Inorganic powder, raw material inorganic powder set, composite material, and composite sheet

Abstract

An inorganic powder according to the present invention contains an alumina powder and a ferrite powder, and when thermal conductivity is T(W / m•K) and magnetic permeability at 100 MHz is M, T and M satisfy TxM ≥ 12.0, T ≥ 2.5, and M ≥ 3.0.

Description

Inorganic powders, raw material inorganic powder sets, composite materials, and composite sheets

[0001] The present invention relates to inorganic powders, raw material inorganic powder sets, composite materials, and composite sheets.

[0002] Various developments have been made regarding mixed inorganic powders containing alumina powder and ferrite powder. As an example of this type of technology, the technology described in Patent Document 1 is known. Patent Document 1 describes measurement results for a thermal conductive sheet containing alumina, ferrite powder, and silicone, with Comparative Example 2 showing a thermal conductivity of 1 W / m·K and a magnetic permeability of 6.28, and Comparative Example 4 showing a thermal conductivity of 1.5 W / m·K and a magnetic permeability of 6.

[0003] Japanese Patent Publication No. 2004-047965

[0004] However, as a result of our investigation, we found that there is room for improvement in both thermal conductivity and magnetic permeability in the mixture of alumina and ferrite powder described in Patent Document 1.

[0005] The inventors have discovered that in inorganic powders containing ferrite powder and alumina powder, both thermal conductivity and magnetic permeability can be adjusted by controlling the particle packing. Based on this finding, further intensive research has led to the discovery that by adding ferrite powder with relatively small particle size to an inorganic powder having predetermined thermal conductivity and magnetic permeability, the integrated value of thermal conductivity and magnetic permeability can be controlled to a value above a predetermined value, thereby realizing an inorganic powder with excellent high thermal conductivity and high magnetic permeability, and thus completing the present invention.

[0006] According to one aspect of the present invention, the following inorganic powders, raw material inorganic powder sets, composite materials, and composite sheets are provided.

