Spherical alumina powder

Abstract

To provide spherical alumina powder with which a resin composition having a high heat conductivity can be provided despite the spherical alumina powder having a D50 of 0.1 to 40 μm.SOLUTION: Spherical alumina powder has a D50 of 0.1 to 40 μm, a circularity of 0.90 or more and 1.00 or less, an α-conversion ratio of 60% or more and 100% or less, and a particle surface roughness shown as the following equation (1) of 1.14 or more and 1.35 or less. Equation (1): the particle surface roughness=BET specific surface area A / sphere-equivalent specific surface area Sa calculated from particle size distribution.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to spherical alumina powder and a method for producing the same. [Background technology]

[0002] In recent years, mobile devices such as smartphones, as well as electronic devices installed in vehicles, have become remarkably smaller, lighter, and thinner. As a result, the density of electronic components such as IC chips and memory mounted on printed circuit boards inside electronic devices is increasing, and the heat density inside electronic devices is tending to increase even more. When the heat density inside electronic devices increases, the temperature rise due to the heat generated inside the device becomes significant, leading to a decrease in the operating performance and reliability of electronic components. Therefore, it is necessary to quickly transfer the heat generated from electronic components to the outside and dissipate it. Thus, the need to improve the thermal conductivity of the packaging materials and substrate materials of electronic devices is becoming even more important.

[0003] The most common method for solving the above problems is to fill insulating resin materials that constitute the packaging and substrate materials of electronic devices with highly thermally conductive inorganic material powder as a filler, achieving a high packing density. Alumina, magnesia, boron nitride, and aluminum nitride are known as highly thermally conductive inorganic material powders, but alumina powder is generally used most often from the viewpoint of chemical resistance and moisture absorption stability.

[0004] The inorganic material powder is preferably spherical in shape, which facilitates mixing with resin at a high packing density. Spherical alumina powder is generally known to be produced by a method called thermal spraying, in which Bayer process alumina, the raw material, is sprayed into a flame and rapidly cooled while melting to form spheres. The thermal spraying method is described in Patent Document 1.

[0005] However, with conventional thermal spraying methods, when the particle size is large, around 50 μm, spherical alumina with a high α-alumina content (hereinafter also referred to as the α-conversion rate) can be obtained. However, as the particle size decreases, the content of low-temperature phases such as δ-alumina increases, leading to problems such as a decrease in the thermal conductivity of the spherical alumina. Therefore, it was considered to increase the α-conversion rate by heat-treating the spherical alumina (Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-147711 [Patent Document 2] Japanese Patent Publication No. 2014-9140 [Overview of the project] [Problems that the invention aims to solve]

[0007] When the gelatinization rate of spherical alumina is increased by heat treatment, the surface roughness of the spherical alumina increases due to the heat treatment, reducing its kneadability with resin. As a result, there was a problem that the thermal conductivity of the resin material filled with spherical alumina could not be increased. On the other hand, conventional spherical alumina, due to its excellent filling properties and fluidity, tends to settle in the kneaded and filled resin composition, and segregation may occur between the resin layer with lower thermal conductivity and the layer where the spherical alumina powder is packed. This leads to a further decrease in thermal conductivity and the occurrence of performance variations.

[0008] This disclosure provides spherical alumina powder that can provide a resin composition with high thermal conductivity even when the spherical alumina powder has a D50 of 0.1 to 40 μm. This disclosure further provides a resin composition and a prepreg containing spherical alumina powder. [Means for solving the problem]

[0009] This disclosure concerns the following matters: [1] The D50 is 0.1 to 40 μm, The circularity is 0.90 or more and 1.00 or less, The α conversion rate is 60% or more and 100% or less, A spherical alumina powder having a particle surface roughness represented by the following formula (1) of 1.14 or more and 1.35 or less. Formula (1); Particle surface roughness = BET specific surface area A / Spherical equivalent specific surface area Sa calculated from the particle size distribution [2] The specific gravity is 3.80 g / cm 3 The spherical alumina powder according to [1] above. [3] The BET specific surface area A is 0.1 m 2 / g or more and 2.0 m 2 / g The spherical alumina powder according to [1] or [2] above. [4] The spherical alumina powder according to any one of [1] to [3], having an oil absorption rate of 30% or more and 50% or less. [5] A resin composition containing the spherical alumina powder according to any one of [1] to [4] and a resin. [6] A prepreg in which the resin composition according to [5] is impregnated into a base material. [7] A cured product of the prepreg according to [6] or a laminate thereof. [8] [7] The cured product according to, A metal-clad laminate including a metal foil disposed on at least one main surface of the cured product. [9] The resin composition according to [5] for use as a sealing material for an electronic component device.

[10] An electronic component device including an element and a cured product of the resin composition according to [5] for sealing the element.

[11] A high-temperature raising step of forming a high-temperature region inside the furnace by a burner that forms a flame, A spheroidizing step is performed to generate spherical alumina powder before heat treatment by introducing raw material alumina powder into the furnace and heating and melting it. A cooling and washing step is performed by immersing the pre-heat-treated spherical alumina powder in cooling and washing water in a water tank to cool and wash the pre-heat-treated spherical alumina powder. A recovery step is to separate the spherical alumina powder before heat treatment from the cooling wash water and recover the spherical alumina powder before heat treatment. A heat treatment step to obtain spherical alumina powder by heat-treating the recovered spherical alumina powder before heat treatment at 1100-1300°C in an atmospheric environment, A method for producing spherical alumina powder containing [the specified substance]. [Effects of the Invention]

[0010] According to this disclosure, it is possible to provide spherical alumina powder that can give a resin composition with high thermal conductivity even when the spherical alumina powder has a D50 of 0.1 to 40 μm. Furthermore, according to this disclosure, it is possible to provide a resin composition and a prepreg containing spherical alumina powder. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows the process flow of a method for producing spherical alumina powder before heat treatment according to one embodiment. [Figure 2] This is a schematic diagram showing the configuration of a manufacturing equipment applicable to the process flow in Figure 1. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described below. The embodiments described below are representative examples of the present invention and are not limited to them.

