the non-curing thermally conductive silicone grease is 100 wt. %.

[0180] When the thermally conductive silicone composition is in the form of an uncurable thermally conductive silicone grease it is usually sandwiched between a heat source and an air-cooled or liquid-cooled heat sink or heat spreader, where the heat source may be, for example, a bare semiconductor die or a lidded semiconductor package. They are typically used to for transporting waste heat from electronic devices in laptops, computing servers, automotive components and photovoltaic devices, including CPUs (central processing units), GPUs (graphics processing units) andIGBTs (insulated-gate bipolar transistors). In a second embodiment the present disclosure provides a thermally conductive silicone composition in tire form of a peroxide curable thermally conductive silicone rubber composition comprising a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof; and which is present in tire composition in an amount of from 4 wt. % to about 19 or 20 wt. % of the composition, alternatively from 5 to about 19 or 20 wt. % of tire composition, alternatively from 5 to 17.5 wt. % of tire composition, alternatively from 7.5 to 17.5 wt. % of the composition, alternatively the difference between lOOwt. % and the cumulative amount of all other ingredients present in the composition;

[0181] b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition, alternatively from 65 wt. % to 90 wt.%, in one embodiment the thermally conductive filler has a volume median particle diameter of between 0.1-100 micrometres (pm) measured by laser diffraction particle size analysis;

[0182] c) preformed silicone elastomeric particulates, which may be made from new compositions or are physically recycled and / or reclaimed silicone elastomeric particulates (c), preferably have an average particle size of 1 mm or less and are present in an amount of from 0.5 to 30 wt. % of the composition and

[0183] f) an organic peroxide curing agent (sometimes referred to as a free-radical initiator), utilised in a curable thermally conductive 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 composition.

[0184] The total wt. % of the composition is 100 wt. %. The composition may also contain one or more optional additives selected from compression set additives, reinforcing fillers, semi-reinforcing fillers, treating agents for rendering fillers hydrophobic pigments and / or coloring agents and flame retardants in amounts indicated again providing the total wt. % of tire composition is 100 wt. %.In a third embodiment the present disclosure provides a thermally conductive silicone composition in tire form of a hydrosilylation (addition) curable thermally conductive silicone rubber composition comprising a) one or more organopolysiloxane polymers which comprises an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof; and which is present in the composition in an amount of from 4 wt. % to about 19 or 20 wt. % of the composition, alternatively from 5 to about 19 or 20 wt. % of the composition, alternatively from 5 to 17.5 wt. % of the composition, alternatively from 7.5 to 17.5 wt. % of the composition, alternatively the difference between lOOwt. % and the cumulative amount of all other ingredients present in the composition;

[0185] b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition, alternatively from 65 wt. % to 90 wt.%, in one embodiment the thermally conductive filler has a volume median particle diameter of between 0.1-100 micrometres (pm) measured by laser diffraction particle size analysis;

[0186] c) preformed silicone elastomeric particulates, which may be made from new compositions or are physically recycled and / or reclaimed silicone elastomeric particulates (c), preferably have an average particle size of 1 mm or less and are present in an amount of from 0.5 to 30 wt. % of the composition. d) an organosilicon compound having an average of at least two or an average of at least three silicon bonded hydrogen groups (Si-H groups), present in an amount of from 0.1 to 10 wt. % of the thermally conductive silicone rubber composition, alternatively 0.1 to 7.5wt. % of the thermally conductive silicone rubber composition, alternatively 0.5 to 7.5wt. %, further alternatively from 0.5% to 5 wt. % of the thermally conductive silicone rubber composition.

[0187] e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof, in an amount dependent on the form / concentration in which the catalyst is provided, within the range of from 0.001 to 3.0 wt. % of the composition, alternatively from 0.001 to 1.5 wt. % of the composition, alternatively from 0.01-1.5 wt. %, alternatively 0.01 to 0.1.0 wt. %, of the thermally conductive silicone rubber composition.

[0188] The total wt. % of the composition is 100 wt. %. The composition may also contain one or more optional additives selected from cure inhibitors and / or, compression set additives, reinforcing fillers, semi-reinforcing fillers, treating agents for rendering fillers hydrophobic pigments and / or coloring agents and flame retardants in amounts indicated again providing the total wt. % of the composition is 100 wt. %.

