JP7598725B2 - Composite Particle Materials - Google Patents

Description

The present invention relates to a composite particle material with excellent storage stability.

Aluminum oxide and aluminum nitride have been used in a wide range of applications, including as various heat dissipation materials, coatings for products, electronic components, and heat dissipation parts for semiconductor manufacturing equipment, due to their high heat dissipation properties, wear resistance, and chemical stability. Thermally conductive composite materials using these materials are also being developed.
However, when these compounds are contained in paints, coating materials, inks, and the like, there is currently a problem that the storage stability, that is, the dispersibility of the settled particles, tends to deteriorate.

On the other hand, examples of organic-inorganic composite materials made of resin particle materials and inorganic particles include:
1) A composite particulate material having a resin particulate material and an inorganic particulate material having a particle size smaller than that of the resin particulate material and fused to a surface of the resin particulate material, the composite particulate material satisfying the following conditions (a), (b), and (c): (a) a sphericity of 0.8 or more, (b) a volume average particle size of 0.1 to 100 μm, and (c) the inorganic particulate material is formed from an inorganic oxide and has OH groups formed on the surface by fusion (see, for example, Patent Document 1).
2) A fine powder-coated amine in which the surface of a solid amine, which is an aromatic amine or an aliphatic amine having a melting point of 50° C. or higher and a median particle size of 20 μm or less, is coated with at least one fine powder having a median particle size of 2 μm or less selected from the group consisting of polyvinyl chloride, titanium oxide, calcium carbonate, clay, carbon, alumina, talc, zinc oxide and silica, and which has a calorific value of 220 J/g or less at the second absorption peak measured by a differential scanning calorimeter (see, for example, Patent Document 2).
3) Organic-inorganic composite particles comprising a vinyl-based polymer, which is a polymer of a polymerizable vinyl-based monomer, and inorganic particles made of at least one of an inorganic oxide and an inorganic nitride, the inorganic particles having a thermal conductivity of 10 W/(m·K) or more, the inorganic particles being surface-treated with at least one polymerizable compound selected from the group consisting of an acidic phosphate ester having no polymerizable functional group, a carboxylic acid having a polymerizable functional group, an acidic phosphate ester having a polymerizable functional group, and a lactone having a polymerizable functional group, the at least one polymerizable compound being bonded to the vinyl-based polymer, and the inorganic particles being unevenly distributed in one or more layers on the surface of the organic-inorganic composite particles; a thermally conductive filler for a heat dissipation sheet or heat dissipation grease (see, for example, Patent Document 3);
etc. are known.

However, the above Patent Documents 1 to 3 each concern a composite material in which a resin particle material or the like is coated or fused with an inorganic particle material or inorganic particles. Patent Document 1 provides low viscosity, low dielectric properties, and high adhesion when formed into a slurry, Patent Document 2 provides good breaking strength when used as a curing agent component in a one-part heat-curable composition, and Patent Document 3 provides flexibility and light weight to a thermally conductive resin composition. These differ from the present invention in terms of purpose, technical concept (structure, action, and effect), etc.

International Publication No. WO 2018/212279 (Claims, Examples, etc.) International Publication No. WO 2017/077722 (Claims, Examples, etc.) JP 2018-172574 A (Claims, Examples, etc.)

The present invention is made in consideration of the problems and current state of the prior art described above, and aims to solve these problems, and to provide a composite particulate material that has good compatibility with varnishes and the like, does not settle when used in coating materials such as paints, ink materials, etc., has excellent dispersibility, and has excellent storage stability and thermal conductivity.

In view of the above-mentioned problems in the past, the inventors conducted intensive research and discovered that a composite particle material having thermally conductive particles and a resin material, which is composed of specific thermally conductive particles and a specific resin material, can be obtained, and thus completed the present invention.

That is, the composite particulate material of the present invention is a composite particulate material having thermally conductive particles and a resin material, and is characterized by satisfying the following conditions (a) and (b).
(a) The thermally conductive particles are at least one selected from aluminum oxide and aluminum nitride.
(b) The resin material is at least one selected from urethane, urea, and urea-urethane.
The resin material (b) preferably accounts for 5% by mass or more of the thermally conductive particles (a).

