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., otherwise referred to as relative 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 seat 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 wate 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 electronic 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 weight % (wt. %) of the composition generally result in tire un-cured compositions or pre-cured materials having significantlyincreased viscosities causing impaired handling characteristics and additionally, in the latter case, 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 the 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 the 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 (75%+).

[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) at least one thermoplastic component having an average particle size of 0.1 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] (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] Thermoplastic component (c) is preferably either pre-formed or is dispersed in-situ by melt blending through a melt blending procedure in or with at least Component (a).

[0028] There is also provided a method for making a thermally conductive silicone composition, which comprises mixing the following components:

[0029] 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;

[0030] b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the thermally conductive filler composition; and

[0031] c) at least one thermoplastic component having an average particle size of 0.1 mm or less, in an amount of from 0.5 to 30 wt. % of the composition,

[0032] 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)

[0033] wherein components (d) and (e) are:

[0034] (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

[0035] e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and

[0036] f) is an organic peroxide curing agent;

[0037] to form a curable thermally conductive silicone rubber composition and curing said curable thermally conductive silicone rubber composition.

[0038] 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 byIntroducing a component (c) comprising at least one thermoplastic component having an average particle size of 0.1 mm or less, in an amount of from 0.5 to 30 wt. % of the composition in a particulate form or by melt blending with some or all of component (a) which composition otherwise comprising 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;

[0039] 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)

[0040] wherein components (d) and (e) are:

[0041] d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; and

[0042] e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and

[0043] f) is an organic peroxide curing agent;

[0044] to form a curable thermally conductive silicone rubber composition and curing said curable thermally conductive silicone rubber composition.

[0045] There is also provided a use of of a component (c) comprising at least one thermoplastic component having an average particle size of 0.1 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 hydrosilylation (addition) curable thermally conductive silicone rubber composition otherwise comprising the following components:

[0046] 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;

[0047] 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)

[0048] wherein components (d) and (e) are:

[0049] d) an organosilicon compound having at least two Si-H groups per molecule or at least three Si-H groups per molecule; and

[0050] e) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and

[0051] f) is an organic peroxide curing agent;

[0052] to form a curable thermally conductive silicone rubber composition.The total weight % (wt. %) of each of the above compositions is 100 wt. %.

[0053] 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 a non-curing thermally conductive silicone grease, said non-curing thermally conductive silicone grease does not contain component (e) or component (f). 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:

[0054] density of the thermally conductive silicone composition: density of water at 4°C

[0055] 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).

[0056] 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 thermal ly conductive fillers already present in a composition. While it is believed a significant amount of thermally conductive fillers say 65 wt. % will always be required to make a thermally conductive silicone composition suitably thermally conductive, the addition of further conductive can be limited by excluding the 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.

[0057] 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.

[0058] Component (a)

[0059] 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.

[0060] 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.

[0061] Each organopolysiloxane polymer of component (a) comprises multiple siloxy units, of formula (I):

[0062] R’aSiO(4-a) / 2 (I)

[0063] The subscript “a” is 0, 1, 2 or 3.

[0064] 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 SiO4 / 2. 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.

[0065] 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.

[0066] Substituted aliphatic hydrocarbyl group are preferably non-halogenated substituted alkyl groups.

[0067] 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.

[0068] 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

[0069] 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 dimethyhnethylvinyl 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. Preferably component (a) has a zero-shear viscosity of at least lOmPa.s at 25°C. Unless otherwise indicated viscosity measurements provided are zero-shear viscosity (η0)) 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.

[0070] In a still further the viscosity measurements may be obtained using an ARES parallel plate rheometer. (TA Instruments) with a dynamic frequency sweep was performed from 0.1 to 100 rad / s using 0.1% strain, 25 mm plates, and a 2 mm gap. The latter was preferred herein.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 the difficulty in measuring the viscosity of such highly viscous fluids, often referred to as silicone gums, it is usually preferred to provide 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 lOOmm / 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.

[0071] 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 the silicone gums used as component (a) herein were determined using a Waters 2695 Separations Module equipped with a vacuum degasser, and a Waters 2414 refractive index detector (Waters Corporation of MA, USA). The analyses were performed using certified grade toluene flowing at 1.0 mL / min as the eluent. Data collection and analyses were performed using Waters Empower GPC software.

[0072] 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).

[0073] 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.

[0074] 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 between100 wt. % and the cumulative wt. % of the other components / ingredients of the thermally conductive silicone composition.

[0075] Component (b)

[0076] 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.

[0077] 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;

[0078] 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;

[0079] 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;

[0080] Metal oxides such as, aluminium oxide (alumina), zinc oxide, silicon oxide, magnesium oxide, beryllium oxide, chromium oxide and titanium oxide;

[0081] metal hydroxides such as magnesium hydroxide, aluminum hydroxide, barium hydroxide and calcium hydroxide;

[0082] metal nitrides, such as boron nitride, aluminum nitride and silicon nitride;

[0083] metal carbides such as silicon carbide, include boron carbide and titanium carbide; and

[0084] 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.

[0085] 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.

[0086] Of the above, aluminium oxide, aluminum hydroxide, aluminium nitride, boron nitride and mixtures thereof are preferred.

