Spherical alumina powder

Abstract

This spherical alumina powder has a hydrogen-bonding OH group density of 12.0 groups / nm2 or less as determined by a specific procedure.

Description

Technical Field

[0001] The present invention relates to spherical alumina powder.

Background Art

[0002] Various developments have been made on spherical alumina powder so far. As this type of technology, for example, the technology described in Patent Document 1 is known. Patent Document 1 describes spherical alumina powder having an average particle diameter (D50) of 50 μm or less and a sphericity of 0.9 or more (Claim 1 of Patent Document 1, etc.).

Prior Art Documents

Patent Documents

[0003] <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ Using the spherical alumina powder, the amount of moisture V1 (ppm) derived from hydrogen-bonded OH groups generated from above 200 °C to 550 °C and the amount of moisture V2 (ppm) derived from isolated OH groups generated from above 550 °C to 900 °C are measured by the Karl Fischer method. The specific surface area S (m 2 / g) of the spherical alumina powder is measured by the BET one-point method using nitrogen gas adsorption. Using the obtained V1 and S, the above hydrogen-bonded OH group density (number / nm 2 ) is calculated from Equation 1: 0.0668 × V1 / S. 2. The spherical alumina powder according to 1., where the density of isolated OH groups calculated from Equation 2: 0.0668 × V2 / S using V2 and S obtained based on the above procedure is 7.0 number / nm 2 or less, spherical alumina powder. 3. The spherical alumina powder according to 1. or 2., where the specific surface area (S) of the spherical alumina powder measured by the BET one-point method using nitrogen gas adsorption is 0.5 m 2 / g or more and 2.5 m 2 / g or less, spherical alumina powder. 4. The spherical alumina powder according to any one of 1. to 3., where the loose bulk density measured by the following procedure is 1.10 g / cm 3 or more and 1.50 g / cm 3 or less, spherical alumina powder. (Procedure) The spherical alumina powder is allowed to fall naturally from a height of 25 cm at an input rate of 5 to 10 g per minute and is put into the measuring cup of 100 cm 3 , and a heap cup is prepared until it overflows from the cup. Subsequently, for the heap cup, without tapping, after scraping off the overflow on the upper surface of the cup, the mass (g) of the spherical alumina powder filled in the cup is measured, and the loose bulk density (g / cm 3 ) is calculated. On the other hand, for the overflowing cup, after tapping it 180 times in the vertical direction (stroke length 2 cm, 1 second / tap), and leveling off the excess on the top of the cup, the mass (g) of the spherical alumina powder filled in the cup was measured, and the bulk density (g / cm³) was determined. 3 Calculate ). 5. The spherical alumina powder described in 1. to 4., When the loose bulk density measured in the above procedure is A and the firm bulk density is P, Spherical alumina powder having a compression degree of 35% or more and 55% or less, calculated based on ((PA) / P) × 100. 6. A spherical alumina powder as described in any one of items 1 to 5, In the volume frequency particle size distribution measured by the wet laser diffraction scattering method, the particle size at which the cumulative value reaches 25% is defined as D. 25 The particle size at which the cumulative value reaches 97% is D 97 In that case, D 97 / D 25 However, it is spherical alumina powder with a pH between 8.0 and 30.0. 7. A spherical alumina powder as described in any one of 1. to 6., In the volume frequency particle size distribution measured by the wet laser diffraction scattering method, the particle size at which the cumulative value reaches 50% is defined as D. 50 The particle size at which the cumulative value reaches 97% is D 97 In that case, D 97 / D 50 However, it is spherical alumina powder with a coefficient between 5.0 and 20.0. [Effects of the Invention]

[0007] According to the present invention, a spherical alumina powder with excellent thermal conductivity when used in resin molding materials is provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing the configuration of a thermal spraying apparatus. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings. In all drawings, similar components are denoted by the same reference numerals, and their descriptions are omitted as appropriate. Also, the drawings are schematic diagrams and do not correspond to the actual dimensional ratios.

[0010] The spherical alumina powder of this embodiment will now be described.

