Polyaddition-crosslinkable silicone composition for preparing thermally conductive silicone elastomer

Abstract

The present invention relates to silicone compositions that are crosslinked by polyaddition reaction, intended to produce thermally conductive components. Said silicone compositions comprise at least one organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group bonded to silicon, at least one organopolysiloxane B having, per molecule, at least two SiH units, a catalytically effective amount of at least one polyaddition catalyst C, a thermally conductive filler D, and a non-reactive organopolysiloxane E that is liquid at room temperature, characterized in that the non-reactive organopolysiloxane E that is liquid at room temperature contains between 130 ppm and 1000 ppm by mass of OH groups bonded to silicon.

Description

[0001] DESCRIPTION

[0002] TITLE: Polyaddition crosslinkable silicone composition for the preparation of thermally conductive silicone elastomer

[0003] technical field

[0004] The present invention relates to new silicone compositions crosslinking by polyaddition reaction, intended to produce thermally conductive elements particularly for the field of electronics and automotive, especially for the field of electric vehicles.

[0005] Prior art

[0006] Thermally conductive silicone elastomers are well known for their remarkable heat transfer properties, resistance to hot and cold temperatures, and electrical insulation. They are used particularly in electrical and electronic applications, and in the automotive sector. Specifically in the automotive sector, thermally conductive silicone elastomers are used in the batteries of electric and hybrid vehicles (EVs and HEVs) to dissipate heat from the battery cells and onboard electronics.

[0007] Thermally conductive silicone formulations have been described in the prior art. As early as 1981, US patent 4,292,223 described thermally conductive elastomers comprising organopolysiloxanes, a particulate filler, and a viscosity modifier.

[0008] The amount of thermally conductive fillers in silicone compositions is high, typically exceeding 50% by weight, and even exceeding 70% by weight. One of the design challenges of thermally conductive silicones lies in adding such large quantities of thermally conductive fillers while minimizing the impact on the composition's fluidity. This is particularly critical for so-called "potting" compositions, whose viscosity must be low, typically less than

[0009] 10,000 mPa.s, despite a high concentration of thermally conductive charges.

[0010] Several solutions have been proposed in the prior art to control the viscosity of thermally conductive silicone compositions. One method involves carefully selecting the type of filler, its shape, and its size. For example, Elkem Silicones' application WO 2021 / 260279 Al proposes selecting certain fillers with specific dimensions, with a required ratio between large and small particles. Shin-Etsu Chemical's patent EP 1 788 031 B 1 describes a thermally conductive silicone elastomer comprising, for every 100 parts by weight of a heat-curable organopolysiloxane composition, 10 to 2000 parts by weight of a metallic silicon powder having an average particle size of less than 100 µm. Another method involves changing the medium of the silicone formulation or adding a solvent. However, solvent evaporation generates volatile compounds, which pose health and environmental risks.Finally, another method involves treating the thermally conductive fillers to improve their compatibility with the silicone matrix. For example, international patent application WO 2023 / 283819 Al, filed by Dow Silicones and Dow Global Technologies, describes a self-adhesive, thermally conductive silicone composition comprising, among other things, a thermally conductive filler and a treatment agent, in combination with an adhesion-promoting agent containing both a hydrogen atom bonded to a silicon atom and at least one alkoxy group bonded to a silicon atom. However, the addition of a treatment agent to the formulation can negatively impact the mechanical properties of the silicone elastomer, and exudation of the treatment agents from the silicone matrix has been observed.Momentive's patent application JP 2007-119589 A describes a thermally conductive silicone elastomer composition with high elongation and a high thermally conductive filler content. Wacker Chemie AG's international patent application WO 2023 / 242193 Al also describes a thermally conductive silicone composition with good storage stability and heat resistance.

[0011] The object of the present invention is to propose a new thermally conductive silicone composition, solving the problems mentioned above, and possessing both a high thermally conductive filler content, good thermal conductivity, and low viscosity.

[0012] Summary of the invention

[0013] The present invention relates to a silicone composition that can be crosslinked by polyaddition reaction, comprising:

[0014] - at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon,

[0015] - at least one organopolysiloxane B having, per molecule, at least two SiH motifs,

[0016] - a catalytically effective amount of at least one C polyaddition catalyst, and

[0017] - a thermally conductive charge D, and

[0018] - a non-reactive organopolysiloxane liquid at room temperature E, characterized in that the non-reactive organopolysiloxane liquid at room temperature E contains between 130 ppm and 1000 ppm mass of OH groups linked to silicon.

[0019] Detailed description of the invention

[0020] Unless otherwise stated, all the viscosities of the silicone oils discussed herein correspond to a dynamic viscosity at 25°C known as "Newtonian," that is, the dynamic viscosity measured, in a manner known per se, with a Brookfield viscometer at a shear rate gradient sufficiently low for the measured viscosity to be independent of the rate gradient. In the following section concerning the description of organopolysiloxane A, the following nomenclature has been used to represent the siloxyl units:

[0021] M: siloxyl motif R SiOi / z,

[0022] M V1 : siloxyl motif chosen from YR^SiOi / z and Y2R 1 SiOi / 2, preferably YR^SiOi / z,

[0023] D: siloxyl motif R^SiCh / z,

[0024] D V1 : siloxyl motif chosen from Y2SiO22 and YR 1 SiÛ2 / 2, preferably YR 1 SiÛ2 / 2,

[0025] T: siloxyl motif R^iCh / z,

[0026] Q: SiC>4 / 2 siloxyl motif, with Y and R 1 such that: Y represents a C2-C12 alkenyl group, preferably a vinyl group; R 1 represents a monovalent hydrocarbon group having from 1 to 16 carbon atoms, preferably chosen from alkyl groups having from 1 to 8 carbon atoms such as methyl, ethyl, propyl groups, cycloalkyl groups having from 3 to 8 carbon atoms and aryl groups having from 6 to 12 carbon atoms.

