Method for manufacturing dielectric layer, resin composition, and laminate comprising dielectric layer

Abstract

The manufacturing method according to the present disclosure is a method for manufacturing a dielectric layer provided in a reflection-type electromagnetic wave absorber, including: a step of preparing a resin composition containing at least one dielectric compound and a resin component, and having a relative dielectric constant of 10.0 or more at a frequency of 3.7 GHz or 90 GHz; and a step of forming a dielectric layer having a thickness of 20 to 7000 μm from the resin composition. The resin composition according to the present disclosure is used for forming a dielectric layer provided in a reflection-type electromagnetic wave absorber, and contains at least one dielectric compound and a resin component, and has a relative dielectric constant of 10.0 or more at a frequency of 3.7 GHz or 90 GHz.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing a dielectric layer in a reflective electromagnetic wave absorber, a resin composition for forming the dielectric layer, and a laminate containing the dielectric layer. Background Technology

[0002] In recent years, the rapid increase in information volume, the high speed of mobile devices, autonomous driving, and the practical application of IoT (Internet of Things) have led to an increasing demand for communication, radar, and security scanners capable of handling various situations. Along with this, technologies utilizing next-generation electromagnetic waves such as 5G, millimeter waves, and terahertz waves for high-speed wireless communication are developing rapidly.

[0003] Products utilizing electromagnetic waves may interfere with electromagnetic waves emitted from other electronic devices, causing malfunctions. As a means to prevent this, reflective electromagnetic wave absorbers, known as λ / 4 type absorbers, are known. Patent Document 1 discloses an electromagnetic wave absorber having a dielectric layer between a resistive film containing extremely fine conductive fibers and an electromagnetic wave reflector. Patent Document 2 discloses an electromagnetic wave absorber comprising a first layer as a dielectric layer or a magnetic layer, and a conductive layer disposed on at least one side of the first layer, wherein the relative permittivity of the first layer is 1 to 10.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-311330

[0007] Patent Document 2: International Publication No. 2018 / 230026 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The dielectric layer in a reflective electromagnetic wave absorber is used to cause interference between the incident electromagnetic wave and the reflected electromagnetic wave. The thickness of the dielectric layer is set based on the following formula.

[0010] d=λ / (4(ε r ) 1 / 2 )

[0011] In the formula, λ represents the wavelength of the electromagnetic wave to be reduced (unit: m), and ε rThe dielectric constant represents the relative permittivity of the material constituting the dielectric layer, and d represents the thickness of the dielectric layer (in meters). The phase of the incident electromagnetic wave and the phase of the reflected electromagnetic wave can be offset by π to achieve reflection attenuation. Previously, in order to achieve sufficient reflection attenuation, it was necessary to increase the thickness of the dielectric layer. Therefore, there is still room for improvement in terms of the fabrication efficiency and space saving of the dielectric layer.

[0012] This disclosure provides a method for efficiently manufacturing a dielectric layer for use in a reflective electromagnetic wave absorber, which achieves excellent reflection attenuation. Additionally, this disclosure provides a resin composition for forming the dielectric layer, and a laminate comprising the dielectric layer.

[0013] Methods for solving problems

[0014] One aspect of this disclosure relates to a method for manufacturing a dielectric layer in a reflective electromagnetic wave absorber. The method includes: preparing a resin composition containing at least one dielectric compound and a resin component, and having a relative permittivity greater than 10.0 at a frequency of 3.7 GHz or 90 GHz; and forming a dielectric layer of 20 to 7000 μm thickness composed of the resin composition.

[0015] In the invention described in Patent Document 2, it is known that in order to achieve good electromagnetic wave absorption performance in a bandwidth of 50 to 100 GHz and in a bandwidth of 2 GHz or more, the relative permittivity of the first layer is set in the range of 1 to 10 (see paragraph

[0016] of Patent Document 2). In contrast, in this disclosure, the relative permittivity of the dielectric layer is set to a value higher than 10.0. This is based on the following technical idea. That is, for example, if we consider the 76 GHz automotive millimeter-wave radar to be applied, the permissible value of the occupied frequency bandwidth is limited to the range of 500 MHz (Japan) to 1 GHz (other countries). In this approximately 1 GHz band, sometimes it is sufficient to meet the requirements of adequate absorption performance (e.g., -20 dB). That is, when it is not necessary to extend the absorption bandwidth, it is useful to prioritize the manufacturing efficiency and space saving of the dielectric layer by increasing the relative permittivity of the dielectric layer and making the dielectric layer thinner. Generally speaking, the relative permittivity of the dielectric layer tends to decrease as the frequency increases. If the relative permittivity at frequencies of 3.7 GHz or 90 GHz is higher than 10.0, the dielectric layer disclosed herein can be used as an electromagnetic wave absorber for 5G (28 GHz) or millimeter-wave radar (76 GHz) to fully address the aforementioned issues.