According to the present invention, a composite particle material is provided which has good compatibility with varnishes, does not settle when used in coating materials such as paints or ink materials, has excellent dispersibility, and has excellent storage stability and thermal conductivity.
The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention as claimed.

1( a ) to 1 ( c ) are schematic diagrams showing respective embodiments of the composite particulate material of the present invention.

Embodiments of the present invention are described in detail below. However, please note that the technical scope of the present invention is not limited to the embodiments described in detail below, but extends to the inventions described in the claims and their equivalents.

The composite particulate material of the present invention is a composite particulate material having thermally conductive particles and a resin material, and is characterized in that it satisfies the following conditions (a) and (b).
(a) The thermally conductive particles are at least one selected from aluminum oxide and aluminum nitride.
(b) The resin material is at least one selected from urethane, urea, and urea-urethane.

The thermally conductive particles of component (a) used in the present invention are at least one type selected from aluminum oxide and aluminum nitride (either alone or in combination), and preferably have a thermal conductivity of 15 W/(m K) or more, and more preferably 20 W/(m K) or more.
When the thermal conductivity of the heat-conducting particles is less than 15 W/(m·K), the thermal conductivity of the composite particle material is low.
In the present invention, the thermal conductivity is a value measured using a thermal conductivity meter (thermal conductivity measuring device TCi Max-K, manufactured by Rigaku).

There are no particular limitations on the thermally conductive particles used, as long as they have a conductivity of 15 W/(m·K) or more, and various types of aluminum oxide and aluminum nitride can be used. These thermally conductive particles may be spherical or irregular in shape, and may be used alone or in combination of two or more types.
Aluminum oxide is advantageous in that it has high water resistance and thermal stability, so that a thermally conductive composite particulate material can be stably produced, and is inexpensive, so that a composite particulate material can be realized at low cost.Also, aluminum nitride particles are advantageous in that the thermal conductivity of the particles is high, so that the addition of a small amount of the particles can relatively increase the thermal conductivity of the composite particulate material.
The aluminum oxide (alumina) used has a thermal conductivity of 15 to 40 W/(m·K), and the aluminum nitride particles have a thermal conductivity of 150 to 170 W/(m·K).

The average particle size of these thermally conductive particles varies depending on the application of the composite particulate material. However, from the viewpoint of further improving the effects of the present invention and improving the yield of the composite particulate material, it is preferable that the average particle size of the thermally conductive particles is within the range of 0.1 to 70 μm, and even more preferably within the range of 3 to 50 μm.
By making the average particle diameter of the thermally conductive particles 0.1 μm or more, it is possible to further suppress the generation of resin material by-products that are not compounded with the thermally conductive particles during production, and by making it 70 μm or less, it is possible to further suppress the generation of thermally conductive particle by-products that are not compounded with the resin particles.
In this specification, the "average particle size" of inorganic particles means the average particle size (Mv) at which the cumulative fraction in a volume-based particle size distribution measured with a laser diffraction particle size distribution analyzer is 50%.

The content of these thermally conductive particles in the composite particle material (of the total amount) is preferably 50 to 90% by mass. If the amount of thermally conductive particles contained in the composite particle material is less than 50% by mass, the resin material component in the composite particles may inhibit thermal conductivity, making it impossible to provide sufficient thermal conductivity. On the other hand, if it exceeds 90% by mass, dispersibility may be insufficient, and storage stability may be impaired.

The resin material of component (b) used in the present invention is at least one selected from urethane, urea, and urea-urethane (either alone or in combination of two or more).
These urethane, urea, and urea-urethane resin materials are specifically selected from the standpoint of ease of preparation of the composite particle material, quality, and ability to produce a composite particle material with excellent dispersibility, and the effects of the present invention cannot be obtained with other resin materials, such as melamine components.
In order to obtain sufficient dispersibility, it is preferable that the resin material (b) is contained in an amount of 5% by mass or more, and more preferably 10 to 50% by mass, based on the thermally conductive particles (a).
If the resin material (b) is less than 5% by mass, the thermally conductive particles will not be sufficiently coated with the resin material, resulting in reduced dispersibility. On the other hand, if the resin material (b) is 50% by mass or more, the amount of resin material will be too large compared to the thermally conductive particles, resulting in a large amount of by-products other than the composite particle material.

