JP2014049526A - Electromagnetic wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighter electromagnetic wave absorber capable of absorbing electromagnetic waves having low frequencies of 1 GHz or lower.SOLUTION: An electromagnetic wave absorber which is light and absorbs electromagnetic waves having low frequencies, includes a conductor having a volume resistivity of 1 Ω m or less and a semi-insulating material formed by a resin including at least one type of a dielectric body chosen from water, glycols, and a ferroelectric substance and having a volume resistivity of 1 kΩ m or more and 10 GΩ or less, and generates electromotive force having an absolute value of 10 mV or more when the conductor and the semi-insulating material are made contacted with each other.

Description

  The present invention relates to an electromagnetic wave absorber that absorbs harmful electromagnetic waves.

  In recent years, with the progress of the use of electromagnetic waves, electromagnetic interference due to unnecessary electromagnetic waves, malfunction of electronic devices, and the like have become major problems. In order to solve this problem, a method of preventing the intrusion of an external electromagnetic wave and preventing the propagation of the generated electromagnetic wave to the outside using an electromagnetic wave shielding material, or a method of absorbing the electromagnetic wave itself using an electromagnetic wave absorber is used. The electromagnetic wave shielding material is effective for preventing transmission of electromagnetic waves, but measures against reflected waves are required. On the other hand, the electromagnetic wave absorber converts the absorbed electromagnetic wave into thermal energy, and can substantially eliminate the absorbed electromagnetic wave.

  The electromagnetic wave absorber was first started in the 1930s by the French company Naamlouze Vennotschach Machinerieen who obtained a French patent. It was put into practical use on a submarine during World War II. A rubber sheet was obtained by dispersing a carbonyl iron material, and a resistor sheet and a plastic dielectric were stacked. Thereafter, a quarter-wave type wave absorber was developed in the United States in which a sheet having a sheet resistance of 377 ohms was provided at a distance of λ / 4 from the back conductor plate. In 1953, a pyramidal wave absorber was developed.

  Known electromagnetic wave absorbers include magnetic electromagnetic wave absorbers utilizing magnetic loss, dielectric electromagnetic wave absorbers utilizing dielectric loss, conductive electromagnetic wave absorbers utilizing resistance loss, and λ / 4 type electromagnetic wave absorbers. (For example, Non-Patent Document 1). As a magnetic electromagnetic wave absorber, for example, a ferrite sintered body or rubber ferrite is used, or a method of absorbing using a soft magnetic material such as Sendust, Permalloy, silicon steel plate, Fe-based amorphous, Co-based amorphous, or nanogranular film is used. Although used (for example, patent document 1), there exists a problem of generation | occurrence | production of an eddy current. In addition, these metals are heavy and the material is expensive. As the dielectric electromagnetic wave absorber, for example, rubber carbon mixed with carbon powder such as carbon black or graphite is used (for example, Patent Document 2). Moreover, as a conductive electromagnetic wave absorber, for example, carbon powder or metal fiber dispersed is used (for example, Patent Document 3). In addition, the λ / 4 type electromagnetic wave absorber can obtain a higher electromagnetic wave absorption ability by setting the thickness to ¼ of the wavelength of the target electromagnetic wave, and the reflected waves cancel each other out by interference. There is a problem of thickening. Thus, attempts have been made to change the wavelength by changing the dielectric constant or permeability of the electromagnetic wave absorber, but there is a limit to the change in wavelength (for example, Patent Document 4).

JP 62-90909 A JP 2007-019287 A JP 2000-278032 A JP 2002-76681 A

Supervised by Osamu Hashimoto, "Latest Technology and Applications of New Wave Absorber", published by CMMC, 1999

  Conventionally, a material selected in advance according to the absorption frequency is used for the electromagnetic wave absorber, and a method of changing the thickness is used in order to satisfy a desired absorption frequency and a maximum absorption amount at the frequency. ing. In recent years, hybrid cars and electric cars have begun to spread, but these cars use 400 to 600V direct current. However, this direct current has a lot of switching noise and is a source of low frequency noise. However, an electromagnetic wave absorber for an electromagnetic wave having a low frequency of 10 MHz or less, which has an influence on carcinogenicity and malfunction of an electronic device in the vicinity of 1 GHz or a human body, does not satisfy thinness and lightness. For example, a λ / 4 type electromagnetic wave absorber requires a thickness of about 50 cm even at 100 MHz, and at a frequency lower than that, a thickness greater than that is required, making it difficult to put to practical use. In order to reduce the weight of hybrid vehicles and electric vehicles, there is a need for lighter electromagnetic wave absorbers that can absorb electromagnetic waves at low frequencies, for example, 1 GHz or less, and further 10 MHz or less.

