Thermally conductive composition

Abstract

Provided is a thermally conductive composition in which an increase in viscosity can be suppressed even if the content of an inorganic powdered filler is increased.　This thermally conductive composition contains a base oil and an inorganic powdered filler, wherein the composition further containing a titanate-based coupling agent and / or an aluminate-based coupling agent.

Description

Thermally conductive composition

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

[0002] Among the semiconductor components used in electronic devices, there are heat-generating components that generate heat during use, such as computer CPUs, Peltier elements, LEDs, and power semiconductors for power supply control such as inverters.

[0003] To protect these heat-generating components from heat and ensure their normal function, one method is to conduct the generated heat to a heat-dissipating component (cooling device) such as a heat spreader or heat sink. Thermally conductive grease is applied between these heat-generating and heat-dissipating components to ensure close contact between them, and is used to efficiently conduct the heat from the heat-generating component to the heat-dissipating component. Thermally conductive grease is a grease-like composition in which a large amount of inorganic powder filler with high thermal conductivity (metal oxides such as zinc oxide and aluminum oxide, inorganic nitrides such as boron nitride, silicon nitride, and aluminum nitride, and metal powders such as aluminum and copper) is dispersed in a base oil such as liquid hydrocarbon, silicone oil, or fluorinated oil.

[0004] More specifically, thermally conductive grease is applied to the thermal contact interface between a heat-generating component such as a computer CPU and a heat-dissipating component such as a heat sink, and between a heat-generating component such as a high-output inverter mounted on a hybrid vehicle or electric vehicle and a heat-dissipating component such as a heat spreader. In recent years, semiconductor elements in these electronic devices have become smaller and more powerful, resulting in increased heat density and heat output, and are increasingly being installed in close proximity to other heat-generating semiconductor components.

[0005] For example, Patent Document 1 describes a technology related to a thermally conductive grease containing a specific antioxidant in a predetermined proportion, and states that this thermally conductive grease has high thermal conductivity, consistency, and thermal stability at high temperatures.

[0006] JP 2019-081841 A

[0007] Although the thermal conductivity of a thermally conductive composition containing an inorganic powder filler can be improved by increasing the content of the inorganic powder filler, increasing the content of the inorganic powder filler also increases the viscosity of the thermally conductive composition.

[0008] If the viscosity of the thermally conductive composition increases, the desired properties of the thermally conductive composition may not be obtained, for example, when the thermally conductive composition is used as a thermally conductive grease, such as insufficient coatability, etc. Thus, the thermally conductive composition is required to have a viscosity that does not increase significantly even when the content of the inorganic powder filler is increased.

[0009] An object of the present invention is to provide a thermally conductive composition that can suppress an increase in viscosity even when the content of inorganic powder filler is increased.

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that a thermally conductive composition containing a specific coupling agent can solve the above-mentioned problems, thereby completing the present invention.

[0011] A first aspect of the present invention is a thermally conductive composition containing a base oil and an inorganic powder filler, and the thermally conductive composition further contains at least one of a titanate-based coupling agent or an aluminate-based coupling agent.

[0012] A second aspect of the present invention is the thermally conductive composition according to the first aspect of the present invention, wherein the total content of the titanate-based coupling agent and the aluminate-based coupling agent is 3% by volume or more and 30% by volume or less of the total amount of the thermally conductive composition.

[0013] A third aspect of the present invention is the thermally conductive composition according to the first or second aspect of the present invention, wherein the inorganic powder filler is at least one selected from the group consisting of copper, aluminum, zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride, and silicon carbide.

[0014] A fourth aspect of the present invention is the thermally conductive composition according to the first or second aspect of the present invention, wherein the base oil is at least one selected from the group consisting of mineral oil, synthetic hydrocarbon oil, diester, polyol ester, and phenyl ether.

[0015] The thermally conductive composition of the present invention can effectively suppress an increase in viscosity even when the content of the inorganic powder filler is increased.

[0016] Specific embodiments of the present invention (hereinafter referred to as "present embodiments") will be described in detail below. Note that the present invention is not limited to the following embodiments, and can be practiced with appropriate modifications within the scope of the object of the present invention. Furthermore, in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "X or more and Y or less."

