Radio wave absorber

Abstract

The technical problem to be solved by the present invention is to provide a radio wave absorber which has good radio wave absorption for oblique incidence, especially for oblique incidence of radio waves near 60 GHz. The technical problem is solved by a radio wave absorber which, in the measurement of circularly polarized waves with an incidence of 45°, has an absorption performance of more than 15 dB in the 55-65 GHz band and an absorption range of more than 4 GHz.

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave absorber. Background Art

[0002] In recent years, the popularity of portable communication devices such as mobile phones and smart phones has been rapidly advancing. In addition, a large number of electronic devices are also installed in vehicles, etc., and problems such as radio interference caused by the radio waves and noise generated by them, and failures of other electronic devices have occurred frequently. As a countermeasure to prevent such radio interference and failures, various radio wave absorbers are being studied. For example, Patent Document 1 discloses an electromagnetic wave absorber having a bandwidth of more than 2 GHz in a frequency band of 60 to 90 GHz and an electromagnetic wave absorption amount of more than 20 dB.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-098367 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] Depending on the purpose of the radio wave absorber, the radio wave absorber may not be configured so that the radio wave is incident from the normal direction. In this case, the absorbency of obliquely incident radio waves is very important. The inventors have conducted research focusing on this point and found that the conventional radio wave absorbers can already cope with radio waves incident from the normal direction, but cannot fully absorb obliquely incident radio waves.

[0008] Therefore, the present invention aims to provide a radio wave absorber having good radio wave absorption performance at oblique incidence, and in particular, to provide a radio wave absorber having good radio wave absorption performance at oblique incidence of radio waves around 60 GHz.

[0009] Technical solutions to solve problems

[0010] In the course of the research, the inventors found that by optimizing the characteristics at 45-degree incidence, it is possible to exhibit good radio wave absorption properties for incident waves from various angles. Furthermore, based on the above findings, the inventors conducted further research and found a radio wave absorber that can solve the above technical problems. In the measurement of circularly polarized waves incident at 45 degrees, the radio wave absorber has an absorption performance of 15 dB or more in the 55-65 GHz band and an absorption range of more than 4 GHz. The inventors continued their research based on the above findings and completed the present invention.

[0011] That is, the present invention includes the following embodiments.

[0012] Item 1. A radio wave absorber having an absorption performance of 15 dB or more in the 55 to 65 GHz band in a measurement of a circularly polarized wave incident at 45° and having an absorption range of 4 GHz or more.

[0013] Item 2. The radio wave absorber according to Item 1, comprising a resistor film, a dielectric layer, and a reflective layer.

[0014] Item 3. The radio wave absorber according to Item 2, wherein the resistance value of the resistance film is 250 to 520 Ω / □.

[0015] Item 4: The radio wave absorber according to Item 2 or 3, which satisfies the formula (1): 950≤d×√ε≤1500,

[0016] Wherein, d represents the thickness of the dielectric layer (μm), and ε represents the relative dielectric constant of the dielectric layer.

[0017] Item 5. The radio wave absorber according to any one of Items 2 to 4, wherein the dielectric layer has a relative dielectric constant of 1 to 10.

[0018] Item 6. The radio wave absorber according to any one of Items 2 to 5, wherein the resistive film includes a barrier layer.

[0019] Item 7. The radio wave absorber according to any one of Items 2 to 6, wherein the resistor film contains molybdenum.

[0020] Item 8. The radio wave absorber according to Item 7, wherein the resistor film further contains nickel and chromium.

[0021] Item 9. The radio wave absorber according to any one of Items 2 to 8, wherein a surface roughness (Rz) of a surface of the reflective layer on the dielectric layer side is 1 μm or more and 10 μm or less.

[0022] Item 10. The radio wave absorber according to any one of Items 2 to 9, further comprising a support, wherein the surface tension of the outermost surface of the radio wave absorber on the support side is 35 dyn / cm or more.

[0023] Item 11. The radio wave absorber according to Item 10, wherein the total light transmittance of the support is 30% or less.

[0024] Item 12. A component for a λ / 4 type radio wave absorber, which has a resistor film and a dielectric layer, and when an aluminum plate with a thickness of 10 μm is laminated on the other surface of the dielectric layer, in the measurement of a circularly polarized wave incident at 45°, the component for a radio wave absorber has an absorption performance of 15 dB or more in the frequency band of 55 to 65 GHz and an absorption range of more than 4 GHz.

[0025] Effects of the Invention

[0026] According to the present invention, it is possible to provide a radio wave absorber having excellent radio wave absorptivity for oblique incidence, particularly for oblique incidence of radio waves near 60 GHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] [ Figure 1 ] is a schematic cross-sectional view showing an example of the radio wave absorber of the present invention.

[0028] [ Figure 2 The figure above is a schematic cross-sectional view showing an example of a component for a radio wave absorber of the present invention. The figure below is a schematic cross-sectional view showing an example of an adherend that is arranged in contact with the component and can function as a reflective layer.

[0029] [ Figure 3 ] is a schematic cross-sectional view showing an example of the use of the radio wave absorber of the present invention (an example of a form in which it is arranged on a shell via an adhesive). DETAILED DESCRIPTION

[0030] In this specification, the expressions “including” and “comprising” include the concepts of “including”, “comprising”, “substantially including” and “comprising only”.

[0031] The present invention, in one embodiment, relates to a radio wave absorber (sometimes referred to as "radio wave absorber of the present invention" in the present invention specification), wherein in the measurement of circularly polarized waves incident at 45°, the radio wave absorber has an absorption performance of 15 dB or more in the 55 to 65 GHz band and an absorption range of 4 GHz or more. This will be described below.

[0032] <1. Characteristics>

[0033] The radio wave absorber of the present invention has the following characteristics (sometimes referred to as "characteristics of the present invention" in this specification), that is, in the measurement of circularly polarized waves incident at 45°, the absorption performance of the radio wave absorber in the 55-65 GHz band is 15 dB or more, and the absorption range is above 4 GHz. By having this characteristic, the radio wave absorber can exhibit good radio wave absorption properties against incident waves from various angles.

[0034] The “absorption range in which the absorption performance is 15 dB or more in the 55 to 65 GHz band” refers to the width (unit: GHz) of the frequency band in which the absorption performance is 15 dB or more (=reflection attenuation is -15 dB or less) in the 55 to 65 GHz band.

[0035] The above-mentioned absorption range can be measured by the following method.