[0087] The shape of the thermally conductive filler particles is not specifically restricted, e.g., they may be powders and / or fibres, however, rounded or spherical particles may prevent viscosity increase to an undesirable level given the 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 tire exact amount added to the curable composition, as well as the bondline thickness of the device in which tire cured silicone-based product of the composition will be used. In some particular instances, tirethermally 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 80 micrometres, 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).

[0088] 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).

[0089] 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.

[0090] 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)

[0091] Component (c) is at least one thermoplastic component having an average particle size of 0.1 mm or less, Given component (c) is thermoplastic it may be either pre-formed or dispersed in-situ through a melt blending procedure with at least Component (a) to have an average particle size of 0.1 mm or less, alternatively 0.05mm in the final dispersion in an amount of from 0.5 to 30 wt. % of the of the thermally conductive silicone 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 the composition, alternatively in an amount of from 0.5 to 15 wt. % of the composition.

[0092] The thermoplastic component (c) may be made from new (aka “virgin”) materials or is recycled (meaning physically recycled or chemically recycled), and / or reclaimed thermoplastic components. In one embodiment the thermoplastic component (c) is recycled and / or reclaimed thermoplastic (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 thermoplastic component particulates present in the final thermally conductive composition is given irrespective of its method of preparation and irrespective to their initial size or form.

[0095] For example, in the case of virgin, recycled and / or reclaimed thermoplastic particulates (c) being utilised it is tire average particle size of particulates subsequent to mixing tire thermoplastic component (c) with atleast component (a). The use of virgin or recycled / reclaimed thermoplastic as component (c) provides a more sustainable and lower density thermally conductive silicone composition selected from non-curing thermally conductive silicone greases or curable thermally conductive silicone rubber compositions offering a lower carbon footprint to the user by enabling replacement of a proportion of new silicone composition, for example replacing at least 0.5 wt. %, alternatively at least 1 wt. % alternatively at least 2 wt. %, alternatively at least 5 wt. %, alternatively at least 10 wt. % new silicone compositions, with domains formed from the thermoplastic component, from a variety of sources, sufficiently dispersed within thermally conductive silicone compositions which provide useful elastomeric properties thereto. Hence, this solution provides both the benefit, of enhanced sustainability and reduced cost and density associated with producing the equivalent displaced volume of new highly filled compositions as well as providing an outlet for recycled thermoplastic content, a high value, more environmentally attractive alternative to incineration or landfilling as an end-of-life option for the thermoplastics used in the preparation of the preformed thermoplastic particulates.

[0096] However, the thermoplastic material may alternatively be used to form a non-continuous phase in a silicone composition (which provides the continuous phase, through melt blending of the silicone base comprising for example, polymer(a) or polymer (a) and / filler (b) or polymer / resin masterbatch. The thermoplastic is mixed into the silicone at a temperature above the melting temperature thereof to create a dispersion in a mixer (like an extruder or Haake mixer). The thermoplastic itself can be fed to the mixer in any size, typically as resins, pellets, beads, flakes or chopped fibres or chopped fabrics. There the plastic can be granulated, shredded or cut down to any size amenable for feeding from any form factor whether a plastic article, monolith, sheet, fabric, or it may be pre -formed into its final form as through an extrusion or through a pelletization or grinding process after any shaping or forming process.

[0097] The thermoplastics may be prepared by co-extrusion or other known melt co-processing technique of the thermoplastic in an organopolysiloxane at a temperature above the melt transition temperature (Tm) of the thermoplastic. The thermoplastics can be virgin or recycled and can be selected from any thermoplastic resin. In some preferable embodiments, component (c) is a thermoplastic component that is dispersed in-situ through a melt blending procedure with at least Component (a) to form a discontinuous phase of component (c) in a continuous phase of at least the silicone polymer (a).

[0098] Examples of melt blending procedures to form such a dispersion of component (c) can be found in previously filed patent application cases with the US2024 / 0141111, US2024 / 0132721 and WO2023055872 which are incorporated by reference.

[0099] Whether pre-formed or dispersed in-situ, the thermoplastic particulates (c) may be made from virgin thermoplastics or may be derived from a recycling / reclaiming process derived from any suitable source. The original thermoplastic form may be dense or have inclusions or voids, as in foams.

[0100] Regardless of whether Component C is preformed thermoplastic or in-situ dispersed through a melt blending process, when the thermoplastic component c is the result of recycling, the source of thethermoplastics may be from, for example, post-industrial scrap or waste, pre-consumer scrap or waste, or post-consumer scrap or waste. For the avoidance of doubt and for the sake of this disclosure physically (mechanically) recycled / reclaimed particulates have their original chemical structure largely preserved with minimal degradation of the original polymer structure, whereas chemically recycled materials are reduced to monomeric or oligomeric components that are then re-polymerized back into a recycled polymer that may or may not be the same in structure and composition as the original.

[0101] When the origin of the thermoplastic component (c) is unknown a priori, the thermoplastic material 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 including infrared 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).

[0102] In the embodiments where the thermoplastic Component (c ) is introduced as pre-formed particulates to have an average particle size of 0.1 nun or less, alternatively 0.05mm in the final dispersion, it herein may be made from any appropriate method for the thermoplastic material concerned and may be prepared in the form of 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. Examples of methods which may be utilised to generate the pre-formed particulates include, for the sake of example, cryomilling (at liquid nitrogen temperatures), using milling equipment known in the 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 thermoplastic material is pulverized by an intense water stream.