[0011] The spherical alumina powder of this embodiment has a hydrogen-bonding OH group density of 12.0 groups / nm. 2 It is configured as follows:

[0012] Hydrogen-bonded OH group density is one indicator that represents the amount of OH groups attached to the surface of spherical alumina powder. The density of hydrogen-bonded OH groups can be measured according to the following procedure. Using the spherical alumina powder, the amount of water V1 (ppm) derived from hydrogen-bonded OH groups generated from the temperature increase from over 200°C to 550°C is measured by the Karl Fischer method. The specific surface area S(m²) of the spherical alumina powder was determined by the BET 1-point method using nitrogen gas adsorption. 2 Measure the amount ( / g). Using the obtained V1 and S, the above hydrogen bonding OH group density (groups / nm) 2 ) is calculated from formula 1: 0.0668 × V1 / S.

[0013] In this embodiment, when a sample is placed in a moisture vaporizer and the generated moisture is measured by Karl Fischer coulometric titration while heating, the moisture generated up to a temperature of 200°C is defined as "physically adsorbed water," the moisture generated from 200°C up to 550°C is defined as "moisture derived from hydrogen-bonded OH groups," and the moisture generated from 550°C up to 900°C is defined as "moisture derived from isolated OH groups."

[0014] The upper limit for the hydrogen-bonding OH group density of spherical alumina powder is 12.0 groups / nm. 2 Preferably 10.0 pieces / nm 2More preferably, 9.5 particles / nm 2 The following is the result. This makes it possible to improve the thermal conductivity of molded articles made from resin molding materials containing spherical alumina powder. The lower limit of the hydrogen-bonding OH group density mentioned above is, for example, 3.0 groups / nm. 2 Preferably 4.0 pieces / nm 2 Above, a comfortable 5.0 pieces / nm 2 That concludes the explanation. This will improve liquidity.

[0015] Although the detailed mechanism is not clear, it is thought that by controlling the upper limit of the hydrogen-bonding OH group density of the spherical alumina powder to below a predetermined value, the surface of the spherical alumina powder (thermally conductive filler) in the resin molding material (resin composition) after molding becomes suitable, thereby improving the thermal conductivity.

[0016] The upper limit of the isolated OH group density in spherical alumina powder is, for example, 7.0 groups / nm. 2 Preferably 5.0 pieces / nm 2 More preferably, 4.0 pieces / nm 2 The following is the result. This improves the thermal conductivity of the molded body. The lower limit of the above-mentioned isolated OH group density is, for example, 0.5 groups / nm. 2 Preferably, the above is 1.0 particles / nm. 2 Above, a comfortable 1.5 particles / nm 2 That concludes the explanation. This will improve liquidity.

[0017] The lower limit of the specific surface area (S) of spherical alumina powder measured by the BET1-point method using nitrogen gas adsorption is, for example, 0.2 m². 2 / g or more, preferably 0.4m 2 / g or more, more preferably 0.5m 2 It is above / g. This improves liquidity. The above upper limit for specific surface area (S) is, for example, 3.0 m². 2 Less than or equal to / g, preferably 2.5m 2 Less than or equal to / g, more preferably 2.2m 2It is less than / g. This improves thermal conductivity.

[0018] In this embodiment, the hydrogen-bonding OH group density and the isolated OH group density can be controlled by appropriately selecting, for example, the raw material components of the spherical alumina powder and the method for producing the spherical alumina powder. Among these, for example, appropriately controlling the molten flame conditions such as the raw material supply amount, raw material particle size, flame temperature, combustible gas, combustion aiding gas, and dispersion gas; heating the carrier gas of the raw material; using alumina raw material powders of different particle sizes in combination; and appropriately adjusting the opening during the classification process are examples of factors that can bring the hydrogen-bonding OH group density and the isolated OH group density into a desired numerical range.

[0019] The spherical alumina powder may be configured such that, when the loose bulk density is A and the hard bulk density is P, the degree of compression, calculated based on ((PA) / P) × 100, is, for example, 35% or more and 55% or less.

