Spherical alumina powder

Abstract

The present invention provides a spherical alumina powder in which, in a volume frequency particle size distribution measured by a laser diffraction scattering method based on a wet method, when D10 is the particle size at which the cumulative value is 10%, D50 is the particle size at which the cumulative value is 50%, and D97 is the particle size at which the cumulative value is 97%, (D97-D10) / D50 is 4.2-20.0.

Description

Technical Field

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

[0002] To date, various developments have been made on spherical alumina powder. As such a technique, for example, the technique described in Patent Document 1 is known. Patent Document 1 describes a spherical alumina powder having an average particle diameter (D 50 ) of 50 μm or less and a true sphericity of 0.9 or more (Claim 1 of Patent Document 1, etc.).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-193493 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] However, as a result of the research by the present inventors, it has been found that there is room for improvement in terms of burr generation when the spherical alumina powder described in Patent Document 1 is used in a resin molding material.

[0008] Means for Solving the Technical Problem

[0009] As a result of further research by the present inventors, it has been found that by appropriately controlling (D 97 -D 10 ) / D 50 , which is one of the particle size distributions of the spherical alumina powder, burr generation during molding using a resin molding material containing the same can be suppressed, and thus the present invention has been completed.

[0010] According to one aspect of the present invention, the following spherical alumina powder is provided.

[0011] 1. A spherical alumina powder, wherein

[0012] in the volume frequency particle size distribution measured by a wet-based laser diffraction scattering method, when the particle diameter at which the cumulative value becomes 10% is defined as D 10 , the particle diameter at which the cumulative value becomes 50% is defined as D 50 , and the particle diameter at which the cumulative value becomes 97% is defined as D 97 ,

[0013] (D 97 -D 10 ) / D 50 is 4.2 or more and 20.0 or less.

[0014] 2. The spherical alumina powder according to 1., wherein

[0015] D 97 / D 50 is 5.0 or more and 20.0 or less.

[0016] 3. The spherical alumina powder according to 1. or 2., wherein

[0017] the thixotropic index of the resin varnish for evaluation containing the spherical alumina powder measured according to the following steps is 0.10 or more and 0.80 or less.

[0018] (Steps)

[0019] Mix the spherical alumina powder with a liquid bisphenol F type epoxide at 25 °C so that the content becomes 83% by mass to obtain the above-mentioned resin varnish for evaluation.

[0020] Next, in the obtained resin varnish for evaluation, use a rheometer to measure the viscosity (η1) when measured at a shear rate of 2 [1 / s] and the viscosity (η 20 ) at 25 °C when measured at a shear rate of 20 [1 / s]. Calculate the above-mentioned thixotropic index according to η 20 / η1.

[0021] 4. The spherical alumina powder according to any one of 1. to 3., wherein

[0022] the shear rate in the test sample of the resin composition: the viscosity η 20 at 20 [1 / s] is 10 Pa·s or more and 200 Pa·s or less.

[0023] 5. The spherical alumina powder according to any one of 1. to 4., wherein

[0024] the loose bulk density measured according to the following steps is 1.10 g / cm 3 or more and 1.50 g / cm 3 or less.

[0025] (Steps)

[0026] Let the spherical alumina powder fall naturally from a height of 25 cm at an input rate of 5 to 10 g per minute and input it into the inside of a measuring cup of 100 cm 3 until it overflows from the cup to prepare a full cup.

[0027] Next, without tamping the full cup, scrape off the part that has overflowed onto the upper surface of the cup, then measure the mass (g) of the spherical alumina powder filled in the cup, and calculate the loose bulk density (g / cm 3 ).

[0028] On the other hand, after tamping and filling the cup 180 times in the up-and-down direction under the conditions of a stroke length of 2 cm and 1 time per second, the portion that overflows to the upper surface of the cup is scraped off, and then the mass (g) of the spherical alumina powder filled in the cup is measured, and the tapped bulk density (g / cm 3 ) is calculated.

[0029] 6. The spherical alumina powder according to any one of 1. to 5., wherein

[0030] when the loose bulk density measured by the above steps is set as A and the tapped bulk density is set as P,

[0031] the degree of compressibility calculated according to ((P - A) / P)×100 is 35% or more and 55% or less.

