Alumina particles and resin composition using same

Abstract

The alumina particles have a particle diameter D50 of 2.0 [mu] m to 30.0 [mu] m (inclusive) at a cumulative particle size distribution of 50% by number from the particle side, an alphalation rate of 60.0% or more, and satisfy the following formula (1). D50 * SA * AD < = 222.00 (1) where D50 is the particle diameter D50 ([mu] m), SA is the specific surface area (m2 / g) of the alumina particles, and AD is the apparent density (g / cm3) of the alumina particles. The purpose of the present invention is to provide alumina particles capable of forming a resin composition having low dielectric loss when used as a filler for a resin composition.

Description

Technical Field

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

[0002] The heat generated by energizing an electronic component is dissipated through a heat sink. A technique of filling a heat dissipation material between an electronic component and a 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 alumina particles, a method of melting a pulverized product of fused alumina by a flame melting method and rapidly cooling by spraying water into a 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 a heat dissipation material is disposed near an electronic component, a low dielectric loss is desired. Therefore, alumina particles capable of forming a resin composition having a low dielectric loss are required.

[0010] However, regarding the alumina particles described in Patent Document 1, no study has been made on forming a resin composition having a low dielectric loss.

[0011] In view of such a situation, an object of one embodiment of the present invention is to provide alumina particles that are alumina particles used as a filler for a resin composition and can form a resin composition having a low dielectric loss. Further, an object of another embodiment of the present invention is to provide a resin composition using such alumina particles.

[0012] Means for Solving the Problems

[0013] Aspect 1 of the present invention is alumina particles, wherein the particle diameter D50 of 50% cumulative by number from the fine particle side in the cumulative particle size distribution is 2.0 μm or more and 30.0 μm or less.

[0014] The α conversion rate is 60.0% or more and satisfies the following formula (1).

[0015] D50 × SA × AD ≤ 222.00 (1)

[0016] Wherein, D50 is the aforementioned particle size D50 (μm),

[0017] SA is the specific surface area of the alumina particles (m 2 / g),

[0018] AD is the apparent density of the alumina particles (g / cm 3 ).

[0019] Mode 2 of the present invention is the alumina particles as described in Mode 1, and its roundness is 0.90 or more.

[0020] Mode 3 of the present invention is the alumina particles as described in Mode 1 or 2, and its apparent density is 3.60 g / cm 3 or more and less than 3.96 g / cm 3 .

[0021] Mode 4 of the present invention is the alumina particles as described in any one of Modes 1 to 3, wherein 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 160.0% or less.

[0022] Mode 5 of the present invention is the alumina particles as described in any one of Modes 1 to 4, and its moisture content is 1400 ppm or less.

[0023] Mode 6 of the present invention is a resin composition, which contains a resin and the alumina particles as described in any one of Modes 1 to 5.

[0024] Effects of the Invention

[0025] By using the alumina particles according to an embodiment of the present invention as a filler, a resin composition with low dielectric loss can be obtained. Description of the Drawings

[0026] Figure 1 Figure 1 It is a schematic diagram showing the apparatus for implementing the flame melting process in the manufacturing method of alumina particles. Detailed Embodiments

[0027] [Embodiment 1: Alumina Particles]

[0028] ​​In Embodiment 1 of the present invention, the alumina particles are used by being mixed with a resin as a filler for a resin composition. Regarding the alumina particles, the particle size D50 at the 50% cumulative number from the fine particle side in the cumulative particle size distribution is 2.0 μm or more and 30.0 μm or less, the α-conversion rate is 60.0% or more, and the following formula (1) is satisfied.

[0029] D50 × SA × AD ≤ 222.00 (1)

[0030] Wherein, D50 is the aforementioned particle size D50 (μm),

[0031] SA is the specific surface area of the alumina particles (m 2 / g),

[0032] AD is the apparent density of the alumina particles (g / cm 3 ).

[0033] The inventors of the present application newly discovered that the value of the left side (D50 × SA × AD) of formula (1) is correlated with the dielectric loss (tanδ) of a resin composition using alumina particles as a filler, and conducted in-depth research. And for the first time, it was found that when the value of the left side of formula (1) is 222.00 or less, a resin composition with a low dielectric loss can be formed, thus completing the invention related to the present embodiment.

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

[0035] (Particle size D50 at the 50% cumulative number from the fine particle side in the cumulative particle size distribution)

[0036] Embodiment 1 of the present invention targets alumina particles with a particle size D50 at the 50% cumulative number from the fine particle side in the cumulative particle size distribution (hereinafter sometimes simply referred to as "D50") of 2.0 μm or more and 30.0 μm or less. The particle size D50 of the alumina particles is preferably 4.0 μm or more and 28.0 μm or less.

