Alumina particles and resin composition using the same

Abstract

[The technical problem to be solved] The present invention provides an alumina particle that is used as a filler in a resin composition and can improve the thermal conductivity of the resin composition more than before. Technical means to solve the problem The solution to this problem is an alumina particle whose cumulative particle size distribution, from the microparticle side, has a cumulative particle size D50 exceeding 100 μm, an α-alkalinity of over 90%, and is a single crystal of α-alumina. The Na content of the alumina particles is preferably below 800 ppm. Furthermore, the cumulative particle size distribution, from the microparticle side, has a cumulative particle size D10 preferably between 70 and 135 μm.

Description

[Technical Field]

[0001] This disclosure relates to alumina particles and resin compositions using alumina particles. [Previous Technology]

[0002] The heat generated by an electronic component when it is powered on is dissipated via a heat sink. To improve heat dissipation efficiency, a technique is known of filling the space between the electronic component and the heat sink with a heat-dissipating material.

[0002] As a heat dissipation component, resin compositions containing resin and inorganic particles are known, and alumina particles can be used as inorganic particles (for example, Patent Documents 1 to 3).

[0003] Patent Document 1 discloses alumina particles with an α-phase content of 40% or less, an average roundness of 0.95 or more, and an average particle size of 100 μm or less, which are alumina particles capable of improving flowability when highly filled in resin. Regarding the manufacturing method of the alumina particles, a method is disclosed in which pulverized fused alumina is melted by flame melting and then rapidly cooled by spraying water into the furnace.

[0004] Patent Document 2 discloses alumina particles with an average sphericity of 0.93 or higher and an α-ratio of 95% or higher, which can improve the viscosity and flowability of compositions when formulated into resins, etc. Regarding the manufacturing method of the alumina particles, a method is disclosed that uses metallic aluminum powder, alumina powder, or a mixture of both as raw materials, melts them by flame melting, cools and solidifies them, and then performs reheat treatment.

[0005] Patent document 3 discloses a method for obtaining spherical fused alumina particles with an average particle size of 5 to 4000 μm by using a jet mill to pulverize fused alumina and remove the edges of the fused alumina particles.

[0005] [Previous Technical Documents]

[0005] [Patent Documents]

[0006] Patent Document 1: International Publication No. 2009 / 133904

[0006] Patent Document 2: International Publication No. 2008 / 053536

[0006] Patent Document 3: Japanese Patent Application Publication No. 2006-169090

[0007] In recent years, the increasing integration of ICs in electronic devices has led to increased heat generation from ICs, and the use of high-current driven electronic components due to the electrification of electric vehicles, aircraft, etc., has also increased heat generation in electronic components. To achieve more effective heat dissipation, it is necessary to further improve the thermal conductivity of the resin composition. To achieve even more effective heat dissipation, it is also necessary to minimize the interface between the resin and the filler (alumina particles) used in the resin composition, which requires larger alumina particle sizes.

[0008] However, the alumina particles disclosed in Patent Documents 1 and 2 do not examine how to further improve the thermal conductivity of the resin composition.

[0008] The thermal conductivity of the alumina particles in Patent Document 3 when mixed with resin to form a resin composition is not considered sufficient.

[0009] In view of this situation, one embodiment of the present invention aims to provide alumina particles that are used as fillers in resin compositions and can improve the thermal conductivity of the resin compositions more than before. Furthermore, another embodiment of the present invention aims to provide a resin composition using alumina particles.

[0010] The present invention sample 1 is an alumina particle, wherein the cumulative particle size distribution from the microparticle side has a cumulative 50% particle size D50 of more than 100 μm, an α-oxidation rate of more than 90%, and the α-alumina is a single crystal.

[0011] The second state of the present invention is the alumina particles as described in the first state above, wherein the Na content is 800 ppm or less.

[0012] The present invention sample 3 is an alumina particle as described in sample 1 or sample 2 above, wherein the cumulative particle size distribution from the particle side has a cumulative particle size D10 of 70 to 135 μm.

[0013] The present invention sample 4 is an alumina particle as described in any of the above-described samples 1 to 3, wherein the cumulative particle size distribution from the particle side has a cumulative particle size D90 of 130 to 200 μm.

[0014] The present invention sample 5 is an alumina particle as described in any one of the above-described samples 1 to 4, having a sphericity of 0.90 to 1.00.

[0015] The present invention sample 6 is an alumina particle as described in any one of the above-described samples 1 to 5, having a density of 3.80 g / cm3 or more.

[0016] The present invention sample 7 is a resin composition containing resin and alumina particles as described in any one of the above samples 1 to 6.

[0017] By using alumina particles according to one embodiment of the present invention as a filler, a resin composition with high thermal conductivity can be obtained. [Simplified Explanation of the Diagram]

[0018] Figure 1 is a schematic diagram of an apparatus used to perform the flame melting step in a method for manufacturing alumina particles.

[0018] Figure 2 is a conceptual diagram of a device for measuring the thermal diffusivity of an alumina particle using the temperature wave analysis method (TWA).

[0018] Figure 3 is a schematic diagram used to illustrate the calculation method of particle defect rate.

Implementation Method

[0019] [Alumina particles]

[0019] The alumina particles of this invention are used as fillers in resin compositions, and are mixed with and used in resins. The cumulative particle size distribution of the alumina particles has a cumulative 50% particle size D50 exceeding 100 μm from the microparticle side, an α-alumina content of 90% or more, and α-alumina is a single crystal. By having these characteristics, the thermal conductivity of the resin composition can be improved. Each feature is described in detail below.

[0020] (Cumulative particle size distribution, the cumulative particle size D50 from the microparticle side)

[0020] In the alumina particles of the present invention, the cumulative particle size distribution from the microparticle side, the cumulative particle size D50 (hereinafter sometimes simply referred to as "D50") is greater than 100 μm. When used as a filler in a resin composition, it can be inferred that a resin composition with high thermal conductivity can be obtained for the following reasons.

[0021] When the D50 of alumina particles is large, the total surface area per unit mass of alumina particles decreases. Therefore, when mixing alumina particles and resin in a predetermined ratio to prepare a resin composition, using alumina particles with a large average particle size can reduce the total area of ​​the interface between the alumina particles and the resin. Since the interface between alumina particles and resin scatters phonons that are to propagate, it is believed that thermal conductivity can be improved by reducing the total area of ​​the interface.

[0022] Since the D50 of the alumina particles in the embodiments of the present invention exceeds 100 μm, compared with the case where the D50 is less than 100 μm, the total interfacial area when mixed with the resin in a predetermined ratio can be reduced, and a resin composition with high thermal conductivity can be manufactured.

[0022] The D50 of the alumina particles is preferably 105 μm or more, more preferably 110 μm or more, and particularly preferably 115 μm or more. There is no particular limitation on the upper limit, but from the viewpoint of good compatibility with resin and suitability as a filler for resin compositions, it is preferably 160 μm or less, more preferably 155 μm or less, more preferably 150 μm or less, even more preferably 140 μm or less, and particularly preferably 135 μm or less. If it is greater than 160 μm, even in embodiments of the present invention, it is undesirable because the sphericity of the alumina particles is likely to decrease.

[0023] The D50 of alumina particles is determined by measuring the particle size distribution of alumina particles according to the principle of dynamic image analysis based on ISO 13322-2, and the cumulative particle size (D50) from the microparticle side is obtained by using the cumulative particle size distribution obtained from the measurement results. As a measuring device, for example, a CAMSIZER (manufactured by VERDER Scientific) is used. The sample is placed into the device in sequence, and while the agglomerated particles are dispersed by dry air, the particles passing in front of the camera are measured.

[0024] (α-conversion rate)

[0024] Since α-alumina has high thermal conductivity, the thermal conductivity of alumina particles can be increased by increasing the α-alumina content in the alumina particles. In the embodiments of the present invention, the α-alumina content of the alumina particles has an α-alumina content of over 90%. Therefore, alumina particles with high thermal conductivity can be obtained.

[0024] The α-oxidation rate of alumina particles is preferably above 95%, and the best is 100%.

[0025] In this specification, "α-alumina content" refers to the percentage (volume %) of α-alumina relative to the total alumina contained in the alumina particles.