[0189] It will be appreciated that as described above there is provided a method for making a thermally conductive silicone rubber composition as described above which comprises mixing components (a), (b) and (c) to form a non-curing thermally conductive silicone grease, or mixing components (a), (b), (c) and (f) to form a peroxide curable thermally conductive silicone rubber composition or mixing components (a), (b), (c), (d) and (e) to form a hydrosilylation curable thermally conductive silicone rubber composition.When the thermally conductive silicone composition is in the form of a hydrosilylation (addition) curable thermally conductive silicone rubber composition, mixtures of the aforementioned components (a), (d), and (e) may begin to cure at ambient temperature. Hence, the thermally conductive silicone rubber compositions as hereinbefore described may be stored in two parts which are mixed together immediately before use when the composition is not prepared for immediate use. In such a case, the two parts are generally referred to as Part (A) and Part (B) and are designed to keep components (d) the cross-linker(s) and (e) the catalyst(s) apart to avoid premature cure.

[0190] Typically, in such cases a Part A composition may comprise components (a), and (e) and optionally either or both of (b), (c) and Part B will comprise components (a), and (d) and typically the remainder of (b), (c) and when present, cure inhibitor.

[0191] Other optional additives, when present in the hydrosilylation (addition) curable thermally conductive silicone rubber composition, may be in either Part A or Part B providing they do not negatively affect the properties of any other component (e.g., catalyst inactivation). The part A and part B of hydrosilylation (addition) curable thermally conductive silicone rubber composition are mixed together shortly prior to use to initiate cure of the full composition into a silicone elastomeric material. The compositions can be designed to be mixed in any suitable weight ratio e.g., part A : part B may be mixed together in weight ratios of from 100 : 1 to 1 : 150 most preferred is a weight ratio of 1 : 100. Typically, the part A and part B compositions are mixed together using a suitable means prior to use.

[0192] Components in each of Par t A and / or Part B may be mixed together individually or may be intr oduced into the composition in pre-prepared in combinations for, e.g., ease of mixing the final composition. For example, components (a) and (b) may be mixed together to form a base composition. In such cases the treating agent, if present, is usually introduced into the mixture so that the thermally conductive filler (b) can be treated in-situ. Alternatively, the thermally conductive filler (b) may be pre-treated with treating agent although this is not preferred. The resulting base material can be split into two or more parts, typically part A and part B and appropriate additional components and additives may be added, if and when required.

[0193] Alternatively, when the thermally conductive silicone composition is curable e.g., in the form of a hydrosi ly lation (addition) curable thermally conductive silicone rubber composition or a curable peroxide composition, said composition herein may be prepared by combining all of components together at ambient temperature into a one-part composition in cases where the composition is to be used immediately. Typically, a base is prepared first to enable the thermally conductive fdlers to be treated in-situ and then the remaining ingredients can be introduced into the mixture in any suitable order.

[0194] 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. However, when component (a) is a gum mixing is preferably undertaken, as previously indicated using a two-roll mill or a kneader mixer. Cooling of components during mixing may be desirable to avoid premature curing of die composition.In a still further approach, a one-part curable thermally conductive silicone composition may be cured via a latent heat cure approach, in which an encapsulated catalyst is utilised and the encapsulant melts / softens under heat.

[0195] Hence, in tire case of a process for the manufacture of a one part thermally conductive silicone rubber composition as hereinbefore described the process may comprise tire steps of

[0196] (i) preparing a hydrophobically heated thermally conductive filler base by mixing together components (a) and (c) together with a treating agent if desired at a temperature in the range of from 75°C to 150°C, alternatively from 80 °C to 140 °C, alternatively 90 °C to 130 °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 thermally conductive filler is in -situ treated and thoroughly mixed into component (a) and then cooling the resulting base to approximately room temperature (23°C to 25°C)

[0197] (ii) introducing component (e) the catalyst (catalyst composition e.g., Karstedt’s catalyst) component (c) preformed silicone elastomeric particulates, and if desired optional cure inhibitor (e.g., Ethynyl Cyclohexanol (ETCH)) and any other optional additives in any suitable order, or simultaneously and mixing to homogeneity.

