Thermally conductive grease composition

Abstract

A thermally conductive grease composition comprising a base oil and thermally conductive fillers, wherein the thermally conductive fillers include a filler A that is zinc oxide and fillers that are each aluminum nitride, the fillers that are each aluminum nitride include a filler B and a filler C, the filler B has the smallest volume average particle diameter among the fillers that are each aluminum nitride, the filler C has the largest volume average particle diameter among the fillers that are each aluminum nitride, and the volume average particle diameter of the filler A is smaller than the volume average particle diameter of the filler B.

Description

Thermally conductive grease composition

[0001] The present disclosure relates to a thermally conductive grease composition.

[0002] Among semiconductor components used in electronic devices and the like, there are components that generate heat during use, such as a computer's CPU (Central Processing Unit) and power semiconductors for power control. In order to protect these semiconductor components from heat and allow them to function normally, there is a method of conducting the generated heat to a heat dissipation component such as a heat sink to dissipate the heat. A thermally conductive grease composition is applied between a heat-generating component such as a semiconductor component and a heat dissipation component to bring them into close contact, and is used to enhance heat conduction.

[0003] In thermally conductive grease compositions, thermally conductive fillers selected from various thermally conductive materials are used to improve thermal conductivity. As thermally conductive materials, for example, metal oxides such as zinc oxide and aluminum oxide, nitrides such as silicon nitride, aluminum nitride, and boron nitride, and metal powders such as aluminum, copper, and silver are used. Among such thermally conductive materials, aluminum nitride is known as a thermally conductive material having high thermal conductivity, and various improvements have been proposed (see, for example, Patent Documents 1 and 2).

[0004] Patent Document 1: Japanese Unexamined Patent Publication No. 2017-014445 Patent Document 2: International Publication No. WO 2014 / 123247

[0005] Along with the miniaturization and higher density of electronic devices, there is a demand for thermally conductive grease compositions having high thermal conductivity (specifically, 8 W / (m·K) or higher). Thermally conductive grease compositions are also required to have coatability and heat resistance. However, the reality is that a thermally conductive grease composition having high thermal conductivity of 8 W / (m·K) or higher and excellent coatability and heat resistance has not yet been obtained.

[0006] An object to be solved by an embodiment of the present disclosure is to provide a thermally conductive grease composition that has high thermal conductivity (specifically, 8 W / (m·K) or higher) and is excellent in coatability and heat resistance.

[0007] This disclosure includes the following embodiments: <1> A thermal conductive grease composition comprising a base oil and a thermal conductive filler, wherein the thermal conductive filler comprises filler A, which is zinc oxide, and filler C, the aluminum nitride filler comprises filler B and filler C, filler B has the smallest volume average particle diameter among the aluminum nitride fillers, filler C has the largest volume average particle diameter among the aluminum nitride fillers, and the volume average particle diameter of filler A is smaller than the volume average particle diameter of filler B, the thermal conductive grease composition. <2> The thermal conductive grease composition according to <1>, wherein the volume average particle diameter of filler C is 40 μm or more and less than 200 μm, the thermal conductive grease composition according to <1> or <2>, wherein the total content of filler B and filler C is greater than the content of filler A, the thermal conductive grease composition according to <1> or <2>. <4> A thermal conductive grease composition according to any one of <1> to <3>, wherein the ratio of the content of filler A to the total content of aluminum nitride fillers is 0.35 or more and less than 1 by mass. <5> A thermal conductive grease composition according to any one of <1> to <4>, wherein the ratio of the content of filler C to the content of filler B is 1 or more and 10 or less by mass. <6> A thermal conductive grease composition according to any one of <1> to <5>, wherein the total content of thermal conductive fillers is 90% by mass or more and 98% by mass or less of the total amount of the thermal conductive grease composition. <7> A thermal conductive grease composition according to any one of <1> to <6>, wherein the base oil contains polyalphaolefin and organic acid ester.

[0008] According to one embodiment of the present disclosure, a thermally conductive grease composition is provided that has high thermal conductivity (specifically, 8 W / (m·K) or higher) and excellent applicability and heat resistance.

[0009] Figure 1 is a diagram illustrating the preparation of a sample for measuring spreading consistency. Figure 2 is a diagram illustrating the measurement of spreading consistency.

[0010] The following describes an example embodiment of this disclosure. These descriptions and examples are illustrative and do not limit the scope of the invention. In numerical ranges described stepwise in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the value shown in the example.

[0011] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if multiple types of the substance corresponding to each component are present in the composition, unless otherwise specified, it refers to the total amount of those multiple types of substances present in the composition.