[0025] The α-phase ratio is determined by powder X-ray diffraction of alumina particles. From the obtained diffraction spectrum, the peak height (I25.6) of the α phase (012 plane) appearing at the position of 2θ=25.6° and the peak height (I46) of the γ phase, η phase, χ phase, κ phase, θ phase and δ phase appearing at the position of 2θ=46° are obtained and calculated by the following formula (1).

[0025] α conversion rate = I25.6 / (I25.6+I46) x 100(%) (1)

[0026] In addition, although the α-oxidation rate of the alumina particles in the embodiments of the present invention is ideally 100%, it may also contain, for example, about 10% or less of alumina other than α-alumina (δ-alumina, θ-alumina, etc.), without affecting the purpose of the present invention.

[0026] Furthermore, aluminum oxide other than α-alumina can be included in any form. For example, α-alumina and aluminum oxide other than α-alumina can be included simultaneously within a single aluminum oxide particle. Alternatively, one aluminum oxide particle may consist only of α-alumina, while other aluminum oxide particles may consist only of aluminum oxide other than α-alumina, and these aluminum oxide particles may exist in a mixed manner.

[0027] (α-alumina is a single crystal)

[0027] In embodiments of the present invention, the manufacturing conditions are controlled such that the α-alumina contained in the alumina particles is a single crystal. As described above, α-alumina has high thermal conductivity, especially when it is a single crystal, it has a higher thermal conductivity than polycrystalline α-alumina. Therefore, by containing α-alumina in a single crystal form in the alumina particles, the thermal conductivity of the alumina particles can be further improved.

[0027] Alternatively, a small amount (e.g., less than 10%) of polycrystalline α-alumina may be contained simultaneously with single-crystal α-alumina without hindering the purpose of the present invention.

[0028] The α-alumina in the alumina particles can be confirmed to be a single crystal by SEM-EBSD. In the Phase MAP, it can be determined whether it is α-alumina or alumina other than α-alumina. Then, in the Image Quality (IQ) MAP, it can be determined whether it is a single crystal or polycrystalline by whether there are clear grain boundaries in the alumina particles.

[0028] The Debye-Scherrer method can also be used to confirm that α-alumina is a single crystal.

[0029] In an embodiment of the present invention, the Na content of the alumina particles is preferably below 800 ppm.

[0029] When using alumina particles as a filler in resin compositions, if the Na content is high (e.g., 1000 ppm or more), it may adversely affect electronic components and other components placed adjacent to the resin composition. Furthermore, since Na present in alumina particles causes phonon scattering, it was previously believed that if the Na content was, for example, 100 ppm or more, the thermal conductivity of alumina particles would be too low, making them unsuitable as a filler in resin compositions. Therefore, it was previously thought that when using alumina particles as a filler in resin compositions, the Na content must be set to less than 100 ppm.

[0030] In contrast, the inventors of this case discovered that by having a D50 greater than 100 μm and an α-alkalinity of over 90%, the contained α-alumina is a single crystal, and even with a Na content of over 100 ppm, it can achieve a thermal conductivity suitable for use as a filler in resin compositions. In particular, a Na content of 800 ppm or less is preferred, as it can improve the thermal conductivity of the alumina particles.

[0030] In this specification, "Na content" refers to the content obtained by conversion of oxides, and refers to the content of Na2O (mass ppm) in alumina particles when the alumina content (converted to Al2O3) in the alumina particles is set as 100% by mass.

[0031] The Na content is preferably below 700ppm, and ideally below 600ppm.

[0032] There is no particular limitation on the lower limit of Na content, for example, it is 1 ppm or more. In the following cases, it is preferable to increase the lower limit of Na content (e.g., greater than 20 ppm).

[0032] Na is sometimes contained in the raw materials (alumina raw material particles) used to manufacture alumina particles. In order to make the Na content of alumina particles extremely low, it is necessary to perform a treatment to remove Na from the raw materials from the entire alumina particles (the surface and interior of the alumina particles). Since the alumina particles of the embodiments of the present invention are dense, it is difficult to remove Na from the interior of the alumina particles by washing them with water as described below.

[0032] However, as described above, the alumina particles according to embodiments of the present invention can be used as fillers in resin compositions even if the Na content is 100 ppm or more. Therefore, it is preferable to allow a certain amount of Na content in order to omit the treatment for removing Na.

[0032] The Na content is preferably more than 20 ppm, more than 30 ppm, more than 50 ppm or more than 80 ppm, and more preferably more than 100 ppm.

[0033] Of the Na contained in the alumina particles, the Na present on the surface can be easily washed away by water. Since the Na that may adversely affect electronic components is mainly the Na present on the surface of the alumina particles, washing the alumina particles with water before mixing them with the resin as a filler in the resin composition can reduce adverse effects on electronic components. However, since only a trace amount of Na present near the surface of the alumina particles can be removed by water washing, it is difficult to confirm a significant reduction in Na content even when comparing the measured values ​​of Na content in the alumina particles before and after water washing.

[0033] Furthermore, since the Na that reduces the thermal conductivity of alumina particles is mainly Na present inside the alumina particles, it is speculated that even if the alumina particles are washed with water, the thermal conductivity of the alumina particles will not increase much.

[0034] The Na content of alumina particles can be quantified by conventional methods such as glow discharge mass spectrometry, inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), and fluorescence determination, but inductively coupled plasma mass spectrometry (ICP-MS) is preferred.

[0035] The cumulative particle size distribution of alumina particles, with the cumulative particle size D10 of 10% from the microparticle side, preferably 70 μm or more, more preferably 75 μm or more or 80 μm or more, and particularly preferably 90 μm or more. D10 is preferably 135 μm or less, more preferably 125 μm or less, 120 μm or less, 115 μm or less, 110 μm or less, or 105 μm or less.

[0035] Furthermore, the cumulative particle size distribution of alumina particles, with 90% of the particle size D90 accumulating from the microparticle side, is preferably 130 to 200 μm. D90 is more preferably 130 to 190 μm, and particularly preferably 130 to 180 μm.

[0035] Alumina particles with such a particle size are preferred because they have good flowability, can be filled in large quantities in the resin, and are easy to handle.

[0036] Furthermore, the alumina particles preferably have a sharp particle size distribution, with D90 / D10 preferably below 3.0, and more preferably below 2.0. The sharper the particle size distribution of the alumina particles, the higher the replenishment rate (recovery rate) of the particles after melting and manufacturing, resulting in better productivity. In addition, alumina particles with a sharp particle size distribution are preferred because they are easier to use as fillers in resin compositions and offer increased selectivity and flexibility when mixed with other particles.

[0037] Furthermore, to ensure that the alumina particles, as the final product, are free of particulates and coarse particles, it is preferable to classify or screen the alumina raw material particles or the manufactured alumina particles. For example, if the alumina raw material particles are classified or screened to remove particulates and coarse particles before being used to manufacture alumina particles, the particulates and coarse particles in the resulting alumina particles can be reduced. Alternatively, the manufactured alumina particles can also be classified or screened to remove particulates and coarse particles.

[0038] In alumina particles that do not contain coarse particles, from the viewpoint of improving sphericity, the cumulative particle size distribution from the microparticle side, the cumulative particle size D100 (i.e., the maximum particle size) is preferably 500 μm or less, more preferably 400 μm or less, and especially preferably 300 μm or less.

[0039] In embodiments of the present invention, when alumina particles are manufactured using alumina raw material particles, polycrystalline alumina particles, alumina particles with low α-saturation, or low-density alumina particles are easily formed. Therefore, it is particularly preferred to remove the particles from the alumina raw material particles, or to remove the particles from the manufactured alumina particles.

[0040] The determination of D10, D90, and D100 of alumina particles can be performed using the same method and apparatus as the determination of D50 described above. The particle size distribution of alumina particles is determined according to the principle of dynamic image analysis based on ISO 13322-2, and the cumulative particle size distribution obtained from the measurement results is used to determine the cumulative 10% particle size (D10), 90% particle size (D90), and 100% particle size (D100) from the microparticle side. As the measuring apparatus, for example, a CAMSIZER (manufactured by VERDER Scientific) is used. The sample is placed sequentially into the apparatus, and while the agglomerated particles are dispersed by dry air, the particles passing in front of the camera are measured.

