WO2017104710A1 - 電磁波吸収体およびそれを備えた電磁波吸収体付成形体 - Google Patents
電磁波吸収体およびそれを備えた電磁波吸収体付成形体 Download PDFInfo
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- WO2017104710A1 WO2017104710A1 PCT/JP2016/087247 JP2016087247W WO2017104710A1 WO 2017104710 A1 WO2017104710 A1 WO 2017104710A1 JP 2016087247 W JP2016087247 W JP 2016087247W WO 2017104710 A1 WO2017104710 A1 WO 2017104710A1
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- electromagnetic wave
- wave absorber
- resistance
- absorber according
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
- H01Q17/004—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems using non-directional dissipative particles, e.g. ferrite powders
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/28—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0075—Magnetic shielding materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
- G01S13/931—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of land vehicles
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
- H05K9/0088—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising a plurality of shielding layers; combining different shielding material structure
Definitions
- the present invention relates to an electromagnetic wave absorber for preventing electromagnetic interference and a molded body with an electromagnetic wave absorber provided with the same.
- millimeter waves wavelengths of about 1 to 10 mm, frequencies of 30 to 300 GHz
- electromagnetic waves in the quasi-millimeter wave region are increasingly used as information communication media.
- a collision prevention system that detects obstacles and automatically brakes, measures the speed and distance of surrounding vehicles, and controls the speed and distance of the vehicle. Is progressing.
- an electromagnetic wave absorber that absorbs unnecessary electromagnetic waves in order to ensure the performance of these systems.
- ⁇ / 4 type a type in which an electromagnetic wave reflection layer, a dielectric layer having a thickness of ⁇ / 4 ( ⁇ is the wavelength of a target electromagnetic wave), and a resistive thin film layer are provided.
- ⁇ is the wavelength of a target electromagnetic wave
- Patent Document 1 proposes an electromagnetic wave absorber that exhibits excellent characteristics of functioning over a wide range of incident angles.
- the present invention has been made in view of such circumstances, and provides a ⁇ / 4 type electromagnetic wave absorber capable of maintaining its performance for a long period of time and a molded body with an electromagnetic wave absorber provided with the same. It is the purpose.
- the present invention provides a dielectric layer made of a polymer film, a resistance layer mainly composed of indium tin oxide (hereinafter referred to as “ITO”) on the first surface of the dielectric layer, And an electromagnetic wave absorber having a conductive layer having a sheet resistance lower than that of the resistance layer on the second surface of the dielectric layer, and tin oxide (hereinafter referred to as “SnO 2 ”) contained in the ITO of the resistance layer.
- An electromagnetic wave absorber having a content of 20 to 40% by weight is defined as a first gist.
- the resistance layer includes an electromagnetic wave absorber containing a component other than ITO, and among the electromagnetic wave absorbers according to the second aspect, the resistance layer
- the electromagnetic wave absorber in which the component other than ITO is at least one selected from the group consisting of silicon oxide, magnesium oxide and zinc oxide is a third aspect, and among the electromagnetic wave absorbers of the first to third aspects,
- An electromagnetic wave absorber in which the conductive layer is made of ITO is a fourth aspect, and among the electromagnetic wave absorbers of the fourth aspect, an electromagnetic wave absorber in which SnO 2 contained in the conductive layer ITO is 5 to 15% by weight.
- the conductive layer is at least one of aluminum (hereinafter referred to as “Al”), copper (hereinafter referred to as “Cu”), and alloys thereof.
- Electromagnetic wave absorber comprising And sixth gist of.
- an electromagnetic wave absorber in which the sheet resistance of the resistance layer is set in the range of 300 to 500 ⁇ / ⁇ is a seventh aspect, and the first to seventh aspects of the invention.
- an electromagnetic wave absorber in which the thickness of the resistance layer is set in a range of 20 to 100 nm is an eighth gist.
- an electromagnetic wave absorber comprising a polymer film having a dielectric constant of 2.0 to 20.0 as a dielectric layer.
- the polymer film of the dielectric layer was selected from the group consisting of ethylene vinyl acetate copolymer, vinyl chloride, urethane, acrylic, acrylic urethane, polyethylene, silicone, and polyethylene terephthalate.
- the electromagnetic wave absorber consisting of at least one is defined as a tenth aspect.
- an electromagnetic wave absorber in which a coating layer is provided between at least one of the dielectric layer and the resistance layer and between the dielectric layer and the conductor layer.
- the coating layer has silicon oxide (SiO 2 , SiO), silicon nitride (SiN), aluminum oxide (Al 2 O 3 ), aluminum nitride (
- An electromagnetic wave absorber made of at least one selected from the group consisting of (AlN), niobium oxide (Nb 2 O 5 ), tin silicon oxide (STO), and aluminum-containing zinc oxide (AZO) is a twelfth aspect
- an electromagnetic wave absorber having a coating layer thickness set in the range of 5 to 100 nm is a thirteenth aspect.
- an electromagnetic wave absorber further provided with an adhesive layer, and the adhesive layer provided on the outside of the conductive layer is a fourteenth aspect.
- a molded body with an electromagnetic wave absorber provided with the electromagnetic wave absorber of the gist is defined as a fifteenth gist.
- the present inventors focused on the problem that it is necessary to further improve the reliability of the collision prevention system, aiming not only to reduce the cost of the electromagnetic wave absorber but also to maintain its excellent performance over a long period of time. And conducted intensive research.
- the ⁇ / 4 type electromagnetic wave absorber has a resistance layer mainly composed of ITO on the first surface of the dielectric layer made of a polymer film, and the second surface has It has been found that the above problems can be solved by forming a laminate having a conductive layer having a low sheet resistance and containing 20 to 40% by weight of SnO 2 in the ITO of the resistance layer, and has reached the present invention.
- the SnO 2 content of the resistance layer of the present invention can be measured by, for example, X-ray photoelectron spectroscopy (XPS) or electron beam microanalyzer (EPMA).
- XPS X-ray photoelectron spectroscopy
- EPMA electron beam microanalyzer
- the sheet resistance of the resistance layer and the conductive layer of the present invention can be measured by, for example, a contact type (4-end needle method) or non-contact type (eddy current method) resistance measurement method.
- the “main component” means a component that affects the properties of the material.
- the content of the component is usually 50% by weight or more of the whole material, and the whole consists of the main component only. Cases are also included.
- the electromagnetic wave absorber of the present invention has a resistance layer mainly composed of ITO on the first surface of the dielectric layer made of a polymer film, and has a sheet resistance lower than that of the resistance layer on the second surface.