[0198] Once prepared because of the reactivity of the components (a), (d) and (e) the composition will cure. Typically, cure will take place at a temperature between 80°C and 180 °C, alternatively between 100 °C and 170°C, alternatively between 120 °C and 170°C. This 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, e.g., from 2 to 10 minutes or as otherwise desired or required.

[0199] In comparison when the one part thermally conductive silicone rubber composition comprises system (f) as hereinbefore described. A base is first prepared and then all the additional ingredients are added with tire peroxide catalyst added last. The composition is then cured at a temperature of between 90°C and about 350°C, dependent on tire methodology used.

[0200] The present thermally conductive silicone rubber composition may alternatively be further processed by injection moulding, encapsulation moulding, press moulding, dispenser moulding, extrusion moulding, transfer moulding, press vulcanization, centrifugal casting, calendaring, bead application or blow moulding. As and when required samples may be additionally post-cured by heating to a temperature of 130°C to 200°C for up to 4 Hours.

[0201] In the case of a process for the manufacture of a two-part hydrosilylation curable thermally conductive silicone rubber composition as hereinbefore described the process may comprise the steps

[0202] (i) the same as step (i) for the preparation of the one-part composition above,

[0203] (ii) dividing the resulting mixture into two parts, part A and part B and introducing tire catalyst (e) into part A and the cross-linker (d) and cure inhibitor (if present) in the part B composition. (iii) Introducing any other optional additives into either or both part A and part B;(iv) Storing the part A and part B compositions separately.

[0204] Typically, when utilised the part A and part B compositions are thoroughly mixed in a suitable weight ratio as described above, e.g., in a weight ratio of about 1 : 100 immediately before use in order to avoid premature cure. Cure is then undertaken as described above for the one -part composition.

[0205] The thermally conductive silicone rubber composition as hereinbefore described may be used in any suitable application for which prior art thermally conductive silicone rubber compositions are utilised. Thermally conductive silicone rubber compositions may be used in a wide variety of applications, including for the sake of example in automotive and electronics applications including heat transfer pads for electric vehicles (EVs), heat transfer media for electrical chargers and charging cables, heat transfer gaskets for EVs, under hood cooling parts for EVs, heat transfer pads for keypads, printed circuit boards (PCBs), central processing units (CPUs) and hard drives, heat dissipation parts for motor drive module and control module, heat dissipation parts for imaging display section of light emitting diode (LED) projectors, image processing module of security surveillance cameras, heat dissipation parts for broadband cellular networks, e.g. 5G (fifth generation technology standard for broadband cellular networks) and communication electronics devices. It will be appreciated that Utilization of waste silicone rubber particulates into the composition makes the end product more sustainable.

[0206] EXAMPLES

[0207] All viscosities were measured at 25°C unless otherwise indicated. Unless otherwise indicated Viscosities of individual components in tire following examples were zero-shear viscosity measurements obtained by using commercial rheometers such as an Anton-Parr MCR-301 rheometer or a TA Instruments AR-2000 rheometer equipped with cone-and-plate fixtures of suitable diameter to generate adequate torque signal at a series of low shear rates, such as 0.01 s'1, 0.1 s'1and 1.0 s'1while not exceeding the torque limits of the transducer.

[0208] A series of compositions for examples and comparative Examples were prepared and are depicted in Tables la and lb.

[0209] Table la: Thermally conductive silicone rubber base (TC base 1)

[0210]

[0211] In the above,

[0212] Silicone Rubber Gum 1 is a dimethylvinylsiloxy terminated dimethyl Siloxane, Dimethylvinylsiloxy terminated having a Williams plasticity of about 148 in accordance with ASTM D-926-08.Treating agent 1 a trimethoxysiloxy-terminated and dimethylvinylsiloxy terminated polydimethyl siloxane, having a kinematic viscosity of 25 mm / s2measured at 25 °C using a glass capillary viscometer in accordance with ASTM D-445.

[0213] Thermally conductive filler 1 was a crushed alumina thermally conductive filler sold under the product reference ALM -41 -01 by Sumitomo Chemical Co of Tokyo Japan. It has an average particle size of 2ym (manufacturer’s information).

