WO2020111159A1 - Quasi-millimeter wave/millimeter wave band electric wave absorption sheet and quasi-millimeter wave/millimeter wave band electric wave absorption method - Google Patents

Abstract

The present invention provides a light-weight and flexible sheet-like electric wave absorber particularly having an excellent electric wave absorption performance in the frequency of a quasi-millimeter wave band. This quasi-millimeter wave/millimeter wave band electric wave absorption sheet is provided with: an electric wave reflection layer (A); and an electric wave absorption layer (B) that is disposed in parallel on top of the electric wave reflection layer (A), wherein the film thickness of the electric wave absorption layer (B) is within the range of 400-1000 µm, regarding the relative permeability (µr=µ'+µ"i) of the electric wave absorption layer (B) in a frequency of 24 GHz, a real part µ' is 1.0-1.50, and the absolute value of an imaginary part µ" is 0 or more but less than 1.0, and regarding the relative dielectric constant (ɛr=ɛ'+ɛ"i) of the electric wave absorption layer (B) in the frequency of 24 GHz, a real part ɛ' is 14-25, and the absolute value of an imaginary part ɛ" is in the range of 4-10.

Description

Quasi-millimeter wave/millimeter wave band electromagnetic wave absorption sheet and quasi-millimeter wave/millimeter wave wave absorption method

The present invention relates to a radio wave absorption sheet and a radio wave absorption method.

Radio waves are radiated from communication devices such as radios, televisions, and wireless communications, but in addition to this, radio waves are also radiated from electronic devices such as mobile phones and personal computers, which have rapidly increased due to recent advances in information technology. Therefore, as a method for avoiding malfunctions due to radio waves in electronic devices, communication devices, etc., a radio wave absorber (Electro Magnetic Absorber, EMA) that efficiently absorbs radio waves and converts the absorbed radio waves into heat energy. Is often installed near or far from the radio wave generation site.

An example of installing a radio wave absorber far away from a radio wave generation site is, for example, an automatic toll collection system (ETC) application on a highway. When a car passes through the exit of a tollgate on an expressway, ETC uses microwaves with a frequency of 5.8 GHz between the roadside device antenna and the vehicle-mounted device antenna provided at the tollgate to provide billing information. It is a system to exchange. At the tollgate where this ETC system is installed, microwaves radiated from the antenna may be reflected on the roof of the tollgate, and unnecessary radio waves may leak from the adjacent ETC lane, causing communication problems. There is. Therefore, a radio wave absorber is installed between the roof of the tollgate and the ETC lane to suppress communication abnormality. (Patent Document 1, etc.)
As described above, the electromagnetic wave absorber is widely used, and various electromagnetic wave absorbers of various materials and shapes have been developed according to the purpose and application.

There are pyramid type electromagnetic wave absorbers and laminated type electromagnetic wave absorbers as electromagnetic wave absorbers that absorb in a wide band.

A pyramid type electromagnetic wave absorber is a type of electromagnetic wave absorber in which the energy of the electromagnetic wave is attenuated while the electromagnetic wave passes through the inside of the absorber. Patent Document 2 discloses a radio wave in which a material obtained by kneading a conductive material such as carbon black or graphite with a foamable organic resin such as foamed polyethylene as a base material is molded into a shape in which a plurality of pyramids are connected. An absorber is described. Since the electromagnetic wave absorber itself has a shape like a pyramid, the cross-sectional area of the electromagnetic wave absorber surface (direction of arrival of electromagnetic waves) can be reduced, and the reflection of incident electromagnetic waves on the surface can be suppressed, and the inside of the absorber can be suppressed. It is considered that the radio waves entering the inside of the absorber can be efficiently converted into thermal energy as the radio waves easily enter and the cross-sectional area of the absorber increases.

On the other hand, a laminated type electromagnetic wave absorber absorbs an electromagnetic wave by laminating an electromagnetic wave reflection layer and a plurality of electromagnetic wave absorption layers. For example, in Patent Document 3, a metal powder and a bond are formed on the surface of a metal plate. A radio wave absorber having a magnetic loss layer containing an agent is disclosed.

In recent years, electronic devices and communication devices have shifted to products that use high-frequency radio waves. For example, application of millimeter-wave radar has been attempted to support collision prevention of automobiles. Although radio wave absorbers that absorb radio waves in the millimeter wave band have been developed, most of them are pyramid type, and there is a problem that the base material is deteriorated/deformed due to aging, heat, etc., and the radio wave absorption is reduced. It was Further, since the pyramid type electromagnetic wave absorber is bulky, it is difficult to attach the pyramid type electromagnetic wave absorber depending on the installation location, and the manufacturing process is complicated.

Furthermore, the conventional laminated wave absorber did not reach a sufficient level regarding the absorption frequency bandwidth of the millimeter wave band. For this reason, it is technically difficult to design a lightweight and flexible electromagnetic wave absorber that absorbs a wide range of millimeter waves and can be attached to a curved surface.

In order to meet such needs, the present inventor can sufficiently absorb radio waves in the millimeter wave band by combining a plurality of radio wave absorption layers having a specific dielectric constant with respect to the radio wave reflection layer in Patent Document 4. Proposed an electromagnetic wave absorption sheet. However, the radio wave absorbing sheet described in Patent Document 4 has a thicker film because the radio wave absorbing layer has a laminated structure, and further thinning has been desired. Further, the radio wave absorption sheet is designed by paying attention to radio waves in the millimeter wave band, and has poor radio wave absorption characteristics in the quasi-millimeter wave band.

Millimeter waves and quasi-millimeter waves are not clearly defined, but quasi-millimeter waves refer to radio waves of 20 GHz to 30 GHz (wavelength is 10 mm to 15 mm) and millimeter waves are 30 GHz to 300 GHz (wavelength is 1 mm to 10 mm). There are many.

A millimeter-wave radar is suitable for detecting collision objects in front of a vehicle as a collision prevention support radar, but quasi-millimeter waves are used for detecting collision objects around the vehicle on the rear or side of the vehicle. There is. In addition, quasi-millimeter-wave radio waves are about to be used in the next-generation wireless communication system “5G” (5th generation mobile communication system: 5th Generation) that enables high-speed, large-capacity, connection of a large number of terminals, and the like.