[0103] Whether pre-formed or generated in-situ by the melt blending process, the resulting thermoplastic particulates in the dispersed phase of the thermally conductive compositions preferably have an average particle size of 0.1 mm or less, alternatively 0.05mm or less. Smaller particle sizes are preferable to minimize stress-concentrating defects in a new article as well as allowing use in thinner gaps applications, but larger particle sizes can also help manage processability of the final thermally conductive compositions.

[0104] If desired for more accurate particle size measurements samples can be measured using laser diffraction with e.g., a Beckman Coulter™ LS 13 320 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 thermoplastics as component (c) into the composition can make the end product more sustainable and the technique described herein provides increased thermal conductivity at same or lower specific density and also maintains the same level of conductivity at lower specific density.

[0105] The thermoplastic component (c) may be any suitable type of thermoplastic providing suitable particulates are preparable. Component (c) may be made from acrylonitrile-butadiene-styrene, polyphenyl ene / styrene blends, polystyrenes, polycarbonates (PC); polyurethane, styrene resin, polyethylene, polypropylene, acrylic, polyacrylates, polymethacrylates, polyacrylamides, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT); polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide (PA), such as nylon 6 (PA 6) nylon 6,6 (PA6,6) and nylon 6,10; blends of polyamide resins with syndiotactic polystyrene, polyimide, fluoropolymers, and liquid crystal resin, non-resin containing polyetherimides; phenolic resins, epoxy resins, epoxy mold compounds urea resins, melamine resins, alkyd resins, acrylonitrile-butadiene-styrenes, styrene-modified poly(phenylene oxides), poly(phenylene sulfides), vinyl esters or polyphthalamides and combinations thereof.

[0106] In some cases, the thermoplastic is selected from among polyamides, polyesters, polyolefins, polyacetals, polylphthalamides, polyoxymethylenes, polyphenylenesulfides, or a combination thereof. In some embodiments, the thermoplastic phase can be compatibilized through a reactive extrusion technique. Alternatively, the thermoplastic is selected from polyamides, polyesters, polyolefins, polyacetals, polylphthalamides and blends thereof. Specific examples of the thermoplastic include but are not limited to nylons such as nylon 6, nylon 6,6, nylon 12, polyethylene terephthalate, polyethylene, polypropylene, polyoxymethylene (POM), polybutylene terephthalate (PBT), polycyclohexylene dimethylene terephthalate (PCT), polytetrafluoroethylene (PTFE), copolymers of fluorinated thermoplastics such as ethylene tetrafluoroethylene (ETFE) and fluorinated ethylene propylene (FEP) and / or polyphenylenesulfide (PPS).

[0107] 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;

[0108] Component (d)

[0109] Component (d) of a 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 the 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 all of Component (d) mayalternatively have two silicon bonded hydrogen atoms per molecule when polymer (a) has greater than two unsaturated groups per molecule.

[0110] 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.

[0111] 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 100mPa.s at 25°C, they may be measured using a glass capillary viscometer in accordance with ASTM D-445.

[0112] 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 the silicon-bonded organic groups used in component (d) are alkyl groups, alternatively methyl, ethyl or propyl groups.

[0113] Examples of the organosilicon compound having an average of at least two or an average of at least three Si-H groups per molecule (d) include but are not limited to:

[0114] (a’) trimethylsiloxy-terminated methylhydrogenpolysiloxane,

[0115] (b’) trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxane,

[0116] (c’) dimethylhydrogensiloxy-terminated dimethylsiloxane-methylhydrogensiloxane copolymers, (d’) dimethylsiloxane-methylhydrogensiloxane cyclic copolymers,

[0117] (e’) copolymers and / or silicon resins consisting of (CHshHSiOi / z units, (CHs SiOie units and SiO4 / 2 units,

[0118] (f ’) copolymers and / or silicone resins consisting of (CH ihHSiOi / j units and SiC>4 / 2 units,

[0119] (g’) Methylhydrogensiloxane cyclic homopolymers having between 3 and 10 silicon atoms per molecule;

[0120] (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.

[0121] alternatively, component (c), the cross-linker, may be a filler, e.g., silica treated with one of the above, and mixtures thereof.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Generally, this is determined by calculating the total weight % of alkenyl groups in the composition, e.g., vinyl [V] and the total weight % of silicon bonded hydrogen [H] in tire composition and given the molecular weight of hydrogen is 1 and of vinyl is 27 the molar ratio of silicon bonded hydrogen to vinyl is 27[H] / [V].

[0126] 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 rubber composition, alternatively 0.5 to 7.5wt. %, further alternatively from 0.5% to 5 wt. % of the thermally conductive silicone rubber composition.

[0127] Component (e)

[0128] 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.

[0129] 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 (PtCl₂.(olefin)₂ and H(PtCl₃.olefin), preference being given in this context to the use of alkenes having 2 to 8 carbon atoms, such as ethylene, propylene, isomers of butene and of octene, or cycloalkanes having 5 to 7 carbon atoms, such as cyclopentene, cyclohexene, and cycloheptene. Other soluble platinum catalysts are, for tire sake of example a platinum-cyclopropane complex of the formula (PtCl₂C₃H₆)₂, 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. (Ph₃P)₂PtCl₂; and complexes of platinum with vinylsiloxanes, such as sym-divinyltetramethyldisiloxane.

