Spherical alumina powder

Abstract

The invention provides spherical aluminum oxide powder and a preparation method thereof. When S1 is the sphericity degree having a particle diameter of 5 [mu] m or more and less than 10 [mu] m, S2 is the sphericity degree having a particle diameter of 10 [mu] m or more and less than 20 [mu] m, S3 is the sphericity degree having a particle diameter of 20 [mu] m or more and less than 30 [mu] m, and S4 is the sphericity degree having a particle diameter of 30 [mu] m or more and less than 45 [mu] m in the spherical alumina powder as measured using a wet flow image analyzer, S1 is the sphericity degree having a particle diameter of 5 [mu] m or more and less than 10 [mu] m. When a sphericity degree having a particle diameter of 45 [mu] m or more is set as S5, at least two or more of S1, S2, S4, and S5 are 0.85 or more, and S3 is 0.84 or less.

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 powders. As such a technique, for example, the technique described in Patent Document 1 is known. In Patent Document 1, there is described a spherical alumina powder having an average particle size (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] However, as a result of the study 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.

[0007] As a result of further study by the present inventors, it has been found that by appropriately controlling the sphericity of the spherical alumina powder in each particle size grade, burr generation during molding using a resin molding material containing the same can be suppressed, and thus the present invention has been completed.

[0008] According to one aspect of the present invention, the following spherical alumina powder is provided.

[0009] 1. A spherical alumina powder, wherein

[0010] when the sphericity of the spherical alumina powder having a particle size of 5 μm or more and less than 10 μm measured using a wet flow type image analysis device is set as S1, the sphericity of the particle size of 10 μm or more and less than 20 μm is set as S2, the sphericity of the particle size of 20 μm or more and less than 30 μm is set as S3, the sphericity of the particle size of 30 μm or more and less than 45 μm is set as S4, and the sphericity of the particle size of 45 μm or more is set as S5,

[0011] at least two or more of S1, S2, S4, and S5 are 0.85 or more,

[0012] S3 is 0.84 or less.

[0013] 2. The spherical alumina powder according to 1., wherein

[0014] When the average sphericity obtained by averaging the values of S1, S2, S3, S4, and S5 (excluding those with a value of 0) is defined as S AVE S AVE is 0.80 or more.

[0015] 3. The spherical alumina powder according to 1. or 2., wherein

[0016] 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.

[0017] (Steps)

[0018] Let the spherical alumina powder naturally fall from a height of 25 cm at an input rate of 5 to 10 g per minute and be put into the inside of a measuring cup of 100 cm 3 until it overflows from the cup, thereby preparing a full cup.

[0019] Next, without tapping 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 ).

[0020] On the other hand, after tapping the full cup 180 times in the up and down direction (stroke length 2 cm, 1 time / second), 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 tapped bulk density (g / cm 3 ).

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

[0022] when the loose bulk density measured by the above steps is defined as A and the tapped bulk density is defined as P,

[0023] the degree of compressibility calculated according to ((P - A) / P) × 100 is 35% or more and 55% or less.

[0024] 5. The spherical alumina powder according to any one of 1. to 4., wherein

[0025] in the volume frequency particle size distribution measured by the wet laser diffraction scattering method, when the particle size at which the cumulative value becomes 25% is defined as D 25 and the particle size at which the cumulative value becomes 97% is defined as D 97 then

[0026] D 97 / D 25It is 8.0 or more and 30.0 or less.

[0027] 6. The spherical alumina powder according to any one of 1. to 5., wherein

[0028] In the volume frequency particle size distribution measured by the wet laser diffraction scattering method, the particle size at which the cumulative value becomes 50% is defined as D 50 and the particle size at which the cumulative value becomes 97% is defined as D 97 when

[0029] D 97 / D 50 is 5.0 or more and 20.0 or less.

[0030] According to the present invention, there is provided a spherical alumina powder having excellent burr suppression when used in a resin molding material. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic cross-sectional view showing the structure of a spraying device. DETAILED DESCRIPTION OF THE INVENTION

[0032] 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 constituent elements, and the description is appropriately omitted. And, the drawings are schematic views and do not match the actual dimensional ratios.

[0033] The spherical alumina powder of the present embodiment will be described.