[0214] Thermally conductive filler 2 was a spherical alumina sold under the tradename DAM-40K by the Denka Company limited. It is a spherical form of alumina with a volume median particle diameter size of 40 pm (manufacturer’s information).

[0215] Thermally Conductive base 1 (TC Base 1) manufacturing Process

[0216] TC base 1 as depicted in Table la was prepared in a Baker Perkins double arm kneader style mixer with dispersion blades. Silicone Rubber Gum 1 and the treating agent were first introduced and mixed. The thermally conductive fillers were then added in 5 equal parts. After all the thermally conductive fillers had been introduced, tire mixture was further mixed whilst being heated to a temperature of greater than 120°C under vacuum heated vacuum at greater than 20inHg (0.34MPa).

[0217] In Table lb additional polymer or alternative varieties of component (c) silicone rubber particulates were introduced into the TC base 1 prepared in accordance with tire composition of Table la. TC base 1 was added into a Rlieomix 600 bowl on tire Haake mixer and then the additional gum or component (c) ingredients were added in a specified amount with respect to 100 parts by weight of TC base 1 and everything was mixed together to form a silicone grease which was non-curing.

[0218] Table lb: Thermally conductive silicone greases C. 1 and Ex. 1 to 3 which examples containing silicone rubber particulates were added (wt. %).

[0219]

[0220] In the above masterbatch 1 is depicted in Table la and silicone rubber gum 1 is described above.

[0221] Silicone rubber particulates 1: was a post-industrially recycled airbag article containing 10 wt.% nylon fibers and 90 wt.% cured silicone elastomer widi an average particle size of 150pm. It is non-tliermally conductive.

[0222] Silicone rubber particulates 2 was recycled silicone rubber made from grinding the elastomeric product of a commercially available silicone rubber product sold under the trademark SILASTIC™ LCF 3600Coating Liquid Silicone Rubber sold by Dow Silicones Corporation. It had a durometer hardness of approximately 40 to 45 shore A (ASTM D2240) and is non-thermally conductive. The average size of the particulates was approximately 200pm.

[0223] Silicone rubber particulates 3 was recycled silicone rubber made from grinding the elastomeric product of a commercially available silicone rubber product sold under the trademark SILASTIC™ LCF 3760 Coating Liquid Silicone Rubber sold by Dow Silicones Corporation. It had a durometer hardness of approximately 10 shore A (ASTM D2240) and is non-thermally conductive. The average size of the particulates was approximately 400pm.

[0224] Each silicone grease was subsequently assessed for its specific gravity and thermal conductivity.

[0225] A number of cure packages were assessed by being combined into samples of the silicone grease compositions of Table lb. Each cure package was assessed independently with each grease of Table lb to provide a variety of cured thermally conductive silicone materials. Each grease was mixed with the ingredients of each cure package in the amounts indicated relative to 100 parts by weight of the grease to form a version of the hydrosilylation cure composition, peroxide composition 1 and peroxide composition 2 and each of the resulting C. 1 and Ex. 1 to 3 cure compositions were also assessed for their thermal conductivity

[0226] The curable thermally conductive compositions using assorted cure packages are depicted in Table 1c below.

[0227] Table 1c: Curable thermally conductive compositions provided by adding tire cure packages below measured in parts by weight per 100 parts by weight of tire respective thermally conductive grease of Table lb.

[0228]

[0229] In the above,

[0230] CDA-6S was ADK STAB CDA-6S a metal deactivator commercially available from Adeka Corporation;

[0231] Cross-linker was a branched oligomeric trimethylsilyl-terminated polydimethylsiloxane-polyhydridomethylsiloxane copolymer with an average of one T branched unit per chain with a viscosityof 16 mm2 / s measured at 25 °C using a glass capillary viscometer in accordance with ASTM D-445and including 0.81 wt.% H in tire form of Si bonded hydrogen

[0232] Peroxide 1 was Luperox™ 101SIL45 organic peroxide which is commercially available from Arkema and is a 45-48% active weight formulation of 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexanepure dispersed on silica filler.

[0233] Peroxide 2 was Xiameter™ RBM-9020 Modifier which is commercially available from Dow Silicones Corporation and is a peroxide masterbatch comprising approximately 50 wt. % of peroxide in silicone oil. The above cure systems were prepared on a 2-roll mill and milled and subsequently were cured. After samples were well mixed the finished compound was removed from the mill.

