JP2008182045A - Radio wave absorber and ITS / DSRC facility - Google Patents

Abstract

An object of the present invention is to provide a radio wave absorber excellent in durability and inexpensive, and an ETC facility using the radio wave absorber.
A radio wave absorber according to the present invention is a laminated glass formed by sandwiching an intermediate film made of PVB or EVA between two glass plates 16, 18. A conductive film 20 having a predetermined resistance value is formed on the contact surface, and a conductive film 22 having a predetermined resistance value is formed on the contact surface of the glass plate 18 with the intermediate film 14. The conductive films 20 and 22 are transparent tin oxide (SnO ₂ ), and are coated on the glass surface by a CVD method.
[Selection] Figure 1

Description

  The present invention relates to a radio wave absorber and an ETC system, and particularly to a radio wave absorber excellent in durability and an ITS / DSRC facility in which the radio wave absorber is installed.

  In ITS (Intelligent Transport Systems), services that perform wireless communication between roadside devices (wireless devices installed on the roadside) and onboard devices (wireless devices mounted on vehicles) have been put into practical use. . This technology is called DSRC (Dedicated Short Range Communication). As an example of ITS / DSRC facilities, there is ETC (Electronic Toll Collection) on the popular highway, which is used in a non-stop automatic toll payment system. ing.

  In the future, DSRC is expected to be used in various information service fields such as logistics information in addition to the application of DSRC such as toll parking lots, gas stations and fast food stores in urban areas.

  DSRC uses radio waves of 5.8 GHz, but for the purpose of reducing malfunction of equipment due to unnecessary radio waves caused by irregular reflection of radio waves, a radio wave absorber for absorbing unnecessary radio waves is installed around the system. Yes.

  Taking the ETC on the highway as an example, the installation location is the lower part of the canopy of the toll gate, the lower part of the roadside antenna structure (often attached to a structure called a gantry), the transparent partition of the toll gate island, And road pavement. For example, carbon-added foamed polyethylene-based radio wave absorbers are used in the lower part of the canopy and the roadside antenna structure. In addition, for example, a polycarbonate (PC) plate material is used for the partition walls of the charge island. A wave absorber with a sandwiched structure is used. This island partition is required to be transparent in consideration of safety. Furthermore, for example, a pavement material mixed with a magnetic material is used for road pavement.

  By the way, Patent Document 1 discloses a radio wave absorber including a transparent plate-like dielectric made of PC and a resistance film formed on one surface of the dielectric. In this radio wave absorber, the amount of electromagnetic wave absorption is determined by using the impedance on the incident side when an electromagnetic wave is incident from the surface on which the dielectric resistive film is not formed, and the electromagnetic wave absorption amount is 10 dB or more. The thickness and the sheet resistance of the resistance film are determined.

  In addition, the radio wave absorber disclosed in Patent Document 2 has a resistance film formed on the opposite side of a radio wave incident surface of a single glass plate or laminated glass that is a transparent dielectric material, and electromagnetic waves are incident from the surface of the dielectric material. The thickness of the dielectric is determined such that the electromagnetic wave absorption obtained using the impedance on the incident side is 10 dB or more.

Further, Patent Document 3 discloses a transparent radio wave absorber formed by laminating a plurality of resin plates such as PC and acrylic resin (AC). The radio wave absorber includes a first transparent resin layer, a resistance film layer, a second transparent resin layer, and a conductive film layer from the surface side which is a radio wave incident surface, and further, a first transparent resin is provided on the back surface side of the conductive film layer. A third transparent resin layer having a thickness different from the thickness of the layer is provided.
JP 2006-135031 A JP 2006-186725 A JP 2005-86022 A

  However, as a transparent shielding / absorbing material used for the partition of the charge island, those using PC as in Patent Documents 1 and 3 have a high impact property but a weak scratch property. Also, PC has a large coefficient of thermal expansion, and it deforms when the temperature difference between the front and back surfaces is large due to solar radiation, etc., and the conductive film layer or PC / adhesive layer on the PC peels off due to expansion / contraction due to temperature change It may occur. Even if the surface of the PC plate is subjected to a weather-resistant coating treatment or the like, there is a risk of peeling when pebbles or the like collide, and there is a problem that it is difficult to maintain transparency for a long period of time. Furthermore, when the radio wave absorber is self-supporting, the distortion is large, and the reflected image when the headlamp is irradiated particularly at night may give the driver an unpleasant feeling.

