Method for producing spherical inorganic oxide powder

Abstract

To provide a method for producing a spherical inorganic oxide powder, by which the spherical inorganic oxide powder in which the amount of Na + present on the surfaces of particles is reduced can simply be produced in a small scale facility in a short time.SOLUTION: A method for producing a spherical inorganic oxide powder, comprising a temperature increasing step of forming a high-temperature region inside a furnace by a burner that forms a flame, a spheroidizing step of charging a raw material inorganic oxide powder into the furnace and heating and melting the raw material inorganic oxide powder to produce a spherical inorganic oxide powder, a cooling and washing step of charging the spherical inorganic oxide powder into cooling and washing water in a water tank to cool and wash the spherical inorganic oxide powder, and a recovery step of separating the spherical inorganic oxide powder from the cooling and washing water to recover the spherical inorganic oxide powder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a spherical inorganic oxide powder. [Background technology]

[0002] Thermally conductive inorganic oxide powders are used as heat-dissipating fillers in the encapsulation resins of electronic components, providing the encapsulation resin with the ability to dissipate heat generated during component operation. In recent years, advances in electronics technology and AI analysis technology have led to a rapid increase in the heat density of electronic circuits and components. Therefore, there is a demand for spherical inorganic oxide fillers that have high thermal conductivity and are easy to fill into resins. Spherical alumina powder, which is relatively inexpensive and chemically stable, has long been widely used as such a filler.

[0003] Spherical alumina powder is generally produced by the flame fusion method, in which raw alumina powder is sprayed into a flame. Raw alumina powder is generally produced industrially by the Bayer process, in which bauxite ore is dissolved with caustic soda and refined. Raw alumina powder produced by the Bayer process contains Na, which is derived from caustic soda, inside and on the surface of the particles. + The alumina powder obtained by spheroidizing such raw alumina powder contains a large amount of Na (sodium ions). + Na + When alumina powder with a large amount of Na on the surface is used in semiconductor products, etc. + Therefore, in semiconductor applications, Na is not recommended. + It is desirable to use reduced amounts of alumina powder.

[0004] Na present on the surface of alumina particles +As a method for reducing the amount of ionic impurities, a method for washing spherical alumina with ion-exchanged water produced using an ion-exchange resin, which has a lower dissolved ion concentration than ordinary tap water, is known (Patent Document 1).A method for washing spherical alumina produced by a flame fusion method, which is recovered in a cyclone and then supplied to a washing tank, has also been disclosed (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-281063 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-75062 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method of Patent Document 1 requires a large-scale device for generating ion-exchanged water required for washing a large amount of alumina powder during mass production, which increases facility construction costs and production costs, and requires a large site for arranging the large facility. Furthermore, the production time increases, which increases production costs. In the method of Patent Document 2, spherical alumina produced by the flame fusion method is introduced into a washing tank via a recovery mechanism, which takes a long time to process, requires larger facilities, increases costs, and increases thermal history, which affects the powder properties.

[0007] The present disclosure provides Na present on the particle surface. + The present invention provides a method for easily producing spherical inorganic oxide powder with a reduced amount of inorganic oxide in a short time using small-scale equipment. [Means for solving the problem]

[0008] The contents of the present disclosure relate to the following: [1] a high temperature process in which a high temperature region is formed inside the furnace by a burner that forms a flame; a spheroidizing step of generating spherical inorganic oxide powder by adding a raw inorganic oxide powder to the furnace and heating and melting the raw inorganic oxide powder; a cooling and washing step in which the spherical inorganic oxide powder is cooled and washed by putting the spherical inorganic oxide powder into cooling and washing water in a water tank; a recovery step of separating the spherical inorganic oxide powder from the cooling and washing water and recovering the spherical inorganic oxide powder; A method for producing a spherical inorganic oxide powder, comprising: [2] The method for producing a spherical inorganic oxide powder according to [1], wherein the spherical inorganic oxide powder is introduced into the cooling and washing water within 5 seconds after leaving the furnace. [3] The method for producing a spherical inorganic oxide powder according to [1] or [2], further comprising a pre-cooling step of spraying water onto the spherical inorganic oxide powder to pre-cool the spherical inorganic oxide powder. [4] The method for producing a spherical inorganic oxide powder according to any one of [1] to [3], further comprising a drying step of drying the spherical inorganic oxide powder after separation. [5] The method for producing a spherical inorganic oxide powder according to any one of [1] to [4], wherein the raw inorganic oxide powder is an alumina powder. [6] The method for producing a spherical inorganic oxide powder according to any one of [1] to [5], wherein the spherical inorganic oxide powder has a circularity of 0.90 or more. [7] The method for producing a spherical inorganic oxide powder according to any one of [1] to [6], wherein the furnace has a cylindrical shape. [Effects of the Invention]

