LIGHT ALLOY-CONTAINING THERMAL PASTES

Description

[0001] The present invention relates to thermally conductive silicone compositions, their preparation and use. State of the art

[0002] Thermally conductive silicone compounds are widely used for thermal management in the automotive and electronics industries. Important dosage forms include thermally conductive adhesives, thermal pads, gap fillers, and potting compounds. Of these applications, gap fillers for lithium-ion batteries in electric vehicles represent by far the largest application in terms of volume. Gap fillers are thermally conductive elastomers that completely and permanently fill air gaps caused by manufacturing tolerances, height differences, or different expansion coefficients, thus minimizing thermal resistance, for example, between electronic components and cooling housings or heat sinks.

[0003] The state of the art includes various thermally conductive fillers that are added to silicone to increase thermal conductivity. However, these have serious disadvantages. Ceramic fillers, such as aluminum oxide, have a very high density and thus significantly increase the weight of the components. They are also comparatively expensive. Many thermally conductive metallic fillers, such as finely divided copper and silver particles, are also unsuitable for gap fillers due to their high density and cost.

[0004] Many other highly thermally conductive fillers, such as carbonanotubes, boron nitride and aluminum nitride, can only be used to a limited extent, in small quantities or in special applications due to their comparatively high price.

[0005] The state of the art includes various thermally conductive silicone compositions that contain metal particles as thermally conductive fillers. The use of chemically pure metal particles often has disadvantages. Metal particles based on copper, silver, or gold, for example, have high thermal conductivity, but significantly increase the weight and cost of the components. Aluminum particles have a low density and high thermal conductivity, but due to their electrical conductivity, they are unsuitable for many applications, such as electronics or electromobility. Chemically pure silicon particles are electrically insulating, but they are very brittle and have a high Mohs hardness, making them very abrasive.

[0006] The use of alloys makes it possible to combine the advantageous properties of different metals and create new compounds with improved properties.

[0007] The advantageous properties of metal alloys based on light metals, in particular aluminum and silicon, are described, for example, in US2001051673, US4292223, CN109749427, CN109749292.

[0008] However, according to the state of the art, the metal alloy particles are not suitable for use as gap fillers in lithium-ion batteries for electric vehicles: US2001051673 describes the advantageous properties of alloy particles with an average particle size of 0.5 to 20 µm. However, the use of such finely divided metal particles is disadvantageous because such small particles have a comparatively low minimum ignition energy and are therefore potentially explosive due to dust explosions. They require complex and costly safety precautions during processing. Furthermore, gap fillers containing such finely divided alloy particles do not meet the required fire behavior according to UL94 V-0.

[0009] It has also been shown that gap fillers containing alloy particles with a comparatively narrow particle size distribution do not meet the required fire behavior according to UL94 V-0. The disadvantage of ground alloy particles is that such particles have a large surface area and bind a large amount of polymer. This significantly increases the viscosity of the silicone composition. Only mixtures with comparatively low filler contents and low thermal conductivity can be produced. At higher filler contents, the composition becomes very stiff and can no longer be processed using conventional methods, such as dispensing. It has also been shown that silicone compositions containing ground alloy particles are comparatively highly flammable.

[0010] US 2019 / 100650 A1 discloses a thermally conductive silicone composition containing metal particles as filler, wherein aluminum particles with an average diameter of 2 or 9 µm can be used. According to claim 5 of this disclosure, the particles can be present as an alloy.

[0011] The object of the present invention was therefore to provide thermally conductive silicone elastomer compositions which do not exhibit the above-mentioned disadvantages of the prior art and which combine the properties of low density, low cost and high thermal conductivity.

[0012] This object is achieved by the crosslinkable, thermally conductive silicone compositions (Y) according to the invention, which contain comparatively large light metal alloy particles with an average particle size of 25 to 150 µm, a predominantly rounded surface shape, and which simultaneously exhibit a particularly large or broad particle distribution. Completely surprisingly, experiments have shown that these silicone compositions (Y) according to the invention exhibit significantly reduced flammability.

[0013] In the context of the present invention, light metal alloy particles with a "predominantly rounded surface shape" are understood to mean those that have a spherical to oval, spattered or nodular shape with simultaneously smooth and curved surfaces. Figures 1 a to 1 cshow, by way of example, the predominantly rounded surface shape of these light metal alloy particles according to the invention. Light metal alloy particles according to the invention with a predominantly rounded surface shape are produced using a melting process. This means that the light metal alloy particles according to the invention must be obtained in the final production step by solidification from a melt and not by mechanical comminution of the solid material. This can be achieved, for example, by plasma rounding or by atomization of the melt (atomization). Atomization is the preferred process.

[0014] Light metal alloy particle shapes not according to the invention show, by way of example, the Figures 2a and 2b with angular and pointed particle surfaces. These are produced by grinding, crushing, or grinding processes.

[0015] The metallic light metal alloy particles according to the invention are therefore neither angular nor pointed. However, they can contain such particles to the extent of an impurity without impairing their inventive effect.

[0016] The subject of the present invention is a crosslinkable, thermally conductive silicone composition (Y) containing 5-60 vol.% of a crosslinkable silicone composition (S) and 40-95 vol.% of at least one thermally conductive filler (Z) with a thermal conductivity of at least 5 W / mK, with the proviso that the crosslinkable, thermally conductive silicone compositions (Y) have a thermal conductivity of at least 0.6 W / mK, and at least 20 vol% metallic light metal alloy particles are contained as thermally conductive fillers (Z), which meet the following characteristics: a) their average diameter x50 is in the range 25-150 µm; b) they are produced in the last production step using a melting process and have a predominantly rounded surface shape; c) their distribution width SPAN ((x90-x10) / x50) is at least 0.40, and the light metal alloy particles contain as main constituent at least 60 wt.% of a light metal or a light semi-metal selected from B, C, S, P, Be, Mg, Ca, Al or Si.

[0017] In the context of this invention, the terms thermally conductive, thermoconductive or thermally conductive are synonymous.

[0018] For the purposes of this invention, thermally conductive fillers (Z) are understood to mean all fillers with a thermal conductivity of at least 5 W / mK.

[0019] For the purposes of this invention, thermally conductive silicone composition (Y) is understood to mean silicone compositions which significantly exceed the thermal conductivity of a filler- and additive-free polydimethylsiloxane, typically about 0.2 W / mK, characterized in that they have a thermal conductivity of at least 0.6 W / mK.

[0020] For the purposes of this invention, all parameters describing the particle size (parameter: mean diameter x50) and the particle size distribution (parameters: standard deviation sigma and distribution width SPAN) refer to a volume-related distribution. These parameters can be determined, for example, using dynamic image analysis according to ISO 13322-2 and ISO 9276-6, for example, using a Camsizer X2 from Retsch Technology.

[0021] In order not to make the number of pages of the description of the present invention too extensive, only the preferred embodiments of the individual features are listed in the text.

[0022] However, the knowledgeable reader should explicitly understand this type of disclosure to mean that every combination of different preference levels is explicitly disclosed and explicitly desired. Crosslinkable silicone composition (S)

[0023] Silicones known to the person skilled in the art from the prior art can be used as the crosslinkable silicone composition (S), such as addition-crosslinking, peroxide-crosslinking, condensation-crosslinking, or radiation-crosslinking silicone compositions (S). Preference is given to using addition-crosslinking or peroxide-crosslinking silicone compositions (S).

[0024] Peroxide-crosslinking silicone compositions (S) have long been known to those skilled in the art. In the simplest case, they contain at least one organopolysiloxane with at least two crosslinkable groups per molecule, such as methyl or vinyl groups, and at least one suitable organic peroxide catalyst. If the compositions according to the invention are crosslinked by means of free radicals, organic peroxides serving as a source of free radicals are used as crosslinking agents. Examples of organic peroxides are acyl peroxides, such as dibenzoyl peroxide, bis(4-chlorobenzoyl) peroxide, bis(2,4-dichlorobenzoyl) peroxide, and bis(4-methylbenzoyl) peroxide; alkyl peroxides and aryl peroxides, such as di-tert-butyl peroxide, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, dicumyl peroxide, and 1,3-bis(tert-butylperoxyisopropyl)benzene; perketals such as 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane; Peresters such as diacetyl peroxydicarbonate, tert-butyl perbenzoate, tert.-butylperoxy-isopropylcarbonate, tert-butylperoxy-isonona-noate, dicyclohexyl peroxydicarbonate and 2,5-dimethyl-hexane-2,5-diperbenzoate.

[0025] One type of organic peroxide or a mixture of at least two different types of organic peroxides can be used.

[0026] Particular preference is given to using addition-curing silicone compositions (S).

[0027] Addition-crosslinking silicone compositions (S) used according to the invention are known in the prior art and, in the simplest case, contain (A) at least one linear compound having radicals with aliphatic carbon-carbon multiple bonds, (B) at least one linear organopolysiloxane having Si-bonded hydrogen atoms, or instead of (A) and (B) (C) at least one linear organopolysiloxane having SiC-bonded radicals with aliphatic carbon-carbon multiple bonds and Si-bonded hydrogen atoms, and (D) at least one hydrosilylation catalyst.