[0027] As examples of terminal patterns M and M V1 Examples include trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy, and dimethylhexylsiloxy.

[0028] As examples of patterns D and D V1 Examples include dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy.

[0029] Examples of T motifs include the methylsiloxy group.

[0030] Organopolysiloxane A, having, per molecule, at least one, preferably at least two C2-C12 alkenyl groups linked to silicon, can preferably be an organopolysiloxane formed:

[0031] - of at least one, preferably at least two siloxyl motifs of the following formula: Y a R 1 bSiO(4- a -b) / 2 in which Y represents a C2-C12 alkenyl group, preferably a vinyl group; R 1 represents a monovalent hydrocarbon group having from 1 to 16 carbon atoms, preferably chosen from alkyl groups having from 1 to 8 carbon atoms such as methyl, ethyl, propyl groups, cycloalkyl groups having from 3 to 8 carbon atoms and aryl groups having from 6 to 12 carbon atoms; a = 1 or 2, b = 0, 1 or 2 and the sum a+b = 1, 2 or 3, and

[0032] - possibly with the following formula patterns: R 1 c SiO(4- C ) / 2 in which R 1 has the same meaning as above and c = 0, 1, 2 or 3.

[0033] It is understood in the formulas above that, if several groups R 1 are present, they may be identical or different from each other.

[0034] Organopolysiloxane A, having at least one C2-C12 alkenyl group linked to silicon per molecule, can have a linear, branched, or cyclic structure.

[0035] According to one embodiment, the organopolysiloxane A, having at least one C2-C12 alkenyl group linked to silicon per molecule, may preferably be a linear organopolysiloxane essentially composed of D and / or D siloxyl motifs V1 , and terminal siloxyl motifs M and / or M V1Examples of linear organopolysiloxanes that could be organopolysiloxanes according to the invention are:

[0036] - a poly(dimethylsiloxane) with dimethylvinylsilyl ends;

[0037] - a poly(dimethylsiloxane-co-methylphenylsiloxane) with dimethylvinylsilyl ends;

[0038] - a poly(dimethylsiloxane-co-methylvinylsiloxane) with dimethylvinylsilyl ends; and

[0039] - a poly(dimethylsiloxane-co-methylvinylsiloxane) with trimethyl-silyl ends.

[0040] Preferably, the organopolysiloxane contains terminal dimethylvinylsilyl motifs and even more preferably the organopolysiloxane is a poly(dimethylsiloxane) with dimethylvinylsilyl ends.

[0041] Preferably, the organopolysiloxane A compound has a mass content of alkenyl motifs between 0.01% and 10%, preferably between 0.1% and 5% (mass % of alkenyl motifs, based on the total weight of organopolysiloxane A).

[0042] The organopolysiloxanes A are preferably oils with a dynamic viscosity between 50 mPa.s and 100,000 mPa.s, more preferably between 50 mPa.s and 50,000 mPa.s, and more preferably between 100 mPa.s and 10,000 mPa.s. The dynamic viscosity is measured at 25°C in a manner known per se, with a Brookfield viscometer at a shear rate gradient sufficiently low so that the measured viscosity is independent of the rate gradient.

[0043] According to a preferred embodiment, organopolysiloxane A may contain hydroxyl groups (OH) attached to siloxy motifs at the chain ends and / or in the middle of the chain. Organopolysiloxane A may preferably contain between 130 ppm and 1000 ppm of silicon-bonded OH groups, preferably between 150 ppm and 900 ppm. The content of silicon-bonded OH groups in organopolysiloxane A is a mass content (OH weight / sample weight). It can be measured by an infrared method after deuteration, as described in "Measurement of Trace Silanol in Siloxanes by IR Spectroscopy" by Elmer D. Lipp, Applied Spectroscopy vol. 45, no. 3, 1991, pp. 477-483. For this purpose, a sample is analyzed using a Fourier transform infrared (FTIR) spectrophotometer.

[0044] According to a preferred embodiment, organopolysiloxane A may have a T-type siloxyl motif content ranging from 100 ppm to 1200 ppm, more preferably from 200 ppm to 1000 ppm, and even more preferably from 300 ppm to 800 ppm. In this text, the T-type siloxyl motif content in organopolysiloxane A is a mass content, representing the weight of the T motif "SiCh / 2" relative to the total percentage of organopolysiloxane A. It can be measured, in a manner known to those skilled in the art, by any suitable assay method. Alternatively, it can be calculated theoretically by taking into account the mass of T motifs introduced into the reaction medium during the synthesis of organopolysiloxane A. According to one embodiment, organopolysiloxane A may have a residual acidity content.The residual acidity content may be greater than or equal to 5 ppm, preferably between 6 ppm and 100 ppm, and more preferably between 10 ppm and 100 ppm.

[0045] According to another embodiment, organopolysiloxane A exhibits no, or no significant, residual acidity. The residual acidity content may be strictly less than 5 ppm, preferably less than 4 ppm, and more preferably less than 3 ppm. Without being bound by this theory, the inventors believe that the absence of significant residual acidity in organopolysiloxane A has the advantage of improving the long-term stability of said organopolysiloxane, particularly at high temperatures. Consequently, the polyaddition-crosslinkable silicone composition according to the present invention may exhibit better long-term stability and a longer shelf life.

[0046] In this text, acidity is expressed in ppm mass equivalent of HCl (hydrochloric acid), i.e., mg / kg of HCl equivalents. Acidity can be measured using a UV-visible spectrophotometer by measuring the difference in transmittance between the analyzed sample and a standard obtained by adding known, measured amounts of HCl.

[0047] The organopolysiloxane A according to the invention can be selected from commercially available compounds meeting the stated specifications. Alternatively, it can be synthesized using methods known in the technical field.

