Thermally conductive grease composition

Abstract

The thermally conductive grease composition of the present invention contains a base oil (A) and thermally conductive particles (B), wherein the thermally conductive particles (B) include aluminum nitride (B1) with an average particle size D50 of less than 70 μm and aluminum nitride (B2) with an average particle size D50 of 70 μm or more.

Description

Technical Field

[0001] This invention relates to a thermally conductive grease composition. This application claims priority based on Japan Patent Application No. 2024-193596, filed on November 5, 2024, the contents of which are incorporated herein by reference. Prior Technology

[0002] In electronic devices such as computers, automotive parts, and mobile phones, heat sinks and other cooling components are typically used to dissipate heat generated by heat-generating elements such as semiconductor components or mechanical parts. Thermal grease is used to improve the heat conduction efficiency of these cooling components.

[0003] For example, Patent Document 1 discloses a thermally conductive grease that transfers heat from a heating element to a cooling component, and contains: a base oil comprising at least one selected from a copolymer of an unsaturated dialkyl dicarboxylate and an α-olefin, and a polyα-olefin; a dispersant comprising a phosphoric acid anionic surfactant; and a thermally conductive filler. The disclosed thermally conductive grease possesses a lower viscosity than previous methods when the type and amount of thermally conductive filler are the same, i.e., superior thermal conductivity. [Previous Technical Documents] [Patent Literature]

[0004] [Patent Document 1] International Publication No. 2021 / 186875 Summary of the Invention

[0005] [The problem the invention aims to solve] In recent years, with the miniaturization and high performance of electronic devices, there is a demand for a thermally conductive grease composition with a thermal conductivity that is even higher than that of the previous thermally conductive grease compositions described in Patent Document 1.

[0006] The present invention was made in view of the above circumstances, and its object is to provide a thermally conductive grease composition with high thermal conductivity. [Technical means to solve the problem]

[0007] To address the aforementioned issues, the present invention employs the following configuration. [1] A thermally conductive grease composition comprising a base oil (A) and thermally conductive particles (B), wherein the thermally conductive particles (B) comprise aluminum nitride (B1) with an average particle size D50 of less than 70 μm and aluminum nitride (B2) with an average particle size D50 of 70 μm or more. [2] The thermally conductive grease composition as described in [1] wherein the average particle size D50 of the aluminum nitride (B2) exceeds 100 μm. [3] The thermally conductive grease composition as described in [1] or [2] includes aluminum nitride (B11) with an average particle size D50 of less than 3 μm, aluminum nitride (B12) with an average particle size D50 of more than 3 μm but less than 70 μm, and aluminum nitride (B2) with an average particle size D50 of more than 70 μm. [Effects of the Invention]

[0008] According to the present invention, a thermally conductive grease composition with high thermal conductivity can be provided. Implementation

[0009] (Thermal conductive grease composition) The thermally conductive grease composition of this embodiment contains a base oil (A) and thermally conductive particles (B).

[0010] Thermal grease refers to grease used to improve thermal conductivity by being applied between the heating element and the cooling component and filling the gap.

[0011] <Base Oil (A)> The thermally conductive grease composition of this embodiment contains a base oil (A). The base oil (A) has a kinematic viscosity of at 40°C preferably of 10 mm² / s or more, preferably of 20 mm² / s or more, and even more preferably of 40 mm² / s or more. The base oil (A) has a kinematic viscosity of less than 700 mm² / s at 40°C, more preferably less than 650 mm² / s, and even more preferably less than 450 mm² / s.

[0012] When the kinematic viscosity of the base oil (A) of the thermally conductive grease composition of this embodiment is within the above-mentioned preferred range at 40°C, the base oil (A) and the thermally conductive particles are not easily separated.

[0013] For example, the kinematic viscosity of the base oil (A) at 40°C is preferably 10 mm² / s or more than 700 mm² / s, more preferably 20 mm² / s or more than 650 mm² / s, and even more preferably 40 mm² / s or more than 450 mm² / s.

