TW201330764A - Electromagnetic wave absorber and method for manufacturing electromagnetic wave absorber - Google Patents

Abstract

Provided are an electromagnetic wave absorber and a method for manufacturing an electromagnetic wave absorber wherein electric permittivity is increased while the content of a carbon-based material included in a dielectric layer is minimized, the electromagnetic wave absorber being lightweight, having excellent workability, and having a high performance of electromagnetic wave absorbency free of nonuniformities. An electromagnetic wave absorber comprises a dielectric layer (3) and an electromagnetic wave reflecting layer (4), uses a carbon-based material as an electromagnetic wave absorbing material, and has a frequency band of 4.9 to 7.05 GHz, the dielectric layer (3) being configured from vulcanized rubber containing the carbon-based material.

Description

Electromagnetic wave absorber and method of manufacturing electromagnetic wave absorber

The present invention relates to an electromagnetic wave absorber and a method of manufacturing an electromagnetic wave absorber that absorb electromagnetic waves emitted from a communication device or the like.

In recent years, with the spread of various communication devices including mobile phones, various radio wave interferences such as malfunction of electrical and electronic equipment or leakage of information caused by electromagnetic wave noise have become increasingly serious. Moreover, there are also flaws in which electromagnetic waves have an adverse effect on the human body. Therefore, a method of preventing an adverse effect caused by electromagnetic waves by using an electromagnetic wave absorber that absorbs electromagnetic waves has been conventionally performed. Specifically, an electromagnetic wave absorber is disposed on a wall portion around an electronic device that emits electromagnetic waves, or an electromagnetic wave absorber is disposed on a wall of a building, thereby absorbing electromagnetic waves emitted from the electronic device.

Further, it is desirable that the electromagnetic wave absorber as described above be thinned and lightened. For example, in the Electronic Toll Collection (ETC) used in toll stations of highways, in order to prevent the malfunction of the vehicle-mounted device caused by electromagnetic interference between adjacent lanes, it is necessary to be in the ceiling or side wall of the toll booth. The electromagnetic wave absorber is attached, and the electromagnetic wave absorber is required to be thinned and lightened.

Here, in order to absorb electromagnetic waves, it is necessary to use an electromagnetic wave absorber corresponding to the frequency band of the electromagnetic wave to be absorbed. For example, as the microwave emitted from the communication device, there are electromagnetic waves of a frequency of 2.4 GHz and 5.2 GHz used in a wireless LAN (Local Area Network), and electromagnetic waves of a frequency of 5.8 GHz used in ETC. Absorb this micro For the wave, it is necessary to use an electromagnetic wave absorber corresponding to the frequency band.

For example, Japanese Laid-Open Patent Publication No. 2003-158395 discloses an electromagnetic wave absorber in which 1 to 10 parts by weight of a nanometer-sized carbon material is blended in a resin, and a wide frequency near 1 to 20 GHz can be obtained. A relatively high electromagnetic wave absorption performance is obtained in the domain. Further, Japanese Laid-Open Patent Publication No. 2004-311586 discloses an electromagnetic wave absorber comprising a specific resin component and a carbon black having a specific nitrogen adsorption specific surface area powder, and the density is set to 0.3 g/cm ^{3 .} The following foams are available for electromagnetic wave absorption at 8 to 12.5 GHz to attenuate electromagnetic waves by more than 8 dB.

Further, as described in Japanese Laid-Open Patent Publication No. 2004-311586, the electromagnetic wave band (peak frequency) which is a reflection of electromagnetic wave absorption characteristics and the attenuation rate in the frequency band basically depend on the absorption electromagnetic wave contained in the electromagnetic wave absorption body. The type and amount of the substance, and the thickness of the absorber. The type of the substance that absorbs electromagnetic waves includes a magnetic material such as ferrite iron and a conductive material (dielectric material) such as graphite. The former is heavy, and therefore it is preferable to use a conductive material as an electromagnetic wave absorber. Further, the complex dielectric constant indicates the type of the conductive material, and the reflection-free curve in which the reflection of the electromagnetic wave absorber is theoretically disappeared can be calculated. Further, the thickness of the electromagnetic wave absorber which can efficiently reduce the reflection of a certain wavelength λ depends on the complex dielectric constant. In other words, it can be said that the complex dielectric constant depends on the thickness of the electromagnetic wave absorber.

Further, the larger the real part of the complex dielectric coefficient, the thinner the thickness of the absorber at the frequency at which the absorption effect is maximized. Further, the larger the imaginary part of the complex dielectric coefficient, the better the electromagnetic wave is absorbed.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2003-158395

Patent Document 2: Japanese Patent Laid-Open Publication No. 2004-311586

Here, the electromagnetic wave absorber including the carbon-based material as the electromagnetic wave absorbing material in the above-described Patent Documents 1 and 2 has a smaller specific gravity than the magnetic material such as the ferrite-grained iron, and is lighter, but cannot be absorbed. A better electromagnetic wave absorber. The reason for this is that if the dielectric constant is not increased as described above, the absorption performance is not good, and in order to increase the dielectric constant, it is necessary to charge the electromagnetic wave absorbing material at a high density, so that the formability is deteriorated, and the sheet becomes brittle. problem. Further, when a large amount of carbon-based material is contained, there is a problem in that voids are generated inside due to poor dispersion of the carbon-based material, or electromagnetic wave absorption performance is uneven.

The present invention has been made to solve the above problems, and an object of the invention is to provide an electromagnetic wave absorber and a method for producing an electromagnetic wave absorber having the following properties: by using a vulcanized rubber as a dielectric layer, the dielectric layer is suppressed. The content of the carbon-based material increases the dielectric constant, and is lightweight and excellent in workability, and has high-performance electromagnetic wave absorption performance without unevenness.