[0016] One aspect of this disclosure relates to a resin composition for forming a dielectric layer in a reflective electromagnetic wave absorber. The resin composition contains at least one dielectric compound and a resin component, and has a relative permittivity greater than 10.0 at a frequency of 3.7 GHz or 90 GHz. Preferably, the dielectric compound is in the form of, for example, powder, and its relative permittivity is higher than that of the resin component. Specific examples of the dielectric compound include metallic compounds such as titanium oxide and barium titanate. Preferably, the relative permittivity of the resin component at a frequency of 3.7 GHz or 90 GHz is, for example, 2.5 to 9.5.

[0017] Preferably, the resin composition itself is adhesive. By forming the dielectric layer from the adhesive resin composition, the dielectric layer can be effectively attached to the object component. Preferably, the adhesion of the resin composition to the 304 stainless steel sheet is 1.0 N / 25 mm or more.

[0018] One aspect of this disclosure relates to a laminate comprising a dielectric layer. The laminate includes:

[0019] The dielectric layer is composed of the above-described resin composition, and an adhesive layer is disposed on at least one side of the dielectric layer. According to this configuration, the dielectric layer can be effectively attached to the object component via the adhesive layer.

[0020] The effects of the invention

[0021] According to this disclosure, an efficient method for manufacturing a dielectric layer is provided, the dielectric layer being a dielectric layer for a reflective electromagnetic wave absorber, which achieves excellent reflection attenuation. Additionally, according to this disclosure, a resin composition for forming the dielectric layer and a laminate comprising the dielectric layer are provided. Attached Figure Description

[0022] [ Figure 1 ] Figure 1 This is a schematic cross-sectional view illustrating a first embodiment of the laminate involved in this disclosure.

[0023] [ Figure 2 ] Figure 2 This is a schematic cross-sectional view illustrating a second embodiment of the laminated body involved in this disclosure. Detailed Implementation

[0024] Hereinafter, several embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that in the drawings, identical or equivalent parts are labeled with the same symbols, and repeated descriptions are omitted. Furthermore, unless otherwise specified, positional relationships such as top, bottom, left, and right are based on the positional relationships shown in the drawings. In addition, the scale of the drawings is not limited to the scale shown.

[0025] <First Implementation>

[0026] Figure 1 This diagram schematically shows a cross-sectional view of a reflective electromagnetic wave absorber according to the first embodiment. The electromagnetic wave absorber 10 shown is a film or sheet, having a stacked structure comprising an electromagnetic wave transmitting layer 1, a dielectric layer 3, and a reflective layer 4 in sequence. It should be noted that the overall thickness of the film-type electromagnetic wave absorber is, for example, 24 to 250 μm. On the other hand, the overall thickness of the sheet-type electromagnetic wave absorber is, for example, 0.25 to 7.1 mm.

[0027] (Electromagnetic wave transmission layer)

[0028] The electromagnetic wave transmission layer 1 is a layer used to guide electromagnetic waves incident from the outside to the dielectric layer 3. That is, the electromagnetic wave transmission layer 1 is a layer used for impedance matching according to the environment or layer configuration in which the electromagnetic wave absorber 10 is used, thereby obtaining an electromagnetic wave absorber 10 with a large reflection attenuation. When the electromagnetic wave absorber 10 is used in air (impedance: 377Ω / □), the sheet resistance of the electromagnetic wave transmission layer 1 can be set according to the relative permittivity of the dielectric layer 3. For example, if the relative permittivity of the dielectric layer 3 is greater than 10 at 3.7 GHz, the sheet resistance of the electromagnetic wave transmission layer 1 can be set in the range of 200–800 Ω / □, or in the range of 350–400 Ω / □. When the relative permittivity of dielectric layer 3 at 90GHz is greater than 10, the thin-film resistance of electromagnetic wave transmission layer 1 can be set in the range of 200 to 800 Ω / □, or in the range of 350 to 400 Ω / □.

[0029] The electromagnetic wave transmission layer 1 contains a conductive inorganic or organic material. Examples of conductive inorganic materials include nanoparticles and / or nanowires selected from the group consisting of indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), carbon nanotubes, graphene, Ag, Al, Au, Pt, Pd, Cu, Co, Cr, In, Ag-Cu, Cu-Au, and Ni. Examples of conductive organic materials include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, and polypyrrole derivatives. Particularly from the viewpoints of flexibility, film-forming properties, stability, and a sheet resistance of 377 Ω / □, a conductive polymer containing polyethylene dioxythiophene (PEDOT) is preferred. The electromagnetic wave transmission layer 1 may also contain a mixture of polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PPS) (PEDOT / PSS).

