Process for producing spherical alumina powder and production apparatus

Abstract

Provided is a method for producing a spherical alumina powder, including: a high-temperature forming step of forming a high-temperature region on the inside of a furnace by a burner that forms a flame; a spheroidizing step of generating a pre-heat treatment spherical alumina powder by feeding a raw material alumina powder into the furnace and heating and melting; a cooling and washing step of cooling and washing the pre-heat treatment spherical alumina powder by feeding the pre-heat treatment spherical alumina powder into cooling and washing water in a water tank; and a recovery step of separating the pre-heat treatment spherical alumina powder from the cooling and washing water and recovering the pre-heat treatment spherical alumina powder.

Description

[0001] This application is a divisional application of the invention patent application with application number 202580002060.3, invention title "Spherical Alumina Powder", application date February 5, 2025, and entry into the Chinese national phase on October 10, 2025. Technical Field

[0002] This disclosure relates to a method and apparatus for manufacturing spherical alumina powder. Background Technology

[0003] In recent years, the miniaturization, weight reduction, and thinning of mobile devices, such as smartphones, and electronic devices in vehicles have become increasingly significant. As a result, the density of electronic components such as IC chips and memory chips mounted on printed circuit boards inside these devices continues to rise, leading to a gradual increase in the heat density within the devices. If the heat density inside electronic devices increases, the accompanying temperature rise becomes significant, resulting in reduced performance and reliability of the electronic components. Therefore, it is necessary to rapidly transfer the heat generated by electronic components to the outside for heat dissipation. Consequently, the necessity of improving the thermal conductivity of packaging and substrate materials for electronic devices has further increased.

[0004] As a means of solving the above problems, the mainstream method is to fill the insulating resin material constituting the packaging material and substrate material of electronic devices with a high filling rate of inorganic material powder with high thermal conductivity as a filler. As inorganic material powder with high thermal conductivity, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, etc. are known, but from the point of view of chemical resistance and moisture stability, aluminum oxide powder is generally used most often.

[0005] The inorganic material powder is preferably in a spherical shape, which allows for easy mixing with resin at a high filling rate. It is known that spherical alumina powder is generally manufactured using a so-called spraying method, where Bayer process alumina is sprayed into a flame, melted, and rapidly cooled, thereby achieving spheroidization. The spraying method is described in Patent Document 1.

[0006] However, in conventional spraying methods, when the particle size is large, around 50 μm, spherical alumina with a high α-alumina content (hereinafter also referred to as α-alumina ratio) can be obtained. But as the particle size decreases, the content of low-temperature phases such as δ-alumina increases, resulting in a decrease in the thermal conductivity of the spherical alumina. Therefore, a study was conducted on improving the α-alumina ratio by heat treatment (Patent Document 2).

[0007] Existing technical documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 11-147711

[0009] Patent Document 2: Japanese Patent Application Publication No. 2014-9140 Summary of the Invention

[0010] When the α-aggregate ratio is improved by heat-treating spherical alumina, the surface roughness of the alumina increases due to this heat treatment, reducing its miscibility with the resin. Therefore, the resin material filled with spherical alumina suffers from low thermal conductivity. On the other hand, conventional spherical alumina, due to its excellent filling and flow properties, tends to settle easily in mixed-filled resin compositions, sometimes resulting in segregation between the resin layer with lower thermal conductivity and the layer filled with spherical alumina powder. This further reduces thermal conductivity and leads to uneven performance.

[0011] This disclosure provides a spherical alumina powder, which, even with a D50 of 0.1 to 40 μm, can yield resin compositions with high thermal conductivity. This disclosure also provides resin compositions and prepregs comprising spherical alumina powder.

[0012] This disclosure pertains to the following matters.

[0013] [1]

[0014] A spherical alumina powder,

[0015] D50 ranges from 0.1 to 40 μm.

[0016] Roundness is 0.90 or higher and 1.00 or lower.

[0017] The alpha conversion rate is above 60% and below 100%.

[0018] The particle surface roughness expressed by the following formula (1) is greater than 1.14 and less than 1.35.

[0019] Equation (1): Particle surface roughness

[0020] =BET specific surface area A / Sphere converted specific surface area Sa based on particle size distribution

[0021] [2]

[0022] The spherical alumina powder described in [1] has a specific gravity of 3.80 g / cm³. 3 above.

[0023] [3]

[0024] According to the spherical alumina powder described in [1] or [2], the BET specific surface area A is 0.1 or more and 2.0 or less.

[0025] [4]

[0026] The spherical alumina powder according to any one of [1] to [3] has an oil absorption rate of 30% or more and 50% or less.

[0027] [5]

[0028] A resin composition comprising any one of [1] to [4] spherical alumina powder and resin.

[0029] [6]

[0030] A prepreg impregnated in a substrate with the resin composition described in [5].

[0031] [7]

[0032] A cured product is a cured product of the prepreg or its laminate described in [6].

[0033] [8]

[0034] A metal-clad laminate, comprising:

[0035] [7] The solidified product, and

[0036] A metal foil disposed on at least one main surface of the cured material.

[0037] [9]

[0038] The resin composition described in [5] is used as a sealing material for electronic component devices.

[0039]

[10]

[0040] An electronic component device comprising an element and a cured resin composition of [5] sealing the element.

[0041]

[11]

[0042] A method for manufacturing spherical alumina powder, comprising:

[0043] The high-temperature process involves creating a high-temperature zone inside the furnace using a burner that generates a flame.

[0044] The spheroidization process involves feeding raw alumina powder into the furnace and heating it to melt, thereby generating spherical alumina powder before heat treatment.

[0045] The spherical alumina powder before heat treatment is immersed in cooling and cleaning water in a water tank to carry out the cooling and cleaning process of the spherical alumina powder before heat treatment.

[0046] The recovery process of separating the spherical alumina powder before heat treatment from the cooling and cleaning water to recover the spherical alumina powder before heat treatment; and

[0047] The heat treatment process involves heat-treating the recovered spherical alumina powder before heat treatment at 1100~1300℃ in an atmospheric atmosphere to obtain spherical alumina powder.

[0048] According to this disclosure, a spherical alumina powder can be provided, which, even spherical alumina powder with a D50 of 0.1 to 40 μm, can yield a resin composition with high thermal conductivity. Furthermore, according to this disclosure, a resin composition comprising spherical alumina powder and a prepreg can be provided.

[0049] This disclosure also covers the following matters.

[0050]

[12] A method for manufacturing spherical alumina powder, comprising:

[0051] The high-temperature process involves creating a high-temperature zone inside the furnace using a burner that generates a flame.

[0052] The spheroidization process involves feeding raw alumina powder into the furnace and heating it to melt, thereby generating spherical alumina powder before heat treatment.