[0130] Hence, specific examples of suitable platinum-based catalysts of component (e) include

[0131] (i) complexes of chloroplatinic acid with organosiloxanes containing ethylenically unsaturated hydrocarbon groups are described in US 3,419,593;

[0132] (ii) chloroplatinic acid, either in hexahydrate form or anhydrous form;

[0133] (iii) a platinum-containing catalyst which is obtained by a method comprising reacting chloroplatinic acid with an aliphatically unsaturated organosilicon compound, such as divinyltetramethyldisiloxane;

[0134] (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;

[0135] (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 the encapsulant melts / softens under heat;and / or

[0136] (vi) Karstedt’s catalyst is a Pt2(divinyl tetramethyl disiloxane)a complex typically containing from 30 to 50 wt. % platinum metal in the 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 tire 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 tire 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.

[0137] 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 the catalyst. The catalyst may be added as a single species or as a mixture of two or more different species. Typically, dependent on the form / concentration in which the catalyst is provided 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 the form of a hydrosilylation (addition) curable thermally conductive silicone rubber composition.

[0138] 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:

[0139] Component (f)

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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 between 1. OW / mK and 2. OW / mK, (ISO 22007-2 - hot disk method).

[0145] It has been found that rather than by the traditional route of further increasing the thermal conductivity of 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 therefrom, the addition of component (c) the thermoplastic particulates in an amount of from 0.5 to 30 wt. % causes the thermal conductivity to be increased without increasing the specific gravity thereof by effectively reducing the volume of the thermally conductive silicone compositions or the cured silicone-based products resulting therefrom, in which the conductive filler can be situated, i.e., concentrating the thermally conductive filler content.

[0146] 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.

[0147] One advantage herein when using such fillers in combination with the compositions herein result in said cured silicone -based products retaining their 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.Optional Reinforcing and semi-reinforcing fillers

[0150] Whilst not preferred given the requirement herein for high thermal conductivity, one optional additive in the thermally conductive silicone compositions as described herein is at least one silica or calcium carbonate reinforcing or semi-reinforcing filler(s).

[0151] 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 9277: 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 heating 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 trifluoropropylmethylsiloxane, 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 hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes, such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane and; hydroxyldimethyl terminated polydimethylmethylvinyl siloxane, octamethyl cyclotetrasiloxane, and silanes including but not limited tomethyltriethoxysilane, dimethyldiethoxysilane and / or vinyltriethoxysilane. A small amount of water can be added together with the 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 the 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 the 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 or used as the non-curable grease.

[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, 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, P-naphthol pigments, naphthol AS pigments, benzimidazolone pigments, diazo condensation pigment, isoindolinone, and isoindoline pigments, polycyclic pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, and diketopyrrolo pyrrole pigments.Flame Retardants

[0163] 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.

[0164] Further Additional optional components when the thermally conductive silicone composition is a curable thermally conductive silicone rubber composition

[0165] When the thermally conductive silicone compositions are curable thermally conductive silicone rubber compositions, they may additionally include compression set additives and when the curable thermally conductive silicone rubber compositions are hydrosilylation (addition) curable they may additionally include cure inhibitors.

[0166] Optional Compression Set Additives

[0167] 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 measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As a rubber 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, 1,2-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.

[0168] Optional hydrosilylation reaction cure inhibitors

[0169] When the thermally conductive silicone composition is a hydrosilylation (addition) curable thermally conductive silicone rubber composition, said composition may also comprise one or more optionalhydrosilylation 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 and diesters, conjugated ene-ynes, hydroperoxides, nitriles, and diaziridines. Alkenyl-substituted siloxanes as described in US3989667 may be used, of which cyclic methylvinylsiloxanes are preferred.

[0170] 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.

[0171] Examples of acetylenic alcohols and their derivatives include 1-ethynyl-1-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.

[0172] 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.

[0173] In one embodiment the inhibitor, when present, is selected from 1-ethynyl-1-cyclohexanol (ETCH) and / or 2-methyl-3-butyn-2-ol and is present in an amount of greater than zero to 0.1 wt. % of the composition.

[0174] Hence, in one alternative, the present disclosure provides a thermally conductive silicone composition in the form of a non-curing thermally conductive silicone grease which comprises:

[0175] 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 lOOwt. % and tire cumulative amount of all other ingredients present in tire composition;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 micrometers (pm) measured by laser diffraction particle size analysis;

[0176] c) at least one thermoplastic component having an average particle size of 0.1 mm or less and are present in an amount of from 0.5 to 30 wt. % of the composition.

[0177] 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.

[0178] The total wt. % of the non-curing thermally conductive silicone grease is 100 wt. %. When the above composition is a non-curing thermally conductive silicone grease, in one embodiment said non-curing thermally conductive silicone grease does not contain component (e) or component (f).

[0179] When tire 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 semi conductor 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) and IGBTs (insulated-gate bipolar transistors). In a second embodiment the present disclosure provides a thermally conductive silicone composition in the 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 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;

[0180] 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;

[0181] c) at least one thermoplastic component having an average particle size of 0.1 mm or less and are present in an amount of from 0.5 to 30 wt. % of the composition.