[0017] 1. Thermally conductive composition The thermally conductive composition according to the present embodiment contains a base oil and an inorganic powder filler, and further contains at least one of a titanate-based coupling agent and an aluminate-based coupling agent.

[0018] By including such a specific coupling agent, it is possible to effectively suppress an increase in viscosity even if the content of the inorganic powder filler is increased.

[0019] The thermally conductive composition according to the present embodiment can be used as a thermally conductive composition for forming a thermally conductive layer that is disposed between a heat-generating component such as a computer CPU, a Peltier element, an LED, or a power semiconductor for power supply control such as an inverter, and a heat-dissipating component such as a heat spreader or a heat sink, and that conducts heat from the heat-generating component to the heat-dissipating component, thereby dissipating the heat from the heat-generating component.

[0020] The thermally conductive composition according to the present embodiment can be used as a semi-solid or semi-fluid thermally conductive grease at room temperature. Furthermore, the thermally conductive composition according to the present embodiment can also be used as a thermally conductive paste that is fluid at room temperature by adding, for example, a diluent.

[0021] The thermally conductive layer formed by the thermally conductive composition according to the present embodiment may be solid, semi-solid, or semi-fluid. The thermally conductive composition according to the present embodiment may contain, for example, a thermoplastic resin, and may be a phase-change type thermally conductive sheet that exhibits increased fluidity at high temperatures.

[0022] Each component contained in the thermally conductive composition will be described below.

[0023] (1) Inorganic powder filler The inorganic powder filler imparts high thermal conductivity to the thermally conductive composition. The inorganic powder filler used in this embodiment is not particularly limited as long as it has a higher thermal conductivity than the base oil, but powders such as metal oxides, inorganic sulfides, inorganic nitrides, metals (including alloys), silicon compounds (silica), carbon materials (including carbon materials, diamonds, fullerenes, etc.) are preferably used. The type of inorganic powder filler may be one type, or two or more types may be used in combination.

[0024] For example, when electrical insulation is required for the thermally conductive composition, powders of non-conductive materials such as semiconductors or ceramics, such as zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride, boron nitride, silicon carbide, silicon compounds (silica), and diamond, can be suitably used. When higher thermal conductivity is required without electrical insulation, powders of copper, silver, aluminum, and alloys containing these can be used. Furthermore, a combination of metal powder and powder of a non-conductive material may also be used.

[0025] Among these inorganic powder fillers, it is preferable to use one or more selected from the group consisting of copper, aluminum, zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride and silicon carbide.

[0026] Furthermore, the inorganic powder filler used in the thermally conductive composition according to this embodiment may be an inorganic powder filler having one type of average particle size, or a plurality of inorganic powder fillers having different average particle sizes may be used.

[0027] When using multiple inorganic powder fillers with different average particle sizes, it is preferable to use three or more types of inorganic powder fillers with different average particle sizes, depending on the expected thickness of the thermally conductive layer, and including at least a first inorganic powder filler with an average particle size in the range of 30 μm to 200 μm, a second inorganic powder filler with an average particle size in the range of 1 μm to 30 μm, and a third inorganic powder filler with an average particle size in the range of 0.1 μm to 1 μm.

[0028] By including an inorganic powder filler having an average particle size in this range, it is possible to suppress turbulence of the inorganic powder filler in the thermally conductive composition, thereby improving the fluidity, and as a result, it is possible to make the thermally conductive composition spread uniformly. The average particle size of the inorganic powder filler can be calculated as the volume average diameter of the particle size distribution measured by a laser diffraction scattering method (in accordance with JIS R 1629:1997).

[0029] An inorganic powder filler having an average particle size smaller than that of the third inorganic powder filler may be further added within a range that does not impair the flowability of the thermally conductive composition.

[0030] The content of the inorganic powder filler is preferably 50% by volume or more and 90% by volume or less, more preferably 55% by volume or more and 85% by volume or less, and even more preferably 60% by volume or more and 80% by volume or less, relative to 100% by volume of the thermally conductive composition.