[0041] The sphericity of the alumina particles is preferably 0.90 to 1.00, which can make them well mixed with the resin, improve the flowability of the compound after mixing, and reduce the wear of other components caused by the alumina particles.

[0041] Since alumina particles are typically hard particles, a sphericity of 0.90 or higher is preferred for use as a filler in resin compositions for electronic components. However, it is difficult to obtain alumina particles with a sphericity of 0.90 or higher by simply colliding or crushing alumina particles with low sphericity. Furthermore, there is a risk of generating a large amount of fine powder due to prolonged impacting and crushing. In addition, there is a risk that the new hydrophilic surface created by crushing may reduce the miscibility with the resin.

[0042] Sphericity (SPHT) is analyzed according to ISO 9276-6. It is obtained by SPHT=4πA / P2. In the formula, A is the measured value of the area of ​​the projected particle image, and P is the measured value of the perimeter of the particle projection image.

[0042] The sphericity of alumina particles is determined by a measuring device (e.g., CAMSIZER X2 (manufactured by VERDER Scientific)) based on the principle of dynamic image analysis according to ISO 13322-2.

[0043] The density of the alumina particles is preferably above 3.80 g / cm3.

[0043] If internal voids exist in alumina particles, the thermal conductivity of the alumina particles will decrease. Therefore, alumina particles with few internal voids are ideal. As for methods to confirm internal voids, there are methods that directly observe them through image analysis such as cross-sectional SEM images and X-ray fluoroscopy images, and methods that indirectly confirm them by measuring the density of alumina particles.

[0043] The density of the alumina particles is preferably above 3.80 g / cm3, so as to obtain alumina particles with little internal voids (or no internal voids), that is, alumina particles with high thermal conductivity.

[0043] The density of the alumina particles is preferably 3.85 g / cm3 or higher, 3.88 g / cm3 or higher, or 3.89 g / cm3 or higher, and preferably 3.90 g / cm3 or higher.

[0044] The density of the alumina particles was determined by the specific gravity bottle method according to JIS R 1620-1995. The number of measurements was set to at least 5. For example, an AccuPyc 1330 (Micromeritics) could be used for the determination.

[0045] In embodiments of the present invention, the thermal conductivity (W / mK) of one alumina particle can be improved. Preferably, the thermal conductivity of one alumina particle is 25 W / mK or higher, more preferably 28 W / mK or higher, particularly preferably 30 W / mK or higher, and most preferably 33 W / mK or higher.

[0046] [Method for manufacturing alumina particles]

[0046] The following describes a method for manufacturing alumina particles according to embodiments of the present invention.

[0046] The raw material for the alumina particles is composed of single-crystal α-alumina, and the cumulative particle size distribution from the microparticle side has a cumulative particle size D50 of more than 100 μm. Then, alumina particles are manufactured from the alumina raw material particles by flame melting.

[0047] The prevailing view to date is that since the raw material particles melt when they are placed in a flame, the crystal structure of the raw material particles is reset, and therefore the properties of the crystal structure of the raw material particles do not affect the crystal structure of the particles after they are spheroidized by the flame. However, it has been unexpectedly discovered that when single crystal particles are used as raw material particles, the properties of the crystal structure of the raw material particles can be inherited even after spheroidization.

[0048] In the flame melting step, for example, the apparatus shown in FIG1 is used. By means of the flame melting step, alumina particles with an α-oxidation rate of 90% or more and α-alumina as single crystals can be obtained.

[0048] In order to effectively utilize the crystal structure of single-crystal alumina after using raw material particles of single-crystal alumina and spheroidizing them, the particle size of the alumina raw material particles used, the supply rate of the alumina raw material particles to the flame melting furnace of the device, the intensity of the flame, and the distance between the flame and the alumina raw material particles are controlled.

[0049] In order to manufacture alumina particles with a D50 greater than 100 μm, alumina raw material particles with a D50 of, for example, 110 μm or greater are used. The D50 of the alumina raw material particles is preferably 120 μm or greater, for example, 150 μm.

[0050] Furthermore, even if the D50 of the alumina raw material particles is, for example, 110 μm or more, each individual alumina raw material particle will contain particles with a particle size less than 110 μm. Therefore, the resulting alumina particles will also contain polycrystalline α-alumina and / or alumina other than α-alumina. However, by setting the D50 of the alumina raw material particles to 110 μm or more, the content of polycrystalline α-alumina and / or alumina other than α-alumina can be suppressed to a small amount acceptable in this invention.

[0051] In addition, there are known methods for manufacturing alumina particles using granulated raw material particles via flame melting, but sometimes the resulting alumina particles contain a large number of internal voids. In the present invention, since ungranulated single-crystal α-alumina itself is used as the alumina raw material particle, high-density alumina particles with few (or no) internal voids can be obtained.

[0052] The D50 of alumina raw material particles can be determined by the same method as the above-mentioned method for determining the D50 of alumina particles.

[0052] The alumina raw material particles can be confirmed to be single-crystal α-alumina by the same method as the above method for confirming that the α-alumina in the alumina particles is a single crystal.

[0053] Regarding the raw materials for alumina particles, sapphire and single-crystal α-alumina produced by melt growth methods such as the CZ method, the Verneuil method, the Kyropoulos method, the Bridgman method, and the EFG method can be used. By pulverizing these raw materials and sieving them with a mesh size of the desired pore size, alumina particles with a predetermined D50 can be prepared.

[0054] The alumina raw material particles may contain a small amount (e.g., less than 10% by mass) of alumina other than α-alumina (δ-alumina, θ-alumina, etc.). In addition, they may also contain a small amount (e.g., less than 10% by mass) of polycrystalline α-alumina at the same time as monocrystalline α-alumina. Neither of these shall affect the purpose of the present invention.

[0055] In the flame melting step, the supply of alumina raw material particles, fuel gas and oxygen is preferably satisfied by the following formulas (2) and (3).

[0055]

[0055]

[0055] Here, F is the supply of fuel gas (Nm3 / hour), S is the supply of oxygen (Nm3 / hour), and R is the supply of alumina raw material particles (kg / hour).

[0055] In addition, the oxygen supply (S) is the sum of the combustion oxygen supply and the carrier oxygen supply. The carrier oxygen is oxygen mainly used for transporting alumina raw material particles, but after transportation, it will be used for combustion in the same way as the combustion oxygen.

[0056] As specified in Formula (2), the ratio (R / F) of the supply amount of alumina raw material particles to the supply amount of fuel gas is preferably 0.625 kg / Nm3 or more and 5.000 kg / Nm3 or less. Furthermore, as specified in Formula (3), the ratio (R / S) of the supply amount of alumina raw material particles to the supply amount of oxygen is preferably 0.125 kg / Nm3 or more and 1.500 kg / Nm3 or less.

[0057] The supply rate of fuel gas F (Nm3 / hour) and the supply rate of oxygen S (Nm3 / hour) are factors that determine the flame intensity in the furnace during the flame melting process. In the flame melting process, R / F and R / S both become indicators of the relationship between the flame intensity in the furnace and the supply rate of alumina raw material particles.

[0057] When R / F and R / S increase, the supply of alumina raw material particles is greater, and the energy that each alumina raw material particle can obtain from the flame decreases (i.e., the melting of alumina raw material particles is suppressed).

[0057] When R / F and R / S decrease, the supply of alumina raw material particles is less, and the energy that each alumina raw material particle can obtain from the flame increases (i.e., the melting of alumina raw material particles is promoted).

[0058] Therefore, controlling R / F and R / S is a method for controlling the melting state of alumina raw material particles in the flame melting step. When R / F and R / S are each within a better range, spheroidization can be achieved in the flame melting step while maintaining the raw material particle crystal structure of the alumina raw material particles.

[0059] The R / F is preferably above 0.625 kg / Nm3 and below 4.500 kg / Nm3, and particularly preferably above 1.000 kg / Nm3 and below 4.500 kg / Nm3.

[0059] The R / S is preferably above 0.125 kg / Nm3 and below 1.333 kg / Nm3, the particularly good is above 0.125 kg / Nm3 and below 1.250 kg / Nm3, and the best is above 0.200 kg / Nm3 and below 1.000 kg / Nm3.

