Alumina particles and resin composition using same

Abstract

The alumina particles have a particle diameter D50 of more than 55.0 [mu] m and 100.0 [mu] m or less at 50% of the cumulative particle size distribution from the particle side, an alphalation rate of 70.0% 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 1.0-110.0%. 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] 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 to improve 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 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 size 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 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 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, research on forming a resin composition having a low dielectric loss has not been conducted.

[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 in which the particle size D50 of 50% cumulative from the fine particle side in the cumulative particle size distribution is greater than 55.0 μm and 100.0 μm or less,

[0014] The α-ratio is 70.0% or more,

[0015] 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 110.0% or less.

[0016] In Mode 2 of the present invention, the alumina particles are as described in Mode 1, and the crystal defect rate thereof is 30.0% or less.

[0017] In Mode 3 of the present invention, the alumina particles are as described in Mode 1 or 2, and the roundness thereof is 0.85 or more.

[0018] 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).

[0019] D50 × SA × AD ≤ 38.00 (1)

[0020] Wherein, D50 is the aforementioned particle size D50 (μm),

[0021] SA is the specific surface area of the alumina particles (m 2 / g),

[0022] AD is the apparent density of the alumina particles (g / cm 3 ).

[0023] In Mode 5 of the present invention, the resin composition contains a resin and the alumina particles as described in any one of Modes 1 to 4.

[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 having a low dielectric loss can be obtained. Description of the Drawings

[0026] Figure 1 Figure 1 It is a schematic diagram showing an apparatus for carrying out a flame melting process in a method for manufacturing alumina particles.

[0027] Figure 2 Figure 2 It is a schematic diagram for explaining a calculation method of the particle defect rate. Detailed Embodiments

[0028] [Embodiment 1: Alumina Particles]

[0029] ​​​​The alumina particles according to Embodiment 1 of the present invention are used by being mixed with a resin as a filler for a resin composition. Regarding the alumina particles, the particle diameter D50 of the cumulative 50% in terms of the number from the fine particle side of the cumulative particle size distribution is greater than 55.0 μm and 100.0 μm or less, the α conversion rate is 70.0% 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 100.0% or less.

[0030] The inventors of the present application have found for the first time that alumina particles satisfying the above characteristics can reduce the dielectric loss (tan δ) of a resin composition using the alumina particles as a filler, and thus have completed the invention according to this embodiment.

[0031] Regarding the characteristics of the alumina particles according to Embodiment 1, the following will be described in detail.

[0032] (Particle diameter D50 of the cumulative 50% in terms of the number from the fine particle side of the cumulative particle size distribution)

[0033] Embodiment 1 of the present invention targets alumina particles having a particle diameter D50 (hereinafter sometimes simply referred to as "D50") of the cumulative 50% in terms of the number from the fine particle side of the cumulative particle size distribution that is greater than 55.0 μm and 100.0 μm or less. The particle diameter D50 of the alumina particles is preferably 57.0 μm or more and 90.0 μm or less.

[0034] 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 diameter (D50) of the cumulative 50% in terms of the number from the fine particle side is obtained. As a measurement 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 agglomerated particles with dry air.

[0035] (α conversion rate)

[0036] Regarding the alumina particles according to Embodiment 1 of the present invention, the α conversion rate as an index of the content of α-alumina is 70.0% or more, preferably 75.0% or more. The upper limit of the α conversion rate is not particularly limited and may be 100% or less, or may be 99.0% 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.

[0037] 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.

[0038] Regarding the α-phase conversion rate, alumina particles are measured using powder X-ray diffraction, and based on the obtained diffraction spectrum, the peak height (I 25.6 ) of the α-phase ((012) plane) that appears at the position of 2θ = 25.6° and the peak height (I 46 ) that appears at the position of 2θ = 46° and is caused by the γ-phase, η-phase, χ-phase, κ-phase, θ-phase, and δ-phase are calculated by the following formula (2).

[0039] α-phase conversion rate = I 25.6 / (I 25.6 +I 46 )×100(%) (2)

[0040] It should be noted that the alumina particles related to Embodiment 1 of the present invention may also contain, for example, 30.0% or less of alumina other than α-alumina (δ-alumina, θ-alumina, etc.), which does not hinder the purpose of the present invention.

[0041] 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 can 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 and present.

[0042] (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)

[0043] 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.