- a ⁇ / 4-type electromagnetic wave absorber having a conductive layer Therefore, it is easy to design according to the target frequency, and a relatively inexpensive material can be used, so that it can be manufactured at a low cost.
- the SnO 2 contained in the ITO of the resistance layer is 20 to 40% by weight, the amorphous structure is extremely stable, and the sheet resistance of the resistance layer can be improved even when a temporal change or an environmental change is applied. The fluctuation can be kept below 15%, and the electromagnetic wave absorption effect can be exhibited for a long time.
- the inclusion of a component other than ITO in addition to ITO, the main component of which is the resistance layer, can increase the durability of the resistance layer and maintain the sheet resistance value of the resistance layer with accuracy over a long period of time. it can.
- a transparent electromagnetic wave absorber can be provided, and not only can it be applied to a part that requires transparency, but also the transparent electromagnetic wave absorber is scheduled to be attached. Since a site
- the conductive layer is made of at least one of Al, Cu, and alloys thereof, the sheet resistance value can be more easily lowered, so that reflection close to total reflection can be realized, and the absorption capacity of the electromagnetic wave absorber can be further increased. Can be increased.
- the electromagnetic wave can be effectively attenuated.
- a resistance layer having a desired sheet resistance can be formed with a high thickness accuracy, and therefore, an electromagnetic wave absorption having a more uniform electromagnetic wave absorption effect. It can be a body.
- the dielectric layer When the dielectric layer is made of a polymer film having a relative dielectric constant of 2.0 to 20.0, the dielectric layer can be set to a thickness that can be easily controlled, so that the electromagnetic wave absorber has a more uniform electromagnetic wave absorption effect. It can be.
- the polymer film of the dielectric layer is made of at least one selected from the group consisting of ethylene vinyl acetate copolymer, vinyl chloride, urethane, acrylic, acrylic urethane, polyethylene, silicone, polyethylene terephthalate, cost and dimensional accuracy It is possible to provide an electromagnetic wave absorber that is balanced and easy to use.
- the components in the dielectric layer are contained in the resistive layer or the conductive layer. Therefore, the sheet resistance of the resistance layer or the conductor layer is not influenced by the components in the dielectric layer, and can maintain a stable value for a long period of time. .
- the coating layer is made of at least one selected from the group consisting of SiO 2 , SiN, Al 2 O 3 , AlN, Nb 2 O 5 , STO, and AZO
- the component in the dielectric layer has resistance. Since diffusion into the layer or the conductor layer can be more reliably prevented, a high absorption capacity can be maintained over a long period of time.
- the thickness of the coating layer is set in the range of 5 to 100 nm, the stability and durability of the sheet resistance of the resistance layer or the conductor layer are particularly excellent.
- the adhesive layer is an electromagnetic wave absorber provided on the outer side of the conductive layer (opposite side of the dielectric layer side), the adhesive layer can be easily attached to another member (attached member). In addition, by fixing the mounting position of the electromagnetic wave absorber, it is possible to stably maintain an excellent electromagnetic wave absorbing ability.
- the molded body with an electromagnetic wave absorber provided with these electromagnetic wave absorbers always exhibits excellent electromagnetic wave absorbing ability more stably because the electromagnetic wave absorber is accurately arranged at a fixed position. Can do.
- the electromagnetic wave absorber of the present invention is composed of a laminate having a resistance layer A, a dielectric layer B, and a conductive layer C in this order, for example, as shown in FIG.
- the dielectric layer B is made of a laminated film in which a resin layer b2, a resin layer b1, and a resin layer b2 are laminated in this order.
- each part is shown typically and is different from the actual thickness, size, etc. (the same applies to the following figures).
- this electromagnetic wave absorber when an electromagnetic wave ( ⁇ O ) having a wavelength (frequency) to be absorbed is incident, the electromagnetic wave caused by reflection (surface reflection) on the surface of the resistance layer A and reflection (back surface reflection) on the surface of the conductive layer C ) / 4 type electromagnetic wave absorber which is set so as to interfere with the electromagnetic wave caused by In the ⁇ / 4 type electromagnetic wave absorber, as shown in the following formula (1), the electromagnetic wave ( ⁇ ) to be absorbed by the thickness (t) of the dielectric layer B and the relative dielectric constant ( ⁇ r ). It is known to determine the wavelength (frequency) of O ). That is, by appropriately setting the material and thickness of the dielectric layer B, it is possible to set an electromagnetic wave having a wavelength (frequency) to be absorbed. Each structure of the said electromagnetic wave absorber is demonstrated in order below. [Formula 1]
- the resistance layer A is disposed to reflect an electromagnetic wave having a target wavelength (frequency) near the surface of the electromagnetic wave absorber.
- This resistance layer A contains ITO as a main component, and the weight percent concentration of SnO 2 in the ITO is 20 to 40% by weight, more preferably 25 to 35% by weight of SnO 2 .
- the resistance layer A has an amorphous structure that is extremely stable because the amount of SnO 2 contained in the ITO is within the above range, and can suppress fluctuations in the sheet resistance of the resistance layer A even in a high-temperature and high-humidity environment. it can.
- ITO that is generally used contains 5 to 15% by weight of SnO 2 and is different from that used in the resistance layer A of the present invention.
- ITO containing 5 to 15% by weight of SnO 2 is formed as an amorphous film without annealing, a resistance layer of 300 to 500 ⁇ / ⁇ can be easily obtained. It cannot be used as a resistance layer of a radio wave absorber because it crystallizes due to environmental changes such as heat and the resistance value varies greatly. Further, when ITO containing 5 to 15% by weight of SnO 2 is formed into a polycrystalline structure by annealing, it has long-term stability, but on the other hand, the conductivity becomes too high.
- the resistance layer A may contain components other than ITO, and examples of such components include silicon oxide soot, magnesium oxide, and zinc oxide.
- a component other than ITO is contained in the resistance layer A, it is preferably a very small amount, for example, preferably 0.5 to 10 parts by weight, more preferably 1 to 1 part by weight with respect to 100 parts by weight of ITO. 5 parts by weight.
- the resistance layer A contains a component other than ITO, the thickness of the resistance layer A can be increased without changing the sheet resistance value, so that the durability of the resistance layer A can be enhanced. Therefore, the sheet resistance value of the resistance layer A can be accurately maintained over a longer period.
- the sheet resistance of the resistance layer A is preferably set in the range of 300 to 500 ⁇ / ⁇ , and more preferably in the range of 350 to 450 ⁇ / ⁇ . This is because the electromagnetic resistance can be effectively attenuated when the sheet resistance of the resistance layer A is within the above range.
