JP2012020900A - Spherical alumina powder, and method of production and application thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spherical alumina powder which, when used for a resin composition, does not degenerate its viscosity characteristics and strengthens adhesiveness to a resin; its production method; and a resin composition obtained by using the spherical alumina powder.SOLUTION: The spherical alumina powder has 3 vol.% or less of content of particles having particle sizes of 0.5 μm or less by a laser diffractive scattering method, an average particle size of 1.0-3.5 μm, a specific surface area of 2.0-6.0 m/g, and an average sphericity of 0.90 or higher. The production method for the spherical alumina powder includes spraying an alcohol slurry of an ultrafine alumina powder having a specific surface area of 10-20 m/g into a flame at 1,300-1,650°C. Preferably, a supporting gas is air, air containing an inactive gas, or oxygen containing an inactive gas.

Description

The present invention relates to spherical alumina powder, a method for producing the same, and use.

  In recent years, with the increase in performance and functionality of electronic devices, heat dissipation of electronic components has become a problem. In order to improve the heat dissipation characteristics of the electronic member, a resin or rubber may be highly filled with a heat conductive filler such as alumina.

  When a general Bayer method alumina powder is highly filled in a silicone resin, the heat conduction characteristics of alumina cannot be fully utilized due to a remarkable thickening phenomenon. In order to solve this, Patent Document 1 proposes that a spherical alumina powder is obtained by spraying aluminum hydroxide powder or a slurry of aluminum hydroxide powder into a flame from a feed tube having a strong dispersion function.

  When spherical alumina powder is highly filled in resin or rubber, the mechanical strength is remarkably lowered, and therefore there is a need for improvement in applications where reliability is required. Patent Document 2 proposes a method for improving the strength of an epoxy resin composition by surface-treating spherical alumina with an acrylic silane coupling agent. The influence of the interaction between the silane coupling agent and the resin is large, and the spherical alumina treated with the acrylic silane coupling agent cannot improve the strength universally for resins other than the epoxy resin. There is a need for spherical alumina powders that can be used universally in various resin systems.

  Patent Document 3 proposes a method of obtaining spherical alumina having a smooth surface by spraying and burning a combustible liquid containing an aluminum-containing compound. Since the spherical alumina in this invention has a smooth surface, when the resin is filled, the bonding area between the spherical alumina and the resin cannot be increased, and there is room for improvement in strength characteristics.

Japanese Patent Laid-Open No. 2001-19425 JP 2005-68258 A Japanese Patent Laid-Open No. 11-147711

  The present invention relates to a spherical alumina powder capable of further improving the adhesion to a resin without deteriorating the viscosity characteristics of the resin composition when used in a resin composition, a method for producing the same, and a resin composition using the same It provides things.

The present invention solves the above problems by the following means.
(1) The content of particles of 0.5 μm or less in particle size distribution measurement by laser diffraction scattering method is 3% by volume or less, the average particle size is 1.0 to 3.5 μm, and the specific surface area is 2.0 to 6.0 m. A spherical alumina powder characterized by ² / g and an average sphericity of 0.90 or more.
(2) A spherical inorganic powder comprising the spherical alumina powder described in (1) above.
(3) A spherical inorganic powder comprising 3 to 15% by mass of the spherical alumina powder according to (1).
(4) A resin composition comprising the spherical alumina powder according to (1).
(5) A resin composition comprising the spherical inorganic powder according to (2) or (3).
(6) A heat radiating member using the resin composition according to (4) or (5).
(7) A heat dissipation sheet using the resin composition according to (4) or (5).
(8) The production of spherical alumina powder according to (1) above, wherein an alcohol slurry of ultrafine alumina powder having a specific surface area of 10 to 20 m ² / g is sprayed into a flame having a flame temperature of 1300 to 1650 ° C. Method.
(9) The method for producing a spherical alumina powder as described in (8) above, wherein the auxiliary combustion gas is air, air containing an inert gas, or oxygen containing an inert gas.

  By using the spherical alumina powder of the present invention, it is possible to remarkably improve the adhesion with the resin and increase the strength of the resin composition without deteriorating the viscosity characteristics of the resin composition when used in the resin composition. it can.

