WO2020241716A1 - Alumina powder, resin composition, heat dissipating component, and method for producing coated alumina particles - Google Patents

Abstract

The purpose of the present invention is to provide alumina particles which are capable of suppressing an increase in viscosity when included in a resin, and which make a resin composition containing the resin highly heat conductive. An alumina powder according to the present invention contains coated alumina particles that each comprise an alumina particle and a coating layer coating the alumina particle, and that each have a projected area equivalent circle diameter of 1 µm or greater as determined by microscopy. The coating layer contains aluminum nitride, and the average sphericity of the coated alumina particles is 0.85 to 0.97.

Description

Manufacturing method of alumina powder, resin composition, heat dissipation parts, and coated alumina particles

The present invention relates to a method for producing alumina powder, a resin composition, heat radiating parts, and coated alumina particles.

In recent years, the miniaturization and high performance of electrical equipment have been progressing. With the miniaturization and higher performance, the mounting density of electronic components constituting electric devices is increasing, and the need to effectively dissipate heat generated from electronic components is increasing.

In addition, in power device applications such as electric vehicles that can suppress the environmental load, a high voltage may be applied to electronic components or a large current may flow. In this case, a high amount of heat is generated, and in order to deal with the high amount of heat generated, there is an increasing demand for more effectively releasing heat than before. As a technique for meeting such a demand, for example, Patent Document 1 discloses a resin composition containing three kinds of alumina fillers. Further, Patent Document 2 discloses alumina-blended particles containing spherical alumina particles and non-spherical alumina particles, and a resin composition containing the particles. Further, Patent Document 3 describes, as a heat conductive filler, a core made of at least one of alumina and aluminum nitride and a surface layer made of aluminum nitride having a thickness of 1.1 μm or more formed on the surface of the core. The aluminum nitride-based particles provided are disclosed.

Japanese Unexamined Patent Publication No. 2009-164093 JP-A-2009-274929 Japanese Unexamined Patent Publication No. 2012-41253

However, in Patent Documents 1 and 2, the specific surface area of the alumina particles is high, the average sphericity is low, and the resin contains a distorted shape. Therefore, the resin is thickened when the alumina particles are filled, and the alumina particles are contained in a high proportion. It has a problem that it is difficult to fill with. Therefore, the moldability is low, and the thermal conductivity of the obtained heat-dissipating component is also low.

Further, in Patent Document 3, aluminum nitride-based particles are obtained by microwave irradiation, but spherical particles cannot be obtained by this manufacturing method. Therefore, as described above, since the aluminum nitride-based particles described in Patent Document 3 also have a poor shape, the resin is thickened when the aluminum nitride-based particles are filled, and it is difficult to highly fill the aluminum nitride-based particles. Has. After all, even if the aluminum nitride based particles described in Patent Document 3 are used, the moldability is low and the thermal conductivity of the obtained heat radiating component is low.

The present invention has been made in view of such a problem, and is a specific coated alumina capable of suppressing an increase in viscosity when filled in a resin and realizing high thermal conductivity of a resin composition containing the resin. It is an object of the present invention to provide an alumina powder containing particles, a resin composition containing the alumina powder, a heat radiating component, and a method for producing coated alumina particles.

As a result of diligent research to achieve the above object, the present inventors can suppress an increase in viscosity of the alumina powder containing specific coated alumina particles when the resin is filled with the alumina powder, and the alumina powder can be used. It has been found that a resin composition and heat-dissipating parts capable of achieving high thermal conductivity can be obtained by including the mixture, and the present invention has been completed.

That is, the present invention is as follows.
[1]
Alumina powder containing alumina particles and a coating layer for coating the alumina particles, and having a projected area circle equivalent diameter of 1 μm or more and 300 μm or less by microscopy, wherein the coating layer is aluminum nitride. Alumina powder containing, and the average sphericality of the coated alumina particles is 0.85 or more and 0.97 or less.
[2]
The alumina powder according to [1], wherein the alumina powder has a plurality of peaks in a particle size range of 2 μm or more and 200 μm or less in a volume-based frequency particle size distribution by a laser diffraction / scattering method.
[3]
The alumina powder according to [1] or [2], wherein the proportion of the coated alumina particles having a sphericity of 0.80 or less is 15% or less based on the number of the coated alumina particles.
[4]
The alumina powder according to any one of [1] to [3], wherein the average particle size of the coated alumina particles is 30 μm or more and 150 μm or less, which is measured by a laser diffraction / scattering type particle size distribution measuring machine.
[5]
The alumina powder according to any one of [1] to [4], wherein the content of aluminum nitride in the coated alumina particles is 10% by mass or more and 40% by mass or less.

[6]
The alumina powder according to any one of [1] to [5], wherein the total content of alumina and aluminum nitride in the alumina powder is 80% by mass or more.
[7]
The alumina powder according to any one of [1] to [6], wherein the amount of carbon in the coated alumina particles is 0.3% by mass or less.
[8]
A resin composition containing a resin and the alumina powder according to any one of [1] to [7].
[9]
The resin composition according to [8], wherein the resin contains at least one selected from the group consisting of silicone resin, epoxy resin, urethane resin, and acrylic resin.

[10]
A heat-dissipating component containing the alumina powder according to any one of [1] to [7] or the resin composition according to [8] or [9].
[11]
The method for producing a coated alumina powder according to [1], wherein a mixture containing the raw material alumina powder and carbon powder is calcined at a temperature of 1500 ° C. or higher and 1700 ° C. or lower in a reducing atmosphere containing nitrogen gas. The first step of obtaining the first calcined powder and the second step of further calcining the first calcined powder at a temperature of 600 ° C. or higher and 900 ° C. or lower in an air atmosphere to obtain the coated alumina particles. The average particle size of the carbon powder is 30 nm or more and 70 nm or less, the bulk density is 0.10 g / cm ³ or more and 0.20 g / cm ³ or less, and the specific surface area is 20 m ² / g or more and 60 m ² / g. The manufacturing method is as follows.

According to the present invention, an alumina powder capable of suppressing an increase in viscosity when filled in a resin and realizing high thermal conductivity of a resin composition containing the resin, a resin composition containing the alumina powder, a heat radiating component, and the like. And a method for producing coated alumina particles can be provided.

It is an image of the cross-sectional EPMA analysis of the coated alumina particles according to this embodiment.

Hereinafter, a mode for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and the present invention is not limited to the present embodiment.

[Alumina powder]
The alumina powder of the present embodiment contains one or more of the coated alumina particles according to the present embodiment described later. As will be described later, the alumina powder of the present embodiment may contain a filler other than the coated alumina particles, particularly an inorganic filler. When the alumina powder of the present embodiment is a filler other than the coated alumina particles and contains a filler other than the inorganic filler, it should be referred to as a simple powder rather than an alumina powder. Further, when the alumina powder of the present embodiment contains an inorganic filler other than the coated alumina particles (however, it does not contain a filler other than the inorganic filler), it should be referred to as an inorganic powder. However, in the present specification, "alumina powder" is used in a concept that includes them.

(Coated alumina particles)
The coated alumina particles according to the present embodiment have alumina particles and a coating layer that covers the alumina particles and contains aluminum nitride, has a projected area circle equivalent diameter of 1 μm or more and 300 μm or less by microscopic method, and has an average spherical shape. The degree is 0.85 or more and 0.97 or less. Hereinafter, unless otherwise specified, the coated alumina particles according to this embodiment are also simply referred to as “coated alumina particles”.

The coated alumina particles are derived from the alumina particles contained in the raw material alumina powder (hereinafter, simply referred to as "raw material alumina powder") described later.

By using the alumina powder of the present embodiment containing the coated alumina particles containing aluminum nitride in the coating layer for the resin composition and the heat radiating component, the average sphericity described later is set within a predetermined numerical range, and particularly the resin composition. And the thermal conductivity of heat-dissipating parts is increased. The coating layer may contain an unavoidable component such as aluminum nitride generated in the process of forming the coating layer.

The thickness of the coating layer according to the present embodiment is preferably 0.8 μm or more and 12 μm or less, and 1.5 μm or more and 7.5 μm or less can preferably suppress an increase in viscosity when the resin is filled. Alternatively, it is more preferable because it is possible to further realize high thermal conductivity of the resin composition containing the resin. When alumina powder having a coating layer thickness within the above range in the coated alumina particles is used, a heat path can be efficiently formed and heat tends to be sufficiently conducted. The thickness of the coating layer is measured by the method described in Examples.

