Thermally conductive silicone composition

Abstract

The invention relates to thermally conductive silicone compositions, as well as to the production and use thereof.

Description

[0001] WA12340S / Dr.MK

[0002] Thermally conductive silicone composition

[0003] The present invention relates to thermally conductive silicone compositions, their production and use.

[0004] State of the art

[0005] Thermally conductive silicone compounds are widely used for thermal management in the automotive and electronics industries. These compounds contain a high proportion of thermally conductive filler dispersed in a silicone polymer. Generally, larger particles are preferred because, at the same filler density, fewer filler / matrix phase transitions impede heat flow. The gaps between the large filler particles are often filled with filler fractions exhibiting a smaller particle size distribution.

[0006] However, these highly filled compositions tend to segregate the filler, which means they have a limited shelf life and require extensive stirring before processing into the final product.

[0007] The state of the art therefore includes the use of inorganic rheology modifiers to increase the storage stability of thermally conductive silicone compositions. These are usually very fine particles with a very high surface area, such as pyrogenic silica or platelet-shaped particles like boron nitride or layered silicates. These increase the viscosity of the composition and thus slow down segregation. However, this increase in viscosity has a very detrimental effect on processability, which severely limits the amount of such inorganic rheology modifiers used and consequently renders them insufficiently effective. Shear-thinning systems are also known, in which the shear-thinning effect is achieved by adding thixotropic additives, such as WA12340S / Dr.MK.

[0008] 2. So-called "organoclay" compounds. These naturally occurring organotones are two-dimensional inorganic materials with a layered structure, such as montmorillonite or bentonite. The addition of such layered organotones to non-crosslinking silicone compositions is described, for example, in US2023032719A. To achieve a suitable shear-thinning effect, this document defines the increase, and thus a minimum achievable "Thixotropic Index" value, that the thermally conductive composition containing 50-74 vol.% thermally conductive fillers must reach. This "Thixotropic Index" is calculated from the ratio of the maximum viscosity to the minimum viscosity of the final thermally conductive composition, with these viscosities being determined by oscillation measurement.However, the use of organotones is disadvantageous because they have comparatively poor thermal conductivity, thus reducing the effectiveness of the thermally conductive silicone composition. Furthermore, due to their large BET surface area, organotones also cause an undesirable increase in viscosity under increased shear stress, which impairs overall processability.

[0009] Therefore, there remains a great need for thermally conductive silicone compositions that do not exhibit the aforementioned disadvantages of the state of the art and show good storage stability, good processability, and still good thermal conductivity.

[0010] Completely unexpectedly, it turned out that the present thermally conductive silicone composition (Y) according to the invention solves this problem. WA12340S / Dr.MK

[0011] 3

[0012] The present invention therefore relates to a thermally conductive silicone composition (Y) comprising

[0013] -5-40 vol% silicone composition (S) ;

[0014] -60-95 vol% of at least one thermally conductive filler (Z) with a thermal conductivity of at least 2 W / mK, wherein (Z) contains at least one thermally conductive filler (ZI) characterized in that its mean diameter d50 is 10-200 pm, and at least one thermally conductive filler (Z2) characterized in that a) its mean diameter d50 is 0.1 to 6 pm, b) its BET is 3.5 to 15 m 2 / g is, c) its particle-specific thixotropy index (0.5 / 10)

[0015] [= ps-TI ( 0 , 5 / 10 ) ] is at least 5, where the ps-TI ( 0 , 5 / 10 ) value is determined as the ratio of the dynamic viscosity at 25°C and a shear rate of 0.5 s -1viscosity at 25°C and a shear rate of 10 s -1 and these viscosities are measured in the following standardized form:

[0016] 20 vol.% (Z2) in a linear polydimethylsiloxane terminated with vinyl dimethylsilyl groups, with a dynamic viscosity of 1000 mPas at 25°C, wherein the amount of (Z2) is 3-20 vol.%, based on the total silicone composition (Y) .

[0017] The determination and measurement methods revealed in the examples below are used. WA12340S / Dr.MK

[0018] 4

[0019] In order to avoid making the number of pages in the description of the present invention too extensive, only the preferred embodiments of the individual features are listed below.

[0020] The expert reader should understand this type of disclosure explicitly as meaning that every combination of different levels of preference is explicitly stated and explicitly desired.

[0021] For clarification, it should also be noted that the quantities of each individual component used in the compositions according to the invention are selected such that they always add up to 100 wt.% or 100 vol.%.

[0022] Silicone composition (S)

[0023] According to the invention, all crosslinking and non-crosslinking silicone compositions known in the prior art can be used. Furthermore, hybrid systems, i.e., those based on silane-crosslinking polymers, are also suitable as silicone compositions (S).

[0024] Addition-curing silicone compositions (S) are preferred.

[0025] Non-crosslinking silicone compositions (S)

[0026] Non-netting silicone composition (S) contains:

[0027] One or a mixture of at least two organopolysiloxanes (T) having the following properties:

[0028] -they are linear, branched or cyclic, preferably linear

[0029] -terminated on both ends, or Si-OH terminal on one end or alkoxy-silyl terminal on one end, preferably terminated on both ends WA12340S / Dr.MK

[0030] 5

[0031] -the Si-bound side and end groups R 1 These are independently substituted or unsubstituted CI to C18 hydrocarbon groups, preferably C1-C10 monovalent hydrocarbon groups. Examples of R 1Suitable compounds include linear, branched, and cyclic alkyl, alkenyl, aryl, aralkyl, and haloalkyl groups. Suitable pure alkyl groups include methyl, ethyl, propyl, hexyl, and octyl groups. Suitable branched alkyl groups include isopropyl, isobutyl, tert-butyl, and 2-ethylhexyl groups. Suitable cyclic alkyl groups include cyclopentyl and cyclohexyl groups. Suitable alkenyl groups are vinyl and allyl groups. Suitable aryl groups include phenyl and tolyl groups. Suitable aralkyl groups include 2-phenylethyl and 2-methyl-2-phenylethyl groups. Suitable haloalkyl groups include 3,3,3-trifluoropropyl, 2-(nonafluorobutyl)ethyl, and 2-(heptadecafluorooctyl)ethyl groups. As R 1 The methyl or phenyl groups are preferred.

