Alumina particles and resin compositions using the same

Abstract

To provide alumina particles which are used as a filler for a resin composition and can improve the thermal conductivity of a resin composition in comparison with a conventional one.SOLUTION: Alumina particles have a cumulative 50% particle diameter D50 of more than 100 μm from the fine particle side of the cumulative particle size distribution, an α conversion rate of 90% or more, and α-alumina being a single crystal. The alumina particles preferably have a Na content of 800 ppm or less. The alumina particles preferably have a cumulative 10% particle size D10 of 70 to 135 μm from the fine particle side of the cumulative particle size distribution.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to alumina particles and resin compositions using them. [Background technology]

[0002] The heat generated when an electronic component is energized is dissipated through a heat sink. To improve heat dissipation efficiency, a technique is known in which the space between the electronic component and the heat sink is filled with a heat-dissipating material. One type of heat dissipation component is a resin composition containing resin and inorganic particles, and it is known that alumina particles can be used as the inorganic particles (for example, Patent Documents 1-3).

[0003] Patent Document 1 discloses alumina particles that can improve fluidity when densely packed into a resin, 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. As a method for producing alumina particles, a method is disclosed in which pulverized electrofused alumina is melted by flame melting and rapidly cooled by spraying water into the furnace.

[0004] Patent Document 2 discloses alumina particles that can improve the viscosity and fluidity of a composition when blended with resins, etc., having an average sphericity of 0.93 or higher and an alumina α-ratio of 95% or higher. A method for producing alumina particles is disclosed, in which metallic aluminum powder, alumina powder, or a mixture of both are used as raw materials, which are melted by flame melting, cooled and solidified, and then reheated.

[0005] Patent Document 3 discloses a method for obtaining rounded electrofused alumina particles with an average particle size of 5 to 4000 μm by crushing electrofused alumina using a jet mill and removing the edges of the electrofused alumina particles. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2009 / 133904 [Patent Document 2] International Publication No. 2008 / 053536 [Patent Document 3] Japanese Patent Publication No. 2006-169090 [Overview of the project] [Problems that the invention aims to solve]

[0007] In recent years, the increased heat generation in ICs due to the high integration of ICs in electronic devices, and the increased heat generation in electronic components due to the use of high-current driven electronic components in electric vehicles, aircraft, etc., have become problematic. To achieve more effective heat dissipation, it is necessary to further improve the thermal conductivity of resin compositions. To achieve more effective heat dissipation, it is also necessary to minimize the interface between the resin and filler (alumina particles) used in the resin composition, that is, to increase the particle size of the alumina particles.

[0008] However, the alumina particles disclosed in Patent Documents 1 and 2 have not been studied for further improvement of the thermal conductivity of the resin composition. The alumina particles described in Patent Document 3, when mixed with a resin to form a resin composition, are not considered sufficient in terms of thermal conductivity.

[0009] In view of these circumstances, one embodiment of the present invention aims to provide alumina particles used as a filler for resin compositions, which 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. [Means for solving the problem]

[0010] One aspect of the present invention is: The particle size D50 at the 50% cumulative particle size distribution from the finest particle side is over 100 μm, the alpha-adsorption rate is 90% or higher, and the α-alumina is a single-crystal alumina particle.

[0011] Aspect 2 of the present invention is, The alumina particles are as described in Embodiment 1, wherein the Na content is 800 ppm or less.

[0012] A third aspect of the present invention is: The alumina particles are as described in embodiment 1 or 2, wherein the particle size D10 of the cumulative 10% from the finest particle side of the cumulative particle size distribution is 70 to 135 μm.

[0013] Aspect 4 of the present invention is The alumina particles are as described in any of embodiments 1 to 3, wherein the particle size D90 at the cumulative 90% from the finest particle side of the cumulative particle size distribution is 130 to 200 μm.

[0014] Aspect 5 of the present invention is The alumina particles are those described in any one of embodiments 1 to 4, having a roundness of 0.90 to 1.00.

[0015] Aspect 6 of the present invention is, Density is 3.80 g / cm³ 3 The above describes the alumina particles as described in any one of embodiments 1 to 5.

[0016] Aspect 7 of the present invention is This is a resin composition comprising a resin and alumina particles as described in any one of embodiments 1 to 6. [Effects of the Invention]

[0017] By using alumina particles according to one embodiment of the present invention as a filler, a resin composition having high thermal conductivity can be obtained. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic diagram showing the apparatus for carrying out the flame melting process in a method for producing alumina particles. [Figure 2] Figure 2 is a conceptual diagram of a thermal diffusivity measuring device for performing thermal wave analysis (TWA) on a single alumina particle. [Figure 3] Figure 3 is a schematic diagram illustrating the method for calculating the particle defect rate. [Modes for carrying out the invention]

[0019] [Alumina particles] The alumina particles according to the embodiment of the present invention are intended for use as a filler in resin compositions, mixed with resins. The alumina particles have a particle size D50 of over 100 μm at the 50% end of the cumulative particle size distribution from the finest end, an α-conjugation rate of 90% or more, and α-alumina as a single crystal. These characteristics improve the thermal conductivity of the resin composition. Each characteristic is described in detail below.

[0020] (D50: Particle size at 50% of the cumulative particle size distribution, starting from the finest particle side) In the alumina particles according to the embodiment of the present invention, the particle size D50 (hereinafter sometimes simply referred to as "D50") at the cumulative 50% from the finest particle side of the cumulative particle size distribution is greater than 100 μm. When used as a filler for resin compositions, it is presumed that a resin composition with high thermal conductivity can be obtained for the following reasons.

[0021] When the D50 of alumina particles is large, the total surface area of ​​the alumina particles per unit mass (total surface area) decreases. Therefore, when manufacturing a resin composition by mixing alumina particles and resin in a predetermined ratio, using alumina particles with a larger average particle size can reduce the total surface 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 reducing the total surface area of ​​the interface can improve thermal conductivity.

[0022] In the embodiment of the present invention, the alumina particles have a D50 of more than 100 μm, which reduces the total surface area of ​​the interface when mixed with the resin in a predetermined ratio compared to the case where the D50 is 100 μm or less, making it possible to produce a resin composition with high thermal conductivity. The D50 of the alumina particles is preferably 105 μm or more, more preferably 110 μm or more, and particularly preferably 115 μm or more. There is no particular upper limit, but from the viewpoint of improving the kneadability with resins and from the viewpoint of application to fillers for resin compositions, it is preferably 160 μm or less, more preferably 155 μm or less, more preferably 150 μm or less, even more preferably 140 μm or less, and particularly preferably 135 μm or less. If it exceeds 160 μm, it is undesirable because there is a high possibility that the roundness of the alumina particles will be low even in the embodiments of the present invention.

[0023] The D50 of alumina particles is determined by measuring the particle size distribution of the alumina particles based on the principle of dynamic image analysis in accordance with ISO 13322-2. The cumulative particle size distribution obtained from the measurement results is used to determine the particle size (D50) at which 50% of the particles are accumulated from the finest particles. As a measuring device, for example, a CAMSIZER (manufactured by VERDER Scientific) is used, in which the sample is sequentially introduced into the device, and the particles passing in front of the camera are measured while aggregated particles are dispersed with dry air.

[0024] (gelatinization rate) Because α-alumina has high thermal conductivity, the thermal conductivity of alumina particles can be increased by increasing the α-alumina content in the alumina particles. In the embodiment of the present invention, the α-conversion rate, which is an indicator of the α-alumina content, is high at 90% or more. Therefore, alumina particles with high thermal conductivity can be obtained. The gelatinization rate of the alumina particles is preferably 95% or higher, and most preferably 100%.

