Inorganic powder and method for producing inorganic powder

Abstract

An inorganic powder according to the present invention includes spherical alumina powder having an average particle size of from 20 μm to 50 μm and spherical silica powder having a dielectric loss tangent at 1 GHz of 2.0×10-3 or less and an average particle size of from 0.5 μm to 10 μm.

Description

Inorganic powder and method for producing inorganic powder

[0001] The present invention relates to an inorganic powder and a method for producing the inorganic powder.

[0002] Various developments have been made on inorganic powders up to now. For example, Patent Document 1 describes spherical alumina powder, and Patent Document 2 describes spherical silica powder.

[0003] International Publication No. 2022 / 210928 Japanese Patent Application Laid-Open No. 2000-191317

[0004] However, when the spherical alumina powder described in Patent Document 1 is used, the thermal conductivity of the inorganic powder can be improved, but the dielectric loss tangent can be reduced. On the other hand, when the spherical silica powder described in Patent Document 2 is used after being subjected to a dielectric reduction treatment, the dielectric loss tangent of the inorganic powder can be reduced, but the thermal conductivity can be reduced. That is, as a result of the inventor's investigations, it has been found that the thermal conductivity and the dielectric loss tangent exhibit a trade-off characteristic in inorganic powders containing spherical alumina powder and / or spherical silica powder.

[0005] After further investigation, the inventors discovered that by appropriately selecting the particle sizes of the spherical alumina powder and spherical silica powder, and filling the gaps between the large-particle-diameter spherical alumina powder with small-particle-diameter spherical silica powder that has a low dielectric tangent, it is possible to improve both the thermal conductivity and the dielectric tangent, which are trade-off characteristics, and thus completed the present invention.

[0006] According to one aspect of the present invention, there are provided the following inorganic powder and method for producing the inorganic powder.

[0007] 1. Spherical alumina powder with an average particle size of 20 μm or more and 50 μm or less and a dielectric loss tangent of 2.0 × 10 at 1 GHz －３2. The inorganic powder according to 1., wherein the spherical silica powder comprises at least one of spherical silica powder A having an average particle diameter of 0.5 μm to 4.0 μm and spherical silica powder B having an average particle diameter of 4.0 μm to 10 μm. 3. The inorganic powder according to 1. or 2., wherein the spherical silica powder has a specific surface area of ​​4.0 m or less. ２ / g over 10.0m ２ / g or less, and a spherical silica powder A having a specific surface area of ​​0.5 m ２ / g or more 4.0m ２ / g or less. 4. The inorganic powder according to 2. or 3., wherein the volumetric content ratio of the spherical silica powder A to the spherical silica powder B in the spherical silica powder is 30 vol%:70 vol% or more and 70 vol%:30 vol% or less. 5. The inorganic powder according to any one of 1. to 4., wherein the volumetric content ratio of the spherical alumina powder to the spherical silica powder is 25 vol%:75 vol% or more and 60 vol%:40 vol% or less. 6. The inorganic powder according to any one of 1. to 5., wherein the particle size frequency distribution of the inorganic powder has a maximum peak in the range of 20 μm or more and 50 μm or less. 7. The inorganic powder according to 6., wherein the frequency of the maximum peak is 10% or more. 8. The inorganic powder according to 1. to 7. 9. The inorganic powder according to any one of items 1. to 9., wherein, in a particle size frequency distribution of the inorganic powder, when the inorganic powder is divided into five particle size classes of more than 1.5 μm and not more than 2 μm, more than 2 μm and not more than 3 μm, more than 3 μm and not more than 4 μm, more than 4 μm and not more than 6 μm and not more than 8 μm, the average frequency of the five particle size classes is 2% to 10%. 9. The inorganic powder according to item 8., wherein the difference between the maximum value among the frequencies of the five particle size classes and the average value is 3% or less. 10. The inorganic powder according to any one of items 1. to 9., wherein a resin varnish for evaluation containing the inorganic powder has a thixotropy index of 0.01 to 0.10, measured according to the following procedure. (Procedure) The inorganic powder is mixed with a liquid bisphenol F-type epoxy (Epikote 807) at 25°C so that the content is 75% by mass, to obtain the resin varnish for evaluation. Next, the viscosity (η) of the obtained resin varnish for evaluation was measured at 25°C and a shear rate of 1 [1 / s] using a rheometer. １ ), and viscosity (η １００ Using the measured viscosity, the equation: η １ / η １００11. Spherical alumina powder having an average particle size of 20 μm or more and 50 μm or less and a dielectric loss tangent of 2.0 × 10 at 1 GHz are calculated based on the above. －３ A method for producing an inorganic powder, comprising a mixing step of mixing a spherical silica powder having an average particle diameter of 4 μm or more and 10 μm or less with the above.