[0182] and

[0183] f). an organic peroxide curing agent (sometimes referred to as a free -radical initiator), utilised in a curable thermally conductive silicone 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.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 the composition is 100 wt. %.

[0184] In a third embodiment the present disclosure provides a thermally conductive silicone composition in the 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) at least one thermoplastic component having an average particle size of 0.1 mm or less, preferably have an average particle size of 0.1 mm or less and are present in an amount of from 0.5 to 30 wt. % of the composition.

[0187] 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.

[0188] 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.

[0189] 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. %.

[0190] 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.

[0191] When relying on melt blending to disperse component (c) into component (a), component (a) will form a continuous phase with thermoplastic Component (c) which may be optionally reactively compatibilized, such as by known reactive extrusion methods. It is to be understood that optimal dispersion may be had by using a polymer component that is of comparable viscosity to the melt viscosity of the thermoplastic component at the melt blending process conditions. As such, an initial dispersion of Component (c) can then be combined with additional components of the present composition to give a final thermally conductive composition. Because methods of in-situ dispersion of Component (c) through melt blending in at least some portion of Component (a) allow Compoent (c) to be introduced in any form factor and size that is amenable to feeding into a mixer or melt blending apparatus, these preferred embodiments can save on the energy, process time.

[0192] The melt blending procedure may comprise mixing components (a) and (c) at an elevated temperature greater than a melting transition temperature of component (c), optionally in the presence of components (b) to give a mixture. The preparation method also comprises reducing the elevated temperature of the mixture to a reduced temperature less than the melting transition temperature of component (c) to provide the silicone-thermoplastic intermediate composition.

[0193] For example, when component (a) is a low viscosity polymer e.g. having a viscosity of 10,000mPa.s at 25°C or less, the mixing process may include any method typically utilized with liquids or viscous materials. Similarly, the elevated temperature is selected based on a melting or softening point temperature of the thermoplastic polymer (c), The elevated temperature is generally greater than the melting or softening point temperature of the thermoplastic polymer (c). Components (a) and (c) may be combined and mixed in the presence of components (b) if desired.

[0194] Reduction of the elevated temperature may take place within the vessel or extruder in which components (a) and (c) are mixed or may be after removal thereof. The temperature may be reduced naturally via ambient exposure, or accelerated by selectively controlling temperature, e.g. by active cooling. The reduced temperature is less than the melting or softening point temperature of component (c) and allows for solidification or hardening of component (c).

[0195] In certain embodiments, the method further comprises the step of introducing components (b) (d) and (e) or components (b) and (f) to give a curable thermally conductive composition after the step of reducing the elevated temperature. Components (d) and (e) or component (f) may be combined with the mixture in the vessel or extruder, or after removal of the mixture therefrom.

[0196] As a result, the component (a) and (c) mixture as introduced above, includes

[0197] (1) a continuous phase comprising the silicone component (a); and(2) a discontinuous phase comprising the thermoplastic polymer (c). When present, the thermally conductive filler (b) is typically present in the discontinuous phase (2).

[0198] When the thermally conductive silicone composition is in the form of a hydrosilylation (addition) curable thermally conductive silicone rubber composition, and component (c) is in particulate form, 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.

[0199] 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.

[0200] 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 thermoplastic 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 prefened 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.

[0201] Components in each of Part A and / or Part B may be mixed together individually or may be introduced into the composition in pre-prepared in combinations for, e.g., ease of mixing the final composition. For example, components (a) and (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. Tire 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.

[0202] Alternatively, when the thermally conductive silicone composition is curable e.g., in the form of a hydrosilylation (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 fillers to be treated in-situ and then the remaining ingredients can be introduced into the mixture in any suitable order, In this case component (a) and (c) may undergo a form of melt blending in an initial step alone or in conjunction with component (b). Any mixing techniques and devices described in the prior art can be used for this purpose. The particular device to be used will be determined by 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 the composition.

[0203] 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.

[0204] Hence, in the case of a process for the manufacture of a one part thermally conductive silicone rubber composition as hereinbefore described the process may comprise the steps of

[0205] (i) preparing a hydrophobically treated thermally conductive filler base by mixing together components (a) and (b) or a melt blended mixture of components (a) and (c) with component (b) together with a treating agent if desired at a temperature in the range of from 75°C to 150°C but preferably mellow the melt temperature of component (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) (ii) introducing component (e) the catalyst (catalyst composition e.g., Karstedt’s catalyst) component (c) preformed thermoplastic particulates (when present), 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.

[0206] 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 but preferably below the melt temperature of component (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.

[0207] In comparison when the one part thermally conductive silicone rubber composition comprises component(f) as hereinbefore described. A base is first prepared as described above and then all the additional ingredients are added with the peroxide catalyst added last. The composition is then cured at a temperature of between 90°C and about 350°C,but preferably below the melt temperature of component (c) dependent on the methodology used.

[0208] 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 of130°C to 200°C for up to 4 Hours, however this should again preferably be at a temperature below the melt temperature of component (c).

[0209] 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

[0210] (i) the same as step (i) for the preparation of the one-part composition above,

[0211] (ii) dividing the resulting mixture into two parts, part A and part B and introducing the 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;

[0212] (iv) Storing the part A and part B compositions separately.

[0213] 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.

[0214] 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.

