Inorganic powder and method for producing inorganic powder

Abstract

To provide an inorganic powder with excellent thermal conductivity and dielectric loss tangent.SOLUTION: An inorganic powder includes spherical alumina powder having an average particle size of from 20 μm or more to 50 μm or less, 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 or more to 10 μm or less.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when using the spherical alumina powder described in Patent Document 1 above, the thermal conductivity of the inorganic powder can be improved, but the dielectric tangent may be reduced. On the other hand, when using a low-dielectric treated spherical silica powder of Patent Document 2 above, the dielectric tangent of the inorganic powder can be reduced, but the thermal conductivity may be decreased. That is, as a result of the study by the present inventors, it has been found that in inorganic powder containing spherical alumina powder and / or spherical silica powder, the thermal conductivity and the dielectric tangent exhibit a trade-off characteristic.

Means for Solving the Problems

[0005] As a result of further studies by the present inventors, by appropriately selecting the particle sizes of the spherical alumina powder and the spherical silica powder, and using an inorganic powder in which the gaps between the large-particle-sized spherical alumina powders having high thermal conductivity are filled with small-particle-sized spherical silica powders having low dielectric loss tangent, it has been found that both the thermal conductivity and the dielectric loss tangent, which are trade-off characteristics, can be improved, and the present invention has been completed.

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

[0007] 1. Spherical alumina powder having an average particle diameter of 20 μm or more and 50 μm or less, and Spherical silica powder having a dielectric loss tangent of 2.0×10 -3 or less at 1 GHz and an average particle diameter of 0.5 μm or more and 10 μm or less, an inorganic powder. 2. The inorganic powder according to 1., wherein the spherical silica powder contains 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 more than 4.0 μm and 10 μm or less, an inorganic powder. 3. The inorganic powder according to 1. or 2., wherein the spherical silica powder contains at least one of spherical silica powder A having a specific surface area of more than 4.0 m 2 / g and 10.0 m 2 / g or less and spherical silica powder B having a specific surface area of 0.5 m 2 / g or more and 4.0 m 2 / g or less, an inorganic powder. 4. The inorganic powder according to 2. or 3., wherein in the spherical silica powder, the volume-based content ratio of the spherical silica powder A and the spherical silica powder B is 30 vol%:70 vol% or more and 70 vol%:30 vol% or less, an inorganic powder. 5. The inorganic powder according to any one of 1. to 4., wherein the volume-based content ratio of the spherical alumina powder and the spherical silica powder is 25 vol%:75 vol% or more and 60 vol%:40 vol% or less, an inorganic powder. 6. An inorganic powder according to any one of 1. to 5., In the particle size frequency distribution of the inorganic powder, an inorganic powder having a maximum peak in the range of 20 μm or more and 50 μm or less. 7. The inorganic powder according to 6., The inorganic powder, wherein the frequency of the maximum peak is 10% or more. 8. An inorganic powder according to any one of 1. to 7., In the particle size frequency distribution of the inorganic powder, when divided into five particle size classes of more than 1.5 μm and 2 μm or less, more than 2 μm and 3 μm or less, more than 3 μm and 4 μm or less, more than 4 μm and 6 μm or less, and more than 6 μm and 8 μm or less, the average value of the frequencies of the five particle size classes is 2% or more and 10% or less. An inorganic powder. 9. The inorganic powder according to 8., The inorganic powder, wherein the difference between the maximum value and the average value of the frequencies of the five particle size classes is 3% or less. 10. An inorganic powder according to any one of 1. to 9., The inorganic powder, wherein the thixotropy index of the resin varnish for evaluation containing the 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) in a liquid state at 25 ° C so that the content is 75% by mass to obtain the above resin varnish for evaluation. Subsequently, in the obtained resin varnish for evaluation, using a rheometer, the viscosity (η 1 ) when measured at a shear rate of 1 [1 / s] at 25 ° C, and the viscosity (η 100 ) when measured at a shear rate of 100 [1 / s] are measured. Using the measured viscosities, the above thixotropy index is calculated based on the formula: η 1 / η 100 . 11. Spherical alumina powder with an average particle size of 20 μm or more and 50 μm or less, and The dielectric loss tangent at 1 GHz is 2.0×10 -3 or less, spherical silica powder with an average particle size of 4 μm or more and 10 μm or less, and A method for producing an inorganic powder, including a mixing step of mixing

Advantages of the Invention

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

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and the description will be omitted as appropriate. Also, the drawings are schematic views and do not match the actual dimensional ratios.