[0053] The spherical alumina powder before heat treatment is immersed in cooling and cleaning water in a water tank to perform a cooling and cleaning process for the spherical alumina powder before heat treatment; and

[0054] The recovery process involves separating the spherical alumina powder before heat treatment from the cooling and cleaning water to recover the spherical alumina powder before heat treatment.

[0055]

[13] An apparatus for manufacturing spherical alumina powder, comprising:

[0056] The high-temperature section forms a high-temperature zone inside the spherical furnace by a burner that generates a flame;

[0057] The spherical part of the spherical alumina powder before heat treatment is generated by feeding raw alumina powder into the spherical furnace and heating and melting it.

[0058] The cooling and cleaning section involves immersing the pre-heat-treated spherical alumina powder in cooling and cleaning water within a stirring and cooling tank for cooling and cleaning the pre-heat-treatment spherical alumina powder; and

[0059] The recovery section is used to separate the spherical alumina powder before heat treatment from the cooling and cleaning water to recover the spherical alumina powder before heat treatment. Attached Figure Description

[0060] Figure 1 This is a diagram illustrating the process flow of a method for manufacturing spherical alumina powder before heat treatment according to one embodiment.

[0061] Figure 2 It means that it can be applied to Figure 1 A schematic diagram of the structure of the manufacturing equipment for the process flow. Detailed Implementation

[0062] Hereinafter, embodiments of the present invention will be described. Furthermore, the embodiments described below are representative examples of the present invention and are not intended to limit the scope of the invention.

[0063] In this specification, when multiple upper or lower limits are specified, a range of values ​​can be created based on all combinations of the upper and lower limits. Similarly, when multiple ranges of values ​​are specified, different ranges of values ​​can be created by individually selecting and combining the upper and lower limits from these ranges.

[0064] [Spherical alumina powder]

[0065] In one embodiment, the spherical alumina powder is a spherical alumina powder with a D50 of 0.1 to 40 μm, a roundness of 0.90 or more and 1.00 or less, an α-saturation of 60% or more and 100% or less, and a particle surface roughness of 1.14 or more and 1.35 or less as expressed by the following formula (1).

[0066] Equation (1): Particle surface roughness

[0067] =BET specific surface area A / Sphere converted specific surface area Sa based on particle size distribution

[0068] Spherical alumina powder has a high α-saturation rate and a particle surface roughness within an appropriate range from a filling perspective, resulting in high thermal conductivity. Furthermore, it is less prone to segregation in resin compositions and readily forms uniform particle contact points. Therefore, spherical alumina powder can yield resin compositions with high thermal conductivity.

[0069] (D50)

[0070] The D50 of the spherical alumina powder is 0.1 μm or more, preferably 0.5 μm or more, and more preferably 1.0 μm or more. The D50 of the spherical alumina powder is 40 μm or less, preferably 10 μm or less, and more preferably 5.0 μm or less. If the D50 is 0.1 μm or more, the thermal conductivity can be improved. If the D50 is 40 μm or less, the filling performance with resin can be improved.

[0071] D50 is the 50% particle size in the volume-based cumulative particle size distribution measured using a laser diffraction scattering particle size distribution measuring device, determined by the method described in the examples.

[0072] (α-conversion rate)

[0073] The α-saturation rate of the spherical alumina powder is 60% or more, preferably 70% or more, and more preferably 80% or more. A higher α-saturation rate generally leads to improved thermal conductivity. The α-saturation rate of the spherical alumina powder is 100% or less, and can be 99% or less or 98% or less.

[0074] In X-ray diffraction determination, the maximum peak intensity of the α-alumina crystalline phase at a diffraction angle of 2θ = 35.2° ± 0.2° is set as X. For the crystalline phase other than α-alumina, the maximum peak intensity at a diffraction angle of 2θ = 67.3° ± 0.2° is set as Y. The α-alumina crystalline phase is calculated using the following formula (2).

[0075] Equation (2): α-conversion rate = (X / (X+Y)) × 100 (%)

[0076] (Particle surface roughness A / Sa)

[0077] In this specification, particle surface roughness refers to the value calculated using the following formula (1).

[0078] Equation (1): Particle surface roughness

[0079] =BET specific surface area A / Sphere converted specific surface area Sa based on particle size distribution

[0080] The surface roughness of the spherical alumina powder particles is 1.14 or higher, preferably 1.16 or higher, and more preferably 1.20 or higher. The surface roughness of the spherical alumina particles is 1.35 or lower, preferably 1.31 or lower, and more preferably 1.29 or lower. If the particle surface roughness is 1.14 or higher, the sedimentation of alumina particles in the resin composition can be suppressed. If the particle surface roughness is 1.35 or lower, the filling properties of the resin can be improved.

[0081] (BET specific surface area A)

[0082] The BET specific surface area A of the spherical alumina powder is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1.0 or more. The BET specific surface area A of the spherical alumina powder is preferably 2.0 or less, more preferably 1.7 or less, and even more preferably 1.5 or less. If the BET specific surface area A is 0.1 or more, the heat dissipation is excellent. If the BET specific surface area A is 2.0 or less, the resin filling performance can be improved.

[0083] In this specification, the BET specific surface area A is a value calculated according to "6.2 Flow method (3.5) Single point method" of JIS R 1626:1996 (Determination of specific surface area of ​​fine ceramic powder by gas adsorption BET method). As a pretreatment, the sample was heated to 180°C, nitrogen gas was introduced for 20 minutes, and nitrogen gas was used as the adsorbate for the determination.

[0084] (Spherical converted specific surface area Sa calculated based on particle size distribution)

[0085] In this specification, the sphere equivalent specific surface area Sa (also known as sphere equivalent specific surface area Sa) calculated based on the particle size distribution is determined by the method described in the examples.

[0086] The spherical specific surface area Sa of the spherical alumina powder is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1.0 or more. The spherical specific surface area Sa of the spherical alumina powder is preferably 2.0 or less, more preferably 1.7 or less, and even more preferably 1.5 or less. If the spherical specific surface area Sa is 0.1 or more, the heat dissipation is excellent. If the spherical specific surface area Sa is 2.0 or less, the resin filling performance can be improved.

[0087] (proportion)

[0088] The preferred specific gravity of the spherical alumina powder is 3.80 g / cm³. 3 The above, more preferably 3.85 g / cm³ 3 The above. The preferred specific gravity of the spherical alumina powder is 4.00 g / cm³. 3 The preferred value is 3.97 g / cm³. 3 Below. If the specific gravity is 3.80 g / cm³ 3 The above indicates a high proportion of α-alumina, resulting in excellent thermal conductivity. Specific gravity was determined using the method described in the examples.

[0089] (Roundness)

[0090] The spherical alumina powder has a roundness of 0.90 or higher, preferably 0.92 or higher, more preferably 0.93 or higher, and even more preferably 0.95 or higher. By definition, the spherical alumina powder has a roundness of 1.00 or lower, but from a productivity point of view, it can be 0.99 or lower. Roundness is determined by the method described in the examples.