[0008] According to the present invention, an inorganic powder having excellent thermal conductivity and dielectric loss tangent, and a method for producing the same are provided.

[0009] FIG. 2 is a graph showing the relationship between thermal conductivity and dielectric loss tangent in inorganic powders of Examples and Comparative Examples.

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all drawings, similar components are designated by similar reference numerals, and descriptions thereof will be omitted where appropriate. Furthermore, the drawings are schematic diagrams and do not correspond to actual dimensional proportions.

[0011] An outline of the inorganic powder of this embodiment will be described.

[0012] The inorganic powder of this embodiment is composed of spherical alumina powder having an average particle diameter of 20 μm or more and 50 μm or less, and a dielectric loss tangent of 2.0×10 at 1 GHz. －３ and a spherical silica powder having an average particle size of 0.5 μm or more and 10 μm or less.

[0013] According to the findings of the present inventors, it has been found that by combining large-particle-sized spherical alumina powder with high thermal conductivity and small-particle-sized spherical silica powder with low dielectric loss tangent, both the thermal conductivity and the dielectric loss tangent can be improved. Although the detailed mechanism is unclear, it is presumed that by forming an appropriate packing structure in the inorganic powder, in which the voids between the spherical alumina powder are filled with spherical silica powder, both the thermal conductivity and the dielectric loss tangent, which are trade-off characteristics, can be improved.

[0014] Furthermore, according to the findings of the present inventors, the larger the particle size of the spherical alumina powder, the higher the thermal conductivity. From the perspective of high thermal conductivity, it is common to select spherical alumina powder with a small particle size to fill the gaps between large-particle spherical alumina powder. However, as the particle size decreases, the specific surface area increases, resulting in an increased dielectric loss tangent. Therefore, from the perspective of low dielectric loss tangent, it is preferable to select spherical silica powder with a small particle size. Furthermore, from the perspective of improving the trade-off characteristics between thermal conductivity and dielectric loss tangent, it is preferable to use spherical silica powder that has been subjected to a low dielectric loss tangent treatment, such as heat treatment, to reduce the amount of physically adsorbed water, hydrogen-bonded silanol groups, and isolated silanol groups on the surface. However, when this small-particle spherical alumina powder is heat-treated in the same way as spherical silica powder, it forms large clumps in the furnace and cannot be used as a powder that has been subjected to a low dielectric loss tangent treatment.

[0015] Hereinafter, each component of the inorganic powder of this embodiment will be described in detail.

[0016] <Spherical alumina powder> The spherical alumina powder is alumina (Al ２ 0 ３ The main component is alumina (Al) in the total amount of alumina powder, calculated by mass. ２ 0 ３ ) in an amount of, for example, 50% or more, preferably 80% or more, and more preferably 90% or more. The spherical alumina powder preferably has a high purity, but the presence of impurities inevitably mixed in from the raw materials or during the production process is acceptable.

[0017] The lower limit of the average particle size of the spherical alumina powder is, for example, 20 μm or more, preferably 25 μm or more, and more preferably 30 μm or more.The upper limit of the average particle size of the spherical alumina powder is, for example, 50 μm or less, preferably 45 μm or less, and more preferably 40 μm or less.

[0018] In this specification, the average particle size refers to the particle size at the point where the cumulative volume from the small particle side reaches 50% (so-called D50) in the volume frequency particle size distribution measured by wet laser diffraction scattering. The measurement sample is prepared by using water as the solvent and pre-treating the powder by applying 200 W output power to a homogenizer for 1 minute to disperse the powder. The volume frequency particle size distribution and particle size frequency distribution can be measured using an "MT-3300EX" manufactured by Nikkiso Co., Ltd.

[0019] The lower limit of the specific surface area of ​​the spherical alumina powder is not particularly limited, but is, for example, 0.1 m ２ The upper limit of the specific surface area of ​​the spherical alumina powder may be, for example, 0.5 m ２ / g or less, preferably 0.35m ２ / g or less.

[0020] In this specification, the specific surface area can be measured by the BET single-point method using nitrogen gas adsorption. Specifically, using a specific surface area measuring device (for example, manufactured by Yuasa Ionics Co., Ltd., device name: MONOSORB), nitrogen gas is used as an adsorption gas and helium gas is used as a carrier gas, and 1 g of a sample is dried and degassed at 300°C for 30 minutes before measurement.

[0021] The upper limit of the α-crystalline phase of the spherical alumina powder is 90% or less, preferably 85% or less, and more preferably 80% or less. This improves the flowability and suppresses the generation of flash when used in a resin molding material. The lower limit of the α-crystalline phase is, for example, 40% or more, preferably 45% or more, and more preferably 50% or more. This improves the thermal conductivity of the resin composition.