- the thickness of the resistance layer A is preferably in the range of 20 to 100 nm, and more preferably in the range of 25 to 60 nm. This is because, when the thickness is too thick or conversely too thin, there is a tendency that the reliability of the sheet resistance value is lowered when a change with time or an environmental change is applied.
- the dielectric layer B is made of a laminated film in which a resin layer b2, a resin layer b1, and a resin layer b2 are laminated in this order (see FIG. 1). Further, the resin layer b2 is not necessarily provided, that is, the dielectric layer B may be formed of a single layer film. However, it is preferable to provide the resin layer b2 on both sides of the resin layer b1 in view of the ease of forming the resin layer b1 with a constant thickness and the ease of forming the resistance layer A and the conductive layer C.
- the relative dielectric constant ( ⁇ r ) in the case where the dielectric layer B is composed of multiple layers is measured by measuring the relative dielectric constant of each layer, and the ratio of the thickness of the obtained dielectric constant to the entire dielectric layer It can be calculated by multiplying and adding these.
- the resin layer b1 are those having an important role in determining the wavelength of the electromagnetic wave (lambda O) to the absorption of the target (frequency), the wavelength of the electromagnetic wave (lambda O) to the absorption of the target (frequency)
- a resin composition having a predetermined relative dielectric constant ( ⁇ r ) is formed to have a predetermined thickness (t) after curing and cured.
- Examples of the resin composition used for the resin layer b1 include ethylene vinyl acetate copolymer (EVA), vinyl chloride, urethane, acrylic, acrylic urethane, polyethylene, silicone, polyethylene terephthalate, polyester, polystyrene, polyimide, polycarbonate, polyamide, polysulfone, Synthetic rubber materials such as polyethersulfone and epoxy, and polyisoprene rubber, polystyrene / butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile / butadiene rubber, butyl rubber, acrylic rubber, ethylene / propylene rubber and silicone rubber It is preferable to use it as a resin component, and it is particularly preferable to use EVA from the viewpoint of moldability and relative permittivity.
- EVA ethylene vinyl acetate copolymer
- EVA vinyl chloride
- urethane acrylic
- acrylic urethane polyethylene
- silicone polyethylene terephthalate
- polyester poly
- the thickness of the resin layer b1 can be further reduced, so that the entire electromagnetic wave absorber can be made thinner.
- these can be used individually or in combination of 2 or more types.
- the thickness of the resin layer b1 is preferably 50 to 2000 ⁇ m, and more preferably 100 to 1000 ⁇ m. If the thickness is too thin, it is difficult to ensure the thickness dimensional accuracy. If the thickness is too thick, the material cost increases.
- the resin layer b2 is a substrate for forming the resistance layer A or the conductive layer C by sputtering or the like, and is used as an auxiliary material for strictly controlling the thickness of the resin layer b1. It is.
- the material of the resin layer b2 is preferably one that can withstand high temperatures such as vapor deposition and sputtering used to form the resistance layer A or the conductive layer C.
- PET polyethylene terephthalate
- PEN polyethylene naphthalate
- acrylic PMMA
- PC polycarbonate
- COP cycloolefin polymer
- PET is preferably used because of its excellent heat resistance and good balance between dimensional stability and cost.
- the resin layer b2 may be made of the same material on both sides of the resin layer b1, or may be made of different materials.
- the thickness of the resin layer b2 is preferably 10 to 125 ⁇ m, more preferably 20 to 50 ⁇ m. This is because if it is too thin, wrinkles and deformation are likely to occur when the resistance layer A is formed, and if it is too thick, the flexibility as an electromagnetic wave absorber is reduced. Moreover, the thickness may be the same on both sides of the resin layer b1, or may be different from each other.
- the conductive layer C is disposed to reflect an electromagnetic wave having a target wavelength (frequency) near the back surface of the electromagnetic wave absorber.
- the sheet resistance of the conductive layer C is set sufficiently lower than the sheet resistance of the resistance layer A.
- examples of the material of the conductive layer C include ITO, Al, Cu, nickel (Ni), chromium (Cr), molybdenum (Mo), and alloys of these metals.
- ITO containing 5 to 15% by weight of SnO 2 is preferably used.
- the thickness of the conductive layer C is preferably 20 to 200 nm, and more preferably 50 to 150 nm. This is because if the thickness is too thick, stress and cracks are easily generated in the conductive layer C, and if the thickness is too thin, it is difficult to obtain a desired low resistance value. Further, the sheet resistance of the conductive layer C is preferably 1/500 to 1/5, and more preferably 1/200 to 1/15 of the sheet resistance of the resistance layer A.
- the resistance layer A is mainly composed of ITO containing 20 to 40% by weight of SnO 2 , even if the electromagnetic wave absorber is changed over time or environmentally, the resistance layer A The variation in sheet resistance can be kept below approximately 15%, and electromagnetic waves having a target wavelength (frequency) can be absorbed over a long period of time.
- the electromagnetic wave absorber is a laminate of the resistance layer A, the dielectric layer B, and the conductive layer C, but the electromagnetic wave absorber may be provided with layers other than these layers. . That is, another layer may be provided outside the resistance layer A, outside the conductive layer C, between the resistance layer A and the dielectric layer B, and between the dielectric layer B and the conductive layer C.
- the durability and weather resistance of the resistance layer A can be improved.
- a coating layer E is provided between the resistance layer A and the dielectric layer B, or a coating layer E ′ is provided between the dielectric layer B and the conductor layer C
- the dielectric layer The component in B can be prevented from diffusing into the resistance layer A or the conductor layer C.
- the sheet resistances of the resistance layer A and the conductor layer C are not affected by the components in the dielectric layer B, and high absorptivity can be maintained over a long period of time.
- the coat layers E and E ′ may be made of the same material between the resistance layer A and the dielectric layer B and between the dielectric layer B and the conductor layer C, or may be made of different materials. It may be. In order to obtain this effect, it is not necessary to provide the coat layers E and E ′ between the resistance layer A and the dielectric layer B and between the dielectric layer B and the conductor layer C. You may provide only in either. However, it is particularly preferable to provide the coat layer E between the resistance layer A and the dielectric layer B. Of course, other layers may be provided between the resistance layer A and the coat layer E and between the conductor layer C and the coat layer E ′.
- the material of the coating layers E and E ′ for example, SiO 2 , SiN, Al 2 O 3 , AlN, Nb 2 O 5 , STO, AZO and the like can be used, and among them, when AIN and AZO are used, This is preferable because the durability of the resistance layer A or the conductor layer C can be further increased.