  Accordingly, an object of the present invention is to provide a lighter electromagnetic wave absorber that can absorb an electromagnetic wave having a low frequency of 1 GHz or less.

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, the present invention includes a semi-insulator made of a resin containing at least one dielectric and a conductor, and the semi-insulator and the conductor are brought into contact with each other by contact. The present invention has been completed by finding that a material that generates an electromotive force of a predetermined value or more in the meantime can absorb low-frequency electromagnetic waves. That is, the electromagnetic wave absorber of the present invention comprises a conductor having a volume resistivity of 1 Ω · m or less and a semi-insulator composed of a resin containing at least one dielectric and having a volume resistivity of 1 kΩ · m to 10 GΩ. In addition, when the conductor and the semi-insulator are brought into contact with each other, an electromotive force having an absolute value of 10 mV or more is generated.

  According to the present invention, it is possible to provide a lighter electromagnetic wave absorber that can absorb an electromagnetic wave having a low frequency of 1 GHz or less.

It is a graph which shows the relationship between the electromagnetic wave shielding effect and frequency in Example 1 and Comparative Examples 1a and 1b. It is a graph which shows the relationship between the electromagnetic wave shielding effect and frequency in Example 2, Comparative example 1a, and Comparative example 2. It is a graph which shows the relationship between the electromagnetic wave shielding effect in Example 3, and the comparative example 3, and a frequency. It is a graph which shows the relationship between the electromagnetic wave shielding effect in Example 4, and the comparative example 4, and a frequency. It is a graph which shows the relationship between the electromagnetic wave shielding effect in Example 5, and the comparative example 5, and a frequency. It is a graph which shows the relationship between the electromagnetic wave shielding effect in Example 5, and the comparative example 6, and a frequency. It is a graph which shows the relationship between the electromagnetic wave shielding effect and frequency in Example 7 and Comparative Example 1a. It is a graph which shows the relationship between the electromagnetic wave shielding effect in Comparative Example 8, and a frequency. It is a graph which shows the relationship between the electromagnetic wave shielding effect in Comparative Example 8, and a frequency. It is a graph which shows the relationship between the electromagnetic wave shielding effect in Example 6, and the comparative example 9, and a frequency.

Hereinafter, embodiments of the present invention will be described in detail.
The electromagnetic wave absorber of the present invention includes a conductor having a volume resistivity of 1 Ω · m or less and a semi-insulator having a volume resistivity of 1 kΩ · m to 10 GΩ, which is made of a resin containing at least one dielectric. When the conductor and the semi-insulator are brought into contact with each other, an electromotive force having an absolute value of 10 mV or more is generated.

(conductor)
The conductor used in the present invention is a material having a volume resistivity of 1 Ω · m or less, preferably 1 mΩ · m or less, more preferably 0.1 mΩ · m or less. Specifically, conductive polymers such as polyethylenedioxythiophene (PEDOT), polyaniline, polyacetylene, polypyrrole, gold, silver, copper, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, chromium, Metals such as lead, titanium and manganese, alloys of these metals such as brass, stainless steel, metal oxides such as conductive zinc oxide, carbon materials, organic conductive fibers obtained by conducting conductive treatment on the surface of synthetic fibers, etc. it can. A plurality of different kinds of conductors may be combined.

  The shape and form of the conductor are not particularly limited, and for example, a film, sheet, mesh, honeycomb, powder, or fiber can be used. Preferred conductors are stainless steel fibers, carbon fibers, and organic conductive fibers with a metal sputtered on the surface.

