ALUMINUM-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 aluminum particles as a thermally conductive filler. These are comparatively lightweight and inexpensive. Furthermore, aluminum, as a semiconductor, has extremely low electrical conductivity. However, the aluminum particles according to the state of the art are not suitable for use as gap fillers in lithium-ion batteries for electric vehicles: The state of the art uses very finely divided aluminum particles with an average particle size of less than 20 µm. The use of aluminum particles smaller than 20 µm is disadvantageous because such small particles have a comparatively low minimum ignition energy and are therefore hazardous to dust explosions, requiring complex and costly safety precautions during processing. Furthermore, gap fillers containing such finely divided aluminum particles do not meet the required fire behavior according to UL94 V-0.

[0006] Another disadvantage of very fine or ground aluminum particles is that such particles have a comparatively large surface area and bind a large amount of polymer. This significantly increases the viscosity of the silicone composition, so that only mixtures with comparatively low filler levels and low thermal conductivity can be produced. At higher filler levels, 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 aluminum particles are comparatively highly flammable.

[0007] There are numerous patents that disclose the use of finely divided aluminum particles in thermally conductive silicone compositions, for example, in US2007167564, US2002014692, US2003049466, US2018022977, JP2014037460, WO21079714, US2011163460, US2016208156, JP2010013521, JP2014037460, US2016060462, and US2016068732. None of these documents disclose any details regarding the shape of the particles, and only a very broad definition of the average particle diameter is provided. The specific examples disclose the use of very fine aluminum particles <20 µm.

[0008] However, this use of very small aluminum particles <20 µm is associated with a major disadvantage. Since they have a comparatively low minimum ignition energy and are therefore subject to dust explosion hazard, they require complex and costly safety precautions during processing. In addition, silicone compositions containing such fine-particle aluminum particles do not meet the required fire behavior according to UL94 V-0 and are therefore not suitable for use as gap fillers in lithium-ion batteries. Another disadvantage is that such fine-particle aluminum particles have a large surface area and bind a large amount of polymer. This greatly increases the viscosity of the silicone composition. Only mixtures with comparatively low filler contents and low thermal conductivity can be produced.

[0009] US2017002248 claims thermal interface materials with a high thermal conductivity of >6 W / mK and a low secant modulus of elasticity. A wide selection of possible matrix materials is mentioned (thermoplastics, thermosets, polymers). A wide selection of possible thermally conductive fillers is disclosed, such as metal oxides, nitrides or ceramics, including metallic aluminum, although no further specification of shape and size is given. The examples disclose addition-curable silicone compositions, silicone oil and mineral oil as matrix materials and exclusively combinations of aluminum oxide and metallic aluminum as fillers, with three types of aluminum oxide of different sizes and four types of aluminum (Al-1: 150 µm, Al-2: 80 µm, Al-3: 5 µm, Al-4: 50 µm) of different sizes being mixed, all types being spherical. The content of aluminum particles is greater than 42 wt.-% and the aluminum oxide particle content is greater than 37 wt.%. The proportion of added small aluminum particles < 20 µm (particles, for example, Al-3) relative to the total amount of aluminum particles is greater than 20% in each case. The addition and content of very small aluminum particles < 20 µm is associated with the disadvantages mentioned above. Due to the use of large amounts of aluminum oxide, such thermal interface materials are also very expensive to produce and have a comparatively high density of greater than 2.69 g / ml.

[0010] 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.

[0011] This object is achieved by the crosslinkable, thermally conductive silicone compositions (Y) according to the invention, which contain comparatively large aluminum particles with an average particle size of 20 to 150 µm, a predominantly rounded surface shape, and which simultaneously exhibit a particularly large or broad particle distribution. Completely surprisingly, experiments have found that these silicone compositions (Y) according to the invention exhibit significantly reduced flammability.

