Alumina particles and resin composition using same

Abstract

The alumina particles have a particle diameter D50 of more than 30.0 [mu] m and 55.0 [mu] m or less at 50% of the cumulative particle size distribution from the particle side, an alphalation rate of 60.0% or more, and a ratio (L2 / L1) of a total length L2 of boundary lines inside the alumina particles to a length L1 of an outer edge of the alumina particles of 1.0% or more and 90.0% or less. The purpose of the present invention is to provide alumina particles which, when used as a filler for a resin composition, can reduce the viscosity of a mixture with a resin and can form a resin composition having low dielectric loss.

Description

Technical Field

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

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

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

[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 manufacturing the alumina particles, a method of melting a pulverized product of fused alumina by a flame melting method and rapidly cooling by spraying water into the furnace is disclosed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2009 / 133904 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Since the resin composition used as the heat dissipation material is disposed near the electronic component, a low dielectric loss is desired. Therefore, alumina particles capable of forming a resin composition with a low dielectric loss are required.

[0010] In addition, in recent years, due to the miniaturization of electronic devices and the high integration of ICs, the gap between the electronic component and the heat sink has become narrower. The resin composition disposed between the electronic component and the heat sink is required to be able to be molded in this narrow gap (that is, to have excellent moldability). Therefore, it is desired to suppress the viscosity of the mixture of the alumina particles and the resin to a low level, and alumina particles capable of reducing the viscosity of the mixture are required.

[0011] In order to meet these requirements, alumina particles capable of reducing the viscosity of the mixture with the resin and capable of forming a resin composition with a low dielectric loss are required.

[0012] However, regarding the alumina particles described in Patent Document 1, no study has been made on forming a resin composition with a low dielectric loss.

[0013] In view of such a situation, an object of an embodiment of the present invention is to provide alumina particles that are used as fillers for resin compositions, can reduce the viscosity of a mixture with a resin, and can form a resin composition with low dielectric loss. Further, an object of another embodiment of the present invention is to provide a resin composition using such alumina particles.

[0014] Means for Solving the Problem

[0015] In Mode 1 of the present invention, the alumina particles have a cumulative particle size distribution such that the particle size D50 at which the cumulative number from the fine particle side reaches 50% is greater than 30.0 μm and 55.0 μm or less.

[0016] The α - conversion rate is 60.0% or more.

[0017] The ratio (L2 / L1) of the total length L2 of the boundary lines inside the alumina particles to the length L1 of the outer edge of the alumina particles is 1.0% or more and 90.0% or less.

[0018] In Mode 2 of the present invention, the alumina particles are as described in Mode 1, and the crystal defect rate is less than 20.0%.

[0019] In Mode 3 of the present invention, the alumina particles are as described in Mode 1 or 2, and the roundness is 0.85 or more.

[0020] In Mode 4 of the present invention, the alumina particles are as described in any one of Modes 1 to 3 and satisfy the following formula (1).

[0021] 3.00 ≤ D50 × SA × AD ≤ 25.00 (1)

[0022] Wherein, D50 is the aforementioned particle size D50 (μm).

[0023] SA is the specific surface area of the alumina particles (m 2 / g).

[0024] AD is the apparent density of the alumina particles (g / cm 3 ).

[0025] In Mode 5 of the present invention, the alumina particles are as described in any one of Modes 1 to 4, and the moisture content is less than 62 ppm.

[0026] In Mode 6 of the present invention, the resin composition contains a resin and the alumina particles as described in any one of Modes 1 to 5.

[0027] Effects of the Invention

[0028] By using the alumina particles according to an embodiment of the present invention as a filler, it is possible to reduce the viscosity of the mixture with the resin and obtain a resin composition having a low dielectric loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Figure 1 It is a schematic diagram of an apparatus for carrying out a flame melting process in a method for manufacturing alumina particles.

[0030] Figure 2 Figure 2 It is a schematic diagram for explaining a calculation method of the particle defect rate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] [Embodiment 1: Alumina Particles]

[0032] The alumina particles according to Embodiment 1 of the present invention are used for mixing with a resin as a filler for a resin composition. Regarding the alumina particles, the particle size D50 of the cumulative 50% in terms of the number from the fine particle side of the cumulative particle size distribution is greater than 30.0 μm and 55.0 μm or less, the α - conversion rate is 60.0% or more, and the ratio (L2 / L1) of the total length L2 of the boundary lines inside the alumina particles to the length L1 of the outer edge of the alumina particles is 1.0% or more and 90.0% or less.

[0033] The inventors of the present application have found for the first time that alumina particles satisfying the above characteristics can reduce the dielectric loss (tanδ) of a resin composition using the alumina particles as a filler, and thus completed the invention according to this embodiment.

[0034] Regarding the characteristics of the alumina particles according to Embodiment 1, they will be described in detail below.

[0035] (Particle Size D50 of the Cumulative 50% in Terms of the Number from the Fine Particle Side of the Cumulative Particle Size Distribution)

[0036] Embodiment 1 of the present invention targets alumina particles in which the particle size 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 30.0 μm and 55.0 μm or less. The particle size D50 of the alumina particles is preferably 35.0 μm or more and 50.0 μm or less.

[0037] ​​​​Regarding the D50 of the alumina particles, the particle size distribution of the alumina particles is measured based on the principle of dynamic image analysis in accordance with ISO 13322-2. 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 determined. As the measuring device, for example, CAMSIZER (manufactured by VERDER Scientific) is used. The sample is sequentially introduced into the device, and the particles passing in front of the camera are measured while dispersing the aggregated particles with dry air.

[0038] (α conversion rate)

[0039] Regarding the alumina particles according to Embodiment 1 of the present invention, the α conversion rate, which is an index of the content of α-alumina, is 60.0% or more, preferably 65.0% or more. The upper limit of the α conversion rate is not particularly limited and may be 100% or less, and may be 99.6% or less. Since the thermal conductivity of α-alumina is high, by increasing the content of α-alumina in the alumina particles, the thermal conductivity of the alumina particles can be increased.