(Semi-insulator)
The semi-insulator used in the present invention is a resin containing at least one dielectric. The volume resistivity of the semi-insulator is 1 kΩ · m to 10 GΩ · m, preferably 10 kΩ · m to 1 GΩ · m, more preferably 100 kΩ · m to 1 GΩ · m.

  The resin used for the semi-insulator is polyvinyl chloride, chlorinated polyethylene, chlorinated polypropylene, polyethylene, polypropylene, polyvinyl acetate, vinyl acetate copolymer, (meth) acrylic copolymer, styrene acrylic resin, polyvinylidene fluoride Polymers such as polyisoprene, acrylonitrile polymers, styrene-butadiene rubber, butadiene rubber, natural rubber, isoprene rubber, polystyrene, styrene acrylic copolymer, polyester, polyurethane, and polyamide can be used. An acrylonitrile-based polymer is preferable.

  Examples of acrylonitrile polymers include polyacrylonitrile, acrylonitrile- (meth) acrylic acid ester copolymer, acrylonitrile-styrene- (meth) acrylic acid ester copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer. Examples thereof include mer and acrylonitrile-styrene copolymer.

  The content of the resin in the semi-insulator is 50 to 99.99% by weight, preferably 80 to 99% by weight. This is because if the amount is less than 50% by weight, the electromotive force becomes small. Moreover, it is because it becomes difficult to generate an electromotive force if all are made of a polymer.

  Further, as the resin, a polymer having a glass transition point equal to or lower than the use temperature of the electromagnetic wave absorber is used. This is because the electromotive force is reduced when a polymer having a glass transition point higher than the operating temperature is used.

  As the at least one dielectric used in the present invention, a substance having a relative dielectric constant of 20 or more can be used. Specific examples include water; alcohols such as methanol and ethanol; glycols such as ethylene glycol, diethylene glycol and propylene glycol; glycerin; and ferroelectrics. Specific examples of ferroelectrics include guanidines such as guanidine aluminum sulfate; perovskites such as barium titanate, barium zirconate titanate, lead titanate and potassium niobate; glycines such as triglycine sulfate; Rochelle salts such as antimony, Rochelle salt and deuterium Rochelle salt; alkali dihydrogen phosphates such as potassium dihydrogen phosphate; Preferred dielectrics are water, glycols, and Rochelle salts.

  The content of the dielectric in the semi-insulator is 0.5 to 50% by weight, preferably 2 to 30% by weight, more preferably 2 to 10% by weight. This is because when the amount is less than 0.5% by weight, an electromotive force is hardly generated, and when the amount is more than 50% by weight, the electromotive force decreases.

  In the present invention, when the conductor and the semi-insulator are brought into contact with each other, it is necessary to generate an electromotive force having an absolute value of 10 mV or more. Preferably, the absolute value of the electromotive force is 20 mV or more. This is because if the absolute value of the electromotive force is less than 10 mV, the ability to absorb low-frequency electromagnetic waves decreases. In the present invention, when an electric body and a semi-insulator are brought into contact with each other, an electromotive force having an absolute value of 10 mV or more is generated. Is provided, a potential difference having an absolute value of 10 mV or more is generated between the pair of electrodes. Here, bringing the conductor and the semi-insulator into contact refers to laminating in a planar shape by applying pressure as necessary. Moreover, the measured value in room temperature (20 +/- 5 degreeC) is used for the electromotive force of this invention.

  In the present invention, the electrical resistance of the composite in which the conductor and the semi-insulator are in contact is 100 kΩ to 1 GΩ, preferably 500 kΩ to 500 MΩ. This is because if it is less than 100 kΩ, an electromotive force is hardly generated. Moreover, even if it is larger than 1 GΩ, an electromotive force is hardly generated.

  In order to make the absolute value of the electromotive force 10 mV or more, it can be performed by changing the kind of dielectric material contained in the semi-insulator and its content.

The semi-insulator can be manufactured, for example, by the following method.
Blending resin and dielectric using a blender or kneader, pressing or extrusion molding, blending emulsion or solution resin and dielectric with a stirrer, casting by blowing water or solvent, printing method It can be produced using a coating method or the like.