In order to achieve the above object, an electromagnetic wave absorber of the present invention is characterized by comprising a dielectric layer and an electromagnetic wave reflective layer laminated on one surface of the dielectric layer, and the dielectric layer includes a vulcanized rubber containing a carbon-based material.

Further, the electromagnetic wave absorber of the present invention is characterized in that the above vulcanized rubber Natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, nitrile rubber, chloroprene rubber, ethylene propylene rubber, butyl rubber with sulfur or organic peroxide as vulcanizing agent A vulcanized rubber obtained by vulcanizing any rubber material.

Moreover, the electromagnetic wave absorber of the present invention is characterized in that the carbon-based material is flaky graphite.

Further, the electromagnetic wave absorber of the present invention is characterized in that it has a peak frequency of electromagnetic wave absorption of 20 dB or more in a frequency band of 4.9 to 7.05 GHz.

Moreover, the electromagnetic wave absorber of the present invention is characterized in that the rubber-based material constituting the vulcanized rubber is set to be 90 to 160 parts by weight per 100 parts by weight.

Further, the electromagnetic wave absorber of the present invention is characterized in that it is produced by a first mixing step of kneading a rubber-based material and the carbon-based material, and a mixture obtained by the first mixing step. a second mixing step of re-kneading by adding a vulcanizing agent and a vulcanization accelerator; a step of processing the mixture obtained by the second mixing step into a sheet shape; and applying the above-mentioned mixture processed into a sheet shape to a specific The step of forming the above dielectric layer by heating at a temperature to carry out a vulcanization reaction.

Moreover, the electromagnetic wave absorber of the present invention is characterized in that the amount of the vulcanizing agent added in the second mixing step is 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material.

Moreover, the method for producing an electromagnetic wave absorber according to the present invention includes a first mixing step of kneading a rubber-based material and the carbon-based material, and adding a vulcanizing agent to the mixture obtained by the first mixing step. a second mixing step of re-kneading the vulcanization accelerator; The step of processing the mixture obtained in the second mixing step into a sheet shape; and the step of forming the dielectric layer by performing a vulcanization reaction by heating the above-mentioned mixture processed into a sheet shape at a specific temperature.

Moreover, the method for producing an electromagnetic wave absorber of the present invention is characterized in that the rubber-based material is natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, nitrile rubber, and neoprene rubber. Any one of ethylene propylene rubber and butyl rubber, wherein the vulcanizing agent is sulfur or an organic peroxide.

Moreover, the method for producing an electromagnetic wave absorber according to the present invention is characterized in that the carbon-based material is flaky graphite.

Further, in the method for producing an electromagnetic wave absorber of the present invention, the amount of the carbon-based material contained in the dielectric layer is 90 to 160 parts by weight per 100 parts by weight of the rubber-based material.

Further, in the method for producing an electromagnetic wave absorber of the present invention, the amount of the vulcanizing agent added in the second mixing step is 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material.

According to the electromagnetic wave absorber of the present invention having the above-described configuration, since the dielectric layer is formed of a vulcanized rubber containing a carbon-based material, it is compared with other rubber-based materials or resins, inorganic binders, inorganic/organic materials which are not vulcanized. When a mixed adhesive or the like is used for the dielectric layer, the content of the carbon-based material contained in the dielectric layer can be suppressed and the dielectric constant can be increased. Further, the shape of the dielectric layer can be changed little, so that the change in absorption performance can be made small. Therefore, it is lightweight and excellent in processability, and has high performance without unevenness. Electromagnetic wave absorber for electromagnetic wave absorption performance. Further, weather resistance and heat resistance can be improved. Further, by increasing the dielectric constant of the dielectric layer, it is possible to reduce the thickness of the electromagnetic wave absorber. Further, the electromagnetic wave absorber can be thinned and the peak frequency can be shifted to the low frequency side. For example, even in the case of a film-shaped electromagnetic wave absorber of about 1.6 mm, the amount of reflection attenuation (electromagnetic wave absorption amount) can be sufficiently absorbed in the frequency band of 4.9 to 7.05 GHz.

Further, according to the electromagnetic wave absorber of the present invention, natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, nitrile rubber, chlorine is used because sulfur or an organic peroxide is used as a vulcanizing agent. A vulcanized rubber obtained by vulcanizing any of the rubber-based materials of the butadiene rubber, the ethylene propylene rubber, and the butyl rubber can provide an electromagnetic wave absorber which is lightweight and excellent in workability.

Further, according to the electromagnetic wave absorber of the present invention, since the dielectric layer includes a layer in which scaly graphite is dispersed with respect to the vulcanized rubber, the effective dielectric constant of the dielectric layer can be increased. As a result, thinning and weight reduction of the dielectric layer can be achieved.

Further, according to the electromagnetic wave absorber of the present invention, since the electromagnetic wave absorption amount is 20 dB or more in the frequency band of 4.9 to 7.05 GHz, sufficient electromagnetic wave absorption performance can be realized when electromagnetic waves in the frequency band of 4.9 to 7.05 GHz are absorbed. .

Further, according to the electromagnetic wave absorber of the present invention, since the amount of the carbon-based material contained in the dielectric layer is 90 to 160 parts by weight per 100 parts by weight of the rubber-based material constituting the vulcanized rubber, it is possible to suppress the inclusion thereof. The content of carbon-based materials. As a result, it is possible to prevent the formability from being deteriorated and the sheet becoming brittle. And other issues. Further, when a large amount of carbon-based material is contained, it is possible to prevent voids from occurring inside or uneven electromagnetic wave absorbing performance due to poor dispersion of the carbon-based material.