[0032] The process for producing end-stopped organopolysiloxanes has long been known to those skilled in the art and is carried out, for example, from dichlorodimethylsilane in the presence of water to linear, end-stopped polymethylpolysiloxanes.

[0033] The dynamic viscosity of these organopolysiloxanes (T) ranges from 35 to 1,000,000 mPas, preferably 50 to 100,000 mPas at 25 °C. They have been known in the art for a long time and are often referred to as silicone oils.

[0034] Non-curing silicone compositions (S) may optionally contain all other additives that have previously been used in the production of non-curing silicone compositions. WA12340S / Dr.MK

[0035] 6

[0036] Crosslinking silicone compositions (S)

[0037] Silicones known to the person skilled in the art can be used as crosslinkable silicone compositions (S ), such as addition-curing, peroxide-curing, condensation-curing or radiation-curing silicone composition tongues (S ).

[0038] The addition-curing silicone compositions (S) used according to the invention are known in the prior art and in the simplest case contain

[0039] (A) at least one linear compound having residues with aliphatic carbon to ff multiple bonds,

[0040] (B) at least one linear organopolysiloxane with Si-bound hydrogen atoms, or instead of (A) and (B)

[0041] (C) at least one linear organopolysiloxane having SiC-bonded residues with aliphatic carbon-carbon multiple bonds and Si-bonded hydrogen atoms, and

[0042] ( D) at least one hydrosilylation catalyst .

[0043] The addition-curing silicone compositions (S) can be one-component silicone compositions as well as two-component silicone compositions.

[0044] In two-component silicone compositions (S), the two components of the inventive, addition-curing WA12340S / Dr.MK

[0045] 7

[0046] Silicon compositions (S) contain all components in any combination, generally with the proviso that one component does not simultaneously contain siloxanes with aliphatic multiple bonds, siloxanes with Si-bound hydrogen and catalyst, i.e., essentially not simultaneously contain the components (A) , (B) and (D) or (C) and (D).

[0047] The compounds (A) and (B) or (C) used in the addition-curing 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 aliphatic unsaturated residues and (B) has at least three silicon-bound hydrogen atoms, or compound (A) has at least three aliphatic unsaturated residues and siloxane (B) has at least two silicon-bound hydrogen atoms, or alternatively, instead of compounds (A) and (B), siloxane (C) is used, which has aliphatic unsaturated residues and silicon-bound hydrogen atoms in the above-mentioned ratios. Mixtures of (A) and (B) and (C) with the above-mentioned ratios of aliphatic unsaturated residues and silicon-bound hydrogen atoms are also possible.

[0048] The addition-curing silicone composition (S) according to the invention typically contains 40-99.0 wt.%, preferably 45-95 wt.%, and particularly preferably 50-90 wt.% (A). The addition-curing silicone composition (S) according to the invention typically contains 1-60 wt.%, preferably 3-50 wt.%, and particularly preferably 8-40 wt.% (B). If the addition-curing 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.% (C) based on the total amount of the addition-curing silicone composition (S) according to the invention. WA12340S / Dr.MK

[0049] 8

[0050] The compound (A) used according to the invention can be silicon-free organic compounds with preferably at least two aliphatic unsaturated groups, as well as organosilicon compounds with preferably at least two aliphatic unsaturated groups, or mixtures thereof.

[0051] 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-diene,

[0052] 1.3-Diisoproppenylbenzene, vinyl group-containing polybutadiene,

[0053] 1 . 4-Divinylcyclohexan, 1 , 3 , 5-Triallylbenzol , 1 , 3 , 5-Trivinylben- zol , 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-octa- dien- ( l , 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' -Diallylharnstof f , Triallylamin, Tris ( 2-methylallyl ) amin, 2 , 4 , 6-Triallyloxy- l , 3 , 5-triazin, Tri- allyl-s-triazin-2 , 4 , 6 ( 1H, 3H, 5H) -trion, Diallylmalonsäureester, Polyethylenglykoldiacrylat , Polyethylenglykol Dimethacrylat , Poly ( propyl engly ko 1 ) methacrylat .

[0054] Preferably, the addition-curing silicone compositions (S) according to the invention contain as component (A) at least one aliphatic unsaturated organosilicon compound, wherein all aliphatic unsaturated organosilicon compounds used previously in addition-curing compositions can be employed, such as silicone block copolymers with urea segments, silicone block copolymers with WA12340S / Dr.MK

[0055] 9

[0056] 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.

[0057] Organosilicon compounds (A) which have SiC-bound residues with aliphatic carbon-carbon multiple bonds are preferably linear or branched organopolysiloxanes from units of the general formula (I)

[0058] R 4 a R 5 bS i 0 ( 4 -ab ) / 2 (I) is used, where

[0059] R 4 independent of each other, the same or different, an organic or inorganic residue free of aliphatic carbon to ff multiple bonds,

[0060] R 5 independently of each other, identical or different, a monovalent, substituted or unsubstituted, SiC-bonded hydrocarbon residue with 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 residues R 5 each molecule.