[0009] According to the manufacturing method of the present disclosure, Na present on the particle surface + The present invention makes it possible to easily produce spherical inorganic oxide powders with reduced amounts of inorganic particles in a short time using small-scale equipment. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a diagram showing a process flow of a method for producing a spherical inorganic oxide powder according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a manufacturing device applicable to the process flow of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described. Note that the embodiments described below are representative examples of the present invention, and the present invention is not limited thereto.

[0012] In this specification, when multiple upper or lower limits are listed, numerical ranges can be created from all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining the upper and lower limits from those numerical ranges.

[0013] In this specification, D50 refers to the 50% particle size in the volume-based cumulative particle size distribution measured using an electrical resistance particle size distribution analyzer (Beckman Coulter, Multisizer 4) with a measurement aperture of 30 μm to 280 μm, selected according to the particle size of the raw inorganic material powder and the spherical inorganic material powder. The measurement aperture is selected as follows: a 30 μm aperture if the powder is composed of particles 16 μm or less, a 100 μm aperture if the powder is composed of particles 1 μm to 50 μm, a 200 μm aperture if the powder is composed of particles 2 μm to 102 μm, and a 280 μm aperture if the powder is composed of particles 4 μm or larger.

[0014] <Method for producing spherical inorganic oxide powder> In one embodiment, the method for producing spherical inorganic oxide powder includes a high-temperature step of forming a high-temperature region inside a furnace using a burner that forms a flame, a spheroidizing step of producing spherical inorganic oxide powder by charging a raw inorganic oxide powder into the furnace and heating and melting it, a cooling and washing step of charging the spherical inorganic oxide powder into cooled washing water in a water tank to cool and wash the spherical inorganic oxide powder, and a recovery step of separating the spherical inorganic oxide powder from the cooled washing water and recovering the spherical inorganic oxide powder. The method for producing spherical inorganic oxide powder includes a high-temperature step of forming a high-temperature region inside a furnace using a burner that forms a flame, a spheroidizing step of producing spherical inorganic oxide powder by charging the raw inorganic oxide powder into cooled washing water in a water tank to cool and wash the spherical inorganic oxide powder, and a recovery step of separating the spherical inorganic oxide powder from the cooled washing water and recovering the spherical inorganic oxide powder. Since the concentration of ionic impurities present on the particle surfaces can be reduced by simultaneously cooling and washing the spherical inorganic oxide powder, the method for producing spherical inorganic oxide powder can easily and quickly remove Na present on the particle surfaces using small-scale equipment at low cost without preparing a large site or using expensive, large-scale equipment such as an ion-exchange water generator. + It is possible to produce spherical inorganic oxide powders with reduced amounts of ammonium nitrate and other ionic impurities.

[0015] (Raw material inorganic oxide powder) The raw inorganic oxide powder is not limited, but may be at least one selected from silica powder, alumina powder, zirconia powder, magnesia powder, and titania powder, and is preferably alumina powder. Alumina is inexpensive, stable against acids and alkalis, has high thermal conductivity, and has insulating properties, and therefore has excellent cost performance as a thermally conductive filler. There are no particular restrictions on the alumina powder, but Na + It is preferable to use a small amount. + A specific example of alumina powder with a small amount of sodium is low-soda alumina powder produced by the Bayer process. + The concentration is preferably 500 ppm or less, more preferably 400 ppm or less. + The lower limit of the concentration is not limited, but may be, for example, 1 ppm, 10 ppm, or 100 ppm. + The concentration was measured using an IPC emission spectrophotometer. 20 g of raw inorganic oxide powder is weighed into a polytetrafluoroethylene container, immersed in 200 mL of ultrapure water, heated at 95°C for 5 hours, and then cooled. The supernatant liquid in the cooled container is collected as the extract.

[0016] The shape of the raw inorganic oxide powder is not limited, but a non-spherical shape is preferred for the purpose of obtaining a spherical inorganic oxide powder. The circularity of the raw inorganic oxide powder may be less than 0.90, 0.86 or less, or 0.84 or less.

