Inorganic filler powder, thermally conductive polymer composition, method for producing inorganic filler powder

Abstract

To provide inorganic filler powder capable of yielding a thermally conductive polymer composition of excellent heat conductivity and low hardness at a low cost, a thermally conductive polymer composition using the same, and a method of producing the inorganic filler powder.SOLUTION: The inorganic filler powder structured in such a manner that at least a part of a surface of an inorganic particle having a particle size of 1 μm or more is covered with an inorganic fine particle having a particle size of 10 nm or more and smaller than 0.1 μm, is characterized in that a coverage rate of the surface of the inorganic particle covered with the fine inorganic particle is 30% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an inorganic filler powder used as a thermally conductive material, a thermally conductive polymer composition, and a method for producing the inorganic filler powder.

Background Art

[0002] In recent years, with the development of electric vehicles, fuel cell vehicles, etc., the current in electrical components has been increasing, and the amount of heat generated from electrical components is also increasing. For example, a lithium-ion battery for an automobile generates a large amount of heat because it outputs a large current of electric power continuously for a long time, and it is necessary to efficiently dissipate the generated large amount of heat to the outside. For this reason, a thermally conductive polymer composition having excellent thermal conductivity may be used as a heat dissipation member in a portion where insulation is required for an electrical component that outputs a large current, such as a lithium-ion battery.

[0003] Conventionally, as a thermally conductive polymer composition, an inorganic filler powder made of an inorganic material having excellent thermal conductivity is dispersed in a matrix material such as a resin having excellent insulation and moldability. As the inorganic filler powder, aluminum oxide (alumina: Al2O3), aluminum nitride (AlN), silicon dioxide (SiO2), silicon nitride (SiN), magnesium oxide (MgO), etc. are generally used from the viewpoints of thermal conductivity and specific gravity.

[0004] The thermal conductivity of the thermally conductive polymer composition can be improved by increasing the content of the inorganic filler powder. As an example, in order to obtain a thermally conductive polymer composition having a high thermal conductivity of 5 W / mK or more, it is necessary to knead 1100 parts by mass or more of the inorganic filler powder with respect to 100 parts by mass of the matrix material.

[0005] However, increasing the inorganic filler powder content in the matrix material also increases the hardness of the resulting thermally conductive polymer composition, leading to problems such as reduced fluidity and moldability. For this reason, for example, Patent Documents 1 and 2 disclose polymer compositions that use spherical alumina particles as inorganic filler powder, thereby keeping the hardness low even when the inorganic filler powder content is increased, and that are easy to knead. Patent Document 3 also discloses an alumina filler in which γ-alumina particles are formed on the surface of α-alumina particles. Furthermore, Patent Document 4 discloses the addition of low-hardness inorganic powder to a resin for the purpose of reducing wear on resin molding dies. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4361997 [Patent Document 2] Japanese Patent Publication No. 2012-121742 [Patent Document 3] Special Publication No. 6-51778 [Patent Document 4] Japanese Patent Publication No. 2011-16962 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the spherical alumina particles used in the resin compositions disclosed in Patent Documents 1 and 2 have the drawback of having a complex manufacturing process and high manufacturing costs. Furthermore, the method of forming γ-alumina particles on the surface of α-alumina particles, as disclosed in Patent Document 3, also has the drawback of high manufacturing costs because it requires a heating process at high temperatures. Furthermore, the method disclosed in Patent Document 4 had the problem that adding a large amount of low-hardness inorganic powder to high-hardness inorganic powder reduced the fluidity of the resin.

[0008] This invention has been made in consideration of these circumstances, and aims to provide an inorganic filler powder that can be used to obtain a thermally conductive polymer composition with excellent thermal conductivity and low hardness at low cost, a thermally conductive polymer composition using the same, and a method for producing the inorganic filler powder. [Means for solving the problem]

[0009] To solve the above problems, the present invention proposes the following means. In other words, the inorganic filler powder of the present invention comprises inorganic particles (excluding those with metal coating) with a particle size of 1 μm or more, and inorganic fine particles (excluding those with metal coating) with a particle size of 10 nm or more and less than 0.1 μm. By fixing it in place The structure is coated (excluding sintered structures), the coverage rate of the inorganic particles on the surface of the inorganic particles is 30% or more, and the inorganic particles and inorganic fine particles are characterized by being one of aluminum oxide, silicon carbide, aluminum nitride, silicon nitride, silicon dioxide, or magnesium oxide. At least a portion of the surface of the inorganic particles (excluding those with metal coatings) consists of inorganic fine particles (excluding those with metal coatings) with a particle size of 10 nm or more and less than 0.1 μm. By fixing it in place Covered structure (Excluding sintered products) The present invention is characterized by the production of inorganic filler powder.