[0234] A solid “puck” of each cured sample was formed using a metal mold. The finished puck was 12.5mm high and 25.4mm diameter. A release spray was applied to the mold prior to manually packing the mold. A minimum of 2 were made for each composition.

[0235] A small slab of each cured material was also pressed using a Hot press (16” Greened Press (40.64cm). The material was sheeted from the 2-roll mill and pressed into a slab using a steel chase. A 0.04 inch (10.16mm) thick aluminum backer plate and a sheet of release liner were used to prevent sticking to the samples to the backer plate.

[0236] Samples were assessed for their specific gravity according to ASTM D792 using a Mettler Toledo AT261 Delta Range scales apparatus to collect the weights.

[0237] Thermal conductivity testing was undertaken in accordance with ISO 22007-2 using a plastic cup with 9mm depth and 35mm diameter. The testing of the uncured greases was completed on a Hot disk™ TPS 2500 thermal analyzer (commercially available from Hot Disk AB of Sweden).

[0238] Each test was repeated 3 times on each sample through a scheduled procedure with a 3-minute wait between each individual test. During the testing the sample remained in place, undisturbed.

[0239] Thermal Conductivity Testing on cured samples

[0240] Thermal Conductivity Testing on the cured samples was also completed using the Hot disk™ TPS2500 Thermal Analyzer. The 2 cured pucks were placed above and below the probe. A small spreader plate was placed on the top of the sample-probe-sample sandwich. A thumb style screw was tightened to compress the samples together until good contact was made with the probe. The cover was placed over this for safety. The settings on the Hot disk™ TPS 2500 thermal analyzer were 200mW; 11.2mm, and 10 seconds. The cover was placed over the test apparatus and test started using the computer. Each test was repeated 3 times on each sample through a scheduled procedure with a 3-minute wait between each individual test. During the testing the sample remained in place, undisturbed.Table Id: Specific gravity and thermal conductivity results for C. 1 and Ex. 1 to 3.

[0241]

[0242] The specific gravity results were obtained from silicone greases of Table lb. TC uncured is intended to refer to the thermal conductivity of the silicone greases described in Table lb. The TC cured results are the thermal conductivity of the curable compositions made by mixing tire greases with the cure packages depicted in Table 1c. The thermal conductivity results were not affected by the cure package selected and as such the same results were obtained for each cure package.

[0243] It can be seen that in each of the comparative C. 1 and Ex. 1 to 3 the specific gravity remained substantially tire same for all samples. However, the thermal conductivity of the uncured grease samples of each of Ex. 1 to 3 increased as compared to the C. 1. Likewise cured samples of Ex. 1 to 3 all increased the thermal conductivity.

[0244] A masterbatch was prepared for a further set of examples. The composition of the masterbatch, masterbatch 2, is provided in Table 2a below.

[0245] Table 2a: Masterbatch 2 composition

[0246]

[0247] TCP20 is a thermally conductive filler commercially available from Toyal America and Inc which is a form of spherical aluminum having a median particle size of 20 micrometers (supplier information). ZOCO 104 is a thermally conductive filler commercially available from Zochem LLC which is a zinc oxide having a surface area of 5 meters squared per gram (supplier information).

[0248] SP30 is a thermally conductive filler commercially available from Saint Gobain Group and is a form of boron nitride platelets having a median particle size of 30 micrometres.organopolysiloxane polymer 1 was a Di-vinyldimethoxysiloxy-terminated polydimethyl siloxane having an average kinetic / kinematic viscosity of sixty-five centimeter squared per second (65 centiStokes), a specific gravity at 25°C of 0.97.

[0249] Treating Agent: was a linear polysiloxane having the following average composition:

[0250] : (CH3)3SiOi / 2[(CH3)2Si02 / 2]iio(CH30)3SiOi / 2 Its method of preparation is described in US2006 / 0100336

[0251] The masterbatch was prepared by introducing and mixing the different ingredients together in a 1 (US) gallon (3.785 litres) planetary mixer.