[0012] In the context of the present invention, aluminum particles with a "predominantly rounded surface shape" are understood to mean those that have a spherical to oval, spiky 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 aluminum particles according to the invention. Aluminum particles according to the invention with a predominantly rounded surface shape are produced using a melting process. This means that the aluminum 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.

[0013] Non-inventive aluminum particle shapes show, by way of example, the Figures 2 a and 2 b with angular and pointed particles. These are produced by grinding, crushing, or grinding processes.

[0014] Metallic aluminum particles according to the invention with a predominantly rounded surface shape are therefore neither angular nor pointed. However, they can contain such particles to the extent of an impurity without impairing their inventive effect.

[0015] The subject of the present invention is thus a crosslinkable, thermally conductive silicone composition (Y) containing 5-50 vol.% of a crosslinkable silicone composition (S) and 50-95 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 composition (Y) has a thermal conductivity of at least 0.6 W / mK, and at least 20 vol% metallic aluminum particles are contained as thermally conductive fillers (Z), which meet the following characteristics: a) their average diameter x50 is in the range 20-150 µm; b) they are produced in the last manufacturing 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.

[0016] In the context of this invention, the terms thermally conductive, thermoconductive or thermally conductive are synonymous.

[0017] 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.

[0018] For the purposes of this invention, thermally conductive silicone composition (Y) is understood to mean those 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.

[0019] For the purposes of this invention, all parameters describing the particle size (parameter: mean diameter x50) or the particle size distribution (parameter: 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.

[0020] In order to avoid making 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 description.

[0021] 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)

[0022] 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).

[0023] 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-dimethylhexane-2,5-diperbenzoate.

[0024] One type of organic peroxide or a mixture of at least two different types of organic peroxides can be used.

[0025] Particular preference is given to using addition-curing silicone compositions (S).

[0026] 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.

[0027] The addition-curing silicone compositions (S) can be one-component silicone compositions as well as two-component silicone compositions.

[0028] 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).

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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, Triallyl-s-triazin-2,4,6(1H,3H,5H)-trion, Diallylmalonsäureester, Polyethylenglykoldiacrylat, Polyethylenglykol Dimethacrylat, Poly(propylenglykol)methacrylat.

[0033] 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.

[0034] As organosilicon compounds (A) which have SiC-bonded radicals with aliphatic carbon-carbon multiple bonds, preferably linear or branched organopolysiloxanes comprising units of the general formula (I) R 4< a R 5< b SiO (4-ab) / 2 ( I) is used, whereby R 4< independently of one another, identical or different, an organic or inorganic radical free from aliphatic carbon-carbon multiple bonds, R 5< independently of one another, identically or differently, denote 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 per molecule.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 mentioned 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.

[0040] 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.

[0041] The residue R 5< can be any group that is accessible to an addition reaction (hydrosilylation) with a SiH-functional compound.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] All hydrogen-functional organosilicon compounds which have previously been used in addition-crosslinkable compositions can be used as organosilicon compound (B).

[0047] 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) are used, 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) with at least three, particularly preferably at least four Si-bonded hydrogen atoms per molecule.

[0048] 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.%.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The components (A) and (B) used according to the invention are commercially available products or can be prepared by processes commonly used in chemistry.

[0055] 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).

[0056] 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.

[0057] Examples of organopolysiloxanes (C) are those consisting of SO 4 / 2 , R 4< 3 SiO 1 / 2 -, R 4< 2 R 5< SiO 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.

[0058] 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.

[0059] 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, for example, 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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. %.

[0064] 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 E.

[0065] 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 amounts 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.

[0066] 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, dispersants, adhesion promoters, pigments, dyes, plasticizers, organic polymers, heat stabilizers, etc. Thermally conductive filler (Z)

[0067] 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 aluminum particles as thermally conductive fillers (Z), which must also meet at least the further specific features a) to c), and the total amount of thermally conductive fillers (Z) is at least 50 vol.%. a) The average diameter x50 of these metallic aluminum particles (Z) according to the invention is in the range 20-150 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 aluminum 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 aluminum 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.