- the thickness of the coat layers E and E ′ is preferably in the range of 5 to 100 nm, more preferably in the range of 10 to 50 nm. If the thickness is too thin, the effect of improving the durability of the resistance layer A or the conductor layer C may be poor. If the thickness is too thick, the coating layers E and E ′ are likely to crack, and the effect of improving the durability is stable. This is because there is a tendency that cannot be exhibited.
- an adhesive layer F may be provided outside the conductive layer C (opposite the dielectric layer side) as shown in FIG. Providing the adhesive layer F not only facilitates attachment to other members (attached members), but also can stably maintain excellent electromagnetic wave absorption ability by fixing the attachment position of the electromagnetic wave absorber. It becomes possible. Of course, another layer can also be provided between the conductive layer C and the adhesive layer F.
- an adhesive such as a rubber adhesive, an acrylic adhesive, a silicone adhesive, and a urethane adhesive can be used. It is also possible to use adhesives such as emulsion adhesives, rubber adhesives, epoxy adhesives, cyanoacrylic adhesives, vinyl adhesives, silicone adhesives, etc., depending on the material and shape of the mounted member It can be selected appropriately. Among them, an acrylic pressure-sensitive adhesive is preferably used from the viewpoint of exhibiting adhesive force over a long period of time and having high attachment reliability.
- the electromagnetic wave absorber (see FIG. 1) shown in the embodiment of the present invention can be manufactured, for example, as follows.
- the resistance layer A is formed on the resin layer b2 formed into a film shape.
- the conductive layer C is formed on the resin b2 formed in a film shape different from the above (below in FIG. 4 (II)).
- the resistance layer A and the conductive layer C can be formed by sputtering, vapor deposition, or the like. Of these, it is preferable to use sputtering because the resistance value and thickness can be strictly controlled.
- a resin composition for forming the resin layer b1 is applied to the opposite surface of the resin layer b2 on which the conductive layer C is formed, on which the conductive layer C is formed, printing, extrusion molding, etc. I do.
- the opposite surface in which the resistance layer A was formed of the resin layer b2 in which the resistance layer A was formed was piled up, and after adjusting the thickness of a resin composition, this was hardened and resin This is layer b1.
- the electromagnetic wave absorber in which the resistance layer A, the dielectric layer B (a composite film composed of the resin layer b2, the resin layer b1, and the resin layer b2) and the conductive layer C shown in FIG. 1 are laminated in this order is obtained. Can do.
- an electromagnetic wave absorber that effectively absorbs electromagnetic waves having a target wavelength (frequency) can be obtained. Moreover, since the resistance layer A and the conductive layer C can be formed separately, the time required for the production of the electromagnetic wave absorber can be shortened, and the production can be carried out at a low cost.
- the dielectric layer B is formed only by the resin layer b1
- a film-like resin layer b1 having a predetermined thickness is prepared, and the first resin layer b1 is formed with respect to the first resin layer b1.
- the resistance layer A may be formed on the surface and the conductive layer C may be formed on the second surface.
- the coating layer E when the coating layer E is provided between the resistance layer A and the dielectric layer B, for example, in FIG. 4 (I), the coating layer E is previously formed on the resin layer b2.
- the resistance layer A may be formed on the coating layer E by coating or the like.
- the coat layer E ′ is provided between the dielectric layer B and the conductor layer C, in FIG. 4 (II), the coat layer E ′ is previously formed on the resin layer b2 by coating or the like.
- the resistive layer C may be formed on the coat layer E ′.
- the adhesive layer F when the adhesive layer F is provided, for example, after the electromagnetic wave absorber shown in FIG. 1 is prepared, the adhesive is disposed outside the conductive layer C (on the side opposite to the dielectric layer side). Alternatively, it can be formed by applying an adhesive or the like.
- FIG. 6 shows an electromagnetic wave absorber according to another embodiment of the present invention.
- the dielectric layer B is composed of a single resin layer b1, and the dielectric layer B has the resistance layer A directly on the first surface and the conductive layer C directly on the second surface.
- reference numeral D denotes a resin layer that becomes a substrate when the resistance layer A and the conductive layer C are formed by sputtering or the like.
- the other parts are the same as in the above embodiment, and the same effects as in the above embodiment are achieved.
- the resin layer D serves as a coating layer for the resistance layer A and the conductive layer C, respectively, and these layers can be protected from the outside.
- the material of the resin layer D is preferably one that can withstand high temperatures such as vapor deposition and sputtering used to form the resistance layer A or the conductive layer C.
- the material of the resin layer D is preferably one that can withstand high temperatures such as vapor deposition and sputtering used to form the resistance layer A or the conductive layer C.
- PET polyethylene terephthalate
- PEN polyethylene naphthalate
- PEN acrylic
- PC polycarbonate
- COP cycloolefin polymer
- PET is preferably used because of its excellent heat resistance and good balance between dimensional stability and cost.
- the resin layer D may be made of the same material on both the resistance layer A side and the conductive layer C side, or may be made of different materials.
- the electromagnetic wave absorber of another embodiment shown in FIG. 6 may be provided between the layers as in the above embodiment. Specifically, it is the same as that shown in the previous embodiment, and has the same effect.
- another layer may be provided outside the resin layer D, between the resistance layer A and the dielectric layer B (resin layer b1), and between the dielectric layer B (resin layer b1) and the conductive layer C.
- the other layers include the coating layers E and E 'and the adhesive layer F, but other layers may be used.
- a coat layer E is provided between the resistance layer A and the dielectric layer B (resin layer b1), and a coat layer E ′ is provided between the dielectric layer B (resin layer b1) and the conductive layer C.
- An example is shown. Also in this example, the components in the dielectric layer B are effectively prevented from diffusing into the resistance layer A and the conductor layer C.
- FIG. 8 shows an example in which a coat layer E is further provided between the resistance layer A and the resin layer D, and a coat layer E ′ is provided between the conductive layer C and the resin layer D.
- the resistance layer A and the conductor layer C can be reliably protected, fluctuations in the sheet resistance can be prevented over a long period of time, and the reliability can be further improved.
- the electromagnetic wave absorber of another embodiment shown in FIG. 6 can be manufactured as follows, for example.
- the resistance layer A is formed on the resin layer D formed into a film shape (below in FIG. 9 (I)). Further, as shown in FIG. 9 (II), a conductive layer C is formed on a resin layer D formed in a film shape different from the above.
- the resistance layer A and the conductive layer C can be formed by sputtering, vapor deposition, or the like. Of these, it is preferable to use sputtering because the resistance value and thickness can be strictly controlled.
