Alumina particles and resin composition using same

Abstract

The alumina particles have a particle diameter D50 of more than 200 [mu] m at a cumulative particle size distribution of 50% by number from the particle side, a roundness of 0.90 or more, and an alpha rate of 90.0% or more.

Description

Technical Field

[0001] The present disclosure relates to alumina particles and a resin composition using the same. Background Art

[0002] The heat generated by energizing an electronic component is dissipated through a heat sink. A technique is known in which a heat dissipation material is filled between the electronic component and the heat sink in order to improve the heat dissipation efficiency.

[0003] As one of the heat dissipation members, a resin composition containing a resin and inorganic particles is known, and alumina particles can be used as the inorganic particles (for example, Patent Documents 1 to 3).

[0004] In Patent Document 1, as alumina particles capable of improving the fluidity when highly filled in a resin, alumina particles having an α-phase content of 40% or less, an average circularity of 0.95 or more, and an average particle diameter of 100 μm or less are disclosed. As a method for producing the alumina particles, a method is disclosed in which a pulverized product of fused alumina is melted by a flame melting method and quenched by spraying water into the furnace.

[0005] In Patent Document 2, as alumina particles capable of improving the viscosity and fluidity of a composition when incorporated into a resin or the like, alumina particles having an average sphericity of 0.93 or more and an α-rate of alumina of 95% or more are disclosed. As a method for producing the alumina particles, the following method is disclosed: using metal aluminum powder, alumina powder, or a mixture of both as a raw material, melting it by a flame melting method, cooling and solidifying it, and then performing a reheating treatment.

[0006] Patent Document 3 discloses the following method: pulverizing fused alumina using a jet mill and removing the edges of the fused alumina particles, thereby obtaining round-shaped fused alumina particles having an average particle diameter of 5 to 4000 μm.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: International Publication No. 2009 / 133904

[0010] Patent Document 2: International Publication No. 2008 / 053536

[0011] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2006-169090 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] In recent years, the increase in the heat generation in ICs due to the high integration of ICs in electronic devices, and the increase in the heat generation in electronic components caused by the use of high-current-driven electronic components in the electrification of electric vehicles, aircraft, etc. have become problems. In order to achieve more effective heat dissipation, it is required to further increase the thermal diffusivity of the resin composition. In order to achieve more effective heat dissipation, it is also required to minimize the interface between the resin and the filler (aluminum oxide particles) used in the resin composition as much as possible, that is, to increase the particle size of the aluminum oxide particles.

[0014] However, regarding the aluminum oxide particles disclosed in Patent Documents 1 and 2, there is no research on further increasing the thermal diffusivity of the resin composition.

[0015] In the case where the aluminum oxide particles of Patent Document 3 are mixed with a resin to form a resin composition, the thermal diffusivity is not sufficient.

[0016] In view of such a situation, an object of one embodiment of the present invention is to provide aluminum oxide particles that are used as a filler for a resin composition and can increase the thermal diffusivity of the resin composition compared to the prior art. In addition, another object of the present invention is to provide a resin composition using such aluminum oxide particles.

[0017] Means for Solving the Problem

[0018] Mode 1 of the present invention is aluminum oxide particles, wherein the particle size D50 of the cumulative particle size distribution at 50% cumulative from the fine particle side is greater than 200 μm, the roundness is 0.90 or more, and the α conversion rate is 90.0% or more.

[0019] Mode 2 of the present invention is the aluminum oxide particles according to Mode 1, and the angle of repose is less than 32°.

[0020] Mode 3 of the present invention is the aluminum oxide particles according to Mode 1 or 2, and the apparent density is 3.75 g / cm 3 to 3 3.96 g / cm or less.

[0021] Mode 4 of the present invention is the aluminum oxide particles according to any one of Modes 1 to 3, and the tapped density is 1.70 g / cm 3 or more.

[0022] Mode 5 of the present invention is the aluminum oxide particles according to any one of Modes 1 to 4, and the difference between the particle size D90 of the cumulative particle size distribution at 90% cumulative from the fine particle side and the particle size D10 of the cumulative particle size distribution at 10% cumulative from the fine particle side is less than 124 μm.

[0023] Embodiment 6 of the present invention is the alumina particles as described in any one of Embodiments 1 to 5, which contain first alumina particles, and the value of "Threshold", which is the brightness parameter when binarizing the stereomicroscope image using image analysis software (ImageJ), of the first alumina particles is 100 or more and less than 200.

[0024] Embodiment 7 of the present invention is the alumina particles as described in Embodiment 6, wherein the average value of the Feret's diameter of the aforementioned first alumina particles is greater than 180 μm.

[0025] Embodiment 8 of the present invention is the alumina particles as described in Embodiment 6 or 7, wherein the ratio of the average value of the minimum Feret's diameter of the aforementioned first alumina particles to the average value of the Feret's diameter is 0.70 or more.

[0026] Embodiment 9 of the present invention is the alumina particles as described in any one of Embodiments 6 to 8, wherein the average value of the fracture strength of the aforementioned first alumina particles in the particle compression test is greater than 25.9 MPa.

[0027] Embodiment 10 of the present invention is the alumina particles as described in any one of Embodiments 1 to 9, which contain second alumina particles, and the value of "Threshold", which is the brightness parameter when binarizing the stereomicroscope image using image analysis software (ImageJ), of the second alumina particles is 200 or more and 255 or less.

[0028] Embodiment 11 of the present invention is the alumina particles as described in Embodiment 10, wherein the average value of the Feret's diameter of the aforementioned second alumina particles is greater than 180 μm.

[0029] Embodiment 12 of the present invention is the alumina particles as described in Embodiment 10 or 11, wherein the ratio of the average value of the minimum Feret's diameter of the aforementioned second alumina particles to the average value of the Feret's diameter is 0.70 or more.

[0030] Embodiment 13 of the present invention is the alumina particles as described in any one of Embodiments 10 to 12, wherein the average value of the strain at fracture of the aforementioned second alumina particles in the particle compression test is less than 0.074.

[0031] Embodiment 14 of the present invention is a resin composition, which contains a resin and the alumina particles as described in any one of Embodiments 1 to 13.

[0032] Effects of the Invention

[0033] By using the alumina particles according to an embodiment of the present invention as a filler, a resin composition having a high thermal diffusivity can be obtained. Description of the Drawings

[0034] Figure 1 This is an example of a graph showing strain - strength (MPa) obtained from a compression test of particles in accordance with JIS R1639 - 5.

[0035] Figure 2 This is a conceptual diagram of an apparatus for measuring the thermal diffusivity of a single alumina particle. Detailed Description of the Invention

[0036] [Alumina Particles]

[0037] The alumina particles according to the embodiment of the present invention are used by being mixed with a resin as a filler for a resin composition. Regarding the alumina particles, the particle diameter D50 of the cumulative 50% in terms of the number from the fine particle side of the cumulative particle size distribution is greater than 200 μm, the roundness is 0.90 or more, and the α - conversion rate is 90.0% or more. By having these characteristics, the thermal diffusivity of the resin composition can be improved. Each characteristic will be described in detail below.

[0038] (Particle diameter D50 of the cumulative 50% in terms of the number from the fine particle side of the cumulative particle size distribution)

[0039] In the alumina particles according to the embodiment of the present invention, the particle diameter D50 of the cumulative 50% in terms of the number from the fine particle side of the cumulative particle size distribution (hereinafter, sometimes simply referred to as “D50”) is greater than 200 μm. When used as a filler for a resin composition, it is presumed that for the following reasons, a resin composition with a high thermal diffusivity can be obtained.

