JP2013201359A - Electromagnetic wave absorber and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorber which is lightweight and excellent in processability and has high electromagnetic wave absorbing performance in a low frequency band, and a method for manufacturing the electromagnetic wave absorber.SOLUTION: An electromagnetic wave absorbing sheet 1 for a frequency band of 4.9-7.05 GHz is constituted by laminating a DCF 2, a dielectric layer 3, and an electromagnetic wave reflecting layer 4. The electromagnetic wave absorbing sheet 1 is configured such that a first resin layer 5, which is between the dielectric layer 3 and the DCF 2 and bonds opposing surfaces of the dielectric layer 3 and the DCF 2 to each other, has a thickness D of 5-300 μm.

Description

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

  In recent years, with the spread of various communication devices such as mobile phones, various problems of radio interference such as malfunction of electric / electronic devices and leakage of information due to electromagnetic noise have become serious. In addition, there is a possibility that electromagnetic waves may adversely affect the human body. Therefore, conventionally, a method for preventing an adverse effect due to electromagnetic waves has been performed by using an electromagnetic wave absorber that absorbs electromagnetic waves. Specifically, the electromagnetic wave emitted from the electronic device is absorbed by arranging the electromagnetic wave absorber on the wall around the electronic device that emits the electromagnetic wave, or arranging the electromagnetic wave absorber on the wall of the building. Was.

  The electromagnetic wave absorber as described above has been desired to be thin and light. For example, in the non-stop automatic toll collection system (ETC) used in tollgates on expressways, in order to prevent malfunction of on-vehicle equipment due to electromagnetic wave interference between adjacent lanes, electromagnetic waves are generated on the ceiling and side walls of the toll booth. It is necessary to attach an absorber, and it is necessary to reduce the thickness and weight of the electromagnetic wave absorber.

  Here, in order to absorb electromagnetic waves, it is necessary to use an electromagnetic wave absorber corresponding to the frequency band of the electromagnetic waves to be absorbed. For example, microwaves emitted from communication devices include 2.4 GHz and 5.2 GHz frequency electromagnetic waves used for wireless LAN, and 5.8 GHz frequency electromagnetic waves used for ETC, and absorb these microwaves. Therefore, it is necessary to use an electromagnetic wave absorber corresponding to the frequency band.

For example, Japanese Patent Application Laid-Open No. 2003-158395 discloses an electromagnetic wave absorber that can obtain relatively high electromagnetic wave absorption performance in a wide frequency range near 1 to 20 GHz in which 1 to 10 parts by weight of a nanosized carbon material is blended in a resin. ing. Japanese Patent Application Laid-Open No. 2004-311586 discloses a foamed electromagnetic wave comprising a predetermined resin component and powdered carbon black having a specific nitrogen adsorption specific surface area, and having a density set to 0.3 g / cm ³ or less. An electromagnetic wave absorber that is an absorber and can obtain an electromagnetic wave absorbing performance that attenuates an electromagnetic wave by 8 dB or more at 8 to 12.5 GHz is disclosed.

JP2003-158395A (page 3-4) Japanese Patent Laying-Open No. 2004-311586 (page 5-6)

  By the way, as described in Patent Document 1, an electromagnetic wave band (peak frequency) for reducing reflection, which is an electromagnetic wave absorption characteristic, and an attenuation factor in the band are basically substances that absorb electromagnetic waves contained in the electromagnetic wave absorber ( Hereinafter, it is determined by the type and amount of the electromagnetic wave absorbing material) and the thickness of the electromagnetic wave absorbing layer (that is, the dielectric layer).

  Specifically, the thickness of the electromagnetic wave absorbing layer that can efficiently reduce reflection at a certain wavelength λ is determined by the complex relative dielectric constant of the electromagnetic wave absorbing layer. As the real part of the complex dielectric constant increases, the thickness of the electromagnetic wave absorption layer at the frequency (matching frequency) at which the absorption effect is maximized can be reduced. In addition, the larger the imaginary part of the complex dielectric constant, the better the electromagnetic wave is absorbed. If the complex relative dielectric constant is fixed, the thickness of the electromagnetic wave absorbing layer corresponding to the matching frequency needs to be increased as the matching frequency is shifted to the lower frequency side.

  That is, an electromagnetic wave absorber having a high absorption amount in a low frequency band (for example, 4.9 to 7.05 GHz) has a high density of the electromagnetic wave absorbing material in order to increase the thickness of the electromagnetic wave absorption layer or increase the dielectric constant. It was necessary to charge. However, if the thickness of the electromagnetic wave absorbing layer is increased, the electromagnetic wave absorber cannot be reduced in thickness and weight. Moreover, when the electromagnetic wave absorbing material is charged at a high density, problems such as poor formability and brittleness of the sheet occur. Furthermore, when a large amount of the electromagnetic wave absorbing material is contained, there is a problem that voids are generated inside due to poor dispersion of the electromagnetic wave absorbing material, and electromagnetic wave absorbing performance varies.

  The present invention has been made in order to solve the above-described conventional problems. The thickness of the resin layer for joining the dielectric layer and the divided conductive film layer is increased while the divided conductive film layer is laminated on the dielectric layer. By defining, it aims at providing the manufacturing method of the electromagnetic wave absorber and electromagnetic wave absorber which are lightweight, excellent in workability, and have high electromagnetic wave absorption performance in a low frequency band.

  In order to achieve the above object, an electromagnetic wave absorber according to claim 1 of the present application includes a dielectric layer made of a matrix containing an electromagnetic wave absorbing material, a divided conductive film layer laminated on one surface of the dielectric layer, An electromagnetic wave reflection layer laminated on the other surface of the dielectric layer, and a resin layer between the dielectric layer and the divided conductive film layer and bonding the opposing surfaces of the dielectric layer and the divided conductive film layer to each other The thickness of the resin layer is 5 μm to 300 μm, the thickness of the dielectric layer is 1000 μm or less, and the electromagnetic wave absorbing material contained in the dielectric layer is the matrix 100. It is 130 weight part or less with respect to a weight part, Comprising: The peak frequency is 6.4 GHz or less, It is characterized by the above-mentioned.