[0031] (2) Base Oil The base oil imparts high lubricity to the thermally conductive composition. Various base oils can be used as the base oil, including, for example, hydrocarbon-based base oils such as mineral oils and synthetic hydrocarbon oils, ester-based base oils such as diesters and polyol esters, ether-based base oils such as (poly)phenyl ethers, phosphate esters, silicone oils, and fluorine oils. The base oils may be used alone or in combination of two or more.

[0032] Among these, it is preferable to use a base oil containing at least one selected from the group consisting of hydrocarbon-based base oils (mineral oils, synthetic hydrocarbon oils), ester-based base oils, and ether-based base oils. These base oils do not contain siloxane, and the inclusion of such a base oil can prevent contact failure and improve the long-term reliability of electronic devices.

[0033] The mineral oil may be, for example, a mineral oil-based lubricating oil fraction refined by an appropriate combination of refining techniques such as solvent extraction, solvent dewaxing, hydrorefining, hydrocracking, wax isomerization, etc., and may be 150 neutral oil, 500 neutral oil, bright stock, high viscosity index base oil, etc. The mineral oil used as the base oil is preferably a highly hydrorefined high viscosity index base oil.

[0034] Examples of synthetic hydrocarbon oils include alpha olefins produced from raw materials such as ethylene, propylene, butene, and derivatives thereof, which are polymerized singly or in combination of two or more. Preferred examples of alpha olefins include those having 6 to 14 carbon atoms.

[0035] Specific examples of synthetic hydrocarbon oils include polyalphaolefins (PAO), which are oligomers of 1-decene or 1-dodecene, polybutene, which is an oligomer of 1-butene or isobutylene, and cooligomers of ethylene or propylene with alphaolefins.Alkylbenzenes and alkylnaphthalenes can also be used.

[0036] Examples of ester-based base oils include diesters and polyol esters. Examples of diesters include esters of dibasic acids such as adipic acid, azelaic acid, sebacic acid, and dodecanedioic acid. The dibasic acid is preferably an aliphatic dibasic acid having 4 to 36 carbon atoms. The alcohol residue constituting the ester moiety is preferably a monohydric alcohol residue having 4 to 26 carbon atoms. Examples of polyol esters include esters of neopentyl polyols having no hydrogen atom on the β-position carbon, specifically carboxylic acid esters such as neopentyl glycol, trimethylolpropane, and pentaerythritol. The carboxylic acid residue constituting the ester moiety is preferably a monocarboxylic acid residue having 4 to 26 carbon atoms.

[0037] In addition to the above, the ester-based base oil may also be an ester of a dihydric aliphatic alcohol such as ethylene glycol, propylene glycol, butylene glycol, 2-butyl-2-ethylpropanediol, or 2,4-diethylpentanediol with a linear or branched saturated fatty acid. As the linear or branched saturated fatty acid, a monovalent linear or branched saturated fatty acid having from 4 to 30 carbon atoms is preferred.

[0038] Examples of ether-based base oils include polyglycols and (poly)phenyl ethers. Examples of polyglycols include polyethylene glycol, polypropylene glycol, and derivatives thereof. Examples of (poly)phenyl ethers include alkylated diphenyl ethers such as monoalkylated diphenyl ether and dialkylated diphenyl ether, alkylated tetraphenyl ethers such as monoalkylated tetraphenyl ether and dialkylated tetraphenyl ether, and alkylated pentaphenyl ethers such as pentaphenyl ether, monoalkylated pentaphenyl ether, and dialkylated pentaphenyl ether. Examples of phosphate esters include triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, and trixylenyl phosphate.

[0039] Here, the thermally conductive layer formed by the thermally conductive composition according to this embodiment is exposed to high temperatures for a long period of time, mainly due to heat-generating components. Therefore, it is desirable that the base oil contained in the thermally conductive composition has excellent thermal oxidation stability. Among the above-mentioned base oils, synthetic base oils are preferred, and synthetic hydrocarbon oils, ester-based base oils, and ether-based base oils are preferred. Among these base oils, polyalphaolefins are preferred as synthetic hydrocarbon oils, polyol esters are preferred as ester-based base oils, and (poly)phenyl ethers are preferred as ether-based base oils, as they have particularly excellent thermal oxidation stability.