  On the other hand, foamed polyethylene-based radio wave absorbers used in the lower part of the canopy and the roadside antenna structure are inferior in weather resistance and absorbable water, so they are protected by a resin cover material such as PC. Often. However, this radio wave absorber cannot completely avoid the intrusion of moisture. The penetration of water into the radio wave absorber and the peeling off of the electromagnetic wave reflector (the electromagnetic wave reflector is also composed of a conductive film. In particular, in the case of a film, it is also referred to as an electromagnetic wave reflective film) cause a significant decrease in radio wave absorption performance. It was.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a radio wave absorber excellent in durability and inexpensive, and an ETC system using the radio wave absorber.

  In order to achieve the above object, the invention according to claim 1 includes, from the electromagnetic wave incident surface side, a glass with a conductive film, a resin sheet having a lower dielectric constant than the glass, and a glass with a conductive film in this order. The conductive film is an electromagnetic wave absorber disposed so as to face the resin sheet, and the sheet resistance value of the conductive film on the electromagnetic wave incident surface side is larger than the sheet resistance value of the other conductive film, The electromagnetic waves are transmitted through the conductive film on the electromagnetic wave incident surface side, reflected by the other conductive film, and canceled by the reflected electromagnetic waves. Each of the conductive films has transparency, and Sn. It is characterized by being a film mainly composed of one or more metal oxides selected from the group consisting of In and Zn.

  The invention according to claim 2 is characterized in that, in claim 1, the resin sheet is EVA or PVB.

  Here, EVA is an ethylene vinyl acetate resin, and PVB is polyvinyl butyral.

According to a third aspect of the present invention, in any one of the first or second aspects, the conductive film is a film mainly composed of tin oxide coated by CVD.
Here, CVD is a chemical vapor deposition (chemical vapor deposition) method.

  A fourth aspect of the present invention is the method according to the first, second, or third aspect, wherein the surface of the glass opposite to the conductive film of the conductive film-containing glass on the electromagnetic wave incident surface side is subjected to water repellency or hydrophilic treatment. It is characterized by being.

  The invention of the ITS / DSRC facility according to claim 5 is characterized in that the electromagnetic wave absorber according to any one of claims 1, 2, 3, or 4 is installed between adjacent ITS / DSRC facilities. Yes.

  According to the radio wave absorber according to claim 1, a laminated glass having a long-term use record in the construction field is a basic configuration, and a conductive film that transmits electromagnetic waves and an electromagnetic wave are reflected on the intermediate film side of the laminated glass. Since there is a conductive film, it does not come into direct contact with moisture such as rain and is not easily affected by water. In this configuration, the resin sheet itself may be used as the intermediate film, or the resin sheet and the intermediate film may be different. In addition, since the glass itself as the base material does not absorb moisture, the conductive film and moisture do not come into contact with each other through the glass and are hardly affected by water. Further, the glass itself has an expansion coefficient lower than that of PC and the like, and is excellent in durability since the expansion and contraction of the glass due to temperature change is small and the possibility of peeling of the conductive film is very small. Further, since it is made into laminated glass, it is stronger than a single glass (one glass), has less expansion and contraction, and can reduce the possibility of peeling of the conductive film. Further, unlike the prior art, a protective cover material is not required, and the conductive film is mainly composed of one or more metal oxides selected from the group consisting of Sn, In and Zn having transparency. Compared to the conductive film, the scratch resistance is strong and the durability is excellent.

  According to the radio wave absorber according to claim 2, since the resin sheet is EVA or PVB, the interlayer film for laminated glass can be used as it is.

  According to the radio wave absorber according to the third aspect, since tin oxide having transparency is used as the conductive film and this is coated on the glass by the CVD method, the structure is inexpensive.

  According to the radio wave absorber according to claim 4, since the glass surface opposite to the conductive film of the glass with the conductive film on the electromagnetic wave incident surface side is subjected to water repellency or hydrophilic treatment, Excellent. Because it is excellent in transparency, it is excellent in safety because it is easy to check the field of view through the radio wave absorber on rainy days. In addition, since there are many types of water-repellent or hydrophilic treatment methods in which a raw material liquid such as a water-repellent liquid or a hydrophilic liquid is applied to the surface of a substrate and heated and fired to create a water-repellent film or a hydrophilic film When a glass substrate is used, conditions for heating and baking can be set wider than when a PC substrate or the like is used, the selection range of raw material liquids is increased, and manufacturing is simple and low cost can be expected.

