Thermally conductive grease composition

Abstract

Disclosed is a thermally conductive grease composition which contains a base oil (A) and thermally conductive particles (B), wherein: the content of the thermally conductive particles (B) is not less than 79% by mass but less than 92% by mass relative to the total amount of the thermally conductive grease composition; the thermally conductive particles (B) contain aluminum nitride (B1) that has an average particle diameter D50 of less than 30 µm and aluminum nitride (B2) that has an average particle diameter D50 of 30 µm or more; and the mass ratio ((B2) / (B1)) of the content of the aluminum nitride (B2) to the content of the aluminum nitride (B1) is 1-3.

Description

Thermally conductive grease composition

[0001] This invention relates to a thermally conductive grease composition. This application claims priority under Japanese Patent Application No. 2024-185374, filed in Japan on October 21, 2024, the contents of which are incorporated herein by reference.

[0002] In electronic devices such as computers, automotive parts, and mobile phones, cooling components such as heat sinks are commonly used to dissipate heat generated from heat-generating elements such as semiconductor elements and mechanical parts, and thermally conductive grease is used to improve the heat transfer efficiency to the cooling components.

[0003] For example, Patent Document 1 discloses a thermal conductive grease for transferring heat from a heating element to a cooling component, comprising a base oil consisting of at least one selected from a copolymer of an unsaturated dialkyl dicarboxylic acid ester and an α-olefin, and a poly-α-olefin, a dispersant consisting of a phosphate-based anionic surfactant, and a thermal conductive filler. This thermal conductive grease is disclosed to have the characteristic of having a lower viscosity than conventional greases when the type and amount of thermal conductive filler are the same, i.e., it has excellent thermal conductivity.

[0004] International Publication No. 2021 / 186875

[0005] Generally, the heat dissipation characteristics of a thermally conductive grease composition improve with decreasing viscosity, provided that the type and content of the thermally conductive filler are the same. This is because lower viscosity greases tend to be thinner when pressed under the same load, thus reducing thermal resistance. With the recent miniaturization and increased performance of electronic devices, there is a demand for thermally conductive grease compositions with even lower viscosity than conventional thermally conductive grease compositions, such as those described in Patent Document 1.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a low-viscosity thermally conductive grease composition.

[0007] In order to solve the above problems, the present invention adopts the following configuration. [1] A thermally conductive grease composition containing a base oil (A) and thermally conductive particles (B), wherein the content of the thermally conductive particles (B) is 79% by mass or more and less than 92% by mass based on the total amount of the thermally conductive grease composition, and the thermally conductive particles (B) include aluminum nitride (B1) having an average particle diameter D50 of less than 30 μm and aluminum nitride (B2) having an average particle diameter D50 of 30 μm or more, and the mass ratio ((B2) / (B1)) of the content of the aluminum nitride (B1) to the content of the aluminum nitride (B2) is 1 to 3. [2] The thermally conductive grease composition according to [1], further containing one or more compounds selected from the group consisting of phosphate esters, phosphite esters, and salts of phosphite esters.

[0008] According to the present invention, a thermally conductive grease composition with low viscosity can be provided.

[0009] (Thermally Conductive Grease Composition) The thermally conductive grease composition of the present embodiment contains a base oil (A) and thermally conductive particles (B).

[0010] A thermally conductive grease is a grease used to coat between a heat generating body and a cooling component and fill the gap to increase the thermal conductivity.

[0011] <Base Oil (A)> The thermally conductive grease composition of the present embodiment contains a base oil (A). The kinematic viscosity of the base oil (A) at °C is preferably 10 mm ２ / s or more, more preferably 20 mm ２ / s or more, and even more preferably 40 mm ２ / s or more. The kinematic viscosity of the base oil (A) at 40 °C is preferably 700 mm ２ / s or less, more preferably 650 mm ２ / s or less, and even more preferably 450 mm ２ / s or less.

[0012] When the kinematic viscosity of the base oil (A) of the thermally conductive grease composition of the present embodiment at 40 °C is within the above preferable range, it becomes difficult for the base oil (A) and the thermally conductive particles to separate.

[0013] For example, the kinematic viscosity of base oil (A) at 40°C is 10 mm ２ / s or more and 700 mm ２ / s or less, preferably 20 mm ２ / s or more and 650 mm ２ / s or less, more preferably 40 mm ２ / s or more and 450 mm ２ / s or less is even more preferable.