[0034] The spherical alumina powder of the present embodiment is configured as follows: when the sphericity of particles having a particle size of 5 μm or more and less than 10 μm measured by a wet flow type image analysis device is defined as S1, the sphericity of particles having a particle size of 10 μm or more and less than 20 μm is defined as S2, the sphericity of particles having a particle size of 20 μm or more and less than 30 μm is defined as S3, the sphericity of particles having a particle size of 30 μm or more and less than 45 μm is defined as S4, and the sphericity of particles having a particle size of 45 μm or more is defined as S5, at least two or more of S1, S2, S4, and S5 are 0.85 or more, and S3 satisfies 0.84 or less.

[0035] Although the detailed mechanism is not yet clear, it is considered that by controlling the sphericity for each of the above particle size grades, appropriate viscoelastic properties can be achieved in the resin molding material (resin composition) when compounded into the resin, and thus burr generation during molding can be suppressed.

[0036] Regarding S1, S2, S3, S4, and S5, as long as at least two of them are 0.85 or more, it is sufficient, and preferably three or more, more preferably four or more. Thus, it is possible to suppress the generation of burrs when molding a resin molding material containing spherical alumina powder.

[0037] Moreover, the upper limit of S3 only needs to satisfy 0.84 or less, preferably 0.83 or less, more preferably 0.82 or less. Thus, it is possible to suppress the generation of burrs when molding the resin molding material.

[0038] In addition, the lower limit of S3 is not particularly limited and can be 0.60 or more, or 0.70 or more.

[0039] Let the average sphericity obtained from the average of S1, S2, S3, S4, and S5 (excluding those with a value of 0) be S. AVE .

[0040] S AVE The lower limit of S is, for example, 0.80 or more, preferably 0.82 or more, more preferably 0.84 or more. Thus, it is possible to improve the fluidity of the resin molding material. In addition, the upper limit of S AVE can be set to 0.99 or less, for example.

[0041] In the present embodiment, for example, by appropriately selecting the raw material composition of the spherical alumina powder or the manufacturing method of the spherical alumina powder, etc., it is possible to control the sphericity in each particle size grade of the above S1, S2, S3, S4, and S5 or S AVE . Among these, for example, elements such as appropriately controlling the molten flame conditions such as the raw material supply amount, raw material particle size, flame temperature, combustible gas, combustion-supporting gas, and dispersion gas, elements for heating the carrier gas of the raw material (the elements in (iv) below), and elements of using alumina raw material powders with different particle sizes can be cited as elements for setting the sphericity in each particle size grade of the above S1, S2, S3, S4, and S5 or S AVE within the desired numerical range.

[0042] For example, in order to control the sphericity in each particle size grade, the following can be cited: (i) if the raw material supply amount is reduced, the sphericity increases, and if the raw material supply amount is increased, the sphericity decreases; (ii) when supplying the raw material into the flame, by improving the dispersibility of the raw material, the agglomeration is reduced and the sphericity increases, and the target particle size can be obtained; (iii) if the particle sizes of multiple raw materials are close to the average particle size, the sphericity increases, and the farther away from the average particle size, the more the sphericity decreases; (iv) the higher the flame temperature, the more the sphericity increases, and the lower the flame temperature, the more the sphericity decreases; (v) the higher the temperature of the combustible gas, the more the sphericity increases, and the lower the temperature of the combustible gas, the more the sphericity decreases; (vi) the closer the combustion-supporting gas is to the stoichiometric ratio, the more the sphericity increases, and the farther away from the stoichiometric ratio, the more the sphericity decreases; (vii) by appropriately introducing the dispersing gas, the agglomeration is reduced and the sphericity increases, etc.

[0043] 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 density is set as P, the compressibility calculated according to ((P - A) / P)×100 is, for example, 35% or more and 55% or less.

[0044] Regarding the loose bulk density, tapped density, and compressibility, they can be measured according to the following steps under the conditions of room temperature of 25°C and humidity of 55%.

[0045] Let the spherical alumina powder naturally fall from a height of 25 cm at an input rate of 5 - 10 g per minute and be input into the inside of a measuring cup of 100 cm 3 until it overflows from the cup, thereby preparing a cup filled to the brim.

[0046] Next, without tapping the filled 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 ).

[0047] On the other hand, after tapping the filled cup 180 times in the up-and-down direction (stroke length 2 cm, 1 time / second), 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 tapped density (g / cm 3 ).

[0048] Using the loose bulk density (A) and tapped density (P) obtained by the above steps, calculate the compressibility (%) according to ((P - A) / P)×100.

[0049] The lower limit of the 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.