Further, according to the electromagnetic wave absorber of the present invention, the vulcanizing agent and the vulcanization accelerator are added to the mixture obtained by the first mixing step by the first mixing step of kneading the rubber-based material and the carbon-based material. a second mixing step of re-kneading, a step of processing the mixture obtained by the second mixing step into a sheet shape, and a vulcanization reaction by heating the mixture processed into a sheet at a specific temperature to form a dielectric layer Since the step is produced, the vulcanization reaction treatment of the dielectric layer can be appropriately performed to form a dielectric layer by vulcanizing rubber containing a carbon-based material.

Further, according to the electromagnetic wave absorber of the present invention, since the amount of the vulcanizing agent added when the dielectric layer is formed is 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material, the dielectric constant can be made large. The ground rises. As a result, it is possible to provide an electromagnetic wave absorber having electromagnetic wave absorption performance without unevenness and high performance.

Further, according to the method for producing an electromagnetic wave absorber of the present invention, the first mixing step of kneading the rubber-based material and the carbon-based material is included, and the vulcanizing agent and the vulcanization accelerator are added to the mixture obtained by the first mixing step. And a second mixing step of re-kneading, a step of processing the mixture obtained by the second mixing step into a sheet shape, and a vulcanization reaction by heating the mixture processed into a sheet at a specific temperature to form a dielectric layer In the step, the vulcanization reaction treatment of the dielectric layer can be appropriately performed to form a dielectric layer by vulcanizing rubber containing a carbon-based material.

Further, according to the method for producing an electromagnetic wave absorber of the present invention, natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyronitrile are used because sulfur or an organic peroxide is used as a vulcanizing agent. A vulcanized rubber obtained by vulcanizing any rubber material such as rubber, chloroprene rubber, ethylene propylene rubber or butyl rubber is used as a vulcanized rubber which forms a dielectric layer, so that an electromagnetic wave absorber which is lightweight and excellent in workability can be provided.

Moreover, according to the method for producing an electromagnetic wave absorber of the present invention, since the dielectric layer includes a layer in which scaly graphite is dispersed with respect to the vulcanized rubber, the effective dielectric constant of the dielectric layer can be increased. As a result, thinning and weight reduction of the dielectric layer can be achieved.

Further, according to the method for producing an electromagnetic wave absorber of the present invention, the amount of the carbon-based material contained in the dielectric layer is 90 to 160 parts by weight per 100 parts by weight of the rubber-based material constituting the vulcanized rubber, thereby suppressing The content of the carbon-based material contained. As a result, problems such as deterioration of formability and brittleness of the sheet can be prevented. Further, when a large amount of carbon-based material is contained, it is possible to prevent voids from occurring inside or uneven electromagnetic wave absorbing performance due to poor dispersion of the carbon-based material.

Further, according to the method for producing an electromagnetic wave absorber of the present invention, the amount of the vulcanizing agent added when the dielectric layer is formed is 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material, so that the dielectric constant can be obtained. Increased to a large extent. As a result, it is possible to provide an electromagnetic wave absorber having electromagnetic wave absorption performance without unevenness and high performance.

Hereinafter, the electromagnetic wave absorber and electromagnetic wave absorption of the present invention will be described with reference to the drawings. The embodiment of the method of manufacturing the body will be described in detail.

First, the configuration of the electromagnetic wave absorption sheet 1 as the electromagnetic wave absorber of the present invention will be described based on Fig. 1 . Fig. 1 is an explanatory view showing an electromagnetic wave absorptive sheet 1 of the present invention.

As shown in FIG. 1, the electromagnetic wave absorption sheet 1 of the present invention mainly comprises a dielectric layer 3 and an electromagnetic wave reflection layer 4. Further, the dielectric layer 3 and the electromagnetic wave reflective layer 4 are sequentially laminated with respect to the incident direction of the electromagnetic wave. Moreover, FIG. 1 shows an example in which the electromagnetic wave absorbing sheet 1 is bonded to the adherend 5 such as a wall via the adhesive layer 6. Further, the front surface of the dielectric layer 3 is covered with a protective film 7 such as a fluorine-based polymer film excellent in weather resistance and heat resistance.

Here, the dielectric layer 3 is formed of a vulcanized rubber in which an electromagnetic wave absorbing material is dispersed. Further, as the vulcanized rubber used in the dielectric layer 3, natural rubber (NR, Nature Rubber), isoprene rubber (IR, Isoprene Rubber), and dibutyl are used as vulcanizing agents using sulfur or an organic peroxide as a vulcanizing agent. Butadiene Rubber (BR), Styrene Butadiene Rubber (SBR), Nitrile Butadiene Rubber (NBR), Chloroprene Rubber (CR, Chloroprene Rubber), Ethylene Propylene Rubber ( A rubber material such as EPDM, Ethylene Propylene Diene Monomer, or Isobutylene Isoprene Rubber is vulcanized, and it is particularly preferable to use a vulcanized rubber obtained by vulcanizing EPDM rubber. Further, which of the sulfur or the organic peroxide is used as the vulcanizing agent is appropriately selected depending on the type of the rubber-based material. Further, as the vulcanized rubber used in the dielectric layer 3, it is preferable to use a material which can be respectively connected to the electromagnetic wave reflective layer 4 and the protective film 7.

EPDM rubber is versatile because it is excellent in weather resistance and chemical resistance and is cheaper than enamel rubber and fluororubber. Further, it is characterized in that sulfur or an organic peroxide is used as a vulcanizing agent for EPDM rubber. The type of the sulfur or the organic peroxide to be used is not particularly limited. For example, one type or two or more types may be used: sulfur, di-tert-butyl peroxide, dicumyl peroxide (DCP, Dicumyl). Peroxide), α,α'-bis(t-butylperoxide)-p-diisopropylbenzene or 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2, 5-Dimethyl-2,5-di(t-butylperoxy)hexyne-3, or 2,5-dimethyl-2,5-di(perylenebenzhydryl peroxide)hexane Suitable for di-tert-butyl-3,3,5-trimethylcyclohexane or tert-butyl hydroperoxide.