[0048] The silicone composition preferably comprises 1% to 50% by weight of organopolysiloxane A, and even more preferably 2% to 40% by weight of organopolysiloxane A. According to one embodiment, the silicone composition may comprise 1% to 40%, preferably 1% to 30%, more preferably 1.5% to 20%, and even more preferably 2% to 10%, by weight of organopolysiloxane A. According to another embodiment, the silicone composition may comprise 2% to 50%, preferably 3% to 40%, more preferably 4% to 40%, and even more preferably 5% to 30%, by weight of organopolysiloxane A.

[0049] In the following section concerning the description of organopolysiloxane B, the following nomenclature has been used to represent the siloxyl motifs:

[0050] M: siloxyl motif R SiOw,

[0051] M': siloxyl motif R 2 2HSiOi / 2,

[0052] D: siloxyl motif R 22SiC>2 / 2,

[0053] D': siloxyl motif R 2 HsiC>2 / 2,

[0054] T: siloxyl motif R 2 SiC>3 / 2,

[0055] Q: SiCl / 2 siloxyl motif, with R 2 representing a monovalent radical having from 1 to 12 carbon atoms. Organopolysiloxane B is an organopolysiloxane having, per molecule, at least two SiH units. It is therefore an organohydrogenopolysiloxane compound. Preferably, organopolysiloxane B comprises at least three SiH units.

[0056] Organopolysiloxane B may advantageously be an organopolysiloxane comprising at least two, preferably at least three, siloxyl units of the following formula: HdR 2 e SiO(4-de) / 2 in which R 2 represents a monovalent radical having from 1 to 12 carbon atoms, d = 1 or 2, e = 0, 1 or 2 and d+e = 1, 2 or 3; and possibly other motifs of the following formula: R 2 fSiO<4-f) / 2 in which R2 has the same meaning as above, and f = 0, 1, 2, or 3.

[0057] It is understood that, if several R groups 2 are present in the formulas above, they may be identical or different from each other.

[0058] Preferably, R 2 can represent a monovalent radical chosen from the group consisting of alkyl groups having 1 to 8 carbon atoms, possibly substituted by at least one halogen atom such as chlorine or fluorine, cycloalkyl groups having 3 to 8 carbon atoms, and aryl groups having 6 to 12 carbon atoms. R 2 can advantageously be chosen from the group consisting of methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl.

[0059] The symbol d is preferably equal to 1.

[0060] Organopolysiloxane B can have a linear, branched, or cyclic structure. The degree of polymerization is preferably greater than or equal to 2. Generally, it is less than 5000. Preferably, the viscosity of organopolysiloxane B is between 1 mPa.s and 5000 mPa.s, more preferably between 1 mPa.s and 2000 mPa.s, and even more preferably between 5 mPa.s and 1000 mPa.s.

[0061] In the case of linear polymers, these are essentially composed of D and / or D' siloxyl units, and terminal M and / or M' siloxyl units. In the case of cyclic polymers, these are essentially composed of D and / or D' siloxyl units. Examples of organohydrogenopolysiloxanes that could be organopolysiloxanes B according to the invention are:

[0062] - a poly(dimethylsiloxane) with hydrogenodimethylsilyl ends;

[0063] - a poly(dimethylsiloxane-co-methylhydrogenosiloxane) with trimethylsilyl ends;

[0064] - a poly(dimethylsiloxane-co-methylhydrogenosiloxane) with hydrogenodimethylsilyl ends;

[0065] - a poly(methylhydrogenosiloxane) with trimethysilyl ends; and

[0066] - a cyclic poly(methylhydrogenosiloxane).

[0067] When organopolysiloxane B has a branched structure, it is preferably chosen from the group consisting of silicone resins with the following formulas:

[0068] - M'Q where hydrogen atoms bonded to silicon atoms are carried by the M groups;

[0069] - MM'Q where hydrogen atoms bonded to silicon atoms are carried by part of the M motifs;

[0070] - MD'Q where hydrogen atoms bonded to silicon atoms are carried by the D groups;

[0071] - MDD'Q where hydrogen atoms bonded to silicon atoms are carried by a part of the D groups;

[0072] - MM'TQ where hydrogen atoms bonded to silicon atoms are carried by part of the M motifs;

[0073] - MM'DD'Q where hydrogen atoms bonded to silicon atoms are carried by part of the M and D motifs;

[0074] - and their mixtures.

[0075] Preferably, organopoly siloxane B has a mass content of hydrogenosilyl Si-H functions between 0.2% and 91%, more preferably between 3% and 80%, and even more preferably between 15% and 70%.

[0076] The silicone composition according to the invention preferably comprises 0.1% to 15% by weight, and more preferably 0.5% to 10% by weight, of organopoly siloxane B. The silicone composition according to the invention may comprise an organopolysiloxane B or a mixture of several organopolysiloxanes B, for example a mixture of a poly(dimethylsiloxane) with hydrogenodimethylsilyl ends and an organopolysiloxane having, per molecule, at least three SiH motifs.

[0077] Advantageously, the molar ratio of Si-H hydrogenosiloxane functions of organopolysiloxanes B to alkene functions of organopolysiloxanes A is between 0.2 and 10, preferably between 0.5 and 5.

[0078] The polyaddition catalyst C can be chosen from platinum and rhodium compounds, but also from silicon compounds such as those described in patent applications WO 2015 / 004396 and WO 2015 / 004397, germanium compounds such as those described in patent application WO 2016 / 075414, nickel, cobalt, or iron complexes such as those described in patent applications WO 2016 / 071651, WO 2016 / 071652, WO 2016 / 071654, WO 2018 / 115601, WO 2019 / 008279, WO 2019 / 138194, WO 2023 / 031524, and WO 2023 / 031525, or manganese complexes such as those described in applications WO 2023 / 139322 and WO 2024 / 146993. Catalyst C is preferably a compound derived from at least one metal belonging to the platinum group. Such catalysts are well known. In particular, complexes of platinum and an organic product described in US patents 3,159,601, 3,159,602, 3,220,972 and European patents EP 0.057.459, EP 0.188.978 and EP 0.190 can be used.530, the platinum and vinyl organosiloxane complexes described in US patents 3,419,593, 3,715,334, 3,377,432 and 3,814,730.