[0091] (oil absorption rate)

[0092] The oil absorption rate of the spherical alumina powder is preferably 30% or more, more preferably 35% or more, and even more preferably 38% or more. The oil absorption rate of the spherical alumina powder is preferably 50% or less, more preferably 45% or less, and even more preferably 43% or less. If the oil absorption rate is 30% or more, the sedimentation of alumina particles in the resin composition can be suppressed. If the oil absorption rate is 50% or less, the filling properties of the resin can be improved. The oil absorption rate is determined using the method described in the examples.

[0093] [Method for manufacturing spherical alumina powder]

[0094] Spherical alumina powder obtained by conventional flame melting is manufactured using a known method as follows: raw material powders that can serve as aluminum sources, such as alumina powder, aluminum hydroxide powder, or metallic aluminum powder, are placed into a high-temperature flame to melt the raw material powders. After spheroidizing the particles due to surface tension, the powders are cooled to a temperature suitable for collection by air cooling, and then collected using a collection device. In this method, because cooling after melting is slow, the crystallization of the alumina particles progresses during cooling, resulting in increased particle surface roughness. Furthermore, since the temperature profile from spheroidization to cooling is not controlled, the degree of crystallization progression during cooling is uneven. Therefore, when heat-treating such conventional spherical alumina powder, it is difficult to control the α-spheroidization rate and particle surface roughness within the expected range.

[0095] On the other hand, the inventors have discovered that by spheroidizing the raw material powder using the aforementioned known method, and then immediately cooling the high-temperature powder in a water bath, and by heat-treating the spherical alumina powder after cleaning away impurities such as sodium and calcium components that may induce particle melting and sintering from the particle interior to the surface, spherical alumina powder with α-scaling rate and particle surface roughness controlled within a desired range can be obtained. Hereinafter, the spherical alumina powder before heat treatment will be referred to as pre-heat-treated spherical alumina powder, and the spherical alumina powder after heat treatment will be referred to as spherical alumina powder, and exemplary manufacturing methods for them will be described.

[0096] (Method for manufacturing spherical alumina powder before heat treatment)

[0097] One embodiment of the method for manufacturing spherical alumina powder before heat treatment includes: a high-temperature step of forming a high-temperature zone inside a furnace by a burner forming a flame; a spheroidization step of generating spherical alumina powder before heat treatment by feeding raw alumina powder into the furnace and heating and melting it; a cooling and cleaning step of cooling and cleaning the spherical alumina powder before heat treatment by immersing it in cooling and cleaning water in a water tank; and a recycling step of separating the spherical alumina powder before heat treatment from the cooling and cleaning water to recover the spherical alumina powder before heat treatment. Figure 1 This describes a process flow for manufacturing spherical alumina powder before heat treatment according to one embodiment. By simultaneously cooling and cleaning the spherical alumina powder before heat treatment, it is possible to manufacture Na, which exists on the particle surface and may lead to particle melting and sintering, at low cost and in a short time. + The amount of other ionic impurities was reduced in the spherical alumina powder before heat treatment.

[0098] <Raw material: Alumina powder>

[0099] There are no particular restrictions on the raw material alumina powder, but Na is preferred.+ Small quantities of powder. As Na + Specific examples of small quantities of alumina powder include low-sodium alumina powder produced by the Bayer process.

[0100] The shape of the raw alumina powder is not limited, but non-spherical shape is preferred from the perspective of obtaining spherical alumina powder before heat treatment. The sphericity of the raw alumina powder is, for example, less than 0.90, 0.86 or less, or 0.84 or less.

[0101] From the viewpoint of obtaining spherical alumina powder before heat treatment with a size suitable for heat dissipation filler, the D50 of the raw alumina powder is preferably 0.1 μm or more and 40 μm or less. From the same viewpoint, the D50 is more preferably 0.5 μm or more and 10 μm or less, and even more preferably 1.0 μm or more and 5 μm or less.

[0102] <Furnace>

[0103] Examples of furnaces include vertical and horizontal furnaces. The shape of the furnace is not limited; examples include cylindrical and hexagonal prism shapes, among others. Cylindrical shapes are preferred because they facilitate uniform temperature control within the furnace. A cylindrical shape means that at least a portion of the furnace is cylindrical, but it may also include portions of other shapes. A prismatic shape means that at least a portion of the furnace is prismatic, but it may also include portions of other shapes. From the viewpoint of improving capture efficiency, the downstream portion of the furnace is preferably an inverted conical shape that narrows towards the discharge port.

[0104] The material of the furnace is not limited, but from the viewpoint of reducing contamination of the spherical alumina powder before heat treatment by impurities, stainless steel is preferred for the inner wall. A water-cooling jacket can be installed around the furnace to cool it.

[0105] <High-temperature processing>

[0106] The high-temperature process is a process in which a burner that generates flames creates a high-temperature zone inside the furnace.

[0107] A burner is a device that forms a flame in a furnace by appropriately mixing a combustible gas with an oxidizing gas. Combustible gas is supplied to the burner from a combustible gas supply source, and oxidizing gas is supplied to the burner from an oxidizing gas supply source. Examples of combustible gases include liquefied natural gas (LNG) and liquefied petroleum gas (LPG). Examples of oxidizing gases include air, oxygen, and oxygen-enriched air.

[0108] The temperature of the high-temperature zone is preferably above 2100°C. The temperature of the high-temperature zone is preferably below 2500°C, more preferably below 2300°C. If the temperature is above 2100°C, it is above the melting point of alumina, thus easily improving the sphericity of the obtained alumina powder. If the temperature is below 2500°C, it is within the heat resistance range of a typical burner, thus being cost-effective.

[0109] <Spheroidizing process>

[0110] The spheroidizing process is a process of generating spherical alumina powder before heat treatment by feeding raw alumina powder into a furnace and heating it to melt. In the spheroidizing process, a carrier gas for supplying the raw alumina powder can be used as needed. Examples of carrier gases include at least one selected from air, nitrogen, oxygen, and carbon dioxide.

[0111] <Pre-cooling process>

[0112] The method for manufacturing spherical alumina powder before heat treatment preferably includes a pre-cooling step of pre-cooling the spherical alumina powder before heat treatment. The pre-cooling step is performed after the spheroidization step and before the cooling and cleaning step. The equipment for pre-cooling is preferably located outside the high-temperature zone of the furnace or between the furnace and the water tank used in the cooling and cleaning step. This allows the spherical alumina powder before heat treatment, which is placed in the cooling and cleaning water in the cooling and cleaning tank during the cooling and cleaning step, to be cooled to a preferred temperature in a short time.

[0113] Pre-cooling is preferably performed by spraying water onto the spherical alumina powder before heat treatment. Examples of devices for spraying water include sprayers.

