EP4172276A1

EP4172276A1 - Thermally conductive silicone compositions

Info

Publication number: EP4172276A1
Application number: EP21740116.5A
Authority: EP
Inventors: Aurélie PELLE; Lucile FAUVRE; Julie DUBOIS
Original assignee: Elkem Silicones France SAS
Current assignee: Elkem Silicones France SAS
Priority date: 2020-06-25
Filing date: 2021-06-24
Publication date: 2023-05-03
Also published as: CN116209720A; JP2023533466A; KR20230029862A; WO2021260279A1; US20230250283A1

Abstract

The present invention relates to organopolysiloxane compositions comprising an organopolysiloxane having, per molecule, at least two alkenyl groups, an organopolysiloxane having, per molecule, at least two SiH units, a hydrosilylation catalyst, and a thermally conductive filler, the thermally conductive filler comprising at least 40% by weight of metallic silicon, and a specific particle size distribution. The invention further relates to a silicone elastomer which can be obtained by cross-linking and/or curing the composition, as well as its use as a thermally conductive material for coating or filling, in particular for the automotive field, in particular for the field of electric vehicles.

Description

DESCRIPTION

TITLE: THERMOCONDUCTIVE SILICONE COMPOSITIONS

Technical field The present invention relates to novel organopolysiloxane compositions crosslinking by polyaddition, intended to produce thermally conductive elements in particular for the automotive field, in particular for the field of electric vehicles.

STATE OF THE PRIOR ART Thermally conductive silicone elastomers are well known for their remarkable properties of heat transfer, thermal resistance to hot and cold, and electrical insulation. They are used in particular in electrical and electronic applications, and in the automotive industry. In particular in the automotive field, thermally conductive silicone elastomers are used in the batteries of electric vehicles and hybrid vehicles (“EV” and “HEV” according to English terminology) to remove heat from the cells of battery packs and of on-board electronics.

Thermally conductive silicone formulations have been described in the prior art. As early as 1981, US Pat. No. 4,292,223 described thermally conductive elastomers comprising organopolysiloxanes, a particulate filler and a viscosity modifier. The particulate filler comprises silica and a thermally conductive metal powder. The content by weight of metal powder is however only from 0.5: 1 to 2.5: 1, in powder / polymer mass ratio, and the maximum thermal conductivity obtained is only 11.7.10 ⁴ cal / s. .cm. ° C, or 0.5 W / mK, which is not sufficient for the desired applications. Currently, it is desirable to achieve thermal conductivity greater than 2.0 W / mK, preferably at least 3.0 W / mK

Traditionally, metal oxide powders have been employed to improve the thermal conductivity of elastomers, for example aluminum trihydrate (ATH), aluminum oxide and / or magnesium oxide (see for example the application US Patent 2019/0161666). However, the addition of these thermally conductive fillers at very high concentration is responsible for increasing the density of the elastomer. For the intended fields of application, such as the automobile, the density of the elastomeric material is a very important property. It is desirable to obtain a thermally conductive elastomer material, the density of which is preferably less than 4 g / cm ³ , more preferably less than 3 g / cm ³ , more preferably less than 2.5 g / cm ³ , and even more preferably less than 2 g / cm ³ . Patent application JP 2000-063670 describes a thermally conductive silicone elastomer containing metallic silicon as thermally conductive filler. Patent EP 1,788,031 also describes the use of metallic silicon powder in silicone elastomers as a thermally conductive filler in order to obtain high thermal conductivity and good storage stability. However, the maximum thermal conductivity obtained in this document is between 0.6 W / mK and 1.0 W / mK In the same way, the patent application JP 2007-311628 describes a thermally conductive elastomer film in which a silicon powder metallic is used as a thermally conductive filler and electrical insulator. Preferably, said metallic silicon powder has a particle size of less than 20 µm. Patent application KR 20120086249 describes a method of preparing a thermally conductive silicone elastomer containing a thermally conductive powder filler and a hollow filler made of organic resin. According to this document, use will preferably be made of a thermally conductive powder having particles with a diameter of between 3 and 15 μm. It is specified that the silicone elastomer obtained can have a thermoconductivity of between 0.15 W / mK and 3.0 W / m. K. However, in the examples, the thermal conductivity does not exceed 0.41 W / mK

In another technical field, patent JP524573 describes thermally conductive heat-sealing rolls and bands using a silicone elastomer layer comprising a metallic silicon powder. The thermal conductivity obtained is 2 W / m.K.

It would be desirable to have a thermally conductive silicone elastomer having both a high thermal conductivity, preferably greater than 2.0 W / mK or 3.0 W / mK, and a low density, preferably less than 3 g /. cm ³ or 2 g / cm ³ . In addition, it is necessary for this silicone elastomer to have a consistency allowing its implementation and its use in the desired technical fields. Indeed, the inventors have observed that the composition could become powdery if the fillers were poorly chosen, and the preparation of the elastomer then became impossible.

The object of the present invention is to provide a novel thermally conductive organopolysiloxane composition, solving the above-mentioned problems, and having both high thermal conductivity, low density, and good processability.