[0037] Regarding the D50 of the alumina particles, based on the principle of dynamic image analysis in accordance with ISO 13322-2, the particle size distribution of the alumina particles is measured, and using the cumulative particle size distribution obtained from the measurement results, the particle size (D50) at the 50% cumulative number from the fine particle side is obtained. As the measuring device, for example, CAMSIZER (manufactured by VERDER Scientific) is used, the sample is sequentially introduced into the device, and while dispersing the agglomerated particles with dry air, the particles passing in front of the camera are measured.

[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 62.0% or more. The upper limit of the α-conversion rate is not particularly limited and may be 100% or less, may be 99.0% or less, or may be 98.0% or less. Since α-alumina has high thermal conductivity, 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 alumina contained in the alumina particles.

[0041] Regarding the α-conversion rate, the alumina particles are measured by powder X-ray diffraction method, and the peak height (I 25.6 ) of the α-phase ((012) plane) appearing at the position of 2θ = 25.6° and the peak height (I 46 ) formed due to γ-phase, η-phase, χ-phase, κ-phase, θ-phase and δ-phase appearing at the position of 2θ = 46° are obtained from the obtained diffraction spectrum, and are 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, alumina other than α-alumina can be contained in any manner. For example, α-alumina and alumina other than α-alumina can be contained inside one alumina particle at the same time. 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] (Satisfying formula (1): D50 × SA × AD ≤ 222.00)

[0046] The following formula (1) is obtained by transforming a general formula representing the relationship between the particle size and the specific surface area of the particles.

[0047] D50 × SA × AD ≤ 222.00 (1)

[0048] Among them, D50 is the aforementioned particle size D50 (μm),

[0049] SA is the specific surface area of the alumina particles (m2 / g),

[0050] AD is the apparent density of alumina particles (g / cm 3 ).

[0051] According to the general formula representing the relationship between the particle size and specific surface area of particles, 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 left side (D50 × SA × AD) of formula (1) becomes 6. When the specific surface area SA becomes larger, the value of the left side becomes larger, and when the apparent density AD is less than the theoretical density, the value of the left side becomes smaller.

[0052] The alumina particles according to this embodiment can reduce the dielectric loss (tanδ) of the resin composition using the alumina particles as a filler by satisfying the above formula (1) (that is, the value of D50 × SA × AD of the alumina particles is 222.00 or less).

[0053] Although the reason why the dielectric loss of the resin composition containing alumina particles can be suppressed to a low level when the value of D50 × SA × AD of the alumina particles becomes 222.00 or less is not certain, it is considered that the apparent density AD and surface area of the alumina particles affect the dielectric loss of the resin composition. For example, when the apparent density AD of the alumina particles is too low, the dielectric loss of the resin composition increases. It is speculated that if the specific surface area SA of the alumina particles is too high, the interface with the resin increases, and thus the dielectric loss of the resin composition becomes high.

[0054] The value of D50 × SA × AD of the alumina particles is preferably 200.00 or less, more preferably 100.00 or less, further preferably 60.00 or less, still further preferably 45.00 or less, particularly preferably 30.00 or less, preferably 2.00 or more, more preferably 2.50 or more, further preferably 3.00 or more, still further preferably 5.00 or more, particularly preferably 8.00 or more.

[0055] The calculation of formula (1) uses the values obtained under the following conditions.

[0056] The particle size D50 (μm) is measured by the above-mentioned measurement method, and the value rounded to one decimal place is used.

[0057] The specific surface area SA (m 2 / g) is measured by the method described later, and the value rounded to two decimal places is used.

[0058] The apparent density AD (g / cm 3 ) is measured by the method described later, and the value rounded to two decimal places is used.

[0059] (Specific surface area SA of alumina particles)

[0060] The specific surface area SA of the alumina particles is the BET specific surface area measured by the nitrogen adsorption method based on JIS Z 8830:2013.

[0061] The specific surface area becomes an index indicating the degree of concavity and convexity of the particles. If the surface of the alumina particles has less concavity and convexity, when used as a filler for a resin composition, the interface with the resin becomes less, and as a result, it can be expected to reduce the dielectric loss of the resin composition.

[0062] The specific surface area SA of the alumina particles is preferably 10.0 m 2 / g or less, more preferably 8.0 m 2 / g or less, further preferably 6.5 m 2 / g or less, even more preferably 3.0 m 2 / g or less, particularly preferably 1.5 m 2 / g or more.