(Production method)
The electromagnetic wave absorber of the present invention can be produced using various methods depending on the shape and form of the conductor.
For example, when the conductor has a plate shape, the semi-insulator may be laminated and manufactured by pressure bonding or coating. The same applies if the conductor is a film, mesh, honeycomb, or nonwoven fabric.

  In addition, when the conductor is in the form of powder or short fiber, it may be molded by blending the conductor with a semi-insulating resin, or the conductive layer is formed by molding the powder or short fiber conductor with a binder. Then, a semi-insulator may be applied thereon.

  Alternatively, a conductor layer may be formed on insulating paper or a resin film by coating, printing, vapor deposition, or the like, and a semi-insulator layer may be formed on the conductor layer. Alternatively, a semi-insulator layer may be formed on an insulating paper or resin film by coating, printing, pressure bonding, or the like, and a conductor layer may be formed on the semi-insulator layer. When forming a conductor layer or semi-insulator layer on insulating paper or resin film, it may be formed on the front surface of paper or resin film, or it may be formed in various pattern shapes as required. May be.

  Note that the conductor and the semi-insulator are not limited to one type, and a plurality of types may be used in combination. Moreover, it can also be used in combination with a conventional electromagnetic wave absorber or electromagnetic wave shielding material.

(Evaluation of electromagnetic wave absorption characteristics)
The electromagnetic wave absorber of the present invention can be obtained by a method (hereinafter referred to as the KEC method) using an electromagnetic shielding effect measuring device developed at KEC (Kansai Electronics Industry Promotion Center; The electromagnetic wave absorption characteristics were evaluated. The electromagnetic wave shield measurement by the KEC method receives the electromagnetic wave emitted from the transmitting antenna with the receiving antenna, puts the test piece between them, and measures the amount of electromagnetic wave transmitted, resulting in the effects of both reflection and absorption of the electromagnetic wave. Is to measure.

  A material with higher conductivity reflects more electromagnetic waves. Therefore, what is generally referred to as a shielding material reflects electromagnetic waves using a conductive material. For example, when iron or nickel having a high magnetic permeability and high conductivity is used, a low frequency electromagnetic wave is reflected, so that a high electromagnetic shielding effect is obtained. Furthermore, a high electromagnetic wave absorption effect due to magnetism is obtained for high frequencies in the vicinity of 1 GHz.

  On the other hand, since the semi-insulator used in the present invention has a large volume resistivity, the conductivity does not increase even when combined with a conductor. Therefore, it is unlikely that low frequency electromagnetic waves are reflected. Then, when the electromagnetic wave absorber of the present invention was used, the reason why the amount of low-frequency electromagnetic wave transmitted decreased was that the low-frequency electromagnetic wave was absorbed by the electromagnetic wave absorber of the present invention. Although the cause of this is under investigation, it is thought that the polarity of the semi-insulator used in the present invention is easily reversed, and low-frequency electromagnetic energy is absorbed in the process of polarity reversal by electromagnetic waves.

This will be described in detail below.
In the present invention, since conductors are combined and a semi-insulator having electrical insulation in a region having an antistatic effect is combined, it is clear that the expression of the potential difference is not due to static electricity. In general, as a potential difference using a metal, a tendency of ionization of a metal using a metal and an electrolyte having a low electrical resistance is known. However, the potential difference in the present invention is also manifested in carbon or a conductive polymer. On the other hand, the onset of the potential difference is instantaneous at the same time as the measurement, and is different from that due to the ionization tendency because the semi-insulating region having a relatively high resistance is used.

  The standard oxidation-reduction potential is shown below (Tokyo Electroplating Industry Association plating-related data collection, standard electrode potential of various metals, http://www.tmk.or.jp/datapdf/data51.pdf).

  When a semi-insulator is used, a potential difference is developed between the same metals, and further, carbon and a conductive polymer are also developed. Therefore, this is not due to a difference in ionization tendency.

  On the other hand, the following values have been reported for the Seebeck coefficient as an index of thermoelectromotive force (Moffat, R., “Notes on Using Thermocouples”, Electronics Cooling, Vol. 3, No. 1, 1997).