In this way, it is predicted that the number of devices that utilize not only millimeter waves but also quasi-millimeter waves will increase in the near future, and the development of radio wave absorbers with excellent radio wave absorption characteristics in the quasi-millimeter wave band is also required. There is.

Japanese Patent Laid-Open No. 2001-217645 JP-A-6-334382 Japanese Unexamined Patent Publication No. 8-288688 WO2018/124131

The present invention has an object to provide a sheet-shaped electromagnetic wave absorber having excellent electromagnetic wave absorption performance at high frequencies, particularly in the quasi-millimeter wave band, and an electromagnetic wave absorption method using the same.

The present inventor, as a result of diligent studies on the above-mentioned problems, paid attention to the film thickness, relative permeability and relative permittivity of the radio wave absorption layer combined with the radio wave reflection layer. And when the film thickness of the electromagnetic wave absorption layer is in a specific range and the relative permeability and relative permittivity of the electromagnetic wave absorption layer at a frequency of 24 GHz have a specific relationship, the electromagnetic wave absorption characteristics should be greatly expressed especially in the quasi-millimeter wave band. Found.

That is, the present invention is
A radio wave absorption sheet for quasi-millimeter wave/millimeter wave band, comprising a radio wave reflection layer (A) and a radio wave absorption layer (B) arranged in parallel on the radio wave reflection layer (A),
The film thickness of the radio wave absorption layer (B) is in the range of 400 to 1000 μm,
The real part μ′ of the relative magnetic permeability (μr=μ′+μ″i) of the radio wave absorbing layer (B) at a frequency of 24 GHz is in the range of 1.0 to 1.50, and the absolute value of the imaginary part μ″ is 0 or more and less than 1.0,
The relative part of the relative permittivity (εr=ε′+ε″i) of the radio wave absorbing layer (B) at a frequency of 24 GHz is in the range of 14 to 25, and the absolute value of the imaginary part ε″ is 4 to 10 Within range,
A quasi-millimeter wave/millimeter wave band radio wave absorption sheet, and a quasi-millimeter/millimeter wave band radio wave absorption method using the radio wave absorption sheet, and a radio wave reflector that causes a malfunctioning radio wave interference, The present invention relates to a method for preventing radio interference, in which a radio wave absorption sheet is installed or the radio wave absorption sheet described above is installed between the radio wave reflector and the radio wave reception device.

The radio wave absorption sheet of the present invention can exhibit a high level of radio wave absorption in the quasi-millimeter wave band. This radio wave absorption sheet can absorb high frequency radio waves such as quasi-millimeter waves and millimeter waves efficiently, so installing it near equipment that uses high frequency radio waves prevents malfunctions. It is applicable to various uses.

Also, since this electromagnetic wave absorption sheet is thin, has excellent flexibility and durability, it can be attached to a wide variety of base materials.

FIG. 1 is a schematic diagram showing the relationship between the respective layers constituting the radio wave absorption sheet. FIG. 2 is an example of a radio wave absorption characteristic chart in the quasi-millimeter wave band.

An embodiment of a quasi-millimeter wave/millimeter wave band electromagnetic wave absorption sheet according to the present invention will be described below with reference to the accompanying drawings. In the present specification, the quasi-millimeter wave band means 20 to 30 GHz including frequencies for automatic traveling and 5G communication, and the millimeter wave band means 76 to 81 GHz which is a frequency for collision prevention and automatic traveling. To do.

FIG. 1 is a schematic diagram showing the relationship of each layer constituting the radio wave absorption sheet according to the present invention.

In FIG. 1, a radio wave absorbing layer (B) and a protective layer (C) are sequentially stacked on the radio wave reflecting layer (A). The radio wave absorption sheet is used so that the radio wave α enters from the protective layer (C) side. Although spaces are provided between the layers in FIG. 1 for the sake of explanation, the layers are usually in close contact with each other in the present invention.

<Radio wave reflection layer (A)>
The radio wave reflection layer (A) reflects the radio wave α that has passed through the radio wave absorption layer (B) described later while being attenuated and reached the reflection layer A on its surface.

The material of the radio wave reflection layer (A) is not limited, but a metal sheet is generally used. The metal sheet also includes a metal foil. Examples of the type of metal include tin, brass, copper, iron, nickel, stainless steel, aluminum, and the like, and a mesh-shaped metal sheet may be used.

The thickness of the radio wave reflection layer (A) is not particularly limited, but is preferably in the range of 25 to 500 μm from the viewpoint of flexibility of the finally obtained radio wave absorption sheet and installation workability. And particularly preferably in the range of 30 to 300 μm.

In this specification, the film thickness can be obtained by observing a cross section of a test body using an SEM, arbitrarily selecting three positions from the obtained image, and averaging the selected values.

<Radio wave absorption layer (B)>
In FIG. 1, the radio wave absorption layer (B) is arranged in parallel on the radio wave reflection layer (A), and the relative permittivity and the film thickness at 24 GHz satisfy specific conditions.

<<Relative permeability and relative permittivity>>
In the present invention, it is important that the frequency for determining the relative magnetic permeability and the relative permittivity is 24 GHz. In the present specification, the relative magnetic permeability μr is a value represented by the following formula (1).

In the above formula (1), μr is the relative permeability, μ′ is the real part of the relative permeability, and μ″ is the imaginary part of the relative permeability, where i=√(−1). ..

Further, the magnetic permeability μ at 24 GHz of the material is a value represented by the following formula (2). The relative magnetic permeability μr defined in the present invention indicates the ratio of the magnetic permeability μ of the material to the magnetic permeability μ0 of vacuum, and has no unit.

For example, when the relative permeability μr is represented by μr=1.5−0.3i, “the real part μ′ of the relative permeability” is 1.5, and the absolute value of “the imaginary part μ of the relative permeability”. Is 0.3.

Further, in the present specification, the relative permittivity εr is a value represented by the following formula (3).

In the above equation (3), εr is the relative permittivity, ε′ is the real part of the relative permittivity, and ε″ is the imaginary part of the relative permittivity, where i=√(−1). ..