[0014] The base oil (A) has a kinematic viscosity of at 100°C preferably of 2 mm² / s or more, preferably of 5 mm² / s or more, and even more preferably of 7 mm² / s or more. The base oil (A) has a kinematic viscosity of less than 70 mm² / s at 100°C, more preferably less than 65 mm² / s, and even more preferably less than 60 mm² / s.

[0015] When the kinematic viscosity of the base oil (A) of the thermally conductive grease composition of this embodiment is within the above-mentioned preferred range at 100°C, the base oil (A) and the thermally conductive particles are not easily separated.

[0016] For example, the kinematic viscosity of the base oil (A) at 100°C is preferably 2 mm² / s or more and 70 mm² / s or less, more preferably 5 mm² / s or more and 65 mm² / s or less, and even more preferably 7 mm² / s or more and 60 mm² / s or less.

[0017] The kinematic viscosity at 40°C and 100°C mentioned in this specification refers to the kinematic viscosity at 40°C as measured according to JIS K2283:2000.

[0018] Examples of base oils (A) for the thermally conductive grease composition of this embodiment include synthetic oils and mineral oils.

[0019] Synthetic Oils Examples of synthetic oils include: polyolefin base oils such as poly-α-olefins, ester base oils such as diesters and polyol esters, polyalkyl glycols, alkylbenzenes, alkylnaphthalenes, ether base oils, silicone oils, and fluorinated oils. As a synthetic oil, among the above, polyolefins are preferred from the viewpoints of availability, cost, viscosity characteristics, and oxidative stability, and poly-α-olefins (PAO) are even more preferred. The base oil (A) of the thermally conductive grease composition of this embodiment can be a single synthetic oil or a mixture of multiple synthetic oils.

[0020] Mineral Oil As a mineral oil, distillate obtained by atmospheric distillation of crude oil can be used. Alternatively, lubricating oil fractions obtained by further vacuum distillation of the distillate can be used, refined through various refining processes. As a refining process, hydrogenation refining, solvent extraction, solvent dewaxing, hydrogenation dewaxing, sulfuric acid washing, and clay treatment can be appropriately combined. By combining these refining processes in an appropriate sequence, mineral oil can be obtained. Alternatively, a mixture of several refined oils with different properties can be used, obtained by combining different crude oils or distillates to different refining processes.

[0021] As a mineral oil, it may use Group I base oil (hereinafter referred to as "API Group I base oil"), Group II base oil (hereinafter referred to as "API Group II base oil"), or Group III base oil (hereinafter referred to as "API Group III base oil"), or a mixture thereof. API Group I base oils are mineral oil base oils with a sulfur content exceeding 0.03% by mass and / or a saturated content not exceeding 90% by mass, and a viscosity index of 80 or higher but not exceeding 120. API Group II base oils are mineral oil base oils with a sulfur content of less than 0.03% by mass, a saturated content of more than 90% by mass, and a viscosity index of more than 80 but less than 120. API Group III base oils are mineral oil base oils with a sulfur content of less than 0.03% by mass, a saturated content of more than 90% by mass, and a viscosity index of more than 120.

[0022] The base oil (A) of the thermally conductive grease composition of this embodiment can be a single mineral oil or a mixture of multiple mineral oils. In a mixture of multiple mineral oils, the API classifications of these mineral oils can be the same or different.

[0023] The base oil (A) of the thermally conductive grease composition of this embodiment can be either mineral oil or synthetic oil, or a mixture of mineral oil and synthetic oil. The base oil (A) of the thermally conductive grease composition of this embodiment preferably contains synthetic oil, and more preferably contains poly-α-olefin.

[0024] The content of base oil (A) in the thermally conductive grease composition of this embodiment is preferably 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass or more, relative to the total amount of the thermally conductive grease composition. The content of base oil (A) in the thermally conductive grease composition of this embodiment is preferably 21% by mass or less, more preferably 15% by mass or less, and even more preferably 13% by mass or less, relative to the total amount of the thermally conductive grease composition. For example, the content of base oil (A) in the thermally conductive grease composition of this embodiment is preferably 2% by mass or more and 21% by mass or less relative to the total amount of the thermally conductive grease composition, more preferably 2.5% by mass or more and 15% by mass or less, and even more preferably 3% by mass or more and 13% by mass or less.