Summary of the invention

The present invention relates to an organopolysiloxane composition X comprising:

- at least one organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon, - at least one organopolysiloxane B having, per molecule, at least two SiH units,

- a catalytically effective amount of at least one hydrosilylation catalyst C, and

a thermally conductive filler D, characterized in that said thermally conductive filler D comprises at least 40% by weight of metallic silicon, said thermally conductive filler D comprises between 3% and 22% of particles having a diameter less than or equal to 2 μm, and the particle size distribution is such that the d90 / d10 ratio of said filler is greater than or equal to 20.

Another subject of the present invention relates to a two-component system P precursor of the organopoly siloxane composition X as defined above and comprising the constituents A, B, C, and D as defined above, said two-component system. component P being characterized in that it is presented in two distinct parts PI and P2 intended to be mixed to form said organopolysiloxane composition X, and in that one of the parts PI or P2 comprises catalyst C and does not include l organopolysiloxane B, while the other part PI or P2 comprises organopolysiloxane B and does not include catalyst C.

Another subject of the present invention relates to a silicone elastomer capable of being obtained by crosslinking and / or curing of the organopolysiloxane composition X as defined above, as well as the use of the silicone elastomer as a thermally conductive coating material. or filling, in particular for the automotive field, in particular for the field of electric vehicles.

Another object of the present invention relates to a process for preparing a silicone elastomer comprising the following steps: a) providing a two-component system P comprising all the components of the organopolysiloxane composition X as defined above; b) mixing the two parts of said two-component system P to obtain the organopolysiloxane composition X; and c) allowing said organopolysiloxane composition X to crosslink and / or harden to obtain said silicone elastomer.

Finally, the present invention relates to an intermediate composition comprising:

- at least one organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon, and

- a thermally conductive filler D, characterized in that said thermally conductive filler D comprises at least 40% by weight of metallic silicon, said thermally conductive filler D comprises between 3% and 22% of particles having a diameter less than or equal to 2 mhi, and the size distribution of the particles is such that the d90 / d10 ratio of said filler is greater than or equal to 20.

Detailed description of the invention

Unless otherwise indicated, all the viscosities of the silicone oils referred to in the present disclosure correspond to a dynamic viscosity quantity at 25 ° C called “Newtonian”, that is to say the dynamic viscosity which is measured, in a manner known per se, with a Brookfield viscometer at a sufficiently low shear rate gradient so that the measured viscosity is independent of the speed gradient.

The organopolysiloxane composition X according to the present invention comprising at least the following components A, B, C, and D:

- an organopolysiloxane A having, per molecule, at least two C 1 -G alkenyl groups, bonded to silicon,

- an organopolysiloxane B having, per molecule, at least two SiH units,

- a hydrosilylation catalyst C, and

- a thermally conductive load D.

The organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon, can in particular be formed:

- at least two siloxyl units of the following formula: Y _a R ¹ _b SiO ₍ 4- _ab ) / 2 in which:

Y is C2-C6 alkenyl, preferably vinyl,

R ¹ is a monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably chosen from alkyl groups having 1 to 8 carbon atoms such as methyl, ethyl, propyl, cycloalkyl groups having 3 to 8 atoms carbon and aryl groups having 6 to 12 carbon atoms, and a = 1 or 2, b = 0, 1 or 2 and the sum of a + b = 1, 2 or 3; and

- optionally of units of the following formula: R ¹ _c SiO ₍ 4- _C ) / 2 in which R ¹ has the same meaning as above and c = 0, 1, 2 or 3.

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

These organopolysiloxanes A can have a linear structure, essentially consisting of “D” siloxyl units chosen from the group consisting of siloxyl units Y2S1O2 _/ 2, YR ¹ Si0 _2/2 and R ^ SIIOM, and end siloxyl units “M” chosen. among the group formed by YR / SiOi siloxyl units. Y2R ¹ SiOi / 2 and R '; SiO 2- The symbols Y and R ¹ are as described above.

As examples of terminal "M" units, mention may be made of trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxy groups.

As examples of "D" units, mention may be made of dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy groups.

Examples of linear organopolysiloxanes which may be organopolysiloxanes A according to the invention are:

- a poly (dimethylsiloxane) with dimethylvinylsilyl ends;

- a poly (dimethylsiloxane-co-methylphenylsiloxane) with dimethyl-vinylsilyl ends;

- unpoly (dimethylsiloxane-co-methylvinylsiloxane) with dimethyl-vinylsilyl ends;

- a poly (dimethylsiloxane-co-methylvinylsiloxane) with trimethyl-silyl ends; and

- a cyclic poly (methylvinylsiloxane).

In the most recommended form, organopolysiloxane A contains terminal dimethylvinylsilyl units and even more preferably organopolysiloxane A is a poly (dimethylsiloxane) with dimethylvinylsilyl ends.

Silicone oil generally has a viscosity of between 1 mPa.s and 2,000,000 mPa.s. Preferably, said organopolysiloxanes A are oils with a dynamic viscosity of between 20 mPa.s and 100,000 mPa.s, preferably between 20 mPa.s and 80,000 mPa.s at 25 ° C, and more preferably between 100 mPa.s and 50,000 mPa.s.