[0040] In this specification, the so-called "α conversion rate" refers to the content ratio (volume %) of α-alumina with respect to all the alumina contained in the alumina particles.

[0041] Regarding the α conversion rate, the alumina particles are measured by powder X-ray diffraction method, and from 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 ) of the peaks formed due to 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 (2).

[0042] α conversion rate = I 25.6 / (I 25.6 +I 46 )×100 (%) (2)

[0043] It should be noted that the alumina particles according to Embodiment 1 of the present invention may also contain, for example, 40.0% or less of alumina other than α-alumina (δ-alumina, θ-alumina, etc.), which does not hinder the object of the present invention.

[0044] In addition, the alumina other than α-alumina can be contained in any manner. For example, α-alumina and alumina other than α-alumina can be simultaneously contained inside one alumina particle. In addition, it may be that some alumina particles contain only α-alumina, and other alumina particles contain only alumina other than α-alumina, and these alumina particles are mixed.

[0045] (Ratio of the total length L2 of the boundary lines inside the particle to the length L1 of the outer edge of the alumina particle)

[0046] The fewer the grain boundaries and voids inside the alumina particle, the lower the dielectric loss of the alumina particle. Therefore, as an index of the grain boundary content inside the alumina particle, 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 particle.

[0047] When the length of the outer edge of one alumina particle is set as L1 and the total length of the boundary lines possessed by the alumina particle is set as L2, the alumina particle with a small value of L2 / L1 can be said to be an alumina particle with a small content of boundary lines and a low dielectric loss. In particular, (L2 / L1) (%) is preferably 1.0% or more and 90.0% or less. When used as a filler for a resin composition, the dielectric loss of the resin composition can be further reduced. (L2 / L1) is more preferably 5.0% or more, further preferably 10.0% or more, particularly preferably 20.0% or more, more preferably 80.0% or less, further preferably 60.0% or less, still further preferably 50.0% or less, and particularly preferably 40.0% or less. In the case of using granulated raw material particles, polycrystalline raw material particles, and manufacturing alumina particles by the flame fusion method, the value of L2 / L1 becomes particularly large, and even if subsequent processes such as reheating are performed, it cannot be significantly reduced.

[0048] It should be noted that the "total length L2 of the boundary lines" is the sum of the boundary lines contained inside the alumina particle and does not include the outer edge of the alumina particle. The total length L2 of the boundary lines is obtained by adding the total length L3 of the grain boundaries inside the alumina particle and the total length L4 of the inner walls of the voids (when there are voids inside the alumina particle) (that is, L2 = L3 + L4).

[0049] The measurement of L1, L2, L3, and L4 is preferably performed on alumina particles formed of α-alumina.

[0050] (Particle internal defect rate)

[0051] When voids or amorphous layers (referred to as "defects of the particle") are contained inside the alumina particle, it becomes a cause for increasing the dielectric loss. Therefore, the particle internal defect rate of the alumina particle is preferably low, particularly preferably less than 20.0%, more preferably less than 12.0%, and particularly preferably 10.0% or less. Thereby, when the alumina particle is used as a filler for a resin composition, the dielectric loss of the resin composition can be further reduced.

[0052] Regarding the defect rate within the particles, for alumina particles in a thinly dispersed state on a substrate, X-ray transmission images are taken using X-ray CT scanning. For all over 20 alumina particles within the obtained X-ray transmission images, the defects of the particles are confirmed. The defects of the particles are observed as light gray portions inside the alumina particles in the X-ray transmission images of the alumina particles, within the non-defective portions (non-defective portions: observed as white portions) of the alumina particles.

[0053] For the X-ray transmission photographs, using image processing software or the like, the total area Sa of the alumina particles, the area Sb of the non-defective portions within the alumina particles, and the area Sc of the defective portions within the alumina particles are obtained. It should be noted that among the respective areas, the equation Sa = Sb + Sc holds.

[0054] And, Sc / Sa is expressed as a percentage and set as the defect rate within the particles (%).

[0055] (Satisfying formula (1): 3.00 ≤ D50 × SA × AD ≤ 25.00)

[0056] The following formula (1) is obtained by transforming a general formula representing the relationship between the particle size and the specific surface area.

[0057] 3.00 ≤ D50 × SA × AD ≤ 25.00 (1)

[0058] Among them, D50 is the aforementioned particle size D50 (μm),

[0059] SA is the specific surface area of the alumina particles (m 2 / g),

[0060] AD is the apparent density of the alumina particles (g / cm 3 ).

[0061] According to the general formula representing the relationship between the particle size and the specific surface area, when the alumina particles are spherical, the surface of the alumina particles is smooth, and the apparent density of the alumina particles is the theoretical density (3.98 g / cm 3 ), the value of the middle term (D50 × SA × AD) of formula (1) becomes 6. When the specific surface area SA becomes larger, the value of the middle term becomes larger, and when the apparent density AD is less than the theoretical density, the value of the middle term becomes smaller.

[0062] The alumina particles according to the present embodiment preferably satisfy the above formula (1) (that is, the value of D50 × SA × AD of the alumina particles is 3.00 or more and 25.00 or less), which can further reduce the viscosity and dielectric loss (tanδ) of the resin composition using the alumina particles as a filler.

[0063] Although the reason why the value of D50×SA×AD of alumina particles can affect the viscosity and dielectric loss of the resin composition containing alumina particles is uncertain, it is considered that the apparent density AD and specific surface area SA of alumina particles affect the viscosity and dielectric loss of the resin composition. For example, when the apparent density AD of alumina particles is too low, the dielectric loss of the resin composition increases. It is speculated that if the specific surface area SA of alumina particles is too high, the interface with the resin increases, so the viscosity and dielectric loss of the resin composition become high.