- a resin composition for forming the resin layer B is applied to the surface of the resin layer D on which the conductive layer C is formed, on which the conductive layer C is formed, printing, extrusion molding, and the like.
- the surface in which the resistance layer A was formed of the resin layer D in which the resistance layer A was formed was piled up, and after adjusting the thickness of the said resin composition, this was hardened and resin Let it be layer B (resin layer b1).
- the electromagnetic wave absorber in which the resin layer D, the resistance layer A, the dielectric layer B (resin layer b1), the conductive layer C, and the resin layer D shown in FIG. 6 are laminated in this order can be obtained.
- the resin layer B is composed of a single resin layer b1
- the wavelength (frequency) of the electromagnetic wave to be set can be set accurately.
- the resistance values of the resistance layer A and the conductive layer C can be strictly controlled, it is possible to manufacture an electromagnetic wave absorber that can maintain excellent electromagnetic wave absorption ability for a long period of time.
- the coat layer E when the coat layer E is provided between the resistance layer A and the dielectric layer B, for example, the coat layer E is sputtered on the resistance layer A in FIG. Or by chemical vapor deposition (CVD), coating, or the like.
- CVD chemical vapor deposition
- the coat layer E ′ is provided between the dielectric layer B and the conductor layer C, the coat layer E ′ is sputtered, CVD, coated, etc. on the conductive layer C in FIG. 9 (II). May be formed.
- a coat layer E is further provided between the resin layer D and the resistance layer A, for example, in FIG. May be formed by sputtering, CVD, coating, or the like, and the resistance layer A may be formed on the coating layer E.
- the coat layer E ′ is provided between the conductor layer C and the resin layer D, the coat layer E ′ is formed on the resin layer D in advance by sputtering, CVD, coating, etc. in FIG.
- the resistance layer C may be formed on the coat layer E ′.
- Test Examples using ITO containing SnO 2 20 wt% 2 and Test Example 3 using the ITO containing SnO 2 30% by weight show high evaluation, and it turns out that it is excellent in durability. It can also be seen that Test Example 7 in which ITO containing 20% by weight of SnO 2 was used for the resistance layer and a base coat layer was provided on the resistance layer was also excellent in durability.
- Examples 1 to 14 and Comparative Examples 1 to 4 were produced as shown below. Further, Examples 15 to 34 were produced as described later in accordance with the embodiment shown in FIG. With respect to the electromagnetic wave absorbers of Examples 1 to 34 and Comparative Examples 1 to 4, the return loss after 1000 hours was measured in the initial stage and at a temperature of 120 ° C. according to the following indices, and evaluated. Then, the evaluation results of the return loss after 1000 hours at the initial stage and at the temperature of 120 ° C. were applied to the following indices to evaluate the electromagnetic wave absorption ability. The obtained results are shown in Table 2 and Table 3 together.
- Example 1 In accordance with the method shown in the embodiment of FIG. 1 above, first, on a film-like resin layer b2 made of PET (Mitsubishi Chemical Polyester Co., Ltd .: Mitsubishi Diafoil), 30 weight so as to have a sheet resistance of 430 ⁇ / ⁇ Resistance layer A was formed using ITO containing% SnO 2 . Further, ITO containing 10% by weight of SnO 2 is laminated on another film-like resin layer b2 (manufactured by Mitsubishi Chemical Polyester Co., Ltd .: Mitsubishi Diafoil), and the temperature is 150 ° C. for 1 hour with respect to the ITO.
- a film-like resin layer b2 made of PET (Mitsubishi Chemical Polyester Co., Ltd .: Mitsubishi Diafoil)
- ITO containing 10% by weight of SnO 2 is laminated on another film-like resin layer b2 (manufactured by Mitsubishi Chemical Polyester Co., Ltd .: Mitsubishi Diafoil), and the temperature is 150 ° C. for 1
- the conductive layer C having a sheet resistance of 20 ⁇ / ⁇ was formed by performing the annealing process of FIG.
- a resin layer (EVA composition) obtained by press-molding a resin composition (EVA composition) to a predetermined thickness is placed on the opposite side of the surface on which the conductive layer C is formed of the resin layer b2 on which the conductive layer C is formed.
- the previous resin layer b2 was overlapped so as to match the surface opposite to the surface on which the layer A was formed, and the resin composition was cured to form a resin layer b1 to obtain a target electromagnetic wave absorber.
- the dielectric constant of the dielectric layer B was 2.45.
- Examples 2 and 3 Comparative Examples 1 and 2>
- the target electromagnetic wave absorber was obtained in the same manner as in Example 1 except that the resistance layer A was formed in place of the SnO 2 blending amount in% by weight shown in Table 2.
- Example 4 The target electromagnetic wave absorber is obtained in the same manner as in Example 1 except that the conductive layer C is formed using Al so as to have a sheet resistance of 2 ⁇ / ⁇ , and the resistance layer A is formed so as to have a sheet resistance of 380 ⁇ / ⁇ . It was.
- Examples 5 to 8> A target electromagnetic wave absorber was obtained in the same manner as in Example 1 except that the resistance layer A was formed so as to have the sheet resistance shown in Table 2.
- Example 9 to 11 A target electromagnetic wave absorber was obtained in the same manner as in Example 1 except that the dielectric layer B was formed using the materials shown in Table 2. The relative dielectric constant of the dielectric layer B at this time was 2.45 in Example 9, 2.7 in Example 10, and 2.55 in Example 11.
- Example 12 to 15 A target electromagnetic wave absorber was obtained in the same manner as in Example 1 except that the thickness of the resistance layer A was changed to the thickness shown in Table 2.
- Example 16 Example 1 except that the resistance layer A is formed to a thickness of 50 nm using ITO containing 30% by weight of SnO 2 and 2.5% by weight of SiO 2 , and the dielectric layer B is formed using acrylic. Thus, an intended electromagnetic wave absorber was obtained.
- Example 3 The target electromagnetic wave was formed in the same manner as in Example 1 except that the conductive layer C was formed using ITO containing 30% by weight of SnO 2 so as to have a sheet resistance of 430 ⁇ / ⁇ (the same sheet resistance as that of the resistance layer A). An absorber was obtained.
- Example 4 A target electromagnetic wave absorber was obtained in the same manner as in Example 1 except that the conductive layer C was formed using aluminum-doped zinc oxide (AZO) so as to have a sheet resistance of 600 ⁇ / ⁇ .
- AZO aluminum-doped zinc oxide
- the sheet resistance becomes 430 ⁇ / ⁇ on the film-like resin layer D (Mitsubishi Chemical Polyester Co., Ltd .: Mitsubishi Diafoil) made of PET.