[0010] According to the present invention, by creating a structure in which a portion of the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm, it is possible to realize an inorganic filler powder with high thermal conductivity when kneaded with a matrix material at a lower cost compared to the conventional method using spherical alumina particles. Furthermore, by mixing the inorganic filler powder of the present invention with a matrix material, a thermally conductive polymer composition that is flexible and has excellent shape conformability can be obtained.

[0011] Furthermore, in the present invention, the inorganic particles and inorganic fine particles may also contain aluminum oxide.

[0012] The thermally conductive polymer composition of the present invention is characterized in that the inorganic filler powder described in each of the above items is mixed with a matrix material containing at least one of a resin material, an elastomer material, and a rubber material.

[0013] Further, in the present invention, the thermally conductive polymer composition may contain 1200 parts by mass or more of the inorganic filler powder with respect to 100 parts by mass of the matrix material. [[ID= 6]]

[0014] The method for producing the inorganic filler powder of the present invention is to rotate and flow a raw material slurry obtained by mixing an inorganic raw material powder and a solvent at a peripheral speed of 10 m / s or more to polish the inorganic raw material powder, thereby obtaining a fluid in which Inorganic particles (excluding those coated with metal) and Inorganic fine particles (excluding those coated with metal) are generated in the solvent. The method has a fluid polishing step and a drying step of removing the solvent from the fluid and attaching the inorganic fine particles to the surface of the inorganic particles. The inorganic particles and the inorganic fine particles are any of aluminum oxide, silicon carbide, aluminum nitride, silicon nitride, silicon dioxide, and magnesium oxide. The present invention provides a method for producing an inorganic filler powder having a structure in which at least a portion of the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm. This is the feature.

[0015] Further, in the present invention, the inorganic raw material powder may be fused alumina powder.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide an inorganic filler powder capable of obtaining a thermally conductive polymer composition having excellent thermal conductivity and low hardness at low cost, a thermally conductive polymer composition using the same, and a method for producing the inorganic filler powder.

Brief Description of the Drawings

[0017] [Figure 1] It is an electron micrograph (10,000 times) showing the inorganic filler powder of the present embodiment. [Figure 2] It is an enlarged schematic view showing one particle of the inorganic filler powder. [Figure 3]It is an image obtained by trimming and binarizing an arbitrary rectangular region of an electron micrograph of inorganic filler powder. [Figure 4] It is an enlarged schematic view showing the thermally conductive polymer composition of the present embodiment. [Figure 5] It is an electron micrograph of the inorganic filler powder used in Verification Example 1 (polishing time: 3 minutes). [Figure 6] It is an electron micrograph of the inorganic filler powder used in Verification Example 1 (polishing time: 30 minutes). [[ID=!0]] [Figure 7] It is an electron micrograph of the inorganic filler powder used in Verification Example 1 (polishing time: 45 minutes). [Figure 8] It is an electron micrograph of the inorganic filler powder used in Verification Example 1 (polishing time: 60 minutes). [Figure 9] It is a graph showing the results of Verification Example 2.

Mode for Carrying Out the Invention

[0018] Hereinafter, with reference to the drawings, an inorganic filler powder according to an embodiment of the present invention, a thermally conductive polymer composition using the same, and a method for producing the inorganic filler powder will be described. The embodiments shown below are specifically described to better understand the gist of the invention, and do not limit the present invention unless otherwise specified.

[0019] (Inorganic Filler Powder) The inorganic filler powder is a thermally conductive material for obtaining a thermally conductive polymer composition by mixing with a matrix material. The inorganic filler powder according to an embodiment of the present invention is aluminum oxide (alumina: Al2O3) in the form of fine powder.

