Thermal interface material

Abstract

The invention relates to a thermal interface material, such as thermally conductive pads or thermally conductive sheets, having a good compromise between thermal conductivity and electrical resistivity. The material is based on: - 100 phr of silicone rubber; - from 500 to 1300 phr of a thermally conductive filler comprising alumina and silicon carbide, the alumina and the silicon carbide representing more than 90% by weight of the thermally conductive filler, the total percentage by volume of the alumina and of the silicon carbide in the thermal interface material being within a range extending from 45 to 70%, and the ratio between the percentage by volume of the silicon carbide and the total percentage by volume of the thermally conductive filler being within a range extending from 0.02 to 0.4; - from 15 to 150 phr of silicone oil; and - from 0.2 to 5 phr of a crosslinking agent, the crosslinking agent preferably being a peroxide, the percentages by volume being expressed relative to the sum of the volumes of the constituents of the interface material.

Description

[0001] THERMAL INTERFACE MATERIAL

[0002] The present invention relates to a thermal interface material usable in particular for extracting heat from an element by generating, for example in the field of accumulator batteries.

[0003] Lithium-ion technology is increasingly used in batteries for electric vehicles, whose propulsion requires very high-power batteries. This technology demands an optimal operating temperature range for the battery, both to fully utilize the available power and, more importantly, to prevent damage during repeated charge / discharge cycles. Indeed, the high electrical power involved during use (battery discharging) or during regenerative braking (battery charging) generates significant heat. To prevent this type of damage, battery temperature regulation / control systems called BMS (Battery Management Systems) are generally used.The thermal component of a BMS typically includes heat exchangers with circulating heat transfer fluids (cooling table) and thermal interface materials (TMMs) that extract heat from the coil. These TMMs (or thermal interfaces) are called TMMs or TIMs (Thermal Management / Interface Materials). TMMs come in several forms: gap fillers and pads.

[0004] Space fillers are liquid compositions that are cross-linked at room temperature to solidify the filling of interstitial volumes between the drum kit and the cooling table. Pads, on the other hand, are solid compositions that are formed into plates of a specific thickness. Placing the pads in the drum packs requires mechanical compression to ensure close contact between the drum kit and the cooling table. This placement requires a high degree of deformability to prevent the pads from breaking.

[0005] The thermal conductivity required of the pads generally necessitates a high volume percentage of thermally conductive fillers in the TMM composition. However, increasing the thermally conductive filler content must not compromise the electrical resistivity of the pads.

[0006] 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+06 ohm.m, preferably greater than 10E+09 ohm.m. Document CN105754341A describes that compositions based on silicone elastomer including, among other things, spherical alumina, silicon carbide, silicone oil and 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, exhibit thermal conductivity, strength and tensile strength properties.

[0007] Continuing her 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 thermal conductivity while maintaining sufficient electrical resistivity.

[0008] Thus, the invention relates to a thermal interface material comprising:

[0009] - 100 pieces of silicone rubber

[0010] - 500 to 1,300 pieces of a thermally conductive filler comprising alumina and silicon carbide, with alumina and silicon carbide representing more than 90% by mass of the thermally conductive filler, the total volume percentage of alumina and silicon carbide in the thermal interface material being in the range of 45 to 70% and the ratio between the volume percentage of silicon carbide and the total volume percentage of the thermally conductive filler being in the range of 0.02 to 0.4,

[0011] - 15 to 150 pieces of silicone oil, and

[0012] - 0.2 to 5 parts of a crosslinking agent, the crosslinking agent preferably being a peroxide, the volume percentages being expressed in relation to the sum of the volumes of the constituents of the interface material.

[0013] I- DEFINITIONS

[0014] The term "composition based on" refers to a composition comprising a mixture and / or the in situ reaction product of the various constituents used, some of which may react and / or are intended to react with each other, at least partially, during the different manufacturing phases of the composition; the composition may thus be in a fully or partially crosslinked state or in a non-crosslinked state. "Elastomeric matrix" refers to all the elastomers in the composition. The term "part by weight per hundred parts by weight of elastomer" (or pw) refers, for the purposes of this invention, to the proportion, by mass per hundred parts of elastomer, present in the rubber composition in question.