[0114] <Cooling and Cleaning Process>

[0115] The cooling and cleaning process involves simultaneously immersing the pre-heat-treated spherical alumina powder in cooling and cleaning water within a water tank, thereby cooling and cleaning the powder. Compared to performing cooling and cleaning as separate processes, such as air-cooling the pre-heat-treated spherical alumina powder after the spheroidization process while simultaneously collecting it using a cyclone separator or similar device and then cleaning the collected powder, this simultaneous cooling and cleaning allows for smaller equipment scale and shorter overall process time. Furthermore, it helps suppress uneven crystallinity. Because the method for manufacturing pre-heat-treated spherical alumina powder involves a shorter thermal path, it is possible to produce pre-heat-treated spherical alumina powder with a low BET specific surface area.

[0116] Cooling and cleaning water is stored in the tank for simultaneously cooling and cleaning the spherical alumina powder before heat treatment. To improve cleaning efficiency, it is preferable to agitate the cooling and cleaning water with a mixer. There are no limitations on the cooling and cleaning water; tap water is an example.

[0117] From the viewpoint of effectively reducing ionic impurities present on the surface of spherical alumina powder before heat treatment, the temperature of the cooling cleaning water is preferably 50°C or higher, more preferably 70°C or higher. From the viewpoint of suppressing damage to the furnace body caused by heat load, the temperature of the cooling cleaning water is preferably 80°C or lower.

[0118] In the cooling and cleaning process, the spherical alumina powder before heat treatment is preferably added to the cooling and cleaning water within 5 seconds after leaving the furnace. By adding it within 5 seconds, the BET specific surface area of ​​the spherical alumina powder before heat treatment can be suppressed to a low level. By adding it within 5 seconds, the unevenness of the crystallinity of the spherical alumina powder before heat treatment can be suppressed.

[0119] In the cooling and cleaning process, the temperature of the spherical alumina powder before heat treatment, before being immersed in the cooling and cleaning water, is preferably below 200°C, more preferably below 100°C. It is even more preferable that the temperature of the spherical alumina powder after leaving the furnace and before being immersed in the cooling and cleaning water is below 200°C, particularly preferably below 100°C. If the temperature is below 200°C, the possibility of the cooling and cleaning water in the tank overheating and evaporating is small, thus facilitating stable production.

[0120] The temperature of the spherical alumina powder before heat treatment can be determined using the simulation software Ansys Fluent (Ansys Corporation).

[0121] <Recycling Process>

[0122] The recovery process involves separating the spherical alumina powder before heat treatment from the cooling and cleaning water, and then recovering the spherical alumina powder before heat treatment. There are no limitations on the recovery method; examples include allowing the spherical alumina powder dispersed in the cooling and cleaning water to settle, and then removing the supernatant using a pump or similar device. This method can clean and remove Na adhering to the particle surface. + Ca 2+ Plasmonic impurities are preferred.

[0123] <Drying Process>

[0124] The method for manufacturing spherical alumina powder before heat treatment preferably includes a drying step. The drying step is a process of drying the spherical alumina powder before heat treatment after the cooling and cleaning water has been separated. In the drying step, residual moisture from the recycling process is removed. The drying method is not limited and can be either natural drying or heat drying.

[0125] <Apparatus for manufacturing spherical alumina powder before heat treatment>

[0126] Hereinafter, the preferred configuration of the manufacturing apparatus used in the method for manufacturing spherical alumina powder before heat treatment according to one embodiment will be described in detail with the help of the accompanying drawings. Furthermore, in the following description, for ease of understanding and convenience, the parts that are characteristic are emphasized, and the size ratios of each component may not be the same as those of the actual apparatus.

[0127] use Figure 2 The apparatus for manufacturing spherical alumina powder before heat treatment is described. For example... Figure 2 As shown, the apparatus for manufacturing spherical alumina powder before heat treatment is generally composed of the following components: a hopper 1 for storing and feeding raw materials; a spheroidizing burner 2; a water-cooled jacketed spheroidizing furnace 3 (also called a spheroidizing furnace 3) for spheroidizing; a stirring cooling tank 4 for cleaning and cooling the spherical alumina powder before heat treatment; a separation tank 5 for separating the collected spherical alumina powder before heat treatment from a large amount of moisture and removing the spherical alumina powder before heat treatment; and a drying apparatus 6 for drying the spherical alumina powder before heat treatment containing residual moisture to obtain dry powder.

[0128] The raw material hopper 1 is equipped with a feeding device, which can quantitatively supply raw alumina powder to the spheroidizing burner 2. The spheroidizing burner 2 supplies the raw alumina powder from the raw material hopper 1 into the spheroidizing furnace 3. Alternatively, a powder conveying carrier gas can be used to supply the raw alumina powder to the spheroidizing burner 2.

[0129] The spherical burner 2 is installed in the spherical furnace 3. Combustible gas is supplied to the spherical burner 2 from a combustible gas supply source (not shown) and combustion-supporting gas is supplied to the spherical burner 2 from a combustion-supporting gas supply source (not shown). The spherical burner 2 is able to form a flame in the spherical furnace 3.

[0130] The spheroidizing furnace 3 is a cylindrical vertical furnace with an inverted conical shape at the bottom that narrows towards the discharge port. Inside the spheroidizing furnace 3, raw alumina powder is heated and melted in a high-temperature zone formed by a flame to generate spherical alumina powder before heat treatment.

[0131] A sprayer 10 is installed inside the spheroidizing furnace 3. By spraying water onto the spheroidized alumina powder before heat treatment, which is leaving the high-temperature zone, the spheroidized alumina powder can be pre-cooled. Figure 2 In the process, the sprayer is set inside the spheroidizing furnace 3, but as long as it is on the path of the spheroidized alumina powder after it leaves the high-temperature area before it comes into contact with the cooling and cleaning water, the sprayer can be set at any position.

[0132] The spheroidizing furnace 3 is connected to the stirring cooling tank 4 via a short pipe. Furthermore, a conduit is provided on the short pipe, which connects to a scrubber-type collection device 8 and an exhaust device 9, enabling the combustion exhaust to be discharged outside the system. Moreover, since the combustion exhaust contains tiny spherical alumina powder particles from before heat treatment, it is preferable to pass it through the scrubber-type collection device 8 to separate and remove the tiny powder particles from the gas, and then discharge the purified combustion exhaust through the exhaust device 9. Figure 2 In the process, there is no gap between the spheroidizing furnace 3, the short tube and the stirring cooling tank 4, but there may be gaps between them.

[0133] The stirring cooling tank 4 stores cooling and cleaning water for simultaneously cooling and cleaning the spherical alumina powder before heat treatment. The cooling and cleaning water in the stirring cooling tank 4 is stirred by a mixer to improve cleaning efficiency. A cooling water pump 7 is connected to the stirring cooling tank 4, and the cooling water pump 7 is connected to a sprayer 10, with piping configured to circulate the cooling and cleaning water in the tank.