Also, the dielectric constant ε (F/m) of the material at 24 GHz is a value represented by the following formula (4). The relative permittivity εr defined in the present invention indicates the ratio of the permittivity ε (F/m) of the material to the permittivity ε0 (F/m) in vacuum, and has no unit.

For example, when the relative permittivity εr is represented by εr=5-3i, the “real part of relative permittivity ε′” is 5 and the “absolute value of imaginary part ε” of relative permittivity” is 3. And

In the present invention, the measurement of the relative permeability μr and the relative permittivity εr at a frequency of 24 GHz is performed by the free space S parameter method (reflection transmission method). For example, a vector type network analyzer (“PNA-X” product name, manufactured by KEYSIGHT) is used as a relative permittivity measuring device, a free space fixture and a calibration metal plate are used, and “N1500 material characteristic suite” (product name, KEYSIGHT (Manufactured by the company, software), and can be obtained by simulation from the measured value of the S parameter.

Since the relative permeability and the relative permittivity change depending on the frequency, the relative permeability and the relative permittivity data for each frequency are acquired within the frequency range of 20 to 30 GHz, and the relative permeability at the frequency of 24 GHz is selected from the data. The values of magnetic susceptibility and relative permittivity shall be selected.

In the radio wave absorption sheet of the present invention, the radio wave absorption layer (B) has a real part μ′ of relative permeability within a range of 1.0 to 1.5 at a frequency of 24 GHz and an imaginary part μ″ of relative permeability. Is less than 1.0, the real part ε′ of the relative permittivity is in the range of 14 to 25, and the imaginary part ε″ of the relative permittivity is in the range of 4 to 10. is there. The real part μ'of the relative permeability is 1.0 to 1.3, the absolute value of the imaginary part μ" of the relative permeability is less than 0.5, and the real part ε'of the relative permittivity is 18 to 23. More preferably, the absolute value of the imaginary part ε″ of the dielectric constant is within the range of 5 to 8.

When the real part μ'of the relative permeability of the electromagnetic wave absorbing layer (B) is less than 1.0, the electromagnetic wave absorption amount of the quasi-millimeter wave/millimeter wave band of the electromagnetic wave absorbing sheet decreases, while when it exceeds 1.5, the electromagnetic wave absorption becomes large. This is not preferable because the amount of electromagnetic wave absorption and durability in the quasi-millimeter wave/millimeter wave band of the sheet tend to decrease. Further, if the absolute value of the imaginary part μ" of the relative magnetic permeability exceeds 1.0, the radio wave absorption amount and durability in the quasi-millimeter wave/millimeter wave band of the radio wave absorption sheet tend to be reduced, which is not preferable. When the real part ε'of the dielectric constant is less than 14, the electromagnetic wave absorption amount in the quasi-millimeter wave/millimeter wave band of this electromagnetic wave absorption sheet is low, and even when it exceeds 25, the electromagnetic wave in the quasi-millimeter wave/millimeter wave band of this electromagnetic wave absorption sheet is low. If the absolute value of the imaginary part ε″ of the relative permittivity of the electromagnetic wave absorbing layer (B) is less than 4, the electromagnetic wave absorption amount in the quasi-millimeter wave/millimeter wave band is low, while the absorption amount tends to decrease. If it exceeds 10, the amount of radio wave absorption in the quasi-millimeter wave/millimeter wave band is reduced, which is not preferable.

The radio wave absorption layer (B) can be a film or coating containing a dielectric powder and a binder. The film or coating may be, for example, a film obtained by molding a dispersion obtained by dispersing dielectric powder in a binder into a film, or a radio wave absorbing paint containing the binder, the dielectric powder and a solvent. It may be a coating film formed by applying the composition and drying it.

《Binder》
A polymer is mainly used as the binder. Specific examples include ester rubber, chlorosulfonated polyethylene rubber, chlorinated rubber, ethylene propylene diene rubber, chloroprene rubber, natural rubber, styrene butadiene rubber, isoprene rubber, butadiene rubber, butyl rubber, ethylene propylene rubber, acrylonitrile butadiene rubber, chlorine. Rubber components such as chlorinated butyl rubber, chlorinated polyethylene rubber, chlorinated polypropylene rubber, chlorinated ethylene propylene rubber, brominated butyl rubber; polyimide, polyphenylene sulfide, shellac, rosin, polyolefin resin, chlorinated polyolefin resin, hydrocarbon resin, vinylidene chloride Resin components such as resin, polyamide resin, polyetherketone resin, vinyl chloride resin, polyester resin, alkyd resin, phenol resin, epoxy resin, acrylic resin, urethane resin, silicone resin, cellulose resin, vinyl acetate resin, etc. A combination and the like can be mentioned. Among these, preferably ethylene propylene diene rubber, chlorinated polyethylene rubber, chlorinated polypropylene rubber, chlorinated ethylene propylene rubber, chloroprene rubber, ethylene propylene rubber, polyolefin resin, chlorinated polyolefin resin, polyester resin, alkyd resin, phenol resin, Examples thereof include epoxy resin, acrylic resin, urethane resin, silicone resin, polyisocyanate resin, amino resin, and combinations thereof.

<<Powder with dielectric properties>>
As the dielectric powder, any material and shape can be used as long as it has dielectric properties. Specific examples include, for example, ferrite, sendust, Fe-Cr-Al alloy, Fe-Si-Cr alloy, Fe-Al-Si alloy, permalloy, carbonyl iron, α-alumina, β-alumina, corundum, and chromium oxide. , Cerium oxide, titanium oxide, ITO, silicon oxide compounds, silicon nitride, boron nitride, silicon carbide, silicon carbide, titanium carbide, calcium carbonate, barium sulfate, benzoguanamine, crosslinked polystyrene, polyethylene, silicone resin, polytetrafluoroethylene A powder of a material selected from the group consisting of carbon, carbons, barium titanate, and combinations thereof.

The average particle diameter of the dielectric powder is preferably 0.001 to 500 μm, more preferably 0.01 to 100 μm. When the dielectric powder has a needle-like shape, the average minor axis is preferably 0.001 to 500 μm, and more preferably 0.01 to 100 μm.

In the present specification, the average particle size or the average minor axis of the dielectric powder can be obtained by observing the SEM image of the radio wave absorption sheet of the present invention using SEM.