[0044] 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 L2 / L1 value can be said to be an alumina particle with a small content of boundary lines and a low dielectric loss. In particular, when (L2 / L1) (%) is 1.0% or more and 110.0% 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, more preferably 80.0% or less, further preferably 60.0% or less, and particularly preferably 40.0% or less. In the case of using granulated raw material particles as polycrystalline raw material particles and manufacturing alumina particles by the flame melting method, the value of L2 / L1 becomes particularly large, and even if subsequent processes such as reheating are performed, it cannot be significantly reduced.

[0045] 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 voids (when there are voids inside the alumina particle) L4 (that is, L2 = L3 + L4).

[0046] The measurement of L1, L2, L3, and L4 is preferably performed on alumina particles formed of α-alumina.

[0047] (Intra-particle defect rate)

[0048] When voids or amorphous layers (referred to as "defects of the particles") are contained inside the alumina particles, it becomes a cause for increasing the dielectric loss. Therefore, the intra-particle defect rate of the alumina particles is preferably low, particularly preferably 30.0% or less, and more preferably 20.0% or less. Thereby, when the alumina particles are used as a filler for a resin composition, the dielectric loss of the resin composition can be further reduced.

[0049] Regarding the intra-particle defect rate, for alumina particles in a thinly dispersed state on a substrate, an X-ray transmission image is taken using X-ray CT scanning, and for all 20 or more alumina particles in the obtained X-ray transmission image, the defects of the particles are confirmed. The defects of the particles are observed as light gray parts inside the non-defective parts (non-defective parts: observed as white parts) inside the alumina particles in the X-ray transmission image of the alumina particles.

[0050] For an X-ray transmission photograph, the total area Sa of alumina particles, the area Sb of the non-defective portion within the alumina particles, and the area Sc of the defective portion within the alumina particles are obtained using image processing software or the like. It should be noted that among the respective areas, the equation Sa = Sb + Sc holds.

[0051] Furthermore, Sc / Sa is expressed as a percentage and is defined as the defect rate within the particles (%).

[0052] (Satisfying formula (1): D50 × SA × AD ≤ 38.00)

[0053] The following formula (1) is obtained by transforming a general formula representing the relationship between the particle size and the specific surface area.

[0054] D50 × SA × AD ≤ 38.00 (1)

[0055] Among them, D50 is the aforementioned particle size D50 (μm),

[0056] SA is the specific surface area of the alumina particles (m 2 / g),

[0057] AD is the apparent density of the alumina particles (g / cm 3 ).

[0058] 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 left side (D50 × SA × AD) of formula (1) becomes 6. When the specific surface area SA increases, the value of the left side increases, and when the apparent density AD is less than the theoretical density, the value of the left side decreases.

[0059] 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 38.00 or less), which can further reduce the dielectric loss (tanδ) of the resin composition using the alumina particles as a filler.

[0060] Although the reason why the value of D50 × SA × AD of the alumina particles can affect the dielectric loss of the resin composition containing the alumina particles is not certain, it is considered that the apparent density AD and the 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.

[0061] The value of D50×SA×AD of the alumina particles is more preferably 35.00 or less, further preferably 30.00 or less, particularly preferably 20.00 or less, more preferably 1.00 or more, further preferably 2.00 or more, and particularly preferably 3.00 or more.

[0062] The calculation of formula (1) uses the values obtained under the following conditions.

[0063] The particle size D50 (μm) is measured by the above-mentioned measurement method, and the value rounded to one decimal place is used.

[0064] The specific surface area SA (m 2 / g) is measured by the method described below, and the value rounded to two decimal places is used.

[0065] The apparent density AD (g / cm 3 ) is measured by the method described below, and the value rounded to two decimal places is used.

[0066] (Specific surface area SA of alumina particles)

[0067] 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.

[0068] 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.

[0069] The specific surface area SA of the 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, even more preferably 0.5 m 2 / g or less, particularly preferably 0.3 m 2 / g or less.

[0070] The specific surface area SA of the alumina particles can be 0.005 m 2 / g or more, or can be 0.01 m 2 / g or more.

[0071] (Apparent density AD of alumina particles)

[0072] The apparent density AD of the alumina particles was measured by the pycnometer method in accordance with JIS R 1620-1995. The number of measurements was set to 5 or more, and the average value was used. For example, AccuPyc 1330 (Micromeritics) can be used during the measurement.