[0068] It is irrelevant whether a single fraction of aluminum particles (Z) is used whose SPAN lies within the inventive range, or whether two or more fractions of aluminum particles are mixed, thereby achieving the inventive particle size distribution range according to feature c) of the inventive aluminum particles (Z). If two or more fractions of aluminum particles are mixed, this can be done before mixing with one or more components of the inventive composition, or the fractions of aluminum particles can also be mixed separately with one or more components of the inventive composition. The order of addition is irrelevant.

[0069] Preferably, a maximum of four fractions of aluminum particles are mixed and thus the distribution range according to the invention is achieved, preferably a maximum of three fractions of aluminum particles are mixed and thus the distribution range according to the invention is achieved, particularly preferably a maximum of two fractions of aluminum particles according to the invention are used and thus the distribution range according to the invention is achieved, particularly preferably only a single aluminum powder according to the invention is used.

[0070] Metallic aluminum exhibits several highly advantageous properties for use as a thermally conductive filler (Z). For example, the exceptionally high thermal conductivity of aluminum particles (Z) improves the thermal conductivity of the thermoconductive silicone composition (Y) produced from them. The low density of the aluminum particles (Z) reduces the weight of the composition and the components produced from it, helping to save costs. The electrical conductivity can be reduced, if required by the application, using state-of-the-art methods, for example, by surface oxidation. The low Mohs hardness of the aluminum particles (Z) reduces abrasion during processing. Those skilled in the art will understand that the aforementioned advantages are lost in whole or in part as the purity of the aluminum decreases.The purity of the aluminum particles (Z) according to the invention and thus the aluminum content is at least 80%, preferably at least 90%, particularly preferably at least 95%.

[0071] The skilled person is also aware that metallic aluminum particles are flammable under certain conditions and that the dusts are explosive. The skilled person also knows 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 aluminum particles below 20 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 dangerous to handle and require complex and costly safety precautions during processing. Furthermore, it has been shown that compositions containing very small aluminum particles below 20 µm are comparatively highly flammable and do not meet the UL94 V-0 flammability class for gap fillers in lithium-ion batteries.

[0072] The aluminum particles (Z) according to the invention preferably contain less than 20% by weight, more preferably less than 15% by weight, particularly preferably less than 10% by weight of a particle fraction having a diameter of less than or equal to 20 µm, in each case based on the total amount of aluminum particles.

[0073] The aluminum particles (Z) according to the invention preferably contain less than 15% by weight, more preferably less than 10% by weight, particularly preferably less than 5% by weight of a particle fraction having a diameter of less than or equal to 10 µm, in each case based on the total amount of aluminum particles.

[0074] The inventive aluminum particles (Z) preferably contain at most 1.5 wt.% aluminum particles smaller than 2 µm, preferably at most 1 wt.%, particularly preferably at most 0.5 wt.%, in each case based on the total amount of aluminum particles. Particularly preferred aluminum particles are essentially free of particle fractions smaller than 2 µm.

[0075] In a particularly preferred embodiment, there is no intentional addition of aluminum 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 aluminum particles less than or equal to 5 µm.

[0076] Larger aluminum particles with an average particle size of over 20 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 aluminum particles larger than 20 µm proved to be comparatively highly flammable and did not meet the UL94 V-0 flammability rating for gap fillers in lithium-ion batteries.

[0077] Aluminum particles with an average particle size of over 150 µm are unsuitable for many applications of thermally conductive silicone compositions, as such large-grained aluminum particles often do not fit into the fine gaps that must be filled with gap fillers, for example. Furthermore, it has been very unexpectedly found that even such large-grained aluminum particles exhibit comparatively high flammability.

[0078] 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 aluminum particles (Z) according to the invention, which simultaneously satisfy features a) to c), in the required minimum amounts.