[0050] The upper limit of the compression ratio is, for example, 55% or less, preferably 53% or less, and more preferably 50% or less. Thereby, the mixing property of the resin and the spherical alumina powder can be improved.

[0051] The spherical alumina powder can be configured such that the loose bulk density (A) becomes 1.10 g / cm 3 or more and 1.50 g / cm 3 or less.

[0052] 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. Thereby, it is possible to improve the denseness and the strength in the molded body of the resin molding material.

[0053] 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. Thereby, the mixing property of the resin and the spherical alumina powder can be improved.

[0054] By measuring the volume frequency particle size distribution in the spherical alumina powder by the wet laser diffraction scattering method, in the obtained volume frequency particle size distribution, the particle size at which the cumulative value becomes 25% is defined as D 25 , the particle size at which the cumulative value becomes 50% is defined as D 50 , and the particle size at which the cumulative value becomes 97% is defined as D 97 .

[0055] D 97 / D 25 The lower limit of is, for example, 8.0 or more, preferably 9.0 or more, and more preferably 10.0 or more. Thereby, the particle size distribution has a certain width, and the fluidity and moldability can be improved.

[0056] D 97 / D 25 The upper limit of is, for example, 30.0 or less, preferably 20.0 or less, and more preferably 18.0 or less. Thereby, the particle size of the coarse particles becomes sharp, and the molding failure of the molded body caused by the coarse particles can be suppressed.

[0057] D 97 / D 50 The lower limit of is, for example, 5.0 or more, preferably 5.5 or more, and more preferably 6.0 or more. Thereby, the particle size distribution has a certain width, and the fluidity and moldability can be improved.

[0058] D97 / D 50 The upper limit of / D 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 molding defects of the molded body caused by the coarse particles can be suppressed.

[0059] D 90 The lower limit of D is, for example, 20.0 μm or more, preferably 25.0 μm or more, more preferably 30.0 μm or more.

[0060] D 90 The upper limit of D is, for example, 80.0 μm or less, preferably 70.0 μm or less, more preferably 60.0 μm or less.

[0061] 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. At the time of measurement, water is used as the solvent, and a homogenizer is used to apply an output of 200 W for 1 minute for dispersion treatment as a pretreatment. And 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 material of the powder is considered. For example, for amorphous silica, the refractive index was measured as 1.50, and for alumina, the refractive index was measured as 1.68.

[0062] A method for manufacturing the spherical alumina powder of the present embodiment will be described.

[0063] Regarding the spherical alumina powder, for example, an 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 manufacturing. 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 treatments as needed. A variety of raw material powders with different particle sizes are used in the alumina raw material powder.

[0064] An example of a schematic diagram of a spraying device for manufacturing the molten spherical particles is shown in Figure 1 in.

[0065] Figure 1The spraying device 100 is composed of a melting furnace 2 provided with a burner 1, a cyclone 4 for classifying the molten spherical particles generated by the high-temperature exhaust gas of the flame by suction of a blower 9, and a bag filter 8 for recovering the fine powder that cannot be captured by the cyclone 4.

[0066] 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.

[0067] The high-temperature exhaust gas is cooled by using pipes 3 and 5 equipped with water-cooled jackets.

[0068] An unillustrated suction gas volume control valve and a gas exhaust port may be connected to the blower 9.

[0069] An unillustrated captured powder extraction device may be connected to the lower parts of the melting furnace 2, the cyclone 4, and the bag filter 8.

[0070] 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 in the conveying process of the molten spherical product, or can be captured together and carried out in other pipelines.

[0071] 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.

[0072] As the combustion-supporting gas, for example, a gas containing oxygen can be used. Generally, it is inexpensive and most preferred to use pure oxygen of 99% by 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 combustion-supporting gas.

[0073] 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 dry or wet by slurrying with water or the like.

[0074] A material obtained by blending the spherical alumina powder of the present invention into a resin composition can be preferably used as a resin molding material.

[0075] The resin composition contains a resin or known resin additives in addition to the spherical alumina powder of the present invention.

[0076] 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. Moreover, in the mixed inorganic powder, the content of other fillers can be, for example, 1 to 20% by mass, 3 to 15% by mass with respect to 100% by mass of the spherical alumina powder.

[0077] In addition, in this specification, unless otherwise specifically stated, "~" means including the upper limit value and the lower limit value.

[0078] 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.

[0079] For the average particle diameter of other fillers, for example, fillers of about 5 to 100 μm are used, and there is no particular limitation on its particle size structure and shape.