  The electromagnetic wave absorber according to claim 2 is the electromagnetic wave absorber according to claim 1, wherein the divided conductive film layer has a structure in which a plurality of rectangular conductive films are arranged at predetermined intervals. The size of one side of the film is 2.0 mm to 10.0 mm, and the conductive film is arranged at an interval of 0.1 mm to 1.5 mm.

The electromagnetic wave absorber according to claim 3 is the electromagnetic wave absorber according to claim 1 or 2, wherein the dielectric layer is made of a matrix containing a carbon-based material and is measured by a waveguide method. The relative permittivity is characterized in that the real part (ε _r ′) satisfies the range of 20 to 120 and the imaginary part (ε _r ″) satisfies the range of 2 to 16.

  The electromagnetic wave absorber according to claim 4 is the electromagnetic wave absorber according to claim 3, wherein the electromagnetic wave absorbing material is flake graphite.

  The electromagnetic wave absorber according to claim 5 is the electromagnetic wave absorber according to claim 3 or 4, wherein the dielectric layer is made of vulcanized rubber containing the electromagnetic wave absorbing material.

  The electromagnetic wave absorber according to claim 6 is the electromagnetic wave absorber according to any one of claims 1 to 5, wherein the dielectric layer has a complex relative dielectric constant measured by a waveguide method. When the part is compared with the value of the imaginary part that satisfies the same non-reflection condition, the value of the imaginary part is lower than the value of the imaginary part that satisfies the non-reflection condition.

  An electromagnetic wave absorber according to claim 7 is the electromagnetic wave absorber according to any one of claims 1 to 6, wherein an electromagnetic wave absorption amount is 20 dB or more in a frequency band of 4.9 to 7.05 GHz. It is characterized by having.

  Furthermore, the manufacturing method of the electromagnetic wave absorber which concerns on Claim 8 is a manufacturing method of the electromagnetic wave absorber which manufactures the electromagnetic wave absorber in any one of the said Claim 1 thru | or 7.

The electromagnetic wave absorber according to claim 1, having the above-described configuration, includes a divided conductive film layer laminated on one surface of the dielectric layer, and is further provided between the dielectric layer and the divided conductive film layer. The thickness of the resin layer that joins the opposing surfaces of the layer and the divided conductive film layer to each other is set to 5 μm to 300 μm, so that the thickness of the dielectric layer is 1000 μm or less, and the electromagnetic wave absorbing material contained in the dielectric layer Even if it is 130 parts by weight or less with respect to 100 parts by weight of the matrix, the peak frequency can be made 6.4 GHz or less. An electromagnetic wave absorber having high electromagnetic wave absorbing performance can be provided. For example, even a thin-film electromagnetic wave absorber having a thickness of about 1.0 to 1.3 mm can achieve a sufficient amount of reflection attenuation (electromagnetic wave absorption) in a frequency band of 6.4 GHz or less. is there.
Further, by suppressing the content of the electromagnetic wave absorbing material to be contained in the dielectric layer, it is possible to provide an electromagnetic wave absorber that is lightweight, excellent in workability, and has high performance electromagnetic wave absorbing performance without variation.
On the other hand, by using the DCF structure, the dielectric constant can be further increased. Further, by increasing the dielectric constant, it is possible to further reduce the thickness and weight of the electromagnetic wave absorber.

  In addition, according to the electromagnetic wave absorber according to claim 2, sufficient electromagnetic wave absorption characteristics can be obtained by setting appropriate values for the length of one side of the conductive film and the arrangement interval of the conductive film, which are DCF parameters. It is possible to reduce the thickness and weight of the dielectric layer and the DCF in the state of having the.

  According to the electromagnetic wave absorber according to claim 3, in the electromagnetic wave absorber using a carbon-based material as the electromagnetic wave absorbing material, a sufficient electromagnetic wave can be obtained without increasing the proportion of the carbon-based material by using a DCF structure. Absorption performance can be obtained. That is, it is possible to increase the effective dielectric constant of the dielectric layer and design the electromagnetic wave absorber including the divided conductive film layer and the dielectric layer so as to satisfy the non-reflection condition. Thereby, the electromagnetic wave that has entered the electromagnetic wave absorber can be greatly attenuated.

  In addition, according to the electromagnetic wave absorber according to claim 4, since the dielectric layer is composed of a layer in which scaly graphite is dispersed in the matrix, the effective dielectric constant of the dielectric layer can be increased. As a result, it is possible to reduce the thickness and weight of the dielectric layer.

  Further, according to the electromagnetic wave absorber according to claim 5, since the dielectric layer is formed by vulcanized rubber containing the electromagnetic wave absorbing material, other rubber-based materials that are not vulcanized, resin, inorganic binder, inorganic -Compared with the case where an organic hybrid binder etc. are used for a dielectric material layer, it becomes possible to raise a dielectric constant, suppressing content of the electromagnetic wave absorption material contained in a dielectric material layer. Furthermore, weather resistance and heat resistance can be improved.

  Further, according to the electromagnetic wave absorber according to claim 6, when the real part of the complex relative permittivity of the dielectric layer is compared with the value of the imaginary part satisfying the same antireflection condition, the imaginary condition satisfying the antireflection condition is satisfied. Since the value of the imaginary part is lower than the value of the part, the electromagnetic wave absorbing sheet including the DCF and the dielectric layer can be designed to satisfy the non-reflection condition. Thereby, it is possible to attenuate the electromagnetic wave that has entered the electromagnetic wave absorbing sheet.