[0025] In this specification, "alpha-conversion rate" refers to the percentage (by volume) of alpha-alumina relative to the total alumina contained in the alumina particles. The alpha-adsorption rate is determined by measuring the alumina particles using powder X-ray diffraction and analyzing the obtained diffraction spectrum, specifically the peak height (I) of the α-phase (012 plane) appearing at the position 2θ = 25.6°. 25.6 ) and the peak heights (I) of the γ, η, χ, κ, θ, and δ phases that appear at the position 2θ=46° 46 ) is determined and calculated using the following formula (1). αization rate=I 25.6 / ( I 25.6 +I 46 ) × 100 (%) (1)

[0026] While it is most desirable for the alumina particles in the embodiment of the present invention to have an α-conjugation rate of 100%, they may also contain alumina other than α-alumina (δ-alumina, θ-alumina, etc.) in amounts of, for example, about 10% or less, without hindering the objectives of the present invention. Furthermore, alumina other than α-alumina may be included in any manner. For example, a single alumina particle may contain both α-alumina and alumina other than α-alumina. Alternatively, some alumina particles may consist only of α-alumina, while other alumina particles may consist only of alumina other than α-alumina, and these alumina particles may be mixed together.

[0027] (α-alumina is a single crystal) In the embodiments of the present invention, the manufacturing conditions are controlled so that the α-alumina contained in the alumina particles becomes a single crystal. As described above, α-alumina has high thermal conductivity, and in particular, when it is a single crystal, its thermal conductivity is higher than that of polycrystalline α-alumina. Therefore, by including α-alumina in the alumina particles as a single crystal, the thermal conductivity of the alumina particles can be further improved. Furthermore, the present invention may contain a small amount (for example, about 10% or less) of polycrystalline α-alumina along with single-crystal α-alumina, without hindering the objectives of the present invention.

[0028] The single-crystal nature of α-alumina within alumina particles can be confirmed by SEM-EBSD. Phase MAP is used to determine whether the material is α-alumina or other types of alumina, and then Image Quality (IQ) MAP is used to determine whether the material is single-crystal or polycrystalline based on the presence or absence of clear grain boundaries within the alumina particles. The fact that α-alumina is a single crystal can also be confirmed by the Debye-Scherrer method.

[0029] In the embodiment of the present invention, the alumina particles preferably have a Na content of 800 ppm or less. When alumina particles are used as a filler in resin compositions, a high Na content (e.g., 1000 ppm or more) may adversely affect electronic components and other materials placed adjacent to the resin composition. Furthermore, because the Na present in alumina particles scatters propagating phonons, it was previously believed that a Na content of, for example, 100 ppm or more resulted in too low alumina particle thermal conductivity, making them unsuitable as a filler in resin compositions. For these reasons, it was conventionally considered necessary to keep the Na content below 100 ppm when using alumina particles as a filler in resin compositions.

[0030] In contrast, the inventors of this application have found that, when the D50 is greater than 100 μm, the α-conjugation rate is 90% or more, and the contained α-alumina is single crystal, it is possible to achieve a thermal conductivity suitable for use as a filler for resin compositions even if the Na content is 100 ppm or more. In particular, a Na content of 800 ppm or less is preferable, as this can improve the thermal conductivity of the alumina particles. In this specification, "Na content" refers to the content calculated on an oxide basis, where the alumina contained in the alumina particles (calculated as Al2O3) is considered to be 100% by mass, and the Na contained in the alumina particles is calculated as Na2O, resulting in the Na2O content (mass ppm).

[0031] The Na content is more preferably 700 ppm or less, and particularly preferably 600 ppm or less.

[0032] The lower limit of the Na content is not particularly limited, but for example, it is 1 ppm or more. Under the following circumstances, it is preferable to raise the lower limit of the Na content (for example, to more than 20 ppm). Na may be present in the raw materials (alumina raw material particles) used to manufacture alumina particles. In order to reduce the Na content of alumina particles to an extremely low level, it is necessary to perform a treatment to remove the Na derived from the raw materials from the entire alumina particle (the surface and interior of the alumina particle). Because the alumina particles according to the embodiment of the present invention are dense, it is difficult to remove Na from the interior of the alumina particles by water washing of the alumina particles as described later. However, as described above, the alumina particles according to the embodiment of the present invention can be used as a filler for resin compositions even if the Na content is 100 ppm or more. Therefore, it is preferable to allow a certain amount of Na content in order to omit the treatment for removing Na. The Na content is preferably more than 20 ppm, more than 30 ppm, more than 50 ppm, or more than 80 ppm, and more preferably 100 ppm or more.

[0033] 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 the Na present on the surface of the alumina particles, washing the alumina particles with water before mixing them with resin as a filler for resin compositions can reduce adverse effects on electronic components. However, since the Na that can be removed by washing with water is only a very small amount of Na present near the surface of the alumina particles, it is difficult to confirm a significant decrease in Na content by comparing the measured Na content of alumina particles before and after washing with water. Furthermore, since the sodium that reduces the thermal conductivity of alumina particles is mainly the sodium present inside the alumina particles, it is presumed that washing the alumina particles with water will not significantly improve their thermal conductivity.

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

[0035] The alumina particles preferably have a particle size D10 of 10% of the cumulative particle size distribution from the finer end, which is 70 μm or larger, more preferably 75 μm or larger, or 80 μm or larger, and particularly preferably 90 μm or larger. D10 is preferably 135 μm or smaller, and more preferably 125 μm or smaller, 120 μm or smaller, 115 μm or smaller, 110 μm or smaller, or 105 μm or smaller. Furthermore, it is preferable that the alumina particles have a particle size D90 of 130 to 200 μm at the cumulative 90% of the cumulative particle size distribution from the finer side. More preferably, D90 is 130 to 190 μm, and particularly preferably 130 to 180 μm. Alumina particles with such particle size are preferable because they have good fluidity, can be filled in large quantities in resin, and are easy to handle.

[0036] Furthermore, it is preferable that the alumina particles have a sharp particle size distribution, with D90 / D10 being preferably 3.0 or less, and more preferably 2.0 or less. The sharper the particle size distribution of the alumina particles, the better the particle capture rate (recovery rate) after melting and manufacturing the alumina particles, resulting in improved productivity. In addition, alumina particles with a sharp particle size distribution are easier to use as fillers for resin compositions, and are preferable because they increase selectivity and flexibility when mixing with other particles.

[0037] Furthermore, it is preferable to classify or sieve the alumina raw material particles or the manufactured alumina particles so that the final product alumina particles do not contain fine or coarse particles. For example, if the alumina raw material particles are classified or sieved to remove fine and coarse particles before being used in the manufacture of alumina particles, the amount of fine and coarse particles in the resulting alumina particles can be reduced. Alternatively, the manufactured alumina particles may be classified or sieved to remove fine and coarse particles.

[0038] In alumina particles that do not contain coarse grains, from the viewpoint of improving roundness, the particle size D100 (i.e., the maximum particle size) at which 100% of the cumulative particle size distribution is accumulated from the fine grain side is preferably 500 μm or less, more preferably 400 μm or less, and particularly preferably 300 μm or less.

[0039] In the embodiments of the present invention, when alumina particles are produced using fine alumina raw material particles, they tend to become polycrystalline alumina particles, alumina particles with a low alpha-gelatinization rate, or low-density alumina particles. Therefore, it is particularly preferable to remove the fine particles from the alumina raw material particles or the fine particles from the alumina particles after production.