[0020] Loose bulk density, firm bulk density, and compressibility can be measured under room temperature of 25°C and humidity of 55% by following the procedure below. The spherical alumina powder is added at a rate of 5-10g per minute, allowed to fall naturally from a height of 25cm, and then 100cm 3 Pour the mixture into the measuring cup and continue until it overflows, preparing a heaping cup. Next, for the overflowing cup, without tapping, the amount that overflowed from the top of the cup was leveled off, and the mass (g) of the spherical alumina powder filled in the cup was measured, and the loose bulk density (g / cm³) was determined. 3 Calculate ). On the other hand, for the overflowing cup, after tapping it 180 times in the vertical direction (stroke length 2 cm, 1 second / tap), and leveling off the excess on the top of the cup, the mass (g) of the spherical alumina powder filled in the cup was measured, and the bulk density (g / cm³) was determined. 3 Calculate ). Using the loose bulk density (A) and the hard bulk density (P) obtained by the above procedure, the degree of compressibility (%) is calculated based on ((PA) / P) × 100.

[0021] The lower limit of the degree of compression is, for example, 35% or more, preferably 38% or more, and more preferably 40% or more. This improves the handling properties of the spherical alumina powder. The upper limit of the compression is, for example, 55% or less, preferably 53% or less, and more preferably 50% or less. This improves the miscibility between the resin and the spherical alumina powder.

[0022] The spherical alumina powder has a loose bulk density (A) of 1.10 g / cm³. 3 More than 1.50g / cm 3 It may be configured as follows: The lower limit of the loose bulk density (A) is, for example, 1.10 cm. 3 / g or more, preferably 1.15cm 3 / g or more, more preferably 1.20cm 3 It is 1 / g or more. This improves density and has the potential to improve the strength of molded articles made from resin molding materials. The upper limit of the loose bulk density (A) is, for example, 1.50 cm 3 Less than or equal to / g, preferably 1.45cm 3 Less than or equal to / g, more preferably 1.40cm 3 The amount is less than / g. This improves the miscibility between the resin and the spherical alumina powder.

[0023] The volume frequency particle size distribution of spherical alumina powder was measured by a wet laser diffraction scattering method, and the particle size at which the cumulative value reached 25% in the obtained volume frequency particle size distribution was defined as D 25 The particle size at which the cumulative value reaches 50% is D 50 The particle size at which the cumulative value reaches 97% is D 97 Let's assume that.

[0024] D 97 / D 25The lower limit is, for example, 8.0 or higher, preferably 9.0 or higher, and more preferably 10.0 or higher. This ensures that the particle size distribution has a certain range, improving fluidity and moldability. D 97 / D 25 The upper limit is, for example, 30.0 or less, preferably 20.0 or less, and more preferably 18.0 or less. This makes the particle size of coarse particles sharper, and mold defects in the molded product caused by coarse particles can be suppressed.

[0025] D 97 / D 50 The lower limit is, for example, 5.0 or higher, preferably 5.5 or higher, and more preferably 6.0 or higher. This ensures that the particle size distribution has a certain range, improving fluidity and moldability. D 97 / D 50 The upper limit is, for example, 20.0 or less, preferably 10.0 or less, and more preferably 8.0 or less. This makes the particle size of coarse particles sharper, and can suppress molding defects in the molded article caused by coarse particles.

[0026] D 90 The lower limit is, for example, 20.0 μm or more, preferably 25.0 μm or more, and more preferably 30.0 μm or more. D 90 The upper limit is, for example, 80.0 μm or less, preferably 70.0 μm or less, and more preferably 60.0 μm or less.

[0027] The particle size distribution of spherical alumina powder is a value based on particle size measurement by laser diffraction scattering, and can be measured using a particle size distribution analyzer such as the "Model LS-13230" (manufactured by Beckman Coulter). For measurement, water was used as the solvent, and as a pretreatment, the powder was dispersed using a homogenizer at a power of 200W for 1 minute. The PIDS (Polarization Intensity Differential Scattering) concentration was adjusted to 45-55%. The refractive index of water was set to 1.33, and the refractive index of the powder material was taken into consideration. For example, a refractive index of 1.50 was used for amorphous silica and 1.68 for alumina.

[0028] The method for producing the spherical alumina powder of this embodiment will now be described.

