JPWO2012124290A1 - Radio wave absorbing particle manufacturing method, radio wave absorbing particle manufactured by the method, and radio wave absorber - Google Patents

Abstract

The inorganic particle slurry containing the inorganic particles and the conductive filler slurry containing the conductive filler are mixed to prepare a mixed slurry, and the sprayed slurry is sprayed and dried using the spray dryer method, so that the inorganic particles are dried. And electromagnetic wave absorbing particles composed of conductive filler.

Description

  The present invention relates to a method for producing radio wave absorbing particles, a radio wave absorbing particle produced by the method, and a radio wave absorber.

  In recent years, advances in wireless communication technology and infrastructure development of wireless communication systems have progressed, and the use of radio waves such as mobile phones, wireless local area networks (LANs) and automatic fee collection systems (ETCs) has been rapidly progressing.

  Under the use of radio waves, it is required to make the device operate normally without being affected by external radio waves (immunity problem) and to prevent the device from emitting radio waves that affect others (emission problem). Radio wave absorbers that absorb unnecessary radio waves and suppress reflected waves have attracted attention.

  This radio wave absorber is generally known as a molded body in which a ferrite sintered body, a magnetic powder such as ferrite, or a conductive powder such as carbon black is dispersed in a synthetic resin or rubber. The radio wave energy is converted into heat energy and absorbed by magnetic loss.

  As a wave absorber using dielectric loss and conductive loss, for example, non-conductive foam made of conductive foam particles made of vinylidene chloride resin and thermoplastic organic polymer (for example, vinylidene chloride resin). Radio wave absorbing particles in which the particles are fused to each other have been proposed. This conductive foamed particle comprises a conductive layer having a conductive powder on the surface of a thermoplastic organic polymer foamed particle, and an overcoat thin layer of an organic polymer that prevents the conductive powder in the conductive layer from falling off have. And it is described that such a structure can provide radio wave absorbing particles having excellent mechanical strength and stable shape retention for a long period of time (see, for example, Patent Document 1).

JP-A-11-209505

  However, since the electromagnetic wave absorber described in Patent Document 1 uses dielectric loss, the conductive material alone does not exhibit radio wave absorption characteristics. That is, in Patent Document 1, conductive foam particles and non-conductive foam particles are mixed, and the mixture is heated in a molding die to fuse the conductive foam particles and the non-conductive foam particles. Therefore, the manufacturing process is complicated.

  Therefore, the present invention has been made in view of the above-described problems, and the radio wave absorbing particles that are constituent particles of a radio wave absorber that exhibits radio wave absorption characteristics without undergoing a fusion process with a non-conductive material. It is an object of the present invention to provide a manufacturing method and radio wave absorbing particles and radio wave absorbers manufactured by the method.

  In order to achieve the above object, the method for producing radio wave absorbing particles of the present invention comprises mixing an inorganic particle slurry containing inorganic particles and a conductive filler slurry containing a conductive filler to produce a mixed slurry, It is characterized by granulating radio wave absorbing particles composed of inorganic particles and conductive fillers by spraying and drying the mixed slurry using a spray dryer method.

  According to this configuration, it is possible to manufacture radio wave absorbing particles that can obtain a radio wave absorber excellent in radio wave absorption characteristics in which a conductive three-dimensional network is formed simply by filling a container and accumulating it. Therefore, it is possible to obtain a radio wave absorber that exhibits radio wave absorption characteristics without going through the process of fusing the conductive foam particles and the non-conductive foam particles.

  Further, the radio wave absorbing particles can be mass-produced by a simple method of spraying and drying the mixed slurry by the spray dryer method.

  In the method for producing radio wave absorbing particles of the present invention, the blending amount of the conductive filler in the mixed slurry may be 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

  According to this configuration, it is possible to form a stable conductive network without causing the disadvantage that the radio wave absorption characteristics are degraded.

  In the method for producing radio wave absorbing particles of the present invention, the inorganic particles may be alumina particles, and the conductive filler may be carbon particles.

  According to this configuration, since the alumina particles have an appropriate weight, when the electromagnetic wave absorbing particles are filled in the container to form the electromagnetic wave absorber, the contact between the particles can be maintained by the weight of the electromagnetic wave absorbing particles. It becomes possible. Therefore, a stable conductive network can be formed, and as a result, the radio wave absorption characteristics can be improved. Further, by using carbon particles, it is possible to improve the conductivity with a small amount of the conductive filler and obtain a radio wave absorber excellent in radio wave absorption characteristics.

  In the method for producing radio wave absorbing particles of the present invention, the inorganic particle slurry contains a dispersant, and the amount of the dispersant in the inorganic particle slurry is 0.5 parts by mass or more with respect to 100 parts by mass of the inorganic particles. There may be.

  According to this configuration, since the dispersant also serves as a binder, the strength of the radio wave absorption particles is improved, and when using the radio wave absorption particles, the disadvantage that the radio wave absorption particles are damaged by their own weight is avoided. It becomes possible.

  In the method for producing radio wave absorbing particles of the present invention, the inorganic particles may be titania particles and the conductive filler may be carbon particles.

  According to this configuration, compared with the case where alumina particles are used as inorganic particles, the amount of carbon particles added is reduced (that is, with a small amount of carbon particles added), and a desired frequency band (for example, around 6 GHz). An electromagnetic wave absorber that absorbs the electromagnetic wave can be obtained. Further, by using carbon particles, it is possible to improve the conductivity with a small amount of the conductive filler and obtain a radio wave absorber excellent in radio wave absorption characteristics.

  In the method for producing radio wave absorbing particles of the present invention, the inorganic particles may be a ceramic tile substrate, and the conductive filler may be carbon particles.