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

[0041] The alumina particles preferably have a roundness of 0.90 to 1.00, which allows for good mixing with the resin, enhances the fluidity of the composite after mixing, and further reduces wear of other components by the alumina particles. Since alumina particles are generally hard particles, it is preferable that the roundness is 0.90 or more for use as a filler for a resin composition of an electronic component. However, it is difficult to obtain alumina particles with a roundness of 0.90 or more by simply colliding alumina particles with low roundness or by simply pulverizing alumina particles with low roundness. Furthermore, if such collisions and pulverizations are carried out for a long time, there is a risk of generating a large amount of fine powder. In addition, the newly generated hydrophilic surface caused by pulverization may reduce the miscibility with the resin.

[0042] The roundness (SPHT) was analyzed in accordance with ISO 9276-6. SPHT = 4πA / P 2 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. The roundness of the alumina particles is measured by a measuring device (for example, CAMSIZER X2 (manufactured by VERDER Scientific)) based on the principle of dynamic image analysis in accordance with ISO 13322-2.

[0043] The alumina particles preferably have a density of 3.80 g / cm 3 or more. If internal voids exist in the alumina particles, the thermal conductivity of the alumina particles will be low. Therefore, it is desirable that the alumina particles have few internal voids. As a method for confirming internal voids, there are a method of directly observing by image analysis such as a cross-sectional SEM image or an X-ray fluoroscopic image, and a method of indirectly confirming by measuring the density of the alumina particles. The density of the alumina particles is preferably 3.80 g / cm 3 or more, and alumina particles with a small amount of internal voids (or no internal voids), that is, alumina particles with high thermal conductivity can be obtained. The density of the alumina particles is more preferably 3.85 g / cm 3 or more, 3.88 g / cm 3 or more, or 3.89 g / cm 3 or more, and particularly preferably 3.90 g / cm 3 or more.

[0044] The density of alumina particles shall be measured by the pycnometer method in accordance with JIS R 1620-1995. Measurements shall be taken at least five times. For example, an AccuPic 1330 (Micromeritics) can be used for measurement.

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

[0046] [Method for producing alumina particles] A method for producing alumina particles according to an embodiment of the present invention will be described. The raw material for the alumina particles consists of single-crystal α-alumina, and the alumina raw material particles used have a cumulative particle size D50 of over 100 μm, representing 50% of the cumulative particle size distribution from the finer side. Then, the alumina particles are manufactured from the alumina raw material particles by flame melting.

[0047] Until now, the prevailing theory was that when raw material particles are placed in a flame, they melt and their crystalline structure is reset, so the characteristics of the raw material particles' crystalline structure do not affect the crystalline structure of the particles after they are spheroidized by the flame. However, we unexpectedly discovered that when single-crystal particles are used as raw material particles, the characteristics of the raw material particles' crystalline structure can be retained even after spheroidization.

[0048] In the flame melting process, for example, an apparatus like the one shown in Figure 1 is used. Through the flame melting process, alumina particles with an α-conjugation rate of 90% or more and α-alumina as a single crystal can be obtained. Using single-crystal alumina raw material particles, and in order to preserve the characteristics of the single-crystal alumina crystal structure 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 flame intensity, and the distance between the flame and the alumina raw material particles are controlled.

[0049] To produce alumina particles with a D50 of over 100 μm, alumina raw material particles with a D50 of, for example, 110 μm or more are used. The D50 of the alumina raw material particles is preferably 120 μm or more, for example, 150 μm.

[0050] Even if the D50 of the alumina raw material particles is, for example, 110 μm or larger, individual alumina raw material particles may include particles with a diameter of less than 110 μm. Therefore, the resulting 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 larger, the content of polycrystalline α-alumina and / or alumina other than α-alumina can be reduced to a small amount permissible under the present invention.

[0051] Furthermore, while a conventional method of producing alumina particles using granulated raw material particles by flame melting is known, the resulting alumina particles sometimes contain many internal voids. In the present invention, since ungranulated single-crystal α-alumina itself is used as the alumina raw material particle, it is possible to obtain high-density alumina particles with few (or no) internal voids.

[0052] The D50 of alumina raw material particles can be measured using the same method as described above for measuring the D50 of alumina particles. The fact that the alumina raw material particles are single-crystal α-alumina can be confirmed by the same method used to confirm that the α-alumina in the alumina particles described above is single-crystal.

[0053] As raw materials for alumina raw material particles, sapphire and single-crystal α-alumina produced by melt growth methods such as the CZ method, Bernoulli method, Chiroporous method, Bridgman method, and EFG method can be used. By crushing these raw materials and sieving them with a mesh of the desired opening, alumina raw material particles with a predetermined D50 can be prepared.

[0054] The alumina raw material particles may contain small amounts (for example, about 10% by mass or less) of alumina other than α-alumina (δ-alumina, θ-alumina, etc.), and may also contain small amounts (for example, about 10% by mass or less) of polycrystalline α-alumina along with single-crystal α-alumina, and neither of these will hinder the objectives of the present invention.

[0055] In the flame melting process, it is preferable that the supply amounts of alumina raw material particles, fuel gas, and oxygen gas satisfy the following equations (2) and (3). 0.625 ≤ R / F (kg / Nm) 3 ) ≤ 5.000 (2) 0.125 ≤ R / S (kg / Nm) 3 ) ≤ 1.500 (3) Here, F is the amount of fuel gas supplied (Nm³ 3 ( / hour), S is the oxygen gas supply rate (Nm³) 3 R is the supply rate of alumina raw material particles (kg / hour), where R is the supply rate of alumina raw material particles (kg / hour). The oxygen gas supply amount (S) is the sum of the supply amount of combustion oxygen gas and the supply amount of carrier oxygen gas. The carrier oxygen gas is primarily used to transport alumina raw material particles, but after transport, it is used for combustion in the same way as combustion oxygen gas.

[0056] As defined in equation (2), the ratio of the supply amount of alumina raw material particles to the supply amount of fuel gas (R / F) is 0.625 kg / Nm³ 3 More than 5.000kg / Nm 3 The following is preferable. Also, as defined in formula (3), the ratio of the supply amount of alumina raw material particles to the supply amount of oxygen gas (R / S) is 0.125 kg / Nm³. 3 More than 1.500kg / Nm 3 The following is preferable:

[0057] Fuel gas supply amount F(Nm 3 (per hour) and the oxygen gas supply rate S (Nm³) 3R / F (Rate / Time) is a factor that determines the intensity of the flame inside the furnace during the flame melting process. Both R / F and R / S are indicators of the relationship between the intensity of the flame inside the furnace and the supply rate of alumina raw material particles during the flame melting process. When R / F and R / S are large, the supply of alumina raw material particles is large, and the amount of energy supplied from the flame to each alumina raw material particle is small (i.e., the melting of the alumina raw material particles is suppressed). When R / F and R / S are small, the supply of alumina raw material particles is small, and the amount of energy supplied from the flame to each alumina raw material particle is large (i.e., the melting of the alumina raw material particles is accelerated).

[0058] Therefore, controlling R / F and R / S is one method for controlling the melting state of alumina raw material particles in the flame melting process. When both R / F and R / S are within a preferred range, the alumina raw material particles can be spheroidized in the flame melting process while maintaining the crystalline structure of the raw material particles.

