JP6905834B2 - Method of manufacturing electromagnetic wave absorber and electromagnetic wave absorber - Google Patents

Description

The present invention relates to an electromagnetic wave absorber and a method for producing the electromagnetic wave absorber, and more specifically, to an electromagnetic wave absorber having an absorption property for electromagnetic waves in a frequency band (W band) of 75 GHz to 110 GHz.

In recent years, a collision avoidance support system has become widespread as one of the so-called Advanced Driver Assistance Systems (ADAS). In a collision avoidance support system, a millimeter-wave radar device is usually used to detect an object in front of a vehicle (for example, another vehicle, a pedestrian, an obstacle, etc.). The millimeter-wave radar device includes an antenna that emits an electromagnetic wave of a predetermined frequency (for example, 76 GHz) and an electromagnetic wave absorber that absorbs the electromagnetic wave of the frequency, and irradiates the object with the electromagnetic wave in a directional manner. It is configured so that it can be done. The absorbency means a property of absorbing an electromagnetic wave having a predetermined frequency and transmitting an electromagnetic wave other than the frequency without absorbing the electromagnetic wave. As such an electromagnetic wave absorber, one in which a carbon material (carbon-based particles) acting as a resistor is dispersed in a resin material is known (see, for example, Patent Document 1).

By the way, since the electromagnetic wave absorber of the above-mentioned conventional example has a low absorption rate for electromagnetic waves in a predetermined frequency band of about 40%, it is necessary to increase the electromagnetic wave absorption rate. As a method of increasing the electromagnetic wave absorption rate, it is conceivable to increase the content of the carbon material to increase the conductivity. However, since the carbon material is bulky, there is a problem that it is difficult to increase the content of the carbon material in the resin material.

Japanese Unexamined Patent Publication No. 2015-15373

In view of the above points, the present invention manufactures an electromagnetic wave absorber and an electromagnetic wave absorber having excellent absorption performance for electromagnetic waves in the frequency band of 75 GHz to 110 GHz even if the content of the carbon material in the resin material is small. The challenge is to provide a method.

In order to solve the above problems, the electromagnetic wave absorber of the present invention, which has absorbency against electromagnetic waves in a predetermined frequency band, is a resin material formed into a predetermined shape and a carbon material dispersed in the resin material. It is composed of a sintered body obtained by sintering the above with silver fine particles, and is characterized by containing 4 to 11 parts by weight of the silver fine particles with respect to 100 parts by weight of the resin material. In this case, it is preferable that the carbon material is contained in an amount of 4 to 11 parts by weight with respect to 100 parts by weight of the resin material. Further, in order to solve the above problems, the electromagnetic wave absorber of the present invention having absorbency to electromagnetic waves in a predetermined frequency band is dispersed in a resin material formed into a predetermined shape and the resin material. It is composed of a sintered body obtained by sintering a carbon material through silver fine particles, and is characterized by containing 4 to 11 parts by weight of the carbon material with respect to 100 parts by weight of the resin material.

According to the present invention, a carbon material is sintered with silver fine particles to form a low-resistance sintered body, and the sintered body is dispersed in a resin material, so that the conductivity is increased even if the content of the carbon material is small. As a result, an electromagnetic wave absorber having excellent absorption performance for electromagnetic waves in a predetermined frequency band can be obtained. According to the examples described later, it was confirmed that it has an absorption rate of 99% or more with respect to electromagnetic waves in the frequency band of 75 GHz to 110 GHz and exhibits excellent absorption performance.

In the present invention, as the carbon material, particles, powders, spheres, rods, flat plates, fibrous, hollow, square or lumps can be used, for example, carbon black, acetylene black, and the like. It can be used by selecting from carbon nanotubes, carbon nanofibers, graphene and fullerenes.

In the present invention, the average particle size of the silver fine particles is preferably 1 nm to 100 nm .

In the method for producing an electromagnetic wave absorber of the present invention, which manufactures an electromagnetic wave absorber capable of absorbing electromagnetic waves in a predetermined frequency band, the electromagnetic wave absorber is formed into a resin material formed into a predetermined shape and the resin material is contained therein. The process of producing a carbon material to which a dispersed carbon material is sintered via silver fine particles and to which the silver fine particles are attached is mixed with the carbon material to which the silver fine particles are attached and a resin material. The step of forming the mixture obtained by mixing into a predetermined shape and drying, and the step of heating the dried product obtained by drying at a temperature of 180 to 300 ° C. and sintering the carbon material with silver fine particles. It is characterized by including a step of performing.