[0079] Alternatively, a polyaddition photocatalyst can be used. Such a catalyst can be activated by irradiation, preferably by UV irradiation. A platinum-based photocatalyst can be chosen, for example, from: platinum bis(acetylacetonate), platinum trimethyl(acetylacetonate), platinum trimethyl(2,4-pentanedione), platinum trimethyl(3,5-heptanedione), platinum trimethyl(methyl acetoacetate), platinum bis(2,4-pentanedione), platinum bis(2,4-hexanedione), platinum bis(2,4-heptanedione), platinum bis(3,5-heptanedione), and platinum bis(l-phenyl-l,3-butanedione).

[0080] Preferably, catalyst C is a platinum-derived compound. In this case, the mass quantity of catalyst C, calculated by weight of platinum-metal, is generally between 2 ppm and 400 ppm by mass, preferably between 5 ppm and 200 ppm, based on the total weight of the silicone composition.

[0081] Preferably, catalyst C is a Karstedt platinum.

[0082] The polyaddition-curable silicone composition according to the present invention is characterized in particular by the fact that it comprises a thermally conductive filler D. This filler may consist of a single filler or a mixture of fillers having a different chemical nature and / or a different structure and / or a different particle size. According to one embodiment of the present invention, the thermally conductive filler D consists of a mixture of at least two fillers or at least three fillers having a different chemical nature and / or particle size. According to another embodiment of the present invention, the thermally conductive filler D consists of a single filler.

[0083] The total weight of the thermally conductive filler D in the polyaddition reaction crosslinkable silicone composition is preferably greater than 50%, more preferably greater than 60%, and even more preferably between 70% and 95%, by weight relative to the total weight of the polyaddition reaction crosslinkable silicone composition.

[0084] The thermally conductive filler D may contain one or more fillers of different kinds known to those skilled in the art for their thermally conductive properties, including metals, alloys, metal oxides, metal hydroxides, metal nitrides, metal carbides, metal silicides, carbon, soft magnetic alloys, and ferrites. The thermal conductivity of these fillers is preferably greater than 10 W / mK, more preferably greater than 20 W / mK, and even more preferably greater than 50 W / mK. They may, in particular, be chosen from the group consisting of alumina, aluminum trihydrate (ATH), aluminum, silica, metallic silicon, silicon carbide, silicon nitride, magnesium oxide, magnesium carbonate, boron nitride, zinc oxide, aluminum nitride, and carbon, for example, carbon black, diamond, carbon nanotubes, graphite, and graphene.Preferably, the thermally conductive charge D may comprise a thermally conductive charge selected from the group consisting of an alumina charge, an aluminum trihydrate (ATH) charge, an aluminum charge, a silica charge, a metallic silicon charge, a zinc oxide charge, an aluminum nitride charge, a boron nitride charge, and mixtures thereof. Even more preferably, the thermally conductive charge D may comprise a thermally conductive charge selected from the group consisting of an alumina charge, an aluminum trihydrate (ATH) charge, a zinc oxide charge, a silica charge, and mixtures thereof.

[0085] The thermally conductive charge D can have any shape known to those skilled in the art, for example, a sphere, a needle, a disc, a rod, or an indefinite shape. Preferably, the thermally conductive charge is spherical or an indefinite shape. When different thermally conductive charges are used in mixtures, they can have the same shape or different shapes.

[0086] The thermally conductive filler(s) can be used as is or they can undergo surface treatment. This surface treatment typically aims to improve the dispersibility of the filler within the organopolysiloxane composition and / or to enhance the thermal stability of the composition. Furthermore, heat treatment can improve the physical stability of the composition by preventing sedimentation, exudation, or increased viscosity.

[0087] The surface treatment said may be a heat treatment, a chemical treatment, a physical treatment, or combinations thereof, including a combination of a heat treatment and a chemical treatment.

[0088] According to the preferred embodiment, the thermally conductive filler can be treated with organosilicon compounds commonly used for this purpose. The polyaddition reaction crosslinkable silicone composition according to the invention can therefore include a thermally conductive filler treatment agent. These agents include:

[0089] - organosiloxanes, particularly methylpolysiloxanes such as hexamethyldisiloxane and

[0090] 1 ' octamethylcyclotetrasiloxane,

[0091] - organosilazanes, particularly methylpolysilazanes such as hexamethyldisilazane, divinyltetramethyldisilazane and hexamethylcyclotrisilazane,

[0092] - Chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane and dimethylvinylchlorosilane,

[0093] - alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, an (alkyl in CL- Cixjtrimethoxysilane such as octyltrimethoxysilane, vinyltrimethoxysilane, dimethylvinylethoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltriacetoxysilane, allyltrimethoxysilane, butenyltrimethoxysilane, hexenyltrimethoxysilane, gamma-methacryloxyproyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane.

[0094] Preferably, the thermally conductive charge can be treated with an alkoxysilane, in particular an alkyl Cl-C ixjtrimcthox silane, or with an organosilazane, in particular hexamethyldisilazane (HMDZ) and divinyltetramethyldisilazane, or a mixture thereof, in particular a mixture of HMDZ and divinyltetramethyldisilazane. When the thermally conductive charge is treated with a chemical agent, in particular an organosilazane, water may typically be added.

[0095] The silicone composition crosslinkable by polyaddition reaction according to the invention preferably comprises 0.05% to 5% of a thermally conductive filler treatment agent, and more preferably 0.1% to 3% by weight, relative to the total weight of the silicone composition crosslinkable by polyaddition reaction according to the invention.

[0096] A heat treatment of the thermally conductive load may consist of subjecting said load to a temperature between 70°C and 200°C for a period of between 1 hour and 4 hours.