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

[0012] The inorganic powder of this embodiment is spherical alumina powder with an average particle diameter of 20 μm or more and 50 μm or less, and the dielectric tangent at 1 GHz is 2.0×10 -3 or less, and spherical silica powder with an average particle diameter 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 spherical alumina powder with a large particle diameter having high thermal conductivity and spherical silica powder with a small particle diameter having a low dielectric tangent, both the thermal conductivity and the dielectric tangent can be improved. Although the detailed mechanism is not clear, it is presumed that in the inorganic powder, by forming an appropriate filling structure in which the spherical silica powder fills the gaps between the spherical alumina powders, both the thermal conductivity and the dielectric tangent, which are trade-off characteristics, can be improved.

[0014] According to the findings of the present inventors, the larger the particle size of the spherical alumina powder, the higher the thermal conductivity can be. From the perspective of high thermal conductivity, in order to fill the gaps between the spherical alumina powders with large particle sizes, it is a common idea to select spherical alumina powders with small particle sizes. However, since the specific surface area increases as the particle size decreases, the dielectric loss tangent will increase. Therefore, from the perspective of low dielectric loss tangent, it is preferable to select spherical silica powders with small particle sizes. Furthermore, from the perspective of improving the trade-off characteristics between thermal conductivity and dielectric loss tangent, as the spherical silica powder with small particle sizes, it is preferable to use a spherical silica powder with low dielectric loss tangent treatment in which the amounts of physically adsorbed water, hydrogen-bonded silanol groups, and isolated silanol groups on the surface are reduced by heat treatment or the like. In addition, when this spherical alumina powder with small particle sizes is heat-treated in the same manner as the spherical silica powder, it becomes a large lump in the furnace and cannot be used as a powder with low dielectric treatment.

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

[0016] <Spherical alumina powder> The spherical alumina powder may contain alumina (Al 2 0 3 ) as the main component. The main component means that, in the total amount of the alumina powder, in terms of mass, alumina (Al 2 0 3 ) is contained, for example, in an amount of 50% or more, preferably 80% or more, more preferably 90% or more. The spherical alumina powder preferably has a high purity, but the presence of impurities inevitably mixed in the raw materials and the manufacturing process is tolerated.

[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, 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, more preferably 40 μm or less.

[0018] In this specification, the average particle diameter means the particle diameter (so-called D50) at the point where the cumulative volume from the small particle side becomes 50% in the volume frequency particle size distribution measured by the wet laser diffraction scattering method. For the measurement sample, water is used as the solvent. As a pretreatment, a sample obtained by dispersing the powder by applying an output of 200 W using a homogenizer for 1 minute is used. The volume frequency particle size distribution and the particle diameter frequency distribution can be measured by "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. For example, it may be 0.1 m 2 / g or more. The upper limit of the specific surface area of the spherical alumina powder is, for example, 0.5 m 2 / g or less, preferably 0.35 m 2 / g or less.

[0020] In this specification, the specific surface area can be measured by the BET one-point method by nitrogen gas adsorption. Specifically, using a specific surface area measuring device (for example, manufactured by Yuasa Ionics, device name: MONOSORB), nitrogen gas as the adsorption gas and helium gas as the carrier gas, after drying and degassing 1 g of the sample under the conditions of 300 °C for 30 minutes, the measurement can be performed.

