JP2008124154A - Radio wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a durable radio wave absorber where the surface resistivity of a resistive film is nearly fixed for a long term, and initially satisfactory radio wave absorption performance can be maintained for a long term. <P>SOLUTION: The radio wave absorber A is provided with a resistive film 2 on one side of a dielectric layer 1 and a radio wave reflector 3 on the opposite side of the dielectric layer 1, and gas barrier films 5 and 5 are stacked on both surfaces of the resistive film 2. Thus, the invasion and contact of moisture (open air containing water content) into/with the resistive film 2 can be blocked with the gas barrier films 5 and 5, and an influence of heat or light on the resistive film 2 can be also reduced, so as to keep the surface resistivity of the resistive film 2 nearly constant, prevent the degradation of radio wave absorbing performance due to a change in surface resistivity, and maintain initially satisfactory radio wave absorption performance for a long term. As a result, the durability and reliability can be extensively improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a radio wave absorber that is used to eliminate radio wave interference and malfunction in the ITS field such as an ETC toll gate on a highway, for example, particularly a radio wave absorber that has transparency, and has a good radio wave absorption performance. The present invention relates to a radio wave absorber excellent in durability that can be maintained for a period of time.

  At the ETC tollgate on the expressway, malfunctions due to ETC radio waves have occurred about 0.03%. To eliminate this, radio wave absorbers, especially each other's lanes, can be seen between the lanes of the tollgate. It is desired to install a radio wave absorber having transparency. A transparent PET (polyethylene terephthalate) film in which a resistive thin film is formed by vapor-depositing a metal oxide such as ITO on one side of a dielectric made of transparent acrylic resin, etc., as a transparent radio wave absorber that eliminates such malfunctions Etc., and a radio wave reflector such as a metal wire grating or a metal thin film that transmits light on the opposite surface of the dielectric is known (Patent Document 1).

  This radio wave absorber has good transparency because a metal oxide such as ITO is deposited to form a resistive thin film. However, since the resistive thin film deposited with ITO or the like has poor weather resistance, there is a problem that when the above-described radio wave absorber is used outdoors, the resistive thin film deteriorates within a short period of time and the radio wave absorbing performance is impaired. .

  Therefore, in order to solve the above problem, the present applicant has a transparent dielectric layer between a transparent resistive film containing ultrafine conductive fibers and a radio wave reflector that transmits light, and the outside of the resistive film. A transparent radio wave absorber provided with a transparent protective layer was proposed (Patent Document 2). In this transparent wave absorber, the resistive film containing ultrafine conductive fibers has good transparency comparable to the ITO resistive thin film, and the resistance film substrate containing ultrafine conductive fibers can be freely selected By selecting a base material with good weather resistance, it is possible to improve weather resistance compared to ITO resistive thin film, and to eliminate the concern that it will deteriorate in a short period of time and cause a significant decrease in radio wave absorption performance It is.

However, this transparent radio wave absorber has a problem that it is difficult to maintain good radio wave absorption performance over a long period of time because the electric resistance (surface resistivity) of the resistance film changes. It was also seen in transparent wave absorbers. Therefore, the present inventor has developed a transparent radio wave absorber that has improved durability by sealing the resistance film from the outside air containing moisture, but when used outdoors, it has long-term radio wave absorption performance. It has been found that maintenance is not sufficient. The cause is not clear, but it is presumed that heat and light are greatly influenced in addition to moisture (humidity) in the air.
JP-A-5-335832 JP-A-2005-311330

  The present invention has been made to cope with the above-mentioned problems. The electric resistance (surface resistivity) of the resistance film is substantially constant over a long period of time, and the initial good radio wave absorption performance is maintained over a long period of time. An object of the present invention is to provide a radio wave absorber having excellent durability.

  In order to solve the above problems, the radio wave absorber of the present invention is a radio wave absorber having a resistance film on one side of a dielectric layer and a radio wave reflector on the opposite side of the dielectric layer, A gas barrier film is laminated on both sides of the membrane.

  In the present invention, as in the radio wave absorber of claim 2, the periphery of the composite laminate formed by laminating the gas barrier film on both sides of the resistance film, or the periphery and both sides, or the periphery and one side is bonded to the adhesive. In addition, as in the radio wave absorber according to claim 3, a surface coating layer is provided on one side of the dielectric layer, and the composite laminate is provided between the dielectric layer and the surface coating layer. It is preferable to provide it. In that case, a plurality of composite laminates are provided between the dielectric layer and the surface coating layer as in the radio wave absorber of claim 4, and a plurality of composite laminates are provided as in the radio wave absorber of claim 5. An air layer or other dielectric layer may be formed between the bodies, and an air layer or other dielectric material is provided between the composite laminate and the surface covering layer as in the radio wave absorber according to claim 6. A layer may be formed. Further, as in the radio wave absorber of claim 7, a composite laminate may be provided on the opposite side of the dielectric layer provided on both sides of the radio wave reflector from the radio wave reflector.

In the present invention, as in the radio wave absorber of claim 8, the gas barrier film has a water vapor permeability of 5.0 (g / m ² · day) or less and 5.0 (cc / m ² · day · atm), a single-layer or multi-layer synthetic resin film having an oxygen permeability of less than or equal to, specifically, polyvinyl alcohol, polyethylene terephthalate, ultra-low density polyethylene, such as the radio wave absorber of claim 9. , Polyvinyl chloride, polyvinylidene chloride, fluorine-based resin, polyamide-based resin, ethylene-vinyl alcohol copolymer, polyphenylene sulfide, polyacrylonitrile, alone or in combination of two or more synthetic resins A resin film is preferably used. More preferably, as in the radio wave absorber according to claim 10, at least one surface of the single-layered or multilayered synthetic resin film, or an interface between layers of the multilayered synthetic resin film, silica, aluminum oxide Any one of magnesium oxide or two or more vapor-deposited layers are formed. The water vapor permeability is a value measured according to JIS K 7129, and the oxygen permeability is JIS K 7126.

  Furthermore, in the present invention, as in the radio wave absorber of claim 11, the resistance film is a film containing ultrafine conductive fibers, and the fine conductive fibers are dispersed without agglomeration and are in contact with each other, The surface coating layer is a synthetic resin plate containing an ultraviolet absorber as in the radio wave absorber of claim 12, and the electrode is attached to the resistance film as in the radio wave absorber of claim 13. 14 is sealed with an adhesive, as in the case of the radio wave absorber of 14, or the ethylene vinyl acetate copolymer resin system in which the adhesive has heat resistance at 80 ° C., as in the radio wave absorber of claim 15. It is preferably a polycarbonate ester resin-based hot-melt adhesive sheet, and each constituent member is preferably transparent as in the radio wave absorber of claim 16.

  Here, “without agglomeration” means that there is no agglomerate having an average diameter of 0.5 μm or more when the resistance film is observed with a microscope, and “contact” means that an ultrafine conductive fiber is actually used. It means both the case where it is in contact with the case and the case where the fine conductive fiber is approaching with a small gap that allows conduction. Further, the transparency means that the haze as an optical characteristic is 10% or less.

  When the gas barrier film is disposed on both sides of the resistance film as in the radio wave absorber of the present invention, the gas barrier film has low water vapor permeability and oxygen permeability, and therefore moisture (outside air containing moisture) with respect to the resistance film. Is substantially cut off, and the influence of heat and light is reduced, so that the surface resistivity of the resistive film is kept substantially constant. Therefore, the deterioration of the radio wave absorption performance due to the change (increase / decrease) in the surface resistivity is prevented, and the initial good radio wave absorption performance can be maintained over a long period of time, so that the durability and reliability are greatly improved.

  In the radio wave absorber according to claim 2, since the resistance film is hermetically sealed by the gas barrier film on both sides of the resistance film and the adhesive that seals the periphery of the resistance film, contact between the resistance film and moisture is blocked. In addition, the influence of heat and light is reduced, and the surface resistivity of the resistance film is kept substantially constant.

  In the radio wave absorber of claim 3, the composite laminate is covered and protected by the surface coating layer, and the resistance film of the composite laminate is double-sealed by the surface coating layer. It becomes stronger and the influence of heat and light is further reduced.

