Inorganic powder

Abstract

To provide an inorganic powder with excellent heat dissipation and dielectric loss.SOLUTION: An inorganic powder contains spherical alumina powder and spherical silica powder. When the dielectric loss tangent at 1 GHz is defined as D×10-4 and the thermal conductivity is defined as T (W / m K) in the inorganic powder, D and T satisfy T≥0.14D+1.03.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to 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 decrease. On the other hand, when using a spherical silica powder obtained by subjecting the spherical silica powder of Patent Document 2 above to a low dielectric treatment, the dielectric tangent of the inorganic powder can be reduced, but the thermal conductivity may decrease. That is, as a result of the study by the present inventor, it has been found that in an 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 study by the present inventor, by appropriately selecting the particle sizes of the spherical alumina powder and the spherical silica powder, the trade-off characteristic between the thermal conductivity and the dielectric tangent can be improved. Thus, it has been found that the heat dissipation property of the inorganic powder in practical use can be enhanced while reducing the dielectric loss, and the present invention has been completed.

[0006] According to one aspect of the present invention, the following inorganic powders are provided.

[0007] 1. An inorganic powder containing spherical alumina powder and spherical silica powder, wherein the dielectric tangent at 1 GHz in the inorganic powder measured according to the following procedure A is D×10 -4 and when the thermal conductivity in the inorganic powder measured according to the following procedure B is T (W / m·K), an inorganic powder in which D and T satisfy T≧0.14D+1.03. (Procedure A) Using a measurement sample filled with the inorganic powder in a Teflon tube, measure the dielectric tangent at 1 GHz above by the cavity resonator perturbation method. (Procedure B) Using a mixture of 70% by volume of the inorganic powder and 30% by volume of a liquid silicone resin, for a sheet-like sample with a thickness of 3 mm obtained by drying treatment, measure the above thermal conductivity by the heat flow meter method in accordance with ASTM E 1530. 2. The inorganic powder according to 1., wherein D and T satisfy 0<D≦17 and 2.2≦T≦8.0. 3. The inorganic powder according to 1. or 2., wherein the inorganic powder has a maximum peak in the range of 20 μm or more and 50 μm or less in the particle size frequency distribution of the inorganic powder. 4. The inorganic powder according to 3., wherein the frequency of the maximum peak is 10% or more. 5. The inorganic powder according to any one of 1. to 4., wherein when the particle size frequency distribution of the inorganic powder 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, the average value of the frequencies of the five particle size classes is 2% or more and 10% or less. 6. The inorganic powder according to 5., wherein the difference between the maximum value and the average value among the frequencies of the five particle size classes is 3% or less. 7. The inorganic powder according to any one of 1. to 6., 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) 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] and the viscosity (η 100 ) measured at a shear rate of 100 [1 / s] are measured at 25°C. Using the measured viscosities, the above-mentioned thixotropy index is calculated based on the formula: η 100 / η 1 .

Advantages of the Invention

[0008] According to the present invention, there are provided an inorganic powder excellent in heat dissipation and dielectric loss, 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. The drawings are schematic views and do not match the actual dimensional ratios.

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

[0012] The inorganic powder of this embodiment is an inorganic powder containing spherical alumina powder and spherical silica powder, wherein the dielectric loss tangent at 1 GHz in the inorganic powder, measured according to the following procedure A, is D×10 -4 and wherein the thermal conductivity in the inorganic powder, measured according to the following procedure B, is T (W / m·K), D and T satisfy T≧0.14D+1.03. (Procedure A) Using a measurement sample filled with the inorganic powder in a Teflon tube, the dielectric loss tangent at 1 GHz is measured by the cavity resonator perturbation method. (Procedure B) Using a sheet-like sample with a thickness of 3 mm obtained by drying a mixture of 70% by volume of the inorganic powder and 30% by volume of a liquid silicone resin, the thermal conductivity is measured by the heat flow meter method in accordance with ASTM E 1530.

[0013] It is preferable that D and T satisfy 0<D≦17 and 2.2≦T≦8.0. In this case, the upper limit of D is preferably 16 or less, more preferably 15 or less. Also, the lower limit of T is preferably 2.3 or more, more preferably 2.4 or more. On the other hand, the upper limit of T may be preferably 7 or less, 6 or less, or 5 or less. The lower limit of D is not particularly limited, but may be 0.1 or more or 1 or more.