[0028] The addition-curing silicone compositions (S) can be one-component silicone compositions as well as two-component silicone compositions.

[0029] In the case of two-component silicone compositions (S), the two components of the addition-crosslinking silicone compositions (S) according to the invention can contain all constituents in any combination, generally with the proviso that one component does not simultaneously contain siloxanes with aliphatic multiple bonds, siloxanes with Si-bonded hydrogen and catalyst, i.e. essentially not simultaneously contain the constituents (A), (B) and (D) or (C) and (D).

[0030] The compounds (A) and (B) or (C) used in the addition-crosslinking silicone compositions (S) according to the invention are known to be selected such that crosslinking is possible. For example, compound (A) has at least two aliphatically unsaturated radicals and (B) at least three Si-bonded hydrogen atoms, or compound (A) has at least three aliphatically unsaturated radicals and siloxane (B) has at least two Si-bonded hydrogen atoms, or instead of compound (A) and (B), siloxane (C) is used, which has aliphatically unsaturated radicals and Si-bonded hydrogen atoms in the above-mentioned ratios. Mixtures of (A) and (B) and (C) with the above-mentioned ratios of aliphatically unsaturated radicals and Si-bonded hydrogen atoms are also possible.

[0031] The addition-crosslinking silicone composition (S) according to the invention typically contains 30-99.0 wt.%, preferably 40-95 wt.%, and particularly preferably 50-90 wt.% of (A). The addition-crosslinking silicone composition (S) according to the invention typically contains 1-70 wt.%, preferably 3-50 wt.%, and particularly preferably 8-40 wt.% of (B). If the addition-crosslinking silicone composition according to the invention contains component (C), it typically contains at least 30 wt.%, preferably at least 45 wt.%, and particularly preferably at least 58 wt.% of (C), based on the total amount of addition-crosslinking silicone composition (S) according to the invention.

[0032] The compound (A) used according to the invention can be silicon-free organic compounds having preferably at least two aliphatically unsaturated groups and organosilicon compounds having preferably at least two aliphatically unsaturated groups or mixtures thereof.

[0033] Examples of silicon-free organic compounds (A) are 1,3,5-trivinylcyclohexane, 2,3-dimethyl-1,3-butadiene, 7-methyl-3-methylene-1,6-octadiene, 2-methyl-1,3-butadiene, 1,5-hexadiene, 1,7-octadiene, 4,7-methylene-4,7,8,9-tetrahydroindene, methylcyclopentadiene, 5-vinyl-2-norbornene, bicyclo[2.2.1]hepta-2,5-dien, 1,3-Diisoproppenylbenzol, vinylgruppenhaltiges Polybutadien, 1,4-Divinylcyclohexan, 1,3,5-Triallylbenzol, 1,3,5-Trivinylbenzol, 1,2,4-Trivinylcyclohexan, 1,3,5-Triisopropenylbenzol, 1,4-Divinylbenzol, 3-Methyl-heptadien-(1,5), 3-Phenyl-hexadien-(1,5), 3-Vinyl-hexadien-(1,5 und 4,5-Dimethyl-4,5-diethyl-octadien-(1,7), N,N'-Methylen-bis-acrylsäureamid, 1,1,1-Tris(hydroxymethyl)-propan-triacrylat, 1,1,1-Tris(hydroxymethyl)propan-trimethacrylat, Tripropylenglykol-diacrylat, Diallylether, Diallylamin, Diallylcarbonat, N,N'-Diallylharnstoff, Triallylamin, Tris(2-methylallyl)amin, 2,4,6-Triallyloxy-1,3,5-triazin, Tri-allyl-s-triazin-2,4,6(1H,3H,5H)-trion, Diallylmalonsäureester, Polyethylenglykoldiacrylat, Polyethylenglykol Dimethacrylat, Poly(propylenglykol)methacrylat.

[0034] The addition-crosslinking silicone compositions (S) according to the invention preferably contain as component (A) at least one aliphatically unsaturated organosilicon compound, it being possible to use all aliphatically unsaturated organosilicon compounds previously used in addition-crosslinking compositions, such as, for example, silicone block copolymers with urea segments, silicone block copolymers with amide segments and / or imide segments and / or ester-amide segments and / or polystyrene segments and / or silarylene segments and / or carborane segments and silicone graft copolymers with ether groups.

[0035] As organosilicon compounds (A) which have SiC-bonded radicals with aliphatic carbon-carbon multiple bonds, linear or branched organopolysiloxanes comprising units of the general formula (I) R 4< a R 5< b SiO (4-ab) / 2 (I) are preferably used. where R 4< are independently, identical or different, an organic or inorganic radical free of aliphatic carbon-carbon multiple bonds, R 5< are independently, identical or different, a monovalent, substituted or unsubstituted, SiC-bonded hydrocarbon radical having at least one aliphatic carbon-carbon multiple bond, a is 0, 1, 2 or 3, and b is 0, 1 or 2, with the proviso that the sum a + b is less than or equal to 3 and at least 2 radicals R 5< are present per molecule.

[0036] The radical R 4< can be mono- or polyvalent radicals, wherein the polyvalent radicals, such as bivalent, trivalent and tetravalent radicals, then link several, such as two, three or four, siloxy units of the formula (I) to one another.

[0037] Further examples of R 4< are the monovalent radicals -F, -Cl, -Br, OR 6< , -CN, -SCN, -NCO and SiC-bonded, substituted or unsubstituted hydrocarbon radicals which may be interrupted by oxygen atoms or the group -C(O)-, as well as divalent radicals which are Si-bonded on both sides according to formula (I). If the radical R 4< is a SiC-bonded, substituted hydrocarbon radical, preferred substituents are halogen atoms, phosphorus-containing radicals, cyano radicals, -OR 6< , -NR 6< -, -NR 6< 2 , -NR 6< -C(O)-NR 6< 2 , -C(O)-NR 6< 2 , -C(O)R 6< , -C(O)OR 6< , -SO 2 -Ph and - C 6 F 5 . R 6< independently of one another, identically or differently, denote a hydrogen atom or a monovalent hydrocarbon radical having 1 to 20 carbon atoms and Ph is the phenyl radical.

[0038] Examples of radicals R 4< are alkyl radicals such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, isopentyl, neo-pentyl, tert-pentyl, hexyl radicals such as n-hexyl, heptyl radicals such as n-heptyl, octyl radicals such as n-octyl and iso-octyl radicals such as 2,2,4-trimethylpentyl, nonyl radicals such as n-nonyl, decyl radicals such as n-decyl, dodecyl radicals such as n-dodecyl, and octadecyl radicals such as n-octadecyl, cycloalkyl radicals such as cyclopentyl, Cyclohexyl, cycloheptyl and methylcyclohexyl radicals, aryl radicals such as phenyl, naphthyl, anthryl and phenanthryl radicals, alkaryl radicals such as o-, m-, p-tolyl radicals, xylyl radicals and ethylphenyl radicals, and aralkyl radicals such as benzyl, α- and β-phenylethyl radicals.

[0039] Examples of substituted radicals R 4< are haloalkyl radicals, such as the 3,3,3-trifluoro-n-propyl radical, the 2,2,2,2',2',2'-hexafluoroisopropyl radical, the heptafluoroisopropyl radical, haloaryl radicals, such as the o-, m- and p-chlorophenyl radical, -(CH 2 )-N(R 6< )C(O)NR 6< 2 , -(CH 2 ) o -C(O)NR 6< 2 , - (CH 2 ) o -C(O)R 6< , - (CH 2 ) o -C(O)OR 6< , - (CH 2 ) o -C(O)NR 6< 2 , - (CH 2 )-C(O)- (CH 2 ) p C(O)CH 3 , -(CH 2 )-O-CO-R 6< , - (CH 2 )-NR 6< -(CH 2 ) p -NR 6< 2 , - (CH 2 ) o -O-(CH 2 ) p CH(OH)CH 2 OH, - (CH 2 ) o (OCH 2 CH 2 ) p OR 6< , - (CH 2 ) o -SO 2 -Ph and - (CH 2 ) o -OC 6 F 5 , where R 6< and Ph have the meanings given above and o and p are identical or different integers between 0 and 10.

[0040] Examples of R 4< which are divalent radicals which are Si-bonded on both sides according to formula (I) are those which are derived from the monovalent examples given above for radical R 4< in that an additional bond occurs through substitution of a hydrogen atom. Examples of such radicals are - (CH 2 )-, -CH(CH 3 )-, -C(CH 3 ) 2 -, -CH(CH 3 )-CH 2 -, -C 6 H 4 -, -CH(Ph)-CH 2 -, -C(CF 3 ) 2 -, -(CH 2 ) o -C 6 H 4 -(CH 2 ) o -, - (CH 2 ) o -C 6 H 4 -C 6 H 4 -(CH 2 ) o -, - (CH 2 O) p , (CH 2 CH 2 O) o , - (CH 2 ) o -O x -C 6 H 4 -SO 2 -C 6 H 4 -O x -(CH 2 ) o -, where x is 0 or 1, and Ph, o and p have the meaning given above.