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

[0015] When the kinematic viscosity of base oil (A) of the thermal conductivity grease composition of the present embodiment at 100°C is within the above preferable range, it becomes difficult for base oil (A) and the thermal conductivity particles to separate.

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

[0017] The kinematic viscosities at 40°C and 100°C in this specification mean the kinematic viscosity at 40°C measured in accordance with JIS K2283:2000.

[0018] Examples of base oil (A) of the thermal conductivity grease composition of the present embodiment include synthetic oil and mineral oil.

[0019] <<Synthetic Oils>> Examples of synthetic oils include polyolefins such as poly-α-olefins, ester base oils such as diesters and polyol esters, polyalkylene glycols, alkylbenzenes, alkylnaphthalenes, ether base oils, silicone oils, and fluorine oils. Among the above, polyolefins are preferred as synthetic oils from the viewpoint of availability, cost, viscosity characteristics, and oxidation stability, and poly-α-olefins (PAO) are more preferred. As the base oil (A) of the thermally conductive grease composition of this embodiment, one type of synthetic oil may be used alone, or a mixture of multiple synthetic oils may be used.

[0020] ≪Mineral Oil≫ As mineral oil, distillate obtained by atmospheric distillation of crude oil can be used. In addition, lubricating oil fractions obtained by further vacuum distillation of this distillate and then refined through various refining processes can also be used. As refining processes, hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, and clay treatment can be combined as appropriate. Mineral oil can be obtained by combining these refining processes in an appropriate order. Alternatively, a mixture of multiple refined oils with different properties obtained by subjecting different crude oils or distillates to different refining process combinations may be used.

[0021] As the mineral oil, you can use base oils from API Group I (hereinafter referred to as "API Group I base oil"), Group II (hereinafter referred to as "API Group II base oil"), or Group III (hereinafter referred to as "API Group III base oil") according to the API base oil classification, or a mixture thereof. API Group I base oil is a mineral oil-based base oil with a sulfur content of more than 0.03% by mass and / or a saturation content of less than 90% by mass, and a viscosity index of 80 or more and less than 120. API Group II base oil is a mineral oil-based base oil with a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 80 or more and less than 120. API Group III base oil is a mineral oil-based base oil with a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 120 or more.

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

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

[0024] The base oil (A) content of the thermal conductive grease composition of this embodiment is preferably 8% by mass or more, more preferably 9% by mass or more, and even more preferably 10% by mass or more, based on the total amount of the thermal conductive grease composition. The base oil (A) content of the thermal conductive grease composition of this embodiment is preferably 21% by mass or less, more preferably 19% by mass or less, and even more preferably 17% by mass or less, based on the total amount of the thermal conductive grease composition. For example, the base oil (A) content of the thermal conductive grease composition of this embodiment is preferably 8% by mass or more and 21% by mass or less, more preferably 9% by mass or more and 19% by mass or less, and even more preferably 10% by mass or more and 17% by mass or less, based on the total amount of the thermal conductive grease composition.

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

[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, carbonized resin fibers, and graphitized resin fibers.

[0027] The thermally conductive particles (B) include aluminum nitride (B1) with an average particle diameter D50 of less than 30 μm and aluminum nitride (B2) with an average particle diameter D50 of 30 μm or more.

[0028] ≪Aluminum Nitride (B1)≫ Aluminum nitride (B1) has an average particle diameter D50 of less than 30 μm, preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. The average particle diameter D50 of the thermally conductive particles (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 diameter D50 of the thermally conductive particles (B1) is preferably 0.1 μm or more and less than 30 μm, more preferably 0.1 μm or more and 20 μm or less, even more preferably 0.3 μm or more and 15 μm or less, and particularly preferably 0.5 μm or more and 10 μm or less.

[0029] The thermal conductive grease composition of this embodiment preferably contains two or more types of thermal conductive particles (B1). The thermal conductive particles (B1) preferably include thermal conductive particles (B11) having an average particle diameter D50 of 0.1 μm or more and less than 5 μm, and thermal conductive particles (B12) having an average particle diameter D50 of 5 μm or more and less than 30 μm.

[0030] The thermally conductive particles (B11) have an average particle diameter D50 of 0.1 μm or more and less than 5 μm, preferably 0.2 μm or more and 3 μm or less, more 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. The thermally conductive particles (B12) have an average particle diameter D50 of 5 μm or more and less than 30 μm, preferably 6 μm or more and 25 μm or less, more preferably 7 μm or more and 15 μm or less, and even more preferably 7 μm or more and 10 μm or less.