In the present invention, in the step of producing the carbon material to which the silver fine particles are attached, a dispersion liquid obtained by dispersing the silver fine particles covered with a surfactant in a low polar solvent is obtained, and the carbon material is mixed with the dispersion liquid. It is preferable to include a step of adding a polar solvent to the dispersion liquid in which the carbon material is mixed and a step of precipitating the carbon material to which the silver fine particles covered with the surfactant are attached.

In the present invention, when the dried product is heated at 180 to 300 ° C., the surfactant is at least one selected from fatty acids having 6 to 18 carbon atoms and aliphatic amines having 6 to 18 carbon atoms. It is preferable to use it. According to this, even when heating at a relatively low temperature of 180 to 300 ° C., the surfactant can be desorbed, and the surfactant can be prevented from remaining attached to the silver fine particles.

In the present invention, the low-polarity solvent is at least one liquid hydrocarbon selected from octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, xylene, cyclododecane, cyclododecane, octylbenzene, and dodecylbenzene. Can be used alone or in combination.

The figure which shows typically the electromagnetic wave absorber of embodiment of this invention. The process drawing explaining the manufacturing method of the electromagnetic wave absorber of embodiment of this invention. (A) is a schematic diagram for explaining step 1 shown in FIG. 2, and (b) is a schematic diagram for explaining step 3 shown in FIG. The graph which plotted the complex relative permittivity measured in Example 1 of this invention. The graph which shows the electromagnetic wave absorption rate obtained in Example 1 of this invention. A STEM image of the electromagnetic wave absorbing sheet produced in Example 1 of the present invention. The graph which plotted the complex relative permittivity measured in Example 2 of this invention. The graph which shows the electromagnetic wave absorption rate obtained in Example 2 of this invention. The graph which plotted the complex relative permittivity measured in the comparative example 1. The graph which shows the electromagnetic wave absorption rate obtained in the comparative example 1. FIG. The graph which plotted the complex relative permittivity measured in the comparative example 2. The graph which shows the electromagnetic wave absorption rate obtained in the comparative example 2.

Hereinafter, the electromagnetic wave absorber according to the embodiment of the present invention will be described by taking a sheet-like one as an example. With reference to FIG. 1, the electromagnetic wave absorber EA is a sintered body obtained by sintering a resin material 1 formed into a sheet shape and a carbon material 21 dispersed in the resin material 1 via silver fine particles 22. It is composed of 2.

Examples of the resin material 1 include polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyester, polyvinyl butyral, ethylene / vinyl acetate copolymer resin (EVA resin), acrylonitrile / styrene copolymer resin (AS resin), and acrylonitrile / butadiene. -A styrene copolymer resin (ABS resin), acrylonitrile / ethylene / styrene copolymer resin (AES resin), polyamide resin, fluororesin, etc. can be selected and used, but isolated electron pairs can be used. It is preferable to use one having a functional group such as a butyral group, an acetyl group or a hydroxyl group. The silver fine particles 22 can be easily coordinated to the functional group having such a lone electron pair, and the aggregation of the silver fine particles 22 in the resin material 1 can be suppressed, and as a result, the dispersibility of the silver fine particles 22 can be improved. Can be enhanced. Therefore, polyvinyl butyral can be preferably used as the resin material 1.

As the carbon material 21, particles, powders, spheres, rods, flat plates, fibers, hollows, horns or lumps can be used, for example, carbon black, acetylene black, carbon nanotubes, carbon nano. At least one selected from fiber, carbon filler, graphene and fullerene can be used.

As the silver fine particles 22, those having an average particle diameter in the range of 1 nm to 100 nm can be used. If the average particle size is less than 1 nm, the specific surface area of the silver fine particles 22 becomes large, and the content of the surfactant 24 that coats the surface of the silver fine particles 22 becomes too large. The agent 24 may not be sufficiently desorbed, and if the average particle size exceeds 100 nm, the sintering of the carbon material 21 via the silver fine particles 22 may be insufficient. The average particle size is a value obtained based on the particle size analysis by the dynamic light scattering method of JISZ8828.

Next, with reference to FIG. 2, the method for manufacturing the electromagnetic wave absorber EA will be described by taking the case of manufacturing an electromagnetic wave absorbing sheet as an example.