[0041] The radical R 4< is preferably a monovalent, SiC-bonded, optionally substituted hydrocarbon radical having 1 to 18 carbon atoms and free from aliphatic carbon-carbon multiple bonds, particularly preferably a monovalent, SiC-bonded hydrocarbon radical having 1 to 6 carbon atoms and free from aliphatic carbon-carbon multiple bonds, in particular the methyl or phenyl radical.

[0042] The residue R 5< can be any group that is accessible to an addition reaction (hydrosilylation) with a SiH-functional compound.

[0043] If the radical R 5< is a SiC-bonded, substituted hydrocarbon radical, halogen atoms, cyano radicals and -OR 6< are preferred as substituents, where R 6< has the meaning given above.

[0044] The radical R 5< preferably comprises alkenyl and alkynyl groups having 2 to 16 carbon atoms, such as vinyl, allyl, methallyl, 1-propenyl, 5-hexenyl, ethynyl, butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, vinylcyclohexylethyl, divinylcyclohexylethyl, norbornenyl, vinylphenyl and styryl radicals, with vinyl, allyl and hexenyl radicals being particularly preferably used.

[0045] The molecular weight of component (A) can vary within wide limits, for example between 10 2 < and 10 6 < g / mol. For example, component (A) can be a relatively low molecular weight alkenyl-functional oligosiloxane, such as 1,2-divinyltetramethyldisiloxane, but also a high-polymer polydimethylsiloxane containing chain-positioned or terminal Si-bonded vinyl groups, e.g., with a molecular weight of 10 5 < g / mol (number average determined by NMR). The structure of the molecules constituting component (A) is also not fixed; in particular, the structure of a higher molecular weight, i.e., oligomeric or polymeric siloxane can be linear, cyclic, branched, or even resinous or network-like. Linear and cyclic polysiloxanes are preferably composed of units of the formula R 4< 3 SiO 1 / 2 , R 5< R 4< 2 SiO 1 / 2 , R 5< R 4< SiO 1 / 2 and R 4< 2 SiO 2 / 2 , where R 4< and R 5< have the meaning given above.Branched and network-like polysiloxanes additionally contain trifunctional and / or tetrafunctional units, with those of the formulas R 4< SiO 3 / 2 , R 5< SiO 3 / 2 , and SiO 4 / 2 being preferred. Of course, mixtures of different siloxanes that satisfy the criteria of component (A) can also be used.

[0046] Particularly preferred as component (A) is the use of vinyl-functional, substantially linear polydiorganosiloxanes having a viscosity of 10 to 100,000 mPa•s, particularly preferably 15 to 20,000 mPa•s, especially preferably 20 to 2,000 mPa•s, in each case at 25°C.

[0047] All hydrogen-functional organosilicon compounds which have previously been used in addition-crosslinkable compositions can be used as organosilicon compound (B).

[0048] As organopolysiloxanes (B) containing Si-bonded hydrogen atoms, preferably linear, cyclic or branched organopolysiloxanes comprising units of the general formula (III) R 4< c H d SiO (4-cd) / 2 (III) where R 4< has the meaning given above, c is 0, 1, 2 or 3, and d is 0, 1 or 2, with the proviso that the sum of c + d is less than or equal to 3 and at least two Si-bonded hydrogen atoms are present per molecule. Preferably, at least one organopolysiloxane (B) having at least three, particularly preferably at least four Si-bonded hydrogen atoms per molecule is present.

[0049] The organopolysiloxane (B) used according to the invention preferably contains Si-bonded hydrogen in the range of 0.01 to 1.7 weight percent (wt.%), based on the total weight of the organopolysiloxane (B). Preferably in the range 0.02-0.8 wt.%, particularly preferably in the range 0.03-0.3 wt.%.

[0050] The molecular weight of component (B) can also vary within wide limits, for example, between 10 2 and 10 6 g / mol. Component (B) can, for example, be a relatively low-molecular SiH-functional oligosiloxane, such as tetramethyldisiloxane, but also a high-polymer polydimethylsiloxane containing chain- or terminal SiH groups, or a silicone resin containing SiH groups.

[0051] The structure of the molecules forming component (B) is also not fixed; in particular, the structure of a higher molecular weight, i.e. oligomeric or polymeric SiH-containing siloxane can be linear, cyclic, branched or even resinous, network-like. Linear and cyclic polysiloxanes (B) are preferably composed of units of the formula R 4< 3 SiO 1 / 2 , HR 4< 2 SiO 1 / 2 , HR 4< SiO 2 / 2 and R 4< 2 SiO 2 / 2, where R 4< has the meaning given above. Branched and network-like polysiloxanes additionally contain trifunctional and / or tetrafunctional units, with preference being given to those of the formulas R 4< SiO 3 / 2 , HSiO 3 / 2 and SiO 4 / 2 , where R 4< has the meaning given above.

[0052] Of course, mixtures of different siloxanes that meet the criteria of component (B) can also be used. Particular preference is given to the use of low-molecular-weight SiH-functional compounds such as tetrakis(dimethylsiloxy)silane and tetramethylcyclotetrasiloxane, as well as higher-molecular-weight, SiH-containing siloxanes such as poly(hydrogenmethyl)siloxane and poly(dimethylhydrogenmethyl)siloxane, or analogous SiH-containing compounds in which some of the methyl groups are replaced by 3,3,3-trifluoropropyl or phenyl groups.

[0053] Particularly preferred as component (B) is the use of SiH-containing, substantially linear poly(hydrogenmethyl)siloxanes and poly(dimethylhydrogenmethyl)siloxanes, which may also be hydrogendimethylsiloxy-terminated, having a viscosity in the range from 1 to 100,000 mPa•s, preferably in the range from 2 to 1,000 mPa•s, particularly preferably in the range from 3 to 750 mPa•s, especially preferably in the range from 5 to 500 mPa•s, in each case at 25°C, and the use of hydrogendimethylsiloxy-terminated polydimethylsiloxanes having a viscosity of from 10 to 100,000 mPa•s, particularly preferably from 15 to 20,000 mPa•s, especially preferably from 20 to 2,000 mPa•s, in each case at 25°C, and mixtures thereof.

[0054] Component (B) is preferably present in the crosslinkable silicone compositions (S) according to the invention in an amount such that the molar ratio of SiH groups to aliphatically unsaturated groups from (A) is from 0.1 to 10, particularly preferably between 0.5 and 5.0, in particular between 0.5 and 3.

[0055] The components (A) and (B) used according to the invention are commercially available products or can be prepared by processes commonly used in chemistry.

[0056] Instead of components (A) and (B), the silicone compositions (S) according to the invention may contain organopolysiloxanes (C) that simultaneously contain aliphatic carbon-carbon multiple bonds and Si-bonded hydrogen atoms. The silicone compositions (S) according to the invention may also contain all three components (A), (B), and (C).

[0057] If siloxanes (C) are used, they are preferably those consisting of units of the general formulas (IV), (V) and (VI) R 4< f SiO 4 / 2 (IV) R 4< g R 5< SiO 3-g / 2 (V) R 4< h HSiO 3-h / 2 (VI) where R 4< and R 5< have the meaning given above f 0, 1, 2 or 3, g 0, 1 or 2 and h 0, 1 or 2, with the proviso that at least 2 residues R 5 and at least 2 Si-bonded hydrogen atoms are present.

[0058] Examples of organopolysiloxanes (C) are those consisting of SO 4 / 2 , R 4< 3 SiO 1 / 2 -, R 4< 2 R 5< OSi 1 / 2 - and R 4< 2 HSiO 1 / 2 - units, so-called MP resins, whereby these resins may additionally contain R 4< SiO 3 / 2 - and R 4< 2 SiO units, as well as linear organopolysiloxanes essentially consisting of R 4< 2 R 5< SiO 1 / 2 -, R 4< 2 SiO and R 4< HSiO units with R 4< and R 5< equal to the meaning given above.

[0059] The organopolysiloxanes (C) preferably have an average viscosity of 0.01 to 500,000 Pa•s, particularly preferably 0.1 to 100,000 Pa•s, each at 25°C. Organopolysiloxanes (C) can be prepared by methods commonly used in chemistry.

[0060] All heat- or UV-curing catalysts known in the art can be used as the hydrosilylation catalyst (D). Component (D) can be a platinum group metal, for example platinum, rhodium, ruthenium, palladium, osmium, or iridium, an organometallic compound, or a combination thereof. Examples of component (D) are compounds such as hexachloroplatinic(IV) acid, platinum dichloride, platinum acetylacetonate, and complexes of said compounds encapsulated in a matrix or a core-shell structure. Low-molecular-weight platinum complexes of organopolysiloxanes include 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes with platinum. Further examples are platinum phosphite complexes or platinum phosphine complexes.For light- or UV-curing compositions, alkyl platinum complexes such as derivatives of cyclopentadienyltrimethylplatinum(IV), cyclooctadienyldimethylplatinum(II), or diketonato complexes such as bisacetylacetonatoplatinum(II) can be used to initiate the addition reaction with the aid of light. These compounds can be encapsulated in a resin matrix.

[0061] The concentration of component (D) is sufficient to catalyze the hydrosilylation reaction of components (A), (B), and (C) when exposed to generate the heat required in the process described herein. The amount of component (D) can be between 0.1 and 1000 parts per million (ppm), 0.5 and 100 ppm, or 1 and 25 ppm of the platinum group metal, depending on the total weight of the components. The cure rate may be slow if the platinum group metal content is below 1 ppm. The use of more than 100 ppm of the platinum group metal is uneconomical or reduces the storage stability of the silicone composition.