[0015] In this document, unless expressly stated otherwise, all percentages (%) shown are percentages (%) by mass.

[0016] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​from greater than a to less than b (that is, excluding the bounds a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (that is, including the strict bounds a and b). In this context, when an interval of values ​​is designated by the expression "from a to b," it also and preferably refers to the interval represented by the expression "between a and b."

[0017] 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 the mixture, multiplied by one hundred. In the case of the volume percentage of a component in a 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.

[0018] The compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they may be partially or entirely derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of previously used materials; that is, they may be partially or entirely produced through a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, polymers, plasticizers, fillers, etc.

[0019] II- DESCRIPTION OF THE INVENTION

[0020] II- 1 Silicone rubber (elastomer matrix)

[0021] According to the invention, silicone rubber constitutes the elastomeric matrix of the thermal interface material, which is therefore 100 parts per unit area (P / m³) of silicone rubber. The silicone rubber can have a mass average molar density (Mw) in the range of 150 to 1000 kg / mol. Below 150 kg / mol, the silicone rubber exhibits a consistency and viscoelastic behavior that make its handling and processing complex. Furthermore, if the Mw of the silicone rubber is too low, the crosslinking efficiency is reduced. Above 1000 kg / mol, the silicone rubber has a high consistency, making its processing complex and requiring significant energy input. Preferably, the silicone rubber has an Mw in the range of 300 to 1000 kg / mol, and even more preferably, 500 to 800 kg / mol.

[0022] 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").

[0023] The thermal interface material according to the invention may comprise a single or a mixture of silicone rubbers having 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.

[0024] According to a preferred embodiment, the silicone rubber is either functional or non-functional, preferably functional.

[0025] Silicone rubber may contain vinyl functionalities. The amount of vinyl functionalities in silicone rubber may be less than 2%, preferably less than 1%, and preferably less than 0.5%. When silicone rubber contains vinyl functionalities, the mole fraction of vinyl functionalities within the silicone rubber may be between 0.01% and 2%, preferably between 0.05% and 1%, and preferably between 0.08% and 0.5%. Advantageously, silicone rubber contains vinyl functionalities, preferably with a mole fraction within the aforementioned ranges.

[0026] The mole fraction of vinyl function within silicone rubber is determined by NMR spectroscopy 1 H, 13C. NMR spectra are recorded on a Brüker Avance III 500 MHz spectrometer equipped with a 5 mm BBIz-grad "broadband" cryo-probe. The quantitative 'H' NMR experiment uses a single 30° pulse sequence and a 5-second repetition delay between each acquisition. 64 to 256 accumulations are performed. The NMR experiment 13 Quantitative C-scanning uses a simple 30° pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. Two-dimensional experiments are used to determine the structure of the polymers. NMR measurements are carried out at 25°C with the copolymers in solution in a deuterated solvent (approximately 25 mg of elastomer in µL), generally deuterated chloroform (CDCh).

[0027] As an example of silicone rubber useful for the purpose of the invention and available commercially, we can cite Elastosil® R401-10, Elastosil® R401-25, Elastosil® R401-30, Elastosil® R401-50, Elastosil® R401-70, Elastosil® R401-75 or Elastosil® R401-90 from the Wacker company.

[0028] II-2 Thermally conductive load

[0029] The thermal interface material according to the invention is based on 500 to 1300 parts per annum of a thermally conductive filler comprising alumina and silicon carbide (SiC).

[0030] The thermally conductive charge may include thermally conductive charges other than alumina and silicon carbide, but this is neither required nor preferred.

[0031] Advantageously, alumina and silicon carbide constitute more than 95% by mass, preferably 100% by mass of the thermally conductive charge.

[0032] According to a preferred embodiment, the total volume percentage of alumina and silicon carbide in the thermal interface material is in the range of 50 to 65%.