[0063] The specific surface area SA of the alumina particles can be 0.01 m 2 / g or more, and can be 0.02 m 2 / g or more.

[0064] (Apparent density AD of alumina particles)

[0065] The apparent density AD of the alumina particles is measured by the pycnometer method in accordance with JIS R 1620-1995. The number of measurements is set to 5 or more, and the average value is used. For example, AccuPyc 1330 (Micromeritics) can be used in the measurement.

[0066] The apparent density of the alumina particles is preferably 3.60 g / cm 3 or more and less than 3.96 g / cm 3 , more preferably 3.93 g / cm 3 or less, further preferably 3.92 g / cm 3 or less, further preferably 3.65 g / cm 3 or more and 3.89 g / cm 3 or less, particularly preferably 3.70 g / cm 3 or more and 3.80 g / cm 3 or less. If the density is within the above range, it is easy to obtain a resin composition with low dielectric loss when used as a filler for a resin composition.

[0067] (True roundness of alumina particles)

[0068] The roundness of the alumina particles is preferably 0.90 or more, more preferably 0.93 or more and 1.00 or less. When within this range, the kneadability with the resin can be made good, the fluidity of the kneaded composite can be improved, and furthermore, the wear of other components caused by the alumina particles can be reduced. Therefore, it is suitable as a filler for a resin composition for electronic components.

[0069] It should be noted that the following aspects should be paid attention to: Since alumina particles are usually hard particles, if only alumina particles with low roundness collide with each other or alumina particles with low roundness are crushed, it is difficult to make the value of D50×SA×AD as described above appropriate, and furthermore, it is difficult to obtain alumina particles with a roundness of 0.90 or more. In order to make the value of D50×SA×AD of the alumina particles appropriate and improve the roundness by collision and crushing, it is necessary to perform collision and crushing for a long time. However, in this case, a large amount of fine powder of alumina is generated, which may cause the particle size D50 of the alumina particles to be excessively reduced or the dielectric loss of the resin composition to increase. In addition, the new hydrophilic surface generated on the surface of the alumina particles due to crushing will reduce the mixing property with the alumina particle resin, so it may not be suitable as a filler for the resin composition. In addition, there are many minute defects on the aforementioned hydrophilic surface, and the dielectric loss may increase.

[0070] The roundness (SPHT) is analyzed in accordance with ISO 9276-6. According to SPHT = 4πA / P 2 it is obtained. 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.

[0071] The roundness of the alumina particles is measured by a measuring device (for example, CAMSIZER X2 (manufactured by VERDER Scientific)) based on the principle of dynamic image analysis in accordance with ISO 13322-2.

[0072] (The 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)

[0073] The fewer the grain boundaries and voids inside the alumina particles, the lower the dielectric loss of the alumina particles. Therefore, as an index of the grain boundary content inside the alumina particles, the ratio (L2 / L1) of the total length L2 of the boundary lines to the length L1 of the outer edge is introduced. L1 and L2 are obtained from the cross-sectional observation of the alumina particles.

[0074] When the length of the outer edge of one alumina particle is set as L1 and the total length of the boundary lines of 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 160.0% 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 130.0% or less, further preferably 100.0% or less, and particularly preferably 80.0% or less. In the case of using granulated raw material particles as raw material particles of polycrystals and manufacturing alumina particles by the flame fusion method, the value of L2 / L1 particularly increases, and even through subsequent processes such as reheating, it cannot be significantly reduced.

[0075] It should be noted that the "total length of boundary lines L2" 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 of boundary lines L2 is obtained by adding the total length of grain boundaries L3 inside the alumina particle and the total length of the inner walls of the cavities (when there are cavities inside the alumina particle) L4 (that is, L2 = L3 + L4).

[0076] The measurement of L1, L2, L3, and L4 is preferably performed on alumina particles obtained from α-alumina.

[0077] (Water content of alumina particles)

[0078] When the water content of the alumina particles (the water content contained in the alumina particles) is high, the dielectric loss of the resin composition made using the alumina particles becomes large. In addition, if the amount of water brought in by the alumina particles is large, the water seeps out from the resin, which may have an adverse effect on electronic components and the like arranged adjacent to the resin composition. Therefore, the amount of water brought in by the alumina particles is preferably as small as possible.

[0079] The water content of the alumina particles is preferably 1400 ppm or less, more preferably 1000 ppm or less, further preferably 500 ppm or less, still further preferably 300 ppm or less, and particularly preferably 140 ppm or less.

[0080] 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 "Method for Determination of Water in Chemical Products".