[0079] The crosslinkable silicone composition (Y) according to the invention contains at least 20 vol% of such metallic aluminum 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 aluminum particles (Z), the desired advantageous effects of the metallic aluminum, for example, the low density and high thermal conductivity, are no longer sufficiently present.

[0080] The prior art knows various methods for producing finely divided metal particles. The aluminum particles (Z) according to the invention are preferably produced from a molten state, as a result of which 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 have been 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 an aluminum melt is first produced and then comminution, for example by atomization.Preferably, the aluminum particles according to the invention are brought into the solid form according to the invention by spraying or atomizing, also called atomization, an aluminum melt and subsequent cooling.

[0081] Suitable processes for producing the aluminum 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 ". and at the same time satisfy the features a) to c) of the invention.

[0082] The production process for the metallic aluminum particles (Z) according to the invention is preferably carried out such that the particles are obtained in their predominantly rounded surface shape according to the invention, thus fulfilling features a) - c) and being essentially free of angular or pointed particles. The solidified particles can be separated by size in a subsequent process step using conventional methods, e.g., by screening or sifting. These processes allow agglomerates and bonded particles to be separated, but essentially no particles are destroyed.

[0083] Predominantly rounded or substantially free from 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 interfere with their effect according to the invention.

[0084] The crosslinkable silicone composition (Y) according to the invention may contain, in addition to these metallic aluminum 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 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, metallic silicon powder, aluminum hydroxide, and aluminum oxide, with metallic silicon powder and aluminum hydroxide being particularly preferred. The shape of the further filler is fundamentally unrestricted. The particles may, for example, be 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.

[0085] 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 6.0 g / cm 3 , preferably at most 4.5 g / cm 3 , particularly preferably at most 3.0 g / cm 3 .

[0086] 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 .

[0087] 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 .

[0088] Preferred crosslinkable silicone compositions (Y) according to the invention contain, as the thermally conductive filler (Z), the metallic aluminum 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).

[0089] If the preferred compositions according to the invention contain the metallic aluminum 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.

[0090] The total amount of thermally conductive fillers (Z) in the crosslinkable, thermally conductive silicone composition (Y) according to the invention is 50-95 vol.%, preferably 60-90 vol.%, more preferably 65-88 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.

[0091] 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.

[0092] 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).

[0093] 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.

[0094] 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< .

[0095] The silicone compositions according to the invention are predominantly free of volatile organic solvents, as these can generate flammable vapors and / or lead to undesirable shrinkage during or after crosslinking. "Predominantly free" means that no solvents are intentionally added, but may only be present in small amounts (less than 0.1 wt.%) as impurities in the inventive components of the silicone compositions according to the invention.

[0096] 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.

[0097] 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.

[0098] In a preferred embodiment, there is no intentional addition of aluminum 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 aluminum particles less than or equal to 5 µm, since this is associated with a particular safety risk in technical production.

[0099] The crosslinkable silicone composition (Y) according to the invention can be provided as a one-, two-, or multi-component mixture. Examples include two-component, thermosetting compositions (Y) or one-component UV-crosslinkable compositions (Y). This has also long been known to the skilled person.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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).

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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< .

[0108] The crosslinked silicone products according to the invention preferably correspond to flammability class UL94 V-0.

[0109] 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.

[0110] 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

[0111] 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.

[0112] 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

[0113] 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

[0114] 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

[0115] 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 .

[0116] The following examples describe the basic feasibility of the present invention, without, however, limiting it to the contents disclosed therein.

[0117] 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 aluminum powders and aluminum powder mixtures used according to the invention and not according to the invention

[0118] Table 1 summarizes the properties of the aluminum powders according to the invention and those not according to the invention used in the examples.

[0119] Examples 1-6 and 8 according to the invention use aluminum powder according to the invention, which was obtained by inert gas atomization and thus has a predominantly rounded surface shape and also has a comparatively broad particle size distribution according to the invention.