[0059] R / F is more preferably 0.625 kg / Nm 3 More than 4.500kg / Nm 3 The following, and particularly preferably 1,000 kg / Nm 3 More than 4.500kg / Nm 3 The following applies: R / S is more preferably 0.125 kg / Nm 3 More than 1.333kg / Nm 3 The following, and particularly preferably 0.125 kg / Nm 3 More than 1.250kg / Nm 3 The following is the case, most preferably 0.200 kg / Nm 3 More than 1.000kg / Nm 3 The following applies:

[0060] Furthermore, the fuel gas supply amount F is 20 Nm³ 3It is preferable that the time is less than / hour. The flame length can be changed by the amount of fuel gas supplied; the more fuel gas supplied, the longer the flame length becomes, and the longer the residence time of the particles in the flame. The less fuel gas supplied, the shorter the flame length becomes, and the shorter the residence time of the particles in the flame can be made. In other words, the residence time of the alumina raw material particles in the flame can be changed, and the degree of melting (time) of the alumina raw material particles in the flame can be changed. Furthermore, the alpha-gelatinization rate and density of the alumina particles can be increased while maintaining the crystalline structure of the raw material particles.

[0061] 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.

[0062] Furthermore, by producing alumina particles through such a flame melting process, the Na content of the resulting alumina particles can be reduced compared to the Na content of the alumina raw material particles.

[0063] In the flame melting process, when solidifying the molten alumina raw material particles, the cooling rate may be slowed by passing through a region of 600°C to 1500°C, preferably 800°C to 1400°C, and more preferably 1000°C to 1300°C. By passing through such a region and solidifying the spherical alumina particles, the alpha-gelatinization rate can be increased.

[0064] As a post-processing step following the flame melting process described above, a step of reheating the cooled and solidified alumina particles before collection may be included. By reheating the cooled and solidified alumina particles, the proportion of alumina other than α-alumina can be reduced, and the α-gelatinization rate can be increased. The temperature for the reheating step is preferably 900°C or higher, and more preferably 1000°C or higher. Methods of reheating include external heating using a heater or heating by re-combustion of gas.

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

[0066] The alumina particles according to the embodiment of the present invention can improve thermal conductivity without impairing the flexibility characteristic of the resin, so the blending ratio is preferably 5 to 75 volume% of the resin and 95 to 25 volume% of the alumina particles relative to the resin composition (composite).

[0067] A method for producing a resin composition will be described. A resin composition can be obtained by mixing the alumina particles and resin of the present invention using a commonly known method. For example, if 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 curing agents, mixing methods, and curing methods can be used. On the other hand, if the resin is solid (e.g., polyolefin resin or acrylic resin), the desired resin composition can be obtained by mixing the alumina particles and the resin and then kneading them using a known method such as melt kneading.

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

[0069] Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers; fluorine-based polymers such as polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, 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; polyimides; polyamide-imides; polymethacrylic acid esters such as polymethacrylic acid and polymethyl methacrylate; polyacrylic acids; polycarbonates; polyphenylene sulfide; polysulfone; polyethersulfone; polyethernitrile; polyetherketone; polyketone; liquid crystal polymers; silicone resins; and ionomers.

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

[0071] Examples of thermosetting resins include crosslinked rubber, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, and diallyl phthalate resin. Specific examples of 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, urethane rubber, and silicone rubber.

[0072] From the viewpoint of processability and properties, polyolefin resins, acrylic resins, polyimide resins, polyamide resins, polyamide-imide resins, epoxy resins, phenolic resins, and silicone resins are preferably used.

[0073] Furthermore, these resin compositions may optionally contain, individually or in combination of two 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 mold release agents, as long as they do not impair the effects of the invention.

[0074] The alumina particles and the resin composition containing said alumina particles according to this embodiment are particularly suitable for heat dissipation material applications. Therefore, one aspect of this disclosure provides heat-dissipating alumina particles and a heat-dissipating resin composition.

[0075] However, the alumina particles and resin compositions according to this embodiment may possess low dielectric loss properties by further possessing the properties described in [Other Properties] below. Thus, in another embodiment of this disclosure, low dielectric loss alumina particles and low dielectric loss resin compositions can be provided. In yet another embodiment of this disclosure, it is also possible to provide heat-dissipating and low dielectric loss alumina particles and heat-dissipating and low dielectric loss resin compositions by utilizing both heat dissipation and low dielectric loss properties.

[0076] [Other physical properties] The alumina particles according to this embodiment, and the resin composition containing said alumina particles, further possess the following properties, thereby enabling the creation of a resin composition with low dielectric loss. The "other physical properties" described below can be measured using the measurement methods described in the examples.

[0077] (Intraparticle defect rate) The presence of voids or amorphous layers (referred to as "particle defects") within alumina particles increases dielectric loss. Therefore, it is preferable for alumina particles to have a low defect rate, particularly 20% or less, and more preferably 15% or less. This allows for a further reduction in the dielectric loss of the resin composition when alumina particles are used as a filler for the resin composition.

[0078] (Average aspect ratio of impurity particles) The alumina particles may contain impurity particles (elongated, non-circular alumina particles). Preferably, the average aspect ratio of the impurity particles is greater than 1.2 and less than or equal to 5.0, and particularly less than or equal to 3, or less than or equal to 2.5. The inclusion of small amounts of such impurity particles in the alumina particles improves the packing density of the alumina particles when used as a filler for resin compositions, thereby further reducing the dielectric loss of the resin composition.

[0079] (The ratio of the total length L2 of the internal boundary lines of an alumina particle to the length L1 of the outer edge of the particle) The fewer grain boundaries and cavities within an alumina particle, the lower its dielectric loss. Therefore, the ratio of the total length L2 of the boundary lines to the length L1 of the outer edge (L2 / L1) is introduced as an indicator of the grain boundary content within an alumina particle.

[0080] When L1 is the length of the outer edge of a single alumina particle and L2 is the total length of the boundary lines of that alumina particle, alumina particles with a small L2 / L1 value can be said to have a low boundary line content and low dielectric loss. In particular, it is preferable that (L2 / L1)(%) is 100% or less, as this can further reduce the dielectric loss of the resin composition when used as a filler for resin compositions. (L2 / L1) is more preferably 80% or less, even more preferably 50% or less, and particularly preferably 40% or less.

[0081] Note that the "total boundary line length L2" is the sum of the boundary lines contained within the alumina particles, and does not include the outer edges of the alumina particles. The total boundary line length L2 is the sum of the total grain boundary lengths L3 within the alumina particles and (if there are cavities within the alumina particles) the total length of the inner walls of those cavities L4 (i.e., L2 = L3 + L4). Measurements of L1, L2, L3, and L4 are preferably performed using alumina particles made of α-alumina.

[0082] (Number of contact points between alumina particles in the resin composition) In a resin composition, an increase in the number of contact points between adjacent alumina particles (i.e., the number of interparticle interfaces) increases the dielectric loss of the resin composition. Therefore, the number of contact points between alumina particles in a resin composition should be 40 or less within an observation area of ​​650 μm × 750 μm (observation area 1 mm). 2 It is preferable that the number of particles per unit be 82 or less, which can further reduce the dielectric loss of the resin composition when used as a filler for resin compositions.

[0083] The number of contact points between alumina particles is measured within the observation area of ​​1 mm. 2 Converted to 65 pieces / mm 2 More preferably, the following, 50 pieces / mm 2 The following, or 30 pieces / mm 2 The following is particularly preferable: For heat dissipation characteristics, the number of contact points between alumina particles should be one or more within an observation area of ​​650 μm × 750 μm (observation area 1 mm). 2 It is preferable that each unit is equivalent to 2 or more units. Furthermore, the number of contact points between alumina particles can serve as an indicator of the degree of particle dispersion; the fewer the number of contact points, the more uniformly dispersed the alumina particles are in the resin.