In addition, in the present invention, the amount of the vulcanizing agent to be used may be appropriately determined depending on the type of the rubber-based material to be used, and the like. For example, it is preferably 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material. It is preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight. Further, in the present invention, sulfinamide, thiuram, thiourea, thiazole or the like as a vulcanization accelerator; zinc oxide or stearic acid as a promoter; Rubber chemicals, softeners, anti-aging agents, etc. In addition, the type and amount of the vulcanization accelerator can be appropriately determined depending on the type of the vulcanizing agent to be used, and the like, for example, 0.1 to 20 parts by weight, preferably 0.5 to 100 parts by weight per 100 parts by weight of the rubber-based material. 10 parts by weight, more preferably 1 to 5 parts by weight.

Further, in the vulcanized rubber of the present invention, a mixture containing at least EPDM rubber, an organic peroxide or sulfur as a component may be added, and components other than the above-mentioned essential components may be added within a range not detracting from the above characteristics.

Particularly in the present invention, 2-mercaptobenzimidazole is preferably used as an anti-aging agent. By adding 2-mercaptobenzimidazole, it has an effect of preventing a low molecular weight due to decomposition of the propylene portion of the EPDM rubber due to the organic peroxide. Further, an anti-aging agent other than the above may be used in combination, for example, 2,2,4-trimethyl-1,2-dihydroquinoline or 4,4'-bis(α,α'-dimethylbenzyl group Diphenylamine and the like.

Further, in the EPDM rubber of the present invention, for example, paraffin wax such as chlorinated paraffin or a dry oil such as a wax, a naphthene, an aromatic, an asphalt, or a linseed oil, or an animal or vegetable oil may be added in order to adjust the formability and the like. As a softening agent, petroleum-based oils, various low molecular weight polymers, phthalates, phosphates, stearic acid or esters thereof, alkylsulfonates, adhesion-imparting agents, and the like. Further, since stearic acid or an ester thereof is also useful as a lubricant, it can be exemplified as a component in which various lubricants can be blended.

Further, it may be added to the EPDM rubber of the present invention as needed: talc or calcium carbonate, magnesium carbonate, citric acid or a salt thereof, clay, mica powder, aluminum hydroxide, magnesium hydroxide, zinc white, bentonite, carbon black, dioxide Fillers such as barium, alumina, aluminum citrate, acetylene black, aluminum powder, calcium oxide; and, in addition, plasticizers or antioxidants, pigments, colorants, mildew inhibitors and the like. Further, the above-mentioned calcium oxide is useful as a moisture absorbent, and zinc white is useful as a stabilizer. Therefore, examples in which various stabilizers or reinforcing agents can be blended may be mentioned.

Moreover, the dielectric layer 3 in the present invention is formed by adding an additive such as the above-mentioned vulcanizing agent to a rubber-based material as described below, and then heating the mixture to carry out a vulcanization reaction treatment. Among them, when they are formed, they can also borrow After the mixture is molded into a specific form such as a sheet, the formed body is heat-treated. In this case, the formed body can be formed into any form by a suitable method, and the form thereof is not particularly limited.

Therefore, the object to be vulcanized may be formed into a sheet or other form by a suitable means such as by a kneader or a roll, a Banbury mixer, extrusion molding, or the like, or may be a specific mold. Further, it is formed into a specific form having irregularities or the like by an appropriate method such as injection molding or press molding. Further, in the present invention, heat treatment is carried out especially after forming into a sheet shape.

Further, the size of the molded body of the mixture before heating is arbitrary, and can be appropriately determined depending on the form of the target dielectric layer 3 and the like. For example, in the present invention, it is formed into a sheet having a thickness of about 1.6 mm.

The above-mentioned sulfurization reaction treatment can be carried out according to the conditions suitable for the prior art depending on the decomposition temperature of the sulfur or organic peroxide to be used and the like. The general heating temperature is 200 ° C or lower, preferably about 140 ° C to 180 ° C. Further, the heating method is carried out by conveying the sheet to a hot press or a heated roll surface or the like.

On the other hand, as the electromagnetic wave absorbing material contained in the dielectric layer 3, a carbon-based material is used. In addition, examples of the carbon-based material include carbon black, graphite, carbon nanotubes, and carbon fibers, but are not limited thereto. In the present invention, anisotropic flaky graphite is particularly used as the electromagnetic wave absorbing material. Moreover, it is preferable to contain a carbon-based material in a ratio of 90 to 160 parts by weight, preferably 110 to 140 parts by weight, based on 100 parts by weight of the rubber-based material. If the proportion of the carbon-based material is too large, the formability is deteriorated, and the sheet is deteriorated. Become brittle and other issues. On the other hand, if the ratio of the carbon-based material is too small, the dielectric constant cannot be increased. In the present invention, the dielectric constant can be increased by using the vulcanized rubber as the dielectric layer 3, so that the same thickness and the same dielectric constant can be reduced as compared with the prior electromagnetic wave absorptive sheet which does not use the vulcanized rubber. The content of the carbon-based material at the time of dielectric layer 3. For example, in the electromagnetic wave absorbing sheet which does not use a vulcanized rubber, the carbon-based material is usually contained in a ratio of 160 parts by weight or more based on 100 parts by weight of the rubber-based material, and in the present invention, it can be reduced to The ratio is 90 to 160 parts by weight, preferably 110 to 140 parts by weight, based on 100 parts by weight of the rubber-based material.