[0061] With the remainder R 4These can be monovalent or polyvalent residues, with the polyvalent residues, such as bivalent, trivalent, and tetravalent residues, then linking several, such as two, three, or four, siloxy units of formula (I) together. WA12340S / Dr.MK

[0062] 10

[0063] More examples of R 4 are the monovalent residues -F, -Ci, -Br, OR 6 -ON, -SON, -NCO and SiC-bonded, substituted or unsubstituted hydrocarbon residues, which may be interrupted by oxygen atoms or the group -C(O)-, as well as divalent residues bonded to Si on both sides according to formula (I). If residue R 4 In the case of SiC-bonded, substituted hydrocarbon residues, preferred substituents are halogen atoms, phosphorus-containing residues, cyano residues, -OR 6 , -NR 6 -, - NR 6 2, -NR 6 -C (0) -NR 6 2, -C(O)-NR 6 2, -0(0) R 6 , -0(0) OR 6, -SO2-Ph and -CeFs. Here, R means 6 independently of each other, the same or different, a hydrogen atom or a monovalent hydrocarbon residue with 1 to 20 carbon atoms and Ph equal to the phenyl residue.

[0064] Examples of residues R 4These are alkyl groups, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-bulyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl, and tert-pentyl groups; hexyl groups, such as n-hexyl; heptyl groups, such as n-heptyl; octyl groups, such as n-octyl and iso-octyl groups, such as 2,2,4-trimethylpentyl; nonyl groups, such as n-nonyl; decyl groups, such as n-decyl; dodecyl groups, such as n-dodecyl, and octadecyl; cycloalkyl groups, such as cyclopentyl. Cyclohexyl, cycloheptyl and methylcyclohexyl groups, aryl groups such as phenyl, naphthyl, anthryl and phenanthryl groups, alkaryl groups such as o-, m-, p-tolyl groups, xylyl groups and ethylphenyl groups, and aralkyl groups such as benzyl, α- and β-phenylethyl groups.

[0065] Examples of substituted residues R 4are halogenalkyl groups, such as the 3,3,3-trifluoro-n-propyl group, the 2,2,2,2,2',2',2'-hexafluoroisopropyl group, the heptafluoroisopropyl group, halogenaryl groups, such as the o-, m- and p-chlorophenyl group, - (CH2)- N (R 6 ) c (o) NR 6 2, - (CH2) OC (O) NR 6 2, - (CH2) O -C (0) R 6 , - (CH2) O -C (0) 0R 6 , - WA12340S / Dr.MK

[0066] 11

[0067] (CH2) oC (0) NR 6 2, - (CH2) -c (0) - (CH2) pC (0) CH3, - (CH2) -O-CO-R 6 , - (CH2)- NR 6 - ( CH2) P -NR 6 2, - (CH2) oO- (CH2) pCH (OH) CH2OH, -

[0068] (CH2) O (OCH2CH2) P 0R 6 , - (CH2) o -S02-Ph and - (CH2) o -0-C6F5, where R 6 and Ph corresponds to the meaning given above, and o and p mean the same or different integers between 0 and 10.

[0069] Examples of R 4Equally divalent, Si-bonded residues according to formula (I) are those that differ from the preceding residue R 4 The aforementioned monovalent examples can be derived by adding a hydrogen atom through substitution; examples of such residues are - (CH2)-, -CH(CH3)-, -C(CH3)2-, -CH (CH3) -CH2-, -C6H4-, -CH (Ph) -CH2-, -C(CF3)2-, - (CH2) O -C6H4- (CH2) O-, - (CH2) O -C6H4-C6H4- (CH2) O-, - (CH2O)p, (CH2CH20) O, - (CH2) O-0X-C6H4-S02-C6H4-0X- (CH2) O-, where x is 0 or 1, and Ph, o and p have the meanings given above.

[0070] Preferably, the remainder is R. 4around a monovalent, SiC-bonded, optionally substituted hydrocarbon residue free of aliphatic carbon-carbon multiple bonds with 1 to 18 carbon atoms, particularly preferably around a monovalent, SiC-bonded hydrocarbon residue free of aliphatic carbon-carbon multiple bonds with 1 to 6 carbon atoms, in particular around the methyl or phenyl residue.

[0071] With the remainder R 5 These can be any groups accessible to an attachment reaction (hydrosilylation) with a SiH-functional compound.

[0072] If the remainder is R 5 The substituents are SiC-bound, substituted hydrocarbon residues, WA12340S / Dr.MK

[0073] 12

[0074] Halogen atoms, cyano residues and -OR 6 preferably , where R 6 which has the above-mentioned meaning.

[0075] Preferably, the remainder is R.5 around alkenyl and alkynyl groups with 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 groups, wherein vinyl, allyl and hexenyl groups are particularly preferred.

[0076] The molecular weight of component (A) can vary within wide limits, approximately between 10 2 and 10 6 g / mol. Thus, component (A) can be, for example, a relatively low-molecular-weight alkenyl functional oligosiloxane, such as 1,2-divinyltetramethyldisiloxane, but also a high-polymer polydimethylsiloxane possessing chain- or terminal Si-bonded vinyl groups, e.g., with a molecular weight of 10 5g / mol (number average determined by NMR). The structure of the molecules forming component (A) is also not specified; 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 formula R 4 aSiOi / 2 , R 5 R 4 2SiOi / 2 , R 5 R 4 SiOi / 2 and R 4 2SiO2 / 2 composite, where R 4 and R 5 the meaning given above. Branched and network-like polysiloxanes additionally contain trifunctional and / or tetrafunctional units, those of formula R 4 SiOa / 2 , R 5 SiO₂ and S₂O₄ are preferred. Of course, mixtures of different siloxanes that meet the criteria of component (A) can also be used. WA12340S / Dr.MK

[0077] 13

[0078] Particularly preferred as component (A) is the use of vinyl-functional, essentially linear polydiorganosiloxanes with a viscosity of 10 to 100,000 mPa*s, particularly preferably of 15 to 20,000 mPa*s, and particularly preferably 20 to 2,000 mPa*s, each at 25°C.

[0079] All hydrogen-functional organosilicon compounds that have previously been used in addition-crosslinkable compositions can be used as organosilicon compounds (B).