[0021] The upper limit of the α-crystalline phase of the spherical alumina powder is 90% or less, preferably 85% or less, more preferably 80% or less. Thereby, the fluidity when used in a resin molding material can be improved, and the generation of burrs can be suppressed. Also, the lower limit of the above α-crystalline phase is, for example, 40% or more, preferably 45% or more, more preferably 50% or more. Thereby, the thermal conductivity of the resin composition can be improved.

[0022] The content rate of the α-crystalline phase in the spherical alumina powder is measured by the following method. Using NIST-676a (α-alumina), which is an intensity standard substance for X-ray diffraction (XRD), and θ·δ·γ-alumina, after weighing each alumina to a total of 2 g, it is mixed for 15 minutes using a pulverizer to prepare samples for calibration curve creation. Then, for each sample, using an enclosed tube type X-ray diffractometer (D8 ADVANCE (trade name) manufactured by Bruker), the integrated intensity (Cps×deg) is calculated under the following measurement conditions to create a calibration curve. For the measurement of the content rate of the α crystal phase, three diffraction peaks in α-alumina (2θ = 25.6° (012), 35.2° (104), and 2θ = 43.4° (113)) are used. (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° · Solar slit: 2.5 deg Subsequently, using spherical alumina powder, the diffraction peak area (Y) of the (113) plane derived from the α crystal phase of alumina is measured, and using the above calibration curve, the content rate of the α crystal phase is calculated. Note that for the measurement, diffraction peaks detected at 2θ = 10° or more and 70° or less are used. Also, using spherical alumina powder, the diffraction peak area (Y) of the (113) plane derived from the α crystal phase of alumina is measured, and using the above calibration curve, the content rate of the α crystal phase is calculated. Note that for the measurement, diffraction peaks detected at 2θ = 10° or more and 70° or less are used.

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

[0024] The spherical alumina powder of this embodiment has a sphericity of S when the particle size measured using a wet flow type image analyzer is 5 μm or more and less than 10 μm 1 , a sphericity of S when the particle size is 10 μm or more and less than 20 μm 2 , a sphericity of S when the particle size is 20 μm or more and less than 30 μm 3 , a sphericity of S when the particle size is 30 μm or more and less than 45 μm 4 , a sphericity of S when the particle size is 45 μm or more 5 . When this is the case, at least two or more of S 1 , S 2 , S 4 , and S 5 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 may contain silica (SiO 2 ) as the main component. The main component means that, in the total amount of the silica powder, silica (SiO 2 ) is contained, for example, at 80% or more, preferably 90% or more, and more preferably 95% or more in terms of mass conversion. The spherical silica powder preferably has a high purity, but the presence of impurities inevitably mixed in during the raw material and manufacturing processes is tolerated.

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

[0027] In this specification, the dielectric loss tangent of the powder at 1 GHz can be measured by the cavity resonator perturbation method using a measurement sample filled with the powder 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, 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 or less, more preferably 5.0 μm or less.

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

[0030] The amorphous ratio of the spherical silica powder is measured from the intensity ratio of specific diffraction peaks by performing X-ray diffraction analysis in the range of 2θ of CuKα ray from 26° to 27.5° using a powder X-ray diffractometer (for example, the product name "Model MiniFlex" manufactured by Rigaku Corporation). In the case of silica powder, the main peak of crystalline silica exists at 26.7°, but there is no peak in amorphous silica. When amorphous silica and crystalline silica are mixed, a peak height of 26.7° corresponding to the ratio of crystalline silica is obtained. Then, from the ratio of the X-ray intensity of the sample to the X-ray intensity of the crystalline silica standard sample, the mixing ratio of crystalline silica (X-ray diffraction intensity of the sample / X-ray diffraction intensity of crystalline silica) is calculated, and the amorphous ratio (%) can be calculated from the formula, amorphous ratio (%) = (1 - mixing ratio of crystalline silica) × 100.