[0022] The content of the α-crystalline phase in spherical alumina powder is measured using the following method. Using NIST-676a (α-alumina), an intensity standard for X-ray diffraction (XRD), and θ, δ, and γ-alumina, each alumina is weighed out to a total of 2 g, and then mixed for 15 minutes in a crusher to prepare a sample for creating a calibration curve. Then, for each sample, a sealed tube X-ray diffractometer (D8 ADVANCE (trade name) manufactured by Bruker) is used to calculate the integrated intensity (Cps × deg) under the following measurement conditions, and a calibration curve is created. The content of the α-crystalline phase is measured using three diffraction peaks in α-alumina (2θ = 25.6° (012), 35.2° (104), and 2θ = 43.4° (113)). (Measurement conditions) θ-θ scan Tube voltage: 40 kV Tube current: 40 mA X-ray source: CuKα (λ = 1.54056 Å) Slit: DS, 0.5° Soller slit: 2.5° Next, using spherical alumina powder, the diffraction peak area (Y) of the (113) plane derived from the α-crystalline phase of alumina is measured, and the content of the α-crystalline phase is calculated using the above-mentioned calibration curve. Note that the measurement uses a diffraction peak detected at 2θ = 10° or more and 70° or less. Also, using spherical alumina powder, the diffraction peak area (Y) of the (113) plane derived from the α-crystalline phase of alumina is measured, and the content of the α-crystalline phase is calculated using the above-mentioned calibration curve. Note that the measurement uses a diffraction peak detected at 2θ = 10° or more and 70° or less.

[0023] The crystallite size of the alumina obtained by X-ray diffraction measurement using Cu-Kα may be, for example, 400 nm to 800 nm, 450 nm to 750 nm, or 500 nm to 700 nm. This can improve the bending strength of the resin composition. The crystallite size can be calculated from the obtained powder X-ray diffraction pattern by quantitative analysis using Rietveld analysis with powder X-ray diffraction pattern analysis software TOPAS attached to the powder X-ray diffractometer.

[0024] The spherical alumina powder of this embodiment has a sphericity of S when the particle diameter is 5 μm or more and less than 10 μm as measured using a wet flow type image analyzer. １ The sphericity of particles with a diameter of 10 μm or more and less than 20 μm is S ２The sphericity of particles with a diameter of 20 μm or more and less than 30 μm is S ３ The sphericity of particles with a diameter of 30 μm or more and less than 45 μm is S ４ The sphericity of particles with a diameter of 45 μm or more is S ５ When this is done, S １ , S ２ , S ４ , and S ５ At least two of the above are 0.85 or more, preferably three or more are 0.85 or more, and more preferably four or more are 0.85 or more.

[0025] <Spherical Silica Powder> The spherical silica powder is silica (SiO ２ The main component is silica (SiO) in terms of mass in the total amount of silica powder. ２ ) in an amount of, for example, 80% or more, preferably 90% or more, and more preferably 95% or more. The spherical silica powder preferably has a high purity, but the presence of impurities inevitably mixed in from the raw materials or during the production process is acceptable.

[0026] The upper limit of the dielectric loss tangent of spherical silica powder at 1 GHz is 2.0 × 10 －３ or less, preferably 1.5 × 10 －３ or less, more preferably 1.0 × 10 －３ The lower limit of the dielectric loss tangent of the spherical silica powder at 1 GHz is not particularly limited, but is, for example, 3.0 × 10 －4 or more, 5.0 × 10 －4 More than that is fine.

[0027] In this specification, the dielectric loss tangent of a powder at 1 GHz can be measured by a cavity resonator perturbation method using a measurement sample in which the powder is filled in a Teflon tube.

[0028] The lower limit of the average particle size of the spherical silica powder is, for example, 0.5 μm or more, preferably 1.0 μm or more, and more preferably 1.2 μm or more. The upper limit of the average particle size of the spherical silica powder is, for example, 10 μm or less, preferably 7.5 μm or less, and more preferably 5.0 μm or less.

[0029] The spherical silica powder contains either or both of amorphous and crystalline silica. The amorphous content of the spherical silica powder is, for example, 95.0% or more, preferably 97.0% or more, and more preferably 99.0% or more.