The amount of the dielectric powder contained in the radio wave absorption layer (B) is preferably 100 to 700 parts by mass, more preferably 200 to 500 parts by mass, based on 100 parts by mass of the binder.

Note that, as the powder having the above-mentioned dielectric property, it is suitable to include ferrite as a part of its component from the viewpoint of the radio wave absorptivity in the quasi-millimeter wave/millimeter wave band of the radio wave absorption sheet of the present invention.

In the present specification, ferrite refers to a complex oxide containing iron oxide and a metal in a part of its structure, and there is no limitation on the manufacturing method, shape, structure and the like. Among them, as a metal compounded with iron, at least one metal selected from manganese, zinc, nickel, cobalt, copper, barium, strontium, silicon, and aluminum, preferably at least two metals are chemically contained. Ferrite is preferred.

Preferable examples of ferrites containing a chemical structure of at least one metal in a part of iron oxide include, for example, zinc-based ferrite, cobalt-based ferrite, magnesium-based ferrite, barium-based ferrite, strontium-based ferrite, and these Combinations and the like can be mentioned.

Preferable examples of the ferrite containing at least two metals in a part of iron oxide in a chemical structure include, for example, manganese/zinc ferrite, manganese/nickel ferrite, nickel/zinc ferrite, copper/zinc ferrite, And combinations thereof.

When the dielectric powder contains ferrite, the amount of ferrite contained in the radio wave absorption layer (B) is preferably 150 to 650 parts by mass, more preferably 200 to 650 parts by mass, based on 100 parts by mass of the binder. 500 parts by mass.

Further, as the powder having the above-mentioned dielectric property, it is preferable that a silicon oxide-containing compound is included as a part of the component thereof from the viewpoint of the radio wave absorption and durability in the quasi-millimeter wave/millimeter wave band of the radio wave absorption sheet of the present invention. Are suitable.

Examples of the silicon oxide-containing compound in the present invention include silicon dioxide such as silica, and talc, diatomaceous earth, wollastonite, and other various silicon dioxide and minerals composed of metal oxides, as well as compounds containing silicon oxide in their composition. Included.

When the dielectric powder contains a silicon oxide-containing compound, the amount of the silicon oxide-containing compound contained in the radio wave absorbing layer (B) is preferably 0.5 to 50 parts by mass, based on 100 parts by mass of the binder. , And more preferably 1 to 10 parts by mass.

Further, as the above-mentioned dielectric powder, it is suitable to include carbons as a part of its components from the viewpoint of the radio wave absorption, flexibility and durability in the quasi-millimeter wave/millimeter wave band of the radio wave absorption sheet of the present invention. ing.

The carbons that can be used in the present invention are not limited in shape, manufacturing method, etc., and may be conductive or insulating. Specific examples include carbon black, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerenes, artificial diamond, graphite, and combinations thereof.

When the powder having dielectric properties contains carbons, the amount of carbons contained in the radio wave absorption layer (B) is preferably 1 to 50 parts by mass, and more preferably 100 parts by mass of the binder. It is 2 to 30 parts by mass.

The film thickness of the electromagnetic wave absorption layer (B) is also an important factor in achieving high level of electromagnetic wave absorption in the quasi-millimeter wave/millimeter wave band region. In the present invention, the thickness of the radio wave absorbing layer (B) is in the range of 400 to 1000 μm, preferably 450 to 900 μm, and particularly preferably 500 to 800 μm. When the film thickness of the electromagnetic wave absorbing layer (B) is less than 400 μm, the electromagnetic wave absorbing property of this electromagnetic wave absorbing sheet in the quasi-millimeter wave/millimeter wave band deteriorates, while even when it exceeds 1000 μm, the electromagnetic wave in the quasi-millimeter wave/millimeter wave band Absorbency is reduced.

In addition, in the present invention, in addition to the relative permittivity and film thickness of the radio wave absorption layer (B), the tangent delta value is important as an index having radio wave absorptivity in the quasi-millimeter wave/millimeter wave band.

If the electromagnetic wave absorbing layer (B) has a tangent delta value in the range of 0.25 to 0.70 in addition to the conditions of relative permeability, relative permittivity and film thickness, the electromagnetic wave absorbing sheet of the present invention. This is preferable because it has good radio wave absorption in the quasi-millimeter wave/millimeter wave band.

The tangent delta value is a numerical value representing the degree of electric energy loss in the dielectric body, and in this specification, it is a value obtained by calculating the absolute value of the imaginary part/real part ratio of the relative permittivity.

In the present invention, the radio wave absorption layer (B) may have a single layer structure or a multi-layer structure, but when the radio wave absorption layer (B) has a single layer structure, the radio wave absorption sheet which is the final product. It is effective because it can reduce the time required for manufacturing, and has moderate electromagnetic wave absorbability and flexibility in the quasi-millimeter wave/millimeter wave band.

<Protective layer (C)>
In FIG. 1, the protective layer (C) is disposed in parallel with the upper portion of the radio wave absorption layer (B), and the radio wave absorption sheet of the present invention has a radio wave absorption property in desired quasi-millimeter wave/millimeter wave band. And, if necessary, to provide durability. Then, as shown in FIG. 1, it is important that the radio wave absorption layer (B) is disposed on the radio wave reflection layer (A) and the protection layer (C) is disposed on the radio wave absorption layer (B) in this order. Is.

Further, by providing the protective layer (C), it is possible to protect each layer located below the protective layer (C) and also to impart durability to the electromagnetic wave absorbing sheet.

The protective layer (C) may be a molded film or a coating film obtained by applying a coating composition and drying. The protective layer (C) may have a single-layer structure or a multi-layer structure.

In the present invention, the material of the protective layer (C) is not particularly limited, but a film containing a polymer (synthetic resin) as a binder is suitable. Examples of such a polymer include the same compounds as exemplified in the explanation of the radio wave absorption layer (B), and among them, a resin selected from vinyl chloride resin, polyurethane resin and polyolefin resin is preferable.

As the film containing a polyurethane resin in the present specification, not only a film using a polyurethane resin as a binder, but also a film obtained by mixing a component containing a hydroxyl group-containing resin and a polyisocyanate, coating and curing the same is a polyurethane resin. Include as a film.