[0032] Advantageous Effects of the Invention

[0033] According to the present invention, there is provided a spherical alumina powder excellent in burr suppression when used in a resin molding material. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic cross-sectional view showing the structure of a thermal spraying apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in all the drawings, the same reference numerals are assigned to the same components, and the description will be appropriately omitted. And the drawings are schematic views and do not match the actual dimensional ratios.

[0036] The spherical alumina powder of the present embodiment will be described.

[0037] The volume frequency particle size distribution in the spherical alumina powder is measured by a wet-based laser diffraction scattering method. In the obtained volume frequency particle size distribution, the particle size at which the cumulative value becomes 10% is set as D 10 , the particle size at which the cumulative value becomes 50% is set as D 50 , and the particle size at which the cumulative value becomes 97% is set as D 97 .

[0038] The spherical alumina powder of the present embodiment is configured to belong to one of the particle size distributions, and (D 97 - D 10 ) / D 50 becomes 4.2 or more and 20.0 or less.

[0039] (D 97 - D 10 ) / D 50The lower limit is 4.2 or more, preferably 4.5 or more, more preferably 5.0 or more. Thus, it is possible to suppress the generation of burrs when molding a resin molding material containing spherical alumina powder.

[0040] And, (D 97 -D 10 ) / D 50 The upper limit is 20.0 or less, preferably 15.0 or less, more preferably 10.0 or less. Thus, the particle size distribution does not become too wide or D 50 does not become too small, within an appropriate range, so that the fluidity and fillability of the powder itself can be improved.

[0041] D 97 -D 50 The lower limit is, for example, 5.0 or more, preferably 5.5 or more, more preferably 6.0 or more. Thus, the particle size distribution has a certain width, and the fluidity and moldability can be improved.

[0042] And, D 97 -D 50 The upper limit is, for example, 20.0 or less, preferably 10.0 or less, more preferably 8.0 or less. Thus, the particle size of the coarse particles becomes sharp, and the molding defect of the molded body caused by the coarse particles can be suppressed.

[0043] D 50 The lower limit is, for example, 2.0 μm or more, preferably 3.0 μm or more, more preferably 4.0 μm or more.

[0044] And, D 50 The upper limit is, for example, 15.0 μm or less, preferably 9.0 μm or less, more preferably 8.5 μm or less.

[0045] D 90 The lower limit is, for example, 20.0 μm or more, preferably 25.0 μm or more, more preferably 30.0 μm or more.

[0046] And, D 90 The upper limit is, for example, 80.0 μm or less, preferably 70.0 μm or less, more preferably 60.0 μm or less.

[0047] The particle size distribution of the spherical alumina powder is based on the values measured by the laser diffraction scattering method. As a particle size distribution measuring machine, for example, "Model LS-13230" (manufactured by Beckman Instruments, Inc.) can be used for measurement. During the measurement, water is used as the solvent, and a homogenizer is used to apply a power of 200 W for 1 minute for dispersion treatment as a pretreatment. Also, it is prepared in such a way that the PIDS (Polarization Intensity Differential Scattering) concentration becomes 45 to 55%. In addition, the refractive index of water is 1.33, and for the refractive index of the powder, the refractive index of the powder material is considered. For example, for amorphous silica, the refractive index was set to 1.50 for measurement, and for alumina, the refractive index was set to 1.68 for measurement.

[0048] Although the detailed mechanism is not yet clear, it is considered that by controlling the particle size distribution of the above spherical alumina powder, appropriate viscoelastic properties can be achieved in the resin molding material (resin composition) when compounded into the resin, so burr generation can be suppressed during molding.

[0049] In the present embodiment, for example, by appropriately selecting the raw material components of the spherical alumina powder or the manufacturing method of the spherical alumina powder, etc., the above (D 97 -D 10 ) / D 50 and D 97 / D 50 . Among these, for example, elements such as appropriately controlling the raw material supply amount, raw material particle size, flame temperature, combustible gas, combustion-supporting gas, dispersion gas, etc. of the melting flame conditions, elements for heating the carrier gas of the raw material, elements of using alumina raw material powders with different particle sizes, and elements for appropriately adjusting the opening degree during the classification treatment can be cited as elements for setting the above (D 97 -D 10 ) / D 50 and D 97 / D 50 within the desired numerical range.