[0215] Utilization of waste silicone rubber particulates into the composition makes the end product more sustainable and the technique described herein provides increased thermal conductivity at same or lower specific density and also maintains the same level of conductivity at lower specific density, EXAMPLES

[0216] All viscosities were measured at 25°C unless otherwise indicated. Unless otherwise indicated Viscosities of individual components in the 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.

[0217] A series of compositions for examples and comparative Examples were prepared and are depicted in Tables la and lb.Table la: Thermally conductive silicone base (TC base 1)

[0218] TC base 1 (wt. %)

[0219] Silicone Rubber Gum 1 12

[0220] Treating agent 1 1

[0221] Thermally conductive filler 1 35.2

[0222] Thermally conductive filler 2 52.8

[0223]

[0224] In the above,

[0225] 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.

[0226] Treating agent 1 is a trimethoxysiloxy-terminated and dimethylvinylsiloxy terminated polydimethyl siloxane, having a kinematic viscosity of 25 mm / s² measured at 25 °C using a glass capillary viscometer in accordance with ASTM D-445.

[0227] 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 2pm (manufacturer’s information).

[0228] 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).

[0229] Thermally Conductive base 1 (TC Base 1) manufacturing Process

[0230] 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, the 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).

[0231] In Table lb additional polymer or varieties component (c) masterbatches 1 to 6 (thermoplastic particulates MB 1 - MB 6) were introduced into the TC base 1 prepared in accordance with the composition of Table la. TC base 1 was added into a Rheomix 600 bowl on the 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 noncuring.Table lb: Thermally conductive silicone greases C. 1 and Ex. 1 to 6 which examples containing thermoplastic particulate masterbatches were added (wt. %)

[0232] C. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Masterbatch 1 91 91 91 91 91 91 91

[0233] Silicone Rubber Gum 1 9

[0234] Thermoplastic dispersion MB 1 9

[0235] Thermoplastic dispersion MB 2 9

[0236] Thermoplastic dispersion MB 3 9

[0237] Thermoplastic dispersion MB 4 9

[0238] Thermoplastic dispersion MB 5 9

[0239] Thermoplastic dispersion MB 6 9

[0240]

[0241] Thermoplastic dispersion MB 1 was 30 wt. % of linear low-density polyethylene from Dow dispersed in-situ as described above in silicone Rubber Gum 1 to have a particle size of 50pm (0.05 mm) in the dispersion;

[0242] Thermoplastic dispersion MB 2 was 40 wt. % of linear low-density polyethylene from Dow dispersed in-situ as described above in silicone Rubber Gum 1 to have a particle size of 50pm (0.05 mm) in the dispersion;

[0243] Thermoplastic dispersion MB 3 was 40 wt. % of high-density polyethylene from Dow dispersed in-situ as described above in silicone Rubber Gum 1 to have a particle size of 50pm (0.05 mm) in the dispersion;

[0244] Thermoplastic dispersion s MB 4 was 30 wt. % of high-density polyethylene from Dow dispersed in-situ as described above in silicone Rubber Gum 1 to have a particle size of 50pm (0.05 mm) in the dispersion;

[0245] Thermoplastic dispersion MB 5 was 30 wt. % of nylon 12 from Arkema dispersed in-situ as described above in silicone Rubber Gum 1 to have a particle size of 50pm (0.05 mm) in tire dispersion;

[0246] Thermoplastic dispersion MB 6 is 29.4 wt. % of nylon 12 from Arkema dispersed in-situ as described above in silicone Rubber Gum 1 to have a particle size of 50pm (0.05 mm) in tire dispersion;

[0247] Silicone rubber base 1 comprises approximately 78% of silicone rubber gum 2 and 22 % of treated fumed silica 1;

[0248] Silicone rubber gum 2 is a vinyldimethylsiloxy-end capped polydimethyl-vinylmethylsiloxane copolymer with about 675 ppm by weight of vinyl (by FTIR), having a Williams plasticity of 153 mm / 100; and

[0249] Fumed silica 1 was CAB-O-SIL™ MS-75D fumed silica sold commercially by the Cabot Corporation A Haake mixer was provided. The Haake mixer was preheated to a Thermoplastic Polymer Melting Temperature, depending on the Thermoplastic Component (c) used, as understood in the art. The Haake mixer was started at a rate of 75 rpm. Component (a) was added to the Haake mixer and allowed to mixfor 5 minutes. If the Thermoplastic Component (c) was observed to have a tendency to phase separate, a small amount of an optional silicone fluid was used as a mixing aid to coat the mixing bowl of the Haake mixer to prevent the Thermoplastic Component (c) from sticking to the metal of tire Haake mixer.

[0250] Thermoplastic Component (c) was added to the Haake mixer while mixing. The ingredients were allowed to mix for 5 minutes to fully melt and disperse component (c) throughout component (a). Unless using a compatibilizer the resulting mixture was removed for cooling after 5 additional minutes of mixing. If a compatibilizer was used, the compatibilizer was added in increments by a syringe to the mixer. Once the compatibilizer was fully incorporated, the materials were mixed for 10 minutes to facilitate compatibilization to give a hybrid composition. The Haake mixer was stopped, and the hybrid composition was removed from mixing blades of the Haake mixer to cool.

[0251] Each silicone grease was subsequently assessed for its specific gravity and thermal conductivity.