  Moreover, according to the electromagnetic wave absorber of claim 7, since the electromagnetic wave absorption has a peak frequency of 20 dB or more in the frequency band of 4.9 to 7.05 GHz, the frequency band of 4.9 to 7.05 GHz It is possible to realize sufficient electromagnetic wave absorption performance when absorbing electromagnetic waves.

  Furthermore, according to the method for producing an electromagnetic wave absorber according to claim 8, an electromagnetic wave absorber having high electromagnetic wave absorption performance in a low frequency band while suppressing the content of the electromagnetic wave absorbing material to be contained in the dielectric layer is provided. Is possible.

It is explanatory drawing shown about the electromagnetic wave absorption sheet which concerns on this invention. It is the schematic diagram which showed the structure of DCF formed in the electromagnetic wave absorption sheet which concerns on this invention. It is the figure which showed the relationship between the thickness of the 1st resin layer in Examples 1-4 and the electromagnetic wave absorption sheet of the comparative example 1, and a matching frequency.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying an electromagnetic wave absorber and an electromagnetic wave absorber manufacturing method according to the present invention will be described in detail with reference to the drawings.

  First, the structure of the electromagnetic wave absorbing sheet 1 which is an electromagnetic wave absorber according to the present invention will be described with reference to FIG. FIG. 1 is an explanatory view showing an electromagnetic wave absorbing sheet 1 according to the present invention.

  As shown in FIG. 1, the electromagnetic wave absorbing sheet 1 according to the present invention basically includes a divided conductive film layer (hereinafter referred to as DCF) 2, a dielectric layer 3, and an electromagnetic wave reflection layer 4. Also, the DCF 2, the dielectric layer 3, and the electromagnetic wave reflection layer 4 are laminated in this order with respect to the incident direction of the electromagnetic wave. In addition, a first resin layer 5 is provided between the DCF 2 and the dielectric layer 3 to join the facing surfaces of the DCF 2 and the dielectric layer 3 to each other. Similarly, a second resin layer 6 is provided between the dielectric layer 3 and the electromagnetic wave reflection layer 4 to join the opposing surfaces of the dielectric layer 3 and the electromagnetic wave reflection layer 4 to each other. FIG. 1 shows an example in which the electromagnetic wave absorbing sheet 1 is attached to an adherend 7 such as a wall via an adhesive layer 8. Further, the front surface of the DCF 2 is covered with a protective film 9 such as a fluorine polymer film having excellent weather resistance and heat resistance. The thickness D of the first resin layer 5 is 5 μm to 300 μm, preferably 5 μm to 100 μm, more preferably 5 μm to 50 μm, as will be described later.

Here, the DCF 2 has a periodic structure in which square conductive films 11 made of a conductive material (for example, copper foil) are arranged at equal intervals. FIG. 2 is a schematic diagram showing the structure of DCF2.
As shown in FIG. 2, the DCF 2 of the present invention is configured by disposing a copper foil conductive film 11 having a length of one side a with respect to a PI (polyimide) film 12 at an interval b. Further, the length a of one side of the conductive film 11 is 2.0 mm to 10.0 mm, and the arrangement interval b of the conductive film 11 is preferably 0.1 mm to 1.5 mm. By setting a and b to appropriate numerical ranges, the effective dielectric constant of the electromagnetic wave absorbing sheet 1 can be greatly increased as described later.

  When electromagnetic waves are incident on the DCF 2 perpendicularly, a current flows through the edge portion of the conductive film 11, and an electric field is accumulated in the gap portion of the conductive film 11 (between adjacent conductive films 11). That is, the phase is delayed, and the effective dielectric constant of the electromagnetic wave absorbing sheet 1 can be greatly increased (both the real part and the imaginary part of the complex relative dielectric constant are increased). Therefore, the electromagnetic wave absorbing sheet 1 using DCF 2 can be made thinner and lighter than the conventional λ / 4 type wave absorber. Moreover, it becomes possible to shift the matching frequency to a lower frequency side with the thinning of the electromagnetic wave absorbing sheet 1.

In addition, the thickness d of the electromagnetic wave absorbing sheet 1 including the DCF 2, the dielectric layer 3, and the electromagnetic wave reflection layer 4 is applied to the wavelength λ of the electromagnetic wave that is absorbed from an application to be attached to the wall surface or ceiling. It is desirable to make the range satisfying 01 to 0.05. Therefore, for example, at a design frequency of 5.8 GHz, it is desirable that d = 0.51 mm to 2.59 mm. Further, it is desirable that the weight per unit area of the electromagnetic wave absorber sheet 1 is in the range of ^{1000g / m 2 ~2000g / m 2} .

  In addition, the material which comprises the electrically conductive film 11 of DCF2 is not restricted to copper foil, Aluminum, gold | metal | money, silver, a conductive film, etc. may be sufficient. Alternatively, the conductive film 11 may be directly disposed on the dielectric layer 3 without using the PI film 12.

  On the other hand, the dielectric layer 3 is formed of a matrix in which an electromagnetic wave absorbing material is dispersed. The matrix used for the dielectric layer 3 includes a rubber material, a resin, an inorganic binder, an inorganic / organic hybrid binder, and the like. For example, the matrix is formed of a vulcanized rubber in which an electromagnetic wave absorbing material is dispersed. As the vulcanized rubber used for the dielectric layer 3, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), chloroprene rubber ( CR), ethylene propylene rubber (EPDM), rubber material such as butyl rubber (IIR), which is vulcanized with sulfur or organic peroxide as vulcanizing agent, especially vulcanized rubber vulcanized with EPDM rubber It is desirable to use Whether sulfur or an 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 for the dielectric layer 3, it is desirable to use materials that can be bonded to the first resin layer 5 and the second resin layer 6, respectively.