[0036] The radio wave absorption measuring device was composed of a PNA microwave network analyzer N5227A (manufactured by Keysight), a PNA-X series 2-port millimeter wave controller N5261A (manufactured by Keysight), and a horn antenna FSS-07 (manufactured by HVS). The radio wave absorption measuring device was used to measure the radio wave absorption amount of the radio wave absorber in the E band (60 to 90 GHz) and the U band (40 to 60 GHz) in accordance with JIS R1679.

[0037] It should be noted that the radio wave is incident on the front of the measurement sample at 45 degrees, and the horn antenna is installed at the same angle relative to the perpendicular line of the center of the measurement sample surface. The electric field of the incident wave is perpendicular to the incident surface (TE wave) and the reflection coefficient ΓTE is measured.

[0038] Subsequently, the reflection coefficient ΓTM was measured by the same method in a state where the electric field of the incident wave was parallel to the incident plane (TM wave).

[0039] The average value of the reflection coefficients ГTE and ГTM is defined as the reflection coefficient ГCP of the circularly polarized wave.

[0040] Using the above coefficients, the reflection loss amount for circularly polarized waves was calculated by -20log|ГCP|. The absolute value of the reflection loss amount was defined as the absorption performance.

[0041] The absorption range is preferably 5 GHz or more, more preferably 6 GHz or more, further preferably 8 GHz or more, further preferably 9 GHz or more, and particularly preferably 9.5 GHz or more. Since the absorption range is within the frequency band of 55 to 65 GHz, the upper limit is 10 GHz.

[0042] <2. Composition>

[0043] The structure of the radio wave absorber of the present invention is not particularly limited as long as it has the characteristics of the present invention. For example, a known structure of a radio wave absorber can be adopted. In one embodiment, the radio wave absorber of the present invention has a structure such as a resistance film, a dielectric layer, and a reflection layer. That is, in one embodiment, the radio wave absorber of the present invention is a λ / 4 type radio wave absorber. This embodiment will be described below.

[0044] <2-1. Resistor Film>

[0045] The resistance film is not particularly limited as long as it includes a layer that can function as a resistance layer in the radio wave absorber.

[0046] The resistance value of the resistor film is not particularly limited as long as it can satisfy the characteristics of the present invention. By adjusting the resistance value of the resistor film, the absorption range in the characteristics of the present invention can be adjusted. The resistance value of the resistor film can be, for example, 200 to 600Ω / □. In this range, it is more preferably 250Ω / □ or more, more preferably 300Ω / □ or more, and particularly preferably 330Ω / □ or more. In this range, it is more preferably 520Ω / □ or less, more preferably 450Ω / □ or less, and particularly preferably 390Ω / □ or less.

[0047] The resistance value of the resistor film can be measured by a four-terminal method using a surface resistivity meter (manufactured by MITSUBISHI CHEMICAL ANALYTECH CO., LTD., trade name “Loresta-EP”).

[0048] The thickness of the resistor film is not particularly limited as long as it satisfies the resistance value of the characteristics of the present invention. The thickness of the resistor film is, for example, 1 nm to 200 nm, preferably 2 nm to 100 nm, and more preferably 2 nm to 50 nm.

[0049] The layer structure of the resistor film is not particularly limited. The resistor film may be composed of a single layer or a combination of two or more layers.

[0050] <2-1-1. Resistance layer>

[0051] <2-1-1-1. Resistor layer containing ITO>

[0052] As the resistor layer, for example, indium tin oxide (hereinafter referred to as "ITO") can be used. Among them, from the viewpoint that the amorphous structure is extremely stable and the variation of the sheet resistance of the resistor layer can be suppressed even in a high temperature and high humidity environment, it is preferred to use a substance containing ITO containing 1 to 40% by weight of SnO2, and more preferably to use a substance containing ITO containing 2 to 35% by weight of SnO2. The content of the ITO in the resistor layer is, for example, 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, further preferably 95% by weight or more, and usually less than 100% by weight.

[0053] <2-1-1-2. Resistor layer containing molybdenum>

[0054] As the resistor layer, a resistor layer containing molybdenum is preferably used from the viewpoint of facilitating the adjustment of durability and sheet resistance. The lower limit of the content of molybdenum is not particularly limited, but from the viewpoint of further improving durability, it is preferably 5% by weight, more preferably 7% by weight, more preferably 9% by weight, more preferably 11% by weight, particularly preferably 13% by weight, very preferably 15% by weight, and most preferably 16% by weight. In addition, the upper limit of the content of molybdenum is preferably 70% by weight, more preferably 30% by weight, more preferably 25% by weight, and more preferably 20% by weight from the viewpoint of facilitating the adjustment of the surface resistance value.

[0055] When the resistor layer contains molybdenum, it is more preferable to further contain nickel and chromium. By making the resistor layer contain nickel and chromium in addition to molybdenum, a radio wave absorber with better durability can be obtained. As alloys containing nickel, chromium and molybdenum, for example, various grades such as Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X can be cited.

[0056] When the resistor layer contains molybdenum, nickel and chromium, the molybdenum content is preferably 5% by weight or more, the nickel content is 40% by weight or more, and the chromium content is 1% by weight or more. By making the contents of molybdenum, nickel and chromium within the above range, a radio wave absorber with better durability can be obtained. The molybdenum, nickel and chromium contents are further preferably 7% by weight or more, 45% by weight or more, and 3% by weight or more. The molybdenum, nickel and chromium contents are more preferably 9% by weight or more, 47% by weight or more, and 5% by weight or more. The molybdenum, nickel and chromium contents are further preferably 11% by weight or more, 50% by weight or more, and 10% by weight or more. The molybdenum, nickel and chromium contents are particularly preferably 13% by weight or more, 53% by weight or more, and 12% by weight or more. The molybdenum, nickel and chromium contents are very preferably 15% by weight or more of molybdenum, 55% by weight or more of nickel and 15% by weight or more of chromium. The molybdenum, nickel and chromium contents are most preferably 16% by weight or more of molybdenum, 57% by weight or more of nickel and 16% by weight or more of chromium. In addition, the nickel content is preferably 80% by weight or less, more preferably 70% by weight or less, and even more preferably 65% ​​by weight or less. The upper limit of the chromium content is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 35% by weight or less.

[0057] The resistor layer may contain metals other than the molybdenum, nickel and chromium. Examples of such metals include iron, cobalt, tungsten, manganese and titanium. When the resistor layer contains molybdenum, nickel and chromium, the upper limit of the total content of the metals other than molybdenum, nickel and chromium is preferably 45% by weight, more preferably 40% by weight, further preferably 35% by weight, further preferably 30% by weight, particularly preferably 25% by weight, and very preferably 23% by weight from the viewpoint of durability of the resistor layer. The lower limit of the total content of the metals other than molybdenum, nickel and chromium is, for example, 1% by weight or more.