[0062] The addition-crosslinking silicone compositions (S) can optionally contain all other additives that have also been used previously to produce addition-crosslinkable compositions. Examples of actively reinforcing fillers (E) that do not fall under the definition of thermally conductive fillers (Z) that can be used as components in the addition-crosslinking silicone compositions (Y) according to the invention are fumed or precipitated silicas with BET surface areas of at least 50 m² / g, as well as carbon blacks and activated carbons such as furnace black and acetylene black, with fumed and precipitated silicas with BET surface areas of at least 50 m² / g being preferred.

[0063] The silica fillers (E) mentioned may be hydrophilic in nature or hydrophobized by known methods. Preferred fillers (E) have a carbon content of at least 0.01 to a maximum of 20 wt.%, preferably between 0.1 and 10 wt.%, particularly preferably between 0.5 and 6 wt.%, as a result of a surface treatment.

[0064] In the addition-crosslinking silicone composition (S) according to the invention, component (E) is preferably used as a single or likewise preferably as a mixture of several finely divided fillers. The content of actively reinforcing filler in the crosslinkable silicone compositions (S) according to the invention is in the range from 0 to 50 wt. %, preferably 0 to 30 wt. %, more preferably 0 to 10 wt. %.

[0065] The crosslinkable addition-curing silicone compositions (S) are particularly preferably characterized in that the filler (E) is surface-treated. The surface treatment is achieved by the processes known in the prior art for hydrophobizing finely divided fillers.

[0066] The addition-crosslinking silicone composition (S) according to the invention may contain alkyltrialkoxysilanes (F) as further additives to reduce its viscosity. If they are present, they are preferably present in an amount of 0.1-8 wt. %, more preferably 0.2-6 wt. %, based on the total mass of silicone composition (S). The alkyl group may be a saturated or unsaturated, linear or branched alkyl group having 2 to 20, preferably 8-18, carbon atoms, and the alkoxy groups may have 1 to 5 carbon atoms. Examples of the alkoxy groups include methoxy groups, ethoxy groups, propoxy groups, and butoxy groups, with methoxy groups and ethoxy groups being particularly preferred. Preferred for (F) are n-octyl-trimethoxysilane, n-decyl-trimethoxysilane, n-dodecyl-trimethoxysilane, n-hexadecyltrimethoxysilane and n-octadecyl-trimethoxysilane.

[0067] The addition-crosslinking silicone composition (S) according to the invention may optionally contain further additives as constituents in a proportion of up to 70% by weight, preferably up to 42% by weight, based in each case on the addition-crosslinking silicone composition (S) according to the invention, which additives differ from the thermally conductive fillers (Z) according to the invention and from the additives (E) and (F). These additives may be, for example, inactive fillers, resinous polyorganosiloxanes other than the siloxanes (A), (B), and (C), non-reinforcing fillers, fungicides, fragrances, rheological additives, corrosion inhibitors, oxidation inhibitors, light stabilizers, flame-retardants, and agents for influencing electrical properties, dispersing aids, solvents, adhesion promoters, pigments, dyes, plasticizers, organic polymers, heat stabilizers, etc. Thermally conductive filler (Z)

[0068] The crosslinkable thermally conductive silicone composition (Y) according to the invention contains at least one thermally conductive filler (Z) having a thermal conductivity of at least 5 W / mK, with the proviso that the crosslinkable thermally conductive silicone compositions (Y) contain at least 20 vol.% metallic light metal alloy particles as thermally conductive fillers (Z), which must also meet at least the further special features a) to c), and the total amount of thermally conductive fillers (Z) is at least 40 vol.%. a) The average diameter x50 of these metallic light metal alloy particles (Z) according to the invention is in the range 25-150 µm, preferably in the range 30-140 µm, more preferably in the range 40-130 µm, particularly preferably in the range 50-125 µm. b) The metallic light metal alloy particles (Z) according to the invention are produced in the last production step using a melting process and thus have a predominantly rounded surface shape. c) The particle size distribution width (SPAN) is defined as SPAN = (x90 - x10) / x50. The SPAN of the metallic light metal alloy particles (Z) according to the invention is at least 0.4, preferably at least 0.5, more preferably at least 0.6, and especially preferably at least 0.7. In a preferred embodiment, the SPAN is between 0.7 and 2.5, in particular between 0.75 and 2.

[0069] It is irrelevant whether a single fraction of light metal alloy particles (Z) is used whose SPAN lies within the inventive range, or whether two or more fractions of light metal alloy particles are mixed, thereby achieving the inventive particle size distribution range according to feature c) of the inventive light metal alloy particles (Z). If two or more fractions of light metal alloy particles are mixed, this can be done before mixing with one or more components of the inventive composition, or the fractions of light metal alloy particles can also be mixed separately with one or more components of the inventive composition. The order of addition is irrelevant.

[0070] Preferably, a maximum of four fractions of light metal alloy particles are mixed and thus the distribution width according to the invention is achieved, preferably a maximum of three fractions of light metal alloy particles are mixed and thus the distribution width according to the invention is achieved, particularly preferably a maximum of two fractions of light metal alloy particles according to the invention are used and thus the distribution width according to the invention is achieved, particularly preferably only a single light metal alloy particle according to the invention is used.

[0071] Metallic light metal alloys exhibit several very advantageous properties for use as thermally conductive fillers (Z). For example, the exceptionally high thermal conductivity of light metal alloy particles, such as those based on aluminum, silicon, or magnesium (Z), improves the thermal conductivity of the thermoconductive silicone composition (Y) produced from them. The low density of the light metal alloy particles (Z) reduces the weight of the composition and the components produced from it, helping to save costs.Other properties, such as electrical conductivity, Mohs hardness and brittleness, can be specifically adjusted and optimized over a wide range depending on the application requirements by combining different alloying metals and the ratio of the alloy components, and thus, for example, electrically conductive or electrically insulating silicone compositions can be produced, or the abrasiveness of the particles can be reduced.

[0072] The light metal alloy according to the invention contains as main component at least 60 wt.%, preferably at least 70 wt.%, preferably at least 80 wt.%, in particular at least 90 wt.% of a light metal or a light semi-metal selected from B, C, S, P, Be, Mg, Ca, Al or Si.

[0073] Preferred light metal alloys contain as main components at least 60 wt.%, preferably at least 70 wt.%, preferably at least 80 wt.%, in particular at least 90 wt.% of a light metal or a light semi-metal selected from Al, Ca, Mg or Si, with Al and Si being particularly preferred as main components.

[0074] In a particularly preferred embodiment, the light metal alloys are substantially free of heavy metals.

[0075] Those skilled in the art are aware that metallic light metal alloy particles are flammable under certain conditions and that the dusts are explosive. Those skilled in the art also know that the risk of dust formation, the flammability, and the explosiveness of metal powders increase significantly with decreasing particle size. For this reason, very small light metal alloy particles below 25 µm are unsuitable for many applications, for example, as fillers for gap fillers in lithium-ion batteries. Due to their low minimum ignition energy, such particles are hazardous to handle and require complex and costly safety precautions during processing. Furthermore, it has been shown that compositions containing very small light metal alloy particles below 25 µm are comparatively highly flammable and do not meet the UL94 V-0 flammability class for gap fillers in lithium-ion batteries.

[0076] The light metal alloy particles according to the invention preferably contain less than 20 wt.%, preferably less than 15 wt.%, particularly preferably less than 10 wt.% of a particle fraction with a diameter of less than or equal to 20 µm, in each case based on the total amount of light metal alloy particles.

[0077] The light metal alloy particles according to the invention preferably contain less than 15 wt.%, preferably less than 10 wt.%, particularly preferably less than 5 wt.% of a particle fraction with a diameter of less than or equal to 10 µm, in each case based on the total amount of light metal alloy particles.

[0078] In a particularly preferred embodiment, there is no intentional addition of light metal alloy particles with an average diameter of less than or equal to 20 µm, particularly preferably less than or equal to 10 µm, in particular of light metal alloy particles less than or equal to 5 µm.

[0079] Larger light metal alloy particles with an average particle size of over 25 µm exhibit a comparatively high minimum ignition energy and are therefore easier and safer to process in industrial processes. However, compositions containing non-inventive ground, angular light metal alloy particles larger than 25 µm proved to be comparatively highly flammable and did not meet the UL94 V-0 flammability rating for gap fillers in lithium-ion batteries.

[0080] Light metal alloy particles with an average particle size of over 150 µm are unsuitable for many applications of thermally conductive silicone compositions, as such large-grained light metal alloy particles often do not fit into the fine gaps that need to be filled with gap fillers, for example. Furthermore, it has been very unexpectedly found that even such large-grained light metal alloy particles exhibit comparatively high flammability.

[0081] Completely surprisingly, it has been found that the crosslinkable silicone compositions (Y) according to the invention are thermally conductive and at the same time flame-resistant if they contain metallic light metal alloy particles according to the invention which simultaneously satisfy features a) to c) in the required minimum amounts.