[0040] These polyalphaolefins, (poly)phenyl ethers, and polyol esters may be used alone, but it is preferable to use two or more of them in combination. When used in combination, it is particularly preferable to use a base oil group consisting of polyalphaolefins or (poly)phenyl ethers in combination with a polyol ester, as this allows for the preparation of a thermally conductive composition with a relatively high viscosity index, high consistency when prepared, and excellent coatability. In this case, the content ratio of the base oil group consisting of polyalphaolefins or (poly)phenyl ethers to the polyol ester is preferably 95:5 to 30:70, more preferably 90:10 to 50:50, and even more preferably 85:15 to 65:35 by mass.

[0041] The kinematic viscosity of the base oil is 10 mm at 40°C. ２ / s or more 1200mm ２ It is preferable that the kinematic viscosity at 40°C is 10 mm / s or less. ２ By setting the kinematic viscosity at 40°C to 1200 mm / s or more, evaporation of the base oil and oil separation at high temperatures tend to be suppressed, which is preferable. ２ / s or less is preferable because it is easy to obtain high consistency.

[0042] The content of the base oil is preferably 5% by volume or more and 30% by volume or less, more preferably 7% by volume or more and 27% by volume or less, and even more preferably 8% by volume or more and 25% by volume or less, relative to 100% by volume of the thermally conductive composition.

[0043] (3) Coupling Agent The coupling agent is adsorbed onto the surface of the inorganic powder filler to reduce the viscosity of the thermally conductive composition. A coupling agent is a compound that acts to chemically bond organic and inorganic materials. The coupling agent's adsorption onto the surface of the inorganic powder filler can increase the affinity with the base oil.

[0044] Here, the thermally conductive composition according to the present embodiment is characterized by containing at least one of a titanate-based coupling agent and an aluminate-based coupling agent among such coupling agents.

[0045] The titanate-based coupling agent is a coupling agent containing titanium (Ti) as a constituent element, and the aluminate-based coupling agent is a coupling agent containing aluminum (Al) as a constituent element.

[0046] The inclusion of such a specific coupling agent can suppress an increase in the viscosity of the thermally conductive composition. Although the reason for this is not entirely clear, it is thought that the specific coupling agent is more likely to adsorb densely to the surface of the inorganic powder filler in the thermally conductive composition, thereby increasing the hydrophobicity of the surface of the inorganic powder filler, thereby improving affinity with the base oil compared to other dispersants, etc. Note that the titanate-based coupling agent and the aluminate-based coupling agent may be used alone or in combination.

[0047] Even more surprisingly, the inventors' research has revealed that increasing the content of the titanate-based coupling agent or the aluminate-based coupling agent not only further reduces the viscosity of the thermally conductive composition but also increases the thermal conductivity of the thermally conductive layer formed from the thermally conductive composition.

[0048] Known titanate coupling agents can be used, and are not particularly limited, but examples thereof include titanate coupling agents having a hydrocarbon group such as alkyl titanates. Specific examples include titanate coupling agents such as isopropyl triisostearoyl titanate, isopropyl tri(dioctyl pyrophosphate) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, isopropyl tri-n-dodecylbenzenesulfonyl titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, and tetraisopropyl bis(dioctyl phosphite) titanate.

[0049] Commercially available titanate coupling agents include the PLENACT series manufactured by Ajinomoto Fine-Techno Co., Ltd. and the ORGATIX series manufactured by Matsumoto Fine Chemical Co., Ltd.

[0050] Known aluminate coupling agents can be used, and are not particularly limited. Examples of the aluminate coupling agent include aluminum alkyl acetoacetates and dialkylates such as acetoalkoxy aluminum dialkylate and aluminum ethyl acetoacetate-diisopropylate; aluminum alkenyl acetoacetates and dialkylates; aluminum trisethyl acetoacetate, aluminum bisethyl acetoacetate-monoacetylacetonate, and aluminum trisacetylacetonate.

