JP2008124155A - 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 silica vapor deposition layers 5 and 5 are stacked on both surfaces of the resistive film 2. Thus, an influence of moisture (open air containing water content), heat, light, etc. on the resistive film 2 can be substantially blocked with the silica vapor deposition layers 5 and 5, 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.

  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 silica vapor deposition layer is disposed on both sides of the film.

  In the present invention, as in the radio wave absorber according to claim 2, the silica vapor deposition layer is formed on each of the opposing surfaces of the dielectric layer and the surface coating layer provided on one side thereof, and is formed on both sides of the resistance film. It may be arranged and the periphery of the resistance film may be sealed with an adhesive. Further, as in the radio wave absorber according to claim 3, a synthetic resin film having a silica vapor deposition layer formed on one side is laminated on both sides of the resistance film, and the silica vapor deposition layer is arranged on both sides of the resistance film. The circumference of the body, or the circumference and both sides, or the circumference and one side may be sealed with an adhesive. Further, as in the radio wave absorber according to claim 4, a laminate of other synthetic resin films laminated on both sides of a synthetic resin film having a silica vapor deposition layer formed on one side is laminated on both sides of a resistance film, and a silica vapor deposition layer is formed. You may arrange | position on the both surfaces side of a resistance film, and may seal the circumference | surroundings of this composite laminated body, a circumference | surroundings and both surfaces, or a circumference | surroundings and one side with an adhesive agent. In that case, polyvinyl alcohol, polyethylene terephthalate, ultra-low density as a synthetic resin film or other synthetic resin film having a silica vapor deposition layer formed on one side thereof as in the radio wave absorber of claim 5 and the radio wave absorber of claim 6 It is preferable to use a synthetic resin film of any one of polyethylene, polyvinyl chloride, polyvinylidene chloride, fluorine resin, polyamide resin, ethylene-vinyl alcohol copolymer, polyphenylene sulfide, and polyacrylonitrile.

  In the present invention, it is preferable to provide a surface coating layer on one side of the dielectric layer and provide the above composite laminate between the dielectric layer and the surface coating layer as in the radio wave absorber according to claim 7. 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 8, or a plurality of radio wave absorbers of claim 9, An air layer or other dielectric layer is formed between the composite laminates, or an air layer or other dielectric layers are provided between the composite laminate and the surface covering layer as in the radio wave absorber according to claim 10. May be formed. Further, as in the radio wave absorber according to claim 11, each of the composite laminates 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.

  Further, as in the radio wave absorber according to claim 12, the resistance film is a film containing ultrafine conductive fibers, and the ultrafine conductive fibers are dispersed without contacting each other, and are in contact with each other. The surface coating layer is a synthetic resin plate containing an ultraviolet absorber as in the absorber, the electrode is attached to the resistance film as in the radio wave absorber according to claim 14, and the radio wave absorption according to claim 15 The four side surfaces are sealed with an adhesive as in the body, and the adhesive is an ethylene-vinyl acetate copolymer resin system or polycarbonate ester having heat resistance at 80 ° C. as in the radio wave absorber according to claim 16. It is preferable that it is a resin-based hot-melt adhesive sheet, and that each constituent member has transparency as in the radio wave absorber of claim 17.

  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 silica vapor deposition layers are arranged on both sides of the resistance film as in the radio wave absorber of the present invention, the influence of moisture (external air including moisture), heat, light, etc. on the resistance film is substantially affected by the silica vapor deposition layer. Therefore, the surface resistivity of the resistive film is kept almost constant as supported by the experimental data 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.

  The radio wave absorber according to claim 2 has the simplest configuration, but the resistance film includes a dielectric layer and a surface coating layer having a silica vapor deposition layer formed on the opposite surface, and an adhesive that seals the periphery of the resistance film. As a result, the influence of moisture, heat, light, etc. is substantially blocked, and the surface resistivity of the resistive film is kept substantially constant.

  In the radio wave absorber of claim 3, the water vapor permeability and oxygen permeability of the synthetic resin film (silica vapor deposition film) having the silica vapor deposition layer formed on one side are low, and the resistance film in the composite laminate is disposed on both sides thereof. Furthermore, since the silica vapor deposition film and the adhesive that seals the periphery of the composite laminate are sealed, the influence of moisture, heat, light, etc. on the resistance film is substantially blocked, and the surface resistance of the resistance film The rate is kept almost constant.

  The radio wave absorber according to claim 4 is a composite laminate in which a water vapor permeability and an oxygen permeability of a synthetic resin film in which a silica vapor deposition layer is formed on one side are laminated with another synthetic resin film (laminate) are further reduced. Since the resistance film in the body is sealed by the above-described laminate disposed on both sides thereof and the adhesive that seals the periphery of the composite laminate, etc., the resistance film is affected by moisture, heat, light, etc. It is blocked more reliably and the surface resistivity of the resistive film is kept almost constant. Moreover, since the above laminate has a thickness suitable for handling, it is easy to handle at the time of manufacturing the radio wave absorber.

In the radio wave absorber according to claim 5, since the synthetic resin film having the silica vapor deposition layer formed on one side is a polyvinyl alcohol film or a polyethylene terephthalate film, the water vapor permeability and the oxygen permeability are extremely low. The silica vapor deposited film formed on one side of the alcohol film has a water vapor permeability of 0.1 (g / m ² · day) or less and an oxygen permeability of 0.1 (cc / m ² · day · atm) or less. And like the electromagnetic wave absorber of Claim 6, what laminated | stacked the polyethylene terephthalate film or the ultra-low-density polyethylene film on said silica vapor deposition film becomes still lower in water vapor permeability and oxygen permeability. Therefore, since the electromagnetic wave absorber according to claims 5 and 6 has an extremely strong effect of blocking the influence of moisture, heat, light, etc. on the resistance film, the durability is remarkably improved, and the initial goodness over a long period of time. The radio wave absorption performance can be maintained. The water vapor permeability is a value measured according to the method of JIS K 7129, and the oxygen permeability is a value measured according to the method of JIS K 7126.