[0073] The apparent density of the 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, and even more preferably 3.93 g / cm 3 or less, and even more preferably 3.68 g / cm 3 or more and 3.92 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 the resin composition.

[0074] (True roundness of alumina particles)

[0075] The true roundness of the alumina particles is preferably 0.85 or more, more preferably 0.90 or more. 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 the resin composition of electronic components.

[0076] 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 0.85 or more, especially 0.90 or more, if only alumina particles with low true roundness are made to collide with each other or if alumina particles with low true roundness are pulverized. In order to improve the true roundness of the alumina particles by collision and pulverization, it is necessary to carry out collision and pulverization for a long time. 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 pulverization will reduce the mixing property with the alumina particle resin, so it may not be suitable as a filler for the resin composition. Furthermore, there are many minute defects on the aforementioned hydrophilic surface, and the dielectric loss may increase.

[0077] The true 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.

[0078] The true roundness of the alumina particles is measured using a measuring device (e.g., CAMSIZER X2 (manufactured by VERDER Scientific)) based on the principle of dynamic image analysis in accordance with ISO 13322-2.

[0079] (Particle size distribution: D90 - D10)

[0080] The particle size distribution of the alumina particles can be evaluated by the difference (D90 - D10) between the particle diameter D10 at which the cumulative number from the fine particle side of the cumulative particle size distribution reaches 10% and the particle diameter D90 at which the cumulative number from the fine particle side of the cumulative particle size distribution reaches 90%. The smaller D90 - D10 is, the narrower the particle size distribution, and it can be said that the alumina particles have a consistent particle diameter. D90 - D10 is preferably 20.0 μm or more and 90.0 μm or less, more preferably 30.0 μm or more and 85.0 μm or less, and particularly preferably 35.0 μm or more and 80.0 μm or less.

[0081] As described above, the alumina particles according to Embodiment 1 are used as a filler for a resin composition, and thus a resin composition with low dielectric loss can be manufactured.

[0082] When the alumina particles according to Embodiment 1 are further mixed (kneaded) with a resin, the viscosity of the mixture can be suppressed to be low. Therefore, even when the gap between the electronic component and the heat sink is narrow, the resin composition can be appropriately disposed in the narrow gap.

[0083] [Manufacturing method of alumina particles]

[0084] The manufacturing method of the alumina particles according to Embodiment 1 of the present invention will be described.

[0085] Among the raw materials of the alumina particles, alumina raw material particles mainly formed of single crystal α-alumina, having a particle diameter D50 at which the cumulative number from the fine particle side of the cumulative particle size distribution is greater than 53.0 μm and 110.0 μm or less, are mainly used. Then, the alumina particles are manufactured from the alumina raw material particles by the flame fusion method.

[0086] So far, the general view is that when the raw material particles are put into a flame, they will melt and the crystal structure of the raw material particles is reset, so 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.

[0087] 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 70.0% or more and satisfying the above formula (1) can be obtained.

[0088] In order to use raw material particles of single-crystalline alumina and effectively utilize the crystal structure characteristics of single-crystalline 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 device, the intensity of the flame, the distance between the flame and the alumina raw material particles, etc. are controlled.

[0089] In order to manufacture alumina particles with a D50 greater than 55.0 μm and 100.0 μm or less, alumina raw material particles with a D50, for example, greater than 53.0 μm and 110.0 μm or less are used. The D50 of the alumina raw material particles is preferably 55.0 μm or more and 105.0 μm or less, for example, 64.0 μm.

[0090] It should be noted 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.

[0091] It should be noted that even if the D50 of the alumina raw material particles is, for example, greater than 53.0 μm and 110.0 μm or less, as each alumina raw material particle, it may contain particles with a particle size of 53.0 μm or less and particles with a size greater than 110.0 μm. 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 53.0 μm and 110.0 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.

[0092] In addition, conventionally, a method of manufacturing alumina particles by using granulated raw material particles or polycrystalline raw material particles and using 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-crystalline α-alumina itself without granulation is used as the alumina raw material particles, alumina particles with a small L2 / L1 value can be obtained.

[0093] 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.

[0094] The case where the alumina raw material particles are single-crystalline 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, it can be judged whether it is single-crystalline or polycrystalline according to the presence or absence of clear grain boundaries in the alumina particles.

[0095] It is also possible to confirm that α-aluminum oxide is a single crystal by using the Debye-Scherrer method.