Manufacturing process schematic Spherical alumina powder SEM photo

Hereinafter, the present invention will be described in detail.
The present invention is a spherical alumina powder that is not easily unraveled in the kneading / molding process of the composition. The spherical alumina powder of the present invention does not deteriorate the viscosity characteristics of the resin composition when used in the resin composition. Since the spherical alumina powder of the present invention has a large surface area, the contact area with the resin is increased, and the strength of the resin composition can be increased.

Production of Spherical Alumina Powder Spherical alumina powder was produced using the equipment shown in FIG. Briefly, an alcohol slurry of ultrafine alumina powder is sprayed into the flame from the top of the furnace in a mist, and the resulting spherical alumina powder is conveyed to a bag filter with a blower and collected. Atmax nozzle type BN500 manufactured by Atmax Co., Ltd. was used for dispersing the raw material slurry. The flame was formed by using LPG as the fuel gas, air as the auxiliary combustion gas, air added with nitrogen gas, or oxygen added with nitrogen gas, and injected from a combustion burner set in the furnace body. Air compressed by a compressor was used as a dispersion gas for the raw slurry. The fuel gas flow rate ^{5 Nm} 3 / Hr, assisting gas flow rate 25 Nm ³ / Hr, dispersed gas was carried out at 100 Nm ³ / Hr.

Control of the particle content of 0.5 μm or less of the spherical alumina powder The particle content of 0.5 μm or less of the spherical alumina powder can be controlled by adjusting the specific surface area of the ultrafine alumina powder as a raw material. Considering the strength characteristics of the resin composition, the particle content of 0.5 μm or less of the spherical alumina powder is 3% by volume or less in the laser diffraction scattering method particle size distribution measurement.
If the number of particles of 0.5 μm or less increases, the strength characteristics are hardly expressed. The specific surface area of the ultrafine alumina powder is preferably 20 m ² / g or less.

Control of the average particle diameter of the spherical alumina powder The particle diameter of the spherical alumina powder can be controlled by adjusting the specific surface area of the raw ultrafine alumina powder and the alcohol slurry concentration of the ultrafine alumina powder. When used in a resin composition, the average particle size of the spherical alumina powder is preferably small in that the viscosity property of the resin composition is not deteriorated. However, if the average particle size is too small, strength characteristics are exhibited. It becomes difficult to do. Considering the compatibility between the viscosity and strength characteristics, the spherical alumina powder preferably has an average particle size of 1.0 to 3.5 μm.
The higher the specific surface area of the ultrafine alumina powder, the larger the average particle size of the spherical alumina powder produced. As for the alcohol slurry concentration of the ultrafine alumina powder, the higher the ultrafine alumina powder concentration, the larger the average particle size of the spherical alumina powder produced. The alcohol slurry concentration is preferably 10 to 30% by mass.

Control of specific surface area of spherical alumina powder The specific surface area of spherical alumina powder should be controlled by adjusting the flame temperature according to the specific surface area of the raw ultrafine alumina powder, the alcohol slurry concentration of the ultrafine alumina powder and the oxygen concentration of the auxiliary combustion gas. Can do. Considering the balance of strength characteristics of the resin composition, the specific surface area of the spherical alumina powder is 2.0 to 6.0 m ² / g.
Increasing the specific surface area of the ultrafine alumina powder as a raw material increases the specific surface area of the spherical alumina powder produced. If the specific surface area of ultrafine alumina becomes too high, the viscosity characteristics of the resin composition will deteriorate when used in the resin composition. The specific surface area of the ultrafine spherical alumina powder is 10 to 20 m ² / g. When the alcohol slurry concentration is diluted, the specific surface area of the spherical alumina powder produced increases. The alcohol slurry concentration is preferably 10 to 30% by mass. Further, when the oxygen concentration of the auxiliary combustion gas is reduced, the flame temperature is lowered and the specific surface area of the spherical alumina powder can be increased. As for the flame temperature, 1300 to 1650 ° C. is an appropriate range.