[0025] <Thermal Conductive Particles (B)> The thermally conductive grease composition of this embodiment contains thermally conductive particles (B). Examples of thermally conductive particles (B) include: metals, metal oxides, metal nitrides, metal hydroxides, metal carbides, graphite, carbon fibers, etc.

[0026] Examples of metals include aluminum, silver, copper, and nickel. Examples of metal oxides include aluminum oxide, magnesium oxide, and zinc oxide. Examples of metal nitrides include boron nitride and aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. Examples of metal carbides include silicon carbide. Examples of carbon fibers include pitch-based carbon fibers, PAN-based carbon fibers, fibers obtained by carbonizing resin fibers, and fibers obtained by graphitizing resin fibers.

[0027] The thermally conductive particles (B) include aluminum nitride (B1) with an average particle size D50 of less than 70 μm and aluminum nitride (B2) with an average particle size D50 of more than 70 μm.

[0028] <<Aluminum Nitride (B1)>> The average particle size D50 of aluminum nitride (B1) is less than 70 μm, preferably less than 60 μm, more preferably less than 55 μm, and even more preferably less than 50 μm. The average particle size D50 of aluminum nitride (B1) is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. For example, the average particle size D50 of aluminum nitride (B1) is preferably 0.1 μm or more and not more than 70 μm, more preferably 0.1 μm or more and not more than 60 μm, further preferably 0.3 μm or more and not more than 55 μm, and even more preferably 0.5 μm or more and not more than 50 μm.

[0029] Aluminum nitride (B1) preferably includes aluminum nitride (B11) with an average particle size D50 of less than 3 μm and aluminum nitride (B12) with an average particle size D50 of more than 3 μm but less than 70 μm.

[0030] The average particle size D50 of aluminum nitride (B11) is less than 3 μm, preferably less than 2.5 μm, more preferably less than 2 μm, and even more preferably less than 1.5 μm. The average particle size D50 of aluminum nitride (B11) is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and particularly preferably 0.5 μm or more. For example, the average particle size D50 of aluminum nitride (B11) is preferably 0.1 μm or more and 3 μm or less, more preferably 0.2 μm or more and 2.5 μm or less, further preferably 0.3 μm or more and 2 μm or less, and even more preferably 0.5 μm or more and 1.5 μm or less.

[0031] The aluminum nitride (B12) has an average particle size D50 of more than 3 μm, preferably more than 3.5 μm, more preferably more than 4 μm, and even more preferably more than 4.5 μm. The average particle size D50 of aluminum nitride (B12) is less than 70 μm, preferably less than 65 μm, more preferably less than 60 μm, and even more preferably less than 55 μm. For example, the average particle size D50 of aluminum nitride (B12) is preferably 3.5 μm or more and 65 μm or less, more preferably 4 μm or more and 60 μm or less, and even more preferably 4.5 μm or more and 55 μm or less.

[0032] In the thermally conductive grease composition of this embodiment, the mass ratio of aluminum nitride (B11) content to aluminum nitride (B12) content ((B12) / (B11)) is preferably 1 to 3, more preferably 1 to 2, and even more preferably 1 to 1.5.

[0033] <<Aluminum Nitride (B2)>> The average particle size D50 of aluminum nitride (B2) is 70 μm or more, preferably more than 100 μm, more preferably more than 110 μm, and even more preferably more than 120 μm. The average particle size D50 of aluminum nitride (B2) is preferably less than 150 μm, more preferably less than 140 μm, and even more preferably less than 130 μm. For example, the average particle size D50 of aluminum nitride (B2) is 70 μm or more and 150 μm or less, preferably more than 100 μm and less than 140 μm, more preferably more than 110 μm, and even more preferably more than 120 μm and less than 130 μm.

[0034] In this specification, the average particle size D50 is the particle size that accounts for 50% of the cumulative volume ratio from the small particle side in the cumulative particle size distribution curve obtained by laser diffraction / scattering particle size distribution measurement. The average particle size D50 of aluminum nitride can be determined using a commercially available laser diffraction / scattering particle size distribution measuring device.