  According to this configuration, since the ceramic tile base has a small density and is inexpensive, an inexpensive and lightweight radio wave absorber can be obtained by using the ceramic tile base as the inorganic particles. Further, by using carbon particles, it is possible to improve the conductivity with a small amount of the conductive filler and obtain a radio wave absorber excellent in radio wave absorption characteristics.

  In addition, the method for producing radio wave absorbing particles of the present invention is a radio wave absorbing particle that can obtain a radio wave absorber excellent in radio wave absorption characteristics in which a conductive three-dimensional network is formed simply by filling a container and accumulating it. It has an excellent characteristic that it can be manufactured. Therefore, the present invention is suitably used for the radio wave absorbing particles manufactured by the radio wave absorbing particle manufacturing method of the present invention and the radio wave absorber in which the radio wave absorbing particles are integrated.

  According to the present invention, it is possible to manufacture a radio wave absorbing particle that can obtain a radio wave absorber excellent in radio wave absorption characteristics in which a conductive three-dimensional network is formed, by simply filling the container with the radio wave absorbing particle and accumulating it. be able to.

It is sectional drawing which shows the structure of the electromagnetic wave absorption particle which concerns on embodiment of this invention. It is the schematic which shows the whole structure of the spray dryer apparatus used in the manufacturing method of the electromagnetic wave absorption particle which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the droplet produced | generated in the spray dryer process in the manufacturing method of the electromagnetic wave absorption particle which concerns on embodiment of this invention. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorption particle obtained in Examples 1-5 and Example 15. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorption particle obtained in Examples 6-10. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorption particle obtained in Examples 11-12 and Example 16. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorption particle obtained in Example 1 and Examples 13-14. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorption particle obtained in Examples 17-25. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorption particle obtained in Examples 26-33. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorption particle obtained in Examples 34-37.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

  FIG. 1 is a cross-sectional view showing the structure of radio wave absorbing particles according to an embodiment of the present invention.

  As shown in FIG. 1, the radio wave absorbing particle 1 of the present embodiment is a granule formed by a plurality of inorganic particles (core particles) 2 that are dielectrics and a plurality of conductive fillers 4 gathered together. .

  The radio wave absorbing particle 1 absorbs unnecessary electromagnetic waves such as noise generated from electronic components constituting the electronic device, for example. The radio wave absorbing particle 1 acts to protect the electronic device from external electromagnetic waves and noise. In addition, it has an effect of preventing noise generated from the electronic device from leaking to the outside.

  In addition, by filling the electromagnetic wave absorbing particles 1 in a container or other storage member, for example, an electromagnetic wave absorber used in a wireless LAN, an ETC (Electronic Toll Collection), an anechoic chamber, heat resistance, or incombustibility is required. The radio wave absorbing particle 1 is used as a material for forming the radio wave absorber.

  That is, the electromagnetic wave absorbing particles 1 which are granules formed by the inorganic particles 2 and the conductive fillers 4 are filled in a container and accumulated, thereby combining a conductive three-dimensional network with a conductor and a dielectric. A radio wave absorber having a structure can be easily manufactured.

  In addition, as described above, the radio wave absorber can be used for various purposes. However, since the frequency band used for next-generation wireless communication such as the above-described wireless LAN and ETC is 2.4 to 10 GHz, It can be suitably used as a radio wave absorber that absorbs electromagnetic waves in a frequency band near 6 GHz.

  Further, as shown in FIG. 1, in the radio wave absorbing particle 1, the conductive filler 4 is distributed throughout the radio wave absorbing particle 1, and the density of the conductive filler 4 from the center of the radio wave absorbing particle 1 toward the surface. The slope of the distribution is large.

  That is, a large number of conductive fillers 4 are distributed on the surface of the radio wave absorbing particles 1, and a conductive layer 3 composed of a large number of conductive fillers 4 is formed on the surface of the conductive particles 1.

  On the other hand, as shown in FIG. 1, the inorganic particles 2 are uniformly distributed throughout the radio wave absorbing particles 1. Within the radio wave absorbing particles 1, a small number of inorganic particles 2 are uniformly distributed between the inorganic particles 2. The conductive filler 4 is located.

  Although not shown, when the conductive filler 4 concentrates on one inorganic particle 2 inside the radio wave absorbing particle 1, the inorganic particle 2 covered with the conductive filler 4 is formed. .

  The inorganic particles 2 are not particularly limited, but ceramic particles are preferably used from the viewpoint of forming a stable conductive network and improving radio wave absorption characteristics. As the ceramic particles, alumina particles, titania particles, clay, kaolin, glass particles, mullite particles, zirconia particles, zircon particles, and magnesia particles are preferably used as heat-resistant ceramic particles and ceramic tile bases, At least one of these can be used.

  That is, by using the above-mentioned ceramic particles (alumina particles, titania particles, etc.) as the inorganic particles 2, the ceramic particles have an appropriate weight, so the radio wave absorber particles 1 are filled in a container to form a radio wave absorber. In doing so, it becomes possible to maintain contact between the particles due to the weight of the radio wave absorbing particles 1. Therefore, a stable conductive network can be formed, and as a result, the radio wave absorption characteristics can be improved. Moreover, since the above-mentioned ceramic particles are excellent in heat resistance and nonflammability, it is possible to obtain a radio wave absorber that requires heat resistance and nonflammability by using such ceramic particles.

  The “conductive network” referred to here is a conductive tertiary formed by filling the wave absorbing particles 1 into a container and accumulating them, so that the plurality of wave absorbing particles 1 are in contact with each other or close to each other. Say the original network.

  In addition, by using titania particles having a dielectric constant higher than that of alumina particles as inorganic particles 2, the amount of conductive filler 4 (carbon particles) added can be reduced as compared with the case of using alumina particles (that is, A radio wave absorber that absorbs electromagnetic waves in a desired frequency band (for example, around 6 GHz) can be obtained with a small amount of added carbon particles.