[0050] In the present embodiment, the thixotropic index of the evaluation resin varnish containing the spherical alumina powder is, for example, 0.10 or more and 0.80 or less.

[0051] Regarding the thixotropic index of the evaluation resin varnish, it can be measured according to the following steps.

[0052] The spherical alumina powder was mixed with liquid bisphenol F type epoxy resin (EPIKOTE 807) at 25 °C so that the content became 83% by mass, thereby obtaining the above-mentioned resin varnish for evaluation.

[0053] Next, in the obtained resin varnish for evaluation, a rheometer was used to measure the viscosity (η1) when measured at a shear rate of 2 [1 / s] and the viscosity (η 20 ) when measured at a shear rate of 20 [1 / s]. The above thixotropic index was calculated according to η 20 / η1.

[0054] The lower limit of the above thixotropic index is, for example, 0.10 or more, preferably 0.12 or more, and more preferably 0.15 or more. Thereby, the wire sweep property of the resin molding material can be improved.

[0055] And, the upper limit of the above thixotropic index is, for example, 0.80 or less, preferably 0.70 or less, and more preferably 0.60 or less. Thereby, the moldability of the resin molding material can be improved.

[0056] The lower limit of the viscosity (η1) at a shear rate of 1 [1 / s] in the above resin varnish for evaluation is, for example, 100 Pa·s or more, preferably 120 Pa·s or more, and more preferably 150 Pa·s or more. Thereby, the operability of the resin molding material can be improved.

[0057] And, the upper limit of the above viscosity (η1) is, for example, 1000 Pa·s or less, preferably 800 Pa·s or less, and more preferably 600 Pa·s or less. Thereby, the operability of the resin molding material can be improved or the wire deformation caused by the flow pressure during molding can be suppressed.

[0058] The spherical alumina powder can be configured as follows: when the loose bulk density measured by the following steps is set as A and the tapped bulk density is set as P, the compressibility calculated according to ((P - A) / P)×100 is, for example, 35% or more and 55% or less.

[0059] Regarding the loose bulk density, tapped bulk density, and compressibility, they can be measured according to the following steps under the conditions of room temperature 25 °C and humidity 55%.

[0060] The spherical alumina powder was allowed to fall naturally from a height of 25 cm at an input rate of 5 - 10 g per minute and was put into the inside of a measuring cup of 100 cm 3 until it overflowed from the cup, thereby preparing a full cup.

[0061] Next, for the filled cup, without tamping, the portion that has overflowed onto the upper surface of the cup is scraped off, and then the mass (g) of the spherical alumina powder filled in the cup is measured, and the loose bulk density (g / cm 3 ) is calculated.

[0062] On the other hand, for the filled cup, after tamping under the condition of 180 times in the vertical direction (stroke length 2 cm, 1 time / second), the portion that has overflowed onto the upper surface of the cup is scraped off, and then the mass (g) of the spherical alumina powder filled in the cup is measured, and the tapped bulk density (g / cm 3 ) is calculated.

[0063] Using the loose bulk density (A) and the tapped bulk density (P) obtained through the above steps, the degree of compressibility (%) is calculated according to ((P - A) / P)×100.

[0064] The lower limit of the degree of compressibility is, for example, 35% or more, preferably 38% or more, and more preferably 40% or more. Thus, the operability of the spherical alumina powder can be improved.

[0065] And, the upper limit of the degree of compressibility is, for example, 55% or less, preferably 53% or less, and more preferably 50% or less. Thus, the mixing property of the resin and the spherical alumina powder can be improved.

[0066] The spherical alumina powder can be configured as follows: the loose bulk density (A) is 1.10 g / cm 3 or more and 1.50 g / cm 3 or less.

[0067] The lower limit of the loose bulk density (A) is, for example, 1.10 cm 3 / g or more, preferably 1.15 cm 3 / g or more, and more preferably 1.20 cm 3 / g or more. Thus, it is possible to improve the denseness and the strength in the molded body of the resin molding material.

[0068] And, the upper limit of the loose bulk density (A) is, for example, 1.50 cm 3 / g or less, preferably 1.45 cm 3 / g or less, and more preferably 1.40 cm 3 / g or less. Thus, the mixing property of the resin and the spherical alumina powder can be improved.