[0017] The D50 of the raw inorganic oxide powder is preferably 0.1 μm or more and 100 μm or less from the viewpoint of obtaining spherical inorganic oxide powder of a size suitable for a thermally conductive filler, more preferably 0.5 μm or more and 50 μm or less, even more preferably 1.0 μm or more and 15 μm or less, and particularly preferably 1.0 μm or more and 6 μm or less from the same viewpoint. is.

[0018] (furnace) Examples of the furnace include a vertical furnace and a horizontal furnace. The shape of the furnace is not limited, and examples include a cylindrical shape and a polygonal prism shape such as a hexagonal prism. A cylindrical shape is preferred because it is easy to uniformly control the temperature inside the furnace. A cylindrical shape means that at least a portion of the furnace is cylindrical, and may include portions of other shapes. A polygonal prism shape means that at least a portion of the furnace is polygonal prism, and may include portions of other shapes. From the viewpoint of improving collection efficiency, the downstream portion of the furnace is preferably an inverted cone shape that narrows toward the discharge hole.

[0019] Although the material of the furnace is not limited, the inner wall is preferably made of stainless steel in order to reduce contamination of the spherical inorganic oxide powder with impurities. A water-cooled jacket may be provided around the periphery of the furnace to cool it.

[0020] (High temperature process) The high temperature process is a process in which a high temperature region is formed inside the furnace by a burner that forms a flame.

[0021] A burner is a device that mixes a suitable amount of a combustion-sustaining gas with a combustible gas to form a flame in a furnace. The burner is supplied with a combustible gas from a combustible gas supply source, and a combustion-sustaining gas from a combustion-sustaining gas supply source. Examples of combustible gases include liquefied natural gas (LNG) and LPG. Examples of combustion-sustaining gases include air, oxygen gas, and oxygen-enriched air.

[0022] The temperature of the high-temperature zone may be set appropriately depending on the melting point of the raw inorganic oxide powder used. The temperature of the high-temperature zone is, for example, 1800°C or higher, or 2100°C or higher. The temperature of the high-temperature zone is preferably 2500°C or lower, more preferably 2300°C or lower. A temperature of 2500°C or lower is within the heat resistance range of a typical burner, which is advantageous in terms of cost. When alumina powder is used as the raw inorganic oxide powder, the temperature of the high-temperature zone is preferably 2100°C or higher. A temperature of 2100°C or higher is above the melting point of alumina, which makes it easy to increase the circularity of the resulting alumina powder.

[0023] (Spheroidization process) The spheroidization step is a step in which a raw inorganic oxide powder is charged into a furnace and heated and melted to produce a spherical inorganic oxide powder. In the spheroidization step, a carrier gas for supplying the raw inorganic oxide powder may be used as needed. Examples of the carrier gas include at least one selected from air, nitrogen, oxygen, and carbon dioxide.

[0024] (Pre-cooling process) The method for producing a spherical inorganic oxide powder preferably includes a pre-cooling step in which the spherical inorganic oxide powder is pre-cooled. The pre-cooling step is carried out after the spheroidizing step and before the cooling and washing step. The equipment for pre-cooling is preferably provided 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 inorganic oxide powder to be cooled to a desired temperature in a short time before being poured into the cooling and washing water in the water tank in the cooling and washing step.

[0025] Pre-cooling is preferably carried out by spraying water onto the spherical inorganic oxide powder. Pre-cooling may also be carried out by spraying air, an inert gas, or other gas onto the spherical inorganic oxide powder. Equipment for spraying water includes a shower.

[0026] (Cooling and washing process) The cooling and washing step is a step in which the spherical inorganic oxide powder is poured into cooled washing water in a water tank to simultaneously cool and wash the spherical inorganic oxide powder. By simultaneously cooling and washing, the equipment can be made smaller and the overall process time can be shortened compared to when cooling and washing are performed as separate steps, for example, when the spherical inorganic oxide powder is air-cooled after the spheroidizing step and recovered in a collector such as a cyclone, and the recovered spherical inorganic oxide powder is then washed. The method for producing spherical inorganic oxide powder can produce spherical inorganic oxide powder with a low BET specific surface area because of its short thermal history.