Further, in the dielectric layer 3 of the present invention, it is preferable that the flaky graphite is dispersed in the vulcanized rubber in a state of being aligned in a direction perpendicular to the incident direction of the electromagnetic wave. Further, by making the surface of the scaly graphite perpendicular to the incident direction of the electromagnetic wave, the value of the real part can be increased without increasing the value of the imaginary part of the complex permittivity of the electromagnetic wave absorbing sheet 1 to a large extent. As a result, the complex permittivity of the electromagnetic wave absorbing sheet 1 can be shifted to the high dielectric constant side, and the non-reflective condition can be satisfied, whereby the electromagnetic wave absorbing sheet 1 can be thinned and lightened.

Further, the complex dielectric constant of the dielectric layer 3 measured by the coaxial tube method or the waveguide method is designed such that the electromagnetic wave absorbing sheet 1 including the dielectric layer 3 satisfies the non-reflective condition.

On the other hand, the electromagnetic wave reflective layer 4 is a layer serving as a reflection mechanism for reflecting incident electromagnetic waves, which is formed by a metal plate such as aluminum, copper, iron or stainless steel, or by vacuum evaporation or plating. Applied to polymer When a film of the above-mentioned metal is formed on the film, a resin such as carbon fiber is used to reinforce the resin or the like. Further, for the method of laminating the dielectric layer 3 and the electromagnetic wave reflective layer 4, for example, there is a method in which heat is directly applied, and a method in which a thinner adhesive which does not affect the electromagnetic wave absorption characteristics is subjected to a subsequent method. Further, the incident direction of the electromagnetic wave with respect to the electromagnetic wave absorbing sheet 1 is designed to be incident from the surface opposite to the surface on which the electromagnetic wave reflection layer 4 is laminated. Here, in FIG. 1, although the incident direction of the electromagnetic wave is perpendicular to the electromagnetic wave reflective layer 4, the incident direction may not be perpendicular to the electromagnetic wave reflective layer 4.

Further, in the electromagnetic wave absorptive sheet 1 of the present invention, an adhesive layer 6 for attachment to the adherend 5 may be provided as needed. The adhesive layer 6 can be formed by a suitable adhesive, and is preferably an adhesive layer from the viewpoint of ease of handling and the like. Further, a suitable adhesive substance can be used in the formation of the adhesive layer. In general, for example, a rubber-based adhesive or an acrylic adhesive, a polyoxygen-based adhesive or a vinyl alkyl ether-based adhesive, a polyvinyl alcohol-based adhesive, or a polyvinylpyrrolidone-based adhesive, An organic adhesive such as a polypropylene amide-based adhesive or a cellulose-based adhesive.

Further, the adhesive layer 6 can be provided in a suitable stage until the electromagnetic wave absorbing sheet 1 is attached to the adherend 5 . Therefore, it can be set in advance on the electromagnetic wave absorbing sheet 1, or can be provided after the electromagnetic wave absorbing sheet 1 is formed.

The attachment of the layer 6 to the electromagnetic wave absorbing sheet 1 can be carried out by a suitable method such as a roll method such as a roll method, a sheet forming method such as a doctor blade method or a gravure roll coating method, or the like. a manner in which the substance is attached to the electromagnetic wave absorbing sheet 1; or an adhesive layer 6 is formed on the spacer as described above. A method of moving it to an electromagnetic wave absorbing sheet or the like.

Further, the thickness of the attached adhesive layer 6 can be determined depending on the purpose of use, and is usually set to 1 to 500 μm. In addition, when the provided adhesive layer 6 is exposed on the surface, it may be covered with a separator or the like as needed to prevent contamination or the like from being adhered to the adherend 5 .

Further, the protective film 7 includes a film formed of a fluorine-based resin, more specifically, a fluorine-based polymer, a coating layer, a immersion film, and the like. Further, the fluorine-based polymer forming the protective film 7 can be suitably used, and is not particularly limited. For example, polytetrafluoroethylene or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer or ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene (PCTFE, Polychlorotrifluoroethylene) Or an ethylene-chlorotrifluoroethylene copolymer (ECTFE, Ethylene-chlorotrifluoroethylene), polyvinylidene fluoride (PVDF) or polyvinyl fluoride (PVF, Polyvinyl Fluoride). These fluorine-based polymers are excellent in environmental resistance such as ozone resistance, weather resistance, and heat resistance. Further, in the above fluorine-based polymer, a plurality of fluorine-based polymers may be used. Further, a reinforcing substrate such as a fiber may be mixed into the protective film 7 as needed.

Further, the protective film 7 can also be formed by using a suitable polymer other than the fluorine-based polymer for the purpose of improving physical properties and the like. In particular, the amount of the fluorine-based polymer is 80% by weight or less, preferably 50% by weight or less, and more preferably 20% by weight or less, from the viewpoint of maintaining the weather resistance.

Moreover, the thickness of the protective film 7 is preferably 0.1 μm or more from the viewpoints of strength, weather resistance, and the like. For example, set to 20 μm. Further, the protective film 7 may be omitted.

The electromagnetic wave absorptive sheet 1 of the present invention having the above-described configuration can be preferably used for electromagnetic wave countermeasures such as buildings such as an ETC toll booth or a gas station, a vehicle guard rail such as a guard rail, and a building such as a high-rise building. Further, since the electromagnetic wave absorbing sheet 1 of the present invention uses vulcanized rubber in the dielectric layer 3, it is compared with other rubber-based materials which are not vulcanized, or resins, inorganic binders, inorganic/organic hybrid binders, and the like. In addition, weather resistance and heat resistance can be improved. Moreover, when the protective film 7 is provided, the weather resistance and the abrasion resistance can be further improved, and it can be preferably used for outdoor use or the like.

Example

Hereinafter, embodiments of the invention will be described.

First, the manufacturing steps of the electromagnetic wave absorptive sheet 1 of the present embodiment will be described.

