THERMAL INTERFACE MATERIAL

Abstract

The invention relates to a thermal interface material, such as thermally conductive pads or thermally conductive sheets, exhibiting a good compromise between thermal conductivity and electrical resistivity. The material is based on at least one elastomeric matrix comprising 85 to 100 parts per annum of silicone rubber having a mass average molar mass, Mw, in the range of 150 to 1,000 kg / mol, 500 to 1,300 parts per annum of a thermally conductive filler comprising alumina and graphite, the volume percentage of graphite in the thermally conductive filler being in the range of 2% to 12%, and the total volume percentage of alumina and graphite in the thermally conductive filler being greater than 55%, 15 to 150 parts per annum of silicone oil having a viscosity at 25°C less than 150,000 mPa.s, and 0.2 to 5 parts per annum of a crosslinking agent.

Description

Title of the invention: THERMAL INTERFACE MATERIAL

[0001] The present invention relates to a thermal interface material which can be used in particular to extract heat from an element by generating it, for example in the field of accumulator batteries.

[0002] Lithium-ion technology is increasingly used in batteries for electric vehicles whose propulsion requires the use of very high-power batteries. This technology requires an optimal operating temperature range for the battery, on the one hand to fully benefit from the reserve power but also and above all to avoid damage during repeated charge / discharge cycles. Indeed, the high electrical powers involved during use (battery discharging) or during recovery (battery charging) cause significant heating. To prevent this type of damage, battery temperature regulation / control systems called BMS (Battery Management System) are generally used.The thermal component of the BMS typically includes heat exchangers with circulating heat transfer fluids (cooling table) and thermal relays that extract heat from the coil. These thermal relays (or thermal interfaces) are called TMMs or TIMs (Thermal Management / Interface Materials). TMMs come in several forms: gap fillers and pads.

[0003] Space fillers are liquid compositions that are crosslinked at room temperature to freeze the filling of interstitial volumes between the battery and the cooling table. The pads are solid compositions that are shaped into plates of given thickness. The placement of the pads in the battery packs requires mechanical crushing to ensure intimate contact between the battery and the cooling table. This placement requires high deformability so as not to lead to rupture of the pads.

[0004] The thermal conduction property that the pads must have generally requires a high volume percentage of thermally conductive fillers in the composition of the TMM. However, the increase in the thermally conductive filler content must not be at the expense of the electrical resistivity of the pads.

[0005] There is therefore a real need to find a good balance between a thermal conductivity greater than 1.5 W / mK, preferably greater than 2 W / mK, and an electrical resistivity greater than 10E+03 ohm.m, preferably greater than 10E+09 ohm.m.

[0006] Document CN112831187A describes elastomer-based compositions silicone comprising spherical alumina, alumina nitride, silicone oil and 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, exhibit good thermal conductivity, strength and breaking strength.

[0007] Continuing its research, the Applicant unexpectedly discovered that the combined use of silicone rubber, a specific mixture of thermally conductive fillers in certain proportions, silicone oil and crosslinking agent, at particular rates, makes it possible to solve the aforementioned technical problem by further improving the thermal conductivity while maintaining sufficient electrical resistivity.

[0008] Thus, the invention relates to a thermal interface material based on at least: - an elastomeric matrix comprising 85 to 100 parts per unit area of ​​silicone rubber having a mass average molar mass, Mw, in the range of 150 to 1000 kg / mol, - from 500 to 1,300 pce of a thermally conductive filler comprising alumina and graphite, the volume percentage of graphite in the thermally conductive filler being in the range from 2% to 12%, and the total volume percentage of alumina and graphite in the thermally conductive filler being greater than 55%, - from 15 to 150 pce of silicone oil having a viscosity at 25°C of less than 150,000 mPa.s, and - from 0.2 to 5 pce of a crosslinking agent. I- DEFINITIONS

[0009] The expression "composition based on" means a composition comprising the mixture and / or the in situ reaction product of the different constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the different phases of manufacture of the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state. The term "elastomer matrix" means all the elastomers in the composition.

[0010] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts of elastomer present in the rubber composition considered.

[0011] In this document, unless expressly indicated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0012] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the range of values ​​from more than a to less than b (i.e., excluding limits a and b) while any interval of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict limits a and b). In the present, when an interval of values ​​is designated by the expression "from a to b", we also and preferentially designate the interval represented by the expression "between a and b".