Optionally, the organopolysiloxanes A can also contain “T” siloxyl units (R'SiCLi) and / or “Q” siloxyl units (S1O4 _/ 2). The R ¹ symbols are as described above. The organopolysiloxanes A then exhibit a branched structure. Examples of branched organopolysiloxanes which may be organopolysiloxanes A according to the invention are:

- a poly (dimethylsiloxane) (methylsiloxane) with trimethylsilyl and dimethylvinylsilyl ends, consisting of “M” trimethylsiloxy, “M” dimethylvinylsiloxy, “D” dimethylsiloxy and “T” methylsiloxy units;

a resin consisting of “M” trimethylsiloxy, “M” dimethylvinylsiloxy and “Q” units; and

a resin consisting of “M” trimethylsiloxy, “D” methylvinylsiloxy and “Q” units. However, according to one embodiment, the organopolysiloxane composition X does not comprise branched organopolysiloxanes or resins comprising C2-C6 alkenyl units. Preferably, the organopolysiloxane compound A has a content by mass of alkenyl unit of between 0.001% and 30%, preferably between 0.01% and 10%, preferably between 0.02 and 5%.

The organopolysiloxane composition X preferably comprises from 5% to 30% of organopolysiloxane A, more preferably from 8% to 15% by weight of organopolysiloxane A, relative to the total weight of the organopolysiloxane composition X.

The organopolysiloxane composition X can comprise a single organopolysiloxane A or a mixture of several organopolysiloxanes A having, for example, different viscosities and / or different structures.

Organopolysiloxane B is an organohydrogenpolysiloxane compound comprising per molecule at least two, and preferably at least three, hydrogenosilyl functions or Si — H units. The organopolysiloxane composition X can comprise a single organohydrogenpolysiloxane B or a mixture of several organohydrogenpolysiloxanes B having, for example, different viscosities and / or different structures. The organohydrogenpolysiloxane B can advantageously be an organopolysiloxane comprising at least two, preferably at least three, siloxyl units of the following formula: in which :

- the R ² radicals, which are identical or different, represent a monovalent radical having 1 to 12 carbon atoms,

- d = 1 or 2, e = 0, 1 or 2 and d + e = l, 2 or 3; and optionally other units of the following formula: R ² _f SiO ₍ 4-f> / 2 in which R ² has the same meaning as above, and f = 0, 1, 2, or 3.

It is understood in the above formulas that, if several R ² groups are present, they can be identical or different from each other. Preferably, R ² can represent a monovalent radical chosen 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 from 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.

In the above formula, the symbol d is preferably equal to 1. The organohydrogenpolysiloxane 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. When it comes to linear polymers, they consist essentially of siloxyl units chosen from the units of the following formulas D: R ² ₂ Si0 _2/2 or D ': R ² HSi0 _2/2 , and of siloxyl units terminals chosen from the units of the following formulas M: R ² 3SiOi _{/ 2} or M ': R ² 2HSiOi / 2 where R ² has the same meaning as above.

Examples of organohydrogenpolysiloxanes which may be organopolysiloxanes B according to the invention comprising at least two hydrogen atoms bonded to a silicon atom are:

- a poly (dimethylsiloxane) with hydrogenodimethylsilyl ends;

- a poly (dimethylsiloxane-co-methylhydrogenosiloxane) with trimethyl-silyl ends;

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

- a poly (methylhydrogenosiloxane) with trimethylsilyl ends; and

- a cyclic poly (methylhydrogenosiloxane).

When the organohydrogenpolysiloxane B has a branched structure, it is preferably chosen from the group consisting of the silicone resins of the following formulas:

- M’Q where the hydrogen atoms bonded to silicon atoms are carried by the M groups,

- MM'Q where the hydrogen atoms bonded to silicon atoms are carried by part of the M units,

- MD’Q where the hydrogen atoms bonded to silicon atoms are carried by the D groups,

- MDD’Q where the hydrogen atoms bonded to silicon atoms are carried by part of the D groups,

- MM'TQ where the hydrogen atoms bonded to silicon atoms are carried by part of the M units,

- MM'DD'Q where the hydrogen atoms bonded to silicon atoms are carried by part of the M and D units,

- and their mixtures, with M, M ', D and D' as defined above, T: siloxyl unit of formula R ² ₃ SiOi _{/ 2} and Q: siloxyl unit of formula S1O4 / 2 where R ² has the same meaning as above.

Preferably, the organohydrogenpolysiloxane compound 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%.

Considering the whole of the organopolysiloxane composition X, the molar ratio of the hydrogenosilyl Si-H functions to the alkenes functions can advantageously be between 0.2 and 20, preferably between 0.5 and 15, more preferably between 0.5 and 10, and even more preferably between 0.5 and 5. Preferably, the viscosity of the organohydrogenpolysiloxane 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.

The organopolysiloxane composition X preferably comprises from 0.1% to 10% of organohydrogenopolysiloxane B, and more preferably from 0.5% to 5% by weight, relative to the total weight of the organopolysiloxane composition X.

The hydrosilylation catalyst C can 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 applications WO 2016/075414 or complexes of nickel, cobalt or iron such as those described in patent applications WO 2016/071651, WO 2016/071652 and WO 2016/071654. Catalyst C is preferably a compound derived from at least one metal belonging to the platinum group. These catalysts are well known. It is possible, in particular, to use the complexes of platinum and of 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 complexes platinum and vinylated organosiloxanes described in US Patents 3,419,593, US 3,715,334, US 3,377,432 and US 3,814,730.

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

Preferably, catalyst C is a Karstedt platinum.

