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, and a thermally conductive filler D, characterized in that the organopolysiloxane A has a linear structure, a viscosity at 25°C of between 50 mPa·s and 200 mPa·s, and contains between 130 ppm and 1000 ppm by mass of OH groups bonded to silicon.

Description

[0001] DESCRIPTION

[0002] TITLE: Poly-addition 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 in particular for the electronics and automotive fields, in particular for the field of electric vehicles.

[0005] State of the prior art

[0006] Thermally conductive silicone elastomers are well known for their remarkable heat transfer properties, thermal resistance to hot and cold, and electrical insulation. They are used in particular in electrical and electronic applications, and in the automotive field. Particularly in the automotive field, thermally conductive silicone elastomers are used in the batteries of electric vehicles and hybrid vehicles (EV and HEV) to evacuate heat from battery pack cells and on-board 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 filler in silicone compositions is high, typically greater than 50% by weight, or even greater than 70% by weight. One of the challenges in designing thermally conductive silicones lies in adding such large amounts of thermally conductive fillers while minimizing the impact on the fluidity of the composition. 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 fillers.

[0010] Several solutions have been proposed in the prior art to control the viscosity of thermally conductive silicone compositions. One method consists of carefully choosing the type of filler, its shape and its size. For example, application WO 2021 / 260279 A1 from Elkem Silicones proposes the selection of certain fillers having specific dimensions, with a ratio to be respected between large and small particles. Patent EP 1 788 031 B1 from Shin-Etsu Chemical describes a thermally conductive silicone elastomer comprising, per 100 parts by weight of a heat-crosslinkable organopolysiloxane composition, from 10 to 2000 parts by weight of a metallic silicon powder having an average particle size of less than 100 μm. Another method consists of changing the medium of the silicone formulation or adding a solvent. However, the evaporation of the solvent generates volatile compounds, linked to risks for hygiene and the environment.Finally, another method consists of treating the thermally conductive fillers so as to improve their compatibility with the silicone matrix. For example, international patent application WO 2023 / 283819 A1, filed by Dow Silicones and Dow Global Technologies, describes a self-adhesive thermally conductive silicone composition comprising in particular a thermally conductive filler and a treatment agent, in combination with an adhesion promoting agent containing at the same time 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 in the formulation can have negative impacts on the mechanical properties of the silicone elastomer, and phenomena of exudation of the treatment agents from the silicone matrix are noted.

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

[0012] Summary of the invention

[0013] The subject of the present invention is a silicone composition crosslinkable by polyaddition reaction comprising:

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

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

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

[0017] - a thermally conductive filler D, characterized in that the organopolysiloxane A has a linear structure, a viscosity at 25°C of between 50 mPa.s and 200 mPa.s, and contains between 130 ppm and 1000 ppm by mass of OH groups linked to silicon.

[0018] Detailed description of the invention

[0019] Unless otherwise indicated, all viscosities of the silicone oils discussed in this disclosure correspond to a dynamic viscosity quantity at 25°C known as “Newtonian”, i.e. the dynamic viscosity which is measured, 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.

[0020] In the following section concerning the description of organopolysiloxane A, the following nomenclature has been used to represent the siloxyl units: with Y and R 1such that: Y represents a C2-C12 alkenyl group, preferably a vinyl group; R 1 represents a monovalent hydrocarbon group having from 1 to 12 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.

[0021] As examples of terminal motifs M and M V1 , we can cite the trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxy groups.

[0022] As examples of patterns D and D V1 , we can cite the dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy groups.

[0023] Examples of T units include the methylsiloxy group.

[0024] Organopoly siloxane A having, per molecule, at least one C2-C12 alkenyl group bonded to silicon, has a linear structure. By “linear structure” is meant a structure which does not contain, or substantially does not contain, siloxy units T and / or Q. The content of siloxy units T and / or Q is preferably less than or equal to 0.1% (% by mass of the units T and / or Q, based on the total weight of organopoly siloxane A).

[0025] Organopoly siloxane A can have the following general average formula: in which

[0026] - Y represents a C2-C12 alkenyl group, preferably a vinyl group;

[0027] - R 1represents a monovalent hydrocarbon group having from 1 to 12 carbon atoms, preferably selected 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; and

[0028] - a, b and c are such that a > 0, b > 0, a+b =2, c > 1, preferably c is between 1 and 200, and the mass concentration of OH groups bonded to silicon is between 130 ppm and 1000 ppm (ppm mass, based on the total weight of the organopoly siloxane A).