Also, it is suitable that the protective layer (C) contains a pigment from the viewpoint of the durability of the radio wave absorption sheet. As the pigment, a color pigment and an extender pigment can be used.

The color pigment can be appropriately selected according to the design, use, and purpose. Further, as the coloring pigment, conventionally known pigments can be used. Specific examples of the coloring pigment include, for example, black pigments such as carbon black, copper oxide, ferrosoferric oxide, manganese dioxide, aniline black and activated carbon; yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, Yellow pigments such as nickel titanium yellow, navel yellow, naphthol yellow S, hansa yellow, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake; red iron oxide, cadmium red, red lead, mercury sulfide, cadmium. , Permanent Red 4R, Resole Red, Pyrozolone Red, Watching Red, Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B; Red Pigment; Navy Blue, Cobalt Blue, Blue pigments such as Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue, Metal-Free Phthalocyanine Blue, Phthalocyanine Blue Partial Chloride, Fast Sky Blue, Induslen Blue BC; Chrome Green, Chromium Oxide, Pigment Green B, Malachite Green Lake, Final And green pigments such as yellow green G; white pigments such as zinc white, titanium oxide, antimony white, zinc sulfide, and combinations thereof; and the like. On the other hand, examples of extender pigments include silica, talc, mica, calcium carbonate, clay, kaolin, barium sulfate, and combinations thereof.

The blending amount of the coloring pigment varies depending on the type used, but in general, from the viewpoint of the concealing property of the protective layer (C), the radio wave absorbing property in the quasi-millimeter wave/millimeter wave band, flexibility and durability, the protective layer is generally used. It is preferably in the range of 0.1 to 300 parts by mass, particularly preferably in the range of 5 to 150 parts by mass, based on the mass of the polymer contained in the colored film constituting (C).
The amount of the extender pigment to be blended is preferably in the range of 1 to 200 parts by mass, based on the mass of the polymer contained in the colored film from the viewpoint of radio wave absorption in the quasi-millimeter wave/millimeter wave band, flexibility and durability. And particularly preferably in the range of 2 to 100 parts by mass.

The hiding ratio of the protective layer (C) is preferably 50% or more, and it is particularly preferable to use one having a hiding ratio of 70% or more.

In the present specification, the hiding ratio of the protective layer (C) is, for example, a hiding ratio test paper conforming to the B method of JIS K56004-1, the protective layer (C) is placed, and the tristimulus is applied via the protective layer (C). The value Y is measured in each of the white part (YW) and the black part (YB), and YB/YW is calculated as a percentage.

In the present invention, the film thickness of the protective layer (C) is preferably in order to exert a high level of radio wave absorption in the quasi-millimeter wave/millimeter wave band region and to improve flexibility and durability. It is in the range of 30 to 200 μm, particularly preferably in the range of 50 to 100 μm.

In the present invention, as the relative dielectric constant of the protective layer (C) alone at a frequency of 24 GHz, the real part ε′ is 1.5 to 8.0, preferably 2.0 to 5.0, and the relative dielectric constant is It is suitable that the absolute value of the imaginary part ε″ is less than 1.0, particularly preferably less than 0.1, and the tangent delta value is less than 0.1, particularly less than 0.01. Are suitable.

<Electromagnetic wave absorption sheet>
The radio wave absorption sheet of the present invention comprises a radio wave reflection layer (A), a radio wave absorption layer (B), and, if necessary, a protective layer (C), and a known method can be used to attach each layer. Used. Each layer may be formed by applying a liquid coating material and drying it, but when forming by film sticking, an adhesive layer (P) may be provided between each film as needed.

<Adhesive layer (P)>
The adhesive layer (P) is a layer provided as necessary for the purpose of improving the adhesiveness between the layers and improving the durability of the present radio wave absorption sheet, and a known adhesive or pressure-sensitive adhesive can be used.

The form of the adhesive or pressure-sensitive adhesive forming the adhesive layer (P) may be any of water dispersion system, solution system, two-liquid mixture system, solid system, and tape system. Although the material is not particularly limited, it may be an organic adhesive or an adhesive, or an inorganic adhesive or an adhesive.

Examples of organic adhesives or adhesives include vinyl acetate-based, vinyl acetate resin emulsion-based, vinyl resin-based, ethylene-vinyl acetate resin-based, polyvinyl acetate resin-based, epoxy resin-based, polyvinyl alcohol-based, ethylene vinyl acetate System, vinyl chloride system, α-olefin system, acrylic resin system, polyamide system, polyimide system, cellulose system, polyvinylpyrrolidone system, polystyrene system, polystyrene resin system, cyanoacrylate system, polyvinyl acetal system, urethane resin system, polyolefin resin system , Polyvinyl butyral resin system, polyaromatic system, urea resin system, melamine resin system, phenol resin system, resorcinol system, chlorobrene rubber system, nitrile rubber system, styrene butadiene rubber system, polybenzimidazole system, thermoplastic elastomer -Based, butyl rubber-based, silicone-based, modified silicone-based, silylated urethane-based, urethane rubber-based, polysulfite-based, acrylic rubber-based and other synthetic adhesives; and starch-based, natural rubber-based, asphalt, glue, gum arabic , Natural adhesives or pressure sensitive adhesives such as lacquer, casein, soybean protein and pine nuts; reactive hot melt adhesives or pressure sensitive adhesives.

Examples of inorganic adhesives or adhesives include sodium silicate, cement-based (Portland cement, plaster, gypsum, magnesium cement, litharge cement, dental cement, etc.) and ceramics.

Among the above-mentioned adhesives or pressure-sensitive adhesives, the use of synthetic adhesives or pressure-sensitive adhesives is suitable from the viewpoint of the flexibility of the present electromagnetic wave absorption sheet, the electromagnetic wave absorption in the quasi-millimeter wave/millimeter wave band, and the durability. ..

The film thickness of the adhesive layer (P) is not particularly limited, but can be generally 100 μm or less from the viewpoint of radio wave absorption in the quasi-millimeter wave/millimeter wave band, and particularly 7 to 80 μm. Can be in the range of.