The organopolysiloxane composition X according to the present invention is characterized in that it comprises a thermally conductive filler D. This can consist of a single filler or of a mixture of fillers having a different chemical nature and / or a structure different and / or different grain size. According to a preferred 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 preferred embodiment of the present invention, the thermally conductive filler D consists of a single filler.

The total weight of the thermally conductive filler D in the organopolysiloxane composition X is preferably greater than 70%, more preferably greater than 75%, and even more preferably between 80% and 95%, by weight relative to the weight total composition organopolysiloxane X. According to a particularly advantageous embodiment of the present invention, the total weight of the thermally conductive filler D in the organopolysiloxane composition X is greater than or equal to 85%. This particularly high content of thermally conductive filler makes it possible to achieve very high thermal conductivities.

Said thermally conductive filler D comprises at least 40% by weight of metallic silicon, preferably at least 50% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight, and most preferably at least 60% by weight. even more preferred at least 80% by weight.

According to a first embodiment, the thermally conductive filler D comprises between 60% and 99.99% by weight of metallic silicon, preferably between 65% and 99.95% by weight, more preferably between 70% and 99, 9% by weight, more preferably between 70% and 99% by weight, more preferably between 75% and 97% by weight, more preferably between 80% and 95% by weight.

In addition to metallic silicon, the thermally conductive filler D may contain one or more other fillers of a different nature known to those skilled in the art for their thermally conductive properties, in particular from metals, alloys, metal oxides, metal hydroxides, metal nitrides. , metallic carbides, metallic silicides, carbon, soft magnetic alloys and ferrites. The thermal conductivity of these charges 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 l 'alumina, aluminum trihydrate (ATH), aluminum, silicon carbide, silicon nitride, magnesium oxide, magnesium carbonate, boron nitride, zinc oxide, nitride aluminum, and carbon, for example carbon black, diamond, carbon nanotubes, graphite and graphene. Preferably, the thermally conductive filler D may comprise, in addition to metallic silicon, a thermally conductive filler chosen from the group consisting of an alumina filler, an aluminum trihydrate (ATH) filler, an aluminum filler, a filler. silica, zinc oxide filler, aluminum nitride filler, boron nitride filler, and mixtures thereof. Even more preferably, the thermally conductive filler D can comprise, in addition to metallic silicon, in addition to metallic silicon, a thermally conductive filler chosen from the group consisting of an alumina filler, an aluminum trihydrate (ATH) filler. , a zinc oxide filler, a silica filler, and mixtures thereof. The thermally conductive filler D can comprise between 0.01% and 60% by weight of thermally conductive filler which is not metallic silicon, preferably between 0.05% and 50% by weight, more preferably between 0, 1% and 40% by weight, more preferably between 1% and 30% by weight, more preferably between 3% and 25% by weight, more preferably between 5% and 20% by weight.

According to another embodiment, the thermally conductive filler D comprises 100% by weight of metallic silicon, i.e. the thermally conductive filler D consists of metallic silicon, to the exclusion of any other thermally conductive filler of a different chemical nature. Thus, preferably:

- the organopolysiloxane composition X does not contain alumina, and / or

- the organopolysiloxane composition X does not contain aluminum trihydrate (ATH), and / or

- the organopolysiloxane composition X does not contain zinc oxide, and / or

- the organopolysiloxane composition X does not contain silica.

The thermally conductive filler D according to the invention has certain particle size characteristics.

On the one hand, the thermally conductive filler D comprises between 3% and 22% (by volume) of particles having a diameter less than or equal to 2 µm (micrometers). More preferably, the thermally conductive filler D comprises between 3% and 20% (by volume) of particles having a diameter less than or equal to 2 μm (micrometers). Even more preferably, the thermally conductive filler D comprises between 6% and 18% (by volume) of particles having a diameter less than or equal to 2 μm.

On the other hand, the size distribution of the particles is such that the d90 / d10 ratio of said filler is greater than or equal to 20. More preferably, the size distribution of the particles is such that the d90 / d10 ratio of said filler. charge is greater than or equal to 30. The d90 / d10 ratio of said charge may advantageously be less than 200, preferably less than 100.

In the present text, the particle size distribution of the charges is measured by a laser diffraction method. The content of particles having a diameter less than or equal to 2 μm is a volume content, obtained by summing the volume of all the particles having a diameter measured by laser diffraction less than or equal to 2 μm. “D90” corresponds to the characteristic diameter corresponding to 90% of the cumulative frequency by volume of the particle size distribution of the filler. “D10” corresponds to the characteristic diameter corresponding to 10% of the cumulative frequency by volume of the particle size distribution of the filler.

The thermally conductive charge (s) may have a specific surface area, measured according to BET methods, of at least 0.1 m ² / g. Typically, the specific surface is less than or equal to 3000 m ² / g. Preferably, the thermally conductive filler (s) can have a specific surface area, measured according to the BET methods, between 0.1 m ² / g and 100 m ² / g, or even between 0.1 m ² / g and The thermally conductive filler D can 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 else an undefined shape. Preferably, the thermally conductive filler has a spherical shape or an undefined shape. When different thermally conductive fillers are used in mixtures, the latter may have the same shape or different shapes.