[0027] The water tank stores cooling washing water for cooling and washing the spherical inorganic oxide powder. To improve the washing efficiency, it is preferable to stir the cooling washing water with a stirrer. The cooling washing water is not limited to, but may be, for example, city water.

[0028] 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 inorganic oxide powder. The temperature of the cooling and washing water is preferably 80° C. or lower, from the viewpoint of suppressing damage to the furnace body due to heat load.

[0029] In the cooling and washing step, it is preferable that the spherical inorganic oxide powder is added to the cooling and washing water within 5 seconds after leaving the furnace. Adding the powder within 5 seconds can keep the BET specific surface area of ​​the spherical inorganic oxide powder low. Adding the powder within 5 seconds can increase production efficiency.

[0030] In the cooling and washing step, the temperature of the spherical inorganic oxide powder added to the cooling and washing water is preferably 200° C. or less, and more preferably 100° C. or less. More preferably, the temperature of the spherical inorganic oxide powder from the time it leaves the furnace until it is added to the cooling and washing water is 200° C. or less, and particularly preferably 100° C. or less. If the temperature is 200° C. or less, there is little risk of the cooling and washing water in the water tank overheating and evaporating, which facilitates stable production.

[0031] The temperature of the spherical inorganic oxide powder can be determined using simulation software Ansys Fluent (Ansys, Inc.).

[0032] (Recovery process) The recovery step is a step of separating the spherical inorganic oxide powder from the cooled washing water and recovering the spherical inorganic oxide powder. The recovery method is not limited, but includes a method of settling the spherical inorganic oxide powder dispersed in the cooled washing water and removing the supernatant water with a pump or the like. This method removes Na adhering to the particle surface. + , Ca 2+ This is preferable because it is possible to wash away ionic impurities such as ammonium hydroxide and the like.

[0033] (drying process) The method for producing a spherical inorganic oxide powder preferably includes a drying step. The drying step is a step of drying the spherical inorganic oxide powder from which the cooling and washing water has been separated. In the drying step, moisture remaining after the recovery step is removed. The drying method is not limited, and may be natural drying or heat drying.

[0034] <Spherical inorganic oxide powder manufacturing equipment> Hereinafter, a preferred embodiment of a manufacturing apparatus used in a method for manufacturing a spherical inorganic oxide powder according to the present invention and its configuration will be described in detail with reference to the drawings. Note that the drawings used in the following description focus on the characteristic parts for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of the components may not necessarily be the same as those of an actual apparatus.

[0035] The spherical inorganic oxide powder manufacturing apparatus will be described with reference to Figure 2. As shown in Figure 2, the spherical inorganic oxide powder manufacturing apparatus is generally composed of a hopper 1 for storing and charging raw materials, a spheroidizing burner 2, a water-cooled jacket-type spheroidizing furnace 3 (also referred to as spheroidizing furnace 3) for spheroidizing, a stirring and cooling tank 4 for washing and cooling the spherical inorganic oxide powder, a separation tank 5 for separating the collected spherical inorganic oxide powder from a large amount of water and extracting the spherical inorganic oxide powder, and a drying device 6 for drying the spherical inorganic oxide powder with remaining water to obtain a dry spherical inorganic oxide powder.

[0036] The raw material hopper 1 is equipped with a feeder device and the like, which allows the raw material inorganic oxide powder to be quantitatively supplied to the spheroidizing burner 2. This spheroidizing burner 2 supplies the raw material inorganic oxide powder supplied from the raw material hopper 1 into the spheroidizing furnace 3. It is also possible to supply the inorganic oxide powder to the spheroidizing burner 2 using a carrier gas for transporting the powder.

[0037] The spheroidizing burner 2 is provided in the spheroidizing furnace 3. A combustible gas is supplied to the spheroidizing burner 2 from a combustible gas supply source (not shown), and a combustion-sustaining gas is supplied to the spheroidizing burner 2 from a combustion-sustaining gas supply source (not shown). The spheroidizing burner 2 can form a flame in the spheroidizing furnace 3.

[0038] The spheroidizing furnace 3 is a cylindrical vertical furnace, and the lower part of the furnace has an inverted cone shape that narrows toward the discharge hole. In the spheroidizing furnace 3, the raw inorganic oxide powder is fed into a high-temperature region formed by a flame and heated to melt, thereby producing spherical inorganic oxide powder.