In the present invention, in order to exert a high level of radio wave absorption in the quasi-millimeter wave/millimeter wave band, the outermost surface of the radio wave absorption sheet (the radio wave absorption layer (B) side, the protective layer if there is a protective layer (C)) The (C) side) has a surface roughness Sa (arithmetic mean surface roughness) of 150 to 6000 nm, preferably 200 to 5500 nm, and a Sq (root mean square height surface roughness) of 200 to 7,000 nm, preferably 300. It is desirable to adjust the thickness within the range of up to 6000 nm.

In the present invention, the roughness parameters Sa (arithmetic mean roughness) and Sq (root mean square height) are based on the method specified in ISO 25178, using images of the surface of the test body taken under the following conditions. It was measured.
・Device: Optical interference microscope (Counter GT-1 manufactured by Bruker AXS)
-Objective lens: 5 times-Internal lens (eyepiece): 0.55 times-Measurement range: Width 6 mm/length: 1.7 mm.

<Radio wave absorption method>
The present invention provides a radio wave absorbing method for absorbing radio waves in the quasi-millimeter wave/millimeter wave band by using the radio wave absorbing sheet as described above.

Further, the present invention is to install the above-mentioned radio wave absorbing sheet on a radio wave reflecting body which causes a radio wave trouble of malfunction, or to install the above radio wave absorbing sheet between the radio wave reflecting body and a radio wave receiving device. It is intended to provide a method of preventing electromagnetic interference that is installed.

The radio wave absorption sheet of the present invention described above can have a total film thickness of 0.5 to 1.5 mm, particularly 0.6 to 1 mm, and is extremely flexible. In the case of paint, the film thickness after drying may be within this range. Therefore, it can be easily attached to radio wave reflectors of various shapes.

The radio wave reflector for installing the radio wave absorbing sheet of the present invention directly or in the vicinity thereof is particularly a product/structure which is in an environment where radio waves in the quasi-millimeter wave and the millimeter wave, particularly in the quasi-millimeter wave band are generated. There is no limit.

Some specific examples are car travel such as medians, tunnel inner walls, sound insulation walls, sound insulation walls, road signs, guardrails, road reflection mirrors, telephone poles, traffic lights, traffic signs, street trees, road lighting poles, etc. Examples include goods and structures near roads, automobile factories and maintenance areas, and wall surfaces of rooms.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples. In addition, "part" and "%" in the following examples mean "mass part" and "mass %", respectively.

<Manufacture of electromagnetic wave absorption sheet>
Example 1
An aluminum foil (Al foil) having a length of 30 cm, a width of 30 cm, and a thickness of 50 μm is provided with a 10 μm adhesive layer (acrylic adhesive), and 100 parts of chlorinated polyethylene rubber is coated with MnZn ferrite (manganese). -Zinc-based ferrite, average particle size 0.7 μm) 350 parts, insulating carbon 350 parts, and silica 3 parts are kneaded and molded to obtain a single-layer structure sheet having a thickness of 570 μm, which is further laminated. An adhesive layer (acrylic adhesive) having a thickness of 10 μm was provided thereon, and a protective sheet (note) having a thickness of 80 μm was attached to obtain a radio wave absorption sheet (X-1).

(Note) Protective sheet: Colored film containing vinyl chloride resin and titanium oxide. The amount of titanium oxide was 80 parts with respect to 100 parts of the vinyl chloride resin.

Examples 2-15 and Comparative Examples 1-9
Sheet-shaped electromagnetic wave absorption sheets (X-2) to (X-24) were prepared in the same manner as in Example 1 except that the materials and thicknesses of the electromagnetic wave absorption layer and the protective layer were as shown in Tables 1 to 4. Got In the table, phr means the mass ratio of each component to 100 parts by mass of the binder. Further, in the table, j described in the column of the relative dielectric constant of the protective layer has the same meaning as i representing the relative dielectric constant of the radio wave absorption layer. Therefore, the real part of the relative permittivity of the protective layer of Example 1 is 3.8, and the absolute value of the imaginary part is 0.08.

Comparative Example 10
An aluminum foil having a length of 30 cm, a width of 30 cm, and a thickness of 50 μm is provided with a 10 μm adhesive layer, and 790 parts of manganese-zinc ferrite is kneaded with 100 parts of EPDM rubber (ethylene propylene diene rubber). Then, the sheet (1) having a film thickness of 550 μm obtained by molding was laminated, and further, 300 parts of barium ferrite was kneaded with 100 parts of ethylene propylene diene rubber, and molded to obtain A sheet (2) with a film thickness of 950 μm is laminated, and a commercially available white marking film with a thickness of 80 μm (a design film with an adhesive, a fan tack sheet: Kampe Fan Tuck Center Co., Ltd.) is attached on the sheet (2) to form an electromagnetic wave absorption sheet. (X-25) was obtained. In the radio wave absorbing sheet (X-25), the relative permittivity of the sheet (1) at a frequency of 79 GHz is ε=34-4.5i, and the relative permittivity of the sheet (2) is ε=2.5-0. .2i. The radio wave absorption sheet (X-25) has a total film thickness of 1.64 mm, the radio wave absorption layer portion has a laminated structure, and the thickness of the portion is 1.5 mm.

(Note) MnZn ferrite: Manganese/zinc ferrite, average particle size 0.7 μm,
(Note) Insulating carbon: Insulating carbon black, average particle size 20 nm,
(Note) Conductive carbon: conductive carbon black, average particle size 34 nm,
(Note) Silica: average particle diameter 6 μm,
(Note) Ba ferrite: barium ferrite, average particle diameter 2 μm,
(Note) Barium titanate: average particle size 2 μm,
(Note) Fe-Al-Si alloy: An alloy of iron, aluminum and silicon.

<Evaluation test>
The electromagnetic wave absorbing sheets (X-1) to (X-25) prepared in the above Examples and Comparative Examples were evaluated according to the following criteria and methods, and the properties of each electromagnetic wave absorbing sheet are shown in Tables 1 to 4. .. In Tables 1 to 4, the relative permittivity and relative permeability of the electromagnetic wave absorbing layer (B) and the protective layer (C), the thickness of the electromagnetic wave absorbing sheet, and the roughness parameters Sa and Sq are the methods described in the specification. It was sought by.