[0051] The total content of the titanate-based coupling agent and the aluminate-based coupling agent contained in the thermally conductive composition is not particularly limited, but is preferably 3 vol% or more and 30 vol% or less, more preferably 7 vol% or more and 25 vol% or less, and even more preferably 12 vol% or more and 20 vol% or less, relative to 100 vol% of the thermally conductive composition. When the total content of the titanate-based coupling agent and the aluminate-based coupling agent is 3 vol% or more, relative to 100 vol% of the thermally conductive composition, the viscosity of the thermally conductive composition can be more effectively reduced. When the total content of the titanate-based coupling agent and the aluminate-based coupling agent is 30 vol% or less, relative to 100 vol% of the thermally conductive composition, the content of the inorganic powder filler and the base oil can be relatively increased, thereby imparting high thermal conductivity and lubricity to the thermally conductive composition.

[0052] Furthermore, the total content of the titanate-based coupling agent and the aluminate-based coupling agent relative to 100 parts by volume of the inorganic powder filler contained in the thermally conductive composition is preferably 5 parts by volume or more and 35 parts by volume or less, more preferably 10 parts by volume or more and 30 parts by volume or less, and even more preferably 15 parts by volume or more and 25 parts by volume or less.

[0053] The effect of further reducing the viscosity of the thermally conductive composition by increasing the total content of the titanate-based coupling agent and the aluminate-based coupling agent cannot be obtained, for example, when a coupling agent or dispersant other than these coupling agents is used. The thermally conductive composition according to this embodiment contains the titanate-based coupling agent and the aluminate-based coupling agent, so that an increase in viscosity can be effectively suppressed even when the content of the inorganic powder filler is increased.

[0054] (4) Other Additives In order to enhance various properties of the thermally conductive composition, other additives may be added depending on the application, such as thickeners, antioxidants, bleed-out inhibitors, resins, diluents, viscosity index improvers, etc.

[0055] The thermally conductive composition according to this embodiment may contain a thickener as needed. Although the thickener is not an essential component of the thermally conductive composition according to this embodiment, for example, when the thermally conductive composition is used as a thermally conductive grease, by adding a thickener, the consistency of the thermally conductive grease can be controlled and the coatability of the thermally conductive composition can be improved.

[0056] Examples of thickeners include lithium soap, lithium complex soap, calcium soap, calcium complex soap, aluminum soap, aluminum complex soap, urea compounds, sodium terephthalamate, polytetrafluoroethylene, organo-bentonite, silica gel, petroleum wax, fluororesin, and polyethylene wax.

[0057] The thermally conductive composition according to the present embodiment may contain an antioxidant as needed. Although the antioxidant is not an essential component of the thermally conductive composition according to the present embodiment, the inclusion of an antioxidant can suppress oxidation of the base oil contained in the thermally conductive composition.

[0058] Examples of the antioxidant include amine-based antioxidants and phosphorus-based antioxidants. The amine-based antioxidant is not particularly limited, and examples of aromatic amine-based antioxidants such as alkylated diphenylamines, alkylated phenylnaphthylamines, and phenylenediamines can be used. Examples of alkylated diphenylamines that can be used include diphenylamine, p,p'-dibutyldiphenylamine, p,p'-dipentyldiphenylamine, p,p'-dihexyldiphenylamine, p,p'-diheptyldiphenylamine, p,p'-dioctyldiphenylamine, and p,p'-dinonyldiphenylamine, as well as mixed alkyldiphenylamines having 4 to 9 carbon atoms. Examples of alkylated phenylnaphthylamines that can be used include N-phenyl-α-naphthylamine, N-butylphenyl-α-naphthylamine, N-pentylphenyl-α-naphthylamine, N-hexylphenyl-α-naphthylamine, N-heptylphenyl-α-naphthylamine, N-octylphenyl-α-naphthylamine, and N-nonylphenyl-α-naphthylamine. Examples of phenylenediamines that can be used include p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine.