[0096] As the raw material of the alumina raw material particles, sapphire, and single crystal α-alumina produced by melt growth methods such as the Czochralski method, Verneuil method, Kyropoulos method, Bridgman method, and EFG method can be used. By crushing these raw materials and screening them with a sieve of a desired mesh size, alumina raw material particles with a specified D50 can be prepared.

[0097] The alumina raw material particles may contain a small amount (for example, about 10% by mass or less) of alumina other than α-aluminum oxide (δ-aluminum oxide, θ-aluminum oxide, etc.). In addition, a small amount (for example, about 10% by mass or less) of polycrystalline α-aluminum oxide may be included together with the single crystal α-aluminum oxide, which does not hinder the object of the present invention.

[0098] 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).

[0099] 0.625 ≤ R / F (kg / Nm 3 ) ≤ 17.000 (3)

[0100] 0.125 ≤ R / S (kg / Nm 3 ) ≤ 3.400 (4)

[0101] Herein, 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).

[0102] 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.

[0103] 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.

[0104] The supply amount F (Nm 3 / h) of 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 in the flame melting process.

[0105] 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).

[0106] 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).

[0107] 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 the preferred ranges respectively, in the flame melting process, spheroidization can be carried out while effectively utilizing the crystal structure characteristics of the raw material particles of alumina raw material particles.

[0108] 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.

[0109] R / S is more preferably 0.300 kg / Nm 3 or more and 3.000 kg / Nm 3 or less, and particularly preferably 0.600 kg / Nm 3 or more and 3.000 kg / Nm 3 or less.

[0110] In addition, the supply amount F of fuel gas is preferably less than 20 Nm 3 / h. By the supply amount of fuel gas, the flame length can be changed. The more the supply amount of fuel gas, the longer the flame length and the longer the residence time of particles in the flame. The smaller the supply amount of fuel gas, the shorter the flame length and the residence time of particles in the flame can be shortened. That is, the residence time of alumina raw material particles in the flame can be changed, and the melting degree (time) of alumina raw material particles in the flame can be changed. In addition, alumina particles with a small L2 / L1 value can be obtained while effectively utilizing the crystal structure characteristics of the raw material particles of alumina raw material particles.

[0111] 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.

[0112] 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.

[0113] As a subsequent process to the above-mentioned 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.

[0114] [Embodiment 2: Resin Composition]

[0115] 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 contains a resin and the alumina particles according to Embodiment 1 of the present invention.

[0116] 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, the mixing ratio thereof with respect to the resin composition (composite) is preferably in the ratio of 5 to 75 vol% of the resin and 95 to 25 vol% of the alumina particles.

[0117] The manufacturing method of the resin composition will be described.

[0118] Using a known method that is commonly used, the alumina particles according 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 a liquid epoxy resin, etc.), after mixing the liquid resin, the alumina particles, and a curing agent, it can be cured by heat, ultraviolet rays, etc., whereby a resin composition can be obtained. Known curing agents and methods can be used for the curing agent, mixing method, and curing method. On the other hand, when the resin is in a solid state (such as a polyolefin resin, an 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.

[0119] As the resin used in the resin composition, it can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. It should be noted that the resin can be used alone as 1 type, or 2 or more types can be used in combination.

[0120] Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, poly-4-methyl-1-pentene, 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 (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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] In addition, in these resin compositions, if necessary, known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, anti-blocking agents, antistatic agents, leveling agents, and mold release agents can be appropriately blended singly or in combination of two or more without impairing the effects of the invention.

[0125] The alumina particles and the resin composition containing the alumina particles according to this embodiment are particularly suitable for use as heat dissipation materials with low dielectric loss.

[0126] Examples

[0127] (1) Manufacture of alumina particles

[0128] Alumina raw material particles (raw material particles 1 and 2) 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 64.0 μm, and the D50 of raw material particle 2 was 81.0 μm. The D50 of the alumina raw material particles was measured by the laser diffraction method. Laser light was irradiated onto the sample dispersed in water, and its diffraction was measured to obtain the particle size. The measuring device used was the CILAS model 1090L.

[0129] Using Figure 1 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 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 sample No. 7 was not subjected to flame melting.