[0069] The manufacturing method of the spherical alumina powder of the present embodiment will be described.

[0070] Regarding spherical alumina powder, for example, alumina raw material powder is supplied into a high-temperature flame formed by the combustion reaction of a combustible gas and an oxidizing gas, and melted and spheroidized above its melting point for production. The particles obtained by this melting flame method are called molten spherical particles. The obtained molten spherical particles can be further subjected to classification and screening processes as needed. In the alumina raw material powder, raw material powders with various different particle sizes are used.

[0071] An example of a schematic diagram of a thermal spraying device for manufacturing molten spherical particles is shown in Figure 1 Figure.

[0072] Figure 1 The thermal spraying device 100 shown in Figure consists of a melting furnace 2 provided with a burner 1, a cyclone 4 for classifying the molten spherical particles generated from the high-temperature exhaust gas of the flame by suction of a blower 9, and a bag filter 8 for recovering fine powder that cannot be captured by the cyclone 4.

[0073] The melting furnace 2 is composed of a vertical furnace body, but is not limited thereto, and may also be a so-called horizontal furnace or inclined furnace in a horizontal form with the flame blown in the horizontal direction.

[0074] The high-temperature exhaust gas is cooled using pipes 3 and 5 equipped with a water-cooled jacket.

[0075] A suction gas volume control valve and a gas exhaust port (not shown) may be connected to the blower 9.

[0076] A captured powder extraction device (not shown) may be connected to the lower parts of the melting furnace 2, the cyclone 4, and the bag filter 8.

[0077] Regarding classification, known equipment such as a gravity settling chamber, a cyclone, and a classifier with rotating blades can be used. Regarding this classification operation, it can be integrated and carried out in the conveying process of the molten spherical product, or it can be captured together and carried out in other pipelines.

[0078] As the combustible gas, for example, one or more of acetylene, propane, butane, etc. can be used, but propane, butane, or a mixed gas thereof with relatively small calorific value is preferred.

[0079] As the oxidizing gas, for example, a gas containing oxygen can be used. Generally, it is inexpensive and most preferred to use pure oxygen of 99 mass% or more. In order to reduce the calorific value of the gas, an inert gas such as air or argon can also be mixed into the oxidizing gas.

[0080] As the alumina raw material powder of the raw material powder, for example, alumina powder with an average particle size of 3 to 70 μm can be used. The supply of aluminum hydroxide powder into the high-temperature flame can be either dry or wet by slurrying with water or the like.

[0081] Preferably, a material obtained by incorporating the spherical alumina powder of the present invention into a resin composition can be used as a resin molding material.

[0082] In addition to the spherical alumina powder of the present invention, the resin composition further contains a resin or known resin additives, etc.

[0083] In the resin composition, the spherical alumina powder can be used alone or in combination with other fillers. In the resin composition, 10 to 99% by mass of the spherical alumina powder can be contained, or 10 to 99% by mass of a mixed inorganic powder containing the spherical alumina powder and other fillers can also be contained. And, in the mixed inorganic powder, the content of other fillers can be, for example, 1 to 20% by mass, 3 to 15% by mass relative to 100% by mass of the spherical alumina powder.

[0084] In addition, in this specification, unless otherwise specifically stated, "~" means including the upper limit value and the lower limit value.

[0085] As the above-mentioned other fillers, for example, crystalline silica, fused silica, titanium dioxide, silicon nitride, aluminum nitride, silicon carbide, talc, calcium carbonate, etc. can be cited.

[0086] For the average particle size of other fillers, for example, fillers of about 5 to 100 μm are used, and there are no particular restrictions on its particle size structure and shape.

[0087] As the above-mentioned resin, for example, epoxy resin, silicone resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide and other polyamides, polybutylene terephthalate, polyethylene terephthalate and other polyesters, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylate rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, etc. These can be used alone or in combination of two or more.

[0088] Regarding the resin composition, for example, it can be manufactured by the following steps: after mixing the raw material components in a specified ratio using a blender or Henschel mixer, etc., kneading using a heating roll, kneader, single-screw or twin-screw extruder, etc. to obtain a substance, and then cooling and pulverizing the substance.