  In the radio wave absorber according to the seventh aspect, 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. The action of blocking the influence of the above becomes stronger.

  The radio wave absorber according to claim 8 has a disadvantage in the resistance film of one composite laminate during a long-term use, 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 9 or the radio wave absorber according to claim 10 includes an air layer or other 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 11 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 12, 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 of claim 13 is used outdoors, the resistance film, 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 14 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 measuring 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 15, since the four circumferential side surfaces are sealed with an adhesive, it is possible to reliably prevent moisture from entering, and in the radio wave absorber according to claim 16, the adhesive is 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 17 can see the other side through the radio wave absorber and can also brighten the periphery thereof. 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 a basic embodiment of the present invention, FIGS. 9A, 9B, and 9C are schematic cross-sectional views showing a resistance film of the radio wave absorber, and FIG. It is the model which shows the dispersion state which looked at the carbon nanotube of the resistance film from the front.

  The radio wave absorber A includes a resistive film 2 on one side (front surface side: radio wave incident surface side) of the transparent dielectric layer 1 and is transparent on the opposite surface side (back surface side) of the dielectric layer 1 (see FIG. The resistive film 2 is provided between the dielectric layer 1 and the transparent surface coating layer 4 on one side thereof. And the transparent silica vapor deposition layers 5 and 5 are formed in the opposing surface of the dielectric material layer 1 and the surface coating layer 4, respectively, and the resistance film 2 is pinched | interposed by the silica vapor deposition layers 5 and 5 from both surface sides. Yes. The periphery of the resistance film 2 is sealed with an adhesive 6, and the outer periphery of the dielectric layer 1 and the surface coating layer 4 in which the silica vapor-deposited layers 5 and 5 are formed on the opposite surfaces is bonded by the adhesive 6. ing. Further, the radio wave reflector 3 and the back surface coating layer 7 are provided on the opposite surface side (back surface side) of the dielectric layer 1, and the dielectric layer 1, the radio wave reflector 3, the back surface coating layer 7, and the like. Are integrated with an adhesive.

  In the above radio wave absorber A, it is necessary to adhere the outer peripheral portion of the surface coating layer 4 to the dielectric layer 1 with the adhesive 6 in order to seal the resistance film 2. The layer 7 may simply be superimposed on the back side of the dielectric layer 1. However, it is preferable that the dielectric layer 1, the radio wave reflector 3, and the back surface coating layer 7 are integrated with an adhesive or the like as in this embodiment because the handling property is improved.

  Such a radio wave absorber A has an action in which the silica vapor deposition film 5 substantially blocks the influence of moisture, heat, light, etc. on the resistance film 2, and a dielectric layer in which the silica vapor deposition film 5 is formed on the opposing surface. 1 and the surface coating layer 4 and the adhesive 6 around the resistance film 2, the resistance film 2 is hermetically sealed, so that the resistance film 2 is affected by moisture (outside air containing moisture), heat, light, and the like. The surface resistivity of the resistive film 2 is substantially kept 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 silica deposition layer 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 compared to methyl methacrylate resin, but by adding a UV absorber or using a resin plate having excellent weather resistance, which will be described later, as the surface coating layer 4, weather resistance sufficient for practical use is obtained. Sex can be imparted.

  The dielectric layer 1 made of synthetic resin or glass as described above also serves to seal the back surface of the resistance film 2 and prevent permeation of outside air containing moisture from the back surface.

  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 of the opposing surfaces of the dielectric layer 1 or the surface coating layer 4. The surface resistivity of 280 to 400Ω / □ is obtained by adjusting various conditions such as the content of the ultrafine conductive fiber, the coating thickness, and the 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 solution to one of the opposing surfaces of the dielectric layer 1 or the surface coating layer 4 as described above, but other methods, for example, the coating solution is applied to a release film. Is applied to form a resistance film, and if necessary, an adhesive layer is formed thereon to form a transfer film, and this transfer film is pressure-bonded to one opposing surface of the dielectric layer 1 or the surface coating layer 4 Then, the resistance film or the resistance film and the adhesive layer are transferred, or the coating liquid is applied to one side of a different kind of thermoplastic resin film that is the same or compatible with the dielectric layer 1 or the surface coating layer 4 to resist. A film 2 may be formed, and this resistive film forming film may be formed by adopting a method of thermocompression bonding to one opposing surface of the dielectric layer 1 or the surface coating layer 4.

  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. 9A, the carbon nanotubes 2a are dispersed in the binder 2b in a three-dimensional structure in the above dispersed state. As shown in FIG. 9B, 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. Are dispersed in contact with each other, or some of the carbon nanotubes 2a are inside the binder 2b as shown in FIG. 9 (a), and the other carbon nanotubes 2a are binders as shown in FIG. 9 (b). 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. 9C, the carbon nanotubes are dispersed in the above-mentioned dispersed 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. 10 schematically shows the dispersion state of the carbon nanotubes 2a as viewed from the front. As can be understood from FIG. 10, 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 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 a synthetic resin or glass having the same transparency as the dielectric layer 1, and the surface coating layer 4 seals the resistance film 2 to moisture ( It is provided for the purpose of shielding from the outside air containing moisture) and for the purpose of protecting the resistance film 2 and the dielectric layer 1 from ultraviolet deterioration due to direct sunlight. Furthermore, the surface coating layer 4 made of synthetic resin can also prevent damage due to flying object collision. 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, the dielectric layer 1 and the resistance film 3 from damage caused by flying object collisions and UV deterioration caused by direct sunlight. In addition, the same resin plate as the surface coating 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 an ultraviolet absorber were added to improve weather resistance. A synthetic resin plate such as a polyester or olefin having the same thickness having transparency and particularly a polycarbonate resin plate containing an ultraviolet absorber is preferably used.