The coated alumina particles according to the present embodiment have a projected area circle equivalent diameter of 1 μm or more and 300 μm or less and an average sphericity of 0.85 or more and 0.97 or less according to the following microscopy. If the average sphericity of the coated alumina particles is in the above range, it becomes difficult to thicken the resin when the coated alumina particles are filled. When the alumina powder of the present embodiment contains the coated alumina particles, the alumina powder can be filled in the resin at a high ratio. As a result, a heat path can be efficiently and well formed in the resin, and a resin composition having high thermal conductivity and a heat radiating component can be obtained. The average sphericity is preferably 0.87 or more and 0.96 or less, and 0.89 or more and 0.95 or less, from the viewpoint of reducing frictional resistance when filled in resin and increasing the contact area between particles. More preferably. When the alumina powder of the present embodiment contains the coated alumina particles having the above average sphericality in the above range, the fluidity of the alumina powder containing the coated alumina particles is further improved in the resin, and the frictional resistance with the resin is further improved. Is reduced, and an increase in viscosity when the resin is filled with alumina powder can be suppressed. Further, the contact between the alumina particles including the coated alumina particles becomes more sufficient, and the contact area becomes larger. As a result, the heat path can be efficiently formed, so that a resin composition having higher thermal conductivity and a heat radiating component can be obtained. There is a tendency. The average sphericity is measured, for example, by the following microscopy. That is, the particle image taken by a scanning electron microscope, a transmission electron microscope, or the like is taken into an image analyzer, and the projected area (A) and the peripheral length (PM) of the particles are measured from the photograph. Assuming that the area of a perfect circle having the same peripheral length as the peripheral length (PM) is (B), the sphericity of the particle is A / B. Therefore, assuming a perfect circle having the same peripheral length as the peripheral length (PM) of the sample, PM = 2πr and B = πr ² , so B = π × (PM / 2π) ² and the individual particles The sphericity is sphericity = A / B = A × 4π / (PM) ² . The sphericity of 200 arbitrary particles having a projected area circle-equivalent diameter of 1 μm or more and 300 μm or less is obtained as described above, and the arithmetic mean value thereof is taken as the average sphericity. The specific measurement method is as described in the examples. The projected area circle-equivalent diameter refers to the diameter of a perfect circle having the same projected area as the projected area (A) of the particles.

In the alumina powder of the present embodiment, the proportion of the coated alumina particles having a sphericity of 0.80 or less in the coated alumina particles according to the present embodiment is preferably 15% or less on a number basis, and 10 on a number basis. More preferably, it is less than%. The fact that the proportion of coated alumina particles having a spherical degree of 0.80 or less is 15% or less based on the number of particles means that coated alumina particles having few coalesced particles or cracked particles that cause thickening when the resin is filled with alumina powder It means that it is an alumina powder containing, and is preferable in that respect. In addition, there is a tendency that wear of the device and the mold can be reduced. The proportion of the coated alumina particles is, for example, 0.5% or more on a number basis. The diameter equivalent to the projected area circle by the microscope method is usually 200 μm or less.

In the alumina powder of the present embodiment, the proportion of the coated alumina particles having a sphericity of more than 0.80 and 0.83 or less in the coated alumina particles according to the present embodiment is 10% or less on a number basis. It is preferably 5% or less on a number basis. The fact that the proportion of coated alumina particles having a spherical degree in the above range is 10% or less means that alumina containing coated alumina particles having less coalesced particles or cracked particles that cause thickening when the resin is filled with alumina powder. It means that it is a powder, which is preferable. In addition, there is a tendency that wear of the device and the mold can be reduced. The proportion of the coated alumina particles is, for example, 0.5% or more on a number basis. The diameter equivalent to the projected area circle by the microscope method is usually 200 μm or less.

With the coated alumina particles according to the present embodiment, the contact between the alumina powders containing the coated alumina particles becomes better, the heat path can be formed efficiently and satisfactorily, and a resin composition having higher thermal conductivity and heat dissipation parts can be obtained. From the viewpoint of surface smoothness when the resin composition is formed, the average particle size is preferably 30 μm or more and 150 μm or less, more preferably 30 μm or more and 130 μm or less, and 40 μm or more and 120 μm or less. More preferably. When the average particle size is 30 μm or more, the heat path can be formed more efficiently in the resin composition and the heat radiating component, and the heat tends to be conducted more sufficiently. Further, when the average particle size is 150 μm or less, the smoothness of the surface of the heat radiating component is further improved, and the thermal resistance at the interface between the heat radiating component and the heat source is reduced, so that the thermal conductivity can be further improved. I tend to be able to do it. In the present embodiment, the particle size and the average particle size are measured by a laser diffraction / scattering type particle size distribution measuring machine. The specific measurement method is as described in the examples.

The content of aluminum nitride in the coated alumina particles according to the present embodiment is preferably 10% by mass or more and 40% by mass or less, and since high thermal conductivity of the resin composition can be further realized, 15% by mass or more and 35% by mass. More preferably, it is less than%. When coated alumina particles having an aluminum nitride content within the above range are used, the heat path can be formed more efficiently, and heat tends to be conducted more sufficiently. When the content is 10% by mass or more, the coating layer of aluminum nitride becomes thicker, so that the effect of improving the thermal conductivity by coating the aluminum nitride tends to be further enhanced. When the content is 40% by mass or less, the fine irregularities of the coating layer can be further reduced, so that the moldability of the resin composition and the heat radiating component is further improved, and the voids in the heat radiating component tend to be further reduced. The content of aluminum nitride is measured by the method described in Examples.

The carbon content in the coated alumina particles according to the present embodiment is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and further preferably 0.1% by mass or less. preferable. The amount of carbon in the coated alumina particles is, for example, 0.01% by mass or more. When the amount of carbon is in the above range, it tends to have better thermal conductivity, and carbon, which is a conductor, is reduced as much as possible. Therefore, the resin composition has high insulation and thermal conductivity. Objects and heat-dissipating parts can be obtained more effectively and reliably. The amount of carbon in the coated alumina particles is measured by the method described in Examples. Further, the carbon in the coated alumina particles is mainly derived from the carbon powder mixed with the raw material alumina powder. The carbon powder is used when producing the coated alumina particles according to the present embodiment, as described later in the method for producing coated alumina particles.

The specific surface area of the coated alumina particles according to the present embodiment, it is preferable, 0.03 m ² / g or more 0.12 m ² / g or less or less 0.02 m ² / g or more 0.15 m ² / g Is more preferable. When the specific surface area is within the above range, it is easy to suppress an increase in viscosity when the resin is filled with alumina powder containing specific coated alumina particles, and a resin composition having higher thermal conductivity and heat-dissipating parts can be obtained. It works. In this embodiment, the specific surface area is measured by the BET flow method, and the specific measuring method is as described in the examples.

(Alumina powder)
In the alumina powder of the present embodiment, the total content of alumina and aluminum nitride is preferably 80% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more. It is preferably 99% by mass or more, and even more preferably 99% by mass or more. The upper limit of the total content is, for example, 100% by mass. Alumina powder having a total content of alumina and aluminum nitride within the above range has a resin composition having higher thermal conductivity because the amount of unavoidable components such as aluminum oxynitride, which tends to obstruct the thermal pathway, is further reduced. There is a tendency to obtain objects and heat-dissipating parts. The total content of alumina and aluminum nitride is measured by the method described in Examples.

The alumina powder of the present embodiment preferably has a plurality of peaks in a particle size range of 2 μm or more and 200 μm or less in the volume-based frequency particle size distribution by the laser diffraction / scattering method. As a result, the alumina powder of the present embodiment is efficiently filled in the resin to form a heat path, high thermal conductivity can be realized, and an increase in the viscosity of the resin composition is suppressed. Here, in the present embodiment, the peak is the maximum detected in the particle size range obtained by dividing the particle size range of 0.01 μm or more and 3500 μm or less into 100 in the volume-based frequency particle size distribution by the laser diffraction / scattering method. Refer to a point. In addition, if there is a shoulder in the detected peak, that shoulder is also counted as a peak. The shoulder is detected by the curvature of the peak given by the second derivative, and has an inflection point in the peak, that is, the presence of more particle components having a specific particle size.