As regards the thermally conductive filler of metallic silicon, this can be obtained by any method well known to those skilled in the art. According to a first embodiment, the thermally conductive filler in metallic silicon is a powder obtained by chemical reduction of silica then grinding in a crusher or an industrial grinder. According to a second embodiment, the thermally conductive filler of metallic silicon is a powder obtained from fragments of metallic silicon wafers and chips from the semiconductor industry, which have been finely cut or ground. According to a third embodiment, the thermally conductive filler in metallic silicon is a spherical powder obtained by melting metallic silicon at high temperature, by atomizing the molten silicon, then by cooling or by solidifying the spherical particles obtained. The metallic silicon can be monocrystalline or polycrystalline. The classification of the thermally conductive filler in metallic silicon can be carried out according to methods known to those skilled in the art, for example by dry classification or by wet classification, or by a succession of several classification steps of the same or different type.

The thermally conductive silicon metal filler is typically greater than 50%, or greater than 80%, or greater than 95% (by weight) pure. However, it is known that the surface of a metallic silicon filler can be covered with a silicon oxide layer. The appearance of this silicon oxide layer can be natural or caused by certain treatments. It can advantageously give the load better thermal stability.

The thermally conductive fillers made of metallic silicon can be used as such or they can undergo a surface treatment. 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 can improve the physical stability of the composition, avoiding the phenomena of settling or exudation, or even an increase in viscosity.

Said surface treatment can be a heat treatment, a chemical treatment, a physical treatment, or their combinations, in particular the combination of a chemical treatment and a chemical treatment. According to a preferred embodiment, the thermally conductive filler made of metallic silicon can be treated with organosilicon compounds usually used for this use. The organopolysiloxane composition X according to the invention can therefore comprise an agent for treating the thermally conductive filler E. Among these agents are:

- organosiloxanes, in particular methylpolysiloxanes such as hexamethyldisiloxane and 1 ’octamethylcy clotetrasiloxane,

- organosilazanes, in particular methylpolysilazanes such as hexamethyldisilazane, divinyltetramethyldisilazane and hexamethylcyclotrisilazane,

- chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane and dimethylvinylchlorosilane,

- alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, octyltrimethoxysilane, vinyltrimethoxysilane, dimethylvinylethoxysilane, vinyltri (2-methoxyethoxy) silane, vinyltriacetoxysilane, allyltrimethoxysilane, the butenyltrimethoxysilane, hexenyltrimethoxysilane, gamma-methacryloxyproyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, trimethylmethoxy and trimethylethoxysilane.

More preferably, the thermally conductive filler made of metallic silicon can be treated with an alkoxysilane, in particular octyltrimethoxysilane, or with an organosilazane, in particular hexamethyldisilazane (HMDZ) and divinyltetramethyldisilazane, or a mixture of these, in particular a mixture of these HMDZ and divinyltetramethyldisilazane. When the thermally conductive filler is treated with a chemical agent, especially an organosilazane, water can typically be added.

The organopolysiloxane composition X preferably comprises from 0.1% to 5% of an agent for treating the thermally conductive filler E, and more preferably from 1% to 3% by weight, relative to the total weight of the organopolysiloxane composition X.

A heat treatment of the thermally conductive filler in metallic silicon can consist in subjecting said filler to a temperature of between 100 ° C and 200 ° C for a period of between 1 hour and 4 hours.

By physical treatment is meant the addition to the thermally conductive charge of a physical treatment agent which interacts with said charge in an essentially physical and non-chemical manner, for example by ionic interaction or by hydrogen bonds. Typically, a physical treatment agent can be an organopolysiloxane comprising in OH groups. According to one embodiment, the surface treatment can be carried out before incorporation of the thermally conductive filler in the organopolysiloxane composition. According to an alternative embodiment, the treatment of the thermally conductive filler can be carried out in situ, during the preparation of the organopolysiloxane composition.

In addition to the components A, B, C, and D already mentioned above, the organopolysiloxane composition X according to the present invention can optionally comprise other components.

According to one embodiment, the organopolysiloxane composition X according to the present invention can optionally comprise a filler E which is not a thermally conductive filler.

According to one embodiment, the organopolysiloxane composition X according to the present invention can optionally comprise a crosslinking inhibitor F. The function of the inhibitor F is to slow the hydrosilylation reaction. The crosslinking inhibitor F can be chosen from the following compounds:

- an organopolysiloxane, advantageously cyclic, and substituted by at least one alkenyl, tetramethylvinyltetrasiloxane being particularly preferred,

- pyridine,

- organic phosphines and phosphites,

- unsaturated amides,

- alkylated maleates, and

- acetylenic alcohols.

Preferably, the crosslinking inhibitor F is an acetylenic alcohol of formula (R ¹ ) (R ² ) C (OH) -C = CH, in which:

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

- 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 possibly forming a ring, and

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

Said alcohols are preferably chosen from those having a boiling point greater than 250 ° C. Mention may be made, by way of examples, of the following products which are commercially available: 1-ethynyl-l-cyclohexanol, methyl-3-dodécyne-l-ol-3, trimethyl-3,7,1 l-dodécyne -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. Preferably, the crosslinking inhibitor F is 1-ethynyl-1-cyclohexanol.

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 can typically be present in an amount of 3000 ppm at most, preferably at a rate of 100 ppm to 2000 ppm relative to the total weight of the organopolysiloxane composition X.