Control of average sphericity of spherical alumina powder The average sphericity of spherical alumina powder can be controlled by adjusting the feed amount of the alcohol slurry of ultrafine alumina powder. When the feed amount is increased, the probability that the spherical alumina powders come into contact with each other in the furnace increases, and the average sphericity decreases. When the average sphericity of the spherical alumina powder is lowered, the viscosity characteristics are deteriorated. Considering the viscosity characteristics of the resin composition, the average sphericity of the spherical alumina powder is 0.90 or more.
The feed amount of the alcohol slurry of the ultra fine alumina powder is preferably 45 L / Hr or less.

As the alcohol, lower alcohols having a small number of carbon atoms such as methanol, ethanol, propanol, butanol, isopropyl alcohol and the like are preferable, and methanol and ethanol are particularly preferable among them.

Specific surface area measurement The specific surface area measurement was performed using the AUTOMATIC SURFACE ANALYZER MODEL-4232II by Microdata.

Laser diffraction scattering method particle size distribution measurement For confirmation of the particle content of 0.5 μm or less of the alumina powder and measurement of the average particle diameter, a laser diffraction scattering method particle size distribution measuring device LS-230 manufactured by Beckman Coulter, Inc. was used. The particle size distribution was measured using ion-exchanged water as a solvent at a pump speed of 60 rpm. In order to analyze the particle size distribution, a refractive index parameter is required. Since the sample to be measured this time is a solvent to be dispersed with alumina, water (1.333) and alumina (1.768) were used for the refractive index. The analysis of the particle size distribution was performed by volume-cumulative. The sample for particle size distribution measurement is introduced as an aqueous slurry. For aqueous slurry, after adding 0.5 ml of ethanol and 5 ml of ion-exchanged water to 0.04 g of spherical alumina powder, an ultrasonic generator UD-200 manufactured by Tommy Seiko Co., Ltd. (with ultra-trace chip TP-030 attached) For 30 seconds.

Flame temperature measurement The flame temperature at the time of melting was measured using an IS5 / F radiation thermometer manufactured by Impac with a burner installed outside the furnace. The temperature was measured while feeding a methanol slurry of ultrafine alumina.

Average sphericity measurement The average sphericity measurement was performed using a flow type particle image analyzer FPIA-3000 manufactured by Sysmex. The flow-type particle image analyzer can analyze the circumference of a single particle projection image and the circumference of a circle corresponding to the area of the particle projection image, and the formula (circularity) = (perimeter of the particle projection image) / (Circumference of the circle corresponding to the area of the particle projection image), the degree of circularity can be calculated. The average sphericity is the square of the average circularity. In this measurement of the average sphericity, data on the circularity of 36,000 particles were collected. The circularity data obtained by the measurement was reanalyzed for a region having a particle diameter of 0.992 to 9.961 μm, and the average circularity was recalculated. The average sphericity in the present invention is obtained by squaring the average circularity obtained by reanalysis. This measurement was performed with a high-magnification imaging unit, and LUCPLFLN 20 × (magnification 20 times) was used for the objective lens, and AND-40C-70 (transmittance 70%) was used for the ND filter. The pretreatment for measuring the average circularity is carried out by weighing 0.05 g of a sample into a 20 ml glass beaker container, adding 10 ml of a 25% by mass aqueous solution of propylene glycol, and then dispersing for 3 minutes with an ultrasonic disperser. All of the pretreated solution is put into FPIA-3000 and measured by the HPF mode / quantitative count (total count of 36000, number of repeated measurements once).

Since the spherical alumina powder of the present invention has a large surface area, the contact area with the resin is widened, and the adhesion can be further improved. Examples of the resin of the heat radiating member containing the spherical alumina powder or the spherical inorganic powder of the present invention include epoxy resins, phenol resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyimides, polyamideimides, and polyetherimides. Polyester such as polyamide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber / styrene) resin, AES (Acrylonitrile / ethylene / propylene / diene rubber-styrene) resin, EVA (ethylene vinyl acetate copolymer) resin, or the like can be used. In addition, as the resin of the heat dissipation sheet containing the spherical alumina powder or the spherical inorganic powder of the present invention, urethane rubber, acrylic rubber, ethylene propylene rubber, urethane rubber, or the like can be used.