(Manufacturing procedure of Example 1)

First, EPDM rubber (ethylene propylene terpolymer, Mitsui Chemicals Co., Ltd. EPT #4021), flaky graphite (Ito graphite W-5), zinc oxide, and stearic acid were kneaded using a Banbury mixer. Further, the amount of the flaky graphite added was 130 parts by weight based on 100 parts by weight of the EPDM rubber.

Then, a sulfur-based vulcanizing agent (Aichi, Alpha Gran S-50EN), a vulcanization accelerator (Ouchi Revital Chemical Co., Ltd., Nocceler CZ, Nocceler DM) was added to the obtained mixture, and the kneading was performed again. . In addition, the amount of the vulcanizing agent added was 0.25 parts by weight, and the amount of the vulcanization accelerator added was 1 part by weight, based on 100 parts by weight of the EPDM rubber.

Thereafter, the obtained mixture was processed into a sheet having a thickness of about 1.6 mm by an extruder, and heated by a hot press (185 ° C, 0.2 MPa) for 5 minutes to carry out a vulcanization reaction treatment to prepare a dielectric layer 3.

Further, an aluminum foil (Toyo Aluminum Co., Ltd., aluminum foil #80) was attached to the surface of one of the obtained sheets by means of an adhesive tape.

After the bonding, the sheet was cut to a standard size and processed into a sheet of 300 mm × 300 mm to prepare an electromagnetic wave absorbing sheet 1.

(Manufacturing steps of Examples 2 to 11)

The dielectric layer 3 was produced by changing the type and amount of the vulcanizing agent and the vulcanization accelerator, respectively. Other production conditions were the same as in the first embodiment. In addition, the kind and addition amount of the vulcanizing agent and vulcanization accelerator of each Example are described in Table 1 mentioned later.

(Manufacturing procedure of Comparative Example 1)

The dielectric layer 3 was produced without adding a vulcanizing agent to the vulcanization reaction treatment of the EPDM rubber. Other production conditions were the same as in the first embodiment.

(Evaluation results of the examples and comparative examples [dielectric coefficient measurement])

Using the network analyzer of Agilent Technologies Co., Ltd. and the C-band waveguide of Kanto Electronics, the electromagnetic wave absorption sheets of Examples 1 to 11 and Comparative Example 1 obtained in the above examples were introduced at a frequency of 4.9 to 7.05 GHz. Determination of electrical coefficient. The production conditions and measurement results of the respective measurement objects are shown in Table 1. Further, the results of Table 1 are graphically shown in Figs. 2 to 4 .

As shown in Table 1 and Figs. 2 to 4, the actual dielectric constants of the dielectric layer 3 were compared with those of the first to the eleventh examples using the vulcanized rubber as the dielectric layer 3 and the comparative example 1 in which the vulcanization was not performed. Both (εr') and imaginary part (εr") increased to a large extent. Further, Examples 8 to 11 using an organic peroxide as a vulcanizing agent were compared with Examples 1 to 7 using a sulfur system. The imaginary part (εr" of the complex dielectric coefficient of the electric layer 3 has almost no difference, while the real part (εr') slightly rises. Further, in Examples 1 to 3 in which the amount of the vulcanizing agent added was changed, the difference in dielectric constant was hardly found. Similarly, the difference in dielectric constant was not found in Examples 4 to 7 and Examples 8 to 11 in which the amount of the vulcanization accelerator was changed. Among them, in Example 4 in which no vulcanization accelerator was added, the real part (εr') of the dielectric constant of the dielectric layer 3 was slightly lowered as compared with Examples 5 to 7 in which the vulcanization accelerator was added.

Therefore, there is basically no correlation between the amount of the vulcanizing agent or the vulcanization accelerator added and the rate of increase of the dielectric constant, and the dielectric constant can be sufficiently increased as long as the amount required for the vulcanization reaction is added. Further, even when a vulcanizing agent or a vulcanization accelerator of a desired amount or more is added, the dielectric constant is not lowered. Therefore, the amount of the vulcanizing agent to be added is, for example, 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, and more preferably 1 to 5 parts by weight, per 100 parts by weight of the rubber-based material. Further, the amount of the vulcanization accelerator added is 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, and more preferably 1 to 5 parts by weight per 100 parts by weight of the rubber-based material.

Further, in the electromagnetic wave absorptive sheets 1 of the first to eleventh embodiments, the dielectric constant can be increased by using the vulcanized rubber in the dielectric layer 3, so that it can be reduced as compared with the comparative example 1 in which the vulcanized rubber is not used. Addition of a carbon-based material (for example, a ring-shaped graphite) of the dielectric layer 3 of the same thickness and the same dielectric constant the amount. Further, the shape change of the dielectric layer 3 can be made small, so that the change in the absorption performance can be made small. Therefore, it is possible to provide an electromagnetic wave absorber which is lightweight and excellent in workability and has electromagnetic wave absorbing performance without unevenness and high performance.

(Evaluation results of the examples and comparative examples [Measurement of electromagnetic wave attenuation amount])

The embodiment obtained in the above embodiment was carried out using a network analyzer (Agilent Technologies, Inc.), a reflection attenuation amount measuring device (KEYCOM Co., Ltd., lens antenna method/oblique incident type), and a circularly polarized wave antenna WR159. The electromagnetic wave absorption sheets of 1 to 11 and Comparative Example 1 were measured for the amount of reflection attenuation (electromagnetic wave absorption amount) of electromagnetic waves having a frequency of 4.9 to 7.05 GHz. The measurement results are shown in Figs. 5 to 7 .