[0058] When the resistor layer contains iron, from the viewpoint of durability of the resistor layer, the upper limit of the content is preferably 25% by weight, the upper limit is more preferably 20% by weight, the upper limit is more preferably 15% by weight, and the lower limit is preferably 1% by weight. When the resistor layer contains cobalt and / or manganese, from the viewpoint of durability of the resistor layer, the upper limit of the content is preferably 5% by weight, the upper limit is more preferably 4% by weight, the upper limit is more preferably 3% by weight, and the lower limit is preferably 0.1% by weight. When the resistor layer contains tungsten, from the viewpoint of durability of the resistor layer, the upper limit of the content is preferably 8% by weight, the upper limit is more preferably 6% by weight, the upper limit is more preferably 4% by weight, and the lower limit is preferably 1% by weight.

[0059] The resistor layer may also contain silicon and / or carbon. When the resistor layer contains silicon and / or carbon, the content of the silicon and / or carbon is preferably 1% by weight or less, and more preferably 0.5% by weight or less, respectively and independently. In addition, when the resistor layer contains silicon and / or carbon, the content of the silicon and / or carbon is preferably 0.01% by weight or more.

[0060] The resistance value of the resistor layer is not particularly limited as long as it satisfies the characteristics of the present invention. The absorption range in the characteristics of the present invention can be adjusted by adjusting the resistance value of the resistor layer. The resistance value of the resistor layer can be, for example, 200 to 600 Ω / □. In this range, it is more preferably 250 to 520 Ω / □, more preferably 300 to 450 Ω / □, and particularly preferably 330 to 390 Ω / □.

[0061] The thickness of the resistor layer is not particularly limited as long as it satisfies the characteristic resistance value of the present invention. The thickness of the resistor layer is, for example, 1 nm to 200 nm, preferably 2 nm to 100 nm, and more preferably 2 nm to 50 nm.

[0062] The layer structure of the resistor layer is not particularly limited. The resistor layer may be composed of a single resistor layer or a combination of two or more resistor layers.

[0063] <2-1-2. Barrier layer>

[0064] From the viewpoint of durability, the resistor film preferably includes a barrier layer. The barrier layer is disposed on the surface of at least one of the resistor layers. The barrier layer will be described in detail below.

[0065] The barrier layer is not particularly limited as long as it is a layer that can protect the resistor layer and inhibit its degradation. The raw material of the barrier layer is, for example, a metal compound, a metalloid compound, preferably an oxide, nitride, nitride oxide, etc. of a metal or metalloid. The barrier layer may also contain components other than the raw materials as long as the effect of the present invention is not significantly impaired. In this case, the amount of the raw materials in the barrier layer is, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 99% by mass or more, and usually less than 100% by mass.

[0066] Examples of the metal element contained in the barrier layer include titanium, aluminum, niobium, cobalt, nickel, etc. Examples of the metalloid element contained in the barrier layer include silicon, germanium, antimony, bismuth, etc.

[0067] Examples of the oxide include MO X A compound represented by [wherein X is a number satisfying the formula: n / 100≤X≤n / 2 (n is the valence number of the metal or metalloid), and M is a metal element or a metalloid element].

[0068] As the nitride, for example, MN y A compound represented by [wherein Y is a number satisfying the formula: n / 100≤Y≤n / 3 (n is the valence number of the metal or metalloid), and M is a metal element or a metalloid element].

[0069] As the nitrided oxide, for example, MO X N y A compound represented by [wherein X and Y satisfy: n / 100≤X, n / 100≤Y, and X+Y≤n / 2 (n is the valence number of the metal or metalloid), and M is a metal element or a metalloid element].

[0070] The oxidation number X of the oxide or nitride oxide can be obtained by, for example, x or MO x N y The cross section of the layer is subjected to elemental analysis using FE-TEM-EDX (e.g., "JEM-ARM200F" manufactured by JEOL Ltd.), and the x N y The valence of the oxygen atom can be calculated by calculating X from the element ratio of M and O per unit area of ​​the cross section of the layer.

[0071] Regarding the nitride number Y of the nitride or nitride oxide, for example, the valence of the nitrogen atom can be calculated by calculating Y based on the element ratio of M and N per unit area of ​​the cross-section of the layer containing MNy or MOxNy by performing elemental analysis on the cross-section of the layer containing MNy or MOxNy using FE-TEM-EDX (for example, "JEM-ARM200F" manufactured by JEOL Ltd.).

[0072] Specific examples of the raw materials of the barrier layer include SiO2, SiO x , Al2O3, MgAl2O4, CuO, CuN, TiO2, TiN, AZO (aluminum-doped zinc oxide), etc.

[0073] The thickness of the barrier layer is not particularly limited. The thickness of the barrier layer is, for example, 1 nm to 200 nm, preferably 1 nm to 100 nm, and more preferably 1 nm to 20 nm.

[0074] The layer structure of the barrier layer is not particularly limited. The barrier layer may be composed of a single barrier layer or a combination of two or more barrier layers.

[0075] <2-2. Dielectric layer>

[0076] The dielectric layer is not particularly limited as long as it can function as a dielectric at the target wavelength in the radio wave absorber. The dielectric layer is not particularly limited, and examples thereof include resin sheets and adhesives.

[0077] The resin sheet is not particularly limited as long as it is a sheet containing resin as a raw material. The resin sheet may also contain components other than the resin as long as the effect of the present invention is not significantly impaired. In this case, the total amount of the resin in the resin sheet is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and usually less than 100% by mass.

[0078] The resin is not particularly limited, and for example, synthetic resins such as ethylene vinyl acetate copolymer (EVA), vinyl chloride, urethane, acrylic acid, acrylic urethane, polyolefin, polyethylene, polypropylene, polysiloxane, polyethylene terephthalate, polyester, polystyrene, polyimide, polycarbonate, polyamide, polysulfone, polyethersulfone, epoxy resin, and synthetic rubber materials such as polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, butyl rubber, acrylic rubber, ethylene-propylene rubber, and polysiloxane rubber are preferably used as the resin component. One of these may be used alone, or two or more of them may be used in combination.

[0079] The dielectric layer can also be foam or adhesive.

[0080] The dielectric layer may be a material having adhesive properties. Therefore, when a dielectric having no adhesive properties is laminated to other layers via an adhesive layer, the dielectric and the adhesive layer are collectively referred to as a "dielectric layer". From the viewpoint of facilitating lamination with adjacent layers, the dielectric layer preferably includes an adhesive layer.

