Alumina particles and resin composition using the same

Abstract

The present invention provides alumina particles used as a filler for a resin composition and capable of improving the thermal conductivity of the resin composition compared with the past. An alumina particle has a cumulative particle size distribution in which the particle size D50 at which 50% is accumulated from the fine particle side is more than 100 μm, an α conversion rate of 90% or more, and α-alumina is a single crystal. The Na content of the alumina particle is preferably 800 ppm or less. In addition, the particle size D10 at which 10% is accumulated from the fine particle side in the cumulative particle size distribution of the alumina particle is preferably 70 to 135 μm.

Description

Technical Field

[0001] This disclosure relates to alumina particles and resin compositions using the same. Background Technology

[0002] Heat generated by energizing electronic components is dissipated via a heat sink. To improve heat dissipation efficiency, techniques are known for filling the space between the electronic components and the heat sink with a heat-dissipating material.

[0003] As one of the heat dissipation components, resin compositions containing resin and inorganic particles are known, and alumina particles can be used as inorganic particles (for example, Patent Documents 1-3).

[0004] Patent Document 1 discloses alumina particles with an α-phase content of 40% or less, an average sphericity of 0.95 or more, and an average particle size of 100 μm or less as alumina particles capable of improving flowability when highly filled in resin. As a method for manufacturing alumina particles, a method is disclosed in which pulverized fused alumina is melted by flame melting and then rapidly cooled by spraying water into the furnace.

[0005] Patent Document 2 discloses alumina particles with an average sphericity of 0.93 or higher and an α-ratio of 95% or higher, which are capable of improving the viscosity and flowability of compositions when formulated with resins, etc. As a method for manufacturing alumina particles, a method is disclosed that uses metallic aluminum powder, alumina powder, or a mixture of both as raw materials, melts them by flame melting, cools and solidifies them, and then performs reheat treatment.

[0006] Patent document 3 discloses a method for obtaining spherical fused alumina particles with an average particle size of 5 to 4000 μm by using a jet mill to pulverize fused alumina and remove the edges of the fused alumina particles.

[0007] Existing technical documents

[0008] Patent documents

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

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

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

[0012] In recent years, the increased heat generation of ICs due to their high integration in electronic devices, and the use of high-current driven electronic components in electric vehicles, aircraft, and other electric applications, has become a problem. To achieve more effective heat dissipation, it is necessary to further improve the thermal conductivity of the resin composition. To achieve even more effective heat dissipation, it is also necessary to minimize the interface between the resin and the filler (alumina particles) used in the resin composition, i.e., to increase the particle size of the alumina particles.

[0013] However, the alumina particles disclosed in Patent Documents 1 and 2 have not been studied to further improve the thermal conductivity of the resin composition.

[0014] When the alumina particles in Patent Document 3 are mixed with resin to form a resin composition, it is difficult to say that the thermal conductivity is sufficient.

[0015] In view of this situation, one embodiment of the present invention aims to provide alumina particles that, when used as a filler in a resin composition, can improve the thermal conductivity of the resin composition compared to conventional methods. Furthermore, another embodiment of the present invention aims to provide a resin composition using alumina particles.

[0016] Method 1 of the present invention is an alumina particle with a cumulative particle size distribution where 50% of the particle size D50 from the microparticle side exceeds 100 μm, an α-oxidation rate of over 90%, and the α-alumina is a single crystal.

[0017] Method 2 of the present invention is the alumina particles according to Method 1, wherein the Na content is less than 800 ppm.

[0018] The third embodiment of the present invention is the alumina particles according to the first or second embodiment, wherein the cumulative particle size distribution, from the microparticle side, cumulatively includes 10% of the particle size D10, which is 70 to 135 μm.

[0019] The fourth embodiment of the present invention is alumina particles according to any one of embodiments 1 to 3, wherein the cumulative particle size distribution, from the microparticle side, cumulatively has a particle size D90 of 130 to 200 μm.

[0020] The fifth embodiment of the present invention is alumina particles according to any one of embodiments 1 to 4, wherein the sphericity is 0.90 to 1.00.

[0021] In embodiment 6 of the present invention, the alumina particles are according to any one of embodiments 1 to 5, wherein the density is 3.80 g / cm³. 3 above.

[0022] Embodiment 7 of the present invention is a resin composition comprising a resin and alumina particles as described in any one of embodiments 1 to 6.

[0023] By using alumina particles as filler according to one embodiment of the present invention, a resin composition with high thermal conductivity can be obtained. Attached Figure Description

[0024] Figure 1 This is a simplified diagram of the apparatus used to perform the flame melting process in a method for manufacturing alumina particles.

[0025] Figure 2 This is a conceptual diagram of an apparatus for measuring the thermal diffusivity of an alumina particle using the temperature wave thermal analysis (TWA) method.

[0026] Figure 3 This is a schematic diagram illustrating the calculation method for particle defect rate. Detailed Implementation

[0027] [Alumina particles]

[0028] The alumina particles of this invention are used as fillers in resin compositions and mixed with resin. The cumulative particle size distribution of the alumina particles has a cumulative 50% particle size D50 exceeding 100 μm from the microparticle side, an α-alumina content of 90% or more, and the α-alumina is a single crystal. These characteristics improve the thermal conductivity of the resin composition. Each characteristic is described in detail below.

[0029] (Cumulative particle size distribution, accumulating 50% of the particle size D50 from the microparticle side)

[0030] In the alumina particles of this embodiment, the cumulative particle size distribution, from the microparticle side, has a cumulative 50% particle size D50 (hereinafter sometimes simply referred to as "D50") exceeding 100 μm. When used as a filler in a resin composition, it is presumed that a resin composition with high thermal conductivity can be obtained for the following reasons.

[0031] When the D50 of alumina particles is large, the total surface area per unit mass of alumina particles decreases. Therefore, when manufacturing a resin composition by mixing alumina particles and resin in a specified ratio, using alumina particles with a large average particle size can reduce the total area of ​​the interface between the alumina particles and the resin. Since the interface between alumina particles and resin scatters propagating phonons, it is believed that thermal conductivity can be improved by reducing the total interface area.

[0032] Since the alumina particles of the present invention have a D50 of more than 100 μm, compared with the case where the D50 is less than 100 μm, the total interface area when mixed with the resin in a specified ratio can be reduced, and a resin composition with high thermal conductivity can be manufactured.

[0033] The D50 of the alumina particles is preferably 105 μm or more, more preferably 110 μm or more, and particularly preferably 115 μm or more. While there is no particular upper limit, from the viewpoint of good compatibility with resins and for use as a filler in resin compositions, it is preferably 160 μm or less, more preferably 155 μm or less, even more preferably 150 μm or less, further preferably 140 μm or less, and particularly preferably 135 μm or less. If the particle size exceeds 160 μm, even in embodiments of the present invention, the sphericity of the alumina particles is likely to decrease, and therefore this is not preferred.

[0034] The D50 of alumina particles is determined based on the principle of dynamic image analysis according to ISO 13322-2. The cumulative particle size distribution of alumina particles is calculated using the cumulative particle size distribution obtained from the measurement results, and the particle size at the cumulative 50% from the microparticle side (D50) is determined. As a measuring device, for example, a CAMSIZER (manufactured by VERDER Scientific) is used. The sample is sequentially placed into the device, and the particles are measured as they pass through the camera while the aggregated particles are dispersed using dry air.

[0035] (α-conversion rate)

[0036] Because α-alumina has high thermal conductivity, the thermal conductivity of alumina particles can be increased by increasing the α-alumina content. In the embodiments of the present invention, the α-alumina content of the alumina particles has an α-alumina content of over 90%. Therefore, alumina particles with high thermal conductivity can be obtained.

[0037] The α-oxidation rate of alumina particles is preferably above 95%, and most preferably 100%.

[0038] In this specification, "α-alumina content" refers to the percentage (volume %) of α-alumina relative to the total alumina contained in the alumina particles.

[0039] The α-phase density was determined by powder X-ray diffraction of alumina particles. The peak height (I) of the α-phase (012 plane) appearing at 2θ = 25.6° was calculated from the obtained diffraction spectrum. 25.6 ) and the peak heights (I) of the γ phase, η phase, χ phase, κ phase, θ phase, and δ phase appearing at the position of 2θ = 46°. 46 ), which is calculated by the following formula (1).