  EPDM rubber is widely used because it is excellent in weather resistance and chemical resistance and is less expensive than silicon rubber and fluoro rubber. In addition, as a vulcanizing agent for EPDM rubber, sulfur or an organic peroxide is used. The kind of sulfur or organic peroxide to be used is not particularly limited. For example, sulfur, di-t-butyl peroxide, dicumyl peroxide (DCP), α, α′-bis (t-butylperoxy) -p -Diisopropylbenzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, and 2 1,5-dimethyl-2,5-di (t-benzoylperoxy) hexane, di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butyl hydroperoxide, etc. Species or two or more can be used.

  Further, in the present invention, the amount of the vulcanizing agent can be appropriately determined according to the type of the rubber-based material to be used. For example, 0.1 to 20 parts by weight, preferably 0, per 100 parts by weight of the rubber-based material. 5 to 10 parts by weight, more preferably 1 to 5 parts by weight. In the present invention, sulfenamide-based, thiuram-based, thiourea-based, thiazole-based, etc. as vulcanization accelerators, zinc oxide, stearic acid, etc. as acceleration aids, oils, softeners, anti-aging as rubber chemicals Each agent can be used in combination. The type and amount of the vulcanization accelerator can be appropriately determined according to the type of the vulcanizing agent used. For example, 0.1 to 20 parts by weight, preferably 0, per 100 parts by weight of the rubber-based material. 5 to 10 parts by weight, more preferably 1 to 5 parts by weight.

  Further, the vulcanized rubber of the present invention is composed of an admixture containing at least EPDM rubber, organic peroxide or sulfur as a component, but other than the essential components may be added as long as the above characteristics are not impaired. .

  In particular, in the present invention, 2-mercaptobenzimidazole is preferably used as an anti-aging agent. By adding 2-mercaptobenzimidazole, there is an effect of preventing a reduction in molecular weight due to decomposition of the propylene portion of the EPDM rubber by the organic peroxide. Other anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline and 4,4′-bis (α, α′-dimethylbenzyl) diphenylamine can also be used in combination.

  In addition, the EPDM rubber of the present invention has a softening agent for the purpose of adjusting moldability, for example, dry oils such as paraffins such as chlorinated paraffins, waxes, naphthenes, aromas, asphalts, and linseed oil. Animal and vegetable oils, petroleum oils, various low molecular weight polymers, phthalic acid esters, phosphoric acid esters, stearic acid and its esters, alkylsulfonic acid esters, tackifiers and the like can also be added. In addition, stearic acid and its esters are useful as a lubricant, and therefore can be listed as examples of components in which various lubricants can be blended.

  Further, the EPDM rubber of the present invention includes talc, calcium carbonate, magnesium carbonate, silicic acid and its salts, clay, mica powder, aluminum hydroxide, magnesium hydroxide, zinc white, bentonine, carbon black, silica, alumina, aluminum. An appropriate compounding agent such as a filler such as silicate, acetylene black, aluminum powder, and calcium oxide, and a plasticizer, an antioxidant, a pigment, a colorant, and an antifungal agent can be added as necessary. The calcium oxide is useful as a hygroscopic agent, and the zinc white is useful as a stabilizer. Therefore, examples of components that can contain various stabilizers and reinforcing agents are given.

  The dielectric layer 3 in the present invention is formed by adding an additive such as the above-described vulcanizing agent to a rubber-based material as described later, and then heating the mixture to perform a vulcanization reaction treatment. However, when forming the mixture, it is also possible to form the mixture by, for example, forming the mixture into a predetermined form such as a sheet and then heat-treating the formed body. In that case, the molded body may be molded into an arbitrary form by an appropriate method, and the form is not particularly limited.

  Therefore, the object of vulcanization treatment may be a mixture obtained by molding the mixture into a sheet or other form by an appropriate method such as mixing roll, calendar roll, Banbury mixer, extrusion molding, etc. It may be formed into a predetermined form having irregularities or the like by an appropriate method such as injection molding or press molding. In the present invention, the heat treatment is performed after the sheet is formed.

  Moreover, the dimension of the molded body of the mixture before heating is arbitrary, and can be appropriately determined according to the target form of the dielectric layer 3 and the like. For example, in the present invention, it is formed into a sheet having a thickness of about 1.0 to 1.3 mm.

  The vulcanization reaction treatment described above can be performed under appropriate conditions according to the prior art depending on the sulfur used, the decomposition temperature of the organic peroxide, or the like. The general heating temperature is 200 ° C. or less, preferably about 140 ° C. to 180 ° C. As a heating method, a sheet is conveyed to the surface of a hot press or a heated roller.

  On the other hand, as the electromagnetic wave absorbing material included in the dielectric layer 3, a carbon-based material is used. Examples of the carbon-based material include, but are not limited to, carbon black, graphite, carbon nanotube, and carbon fiber. In the present invention, anisotropic scaly graphite is particularly used as the electromagnetic wave absorbing material. The carbon-based material is desirably contained in a proportion of 90 to 160 parts by weight, preferably 110 to 130 parts by weight with respect to 100 parts by weight of the rubber-based material. If the proportion of the carbon-based material is excessive, problems such as poor formability and brittleness of the sheet occur. On the other hand, if the proportion of the carbon-based material is too small, the dielectric constant cannot be increased. However, since the dielectric constant can be increased by laminating DCF2 and using vulcanized rubber as the dielectric layer 3 in the present invention, the dielectric having the same thickness and the same dielectric constant as compared with the conventional electromagnetic wave absorbing sheet. It becomes possible to reduce the content of the carbon-based material when forming the body layer 3. For example, in the conventional electromagnetic wave absorbing sheet, the carbon-based material is generally contained in a ratio of 160 parts by weight or more with respect to 100 parts by weight of the rubber-based material, whereas in the present invention, 100% by weight of the rubber-based material. 90 to 160 parts by weight, preferably 110 to 130 parts by weight with respect to parts.