[0089] The above describes the embodiments of the present invention, but these are examples of the present invention, and various structures other than the above can be adopted. And, the present invention is not limited to the above embodiments, and variations, improvements, etc. within the scope capable of achieving the object of the present invention are also included in the present invention.

[0090] Example

[0091] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to any of the descriptions of these examples.

[0092] <Manufacture of spherical alumina powder>

[0093] Using Figure 1 the thermal spraying device 100 shown in the figure, spherical alumina powder was manufactured.

[0094] Figure 1 The thermal spraying device 100 shown in the figure includes a melting furnace 2, a burner 1 provided above the melting furnace 2, and a capture system pipeline directly connected to the lower part of the melting furnace 2 and composed of a cyclone 4 and a bag filter 8.

[0095] The burner 1 has a double-tube structure capable of forming an inner flame and an outer flame, is provided at the top of the melting furnace 2, and is respectively connected to a combustible gas supply pipe 11, an auxiliary combustion gas supply pipe 12, and a raw material supply pipe 13.

[0096] In the melting furnace 2, raw material powder can be supplied into the high-temperature flame through the raw material supply pipe 13 and melted to form spherical molten particles. The molten spherical particles that have passed through the melting furnace 2 are sucked by a blower 9 together with the combustion exhaust gas, move through the air in the pipes 3 and 5, and are classified and captured using a cyclone 4 or a bag filter 8.

[0097] (Example 1)

[0098] Using the above thermal spraying device 100, LPG was supplied as the combustible gas from the combustible gas supply pipe 11, and oxygen was supplied as the auxiliary combustion gas from the auxiliary combustion gas supply pipe 12. In the burner 1, a high-temperature flame was formed by the combustion of LPG and oxygen.

[0099] Secondary air was supplied to the cyclone 4 through a rotary valve (not shown) provided in the pipe 3. The secondary air used the air in the atmosphere. And the opening degree (lower opening degree) of the valve in the lower part of the cyclone 4 was set to 100%.

[0100] In addition, as the raw material powder, various alumina powders having a maximum value in the range of the average particle size (D 50 ) of 2 to 45 μm were used. Regarding the supply amount, the carrier gas of the raw material heated to 500 °C was set to 15 Nm 3 / hr, the combustible gas of the burner was set to 5 Nm 3 / hr, and the auxiliary combustion gas was set to 10 Nm 3 / hr. The molten spherical particles captured by the bag filter 8 were recovered as spherical alumina powder.

[0101] (Examples 2 to 5)

[0102] When performing classification treatment in the manufacture of spherical alumina powder, the lower opening was changed to 20%, 25%, 35%, and 45% respectively. Except for this, the spherical alumina powder was recovered in the same manner as in Example 1 above.

[0103] (Comparative Example 1)

[0104] Spherical alumina fine powder (manufactured by Denka Company Limited., DAW-01, average particle size D 50 : 2 μm) was added to the spherical alumina powder recovered in the same manner as in Example 1 to adjust the particle size distribution in Table 1, thereby obtaining the spherical alumina powder of Comparative Example 1.

[0105] (Comparative Example 2)

[0106] Spherical alumina coarse powder (manufactured by Denka Company Limited., DAW-70, average particle size D 50 : 45 μm) was added to the spherical alumina powder recovered in the same manner as in Example 1 to adjust the particle size distribution in Table 1, thereby obtaining the spherical alumina powder of Comparative Example 2.

[0107] <Loose bulk density, tapped bulk density>

[0108] In the obtained spherical alumina powder, under the conditions of room temperature 25 °C and humidity 55%, the loose bulk density and tapped bulk density were measured using a powder tester (manufactured by Hosokawa Micron Corporation, PT-E type).

[0109] The specific steps are as follows.

[0110] The spherical alumina powder as the measurement sample was allowed to fall naturally from a height of 25 cm at an input rate of 5 to 10 g per minute and was put into the inside of a 100 cm 3 measurement cup until it overflowed from the cup, thereby preparing a full cup.

[0111] Next, for the full cup, after scraping off the part that overflowed onto the upper surface of the cup without tamping, the mass (g) of the spherical alumina powder filled in the cup was measured, and the loose bulk density (g / cm 3 ) was calculated.