According to one embodiment, the organopolysiloxane composition X according to the present invention can optionally comprise other additives traditionally used in this technical field by a person skilled in the art, for example an adhesion promoter, a dye, a fire retardant, a rheological agent such as a thixotropic agent, etc.

According to one embodiment, the organopolysiloxane composition X according to the present invention can 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 can preferably be chosen from the compounds themselves containing a low level of volatile organic compounds.

According to a preferred embodiment, the organopolysiloxane composition X according to the invention comprises:

- from 5% to 30%, preferably from 8% to 15%, of an organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon,

- from 0.1% to 10%, preferably from 0.5% to 5%, of an organopolysiloxane B having, per molecule, at least two SiH units,

- from 2 ppm to 400 ppm, preferably from 5 ppm to 200 ppm, of a hydrosilylation catalyst C,

- from 70% to 95%, preferably from 80% to 95% of a thermally conductive load D,

- from 0.1% to 5%, preferably from 1% to 3%, of an agent for treating the thermally conductive filler E,

- from 100 ppm to 3000 ppm, preferably from 100 ppm to 2000 ppm of a crosslinking inhibitor F.

The percentages and ppm are percentages and ppm by mass. The quantity by weight of catalyst C is calculated by weight of platinum metal.

A subject of the present invention is also the silicone elastomer obtained or capable of being obtained by crosslinking and / or curing of the organopolysiloxane composition X such as defined above, the process for obtaining said elastomer, as well as the intermediate compositions used during this process for obtaining.

The organopolysiloxane composition X as defined above is particularly suitable for the preparation of a silicone elastomer having thermally conductive properties. According to one embodiment, said elastomer is prepared from a two-component system P comprising all the components of the organopolysiloxane composition X.

In particular, the present invention also relates to a two-component system P precursor of the organopolysiloxane composition X as defined above, comprising at least the components A, B, C, and D, said two-component system P being characterized in that it is in two distinct PI and P2 parts intended to be mixed to form said organopolysiloxane composition X, and in that one of the PI or P2 parts comprises catalyst C and does not include organopolysiloxane B , while the other PI or P2 part comprises the organopolysiloxane B and does not include the catalyst C.

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 P comprising all the components of the organopolysiloxane composition X as defined above; b) mixing the two parts of said two-component system P to obtain the organopolysiloxane composition X; and c) allowing said organopolysiloxane composition X to crosslink and / or harden to obtain said silicone elastomer.

According to a preferred embodiment, the PI part comprises:

- all or part of the organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon,

- the hydrosilylation catalyst C,

- all or part of the thermally conductive load D,

- optionally the treatment agent for the thermally conductive load E, and part P2 includes:

- optionally a part of the organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon,

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

- all or part of the thermally conductive load D,

- optionally the treatment agent for the thermally conductive load E,

- optionally the crosslinking inhibitor F. 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. Advantageously, the thermally conductive filler D can be present in part PI and in part P2, in an identical content. Thus, the total content of thermally conductive filler D remains invariable in the organopolysiloxane composition X regardless of the rate of mixing of the parts PI and P2.

Each of the parts PI and P2 according to the present invention can be obtained by mixing the various components in an appropriate device known to those skilled in the art.

According to a particularly advantageous embodiment of the present invention, the PI part, the P2 part or the two PI and P2 parts 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 treatment agent for the thermally conductive filler E.

A subject of the present invention is also an intermediate composition comprising:

Said organopolysiloxane A and said thermally conductive filler D are preferably as described above.

Advantageously, the total weight of the thermally conductive filler D in the intermediate composition is greater than 70%, more preferably greater than 75%, and more preferably greater than 80%, and even more preferably between 85% and 98% by weight relative to the total weight of the intermediate composition. This intermediate composition, particularly rich in thermally conductive filler D, makes it possible, after dilution with other components, to easily obtain the organopolysiloxane composition X or precursor parts PI and / or P2. The intermediate composition according to the present invention can be obtained by mixing at least the organopolysiloxane A and the thermally conductive filler D by means of a device known to those skilled in the art, for example a Z-arm mixer or a butterfly mixer. . Optionally, the thermally conductive filler D can undergo a treatment surface treatment, which can be heat treatment, chemical treatment, or a combination of heat treatment and chemical treatment. The intermediate composition may optionally comprise an agent for treating the thermally conductive filler E, as described above. Heat treatment can be performed on the thermally conductive filler before it is mixed into the intermediate composition. Alternatively, the intermediate composition can be subjected to a heat treatment after mixing the organopolysiloxane A, the thermally conductive filler D, and optionally the treatment agent for the thermally conductive filler E.

Advantageously, the organopolysiloxane composition X, as well as the parts PI and P2 of the two-component system P precursor of the organopolysiloxane composition X, have good processability. Indeed, despite the presence of a very high thermally conductive filler content, said compositions are advantageously pasty and non-powdery, which makes them easy to handle, in particular extrudable. It is to the credit of the inventors to have succeeded in determining the good characteristics of the thermally conductive filler allowing this technical result to be achieved.