The alumina powder of the present embodiment has one or more peaks derived from the coated alumina particles in the particle size range of 0.01 μm or more and 3500 μm or less in the volume-based frequency particle size distribution by the laser diffraction scattering method. The alumina powder of the present embodiment has a plurality of peaks derived from the coated alumina particles according to the present embodiment in a particle size range of 0.01 μm or more and 3500 μm or less in the volume-based frequency particle size distribution by the laser diffraction / scattering method. You may.

Alumina powder having such a particle size distribution can be obtained, for example, by containing two or more kinds of coated alumina particles having one peak in the above particle size range and having different average particle diameters from each other.

Further, the alumina powder of the present embodiment may contain a filler other than the coated alumina particles according to the present embodiment. Even in this case, in the volume-based frequency particle size distribution by the laser diffraction / scattering method, the peak derived from the coated alumina particles according to the present embodiment and the coated alumina thereof are usually found in the particle size range of 0.01 μm or more and 3500 μm or less. Two or more peaks will be detected, including peaks derived from fillers other than particles. Examples of the filler include an inorganic filler. Specifically, coated alumina particles other than the coated alumina particles according to the present embodiment, alumina particles having no coating layer (that is, uncoated), magnesia, aluminum nitride, silicon nitride, yttrium oxide, boron nitride, calcium oxide. , Iron oxide, and boron oxide. As described above, the alumina powder of the present embodiment also contains an inorganic material other than alumina such as aluminum nitride, and thus corresponds to the inorganic powder in that respect.

Examples of the coated alumina particles other than the coated alumina particles include coated alumina particles having an alumina particle and a coating layer for coating the alumina particle, and having a projected area circle equivalent diameter of less than 1 μm by microscopy. Examples of the coating layer in this case include aluminum nitride and silicon nitride.

Further, as the coated alumina particles other than the coated alumina particles according to the present embodiment, the alumina particles and the coating layer for coating the alumina particles are provided, and the projected area circle equivalent diameter by microscopy is 1 μm or more and 300 μm or less. Examples of the alumina particles include coated alumina particles that do not contain aluminum nitride as the coating layer. Examples of the coating layer in this case include silicon nitride.

These fillers may be fillers surface-treated with a known silane coupling agent or the like.
The alumina powder of the present embodiment may contain one or more of these fillers together with the coated alumina particles according to the present embodiment.

In the alumina powder of the present embodiment, the content of the coated alumina particles according to the present embodiment is preferably 20% by volume or more and 80% by volume or less, and 25% by volume or more and 75% by volume, based on the total amount of the alumina powder. More preferably, it is less than%. In the present embodiment, when the alumina powder contains two or more kinds of coated alumina particles according to the present embodiment having different average particle diameters, the content of the coated alumina particles is the total amount thereof. To do. By containing the coated alumina particles within the above range, the alumina powder according to the present embodiment can further suppress the increase in viscosity when filled in the resin, and the resin composition containing the resin can be highly thermally conductive. It can be realized more.

Further, in the alumina powder of the present embodiment, from the viewpoint of improving the thermal conductivity, the coated alumina particles according to the present embodiment and the coated alumina particles other than the coated alumina particles according to the present embodiment are used with respect to the total amount of the alumina powder. The total content of the uncoated alumina particles (hereinafter referred to as “coated alumina particles and the like”) is preferably 80% by volume or more and 100% by volume or less, and is 85% by volume or more and 100% by volume or less. Is more preferable. Since the coated alumina particles and the like are contained within the above range, the alumina powder according to the present embodiment has the effect of increasing the thermal conductivity of the resin composition.

As described above, the alumina powder of the present embodiment preferably has a plurality of peaks, that is, two or more peaks, and more preferably two or more and four or less peaks in a particle size range of 2 μm or more and 200 μm or less. It is more preferable to have three peaks. It should be noted that each peak is the first to be detected from the fine particle side (that is, the 0.01 μm side) in the particle size region where the particle size is 0.01 μm or more and 3500 μm or less in the volume-based frequency particle size distribution by the laser diffraction scattering method. A particle having a peak is referred to as a first particle, a particle having a second peak is referred to as a second particle, and a particle having an nth peak in sequence is referred to as an nth particle. That is, the number of detected peaks is n. The particles to be detected may be only the coated alumina particles according to the present embodiment, or may be fillers other than the coated alumina particles, but the fillers other than the coated alumina particles according to the present embodiment may be used. , One or more of coated alumina particles and uncoated alumina particles other than the coated alumina particles according to the present embodiment is preferable.

In the alumina powder of the present embodiment, when the number of peaks n is 2, the position of the peak derived from the first particle is detected in the particle size range of 3 μm or more and 15 μm or less, and the position of the peak derived from the second particle is , It is preferable that the particle size range is 30 μm or more and 150 μm or less. Further, it is preferable that the second particles are coated alumina particles according to the present embodiment, and in addition, it is more preferable that the first particles are uncoated alumina particles.
The content of the first particles in the alumina powder of the present embodiment is 25% by volume or more and 55% by volume or less, and 30% by volume or more and 50% by volume or less from the viewpoint of suppressing the increase in viscosity of the resin composition. It is preferably 35% by volume or more and 45% by volume or less. The content of the second particles is preferably 45% by volume or more and 75% by volume or less, preferably 50% by volume or more and 70% by volume or less, and 55% by volume or more and 65% by volume, from the viewpoint of suppressing the increase in viscosity of the resin composition. More preferably, it is by volume or less. The total of the first particle and the second particle is 100% by volume.
The average particle size of the first particles is preferably 4.0 μm or more and 12 μm or less, and more preferably 5.0 μm or more and 10 μm or less, from the viewpoint of suppressing the increase in viscosity of the resin composition. The average particle size of the second particles is preferably 35 μm or more and 140 μm or less, and more preferably 40 μm or more and 130 μm or less, from the viewpoint of suppressing the increase in viscosity of the resin composition.

When the number of peaks n is 3, the position of the peak derived from the first particle is detected in the particle size range of 0.3 μm or more and 1.0 μm or less, and the position of the peak derived from the second particle is 3.0 μm. It is preferable that the position of the peak derived from the third particle is detected in the particle size range of 30 μm or more and 150 μm or less.
The content of the first particles in the alumina powder of the present embodiment is 10% by volume or more and 25% by volume or less, preferably 12% by volume or more and 18% by volume or less, and 13% by volume or more and 17% by volume or less. More preferably. The content of the second particles is 20% by volume or more and 55% by volume or less, preferably 25% by volume or more and 41% by volume or less, and more preferably 30% by volume or more and 39% by volume or less. .. Further, the content of the third particle is 35% by volume or more and 55% by volume or less, preferably 47% by volume or more and 57% by volume or less, and more preferably 48% by volume or more and 53% by volume or less. .. When the content of each particle is within the above range, the resin can be filled with alumina powder at a high ratio, which is preferable from the viewpoint of suppressing an increase in the viscosity of the resin composition. The total of the first particle, the second particle, and the third particle is 100% by volume.

In this case, the average particle size of the first particles is preferably 0.3 μm or more and 1.0 μm or less, more preferably 0.4 μm or more and 0.9 μm or less, and 0.5 μm or more and 0.8 μm or less. Is more preferable. When the average particle size of the first particles is 0.3 μm or more, the gaps between the particles are efficiently filled, the thermal conductivity can be improved, and the effect of suppressing the increase in viscosity of the resin composition tends to be obtained. is there. Further, when the average particle size of the first particles is 1.0 μm or less, the content of the first particles is about the same as that when the average particle size exceeds 1.0 μm. The number of particles tends to increase, and the number of thermal paths between particles also tends to increase. On the other hand, when the average particle size exceeds 1.0 μm, the number of heat paths between particles tends to decrease. Further, when the average particle size exceeds 1.0 μm, the heat conduction in the first particle is rapid, but the heat conduction in a small number of heat paths becomes rate-determining, and the heat when viewed as a whole powder. Conductivity tends to be low. However, when the average particle size is 1.0 μm or less, the particle size of each particle is small and the number of heat paths is large, so that heat conduction in the first particle and heat conduction in the heat path between particles can be achieved. Large differences are unlikely to occur, and as a result of high heat conduction uniformity, heat conductivity tends to be high.