  The silica vapor deposition layer 5 formed on the opposing surface of the dielectric layer 1 and the surface coating layer 4 has a function of blocking the influence of moisture, heat, and light on the resistance film 2 and has a vapor deposition thickness of 0. Those deposited by vapor deposition so as to be about 5 nm to 500 nm are preferable. When the amount of silica deposition is less than the above range, the action of blocking the influence of moisture, heat, light, etc. on the resistance film 2 is reduced, so that the surface resistivity of the resistance film 2 changes and the initial radio wave absorption performance is prolonged. It becomes difficult to maintain over. Moreover, the silica vapor deposition layer 5 is likely to be cracked or peeled off, or the transparency is deteriorated. On the other hand, if the silica deposition amount exceeds the above range, the material is wasted.

  The adhesive 6 adheres the outer peripheral portions of the dielectric layer 1 and the surface coating layer 4 to seal the periphery of the resistance film 2, and prevents the penetration of moisture from the periphery to the resistance film 2. Prevents changes in surface resistivity over time (increase / decrease), such as polyurethane, ethylene-vinyl acetate copolymer, ethylene monocarboxylic acid vinyl ester copolymer, ethylene-acrylic acid vinyl ester Hot melt adhesive sheet such as copolymer system, polycarbonate ester system, silicone system, epoxy system, acrylic system, organopolysiloxane system, carbamate system, vinyl system, hydrolyzable silyl group system, silylated urethane system, Uses curable adhesives (sealing agents) such as polyoxyalkylene polymer systems, and synthetic resin coating solutions in which resin is dissolved in a solvent. It is. 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. These adhesives are preferably colorless and transparent, but like the transparent radio wave absorber A of this embodiment, the outer peripheral portions of the dielectric layer 1 and the surface coating layer 4 are bonded to each other to form a resistance film. When sealing the periphery of 2 or when sealing and sealing the four circumferential sides of the radio wave absorber with an adhesive as described later, an opaque adhesive may be used.

  The radio wave absorber A as described above can be manufactured, for example, by the following method. First, the dielectric layer 1 and the surface coating layer 4 made of the synthetic resin plate or the like in which the silica vapor deposition film 5 is formed on one side so as to have the above-described vapor deposition amount are prepared. Then, a coating liquid is prepared by thoroughly mixing ultrafine conductive fibers such as carbon nanotubes, a solvent, the binder as necessary, and the dispersant as necessary, and the coating liquid is mixed with the dielectric layer 1 or The resist film 2 having a surface resistivity of 280 to 400 Ω / □ is formed by applying the coating on any one of the silica vapor deposition layers 5 of the surface coating layer 4 except for the outer peripheral portion. Next, the hot-melt adhesive sheet having a narrow width is disposed as the adhesive 6 on the outer periphery of the dielectric layer 1 or the surface coating layer 4, and the dielectric layer 1 and the surface coating layer 4 are overlapped with each other. The radio wave reflector 3 is overlapped on the opposite surface of 1 and the hot melt adhesive sheet is disposed as an adhesive, and the back surface coating layer 5 made of the synthetic resin plate is overlapped thereon (back surface). The laminate is heated while being sandwiched between upper and lower gloss plates to soften and melt the hot melt adhesive sheet, thereby bonding the outer peripheral portions of the dielectric layer 1 and the surface coating layer 4 to the periphery of the resistance film 2. The radio wave absorber 3 is manufactured by adhering the radio wave reflector 3 and the back surface coating layer 7 to the opposite surface of the dielectric layer 1. The radio wave absorber A obtained in this way can give good transparency (visibility) by setting its total light transmittance to 40% or more and haze to 10% or less.

  If the radio wave absorber A does not have transparency but has translucency, 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. The haze may be increased by using the above-described materials, or by forming fine irregularities on the outer surface of the surface coating layer 4 or the back surface coating layer 7. 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. Moreover, depending on the case, you may abbreviate | omit either one of the silica vapor deposition layers 5 and 5 formed in the opposing surface of the dielectric material layer 1 and the surface coating layer 4. FIG.

  As in the radio wave absorber A having transparency according to this embodiment, the dielectric layer 1 and the surface coating layer 4 on which the silica vapor deposition layer 5 that blocks the influence of moisture, heat, light, etc. on the resistance film 2 is formed; When the resistance film 2 is hermetically sealed by the adhesive 6 around the film 2, the contact between the resistance film 2 and moisture (moisture in the outside air) is cut off, and the influence of heat and light is also blocked. Therefore, the surface resistivity of the resistance film 2 is kept substantially constant. Therefore, the deterioration of the radio wave absorption performance due to the change in the surface resistivity of the resistance film 2 is prevented, and the initial good radio wave absorption performance is maintained over a long period of time, so that the durability and reliability are greatly improved. Moreover, since the radio wave absorber A has a very good dispersion state of the carbon nanotubes in the resistance film 2 and a high frequency of contact with each other, and can ensure a predetermined surface resistivity with a small content, the transparency of the resistance film 2 Therefore, the transparency of the radio wave absorber A is improved accordingly. In addition, 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 UV deterioration, and prevent damage caused by flying objects. You can also