[0081] (Particle size distribution: D90 / D50)

[0082] The particle size distribution of the alumina particles can be evaluated by the value (D90 / D50) of the particle diameter D90 at the cumulative 90% from the fine particle side of the cumulative particle size distribution relative to the particle diameter D50. When D90 / D50 is close to 1, it can be said that the particle size distribution is narrow, and the alumina particles have a uniform particle diameter. D90 / D50 is preferably 1.0 or more and 5.0 or less, more preferably 1.5 or more and 4.0 or less, and particularly preferably 2.0 or more and 3.8 or less.

[0083] (Tap density)

[0084] A high tap density of the alumina particles means that the alumina particles can be packed tightly. When using alumina particles with a high tap density to form a resin composition, it can be expected that more alumina particles can be kneaded, and the fluidity of the kneaded composite can be improved. In addition, when the tap density is high, the alumina particles are not easily scattered and are easy to handle.

[0085] The tap density is preferably 1.8 g / cm 3 or more and 3.0 g / cm 3 or less, more preferably 2.2 g / cm 3 or more and 2.8 g / cm 3 or less.

[0086] The tap density is measured in accordance with the description in JIS Z 2512:2012 "Metal Powders - Method for Determination of Tap Density".

[0087] [Manufacturing method of alumina particles]

[0088] The manufacturing method of the alumina particles according to Embodiment 1 of the present invention will be described.

[0089] In the raw materials of the alumina particles, alumina raw material particles mainly formed of single crystal α-alumina and having a particle diameter D50 at the cumulative 50% from the fine particle side of the cumulative particle size distribution of 1.0 μm or more and 29.0 μm or less are mainly used. Then, alumina particles are manufactured from the alumina raw material particles by the flame fusion method.

[0090] So far, the general view is that when the raw material particles are put into the 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.

[0091] In the flame fusion process, for example, a device as shown in Figure 1 is used. Through the flame fusion process, alumina particles with an α conversion rate of 60.0% or more and satisfying the above formula (1) can be obtained.

[0092] In order to use raw material particles of single-crystal alumina and effectively utilize the crystal structure characteristics of single-crystal alumina even after spheroidization, the particle size of the alumina raw material particles used, the supply rate of the alumina raw material particles into the flame melting furnace of the apparatus, the intensity of the flame, the distance between the flame and the alumina raw material particles, etc. are controlled.

[0093] In order to manufacture alumina particles with a D50 of 2.0 μm or more and 30.0 μm or less, alumina raw material particles with a D50 of, for example, 1.0 μm or more and 29.0 μm or less are used. The D50 of the alumina raw material particles is preferably 1.5 μm or more and 28.0 μm or less, and is, for example, 2.7 μm.

[0094] It should be noted that even if the D50 of the alumina raw material particles is, for example, 1.0 μm or more and 29.0 μm or less, as each alumina raw material particle, particles with a particle size smaller than 1.0 μm and particles with a particle size larger than 29.0 μm may be included. Therefore, the obtained alumina particles may contain polycrystalline α-alumina and / or alumina other than α-alumina. However, by making the D50 of the alumina raw material particles 1.0 μm or more and 29.0 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 allowable range of the present invention.

[0095] In addition, conventionally, a method of manufacturing alumina particles using granulated raw material particles or polycrystalline raw material particles by a 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 that has not been granulated is used as the alumina raw material particles, alumina particles with a small L2 / L1 value can be obtained.

[0096] The D50 of the alumina raw material particles can be measured by the same method as the measurement method of the D50 of the above-mentioned alumina particles.

[0097] The case where the alumina raw material particles are single-crystal α-alumina 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, whether it is single crystal or polycrystalline can be judged based on the presence or absence of clear grain boundaries in the alumina particles.

[0098] Whether α-alumina is single crystal can also be confirmed by the Debye-Scherrer method.

[0099] As raw materials for 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 pulverizing these raw materials and sieving them using a sieve with a desired mesh size, alumina raw material particles with a specified D50 can be prepared.

[0100] The alumina raw material particles may contain a small amount (e.g., about 10% by mass or less) of alumina other than α-alumina (δ-alumina, θ-alumina, etc.). In addition, a small amount (e.g., about 10% by mass or less) of polycrystalline α-alumina may be contained together with the single crystal α-alumina, which does not hinder the purpose of the present invention.

[0101] In the flame melting process, the supply amounts of the alumina raw material particles, fuel gas, and oxygen preferably satisfy the following formulas (3) and (4).