[0082] The crosslinkable silicone composition (Y) according to the invention contains at least 20 vol% of such metallic light metal alloy particles (Z), preferably at least 25 vol%, more preferably at least 30 vol%, and particularly preferably at least 35 vol%. If the silicone composition (Y) contains smaller amounts of metallic light metal alloy particles (Z), the desired advantageous effects of the metallic light metal alloy particles, for example, the low density and high thermal conductivity, are no longer sufficiently present.

[0083] The prior art knows various methods for producing finely divided metal particles. The light metal alloy particles (Z) according to the invention are produced from a molten state, whereby they have a comparatively smooth surface and are essentially free of fractures, sharp edges, and pointed corners. This distinguishes them from conventional ground particles, which were brought into their final shape, for example, by breaking, grinding, or milling. It is irrelevant whether the particles are cold-comminuted in a first process step, for example by grinding, and then brought into a molten form by heating above the melting point, for example by heat treatment in a hot zone, for example by means of a plasma, or whether a melt is first produced and then comminuted, for example by atomization.Preferably, the light metal alloy particles according to the invention are brought into the solid form according to the invention by spraying or atomizing, also called atomization, a light metal alloy melt and subsequent cooling.

[0084] Suitable processes for producing the light metal alloy particles (Z) according to the invention are known to the person skilled in the art and are described, for example, in Chapter 2.2 in "Powder Metallurgy: Technologies and Materials," Schatt, Werner, Wieters, Klaus-Peter, Kieback, Bernd, pp. 5-48, ISBN 978-3-540-681112-0, e-book: https: / / doi.org / 10.1007 / 978-3-540-68112-0 2. Preferred processes for producing the light metal alloy particles (Z) according to the invention are inert gas atomization, also called gas atomization, pressurized water atomization, also called liquid atomization or water atomization, or melt centrifugal atomization or rotary atomization.

[0085] The described processes allow the production of metallic light metal alloy particles in a very diverse particle size range, particularly in the average particle size range from a few micrometers to a few millimeters. Furthermore, the metallic light metal alloy particles can be produced in very different grain shapes, for example, "splashed," i.e., very irregular, nodular, ellipsoidal, or spherical, and with a highly variable particle size distribution. Regardless of the grain shape, these particles produced by a melting process exhibit a comparatively smooth surface according to the invention and are essentially free of fractures, sharp edges, and pointed corners.

[0086] Completely surprisingly, it has been found that only those light metal alloy particles which are produced by a melting process and thus have a predominantly rounded surface shape and at the same time satisfy the features a) to c) according to the invention exhibit advantageous properties according to the invention, in particular a comparatively low combustibility.

[0087] The production process for the metallic light metal alloy particles (Z) according to the invention is preferably carried out in such a way that the particles are obtained in their predominantly rounded surface shape according to the invention and thus satisfy features a) - c) and are essentially free of angular or pointed particles. The solidified particles can be separated according to size in a subsequent process step using conventional methods, e.g. by classifying by sieving or by sifting. In these processes, agglomerates and stuck-together particles can be separated, but essentially no particles are destroyed. Predominantly rounded or essentially free of means that the presence of such particles is tolerated to the extent of contamination of the particles (Z) according to the invention and does not impair their inventive effect.

[0088] The crosslinkable silicone composition (Y) according to the invention can contain, in addition to these metallic light metal alloy particles (Z), further thermally conductive fillers (Z) with thermal conductivity greater than 5 W / mK. Examples of such further thermally conductive fillers (Z) are magnesium oxide, metallic aluminum powder, metallic silicon powder, metallic silver powder, zinc oxide, boron nitride, aluminum carbide, aluminum nitride, aluminum hydroxide, aluminum oxide, graphite, etc. Preferred further fillers are aluminum powder, magnesium oxide, aluminum hydroxide, zinc oxide, and aluminum oxide. Particularly preferred fillers are zinc oxide, aluminum hydroxide, and aluminum oxide, with aluminum hydroxide being particularly preferred. The shape of the further filler is fundamentally unrestricted. The particles can be, for example, spherical, ellipsoidal, acicular, tubular, platelet-shaped, fibrous, or irregularly shaped.They are preferably spherical, ellipsoidal, or irregularly shaped. The average diameter of the additional thermally conductive fillers (Z) is preferably in the range 0.01-150 µm, preferably in the range 0.1-100 µm, particularly preferably in the range 0.2-80 µm, in particular in the range 0.4-60 µm.

[0089] Fillers with very high density are disadvantageous in applications such as aircraft and electric vehicles, as they significantly increase the weight of the components. Preferably, the additional thermally conductive fillers (Z) have a density of at most 5.0 g / cm 3 , preferably at most 3.8 g / cm 3 , particularly preferably at most 3.0 g / cm 3 .

[0090] The crosslinkable silicone composition (Y) according to the invention preferably contains less than 16% by weight, preferably less than 14% by weight, particularly preferably less than 12% by weight of a further thermally conductive filler (Z) having a density of greater than 5.0 g / cm 3 . In a particularly preferred embodiment, the crosslinkable silicone composition (Y) according to the invention is free of further thermally conductive fillers (Z) having a density of greater than 5.0 g / cm 3 .

[0091] The crosslinkable silicone composition (Y) according to the invention preferably contains less than 35% by weight, preferably less than 30% by weight, particularly preferably less than 25% by weight, especially preferably less than 20% by weight of a further thermally conductive filler (Z) having a density of greater than 3.0 g / cm 3 . In a particularly preferred embodiment, the crosslinkable silicone composition (Y) according to the invention is free of further thermally conductive fillers (Z) having a density of greater than 3.0 g / cm 3 .

[0092] Preferred crosslinkable silicone compositions (Y) according to the invention contain, as the thermally conductive filler (Z), the metallic light metal alloy particles according to the invention as the sole thermally conductive filler (Z) or in combination with up to two further thermally conductive fillers (Z). Impurities of up to 5% are not considered as further fillers (Z).

[0093] If the preferred compositions according to the invention contain the metallic light metal alloy particles (Z) according to the invention as the only thermally conductive filler (Z) with a thermal conductivity greater than 5 W / mK, a rheology modifier or thickener is preferably added to prevent the filler from settling. Suitable rheology modifiers are known to those skilled in the art, with hydrophobic silica, such as component (E), being preferred.

[0094] The total amount of thermally conductive fillers (Z) in the crosslinkable, thermally conductive silicone composition (Y) according to the invention is 40-95 vol.%, preferably 50-90 vol.%, more preferably 60-88 vol.%. If the silicone composition (Y) contains smaller amounts of thermally conductive filler (Z), sufficient thermal conductivity is not achieved. If the silicone composition (Y) contains larger amounts of thermally conductive filler (Z), the composition (Y) becomes difficult to process, as it becomes highly viscous or even crumbly.

[0095] The uncrosslinked thermally conductive silicone compositions (Y) according to the invention have a thermal conductivity of at least 0.6 W / mK, preferably at least 0.8 W / mK, preferably at least 1.2 W / mK, in particular at least 1.5 W / mK.

[0096] The viscosity of the uncrosslinked, thermoconductive silicone compositions (Y) according to the invention can vary within a very wide range and be adapted to the requirements of the application. The viscosity of the uncrosslinked, thermoconductive silicone compositions (Y) according to the invention is preferably adjusted via the content of thermoconductive filler (Z) and / or the composition of the silicone composition (S), according to customary methods from the prior art. These are known to the person skilled in the art. The viscosity is preferably adjusted via the selection and combination of components (A), (B), and (C) and optionally adding a rheology modifier and / or an active filler (E) and / or an alkyltrialkoxysilane (F).

[0097] The dynamic viscosity of the uncrosslinked, thermally conductive silicone compositions (Y) according to the invention is preferably in the range 100 - 1 000 000 mPa•s, preferably in the range 1 000 - 750 000 mPa•s, particularly preferably in the range 2 000 - 500 000 mPa•s, in particular at most 250 000 mPa•s, in each case at shear rate D = 10 s -1< and 25 °C.

[0098] The density of the uncrosslinked silicone compositions (Y) according to the invention is less than 3.5 g / cm 3< , preferably less than 3.0 g / cm 3< , preferably less than 2.6 g / cm 3< , in particular less than 2.3 g / cm 3< .

[0099] Another object of the present invention is a process for preparing the crosslinkable silicone compositions (Y) according to the invention by mixing the individual components.

[0100] The components can be mixed using conventional continuous and discontinuous processes known in the art. All known devices are suitable as mixing devices. Examples include uniaxial or biaxial continuous mixers, twin-roll mixers, Ross mixers, Hobart mixers, dental mixers, planetary mixers, kneaders, Henschel mixers, or similar mixers. Mixing is preferably carried out in a planetary mixer, a kneader, or a continuous mixer. The crosslinkable silicone composition (Y) can optionally be heated during mixing; mixing is preferably carried out in a temperature range of 15-40°C. The procedure for preparing the preferred addition-crosslinkable silicone compositions (S) is also known to those skilled in the art. In principle, the components can be added in any order.For example, components e) and optionally g) can be premixed and then mixed with components a) and / or b). The mixture can optionally also be heated and / or evacuated. Preferably, at least a portion of a) and the alkoxysilane g) are mixed, followed by the thermally conductive filler(s) (Z). Production preferably takes place without active heating.