[0035] In the thermally conductive grease composition of this embodiment, the mass ratio of aluminum nitride (B1) content to aluminum nitride (B2) content ((B2) / (B1)) is preferably 1 to 5, more preferably 1 to 2.5, and even more preferably 1.5 to 2.

[0036] Thermally conductive particles (B) can be used alone or in combination. The content of thermally conductive particles (B) in the thermally conductive grease composition of this embodiment is preferably 79% by mass or more, more preferably 85% by mass or more, and even more preferably 87% by mass or more, relative to the total amount of the thermally conductive grease composition. The content of thermally conductive particles (B) in the thermally conductive grease composition of this embodiment is preferably 98% by mass or less, more preferably 97.5% by mass or less, and even more preferably 97% by mass or less, relative to the total amount of the thermally conductive grease composition. For example, the content of thermally conductive particles (B) in the thermally conductive grease composition of this embodiment is preferably 79% by mass or more and 98% by mass or less relative to the total amount of the thermally conductive grease composition, more preferably 85% by mass or more and 97.5% by mass or less, and even more preferably 87% by mass or more and 97% by mass or less.

[0037] <Any ingredient> The thermally conductive grease composition of this embodiment may also contain any components other than the base oil (A) and thermally conductive particles (B) described above. Examples of such arbitrary components include: acidic phosphate esters, phosphites or their salts, thickeners, anti-wear agents, antioxidants, rust inhibitors, corrosion inhibitors, tackifiers, anti-diffusion agents, and flame retardants.

[0038] <Acidic phosphate esters> Examples of acidic phosphate esters include: one or more compounds selected from the group consisting of compounds represented by the following general formula (C-1) (C1), compounds represented by the following general formula (C-2) (C2), and compounds represented by the following general formula (C-3) (C3).

[0039] [Chemistry 1] In formula (C-1), Rc1 and Rc2 are independently hydrogen atoms and aliphatic hydrocarbon groups with 18 or more carbon atoms, respectively. There is no case where both Rc1 and Rc2 are hydrogen atoms. In formula (C-2), Rc3 and Rc4 are each an aliphatic hydrocarbon group with 18 or more carbon atoms. l is an integer from 1 to 5. m is an integer from 1 to 5. In formula (C-3), Rc5 is an aliphatic hydrocarbon group with 18 or more carbon atoms. n is an integer from 1 to 5.

[0040] <<Compound (C1)>> The compound (C1) is the compound represented by the following general formula (C-1).

[0041] [Chemistry 2] [In formula (C-1), Rc1 and Rc2 are independently hydrogen atoms and aliphatic hydrocarbon groups with 18 or more carbon atoms, respectively. There is no case where both Rc1 and Rc2 are hydrogen atoms.]

[0042] In the above formula (C-1), the aliphatic hydrocarbon groups with 18 or more carbon atoms in Rc1 and Rc2 are preferably aliphatic hydrocarbon groups with 18 to 40 carbon atoms, more preferably aliphatic hydrocarbon groups with 18 to 30 carbon atoms, and even more preferably aliphatic hydrocarbon groups with 18 to 25 carbon atoms.

[0043] In the above general formula (C-1), the aliphatic hydrocarbon groups with 18 or more carbon atoms in Rc1 and Rc2 can be straight-chain or branched, and can be saturated or unsaturated aliphatic hydrocarbon groups.

[0044] In the above general formula (C-1), examples of aliphatic hydrocarbon groups in Rc1 and Rc2 include: alkyl, alkenyl, alkadienyl, alkanetrienyl, etc.

[0045] Examples of alkyl groups with 18 or more carbon atoms include octadecyl, nonadecanyl, eicosyl, and dodecyl. Examples of alkenyl groups with 18 or more carbon atoms include: octadecenyl, 19decenyl, 20decenyl, and 21decenyl. Furthermore, the position of the double bond is arbitrary; for example, oleyl (9-octadecenyl) can be cited.

