WO2025052820A1 - Thermally conductive composition - Google Patents

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

The present invention relates to a thermally conductive composition.

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 control such as inverters.

In order to protect these heat-generating components from heat and allow them to function normally, there is a method of dissipating the generated heat by conducting it to heat-dissipating components (cooling devices) such as heat spreaders and heat sinks. Thermally conductive grease is applied between these heat-generating components and heat-dissipating components so that they come into close contact with each other, and is used to efficiently conduct the heat from the heat-generating components to the heat-dissipating components. 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 fluorine oil.

More specifically, thermally conductive grease is applied to the thermal contact interface between heat-generating parts, such as a computer CPU, and heat-dissipating parts, such as a heat sink, and between heat-generating parts, such as high-output inverters mounted on hybrid and electric vehicles, and heat-dissipating parts, such as a heat spreader. In recent years, the semiconductor elements in these electronic devices have become smaller and more powerful, resulting in increased heat density and amount of heat generated, and they are often installed in close proximity to other heat-generating semiconductor parts.

For example, Patent Document 1 describes technology related to thermally conductive grease that contains a specific antioxidant in a specified ratio. Patent Document 1 describes that this thermally conductive grease has high thermal conductivity, consistency, and thermal stability at high temperatures.

JP 2019-081841 A

Thermal conductivity of a thermally conductive composition containing an inorganic powder filler can be improved by increasing the content of the inorganic powder filler. On the other hand, increasing the content of the inorganic powder filler increases the viscosity of the thermally conductive composition.

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, and the like. For this reason, a thermally conductive composition is required to have a viscosity that does not increase significantly even if the content of inorganic powder filler is increased.

The present invention aims to provide a thermally conductive composition that can suppress an increase in viscosity even when the content of inorganic powder filler is increased.

The inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that a thermally conductive composition containing a specific coupling agent could solve the above problems, which led to the completion of the present invention.

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

The second aspect of the present invention is the thermally conductive composition according to the first invention, in which 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.

The third aspect of the present invention is a thermally conductive composition according to the first or second invention, in which the inorganic powder filler is one or more selected from the group consisting of copper, aluminum, zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride, and silicon carbide.

The fourth aspect of the present invention is a thermally conductive composition according to the first or second invention, in which the base oil is one or more selected from the group consisting of mineral oil, synthetic hydrocarbon oil, diester, polyol ester, and phenyl ether.

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

Below, a specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the following embodiment, and can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, in this specification, the expression "X to Y" (X and Y are arbitrary numbers) means "X or more and Y or less."

≪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.

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

The thermally conductive composition according to this 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 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.

The thermally conductive composition according to this embodiment can be used as a semi-solid or semi-liquid thermally conductive grease at room temperature. Furthermore, the thermally conductive composition according to this embodiment can also be used as a liquid thermally conductive paste at room temperature by, for example, adding a diluent.

The thermally conductive layer formed by the thermally conductive composition according to this embodiment may be solid, semi-solid, or semi-liquid. The thermally conductive composition according to this embodiment may be a phase-change type thermally conductive sheet that has increased fluidity at high temperatures, for example, by containing a thermoplastic resin.

The components contained in the thermally conductive composition are explained below.

(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), and 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.

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. Also, a combination of metal powder and powder of a non-conductive material may be used.

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.

The inorganic powder filler used in the thermally conductive composition according to this embodiment may be an inorganic powder filler with one type of average particle size, or multiple inorganic powder fillers with different average particle sizes may be used.

When using multiple inorganic powder fillers with different average particle sizes, depending on the expected thickness of the thermally conductive layer, it is preferable to use, for example, three or more types of powders with different average particle sizes, 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.

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 and improve the fluidity, which results in the thermally conductive composition spreading 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 the laser diffraction scattering method (in accordance with JIS R 1629:1997).

In addition, an inorganic powder filler having an average particle size smaller than that of the third inorganic powder filler may be further added as long as it does not impair the flowability of the thermally conductive composition.

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.

(2) Base oil The base oil provides high lubricity to the thermally conductive composition. As the base oil, various base oils can be used, for example, mineral oil, hydrocarbon-based base oils such as 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.

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 prevents contact failure and provides excellent long-term reliability for electronic devices.

Mineral oils that can be used include those that are obtained by refining mineral oil lubricating oil fractions through an appropriate combination of refining techniques such as solvent extraction, solvent dewaxing, hydrorefining, hydrocracking, and wax isomerization, and include 150 neutral oil, 500 neutral oil, bright stock, and high viscosity index base oils. Highly hydrorefined high viscosity index base oils are preferred as the mineral oils used as base oils.