Further, the average particle size of the second particles is preferably 3.0 μm or more and 15 μm or less, more preferably 4.0 μm or more and 12 μm or less, from the viewpoint of suppressing the increase in viscosity of the resin composition. It is more preferably 0 μm or more and 10 μm or less. When the average particle size of the second particles is in the above range, the second particles are efficiently filled in the gaps between the particles, the thermal conductivity can be improved, and the effect of suppressing the increase in viscosity of the resin composition is obtained. Tend to be.

The average particle size of the third particles is preferably 30 μm or more and 140 μm or less, more preferably 35 μm or more and 135 μm or less, and 45 μm or more and 130 μm or less from the viewpoint of suppressing the increase in viscosity of the resin composition. It is even more preferably 60 μm or more and 120 μm or less. When the average particle diameter of the third particles is 30 μm or more, the thermal pathway can be efficiently formed by the contact between the particles, so that the thermal conductivity tends to be improved. Further, the filling rate tends to be increased by reducing the specific surface area of the particles. Further, when the average particle diameter of the third particle is 140 μm or less, the surface smoothness of the obtained heat radiating component can be maintained, and the contact resistance at the particle interface can be reduced, so that the thermal conductivity Tends to be able to increase.

Further, the average sphericity of the first particles is preferably 0.82 or more and 0.94 or less, preferably 0.84, from the viewpoint of reducing the frictional resistance when filled in the resin and increasing the contact area between the particles. It is more preferably 0.92 or less.
The average sphericity of the second particles is preferably 0.82 or more and 0.94 or less, preferably 0.84 or more and 0, from the viewpoint of reducing the frictional resistance when filled in the resin and increasing the contact area between the particles. It is more preferably .92 or less.
The average sphericity of the third particle is preferably 0.82 or more and 0.94 or less, preferably 0.84 or more and 0, from the viewpoint of reducing the frictional resistance when filled in the resin and increasing the contact area between the particles. It is more preferably .92 or less.

The content of the α crystal phase in the first particles is preferably 80% by mass or more, more preferably 90% by mass or more, from the viewpoint of improving the thermal conductivity. The upper limit is, for example, 100% by mass.
The content of the α crystal phase in the second particles is preferably 80% by mass or more, more preferably 90% by mass or more, from the viewpoint of improving the thermal conductivity. The upper limit is, for example, 100% by mass.
The content of the α crystal phase in the third particle is preferably 80% by mass or more, and more preferably 90% by mass or more, from the viewpoint of improving the thermal conductivity. The upper limit is, for example, 100% by mass.

In the present embodiment, the first particles are preferably uncoated alumina particles from the viewpoint of further improving the fluidity.
The second particles include uncoated alumina particles, coated alumina particles other than the coated alumina particles according to the present embodiment, and coated alumina particles according to the present embodiment from the viewpoint of improving fluidity and thermal conductivity. It is preferably present, and more preferably uncoated alumina particles.
From the viewpoint of improving the thermal conductivity, the third particles are preferably coated alumina particles according to the present embodiment, uncoated alumina particles, and coated alumina particles other than the coated alumina particles according to the present embodiment. More preferably, the coated alumina particles according to the present embodiment.
Examples of the uncoated alumina particles include spherical alumina particles.

When the number of peaks n is 4, the position of the peak derived from the first particle is detected in the particle size range of 0.05 μm or more and 0.2 μm or less, and the position of the peak derived from the second particle is 0.3 μm or more. The position of the peak derived from the third particle is detected in the particle size range of 1.0 μm or less, and the position of the peak derived from the third particle is detected in the particle size range of 3.0 μm or more and 15 μm or less, and the position of the peak derived from the fourth particle is 30 μm or more. It is preferable to detect in a particle size range of 150 μm or less. In the alumina powder of the present embodiment, the position of the peak derived from the first particles is detected in the particle size range of 0.07 μm or more and 0.1 μm or less from the viewpoint of suppressing the increase in viscosity of the resin composition, and the second particles. The position of the peak derived from is detected in the particle size range of 0.4 μm or more and 0.9 μm or less, and the position of the peak derived from the third particle is detected in the particle size range of 4.0 μm or more and 12 μm or less. It is more preferable that the position of the peak derived from the particles of is detected in the particle size range of 35 μm or more and 140 μm or less. Further, it is preferable that the fourth particle is the coated alumina particle according to the present embodiment, and in addition, the first particle, the second particle and the third particle are uncoated alumina particles. preferable.

The content of the first particles in the alumina powder of the present embodiment is 0.5% by volume or more and 5.0% by volume or less, and 1.0% by volume or more 4 from the viewpoint of suppressing the increase in viscosity of the resin composition. It is preferably 0.0% by volume or less, and more preferably 1.5% by volume or more and 3.0% by volume or less. From the viewpoint of suppressing the increase in viscosity of the resin composition, the content of the second particles is preferably 9% by volume or more and 20% by volume or less, preferably 11% by volume or more and 18% by volume or less, and 12% by volume or more and 17%. More preferably, it is by volume or less. The content of the third particles is preferably 19% by volume or more and 45% by volume or less, preferably 24% by volume or more and 41% by volume or less, and 29% by volume or more and 39% by volume, from the viewpoint of suppressing the increase in viscosity of the resin composition. More preferably, it is by volume or less. The content of the fourth particles is preferably 43% by volume or more and 60% by volume or less, preferably 45% by volume or more and 57% by volume or less, and 46% by volume or more and 53% by volume, from the viewpoint of suppressing the increase in viscosity of the resin composition. More preferably, it is by volume or less. The total of the first particle, the second particle, the third particle, and the fourth particle is 100% by volume.

Further, the average particle size of the first particles is preferably 0.05 μm or more and 0.2 μm or less, and more preferably 0.07 μm or more and 0.1 μm or less, from the viewpoint of suppressing the increase in viscosity of the resin composition. preferable. The average particle size of the second particles is preferably 0.3 μm or more and 1.0 μm or less, and more preferably 0.4 μm or more and 0.9 μm or less, from the viewpoint of suppressing the increase in viscosity of the resin composition. The average particle size of the third particles is preferably 3.0 μm or more and 15 μm or less, and more preferably 4.0 μm or more and 12 μm or less, from the viewpoint of suppressing the increase in viscosity of the resin composition. The average particle size of the fourth particles is preferably 30 μm or more and 150 μm or less, and more preferably 35 μm or more and 140 μm or less, from the viewpoint of suppressing the increase in viscosity of the resin composition.

In the present embodiment, the total content of all the first to nth particles in the alumina powder is preferably 98% by volume or more, preferably 99% by volume or more, from the viewpoint of improving the thermal conductivity. Is more preferable. The upper limit of the content rate is 100% by volume.

(Manufacturing method of coated alumina particles)
In the method for producing coated alumina particles according to the present embodiment, for example, a mixture containing raw material alumina powder and carbon powder is calcined at a temperature of 1500 ° C. or higher and 1700 ° C. or lower in a reducing atmosphere containing nitrogen gas. The first step of obtaining the first calcined powder and the second step of further calcining the first calcined powder at a temperature of 600 ° C. or higher and 900 ° C. or lower in an air atmosphere to obtain coated alumina particles according to the present embodiment. It is obtained by using a step including. By this production method, coated alumina particles containing aluminum nitride in the coating layer and having an average sphericity in a predetermined high range can be obtained. When the alumina particles of the present embodiment contain the coated alumina particles, thickening can be suppressed, and a resin composition and heat-dissipating parts having high thermal conductivity can be obtained. The details will be described below.

In the first step, first, the raw material alumina powder and the carbon powder are mixed so as to have a predetermined mixing ratio using a predetermined mixer. The mixing method is not particularly limited as long as the raw material alumina powder and the carbon powder can be uniformly mixed, and either wet mixing or dry mixing may be used. Examples of such a mixing method include ball mill mixing. The mixing ratio of the raw material alumina powder and the carbon powder takes into consideration the mixing ratio of the stoichiometry of the raw material alumina powder and the carbon powder, and from the viewpoint of forming a reaction atmosphere, the carbon powder is based on 100 parts by mass of the raw material alumina powder. It is preferably 10 parts by mass or more and 50 parts by mass or less, and more preferably 15 parts by mass or more and 45 parts by mass or less.