The silicone elastomer which is the subject of the present invention, obtained or capable of being obtained by crosslinking and / or curing of the organopolysiloxane composition X, advantageously exhibits a thermal conduction greater than or equal to 1 W / mK, preferably greater than or equal to 1.5 W / mK, more preferably greater than or equal to 2 W / mK, more preferably greater than or equal to 3 W / mK, and even more preferably between 3 W / mK and 7 W / mK

In addition, said silicone elastomer advantageously has a density of less than or equal to 4 g / cm ³ , preferably less than or equal to 3 g / cm ³ , more preferably less than 2 g / cm ³ .

Advantageously, the silicone elastomer according to the present invention can easily be recycled after use. Indeed, this elastomer preferably contains a very high silicon element content, in particular when the thermally conductive filler itself contains a very high metallic silicon content. The used silicone elastomer can advantageously be recycled using combustion furnaces.

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 coating material (ie “potting” according to English terminology) or filling (ie “gap-filler” according to English terminology. Anglo-Saxon), in particular for batteries, for example the batteries of electric vehicles and hybrid vehicles, but also stationary batteries. In the field of electronics, the silicone elastomer according to the invention can advantageously be used as a thermally conductive material in 5G devices.

EXAMPLES

The silicone compositions described as an example below were obtained from the following raw materials:

A: End-of-chain vinylated silicone oil, having a vinyl group content of 1.2% by weight, viscosity = 100 mPa.s

B 1: Hydrogen dimethylpolysiloxane oil with chain end SiH groups (a / w), having a vinyl group content of SiH of 5.7% by weight, viscosity = 8.5 mPa.s B2: Poly (methylhydrogen) oil (dimethyl) siloxane with SiH groups in the middle and end of the chain (a / w), having a vinyl group content of SiH of 7.3% by weight, viscosity = 30 mPa.s

C: Karstedt platinum catalyst, containing 10% by weight of platinum metal

DI: silicon powder (purity> 99%), dl0 = 42.3 pm, d50 = 70 pm, d90 = 112 pm, dl00 = 200 pm

D2: silicon powder (purity> 99%), dl0 = 15 pm, d50 = 31.6 pm, d90 = 54 pm, dl00 = 100 pm

D3: silicon powder (purity> 99%), dl0 = 6.4 pm, d50 = 10.4 pm, d90 = 16.4 pm, dl00 = 30 pm

D4: silicon powder (purity> 99%), dl0 = 2 pm, d50 = 10.7 pm, d90 = 26 pm, dl00 = 60 pm

D5: silicon powder (purity> 99%), dl0 = 0.9 pm, d50 = 2.7 pm, d90 = 5.3 pm, dl00 = 10 pm

D6: silicon powder (purity> 99%), dl0 = 4.0 pm, d50 = 10 pm, d90 = 25

D7: alumina powder, d10 = 1 pm, d50 = 5.7 pm, d90 = 12.3 pm

D8: alumina powder, d10 = 18 pm, d50 = 46 pm, d90 = 73 pm

D9: alumina powder, d10 = 0.3 pm, d50 = 2.4 pm, d90 = 18 pm

D10: zinc oxide powder, d10 = 0.2 pm, d50 = 1.5 pm, d90 = 5 pm

El: octyltrimethoxysilane

F: 1-ethynyl-l-cyclohexanol (ECH)

In the examples which follow, the particle size distribution of the fillers is measured by a laser diffraction method:

- "d10" corresponds to the characteristic diameter corresponding to 10% of the cumulative frequency by volume of the particle size distribution of the filler.

- "d50" corresponds to the characteristic diameter corresponding to 50% of the cumulative frequency by volume of the particle size distribution of the filler.

- "d90" corresponds to the characteristic diameter corresponding to 90% of the cumulative frequency by volume of the particle size distribution of the filler.

- "d100" corresponds to the characteristic diameter corresponding to 100% of the cumulative frequency by volume of the particle size distribution of the filler.

the content of particles having a diameter less than or equal to 2 μm is a volume content, obtained by summing the volume of all the particles having a diameter measured by laser diffraction less than or equal to 2 μm. Examples 1 to 17:

Silicone compositions corresponding to parts PI and P2 were prepared according to the following protocol:

For the PI part: the thermally conductive filler D, the silicone oil A and the catalyst C were mixed in a Speed Mixer at 1800 rpm according to the concentration indicated in Table 1 below. The concentration of thermally conductive fillers is 85%.

For part P2: the thermally conductive filler D, silicone oil A, silicone oils B 1 and B2, and G 1-ethynyl-l-cyclohexanol F were mixed in a Speed Mixer at 1800 rpm depending on the concentration shown in Table 1 below. The concentration of thermally conductive fillers is 85%.

[Table 1]

Examples 1 to 17 were carried out by following the manufacturing protocol described above, by varying the thermally conductive load D as described in Table 2 and Table 3 below. The processability of the compositions obtained was evaluated visually, and classified as: "-" = very poor - powdery appearance "-" = poor - appearance of a crumble, aggregates "+" = good - pasty appearance "+ + ”= Very good - pasty and smooth appearance.

The results are shown in Table 2 and Table 3 below.

[Table 2] [Table 3] Examples 18 to 22

Examples 18 to 22 were carried out by mixing with the Speed Mixer (stirring for 2 times 2 minutes at 1800 revolutions per minute) 85% of thermally conductive fillers D with 15% of silicone oil A, by varying the thermally conductive load D as described. in Table 4 below. The processability of the compositions obtained was visually evaluated as described above. The thermal conductivity and the density of an elastomeric material which could be obtained from the exemplified compositions were estimated by calculation.