The composite particle material of the present invention is in the form of composite particles in which the thermally conductive particles of the component (a) are coated with the resin material of the component (b). The coating form can be one in which a total of 50% or more of the surface area of the thermally conductive particles is coated. Even if the particles are not completely coated (100% of the total surface area is coated), the effects of the present invention can be achieved as long as a total of at least 50% of the total surface area is coated, and more preferably a total of 70% to 100% of the total surface area.
1(a) to (c) are schematic diagrams showing various embodiments of the composite particulate material of the present invention, in which (a) is composite particulate material A in a form in which the approximately spherical surfaces of the thermally conductive particles 10 are covered with a resin material 20 at 60% of the total surface area (40% of the thermally conductive particles are exposed), (b) is composite particulate material B in a form in which the approximately spherical surfaces of the thermally conductive particles 10 are covered with a resin material 20, 20... at a total of 70% of the total surface area (30% (in total) of the thermally conductive particles are exposed), and (c) is composite particulate material C in a form in which the approximately spherical surfaces of the thermally conductive particles 10 are completely covered with a resin material 20 (100% of the total surface area).

In the present invention, the composite particulate material obtained may be spherical, ellipsoidal, or irregular in shape, but is preferably spherical in shape, since this results in a more densely packed state and higher thermal conductivity when used in coating materials such as paints.
In the present invention (including the examples described later), the shape of the composite particulate material, the coating form of the resin material, and the coating surface area can be calculated by SEM (scanning electron microscope) observation, etc., and the surface area can be easily calculated by using analysis software. For the SEM observation, etc., an S-4700 manufactured by Hitachi High-Technologies Corporation was used.

The average particle diameter (Mv) of the obtained composite particulate material will vary depending on the application of the composite particulate material. However, in order to further improve the effects of the present invention and to obtain a composite particulate material with high thermal conductivity, the average particle diameter is preferably within the range of 0.3 to 100 μm, and more preferably within the range of 5 to 70 μm.
By making the average particle diameter of this composite particulate material 0.3 μm or more, it is possible to obtain a composite particulate material with even higher thermal conductivity, and by making it 100 μm or less, it is possible to obtain a composite particulate material with even better dispersibility and storage stability.

As described above, the composite particle material of the present invention may be produced by any method as long as the thermally conductive particles of component (a) are covered with the resin material of component (b) over a total area of at least 50% in total. Preferably, however, the composite particle material is produced by forming at least the thermally conductive particles of component (a) into a shell made of a coating material (wall material) of the resin material of component (b), or by encapsulating the thermally conductive particles in this shell (shell layer).
More preferably, the thermally conductive particles of component (a) and a poorly water-soluble medium having a specific gravity of less than 1 at 20°C are encapsulated in a shell (shell layer) made of the resin material of component (b). For example, the thermally conductive particles of component (a) and a poorly water-soluble medium having a specific gravity of less than 1 at 20°C can be microencapsulated to have the above-mentioned specified average particle size, specifically, encapsulated in a shell (shell layer) made of a coating material (wall material) of the resin material of component (b).
Examples of the production method include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, a liquid hardening coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melting dispersion cooling method, an air suspension coating method, and a spray drying method.

Usable poorly water-soluble media having a specific gravity of less than 1 at 20° C. are not particularly limited as long as they satisfy the above physical properties, and examples thereof include media such as organic solvents having a specific gravity of less than 1 at 20° C. In the present invention, “poorly water-soluble” refers to a medium having a solubility of 0.1 mg or less in 100 ml of water.
Examples of usable poorly water-soluble media having a specific gravity of less than 1 at 20° C. include alkyl-phenols such as ortho-secondary butylphenol, alkylaryls such as dodecylbenzene, aliphatic carboxylates such as saturated or unsaturated carboxylate alkyl esters such as octyl oleate, isopropyl myristate, isopropyl palmitate, myristyl myristate, stearyl stearate, and isopropyl oleate, aliphatic dicarboxylates such as carboxylate dialkyl esters such as dioctyl adipate, phosphate triesters such as trialkyl phosphates such as tributyl phosphate, aromatic carboxylates such as benzoate alkyl esters such as butyl benzoate, and phthalate dialkyl esters such as ditridecyl phthalate, and ketones such as diisobutyl ketone.
These organic solvent media may be used alone or in combination of two or more in an appropriate ratio.