[0030] The amorphous fraction of spherical silica powder is measured by X-ray diffraction analysis using a powder X-ray diffractometer (e.g., RIGAKU Corporation, product name "Model MiniFlex") in the 2θ range of 26° to 27.5° with CuKα radiation, and the measurement is based on the intensity ratio of specific diffraction peaks. In the case of siliceous powder, crystalline silica has a main peak at 26.7°, while amorphous silica does not have a peak. When amorphous silica and crystalline silica are mixed, a peak height of 26.7° corresponding to the proportion of crystalline silica is obtained. Then, the crystalline silica mixing ratio (X-ray diffraction intensity of sample / X-ray diffraction intensity of crystalline silica) is calculated from the ratio of the X-ray intensity of the sample to the X-ray intensity of a crystalline silica standard sample, and the amorphous fraction (%) can be calculated using the formula: amorphous fraction (%) = (1 - crystalline silica mixing ratio) x 100.

[0031] The spherical silica powder has an average circularity of, for example, 0.85 or more, preferably 0.90 or more, and more preferably 0.95 or more, which can prevent an increase in viscosity and a decrease in flowability when the silica powder is mixed with a resin.

[0032] The average sphericity of silica powder can be measured using a powder image analyzer (FPIA-3000). Specifically, after dispersing a sample in pure water, the liquid is passed through a planar extensional flow cell, and 100 or more particles of amorphous silica powder moving through the cell are recorded as images using an objective lens. The average circularity is calculated from these recorded images and the following formula (1). In formula (1), HD represents the circular equivalent diameter, which is determined from the ratio of the projected area of ​​the target particle to the area of ​​a perfect circle. PM represents the projected perimeter of the target particle. The average value of 200 particles of silica powder calculated in this way is defined as the average circularity. Formula (1): Average circularity = π HD / PM. From this average circularity, the formula: Average sphericity = (average circularity) ２ The average sphericity is calculated by the following.

[0033] The inorganic powder of this embodiment may contain one or more types of spherical silica powders having different average particle sizes.

[0034] The spherical silica powder may contain at least one of spherical silica powder A having an average particle size of 0.5 μm or more and 4.0 μm or less, and spherical silica powder B having a specific surface area of ​​4.0 μm or more and 10 μm or less. By containing spherical silica powder A having a fine particle size and spherical silica powder B having a small particle size in the inorganic powder, it is possible to further increase the packing density in the spherical alumina powder.

[0035] The lower limit of the average particle size of the spherical silica powder A is, for example, 0.5 μm or more, preferably 1.0 μm or more, and more preferably 1.2 μm or more. The upper limit of the average particle size of the spherical silica powder A is, for example, 4.0 μm or less, preferably 3.0 μm or less, and more preferably 2.0 μm or less.

[0036] The lower limit of the average particle size of the spherical silica powder B is, for example, more than 4.0 μm, preferably 5.0 or more, more preferably 6.0 or more. The upper limit of the average particle size of the spherical silica powder B is, for example, 10 μm or less, preferably 9.0 or less, more preferably 8.0 or less.

[0037] In addition, the spherical silica powder has a specific surface area of ​​4.0 m ２ / g over 10.0m ２ / g or less, and a spherical silica powder A having a specific surface area of ​​0.5 m ２ / g or more 4.0m ２ / g or less spherical silica powder B.

[0038] The lower limit of the specific surface area of ​​the spherical silica powder A is, for example, 4.0 m ２ / g, preferably more than 4.5m ２ / g or more, more preferably 5.0m ２ The upper limit of the specific surface area of ​​the spherical silica powder A is, for example, 10.0 m ２ / g or less, preferably 8.0 or less, and more preferably 6.0 or less.

[0039] The lower limit of the specific surface area of ​​the spherical silica powder B is, for example, 0.5 m ２ / g or more, preferably 1.0 or more, more preferably 1.5m ２The upper limit of the specific surface area of ​​the spherical silica powder B is, for example, 4.0 m ２ / g or less, preferably 3.0m ２ / g or less, more preferably 2.0m ２ / g or less.

[0040] The volumetric content ratio of spherical silica powder A to spherical silica powder B in the spherical silica powder is, for example, 30 vol%:70 vol% to 70 vol%:30 vol%, preferably 35 vol%:65 vol% to 65 vol%:35 vol%, and more preferably 40 vol%:60 vol% to 60 vol%:40 vol%. The lower limit of the total content of the spherical alumina powder and spherical silica powder in 100 mass% of the inorganic powder is, for example, 90 mass% or more, preferably 95 mass% or more, and more preferably 99 mass% or more. The upper limit of the total content is, but is not particularly limited to, 100 mass% or less.

[0041] The volumetric content ratio of the spherical alumina powder and the spherical silica powder in the inorganic powder is, for example, 25 vol%:75 vol% to 75 vol%:25 vol%, preferably 35 vol%:65 vol% to 65 vol%:35 vol%, and more preferably 40 vol%:60 vol% to 60 vol%:40 vol%.