[0039] A shower 10 is provided inside the spheroidizing furnace 3. The spherical inorganic oxide powder can be pre-cooled by spraying water onto the spherical inorganic oxide powder that has left the high-temperature region using the shower 10. In Fig. 2, the shower is provided inside the spheroidizing furnace 3, but the shower may be provided at any location on the path from when the spherical inorganic oxide powder leaves the high-temperature region until it comes into contact with the cooling wash water.

[0040] The spheroidizing furnace 3 is connected to the stirring and cooling tank 4 via a short pipe. The short pipe is equipped with a duct or the like, which is connected to a scrubber-type collector 8 and an exhaust device 9, allowing the combustion exhaust gas to be discharged outside the system. Since the combustion exhaust gas contains fine spherical inorganic oxide powder, it is desirable to pass the combustion exhaust gas through the scrubber-type collector 8 to separate and remove the fine powder from the gas, and then discharge the purified combustion exhaust gas via the exhaust device 9. In FIG. 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.

[0041] Cooling and washing water for cooling and washing the spherical inorganic oxide powder is stored in the stirring and cooling tank 4. The cooling and washing water in the stirring and cooling tank 4 is stirred by an agitator 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, and piping is provided so that the cooling and washing water in the tank can be recycled and reused.

[0042] A separation tank 5 is connected to the stirring and cooling tank 4 to separate the collected spherical inorganic oxide powder from the cooling and washing water, and a slurry containing the spherical inorganic oxide 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 is separated from the solid matter, and the water is returned to the system via the cooling water pump 7 and circulated. At this time, Na adhering to the particle surfaces is + The solid matter is fed to a drying device 6, where the remaining moisture adhering thereto is dried, thereby obtaining a spherical inorganic oxide powder with a small amount of ionic impurities.

[0043] This manufacturing apparatus does not require the installation of expensive, large-scale equipment such as an ion-exchange water apparatus, and allows the production of spherical inorganic oxide powder with a small amount of ionic impurities using a small-scale spheroidizing facility.

[0044] <Spherical inorganic oxide powder> (D50) The D50 of the spherical inorganic oxide powder is preferably 0.1 μm or more and 100 μm or less from the viewpoint of a size suitable for a heat dissipating filler, more preferably 0.5 μm or more and 50 μm or less, even more preferably 1.0 μm or more and 15 μm or less, and particularly preferably 1.0 μm or more and 6 μm or less from the same viewpoint.

[0045] (BET specific surface area) The BET specific surface area of ​​the spherical inorganic oxide powder is preferably 0.01 m 2 / g or more 10m 2 / g or less. 2 From the same viewpoint, the BET specific surface area is more preferably 0.05 m 2 / g or more, more preferably 0.4m 2 The BET specific surface area of ​​the spherical inorganic oxide powder is preferably 10 m / g or more in order to improve the mixing property with a resin composition or the like. 2 / g or less, more preferably 5m 2 / g or less, more preferably 2m 2 / g or less. In this specification, the BET specific surface area is a value measured in accordance with JIS R 1626:1996.

[0046] (Circularity) The circularity of the spherical inorganic oxide powder is preferably 0.90 or more. When the circularity is 0.90 or more, the spherical inorganic oxide powder has excellent packing properties, and as a result, excellent heat dissipation properties. From the same viewpoint, the circularity is more preferably 0.92 or more, and even more preferably 0.93 or more. By definition, the circularity is 1.00 or less, but from the viewpoint of productivity, it may be 0.99 or less. The circularity is measured by the method described in the examples.

[0047] (electrical conductivity) The electrical conductivity of the extract obtained by extracting components from a spherical inorganic oxide powder using the following procedure is preferably 50 μS / cm or less. A conductivity of 50 μS / cm or less is preferable because it can suppress the diffusion of ionic impurities that inhibit insulation into the resin. From the same perspective, the electrical conductivity of the extract is more preferably 25 μS / cm or less, and even more preferably 20 μS / cm or less. The lower limit of the electrical conductivity is not limited, but may be, for example, 1 μS / cm or 3 μS / cm. 20 g of spherical inorganic oxide powder is weighed into a polytetrafluoroethylene container, immersed in 200 mL of ultrapure water, heated at 95°C for 5 hours, and then cooled. The supernatant liquid in the cooled container is collected as the extract.