[0030] Regarding the thin-film resistance value of the electromagnetic wave transmission layer 1, when the resistivity ρ (Ω·m) of the conductive material and the thickness t (m) of the conductive material are taken as the thin-film resistance value of the conductive material, it is expressed as σ = ρ / t. Therefore, it can be appropriately set according to the selection of conductive inorganic or organic materials and the adjustment of the film thickness. When the electromagnetic wave transmission layer 1 is composed of inorganic materials, the thickness (film thickness) of the electromagnetic wave transmission layer 1 is preferably set in the range of 0.1 nm to 100 nm, more preferably in the range of 1 nm to 50 nm. When the film thickness is 0.1 nm or more, it is easy to form a uniform film, thereby tending to more fully realize the function of the electromagnetic wave transmission layer 1. On the other hand, when the film thickness is 100 nm or less, sufficient flexibility can be maintained, tending to more reliably prevent cracking in the film due to external factors such as bending and stretching after film formation, and suppress damage or shrinkage caused by heat to the substrate. When the electromagnetic wave transmission layer 1 is made of an organic material, its thickness (film thickness) is preferably set in the range of 0.1 to 2.0 μm, more preferably in the range of 0.1 to 0.4 μm. When the film thickness is 0.1 μm or more, it is easier to form a uniform film, thereby tending to more fully realize its function as the electromagnetic wave transmission layer 1. On the other hand, when the film thickness is 2.0 μm or less, sufficient flexibility can be maintained, tending to more reliably prevent cracking in the film due to external factors such as bending and stretching after film formation.

[0031] As film-forming methods, dry coating and wet coating methods can be listed.

[0032] Dry coating methods include resistance heating or induction heating, vacuum evaporation using ion beams (EB), and sputtering. In resistance heating, material is placed in a ceramic crucible, and a voltage is applied to a heater surrounding the crucible to allow current to flow. The crucible is heated in a vacuum, causing the inorganic material to evaporate from the opening and adhere to the substrate to form a film. The film-forming speed is adjusted by controlling the distance between the material and the substrate, the voltage applied to the heater, and the current. For batch film forming, the film-forming time is controlled by the shutter opening and closing time; for roll forming, the film-forming time is controlled by linear speed, thus controlling the film thickness. Ion beams work by passing current through a filament in a vacuum, releasing electrons. These electrons are then focused directly onto the material using an electromagnetic lens, causing the inorganic material to heat, evaporate, and adhere to the substrate to form a film. This method is used for inorganic materials requiring high heat for evaporation or for situations requiring high film-forming rates. The film-forming speed is adjusted by controlling the distance between the material and the substrate, the amount of electrons generated by the filament using current, and the irradiation position or range (aperture) of the material using an electromagnetic lens. The film-forming time is controlled by the shutter opening and closing time or linear velocity, thus controlling the film thickness. In sputtering, rare gases such as Ar are mainly introduced onto a target made of inorganic materials. A voltage is applied to plasmaize the Ar, causing it to collide with the voltage-accelerated target, physically ejecting the material (sputtering) and adhering it to the substrate to form a film. For inorganic materials that cannot be film-formed using vacuum evaporation, sputtering can potentially produce films. The film-forming speed is adjusted by controlling the distance between the target and the substrate, the applied current to the target, and the Ar gas pressure. The film-forming time is controlled by the shutter opening and closing time or linear velocity, thus controlling the film thickness. This method is mainly used for film-forming inorganic materials.

[0033] Wet coating is a method of applying materials to a substrate. It involves dissolving or dispersing materials that are solid at room temperature and pressure in a suitable solvent to create an ink. After coating, the solvent is removed by drying to form a film. Coating methods include die coating, microgravure coating, rod gravure coating, and gravure coating. A common element is controlling the solid content of the ink. In die coating, this involves controlling the gap between the die opening, the substrate, and the coating head. In microgravure coating, rod gravure coating, and gravure coating, this involves controlling the line count, depth, and rotation ratio of the printing plate to apply the ink to the substrate. Drying controls the film thickness. It is mainly used when forming films from organic materials and a portion of inorganic dispersed materials.

[0034] The thin-film resistivity of electromagnetic wave transmission layer 1 can be measured, for example, using Loresta GP MCP-T610 (trade name, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0035] (Dielectric layer)

[0036] The dielectric layer 3 is a layer used to cause interference between the incident electromagnetic wave and the reflected electromagnetic wave. The thickness and other properties of the dielectric layer 3 are set in a manner that satisfies the conditions expressed by the following formula.

[0037] d=λ / (4(ε r ) 1 / 2 )

[0038] In the formula, λ represents the wavelength of the electromagnetic wave to be suppressed (unit: m), ε r d represents the relative permittivity of the material constituting dielectric layer 3, and d represents the thickness of dielectric layer 3 (in meters). Reflection attenuation is achieved by shifting the phase of the incident electromagnetic wave and the phase of the reflected electromagnetic wave by π.