[0102] 0.625 ≤ R / F (kg / Nm 3 ) ≤ 17.000 (3)

[0103] 0.125 ≤ R / S (kg / Nm 3 ) ≤ 3.400 (4)

[0104] Wherein, F is the supply amount of the fuel gas (Nm 3 / hour), S is the supply amount of oxygen (Nm 3 / hour), and R is the supply amount of the alumina raw material particles (kg / hour).

[0105] 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 used to carry the alumina raw material particles, but after transportation, it is used for combustion in the same way as the combustion oxygen.

[0106] As specified in formula (3), the ratio (R / F) of the supply amount of the alumina raw material particles to the supply amount of the fuel gas is preferably 0.625 kg / Nm 3 or more and 17.000 kg / Nm 3 or less. In addition, as specified in formula (4), the ratio (R / S) of the supply amount of the 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.

[0107] The supply amount of the fuel gas F (Nm 3 / h) and the supply amount S (Nm 3 / h) 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.

[0108] 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).

[0109] 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).

[0110] Therefore, controlling R / F and R / S is one 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, in the flame melting process, spheroidization can be carried out while effectively utilizing the crystal structure characteristics of the raw material particles of the alumina raw material particles.

[0111] R / F is more preferably 1.000 kg / Nm 3 to 10.000 kg / Nm 3 below, and particularly preferably 2.000 kg / Nm 3 to 10.000 kg / Nm 3 below.

[0112] R / S is more preferably 0.300 kg / Nm 3 to 3.000 kg / Nm 3 below, and particularly preferably 0.600 kg / Nm 3 to 3.000 kg / Nm 3 below.

[0113] In addition, the supply amount F of the fuel gas is preferably less than 20 Nm 3 / h. By 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 smaller 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 particles.

[0114] As the fuel gas in the present invention, for example, propane, butane, propylene, acetylene, hydrogen, etc. can be cited. Propane (for example, liquefied propane gas (LPG)) is particularly preferred.

[0115] 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 increased.

[0116] 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 increased. 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, heating from the outside using a heater or the like, heating based on gas combustion again, etc. can be applied.

[0117] [Embodiment 2: Resin Composition]

[0118] 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. The resin composition includes a resin and the alumina particles according to Embodiment 1 of the present invention.

[0119] The alumina particles according to Embodiment 1 of the present invention can reduce the dielectric loss without impairing the flexibility inherent in the resin. Therefore, its mixing ratio is preferably 5 to 75% by volume of the resin and 95 to 25% by volume of the alumina particles with respect to the resin composition (composite).

[0120] The manufacturing method of the resin composition will be described.

[0121] By mixing the alumina particles according to Embodiment 1 of the present invention with a resin using a generally used known method, 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., thereby obtaining a resin composition. 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 and the resin, it can be kneaded using a known method such as melt kneading, thereby obtaining the target resin composition.

[0122] 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 kind, or two or more kinds can be used in combination.

[0123] Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer, 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, polyamide-imide, 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.

[0124] 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.

[0125] Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, 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.

[0126] 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.

[0127] In addition, in these resin compositions, as needed, known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, anti-blocking agents, antistatic agents, leveling agents, and mold release agents can be appropriately blended alone or in two or more kinds within the range not impairing the effects of the invention.

[0128] The alumina particles according to this embodiment and the resin composition containing the alumina particles are particularly suitable for use as heat dissipation materials with low dielectric loss.

[0129] Examples

[0130] (1) Manufacture of alumina particles

[0131] Alumina raw material particles (raw material particles 1 to 3) formed of single crystal alumina were prepared. The D50 of each raw material particle was measured. As a result, the D50 of raw material particle 1 was 2.7 μm, the D50 of alumina raw material particle 2 was 4.6 μm, and the D50 of alumina raw material particle 3 was 21.8 μm. The D50 of the alumina raw material particles was measured by the laser diffraction method. Laser light was irradiated to a sample dispersed in water, and its diffraction was measured to obtain the particle size. The measuring device used was a CILAS model 1090L.

[0132] Using Figure 1 such a device as shown, alumina particles were prepared from the alumina raw material particles. The oxygen from the oxygen supply system 10 was split, and one part (carrier oxygen 11) was supplied to the feeder 30, and the other part (combustion oxygen 12) was 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 from 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.

[0133] As the ratio of the supply amount F (Nm 3 / h) of the fuel gas, the supply amount S (Nm 3 / h) of oxygen, and the supply amount R (kg / h) of the alumina raw material particles, R / F and R / S are summarized in Table 1. 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 1, the columns of R / F and R / S being "-" means that flame melting was not performed.