As the raw material alumina powder, for example, various alumina particles having a crystal structure of α, γ, θ, and η can be used. The alumina particles are usually spherical. Specifically, the average sphericity of the alumina particles having a projected area circle equivalent diameter of 1 μm or more and 300 μm or less contained in the raw material alumina powder is usually 0.90 or more and 0.91 or more. It is preferably 0.99 or less, and more preferably 0.92 or more and 0.98 or less. The upper limit of the average sphericity is, for example, 1.00. When the average sphericity is in the above range, the mixture of the raw material alumina powder and the carbon powder becomes more uniform, and the reaction is promoted.

The average particle size of the raw material alumina powder is preferably 25 μm or more and 140 μm or less, preferably 30 μm or more and 130 μm or less, because the carbon reduction nitriding reaction is more likely to proceed when the average particle size is larger than that of the carbon powder described later. Is more preferable.

The specific surface area of the alumina raw material powder is preferably from 0.03 m ² / g or more 0.30 m ² / g, more preferably not more than 0.05 m ² / g or more 0.25 m ² / g. When the specific surface area is in the above range, the mixture of the raw material alumina powder and the carbon powder becomes more uniform, and the reaction is promoted.

The carbon powder according to the present embodiment has an average particle size of 30 nm or more and 70 nm or less, a bulk density of 0.10 g / cm ³ or more and 0.20 g / cm ³ or less, and a specific surface area of 20 m ² / g. It is 60 m ² / g or less. By using such carbon powder, a large amount of carbon powder adheres to the surface of the alumina particles, and in the reaction between the raw material alumina powder and nitrogen at high temperature, the carbon powder contributes as a spacer and coalesces the alumina particles. Can be suppressed, and coated alumina particles having a high degree of sphere can be suitably produced.

The average particle size of the carbon powder is preferably 35 nm or more and 65 nm or less from the viewpoint of improving the effect of preventing coalescence of alumina particles.

The bulk density of the carbon powder is preferably 0.10 g / cm ³ or more and 0.20 g / cm ³ or less, and preferably 0.12 g / cm ³ or more and 0.18 g / cm ³ or less. When the bulk density is in the above range, the carbon powder adheres more uniformly to the surface of the alumina particles, and the reaction is promoted. In this embodiment, the bulk density is measured by the method described in the examples.

Further, the specific surface area of the carbon powder is preferably 20 m ² / g or more and 60 m ² / g or less, and preferably 25 m ² / g or more and 55 m ² / g or less. When the specific surface area is within the above range, the effect of preventing coalescence of alumina particles is improved.

The total pore volume of the carbon powder is preferably 1 mL / g or more and 4 mL / g or less, and more preferably 1.5 mL / g or more and 3 mL / g or less. When the total pore volume is in the above range, nitrogen gas easily penetrates into carbon, and the above carbon reduction nitriding reaction is more likely to proceed in the carbon powder. In this embodiment, the total pore volume is measured by the method described in Examples.

Examples of the carbon powder include carbon black such as acetylene black, furnace black, and thermal black, and powdered graphite. As the carbon powder, acetylene black is preferable from the viewpoint of purity and the like.

In the first step, the mixture is calcined at a temperature of 1500 ° C. or higher and 1700 ° C. or lower in a reducing atmosphere containing nitrogen gas to obtain a first calcined powder. The formation of the coating layer containing aluminum nitride on the surface of the raw material alumina powder proceeds based on the following formula showing the carbon reduction nitriding reaction.
Al ₂ O ₃ + 3C + N ₂ → 2AlN + 3CO
The gas reducing atmosphere containing nitrogen gas can be obtained, for example, by using a reducing atmosphere furnace that circulates in a refining apparatus to remove oxygen and water. Further, the gas may contain an unavoidable component such as carbon dioxide gas in addition to nitrogen gas.

When firing the mixture, it is preferable to supply nitrogen gas to the mixture at 1 L / min or more and 10 L / min from the viewpoint of reaction promotion and productivity. More preferably, it is supplied at 3 L / min or more and 7 L / min.

The firing temperature in the first step is preferably 1550 ° C. or higher and 1650 ° C. or lower from the viewpoint of controlling the coating layer and the sphericity of the coated alumina particles according to the present embodiment. Further, the firing time is usually 4 hours or more and 12 hours or less in consideration of productivity. The larger the amount of nitrogen gas, the higher the firing temperature, and the longer the firing time, the thicker the coating layer tends to be.

In the second step, the first calcined powder obtained in the first step is further calcined at a temperature of 600 ° C. or higher and 900 ° C. or lower in an air atmosphere to obtain coated alumina particles. By firing the first fired powder in the second step, the remaining carbon powder can be removed, and the coated alumina particles according to the present embodiment can be obtained.
The firing temperature in the second step is preferably 650 ° C. or higher and 850 ° C. or lower from the viewpoint of controlling the carbon content of the coated alumina particles according to the present embodiment. Further, the firing time is preferably 2 hours or more and 6 hours or less in consideration of the fact that carbon powder can be efficiently removed.

Further, in the second step, when the first calcined powder is calcined, air is supplied to the first calcined powder at 1 L / min or more and 3 L / min to control the carbon content of the coated alumina particles according to the present embodiment. From the point of view, it is preferable. More preferably, it is supplied at 1.5 L / min or more and 2.5 L / min.

(Alumina powder manufacturing method)
As the alumina powder according to the present embodiment, one kind of coated alumina particles according to the present embodiment may be used as it is. Further, the alumina powder according to the present embodiment may be obtained by appropriately mixing two or more kinds of coated alumina particles. Further, the alumina powder according to the present embodiment may be obtained by appropriately mixing at least one kind of coated alumina particles according to the present embodiment with other fillers and the like. Examples of the mixing method include ball mill mixing.

[Resin composition and method for producing the same]
The resin composition according to the present embodiment contains at least a resin and an alumina powder according to the present embodiment. By containing the above alumina powder, the resin composition according to the present embodiment can suppress thickening and have high thermal conductivity.

(resin)
As the resin, various polymer compounds such as thermoplastic resin and its oligomers and elastomers can be used. For example, epoxy resin, phenol resin, melamine resin, urea resin, unsaturated polyester, urethane resin, acrylic resin, and Fluorine resin; polyamides such as polyimide, polyamideimide, and polyetherimide; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyester, polysulfone, liquid crystal polymer, polyether sulfone, polycarbonate, maleimide modified resin, ABS (Acrylonitrile / butadiene / styrene) resin, AAS (acrylonitrile / acrylic rubber / styrene) resin, AES (acrylonitrile / ethylene / propylene / diene rubber / styrene) resin, EVA (ethylene vinyl acetate copolymer) resin, silicone resin, etc. Can be used. These resins can be used alone or in admixture of two or more.

Among these resins, epoxy resin, phenol resin, urethane resin, acrylic resin, fluororesin, polyimide, polyphenylene sulfide, polycarbonate, ABS resin, and silicone resin are preferable, and silicone resin and epoxy are preferable from the viewpoint of obtaining high heat dissipation characteristics. Resins, urethane resins, and acrylic resins are more preferred, and silicone resins are even more preferred.
As the silicone resin, it is preferable to use a rubber or gel obtained from a one-component or two-component addition reaction type liquid silicone having an organic group such as a methyl group and a phenyl group. Examples of such rubber or gel include "YE5822A solution / YE5822B solution (trade name)" manufactured by Momentive Performance Materials Japan LLC and "SE1885A solution / SE1885B solution" manufactured by Toray Dow Corning Co., Ltd. Product name) ”and so on.

(Contents of alumina powder and resin)
In the resin composition of the present embodiment, from the viewpoint of improving the thermal conductivity, the content of the alumina powder according to the present embodiment is 67% by volume or more and 88% by volume or less with respect to the total amount of the resin composition. It is preferably 71% by volume or more and 85% by volume or less. Since the alumina powder according to the present embodiment is difficult to thicken even when filled in the resin, it is possible to suppress the thickening of the resin composition even if it is contained in the resin composition within the above range. ..

In the resin composition of the present embodiment, from the viewpoint of moldability of the resin composition, the content of the resin according to the present embodiment is 12% by volume or more and 33% by volume or less with respect to the total amount of the resin composition. Is preferable, and more preferably 15% by volume or more and 29% or less.