[0042] The inorganic powder may have a maximum peak in the particle size frequency distribution in the range of 20 μm or more and 50 μm or less, preferably 30 μm or more and 45 μm or less, and more preferably 35 μm or more and 40 μm or less.

[0043] The lower limit of the frequency of the maximum peaks in the range of 20 μm to 50 μm is, for example, 10% or more, preferably 12.5% ​​or more, and more preferably 15.0% or more. The upper limit of the frequency of the maximum peaks is not particularly limited, but is, for example, 40% or less, preferably 30% or less, and more preferably 20% or less.

[0044] In the particle size frequency distribution of an inorganic powder, the particles are divided into five particle size classes: greater than 1.5 μm and less than 2 μm, greater than 2 μm and less than 3 μm, greater than 3 μm and less than 4 μm, greater than 4 μm and less than 6 μm, and greater than 6 μm and less than 8 μm. In this case, the lower limit of the average frequency of the five particle size classes is, for example, 2% or more, preferably 3% or more, more preferably 4% or more, and even more preferably 5.5% or more. The upper limit of the average frequency of the five particle size classes is, for example, 10% or less, preferably 9% or less, and more preferably 8% or less.

[0045] The upper limit of the difference between the maximum value and the average value among the frequencies of the five particle size classes is, for example, 3% or less, preferably 2.5% or less, and more preferably 2.2% or less. The lower limit of the difference between the maximum value and the average value is, for example, 0.3% or more, preferably 0.9% or more, and more preferably 1.5% or more.

[0046] In the particle size frequency distribution of the inorganic powder, the upper limit of the frequency in the particle size class of 1 μm or less is, for example, 5% or less, preferably 3% or less, more preferably 2.5% or less. The lower limit of the frequency in the particle size class of 1 μm or less is not particularly limited, but may be 0% or more.

[0047] In the particle size frequency distribution of the inorganic powder, the upper limit of the frequency in the particle size class of more than 128 μm and not more than 192 μm is, for example, not more than 2%, preferably not more than 1.0%, more preferably not more than 0.8%. The lower limit of the frequency in the particle size class of 1 μm or less is not particularly limited, but may be not less than 0%.

[0048] The inorganic powder of this embodiment may be configured so that the thixotropy index of the resin varnish for evaluation of the inorganic powder, measured according to the following procedure, is, for example, 0.01 or more and 0.10 or less, preferably 0.01 or more and 0.09 or less, and more preferably 0.02 or more and 0.07 or less.

[0049] By setting the thixotropy index to the upper limit or less, the moldability of the resin composition can be improved, and by setting the thixotropy index to the lower limit or more, the flash characteristics of the resin composition can be improved.

[0050] The procedure for measuring the viscosity and thixotropy index of a resin varnish for evaluation will be described. First, an inorganic powder is mixed with a bisphenol F-type epoxy (Epikote 807) that is liquid at 25°C so that the content is 75% by mass, to obtain a resin varnish for evaluation. Next, the viscosity (η １ ), viscosity (η １００ ) is measured. Then, the viscosity obtained is used to calculate the viscosity using the formula: η １００ / η １ The thixotropy index is calculated from the above.

[0051] In this embodiment, it is possible to control the thermal conductivity, dielectric loss tangent, or thixotropy index of the resin varnish to be evaluated in the inorganic powder by appropriately selecting, for example, the type and amount of each component contained in the inorganic powder, the preparation method of the inorganic powder, etc. Among these, for example, the use of a large particle size spherical alumina powder with high thermal conductivity in combination with a small particle size spherical silica powder with low dielectric loss tangent, or appropriately adjusting the content ratio thereof, can be cited as factors for setting the thermal conductivity, dielectric loss tangent, or thixotropy index of the resin varnish to be evaluated in the inorganic powder in the desired numerical range.

[0052] A method for producing the inorganic powder of this embodiment will be described. An example of the method for producing the inorganic powder of this embodiment is to use a spherical alumina powder having an average particle size of 20 μm or more and 50 μm or less and a dielectric loss tangent of 2.0×10 at 1 GHz. －３ and a spherical silica powder having an average particle diameter of 4 μm or more and 10 μm or less. That is, the inorganic powder is obtained by producing the above-mentioned spherical alumina powder and the above-mentioned spherical silica powder and mixing them together.

[0053] <Method for producing spherical alumina powder> Spherical alumina powder is produced, for example, by supplying an 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 and spheroidizing the powder at a temperature equal to or higher than its melting point. The obtained molten spherical particles may be further subjected to classification and sieving treatment, if necessary.