[0013] In this specification, if multiple upper or lower limits are given, a numerical range can be created from all combinations of upper and lower limits. Similarly, if multiple numerical ranges are given, separate numerical ranges can be created by individually selecting and combining upper and lower limits from those ranges.

[0014] [Spherical alumina powder] In one embodiment, the spherical alumina powder has a D50 of 0.1 to 40 μm, a circularity of 0.90 to 1.00, an α-gelatinization rate of 60% to 100%, and a particle surface roughness of 1.14 to 1.35 as shown in the following formula (1). Equation (1); Particle surface roughness = BET specific surface area A / Spherical equivalent specific surface area Sa calculated from particle size distribution Spherical alumina powder has a high gelatinization rate and a particle surface roughness within an appropriate range from the viewpoint of packing, resulting in high thermal conductivity of its own, and is less prone to segregation in the resin composition, making it easy to form uniform particle contact points. Therefore, spherical alumina powder can provide a resin composition with high thermal conductivity.

[0015] (D50) The D50 of the spherical alumina powder is 0.1 μm or larger, preferably 0.5 μm or larger, and more preferably 1.0 μm or larger. The D50 of the spherical alumina powder is 40 μm or smaller, preferably 10 μm or smaller, and more preferably 5.0 μm or smaller. A D50 of 0.1 μm or larger can increase thermal conductivity. A D50 of 40 μm or smaller can improve fillability in resins.

[0016] D50 is the 50% particle size in the volume-based cumulative particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer, and is measured by the method described in the examples.

[0017] (gelatinization rate) The gelatinization rate of the spherical alumina powder is 60% or higher, preferably 70% or higher, and more preferably 80% or higher. A higher gelatinization rate is expected to improve thermal conductivity. The gelatinization rate of the spherical alumina powder is 100% or lower, and may be 99% or lower, or 98% or lower.

[0018] The alpha-conversion rate is calculated using the following equation (2), where X is the maximum peak intensity of the α-alumina crystal phase at a diffraction angle of 2θ = 35.2° ± 0.2° in X-ray diffraction measurements, and Y is the maximum peak intensity of the crystal phase other than α-alumina at a diffraction angle of 2θ = 67.3° ± 0.2°. Formula (2); alpha conversion rate=(X / (X+Y))×100(%)

[0019] (Particle surface roughness A / Sa) In this specification, particle surface roughness is the value calculated by the following formula (1). Equation (1); Particle surface roughness = BET specific surface area A / Spherical equivalent specific surface area Sa calculated from particle size distribution The particle surface roughness of the spherical alumina powder is 1.14 or higher, preferably 1.16 or higher, and more preferably 1.20 or higher. The particle surface roughness of the spherical alumina is 1.35 or lower, preferably 1.31 or lower, and more preferably 1.29 or lower. When the particle surface roughness is 1.14 or higher, sedimentation of alumina particles in the resin composition is suppressed. When the particle surface roughness is 1.35 or lower, the packing ability into the resin can be improved.

[0020] (BET specific surface area A) The BET specific surface area A of the spherical alumina powder is preferably 0.1 m 2 / g The above is more comfortable 0.5 m 2 / g More preferably 1.0 m 2 / g That concludes the explanation. The BET specific surface area A of the spherical alumina powder is preferably 2.0 m 2 / g More precisely, 1.7m 2 / g Hereinafter, more preferably 1.5 m 2 / g is as follows. The BET specific surface area A is 0.1 m 2 / g or more, and it has excellent heat dissipation. When the BET specific surface area A is 2.0 m 2 / g or less, the filling property into the resin can be enhanced.

[0021] In this specification, the BET specific surface area A is a value measured and calculated in accordance with "6.2 Flow method (3.5) One-point method" of JIS R 1626:1996 (Method for measuring specific surface area of fine ceramics powder by gas adsorption BET method). The measurement is carried out using nitrogen gas as the adsorbate after heating the sample to 180 °C and flowing nitrogen gas for 20 minutes as a pretreatment.

[0022] (Spherical equivalent specific surface area Sa calculated from the particle size distribution) In this specification, the spherical equivalent specific surface area Sa (also referred to as spherical equivalent specific surface area Sa) calculated from the particle size distribution can be obtained by the method described in the examples.

[0023] The spherical equivalent specific surface area Sa of the spherical alumina powder is preferably 0.1 m 2 / g or more, more preferably 0.5 m 2 / g or more, still more preferably 1.0 m 2 / g or more. The spherical equivalent specific surface area Sa of the spherical alumina powder is preferably 2.0 m 2 / g or less, more preferably 1.7 m 2 / g or less, still more preferably 1.5 m 2 / g is as follows. When the spherical equivalent specific surface area Sa is 0.1 m2 / g The above results in excellent heat dissipation. The spherical equivalent specific surface area Sa is 2.0 m 2 / g The following conditions can improve the ability to fill the resin.

[0024] (specific gravity) The specific gravity of the spherical alumina powder is preferably 3.80 g / cm³. 3 More preferably, 3.85 g / cm³ 3 That concludes the explanation. The specific gravity of the spherical alumina powder is preferably 4.00 g / cm³. 3 More preferably, 3.97 g / cm³ 3 The following is the specific gravity: 3.80 g / cm³ 3 The above characteristics indicate a high proportion of α-alumina, resulting in excellent thermal conductivity. The specific gravity is 4.00 g / cm³. 3 The following conditions result in a high proportion of α-alumina and excellent thermal conductivity. The specific gravity can be determined by the method described in the examples.

[0025] (Circularity) The circularity of the spherical alumina powder is 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 circularity of the spherical alumina powder is 1.00 or lower, but from the viewpoint of productivity, it may be 0.99 or lower. The circularity is measured by the method described in the examples.