[0097] In one embodiment, the surface treatment can be carried out before the thermally conductive filler is incorporated into the silicone composition. In an alternative embodiment, the treatment of the thermally conductive filler can be carried out in situ, during the preparation of the silicone composition.

[0098] The polyaddition-curable silicone composition according to the invention comprises a room-temperature liquid non-reactive organopolysiloxane E. In this context, the term "non-reactive" means that this organopolysiloxane does not participate in the polyaddition reaction leading to the crosslinking of the elastomer. In particular, said room-temperature liquid non-reactive organopolysiloxane E does not contain alkenyl or alkynyl functional groups, especially vinyl functional groups. Preferably, said room-temperature liquid non-reactive organopolysiloxane E is a linear diorganopolysiloxane blocked at each end of its chain by a triorganosiloxy motif, the organic radicals of which, bonded to the silicon atoms, are selected from alkyl radicals having from 1 to 8 carbon atoms. It can typically be a trimethylsiloxy-terminated polydimethylsiloxane (commonly called PDMS).The non-reactive organopolysiloxane, liquid at room temperature E, preferably has a viscosity between 50 mPa.s and 1000 mPa.s, preferably between 50 mPa.s and 500 mPa.s, more preferably between 80 mPa.s and 200 mPa.s. The dynamic viscosity is measured at 25°C in a manner known per se, with a Brookfield viscometer at a shear rate gradient sufficiently low so that the measured viscosity is independent of the rate gradient.

[0099] According to the invention, the non-reactive liquid organopolysiloxane E, at room temperature, contains between 130 ppm and 1000 ppm of silicon-bound OH groups, preferably between 150 ppm and 900 ppm. The content of silicon-bound OH groups in the non-reactive organopolysiloxane compound E is a mass content (OH weight / sample weight). It can be measured by an infrared method after deuteration, as described in "Measurement of Trace Silanol in Siloxanes by IR Spectroscopy" by Elmer D. Lipp, Applied Spectroscopy vol. 45, no. 3, 1991, pp. 477-483. To do this, a sample is analyzed using a Fourier transform infrared (FTIR) spectrophotometer. The silicone composition crosslinkable by polyaddition reaction according to the invention comprises (by weight relative to the total weight of the silicone composition) from 2% to 45%, preferably from 5% to 30%, of a non-reactive organopolysiloxane liquid at room temperature E.

[0100] The silicone composition crosslinkable by polyaddition reaction according to the invention may further comprise other compounds, in particular:

[0101] - at least one mineral filler, in particular silica, quartz, or a mixture thereof;

[0102] - a crosslinking inhibitor;

[0103] - a coloring base;

[0104] - optionally other charges.

[0105] According to a preferred embodiment, the silicone composition comprises a mineral filler F, which is preferably a combustion silica or a precipitation silica. The silica-type mineral fillers preferably have a specific surface area, measured according to BET methods, of at least 10 m². 2 / g, notably between 50 m 2 / g and 400 m 2 / g, preferably greater than 70 m 2 / g, an average primary particle size of less than 0.1 pm (micrometer) and an apparent density of less than 200 g / liter. Preferably, the mineral charge F is a combustion silica with a specific surface area between 10 m² 2 / g and 300 m 2 / g.

[0106] Mineral fillers of the silica type, preferably hydrophilic, can be incorporated directly into the silicone composition or optionally treated with a compatibilizing agent. Alternatively, these silicas can be treated with one or more organosilicon compounds, for example organosilane or organosilazane, commonly used for this purpose. These compounds include methylpolysiloxanes such as hexamethyldisiloxane, octamethylcyclo-tetrasiloxane, methylpolysilazanes such as hexamethyldisilazane, hexamethylcyclotrisilazane, tetramethyldivinyldisilazane, chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane, alkoxysilanes such as dimethyldimethoxysilane, dimethylvinylethoxysilane, trimethyhnethoxysilane.These compounds can be used alone or in mixtures (see French patents FR 1 126 884, FR 1 136 885, FR 1 236 505 and English patent GB 1 024 234).

[0107] Silica can optionally be pre-dispersed in a silicone oil to obtain a suspension. A preferred method is to use a treated combustion silica suspension, notably with hexamethyldisilazane, in a polyorganosiloxane oil, particularly a vinylized one.

[0108] Alternatively or in addition, the silicone composition according to the invention may also contain at least one other mineral filler, namely quartz. Preferably, natural ground quartz with an average particle size of less than 10 microns is used. The quartz may optionally be treated to improve its compatibility with organopolysiloxanes.

[0109] Other mineral fillers can be considered, including packing fillers such as diatomaceous earth, calcium carbonate, and / or kaolin. In one embodiment, the polyaddition-curable silicone composition according to the invention may optionally include a crosslinking inhibitor G. The function of the inhibitor G is to slow down the polyaddition reaction. The crosslinking inhibitor G may be selected from the following compounds:

[0110] - an organopolysiloxane, advantageously cyclic, and substituted by at least one alkenyl, tetramethyltetravinylcyclotetrasiloxane being particularly preferred,

[0111] - pyridine,

[0112] - organic phosphines and phosphites,

[0113] - unsaturated amides,

[0114] - alkylated maleates, and

[0115] - acetylenic alcohols, preferably an acetylenic alcohol of formula (R 1 (R 2 )C(OH)-C=CH, in which:

[0116] - R 1 is a linear or branched alkyl radical, or a phenyl radical,

[0117] - R 2 is a hydrogen atom, a linear or branched alkyl radical, or a phenyl radical,

[0118] - the radicals R 1 , R 2 and the carbon atom located alpha to the triple bond, which may eventually form a ring, and

[0119] - the total number of carbon atoms contained in R 1 and R 2 being at least 5, preferably from 9 to 20.