  In addition, since the ceramic tile base has a small density and is inexpensive, by using the ceramic tile base as the inorganic particles 2, an inexpensive and light-weight wave absorber can be obtained.

  The term “ceramic tile base” as used herein refers to a ceramic tile base specified in JIS A5209, which is a clay material containing quartz, feldspar, porcelain stone, and wax. say.

  In addition, as the ceramic tile base, a slurry-like commercial product (for example, trade name: N-300 manufactured by Yamase Co., Ltd.) can be used.

  The shape of the inorganic particles 2 is not particularly limited, and may be any shape such as a spherical shape, a granular shape, a needle shape, a flake shape, and a plate shape, but from the viewpoint of forming a homogeneous network structure, The shape of the particles 2 is preferably spherical.

  Moreover, as the inorganic particles 2, it is preferable to use particles having an average particle diameter of 0.1 μm or more and 10 μm or less.

  The “average particle size” as used herein refers to a 50% particle size (D50), a particle size distribution measuring device (Nikkiso Co., Ltd., Nanotrac (registered trademark) particle size distribution measuring device applying the laser Doppler method. UPA-EX150) etc.

  The conductive filler 4 is not particularly limited, but in this embodiment, carbon particles such as carbon black and carbon nanotubes, metal particles such as gold, silver and copper, indium-tin oxide (ITO), tin -Conductive ceramic particles of metal oxides such as antimony oxide (ATO), indium-zinc oxide (IZO), gallium-zinc oxide (GZO), zinc oxide (ZnO), tin oxide (SnO) are used Are preferably used, and at least one of them can be used.

  Among these, carbon particles having excellent conductivity are used from the viewpoint of being inexpensive and lightweight, and improving conductivity with a small amount of the conductive filler 4 to obtain a radio wave absorber excellent in radio wave absorption characteristics. It is preferable to do.

  The shape and size of the conductive filler 4 depend on the shape and size of the inorganic particles 2, and the conductive filler 4 has a particle form similar to the inorganic particles 2. The shape of the conductive filler 4 is not particularly limited, and may be any shape such as a spherical shape, a granular shape, a needle shape, a flake shape, and a plate shape.

  Next, a method for producing radio wave absorbing particles according to an embodiment of the present invention will be described.

  In this embodiment, the inorganic particle slurry containing the inorganic particles 2 and the conductive filler slurry containing the conductive filler 4 are mixed to produce a mixed slurry, and the mixed slurry is sprayed using a spray dryer method. It is characterized in that it is dried to granulate the radio wave absorbing particles 1 composed of inorganic particles and conductive fillers.

  With such a configuration, the radio wave absorbing particles 1 can be mass-produced by a simple method of spraying and drying the mixed slurry by a spray dryer method.

  The manufacturing method of this embodiment includes an inorganic particle slurry preparation step, a conductive filler slurry preparation step, a mixed slurry preparation step, and a spray dryer step.

<Inorganic particle slurry preparation process>
First, water (ion exchange water), inorganic particles 2, a dispersing agent, and a pulverizing material are put into a resin container (for example, a resin pot), and mixing and pulverization are performed for a predetermined time using a pot mill stand. To make a slurry. Next, the slurry mixed with the pulverized material is passed through a sieve to separate the slurry and the pulverized material, whereby an inorganic particle slurry containing the inorganic particles 2 is obtained.

  The dispersant is for promoting the dispersion of the inorganic particles 2 to prevent the aggregation of the inorganic particles 2 and improving the solid content concentration of the inorganic particles. In this embodiment, the dispersant is dispersed in the inorganic particle slurry. It is preferable to set the compounding amount of the agent so as to be a ratio of 0.5 parts by mass or more with respect to 100 parts by mass of the inorganic particles.

  This is because when the blending amount of the dispersant is 0.5 parts by mass or more, the dispersant also plays a role as a binder, and the strength of the radio wave absorption particles 1 is improved. This is because it is possible to avoid the disadvantage that the particles 1 are damaged by their own weight.

  Examples of the dispersant include an aqueous dispersant for polycarboxylic acid, inorganic dispersants such as sodium phosphate, sodium polyphosphate, sodium citrate, and sodium silicate, amines, pyridine, polyacrylic acid, and polycarboxylic acid. Organic dispersants such as metal salts or ammonium salts can be used.

  Further, the pulverized material is for destroying the aggregated inorganic particles 2 and promoting the dispersion of the inorganic particles 2. For example, when alumina particles are used as the inorganic particles 2, coarse particles and aggregates exist in the alumina particles. Therefore, using the pulverized material, the alumina particles are crushed simultaneously with mixing, and the coarse particles and aggregates are separated. Destroy.

  A cobblestone or the like can be used as this crushing material.

  Further, during the mixing, in order to prevent re-aggregation of the inorganic particles, the above-mentioned dispersant is simultaneously added to promote dispersion.

  Moreover, it is good also as a structure which uses additives, such as a binder, a plasticizer, a lubricant, and an antifoamer.

<Conductive filler slurry preparation process>
A conductive filler slurry containing the conductive filler 4 is obtained by dispersing the conductive filler 4 (for example, carbon black or carbon nanotube when carbon particles are used) in water (ion exchange water).

  A commercially available conductive filler slurry may be used. For example, carbon slurry (manufactured by Lion Corporation, trade name: W-356A, carbon content: 8% by mass) can be used.

<Mixed slurry preparation process>
First, a conductive filler slurry is added to the prepared inorganic particle slurry, and mixed for a predetermined time using a stirrer. Next, a binder and a lubricant are added and mixed for a predetermined time to obtain a mixed slurry in which the inorganic particle slurry and the conductive filler slurry are mixed. In addition, in this process, you may add the above-mentioned dispersing agent and crushing material as needed.