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

[0032] The average sphericity of the silica powder can be measured using a powder image analyzer (FPIA-3000). Specifically, after dispersing the sample in pure water, the liquid is flowed into a planar extensional flow cell, and 100 or more amorphous silica powders moving in the cell are recorded as images with an objective lens, and the average circularity is calculated from this recorded image and the following formula (1). In formula (1), HD represents the equivalent circle diameter and is obtained 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 silica powders 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 is used to obtain the average sphericity.

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

[0034] The spherical silica powder may contain 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 a specific surface area of more than 4.0 μm and 10 μm or less. By including spherical silica powder A with a small particle diameter and spherical silica powder B with a small particle diameter in the inorganic powder, it becomes possible to further increase the packing density in the spherical alumina powder.

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

[0036] The lower limit of the average particle diameter of 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 diameter of spherical silica powder B is, for example, 10 μm or less, preferably 9.0 or less, more preferably 8.0 or less.

[0037] Also, the spherical silica powder has a specific surface area of 4.0 m2 / g is greater than 10.0 m 2 Spherical silica powder A with a specific surface area of less than 0.5 m 2 / g or more and 4.0 m 2 / g or less, and may contain at least one of spherical silica powder B.

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

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

[0040] In the spherical silica powder, the volume conversion content ratio of spherical silica powder A and spherical silica powder B is, for example, 30% by volume: 70% by volume to 70% by volume: 30% by volume, preferably 35% by volume: 65% by volume to 65% by volume: 35% by volume, more preferably 40% by volume: 60% by volume to 60% by volume: 40% by volume.

[0041] In the inorganic powder, the volume conversion content ratio of spherical alumina powder and spherical silica powder is, for example, 25% by volume: 75% by volume to 75% by volume: 25% by volume, preferably 35% by volume: 65% by volume to 65% by volume: 35% by volume, more preferably 40% by volume: 60% by volume to 60% by volume: 40% by volume.

[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, more preferably 35 μm or more and 40 μm or less.

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

[0044] In the particle size frequency distribution of the inorganic powder, it is assumed that it is divided into five particle size classes of more than 1.5 μm and 2 μm or less, more than 2 μm and 3 μm or less, more than 3 μm and 4 μm or less, more than 4 μm and 6 μm or less, and more than 6 μm and 8 μm or less. At this time, the lower limit of the average value of the frequencies of the five particle size classes is, for example, 2% or more, preferably 3% or more, more preferably 4% or more, still more preferably 5.5% or more. The upper limit of the average value of the frequencies of the five particle size classes is, for example, 10% or less, preferably 9% or less, 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, 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, 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 exceeding 128 μm and not exceeding 192 μm is, for example, 2% or less, preferably 1.0% or less, more preferably 0.8% 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.

[0048] The inorganic powder of this embodiment may be configured such that the thixotropic index of the resin varnish for evaluating the inorganic powder, which is 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, more preferably 0.02 or more and 0.07 or less.

[0049] By setting the thixotropic index to be equal to or less than the above upper limit, the moldability of the resin composition can be improved. By setting the thixotropic index to be equal to or greater than the above lower limit, the burr characteristics of the resin composition can be improved.

[0050] The procedure for measuring the viscosity and thixotropic index of the resin varnish for evaluation will be described. First, the inorganic powder is mixed with bisphenol F type epoxy (Epicoat 807) which is liquid at 25°C so that the content becomes 75% by mass to obtain a resin varnish for evaluation. Subsequently, for the obtained resin varnish for evaluation, the viscosity (η 1 ) when measured at a shear rate of 1 [1 / s] and the viscosity (η 100 ) when measured at a shear rate of 100 [1 / s] are measured using a rheometer at 25°C. After that, using the obtained viscosities, the thixotropic index is calculated from the formula: η 100 / η 1

[0051] In this embodiment, for example, by appropriately selecting the types and blending amounts of the respective components contained in the inorganic powder, the preparation method of the inorganic powder, etc., it is possible to control the thermal conductivity, dielectric tangent, or thixotropic index of the evaluation resin varnish in the inorganic powder. Among these, for example, combining and using in combination a spherical alumina powder with a large particle diameter having a high thermal conductivity and a spherical silica powder with a small particle diameter having a low dielectric tangent, appropriately adjusting their content ratios, etc. are cited as elements for setting the thermal conductivity, dielectric tangent, or thixotropic index of the evaluation resin varnish in the organic powder within a desired numerical range.