[0012] In this disclosure, "mass%" and "weight%" are synonymous, and "parts by mass" and "parts by weight" are synonymous. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, "JIS" is used as an abbreviation for Japanese Industrial Standards.

[0013] In this disclosure, unless otherwise specified, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are determined by gel permeation chromatography (GPC) analysis using a TSKgel SuperHM-H column (a trade name of Tosoh Corporation), detecting the molecular weight using a differential refractometer with a solvent PFP (pentafluorophenol) / chloroform = 1 / 2 (mass ratio), and converting it using polystyrene as a standard substance.

[0014] <Thermal Conductive Grease Composition> The thermal conductive grease composition according to this disclosure is a thermal conductive grease composition comprising a base oil and a thermal conductive filler, wherein the volume average particle diameter of filler A is smaller than the volume average particle diameter of filler B, and the volume average particle diameter of filler B is smaller than the volume average particle diameter of filler C.

[0015] The thermally conductive grease composition according to this disclosure, with the above configuration, has high thermal conductivity (specifically, 8 W / (m·K) or higher), excellent applicability and heat resistance. The reason for this is not clear, but it is presumed to be as follows.

[0016] Regarding high thermal conductivity, generally, using large-particle fillers reduces interfacial loss per unit volume, thus increasing thermal conductivity. Combining this with small-particle fillers results in close packing, which is thought to yield even higher thermal conductivity. Regarding applicability, large-particle fillers have less contact per unit volume, reducing resistance and friction and lowering viscosity. Furthermore, using medium-particle fillers acts as a binder, which is thought to increase smoothness. Regarding heat resistance, using large-particle fillers reduces the specific surface area per unit volume and increases the amount of base oil covering the fillers per unit volume, so it is thought to withstand some bleeding and evaporation. The inventors have found that grease compositions using only zinc oxide have good heat resistance, and by adding zinc oxide as a small-particle filler to a composition containing aluminum nitride as a medium-particle and large-particle filler, the dispersed zinc oxide covers the highly thermally conductive aluminum nitride, thus achieving both high thermal conductivity and applicability. The thermally conductive filler in this disclosure includes filler A, which is zinc oxide, and fillers B and C, which are aluminum nitride. The volume-average particle sizes of fillers A, B, and C are such that filler A is smaller than filler B, and filler B is smaller than filler C. As a result, fillers A, B, and C function as the small-particle-size filler, medium-particle-size filler, and large-particle-size filler, respectively, and are presumed to have high thermal conductivity (specifically, 8 W / (m·K) or higher), excellent coatability and heat resistance.

[0017] On the other hand, if only aluminum nitride of a single particle size is used as a thermally conductive filler, the viscosity increases, the thermally conductive grease composition hardens, and the applicability decreases. Combining aluminum nitride with different particle sizes can suppress the increase in viscosity and achieve high thermal conductivity, but it reduces the heat resistance of the thermally conductive grease composition. Furthermore, if only one type of aluminum nitride and one type of zinc oxide are combined, depending on the combination, high thermal conductivity up to 7 W / (m·K) can be achieved, but it is not possible to obtain a thermally conductive grease composition with high thermal conductivity of 8 W / (m·K) or higher, as well as good applicability and heat resistance.

[0018] The following describes in detail each component contained in the thermally conductive grease composition relating to this disclosure.

[0019] (Base Oil) The thermally conductive grease composition according to this disclosure contains a base oil. The base oil is not particularly limited and includes, for example, mineral oil, synthetic hydrocarbon oil, organic acid ester, phosphate ester, silicone oil, and fluorine oil. The base oil may be included in the thermally conductive grease composition alone or in combination of two or more types.

[0020] Examples of mineral oils include those obtained by refining the lubricating oil fraction of crude oil using a combination of refining methods such as solvent refining, hydrorefining, hydrocracking, and hydrodeswaxing. In addition, examples of mineral oils include highly refined paraffinic mineral oils obtained by subjecting hydrorefined oils, catalytic isomerized oils, etc., to treatments such as solvent dewaxing or hydrodeswaxing.

[0021] Examples of synthetic hydrocarbon oils include polyalphaolefins. Examples of polyalphaolefins include alphaolefins produced from ethylene, propylene, butene, and their derivatives as raw materials, either individually or in combination of two or more, and polymerized. The polyalphaolefin is preferably a polymer of alphaolefin having 6 to 18 carbon atoms. The polyalphaolefin preferably contains at least one selected from the group consisting of polymers of 1-decene and polymers of 1-dodecene.