- a resistance layer A was formed using ITO containing 30% by weight of SnO 2, and a coating layer E made of SiO 2 was formed on the resistance layer A to a thickness of 20 nm.
- ITO containing 10% by weight of SnO 2 is laminated on another film-like resin layer D (Mitsubishi Chemical Polyester Co., Ltd .: Mitsubishi Diafoil), and the temperature is 150 ° C. for 1 hour with respect to the ITO.
- the conductive layer C having a sheet resistance of 20 ⁇ / ⁇ was formed by performing the annealing process of FIG.
- a coat layer E ′ made of SiO 2 was formed on the conductive layer C to a thickness of 20 nm.
- a resin composition (EVA composition) that has been press-molded to a predetermined thickness is placed.
- a resin layer D on which the previous resistance layer A is formed is coated with the coat layer E.
- the resin composition was layered so as to face the resin composition, and the resin composition was cured to obtain a resin layer B (b1), thereby obtaining the target electromagnetic wave absorber.
- the dielectric constant of the dielectric layer B was 2.45.
- Example 18 In accordance with Example 17, a resistance layer A, a dielectric layer B, a conductive layer C, and coating layers E and E ′ were formed to obtain a target electromagnetic wave absorber so as to have the configuration shown in Table 3.
- the relative dielectric constant when acrylic is used is 2.55
- the relative dielectric constant when urethane is 2.7
- the relative dielectric constant when SEPS is used is 2.4
- the relative dielectric constant when EPT was used was 2.3
- the relative dielectric constant when silicone was used was 2.7.
- the coat layer E ′ was not formed, and Al was laminated directly on the resin layer b2.
- Examples 1 to 36 all have good electromagnetic wave absorption ability and maintain their performance for a long time even when the surrounding environment changes. This is because, as shown in the results of Table 1, the resistance layers A of Examples 1 to 36 maintain the sheet resistance set over a long period even in a heating environment. In particular, it can be seen that Examples 17 to 36 having at least one of the coat layer E and the coat layer E ′ have extremely excellent electromagnetic wave absorbing ability.
- Comparative Examples 1 and 2 since the amount of SnO 2 added to ITO of the material of the resistance layer A is small or large, when the surrounding environment changes, the resistance value of the resistance layer A changes over time. However, the initial excellent electromagnetic wave absorption ability could not be maintained for a long time. In Comparative Examples 3 and 4, since the sheet resistance of the conductive layer C is the same as or higher than the sheet resistance of the resistance layer A, sufficient electromagnetic wave absorbing ability cannot be obtained.
- the electromagnetic wave absorber of the above implementation is always installed in a member that may receive unnecessary radio waves, such as a vehicle body member, in addition to being attached to any part of a member that wants to absorb unnecessary radio waves.
- the electromagnetic wave absorber can be disposed at a fixed position, and more stable electromagnetic wave absorbing ability can be exhibited.
- Examples of such a member include resin molded bodies such as bumpers, grilles, fenders, spoilers, emblems, brackets, and bumper beams, and metal molded bodies. Therefore, the formed body provided with the electromagnetic wave absorber of the present invention can exhibit excellent electromagnetic wave absorbing ability more stably.