  Here, in this embodiment, it is preferable to set the blending amount of the conductive filler in the mixed slurry so as to be a ratio of 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles. .

  This is because when the blending amount of the conductive filler is less than 0.5 parts by mass, the content of the conductive filler 4 is small, which may cause a problem that the radio wave absorption characteristics of the radio wave absorbing particles 1 are deteriorated. Because there is. Moreover, when the compounding amount of the conductive filler is larger than 10 parts by mass, the conductivity is excessively improved, so that it is difficult to convert the electromagnetic wave into heat, and as a result, there is a disadvantage that the radio wave absorption characteristic is deteriorated. This is because it may occur. That is, by setting the blending amount of the conductive filler to 0.5 parts by mass or more and 10 parts by mass or less, it is possible to form a stable conductive network without causing the disadvantage that the radio wave absorption characteristic is deteriorated. become.

  In this step, first, the prepared inorganic particle slurry is weighed, and the mass of the inorganic particles contained in the inorganic particle slurry is calculated. Next, based on the calculated mass of the inorganic particles, the conductive filler slurry was weighed and weighed so that the blending amount of the conductive filler was 1.4 parts by mass or more with respect to 100 parts by mass of the inorganic particles. By adding and mixing the conductive slurry to the weighed inorganic particle slurry, a mixed slurry is obtained.

  As a binder, the binder conventionally used for granulation of the ceramic granule can be used. For example, synthetic water-soluble polymers such as polyvinyl alcohol, acrylic acid, polyacrylic acid amide, isobutylene-maleic anhydride copolymer, starches, saccharides, derivatives thereof, and cellulose derivatives may be used alone or in combination. Can be used.

  Moreover, the compounding quantity of the binder in a mixing slurry is set so that it may become a ratio of 0.25 mass part or more and 1.5 mass parts or less with respect to a total of 100 mass parts of the inorganic particle 2 and the electroconductive filler 4. FIG.

  The lubricant is used to improve the slipperiness of the surface of the radio wave absorbing particles 1 and to smoothly put the radio wave absorbing particles 1 into the container. As this lubricant, for example, an aqueous lubricant of fatty acid (for example, stearic acid) can be used. In addition, when slipping on the particle surface is necessary, such as when charging into a container having a complicated shape, for example, the blending amount of the lubricant in the mixed slurry is 100 parts by mass in total of the inorganic particles and the conductive filler. It is good to set to 0.14 mass part.

  In this step, the mass of the conductive filler 4-contained in the weighed conductive filler slurry is calculated, and based on the calculated mass of the inorganic particles 2 and the calculated mass of the conductive filler 4. Then, a binder and a lubricant are added so as to have the above-mentioned blending ratio.

<Spray dryer process>
Next, the radio wave absorbing particles 1 are produced by mixing the inorganic particle slurry containing the inorganic particles 2 and the conductive filler slurry containing the conductive filler 4 and treating the mixed slurry using a spray dryer method.

  FIG. 2 is a schematic view showing an overall configuration of a spray dryer apparatus used in the method for producing radio wave absorbing particles according to the embodiment of the present invention.

  As shown in FIG. 2, the spray dryer apparatus 10 includes a granulation chamber 11 in which the radio wave absorbing particles 1 are granulated, a rotating disk (atomizer) 12 that sprays the mixed slurry into droplets, and a rotating disk 12. And a slurry supply pipe 14 for supplying the mixed slurry to the rotating disk 12.

  The motor 13 includes a shaft 15 that is rotationally driven, and the rotary disk 12 is attached to the shaft 15. The rotating disk 12 is configured to rotate integrally with the shaft 15.

  In this step, first, the prepared mixed paste is supplied to the rotating disk 12 via the slurry supply pipe 14. Then, due to the centrifugal force of the rotating disk 12, the mixed slurry is sprayed in the horizontal direction (in the direction of arrow A in the figure) to become fine droplets (atomized liquid) 16.

  As shown in FIG. 3, the droplet 16 has a spherical shape due to its own surface tension, and the inorganic particles 2 and the conductive filler 4 are dispersed in the water droplet 6.

  The sprayed droplets 16 are dried by hot air 17 blown into the granulation chamber 11 by a hot air generator (not shown) to produce the radio wave absorbing particles 1 shown in FIG.

  At this time, the moisture in the droplet 16 is released to the outside while evaporating, and the remaining inorganic particles 2 and the conductive filler 4 are aggregated to form the radio wave absorbing particles 1, but compared to the inorganic particles 2, Since the conductive filler 4 having a small specific gravity moves to the surface side of the radio wave absorption particles 1 together with moisture, the conductive fillers 4 are distributed on the surface of the radio wave absorption particles 1 as shown in FIG. In addition, although there are conductive fillers 4 left from the movement of moisture and remaining inside the particles, the amount thereof is smaller than the amount of conductive fillers 4 moving to the surface side. Therefore, as described above, in the radio wave absorbing particle 1, the conductive filler 4 is distributed throughout the radio wave absorbing particle 1, and the gradient of the density distribution of the conductive filler 4 from the center of the radio wave absorbing particle 1 toward the surface. Becomes larger. As a result, a conductive layer 3 composed of a large number of conductive fillers 4 is formed on the surface of the radio wave absorbing particles 1.

  The produced radio wave absorbing particles 1 are recovered from a recovery port 18 formed in the lower part of the granulation chamber 11.

  Then, by filling and laminating the wave absorbing particles 1 formed in this way into a container, a wave absorber composed of a composite structure of a conductive three-dimensional network and a conductor and a dielectric is easily manufactured. can do.