[0252] 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 tire resulting C. 1 and Ex. 1 to 6 cure compositions were also assessed for their thermal conductivity

[0253] The curable thermally conductive compositions using assorted cure packages are depicted in Table 1c below.

[0254] Table 1c: Curable thermally conductive compositions provided by adding the cure packages below measured in parts by weight per 100 parts by weight of the respective thermally conductive grease of Table lb.

[0255] Hydrosilylation Peroxide curable Peroxide curable Curable composition composition 1 composition 2 Grease (Table lb) 100 100 100

[0256] CDA-6S 0.1

[0257] Ethynyl Cyclohexanol (ETCH) 0.1

[0258] Cross -linker 0.12 0.12 0.12

[0259] Pt catalyst masterbatch 0.27

[0260] Peroxide 1 0.2

[0261] Peroxide 2 0.2

[0262]

[0263] CDA-6S was ADK STAB CDA-6S a metal deactivator commercially available from Adeka Corporation.Cross-linker was a branched oligomeric trimethylsilyl-terminated polydimethylsiloxane-polyhydridomethylsiloxane copolymer with an average of one T branched unit per chain with a viscosity of 16 mm2 / s measured at 25 °C using a glass capillary viscometer in accordance with ASTM D-445and including 0.81 wt.% H in the form of Si bonded hydrogen.

[0264] 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)hexane pure dispersed on silica filler.

[0265] 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 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.

[0266] 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.

[0267] 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.

[0268] Samples were assessed for their specific gravity according to ASTM D792 using a Mettler Toledo AT261 DeltaRange scales apparatus to collect tire weights.

[0269] 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).

[0270] Thermal conductivity testing was undertaken in accordance with ISO 22007-2. The testing of the uncured greases was completed on a Hot disk™ TPS 2500 thermal analyzer (commercially available from Hot Disk AB of Sweden).

[0271] 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.

[0272] Thermal Conductivity Testing on cured samples

[0273] 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 tire testing tire sample remained in place, undisturbed.Table Id: Specific gravity and thermal conductivity results for C. 1 and Ex. 1 to 6 both non-curing and cured

[0274] Thermal Conductivity Thermal Conductivity

[0275] Specific Gravity

[0276] of Uncured Compound (W / mK) of Cured Article (W / mK)

[0277] C. 1 2.3727 1.08 1.20

[0278] Ex. 1 2.3722 1.23 1.27

[0279] Ex. 2 2.3676 1.29 1.30

[0280] Ex. 3 2.3762 1.29 1.46

[0281] Ex.4 2.3826 1.26 1.31

[0282] Ex. 5 2.4038 1.24 1.33

[0283] Ex. 6 2.4127 1.215 1.314

[0284]

[0285] 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.

[0286] It can be seen that in each of the comparative C. 1 and Ex. 1 to 6 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.

[0287] Table 2a: Masterbatch 2 composition

[0288] Wt. %

[0289] TCP-20 55.44

[0290] ZOCO 104 27.64

[0291] SP30 3.50

[0292] organopolysiloxane polymer 1 11.67

[0293] Treating agent 1.60

[0294] n-decyltrimethoxysilane 0.15

[0295]

[0296] 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 micrometres (supplier information). ZOCO 104 is a thermally conductive filler commercially available from Jochem LLC which is a zinc oxide having a surface area of 5 meters squared per gram (supplier information).SP30 is a thermally conductive filler commercially available from Saint Gobin Group and is a form of boron nitride platelets having a median particle size of 30 micrometers.

[0297] organopolysiloxane polymer 1 was a Di-vinyldimethoxysiloxy-terminated polydimethyl siloxane having an average kinetic / kinematic viscosity of sixty-five cm2 / s (65 centistokes) and a specific gravity at 25 °C of 0.97.

[0298] Treating Agent: was a linear polysiloxane having the following average composition:

[0299] (CH₃)₃SiO₁ / ₂[(CH₃)₂SiO₂ / ₂]₁₁₀(CH₃O)₃SiO₁ / ₂. Its method of preparation is described in US2006 / 0100336. The masterbatch was prepared by introducing and mixing the different ingredients together in a 1 (US) gallon (3.785 litres) planetary mixer.

[0300] 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 or a non-curing thermally conductive silicone grease are depicted in Table 2b below:

[0301] Table 2b: Thermally conductive silicone greases C. 2 and C. 3 and Ex. 7 & 8 which examples containing thermoplastic particulate masterbatches were added in parts by weight per 100 parts of Masterbatch 2 C.2 C. 3 Ex. 7 Ex. 8

[0302] Masterbatch 2 100 100 100 100

[0303] organopolysiloxane polymer 1 4

[0304] Silicone Rubber Gum 1 4

[0305] Thermoplastic particulates MB 4 4

[0306] 1 Thermoplastic particulates MB 2 4

[0307] Thermal conductivity (W / mK) 2.43 2.64 3.28 3.90

[0308]

[0309] The thermal conductivity results were measured in accordance with ISO 22007-2 - hot disk method and showed that the 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 thermoplastic elastomeric particulates.

Claims

1. 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 thereof;b) at least one thermally conductive filler in an amount of from 65 to 95 wt. % of the composition;andc)at least one thermoplastic component having an average particle size of 0.1 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 (sometimes referred to as a free -radical initiator).