[0060] Furthermore, the fuel gas supply rate F is preferably less than 20 Nm³ / hour. The flame length can be changed by the fuel gas supply rate; the greater the fuel gas supply rate, the longer the flame length, and the longer the residence time of the particles in the flame. The smaller the fuel gas supply rate, the shorter the flame length, and the shorter the residence time of the particles in the flame. That is, the residence time of alumina raw material particles in the flame can be changed, and the melting degree (time) of alumina raw material particles in the flame can be changed. In addition, while maintaining the crystal structure of alumina raw material particles, the α-oxidation rate and density of alumina particles can be further improved.

[0061] The fuel gas in this invention may include, for example, propane, butane, propylene, acetylene, hydrogen, etc. Propane (e.g., liquefied propane (LPG)) is particularly preferred.

[0062] Furthermore, by manufacturing alumina particles through such a flame melting step, the Na content of the obtained alumina particles can be reduced to below the Na content of the alumina raw material particles.

[0063] In the flame melting step, when solidifying the molten alumina raw material particles, in order to slow down the cooling rate, they can be allowed to pass through a region of 600°C to 1500°C, preferably a region of 800°C to 1400°C, and more preferably a region of 1000°C to 1300°C. By solidifying the spheroidized alumina particles through the above-mentioned regions, the α-alloying rate can be further improved.

[0064] As a subsequent step to the above-described flame melting step, a reheating step can be applied before recovering the cooled and solidified alumina particles. By reheating the cooled and solidified alumina particles, the proportion of alumina other than α-alumina can be reduced, and the α-oxidation rate can be further increased. The temperature of the reheating step is preferably, for example, 900°C or higher, and more preferably 1000°C or higher. The reheating method can be external heating using a heater or the like, or heating by re-combustion of gas.

[0065] [Resin Composition]

[0065] By using the alumina particles of the embodiments of the present invention as a filler for resin compositions, resin compositions with high thermal conductivity can be obtained. The resin composition system comprises resin and the alumina particles of the embodiments of the present invention.

[0066] Since the alumina particles of the present invention can improve thermal conductivity without impairing the inherent softness of the resin, the preferred formulation ratio is 5 to 75% by volume of resin and 95 to 25% by volume of alumina particles relative to the resin composition (composite).

[0067] The following describes the manufacturing method of the resin composition.

[0067] The resin composition can be obtained by mixing the alumina particles of the present invention with the resin using conventional methods. For example, when the resin is liquid (e.g., liquid epoxy resin), the resin composition can be obtained by mixing the liquid resin, alumina particles, and a hardener, and then curing it with heat or ultraviolet light. The hardener, mixing method, and curing method can be conventional materials and methods. On the other hand, when the resin is solid (e.g., polyolefin resin, acrylic resin, etc.), the desired resin composition can be obtained by mixing the alumina particles and the resin and then kneading it using conventional methods such as melt kneading.

[0068] The resin used in the resin composition may be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. In addition, one type of resin may be used alone, or two or more types may be used in combination.

[0069] Examples of thermoplastic resins include: polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; vinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymer; polyvinyl alcohol; polyvinyl acetal; polyvinylidene fluoride and polytetrafluoroethylene; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymer; and propylene. Acrylonitrile-butadiene-styrene copolymer (ABS) resin, polyphenylene ether copolymer (PPE) resin, modified PPE resin, aliphatic polyamides, aromatic polyamides, polyimide, polyamide-imide, polymethacrylic acid, polymethyl methacrylate and other polymethacrylates, polyacrylic acid, polycarbonate, polyphenylene sulfide, polyurethane, polyetherurethane, polyether nitrile, polyether ketone, polyketone, liquid crystal polymers, polysiloxane resins, ionomers, etc.

[0070] Examples of thermoplastic elastomers include: styrene-butadiene block copolymers or their hydrogenated forms, styrene-isoprene block copolymers or their hydrogenated forms, 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.

[0071] Examples of thermosetting resins include: cross-linked rubber, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, etc. Specific examples of cross-linked 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, amine ester rubber, and polysiloxane rubber.

[0072] From the viewpoint of processability and properties, it is preferable to use polyolefin resins, acrylic resins, polyimide resins, polyamide resins, polyamide-imide resins, epoxy resins, phenolic resins, and polysiloxane resins.

[0073] Furthermore, these resin compositions may, as needed, appropriately incorporate one or more conventional additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, anti-caking agents, antistatic agents, leveling agents, and release agents, without impairing the effects of the present invention.

[0074] The alumina particles and the resin composition containing the alumina particles of this embodiment are particularly suitable for use as heat dissipation materials. Therefore, in one embodiment disclosed herein, heat-dissipating alumina particles and a heat-dissipating resin composition can be provided.

[0075] However, the alumina particles and resin composition of this embodiment possess the properties described below [other physical properties], and therefore can have the characteristic of low dielectric loss. Therefore, in another aspect of this disclosure, alumina particles with low dielectric loss and a resin composition with low dielectric loss can be provided. In yet another aspect of this disclosure, alumina particles with heat dissipation / low dielectric loss and a resin composition with heat dissipation / low dielectric loss can also be provided by simultaneously utilizing both heat dissipation and low dielectric loss characteristics.

[0076] [Other physical properties]

[0076] The alumina particles and the resin composition containing the alumina particles of this embodiment can be used to obtain a resin composition with low dielectric loss by having the following properties. The [other physical properties] described below can be measured using the measurement methods described in the examples.

[0077] (Intraparticle defect rate)

[0077] If the alumina particles contain voids or amorphous layers (also referred to as "particle defects"), it will cause an increase in dielectric loss. Therefore, it is preferable to have a low defect rate within the alumina particles, especially below 20%, and even more preferably below 15%. In this way, when alumina particles are used as a filler in resin compositions, the dielectric loss of the resin composition can be further reduced.

[0078] (Average aspect ratio of impurity particles)

[0078] The alumina particles may contain impurity particles (non-circular but elongated alumina particles). The average aspect ratio of the impurity particles is preferably greater than 1.2 and less than 5.0, and particularly preferably less than 3 or less, or less than 2.5. By containing a small amount of such impurity particles, the alumina particles can be used as a filler in resin compositions to increase the filling rate of the alumina particles and further reduce the dielectric loss of the resin composition.

[0079] (The ratio of the total length L2 of the boundary line inside the alumina particle to the length L1 of the outer edge of the alumina particle)

[0079] The smaller the grain boundaries and cavities inside the alumina particles, the lower the dielectric loss of the alumina particles. Therefore, the ratio of the total boundary length L2 to the outer edge length L1 (L2 / L1) is introduced as an indicator of the grain boundary content inside the alumina particles.

[0080] When the outer edge length of an alumina particle is defined as L1, and the total length of the boundary lines of this alumina particle is defined as L2, alumina particles with a small L2 / L1 value can be considered as alumina particles with low boundary line content and low dielectric loss. It is especially preferable that (L2 / L1) is 100% or less, as it can further reduce the dielectric loss of the resin composition when used as a filler in resin compositions. (L2 / L1) is more preferably 80% or less, even more preferably 50% or less, and most preferably 40% or less.

[0081] Furthermore, the "total length of the boundary line L2" refers to the sum of the boundary lines contained within the alumina particle, excluding the outer edge of the alumina particle. The total length of the boundary line L2 is set as the sum of the total length of the grain boundary L3 within the alumina particle and the total length of the inner wall of the cavity (when there is a cavity inside the alumina particle) L4 (i.e., L2 = L3 + L4).

[0081] The determination of L1, L2, L3 and L4 is preferably performed using alumina particles composed of α-alumina.

[0082] (Number of contact points between alumina particles in the resin composition)

[0082] In resin compositions, the dielectric loss of the resin composition increases when the number of contacts between adjacent alumina particles (i.e., the number of interparticle interfaces) increases. Therefore, the number of contacts between alumina particles in the resin composition is preferably 40 or less (equivalent to 82 or less per 1 mm²) within an observation range of 650 μm × 750 μm, which can further reduce the dielectric loss of the resin composition when used as a filler for resin compositions.

[0083] For an observation area of ​​1 mm², the number of contact points between alumina particles is preferably 65 or less per mm², more preferably 50 or less per mm², or 30 or less per mm². For heat dissipation characteristics, the number of contact points between alumina particles is preferably more than one in an observation area of ​​650 μm × 750 μm (equivalent to more than two per 1 mm² observation area).