[0130] As the supply amount F (Nm 3 / h) of the fuel gas and the supply amount S (Nm 3The ratios of R / F and R / S, which are the ratio of the supply rate R (kg / hour) of the alumina raw material particles to the supply rate F (Nm³ / hour) and the supply rate S (Nm³ / hour), respectively, are summarized in Table 1. It should be noted that the supply rate of oxygen S is the sum of the supply rate of carrier oxygen 11 and the supply rate of combustion oxygen 12. The supply rate of the fuel gas F is less than 20 Nm³ 3 / hour. In sample number 7 in Table 1, the entries in the R / F and R / S columns being "-" means that flame melting is not performed.

[0131] [Table 1]

[0132] 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 6.667 1.333 Example 2 Raw material particles 1 4.444 0.889 Example 3 Raw material particles 1 3.333 0.667 Example 4 Raw material particles 1 2.778 0.556 Example 5 Raw material particles 1 2.500 0.500 Example 6 Raw material particles 1 0.556 0.111 Comparative example 7 Raw material particles 1 Example 8 Raw material particles 2 3.000 0.600 Example 9 Raw material particles 2 1.250 0.250

[0133] Various measurements were performed on the obtained alumina particles (sample numbers 1 to 9). It should be noted that "sample number 7" of the alumina particles is the same as raw material particle 1.

[0134] (2) Measurement of the particle size D10, D50, D90, and roundness of the alumina particles

[0135] The particle size distribution of the alumina particles was measured to obtain the particle size D50. In addition, for some samples, the particle sizes D10 and D90 were also obtained.

[0136] The particle size distribution and roundness 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 dry. The sample was sequentially introduced into the device, and while dispersing the aggregated particles with dry air at 50 kPa, the particles passing in front of the camera were measured. The weighed 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 is 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 for the particle size was set as volume.

[0137] The roundness (SPHT) was analyzed in accordance with ISO 9276-6. It was obtained according to SPHT = 4πA / P 2 where 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.

[0138] The particle size D50, the difference between the particle size D10 and D90 (D90 - D10), and the roundness of each alumina particle are shown in Table 2.

[0139] [Table 2]

[0140] Specimen number D50 (μm) D90 - D10 Roundness Example 1 66.0 69.9 0.90 Example 2 72.5 68.6 0.90 Example 3 65.3 60.1 0.96 Example 4 60.5 60.8 0.96 Example 5 61.2 62.1 0.95 Example 6 63.9 47.1 0.96 Comparative example 7 64.0 69.3 0.71 Example 8 79.2 83.9 0.90 Example 9 78.4 76.6 0.91

[0141] (3) Measurement of the apparent density AD of the alumina particles

[0142] Measure the apparent density AD of the alumina particles.

[0143] The apparent density AD is measured in accordance with JIS R 1620-1995. The measurement method and conditions are as follows.

[0144] · Measurement method: Gas displacement method

[0145] · Drying of the sample: 200 °C, for 8 hours or more

[0146] · Equipment used: AccuPyc 1330 (manufactured by Micromeritics)

[0147] · Measurement conditions

[0148] Number of purge times: 10 times

[0149] Purge filling pressure: 15.0 psig

[0150] Number of measurement times: 5 times

[0151] Measurement filling pressure: 15.0 psig

[0152] Equilibrium pressure: 0.005 psig / minute

[0153] Measurement after setting accuracy: Yes

[0154] Deviation allowable error: 0.05%

[0155] Sample unit size: 10 cm 3

[0156] The measurement results are shown in Table 3.

[0157] [Table 3]

[0158] Specimen number <![CDATA[Apparent density AD (g / cm 3 )]]> Example 1 3.91 Example 2 3.90 Example 3 3.83 Example 4 3.83 Example 5 3.84 Example 6 3.65 Comparative example 7 3.96 Example 8 3.89 Example 9 3.89

[0159] (4) Measurement of the α-phase conversion rate of the alumina particles

[0160] Measure the α-phase conversion rate of the alumina particles.

[0161] Regarding the α-phase conversion rate, a powder X-ray diffractometer (manufactured by Rigaku) is used to measure the sample of the alumina particles to obtain a diffraction spectrum. The measurement conditions are as follows: X-ray source: CuKα, X-ray output power: 45 kV, 200 mA, scanning speed: 10 deg / minute.

[0162] Based on the obtained diffraction spectrum, determine the peak height (I) of the α-phase ((012) plane) that appears at the position of 2θ = 25.6°. 25.6) and the peak height (I 46 ) resulting from the γ-phase, η-phase, χ-phase, κ-phase, θ-phase and δ-phase that appears at the position of 2θ = 46° is calculated by the following formula (2).