[0020] Alumina is used as a filler for the thermally conductive polymer composition because the thermal conductivity of alumina is relatively high, about 30 W / m·K. In addition to the alumina used in this embodiment, other thermally conductive inorganic material powders such as silicon carbide (SiC), aluminum nitride (AlN), silicon nitride (SiN), silicon dioxide (SiO2), and magnesium oxide (MgO) can be used as inorganic filler powders.

[0021] The inorganic filler powder of this embodiment is obtained by polishing electrofused alumina powder (inorganic raw material powder), and has a structure in which at least a portion of the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm.

[0022] Figure 1 is an electron microscope image (10,000x magnification) of the inorganic filler powder of this embodiment. Figure 2 is a magnified schematic diagram showing a single particle of the inorganic filler powder. As shown in Figures 1 and 2, the inorganic filler powder of this embodiment has a structure in which a portion of the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm. The inorganic fine particles constituting the inorganic filler powder are attached (adhered) to the surface of the inorganic particles. In the following explanation, "inorganic particles" refers to alumina particles with a particle size of 1 μm or larger, and "inorganic fine particles" refers to alumina particles with a particle size of 10 nm or larger and less than 0.1 μm.

[0023] The surface coverage rate of inorganic particles by inorganic fine particles constituting such inorganic filler powder is said to be 30% or more. The coverage rate referred to here is the ratio (%) of the surface area (plane) of inorganic microparticles to the surface area (plane) of inorganic particles when an arbitrary range of inorganic filler powder is viewed in plan view. As an example of measuring this coverage rate, as shown in Figure 3, an image is prepared by cropping an arbitrary rectangular region from an electron microscope image of inorganic filler powder (for example, at a magnification of about 10,000 to 100,000 times) and binarizing it. In such an image, the parts where inorganic particles are exposed are shown in black, and the parts covered by inorganic microparticles are shown in white. Then, by calculating the area occupied by the white region (area covered by inorganic microparticles) relative to the area of ​​the cropped rectangular region (surface area of ​​inorganic particles) using image processing, the coverage rate (%) can be obtained.

[0024] The inorganic filler powder of this embodiment, as described above, has a structure in which a portion of the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm. Compared to conventional methods using spherical alumina particles, this embodiment enables the creation of an inorganic filler powder with high thermal conductivity when mixed with a matrix material at a lower cost. Furthermore, by mixing the inorganic filler powder of this embodiment with a matrix material, a flexible, shape-following, and highly thermally conductive polymer composition can be obtained.

[0025] (Thermally conductive polymer composition) Figure 4 is an enlarged schematic diagram showing the thermally conductive polymer composition of this embodiment. The thermally conductive polymer composition of this embodiment consists of the inorganic filler powder of this embodiment dispersed in a matrix material. For example, it may be a paste-like mixture in which 1200 parts by mass or more of the inorganic filler powder of this embodiment is mixed with 100 parts by mass of the matrix material. For example, the thermally conductive polymer composition of this embodiment can be obtained by mixing 1200 to 7000 parts by mass of the inorganic filler powder of this embodiment with 100 parts by mass of resin.

[0026] The matrix material into which the inorganic filler powder is mixed may contain at least one of the following: a resin material, an elastomer material, and a rubber material. The matrix material is not particularly limited to resin materials, and known resin materials can be used. Specifically, examples include hydrocarbon resins, unsaturated polyester resins, acrylic resins, vinyl ester resins, epoxy resins, xyleneformaldehyde resins, guanamine resins, diallyl phthalate resins, phenolic resins, furan resins, polyimide resins, melamine resins, urea resins, and the like.

[0027] The matrix material is not particularly limited to elastomer materials, and known elastomer materials can be used. Specifically, examples include polystyrene elastomers, polyvinyl chloride elastomers, polyurethane elastomers, polyester elastomers, polyamide elastomers, and the like.

[0028] The matrix material is not particularly limited to rubber materials, and any known rubber material can be used. Specifically, it can be either natural rubber or synthetic rubber, for example, urethane rubber, silicone rubber, or fluororubber.