[0040] α-conversion rate = I 25.6 / (I 25.6 +I 46 )×100(%)(1)

[0041] It should be noted that although the α-oxidation rate of the alumina particles in the embodiments of the present invention is ideally 100%, it may also contain, for example, less than 10% of alumina other than α-alumina (δ-alumina, θ-alumina, etc.), without affecting the purpose of the present invention.

[0042] Alternatively, aluminum oxide other than α-alumina can be included in any way. For example, an aluminum oxide particle may contain both α-alumina and aluminum oxide other than α-alumina simultaneously. Alternatively, one aluminum oxide particle may consist only of α-alumina, and another aluminum oxide particle may consist only of aluminum oxide other than α-alumina, with these aluminum oxide particles existing in a mixture.

[0043] (α-alumina is a single crystal)

[0044] In embodiments of the present invention, manufacturing conditions are controlled such that the α-alumina contained in the alumina particles is a single crystal. As described above, α-alumina has high thermal conductivity, especially when it is a single crystal, its thermal conductivity is higher than that of polycrystalline α-alumina. Therefore, by containing α-alumina in a single crystal form in the alumina particles, the thermal conductivity of the alumina particles can be further improved.

[0045] It should be noted that a small amount (e.g., less than about 10%) of polycrystalline α-alumina may also be included together with single-crystal α-alumina without affecting the purpose of the present invention.

[0046] SEM-EBSD can be used to confirm that α-alumina in alumina particles is a single crystal. Phase MAP can be used to determine whether it is α-alumina or other types of alumina. Then, Image Quality (IQ) MAP can be used to determine whether it is a single crystal or polycrystalline by checking for the presence of clear grain boundaries in the alumina particles.

[0047] The Debye-Scherrer method can also be used to confirm that α-alumina is a single crystal.

[0048] In embodiments of the present invention, the Na content of the alumina particles is preferably below 800 ppm.

[0049] When using alumina particles as a filler in resin compositions, a high Na content (e.g., 1000 ppm or more) may adversely affect electronic components or similar devices placed adjacent to the resin composition. Furthermore, because Na present in alumina particles scatters propagating phonons, a Na content of, for example, 100 ppm or more is considered to result in excessively low thermal conductivity in the alumina particles, making them unsuitable as fillers in resin compositions. Therefore, it has been conventionally believed that when using alumina particles as a filler in resin compositions, the Na content must be less than 100 ppm.

[0050] In contrast, the inventors of this application have discovered that by having a D50 greater than 100 μm, an α-alkalinity of 90% or more, and containing single-crystal α-alumina, a thermal conductivity suitable for use as a filler in resin compositions can be achieved even with a Na content of 100 ppm or more. In particular, a Na content of 800 ppm or less is preferred, as this can improve the thermal conductivity of the alumina particles.

[0051] In this specification, "Na content" refers to the content calculated by oxide conversion, specifically the Na2O content (mass ppm) when the alumina content (converted to Al2O3) in the alumina particles is set to 100% by mass and the Na content in the alumina particles is converted to Na2O.

[0052] The Na content is more preferably 700 ppm or less, and particularly preferably 600 ppm or less.

[0053] There is no particular limitation on the lower limit of Na content, such as 1 ppm or higher. In the following cases, it is preferable to make the lower limit of Na content higher (e.g., above 20 ppm).

[0054] Sodium (Na) is sometimes contained in the raw materials used to manufacture alumina particles (alumina raw material particles). To achieve extremely low Na content in the alumina particles, a process is required to remove Na from the raw materials from the alumina particles as a whole (both the surface and interior of the alumina particles). Because the alumina particles of the embodiments of the present invention are dense, it is difficult to remove Na from the interior of the alumina particles by water washing as described below.

[0055] However, as described above, the alumina particles of the embodiments of the present invention can be used as fillers in resin compositions even if the Na content is 100 ppm or more. Therefore, in order to omit the Na removal process, a certain level of Na content is preferably allowed.

[0056] The Na content is preferably greater than 20 ppm, greater than 30 ppm, greater than 50 ppm, or greater than 80 ppm, and more preferably greater than 100 ppm.

[0057] Of the sodium (Na) contained in alumina particles, the Na present on the surface can be easily washed away with water. Since the Na that may adversely affect electronic components is mainly present on the surface of the alumina particles, washing the alumina particles with water before mixing them with the resin as a filler in the resin composition can reduce adverse effects on electronic components. However, since only a trace amount of Na present near the surface of the alumina particles can be removed by water washing, it is difficult to confirm a significant reduction in Na content even when comparing the measured values ​​of Na content in the alumina particles before and after water washing.

[0058] Furthermore, since the Na that reduces the thermal conductivity of alumina particles is mainly Na present inside the alumina particles, it is speculated that even if the alumina particles are washed with water, the thermal conductivity of the alumina particles will not increase much.

[0059] The Na content of alumina particles can be quantified by known methods such as glow discharge mass spectrometry, inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), and fluorescence measurement, with inductively coupled plasma mass spectrometry (ICP-AES) being particularly preferred.

[0060] The cumulative particle size distribution of alumina particles, with the cumulative particle size D10 representing 10% from the microparticle side, preferably 70 μm or more, more preferably 75 μm or more or 80 μm or more, and particularly preferably 90 μm or more. D10 is preferably 135 μm or less, more preferably 125 μm or less, 120 μm or less, 115 μm or less, 110 μm or less, or 105 μm or less.

[0061] Furthermore, the cumulative particle size distribution of alumina particles, with 90% of the particle size accumulated from the microparticle side, is preferably 130–200 μm. D90 is more preferably 130–190 μm, and particularly preferably 130–180 μm.

[0062] Alumina particles with this particle size are preferred because they have good flowability, can be filled in large quantities in resins, and are easy to handle.

[0063] Furthermore, the alumina particles preferably have a sharp particle size distribution, with D90 / D10 preferably below 3.0, and more preferably below 2.0. The sharper the alumina particle size distribution, the higher the replenishment rate (recovery rate) of the particles after melting and manufacturing, resulting in better productivity. Additionally, alumina particles with a sharp particle size distribution are preferred because they are easier to use as fillers in resin compositions and offer increased selectivity and flexibility when mixed with other particles.

[0064] It should be noted that, in order to ensure that the alumina particles, as the final product, are free of particulates and coarse particles, it is preferable to grade or screen the alumina raw material particles or the manufactured alumina particles. For example, if the alumina raw material particles are graded or screened to remove particulates and coarse particles before being used in the manufacture of alumina particles, the particulates and coarse particles in the obtained alumina particles can be reduced. Alternatively, the manufactured alumina particles can also be graded or screened to remove particulates and coarse particles.

[0065] For alumina particles that do not contain coarse particles, from the viewpoint of improving sphericity, the cumulative particle size distribution from the microparticle side, the cumulative particle size D100 (i.e., the maximum particle size) is preferably 500 μm or less, more preferably 400 μm or less, and particularly more preferably 300 μm or less.

[0066] In embodiments of the present invention, when alumina particles are manufactured using alumina raw material particles, they tend to become polycrystalline alumina particles, alumina particles with low alpha content, or low-density alumina particles. Therefore, it is particularly preferable to remove the particles from the alumina raw material particles or the particles from the manufactured alumina particles.

[0067] The D10, D90, and D100 of alumina particles can be determined using the same method and apparatus as the D50 determination described above. Based on the principle of dynamic image analysis according to ISO 13322-2, the particle size distribution of alumina particles is determined. Using the cumulative particle size distribution obtained from the measurement results, the cumulative 10% particle size (D10), 90% particle size (D90), and 100% particle size (D100) from the particle side are calculated. As the measuring apparatus, for example, a camera (manufactured by Verder Scientific) is used. The sample is sequentially placed into the apparatus, and the particles are measured while the aggregated particles are dispersed using dry air, as they pass through the camera.

[0068] The sphericity of alumina particles is preferably 0.90 to 1.00, which can improve the compatibility with resin and enhance the flowability of the compound after mixing, thereby reducing the wear of other components caused by alumina particles.

[0069] Since alumina particles are typically hard particles, a sphericity of 0.90 or higher is preferred when using them as fillers in resin compositions for electronic components. However, it is difficult to obtain alumina particles with a sphericity of 0.90 or higher simply by colliding or crushing alumina particles with low sphericity. Furthermore, there is a risk of generating a large amount of fine powder due to prolonged collisions and crushing. In addition, the new hydrophilic surfaces created by crushing may reduce the miscibility with the resin.