[0081] The relative dielectric constant of the dielectric layer is not particularly limited as long as it satisfies the characteristics of the present invention. By adjusting the relative dielectric constant of the dielectric layer (especially by adjusting the value of the formula (1) described later), the absorption range in the characteristics of the present invention can be adjusted. The relative dielectric constant of the dielectric layer is, for example, 1 to 20, preferably 1 to 15, more preferably 1 to 10, and further preferably 1 to 5.

[0082] The thickness of the dielectric layer is not particularly limited as long as it satisfies the characteristics of the present invention. By adjusting the thickness of the dielectric layer (particularly by adjusting the value of the formula (1) described later), the absorption range in the characteristics of the present invention can be adjusted. The thickness of the dielectric layer can be, for example, 300 to 1500 μm, preferably 600 to 980 μm, and more preferably 700 to 860 μm.

[0083] As a method for adjusting the absorption range in the characteristics of the present invention, the dielectric layer preferably satisfies the formula (1): (where d represents the thickness of the dielectric layer (μm), and ε represents the relative dielectric constant of the dielectric layer). The preferred lower limit is 1000, the more preferred lower limit is 1100, and the particularly preferred lower limit is 1150. The preferred upper limit is 1400, the more preferred upper limit is 1300, and the particularly preferred upper limit is 1250.

[0084] When the dielectric layer includes multiple layers, the value of each layer is obtained and the total is calculated. For example, when the dielectric layer includes dielectric layer 1 and dielectric layer 2 (such as adhesive tape, etc.), By calculating "thickness of dielectric layer 1 × (relative dielectric constant of dielectric layer 1) 0.5 " and "the thickness of dielectric layer 2 × (relative dielectric constant of dielectric layer 2) 0.5 ” is calculated by the sum of .

[0085] The thickness of the dielectric layer can be measured by Nikon DIGIMICRO STANDMS-11C + Nikon DIGIMICRO MFC-101.

[0086] The relative dielectric constant of the dielectric layer can be measured at 10 GHz by a cavity resonator perturbation method using a network analyzer, a cavity resonator, or the like.

[0087] The layer structure of the dielectric layer is not particularly limited. The dielectric layer may be composed of one dielectric layer alone, or may be composed of a multilayer combination of two or more dielectric layers. For example, a dielectric layer having a three-layer structure including a dielectric having no adhesiveness and an adhesive layer disposed on both sides thereof, a dielectric layer having a one-layer structure including a dielectric having adhesiveness, etc. may be cited.

[0088] <2-3. Reflective layer>

[0089] The reflective layer is not particularly limited as long as it can function as a reflective layer for radio waves in the radio wave absorber. The reflective layer is not particularly limited, and examples thereof include metal films.

[0090] The metal film is not particularly limited as long as it is a layer containing metal as a raw material. The metal film may also contain components other than metals as long as the effect of the present invention is not significantly impaired. In this case, the total amount of metal in the metal film is, for example, 30% by mass or more, preferably 50% by mass or more, more preferably 75% by mass or more, further preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, very preferably 99% by mass or more, and usually less than 100% by mass.

[0091] The metal is not particularly limited, and examples thereof include aluminum, copper, iron, silver, gold, chromium, nickel, molybdenum, gallium, zinc, tin, niobium, and indium. In addition, metal compounds, such as ITO, can also be used as raw materials for the metal film. These can be a single species or a combination of two or more species.

[0092] The thickness of the reflective layer is not particularly limited and is, for example, 1 μm to 500 μm, preferably 2 μm to 200 μm, and more preferably 5 μm to 100 μm.

[0093] In a preferred embodiment of the present invention, the surface roughness (Rz) of the surface on the dielectric layer side of the reflective layer is preferably 1 μm to 10 μm. Within this range, good adhesion between the dielectric layer and the reflective layer can be exerted, and better radio wave absorption can be exerted. The surface roughness (Rz) is preferably 1 μm to 8 μm, more preferably 1 μm to 5 μm.

[0094] In a preferred embodiment of the present invention, the surface roughness (Rz) of the surface on the opposite side of the dielectric layer side of the reflective layer is 1 μm or more. Thus, good adhesion with the layer (e.g., adhesive layer) laminated on the opposite side of the dielectric layer side of the reflective layer can be exerted, and the radio wave absorber of the present invention can be more easily mounted on other components (e.g., devices in a vehicle, etc.). The surface roughness (Rz) is preferably 30 μm or less, more preferably 2 μm or more and 15 μm or less.

[0095] The surface roughness (Rz) of the reflective layer can be measured as follows. The surface roughness (Rz) can be measured by measuring the concavity and convexity of the reflective layer surface using a color 3D laser microscope (VK8710 (manufactured by Keyence) or its equivalent). Specifically, referring to JIS B0601:2001, using a 50x objective lens, the Rz of any five locations on the surface of the reflective layer within a range of 10 μm×10 μm is measured, and the average value is obtained.

[0096] The surface roughness (Rz) of the reflective layer can be adjusted according to or with reference to known methods for adjusting surface roughness, for example, by applying fine metal particles using metal plating technology or by cutting the surface using physical or chemical methods.

[0097] The layer structure of the reflective layer is not particularly limited. The reflective layer may be composed of a single reflective layer or a combination of two or more reflective layers.

[0098] <2-4. Support>

[0099] When the radio wave absorber of the present invention has a resistive film, it is preferred to further have a support. This can protect the resistive film, thereby improving the durability of the radio wave absorber. There is no particular limitation on the support as long as it is sheet-shaped. There is no particular limitation on the support, and examples thereof include resin substrates.

[0100] As long as the resin substrate is a substrate containing resin as a raw material and is in a sheet shape, there is no particular restriction. As long as the effect of the present invention is not significantly impaired, the resin substrate may also include components other than the resin. For example, from the perspective of adjusting the relative dielectric constant, titanium oxide or the like may also be included. At this time, the total amount of the resin in the resin substrate is, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 99% by mass or more, and usually less than 100% by mass.

[0101] As resin, there is no particular limitation, for example, polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate, and modified polyester, polyethylene (PE) resin, polypropylene (PP) resin, polystyrene resin, polyolefin resins such as cyclic olefin resins, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polyvinyl acetal resins such as polyvinyl butyral (PVB), polyetheretherketone (PEEK) resin, polysulfone (PSF) resin, polyethersulfone (PES) resin, polycarbonate (PC) resin, polyamide resin, polyimide resin, acrylic resin, triacetylcellulose (TAC) resin, etc. These can be used alone or in combination of two or more.

[0102] Among them, polyester resins are preferred from the viewpoint of productivity and strength, and polyethylene terephthalate is more preferred.