[0083] In addition, the number of contact points between alumina particles can be used as an indicator of the degree of particle dispersion. That is, the fewer the number of contact points, the more uniformly the alumina particles are dispersed in the resin.

[0084] (BET specific surface area of ​​alumina particles)

[0084] Due to the small surface roughness and low specific surface area of ​​the alumina particles in this embodiment, it is difficult to accurately determine the BET specific surface area using the N2 gas adsorption method. The N2-BET specific surface area is preferably 0.05 m² / g or less, 0.02 m² / g or less, more preferably 0.01 m² / g or less, and most preferably less than 0.01 m² / g. Furthermore, the alumina particles in Tests No. 3 to 6 did not reach 0.01 m² / g in the N2-BET specific surface area determination. Therefore, by using krypton (Kr) as the adsorption gas to determine the BET specific surface area, the BET specific surface area of ​​alumina particles with low specific surface area can be determined more accurately.

[0085] If the surface of the alumina particles has fewer irregularities, then when used as a filler in resin compositions, the interface between the particles and the resin is reduced, resulting in a decrease in the dielectric loss of the resin composition. Therefore, the BET specific surface area S1 (m² / g) of the alumina particles is preferably 0.10 m² / g or less, which further reduces the dielectric loss of the resin composition when used as a filler in resin compositions. The Kr-BET specific surface area S1 is preferably 0.08 m² / g or less, and particularly preferably 0.07 m² / g or less.

[0085] The specific surface area S1 of Kr-BET can be above 0.01m2 / g or above 0.02m2 / g.

[0086] Regarding another indicator of the surface roughness of alumina particles, there is the ratio (S1 / S2) ( / g) of the BET specific surface area S1 (m2 / g) using krypton to the area S2 (m2) of an ideal sphere. (S1 / S2) is preferably 95 × 10⁵ / g or less, which can further reduce the dielectric loss of the resin composition when used as a filler in resin compositions. (S1 / S2) is more preferably 40 × 10⁵ / g or less, and particularly preferably 20 × 10⁵ / g or less.

[0086] The ideal sphere area S2 (m2) is the surface area of ​​a true spherical particle with diameter D50, and is obtained by the surface area formula of a sphere (4πr2).

[0087] In addition, another method for confirming the unevenness of the particle surface can be to use the pore distribution, pore volume, etc. The pore volume of alumina particles will be described later.

[0088] (Moisture content entrained in alumina particles and resin)

[0088] If the alumina particles contain a large amount of water, the dielectric loss of the resin composition manufactured using these alumina particles will increase. Furthermore, if the alumina particles contain a large amount of water, moisture will seep out of the resin, potentially causing adverse effects on electronic components or other components placed adjacent to the resin composition. Therefore, it is preferable to have a low amount of water contained in the alumina particles.

[0089] As an indicator of the amount of moisture carried by alumina particles, the ratio of the amount of moisture carried by the alumina particles ΔMa to the amount of moisture carried by the resin ΔMr (ppm) is (ΔMa / ΔMr).

[0089] ΔMa / ΔMr is preferably 0.2 or less, and more preferably 0.1 or less. Since the water content ΔMa entrained by alumina particles is extremely small compared to the water content entrained by polyimide resin, the dielectric loss of the resin composition can be further reduced when alumina particles are used as a filler in the resin composition.

[0090] (Pore volume of alumina particles)

[0090] When determining the pore volume of alumina particles by krypton adsorption, the pore volume is preferably below 0.0003 cm3 / g.

[0090] Both pore volume and Kr-BET specific surface area are indicators of the unevenness of particle surfaces. By controlling the pore volume of the first alumina particles within the above-mentioned range, the formability of the mixture can be further improved.

[0091] The pore volume is preferably 0.00009 cm3 / g or less, and particularly preferably 0.00007 cm3 / g or less. The lower limit of the pore volume is not particularly limited, for example, it may be 0.000001 cm3 / g or more, or 0.000005 cm3 / g or more.

[0091] (Example)

[0092] (Preparation of alumina raw material particles)

[0092] Raw material 1 was prepared, consisting of monocrystalline alumina particles. Raw material 2 consisted of monocrystalline alumina particles, which had been screened to remove particles smaller than 50 μm. Both types of alumina particles had angular shapes.

[0092] The physical properties of raw material 1 and raw material 2 are shown in Table 1. In addition, the method for determining the physical properties of alumina raw material particles is the same as the method for determining the physical properties of alumina particles described later.

[0093] [Table 1]

[0094] (Manufacturing of alumina particles)

[0094] Alumina particles are prepared using the apparatus shown in FIG. 1. Oxygen from the oxygen supply system 10 is split, with one portion (carrier oxygen 11) supplied to the feeder 30 and the other portion (combustion oxygen 12) supplied to the burner 41 of the flame melting furnace 40. The alumina raw material particles supplied to the feeder 30 are conveyed to the burner 41 of the flame melting furnace 40 via the carrier oxygen 11. In addition, combustion gas (LPG) is supplied to the burner 41 by the gas supply system 20. In the burner 41, a high-temperature flame of 2150°C or higher is formed by the fuel gas and the combustion oxygen 12, and the alumina raw material particles dispersed in the carrier oxygen 11 are supplied thereto. Thereby, the alumina raw material particles are melted and spheroidized in the flame melting furnace 40. The spheroidized alumina particles are then classified by a cyclone separator 50, and replenished alumina particles are obtained in the cyclone separator 50.

[0095] In samples No. 1 to 4, the obtained alumina particles were used directly in various determinations. In samples No. 5 and 6, the following additional treatment was performed.

[0095] In Sample No. 5, alumina raw material particles (raw material 1) were sieved using a sieve with a pore size of 132 μm, and the alumina raw material particles remaining on the sieve were used as raw material. Furthermore, the obtained alumina particles were acid-washed to remove Na before being used in various determinations.

[0095] In sample No. 6, the obtained alumina particles were graded using a sieve with a pore size of 70 μm and a sieve with a pore size of 135 μm, and then used for various determinations.

[0096] The ratios R / F and R / S of the fuel gas supply rate F (Nm3 / hour), the oxygen supply rate S (Nm3 / hour), and the alumina raw material particle supply rate R (kg / hour) in the flame melting step are summarized in Table 2. Furthermore, the oxygen supply rate S is the sum of the supply rates of the carrier oxygen 11 and the combustion oxygen 12. The fuel gas supply rate F is less than 20 Nm3 / hour.

[0097] [Table 2]

[0098] (1) Determination of particle size D10, D50, D90 and sphericity of alumina particles

[0098] The particle size distribution of alumina particles in samples No.1 to No.6 was determined, and the average value of alumina particles, the cumulative 10% particle size D10, the cumulative 50% particle size D50, and the cumulative 90% particle size D90 were obtained.

[0099] The particle size distribution and sphericity of alumina particles were determined using a CAMSIZER X2 (manufactured by VERDER Scientific) device based on the principle of dynamic image analysis according to ISO 13322-2. The measurement was dry; samples were placed sequentially into the device, and while the aggregated particles were dispersed by dry air at 50 kPa, the particles passing in front of the camera were measured. A 3g sample was weighed and counted as one measurement. The same measurement was repeated three times, and the particle size distribution and sphericity were analyzed by the cumulative average of these results. The particle size was defined as the circular equivalent particle size. The circular equivalent particle size refers to the particle size of a sphere with the same area as the projected particle image. Furthermore, the particle size was set as the reference for volume.

[0099] The circularity (SPHT) was analyzed according to ISO 9276-6. It was obtained from SPHT = 4πA / P². In this formula, A is the measured area of ​​the projected particle image, and P is the measured perimeter of the projected particle image.

[0100] These measurement results are shown in Table 3.

[0101] [Table 3]

[0102] (2) Determination of the density of alumina particles

[0102] The density of alumina particles in samples No.1 to No.6 was determined. The results are shown in Table 4.

[0102] Density was determined according to JIS R 1620-1995. The determination method and conditions are as follows.

[0102] ‧Determination method: Gas displacement method

[0102] ‧Sample drying: 200℃, for more than 8 hours.