[0120] The said acetylenic alcohols are preferably chosen from those having a boiling point above 250°C. Examples include the following commercially available products: 1-ethynyl-1-cyclohexanol, 3-methyl-3-dodecyne-1-ol-3, 3,7,11-trimethyl-3,7,11-dodecyne-1-ol-3, diphenyl-1,1-propyne-2-ol-1, 3-ethyl-6-nonyne-1-ol-3 and 3-methyl-3-pentadecyne-1-ol-3.

[0121] Preferably, the G crosslinking inhibitor is 1-ethynyl-l-cyclohexanol or tetramethyltetravinylcyclotetrasiloxane.

[0122] Depending on the process used to produce the silicone elastomer according to the invention, the presence of the inhibitor may or may not be necessary. If required, such a crosslinking inhibitor can typically be present at a maximum concentration of 3000 ppm, preferably at a concentration of 100 ppm to 2000 ppm relative to the total weight of the silicone composition crosslinkable by polyaddition reaction according to the invention.

[0123] According to one embodiment, the silicone composition crosslinkable by polyaddition reaction according to the present invention may optionally include other additives traditionally used in this technical field by those skilled in the art, for example an adhesion promoter, a colorant, a flame retardant, a rheological agent such as a thixotropic agent, etc.

[0124] According to one embodiment, the polyaddition-curable silicone composition of the present invention may contain a low level of volatile organic compounds, typically less than 100 pgC / g, preferably less than 70 pgC / g, or even less than 50 pgC / g. For this purpose, the organopolysiloxane compounds used in the composition of the present invention may preferably be selected from compounds that themselves contain a low level of volatile organic compounds.

[0125] According to one embodiment, the silicone composition crosslinkable by polyaddition reaction according to the invention comprises (by weight relative to the total weight of the silicone composition):

[0126] - from 1% to 50% of at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon,

[0127] - from 0.1% to 15% of at least one organopolysiloxane B having, per molecule, at least two SiH motifs,

[0128] - from 2 ppm to 400 ppm of at least one platinum-derived C polyaddition catalyst (by weight of platinum-metal),

[0129] - from 50% to 95% of a thermally conductive load D, and

[0130] - 2% to 45% of at least one non-reactive liquid organopolysiloxane at room temperature E.

[0131] According to another embodiment, the polyaddition reaction crosslinkable silicone composition according to the invention comprises (by weight relative to the total weight of the silicone composition):

[0132] - 2% to 40% of at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon,

[0133] - 0.5% to 10% of at least one organopolysiloxane B having, per molecule, at least two SiH motifs,

[0134] - from 5 ppm to 200 ppm of at least one platinum-derived C polyaddition catalyst (by weight of platinum-metal),

[0135] - from 60% to 95% of a thermally conductive load D,

[0136] - 5% to 30% of at least one non-reactive liquid organopolysiloxane at room temperature E,

[0137] - from 0% to 5% of a mineral filler F, and

[0138] - from 0 ppm to 3000 ppm of a G crosslinking inhibitor.

[0139] According to yet another embodiment, the polyaddition reaction crosslinkable silicone composition according to the invention comprises (by weight relative to the total weight of the silicone composition):

[0140] - 2% to 40% of at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon,

[0141] - 0.5% to 10% of at least one organopolysiloxane B having, per molecule, at least two SiH motifs,

[0142] - from 5 ppm to 200 ppm of at least one platinum-derived C polyaddition catalyst (by weight of platinum-metal),

[0143] - from 70% to 95% of a thermally conductive load D,

[0144] - 5% to 30% of at least one non-reactive liquid organopolysiloxane at room temperature E. - 0.01% to 1% of a mineral filler F, and

[0145] - from 100 ppm to 2000 ppm of a G crosslinking inhibitor.

[0146] According to one embodiment, the silicone composition according to the invention can be prepared from a two-component (or multi-component) system characterized in that it is in two (or more) distinct parts intended to be mixed to form said silicone composition. In particular, in the case of preferred silicone compositions as described above, the silicone composition can be prepared from a two-component system characterized in that one part comprises catalyst C and does not comprise organopolysiloxane B, while the other part comprises organopolysiloxane B and does not comprise catalyst C. Other multi-component systems may be provided to improve shelf life and / or optimize the viscosity of each of the components.For example, the silicone composition according to the invention can be prepared from a three-component system characterized in that it is presented in three distinct parts intended to be mixed to form said silicone composition.

[0147] According to a preferred embodiment, the silicone composition according to the invention is in two distinct parts PI and P2 intended to be mixed to form said silicone composition, part PI comprising:

[0148] - all or part of the organopolysiloxane A having, per molecule, at least one alkenyl group in the C2-C12 position linked to silicon,

[0149] - the polyaddition catalyst C,

[0150] - all or part of the thermally conductive charge D, optionally with the thermally conductive charge treatment agent,

[0151] - all or part of the non-reactive liquid organopolysiloxane at room temperature E, and part P2 comprising:

[0152] - optionally a portion of the organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon,

[0153] - organopolysiloxane B having, per molecule, at least two SiH motifs,

[0154] - all or part of the thermally conductive charge D, optionally with the thermally conductive charge treatment agent,

[0155] - all or part of the non-reactive liquid organopolysiloxane at room temperature E,

[0156] - optionally the G crosslinking inhibitor.

[0157] The thermally conductive charge D may be present in part PI, in part P2 or in both parts PI and P2, with identical or different contents between parts PI and P2.

[0158] Advantageously, the thermally conductive filler D can be present in both portion PI and portion P2 in identical proportions. Thus, the total content of thermally conductive filler D remains constant in the polyaddition-curable silicone composition regardless of the mixing ratio of portions PI and P2. Each of portions PI and P2 according to the present invention can be obtained by mixing the various components in a suitable device known to those skilled in the art. According to a particularly advantageous embodiment of the present invention, portion PI, portion P2, or both portions PI and P2 can be obtained from an intermediate composition comprising all or part of the organopolysiloxane A and all or part of the thermally conductive filler D, as well as optionally the thermally conductive filler treatment agent.