[0013] The volume percentage of a component in a mixture is defined as the volume of the component divided by the sum of the volumes of all the components used to make that mixture, multiplied by one hundred. In the case of the volume percentage of a component in the thermal interface material, it is defined as the volume of the component divided by the sum of the volumes of all the components used to make the thermal interface material before crosslinking.

[0014] The compounds mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already used, that is to say, they may be partially or totally derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, polymers, plasticizers, fillers, etc. II- DESCRIPTION OF THE INVENTION II-1 Elastomeric Matrix

[0015] According to the invention, the elastomer matrix of the thermal interface material is based on 85 to 100 phr of silicone rubber having a mass-average molar mass (Mw) in a range from 150 to 1,000 kg / mol. Below 150 kg / mol, the silicone rubber has a consistency and viscoelastic behavior of the silicone such that it is difficult to handle and implement. In addition, if the Mw of the silicone rubber is too low, the effectiveness of the crosslinking is reduced. Above 1,000 kg / mol, the silicone rubber has a high consistency and its implementation becomes complex and requires significant transformation energies. Preferably, the silicone rubber has an Mw in a range from 300 to 900 kg / mol, preferably from 500 to 800 kg / mol.

[0016] The macrostructure (Mw, Mn and Ip) of silicone rubber is determined by size exclusion chromatography (SEC): tetrahydrofuran solvent; temperature 35°C; concentration 1 g / l; flow rate 1 ml / min; solution filtered on a 0.45 pm porosity filter before injection; Moore calibration with polystyrene standards; set of 3 "WATERS" columns in series ("STYRAGEL" HR4E, HR1 and HR0.5); detection by differential refractometer ("WATERS 2410") and its associated operating software ("WATERS EMPOWER").

[0017] The thermal interface material according to the invention may comprise a single or a A silicone rubber blend exhibiting the aforementioned Mw values. In particular, the silicone rubber is selected from the group consisting of polydimethylsiloxanes (PDMS), polymethylarylsiloxanes (especially polymethylphenylsiloxanes), and mixtures thereof. Preferably, the silicone rubber is selected from the group consisting of PDMS and mixtures thereof.

[0018] The silicone rubber may have vinyl functions. The silicone rubber may, for example, not have a vinyl function or have one at a molar level which is less than 2%, preferably less than 1%, preferably less than 0.5%. When the silicone rubber has vinyl functions, the molar fraction of vinyl functions within the silicone rubber may be between 0.01% and 2%, preferably between 0.05% and 1%, preferably between 0.08% and 0.5%.

[0019] The mole fraction of vinyl functional group within silicone rubber is determined by ¹H,¹³C NMR spectroscopy. The NMR spectra are recorded on a Brüker Avance III 500 MHz spectrometer equipped with a 5 mm BBIz-grad "broadband" cryo-probe. The quantitative ¹H NMR experiment uses a single 30° pulse sequence and a 5-second repetition delay between each acquisition. 64 to 256 accumulations are performed. The quantitative ¹³C NMR experiment uses a single 30° pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. The two-dimensional ¹H / ¹³C experiments are used to determine the polymer structure. The NMR measurements are performed at 25°C. the copolymers being in solution in a deuterated solvent (approximately 25mg of elastomer in ImL), generally deuterated chloroform (CDC13).

[0020] The elastomer matrix may comprise elastomers other than silicone rubber, but this is neither mandatory nor preferred. Preferably, the elastomer matrix does not comprise any elastomer other than silicone rubber having an Mw in a range from 150 to 1000 kg / mol or comprises less than 15 phr, preferably less than 10 phr, preferably less than 5 phr. More preferably, the elastomer matrix comprises only, i.e. 100 phr, silicone rubber having an Mw in a range from 150 to 1000 kg / mol, preferably from 300 to 900 kg / mol, preferably from 500 to 800 kg / mol.