(Other ingredients)
In addition to the alumina powder and the resin according to the present embodiment, the resin composition of the present embodiment may contain, if necessary, molten silica, crystalline silica, zirconium, calcium silicate, as long as the characteristics of the present embodiment are not impaired. Inorganic fillers such as calcium carbonate, silicon carbide, aluminum nitride, boron nitride, beryllia, and zirconia; nitrogen-containing compounds such as melamine and benzoguanamine, oxazine ring-containing compounds, and phosphate compounds of phosphorus compounds, aromatic condensed phosphates, And flame-retardant compounds such as halogen-containing condensed phosphoric acid ester; may contain additives and the like. Additives include reaction retarders such as dimethyl maleate, curing agents, curing accelerators, flame retardants, flame retardants, colorants, tackifiers, UV absorbers, antioxidants, optical brighteners, and light. Examples thereof include sensitizers, thickeners, lubricants, defoaming agents, surface conditioners, brighteners, and polymerization inhibitors. These components may be used alone or in admixture of two or more. In the resin composition of the present embodiment, the content of other components is usually 0.1% by mass or more and 5% by mass or less, respectively.

(Manufacturing method of resin composition)
Examples of the method for producing the resin composition of the present embodiment include a method of sufficiently stirring the resin, the alumina powder, and other components as needed. In the resin composition of the present embodiment, for example, a predetermined amount of each component is blended with a blender, a Henschel mixer or the like, kneaded with a heating roll, a kneader, a uniaxial or biaxial extruder or the like, cooled, and then pulverized. Can be manufactured by

[Heat dissipation parts]
The heat radiating component according to the present embodiment includes the alumina powder or the resin composition according to the present embodiment. By using the above alumina powder or resin composition, the heat radiating component according to the present embodiment can realize high thermal conductivity, that is, can have high heat radiating property. Examples of the heat radiating component include a heat radiating sheet, heat radiating grease, heat radiating spacer, semiconductor encapsulant, and heat radiating paint (heat radiating coating agent).

The heat dissipation sheet is usually an insulating heat conductive sheet for removing heat generated from heat-generating electronic components and electronic devices. The heat radiating sheet is not particularly limited as long as it contains the alumina powder or resin composition according to the present embodiment. Examples of the material other than the alumina powder contained in the heat radiating sheet of the present embodiment include silicone rubber. The heat radiating sheet is mainly used by being attached to a heat radiating fin or a metal plate. The heat radiating sheet can be obtained, for example, by molding the alumina powder according to the present embodiment and silicone rubber into a sheet by a solvent casting method, an extrusion film formation, or the like. It is preferable to defoam when forming into a sheet. The thickness of the heat radiating sheet is usually preferably 10 μm or more and 300 μm or less.

The heat radiating grease is usually applied between the heat generating member and the heat radiating member, and is used to efficiently conduct the heat generated by the heat radiating member to the heat radiating member to promote heat dissipation. The thermal grease is not particularly limited as long as it contains the alumina powder or resin composition of the present embodiment. Examples of materials other than the alumina powder contained in the thermal paste of the present embodiment include organosilicon compounds such as silicone oil and hydrocarbon-based synthetic oils such as poly α-olefin oil. The thermal grease can be obtained, for example, by dispersing the alumina powder of the present embodiment in an organosilicon compound or a hydrocarbon-based synthetic oil to make it semi-solid. Further, the thermal grease may be obtained by making this resin composition into a semi-solid state by using a resin composition in which the alumina powder of the present embodiment is dispersed in an organosilicon compound or a hydrocarbon-based synthetic oil. Good.

The heat dissipation spacer is usually used to fill the space between the heat-generating electronic components and devices and the case that houses them. By using this heat radiating spacer, the heat generated from the heat-generating electronic component and the electronic device can be directly transferred to the case of the electronic device and radiated. The heat radiating spacer is not particularly limited as long as it contains the alumina powder or resin composition of the present embodiment. Examples of the material other than the alumina powder contained in the heat radiating spacer of the present embodiment include silicone rubber. The heat radiating spacer can usually be obtained by the same method as the heat radiating sheet, but its thickness is thicker than that of the heat radiating sheet.

The semiconductor encapsulant is used to remove heat generated from electronic components such as semiconductor elements and to protect the electronic components from external stimuli. The semiconductor encapsulant is not particularly limited as long as it contains the alumina powder or resin composition of the present embodiment. For the semiconductor encapsulant, for example, the alumina powder or resin composition of the present embodiment and various known additives or solvents generally used for encapsulant materials are mixed using a known mixer. Can be manufactured in. As a method for adding various components and solvents at the time of mixing, generally known methods can be appropriately applied and are not particularly limited.

The heat-dissipating paint is applied to mechanical parts, electric products, electric parts, etc. that have a heat source, and is used to improve the heat-dissipating properties of those parts. The heat-dissipating paint is not limited as long as it contains the alumina powder or resin composition of the present embodiment and a solvent. Since the alumina powder of the present embodiment can suppress an increase in viscosity when the resin is filled with the alumina powder, it is possible to maintain a suitable viscosity even in a solvent. Examples of the solvent include water, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, propyl acetate, butyl acetate, cyclohexanone, ethylbenzene, xylene, methyl methacrylate, and 1-butanol. These solvents can be used alone or in admixture of two or more. Further, examples of mechanical parts include engines, boilers, blowers, and pumps. Examples of electrical products include lighting, solar cell modules, and refrigerators. Examples of the electric component include a circuit board.

Examples and comparative examples are shown below to explain the present invention in detail, but the present invention is not limited to these examples.

〔Evaluation methods〕
(1) Average Spherical Degree and Ratio of Coated Alumina Particles The coated alumina particles were separated from the alumina powder using a sieve product using a JIS standard stainless steel test sieve having a mesh size of 53 μm.
As described in the above microscope method, the particle image taken by a scanning electron microscope (JSM-6301F type manufactured by JEOL Ltd.) is taken into an image analyzer (“MacView Ver.4” (trade name) manufactured by Mountech Co., Ltd.) and photographed. The projected area (A) and the peripheral length (PM) of the particles were measured from. Using these values, the sphericity of each particle and its ratio were obtained, and the arithmetic mean value of the sphericity of each particle was taken as the average sphericity. For reference, an SEM image (500 times) of the coated alumina particles according to this embodiment is shown in FIG.

(2) Average particle size and particle size distribution (number of peaks)
The average particle size and particle size distribution (number of peaks) were measured by a laser diffraction light scattering method particle size distribution measuring device (manufactured by Malvern, product name "Mastersizer 3000", wet dispersion unit: Hydro MV mounted). In the measurement, water was used as the solvent, and 200 W output was applied for 2 minutes as a pretreatment using the ultrasonic generator UD-200 (with ultratrace chip TP-040) (product name) manufactured by Tomy Seiko. Distributed processing was performed. The particles after the dispersion treatment were dropped onto the dispersion unit so that the laser scattering intensity was 10 to 15%. The stirring speed of the dispersion unit stirrer was 1750 rpm, and there was no ultrasonic mode. The particle size distribution analysis was performed by dividing the particle size range of 0.01 to 3500 μm into 100 parts. 1.33 was used for the refractive index of water, and 1.768 was used for the refractive index of the alumina particles and the coated alumina particles. In the measured mass-based particle size distribution, the particles having a cumulative mass of 50% were defined as the average particle size. The peak was set as the maximum point detected in the above particle size range.

(3) Content of Aluminum Nitride in Coated Alumina Particles The coated alumina particles were separated from the alumina powder using a sieve product using a JIS standard stainless steel test sieve having a mesh size of 53 μm.
The content of aluminum nitride in the coated alumina particles (hereinafter, also referred to as “AlN content”) was measured by Rietveld analysis of the powder X-ray diffraction pattern. The coated alumina particles were packed in a sample holder and measured using an X-ray diffractometer (“D8 ADVANCE” (product name) manufactured by Bruker Co., Ltd., detector: LyncEye (product name)). The measurement conditions are X-ray source: CuKα (λ = 1.5406Å), measurement method: continuous scanning method, scanning speed: 0.017 ° / 2.0sec, tube voltage: 45kV, tube current: 360mA, divergence slit: 0. 5.5 °, solar slit: 4 °, measurement range: 2θ = 10 to 70 °. Based on the obtained X-ray diffraction pattern, the content of aluminum nitride was determined by quantitative analysis by Rietveld analysis using analysis software TOPAS.