[0252] 100 parts by weight of masterbatch 2 was then mixed with 4 parts by weight of either silicone polymer or preformed silicone elastomeric particulates to form a non-curing thermally conductive silicone grease by mixing first in a speed mixer, and then in a Haake mixer. The compositions of the orm a non-curing thermally conductive silicone grease are depicted in Table 2b below:

[0253] Tabic 2b: Thermally conductive silicone greases C. 2 and C. 3 and Ex. 4-6which examples containing silicone rubber particulates were added in parts by weight per 100 parts of masterbatch 2.

[0254]

[0255] The thermal conductivity results were measured in accordance with ISO 22007-2 - hot disk method and showed that tire same effect is observed when using low viscosity polymers as well as silicone gums, in that tire thermal conductivity increased in the presence of preformed silicone elastomeric particulates.

Claims

WHAT IS CLAIMED IS:

1. A thermally conductive silicone composition, which comprises the following components: a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereofb) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition;andc) preformed silicone elastomeric particulates having an average particle size of 1 mm or less, in an amount of from 0.5 to 30 wt. % of the composition;which composition is a non-curing thermally conductive silicone grease unless additionally comprising components (d) and (e) when component (a) comprises an average of at least two unsaturated groups per molecule, or component (f)wherein components (d) and (e) are:(d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; and(e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and(f) an organic peroxide curing agent.

2. A thermally conductive silicone composition in accordance with claim 1 which is a non-curing thermally conductive silicone grease comprising components (a), (b) and (c) and has a thermal conductivity of at least 1.0 W / mK, measured in accordance with ISO 22007-2 - hot disk method.

3. A thermally conductive silicone composition in accordance with claim 1 which is a peroxide curable thermally conductive silicone rubber composition comprising components (a), (b), (c) and (f) or a hydrosilylation curable thermally conductive silicone rubber composition comprising components (a), (b), (c), (d) and (e) and which in each case upon cure has a thermal conductivity of at least 1.0 W / mK, measured in accordance with ISO 22007-2 - hot disk method.

4. A thermally conductive silicone composition in accordance with claim 1 , 2 or 3 wherein the preformed silicone elastomeric particulates (c) are new particulates or are made from a recycling / reclaiming process using post-industrial waste or post-consumer waste obtained from one or more of condensation cured (RTV) silicone elastomers, silicone rubber elastomers prepared from hydrosilylation curable compositions, silicone rubber elastomers prepared from peroxide free-radical cure compositions or U silicone rubber elastomers prepared from UV cure compositions using photoinitiators or photo-catalysts.

5. A thermally conductive silicone composition in accordance with claim 1, 2, 3 or 4 wherein the thermally conductive silicone compositions additionally comprise one or more rheology modifiers, reinforcing fillers, semi-reinforcing fillers, treating agents for rendering fillers hydrophobic, pigments and / or coloring agents, mold release agents, adhesion promoters, cure modifiers, anti-oxidants, heat stabilizers, metal deactivators Acid scavengers, green strength modifiers, species for oil bleed / lubrication and flame retardants.

6. A thermally conductive silicone composition in accordance with claim 1, 2, 3 or 4 wherein when the thermally conductive silicone compositions are curable thermally conductive silicone rubber compositions, they additionally include one or more compression set additives and when tire curable thermally conductive silicone rubber compositions are hydrosilylation curable they additionally include one or more cure inhibitors.

7. A thermally conductive silicone composition in accordance with claim 1, 2, 3, 4, 5 or 6 wherein organopolysiloxane polymer (a) has a zero shear viscosity of at least lOmPa.s at 25°C and / or is a silicone gum having a Williams plasticity value of at least 50mm / 100 in accordance with ASTM D926-08 or wherein component (c) is present in the composition in an amount of from 0.5 to 15 wt. % of the composition or both of the above.

8. A method for making a thermally conductive silicone composition in accordance with any preceding claim which comprises mixing components (a), (b) and (c) to form a non-curing thermally conductive silicone grease, or mixing components (a), (b), (c) and (f) to form a peroxide curable thermally conductive silicone rubber composition or mixingwherein components (a), (b), (c), (d) and (e) to form a hydrosilylation curable thermally conductive silicone rubber composition.