[0046] In the above general formula (C-1), the aliphatic hydrocarbon group in Rc1 and Rc2 is preferably alkenyl, alkadienyl, or alktrienyl, and more preferably alkenyl.

[0047] In the above general formula (C-1), Rc1 and Rc2 are respectively preferably alkenyl groups with 18 to 40 carbon atoms, more preferably alkenyl groups with 18 to 30 carbon atoms, and even more preferably alkenyl groups with 18 to 25 carbon atoms, and especially preferably oleyl groups.

[0048] Compound (C1) can be used alone or in combination of multiple compounds.

[0049] <<Compound (C2)>> The compound (C2) is the compound represented by the following general formula (C-2).

[0050] [Chemistry 3] [In formula (C-2), Rc3 and Rc4 are each independently an aliphatic hydrocarbon group with 18 or more carbon atoms. l is an integer from 1 to 5. m is an integer from 1 to 5.]

[0051] In the above general formula (C-2), the aliphatic hydrocarbon groups with 18 or more carbon atoms in Rc3 and Rc4 can be the same as the aliphatic hydrocarbon groups with 18 or more carbon atoms in Rc1 and Rc2.

[0052] In the above general formula (C-2), l is an integer from 1 to 5, preferably an integer from 2 to 4, and even more preferably an integer of 2 or 3.

[0053] In the above general formula (C-2), m is an integer from 1 to 5, preferably an integer from 2 to 4, and even more preferably an integer of 2 or 3.

[0054] Compound (C2) can be used alone or in combination of multiple compounds.

[0055] <<Compound (C3)>> The compound (C3) is the compound represented by the following general formula (C-3).

[0056] [Chemistry 4] [In formula (C-3), Rc5 is an aliphatic hydrocarbon group with 18 or more carbon atoms. n is an integer from 1 to 5.]

[0057] In the above general formula (C-3), the aliphatic hydrocarbon group with 18 or more carbon atoms in Rc5 can be the same as the aliphatic hydrocarbon group with 18 or more carbon atoms in Rc1 and Rc2.

[0058] In the above general formula (C-3), n is an integer from 1 to 5, preferably an integer from 2 to 4, and even more preferably an integer of 2 or 3.

[0059] The compound (C3) can be used alone or in combination of multiple compounds.

[0060] When the thermally conductive grease composition contains acidic phosphate esters, their content relative to the total amount of the thermally conductive grease composition is, for example, 0.1 to 20% by mass. Acidic phosphate esters can be used alone or in combination of multiple acidic phosphate esters.

[0061] <phosphites or their salts> The thermally conductive grease composition of this embodiment may also contain phosphites or their salts. Examples of phosphite esters include: dibutyl phosphite, di(nonylphenyl) phosphite, monolaurate phosphite, dilaurate phosphite, monomyristate phosphite, dimyristate phosphite, monopalmitate phosphite, dipalmitate phosphite, monostearate phosphite, distearate phosphite, monooleate phosphite, dioleate phosphite, di(tetracoyl) phosphite, etc.

[0062] Examples of salts of phosphites include alkali metal salts of phosphites and amine salts of phosphites.

[0063] Examples of alkali metals that can be used as raw materials for alkali metal salts of phosphites include sodium and potassium.

[0064] Examples of amines that can be used as raw materials for amine salts of phosphites include monoamines, polyamines, and alkanolamines.

[0065] Examples of monoamines include primary, secondary, and tertiary amines. As primary amines, examples include: ethylamine, n-propylamine, butylamine, 1-ethylbutylamine, 1,3-propanediamine, cyclohexylamine, etc. As secondary amines, examples include: diethylamine, di-n-propylamine, di-n-butylamine, 4,4'-diaminodiphenylamine, diethyltriamine, tetraethylpentamine, N-(2-aminoethyl)ethanolamine, etc. As tertiary amines, examples include: dimethylethylamine, diethylmethylamine, triethylamine, tributylamine, etc.

[0066] As alkanolamines, examples include monoethanolamine, diethanolamine, triethanolamine, diethylethanolamine, propanolamine, etc.