[0022] Examples of organic acid esters include monoesters, diesters, and polyol esters. Examples of monoesters include esters of a monobasic acid and an alcohol. Examples of monobasic acids include fatty acids such as butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, eicosanoic acid, docosanoic acid, palmitoleic acid, oleic acid, and ricinoleic acid; acrylic acid; methacrylic acid; etc. Examples of alcohols used in the synthesis of monoesters include oleyl alcohol, lauryl alcohol, methanol, ethanol, pentanol, hexanol, ethylene glycol, propylene glycol, glycerol, neopentyl glycol, trimethylolmethane, trimethylolethane, trimethylolpropane, trimethylolbutane, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, and lauryl alcohol.

[0023] Examples of diesters include esters of a dibasic acid and an alcohol. Examples of dibasic acids include adipic acid, azelaic acid, sebacic acid, and dodecanediic acid. The alcohol used in the synthesis of the diester may be a monohydric alcohol or a polyhydric alcohol having two or more hydroxyl groups in one molecule. The same alcohol used in the synthesis of monoesters can be used for the synthesis of diesters.

[0024] Examples of polyol esters include esters of polyols and saturated fatty acids. Examples of polyols include dihydric alcohols and polyols in which there is no hydrogen atom on the carbon at the β position relative to the hydroxyl group. Examples of dihydric alcohols include ethylene glycol, propylene glycol, butylene glycol, 2-butyl-2-ethylpropanediol, and 2,4-diethylpentanediol. Specific examples of polyols in which there is no hydrogen atom on the carbon at the β position relative to the hydroxyl group include neopentyl glycol, trimethylolpropane, and pentaerythritol. Examples of saturated fatty acids are not particularly limited and include, for example, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, and behenic acid.

[0025] Examples of phosphate esters include triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, and trixylenyl phosphate. Examples of silicone oils include polysiloxanes such as dimethylpolysiloxane and methylphenylpolysiloxane; modified silicones; and others. Examples of fluorinated oils include perfluoropolyethers.

[0026] From the viewpoint of a good balance between high thermal conductivity and coatability, the base oil preferably contains polyalphaolefin and organic acid ester. Furthermore, while the application of a base oil containing low molecular weight siloxane gas may cause contact failure due to the low molecular weight siloxane gas, the application of polyalphaolefin and organic acid ester is also preferable from the viewpoint of preventing contact failure due to low molecular weight siloxane gas.

[0027] The polyalphaolefin content is preferably 70% to 99% by mass, more preferably 80% to 99% by mass, and even more preferably 85% to 99% by mass, based on the total content of polyalphaolefin and organic acid esters.

[0028] The base oil content is preferably 2.0% by mass or more and 8.5% by mass or less, more preferably 3.0% by mass or more and 8.0% by mass or less, and even more preferably 3.5% by mass or more and 7.0% by mass or less, based on the total amount of the thermal conductive grease composition.

[0029] From the viewpoint of high thermal conductivity and coatability, the base oil should have a kinematic viscosity of 10 mm at 40°C (also referred to as 40°C kinematic viscosity). ２ / s or more 600mm ２ Preferably, it should be less than or equal to 20 mm ２ / s or more 450mm ２ It is more preferable that the kinematic viscosity is less than or equal to / s. The kinematic viscosity at 40°C is a value measured according to the kinematic viscosity test method of JIS K 2283:2000.

[0030] (Thermal Conductive Filler) The thermal conductive grease composition according to this disclosure contains a thermal conductive filler. In this disclosure, a thermal conductive filler is a filler with a thermal conductivity of 5 W / (m·K) or higher. The thermal conductivity of the thermal conductive filler is a value measured by the laser flash method (JIS R1611:2010).

[0031] The shape of the thermally conductive filler is not particularly limited. The thermally conductive filler may be granular, crushed, spherical, or any other shape. One preferred form of the thermally conductive filler is spherical.

[0032] In this disclosure, the thermally conductive filler comprises filler A, which is zinc oxide, and filler C, wherein the aluminum nitride filler comprises filler B and filler C, where filler B has the smallest volume-average particle diameter among the aluminum nitride fillers, filler C has the largest volume-average particle diameter among the aluminum nitride fillers, and the volume-average particle diameter of filler A is smaller than the volume-average particle diameter of filler B.

[0033] In the following, filler A (zinc oxide), filler B (aluminum nitride), and filler C (aluminum nitride) may be simply referred to as filler A, filler B, and filler C, respectively.