  The radio wave absorber according to claim 4 has a disadvantage in the resistance film of one composite laminate during long-term use, and even when the surface resistivity deviates from a predetermined range and the radio wave absorption function is not exhibited, The surface resistivity can be maintained within a predetermined range by the resistance film of another composite laminate, and the radio wave absorption performance can be exhibited over a long period of time. Moreover, the frequency band in which the radio wave absorption performance (return loss) is expressed can be widened by the resistive films of the plurality of composite laminates.

  The radio wave absorber according to claim 5 or the radio wave absorber according to claim 6 includes an air layer or another dielectric layer between the composite laminate, an air layer between the composite laminate and the surface coating layer, or other The thickness of the whole wave absorber can be increased and adjusted by the dielectric layer. The radio wave absorber according to claim 7 can reflect the radio wave propagating from both sides by the central radio wave reflector and absorb it by the resistance film of each composite laminate, and can share the radio wave reflector. Therefore, an inexpensive radio wave absorber can be obtained.

In the radio wave absorber according to claim 8, the water vapor permeability and the oxygen permeability of the gas barrier film are 5.0 (g / m ² · day) or less and 5.0 (cc / m ² · day · atm) or less, respectively. Therefore, it is sufficient to block moisture (outside air containing water) against the resistance film. Specific examples of such a gas barrier film include polyvinyl alcohol and polyethylene used in the radio wave absorber according to claim 9. Single terephthalate, ultra-low density polyethylene, polyvinyl chloride, polyvinylidene chloride, fluorine resin, polyamide resin, ethylene-vinyl alcohol copolymer, polyphenylene sulfide, polyacrylonitrile, or a single resin composed of two or more synthetic resins It is a synthetic resin film of a layer or a multilayer. In particular, as in the radio wave absorber according to claim 10, at least one surface of the single-layer or multi-layer synthetic resin film or an interface between layers of the multi-layer synthetic resin film is made of silica, aluminum oxide, or magnesium oxide. When either one or two or more kinds of vapor deposition layers are formed, these vapor deposition layers such as silica have a strong effect of blocking the influence of moisture, heat, and light on the resistance film, so that the water vapor permeability and oxygen permeability And the contact of moisture with the resistive film is almost completely cut off, the influence of heat and light is almost eliminated, the surface resistivity of the resistive film is kept almost constant, and the initial good condition over a long period of time Radio wave absorption performance is maintained. The multi-layer synthetic resin film has an advantage that the blocking action of moisture and the like is improved and the handling is easy as the thickness is increased as compared with the single-layer synthetic resin film.

  In the radio wave absorber according to claim 11, since the ultrafine conductive fibers contained in the resistance film are extremely thin and are dispersed and in contact with each other without agglomeration, the resistance film has good transparency and is in contact and conduction. The number of contributing ultrafine conductive fibers is relatively large and the contact frequency is high. Therefore, it is possible to secure a predetermined surface resistivity even if the content of the ultrafine conductive fiber is reduced, and the transparency of the resistance film can be further improved by the amount that the ultrafine conductive fiber can be reduced.

  When the radio wave absorber according to claim 12 is used outdoors, the resistance coating, the dielectric layer, and the radio wave reflector are protected from ultraviolet rays or the like by the surface coating layer made of a synthetic resin plate containing an ultraviolet absorber. The weather resistance is improved, and the surface coating layer made of a synthetic resin plate is strong, so that damage to the composite laminate or dielectric layer due to flying objects can be prevented.

  The radio wave absorber according to claim 13 monitors the change in the surface resistivity of the resistive film by applying a tester's needle to the electrode attached to the resistive film, and measures the surface resistivity of the resistive film as needed, thereby absorbing the radio wave. Can be analogized.

  In the radio wave absorber according to claim 14, since the four circumferential side surfaces are sealed with an adhesive, it is possible to reliably prevent the intrusion of moisture, and the radio wave absorber according to claim 15 has an adhesive of 80 ° C. Since it is a hot-melt adhesive sheet of a specific resin having heat resistance, even if it is heated outdoors in direct sunlight, the adhesive does not soften and the sealing performance does not deteriorate. The radio wave absorber according to claim 16 can be seen from the other side of the radio wave absorber, and the surrounding area can be brightened. For example, the radio wave absorber is installed between lanes of the ETC toll booth to prevent ETC malfunction. It is suitable as a body.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of a radio wave absorber according to an embodiment of the present invention, FIGS. 7A, 7B, and 7C are schematic cross-sectional views showing a resistance film of the radio wave absorber, and FIG. It is a schematic diagram which shows the dispersion state which looked at the carbon nanotube from the front.

  The radio wave absorber A includes a translucent resistance film 2 on one side (front surface side: radio wave incident surface side) of the translucent dielectric layer 1, and on the opposite surface side (rear surface side) of the dielectric layer 1. A transparent (light transmissive) radio wave reflector 3 is provided, and transparent gas barrier films 5 and 5 having low water vapor permeability and oxygen permeability are laminated on both surfaces of the resistance film 2. Yes. The composite laminate of the resistance film 2 and the gas barrier films 5 and 5 is disposed between the dielectric layer 1 and the transparent surface coating layer 4 on one side thereof, and the transparent adhesive 6 is applied. The dielectric layer 1, the composite laminate, and the surface coating layer 4 are bonded together, and the periphery of the composite laminate is sealed with the adhesive 6. The radio wave reflector 3 and the transparent back surface coating layer 7 are overlapped on the opposite surface side (back surface side) of the dielectric layer 1 and integrated with an adhesive or the like.

  The composite laminate does not have to be adhered to the dielectric layer 1 and the surface coating layer 7 via the adhesive 6 as in the above-described radio wave absorber A, but at least the dielectric layer 1 and the surface coating layer. It is sufficient to seal the periphery of the composite laminate by adhering the outer periphery of the composite laminate 7 with the adhesive 6. Further, the radio wave reflector 3 and the back surface coating layer 7 may be simply overlapped on the back surface side of the dielectric layer 1, but the dielectric layer 1, the radio wave reflector 3, and the back surface coating layer 7 like the above-described radio wave absorber A. Is preferably integrated with an adhesive or the like because the handling property is improved.

  In this radio wave absorber A, both surfaces of the resistance film 2 are covered in triplicate by the gas barrier film 5 having a low water vapor permeability and oxygen permeability, the adhesive 6, and the dielectric layer 1 or the surface coating layer 4. In addition, since the periphery of the composite laminate of the resistance film 2 and the gas barrier film 5 is sealed with an adhesive 6 and sealed, moisture (outside air containing moisture) enters and contacts the resistance film 2. At the same time, the influence of heat and light on the resistance film 2 is reduced, and the surface resistivity of the resistance film 2 is kept substantially constant within a predetermined range (within a range of 280 to 400 Ω / □ described later). Therefore, the deterioration of the radio wave absorption performance due to the change (increase / decrease) in the surface resistivity is prevented, and the initial good radio wave absorption performance can be maintained over a long period of time, so that the durability and reliability are greatly improved. Of the constituent members, the dielectric layer 1, the resistance film 2, the surface coating layer 4, the gas barrier film 5, and the back surface coating layer 7 are all transparent, and the radio wave reflector 3 is also transparent or light transmissive. Therefore, the radio wave absorber A made of these components has transparency.

  The dielectric layer 1 is made of a synthetic resin or glass having a high dielectric constant, and the thickness of the dielectric layer 1 is within a range of 0.5 to 15 mm in consideration of use and practical strength. Λ / 4 wave absorber theory (λ: wavelength of radio wave in the dielectric layer 1). In view of the secondary bending workability, it is desirable to form the dielectric layer 1 with a thermoplastic synthetic resin rather than glass, and further considering the heat resistance and transparency when used outdoors, the melting point and light transmittance. It is desirable to form the dielectric layer 1 with an acrylic resin (such as methyl methacrylate), an olefin resin (polyethylene, polypropylene, cycloolefin polymer, etc.), a polyester resin (polycarbonate, polyethylene terephthalate, etc.) or the like that is high. Among these, polycarbonate resin has excellent mechanical strength, total light transmittance is 85% or more (thickness 3 mm), and haze is 1.0% or less. The dielectric layer 1 of a transparent wave absorber is particularly preferably used. Polycarbonate is somewhat inferior in weather resistance to methyl methacrylate resin, but it is sufficient for practical use by adding an ultraviolet absorber or using a resin plate having excellent weather resistance described later as the surface coating layer 4. Good weather resistance.