[0084] (BET specific surface area of ​​alumina particles) The alumina particles according to this embodiment have few surface irregularities and a low specific surface area, making it difficult to accurately measure the BET specific surface area using the N2 gas adsorption method. The N2-BET specific surface area value is 0.05 m². 2 / g or less, 0.02m 2 Preferably less than / g, and 0.01m 2 Less than or equal to / g is more preferable, and 0.01m 2 A value of less than / g is particularly preferred. Note that the alumina particles in tests No. 3-6 had a specific surface area of ​​0.01 m² according to N2-BET measurement. 2 The value was less than / g. Therefore, by measuring the BET specific surface area using krypton gas (Kr) as the adsorption gas, the BET specific surface area of ​​alumina particles with a low specific surface area can be measured more accurately.

[0085] When alumina particles have fewer surface irregularities, the interface with the resin is reduced when used as a filler for resin compositions, resulting in lower dielectric loss in the resin composition. Therefore, alumina particles have a BET specific surface area S1(m²) using Kr gas. 2 ( / g) is 0.10m 2 It is preferable that the value be less than or equal to / g, and when used as a filler for resin compositions, it can further reduce the dielectric loss of the resin composition. The Kr-BET specific surface area S1 is 0.08 m². 2 It is more preferable that it be less than or equal to / g, and 0.07m 2 It is particularly preferable that the amount be less than or equal to / g. The specific surface area S1 of Kr-BET is 0.01 m². 2 It may be 0.02m or more. 2 It may be more than / g.

[0086] Another indicator of surface roughness of alumina particles is the ideal sphere area S²(m²). 2 ) for the BET specific surface area S1(m²) using Kr gas 2 There is a ratio (S1 / S2)( / g) of (S1 / S2). 5 It is preferable that the ratio be less than or equal to / g, and when used as a filler for resin compositions, it can further reduce the dielectric loss of the resin composition. (S1 / S2) is 40 × 10 5 It is more preferable that it be less than or equal to / g, 20 × 10 5 It is particularly preferable that the amount be less than or equal to / g. Ideal sphere area S2(m 2) is the surface area of ​​a perfectly spherical particle with a diameter D50, and the formula for the surface area of ​​a sphere is (4πr²). 2 )

[0087] Furthermore, the surface irregularities of the particles can also be evaluated using methods such as pore distribution and pore volume. The pore volume of alumina particles will be discussed later.

[0088] (Moisture content of alumina particles and resin) If the amount of moisture carried by the alumina particles (the amount of moisture contained in the alumina particles) is high, the dielectric loss of the resin composition made using those alumina particles will increase. Furthermore, if the amount of moisture carried by the alumina particles is high, moisture may seep out of the resin, potentially adversely affecting electronic components and other items placed adjacent to the resin composition. Therefore, it is preferable to have a low amount of moisture carried by the alumina particles.

[0089] As an indicator of the amount of moisture carried by alumina particles, we introduce the ratio of the amount of moisture carried by alumina particles ΔMa to the amount of moisture carried by the resin ΔMr (ppm) (ΔMa / ΔMr). It is preferable that ΔMa / ΔMr is 0.2 or less, and more preferably 0.1 or less. Since the amount of moisture ΔMa carried in by the alumina particles is extremely small compared to the amount of moisture carried in by the polyimide resin, the dielectric loss of the resin composition can be further reduced when alumina particles are used as a filler for the resin composition.

[0090] (Pore volume of alumina particles) When the pore volume of alumina particles was measured by the krypton adsorption method, the pore volume was 0.0003 cm³. 3 It is preferable that the value be less than or equal to / g. Pore ​​volume, like Kr-BET specific surface area, serves as an indicator of the degree of surface irregularity of the particles. By controlling the pore volume of the first alumina particles within the above range, the moldability of the mixture can be further improved.

[0091] The above pore volume is 0.00009 cm³. 3 It is more preferable that it be less than or equal to / g, and 0.00007cm3 It is particularly preferable that the pore volume be less than or equal to / g. The lower limit of the pore volume is not particularly limited, but for example, 0.000001 cm³ 3 It may be greater than or equal to / g, and even more so, 0.000005cm 3 It may be more than / g. [Examples]

[0092] (Preparation of alumina raw material particles) Raw material 1 consisted of single-crystal alumina particles. Raw material 2 consisted of different single-crystal alumina particles, and particles smaller than 50 μm were removed by sieving. Both alumina raw material particles had an angular shape. Table 1 shows the physical properties of raw material 1 and raw material 2. The method for measuring the physical properties of the alumina raw material particles was the same as the method for measuring the physical properties of the alumina particles described later.

[0093] [Table 1]

[0094] (Manufacturing of alumina particles) Alumina particles were prepared using the apparatus shown in Figure 1. Oxygen gas from the oxygen gas supply system 10 was split, with one (carrier oxygen gas 11) supplied to the feeder 30 and the other (combustion oxygen gas 12) supplied to the burner 41 of the flame melting furnace 40. The alumina raw material particles supplied to the feeder 30 were transported to the burner 41 of the flame melting furnace 40 by the carrier oxygen gas 11. Combustion gas (LPG) was also supplied to the burner 41 from the gas supply system 20. In the burner 41, a high-temperature flame of over 2150°C was formed by the fuel gas and combustion oxygen gas 12, and the alumina raw material particles dispersed in the carrier oxygen gas 11 were supplied to it. As a result, the alumina raw material particles were melted and sphericalized in the flame melting furnace 40. Subsequently, the spherical alumina particles were classified in the cyclone 50 to obtain alumina particles trapped in the cyclone 50.

[0095] For samples No. 1 to 4, the obtained alumina particles were used directly for various measurements. For samples No. 5 and 6, the following additional processing was performed. In sample No. 5, alumina raw material particles (raw material 1) were sieved using a sieve with a mesh size of 132 μm, and the alumina raw material particles that made up the sieve were used as the raw material. Furthermore, the obtained alumina particles were acid-washed to remove sodium and then used for various measurements. For sample No. 6, the obtained alumina particles were classified using sieves with mesh sizes of 70 μm and 135 μm, and used for various measurements.

[0096] F(Nm³) of fuel gas supply during the flame melting process 3 ( / hour), oxygen gas supply rate S (Nm³) 3 Table 2 summarizes the ratios R / F and R / S, which are the ratios of the supply rate R (kg / hour) of alumina raw material particles to the supply rate R (kg / hour). Note that the supply rate of oxygen gas S is the sum of the supply rate of carrier oxygen gas 11 and the supply rate of combustion oxygen gas 12. The supply rate of fuel gas F is 20 Nm³ 3 It was less than an hour.

[0097] [Table 2]

[0098] (1) Measurement of particle size D10, D50, D90 and roundness of alumina particles The particle size distribution of alumina particles from samples No. 1 to 6 was measured, and the average particle size, the cumulative particle size D10 at 10%, the cumulative particle size D50 at 50%, and the cumulative particle size D90 at 90% were determined.

[0099] The particle size distribution and roundness of alumina particles were measured using a CAMSIZER X2 instrument (manufactured by VERDER Scientific) based on the principle of dynamic image analysis in accordance with ISO 13322-2. The measurement was performed in a dry manner, with the sample being sequentially introduced into the instrument and the particles passing in front of the camera being measured while the aggregated particles were dispersed with 50 kPa dry air. 3 g of sample was weighed and measured once. The same measurement was repeated three times, and the particle size distribution and roundness were analyzed from the cumulative average of these results. Particle diameter was defined as the equivalent circular particle diameter. The equivalent circular particle diameter is the diameter of a perfectly circular particle that has the same area as the projected particle image. The particle diameter was based on volume. The roundness (SPHT) was analyzed according to ISO 9276-6. SPHT = 4πA / P 2 This was derived from the following equation. In the equation, A is the measured area of ​​the projected particle image, and P is the measured perimeter of the particle projection image.