More preferably, from the viewpoint of further improving the dispersibility of the thermally conductive particles, the medium having the above physical properties is an aliphatic carboxylic acid ester represented by the following formula (I), and more preferably, a monohydric alcohol ester.
R ₁ COOR ₂ ......(I)
[In the above formula (I), _R1 is a linear or branched alkyl group having 4 to 21 carbon atoms, an alkenyl group, or an alkyl group having two or more double bonds, and _R2 is a linear or branched alkyl group having 1 to 21 carbon atoms, an alkenyl group, or an alkyl group having two or more double bonds.]
Examples of the aliphatic carboxylate ester represented by the above formula (I) include fatty acids such as lauric acid (12 carbon atoms), myristic acid (14 carbon atoms), palmitic acid (16 carbon atoms), stearic acid (18 carbon atoms), and arachic acid (20 carbon atoms); and methyl alcohol (1 carbon atom), isopropyl alcohol (3 carbon atoms), isobutyl alcohol (4 carbon atoms), myristyl alcohol (14 carbon atoms), cetyl alcohol (16 carbon atoms), stearyl alcohol (18 carbon atoms), and eicosanyl alcohol (20 carbon atoms). Examples of the medium obtained from alcohol include methyl laurate (specific gravity: 0.87), myristyl myristate (specific gravity: 0.84), octyldodecyl myristate (specific gravity: 0.86), 2-ethylhexyl palmitate (specific gravity: 0.86), stearic acid stearate (specific gravity: 0.83), butyl stearate (specific gravity: 0.86), isopropyl palmitate (specific gravity: 0.85), isopropyl myristate (specific gravity: 0.85), methyl stearate (specific gravity: 0.84), isobutyl oleate (specific gravity: 0.86), etc. These vehicles (monohydric alcohol esters) have a specific gravity of 0.8 to less than 1 and a solubility of 0.05 mg or less in 100 ml of water.

When the aliphatic carboxylic acid ester represented by the above formula (I) is used as the medium having the above physical properties, the particle size distribution (Mv/Mn) of the composite particulate material tends to become narrower, improving dispersibility.
Mv/Mn is used as an index of particle size distribution, where Mv is the volume average particle size and Mn is the number average particle size. In the present invention (including the examples described later), the closer the particle size distribution (Mv/Mn) value of the composite particle material is to 1, the higher the monodispersity of the thermal conductive particles is. The volume average particle size (Mv) and the number average particle size (Mn) are measured using a particle size distribution analyzer HRA9320-X100 (manufactured by Nikkiso Co., Ltd.) as a measuring device, and the volume average particle size (Mv)/number average particle size (Mn) is calculated.

The urethane (polyurethane resin), urea (polyurea resin), and urea-urethane (polyurea resin/polyurethane resin), which are the coating material (wall material) of the resin material of component (b) above, are formed by the reaction of an isocyanate component with an amine component or an alcohol component, etc.

Examples of isocyanate components that can be used include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, transcyclohexane 1,4-diisocyanate, diphenyl ether diisocyanate, and xylylene diisocyanate. anate, hydrogenated xylylene diisocyanate, 2,6-diisocyanate caproic acid, tetramethyl-m-xylylene diisocyanate, tetramethyl-p-xylylene diisocyanate, trimethylhexamethylene diisocyanate, triphenylmethane triisocyanate, tris(isocyanatephenyl)thiophosphate, isocyanate alkyl 2,6-diisocyanate capronate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4-isocyanate methyl octane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate, and the like.
Also, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxy-4,4-biphenyl-diisocyanate, 3,3'-dimethylphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, Examples of the isocyanate include diisocyanates such as cyclohexylene-1,4-diisocyanate, triisocyanates such as 4,4',4''-triphenylmethane triisocyanate and toluene-2,4,6-triisocyanate, tetraisocyanates such as 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate, and isocyanate prepolymers such as an adduct of hexamethylene diisocyanate and trimethylolpropane, an adduct of 2,4-tolylene diisocyanate and trimethylolpropane, an adduct of xylylene diisocyanate and trimethylolpropane, and an adduct of tolylene diisocyanate and hexanetriol. These isocyanate components may be used alone or in combination.