[0134] A separation tank 5 is connected to the stirring and cooling tank 4 to separate the captured spherical alumina powder before heat treatment from the cooling and cleaning water. A slurry containing the spherical alumina powder before heat treatment is supplied from the stirring and cooling tank 4 to the separation tank 5. In the separation tank 5, the cooling and cleaning water and solid matter are separated, and the water is returned to the system for circulation via the cooling water pump 7. At this time, Na+ adhering to the particle surface... + Plasma impurities are removed by washing. The solid material is fed to drying device 6 to dry the attached residual moisture, resulting in spherical alumina powder with few ionic impurities before heat treatment.

[0135] According to this manufacturing apparatus, there is no need to set up expensive and large-scale equipment such as ion exchange water devices, and spherical alumina powder with few ionic impurities before heat treatment can be obtained through small-scale spheroidization equipment.

[0136] (Method for manufacturing spherical alumina powder)

[0137] Spherical alumina powder can be obtained by heat-treating spherical alumina powder in an atmospheric atmosphere at 1100–1300 °C. Heat treatment above 1100 °C promotes the transformation from phases with low thermal conductivity other than the α-crystalline phase, such as amorphous, γ-crystalline, δ-crystalline, and θ-crystalline phases, to the α-crystalline phase with high thermal conductivity. Heat treatment below 1300 °C suppresses surface roughness. Heat treatment below 1300 °C suppresses particle size increase caused by particle fusion.

[0138] The heat treatment time is preferably 1 hour or more, more preferably 1 hour or more but less than 4 hours. If it is 1 hour or more, the transformation time to the target α crystalline phase is sufficient, and the target α concentration is easily achieved. If it is 4 hours or less, the sintering of particles is suppressed, and powder with the target particle size is easily obtained.

[0139] The heat treatment apparatus can be a general apparatus, and specific examples include bogie hearth furnaces, tunnel furnaces, and rotary kilns. The heat treatment atmosphere is not particularly limited, but an atmospheric atmosphere is preferred.

[0140] The method for manufacturing spherical alumina powder may, as needed, include a crushing step to break up the agglomerated particles produced by heat treatment. The method may, as needed, include a classification step to perform a grading process. Heat treatment sometimes produces agglomerated particles formed by the sintering of some particles together. In this case, it is preferable to perform at least one treatment selected from crushing and classification. The crushing process can be wet or dry. Examples of crushing processes include, for instance, using roller mills, ball mills, small-diameter ball mills (also called bead mills), jar mills, media stirring mills, air jet mills, mortars, automatic mixing mortars, tank mills, or jet mills.

[0141] Spherical alumina powder is preferred for applications requiring high thermal conductivity. For example, it can be used as a filler in materials requiring high thermal conductivity, such as heat dissipation materials and semiconductor sealing materials.

[0142] [Resin Composition]

[0143] One embodiment of the resin composition comprises spherical alumina powder and resin. The resin composition can be used as a thermally insulating resin composition or a sealing material, such as a sealing material for electronic component devices. The resin composition is suitable for semiconductor packaging and printed wiring substrates requiring high thermal conductivity.

[0144] Examples of resins include thermosetting resins and thermoplastic resins, with thermosetting resins being preferred. Examples of thermosetting resins include epoxy resins, phenolic resins, unsaturated imide resins, melamine resins and other amino resins, unsaturated polyester resins, allyl resins, dicyclopentadiene resins, silicone resins, and triazine resins. Among these, epoxy resins, which exhibit excellent moldability and electrical insulation properties, are preferred. Resins can be used alone or in combination of two or more types.

[0145] Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, alicyclic epoxy resin, phenolic varnish type epoxy resin, cresol phenolic epoxy resin, bisphenol A phenolic epoxy resin, bisphenol F phenolic epoxy resin, dicyclopentadiene type epoxy resin, naphthalene type epoxy resin, and anthracene type epoxy resin.

[0146] Examples of thermoplastic resins include polyethylene, polypropylene, polystyrene, polyphenylene ether resin, phenoxy resin, polycarbonate resin, polyester resin, polyamide resin, polyamide-imide resin, polyimide resin, xylene resin, polyphenylene sulfide resin, polyetherimide resin, polyether ether ketone resin, and polyetherimide resin.

[0147] The content of spherical alumina powder in the resin composition is preferably 50-90% by volume, more preferably 60-85% by volume. If the content is 50% by volume or more, the thermal conductivity improvement effect brought by the spherical alumina powder is sufficient. If the content is 90% by volume or less, the resin composition has good formability.

[0148] The resin composition may contain inorganic fillers other than spherical alumina. Examples of other inorganic fillers include aluminum hydroxide, zinc oxide, magnesium oxide, magnesium carbonate, magnesium hydroxide, titanium oxide, silicon oxide, and boron nitride. From the viewpoint of improving thermal conductivity, at least one of aluminum hydroxide, zinc oxide, magnesium oxide, and boron nitride is preferred.

[0149] The resin composition may contain optional components other than those listed above. Optional components include curing agents, curing accelerators, flame retardants, UV absorbers, antioxidants, organic solvents, and surface treatment agents.

[0150] Examples of curing agents used in the case of epoxy resins include multifunctional phenolic compounds such as phenolic varnish and cresol varnish; amine compounds such as dicyandiamide, diaminodiphenylmethane, and diaminodiphenyl sulfone; and acid anhydrides such as phthalic anhydride, pyromellitic anhydride, and maleic anhydride. Curing agents can be used alone or in combination of two or more.

[0151] Examples of curing accelerators used in the case of epoxy resins include imidazole compounds and their derivatives; organophosphorus compounds; secondary amines; tertiary amines; and quaternary ammonium salts.

[0152] Examples of imidazole compounds and their derivatives include, for example, imidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-ethyl-4-methylimidazolium, 2-phenylimidazolium, 2-undecylimidazolium, 1-benzyl-2-methylimidazolium, 2-heptadecylimidazolium, 4,5-diphenylimidazolium, 2-methylimidazoline, 2-phenylimidazoline, 2-undecylimidazoline, 2-heptadecylimidazoline, 2-isopropylimidazolium, 2,4-dimethylimidazolium, 2-phenyl-4-methylimidazolium, 2-ethylimidazoline, 2-isopropylimidazoline, 2,4-dimethylimidazoline, and 2-phenyl-4-methylimidazoline. Imidazole compounds and their derivatives can be masked by masking agents. Examples of masking agents include, for example, acrylonitrile, phenylene diisocyanate, toluidine isocyanate, naphthalene diisocyanate, methylene diphenyl isocyanate, and melamine acrylate.

[0153] Examples of organophosphorus compounds include vinylphosphine, propylphosphine, butylphosphine, phenylphosphine, trimethylphosphine, triethylphosphine, tributylphosphine, trioctylphosphine, triphenylphosphine, tricyclohexylphosphine, triphenylphosphine / triphenylborane complexes, and tetraphenylphosphonium tetraphenylborate.