[0034] In this disclosure, the volume-average particle size of the thermally conductive filler is measured by laser diffraction / scattering in accordance with JIS Z 8825:2013 (corresponding international standard: ISO 13320). Specifically, the measurement procedure involves first measuring the volume distribution of the thermally conductive filler in a sample containing the thermally conductive filler using a laser diffraction / scattering particle size analyzer. Then, based on the obtained measurement values ​​(volume distribution), the volume-average particle size of the thermally conductive filler contained in the sample can be determined. As an example of a measuring device, the SALD-7500nano, manufactured by Shimadzu Corporation, can be used as a laser diffraction / scattering particle size analyzer.

[0035] The zinc oxide thermally conductive filler contains filler A, which is zinc oxide. The volume-average particle size of filler A is smaller than the volume-average particle size of filler B, which is aluminum nitride.

[0036] The volume-average particle diameter of filler A is preferably 0.15 μm or more and less than 2 μm, more preferably 0.20 μm or more and 1.5 μm or less, and even more preferably 0.3 μm or more and 1.2 μm or less, from the viewpoint of high thermal conductivity, coatability, and heat resistance. Filler A may consist of only one type or two or more types. When two or more types of filler A are included, it is preferable that each of the two or more types of filler A falls within the above-mentioned volume-average particle diameter range.

[0037] The zinc oxide included as filler A in the thermally conductive filler is not particularly limited as long as it has a volume-average particle size smaller than the volume-average particle size of filler B, and a zinc oxide having a predetermined volume-average particle size can be selected and used from zinc oxide commonly used as a thermally conductive filler.

[0038] • The aluminum nitride thermally conductive filler includes a filler that is aluminum nitride. The filler that is aluminum nitride includes filler B and filler C. The filler that is aluminum nitride may be of two types, filler B and filler C, or may be three or more types including filler B, filler C, and a filler other than filler B and filler C. Filler B has the smallest volume-average particle diameter among the fillers that are aluminum nitride, and filler C has the largest volume-average particle diameter among the fillers that are aluminum nitride. That is, the volume-average particle diameter of filler B is smaller than the volume-average particle diameter of filler C.

[0039] From the viewpoints of high thermal conductivity, coating property and heat resistance, the volume-average particle diameter of filler B is preferably not less than 5 µm and less than 40 µm, more preferably not less than 6 µm and not more than 30 µm, and still more preferably not less than 7.5 µm and not more than 25 µm.

[0040] In a certain aspect, from the viewpoints of high thermal conductivity, coating property and heat resistance, the volume-average particle diameter of filler B is preferably not less than 20 times the volume-average particle diameter of filler A, more preferably not less than 20 times and not more than 50 times, and still more preferably not less than 25 times and not more than 40 times.

[0041] From the viewpoints of high thermal conductivity, coating property and heat resistance, the volume-average particle diameter of filler C is preferably not less than 40 µm and less than 200 µm, more preferably not less than 50 µm and not more than 180 µm, and still more preferably not less than 60 µm and not more than 150 µm. When two or more types of filler C are included, each of the two or more types of filler C preferably falls within the above-mentioned volume-average particle diameter range.

[0042] In a certain aspect, from the viewpoints of high thermal conductivity and coating property, the volume-average particle diameter of filler C is preferably not less than 2 times the volume-average particle diameter of filler B, more preferably not less than 3 times and not more than 8 times, and still more preferably not less than 4 times and not more than 7 times.

[0043] The aluminum nitride contained as filler B in the thermally conductive filler is not particularly limited as long as it has a volume-average particle diameter larger than that of filler A and smaller than that of filler C, and a material having a predetermined volume-average particle diameter can be selected and used from aluminum nitride that is generally used as a thermally conductive filler.

[0044] The aluminum nitride contained as filler C in the thermally conductive filler is not particularly limited as long as it has a volume-average particle diameter smaller than that of filler B, and a material having a predetermined volume-average particle diameter can be selected and used from aluminum nitride that is generally used as a thermally conductive filler.

[0045] From the viewpoints of high thermal conductivity, coatability and heat resistance, the total content of filler B and filler C is preferably greater than the content of filler A.

[0046] From the viewpoint of heat resistance, the ratio of the content of filler A to the total content of fillers that are aluminum nitride (content of filler A / total content of fillers that are aluminum nitride) is preferably 0.35 or more and less than 1, more preferably 0.35 or more and 0.8 or less, and still more preferably 0.4 or more and 0.6 or less, based on mass.

[0047] From the viewpoints of high thermal conductivity and coatability, the ratio of the content of filler C to the content of filler B (content of filler C / content of filler B) is preferably 1 or more and 10 or less, more preferably 1 or more and 5 or less, and still more preferably 1 or more and 3 or less, based on mass.