[0029] The thermally conductive polymer composition of this embodiment exhibits a 40% or greater reduction in hardness compared to conventional thermally conductive polymer compositions obtained by mixing raw material alumina particles (electrofused alumina particles) and resin, at the same blending ratio. This reduction in hardness, i.e., the increased softness, enhances the fluidity of the thermally conductive polymer composition of this embodiment.

[0030] As a result, the thermally conductive polymer composition of this embodiment can improve shape conformability in the filled portion, allowing it to adhere closely to the heat transfer target object without gaps and efficiently transfer heat. Furthermore, compared to conventional thermally conductive polymer compositions that mix raw material alumina particles (electrofused alumina particles) and resin, a larger amount of inorganic filler powder can be mixed in while maintaining the same level of hardness. Therefore, the thermally conductive polymer composition of this embodiment can improve thermal conductivity compared to conventional thermally conductive polymer compositions using raw material alumina particles.

[0031] (Method for producing inorganic filler powder) In manufacturing the inorganic filler powder of this embodiment, first, an inorganic raw material powder is prepared. In this embodiment, particulate electrofused alumina was used as the inorganic raw material powder. Particulate electrofused alumina, produced by the reduction and melting of bauxite in an electric arc furnace, was used as the inorganic raw material powder because it has a large particle size and a broad particle size distribution, and it can be mixed with matrix materials such as resins at a high packing rate, thereby improving the thermal conductivity of the thermally conductive polymer composition. Commercially available electrofused alumina powder can be used as the raw material. For example, electrofused alumina powder that has passed through a sieve with a mesh size of 100 μm can be used.

[0032] Next, the raw material slurry, which is a mixture of this electrofused alumina powder (inorganic raw material powder) and a solvent, is prepared in 10 minutes. m / s The fused alumina powder is polished by causing it to collide with other particles while swirling at the above peripheral speed (flow polishing process). This generates a fluid in which inorganic particles and inorganic fine particles are produced in the solvent.

[0033] As a solvent for forming a slurry from this inorganic raw material powder, fused alumina powder, a stable liquid that does not dissolve alumina, such as water, is used. In this embodiment, ion-exchanged water is used as the solvent. When water is used as the solvent, the concentration of fused alumina powder should be, for example, about 70% to 80% by mass.

[0034] One method for polishing by slurrying (raw material slurry) such electrofused alumina powder and water is, for example, an emulsification and dispersion device (Aspec Disperser ZERO, manufactured by Hiroshima Metal & Machinery Co., Ltd.). In this emulsification and dispersion device, a stirring rotor rotates at high speed inside a water-cooled stator. When the aforementioned electrofused alumina powder and water are introduced into the gap between the stator and the stirring rotor, the rotation of the stirring rotor causes the electrofused alumina powder to become homogeneously dispersed in the water, forming a raw material slurry (dispersion). In this raw material slurry, the particles of electrofused alumina powder collide with each other, resulting in self-polishing.

[0035] The rotor's rotation speed is 10 m / s The peripheral speed is set to 10. m / s The electrofused alumina powder is efficiently polished by swirling flow at the above peripheral speed, generating inorganic particles with a particle size of 1 μm or larger, and inorganic fine particles with a particle size of 10 nm or larger and less than 0.1 μm in the solvent.

[0036] This is thought to be because the collision polishing of the electrofused alumina powder particles removes the sharp edges of the particles, generating inorganic particles, while the removed edges become inorganic microparticles.

[0037] Furthermore, the polishing time for the electrofused alumina powder (inorganic raw material powder) in this particle polishing process should be between 3 minutes and 60 minutes. If the polishing time is less than 3 minutes, there is a concern that sufficient inorganic fine particles will not be generated. Also, if polishing is performed for a long time, there is a concern that the alumina particles will be crushed and become too fine, resulting in too few inorganic particles. If the particles become too fine, the viscosity may become too high during mixing with the resin, resulting in poor moldability, or a sufficient amount of inorganic filler powder may not be mixed into the matrix material, resulting in insufficient improvement in thermal conductivity.

[0038] The emulsifying and dispersing apparatus may be supplied with fused alumina powder and water separately as two liquids, or as a pre-mixed slurry.