  A silane coupling agent or a surface treatment agent may be used for the purpose of improving the adhesion between the spherical alumina powder or the spherical inorganic powder and the resin. Examples of coupling agents that can be used in the present invention include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3 -Glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyl Diethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) -Aminopropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- (1,3 -Dimethyl-ditylidene) propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N- (vinylbenzyl) -2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltriethoxysilane 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis (triethoxysilylpropyl) tetrasulfide, 3-isocyanatopropyltriethoxysilane, etc. Can. A surface treatment agent can also be used in place of the coupling agent. Examples of surface treatment agents include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, hexamethyldisilazane, hexyltrimethoxysilane, and decyltrimethoxysilane. Can be used.

The heat radiating member of the present invention is obtained by containing the spherical alumina powder or the spherical inorganic powder of the present invention in a resin. The content of the spherical alumina powder or the spherical inorganic powder in the resin varies depending on the use, but is preferably 60 to 90% by mass in consideration of the heat conduction characteristics.

Production of spherical alumina powder Production of spherical alumina powder was carried out using the production apparatus shown in FIG. Ultrafine powder alumina powder shown in Table 1 was used as the spherical alumina raw material, and methanol (purity 98%) manufactured by Mitsui Chemicals was used as the alcohol. Table 2 shows the production conditions of the spherical alumina powder and the characteristics of the obtained spherical alumina powder. Gas conditions during spherical alumina production was performed in the fuel gas flow rate ^{5 Nm} 3 / Hr, supporting gas flow rate 25 Nm ³ / Hr, the dispersion gas flow rate 100 Nm ³ / Hr. The fuel gas was LPG, the auxiliary combustion gas was based on air, and the oxygen concentration was adjusted by mixing air and nitrogen or oxygen in a gas mixer. The oxygen concentration was directly measured from the auxiliary gas flowing in the gas pipe using a small gas detector MiniMax4 manufactured by MK Scientific.

Preparation of spherical inorganic powder The spherical alumina powder produced in Table 2 and another inorganic powder were blended in the proportions shown in Table 3 or Table 5 to prepare spherical inorganic powder. Other inorganic powders include spherical alumina powder DAW-45 (average particle size 45 μm), DAW-05 (average particle size 5 μm) manufactured by Denki Kagaku Kogyo, and boron nitride powder SP-7 (average particle size 1) manufactured by Denki Kagaku Kogyo Co., Ltd. 0.5 μm) and spherical silica SFP-20M (average particle size 0.3 μm) manufactured by Denki Kagaku Kogyo Co., Ltd. were used.

Surface treatment with a coupling agent Surface treatment with a coupling agent was performed on the spherical inorganic powder for evaluating the heat dissipating member. Surface treatment with a coupling agent was performed by enclosing 1 kg of spherical inorganic powder, 500 g of alumina balls (20 mm), and a coupling agent in a ball mill (AXB-15 manufactured by Seiwa Giken Co., Ltd.). The ball mill treatment was performed at a rotation speed of 250 rpm and a time of 30 minutes. As a coupling agent, coupling agent KBM-5103 (3-acryloxypropyltrimethoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd. was used. The coupling agent was added in an amount calculated by the following formula.
Addition amount of coupling agent [g] = (mass of spherical alumina powder [g]) × (specific surface area of spherical alumina powder [m ² / g]) / minimum coating area of coupling agent (m ² / g).
KBM-5103 (333 m ² / g) was used as the minimum coating area of the coupling agent.

Heat Dissipation Member Evaluation In Examples 1, 2, 4 to 14, and Comparative Examples 1 to 8, 40% by mass of the resin prepared in the ratio of Table 4 and 60% by mass of the spherical inorganic powder of Table 3 were mixed and meshed in the same direction. Heat kneading was carried out with a shaft extrusion kneader (screw diameter D = 25 mm, kneading disk length 10 Dmm, paddle rotation speed 150 rpm, discharge rate 4.5 kg / h, heater temperature 105 to 110 ° C.). In Example 3, 30% by mass of the resin prepared in the ratio shown in Table 4 and 70% by mass of the spherical inorganic powder shown in Table 3 were mixed and mixed by heating in the same manner. The discharged product was cooled with a cooling press and then pulverized to prepare a resin composition. The bending strength, fluidity, and thermal conductivity were evaluated as follows. The results are shown in Table 3. The influence which the kind of spherical alumina powder has can be confirmed by comparing Examples 1, 2, 8-14, and Comparative Examples 1-7. The influence of the blending ratio of the spherical alumina powder can be confirmed by comparing Examples 2, 4, 5, and 7. The effects of blending BN powder can be confirmed by comparing Examples 2 and 6.