[0154] Examples of secondary amines include morpholine, piperidine, pyrrolidine, dimethylamine, diethylamine, dicyclohexylamine, N-alkylarylamine, piperazine, diallylamine, thiazoline, and thiomorpholine.

[0155] Examples of tertiary amines include benzyldimethylamine, 2-(dimethylaminomethyl)phenol, and 2,4,6-tris(dimethylaminomethyl)phenol.

[0156] Examples of quaternary ammonium salts include tetrabutylammonium iodide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride, benzalkonium chloride, benzyl di(2-hydroxyethyl)ethylammonium chloride, and decyl di(2-hydroxyethyl)methylammonium bromide.

[0157] Curing accelerators can be used alone or in combination with two or more.

[0158] Organic solvents can be used for purposes such as adjusting the viscosity of the resin composition. For example, in the case of impregnating a resin composition into a substrate to manufacture a prepreg, and in the case of coating a resin composition, it is preferable to use an organic solvent to keep the viscosity of the resin composition within an appropriate range. The organic solvent can be removed after the impregnation or coating process.

[0159] Examples of organic solvents include alcohols such as methanol, ethanol, propanol, and butanol; glycol ethers such as methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as butyl acetate and propylene glycol monomethyl ether acetate; ethers such as tetrahydrofuran; aromatic hydrocarbons such as toluene and xylene; nitrogen-containing solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfur-containing solvents such as dimethyl sulfoxide. Organic solvents can be used alone or in combination of two or more.

[0160] From the viewpoint of solubility, methyl isobutyl ketone, methyl ethyl ketone, propylene glycol monomethyl ether and methyl cellosolve are preferred, and from the viewpoint of low toxicity, methyl isobutyl ketone and propylene glycol monomethyl ether are more preferred.

[0161] When dispersing spherical alumina powder in an organic solvent, dispersers such as bead mills, homogenizers, and jet mills can be used to improve dispersibility. Pretreatment of the spherical alumina powder with a surface treatment agent (described later) or overall mixing is also preferred.

[0162] Examples of surface treatment agents include silane coupling agents, titanate coupling agents, and organosilicon oligomers. Spherical alumina powder can also be pretreated with surface treatment agents.

[0163] When a prepreg is manufactured by impregnating a resin composition into a substrate, the total content of components other than organic solvents (also called solid components) in the resin composition is preferably 40 to 90% by mass, more preferably 50 to 85% by mass, relative to the total resin composition.

[0164] [Method for manufacturing the resin composition]

[0165] There is no particular limitation on the method for manufacturing the resin composition. Examples of methods for manufacturing the resin composition include thoroughly mixing the components in a specified amount using a mixer, mixing using a mixing roller, extruder, or similar equipment, and then cooling the mixture. More specifically, examples include stirring and mixing the components in a specified amount, mixing the mixture using a kneader, roller, extruder, or similar equipment preheated to 70-140°C, and then cooling the mixture.

[0166] [Prepreg]

[0167] One embodiment of the prepreg is made by impregnating a resin composition into a substrate.

[0168] Materials used as substrates include, for example, inorganic fibers such as E-glass, D-glass, S-glass, and Q-glass. Forms of substrates include, for example, woven fabrics, non-woven fabrics, rovings, chopped strand mats, and surface mats. The material and form of the substrate are selected according to the intended use and performance requirements; two or more materials and forms may be used individually or in combination as needed. From the viewpoints of heat resistance, moisture resistance, and processability, the substrate can be surface-treated. Examples of surface treatments include those using silane coupling agents and mechanical fiber-opening processes. The thickness of the substrate is, for example, 0.01 to 0.2 mm.

[0169] Prepregs can be manufactured, for example, by impregnating a substrate with a resin composition containing an organic solvent and then removing the organic solvent. The impregnated resin composition can also be partially cured by heating.

[0170] Prepregs are suitable for semiconductor packaging and printed wiring substrates that require high thermal conductivity.

[0171] [Cure of prepreg or its laminate]

[0172] Cured prepregs or their laminates can be manufactured by heating and pressurizing one or more overlapping prepregs. There is no particular limitation on the number of prepreg layers, for example, 2 to 20 layers. Examples of apparatus for heating and pressurizing include multi-stage presses, multi-stage vacuum presses, continuous molding machines, and autoclave molding machines. The heating and pressurizing conditions are selected based on the thermosetting resin, curing agent, etc., used. For example, a temperature of 100–250°C, a pressure of 0.2–10 MPa, and a time of 0.1–5 hours.

[0173] [Metal-clad laminate]

[0174] One embodiment of the metal-clad laminate includes: a cured prepreg or a laminate thereof; and a metal foil disposed on at least one main surface of the cured material. The metal-clad laminate can be manufactured, for example, by stacking 1 to 20 sheets of prepreg and heating and pressing them with the metal foil disposed on one or both sides. The apparatus for heating and pressing, as well as the conditions for heating and pressing, are the same as described above. There are no particular limitations on the metal foil used in electronic component applications. Examples of metal foils include copper foil and aluminum foil.

[0175] [Electronic Components]

[0176] One embodiment of the electronic component device includes an element and a cured resin composition that seals the element. Examples of the element include active elements such as semiconductor chips, transistors, diodes, and thyristors; and passive elements such as capacitors, resistors, and coils.

[0177] As electronic component devices, examples include devices in which components are mounted on support components such as lead frames, wiring carriers, wiring boards, glass, silicon wafers, and organic substrates, and the component portion is sealed with a resin composition. More specifically, there are general resin-sealed ICs such as DIP (Dual Inline Package), PLCC (Plastic Leaded Chip Carrier), QFP (Quad Flat Package), SOP (Small Outline Package), SOJ (Small Outline J-lead package), TSOP (Thin Small Outline Package), and TQFP (Thin Quad Flat Package), which have a structure where components are fixed on lead frames and the component terminals such as pads and lead portions are connected by wire bonding, bumps, etc., and then sealed using a resin composition through transfer molding, etc.; TCP (Tape Carrier Package), which has a structure where components are sealed by a resin composition for connection to a carrier via bumps; and COB (Chip On Board), which has a structure where components are sealed by a resin composition for connection to wiring formed on a support component via wire bonding, flip chip bonding, solder, etc. Board (chip-on-board) modules, hybrid ICs, multi-chip modules, etc.; surface-mounted components with support components having terminals formed on the back for wiring board connection, and components are connected to wiring formed on the support components by bumps or wire bonding, and the components are sealed with a resin composition, such as BGA (Ball Grid Array), CSP (Chip Size Package), MCP (Multi Chip Package).

[0178] Methods for sealing electronic component devices using resin compositions include, for example, low-pressure transfer molding, injection molding, and compression molding. Among these methods, low-pressure transfer molding is commonly used.

[0179] Example

[0180] The present invention will now be described in more detail by way of examples and comparative examples, but the present invention is not limited to the following examples.