[0080] Organopolysiloxanes (B) which have Si-bound hydrogen atoms are preferably linear, cyclic or branched organopolysiloxanes made up of units of the general formula (III)

[0081] R 4 cH d SiO(4-cd) / 2 (III) is used, wherein

[0082] R 4the meaning given above, where c is 0, 1, 2 or 3 and d is 0, 1 or 2, provided that the sum of c + d is less than or equal to 3 and that at least two Si-bonded hydrogen atoms are present per molecule. Preferably, at least one organopolysiloxane (B) is present with at least three, particularly preferably, hydrogen atoms per molecule.

[0083] Preferably, the organopolysiloxane (B) used according to the invention contains Si-bound hydrogen in the range of 0.01 to 1.7 wt.% , based on the total weight of WA12340S / Dr.MK

[0084] 14

[0085] Organopolysiloxane (B) . Preferably in the range of 0.02-0.8 wt.%, particularly preferably in the range of 0.03-0.3 wt.%.

[0086] The molecular weight of component (B) can also vary within wide limits, for example between 10 2 and 10 6g / mol. For example, the component (B) may be a relatively low molecular weight SiH-functional oligosiloxane, such as tetramethyldisiloxane, but also a high polymer polydimethylsiloxane with chain or terminal SiH groups or a silicone resin containing SiH groups.

[0087] The structure of the molecules forming component (B) is also not specified; 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 or network-like. Linear and cyclic polysiloxanes (B) are preferably composed of units of formula R 4 3SiOi / 2, HR 4 2SiOi / 2, HR 4 SiO2 / 2 and R 4 2SiO2 / 2 compound, where R 4the meaning given above. Branched and network-like polysiloxanes additionally contain trifunctional and / or tetrafunctional units, those of formula R 4 SiOa / 2, HSiO3 / 2 and S1O4 / 2 are preferred, where R 4 the meaning given above.

[0088] Of course, mixtures of different siloxanes that meet the criteria of component (B) can also be used. 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-WA12340S / Dr.MK

[0089] 15 containing compounds in which some of the methyl groups are replaced by 3,3,3-trifluoropropyl or phenyl groups.

[0090] Particularly preferred as component (B) is the use of SiH-containing, essentially linear poly(hydrogenmethyl)siloxanes and poly(dimethylhydrogenmethyl)siloxanes with a viscosity in the range of 1 to 100,000 mPa*s, preferably in the range of 2 to 1,000 mPa*s, particularly preferably in the range of 3 to 750 mPa*s, and especially preferably in the range of 5 to 500 mPa*s, each at 25 °C.

[0091] Component (B) is preferably contained in the crosslinkable silicone compositions (S) according to the invention in such an amount that the molar ratio of SiH groups to aliphatic unsaturated groups from (A) is between 0.1 and 10, particularly preferably between 0.5 and 5.0, and especially between 0.5 and 3.

[0092] In a particularly preferred embodiment, the addition-curing silicone composition (S) according to the invention contains

[0093] - at least one, preferably linear, organopolysiloxane (B) with at least three, Si-bonded hydrogen atoms per molecule, and simultaneously

[0094] - at least one Me₂Si-H-terminated, linear polydimethylsiloxane (B) , wherein preferably at least 50 wt% of a Me₂Si-H-terminated, linear polydimethylsiloxane (B) is contained, based on the total amount of organopolysiloxane (B). Me represents the methyl group. WA12340S / Dr.MK

[0095] 16

[0096] The components (A) and (B) used according to the invention are commercially available products or can be produced using methods commonly used in chemistry.

[0097] Instead of components (A) and (B), the silicone compositions (S) according to the invention can contain organopolysiloxanes (0) which simultaneously have aliphatic carbon-carbon multiple bonds and Si-bound hydrogen atoms. The silicone compositions (S) according to the invention can also contain all three components (A), (B), and (C).

[0098] If siloxanes (0) are used, they are preferably those composed of units of the general formulas (IV) , (V) and (VI)

[0099] R 4 fSiO4 / 2(IV)

[0100] R 4 g R 5 SiO 3-g / 2 (V)

[0101] R 4 hHSiO3-h / 2 (VI) where

[0102] R 4 and R 5 The meanings given above are f 0, 1, 2 or 3, g 0, 1 or 2 and h 0, 1 or 2, with the proviso that each molecule has at least 2 R groups. 5and at least 2 Si-bound hydrogen atoms are present.

[0103] Examples of organopolysiloxanes (C) are those made from SiO4 / 3, R 4 3SiOi / 3-, R 4 3R 5 SiOi / 2- and R 4 3HSiOi / 2 units, so-called MQ resins, where these resins additionally contain R 4 SiO3 / 3- and R 4 may contain 3SiO units, as well as linear organopolysiloxanes in WA12340S / Dr.MK

[0104] 17

[0105] Essentially consisting of R 4 2R 5 SiOi / 2- , R SiO- and R 4 HSiO units with R 4 and R 5 same meaning as above.

[0106] 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 using methods commonly used in chemistry.

[0107] Any heat- or UV-curing catalyst 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) include compounds such as hexachloroplatinic(IV) acid, platinum dichloride, platinum acetylacetonate, and complexes of these compounds encapsulated in a matrix or a core-shell-like structure. Low molecular weight platinum complexes of organopolysiloxanes include 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes with platinum. Other 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 diketonatocomplexes 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.

[0108] The concentration of component (D) is sufficient to catalyze the hydrosilylation reaction of components (A), (B), and (O) upon exposure to the heat required in the described process. The amount of component (D) can range from 0.1 to 1000 parts per million (ppm). WA12340S / Dr.MK

[0109] 18

[0110] The platinum group metal content can be 0, 5, and 100 ppm or 1 and 25 ppm, depending on the total weight of the components. The curing rate may be low if the platinum group metal content is below 1 ppm. Using more than 100 ppm of platinum group metal is uneconomical or reduces the storage stability of the silicone composition.

[0111] The addition-curing silicone compositions (S) can optionally contain all other additives that have previously been used to produce addition-curing compositions.