[0163] Degree of α-phase conversion = I 25.6 / (I 25.6 +I 46 )×100(%) (2)

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

[0165] [Table 4]

[0166] Specimen number α - conversion rate (%) Example 1 90.0 Example 2 93.0 Example 3 89.7 Example 4 89.8 Example 5 79.0 Example 6 78.0 Comparative example 7 100.0 Example 8 100.0 Example 9 95.7

[0167] (5) Measurement of the outer edge length L1 of alumina particles and the total length L2 of the boundary lines inside the particles

[0168] Specimens for cross-sectional observation are prepared using alumina particles. In the preparation of specimens for cross-sectional observation, the alumina particles are embedded in resin, and then the resin and alumina particles are cut using a diamond cutter. Then, Pt is evaporated on the cross-section as a protective film, a cross-section is prepared using Ar ion milling, fixed to the SEM specimen stage using Cu double-sided tape, and SEM-EBSD measurement is performed without evaporation. The observation position is determined in such a way that two or more alumina particles are completely within the observation area (i.e., two or more alumina particles do not contact the observation area frame). The measurement is performed on α-alumina particles.

[0169] The following equipment is used for the pretreatment of the sample and EBSD measurement.

[0170] · Equipment used

[0171] Ion milling device: IM-4000 (manufactured by Hitachi, Ltd.)

[0172] Ion sputtering device: E-1030 (manufactured by Hitachi, Ltd.)

[0173] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by JEOL Ltd.)

[0174] Electron backscatter diffraction device: Digiview V (manufactured by TSL)

[0175] The conditions for EBSD measurement are as follows.

[0176] · Measurement area: 500.0 μm × 400.0 μm

[0177] · Acceleration voltage: 20.0 kV

[0178] ·Magnification: ×500

[0179] ·Vacuum degree: 30 Pa

[0180] In the obtained EBSD image, select two or more alumina particles that do not contact the frame of the observation area, and use the image processing software Image J (manufactured by the National Institute of Health) to calculate the average value of the length L1 of the outer edge of each alumina particle. 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.

[0181] 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 (%).

[0182] The measurement results are shown in Table 5.

[0183] [Table 5]

[0184] Specimen number L2 / L1 (%) Example 1 13.4 Example 2 12.1 Example 3 35.2 Example 4 18.7 Example 5 11.8 Example 6 102.0 Comparative example 7 0.0 Example 8 6.3 Example 9 2.3

[0185] Regarding L2 / L1, the alumina particles of sample numbers 1 to 6 and 8 to 9 are within the numerical range specified in Embodiment 1, but the alumina particles of sample number 7 are below this numerical range. The reason is that the alumina particles (alumina raw material particles) of sample number 7 are single-crystal alumina, and there are almost no boundary lines inside the alumina particles.

[0186] (6) Measurement of the specific surface area SA of alumina particles

[0187] Measure the specific surface area SA of alumina particles.

[0188] The method for measuring the specific surface area of powders (solids) based on gas adsorption follows JIS Z8830:2013, and nitrogen is used as the adsorption gas. During the measurement, 1 g of alumina particles are placed in the sample tube, the adsorption-desorption isotherm is obtained, and using the multi-point plotting method, the specific surface area SA (m 2 / g) is calculated.

[0189] The measurement results of the specific surface area SA are shown in Table 6. In addition, the left side of formula (1) (particle size D50 × specific surface area SA × apparent density AD) is also shown.

[0190] [Table 6]

[0191]

[0192] (7) Measurement of the defect rate inside particles

[0193] Measure the defect rate inside alumina particles.

[0194] For alumina particles thinly dispersed on a substrate, use a high-sensitivity X-ray CT scanner (model: nano3DX) manufactured by Rigaku Corporation 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 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.

[0195] 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 areas, the formula Sa = Sb + Sc holds (see Figure 2 ).

[0196] Then, express Sc / Sa as a percentage as the defect rate inside the particles (%).

[0197] The following explains the image processing method for obtaining the areas Sa, Sb, and Sc.