(*) Measurement of quasi-millimeter wave radio wave absorption of each radio wave absorption sheet The radio wave absorption of each radio wave absorption sheet is measured in an anechoic chamber with a radio wave absorber with a radio wave absorption amount of -30 dB or more installed on the wall and floor of the room. , Was measured using a radio wave absorption measuring device. Specifically, the transmission horn antenna and the reception horn antenna included in the radio wave absorption measuring device are arranged so that the incident and reflection angles thereof are 10° with respect to a vertical plane from the floor. And a receiving horn antenna are installed, a metal reflector is placed at a distance of 45 cm from each antenna, and the reflected signal is received by the receiving horn antenna and the radio wave reflectance is set to 100%. .. Next, the metal reflector is removed, and the reflected signal is received by the receiving horn antenna, and the radio wave reflectance thereof is set to 0%. Then, the measurement sample is placed at the position where the metal reflector is placed, and the radio wave reflection amount reflected from the measurement sample surface is measured for frequencies near the quasi-millimeter wave, and the frequency (GHz) is taken as the horizontal axis, and the radio wave absorption amount (dB ) Is a vertical axis, and a radio wave absorption characteristic chart near the quasi-millimeter wave is obtained. FIG. 2 shows an example of a radio wave absorption characteristic chart.

(*) Radio wave absorption amount at peak frequency In the radio wave absorption characteristic chart obtained by the above radio wave absorption amount measurement, the frequency with the highest radio wave absorption amount is defined as the peak frequency (M3), and the radio wave absorption amount at the peak frequency is calculated, It is described inside. It should be noted that the lower the numerical value of the radio wave absorption amount in the table, the greater the radio wave absorption amount and the better.

(*) Bandwidth at which the electromagnetic wave absorption amount is -20 dB or more The difference between the maximum absorption frequency M1 and the minimum absorption frequency M2 in the radio wave absorption amount -20 dB, which is expressed by the following formula. bw=M1-M2.

The larger the number in the table, the wider the bandwidth in the quasi-millimeter wave region, and the better. The symbol "-" in the table means that the width cannot be measured because the amount of radio wave absorption has not reached -20 dB.

(*) Millimeter-wave radio wave absorption measurement of each radio wave absorption sheet In the above quasi-millimeter wave radio wave absorption measurement test, the radio wave reflection amount reflected from the measurement sample was measured for frequencies near the millimeter wave instead of quasi-millimeter wave, A millimeter wave electromagnetic wave absorption characteristic chart having a frequency (GHz) as a horizontal axis and a radio wave absorption amount (dB) as a vertical axis was obtained. The method of obtaining the amount of radio wave absorption at the peak frequency and the bandwidth at which the amount of radio wave absorption is -20 dB or more is the same as in the case of quasi-millimeter wave. In the table, − means that the maximum absorption amount is less than −20 dB.

(*) Flexibility Each of the electromagnetic wave absorption sheets (X-1) to (X-25) is manually bent by 180° with the electromagnetic wave reflection layer facing down, and the bending workability and the surface condition of the bending part are based on the following standards. Was evaluated.
◯: Bending workability is good, and no damage is observed in the bent portion,
Δ: Bending workability is good, but some damage is observed in the bent portion,
X: The bending work is difficult, and significant damage is recognized in the bent portion.

(*durability)
Drop a drop of 5% hydrochloric acid aqueous solution on the surface of the protective layer or the electromagnetic wave absorbing layer side that constitutes each electromagnetic wave absorbing sheet with a dropper, leave it in an atmosphere of 50° C. for 5 hours, then wash with water and observe the spotted spot, The following criteria evaluated.
⊚: No change is observed
○: Some lusteriness is observed in the spot part,
Δ: Luster is clearly observed in the spot part,
X: Swelling or whitening occurs on the coated surface.

(Discussion)
From the results of Tables 1 to 4, the effects of the present invention will be considered below.

Examples 1 to 15 are electromagnetic wave absorption sheets within the range specified by the present invention.

Comparative Examples 1 and 2 are radio wave absorption sheets in which the film thickness of the radio wave absorption layer (B) is out of the range specified in the present invention.

Comparative Examples 3 and 9 are radio wave absorption sheets in which the relative permittivity real part and the imaginary part of the radio wave absorption layer (B) are below the range specified in the present invention.

Comparative Examples 4 and 5 are radio wave absorption sheets in which the real part of the relative magnetic permeability of the radio wave absorption layer (B) exceeds the range specified in the present invention.

Comparative Example 6 is a radio wave absorption sheet in which the imaginary part of the relative magnetic permeability of the radio wave absorption layer (B) exceeds the range specified in the present invention.

Comparative Example 7 is a radio wave absorption sheet that does not have the radio wave reflection layer (A).

Comparative Example 8 is a radio wave absorption sheet in which the real and imaginary parts of the relative permittivity of the radio wave absorption layer (B) exceed the range specified by the present invention.

Comparative Example 10 is a radio wave absorption sheet in which the film thickness of the radio wave absorption layer portion exceeds the range of the present invention.

The following can be said from the electromagnetic wave absorption characteristics in the quasi-millimeter wave and millimeter wave bands, the flexibility test, and the durability test results using the electromagnetic wave absorption sheet prepared above.

The radio wave reflection layer (A) and the radio wave absorption layer (B) are provided and the positional relationship is as specified, the thickness of the radio wave absorption layer (B) is within a predetermined range, and the relative permittivity and relative permeability of the radio wave absorption layer are As long as the magnetic susceptibility is within the predetermined range of the present invention, it is possible to obtain a radio wave absorption sheet which is extremely excellent in quasi-millimeter wave absorption, has a wide bandwidth, has millimeter wave absorption, and is excellent in flexibility and durability.

When the thickness of the electromagnetic wave absorbing layer (B) does not satisfy the condition of the thickness, the quasi-millimeter wave absorbing property of the electromagnetic wave absorbing sheet cannot be sufficiently exerted, but when the thickness of the electromagnetic wave absorbing layer (B) is within the range specified by the present invention. As far as possible, the quasi-millimeter wave absorption and the bandwidth are dramatically increased. (Comparison between Example 1 and Comparative Examples 1 and 2).