[0103] The relative dielectric constant of the support is not particularly limited. The relative dielectric constant of the support is, for example, 1 to 20, preferably 1 to 15, more preferably 1 to 10, and further preferably 1 to 5.

[0104] The thickness of the support is not particularly limited and is, for example, 5 μm to 500 μm, preferably 10 μm to 300 μm, and more preferably 20 μm to 300 μm.

[0105] In a preferred embodiment of the present invention, the surface tension of the outermost surface on the support side of the radio wave absorber (usually the surface on the opposite side of the resistance film side of the support) is preferably 35 dyn / cm or more. When the surface tension takes such a value, excellent antifouling properties can be exerted. As a result, after wiping off the stains, the radio wave absorption is also excellent. The surface tension is more preferably 36 dyn / cm or more.

[0106] The upper limit of the surface tension is not particularly limited, but is preferably 60 dyn / cm or less, more preferably 57 dyn / cm or less, and further preferably 55 dyn / cm or less from the viewpoint of suppressing blocking of supports during production.

[0107] The surface tension can be measured with reference to JIS K 6768 "Plastics - Film and Sheet Wetting Tension Test Method" using a wetting tension test solution (Wako Pure Chemical Industries, Ltd., mixed solution for wetting tension test). The surface tension can be adjusted by selecting the material of the support, mixing additives such as a light reflector and a light absorber.

[0108] In a preferred embodiment of the present invention, the total light transmittance of the support is preferably 30% or less. When the total light transmittance of the support takes such a value, excellent light resistance can be exerted. The more preferred upper limit of the total light transmittance is 20%, and the further preferred upper limit is 16%. The lower limit of the total light transmittance is not particularly limited, for example, 0.01% or more, preferably 0.05% or more, and more preferably 0.1% or more.

[0109] The total light transmittance can be measured using a haze meter ("NDH-4000" manufactured by Nippon Denshoku Co., Ltd. or an equivalent thereof) in accordance with JIS K7105.

[0110] The total light transmittance can be adjusted by selecting the material of the support and mixing additives such as light reflectors and light absorbers.

[0111] As for the support, in order to fully meet the range of the surface tension and the total light transmittance, it is preferred to include a light reflector. The light reflector may be in a state of being mixed with the support material (the resin, etc.), or may be included in a coating layer constituting the surface of the support. Preferably, the light reflector is in a state of being mixed with the support material (the resin, etc.).

[0112] There are no particular restrictions on the light reflector as long as it is a substance that can reflect or scatter ultraviolet light, visible light, etc. (especially ultraviolet light) and does not significantly reduce the radio wave absorption characteristics of the radio wave absorber of the present invention even if it is contained in the support. For example, inorganic powders can be used.

[0113] The average particle size of the inorganic powder is preferably 50 to 400 nm, more preferably 60 to 390 nm, and even more preferably 70 to 380 nm, from the viewpoint of satisfying the above-mentioned ranges of surface tension and total light transmittance.

[0114] Examples of the inorganic powder include metal oxides such as titanium dioxide and zinc oxide. Among them, titanium dioxide is preferably used because it has a large refractive index and greatly scatters light, making it easy to adjust the total light transmittance.

[0115] The average particle size of zinc oxide used as a light reflector is preferably 50 to 400 nm, more preferably 60 to 390 nm, and even more preferably 70 to 380 nm, from the viewpoint of fully satisfying the above-mentioned ranges of surface tension and total light transmittance.

[0116] Examples of commercially available zinc oxide suitable as a light reflecting agent include: MZ-300 (no surface treatment agent, particle size 30 to 40 nm, TAYCA (Co., Ltd.)), MZ-303S (polymethylsiloxane treatment, particle size 30 to 40 nm, TAYCA (Co., Ltd.)), MZ-303M (polydimethylsiloxane treatment, particle size 30 to 40 nm, TAYCA (Co., Ltd.)), MZ-500 (no surface treatment agent, particle size 20 to 30 nm, TAYCA (Co., Ltd.)), MZ-505S (polymethylsiloxane treatment, particle size 20 to 30 nm, TAYCA (Co., Ltd.) AYCA (Co., Ltd.)), MZ-505M (polydimethylsiloxane treatment, particle size 20 to 30 nm, TAYCA (Co., Ltd.)), MZ-700 (no surface treatment agent, particle size 10 to 20 nm, TAYCA (Co., Ltd.)), MZ-707S (polymethylsiloxane treatment, particle size 10 to 20 nm, TAYCA (Co., Ltd.)), FINEX-25 (no surface treatment agent, particle size 60 nm, Sakai Chemical (Co., Ltd.)), FINEX-25LP (polydimethylsiloxane treatment, particle size 60 nm, Sakai Chemical (Co., Ltd.)), FINEX-50 (no surface treatment agent, particle size 20 nm, Sakai Chemical (Co., Ltd.)), FINEX-50LP (polydimethylsiloxane treatment, particle size 20 nm, Sakai Chemical (Co., Ltd.)), FINEX-75 (no surface treatment agent, particle size 10 nm, made by Sakai Chemical (Co., Ltd.)), etc.

[0117] The average particle size of titanium dioxide used as a light reflector is preferably 50 to 400 nm, more preferably 60 to 390 nm, and even more preferably 70 to 380 nm, from the viewpoint of fully satisfying the above-mentioned ranges of surface tension and total light transmittance.

[0118] Specific examples of titanium dioxide suitable as a light reflector include TIPAQUE CR-50 (alumina treated, particle size 25 nm, manufactured by Ishihara Sangyo Co., Ltd.), Bayer titanium R-KB-1 (zinc oxide treated, alumina treated, silica treated, particle size 30 nm to 40 nm, manufactured by Bayer), TIPAQUE TTO-M-1 (zirconium oxide treated, alumina treated, particle size 10 nm to 25 nm, manufactured by Ishihara Sangyo Co., Ltd.), TIPAQUE TTO-D-1 (zirconium oxide treated, alumina treated, particle size 20 nm to 30 nm, manufactured by Ishihara Sangyo Co., Ltd.), SOLAVEIL CT-100, SOLAVEIL CT-200, SOLAVEIL CT-300, SOLAVEIL CT-434 (manufactured by Croda Japan Co., Ltd.), STR-100 series, STR-40 (manufactured by Sakai Chemical Co., Ltd.). However, it is not limited to these examples.

[0119] As a method for adjusting the above-mentioned surface tension and total light transmittance, in addition to mixing the above-mentioned light reflector, for example, a method of coating the surface of the support with a coating containing a light absorber can be cited. In addition, as a method for adjusting the above-mentioned surface tension, a method of treating the target surface with corona discharge treatment, external ray irradiation treatment, ozone treatment, plasma treatment, etc., a method of applying a coating agent, etc. can be cited.