[0054] The alumina raw material powder may be, for example, an alumina powder having an average particle size of about 20 to 50 μm. A plurality of raw material powders having different particle sizes may be used as the alumina raw material powder. The aluminum hydroxide powder may be supplied to the high-temperature flame in a dry manner or in a wet manner by forming a slurry with water or the like.

[0055] <Method for Producing Spherical Silica Powder> In one example of the production method of this embodiment, alumina raw material powder is supplied into a high-temperature flame formed by the combustion reaction of a combustible gas and a combustion supporting gas, and melted and spheroidized at a temperature above its melting point. If necessary, silica powder can be obtained by further classification. Industrially, classification using a sieve or a classifier such as a precision air classifier is preferred, and a dry method is preferred for the classification operation. Dry classification of spherical silica powder can suppress aggregation of the silica powder and improve handleability, etc., compared to raw silica powder produced by a wet method and / or wet classification. The obtained silica powder is preferably stored in a moisture-proof bag.

[0056] The classified silica powder may also be subjected to a heat treatment as a post-treatment. The heat treatment is carried out in a hot air or electric furnace at a temperature of 500 to 1100°C for a predetermined time (e.g., about 1 to 52 hours) such that the heating temperature (°C) × heating time (h) is 1000 to 26400 (°C·h), preferably 1800 to 17600 (°C·h) (e.g., about 2 to 35 hours). Since the specific surface area and average particle size do not change before and after heating at a heating temperature of 500 to 1100°C, it is desirable to carry out the classification step before heating, and then adjust the specific surface area and average particle size to the desired value before heat treatment. After the heat treatment, the silica powder is allowed to cool naturally in an electric furnace, and then collected at 110 to 300°C. It is then further cooled to 25°C in an environment with a humidity of 40% RH or less, and stored at 15 to 25°C. It may also be collected and stored in a moisture-proof aluminum bag.

[0057] The silica powder was stored in a container with a moisture permeability of 0.1 (g / m) under condition B of JIS Z 0208-1976 (temperature 40°C - relative humidity 90%). ２It is preferable to store the product in a moisture-proof bag, such as a moisture-proof aluminum bag or a PET / AL / PE laminate bag, for a storage time of 24 hours or less.

[0058] A resin composition containing the inorganic powder of the present invention can be suitably used as a resin molding material.

[0059] Next, the resin composition of this embodiment will be described.

[0060] The resin composition contains, in addition to the inorganic powder of the present invention, a resin and known resin additives. The inorganic powder may be used alone in the resin composition, or may be mixed with other fillers. The resin composition may contain 10 to 99% by mass of the inorganic powder, or 10 to 99% by mass of a mixed inorganic powder containing the inorganic powder and other fillers. The content of the 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 the inorganic powder.

[0061] In this specification, unless otherwise specified, the range "to" indicates that the upper and lower limits are included.

[0062] Examples of other fillers include titania, silicon nitride, aluminum nitride, silicon carbide, talc, calcium carbonate, etc. The average particle size of the other fillers is about 5 to 100 μm, and there are no particular restrictions on the particle size structure and shape.

[0063] Examples of the resin include epoxy resin, silicone resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyamide such as polyimide, polyamideimide, polyetherimide, polyester such as polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, etc. These may be used alone or in combination of two or more.

[0064] The resin composition can be obtained, for example, by mixing raw material components in a predetermined ratio using a blender, a Henschel mixer, or the like. The obtained mixture may be kneaded, as necessary, using a heated roll, a kneader, a single-screw or twin-screw extruder, or the like, cooled, and then subjected to pulverization, etc. The resin composition of this embodiment can be used for various purposes, but is preferably used, for example, as a high-frequency material.

[0065] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0066] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.

[0067]

[0068] <Raw Materials> The information on the raw materials shown in Table 1 is as follows: Spherical silica powder 1 (spherical silica powder B): Spherical silica powder 4 subjected to the following heat treatment (specific surface area: 2.5 m ２ / g, D50: 6 μm, dielectric loss tangent at 1 GHz: 5 × 10 －４ Spherical silica powder 2 (spherical silica powder A): Spherical silica powder 5 was subjected to the following heat treatment (specific surface area: 5.5 m ２ / g, D50: 2 μm, dielectric loss tangent at 1 GHz: 12 × 10 －４ Spherical silica powder 3: Silica powder (FB-40R, manufactured by Denka Co., Ltd., specific surface area: 0.5 m) ２ / g, D50: 46 μm, dielectric loss tangent at 1 GHz: 2 × 10 －４ Spherical silica powder 4 (spherical silica powder B): Silica powder (FB-5D, manufactured by Denka Co., Ltd., specific surface area: 2.4 m ２ / g, D50: 6 μm, dielectric loss tangent at 1 GHz: 30 × 10 －４ Spherical silica powder 5 (spherical silica powder A): Silica powder (SFP-130MC, manufactured by Denka Co., Ltd., specific surface area: 5.7 m ２ / g, D50: 2 μm, dielectric loss tangent at 1 GHz: 57 × 10 －４ ) (Heat Treatment) The raw material spherical silica was packed into a mullite container and subjected to heat treatment in an air atmosphere at 930°C for 4 hours. After the heat treatment, spherical silica 1 and 2 were stored in aluminum packs (PET / AL / PE laminated bags) with a moisture permeability of 0.1 (g / m2·24h) or less under condition B of JIS Z 0208-1976 (temperature 40°C, relative humidity 90%), and were taken out and used immediately before use.