[0134] [Table 1]

[0135] Specimen number Aluminum oxide raw material particles <![CDATA[R / F(kg / Nm 3 )]]> <![CDATA[R / S(kg / Nm 3 )]]> Example 1 Raw material particles 1 7.000 1.400 Example 2 Raw material particles 1 3.750 0.750 Example 3 Raw material particles 1 3.077 0.613 Example 4 Raw material particles 1 2.500 0.500 Example 5 Raw material particles 1 0.625 0.125 Comparative example 6 Raw material particles 1 - - Example 7 Raw material particles 2 5.714 1.000 Example 8 Raw material particles 1 1.111 0.222 Example 9 Raw material particles 3 1.111 0.222 Example 10 Raw material particles 3 3.333 0.667

[0136] Various measurements were performed on the obtained alumina particles (sample numbers 1 to 10). It should be noted that "sample number 6" of the alumina particles is the same as raw material particle 1.

[0137] (2) Measurement of the particle size D50, D90 and roundness of the alumina particles

[0138] The particle size distribution of the alumina particles was measured, and the particle size D50 and particle size D90 were obtained.

[0139] The particle size distribution and roundness of the alumina particles were measured by a device CAMSIZER X2 (manufactured by VERDER Scientific) based on the principle of dynamic image analysis in accordance with ISO 13322-2. The measurement was performed dry. The sample was sequentially introduced into the device, and while dispersing the agglomerated particles with dry air at 50 kPa, the particles passing in front of the camera were measured. The weighed amount of the measurement sample was 3 g, and the measurement was performed once. The same measurement was repeated three times, and the particle size distribution and roundness were analyzed by cumulative averaging based on these results. The particle size was the equivalent circular particle size. The equivalent circular particle size refers to the particle size of a perfect circle having the same area as the projected particle image. In addition, the basis of the particle size was set to volume.

[0140] The roundness (SPHT) was analyzed in accordance with ISO 9276-6. According to SPHT = 4πA / P 2 It was obtained. 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.

[0141] The particle size D50, the ratio of the particle size D90 to the particle size D50 (D90 / D50), and the roundness of each alumina particle are shown in Table 2.

[0142] [Table 2]

[0143] Specimen number D50 (μm) D90 / D50 Roundness Example 1 8.5 2.2 0.93 Example 2 11.6 3.7 0.94 Example 3 8.7 2.0 0.94 Example 4 9.9 3.3 0.94 Example 5 8.1 2.3 0.94 Comparative example 6 6.0 1.8 0.92 Example 7 18.2 1.8 0.92 Example 8 7.0 1.5 0.95 Example 9 21.4 2.0 0.95 Example 10 26.3 1.7 0.94

[0144] (3) Measurement of the apparent density AD of the alumina particles

[0145] The apparent density AD of the alumina particles was measured.

[0146] The apparent density AD was measured in accordance with JIS R 1620-1995. The measurement method and measurement conditions are as follows.

[0147] · Measurement method: Gas displacement method

[0148] · Drying of the sample: 200 °C, 8 hours or more

[0149] · Device used: AccuPyc 1330 (Micromeritics)

[0150] ·Measurement Conditions

[0151] Number of purge times: 10 times

[0152] Purge filling pressure: 15.0 psig

[0153] Number of measurement times: 5 times

[0154] Measurement filling pressure: 15.0 psig

[0155] Equilibrium pressure: 0.005 psig / minute

[0156] Measurement after setting accuracy: Yes

[0157] Deviation allowable error: 0.05%

[0158] Specimen unit size: 10 cm 3

[0159] The measurement results are shown in Table 3.

[0160] [Table 3]

[0161] Specimen number <![CDATA[Apparent density AD (g / cm 3 )]]> Example 1 3.78 Example 2 3.75 Example 3 3.73 Example 4 3.71 Example 5 3.74 Comparative example 6 3.96 Example 7 3.85 Example 8 3.69 Example 9 3.75 Example 10 3.77

[0162] Regarding the apparent density, the alumina particles of sample numbers 1 to 5 and 7 to 10 are within the preferred numerical range specified in Embodiment 1, but the alumina particles of sample number 6 are outside the preferred numerical range.

[0163] (4) Measurement of the α - conversion rate of alumina particles

[0164] Measure the α - conversion rate of alumina particles.

[0165] Regarding the α - conversion rate, a powder X - ray diffractometer (manufactured by Rigaku Corporation) is used to measure the specimen of alumina particles to obtain a diffraction spectrum. The measurement conditions are carried out at an X - ray source: CuKα, X - ray output power: 45 kV, 200 mA, and scanning speed: 10 deg / minute.