[0040] When the D50 of the alumina particles is large, the total surface area of the alumina particles per unit mass becomes smaller. Therefore, when manufacturing a resin composition by mixing alumina particles and a resin at a specified ratio, by using alumina particles with a large average particle size, the total area of the interfaces between the alumina particles and the resin can be made smaller. It is considered that the interfaces between the alumina particles and the resin scatter the propagating phonons, so by reducing the total area of the interfaces, the thermal diffusivity can be improved.

[0041] Regarding the alumina particles according to the embodiment of the present invention, by making D50 greater than 200 μm, the total area of the interfaces when mixed with the resin at a specified ratio can be made smaller compared to the case where D50 is 200 μm or less, and a resin composition with a high thermal diffusivity can be manufactured.

[0042] The D50 of the alumina particles is preferably 205 μm or more, more preferably 210 μm or more. There is no particular limitation on the upper limit. From the viewpoints of good kneadability with the resin and application as a filler for a resin composition, it is preferably 1000 μm or less, more preferably 800 μm or less, further preferably 600 μm or less, and particularly preferably 500 μm or less.​​

[0043] Regarding the D50 of alumina particles, based on the principle of dynamic image analysis in accordance with ISO 13322-2, the particle size distribution of alumina particles is measured. Using the cumulative particle size distribution obtained from the measurement results, the particle diameter (D50) at which the cumulative number from the fine particle side reaches 50% is obtained. As the measuring device, for example, CAMSIZER (manufactured by VERDER Scientific) is used. The sample is sequentially introduced into the device, and while dispersing the agglomerated particles with dry air, the particles passing in front of the camera are measured.

[0044] (Roundness)

[0045] By making the roundness of the alumina particles 0.90 or more, good kneadability with the resin can be achieved, the fluidity of the kneaded composite can be improved, and furthermore, the wear of other components caused by the alumina particles can be reduced. In addition, it is suitable as a filler for resin compositions for electronic components. The roundness is preferably greater than 0.91.

[0046] In addition, since alumina particles are usually hard particles, it is difficult to obtain alumina particles with a roundness of 0.90 or more by simply colliding alumina particles with low roundness with each other or crushing alumina particles with low roundness. Furthermore, if such collisions and crushing are carried out for a long time, a large amount of fine powder may be generated. In addition, the newly generated hydrophilic surface due to crushing may reduce the mixing property with the resin.

[0047] In addition, the inventors of the present application found that in order to make the D50 greater than 200 μm and the α conversion rate 90.0% or more while making the roundness 0.90 or more, for example, in the case of the flame melting method described in Patent Documents 1 and 2, the energy (heat) may be insufficient. Therefore, the inventors of the present application found that by adopting a high-frequency thermal plasma method with higher energy than the flame melting method, it is possible to make the D50 of the alumina particles greater than 200 μm and the α conversion rate 90.0% or more while making the roundness 0.90 or more.

[0048] The roundness (SPHT) is analyzed in accordance with ISO 9276-6. It is obtained according to SPHT = 4πA / P 2 wherein A is the measured value of the area of the projected particle image, and P is the measured value of the outer perimeter of the particle projected image.

[0049] The roundness of the alumina particles is measured by a measuring device (for example, CAMSIZER X2 (manufactured by VERDER Scientific)) based on the principle of dynamic image analysis in accordance with ISO 13322-2.

[0050] (α conversion rate)

[0051] α-aluminum oxide has high thermal conductivity. Therefore, by increasing the content of α-aluminum oxide in the alumina particles, the thermal conductivity of the alumina particles can be increased. For the alumina particles according to the embodiment of the present invention, the α-conversion rate, which is an index of the content of α-aluminum oxide, is as high as 90.0% or more. Therefore, alumina particles with high thermal conductivity can be obtained.

[0052] The α-conversion rate of the alumina particles is preferably 92.0% or more, more preferably 95.0% or more, and most preferably 100.0%.

[0053] In this specification, the so-called "α-conversion rate" refers to the content ratio (volume %) of α-aluminum oxide with respect to all the alumina contained in the alumina particles.

[0054] Regarding the α-conversion rate, the alumina particles are measured by powder X-ray diffraction method, and based on the obtained diffraction spectrum, the peak height (I 25.6 ) of the α-phase (012) plane that appears at the position of 2θ = 25.6°, and the peak height (I 46 ) that appears at the position of 2θ = 46° and is caused by the γ-phase, η-phase, χ-phase, κ-phase, θ-phase, and δ-phase are calculated by the following formula (1).

[0055] α-conversion rate = I 25.6 / (I 25.6 +I 46 )×100(%) (1)

[0056] It should be noted that for the alumina particles according to the embodiment of the present invention, although the α-conversion rate is most preferably 100%, it may also contain, for example, 10.0% or less of alumina other than α-aluminum oxide (δ-aluminum oxide, θ-aluminum oxide, etc.), which does not hinder the object of the present invention.

[0057] In addition, the alumina other than α-aluminum oxide can be contained in any manner. For example, α-aluminum oxide and alumina other than α-aluminum oxide can be contained simultaneously inside one alumina particle. In addition, it can be that: some alumina particles contain only α-aluminum oxide, and other alumina particles contain only alumina other than α-aluminum oxide, and these alumina particles are mixed and present.

[0058] (Angle of repose)

[0059] The angle of repose of the alumina particles is preferably less than 32°. Thereby, the fluidity of the alumina particles is improved, and they are easily kneaded with the resin, and a resin composition with a high thermal diffusivity can be easily obtained. The angle of repose is more preferably 30° or less. On the other hand, by making the angle of repose a specified value or more, for example, scattering of the alumina particles can be suppressed, the operability can be improved, and it can also contribute to the improvement of the thermal diffusivity of the resin composition. The angle of repose is preferably greater than 14°, and more preferably 18° or more.

[0060] The angle of repose of the alumina particles can be adjusted by known methods. For example, the angle of repose can be adjusted by adjusting the specific surface area, particle size distribution, and / or roundness of the alumina particles.

[0061] The angle of repose of the alumina particles is measured in accordance with the description of JIS R 9301-2-2:1999. As the ambient atmosphere during the measurement of the angle of repose, the temperature is set to 23°C and the humidity is 40%.

[0062] (Apparent density)

[0063] The apparent density of the alumina particles is preferably 3.75 g / cm 3 or more, whereby alumina particles with a small amount of internal voids, that is, alumina particles with high thermal conductivity, can be obtained. On the other hand, by not making the apparent density of the alumina particles too high, they are not easily settled during mixing with the resin and are easily dispersed. Therefore, the apparent density of the alumina particles is preferably 3.96 g / cm 3 or less, and more preferably 3.95 g / cm 3 or less.

[0064] The apparent density of the alumina particles is measured by the pycnometer method in accordance with JIS R 1620:1995. The number of measurements is set to 5 times or more. For example, AccuPyc 1330 (manufactured by Micromeritics) can be used during the measurement.

[0065] (Tap density)

[0066] A high tap density of the alumina particles means that the alumina particles can be tightly packed. When using alumina particles with a high tap density to form a resin composition, it can be expected that more alumina particles can be kneaded, and the fluidity of the kneaded composite can be improved. In addition, when the tap density is high, the alumina particles are not easily scattered and are easy to operate.