[0070] Circularity (SPHT) is analyzed according to ISO 9276-6. SPHT = 4πA / P 2 Calculate the value. In the formula, A is the measured area of ​​the projected particle image, and P is the measured outer perimeter of the particle projection image.

[0071] The sphericity of alumina particles is determined using a measuring device (e.g., CAMSIZER X2 (VERDER Scientific)) based on the principle of dynamic image analysis according to ISO 13322-2.

[0072] The preferred density of alumina particles is 3.80 g / cm³. 3 above.

[0073] If internal voids exist within alumina particles, their thermal conductivity decreases. Therefore, alumina particles with fewer internal voids are preferred. Methods for confirming internal voids include direct observation through image analysis such as cross-sectional SEM images and X-ray fluoroscopy images, and indirect confirmation by measuring the density of the alumina particles.

[0074] The preferred density of alumina particles is 3.80 g / cm³. 3 The above methods yield alumina particles with few (or no) internal voids, i.e., alumina particles with high thermal conductivity.

[0075] The density of alumina particles is more preferably 3.85 g / cm³. 3 Above, 3.88g / cm 3 Above or 3.89 g / cm 3 The above, especially preferred, is 3.90 g / cm³. 3 above.

[0076] The density of alumina particles was determined according to JIS R1620-1995 using the specific gravity bottle method. The determination should be performed at least five times. For example, an AccuPyc 1330 (Micromeritics) can be used for this determination.

[0077] In embodiments of the present invention, the thermal conductivity (W / mK) of one alumina particle can be increased. The thermal conductivity of one alumina particle is preferably 25 W / mK or more, more preferably 28 W / mK or more, particularly preferably 30 W / mK or more, and most preferably 33 W / mK or more.

[0078] [Methods for manufacturing alumina particles]

[0079] The method for manufacturing alumina particles according to embodiments of the present invention will be described.

[0080] The raw material for the alumina particles is composed of single-crystal α-alumina with a cumulative particle size distribution where 50% of the particles have a diameter D50 exceeding 100 μm from the microparticle side. Alumina particles are then manufactured from these raw material particles using a flame melting method.

[0081] The prevailing view until now was that since the raw material particles melt when placed in a flame, their crystal structure is reset, and therefore the inherent nature of the raw material particles' crystal structure does not affect the crystal structure of the particles after being spheroidized by the flame. However, it was unexpectedly discovered that when single-crystal particles are used as raw material particles, the inherent nature of the raw material particles' crystal structure can be inherited even after spheroidization.

[0082] In the flame melting process, for example using... Figure 1The apparatus shown. Through a flame melting process, alumina particles with an α-alumina content of over 90% and α-alumina as single crystals can be obtained.

[0083] In order to effectively utilize the crystal structure of single-crystal alumina after using raw material particles and spherizing them, it is necessary to control 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, and the distance between the flame and the alumina raw material particles.

[0084] To manufacture alumina particles with a D50 greater than 100 μm, alumina raw material particles with a D50 of, for example, 110 μm or greater are used. The D50 of the alumina raw material particles is preferably 120 μm or greater, for example, 150 μm.

[0085] It should be noted that even if the D50 of the alumina raw material particles is, for example, 110 μm or more, each alumina raw material particle may still contain particles with a particle size smaller than 110 μm. Therefore, the obtained alumina particles may contain polycrystalline α-alumina and / or alumina other than α-alumina. However, by setting the D50 of the alumina raw material particles to 110 μm or more, the content of polycrystalline α-alumina and / or alumina other than α-alumina can be suppressed to a small amount permissible by the present invention.

[0086] Furthermore, conventional methods for manufacturing alumina particles using granulated raw material particles via flame melting sometimes result in alumina particles containing a large number of internal voids. In this invention, since ungranulated single-crystal α-alumina itself is used as the alumina raw material particle, high-density alumina particles with few (or no) internal voids can be obtained.

[0087] The D50 of alumina raw material particles can be determined using the same method as the method described above for determining the D50 of alumina particles.

[0088] The alumina raw material particles can be confirmed to be single-crystal α-alumina using the same method as the method described above for confirming that the α-alumina in the alumina particles is a single crystal.

[0089] As raw materials for alumina particles, sapphire and single-crystal α-alumina produced by melt growth methods such as the CZ method, Verneuil method, Kyropoulos method, Bridgman method, and EFG method can be used. By crushing these raw materials and sieving them with a sieve of the desired mesh size, alumina particles with a specified D50 can be prepared.

[0090] The alumina raw material particles may contain a small amount (e.g., less than 10% by mass) of alumina other than α-alumina (δ-alumina, θ-alumina, etc.). In addition, they may also contain a small amount (e.g., less than 10% by mass) of polycrystalline α-alumina together with single-crystal α-alumina, without affecting the purpose of the present invention.

[0091] In the flame melting process, the supply of alumina raw material particles, fuel gas and oxygen preferably satisfies the following formulas (2) and (3).

[0092] 0.625≤R / F(kg / Nm 3 ≤5.000 (2)

[0093] 0.125≤R / S(kg / Nm 3 )≤1.500 (3)

[0094] Here, F represents the supply of fuel gas (Nm³). 3 / hour), S is the oxygen supply (Nm³ / hour). 3 / hour), where R is the supply rate of alumina raw material particles (kg / hour).

[0095] It should be noted that the oxygen supply (S) is the sum of the supply of combustion oxygen and the supply of carrier oxygen. Carrier oxygen is oxygen primarily used for transporting alumina raw material particles, but after transport, it is used for combustion in the same way as combustion oxygen.

[0096] As specified in formula (2), the ratio (R / F) of the alumina raw material particle supply to the fuel gas supply is preferably 0.625 kg / Nm³. 3 ~5.000kg / Nm 3 Furthermore, as specified in formula (3), the ratio (R / S) of the alumina raw material particle supply to the oxygen supply is preferably 0.125 kg / Nm³. 3 ~1.500kg / Nm 3 .

[0097] Fuel gas supply F (Nm 3 / hour) and oxygen supply S (Nm 3 The ratio ( / hour) is a factor that determines the flame intensity in the furnace during the flame melting process. R / F and R / S are both indicators of the relationship between the flame intensity in the furnace and the supply of alumina raw material particles during the flame melting process.

[0098] When R / F and R / S increase, the supply of alumina raw material particles is greater, and the energy given to each alumina raw material particle from the flame decreases (i.e., the melting of alumina raw material particles is suppressed).

[0099] When R / F and R / S decrease, the supply of alumina raw material particles is less, and the energy given to each alumina raw material particle from the flame increases (i.e., it promotes the melting of alumina raw material particles).

[0100] Therefore, controlling the R / F and R / S ratios is a method for controlling the molten state of alumina raw material particles during the flame melting process. When both R / F and R / S are within preferred ranges, spheroidization can be achieved during the flame melting process while maintaining the crystal structure of the alumina raw material particles.

[0101] A more preferred R / F ratio is 0.625 kg / Nm³. 3 ~4.500kg / Nm 3 The preferred value is 1.000 kg / Nm³. 3 ~4.500kg / Nm 3 .

[0102] The preferred R / S ratio is 0.125 kg / Nm³. 3 ~1.333kg / Nm 3 The preferred value is 0.125 kg / Nm³. 3 ~1.250kg / Nm 3 The optimal value is 0.200 kg / Nm³. 3 ~1.000kg / Nm 3 .

[0103] Therefore, the fuel gas supply quantity F is preferably less than 20 Nm³. 3 / hour. The flame length can be altered by the supply of fuel gas; a larger supply results in a longer flame and a longer residence time for particles. Conversely, a smaller supply results in a shorter flame and a shorter residence time for particles. In other words, the residence time of alumina raw material particles in the flame can be changed, thus altering their melting degree (time). Furthermore, the alpha content and density of alumina particles can be further increased while maintaining their crystal structure.

[0104] Examples of fuel gases used in this invention include propane, butane, propylene, acetylene, and hydrogen. Propane (e.g., liquefied propane gas (LPG)) is particularly preferred.

[0105] In addition, by manufacturing alumina particles through such a flame melting process, the Na content of the resulting alumina particles can be lower than that of the raw alumina particles.