[0112] Hybrid systems as silicon composition (S)

[0113] Hybrid systems can also be used as a silicon composition (S) according to the invention. These systems are based on so-called hybrid polymers, i.e., polymers with an organic backbone that possess reactive and crosslinkable alkoxysilyl groups.

[0114] Polymer systems possessing reactive alkoxysilyl groups have long been known in the state of the art. Upon contact with water or atmospheric humidity, these alkoxysilane-terminated polymers are capable of condensing together at room temperature, releasing the alkoxy groups.

[0115] A first special variant of this technology involves the use of so-called α-silane-terminated prepolymers. These possess reactive alkoxysilyl groups linked to an adjacent urethane unit via a methylene spacer. This class of compounds is highly reactive and requires neither tin catalysts nor strong acids or bases to achieve high curing rates upon contact with air. Commercially available α-silane-terminated prepolymers include GENIOS IL® STP-E10 or -E30 from Wacker Chemie AG. WA12340S / Dr.MK

[0116] 19

[0117] A second special variant, particularly interesting for adhesives based on silane-crosslinking polymers, is described, for example, in US2014155545A, corresponding to EP2744842A. These variants contain phenyl silicone resins in addition to the silane-crosslinking polymers. The corresponding resin additives also result in products that exhibit significantly higher hardness after complete curing. A third special variant, particularly interesting for sealants based on silane-crosslinking polymers, is described, for example, in US2017198101A, corresponding to EP3149095A. This patent describes not only the usual, preferably linear, silane-crosslinking polymers, which contain a crosslinkable silane function at both ends of their chain, but also products that have reactive silane groups at only one end of the chain.

[0118] Polymer systems that possess reactive alkoxysilyl groups contain, for example, at least one compound of the formula

[0119] Y-[ (CR 1 2) m-SiRk (OR 2 ) 3-k] z (VII) , where Y represents an x-valent organic polymer residue bound via nitrogen, oxygen, sulfur or carbon, R can be the same or different and represents a monovalent, optionally substituted hydrocarbon residue, R 1 can be the same or different and represents a hydrogen atom or a monovalent, possibly substituted hydrocarbon residue, which may be bonded to the carbon atom via nitrogen, phosphorus, oxygen, sulfur or a carbonyl group, WA12340S / Dr.MK

[0120] 20

[0121] R 2can be the same or different and represents a hydrogen atom or a monovalent, optionally substituted hydrocarbon residue, z is an integer from 1 to 10, preferably 1, 2 or 3, particularly preferably 1 or 2, k can be the same or different and is 0, 1 or 2, preferably 0 or 1, and m can be the same or different and is an integer from 1 to 10, preferably 1, 3 or 4, particularly preferably 1 or 3, in particular 1.

[0122] Hybrid system-based silicone compositions (S) may optionally contain all other additives that have previously been used to manufacture hybrid system-based silicone compositions.

[0123] Thermally conductive fillers (Z)

[0124] Thermally conductive fillers (Z) according to the invention exhibit a thermal conductivity of at least 2 W / mK, preferably at least 5 W / mK.

[0125] According to the invention, thermally conductive fillers (Z) contain at least one thermally conductive filler (ZI) and at least one thermally conductive filler (Z2), wherein the amount of (Z2) is 3-20 vol.%, preferably the amount of (Z2) is 5-15 vol.%, in each case based on the total silicone composition (Y).

[0126] Examples of such thermally conductive fillers (Z) are magnesium oxide, metallic aluminum powder, metallic silicon powder; metallic silver powder, zinc oxide, boron nitride, silicon carbide, aluminum nitride, aluminum hydroxide, aluminum oxide, graphite, etc., as well as mixtures of two or more such WA12340S / Dr.MK

[0127] 21

[0128] Fillers. Preferably silicon powder, boron nitride, aluminum hydroxide, aluminum nitride, aluminum oxide.

[0129] Thermally conductive fillers (ZI)

[0130] Thermally conductive fillers (ZI) according to the invention have a mean diameter d50 of 10 - 200 gm. Preferably they have a mean diameter d50 of 10 - 150 gm, particularly preferably of 15 - 100 gm.

[0131] (ZI) is preferably silicon powder, boron nitride, aluminum hydroxide, aluminum nitride, aluminum oxide, particularly preferably silicon powder, aluminum hydroxide and aluminum oxide.

[0132] In a preferred embodiment, at least 10 vol% metallic silicon powder is used as filler (ZI).

[0133] Thermally conductive fillers (Z2)

[0134] A thermally conductive filler (Z2) according to the invention is characterized in that a) its mean diameter d50 is 0.1 to 6 gm, preferably 0.15 to 5 gm, particularly preferably 0.2 to 4 gm, b) its BET is 3.5 to 15 m 2 / g is preferably 4 to 13 m 2 / g, c) its particle-specific thixotropy index (0.5 / 10)

[0135] [= ps-TI ( 0 , 5 / 10 ) ] is at least 5, preferably at least 6, wherein the ps-TI ( 0 , 5 / 10 ) value is determined as the ratio of the dynamic viscosity at 25°C and a shear rate of 0.5 s-1 to the viscosity at 25°C and a shear rate of 10 s-1 and these viscosities in the following standardized

[0136] Shape to be measured: WA12340S / Dr.MK

[0137] 22

[0138] 20 vol.% (Z2) in a linear polydimethylsiloxane terminated with vinyl dimethylsilyl groups, with a dynamic viscosity of 1000 mPas at 25°C.