[0067] The tap density of the alumina particles is preferably 1.70 g / cm 3 or more, and more preferably 1.80 g / cm 3 or more, further preferably greater than 2.24 g / cm 3 and even more preferably 2.33 g / cm 3 or more.

[0068] The tapped density of the alumina particles was measured in accordance with the description in JIS Z 2512:2012. The sample amount during the tapped density measurement was set to 20 mL.

[0069] (Particle size distribution: D90 - D10)

[0070] The particle size distribution of the alumina particles is preferably sharp. The more sharp the particle size distribution of the alumina particles, the higher the capture rate (recovery rate) of the particles after melt - manufacturing the alumina particles can be improved, and the productivity becomes good. In addition, alumina particles with a sharp particle size distribution are easily used as fillers for resin compositions, and the selectivity and freedom when mixing with other particles increase, so they are preferred. For example, the difference between the particle diameter D90 at the 90% cumulative number from the fine particle side and the particle diameter D10 at the 10% cumulative number from the fine particle side of the cumulative particle size distribution is preferably less than 124 μm, more preferably less than 108 μm, and further preferably 100 μm or less. On the other hand, when the particle size distribution of the alumina particles is relatively wide to a certain extent, small particles enter the gaps between large particles, etc., thereby improving the filling property, enabling more alumina particles to be kneaded with the resin, and contributing to an increase in the thermal diffusivity of the resin composition. Therefore, the difference between D90 and D10 is preferably greater than 45 μm, more preferably 50 μm or more.

[0071] (Particle size distribution: D90 / D50)

[0072] If the large - particle - size side of the particle size distribution of the alumina particles is sharp, the capture rate (recovery rate) of the particles after melt - manufacturing the alumina particles can be further improved, and the productivity becomes good. In addition, when filling the alumina particles into the resin, segregation of the particles in the resin can be suppressed, enabling them to be uniformly present in the resin, and contributing to an increase in the thermal diffusivity of the resin composition. Therefore, for example, D90 / D50 is preferably less than 1.28, more preferably less than 1.21. The lower limit value of D90 / D50 is not particularly limited, and from the viewpoint of manufacturing stability, it is preferably greater than 1.15.

[0073] The D10 and D90 of the alumina particles can be measured by the same method and apparatus as the above - mentioned D50 measurement. Based on the dynamic image analysis principle in accordance with ISO 13322 - 2, the particle size distribution of the alumina particles is measured, and using the cumulative particle size distribution obtained from the measurement results, the particle diameter (D10) at the 10% cumulative number from the fine particle side and the particle diameter (D90) at the 90% cumulative number are obtained. As the measuring apparatus, for example, CAMSIZER (manufactured by VERDER Scientific) is used. The sample is sequentially introduced into the apparatus, and the particles passing in front of the camera are measured while dispersing the agglomerated particles with dry air.

[0074] (Ratio of the total length L2 of the boundary lines inside the particles to the length L1 of the outer edge of the alumina particles)

[0075] The fewer the grain boundaries and voids inside the alumina particles, the more it helps to improve the thermal diffusivity of the alumina particles. Therefore, as an index of the grain boundary content inside the alumina particles, the ratio (L2 / L1) of the total length L2 of the boundary lines to the length L1 of the outer edge is introduced. L1 and L2 are obtained from the cross-sectional observation of the alumina particles.

[0076] When the length of the outer edge of one alumina particle is set as L1 and the total length of the boundary lines that the alumina particle has is set as L2, the alumina particles with a small value of L2 / L1 can be said to be alumina particles with a small content of boundary lines. In particular, (L2 / L1) (%) is preferably less than 112.8%, more preferably 100.0% or less. On the other hand, the value of L2 / L1 is preferably greater than 0%, more preferably greater than 18.3%, and further preferably 20.0% or more. Thereby, the kneadability with the resin can be improved, and when used as a filler for the resin composition, it is easy to improve the thermal diffusivity.

[0077] It should be noted that the "total length L2 of the boundary lines" is the sum of the boundary lines included inside the alumina particles and does not include the outer edge of the alumina particles. The total length L2 of the boundary lines is obtained by adding the total length L3 of the grain boundaries inside the alumina particles and the total length L4 of the inner walls of the voids (when there are voids inside the alumina particles) (that is, L2 = L3 + L4).

[0078] The alumina particles with a large value of L4 / L1 are less likely to settle and are easily dispersed when mixed with the resin, so they are preferred. In particular, the value of L4 / L1 is preferably greater than 16.6%, more preferably 20.0% or more. The upper limit value of L4 / L1 is not particularly limited, and for example, it can be 100.0% or less.

[0079] [Preferred Embodiment 1]

[0080] Hereinafter, preferred embodiments of the present invention will be described. The alumina particles involved in the preferred embodiments of the present invention include the following alumina particles (hereinafter, also referred to as "first alumina particles"), and the value of the "threshold", which is the brightness parameter when binarizing the stereomicroscope image using image analysis software (ImageJ), is 100 or more and less than 200. A stereomicroscope (SZ-X7 manufactured by OLYMPUS) is set in an environment with an illuminance of 270 lx. An objective lens (DF PLAPΟ1X manufactured by OLYMPUS), an LED light source (LCD-21 manufactured by Hayashi Repic), a camera (DP-22 manufactured by OLYMPUS), and a control box (DP2-SAL manufactured by OLYMPUS) are connected to the stereomicroscope. The scale of the LED light source is set to 5, and using the control box, the shooting conditions are set to exposure compensation -3, AE mode: automatic (Auto), white balance: automatic for shooting, thereby obtaining the aforementioned stereomicroscope image.

[0081] By including the first alumina particles, the thermal diffusivity of the particles themselves can be further improved. One of the reasons can be considered as follows. The first alumina particles having the above "threshold" value can be observed as semi-transparent particles in the stereomicroscope image, the content of the boundary lines of light scattering can be small, and the particles can be those with a small L1 / L2. Therefore, it is considered that the first alumina particles can improve the thermal diffusivity of the particles themselves due to the small L1 / L2, etc.

[0082] The average value of the Feret diameter of the first alumina particles is preferably greater than 180 μm. Thereby, the total area of the interface when mixed with the resin at a specified ratio can be made smaller, and a resin composition with a high thermal diffusivity can be manufactured.

[0083] The average value of the Feret diameter of the first alumina particles is more preferably 190 μm or more, and further preferably 200 μm or more. There is no particular limitation on the upper limit. From the viewpoints of good kneadability with the resin and application as a filler for resin compositions, it is preferably 950 μm or less, more preferably 750 μm or less, further preferably 550 μm or less, and particularly preferably 450 μm or less. It should be noted that in this specification, the so-called "Feret diameter" refers to the tangent diameter of the particle in the horizontal direction in the stereomicroscope image of the particle. Regarding the "average value of the Feret diameter of the first alumina particles", any 50 or more first alumina particles are selected from the stereomicroscope images taken under the above conditions, the Feret diameter of each first alumina particle is obtained, and it is used as the arithmetic average.