[0033] According to a preferred embodiment, the ratio between the volume percentage of silicon carbide and the total volume percentage of the thermally conductive filler is in the range of 0.03 to 0.2.

[0034] Alumina can be found in various forms, particularly as particles. Preferably, alumina is present as particles with a median diameter D50 in the range of 2 to 150 pm, preferably 10 to 100 pm, and preferably 20 to 70 pm. D50 represents the particle diameter where 50% of the total particle volume has a smaller diameter and 50% has a larger diameter. Examples of commercially available alumina include Silatherm® 1432-006 or 1432-400, or Silatherm ©VST1432-006 or VST1432-400 from Quarzwerke.

[0035] Silicon carbide can be found in various forms, particularly as crystals. Preferably, silicon carbide is present as crystals with a diameter D50 in the range of 0.2 to 5 pm, preferably 0.3 to 3 pm, and preferably 0.4 to 2 pm. D50 represents the particle diameter where 50% of the total particle volume has a smaller diameter and 50% has a larger diameter.

[0036] Examples of commercially available silicon carbide include synthetic silicon carbides such as SIKA® Sintex 13C silicon carbide from Fiven, or F400 from Presi.

[0037] Advantageously, the rate of thermally conductive charge in the thermal interface material according to the invention is in a range of 600 to 1200 pc, preferably 700 to 1100 pc.

[0038] Whatever the percentage of thermally conductive filler in the thermal interface material useful to the needs of the invention, it is preferable that the total volume percentage of thermally conductive filler in the thermal interface material be in the range of 45% to 70%, preferably 50% to 65%, preferably 52% to 65%.

[0039] II-3 Silicone Oil

[0040] According to an advantageous embodiment of the invention, the silicone oil has a viscosity at 25°C in the range of 20 to 20,000 mPa.s, preferably from 40 to 5,000 mPa.s, preferably from 50 to 2,000 mPa.s.

[0041] The viscosity of silicone oil is determined at 25°C and atmospheric pressure using the Brookfield method. Brookfield viscosity is a well-known characteristic of liquid substances. Apparent viscosity according to the Brookfield method is measured at a given temperature (e.g., 25°C) in accordance with the European and international standard EN ISO 2555 (1999). For example, a type A viscometer (e.g., model RVT) or a type B viscometer (e.g., model HAT) is used, preferably at a rotation frequency of 10 or 20 minutes. 1 with a number of the moving part (1 to 7) adapted to the range of viscosity measured (according to Annex A of standard EN ISO 2555). Viscosity is expressed in mPa.s or centipoise (cP) (1 cP = 1 mPa.s).

[0042] Silicone oils may be functionalized or not. Preferably, silicone oil is a silicone oil without a hydroxyl group and / or a vinyl group. Even more preferably, silicone oil does not have a polar group and / or a group containing a double bond.

[0043] As an example of silicone oil useful for the needs of the invention and available commercially, we can cite the grades AK-50, AK-100, AK-1000, AK-10000 or even the grade AK-100000 from the Wacker company.

[0044] The silicone oil content is within a range of 15 to 150 parts per cubic meter (ppm). Outside this range, it has been found that the mechanical properties (elongation at break, tensile strength) are not satisfactory at thermally conductive load levels according to the invention. Preferably, the silicone oil content in the thermal interface material is within a range of 25 to 130 ppm, and more preferably from 40 to 100 ppm.

[0045] Advantageously, the mass ratio of the thermally conductive charge to the silicone oil is in a range of more than 5 to 50, preferably from 10 to 30, preferably from 15 to less than 25.

[0046] II-4 Crosslinking Agent

[0047] The thermal interface material according to the invention is based on 0.2 to 5 parts per part of a crosslinking agent.

[0048] The crosslinking agent can be any crosslinking agent capable of crosslinking silicone rubber. Advantageously, the crosslinking agent is a peroxide or a mixture of several peroxides. It can 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 for the purposes of this invention.