[0029] It is understood in the above formulas that, if several R groups 1are present, they may be identical or different from each other. Optionally, although this is not shown in the general formula, organopolysiloxane A may contain hydroxy OH groups carried by siloxy units in the middle of the chain, then having the formula R 1 (OH)SiO 2 / 2 - The content of these patterns is however less than 0.1%, preferably between 0% and 0.01% (% by mass of the patterns R 1 (OH)SiO 2 / 2 , based on the total weight of organopolysiloxane A).

[0030] Preferably, the organopolysiloxane compound A has a mass content of alkenyl units of between 0.01% and 10%, preferably between 0.1% and 5% (mass % of alkenyl units, based on the total weight of the organopolysiloxane A).

[0031] Said organopolysiloxanes A are oils with a dynamic viscosity of between 50 mPa.s and 200 mPa.s, preferably between 80 mPa.s and 150 mPa.s, more preferably between 100 mPa.s and 130 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.

[0032] Organopolysiloxane A contains 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. To do this, a sample is analyzed using an FTIR (Fourier Transform Infrared) spectrophotometer.

[0033] According to one embodiment, the 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.

[0034] According to another embodiment, the organopolysiloxane A does not have, or does not have significantly, 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.

[0035] Without wishing to be bound by this theory, the inventors believe that the absence of significant residual acidity in organopolysiloxane A has the advantage of improving the stability over time of said organopolysiloxane, in particular at high temperature. As a result, the silicone composition crosslinkable by polyaddition reaction according to the present invention can have better stability over time and a longer storage life.

[0036] However, the inventors have found that the presence of a residual acidity greater than or equal to 5 ppm, preferably between 6 ppm and 100 ppm, in organopolysiloxane A would, surprisingly, make it possible to reduce the viscosity of the silicone composition crosslinkable by polyaddition reaction according to the present invention and to improve its thixotropic index. In the present text, the acidity is expressed in ppm by mass equivalent HCl (hydrochloric acid), i.e. mg / kg of HCl equivalents. The measurement of the acidity content can be carried out using a UV-visible spectrophotometer, by measuring the difference in transmittance between the analyzed sample and a standard obtained by known metered additions of HCl.

[0037] The organopolysiloxane A according to the invention can be selected from commercially available compounds meeting the stated specifications. Alternatively, it can be synthesized according to methods known in the technical field.

[0038] According to one embodiment, organopolysiloxane A is obtained by ring-opening polymerization (ROP) in the presence of nucleophilic or electrophilic initiators. These synthesis methods are well known to those skilled in the art and are for example described in the article “Ring-Opening Polymerization (ROP) and Catalytic Rearrangement as a Way to Obtain Siloxane Mono- and Telechelics, as Well as Well-Organized Branching Centers: History and Prospects”, Bezlepkina et al, Polymers 2022, 14, 2408. These methods make it possible to effectively control the molecular weight of the polymer by selecting the amount of initiator and the amount of chain blockers. The synthesis of organopolysiloxane A according to the present invention can be carried out by anionic polymerization or by cationic polymerization.For anionic polymerization, the initiator may be chosen from nucleophilic catalysts well known to those skilled in the art. For cationic polymerization, the initiator may be chosen from acid catalysts well known to those skilled in the art.

[0039] The use of chain blockers containing alkenyl (preferably vinyl) functions makes it possible to synthesize organopolysiloxanes having alkenyl (preferably vinyl) groups in terminal positions. The synthesis of organopoly siloxane A according to the present invention can therefore be carried out from cyclic oligosiloxanes, typically hexamethylcyclotrisiloxane (D3) or octamethylcyclotetrasiloxane (D4), and alkenyl, preferably vinyl, chain blockers, typically divinyldimethyldisiloxane (M V12). The content of OH groups bonded to silicon can be controlled by adding a source of OH groups during the synthesis. This source of OH groups can be chosen from: an α,β-dihydroxylated oligo-organosiloxane, an α,β-dihydroxylated polyorganosiloxane, Silox, a hydroxylated silicone resin, or water. Said α,β-dihydroxylated oligo- and polyorganosiloxanes are preferably chosen from those having a low molecular weight, preferably less than 20,000 g / mol, more preferably less than 15,000 g / mol (weight-average molar mass), and / or low viscosity, preferably less than 1,000 mPa.s.

[0040] The term "Silox" refers to mixtures of a,co-dihydroxylated oligo- or polyorganosiloxane and cyclosiloxanes. These mixtures are obtained from the direct synthesis of organochlorosilanes (Rochow synthesis) and the hydrolysis of the resulting chlorosilanes.

[0041] The silicone composition preferably comprises from 5% to 50% by weight of organopolysiloxane A, even more preferably from 10% to 40% by weight of organopolysiloxane A. In the following part concerning the description of organopolysiloxane B, the following nomenclature has been used to represent the siloxyl units: with R 2 representing a monovalent radical having from 1 to 12 carbon atoms.