[0084] The ratio of the average value of the minimum Feret diameter of the first alumina particles to the average value of the Feret diameter is preferably 0.70 or more. Thereby, the total area of the interface when mixed with the resin at a specified ratio can be made smaller, and a resin composition with high thermal diffusivity can be produced. The ratio of the average value of the minimum Feret diameter of the first alumina particles to the average value of the Feret diameter is more preferably 0.75 or more, and further preferably 0.80 or more. The upper limit is not particularly limited, and from the viewpoints of good kneadability with the resin and application as a filler for resin compositions, it is preferably 1.00 or less, and more preferably 0.95 or less. Note that the "minimum Feret diameter" is the shortest distance among the distances between any two points on the outer periphery of the particle in the stereomicroscope image of the particle. Regarding the "average value of the minimum Feret diameter of the first alumina particles", from the stereomicroscope images taken under the aforementioned conditions, the same first alumina particles as those for obtaining the "average value of the Feret diameter of the first alumina particles" are selected, and the minimum Feret diameter of each first alumina particle is obtained, and used as its arithmetic mean.

[0085] Regarding the first alumina particles, it is preferable that the average value of the breaking strength in the compression test of the particles is greater than 25.9 MPa. Thereby, the particles are not easily broken, and as a result, a resin composition having a high thermal diffusivity is obtained. The breaking strength is more preferably 50.0 MPa or more, further preferably 75.0 MPa or more, and further more preferably 100.0 MPa or more. The upper limit of the breaking strength is not particularly limited, and from the viewpoint of productivity, it may be 500 MPa or less, and may be 300 MPa or less.

[0086] The breaking strength of the first alumina particles is measured in the following manner.

[0087] First, a compression test of the particles is carried out in accordance with JIS R1639-5 to obtain a displacement - test force curve graph. Based on the following formula (2), the displacement in this curve graph is converted into strain, and based on the following formula (3), the test force in this curve graph is converted into strength, to obtain Figure 1 a curve graph of strain - strength (MPa) as shown.

[0088] Strain = displacement [μm] / D [μm] ··· (2)

[0089] Strength [MPa] = 2.48 × test force [N] / (π × D 2 ) ··· (3)

[0090] wherein D [μm] is the average value of the major axis and the minor axis of the particles to be tested. Note that the major axis and the minor axis can be measured by observing with a stereomicroscope.

[0091] For any five or more first alumina particles, determine the strength at the breaking point P1 of the curve graph, i.e., the breaking strength s1 (MPa), and take their arithmetic mean as the average value of the breaking strength of the first alumina particles.

[0092] For any five or more of the above-mentioned first alumina particles, the coefficient of variation CV of the breaking strength (i.e., the ratio of the standard deviation to the arithmetic mean) is preferably 50% or less. As a result, the strength deviation becomes smaller, and a resin composition having a high thermal diffusivity is obtained. More preferably, it is 40% or less. There is no particular limitation on the lower limit of the coefficient of variation, and from the viewpoint of productivity, it can be 1% or more, and can be 5% or more.

[0093] The average value of the strain at the breakage of the first alumina particles in the compression test of the particles is not particularly limited. For example, it can be greater than 0.050, can be greater than 0.060, and can be 0.074 or more. There is no particular limitation on the upper limit of the strain, and from the viewpoint of productivity, it can be 0.200 or less.

[0094] The strain at the breakage of the first alumina particles is measured as follows.

[0095] First, conduct a compression test on the particles in accordance with JIS R1639-5 to obtain Figure 1 a curve graph of strain - strength (MPa) as shown.

[0096] Figure 1 In the case where there is a region with a constant slope, set the strain greater than 0 and having the smallest constant slope as the breaking point P1. It should be noted that in the case where there are multiple regions with a constant slope, set the starting point of the region where the difference in strain between the end point and the starting point of the aforementioned region is the largest as the breaking point P1. Take the strain d1 at the breaking point P1 as the strain at the breakage of the first alumina particles.

[0097] For any five or more first alumina particles, determine the strain at the breakage based on the curve graph, and take their arithmetic mean as the average value of the strain at the breakage of the first alumina particles.

[0098] For any five or more of the above-mentioned first alumina particles, the coefficient of variation CV of the strain at the breakage (i.e., the ratio of the standard deviation to the arithmetic mean) is not particularly limited, and can be 50% or less, and can be 40% or less. There is no particular limitation on the lower limit of the coefficient of variation, and from the viewpoint of productivity, it can be 1% or more, and can be 5% or more.

[0099] Regarding the first alumina particles, the coefficient of variation CV (i.e., the ratio of the standard deviation to the arithmetic mean) of the area of the first alumina particles in the stereomicroscope image is preferably 70% or less. Thereby, the fluidity of the alumina particles is improved, and they are easily kneaded with the resin. As a result, a resin composition having a high thermal diffusivity is obtained. The lower limit of this coefficient of variation is not particularly limited, and from the viewpoint of productivity, it can be greater than 45%, can be greater than 50%, and can be 51.5% or more. It should be noted that for the "average value of the area of the first alumina particles", any 50 or more first alumina particles are selected from the stereomicroscope images taken under the above conditions, the area of each first alumina particle is obtained, and the arithmetic mean thereof is taken as the "standard deviation of the area of the first alumina particles".

[0100] Regarding the first alumina particles, the thermal diffusivity of the particles can be made greater than 3.83×10 -6 m 2 / s. Thereby, it is easy to obtain a resin composition having a high thermal diffusivity. This thermal diffusivity is preferably 5.00×10 -6 m 2 / s or more, more preferably 1.00×10 -5 m 2 / s or more. The upper limit of this thermal diffusivity is not particularly limited, and from the viewpoint of productivity, it can be 1.00×10 - 3 m 2 / s or less, and can be 1.00×10 -4 m 2 / s or less. It should be noted that the thermal diffusivity of the first alumina particles can be measured by applying the temperature wave thermal analysis method (TWA method) to microscale measurement.

[0101] [Preferred Embodiment 2]

[0102] Hereinafter, another preferred embodiment of the present invention will be described. The alumina particles involved in another preferred embodiment of the present invention include the following alumina particles (hereinafter, also referred to as "second alumina particles"), and the value of the "threshold", which is the brightness parameter when binarizing the stereomicroscope image using image analysis software (ImageJ), is 200 or more and 255 or less. A stereomicroscope (OLYMPUS SZ-X7) is set in an environment with an illuminance of 270 lx. An objective lens (OLYMPUS DF PLAPΟ1X), an LED light source (Hayashi Repic LCD-21), a camera (OLYMPUS DP-22), and a control box (OLYMPUS DP2-SAL) are connected to the stereomicroscope. The scale of the LED light source is set to 5, and using the control box, the shooting conditions are set to exposure compensation -3, AE mode: automatic, white balance: automatic, and shooting is performed to obtain the aforementioned stereomicroscope image.

[0103] By including the second alumina particles, the kneadability with the resin can be improved, and when used as a filler for a resin composition, the thermal diffusivity can be easily increased. One of the reasons can be considered as follows. The second alumina particles having the above "threshold" value can be observed as white particles in the stereomicroscope image, and have a large content of the boundary lines that can scatter light, and can be particles with a large L1 / L2. Therefore, it is considered that the second alumina particles can improve the kneadability with the resin due to a large L1 / L2, etc.

[0104] The average value of the Feret diameter of the second alumina particles is preferably greater than 180 μm. By including such second alumina particles, the total interfacial area when mixed with the resin at a specified ratio can be made smaller, and a resin composition with a high thermal diffusivity can be manufactured.