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

  In this radio wave absorber B, the resistance film 2 is formed on the opposite surface of the synthetic resin film 8 (silica deposition film) having the silica deposition layer 5 formed on one side, and the silica deposition layer 5 is formed so as to cover the resistance film 2. By laminating another synthetic resin film 8 (silica vapor deposition film) formed on one side, the silica vapor deposition layers 5 and 5 are arranged on both sides of the resistance film 2 via the synthetic resin films 8 and 8. . A transparent composite laminate composed of the resistance film 2 and two silica vapor deposited films is disposed between the dielectric layer 1 and the surface coating layer 4, and the dielectric layer 1 and the composite laminate are bonded with an adhesive 6. The body and the surface coating layer 4 are bonded together to seal the periphery and both surfaces of the composite laminate.

Examples of the synthetic resin film 8 for forming the silica vapor deposition layer 5 include polyvinyl alcohol, polyethylene terephthalate, ultra-low density polyethylene (metathelon-catalyzed low molecular weight polyethylene film), polyvinyl chloride, polyvinylidene chloride, and fluororesin (polyvinylidene fluoride, poly Tetrafluoroethylene, etc.), polyamide resins (polyamide 6, polyamide 66, polyamide 12, polyamide MXD6, etc.), ethylene-vinyl alcohol copolymers, polyphenylene sulfide, polyacrylonitrile synthetic resin films are used. The silica vapor deposition film in which the silica vapor deposition layer 5 is formed on the film has extremely low water vapor permeability and oxygen permeability, and has a remarkable effect of blocking the influence of moisture, heat, light and the like on the resistance film 2. Incidentally, the silica vapor deposition film in which the silica vapor deposition layer 5 is formed on the polyvinyl alcohol film having a thickness of 12 μm has a water vapor permeability of 0.1 (g / m ² · day) or less and an oxygen permeability of 0.1 (cc / M ² · day · atm) or less.

  As the adhesive 6, the above-described hot melt adhesive sheet, in particular, an ethylene vinyl acetate copolymer resin-based or polycarbonate ester resin-based hot melt adhesive sheet having heat resistance at 80 ° C. is preferably used. When these hot-melt adhesive sheets are 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 The outer periphery of the melt-type adhesive sheet wraps around the composite laminate so that the periphery of the composite laminate is naturally sealed, and the respective adhesion interfaces of the dielectric layer 1, the composite laminate, and the surface coating layer 4 Therefore, the radio wave absorber B having excellent transparency can be obtained.

  In the composite laminate of the resistance film 2 and the silica vapor deposition film in the radio wave absorber B, the synthetic resin films 8 and 8 of the silica vapor deposition film are in contact with the resistance film 2. , 5 may be a composite laminate in contact with the resistance film 2. However, like the composite laminate of the radio wave absorber B, the synthetic resin films 8 and 8 of the silica vapor deposition film are in contact with the resistance film 2, and the silica vapor deposition layers 5 and 5 are respectively on the dielectric layer 1 side and the surface coating layer 4. It is more effective to block the influence of moisture (outside air containing moisture), heat, light and the like.

  The other components of the radio wave absorber B, materials such as the dielectric layer 1, the resistance film 2, the radio wave reflector 3, the surface coating layer 4, the silica vapor deposition layer 5, and the back surface coating layer 7 are the same as those of the radio wave absorber A described above. Since these are the same as those, description thereof will be omitted.

  Such a radio wave absorber B can be manufactured, for example, by the following method. First, on the opposite surface of the silica vapor deposition film 8 having the silica vapor deposition layer 5 formed on one side, the above-mentioned coating liquid containing ultrafine conductive fibers is applied to form the resistance film 2 having a surface resistivity of 280 to 400Ω / □. At the same time, a composite laminated body is produced by stacking the silica vapor deposition film 8 on which the resistance film is not formed so as to cover the resistance film, and this is cut to be slightly smaller than the dielectric layer 1 and the surface coating layer 4. A composite laminate of area is obtained. And on one side of the dielectric layer 1 made of the synthetic resin plate or the like, the surface made of the adhesive 6 (hot melt type adhesive sheet), the composite laminate, the adhesive 6 and the synthetic resin plate. The coating layer 4 is overlaid, and the radio wave reflector 3, the hot-melt adhesive sheet, and the back coating layer 7 made of a synthetic resin plate are overlaid on the opposite surface of the dielectric layer 1. The laminate is heated while sandwiched between upper and lower gloss plates to soften and melt the hot-melt adhesive sheet, thereby simultaneously bonding and integrating the composite laminate with the adhesive that wraps around the composite laminate. The electromagnetic wave absorber B is manufactured by bonding and sealing the periphery. 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 B as described above has a low water vapor permeability and oxygen permeability of the synthetic resin film 8 (silica vapor deposition film) on which the silica vapor deposition layer 5 is formed on one side, and is excellent in blocking action on moisture, heat, light, and the like. The resistive film 2 is hermetically sealed by an adhesive 6 that seals the periphery of the composite laminate with the silica-deposited film on both sides thereof, and further, the adhesive 6 on both sides of the composite laminate, the dielectric layer 1, Since the surface coating layer 4 is double or triple sealed, the influence of moisture, heat, light, etc. on the resistance film 2 is sufficiently blocked, and the surface resistivity of the resistance film is kept substantially constant.