  According to the ITS / DSRC facility according to claim 5, when the ETC system which is an example of the ITS / DSRC facility is taken as an example of the radio wave absorber of the present invention, the lower portion of the canopy of the ETC peripheral facility, the lower portion of the roadside antenna structure, When applied to a partition wall of a toll gate island, the radio wave absorber itself is opaque in the prior art. However, the radio wave absorber of the present invention is laminated glass, and thus has translucency and transparency. Therefore, according to the ETC facility where the radio wave absorber is installed, the toll gate can be a bright and releasable space. Furthermore, since it is comprised with the glass which is a nonflammable material, it has nonflammability and is rich in safety compared with the conventional facility.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments will be described below by taking ETC as an example of a radio wave absorber and ITS / DSRC facility according to the present invention according to the attached drawings.

  FIG. 1 is a cross-sectional view of a radio wave absorber 10 according to an embodiment, and FIG. 2 shows an outline of an ETC facility. A radio wave absorber 10 and a roadside antenna structure (gantry) 12 have radio waves Absorber 10 is installed. The ETC facility where the radio wave absorber 10 is installed is not limited to the lower part of the roadside antenna structure 12 and the canopy 13 and can be installed in an ETC facility such as a transparent partition wall of a toll gate island.

  As shown in FIG. 1, the radio wave absorber 10 is a laminated glass configured by sandwiching an intermediate film 14, which is a resin sheet made of PVB or EVA, between two glass plates 16 and 18. Here, the glass plate 16 is a glass plate on the electromagnetic wave incident side, and a conductive film (conductive film on the electromagnetic wave incident surface side) 20 having a predetermined resistance value is formed on the contact surface of the glass plate 16 with the intermediate film 14, and the glass plate 16 is made of glass. A conductive film (the other conductive film) 22 having a predetermined resistance value is formed on the contact surface of the plate 18 with the intermediate film 14.

  The sheet resistance value of the conductive film 20 is set to be larger than the sheet resistance value of the conductive film 22 so that the electromagnetic waves to be absorbed are transmitted through the conductive film 20, reflected by the conductive film 22, and canceled by the reflected electromagnetic waves. It is configured.

These conductive films 20 and 22 have transparency and are composed mainly of one or more metal oxides selected from the group consisting of Sn, In, and Zn. For example, F-doped SnO ₂ (here, (Also simply referred to as tin oxide), antimony-doped SnO ₂ , Sn-doped In ₂ O ₃ (ITO), aluminum-doped ZnO, gallium-doped ZnO, and the like. In the embodiment, transparent tin oxide (SnO ₂ ) is coated on the glass surface by a CVD method.

  In the method of manufacturing the radio wave absorber 10 according to the embodiment, the intermediate film 14 is sandwiched between the two glass plates 16 and 18 in which the tin oxide conductive films 20 and 22 are coated by the CVD method, and this is performed in a predetermined manner by an autoclave. It is manufactured by heating to a temperature and pressing at a predetermined pressure. This manufacturing method is basically the same as the manufacturing method of laminated glass.

  As the glass plates 16 and 18 of laminated glass, float glass used for ordinary construction is desirable. Higher visible transmittance is generally better, but when used as a canopy material (currently a wave absorber is attached to the bottom of the canopy, but the canopy itself is a wave absorber), etc. It is preferable to use a material that can be colored without greatly affecting the electromagnetic properties of the glass, such as heat-absorbing glass.

  As the intermediate film 14 which is a resin sheet, a PVB, EVA film or the like used for laminated glass for construction is used. When the glass edge is exposed, it is suitable to use an EVA film with little influence of water.

  The advantages of the radio wave absorber 10 of the embodiment are listed below.

[Regarding that the surface is glass]
・ It is hard to be charged and there is little contamination by charged objects.
・ Strong durability against ultraviolet rays compared to resin.
・ It is hard to burn.

[Regarding the formation of tin oxide by CVD using tin oxide for the conductive film]
・ Durable. As the conductive film 22, silver having a low resistance value is more desirable. However, when the silver film is glass-coated to form laminated glass, the film may be deteriorated unless attention is paid to moisture intrusion from the edge.
・ It is hard to be damaged. In manufacturing, there is a process of cleaning the glass with film, but the silver film cannot be used because it is easily damaged by the cleaning brush.