  A device using a thermoelectromotive force, such as a Seebeck device or a Peltier device, joins different kinds of conductors and uses a potential difference between the contacts. Its performance is evaluated by the Seebeck coefficient and a figure of merit based on it. However, when different metals are directly joined, electrons move at that moment, and the potential difference cannot be measured. Therefore, two different kinds of metals are joined in a ring shape, the temperature of the two joint surfaces is changed, and the temperature difference is used to generate a potential difference, and vice versa. The method to make it take is taken. Naturally, the same metal does not generate thermoelectromotive force. On the other hand, since the potential difference when the semi-insulator of the present invention is used also occurs between the same metals, it is different from the mechanism of thermoelectromotive force generation by the Seebeck coefficient.

  Here, in the state where one electrode is SUS304 and the semi-insulating resin is sandwiched between various conductors, the potential difference between the conductor and the SUS electrode is measured at room temperature using a digital multimeter VOAC7522 manufactured by Iwatsu Measurement Co., Ltd. The results measured at (20 ° C.) are shown in Table 3 below. The semi-insulating resin uses an acrylic copolymer resin (acrylonitrile / butyl acrylate = 40/60 emulsion-polymerized in water) emulsion as a matrix, and the resin contains 85 parts by weight of solid and 15 parts by weight of diethylene glycol. It mixed and manufactured with the stirrer.

  Since this potential difference occurs instantaneously at the time of measurement with the electrode changed, it can be seen that the charge medium that causes the potential difference is not ions but electrons.

  Here, when comparing the Seebeck coefficient in Table 2 and the potential difference in Table 3 in order from the larger one, it becomes as shown in Table 4 below, and the nickel order does not match.

  However, as shown in Table 5, when the magnitude of the absolute value of the Seebeck coefficient is compared with the magnitude of the absolute value of the potential difference, the order agrees, but the smaller the Seebeck coefficient, the larger the potential difference of the semi-insulator, and the inverse correlation. Therefore, even a contact potential difference such as a thermoelectromotive force involving the Seebeck coefficient cannot be explained.

  When light hits the surface of the metal, metal ions, free electrons, etc. present in a very thin layer of the surface absorb the energy of the light, excite it at a high energy level, and immediately release the energy from the surface. Therefore, the higher the conductivity, the greater the reflection of light from the metal. That is, although it is instantaneous, the state of the metal changes according to the state of the electromagnetic wave. When there is no semi-insulator, it is reflected as it is, but on the surface where the metal is in contact with the semi-insulator, the charge on the contact surface between the semi-insulator and the metal changes depending on the state. It may be considered that due to the presence of electromagnetic waves, the electrical properties of the metal surface change and have a Seebeck coefficient like a dissimilar metal. In accordance with this, the polarity of the semi-insulator changes from the fact that the polarity is reversed between carbon and SUS304. When the polarity of the semi-insulator changes, there is a transfer of charge (electrons), and the semi-insulator has some conductivity, so there is electron traffic in the semi-insulator or at the interface with the conductor, and heat I think it has changed to energy.

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example, this invention is not limited to a following example.

Example 1.
(Production method)
As the conductor, a non-woven fabric of organic conductive fiber (trade name: Sanderlon) (volume resistivity: 0.8 Ω · m) manufactured by Nippon Kashiwa Dyeing Co., Ltd. having a surface weight of about 170 g / m ² was used. The semi-insulating resin uses an acrylic copolymer resin (acrylonitrile / butyl acrylate = 40/60 emulsion polymerized in water) emulsion as a matrix, and the resin is 85 parts by weight in solid content and 15 parts by weight of diethylene glycol in a stirrer. And mixed. A semi-insulator was applied to a sanderon nonwoven fabric so that the surface weight of the semi-insulator was about 500 g / m ² and dried at 50 ° C. to obtain a radio wave absorber. The thickness of the radio wave absorber was 890 μm.