[0112] On the other hand, for the filled cup, after tamping under the condition of 180 times in the up-and-down direction (stroke length 2 cm, 1 time / second), the part overflowing onto the upper surface of the cup was scraped off, and then the mass (g) of the spherical alumina powder filled in the cup was measured, and the tapped bulk density (g / cm 3 ) was calculated.

[0113] When the loose bulk density obtained by the above steps was set as A and the tapped bulk density was set as P, the degree of compressibility (%) was calculated according to the formula: ((P - A) / P) × 100.

[0114] <Particle size distribution>

[0115] For the obtained spherical alumina powder, a particle size distribution measuring device (manufactured by Beckman Instruments, Inc., LS-13230) was used, and the volume frequency particle size distribution was obtained by the laser diffraction scattering method based on the wet method. Water was used as the solvent, and a homogenizer was used to apply a power of 200 W for 1 minute for dispersion treatment as a pretreatment. And it was prepared in such a way that the PIDS (Polarization Intensity Differential Scattering) concentration became 45 - 55%, and the measurement was carried out.

[0116] Based on the obtained volume frequency particle size distribution, the particle diameter D at which the cumulative value became X% was calculated X .

[0117] <Viscosity>

[0118] The obtained spherical alumina powder was mixed with a liquid bisphenol F-type epoxy resin (EPIKOTE 807) at 25 °C in such a way that the content became 83% by mass, thereby obtaining the above-mentioned resin varnish for evaluation.

[0119] For the obtained resin varnish for evaluation, a rheometer (manufactured by Anton Paar) was used to measure the viscosity (η1) when measured at a shear rate of 1 [1 / s] and the viscosity (η 20 ) when measured at a shear rate of 20 [1 / s] at 25 °C. Using the obtained η1, η 20 The "thixotropy index" represented by the formula η 20 / η1 was calculated.

[0120]

[0121] The following evaluations were carried out on the obtained spherical alumina powders of each example and each comparative example.

[0122] The results are shown in Table 1. In Table 1, "-" indicates not measured.

[0123] <Burr suppression>

[0124] Using a Henschel mixer ("FM-20C / I" manufactured by NIPPON COKE & ENGINEERING.CO., LTD.), 90.1 parts by mass of the obtained spherical alumina powder, 4.8 parts by mass of a biphenyl aralkyl phenol type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name: NC-3000, epoxy equivalent 275, softening point 56°C), 3.7 parts by mass of a phenolic resin (phenolic aralkyl resin, MEHC-7800S manufactured by Meiwa-Chemical Industry Co., Ltd.), 0.19 parts by mass of triphenylphosphine (manufactured by HOKKO CHEMICAL INDUSTRY CO., LTD.: TPP), and 0.35 parts by mass of N-phenyl-3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.: KBM-573) were mixed at normal temperature and a rotation speed of 2000 rpm, and the obtained mixture was heated and kneaded using a co-rotating twin-screw extruder (screw diameter D = 25 mm, L / D = 10.2, blade rotation speed 50 - 120 rpm, discharge rate 3.0 kg / Hr, kneaded material temperature 98 - 100°C) to obtain a resin composition.

[0125] For the obtained resin composition, using a burr measurement die with slits of 2 μm, 5 μm, 10 μm, and 30 μm, the resin flowing out into the slits during molding was measured with a vernier caliper under the conditions of a molding temperature of 175°C and a molding pressure of 7.4 MPa, and the values measured in each slit were averaged to obtain the burr length (μm).

[0126] When the burr length is 2 mm or less, it is evaluated that burr generation during molding can be suppressed (good), and when the burr length exceeds 2 mm, it is evaluated that burrs may be generated during molding (bad).

[0127] <Flowability>

[0128] Using the resin composition obtained above, a spiral flow die was used and carried out in accordance with EMMI-1-66 (Epoxy Molding Material Institute; Society of Plastic Industry). The mold temperature was set at 175 °C, the molding pressure was set at 7.4 MPa, and the holding time was set at 90 seconds.

[0129] Those with a spiral flow of 150 cm or more were evaluated as good, and those less than 150 cm were evaluated as bad.