[0021] As an example of silicone rubber useful for the purposes of the invention and commercially available, mention may be made of Elastosil® R401-10, Elastosil® R401-25, Elastosil® R401-30, Elastosil® R401-50, Elastosil®R401-70, Elastosil®R401-75 or Elastosil® R401-90 from the company Wacker. II-2 Thermally conductive charge

[0022] The thermal interface material according to the invention is based on 500 to 1300 pce of a thermally conductive filler comprising alumina and graphite, the the volume percentage of graphite in the thermally conductive filler being in the range from 2% to 12%, and the total volume percentage of alumina and graphite in the thermally conductive filler being greater than 55%.

[0023] The thermally conductive filler may comprise thermally conductive fillers other than alumina and graphite, but this is neither mandatory nor preferred. Advantageously, the total volume percentage of alumina and graphite in the thermally conductive filler is greater than 60%, preferably greater than 75%, preferably greater than 90%. In other words, the thermally conductive filler preferably does not comprise any filler other than alumina and graphite, or comprises less than 40% by mass, preferably less than 25% by mass, preferably less than 10% by mass.

[0024] The total volume percentage of alumina and graphite in the thermally conductive filler may in particular be 100%. In this case, the volume percentage of alumina in the thermally conductive filler is within a range of 88% to 98%.

[0025] The volume percentage of graphite in the thermally conductive charge is preferably in the range of 2% to 10%, preferably 3% to 7%, preferably 4% to 6%.

[0026] In addition, the volume percentage of graphite in the thermal interface material is advantageously within a range of 1% to 7%, preferably 2% to 6%, preferably 2% to 4%.

[0027] The volume percentage of alumina in the thermally conductive charge is preferably in a range from more than 10% to 98%, preferably from 93% to 97%, preferably from 94% to 96%.

[0028] In addition, the volume percentage of alumina in the thermal interface material is advantageously within a range of 44% to 69%, preferably from 48% to 63%, preferably from 53% to 61%.

[0029] The alumina can be in different forms, in particular in the form of particles. Preferably, the alumina is present in the form of particles whose median diameter D50 is in a range from 2 to 150 pm, preferably from 10 to 100 pm, preferably from 20 to 70 pm. The D50 represents the diameter of the particles for which 50% of the volume of all the particles has a smaller diameter and 50% of the volume a larger diameter.

[0030] As an example of commercially available alumina, mention may be made of Silatherm® 1432-006 or 1432-400 or Silatherm ®VST 1432-006 or VST1432-400 from the company Quarzwerke.

[0031] Graphite can be present in different forms, in particular in the form of crystals. Preferably, the graphite is present in the form of crystals whose diameter D90 is in the range of 20 to 60 pm, preferably 30 to 55 pm, preferably 40 to 50 pm. D90 represents the particle diameter for which 90% of the volume of all particles has a smaller diameter and 10% of the volume has a larger diameter.

[0032] Examples of commercially available graphite include synthetic graphites such as TIMREX KS44, TIMREX PP44 or CThermOOl from Imerys, or natural graphites such as M100 from Imerys.

[0033] Advantageously, the rate of the thermally conductive filler in the thermal interface material according to the invention is within a range from 600 to 1,250 phr, preferably from 700 to 1,200 phr, preferably from 800 to 1,100 phr.

[0034] Regardless of the pce rate of thermally conductive filler in the thermal interface material, it is preferable that the volume rate of the thermally conductive filler in the thermal interface material is within a range from 45% to 70%, preferably from 50% to 65%, preferably from 55% to 63%. II-3 Silicone oil

[0035] The thermal interface material according to the invention is based on 15 to 150 pce of silicone oil having a viscosity at 25°C of less than 150,000 rnPa.s.

[0036] The viscosity of silicone oil is determined at 25°C and at atmospheric pressure, according to the “Brookfield” technique. Brookfield viscosity characterizes liquid substances in a known manner. The apparent viscosity according to the Brookfield method is measured at a given temperature (for example at 25°C) according to the European and international standard EN ISO 2555 (1999). For example, a type A viscosimeter (for example model RVT) or type B (for example model HAT) is used at a rotation frequency preferably equal to 10 or 20 min *, with a spindle number (1 to 7) adapted to the measured viscosity range (according to Annex A of standard EN ISO 2555). The viscosity is expressed in rnPa.s or centipoise (cP) (1 cP = 1 rnPa.s).