[0026] (Oil absorption rate) 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. When the oil absorption rate is 30% or more, the settling of alumina particles in the resin composition is suppressed. When the oil absorption rate is 50% or less, the packing ability into the resin can be improved. The oil absorption rate is measured by the method described in the examples.

[0027] [Method for producing spherical alumina powder] Spherical alumina powder produced by the conventional flame melting method is manufactured using a known method in which raw material powders that can serve as an aluminum source, such as aluminum oxide powder, aluminum hydroxide powder, and metallic aluminum powder, are introduced into a high-temperature flame, the raw material powders are melted and the particles are sphericalized by surface tension, and then cooled to a temperature at which they can be collected by air cooling, and finally the powder is collected with a collection device. In such a method, the cooling after melting is carried out slowly, so the crystallization of the alumina particles progresses during the cooling process, and the surface roughness of the particles increases. In addition, since the temperature profile from spheroidization to cooling is not controlled, there is variation in the progress of crystallization during the cooling process. Therefore, when heat treatment is applied to such conventional spherical alumina powder, it is difficult to control the alpha-adsorption rate and particle surface roughness to a desired range.

[0028] On the other hand, the present inventors have found that spherical alumina powder can be obtained by spheroidizing the raw material powder using the known method described above, immediately cooling the high-temperature powder in a water bath, and washing away impurities such as soda and calcium components that may induce particle fusion and sintering by washing the spherical alumina powder, and then subjecting the resulting spherical alumina powder to heat treatment, thereby controlling the alpha-gelatinization rate and particle surface roughness to a desired range. 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 these will be described.

[0029] (Method for producing spherical alumina powder before heat treatment) One embodiment of the method for producing spherical alumina powder before heat treatment includes: a heating step of forming a high-temperature region inside a furnace using a burner that forms a flame; a spheroidizing step of generating spherical alumina powder before heat treatment by introducing raw alumina powder into the furnace and heating and melting it; a cooling and washing step of introducing the spherical alumina powder before heat treatment into cooling and washing water in a water tank to cool and wash the spherical alumina powder before heat treatment; and a recovery step of separating the spherical alumina powder before heat treatment from the cooling and washing water and recovering the spherical alumina powder before heat treatment. Figure 1 shows the process flow of one embodiment of the method for producing spherical alumina powder before heat treatment. By simultaneously cooling and washing the spherical alumina powder before heat treatment, it is possible to induce particle fusion and sintering present on the particle surface at low cost and in a short time. + Furthermore, it is possible to produce pre-heat-treated spherical alumina powder with reduced amounts of other ionic impurities.

[0030] <Raw material: Alumina powder> There are no particular restrictions on the raw material alumina powder, but Na + It is preferable to use a small amount of Na. + Specific examples of alumina powder produced in small quantities include low-soda alumina powder produced by the Bayer process.

[0031] The shape of the raw alumina powder is not limited, but a non-spherical shape is preferred for the purpose of obtaining spherical alumina powder before heat treatment. The circularity of the raw alumina powder is, for example, less than 0.90, 0.86 or less, or 0.84 or less.

[0032] From the viewpoint of obtaining spherical alumina powder before heat treatment of a size suitable for heat dissipation fillers, the D50 of the raw alumina powder is preferably 0.1 μm to 40 μm. From the same viewpoint, D50 is more preferably 0.5 μm to 10 μm, and even more preferably 1.0 μm to 5 μm.

[0033] <Furnace> Examples of furnaces include vertical furnaces and horizontal furnaces. The shape of the furnace is not limited, but examples include cylindrical shapes and polygonal prism shapes such as hexagonal prisms. A cylindrical shape is preferred because it is easier to uniformly control the temperature inside the furnace. A cylindrical shape means that at least a part of the furnace is cylindrical, but it may include parts of other shapes. A polygonal prism shape means that at least a part of the furnace is polygonal prism, but it may include parts of other shapes. From the viewpoint of improving collection efficiency, the downstream part of the furnace is preferably an inverted cone shape with the discharge port side narrowing.

[0034] While the furnace material is not limited, it is desirable that the inner wall be made of stainless steel to minimize contamination of the spherical alumina powder with impurities before heat treatment. A water-cooling jacket may be provided around the outer circumference of the furnace to cool it.

[0035] <High temperature process> The high-temperature process is a process in which a high-temperature region is created inside the furnace by using a burner that forms a flame.

[0036] A burner is a device that mixes a suitable amount of combustion-supporting gas with a combustible gas to form a flame in a furnace. The burner is supplied with combustible gas from a combustible gas source and combustion-supporting gas from a combustion-supporting gas source. Examples of combustible gases include liquefied natural gas (LNG) and LPG. Examples of combustion-supporting gases include air, oxygen gas, and oxygen-enriched air.

[0037] The temperature in the high-temperature region is preferably 2100°C or higher. Preferably, the temperature in the high-temperature region is 2500°C or lower, more preferably 2300°C or lower. A temperature of 2100°C or higher is above the melting point of alumina, making it easier to increase the circularity of the resulting alumina powder. A temperature of 2500°C or lower is within the heat resistance range of a typical burner, which is advantageous in terms of cost.

[0038] <Spheroidization process> The spheroidizing process is a process of producing spherical alumina powder before heat treatment by introducing raw alumina powder into a furnace and heating and melting it. In the spheroidizing process, a carrier gas for supplying the raw alumina powder may be used as needed. Examples of carrier gases include at least one selected from air, nitrogen, oxygen, and carbon dioxide.

[0039] <Pre-cooling process> A method for producing spherical alumina powder before heat treatment preferably includes a pre-cooling step for pre-cooling the spherical alumina powder before heat treatment. The pre-cooling step is performed after the spheroidizing step and before the cooling and washing step. The equipment for pre-cooling is preferably located outside the high-temperature region of the furnace or between the furnace and the water tank used in the cooling and washing step. This allows the spherical alumina powder before heat treatment, which is to be introduced into the cooling and washing water in the water tank during the cooling and washing step, to be cooled to a preferred temperature in a short time.