  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, the composite laminate provided between the dielectric layer 1 and the surface coating layer 4 is different from the composite laminate in the radio wave absorber B described above. That is, the composite laminate in the radio wave absorber C is obtained by laminating other synthetic resin films 9 and 9 with a transparent adhesive on both surfaces of a synthetic resin film 8 (silica vapor deposition film) having a silica vapor deposition layer 5 formed on one side. Then, the resistance film 2 is formed on one synthetic resin film 9 of the laminate, and another laminate is laminated so as to cover the resistance film 2, thereby depositing silica on both sides of the resistance film 2. The layers 5 and 5 are disposed via the synthetic resin films 8 and 9. Then, the transparent composite laminate composed of the resistance film 2 and the two laminates is disposed between the dielectric layer 1 and the surface coating layer 4, and the adhesive 6 is used to bond the dielectric layer 1 and the composite laminate. The surface coating layer 4 is bonded together to seal the periphery and both surfaces of the composite laminate.

  As the other synthetic resin film 9 to be laminated on both sides of the silica vapor-deposited film having the silica vapor-deposited layer 5 formed on one side, a synthetic resin film similar to the synthetic resin film 8 is preferably used. Since the laminated body laminated with a transparent adhesive on both sides of 8 is lower in water vapor permeability and oxygen permeability than the silica vapor deposited film 8, it acts to block the influence of moisture, heat, light, etc. on the resistance film 2. It is prominent and is easy to handle because it has an appropriate thickness.

  In this radio wave absorber C, the composite laminate of the resistance film 2 and the laminate has the synthetic resin films 8 and 8 of the silica vapor deposition film on the resistance film 2 side, and the silica vapor deposition layers 5 and 5 are on the dielectric layer 1 side and the surface. The layers are laminated so as to be on the coating layer 4 side, but conversely, the silica vapor deposition layers 5 and 5 are on the resistance film 2 side, and the synthetic resin films 8 and 8 are on the dielectric layer 1 side and the surface coating layer 4. You may laminate | stack so that it may become a side. However, like this composite laminate of the radio wave absorber C, the composite laminate in which the silica vapor-deposited layers 5 and 5 of the silica vapor-deposited film are laminated so as to be on the dielectric layer 1 side and the surface coating layer 4 side. However, it is more effective in blocking the influence of moisture (outside air containing moisture), heat, light, and the like.

  Other configurations of the radio wave absorber C, the dielectric layer 1, the resistance film 2, the radio wave reflector 3, the surface coating layer 4, the silica vapor deposition layer 5, the adhesive 6, the back surface coating layer 7, the silica vapor deposition film 8, and the like Since the materials are the same as those of the radio wave absorber B described above, the description thereof is omitted.

  Such a radio wave absorber C can be manufactured, for example, by the following method. First, a laminate is prepared by laminating other synthetic resin films 9 and 9 with a transparent adhesive on both sides of a silica vapor-deposited film 8 having a silica vapor-deposited layer 5 formed on one side, and one synthetic resin of this laminate is produced. On the surface of the film 9 (synthetic resin film 9 laminated on the synthetic resin film 8 side of the silica vapor-deposited film), the resistance film 2 is formed by applying a coating liquid containing the above-mentioned ultrafine conductive fibers. Then, a laminated body in which a resistive film is not formed is overlapped so as to cover the resistive film 2 to produce a composite laminated body, which is cut to have a slightly smaller area than the dielectric layer 1 and the surface coating layer 4. A composite laminate is obtained. Next, on one side of the dielectric layer 1 made of a synthetic resin plate or the like, an adhesive 6 [hot melt type adhesive sheet], the above composite laminate, the adhesive 6 and a surface coating layer made of a synthetic resin plate 4, the radio wave reflector 3, the hot-melt adhesive sheet, and the back surface coating layer 7 made of a synthetic resin plate are stacked on the opposite surface of the dielectric layer 1. The laminate is heated while sandwiched between upper and lower gloss plates to soften and melt the hot-melt adhesive sheet, thereby simultaneously bonding and integrating the composite laminate with the adhesive that wraps around the composite laminate. The electromagnetic wave absorber B is manufactured by bonding and sealing the periphery.

  The radio wave absorber C as described above has a water vapor permeability and oxygen of a laminate obtained by laminating other synthetic resin films 9 and 9 on both surfaces of a synthetic resin film 8 (silica vapor deposition film) having a silica vapor deposition layer 5 formed on one side. The permeability is further lower than the water vapor permeability and oxygen permeability of the silica vapor deposited film alone, and the performance of blocking the influence of moisture, heat, light, etc. on the resistance film 2 is excellent. The resistance film 2 in the composite laminate is hermetically sealed with the laminate having the above-described blocking performance disposed on both sides thereof and the adhesive 6 that seals the periphery of the composite laminate. Since the adhesive 6 on both sides of the body, the dielectric layer 1 and the surface coating layer 4 are double and triple sealed, the influence of moisture, heat, light, etc. on the resistance film 2 is more reliably cut off and resistance is increased. The surface resistivity of the film is kept almost constant. In addition, even if cracks or the like occur in the surface coating layer 4 and the outside air containing moisture may invade, the laminate body excellent in blocking performance on both sides of the resistance film 2 Since the outside air is prevented from penetrating to the resistance film 2, durability and reliability are further improved.