  The resistive film 2 has transparency with a surface resistivity with a target value of 376.7Ω / □ that matches the radio wave characteristic impedance in free space so as to be suitable for radio wave absorption in the frequency band 1 to 18 GHz, preferably Surface resistivity of 280 to 400Ω / □, which is a transparent thin film, specifically considering the thickness of the surface coating layer 4 and the dielectric layer 1 and the oblique incidence characteristic (15 ° incidence) of radio wave absorption performance 1 is preferably used, such as a vapor-deposited film of metal oxide such as ITO or a thin film having the same surface resistivity containing ultrafine conductive fibers. In the radio wave absorber A shown in FIG. A resistive film 2 containing fibers is employed.

The resistance film 2 including the ultrafine conductive fiber is a thin film formed by applying a coating liquid in which the ultrafine conductive fiber is dispersed to one side of any one of the gas barrier films 5, and the content of the ultrafine conductive fiber is The surface resistivity of 280 to 400Ω / □ is obtained by adjusting various conditions such as coating thickness and dispersion state. In this embodiment, carbon nanotubes are used as the ultrafine conductive fibers, and the carbon nanotube content in the coating solution is such that the basis weight of the carbon nanotubes is 15 to 450 mg / m ² , preferably 15 to 250 mg / m ^2. The resistance film 2 having a surface resistivity of 280 to 400Ω / □ is formed by adjusting the thickness of the coating film and applying it. In such a resistance film 2, the surface resistivity of the resistance film 2 is substantially determined in accordance with the basis weight (content and concentration) of the carbon nanotubes, and variations in the surface resistivity are less likely to occur. The weight per unit area is determined by observing the resistive film 2 with an electron microscope, measuring the area ratio of the carbon nanotubes in the planar area, and measuring the thickness and specific gravity of the carbon nanotubes (document values of graphite) The value calculated by multiplying the average value 2.2 of 2.1 to 2.3).

  The resistance film 2 is formed by applying a coating liquid on one side of one gas barrier film 5 as described above. For example, when the gas barrier film 5 is thick and close to a sheet or plate, It may be formed by such a method. One method is to apply the above coating solution to a release film to form a resistance film, and if necessary, form an adhesive layer thereon to form a transfer film. This transfer film is used as one gas barrier film. 5 is a method in which the resistance film or the resistance film and the adhesive layer are transferred by pressure-bonding to one side, and the other method is to apply the above-mentioned coating on one side of a thermoplastic resin film of the same type or compatibility with the gas barrier film 5. This is a method in which a liquid is applied to form the resistance film 2, and this resistance film-forming film is thermocompression bonded to one side of one gas barrier film 5.

  As the ultrafine conductive fiber, the above-mentioned carbon nanotube is most preferably used, but other fibers can be used without limitation as long as the surface resistivity of the resistance film 2 can be 280 to 400Ω / □. It is. For example, carbon nanotubes such as carbon nanohorns, carbon nanowires, carbon nanofibers, and graphite fibrils, metal nanotubes such as platinum, gold, silver, nickel, and silicon, ultrafine metal fibers such as nanowires, and metals such as zinc oxide An ultrafine metal oxide fiber such as an oxide nanotube or nanowire having a diameter of 0.3 to 100 nm and a length of 0.1 to 20 μm, preferably 0.1 to 10 μm is used.

  The carbon nanotubes of the resistance film 2 are dispersed without contacting each other and are in contact with each other. Specifically, the carbon nanotubes are separated one by one, or multiple bundles are bundled one by one. They are dispersed and in contact with each other. If the resistance film 2 is made of carbon nanotubes and a binder, as shown in FIG. 7A, the carbon nanotubes 2a are dispersed inside the binder 2b in a three-dimensional structure in the above dispersion state. 7B, a part of the carbon nanotube 2a enters the binder 2b and the other part protrudes or is exposed from the surface of the binder 2b, as shown in FIG. 7B. Are dispersed in contact with each other, or some of the carbon nanotubes 2a are inside the binder 2b as shown in FIG. 7A, and the other carbon nanotubes 2a are binders as shown in FIG. 7B. It protrudes or is exposed from the surface of 2b to form a three-dimensional structure in the dispersed state and to be dispersed and in contact with each other. Further, when the resistance film 2 does not contain a binder, as shown in FIG. 7C, the carbon nanotubes are dispersed in the above-described dispersion state, and are in contact with each other to form a three-dimensional layer of carbon nanotubes. Yes. As the binder, a transparent synthetic resin is preferable for obtaining the transparent resistive film 2.

  FIG. 8 schematically shows the dispersion state of the carbon nanotubes 2a as viewed from the front. As can be understood from FIG. 8, the carbon nanotubes 2a are slightly bent, but each one or 1 The bundles are separated and dispersed in the inside or the surface of the resistive film 2 in a simply intersected state without being intricately entangled with each other, that is, without agglomeration, and are in contact with each other at the intersections. The carbon nanotubes 2a do not need to be separated and dispersed completely one by one or one bundle, and may have a small aggregate that is intertwined with a part of the carbon nanotube 2a. “None” means that there is no agglomerate having an average value of the major axis and the minor axis of 0.5 μm or more, and therefore the average diameter of the agglomerates that are present needs to be less than 0.5 μm.

  In this way, when the carbon nanotubes 2a, which are ultrafine conductive fibers, are slightly bent in the resistance film 2 and separated one by one or one bundle, the three-dimensional structure is dispersed without being intertwined in a complicated manner. Even if the resistance film 2 is bent, the carbon nanotubes 2a only extend or shift, so that the mutual contact is maintained. Therefore, even if this radio wave absorber A is bent, there is almost no increase in surface resistivity, and radio wave absorption performance can be maintained. Therefore, a curved radio wave absorber can be produced, and it can be bent and used at the construction site. it can.

  Since the carbon nanotube 2a has an extremely thin diameter of 0.3 to 80 nm, the resistive film 2 containing the carbon nanotube 2a in an amount corresponding to the above weight per unit area has good transparency. When the nanotubes 2a are dispersed, the number of carbon nanotubes 2a that contribute to contact and conduction without aggregation is relatively increased, and the frequency of contact between the tubes is increased. Therefore, the basis weight of the carbon nanotubes 2a is reduced accordingly. Even so, the surface resistivity (280 to 400Ω / □) can be secured, and the transparency can be further improved by the amount of the carbon nanotubes 2a. Incidentally, the light transmittance (transmittance of light at 550 nm by a spectrophotometer) of the resistive film 2 having a surface resistivity of 280 to 400 Ω / □ containing carbon nanotubes in an amount corresponding to the weight per unit area is 87%. If a radio wave absorber is prepared by selecting the dielectric layer 1 having good transparency and the radio wave reflector 3 having a large amount of light transmission, the total light transmittance is 40% or more and the haze is 10% or less. Thus, it is possible to reliably obtain a radio wave absorber having transparency. A more preferred wave absorber has a total light transmittance of 50% or more and a haze of 10% or less.

  Examples of the carbon nanotube 2a include multi-walled carbon nanotubes having a plurality of carbon walls concentrically around the central axis, and single-walled carbon nanotubes having a single carbon wall around the central axis. The former multi-walled carbon nanotube includes a multi-walled carbon wall having a plurality of cylindrical carbon walls with different diameters around a central axis, and a multi-walled carbon nanotube formed in a spiral shape. Among them, preferable multi-walled carbon nanotubes are those having 2 to 30 layers, more preferably 2 to 15 layers. When such multi-walled carbon nanotubes are dispersed in the dispersed state, the resistance film 2 having a good light transmittance is formed as described above. Most of the multi-walled carbon nanotubes are dispersed in a state of being separated one by one, but the two- or three-layer carbon nanotubes may be dispersed in a bundle.

  On the other hand, the latter single-walled carbon nanotube is a single-walled tube in which the carbon wall is closed in a cylindrical shape around the central axis as described above. Such single-walled carbon nanotubes usually exist in a state where two or more bundles are bundled, the bundles are separated one by one, and the bundles are simply crossed without agglomerating without complicated entanglement. It is dispersed inside or on the surface of the resistive film 2 and is in contact at each intersection. Preferably, a bundle of 10 to 50 single-walled carbon nanotubes is used. Note that the present invention naturally includes a case where the particles are dispersed one by one.