It is generally difficult to form a low resistance tin oxide film on PET, but glass can be easily coated by CVD.
-Compared to the conductive film made of ITO film, tin oxide has lower raw material cost. In the case of an ITO film, a sputtering method is usually required to form a film having a resistance value required in the present invention. The CDV method can be formed at a lower cost than the sputtering method.
・ Especially when forming a thin film of tin oxide by CVD, the raw materials include tin tetrachloride, dimethyltin dichloride, dibutyltin dichloride, tetramethyltin, tetrabutyltin, dioctyltin dichloride, monobutyltin trichloride, dibutyltin diacetate, etc. Can be illustrated. Further, when forming a thin film containing tin oxide as a main component, it is preferable to add an antimony or fluorine compound to the raw material in order to improve the conductivity. Examples of antimony compounds include antimony trichloride and antimony pentachloride. Examples of the fluorine compound include hydrogen fluoride, trifluoroacetic acid, bromotrifluoromethane, and chlorodifluoromethane. Fluorine doped in tin oxide serves as a charge carrier in the tin oxide thin film, and moves charge while substituting for oxygen in tin oxide.

[Regarding forming a conductive film directly on glass]
It has a simple three-layer structure (glass with conductive film-PVB-glass with conductive film) and is easy to manufacture.
-It is advantageous in terms of manufacturing cost, has few interfaces, and is advantageous in terms of durability.

  On the other hand, the electromagnetic wave absorber disclosed in Patent Document 3 has a complicated 9-layer structure (PC-adhesive layer-PET with film (polyethylene terephthalate resin) -adhesive layer-PC-adhesive layer-PET with film-adhesive layer- PC) and PET with a film is very expensive.

[Regarding being laminated glass]
-It has been proven to have a long-lasting construction for construction, and is highly durable. In the cycle test at -20 ° C to 80 ° C, the possibility of causing interfacial foaming and peeling is very small.
Even when it is cracked, the broken pieces are adhered to the intermediate film 14, so that the broken pieces are rarely chipped off.

[Regarding the use of PVB (EVA) for glass and glass interlayer]
-As a configuration, it is desirable to sandwich a low dielectric constant material between glasses. Although it is conceivable to use a plate-like body such as a PC, since it is necessary to separately bond the plate-like body and glass, the adhesive layer and the low-dielectric material have two functions with one material as in the present invention. In order to express, the structure becomes simple and the manufacture is easy.
-In the case of a small lot, it is difficult to produce a PC having a specific thickness at low cost, but PVB has various thicknesses, and the thickness can be easily set by stacking a plurality of films. They simply overlap and do not complicate the process.

[Comparison with prior art]
The difference between the radio wave absorber 10 of the embodiment and Patent Literature 1 and Patent Literature 2 will be described as an example.

  Table 1 shows the configuration of the radio wave absorber.

  Here, the resistance film refers to the conductive film 20, and the electromagnetic wave reflection film refers to the conductive film 22.

The resistance film and the electromagnetic wave reflection film of Comparative Examples 4 and 5 are configured as PET films. Therefore, in Comparative Examples 4 and 5, an acrylic adhesive was used for adhesion between the PC and PET films.
The radio wave absorber was evaluated by the following two methods.

<Electromagnetic wave evaluation 1: Surface reflection performance>
In the vicinity of the ETC, electromagnetic waves of 5.8 GHz transmitted from the antenna may cause abnormal communication as a result of multiple reflections with the road surface, structure, and vehicle, so the road surface and structure are reflected by the radio wave absorber. Measures are taken to prevent waves.

  In the electromagnetic wave evaluation 1, the surface reflection characteristics of comparative examples and examples were evaluated based on the transmission line theory “Osamu Hashimoto, Introduction to Radio Wave Absorber, Morikita Publishing, 1997”. This evaluates the effect of the absorber on reflection reduction within a specific ETC lane. In ETC, circular polarization is used. Specifically, the evaluation was performed as follows.

  A circularly polarized wave (incident wave) can be expressed as a combination of orthogonal linearly polarized waves that are 90 degrees out of phase. (Right circular polarization)

Now, the reflection coefficients of the TM wave and the TE wave are Γ _x and Γ _y , respectively, and are written as follows.

  Then, the circularly reflected wave can be expressed by the following equation.

  In Equation 3, the first term indicates left-handed circular polarization, and the second term indicates right-handed circular polarization.