[0039] The dielectric layer 3 is composed of a resin composition having a relative permittivity greater than 10.0 at a frequency of 3.7 GHz. By making the relative permittivity of the dielectric layer 3 greater than 10.0, as described above, excellent absorption performance (preferably -15 dB, more preferably -20 dB) can be achieved in a specific frequency band. In addition, since the dielectric layer 3 can be thinned, both increased productivity and space saving of the dielectric layer 3 can be achieved to a high degree. The relative permittivity of the dielectric layer 3 at a frequency of 3.7 GHz is preferably greater than 10.0 and less than 30.0, more preferably greater than 10.0 and less than 20.0. By making the relative permittivity of the dielectric layer 3 less than 30.0 at a frequency of 3.7 GHz, it is preferable to form a dielectric layer 3 with sufficient strength. For example, when an excessive amount of dielectric compound is incorporated into the dielectric layer 3 to increase its relative permittivity, the dielectric layer 3 tends to become brittle. The thickness of dielectric layer 3 can be appropriately set according to the frequency band and relative permittivity. For example, when used in the 60GHz, 76GHz, or 90GHz bands of millimeter-wave radar, the thickness of dielectric layer 3 is preferably 100–400 μm, more preferably 250–400 μm. When used in the 3.7GHz, 4.5GHz, or 28GHz bands of 5G communication, the thickness of dielectric layer 3 is preferably 450–7000 μm, more preferably 650–6500 μm. Furthermore, in recent years, when used in the terahertz wave bands, such as the 300GHz or 350GHz bands, which have attracted attention in fields such as next-generation communication standards, metrology / analysis technology, and medicine, the thickness of dielectric layer 3 is preferably 20–80 μm, more preferably 50–80 μm.

[0040] The resin composition constituting dielectric layer 3 contains at least one dielectric compound and a resin component. The relative permittivity of dielectric layer 3 can be adjusted according to the selection and content of the dielectric compound in the resin composition. The content of the dielectric compound is preferably 10 to 300 parts by volume, more preferably 25 to 100 parts by volume, relative to 100 parts by weight of the resin composition. The content of the dielectric compound is preferably 10 to 900 parts by weight, more preferably 25 to 100 parts by weight, relative to 100 parts by mass of the resin composition. By setting the content of the dielectric compound in the resin composition to a lower limit or higher, the relative permittivity of dielectric layer 3 can be sufficiently increased; on the other hand, by setting it to an upper limit or lower, dielectric layer 3 can be efficiently manufactured by wet coating or extrusion molding.

[0041] Examples of dielectric compounds include barium titanate, titanium dioxide, zinc oxide, aluminum oxide, magnesium oxide, niobium oxide, tantalum oxide, vanadium oxide, forsterite (Mg₂SiO₄), and barium magnesium niobate (Ba(Mg)₂SiO₄). 1 / 3 Nb 2 / 3 (O3), barium titanate (Ba3Nd) 9.3 Ti 18 O 54 Metal compounds such as gallium nitride and aluminum nitride are preferred. The dielectric compound is preferably in the form of a powder (e.g., nanoparticles). The relative permittivity of the dielectric compound is preferably higher than that of the resin component. The relative permittivity of the dielectric compound at frequencies of 3.7 GHz or 90 GHz is preferably higher than 10 and less than 5000, more preferably 100 to 5000, and even more preferably 1000 to 5000.

[0042] Examples of resin components include acrylic resin, methacrylic resin, silicone resin, polycarbonate, epoxy resin, phthalate resin, polyvinyl chloride, polyvinyl alcohol formaldehyde, phenolic resin, urea resin, and polychloroprene resin. The relative permittivity of the resin component at a frequency of 3.7 GHz or 90 GHz is preferably 2.5 to 9.5, more preferably 3.5 to 9.5, and even more preferably 5.0 to 9.5.

[0043] The resin composition preferably has adhesive properties. This allows the dielectric layer 3 to be effectively adhered to the surface 4F of the reflective layer 4. Examples of materials that can be used for this purpose include silicone adhesives, acrylic adhesives, and urethane adhesives. These materials can be used as components of the resin, and an adhesive layer made of these materials can be formed on at least one surface of the dielectric layer 3. The adhesion strength of the resin composition itself or the adhesive layer to the 304 stainless steel sheet is preferably 1.0 N / 25 mm or more, and can be 3.0 to 10.0 N / 25 mm or 10.0 to 15.0 N / 25 mm.

[0044] The complex permittivity of dielectric layer 3 is expressed by the following formula. In the formula, i is the imaginary unit, ε' is the real part of the complex permittivity, and ε” is the imaginary part of the complex permittivity.

[0045] Complex permittivity ε=ε'-iε”

[0046] The real part of the complex permittivity is the relative permittivity (the ratio of the permittivity ε₀ to that of vacuum). The imaginary part ε” of the complex permittivity is derived from the value of the dielectric loss tangent tanδ (=ε” / ε’). The relative permittivity and the dielectric loss tangent can be determined using a permittivity measuring device.

[0047] The real part of the complex permittivity of dielectric layer 3 at 3.7 GHz or 90 GHz is preferably greater than 10, more preferably 10.5 to 30, and even more preferably 12 to 20. By making this value greater than 10, it is preferable to achieve excellent absorption performance in a specific frequency band. On the other hand, by making this value less than 30, it is preferable to form dielectric layer 3 with sufficient strength. The imaginary part of the complex permittivity of dielectric layer 3 at 3.7 GHz or 90 GHz is preferably less than 5, more preferably 0 to 3.5, and even more preferably 0 to 3.