[0101] In a preferred embodiment, there is no intentional addition of light metal alloy particles with an average diameter of less than or equal to 20 µm, particularly preferably less than or equal to 10 µm, in particular of light metal alloy particles less than or equal to 5 µm, since this is associated with a particular safety risk in technical production.

[0102] The crosslinkable silicone composition (Y) according to the invention can be provided as a one-, two-, or multi-component mixture. Examples are two-component thermosetting compositions (Y) or one-component UV-crosslinkable compositions (Y). This has also long been known to the person skilled in the art.

[0103] The crosslinkable silicone composition (Y) according to the invention has very good processing properties with regard to fluidity, gap filling properties and layer thickness control and can be applied precisely.

[0104] The temperature condition for curing the silicone composition (Y) curable preferably by hydrosilylation reaction is not limited and is typically in the range of 20 to 180 °C, preferably in the range of 20 to 150 °C, preferably in the range of 20 to 80 °C.

[0105] Another object of the present inventionare the silicone products obtained by filling or applying the crosslinkable silicone composition and subsequent crosslinking / curing. The cured silicone products (e.g., a heat-conducting element) exhibit excellent thermal conductivity and precise layer thicknesses.

[0106] The hardness of the crosslinked, thermoconductive silicone compositions (Y) according to the invention can vary within a very wide range and be adapted to the requirements of the application. For example, comparatively soft and flexible products are preferably used for use as gap fillers, whereas comparatively hard and solid products are preferably used for use as thermoconductive adhesives. The hardness of the crosslinked, thermoconductive silicone compositions (Y) according to the invention is preferably adjusted via the composition of the silicone composition (S), according to customary methods from the prior art. These are known to those skilled in the art. The hardness is preferably adjusted via the selection and combination of components (A), (B), and (C), and optionally by adding a reinforcing filler (E).

[0107] The hardness of the cured silicone product is preferably in the range from 2 according to the Shore 00 method to 100 according to the Shore A method, preferably in the range from 10 according to the Shore 00 method to 85 according to the Shore A method. For use as a gap filler, the hardness of the crosslinked thermoconductive silicone compositions according to the invention is particularly preferably in the range from 15 according to the Shore 00 method to 65 according to the Shore A method.

[0108] The crosslinked silicone products have a thermal conductivity of at least 0.6 W / mK, preferably at least 0.8 W / mK, preferably at least 1.2 W / mK, in particular at least 1.5 W / mK.

[0109] Another object of the present invention isThe use of the crosslinkable silicone composition as a gap filler (= thermally conductive element), thermal pad, thermally conductive adhesive, and potting compound. They are particularly suitable for use as a gap filler for lithium-ion batteries in electric vehicles and as a potting compound for electronic components, for example, in electric vehicles.

[0110] The density of the crosslinked silicone products according to the invention is less than 3.5 g / cm 3< , preferably less than 3.0 g / cm 3< , preferably less than 2.6 g / cm 3< , in particular less than 2.3 g / cm 3< .

[0111] The crosslinked silicone products according to the invention preferably correspond to flammability class UL94 V-0.

[0112] In a preferred embodiment, the density of the crosslinked silicone products according to the invention is less than 2.5 g / cm 3< , the thermal conductivity is greater than 1.8 W / mK and the flammability satisfies UL94 V-0, with the proviso that the dynamic viscosity of the uncrosslinked silicone compositions according to the invention is less than 500,000 mPa•s, in particular less than 250,000, in each case at shear rate D = 10 s -1< and 25 °C.

[0113] In a particularly preferred embodiment, the density of the silicone products according to the invention is less than 2.3 g / cm 3< , the thermal conductivity is greater than 1.8 W / mK, preferably greater than 3.0 W / mK and the flammability satisfies UL94 V-0, with the proviso that the dynamic viscosity of the uncrosslinked silicone compositions according to the invention is less than 500,000 mPa•s, in particular less than 250,000, in each case at shear rate D = 10 s -1< and 25 °C. Measurement methods Measurement of thermal conductivity Lambda

[0114] Thermal conductivity is determined according to ASTM D5470-12 using a TIM tester (Steinbeis Transfer Center for Thermal Management in Electronics, Lindenstr. 13 / 1, 72141 Walddorfhäslach, Germany). The thermal resistance of the sample, which is placed between two test cylinders, is determined by a constant heat flow. The effective thermal conductivity is calculated based on the sample's layer thickness.

[0115] For the measurement, the sample is applied using a template, and the measuring cylinders are manually compressed to a thickness of 1.9–2.0 mm, then any excess material is removed. The thermal conductivity is measured at a constant gap of 1.8–1.6–1.4–1.2–1.0 mm. The results are evaluated using an integrated report generation tool. After a plausibility check (coefficient of determination of the straight line > 0.998), the thermal conductivity lambda is output as the effective thermal conductivity in W / (m*K). Measurement of dynamic viscosity

[0116] The dynamic viscosity was measured on an Anton Paar MCR 302 rheometer in accordance with DIN EN ISO 3219:1994 and DIN 53019 using a flow curve with the following parameters: Measurement type: T / D; Temperature: 25.0 °C; Measuring element: PP25; Measuring gap: 0.50 mm; Shear rate: 0.1 - 10 s -1< ; Time: 120 sec; Measured values: 30. The viscosity is given in Pa•s as an interpolation value at a shear rate of D = 10 s -1< . Measuring density

[0117] The density of the uncrosslinked, thermally conductive silicone compositions was determined according to ISO 1183, and the density of the crosslinked, thermally conductive silicone compositions was determined according to ISO 1184. Particle size and particle shape analysis

[0118] The particle size (mean diameter x50) and particle size distribution (parameter: distribution width SPAN) were analyzed using a Camsizer X2 from Retsch Technology (measurement principle: dynamic image analysis) according to ISO 13322-2 and ISO 9276-6 (type of analysis: dry measurement of powders and granules; measuring range: 0.8 µm - 30 mm; compressed air dispersion with "X-Jet"; dispersion pressure = 0.3 bar). The evaluations were performed volume-based according to the model xc min .

[0119] The following examples describe the basic feasibility of the present invention, without, however, limiting it to the contents disclosed therein.

[0120] In the following examples, all parts and percentages are by weight unless otherwise stated. Unless otherwise stated, the following examples are carried out at ambient atmospheric pressure, i.e., approximately 1000 hPa, and at room temperature, i.e., approximately 20°C, or a temperature that occurs when the reactants are combined at room temperature without additional heating or cooling. Examples Overview of the alloy particles and light metal alloy particle mixtures used according to the invention and not according to the invention

[0121] In the examples according to the invention and not according to the invention, the light metal alloys listed in Table 1 are used. Table 1 alloy A B C D E Al (wt%) 88 2,5 95 77, 9 88 Mg (wt%) 0, 6 Si (wt%) 12 90 17 8, 5 Fe (wt%) 7, 5 Ti (wt%) 5 Cu (wt%) 4, 5 3,5 density (g / ml) 2, 65 2,47 2,76 2,70 2,73

[0122] Table 2 shows the properties of the light metal alloy particles according to the invention (Examples 1 to 7) and non-inventive light metal alloy particles (Comparative Examples C1 to C8) used in the crosslinkable, thermally conductive silicone compositions.

[0123] Examples 1-6 according to the invention use light metal alloy particles according to the invention which were obtained by means of inert gas atomization and are thus predominantly rounded, and also have a comparatively broad particle size distribution according to the invention and thus fulfill all features a) to c) according to the invention.

[0124] The non-inventive comparative examples V1-V4 use non-inventive light metal alloy particles which were obtained by inert gas atomization and are thus predominantly rounded, but have a comparatively narrow, non-inventive particle size distribution and do not fulfill the inventive feature c).