  In order to enhance the dispersibility of the carbon nanotubes, it is desirable to include a dispersant in the resistance film 2. As the dispersant, a polymer dispersant such as an alkyl ammonium salt solution of an acidic polymer, a tertiary amine-modified acrylic copolymer, a polyoxyethylene-polyoxypropylene copolymer, a coupling agent, or the like is preferably used.

  The resistance film 2 may be a thin film made of only carbon nanotubes without a binder, but it is preferable to use a binder for preventing the carbon nanotubes from dropping off, stabilizing the surface resistivity, transparency, and the like. As this binder, thermoplastic resins such as transparent resins such as polyvinyl chloride, polymethyl methacrylate, nitrocellulose, chlorinated polyethylene, chlorinated polypropylene, and vinylidene fluoride are used, and heat and ultraviolet rays are used. Also, a transparent resin such as a curable resin that is cured by electron beam or radiation, such as a silicone resin such as melamine acrylate, urethane acrylate, epoxy resin, polyimide resin, or acrylic-modified silicate is used. Note that a translucent resin may be used as the binder, and even if such a resin is used, the resistive film 2 having transparency can be obtained by making the resistive film 2 thin. In addition, an inorganic material such as colloidal silica may be added to the binder, and in this case, the resistance film 2 having excellent surface hardness and wear resistance is formed.

The gas barrier film 5 laminated on both surfaces of the resistance film 2 has a water vapor permeability of 5.0 (g / m ² · day) or less and an oxygen transmission rate of 5.0 (cc / m ² · day · atm) or less. A single-layer or multi-layer synthetic resin film having a degree is used. A synthetic resin film having water vapor permeability and oxygen permeability larger than the above ranges has insufficient action to block moisture (outside air containing moisture) from entering and contacting the resistance film 2, and the surface resistance of the resistance film 2. Since the rate cannot be kept almost constant, it cannot be used.

  Specific examples of the gas barrier film 5 include polyvinyl alcohol, polyethylene terephthalate, ultra-low density polyethylene (metathelon-catalyzed low molecular weight polyethylene film), polyvinyl chloride, polyvinylidene chloride, fluorine-based resin (polyvinylidene fluoride, polytetrafluoroethylene, etc.) ), Polyamide resin (polyamide 6, polyamide 66, polyamide 12, polyamide MXD6), ethylene-vinyl alcohol copolymer, polyphenylene sulfide, polyacrylonitrile, alone or in combination of two or more synthetic resins Can be mentioned. Among them, any one of polyvinyl alcohol, polyethylene terephthalate, and ultra-low density polyethylene, or a single-layer or multi-layer synthetic resin film made of two or more synthetic resins, for example, a single-layer film of polyvinyl alcohol, a single-layer film of polyethylene terephthalate A multilayer film in which a polyethylene terephthalate film or ultra-low density polyethylene film is laminated with a transparent adhesive on one or both sides of a polyvinyl alcohol film, and an ultra-low density polyethylene film is laminated on one or both sides of a polyethylene terephthalate film with a transparent adhesive The multilayer film is preferably used because it has good gas barrier properties. Particularly, the multilayer film is much more preferable because it is thicker than the single layer film, has excellent gas barrier properties, and is easy to handle. It is use. These gas barrier films vary in gas barrier performance depending on their thickness. Generally, the thinner the thickness, the lower the water vapor transmission rate and oxygen transmission rate. Need to use one.

As shown to (a) of FIG. 9, it is preferable to form any one of silica, aluminum oxide, and magnesium oxide, or two or more vapor-deposited layers 5a on at least one surface of the single-layer gas barrier film 5. Similarly, it is also preferable to form a vapor deposition layer such as silica as described above on at least one side of a multilayer gas barrier film. Further, as shown in FIG. 9 (b), the above-mentioned silica or the like is formed at the interface between the layers of the multi-layer (two layers) gas barrier film 5 in which the other synthetic resin film 52 is laminated on one surface of the synthetic resin film 51. One side of the gas barrier film 5 of a multilayer (three layers) in which the vapor deposition layer 5a is formed or other synthetic resin films 52, 52 are laminated on both surfaces of the synthetic resin film 51 as shown in FIG. It is also preferable to form the vapor deposition layer 5a such as silica described above at the interface between the two layers. Since the vapor deposition layer 5a such as silica has an action of blocking the influence of heat and light in addition to the moisture blocking action, such a vapor deposition layer 5a of silica or the like is used as at least one surface or an interlayer of the gas barrier film 5. When the film is formed at the interface, the invasion of moisture (outside air containing moisture) into the resistance film 2, the action of blocking contact, and the action of blocking the influence of heat and light on the resistance film 2 are greatly improved. The surface resistivity of 2 can be kept substantially constant, and the deterioration of the radio wave absorption performance can be prevented more reliably. Incidentally, when a vapor deposition layer 5a such as silica is formed on a 12 μm thick polyvinyl alcohol film, the water vapor permeability is 0.1 (g / m ² · day) and the oxygen permeability is 0.1 (cc / m ^2). · Day · atm), the water vapor permeability and the oxygen permeability are reduced to about 1/50 compared with the case of the polyvinyl alcohol film alone, and the gas barrier performance is remarkably improved.

  A composite laminate in which the gas barrier film 5 as described above is laminated on both surfaces of the resistance film 2 is formed to be slightly smaller than the dielectric layer 1 and the surface coating layer 4. The dielectric layer 1, the composite laminate, and the surface coating layer 4 are bonded and integrated via the adhesive 6, and the periphery of the composite laminate is sealed with the adhesive 6 and sealed. Yes. In this composite laminate, the resistance film 2 is formed on one surface of one gas barrier film 5 by applying the coating liquid in which the above-mentioned ultrafine conductive fibers are dispersed, and the other gas barrier property is covered so as to cover the resistance film 2. After the films 5 are stacked, the film 5 is cut to a predetermined size. When the vapor-deposited layer 5a such as silica is formed on one side of the gas barrier film 5, one of the gas barrier films 5 is formed. The resistance film 2 is formed on one side where the vapor deposition layer 5a of silica or the like is not formed, and the other gas barrier film 5 is laminated thereon so that the vapor deposition layer 5a of silica or the like is on the surface coating layer 4 side. It is preferable to produce a laminate in order to improve the shielding performance against moisture, heat, light, and the like.

  The radio wave reflector 3 provided on the back side of the dielectric layer 1 is made of a conductive material having transparency or transparency, and is, for example, a conductive mesh material or a metal mesh material having eyes of about 4 to 250 mesh. Alternatively, a metal wire mesh, a metal lattice, a punching metal having a large aperture ratio, or a transparent film formed with a transparent or transparent conductive film having a surface resistivity of 10Ω / □ or less is preferably used.

  The surface coating layer 4 covering the resistance film 2 is a layer made of synthetic resin, glass, or the like having the same transparency as the dielectric layer 1, and the surface coating layer 4 forms moisture (including moisture) on the resistance film 2. It is provided for the purpose of shielding from the outside air) and for the purpose of protecting the composite laminate or dielectric layer 1 in which the gas barrier film 5 is laminated on both sides of the resistance film 2 from ultraviolet deterioration due to direct sunlight, When the surface coating layer 4 is made of a synthetic resin plate, it is possible to prevent damage due to collision of flying objects. Therefore, the thickness of the surface coating layer 4 has an acrylic resin plate having excellent transparency with excellent weather resistance of about 1 to 4 mm, and transparency having improved weather resistance by containing an ultraviolet absorber. Synthetic resin plates such as polyester and olefin having the same thickness are preferably used. In particular, a polycarbonate resin plate containing an ultraviolet absorber is very preferable as the surface coating layer 4 because of its excellent mechanical strength and good weather resistance and transparency.

  Further, the back surface coating layer 7 covering the radio wave reflector 3 is provided for the purpose of protecting the radio wave reflector 3 and the dielectric layer 1 from damage caused by flying object collisions and ultraviolet deterioration due to direct sunlight. Resin plate similar to the layer 4, that is, an acrylic resin plate having a thickness of about 1 to 4 mm with excellent weather resistance and high transparency, and has transparency with increased weather resistance by containing an ultraviolet absorber. A synthetic resin plate such as polyester or olefin having the same thickness, in particular, a polycarbonate resin plate containing an ultraviolet absorber is preferably used.