  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 composed of a composite laminate (silica vapor deposition layer 5 on one side) having the same shape and size as the dielectric layer 1 and the surface coating layer 4 between the dielectric layer 1 and the surface coating layer 4. A dielectric laminate 1 is formed by forming a resistive film 2 on the opposite surface of the silica vapor-deposited film 8 formed in the above, and providing another composite of the vapor-deposited silica film 8 so as to cover the resistive film 2. The radio wave shown in FIG. 2 described above is that the composite laminate and the surface coating layer 4 are bonded and integrated with the adhesive 6 and that the entire four side surfaces of the radio wave absorber are bonded and sealed with the adhesive 60. It is different from the absorber B. Since this radio wave absorber D is adhesively sealed on the entire four sides with an adhesive 60, 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 flat.

  As the adhesive 60 that covers the entire side surface of the radio wave absorber D, the hot-melt adhesive sheet, the curable adhesive (sealing agent), the resin coating liquid, or the like is 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 D, such as the dielectric layer 1, the composite laminate, the radio wave reflector 3, the surface coating layer 4, the adhesive 6, and the back surface coating layer 7 are the same as those of the radio wave absorber B described above. Therefore, explanation is omitted.

  When the radio wave absorber D having such transparency is manufactured, the dielectric layer 1, the composite laminate, the radio wave reflector 3, the front surface coating layer 4, the back surface coating layer 7, and the adhesion are produced when the above radio wave absorber B is manufactured. After the agent 6 (hot melt type adhesive sheet) is laminated in the same shape and size and integrated by thermocompression bonding to produce the main body portion of the radio wave absorber D, the curable mold is applied to the entire four circumferential side surfaces. The adhesive 60 (sealing agent) or the like is applied and cured, and the entire side surface is adhesively sealed.

  Such a radio wave absorber D also has a low water vapor permeability and oxygen permeability of the synthetic resin film 8 (silica vapor deposition film) on which the silica vapor deposition layer 5 is formed on one side, and has an excellent blocking action against moisture, heat, light, and the like. The resistance film 2 is sealed by the silica vapor deposition film 8 and the adhesive 60 on both sides thereof, and further, double and triple sealed by the adhesive 6, the dielectric layer 1 and the surface coating layer 4 on both sides of the composite laminate. Therefore, the influence of moisture, heat, light, etc. on the resistance film 2 is sufficiently blocked, and the surface resistivity of the resistance film is kept substantially constant. Then, the adhesive 6 brings the respective interfaces of the dielectric layer 1, the composite laminate, and the surface coating layer 4 into close contact with each other, thereby reducing light scattering, and thus has an advantage of improving transparency and light transmittance. In addition, since the radio wave reflector 3 and the back surface coating layer 7 are bonded and integrated with the side surface adhesive 60, it is not necessary to bond them with a hot-melt adhesive sheet or the like, and the manufacturing becomes easy.

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

  This radio wave absorber E omits the surface coating layer and the back surface coating layer, and is a composite laminate (resistive film 2 on the opposite surface of the silica deposited film 8 having the silica deposited layer 5 formed on one side) that is slightly smaller than the dielectric layer 1. Is formed on one side (surface) of the dielectric layer 1 and on the opposite side of the dielectric layer 1 so as to cover the resistance film 2. A radio wave reflector 3 is provided, and the surface and periphery of the composite laminate are covered and sealed with an adhesive 6.

  The other components of the radio wave absorber E, the dielectric layer 1, the resistance film 2, the radio wave reflector 3, the silica vapor deposition layer 5, the adhesive 6, and the silica vapor deposition film 8 are the same as those of the radio wave absorber B. Therefore, the description is omitted.

  Such a radio wave absorber E also has a low water vapor permeability and oxygen permeability of the synthetic resin film 8 (silica vapor deposition film) on which the silica vapor deposition layer 5 is formed on one side, and is excellent in blocking action on moisture, heat, light, and the like. Since the resistance film 2 is sealed by the silica vapor deposition film 8 on both sides and the surrounding adhesive 6 and double sealed by the adhesive 6 and the dielectric layer 1 on the surface of the composite laminate, the resistance film The influence of moisture, heat, light, etc. on 2 is sufficiently blocked, and the surface resistivity of the resistance film 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. 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 composed of a composite laminate (the other layer of silica deposited so that the resistive film 2 is formed on the opposite surface of the silica deposited film 8 having the silica deposited layer 5 formed on one side, and the resistive film 2 is covered). As shown in FIG. 4, the air layer 10 is formed between the composite laminate including the film 8 and the surface coating layer 4, and the composite laminate and the surface coating layer 4 are not bonded with an adhesive. Different from the radio wave absorber D. The air layer 10 is formed by spacers 11 provided on the outer peripheral portions of the composite laminate and the surface coating layer 4. This spacer 11 is provided with a belt-like hot melt adhesive sheet having a large thickness, thickly applied with the curable adhesive (sealing agent) or the resin coating liquid described above, or other members such as a belt-like synthetic resin. It is provided by arranging sheets and plates. The air layer 10 may be formed between the dielectric layer 1 and the composite laminate.

  Other configurations of the radio wave absorber F, the dielectric layer 1, the resistance film 2, the radio wave reflector 3, the surface coating layer 4, the silica vapor deposition layer 5, the adhesives 6 and 60, the back surface coating layer 7, and the silica vapor deposition film 8 Since the materials and the like are the same as those of the above-described radio wave absorber D, the description thereof is omitted.

  In such a wave absorber F, when the wave absorber D shown in FIG. 4 is manufactured, a spacer 11 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.

  Such a radio wave absorber F has a low water vapor permeability and oxygen permeability of the synthetic resin film 8 (silica vapor deposition film) having the silica vapor deposition layer 5 formed on one side, and is excellent in blocking action on moisture, heat, light, and the like. In addition, since the resistance film 2 is sealed by the silica vapor deposition film 8 on both sides thereof and the surrounding adhesive 6, moisture contained in the air layer 10 passes through the silica vapor deposition film 8 and comes into contact with the resistance film 2. In addition, since the silica vapor deposition layer 5 sufficiently blocks the influence of heat, light, etc. on the resistance film 2, the surface resistivity of the resistance film 2 is kept substantially constant. The air layer 10 may be provided with a desiccant or the like to remove moisture.