[0125] The non-inventive comparative examples V5-V7 use non-inventive light metal alloy particles which have a comparatively broad particle size distribution, but were obtained by means of grinding processes and are therefore essentially angular and edged and do not meet the inventive feature b). Example 7: Preparation of the light metal alloy particle mixture 7 (according to the invention)

[0126] 100 g of the non-inventive light metal alloy particle from Comparative Example V2, 200 g of the non-inventive light metal alloy particle from Comparative Example V3, 400 g of a non-inventive light metal alloy particle made of alloy A, which has a x50 of 103.5 µm and a SPAN of 0.31 and is produced by means of inert gas atomization and is thus essentially rounded, 200 g of a non-inventive light metal alloy particle made of alloy A, which has a x50 of 134.2 µm and a SPAN of 0.24 and is produced by means of inert gas atomization and is thus essentially rounded, and 100 g of the non-inventive light metal alloy particle from Comparative Example V4 are stirred with a commercially available laboratory stirrer TYPE RW 28 (IKA ®< -Werke GmbH & CO. KG, 79219 Staufen, Germany) mixed homogeneously.A light metal alloy particle mixture according to the invention is obtained which has a x50 of 106.9 µm and a SPAN of 0.77 and is substantially rounded, and fulfils the features a) to c) according to the invention. Comparative Example V8: Production of the light metal alloy particle mixture V8 (not according to the invention)

[0127] 300 g of a non-inventive light metal alloy particle made of alloy A, which has a x50 of 134.2 µm and a SPAN of 0.24 and is produced by inert gas atomization and is thus essentially rounded, and 600 g of the non-inventive light metal alloy particle from Comparative Example V4 are homogeneously mixed using a commercially available laboratory stirrer type RW 28 (IKA ®< -Werke GmbH & CO. KG, 79219 Staufen, Germany). A non-inventive light metal alloy particle mixture is obtained which has a x50 of 153.1 µm and a SPAN of 0.42 and is essentially rounded, and does not meet feature a) of the invention. Abbreviations

[0128] Example VComparative Example PFParticle shape predominantly rounded Surface shape angular According to the invention NEnot according to the invention nbnot determined Table 2: Overview of the properties of the light metal alloy particles e.g. alloy x10 (µm) x50 (µm) x90 (µm) SPANISH PF remark Feature a) Feature c) Feature b) 1 A 15,3 32,1 44,8 0,92 r E 2 A 17,6 37,4 56,8 1,05 r E 3 A 22,4 50,4 69,7 0,94 r E 4A A 28,7 66,1 96,8 1,03 r E 4B B 28,3 66,5 97,9 1,05 r E 4C C 27,8 67,6 95,6 1,00 r E 4D D 26,5 67,8 94,2 1,00 r E 4E E 30,4 66,2 93,5 0,95 r E 5 A 54,5 83,1 126, 5 0,87 r E 6 A 99,3 137,4 170, 4 0,52 r E 7 A 73,5 108,3 153, 6 0,74 r E V1 A 44,2 53,6 63,2 0,35 r NE V2 A 60,2 67,4 75,8 0,23 r NE V3 A 71,5 81,6 93,4 0,27 r NE V4 A 143,8 161,7 182, 4 0,24 r NE V5 A 11,1 36,5 85,9 2,05 e NE V6 A 19,8 96,5 188, 6 1,75 e NE V7 A 3,2 6,2 9,1 0,95 e NE V8 A 111,2 153,1 5 0,42 r NE General Instructions 1 (AV1) for the production of crosslinked, thermoconductive light metal alloy particle-containing silicone moldings (inventive examples 8 to 14 and non-inventive examples V9 to V20) Step 1: Preparation of an addition-curable, thermoconductive light metal alloy particle-containing silicone composition

[0129] 24.5 g of a vinyldimethylsiloxy-terminated polydimethylsiloxane with a viscosity of 1000 mPa.s, 16.3 g of a hydrogendimethylsiloxy-terminated polydimethylsiloxane with a viscosity of 1000 mPa.s, and 1.0 g of a copolymer of dimethylsiloxy, methylhydrogensiloxy, and trimethylsiloxy units, which has a viscosity of 200 mPa.s and a Si-bonded hydrogen content of 0.18 wt.%, were homogenized using a SpeedMixer DAC 400 FVZ (Hauschild & Co KG, Waterkamp 1, 59075 Hamm, Germany) at a speed of 2350 rpm for 25 seconds. The light metal alloy particles were then added in the ratios shown in Table 3 and mixed for 25 seconds at 2350 rpm using the SpeedMixer. The silicone composition containing light metal alloy was stirred with a spatula, mixing in light metal alloy particle residues from the edge of the vessel.The mixture was then homogenized for a further 25 seconds at 2350 rpm using a SpeedMixer and cooled to room temperature.

[0130] For crosslinking, 4.18 g of ELASTOSIL ®< CAT PT (available from Wacker Chemie AG, Hanns-Seidel-Platz 4, 81737 Munich, Germany) were added, corresponding to a mixing ratio of 1 part catalyst solution to 10 parts silicone composition, not including the proportion of thermally conductive filler (Z). The sample was mixed three times for 10 seconds at 2350 rpm using a SpeedMixer, with the sample being stirred with a spatula between each mixing step. A reactive, pasty mass was obtained that could be stored for only a few hours and was immediately processed. Step 2: Production of a cross-linked, thermoconductive light metal alloy particle-containing silicone molded body

[0131] A molded article measuring 207 mm x 207 mm x 2 mm was produced by press vulcanization in a stainless steel mold at 165 °C and 380 N / cm² for 5 minutes using conventional state-of-the-art methods. The vulcanizate was then cured at 200 °C for 4 hours. A homogeneous and elastic molded article was obtained. Example 15 Flammability test

[0132] The flammability test was conducted using a simplified test based on UL 94 V, an Underwriters Laboratories standard for vertical combustion testing, which allows the classification of plastics according to their flame resistance. This method is the most common test for classifying flame-retardant plastics.

[0133] Test pieces 5" (127 mm) long and 0.5" (12.7 mm) wide were punched out from the inventive silicone moldings according to Examples 8 to 14 and the non-inventive silicone moldings according to Comparative Examples C9 to C13 and C18 to C20. The plate is secured vertically at the upper end with a length of 1 / 4" (1 / 4"). A piece of cotton wool is placed 12" (305 mm) below the test plate. The burner is adjusted to produce a blue flame 3 / 4" long. The flame is directed from a distance of 3 / 8" (9.5 mm) onto the lower edge of the plastic plate. After 10 seconds of exposure, the flame is removed. The afterburn time (total time of afterburning and afterglow) of the test piece is recorded. The sample should extinguish immediately after the flame is removed and continue to burn for a maximum of 4 seconds.The test is conducted on five different test pieces, and the average afterburn time is determined. The results are shown in Table 3.

[0134] In the non-inventive comparative experiments V14 to V16, each containing 62.5 vol.% of the non-inventive light metal alloy particles according to the comparative examples V5 to V7, which in particular do not satisfy feature b), a very highly viscous silicone composition was produced which could not be pressed into a suitable silicone molding. Table 3: Silicone compositions containing light metal alloy particles, their properties and properties of the molded articles produced therefrom e.g. Light metal alloy particles used crosslinkable silicone composition Silicone molded body Example according to Table 2 Quantity (g) Content (vol%) Viscosity (Pa•s) Density (g / cm 3 ) hardness Thermal conductivity Afterburn time (s) 8 1 171,6 62,5 6,4 1,94 71 1,8 2 9 2 171,6 62,5 6,0 1,94 75 1,9 2 10 3 171,6 62,5 6,2 1,94 76 2,1 0 11A 4A 171,6 62,5 5,0 1,94 70 2,0 2 11B 4B 178,1 62,5 5,2 2,00 68 1,9 0 11C 4C 190,2 62,5 4,9 2,11 71 1,8 1 11D 4D 198,5 62,5 5,3 2,18 75 1,9 2 11E 4E 244,5 62,5 4,2 2,61 70 1,9 0 12 5 171,6 62,5 3,5 1,94 71 1,9 0 13 6 171,6 62,5 4,3 1,94 85 1,8 1 14 7 171,6 62,5 4,7 1,94 78 2,0 3 V9 V1 171,6 62,5 9,1 1,94 69 2,0 8 V10 V2 171,6 62,5 13,5 1,94 81 1,9 12 V11 V3 171,6 62,5 14,5 1,94 73 2,0 7 V12 V4 171,6 62,5 16,2 1,94 79 2,0 6 V13 V8 171,6 62,5 3,7 1,94 82 1,8 13 V14 V5 171,6 62,5 nb nb nb nb nb V15 V6 171,6 62,5 nb nb nb nb nb V16 V7 171,6 62,5 nb nb nb nb nb V17 V5 100,1 49,2 14,2 1,73 6 1,2 24 V18 V6 100,1 49,2 nb 1,73 17 1,1 22 V19 V7 100,1 49,2 nb 1,73 28 1,3 57

[0135] Comparative examples V9 to V13 and V17 to V19, containing non-inventive light metal alloy particles or mixtures according to Comparative Examples V1-V8, which do not meet one or more of the features a) to c), exhibit comparatively high flammability in the flammability test. Particularly striking was the flammability of the non-inventive comparative sample V19, containing a light metal alloy particle with an average particle size of less than 20 µm. The samples continued to burn after the flame was removed until the molded body was completely combusted.

[0136] Completely unexpectedly, it was found that light metal alloy particles that simultaneously satisfy features a) to c) exhibit the inventive advantage of reduced flammability. Inventive Example 14, it was also completely surprising that by mixing several non-inventive light metal alloy particles, a light metal alloy particle mixture according to the invention can be produced which has the inventive advantageous properties of low flammability, provided the resulting mixture satisfies features a) to c). In contrast, the non-inventive light metal alloy particle mixture from Comparative Example V8 does not satisfy features a) to c) and also does not exhibit the inventive advantages. Example 16 Full flammability test according to UL 94 V

[0137] The inventive silicone moldings from inventive examples 11A and 12 and the non-inventive silicone moldings from non-inventive comparative examples C10, C11, and C18 were subjected to the full flammability test according to UL 94 V and classified as V-0, V-1, or V-2. For many technical applications, particularly for use as gap fillers in electric vehicles, a V-0 classification is required. The results are shown in Table 4. Table 4: e.g. Classification according to UL 94 V remark 11A V-0 E 12 V-0 E V10 V-1 NE V11 V-1 NE V18 V-2 NE Example 17 Production of a crosslinked, thermoconductive silicone molded article containing a in situ Mixture of two light metal alloy particles. (according to the invention)

[0138] According to the general specification AV1, a crosslinkable thermoconductive silicone composition according to the invention was produced, wherein 187.55 g of the light metal alloy particle according to the invention from Example 1 (37.6 vol.% based on the total amount of the thermoconductive silicone composition) and 183.95 g of a non-inventive light metal alloy particle made of alloy A, which has a x50 of 104.9 µm and a SPAN of 0.36 and is produced by means of inert gas atomization and is thus substantially rounded, (36.8 vol.% based on the total amount of the thermoconductive silicone composition) were added separately from one another as light metal alloy particles and in situ to form a light metal alloy particle mixture according to the invention.