[0031] In the thermal conductive grease composition of this embodiment, the mass ratio ((B12) / (B11)) of the content of aluminum nitride (B11) to the content of aluminum nitride (B12) is preferably 0.1 to 2, more preferably 0.5 to 1.5, and even more preferably 0.8 to 1.

[0032] ≪Aluminum Nitride (B2)≫ Aluminum nitride (B2) has an average particle size D50 of 30 μm or more, preferably 30 μm to 150 μm, more preferably 30 μm to 130 μm, and even more preferably 30 μm to 120 μm.

[0033] In this specification, the average particle diameter D50 is the particle diameter at which the cumulative volume proportion from the smallest particle side becomes 50% in the volume-based cumulative particle diameter distribution curve obtained by laser diffraction / scattering particle diameter distribution measurement. The average particle diameter D50 of thermally conductive particles (B) can be measured using a commercially available laser diffraction / scattering particle diameter distribution analyzer.

[0034] In the thermal conductive grease composition of this embodiment, the mass ratio ((B2) / (B1)) of the content of aluminum nitride (B1) to the content of aluminum nitride (B2) is 1 to 3, preferably 1.2 to 2.5, more preferably 1.5 to 2, and even more preferably 1.7 to 2.

[0035] The thermal conductive particles (B) may be used alone or in a mixture of multiple types. The content of thermal conductive particles (B) in the thermal conductive grease composition of this embodiment is preferably 79% by mass or more, more preferably 81% by mass or more, and even more preferably 83% by mass or more, based on the total amount of the thermal conductive grease composition. The content of thermal conductive particles (B) in the thermal conductive grease composition of this embodiment is less than 92% by mass, preferably 91% by mass or less, and more preferably 90% by mass or less, based on the total amount of the thermal conductive grease composition. For example, the content of thermal conductive particles (B) in the thermal conductive grease composition of this embodiment is preferably 79% by mass or more and less than 92% by mass, more preferably 81% by mass or more and 91% by mass or less, and even more preferably 83% by mass or more and 90% by mass or less, based on the total amount of the thermal conductive grease composition.

[0036] <Optional Components> The thermal conductive grease composition of this embodiment may contain optional components other than the base oil (A) and thermal conductive particles (B) described above. Examples of such optional components include acidic phosphate esters, phosphite esters or their salts, thickeners, anti-wear agents, antioxidants, rust inhibitors, corrosion inhibitors, viscosity enhancers, diffusion inhibitors, and flame retardants.

[0037] <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).

[0038] [In formula (C-1), Rc １ and Rc ２ These are, independently, a hydrogen atom and an aliphatic hydrocarbon group having 18 or more carbon atoms. However, Rc １ and Rc ２ None of these can become hydrogen atoms. In formula (C-2), Rc ３ and Rc ４ Each of these is an aliphatic hydrocarbon group having 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), Rc ５ [where n is an aliphatic hydrocarbon group with 18 or more carbon atoms, and n is an integer from 1 to 5]

[0039] Compound (C1) Compound (C1) is a compound represented by the following general formula (C-1).

[0040] [In formula (C-1), Rc １ and Rc ２ These are, independently, a hydrogen atom and an aliphatic hydrocarbon group having 18 or more carbon atoms. However, Rc １ and Rc ２ None of these can become hydrogen atoms.

[0041] In the above formula (C-1), Rc １ and Rc ２The aliphatic hydrocarbon group having 18 or more carbon atoms is preferably an aliphatic hydrocarbon group having 18 to 40 carbon atoms, more preferably an aliphatic hydrocarbon group having 18 to 30 carbon atoms, and even more preferably an aliphatic hydrocarbon group having 18 to 25 carbon atoms.

[0042] In the above general formula (C-1), Rc １ and Rc ２ The aliphatic hydrocarbon group having 18 or more carbon atoms in this compound may be linear or branched, and may be saturated or unsaturated aliphatic hydrocarbon.

[0043] In the above general formula (C-1), Rc １ and Rc ２ Examples of aliphatic hydrocarbon groups in this context include alkyl groups, alkenyl groups, alkadienyl groups, and alkatrineyl groups.

[0044] Examples of alkyl groups with 18 or more carbon atoms include octadecyl, nonadecyl, eicosyl, and henicosyl groups. Examples of alkenyl groups with 18 or more carbon atoms include octadecenyl, nonadecenyl, eicosenyl, and henicosenyl groups. The position of the double bond is arbitrary; for example, an oleyl group (9-octadecenyl group) is one example.