  In addition, it is desirable that the dielectric layer 3 according to the present invention is dispersed in a state where scaly graphite is aligned in a direction perpendicular to the incident direction of electromagnetic waves with respect to the vulcanized rubber. And, by making the surface of the scaly graphite perpendicular to the incident direction of the electromagnetic wave, the value of the real part is increased without greatly increasing the value of the imaginary part of the complex relative dielectric constant of the electromagnetic wave absorbing sheet 1 Can do. As a result, the complex relative permittivity of the electromagnetic wave absorbing sheet 1 can be shifted to the high dielectric constant side and the non-reflection condition can be satisfied, and the electromagnetic wave absorbing sheet 1 can be made thinner and lighter.

The complex dielectric constant measured by the waveguide method of the dielectric layer 3 is such that the real part (ε _r ′) satisfies the range of 20 to 120 and the imaginary part (ε _r ″) ranges from 2 to 16. When the dielectric loss tangent (Tanδ = ε _r ″ / ε _r ′) satisfies the range of 0.05 to 0.5, particularly when compared with the value of the imaginary part where the real part satisfies the same antireflection condition, It is desirable that the value of the imaginary part is lower than the value of the imaginary part that satisfies the non-reflection condition. This is because the effective dielectric constant is increased by arranging the DCF 2 described above (both the real part and the imaginary part of the complex relative dielectric constant are increased), so that the electromagnetic wave absorbing sheet 1 including the DCF 2 and the dielectric layer 3 is not present. In order to satisfy the reflection condition, the dielectric layer 3 alone needs to have a low effective dielectric constant beforehand (both the real part and the imaginary part of the complex relative dielectric constant are lower than the value satisfying the non-reflection condition). is there.

  On the other hand, the electromagnetic wave reflection layer 4 is a layer used as a reflection means for reflecting incident electromagnetic waves, and is a metal plate such as aluminum, copper, iron or stainless steel, or a thin film of the above metal by vacuum deposition or plating on a polymer film. Or a resin reinforced with a conductive material such as carbon fiber. As a method of laminating the dielectric layer 3 and the electromagnetic wave reflection layer 4, there are, for example, a method of directly heat bonding, a method of bonding with a thin adhesive that does not affect the electromagnetic wave absorption characteristics, and the like. Moreover, the incident direction of the electromagnetic wave incident on the electromagnetic wave absorbing sheet 1 is designed so as to be incident from the surface opposite to the surface on which the electromagnetic wave reflection layer 4 is laminated. However, although the incident direction of the electromagnetic wave is perpendicular to the electromagnetic wave reflecting layer 4 in FIG. 1, the incident direction may not be perpendicular to the electromagnetic wave reflecting layer 4.

  In addition, the first resin layer 5 that joins the facing surfaces of the DCF 2 and the dielectric layer 3 to each other and the second resin layer 6 that joins the facing surfaces of the dielectric layer 3 and the electromagnetic wave reflection layer 4 to each other are made of an appropriate resin material. However, the adhesive layer is preferred from the standpoint of easy adhesion work. An appropriate adhesive substance can be used for forming the adhesive layer. In general, for example, rubber adhesives and acrylic adhesives, silicone adhesives and vinyl alkyl ether adhesives, polyvinyl alcohol adhesives and polyvinylpyrrolidone adhesives, polyacrylamide adhesives and cellulose adhesives, etc. The organic type is used.

  In particular, the thickness D of the first resin layer 5 disposed between the DCF 2 and the dielectric layer 3 affects the matching frequency of the electromagnetic wave absorbing sheet 1. Specifically, as will be described later, the matching frequency is basically shifted to the lower frequency side as the thickness D of the first resin layer 5 is thinner. Therefore, in order to realize the electromagnetic wave absorbing sheet 1 having a high absorption amount in a low frequency band (for example, 4.9 to 7.05 GHz), it is important to reduce the thickness D of the first resin layer 5. However, if the thickness D of the first resin layer 5 is too thin, the DCF 2 and the dielectric layer 3 cannot be joined appropriately. Therefore, the thickness D of the first resin layer 5 is 5 μm to 300 μm, preferably 5 μm to 100 μm. More preferably, the thickness is 5 μm to 50 μm.

  Moreover, the electromagnetic wave absorbing sheet 1 according to the present invention can be provided with an adhesive layer 8 for attaching to the adherend 7 as necessary. The adhesive layer 8 can be formed of an appropriate resin material in the same manner as the first resin layer 5 and the second resin layer 6. The adhesive layer 8 can be provided at an appropriate stage until the electromagnetic wave absorbing sheet 1 is attached to the adherend 7. Therefore, it can be provided in advance on the electromagnetic wave absorbing sheet 1 or can be provided after the electromagnetic wave absorbing sheet 1 is formed. Moreover, the thickness of the adhesive layer 8 to be provided can be determined according to the purpose of use, and is generally 5 to 500 μm. In addition, when the provided adhesive layer 8 is exposed on the surface, it can be covered with a separator or the like as necessary until it is adhered to the adherend 7 to prevent contamination or the like.

  The first resin layer 5, the second resin layer 6, and the adhesive layer 8 are formed by an appropriate method such as a rolling method such as a calender roll method or a sheet forming method such as a doctor blade method or a gravure roll coater method. Is applied to the sheet surface, or a suitable method such as a method in which the first resin layer 5, the second resin layer 6 and the adhesive layer 8 are formed on the separator and transferred to the sheet surface in accordance with the above. It's okay. A commercially available adhesive tape may be used.

  The protective film 9 is made of a fluororesin, more specifically, a film formed from a fluoropolymer, a coating layer, an impregnation film, and the like. In addition, as a fluorine-type polymer which forms the protective film 9, a suitable thing can be used and it does not specifically limit. For example, polytetrafluoroethylene, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, ethylene / tetrafluoroethylene copolymer, polychlorotrifluoroethylene (PCTFE), ethylene / Examples thereof include chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF). These fluoropolymers are materials excellent in environmental resistance such as ozone resistance, weather resistance, and heat resistance. Moreover, you may use multiple types of fluorine-type polymer among said fluorine-type polymers. Further, a reinforcing substrate such as a fiber may be mixed into the protective film 9 as necessary.