9. A method of increasing thermal conductivity of a thermally conductive silicone composition selected from a non-curing thermally conductive silicone grease or a curable thermally conductive silicone rubber composition in each case comprising thermally conductive fillers in an amount of from 65 to 95 wt. % of the composition without introducing additional thermally conductive fillers byIntroducing a component (c) comprising preformed silicone elastomeric particulates having an average particle size of 1 mm or less, in an amount of from 0.5 to 30 wt. % of a composition otherwise comprising the following components(a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof;(b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition;to form a non-curing thermally conductive silicone grease unless; or additionally adding components (d) and (e) when component (a) comprises an average of at least two unsaturated groups per molecule, or component (f)wherein components (d) and (e) are:d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; ande) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; andf) is an organic peroxide curing agent;to form a curable thermally conductive silicone rubber composition and curing said curable thermally conductive silicone rubber composition.

10. A method of increasing thermal conductivity of a thermally conductive silicone composition in accordance with claim 8 or 9 wherein the thermally conductive silicone composition is a noncuring thermally conductive silicone grease comprising components (a), (b) and (c) and has a thermal conductivity of at least 1.0 W / mK, measured in accordance with ISO 22007-2 - hot disk method A.

11. A method of increasing thermal conductivity of a thermally conductive silicone composition in accordance with claim 8 or 9 wherein tire thermally conductive silicone composition is a peroxide curable thermally conductive silicone rubber composition comprising components (a), (b), (c) and (f) or a hydrosilylation curable thermally conductive silicone rubber composition comprising components (a), (b), (c), (d) and (e) and which in each case upon cure has a thermal conductivity of at least 1.0 W / mK, measured in accordance with ISO 22007-2 - hot disk method.

12. Use of of a component (c) comprising preformed silicone elastomeric particulates having an average particle size of 1 mm or less, in an amount of from 0.5 to 30 wt. % to increase thermal conductivity of a thermally conductive silicone composition selected from a non-curing thermally conductive silicone grease or a curable thermally conductive silicone rubber composition otherwise comprising the following components(a) one or more organopolysiloxane polymers which may, but do not necessarily, comprise an average of at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl groups, alkynyl groups or a mixture thereof;b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition; to form a non-curing thermally conductive silicone grease unless; or additionally adding components (d) and (e) when component (a) comprises an average of at least two unsaturated groups per molecule, or component (f)wherein components (d) and (e) are:d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; ande) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; andf) is an organic peroxide curing agent;to form a curable thermally conductive silicone rubber composition.

13. Use of of a component (c) in accordance with claim 10 wherein the thermally conductive silicone composition is a non-curing thermally conductive silicone grease comprising components (a), (b) and (c) and has a thermal conductivity of at least 1.0 W / mK, measured in accordance with ISO 22007-2 - hot disk method.

14. Use of a component (c) in accordance with claim 10 wherein the thermally conductive silicone composition is a peroxide curable thermally conductive silicone rubber composition comprising components (a), (b), (c) and (f) or a hydrosilylation curable thermally conductive silicone rubber composition comprising components (a), (b), (c), (d) and (e) and which in each case upon cure has a thermal conductivity of at least 1.0 W / mK, measured in accordance with ISO 22007-2 - hot disk method.

15. A composite article having a heat dissipating surface in contact with a non-curing thermally conductive silicone grease in accordance with any one of claims 1, 2, 4, 5, 6 and 7 or a silicone rubber material which is the cured product of the curable thermally conductive silicone rubber composition with any one of claim 1, 3, 4, 5, 6 or 7.

16. Use of thermally conductive silicone compositions in accordance with any one of claims 1 to 6 in the manufacture of automotive and electronics applications.

17. Use in accordance with claim 16 wherein the automotive and electronics applications may be selected from in heat transfer pads for electric vehicle chargers, heat transfer gaskets for electric vehicles under hood cooling parts for electric vehicles, heat transfer media for electrical chargers and charging cables, heat transfer pads for keypads, printed circuit boards, central processing units and hard drives, heat dissipation parts for motor drive modules and control modules, heat dissipation parts for imaging display section of light emitting diode projectors, image processing module of security surveillance cameras, heat dissipation parts for broadband cellular networks, and communication electronics devices.

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