[0181] <Evaluation Methods>

[0182] (D10, D50, D90)

[0183] 40 mg of sample was added to 50 mL of water containing 2 drops of a nonionic surfactant (TRITON-X; Roche Applied Science) and dispersed ultrasonically for 3 minutes. The dispersion was measured using a laser diffraction scattering particle size distribution analyzer (Microtrac BEL Co., Ltd., MT3300II). The 10%, 50%, and 90% particle sizes in the obtained volumetric cumulative particle size distribution were defined as D10, D50, and D90, respectively.

[0184] (α-conversion rate)

[0185] The α-saturation rate is calculated in X-ray diffraction (XRD) measurements. The maximum peak intensity at a diffraction angle of 2θ = 35.2° ± 0.2° for the α-alumina crystalline phase is designated as X, and the maximum peak intensity at a diffraction angle of 2θ = 67.3° ± 0.2° for the crystalline phases other than α-alumina is designated as Y. The α-saturation rate (%) is calculated using the relationship: α-saturation rate (%) = (X / (X+Y)) × 100. XRD measurements of alumina powder were performed using a PW3040 / 60X'Pert-MRD XRD system (Malvern Panalytical), with a copper X-ray tube bulb, under conditions of 45 kV tube voltage and 40 mA tube current.

[0186] (BET specific surface area A)

[0187] The BET specific surface area A was calculated according to "6.2 Flow Method (3.5) Single Point Method" of JIS R 1626:1996 (Determination of Specific Surface Area by Gas Adsorption BET Method Using Fine Ceramic Powders). Specifically, about 2g of sample was weighed, and after pre-degassing at 180°C for 20 minutes, the sample was placed in an automatic specific surface area measuring device (MOUNTECH, Macsorb, Co., Ltd.). The amount of nitrogen adsorbed was measured using pure nitrogen and a nitrogen-helium mixture (mixing ratio: nitrogen 30 mol%, helium 70 mol%), and the BET specific surface area A was calculated using the single point method.

[0188] (Spherical converted specific surface area Sa calculated based on particle size distribution)

[0189] The spherical equivalent specific surface area (Sa) calculated based on the particle size distribution is derived from particle size distribution data obtained using a laser diffraction scattering particle size distribution measuring device (Microtrac BEL Co., Ltd., MT3300II), and is calculated using the following formula. The sample preparation method is the same as that used in the determination of D10, D50, and D90.

[0190] Number 1

[0191]

[0192] d i V represents the average diameter within particle size range i. i Let ρ represent the relative volume of particle size range i, and ρ represent the specific gravity. The specific gravity calculated using the following method is used as ρ.

[0193] (proportion)

[0194] A 5 mg sample was placed in the sample cell for measurement, and the specific gravity was determined using a dry hydrometer (Shimadzu Corporation, product name: AccuPycII 1340) by gas (helium) displacement method. Specifically, the sample cell for measurement was set up on the dry hydrometer, the volume of the sample was determined by displacement with helium gas, and the specific gravity was calculated by dividing the sample mass by the volume.

[0195] (Roundness)

[0196] Roundness is the average value calculated by the following formula (3) for more than 2000 particles when the product of the particle's projection map is set as S and the perimeter is set as L.

[0197] Equation (3): (4×π×S) / L 2

[0198] Area S and perimeter L were determined using an FPIA-3000 (Malvern Panalytical). As a pretreatment, due to the limited measurement range of the device, approximately 10g of sample was placed in a 200mm diameter metal sieve with a 25μm mesh size, and particles larger than 25μm were removed with shower water. The sieved sample was then transferred to a plastic container as the test sample. Measurement conditions were LPF / HPF standard (20x lens) and bright field, using particle sheath solution (Malvern Panalytical) as the measurement solvent. Following the principle of having at least 2000 effective particles and an effective particle count / total particle count of 55-70%, 2g of the test sample was weighed into a 50mL beaker, 50mL of pure water was added, and the sample was dispersed for 3 minutes using a 200W ultrasonic disperser before being added to the device for measurement. As a post-measurement data processing step, portions with multiple particles on one screen were removed, and roundness was calculated.

[0199] (oil absorption rate)

[0200] Place 10g of sample in a 10cm diameter mortar, and add a small amount of liquid epoxy resin, mixing thoroughly. Repeat adding small amounts of resin until the sample and epoxy resin become a single unit. Calculate the volume of added resin from the weight of the resin at the moment the sample and resin become a single unit, and then calculate the oil absorption rate using the following formula. Furthermore, the volume of the sample is calculated based on the specific gravity determined above.

[0201] Oil absorption rate (%) = (Volume of resin added / (Volume of sample + Volume of resin added)) × 100

[0202] (thermal conductivity)

[0203] Alumina powder was mixed with an epoxy molding compound containing epoxy resin, a polyfunctional phenolic compound as a curing agent, and an organophosphorus compound as a curing accelerator, at the volume filling percentage shown in Table 1. After dilution with methyl ethyl ketone (MEK), the mixture was stirred using a mixing rotor to prepare a varnish with a solids content of 75% by mass. The resulting varnish was applied to a release PET film with a thickness of 200 μm and dried at 110°C for 10 minutes. The dried resin composition was then pulverized. For the molding and testing of the pulverized resin composition as a composite material, the pressure was increased to 10 kN in a heated vacuum pressurizing apparatus while maintaining a heating temperature of 80°C for 3 minutes. When 10 kN was reached, the temperature was increased to 160°C at a rate of 20°C / 3 minutes. When the heating temperature reached 100°C, the pressing pressure was increased from 10 kN to 40 kN. The mixture was held at 160°C for 16 minutes to produce a resin composite material with a thickness of 1 mm. The resin composite material was cured at 175°C for 6 hours to obtain the test composite material. The thermal conductivity was measured using this test composite material.

[0204] Thermal conductivity is calculated by multiplying thermal diffusivity, specific heat capacity at low pressure, and density. Thermal diffusivity was measured using a xenon flash lamp analyzer (NETZSCH JAPAN Co., Ltd., LFA647 HyperFlash). Specific heat capacity at low pressure was calculated from the specific heat capacity of each material and their proportions. Density was measured using an electronic hydrometer (Alfa Mirage Co., Ltd., MDS-3000). Thermal conductivity was calculated by multiplying these components. Furthermore, thermal diffusivity and density were measured at 23°C, and the specific heat capacity at low pressure was calculated using the specific heat capacity at 25°C.

[0205] (Comparative Example 1)

[0206] Raw alumina powder (D50: 1.8 μm) was added to a high-temperature zone of 2200°C created in a furnace by a flame formed from LPG and oxygen, and subjected to spheroidization treatment. The spheroidized alumina powder before heat treatment was immersed in 80°C cooling water in a water tank within 5 seconds of leaving the furnace for cooling and cleaning. The resulting slurry containing the spheroidized alumina powder before heat treatment was separated into a high-concentration slurry and a supernatant in a recycling process. In a drying process, the high-concentration slurry was dried in an atmospheric atmosphere at 180°C to obtain the spheroidized alumina powder before heat treatment.