  FIG. 7 is a cross-sectional view of a radio wave absorber according to still another embodiment of the present invention.

  This radio wave absorber G is composed of an adhesive 6 (hot melt type adhesive sheet) and a composite laminate (silica vapor deposition film 5 having a silica vapor deposition layer 5 formed on one side) on one side (front side) of the dielectric layer 1. A composite laminate in which a resistive film 2 is formed on the opposite surface and another silica vapor deposition film 8 is stacked so as to cover the resistive film 2), the adhesive 6, another dielectric layer 12, The adhesive 6, the composite laminate, the adhesive 6, and the surface coating layer 4 are stacked in this order, and the radio wave reflector 3 and the back surface coating are provided on the opposite surface side (back surface side) of the dielectric layer 1. The layers 7 are stacked and bonded and integrated, and the entire four-circumferential side surfaces of the radio wave absorber are bonded and sealed with an adhesive 60.

  The radio wave absorber G 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 12 interposed therebetween. The dielectric layer 12 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 surface coating layer 4, the silica vapor deposition layer 5, the adhesive 6, 60, the back surface coating layer 7, and the silica vapor deposition film 8 constituting the radio wave absorber G are Since it is the same as what was used by each electromagnetic wave absorber, description is abbreviate | omitted.

  In place of the dielectric layer 12, an air layer may be formed by sandwiching a spacer between two composite laminates. In some cases, the dielectric layer 12 or the air layer is sandwiched. Three or more composite laminates may be provided. Similarly, in the radio wave absorbers B, C, D, E, and F, a plurality of composite laminates may be provided with an air layer or another dielectric layer interposed therebetween.

  In such a radio wave absorber G, the resistance film 2 of each composite laminate is sealed by the silica vapor deposition film 8 on both sides and the adhesive 60 covering the side surfaces, so that moisture, heat, The influence of light or the like is blocked, the surface resistivity of the resistance film 2 is kept almost constant, and the initial radio wave absorption performance is maintained, so that durability and reliability are improved. In addition, if there are two resistance films 2 and 2 as in the case of the radio wave absorber G, a problem occurs in one resistance film 2 during long-term use, and the surface resistivity exceeds 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 be expanded. Since this radio wave absorber G 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.

  When the thickness of the dielectric layer 12 is 6.5 mm, the radio wave absorption performance at 15 ° incidence is good, and when the thickness of the dielectric layer 12 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 12 as described above.

  FIG. 8 is a cross-sectional view of a radio wave absorber according to still another embodiment of the present invention.

  This radio wave absorber H is provided with dielectric layers 1, 1 on both sides of the radio wave reflector 3, and an adhesive 6 (hot melt adhesive) is provided on the opposite side of the dielectric layers 1, 1 to the radio wave reflector 2. Sheet) and the composite laminate (silica vapor deposition layer 5 formed on one side thereof, the resistance film 2 is formed on the opposite side of the silica vapor deposition film 8, and another silica vapor deposition film 8 is formed so as to cover the resistance film 2. The laminated composite laminate), the adhesive 6 and the surface coating layer 4 are overlapped and bonded and integrated, and the entire four side surfaces thereof are bonded to the adhesive 60 [curing adhesive (sealing agent) or resin coating. Liquid].

  In the radio wave absorber H and the radio wave absorber G, the dielectric layer 1 (12), the composite laminate, and the surface coating layer 4 are bonded to each other by an adhesive 6 (hot melt type adhesive sheet). You may adhere | attach only an outer peripheral part. Further, in this radio wave absorber H and the radio wave absorber G, 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 silica vapor deposition layer 5, the adhesives 6, 60, and the silica vapor deposition film 8 constituting the radio wave absorber H are the above-mentioned radio wave absorbers. The description is omitted because it is the same as that used in the above.

  In such a radio wave absorber H, the resistance film 2 of the composite laminate is sealed with the silica vapor deposition films 8 and 8 on both sides and the adhesive 60 covering the side surfaces. The influence of light or the like is blocked, and the surface resistivity of the resistance film 2 is kept substantially 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. In addition, since the radio wave absorber H has 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 any of the above radio wave absorbers A to H, no electrode is attached to the resistance film 2, but an electrode made of a strip-like 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 H, and a radio wave absorbing 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, on the surface of the laminate, the above-mentioned coating solution is applied and dried so that the basis weight of the single-walled carbon nanotube is about 27 mg / m ^2, and a transparent resistive film having a surface resistivity of 300Ω / □ is formed. At the same time, the above laminate having no resistive film was overlapped so as to cover the resistive film, thereby preparing a composite laminate. And this composite laminated body is cut | disconnected to the magnitude | size of 70x70 mm, and the electrode (width 5mm, length 100mm) which consists of a pair of strip | belt-shaped copper foil along two opposing sides is resistance film with a conductive adhesive. And the four corners were adhered to produce a 70 × 70 mm composite laminate with electrodes.