[Table 4]

Example 23

Step 1: Manufacture of an intermediate composition 89% of thermally conductive fillers D, 9% of silicone oil A and 2% of octyltrimethoxysilane

E1 (weight percentages) were mixed in a Z-arm mixer for 30 minutes. The resulting composition was subjected to a heat treatment for 2 hours at 150 ° C.

The thermally conductive filler D consists of 60% by weight of filler D2 and 40% by weight of filler D5. Characteristics of the charge: - rate of particles having a diameter less than or equal to 2 pm = 13.7%

- d90 / dl0 = 32. Step 2: Manufacture of the PI and P2 parts

For part PI: Dilution of the paste obtained in step 1 with silicone oil A and catalyst C according to the concentration indicated in Table 5 below. The concentration of thermally conductive fillers is 85%.

For part P2: Dilution of the mash obtained in step 1 with silicone oil A, silicone oils B1 and B2, and G 1-ethynyl-l-cyclohexanol F. according to the concentration indicated in the table 5 below. The concentration of thermally conductive fillers is 85%. Said dilutions are obtained by mixing in a Speed Mixer at 1800 revolutions per minute. The PI and P2 parts had very good processability.

Step 3: Manufacture of the thermally conductive silicone composition and of the thermally conductive silicone elastomer

The PI and P2 parts obtained in step 2 were mixed in a ratio of 1: 1 with the Speed Mixer. The resulting mixture was degassed in vacuo, then poured into a mold. The mixture contained in the mold was then placed in a heating press, at a pressure of 2 bars, at 100 ° C., for 30 minutes.

[Table 5]

The thermal conductivity of the elastomer was measured according to the transient plane source method (TPS method for "transient place source") as described in standard ISO 22007-2 ("Determination of thermal conductivity and effusivity thermal. Part 2: Transient planar source (hot disk) method ”) using a Hot Disc TPS 2200 device. The thermal conductivity of the elastomer was equal to 3.42 W / mK The density of l elastomer was 1.94 g / cm ³ .

Claims

1. Organopolysiloxane composition X comprising:

- at least one organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon,

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

2. Organopolysiloxane composition X according to claim 1, characterized in that the total weight of the thermally conductive filler D in the organopolysiloxane composition X is between 80% and 95%.

3. Organopolysiloxane composition X according to claim 1 or claim 2, characterized in that said thermally conductive filler D comprises between 3% and 20%, preferably between 6% and 18%, of particles having a diameter less than or equal to 2 μm. .

4. An organopolysiloxane composition X according to any one of claims 1 to 3, characterized in that the size distribution of the particles is such that the d90 / d10 ratio of said filler is greater than or equal to 30.

5. Organopolysiloxane composition X according to any one of claims 1 to 4, characterized in that said thermally conductive filler D comprises at least 70% by weight of metallic silicon.

6. Organopolysiloxane composition X according to any one of claims 1 to 5, characterized in that the thermally conductive filler D comprises 100% by weight of metallic silicon.

7. An organopolysiloxane composition X according to any one of claims 1 to 5, characterized in that the thermally conductive filler D comprises, in addition to metallic silicon, a thermally conductive filler chosen from the group consisting of an alumina filler, a filler of aluminum trihydrate, aluminum filler, silica filler, zinc oxide filler, aluminum nitride filler, boron nitride filler, and mixtures thereof.

8. Organopolysiloxane composition X according to any one of claims 1 to 7, characterized in that it comprises:

- from 70% to 95%, preferably from 80% to 95% of a thermally conductive load D,

9. Bicomponent system P precursor of the organopolysiloxane composition X as defined in any one of claims 1 to 8 and comprising the constituents A, B, C, and D as defined in any one of claims 1 to 8, said two-component system P being characterized in that it is in two distinct parts PI and P2 intended to be mixed to form said organopolysiloxane composition X, and in that one of the parts PI or P2 comprises the catalyst C and does not include organopolysiloxane B, while the other part PI or P2 includes G organopolysiloxane B and does not include catalyst C

10. Silicone elastomer obtainable by crosslinking and / or curing of the organopolysiloxane composition X as defined in any one of claims 1 to 8.

11. Process for preparing a silicone elastomer comprising the following steps: a) providing a two-component system P comprising all the components of the organopolysiloxane composition X as defined in any one of claims 1 to 8; b) mixing the two parts of said two-component system P to obtain the organopolysiloxane composition X; and c) allowing said organopolysiloxane composition X to crosslink and / or harden to obtain said silicone elastomer.

12. Use of the silicone elastomer as defined in claim 10 as a thermally conductive coating or filling material, in particular in the field of electronics, in electrical applications, and in the automotive field.

13. Intermediate composition comprising:

- at least one organopolysiloxane A having, per molecule, at least two C2-C6 alkenyl groups bonded to silicon, and - a thermally conductive filler D, characterized in that said thermally conductive filler D comprises at least 40% by weight of metallic silicon, said thermally conductive filler D comprises between 3% and 22% of particles having a diameter less than or equal to 2 μm, and the size distribution of the particles is such that the ratio d90 / d10 of said filler is greater than or equal to 20.