[0040] Pre-cooling is preferably performed by spraying water onto the spherical alumina powder before heat treatment. Examples of equipment for spraying water include showers.

[0041] <Cooling and cleaning process> The cooling and washing process involves immersing the spherical alumina powder before heat treatment in cooling and washing water in a water tank to simultaneously cool and wash the powder. By performing cooling and washing simultaneously, the equipment can be made smaller and the overall process time shorter compared to when cooling and washing are performed as separate processes, for example, when the spherical alumina powder before heat treatment is collected using a collection device such as a cyclone while being air-cooled after the spheroidizing process, and then the collected spherical alumina powder is washed. In addition, variations in crystallinity can be suppressed. Because the manufacturing method of spherical alumina powder before heat treatment involves less thermal history, it is possible to produce spherical alumina powder before heat treatment with a low BET specific surface area.

[0042] The tank contains cooling water for washing and cooling the spherical alumina powder before heat treatment. To improve washing efficiency, it is preferable to agitate the cooling water with a stirrer. The cooling water can be any type of water, but examples include tap water.

[0043] The temperature of the cooling and washing water is preferably 50°C or higher, more preferably 70°C or higher, from the viewpoint of efficiently reducing ionic impurities present on the surface of the spherical alumina powder before heat treatment. From the viewpoint of suppressing damage to the furnace body due to heat load, the temperature of the cooling and washing water is preferably 80°C or lower.

[0044] In the cooling and washing process, it is preferable that the spherical alumina powder before heat treatment is added to the cooling and washing water within 5 seconds of leaving the furnace. Adding it within 5 seconds helps to keep the BET specific surface area of ​​the spherical alumina powder before heat treatment low. Adding it within 5 seconds also helps to suppress variations in the degree of crystallinity of the spherical alumina powder before heat treatment.

[0045] In the cooling and washing process, the temperature of the pre-heat-treated spherical alumina powder added to the cooling and washing water is preferably 200°C or lower, and more preferably 100°C or lower. Even more preferably, the temperature of the pre-heat-treated spherical alumina powder from the time it leaves the furnace until it is added to the cooling and washing water is 200°C or lower, and particularly preferably 100°C or lower. A temperature of 200°C or lower reduces the risk of the cooling and washing water in the water tank overheating and evaporating, thus facilitating stable production.

[0046] The temperature of spherical alumina powder before heat treatment can be determined using the simulation software Ansys Fluent (Ansys).

[0047] <Recovery Process> The recovery process involves separating the spherical alumina powder before heat treatment from the cooling and washing water, and recovering the spherical alumina powder before heat treatment. While not limited to a specific recovery method, one method involves allowing the spherical alumina powder dispersed in the cooling and washing water to settle, and then removing the supernatant water using a pump or the like. This method removes the Na adhering to the particle surface.+ Ca 2+ This is preferable because it can wash away and remove ionic impurities such as those mentioned above.

[0048] <Drying process> A method for producing spherical alumina powder before heat treatment preferably includes a drying step. The drying step is a step of drying the spherical alumina powder before heat treatment from which the cooling wash water has been separated. In the drying step, any moisture remaining after the recovery step is removed. The drying method is not limited and may be natural drying or heat drying.

[0049] <Manufacturing equipment for spherical alumina powder before heat treatment> The following describes in detail, with reference to figures, a preferred configuration of a manufacturing apparatus and its components used in a method for producing spherical alumina powder before heat treatment according to one embodiment. Note that the figures used in the following description focus on characteristic parts for ease of understanding, and the dimensional ratios of each component may not necessarily be the same as those of the actual apparatus.

[0050] The apparatus for producing spherical alumina powder before heat treatment will be explained using Figure 2. As shown in Figure 2, the apparatus for producing spherical alumina powder before heat treatment is generally configured to include a hopper 1 for storing and feeding raw materials, a spheroidizing burner 2, a water-cooled jacket-type spheroidizing furnace 3 (also called spheroidizing furnace 3) for spheroidizing, a stirring and cooling tank 4 for washing 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 extracting the spherical alumina powder before heat treatment, and a drying device 6 for drying the spherical alumina powder before heat treatment that still contains moisture to obtain dry spherical alumina powder before heat treatment.

[0051] The raw material hopper 1 is equipped with a feeder device and other components, allowing for the quantitative supply of raw alumina powder to the spheroidizing burner 2. This spheroidizing burner 2 supplies the raw alumina powder from the raw material hopper 1 into the spheroidizing furnace 3. It is also possible to supply inorganic oxide powder to the spheroidizing burner 2 using a powder carrier gas.

[0052] The spheroidizing burner 2 is installed in the spheroidizing furnace 3. The spheroidizing burner 2 is supplied with combustible gas from a combustible gas supply source (not shown) and with combustion-supporting gas from a combustion-supporting gas supply source (not shown), and the spheroidizing burner 2 can form a flame inside the spheroidizing furnace 3.

[0053] The spheroidizing furnace 3 is a cylindrical vertical furnace, and the lower part of the furnace has an inverted conical shape, narrowing towards the discharge port. Inside the spheroidizing furnace 3, the raw alumina powder introduced into the high-temperature region formed by the flame is heated and melted to produce spherical alumina powder before heat treatment.

[0054] A shower 10 is provided inside the spheroidizing furnace 3. By spraying water onto the spherical alumina powder before heat treatment after it has left the high-temperature region using the shower 10, the spherical alumina powder before heat treatment can be pre-cooled. In Figure 2, the shower is provided inside the spheroidizing furnace 3, but the shower may be provided at any point along the path from when the spherical alumina powder before heat treatment leaves the high-temperature region until it comes into contact with the cooling wash water.