Bending strength The bending strength was measured according to JIS K 6911 under the room temperature of 20 ° C. using an autograph AG-2000D manufactured by Shimadzu Corporation. A test piece to be measured was molded under the conditions of 175 ° C., 7.4 MPa, and press time 90 seconds, and a test piece having a size of 10 × 4 × 100 mm was prepared.

Fluidity Using a spiral flow mold, heat kneading in a twin-screw extrusion kneader using a transfer molding machine equipped with a spiral flow measurement mold conforming to EMMI-66 (Epoxy Molding Material Institute; Society of Plastic Industry). Then, the spiral flow value of the prepared semiconductor sealing material was measured. The transfer molding conditions were a mold temperature of 175 ° C., a molding pressure of 7.4 MPa, and a press time of 90 seconds.

Thermal conductivity Spherical alumina powder-containing epoxy resin composition is molded into 25 × 25 mm and thickness 3 mm, sandwiched between a 15 × 15 mm copper heater case and a copper plate, set at a tightening torque of 5 kgf / cm, and then made of copper The heater case is applied with power of 15 W and held for 4 minutes, the temperature difference between the copper heater case and the copper plate is measured, and the thermal resistance is measured.
Thermal resistance (℃ / W) = temperature difference between copper heater case and copper plate (℃) / heater power (W)
The thermal conductivity can be calculated from the thermal resistance (° C./W), the heat transfer area [area of the copper heater case] (m ² ), and the molded body thickness (m) when the tightening torque is 5 kgf / cm.
Thermal conductivity (W / m · K) = formed body thickness (m) / {thermal resistance (° C./W)×heat transfer area (m ² )}

Evaluation of Heat Dissipation Sheet Characteristics In Examples 15, 16, 18 to 28, and Comparative Examples 9 to 16, the spherical inorganic powder prepared by Momentive performance Material, 15% by mass of liquid silicone rubber (YE5822 series) and 85% by mass of the spherical inorganic powder prepared in Table 5 % Was mixed to prepare a rubber composition. In Example 17, a rubber composition was prepared by mixing 10% by mass of liquid silicone rubber (YE5822 series) manufactured by Momentive performance Material and 90% by mass of spherical inorganic powder prepared in the ratio shown in Table 5.
Regarding the heat dissipation sheet evaluation, the viscosity, tensile strength, and thermal conductivity were evaluated according to the following. The results are shown in Table 5. The influence which the kind of spherical alumina powder has can be confirmed by comparing Examples 15, 16, 22-28 and Comparative Examples 9-15. The influence of the blending ratio of the spherical alumina powder can be confirmed by comparing Examples 16, 18, 19, and 21. The effect of blending BN powder can be confirmed by comparing Examples 16 and 20.

Viscosity Viscosity measurement was carried out by adding spherical inorganic powder prepared in a ratio shown in Table 5 to liquid silicone rubber YE5822A manufactured by Momentive performance Material and mixed using a stirrer NZ-1100 manufactured by Tokyo Rika Kikai Co., Ltd. The mixed composition was vacuum degassed, and the viscosity was measured with a B-type viscometer TVB-10 manufactured by Toki Sangyo Co., Ltd. The viscosity was measured using a No. 7 spindle at a rotation speed of 20 rpm and a room temperature of 20 ° C.
In addition, 10% by mass of liquid silicone rubber YE5822B manufactured by Momentive performance Material, YE5822A was added to the composition of the liquid silicone rubber YE5822A and spherical inorganic powder prepared above, and after the molding, the silicone rubber was heated at 120 ° C. Hardens to become a heat dissipation member.