[0007] 1. An inorganic powder containing alumina powder and ferrite powder, wherein, when the thermal conductivity is T (W / m·K) and the magnetic permeability at 100 MHz is M, T and M satisfy the following conditions: T × M ≥ 12.0, T ≥ 2.5, and M ≥ 3.0, as measured by the following procedure. (Procedure for measuring thermal conductivity) 78 volume% of the inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 volume% main agent and 2.2 volume% curing agent are mixed using a rotation-revolution mixer. The resulting mixture is processed into a 3 mm thick sheet and heat-treated in a dryer at 120°C for 2 hours to obtain a sample. The obtained sample is cut to a size of 20 mm (length) x 20 mm (width) x 3 mm (thickness). Then, the upper heater, the cut sample, the heat flux meter, the lower heater, and the heat sink are stacked in that order, and the thermal conductivity (W / m·K) is measured by the heat flux meter method in accordance with ASTM E 1530. (Procedure for measuring magnetic permeability) 78 vol% of the mixed inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 vol% of the main component and 2.2 vol% of the curing agent are mixed using a rotating / revolving mixer. The resulting mixture is placed in a mold with an outer diameter of 20 mm and an inner diameter of 8 mm, and the mixing rate is 1 ton / cm². ２A sample is obtained by performing a heat treatment at 150°C for 1 minute while applying pressure. The obtained sample is measured using an impedance / material analyzer to determine the real part (μ') of the complex permeability at 100 MHz, and the measured value is taken as the permeability. 2. An inorganic powder according to 1, wherein the thermal conductivity is 2.7 W / m·K or higher. 3. An inorganic powder according to 1 or 2, wherein the permeability at 100 MHz is 4.6 or higher. 4. An inorganic powder according to any one of 1 to 3, wherein the ferrite powder contains two or three or more types of ferrite particles with different particle sizes. 5. An inorganic powder according to any one of 1 to 4, wherein the ferrite powder contains spherical ferrite and crushed ferrite. 6. An inorganic powder according to any one of 1 to 5, wherein the alumina powder contains two or three or more types of alumina powder with different particle sizes. 7. An inorganic powder described in any one of 1 to 6, wherein the viscosity of the evaluation varnish containing the inorganic powder, as measured by the following procedure, is 40 mPa·s or more and 400 mPa·s or less. (Viscosity measurement procedure) The inorganic powder is mixed with liquid silicone resin at 25°C to a content of 65 volume percent to prepare an evaluation resin varnish. The viscosity (mPa·s) of the obtained evaluation resin varnish is measured using a rheometer at 25°C and a shear rate of 3.6 (1 / s). 8. A raw inorganic powder set comprising alumina powder and ferrite powder, wherein in an inorganic powder sample obtained by mixing the alumina powder and ferrite powder in the same volume ratio, the following conditions are met when the thermal conductivity is measured by the procedure below, T (W / m·K) and the magnetic permeability at 100 MHz is M, such that T and M satisfy T × M ≥ 12.0, T ≥ 2.5, and M ≥ 3.0. (Procedure for measuring thermal conductivity) 78 volume% of the inorganic powder sample and a two-component addition-reaction type liquid silicone resin consisting of 19.8 volume% main agent and 2.2 volume% curing agent are mixed using a rotation-revolution mixer. The resulting mixture is processed into a 3 mm thick sheet and heat-treated in a dryer at 120°C for 2 hours to obtain a sample.The obtained sample is cut to a size of 20 mm (length) x 20 mm (width) x 3 mm (thickness). Then, the upper heater, the cut sample, the heat flux meter, the lower heater, and the heat sink are stacked in that order, and the thermal conductivity (W / m·K) is measured by the heat flux meter method in accordance with ASTM E 1530. (Procedure for measuring magnetic permeability) 78 vol% of the mixed inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 vol% of the main component and 2.2 vol% of the curing agent are mixed using a rotating / revolving mixer. The obtained mixture is placed in a mold with an outer diameter of 20 mm and an inner diameter of 8 mm at a flow rate of 1 ton / cm. ２ A sample is obtained by performing a heat treatment at 150°C for 1 minute while applying pressure. The real part (μ') of the complex permeability at 100 MHz of the obtained sample is measured using an impedance / material analyzer, and the measured value is taken as the permeability. 9. A raw material inorganic powder set as described in 8., comprising a first container containing the alumina powder and a second container containing the ferrite powder. 10. A composite material comprising an inorganic powder as described in any one of 1 to 7. and at least one of an elastomer and a resin. 11. A composite material as described in 10., which is in solid or liquid form. 12. A composite sheet comprising the composite material as described in 10.

[0008] According to the present invention, a novel inorganic powder capable of exhibiting high thermal conductivity and high magnetic permeability, a raw material inorganic powder set, a composite material having high thermal conductivity and high magnetic permeability, and a composite sheet are provided.

[0009] The outline of the inorganic powder of this embodiment will be described.

[0010] The inorganic powder of this embodiment includes alumina powder and ferrite powder, and when the thermal conductivity is measured by the following procedure, and the magnetic permeability at 100 MHz is denoted as T (W / m·K), T and M satisfy the following conditions: T × M ≥ 12.0, T ≥ 2.5, and M ≥ 3.0.

[0011] (Procedure for measuring thermal conductivity) 78 volume% of the inorganic powder and a two-component addition-type liquid silicone resin consisting of 19.8 volume% of the main component and 2.2 volume% of the curing agent are mixed in a rotating / revolving mixer. The resulting mixture is processed into a 3 mm thick sheet and heat-treated in a dryer at 120°C for 2 hours to obtain a sample. The obtained sample is cut to a size of 20 mm (length) x 20 mm (width) x 3 mm (thickness), and the thermal conductivity (W / m·K) is measured in accordance with ASTM E 1530 using the heat flow meter method with the upper heater, the cut sample, a heat flux meter, a lower heater, and a heat sink stacked in that order. (Procedure for measuring magnetic permeability) 78 volume% of the mixed inorganic powder and a two-component addition-type liquid silicone resin consisting of 19.8 volume% of the main component and 2.2 volume% of the curing agent are mixed in a rotating / revolving mixer. The resulting mixture was placed in a mold with an outer diameter of 20 mm and an inner diameter of 8 mm, at a rate of 1 ton / cm². ２ A sample is obtained by heat treatment at 150°C for 1 minute while applying pressure. The real part (μ') of the complex permeability at 100 MHz is measured using an impedance / material analyzer on the obtained sample, and this measured value is taken as the permeability. In order to standardize the evaluation, the thermal conductivity and permeability are measured using the same binder resin (two-component addition reaction type liquid silicone resin) fixed in the same material.