[0049] The term "organic peroxide" refers to an organic compound, that is, one containing carbon, with an -OO- group (two oxygen atoms linked by a single covalent bond). During the crosslinking process, the organic peroxide decomposes at its unstable O-O bond into free radicals. These free radicals enable the formation of the crosslinking bonds. The organic peroxide is preferably selected from the group comprising or consisting of dialkyl peroxides, monoperoxycarbonates, diacyl peroxides, peroxyketals, or peroxyesters.

[0050] 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, α,α'-di-[(t-butylperoxy)isopropyl]benzene, α,α'-di-[(t-amylperoxy)isopropyl]benzene, di-t-amyl peroxide, 1,3,5-tri-[(t-butylperoxy)isopropyl]benzene, 1,3-dimethyl-3-(t-butylperoxy)butanol, and 1,3-dimethyl-3-(t-amylperoxy)butanol.

[0051] Some monoperoxycarbonates such as OO-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate, OO-tert-butyl-O-isopropyl monoperoxycarbonate and OO-tert-amyl-O-2-ethylhexyl monoperoxycarbonate, can also be used.

[0052] Among the diacyl peroxides, the preferred peroxide is benzoyl peroxide.

[0053] Among the peroxyketals, preferred peroxides are chosen from the group comprising or consisting of l,l-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-l,4,7-triperoxynonane (or cyclic trimer of methyl ethyl ketone peroxide), 3,3,5,7,7-pentamethyl-l,2,4-trioxepane, n-butyl 4,4-bis(t-amylperoxy)valerate, ethyl 3,3-di(t-amylperoxy)butyrate, the 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.

[0054] In summary, the organic peroxide is, particularly preferred, chosen 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 peroxyisopropylcarbonate, tert-butyl peroxybenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,3(4)-bis(tert-butylperoxyisopropyl)benzene and mixtures thereof.Preferably, the organic peroxide is chosen from the group consisting of dicumyl peroxide, n-butyl-4,4'- di(tert-butylperoxy)-valerate, OO-(t-butyl) O-(2-ethylhexyl) monoperoxycarbonate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxybenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,3(4)-bis(tert-butylperoxyisopropyl)benzene and mixtures thereof.

[0055] Examples of commercially available peroxides usable within the framework of the present invention include "Dicup" from Hercules Powder Co., "Perkadox Y12" from Noury ​​van der Lande, "Peroximon F40" from Montecatini Edison SpA, "Trigonox" from Noury ​​van der Lande, "Varox" from RT Vanderbilt Co., and "Luperko" from Wallace & Tieman, Inc.

[0056] II-5 Possible Additives

[0057] The thermal interface material may optionally also include all or some of the usual additives typically used for this type of material, for example pigments, protective agents, antioxidants, flame retardants.

[0058] II-6 Preparation of compositions

[0059] Materials according to the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

[0060] - a first thermomechanical working or mixing phase (the 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 Z-blade mixer. These constituents include the silicone rubber (elastomeric matrix), the thermally conductive filler, any other miscellaneous additives, and the crosslinking system. The incorporation of the filler into the elastomeric matrix can be carried out in one or more stages by thermomechanical mixing. The non-productive phase can be carried out at a maximum temperature between 20°C and 60°C, preferably between 30°C and 50°C, for a duration generally between 20 and 60 minutes.

[0061] - a second mechanical working phase (the so-called "productive" phase), which can be carried out in an external mixer such as a roller 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 whole is then mixed for a few minutes, for example between 5 and 15 min.

[0062] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0063] The final composition thus obtained is then calendered, for example in the form of a sheet or a plate.

[0064] These products can then be used to manufacture thermal interface materials such as thermally conductive pads or sheets, according to techniques known to those skilled in the art. The composition can, for example, be molded and cross-linked at a temperature between 130°C and 200°C under pressure to form a thermal interface pad.

[0065] II-7 Thermal Interface Material

[0066] The thermal interface material according to the invention can be used for any application that allows the extraction of heat emitted by an object. For example, it is particularly well suited for transferring the heat emitted by an electric vehicle battery during use or while charging.