- the present invention can retain the performance of absorbing unnecessary electromagnetic waves for a long period of time, it can be suitably used for an electromagnetic wave absorber of a millimeter wave radar used in an automobile collision prevention system.
- an electromagnetic wave absorber of a millimeter wave radar used in an automobile collision prevention system.
- ITS intelligent road traffic systems
- 5G next-generation mobile communication systems
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- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
- Laminated Bodies (AREA)
Abstract
Description
[式1]
抵抗層Aは、対象とする波長(周波)の電磁波を電磁波吸収体の表面近傍で反射させるために配置されるものである。この抵抗層Aは、ITOを主成分としており、ITO中のSnO2の重量%濃度は20~40重量%であり、より好ましくは25~35重量%のSnO2を含有することである。上記抵抗層Aは、ITOに含まれるSnO2の量が上記範囲内であるため非晶質構造が極めて安定であり、高温多湿の環境下においても抵抗層Aのシート抵抗の変動を抑えることができる。なお、汎用されるITOは、通常、5~15重量%のSnO2を含有するものであり、本発明の抵抗層Aで用いるものとは異なっている。5~15重量%のSnO2を含有するITOでは、アニール処理を行わずに非晶質膜として形成した場合には300~500Ω/□の抵抗層を容易に得ることができるが、加熱や加湿熱など環境変化によって結晶化し、抵抗値が大きく変動するために電波吸収体の抵抗層として利用することはできない。また、5~15重量%のSnO2を含有するITOをアニール処理によって多結晶構造化させた場合は長期的な安定性を有するが、一方、導電性が高くなりすぎる。したがって、汎用されるITOを多結晶構造化して300~500Ω/□の抵抗層Aを得ようとすると、その厚みを10nm以下の極薄膜にする必要がある。厚みが10nm以下の極薄層を、設定された通りの厚みに、均一な状態で形成することは極めて困難であるため、抵抗値の制御が極めて困難となる。
誘電体層Bは、樹脂層b2、樹脂層b1、樹脂層b2がこの順に積層された積層フィルムからなっている(図1参照)。また、樹脂層b2は必ずしも設けなくてもよく、すなわち、誘電体層Bは単層フィルムからなっていてもよい。ただし、樹脂層b1を一定の厚みに形成することの容易性や、抵抗層Aおよび導電層Cの形成のし易さから、樹脂層b1の両側に樹脂層b2を設けることが好ましい。誘電体層Bが複層からなる場合の比誘電率(εr)は、それぞれの層の比誘電率を測定し、得られた各比誘電率にその層の誘電体層全体に対する厚みの割合を乗じ、これらを加算することにより算出することができる。
上記樹脂層b1は、吸収の対象とする電磁波(λO)の波長(周波)を決定するのに重要な役割を有するものであり、吸収の対象とする電磁波(λO)の波長(周波)に合わせ、所定の比誘電率(εr)を有する樹脂組成物を、硬化後に所定の厚み(t)となるように形成し、硬化させたものである。樹脂層b1に用いる樹脂組成物としては、エチレン酢酸ビニル共重合体(EVA)、塩化ビニル、ウレタン、アクリル、アクリルウレタン、ポリエチレン、シリコーン、ポリエチレンテレフタレート、ポリエステル、ポリスチレン、ポリイミド、ポリカーボネート、ポリアミド、ポリサルフォン、ポリエーテルサルフォン、エポキシ等の合成樹脂や、ポリイソプレンゴム、ポリスチレン・ブタジエンゴム、ポリブタジエンゴム、クロロプレンゴム、アクリロニトリル・ブタジエンゴム、ブチルゴム、アクリルゴム、エチレン・プロピレンゴムおよびシリコーンゴム等の合成ゴム材料を樹脂成分として用いることが好ましく、とりわけ、成型性と比誘電率の点から、EVAを用いることが好ましい。また、ウレタン、アクリル、アクリルウレタンを用いると、樹脂層b1の厚みをより薄くできるため、電磁波吸収体全体の薄膜化を図ることができる。なお、これらは単独でもしくは2種以上併せて用いることができる。
上記樹脂層b2は、抵抗層Aまたは導電層Cをスパッタ等により形成する際の基板であり、上記樹脂層b1を形成する際に、その厚みを厳密に制御するための補助材として用いられるものである。このような樹脂層b2の材料としては、抵抗層Aまたは導電層Cの形成に用いる蒸着やスパッタ等の高温に耐えうるものであることが好ましく、例えば、ポリエチレンテレフタレート(PET)、ポリエチレンナフタレート(PEN)、アクリル(PMMA)、ポリカーボネート(PC)、シクロオレフィンポリマー(COP)等があげられる。なかでも、耐熱性に優れ、寸法安定性とコストとのバランスがよいことからPETが好ましく用いられる。また、樹脂層b2は、樹脂層b1の両側において同じ材料からなっていてもよいし、それぞれ異なる材料からなっていてもよい。
導電層Cは、対象とする波長(周波)の電磁波を電磁波吸収体の裏面近傍で反射させるために配置されるものである。また、この導電層Cのシート抵抗は、抵抗層Aのシート抵抗より充分に低く設定されている。これらのことから、導電層Cの材料としては、例えば、ITO、Al、Cu、ニッケル(Ni)、クロム(Cr)、モリブデン(Mo)、およびこれらの金属の合金があげられる。なかでも、透明な電磁波吸収体を供することができ、透明性が必要とされる部位への適用が可能となるだけでなく、施工性の改善を図ることができる点から、ITOを用いることが好ましく、なかでも5~15重量%のSnO2を含有するITOが好ましく用いられる。一方で、シート抵抗値をより容易に下げることができ、ノイズをより低減することができる点から、Al、Cuまたはそれらの合金が好ましく用いられる。また、導電層Cの厚みは、20~200nmであることが好ましく、50~150nmであることがより好ましい。厚みが厚すぎると導電層Cに応力やクラックが入り易くなり、薄すぎると所望の低い抵抗値が得られ難くなるためである。また、導電層Cのシート抵抗は、抵抗層Aのシート抵抗の1/500~1/5であることが好ましく、1/200~1/15であることがさらに好ましい。
まず、本発明の実施例および比較例の説明の前に、本発明の電磁波吸収体における抵抗層Aの信頼性を、下記の〔信頼性評価1〕および〔信頼性評価2〕に記載の指標にしたがって評価した。これらの評価は各試験例についてn=5で行い、その平均を各試験例の評価とした。各試験例の評価(信頼性評価1および信頼性評価2)を後記の表1に合わせて示す。
試験例1~10のうち、試験例1~6は、フィルム状の基材(三菱化学ポリエステル社製PET:三菱ダイアホイル)上に、抵抗層を表1に示す材料を用いてスパッタにより形成した。試験例7~10は、上記フィルム状の基材の上に表1に示す材料を用いて抵抗層を形成し、さらに表1に示す材料を用いてその上にコート層を形成した。そして、これらの試験片を温度120℃の雰囲気下にそれぞれ所定時間(24時間、100時間、1000時間)加熱し、加熱後の抵抗層のシート抵抗の、加熱前の抵抗層のシート抵抗に対する変化をシート抵抗変動率(%)として算出し、下記の指標にしたがって評価した。
〇:シート抵抗変動率が10%未満
△:シート抵抗変動率が10%以上15%未満
×:シート抵抗変動率が15%以上