  That is, a radio wave absorber excellent in radio wave absorption characteristics in which a conductive three-dimensional network is formed can be obtained simply by filling the wave-absorbing particles 1 into a container and accumulating them. Therefore, it is possible to obtain a radio wave absorber that exhibits radio wave absorption characteristics without going through the process of fusing the conductive foam particles and the non-conductive foam particles.

  Hereinafter, the present invention will be described based on examples. In addition, this invention is not limited to these Examples, These Examples can be changed and changed based on the meaning of this invention, and they are excluded from the scope of the present invention. is not.

Example 1
(Production of radio wave absorbing particles)
In a 3 liter resin container, 3 kg of cobblestone (manufactured by Nikkato Co., Ltd., material: HD, diameter: 5 mm), 500 g of ion-exchanged water, and polycarboxylic acid as a main component (Chukyo Yushi) 25 g of Co., Ltd., trade name: D-305, polycarboxylic acid content: 40% by mass) was added and mixed by rotating for 10 minutes using a pot mill stand.

  Subsequently, 2000 g of alumina particles (manufactured by Showa Denko KK, trade name: AL-160SG-4, purity 99.48%) having an average particle size of 0.55 μm was added to this mixture in several portions. Mixing and crushing were performed. Thereafter, using a pot mill stand, mixing and crushing were performed for 15 hours to form a slurry, and the mixture was passed through a sieve having an opening of 2 mm to separate the crushed material, thereby obtaining an alumina slurry.

  The dispersant was added so that the amount of the dispersant in the alumina slurry was 0.5 parts by mass with respect to 100 parts by mass of the alumina particles.

  Next, a carbon slurry (manufactured by Lion Corporation, trade name: W-356A, carbon content: 8 mass%) in which carbon black (primary particle size: about 40 nm) is dispersed in water is prepared, and the prepared alumina slurry. To 1000 g, 139 g of carbon slurry was added and mixed for 30 minutes using a stirrer.

  The carbon slurry was added so that the blending amount of the carbon particles in the mixed slurry was 1.4 parts by mass with respect to 100 parts by mass of the alumina particles.

  Next, 11.2 g of an aqueous binder whose main component is polyvinyl alcohol (manufactured by Chukyo Yushi Co., Ltd., trade name: WF-804, polyvinyl alcohol content: 10% by mass) and an aqueous system whose main component is paraffin wax are added to this slurry. 14.5 g of binder (manufactured by Chukyo Yushi Co., Ltd., trade name: WF-610, paraffin wax content: 20% by mass), water-based lubricant whose main component is fatty acid (manufactured by Chukyo Yushi Co., Ltd., trade name: Cerosol 920) , Fatty acid content: 18% by mass) was added and mixed for 1 hour to obtain a mixed slurry of alumina slurry and carbon slurry.

  In addition, the said binder was added so that the compounding quantity of the water-system binder of polyvinyl alcohol in a mixing slurry might be 0.138 mass part with respect to a total of 100 mass parts of an alumina particle and a carbon particle.

  Moreover, the said binder was added so that the compounding quantity of the water-system binder of the paraffin wax in a mixing slurry might be 0.361 mass part with respect to a total of 100 mass parts of an alumina particle and a carbon particle.

  Furthermore, the said lubricant was added so that the compounding quantity of the water-system lubricant in a mixing slurry might be 0.14 mass part with respect to a total of 100 mass parts of an alumina particle and a carbon particle.

  Next, the produced mixed slurry is supplied to a spray dryer apparatus (trade name: FL-12, manufactured by Okawara Chemical Co., Ltd.), and the mixed slurry is sprayed and dried using a spray dryer method, thereby absorbing radio waves. Particles were made.

  In the spray dryer process, the inlet temperature was set to 140 to 160 ° C., the rotation speed of the rotating disk was set to 12000 rpm, and the supply amount of the mixed slurry was set to 40 g / min. Moreover, the average particle diameter of the obtained radio wave absorbing particles was 50 to 60 μm.

(Radio wave absorption characteristics evaluation)
Next, the relative dielectric constant, dielectric loss tangent, relative permeability measuring device (measurement cell manufactured by Keycom Corporation (outer diameter: 7 mm, inner diameter: 3 mm, height: 30 mm) is filled with the produced radio wave absorbing particles. A radio wave absorber is manufactured, a radio wave is transmitted with a vector network analyzer (manufactured by Anritsu Co., Ltd., trade name: 37269E), and the complex dielectric constant is calculated from the value of the transmitted wave transmitted through the cell and the reflected wave reflected by the cell. And the complex permeability was measured.

  Next, by using the radio wave absorber / reflection loss simulation program (manufactured by Keycom Corporation, trade name: DMP-70) from these measured values, the radio wave absorption is calculated by calculating the return loss [dB]. Characteristics were evaluated. The above results are shown in FIG. In addition, it evaluated on the following evaluation conditions.

A: In the measurement frequency band (500 to 10,000 MHz), the return loss is 10 dB or more. ○: In the measurement frequency band (500 to 10,000 MHz), the return loss is 5 dB or more and less than 10 dB. X: In the measurement frequency band (500 to 10,000 MHz). Return loss less than 5dB (Evaluation of particle crushing strength)
Next, using a micro compression tester (manufactured by Shimadzu Corporation, trade name: MCTM-500), JIS R1639-5 (Fine ceramics-measurement method of (condylar) grain characteristics-Part 5: Single? The crushing strength (compressive load and diameter when the radio wave absorbing particles are broken) [MPa] of the produced single radio wave absorbing particles was measured based on (grain crushing strength). The results are shown in Table 1. In addition, it evaluated on the following evaluation conditions.