[0014] Generally, in a mixed powder of spherical alumina powder and spherical silica powder, increasing the content ratio of the spherical alumina powder increases the thermal conductivity but also increases the dielectric loss tangent, and increasing the content ratio of the spherical silica powder decreases the dielectric loss tangent but also decreases the thermal conductivity. That is, in the conventional mixed powder, when the blending ratio of the two is varied, the plot of the thermal conductivity on the vertical axis and the dielectric loss tangent on the horizontal axis shows a trade-off curve, or has characteristics distributed below such a trade-off curve.

[0015] According to the findings of the present inventors, by combining spherical alumina powder with a large particle diameter having a high thermal conductivity and spherical silica powder with a small particle diameter having a low dielectric tangent, the above-described trade-off characteristics can be improved, and it has been found that an inorganic powder having characteristics distributed above the trade-off curve with the thermal conductivity on the vertical axis and the dielectric tangent on the horizontal axis can be realized. 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.

[0016] Also, according to the findings of the present inventors, the larger the particle diameter of the spherical alumina powder, the higher the thermal conductivity can be. From the viewpoint of high thermal conductivity, it is a common idea to select spherical alumina powder with a small particle diameter to fill the gaps between the spherical alumina powders with a large particle diameter. However, since the specific surface area increases as the particle diameter decreases, the dielectric tangent will increase. Therefore, from the viewpoint of low dielectric tangent, it is preferable to select spherical silica powder with a small particle diameter. Furthermore, from the viewpoint of improving the trade-off characteristics between thermal conductivity and dielectric tangent, as the spherical silica powder with a small particle diameter, it is preferable to use spherical silica powder that has been subjected to low dielectric tangent treatment in which the amount of physically adsorbed water, hydrogen-bonding silanol groups, and isolated silanol groups on the surface has been reduced by heat treatment or the like. In addition, when this spherical alumina powder with a small particle diameter 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 powder that has been subjected to low dielectric tangent treatment.

[0017] Hereinafter, each component of the inorganic powder of the present embodiment will be described in detail.

[0018] <Spherical alumina powder> The spherical alumina powder may be any that contains alumina (Al 2 0 3 ) as a main component. The main component means that in the total amount of the alumina powder, in terms of mass, alumina (Al2 0 3 It means containing, for example, 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 during the raw material and manufacturing processes is tolerated.

[0019] 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.

[0020] In this specification, the average particle size of the powder means the particle size (so-called D50) at the point where the cumulative volume from the small particle side is 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, and as a pretreatment, the powder dispersed by applying an output of 200 W using a homogenizer for 1 minute is used. The volume frequency particle size distribution and the particle size frequency distribution can be measured by "MT-3300EX" manufactured by Nikkiso Co., Ltd.

[0021] The lower limit of the specific surface area of the spherical alumina powder is not particularly limited, but 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.

[0022] 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, it can be measured.

[0023] 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. Further, the lower limit of the 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.

[0024] 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 so that the total amount of each alumina is 2 g, it is mixed with a mortar for 15 minutes to prepare a sample 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-crystalline 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 the 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 rate of the α-crystalline phase is calculated using the above calibration curve. Note that for the measurement, diffraction peaks detected at 2θ = 10° or more and 70° or less are used. Also, using the 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 rate of the α-crystalline phase is calculated using the above calibration curve. Note that for the measurement, diffraction peaks detected at 2θ = 10° or more and 70° or less are used.

[0025] 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.

[0026] The spherical alumina powder of the present 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 it is S 1 S 2 S 4 and at least two or more of S 5 are configured to be 0.85 or more, preferably three or more are 0.85 or more, and more preferably four or more are 0.85 or more.

[0027] <Spherical silica powder> The spherical silica powder may be any one containing silica (SiO 2 ) as a main component. The main component means that silica (SiO 2 ) is contained, for example, in an amount of 80% or more, preferably 90% or more, and more preferably 95% or more in terms of mass in the total amount of the silica powder. The spherical silica powder preferably has a high purity, but allows the presence of impurities inevitably mixed in the raw materials and the manufacturing process.

[0028] 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 The following holds. The lower limit of the dielectric loss tangent of the spherical silica powder at 1 GHz is not particularly limited, but for example, it may be 3.0×10 -4 or more, and may be 5.0×10 -4 or more.

[0029] 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.

[0030] The lower limit of the average particle diameter 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 diameter of the spherical silica powder is, for example, 10 μm or less, preferably 7.5 μm or less, more preferably 5.0 μm or less.

[0031] 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.