[0069] Spherical alumina powder 1: Alumina powder (DAW-45, manufactured by Denka Co., Ltd., specific surface area: 0.6 m ２ / g, D50: 45 μm) Spherical alumina powder 2: Alumina powder (DAW-05, manufactured by Denka Co., Ltd., specific surface area: 0.4 m ２ / g, D50: 6 μm) Spherical alumina powder 3: Alumina powder (ASFP-05S, manufactured by Denka Co., Ltd., specific surface area: 8 m ２ / g, D50: 0.6 μm) Spherical alumina powder 4: Alumina powder (DAM-20, manufactured by Denka Co., Ltd., specific surface area: 0.2 m ２ / g, D50: 25μm)

[0070] <Production of inorganic powder> Inorganic powders were produced by mixing the raw material powders according to the types and blending ratios of the spherical silica powder and spherical alumina powder shown in Table 1. The raw material spherical silica and spherical alumina powders and the resulting inorganic powders were evaluated for the following items.

[0071] <Particle size distribution> The volume frequency particle size distribution and particle diameter frequency distribution of the powder were determined by a wet laser diffraction scattering method using a particle size distribution measuring device (MT-3300EX, manufactured by Nikkiso Co., Ltd.). In this case, water was used as the solvent, and as a pretreatment, the powder was dispersed in the solvent using a homogenizer at an output of 200 W for 1 minute, and the dispersion obtained was used as the measurement subject. Based on the obtained volume frequency particle size distribution, the particle diameter (D Ｘ ) was calculated.

[0072] Furthermore, based on the obtained particle size frequency distribution, the following were determined: (i) the presence or absence of a maximum peak in the range of 20 μm to 50 μm, (ii) the frequency of the maximum peak, (iii) the average frequency of the five particle size classes when divided into five particle size classes of more than 1.5 μm and not more than 2 μm, more than 2 μm and not more than 3 μm, more than 3 μm and not more than 4 μm, more than 4 μm and not more than 6 μm, and more than 6 μm and not more than 8 μm, (iv) the difference between the maximum and average frequencies of the five particle size classes, (v) the frequency in the particle size class of 1 μm or less, and (vi) the frequency in the particle size class of more than 128 μm and not more than 192 μm. The results are shown in Table 2.

[0073]

[0074] <Specific Surface Area> The specific surface area of ​​the powder was measured by the BET single-point method using nitrogen gas adsorption. Specifically, using a specific surface area measuring device (manufactured by Yuasa Ionics, device name: MONOSORB) using nitrogen gas as the adsorption gas and helium gas as the carrier gas, 1 g of the sample was dried and degassed at 300°C for 30 minutes before measurement.

[0075] <Method for Measuring Thermal Conductivity> 70% by volume of powder, 16.4% by volume of liquid silicone resin (DOWSIL SE1885A), and 13.6% by volume of liquid silicone resin (DOWSIL SE1885B) were mixed using a planetary / revolutionary mixer. The resulting mixture was processed into a 3 mm thick sheet and heat-treated in a dryer at 120°C for 2 hours to obtain a sample. The resulting sample was cut into a length of 20 mm, a width of 20 mm, and a thickness of 3 mm. The upper heater, sample (cut-out sample), heat flux meter, lower heater, and heat sink were stacked in this order, and measurements were performed using the heat flow meter method in accordance with ASTM E 1530.

[0076] <Dielectric loss tangent> The dielectric loss tangent of the powder was measured using a perturbation type cavity resonator measurement system (manufactured by Keyence Corporation) at a room temperature of 25°C and a frequency of 1.0 GHz. At this time, the powder to be measured had a diameter of 8.2 mm, a thickness of 30 mmt, and a capacity of 1584 mm. ３ Pour the mixture into the Teflon tube while tapping, and ３The powder was filled until the temperature reached 100°C and sealed with tape. The thermal conductivity of the inorganic powder thus obtained is plotted on the vertical axis and the dielectric loss tangent at 1 GHz on the horizontal axis in Figure 1. In Figure 1, the dielectric loss tangent at 1 GHz is expressed as D x 10 －４ When the thermal conductivity is T (W / m·K), a straight line satisfying T=0.14D+1.03 is plotted.