[0067] Specifically, examples of polyamines include: ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, propylenediamine, diethylenepropyltriamine, triethylenepropyltetramine, tetraethylenepropylpentamine, pentaethylenepropylhexamine, butyldiamine, diethylenebutyltriamine, triethylenebutyltetramine, tetraethylenebutylpentamine, pentaethylenebutylhexamine, and other alkyl polyamines; N-alkylethylenediamines such as N-methylethylenediamine, N-ethylethylenediamine, and N-propylethylenediamine; N-alkenylethylenediamines such as N-vinylethylenediamine, N-propenylethylenediamine, and N-butenylethylenediamine; and N-alkyl or N-alkenylalkyl polyamines such as N-alkyldiethylenetriamine, N-alkenyldiethylenetriamine, and N-alkyltriethylenetetramine. Furthermore, the above-mentioned polyamines also include polyamines derived from fats and oils (such as tallow polyamines).

[0068] As a phosphite or its salt, it is preferred to include a compound or its salt represented by the following general formula (X-1).

[0069] [Chemistry 5] [In the formula, Rc1 and Rc2 are independently hydrogen atoms or aliphatic hydrocarbon groups with 16 or more carbon atoms. There is no case where both Rc1 and Rc2 are hydrogen atoms.]

[0070] In the above general formula (X-1), the aliphatic hydrocarbon groups with 16 or more carbon atoms in Rc1 and Rc2 are preferably aliphatic hydrocarbon groups with 16 to 40 carbon atoms, more preferably aliphatic hydrocarbon groups with 16 to 30 carbon atoms, and even more preferably aliphatic hydrocarbon groups with 16 to 25 carbon atoms.

[0071] In the above general formula (X-1), the aliphatic hydrocarbon groups with 16 or more carbon atoms in Rc1 and Rc2 can be straight-chain or branched, and can be saturated or unsaturated aliphatic hydrocarbon groups.

[0072] In the above general formula (X-1), examples of aliphatic hydrocarbon groups in Rc1 and Rc2 include: alkyl, alkenyl, alkadienyl, alkanetrienyl, etc.

[0073] Examples of alkyl groups with 16 or more carbon atoms include palmityl (hexadecyl), stearyl (octadecyl), nonadecanyl, eicosyl, and dodecyl. Examples of alkenyl groups with 16 or more carbon atoms include: hexadecenyl, octadecenyl, nonadecenyl, icosenoenyl, and icosenoenyl. Furthermore, the position of the double bond is arbitrary; for example, oleyl (9-octadecenyl) can be cited.

[0074] In the above general formula (X-1), Rc1 and Rc2 are respectively preferably alkenyl groups with 16 to 40 carbon atoms, more preferably alkenyl groups with 16 to 30 carbon atoms, and even more preferably alkenyl groups with 16 to 25 carbon atoms, and especially preferably oleyl groups.

[0075] Examples of salts of compounds represented by the general formula (X-1) include alkali metal salts and amine salts of compounds represented by the general formula (X-1). Specifically, Rc1 and Rc2 of the compound represented by general formula (X-1) are alkali metal compounds or Rc1 and Rc2 of the compound represented by general formula (X-1) are compounds with a radical obtained by removing a hydrogen atom from the above-mentioned amine.

[0076] When the thermally conductive grease composition contains phosphites or their salts, the content of the phosphite or its salt relative to the total amount of the thermally conductive grease composition is, for example, 0.1 to 20% by mass. A single phosphite or its salt may be used alone, or multiple phosphites or their salts may be used in combination.

[0077] Examples of thickeners include: metal soap-based thickeners; urea-based thickeners; and inorganic thickeners such as bentonite and silicone. When a thermally conductive grease composition contains a thickener, its content relative to the total amount of the thermally conductive grease composition is, for example, 0.1 to 20% by mass. A single thickener may be used alone, or multiple thickeners may be used in combination.