[0012] According to the inventors' findings, it has been discovered that by adding ferrite powder with a relatively small particle size to a mixed powder of ferrite powder and alumina powder, both thermal conductivity and magnetic permeability can be improved. Although the detailed mechanism is not clear, it is presumed that when ferrite powder with a small particle size is added, not only does the magnetic permeability increase, but the particle packing density in the mixed powder also increases, that is, the porosity decreases, which increases the number of heat conduction paths and thus increases the thermal conductivity.

[0013] The sum of thermal conductivity T and magnetic permeability M, T×M, is 12.0 or higher, preferably 12.5 or higher, and more preferably 13.0 or higher. A value above this lower limit allows for a good balance between thermal conductivity and magnetic permeability. The upper limit of T×M is not particularly limited, but may be 30 or lower.

[0014] The lower limit of the thermal conductivity T is 2.5 W / m·K or higher, preferably 2.7 W / m·K or higher, and more preferably 3.0 W / m·K or higher. A value above this lower limit improves heat dissipation. The upper limit of the thermal conductivity T may be, for example, 4.5 W / m·K or lower.

[0015] The lower limit of the magnetic permeability M is, for example, 3.0 or higher, preferably 4.6 or higher, and more preferably 4.9 or higher. A value above the lower limit improves magnetic permeability. The upper limit of the magnetic permeability M may be, for example, 7.0 or lower.

[0016] In this specification, the particles contained in inorganic powders are classified into predetermined particle size ranges, and the particles in each category are defined as follows: Coarse powder is powder with a particle diameter of 50 μm or more and 150 μm or less. Medium powder is powder with a particle diameter of 2 μm or more and less than 50 μm. Ultrafine powder is powder with a particle diameter of less than 2 μm. The particle diameter can be determined based on the particle diameter (d50) at the point where the cumulative volume from the smallest particle side reaches 50% in the volume-based cumulative distribution measured by wet laser diffraction scattering.

[0017] In this embodiment, it is possible to control the cumulative values ​​of thermal conductivity T, magnetic permeability M, T, and M by appropriately selecting, for example, the types and amounts of each component contained in the inorganic powder, the method of preparing the inorganic powder, etc. Among these, for example, using a combination of coarse ferrite powder and ferrite powder with a small particle size (at least one of medium powder and ultrafine powder), using crushed ferrite, and using two or three or more types of alumina powder with different particle sizes are examples of factors that can bring the cumulative values ​​of thermal conductivity T, magnetic permeability M, T, and M into a desired numerical range.

[0018] The components of the inorganic powder in this embodiment will be described in detail below.

[0019] The inorganic powder contains one or more types of alumina powder and one or more types of ferrite powder.

[0020] The ferrite powder may contain two or more types of ferrite particles with different particle sizes. Specifically, the ferrite powder may contain two or three types selected from the group consisting of coarse ferrite powder, medium ferrite powder, and ultrafine ferrite powder. By using ferrite powder with multiple particle sizes, the packing performance of the inorganic powder can be improved.