[0130] <Thermal conductivity>

[0131] Using the resin composition obtained above, the resin composition was injected into a mold provided with a disk-shaped hole having a diameter of 28 mm and a thickness of 3 mm, and after degassing, it was molded at 150 °C for 20 minutes. For the obtained molded body and for the obtained resin composition, using a thermal conductivity measuring device (resin material thermal resistance measuring device “TRM-046RHHT” (product name) manufactured by Hitachi Technologies and Services, Ltd.), the thermal conductivity (W / m·K) was measured by the steady-state method in accordance with ASTM D5470. The resin composition was processed into a width of 10 mm × 10 mm, and the measurement was carried out while applying a load of 2 N on one side.

[0132] Thermal conductivity (W / m·K) = thickness of the molded body (m) / {thermal resistance (°C / W) × heat transfer area (m 2 )}

[0133] Compared with Comparative Example 1, the spherical alumina powders of Examples 1 to 4 showed results capable of suppressing burr generation during molding of the resin composition and improving the thermal conductivity of the resin molding material. Also, the spherical alumina powders of Examples 1 to 4 showed excellent results in terms of fluidity when used in resin molding materials.

[0134] This application claims the priority based on Japanese Patent Application No. 2022-201021 filed on December 16, 2022, and incorporates all the contents of this disclosure therein.

[0135] Symbol description

[0136] 1 - Burner, 2 - Melting furnace, 3 - Pipe, 4 - Cyclone, 5 - Pipe, 8 - Bag filter, 9 - Blower, 11 - Combustible gas supply pipe, 12 - Combustion-supporting gas supply pipe, 13 - Raw material supply pipe, 100 - Thermal spraying device.

Claims

1. A spherical alumina powder, In the volume frequency particle size distribution measured by the wet-based laser diffraction scattering method, the particle size at which the cumulative value becomes 10% is defined as D 10 , the particle size at which the cumulative value becomes 50% is defined as D 50 , the particle size at which the cumulative value becomes 97% is defined as D 97 when (D 97 -D 10 ) / D 50 is 4.2 or more and 20.0 or less.

2. The spherical alumina powder according to claim 1, D 97 / D 50 It is 5.0 or more and 20.0 or less.

3. The spherical alumina powder according to claim 1 or 2, The thixotropic index of the resin varnish for evaluation containing the spherical alumina powder measured according to the following steps is 0.10 or more and 0.80 or less. The steps are as follows: Mix the spherical alumina powder with liquid bisphenol F type epoxide at 25 °C so that the content becomes 83% by mass to obtain the resin varnish for evaluation. Next, for the obtained resin varnish for evaluation, using a rheometer, the viscosity η1 when measured at a shear rate of 2 [1 / s] at 25°C and the viscosity η when measured at a shear rate of 20 [1 / s] are determined. 20 , based on η 20 / η1, the thixotropic index is calculated.

4. The spherical alumina powder according to claim 3, the shear rate in the test sample of the resin composition: the viscosity η at 20 [1 / s] 20 is 10 Pa·s or more and 200 Pa·s or less.

5. The spherical alumina powder according to claim 1 or 2, The loose bulk density measured by the following steps is 1.10 g / cm 3 or more and 1.50 g / cm 3 or less. The steps are as follows: Let the spherical alumina powder fall naturally from a height of 25 cm at an input rate of 5 to 10 g per minute and be put into the interior of a measuring cup of 100 cm 3 until it overflows from the cup, thereby preparing a full cup; Next, for the filled cup, without tamping, the portion that has overflowed onto the upper surface of the cup is scraped off, and then the mass of the spherical alumina powder filled in the cup is measured in g, and the loose bulk density is calculated in g / cm 3 ; On the other hand, for the filled cup, after tamping under the conditions of 180 times in the vertical direction, a stroke length of 2 cm, and 1 time per second, the portion overflowing onto the upper surface of the cup is scraped off, and then the mass of the spherical alumina powder filled in the cup is measured in g, and the tapped bulk density is calculated in g / cm 3 .

6. The spherical alumina powder according to claim 5, When the loose bulk density measured by the above steps is set as A and the tapped bulk density is set as P, The degree of compressibility calculated according to ((P - A) / P)×100 is 35% or more and 55% or less.

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