[0159] The present invention also relates to the silicone elastomer obtained or capable of being obtained by crosslinking the crosslinkable silicone composition by polyaddition reaction as defined above, the process of obtaining said elastomer, as well as the use of said elastomer.

[0160] The silicone composition crosslinkable by polyaddition reaction as defined above is particularly suitable for the preparation of a silicone elastomer having thermoconducting properties.

[0161] An object of the present invention consists of a process for preparing a thermally conductive silicone elastomer comprising the step of allowing said crosslinkable silicone composition to crosslink by polyaddition reaction to obtain said thermally conductive silicone elastomer.

[0162] Another object of the present invention consists of a process for preparing a silicone elastomer comprising the following steps: a) providing a two-component system comprising all the components of the polyaddition reaction crosslinkable silicone composition as defined above; b) mixing the two parts of said two-component system to obtain the polyaddition reaction crosslinkable silicone composition; and c) allowing said polyaddition reaction crosslinkable silicone composition to obtain said thermally conductive silicone elastomer.

[0163] The crosslinking step can vary in duration depending on the silicone composition and temperature. Generally, a silicone elastomer with good properties is obtained after a few minutes or a few hours, depending on the temperature and the concentration of catalyst and inhibitor in the silicone composition. Mixing the components of the two-component (or multi-component) system typically takes place in a mixer (mechanical paddle mixer, low-pressure dynamic mixer, or any other conventional stirring system) at a temperature close to ambient, i.e., between 10°C and 40°C. An increase in the temperature of the silicone composition is sometimes observed during this mixing process, depending on the type of mixer and the applied shear. If it is desired to accelerate the crosslinking of the silicone composition, mixing can be carried out at a higher temperature, advantageously between 40°C and 70°C.

[0164] This silicone elastomer can advantageously be used as a thermally conductive material in various technical fields, particularly in electronics, electrical applications, and the automotive industry. This silicone elastomer can advantageously be used as a thermally conductive potting material, a gap-filler material, or an adhesive thermally conductive material, especially for batteries, such as those used in electric and hybrid vehicles, as well as stationary batteries. The present invention also relates to a battery, preferably an electric or hybrid vehicle battery, comprising the thermally conductive silicone elastomer of the present invention as a potting, filling, or adhesive thermally conductive material.In the field of electronics, the silicone elastomer according to the invention can advantageously be used as a thermally conductive material in 5G devices.

[0165] Advantageously, the polyaddition-curable silicone composition according to the present invention, as well as parts PI and P2 of the two-component system P that serves as a precursor to the polyaddition-curable silicone composition, possess good processability. Indeed, despite the presence of a high thermally conductive filler content, these compositions advantageously remain sufficiently fluid to be easily handled, and in particular extruded.

[0166] It is to the credit of the inventors that they succeeded in determining that the selection of an organopolysiloxane E having a particular content of hydroxy groups makes it possible to advantageously modify the viscosity of the composition.

[0167] The silicone elastomer of the present invention, obtained or obtainable by crosslinking the crosslinkable silicone composition by polyaddition reaction, advantageously exhibits a thermal conductivity of between 0.5 W / mK and 7 W / mK, preferably between 0.9 W / mK and 5 W / mK, and more preferably between 1 W / mK and 3 W / mK.

[0168] Other details or advantages of the invention will become clearer in view of the examples given below, which are for illustrative purposes only.

[0169] Examples

[0170] The silicone compositions described in the example below were obtained from the following raw materials:

[0171] A: Vinylized polydimethylsiloxane chain-end oil, viscosity = 3500 mPa.s

[0172] B: Poly(methylhydrogeno)(dimethyl)siloxane oil with SiH groups in the middle and end of the chain (a / co), having a SiH vinyl group content of 4.7% by weight, viscosity = 300 mPa·s. C: Karstedt platinum catalyst, containing 10% by weight of platinum metal.

[0173] DI: aluminum oxide Al2O3 flakes, D50 = 2 pm, specific surface area = 3.5 m² 2 / g, surface treated;

[0174] D2: aluminum oxide Al2O3, spherical particles, D50 = 9.3 pm, specific surface area = 0.2 m² 2 / g, untreated;

[0175] D3: aluminum oxide Al2O3, flakes, D50 = 19 pm, specific surface area = 0.2 m² 2 / g, untreated; El to E6: PDMS (trimethylsiloxy-terminated polydimethylsiloxane) whose specifications are given in Table 1.

[0176] The analyses were carried out according to the measurement protocols described below:

[0177] Viscosity of silicone oils A: measurement on a Brookfield rotary viscometer (needle no. 1) at a speed of 500 rpm at 25°C.

[0178] Viscosity of silicone compositions: measurement on a Haake rheometer at 25°C, following a program using an ascending and descending shear ramp, from 0 s 1 at 20 seconds 1 in 120 s (l eœ part) then 20 seconds 1 at 0 s 1 in 120 s (2 eme (part). The viscosity values ​​recorded are the values ​​at 10 s 1 and at 1 second 1 obtained during the 2 eme Part of the program (descending ramp). The installation used has a planar / planar geometry. The diameter of the upper plate is 20 mm. The distance between the two plates is 0.500 mm.

[0179] Measurement of silicon-bound OH ([OH]) content: Silicon-bound OH content was measured by infrared spectroscopy, using the post-deuteration method described in "Measurement of Trace Silanol in Siloxanes by IR Spectroscopy" by Elmer D. Lipp, Applied Spectroscopy vol. 45, no. 3, 1991, pp. 477-483. In practice, the calibration curve was constructed from standard solutions with known OH content. The OH content of the sample was calculated by measuring the optical density of the second derivative of the SiOD band at 2726 cm⁻¹ 1 .