[0048] (Reflective layer)

[0049] The reflective layer 4 is used to reflect electromagnetic waves incident from the dielectric layer 3 so that they reach the dielectric layer 3. The thickness of the reflective layer 4 is, for example, 4 to 250 μm, 4 to 12 μm, or 50 to 100 μm.

[0050] The reflective layer 4 is made of a conductive material, and is preferred because it can reflect electromagnetic waves when its sheet resistance is below 100 Ω / □. This material can be either inorganic or organic. Examples of conductive inorganic materials include nanoparticles and / or nanowires containing one or more nanoparticles selected from the group consisting of indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), carbon nanotubes, graphene, Ag, Al, Au, Pt, Pd, Cu, Co, Cr, In, Ag-Cu, Cu-Au, and Ni. Examples of conductive organic materials include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, and polypyrrole derivatives. The conductive inorganic or organic material can be filmed on a substrate with a sheet resistance of 100 Ω / □ or less. From the perspectives of flexibility, film-forming properties, stability, thin-film resistivity, and low cost, it is preferable to use a laminated film (Al-deposited PET film) having a PET film and an aluminum layer vapor-deposited on its surface as the reflective layer.

[0051] <Manufacturing Method of Electromagnetic Wave Absorber>

[0052] The electromagnetic wave absorber 10 is manufactured, for example, via the following steps. First, a roll-shaped dielectric layer is formed. Then, a roll-shaped laminate containing the dielectric layer is formed by a roll-to-roll process. The laminate is cut to a predetermined size, thereby obtaining the electromagnetic wave absorber 10. The roll-shaped dielectric layer can be manufactured via step (A) of preparing the above-described resin composition and step (B) of forming a dielectric layer composed of the resin composition by a roll-to-roll process. When the frequency band of the target application is high (e.g., above 60 GHz), the dielectric layer is sufficiently thin, so the electromagnetic wave absorber 10 can be manufactured by a roll-to-roll process. In contrast, when the frequency band of the target application is low (e.g., below 28 GHz), a thick dielectric layer is required, making it difficult to manufacture by a roll-to-roll process. In this case, the dielectric layer can be formed, for example, by extrusion molding. That is, the manufacturing method can be appropriately selected according to the frequency band of the target application (in other words, the thickness of the dielectric layer).

[0053] There are no particular limitations on the manufacturing methods for dielectric layers and laminates; conventionally known methods such as dry lamination and melt extrusion lamination can be used. Specifically, dielectric layers can be produced by comma coating or die coating, extrusion film formation, or calendering film formation. For example, in comma coating, an appropriate gap is made between the comma roller and the coating roller, allowing the substrate to travel between them. A certain amount of coating liquid is applied to the film through the gap and then dried, thereby forming the film. By using PET or similar materials treated with anti-stick coating as the substrate, dielectric layer monomers can be easily obtained when producing the laminate. Furthermore, if it can be directly coated onto the electromagnetic wave transmission layer or reflective layer, the lamination step during laminate production can be omitted. By adjusting the gap, dielectric layers of any film thickness can be obtained. In die coating, a gap called the coating gap is left on the substrate being transported to the back-up roll. The coating liquid is applied through the die slit and then dried, thereby producing the dielectric layer. By adjusting the supply liquid flow rate, coating gap, and substrate conveying speed, dielectric layers of arbitrary thickness can be obtained. Regarding the substrate, PET with anti-stick treatment, or electromagnetic wave transmission or reflection layers can be used as before. In extrusion film forming, the resin composition for forming the dielectric layer is supplied to a melt extruder heated to a temperature approximately 100°C above the melting point Tm of the resin composition. The resin composition for forming the dielectric layer is melted, extruded into a sheet through a die such as a T-die, and rapidly cooled and solidified by a rotating cooling roller or the like, and then wound up, thereby forming a dielectric layer film. The thickness of the dielectric layer can be controlled by the degree of opening of the resin ejection lip. When a substrate for conveying is required in the film forming apparatus, or when a laminate can be fabricated using resin thermal fusion, lamination can be performed by thermal fusion with an electromagnetic wave transmission or reflection layer. Similarly, in calendering film formation, a mixing roller can be used to melt the resin, and the resin composition is fed between two or more calendering rollers and rotated. The dielectric layer is then formed by calendering, cooling, and winding. The thickness of the dielectric layer can be controlled by adjusting the gap between the calendering rollers. If substrate mounting is possible, the process is the same as before. If the dielectric layer formed by the above film formation method has adhesive properties, a laminate can be formed by bonding it to an electromagnetic wave transmission layer or a reflective layer using a laminator. If the resin composition itself lacks adhesive properties or has weak adhesiveness, an adhesive layer can be formed using dry lamination or the like, and then laminated for bonding. Alternatively, an adhesive layer can be applied to the resin composition itself, dried, and then bonded to an electromagnetic wave transmission layer or reflective layer used in forming the laminate. Another method is to apply an adhesive to the electromagnetic wave transmission layer or reflective layer, dry it, and then dry-laminate it with the dielectric layer to form a laminate.