First, in step S1, silver fine particles 22 are dispersed in a low-polarity solvent 23 to prepare a dispersion liquid, and the carbon material 21 is stirred and mixed with the prepared dispersion liquid (see FIG. 3A). A known homogenizer can be used for stirring and mixing. A dispersion in which the silver fine particles 22 are dispersed in the low polar solvent 23 in advance may be prepared, and the carbon material 21 may be stirred and mixed with the dispersion.

Here, the blending ratio of the silver fine particles 22 can be set in the range of 4 to 11 parts by weight with respect to 100 parts by weight of the resin described later, and the blending ratio of the carbon material 21 is also set with respect to 100 parts by weight of the resin described later. It can be set in the range of 4 to 11 parts by weight. If it is less than 4 parts by weight, the imaginary part of the complex relative permittivity of the electromagnetic wave absorber described later may be low and the electromagnetic wave absorption performance may be insufficient. If it exceeds 11 parts by weight, the imaginary part of the complex relative permittivity may be insufficient. It may become too large and the electromagnetic wave absorption performance may be insufficient. In order to enhance the dispersibility of the silver fine particles 22, the surface of the silver fine particles 22 is covered with the surfactant 24. As the surfactant 24, it is preferable to use at least one selected from fatty acids having 6 to 18 carbon atoms and aliphatic amines having 6 to 18 carbon atoms. Examples of fatty acids having 6 to 18 carbon atoms include hexanoic acid having 6 carbon atoms and 2-ethylbutyric acid; heptanoic acid having 7 carbon atoms, 2-methylhexanoic acid and cyclohexanecarboxylic acid; octanoic acid having 8 carbon atoms and neo. Xanoic acid, 2-ethylhexanoic acid; 9-carbon nonanoic acid; 10-carbon neooctanoic acid, decanoic acid; 11-carbon undecanoic acid; 12-carbon neodecanoic acid, dodecanoic acid; and 14-carbon tetradecanoic acid Palmitic acid having 16 carbon atoms; and at least one selected from stearic acid, oleic acid, linoleic acid, and linolenic acid having 18 carbon atoms can be used alone or in combination. Examples of aliphatic amines having 6 to 18 carbon atoms include hexylamines having 6 carbon atoms, cyclohexylamines and aniline; heptylamines having 7 carbon atoms; octylamines having 8 carbon atoms and 2-ethylhexylamines; 9 carbon atoms. Nonylamine; decylamine with 10 carbon atoms; dodecylamine with 12 carbon atoms; tetradodecylamine with 14 carbon atoms; and stearylamine with 18 carbon atoms, at least one selected from oleylamine can be used alone or in combination. .. For fatty acids and aliphatic amines having less than 6 carbon atoms, the dispersibility of the silver fine particles 22 in the low polar solvent 23 may decrease, while for fatty acids and aliphatic amines having 19 or more carbon atoms, at the temperature described later. The desorption of the surfactant 24 (fatty acid or aliphatic amine) from the surface of the silver fine particles 22 may be insufficient during the heat treatment, and the resistance value of the sintered body 2 may increase. The low protic solvent 23 is, for example, at least one selected from octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, xylene, octylbenzene, dodecylbenzene, decalin, tetraline, cyclododecane, cyclohexylbenzene and cyclododecane. The seeds can be used alone or in combination.

Then, the polar solvent 25 is added (step S2), the mixture is sufficiently stirred, and then the mixture is allowed to stand for a predetermined time (for example, 2 to 12 hours). As a result, as shown in FIG. 3B, the carbon material 21 to which the silver fine particles 22 are attached settles (step S3). As the polar solvent 25, for example, at least one selected from alcohols such as methanol, ethanol and propanol, and ketones such as acetone, methyl ethyl ketone, methyl isopropyl ketone and methyl isobutyl ketone can be used. By removing the supernatant liquid by decantation or the like (step S4), the carbon material 21 to which the silver fine particles 22 are attached is produced. The addition of the polar solvent 25 (step S2) to the removal of the supernatant liquid (step S4) may be repeated a plurality of times.

A resin material is added to the carbon material 21 to which the silver fine particles 22 thus produced are attached (step S5), and the mixture is sufficiently stirred and mixed to obtain a mixture (step S6). A known homogenizer can be used for this stirring / mixing. As the resin material, a powdery material can be used.