Specific examples of amine components that can be used include aliphatic amines such as ethylenediamine, hexamethylenediamine, diaminocyclohexane, piperazine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, iminobispropylamine, diaminoethyl ether, 1,4-diaminobutane, pentamethylenediamine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2-hydroxytrimethylenediamine, diethylaminopropylamine, diaminopropylamine, diaminopropane, 2-methylpentamethylenediamine, and xylylenediamine, as well as m-phenylenediamine, triaminobenzene, 3,5-tolylenediamine, diaminodiphenylamine, diaminonaphthalene, t-butyltoluenediamine, diethyltoluenediamine, and diaminophenol. Among these, aromatic amines such as phenylenediamine, diaminophenol, and triaminobenzene are preferred.

Specific examples of alcohol components that can be used include polyols having two or more hydroxyl groups, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerin, catechol, resorcinol, and hydroquinone. These alcohol components may be used alone or in combination. An alcohol component may also be used in combination with an amine component.

The shell (shell layer) made of urethane, urea, or urea-urethane, which is composed of the coating material (wall material) of the resin material of component (b), can be formed, for example, by 1) forming the shell (shell layer) by interfacial polymerization in a poorly water-soluble medium having the above-mentioned characteristics in which at least one monomer component of urethane, urea, and urethane urea and the thermally conductive particle component of component (a) are dispersed, or by 2) forming the shell (shell layer) by a manufacturing method including an emulsification step in which an oily component (oil phase) containing an isocyanate component is dispersed in a water-based solvent (aqueous phase) to prepare an emulsion, and an interfacial polymerization step in which at least one of an amine component and an alcohol component is added to the emulsion to perform interfacial polymerization.

In the above-mentioned manufacturing method 2), a solvent having a low boiling point can be used when preparing the emulsion. As the low boiling point solvent, a solvent having a boiling point of 100° C. or less can be used, and examples of such a solvent include n-pentane, methylene chloride, ethylene chloride, carbon disulfide, acetone, methyl acetate, ethyl acetate, chloroform, methyl alcohol, ethyl alcohol, tetrahydrofuran, n-hexane, carbon tetrachloride, methyl ethyl ketone, benzene, ethyl ether, and petroleum ether. These solvents may be used alone or in combination.
On the other hand, the aqueous phase used to emulsify the oily phase may contain a protective colloid in advance. As the protective colloid, a water-soluble polymer can be used, which can be appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers, but it is particularly preferable to add polyvinyl alcohol, gelatin, and a cellulose-based polymer compound.
The aqueous phase may contain a surfactant. The surfactant may be appropriately selected from anionic or nonionic surfactants that do not react with the protective colloid to cause precipitation or aggregation. Preferred surfactants include sodium alkylbenzenesulfonate (e.g., sodium lauryl sulfate), dioctyl sodium sulfosuccinate, polyalkylene glycol (e.g., polyoxyethylene nonylphenyl ether), and the like.
The oily phase prepared as above is added to the aqueous phase, emulsified by mechanical force, and then the temperature of the system is increased as necessary to cause interfacial polymerization at the interface of the oily droplets, which can be turned into particles. In addition, desolvation can be performed simultaneously or after the end of the interfacial polymerization reaction. Capsule particles can be obtained by separating the particles from the aqueous phase after the interfacial polymerization reaction and desolvation, washing them, and then drying them.

In the present invention, the content of the poorly water-soluble medium having a specific gravity of less than 1 at 20°C varies depending on the need to arbitrarily control the dispersibility, specific gravity, and particle size, and the need to adjust the content of thermally conductive particles in the composite particulate material, but it is preferable that the content be 3 to 10 mass% relative to the total amount of the composite particulate material.
In addition, the composite particulate material of the present invention can be adjusted so as to have the above-mentioned specified volume average particle diameter for each application, depending on the application of the composite particulate material (for heat-dissipating electronic component materials, ink for writing instruments, paints, etc.).
Furthermore, depending on the purpose, a secondary resin material coating may be provided on the surface of the composite particle material to impart durability or modify the surface properties for practical use.