[0054] <Second Implementation>

[0055] Figure 2 A cross-sectional view of the reflective electromagnetic wave absorber according to the second embodiment is shown schematically. The reflective electromagnetic wave absorber 20 shown in this figure is a film or sheet-like structure having a stacked structure comprising an electromagnetic wave transmission layer 1, a resistive layer 5, a dielectric layer 3, and a reflective layer 4 in sequence. The electromagnetic wave absorber 20 has the same configuration as the electromagnetic wave absorber 10 according to the first embodiment, except that a resistive layer 5 is provided between the electromagnetic wave transmission layer 1 and the dielectric layer 3. The resistive layer 5 will be described below.

[0056] (Resistive layer)

[0057] The resistive layer 5 is used to guide electromagnetic waves incident from the electromagnetic wave transmission layer 1 to the dielectric layer 3. That is, the resistive layer 5 is used for impedance matching according to the environment in which the electromagnetic wave absorber 20 is used or the characteristics of the electromagnetic wave transmission layer 1. For example, when the electromagnetic wave absorber 20 is used in air (impedance: 377 Ω / □) and the real part of the complex permittivity (relative permittivity) of the dielectric layer 3 is 2.9 and the thickness is 50 μm, high reflection attenuation can be obtained when the thin-layer resistance value of the resistive layer 5 is set in the range of 270 to 500 Ω / □.

[0058] The resistive layer 5 is composed of a conductive material. This material can be inorganic or organic. Examples of conductive inorganic materials include nanoparticles and / or nanowires containing one or more nanoparticles selected from the group consisting of indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), carbon nanotubes, graphene, Ag, Al, Au, Pt, Pd, Cu, Co, Cr, In, Ag-Cu, Cu-Au, and Ni. Examples of conductive organic materials include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, and polypyrrole derivatives. From the viewpoints of flexibility, adaptability to wet coating, stability of the film resistance in the atmosphere after film formation, and the film resistance value, it is preferable that the resistive layer 5 is composed of a conductive polymer containing polyethylene dioxythiophene (PEDOT). For example, the resistive layer 5 can be composed of a mixture of polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PPS) (PEDOT / PSS).

[0059] The sheet resistance value of the resistive layer 5 can be appropriately set, for example, by selecting a conductive material and adjusting the thickness of the resistive layer 5. The thickness of the resistive layer 5 is preferably set in the range of 0.1 to 2.0 μm, and more preferably in the range of 0.1 to 0.4 μm. When the thickness is 0.1 μm or more, it is easier to form a uniform film, thus tending to more fully realize its function as the resistive layer 5. On the other hand, when the thickness is 2.0 μm or less, sufficient flexibility can be maintained, tending to more reliably suppress cracking in the film caused by external factors such as bending and stretching after film formation. The sheet resistance value can be measured, for example, using a Loresta GP MCP-T610 (trade name, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0060] According to the electromagnetic wave absorbers 10 and 20 described above, since the dielectric layer 3 has a relative permittivity of over 10.0 at frequencies of 3.7 GHz or 90 GHz, the dielectric layer 3 can be made sufficiently thin. This allows for a high level of improvement in the productivity of the dielectric layer 3 and space saving. Furthermore, according to the electromagnetic wave absorbers 10 and 20, a significant reflection attenuation of 15 dB or more (preferably 20 dB or more) can be achieved.

[0061] The embodiments of this disclosure have been described in detail above, but the present invention is not limited to the above embodiments. For example, in the above embodiments, film-like or sheet-like electromagnetic wave absorbers 10 and 20 are exemplified, but the shape of the electromagnetic wave absorber is not limited to these. For example, Figure 1 , 2 The reflective layer 4 shown may not be layered.

[0062] Example

[0063] The present disclosure will now be described based on embodiments and comparative examples. It should be noted that the present invention is not limited to the following embodiments.

[0064] The dielectric layers involved in the embodiments and comparative examples were fabricated using the following materials.

[0065] (1) Resin composition

[0066] • Acrylic resin: OC-3405 (manufactured by SAIDEN CHEMICAL INDUSTRY CO.,LTD., relative permittivity at 3.7 GHz: 4.2)

[0067] • Silicone resin: MHM-SI500 (manufactured by Nichiei Processing Co., Ltd., relative permittivity at 3.7 GHz: 3.2)

[0068] • Urea resin: C60A10WN (manufactured by BASF Japan, relative permittivity at 3.7 GHz: 4.5)

[0069] (2) Dielectric compounds

[0070] • Barium titanate powder: BT-01 (manufactured by Sakai Chemical Industry Co., Ltd.)

[0071] • Titanium oxide powder: CR-60 (manufactured by Ishihara Sangyo Co., Ltd.)