[0029] Spherical alumina powder is produced, for example, by supplying alumina raw material powder into a high-temperature flame formed by the combustion reaction of a combustible gas and a combustion-supporting gas, and melting it into spheres above its melting point. Particles obtained by this molten flame method are called molten spherical particles. The obtained molten spherical particles may be further subjected to classification and sieving treatment as needed. Multiple raw material powders with different particle sizes are used as the alumina raw material powder.

[0030] Figure 1 shows an example of a schematic diagram of a thermal spraying apparatus used to produce molten spherical particles. The thermal spraying apparatus 100 in Figure 1 consists of a melting furnace 2 equipped with a burner 1, a cyclone 4 for classifying molten spherical particles generated by the high-temperature exhaust gas of the flame using the suction of a blower 9, and a bag filter 8 for collecting fine particles that could not be captured by the cyclone 4. The melting furnace 2 is composed of a vertical furnace body, but is not limited to this; it may also be a horizontal furnace or inclined furnace, which is horizontal in which the flame is blown out horizontally. The high-temperature exhaust gas is cooled by pipes 3 and 5 equipped with water-cooling jackets. The blower 9 may be connected to a suction gas volume control valve (not shown) and a gas exhaust port. A collection and extraction device (not shown) may be connected to the bottom of the melting furnace 2, cyclone 4, and bag filter 8. Classification can be carried out using known equipment such as heavy sedimentation chambers, cyclones, and classifiers with rotating blades. This classification operation may be incorporated into the transport process of the molten spheroidized product, or it may be carried out on a separate line after bulk collection.

[0031] As the flammable gas, one or more types such as acetylene, propane, and butane can be used, but propane, butane, or a mixture thereof with a relatively low calorific value is preferred. As a combustion-supporting gas, for example, a gas containing oxygen is used. Generally, using pure oxygen of 99% by mass or higher is the most inexpensive and preferable option. To reduce the calorific value of the gas, an inert gas such as air or argon can also be mixed with the combustion-supporting gas.

[0032] As the raw material powder, alumina powder with an average particle size of 3 to 70 μm may be used. The aluminum hydroxide powder may be supplied into the high-temperature flame either dry or wet by slurring it with water or the like.

[0033] The spherical alumina powder of the present invention, when incorporated into a resin composition, can be suitably used as a resin molding material.

[0034] The resin composition includes, in addition to the spherical alumina powder of the present invention, a resin and known resin additives. In the resin composition, spherical alumina powder may be used alone or mixed with other fillers. The resin composition may contain 10 to 99% by mass of spherical alumina powder, or 10 to 99% by mass of a mixed inorganic powder containing spherical alumina powder and other fillers. In addition, the content of other fillers in the mixed inorganic powder may be, for example, 1 to 20% by mass or 3 to 15% by mass relative to 100% by mass of spherical alumina powder. In this specification, unless otherwise specified, "~" indicates that it includes both the upper and lower limits.

[0035] Other fillers mentioned above include, for example, crystalline silica, fused silica, titania, silicon nitride, aluminum nitride, silicon carbide, talc, and calcium carbonate. Other fillers typically have an average particle size of around 5 to 100 μm, and there are no particular restrictions on their particle size composition or shape.

[0036] Examples of the above-mentioned resins include epoxy resins, silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyimides, polyamide-imides, polyetherimides and other polyamides, polyesters such as polybutylene terephthalate and polyethylene terephthalate, polyphenylene sulfide, fully aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins. These may be used individually or in combination of two or more types.

[0037] Resin compositions can be manufactured, for example, by blending raw material components in predetermined ratios using a blender or Henschel mixer, then kneading them using a heated roll, kneader, single-screw or twin-screw extruder, cooling, and then grinding the mixture.

[0038] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. [Examples]

[0039] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way to the descriptions of these examples.