[0120] The non-inventive comparative examples V1-V4 use non-inventive aluminum powders 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 satisfy the inventive feature c).

[0121] The non-inventive comparative examples V5-V7 use non-inventive aluminum powders which have a comparatively broad particle size distribution, but were obtained by means of a grinding process and are therefore essentially angular and angular and do not meet the inventive feature b).

[0122] The non-inventive comparative examples V9 and V10 use non-inventive aluminum powders which were obtained by inert gas atomization and are thus predominantly rounded, and also have a comparatively broad particle size distribution, but the particle size is comparatively small and the inventive feature a) is not fulfilled. Example 7: Preparation of aluminum powder mixture 7 (according to the invention)

[0123] 100 g of the non-inventive aluminum powder from Comparative Example V2, 200 g of the non-inventive aluminum powder from Comparative Example V3, 400 g of a non-inventive aluminum powder which has a x50 of 106.2 µm and a SPAN of 0.37 and is produced by means of inert gas atomization and is thus substantially rounded, 200 g of a non-inventive aluminum powder which has a x50 of 133.5 µm and a SPAN of 0.27 and is produced by means of inert gas atomization and is thus substantially rounded, and 100 g of the non-inventive aluminum powder from Comparative Example V4 are mixed homogeneously using a commercially available laboratory stirrer TYPE RW 28 (IKA ®< -Werke GmbH & CO. KG, 79219 Staufen, Germany). An aluminum powder mixture according to the invention is obtained which has a x50 of 107.4 µm and a SPAN of 0.75 and is substantially rounded, and which fulfills the features a)-c) according to the invention. Comparative Example V8: Preparation of the aluminum powder mixture V8 (not according to the invention)

[0124] 300 g of a non-inventive aluminum powder, which has a x50 of 133.5 µm and a span of 0.27 and is produced by inert gas atomization and is thus essentially rounded, and 600 g of the non-inventive aluminum powder 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 aluminum powder mixture is obtained which has a x50 of 155.0 µm and a span of 0.41 and does not meet feature a) of the invention. Abbreviations

[0125] Example VComparative Example PFParticle shape predominantly rounded Surface shape angular According to the invention NEnot according to the invention nbnot determined Table 1: Overview of the aluminum powders used e.g. x10 (µm) x50 (µm) x90 (µm) SPANISH PF remark Feature a) Feature c) Feature b) 1 16,1 31,5 44,8 0,91 r E 2 17,8 35,8 53,3 0,99 r E 3 21,6 48,5 69,3 0,98 r E 4 28,8 65,8 94,6 1,00 r E 5 55,9 81,5 126 0,86 r E 6 99,5 135,6 168,9 0,51 r E 7 71,9 107,1 152,4 0,75 r E 8 47,2 73,1 115,8 0,94 r E v1 43,5 50,9 63,2 0,39 r NE v2 60,5 68,3 75,4 0,22 r NE v3 71,8 81,8 91,6 0,24 r NE v4 146,2 161,5 180,4 0,21 r NE v5 9,9 37,4 83,6 1,97 e NE v6 19,5 94,8 188,3 1,78 e NE v7 2,8 6,1 9,1 1,03 e NE v8 122,3 155 185,1 0,41 r NE v9 3,2 6,0 8,7 0,92 r NE v10 6,2 14,7 23,1 1,15 r NE General Instructions 1 (AV1) for the preparation of crosslinked, thermoconductive aluminum powder-containing silicone moldings (inventive examples 9 to 16 and non-inventive examples V11 to V23) Step 1: Preparation of an addition-curable, thermoconductive aluminum powder-containing silicone composition

[0126] 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 with 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. An aluminum powder was then added to each in the ratio shown in Table 2 and mixed for 25 seconds at 2350 rpm using the SpeedMixer. The silicone composition containing aluminum particles was stirred with a spatula, and aluminum powder residues from the edge of the vessel were mixed in.The mixture was then homogenized for a further 25 seconds at 2350 rpm using a SpeedMixer and cooled to room temperature.