[0120] The layer structure of the support is not particularly limited. The support may be composed of a single support or a combination of two or more supports in multiple layers.

[0121] <2-5. Layer structure>

[0122] When the radio wave absorber of the present invention has a resistive film, a dielectric layer, and a reflective layer, the layers are arranged in an order that enables the radio wave absorption performance to be exhibited. As an example, the resistive film, the dielectric layer, and the reflective layer are arranged in this order.

[0123] Furthermore, when the radio wave absorber of the present invention has a support, as an example, the support, the resistance film, the dielectric layer, and the reflective layer are arranged in this order.

[0124] The radio wave absorber of the present invention may include other layers in addition to the support, the resistor film, the dielectric layer and the reflective layer. The other layers may be disposed on the surface of any one of the support, the resistor film, the dielectric layer and the reflective layer.

[0125] <3. Absorption of obliquely incident radio waves>

[0126] Since the radio wave absorber of the present invention has the characteristics of the present invention (specific characteristics at 45-degree incidence), it can exhibit good radio wave absorption for incidence from various angles (especially incidence of circularly polarized waves), especially for oblique incidence of radio waves near 60 GHz (for example, 55 to 65 GHz) (especially incidence of circularly polarized waves).

[0127] Specific examples of the radio wave absorbency of the radio wave absorber of the present invention are as follows.

[0128] It should be noted that the absorption range in the following specific examples can be measured by the following method.

[0129] The radio wave absorption measuring device is composed of a PNA microwave network analyzer N5227A (manufactured by Keysight Co., Ltd.), a PNA-X series 2-port millimeter wave controller N5261A (manufactured by Keysight Co., Ltd.), and a horn antenna FSS-07 (manufactured by HVS Co., Ltd.). The radio wave absorption measuring device is used to measure the radio wave absorption amount of the radio wave absorber at the E band (60 to 90 GHz) and the U band (40 to 60 GHz) based on JIS R1679. The radio wave is incident on the front of the measurement sample at 20°, 30°, or 60°, and the horn antenna is installed at the same angle relative to the perpendicular line of the center of the measurement sample. The reflection coefficient ΓTE is measured when the electric field of the incident wave is perpendicular to the incident surface (TE wave).

[0130] Subsequently, the reflection coefficient ΓTM was measured by the same method in a state where the electric field of the incident wave was parallel to the incident plane (TM wave).

[0131] The average value of the reflection coefficients ГTE and ГTM is defined as the reflection coefficient ГCP of the circularly polarized wave.

[0132] Using the above coefficients, the reflection loss amount for circularly polarized waves was calculated by -20log|ΓCP|. The absolute value of the reflection loss amount was defined as the absorption performance.

[0133] The radio wave absorber of the present invention preferably exhibits the following radio wave absorbency (radio wave absorbency 1): in the measurement of circularly polarized waves incident at 20°, the absorption range of the radio wave absorber in the 55 to 65 GHz band is 10 dB or more (preferably 15 dB or more) and is 4 GHz or more. The absorption range in radio wave absorbency 1 is preferably 6 GHz or more, more preferably 8 GHz or more, further preferably 9 GHz or more, and further preferably 9.5 GHz or more.

[0134] The radio wave absorber of the present invention preferably exhibits the following radio wave absorbency (radio wave absorbency 2): in the measurement of circularly polarized waves incident at 30°, the absorption range of the radio wave absorber in the 55-65 GHz band is 10 dB or more (preferably 15 dB or more) and is 4 GHz or more. The absorption range in radio wave absorbency 2 is preferably 6 GHz or more, more preferably 8 GHz or more, further preferably 9 GHz or more, and further preferably 9.5 GHz or more.

[0135] The radio wave absorber of the present invention preferably exhibits the following radio wave absorbency (radio wave absorbency 3): in the measurement of circularly polarized waves incident at 60°, the absorption range of the radio wave absorber in the 55-65 GHz band is 10 dB or more (preferably 15 dB or more) and is 4 GHz or more. The absorption range in radio wave absorbency 3 is preferably 6 GHz or more, more preferably 8 GHz or more, further preferably 9 GHz or more, and further preferably 9.5 GHz or more.

[0136] The radio wave absorber of the present invention preferably exhibits at least two (preferably three) radio wave absorbencies selected from the group consisting of radio wave absorbency 1, radio wave absorbency 2, and radio wave absorbency 3.

[0137] Since the above absorption range is within the frequency band of 55 to 65 GHz, the upper limit thereof is 10 GHz.

[0138] <4. Manufacturing method>

[0139] The radio wave absorber of the present invention can be obtained according to or with reference to various methods, such as known manufacturing methods, depending on its structure. For example, when the radio wave absorber of the present invention has a resistive film, a dielectric layer, and a reflective layer, it can be obtained by a method including the steps of sequentially laminating the resistive film, the dielectric layer, and the reflective layer on a support.

[0140] The lamination method is not particularly limited.

[0141] The resistive film can be obtained, for example, by sputtering, vacuum evaporation, ion plating, chemical evaporation, pulsed laser deposition, etc. Among them, sputtering is preferred from the viewpoint of film thickness controllability. The sputtering method is not particularly limited, and for example, DC magnetron sputtering, high-frequency magnetron sputtering, and ion beam sputtering can be cited. In addition, the sputtering device can be a batch type or a roll-to-roll type.

[0142] The dielectric layer and the reflective layer can be stacked, for example, by utilizing the adhesiveness of the dielectric layer.

[0143] <5. Components for λ / 4 type radio wave absorbers>

[0144] The present invention, in one embodiment thereof, relates to a λ / 4 type radio wave absorber component, the component having a resistive film and a dielectric layer, and when an aluminum plate having a thickness of 10 μm is laminated on the other surface of the dielectric layer, in the measurement of circularly polarized waves incident at 45°, the radio wave absorber component has an absorption performance of 15 dB or more in the 55 to 65 GHz band, and an absorption range of 4 GHz or more. It should be noted that, for the aluminum plate having a thickness of 10 μm, an aluminum plate having a surface roughness (Rz) of 4 μm on the surface in contact with the dielectric layer is used.

[0145] The component for a λ / 4 type radio wave absorber is a component that has a resistor film and a dielectric layer in sequence and is used to form a λ / 4 type radio wave absorber by arranging the dielectric layer in such a manner that it is in contact with an adherend that can function as a reflective layer such as a metal. The component for a λ / 4 type radio wave absorber may further have a support body. In this case, the component for a λ / 4 type radio wave absorber has: a support body, a resistor film, and a dielectric layer in sequence. The support body, the resistor film, the dielectric layer, the characteristics of the present invention, and other configurations are the same as those described in relation to the radio wave absorber of the present invention.