[0045] In the above general formula (C-1), Rc １ and Rc ２ The aliphatic hydrocarbon group in is preferably an alkenyl group, an alkadienyl group, or an alkatrineyl group, and more preferably an alkenyl group.

[0046] In the above general formula (C-1), Rc １ and Rc ２ Among the above, each is preferably an alkenyl group having 18 to 40 carbon atoms, more preferably an alkenyl group having 18 to 30 carbon atoms, even more preferably an alkenyl group having 18 to 25 carbon atoms, and particularly preferably an oleyl group.

[0047] Compound (C1) may be used alone or in a mixture of multiple compounds.

[0048] ≪Compound (C2)≫ Compound (C2) is a compound represented by the following general formula (C-2).

[0049] [In formula (C-2), Rc ３ and Rc ４ Each of these is 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.

[0050] In the above general formula (C-2), Rc ３ and Rc ４ In this context, an aliphatic hydrocarbon group with 18 or more carbon atoms is Rc １ and Rc ２ Examples include aliphatic hydrocarbon groups with 18 or more carbon atoms, similar to those found in [the text].

[0051] In the above general formula (C-2), l is an integer between 1 and 5, preferably between 2 and 4, and more preferably between 2 and 3.

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

[0053] Compound (C2) may be used alone or in combination with other compounds.

[0054] ≪Compound (C3)≫ Compound (C3) is a compound represented by the following general formula (C-3).

[0055] [In formula (C-3), Rc ５ [where n is an aliphatic hydrocarbon group with 18 or more carbon atoms, and n is an integer from 1 to 5]

[0056] In the above general formula (C-3), Rc ５ In this context, an aliphatic hydrocarbon group with 18 or more carbon atoms is Rc １ and Rc ２ Examples include aliphatic hydrocarbon groups with 18 or more carbon atoms, similar to those found in [the text].

[0057] In the above general formula (C-3), n is an integer between 1 and 5, preferably between 2 and 4, and more preferably between 2 and 3.

[0058] Compound (C3) may be used alone or in combination with other compounds.

[0059] When a thermally conductive grease composition contains an acidic phosphate ester, its content is, for example, 0.1 to 20% by mass of the total amount of the thermally conductive grease composition. The acidic phosphate ester may be used alone or in a mixture of multiple acidic phosphate esters.

[0060] <Phosphite esters or salts thereof> The thermal conductive grease composition of this embodiment may contain phosphite esters or salts thereof. Examples of phosphite esters include dibutyl hydrogen phosphite, di(nonylphenyl) hydrogen phosphite, monolauryl hydrogen phosphite, dilauryl hydrogen phosphite, monomyristyl hydrogen phosphite, dimyristyl hydrogen phosphite, monopalmytyl hydrogen phosphite, dipalmytyl hydrogen phosphite, monostearyl hydrogen phosphite, distearyl hydrogen phosphite, monooleyl hydrogen phosphite, dioleyl hydrogen phosphite, ditetracosyl hydrogen phosphite, and the like.

[0061] Examples of phosphite ester salts include alkali metal salts of phosphite esters and amine salts of phosphite esters.

[0062] Examples of alkali metals used as raw materials for alkali metal salts of phosphite esters include sodium and potassium.

[0063] Examples of amines used as raw materials for amine salts of phosphite esters include monoamines, polyamines, and alkanolamines.

[0064] Examples of monoamines include primary, secondary, and tertiary monoamines. Specific examples of primary amines include ethylamine, n-propylamine, butylamine, 1-ethylbutylamine, 1,3-diaminopropane, and cyclohexylamine. Specific examples of secondary amines include diethylamine, di-n-propylamine, di-n-butylamine, 4,4'-diaminodiphenylamine, diethylenetriamine, tetraethylenepentamine, and N-(2-aminoethyl)ethanolamine. Specific examples of tertiary amines include dimethylethylamine, diethylmethylamine, triethylamine, and tributylamine.

[0065] Examples of alkanolamines include monoethanolamine, diethanolamine, triethanolamine, diethylethanolamine, and propanolamine.

[0066] Specifically, examples of polyamines include alkylene polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, propylenediamine, dipropylenetriamine, tripylenetetramine, tetrapropylenepentamine, pentapropylenehexamine, butylenediamine, dibutylentriamine, tripbutylenetetramine, tetrabutylenepentamine, and pentabutylenehexamine; 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-alkenylalkylene polyamines such as N-alkyldiethylenetriamine, N-alkenyldiethylenetriamine, and N-alkyltriethylenetetramine. In addition, the above polyamines also include polyamines derived from oils and fats (such as beef tallow polyamines).