[0166] Based on the obtained diffraction spectrum, the peak height (I 25.6 ) of the α - phase (012 plane) appearing at the position of 2θ = 25.6° and the peak height (I 46 ) formed due to the γ - phase, η - phase, χ - phase, K - phase, θ - phase, and δ - phase appearing at the position of 2θ = 46° are obtained and calculated by the following formula (2).

[0167] α - conversion rate = I 25.6 / (I 25.6 +I 46 )×100 (%) (2)

[0168] The measurement results are shown in Table 4.

[0169] [Table 4]

[0170] Specimen number α - conversion rate (%) Example 1 87.9 Example 2 75.6 Example 3 75.1 Example 4 63.2 Example 5 66.6 Comparative example 6 100.0 Example 7 96.8 Example 8 84.5 Example 9 100.0 Example 10 97.5

[0171] (5) Measurement of the total length L2 of the boundary lines inside the particles and the length L1 of the outer edge of the alumina particles

[0172] Cross-sectional observation specimens were prepared using each alumina particle. In the preparation of the cross-sectional observation specimens, the alumina particles were embedded in resin and then the resin and alumina particles were cut using a diamond cutter. Then, Pt was vapor-deposited on the cross-section as a protective film, and the cross-section was prepared using Ar ion milling, fixed to an SEM specimen stage using Cu double-sided tape, and SEM-EBSD measurement was performed without vapor deposition. The observation position was determined such that two or more alumina particles completely entered the observation area (i.e., two or more alumina particles did not contact the observation area frame). The measurement was performed on α-alumina particles.

[0173] The following equipment was used for the pretreatment of the samples and EBSD measurement.

[0174] · Equipment used

[0175] Ion milling device: IM-4000 (manufactured by Hitachi, Ltd.)

[0176] Ion sputtering device: E-1030 (manufactured by Hitachi, Ltd.)

[0177] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by JEOL Ltd.)

[0178] Electron backscatter diffraction device: Digiview V (manufactured by TSL)

[0179] The conditions for EBSD measurement are as follows.

[0180] · Measurement area: 500.0 μm × 400.0 μm

[0181] · Acceleration voltage: 20.0 kV

[0182] · Magnification: ×500

[0183] · Vacuum degree: 30 Pa

[0184] In the obtained EBSD images, more than two alumina particles not in contact with the frame of the observation region 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 edges 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.

[0185] 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 (%).

[0186] The measurement results are shown in Table 5.

[0187] [Table 5]

[0188] Specimen number L2 / L1 (%) Example 1 28.2 Example 2 36.9 Example 3 34.3 Example 4 42.5 Example 5 95.1 Comparative example 6 0.0 Example 7 38.1 Example 8 48.1 Example 9 57.9 Example 10 56.5

[0189] Regarding L2 / L1, the alumina particles of sample numbers 1 to 5 and 7 to 10 are within the preferred numerical range defined in Embodiment 1, but the alumina particles of sample number 6 are below the preferred numerical range. The reason is that the alumina particles (alumina raw material particles) of sample number 6 are single-crystalline alumina, and there are almost no boundary lines inside the alumina particles.

[0190] (6) Measurement of the specific surface area SA of alumina particles

[0191] Measure the specific surface area SA of the alumina particles.

[0192] 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.

[0193] The measurement results are shown in Table 6.

[0194] [Table 6]

[0195] Specimen number <![CDATA[Specific surface area SA (m 2 / g)]]> Example 1 0.38 Example 2 0.26 Example 3 0.32 Example 4 0.26 Example 5 0.40 Comparative example 6 9.37 Example 7 0.28 Example 8 0.53 Example 9 0.28 Example 10 0.20

[0196] The specific surface area of the alumina particles of Sample No. 6 is high, but the specific surface area of the alumina particles of Sample Nos. 1 to 5 formed from the alumina particles (alumina raw material particles) of Sample No. 6 is low. It is considered that the reason is that the surface of the alumina particles becomes smooth due to the flame melting process of the alumina particles of Sample No. 6.

[0197] It is also speculated that the specific surface area of the alumina particles of Sample Nos. 7 to 10 is low because they also undergo the flame melting process.

[0198] (7) Measurement of the moisture content of alumina particles

[0199] 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 "Methods for Determination of Moisture in Chemical Products".

[0200] Apparatus name: Karl Fischer moisture meter (VA-236S manufactured by Mitsubishi Analytech)

[0201] Measurement method: Heated vaporization coulometry

[0202] Catholyte: "Aquamicron AX" (trade name) manufactured by Mitsubishi Chemical

[0203] Anolyte: "Aquamicron CXU" (trade name) manufactured by Mitsubishi Chemical

[0204] Sample amount: 2 g

[0205] The measurement results are shown in Table 7.