  The adhesive 6 bonds and integrates the dielectric layer 1, the composite laminate, and the surface coating layer 4, and seals the periphery of the composite laminate to prevent moisture from entering and contacting the resistance film 2. For example, hot-melt adhesive sheets such as polyurethane, ethylene-vinyl acetate copolymer, ethylene monocarboxylic acid vinyl ester copolymer, ethylene-acrylic acid vinyl ester copolymer, polycarbonate ester, etc. Curable adhesives (sealing agents) such as silicone, epoxy, acrylic, organopolysiloxane, carbamate, vinyl, hydrolyzable silyl group, silylated urethane, polyoxyalkylene polymer ) Or an adhesive such as a synthetic resin coating solution in which a resin is dissolved in a solvent. Among these, an ethylene-vinyl acetate copolymer resin system and a polycarbonate ester resin system suitable for outdoor use which are softened and melted under relatively mild heating conditions to exhibit excellent adhesiveness and have heat resistance at 80 ° C. The hot-melt type adhesive sheet is particularly preferably used, and a silicone-based adhesive exhibiting excellent adhesive performance with tackiness or adhesiveness in a temperature range from room temperature to less than 100 ° C. is particularly preferably used.

  When the above hot melt adhesive sheet is sandwiched between the dielectric layer 1 and the composite laminate and between the composite laminate and the surface coating layer 4 and bonded and integrated by hot pressing, the softened and melted hot There is an advantage that the outer periphery of the melt-type adhesive sheet goes around the composite laminate, and the periphery of the composite laminate is naturally sealed, and the dielectric layer 1, the composite laminate, and the surface coating layer 4 Since light scattering at each bonding interface is reduced, the radio wave absorber A having excellent transparency can be obtained.

  The adhesive 6 is colorless and transparent. For example, when the outer periphery of the dielectric layer 1 and the surface coating layer 4 is bonded to seal the periphery of the composite laminate, it will be described later. As described above, when the four circumferential side surfaces of the radio wave absorber are adhesively sealed with an adhesive, an opaque adhesive may be used.

  The radio wave absorber A as described above can be manufactured, for example, by the following method. First, a coating liquid is prepared by sufficiently mixing ultrafine conductive fibers such as carbon nanotubes, a solvent, the binder as necessary, and the dispersant as necessary. Then, this coating liquid is applied to one side of the gas barrier film 5 to form a resistance film 2 having a surface resistivity of 280 to 400Ω / □, and another gas barrier property is formed so as to cover the resistance film 2. The film 5 is laminated and cut to produce a composite laminate that is slightly smaller than the dielectric layer 1 and the surface coating layer 4.

  Next, on one side of the dielectric layer 1 made of the synthetic resin plate or the like, the adhesive 6 (hot melt type adhesive sheet), the above composite laminate, the adhesive 6 (hot melt type adhesive sheet), and the above The surface coating layer 4 made of a synthetic resin plate is stacked, and the radio wave reflector 3, the hot melt adhesive sheet, and the back surface coating layer 7 made of the synthetic resin plate are stacked on the opposite surface of the dielectric layer 1. The laminate is heated while sandwiching it between the upper and lower gloss plates to soften and melt the hot melt adhesive sheet. At the same time, the adhesive is wrapped around the composite laminate and the periphery of the composite laminate is adhered. Then, the electromagnetic wave absorber A is manufactured by sealing. In addition, the laminate can be produced in the same manner by degassing the laminate, sandwiching it between upper and lower glass substrates, vacuum degassing, and thermocompression bonding. The radio wave absorber A obtained in this way can provide good transparency (visibility) with a total light transmittance of 40% or more and a haze of 10% or less.

  In addition, when the radio wave absorber A that does not have translucency but has translucency is desired, for example, a light diffusing agent or a filler is added in advance as the dielectric layer 1, the surface coating layer 4, or the back surface coating layer 7. What is necessary is just to make a haze high by using a thing or forming a fine unevenness | corrugation in the outer surface of the surface coating layer 4 or the back surface coating layer 7. FIG. When the opaque wave absorber A is desired, it is made opaque by adding a colorant such as a pigment to the synthetic resin or glass to be the dielectric layer 1, the surface coating layer 4, and the back surface coating layer 7, or A metal plate or the like that does not transmit light may be used for the radio wave reflector 3, or carbon may be added to the resistance film 2 to make it opaque.

  The radio wave absorber A as described above has a low water vapor permeability and oxygen permeability of the gas barrier films 5 and 5 on both surfaces of the resistance film 2 and is excellent in blocking moisture (outside air containing moisture). When the vapor-deposited layer 5a such as silica is formed on one side of the gas barrier film 5 or the interface between the layers, the effect of blocking the influence of heat and light on the resistance film 2 is excellent. The resistance film 2 is covered in triplicate by the gas barrier films 5 and 5, the adhesive 6, and the dielectric layer 1 or the surface coating layer 4 excellent in such blocking performance. Since the periphery of the composite laminate with the gas barrier film 5 is sealed with an adhesive 6 and sealed, moisture intrusion and contact with the resistance film 2 are blocked, and heat and light from the resistance film 2 are blocked. The influence is also cut off, and the surface resistivity of the resistance film 2 is kept almost constant within the range of 280 to 400Ω / □. Therefore, the radio wave absorber A is prevented from being deteriorated in radio wave absorption performance due to a change (increase / decrease) in surface resistivity and can maintain good initial radio wave absorption performance over a long period of time. The characteristics are greatly improved. Further, even when used outdoors, the front surface coating layer 4 and the back surface coating layer 7 can protect the resistance film 2, the dielectric layer 1, and the radio wave reflector 3 from ultraviolet deterioration, and prevent damage caused by flying objects. In addition, durability and reliability are further improved. In addition, as described above, this wave absorber A has a good transparency (visibility) with a total light transmittance of 40% or more and a haze of 10% or less, for example, installed between lanes of an ETC toll gate. Therefore, it can be suitably used as a radio wave absorber that prevents ETC malfunction.

  FIG. 2 is a cross-sectional view of a radio wave absorber according to another embodiment of the present invention.

  The radio wave absorber B includes a composite laminate (composite laminate in which gas barrier films 5 and 5 are laminated on both surfaces of the resistance film 2) provided between the dielectric layer 1 and the surface coating layer 4, and the dielectric layer 1 and The above-described radio wave absorber A shown in FIG. 1 is the same as the surface covering layer 4 in that it has the same shape and size, and the entire four side surfaces of the radio wave absorber are adhesively sealed with an adhesive 60. Is different. In this radio wave absorber B, the entire four side surfaces are bonded and sealed with the adhesive 60, so that the surface coating layer 4, the composite laminate, the dielectric layer 1, the radio wave reflector 3, and the back surface coating layer 7 have the same shape and size. As a result, the entire side surface is made flat.

  As the adhesive 60 that covers the entire side surface of the radio wave absorber B, the above-described hot melt adhesive sheet, curable adhesive (sealing agent), resin coating liquid, and the like are used. A curable adhesive (sealing agent) or resin coating solution that can be easily applied to the entire side surface is preferably used.

  The other components of the radio wave absorber B, such as the dielectric layer 1, the resistance film 2, the radio wave reflector 3, the surface coating layer 4, the gas barrier film 5, the adhesive 6 and the back surface coating layer 7 are the same as those described above. Since it is the same as the absorber A, description is abbreviate | omitted.

  The radio wave absorber B having such transparency has a composite laminate in which gas barrier films 5 and 5 are laminated on both surfaces of the dielectric layer 1 and the resistance film 2 when the radio wave absorber A is manufactured. The reflector 3, the front surface coating layer 4, the back surface coating layer 7, and the adhesive 6 (hot melt type adhesive sheet) are laminated so as to have the same shape and size, and thermocompression integrated to form the main body of the radio wave absorber B. After the portion is manufactured, the curable adhesive 60 (sealing agent) or the like is applied and cured on the entire four-side surface, and the entire side surface is adhesively sealed.