[0105] The average value of the Feret diameter of the second alumina particles is more preferably 190 μm or more, and further preferably 200 μm or more. There is no particular limitation on the upper limit. From the viewpoints of good kneadability with the resin and application as a filler for a resin composition, it is preferably 950 μm or less, more preferably 750 μm or less, further preferably 550 μm or less, and particularly preferably 450 μm or less. It should be noted that for the "average value of the Feret diameter of the second alumina particles", any 50 or more second alumina particles are selected from the stereomicroscope images taken under the aforementioned conditions, the Feret diameter of each second alumina particle is determined, and the arithmetic average thereof is calculated.

[0106] The ratio of the average value of the minimum Feret diameter of the second alumina particles to the average value of the Feret diameter is preferably 0.70 or more. Thereby, the total area of the interface when mixed with the resin at a specified ratio can be made smaller, and a resin composition with a high thermal diffusivity can be produced. The ratio of the average value of the minimum Feret diameter of the second particles to the average value of the maximum Feret diameter is more preferably 0.75 or more, further preferably 0.80 or more, and still further preferably 0.85 or more. The upper limit is not particularly limited, and from the viewpoints of good kneadability with the resin and application as a filler for resin compositions, it is preferably 1.00 or less, and more preferably 0.95 or less. It should be noted that for the "average value of the minimum Feret diameter of the second alumina particles", the second alumina particles identical to those for obtaining the "average value of the Feret diameter of the second alumina particles" are selected from the stereomicroscope images taken under the above conditions, and the minimum Feret diameter of each second alumina particle is obtained, and the arithmetic average thereof is taken.

[0107] The average value of the strain at break of the second alumina particles in the compression test of the particles is preferably less than 0.074. Thereby, the dispersion of the particle area can be made smaller, and as a result, it is easy to obtain a resin composition having a high thermal diffusivity. The average value of this strain is more preferably 0.060 or less, and further preferably 0.050 or less. The lower limit of the average value of this strain is not particularly limited, and from the viewpoint of productivity, it can be 0.005 or more, and can be 0.010 or more.

[0108] The average value of the strain at break of the second alumina particles is measured as follows.

[0109] For any five or more second alumina particles, a compression test of the particles is carried out in accordance with JIS R1639-5 to obtain Figure 1 a stress-strain (MPa) curve graph as shown. The strain at break d1 is obtained from each curve graph, and the arithmetic average thereof is taken as the average value of the strain at break of the second alumina particles.

[0110] For any five or more of the above second alumina particles, the coefficient of variation CV of the strain at break (i.e., the ratio of the standard deviation to the arithmetic average) is not particularly limited, and can be 50% or less, and can be 40% or less. The lower limit of this coefficient of variation is not particularly limited, and from the viewpoint of productivity, it can be 1% or more, and can be 5% or more.

[0111] There is no particular limitation on the average value of the fracture strength of the second alumina particles in the particle compression test. For example, it can be less than 100.0 MPa, less than 75.0 MPa, less than 50.0 MPa, or 25.9 MPa or less. There is no particular limitation on the lower limit of the average value of the fracture strength. From the viewpoint of productivity, it can be 5.0 MPa or more, or 10.0 MPa or more.

[0112] The average value of the fracture strength of the second alumina particles is measured as follows.

[0113] For any five or more second alumina particles, a particle compression test is carried out in accordance with JIS R 1639-5 to obtain Figure 1 a stress-strain (MPa) curve graph as shown. The fracture strength s1 (MPa) is obtained from each curve graph, and their arithmetic mean is taken as the average value of the fracture strength of the second alumina particles.

[0114] For any five or more of the above-mentioned second alumina particles, the coefficient of variation CV of the fracture strength (i.e., the ratio of the standard deviation to the arithmetic mean) is preferably 50% or less. As a result, the strength deviation becomes smaller, and a resin composition having a high thermal diffusivity is obtained. More preferably, it is 40% or less. There is no particular limitation on the lower limit of the coefficient of variation. From the viewpoint of productivity, it can be 1% or more, or 5% or more.

[0115] The thermal diffusivity of the second alumina particles is preferably greater than 1.05×10 -6 m 2 / s. Thus, it is easy to obtain a resin composition having a high thermal diffusivity. There is no particular limitation on the upper limit of the thermal diffusivity. From the viewpoint of productivity, it can be less than 1.00×10 -5 m 2 / s, less than 5.00×10 -6 m 2 / s, or 3.83×10 -6 m 2 / s or less. It should be noted that the thermal diffusivity of the second alumina particles can be measured by applying the temperature wave thermal analysis method (TWA method) to microscale measurement.

[0116] Regarding the second alumina particles, it is possible to reduce the dispersion of the particle area. Specifically, the coefficient of variation CV (i.e., the ratio of the standard deviation to the arithmetic mean) of the area of the second alumina particles in the stereomicroscope image can be made less than 51.5%. As a result, the fluidity of the alumina particles is improved, and they are easily kneaded with the resin. Consequently, a resin composition having a high thermal diffusivity is obtained. More preferably, it is 50% or less, and further preferably 45% or less. The lower limit of this coefficient of variation is not particularly limited, and from the viewpoint of productivity, it can be 5% or more, and can be 10% or more. It should be noted that regarding the "average value of the area of the second alumina particles", any 50 or more second alumina particles are selected from the stereomicroscope images taken under the aforementioned conditions, the area of each second alumina particle is determined, and the arithmetic mean thereof is taken as the "standard deviation of the area of the second alumina particles".

[0117] As described above, the preferred embodiments 1 and 2 of the present invention have been described. A more preferred embodiment of the present invention simultaneously satisfies the preferred embodiments 1 and 2 of the present invention (i.e., the alumina particles simultaneously contain the first alumina particles and the second alumina particles). Thus, it is easy to obtain a resin composition having a higher thermal diffusivity. In the stereomicroscope image of the alumina particles, the area ratio of the first alumina particles to the total of the first alumina particles and the second alumina particles is preferably 1 area% or more and 99 area% or less, more preferably 50 area% or more and 99 area% or less, further preferably 60 area% or more and 95 area% or less, and even more preferably 70 area% or more and 90 area% or less. In the stereomicroscope image of the alumina particles, the area ratio of the second alumina particles to the total of the first alumina particles and the second alumina particles is preferably 1 area% or more and 99 area% or less, more preferably 1 area% or more and 50 area% or less, further preferably 5 area% or more and 40 area% or less, and even more preferably 10 area% or more and 30 area% or less.

[0118] [Method for manufacturing alumina particles]

[0119] The method for manufacturing alumina particles according to the embodiment of the present invention will be described.

[0120] In the raw material of the alumina particles, an alumina raw material particle containing single crystal α-alumina and having a particle size D50 of the cumulative 50% from the fine particle side in the cumulative particle size distribution greater than 200 μm is used. And by melting and spheroidizing the alumina raw material particles using the high-frequency thermal plasma method, alumina particles are manufactured. Thus, alumina particles having a D50 greater than 200 μm, a true circularity of 0.90 or more, and an α conversion rate of 90.0% or more are obtained.