[0048] (Na + concentration) The Na content of the extract obtained by extracting components from spherical inorganic oxide powder using the above procedure was + The concentration is preferably 100 ppm or less. If the concentration is less than 100 ppm, Na, which inhibits the insulating properties, is contained. + From the same viewpoint, Na is preferable because it can suppress the diffusion of + The concentration is more preferably 30 ppm or less, and even more preferably 10 ppm or less. + The lower limit of the concentration is not limited, but may be, for example, 1 ppm or 3 ppm.

[0049] According to one embodiment of the method for producing a spherical inorganic oxide powder, ionic impurities present on the surface, particularly Na, can be easily removed using small-scale equipment without preparing a large site or using large-scale equipment to carry out cleaning work. + The spherical inorganic oxide powder produced by this method is filled into a heat dissipating and insulating resin composition, a prepreg, or the like, and is suitable for use in the production of semiconductor packages and printed wiring boards that require high thermal conductivity. [Example]

[0050] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0051] <Raw materials> Raw inorganic oxide powder: Alumina powder

[0052] <Manufacturing method> Examples 1 to 6 The raw alumina powder listed in Table 1 was placed in a high-temperature zone of 2200°C created in the furnace by a flame formed from LPG and oxygen, and subjected to spheroidization. The spherical alumina powder was placed in a water bath at 80°C for cooling and washing within the time period listed in Table 1 after leaving the furnace. The temperature of the spherical alumina powder immediately before being placed in the cooling and washing water is estimated to be approximately 100°C. The resulting slurry containing the spherical alumina powder was separated into a high-concentration slurry and a supernatant liquid in a recovery process. In a drying process, the high-concentration slurry was heat-treated in a dryer under air at an ambient temperature of 180°C to obtain spherical alumina powder. The resulting spherical alumina powder was evaluated as follows. The results are shown in Table 1. (Comparative Examples 1 and 2) The raw alumina powder listed in Table 1 was introduced into a 2200°C high-temperature zone created in the furnace by a flame formed by LPG and oxygen, and subjected to spheroidization. The spherical alumina powder was then transported to a cyclone together with the combustion exhaust gas. The cyclone then collected the spherical alumina powder from the mixed fluid of the spherical alumina powder and combustion exhaust gas transported from the furnace. The collected spherical alumina powder was then transported to a washing tank via a rotary valve at the bottom of the cyclone. The spherical alumina powder was then introduced into 80°C washing water in a water tank and washed. The temperature of the spherical alumina powder immediately before being introduced into the washing water is estimated to be below 50°C. The resulting slurry containing the spherical alumina powder was separated into a high-concentration slurry and a supernatant liquid in a recovery process. In a drying process, the high-concentration slurry was heat-treated in a dryer under air at an ambient temperature of 180°C to obtain spherical alumina powder. The resulting spherical alumina powder was evaluated as follows. The results are shown in Table 1.

[0053] <Evaluation method>

[0054] (BET specific surface area) Measurements were performed using a fully automatic BET specific surface area measuring device (MacsorbHM model-1208, Mountec Co., Ltd.) in accordance with JIS R 1626:1996. The spherical inorganic oxide powder was pretreated by heating to 180°C and passing nitrogen gas through it for 20 minutes. The BET specific surface area was measured using nitrogen gas as the adsorbate by the BET three-point method. The applicable range of the BET method was P / P = 0.00 to 0.95.

[0055] (Circularity) The circularity is the average value of values ​​calculated from the following formula (1) for 2,000 or more particles, where S is the area of ​​the projection of the particle obtained by an image particle size distribution analyzer and L is the perimeter. 4πS / L 2 (1) Measurements of area S and perimeter L were performed using an FPIA-3000 (Malvern Panalytical). As a pretreatment step, due to the instrument's measurement range, approximately 10 g of sample was placed on a 200 mm diameter, 25 μm mesh sieve and showered with water to remove particles larger than 25 μm. The sample that passed through the sieve was transferred to a plastic container and used as the measurement sample. Measurement conditions were LPF / HPF standard (20x lens) and bright field, and ParticleSheath (Malvern Panalytical) was used as the measurement solvent. 2 g of sample was weighed into a 50 mL beaker, 50 mL of pure water was added, and the sample was dispersed in a 200 W ultrasonic disperser for 3 minutes, after which the sample was placed in the instrument and measured. For post-measurement data processing, multiple particles on a single screen were removed, and the circularity was calculated.