[0055] The spheroidizing furnace 3 is connected to the stirring and cooling tank 4 via a short pipe. A duct is provided in the short pipe, and the duct is connected to a scrubber-type collection device 8 and an exhaust device 9, allowing the combustion exhaust gas to be discharged outside the system. Since this combustion exhaust gas contains minute particles of unheated spherical alumina powder, it is desirable to separate and remove the fine powder from the gas by passing it through the scrubber-type collection device 8, and then discharge the purified combustion exhaust gas through the exhaust device 9. In Figure 2, there are no gaps between the spheroidizing furnace 3, the short pipe, and the stirring and cooling tank 4, but gaps may be present between them.

[0056] The stirring and cooling tank 4 contains cooling and washing water for cooling and washing the spherical alumina powder before heat treatment. The cooling and washing water in the stirring and cooling tank 4 is stirred by a stirrer to improve washing efficiency. A cooling water pump 7 is connected to the stirring and cooling tank 4, and the cooling water pump 7 is connected to a shower 10, with piping arranged so that the cooling and washing water in the tank can be circulated.

[0057] A separation tank 5 is connected to the stirring and cooling tank 4 for separating the collected unheated spherical alumina powder from the cooling and washing water. A slurry containing the unheated spherical alumina powder is supplied from the stirring and cooling tank 4 to the separation tank 5. In the separation tank 5, the cooling and washing water and solid matter are separated, and the water is returned to the system via the cooling water pump 7 and circulated. At this time, Na adhering to the particle surface is separated. + Ionic impurities such as these are washed and removed. The solid material is supplied to the drying apparatus 6, and any remaining moisture is dried to obtain spherical alumina powder before heat treatment with fewer ionic impurities.

[0058] This manufacturing apparatus eliminates the need to install expensive and large-scale equipment such as ion exchange water systems, and allows for the production of heat-treated spherical alumina powder with low levels of ionic impurities using a small-scale spheroidizing facility.

[0059] (Method for producing spherical alumina powder) Spherical alumina powder can be obtained by heat-treating the unheated spherical alumina powder in an atmospheric environment at 1100-1300°C. Heat treatment at temperatures above 1100°C promotes the transition from phases other than the α-crystalline phase, which has low thermal conductivity, such as amorphous, γ-crystalline, δ-crystalline, and θ-crystalline phases, to the α-crystalline phase, which has high thermal conductivity. Heat treatment at temperatures below 1300°C can suppress surface roughness. Heat treatment at temperatures below 1300°C can suppress particle size increase due to fusion between particles.

[0060] The heat treatment time is preferably 1 hour or more, and more preferably 1 hour to 4 hours. A time of 1 hour or more allows sufficient time for the transition to the target α-crystalline phase, making it easier to reach the target α-conversion rate. A time of 4 hours or less suppresses sintering between particles, making it easier to obtain powder with the target particle size.

[0061] The heat treatment apparatus may be a general-purpose device, and specific examples include trolley furnaces, tunnel furnaces, and rotary kiln furnaces. The heat treatment atmosphere is not particularly limited, but is preferably an atmospheric atmosphere.

[0062] A method for producing spherical alumina powder may optionally include a crushing step to crush aggregated particles produced by heat treatment. A method for producing spherical alumina powder may optionally include a classification step to perform a classification treatment. In some cases, aggregated particles may be produced when some particles are sintered together by heat treatment. In this case, it is preferable to perform at least one treatment selected from the crushing treatment and the classification treatment. The crushing treatment may be wet or dry. Examples of crushing treatments include using a roll mill, ball mill, small-diameter ball mill (also called a bead mill), pot mill, media stirring mill, air jet mill, mortar and pestle, automatic mixing mortar and pestle, tank crusher, or jet mill.

[0063] Spherical alumina powder is preferably used in applications requiring high thermal conductivity. For example, spherical alumina powder can be used as a filler in materials requiring high thermal conductivity, such as heat dissipation materials and semiconductor encapsulants.

[0064] [Resin composition] One embodiment of the resin composition comprises spherical alumina powder and resin. The resin composition can be used as a heat-dissipating insulating resin composition or a encapsulant, for example, as a encapsulant for electronic components. The resin composition is suitable for semiconductor packages and printed circuit boards where high thermal conductivity is required.

[0065] 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, amino resins such as melamine resins, unsaturated polyester resins, allyl resins, dicyclopentadiene resins, silicone resins, and triazine resins. Among these, epoxy resins, which have excellent moldability and electrical insulation properties, are preferred. The resins may be used individually or in combination of two or more types.

[0066] 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, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, dicyclopentadiene type epoxy resin, naphthalene type epoxy resin, and anthracene type epoxy resin.

[0067] 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, polyetheretherketone resin, and polyetherimide resin.

[0068] The content of spherical alumina powder in the resin composition is preferably 50 to 90% by volume, more preferably 60 to 85% by volume. When the content is 50% by volume or more, the thermal conductivity improvement effect of the spherical alumina powder is sufficient. When the content is 90% by volume or less, the moldability of the resin composition is good.

[0069] The resin composition may contain other inorganic fillers besides spherical alumina. Examples of other inorganic fillers include aluminum hydroxide, zinc oxide, magnesium oxide, magnesium carbonate, titanium oxide, silicon oxide, and boron nitride. Among these, at least one selected from aluminum hydroxide, zinc oxide, magnesium oxide, and boron nitride is preferred from the viewpoint of improving thermal conductivity.

[0070] The resin composition may contain any components other than those listed above. Examples of optional components include curing agents, curing accelerators, flame retardants, ultraviolet absorbers, antioxidants, organic solvents, and surface treatment agents.

[0071] Examples of curing agents include, when using epoxy resins, polyfunctional phenol compounds such as phenol novolac and cresol novolac; amine compounds such as dicyandiamide, diaminodiphenylmethane, and diaminodiphenylsulfone; and acid anhydrides such as phthalic anhydride, pyromellitic anhydride, maleic anhydride, and maleic anhydride copolymers. The curing agent may be used alone or in combination of two or more types.