[0106] In the flame melting process, when solidifying the molten alumina raw material particles, in order to slow down the cooling rate, they can be passed through a region of 600°C to 1500°C, preferably a region of 800°C to 1400°C, and more preferably a region of 1000°C to 1300°C. Passing through such a region solidifies the spheroidized alumina particles, thereby further improving the α-alloying rate.

[0107] As a follow-up step to the aforementioned flame melting process, a process can be performed to reheat the cooled and solidified alumina particles before recycling. By reheating the cooled and solidified alumina particles, the proportion of alumina other than α-alumina can be reduced, and the α-oxidation rate can be further improved. The temperature for the reheating process is preferably 900°C or higher, and more preferably 1000°C or higher. As a reheating method, external heating using a heater or the like, or heating by re-combustion of gas can be used.

[0108] [Resin Composition]

[0109] By using the alumina particles of the present invention as fillers in resin compositions, resin compositions with high thermal conductivity can be obtained. The resin composition comprises a resin and the alumina particles of the present invention.

[0110] Since the alumina particles of the present invention can improve thermal conductivity without compromising the inherent softness of the resin, the preferred ratio of the alumina particles to the resin composition (composite) is 5-75% by volume of resin and 95-25% by volume of alumina particles.

[0111] The method for manufacturing the resin composition is described.

[0112] The resin composition of the present invention can be obtained by mixing the alumina particles and resin using conventionally known methods. For example, when the resin is liquid (e.g., liquid epoxy resin), the resin composition can be obtained by mixing the liquid resin, alumina particles, and a curing agent and then curing it with heat or ultraviolet light. Known substances and methods can be used for the curing agent, mixing method, and curing method. On the other hand, when the resin is solid (e.g., polyolefin resin, acrylic resin, etc.), the target resin composition can be obtained by mixing the alumina particles and resin and then kneading them using known methods such as melt kneading.

[0113] The resin used in the resin composition may be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. It should be noted that one type of resin may be used alone, or two or more types may be used in combination.

[0114] Examples of thermoplastic resins 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, 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, polymethyl methacrylate, etc.; polyacrylic acid; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyether nitrile; polyether ketone; polyketone; liquid crystal polymers; silicone resins; and ionomers.

[0115] Examples of thermoplastic elastomers include styrene-butadiene block copolymers or their hydrides, styrene-isoprene block copolymers or their hydrides, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

[0116] Examples of thermosetting resins include cross-linked rubber, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, and diallyl phthalate resin. Specific examples of cross-linked 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.

[0117] From the perspective of processability and properties, polyolefin resins, acrylic resins, polyimide resins, polyamide resins, polyamide-imide resins, epoxy resins, phenolic resins, and silicone resins are preferred.

[0118] Furthermore, in these resin compositions, as needed and without impairing the effect of the invention, one or more known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, antiblocking agents, antistatic agents, leveling agents, and release agents may be appropriately added.

[0119] The alumina particles and the resin composition containing the alumina particles of this embodiment are particularly suitable for use as heat dissipation materials. Therefore, in one aspect of this disclosure, heat-dissipating alumina particles and a heat-dissipating resin composition can be provided.

[0120] However, the alumina particles and resin composition of this embodiment can possess low dielectric loss characteristics by further possessing the properties described in [Other Properties] below. Therefore, in another aspect of this disclosure, alumina particles with low dielectric loss and a resin composition with low dielectric loss can be provided. In yet another aspect of this disclosure, alumina particles with both heat dissipation and low dielectric loss, as well as a resin composition with both heat dissipation and low dielectric loss, can also be provided by utilizing the characteristics of both heat dissipation and low dielectric loss.

[0121] [Other physical properties]

[0122] The alumina particles and the resin composition containing the alumina particles of this embodiment can be further characterized by having a low dielectric loss resin composition. The "other physical properties" described below can be measured using the measurement methods described in the examples.

[0123] (Intraparticle defect rate)

[0124] If the alumina particles contain voids or amorphous layers (these are referred to as "particle defects"), they contribute to increased dielectric loss. Therefore, the defect rate within the alumina particles is preferably low, particularly preferably 20% or less, and more preferably 15% or less. This allows for further reduction of the dielectric loss of the resin composition when the alumina particles are used as a filler in a resin composition.

[0125] (Average aspect ratio of impurity particles)

[0126] The alumina particles may contain impurity particles (non-circular, elongated alumina particles). The average aspect ratio of the impurity particles is preferably greater than 1.2 and less than 5.0, particularly preferably less than 3 or less or less than 2.5. By including a small number of such impurity particles in the alumina particles, the filling rate of the alumina particles can be increased when used as a filler in a resin composition, and the dielectric loss of the resin composition can be further reduced.

[0127] (The ratio of the total length L2 of the particle's internal boundary line to the length L1 of the alumina particle's outer edge)

[0128] The fewer grain boundaries and cavities inside alumina particles, the lower the dielectric loss of the alumina particles. Therefore, as an indicator of the grain boundary content inside alumina particles, the ratio of the total length L2 of the boundary line to the length L1 of the outer edge (L2 / L1) is introduced.

[0129] When the length of the outer edge of an alumina particle is L1 and the total length of the boundary lines of the alumina particle is L2, an alumina particle with a small L2 / L1 ratio can be considered an alumina particle with a low boundary line content and low dielectric loss. It is particularly preferable that the (L2 / L1) (%) is 100% or less, which can further reduce the dielectric loss of the resin composition when used as a filler in a resin composition. It is more preferable that the (L2 / L1) is 80% or less, more preferably 50% or less, and particularly preferably 40% or less.

[0130] It should be noted that the "total length of the boundary line L2" is the sum of the boundary lines contained within the alumina particle, excluding the outer edge of the alumina particle. The total length of the boundary line L2 is the sum of the total length of the grain boundaries L3 within the alumina particle and the total length of the inner wall of the cavity (when there is a cavity inside the alumina particle) L4 (i.e., L2 = L3 + L4).

[0131] The determination of L1, L2, L3 and L4 is preferably performed using alumina particles composed of α-alumina.

[0132] (Number of contact points between alumina particles in the resin composition)

[0133] In resin compositions, the dielectric loss of the resin composition increases as the number of contacts between adjacent alumina particles (i.e., the number of interparticle interfaces) increases. Therefore, the number of contacts between alumina particles in the resin composition is preferably 40 or less (equivalent to 1 mm) within an observation range of 650 μm × 750 μm. 2 (Observation range is 82 or less), when used as a filler for resin compositions, it can further reduce the dielectric loss of the resin composition.

[0134] The number of contact points between alumina particles is measured within an observation range of 1 mm. 2 The preferred conversion is 65 pieces / mm. 2 The following is particularly preferred: 50 pieces / mm 2 Below or 30 pieces / mm 2 Below. For heat dissipation characteristics, the number of contact points between alumina particles is preferably more than one within an observation range of 650μm × 750μm (equivalent to one contact point per 1mm). 2 (The observation range is two or more).

[0135] In addition, the number of contact points between alumina particles can be used as an indicator of the degree of particle dispersion. It can be said that the fewer the contact points, the more uniformly the alumina particles are dispersed in the resin.

[0136] (BET specific surface area of ​​alumina particles)

[0137] The alumina particles in this embodiment have a low specific surface area due to the small number of surface irregularities, making it difficult to accurately determine the BET specific surface area using the N2 gas adsorption method. A value of 0.05 m² / g is preferred for the N2-BET specific surface area. 2 / g or less, 0.02m 2 / g or less, more preferably 0.01m 2 / g or less, with a particular preference for less than 0.01m 2 / g. It should be noted that the alumina particles in tests No. 3–6 had a N2-BET specific surface area of ​​less than 0.01 m². 2 / g. Therefore, by using krypton (Kr) as the adsorbed gas to determine the BET specific surface area, the BET specific surface area of ​​alumina particles with low specific surface area can be determined more accurately.

[0138] If the surface of alumina particles has fewer irregularities, the interface with the resin is reduced when used as a filler in resin compositions, resulting in lower dielectric losses in the resin composition. Therefore, the BET specific surface area S1(m²) of alumina particles using Kr gas is [not specified]. 2 / g) is preferably 0.10m 2 When used as a filler in resin compositions, a concentration of / g or less can further reduce the dielectric loss of the resin composition. The Kr-BET specific surface area S1 is more preferably 0.08m². 2 / g or less, particularly preferably 0.07m 2 / g or less.

[0139] The specific surface area S1 of Kr-BET can be 0.01m². 2 / g or more, or 0.02m 2 / g or more.