[0052] The manufacturing method of the inorganic powder of this embodiment will be described. An example of the manufacturing method of the inorganic powder of this embodiment is a spherical alumina powder having an average particle diameter of 20 μm or more and 50 μm or less, and a dielectric tangent at 1 GHz of 2.0×10 -3 as follows, and includes a mixing step of mixing with a spherical silica powder having an average particle diameter of 4 μm or more and 10 μm or less. That is, by producing the above spherical alumina powder and the above spherical silica powder respectively and mixing them, an inorganic powder is obtained.

[0053] <Manufacturing method of spherical alumina powder> The spherical alumina powder is produced, for example, by supplying alumina raw material powder into a high-temperature flame formed by a combustion reaction of a combustible gas and an oxidizing gas, and melting and spheroidizing it 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 as necessary.

[0054] As the alumina raw material powder which is the raw material powder, for example, an alumina powder having an average particle diameter of about 20 to 50 μm may be used. A plurality of raw material powders having different particle diameters may be used for the alumina raw material powder. The supply of the aluminum hydroxide powder into the high-temperature flame may be either dry or wet slurried with water or the like.

[0055] <Manufacturing method of spherical silica powder> As an example of the manufacturing method of the present embodiment, for example, alumina raw material powder is supplied into a high-temperature flame formed by a combustion reaction of a combustible gas and an oxidizing gas, and is melted and spheroidized at a temperature equal to or higher than its melting point for production. Further, if necessary, silica powder can be obtained by classification treatment. In addition, for the classification treatment, industrially, classification by a classifier such as a sieve or a precision air classifier is desirable, and the classification operation is preferably a dry method. By dry-classifying the spherical silica powder, aggregation of the silica powder can be suppressed as compared with the case where raw material silica powder manufactured by a wet method and / or wet classification is used, and handling properties and the like can be improved. Note that it is desirable to store the obtained silica powder in a moisture-proof bag.

[0056] In addition, the classified silica powder may be heat-treated as one of the post-treatments. The heat treatment is performed at a temperature of 500 to 1100 °C, and for a predetermined time (for example, 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) for a predetermined time (for example, about 2 to 35 hours), and is treated in a hot air or an electric furnace. If the heating temperature is 500 to 1100 °C, since the specific surface area and the average particle diameter do not change before and after heating, it is desirable to perform the classification step before heating, adjust to the desired specific surface area and average particle diameter, and then perform the heat treatment. After the heat treatment, after natural cooling in an electric furnace, the silica powder is recovered at a temperature of 110 °C to 300 °C, further cooled to 25 °C in an environment with a humidity of 40% RH or less, stored at 15 to 25 °C, and recovered and stored in a moisture-proof aluminum bag.

[0057] As a method for storing the silica powder, it is preferable to store it using a moisture-proof bag having a moisture permeability of 0.1 (g / m 2 ·24h) or less under the conditions B (temperature 40 °C - relative humidity 90%) of JIS Z 0208-1976, for example, a moisture-proof aluminum bag or a PET / AL / PE laminate bag.

[0058] The composition obtained by blending the inorganic powder of the present invention with a resin composition can be suitably used as a resin molding material.

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

[0060] In addition to the inorganic powder of the present invention, the resin composition contains a resin, known resin additives, and the like. In the resin composition, the inorganic powder may be used alone or in combination with other fillers. The resin composition may contain 10 to 99% by mass of the inorganic powder, or may contain 10 to 99% by mass of a mixed inorganic powder containing the inorganic powder and other fillers. Further, in the mixed inorganic powder, the content of other fillers may be, for example, 1 to 20% by mass, 3 to 15% by mass with respect to 100% by mass of the inorganic powder.