A: Crushing strength is 0.3 MPa or more B: Crushing strength is 0.25 MPa or more and less than 0.3 MPa X: Crushing strength is less than 0.25 MPa (Example 2)
In the same manner as in Example 1 except that 168 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 1.7 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 3)
In the same manner as in Example 1 except that 208 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 2.1 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 4)
In the same manner as in Example 1 except that 238 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 2.4 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 5)
In the same manner as in Example 1 above, except that 347 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 3.5 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 6)
Except that 208 g of carbon slurry was added and no binder and lubricant were used so that the amount of carbon in the mixed slurry was 2.1 parts by mass with respect to 100 parts by mass of alumina particles. Radio wave absorbing particles were produced in the same manner as in Example 1 described above. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 7)
208 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 2.1 parts by mass with respect to 100 parts by mass of alumina particles, and the amount of polyvinyl alcohol aqueous binder was Except that 25 g of the polyvinyl alcohol aqueous binder was added to 100 parts by mass with the carbon particles, and that no paraffin wax aqueous binder and lubricant were used. In the same manner as in Example 1 described above, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 8)
Except that 50 g of the polyvinyl alcohol aqueous binder was added so that the blending amount of the polyvinyl alcohol aqueous binder was 0.5 parts by mass with respect to 100 parts by mass in total of the alumina particles and the carbon particles. In the same manner as in Example 7, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

Example 9
Except for adding 100 g of the polyvinyl alcohol aqueous binder so that the blending amount of the polyvinyl alcohol aqueous binder is 1.0 part by mass with respect to 100 parts by mass in total of the alumina particles and the carbon particles. In the same manner as in Example 7, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 10)
Except that 150 g of the polyvinyl alcohol aqueous binder was added so that the blending amount of the polyvinyl alcohol aqueous binder was 1.5 parts by mass with respect to 100 parts by mass in total of the alumina particles and the carbon particles. In the same manner as in Example 7, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 11)
Except that 50 g of the polycarboxylic acid aqueous dispersant was added so that the compounding amount of the polycarboxylic acid aqueous dispersant in the alumina slurry was 1.0 part by mass with respect to 100 parts by mass of the alumina particles. In the same manner as in Example 6, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 12)
Except for adding 100 g of the polycarboxylic acid aqueous dispersant so that the amount of the polycarboxylic acid aqueous dispersant in the alumina slurry is 2.0 parts by mass with respect to 100 parts by mass of the alumina particles, Radio wave absorbing particles were produced in the same manner as in Example 6 described above. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 13)
As alumina particles, alumina particles having an average particle diameter of 0.54 μm (manufactured by Showa Denko KK, trade name: A-161SG, purity: 99.33%) are used as in Example 1 above. Thus, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 14)
Example 1 described above, except that alumina particles having an average particle diameter of 1.0 μm (made by Showa Denko KK, trade name: A-43-M, purity: 99.39%) were used as alumina particles. In the same manner, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 15)
In the same manner as in Example 1 except that 69 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 0.7 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

(Example 16)
Other than adding 12.5 g of the polycarboxylic acid aqueous dispersant so that the amount of the polycarboxylic acid aqueous dispersant in the alumina slurry is 0.25 parts by mass with respect to 100 parts by mass of the alumina particles. Produced electromagnetic wave absorbing particles in the same manner as in Example 6 described above. Thereafter, the radio wave absorption characteristics and the strength were evaluated in the same manner as in Example 1 described above. The above results are shown in FIG.

  As shown in FIGS. 4 to 7, the radio wave absorber in which the radio wave absorbing particles of any of Examples 1 to 14 and 16 are integrated has a return loss of 10 dB or more in the measurement frequency band (500 to 10,000 MHz). It can be seen that the radio wave absorption characteristics are extremely good.

  That is, it is understood that radio wave absorbing particles can be produced by a simple method of mixing an alumina slurry and a carbon slurry and treating the mixed slurry using a spray dryer method. In addition, it can be seen that a radio wave absorber excellent in radio wave absorption characteristics in which a conductive three-dimensional network is formed can be obtained simply by filling the wave-absorbing particles into a container and accumulating them.

  Moreover, in Example 15, in the measurement frequency band (500-10000 MHz), it turns out that reflection attenuation amount is 5 dB or more and less than 10 dB, and an electromagnetic wave absorption characteristic is favorable.

  In addition, compared with Examples 1-14 and 16 described above, the amount of return loss in Example 15 is small. In Example 15, the amount of carbon particles compared to Examples 1-14 and 16 is as follows. Therefore, it is considered that the conductive layer made of carbon particles was not formed with a sufficient thickness on the surface of the radio wave absorbing particles as compared with Examples 1 to 14 and 16.

  Moreover, as shown in Table 1, it can be seen that any of the radio wave absorbing particles of Examples 1 to 15 has a crushing strength of 0.3 MPa or more and an extremely good strength.

  Moreover, in Example 16, crushing strength is 0.25 MPa or more and less than 0.3 MPa, and it turns out that intensity | strength is favorable.

  In addition, in Example 16, the crushing strength is small compared to Examples 1 to 15 described above, because in Example 16, the amount of dispersant is small compared to Examples 1 to 15, It is considered that this is because the dispersant could not sufficiently fulfill the role as a binder as compared with Examples 1 to 15.

  Moreover, as shown in Examples 1-15, the compounding quantity of the binder in a mixing slurry is a ratio of 0.25 mass part or more and 1.5 mass parts or less with respect to 100 mass parts in total of an alumina particle and a carbon particle. It can be seen that the radio wave absorption characteristics and strength are good.

(Example 17)
Except that 495 g of carbon slurry was added so that the compounding amount of carbon in the mixed slurry was 5 parts by mass with respect to 100 parts by mass of alumina particles, and that an aqueous binder and an aqueous lubricant were not used. In the same manner as in Example 1, radio wave absorbing particles were produced.