[0140] As another indicator of the surface roughness of alumina particles, the BET specific surface area S1 (m²) using Kr gas is used. 2 / g) and the ideal sphere area S2(m 2 The ratio of (S1 / S2) to g is preferred. (S1 / S2) is preferably 95 × 10⁻⁶. 5 When used as a filler in resin compositions, a dielectric loss of 40 × 10⁶ g or less can be further reduced. (S1 / S2) is more preferably 40 × 10⁶ g. 5 Below / g, especially preferably 20×10 5 / g or less.

[0141] The area of ​​an ideal sphere is S2(m 2 ) is the surface area of ​​a true spherical particle with a diameter of D50, calculated using the surface area formula for a sphere (4πr). 2 Find the answer.

[0142] In addition, another method to confirm the surface unevenness of particles can be used to evaluate pore distribution and pore volume. The pore volume of alumina particles will be discussed later.

[0143] (Water content introduced by alumina particles and resin)

[0144] If the alumina particles introduce a large amount of water (the amount of water contained in the alumina particles), the dielectric loss of the resin composition made using these alumina particles will increase. Furthermore, if the alumina particles introduce a large amount of water, moisture will seep into the resin, potentially causing adverse effects on electronic components or other components disposed adjacent to the resin composition. Therefore, it is preferable that the alumina particles introduce a small amount of water.

[0145] As an indicator of the amount of moisture introduced by alumina particles, the ratio of the amount of moisture introduced by alumina particles ΔMa to the amount of moisture introduced by the resin ΔMr (ppm) is (ΔMa / ΔMr).

[0146] ΔMa / ΔMr is preferably 0.2 or less, more preferably 0.1 or less. Since the water content ΔMa brought in by alumina particles is extremely small compared to the water content brought in by polyimide resin, the dielectric loss of the resin composition can be further reduced when alumina particles are used as a filler in the resin composition.

[0147] (pore volume of alumina particles)

[0148] When determining the pore volume of alumina particles by krypton adsorption, the preferred pore volume is 0.0003 cm³. 3 / g or less.

[0149] Like Kr-BET specific surface area, pore volume is an indicator of the unevenness of the particle surface. By controlling the pore volume of the first alumina particles within the aforementioned range, the formability of the mixture can be further improved.

[0150] The volume of the aforementioned fine pores is more preferably 0.00009 cm³. 3 / g or less, particularly preferably 0.00007cm 3 / g or less. The lower limit of the above-mentioned pore volume is not particularly limited; for example, it can be 0.000001cm. 3 / g or more, and thus can be 0.000005cm 3 / g or more.

[0151] Example

[0152] (Preparation of alumina raw material particles)

[0153] Raw material 1 is prepared as raw material particles composed of single-crystal alumina. Raw material 2 is raw material particles composed of another type of single-crystal alumina, which are sieved to remove particles smaller than 50 μm. It should be noted that both types of alumina raw material particles have angular shapes.

[0154] The physical properties of raw material 1 and raw material 2 are shown in Table 1. It should be noted that the methods for determining the physical properties of alumina raw material particles are the same as those for determining the physical properties of alumina particles described later.

[0155] [Table 1]

[0156]

[0157] (Manufacturing of alumina particles)

[0158] Use such as Figure 1 The apparatus shown prepares alumina particles. Oxygen from the oxygen supply system 10 is split, with one stream (carrier oxygen 11) supplied to the feeder 30 and the other stream (combustion oxygen 12) supplied to the burner 41 of the flame melting furnace 40. The alumina raw material particles supplied to the feeder 30 are conveyed to the burner 41 of the flame melting furnace 40 via the carrier oxygen 11. Additionally, combustion gas (LPG) is supplied to the burner 41 from the gas supply system 20. In the burner 41, a high-temperature flame of 2150°C or higher is formed by the fuel gas and the combustion oxygen 12, to which the alumina raw material particles dispersed in the carrier oxygen 11 are supplied. Thus, the alumina raw material particles are melted and spheroidized within the flame melting furnace 40. The spheroidized alumina particles are then classified using a cyclone separator 50, and supplementary alumina particles are obtained in the cyclone separator 50.

[0159] In samples No. 1 to 4, the obtained alumina particles were used directly for various determinations. In samples No. 5 and 6, the following additional treatment was performed.

[0160] In Sample No. 5, alumina raw material particles (raw material 1) were sieved using a 132 μm mesh sieve, and the alumina raw material particles remaining on the sieve were used as raw material. Furthermore, the obtained alumina particles were acid-washed to remove Na before being used for various determinations.

[0161] In sample No. 6, the obtained alumina particles were classified using sieves with a mesh size of 70 μm and 135 μm for various determinations.

[0162] The supply amount of fuel gas F (Nm³) in the flame melting process 3 / hour), oxygen supply S (Nm 3The ratios of the supply rate of alumina raw material particles (R / h) and the supply rate of oxygen S (kg / h), i.e., R / F and R / S, are summarized in Table 2. It should be noted that the supply rate of oxygen S is the sum of the supply rates of carrier oxygen 11 and combustion oxygen 12. The supply rate of fuel gas F is less than 20 Nm³. 3 / Hour.

[0163] [Table 2]

[0164]

[0165] (1) Determination of particle size D10, D50, D90 and sphericity of alumina particles

[0166] The particle size distribution of alumina particles in samples No.1 to No.6 was determined, and the average value of alumina particles, the cumulative 10% particle size D10, the cumulative 50% particle size D50, and the cumulative 90% particle size D90 were calculated.

[0167] The particle size distribution and sphericity of alumina particles were determined using a CAMSIZER X2 (manufactured by VERDER Scientific) device based on the principle of dynamic image analysis according to ISO 13322-2. The measurement was a dry method; samples were sequentially placed into the device, and the particles were measured as they passed through the camera while being dispersed using dry air at 50 kPa. 3 g samples were weighed for each measurement. Three identical measurements were repeated, and the cumulative average of these results was used to analyze the particle size distribution and sphericity. The particle size was defined as the equivalent circular diameter. The equivalent circular diameter refers to the diameter of a sphere with the same area as the projected particle image. Furthermore, the particle size was measured using volume as the reference.

[0168] Circularity (SPHT) is analyzed according to ISO 9276-6. SPHT = 4πA / P 2 Calculate the value. In the formula, A is the measured area of ​​the projected particle image, and P is the measured outer perimeter of the particle projection image.

[0169] These measurement results are shown in Table 3.

[0170] [Table 3]

[0171]

[0172] (2) Determination of the density of alumina particles

[0173] The density of alumina particles in samples No. 1 to No. 6 was determined. The results are shown in Table 4.

[0174] Density was determined according to JIS R1620-1995. The determination method and conditions are as follows.

[0175] • Measurement method: Gas displacement method

[0176] • Sample drying: 200℃, for at least 8 hours

[0177] • Device used: AccuPyc 1330 (Micromeritics)

[0178] • Measurement conditions

[0179] 10 blows

[0180] Purge filling pressure: 15.0 psig

[0181] Number of measurements: 5

[0182] Filling pressure measured: 15.0 psig

[0183] Equilibrium pressure: 0.005 psig / min

[0184] Precision setting measurement: Yes

[0185] Tolerance for deviation: 0.05%

[0186] Sample well dimensions: 10cm 3

[0187] (3) Confirmation of the crystallization state of alumina particles

[0188] The crystallinity of alumina particles in samples No. 1–6 was confirmed by EBSD (backscattered electron diffraction). The determination method and conditions are as follows.

[0189] • Use of equipment

[0190] Ion milling equipment: IM-4000 (manufactured by Hitachi, Ltd.)

[0191] Ion sputtering equipment: E-1030 (manufactured by Hitachi, Ltd.)

[0192] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by Nippon Electron Ltd.)

[0193] Backscattered electron diffraction apparatus: Digiview V (TSL fabrication)

[0194] • Measurement conditions

[0195] Accelerating voltage: 20.0kV (EBSD analysis)

[0196] • Measurement steps

[0197] The specimen for cross-sectional observation was prepared as follows. Alumina particles were embedded in resin, and then the resin and alumina particles were cut using a diamond tool. Next, Pt was deposited as a protective film on the cross-section, and the cross-section was prepared by Ar ion milling. It was then fixed to the SEM sample stage with Cu double-sided tape, and EBSD measurements were performed without evaporation.