[0121] Heretofore, a method of manufacturing alumina particles using granulated raw material particles has been known, but a large amount of grain boundaries and internal voids sometimes exist inside the obtained alumina particles. In an embodiment of the present invention, by using single crystal α-alumina itself that has not been granulated as the alumina raw material particles, alumina particles with few (or no) grain boundaries and internal voids and high density can be obtained. In order to effectively utilize the crystal structure characteristics of single crystal alumina even after using the raw material particles of single crystal alumina and spheroidizing them, the particle size of the alumina raw material particles used, the power required to generate plasma (plasma flame), the atmosphere, etc. can be appropriately controlled. It should be noted that as the high-frequency thermal plasma device, a known device can be used.

[0122] In order to manufacture alumina particles with a D50 of more than 200 μm, for example, the particle size of the alumina raw material particles, various conditions in the high-frequency thermal plasma method, etc. are appropriately controlled. Regarding the alumina raw material particles, it is preferable to use alumina raw material particles with a D50 of 210 μm or more, and more preferably to use alumina raw material particles with a D50 of 230 μm or more.

[0123] It should be noted that even if the D50 of the alumina raw material particles is, for example, 210 μm or more, as each alumina raw material particle, particles with a particle size smaller than 210 μm may be included. Therefore, the obtained alumina particles may contain polycrystalline α-alumina and / or alumina other than α-alumina. However, by making the D50 of the alumina raw material particles 210 μm or more, the content of polycrystalline α-alumina and / or alumina other than α-alumina can be more reliably suppressed to a small amount within the allowable range of the present invention.

[0124] The D50 of the alumina raw material particles can be measured using the same method as the measurement method of the D50 of the above-mentioned alumina particles.

[0125] When the alumina raw material particles are single crystal α-alumina, it can be confirmed by the SEM-EBSD method. It is judged whether it is α-alumina or alumina other than α-alumina by PhaseMAP, and then, by Image Quality (IQ) MAP, it can be judged whether it is single crystal or polycrystal based on the presence or absence of clear grain boundaries in the alumina particles.

[0126] That α-alumina is single crystal can also be confirmed by the Debye-Scherrer method.

[0127] As raw materials for alumina raw material particles, sapphire, single crystal α-alumina produced by melt growth methods such as the Czochralski method, Verneuil method, Kyropoulos method, Bridgman method, and EFG method, etc. can be used. By pulverizing these raw materials and screening them using a sieve with a desired mesh number, alumina raw material particles with a specified D50 can be prepared.

[0128] The alumina raw material particles may contain a small amount (e.g., 10.0 mass% or less) of alumina other than α-alumina (such as δ-alumina, θ-alumina, etc.). In addition, they may also contain a small amount (e.g., 10.0 mass% or less) of polycrystalline α-alumina together with single crystal α-alumina, which does not hinder the purpose of the present invention.

[0129] Thus, by adopting the high-energy high-frequency thermal plasma method, alumina particles with a D50 greater than 200 μm and having the aforementioned various physical properties that cannot be achieved by the flame melting method can be obtained. In addition, as such physical properties, in addition to the aforementioned various physical properties, properties such as the hardness and appearance of the particles may also be included. For example, by adopting the high-energy high-frequency thermal plasma method, the above-mentioned first alumina particles and / or second alumina particles can be obtained.

[0130] [Resin composition]

[0131] By using the alumina particles according to the embodiment of the present invention as a filler for the resin composition, a resin composition with a high thermal diffusivity can be obtained. The resin composition contains a resin and the alumina particles according to the embodiment of the present invention.

[0132] The alumina particles according to the embodiment of the present invention can improve the thermal diffusivity without impairing the flexibility inherent to the resin. Therefore, the mixing ratio thereof with respect to the resin composition (composite) is preferably in the ratio of 5 to 75 vol% of the resin and 95 to 25 vol% of the alumina particles.

[0133] A manufacturing method of the resin composition will be described.

[0134] Using a known method that is commonly used, the alumina particles of the present invention are mixed with a resin, whereby a resin composition can be obtained. For example, when the resin is in a liquid state (such as a liquid epoxy resin, etc.), after mixing the liquid resin, alumina particles, and a curing agent, it can be cured by heat or ultraviolet rays, etc., whereby a resin composition can be obtained. Known curing agents and methods can be used for the curing agent, mixing method, and curing method. On the other hand, when the resin is in a solid state (such as a polyolefin resin, acrylic resin, etc.), after mixing the alumina particles with the resin, it can be kneaded using a known method such as melt-kneading, whereby the target resin composition is obtained.

[0135] As the resin used in the resin composition, it can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. It should be noted that the resin can be used alone as 1 type, or 2 or more types can be used in combination.

[0136] Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymers, etc., polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyvinyl acetal, fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer (ABS) resin, polyphenylene ether copolymer (PPE) resin, modified PPE resin, aliphatic polyamides, aromatic polyamides, polyimides, polyamide-imides, polymethacrylic acids, polymethacrylate esters such as polymethyl methacrylate, polyacrylic acids, polycarbonates, polyphenylene sulfide, polysulfones, polyethersulfones, polyether nitriles, polyether ketones, polyketones, liquid crystal polymers, silicone resins, ionomers, etc.

[0137] Examples of thermoplastic elastomers include styrene-butadiene block copolymers or their hydrogenated products, styrene-isoprene block copolymers or their hydrogenated products, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, etc.

[0138] Examples of thermosetting resins include crosslinked rubbers, epoxy resins, phenolic resins, polyimide resins, unsaturated polyester resins, diallyl phthalate resins, etc. Specific examples of crosslinked rubbers include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, polyurethane rubber, and silicone rubber.

[0139] From the viewpoints of processability and properties, it is preferable to use polyolefin resins, acrylic resins, polyimide resins, polyamide resins, polyamideimide resins, epoxy resins, phenolic resins, and silicone resins.

[0140] In addition, in these resin compositions, if necessary, known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, anti-blocking agents, antistatic agents, leveling agents, and mold release agents can be appropriately blended singly or in combination of two or more within a range that does not impair the effects of the invention.

[0141] The alumina particles and the resin composition containing the alumina particles according to the present embodiment are particularly suitable for heat dissipation material applications. Therefore, in one aspect of the present disclosure, heat dissipating alumina particles and a heat dissipating resin composition can be provided.

[0142] Examples

[0143] (Manufacture of alumina particles)

[0144] As raw materials for the alumina particles, particles obtained from single crystal α-alumina and having a cumulative 50% particle size D50 (by number from the fine particle side) of the cumulative particle size distribution greater than 200 μm were prepared. Then, using a known high-frequency thermal plasma device, in an Ar-O2 atmosphere, the alumina raw material particles were melted and spheroidized by the high-frequency thermal plasma method to manufacture the alumina particles of Sample No. 1. In addition, as a comparative example, a sample obtained by melting and spheroidizing alumina raw material particles by the flame melting method was used as Sample No. 2, and the alumina raw material particles themselves were used as Sample No. 3.

[0145] In addition, as raw materials for the alumina particles, the following 5 types of particles were prepared: particles obtained from single crystal α-alumina, having a cumulative 50% particle size D50 (by number from the fine particle side) of the cumulative particle size distribution greater than 200 μm, and having a D50 greater than that of the raw material used in Sample No. 1. For each raw material, using a known high-frequency thermal plasma device, in an Ar-O2 atmosphere, the alumina raw material particles were melted and spheroidized by the high-frequency thermal plasma method to manufacture the alumina particles of Sample Nos. 4 to 8.