[0146] <6. Application>

[0147] The radio wave absorber of the present invention has the performance of absorbing unnecessary radio waves, so it is preferably used in radio wave response components such as optical transceivers, next-generation mobile communication systems (5G), short-range wireless transmission technologies, etc. At the same time, as other uses, it can also be applied to intelligent transportation systems (ITS) for information communication between cars, roads and people, and millimeter wave radars used in car collision avoidance systems to achieve the purpose of suppressing radio wave interference and reducing noise.

[0148] Furthermore, the radio wave absorber of the present invention can exhibit good radio wave absorption at oblique incidence and is therefore suitable for being arranged at an angle (e.g., 10 to 80 degrees, 20 to 60 degrees, or 30 to 60 degrees) relative to the incident direction of the radio wave to be absorbed.

[0149] The frequency of the radio wave to be absorbed by the radio wave absorber of the present invention is preferably 55 to 65 GHz.

[0150] Example

[0151] Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limited to these Examples.

[0152] (1) Manufacturing of radio wave absorbers

[0153] (Example 1)

[0154] As a support, a polyethylene terephthalate (PET) film (relative dielectric constant 3.4, TiO2; 10 wt%) having a thickness of 125 μm and kneaded with titanium oxide (average particle size 200 μm) was prepared.

[0155] On the PET film, a resistive film (barrier layer 1 / resistive layer / barrier layer 2) with a resistance value of 360Ω / □ was formed as follows: First, a gas with a ratio of Ar and O2 adjusted to 1:1 was introduced by DC pulse sputtering, and the pressure was adjusted to 0.2Pa, and a SiO2 layer (barrier layer 1: thickness 10nm) was formed. Next, on barrier layer 1, a resistive layer with a surface resistance value of 355Ω / □ was formed by DC pulse sputtering. Sputtering was performed as follows: using an alloy (composition: 16.4 wt% molybdenum, 55.2 wt% nickel, 18.9 wt% chromium, 5.5 wt% iron, 3.5 wt% tungsten, 0.5 wt% silicon dioxide) as a target, the gas was introduced under the conditions of an output of 0.4kW and an Ar gas flow rate of 100sccm, and the pressure was adjusted to 0.12Pa. Finally, barrier layer 2 (thickness 5nm) was formed in the same manner as barrier layer 1.

[0156] Next, a dielectric composed of a 780 μm thick acrylic double-sided adhesive tape with a relative dielectric constant of 2.4 was laminated on the formed barrier layer 2, and a reflective layer composed of 10 μm thick aluminum (Rz=4.0 μm) was further laminated on the dielectric to obtain a radio wave absorber.

[0157] (Examples 2 to 5, 7 to 12, Comparative Examples 1 to 4)

[0158] A radio wave absorber was obtained in the same manner as in Example 1 except that the resistance value of the resistor film and / or the thickness of the dielectric were changed as shown in Tables 1 and 2.

[0159] (Example 6)

[0160] A radio wave absorber was obtained in the same manner as in Example 1 except that the barrier layer (resistance layer=resistance film) was not formed.

[0161] (Example 13)

[0162] A radio wave absorber was obtained in the same manner as in Example 3 except that the reflective layer was changed to a copper plate having a thickness of 10 μm (Rz=0.9 μm).

[0163] (Example 14)

[0164] A radio wave absorber was obtained in the same manner as in Example 3 except that the reflective layer was changed to a copper plate having a thickness of 10 μm (Rz=12 μm).

[0165] (Example 15)

[0166] A radio wave absorber was obtained in the same manner as in Example 3, except that the support was changed to a polyethylene terephthalate (PET) film (relative dielectric constant 3.2, surface tension 36 dyn / cm). It should be noted that N2 gas was introduced as a processing gas into an atmospheric pressure plasma device (manufactured by Sekisui Chemical Co., Ltd., "AP / TO2", direct electrode type), and plasma treatment was performed by inputting 900 W (140 V-6.4 A) of power to generate plasma gas, and transporting it at a speed of 15 m / min, thereby adjusting the surface tension of the support surface. It should be noted that the slit area for plasma treatment was set to 200 mm 2 (200 mm in the width direction of the film and 1 mm in the length direction).

[0167] (Example 16)

[0168] A polyethylene terephthalate (PET) film (TiO2; 7 wt%) with a thickness of 125 μm and kneaded with titanium oxide (average particle size 200 μm) was prepared. A liquid hard coating material was applied to the surface of the support opposite to the surface in contact with the resistance layer using a wire rod coater, and the coated film was further heated and dried in an oven at 100°C for 1 minute. Next, the dried coated film was irradiated with ultraviolet rays (irradiation dose: 300 mJ / cm 2 ), and a hard coating layer with a thickness of 2 μm was arranged on the support. As the hard coating material, a liquid hard coating material (solid content concentration: 40 wt%) was prepared by adding a mixed solvent of toluene and methyl isobutyl ketone (MIBK) in a ratio of 5:5 (weight ratio) to an acrylic oligomer containing a photopolymerizing agent. Except that the prepared PET film with a hard coating layer (relative dielectric constant 3.4, surface tension 32 dyn / cm) was used as the support, a radio wave absorber was obtained in the same manner as in Example 3.

[0169] (2) Determination of characteristics

[0170] In the measurement of circularly polarized waves incident at 45°, the absorption range in which the absorption performance was 15 dB or more in the 55 to 65 GHz band was measured. Specifically, the measurement was performed as follows.

[0171] The radio wave absorption measuring device is composed of a PNA microwave network analyzer N5227A (manufactured by Keysight Co., Ltd.), a PNA-X series 2-port millimeter wave controller N5261A (manufactured by Keysight Co., Ltd.), and a horn antenna FSS-07 (manufactured by HVS Co., Ltd.). The radio wave absorption measuring device is used to measure the radio wave absorption amount of the radio wave absorber in the E band (60 to 90 GHz) and the U band (40 to 60 GHz) based on JIS R1679. The radio wave is incident on the front of the measurement sample at 45°, and the horn antenna is installed at the same angle relative to the perpendicular line of the center of the measurement sample. The reflection coefficient ΓTE is measured when the electric field of the incident wave is perpendicular to the incident surface (TE wave).

[0172] Subsequently, the reflection coefficient ΓTM was measured by the same method in a state where the electric field of the incident wave was parallel to the incident plane (TM wave).