[0048] The total content of the thermally conductive filler is preferably 90% by mass or more and 98% by mass or less, more preferably 92% by mass or more and 97% by mass or less, and still more preferably 94% by mass or more and 96% by mass or less, relative to the total amount of the thermally conductive grease composition.

[0049] The total content of the thermally conductive filler is preferably 60% to 98% by volume, more preferably 65% ​​to 95% by volume, and even more preferably 70% to 90% by volume, based on the total volume of the thermally conductive grease composition.

[0050] The thermally conductive grease compositions relating to this disclosure may contain other thermally conductive fillers other than zinc oxide and aluminum nitride, to the extent that the effects relating to this disclosure are achieved. The material of the other thermally conductive fillers is not particularly limited, but examples include magnesium oxide, aluminum oxide, titanium oxide, boron nitride, carbon, silicon carbide, silica, and the like.

[0051] The thermally conductive filler may be a surface-treated thermally conductive filler. A surface-treated thermally conductive filler may contribute to improved affinity with other components other than the thermally conductive filler.

[0052] The surface treatment of the thermally conductive filler is not particularly limited and may be a physical or chemical treatment. Known treatments that can treat the surface of the particles constituting the thermally conductive filler can be applied. The surface treatment is preferably a treatment using a surface treatment agent.

[0053] Examples of surface treatment agents include silane-based coupling agents, titanium-based coupling agents, carboxylic acid-based coupling agents, phosphate-based coupling agents, fatty acids, polymer compounds, surfactants, and oils and fats.

[0054] From the viewpoint of dispersibility, the thermally conductive filler may be surface-treated with a silane-based coupling agent as a surface treatment agent.

[0055] (Dispersant) The thermally conductive grease composition according to this disclosure preferably contains a dispersant. Various dispersants can be used as the dispersant, and it is preferable that the dispersant is a compound having a lipophilic portion and a functional group that adsorbs to calcium carbonate particles and thermally conductive fillers. Specifically, examples of dispersants include carboxylic acid compounds and polyalkylene glycol compounds.

[0056] Carboxylic acid compounds are compounds that have at least one carboxyl group in their molecule. Examples of carboxylic acid compounds include fatty acids and polycarboxylic acids (i.e., compounds that have two or more carboxyl groups in one molecule).

[0057] The molecular weight of the carboxylic acid compound is preferably 100 to 2000, more preferably 150 to 1500, and even more preferably 200 to 1000.

[0058] When a molecular weight distribution exists for a carboxylic acid compound, the molecular weight of the carboxylic acid compound refers to the weight-average molecular weight in polystyrene equivalent, measured by gel permeation chromatography (GPC). The measurement conditions and equipment are as follows: Measurement device: Shodex GPC-101 Column: Shodex GPC LF-804 (Number of columns: 3) Detector: RI (Differential refractive detector) Temperature: 40°C Mobile phase: THF (Tetrahydrofuran) Flow rate: 1 mL / min Sample concentration: 1.0 mass% / vol% Sample injection volume: 100 μL

[0059] Examples of fatty acids, which are embodiments of carboxylic acid compounds, include saturated fatty acids and unsaturated fatty acids. Examples of saturated fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid. Examples of unsaturated fatty acids include caproleic acid, lindelic acid, myristoleic acid, palmitoleic acid, zomalic acid, peteroceric acid, peteroceraidic acid, oleic acid, elaidic acid, pasenic acid, codoic acid, gondouic acid, cetoleic acid, erucic acid, brassic acid, ceracoleic acid, linoleic acid, linoleidic acid, linolenic acid, and arachidonic acid.

[0060] Other embodiments of the carboxylic acid compound include Hypermer KD-4, Hypermer KD-9, Hypermer KD-9-SS, Hypermer KD-12, and Hypermer KD-16, all manufactured by Croda Japan Co., Ltd.

[0061] Polyalkylene glycol compounds are polymer compounds having a repeating ether bond structure, and are produced, for example, by ring-opening polymerization of cyclic ethers. Polyalkylene glycol compounds having hydroxyl groups are preferred.

[0062] Polyalkylene glycol compounds containing hydroxyl groups tend to be highly adhesive. Therefore, surface modifiers adsorbed onto the surface of thermally conductive fillers adhere to the substrate, improving the dispersibility of thermoplastic fillers and contributing to the suppression of the pump-out phenomenon.

[0063] Examples of polyalkylene glycol compounds having a hydroxyl group include polyalkylene glycol and etherified polyalkylene glycols. Examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, and polybutylene glycol.