[0102] ‧Used device: AccuPyc1330 (Made by Micromeritics)

[0102] ‧Determination conditions

[0102] Number of rinsing (purge): 10 times

[0102] Flush filling pressure: 15.0 psig

[0102] Number of measurements: 5

[0102] Measured filling pressure: 15.0 psig

[0102] Balance pressure: 0.005 psig / min

[0102] Setting the accuracy measurement: Yes

[0102] Tolerance for dispersion: 0.05%

[0102] Sample groove size: 10cm³

[0103] (3) Confirmation of the crystallization state of alumina particles

[0103] The crystallization state of alumina particles in samples No. 1 to 6 was confirmed by EBSD (electron backscatter diffraction). The measurement method and conditions are as follows.

[0103] ‧Using equipment

[0103] Ion polishing device: IM-4000 (manufactured by Hitachi, Ltd.)

[0103] Ion sputtering apparatus: E-1030 (manufactured by Hitachi, Ltd.)

[0103] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by Japan Electronics Corporation)

[0103] Backscattered electron diffraction device: Digiview V (TSL manufacturing)

[0103] ‧Determination conditions

[0103] Accelerating voltage: 20.0kV (EBSD analysis)

[0104] ‧Measurement Procedure

[0104] Samples for cross-sectional observation were prepared as follows: Alumina particles were embedded in resin, and the resin and alumina particles were cut using a diamond cutter. Pt was then deposited as a protective film on the cross-section, and the cross-section was modulated by Ar ion polishing. The sample was fixed to the SEM stage with Cu double-sided tape, and EBSD measurements were performed without evaporation.

[0104] In the EBSD measurement, the proportion of particles in α-alumina particles without grain boundaries observed is determined as ○ when the proportion of particles without grain boundaries observed in the same area of ​​at least 400x250μm is greater than 80% relative to the total number of alumina particles in the measurement field, and is determined as × when the proportion of particles in α-alumina particles without grain boundaries observed is less than 80%.

[0105] (4) Determination of Na content in alumina particles

[0105] Determine the Na content of alumina particles in samples No. 1 to 6. Detailed determination methods and conditions are as follows.

[0105] ‧Sample and quantity: Alumina particles, 2 samples in total

[0105] ‧Analysis and testing items

[0105] Quantitative Analysis of Na

[0105] ‧Analytical and experimental methods:

[0105] Quantitative analysis of Na: acid dissolution / ICP-AES method

[0106] A powder sample (alumina particles) was measured in a sealed container, acid was added, and the sample was subjected to pressurized acid decomposition treatment. After cooling, the sample was diluted with ultrapure water to obtain the analytical sample. The amount of Na in the analytical sample was then determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry), and the Na content in the powder sample (alumina powder) was calculated.

[0107] (5) Determination of α-oxidation rate of alumina particles

[0107] The α-oxidation rate of alumina particles in samples No.1 to No.6 was determined. The results are shown in Table 4.

[0107] The α-saturation rate was determined by measuring the diffraction spectrum of alumina particles in a sample using a powder X-ray diffraction apparatus (Rigaku Electron). The measurement conditions were as follows: X-ray source: CuKα, X-ray output: 45kV, 200mA, scan rate: 10deg / min.

[0107] From the obtained diffraction spectrum, the peak height (I25.6) of the α phase (012 plane) appearing at the position of 2θ=25.6°, and the peak height (I46) of the γ phase, η phase, χ phase, κ phase, θ phase and δ phase appearing at the position of 2θ=46° are obtained and calculated by the following formula (1).

[0107] α-conversion rate = I25.6 / (I25.6+I46) x 100(%) (1)

[0108] These measurement results, confirmation results and calculation results are summarized in Table 4.

[0109] [Table 4]

[0110] (6) Determination of thermal diffusivity and thermal conductivity of resin components (complexes)

[0110] Epoxy resin (main agent: room temperature curing type 53 embedding resin (manufactured by Sanki Co., Ltd.) 010-8140, curing agent: room temperature curing type 53 embedding resin (manufactured by Sanki Co., Ltd.) 010-8143) and alumina particles (raw material 1, sample No. 1 to 6) are mixed in the proportions shown in Table 5 and stirred using a Rentarō stirrer (trade name) (manufactured by THINKY CORPORATION) to obtain an epoxy resin-filler (alumina particles) composite.

[0111] A glass fiber tape is bonded to a PET film to prepare a model that determines the shape of the film, and this model is placed on an aluminum plate. The mixed composite is poured into the model, and a PET film is stacked on top of it in a way that prevents air from entering. Another aluminum plate is then placed on top, and the mixture is heated to 50 to 70°C and left to stand to allow the resin to harden. The hardening time is approximately 3 hours at 50°C and approximately 1 hour at 70°C.

[0111] After hardening, the aluminum plate is cooled down to about room temperature. Two PET films are peeled off from both sides of the hardened composite to obtain a sheet sample of the composite for testing.

[0112] The thermal diffusivity, specific heat and density of the obtained sheet sample were measured, and the thermal conductivity was obtained.

[0112] Thermal diffusivity was measured at room temperature using temperature wave analysis (TWA) on a 10 mm long × 10 mm wide × 0.1 mm thick sheet prepared from the above-mentioned resin composition. The ai-Phase Mobile instrument manufactured by ai-Phase Corporation was used as the measuring device.

[0112] The thermal diffusivity is measured at any three points on a single test sample, and the average value is calculated from the results of these three points. The thermal conductivity is based on the measurement value of the composite sample of "epoxy resin + raw material 1", and the measurement values ​​of other test samples are standardized.

[0112] In addition, as a comparison, sheet samples composed only of epoxy resin were prepared and the same measurements and calculations were performed.

[0113] The specific heat coefficient is calculated based on the mixing ratio of resin and alumina particles, and the values ​​in Table 5 are used.

[0114] Density was determined using an electronic hydrometer MDS-300 (Alfa Mirage Inc.).

[0114] The density is obtained by Archimedes' method (solid density determination) according to the following formula (4). In addition, the specific gravity is obtained by density.

[0114] ρ=A÷(AB)×(ρ0-ρL)+ρL (4)

[0114] Here,

[0114] ρ: Density of the sample (composite)

[0114] A: Weight of the sample measured in the atmosphere

[0114] B: Weight of the sample measured in the replacement fluid (water)

[0114] ρ0: Density of the replacement fluid (water) (1.0000 g / cm3)

[0114] ρL: Density of the atmosphere (0.0012 g / cm3).

[0115] The thermal conductivity is obtained by substituting the measured thermal diffusivity, specific heat and density into the following formula (5).

[0115] Thermal conductivity = thermal diffusivity × specific heat × density (5)

[0116] These measurement results and calculation results are shown in Table 5.

[0117] [Table 5]

[0118] The following discusses the measurement results.

[0118] The composites using alumina particles from Samples No. 1, 3 to 6, which meet the requirements of the embodiments of this invention, exhibit excellent thermal properties (thermal diffusivity, thermal conductivity). On the other hand, the composites using alumina particles from Sample No. 2, which do not meet the requirements of the embodiments of this invention, have poor thermal properties.

[0119] (7) Thermal diffusivity and thermal conductivity of alumina particles

[0119] For samples No. 1 and 3 to 5, the thermal diffusivity and thermal conductivity of a single alumina particle were further measured. In the embodiments of this specification, the thermal diffusivity of a single alumina particle was successfully measured.

[0119] The method for determining the thermal diffusivity of an alumina particle is to apply temperature wave analysis (TWA) to microscale measurement. Figure 2 shows a conceptual diagram of the apparatus used to determine the thermal diffusivity of an alumina particle.

[0120] A thermoelectric microsensor is pressed onto a sample 70 (an alumina particle). The thermal diffusivity is determined by measuring the frequency dependence of the phase difference caused by the propagation of the temperature wave generated by the alternating current heating of the function generator via a resistive micro-heater using a biphase lock-in amplifier 80. The diameter of the sample 70 is approximately 110 μm, the thickness of the sample 70 is 67 μm, the measurement frequency is 2.7 kHz to 4.9 kHz, and the sensor size is 8 μm × 9 μm.

[0120] In addition, the thermal conductivity was obtained from the measured thermal diffusivity using the following formula (5). The specific heat was 0.779 kJ / kg‧K, and the density was the value recorded in Table 4.

[0120] Thermal conductivity = thermal diffusivity × specific heat × density (5)

[0121] These measurement results and calculation results are shown in Table 6.