  In such a wave absorber B, both surfaces of the resistance film 2 are covered in triplicate by the gas barrier film 5 having a low water vapor transmission rate and low oxygen transmission rate, the adhesive 6 and the dielectric layer 1 or the surface coating layer 4. In addition, since the periphery of the composite laminate is sealed with the adhesive 60 and sealed, moisture intrusion into the resistance film 2 and the influence of heat and light are blocked, and the surface resistivity of the resistance film 2 is almost equal. Kept constant. The adhesive 6 causes the interfaces of the dielectric layer 1, the composite laminate, and the surface coating layer 4 to be in close contact with each other, thereby reducing light scattering, thereby improving transparency and light transmittance. Since 3 and the back surface coating layer 7 are bonded and integrated by the side surface adhesive 60, it is not necessary to bond them with a hot-melt adhesive sheet or the like, and the manufacturing is facilitated.

  FIG. 3 is a cross-sectional view of a radio wave absorber according to still another embodiment of the present invention.

  In this radio wave absorber C, a front surface coating layer and a back surface coating layer are omitted, and a composite laminated body (composite laminated body in which gas barrier films 5 and 5 are laminated on both surfaces of the resistance film 2) that is slightly smaller than the dielectric layer 1. The dielectric layer 1 is provided on one surface (front surface), the radio wave reflector 3 is provided on the opposite surface of the dielectric layer 1, and the surface and periphery of the composite laminate are covered and sealed with an adhesive 6.

  Since the other components of the radio wave absorber C, the dielectric layer 1, the resistance film 2, the radio wave reflector 3, the gas barrier film 5, and the adhesive 6 are the same as those of the radio wave absorber A, description thereof is omitted. To do.

  In such a radio wave absorber C, both surfaces of the resistance film 2 are double-covered by the gas barrier film 5 having a low water vapor transmission rate and low oxygen transmission rate, and the adhesive 6 or the dielectric layer 1, and a composite laminate Since the periphery of the body is sealed with the adhesive 60 and sealed, moisture intrusion into the resistance film 2 and the influence of heat and light are blocked, and the surface resistivity of the resistance film 2 is kept almost constant. . And there is also an advantage that transparency and light transmittance are improved as much as the surface coating layer and the back surface coating layer are omitted.

  FIG. 4 is a cross-sectional view of a radio wave absorber according to still another embodiment of the present invention.

  This radio wave absorber D is formed by forming an air layer 8 between a composite laminate (composite laminate in which gas barrier films 5 and 5 are laminated on both surfaces of the resistance film 2) and the surface coating layer 4, and composited with an adhesive. 2 is different from the above-described radio wave absorber B shown in FIG. 2 in that the laminated body and the surface coating layer 4 are not bonded. The air layer 8 is formed by spacers 9 provided on the outer peripheral portions of the composite laminate and the surface coating layer 4. This spacer 9 is provided with a strip-shaped hot melt adhesive sheet having a large thickness, thickly applied with the above-mentioned curable adhesive (sealing agent) or resin coating liquid, or other members such as a strip-shaped synthetic resin. It is provided by arranging sheets and plates. The air layer 8 may be formed between the dielectric layer 1 and the composite laminate.

  Other configurations of the radio wave absorber D, the dielectric layer 1, the resistance film 2, the radio wave reflector 3, the surface coating layer 4, the gas barrier film 5, the adhesives 6 and 60, the material of the back surface coating layer 7 and the like are described above. Since these are the same as those of the electromagnetic wave absorber B, description thereof will be omitted.

  In such a wave absorber D, when the wave absorber B shown in FIG. 2 is manufactured, a spacer 9 is disposed around the composite laminate overlaid on the dielectric layer 1, and a surface coating layer is formed thereon. By superimposing 4, it can be easily manufactured.

  In such a wave absorber F, both surfaces of the resistance film 2 are doubled by the gas barrier film 5 having a low water vapor transmission rate and low oxygen transmission rate and the surface coating layer 4 or the adhesive 6 and the dielectric layer 1. Or since it is covered in triplicate and the periphery of the composite laminate is sealed with an adhesive 60 and sealed, moisture is prevented from entering from the outside and the resistance film 2 is affected by heat and light. In addition, since the moisture contained in the air layer 8 does not pass through the gas barrier film 5 and come into contact with the resistance film 2, the surface resistivity of the resistance film 2 is kept substantially constant. The air layer 8 may be provided with a desiccant to remove moisture.

  FIG. 5 is a cross-sectional view of a radio wave absorber according to still another embodiment of the present invention.

  In this radio wave absorber E, an adhesive 6 (hot melt type adhesive sheet) and a composite laminate (gas barrier films 5 and 5 are laminated on both sides of the resistance film 2 on one side (front side) of the dielectric layer 1 are laminated. The composite laminate), the adhesive 6, the other dielectric layer 10, the adhesive 6, the composite laminate, the adhesive 6, and the surface coating layer 4 in this order. The radio wave reflector 3 and the back surface coating layer 7 are overlapped on the opposite surface side (back surface side) of the dielectric layer 1, and these are bonded and integrated, and the entire four side surfaces of the radio wave absorber are bonded and sealed with an adhesive 60. It is a thing.

  This radio wave absorber E is different from the above radio wave absorbers in that two composite laminates are provided on one side of the dielectric layer 1 with the other dielectric layer 10 interposed therebetween. The dielectric layer 10 is made of the same resin or glass as the dielectric layer 1, and has a thickness of about 0.1 to 5 mm. The dielectric layer 1, the resistance film 2, the radio wave reflector 3, the front surface coating layer 4, the gas barrier film 5, the adhesives 6, 60, and the back surface coating layer 7 that constitute the radio wave absorber E The description is omitted because it is the same as that used in FIG.

  Instead of the dielectric layer 10 described above, an air layer may be formed by sandwiching a spacer between two composite laminates. In some cases, the dielectric layer 10 or the air layer is sandwiched. Three or more composite laminates may be provided. Similarly, in the radio wave absorbers B, C and D, a plurality of composite laminates may be provided with an air layer or another dielectric layer interposed therebetween.

  In such a radio wave absorber E, the resistance film 2 of each composite laminate is composed of a gas barrier film 5 having a low water vapor transmission rate and low oxygen transmission rate on both sides, an adhesive 6, and dielectric layers 1 and 10 or In addition to being covered in triplicate by the surface coating layer 4, the side surfaces of each composite laminate are sealed and sealed with the adhesive 60, so that the intrusion of moisture into the resistance film 2, the influence of heat and light is blocked, The surface resistivity of the resistance film 2 is kept almost constant, and the initial radio wave absorption performance is maintained. In addition, if there are two resistance films 2 and 2 as in the case of this electromagnetic wave absorber E, in the unlikely event that one resistance film 2 is in use during a long period of use, the surface resistivity deviates from the range of 280 to 400 Ω / □ Even so, the other resistance film 2 can maintain the surface resistivity within the above range and maintain the radio wave absorption performance, so that the durability and reliability are further improved. The frequency band in which (return loss) appears can also be expanded. Since this radio wave absorber E is provided with two composite laminates, the transparency is slightly lowered and the total light transmittance is in the range of 30% or more, but the haze is 10% or less, so the transparency is good.

  In addition, when the thickness of the dielectric layer 10 is 6.5 mm, the radio wave absorption performance at 15 ° incidence is good, and when the thickness of the dielectric layer 10 is 7.0 mm, the radio wave absorption performance at 45 ° incidence is good. It is preferable to provide the composite laminate with an interval of 0.5 mm, with the dielectric layer 10 as described above.

  FIG. 6 is a cross-sectional view of a radio wave absorber according to still another embodiment of the present invention.

  This radio wave absorber F is provided with dielectric layers 1, 1 on both sides of the radio wave reflector 3, and an adhesive 6 (hot melt type adhesive) on the opposite side of the dielectric layers 1, 1 from the radio wave reflector 2. Sheet), a composite laminate (composite laminate in which the gas barrier films 5 and 5 are laminated on both surfaces of the resistance film 2), the adhesive 6 and the surface coating layer 4 are stacked and integrated. The entire four-side surface is adhesively sealed with an adhesive 60 [curing adhesive (sealing agent) or resin coating solution].

  In the radio wave absorber F and the radio wave absorber E, the dielectric layer 1 (10), the composite laminate, and the surface coating layer 4 are bonded to each other by the adhesive 6 (hot melt type adhesive sheet). You may adhere | attach only an outer peripheral part. Further, in this radio wave absorber F and the above radio wave absorber E, the four side surfaces are adhesively sealed with an adhesive 60 [curing adhesive (sealing agent) or resin coating liquid], but the adhesive 6 ( A hot-melt adhesive sheet) may be bonded by thermocompression.