When considering an ETC antenna system, the first term Γ ^e may be used as a reflection coefficient.

  Therefore, the reflection coefficient at ETC is given by Equation 3,

Thus, Γ _x and Γ _y are obtained from the transmission line theory.

  The reflection attenuation amount of TYPE-B described in the same document (20 dB or more when the incident angle θ is in the range of 0 ° to 47.5 °) was evaluated as having no influence of electromagnetic waves.

  Return loss RL is

(Unit dB).

  The larger this value, the smaller the amount of reflection. When this value is 0 dB, complete reflection is indicated.

  In general, this return loss is often referred to as radio wave absorption.

<Electromagnetic wave evaluation 2: shielding performance>
If nothing is present on the back surface, the radio wave absorber may be evaluated only by the reflection attenuation amount (electromagnetic wave evaluation 1) on the front surface. However, in general, there is often some structure on the back surface of the radio wave absorber, and it is necessary to consider a reflected wave that is transmitted through the electromagnetic wave absorber and reflected from the structure. That is, when a material having a low electromagnetic shielding performance (high transmission performance) is used for the partition walls of the ETC lane, the electromagnetic waves are transmitted through the material, reflected to a vehicle or the like traveling in an adjacent lane, and transmitted through the material again. Incident into the lane and electromagnetic crosstalk occurs. Further, when the ETC lanes are adjacent to each other, the electromagnetic waves of one ETC lane may pass through the material and enter the vehicle-mounted device of the vehicle passing through the other ETC lane.

  Therefore, the radio wave absorber is also required to have shielding performance.

  The electromagnetic wave evaluation 2 is an evaluation of the electromagnetic wave evaluation 1 in a state in which a metal reflector is attached to the back surface of the radio wave absorber. The reflected wave from the radio wave absorber, the wave that passes through the radio wave absorber, and is reflected by the metal reflector Measure the interaction of electromagnetic waves. When the shielding performance of the electromagnetic wave absorber is large, the difference between the results of the electromagnetic wave evaluation 1 and the electromagnetic wave evaluation 2 is small. On the other hand, when the shielding performance is small, the influence of the metal reflector attached to the back surface appears strongly, and the return loss RL obtained in the electromagnetic wave evaluation 2 becomes a small value (close to complete reflection) as 0 dB.

  In the electromagnetic wave evaluation 2 as well, it is evaluated that there is no influence of the electromagnetic wave when the reflection attenuation amount (incident angle θ is in the range of 0 ° to 47.5 °) is 20 dB or more.

(Example)
Electromagnetic wave evaluation 1 and electromagnetic wave evaluation 2 were performed on the electromagnetic wave absorber of the example by changing the incident angle of an electromagnetic wave of 5.8 GHz. The results are shown in FIG. The vertical axis represents the return loss (radio wave absorption). When compared at an incident angle of 0 degree, the electromagnetic wave evaluation 1 is 24 dB, and the electromagnetic wave evaluation 2 is 22 dB. Both the electromagnetic wave evaluations 1 and 2 satisfy 20 dB or more when the incident angle θ is in the range of 0 ° to 47.5 °, which indicates that there is no influence of the electromagnetic wave in the specific lane and the lane adjacent to the specific lane. Moreover, even if it installs in a metallic structure, an Example has shown that it can receive the performance as an absorber, without being influenced by it. In addition, evaluation 1 and evaluation 2 described in FIGS. 3, 4, 5, and 6 represent electromagnetic wave evaluation 1 and electromagnetic wave evaluation 2.

(In the case of Comparative Examples 1 and 2)
Comparative examples 1 and 2 were also evaluated in the same manner as the examples. The results are shown in FIG.

  Comparative Example 2 has a small performance of about 15 dB even in the electromagnetic wave evaluation 1, and is difficult to use for the ETC system. In Comparative Example 1, the incident angle θ in the electromagnetic wave evaluation 1 is in the range of 0 ° to 47.5 ° and satisfies 20 dB or more. However, in the electromagnetic wave evaluation 2, both are substantially 0 dB in the electromagnetic wave evaluation 2 (Comparative Example 2). In the electromagnetic wave evaluation 2, the graphs do not appear to overlap, but are approximately 0 dB). That is, Comparative Example 1 can be expected to be effective only in a specific ETC lane, but in an adjacent ETC lane, electromagnetic waves emitted from the specific ETC lane are transmitted through the radio wave absorber and affected. . Further, when there is a large reflection behind the comparative example 1, such as a metal structure, it is strongly affected, so that it is difficult to use in the special ETC lane.