[0122] [Table 6]

[0123] The alumina particles in samples No. 1 and 3 to 5 showed values ​​of thermal diffusivity and thermal conductivity similar to those measured for monocrystalline α-alumina blocks. Furthermore, the thermal conductivity of polycrystalline α-alumina particles measured in the preliminary experiment was 15 W / mK. It was found that by using monocrystalline α-alumina particles, approximately twice the thermal conductivity was achieved compared to polycrystalline α-alumina.

[0124] (8) Determination of intraparticle defect rate

[0124] Determine the intraparticle defect rate of alumina particles in samples No.1 to 4 and 6.

[0124] X-ray transmission images of alumina particles in a thinly dispersed state on a substrate within a 0.7 mm × 0.7 mm area were obtained using a high-sensitivity X-ray CT scanner (model: nano3DX) manufactured by Rigaku Co., Ltd. Defects in all 20 or more alumina particles in the obtained X-ray transmission images were confirmed. Particle defects refer to voids or amorphous layers existing within the particles, and are observed as light gray areas within the defect-free portions (non-defect portions: observed as white areas) of the alumina particles in the X-ray transmission images.

[0124] Using the image processing software ImageJ (made by the National Institute of Health), the area SA of the entire alumina particle, the area SB of the non-defect portion within the alumina particle, and the area SC of the defect portion within the alumina particle were obtained from the X-ray transmission image. Furthermore, the equation SA = SB + SC holds true for each area.

[0124] Then, SC / SA is expressed as a percentage and is used as the intraparticle defect rate (%).

[0125] The following describes the image processing method used to obtain the areas SA, SB and SC.

[0125] Using the image processing software "Image J", an image of an alumina particle containing voids was cut out from an image obtained from an X-ray transmission photograph and binary converted. The area SA of the entire alumina particle was obtained using the "Analyze Particles" function. In the image obtained from the X-ray transmission photograph, the brightness of the non-defective portion of the alumina particle is the lowest, followed by the brightness of the defective portion within the particle, and then the brightness of the area surrounding the alumina particle (background) is the highest. Therefore, during binary conversion, it is necessary to convert the brightness of the defective portion and the background to the same level. This image processing is performed by adjusting the contrast and the "Convolve" filter. The area of ​​the region after removing the light gray portion belonging to the defective portion from the alumina particle (i.e., the area SB of the non-defective portion) was measured.

[0126] In the particle analysis command, measure the area SA of the alumina particle when it includes both the non-defect portion (area SB) and the defect portion (area SC) inside the alumina particle (with Include Holes enabled and confirmed), and the area when it does not include the defect portion inside the alumina particle (i.e., the area SB of the non-defect portion) (with Include Holes disabled). Calculate the area SC (=SA-SB) from the obtained areas SA and SB.

[0127] A lower intraparticle defect rate (SC / SA) means fewer voids or amorphous layers within the alumina particles. Therefore, a low intraparticle defect rate is preferable for alumina particles, especially below 20%, and more preferably below 15%. This allows for a further reduction in the dielectric loss of resin compositions when alumina particles are used as fillers.

[0128] The calculation results are shown in Table 7.

[0129] [Table 7]

[0130] (9) Determination of the aspect ratio of impurity particles

[0130] X-ray transmission images of alumina particles in samples No. 1 to 6 in the range of 0.7 mm × 0.7 mm were obtained using a high-sensitivity X-ray CT scanner (model: nano3DX) manufactured by Rigaku Co., Ltd.

[0130] Taking all alumina particles in the X-ray transmission image as the evaluation object, the aspect ratio of all alumina particles in the evaluation object was obtained by using the image processing software ImageJ (manufactured by the National Institute of Health). In addition, the aspect ratio was obtained by taking the particle size of the alumina particle in the direction orthogonal to the maximum diameter as the minimum diameter, and expressing it as the ratio of the maximum diameter to the minimum diameter.

[0131] Impurity particles contained in the alumina particles of the evaluation object are defined as those that are extracted from the alumina particles of the evaluation object in the top 1% of terms, starting from the highest aspect ratio. Then, the average aspect ratio of the impurity particles is calculated.

[0132] The average aspect ratio of the impurity particles is preferably greater than 1.2 and less than 5.0, and preferably less than 3 or less or less than 2.5. Since the alumina particles contain a small number of impurity particles (slender particles with high aspect ratio), when used as a filler in resin compositions, the filling rate of alumina particles can be increased, and the dielectric loss of the resin composition can be further reduced.

[0133] The measurement results are shown in Table 8.

[0134] [Table 8]

[0135] (10) Determination of the length L1 of the outer edge of the alumina particles and the total length L2 of the boundary line inside the particles.

[0135] Alumina particles from samples No. 1 to 6 were used to prepare specimens for cross-sectional observation. In the preparation of the specimens for cross-sectional observation, alumina particles were embedded in resin, and the resin and alumina particles were cut using a diamond cutter. Then, Pt was deposited as a protective film on the cross-section, and the cross-section was modulated using Ar ion polishing. It was then fixed to the SEM specimen stage with Cu double-sided tape, and SEM-EBSD measurements were performed without evaporation. The observation position was determined by ensuring that two or more alumina particles were completely within the observation area (i.e., two or more alumina particles did not contact the border of the observation area). Measurements were performed using α-alumina particles.

[0136] The following equipment was used for sample pretreatment and EBSD determination.

[0136] ‧Using equipment

[0136] Ion polishing device: IM-4000 (manufactured by Hitachi, Ltd.)

[0136] Ion sputtering apparatus: E-1030 (manufactured by Hitachi, Ltd.)

[0136] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by Japan Electronics Corporation)

[0136] Backscattered electron diffraction device: Digiview V (TSL manufacturing)

[0137] The conditions for EBSD determination are as follows.

[0137] ‧Measurement area: 500.0μm × 400.0μm

[0137] ‧Accelerating voltage: 20.0kV

[0137] ‧Magnification:×500

[0137] ‧Low vacuum: 30Pa

[0138] In the obtained EBSD image, select two or more alumina particles that do not contact the border of the observation area, and calculate the average value of the length L1 of the outer edge of each alumina particle using the image processing software ImageJ (manufactured by the National Institute of Health). Also calculate the total length L2 of the boundary lines. The "total length L2 of the boundary lines" is the sum of the boundary lines contained within the alumina particle, excluding the outer edge of the alumina particle. The total length L2 of the boundary lines is obtained by adding the total length of the grain boundaries within the alumina particle to the total length of the inner wall of the cavity (if there is a cavity within the alumina particle).

[0139] The ratio of the total length L2 of the boundary line to the length L1 of the outer edge (L2 / L1) is expressed as a percentage (%). The more grain boundaries and / or cavities inside the alumina particles, the larger the value of L2 / L1 (%).

[0139] The fewer grain boundaries and cavities within the alumina particles, the lower the dielectric loss of the alumina particles. That is, the smaller the L2 / L1 value, the lower the dielectric loss of the alumina particles. It is especially preferable that the L2 / L1 of the alumina particles is 100% or less, which can further reduce the dielectric loss of the resin composition when used as a filler in resin compositions. It is more preferably 80% or less (L2 / L1), even more preferably 50% or less, and most preferably 40% or less.

[0140] Observations of the particles' interiors showed that the comparative example particles had voids of about tens of μm, and even grain boundaries were observed in addition to tiny voids of several μm. The particles of the embodiment had tiny voids of several μm.

[0141] The measurement results are shown in Table 9.

[0142] [Table 9]

[0143] (11) Determination of the number of contact points between alumina particles in the resin composition (complex)

[0143] Polyimide resin (manufactured by Ube Industries, clear varnish A) and alumina particles of samples No. 2 to 5 were mixed at a volume ratio of 20:80. A film was prepared from the mixture using a bar coater, and the film was fired in an N2 gas environment to prepare an alumina-resin composite. The cross-section along the thickness direction of the composite was exposed by Ar ion milling, and this cross-section was observed.

[0144] The following apparatus and conditions were used to cut and observe the cross-section.

[0144] ‧ Section cutting: Creating a section using a grinding device.

[0144] Device: E-3500 (made by Hitachi)

[0144] ‧Sectional observation: Observed using a laser scanning microscopy (LSM).