[0173] The average value of the reflection coefficients ГTE and ГTM is defined as the reflection coefficient ГCP of the circularly polarized wave.

[0174] Using the above coefficients, the reflection loss amount for circularly polarized waves was calculated by -20log|ΓCP|. The absolute value of the reflection loss amount was defined as the absorption performance.

[0175] The results are shown in Tables 1 and 2.

[0176] (3) Evaluation of the absorption of obliquely incident radio waves 1

[0177] The absorption of obliquely incident radio waves was evaluated. The measurement method was the same as that for circularly polarized waves incident at 45°, except that the incident angle of the radio waves and the angle of the horn antenna were changed. The absorption range in which the absorption performance was 10 dB or more was measured in the 55-65 GHz band.

[0178] The results are shown in Tables 1 and 2.

[0179]

[0180]

[0181] (4) Evaluation of the absorption of obliquely incident radio waves 2

[0182] The same method as the above-mentioned radio wave absorbency evaluation 1 was used for evaluation except that the absorption range of the absorption performance of 15 dB or more was measured. As a result, the absorption range at 20 degrees of incidence was 9 GHz for Example 1, 9 GHz for Example 2, 1 GHz for Example 5, and 9 GHz for Example 6. The absorption range at 30 degrees of incidence was 10 GHz for Example 1, 6 GHz for Example 2, 1 GHz for Example 5, and 10 GHz for Example 6. The absorption range at 60 degrees of incidence was 10 GHz for Example 1, 1 GHz for Example 2, 8 GHz for Example 3, 6 GHz for Example 4, 6 GHz for Example 5, and 10 GHz for Example 6.

[0183] (5) Evaluation of Adhesion Strength (Dielectric Layer / Reflective Layer)

[0184] The obtained radio wave absorbers of Examples 3, 13 and 14 were cut into short strips of 10 mm width to make test pieces, so that the opposite side of the dielectric layer facing the reflective layer was exposed. The exposed surface was fixed to the base of the measuring device by double-sided adhesive tape (9708, manufactured by 3M Company). According to JIS Z0237, the reflective layer of the test sample was subjected to a tensile test in the 180° direction at a peeling speed of 300 mm / min, and the 180° adhesion (N / 10mm) was measured. The adhesion between the dielectric layer / reflective layer was set to ○ if it was above 5N / 10mm, and to × if it was less than 5N / 10mm.

[0185] (6) Evaluation of antifouling properties (radio wave absorption after wiping off oil stains)

[0186] After dropping one drop of salad oil on the surface of the support body of the obtained radio wave absorber of Examples 3, 15 and 16 opposite to the side facing the resistor film, the surface was wiped back and forth 20 times with a wiping cloth containing petroleum ether (Ligroin) (trade name: CleanWiper SF30C manufactured by Kuraray Co., Ltd.). Then, the characteristics were measured in the same manner as the measurement, and the change in the amount of radio wave absorption at 60 GHz at 45° incidence was rated as ○ when it was within 5 dB, and rated as × when it was greater than 5 dB.

[0187] (7) Evaluation of light resistance

[0188] The obtained radio wave absorbers of Examples 3, 15 and 16 were exposed for 1000 hours using a sunlight weathering test box (S-80, manufactured by SugaTest Instruments Co., Ltd.) under the conditions of a sunlight carbon arc lamp and a relative humidity of 60%. Then, the characteristics were measured in the same manner as the measurement, and the change in the amount of radio wave absorption at 60 GHz at 45° incidence was set to ○ when it was within 5 dB, and to × when it was greater than 5 dB.

[0189] The results are shown in Tables 3 and 4.

[0190] [Table 3]

[0191]

[0192] [Table 4]

[0193]

[0194] Explanation of symbols

[0195] 1 Support

[0196] 2 Resistor film

[0197] 3 Dielectric layer

[0198] 4 Reflection layer

[0199] 5 Adhesive layer

[0200] 6 box

Claims

1. A radio wave absorber comprising a resistive film and a dielectric layer, wherein in a measurement of a circularly polarized wave incident at 45°, the radio wave absorber has an absorption performance of 15 dB or more in a frequency band of 55 to 65 GHz and an absorption range of 4 GHz or more, and The resistance value of the resistor film is 200 to 600Ω / □, and The radio wave absorber satisfies the formula (1): 950≤d×√ε≤1500, Wherein, d represents the thickness of the dielectric layer (μm), and ε represents the relative dielectric constant of the dielectric layer.

2. The radio wave absorber according to claim 1, comprising a reflecting layer.

3. The radio wave absorber according to claim 2, wherein: The resistance film, the dielectric layer, and the reflective layer are arranged in this order.

4. The radio wave absorber according to claim 1 or 2, wherein: The resistance value of the resistance film is 250 to 520Ω / □.

5. The radio wave absorber according to claim 1 or 2, which satisfies the formula (1): 950≤d×√ε≤1400, Wherein, d represents the thickness of the dielectric layer (μm), and ε represents the relative dielectric constant of the dielectric layer.

6. The radio wave absorber according to claim 1 or 2, wherein: The relative dielectric constant of the dielectric layer is 1-10.

7. The radio wave absorber according to claim 1 or 2, wherein: The resistive film includes a barrier layer.

8. The radio wave absorber according to claim 1 or 2, wherein: The resistor film contains molybdenum.

9. The radio wave absorber according to claim 8, wherein: The resistor film further contains nickel and chromium.

10. The radio wave absorber according to claim 2, wherein: The surface roughness (Rz) of the surface of the reflective layer on the dielectric layer side is 1 μm or more and 10 μm or less.

11. The radio wave absorber according to claim 1 or 2, further comprising a support.

12. The radio wave absorber according to claim 11, wherein: The surface tension of the outermost surface of the radio wave absorber on the support side is 35 dyn / cm or more.

13. The radio wave absorber according to claim 11, wherein: The support has a thickness of 5 μm to 500 μm.

14. The radio wave absorber according to claim 11, wherein The total light transmittance of the support is less than 30%.

15. A component for a λ / 4 type radio wave absorber, comprising a resistance film and a dielectric layer, When an aluminum plate having a thickness of 10 μm is laminated on the other surface of the dielectric layer, in the measurement of circularly polarized waves incident at 45°, the component for radio wave absorber has an absorption performance of 15 dB or more in the 55 to 65 GHz band, and an absorption range of 4 GHz or more, and The resistance value of the resistor film is 200 to 600Ω / □, and The radio wave absorber satisfies the formula (1): 950≤d×√ε≤1500, Wherein, d represents the thickness of the dielectric layer (μm), and ε represents the relative dielectric constant of the dielectric layer.

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