[0067] The thermal interface material according to the invention can be in any shape and thickness that allows 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 the range of 0.2 to 10 mm, preferably 0.5 to 8 mm, and preferably 1 to 6 mm.

[0068] III- EXAMPLES

[0069] III- 1 Preparation of compositions

[0070] In the following examples, the rubber compounds were prepared as described in section II.6 above. Specifically, the "non-productive" phase was carried out in a 0.6-liter Z-blade mixer (LINDEN Type LKB II) for 20 minutes at an average paddle speed of 30 rpm until a constant maximum temperature of 50°C was reached. The "productive" phase was carried out in a roller tool at 40°C for 5 to 10 minutes. The compound was then crosslinked at 150°C for 30 minutes under pressure. From the resulting crosslinked plates, test specimens were cut to measure thermal conductivity, electrical resistivity, and tensile mechanical properties (modulus and elongation).

[0071] III-2 Measurements and tests used

[0072] Thermal conductivity

[0073] Cylindrical samples measuring 40 mm x 8 mm were prepared by molding. A Hotdisk TPS 1000 instrument was used to determine thermal conductivity using the Transient Plane Source (TPS) method. A heat flux of 80 mW was applied to the sample for 10 seconds. The thermal conductivity of the sample was thus determined by the observed temperature change, which was itself determined by measuring the change in electrical resistance of the material via a Wheatstone bridge within the sample.

[0074] Electrical resistivity

[0075] Electrical resistivity was measured using the KEITHLEY 6517B resistance electrometer. A disc-shaped specimen of the cross-linked composition, 10 mm in diameter and 1.5 to 2 mm thick, was placed between two steel pads of the same diameter and secured with a mini clamp to ensure close contact between the specimen and the pads. Each of the steel pads on either side of the specimen was connected to the electrometer's voltage source. A voltage of 100 V was applied, and the resistivity was determined using Ohm's law. The results are expressed in ohm-meters (Ω·m). When the electrical resistivity was too low to be measured, the notation "ND" for "not detectable" was recorded in the tables below.

[0076] Mechanical properties

[0077] These tensile tests determine the elastic stresses and fracture properties. Processing the tensile recordings also allows for plotting the modulus curve as a function of elongation. The modulus used here is the nominal (or apparent) secant modulus measured at the first elongation, calculated by referring to the initial cross-section of the specimen. The tensile stresses (CR in MPa) and elongations at break (AR in %) are measured at 23°C ± 2°C, according to standard NF T 46-002 of September 1988. The tensile energy is equal to the product of the elongation at break and the tensile stress.

[0078] III-3 Tests of rubber compositions The examples presented below are intended to compare the thermal conductivity and electrical resistivity properties of compositions according to the present invention (Cl to C6)

[0079] 5 Table 1 presents the compositions tested (in pieces), as well as the results obtained.

[0080] The compositions according to the invention (Cl to C6) differ from the control compositions (Tl to T3) in that they include silicon carbide in the composition.

[0081] 10 The control compositions T1, T2 and T3 contain only alumina at 64%, 59% and 54% respectively by volume fraction and do not conform to the invention.

[0082] The compositions according to the invention Cl to C6 comprise 64% (Cl and C2), 59% (C2 and C3) and 54% (C4 and C5) of total volume fraction of alumina and silicon carbide as well as a volume fraction of silicon carbide of 2% in Cl, C3 and C5 and of 5% in C2, C4 and C6.

[0083] [Table 1]

[0084]

[0085] (a) Wacker company R401 / 30 silicone elastomer with mass Mw=740Kg / mol.

[0086] (b) Silatherm 1432-006 alumina from the Quarzwerke company, size D 50 is 46pm

[0087] (c) SIKA® Sintex 13C silicon carbide from the company FIVEN, size D 50 is 0.6pm.

[0088] 5 (d) Wacker AK 100 silicone oil with a viscosity of 100 cp and a mass of Mn=5kg / mol,

[0089] Mw=9 kg / mol (SEC RI PDMS).