[0072] (Examples 1-3 and Comparative Examples 1 and 2)

[0073] Resin compositions with the compositions shown in Table 1 were prepared. Regarding the resin compositions involved in the Examples and Comparative Examples, the following items were evaluated.

[0074] (1) Determination of relative permittivity

[0075] According to the method described in JIS C2138:2007, the relative permittivity of the resin composition was determined using a cavity resonator method dielectric constant measuring apparatus within a frequency range of 1 MHz to 1 GHz, under conditions of 25°C and 50% relative humidity. Five samples were prepared at each level, and five measurements were performed. The measured values ​​of the relative permittivity at frequencies of 1 MHz, 500 MHz, and 1 GHz were plotted as a semi-logarithmic graph, yielding an approximate straight line. It should be noted that frequency was used as the horizontal axis (logarithmic scale), and the value of the relative permittivity was used as the vertical axis. The relative permittivity at 3.7 GHz and 90 GHz was calculated based on this approximate straight line. The values ​​of the relative permittivity calculated from the five measurements are recorded in Table 1.

[0076] (2) Evaluation of the adhesiveness of the resin composition

[0077] The adhesive strength of the resin composition was evaluated according to the method described in JIS Z0237:2009. The resin compositions involved in the examples and comparative examples were processed into films with a thickness of 0.2 mm and then cut to obtain specimens with a width of 25 mm. On the other hand, a stainless steel 304 sheet with one side mirror-finished was prepared. After placing the specimen on this surface, it was pressed together by passing a 2 kg roller back and forth twice. After standing for 30 minutes, the specimen was peeled relative to the stainless steel 304 sheet at a 180° angle using a tensile testing machine, and the peel strength was measured. The peel speed was set to 300 mm / min. The results are shown in Table 1.

[0078] (3) Evaluation of the adhesion of laminates

[0079] Although acrylic resin (OC-3405) has adhesive properties, as shown in the results of Examples 2 and 3 in Table 1, the adhesive strength of the resin composition decreases with increasing volume fraction of the dielectric compound. Therefore, another sample was prepared by laminating acrylic resin (OC-3405) without the dielectric compound onto one side of a film made from the resin compositions described in Examples 2 and 3 using wire rod #5. The adhesive strength of the adhesive layer composed of this acrylic resin was evaluated in the same manner as above. The results are shown in Table 1.

[0080] (4) Evaluation of the thickness of the dielectric layer

[0081] Dielectric layers of the thicknesses shown in Table 1 are formed by die coating. The thicknesses shown in Table 1 are assumed to be for 90GHz mobile communication. It should be noted that since the dielectric layer thickness that can be formed by one coating is about 200μm, only two coatings are required in Examples 1 to 3, while three coatings are required in Comparative Examples 1 and 2.

[0082] (5) Evaluation of the number of rolls of rice

[0083] Table 1 shows the number of meters of dielectric material wound on a core with an inner diameter of 3 inches and a wall thickness of 4 mm (outer diameter of 84.2 mm) using a device with a maximum diameter of 700 mm. In Examples 1-3, more than 1450 m of dielectric material can be wound on a single roll, whereas in Comparative Examples 1 and 2, the amount of dielectric material wound on a single roll is limited to less than 1000 m.

[0084] [Table 1]

[0085]

[0086] (Example 4 and Comparative Example 3)

[0087] Resin compositions with the compositions shown in Table 2 were prepared. For these resin compositions, the evaluations described in (1) to (3) and (5) above were performed in the same manner as in Example 1. It should be noted that since the urethane resin used as the resin component lacks adhesiveness, a sample was separately prepared by laminating an acrylic resin (OC-3405) without dielectric compounds onto one side of a film made from the resin composition using wire rod #5. The adhesive strength of the adhesive layer composed of this acrylic resin was evaluated in the same manner as described above. Furthermore, the evaluation of (4) was performed as follows.

[0088] (4) Evaluation of the thickness of the dielectric layer

[0089] The dielectric layers with the thicknesses shown in Table 2 are formed by calendering. The thicknesses shown in Table 2 are assumed to be for 3.7 GHz communication. It should be noted that the thickness of the dielectric layer that can be formed by one calendering process is approximately 800 μm.

[0090] [Table 2]

[0091]

[0092] (Example 5 and Comparative Example 4)

[0093] Resin compositions with the compositions shown in Table 3 were prepared. These resin compositions were evaluated in the same manner as in Example 4, as in (1) to (3) and (5). Evaluation of (4) was carried out as follows.

[0094] (4) Evaluation of the thickness of the dielectric layer

[0095] The dielectric layer with the thickness shown in Table 3 is formed by calendering. The thicknesses shown in Table 3 are assumed to be for 28 GHz communication. However, since there is no data on the relative permittivity of the dielectric layer at 28 GHz, the thickness of the dielectric layer is set based on the relative permittivity at 3.7 GHz.