[0042] 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.

[0043] The organopolysiloxane B may advantageously be an organopolysiloxane comprising at least two, preferably at least three, siloxyl units of the following formula: in which R 2represents 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 units of the following formula: in which R 2 has the same meaning as above, and f = 0, 1, 2, or 3.

[0044] It is understood that, if several R groups 2 are present in the above formulas, they can be the same or different from each other.

[0045] Preferably, R 2 may represent a monovalent radical selected from the group consisting of alkyl groups having 1 to 8 carbon atoms, optionally 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 2may advantageously be selected from the group consisting of methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl.

[0046] The symbol d is preferably equal to 1.

[0047] Organopolysiloxane B may 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.

[0048] When linear polymers are concerned, these are essentially constituted of siloxyl units D and / or D', and of terminal siloxyl units M and / or M'. When cyclic polymers are concerned, these are essentially constituted of siloxyl units D and / or D'. Examples of organohydrogenpolysiloxanes which may be organopolysiloxanes B according to the invention are:

[0049] - a poly(dimethylsiloxane) with hydrogenodimethylsilyl ends;

[0050] - a poly(dimethylsiloxane-co-methylhydrogensiloxane) with trimethylsilyl ends;

[0051] - a poly(dimethylsiloxane-co-methylhydrogensiloxane) with hydrogenodimethylsilyl ends;

[0052] - a poly(methylhydrogensiloxane) with trimethylsilyl ends; and

[0053] - a cyclic poly(methylhydrogensiloxane).

[0054] When organopolysiloxane B has a branched structure, it is preferably chosen from the group consisting of silicone resins of the following formulae:

[0055] - M'Q where the hydrogen atoms linked to silicon atoms are carried by the M groups;

[0056] - MM'Q where the hydrogen atoms linked to silicon atoms are carried by part of the M motifs;

[0057] - MD'Q where the hydrogen atoms linked to silicon atoms are carried by the D groups;

[0058] - MDD'Q where the hydrogen atoms linked to silicon atoms are carried by part of the D groups;

[0059] - MM'TQ where the hydrogen atoms linked to silicon atoms are carried by part of the M motifs;

[0060] - MM'DD'Q where the hydrogen atoms linked to silicon atoms are carried by part of the M and D motifs;

[0061] - and their mixtures.

[0062] Preferably, the organopolysiloxane B has a mass content of hydrogenosilyl Si-H functions of between 0.2% and 91%, more preferably between 3% and 80% and even more preferably between 15% and 70%.

[0063] The silicone composition according to the invention preferably comprises 0.1% to 15% by weight, and more preferably from 0.5% to 10% by weight, of organopolysiloxane 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 of organopolysiloxane having, per molecule, at least three SiH units.

[0064] Advantageously, the molar ratio of the hydrogenosilyl functions Si-H of the organopolysiloxanes B to the alkene functions of the organopolysiloxanes A is between 0.2 and 10, preferably between 0.5 and 5.

[0065] The polyaddition catalyst C may in particular 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. These catalysts are well known. In particular, it is possible to use the complexes of platinum and an organic product described in US patents 3,159,601, US 3,159,602, US 3,220,972 and European patents EP 0.057.459, EP 0.188.978 and EP 0.190.530, the platinum and vinyl organosiloxane complexes described in US patents 3,419,593, US 3,715,334, US 3,377,432 and US 3,814,730.

[0066] Alternatively, a polyaddition photocatalyst may be used. Such a catalyst may be activated by irradiation, preferably by UV irradiation. A platinum-based photocatalyst may be selected, 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(1-phenyl-1,3-butanedione).

[0067] Preferably, catalyst C is a compound derived from platinum. In this case, the weight quantity of catalyst C, calculated as the 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.

[0068] Preferably, catalyst C is a Karstedt platinum.

[0069] The silicone composition crosslinkable by polyaddition reaction according to the present invention is characterized in particular by the fact that it comprises a thermally conductive filler D. This 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 a different particle size. According to another embodiment of the present invention, the thermally conductive filler D consists of a single filler.

[0070] The total weight of the thermally conductive filler D in the silicone composition crosslinkable by polyaddition reaction 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 silicone composition crosslinkable by polyaddition reaction.

[0071] The thermally conductive filler D may contain one or more fillers of different nature known to those skilled in the art for their thermally conductive properties, in particular among 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 filler D may comprise a thermally conductive filler selected from the group consisting of an alumina filler, an aluminum trihydrate (ATH) filler, an aluminum filler, a silica filler, a metallic silicon filler, a zinc oxide filler, an aluminum nitride filler, a boron nitride filler, and mixtures thereof. Even more preferably, the thermally conductive filler D may comprise a thermally conductive filler selected from the group consisting of an alumina filler, an aluminum trihydrate (ATH) filler, a zinc oxide filler, a silica filler, and mixtures thereof.