[0072] Examples of curing accelerators, when using epoxy resins, include imidazole compounds and their derivatives; organophosphorus compounds; secondary amines; tertiary amines; and quaternary ammonium salts.

[0073] Examples of imidazole compounds and their derivatives include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 4,5-diphenylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, 2-phenyl-4-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, and 2-phenyl-4-methylimidazole. Imidazole compounds and their derivatives may be masked with a masking agent. Examples of masking agents include acrylonitrile, phenylenediisocyanate, toluidine isocyaninate, naphthalene diisocyanate, methylene bisphenyl isocyanate, and melamine acrylate.

[0074] Examples of organophosphorus compounds include ethylenephosphine, propylphosphine, butylphosphine, phenylphosphine, trimethylphosphine, triethylphosphine, tributylphosphine, trioctylphosphine, triphenylphosphine, tricyclohexylphosphine, triphenylphosphine / triphenylborane complexes, and tetraphenylphosphonium tetraphenylborate.

[0075] Examples of secondary amines include morpholine, piperidine, pyrrolidine, dimethylamine, diethylamine, dicyclohexylamine, N-alkylarylamine, piperazine, diallylamine, thiazoline, and thiomorpholine.

[0076] Examples of tertiary amines include benzyldimethylamine, 2-(dimethylaminomethyl)phenol, and 2,4,6-tris(dimethylaminomethyl)phenol.

[0077] 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.

[0078] The curing accelerator may be used alone or in combination of two or more types.

[0079] Organic solvents can be used to adjust the viscosity of the resin composition, etc. For example, when manufacturing a prepreg by impregnating a substrate with a resin composition, and when coating with a resin composition, it is preferable to use an organic solvent to adjust the viscosity of the resin composition to an appropriate range. The organic solvent may be removed after the impregnation or coating process.

[0080] 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 atom-containing solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfur atom-containing solvents such as dimethyl sulfoxide. Organic solvents may be used individually or in combination of two or more.

[0081] Among these, methyl isobutyl ketone, methyl ethyl ketone, propylene glycol monomethyl ether, and methyl cellosolve are preferred from the viewpoint of solubility, and methyl isobutyl ketone and propylene glycol monomethyl ether are more preferred from the viewpoint of low toxicity.

[0082] When dispersing spherical alumina powder in an organic solvent, dispersers such as bead mills, homogenizers, and jet mills can be used to improve dispersibility. It is also preferable to pre-treat the spherical alumina powder with a surface treatment agent described later, or to perform integral blending.

[0083] Examples of surface treatment agents include coupling agents such as silane coupling agents and titanate coupling agents, and silicone oligomers. The spherical alumina powder may be pre-treated with a surface treatment agent.

[0084] When a prepreg is manufactured by impregnating a substrate with a resin composition, the total content of components other than organic solvents (also called solids) in the resin composition is preferably 40 to 90% by mass, more preferably 50 to 85% by mass, relative to the entire resin composition.

[0085] [Method for producing resin compositions] The method for producing the resin composition is not particularly limited. Examples of methods for producing the resin composition include thoroughly mixing predetermined amounts of components using a mixer, kneading the mixture using a mixing roll, extruder, etc., and then cooling it. More specifically, a method may be used in which predetermined amounts of components are stirred and mixed, the mixture is kneaded using a kneader, roll, extruder, etc., preheated to 70-140°C, and then cooled.

[0086] [Prepreg] In one embodiment, the prepreg is in which a resin composition is impregnated into a substrate.

[0087] Examples of substrate materials include inorganic fibers such as E-glass, D-glass, S-glass, and Q-glass. Examples of substrate forms include woven fabrics, non-woven fabrics, rawhide, chopped strand mats, and surfacing mats. The substrate material and form are selected according to the intended application and performance, and can be used individually or in combination of two or more materials and forms as needed. From the viewpoint of heat resistance, moisture resistance, and processability, the substrate may be surface-treated. Examples of surface treatments include surface treatment with silane coupling agents and mechanical fiber opening treatment. The thickness of the substrate is, for example, 0.01 to 0.2 mm.

[0088] A prepreg 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 may be partially cured by heating.

[0089] Prepregs are suitable for semiconductor packages and printed circuit boards that require high thermal conductivity.

[0090] [Cured prepreg or its laminate] Cured prepregs or laminates thereof can be manufactured by heating and pressurizing one or more layers of prepreg. The number of layers of prepreg is not particularly limited, but is typically 2 to 20. Examples of equipment for heating and pressurizing include multi-stage presses, multi-stage vacuum presses, continuous molding machines, and autoclave molding machines. The heating and pressurizing conditions should be selected according to the thermosetting resin, curing agent, etc. used. For example, a temperature of 100 to 250°C, a pressure of 0.2 to 10 MPa, and a time of 0.1 to 5 hours.

[0091] [Metal-clad laminate] A metal-clad laminate according to one embodiment 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 pressurizing them with metal foils placed on one or both sides. The apparatus for heating and pressurizing, as well as the heating and pressurizing conditions, are the same as described above. The metal foil is not particularly limited as long as it is used for electronic component applications. Examples of metal foils include copper foil and aluminum foil.

[0092] [Electronic Components and Devices] An electronic component device according to one embodiment comprises an element and a cured resin composition that encapsulates the element. Examples of elements include active elements such as semiconductor chips, transistors, diodes, and thyristors, and passive elements such as capacitors, resistors, and coils.