(Measurement of electromotive force of complex)
The potential difference (electromotive force) between the obtained electromagnetic wave absorber conductor and the surface of the coated semi-insulator was measured at room temperature (20 ° C.) using a digital multimeter VOAC7522 manufactured by Iwatatsu Measurement Co., Ltd. Table 6 shows the measurement results. However, the potential difference between the two surfaces of the conductor and resin alone was measured.

(Electromagnetic wave shielding effect measurement)
The obtained electromagnetic wave absorber was measured by the KEC method. The measurement frequency is 0.1 MHz to 1 GHz. The measurement results are shown in FIG.

Example 2
(Production method)
Sanderon nonwoven fabric was used as the conductor. The semi-insulating resin uses an emulsion of a carboxyl group-modified acrylonitrile-butadiene copolymer (Tg: −15 ° C.) having an acrylonitrile content of 40% by weight as a matrix, and the resin has a solid content of 85 parts by weight. It was produced by mixing 15 parts by weight of Rochelle salt with a stirrer. The semi-insulator was applied to a non-woven fabric of Sanderon so that the surface weight of the semi-insulator was about 150 g / m ² and dried at 50 ° C. The thickness of the radio wave absorber was 1022 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Example 3
(Production method)
A 100th stainless mesh (1038 stainless steel 100, 16151 purchased from Tokyu Hands) (volume resistivity: 7 × 10 ⁻⁷ Ω · m) having a surface weight of about 425 g / m ² was used as the conductor. The semi-insulating resin uses an emulsion of a carboxyl group-modified acrylonitrile-butadiene copolymer (Tg-15 ° C.) having an acrylonitrile content of 40% by weight as a matrix, and the resin is 85 parts by weight in solids and Rochelle salt. It was produced by mixing 15 parts by weight with a stirrer. A stainless mesh was placed on the release paper so that the surface weight of the semi-insulator was about 200 g / m ² , the semi-insulator was applied so that the mesh holes were filled, and dried at 50 ° C. The thickness of the radio wave absorber was 298 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Example 4
(Production method)
As a conductor, an aluminum punching plate having a surface weight of about 600 g / m ² (aluminum punching plate A-12 purchased from Tokyu Hands, 3φ × 5 surface removed with sandpaper) (volume resistivity: About 3 × 10 ⁻⁸ Ω · m) was used. As the semi-insulating resin, an emulsion of a carboxyl group-modified acrylonitrile-butadiene copolymer (Tg-15 ° C.) having an acrylonitrile content of 40% by weight was used. The resin was mixed with 85 parts by weight of solid and 15 parts by weight of Rochelle salt with a stirrer.
The aluminum punching plate was placed on the release paper so that the surface weight of the semi-insulator was about 200 g / m ² , the semi-insulator was applied so that the punch holes were filled, and dried at 50 ° C. The thickness of the radio wave absorber was 588 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Example 5 FIG.
(Production method)
A carbon fiber (A sheet made by Unitika) (volume resistivity: about 2 × 10 ⁻⁵ Ω · m) having a surface weight of about 115 g / m ² was used as the conductor. The semi-insulating resin used as the matrix is an emulsion of a carboxyl group-modified acrylonitrile-butadiene copolymer (Tg-15 ° C) with an acrylonitrile content of 40% by weight. It was produced by mixing 15 parts by weight with a stirrer. The semi-insulator was applied to the carbon fiber so that the surface weight of the semi-insulator was about 100 g / m ² and dried at 50 ° C. The thickness of the radio wave absorber was 555 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG. The numerical values of the electromagnetic wave shielding effect at 1 MHz and 500 MHz are shown in Table 7.

Example 6
(Production method)
Unitika A sheet was used as the conductor. As a semi-insulating resin as a matrix, an emulsion of a carboxyl group-modified acrylonitrile-butadiene copolymer (Tg: −15 ° C.) having an acrylonitrile content of 40% by weight was used. The resin was mixed with 85 parts by weight of solid and 15 parts by weight of Rochelle salt with a stirrer. The mixture was poured into a predetermined mold and dried at 50 ° C. The obtained sheet was left under high humidity, 5% by weight of water was hydrated, and heat-sealed to carbon fiber with a hot press under the conditions of 50 ° C. and 10 MPa to obtain an electromagnetic wave absorber. The thickness of the radio wave absorber was 1060 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG. The numerical values of the electromagnetic wave shielding effect at 1 MHz and 500 MHz are shown in Table 7.