(Radio wave absorption characteristics evaluation)
Next, the prepared electromagnetic wave absorbing particles are filled in an acrylic container (height: 300 mm, width: 300 mm, thickness: 10 mm) to produce an electromagnetic wave absorber, and a vector network analyzer (manufactured by Anritsu Co., Ltd., trade name: 37269E) and a lens antenna type return loss measuring device (manufactured by Keycom Corporation, trade name: LAF-2.6A modified), and JIS R1679 (radio wave absorption characteristic measurement method in millimeter wave band of radio wave absorber) ), The radio wave absorption characteristics were measured and evaluated by measuring the amount of reflection of the radio wave absorber with respect to normal incidence. The measurement was performed in the range of 2.6 to 15 GHz. The above results are shown in FIG. In addition, it evaluated on the following evaluation conditions.

A: Return loss is 10 dB or more in the measurement frequency band (2.6 to 15 GHz) B: Return loss is 5 dB or more and less than 10 dB in the measurement frequency band (2.6 to 15 GHz) ×: Measurement frequency band (2. 6 to 15 GHz), the return loss is less than 5 dB (Example 18)
Radio wave absorbing particles in the same manner as in Example 17 except that 297 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 3 parts by mass with respect to 100 parts by mass of alumina particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 19)
In the same manner as in Example 17 except that 248 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 2.5 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 20)
Radio wave absorbing particles in the same manner as in Example 17 except that 198 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 2 parts by mass with respect to 100 parts by mass of alumina particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 21)
In the same manner as in Example 17 except that 149 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 1.5 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 22)
Radio wave absorbing particles in the same manner as in Example 17 except that 99 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 1 part by mass with respect to 100 parts by mass of alumina particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 23)
In the same manner as in Example 17 except that 49 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 0.5 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 24)
In the same manner as in Example 17 except that 743 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 7.5 parts by mass with respect to 100 parts by mass of alumina particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 25)
Radio wave absorbing particles in the same manner as in Example 17 except that 990 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 10 parts by mass with respect to 100 parts by mass of alumina particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 26)
(Production of radio wave absorbing particles)
In a 3 liter resin container, 3 kg of cobblestone (manufactured by Nikkato Co., Ltd., material: HD, diameter: 5 mm), 700 g of ion-exchanged water, and polycarboxylic acid as a main component (Chukyo Yushi) 4.2 g of Co., Ltd., trade name: D-305, polycarboxylic acid content: 40% by mass) was added and mixed by rotating for 10 minutes using a pot mill mount.

  Next, 2100 g of titania particles (manufactured by Fuji Titanium Industry Co., Ltd., trade name: high-purity titanium oxide TM-1) having an average particle diameter of 0.62 μm were added to this mixture in several portions, and mixed and dissolved. Crushed. Then, using a pot mill stand, mixing and crushing were performed for 15 hours to form a slurry, and passed through a sieve having an opening of 2 mm to separate the crushed material, thereby obtaining a titania slurry.

  The dispersant was added so that the amount of the dispersant in the titania slurry was 0.08 parts by mass with respect to 100 parts by mass of the titania particles.

  Next, a carbon slurry (manufactured by Lion Corporation, trade name: W-356A, carbon content: 8% by mass) in which carbon black (primary particle size: about 40 nm) is dispersed in water is prepared and produced. To 1000 g, 468 g of carbon slurry was added and mixed for 30 minutes using a stirrer.

  In addition, carbon slurry was added so that the compounding quantity of the carbon particle in a mixing slurry might be 5 mass parts with respect to 100 mass parts of titania particles, and the mixed slurry of the titania slurry and the carbon slurry was obtained.

  Next, the produced mixed slurry is supplied to a spray dryer apparatus (trade name: FL-12, manufactured by Okawara Chemical Co., Ltd.), and the mixed slurry is sprayed and dried using a spray dryer method, thereby absorbing radio waves. Particles were made.

  In the spray dryer process, the inlet temperature was set to 140 to 160 ° C., the rotation speed of the rotating disk was set to 12000 rpm, and the supply amount of the mixed slurry was set to 40 g / min. Moreover, the average particle diameter of the obtained radio wave absorbing particles was 50 to 60 μm.

  Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 27)
Radio wave absorbing particles in the same manner as in Example 26 except that 281 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 3 parts by mass with respect to 100 parts by mass of titania particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 26 described above. The above results are shown in FIG.

(Example 28)
In the same manner as in Example 26 described above except that 234 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 2.5 parts by mass with respect to 100 parts by mass of titania particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 26 described above. The above results are shown in FIG.

(Example 29)
Radio wave absorbing particles in the same manner as in Example 26 except that 187 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 2 parts by mass with respect to 100 parts by mass of titania particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 26 described above. The above results are shown in FIG.

(Example 30)
In the same manner as in Example 26 described above, except that 140 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 1.5 parts by mass with respect to 100 parts by mass of titania particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 26 described above. The above results are shown in FIG.

(Example 31)
Radio wave absorbing particles in the same manner as in Example 26 except that 94 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 1 part by mass with respect to 100 parts by mass of titania particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 26 described above. The above results are shown in FIG.

(Example 32)
In the same manner as in Example 26 described above, except that 47 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 0.5 parts by mass with respect to 100 parts by mass of titania particles. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 26 described above. The above results are shown in FIG.

(Example 33)
Radio wave absorbing particles in the same manner as in Example 26 except that 936 g of carbon slurry was added so that the amount of carbon in the mixed slurry was 10 parts by mass with respect to 100 parts by mass of titania particles. Was made. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 26 described above. The above results are shown in FIG.

(Example 34)
(Production of radio wave absorbing particles)
Carbon slurry (manufactured by Lion Corporation, trade name: W-356A, carbon content: 8% by mass) in which carbon black (primary particle size: about 40 nm) is dispersed in water, and slurry of ceramic tile base (Yamase) Co., Ltd., trade name: N-300) was prepared.