[0090] (e) Dicumyl peroxide from Sigma-Aldrich

[0091] The results obtained indicate that thermal conductivity increases significantly when a portion of the alumina is replaced by silicon carbide (at 2% and 5% volume fractions) (Cl, C2 compared to T1; C3 and C4 compared to T2; and C5 and C6 compared to T3). Furthermore, and surprisingly, thermal conductivity evolves almost exponentially for a linear variation in the total volume fraction of the charge. In other words, the increase in thermal conductivity does not follow a linear variation with respect to the volume fraction of the thermally conductive charge; in fact, surprisingly, thermal conductivity increases much more rapidly than the volume fraction of the conductive charge.

[0092] The results obtained also show that the electrical resistivity is maintained above 1.01 E+06 ohm.m regardless of the volume fraction of silicon carbide introduced (2 or 5% by volume) and regardless of the voltage applied to determine this property. These values ​​correspond to compositions considered to be electrically insulating, just like the comparative control compositions T1, T2, and T3. It is clear that for a given volume fraction of thermally conductive filler, the partial replacement of alumina with silicon carbide allows for an increase in thermal conductivity while maintaining electrical insulating properties compared to compositions containing only alumina.

Claims

Demands 1. Thermal interface material comprising: 100 parts per annum of silicone rubber, 500 to 1,300 parts per annum of a thermally conductive filler comprising alumina and silicon carbide, the alumina and silicon carbide representing more than 90% by mass of the thermally conductive filler, the total volume percentage of alumina and silicon carbide in the thermal interface material being in the range of 45 to 70% and the ratio of the volume percentage of silicon carbide to the total volume percentage of the thermally conductive filler being in the range of 0.02 to 0.4, 15 to 150 parts per annum of silicone oil, and 0.2 to 5 parts per annum of a crosslinking agent, the crosslinking agent preferably being a peroxide, the volume percentages being expressed as a sum of the volumes of the constituents of the interface material.

2. Thermal interface material according to claim 1, wherein alumina and silicon carbide constitute more than 95% by mass, preferably 100% by mass of the thermally conductive filler.

3. Thermal interface material according to any one of the preceding claims, wherein the silicone rubber is functional, preferably it has vinyl functions.

4. Thermal interface material according to any one of the preceding claims, wherein silicone rubber is selected from the group consisting of polydimethylsiloxanes (PDMS), polymethylarylsiloxanes and mixtures thereof, preferably silicone rubber is selected from the group consisting of polydimethylsiloxanes and mixtures thereof.

5. Thermal interface material according to any one of the preceding claims, wherein the rate of thermally conductive charge is in the range of 600 to 1200 pc, preferably 700 to 1100 pc.

6. Thermal interface material according to any one of the preceding claims, wherein the total volume percentage of alumina and carbide of silicon in the thermal interface material is in a range of 50 to 65%.

7. Thermal interface material according to any one of the preceding claims, wherein the ratio between the volume percentage of silicon carbide and the total volume percentage of the thermally conductive filler is in the range of 0.03 to 0.

2.

8. Thermal interface material according to any one of the preceding claims, wherein the volume percentage of the thermally conductive filler in the thermal interface material is in the range of 50% to 65%, preferably 52% to 65%.

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

10. Thermal interface material according to any one of the preceding claims, wherein the silicon carbide is present in the form of crystals having a diameter D50 in the range of 0.2 to 5 pm, preferably 0.3 to 3 pm, preferably 0.4 to 2 pm.

11. Thermal interface material according to any one of the preceding claims, wherein the silicone oil has a viscosity at 25°C in the range of 20 to 20,000 mPa.s, preferably 40 to 5,000 mPa.s, preferably 50 to 2,000 mPa.s.

12. Thermal interface material according to any one of the preceding claims, wherein the silicone oil content is in the range of 25 to 130 parts per annum, preferably further from 40 to 100 parts per annum.

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, tert-butylcumyl 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 mixtures thereof.

14. Thermal interface material according to any one of the preceding claims, 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 the range of 0.2 to 10 mm, preferably 0.5 to 8 mm, preferably 1 to 6 mm.

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