[0032] 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-based powder, crystalline silica has a main peak at 26.7°, but amorphous silica has no peak. When amorphous silica and crystalline silica are mixed, a peak height of 26.7° corresponding to the ratio of crystalline silica is obtained. Then, the mixing ratio of crystalline silica (X-ray diffraction intensity of the 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 the crystalline silica standard sample, and the amorphous ratio (%) can be calculated from the formula, amorphous ratio (%) = (1 - mixing ratio of crystalline silica) × 100.

[0033] 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.

[0034] 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. 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 length 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 average sphericity is obtained by the formula: average sphericity = (average circularity) 2

[0035] The inorganic powder of this embodiment may contain one or more kinds of spherical silica powders having different average particle diameters.

[0036] 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 the spherical silica powder A with a small particle diameter and the 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.

[0037] The lower limit of the average particle diameter of the 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 the spherical silica powder A is, for example, 4.0 μm or less, preferably 3.0 or less, more preferably 2.0 or less.

[0038] ​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.

[0039] In addition, the spherical silica powder may contain 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.

[0040] The lower limit of the specific surface area of spherical silica powder A is, for example, more than 4.0 m 2 / g, preferably 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.

[0041] 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.

[0042] In the spherical silica powder, the volume conversion content ratio of spherical silica powder A and spherical silica powder B is, for example, 30 vol%:70 vol% to 70 vol%:30 vol%, preferably 35 vol%:65 vol% to 65 vol%:35 vol%, more preferably 40 vol%:60 vol% to 60 vol%:40 vol%.

[0043] In the inorganic powder, the volume-based 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.

[0044] 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.

[0045] The lower limit of the frequency of the maximum peak in the range of 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.

[0046] In the particle size frequency distribution of the inorganic powder, it is assumed to be 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.

[0047] 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.

[0048] 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.

[0049] 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 192 μm or less 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.

[0050] The inorganic powder of the present embodiment may be configured such that the thixotropic 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, more preferably 0.02 or more and 0.07 or less.

[0051] By setting the thixotropic index to be equal to or less than the upper limit, the moldability of the resin composition can be improved. By setting the thixotropic index to be equal to or more than the lower limit, the burr characteristics of the resin composition can be improved.

[0052] 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) in a liquid state at 25 °C so that the content is 75% by mass to obtain a resin varnish for evaluation. Subsequently, for the obtained resin varnish for evaluation, using a rheometer, the viscosity (η 1 ) measured at a shear rate of 1 [1 / s] and the viscosity (η 100 ) measured at a shear rate of 100 [1 / s] are measured at 25 °C. Then, using the obtained viscosities, the thixotropic index is calculated from the formula: η 100 / η 1

[0053] 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 having a large particle diameter with high thermal conductivity and a spherical silica powder having a small particle diameter with a low dielectric tangent, appropriately adjusting their content ratios, etc. are cited as factors for setting the thermal conductivity, dielectric tangent, or thixotropic index of the evaluation resin varnish in the organic powder within a desired numerical range.

[0054] 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 mixing step of mixing a spherical alumina powder having an average particle diameter of 20 μm or more and 50 μm or less and a spherical silica powder having a dielectric tangent of 2.0×10 -3 as follows and having an average particle diameter of 4 μm or more and 10 μm or less. That is, the above spherical alumina powder and the above spherical silica powder are each manufactured, and by mixing these, an inorganic powder is obtained.

[0055] <Manufacturing method of spherical alumina powder> The spherical alumina powder is manufactured, 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.

[0056] As the alumina raw material powder which is the raw material powder, for example, 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.

[0057] <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 a combustion-supporting gas, and is melted and spheroidized at a temperature equal to or higher than its melting point for manufacturing. 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.

[0058] 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 for a predetermined time (for example, about 2 to 35 hours) such that it is 1800 to 17600 (°C·h), 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 state 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 may be recovered and stored in a moisture-proof aluminum bag.

[0059] 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 ·24 h) 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.

[0060] The composition obtained by blending the inorganic powder of the present invention into a resin composition can be suitably used as a resin molding material.

[0061] Next, the resin composition of the present embodiment will be described.

[0062] The resin composition contains, in addition to the inorganic powder of the present invention, 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.

[0063] In this specification, "~" represents inclusion of the upper limit value and the lower limit value unless otherwise specified.

[0064] 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 thereof.

[0065] 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.