(4) Carbon Amount Coated alumina particles were separated from the alumina powder using a sieve product using a JIS standard stainless steel test sieve having a mesh size of 53 μm.
Then, the carbon amount in the coated alumina particles was measured using a carbon / sulfur simultaneous analyzer (CS-444LS type (trade name) manufactured by LECO), and the carbon amount was quantified by a calibration curve method. Specifically, first, a calibration curve was obtained using 63 carbon steel, which is a standard sample of Japanese steel, as a standard substance. After that, 0.3 g of the coated alumina particles obtained in Examples and Comparative Examples were used as a combustion improver for metallic iron (“IRON CHIP” (product name) manufactured by LECO) and metallic tungsten (“CECOCEL II” manufactured by LECO). along with the product name)), in an oxygen atmosphere, a carbon-containing material is completely degraded, and oxidative combustion until all carbon is converted into CO _2, the generated amount of CO ₂ as measured by infrared detector, carbon I asked for the amount.

(5) Thickness of coating layer The coated alumina particles were separated from the alumina powder using a sieve product using a JIS standard stainless steel test sieve having a mesh size of 53 μm.
As shown in FIG. 1, the thickness of the coating layer in the coated alumina particles was measured by cross-sectional EPMA analysis. First, the coated alumina particles were embedded in a G-2 epoxy resin (manufactured by Gatan), and osmium coating was performed after cross-sectional milling. The coated sample was subjected to N element mapping analysis using an electron probe microanalyzer (JXA-8230 (product name) manufactured by JEOL Ltd.). The accelerating voltage was 15 kV, and the irradiation current was 5 × ^10-8 A. The obtained mapping image was taken into an image analyzer (“MacView Ver.4” (trade name) manufactured by Mountech Co., Ltd.), and the thickness of the coating layer was determined. The thickness of 10 points was obtained for one particle, and the arithmetic mean value was taken as the thickness of the coating layer of one particle. The thickness of the coating layer of 200 arbitrary particles obtained in this manner was determined, and the arithmetic mean value thereof was taken as the thickness of the coating layer in the coated alumina particles.

(6) Specific Surface Area The coated alumina particles were separated from the alumina powder using a sieve product using a JIS standard stainless steel test sieve having a mesh size of 53 μm.
The specific surface area was measured using HM-Model 1208 manufactured by Macsorb. Prior to the measurement, the coated alumina particles were pretreated by heating at 300 ° C. for 18 minutes in a nitrogen gas atmosphere. A mixed gas of 30% nitrogen and 70% helium was used as the adsorbed gas, and the flow rate was adjusted so that the indicated value of the main body flow meter was 25 ml / min.

(7) Bulk Density The bulk density of the carbon powder was measured according to JIS K 5101-12-2.

(8) Total Pore Volume The total pore volume of the carbon powder was measured by a mercury injection method using a pore distribution measuring device (AutoPore IV 9520 type (trade name) manufactured by Shimadzu Corporation).

(9) Total content of alumina and aluminum nitride in alumina powder The total content of alumina and aluminum nitride in alumina powder (hereinafter, also referred to as “total content”) is a powder X-ray diffraction pattern. It was measured by Rietveld analysis. X-ray diffraction measurement was carried out in the same procedure as the content of aluminum nitride in the alumina powder described above, and based on the obtained X-ray diffraction pattern, quantitative analysis by Rietveld analysis using the analysis software TOPAS was performed to obtain alumina. The content of aluminum nitride was determined.

(10) Viscosity The alumina powders obtained in Examples and Comparative Examples were added to silicone oil (“KF96-100cs” (product name) manufactured by Shin-Etsu Chemical Co., Ltd.) so that the filling rate of the alumina powder was 75 vol%. did. This was mixed for 30 seconds at a rotation speed of 2200 rpm using a rotation / revolution mixer (“Awatori Rentaro ARE-310” (product name) manufactured by Shinky Co., Ltd.), and then vacuum defoamed to obtain a resin composition. The shear viscosity of the obtained resin composition was measured using a rheometer (“MCR102” (product name) manufactured by Antonio-Par). The measurement conditions were temperature: 30 ° C., plate: φ25 mm parallel plate, gap: 1 mm. Shear rate measured while continuously changing from 0.01s ^-1 to 10s ^-1, was read viscosity at a 5s ^-1.

(11) Thermal conductivity The alumina powders obtained in Examples and Comparative Examples were mixed with silicone resin (SE-1885A solution and B solution manufactured by Toray Dow Corning Co., Ltd.) so that the filling rate of the alumina powder was 80 vol%. I put it in. This was stirred and mixed, vacuum defoamed, processed to a thickness of 3 mm, and heated at 120 ° C. for 5 hours to obtain a resin composition. The obtained resin composition is subjected to thermal conductivity by a steady-state method based on ASTM D5470 using a thermal conductivity measuring device (Hitachi Technology and Service Co., Ltd. resin material thermal resistance measuring device "TRM-046RHHT" (product name)). It was measured. The resin composition was processed into a width of 10 mm × 10 mm, and measurement was carried out while applying a load of 2N.

[Example 1]
In Example 1, as the raw material alumina powder used for producing the coated alumina particles, DAW-90 (product name) manufactured by Denka Co., Ltd. (average sphericity: 0.91, average particle diameter: 91 μm, specific surface area: 0). .1 m ² / g) was used.
In addition, as acetylene black, which is a carbon powder, HS-100 (product name) manufactured by Denka Co., Ltd. (average particle size: 46 nm, bulk density: 0.15 g / cm ³ , specific surface area: 40 m ² / g, total fineness. Pore volume: 2.1 mL / g) was used.
50 g of alumina powder as a raw material and 20 g of carbon powder are mixed by a ball mill, nitrogen gas is supplied at an amount of 7 L / min, and firing is performed in a nitrogen atmosphere under the conditions of a firing temperature of 1650 ° C. and a firing time of 12 hours. (First step). Then, air was supplied at an amount of 2 L / min and calcined in an air atmosphere under the conditions of a firing temperature of 700 ° C. and a firing time of 4 hours to obtain coated alumina particles A. Regarding the coated alumina particles A, the average sphericity of the coated alumina particles of 1 μm or more and 300 μm or less, the ratio of the coated alumina particles having a sphericity of 0.80 or less, the average sphericity, the content of AlN in the whole, and the thickness of the coating layer are determined. The measurements were taken and the results are shown in Table 1.
AA-05 (product name) manufactured by Sumitomo Chemical Co., Ltd. as the ultrafine powder alumina 1 and DAW-07 manufactured by Denka Co., Ltd. as the fine powder alumina 2 in the ratio (volume%) shown in Table 1 (. The product name) was prepared as an alumina powder by blending coated alumina particles A as the coarse powder alumina 3. The physical properties of the obtained alumina powder were evaluated, and the results are shown in Table 1.