The mixture obtained in step S6 is poured into a predetermined container for molding, and this is dried for a predetermined time (for example, 6 to 12 hours) to obtain a dried product (step S7). The drying temperature can be set in the range of 60 to 100 ° C. Finally, the dried body is heat-pressed at a temperature of 180 to 300 ° C. and a pressure of 5 to 15 MPa (step S8) to obtain an electromagnetic wave absorbing sheet having a predetermined shape. By applying pressure during this heat treatment, the distance between the carbon materials 21 becomes shorter, and sintering becomes easier.

By the way, the electromagnetic wave absorption rate A (dB) when a plane wave is vertically incident on an electromagnetic wave absorber EA such as a metal-lined one-layer electromagnetic wave absorbing sheet can be expressed by the following equation (1).

_{Z in in the} equation (1) is the input impedance of the electromagnetic wave absorber EA normalized by the wave impedance in vacuum, and can be expressed by the following equation (2).

In equation (2), ε ^* is the complex relative permittivity, j is the imaginary unit, f is the frequency of the electromagnetic wave (Hz), d is the thickness of the electromagnetic wave absorber EA (m), and C ₀ is the speed of light in vacuum (= about). It is 3 × 10 ⁸ (m / s)).

From the above equation (1), when Z _in = 1, the electromagnetic wave absorption rate A (dB) becomes maximum. Therefore, assuming that the left side of the above equation (2) is 1, the following equation (3) can be obtained as an equation satisfying the condition that the electromagnetic wave absorption rate A is maximized (hereinafter referred to as “non-reflection condition”).

Equation (3) is a function of the complex relative permittivity ε ^* , that is, an equation expressing the non-reflection condition. There are innumerable ^{complex relative permittivity ε *} that satisfy equation (3). This equation (3) can be approximated as the following equation (4).

N in the equation (4) is a value called the order of the equation (non-reflective curve described later) expressing the non-reflective condition, and takes the values of n = 1, 2, 3, 4, .... Of these, in the equation (4), the thickness d (m) of the electromagnetic wave absorber EA becomes the minimum when n = 1. Therefore, by substituting n = 1 into the equation (4), the following equation (5) is obtained.

Further, the complex relative permittivity ε ^* can be expressed by the following equation (6).

In equation (6), ε'is ^{the real part of the complex relative permittivity ε *} , and ε'' is the imaginary part of ^{the complex relative permittivity ε *.} From the equations (5) and (6), the following equations (7) and (8) can be obtained. From these equations (7) and (8), the following equation (9) can be obtained.

Equation (9) is an approximate equation that satisfies the non-reflection condition when the thickness of the electromagnetic wave absorber EA is the smallest. Then, the curve represented by the equation (9) in the ε'−ε'' plane (complex plane) is called a non-reflective curve. ^{In order to fit the real part ε'and the imaginary part ε'' of the complex relative permittivity ε *} to this non-reflective curve, it is necessary to increase the conductivity of the electromagnetic wave absorber EA. It is difficult to increase the content.

According to the present embodiment, the carbon material 21 is sintered with the silver fine particles 22 to obtain a low-resistance sintered body 2, and the sintered body 2 is dispersed in the resin material 1, so that the content of the carbon material 21 is increased. At a minimum, the conductivity can be increased. By increasing the conductivity of the electromagnetic wave absorber EA in this way, the real part ε'and the imaginary part ε'' ^{of the complex relative permittivity ε * can be fitted to the non-reflection condition.} Therefore, if the thickness of the electromagnetic wave absorber EA is appropriately set according to the frequency of the electromagnetic wave to be absorbed, it is possible to provide excellent absorption performance for the electromagnetic wave of the frequency.

Hereinafter, examples in which the embodiments of the present invention are more embodied will be described.

