JPH0682942B2 - Radio wave absorber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radio wave absorber having excellent mechanical strength and rigidity.

[Conventional technology]

In recent years, the use of radio waves has been rapidly expanding mainly in the mobile communication field toward the realization of an advanced information society. In addition, various electronic devices have come into widespread use along with the innovative progress of today's microelectronics technology. Against this background, electromagnetic interference due to unwanted radio waves generated by various wireless devices, electronic devices, etc. tends to increase year by year, and therefore good electromagnetic environment (EMC) in buildings There is an urgent need to develop a high-performance electromagnetic wave absorber that is necessary to maintain the environment. It is important that the material used for the radio wave absorber is a material with large electric loss and magnetic loss that effectively attenuates electromagnetic energy. Conventionally, various ohmic loss materials, dielectric loss materials, magnetic loss materials that meet this requirement Materials are being developed and provided.

As the most representative radio wave absorber, a material in which carbon is held by an insulating resin material such as urethane foam, or a material in which carbon is mixed with rubber or plastic is known.

[Problems to be Solved by the Invention]

However, the type that uses urethane foam as a holding material has a drawback that it requires skill in molding work such as demolding and processing because the material itself is soft and cannot hold a desired shape by itself. . In addition, in the case of using rubber, plastic, etc. as a matrix, it is difficult to uniformly disperse carbon, and the strength and weather resistance of the formed structure are insufficient and it cannot be applied as a building material. There is a point. For this reason, a method of mixing a fiber reinforcing material such as carbon fiber in order to reinforce the structure has been proposed, but it has not yet been achieved to impart uniform mechanical strength and rigidity.

The inventors of the present invention confirmed that the activated carbon powder and granules meet this requirement as a result of conducting multifaceted test research on a material in which the holding material itself has a dielectric loss property and good moldability. It has been developed. Therefore, an object of the present invention is to provide a radio wave absorber having a formed structure having excellent mechanical strength and rigidity and an appropriate radio wave absorption performance.

[Means for Solving the Problems]

A radio wave absorber according to the present invention for achieving the above object is a component obtained by mixing a conductive carbon black and / or carbon fiber as a dispersant with a resin binder and a carbon paste mixed with activated carbon powder particles. The structural feature is that the molded product has a composition.

As the activated carbon constituting the holding base material in the present invention, charcoal, sawdust charcoal, coconut shell charcoal, a granular material obtained by activating coal, etc., with an appropriate particle size distribution particularly in the range of particle size 10 to 100 mesh. The mixture is effectively used.

Carbon powder, carbon fiber or both of them are mixed with a resin binder in the activated carbon powder. Conductive carbon black is effective as the carbon powder. The carbon fiber may be polyacrylonitrile-based, rayon-based or pitch-based, and is usually 1 to 3 m.
It is used as a chop cut to about m.

Conductive carbon black and / or carbon fibers are, for example, vinyl acetate / ethylene-based, vinyl acetate / ethylene /
Mixed with activated carbon powder in a state of being mixed with a resin binder such as acrylic type, styrene / vinyl chloride type, styrene / butadiene type, acrylic type, styrene / acrylic type, formalin type (urea, melamine, phenol, resorcinol resin, etc.) However, particularly good results are obtained when a commercially available carbon paste in which conductive carbon black is suspended in the binder component is used in advance.

It is desirable to mix these conductive carbon black and / or carbon fibers so that the blending ratio is 10 to 20 g / l with respect to the activated carbon powder or granules. It becomes difficult to secure. As described above, the electromagnetic wave absorber of the present invention is obtained by molding the component composition obtained by mixing the carbon powder and / or carbon fiber with the resin binder into the activated carbon powder or granular material into a desired wedge shape, pyramid, plate shape or the like. Is formed.

This radio wave absorber may be coated or impregnated with a material for the purpose of making it non-combustible or may be colored with a pigment in order to be used for the same purpose as other building materials.

[Action]

According to the present invention, a component composition in which a powdery or granular material of activated carbon having originally good dielectric loss characteristics and good moldability is used as a holding material, and conductive carbon black and / or carbon fiber is mixed therein via a resin binder. Since it is configured as a molded body of (1), it can be provided as a molded body excellent in radio wave absorption, strength and rigidity suitable for the frequency of the radio wave to be constantly absorbed. Moreover, since the component composition is mainly composed of carbon, it is possible to obtain a radio wave absorber having good weather resistance and suitable as a building material.