[0139] A thermally conductive filler (Z2) according to the invention is preferably characterized in that d) the particle-specific thixotropy index (1 / 10)

[0140] [= ps-TI (l / 10) ] is at least 4, preferably at least 5 and particularly preferably at least 6, wherein the ps-TI ( 1 / 10 ) value is determined as the ratio of the dynamic viscosity at 25°C and a shear rate of 1 s -1 viscosity at 25°C and a shear rate of 10 s -1 and these viscosities are measured in the following standardized form:

[0141] 20 vol.% (Z2) in a linear polydimethylsiloxane terminated with vinyl dimethylsilyl groups, with a dynamic viscosity of 1000 mPas at 25°C,

[0142] Furthermore, the thermally conductive filler (Z2) according to the invention preferably has a density of at most 6.0 g / cm³. 3 , preferably no more than 4.5 g / cm³ 3 The use of high-density fillers is disadvantageous because it increases the weight of the components.

[0143] Preferred thermally conductive fillers (Z2) also exhibit a band gap greater than 3 eV, preferably greater than 3.5 eV, and particularly preferably greater than 4 eV at 300 K. Preferred thermally conductive fillers (Z2) are therefore electrical insulators. WA12340S / Dr.MK

[0144] 23

[0145] (Z2) is preferably zinc oxide, boron nitride, aluminium hydroxide, aluminium nitride, aluminium oxide, particularly preferably boron nitride, aluminium nitride, aluminium hydroxide and aluminium oxide, especially aluminium hydroxide and aluminium oxide.

[0146] Thermally conductive silicone composition (Y)

[0147] They can exist as one-, two- or multi-component compounds.

[0148] In the silicone composition (Y), addition-curing silicone compositions (S) are preferably used.

[0149] Completely unexpectedly, it turns out that the combination of the thermally conductive fillers ( ZI ) and ( Z2 ) according to the invention provides the required viscosity, stability and rheology of the thermally conductive silicone composition according to the invention.

[0150] (Y) can be set.

[0151] This means that preferably no thixotropic additives are used in (Y). Thixotropic additives within the meaning of this invention are those that are known from the prior art and differ from

[0152] (Z) distinguish.

[0153] Furthermore, rheology modifiers are preferably not used.

[0154] Rheology modifiers within the meaning of this invention are those which are known from the prior art and which differ from (Z).

[0155] Furthermore, the silicone compositions (Y) according to the invention exhibit a particularly high electrical dielectric strength after curing.

[0156] The 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. WA12340S / Dr.MK

[0157] 24

[0158] Another object of the present invention is a method for producing the thermoconductive silicone compositions (Y) according to the invention by mixing the individual components.

[0159] The components can be mixed using conventional continuous and batch processes of the prior art. All known devices are suitable as mixing equipment. Examples include uniaxial or biaxial continuous mixers, twin roller mixers, Ross mixers, Hobart mixers, dental mixers, planetary mixers, kneaders, Henschel mixers, or similar mixers. Preferably, mixing is carried out in a planetary mixer, a kneader, or a continuous mixer. The procedure for preparing the silicone compositions (Y) is known to those skilled in the art. In principle, the components can be added in any order.

[0160] The production of the silicone compositions (Y) according to the invention based on hybrid system as silicone composition (S) is preferably carried out under exclusion of moisture.

[0161] Another aspect of the present invention is the use of the thermally conductive silicone composition (Y) as

[0162] Thermal paste, also known as a gap filler (heat-conducting element), thermal pads, thermally conductive adhesives, and potting compounds, are used to dissipate heat from heat sources, for example, in electronic devices.

[0163] The thermally conductive silicone composition (Y) is applied to heat generators or heat sinks, or they are coated with it and crosslinked if a crosslinkable system is present.

[0164] Heat generators are found in electronic power supply systems and electronic devices, such as supply transistors, power modules, transistors, WA12340S / Dr.MK

[0165] 25

[0166] Thermocouples and temperature sensors; heat-generating electronic components, e.g., integrated circuit components such as CPUs and batteries. Suitable heat sinks include heat-dissipating components such as heat spreaders, heat sinks, and cooling fins.

[0167] Examples

[0168] The following examples describe the basic feasibility of the present invention, without, however, limiting it to the contents disclosed therein.

[0169] In the following examples, all references to parts and percentages, unless otherwise stated, refer to weight. Unless otherwise stated, the following examples are performed at atmospheric pressure, i.e., approximately 1000 hPa, and at room temperature, i.e., approximately 20 °C, or at a temperature that occurs when the reactants are combined at room temperature without additional heating or cooling.

[0170] Measurement methods

[0171] BET surface

[0172] BET surface area is determined according to DIN 66131 (with nitrogen).

[0173] Particle size distribution of the thermally conductive fillers (Z)

[0174] Within the scope of the present invention, particle size determination and visualization of the particle size distribution were performed on a FLOWSYNC measuring device from Microtrac with integrated tri-laser technology according to ISO 13320:2020. Additional information about the particle shape was obtained via dynamic image analysis according to ISO 13322-2. WA12340S / Dr.MK

[0175] Measurement configuration:

[0176] Laser diffraction: 3 red lasers (780 nm)

[0177] Dynamic image analysis: High-resolution camera: 5.2 megapixels

[0178] (2560 x 2048 px) , up to 60 fps at maximum resolution

[0179] Settings :

[0180] Measurement method: Wet measurement; Dispersing agent: Isopropanol; Ultrasound intensity [W]: 100%, Ultrasound time: 60 s, Circulation velocity: 40%, Measurement duration: 30 s, Number of measurements: 2, Measurement temperature: 23.0 ± 1.5 °C, Particle evaluation: Unknown non-spherical, Refractive index: 1.70; Transparency: Transparent

[0181] In wet measurements using FLOWSYNC, the material is dispersed in isopropanol, treated with ultrasound, and continuously circulated within the measuring cell throughout the entire measurement. During the measurement, a laser beam strikes the well-dispersed sample, and the resulting scattered light pattern is used to calculate the particle size distribution. Images of the sample are also captured synchronously with the scattered light pattern using a high-resolution, high-speed camera. The particle size distribution is determined from the overall sample dispersion, optionally based on laser diffraction analysis, dynamic image analysis, or a combination of both.