The thermally conductive composite particulate material of the present invention has a slightly different structure from that of a general thermally conductive composite particulate material. That is, in a general thermally conductive composite particulate material, the core/shell have different compositions, so that there is a clear interface between the two. On the other hand, the thermally conductive composite particulate material of the present invention has a structure in which the components constituting the shell have a lower density toward the center, which makes it easier for the encapsulated thermally conductive particles to be oriented toward the outside of the shell. In the present invention (including the examples described later), the structure in which the components constituting the shell have a lower density toward the center can be confirmed by observing the cross-sectional shape of the composite particulate material with an electron microscope or the like, but is not limited to this method.
In addition, when an aliphatic carboxylic acid ester represented by the above formula (I) is used as a poorly water-soluble medium having a specific gravity of less than 1 at 20°C, the particle size distribution (Mv/Mn) of the composite particulate material tends to become narrower, making it easier to maintain a more uniform state during storage, thereby improving storage stability.
This particle size distribution (Mv/Mn) is preferably 1 to 10, and more preferably 1 to 8. If Mv/Mn exceeds 10, the voids between the particles will be reduced, resulting in a sparsely packed state when used in a coating material such as a paint, and thus reduced thermal conductivity.

In the composite particle material of the present invention thus configured, a resin material having the above-mentioned characteristics is formed on the surface of thermally conductive particles having the above-mentioned characteristics, thereby reducing the interfacial tension between the thermally conductive particles and varnishes, etc., and providing a composite particle material having good compatibility with varnishes, etc., which does not settle even when used in coating materials such as paints, ink materials, etc., and which has excellent dispersibility and thermal conductivity with excellent storage stability.
In the composite particulate material of the present invention, if a fatty acid carboxylate is used as a poorly water-soluble medium having a specific gravity of less than 1 at 20°C, the particle size distribution (Mv/Mn) tends to be narrower and a more uniform state is more easily maintained during storage, thereby improving storage stability.

The composite particulate material of the present invention is a composite particulate material with excellent thermal conductivity and storage stability, and can therefore be suitably used as various heat dissipation materials, coatings for heat dissipation products, and components with heat dissipation functions for electronic components and semiconductor manufacturing equipment.

Next, the present invention will be described in more detail with reference to manufacturing examples, working examples, and comparative examples, but the present invention is not limited to the following examples. Note that "parts" in the following manufacturing examples means "parts by mass."

Thermally conductive composite particulate materials were produced according to the following Production Examples 1 to 5.
[Production Example 1: Particle 1]
As an oil phase solution, 9.6 parts of myristyl myristate (specific gravity: 0.84) were heated to 60°C, while 18.0 parts of aluminum oxide (average particle size 5 μm, thermal conductivity 31 W/(m·K)) were added and thoroughly dispersed. Next, 7.2 parts of isocyanate prepolymer (Takenate D-101E, NV=75%, manufactured by Mitsui Chemicals) were added, and 2 parts of ethylene glycol monobenzyl ether were further added. As an aqueous phase solution, 15 parts of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) were dissolved in 600 parts of distilled water, and the oil phase solution was added thereto, and the mixture was emulsified and mixed with a homogenizer to complete the polymerization. The obtained dispersion was centrifuged to obtain a composite particle material. The particle size distribution (Mv/Mn) was 2.5, and the volume average particle size (Mv) was 25.3 μm.

[Production Example 2: Particle 2]
As an oil phase solution, 9.6 parts of stearyl stearate (specific gravity: 0.83) was heated to 80° C. while 18 parts of aluminum oxide (average particle size: 5 μm, thermal conductivity: 31 W/(m·K)) was added. Next, 3.6 parts of an isocyanate prepolymer (Takenate D-110N, NV=75%, manufactured by Mitsui Chemicals) was added, and 2 parts of ethylene glycol monobenzyl ether was further added. The aqueous phase solution was prepared by dissolving 15 parts of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) in 600 parts of distilled water, adding the oil phase solution, and then adding 6 parts of hexamethylenediamine. After the addition, the mixture was emulsified and mixed with a homogenizer to complete the polymerization. The resulting dispersion was centrifuged to obtain a composite particle material. The particle size distribution (Mv/Mn) was 3.2, and the volume average particle size was 1.0. The diameter (Mv) was 30.7 μm.

[Production Example 3: Particle 3]
In the above Production Example 1, aluminum oxide was replaced with aluminum nitride (average particle size: 1.2 μm, thermal conductivity: 150 W/(m·K)), and myristyl myristate was replaced with methyl laurate (specific gravity: 0.87). Other than the above, a composite particle material was obtained according to the recipe of Example 1. The particle size distribution (Mv/Mn) was 2.3, and the volume average particle size (Mv) was 25.5 μm.