[0127] 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 processed directly. Step 2: Production of a cross-linked, thermoconductive aluminum powder-containing silicone molded body

[0128] 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 17 Flammability test

[0129] The flammability test is performed 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.

[0130] Test pieces 5" (127 mm) long and 0.5" (12.7 mm) wide were punched out from the inventive silicone moldings according to Examples 9 to 16 and the non-inventive silicone moldings according to Comparative Examples V11 to V15 and V19 to V21. 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 2.

[0131] In the non-inventive comparative experiments V16 to V18, each containing 62.5 vol.% of the non-inventive aluminum 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 2: Composition and flammability of aluminum powder-containing silicone compositions e.g. Aluminum powder according to Table 1 crosslinkable silicone composition Silicone molded body e.g. Quantity (g) Content (vol%) Viscosity (Pa•s) Density (g / cm 3 ) hardness Thermal conductivity Afterburn time (s) 9 1 213,2 62,5 6,1 2,05 74 1,7 3 10 2 213,2 62,5 6,3 2,05 72 2,0 1 11 3 213,2 62,5 5,9 2,05 71 1,9 0 12 4 213,2 62,5 5,0 2,05 70 2,0 2 13 5 213,2 62,5 4,8 2,05 74 1,8 0 14 6 213,2 62,5 3,8 2,05 83 1,8 2 15 7 213,2 62,5 4,1 2,05 74 1,9 2 16 8 213,2 62,5 7,4 2,05 86 2,0 3 V11 V1 213,2 62,5 10,1 2,05 75 1,9 6 V12 V2 213,2 62,5 12,5 2,05 72 1,9 15 V13 V3 213,2 62,5 15,3 2,05 81 1,9 5 V14 V4 213,2 62,5 13,2 2,05 83 2,0 9 V15 V8 213,2 62,5 5,2 2,05 78 1,9 20 V16 V5 213,2 62,5 nb nb nb nb nb V17 V6 213,2 62,5 nb nb nb nb nb V18 V7 213,2 62,5 nb nb nb nb nb V19 V5 124,3 49,2 12,7 1,82 4 1,1 21 V20 V6 124,3 49,2 nb 1,82 12 1,2 23 V21 V7 124,3 49,2 nb 1,82 31 1,1 70 V22 V9 213,2 62,5 12,2 2,05 87 1,9 26 V23 V10 213,2 62,5 8,3 2,05 78 1,9 11

[0132] The flammability test showed that comparative examples V11 to V15 and V19 to V23, containing a non-inventive aluminum powder or a non-inventive aluminum powder mixture according to comparative examples V1-V10, which does not meet one or more of the features a) to c), exhibit comparatively high flammability. Particularly striking was the flammability of the non-inventive comparative sample V21, containing an aluminum powder with an average particle size of less than 20 µm. The sample continued to burn after the flame was removed until the molded body was completely combusted.

[0133] Completely unexpectedly, it was found that aluminum powders that simultaneously fulfill features a) to c) exhibit the inventive advantage of reduced flammability. Inventive Example 15, it was also completely surprising that by mixing several non-inventive aluminum powders, an inventive aluminum powder mixture can be produced that has the inventive advantageous properties of low flammability, provided the resulting mixture fulfills features a) to c). In contrast, the non-inventive aluminum powder mixture from Comparative Example V8 does not fulfill features a) to c) and also does not exhibit the inventive advantages. Example 18 Full flammability test according to UL 94 V

[0134] The inventive silicone moldings from inventive examples 12 and 13 and the non-inventive silicone moldings from non-inventive comparative examples V11, V12, and V20 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 3. Table 3: Flammability test according to UL 94 V e.g. Classification according to UL 94 V remark 12 V-0 E 13 V-0 E V12 V-1 NE V13 V-1 NE V20 V-2 NE Example 19 Production of a crosslinked, thermoconductive silicone molded article containing a in situ Mixture of two aluminum powders. (according to the invention)