[0096] [Table 3]

[0097]

[0098] (Example 6 and Comparative Example 5)

[0099] Resin compositions with the compositions shown in Table 4 were prepared. These resin compositions were evaluated in the same manner as in Example 4, as in steps (1) to (3) and (5). The evaluation of (4) is as follows.

[0100] (4) Evaluation of the thickness of the dielectric layer

[0101] The dielectric layer with the thickness shown in Table 4 is formed by calendering. The thicknesses shown in Table 4 are assumed to be for 60 GHz communication. However, since there is no data on the relative permittivity of the dielectric layer at 60 GHz, the thickness of the dielectric layer is set based on the relative permittivity at 90 GHz.

[0102] [Table 4]

[0103]

[0104] (Example 7 and Comparative Example 6)

[0105] Resin compositions with the compositions shown in Table 5 were prepared. These resin compositions were evaluated in the same manner as in Example 4, as in (1) to (3) and (5). Evaluation of (4) was carried out as follows.

[0106] (4) Evaluation of the thickness of the dielectric layer

[0107] The dielectric layer with the thicknesses shown in Table 5 is formed by calendering. The thicknesses shown in Table 5 are assumed to be for 350 GHz communication. However, since there is no data on the relative permittivity of the dielectric layer at 350 GHz, the thickness of the dielectric layer is set based on the relative permittivity at 90 GHz.

[0108] [Table 5]

[0109]

[0110] Explanation of symbols

[0111] 1…Electromagnetic wave transmission layer, 3…Dielectric layer, 4…Reflective layer, 4F…Surface, 5…Resistive layer, 10, 20…Reflective electromagnetic wave absorber

Claims

1. A method for manufacturing a dielectric layer, which is a method for manufacturing a dielectric layer possessed by a reflective electromagnetic wave absorber, comprising: The step of preparing a resin composition, wherein the resin composition contains at least one dielectric compound and a resin component, and has a relative permittivity greater than 10.0 at a frequency of 3.7 GHz or 90 GHz; and The step of forming a dielectric layer with a thickness of 20 to 7000 μm composed of the resin composition. The dielectric compound is at least one of titanium oxide and barium titanate. The resin component has a relative permittivity of 2.5 to 9.5 at frequencies of 3.7 GHz or 90 GHz. The resin component is at least one of acrylic resin, silicone resin, and urethane resin. The content of the dielectric compound is 10 parts by volume or more and less than 100 parts by volume relative to 100 parts by volume of the resin composition. The content of the dielectric compound is 10 parts by weight or more and less than 100 parts by weight relative to 100 parts by weight of the resin composition. According to the method described in JIS C2138:2007, the relative permittivity of the resin composition was measured using a cavity resonator method dielectric constant measuring device in the frequency range of 1MHz to 1GHz under conditions of 25°C and 50% relative humidity. The measured values ​​of the three relative permittivity at frequencies of 1MHz, 500MHz and 1GHz were plotted as a semi-logarithmic graph to draw an approximate straight line. The relative permittivity at 3.7GHz and 90GHz was calculated based on this approximate straight line.

2. A resin composition comprising a dielectric layer for forming a reflective electromagnetic wave absorber. The resin composition contains: At least one dielectric compound, and Resin components, Furthermore, its relative permittivity is higher than 10.0 at frequencies of 3.7 GHz or 90 GHz. The dielectric compound is at least one of titanium oxide and barium titanate. The resin component has a relative permittivity of 2.5 to 9.5 at frequencies of 3.7 GHz or 90 GHz. The resin component is at least one of acrylic resin, silicone resin, and urethane resin. The content of the dielectric compound is 10 parts by volume or more and less than 100 parts by volume relative to 100 parts by volume of the resin composition. The content of the dielectric compound is 10 parts by weight or more and less than 100 parts by weight relative to 100 parts by weight of the resin composition. According to the method described in JIS C2138:2007, the relative permittivity of the resin composition was measured using a cavity resonator method dielectric constant measuring device in the frequency range of 1MHz to 1GHz under conditions of 25°C and 50% relative humidity. The measured values ​​of the three relative permittivity at frequencies of 1MHz, 500MHz and 1GHz were plotted as a semi-logarithmic graph to draw an approximate straight line. The relative permittivity at 3.7GHz and 90GHz was calculated based on this approximate straight line.

3. The resin composition according to claim 2, wherein, The relative permittivity of the dielectric compound is higher than that of the resin component.

4. The resin composition according to claim 2 or 3, wherein it has adhesive properties.

5. The resin composition according to claim 4, wherein the adhesion to a 304 stainless steel sheet is 1.0 N / 25 mm or more.

6. A layered body, comprising: The dielectric layer formed by the resin composition according to any one of claims 2 to 5, and An adhesive layer disposed on at least one surface of the dielectric layer The adhesive layer is composed of at least one of silicone adhesive, acrylic adhesive, and urethane adhesive. The adhesion of the adhesive layer to the 304 stainless steel plate is greater than 1.0 N / 25 mm.

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