[0021] The shape of the particles contained in the above ferrite powder is not particularly limited, but may be spherical, crushed, or the like. The above ferrite powder may contain at least one of spherical ferrite and crushed ferrite, but it is preferable to contain both spherical ferrite and crushed ferrite. In one embodiment, the coarse ferrite powder is preferably spherical. Furthermore, it is preferable that at least one of the ferrite medium powder and ferrite ultrafine powder contains crushed material, and it is preferable that each of them contains crushed material. In the inorganic powder of this embodiment, the thermal conductivity can be further increased by containing crushed ferrite, preferably at least one of crushed ferrite medium powder and crushed ferrite ultrafine powder. Although the detailed mechanism is not clear, it is presumed that the thermal conductivity can be further increased because the crushed ferrite reduces the distance between alumina powder particles and increases the contact points between alumina powder particles.

[0022] The ferrite powder content in the inorganic powder is, for example, 80 to 160 volume%, preferably 90 to 110 volume%, and more preferably 95 to 105 volume%, based on 100 volume% of alumina powder. In this specification, "~" indicates that the upper and lower limits are included unless otherwise specified.

[0023] When the ferrite powder contains crushed ferrite, the crushed ferrite content is, for example, 5 to 60% by volume, preferably 10 to 35% by volume, and more preferably 15 to 30% by volume, of 100% by volume of the ferrite powder.

[0024] When the ferrite powder contains at least one of ferrite medium powder and ferrite ultrafine powder, the content of ferrite medium powder and ferrite ultrafine powder is, for example, 5 to 60% by volume, preferably 10 to 50% by volume, and more preferably 15 to 40% by volume, of 100% by volume of the ferrite powder.

[0025] Examples of ferrites include Mg-Zn ferrite, Mn-Zn ferrite, Mn-Mg ferrite, Cu-Zn ferrite, and Ni-Zn ferrite. These may be used individually or in combination of two or more.

[0026] The ferrite powder may be surface-treated with a silane coupling agent, or it may be untreated with no silane coupling agent adhering to its surface.

[0027] The alumina powder may contain two or more types of alumina powder with different particle sizes. Specifically, the alumina powder may contain two or three types selected from the group consisting of coarse alumina powder, medium alumina powder, and ultrafine alumina powder. By using alumina powder with multiple particle sizes, the packing properties of the inorganic powder can be improved. Furthermore, at least one, preferably two, and more preferably all of the coarse alumina powder, medium alumina powder, and ultrafine alumina powder may contain spherical alumina.

[0028] When the alumina powder contains at least one of alumina medium powder and alumina ultrafine powder, the content of alumina medium powder and alumina ultrafine powder is, for example, 5 to 60% by volume, preferably 10 to 50% by volume, and more preferably 15 to 40% by volume, of 100% by volume of the alumina powder.

[0029] Alumina powder is made from alumina (Al ２ 0 ３ Any product that contains alumina (Al) as its main component is acceptable. The main component is alumina (Al) in terms of mass in the total amount of alumina powder. ２ 0 ３ This means that it contains 90% or more by mass of ). While a higher purity is preferable for alumina powder, the presence of impurities that inevitably get mixed in during the raw material or manufacturing process is acceptable.

[0030] The alumina powder has a lower limit of sphericity measured using a wet flow-type image analysis device, for example, 0.90 or higher, preferably 0.91 or higher, and more preferably 0.92 or higher. This improves packing performance. On the other hand, there is no particular upper limit to the sphericity.

[0031] The alumina powder may be surface-treated with a silane coupling agent, or it may be untreated with no silane coupling agent adhering to the surface.

[0032] Alumina powder is produced, for example, by supplying 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 it above its melting point.

[0033] The inorganic powder may or may not contain other inorganic powders other than ferrite powder and alumina powder. Examples of other inorganic powders include soft magnetic powders such as iron alloys, and thermally conductive powders such as copper, aluminum, silica, zinc oxide, magnesia, titania, aluminum nitride, silicon nitride, boron nitride, and silicon carbide. The content of ferrite powder and alumina powder in the inorganic powder is, for example, 50 to 100% by volume, preferably 80 to 99.9% by volume, and more preferably 80 to 99.5% by volume, based on 100% by volume of the inorganic powder.