[0067] Preferably, the phosphite ester or its salt includes a compound represented by the following general formula (X-1) or its salt.

[0068] [In the formula, Rc １ and Rc ２ Each of these is independently a hydrogen atom or an aliphatic hydrocarbon group having 16 or more carbon atoms. However, Rc １ and Rc ２ None of these can become hydrogen atoms.

[0069] In the above general formula (C-1), Rc １ and Rc ２ The aliphatic hydrocarbon group having 16 or more carbon atoms is preferably an aliphatic hydrocarbon group having 16 to 40 carbon atoms, more preferably an aliphatic hydrocarbon group having 16 to 30 carbon atoms, and even more preferably an aliphatic hydrocarbon group having 16 to 25 carbon atoms.

[0070] In the above general formula (C-1), Rc １ and Rc ２ The aliphatic hydrocarbon group having 16 or more carbon atoms in this compound may be linear or branched, and may be saturated or unsaturated aliphatic hydrocarbon.

[0071] In the above general formula (C-1), Rc １ and Rc ２ Examples of aliphatic hydrocarbon groups in this context include alkyl groups, alkenyl groups, alkadienyl groups, and alkatrineyl groups.

[0072] Examples of alkyl groups having 16 or more carbon atoms include palmityl group (hexadecyl group), stearyl group (octadecyl group), nonadecyl group, eicosyl group, and henicosyl group. Examples of alkenyl groups having 16 or more carbon atoms include hexadecenyl group, octadecenyl group, nonadecenyl group, eicocenyl group, and henicosenyl group. The position of the double bond is arbitrary; for example, an oleyl group (9-octadecenyl group) is one example.

[0073] In the above general formula (C-1), Rc １ and Rc ２Among the above, each is preferably an alkenyl group having 16 to 40 carbon atoms, more preferably an alkenyl group having 16 to 30 carbon atoms, even more preferably an alkenyl group having 16 to 25 carbon atoms, and particularly preferably an oleyl group.

[0074] Examples of salts of the compound represented by the general formula (C-1) include alkali metal salts of the compound represented by the general formula (C-1), amine salts of the compound represented by the general formula (C-1), etc. Specifically, Rc of the compound represented by the general formula (C-1) １ and Rc ２ Compounds in which the Rc is an alkali metal or compound represented by the general formula (C-1) １ and Rc ２ This compound is a group obtained by removing one hydrogen atom from the amine mentioned above.

[0075] If the thermally conductive grease composition contains a phosphite ester or a salt thereof, its content is, for example, 0.1 to 20% by mass of the total amount of the thermally conductive grease composition. The phosphite ester or a salt thereof may be used alone, or multiple phosphite esters or salts thereof may be used in mixture form.

[0076] Examples of thickeners include metal soap-based thickeners, urea-based thickeners, bentonite, and inorganic thickeners such as silica gel. When a thermal conductive grease composition contains a thickener, its content is, for example, 0.1 to 20% by mass of the total amount of the thermal conductive grease composition. The thickener may be used alone or in a mixture of multiple thickeners.

[0077] Examples of anti-wear agents include organozinc compounds such as zinc dialkyldithiophosphate and zinc dialkyldithiocarbamate; sulfur-containing compounds such as molybdenum dialkyldithiocarbamate, dihydrocarbyl polysulfide, sulfur esters, thiazole compounds, and thiadiazole compounds; and phosphorus-containing compounds such as phosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, and phosphite esters. When a thermal conductive grease composition contains an anti-wear agent, its content is preferably, for example, 0.1 to 10% by mass, and more preferably 0.5 to 1.5% by mass, relative to the total amount of the thermal conductive grease composition. The anti-wear agent may be used alone or in combination of multiple anti-wear agents.

[0078] Examples of antioxidants include phenolic compounds such as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol; and amine compounds such as diphenylamine, dialkyldiphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl-α-naphthylamine. When the thermal conductive grease composition contains an antioxidant, its content is, for example, 0.5 to 10% by mass of the total amount of the thermal conductive grease composition. The antioxidant may be used alone or in a mixture of multiple antioxidants.