[0064] Examples of etherified polyalkylene glycols include compounds in which polyalkylene glycol and a hydrocarbon group are linked by an ether bond. The number of carbon atoms in the hydrocarbon group contained in the etherified polyalkylene glycol can be, for example, 12 to 65. The structure of the hydrocarbon group is not particularly limited and may be linear, branched, or cyclic.

[0065] Examples of etherified polyalkylene glycols include polyoxyethylene monooleyl ether, polyoxyethylene monostearyl ether, polyoxyethylene monocetyl ether, and polyoxyethylene lanolin alcohol. From the viewpoint of good dispersibility and suppression of the pump-out phenomenon, polyoxyethylene lanolin alcohol is preferred.

[0066] The dispersant content is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably 0.1% by mass or more and 0.7% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less, based on the total amount of the thermal conductive grease composition.

[0067] The dispersant may be included in the thermal conductive grease composition alone or in combination of two or more types. When the thermal conductive grease composition contains two or more types of dispersants, the above content refers to the total content of the dispersants.

[0068] (Other Additives) The thermal conductive grease composition according to this disclosure may contain other additives in addition to the components described above. Examples of other additives include antioxidants, pump-out inhibitors, rust inhibitors, corrosion inhibitors, thickeners, and cleaning agents.

[0069] The thermally conductive grease composition may also contain a colorant comprising a leuco dye and a color developer as other additives. In one embodiment, the thermally conductive grease composition may contain a encapsulated pigment in which a leuco dye, a color developer, and a color change temperature regulator are encapsulated by a known encapsulation method. The inclusion of such a encapsulated pigment in the thermally conductive grease composition allows for visual confirmation of the temperature distribution. The leuco dye is preferably an electron-donating color-developing organic compound, such as triphenylmethane compounds, spiropyran compounds, fluorane compounds, diphenylmethane compounds, rhodamine lactam compounds, indolylphthalide compounds, leucoauramine compounds, and pyridine compounds. The color developer is preferably an electron-accepting compound, such as diphenylacetic acid, 3,3-diphenylpropionic acid, and triphenylacetic acid. The color change temperature regulator is preferably a reaction medium that induces electron transfer reactions by electron-donating color-developing organic compounds and electron-accepting compounds. Examples include alcohol compounds, ester compounds, ketone compounds, ether compounds, acid amide compounds, azomethine compounds, fatty acid compounds, and hydrocarbon compounds.

[0070] (Physical Properties of Thermally Conductive Grease Composition) -Thermal Conductivity- The thermal conductivity of the thermally conductive grease composition according to this disclosure is 8.0 W / (m·K) or higher, preferably 8.5 W / (m·K) or higher, and more preferably 9.0 W / (m·K) or higher. The upper limit of the thermal conductivity is not particularly limited, and from the viewpoint of applicability, for example, it is 50 W / (m·K) or lower.

[0071] Thermal conductivity shall be measured in accordance with ISO 22007-2. For measuring thermal conductivity, a device such as the TPS2500S manufactured by Kyoto Electronics Manufacturing Co., Ltd. can be used.

[0072] -Shear Viscosity- From the viewpoint of applicability, the shear viscosity of the thermally conductive grease composition according to this disclosure is preferably 1000 Pa·s or less, more preferably 50 Pa·s to 900 Pa·s, even more preferably 100 Pa·s to 700 Pa·s, and particularly preferably 100 Pa·s to 500 Pa·s, measured at a measurement temperature of 25°C and a shear rate of 10 [1 / s].

[0073] In this disclosure, shear viscosity is measured using a viscoelasticity measuring device under the conditions of a measurement temperature of 25°C and a predetermined shear rate. As a viscoelasticity measuring device, for example, product name: MCR102e, manufactured by Anton Paar, can be used.

[0074] -Heat Resistance- The heat resistance of the thermal conductive grease composition according to this disclosure is evaluated by tracking the change in spread consistency over time for the thermal conductive grease composition subjected to a predetermined thermal load, and by the time (h) until the spread consistency reaches 140. In this disclosure, if the time (h) until the spread consistency reaches 140 is 600 (h) or more, the thermal conductive grease composition is determined to have heat resistance. Details of the measurement method and measurement conditions for "spread consistency" will be described later in the examples.

[0075] (Applications) The thermally conductive grease composition according to this disclosure has excellent thermal conductivity, applicability, and heat resistance, and can be applied to the gaps between various heat-generating elements and heat sinks. Examples of heat-generating elements include semiconductor components, and examples of heat sinks include heat sinks.

[0076] (Method for producing a thermally conductive grease composition) The method for producing a thermally conductive grease composition is not particularly limited, and a base oil and a thermally conductive filler may be mixed with a dispersant, preferably, and other additives may be mixed as needed. The mixing order of the base oil and each component is not particularly limited, and each component may be mixed sequentially with the base oil.