[0034] The inorganic powder of this embodiment may be configured such that the viscosity of the evaluation varnish measured by the following procedure is, for example, 40 mPa·s or more and 400 mPa·s or less, preferably 45 to 300 mPa·s, and more preferably 50 to 250 mPa·s. (Viscosity measurement procedure) The inorganic powder is mixed with liquid silicone resin at 25°C to a content of 65 volume% to prepare an evaluation resin varnish. The viscosity (mPa·s) of the obtained evaluation resin varnish is measured using a rheometer at 25°C and a shear rate of 3.6 (1 / s).

[0035] The raw material inorganic powder set of the present embodiment includes alumina powder and ferrite powder. In the raw material inorganic powder set, for an inorganic powder sample obtained by mixing alumina powder and ferrite powder at the same volume ratio, when the thermal conductivity measured by the above procedure is defined as T (W / m·K), and the magnetic permeability at 100 MHz is defined as M, T and M satisfy T×M≧12.0, T≧2.5, and M≧3.0.

[0036] In the raw material inorganic powder set, the alumina powder and the ferrite powder may be stored in a state separated from each other. Specifically, the raw material inorganic powder set may include a first container containing alumina powder and a second container containing ferrite powder. In each of the first container and the second container, coarse powder, medium powder and ultrafine powder may be stored in a state separated from each other, or may be contained in a state where at least two or more types are mixed. For example, the coarse powder and the medium powder may be in a mixed state, and the ultrafine powder may be in a state dispersed in a solvent.

[0037] The composite material of the present embodiment may include the above-mentioned inorganic powder and at least one of an elastomer and a resin.

[0038] As the elastomer, known rubbers can be used, and examples thereof include silicone rubber, urethane rubber, acrylic rubber, butyl rubber, ethylene propylene rubber, urethane rubber, ethylene vinyl acetate copolymer, and the like. As the resin, known polymers can be used, and examples thereof include epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyimides, polyamideimides, polyamides such as polyetherimide, polyesters such as polybutylene terephthalate and polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin.

[0039] The composite material may contain other components depending on the application. Examples of other components include flame retardants, reaction retarders, crosslinking agents, silane coupling agents, and silicone oils.

[0040] The composite material can be used as a molding material, and is solid or liquid at room temperature. The solid composite material may be a molding material in the form of powder, granules, pellets, or the like. Further, the liquid composite material may contain a solvent as required.

[0041] There is no particular limitation on the form of the molded article formed from the composite material, but the molded article is preferably a composite sheet containing the above composite material.

[0042] Molded articles of the composite material are used in various applications that require electromagnetic wave absorption, or both electromagnetic wave absorption and heat dissipation. One example is a heat dissipating member for electronic devices. A heat dissipating member for electronic devices is an interposed material used, for example, when attaching a CPU or the like to a heat sink such as a heat dissipating fin or a metal plate. A sheet shape with a thickness of 0.1 to 6 mm, particularly 0.2 to 2 mm, is common for the heat dissipating member. The planar shape of the sheet may be any shape that can be in close contact with or embedded in an electronic component such as a CPU, and examples thereof include polygons such as triangles, quadrilaterals, and hexagons, circles, ellipses, and the like. Furthermore, irregularities may be provided on the surface to facilitate close contact or embedding.

[0043] The embodiments of the present invention have been described above, but these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like made within the range that can achieve the object of the present invention are included in the present invention.

[0044] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited in any way by the description of these examples.

[0045] The raw materials shown in Table 1 are as follows. (Ferrite powder) ・Coarse powder F: Spherical ferrite (TSF-10A manufactured by Toda Kogyo Corporation, particle diameter (d50): 100 μm) ・Medium powder F1: Spherical ferrite (TSF-03A manufactured by Toda Kogyo Corporation, particle diameter (d50): 35 μm) ・Medium powder F2: Crushed ferrite (particle diameter (d50): 8 μm): NiO, ZnO, CuO, Fe ２ O ３ were mixed in predetermined amounts, and the ferrite obtained by firing at 1200°C was pulverized to obtain the powder. ・Ultrafine powder F: Crushed ferrite (particle diameter (d50): 0.8 μm): Obtained by further pulverizing medium powder F2.