[0040] <Manufacturing of spherical alumina powder> Spherical alumina powder was produced using the thermal spraying apparatus 100 shown in Figure 1. The thermal spraying apparatus 100 shown in Figure 1 comprises a melting furnace 2, a burner 1 installed on top of the melting furnace 2, and a collection system line consisting of a cyclone 4 and a bag filter 8 installed directly connected to the bottom of the melting furnace 2. Burner 1 has a double-tube structure capable of forming an inner flame and an outer flame, and is installed at the top of the melting furnace 2, to which the combustible gas supply pipe 11, the auxiliary combustion gas supply pipe 12, and the raw material supply pipe 13 are connected. In the melting furnace 2, raw material powder is supplied into a high-temperature flame from the raw material supply pipe 13 and melted to form spherical molten spherical particles. The molten spherical particles that have passed through the melting furnace 2 are sucked in by the blower 9 along with the combustion exhaust gas, move through the pipes 3 and 5 by air, and are classified and collected by the cyclone 4 or bag filter 8.

[0041] (Example 1) Using the thermal spraying apparatus 100 described above, LPG was supplied as a combustible gas from the combustible gas supply pipe 11, and atmospheric air was supplied as a combustion aid gas from the combustion aid gas supply pipe 12. A high-temperature flame was formed in the burner 1 by the combustion of LPG and oxygen. Secondary air is supplied to cyclone 4 by a rotary valve (not shown) installed in piping 3. Atmospheric air was used as the secondary air. The degree of opening / closing of the lower valve in cyclone 4 (lower opening) was set to 100%. Furthermore, the raw material powder has an average particle size (D 50 Multiple alumina powders with maximum values ​​in the range of 2 to 45 μm were used. The supply amount was 15 Nm³ of carrier gas for the raw materials heated to 500°C. 3 / hr, the burner's flammable gas is 5Nm 3 / hr, auxiliary gas at 10Nm³ 3 The value was set to / hr. The molten spherical particles collected by the bag filter 8 were recovered as spherical alumina powder.

[0042] (Examples 2-4) In the production of spherical alumina powder, the spherical alumina powder was recovered in the same manner as in Example 1 above, except that the lower opening was changed to 20%, 25%, and 35% during the classification process.

[0043] (Comparative Example 1) In the production of spherical alumina powder, the spherical alumina powder was recovered in the same manner as in Example 1, except that an unheated carrier gas was used.

[0044] <Loose bulk density, firm bulk density> The loose and hard bulk densities of the obtained spherical alumina powder were measured using a powder tester (Hosokawa Micron Corporation, PT-E type) under conditions of room temperature (25°C) and humidity (55%). The specific steps are as follows: The spherical alumina powder, which is the measurement sample, is allowed to fall naturally from a height of 25 cm at a rate of 5-10 g per minute, and then measured at 100 cm. 3 I poured it into the measuring cup and continued until it overflowed, preparing a heaping cup. Next, for the overflowing cup, without tapping, the amount that overflowed from the top of the cup was leveled off, and the mass (g) of the spherical alumina powder filled in the cup was measured, and the loose bulk density (g / cm³) was determined. 3 ) was calculated. On the other hand, for the overflowing cup, after tapping it 180 times in the vertical direction (stroke length 2 cm, 1 second / tap), and leveling off the excess on the top of the cup, the mass (g) of the spherical alumina powder filled in the cup was measured, and the bulk density (g / cm³) was determined. 3 ) was calculated. When the loose bulk density obtained using the above procedure is denoted as A and the stiff bulk density as P, the degree of compressibility (%) was calculated based on the formula: ((PA) / P) × 100.

[0045] <Specific surface area> The specific surface area of ​​the powder was measured using the BET single-point method with nitrogen gas adsorption. Specifically, using a specific surface area measuring device ("Macsorb HM model-1208" manufactured by MACSORB), nitrogen gas was used as the adsorbed gas and helium gas was used as the carrier gas. After drying and degassing 1 g of the sample at 300 °C for 15 minutes, the measurement was carried out.

[0046] <Moisture content> The moisture content in the powder was measured by the Karl Fischer method. Specifically, using a trace moisture measuring device (model CA-05 manufactured by Mitsubishi Chemical Corporation), the powder was set in a quartz tube in a moisture vaporization mechanism, and while heating from room temperature to 900 °C with an electric heater, dehydrated argon gas was supplied as the carrier gas. The water vapor volatilized from the powder surface was led to a moisture measuring mechanism, and the moisture content (ppm) was measured. The moisture generated until the heating temperature of the electric heater reached 200 °C was regarded as physically adsorbed water, the moisture generated until exceeding 200 °C and reaching 550 °C was regarded as moisture (V1) derived from hydrogen-bonded OH groups, and the moisture generated until exceeding 550 °C and reaching 900 °C was regarded as moisture (V2) due to dehydration condensation of isolated OH groups.