[0093] Examples of electronic component devices include those in which elements are mounted on support members such as lead frames, pre-wired tape carriers, wiring boards, glass, silicon wafers, and organic substrates, and the resulting element portion is sealed with a resin composition. More specifically, common resin-encapsulated 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) have a structure in which elements are fixed on a lead frame, the terminal parts of the elements such as bonding pads are connected to the lead parts by wire bonding, bumps, etc., and then sealed using a resin composition by transfer molding, etc.; TCP (Tape Carrier Package) has a structure in which elements connected to a tape carrier by bumps are sealed with a resin composition; and COB (Chip On) has a structure in which elements connected to wiring formed on a support member by wire bonding, flip-chip bonding, solder, etc., are sealed with a resin composition. Examples include board modules, hybrid ICs, multi-chip modules, etc.; BGA (Ball Grid Array), CSP (Chip Size Package), MCP (Multi Chip Package), etc., which have a structure in which elements are mounted on the surface of a support member having terminals for connecting to a wiring board formed on the back surface, the elements and wiring formed on the support member are connected by bump or wire bonding, and then the elements are sealed with a resin composition.

[0094] Methods for encapsulating electronic components using resin compositions include, for example, low-pressure transfer molding, injection molding, and compression molding. Of these, low-pressure transfer molding is the most common. [Examples]

[0095] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0096] <Evaluation Method> (D10, D50, D90) 40 mg of the sample was added to 50 mL of water containing 2 drops of a nonionic surfactant (TRITON-X; Roche Applied Science), and dispersed by ultrasound for 3 minutes. This dispersion was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac-Bell, MT3300II). The 10%, 50%, and 90% particle sizes in the obtained volume-based cumulative particle size distribution were determined as D10, D50, and D90, respectively.

[0097] (gelatinization rate) The alpha-conversion rate was calculated using the relationship (%) = (X / (X+Y)) × 100, where X is the maximum peak intensity of the α-alumina crystal phase at a diffraction angle 2θ = 35.2° ± 0.2°, and Y is the maximum peak intensity of the crystal phase other than α-alumina at a diffraction angle 2θ = 67.3° ± 0.2°. X-ray diffraction measurements of alumina powder were performed using an X-ray diffractometer PW3040 / 60X'Pert-MRD (Malvern Panalytical), with a copper X-ray tube, a tube voltage of 45kV, and a tube current of 40mA.

[0098] (BET specific surface area A) The BET specific surface area A was measured and calculated in accordance with "6.2 Flow method (3.5) Single-point method" of JIS R 1626:1996 (Method for measuring the specific surface area of ​​fine ceramic powder by gas adsorption BET method). Specifically, approximately 2 g of sample was weighed out, pre-degassed at 180°C for 20 minutes, and then placed in an automatic specific surface area measuring device (Macsorb, Mountec Co., Ltd.). The amount of nitrogen gas adsorbed was measured using pure nitrogen and a nitrogen-helium mixed gas (mixing ratio: nitrogen 30 mol%, helium 70 mol%), and the BET specific surface area A was calculated using the single-point method.

[0099] (Spherical equivalent specific surface area Sa calculated from particle size distribution) The spherical specific surface area (Sa) calculated from the particle size distribution was determined using the following formula based on particle size distribution data obtained with a laser diffraction / scattering particle size distribution analyzer (Microtrac-Bell Co., Ltd., MT3300II). The sample preparation method was the same as that used for measurements of D10, D50, and D90.

number

[0100] (specific gravity) A 5 mg sample was placed in a sample cell for measurement, and its specific gravity was measured using a dry densimeter (Shimadzu Corporation, product name: Accupic II 1340) by the gas (helium) displacement method. Specifically, the sample cell was set in the dry densimeter, and the volume of the sample was determined by displacement with helium gas. The specific gravity was then calculated by dividing the sample mass by this volume.

[0101] (Circularity) Circularity is the average value calculated using the following formula (3) for 2000 or more particles, where S is the area of ​​the projection of the particle and L is its perimeter. Equation (3); (4×π×S) / L 2 Area S and perimeter L were measured using an FPIA-3000 (Malvern Panalytical). As a pretreatment, due to the instrument's measurement range, approximately 10g of the sample was placed in a 200mm diameter, 25μm mesh sieve, and particles larger than 25μm were removed with shower water. The sample below the sieve was transferred to a plastic container and used as the measurement sample. The measurement conditions were LPF / HPF standard (20x lens) and bright-field, and particle sheath (Malvern Panalytical) was used as the measurement solvent. To ensure that the number of effective particles was 2000 or more and the ratio of effective particles to total particles was 55-70%, 2g of the measurement sample was weighed into a 50mL beaker, 50mL of pure water was added, and the sample was dispersed in a 200W ultrasonic disperser for 3 minutes before being placed in the instrument and measured. As a post-measurement data processing, multiple particles on a single screen were removed, and the circularity was calculated.

[0102] (Oil absorption rate) A 10g sample was placed in a 10cm diameter mortar, and a small amount of liquid epoxy resin was added dropwise and thoroughly mixed with the sample. This process of adding small amounts of resin was repeated until the sample and epoxy resin formed a single mass. The volume of the added resin was calculated from the weight of the resin at the point when the sample and resin formed a single mass, and the oil absorption rate was calculated using the following formula. The volume of the sample was calculated from the specific gravity measured above. Oil absorption rate (%) = (Volume of resin added / (Volume of sample + Volume of resin added)) × 100

[0103] (Thermal conductivity) Alumina powder was mixed with epoxy resin, a polyfunctional phenol compound as a curing agent, and an organophosphorus compound as a curing accelerator at the volume filling rate shown in Table 1. The mixture was diluted with methyl ethyl ketone and stirred using a mix rotor to produce a varnish with a solid content of 75% by mass. The resulting varnish was coated onto a release PET film to a thickness of 200 μm and dried at a temperature of 110°C for 10 minutes. The dried resin composition was then pulverized. To form a composite for measurement using the pulverized resin composition, the press pressure was increased to 10 kN while holding the heating temperature at 80°C for 3 minutes in a heated vacuum press. Once 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 press pressure was increased from 10 kN to 40 kN. The heating temperature reached 160°C and was held for 16 minutes to produce a resin composite with a thickness of 1 mm. A resin composite was cured at 175°C for 6 hours to obtain a composite for measurement. The thermal conductivity of this composite was then measured.