(Example 1)
4 parts by weight of silver fine particles (trade name "Ag Nanometal Ink L-Ag1T" made by ULVAC) is mixed with 11 parts by weight of particulate carbon material (trade name "Vurcan XC-72R" made by Cabot), and a small amount thereof is added. (100 parts by weight) of toluene was added, and the mixture was sufficiently stirred and mixed with a homogenizer at 25 ° C. (10 minutes or more). Ethanol having a volume (500 parts by weight) five times that of toluene was added thereto, and the mixture was sufficiently stirred. After stopping the stirring, the carbon material to which the silver fine particles were attached was precipitated by allowing it to stand for 12 hours. After removing the supernatant, add 100 parts by weight of resin (trade name "Polyvinyl butyral 630" manufactured by Wako Pure Chemical Industries, Ltd.), add 300 parts by weight of ethanol, and stir sufficiently (10 minutes or more) with a homogenizer. Mixing gave a mixture. This mixture was poured into a film container having a size of 150 mm × 150 mm × 50 mm and dried at 60 ° C. for 12 hours to obtain a dried product. This dried product was heat-pressed at 200 ° C. and 10 MPa for 1 hour to prepare an electromagnetic wave absorbing sheet having a size of 150 mm × 150 mm × 1 mm. The complex relative permittivity in the frequency band of 75 to 110 GHz of the prepared electromagnetic wave absorbing sheet was measured by the free space method. The result of plotting the measured complex relative permittivity is shown in FIG. According to this, it was confirmed that the complex relative permittivity was plotted near the non-reflective curve. Based on the measured complex relative permittivity, when the thickness of the electromagnetic wave absorbing sheet is changed to 0.28, 0.30, 0.32, 0.34, 0.36, 0.38 mm, the formula (1) ) Is shown in FIG. According to this, it was found that by appropriately setting the thickness of the electromagnetic wave absorption sheet, it has an excellent electromagnetic wave absorption rate of 20 dB or more (99% or more) in the frequency band of 75 to 110 GHz, and exhibits excellent absorption performance. rice field.

A sample in which the cross section of the electromagnetic wave absorbing sheet prepared in Example 1 was sliced was prepared by a focused ion beam (FIB) method, and the sample was observed with a scanning transmission electron microscope (STEM). The bright field image of the STEM is shown in FIG. According to this, it was found that the silver fine particles 22 adhered to the carbon material 21 to form the sintered body 2, and the sintered body 2 was dispersed in the resin material 1.

(Example 2)
By the same method as in Example 1 above, except that 11 parts by weight of silver fine particles (trade name "L-Ag1T" manufactured by ULVAC) are blended and the temperature of the heat press treatment of the dried product is set to 180 ° C. An electromagnetic wave absorbing sheet was prepared. The complex relative permittivity in the frequency band of 75 to 110 GHz of the prepared electromagnetic wave absorbing sheet was measured by the free space method in the same manner as in Example 1 above. The result of plotting the measured complex relative permittivity is shown in FIG. According to this, it was confirmed that the complex relative permittivity was plotted near the non-reflective curve. Based on the measured complex relative permittivity, when the thickness of the electromagnetic wave absorbing sheet is changed to 0.28, 0.30, 0.32, 0.34, 0.36, 0.38 mm, the formula (1) ) Is shown in FIG. According to this, it was found that by appropriately setting the thickness of the electromagnetic wave absorption sheet, it has an excellent electromagnetic wave absorption rate of 20 dB or more (99% or more) in the frequency band of 75 to 110 GHz, and exhibits excellent absorption performance. rice field.

Next, a comparative example with respect to the above embodiment will be described.

(Comparative Example 1)
In Comparative Example 1, a small amount (100 parts by weight) of silver fine particles (trade name “L-Ag1T” manufactured by ULVAC) was added to 4 parts by weight without blending a carbon material (trade name “Vurcan XC-72R” manufactured by Cabot). Toluene was added, and the mixture was sufficiently stirred and mixed with a homogenizer at 25 ° C. (10 minutes or more). Ethanol having a volume (500 parts by weight) five times that of toluene was added thereto, and the mixture was sufficiently stirred. After stopping the stirring, the silver fine particles were allowed to settle for 12 hours. Then, an electromagnetic wave absorption sheet was produced in the same manner as in Example 1 above. The complex relative permittivity in the frequency band of 75 to 110 GHz of the prepared electromagnetic wave absorbing sheet was measured by the free space method in the same manner as in Example 1 above. The result of plotting the measured complex relative permittivity is shown in FIG. According to this, it was confirmed that the complex relative permittivity was plotted in the region away from the non-reflective curve. Based on the measured complex relative permittivity, when the thickness of the electromagnetic wave absorbing sheet is changed to 0.52, 0.56, 0.60, 0.64, 0.68, 0.72 mm, the equation (1) ) Is shown in FIG. According to this, it was found that the electromagnetic wave absorption rate was less than 20 dB in the frequency band of 75 to 110 GHz even if the thickness of the electromagnetic wave absorption sheet was changed.