  The solid content of the slurry of the ceramic tile base was 67.6% by mass, and one containing 61% by mass of clay and 39% by mass of feldspar was used.

  Next, 422 g of carbon slurry was added to 1000 g of the ceramic tile base slurry, and mixed for 1 hour using a stirrer.

  In addition, carbon slurry is added so that the compounding amount of the carbon particles in the mixed slurry is 5 parts by mass with respect to 100 parts by mass of the ceramic tile base, and the slurry of the ceramic tile base and the carbon slurry is mixed. Got.

  Next, the produced mixed slurry is supplied to a spray dryer apparatus (trade name: FL-12, manufactured by Okawara Chemical Co., Ltd.), and the mixed slurry is sprayed and dried using a spray dryer method, thereby absorbing radio waves. Particles were made.

  In the spray dryer process, the inlet temperature was set to 140 to 160 ° C., the rotation speed of the rotating disk was set to 12000 rpm, and the supply amount of the mixed slurry was set to 40 g / min. Moreover, the average particle diameter of the obtained radio wave absorbing particles was 50 to 60 μm.

  Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 17 described above. The above results are shown in FIG.

(Example 35)
Except that 296 g of carbon slurry was added so that the compounding amount of carbon in the mixed slurry was 3.5 parts by mass with respect to 100 parts by mass of the ceramic tile substrate, the same as in Example 32 above. Then, radio wave absorbing particles were produced. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 32 described above. The above results are shown in FIG.

(Example 36)
In the same manner as in Example 32 described above, except that 169 g of carbon slurry was added so that the blending amount of carbon in the mixed slurry was 2 parts by mass with respect to 100 parts by mass of the ceramic tile substrate. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 32 described above. The above results are shown in FIG.

(Example 37)
In the same manner as in Example 32 described above, except that 84 g of carbon slurry was added so that the blending amount of carbon in the mixed slurry was 1 part by mass with respect to 100 parts by mass of the ceramic tile substrate. Absorbent particles were prepared. Thereafter, the radio wave absorption characteristics were evaluated in the same manner as in Example 32 described above. The above results are shown in FIG.

  As shown in FIGS. 8 to 10, the radio wave absorber in which the radio wave absorption particles of any of Examples 17 to 22, 24 to 31, and 33 to 37 are integrated is measured in a measurement frequency band (2.6 to 15 GHz). It can be seen that the return loss is 10 dB or more, and the radio wave absorption characteristics are extremely good.

  That is, to produce radio wave absorbing particles by a simple method of mixing alumina slurry (or titania slurry, ceramic tile substrate slurry) and carbon slurry, and treating the mixed slurry using a spray dryer method. You can see that In addition, it can be seen that a radio wave absorber excellent in radio wave absorption characteristics in which a conductive three-dimensional network is formed can be obtained simply by filling the wave-absorbing particles into a container and accumulating them.

  In Examples 23 and 32, it can be seen that the return loss is 5 dB or more and less than 10 dB in the measurement frequency band (2.6 to 15 GHz), and the radio wave absorption characteristics are good.

  In Example 23, the return loss is small compared to Examples 17 to 22, 24, and 25 described above. In Example 23, the amount of return loss is smaller than that in Examples 17 to 22, 24, and 25. It is considered that the conductive layer made of carbon particles was not formed with a sufficient thickness on the surface of the radio wave absorbing particles as compared with Examples 17 to 22, 24, and 25 because the amount of the particles was small. .

  Similarly, in Example 32, the return loss is small compared to Examples 26 to 31 and 33 described above. In Example 32, the carbon particles are smaller than those in Examples 26 to 31 and 33. This is probably because the conductive layer made of carbon particles was not formed to a sufficient thickness on the surface of the radio wave absorbing particles as compared with Examples 26 to 31 and 33 because of the small amount of the compound.

  As described above, the present invention is suitable for the method of manufacturing radio wave absorbing particles, the radio wave absorbing particles manufactured by the method, and the radio wave absorber.

DESCRIPTION OF SYMBOLS 1 Radio wave absorption particle 2 Inorganic particle 3 Conductive layer 4 Conductive filler 6 Water drop 10 Spray dryer apparatus 11 Granulation chamber 12 Rotating disk 13 Motor 14 Slurry supply pipe 17 Hot air

Claims (8)

  By mixing an inorganic particle slurry containing inorganic particles and a conductive filler slurry containing a conductive filler to produce a mixed slurry, and spraying the mixed slurry using a spray dryer method and drying, A method for producing radio wave absorbing particles, comprising granulating radio wave absorbing particles comprising inorganic particles and the conductive filler.   2. The electromagnetic wave absorbing particle according to claim 1, wherein a blending amount of the conductive filler in the mixed slurry is 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles. Production method.   The method for producing radio wave absorbing particles according to claim 1 or 2, wherein the inorganic particles are alumina particles, and the conductive filler is carbon particles.   The said inorganic particle slurry contains a dispersing agent, The compounding quantity of the said dispersing agent in the said inorganic particle slurry is 0.5 mass part or more with respect to 100 mass parts of said inorganic particles, It is characterized by the above-mentioned. The manufacturing method of the electromagnetic wave absorption particle | grains of description.   The method for producing radio wave absorbing particles according to claim 1 or 2, wherein the inorganic particles are titania particles, and the conductive filler is carbon particles.   The method for producing radio wave absorbing particles according to claim 1 or 2, wherein the inorganic particles are ceramic tile bases, and the conductive filler is carbon particles.   Radio wave absorbing particles produced by the production method according to any one of claims 1 to 6.   A radio wave absorber in which the radio wave absorbing particles according to claim 7 are integrated.

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