[0064] The value of D50×SA×AD of alumina particles is more preferably 21.50 or less, further preferably 18.00 or less, more preferably 3.50 or more, and further preferably 4.00 or more.

[0065] The calculation of formula (1) uses the values obtained under the following conditions.

[0066] The particle size D50 (μm) is measured by the above-mentioned measurement method, and the value rounded to one decimal place is used.

[0067] Specific surface area SA (m 2 / g) is measured by the method described below, and the value rounded to two decimal places is used.

[0068] Apparent density AD (g / cm 3 ) is measured by the method described below, and the value rounded to two decimal places is used.

[0069] (Specific surface area SA of alumina particles)

[0070] The specific surface area SA of alumina particles is the BET specific surface area measured by the nitrogen adsorption method based on JIS Z 8830:2013.

[0071] The specific surface area becomes an index indicating the degree of unevenness of the particles. If the surface of the alumina particles has less unevenness, when used as a filler for the resin composition, the interface with the resin becomes less, and as a result, it can be expected to reduce the viscosity and dielectric loss of the resin composition.

[0072] The specific surface area SA of alumina particles is preferably 5.0 m 2 / g or less, more preferably 2.0 m 2 / g or less, further preferably 1.0 m 2 / g or less, particularly preferably 0.5 m 2 / g or less.

[0073] The specific surface area SA of alumina particles can be 0.005 m 2 / g or more, and can also be 0.010 m 2 / g or more.

[0074] (Apparent density AD of alumina particles)

[0075] The apparent density AD of alumina particles is measured by the pycnometer method in accordance with JIS R 1620 - 1995. The number of measurements is set to be more than 5 times, and the average value is used. For example, AccuPyc 1330 (Micromeritics) can be used during the measurement.

[0076] The apparent density of alumina particles is preferably 3.60 g / cm 3 or more and 3.96 g / cm 3 or less, more preferably 3.95 g / cm 3 or less, further preferably 3.93 g / cm 3 or less, further preferably 3.65 g / cm 3 or more and 3.90 g / cm 3 or less, particularly preferably 3.70 g / cm 3 or more and 3.87 g / cm 3 or less. If the density is within the above range, when used as a filler for resin compositions, it is easy to obtain a resin composition with low viscosity and low dielectric loss.

[0077] (True roundness of alumina particles)

[0078] The true roundness of alumina particles is preferably 0.90 or more, more preferably 0.91 or more and 1.00 or less. When within this range, the kneadability with the resin can be made good, and the fluidity of the kneaded composite can be improved. Furthermore, the wear of other components caused by alumina particles can also be reduced. Therefore, it is suitable as a filler for resin compositions of electronic components.

[0079] It should be noted that the following aspects should be paid attention to: Since alumina particles are usually hard particles, it is difficult to obtain alumina particles with a true roundness of 0.90 or more by simply making alumina particles with low true roundness collide with each other or crushing alumina particles with low true roundness. In order to improve the true roundness of alumina particles by collision and crushing, it is necessary to carry out collision and crushing for a long time. In this case, a large amount of fine powder of alumina is generated, which may cause the D50 of alumina particles to be excessively reduced, or the viscosity and dielectric loss of the resin composition to increase. In addition, the new hydrophilic surface generated on the surface of alumina particles due to crushing will reduce the mixing property with the resin of alumina particles, so it may not be suitable as a filler for resin compositions. Moreover, on the aforementioned hydrophilic surface, there are many minute defects, and the dielectric loss may increase.

[0080] The true roundness (SPHT) is analyzed in accordance with ISO 9276 - 6. According to SPHT = 4πA / P 2Find out. 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 projected image.

[0081] The true 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.

[0082] (Water content of alumina particles)

[0083] When the water content of the alumina particles (the water content contained in the alumina particles) is high, the viscosity and dielectric loss of the resin composition made using the alumina particles increase. In addition, if the amount of water brought in by the alumina particles is large, the water will seep out of the resin, which may have an adverse effect on electronic components and the like arranged adjacent to the resin composition. Furthermore, if the amount of water brought in by the alumina particles is large, the kneadability with the resin deteriorates and the viscosity may increase. Therefore, the less water content brought in by the alumina particles, the better.

[0084] The water content of the alumina particles is preferably 62 ppm or less, more preferably 60 ppm or less, further preferably 55 ppm or less, and particularly preferably 50 ppm or less.

[0085] The water content of the alumina particles is measured based on the Karl Fischer method in accordance with the description in JIS K 0068:2001 "Methods for Determination of Water in Chemical Products".

[0086] As described above, the alumina particles according to Embodiment 1 are used as a filler for the resin composition, whereby a resin composition with low dielectric loss can be manufactured.

[0087] When the alumina particles according to Embodiment 1 are further mixed (kneaded) with the resin, the viscosity of the mixture can be suppressed to be low. Therefore, even when the gap between the electronic component and the radiator is narrow, the resin composition can be appropriately arranged in the narrow gap.

[0088] [Manufacturing method of alumina particles]

[0089] The manufacturing method of the alumina particles according to Embodiment 1 of the present invention will be described.

[0090] In the raw materials of the alumina particles, alumina raw material particles mainly formed of single crystal α-alumina and having a cumulative particle size distribution with a cumulative 50% particle size D50 from the fine particle side greater than 29.0 μm and 70.0 μm or less are mainly used. Then, the alumina particles are manufactured from the alumina raw material particles by the flame fusion method.

[0091] Note that the D50 of the obtained alumina particles can also be controlled by the conditions (such as the supply amounts of alumina raw material particles, fuel gas, and oxygen) during the flame melting process.