[0061] In this specification, "~" represents including the upper limit value and the lower limit value unless otherwise specified.

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

[0063] Examples of the above resins include polyamides such as epoxy resins, silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyimides, polyamideimides, and polyetherimides; polyesters such as polybutylene terephthalate and 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, and the like. 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 quantitative ratio using a blender, a Henschel mixer, or the like. The obtained mixture may be kneaded using a heating roll, a kneader, a single-screw or twin-screw extruder, or the like, and after cooling, it may be pulverized or the like. The resin composition of this embodiment can be used for various applications, and for example, it is preferably used as a material for high frequencies.

[0065] As described above, the embodiments of the present invention have been described, but these are examples of the present invention, and various configurations other than the above can be adopted. Further, the present invention is not limited to the above-described embodiments, and modifications, improvements, etc. within the range that can achieve the object of the present invention are included in the present invention.

Examples

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

[0067]

Table 1

[0068] <Raw materials> The information on the raw materials shown in Table 1 is shown below. · Spherical silica powder 1 (spherical silica powder B): obtained by subjecting spherical silica powder 4 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 ) was used. ) was used. · Spherical silica powder 2 (spherical silica powder A): obtained by subjecting spherical silica powder 5 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 ) was used. · 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 spherical silica was filled into a mullite container and heat-treated at 930 °C for 4 hours in an air atmosphere. Note that spherical silicas 1 and 2 were stored using an aluminum pack (PET / AL / PE laminate bag) with a moisture permeability of 0.1 (g / m2·24 h) or less under the conditions of JIS Z 0208-1976, condition B (temperature 40 °C - relative humidity 90%) after the above heat treatment, and 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: 25 μm)

[0070] <Manufacture of inorganic powder> An inorganic powder was manufactured by mixing each raw material powder according to the types and blending ratios of the spherical silica powder and spherical alumina powder shown in Table 1. The following items were evaluated for each of the raw spherical silica, spherical alumina, and the obtained inorganic powder.

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

[0072] Also, based on the obtained particle size frequency distribution, (i) The presence or absence of a maximum peak in the range of 20 μm or more and 50 μm or less, (ii) The frequency of the maximum peak, (iii) When divided into five particle size classes of more than 1.5 μm and 2 μm or less, more than 2 μm and 3 μm or less, more than 3 μm and 4 μm or less, more than 4 μm and 6 μm or less, and more than 6 μm and 8 μm or less, the average value of the frequencies of the five particle size classes, (iv) The difference between the maximum value and the average value among the 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 192 μm or less were determined. The results are shown in Table 2.

[0073]

Table 2

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

[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 mixer. The resulting mixture was processed into a sheet with a thickness of 3 mm and heat-treated at 120 °C for 2 hours in a dryer to obtain a sample. The obtained sample was cut into a size of length: 20 mm × width: 20 mm × thickness 3 mmt, and was measured by the heat flux meter method in accordance with ASTM E 1530 in a state where it was laminated in the order of an upper heater, a sample (the sample after cutting), a heat flux meter, a lower heater, and a heat sink.

[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) under the conditions of room temperature 25 °C and frequency 1.0 GHz. At this time, the powder to be measured was poured into a Teflon tube with a diameter of φ8.2 mm, a thickness of 30 mmt, and a volume of 1584 mm 3 while tapping, and filled until it reached 1.15 cm 3 and sealed with tape. Note that Fig. 1 shows a plot with the thermal conductivity of the obtained inorganic powder on the vertical axis and the dielectric loss tangent at 1 GHz on the horizontal axis. In Fig. 1, when the dielectric loss tangent at 1 GHz is denoted as D×10 -4 and the thermal conductivity is denoted as T (W / m·K), a straight line satisfying T = 0.14D + 1.03 is drawn.