[0077] <Thixotropy Index> The thixotropy index of the resin varnish for evaluation containing inorganic powder was measured as follows. First, the inorganic powder was mixed with bisphenol F-type epoxy (Epikote 807) that was liquid at 25°C so that the content was 75% by mass, to obtain the above-mentioned resin varnish for evaluation. Next, the viscosity (η １ ), and viscosity (η １００ Using the measured viscosity, the formula: η １００ / η １ The above thixotropy index was calculated based on the above.

[0078] [Overall Evaluation] The inorganic powder of Comparative Example 1, with a spherical alumina powder content of 100% by volume, could be designed to have a high thermal conductivity, but the dielectric loss tangent increased. On the other hand, the inorganic powder of Comparative Example 3, with a spherical silica powder content of 100% by volume, could be designed to have a low dielectric loss tangent, but the thermal conductivity decreased. Thus, for inorganic powders containing spherical alumina powder and spherical silica powder, the thermal conductivity and dielectric loss tangent show a trade-off curve, and it was confirmed that even when the blending ratio was changed as in Comparative Examples 1 to 6, the distribution remained below the trade-off curve. In contrast, it was confirmed that the inorganic powders of Examples 1 to 6, which appropriately combined spherical alumina powders 1 and 4, which have high thermal conductivity and relatively large particle diameters, with spherical silica powders 1 and 2, which have low dielectric loss tangents and relatively small particle diameters due to heat treatment, could improve this trade-off characteristic.

[0079] This application claims priority based on Japanese Patent Application No. 2023-203008, filed November 30, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. Spherical alumina powder with an average particle size of 20 μm to 50 μm and a dielectric loss tangent of 2.0 × 10 at 1 GHz. －３ and a spherical silica powder having an average particle diameter of 0.5 μm or more and 10 μm or less.

2. An inorganic powder according to claim 1, wherein the spherical silica powder comprises at least one of spherical silica powder A having an average particle diameter of 0.5 μm or more and 4.0 μm or less, and spherical silica powder B having an average particle diameter of 4.0 μm or more and 10 μm or less.

3. The inorganic powder according to claim 1 or 2, wherein the spherical silica powder has a specific surface area of ​​4.0 m ２ / g over 10.0m ２ / g or less, and a spherical silica powder A having a specific surface area of ​​0.5 m ２ / g or more 4.0m ２ / g or less.

4. An inorganic powder as described in claim 2, wherein the volumetric content ratio of spherical silica powder A and spherical silica powder B in the spherical silica powder is 30 volume%:70 volume% or more and 70 volume%:30 volume% or less.

5. An inorganic powder according to claim 1 or 2, wherein the volumetric content ratio of the spherical alumina powder and the spherical silica powder is 25 volume%:75 volume% or more and 60 volume%:40 volume% or less.

6. An inorganic powder according to claim 1 or 2, wherein the particle size frequency distribution of said inorganic powder has a maximum peak in the range of 20 μm or more and 50 μm or less.

7. The inorganic powder according to claim 6, wherein the frequency of the maximum peak is 10% or more.

8. An inorganic powder according to claim 1 or 2, wherein when the particle size frequency distribution of the inorganic powder is divided into five particle size classes, namely, from more than 1.5 μm to 2 μm, from more than 2 μm to 3 μm, from more than 3 μm to 4 μm, from more than 4 μm to 6 μm, and from more than 6 μm to 8 μm, the average frequency of the five particle size classes is 2% or more and 10% or less.

9. The inorganic powder according to claim 8, wherein the difference between the maximum value among the frequencies of the five particle size classes and the average value is 3% or less.

10. The inorganic powder according to claim 1 or 2, wherein the thixotropy index of a resin varnish for evaluation containing said inorganic powder, measured according to the following procedure, is 0.01 or more and 0.10 or less. (Procedure) The inorganic powder is mixed with bisphenol F type epoxy (Epicoat 807) that is liquid at 25°C so that the content is 75 mass%, to obtain the above-mentioned resin varnish for evaluation. Next, the viscosity (η １ ), and viscosity (η １００ Using the measured viscosity, the formula: η １ / １００ The above thixotropy index is calculated based on the above.

11. Spherical alumina powder with an average particle size of 20 μm or more and 50 μm or less and a dielectric loss tangent of 2.0 × 10 at 1 GHz －３ A method for producing an inorganic powder, comprising: a mixing step of mixing a spherical silica powder having an average particle diameter of 4 μm or more and 10 μm or less with the above.

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