Synthetic hydrocarbon oils include, for example, alpha-olefins produced from raw materials such as ethylene, propylene, butene, and derivatives thereof, polymerized either alone or in combination of two or more kinds. Preferred alpha-olefins are those with 6 to 14 carbon atoms.

Specific examples of synthetic hydrocarbon oils include polyalphaolefins (PAOs), which are oligomers of 1-decene and 1-dodecene, polybutenes, which are oligomers of 1-butene and isobutylene, and co-oligomers of ethylene or propylene with alpha-olefins. Alkylbenzenes and alkylnaphthalenes can also be used.

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 acids are preferably aliphatic dibasic acids 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 that do not have a 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.

In addition to the above, esters of aliphatic dihydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, 2-butyl-2-ethylpropanediol, and 2,4-diethyl-pentanediol with linear or branched saturated fatty acids can also be used as ester-based base oils. As linear or branched saturated fatty acids, monovalent linear or branched saturated fatty acids having 4 to 30 carbon atoms are preferred.

Ether-based base oils include polyglycols and (poly)phenyl ethers. Polyglycols include polyethylene glycol, polypropylene glycol, and derivatives thereof. (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. Phosphate esters include triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, and trixylenyl phosphate.

Here, the thermally conductive layer formed by the thermally conductive composition according to this embodiment will be exposed to high temperatures for a long period of time, mainly due to heat-generating components. For this reason, it is desirable for the base oil contained in the thermally conductive composition to have excellent thermal oxidation stability. Among the above base oils, synthetic base oils are preferred, and synthetic hydrocarbon oils, ester-based base oils, and ether-based base oils are preferred. Of 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 are particularly excellent in thermal oxidation stability.

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.
In the case of using them in combination, it is preferable to use a base oil group consisting of polyalphaolefin or (poly)phenyl ether in combination with a polyol ester, since this allows the preparation of a thermally conductive composition having a relatively high viscosity index, high consistency, and excellent coatability. In this case, the content ratio of the base oil group consisting of polyalphaolefin or (poly)phenyl ether 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.

The kinetic viscosity of the base oil is preferably 10 mm ² /s or more and 1200 mm ² /s or less at 40° C. By making the kinetic viscosity at 40° C. 10 mm ² /s or more, evaporation of the base oil and oil separation at high temperatures tend to be suppressed, which is preferable. In addition, by making the kinetic viscosity at 40° C. 1200 mm ² /s or less, high consistency can be easily obtained, which is preferable.

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, based on 100% by volume of the thermally conductive composition.

(3) Coupling Agent The coupling agent is adsorbed to the surface of the inorganic powder filler and reduces the viscosity of the thermally conductive composition. The coupling agent is a compound that acts to chemically bond organic materials and inorganic materials. The coupling agent is adsorbed to the surface of the inorganic powder filler, thereby increasing the affinity with the base oil.

The thermally conductive composition according to this embodiment is characterized by containing at least one of these coupling agents, a titanate-based coupling agent or an aluminate-based coupling agent.

Titanate-based coupling agents are coupling agents that contain titanium (Ti) as a constituent element, and aluminate-based coupling agents are coupling agents that contain aluminum (Al) as a constituent element.

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 believed that the specific coupling agent is more likely to be densely adsorbed to the surface of the inorganic powder filler in the thermally conductive composition, and by increasing the hydrophobicity of the surface of the inorganic powder filler, it is possible to increase the affinity with the base oil compared to other dispersants. The titanate-based coupling agent and the aluminate-based coupling agent may be used alone or in combination.

More surprisingly, the inventors' research has revealed that increasing the content of titanate-based coupling agent or 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 by the thermally conductive composition.

　Any known titanate coupling agent can be used, and although there is no particular limitation, for example, a titanate coupling agent having a hydrocarbon group such as an alkyl titanate can be used. Specific examples of titanate coupling agents include 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.

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

　Aluminate-based coupling agents that can be used are not particularly limited and include, for example, aluminum alkyl acetoacetates, dialkylates such as acetoalkoxy aluminum dialkylates and aluminum ethyl acetoacetate-diisopropylate; aluminum alkenyl acetoacetates, dialkylates; aluminum trisethyl acetoacetate, aluminum bisethyl acetoacetate-monoacetylacetonate, aluminum trisacetylacetonate, and other aluminate-based coupling agents.

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 the total content of the titanate-based coupling agent and the aluminate-based coupling agent 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. By having the total content of the titanate-based coupling agent and the aluminate-based coupling agent be 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. By having the total content of the titanate-based coupling agent and the aluminate-based coupling agent be 30 vol% or less, relative to 100 vol% of the thermally conductive composition, it is possible to relatively increase the content of the inorganic powder filler and the base oil, and therefore it is possible to impart high thermal conductivity and lubricity to the thermally conductive composition.

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.