[0047] <OH group density> The OH group density was calculated based on the following formula. OH group density (number / nm 2 ) = 0.0668 × P / Q In the above formula, P (ppm) is the moisture content of the powder measured by the Karl Fischer method in the above <Moisture content>, and Q (m 2 / g) is the specific surface area of the powder measured by the BET one-point method by nitrogen gas adsorption in the above <Moisture content>. Specifically, the hydrogen-bonded OH group density (number / nm 2 ) was calculated based on Equation 1: 0.0668 × V1 / S, and the isolated OH group density was calculated based on Equation 2: 0.0668 × V2 / S.

[0048] <Particle size distribution> The volume frequency particle size distribution of the obtained spherical alumina powder was determined by wet laser diffraction scattering using a particle size distribution analyzer (Beckman Coulter, LS-13230). Water was used as the solvent, and as a pretreatment, the powder was dispersed using a homogenizer at a power of 200W for 1 minute. The PIDS (Polarization Intensity Differential Scattering) concentration was also adjusted to 45-55% for measurement. Based on the obtained volume frequency particle size distribution, the particle size D at which the cumulative value is X% X The result was calculated.

[0049] [Table 1]

[0050] The spherical alumina powders obtained from each example and comparative example were evaluated as follows. The results are shown in Table 1. In Table 1, "-" indicates that measurement was not performed.

[0051] <Barrier suppression> The obtained spherical alumina powder was mixed with 90.1 parts by mass, biphenylene aralkylphenol type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., trade name: NC-3000, epoxy equivalent 275, softening point 56℃) with 4.8 parts by mass, phenol resin (phenol aralkyl resin, manufactured by Meiwa Kasei Co., Ltd., MEHC-7800S) with 3.7 parts by mass, triphenylphosphine (manufactured by Hokko Chemical Industry Co., Ltd.: TPP) with N-phenyl-3-aminopropyl trim 0.35 parts by mass of toxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.: KBM-573) was mixed with a Henschel mixer (manufactured by Nippon Coke Industries Co., Ltd. "FM-20C / I") at room temperature and a rotation speed of 2000 rpm. The resulting mixture was heated and kneaded in a co-meshing twin-screw extruder (screw diameter D=25 mm, L / D=10.2, paddle rotation speed 50~120 rpm, discharge rate 3.0 kg / Hr, kneaded material temperature 98~100°C) to obtain a resin composition.

[0052] The obtained resin composition was molded using a burr measuring mold with slits of 2 μm, 5 μm, 10 μm, and 30 μm. The molding temperature was 175°C and the molding pressure was 7.4 MPa. The resin that flowed out of the slits was measured with calipers, and the values ​​measured in each slit were averaged to determine the burr length (μm). If the burr length was 5 mm or less, it was evaluated as good (successful) as it could suppress burr generation during molding; if it exceeded 5 mm, it was evaluated as poor (potential for burr generation during molding).

[0053] <Liquidity> The resin composition obtained above was used, and the molding process was carried out using a spiral flow mold in accordance with EMMI-1-66 (Epoxy Molding Material Institute; Society of Plastic Industry). The mold temperature was 175°C, the molding pressure was 7.4 MPa, and the holding pressure time was 90 seconds. A spiral flow of 150 cm or more was considered good, while a spiral flow of less than 150 cm was considered poor.