[0072] The thermally conductive filler D may have any shape known to those skilled in the art, for example a spherical shape, a needle shape, a disc shape, a rod shape, or an indefinite shape. Preferably, the thermally conductive filler has a spherical shape or an indefinite shape. When different thermally conductive fillers are used in mixtures, these may have the same shape or different shapes.

[0073] The thermally conductive filler(s) may be used as such or may be surface treated. Said surface treatment typically aims to improve the dispersibility of the filler in the organopolysiloxane composition and / or to improve the thermal stability of the composition. In addition, the heat treatment may improve the physical stability of the composition, by avoiding settling or exudation phenomena, or even an increase in viscosity.

[0074] Said surface treatment may be a heat treatment, a chemical treatment, a physical treatment, or combinations thereof, in particular the combination of a heat treatment and a chemical treatment.

[0075] According to the preferred embodiment, the thermally conductive filler can be treated with organosilicon compounds usually used for this purpose. The silicone composition crosslinkable by poly addition reaction according to the invention can therefore comprise an agent for treating the thermally conductive filler. These agents include:

[0076] - organosiloxanes, in particular methylpolysiloxanes such as hexamethyldisiloxane and

[0077] 1' octamethylcyclotetrasiloxane,

[0078] - organosilazanes, in particular methylpolysilazanes such as hexamethyldisilazane, divinyltetramethyldisilazane and hexamethylcyclotrisilazane, - chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane and dimethylvinylchlorosilane,

[0079] - alkoxysilanes such as methyltrimethoxy silane, methyltriethoxysilane, phenyltrimethoxysilane, ethyltrimethoxy silane, n-propyltrimethoxysilane, a (C6-C alkyl 18 trimethoxy silane such as octyltrimethoxysilane, vinyltrimethoxysilane, dimethylvinylethoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltriacetoxy silane,

[0080] 1' ally Itrimethoxy silane, butenyltrimethoxysilane, hexenyltrimethoxysilane, gamma-methacryloxyproyltrimethoxysilane, dimethyldimethoxy silane, dimethyldiethoxy silane, diphenyldimethoxy silane, trimethylmethoxysilane, and trimethylethoxy silane.

[0081] More preferably, the thermally conductive filler may be treated with an alkoxysilane, in particular a (C6-C alkyl 18 )trimethoxy silane, or by an organosilazane, including hexamethyldisilazane (HMDZ) and divinyltetramethyldisilazane, or a mixture thereof, including a mixture of HMDZ and divinyltetramethyldisilazane. When the thermally conductive filler is treated with a chemical agent, including an organosilazane, water may typically be added.

[0082] The silicone composition crosslinkable by polyaddition reaction according to the invention preferably comprises from 0.05% to 5% of a thermally conductive filler treatment agent, and more preferably from 0.1% to 3% by weight, relative to the total weight of the silicone composition crosslinkable by polyaddition reaction according to the invention.

[0083] A heat treatment of the thermally conductive charge may consist of subjecting said charge to a temperature between 70°C and 200°C for a period between 1 hour and 4 hours.

[0084] According to one embodiment, the surface treatment can be carried out before the incorporation of the thermally conductive filler into the silicone composition. According to an alternative embodiment, the treatment of the thermally conductive filler can be carried out in situ, during the preparation of the silicone composition.

[0085] The silicone composition crosslinkable by polyaddition reaction according to the invention may also comprise other compounds, in particular:

[0086] - at least one mineral filler, in particular silica, quartz, or a mixture of these;

[0087] - a crosslinking inhibitor;

[0088] - a non-reactive organopolysiloxane liquid at room temperature;

[0089] - a coloring base;

[0090] - optionally other charges.

[0091] According to a preferred embodiment, the silicone composition comprises a mineral filler E, 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 m 2 / g, in particular 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. Very preferably, the mineral filler E is a combustion silica with a specific surface area of ​​between 10 m 2 / g and 300 m 2 / g.

[0092] The silica-type mineral fillers, preferably hydrophilic, may be incorporated as such into the silicone composition or may optionally be treated with a compatibilizing agent. According to a variant, these silicas may optionally be treated with one or more organosilicon compounds, for example organosilane or organosilazane, usually 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, trimethylmethoxysilane.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).

[0093] The silica may optionally be predispersed in a silicone oil, so as to obtain a suspension. It is particularly preferred to use a suspension of treated combustion silica, in particular with hexamethyldisilazane, in a polyorganosiloxane oil, in particular vinylated.