(Comparative Example 2)
In Comparative Example 2, silver fine particles (trade name "L-Ag1T" manufactured by ULVAC) were not blended, and a small amount (100 parts by weight) was added to 11 parts by weight of a carbon material (trade name "Vurcan XC-72R" manufactured by Cabot). Toluene was added, and the mixture was sufficiently stirred and mixed with a homogenizer at 25 ° C. (10 minutes or more). Then, an electromagnetic wave absorption sheet was produced in the same manner as in Example 1 above. The complex relative permittivity in the frequency band of 75 to 110 GHz of the prepared electromagnetic wave absorbing sheet was measured by the free space method in the same manner as in Example 1 above. The result of plotting the measured complex relative permittivity is shown in FIG. According to this, it was confirmed that the complex relative permittivity was plotted in the region away from the non-reflective curve. Calculated by Eq. (1) when the thickness of the electromagnetic wave absorbing sheet is changed to 0.28, 0.30, 0.32, 0.34, 0.36 mm based on the measured complex relative permittivity. The electromagnetic absorption rate is shown in FIG. According to this, it was found that the electromagnetic wave absorption rate was less than 20 dB in the frequency band of 75 to 110 GHz even if the thickness of the electromagnetic wave absorption sheet was changed.

The present invention is not limited to the above embodiment. In the above embodiment, the case of manufacturing the electromagnetic wave absorbing sheet has been described, but the shape of the electromagnetic wave absorbing body is arbitrary, and may be formed into a block shape, for example.

EA ... Electromagnetic wave absorber, 1 ... Resin material, 2 ... Sintered body, 21 ... Carbon material, 22 ... Silver fine particles, 23 ... Low polar solvent, 24 ... Surfactant, 25 ... Polar solvent.

Claims (7)

In an electromagnetic wave absorber that absorbs electromagnetic waves in a predetermined frequency band,
It is composed of a resin material molded into a predetermined shape and a sintered body in which a carbon material dispersed in the resin material is sintered via silver fine particles .
An electromagnetic wave absorber containing 4 to 11 parts by weight of the silver fine particles with respect to 100 parts by weight of the resin material. The electromagnetic wave absorber according to claim 1, wherein the carbon material is contained in an amount of 4 to 11 parts by weight based on 100 parts by weight of the resin material. In an electromagnetic wave absorber that absorbs electromagnetic waves in a predetermined frequency band,
It is composed of a resin material molded into a predetermined shape and a sintered body in which a carbon material dispersed in the resin material is sintered via silver fine particles.
An electromagnetic wave absorber containing 4 to 11 parts by weight of the carbon material with respect to 100 parts by weight of the resin material. The electromagnetic wave absorber according to any one of claims 1 to 3, wherein the average particle size of the silver fine particles is 1 nm to 100 nm . A method for manufacturing an electromagnetic wave absorber that manufactures an electromagnetic wave absorber that absorbs electromagnetic waves in a predetermined frequency band. The electromagnetic wave absorber is dispersed in a resin material formed into a predetermined shape and the resin material. In the case of a product composed of a sintered body obtained by sintering a carbon material through silver fine particles.
The process of producing a carbon material with silver fine particles attached,
The step of mixing the carbon material to which the silver fine particles are attached and the resin material, and
The process of molding the mixture obtained by mixing into a predetermined shape and drying it.
A method for producing an electromagnetic wave absorber, which comprises a step of heating a dried product obtained by drying at a temperature of 180 to 300 ° C. and sintering the carbon material with silver fine particles. The step of producing the carbon material to which the silver fine particles are attached is
A step of dispersing silver fine particles covered with a surfactant in a low-polarity solvent to obtain a dispersion liquid, and mixing a carbon material with this dispersion liquid.
The production of the electromagnetic wave absorber according to claim 5, further comprising a step of adding a polar solvent to a dispersion liquid mixed with a carbon material and precipitating a carbon material to which silver fine particles covered with a surfactant are attached. Method. The method for producing an electromagnetic wave absorber according to claim 6, wherein the dried body is heated at 180 to 300 ° C.
The method for producing an electromagnetic wave absorber according to claim 6, wherein the surfactant is at least one selected from a fatty acid having 6 to 18 carbon atoms and an aliphatic amine having 6 to 18 carbon atoms. ..

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