[0054] <Thermal conductivity> Using the resin composition obtained above, the resin composition was poured into a mold with a disc-shaped hole measuring 28 mm in diameter and 3 mm in thickness, and molded at 150°C for 20 minutes after degassing. The thermal conductivity (W / m·K) of the obtained molded body and the obtained resin composition was measured using a thermal conductivity measuring device (Hitachi Technology & Services Co., Ltd. resin material thermal resistance measuring device "TRM-046RHHT" (product name)) in accordance with the steady-state method in accordance with ASTM D5470. The resin composition was processed into a 10 mm wide x 10 mm wide piece, and the measurement was performed while applying a load of 2 N. Thermal conductivity (W / m·K) = Thickness of molded body (m) / {Thermal resistance (°C / W) × Heat transfer area (m²)} 2 )}

[0055] Compared to Comparative Example 1, the spherical alumina powders of Examples 1-4 showed that they could suppress burr formation during molding of resin compositions and improve the thermal conductivity of resin molding materials. Furthermore, the spherical alumina powders of Examples 1-4 showed excellent fluidity when used in resin molding materials.

[0056] This application claims priority based on Japanese Patent Application No. 2022-201019, filed on 16 December 2022, and incorporates all of its disclosures herein. [Explanation of Symbols]

[0057] 1 burner 2. Melting furnace 3 Piping 4 Cyclone 5 Piping 8. Bug Filter 9 Blower 11. Combustible gas supply pipe 12 Combustion aid gas supply pipe 13 Raw material supply pipe 100 Thermal spraying equipment

Claims

1. The hydrogen bonding OH group density, determined according to the procedure in step 1 below, is 5.0 groups / nm² or more and 12.0 groups / nm². ２ The following: Based on the above procedure 1, the isolated OH group density calculated from formula 2: 0.0668 × V2 / S using V2 and S is 7.0 groups / nm² or less. Spherical alumina powder having a loosened bulk density of 1.10 g / cm³ or more and 1.50 g / cm³ or less, as measured in step 2 below. (Step 1) Using the spherical alumina powder, the amount of water V1 (ppm) derived from hydrogen-bonded OH groups generated from above 200°C to 550°C, and the amount of water V2 (ppm) derived from isolated OH groups generated from above 550°C to 900°C are measured by the Karl Fischer method. The specific surface area S (m²) of the spherical alumina powder was determined by the BET 1-point method using nitrogen gas adsorption. ２ Measure the amount (per g). Using the obtained V1 and S, the above hydrogen bonding OH group density (groups / nm) ２ This is calculated from formula 1: 0.0668 × V1 / S. (Step 2) The spherical alumina powder is dropped naturally from a height of 25 cm at a rate of 5 to 10 g per minute into a 100 cm³ measuring cup. This process is continued until the cup overflows, creating a heaping cup. Next, for the overflowing cup, without tapping, the amount that overflowed from the top of the cup was leveled off, and the mass (g) of the spherical alumina powder filled in the cup was measured, and the loose bulk density (g / cm³) was calculated. On the other hand, for the overflowing cup, after tapping it 180 times in the vertical direction (stroke length 2 cm, 1 second / tap), and leveling off the excess on the top surface of the cup, the mass (g) of the spherical alumina powder filled in the cup is measured, and the bulk density (g / cm³) is calculated.

2. The spherical alumina powder according to claim 1, The specific surface area (S) of the spherical alumina powder, as measured by the BET 1-point method using nitrogen gas adsorption, is 0.5 m². ２ / g or more 2.5m ２ Spherical alumina powder with a weight of less than / g.

3. A spherical alumina powder according to claim 1 or 2, When the loose bulk density measured in step 2 above is A and the firm bulk density is P, Spherical alumina powder having a compression degree of 35% or more and 55% or less, calculated based on ((P-A) / P) × 100.

4. A spherical alumina powder according to claim 1 or 2, In the volume frequency particle size distribution measured by the wet laser diffraction scattering method, the particle size at which the cumulative value reaches 25% is defined as D. ２５ The particle size at which the cumulative value reaches 97% is D ９７ In that case, D ９７ / D ２５ Spherical alumina powder in which D / D is 8.0 or more and 30.0 or less.

5. A spherical alumina powder according to claim 1 or 2, In the volume frequency particle size distribution measured by the wet laser diffraction scattering method, the particle size at which the cumulative value reaches 50% is defined as D. ５０ The particle size at which the cumulative value reaches 97% is D ９７ In that case, D ９７ / D ５０ However, spherical alumina powder with a coefficient between 5.0 and 20.0.

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