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

[0101] [Table 3]

[0102] (2) Measurement of the density of alumina particles The density of alumina particles in samples No. 1 to 6 was measured. The measurement results are shown in Table 4. Density was measured in accordance with JIS R 1620-1995. The measurement method and conditions were as follows. • Measurement method: Gas displacement method • Drying of the sample: 200°C for 8 hours or more • Device used: AccuPic 1330 (Micromeritics) • Measurement conditions Number of purges: 10 Purge filling pressure: 15.0 psig Number of measurements: 5 Measured filling pressure: 15.0 psig Equilibrium pressure: 0.005 psig / min Measurement with set precision: Yes Variation tolerance: 0.05% Sample cell dimensions: 10 cm 3

[0103] (3) Confirmation of the crystalline state of alumina particles The crystalline state of alumina particles in samples No. 1-6 was confirmed by EBSD (backscattered electron diffraction). The measurement method and conditions were as follows. ·Equipment used Ion milling machine: IM-4000 (manufactured by Hitachi, Ltd.) Ion sputtering system: E-1030 (manufactured by Hitachi, Ltd.) Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by JEOL Ltd.) Backscatter electron diffraction spectrometer: Digiview V (manufactured by TSL) • Measurement conditions Acceleration voltage: 20.0kV (EBSD analysis)

[0104] • Measurement procedure Samples for cross-sectional observation were prepared as follows: Alumina particles were embedded in resin, and then the resin and alumina particles were cut with a diamond cutter. Subsequently, Pt was deposited on the cross-section as a protective film, and the cross-section was prepared by Ar ion milling. The sample was fixed to the SEM sample stage with Cu double-sided tape, and EBSD measurement was performed without deposition. In EBSD measurements, a "○" was indicated if, in the Phase MAP and Image Quality (IQ) MAP of at least 400 μm × 250 μm of the same region, 80% or more of the α-alumina particles in the measurement field of view did not show grain boundaries, and a "×" was indicated if less than 80% of the α-alumina particles did not show grain boundaries.

[0105] (4) Measurement of the Na content of alumina particles The Na content of alumina particles in samples No. 1 to 6 was measured. The detailed measurement method and conditions were as follows. • Samples and number of samples: Alumina particles, 2 samples in total • Analysis, test items Quantitative analysis of Na • Analysis and testing methods Quantitative Na analysis: Acid dissolution / ICP-AES method

[0106] A powder sample (alumina particles) was weighed into a sealed container, acid was added, and a pressurized acid decomposition treatment was performed. After cooling, it was diluted with ultrapure water to prepare the analytical sample. Then, the amount of Na in the analytical sample was measured using ICP-AES (inductively coupled plasma emission spectrometer), and the Na content contained in the powder sample (alumina powder) was calculated.

[0107] (5) Measurement of the alpha-adsorption rate of alumina particles The gelatinization rate of alumina particles in samples No. 1 to 6 was measured. The measurement results are shown in Table 4. The alpha-adsorption rate was measured using a powder X-ray diffractometer (manufactured by Rigaku Denki Co., Ltd.) on alumina particle samples, and the diffraction spectrum was obtained. The measurement conditions were: X-ray source: CuKα, X-ray output: 45kV, 200mA, scanning speed: 10deg / min. From the obtained diffraction spectrum, the peak height (I) of the α phase (012 plane) appearing at the position 2θ = 25.6° was determined. 25.6 ) and the peak heights (I) of the γ, η, χ, κ, θ, and δ phases that appear at the position 2θ=46° 46 The following equation (1) was used to calculate the value of ). αization rate=I 25.6 / ( I 25.6 +I 46 ) × 100 (%) (1)

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

[0109] [Table 4]

[0110] (6) Measurement of thermal diffusivity and thermal conductivity of resin compositions (composites) Epoxy resin (main component: room-temperature curing embedding resin type 53 (manufactured by Sankei Co., Ltd.) 010-8140, hardener: 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 in the proportions shown in Table 5, and the mixture was stirred and mixed using a foam remover (manufactured by Shinki Co., Ltd.) to obtain an epoxy resin-filler (alumina particle) composite.

[0111] A mold was created by attaching glass cloth-reinforced tape to a PET film to determine the film's outline, and then placed on an aluminum plate. The mixed composite was poured into the mold, and a PET film was placed on top, ensuring no air bubbles were trapped. Another aluminum plate was then placed on top of that, and the mixture was heated to 50-70°C and allowed to stand to cure the resin. The curing time was approximately 3 hours at 50°C and approximately 1 hour at 70°C. After curing was complete, the aluminum plate was allowed to cool, and once its temperature had dropped to room temperature, two PET films were peeled off from both sides of the cured composite to obtain a sheet-like sample of the composite for measurement.

[0112] The thermal diffusivity, specific heat, and density of the obtained sheet-like samples were measured, and the thermal conductivity was determined. The thermal diffusivity was measured at room temperature using thermal wave analysis (TWA) by preparing a 10 mm x 10 mm x 0.1 mm measurement sample from a sheet-like sample of the resin composition described above. The iPhase Mobile, manufactured by iPhase Corporation, was used as the measuring device. For thermal diffusivity, measurements were taken at three arbitrary points on a single sample piece, and the average value was calculated from the results of these three points. For thermal conductivity, the measured values ​​of other samples were normalized using the measured value of the composite sample of "epoxy resin + raw material 1" as the standard. For comparison, a sheet-like sample consisting solely of epoxy resin was prepared and the same measurements and calculations were performed.

[0113] The specific heat was calculated from the mixing ratio of resin and alumina particles, and the values ​​in Table 5 were used.

[0114] Density measurements were performed using an electronic hydrometer MDS-300 (Alpha Mirage Co., Ltd.). The density was determined by the Archimedes method (solid density measurement) based on the following equation (4). Specific gravity was also determined from the density. ρ = A ÷ (AB) × (ρ0 - ρ) L )+ρ L (4) Here, ρ: Density of the sample (composite) A: Weight of the sample measured in air B: Weight of the sample measured in the displacement solution (water) ρ0: Density of the replacement solution (water) (1.0000 g / cm³) 3 ) ρ L Atmospheric density (0.0012 g / cm³) 3 ) That is the case.

[0115] The measured results for thermal diffusivity, specific heat, and density were substituted into the following equation (5) to determine the thermal conductivity. Thermal conductivity = thermal diffusivity × specific heat × density (5)

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

[0117] [Table 5]

[0118] The measurement results will be discussed below. The composites using alumina particles from samples No. 1 and 3-6, which met the requirements of the embodiment of this application, exhibited excellent thermal properties (thermal diffusivity and thermal conductivity). On the other hand, the composite using alumina particles from sample No. 2, which did not meet the requirements of the embodiment of this application, exhibited inferior thermal properties.

[0119] (7) Thermal diffusivity and thermal conductivity of alumina particles For samples No. 1 and 3-5, the thermal diffusivity and thermal conductivity of a single alumina particle were further measured. In the examples described herein, the thermal diffusivity of a single alumina particle was successfully measured. The method for measuring the thermal diffusivity of a single alumina particle is an application of thermal wave analysis (TWA) to microscale measurements. A conceptual diagram of the apparatus for measuring the thermal diffusivity of a single alumina particle is shown in Figure 2.