[0037] Advantageously, the silicone oil has a viscosity at 25°C in a range from 20 to 90,000 rnPa.s, preferably from 40 to 50,000 rnPa.s, preferably from 50 to 20,000 rnPa.s. More preferably, the silicone oil has a viscosity at 25°C in a range from 20 to 20,000 rnPa.s, preferably from 40 to 5,000 rnPa.s, preferably from 50 to 2,000 rnPa.s.

[0038] The silicone oils may or may not be functionalized. Preferably, the silicone oil is a silicone oil having no hydroxyl function and / or no vinyl function. More preferably, the silicone oil has no polar function and / or no function comprising a double bond.

[0039] As an example of silicone oil useful for the purpose of the invention and available in In the trade, we can mention the grades AK-50, AK-100, AK-1000, AK-10000 or even the grade AK-100000 from the Wacker company.

[0040] The level of silicone oil is in a range from 15 to 150 phr. Outside this range, it has been found that the mechanical properties (elongation at break, breaking stress) were not satisfactory at levels of thermally conductive filler in accordance with the invention. Preferably, the level of silicone oil in the thermal interface material is in a range from 20 to 130 phr, preferably from 50 to 120 phr, preferably from 80 to 110 phr.

[0041] Advantageously, the mass ratio of the thermally conductive filler to the silicone oil is within a range from more than 5 to 50, preferably from 10 to 30, preferably from 15 to less than 25. II-4 Crosslinking agent

[0042] The thermal interface material according to the invention is based on 0.2 to 5 pce of a crosslinking agent.

[0043] The crosslinking agent may be any crosslinking agent for crosslinking a silicone rubber. Advantageously, the crosslinking agent is a peroxide or a mixture of several peroxides. It may be any peroxide known to those skilled in the art. Among the peroxides, well known to those skilled in the art, it is preferable to use an organic peroxide in the context of the present invention.

[0044] By "organic peroxide" is meant an organic compound, i.e. containing carbon, comprising a -OO- group (two oxygen atoms linked by a single covalent bond). During the crosslinking process, the organic peroxide decomposes at its unstable 0-0 bond into free radicals. These free radicals allow the creation of the crosslinking bonds.

[0045] The organic peroxide is preferably selected from the group comprising or consisting of dialkyl peroxides, monoperoxycarbonates, diacyl peroxides, peroxyketals or peroxyesters.

[0046] Preferably, the dialkyl peroxides are selected from the group comprising or consisting of dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-amylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(t-amylperoxy)hexyne-3, a,a'-di-[(t-butyl-peroxy)isopropyl]benzene, a,a'-di-[(t-amyl-peroxy)isopropyl]benzene, di-t-amyl peroxide, 1,3,5-tri-[(t-butylperoxy)isopropyl]benzene, l,3-dimethyl-3-(t-butylperoxy)butanol, and l,3-dimethyl-3-(t-amylperoxy)butanol.

[0047] Certain monoperoxycarbonates such as OO-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate, OO-tert-butyl-O-isopropyl monoperoxycarbonate and OO- tert-amyl-O-2-ethyl hexyl monoperoxycarbonate, may also be used.

[0048] Among the diacyl peroxides, the preferred peroxide is benzoyl peroxide.

[0049] Among the peroxyketals, the preferred peroxides are selected from the group comprising or consisting of 1,1-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl 4,4-di-(t-butylperoxy)valerate, ethyl 3,3-di-(t-butylperoxy)butyrate, 2,2-di-(t-amylperoxy)-propane, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane (or methyl ethyl ketone peroxide cyclic trimer), 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, n-butyl 4,4-bis(t-amylperoxy)valerate, 3,3-di(t-amylperoxy)butyrate ethyl, l,l-di(t-butylperoxy)cyclohexane, l,l-di(t-amylperoxy)cyclohexane and mixtures thereof. Preferably, the peroxyesters are selected from the group consisting of tert-butylperoxybenzoate, tert-butylperoxy-2-ethylhexanoate and tert-butylperoxy-3,5,5-trimethylhexanoate.