[0206] [Table 7]

[0207] Specimen number Moisture content of aluminum oxide particles (ppm) Example 1 56.5 Example 2 39.6 Example 3 55.6 Example 4 137.5 Example 5 88.4 Comparative example 6 1462.5 Example 7 157.6 Example 8 222.7 Example 9 169.7 Example 10 110.8

[0208] It is considered that the specific surface area of the alumina particles of Sample Nos. 1 to 5 and 7 to 10 is low, so the amount of moisture adsorbed on the surface of the alumina particles is small. On the other hand, the specific surface area of the alumina particles of Sample No. 6 is high, so the amount of moisture adsorbed on the surface of the alumina particles is large.

[0209] (8) Tap density

[0210] The tap density of the alumina particles is measured.

[0211] The tap density is measured in accordance with the description in JIS Z 2512:2012 "Metal Powders - Method for Determination of Tap Density". Specifically, 20 mL of alumina powder is measured into a 100 mL resin measuring cylinder, and it is gently tapped at a frequency of once per second for 3 minutes. After confirming that the volume of the alumina powder no longer decreases, the mass and volume of the sample are measured, and the tap density is calculated according to the following formula.

[0212] Tap density = sample mass / sample volume

[0213] The measurement results are shown in Table 8.

[0214] [Table 8]

[0215] Specimen number <![CDATA[Tap density (g / cm 3 )]]> Example 1 2.4 Example 2 2.7 Example 3 2.5 Example 4 2.4 Example 5 2.4 Comparative example 6 1.7 Example 7 2.3 Example 8 2.2 Example 9 2.4 Example 10 2.4

[0216] Regarding the tap density, the alumina particles of sample numbers 1 to 5 and 7 to 10 are within the preferred numerical range defined in Embodiment 1, but the alumina particles of sample number 6 are below the preferred numerical range.

[0217] (9) Measurement of the dielectric loss of the resin composition (composite)

[0218] A resin composition (composite) was produced using alumina particles, and its dielectric loss was measured.

[0219] Polypropylene resin (J105G manufactured by Prime Polymer Co., Ltd.) and alumina particles were mixed at a mixing ratio of 60:40 by volume%. Using a compression molding machine, vacuum compression molding was performed under the following conditions to produce an alumina-resin composite with a thickness of 600 μm.

[0220] Under the following measurement conditions, the dielectric loss (tan δ) of the composite was measured.

[0221] · Measuring device: Network analyzer 8720ES (manufactured by Agilent Technologies)

[0222] · Test piece size: 50 mm × 50 mm

[0223] · Measurement frequency: 12 GHz

[0224] · Test environment: 22°C / 59% RH

[0225] The measurement results of the dielectric loss and the calculated values of the left side of formula (1) (particle size D50 × specific surface area SA × apparent density AD) are shown together in Table 9.

[0226] [Table 9]

[0227]

[0228] For the alumina particles of sample numbers 1 to 5 and 7 to 10, the value on the left side of formula (1) is small. Therefore, the resin composition using the alumina particles of sample numbers 1 to 5 and 7 to 10 has a low dielectric loss.

[0229] Regarding the alumina particles (alumina raw material particles) of Sample No. 6, the value on the left side of Formula (1) is significantly large. The resin composition using the alumina particles of Sample No. 6 has a high dielectric loss.

[0230] Description of Reference Numerals

[0231] 10 Oxygen supply system

[0232] 11 Carrier oxygen

[0233] 12 Combustion oxygen

[0234] 20 Fuel gas supply system

[0235] 30 Feeder

[0236] 40 Flame melting furnace

[0237] 50 Cyclone separator

Claims

1. Alumina particles, wherein the particle size D50 at which the cumulative number from the fine particle side in the cumulative particle size distribution is 50% is 2.0 μm or more and 30.0 μm or less, the α - conversion rate is 60.0% or more, and the following formula (1) is satisfied, D50×SA×AD≤222.00 (1) Among them, where 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 ).

2. The alumina particles according to claim 1, having a roundness of 0.90 or more.

3. The alumina particles according to claim 1, having an apparent density of 3.60 g / cm 3 or more and less than 3.96 g / cm 3 .

4. The alumina particles according to claim 1, wherein, 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 160.0% or less.

5. The alumina particles according to claim 1, having a moisture content of 1400 ppm or less.

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

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