[0094] Alternatively or in addition, the silicone composition according to the invention may also contain at least one other mineral filler which is quartz. Preferably, a ground natural 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.

[0095] Other mineral fillers may be considered, including bulking fillers, such as diatomaceous earth, calcium carbonate and / or kaolin.

[0096] According to one embodiment, the silicone composition crosslinkable by polyaddition reaction according to the invention may optionally comprise a crosslinking inhibitor F. The function of the inhibitor F is to slow down the polyaddition reaction. The crosslinking inhibitor F may be chosen from the following compounds:

[0097] - an organopolysiloxane, advantageously cyclic, and substituted by at least one alkenyl, tetramethyltetravinylcyclotetrasiloxane being particularly preferred,

[0098] - pyridine,

[0099] - organic phosphines and phosphites,

[0100] - unsaturated amides,

[0101] - alkylated maleates, and

[0102] - acetylenic alcohols, preferably an acetylenic alcohol of formula (R 1 )(R 2 )C(OH)-C=CH, in which:

[0103] - R 1 is a linear or branched alkyl radical, or a phenyl radical,

[0104] - R 2 is a hydrogen atom, a linear or branched alkyl radical, or a phenyl radical, - the radicals R 1 , R 2 and the carbon atom located alpha to the triple bond which can possibly form a cycle, and

[0105] - the total number of carbon atoms contained in R 1 and R 2 being at least 5, preferably 9 to 20.

[0106] Said acetylenic alcohols are preferably chosen from those having a boiling point above 250°C. Examples which may be mentioned are the following products which are commercially available: 1-ethynyl-1-cyclohexanol, methyl-3-dodecyne-1-ol-3, trimethyl-3,7,11-dodecyne-1-ol-3, diphenyl-1,1-propyne-2-ol-1, ethyl-3-ethyl-6-nonyne-1-ol-3 and methyl-3-pentadecyne-1-ol-3.

[0107] Preferably, the crosslinking inhibitor F is 1-ethynyl-1-cyclohexanol or tetramethyltetravinylcyclotetrasiloxane.

[0108] 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 necessary, such a crosslinking inhibitor may typically be present at a maximum of 3000 ppm, preferably at a maximum of 100 ppm to 2000 ppm relative to the total weight of the silicone composition crosslinkable by polyaddition reaction according to the invention.

[0109] According to one embodiment, the silicone composition crosslinkable by polyaddition reaction according to the invention may optionally comprise a non-reactive organopolysiloxane that is liquid at room temperature G. The non-reactive organopolysiloxanes that are liquid at room temperature have the function of reducing the overall viscosity of the composition. 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. Preferably, said non-reactive organopolysiloxane that is liquid at room temperature G is a linear diorganopolysiloxane blocked at each end of its chain by a triorganosiloxy unit, the organic radicals of which, linked to the silicon atoms, are chosen from alkyl radicals having from 1 to 8 carbon atoms. It may typically be a polydimethylsiloxane with trimethylsiloxy end groups.The non-reactive organopolysiloxane liquid at room temperature G preferably has a viscosity of between 50 mPa 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.

[0110] The silicone composition crosslinkable by polyaddition reaction according to the invention comprises (by weight relative to the total weight of the silicone composition) from 0% to 10%, preferably from 0.1% to 5%, of a non-reactive organopolysiloxane which is liquid at room temperature G.

[0111] According to one embodiment, the silicone composition crosslinkable by polyaddition reaction according to the present invention may optionally comprise other additives traditionally used in this technical field by those skilled in the art, for example an adhesion promoter, a colorant, a fire retardant, a rheological agent such as a thixotropic agent, etc.

[0112] According to one embodiment, the silicone composition crosslinkable by polyaddition reaction according to 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, the organopolysiloxane compounds used in the composition according to the present invention may preferably be chosen from compounds themselves containing a low level of volatile organic compounds.

[0113] 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):

[0114] - from 5% to 50% of at least one organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked to silicon,

[0115] - from 0.1% to 15% of at least one organopolysiloxane B having, per molecule, at least two SiH units,

[0116] - from 2 ppm to 400 ppm of at least one polyaddition catalyst C derived from platinum (by weight of platinum-metal), and

[0117] - from 50% to 95% of a thermally conductive charge D.

[0118] According to another embodiment, the silicone composition crosslinkable by polyaddition reaction according to the invention comprises (by weight relative to the total weight of the silicone composition):

[0119] - from 10% to 40% of at least one organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked to silicon,

[0120] - from 0.5% to 10% of at least one organopolysiloxane B having, per molecule, at least two SiH units,

[0121] - from 5 ppm to 200 ppm of at least one polyaddition catalyst C derived from platinum (by weight of platinum-metal),

[0122] - from 60% to 95% of a thermally conductive charge D,

[0123] - from 0% to 5% of a mineral charge E,

[0124] - from 0 ppm to 3000 ppm of a crosslinking inhibitor F, and

[0125] - from 0% to 10% of a non-reactive organopolysiloxane liquid at room temperature G.