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 a titanate-based coupling agent and an aluminate-based coupling agent, so that it is possible to effectively suppress an increase in viscosity even if the content of the inorganic powder filler is increased.

(4) Other Additives In order to enhance various properties of the thermally conductive composition, other additives may be added depending on the application. Examples of other additives that may be added include a thickener, an antioxidant, a bleed-out inhibitor, a resin, a diluent, a viscosity index improver, etc.

The thermally conductive composition according to this embodiment may contain a thickener as necessary. A thickener is not an essential component of the thermally conductive composition according to this embodiment, but for example, when the thermally conductive composition is to be a thermally conductive grease, the consistency of the thermally conductive grease can be controlled by including a thickener, thereby improving the applicability of the thermally conductive composition.

Thickeners include, for example, 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, polyethylene wax, etc.

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

Examples of the antioxidant include amine-based antioxidants and phosphorus-based antioxidants. The amine-based antioxidant is not particularly limited, and examples of the aromatic amine-based antioxidants that can be used include alkylated diphenylamines, alkylated phenylnaphthylamines, and phenylenediamines. Examples of the 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.

As the phosphorus-based antioxidant, it is preferable to use a phosphite-based antioxidant, and it is more preferable to use an alkylated phenyl phosphite. Specifically, examples of the alkylated phenyl phosphite that can be used include tris(2,4-di-tert-butylphenyl)phosphite, 4,4'-butylidenebis(3-methyl-6-tert-butylphenyl-di-tridecyl phosphite), alkanol(C12-16)-4,4'-isopropylidenediphenol-triphenyl phosphite polycondensate, [hexaalkyl(C8-18)tris(alkyl(C8-9)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite, and [trialkyl(C8-18)tris(alkyl(C8-9)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite. Among these, [hexaalkyl(carbon number 8-18)tris(alkyl(carbon number 8-9)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite or [trialkyl(carbon number 8-18)tris(alkyl(carbon number 8-9)phenyl)]1,1,3-tris(3-tert-butyl-6-methyl-4-oxyphenyl)-3-methylpropane triphosphite can be used.

The thermally conductive composition according to this embodiment may contain a bleed-out inhibitor as necessary. Although the bleed-out inhibitor is not an essential component of the thermally conductive composition according to this embodiment, the inclusion of the bleed-out inhibitor can suppress the bleed-out of the thermally conductive composition.

As the bleed-out inhibitor, a fluorine group-containing surfactant can be used. Here, a 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 preferable. In addition, the fluorine group-containing surfactant is preferably a nonionic surfactant having a fluorine-containing group and a lipophilic group.

When the thermally conductive composition according to this embodiment contains a bleed-out inhibitor, the content of the bleed-out 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 bleed-out inhibitor content of 0.001% by mass or more is preferable because it effectively suppresses the diffusion of the base oil and suppresses bleed-out. 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 preferable because it reduces costs.

The thermally conductive composition according to this embodiment may contain a resin as necessary. If it is desired that the thermally conductive composition according to this embodiment be an elastic body at room temperature and a viscous body by heating, it is preferable that it contain a resin such as ethylene-propylene rubber, ethylene-butylene copolymer, ethylene-butylene-styrene copolymer, or ethylene-propylene-styrene copolymer.

In addition, 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.

Furthermore, if it is desired to make the thermally conductive composition according to this embodiment into a phase-change type thermally conductive sheet in which the fluidity increases at high temperatures, it is preferable for the thermally conductive composition to contain a thermoplastic resin. There are no particular limitations on the thermoplastic resin, and examples of the thermoplastic resin include ester-based resins, acrylic-based resins, rosin-based resins, and cellulose-based resins. The resin may also be a wax-based resin.

Thermoplastic resin contained in the thermally conductive composition according to this embodiment is preferably a wax-based resin in combination with a rosin-based resin, which improves the shape retention of the thermally conductive composition and enhances adhesion to a heating element such as a module, even when the composition is softened by the application of heat.

A wax-based resin is an organic or silicone compound that is solid at room temperature or below and liquefies when heated. The penetration and melting point may be adjusted as appropriate to impart desired properties to the thermally conductive composition. Different types of wax may also be added.

The term "rosin-based resin" refers to a resin that has structural units derived from rosin acid (e.g., abietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid, dehydroabietic acid) as the main component. In order to impart desired properties to the thermally conductive composition, physical properties such as the softening point, acid value, and glass transition point may be appropriately adjusted. Also, different types of rosin-based resins may be added.

In addition, when using a combination of wax-based resin and rosin-based resin, the content ratio of the wax-based resin to the rosin-based resin may be appropriately adjusted to impart desired properties to the thermally conductive composition.