[0050] In summary, the organic peroxide is, particularly preferably, selected from the group consisting of dicumyl peroxide, aryl peroxides, diaryl peroxides, diacetyl peroxide, benzoyl peroxide, dibenzoyl peroxide, ditertbutyl peroxide, tertbutylcumyl peroxide, 2,5-bis(tertbutylperoxy)-2,5-dimethylhexane, n-butyl-4,4'-di(tert-butylperoxy) valerate, OO-(t-butyl)-O-(2-ethylhexyl) monoperoxycarbonate, tert-butyl peroxyisopropyl-carbonate, tert-butyl peroxybenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,3(4)-bis(tert-butylperoxyisopropyl)benzene and their mixtures.More preferably, the organic peroxide is selected from the group consisting of dicumyl peroxide, n-butyl-4,4'-di(tert-butylperoxy)-valerate, OO-(t-butyl) O-(2-ethylhexyl) monoperoxycarbonate, tert-butyl peroxyisopropyl-carbonate, tert-butyl peroxybenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, l,3(4)-bis(tert-butylperoxyisopropyl)benzene and mixtures thereof.

[0051] As examples of peroxides that can be used in the context of the present invention and are commercially available, mention may be made of “Dicup” from the company Hercules Powder Co., “Perkadox Y12” from the company Noury ​​van der Lande, “Peroximon F40” from the company Montecatini Edison SpA, “Trigonox” from the company Noury ​​van der Lande, “Varox” from the company RTVanderbilt Co., or “Luperko” from the company Wallace & Tiernan, Inc. II-5 Possible additives

[0052] The thermal interface material may optionally also comprise all or part of the usual additives usually used in TMM, such as for example pigments, protective agents, antioxidants, flame retardants. II-6 Preparation of compositions

[0053] The materials in accordance with the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: - a first phase of working or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents are introduced into a suitable mixer such as a conventional internal mixer (for example of the "Banbury" type), in particular the elastomer matrix, the thermally conductive filler, any other various additives, with the exception of the crosslinking system. The incorporation of the filler into the elastomer can be carried out in one or more stages by thermomechanical mixing.In cases where the filler is already incorporated, in whole or in part, into the elastomer in the form of a masterbatch, as described, for example, in applications WO 97 / 36724 or WO 99 / 16600, the masterbatch is directly mixed, and where applicable, other elastomers or fillers present in the composition that are not in masterbatch form, as well as any other miscellaneous additives other than the crosslinking system, are incorporated. The non-productive phase can be carried out at high temperature, up to a maximum temperature between 80°C and 150°C, preferably between 100°C and 120°C, for a duration generally between 2 and 10 minutes. - a second phase of mechanical work (so-called "productive" phase), which can be carried out in an external mixer such as a cylinder mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and everything is then mixed for a few minutes, for example between 5 and 15 min.

[0054] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0055] The final composition thus obtained is then calendered, for example, in the form of a sheet or a plate.

[0056] These products can then be used to manufacture thermal interface materials such as thermally conductive pads (or cushions) or thermally conductive sheets, according to techniques known to those skilled in the art. The composition can, in particular, be molded and cross-linked, for example, at a temperature between 130°C and 200°C, under pressure, to form a thermal interface pad. II-7 Thermal interface material

[0057] The thermal interface material according to the invention can be used for any application for extracting the heat emitted by an object. For example, it is particularly well suited to transferring the heat emitted by an electric vehicle battery during use or during charging.

[0058] The thermal interface material according to the invention may be in any form and at any thickness enabling it to perform its function. Preferably, the thermal interface material is chosen from the group consisting of thermally conductive pads and thermally conductive sheets. Furthermore, the thermal interface material preferably has a thickness in a range from 0.2 to 10 mm, preferably from 0.5 to 8 mm, preferably from 1 to 6 mm. III- EXAMPLES III-1 Preparation of compositions

[0059] In the following examples, the rubber compositions were produced as described in point II.6 above. In particular, the “non-productive” phase was carried out in a 0.4 liter mixer for 3.5 minutes, for an average paddle speed of 50 revolutions per minute until a maximum drop temperature of 90°C was reached. The “productive” phase was carried out in a cylinder tool at 40°C for 5 to 10 minutes. The crosslinking of the composition was carried out at a temperature of 150°C for 30 minutes, under pressure. From the crosslinked plates obtained, test pieces were cut out for the purpose of measuring thermal conduction and electrical resistivity. III-2 Measurements and tests used Thermal conductivity