[0126] According to yet another embodiment, the silicone composition crosslinkable by polyaddition reaction according to the invention comprises (by weight relative to the total weight of the silicone composition):

[0127] - from 10% to 40% of at least one organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked to silicon,

[0128] - from 0.5% to 10% of at least one organopolysiloxane B having, per molecule, at least two SiH units, - from 5 ppm to 200 ppm of at least one poly addition catalyst C derived from platinum (by weight of platinum-metal),,

[0129] - from 70% to 95% of a thermally conductive charge D,

[0130] - from 0.01% to 1% of a mineral filler E,

[0131] - from 100 ppm to 2000 ppm of a crosslinking inhibitor F, and

[0132] - from 0% to 10%, preferably from 0.1% to 5%, of a non-reactive organopolysiloxane liquid at room temperature G.

[0133] 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 presented in two (or more) distinct parts intended to be mixed to form said silicone composition. In particular, in the case of the preferred silicone compositions as described above, the silicone composition can be prepared from a two-component system characterized in that one of the parts 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 can be provided to improve the storage 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.

[0134] According to a preferred embodiment, the silicone composition according to the invention is presented in two distinct parts PI and P2 intended to be mixed to form said silicone composition, the part PI comprising:

[0135] - all or part of the organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked to silicon,

[0136] - the poly addition catalyst C,

[0137] - all or part of the thermally conductive filler D, optionally with the thermally conductive filler treatment agent, and part P2 comprising:

[0138] - optionally a part of the organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked to silicon,

[0139] - organopolysiloxane B having, per molecule, at least two SiH units,

[0140] - all or part of the thermally conductive filler D, optionally with the thermally conductive filler treatment agent,

[0141] - optionally the crosslinking inhibitor F.

[0142] The thermally conductive filler D can 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.

[0143] Advantageously, the thermally conductive filler D may be present in the PI part and in the P2 part in an identical content. Thus, the total content of thermally conductive filler D remains invariable in the silicone composition crosslinkable by polyaddition reaction regardless of the mixing rate of the PI and P2 parts. Each of the PI and P2 parts according to the present invention may be obtained by mixing the different components in a suitable device known to those skilled in the art.

[0144] According to a particularly advantageous embodiment of the present invention, the part PI, the part P2 or both parts PI and P2 can be obtained from an intermediate composition comprising all or part of the organopoly siloxane A and all or part of the thermally conductive filler D, as well as optionally the agent for treating the thermally conductive filler.

[0145] 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 for obtaining said elastomer, as well as the use of said elastomer.

[0146] The silicone composition crosslinkable by polyaddition reaction as defined above is particularly suitable for the preparation of a silicone elastomer having thermoconductive properties.

[0147] 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.

[0148] Another subject 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 silicone composition crosslinkable by polyaddition reaction as defined above; b) mixing the two parts of said two-component system to obtain the silicone composition crosslinkable by polyaddition reaction; and c) allowing said silicone composition crosslinkable by polyaddition reaction to crosslink to obtain said thermally conductive silicone elastomer.

[0149] The crosslinking step can have a variable duration depending on the silicone composition and the 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. The mixing of the parts of the two-component (or multi-component) system can typically take place in a mixer (mechanical stirrer with inclined blades, low-pressure dynamic mixer, or any other conventional stirring system) at a temperature close to room temperature, i.e. between 10°C and 40°C. An increase in the temperature of the silicone composition is sometimes observed during this mixing depending on the type of mixer and the shear applied. If it is desired to accelerate the crosslinking of the silicone composition, the mixing can be carried out at a higher temperature, advantageously between 40°C and 70°C.

[0150] Said silicone elastomer can advantageously be used as a thermally conductive material in various technical fields, in particular in the field of electronics, in electrical applications, and in the automotive field. Said silicone elastomer can advantageously be used as a thermally conductive potting material (i.e. "potting" according to English terminology), filling material (i.e. "gap-filler" according to English terminology) or adhesive thermally conductive material, in particular for batteries, for example batteries of electric vehicles and hybrid vehicles, but also stationary batteries. The present invention also relates to a battery, preferably an electric vehicle or hybrid vehicle battery, comprising the thermally conductive silicone elastomer which is the subject of the present invention as a thermally conductive potting material, filling material 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.