If the electromagnetic wave absorbing layer (B) does not satisfy the condition of the relative permittivity, the quasi-millimeter wave absorbing property of the electromagnetic wave absorbing sheet cannot be sufficiently exhibited, but the relative permittivity of the electromagnetic wave absorbing layer (B) falls within the range of the present invention. Only at certain times, millimeter wave absorption and bandwidth will increase dramatically. (Comparison between Example 1 and Comparative Examples 3, 8 and 9).

ㆍThe electromagnetic wave absorbing sheet without the electromagnetic wave reflection layer (A) cannot fully exhibit the quasi-millimeter wave absorbing property of the electromagnetic wave absorbing sheet. However, the combination of all layers dramatically increases the millimeter wave absorption and bandwidth. (Comparison between Example 1 and Comparative Example 7).

When the condition of the relative magnetic permeability of the radio wave absorbing layer (B) is not satisfied, the quasi-millimeter wave absorbing property of the radio wave absorbing sheet cannot be sufficiently exhibited, but the relative magnetic permeability of the radio wave absorbing layer (B) falls within the range specified by the present invention. Only at certain times, millimeter wave absorption and bandwidth are dramatically increased, and durability is also improved. (Comparison between Example 1 and Comparative Examples 4, 5 and 6).

ㆍEven if the electromagnetic wave absorbing layer contains a powder having dielectric properties, the total film thickness is large, and if it has a laminated structure, it has millimeter wave absorption but the quasi-millimeter wave characteristics are not sufficient. (Comparison between Example 1 and Comparative Example 10).

Claims (17)

1. A radio wave reflection layer (A) and a radio wave absorption layer (B) arranged in parallel on the radio wave reflection layer (A),
   The film thickness of the radio wave absorption layer (B) is in the range of 400 to 1000 μm,
   The real part μ′ of the relative magnetic permeability (μr=μ′+μ″i) of the radio wave absorbing layer (B) at a frequency of 24 GHz is in the range of 1.0 to 1.50, and the absolute value of the imaginary part μ″ is 0 or more and less than 1.0,
   The relative part of the relative permittivity (εr=ε′+ε″i) of the radio wave absorbing layer (B) at a frequency of 24 GHz is in the range of 14 to 25, and the absolute value of the imaginary part ε″ is 4 to 10 Within range,
   Electromagnetic wave absorption sheet for quasi-millimeter wave/millimeter wave band.
2. The radio wave absorption layer (B) is a film containing a powder having a dielectric property and a binder,
   The dielectric powder has the following materials:
   Ferrite, sendust, Fe-Cr-Al alloy, Fe-Si-Cr alloy, Fe-Al-Si alloy, permalloy, carbonyl iron, α-alumina, β-alumina, corundum, chromium oxide, cerium oxide, titanium oxide, ITO , Silicon oxide compounds, silicon nitride, boron nitride, silicon carbide, silicon carbide, titanium carbide, calcium carbonate, barium sulfate, benzoguanamine, crosslinked polystyrene, polyethylene, silicone resin, polytetrafluoroethylene, carbons, barium titanate, The radio wave absorption sheet according to claim 1, which is a powder of a material selected from the group consisting of a combination thereof.
3. The radio wave absorption sheet according to claim 2, wherein the powder having dielectric properties contains ferrite as a part of its component.
4. The radio wave absorption sheet according to claim 2 or 3, wherein the dielectric powder contains a silicon oxide-containing compound as a part of its components.
5. The radio wave absorbing sheet according to any one of claims 2 to 4, wherein the powder having dielectric properties contains carbon as a part of its components.
6. 6. The electromagnetic wave absorbing layer (B) according to any one of claims 2 to 5, wherein 100 to 700 parts by mass of the dielectric powder is included based on 100 parts by mass of the binder contained in the electromagnetic wave absorbing layer (B). The electromagnetic wave absorption sheet according to item 1.
7. 7. The radio wave absorption layer (B) according to any one of claims 2 to 6, wherein a film obtained by molding a dispersion obtained by dispersing the powder having the dielectric property in the binder into a film shape. Radio wave absorption sheet.
8. Any one of 2 to 6 wherein the radio wave absorbing layer (B) is a film formed by applying a radio wave absorbing coating composition containing the binder, the powder having the dielectric property, and a solvent and drying the composition. Electromagnetic wave absorption sheet according to the item.
9. The radio wave absorption sheet according to any one of claims 1 to 8, wherein the radio wave absorption layer (B) has a single layer structure.
10. A protective layer (C) is further provided at a position on the outermost surface, and the radio wave reflection layer (A), the radio wave absorption layer (B), and the protection layer (C) are arranged in parallel in this order. 9. The radio wave absorption sheet according to any one of 9 above.
11. The radio wave absorption sheet according to claim 10, wherein the protective layer (C) is a film containing a resin selected from vinyl chloride resin, polyurethane resin and polyolefin resin as a binder.
12. The radio wave absorption sheet according to claim 10 or 11, wherein the protective layer (C) is a colored film containing a coloring agent.
13. When the real part ε′ of the relative dielectric constant (εr=ε′+ε″i) of the protective layer (C) at a frequency of 24 GHz is in the range of 1.5 to 8 and the absolute value of the imaginary part ε″ is 0 or more. The radio wave absorption sheet according to any one of claims 10 to 12, which is less than 1.0.
14. The radio wave absorption sheet according to any one of claims 1 to 13, wherein the surface roughness of the outermost surface is in the range of arithmetic mean roughness of 150 to 6000 nm and root mean square height of 200 to 7,000 nm.
15. The radio wave absorption sheet according to any one of claims 1 to 14, wherein an adhesive layer (P) is provided between at least one of the layers.
16. A method of absorbing radio waves in the quasi-millimeter/millimeter wave band using the radio wave absorbing sheet according to any one of claims 1 to 15.
17. The radio wave absorbing sheet according to any one of claims 1 to 15 is installed on a radio wave reflector that causes electromagnetic interference due to malfunction, or between the radio wave reflector and the radio wave receiving device. A method for preventing radio interference, which comprises installing the radio wave absorption sheet according to any one of claims 1 to 15.

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