[0066] 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, etc., and after cooling, it may be pulverized or the like. The resin composition of this embodiment can be used for various applications, but for example, it is preferably used as a material for high frequencies.

[0067] 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

[0068] 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.

[0069]

Table 1

[0070] <Raw materials> The information on the raw materials shown in Table 1 is shown below. · Spherical silica powder 1 (spherical silica powder B): The one 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): The one 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 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 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.

[0071] · 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)

[0072] <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.

[0073] <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.

[0074] 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.

[0075]

Table 2

[0076] <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 carried out.

[0077] <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 rotating and revolving mixer. The obtained mixture was processed into a sheet with a thickness of 3 mm, heat-treated at 120 °C for 2 hours using a dryer to obtain a sample. The obtained sample was cut into a size of longitudinal width: 20 mm × transverse width: 20 mm × thickness 3 mmt, and was measured by the heat flow meter method 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, in accordance with ASTM E 1530.

[0078] <Dielectric Loss Tangent> The dielectric loss tangent of the powder was measured under the conditions of room temperature 25 °C and frequency 1.0 GHz using a perturbation type cavity resonator measurement system (manufactured by KEYENCE CORPORATION). 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 capacity of 1584 mm 3 while tapping, filled until it reached 1.15 cm 3 and sealed with tape. In addition, a plot of the obtained thermal conductivity of the inorganic powder on the vertical axis and the dielectric loss tangent at 1 GHz on the horizontal axis is shown in FIG. 1. 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.

[0079] <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 became 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] and the viscosity (η100 ) was measured. Using the measured viscosity, the thixotropy index was calculated based on the formula: η 100 / η 1 as described above.

[0080] [Comprehensive Evaluation] The inorganic powder of Comparative Example 1 has a content of spherical alumina powder of 100% by volume, and although its thermal conductivity can be designed to be high, on the contrary, its dielectric tangent increases. On the other hand, the inorganic powder of Comparative Example 3 has a content of spherical silica powder of 100% by volume, and although its dielectric 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 tangent show a trade-off curve, and 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. In contrast, in the inorganic powders of Examples 1 to 6 in which spherical alumina powder 1,4 having a high thermal conductivity and a relatively large particle diameter and spherical silica powder 1,2 having a low dielectric tangent and a relatively small particle diameter due to heat treatment were appropriately combined, it was confirmed that such trade-off characteristics can be improved. When such inorganic powders of Examples 1 to 6 are used as materials for high frequencies, even when the frequency is increased in the high frequency band, compared with Comparative Examples 1 to 6, both reduction of dielectric loss and heat dissipation due to frequency increase etc. can be achieved. Therefore, it was found that they are excellent in dielectric loss and heat dissipation in practical use.

Claims

1. An inorganic powder containing spherical alumina powder and spherical silica powder, The dielectric loss tangent at 1 GHz in the inorganic powder, measured according to the following procedure A, is D×10 －４ and when the thermal conductivity of the inorganic powder measured according to the following Procedure B is T (W / m·K), an inorganic powder in which D and T satisfy T≥0.14D + 1.

03. (Procedure A) Using a measurement sample filled with the inorganic powder in a Teflon tube, the dielectric loss tangent at 1 GHz is measured by the cavity resonator perturbation method. (Procedure B) Using a mixture of 70% by volume of the inorganic powder and 30% by volume of a liquid silicone resin, for a sheet-like sample with a thickness of 3 mm obtained by drying treatment, in accordance with ASTM E 1530, the above thermal conductivity is measured by the heat flow meter method.

2. The inorganic powder according to Claim 1, an inorganic powder in which D and T satisfy 0 < D≤17 and 2.2≤T≤8.

0.

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

4. The inorganic powder according to Claim 3, an inorganic powder in which the frequency of the maximum peak is 10% or more.

5. The inorganic powder according to Claim 1 or 2, 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 in the particle size frequency distribution of the inorganic powder, an inorganic powder in which the average value of the frequencies of the five particle size classes is 2% or more and 10% or less.

6. The inorganic powder according to Claim 5, an inorganic powder in which the difference between the maximum value and the average value among the frequencies of the five particle size classes is 3% or less.

7. The inorganic powder according to Claim 1 or 2, an inorganic powder in which the thixotropic index of an evaluation resin varnish 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) which is liquid at 25°C so that the content is 75% by mass to obtain the above evaluation resin varnish. Subsequently, in the obtained resin varnish for evaluation, using a rheometer, the viscosity (η １ ), 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 １００ / η １ .

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