[0151] Advantageously, the silicone composition crosslinkable by polyaddition reaction according to the present invention, as well as the parts PI and P2 of the two-component system P precursor of the silicone composition crosslinkable by polyaddition reaction, have good processability. Indeed, despite the presence of a high content of thermally conductive filler, said compositions advantageously remain sufficiently fluid to be easily handled, in particular extrudable.

[0152] The silicone composition crosslinkable by polyaddition reaction according to the present invention can advantageously have a viscosity at 25°C at a shear rate of 10 s 1less than 6000 mPa.s, preferably less than 5500 mPa.s, and more preferably between 1000 mPa.s and 5000 mPa.s.

[0153] Furthermore, the silicone composition crosslinkable by polyaddition reaction according to the present invention may advantageously have a thixotropic index of less than 3.00, preferably less than 2.50, and more preferably between 0.50 and 2.00, the thixotropic index being defined as the ratio between the viscosity at 25°C at a shear rate of 10 s 1 and viscosity at 25°C at a shear rate of 1 s -1 .

[0154] Measurement of the viscosity at 25°C of the silicone composition, at a shear rate of 10 s 1 (which can be described as strong shear) or 1 s (which can be qu-a 1lified low shear), can be obtained according to methods known to those skilled in the art. In the examples in this text, these viscosities were obtained using a Haake rheometer, on a plate / plate type installation. The diameter of the upper plate was 20 mm. The gap between the two plates was 0.500 mm.

[0155] It is to the credit of the inventors to have succeeded in determining the good characteristics of organopolysiloxane A making it possible to achieve this technical result. The silicone elastomer which is the subject of the present invention, obtained or capable of being obtained by crosslinking the crosslinkable silicone composition by polyaddition reaction, advantageously has a thermal conductivity of between 0.5 W / mK and 7 W / mK, preferably of between 0.9 W / mK and 5 W / mK, more preferably of between 1 W / mK and 3 W / mK

[0156] Other details or advantages of the invention will appear more clearly from the examples given below for information purposes only.

[0157] Examples

[0158] The silicone compositions described as examples below were obtained from the following raw materials:

[0159] A1 to A14: End-of-chain vinylated polydimethylsiloxane oils whose specifications are given in tables 1 and 3

[0160] B1: Hydrogendimethylpolysiloxane oil with SiH groups at the chain end (a / co), having a SiH vinyl group content of 5.7% by weight, viscosity = 8.5 mPa.s

[0161] B2: Poly(methylhydrogen)(dimethyl)siloxane oil with SiH groups in the middle and end of the chain (a / co), having a SiH vinyl group content of 7.3% by weight, viscosity = 30 mPa.s C: Karstedt platinum catalyst, containing 10% by weight of platinum metal

[0162] D: ATH (aluminum trihydrate) powder;

[0163] E: Combustion silica with hydrophobic treatment with a specific surface area of ​​approximately 15-45 m 2 / g ;

[0164] F: tetramethyltetravinylcyclotetrasiloxane

[0165] The analyses were carried out according to the measurement protocols described below:

[0166] Viscosity of silicone oils A: measured on a Brookfield rotary viscometer (needle no. 1) at a speed of 500 rpm at 25 °C.

[0167] Viscosity of silicone compositions: measurement on a Haake rheometer at 25°C, following a program using an upward and downward shear ramp, from 0 s -1 at 20 se -1 n 120 s ( 1 ere part) then 20 s -1 at 0 s -1 in 120 s ( 1 2 eme part). The viscosity values ​​recorded are the values ​​at 10 s -1 and at 1 s -1 obtained during the 2 emepart of the program (decreasing ramp). The installation used is of plane / plane geometry. The diameter of the upper plate is 20 mm. The distance between the two plates is 0.500 mm.

[0168] Thixotropic index (TI): ratio of viscosity at 25°C at a shear rate of 10 s -1 and viscosity at 25°C at a shear rate of 1 s -1 .

[0169] Measurement of silicon-bonded OH group content (IOHI): The silicon-bonded OH group content was measured by infrared, according to the method after deuteration 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 group content. The OH group content of the sample was calculated by measuring the optical density of the second derivative of the SiOD band at 2726 cm 1 .

[0170] Acidity measurement: The measurement was made using a UV-Vis spectrophotometer equipped with a tube holder accessory. Calibration was done by known metered additions of HCl in a reactive solvent of bromocresol purple in a butanol / toluene mixture. The results are expressed in ppm by mass HCl equivalent.

[0171] Compositions 1 to 9:

[0172] Compositions 1 to 9 were obtained by mixing 27.9% (by weight) different vinylated polydimethylsiloxane oils chain end A1 to A9 and 72.10% (by weight) of thermally conductive filler D. The results of the analyses are given in Table 1:

[0173] [Table 1]

[0174] With a substantially equal oil viscosity, the use of an oil A with an OH group content greater than 130 ppm advantageously makes it possible to reduce the overall viscosity of the composition as well as its thixotropic index.