Tensile strength [Production of spherical inorganic powder-containing silicone rubber composition]
YE5822 (A) and YE5822 (B) manufactured by MOMENTIVE performance materials were used as the liquid silicone rubber, and the ratio of YE5822 (A) to YE5822 (B) was 10: 1 [mass ratio]. The spherical inorganic powder shown in Table 5, YE5822 (A), and YE5822 (B) were mixed for 60 seconds with a planetary agitation / defoaming device (MAZERUSTAR KK-400W), and then molded into a sheet. By heating at 120 ° C., the silicone rubber was cured to produce a spherical inorganic powder-containing silicone rubber composition. The thickness of the spherical inorganic powder-containing silicone rubber composition was 3.0 mm.
[Preparation of tensile strength measurement specimen]
A spherical inorganic powder-containing silicone rubber composition formed into a sheet shape having a thickness of 3.0 mm was punched into a dumbbell shape with a test piece punching blade JIS No. 1 manufactured by Kobunshi Keiki Co., Ltd. to prepare a test piece for measuring tensile strength. .
[Tensile strength measurement]
Tensile strength measurement was performed according to JIS K6251 using Shimadzu Autograph AG-2000D.

Measurement of thermal conductivity After forming a silicone rubber composition containing spherical alumina powder to a size of 25 × 25 mm and a thickness of 3 mm, sandwiching this between a 15 × 15 mm copper heater case and a copper plate, and setting with a tightening torque of 5 kgf / cm Then, 15 W of electric power is applied to the copper heater case and held for 4 minutes, the temperature difference between the copper heater case and the copper plate is measured, and the thermal resistance is measured.
Thermal resistance (℃ / W) = temperature difference between copper heater case and copper plate (℃) / heater power (W)
The thermal conductivity can be calculated from the thermal resistance (° C./W), the heat transfer area [area of the copper heater case] (m ² ), and the molded body thickness (m) when the tightening torque is 5 kgf / cm.
Thermal conductivity (W / m · K) = formed body thickness (m) / {thermal resistance (° C./W)×heat transfer area (m ² )}

  As is apparent from Table 3, the spherical alumina powder of the present invention can significantly improve the adhesion with the resin without deteriorating the viscosity characteristics of the resin composition when used in the resin composition. . The resin composition using the alumina powder of the present invention is suitable for use as a heat dissipation member.

  As is apparent from Table 5, the spherical alumina powder of the present invention can remarkably improve the adhesion with the resin without deteriorating the viscosity characteristics of the resin composition when used in the resin composition. . The resin composition using the alumina powder of the present invention is suitable for use as a heat dissipation sheet.

FIG. 2 shows the spherical alumina particles of the present invention. The spherical alumina particles of the present invention are those in which ultrafine alumina particles are aggregated and pseudo-spheroidized. The spherical alumina particles of the present invention are not easily unraveled in the kneading / molding step of the composition, and do not deteriorate the viscosity characteristics of the compound.

  The spherical alumina powder of the present invention is used as a filler for a resin composition. The resin composition of the present invention can be used for molding compounds such as automobiles, portable electronic devices, industrial devices, and household appliances, heat dissipation sheets, and the like.

(Figure 1)
DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Burner 3 Fuel gas supply pipe 4 Auxiliary combustion gas supply pipe 5 Raw material slurry supply part (Atmax nozzle BN500 type)
6 Bug filter 7 Blower

(Figure 2)
1 spherical alumina particles of the present invention

Claims (9)

The content of particles of 0.5 μm or less in the particle size distribution measurement by laser diffraction scattering method is 3% by volume or less, the average particle size is 1.0 to 3.5 μm, and the specific surface area is 2.0 to 6.0 m ² / g. A spherical alumina powder having an average sphericity of 0.90 or more. A spherical inorganic powder comprising the spherical alumina powder according to claim 1. A spherical inorganic powder comprising 3 to 15% by mass of the spherical alumina powder according to claim 1. A resin composition comprising the spherical alumina powder according to claim 1. A resin composition comprising the spherical inorganic powder according to claim 2. The heat radiating member using the resin composition of Claim 4 or 5. A heat dissipation sheet using the resin composition according to claim 4. The method for producing spherical alumina powder according to claim 1, wherein an alcohol slurry of ultrafine alumina powder having a specific surface area of 10 to 20 m ² / g is sprayed into a flame having a flame temperature of 1300 to 1650 ° C. The method for producing a spherical alumina powder according to claim 8, wherein the auxiliary combustion gas is air, air containing an inert gas, or oxygen containing an inert gas.