  The dielectric layer 1, the resistance film 2, the radio wave reflector 3, the surface coating layer 4, the gas barrier film 5, and the adhesives 6 and 60 that constitute the radio wave absorber F are used for each of the radio wave absorbers described above. Since it is the same as that, the description is omitted.

  In such a radio wave absorber F, the resistance film 2 is composed of the gas barrier films 5 and 5 having low water vapor permeability and oxygen permeability on both sides, the adhesive 6, and the dielectric layer 1 or the surface coating layer 4. In addition to being covered in triplicate, the side surface of the composite laminate is sealed with an adhesive 60 and sealed, so that the intrusion of moisture into the resistance film 2 and the influence of heat and light are blocked, and the surface resistivity of the resistance film 2 Is kept almost constant. In addition, radio waves incident from the surface coating layers 4 and 4 on both sides can be reflected and absorbed by the radio wave reflector 3, and since the radio wave reflector 3 can be shared, an inexpensive radio wave absorber can be obtained. Since this radio wave absorber F has two composite laminates, the transparency is slightly reduced and the total light transmittance is in the range of 30% or more, but the haze is 10% or less, and the transparency is good.

  In any of the above radio wave absorbers A to F, no electrode is attached to the resistance film 2, but an electrode made of a strip-shaped copper foil or the like may be attached to the resistance film 2. When the electrodes are attached in this way, the surface resistivity of the resistive film 2 is monitored at any time by applying the tester's needle to the electrode, and the change in the radio wave absorption performance is monitored. There is an advantage that can be inferred.

  Further, a metal frame is attached around the radio wave absorbers A to F, and a radio wave absorber sheet (for example, a magnetic material such as ferrite is formed on a synthetic rubber or a synthetic resin sheet on the surface of the radio wave incident side of the frame body. May be pasted. If it does in this way, the peripheral part of an electromagnetic wave absorber will be protected by a frame, it will become easy to attach to an ETC toll booth of a highway, etc., and there will be no fear that the components of an electromagnetic wave absorber will disassemble during use. And since the electromagnetic wave which hits a metal frame is absorbed by the electromagnetic wave absorbing sheet, it is possible to prevent the radio wave absorbing performance from being deteriorated by the frame.

  Next, an experiment conducted for confirming the effect of the present invention will be described.

[Experiment 1]
Acid treatment of single-walled carbon nanotubes having a diameter of 1.3 to 1.8 nm synthesized based on the document Chemical Physics Letters, 323 (2000) P580-585 in isopropyl alcohol / water mixture (mixing ratio 3: 1) as a solvent And the polyalkyleneethylene-polyoxypropylene copolymer as a dispersant added and mixed and dispersed uniformly, 0.003% by mass of single-walled carbon nanotubes, and 0.05% by mass of dispersant The coating liquid containing was adjusted.

Laminate a 25 μm thick PET (polyethylene terephthalate) film on both sides of a 12 μm thick commercially available silica deposited film [Rack Barrier S manufactured by Mitsubishi Plastics, Inc.], which is a PVA (polyvinyl alcohol) film formed with a silica deposited layer. Then, a gas barrier film as shown in FIG. 9C, that is, a gas barrier film having a three-layer laminate structure in which a silica vapor deposition layer was formed at the interface between layers was prepared. A transparent resistive film having a surface resistivity of 300Ω / □ is applied to the surface of the gas barrier film by applying the coating solution so that the basis weight of the single-walled carbon nanotubes is about 27 mg / m ^2. In addition, the above-described gas barrier film on which no resistive film was formed was superposed so as to cover the resistive film, thereby preparing a composite laminate. This composite laminate is cut to a size of 70 × 70 mm, and a pair of strip-shaped copper foil electrodes (width 5 mm, length 100 mm) are bonded to the resistance film with a conductive adhesive along two opposite sides. At the same time, the four corners were bonded to produce a 70 × 70 mm composite laminate with electrodes.

  As shown in FIGS. 10A and 10B, 80 mm square hot made of EVA (ethylene-vinyl acetate copolymer resin) as the adhesive 6 is formed on the upper and lower surfaces of the composite laminate 20 with the electrodes 30. Melt type adhesive sheets (thickness 0.5 mm) are stacked, and 80 mm square polycarbonate plates 40 and 40 (thickness 2 mm) are stacked on the top and bottom, and sandwiched from above and below by a 100 mm square gloss plate at 130 ° C. By heating, the hot-melt adhesive sheets 6 and 6 are softened and melted, and the composite laminate 20 with electrodes and the polycarbonate plates 40 and 40 are bonded and integrated, and the outer periphery of the composite laminate 20 with electrodes is bonded to the adhesive. This test body sealed with 6 was produced.

  About this test body, the heat resistance test change of the surface resistivity of a resistance film was investigated at 80 degreeC constant temperature using oven (made by Tabay Espec). The result is shown in the graph of FIG.

For comparison, the above coating solution is applied to one side of an 80 mm square polycarbonate plate (thickness 2 mm) so that the basis weight of single-walled carbon nanotubes is about 27 mg / m ^2, and the surface resistivity is increased. A 300Ω / □ transparent resistance film is formed, and an electrode made of the copper foil is attached to the resistance film, and an 80 mm square polycarbonate plate (thickness 2 mm) is stacked so as to cover the resistance film. A test specimen for comparison was prepared in which the four sides were bonded and sealed with a silicone adhesive (sealing agent). And about this test body for a comparison, the heat test change of the surface resistivity of a resistance film was investigated similarly to the above. The results are also shown in the graph of FIG.

[Experiment 2]
This test body was prepared in the same manner as in Experiment 1, and the humidity resistance change of the surface resistivity of the resistance film was measured at a temperature of 60 ° C. and a humidity of 90% using a constant temperature and humidity chamber (Prasina lucifer, manufactured by Tabai Espec). We examined by condition. The result is shown in the graph of FIG.
For comparison, a test specimen for comparison was prepared in the same manner as in Experiment 1, and the change in the moisture resistance test of the surface resistivity of the resistance film was examined in the same manner as described above. The results are also shown in the graph of FIG.

[Experiment 3]
This test specimen was prepared in the same manner as in Experiment 1, and the outdoor exposure test change in the surface resistivity of the resistive film was measured using the Takiron Co., Ltd. Aboshi factory permanent outdoor exposure test stand (Tainan facing, 45 ° It was installed on a tilt table and examined. The result is shown in the graph of FIG.
For comparison, a test specimen for comparison was prepared in the same manner as in Experiment 1, and the change in the outdoor exposure test of the surface resistivity of the resistive film was examined in the same manner as described above. The results are also shown in the graph of FIG.

  As can be seen from the results of the heat resistance test shown in the graph of FIG. 11, the resistance film of the comparative test specimen gradually increased in surface resistivity with the passage of days, and increased by 17% (51 Ω / □) after 5 days. It was found that it increased by 25% (75Ω / □) over the course of the day and increased by 35% (105Ω / □) over the course of 21 days. Therefore, if it is a radio wave absorber using this resistance film, it will become 375 ohms / square after 10 days, and it will become difficult to absorb a radio wave after this. On the other hand, as in this test body, the resistance film of the composite laminate is sandwiched between gas barrier films, and the upper and lower surfaces and the outer periphery of the composite laminate are bonded and sealed with a hot-melt adhesive sheet. The surface resistivity of the resistive film is decreased by −1% (−3Ω / □) even after the number of days, and the change is extremely small and substantially constant. The change in the surface resistivity of the resistive film is caused by the gas barrier film. It was found that (increase / decrease) was definitely prevented. Therefore, even if the surface resistivity changes, it is in the range of 297 to 300 Ω / □, and the radio wave absorber using the resistance film of such a composite laminate has a long-term radio wave absorption function as far as heat is concerned in external use. You can see that it works.