[0077] <Thixotropy Index> The thixotropy index of the resin varnish for evaluation containing inorganic powder was measured as follows. First, inorganic powder was mixed with bisphenol F type epoxy (Epicoat 807) which was liquid at 25 °C so that the content was 75% by mass to obtain the above-mentioned resin varnish for evaluation. Subsequently, in the obtained resin varnish for evaluation, the viscosity (η 1 ) when measured at a shear rate of 1 [1 / s] at 25 °C using a rheometer, and the viscosity (η100 ) was measured. Using the measured viscosity, the formula: η 100 / η 1 Based on the above, the thixotropy index was calculated.

[0078] [Comprehensive Evaluation] The inorganic powder of Comparative Example 1 has a spherical alumina powder content of 100% by volume, and its thermal conductivity can be designed to be high. On the contrary, its dielectric loss tangent increases. On the other hand, the inorganic powder of Comparative Example 3 has a spherical silica powder content of 100% by volume, and its dielectric loss tangent can be designed to be low. On the contrary, it shows a result of reduced thermal conductivity. Thus, in the inorganic powder containing spherical alumina powder and spherical silica powder, the thermal conductivity and the dielectric loss tangent show a trade-off curve. It was confirmed that even if the blending ratio is changed as in Comparative Examples 1 to 6, it is distributed below the trade-off curve. On the contrary, in the inorganic powders of Examples 1 to 6, in which spherical alumina powder 1,4 with high thermal conductivity and relatively large particle size and spherical silica powder 1,2 with low dielectric loss tangent and relatively small particle size due to heat treatment were appropriately combined, it was confirmed that such trade-off characteristics can be improved.

Claims

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

2. The inorganic powder according to Claim 1, wherein the spherical silica powder includes at least one of spherical silica powder A with an average particle diameter of 0.5 μm or more and 4.0 μm or less, and spherical silica powder B with an average particle diameter of more than 4.0 μm and 10 μm or less, an inorganic powder.

3. The inorganic powder according to Claim 1 or 2, wherein The spherical silica powder has a specific surface area of more than 4.0 m ２ / g and 10.0 m ２ / g or less of spherical silica powder A, and a specific surface area of 0.5 m ２ / g or more and 4.0 m ２ / g or less of at least one of spherical silica powder B, an inorganic powder.

4. The inorganic powder according to Claim 2, wherein in the spherical silica powder, the volume conversion content ratio of the spherical silica powder A and the spherical silica powder B is 30% by volume: 70% by volume or more and 70% by volume: 30% by volume or less, an inorganic powder.

5. The inorganic powder according to Claim 1 or 2, wherein the volume conversion content ratio of the spherical alumina powder and the spherical silica powder is 25% by volume: 75% by volume or more and 60% by volume: 40% by volume or less, an inorganic powder.

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

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

8. The inorganic powder according to Claim 1 or 2, wherein in the particle size frequency distribution of the inorganic powder, when divided into five particle size classes of more than 1.5 μm and 2 μm or less, more than 2 μm and 3 μm or less, more than 3 μm and 4 μm or less, more than 4 μm and 6 μm or less, and more than 6 μm and 8 μm or less, the average value of the frequencies of the five particle size classes is 2% or more and 10% or less, an inorganic powder.

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

10. The inorganic powder according to Claim 1 or 2, wherein the thixotropic index of the resin varnish for evaluation containing the inorganic powder, measured according to the following procedure, is 0.01 or more and 0.10 or less, an inorganic powder. (Procedure) Mix the inorganic powder with bisphenol F type epoxy (Epicoat 807) in a liquid state at 25 °C so that the content is 75% by mass to obtain the above-mentioned resin varnish for evaluation. Subsequently, in the obtained resin varnish for evaluation, using a rheometer, the viscosity (η １ ) measured at a shear rate of 1 [1 / s] at 25°C, and the viscosity (η １００ ) measured at a shear rate of 100 [1 / s] are measured. Using the measured viscosities, the thixotropy index is calculated based on the formula: η １ / η １００ .

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

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