[0039] While other methods such as bead mills and ball mills can be used to grind electrofused alumina powder and water into a slurry, there are concerns about excessive grinding effect and quality degradation due to the inclusion of media such as beads or balls.

[0040] Next, the solvent is removed from the fluid obtained in the particle polishing process, in which inorganic particles and inorganic fine particles are generated in the solvent, thereby producing an inorganic filler powder in which inorganic fine particles are attached to the surface of the inorganic particles (drying process).

[0041] In this drying process, for example, a heated dryer is used to heat the fluid to about 80°C to 100°C, thereby evaporating the solvent from the fluid and causing inorganic fine particles to adhere (fix) to the surface of the inorganic particles during this solvent evaporation process. This results in an inorganic filler powder in which at least a portion of the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm, and the surface coverage rate of the inorganic particles by inorganic fine particles is 30% or more.

[0042] In this embodiment, the particle size is the median diameter (central diameter), i.e., the average particle size D50 at which the cumulative frequency reaches 50%. This average particle size D50 was measured using a laser diffraction scattering particle size distribution analyzer (MT3300EXII: Microtrac-Bell Co., Ltd.).

[0043] (Method for producing a thermally conductive polymer composition) The method for producing the thermally conductive polymer composition of this embodiment involves kneading the inorganic filler powder of this embodiment described above into a matrix material. To knead the inorganic filler powder into the matrix material, such as a resin, a rotary / revolving type mixer (e.g., Neritara: manufactured by Shinky Co., Ltd.) can be used.

[0044] The thermally conductive polymer composition of this embodiment consists of a matrix material containing the inorganic filler powder of this embodiment. For example, the thermally conductive polymer composition of this embodiment can be produced by adding 1200 to 7000 parts by mass of the inorganic filler powder of this embodiment to 100 parts by mass of the matrix material and kneading it with a mixer.

[0045] In this case, the inorganic filler powder has a structure in which at least a portion of the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm. Therefore, compared to the case in which raw alumina particles are used as alumina filler as is, the amount of inorganic filler powder can be increased while maintaining the same hardness or viscosity of the resulting thermally conductive polymer composition. This makes it possible to obtain a thermally conductive polymer composition with high thermal conductivity.

[0046] Although one embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment and its variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Examples]

[0047] The following shows the verification results that confirmed the effects of the present invention. As the inorganic raw material powder, fused alumina powder V325F (average particle size D50 = 11.1 μm: manufactured by Nippon Light Metal Co., Ltd.) was used. The fused alumina powder was mixed with deionized water to make a slurry with a concentration of 72% by mass. Using an emulsification and dispersion device (Aspec Disperser ZERO, manufactured by Hiroshima Metal & Machinery Co., Ltd.), the peripheral speed of the stirring rotor was set to 32 m / s or 35 m / s, and the time was set to 3 minutes, 30 minutes, 45 minutes, and 60 minutes, respectively, to polish the fused alumina powder and obtain a fluid. Next, the fluid was heated to 90°C using a heating furnace to evaporate the water solvent, and the residue was ground in a mortar to obtain inorganic filler powder.

[0048] Then, the obtained inorganic filler powder and a butadiene-based polymer (R-45HT: manufactured by Idemitsu Kosan Co., Ltd.) as a matrix material were kneaded using a rotational / revolving mixer (Awatori Rentaro: manufactured by Shinky Co., Ltd.) to obtain a thermally conductive polymer composition. At this time, 1400 parts by mass of inorganic filler powder were added to 100 parts by mass of matrix material.

[0049] (Verification Example 1) Electron microscope images were taken of the inorganic filler powders obtained for each of the polishing times described above. Figure 5 shows the result for a polishing time of 3 minutes, Figure 6 for a polishing time of 30 minutes, Figure 7 for a polishing time of 45 minutes, and Figure 8 for a polishing time of 60 minutes. In each of the photographs shown in Figures 5 to 8, the black background area is a magnified view of a portion of the surface of a single inorganic particle, and the numerous particles smaller than 0.1 μm displayed on top of this background are inorganic microparticles.