As shown in FIG. 5 to FIG. 7 , it is understood that the examples 1 to 11 using the vulcanized rubber as the dielectric layer 3 have a matching frequency (peak frequency) in which the reflection attenuation amount (electromagnetic wave absorption amount) is 20 dB or more in the frequency band of 4.9 to 7.05 GHz. ). In addition, it is understood that the amount of reflection attenuation (electromagnetic wave absorption amount) is largely increased as compared with Comparative Example 1, and the peak frequency is shifted toward the low frequency side. Further, it is understood that in Examples 8 to 11 in which an organic peroxide is used as a vulcanizing agent, the amount of reflection attenuation (electromagnetic wave absorption amount) is further increased, and the peak frequency is further lowered to a lower frequency than in Examples 1 to 7 in which sulfur is used. Side offset. Also, the peak frequency can be made at a frequency of 5.8 GHz used in the ETC. On the other hand, in Examples 1 to 3 in which the amount of the vulcanizing agent was changed, the difference in the amount of reflection attenuation (electromagnetic wave absorption amount) was hardly found. Similarly, in Examples 4 to 7 and Examples 8 to 11 in which the amount of the vulcanization accelerator was changed, the difference in the amount of reflection attenuation (electromagnetic wave absorption amount) was hardly observed.

Therefore, the amount of vulcanizing agent or vulcanization accelerator added and the amount of reflection attenuation There is basically no correlation (electromagnetic wave absorption amount), and the amount of reflection attenuation (electromagnetic wave absorption amount) can be sufficiently increased as long as the amount required for the vulcanization reaction is added. Moreover, even when a vulcanizing agent or a vulcanization accelerator of a required amount or more is added, the amount of reflection attenuation (electromagnetic wave absorption amount) is not lowered. Therefore, the amount of the vulcanizing agent to be added is, for example, 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, and more preferably 1 to 5 parts by weight, per 100 parts by weight of the rubber-based material. Further, the amount of the vulcanization accelerator added is 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, and more preferably 1 to 5 parts by weight per 100 parts by weight of the rubber-based material.

According to the above, the electromagnetic wave absorptive sheet 1 of the examples 1 to 11 can have a reflection attenuation amount (electromagnetic wave absorption amount) in the frequency band of 4.9 to 7.05 GHz as long as it is a film-like sheet of about 1.6 mm. The amount of reflection attenuation (electromagnetic wave absorption) of the peak frequency of 20 dB or more, more specifically 25 dB or more.

As described above, the electromagnetic wave absorption sheet 1 of the present embodiment includes the dielectric layer 3 and the electromagnetic wave reflection layer 4, and uses a carbon-based material as an electromagnetic wave absorber in the frequency band of 4.9 to 7.05 GHz of the electromagnetic wave absorption material, and is dielectric-coated. The layer 3 includes a vulcanized rubber containing a carbon-based material, and thus can be suppressed as compared with a case where another rubber-based material that does not vulcanize, or a resin, an inorganic binder, an inorganic/organic hybrid binder, or the like is used for the dielectric layer. The content of the carbon-based material (for example, flaky graphite) contained in the dielectric layer 3 increases the dielectric constant. Further, the shape change of the dielectric layer 3 can be made small, so that the change in the absorption performance can be made small. Therefore, it is possible to provide the electromagnetic wave absorption sheet 1 which is lightweight and excellent in workability, and has electromagnetic wave absorption performance without uneven performance. Enter Moreover, weather resistance and heat resistance can also be improved. Further, by increasing the dielectric constant of the dielectric layer 3, the electromagnetic wave absorbing sheet 1 can be thinned. Further, the electromagnetic wave absorbing sheet 1 can be thinned and the matching frequency (peak frequency) can be shifted toward the low frequency side. For example, even a film-like sheet of about 1.6 mm can achieve a reflection attenuation amount (electromagnetic wave absorption amount) in a frequency band of 4.9 to 7.05 GHz as 20 dB or more as a sufficient absorption amount, more specifically 25 The amount of reflection attenuation (electromagnetic wave absorption) of the matching frequency (peak frequency) above dB.

Further, natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, nitrile rubber, chloroprene rubber, ethylene propylene rubber, or the like, using sulfur or an organic peroxide as a vulcanizing agent. The vulcanized rubber obtained by vulcanizing any of the rubber materials of the butyl rubber serves as the vulcanized rubber forming the dielectric layer 3, so that the electromagnetic wave absorbing sheet 1 which is lightweight and excellent in workability can be provided.

Further, since the dielectric layer 3 contains a layer in which scaly graphite is dispersed on the vulcanized rubber, the effective dielectric constant of the dielectric layer 3 can be increased. As a result, thinning and weight reduction of the dielectric layer can be achieved.

In addition, since the matching frequency (peak frequency) of electromagnetic wave absorption amount is 20 dB or more in the frequency band of 4.9 to 7.05 GHz, sufficient electromagnetic wave absorption performance can be realized when electromagnetic waves in the frequency band of 4.9 to 7.05 GHz are absorbed.

In addition, since the amount of the carbon-based material (for example, flaky graphite) contained in the dielectric layer 3 is 90 to 160 parts by weight per 100 parts by weight of the rubber-based material constituting the vulcanized rubber, the carbon contained therein can be suppressed. The content of the material. As a result, problems such as deterioration of formability and brittleness of the sheet can be prevented. Enter Further, in the case where a large amount of carbon-based material is contained, it is possible to cause voids in the interior due to poor dispersion of the carbon-based material or unevenness in electromagnetic wave absorption performance.

In addition, the second mixing step of re-kneading the vulcanizing agent and the vulcanization accelerator by adding the vulcanizing agent and the vulcanization accelerator to the mixture obtained by the first mixing step by the first mixing step of kneading the rubber-based material and the carbon-based material The step of processing the mixture obtained by the second mixing step into a sheet shape and the step of forming the dielectric layer 3 by performing a vulcanization reaction by heating the mixture processed into a sheet at a specific temperature, and thus suitably The vulcanization reaction treatment of the dielectric layer 3 is performed to form the dielectric layer 3 by vulcanized rubber containing a carbon-based material.