  As can be seen from the humidity resistance test results shown in the graph of FIG. 12, the resistance film of the comparative test specimen gradually increases in surface resistivity with the passage of days, and 31.3% (94Ω / □) after 3 days. Increased by 38% (114Ω / □) after 5 days, increased by 46% (138Ω / □) after 10 days, and increased by 52% (156Ω / □) after 21 days It was. Therefore, in the case of a radio wave absorber using this resistance film, it becomes 394Ω / □ after 3 days, and the radio wave is difficult to be absorbed thereafter. On the other hand, like this test body, the resistance film of the composite laminate is sandwiched between gas barrier films, and the upper and lower surfaces and the outer peripheral portion of the composite laminate are bonded and sealed with a hot-melt adhesive sheet. Even when the number of days has passed, the surface resistivity is 0% (0Ω / □), and the change is extremely small and constant, and it is understood that the above-mentioned gas barrier film reliably prevents the change in surface resistivity. It was. Therefore, even if the surface resistivity of the resistance film changes, it is 300 Ω / □, and the radio wave absorber using such a composite laminate resistance film has long-term radio wave absorption performance as far as heat and temperature in external use are concerned. It can be seen that

  As can be seen from the outdoor exposure test results shown in the graph of FIG. 13, the resistance film of the comparative test specimen gradually increased in surface resistance with the passage of days, and 18.5% (55.5Ω / □) after one day. Increased by 23.1% (69Ω / □) after 50 days, increased by 24.3% (73Ω / □) after 100 days, and increased by 25.7% (77Ω / □) after 130 days I found out. Therefore, in the case of a radio wave absorber using this resistance film, it becomes 377 Ω / □ after 100 days, and the radio wave is difficult to be absorbed thereafter. On the other hand, like this test body, the resistance film of the composite laminate is sandwiched between gas barrier films, and the upper and lower surfaces and the outer peripheral portion of the composite laminate are bonded and sealed with a hot-melt adhesive sheet. Even after 130 days have passed since the start of outdoor exposure (March 22, 2006), the surface resistivity of the resistive film increased only by 7.7% (23.1 Ω / □) and there was little change. Therefore, if it is a radio wave absorber using this composite laminate, it becomes 323 Ω / □ after 130 days, maintaining a useful range as a radio wave absorber, and the surface resistivity of the resistance film by the gas barrier film described above. It was found that change (increase) was reliably prevented. In addition, the slope of the graph for 20 days from 110 days after midsummer (July 12, 2006) to 130 days later (August 1, 2006) increased from a maximum of 0.6Ω / □ in 20 days. It is 0.03Ω / □ / day in one day, and the increase in the next one year is 11Ω / □ even if it is assumed to be summer. Therefore, for example, if the initial surface resistivity is 300Ω / □, one year Even if the surface resistivity changes, it is 311 Ω / □, and even for 5 years, it is 355 Ω / □, and the electromagnetic wave absorber using the resistive film of this composite laminate can be used for a long time even when exposed to sunlight. It can be seen that it exhibits radio wave absorption performance. However, if the resistance film is not sandwiched between the gas barrier films, the increase will be 23% (69Ω / □) after 20 days from the start of outdoor exposure, and the increase will be at least 6Ω / □ over 20 days, and will be 0. 3Ω / □ is increased by 109.5Ω / □ in one year, and it is obvious that such a radio wave absorber cannot exhibit radio wave absorption performance for a long period of time when used externally.

  In addition, in the outdoor exposure test results, the rate of increase up to 20 days later is high, so operations such as outdoor exposure stabilization and light irradiation stabilization can be performed on the resistance film in advance, and the surface resistivity can be intentionally increased and stabilized. preferable. This operation can be performed using, for example, a solar simulator WXS-155S-L2, AM1.5GMM (solar pole approximate light) manufactured by Wacom Denso Co., Ltd.

  From the above experimental results, the radio wave absorber of the present invention has a gas barrier film that blocks moisture from entering and contacting the resistance film, and reduces the influence of heat and light on the resistance film, thereby reducing the surface resistance of the resistance film. It is confirmed that the radio wave absorption performance is prevented from deteriorating due to the change in rate, and that the initial good radio wave absorption performance can be maintained over a long period of time.

It is sectional drawing of the electromagnetic wave absorber which concerns on one Embodiment of this invention. It is sectional drawing of the electromagnetic wave absorber which concerns on other embodiment of this invention. It is sectional drawing of the electromagnetic wave absorber which concerns on other embodiment of this invention. It is sectional drawing of the electromagnetic wave absorber which concerns on other embodiment of this invention. It is sectional drawing of the electromagnetic wave absorber which concerns on other embodiment of this invention. It is sectional drawing of the electromagnetic wave absorber which concerns on other embodiment of this invention. (A) (b) (c) is a fragmentary sectional view of a resistance film. It is a schematic diagram which shows the dispersion state which looked at the carbon nanotube contained in a resistive film from the front. (A) (b) (c) is a fragmentary sectional view of the gas-barrier film of the different aspect in which the silica vapor deposition layer was formed. (A) is an exploded side view of the test specimen, and (b) is a plan view of the test specimen. It is a graph which shows the relationship between the surface resistivity of a resistive film and elapsed days by a heat test. It is a graph which shows the relationship between the surface resistivity of a resistive film and elapsed days by a moisture-proof heat test. It is a graph which shows the relationship between the surface resistivity of a resistance film by an outdoor exposure test, and elapsed days.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dielectric layer 2 Resistive film | membrane 2a Carbon nanotube 2b Binder 3 Radio wave reflector 4 Surface coating layer 5 Barrier film 5 rubbed silica Deposition layer 6,60 Adhesive 7 Back surface coating layer 8 Air layer 9 Spacer 20 Composite laminated body 30 Electrodes A, B, C, D, E, F Electromagnetic wave absorber

Claims (16)

  A radio wave absorber having a resistive film on one side of a dielectric layer and a radio wave reflector on the opposite side of the dielectric layer, wherein a gas barrier film is laminated on both sides of the resistive film. Absorber.   The radio wave according to claim 1, wherein the periphery of the composite laminate formed by laminating the gas barrier film on both sides of the resistance film, or the periphery and both sides, or the periphery and one side are sealed with an adhesive. Absorber.   The radio wave absorber according to claim 2, wherein a surface coating layer is provided on one side of the dielectric layer, and a composite laminate is provided between the dielectric layer and the surface coating layer.   4. The radio wave absorber according to claim 3, wherein a plurality of composite laminates are provided so as to overlap each other between the dielectric layer and the surface coating layer.   The radio wave absorber according to claim 4, wherein an air layer or another dielectric layer is formed between the plurality of composite laminates.   The radio wave absorber according to claim 3, wherein an air layer or other dielectric layer is formed between the composite laminate and the surface coating layer.   The radio wave absorber according to claim 2, wherein a composite laminate is provided on each side of the dielectric layer provided on both sides of the radio wave reflector on the side opposite to the radio wave reflector. Synthesis of a single layer or multiple layers in which the gas barrier film has a water vapor permeability of 5.0 (g / m ² · day) or less and an oxygen permeability of 5.0 (cc / m ² · day · atm) or less. The radio wave absorber according to any one of claims 1 to 7, wherein the radio wave absorber is a resin film.   The gas barrier film is polyvinyl alcohol, polyethylene terephthalate, ultra low density polyethylene, polyvinyl chloride, polyvinylidene chloride, fluorine resin, polyamide resin, ethylene-vinyl alcohol copolymer, polyphenylene sulfide, polyacrylonitrile alone or The radio wave absorber according to claim 8, wherein the radio wave absorber is a single-layer or multi-layer synthetic resin film made of two or more kinds of synthetic resins.   A single layer or two or more kinds of vapor deposition layers of silica, aluminum oxide, and magnesium oxide are formed on at least one surface of a single layer or multilayer synthetic resin film, or at the interface between layers of the multilayer synthetic resin film. The radio wave absorber according to claim 8 or 9, characterized in that   11. The radio wave absorption according to claim 1, wherein the resistance film is a film containing ultrafine conductive fibers, and the fine conductive fibers are dispersed without contacting each other and are in contact with each other. body.   The radio wave absorber according to any one of claims 3 to 6, wherein the surface coating layer is a synthetic resin plate containing an ultraviolet absorber.   The radio wave absorber according to any one of claims 1 to 12, wherein an electrode is attached to the resistance film.   The radio wave absorber according to any one of claims 1 to 13, wherein the four side surfaces are sealed with an adhesive.   The radio wave absorber according to claim 2 or 14, wherein the adhesive is an ethylene-vinyl acetate copolymer resin-based or polycarbonate ester resin-based hot-melt adhesive sheet having heat resistance at 80 ° C. .   The radio wave absorber according to any one of claims 1 to 15, wherein each constituent member has transparency.

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