[0050] Then, in each of the electron microscope images shown in Figures 5 to 8, three arbitrary rectangular regions (0.5 μm × 0.5 μm) were set (fields 1 to 3), and after performing the binarization process shown in Figure 3, the coverage rate (%) of inorganic particles by inorganic microparticles was calculated. The results of this coverage rate are shown in Table 1.

[0051] [Table 1]

[0052] Table 1 shows that the coating rate increased with increasing polishing time. A raw material slurry in which fused alumina powder, an inorganic raw material powder, was diffused in a solvent was used. m / sIt was confirmed that by polishing the inorganic raw material powder by swirling it at the peripheral speed described above, it is possible to produce an inorganic filler powder in which the surface of inorganic particles with a particle size of 1 μm or more is coated with inorganic fine particles with a particle size of 10 nm or more and less than 0.1 μm.

[0053] (Verification Example 2) Next, the hardness of each thermally conductive polymer composition was measured using inorganic filler powder polished for 3 minutes (average coverage 21.4%), inorganic filler powder polished for 30 minutes (average coverage 30.1%), inorganic filler powder polished for 45 minutes (average coverage 56.2%), inorganic filler powder polished for 60 minutes (average coverage 90.9%), and electrofused alumina powder, which is a raw material that is not polished (average coverage 14.5%). Hardness measurement: Durometer (Asker Rubber Hardness Tester Type A: Polymer Instruments Co., Ltd.)

[0054] Then, the improvement rate (%) in hardness of the thermally conductive polymer composition using each inorganic filler powder, with respect to the hardness of the thermally conductive polymer composition using electrofused alumina powder as the raw material, was measured. Hardness improvement rate (%) = Hardness of the thermally conductive polymer composition using inorganic filler powder / Hardness of the thermally conductive polymer composition using electrofused alumina powder × 100 These results are shown in Figure 9 as a graph.

[0055] As shown in Figure 9, it was found that by manufacturing a thermally conductive polymer composition using inorganic filler powder with an average coverage rate of 30% or more of inorganic fine particles over inorganic particles, the hardness was reduced by more than 40% compared to conventional thermally conductive polymer compositions using electrofused alumina powder that was not polished, significantly increasing flexibility.

Claims

1. A structure (excluding sintered structures) in which at least a portion of the surface of inorganic particles (excluding those with a metal coating) with a particle size of 1 μm or more is coated by fixing inorganic fine particles (excluding those with a metal coating) with a particle size of 10 nm or more and less than 0.1 μm, wherein the coverage rate of the surface of the inorganic particles by the inorganic fine particles is 30% or more. The inorganic filler powder is characterized in that the inorganic particles and inorganic fine particles are any of aluminum oxide, silicon carbide, aluminum nitride, silicon nitride, silicon dioxide, or magnesium oxide.

2. A thermally conductive polymer composition characterized by mixing the inorganic filler powder described in claim 1 with a matrix material containing at least one of a resin material, an elastomer material, and a rubber material.

3. The thermally conductive polymer composition according to claim 2, characterized in that it contains 1,200 parts by mass or more of the inorganic filler powder with respect to 100 parts by mass of the matrix material.

4. The process includes a fluid polishing step in which a raw material slurry, obtained by mixing inorganic raw material powder and a solvent, is flowed in a swirling manner at a peripheral speed of 10 m / s or more to polish the inorganic raw material powder, thereby obtaining a fluid in which inorganic particles (excluding those coated with metal) and inorganic fine particles (excluding those coated with metal) are generated in the solvent; and a drying step in which the solvent is removed from the fluid and the inorganic fine particles are attached to the surface of the inorganic particles. The inorganic particles and inorganic fine particles are any of aluminum oxide, silicon carbide, aluminum nitride, silicon nitride, silicon dioxide, or magnesium oxide. A method for producing inorganic filler powder, characterized by producing an inorganic filler powder having a structure in which at least a portion of the surface of inorganic particles having a particle size of 1 μm or more is coated with inorganic fine particles having a particle size of 10 nm or more and less than 0.1 μm.

5. The method for producing inorganic filler powder according to claim 4, characterized in that the inorganic raw material powder is electrofused alumina powder.

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