[0180] Compositions 1 to 16:

[0181] Compositions 1 to 16 were obtained by mixing different PDMS oils El to E4 and a thermally conductive filler DI, D2 or D3. The results of the analyses are given in Table 1:

[0182] [Table 1]

[0183]

[0184] At equal viscosity, using a PDMS E with an OH group content greater than 130 ppm advantageously reduces the overall viscosity of the composition. Compositions 17-20:

[0185] Silicone compositions corresponding to parts PI and P2 were prepared according to the following protocol: For part PI: the thermally conductive filler D1, silicone oil A, PDMS E, and catalyst C were mixed according to the concentration indicated in Table 2 below. For part P2: the thermally conductive filler D1, silicone oil A, PDMS E, and silicone oil B were mixed according to the concentration indicated in Table 2 below. The resulting parts PI and P2 were then mixed in a 1:1 ratio.

[0186] [Table 2]

[0187] Compositions were thus obtained with 4 different PDMS oils (E1, E2, E5 and E6) with virtually identical viscosities (100 mPa·s), but varying in OH group content. The results of the analyses on the PI parts are given in Table 3: [Table 3]

Claims

DEMANDS 1. Polyaddition reaction crosslinkable silicone composition comprising: - at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon, - at least one organopolysiloxane B having, per molecule, at least two SiH motifs, - a catalytically effective amount of at least one C polyaddition catalyst, - a thermally conductive charge D, and - a non-reactive organopolysiloxane liquid at room temperature E, characterized in that the non-reactive organopolysiloxane liquid at room temperature E contains between 130 ppm and 1000 ppm mass of OH groups linked to silicon.

2. Silicone composition according to claim 1, wherein the non-reactive organopolysiloxane liquid at room temperature E is a linear diorganopolysiloxane blocked at each end of its chain by a triorganosiloxy motif, the organic radicals of which, linked to the silicon atoms, are selected from alkyl radicals having from 1 to 8 carbon atoms, preferably a polydimethylsiloxane with trimethylsiloxy terminations.

3. Silicone composition according to claim 1 or claim 2, wherein the silicone composition crosslinkable by polyaddition reaction according to the invention comprises (by weight relative to the total weight of the silicone composition) from 2% to 45%, preferably from 5% to 30%, of a non-reactive organopolysiloxane liquid at room temperature E.

4. Silicone composition according to any one of claims 1 to 3, wherein the total weight of the thermally conductive filler D in the polyaddition reaction crosslinkable silicone composition is greater than 50%, more preferably greater than 60%, and even more preferably between 70% and 95%, by weight relative to the total weight of the polyaddition reaction crosslinkable silicone composition.

5. Silicone composition according to any one of claims 1 to 4, wherein organopolysiloxane A contains between 130 ppm and 1000 ppm of silicon-bound OH groups, preferably between 150 ppm and 900 ppm.

6. Silicone composition according to any one of claims 1 to 5, said polyaddition reaction crosslinkable silicone composition comprising, by weight relative to the total weight of the silicone composition: - from 1% to 50% of at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon, - from 0.1% to 15% of at least one organopolysiloxane B having, per molecule, at least two SiH motifs, - from 2 ppm to 400 ppm of at least one platinum-derived C polyaddition catalyst (by weight of platinum-metal), - from 50% to 95% of a thermally conductive load D, and - 2% to 45% of at least one non-reactive liquid organopolysiloxane at room temperature E.

7. Silicone composition according to any one of claims 1 to 5, said polyaddition reaction crosslinkable silicone composition comprising, by weight relative to the total weight of the silicone composition: - 2% to 40% of at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon, - 0.5% to 10% of at least one organopolysiloxane B having, per molecule, at least two SiH motifs, - from 5 ppm to 200 ppm of at least one platinum-derived C polyaddition catalyst (by weight of platinum-metal), - from 60% to 95% of a thermally conductive load D, - 5% to 30% of at least one non-reactive liquid organopolysiloxane at room temperature E, - from 0% to 5% of a mineral filler F, and - from 0 ppm to 3000 ppm of a G crosslinking inhibitor.

8. Silicone composition according to any one of claims 1 to 5, said polyaddition reaction crosslinkable silicone composition comprising, by weight relative to the total weight of the silicone composition: - 2% to 40% of at least one organopolysiloxane A having, per molecule, at least one alkenyl group at C2-C12 linked to silicon, - 0.5% to 10% of at least one organopolysiloxane B having, per molecule, at least two SiH motifs, - from 5 ppm to 200 ppm of at least one platinum-derived C polyaddition catalyst (by weight of platinum-metal), - from 70% to 95% of a thermally conductive load D, - 5% to 30% of at least one non-reactive liquid organopolysiloxane at room temperature E. - from 0.01% to 1% of a mineral filler F, and - from 100 ppm to 2000 ppm of a G crosslinking inhibitor.

9. Silicone composition according to any one of claims 1 to 8, said silicone composition being prepared from a two-component system characterized in that one part comprises catalyst C and does not comprise organopolysiloxane B, while the other part comprises organopolysiloxane B and does not comprise catalyst C.

10. A process for preparing a thermally conductive silicone elastomer comprising the step of allowing a crosslinkable silicone composition to be crosslinked by polyaddition reaction according to any one of claims 1 to 9 to obtain said thermally conductive silicone elastomer.

11. Thermally conductive silicone elastomer obtained or obtainable by crosslinking the crosslinkable silicone composition by polyaddition reaction according to any one of claims 1 to 9.

12. Use of the thermally conductive silicone elastomer according to claim 11, as a thermally conductive material in the field of electronics, in electrical applications, or in the automotive field.

13. Use of the thermally conductive silicone elastomer according to claim 11 as a thermally conductive coating, filling or adhesive material.

14. Battery, preferably an electric vehicle or hybrid vehicle battery, comprising the thermally conductive silicone elastomer according to claim 11 as a thermally conductive encapsulating, filling or thermally conductive adhesive material.

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