[0144] Equipment: OLS4000 (Olympus)

[0144] Measurement mode: Magnification 20x

[0144] Resolution: 1024×1942

[0144] Measurement range: approximately 650 μm in the x-direction and approximately 750 μm in the y-direction

[0145] The number of contact points between alumina particles in the resin composition was confirmed using cross-sectional LSM images. In the cross-sectional LSM images, alumina particles were observed to be gray, and the resin was white. The number of points where the gray alumina particles were in direct contact with each other was taken as the number of contact points between alumina particles, and the number of contact points was counted.

[0145] The number of contact points can be used as an indicator of the degree of particle dispersion. If the dispersion is uniform, the number of contact points between alumina particles will decrease.

[0145] Furthermore, in the resin composition, when the number of junctions between adjacent alumina particles (i.e., the number of interfaces between particles) increases, the dielectric loss of the resin composition will increase.

[0146] In the observation range of 650μm×750μm, the number of contact points between alumina particles is preferably 40 or less (equivalent to 82 or less per 1mm2 observation range), which can further reduce the dielectric loss of the resin composition when used as a filler in the resin composition.

[0146] Based on the observation range of 1 mm2, the number of contact points between alumina particles is preferably 65 or less per mm2, and even more preferably 50 or less per mm2 or 30 or less per mm2.

[0147] The measurement results are shown in Table 10.

[0148] [Table 10]

[0149] (12) Determination of BET specific surface area of ​​alumina particles

[0149] Determine the BET specific surface area of ​​alumina particles in samples No.1 to No.6.

[0149] The method for determining the specific surface area of ​​powders (solids) by gas adsorption is based on JIS Z 8830:2013, using Kr as the adsorbed gas. During the measurement, 1g of alumina particles are placed in a sample tube, and adsorption-desorption isotherms are obtained. The Kr-BET specific surface area S1 (m2 / g) is calculated by multi-point plotting.

[0149] In addition, the ratio (S1 / S2) of the Kr-BET specific surface area S1 (m2 / g) to the ideal sphere area S2 (m2) obtained from D50 is obtained. The ideal sphere area refers to the surface area of ​​a true spherical particle with diameter D50, and is obtained from the surface area formula of a sphere (4πr2).

[0150] If the surface of the alumina particles has fewer irregularities, the interface with the resin will be smaller when used as a filler in a resin composition, resulting in a reduction in the dielectric loss of the resin composition. Both the BET specific surface area and the ratio of the Kr-BET specific surface area to the area of ​​an ideal sphere (S1 / S2) are indicators of the degree of irregularity of the particles.

[0151] The BET specific surface area S1 obtained by the Kr adsorption method is preferably 0.10 m2 / g or less, which can further reduce the dielectric loss of the resin composition when used as a filler in the resin composition. The Kr-BET specific surface area S1 is more preferably 0.08 m2 / g or less, and particularly preferably 0.07 m2 / g or less.

[0151] The specific surface area S1 of Kr-BET can be 0.01m2 / g or more, or 0.02m2 / g or more.

[0152] Furthermore, the ratio of Kr-BET specific surface area to the area of ​​an ideal sphere (S1 / S2) is preferably 95 × 10⁵ / g or less, which can further reduce the dielectric loss of the resin composition when used as a filler in a resin composition. (S1 / S2) is more preferably 40 × 10⁵ / g or less, and particularly preferably 20 × 10⁵ / g or less.

[0153] The measurement results and calculation results are shown in Table 11.

[0154] [Table 11]

[0155] (13) Determination of moisture content entrained in alumina particles and resin

[0155] The moisture content entrained in the alumina particles of samples No. 2 to 3 and No. 5 to 6 was determined as follows. 1 g of alumina particles was pre-weighed and left in the atmosphere for 24 hours; the mass was measured and recorded as the pre-measurement mass Ma1 (g). Then, the alumina particles were dried in a vacuum dryer for 24 hours; the mass was measured and recorded as the post-measurement mass Ma2 (g). The moisture content entrained in the alumina particles, ΔMa (ppm), was defined as (pre-measurement mass Ma1 - post-measurement mass Ma2) / (pre-measurement mass Ma1) × 10⁶.

[0156] The amount of water entrained in the resin is determined as follows.

[0156] A film was prepared from polyimide resin (manufactured by Ube Industries, clear varnish A) using a rod coater, and the film was fired in an N2 gas environment to produce a resin film with a thickness of approximately 300 μm. A 1 cm × 1 cm sample piece was cut from the resin film. The sample piece was left in the atmosphere for 24 hours, and its mass was measured as the mass before measurement Mr1 (g). Then, the polyimide resin was dried in a vacuum dryer for 24 hours, and its mass was measured as the mass after measurement Mr2 (g). The water content ΔMr (ppm) entrained in the polyimide resin was defined as (mass before measurement Mr1 - mass after measurement Mr2) / (mass before measurement Mr1) × 106.

[0157] The ratio (ΔMa / ΔMr) of the water content ΔMa entrained by the alumina particles to the water content ΔMr entrained by the polyimide resin is obtained. ΔMa / ΔMr is preferably 0.2 or less, and more preferably 0.1 or less. Since the water content ΔMa entrained by the alumina particles is extremely small compared to the water content entrained by the polyimide resin, the dielectric loss of the resin composition can be further reduced when alumina particles are used as a filler in the resin composition.

[0158] The calculation results are shown in Table 12.

[0159] [Table 12]

[0160] (14) Determination of dielectric loss of resin composition (composite)

[0160] Polyimide resin (manufactured by Ube Industries, clear varnish A) and alumina particles of samples No. 1 to 6 were mixed at a volume ratio of 20:80. A film was made from the mixture using a bar coater, and the film was fired in an N2 gas environment to produce an alumina-resin composite with a thickness of 800 μm.

[0161] The dielectric loss of the composite was measured under the following conditions.

[0161] ‧Measurement device: HP8510C network analyzer (manufactured by Agilent Technologies)

[0161] ‧Scan signal generator: HP83651A, HP8517B (both manufactured by Agilent Technologies)

[0161] ‧Test piece size: 110mm × 60mm

[0161] ‧Measurement frequency: 10GHz

[0161] ‧Test environment: 22℃ / 59% RH

[0162] The measurement results are shown in Table 13.

[0163] [Table 13]

[0164] No.1 and No.3 to No.6 have low dielectric loss, while No.2 has high dielectric loss.

[0165] (15) Determination of pore volume of alumina particles

[0165] Determine the pore volume of alumina particles in samples No.1 to No.6.

[0165] The method for determining the specific surface area of ​​powders (solids) by gas adsorption is based on JIS Z 8830:2013, and Kr is used as the adsorbed gas. During the measurement, 1g of alumina particles are placed in a sample tube, and adsorption-desorption isotherms are obtained. The pore volume is determined by analyzing the pore volume distribution using a multi-point plotting method.

[0166] When determining the pore volume of alumina particles by krypton adsorption, the pore volume is preferably below 0.0003 cm3 / g.

[0166] Both pore volume and Kr-BET specific surface area are indicators of the surface roughness of particles. By controlling the pore volume of the first alumina particles within the above range, the formability of the mixture can be further improved.

[0167] The pore volume is preferably 0.00009 cm3 / g or less, and particularly preferably 0.00007 cm3 / g or less. The lower limit of the pore volume is not particularly limited, for example, it may be 0.000001 cm3 / g or more, and further may be 0.000005 cm3 / g or more.

[0168] The measurement results are shown in Table 14.

[0169] [Table 14]

Claims

1. An alumina particle having a cumulative particle size distribution where 50% of the particles from the microparticle side have a particle size D50 exceeding 100 μm, an α-oxidation rate of over 90%, and the α-alumina being a single crystal.

2. The alumina particles as described in claim 1 have a Na content of less than 800 ppm.

3. The alumina particles as described in claim 1, wherein the cumulative particle size distribution, from the microparticle side, has a cumulative particle size D10 of 70 to 135 μm.

4. The alumina particles as described in claim 1 have a cumulative particle size distribution in which 90% of the particle size D90 is 130 to 200 μm.

5. The alumina particles as described in claim 1 have a sphericity of 0.90 to 1.

00.

6. The alumina particles as described in claim 1 have a density of 3.80 g / cm3 or higher.

7. A resin composition comprising a resin and alumina particles as described in any one of claims 1 to 6.

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