[0104] Thermal conductivity is calculated by the product of thermal diffusivity, low-pressure specific heat capacity, and density. Thermal diffusivity was measured using a xenon flash analyzer (NETZSCH JAPAN Co., Ltd., LFA647 HyperFlash). Constant-pressure specific heat capacity was calculated from the specific heat capacity of each material and its mixing ratio. Density was measured using an electronic hydrometer (Alpha Mirage Co., Ltd., MDS-3000). Thermal conductivity was calculated from the product of these values. Note that thermal diffusivity and density were measured at 23°C, and the specific heat capacity value at 25°C was used.

[0105] (Comparative Example 1) The raw material alumina powder (D50: 1.8 μm) was introduced into a high-temperature region of 2200°C formed inside a furnace by a flame created by LPG and oxygen, and subjected to a spheroidization treatment. The spherical alumina powder before heat treatment was placed into 80°C cooling wash water in a water tank within 5 seconds of leaving the furnace and cooled and washed. The slurry containing the obtained spherical alumina powder before heat treatment was separated into a high-concentration slurry and a supernatant liquid in the recovery process, and in the drying process the high-concentration slurry was dried in a dryer in an atmospheric atmosphere at an ambient temperature of 180°C to obtain spherical alumina powder 1 before heat treatment.

[0106] (Comparative Example 2) Raw material alumina powder (D50: 1.2 μm) was introduced into a high-temperature region of 2200°C formed inside a furnace by a flame created by LPG and oxygen, and subjected to a spheroidization treatment. The spherical alumina powder before heat treatment was placed into 80°C cooling wash water in a water tank within 5 seconds of leaving the furnace and cooled and washed. The slurry containing the obtained spherical alumina powder before heat treatment was separated into a high-concentration slurry and a supernatant liquid in the recovery process, and in the drying process the high-concentration slurry was dried in a dryer in an atmospheric atmosphere at an ambient temperature of 180°C to obtain spherical alumina powder 2 before heat treatment.

[0107] (Comparative Example 3) Sumitomo Chemical Co., Ltd. Advanced Alumina AA-2

[0108] (Example 1) Spherical alumina powder 1 was heat-treated in a muffle furnace in an air atmosphere at a temperature of 1250°C for 4 hours. After cooling, it was crushed using a wet shear crusher Nanomizer, and then dispersed and classified using a high-speed rotating thin-film classifier Filmix to obtain spherical alumina powder.

[0109] (Example 2) The spherical alumina powder 2 before heat treatment was heat-treated in a muffle furnace at an atmospheric temperature of 1250°C for 4 hours. After cooling, it was crushed and classified using a swirling flow jet mill to obtain spherical alumina powder.

[0110] [Table 1] As shown in Table 1, the thermal conductivity of the resin compositions containing heat-treated spherical alumina powder in Examples 1 and 2 was 2.1 W / m·K and 1.9 W / m·K, respectively. These show superior thermal conductivity compared to the resin compositions containing untreated spherical alumina powder in Comparative Examples 1 and 2. On the other hand, the non-spherical alumina in Comparative Example 3, although not heat-treated, has a high alpha-adsorption rate, and its own thermal conductivity is presumed to be high. However, the thermal conductivity of the resin composition containing non-spherical alumina in Comparative Example 3 is lower than that of Examples 1 and 2. This is thought to be because the particle surface roughness of the non-spherical alumina is too high, resulting in poor packing. More specifically, it is presumed that the poor packing prevents the uniform and sufficient formation of contact points between particles that serve as heat conduction pathways. [Explanation of Symbols]

[0111] 1 Hopper 2. Spheroidizing burner 3. Water-cooled jacket-type spheroidizing furnace 4. Stirring and cooling tank 5 Separation tank 6 Drying equipment 7. Cooling water pump 8. Scrubber-type collection device 9. Exhaust system 10 showers

Claims

1. D50 is 0.1 to 40 μm. The circularity is between 0.90 and 1.

00. The gelatinization rate is between 60% and 100%. The BET specific surface area A is 0.1 m² / g or more and 2.0 m² / g or less. The oil absorption rate is between 30% and 50%. Spherical alumina powder having a particle surface roughness of 1.14 or more and 1.35 or less, as shown by the following formula (1). Formula (1); Particle surface roughness = BET specific surface area A / Spherical equivalent specific surface area Sa calculated from particle size distribution

2. Specific gravity is 3.80 g / cm³ ３ The spherical alumina powder according to claim 1, as described above.

3. A resin composition comprising spherical alumina powder and resin according to claim 1 or 2.

4. A prepreg in which the resin composition described in claim 3 is impregnated into a substrate.

5. A cured product of a prepreg or laminate thereof according to claim 4.

6. The cured product according to claim 5, A metal-clad laminate comprising a metal foil disposed on at least one main surface of the cured material.

7. The resin composition according to claim 3, for use as a encapsulant for electronic component devices.

8. An electronic component device comprising an element and a cured product of the resin composition according to claim 3 for sealing the element.

9. A high-temperature process that creates a high-temperature region inside the furnace using a burner that forms a flame, A spheroidizing step is performed to generate spherical alumina powder before heat treatment by introducing raw material alumina powder into the furnace and heating and melting it. A cooling and washing step is performed by immersing the pre-heat-treated spherical alumina powder in cooling and washing water in a water tank to cool and wash the pre-heat-treated spherical alumina powder. A recovery step is to separate the spherical alumina powder before heat treatment from the cooling wash water and recover the spherical alumina powder before heat treatment. A heat treatment step to obtain spherical alumina powder by heat-treating the recovered spherical alumina powder before heat treatment at 1100 to 1300°C in an atmospheric environment, A method for producing spherical alumina powder containing [the specified substance].

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