[0092] So far, the general view is that when raw material particles are put into a flame, they will melt and the crystal structure of the raw material particles is reset. Therefore, the crystal structure characteristics of the raw material particles will not affect the crystal structure of the particles spheroidized by the flame. However, unexpectedly, it was found that if single crystal particles are used as the raw material particles, the crystal structure characteristics of the raw material particles can also be inherited after spheroidization.

[0093] In the flame melting process, for example, use Figure 1 a device as shown. Through the flame melting process, alumina particles with an α-conversion rate of 60.0% or more and satisfying the above formula (1) can be obtained.

[0094] In order to use single crystal alumina raw material particles and effectively utilize the crystal structure characteristics of single crystal alumina after spheroidization, the particle size of the used alumina raw material particles, the supply rate of the alumina raw material particles into the flame melting furnace of the device, the intensity of the flame, the distance between the flame and the alumina raw material particles, etc. are controlled.

[0095] In order to manufacture alumina particles with a D50 greater than 30.0 μm and 55.0 μm or less, alumina raw material particles with a D50 greater than 29.0 μm and 70.0 μm or less, for example, are used. The D50 of the alumina raw material particles is preferably 32.0 μm or more and 68.0 μm or less, for example, 37.0 μm.

[0096] Note that even if the D50 of the alumina raw material particles is greater than 29.0 μm and 70.0 μm or less, for each alumina raw material particle, particles with a particle size of 29.0 μm or less and particles with a size greater than 70.0 μm may be included. Therefore, the obtained alumina particles may contain polycrystalline α-alumina and / or alumina other than α-alumina, etc. However, by making the D50 of the alumina raw material particles greater than 29.0 μm and 70.0 μm or less, the content of polycrystalline α-alumina and / or alumina other than α-alumina can be suppressed to a small amount within the tolerance of the present invention.

[0097] In addition, conventionally, a method of manufacturing alumina particles using granulated raw material particles or polycrystalline raw material particles by the flame melting method has been known, but a large amount of grain boundaries and internal voids may be contained inside the obtained alumina particles. In the present invention, since single crystal α-alumina itself without granulation is used as the alumina raw material particles, alumina particles with a small L2 / L1 value can be obtained.

[0098] The D50 of the alumina raw material particles can also be measured by the same method as the method for measuring the D50 of the above-mentioned alumina particles.

[0099] In the case where 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 polycrystalline according to whether there are clear grain boundaries in the alumina particles.

[0100] The fact that α-alumina is single crystal can also be confirmed by the Debye-Scherrer method.

[0101] As the raw material of the 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 crushing these raw materials and sieving them with a sieve of the desired mesh number, alumina raw material particles with a specified D50 can be prepared.

[0102] The alumina raw material particles may contain a small amount (for example, about 10% by mass or less) of alumina other than α-alumina (δ-alumina, θ-alumina, etc.), and in addition, may contain a small amount (for example, about 10% by mass or less) of polycrystalline α-alumina together with single-crystal α-alumina, which does not hinder the purpose of the present invention.

[0103] In the flame fusion process, the supply amounts of the alumina raw material particles, fuel gas, and oxygen preferably satisfy the following formulas (3) and (4).

[0104] 0.625 ≤ R / F (kg / Nm 3 ) ≤ 17.000 (3)

[0105] 0.125 ≤ R / S (kg / Nm 3 ) ≤ 3.400 (4)

[0106] Wherein, F is the supply amount of the fuel gas (Nm 3 / h), S is the supply amount of oxygen (Nm 3 / h), and R is the supply amount of the alumina raw material particles (kg / h).

[0107] It should be noted that the supply amount of oxygen (S) is the sum of the supply amount of combustion oxygen and the supply amount of carrier oxygen. The carrier oxygen is mainly for transporting the alumina raw material particles, but after transportation, it is used for combustion in the same way as the combustion oxygen.

[0108] As defined in formula (3), 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 / Nm 3 or more and 17.000 kg / Nm 3 or less. In addition, as defined in formula (4), the ratio (R / S) of the supply amount of alumina raw material particles to the supply amount of oxygen is preferably 0.125 kg / Nm 3 or more and 3.400 kg / Nm 3 or less.

[0109] The supply amount F (Nm 3 / h) of the fuel gas and the supply amount S (Nm 3 / h) of oxygen are factors that determine the flame intensity in the furnace during the flame melting process. Both R / F and R / S are indicators of the relationship between the flame intensity in the furnace and the supply amount of alumina raw material particles during the flame melting process.

[0110] When R / F and R / S increase, the supply amount of alumina raw material particles is large, and the energy provided by the flame to each alumina raw material particle becomes small (i.e., the melting of alumina raw material particles is inhibited).

[0111] When R / F and R / S decrease, the supply amount of alumina raw material particles is small, and the energy provided by the flame to each alumina raw material particle becomes large (i.e., the melting of alumina raw material particles is promoted).

[0112] Therefore, controlling R / F and R / S is a method of controlling the melting state of alumina raw material particles in the flame melting process. When R / F and R / S are within their respective preferred ranges, spheroidization can be carried out in the flame melting process while effectively utilizing the crystal structure characteristics of the raw material particles of alumina raw material particles.

[0113] R / F is more preferably 1.000 kg / Nm 3 or more and 10.000 kg / Nm 3 or less, and particularly preferably 2.000 kg / Nm 3 or more and 10.000 kg / Nm 3 or less.

[0114] R / S is more preferably 0.300 kg / Nm 3 or more and 3.000 kg / Nm 3 or less, and particularly preferably 0.500 kg / Nm 3 or more and 3.000 kg / Nm 3 or less.