[0175] Compositions 10 - 14: Silicone compositions corresponding to parts P1 and P2 were prepared according to the following protocol: For part PI: the thermally conductive filler D, the silicone oil A and the catalyst C were mixed according to the concentration indicated in Table 2 below. For part P2: the thermally conductive filler D, the silicone oil A, silicone oils B1 and B2, and a retarder F were mixed according to the concentration indicated in Table 2 below. The parts PI and P2 thus obtained were mixed in a proportion of 1:1.

[0176] [Table 2]

[0177] Compositions were thus obtained with different vinylated polydimethylsiloxane oils at the chain end A10 to A14, and the results of the analyses on the PI parts are given in table 3:

[0178] [Table 3]

[0179] As with silica-free compositions, it can be seen that the use of an A oil with an OH group content greater than 130 ppm advantageously reduces the overall viscosity of the composition as well as its thixotropic index. The viscosity of compositions with silica is typically higher than the viscosity of compositions without silica. However, silica reduces the settling phenomenon of the parts before crosslinking, and therefore improves its shelf life.

Claims

CLAIMS 1. Silicone composition crosslinkable by poly addition reaction comprising: - at least one organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked 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, and - a thermally conductive filler D, characterized in that the organopolysiloxane A has a linear structure, a viscosity at 25°C of between 50 mPa.s and 200 mPa.s, and contains between 130 ppm and 1000 ppm by mass of OH groups linked to silicon.

2. Silicone composition according to claim 1, in which the organopolysiloxane A has the following general average formula: in which - Y represents a C2-C12 alkenyl group, preferably a vinyl group; - R 1represents a monovalent hydrocarbon group having from 1 to 12 carbon atoms, preferably selected 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; and - a, b and c are such that a > 0, b > 0, a+b =2, c > 1, preferably c is between 1 and 200.

3. Silicone composition according to claim 1 or claim 2, in which the organopolysiloxane A has a residual acidity content greater than or equal to 5 ppm, preferably between 6 ppm and 100 ppm, and more preferably between 10 ppm and 100 ppm.

4. Silicone composition according to claim 1 or claim 2, in which the organopolysiloxane A has a residual acidity content strictly less than 5 ppm, preferably less than 4 ppm, and more preferably less than 3 ppm.

5. Silicone composition according to any one of claims 1 to 4, in which the total weight of the thermally conductive filler D in the silicone composition crosslinkable by polyaddition reaction 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 silicone composition crosslinkable by polyaddition reaction.

6. Silicone composition according to any one of claims 1 to 5, said silicone composition further comprising a mineral filler E, which is preferably a combustion silica or a precipitation silica.

7. Silicone composition according to any one of claims 1 to 6, said silicone composition further comprising a non-reactive organopolysiloxane which is liquid at room temperature G.

8. Silicone composition according to any one of claims 1 to 7, said silicone composition crosslinkable by polyaddition reaction comprising (by weight relative to the total weight of the silicone composition): - from 5% to 50% of at least one organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked to silicon, - from 0.1% to 15% of at least one organopolysiloxane B having, per molecule, at least two SiH units, - from 2 ppm to 400 ppm of at least one polyaddition catalyst C derived from platinum (by weight of platinum-metal), and - from 50% to 95% of a thermally conductive charge D.

9. Silicone composition according to any one of claims 1 to 8, said silicone composition crosslinkable by polyaddition reaction comprising (by weight relative to the total weight of the silicone composition): - from 10% to 40% of at least one organopolysiloxane A having, per molecule, at least one C2-C12 alkenyl group linked to silicon, - from 0.5% to 10% of at least one organopolysiloxane B having, per molecule, at least two SiH units, - from 5 ppm to 200 ppm of at least one polyaddition catalyst C derived from platinum (by weight of platinum-metal), - from 60% to 95% of a thermally conductive charge D, - from 0% to 5% of a mineral charge E, - from 0 ppm to 3000 ppm of a crosslinking inhibitor F, and - from 0% to 10% of a non-reactive organopolysiloxane liquid at room temperature G.

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

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

12. Thermally conductive silicone elastomer obtained or capable of being obtained by crosslinking the crosslinkable silicone composition by polyaddition reaction according to any one of claims 1 to 10.

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

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

15. Battery, preferably an electric vehicle or hybrid vehicle battery, comprising the thermally conductive silicone elastomer according to claim 12 as thermally conductive coating material, filler material or adhesive thermally conductive material.

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