[0120] A thermoelectric microsensor was pressed onto sample 70 (a single alumina particle). The frequency dependence of the phase difference due to the propagation of a temperature wave generated by AC current heating from a function generator to a resistive microheater was measured using a two-phase lock-in amplifier 80 to determine the thermal diffusivity. The diameter of sample 70 was approximately 110 μm, the thickness of sample 70 was 67 μm, the measurement frequency was 2.7 kHz to 4.9 kHz, and the sensor size was 8 μm × 9 μm. Furthermore, the thermal conductivity was determined from the measured thermal diffusivity using the following equation (5). The specific heat was assumed to be 0.779 kJ / kg·K, and the density was the value listed in Table 4. Thermal conductivity = thermal diffusivity × specific heat × density (5)

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

[0122] [Table 6]

[0123] The alumina particles of samples No. 1 and 3-5 showed thermal diffusivity and thermal conductivity values ​​comparable to those measured for bulk single-crystal α-alumina. Furthermore, preliminary experiments on polycrystalline α-alumina particles showed a thermal conductivity of 15 W / mK. This indicates that single-crystal α-alumina exhibits approximately twice the thermal conductivity compared to polycrystalline α-alumina.

[0124] (8) Measurement of the intraparticle defect rate The intraparticle defect rate of alumina particles from samples No. 1-4 and 6 was measured. Alumina particles, thinly dispersed on a substrate, were subjected to X-ray transmission imaging in a 0.7 mm × 0.7 mm area using a high-sensitivity X-ray CT scanner (model: nano3DX) manufactured by Rigaku Corporation. Particle defects were confirmed for all 20 or more alumina particles in the obtained X-ray transmission images. Particle defects are voids or amorphous layers present within the particle, and in the X-ray transmission images of alumina particles, they are observed as light gray areas within the defect-free parts (defect-free areas: observed as white areas) of the alumina particles. X-ray radiographs were processed using the image processing software Image J (manufactured by the National Institute of Health) to determine the total area SA of the 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. The equation SA = SB + SC holds true for each of these areas. Then, SC / SA was expressed as a percentage, and this was defined as the particle defect rate (%).

[0125] The image processing methods for determining the areas SA, SB, and SC are described below. Using the image processing software "Image J," an image of a single alumina particle containing voids was extracted from an image obtained from an X-ray radiograph, binarized, and the area SA of the entire alumina particle was determined using the analysis of "Analyze Particles." In the image obtained from the X-ray radiograph, the non-defective parts of the alumina particle have the lowest brightness, followed by the defective parts within the particle, and then the area surrounding the alumina particle (background) has the highest brightness. Therefore, during the binarization process, image processing is required to convert the brightness of the defective parts and the background to roughly the same level. Such image processing was performed by adjusting the contrast and the filter "Convolve." As a result, the area of ​​the region where the light gray defective parts were removed from the alumina particle (i.e., the area SB of the non-defective parts) was measured.

[0126] In the particle analysis command, the area SA of an alumina particle was measured when both the non-defective portion (area SB) and the defective portion (area SC) within the alumina particle were included (with the "Include holes" checkbox turned ON), and the area SB of the non-defective portion (i.e., the area of ​​the non-defective portion) was measured when the defective portion of the alumina particle was not included (with the "Include holes" checkbox turned OFF). From the obtained areas SA and SB, the area SC (=SA-SB) was calculated.

[0127] A lower intraparticle defect ratio (SC / SA) means that there are fewer voids or amorphous layers within the alumina particles. Therefore, a low intraparticle defect ratio is preferable for alumina particles, particularly preferably 20% or less, and more preferably 15% or less. This can further reduce the dielectric loss of the resin composition when alumina particles are used as a filler for the resin composition.

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

[0129] [Table 7]

[0130] (9) Measurement of the aspect ratio of impurity particles X-ray transmission images of alumina particles from samples No. 1 to 6 were acquired in a 0.7 mm x 0.7 mm area using a high-sensitivity X-ray CT scanner (model: nano3DX) manufactured by Rigaku Corporation. The X-ray transmission images were processed using the image processing software Image J (manufactured by the National Institute of Health). All alumina particles within the X-ray transmission images were evaluated, and the aspect ratio of all evaluated alumina particles was determined. The aspect ratio was calculated as the ratio of the maximum diameter to the minimum diameter, with the minimum diameter being defined as the particle size in the direction perpendicular to the maximum diameter of the alumina particle.

[0131] The impurity particles contained in the alumina particles under evaluation were defined as the top 1% extracted from the alumina particles under evaluation, sorted by aspect ratio. The average aspect ratio of these impurity particles was then calculated.

[0132] The average aspect ratio of the impurity particles is preferably greater than 1.2 and less than or equal to 5.0, and particularly preferably less than or equal to 3, or less than or equal to 2.5. When alumina particles are used as a filler for resin compositions, the packing density of the alumina particles can be improved, and the dielectric loss of the resin composition can be further reduced.

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

[0134] [Table 8]

[0135] (10) Measurement of the length L1 of the outer edge of the alumina particle and the sum of the length L2 of the boundary line inside the particle. Samples for cross-sectional observation were prepared using alumina particles from samples No. 1 to 6. For the preparation of the cross-sectional observation samples, the alumina particles were embedded in resin, and then the resin and alumina particles were cut with a diamond cutter. Subsequently, Pt was deposited as a protective film on the cross-section, and the cross-section was prepared using Ar ion milling. The sample was then fixed to the SEM sample stage with Cu double-sided tape, and SEM-EBSD measurement was performed without deposition. The observation position was determined so that at least two alumina particles were completely contained within the observation area (i.e., no two or more alumina particles came into contact with the frame of the observation area). Measurements were performed using α-alumina particles.

[0136] The following instruments were used for sample preparation and EBSD measurement. ·Equipment used Ion milling machine: IM-4000 (manufactured by Hitachi, Ltd.) Ion sputtering system: E-1030 (manufactured by Hitachi, Ltd.) Ultra-high resolution field emission scanning electron microscope: JSM-7800F Prime (manufactured by JEOL Ltd.) Backscatter electron diffraction spectrometer: Digiview V (manufactured by TSL)

[0137] The conditions for EBSD measurement were as follows: ·Measurement area: 500.0μm×400.0μm • Acceleration voltage: 20.0kV Magnification: ×500 ·Low vacuum: 30Pa

[0138] In the obtained EBSD images, two or more alumina particles not in contact with the observation area frame were selected, and the length L1 of the outer edge of each alumina particle was calculated as the average using the image processing software Image J (National Institutes of Health). The total boundary line length L2 was also calculated. The "total boundary line length L2" is the sum of the boundary lines contained within the alumina particle, and does not include the outer edge of the alumina particle. The total boundary line length L2 was obtained by adding the total length of the grain boundaries inside the alumina particle and (if there is a cavity inside the alumina particle) the total length of the inner wall of that cavity.

[0139] The ratio of the total boundary line length L2 to the outer edge length L1 (L2 / L1) is expressed as a percentage (%). The more grain boundaries and / or cavities there are inside the alumina particles, the larger the value of L2 / L1(%). The fewer grain boundaries and cavities within the alumina particles, the lower the dielectric loss of the alumina particles. In other words, the smaller the L2 / L1 value, the lower the dielectric loss of the alumina particles. In particular, it is preferable that the L2 / L1 of the alumina particles be 100% or less, as this can further reduce the dielectric loss of the resin composition when used as a filler for resin compositions. (L2 / L1) is more preferably 80% or less, even more preferably 50% or less, and particularly preferably 40% or less.

[0140] Observation of the inside of the particles revealed that the comparative example particles had voids of several tens of micrometers in size, as well as fine voids of several micrometers in size and grain boundaries. The example particles had fine voids of several micrometers in size.