[0078] Examples of anti-wear agents include: organozinc compounds such as zinc dialkyldithiophosphate and zinc dialkyldithioaminoformate; sulfur-containing compounds such as molybdenum dialkyldithioaminoformate, dialkyl polysulfides, sulfide esters, thiazole compounds, and thiadiazole compounds; and phosphorus-containing compounds such as phosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, and phosphites. When the thermally conductive grease composition contains an anti-wear agent, its content relative to the total amount of the thermally conductive grease composition is preferably 0.1 to 10% by mass, more preferably 0.5 to 1.5% by mass. One anti-wear agent may be used alone, or multiple anti-wear agents may be used in combination.

[0079] Examples of antioxidants include phenolic compounds such as 2,6-di-tert-butylphenol and 2,6-di-tert-butyl-p-cresol; and amine compounds such as diphenylamine, dialkyldiphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl-α-naphthylamine. When the thermally conductive grease composition contains antioxidants, their content relative to the total amount of the thermally conductive grease composition is, for example, 0.5 to 10% by mass. One antioxidant may be used alone, or multiple antioxidants may be used in combination.

[0080] Examples of rust inhibitors include: amines, neutral or alkaline petroleum-based or synthetic oil-based metal sulfonates, carboxylic acid metal salts, esters, phosphoric acid, phosphates, etc. When a rust inhibitor is present in a thermally conductive grease composition, its content relative to the total amount of the thermally conductive grease composition is, for example, 0.005 to 5% by mass. A single rust inhibitor may be used, or multiple rust inhibitors may be used in combination.

[0081] As corrosion inhibitors, known corrosion inhibitors such as benzotriazole compounds, toluenetriazole compounds, thiadiazole compounds, and imidazole compounds can be used. When the thermally conductive grease composition contains a corrosion inhibitor, its content relative to the total amount of the thermally conductive grease composition is, for example, 0.01 to 10% by mass. A single corrosion inhibitor can be used, or multiple corrosion inhibitors can be used in combination.

[0082] The thermally conductive grease composition of this embodiment contains a base oil (A) and thermally conductive particles (B), wherein the thermally conductive particles (B) include aluminum nitride (B1) with an average particle size D50 of less than 70 μm and aluminum nitride (B2) with an average particle size D50 of 70 μm or more. In previous thermally conductive grease compositions, aluminum nitride with a small particle size (average particle size D50) of approximately 70 μm was used because it was easy to form a thin film during pressing, thereby reducing thermal resistance. However, when the thermally conductive grease composition contains only small-particle aluminum nitride, heat transfer occurs between the small-particle aluminum nitride, thus inevitably reducing thermal conductivity. On the other hand, in thermally conductive grease compositions containing only large-particle aluminum nitride, the gaps become larger, and heat transfer occurs between air particles with lower thermal conductivity, thus reducing heat dissipation characteristics. The thermally conductive grease composition of this embodiment combines aluminum nitride with specific particle sizes, thus solving the above-mentioned problems and achieving higher thermal conductivity. [Example]

[0083] The present invention will be described in more detail below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0084] <Preparation of Thermally Conductive Grease Compositions> The thermally conductive grease compositions of Examples 1-10 and Comparative Examples 1-3 were prepared using the mixing ratios shown in Tables 1-3. The values ​​in Tables 1-3 are mixing ratios (mass%) relative to the total amount of the thermally conductive grease compositions.

[0085] (1) Base oil (A) (A)-1: Poly-α-olefin (kinematic viscosity at 40℃ = 412 mm² / s, density 0.846 g / cm³) •(A)-2: Poly-α-olefin (kinematic viscosity at 40℃ = 47.5 mm² / s, density 0.818 g / cm³)

[0086] (2) Thermally conductive particles (B) •(B)-1: Aluminum nitride (spherical, average particle size D50 0.9 μm) •(B)-2: Aluminum nitride (polyhedral, average particle size D50 5 μm) •(B)-3: Aluminum nitride (polyhedral, average particle size D50 8 μm) •(B)-4: Aluminum nitride (spherical, average particle size D50 30 μm) •(B)-5: Aluminum nitride (spherical, average particle size D50 50 μm) (B)-6: Aluminum nitride (spherical, average particle size D50 80 μm) •(B)-7: Aluminum nitride (spherical, average particle size D50 120 μm) •(B)-8: Aluminum nitride (fibrous, 2-5 μm in diameter, length d50=15 μm and less than 100 μm)

[0087] (3) Acidic phosphate esters (C) •(C)-1: Oil-based acidic phosphate ester (JP518-O, manufactured by Chengbei Chemical Co., Ltd.)