[0182] Dynamic viscosity

[0183] The dynamic viscosity was measured on an Anton Paar "MCR 302" rheometer according to 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; WA12340S / Dr.MK

[0184] 27

[0185] Measured values: 30. The viscosity value in mPa*s is given as an interpolated value at a shear rate of D = 0.5 s- 1, D = 1 s-1 and D = 10 s-1.

[0186] General procedure for determining the particle-specific thixotropic index (VI)

[0187] 20 vol% thermally conductive filler and 80 vol% vinyldimethylsiloxy-terminated polydimethylsiloxane, exhibiting a viscosity of 1000 mPa*s (Polymer 1), are homogenized using a commercially available SpeedMixer DAC 1100.2 VAC-P (Hauschild & Co KG, Waterkamp 1, 59075 Hamm, Germany) at a speed of 800 rpm and 3 mbar vacuum for 100 seconds. The mixture is then stirred with a spatula and homogenized again at a speed of 800 rpm and 3 mbar vacuum for 100 seconds. If necessary, the process is repeated until complete homogeneity is achieved. The dynamic viscosity is then determined, ensuring that no particle separation occurs. If necessary, the samples are homogenized again before measurement.

[0188] The particle-specific thixotropic index ps-TI ( 0 , 5 / 10 ) is determined as the ratio of the dynamic viscosity at 25°C and a shear rate of 0.5 s-1 to the viscosity at 25°C and a shear rate of 10 s-1.

[0189] The particle-specific thixotropic index ps-TI (1 / 10) is determined as the ratio of the dynamic viscosity at 25°C and a shear rate of 1 s-1 to the viscosity at 25°C and a shear rate of 10 s-1.

[0190] Electrical dielectric strength

[0191] The determination of the breakdown voltage is based on DIN.

[0192] EN 60243-1 (VDE 0303-21) on an oil testing device from Baur WA12340S / Dr.MK

[0193] 28

[0194] (BAUR GmbH, Ralf Eisenstraße 8, 6832 Sulz, Austria), type DTA 100, equipped with a glass test tube with plate / plate electrodes using Powersil® TR50 (Wacker Chemie AG, Munich, Germany) as insulating oil. The crosslinkable silicone compositions to be tested are degassed at 1 mbar vacuum and then crosslinked at 90 °C to form a film with dimensions of 80 x 60 x 1 mm.

[0195] thermal conductivity

[0196] The thermal conductivity k is determined according to ASTM D5470, standard test method for determining heat transfer properties, using a TIM tester (Center for Thermal Management (ZFW), STZ Thermal Management in Electronics, Wiederholdstraße 10, 70174 Stuttgart, Germany). The paste-like material is measured between two temperature-controlled test cylinders (temperatures TI = 14 °C, T2 = 40 °C) across gaps of 1.6, 1.4, 1.2, and 1.0 mm under steady-state conditions after preconditioning the paste-like material at 1.8 mm. The thermal conductivity in W / (m K) is calculated from the measured thermal resistance and the gap thickness after plotting the measured values.

[0197] Method for assessing inventory stability (V2)

[0198] For the investigation of storage stability, component 1 of a two-component, crosslinkable, thermally conductive silicone composition was prepared according to General Manufacturing Instructions (V3). The compositions of the thermally conductive silicone compositions according to the invention (Examples 13-24) are summarized in Table 3, and the compositions of the non-inventive reference examples R12-R22 are summarized in Table 4. 100 mL of component 1 of the crosslinkable silicone composition was dissolved in a transparent 185 mL container. WA12340S / Dr.MK

[0199] 29

[0200] PE cups (available from HAUSCHILD GMBH & CO. KG, Waterkamp 1, 59075 Hamm, Germany) were filled and stored at 50 °C for 8 weeks. Storage stability was then assessed using a grading system from 1 to 6, where 1 is the best and 6 is the worst. The criteria for grades 1 to 6 are as follows, with grades 5 and 6 indicating unsuitable performance.

[0201] Note 1: no visible change in the sample

[0202] Note 2: slight sheen on the surface

[0203] Note 3: strong surface gloss

[0204] Note 4: low, local oil separation

[0205] Note 5: increased oil separation in depressions of the surface or formation of a thin oil layer over the entire mass

[0206] Note 6: heavy oil separation or thick oil layer over the entire surface

[0207] General manufacturing instructions (V3) of the inventive examples 13-24 and non-inventive reference examples R12-R22

[0208] The raw materials according to Table 3 of the thermally conductive silicone compositions according to the invention, as well as according to Table 4 of the non-inventive reference examples, are mixed in a commercially available Labotop planetary mixer (PC Laborsystem GmbH, Maispracherstrasse 6, 4312 Mägden, Switzerland), equipped with two beam stirrers and a scraper.

[0209] First, the vinyldimethylsiloxy-terminated polydimethylsiloxane, which has a viscosity of 120 mPa*s (=polymer 2), is added, and then the fillers are added according to the order in Table 3 or 4. Each filler is then processed for 10 minutes at 300 rpm under a slight vacuum.

[0210] (950 mbar) homogeneously incorporated. The resulting pasty mass WA12340S / Dr.MK

[0211] 30 is scraped off from the edge and homogenized for a further 20 minutes at 50 rpm under vacuum (50 mbar).

[0212] Table 1 shows an overview of all fillers used as (Z2):

[0213] FF1 to FF9 = fillers according to the invention (Z2)

[0214] RI to Rll = non-inventive reference fillers (Z2)

[0215] Table 1:

[0216] WA12340S / Dr.MK

[0217] 32

[0218] The fillers (Z2) FF1 to FF9 according to the invention and the non-inventive fillers (Z2) RI to RIO are commercially available materials. R1 was produced by wet milling of silicon. Methods for this are known in the prior art.