[0059] As the phosphorus-based antioxidant, it is preferable to use a phosphite-based antioxidant, and it is more preferable to use alkylated phenyl phosphite. Specific examples of alkylated phenyl phosphites that can be used include tris(2,4-di-tert-butylphenyl)phosphite, 4,4'-butylidenebis(3-methyl-6-tert-butylphenyl-di-tridecyl phosphite), alkanol (having 12 to 16 carbon atoms)-4,4'-isopropylidenediphenol-triphenyl phosphite polycondensates, [hexaalkyl(having 8 to 18 carbon atoms)tris(alkyl(having 8 to 9 carbon atoms)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite, and [trialkyl(having 8 to 18 carbon atoms)tris(alkyl(having 8 to 9 carbon atoms)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite. Among these, [hexaalkyl(C8 to C18)tris(alkyl(C8 to C9)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite or [trialkyl(C8 to C18)tris(alkyl(C8 to C9)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite can be used.

[0060] The thermally conductive composition according to the present embodiment may contain a bleed-out inhibitor as needed. Although the bleed-out inhibitor is not an essential component of the thermally conductive composition according to the present embodiment, the inclusion of the bleed-out inhibitor can suppress bleeding of the thermally conductive composition.

[0061] As the bleed-out inhibitor, a fluorine group-containing surfactant can be used. Here, the fluorine group-containing surfactant means a surfactant having a fluorine group. The structure of the fluorine group is not particularly limited, but is preferably a perfluoroalkyl structure or a perfluoroether structure, and a compound-based surfactant having such a structure is preferred. Furthermore, the fluorine group-containing surfactant is preferably a nonionic surfactant having a fluorine-containing group and a lipophilic group.

[0062] When the thermally conductive composition according to this embodiment contains a bleedout inhibitor, the content of the bleedout inhibitor is preferably 0.001% by mass or more and 1% by mass or less, more preferably 0.1% by mass or more and 0.5% by mass or less, and even more preferably 0.1% by mass or more and 0.2% by mass or less, relative to 100% by mass of the thermally conductive composition. A bleedout inhibitor content of 0.001% by mass or more is preferred because it effectively suppresses the diffusion of the base oil and thereby suppresses bleedout. On the other hand, even if the content of the base oil diffusion inhibitor exceeds 1% by mass, the properties of the base oil diffusion inhibitor do not change significantly. A content of the base oil diffusion inhibitor of 1% by mass or less relative to 100% by mass of the thermally conductive composition is preferred because it reduces costs.

[0063] The thermally conductive composition according to the present embodiment may contain a resin as needed. If it is desired that the thermally conductive composition according to the present embodiment be an elastic body at room temperature and a viscous body when heated, it is preferable that the thermally conductive composition contain a resin such as ethylene-propylene rubber, ethylene-butylene copolymer, ethylene-butylene-styrene copolymer, or ethylene-propylene-styrene copolymer.

[0064] Furthermore, if the thermally conductive composition according to this embodiment is viscous at room temperature and is to be cured by heating, it preferably contains a thermosetting resin such as an epoxy resin and a curing agent.

[0065] Furthermore, when the thermally conductive composition according to the present embodiment is to be made into a phase-change type thermally conductive sheet that exhibits increased fluidity at high temperatures, it is preferable that the thermally conductive composition contain a thermoplastic resin. The thermoplastic resin is not particularly limited, and examples thereof include ester-based resins, acrylic-based resins, rosin-based resins, and cellulose-based resins. The resin may also be a wax-based resin.

[0066] It is particularly preferable to use a wax-based resin and a rosin-based resin in combination as the thermoplastic resin contained in the thermally conductive composition according to this embodiment, which improves the shape retention of the thermally conductive composition and increases adhesion to a heat generating element such as a module even when the thermally conductive composition is softened by the application of heat.

[0067] Wax-based resins are organic or silicone compounds that are solid at room temperature or below and liquefy when heated. The penetration and melting point of the resins may be adjusted to impart desired properties to the thermally conductive composition. Different types of waxes may also be added.

[0068] The rosin-based resin refers to a resin having a structural unit derived from a rosin acid (e.g., abietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid, dehydroabietic acid) as a main component. Physical properties such as the softening point, acid value, and glass transition point may be appropriately adjusted to impart desired properties to the thermally conductive composition. Furthermore, different types of rosin-based resins may be added.