[0046] (Alumina powder) ・Coarse powder A: Spherical alumina (manufactured by Denka Company Limited, DAM-90, particle diameter (d50): 97 μm, specific surface area: 0.1 m ２ / g) ・Medium powder A: Spherical alumina (manufactured by Denka Company Limited, DAM-07, particle diameter (d50): 11 μm, specific surface area: 0.4 m ２ / g) ・Ultrafine powder A: Spherical alumina (manufactured by Denka Company Limited, ASFP-20, particle diameter (d50): 0.3 μm, specific surface area: 10.8 m ２ / g)

[0047] <Inorganic powder> According to the blending ratios shown in Table 1, ferrite powder and alumina powder were mixed to produce the inorganic powders of Examples 1 to 5 and Comparative Example 1, respectively. The inorganic powders of Examples 1 to 5 and Comparative Example 1 in Table 1 were adjusted to contain about 50% by volume of ferrite powder and about 50% by volume of alumina powder.

[0048]

[0049] The following properties and items were evaluated for the obtained inorganic powder.

[0050] <Measurement of Thermal Conductivity> 78 vol% of the obtained inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 vol% of the main component (YE5822A, manufactured by Momentive Performance Materials Japan LLC) and 2.2 vol% of the curing agent (YE5822B) were mixed using a rotation-revolution 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 obtained sample was cut to a size of 20 mm (length) x 20 mm (width) x 3 mm (thickness), and the thermal conductivity (W / m·K) was measured in accordance with ASTM E 1530 using the heat flow meter method with the upper heater, the cut sample, a heat flux meter, a lower heater, and a heat sink stacked in that order. The results are shown in Table 1.

[0051] <Measurement of magnetic permeability> 78 vol% of the mixed inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 vol% of the main component (YE5822A, manufactured by Momentive Performance Materials Japan LLC) and 2.2 vol% of the curing agent (YE5822B) were mixed using a rotating / revolving mixer. The resulting mixture was placed in a mold with an outer diameter of 20 mm and an inner diameter of 8 mm, and the mixing rate was 1 ton / cm². ２ A sample was obtained by heat treatment at 150°C for 1 minute while applying pressure. The real part (μ') of the complex permeability at 100 MHz was measured using an impedance / material analyzer E4991A (manufactured by Agilent Technologies), and this measured value was defined as the permeability described above.

[0052] <Viscosity> The obtained inorganic powder was mixed with liquid silicone resin (main component "YE5822A") at 25°C to a content of 65 volume percent to prepare an evaluation resin varnish. The viscosity (mPa·s) of the obtained evaluation resin varnish was measured using a rheometer at 25°C and a shear rate of 3.6 (1 / s). The results are shown in Table 1.

[0053] The inorganic powders of Examples 1 to 5 showed higher values ​​for both thermal conductivity and magnetic permeability compared to Comparative Example 1. Composite materials using these inorganic powders of Examples 1 to 5 are expected to have high magnetic permeability, excellent noise suppression capabilities, and high thermal conductivity, resulting in superior heat dissipation. The applicable frequency range of this composite material is not limited to 100 MHz.

[0054] This application claims priority based on Japanese Patent Application No. 2025-029790, filed on 27 February 2025, and incorporates all of its disclosures herein.