[0079] Examples of rust inhibitors include amines, neutral or overbasic petroleum-based or synthetic oil-based metal sulfonates, carboxylate metal salts, esters, phosphoric acid, and phosphates. When a thermal conductive grease composition contains a rust inhibitor, its content is, for example, 0.005 to 5% by mass of the total amount of the thermal conductive grease composition. The rust inhibitor may be used alone or in a mixture of multiple rust inhibitors.

[0080] As corrosion inhibitors, known corrosion inhibitors such as benzotriazole compounds, tolyltriazole compounds, thiadiazole compounds, and imidazole compounds can be used. When the thermal conductive grease composition contains a corrosion inhibitor, its content is, for example, 0.01 to 10% by mass of the total amount of the thermal conductive grease composition. The corrosion inhibitor may be used alone or in a mixture of multiple corrosion inhibitors.

[0081] The thermal conductive grease composition of this embodiment contains a base oil (A) and thermal conductive particles (B). The content of thermal conductive particles (B) is 79% by mass or more and less than 92% by mass of the total amount of the thermal conductive grease composition. In addition, the thermal conductive particles (B) include aluminum nitride (B1) with an average particle diameter D50 of less than 30 μm and aluminum nitride (B2) with an average particle diameter D50 of 30 μm or more, and the mass ratio of the content of aluminum nitride (B1) to the content of aluminum nitride (B2) ((B2) / (B1)) is 1 to 3. The thermal conductive grease composition of this embodiment has low viscosity because the content of thermal conductive particles (B) and the mass ratio of aluminum nitride (B1) to aluminum nitride (B2) are within a specific range. This is presumed to be due to the arrangement of aluminum nitride in the thermally conductive grease approaching close packing, reducing the gaps between particles, decreasing the resistance when the base oil moves between particles, and reducing the interaction between particles.

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0083] <Preparation of Thermally Conductive Grease Compositions> The thermally conductive grease compositions of Examples 1 and 2, and the thermally conductive grease compositions of Comparative Examples 1 to 6 were prepared according to the blending ratios shown in Table 1. The values ​​in Table 1 represent the blending ratio (mass%) relative to the total amount of the thermally conductive grease composition.

[0084] (1) Base oil (A) ・(A)-1: Poly-α-olefin (40°C kinematic viscosity = 412 mm) ２ / s, density 0.846g / cm ３ )

[0085] (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 8 μm) ・(B)-3: Aluminum nitride (spherical, average particle size D50 30 μm) ・(B)-4: Aluminum nitride (spherical, average particle size D50 50 μm) ・(B)-5: Aluminum nitride (spherical, average particle size D50 120 μm)

[0086] (3) Acidic phosphate ester (C) ・(C)-1: Oleyl acidic phosphate ester (JP518-O, manufactured by Johoku Chemical Co., Ltd.)

[0087] (4) Additive X-1: Mixture containing phosphite ester (LUBRIZOL 6178, manufactured by Lubrizol Nippon Co., Ltd.)

[0088] [Measurement of rotational viscosity] The rotational viscosity of each example of the thermally conductive grease composition was measured under the following measurement conditions. The results are shown in Table 1. <Measurement conditions> Equipment used: HAAKE MARS3 Measurement temperature: 25℃ Sensor used: Parallel plate type 25 mm Sample thickness: 1 mm Shear rate: 10 s⁻¹

[0089]

[0090] As shown in Table 1, the thermal conductive grease composition of the example was found to have lower viscosity compared to the thermal conductive grease composition of the comparative example. Therefore, it can be seen that the thermal conductive grease composition of the example is easier to thin when pressed under the same load, reducing thermal resistance and thus exhibiting superior heat dissipation characteristics.

[0091] While preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications are possible without departing from the spirit of the invention. The present invention is not limited by the foregoing description, but only by the scope of the appended claims.

Claims

1. A thermally conductive grease composition comprising a base oil (A) and thermally conductive particles (B), wherein the content of the thermally conductive particles (B) is 79% by mass or more and less than 92% by mass of the total amount of the thermally conductive grease composition, the thermally conductive particles (B) comprises aluminum nitride (B1) having an average particle diameter D50 of less than 30 μm and aluminum nitride (B2) having an average particle diameter D50 of 30 μm or more, and the mass ratio ((B2) / (B1)) of the content of aluminum nitride (B1) to the content of aluminum nitride (B2) is 1 to 3.

2. The thermally conductive grease composition according to claim 1, further comprising one or more compounds selected from the group consisting of phosphate esters, phosphite esters, and salts of phosphite esters.

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