Comparative Example 1a.
An electromagnetic wave absorber was produced in the same manner as in Example 1 except that only the conductor was used without using the semi-insulator. The thickness of the radio wave absorber was 890 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 1b.
An electromagnetic wave absorber was produced in the same manner as in Example 1 except that only a semi-insulator was used without using a conductor. The thickness of the radio wave absorber was 845 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 2
An electromagnetic wave absorber was produced in the same manner as in Example 2 except that only the semi-insulator was used without using the conductor. The thickness of the radio wave absorber was 608 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 3
An electromagnetic wave absorber was produced in the same manner as in Example 3 except that only the conductor was used without using the semi-insulator. The thickness of the radio wave absorber was 186 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 4
An electromagnetic wave absorber was produced in the same manner as in Example 4 except that only the conductor was used without using the semi-insulator. The thickness of the radio wave absorber was 498 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 5
An electromagnetic wave absorber was produced in the same manner as in Example 5 except that only the conductor was used without using the semi-insulator. The thickness of the radio wave absorber was 431 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 6
Non-semi-insulating carbon fiber with a solid ratio of 25 parts of styrene butadiene rubber SR-104 (manufactured by Japan A & L Co.) and 25 parts of KN-320 (magnetite manufactured by Toda Kogyo Co., Ltd.) An electromagnetic wave absorber was produced in the same manner as in Example 5 except that a semi-insulator was not used. The thickness of the radio wave absorber was 545 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 7
Thunderon was coated with a methyl methacrylate / butyl acrylate copolymer resin having a Tg of 18 ° C., which was not semi-insulating. An electromagnetic wave absorber was produced in the same manner as in Example 1 except that the semi-insulator was not used. The thickness of the radio wave absorber was 1035 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 1. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 8.
An electromagnetic wave absorbing ferrite composite sheet for ETC (Electronic Toll Collection) in which 100 parts of acrylic resin mainly composed of butyl acrylate and 100 parts of ferrite GP-500 was blended was used as the electromagnetic wave absorber. The thickness of the radio wave absorber was 1005 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIGS.

Comparative Example 9
As a semi-insulating resin, 15 parts of Rochelle salt added to nitrile butadiene rubber and 5% of water were poured into a predetermined mold and dried at 50 ° C. The obtained sheet was hot-pressed and molded at 100 ° C. and 40 MPa. The thickness of the radio wave absorber was 610 μm.

  The electromotive force measurement was performed in the same manner as in Example 1. The results are shown in Table 6. The electromagnetic wave shielding effect measurement was performed in the same manner as in Example 1. The results are shown in FIG.

(result)
As is clear from the comparison between Examples 1 to 6 and the comparative example, in the present invention, the electromagnetic wave absorption characteristics were improved in the measurement frequency range (1 MHz to 1 GHz) by including the conductor and the semi-insulator.

  Comparative Example 1a is an untreated conductive non-woven fabric, and due to its electrical conductivity, a shielding effect of about 20 dB, which seems to be due to reflection of electromagnetic waves, is obtained (FIG. 1). Comparative Example 1b is a semi-insulator of the present invention and is a single film. A single film has almost no electromagnetic shielding effect and is close to 0 dB (FIG. 1).

  On the other hand, in Example 1, a semi-insulating material is applied to a conductive nonwoven fabric, and as can be seen from FIG. 1, the shielding effect is improved by several dB. The reflection of electromagnetic waves is due to electrical conductivity. A semi-insulator has an intermediate electrical conductivity and has almost no shielding effect when used alone. However, when combined, the shielding effect is increased because the electromagnetic wave is absorbed rather than reflected.

  In Example 2, a semi-insulating material is applied to a conductive nonwoven fabric, and as is clear from FIG. 2, the shielding effect is improved by several dB. The reflection of electromagnetic waves is due to electrical conductivity. Semi-insulators have a moderate electrical conductivity and have almost no shielding effect when used alone. However, the combined effect of the semi-insulator is probably due to the absorption of electromagnetic waves, not the reflection of electromagnetic waves.