  As shown in FIGS. 11A and 11B, 80 mm square hot made of EVA (ethylene-vinyl acetate copolymer resin) as an 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 resistive film was examined in the same manner as 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 results are 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. 12, the resistance film of the comparative test specimen gradually increased in surface resistivity with the passage of days, and increased by 17% (51Ω / □) 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, like this test body, the resistance film of the composite laminate is sandwiched between laminates obtained by laminating a PET film on both sides of a silica-deposited PVA film, and the upper and lower surfaces and the outer periphery of the composite laminate are hot melt type. What is adhesively sealed with an adhesive sheet, the surface resistivity of the resistance film is decreased by -1% (-3Ω / □) even after the number of days, and the change is extremely small and substantially constant. It was found that the change (increase / decrease) in the surface resistivity of the resistive film was reliably prevented by the laminate in which the PET film was laminated on both sides of the PVA film. 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. 13, 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 laminates obtained by laminating a PET film on both sides of a silica-deposited PVA film, and the upper and lower surfaces and the outer periphery of the composite laminate are hot melt type. In the case where the adhesive sheet is bonded and sealed, the surface resistivity is extremely small and constant without increasing / decreasing 0% (0Ω / □) even if the number of days passes. It was found that this was definitely prevented. 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. 14, the resistance film of the test specimen for comparison gradually increases with the passage of days, and 18.5% (55.5 Ω / □) 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 laminates obtained by laminating a PET film on both sides of a silica-deposited PVA film, and the upper and lower surfaces and the outer periphery of the composite laminate are hot melt type. Even if 130 days have passed after the start of outdoor exposure (March 22, 2006), the surface resistivity of the resistive film is 7.7% (23. 23%). 1Ω / □) Only increases and there is little change. Therefore, in the case of the radio wave absorber using this composite laminate, it becomes 323Ω / □ after 130 days, and maintains a useful range as the radio wave absorber. It was found that (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 laminates of the PET film laminated on both sides of the silica-deposited PVA film, the increase will be 23% (69Ω / □) after 20 days of outdoor exposure, and the increase will continue to be maximum in 20 days. 6 Ω / □ or more, 0.3 Ω / □ in one day, and 109.5 Ω / □ in one year, and such a wave absorber should exhibit long-term wave absorption performance when used externally under sunlight. It's obvious that you can't.

  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 according to the present invention has the effect of absorbing the radio wave due to the change in the surface resistivity of the resistive film by blocking the influence of moisture, heat, light, etc. on the resistive film by the film on which the silica deposited layer is formed. It is proved that the deterioration of the performance is prevented and 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. 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) 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 2a Carbon nanotube 2b Binder 3 Radio wave reflector 4 Surface coating layer 5 Silica vapor deposition layer 6,60 Adhesive 7 Back surface coating layer 8 Synthetic resin film (silica vapor deposition film)
9 Other synthetic resin films to be laminated 10 Air layer 20 Composite laminate 30 Electrode A, B, C, D, E, F, G, H Wave absorber

Claims (17)

  A radio wave absorber having a resistive film on one side of the dielectric layer and a radio wave reflector on the opposite side of the dielectric layer, wherein a silica vapor deposition layer is disposed on both sides of the resistive film. Radio wave absorber.   A silica vapor deposition layer is formed on the opposing surface of the dielectric layer and the surface coating layer provided on one side of the dielectric layer, arranged on both sides of the resistance film, and the periphery of the resistance film is sealed with an adhesive. The radio wave absorber according to claim 1.   A synthetic resin film having a silica vapor deposition layer formed on one side is laminated on both sides of the resistance film, and the silica vapor deposition layer is arranged on both sides of the resistance film, and the periphery of the composite laminate, or the periphery and both sides, or the periphery. The radio wave absorber according to claim 1, wherein one side is sealed with an adhesive.   This composite laminate is obtained by laminating a synthetic resin film with a silica vapor deposition layer on one side and laminating another synthetic resin film on both sides of the resistance film, and placing the silica vapor deposition layer on both sides of the resistance film. 2. The radio wave absorber according to claim 1, wherein the periphery, or both sides and both sides, or the periphery and one side are sealed with an adhesive.   A synthetic resin film with a silica vapor deposition layer formed on one side is made of polyvinyl alcohol, polyethylene terephthalate, ultra-low density polyethylene, polyvinyl chloride, polyvinylidene chloride, fluorine resin, polyamide resin, ethylene-vinyl alcohol copolymer, polyphenylene sulfide. 5. The radio wave absorber according to claim 3, wherein the electromagnetic wave absorber is a synthetic resin film of any one of polyacrylonitrile.   Other synthetic resin films are polyvinyl alcohol, polyethylene terephthalate, ultra low density polyethylene, polyvinyl chloride, polyvinylidene chloride, fluorine resin, polyamide resin, ethylene-vinyl alcohol copolymer, polyphenylene sulfide, polyacrylonitrile. The radio wave absorber according to claim 4, wherein the radio wave absorber is a synthetic resin film.   7. The radio wave absorption according to claim 3, 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. body.   The radio wave absorber according to claim 7, wherein a plurality of composite laminates are provided so as to overlap each other between the dielectric layer and the surface coating layer.   9. The radio wave absorber according to claim 8, wherein an air layer or another dielectric layer is formed between the plurality of composite laminates.   8. The radio wave absorber according to claim 7, wherein an air layer or another dielectric layer is formed between the composite laminate and the surface coating layer.   7. The radio wave absorber according to claim 3, wherein a composite laminate is provided on each side of the dielectric layer provided on both sides of the radio wave reflector, opposite to the radio wave reflector. .   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 7 to 10, 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 13, wherein an electrode is attached to the resistance film.   The radio wave absorber according to any one of claims 1 to 14, wherein the four side surfaces are sealed with an adhesive.   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. Item 16. The radio wave absorber according to Item 15.   The radio wave absorber according to any one of claims 1 to 16, wherein each constituent member has transparency.

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