[0115] In addition, the supply amount F of the fuel gas is preferably less than 20 Nm3 per hour. By adjusting the supply amount of the fuel gas, the flame length can be changed. The more the supply amount of the fuel gas, the longer the flame length, and the longer the residence time of the particles in the flame. The less the supply amount of the fuel gas, the shorter the flame length, and the residence time of the particles in the flame can be shortened. That is, the residence time of the alumina raw material particles in the flame can be changed, and the melting degree (time) of the alumina raw material particles in the flame can be changed. In addition, alumina particles with a small L2 / L1 value can be obtained while effectively utilizing the crystal structure characteristics of the raw material particles of the alumina raw material.

[0116] Examples of the fuel gas in the present invention include propane, butane, propylene, acetylene, hydrogen, etc. Propane (for example, liquefied propane gas (LPG)) is particularly preferred.

[0117] In the flame melting process, when solidifying the molten alumina raw material particles, in order to slow down the cooling rate, it can be passed through a region of 600°C to 1500°C, preferably a region of 800°C to 1400°C, more preferably a region of 1000°C to 1300°C. By passing through such a region and solidifying the spheroidized alumina particles, the α-conversion rate can be further improved.

[0118] As a subsequent process to the above flame melting process, a process of reheating before recovering the cooled and solidified alumina particles can also be added. By reheating the cooled and solidified alumina particles, the proportion of alumina other than α-alumina can be reduced, and the α-conversion rate can be further improved. As the temperature of the reheating process, for example, it is preferably 900°C or higher, more preferably 1000°C or higher. As the reheating method, external heating using a heater or the like, heating based on gas combustion again, etc. can be applied.

[0119] [Embodiment 2: Resin Composition]

[0120] By using the alumina particles according to Embodiment 1 of the present invention as a filler for a resin composition, a resin composition with low dielectric loss can be obtained. In addition, the alumina particles according to Embodiment 1 of the present invention can suppress the viscosity of the mixture formed by mixing with the resin to a relatively low level. The resin composition includes a resin and the alumina particles according to Embodiment 1 of the present invention.

[0121] The alumina particles according to Embodiment 1 of the present invention can reduce the dielectric loss without impairing the flexibility peculiar to the resin. Therefore, its mixing ratio 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.

[0122] The manufacturing method of the resin composition will be described.

[0123] Using a known method that is commonly used, the alumina particles related to Embodiment 1 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 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 polyolefin resin, acrylic resin, etc.), after mixing the alumina particles with the resin, it can be kneaded by a known method such as melt kneading, whereby the target resin composition is obtained.

[0124] 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 one type, or two or more types can be used in combination.

[0125] Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, 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, polyimide, polyamideimide, polymethacrylic acid, polymethacrylate such as polymethyl methacrylate, polyacrylic acid, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyether nitrile, polyether ketone, polyketone, liquid crystal polymer, silicone resin, ionomer, etc.

[0126] Examples of the thermoplastic elastomer include styrene-butadiene block copolymer or its hydride, styrene-isoprene block copolymer or its hydride, styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, etc.

[0127] Examples of the thermosetting resin include crosslinked rubbers, epoxy resins, phenolic resins, polyimide resins, unsaturated polyester resins, diallyl phthalate resins, etc. Specific examples of the crosslinked rubber 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.

[0128] From the viewpoints 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 silicone resins.

[0129] In addition, in these resin compositions, if necessary, known additives such as a plasticizer, a curing accelerator, a coupling agent, a filler, a pigment, a flame retardant, an antioxidant, a surfactant, a compatibilizer, a weathering agent, an anti-blocking agent, an antistatic agent, a leveling agent, and a mold release agent may be appropriately blended singly or in combination of two or more within a range not impairing the effects of the invention.

[0130] The alumina particles and the resin composition containing the same according to the present embodiment are particularly suitable for use as a heat dissipation material with low dielectric loss.

[0131] Examples

[0132] (1) Production of alumina particles

[0133] Alumina raw material particles (raw material particles 1, 3, and 4) formed of single crystal alumina and raw material particles (raw material particle 2) formed of polycrystalline alumina were prepared. The D50 of each raw material particle was measured and summarized in Table 1. The D50 of the alumina raw material particles was measured by the laser diffraction method. Laser light was irradiated onto a sample dispersed in water, and its diffraction was measured to determine the particle size. The measuring device used was a CILAS model 1090L.

[0134] [Table 1]

[0135] Aluminum oxide raw material particles D50 (μm) Raw material particle 1 37.0 Raw material particle 2 41.0 Raw material particle 3 64.0 Raw material particle 4 53.3

[0136] Use Figure 1In a device as shown, alumina particles were prepared from alumina raw material particles. The oxygen from the oxygen supply system 10 was split, with one part (carrier oxygen 11) supplied to the feeder 30 and the other part (combustion oxygen 12) supplied to the burner 41 of the flame melting furnace 40. The alumina raw material particles supplied to the feeder 30 were transported by the carrier oxygen 11 to the burner 41 of the flame melting furnace 40. In addition, fuel gas (LPG) was supplied from the gas supply system 20 to the burner 41. In the burner 41, a high-temperature flame of 2150 °C or higher was formed by the fuel gas and the combustion oxygen 12, and the alumina raw material particles dispersed in the carrier oxygen 11 were supplied thereto. Thus, in the flame melting furnace 40, the alumina raw material particles were melted and spheroidized. Then, the spheroidized alumina particles were classified by a cyclone separator 50, and the alumina particles captured by the cyclone separator 50 were obtained. It should be noted that the sample No. 6 was not subjected to flame melting.

[0137] The alumina raw material particles used, the supply amount F (Nm 3 / h) of the fuel gas as in the flame melting process, the supply amount S (Nm 3 / h) of oxygen, and the ratios of R / F and R / S of the supply amount R (kg / h) of the alumina raw material particles are summarized in Table 2. It should be noted that the supply amount of oxygen S is the sum of the supply amount of the carrier oxygen 11 and the supply amount of the combustion oxygen 12. The supply amount of the fuel gas F is less than 20 Nm 3 / h. In sample No. 6 in Table 2, the fact that the columns of R / F and R / S become "-" means that no flame melting is performed.