  Comparative Example 3 is a stainless steel mesh, and a shielding effect of about 60 to 70 dB, which is considered to be due to reflection of electromagnetic waves, is obtained due to its electrical conductivity (FIG. 3). In contrast, in Example 3, a semi-insulating material was applied to a stainless steel mesh, and the shielding effect was improved by several dB (FIG. 3).

  Comparative Example 4 is a punching plate in which a large number of round holes are formed in an aluminum plate, and due to its electrical conductivity, a shielding effect of less than 30 dB, which seems to be due to reflection of electromagnetic waves, is obtained (FIG. 4). On the other hand, in Example 4, a semi-insulating material was applied to a punching plate having a large number of round holes in an aluminum plate, and the shielding effect was improved by several dB (FIG. 4).

  Comparative Example 5 is an uncoated carbon fiber, and due to its electrical conductivity, a shielding effect that seems to be due to reflection and absorption of electromagnetic waves is obtained (FIG. 5). In contrast, in Example 5, a semi-insulator was applied to carbon fiber, and the shielding effect was improved by several dB (FIG. 5).

  In Comparative Example 6, an insulating resin is applied to carbon fiber, and the shielding effect is lower by several dB than that obtained by applying a semi-insulator (FIG. 6). In contrast, in Example 5, a semi-insulator was applied to carbon fiber, and the shielding effect was improved by several dB (FIG. 6).

  Comparative Example 1a is an untreated conductive non-woven fabric, and due to its electrical conductivity, a shielding effect of about 20 dB, which seems to be due to reflection of electromagnetic waves, is obtained (FIG. 7). On the other hand, the comparative example 7 apply | coats the insulating acrylic resin to the electroconductive nonwoven fabric, and the shielding effect has fallen several dB (FIG. 7). The reflection of electromagnetic waves is due to electrical conductivity. Insulators have low electrical conductivity and little shielding effect. When combined, the shielding effect decreases because the reflection of electromagnetic waves is prevented and the amount of transmission increases.

  Comparative Example 8 utilizes the magnetic properties (high permeability) of ferrite, and at 1 GHz or less, the effect of electromagnetic wave shielding by electromagnetic wave reflection and electromagnetic wave absorption was not recognized (FIG. 8).

  In Comparative Example 8, at 1 GHz or less, the effect of electromagnetic wave shielding by electromagnetic wave reflection and electromagnetic wave absorption was not recognized, but absorption of electromagnetic waves was observed at 10 GHz to 15 GHz, and peaks of reflection loss were observed at about 11 GHz and 14 GHz. (FIG. 9).

  Comparative Example 9 is a semi-insulator of the present invention and is a single film. A single film has little effect of electromagnetic wave sealing and is close to 0 dB (FIG. 10). In contrast, in Example 6, a semi-insulator was applied to a conductive nonwoven fabric, and the shielding effect was improved by several dB (FIG. 10).

  In Table 6, a film means a semi-insulator film formed by applying to a conductor or a non-semi-insulator film, and a sheet is not a semi-insulator prepared without using a conductor. By semi-insulating or non-semi-insulating sheet. The volume resistivity of the coating or sheet in Table 6 is a value measured according to JIS K7194 by preparing a semi-insulating sheet having a thickness of 2 mm and a non-semi-insulating sheet.

Claims (3)

  A conductor having a volume resistivity of 1 Ω · m or less and a semi-insulator having a volume resistivity of 1 kΩ · m or more and 10 GΩ or less made of a resin containing at least one dielectric, the conductor and the semi-insulator An electromagnetic wave absorber that generates an electromotive force having an absolute value of 10 mV or more when brought into contact.   2. The electromagnetic wave absorber according to claim 1, wherein the dielectric is at least one selected from water, glycols and ferroelectrics.   2. The electromagnetic wave absorber according to claim 1, wherein an electrical resistance of the composite in which the conductor and the semi-insulator are in contact is 100 kΩ to 1 GΩ.

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