[0146] (1) Measurement of particle size D10, D50, D90 and roundness of alumina particles

[0147] The particle size distributions of the alumina particles of Sample Nos. 1 to 8 were measured, and the average value, particle size D10 (cumulative 10% by number), cumulative 50% particle size D50, and cumulative 90% particle size D90 of the alumina particles were determined.

[0148] The particle size distribution and roundness of the alumina particles were measured using the CAMSIZER X2 (manufactured by VERDER Scientific), a device based on the principle of dynamic image analysis in accordance with ISO 13322-2. The measurement was carried out in a dry state. The sample was sequentially introduced into the device, and while dispersing the agglomerated particles using dry air at 50 kPa, the particles passing in front of the camera were measured. The measured sample weighed 3 g and was measured once. The same measurement was repeated three times, and the particle size distribution and roundness were analyzed by cumulative averaging based on these results. The particle size was the equivalent circular diameter. The equivalent circular diameter refers to the diameter of a perfect circle having the same area as the projected particle image. In addition, the basis for the particle size was set as volume.

[0149] The roundness (SPHT) was analyzed in accordance with ISO 9276-6. Based on SPHT = 4πA / P 2 it was calculated. In the formula, A is the measured value of the area of the projected particle image, and P is the measured value of the outer perimeter of the particle projection image.

[0150] (2) Measurement of the α-phase conversion rate of alumina particles

[0151] The α-phase conversion rates of the alumina particles of sample numbers 1 to 8 were measured.

[0152] Regarding the α-phase conversion rate, the sample of the alumina particles was measured using a powder X-ray diffractometer (manufactured by Rigaku Denki Kogyo Co., Ltd.) to obtain a diffraction spectrum. The measurement conditions were as follows: X-ray source: CuKα, X-ray output power: 45 kV, 200 mA, scanning speed: 10 deg / min.

[0153] Based on the obtained diffraction spectrum, the peak height (I 25.6 ) of the α-phase (012) plane appearing at the position of 2θ = 25.6° and the peak height (I 46 ) formed due to the γ-phase, η-phase, χ-phase, κ-phase, θ-phase, and δ-phase appearing at the position of 2θ = 46° were obtained and calculated by the following formula (1).

[0154] α-phase conversion rate = I 25.6 / (I 25.6 + I 46 ) × 100 (%) (1)

[0155] (3) Measurement of the angle of repose of alumina particles

[0156] The angle of repose of the alumina particles of sample numbers 1 to 8 was measured in accordance with the description in JIS R 9301-2-2:1999. The ambient atmosphere during the measurement of the angle of repose was set to a temperature of 23°C and a humidity of 40%.

[0157] (4) Measurement of the apparent density of alumina particles

[0158] The apparent density of the alumina particles of Sample Nos. 1 to 8 was measured in accordance with JIS R 1620:1995. The measurement method and measurement conditions are as follows.

[0159] · Measurement method: Gas displacement method

[0160] · Drying of the sample: 200 °C, for 8 hours or more

[0161] · Apparatus used: AccuPyc 1330 (Micromeritics)

[0162] · Measurement conditions

[0163] Number of purge times: 10 times

[0164] Purge filling pressure: 15.0 psig

[0165] Number of measurement times: 5 times

[0166] Measurement filling pressure: 15.0 psig

[0167] Equilibrium pressure: 0.005 psig / minute

[0168] Measurement after setting the accuracy: Yes

[0169] Deviation allowable error: 0.05%

[0170] Sample unit size: 10 cm 3

[0171] (5) Measurement of the tapped density of the alumina particles

[0172] The tapped density of the alumina particles of Sample Nos. 1 to 8 was measured in accordance with the description in JIS Z 2512:2012. The sample amount during the tapped density measurement was set to 20 mL.

[0173] (6) Measurement of the total length L2 of the boundary lines inside the particles and the length L1 of the outer edge of the alumina particles

[0174] Cross-section observation samples were prepared using the alumina particles of Sample Nos. 1 to 8. In the preparation of the cross-section observation samples, the alumina particles were embedded in resin, and then the resin and the alumina particles were cut using a diamond cutter. Then, Pt was vapor-deposited on the cross-section as a protective film, a cross-section was prepared using Ar ion milling, fixed to the SEM sample stage using Cu double-sided tape, and SEM-EBSD measurement was performed without vapor deposition. The observation position was determined in such a way that two or more alumina particles completely entered the observation area (i.e., two or more alumina particles did not contact the observation area frame). The measurement was performed on α-alumina particles.

[0175] The following equipment is used for the pretreatment of the sample and EBSD measurement.

[0176] · Equipment used

[0177] Ion milling device: IM-4000 (manufactured by Hitachi, Ltd.)

[0178] Ion sputtering device: E-1030 (manufactured by Hitachi, Ltd.)

[0179] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by JEOL Ltd.)

[0180] Electron backscatter diffraction device: Digiview V (manufactured by TSL)

[0181] The conditions for EBSD measurement are as follows.

[0182] · Measurement area: 500.0 μm × 400.0 μm

[0183] · Acceleration voltage: 20.0 kV

[0184] · Magnification: ×500

[0185] · Vacuum degree: 30 Pa

[0186] In the obtained EBSD images, two or more alumina particles that do not contact the frame of the observation area are selected, and the average value of the length L1 of the outer edge of each alumina particle is calculated using the image processing software ImageJ (manufactured by the National Institute of Health). In addition, the total length L2 of the boundary lines is also calculated. The "total length L2 of the boundary lines" is the sum of the boundary lines contained inside the alumina particles and does not include the outer edge of the alumina particles. The total length L2 of the boundary lines is obtained by adding the total length L3 of the grain boundaries inside the alumina particles and (when there are voids inside the alumina particles) the total length L4 of the inner walls of the voids (i.e., L2 = L3 + L4).

[0187] Using L1, L2, and L4 obtained in the above manner, L2 / L1 and L4 / L1 are calculated.

[0188] (7) Stereomicroscopic observation of alumina particles (measurement of the Feret diameter and area of each particle)

[0189] For the alumina particles with sample number 1, a stereomicroscope (OLYMPUS SZ-X7) was set up in an environment with an illuminance of 270 lx. An objective lens (OLYMPUS DF PLAPΟ1X), an LED light source (Hayashi Repic LCD-21), a camera (OLYMPUS DP-22), and a control box (OLYMPUS DP2-SAL) were connected to the aforementioned stereomicroscope. The scale of the LED light source was set to 5, and using the control box, the shooting conditions were set to exposure compensation -3, AE mode: automatic, white balance: automatic, and a stereomicroscope image was taken. Particles with a "threshold" value (i.e., the brightness parameter when performing binarization processing on this stereomicroscope image using image analysis software (ImageJ)) of 100 or more and less than 200 (hereinafter, also referred to as "the first particles") and particles with a "threshold" value of 200 or more and less than 255 (hereinafter, also referred to as "the second particles") were selected. The first particles are translucent in the stereomicroscope image, and the second particles are white in the stereomicroscope image.

[0190] Based on the above stereomicroscope image, for any 50 or more first particles, the average Feret diameter, the average minimum Feret diameter, the average area, and their standard deviations were calculated. Similarly, for any 50 or more second particles, the average Feret diameter, the average minimum Feret diameter, the average area, and their standard deviations were calculated. In addition, the area ratio of the first particles to the total of the first particles and the second particles was calculated, and the result was 84 area% or less.