[0138] [Table 2]

[0139] Specimen number Aluminum oxide raw material particles <![CDATA[R / F(kg / Nm 3 )]]> <![CDATA[R / S(kg / Nm 3 )]]> Example 1 Raw material particle 1 5.714 1.143 Example 2 Raw material particle 1 3.810 0.762 Example 3 Raw material particle 1 3.125 0.625 Example 4 Raw material particle 1 2.857 0.571 Comparative example 5 Raw material particle 2 1.250 0.250 Comparative example 6 Raw material particle 1 - - Example 7 Raw material particle 1 3.333 0.667 Example 8 Raw material particle 3 1.111 0.222 Example 9 Raw material particle 1 2.222 0.444 Example 10 Raw material particle 4 2.222 0.444 Example 11 Raw material particle 4 3.333 0.667

[0140] Various measurements were performed on the obtained alumina particles (sample Nos. 1 to 11). It should be noted that "sample No. 6" of the alumina particles is the same as the raw material particles 1.

[0141] It should be noted that a part of the alumina particles of sample No. 5 was taken and subjected to additional heat treatment to investigate the change in the state of the alumina particles before and after heating. For the alumina particles of sample No. 5, they were in a powdery state before the heat treatment, and if heated at 1350 °C, the alumina particles were welded to each other. Therefore, the various measurements as described below could not be performed on the alumina particles after the heat treatment.

[0142] (2) Measurement of the particle size D50 and roundness of the alumina particles

[0143] The particle size distribution of the alumina particles was measured to obtain the particle size D50.

[0144] The particle size distribution and circularity of the alumina particles were measured using a CAMSIZER X2 (manufactured by VERDER Scientific) based on the principle of dynamic image analysis in accordance with ISO 13322-2. The measurement was performed 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 was weighed at 3 g and measured once. The same measurement was repeated three times, and the particle size distribution and circularity were analyzed based on the cumulative average of these results. The particle size was the equivalent circular diameter. The equivalent circular diameter refers to the diameter of a perfect circle that has the same area as the projected particle image. In addition, the basis for the particle size was set as volume.

[0145] The circularity (SPHT) was analyzed in accordance with ISO 9276-6. According to 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.

[0146] The particle size D50 and circularity of each alumina particle are shown in Table 3.

[0147] [Table 3]

[0148] Specimen number D50 (μm) Circularity Example 1 41.0 0.91 Example 2 42.0 0.93 Example 3 41.3 0.95 Example 4 39.1 0.95 Comparative example 5 41.4 0.95 Comparative example 6 38.0 0.85 Example 7 36.2 0.95 Example 8 51.7 0.95 Example 9 38.2 0.95 Example 10 49.6 0.94 Example 11 51.6 0.94

[0149] (3) Measurement of the apparent density AD of alumina particles

[0150] The apparent density AD of the alumina particles was measured.

[0151] The apparent density AD was measured in accordance with JIS R 1620-1995. The measurement method and conditions are as follows.

[0152] · Measurement method: Gas displacement method

[0153] · Drying of the sample: 200 °C, 8 hours or more

[0154] · Device used: AccuPyc 1330 (Micromeritics)

[0155] · Measurement conditions

[0156] Number of purge times: 10 times

[0157] Purge filling pressure: 15.0 psig

[0158] Number of measurements: 5 times

[0159] Measurement filling pressure: 15.0 psig

[0160] Equilibrium pressure: 0.005 psig / minute

[0161] Measurement after setting the precision: Yes

[0162] Deviation allowable error: 0.05%

[0163] Specimen unit size: 10 cm 3

[0164] The measurement results are shown in Table 4.

[0165] [Table 4]

[0166] Specimen number <![CDATA[Apparent density AD (g / cm 3 )]]> Example 1 3.84 Example 2 3.80 Example 3 3.70 Example 4 3.71 Comparative example 5 3.78 Comparative example 6 3.96 Example 7 3.69 Example 8 3.79 Example 9 3.74 Example 10 3.76 Example 11 3.83

[0167] (4) Measurement of the α - conversion rate of alumina particles

[0168] Measure the α - conversion rate of alumina particles. It should be noted that for sample number 6, the measurement was not carried out.

[0169] Regarding the α - conversion rate, the specimen of alumina particles was measured using a powder X - ray diffractometer (manufactured by Rigaku Corporation) 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.

[0170] 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 γ - phase, η - phase, χ - phase, κ - phase, θ - phase and δ - phase were calculated through the following formula (2).

[0171] α - conversion rate = I 25.6 / (I 25.6 +I 46 )×100 (%) (2)

[0172] The measurement results are shown in Table 5.

[0173] [Table 5]

[0174] Specimen number α - conversion rate (%) Example 1 99.6 Example 2 74.0 Example 3 87.0 Example 4 89.0 Comparative example 5 99.1 Example 7 98.5 Example 8 90.0 Example 9 100.0 Example 10 89.8 Example 11 89.9

[0175] Regarding the α - conversion rate, the alumina particles of sample numbers 1 - 5, 7 - 11 are within the preferred numerical range specified in Embodiment 1.

[0176] (5) Measurement of the total length L2 of the outer edge length L1 of alumina particles and the boundary lines inside the particles

[0177] Each alumina particle was used to prepare a specimen for cross-sectional observation. In the preparation of the specimen for cross-sectional observation, after embedding the alumina particles in resin, the resin and alumina particles were cut using a diamond cutter. Then, Pt was vapor-deposited on the cross-section as a protective film, the cross-section was prepared using Ar ion milling, fixed to the SEM specimen 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., in such a way that two or more alumina particles did not contact the observation area frame). The measurement was carried out using α-alumina particles.