  Further, the protective film 9 may be formed by using an appropriate polymer other than the fluorine-based polymer for the purpose of improving physical properties. However, the combined use amount is 80% by weight or less, preferably 50% by weight or less, more preferably 20% by weight or less of the fluoropolymer from the viewpoint of maintaining weather resistance.

  Moreover, it is preferable that the thickness of the protective film 9 shall be 0.1 micrometer or more from points, such as intensity | strength and a weather resistance. For example, it is 20 μm. The protective film 9 may be omitted.

  The electromagnetic wave absorbing sheet 1 according to the present invention having the above-described configuration is used for the purpose of electromagnetic wave countermeasures such as a building such as an ETC toll gate or a gas station, a guard fence for a vehicle such as a guardrail, or a building such as a high-rise building. It can be preferably used. Moreover, since the electromagnetic wave absorbing sheet 1 according to the present invention uses vulcanized rubber for the dielectric layer 3, other rubber-based materials that are not vulcanized, resins, inorganic binders, inorganic / organic hybrid binders, or the like are used. Compared to, it becomes possible to improve the weather resistance and heat resistance. Further, if the protective film 9 is provided, the weather resistance and scratch resistance can be further improved, which can be preferably used when used outdoors.

Examples of the present invention will be described below.
First, the manufacturing process of the electromagnetic wave absorbing sheet 1 of this example will be described.

(Production process of Example 1)
First, EPDM rubber (ethylene propylene terpolymer, Mitsui Chemicals, Inc. EPT # 4021), scaly graphite (Ito graphite W-5), zinc oxide, and stearic acid were kneaded with a Banbury mixer. In addition, the addition amount of scaly graphite was 120 weight part with respect to 100 weight part of EPDM rubber.
Next, a sulfur-based vulcanizing agent (Tochi Alpha Gran S-50EN) and a vulcanization accelerator (Ouchi Shinko Chemical Co., Ltd. Noxeller CZ, Noxeller DM) are added to the resulting mixture. In addition, kneading was performed again. The amount of vulcanizing agent added was 0.25 parts by weight and the amount of vulcanization accelerator added was 1 part by weight with respect to 100 parts by weight of EPDM rubber.
Thereafter, the obtained mixture is processed into a sheet having a thickness of about 1.0 mm by an extruder, heated by a hot press (185 ° C., 0.2 MPa) for 5 minutes, and subjected to a vulcanization reaction treatment. 3 was produced.
On the other hand, the DCF 2 is produced by disposing a pattern of the conductive film 11 made of copper foil on the PI film 12 by any one of vapor deposition, etching, and printing. In DCF2, the length a of one side of the conductive film 11 is 5.0 mm, and the arrangement interval b of the conductive film 11 is 0.4 mm. Then, the PI film 12 (DCF2) on which the conductive film 11 was disposed was bonded to one surface of the dielectric layer 3 with an adhesive tape (first resin layer 5) having a thickness of 300 μm. In addition, an aluminum foil (Toyo Aluminum Co., Ltd. aluminum foil # 80) was bonded to the other surface of the dielectric layer 3 with the same adhesive tape (second resin layer 6). As the pressure-sensitive adhesive tape, an acrylic pressure-sensitive adhesive containing an acrylic polymer mainly composed of (meth) acrylic acid C1-20 alkyl ester is used.
After the lamination, the electromagnetic wave absorbing sheet 1 was prepared by cutting it into a standard length and processing it into a 300 mm × 300 mm sheet.

(Manufacturing process of Examples 2-4)
The electromagnetic wave absorbing sheet 1 was produced by changing the thickness of the adhesive tape (first resin layer 5) that bonds the DCF 2 and the dielectric layer 3 together. In addition, about conditions, such as the thickness of the adhesive tape of each Example, it describes in Table 1 mentioned later.

(Manufacturing process of Comparative Examples 1-5)
The electromagnetic wave absorbing sheet 1 was produced by changing the thickness of the adhesive tape (first resin layer 5) that bonds the DCF 2 and the dielectric layer 3 together. Furthermore, in Comparative Example 2, the thickness of the dielectric layer 3 was changed. In Comparative Example 3, the amount of scale-like graphite added was 140 parts by weight. Furthermore, in Comparative Example 5, an electromagnetic wave absorbing sheet was produced without providing DCF2. In addition, about conditions, such as the thickness of the adhesive tape of each comparative example, it describes in Table 1 mentioned later.

(Evaluation results of examples and comparative examples [dielectric constant measurement])
For the electromagnetic wave absorbing sheets of Examples 1 to 4 and Comparative Examples 1 to 5 obtained in the above-described Examples, a frequency of 4.9 to 7.05 GHz is used using a network analyzer and Kanto Electronics C-band waveguide. The dielectric constant was measured at. Table 1 shows the manufacturing conditions and measurement results of each measurement object. In particular, with respect to Examples 1 to 4 and Comparative Example 1, FIG. 3 is a graph showing the correspondence between the thickness of the adhesive tape (first resin layer 5) for bonding DCF 2 and dielectric layer 3 to the matching frequency. Shown in

  As shown in Table 1 and FIG. 3, when Examples 1 to 4 and Comparative Example 1 are compared, the thickness of the adhesive tape (hereinafter referred to as the first resin layer 5) that bonds the DCF 2 and the dielectric layer 3 to each other is as follows. It can be seen that the thinner the frequency, the lower the matching frequency. However, in Comparative Example 4 in which the thickness of the first resin layer 5 was 3 μm, the DCF 2 and the dielectric layer 3 could not be bonded appropriately, and the measurement result could not be obtained. Therefore, if the thickness of the first resin layer 5 is 5 μm to 300 μm, preferably 5 μm to 100 μm, more preferably 5 μm to 50 μm, the first resin layer 5 has a high absorption amount in a low frequency band (for example, 4.9 to 7.05 GHz). It can be seen that an electromagnetic wave absorbing sheet can be realized. Specifically, it is possible to realize an electromagnetic wave absorbing sheet having a matching frequency with an electromagnetic wave absorption amount of 20 dB or more in a frequency band of 4.9 to 7.05 GHz (more specifically, 6.4 GHz or less). In particular, in Examples 3 and 4 in which the thickness of the first resin layer 5 is 5 μm to 50 μm, it is possible to position the peak frequency at a frequency around 5.8 GHz used for ETC. Moreover, if the 1st resin layer 5 is made thin, it can also be made thin about the thickness of the whole electromagnetic wave absorption sheet | seat, and it also becomes possible to achieve the thin film thickness and weight reduction of an electromagnetic wave absorption sheet | seat.