[0198] In EBSD measurements, using Phase MAP and Image Quality (IQ) MAP in the same region of at least 400 × 250 μm, relative to the total number of alumina particles in the measurement field, a case where the proportion of α-alumina particles without observed grain boundaries is 80% or more is rated as 0, and a case where the proportion of α-alumina particles without observed grain boundaries is less than 80% is rated as ×.

[0199] (4) Determination of Na content in alumina particles

[0200] The Na content of alumina particles in samples No. 1 to No. 6 was determined. Detailed determination methods and conditions are as follows.

[0201] • Sample and quantity: Alumina particles, a total of 2 samples

[0202] • Analysis and testing projects

[0203] Quantitative analysis of Na

[0204] ·Analytical and experimental methods

[0205] Na Quantitative Analysis: Acid Dissolution / ICP-AES Method

[0206] A powdered sample (alumina particles) was measured in a sealed container, acid was added, and the sample was subjected to pressurized acid decomposition. After cooling, it was diluted with ultrapure water to obtain the analytical sample. Then, the amount of Na in the analytical sample was determined using ICP-AES (Inductively Coupled Plasma Emission Spectrometry), and the Na content contained in the powdered sample (alumina powder) was calculated.

[0207] (5) Determination of the α-oxidation rate of alumina particles

[0208] The α-oxidation rate of alumina particles in samples No. 1 to No. 6 was determined. The results are shown in Table 4.

[0209] The α-saturation rate was determined using a powder X-ray diffraction (RTD) apparatus (Rigaku Electron apparatus) to obtain the diffraction spectrum of the alumina particle sample. The measurement conditions were as follows: X-ray source: CuKα, X-ray output: 45kV, 200mA, scan rate: 10deg / min.

[0210] The peak height (I) of the α phase (012 plane) appearing at position 2θ = 25.6° was determined from the obtained diffraction spectrum.25.6 ) and the peak heights (I) of the γ phase, η phase, χ phase, κ phase, θ phase, and δ phase appearing at the position of 2θ = 46°. 46 ), which is calculated by the following formula (1).

[0211] α-conversion rate = I 25.6 / (I 25.6 +I 46 )×100(%)(1)

[0212] These measurement results, confirmation results, and calculation results are summarized in Table 4.

[0213] [Table 4]

[0214] Sample No. <![CDATA[Density (g / cm 3 )]]> Crystalline state Na content (ppm) Alpha conversion rate (%) Example 1 3.92 ○ 450 98.5 Comparative example 2 3.65 × 40 78.0 Example 3 3.92 ○ 500 97.9 Example 4 3.92 ○ 550 99.3 Example 5 3.92 ○ 170 98.0 Example 6 3.92 ○ 580 94.2

[0215] (6) Determination of thermal diffusivity and thermal conductivity of resin composition (composite)

[0216] Epoxy resin (main agent: room temperature curing embedding resin type 53 (manufactured by SANKEI CO., LTD.) 010-8140, curing agent: room temperature curing embedding resin type 53 (manufactured by SANKEI CO., LTD.) 010-8143) and alumina particles (raw material 1, samples No. 1 to 6) were mixed according to the proportions shown in Table 5, and stirred using Awatori Rentaro (manufactured by Thinky Co., Ltd.) to obtain an epoxy resin-filler (alumina particles) composite.

[0217] Adhesive tape containing glass cloth is applied to a PET film to create a mold that determines the film's shape, which is then placed on an aluminum plate. The mixed composite is poured into the mold, and the PET film is then layered on top, ensuring no air is included. Next, another aluminum plate is placed on top, and the mixture is heated to 50–70°C and allowed to cure. The curing time is approximately 3 hours at 50°C and approximately 1 hour at 70°C.

[0218] After curing, the aluminum plate was cooled down to about room temperature. Two PET films were peeled off from both sides of the cured composite to obtain a sheet sample of the composite for testing.

[0219] For the obtained sheet-like sample, the thermal diffusivity, specific heat and density are measured, and the thermal conductivity is calculated.

[0220] For thermal diffusivity, a test sample measuring 10 mm long × 10 mm wide × 0.1 mm thick was prepared from the sheet sample of the above resin composition, and the measurement was performed at room temperature by temperature wave thermal analysis (TWA method). The ai-Phase Mobile instrument manufactured by ai-Phase Corporation was used as the measuring apparatus.

[0221] Regarding thermal diffusivity, measurements were taken at any three points on a single test sample, and the average value was calculated from these three points. Regarding thermal conductivity, the measured values ​​of other test samples were standardized based on the measured value of the composite sample of "epoxy resin + raw material 1".

[0222] It should be noted that, for comparison, sheet samples made solely of epoxy resin were prepared and subjected to the same measurements and calculations.

[0223] Specific heat is calculated based on the ratio of resin to alumina particles, using the values ​​in Table 5.

[0224] Density was determined using an electronic hydrometer MDS-300 (Alfa Mirage Co., Ltd.).

[0225] The density is determined by Archimedes' method (solid density determination) according to the following formula (4). In addition, the specific gravity is determined from the density.

[0226] ρ=A÷(A-B)×(ρ0-ρ L )+ρ L (4)

[0227] here,

[0228] ρ: Density of the sample (composite)

[0229] A: Weight of the sample measured in the atmosphere

[0230] B: Weight of the sample measured in the replacement solution (water)

[0231] ρ0: Density of the replacement fluid (water) (1.0000 g / cm³) 3 )

[0232] ρ L Atmospheric density (0.0012 g / cm³) 3 ).

[0233] Substitute the measured thermal diffusivity, specific heat, and density into the following equation (5) to obtain the thermal conductivity.

[0234] Thermal conductivity = thermal diffusivity × specific heat × density (5)

[0235] These measurement and calculation results are shown in Table 5.

[0236] [Table 5]

[0237]

[0238] The measurement results will be discussed below.

[0239] The composites using alumina particles from samples No. 1, 3 to 6, which meet the requirements of the embodiments of this application, exhibit excellent thermal properties (thermal diffusivity, thermal conductivity). On the other hand, the composites using alumina particles from sample No. 2, which do not meet the requirements of the embodiments of this application, have poor thermal properties.

[0240] (7) Thermal diffusivity and thermal conductivity of alumina particles

[0241] For samples No. 1 and 3–5, the thermal diffusivity and thermal conductivity of a single alumina particle were further measured. In the embodiments described in this specification, the thermal diffusivity of a single alumina particle was successfully measured.

[0242] The method for determining the thermal diffusivity of an alumina particle is to apply temperature wave thermal analysis (TWA) to microscale measurements. A conceptual diagram of the apparatus used to determine the thermal diffusivity of an alumina particle is shown below. Figure 2 .

[0243] A thermoelectric potential type microsensor is pressed onto sample 70 (an alumina particle). The thermal diffusivity is determined by measuring the frequency dependence of the phase difference caused by the propagation of the temperature wave generated by AC heating via a function generator and a resistive microheater using a two-phase-locked amplifier 80. The diameter of sample 70 is approximately 110 μm, the thickness is 67 μm, the measurement frequency is 2.7 kHz to 4.9 kHz, and the sensor size is 8 μm × 9 μm.

[0244] In addition, the thermal conductivity was calculated using the following formula (5) from the measured thermal diffusivity. The specific heat was 0.779 kJ / kg·K, and the density was calculated using the values ​​listed in Table 4.

[0245] Thermal conductivity = thermal diffusivity × specific heat × density (5)

[0246] These measurement and calculation results are shown in Table 6.

[0247] [Table 6]

[0248]

[0249] The alumina particles in samples No. 1 and 3–5 exhibited thermal diffusivity and thermal conductivity values ​​similar to those measured for bulk single-crystal α-alumina. It should be noted that the thermal conductivity of polycrystalline α-alumina particles measured in the preliminary experiments was 15 W / mK. This indicates that by preparing single crystals, approximately twice the thermal conductivity of polycrystalline α-alumina can be achieved.

[0250] (8) Determination of intraparticle defect rate

[0251] The intraparticle defect rate of alumina particles in samples No.1 to No.4 and No.6 was determined.

[0252] Alumina particles, thinly dispersed on a substrate, were imaged using a Rigaku high-sensitivity X-ray CT scanner (model: nano3DX) within a 0.7 mm × 0.7 mm area. For all 20 or more alumina particles within the obtained X-ray transmission images, particle defects were identified. Particle defects refer to voids or amorphous layers existing within the particles. In the X-ray transmission images of alumina particles, the areas without defects (non-defect areas: observed as white) appear as light gray areas.