The thermally conductive composition according to this embodiment may contain a diluent as necessary. The diluent can reduce the viscosity of the thermally conductive composition. The diluent is not an essential component of the thermally conductive composition according to this embodiment, but by using a thermally conductive composition that contains a diluent, for example, a thermally conductive sheet can be formed by a conventionally known coating method such as screen printing.

Examples of diluents include hydrocarbon solvents, aromatic solvents, ketone solvents, and ester solvents. When the thermally conductive composition according to this 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.

The thermally conductive composition according to this embodiment may contain a viscosity index improver as necessary. The viscosity index improver increases the viscosity of the thermally conductive composition. The viscosity index improver is not an essential component of the thermally conductive composition according to this embodiment, but by including the viscosity index improver, for example, the viscosity of the thermally conductive composition can be adjusted to a preferred range.

An example of a viscosity index improver is an oleophilic polymer with a molecular weight 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. For this reason, 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 high temperature of the thermally conductive composition becomes greater than the cohesive energy, and the viscosity index improver swells, involving the base oil, and the flow resistance of the lubricant increases, making it possible to prevent the viscosity from decreasing at high temperatures.

Viscosity index improvers include polymethacrylate compounds, olefin copolymer compounds, and mixtures of these. Note that the larger the molecular weight, the more likely it is that the main chain will be cut by shear force, resulting in a lower molecular weight, making it difficult to achieve the desired effect. For this reason, it is preferable to adjust the molecular weight of the viscosity index improver according to the desired viscosity.

2. Method for producing thermally conductive composition
The method for producing the thermally conductive composition according to the present embodiment is not particularly limited as long as the components can be mixed uniformly. A typical production 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 produced using a similar method.

The thermal conductivity of the obtained thermally conductive composition at room temperature is preferably 3.0 W/mK or more, more preferably 3.5 W/mK or more, and even more preferably 3.8 W/mK or more. By controlling the components contained so as to obtain such a thermal conductivity, it becomes possible to more effectively transfer heat from heat-generating components to heat-dissipating components. 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.

The shear viscosity (shear rate: 0.01-10/s) of the obtained thermally conductive composition at room temperature depends 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 (Anton Paar MC302e).

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

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.

(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).

(B) Base oil polyol ester oil

(C) Coupling Agent (C-1) Titanate Coupling Agent (Isopropyltri(dioctylpyrophosphate)titanate)
(C-2) Aluminate coupling agent (acetoalkoxyaluminum dialkylate)

(D) Dispersant Polyether carboxylic acid

The above compounds (A) to (D) were blended and mixed as shown in Table 1 below to produce the thermally conductive compositions of Examples 1 to 9 and Comparative Examples 1 to 9. That is, they were placed in a planetary mixer so as to have the contents shown in Table 1. After that, the thermally conductive compositions were produced by kneading three times using a three-roll mill.

Thermal conductivity and viscosity of the thermally conductive compositions manufactured in Examples 1 to 9 and Comparative Examples 1 to 9 were evaluated using the following method.

(1) Measurement of Thermal Conductivity The thermal conductivity of the obtained thermally conductive composition 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.

(2) Viscosity Measurement The shear viscosity of the obtained thermally conductive composition 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.

As can be seen from the above table, the thermally conductive composition of the embodiment containing at least one of a titanate-based coupling agent or an aluminate-based coupling agent can effectively suppress the increase in viscosity.

In particular, the thermally conductive compositions of Examples 2, 3, 5, 6, 8, 9, 11, and 12, in which the content of the titanate-based coupling agent or the aluminate-based coupling agent is 7 volume % or more of the total amount of the thermally conductive composition (or the content ratio of the titanate-based coupling agent or the aluminate-based coupling agent to 100 volume parts of the inorganic powder filler is 10 volume parts 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.

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.

Furthermore, there is no increase in thermal conductivity between the thermally conductive compositions of Comparative Examples 1, 4, and 7, in which the dispersant content is 5 volume % of 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 is 7 volume % or more of the total amount of the thermally conductive composition. From this, it can be seen that the effect of the thermally conductive compositions of Examples 2, 3, 5, 6, 8, 9, 11, and 12 having increased thermal conductivity compared to the thermally conductive compositions of Examples 1, 4, 7, and 10 is an effect caused by the use of a titanate-based coupling agent or an aluminate-based coupling agent.

Claims (4)

A thermally conductive composition comprising a base oil and an inorganic powder filler,
The thermally conductive composition further comprises at least one of a titanate-based coupling agent or an aluminate-based coupling agent. The thermally conductive composition according to claim 1 , wherein a total content of the titanate-based coupling agent and the aluminate-based coupling agent is 3 vol % or more and 30 vol % or less with respect to 100 vol % of the thermally conductive composition. 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. 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.