[0056] (electrical conductivity) 20 g of raw alumina powder or spherical alumina powder was weighed into a polytetrafluoroethylene container, immersed in 200 mL of ultrapure water, heated at 95°C for 5 hours, and then cooled. The supernatant liquid in the cooled container was collected as a component extract, and the electrical conductivity of the supernatant liquid was measured using a commercially available conductivity meter.

[0057] (Na + concentration) 20 g of raw alumina powder or spherical alumina powder was weighed into a polytetrafluoroethylene container, immersed in 200 mL of ultrapure water, heated at 95°C for 5 hours, and then cooled. The supernatant liquid in the cooled container was collected as a component extract and analyzed for Na using an ICP emission spectrometer. + The concentration of was measured.

[0058] [Table 1]

[0059] The spherical alumina powders obtained in Examples 1 to 6 were added to the cooling and washing water within 5 seconds of leaving the furnace. This significantly shortens the processing time and improves production efficiency compared to conventional methods of collecting the alumina powder using a cyclone, hopper, or the like and then washing it. Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, each have a similar D50, but Example 1 and Example 2 exhibit smaller BET specific surface areas. This is thought to be because Example 1 is rapidly cooled and washed, making it difficult for the surface to become highly crystalline. This is preferable from the perspective of improving kneadability into resin. [Explanation of symbols]

[0060] 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. Shower

Claims

1. A method for producing a spherical inorganic oxide powder using a production apparatus in which a spheroidizing furnace is connected to a stirring and cooling tank via a short pipe, wherein there is no gap between the spheroidizing furnace, the short pipe, and the stirring and cooling tank; a high-temperature step of forming a high-temperature region of 1800°C or higher inside the spheroidizing furnace by a burner that forms a flame; a spheroidizing step of producing spherical inorganic oxide powder by heating and melting a raw inorganic oxide powder in the spheroidizing furnace; a cooling and washing step in which the spherical inorganic oxide powder is cooled and washed by pouring the spherical inorganic oxide powder into the cooling and washing water in the stirring and cooling tank; a recovery step of separating the spherical inorganic oxide powder from the cooling and washing water and recovering the spherical inorganic oxide powder; Including, The spherical inorganic oxide powder is introduced into the cooling and washing water within 5 seconds after leaving the spheroidizing furnace; The method for producing a spherical inorganic oxide powder, wherein the raw inorganic oxide powder is an alumina powder.

2. The method for producing a spherical inorganic oxide powder according to claim 1, further comprising a pre-cooling step of spraying water onto the spherical inorganic oxide powder to pre-cool the spherical inorganic oxide powder.

3. 3. The method for producing a spherical inorganic oxide powder according to claim 1, further comprising a drying step of drying the spherical inorganic oxide powder after separation.

4. The method for producing a spherical inorganic oxide powder according to claim 1 or 2, wherein the spherical inorganic oxide powder has a circularity of 0.90 or more.

5. The method for producing a spherical inorganic oxide powder according to claim 1 or 2, wherein the spheroidizing furnace has a cylindrical shape.

6. a high-temperature region in the spheroidizing furnace, in which a high-temperature region of 1800°C or higher is formed by a burner that forms a flame; a spheroidizing section in which alumina powder is introduced as a raw inorganic oxide powder into the spheroidizing furnace and heated to melt it, thereby producing spherical inorganic oxide powder; a cooling and washing section in which the spherical inorganic oxide powder is poured into cooling and washing water in a stirring and cooling tank to cool and wash the spherical inorganic oxide powder; a recovery section for separating the spherical inorganic oxide powder from the cooling wash water and recovering the spherical inorganic oxide powder; Including, the spheroidizing furnace is connected to a 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; The spherical inorganic oxide powder manufacturing apparatus is configured so that the spherical inorganic oxide powder is introduced into the cooling washing water within 5 seconds after leaving the spheroidizing furnace.

7. 7. The apparatus for producing a spherical inorganic oxide powder according to claim 6, further comprising a pre-cooling section for pre-cooling the spherical inorganic oxide powder by spraying water onto the spherical inorganic oxide powder.

8. 8. The apparatus for producing a spherical inorganic oxide powder according to claim 6 or 7, further comprising a drying section for drying the spherical inorganic oxide powder after separation.

9. 8. The apparatus for producing spherical inorganic oxide powder according to claim 6, wherein the spheroidizing furnace has a cylindrical shape.

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