[0080] 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.

[0081] 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 a Henschel mixer, etc., kneading using a heating roll, a kneader, a single-screw or twin-screw extruder, etc. to obtain a substance, and then cooling the substance and pulverizing it.

[0082] 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. Moreover, the present invention is not limited to the above embodiments, and modifications, improvements, etc. within the scope capable of achieving the object of the present invention are also included in the present invention.

[0083] Examples

[0084] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited by any of the descriptions of these examples.

[0085] <Manufacture of spherical alumina powder>

[0086] Using Figure 1 the spraying device 100 shown in the figure, spherical alumina powder was manufactured.

[0087] Figure 1 The 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.

[0088] 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.

[0089] 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.

[0090] (Example 1)

[0091] Using the above 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.

[0092] 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%.

[0093] 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.

[0094] (Examples 2 to 4)

[0095] When performing the classification treatment in the manufacture of spherical alumina powder, the lower opening degrees were changed to 20%, 25%, and 35% respectively. Except for this, the spherical alumina powder was recovered in the same manner as in Example 1 above.

[0096] (Comparative Example 1)

[0097] In the production of spherical alumina powder, the combustible gas of the burner was 7.5 Nm 3 / hr. Other than this, spherical alumina powder was recovered in the same manner as in Example 1.

[0098] <Sphericity>

[0099] For the obtained spherical alumina powder, the sphericity was determined as follows under the conditions of room temperature of 25 °C and humidity of 70%.

[0100] For the obtained spherical alumina powder, the sphericity (S1) of particles with a particle size of 5 μm or more and less than 10 μm, the sphericity (S2) of particles with a particle size of 10 μm or more and less than 20 μm, the sphericity (S3) of particles with a particle size of 20 μm or more and less than 30 μm, the sphericity (S4) of particles with a particle size of 30 μm or more and less than 45 μm, and the sphericity (S5) of particles with a particle size of 45 μm or more were measured using a wet flow type image analysis device (manufactured by Sysmex Corporation, FPIA - 3000).

[0101] [Measurement Procedure]

[0102] Corrected to the current measurement method

[0103] The measurement sample for the above wet flow type image analysis device was adjusted as follows.

[0104] In a 20 - ml glass beaker container, 0.05 g of a sample of spherical alumina powder was weighed, and after adding 10 ml of a 25 mass% aqueous solution of propylene glycol, it was dispersed for 3 minutes using an ultrasonic disperser (ASU - 10M manufactured by AS ONE Co rporation).

[0105] The total amount was put into the FPIA - 3000 and measured in the LPF mode / quantitative counting (total count 100, number of repeated measurements 1) method.

[0106] Using the above wet flow type image analysis device, the perimeter of the projection image of one particle and the perimeter of a circle corresponding to the area of the particle projection image were analyzed, and the circularity was calculated by the following formula.

[0107] Circularity = (Perimeter of particle projection image) / (Perimeter of circle corresponding to area of particle projection image)

[0108] The sphericity and circularity are the average values of the particles included in the range of each particle size grade.

[0109] The sphericity is set to the square value of the roundness for each particle size grade.

[0110] And, the average sphericity (S AVE ) was calculated based on the average value of S1, S2, S3, S4, and S5 (excluding those with a value of 0).

[0111] <Loose bulk density, tapped density>

[0112] In the obtained spherical alumina powder, the loose bulk density and the tapped density were measured using a powder tester (manufactured by Hosokawa Micron Corporation, model PT-E) under the conditions of a room temperature of 25 °C and a humidity of 55%.

[0113] The specific steps are as follows.

[0114] 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 - 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.

[0115] Next, without tapping the full cup, the portion overflowing onto the upper surface of the cup was scraped off, then the mass (g) of the spherical alumina powder filled in the cup was measured, and the loose bulk density (g / cm 3 ) was calculated.

[0116] On the other hand, after tapping the full cup 180 times in the vertical direction (stroke length 2 cm, 1 time per second), the portion overflowing onto the upper surface of the cup was scraped off, then the mass (g) of the spherical alumina powder filled in the cup was measured, and the tapped density (g / cm 3 ) was calculated.

[0117] When the loose bulk density obtained by the above steps is set as A and the tapped density is set as P, the compressibility (%) was calculated according to the formula: ((P - A) / P) × 100.