[0077] Examples are described below, but the thermally conductive grease compositions relating to this disclosure are not limited to these examples.

[0078] <Examples 1-5, Comparative Examples 1-10> Each component listed in the composition column of Table 1 or Table 2 (i.e., base oil, thermally conductive filler, dispersant, and other additives) was blended in the blending ratio (mass%) shown in Table 1 or Table 2. A blank space in the composition column of Table 1 or Table 2 indicates that the corresponding component was not blended.

[0079] In Examples 1 to 5, thermally conductive grease compositions having the compositions shown in Table 1 were prepared. Comparative Examples 5 to 6 and 10 were not greased. Therefore, the performance evaluations described below were not performed for Comparative Examples 5 to 6 and 10.

[0080] <Evaluation> The following performance evaluations were performed using each of the thermal conductive grease compositions obtained in Examples 1 to 5, and the thermal conductive grease compositions of Comparative Examples 1 to 4 and 7 to 9.

[0081] (Thermal Conductivity) Thermal conductivity was measured in accordance with ISO 22007-2. The thermal conductivity measuring device used was a TPS2500S manufactured by Kyoto Electronics Manufacturing Co., Ltd. A thermal conductivity of 8.0 W / (m·K) or higher means that the thermal conductive grease composition has the high thermal conductivity described herein.

[0082] (Heat Resistance) Heat resistance was evaluated by tracking the change in spread consistency over time for a thermally conductive grease composition subjected to a predetermined heat load, and measuring the time (h) until the spread consistency reached 140. A time (h) of 600 (h) or more until the spread consistency reached 140 indicates that the thermally conductive grease composition has heat resistance. The measurement method and conditions for spread consistency were as follows.

[0083] =Measurement Method and Measurement Conditions= (1) Preparation of the Measurement Sample As shown in Figure 1, the thermal conductive grease composition 12 was inserted between two opposing steel plates 11a and 11b via spacers 13a and 13b (height: 200 μm), and then left to stand in a constant temperature bath 10 (150°C) to apply a heat load. The amount of thermal conductive grease composition 12 inserted was 0.25 mL, and the thickness was 200 μm. The thermal conductive grease composition 12 that had been subjected to a heat load for a predetermined time was used as a sample for measuring the spread consistency.

[0084] (2) Measurement of spreading consistency As shown in Figure 2(A), a mold 15 having a filling section (inner diameter φ: 8.0 mm) is placed on the plate 14, and the thermal conductive grease composition 12 (measurement sample) after applying a heat load to the filling section is spread to 0.05 cm. ３ The mixture was filled to the specified volume and molded into a cylinder with a diameter of 8.0 mm. Next, after removing the mold 15 from the molded thermal conductive grease composition 12, a weight 17 and a top plate 18 were placed on the thermal conductive grease composition 12 using a support rod 16, as shown in Figure 2(B). The weight of the weight 17 was 100 g. Next, as shown in Figure 2(C), the support rod 16 was removed, and a load was applied to the thermal conductive grease composition 12 for 5 seconds, after which the weight 17 and top plate 18 were removed. The diameter d2 of the thermal conductive grease composition 12 spread on the plate 14 was measured, and the measured value was substituted into the following formula A to convert it to consistency. Consistency = d2 × 20 - 19.7 ...Formula A

[0085] (Applicability Evaluation) Applicability was evaluated by measuring the shear viscosity using a viscoelasticity measuring device (product name: MCR102e, manufactured by Anton Paar) at a measurement temperature of 25°C and a shear rate of 10¹ / s. A shear viscosity of 500 Pa·s or less measured under the condition of 10¹ / s indicates that the thermally conductive grease composition has excellent applicability.

[0086] The results are shown in Tables 1 and 2.

[0087]

[0088]

[0089] The results shown in Table 1 indicate that each thermally conductive grease composition in the examples has a high thermal conductivity of 8 W / (m·K) or higher, and exhibits excellent applicability and heat resistance. On the other hand, the results shown in Table 2 indicate that Comparative Examples 1-4, which do not contain filler A (zinc oxide), and Comparative Examples 7-9, which contain only one type of aluminum nitride, do not achieve at least one of the following: high thermal conductivity, applicability, and heat resistance. Furthermore, Comparative Examples 5-6 and 10 did not form grease.

[0090] Details of each component in Tables 1 and 2 are described below.