[0207] (Comparative Example 2)

[0208] Raw alumina powder (D50: 1.2 μm) was added to a high-temperature zone of 2200°C created in a furnace by a flame formed from LPG and oxygen, and subjected to spheroidization treatment. The spheroidized alumina powder was then immersed in 80°C cooling water in a water tank within 5 seconds of leaving the furnace for cooling and cleaning. The resulting slurry containing the pre-heat-treated spheroidized alumina powder was separated into a high-concentration slurry and a supernatant in a recycling process. In a drying process, the high-concentration slurry was dried in an atmospheric atmosphere at 180°C to obtain the pre-heat-treated spheroidized alumina powder 2.

[0209] (Comparative Example 3)

[0210] Sumitomo Chemical Co., Ltd. Advanced Alumina AA-2

[0211] (Example 1)

[0212] Spherical alumina powder 1, before heat treatment, was placed in a muffle furnace and heat-treated at 1250°C for 4 hours in an atmospheric atmosphere. After cooling, it was crushed using a wet shear crusher (Nanomizer) and dispersed and classified using a high-speed rotary film classifier (Filmix) to obtain spherical alumina powder.

[0213] (Example 2)

[0214] Spherical alumina powder 2, before heat treatment, was heat-treated in a muffle furnace at 1250°C in an atmospheric atmosphere for 4 hours. After cooling, it was crushed and classified using a rotary air jet mill to obtain spherical alumina powder.

[0215]

[0216] As shown in Table 1, the thermal conductivity of the resin compositions containing heat-treated spherical alumina powder in Examples 1 and 2 were 2.1 W / m·K and 1.9 W / m·K, respectively. This indicates that they exhibit superior thermal conductivity compared to the resin compositions containing untreated spherical alumina powder in Comparative Examples 1 and 2. On the other hand, although the non-spherical alumina in Comparative Example 3 was not heat-treated, its high α-oxidation rate suggests high thermal conductivity. However, the thermal conductivity of the resin composition containing non-spherical alumina in Comparative Example 3 was lower than that in Examples 1 and 2. This is believed to be due to the excessively high surface roughness and poor filling properties of the non-spherical alumina particles. Specifically, it is presumed that the poor filling properties prevent the uniform and sufficient formation of contact points between particles that serve as heat conduction paths.

[0217] Explanation of reference numerals in the attached figures

[0218] 1. Hopper

[0219] 2. Spherical burner

[0220] 3. Water-cooled jacketed spheroidizing furnace

[0221] 4. Stirring and cooling tank

[0222] 5 Separation tank

[0223] 6. Drying device

[0224] 7. Cooling water pump

[0225] 8. Washer-type trapping device

[0226] 9. Exhaust system

[0227] 10 Sprayers

Claims

1. A method for producing a spherical alumina powder, comprising: a high-temperature process of forming a high-temperature region on the inside of a furnace by a burner that forms a flame; a spheroidization process of generating a heat-treated-before spherical alumina powder by feeding a raw material alumina powder into the furnace and heating and melting; a cooling and washing process of cooling and washing the heat-treated-before spherical alumina powder by feeding the heat-treated-before spherical alumina powder into cooling and washing water in a cooling and washing tank; and a recovery process of recovering the heat-treated-before spherical alumina powder by separating the heat-treated-before spherical alumina powder from the cooling and washing water.

2. The method for producing a spherical alumina powder according to claim 1, wherein the high-temperature region is 2100°C or higher.

3. The method for producing a spherical alumina powder according to claim 1 or 2, wherein the heat-treated-before spherical alumina powder is fed into the cooling and washing water within 5 seconds after leaving the furnace.

4. The method for producing a spherical alumina powder according to claim 1 or 2, wherein the high-temperature process, the spheroidization process, and the cooling and washing process are performed using a production device in which a spheroidization furnace is connected to a stirring cooling tank via a short pipe, and there is no gap between the spheroidization furnace, the short pipe, and the stirring cooling tank.

5. The method for producing a spherical alumina powder according to claim 1 or 2, further comprising: a pre-cooling process of pre-cooling the heat-treated-before spherical alumina powder by spraying water onto the heat-treated-before spherical alumina powder.

6. The method for producing a spherical alumina powder according to claim 1 or 2, further comprising: a drying process of drying the heat-treated-before spherical alumina powder after separation.

7. The method for producing a spherical alumina powder according to claim 1 or 2, wherein the furnace is cylindrical.

8. The method for producing a spherical alumina powder according to claim 1 or 2, further comprising: a heat treatment process of obtaining a spherical alumina powder by heat-treating the heat-treated-before spherical alumina powder recovered after recovery at 1100 to 1300°C in an atmosphere.

9. A production device for a spherical alumina powder, comprising: a high-temperature formation site of forming a high-temperature region on the inside of a spheroidization furnace by a burner that forms a flame; a spheroidization site of generating a heat-treated-before spherical alumina powder by feeding a raw material alumina powder into the spheroidization furnace and heating and melting; a cooling and washing site of cooling and washing the heat-treated-before spherical alumina powder by feeding the heat-treated-before spherical alumina powder into cooling and washing water in a stirring cooling tank; and a recovery site of recovering the heat-treated-before spherical alumina powder by separating the heat-treated-before spherical alumina power from the cooling and washing water.

10. The production device for a spherical alumina powder according to claim 9, wherein the high-temperature formation site forms a high-temperature region of 2100°C or higher.

11. The production device for a spherical alumina powder according to claim 9 or 10, configured such that the heat-treated-before spherical alumina powder is fed into the cooling and washing water within 5 second after leaving the spheroidization furnace. ​ ​ ​ ​ ​ ​ ​ 12. The apparatus for manufacturing spherical alumina powder according to claim 9 or 10, The spheroidizing furnace is connected to the stirring and cooling tank via a short pipe, and there is no gap between the spheroidizing furnace, the short pipe, and the stirring and cooling tank.

13. The apparatus for manufacturing spherical alumina powder according to claim 9 or 10, further comprising a pre-cooling section for pre-cooling the spherical alumina powder before heat treatment by spraying water onto the spherical alumina powder before heat treatment.

14. The apparatus for manufacturing spherical alumina powder according to claim 9 or 10, further comprising a drying section for drying the separated, heat-treated spherical alumina powder.

15. The apparatus for manufacturing spherical alumina powder according to claim 9 or 10, wherein the spheroidizing furnace is cylindrical.

16. The apparatus for manufacturing spherical alumina powder according to claim 9 or 10, further comprising a heat treatment section for heat-treating the recovered pre-heat-treatment spherical alumina powder at 1100~1300°C in an atmospheric atmosphere to obtain spherical alumina powder.

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