Claims

1. An inorganic powder containing alumina powder and ferrite powder, wherein, when the thermal conductivity is T (W / m·K) and the magnetic permeability at 100 MHz is M, T and M satisfy the following conditions: T × M ≥ 12.0, T ≥ 2.5, and M ≥ 3.0, as measured by the following procedure. (Procedure for measuring thermal conductivity) 78 volume% of the inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 volume% main agent and 2.2 volume% curing agent are mixed using a rotating / revolving mixer. The resulting mixture is processed into a 3 mm thick sheet and heat-treated in a dryer at 120°C for 2 hours to obtain a sample. The obtained sample is cut to a size of 20 mm (length) x 20 mm (width) x 3 mm (thickness). Then, the upper heater, the cut sample, the heat flux meter, the lower heater, and the heat sink are stacked in that order, and the thermal conductivity (W / m·K) is measured by the heat flux meter method in accordance with ASTM E 1530. (Procedure for measuring magnetic permeability) 78 vol% of the mixed inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 vol% of the main component and 2.2 vol% of the curing agent are mixed using a rotating / revolving mixer. The resulting mixture is placed in a mold with an outer diameter of 20 mm and an inner diameter of 8 mm, and the mixing rate is 1 ton / cm². ２ A sample is obtained by performing a heat treatment at 150°C for 1 minute while applying pressure. The real part (μ') of the complex permeability at 100 MHz of the obtained sample is measured using an impedance / material analyzer, and this measured value is taken as the permeability.

2. The inorganic powder according to claim 1, wherein the thermal conductivity is 2.7 W / m·K or higher.

3. An inorganic powder according to claim 1 or 2, wherein the magnetic permeability at 100 MHz is 4.6 or higher.

4. An inorganic powder according to claim 1 or 2, wherein the ferrite powder contains two or three or more ferrite particles with different particle sizes.

5. An inorganic powder according to claim 1 or 2, wherein the ferrite powder comprises spherical ferrite and crushed ferrite.

6. An inorganic powder according to claim 1 or 2, wherein the alumina powder comprises two or three or more alumina powders with different particle sizes.

7. An inorganic powder according to claim 1 or 2, wherein the viscosity of an evaluation varnish containing the inorganic powder, as measured by the following procedure, is 40 mPa·s or more and 400 mPa·s or less. (Viscosity measurement procedure) An evaluation resin varnish is prepared by mixing the inorganic powder with a liquid silicone resin at 25°C so that the content is 65 volume%. The viscosity (mPa·s) of the obtained evaluation resin varnish is measured using a rheometer at 25°C and a shear rate of 3.6 (1 / s).

8. A raw inorganic powder set comprising alumina powder and ferrite powder, wherein in an inorganic powder sample obtained by mixing the alumina powder and ferrite powder in the same volume ratio, the following conditions are met when the thermal conductivity is measured by the procedure below, T (W / m·K) and the magnetic permeability at 100 MHz is M, such that T and M satisfy T × M ≥ 12.0, T ≥ 2.5, and M ≥ 3.

0. (Procedure for measuring thermal conductivity) 78 volume% of the inorganic powder sample and a two-component addition-reaction type liquid silicone resin consisting of 19.8 volume% main agent and 2.2 volume% curing agent are mixed using a rotation-revolution mixer. The resulting mixture is processed into a 3 mm thick sheet and heat-treated in a dryer at 120°C for 2 hours to obtain a sample. The obtained sample is cut to a size of 20 mm (length) x 20 mm (width) x 3 mm (thickness). Then, the upper heater, the cut sample, the heat flux meter, the lower heater, and the heat sink are stacked in that order, and the thermal conductivity (W / m·K) is measured by the heat flux meter method in accordance with ASTM E 1530. (Procedure for measuring magnetic permeability) 78 vol% of the mixed inorganic powder and a two-component addition-reaction type liquid silicone resin consisting of 19.8 vol% of the main component and 2.2 vol% of the curing agent are mixed using a rotating / revolving mixer. The resulting mixture is placed in a mold with an outer diameter of 20 mm and an inner diameter of 8 mm, and the mixing rate is 1 ton / cm². ２ A sample is obtained by performing a heat treatment at 150°C for 1 minute while applying pressure. The real part (μ') of the complex permeability at 100 MHz of the obtained sample is measured using an impedance / material analyzer, and this measured value is taken as the permeability.

9. A raw material inorganic powder set according to claim 8, comprising a first container containing the alumina powder and a second container containing the ferrite powder.

10. A composite material comprising the inorganic powder of claim 1 or 2, and at least one of an elastomer and a resin.

11. A composite material according to claim 10, wherein the composite material is in a solid or liquid state.

12. A composite sheet comprising the composite material described in claim 10.

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