抵抗層を評価する試験片を信頼性評価1の試験片と同様に作製した。そして、これらの試験片を、温度85℃,湿度85%の雰囲気下にそれぞれ所定時間(24時間、100時間、1000時間)置き、所定時間置いた後の抵抗層のシート抵抗の、所定時間置く前の抵抗層のシート抵抗に対する変化をシート抵抗変動率(%)として算出し、下記の指標にしたがって評価した。
〇:シート抵抗変動率が10%未満
△:シート抵抗変動率が10%以上15%未満
×:シート抵抗変動率が15%以上
JIS R 1679(電波吸収体のミリ波帯における電波吸収特性測定方法)に準拠して、76GHzのミリ波に対する反射減衰量(dB)を測定し、下記の指標にしたがって評価した。なお、上記測定を各実施例、比較例についてn=5で行い、その平均を下記の指標に当てはめ、各実施例、比較例の評価とした。
◎:反射減衰量が30dB以上
〇:反射減衰量が20dB以上30dB未満
△:反射減衰量が10dB以上20dB未満
×:反射減衰量が10dB未満
◎:初期および温度120℃雰囲気下で1000時間経過後の反射減衰量の評価が、いずれも◎であり、電磁波吸収能が非常に優れるもの。
○:初期および温度120℃雰囲気下で1000時間経過後の反射減衰量の評価において、一方の評価が◎であり、もう一方の評価が○であるもの。あるいはいずれも○であり、電磁波吸収能が優れるもの。
△:初期および温度120℃雰囲気下で1000時間経過後の反射減衰量の評価において、一方の評価が◎もしくは○であり、もう一方の評価が△であるもの。あるいはいずれも△であり、ある程度の電磁波吸収能が得られるもの。
×:初期および温度120℃雰囲気下で1000時間経過後の反射減衰量の評価において、少なくとも一方に×があり、電磁波吸収能またはその信頼性に欠けるもの。
上記図1の実施の形態に示す方法に準じて、まず、PETからなるフィルム状の樹脂層b2(三菱化学ポリエステル社製:三菱ダイアホイル)の上に、シート抵抗430Ω/□となるよう30重量%のSnO2を含有するITOを用いて抵抗層Aを形成した。また、別のフィルム状の樹脂層b2(三菱化学ポリエステル社製:三菱ダイアホイル)の上に、10重量%のSnO2を含有するITOを積層し、上記ITOに対し、温度150℃で1時間のアニール処理を行い、多結晶構造化させて、シート抵抗が20Ω/□の導電層Cを形成した。この導電層Cが形成された樹脂層b2の、導電層Cが形成された面の反対面に、樹脂組成物(EVA組成物)を所定厚みにプレス成型したものを載せ、その上に、抵抗層Aが形成された面の反対面を合わせるよう先の樹脂層b2を重ね、上記樹脂組成物を硬化させて樹脂層b1とし、目的の電磁波吸収体を得た。このときの誘電体層Bの比誘電率は2.45であった。
SnO2の配合量を表2に示す重量%に代えて抵抗層Aを形成した以外は、実施例1と同様にして目的の電磁波吸収体を得た。
導電層Cをシート抵抗2Ω/□となるようAlを用いて形成し、抵抗層Aをシート抵抗380Ω/□となるよう形成した以外は、実施例1と同様にして目的の電磁波吸収体を得た。
表2に示すシート抵抗となるよう抵抗層Aを形成した以外は、実施例1と同様にして目的の電磁波吸収体を得た。
表2に示す材料を用いて誘電体層Bを形成した以外は、実施例1と同様にして目的の電磁波吸収体を得た。このときの誘電体層Bの比誘電率は、実施例9が2.45、実施例10が2.7、実施例11が2.55であった。
抵抗層Aの厚みを表2に示す厚みに代えた以外は、実施例1と同様にして目的の電磁波吸収体を得た。
SnO2を30重量%含有するITOおよび2.5重量%のSiO2を用いて抵抗層Aを厚み50nmに形成し、誘電体層Bをアクリルを用いて形成した以外は、実施例1と同様にして目的の電磁波吸収体を得た。
導電層Cをシート抵抗430Ω/□(抵抗層Aと同じシート抵抗)になるよう、30重量%のSnO2を含有するITOを用いて形成した以外は、実施例1と同様にして目的の電磁波吸収体を得た。
導電層Cをシート抵抗600Ω/□となるようアルミニウムドープ酸化亜鉛(AZO)を用いて形成した以外は、実施例1と同様にして目的の電磁波吸収体を得た。
つぎに、上記図7の実施の形態に示す方法に準じて、まず、PETからなるフィルム状の樹脂層D(三菱化学ポリエステル社製:三菱ダイアホイル)の上に、シート抵抗430Ω/□となるよう30重量%のSnO2を含有するITOを用いて抵抗層Aを形成し、この抵抗層Aの上にSiO2からなるコート層Eを厚み20nmに形成した。また、別のフィルム状の樹脂層D(三菱化学ポリエステル社製:三菱ダイアホイル)の上に、10重量%のSnO2を含有するITOを積層し、上記ITOに対し、温度150℃で1時間のアニール処理を行い、多結晶構造化させて、シート抵抗が20Ω/□の導電層Cを形成した。そして、この導電層Cの上にSiO2からなるコート層E’を厚み20nmに形成した。このコート層E’の上に、樹脂組成物(EVA組成物)を所定厚みにプレス成型したものを載せ、その上に、先の抵抗層Aが形成された樹脂層Dを、コート層Eが樹脂組成物に対峙するように重ね、上記樹脂組成物を硬化させて樹脂層B(b1)とし、目的の電磁波吸収体を得た。このときの誘電体層Bの比誘電率は2.45であった。
実施例17に準じて、表3に示す構成となるように、それぞれ抵抗層A、誘電体層B、導電層C、コート層E,E’形成して、目的の電磁波吸収体を得た。なお、誘電体層Bにおいて、アクリルを用いた場合の比誘電率は2.55、ウレタンを用いた場合の比誘電率は2.7、SEPSを用いた場合の比誘電率は2.4、EPTを用いた場合の比誘電率は2.3、シリコーンを用いた場合の比誘電率は2.7であった。また、実施例26ではコート層E’を形成せず、樹脂層b2の上に直接Alを積層した。
B 誘電体層
C 導電層
Claims (15)
- 高分子フィルムからなる誘電体層と、誘電体層の第1の面に酸化インジウムスズを主成分とする抵抗層と、誘電体層の第2の面に上記抵抗層より低いシート抵抗を有する導電層とを有する電磁波吸収体であって、上記抵抗層の酸化インジウムスズに含まれる酸化スズが20~40重量%であることを特徴する電磁波吸収体。
- 上記抵抗層が酸化インジウムスズ以外の成分を含有する請求項1記載の電磁波吸収体。
- 上記抵抗層の酸化インジウムスズ以外の成分が、酸化ケイ素、酸化マグネシウムおよび酸化亜鉛からなる群から選ばれた少なくとも一つである請求項2記載の電磁波吸収体。
- 上記導電層が酸化インジウムスズからなる請求項1~3のいずれか一項に記載の電磁波吸収体。
- 上記導電層の酸化インジウムスズに含まれる酸化スズが5~15重量%である請求項4記載の電磁波吸収体。
- 上記導電層がアルミニウム、銅およびそれらの合金の少なくとも一つからなる請求項1~3のいずれか一項に記載の電磁波吸収体。
- 上記抵抗層のシート抵抗が300~500Ω/□の範囲に設定された請求項1~6のいずれか一項に記載の電磁波吸収体。
- 上記抵抗層の厚みが20~100nmの範囲に設定された請求項1~7のいずれか一項に記載の電磁波吸収体。
- 上記誘電体層が、比誘電率2.0~20.0の高分子フィルムからなる請求項1~8のいずれか一項に記載の電磁波吸収体。
- 上記誘電体層の高分子フィルムが、エチレン酢酸ビニル共重合体、塩化ビニル、ウレタン、アクリル、アクリルウレタン、ポリエチレン、シリコーン、ポリエチレンテレフタレートからなる群から選ばれた少なくとも一つからなる請求項1~9のいずれか一項に記載の電磁波吸収体。
- 上記誘電体層と抵抗層との間および誘電体層と導電体層との間の少なくとも一方に、コート層が設けられた請求項1~10のいずれか一項に記載の電磁波吸収体。
- 上記コート層が、酸化ケイ素、窒化ケイ素、酸化アルミニウム、窒化アルミニウム、酸化ニオブ、スズ・シリコン酸化物およびアルミニウム含有酸化亜鉛からなる群から選ばれた少なくとも一つからなる請求項11記載の電磁波吸収体。
- 上記コート層の厚みが5~100nmの範囲に設定された請求項11または12記載の電磁波吸収体。
- さらに粘着層を備え、上記粘着層が上記導電層の外側に設けられた請求項1~13のいずれか一項に記載の電磁波吸収体。
- 請求項1~14のいずれか一項に記載の電磁波吸収体を備えた電磁波吸収体付成形体。
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