[0219] The thermally conductive filler (Z2) according to the invention is characterized in that a) its mean diameter d50 is 0.1 to 6 gm, b) its BET is 3.5 to 15 m 2 / g is, c) its particle-specific thixotropy index (0.5 / 10)

[0220] [= ps-TI ( 0 , 5 / 10 ) ] is at least 5.

[0221] The fillers Fl to F9 according to the invention fulfill the features a) — c).

[0222] The non-inventive RI to R4 fulfill features a) and c), but their BET surface area is too low and therefore feature b) is not fulfilled.

[0223] The non-inventive R5 and R6 fulfill features a) and c), but their BET surface area is too high and therefore feature b) is not fulfilled.

[0224] The non-inventive R7 to RIO fulfill features a) and b), but their particle-specific thixotropy index (0.5 / 10) is too low and therefore feature c) is not fulfilled.

[0225] The non-inventive Rll fulfills feature a), but its BET surface area is too high and its particle-specific thixotropy index (0.5 / 10) is too low, and therefore features b) and c) are not fulfilled.

[0226] Table 2 shows an overview of all fillers used as (ZI).

[0227] Fabrics:

[0228] F9 to F12 = fillers according to the invention (ZI) WA12340S / Dr.MK

[0229] 33

[0230] Table 2:

[0231] F10 and F12 according to the invention are commercially available fillers. F9 and F11 according to the invention are spherical silicon particles, producible by gas atomization processes according to the prior art.

[0232] To evaluate the storage stability of the thermally conductive silicone compositions, the thermally conductive silicone compositions according to the invention (= Examples 13 to 24) and the non-inventive reference silicone compositions (= Reference Examples R12 to R22) were produced according to the general manufacturing procedure (V3) and subsequently evaluated according to method (V2). The results are summarized in Tables 3 and 4. Quite surprisingly, it is found that the thermally conductive silicone compositions according to the invention, which contain a filler according to the invention (Z2) fulfilling all features a) - c), exhibit improved storage stability.

[0233] Table 3 shows the examples 13 to 24 of the thermally conductive silicone compositions according to the invention and the results regarding their storage stability, thermal conductivity, and dielectric strength. Table 3:

[0234] WA12340S / Dr.MK

[0235] 35

[0236] Table 4 shows the non-inventive reference examples.

[0237] R12 to R22 of the thermally conductive silicone compositions and the results regarding their storage stability, thermal conductivity and dielectric strength

[0238] Table 4:

Claims

WA12340S / Dr.MK 37 Patent claims 1. Containing a thermally conductive silicone composition (Y) -5-40 vol% silicone composition (S) ; -60-95 vol% of at least one thermally conductive filler (Z) with a thermal conductivity of at least 2 W / mK, wherein (Z) contains at least one thermally conductive filler (ZI) characterized in that its mean diameter d50 is 10-200 gm, and at least one thermally conductive filler (Z2) characterized in that a) its mean diameter d50 is 0.1 to 6 gm, b) its BET is 3.5 to 15 m 2 / g is, c) its particle-specific thixotropy index (0.5 / 10) [= ps-TI ( 0, 5 / 10) ] is at least 5, where the ps-TI ( 0 , 5 / 10 ) value is determined as the ratio of the dynamic viscosity at 25°C and a shear rate of 0.5 s -1viscosity at 25°C and a shear rate of 10 s -1 and these viscosities are measured in the following standardized form: 20 vol.% (Z2) in a linear polydimethylsiloxane terminated with vinyl dimethylsilyl groups, with a dynamic viscosity of 1000 mPas at 25°C, wherein the amount of (Z2) is 3-20 vol.%, based on the total silicone composition (Y) . WA12340S / Dr.MK 38 2. Thermally conductive silicone composition (Y) according to claim 1, characterized in that the amount of (Z2) is 5-15 vol.%, based on the total silicone composition (Y) .

3. Thermally conductive silicone composition (Y) according to claim 1 or 2, characterized in that d) the particle-specific thixotropy index (1 / 10) [= ps-TI (l / 10) ] is at least 4, where the ps-TI ( 1 / 10 ) value is determined as the ratio of the dynamic viscosity at 25°C and a shear rate of 1 s -1viscosity at 25°C and a shear rate of 10 s -1 and these viscosities are measured in the following standardized form: 20 vol.% (Z2) in a linear polydimethylsiloxane terminated with vinyl dimethylsilyl groups, with a dynamic viscosity of 1000 mPas at 25°C.

4. Thermally conductive silicone composition (Y) according to one of claims 1 to 3, characterized in that the silicone composition (S) is an addition-curing silicone composition (S).

5. Thermally conductive silicone composition (Y) according to any one of claims 1 to 4, characterized in that it does not contain any rheology modifiers which differ from (Z).

6. Thermally conductive silicone composition (Y) according to one of the Claims 1 to 4, characterized in that it does not contain any thixotropy additives which differ from (Z). WA12340S / Dr.MK 7. Thermally conductive silicone composition (Y) according to any one of claims 1 to 6, characterized in that the density of (Z2) is at most 4.5 g / cm³ 3 amounts.

8. Thermally conductive silicone composition (Y) according to any one of claims 1 to 7, characterized in that the thermally conductive fillers (Z2) have a band gap greater than 3 eV.

9. Thermally conductive silicone composition (Y) according to any one of claims 1 to 8, characterized in that the thermally conductive fillers (Z2) are selected from aluminium oxide and aluminium hydroxide.

10. Thermally conductive silicone composition (Y) according to one of claims 1 to 9, characterized in that at least 10 vol% metallic silicon powder is used as filler (ZI).

11. Method for producing the thermally conductive silicone composition (Y) according to any one of claims 1 to 10, by mixing the individual components.

12. Use of the thermally conductive silicone composition (Y) according to any one of claims 1 to 10, as a thermal paste, as a gap filler (=thermally conductive element), thermal pad, thermally conductive adhesives and potting compound.

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