[0060] Cylindrical samples measuring 40 mm x 8 mm were made by molding. A TPS 1000 device from the Hotdisk brand is used to determine the thermal conductivity by the TPS (Transient Plane Source) method. A heat flux with a power of 80 mW is applied for 10 seconds to the sample. The thermal conductivity of the sample is thus determined by the observed temperature variation, itself determined by a measurement of the variation in electrical resistance of the material via a Wheatstone bridge in the sample. Electrical resistivity

[0061] The electrical resistivity was measured using a KEITHLEY 6517B resistance electrometer. A disc-shaped specimen of the crosslinked composition with a diameter of 10 mm and a thickness of between 1.5 and 2 mm was placed in contact between two steel studs of the same diameter and fixed using a mini clamp to obtain intimate contact between the specimen and the two studs. Each of the steel studs on either side of the specimen were connected to the voltage source of the electrometer. A voltage of 100V was applied and the resistivity was determined by Ohm's law. The results are expressed in Ohm.m. When the electrical resistivity was too low to be measured, the indication "ND" for "not detectable" was reported in the tables below. III-3 Rubber composition tests

[0062] The examples presented below aim to compare the thermal conductivity and electrical resistivity properties of compositions in accordance with the present invention (C1 to C5) with control compositions (T1 to T7).

[0063] Tables 1 and 2 present the compositions tested (in pieces), as well as the results obtained.

[0064] The compositions according to the invention differ from the control compositions in particular by the volume percentage of graphite in the composition.

[0065] [Tables 1] Composition Tl T2 T3 T4 T5 T6 T7 Silicone elastomer (a) 100 100 100 100 100 100 100 Graphite (b) 0 0 185 65 87 130 175 % by volume of (b) in the thermally conductive filler 0% 0% 100% 75% 20% 30% 40% % by volume of (b) in the composition 0% 0% 30% 7.5% 10% 15% 20% Alumina (c) 712 310 0 608 570 500 430 % by volume of (c) in the thermally conductive filler 100% 100% 0% 85% 80% 20% 60% % by volume of (c) in the composition 50% 30% 0% 42.5% 40% 35% 30% Total th. charge 712 310 185 673 657 630 605 % by volume of (b) + (c) in the composition 50% 30% 30% 50% 50% 50% 50% Silicone oil (d) 100 100 100 100 100 100 100 Peroxide (e) 1 1 1 1 1 1 1 Thermal conductivity (W / mK) 1.18 0.50 2.71 2.11 2.46 3.35 4.51 Electrical resistivity (Ohm.m under 100V) 2.5E+ 12 2E+12 ND ND ND ND ND

[0066] (a) Wacker R401 / 70 silicone elastomer and mass Mn= 350k g / mol, mass Mw= 620kg / mol (SEC RI PS) (b) TIMREX KS44 D90 45pm graphite from Imerys (c) Alumina Silatherm 1432-006 from the company Quarzwerke with a D50 size of 46pm (d) Wacker AK100 silicone oil with a viscosity of 100 mPa.s (e) Dicumyl peroxide from Sigma-Aldrich

[0067] [Tables2] Composition Cl C2 C3 C4 C5 Silicone elastomer (a) 100 100 100 100 100 Graphite (b) 43 48 29 54 32 % by volume of (b) in the thermally conductive filler 10% 9% 5.5% 8% 5% % by volume of (b) in the composition 5% 5% 3% 5% 3% Alumina (c) 642 790 822 980 1015 % by volume of (c) in the thermally conductive filler 90% 91% 94.5% 92% 95% % by volume of (c) in the composition 45% 50% 52% 55% 57% Total th. charge 685 838 851 1034 1043 % by volume of (b) + (c) in the composition 50% 55% 55% 60% 60% Silicone oil (d) 100 100 100 100 100 Peroxide (e) 1 1 1 1 1 Thermal conductivity (W / mK) 1.67 2.1 1.8 2.7 2.25 Electrical resistivity (Ohm.m under 100V) l,2E+0 9 1.1E+O 6 1.3E+1 2 9.7E+0 3 4.1E+1 1

[0068] (a) to (e) See Table 1

[0069] The results presented in Tables 1 and 2 above show that the compositions in accordance with the invention all have a thermal conductivity greater than 1.5 W / mK and an electrical resistivity greater than 10E+03 ohm.m. Composition C5 is particularly interesting because it has a thermal conductivity greater than 2 W / mK, and an electrical resistivity greater than 10E+09 ohm.m.