[0178] The following equipment was used in the pretreatment of the sample and the EBSD measurement.

[0179] · Equipment used

[0180] Ion milling device: IM-4000 (manufactured by Hitachi, Ltd.)

[0181] Ion sputtering device: E-1030 (manufactured by Hitachi, Ltd.)

[0182] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by JEOL Ltd.)

[0183] Electron backscatter diffraction device: Digiview V (manufactured by TSL)

[0184] The conditions for the EBSD measurement are as follows.

[0185] · Measurement area: 500.0 μm × 400.0 μm

[0186] · Acceleration voltage: 20.0 kV

[0187] · Magnification: ×500

[0188] · Vacuum degree: 30 Pa

[0189] In the obtained EBSD images, two or more alumina particles that did not contact the observation area frame were selected, and the average value of the length L1 of the outer edge of each alumina particle was calculated using the image processing software Image J (manufactured by the National Institute of Health). In addition, the total length L2 of the boundary lines was 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 of the grain boundaries inside the alumina particles and (in the case where there are voids inside the alumina particles) the total length of the inner walls of the voids.

[0190] The ratio (L2 / L1) of the total length L2 of the boundary lines to the length L1 of the outer edge is expressed as a percentage (%). The more grain boundaries and voids there are inside the alumina particles, the larger the value of L2 / L1 (%).

[0191] The measurement results are shown in Table 6.

[0192] [Table 6]

[0193] Specimen number L2 / L1 (%) Example 1 29.3 Example 2 20.8 Example 3 29.2 Example 4 41.8 Comparative example 5 94.0 Comparative example 6 0.0 Example 7 40.2 Example 8 55.1 Example 9 20.7 Example 10 72.1 Example 11 90.0

[0194] Regarding L2 / L1, the alumina particles of sample numbers 1 to 4 and 7 to 11 are within the numerical range specified in Embodiment 1, but the alumina particles of sample number 5 exceed this numerical range, and the alumina particles of sample number 6 are below this numerical range. The reason for the alumina particles of sample number 5 is that polycrystalline alumina (raw material particles 2) is used as the alumina raw material particles, so many boundary lines from the raw materials still remain after the flame melting process. And the alumina particles (alumina raw material particles) of sample number 6 are single-crystal alumina, and there are almost no boundary lines inside the alumina particles.

[0195] (6) Measurement of the specific surface area SA of alumina particles

[0196] Measure the specific surface area SA of the alumina particles.

[0197] The method for measuring the specific surface area of powders (solids) based on gas adsorption complies with JIS Z8830:2013, and nitrogen is used as the adsorption gas. During the measurement, 1 g of alumina particles is placed in the sample tube, the adsorption-desorption isotherm is obtained, and the specific surface area SA (m 2 / g) is calculated using the multi-point plotting method.

[0198] The measurement results of the specific surface area SA are shown in Table 7. In addition, the middle part (particle size D50 × specific surface area AS × apparent density AD) of formula (1) is also shown.

[0199] [Table 7]

[0200]

[0201] (7) Measurement of the moisture content of alumina particles

[0202] For the moisture content of the alumina particles, based on the Karl Fischer method, the measurement is carried out in accordance with the description in JIS K 0068:2001 "Method for Determining the Moisture in Chemical Products".

[0203] Device name: Karl Fischer moisture meter (VA-236S manufactured by Mitsubishi Analytech)

[0204] Measurement method: Heating vaporization coulometry

[0205] Catholyte: "Aquamicron AX" (trade name) manufactured by Mitsubishi Chemical

[0206] Anolyte: "Aquamicron CXU" (trade name) manufactured by Mitsubishi Chemical

[0207] Sample amount: 2 g

[0208] The measurement results are shown in Table 8.

[0209] [Table 8]

[0210] Specimen number Moisture content of aluminum oxide particles (ppm) Example 1 33 Example 2 37 Example 3 44 Example 4 25 Comparative example 5 62 Comparative example 6 137 Example 7 25 Example 8 40 Example 9 61 Example 10 60 Example 11 53

[0211] Regarding the moisture content, the alumina particles of sample numbers 1 to 4 and 7 to 11 are within the preferred numerical range defined in Embodiment 1, but the alumina particles of sample numbers 5 to 6 exceed the preferred numerical range.

[0212] (8) Measurement of the defect rate inside the particles

[0213] Measure the defect rate inside the alumina particles.

[0214] For alumina particles thinly dispersed on a substrate, high-sensitivity X-ray CT scanning (model: nano3DX) manufactured by Rigaku Corporation is used to take an X-ray transmission image within a range of 0.7 mm × 0.7 mm. For all more than 20 alumina particles in the obtained X-ray transmission image, confirm the defects of the particles. The defects of the particles refer to voids or amorphous layers existing inside the particles. In the X-ray transmission image of the alumina particles, inside the non-defective part (non-defective part: observed as a white part) of the alumina particles, it is observed as a light gray part.

[0215] For the X-ray transmission photograph, use the image processing software Image J (manufactured by the National Institute of Health) to obtain the total area Sa of the alumina particles, the area Sb of the non-defective part inside the alumina particles, and the area Sc of the defective part inside the alumina particles. It should be noted that among the respective areas, the equation Sa = Sb + Sc holds (see Figure 2 ).

[0216] Then, express Sc / Sa as a percentage as the defect rate inside the particles (%).

[0217] The following describes the image processing method for obtaining the areas Sa, Sb, and Sc.

[0218] Using the image processing software "Image J", based on the image obtained from the X-ray transmission photograph, an image of one alumina particle containing voids was cut out, binarized, and analyzed using "Analyze Particles" to obtain the total area Sa of the alumina particle. In the image obtained from the X-ray transmission photograph, the brightness of the non-defective part of the alumina particle is the lowest, followed by the higher brightness of the defective part inside the particle, and the highest brightness of the part around (background) the alumina particle. Therefore, when performing binarization processing, it is necessary to convert the brightness of the defective part and the background to the same level of image processing. Such image processing is carried out by adjusting the contrast and adjusting the "Convolve" filter. Thus, the area of the range after removing the light gray part as the defective part from the alumina particle (i.e., the area Sb of the non-defective part) was measured.