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

[0142] [Table 9]

[0143] (11) Measurement of the number of contact points between alumina particles in a resin composition (composite) Polyimide resin (Varnish A, manufactured by Ube Industries) and alumina particles from samples No. 2 to 5 were mixed in a volume percentage ratio of 20:80. A film was prepared from the mixture using a bar coater, and the film was fired in an N2 atmosphere to produce an alumina-resin composite. The cross-section along the thickness direction of the composite was exposed by Ar ion milling, and the cross-section was observed.

[0144] Cross-sectional cutting and observation were performed using the following equipment and conditions. • Cutting of cross-sections: Cross-section creation using a milling device. Device: E-3500 (Hitachi) • Cross-sectional observation: Observation using a laser microscope (LSM; Laser Scanning Microscopy) Equipment: OLS4000 (manufactured by Olympus) Measurement mode: 20x magnification Resolution: 1024×1942 Measurement range: x-direction approx. 650 μm × y-direction approx. 750 μm

[0145] The number of contact points between alumina particles in the resin composition was determined from cross-sectional LSM images. In cross-sectional LSM images, alumina particles are observed as gray and the resin as white. The number of points where the gray alumina particles are in direct contact with each other was defined as the number of contact points between alumina particles, and the number of contact points was counted. The number of contact points can be an indicator of the degree of particle dispersion; uniform dispersion results in fewer contact points between alumina particles. Furthermore, increasing the number of contact points between adjacent alumina particles (i.e., the number of interparticle interfaces) in the resin composition increases the dielectric loss of the resin composition.

[0146] The number of contact points between alumina particles is 40 or less within an observation area of ​​650 μm × 750 μm (observation area 1 mm). 2 It is preferable that the number of particles per unit be 82 or less, which can further reduce the dielectric loss of the resin composition when used as a filler for resin compositions. The number of contact points between alumina particles is measured within the observation area of ​​1 mm. 2 Converted to 65 pieces / mm 2 More preferably, the following, 50 pieces / mm 2 The following, or 30 pieces / mm 2 The following is particularly preferable:

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

[0148] [Table 10]

[0149] (12) Measurement of the BET specific surface area of ​​alumina particles The BET specific surface area of ​​alumina particles from samples No. 1 to 6 was measured. The specific surface area measurement method for powders (solids) by gas adsorption conforms to JIS Z 8830:2013, and Kr was used as the adsorbent gas. For the measurement, 1 g of alumina particles was placed in a sample tube, and an adsorption / desorption isotherm was obtained. The Kr-BET specific surface area S1(m²) was calculated using the multipoint plotting method. 2 The value per gram ( / g) was calculated. Furthermore, the ideal sphere area S2(m²) obtained from D50 2 ) for the specific surface area S1(m²) of Kr-BET 2 The ratio (S1 / S2) of ( / g) was determined. The area of ​​an ideal sphere is the surface area of ​​a perfectly spherical particle with a diameter of D50, and the formula for the surface area of ​​a sphere is (4πr 2 ) was derived from this.

[0150] When the surface of alumina particles has few irregularities, when used as a filler for a resin composition, the interface with the resin is reduced, and as a result, the dielectric loss of the resin composition can be lowered. Both the BET specific surface area and the ratio (S1 / S2) of the Kr-BET specific surface area to the ideal spherical area serve as indicators of the degree of irregularities of the particles.

[0151] The BET specific surface area S1 by the Kr adsorption method is preferably 0.10 m 2 / g or less, and when used as a filler for a resin composition, the dielectric loss of the resin composition can be further reduced. The Kr-BET specific surface area S1 is 0.08 m 2 / g or less is more preferable, and 0.07 m 2 / g or less is particularly preferable. The Kr-BET specific surface area S1 may be 0.01 m 2 / g or more, and may be 0.02 m 2 / g or more.

[0152] Also, the ratio (S1 / S2) of the Kr-BET specific surface area to the ideal spherical area is preferably 95×10 5 / g or less, and when used as a filler for a resin composition, the dielectric loss of the resin composition can be further reduced. (S1 / S2) is 40×10 5 / g or less is more preferable, and 20×10 5 / g or less is particularly preferable.

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

[0154]

Table 11

[0155] (13) Measurement of the amount of incorporated moisture of alumina particles and resin The water content carried in the alumina particles of Sample Nos. 2 to 3 and 5 to 6 was determined as follows. After weighing 1 g of alumina particles in advance and leaving them in the atmosphere for 24 h, the mass was measured and designated as the mass Ma1 (g) before measurement. Then, after drying the alumina particles in a vacuum dryer for 24 h, the mass was measured and designated as the mass Ma2 (g) after measurement. (Mass Ma1 before measurement - Mass Ma2 after measurement) / (Mass Ma1 before measurement) × 10 6 was defined as the water content ΔMa (ppm) carried in the alumina particles. [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​(14) Measurement of dielectric loss of resin composition (composite) Polyimide resin (Varnish A, manufactured by Ube Industries) and alumina particles from samples No. 1 to 6 were mixed in a volume percentage ratio of 20:80. A film was prepared from the mixture using a bar coater, and the film was fired in an N2 atmosphere to produce an alumina-resin composite with a thickness of 800 μm.

[0161] The dielectric loss of the composite was measured under the following measurement conditions. • Measurement device: Network analyzer HP8510C (manufactured by Agilent Technologies) • Sweep signal generators: HP83651A, HP8517B (both manufactured by Agilent Technologies) • Test specimen dimensions: 110mm x 60mm ·Measurement frequency: 10GHz • Test environment: 22℃ / 59%RH

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

[0163] [Table 13]

[0164] Numbers 1, 3-6, and 2 had low dielectric loss, while number 2 had high dielectric loss.

[0165] (15) Measurement of the pore volume of alumina particles The pore volume of alumina particles from samples No. 1 to 6 was measured. The specific surface area of ​​powders (solids) was measured by gas adsorption in accordance with JIS Z 8830:2013, using kr as the adsorbent gas. For the measurement, 1 g of alumina particles was placed in a sample tube, adsorption / desorption isotherms were obtained, and pore volume distribution analysis was performed using the multi-point plotting method to determine the pore volume.

[0166] When the pore volume of alumina particles was measured by krypton adsorption, the pore volume was 0.0003 cm³. 3 It is preferable that the value be less than or equal to / g. Pore ​​volume, like Kr-BET specific surface area, serves as an indicator of the degree of surface irregularity of the particles. By controlling the pore volume of the first alumina particles within the above range, the moldability of the mixture can be further improved.

[0167] The above pore volume is 0.00009 cm³. 3 It is more preferable that it be less than or equal to / g, and 0.00007cm 3 It is particularly preferable that the pore volume be less than or equal to / g. The lower limit of the pore volume is not particularly limited, but for example, 0.000001 cm³ 3 It may be greater than or equal to / g, and even more so, 0.000005cm 3 It may be more than / g.

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

[0169] [Table 14] [Explanation of symbols]

[0170] 10. Oxygen gas supply system 11. Carrier oxygen gas 12 Combustion oxygen gas 20 Fuel gas supply system 30 feeders 40 Flame melting furnace 50 Cyclone 60 Function Generators 70 samples 80 2 Phase Lock-in Amplifier

Claims

1. The cumulative particle size distribution shows that the particle size D50 at the 50% cumulative point from the finest particle side is greater than 100 μm, the alpha-adsorption rate is 90% or more, and the α-alumina is a single crystal. The roundness is 0.90 to 1.

00. An alumina particle in which, when L1 is the length of the outer edge of the alumina particle and L2 is the total length of the boundary lines it has, L2 / L1 is 40% or less.

2. A resin composition comprising a resin and alumina particles as described in claim 1.

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