[0135] According to the general specification AV1, a crosslinkable thermoconductive silicone composition according to the invention was prepared, wherein 191.0 g of the inventive aluminum powder from Example 1 (37.6 vol.% based on the total amount of the thermoconductive silicone composition) and 187.4 g of a non-inventive aluminum powder, which has a x50 of 106.2 µm and a SPAN of 0.37 and is produced by means of inert gas atomization and is thus substantially rounded off, (36.8 vol.% based on the total amount of the thermoconductive silicone composition) were added separately from one another as aluminum powder and in situ to form an aluminum powder mixture according to the invention.

[0136] A reactive silicone composition according to the invention was obtained with a content of aluminum particles according to the invention of 74.4 vol. % and a dynamic viscosity of 58,600 mPa.s at a shear rate D = 10 s -1 and 25 °C. The thermal conductivity was 4.65 W / mK and the density was 2.19 g / cm 3 . The composition according to the invention has good processability, high thermal conductivity and a low density and is very suitable for use as a gap filler. A crosslinked silicone molding according to the invention was produced according to General Specification AV1. The after-flame time according to Example 17 was 2.1 seconds. According to Example 18, a classification according to UL94 V-0 was achieved. Comparison example V24 Production of a crosslinked silicone molded article containing a in situ Mixture of two aluminum powders. (not according to the invention)

[0137] A crosslinked silicone molded article was produced according to inventive example 19, but 19.0 vol.% of the aluminum powder from example 1 and 18.6 vol.% of a non-inventive aluminum powder, which has a x50 of 106.2 µm and a SPAN of 0.37 and is produced by inert gas atomization and is thus substantially rounded, were used.

[0138] The non-inventive silicone molded article has a non-inventive total content of thermally conductive filler (Z) of 37.6 vol.% and a thermal conductivity of 0.45 W / mK. According to Example 18, it was classified according to UL94 V-1. The composition is unsuitable for use as a gap filler. Example 20 Two-component gap filler (according to the invention) Preparation of the A component

[0139] 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 670.7 g of an inventive aluminum powder, which has a x50 of 79.5 µm and a SPAN of 1.62 and is produced by inert gas atomization and is thus essentially rounded, was added in two portions (first portion 447.1 g, second portion 223.6 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). This yielded an inventive A component having a content of inventive aluminum particles of 55.5 vol.% and a total content of thermally conductive filler of 73.1 vol.%. The pasty composition has a density of 2.46 g / cm 3< , a dynamic viscosity of 57800 mPa•s at shear rate D = 10 s -1< and 25 °C and a thermal conductivity of 3.2 W / mK and is therefore very suitable for use as a gap filler. Production of the B component

[0140] 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 665.2 g of an inventive aluminum powder, which has a x50 of 79.5 µm and a SPAN of 1.62 and is produced by inert gas atomization and thus essentially rounded, was added in two portions (first portion 443.5 g, second portion 221.7 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). This yielded a B component according to the invention with a content of inventive aluminum particles of 55.5 vol.% and a total content of thermally conductive filler of 73.1 vol.%. The pasty composition has a density of 2.46 g / cm 3< , a dynamic viscosity of 42800 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

[0141] 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 1.6. According to Example 18, 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 5-50% by volume of a crosslinkable silicone composition (S) and 50-95% 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 aluminium particles present as thermally conductive fillers (Z) fulfils the following features: a) the median diameter x50 thereof is in the range of 30-150 µm; b) they are produced in the last production step via a melting process and have a predominately rounded surface shape; c) the distribution range SPAN ((x90-x10) / x50) thereof is at least 0.40, 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 aluminium 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 aluminium 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 aluminium 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 aluminium 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 aluminium 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 a gap filler for lithium ion batteries of electrical vehicles.

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