[0198] Use the image processing software "Image J", cut out the image of 1 alumina particle containing voids according to the image obtained from the X-ray transmission photograph, perform binarization, and use the analysis of "Analyze Particles" to obtain the total area Sa of the alumina particles. In the image obtained from the X-ray transmission photograph, the brightness of the non-defective part of the alumina particles is the lowest, followed by the relatively higher brightness of the defective part inside the particles, and the brightness of the part around the alumina particles (background) is the highest. Therefore, when performing binarization processing, it is necessary to perform image processing to convert the brightness of the defective part and the background to the same level. Such image processing is carried out through the adjustment of contrast and the adjustment of "Convolve" filtering. Thereby, measure the area of the range after removing the light gray part as the defective part from the alumina particles (that is, the area Sb of the non-defective part).

[0199] In the particle analysis command, the area Sa (with the Include holes option set to ON), which measures both the non-defective part (area Sb) and the defective part (area Sc) inside the alumina particles, and the area of the non-defective part (i.e., area Sb) without including the defective part inside the alumina particles (with the Include holes option set to OFF) were measured. The area Sc (= Sa - Sb) was calculated based on the obtained areas Sa and Sb.

[0200] The calculation results are shown in Table 7.

[0201] [Table 7]

[0202] Specimen number Internal defect rate of particles (%) Example 1 8.6 Example 2 3.1 Example 3 4.5 Example 4 4.3 Example 5 3.7 Example 6 23.0 Comparative example 7 0.0 Example 8 1.0 Example 9 2.2

[0203] (8) Viscosity measurement of the mixture of alumina particles and resin

[0204] Shear rate-viscosity measurement of the mixture of alumina particles and epoxy resin was carried out.

[0205] 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 to 20 minutes to prepare a mixed sample for viscosity measurement.

[0206] Using HAAKE MARS II (manufactured by Thermo Fisher Scientific), shear rate-viscosity measurement of the mixed sample was carried out.

[0207] The measurement conditions are as follows.

[0208] · Geometry: Φ20 mm parallel plates

[0209] · Shear rate: 0.001 s -1 ~100 s -1

[0210] · Measurement temperature: 23 °C

[0211] · Measurement time: 4 minutes

[0212] At the measurement temperature, on a stable plate, the sample was set up within 10 minutes and the measurement was started.

[0213] Viscosity measurement results at a shear rate of 1 s -1 are shown in Table 8.

[0214] [Table 8]

[0215]

[0216] Among the alumina particles of sample numbers 1 to 6 and 8 to 9, it can be said that the viscosity of the mixture with the resin is low and the moldability is excellent. On the other hand, in the alumina particles of sample number 7, it is known that the viscosity of the mixture with the resin is significantly high and the moldability is lacking.

[0217] (9) Measurement of dielectric loss of 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.) was mixed with any of the alumina particles in sample numbers 1 to 7 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 (tanδ) of the composite was measured.

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

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

[0223] · Measuring frequency: 12 GHz

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

[0225] The measurement results of the dielectric loss are shown in Table 9.

[0226] [Table 9]

[0227] Specimen number of aluminum oxide particles Dielectric loss of resin composition Example 1 <![CDATA[1.69×10 -3 > Example 2 <![CDATA[1.36×10 -3 > Example 3 <![CDATA[9.03×10 -4 > Example 4 <![CDATA[9.34×10 -4 > Example 5 <![CDATA[8.21×10 -4 <!-- 14 -->]]> Example 6 <![CDATA[6.57×10 -4 > Comparative example 7 <![CDATA[4.40×10 -3 > Example 8 <![CDATA[6.29×10 -4 > Example 9 <![CDATA[4.97×10 -4 >

[0228] The D50, α - conversion rate, and L2 / L1 values of the alumina particles of sample numbers 1 to 6 and 8 to 9 are within the ranges specified in Embodiment 1. In addition, the value on the left side of formula (1) is also within the preferred range of Embodiment 1. Therefore, the dielectric loss of the resin composition using the alumina particles of sample numbers 1 to 6 and 8 to 9 is low.

[0229] The dielectric loss of the resin composition using the alumina particles (alumina raw material particles) of sample number 7 is high.

[0230] Explanation 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 diameter D50 at which the cumulative number from the fine particle side in the cumulative particle size distribution is 50% is greater than 55.0 μm and 100.0 μm or less, the α - conversion rate is 70.0% 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 110.0% or less.

2. The alumina particles according to claim 1, wherein the crystal defect rate is 30.0% or less.

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), D50 × SA × AD ≤ 38.00 (1) Among them, D50 is the particle diameter 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. A resin composition comprising a resin and the alumina particles according to any one of claims 1 to 4.

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