[0118] <Particle size distribution>

[0119] 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 determined by the wet laser diffraction scattering method. Water was used as the solvent, and a homogenizer was used to apply an output of 200 W for 1 minute for dispersion treatment as a pretreatment. In addition, it was prepared so that the PIDS (Polarization Intensity Differential Scattering) concentration was 45 to 55%, and the measurement was carried out.

[0120] Based on the obtained volume frequency particle size distribution, the particle diameter D at which the cumulative value became X% was calculated. X 。

[0121] [Table 1]

[0122]

[0123] The following evaluations were performed on the obtained spherical alumina powder of each example and each comparative example.

[0124] The results are shown in Table 1. In Table 1, "-" indicates that the measurement was not performed.

[0125] <Burr suppression>

[0126] 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 terphenyl aralkylphenol 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 (a phenol 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 to 120 rpm, discharge rate 3.0 kg / Hr, kneaded material temperature 98 to 100°C), thereby obtaining a resin composition.

[0127] Regarding the obtained resin composition, using a burr measurement die having 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).

[0128] 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).

[0129] <Flowability>

[0130] 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 to 175°C, the molding pressure was set to 7.4 MPa, and the holding pressure time was set to 90 seconds.

[0131] A spiral flow of 150 cm or more was evaluated as good, and less than 150 cm was evaluated as bad.

[0132] <Thermal conductivity>

[0133] 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.

[0134] Compared with Comparative Example 1, the spherical alumina powders of Examples 1 to 4 showed results capable of suppressing the generation of burrs during the molding of the resin composition. Also, the spherical alumina powders of Examples 1 to 4 showed excellent fluidity when used in resin molding materials and the result of improving the thermal conductivity of the resin molding materials.

[0135] This application claims priority based on Japanese Patent Application No. 2022-201017 filed on December 16, 2022, and incorporates all the contents of this disclosure therein.

[0136] Symbol Explanation

[0137] 1 Burner

[0138] 2 Melting furnace

[0139] 3 Pipe

[0140] 4 Cyclone

[0141] 5 Pipe

[0142] 8 Bag filter

[0143] 9 Blower

[0144] 11 Combustible gas supply pipe

[0145] 12 Combustion-supporting gas supply pipe

[0146] 13 Raw material supply pipe

[0147] 100 Spraying device

Claims

1. A spherical alumina powder, wherein, when the sphericity of the spherical alumina powder having a particle size of 5 μm or more and less than 10 μm measured using a wet flow type image analysis device is set as S1, the sphericity of the particle size of 10 μm or more and less than 20 μm is set as S2, the sphericity of the particle size of 20 μm or more and less than 30 μm is set as S3, the sphericity of the particle size of 30 μm or more and less than 45 μm is set as S4, and the sphericity of the particle size of 45 μm or more is set as S5, at least two or more of S1, S2, S4, and S5 are 0.85 or more, S3 is 0.84 or less.

2. The spherical alumina powder according to claim 1, wherein, When the average sphericity obtained from the average of S1, S2, S3, S4, and S5 is defined as S AVE S AVE is 0.80 or more, excluding those with a median value of 0 among S1, S2, S3, S4, and S5.

3. The spherical alumina powder according to claim 1 or 2, wherein, 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, without lightly tapping the filled cup, scrape off the portion that will overflow onto the upper surface of the cup, measure the mass (g) of the spherical alumina powder filled in the cup, and calculate the loose bulk density (g / cm 3 ); and On the other hand, after tapping the filled cup under the condition of 180 times in the vertical direction, that is, with a stroke length of 2 cm and a condition of 1 second per time, 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 density (g / cm 3 ) is calculated.

4. The spherical alumina powder according to claim 3, wherein, when the loose bulk density measured by the above steps is set as A and the tapped density is set as P, the degree of compressibility calculated according to ((P - A) / P)×100 is 35% or more and 55% or less.

5. The spherical alumina powder according to claim 1 or 2, wherein, In the volume frequency particle size distribution determined by the wet-based laser diffraction scattering method, the particle size at which the cumulative value becomes 25% is defined as D 25 and the particle size at which the cumulative value becomes 97% is defined as D 97 when D 97 / D 25 It is 8.0 or above and 30.0 or below.

6. The spherical alumina powder according to claim 1 or 2, wherein, In the volume frequency particle size distribution determined by the wet-based laser diffraction scattering method, the particle size at which the cumulative value becomes 50% is designated as D 50 and the particle size at which the cumulative value becomes 97% is designated as D 97 when D 97 / D 50 is 5.0 or more and 20.0 or less.

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