〔Example〕

 Hereinafter, the present invention will be described in detail based on examples.

Example 1 Activated carbon powder (particle size: 50 mesh) was mixed with carbon paste (Lion paste W-311N manufactured by Lion Co., Ltd.) containing conductive carbon black as a dispersant so that the carbon content (C amount) was different. These were mixed and molded into a plate-shaped molded body having a length and width of 40 mm and a thickness of 7 mm.

The dielectric constant of each obtained molded body was measured, and the results are shown in Table 1.

The dielectric constant is measured by inserting the test piece in a direct test adapter and using a Q meter at each frequency of 10MHz, 30MHz and 50MHz by the direct measurement method.
And the dielectric constant was calculated by the equation (2).

However, the symbols in the above formula are as follows.

εr: Relative permittivity tanδ: Dielectric loss tangent tx: Sample thickness (cm) t ₀ : Minimum distance between electrodes at resonance without sample (cm) C ₁ : C value at resonance with inductor only (pF) Q ₂ : Q value at resonance when there is no sample and the distance between electrodes is the same as the sample thickness Q ₃ : Q value at resonance when there is a sample From the results shown in Table 1, the dielectric constant of the obtained molded product was appropriate as a radio wave absorber, and the structure of the molded product had excellent mechanical strength and rigidity.

Example 2 Activated carbon powder (particle size 50 mesh) was added to the same carbon paste and carbon fiber chop (length 0.7 m) as in Example 1.
m) are mixed so that the carbon content is 10g / l and the mixture is molded into a 40mm length, 7m thickness.
It was formed into a m-shaped plate. The obtained molded body had a high bending strength and a high elastic modulus, and its dielectric constant showed appropriate electromagnetic wave absorption characteristics as shown in Table 2.

Example 3 An activated carbon / carbon paste mixture having a composition of dielectric constant (εr) 5.0 and dielectric loss (tan δ) 1.0 was molded into a wedge shape shown in FIG. 1 and the theoretical electromagnetic wave absorption was measured.
As a result, the reflection loss (dB) shown in FIG.

〔The invention's effect〕

As described above, the activated carbon having good moldability according to the present invention is used as the holding material, and the carbon powder and / or the carbon fiber is mixed into the holding material to provide the appropriate electromagnetic wave absorption performance and the excellent electromagnetic strength and rigidity. Therefore, it can be expected to be useful when applied to a radio wave absorption wall as a building material.

[Brief description of drawings]

FIG. 1 is a perspective view showing the shape of a radio wave absorber according to an embodiment of the present invention, and FIG. 2 is a graph illustrating a theoretical radio wave absorption amount.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshikazu Takei 2-19-1, Tobita-cho, Chofu-shi, Tokyo Kashima Construction Co., Ltd. Technical Research Institute (72) Inventor Tadahiro Shimazu 1-2-2 Moto-Akasaka, Minato-ku, Tokyo No. 7 Kashima Construction Co., Ltd. (72) Inventor Yoshio Sasanuma 1-2-7 Moto-Akasaka, Minato-ku, Tokyo Kashima Construction Co., Ltd. (72) Inventor Yoshinori Kasashima 2-19-1 Tobita, Chofu-shi, Tokyo No. Kashima Construction Co., Ltd. Technical Research Institute (72) Inventor Eiji Matsushita Moto-Akasaka 1-2-7, Minato-ku, Tokyo Kashima Construction Co., Ltd. (72) Inventor Masaru Fujimoto 776-2, Kawaguchi City, Saitama Prefecture ( 72) Inventor Yoshinaga Katsuzawa 2-229, Suzuki-cho, Kodaira-shi, Tokyo (56) Reference JP 62-111500 (JP, A) Actual 60-129196 (JP, U)

Claims (2)

[Claims] 1. A molded product having a component composition in which a carbon paste obtained by mixing conductive carbon black and / or carbon fiber as a dispersant with a resin binder is mixed with powdered particles of activated carbon. Radio wave absorber. 2. The compounding ratio of conductive carbon black and / or carbon fiber to powder of activated carbon is 10 to 20 g / l.
The radio wave absorber according to claim 1.