Moreover, since the amount of the vulcanizing agent added when the dielectric layer 3 is formed is 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material, the dielectric constant can be largely increased. As a result, it is possible to provide an electromagnetic wave absorber having electromagnetic wave absorption performance without high uniformity.

The present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention.

For example, the mixing conditions, the vulcanization conditions, the sheet forming conditions, the heating conditions, and the like when the electromagnetic wave absorbing sheet 1 is produced are not limited to the conditions described in the above embodiments. For example, the amount of addition, the heating temperature, the heating time, and the like can be appropriately changed.

Further, in the present embodiment, flaky graphite is used as the electromagnetic wave absorbing material dispersed in the dielectric layer 3, but other carbon-based materials may be used.

Moreover, in the present embodiment, although the EPDM rubber is vulcanized, As the vulcanized rubber constituting the dielectric layer 3, other rubber-based materials may be used.

Further, in the present embodiment, dicumyl peroxide (DCP) is used as the vulcanizing agent for the organic peroxide, but other vulcanizing agents may be used.

1‧‧‧Electromagnetic wave absorption sheet

3‧‧‧ dielectric layer

4‧‧‧Electromagnetic wave reflection layer

7‧‧‧Protective film

Fig. 1 is an explanatory view showing an electromagnetic wave absorptive sheet of the present invention.

Fig. 2 is a graph showing the measurement results of the dielectric constants of the electromagnetic wave absorptive sheets of Examples 1 to 3 and Comparative Example 1.

Fig. 3 is a graph showing the measurement results of the dielectric constants of the electromagnetic wave absorptive sheets of Examples 4 to 7 and Comparative Example 1.

Fig. 4 is a graph showing the results of measurement of the dielectric constant of the electromagnetic wave absorptive sheets of Examples 8 to 11 and Comparative Example 1.

Fig. 5 is a graph showing the results of measurement of the electromagnetic wave attenuation amount of the electromagnetic wave absorptive sheets of Examples 1 to 3 and Comparative Example 1.

Fig. 6 is a graph showing the results of measurement of the electromagnetic wave attenuation amount of the electromagnetic wave absorptive sheets of Examples 4 to 7 and Comparative Example 1.

Fig. 7 is a graph showing the results of measurement of the electromagnetic wave attenuation amount of the electromagnetic wave absorptive sheets of Examples 8 to 11 and Comparative Example 1.

1‧‧‧Electromagnetic wave absorption sheet

3‧‧‧ dielectric layer

4‧‧‧Electromagnetic wave reflection layer

5‧‧‧Adhesive body

6‧‧‧Next layer

7‧‧‧Protective film

Claims (12)

An electromagnetic wave absorber comprising: a dielectric layer; and an electromagnetic wave reflecting layer laminated on a surface of the dielectric layer; and the dielectric layer comprises a vulcanized rubber containing a carbon-based material. The electromagnetic wave absorber of claim 1, wherein the vulcanized rubber is a natural rubber, an isoprene rubber, a butadiene rubber, a styrene butadiene rubber, a nitrile rubber, or a chlorine by using sulfur or an organic peroxide as a vulcanizing agent. A vulcanized rubber obtained by vulcanizing any rubber material of butadiene rubber, ethylene propylene rubber, or butyl rubber. The electromagnetic wave absorber of claim 1, wherein the carbonaceous material is flaky graphite. The electromagnetic wave absorber of claim 1, wherein the electromagnetic wave absorption amount is 20 dB or more in a frequency band of 4.9 to 7.05 GHz. The electromagnetic wave absorber of claim 1, wherein the amount of the carbon-based material contained in the dielectric layer is 90 to 160 parts by weight per 100 parts by weight of the rubber-based material constituting the vulcanized rubber. The electromagnetic wave absorber according to any one of claims 1 to 5, which is produced by the first step of kneading a rubber-based material and the carbon-based material; and by the first mixing step a second mixing step of remixing the vulcanizing agent and the vulcanization accelerator in the obtained mixture; a step of processing the mixture obtained by the second mixing step into a sheet shape; and the above processing by processing the above into a sheet shape The mixture is added at a specific temperature The step of forming a dielectric layer by performing a vulcanization reaction by heat. The electromagnetic wave absorber of claim 6, wherein the amount of the vulcanizing agent added in the second mixing step is 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material. A method for producing an electromagnetic wave absorber, comprising: a first mixing step of kneading a rubber-based material and the carbon-based material; and adding a vulcanizing agent and a vulcanization accelerator to the mixture obtained by the first mixing step; a second mixing step of re-kneading; a step of processing the mixture obtained by the second mixing step into a sheet shape; and performing a vulcanization reaction by heating the above-mentioned mixture processed into a sheet at a specific temperature. Thereby the step of forming the above dielectric layer is carried out. The method for producing an electromagnetic wave absorber according to claim 8, wherein the rubber-based material is natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, nitrile rubber, chloroprene rubber, and ethylene. Any of propylene rubber and butyl rubber, and the above vulcanizing agent is sulfur or an organic peroxide. The method for producing an electromagnetic wave absorber according to claim 8, wherein the carbon-based material is flaky graphite. The method for producing an electromagnetic wave absorber according to claim 8, wherein the amount of the carbon-based material contained in the dielectric layer is 90 to 160 parts by weight per 100 parts by weight of the rubber-based material. The method for producing an electromagnetic wave absorber according to any one of claims 8 to 11, wherein the amount of the vulcanizing agent added in the second mixing step is 0.1 to 20 parts by weight per 100 parts by weight of the rubber-based material. .