[0139] A reactive silicone composition according to the invention was obtained with a content of light metal alloy particles according to the invention of 74.4 vol. % and a dynamic viscosity of 61,500 mPa.s at a shear rate D = 10 s -1 and 25 °C. The thermal conductivity was 5.14 W / mK and the density was 2.22 g / cm 3 . The composition according to the invention has good processability, high thermal conductivity and low density and is very suitable for use as a gap filler. A crosslinked silicone molded article according to the invention was produced according to General Specification AV1. The after-flame time according to Example 15 was 0.9 seconds. According to Example 16, a classification according to UL94 V-0 was achieved. Comparison example V20 Production of a crosslinked silicone molded article containing a in situ Mixture of two light metal alloy particles. (not according to the invention)

[0140] A crosslinked silicone molded article was produced according to inventive example 17, but 19.0 vol.% of the light metal alloy particle from example 1 and 18.6 vol.% of a non-inventive light metal alloy particle made of alloy A, which has a x50 of 105.8 µm and a SPAN of 0.35 and is produced by means of inert gas atomization and is thus substantially rounded, were used.

[0141] The non-inventive silicone molded article has a non-inventive total content of thermally conductive filler (Z) of 37.6 vol.% and exhibits a thermal conductivity of 0.48 W / mK. According to Example 16, it was classified according to UL94 V-1. The composition is unsuitable for use as a gap filler. Example 18 Two-component gap filler (according to the invention) Production of the A component

[0142] In a commercially available Labotop planetary mixer (PC Laborsystem GmbH, Maispracherstrasse 6, 4312 Magden, Switzerland), equipped with two bar stirrers and a scraper, 115.4 g of a vinyldimethylsiloxy-terminated polydimethylsiloxane, which has a viscosity of 120 mPa•s, and 1.1 g of WACKER ®< CATALYST EP (available from Wacker Chemie AG, Hanns-Seidel-Platz 4, 81737 Munich, Germany) were mixed at room temperature and a stirrer speed of 300 rpm for 5 minutes. 308.5 g of spherical alumina BAK-5 (available from Shanghai Bestry Performance Materials Co., Ltd. Room 209, Yunchuang Space, 325 Yunqiao Road, Pudong, Shanghai) were added and homogeneously incorporated for 10 minutes at 300 rpm under slight vacuum (950 mbar).Subsequently, a total of 658.29 g of an inventive light metal alloy particle made of alloy A, which has a x50 of 79.2 µm and a SPAN of 1.61 and is produced by inert gas atomization and is thus essentially rounded, was added in two portions (first portion 438.86 g, second portion 219.53 g). After each addition, mixing was carried out for 10 minutes under a slight vacuum (950 mbar) at 300 rpm. The resulting pasty mass was homogenized for a further 10 minutes at 300 rpm under a slight vacuum (950 mbar). An inventive A component was obtained with a content of inventive light metal alloy particles of 55.5 vol.% and a total content of thermally conductive filler of 73.1 vol.%.The pasty composition has a density of 2.43 g / cm 3< , a dynamic viscosity of 53,200 mPa•s at shear rate D = 10 s -1< and 25 °C and a thermal conductivity of 3.4 W / mK and is therefore very suitable for use as a gap filler. Production of the B component

[0143] In a commercially available Labotop planetary mixer (PC Laborsystem GmbH, Maispracherstrasse 6, 4312 Magden, Switzerland), equipped with two bar stirrers and a scraper, 106.5 g of a vinyldimethylsiloxy-terminated polydimethylsiloxane, which has a viscosity of 120 mPa•s, and 9.0 g of a copolymer of dimethylsiloxy and methylhydrogensiloxy and trimethylsiloxy units, which has a viscosity of 200 mPa•s and a content of Si-bonded hydrogen of 0.18 wt.%, were mixed at room temperature and a stirrer speed of 300 rpm for 5 minutes. 306.0 g of spherical alumina BAK-5 (available from Shanghai Bestry Performance Materials Co., Ltd. Room 209, Yunchuang Space, 325 Yunqiao Road, Pudong, Shanghai) were added and homogeneously incorporated for 10 minutes at 300 rpm under slight vacuum (950 mbar).Subsequently, a total of 652.83 g of inventive light metal alloy particles made of alloy A, which has a x50 of 78.8 µm and a SPAN of 1.64 and is produced by inert gas atomization and is thus essentially rounded, were added in two portions (first portion 435.22 g, second portion 217.61 g). After each addition, mixing was carried out for 10 minutes under a slight vacuum (950 mbar) at 300 rpm. The resulting pasty mass was homogenized for a further 10 minutes at 300 rpm under a slight vacuum (950 mbar). A B component according to the invention was obtained with a content of inventive light metal alloy particles of 55.5 vol.% and a total content of thermally conductive filler of 73.1 vol.%.The pasty composition has a density of 2.43 g / cm 3< , a dynamic viscosity of 39500 mPa•s at shear rate D = 10 s -1< and 25 °C and a thermal conductivity of 3.5 W / mK and is therefore very suitable for use as a gap filler. Production of a molded body

[0144] A crosslinked test specimen according to the invention was produced by homogeneously mixing 1 part by weight of the inventive A component and 1 part by weight of the inventive B component and then vulcanizing them according to General Specification AV1. The resulting molded specimen has a Shore A hardness of 1.8. According to Example 16, it was classified according to UL94 V-0. The composition is highly suitable for use as a gap filler.

Claims

1. Crosslinkable, heat-conducting silicone composition (Y) comprising 5-60% by volume of a crosslinkable silicone composition (S) and 40-95% by volume of at least one thermally conductive filler (Z) having a thermal conductivity of at least 5 W / mK, with the proviso that the crosslinkable, heat-conducting silicone composition (Y) has a thermal conductivity of at least 0.6 W / mK, and that at least 20% by volume of metallic light metal alloy particles present as thermally conductive fillers (Z) fulfil the following features: a) their median diameter x50 is in the range of 25-150 µm; b) they are produced in the last production step via a melting process and have a predominantly rounded surface shape; c) their distribution range SPAN ((x90-x10) / x50) is at least 0.40, and the light metal alloy particles contain, as main constituent, at least 60% by weight of a light metal or of a light semimetal selected from B, C, S, P, Be, Mg, Ca, Al and Si, where thermal conductivity and distribution range SPAN are determined by the methods specified in the description.

2. Crosslinkable silicone composition (Y) according to Claim 1, characterized in that it is an additioncrosslinking silicone composition.

3. Crosslinkable silicone composition (Y) according to Claim 1 or 2, characterized in that it contains at least 25% by volume of metallic light metal alloy particles as thermally conductive fillers (Z).

4. Crosslinkable silicone composition (Y) according to any of Claims 1 to 3, characterized in that it contains only one or two further thermally conductive fillers (Z) aside from the metallic light metal alloy particles.

5. Crosslinkable silicone composition (Y) according to any of Claims 1 to 4, characterized in that less than 16% by weight of a further thermally conductive filler (Z) having a density of greater than 5.0 g / cm3 is present.

6. Crosslinkable silicone composition (Y) according to any of Claims 1 to 5, characterized in that the median diameter x50 of the metallic light metal alloy particles is in the range of 40-130 µm.

7. Crosslinkable silicone composition (Y) according to any of Claims 1 to 6, characterized in that the metallic light metal alloy particle contains less than 20% by weight of a particle fraction having a diameter of not more than 20 µm based on the total amount of light metal alloy particles.

8. Crosslinkable silicone composition (Y) according to any of Claims 1 to 7, characterized in that it has a thermal conductivity of at least 0.8 W / mK.

9. Crosslinkable silicone composition (Y) according to any of Claims 1 to 8, characterized in that it has a dynamic viscosity, determined by the method specified in the description, of 1000-750 000 mPa•s, in each case at shear rate D = 10 s-1 and 25°C.

10. Process for producing the inventive crosslinkable silicone compositions according to any of Claims 1 to 9 by mixing the individual components.

11. Silicone product obtainable by dispensing or applying and then curing the inventive crosslinkable silicone compositions according to any of Claims 1 to 9.

12. Use of the crosslinkable silicone composition according to any of Claims 1 to 9 as a gap filler (= heat-conducting element), heat-conducting pad, heat-conducting adhesives and encapsulating compounds.

13. Use according to Claim 12 as gap filler for lithium ion batteries of electrical vehicles.

14. Use according to Claim 12 as encapsulating compound in electrical vehicles.