[0069] When a wax-based resin and a rosin-based resin are used in combination, the content ratio of the wax-based resin to the rosin-based resin may be adjusted appropriately to impart desired properties to the thermally conductive composition.

[0070] The thermally conductive composition according to the present embodiment may contain a diluent as needed. The diluent can reduce the viscosity of the thermally conductive composition. Although the diluent is not an essential component of the thermally conductive composition according to the present embodiment, for example, a thermally conductive composition containing a diluent can be used to form a thermally conductive sheet by a conventional coating method such as screen printing.

[0071] Examples of diluents include hydrocarbon solvents, aromatic solvents, ketone solvents, and ester solvents. When the thermally conductive composition according to the present embodiment contains a diluent, the flash point and boiling point of the diluent may be appropriately adjusted to impart desired properties to the thermally conductive composition.

[0072] The thermally conductive composition according to the present embodiment may contain a viscosity index improver as needed. The viscosity index improver increases the viscosity of the thermally conductive composition. Although the viscosity index improver is not an essential component of the thermally conductive composition according to the present embodiment, for example, by including a viscosity index improver, the viscosity of the thermally conductive composition can be adjusted to a preferred range.

[0073] Examples of viscosity index improvers include lipophilic polymers with molecular weights of 10,000 to 1,500,000. At low temperatures, the cohesive energy of the viscosity index improver is greater than the affinity between the polymer and the solvent. Therefore, when the viscosity index improver is contained in a thermally conductive composition, the viscosity index improver is dissolved in the base oil in a contracted state. As a result, the kinetic energy increased by the temperature rise of the thermally conductive composition becomes greater than the cohesive energy, and the viscosity index improver swells, drawing in the base oil. This increases the flow resistance of the lubricant, making it possible to prevent a decrease in viscosity at high temperatures.

[0074] Examples of viscosity index improvers include polymethacrylate compounds, olefin copolymer compounds, and mixtures thereof. The larger the molecular weight, the more likely the main chain is cleaved by shear force, resulting in a lower molecular weight, making it difficult to achieve the desired effect. Therefore, it is preferable to adjust the molecular weight of the viscosity index improver according to the desired viscosity.

[0075] 2. Manufacturing Method of Thermally Conductive Composition The manufacturing method of the thermally conductive composition according to this embodiment is not particularly limited as long as the components can be mixed uniformly. A typical manufacturing method is to mix the components using a planetary mixer, a rotation-revolution mixer, or the like, and then knead the components uniformly using a three-roll mill. The thermally conductive paste described below can also be manufactured using a similar method.

[0076] The thermal conductivity of the obtained thermally conductive composition at room temperature is preferably 3.0 W / mK or more, preferably 3.5 W / mK or more, and more preferably 3.8 W / mK or more. By controlling the components contained so as to achieve such a thermal conductivity, it becomes possible to more effectively transfer heat from a heat-generating component to a heat-dissipating component. The thermal conductivity of the thermally conductive composition can be measured, for example, using a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0077] The shear viscosity (shear rate: 0.01 to 10 / s) of the obtained thermally conductive composition at room temperature varies depending on the types of components contained, but is preferably 450 Pa·s or less, more preferably 430 Pa·s or less, and even more preferably 425 Pa·s or less. The shear viscosity of the thermally conductive composition can be measured using a rheometer (MC302e manufactured by Anton Paar).

[0078] EXAMPLES The present invention will be described in detail below based on examples and comparative examples of the present invention, but the present invention is not limited to the following examples in any way.

[0079] 1. Production of Thermally Conductive Compositions Thermally conductive compositions having the compositions shown in Table 1 below were produced using the materials (A) to (D) below.

[0080] (A) Inorganic powder filler Zinc oxide 1: average particle size 5 μm Zinc oxide 2: average particle size 2 μm Zinc oxide 3: average particle size 0.6 μm Aluminum oxide 1: average particle size 5 μm Aluminum 1: average particle size 5 μm The average particle size of each inorganic powder filler was measured by a laser diffraction scattering method using a particle size distribution measuring device (SALD-7000 manufactured by Shimadzu Corporation).