[Example 2]
In Example 2, as the raw material alumina powder used for producing the coated alumina particles, DAW-70 (product name) manufactured by Denka Co., Ltd. (average sphericalness: 0.92, average particle diameter: 70 μm, specific surface area: 0). .1 m ² / g) was used to produce coated alumina particles B in the same manner as in Example 1 except that the firing temperature in the first step was changed to 1550 ° C. and the firing time was changed to 4 hours. The same measurements as in Example 1 were performed and the results are shown in Table 1.
Table 1 shows the same as in Example 1 except that DAW-05 (product name) manufactured by Denka Co., Ltd. was used as the fine powder alumina 2 and coated alumina particles B were used as the coarse powder alumina 3. Alumina powder was obtained by compounding (% by volume). In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Example 3]
In Example 3, as the raw material alumina powder used for producing the coated alumina particles, DAS-30 (product name) manufactured by Denka Co., Ltd. (average sphericalness: 0.93, average particle diameter: 30 μm, specific surface area: 0). Using .2 m ² / g), coated alumina particles C were produced in the same manner as in Example 1 except that the firing temperature in the first step was changed to 1500 ° C. and the firing time was changed to 4 hours. The same measurements as in Example 1 were performed and the results are shown in Table 1.
Table 1 shows the same as in Example 1 except that DAW-05 (product name) manufactured by Denka Co., Ltd. was used as the fine powder alumina 2 and coated alumina particles C were used as the coarse powder alumina 3. Alumina powder was obtained by compounding (% by volume). In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Example 4]
In Example 4, as the raw material alumina powder used for producing the coated alumina particles, DAW-120 (product name) manufactured by Denka Co., Ltd. (average sphericalness: 0.91, average particle diameter: 115 μm, specific surface area: 0). Coated alumina particles D were produced in the same manner as in Example 1 except that 1 m ² / g) was used. The same measurements as in Example 1 were performed and the results are shown in Table 1.
Table 1 shows the same as in Example 1 except that DAW-10 (product name) manufactured by Denka Co., Ltd. was used as the fine powder alumina 2 and coated alumina particles D were used as the coarse powder alumina 3. Alumina powder was obtained by compounding (% by volume). In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Example 5]
In Example 5, coated alumina particles E were produced in the same manner as in Example 1 except that the firing temperature in the first step was changed to 1600 ° C. The same measurements as in Example 1 were performed and the results are shown in Table 1.
Alumina powder was obtained by the formulation (volume%) shown in Table 1 in the same manner as in Example 1 except that coated alumina particles E were used as the coarse powder alumina 3. In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Example 6]
In Example 6, as the raw material alumina powder used for producing the coated alumina particles, DAW-45 (product name) manufactured by Denka Co., Ltd. (average sphericalness: 0.92, average particle diameter: 43 μm, specific surface area: 0). Using .2 m ² / g), coated alumina particles F were produced in the same manner as in Example 1 except that the firing temperature in the first step was changed to 1600 ° C. and the firing time was changed to 8 hours. The same measurements as in Example 1 were performed and the results are shown in Table 1.
Table 1 shows the same as in Example 1 except that DAW-05 (product name) manufactured by Denka Co., Ltd. was used as the fine powder alumina 2 and coated alumina particles F were used as the coarse powder alumina 3. Alumina powder was obtained by compounding (% by volume). In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Example 7]
In Example 7, as the raw material alumina powder used for producing the coated alumina particles, DAW-70 (product name) manufactured by Denka Co., Ltd. (average sphericalness: 0.92, average particle diameter: 70 μm, specific surface area: 0). The coated alumina particles G were produced in the same manner as in Example 1 except that the firing temperature in the first step was changed to 1600 ° C. using 1 m ² / g). The same measurements as in Example 1 were performed and the results are shown in Table 1.
Table 1 shows the same as in Example 1 except that DAW-05 (product name) manufactured by Denka Co., Ltd. was used as the fine powder alumina 2 and coated alumina particles G were used as the coarse powder alumina 3. Alumina powder was obtained by compounding (% by volume). In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Example 8]
In Example 8, as the raw material alumina powder used for producing the coated alumina particles, DAW-120 (product name) manufactured by Denka Co., Ltd. (average sphericalness: 0.91, average particle diameter: 115 μm, specific surface area: 0). The coated alumina particles H were produced by the same method as in Example 1 except that the firing temperature in the first step was changed to 1600 ° C. using 1 m ² / g). The same measurements as in Example 1 were performed and the results are shown in Table 1.
Table 1 shows the same as in Example 1 except that DAW-10 (product name) manufactured by Denka Co., Ltd. was used as the fine powder alumina 2 and coated alumina particles H were used as the coarse powder alumina 3. Alumina powder was obtained by compounding (% by volume). In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Example 9]
Alumina powder was produced and evaluated in the same manner as in Example 7 except that the blending ratio of alumina was changed to the ratio (volume%) shown in Table 1. The results are shown in Table 1.

[Example 10]
Alumina powder was produced and evaluated in the same manner as in Example 7 except that the blending ratio of alumina was changed to the ratio (volume%) shown in Table 1. The results are shown in Table 1.

[Comparative Example 1]
In Comparative Example 1, DAW-05 (product name) manufactured by Denka Co., Ltd. was used as the fine powder alumina 2, and DAW-45 manufactured by Denka Co., Ltd. was used as the coarse powder alumina 3 instead of the coated alumina particles A. (Product name) The formulation (volume) shown in Table 1 is the same as in Example 1 except that (average sphericalness: 0.92, average particle size: 43 μm, specific surface area: 0.2 m ² / g) is used. %) To obtain an alumina powder. In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

[Comparative Example 2]
In Comparative Example 2, as the raw material alumina powder used for producing the coated alumina particles, DAW-45 (product name) manufactured by Denka Co., Ltd. (average sphericalness: 0.92, average particle diameter: 43 μm, specific surface area: 0). Using .2 m ² / g), coated alumina particles a were produced in the same manner as in Example 1 except that the firing temperature in the first step was changed to 1650 ° C. and the firing time was changed to 30 hours. The same measurements as in Example 1 were performed and the results are shown in Table 1. The coated alumina particles a did not correspond to the coated alumina particles according to the present embodiment.
The formulation shown in Table 1 (volume%) was the same as in Example 1 except that DAW-05 manufactured by Denka Co., Ltd. was used as the fine powder alumina 2 and coated alumina particles a were used as the coarse powder alumina 3. ), Alumina powder was obtained. In addition, the same measurements as in Example 1 were performed, and the results are shown in Table 1.

This application is based on a Japanese patent application filed on May 30, 2019 (Japanese Patent Application No. 2019-101604), the contents of which are incorporated herein by reference.

According to the coated alumina powder of the present invention, it is possible to suppress an increase in viscosity when filling the resin, and it is possible to realize high thermal conductivity of the resin composition containing the resin. Therefore, it is particularly useful for applications of heat-dissipating parts such as heat-dissipating sheets, heat-dissipating greases, heat-dissipating spacers, semiconductor encapsulants, and heat-dissipating paints (heat-dissipating coating agents).

Claims (11)

1. An alumina powder containing alumina particles and a coating layer covering the alumina particles, and having a projected area circle equivalent diameter of 1 μm or more and 300 μm or less by microscopy.
   The coating layer contains aluminum nitride and contains
   The average sphericity of the coated alumina particles is 0.85 or more and 0.97 or less.
   Alumina powder.
2. The alumina powder according to claim 1, wherein the alumina powder has a plurality of peaks in a particle size range of 2 μm or more and 200 μm or less in a volume-based frequency particle size distribution by a laser diffraction / scattering method.
3. The alumina powder according to claim 1 or 2, wherein the proportion of the coated alumina particles having a sphericity of 0.80 or less is 15% or less based on the number of the coated alumina particles.
4. The alumina powder according to any one of claims 1 to 3, wherein the average particle size of the coated alumina particles is 30 μm or more and 150 μm or less, which is measured by a laser diffraction / scattering type particle size distribution measuring machine.
5. The alumina powder according to any one of claims 1 to 4, wherein the content of aluminum nitride in the coated alumina particles is 10% by mass or more and 40% by mass or less.
6. The alumina powder according to any one of claims 1 to 5, wherein the total content of alumina and aluminum nitride in the alumina powder is 80% by mass or more.
7. The alumina powder according to any one of claims 1 to 6, wherein the amount of carbon in the coated alumina particles is 0.3% by mass or less.
8. A resin composition containing a resin and the alumina powder according to any one of claims 1 to 7.
9. The resin composition according to claim 8, wherein the resin contains at least one selected from the group consisting of silicone resin, epoxy resin, urethane resin, and acrylic resin.
10. A heat-dissipating component containing the alumina powder according to any one of claims 1 to 7 or the resin composition according to claim 8 or 9.
11. The method for producing coated alumina particles according to claim 1.
    The first step of obtaining a first calcined powder by calcining a mixture containing the raw material alumina powder and carbon powder at a temperature of 1500 ° C. or higher and 1700 ° C. or lower in a reducing atmosphere containing nitrogen gas.
    The first step of calcining the first calcined powder in an air atmosphere at a temperature of 600 ° C. or higher and 900 ° C. or lower to obtain the coated alumina particles is included.
    The average particle size of the carbon powder is 30 nm or more and 70 nm or less, the bulk density is 0.10 g / cm ³ or more and 0.20 g / cm ³ or less, and the specific surface area is 20 m ² / g or more and 60 m ² / g or less. ,Production method.

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