[0088] (4) Additives X-1: A mixture containing phosphites (LUBRIZOL 6178, manufactured by Lubrizol Corporation, Japan)

[0089] [Determination of thermal conductivity] At room temperature (25°C), thermally conductive grease was directly applied to the surface of the MTPS sensor, and the thermal conductivity was measured. The results are shown in Tables 1-3. <Measurement Conditions> Machine used: C-Therm TRIDENT MTPS sensor The "ND" in the table means that the material is not greased and its thermal conductivity cannot be measured.

[0090] [Table 1] Example 1 Example 2 Comparative Example 1 (A)-1 7.60 9.5 (A)-2 10 (B)-1 18.20 17.10 (B)-2 (B)-3 14.30 (B)-4 (B)-5 (B)-6 (B)-7 62.50 58.60 90 (B)-8 11.30 (C)-1 0.40 0.5 (X)-1 (B2) / (B1) 4.05 1.87 Thermal conductivity [W / mK] 6.0 4.2 1.8

[0091] [Table 2] Example 3 Example 4 Example 5 Comparative Example 2 Comparative Example 3 (A)-1 8.00 8.00 8.00 (A)-2 7.60 5.70 (B)-1 16.71 17.07 (B)-2 22.00 37.00 42.00 (B)-3 75.29 76.93 (B)-4 (B)-5 (B)-6 (B)-7 70.00 55.00 50.00 (B)-8 (C)-1 0.40 0.30 (X)-1 (B2) / (B1) 3.18 1.49 1.19 Thermal conductivity [W / mK] 4.2 5.1 4.4 3.8 ND

[0092] [Table 3] Example 6 Example 7 Example 8 Example 9 Example 10 (A)-1 3.80 2.85 3.80 5.70 5.70 (B)-1 18.20 18.20 18.20 17.80 17.78 (B)-2 (B)-3 15.30 15.30 15.30 15.00 14.92 (B)-4 (B)-5 (B)-6 62.50 (B)-7 62.50 63.50 61.20 61.30 (B)-8 (C)-1 0.20 0.15 0.20 0.30 (X)-1 0.30 (B2) / (B1) 1.87 1.90 1.87 1.87 1.87 Thermal conductivity [W / mK] 10.3 11.6 9.6 6.8 7.1

[0093] As shown in Tables 1-3, it can be seen that the thermal conductivity of the thermally conductive grease compositions in the examples is higher than that of the comparative examples.

[0094] The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications can be made to the structure without departing from the spirit of the present invention. The present invention is not limited to the above description, but only to the appended claims.

Claims

1. A thermally conductive grease composition comprising a base oil (A) and thermally conductive particles (B), wherein the base oil (A) comprises a poly-α-olefin, the thermally conductive particles (B) comprise aluminum nitride (B1) with an average particle size D50 of less than 70 μm and aluminum nitride (B2) with an average particle size D50 of 70 μm or more, and the aluminum nitride (B1) comprises aluminum nitride (B11) with an average particle size D50 of less than 3 μm and aluminum nitride (B12) with an average particle size D50 of more than 3 μm but less than 70 μm.

2. The thermally conductive grease composition of claim 1, wherein the average particle size D50 of the aluminum nitride (B2) exceeds 100 μm.

3. The thermally conductive grease composition of claim 1 or 2, wherein the mass ratio of the content of aluminum nitride (B1) to the content of aluminum nitride (B2) ((B2) / (B1)) is 1.19 to 5.

4. The thermally conductive grease composition of claim 1 or 2, wherein the mass ratio of the content of aluminum nitride (B1) to the content of aluminum nitride (B2) ((B2) / (B1)) is 1.5 to 2.

5. The thermally conductive grease composition of claim 1 or 2, further comprising an acidic phosphate ester, a phosphite ester, or a salt of a phosphite ester.