[0081] (B) Base oil: polyol ester oil

[0082] (C) Coupling Agents (C-1) Titanate Coupling Agent (Isopropyltri(dioctylpyrophosphate)titanate) (C-2) Aluminate Coupling Agent (Acetoalkoxyaluminum Dialkylate)

[0083] (D) Dispersant Polyether carboxylic acid

[0084] The thermally conductive compositions of Examples 1 to 9 and Comparative Examples 1 to 9 were prepared by blending and mixing the above compounds (A) to (D) as shown in Table 1 below. That is, they were placed in a planetary mixer so as to have the contents shown in Table 1. Then, kneading was carried out three times using a three-roll mill to prepare the thermally conductive compositions.

[0085] The thermal conductivity and viscosity of the thermally conductive compositions produced in Examples 1 to 9 and Comparative Examples 1 to 9 were evaluated by the following methods.

[0086] (1) Measurement of Thermal Conductivity The thermal conductivity of the obtained thermally conductive compositions was measured. Specifically, the thermal conductivity of the thermally conductive compositions of Examples 1 to 9 and Comparative Examples 1 to 9 was measured at room temperature using a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0087] (2) Viscosity Measurement The shear viscosity of the obtained thermally conductive compositions was measured. Specifically, the thermally conductive compositions of Examples 1 to 9 and Comparative Examples 1 to 9 were measured at 0.01 to 10 / s using a rheometer (MC302e manufactured by Anton Paar) capable of controlling the measurement environment temperature, and evaluated at room temperature. The viscosity at 6 / s was used for comparison as the viscosity value during printing.

[0088]

[0089] As can be seen from the above table, the thermally conductive compositions of the examples containing at least one of a titanate-based coupling agent and an aluminate-based coupling agent can effectively suppress an increase in viscosity.

[0090] In particular, the thermally conductive compositions of Examples 2, 3, 5, 6, 8, 9, 11, and 12, in which the content of the titanate coupling agent or the aluminate coupling agent was 7% by volume or more of the total amount of the thermally conductive composition (or the content ratio of the titanate coupling agent or the aluminate coupling agent per 100 parts by volume of the inorganic powder filler was 10 parts by volume or more), had a reduced viscosity compared to the thermally conductive compositions of Examples 1, 4, 7, and 10. Furthermore, the thermally conductive compositions of Examples 2, 3, 5, 6, 8, 9, 11, and 12 had an increased thermal conductivity compared to the thermally conductive compositions of Examples 1, 4, 7, and 10.

[0091] On the other hand, the thermally conductive compositions of Comparative Examples 1 to 9, which contain a dispersant instead of a coupling agent, are unable to effectively suppress the increase in viscosity.

[0092] Furthermore, no increase in thermal conductivity was observed between the thermally conductive compositions of Comparative Examples 1, 4, and 7, in which the dispersant content was 5% by volume based on the total amount of the thermally conductive composition, and the thermally conductive compositions of Comparative Examples 2, 3, 5, 6, 8, and 9, in which the dispersant content was 7% by volume or more based on the total amount of the thermally conductive composition. This indicates that the effect of the thermally conductive compositions of Examples 2, 3, 5, 6, 8, 9, 11, and 12, in which the thermal conductivity was increased compared to the thermally conductive compositions of Examples 1, 4, 7, and 10, was due to the use of a titanate-based coupling agent or an aluminate-based coupling agent.

Claims

1. A thermally conductive composition comprising a base oil and an inorganic powder filler, said thermally conductive composition further comprising at least one of a titanate-based coupling agent or an aluminate-based coupling agent.

2. The thermally conductive composition according to claim 1, wherein the total content of the titanate-based coupling agent and the aluminate-based coupling agent is 3 vol. % or more and 30 vol. % or less, based on 100 vol. % of the thermally conductive composition.

3. The thermally conductive composition according to claim 1 or 2, wherein the inorganic powder filler is at least one selected from the group consisting of copper, aluminum, zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride and silicon carbide.

4. The thermally conductive composition according to claim 1 or 2, wherein the base oil is at least one selected from the group consisting of mineral oils, synthetic hydrocarbon oils, diesters, polyol esters and phenyl ethers.

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