  Further, in Comparative Example 2, the thickness of the dielectric layer 3 was reduced as compared with Examples 1 to 4 and Comparative Example 1. As a result, even if the thickness of the first resin layer 5 is made thicker than 300 μm, the thickness and weight of the entire electromagnetic wave absorbing sheet can be set to the same level as in Examples 1 to 4. However, by reducing the thickness of the dielectric layer 3, the matching frequency is shifted to the high frequency side. Therefore, the electromagnetic wave absorbing sheet of Comparative Example 2 cannot realize a matching frequency having an electromagnetic wave absorption amount of 20 dB or more in the frequency band of 4.9 to 7.05 GHz (the matching frequency is 7.05 GHz or more).

  In Comparative Example 3, it can be seen that the dielectric constant of the dielectric layer 3 is increased by increasing the density of scaly graphite, which is an electromagnetic wave absorbing material, as compared with Comparative Example 1. And since the matching frequency is also shifted to the low frequency side accordingly, even if the thickness of the first resin layer 5 is made thicker than 300 μm, the matching frequency is lowered to the same level as in Examples 1 to 4 of 300 μm or less. It is possible to shift to a band (eg 6.4 GHz). However, in Comparative Example 3, the density of the scaly graphite is increased, so that the workability is deteriorated, for example, a problem occurs in the sheet appearance and shape. In addition, voids may be generated inside, and electromagnetic wave absorption performance may vary. In addition, it is desirable that the addition amount of the scaly graphite as the electromagnetic wave absorbing material is 130 parts by weight or less with respect to 100 parts by weight of the EPDM rubber.

  Moreover, since the DCF 2 is not provided in the comparative example 5 as compared with the first to fourth embodiments, the effect of increasing the dielectric constant by the DCF 2 cannot be obtained. Therefore, in order to shift the matching frequency to the low frequency band (for example, 5.9 GHz) to the same level as in the first to fourth embodiments where the DCF 2 is provided, it is necessary to increase the thickness of the dielectric layer 3 to 1.65 mm. I understand that. As a result, it is difficult to reduce the weight and thickness of the electromagnetic wave absorbing sheet.

  From the above, in the electromagnetic wave absorbing sheet 1 of Examples 1 to 4 in which the thickness of the first resin layer 5 is 5 μm to 300 μm, preferably 5 μm to 100 μm, more preferably 5 μm to 50 μm, the thickness of the dielectric layer 3 is 1000 μm. 6.4 GHz or less even when the electromagnetic wave absorbing material 1 is less than 130 parts by weight with respect to 100 parts by weight of the matrix (ie, the thickness of the electromagnetic wave absorbing sheet 1 is 1300 μm or less). In this frequency band, it is possible to achieve a reflection attenuation amount (electromagnetic wave absorption amount) having a matching frequency of 20 dB or more, which is a sufficient absorption amount of reflection attenuation amount (electromagnetic wave absorption amount).