(In the case of Comparative Example 3)
Comparative Example 3 was also evaluated in the same manner as the Example. The results are shown in FIG.

Comparative Example 3 is a single glass, but in electromagnetic wave evaluation 1, it has good performance at an incident angle of 0 degree, but in electromagnetic wave evaluation 2, it is almost 0 dB at the measured angle, and it is affected by the adjacent ETC lane. Indicates. In addition, here, there is no resistance film, but a glass plate with a film having a very large resistance value such as a resistance value of 10 ⁵ Ω / □ described in Patent Document 2 shows similar results. I can think of it.

(Comparative examples 4 and 5)
Similarly, Comparative Examples 4 and 5 were also evaluated. The results are shown in FIG.
Comparative Example 4 is a PC laminated material described in Patent Document 3 (corresponding to the examples in Table 1 of Patent Document 3). The values of the electromagnetic wave evaluation 1 and the electromagnetic wave evaluation 2 are almost the same, the incident angle θ is 20 dB or more in the range of 0 ° to 47.5 °, and only the electromagnetic wave evaluation is similar to the invention of the present application. It is not suitable for an electromagnetic wave absorber for ECT.

  Further, comparing the configurations of the example and the comparative example 4, the relative dielectric constant of the glass is ε = 7−j0.1, while the dielectric constant of PC is as large as ε = 2.75−j0.01. Since the wavelength of the radio wave propagating through the medium having a high dielectric constant is compressed, the embodiment can be made an absorber thinner than the comparative example 4, and more as a partition wall installed on a narrow ETC island. This is a preferred form. Further, if a PC material having the same thickness as that of the example is referred to as Comparative Example 5, in Comparative Example 5, the electromagnetic wave absorption characteristics are not matched, and reflection on the surface becomes large. Becomes smaller.

  A thin radio wave absorber using glass, which is an essential component of the present invention, is also desirable in that it is less likely to be restricted in terms of installation.

  The measurement result of an Example and Comparative Examples 1-5 and the durability comprehensive evaluation mentioned later are shown.

  -Indicates that evaluation is not performed.

  Comparative Examples 1 and 2 described in Table 2 are the configurations of Table 3 described in Patent Document 1, and Comparative Example 3 is the configuration of Patent Document 2. The configurations of Patent Documents 1 and 2 prevent the influence on the adjacent ETC lane. I can't.

(Total durability evaluation)
The following weather resistance test and scratch resistance test were performed on the examples and comparative examples 4 and 6 that passed the electromagnetic wave evaluations 1 and 2 as the radio wave absorber.

  Evaluation 1) As a weather resistance test, a sunshine carbon arc weather resistance tester (weather meter) was visually evaluated after a weather resistance test at 2000 hr. There was no problem that the appearance did not change.

  Evaluation 2) As a weather resistance test, visual evaluation after a weather resistance test at 90 ° C. for 90 days at 60 ° C. There was no problem that the appearance did not change.

  Evaluation 3) As a weather resistance test, a thermal cycle −20 ° C. → 80 ° C. (95%) 2 cycles / day Visual evaluation at 90 days. There was no problem that the appearance did not change.

  Evaluation 4) As an abrasion resistance test, Taber abrasion test (JIS K7204) 500 g loading Haze evaluation was performed by a single beam method as an evaluation based on the Haze value after 500 times. A haze of 3 or less was regarded as no problem.

  Evaluation 5) As a scratch resistance test, as a cleaning test of a resistance film and an electromagnetic wave reflection film (conductive film), a glass substrate coated with 20 Ω / □ of tin oxide is compared with a 20 Ω / □ coating of Ag film on the glass as a comparison. A prototype was manufactured with a normal laminated glass production line using the substrate, and the degree of damage to the electromagnetic wave reflection film in the glass cleaning process was evaluated. There was no problem that the appearance did not change.

  The process is glass cleaning ⇒ interlayer lamination ⇒ preheating ⇒ autoclave.

  Comprehensive evaluation) As a result of the evaluations 1 to 4, all the problems were evaluated as “good”. The results are shown in Table 3.