[0091] (Base oil) - Polyalphaolefin - Polyalphaolefin 1; Product name: DURASYN-168, manufactured by INEOS Oligomeres, polyalphaolefin (polymer of 1-decene), kinematic viscosity at 40°C: 46.4 mm ２ / s Polyalphaolefin 2; Product name: DURASYIN-170INEOS, manufactured by Oligomeres, polyalphaolefin (polymer of 1-decene), kinematic viscosity at 40°C: 65.3 mm ２ / s Polyalphaolefin 3; Product name: DURASYN-180R, manufactured by INEOS Oligomeres, kinematic viscosity at 40°C: 935 mmHg ２ / s -Organic acid ester- Lauryl methacrylate; Product name: Light Ester L, manufactured by Kyoeisha Chemical Co., Ltd., Lauryl methacrylate

[0092] (Thermally conductive fillers) - Zinc oxide (Filler A) - Zinc oxide 1; Product name: Zinc oxide type 1, manufactured by Sakai Chemical Co., Ltd., zinc oxide particles, volume average particle diameter 0.6 μm - Aluminum nitride (Filler B and Filler C) - Aluminum nitride 1; Product name: HF-01Dh, manufactured by Tokuyama Corporation, aluminum nitride (AlN) particles, surface treated, volume average particle diameter 1 μm - Aluminum nitride 2; Product name: HF-01D, manufactured by Tokuyama Corporation, aluminum nitride (AlN) particles, no surface treatment, volume average particle diameter 1 μm - Aluminum nitride 3; Product name: HF-20h, manufactured by Tokuyama Corporation, aluminum nitride (AlN) particles, surface treated, volume average particle diameter 17.8 μm - Aluminum nitride 4; Product name: HF-20, manufactured by Tokuyama Corporation, aluminum nitride (AlN) particles, no surface treatment, volume average particle diameter 17.8 μm - Aluminum nitride 5; Product name: HFS-80, manufactured by Tokuyama Corporation, aluminum nitride (AlN) particles, no surface treatment, volume average particle size 80 μm - Aluminum nitride 6; Product name: HFS-120, manufactured by Tokuyama Corporation, aluminum nitride (AlN) particles, no surface treatment, volume average particle size 120 μm

[0093] (Dispersants) ・Dispersant 1: Product name: Hypermer KD-9, manufactured by Croda Japan, carboxylic acid compound, polycarboxylic acid, weight-average molecular weight: 760 ・Dispersant 2: Product name: Polycol 15, manufactured by Croda Japan, polyoxyethylene lanolin alcohol

[0094] (Other Additives) - Antioxidants - Antioxidant: Irganox L57, manufactured by BASF Japan, reaction product of N-phenylbenzeneamine and 2,4,4-trimethylpentene - Pump-out Inhibitor - Calcium Carbonate: Product name: Shirotsuka, manufactured by Shiraishi Kogyo Co., Ltd., calcium carbonate particles surface-treated with rosin-based compounds, volume average particle size 30 nm

[0095] 10 Constant temperature bath 11a, 11b Steel plate 12 Thermal conductive grease composition 13a, 13b Spacer 14 Plate 15 Formwork 16 Support rod 17 Weight 18 Top plate d1, d2 Diameter of the sample for measurement

[0096] The disclosure of Japanese Patent Application No. 2025-057243, filed on 28 March 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A thermally conductive grease composition comprising a base oil and a thermally conductive filler, wherein the thermally conductive filler comprises filler A, which is zinc oxide, and filler C, wherein the aluminum nitride filler comprises filler B and filler C, where filler B has the smallest volume-average particle diameter among the aluminum nitride fillers, filler C has the largest volume-average particle diameter among the aluminum nitride fillers, and the volume-average particle diameter of filler A is smaller than the volume-average particle diameter of filler B.

2. The thermally conductive grease composition according to claim 1, wherein the volume-average particle diameter of the filler C is 40 μm or more and less than 200 μm.

3. The thermal conductive grease composition according to claim 1 or claim 2, wherein the total content of filler B and filler C is greater than the content of filler A.

4. The thermal conductive grease composition according to claim 1 or claim 2, wherein the ratio of the content of filler A to the total content of the aluminum nitride filler is 0.35 or more and less than 1 by mass.

5. The thermal conductive grease composition according to claim 1 or claim 2, wherein the ratio of the content of filler C to the content of filler B is 1 or more and 10 or less by mass.

6. The thermal conductive grease composition according to claim 1 or claim 2, wherein the total content of the thermal conductive filler is 90% by mass or more and 98% by mass or less of the total amount of the thermal conductive grease composition.

7. The thermally conductive grease composition according to claim 1 or claim 2, wherein the base oil comprises a polyalphaolefin and an organic acid ester.

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