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 component (c) is selected from particulates of one or more of acrylonitrile-butadiene-styrene, polyphenylene / styrene blends, polystyrenes, polycarbonates (PC); polyurethane, styrene resin, polyethylene, polypropylene, acrylic, polyacrylates, polymethacrylates, polyacrylamides, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT); polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide (PA), such as nylon 6 (PA 6) nylon 6,6 (PA6,6) and nylon 6,10; blends of polyamide resins with syndiotactic polystyrene, polyimide, fluoropolymers, and liquid crystal resin, non-resin containingpoly etherimides; phenolic resins, epoxy resins, epoxy mold compounds urea resins, melamine resins, alkyd resins, acrylonitrile-butadiene-styrenes, styrene-modified poly(phenylene oxides), poly(phenylene sulfides), vinyl esters or polyphthalamides and combinations thereof.

5. A thermally conductive silicone composition in accordance with claim 1, 2, 3 or 4 wherein component (c) is selected from particulates of one or more of a nylon, polyethylene terephthalate, polyethylene, polypropylene, polyoxymethylene (POM), polybutylene terephthalate (PBT), polycyclohexylene dimethylene terephthalate (PCT), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP) and / or polyphenylenesulfide (PPS).

6. A thermally conductive silicone composition in accordance with claim 1, 2, 3, 4 or 5 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 retardant.

7. A thermally conductive silicone composition in accordance with claim 1, 2, 3, 4 or 5 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 the curable thermally conductive silicone rubber compositions are hydrosilylation curable they additionally include one or more cure inhibitors.

8. A thermally conductive silicone composition in accordance with any preceding claim wherein organopolysiloxane polymer (a) has a zero shear viscosity of at least 10mPa.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.

9. A method for making a thermally conductive silicone rubber 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 mixing components (a), (b), (c), (d) and (e) to form a hydrosilylation curable thermally conductive silicone rubber composition.

10. 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 either Introducing a component (c) comprising at least one thermoplastic component having an average particle size of 0.1 mm or less, in an amount of from 0.5 to 30 wt. % of the composition in a particulate form or by melt blending with some or all of component (a) which 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 hydrosi ly lation 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.

11. A method of increasing thermal conductivity of a thermally conductive silicone composition in accordance with claim 9 wherein component (c) is selected from particulates of one or more of acrylonitrile -butadiene-styrene, polyphenylene / styrene blends, polystyrenes, polycarbonates (PC); polyurethane, styrene resin, polyethylene, polypropylene, acrylic, polyacrylates, polymethacrylates, polyacrylamides, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT); polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide (PA), such as nylon 6 (PA 6) nylon 6,6 (PA6,6) and nylon 6,10; blends of polyamide resins with syndiotactic polystyrene, polyimide, fluoropolymers, and liquid crystal resin, non-resin containing polyetherimides; phenolic resins, epoxy resins, epoxy mold compounds urea resins, melamine resins, alkyd resins, acrylonitrile- butadiene-styrenes, styrene-modified poly(phenylene oxides), poly(phenylene sulfides), vinyl esters or polyphthalamides and combinations thereof.

12. A method of increasing thermal conductivity of a thermally conductive silicone composition in accordance with claim 9 wherein component (c) is selected from particulates of one or more of a nylon, polyethylene terephthalate, polyethylene, polypropylene, polyoxymethylene (POM), polybutylene terephthalate (PBT), polycyclohexylene dimethylene terephthalate (PCT), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP) and / or polyphenylenesulfide (PPS).

13. Use of of a component (c) comprising at least one thermoplastic component having an average particle size of 0.1 mm or less, in an amount of from 0.5 to 30 wt. % of tire composition to increase thermal conductivity of a thermally conductive silicone composition selected from a non-curing thermally conductive silicone grease or a hydrosilylation 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.

14. Use of of a component (c) in accordance with claim 12 wherein component (c) is selected from particulates of one or more of acrylonitrile-butadiene-styrene, polyphenyl ene / styrene blends, polystyrenes, polycarbonates (PC); polyurethane, styrene resin, polyethylene, polypropylene, acrylic, polyacrylates, polymethacrylates, polyacrylamides, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT); polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide (PA), such as nylon 6 (PA 6) nylon 6,6 (PA6,6) and nylon 6,10; blends of polyamide resins with syndiotactic polystyrene, polyimide, fluoropolymers, and liquid crystal resin, non-resin containing polyetherimides; phenolic resins, epoxy resins, epoxy mold compounds urea resins, melamine resins, alkyd resins, acrylonitrile-butadiene-styrenes, styrene-modified poly (phenylene oxides), poly(phenylene sulfides), vinyl esters or polyphthalamides and combinations thereof.

15. Use of of a component (c) in accordance with claim 12 wherein component (c) is selected from particulates of one or more of a nylon, polyethylene terephthalate, polyethylene, polypropylene, polyoxymethylene (POM), polybutylene terephthalate (PBT), polycyclohexylene dimethylene terephthalate (PCT), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP) and / or polyphenylenesulfide (PPS).

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

17. Use of thermally conductive silicone rubber compositions in accordance with any one of claims 1 to 7 in the manufacture of automotive and electronics applications.

18. Use in accordance with claim 16 wherein the automotive and electronics applications is 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 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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