[0253] The area SA of the entire alumina particle, the area SB of the non-defective portion within the alumina particle, and the area SC of the defective portion within the alumina particle were calculated using ImageJ (made by the National Institute of Health) image processing software from the X-ray transmission image. It should be noted that the formula SA = SB + SC holds true for all areas.

[0254] Then, the SC / SA ratio is expressed as a percentage, which is the intraparticle defect rate (%).

[0255] The following describes the image processing method used to calculate the areas SA, SB, and SC.

[0256] Using the image processing software "Image J", an image of an alumina particle containing voids was extracted from an image obtained from an X-ray transmission image and binarized. The area SA of the entire alumina particle was calculated using the "Analyze Particles" function. In the X-ray transmission image, the non-defective portion of the alumina particle had the lowest brightness, followed by the brighter defective portion within the particle, and then the brightest portion surrounding the alumina particle (background). Therefore, during binarization, the brightness of the defective portion and the background needed to be converted to the same level. This image processing was performed by adjusting the contrast and the "Convolve" filter. Thus, the area of ​​the region remaining after removing the light gray portion (considered a defect) from the alumina particle was measured (i.e., the area SB of the non-defective portion).

[0257] In the particle analysis command, the area SA of the alumina particle is measured when both the non-defective portion (area SB) and the defective portion (area SC) inside the alumina particle are included (with Include holes checked), and the area SB of the non-defective portion is measured when the alumina particle is not included (with Include holes checked). The area SC is calculated from the obtained areas SA and SB (= SA - SB).

[0258] A lower intraparticle defect ratio (SC / SA) means fewer voids or amorphous layers within the alumina particles. Therefore, the intraparticle defect ratio of alumina particles is preferably low, particularly preferably 20% or less, and more preferably 15% or less. This further reduces the dielectric loss of the resin composition when alumina particles are used as a filler in a resin composition.

[0259] The calculation results are shown in Table 7.

[0260] [Table 7]

[0261] Sample No. Intraparticle defect rate (%) Example 1 2.1 Comparative example 2 23.0 Example 3 12.4 Example 4 3.7 Example 6 13.5

[0262] (9) Determination of the aspect ratio of impurity particles

[0263] X-ray transmission images of alumina particles from samples No. 1 to 6 within a range of 0.7 mm × 0.7 mm were captured using a high-sensitivity X-ray CT scanner (model: nano3DX) manufactured by Rigaku Corporation.

[0264] The X-ray transmission image was processed using ImageJ (made by the National Institute of Health) image processing software. Using all alumina particles within the X-ray transmission image as the evaluation object, the aspect ratio of all alumina particles in the evaluation object was determined. It should be noted that the aspect ratio is calculated by taking the particle diameter in the direction orthogonal to the maximum diameter as the minimum diameter and expressing it as the ratio of the maximum diameter to the minimum diameter.

[0265] Impurity particles in the alumina particles being evaluated are defined as the top 1% extracted from the alumina particles in descending order of aspect ratio. Then, the average aspect ratio of the impurity particles is calculated.

[0266] The average aspect ratio of the impurity particles is preferably greater than 1.2 and less than 5.0, particularly preferably less than 3 or less or less than 2.5. By including a small number of impurity particles (slender particles with a high aspect ratio) in the alumina particles, the filling rate of the alumina particles can be increased when used as a filler in a resin composition, and the dielectric loss of the resin composition can be further reduced.

[0267] The measurement results are shown in Table 8.

[0268] [Table 8]

[0269] Sample No. Average aspect ratio of impurity particles Example 1 1.9 Comparative example 2 1.2 Example 3 1.5 Example 4 2.4 Example 5 1.4 Example 6 1.9

[0270] (10) Determination of the length L1 of the outer edge of alumina particles and the total length L2 of the inner boundary line of the particles.

[0271] Cross-sectional observation specimens were prepared using alumina particles from samples No. 1 to 6. In the preparation of these specimens, alumina particles were embedded in resin, and then the resin and alumina particles were cut using a diamond tool. Next, Pt was deposited as a protective film on the cross-section, and the cross-section was prepared by Ar ion milling. The specimens were then fixed to the SEM stage using Cu double-sided tape, and SEM-EBSD measurements were performed without evaporation. The observation position was determined by ensuring that two or more alumina particles were completely within the observation area (i.e., two or more alumina particles did not contact the edge of the observation area). Measurements were performed using α-alumina particles.

[0272] The following equipment is used for sample pretreatment and EBSD determination.

[0273] • Use of equipment

[0274] Ion milling equipment: IM-4000 (manufactured by Hitachi, Ltd.)

[0275] Ion sputtering equipment: E-1030 (manufactured by Hitachi, Ltd.)

[0276] Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by Nippon Electron Ltd.)

[0277] Backscattered electron diffraction apparatus: Digiview V (TSL fabrication)

[0278] The conditions for EBSD determination are as follows.

[0279] • Measurement area: 500.0 μm × 400.0 μm

[0280] Accelerating voltage: 20.0kV

[0281] ·Magnification:×500

[0282] • Low vacuum level: 30Pa

[0283] In the obtained EBSD image, select two or more alumina particles that do not contact the border of the observation area, and calculate the average value of the length L1 of the outer edge of each alumina particle using the image processing software Image J (made by the National Institute of Health). Also calculate the total length L2 of the boundary lines. The "total length L2 of the boundary lines" is the sum of the boundary lines contained within the alumina particle, excluding the outer edge of the alumina particle. The total length L2 of the boundary lines is obtained by adding the total length of the grain boundaries within the alumina particle to the total length of the inner walls of the cavities (when there are cavities within the alumina particle).

[0284] The ratio of the total length L2 of the boundary line to the length L1 of the outer edge (L2 / L1) is expressed as a percentage (%). The more grain boundaries and / or cavities inside the alumina particles, the larger the value of L2 / L1 (%).

[0285] The fewer grain boundaries and cavities within the alumina particles, the lower the dielectric loss of the alumina particles. That is, the smaller the L2 / L1 value, the lower the dielectric loss of the alumina particles. In particular, the L2 / L1 of the alumina particles is preferably 100% or less, which can further reduce the dielectric loss of the resin composition when used as a filler in a resin composition. The L2 / L1 is more preferably 80% or less, more preferably 50% or less, and particularly preferably 40% or less.

[0286] Based on observations of the particles' interiors, the comparative example particles had voids of approximately tens of μm, and in addition to these tiny voids of several μm, grain boundaries were also observed. The example particles had tiny voids of several μm.

[0287] The measurement results are shown in Table 9.

[0288] [Table 9]

[0289] Sample No. L2 / L1 (%) Example 1 44 Comparative example 2 102 Example 3 14 Example 4 31 Example 5 13 Example 6 23

[0290] (11) Determination of the number of contact points between alumina particles in the resin composition (complex)

[0291] Polyimide resin (Ube Industries varnish A) and alumina particles from samples No. 2-5 were mixed at a volume ratio of 20:80. A film was prepared from this mixture using a bar coater, and the film was fired in a nitrogen atmosphere to prepare an alumina-resin composite. A cross-section along the thickness direction of the composite was exposed by Ar ion milling, and the cross-section was observed.

[0292] The following apparatus and conditions are used to cut out and observe the cross-section.

[0293] • Section cutting: The section is created using a milling machine.

[0294] Device: E-3500 (made by Hitachi)

[0295] • Cross-sectional observation: Observation using a laser scanning microscopy (LSM).

[0296] Device: OLS4000 (Made by Olympus)

[0297] Measurement mode: Magnification 20x

[0298] Resolution: 1024×1942

[0299] Measurement range: approximately 650 μm in the x-direction and approximately 750 μm in the y-direction.

[0300] The number of contact points between alumina particles in the resin composition was confirmed using cross-sectional LSM images. In the cross-sectional LSM images, alumina particles were observed to be gray, and the resin was white. The number of points where the gray alumina particles were in direct contact with each other was taken as the number of contact points between alumina particles, and the number of contact points was counted.

[0301] The number of contact points can be used as an indicator of the degree of particle dispersion. If the particles are uniformly dispersed, the number of contact points between them will be smaller.

[0302] In addition, in the resin composition, the dielectric loss of the resin composition increases when the number of junctions between adjacent alumina particles (i.e., the number of interparticle interfaces) increases.