Claims

Claims

1. Thermal interface material based on at least: - an elastomer matrix comprising from 85 to 100 phr of silicone rubber having a mass average molar mass, Mw, in a range from 150 to 1,000 kg / mol, - from 500 to 1,300 phr of a thermally conductive filler comprising alumina and graphite, the volume percentage of graphite in the thermally conductive filler being in a range from 2% to 12%, and the total volume percentage of alumina and graphite in the thermally conductive filler being greater than 55%, - from 15 to 150 phr of silicone oil having a viscosity at 25°C of less than 150,000 mPa.s, and - from 0.2 to 5 phr of a crosslinking agent.

2. The thermal interface material of claim 1, wherein the silicone rubber is selected from the group consisting of polydimethylsiloxanes (PDMS), polymethylarylsiloxanes and mixtures thereof, preferably the silicone rubber is selected from the group consisting of polydimethylsiloxanes and mixtures thereof.

3. Thermal interface material according to any one of the preceding claims, wherein the rate of the thermally conductive filler is in a range from 600 to 1250 phr, preferably from 700 to 1200 phr, preferably from 800 to 1100 phr.

4. A thermal interface material according to any preceding claim, wherein the total volume percentage of alumina and graphite in the thermally conductive filler is greater than 60%, preferably greater than 75%, preferably greater than 90%.

5. Thermal interface material according to any one of the preceding claims, wherein the volume percentage of graphite in the thermally conductive filler is in a range from 2% to 10%, preferably from 3% to 7%, preferably from 4% to 6%.

6. A thermal interface material according to any preceding claim, wherein the volume percentage of graphite in the thermal interface material is within a range ranging from 1% to 7%, preferably from 2% to 6%, preferably from 2% to 4%.

7. A thermal interface material according to any preceding claim, wherein the volume percentage of the thermally conductive filler in the thermal interface material is in a range from 45% to 70%, preferably from 50% to 65%, preferably from 55% to 63%.

8. Thermal interface material according to any one of the preceding claims, in which the alumina is present in the form of particles whose median diameter D50 is in a range from 2 to 150 pm, preferably from 10 to 100 pm, preferably from 20 to 70 pm.

9. Thermal interface material according to any one of the preceding claims, wherein the graphite is present in the form of crystals whose diameter D90 is in a range from 20 to 60 pm, preferably from 30 to 55 pm, preferably from 40 to 50 pm.

10. A thermal interface material according to any preceding claim, wherein the silicone oil has a viscosity at 25°C in a range of 20 to 20,000 mPa.s, preferably 40 to 5,000 mPa.s, preferably 50 to 2,000 mPa.s.

11. Thermal interface material according to any one of the preceding claims, wherein the silicone oil content is in a range from 20 to 130 phr, preferably from 50 to 120 phr, preferably from 80 to 110 phr.

12. A thermal interface material according to any preceding claim, wherein the mass ratio of the thermally conductive filler to the silicone oil is in a range of more than 5 to 50, preferably 10 to 30, preferably 15 to less than 25.

13. Thermal interface material according to any one of the preceding claims, wherein the crosslinking agent is an organic peroxide preferably selected from the group consisting of dicumyl peroxide, aryl peroxides, diaryl peroxides, diacetyl peroxide, benzoyl peroxide, dibenzoyl peroxide, ditertbutyl peroxide, tertbutylcumyl peroxide, 2,5-bis(tertbutylperoxy)-2,5-dimethylhexane, n-butyl-4,4'-di(tert-butylperoxy) valerate, OO-(t-butyl)-O-(2-ethylhexyl) monoperoxycarbonate, tert-butyl per- oxyisopropylcarbonate, tert-butyl peroxybenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, l,3(4)-bis(tert-butylperoxyisopropyl)benzene and mixtures thereof.

14. A thermal interface material according to any preceding claim, said material being selected from the group consisting of thermally conductive pads and thermally conductive sheets.

15. Thermal interface material according to any one of the preceding claims, said material having a thickness in a range from 0.2 to 10 mm, preferably from 0.5 to 8 mm, preferably from 1 to 6 mm.