[0219] In the particle analysis command, the area Sa (with the option of Include holes set to ON) when measuring both the non-defective part (area Sb) and the defective part (area Sc) inside the alumina particle, and the area (i.e., the area Sb of the non-defective part) when not including the defective part inside the alumina particle (with the option of Include holes set to OFF) were measured. The area Sc (= Sa - Sb) was calculated based on the obtained areas Sa and Sb.

[0220] The calculation results are shown in Table 9.

[0221] [Table 9]

[0222] Specimen number Internal defect rate of particles (%) Example 1 3.0 Example 2 3.0 Example 3 2.0 Example 4 5.0 Comparative example 5 12.0 Comparative example 6 0.0 Example 7 2.0 Example 8 1.0 Example 9 1.0 Example 10 1.0 Example 11 1.0

[0223] (9) Viscosity measurement of the mixture of alumina particles and resin

[0224] Shear rate-viscosity measurement of the mixture of alumina particles and epoxy resin was carried out.

[0225] Epoxy resin (Epoxy binder jER828 manufactured by Mitsubishi Chemical) and alumina particles were mixed at a mixing ratio of 45:55 by volume% (equivalent to about 0.5 g of epoxy resin: about 2.0 g of alumina particles). Using a mortar, the alumina particles and epoxy resin were manually mixed for about 10 - 20 minutes to prepare a mixed sample for viscosity measurement.

[0226] Using HAAKE MARS II (manufactured by Thermo Fisher Scientific), shear rate-viscosity measurement of the mixed sample was carried out.

[0227] The measurement conditions are as follows.

[0228] · Geometric structure: Φ20mm parallel plates

[0229] · Shear rate: 0.001 s -1 ~100 s -1

[0230] · Measurement temperature: 23 °C

[0231] · Measurement time: 4 minutes

[0232] At the measurement temperature, on a stable plate, complete the sample setting within 10 minutes and start the measurement.

[0233] Shear rate 10 s -1 The measurement results of the viscosity at this time are shown in Table 10.

[0234] [Table 10]

[0235]

[0236] (10) Measurement of the dielectric loss of the resin composition (composite)

[0237] For sample numbers 1 to 4 and 7 to 11, use alumina particles to prepare the resin composition (composite) and measure its dielectric loss. It should be noted that for the alumina particles of sample numbers 5 to 6 with high viscosity of the mixture with the resin, the resin composition (composite) was not prepared.

[0238] Mix polypropylene resin (J105G manufactured by Prime Polymer Co., Ltd.) and alumina particles at a mixing ratio of 60:40 by volume%. Use a compression molding machine to perform vacuum compression molding under the following conditions to produce an alumina-resin composite with a thickness of 600 μm.

[0239] Under the following measurement conditions, measure the dielectric loss (tanδ) of the composite.

[0240] · Measuring device: Network analyzer 8720ES (manufactured by Agilent Technologies)

[0241] · Test piece size: 50 mm × 50 mm

[0242] · Measurement frequency: 12 GHz

[0243] · Test environment: 22 °C / 59% RH

[0244] The measurement results of the dielectric loss are shown in Table 11.

[0245] [Table 11]

[0246] Specimen number of aluminum oxide particles Dielectric loss of resin composition Example 1 <![CDATA[1.55×10 -4 > Example 2 <![CDATA[2.95×10 -4 > Example 3 <![CDATA[3.38×10 -4 > Example 4 <![CDATA[3.56×10 -4 > Example 7 <![CDATA[2.30×10 -4 > Example 8 <![CDATA[4.63×10 -4 > Example 9 <![CDATA[1.75×10 -4 > Example 10 <![CDATA[6.80×10 -4 > Example 11 <![CDATA[7.67×10 -4 >

[0247] Regarding the alumina particles of sample numbers 1 to 4 and 7 to 11, the values of D50, the α conversion rate, and L2 / L1 are within the ranges specified in Embodiment 1. In addition, the intermediate value of formula (1) is also within the preferred range of Embodiment 1. Therefore, the resin composition using the alumina particles of sample numbers 1 to 4 and 7 to 11 has a low dielectric loss.

[0248] Description of Reference Numerals

[0249] 10 Oxygen supply system

[0250] 11 Carrier oxygen

[0251] 12 Combustion oxygen

[0252] 20 Fuel gas supply system

[0253] 30 Feeder

[0254] 40 Flame melting furnace

[0255] 50 Cyclone separator

Claims

1. Alumina particles, wherein the particle size D50 at the 50% cumulative number from the fine particle side of the cumulative particle size distribution is greater than 30.0 μm and 55.0 μm or less, the α - conversion rate is 60.0% or more, the ratio (L2 / L1) of the total length L2 of the boundary lines inside the alumina particles to the length L1 of the outer edge of the alumina particles is 1.0% or more and 90.0% or less.

2. The alumina particles according to claim 1, wherein the crystal defect rate is less than 20.0%.

3. The alumina particles according to claim 1, wherein the roundness is 0.85 or more.

4. The alumina particles according to claim 1, which satisfy the following formula (1), 3.00 ≤ D50 × SA × AD ≤ 25.00 (1) Among them, D50 is the particle size D50 (μm), SA is the specific surface area of the alumina particles (m 2 / g), AD is the apparent density of alumina particles (g / cm 3 ).

5. The alumina particles according to claim 1, wherein the moisture content is less than 62 ppm.

6. A resin composition comprising a resin and the alumina particles according to any one of claims 1 to 5.

Images