As described above, the electromagnetic wave absorbing sheet 1 according to the present embodiment is composed of the DCF 2, the dielectric layer 3, and the electromagnetic wave reflecting layer 4, and is an electromagnetic wave absorber in the frequency band of 4.9 to 7.05 GHz. The thickness of the first resin layer 5 between the dielectric layer 3 and the DCF 2 and joining the opposing surfaces of the dielectric layer 3 and the DCF 2 to each other is set to 5 μm to 300 μm. It is possible to provide the electromagnetic wave absorbing sheet 1 having high electromagnetic wave absorbing performance in a low frequency band while suppressing the content of the electromagnetic wave absorbing material (for example, scaly graphite). For example, even when the electromagnetic wave absorbing sheet 1 is in the form of a thin film having a thickness of about 1.0 to 1.3 mm, a sufficient amount of reflection attenuation (electromagnetic wave absorption) is achieved in the frequency band of 4.9 to 7.05 GHz. It is possible.
Moreover, by suppressing the content of an electromagnetic wave absorbing material (for example, scaly graphite) to be contained in the dielectric layer 3, an electromagnetic wave absorbing sheet 1 that is lightweight, excellent in workability, and has high performance electromagnetic wave absorbing performance without variation is provided. Is possible.
On the other hand, by using the DCF structure, the dielectric constant can be further increased. Further, by increasing the dielectric constant, it is possible to further reduce the thickness and weight of the electromagnetic wave absorbing sheet 1.
The dielectric layer 3 is made of a matrix containing a carbon-based material, and the measured value of the complex dielectric constant measured by the waveguide method satisfies the range where the real part (ε _r ′) is 20 to 120 and is imaginary. Part (ε _r ″) satisfies the range of 2 to 16, and the dielectric loss tangent (Tanδ = ε _r ″ / ε _r ′) satisfies the range of 0.05 to 0.5. By using the DCF structure in the electromagnetic wave absorbing sheet 1 used, sufficient electromagnetic wave absorbing performance can be obtained without increasing the proportion of the carbon-based material. That is, the effective dielectric constant of the dielectric layer 3 can be increased, and the electromagnetic wave absorbing sheet 1 including the DCF 2 and the dielectric layer 3 can be designed to satisfy the non-reflection condition. As a result, the electromagnetic wave entering the electromagnetic wave absorbing sheet 1 can be greatly attenuated.
Further, since the dielectric layer 3 is made of a layer in which scaly graphite is dispersed in the matrix, the effective dielectric constant of the dielectric layer 3 can be increased. As a result, the dielectric layer 3 can be made thinner and lighter.
In addition, since the dielectric layer 3 is composed of vulcanized rubber containing carbon-based material, other rubber-based materials that are not vulcanized, resin, inorganic binder, inorganic / organic hybrid binder, etc. are used for the dielectric layer. In comparison with the above, it is possible to increase the dielectric constant while suppressing the content of the carbon-based material (for example, flaky graphite) contained in the dielectric layer 3. Further, the change in shape of the dielectric layer 3 can be reduced, and the change in absorption performance can be reduced. Therefore, it is possible to provide the electromagnetic wave absorbing sheet 1 that is lightweight, excellent in workability, and has high performance electromagnetic wave absorbing performance without variation. Furthermore, weather resistance and heat resistance can be improved.
Moreover, since the electromagnetic wave absorption amount has a matching frequency (peak frequency) of 20 dB or more in the frequency band of 4.9 to 7.05 GHz, sufficient electromagnetic waves are absorbed when absorbing electromagnetic waves in the frequency band of 4.9 to 7.05 GHz. Absorption performance can be realized.
In addition, by setting the length a of one side of the conductive film 11 which is a parameter of the DCF 2 and the value b of the arrangement interval of the conductive film 11 to appropriate values, the dielectric layer 3 can have sufficient electromagnetic wave absorption characteristics. In addition, the DCF 2 can be made thinner and lighter.
Further, when the real part of the complex relative permittivity of the dielectric layer 3 is compared with the value of the imaginary part satisfying the same non-reflection condition, the value of the imaginary part is lower than the value of the imaginary part satisfying the non-reflection condition. Therefore, the electromagnetic wave absorbing sheet including the DCF 2 and the dielectric layer 3 can be designed so as to satisfy the non-reflection condition. Thereby, it is possible to attenuate the electromagnetic wave that has entered the electromagnetic wave absorbing sheet.

In addition, this invention is not limited to the said Example, Of course, various improvement and deformation | transformation are possible within the range which does not deviate from the summary of this invention.
For example, the mixing conditions, vulcanization conditions, sheet forming conditions, heating conditions, and the like at the time of manufacturing the electromagnetic wave absorbing sheet 1 are not limited to the conditions described in the above examples. For example, the addition amount, heating temperature, heating time, etc. can be appropriately changed.

  In this embodiment, an adhesive such as an adhesive tape is used as the first resin layer 5 that joins the opposing surfaces of the dielectric layer 3 and the DCF 2 to each other, but other resin materials may be used.

  In the present embodiment, scaly graphite is used as the electromagnetic wave absorbing material dispersed in the dielectric layer 3, but other carbon-based materials or magnetic materials such as ferrite may be used.

  In this embodiment, the vulcanized rubber constituting the dielectric layer 3 is a vulcanized EPDM rubber, but other rubber-based materials may be used. Further, the dielectric layer 3 may be composed of a matrix other than vulcanized rubber.

  In this embodiment, dicumyl peroxide (DCP) is used as the organic peroxide-based vulcanizing agent, but other vulcanizing agents may be used.

  In the present embodiment, the conductive film 11 disposed in the DCF 2 has a square shape, but may have another shape (for example, a rectangular shape).

1 Electromagnetic wave absorbing sheet 2 DCF
3 Dielectric layer 4 Electromagnetic wave reflection layer 5 First resin layer 6 Second resin layer 9 Protective film

Claims (8)

A dielectric layer comprising a matrix containing an electromagnetic wave absorbing material;
A split conductive film layer laminated on one surface of the dielectric layer;
An electromagnetic wave reflection layer laminated on the other surface of the dielectric layer;
A resin layer that is between the dielectric layer and the divided conductive film layer and that joins the opposing surfaces of the dielectric layer and the divided conductive film layer to each other;
The resin layer has a thickness of 5 μm to 300 μm,
The dielectric layer has a thickness of 1000 μm or less,
The electromagnetic wave absorbing material contained in the dielectric layer is 130 parts by weight or less with respect to 100 parts by weight of the matrix,
An electromagnetic wave absorber having a peak frequency of 6.4 GHz or less. The divided conductive film layer has a structure in which a plurality of rectangular conductive films are arranged at predetermined intervals,
The size of one side of the conductive film is 2.0 mm to 10.0 mm,
The electromagnetic wave absorber according to claim 1, wherein the conductive films are arranged at intervals of 0.1 mm to 1.5 mm. The dielectric layer is
The complex dielectric constant measured by the waveguide method is
The real part (ε _r ′) satisfies the range of 20 to 120,
The electromagnetic wave absorber according to claim 1, wherein an imaginary part (ε _r ″) satisfies a range of 2 to 16.   The electromagnetic wave absorber according to claim 3, wherein the electromagnetic wave absorbing material is flaky graphite.   The electromagnetic wave absorber according to claim 3 or 4, wherein the dielectric layer is made of a vulcanized rubber containing the electromagnetic wave absorbing material.   The dielectric layer has a complex relative permittivity measured by the waveguide method, and the real part is compared with the value of the imaginary part satisfying the antireflection condition with the same value, compared with the value of the imaginary part satisfying the antireflection condition. The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorber has a low imaginary part value.   The electromagnetic wave absorber according to any one of claims 1 to 6, wherein the electromagnetic wave absorber has a peak frequency of 20 dB or more in a frequency band of 4.9 to 7.05 GHz. The manufacturing method of the electromagnetic wave absorber which manufactures the electromagnetic wave absorber in any one of the said Claim 1 thru | or 7.

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