[Production Example 4: Particle 4]
In the above Production Example 2, aluminum oxide was replaced with aluminum nitride (average particle size: 1.2 μm, thermal conductivity: 150 W/(m·K)), and stearyl stearate was replaced with 2-ethylhexyl palmitate (specific gravity: 0.86). Except for the above change, a composite particle material was obtained according to the recipe of Example 2. The particle size distribution (Mv/Mn) was 2.4, and the volume average particle size (Mv) was 24.7 μm.

[Production Example 5: Particle 5]
As an oil phase solution, 9.6 parts of myristyl myristate (specific gravity: 0.84) was heated to 60° C. while 18 parts of aluminum oxide (average particle size: 5 μm, thermal conductivity: 31 W/(m·K)) was added. After adding 0 parts of the oil and dispersing thoroughly, the mixture was added to 400 parts of an aqueous solution of methyl vinyl ether-maleic anhydride copolymer resin (GANTREZAN-179: GAF CHEMICALS) adjusted to 95° C. and pH 4, and the mixture was heated and stirred to form oil droplets. Then, 20 parts of a 50% aqueous solution of methylolmelamine was gradually added as an encapsulation agent, and the mixture was emulsified with a homogenizer to complete the polymerization. The obtained dispersion was centrifuged to obtain a composite particle material. The particle size distribution (Mv/Mn) was 2.8, and the volume average particle size (Mv) was 32.7 μm.

[Examples 1 to 4 and Comparative Examples 1 to 3]
Using each of the composite particulate materials obtained in Production Examples 1 to 5 above, coating compositions were prepared in a conventional manner according to the blending compositions (composite particulate material + various varnishes) shown in Table 1 below.
The volume average particle diameter (Mv), volume average particle diameter (Mv), and surface state in accordance with FIGS. 1(a) to (c) of each of the composite particle materials obtained in Production Examples 1 to 5 are shown in Table 1 below.
The resulting coating compositions were evaluated for viscosity (25° C., mPa·s) and storage stability by the following evaluation methods.

(Method of measuring viscosity)
For each of the obtained coating compositions (each of the dispersions), the viscosity was measured by the following method, and the storage stability was evaluated by measuring the viscosity at a shear rate of 3.8/s at 25° C. The lower the viscosity, the better.

(Method of evaluating storage stability)
Next, the dispersion obtained above was stored in a thermostatic chamber at 50° C. for one week to accelerate aging, and the viscosity of the dispersion after aging was measured in the same manner as in the "Viscosity measurement" described above. The rate of change in viscosity before and after storage at 50° C. for one week was calculated and evaluated on a three-level scale according to the following criteria.
The presence of sediment shall be confirmed by visual inspection.
A: The viscosity change rate was within ±10% and no sediment was observed.
B: The viscosity change rate exceeded ±10% and sediment was observed.
C: The viscosity change rate exceeded ±20% and sediment was observed.

Considering Table 1 above, it has been confirmed that Examples 1 to 4, which fall within the scope of the present invention, have good dispersibility even after time has passed, compared to Comparative Examples 1 to 3, which fall outside the scope of the present invention, and a composite particle material having excellent thermal conductivity and excellent storage stability is obtained.

The resulting composite particle material has excellent thermal conductivity and storage stability, making it suitable for use as a variety of heat dissipation materials, coatings for heat dissipation products, and components with heat dissipation functions for electronic components and semiconductor manufacturing equipment.

A Composite particle material B Composite particle material C Composite particle material 10 Thermally conductive particles 20 Resin material

Claims (2)

A composite particle material in which thermally conductive particles are coated with a resin material in advance , the composite particle material being characterized in that it satisfies the following conditions (a) and (b), the resin material is contained in an amount of 5 to 50 mass% relative to the thermally conductive particles, and the average particle diameter (Mv) of the composite particle material is 0.3 to 100 μm .
(a) The thermally conductive particles are at least one selected from aluminum oxide and aluminum nitride.
(b) The resin material is at least one selected from urethane, urea, and urea-urethane. 2. The composite particle material according to claim 1, characterized in that the composite particles are coated such that a total of 50% or more of the surface area of the thermally conductive particles is coated .

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