[0191] (8) Compression test of alumina particles (measurement of the average crushing strength and the average strain at break)

[0192] The compression tests of the first particles and the second particles were carried out in accordance with JISR1639-5 to obtain a displacement - test force curve graph. Based on the following formula (2), the displacement in this curve graph was converted into strain, and based on the following formula (3), the test force in this curve graph was converted into strength, obtaining a strain - strength curve graph.

[0193] Strain = displacement [m] / D [m] ··· (2)

[0194] Strength [MPa] = 2.48 × test force [N] / (π × D 2 ) ··· (3)

[0195] Among them, D [m] is the average of the major axis and the minor axis of the particles under test. It should be noted that the major axis and the minor axis were measured by observing with a stereomicroscope.

[0196] For any five first particles, the strength of the breaking point P1 of the curve graph is obtained as the breaking strength s1 (MPa), and their arithmetic mean is taken as the average breaking strength of the first particles, and its standard deviation is taken as the standard deviation of the breaking strength of the first particles. In addition, for any five first particles, the strain d1 at break is obtained from each curve graph, and their arithmetic mean is taken as the average strain at break of the first particles, and its standard deviation is taken as the standard deviation of the strain at break of the first particles. In addition, by performing the same operation, the average value of the breaking strength of the second particles and its standard deviation, and the average value of the strain at break of the second particles and its standard deviation are obtained.

[0197] (9) Measurement of the thermal diffusivity of alumina particles

[0198] Regarding the thermal diffusivities of the first particles and the second particles, the temperature wave thermal analysis method (TWA method) is applied to microscale measurement for determination. Specifically, in the conceptual diagram ( Figure 2 ) of the apparatus for measuring the thermal diffusivity of one alumina particle, a thermoelectromotive force type microsensor is pressed against the specimen 70 (one alumina particle). The frequency dependence of the phase difference caused by the propagation of the temperature wave generated by the AC energization heating of the resistance type microheater by the function generator is measured by a two-phase lock-in amplifier 80 to determine the thermal diffusivity. For the specimen 70, the diameter of particle 1 is about 180 μm and the thickness is about 100 μm, the diameter of particle 2 is about 170 μm and the thickness is about 100 μm, the measurement frequency is 1.6 kHz to 4.9 kHz, and the sensor size is 20 μm × 20 μm.

[0199] (10) Measurement of the thermal diffusivity of the resin composition (composite)

[0200] Epoxy resin (main agent: room temperature curing type embedded resin 53 type (manufactured by SANKEI Co., Ltd.) 010 - 8140, curing agent: room temperature curing type embedded resin 53 type (manufactured by SANKEI Co., Ltd.) 010 - 8143) and alumina particles (raw material 1, sample numbers 1 to 8) are mixed at a mixing ratio (volume ratio) of 50:50, and stirred and mixed using Awatori Rentaro (manufactured by Thinky Corporation) to obtain a composite of epoxy resin - filler (alumina particles).

[0201] A 1 cm × 10 cm frame is made on an aluminum plate, and a PET film coated with a release agent is pasted on the back of the aluminum plate. The stirred composite is injected, and a PET film coated with a release agent is pasted on top. Further, a metal roller is used to fuse the composite in the frame. Further, another aluminum plate is placed thereon, heated at 100 °C for 1 hour and allowed to stand to cure the composite. After curing is completed, it is left to cool. After the temperature of the aluminum plate drops to around room temperature, the two PET films are peeled off from both sides of the cured composite to obtain a sheet-like specimen for measuring the thermal diffusivity of the composite.

[0202] For the obtained sheet-like specimen, the thermal diffusivity is measured.

[0203] Regarding the thermal diffusivity, a measurement specimen piece with a length of 10 mm × width of 10 mm × thickness of 1 mm is made from the sheet-like specimen of the above resin composition, and the measurement is carried out at room temperature using the temperature wave thermal analysis method (TWA method). As the measurement device, Ai-Phase·Mobile manufactured by Ai-Phase Co., Ltd. is used.

[0204] Regarding the thermal diffusivity, for one measurement specimen piece, the measurement is carried out at three arbitrary points, and based on the measurement results of these three points, the average value is calculated as the measured value.

[0205] These measurement results and calculation results are shown in Tables 1 and 2.

[0206] [Table 1]

[0207]

[0208] [Table 2]

[0209]

[0210] Regarding the measurement results, the following research is carried out.

[0211] As shown in Table 1, for the composites using the alumina particles of specimen numbers 1 and 4 - 8 that meet the requirements of the embodiments of the present application, excellent thermal diffusivity is shown. On the other hand, for the composites using the alumina particles of specimen numbers 2 and 3 that do not meet the requirements of the embodiments of the present application, the thermal diffusivity is poor.

[0212] In addition, as shown in Table 2, for the first particles that meet the requirements of the preferred embodiments of the present application, the thermal diffusivity of the particles is high. In addition, for the second particles that meet the requirements of another preferred embodiment of the present application, the dispersion of the particle area (i.e., the coefficient of variation of the particle area) is small.

Claims

1. Alumina particles, wherein the particle diameter D50 at which the cumulative number of particles from the fine particle side in the cumulative particle size distribution is 50% is greater than 200 μm, the roundness is 0.90 or more, and the α-conversion rate is 90.0% or more.

2. The alumina particles according to claim 1, wherein the angle of repose is less than 32°.

3. The alumina particles according to claim 1, having an apparent density of 3.75 g / cm 3 or more and 3.96 g / cm 3 or less.

4. The alumina particles according to claim 1, having a tapped density of 1.70 g / cm 3 or more.

5. The alumina particles according to claim 1, wherein the difference between the particle diameter D90 at which the cumulative number of particles from the fine particle side in the cumulative particle size distribution is 90% and the particle diameter D10 at which the cumulative number of particles from the fine particle side in the cumulative particle size distribution is 10% is less than 124 μm.

6. The alumina particles according to claim 1, which contain first alumina particles, and the value of the "threshold", which is the brightness parameter when the stereomicroscope image is binarized using image analysis software (ImageJ), of the first alumina particles is 100 or more and less than 200.

7. The alumina particles according to claim 6, wherein The average value of the Feret diameter of the first alumina particles is greater than 180 μm.

8. The alumina particles according to claim 6, wherein The ratio of the average value of the minimum Feret diameter of the first alumina particles to the average value of the Feret diameter is 0.70 or more.

9. The alumina particles according to claim 6, wherein, The average value of the crushing strength of the first alumina particles in the particle compression test is greater than 25.9 MPa.

10. The alumina particles according to claim 1, which contain second alumina particles, and the value of the "threshold", which is the brightness parameter when the stereomicroscope image is binarized using image analysis software (ImageJ), of the second alumina particles is 200 or more and 255 or less.

11. The alumina particles according to claim 10, wherein, The average value of the Feret diameter of the second alumina particles is greater than 180 μm.

12. The alumina particles according to claim 10, wherein, The ratio of the average value of the minimum Feret diameter of the second alumina particles to the average value of the Feret diameter is 0.70 or more.

13. The alumina particles according to claim 10, wherein, The average value of the strain at break of the second alumina particles in the particle compression test is less than 0.

074.

14. A resin composition comprising a resin and the alumina particles according to any one of claims 1 to 13.

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