  In Comparative Example 4 using PC, yellowing was strongly recognized in Evaluation 1 due to the influence of ultraviolet rays. Also, in evaluation 4, which is an evaluation of the ease of scratching, a large change in Haze was recognized before and after the experiment. Some PC materials have a weather-grade surface treatment, but in an environment where many automobiles pass, there is a strong possibility that the surface protection material will be lost and affected by ultraviolet rays.

  In Comparative Example 4, Ag was used as the electromagnetic wave reflecting material. Since Ag is inferior in moisture resistance, in Experiments 1, 2, and 3, discoloration was observed due to moisture penetrating from the end face.

  Moreover, in evaluation 5, many scratches were observed on the resistance film surface in the glass cleaning step necessary for the manufacturing process with the substrate coated with 20 Ω / □ of the Ag film on the glass. Since the Ag film is used, it is not suitable for the manufacturing process having a glass cleaning process. In the case of using the tin oxide film as in the example, the tin oxide film has scratch resistance, and is particularly suitable for the manufacturing line. It is possible to manufacture with a normal laminated glass production line without taking any measures.

  From these, in an Example, since abnormality is not recognized by each evaluation, it is suitable also for the utilization in an outdoor environment, and since it can manufacture using a normal manufacturing line, it can manufacture easily.

  FIG. 7 shows a design example of the conductive film 20 and the PVB intermediate film of the electromagnetic wave absorber.

  The three values of the thickness of the glass plate 16, the thickness of PVB as the intermediate film 14 (resin sheet), and the resistance value of the conductive film 20 are correlated with three values that can reduce electromagnetic waves. However, the glass is required to have a thickness of 3 mm or more because a force is applied when forming into a laminated glass. In addition, since two sheets of glass are used, the laminated glass becomes heavier, so we don't want to make the glass thicker to reduce weight. For this reason, a suitable glass thickness is 3 mm. Further, the thickness of the glass plate 18 is not related to electromagnetic wave absorption, but is 3 mm like the thickness of the glass plate 16. The conductive film 22 only needs to have a function of reflecting electromagnetic waves, and the resistance value may be 20Ω / □ or less.

  For this reason, when the optimum range of the PVB thickness and the resistance value of the conductive film 20 when the thickness of the glass plates 16 and 18 is 3 mm is obtained, it is the inner side surrounded by the line of the graph of FIG. The unit of the vertical axis is mil, and mil is 1 mil = 0.0254 mm.

Sectional drawing of the electromagnetic wave absorber which concerns on embodiment of this invention Explanatory drawing which showed the canopy of the ETC facility where the electromagnetic wave absorber shown in FIG. 1 is installed The graph which showed the return loss with respect to the incident angle of the electromagnetic wave absorber of embodiment A graph showing the return loss with respect to the incident angle of a conventional wave absorber A graph showing the return loss with respect to the incident angle of a conventional wave absorber A graph showing the return loss with respect to the incident angle of a conventional wave absorber The graph which showed the optimal range of the PVB thickness when the glass plate thickness is 3 mm and the resistance value of the conductive film 20

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Wave absorber, 12 ... Gantry, 13 ... Canopy, 14 ... Intermediate film (resin sheet), 16 ... Glass plate, 18 ... Glass plate, 20 ... Conductive film, 22 ... Conductive film

Claims (5)

From the electromagnetic wave incident surface side, a glass with a conductive film, a resin sheet having a lower dielectric constant than the glass, and a glass with a conductive film are disposed in this order, and the conductive film is disposed so as to face the resin sheet, respectively. An electromagnetic wave absorber,
The sheet resistance value of the conductive film on the electromagnetic wave incident surface side is larger than the sheet resistance value of the other conductive film, and the electromagnetic wave to be absorbed passes through the conductive film on the electromagnetic wave incident surface side and is reflected by the other conductive film. Configured to counteract by reflected electromagnetic waves,
Each of the conductive films has transparency and is a film mainly composed of one or more metal oxides selected from the group consisting of Sn, In, and Zn.   The radio wave absorber according to claim 1, wherein the resin sheet is EVA or PVB.   The radio wave absorber according to claim 1, wherein each of the conductive films is a film mainly composed of tin oxide coated by CVD.   4. The radio wave according to claim 1, wherein the glass surface opposite to the conductive film of the glass with a conductive film on the electromagnetic wave incident surface side is subjected to water repellency or hydrophilic treatment. Absorber.   An ETC system, wherein the radio wave absorber according to any one of claims 1, 2, 3 and 4 is installed between adjacent ITS / DSRC facilities.

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