[0303] The number of contact points between alumina particles is preferably less than 40 within an observation range of 650 μm × 750 μm (equivalent to 1 mm). 2 (Observation range is 82 or less), when used as a filler for resin compositions, it can further reduce the dielectric loss of the resin composition.

[0304] The number of contact points between alumina particles is measured within an observation range of 1 mm. 2 The preferred conversion is 65 pieces / mm. 2 The following is particularly preferred: 50 pieces / mm 2 Below or 30 pieces / mm 2 the following.

[0305] The measurement results are shown in Table 10.

[0306] [Table 10]

[0307]

[0308] (12) Determination of BET specific surface area of ​​alumina particles

[0309] The BET specific surface area of ​​alumina particles in samples No.1 to No.6 was determined.

[0310] The method for determining the specific surface area of ​​powders (solids) using gas adsorption is based on JIS Z 8830:2013, using Kr as the adsorbed gas. During the measurement, 1g of alumina particles are placed in a sample tube, and adsorption-desorption isotherms are obtained. The Kr-BET specific surface area S1 (m²) is calculated using a multi-point plotting method. 2 / g).

[0311] In addition, calculate the Kr-BET specific surface area S1 (m²). 2 / g) and the ideal sphere area S2 (μm) calculated from D502 The ratio of S1 to S2. The area of ​​an ideal sphere is the surface area of ​​a true sphere with a diameter of D50, which is given by the surface area formula for a sphere (4πr²). 2 Find the answer.

[0312] If the surface of alumina particles has fewer irregularities, the interface between the particles and the resin is reduced when used as a filler in resin compositions, resulting in lower dielectric losses in the resin compositions. The BET specific surface area and the ratio of the Kr-BET specific surface area to the area of ​​an ideal sphere (S1 / S2) are both indicators of the degree of particle irregularity.

[0313] The optimal BET specific surface area S1 based on the Kr adsorption method is 0.10 m². 2 When used as a filler in resin compositions, a concentration of / g or less can further reduce the dielectric loss of the resin composition. The Kr-BET specific surface area S1 is more preferably 0.08m². 2 / g or less, particularly preferably 0.07m 2 / g or less.

[0314] The specific surface area S1 of Kr-BET can be 0.01m². 2 / g or more, or 0.02m 2 / g or more.

[0315] Furthermore, the ratio of Kr-BET specific surface area to the area of ​​an ideal sphere (S1 / S2) is preferably 95 × 10⁻⁶. 5 When used as a filler in resin compositions, a dielectric loss of 40 × 10⁶ g or less can be further reduced. (S1 / S2) is more preferably 40 × 10⁶ g. 5 Below / g, especially preferably 20×10 5 / g or less.

[0316] The measurement and calculation results are shown in Table 11.

[0317] [Table 11]

[0318]

[0319] (13) Determination of moisture content carried over by alumina particles and resin

[0320] The moisture content of alumina particles in samples No. 2-3 and 5-6 was calculated as follows. 1 g of alumina particles was pre-weighed and left in the atmosphere for 24 hours; the mass was measured and recorded as the initial mass Ma1 (g). Then, the alumina particles were dried in a vacuum dryer for 24 hours; the mass was measured and recorded as the final mass Ma2 (g). The result was calculated as (initial mass Ma1 - final mass Ma2) / (initial mass Ma1) × 10⁻¹⁰. 6ΔMa (ppm) is defined as the amount of water introduced by alumina particles.

[0321] The amount of water introduced by the resin is calculated as follows.

[0322] A film was prepared from polyimide resin (Ube Industries varnish A) using a rod coater. This film was then fired in a nitrogen atmosphere to produce a resin film approximately 300 μm thick. 1 cm × 1 cm sample pieces were cut from the resin film. The sample pieces were left to stand in the atmosphere for 24 hours, and their mass was measured; this was recorded as the initial mass Mr1 (g). Then, the polyimide resin was dried in a vacuum dryer for 24 hours, and its mass was measured; this was recorded as the final mass Mr2 (g). The formula (initial mass Mr1 - final mass Mr2) / (initial mass Mr1) × 10⁻¹⁰ was calculated. 6 Defined as the amount of water introduced by the polyimide resin, ΔMr (ppm).

[0323] The ratio (ΔMa / ΔMr) of the water-carrying content ΔMa of the alumina particles to the water-carrying content ΔMr of the polyimide resin is calculated. ΔMa / ΔMr is preferably 0.2 or less, more preferably 0.1 or less. Since the water-carrying content ΔMa of the alumina particles is extremely small compared to that of the polyimide resin, the dielectric loss of the resin composition can be further reduced when alumina particles are used as a filler in the resin composition.

[0324] The calculation results are shown in Table 12.

[0325] [Table 12]

[0326]

[0327] (14) Determination of dielectric loss of resin composition (composite)

[0328] Polyimide resin (Ube Industries varnish A) and alumina particles from samples No. 1 to 6 were mixed at a volume ratio of 20:80. A film was prepared from the mixture using a bar coater, and the film was fired in a nitrogen atmosphere to produce an alumina-resin composite with a thickness of 800 μm.

[0329] The dielectric loss of the composite was measured under the following conditions.

[0330] • Measurement apparatus: HP8510C network analyzer (manufactured by Agilent Technologies)

[0331] • Scan signal generators: HP83651A and HP8517B (both manufactured by Agilent Technologies)

[0332] • Test piece size: 110mm × 60mm

[0333] • Measurement frequency: 10GHz

[0334] • Test environment: 22℃ / 59%RH

[0335] The measurement results are shown in Table 13.

[0336] [Table 13]

[0337] Sample No. Dielectric loss Example 1 0.0032 Comparative example 2 0.0049 Example 3 0.0029 Example 4 0.0027 Example 5 0.0028 Example 6 0.0029

[0338] Dielectric loss is low for grades 1 and 3-6, while dielectric loss is high for grade 2.

[0339] (15) Determination of the pore volume of alumina particles

[0340] The pore volume of alumina particles in samples No.1 to No.6 was determined.

[0341] The method for determining the specific surface area of ​​powders (solids) using gas adsorption is based on JIS Z 8830:2013, using Kr as the adsorbed gas. During the measurement, 1g of alumina particles are placed in a sample tube, and adsorption-desorption isotherms are obtained. The pore volume distribution is analyzed using a multi-point plotting method to determine the pore volume.

[0342] When determining the pore volume of alumina particles by krypton adsorption, the preferred pore volume is 0.0003 cm³. 3 / g or less.

[0343] Like Kr-BET specific surface area, pore volume is an indicator of the unevenness of the particle surface. By controlling the pore volume of the first alumina particles within the aforementioned range, the formability of the mixture can be further improved.

[0344] The volume of the aforementioned fine pores is more preferably 0.00009 cm³. 3 / g or less, particularly preferably 0.00007cm 3 / g or less. The lower limit of the above-mentioned pore volume is not particularly limited; for example, it can be 0.000001cm. 3 / g or more, and thus can be 0.000005cm 3 / g or more.

[0345] The measurement results are shown in Table 14.

[0346] [Table 14]

[0347]

[0348] Symbol Explanation

[0349] 10. Oxygen Supply System

[0350] 11. Carrier oxygen

[0351] 12. Combustion of oxygen

[0352] 20. Fuel gas supply system

[0353] 30 Feeder

[0354] 40 Flame Melting Furnace

[0355] 50 Cyclone Separator

[0356] 60 Function Generator

[0357] 70 samples

[0358] 80 2 phase-locked amplifier

Claims

1. An alumina particle, wherein the cumulative particle size distribution, from the microparticle side, has a cumulative particle size D50 exceeding 100 μm, an α-oxidation rate of over 90%, and the α-alumina is a single crystal. The cumulative particle size distribution, with the cumulative 10% of the particle size D10 from the microparticle side, is 70–135 μm. The cumulative particle size distribution, starting from the microparticle side, shows that 90% of the particle size, D90, is 130–200 μm.

2. The alumina particles according to claim 1, wherein, The Na content is below 800 ppm.

3. The alumina particles according to claim 1, wherein, The roundness is 0.90 to 1.

00.

4. The alumina particles according to claim 1, wherein, The density is 3.80 g / cm³. 3 above.

5. A resin composition comprising a resin and alumina particles according to any one of claims 1 to 4.

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