Electromagnetic wave absorber and laminated body for electromagnetic wave absorber

Abstract

An electric wave absorber (1a) includes a resistance layer (10), a reflector (30), and a dielectric layer (20). The resistance layer (10) includes a plurality of carbon nanotubes (11). The resistance layer (10) has a resistivity of 1.5 Ω·cm or less. The reflector (30) reflects an electric wave. The dielectric layer (20) is disposed between the resistance layer (10) and the reflector in a thickness direction of the resistance layer (10).

Description

Technical Field

[0001] This invention relates to electromagnetic wave absorbers and laminates for electromagnetic wave absorbers. Background Technology

[0002] Previously, it was known that electromagnetic wave absorbers had a dielectric layer between the resistive layer and the electromagnetic wave reflector.

[0003] For example, Patent Document 1 describes an electromagnetic wave absorber comprising a resistive film, an electromagnetic wave reflector, and a dielectric layer. The resistive film contains extremely fine conductive fibers such as carbon nanotubes. The electromagnetic wave absorber has a dielectric layer between the resistive film and the electromagnetic wave reflector, and the thickness of the dielectric layer is designed based on the λ / 4 electromagnetic wave absorber theory.

[0004] Furthermore, Patent Document 2 describes an electromagnetic wave absorbing sheet. The electromagnetic wave absorbing sheet is manufactured by coating at least one side of a sheet-like substrate (A) with an electromagnetic wave absorbing coating composition (B). The electromagnetic wave absorbing coating composition (B) contains carbon nanomaterials (a), resin (b), and solvent (c). The sheet-like substrate (A) can be a dielectric sheet. A λ / 4 type electromagnetic wave absorber structure can be obtained by attaching the electromagnetic wave absorbing sheet to a metal casing or attaching an electromagnetic wave absorbing sheet with a reflective layer on the other side of the dielectric sheet to a plastic casing. The carbon nanomaterials (a) are, for example, conductive multilayer carbon nanotubes.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2005-311330

[0008] Patent Document 2: Japanese Patent Application Publication No. 2006-114877 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] With the advancement of technologies such as communication and autonomous driving, it is conceivable that there will be a need for electromagnetic wave absorbers that can be used in various environments. For example, electromagnetic wave absorbers may require both high tensile strength and high durability in high temperature and high humidity environments. On the other hand, according to Patent Documents 1 and 2, there has been no research on electromagnetic wave absorbers with a resistive layer that can simultaneously achieve high tensile strength and high durability in high temperature and high humidity environments.

[0011] In view of this, the present invention provides an electromagnetic wave absorber and a laminate for electromagnetic wave absorbers that have a resistive layer that is advantageous from the viewpoint of high tensile strength and high durability in high temperature and high humidity environments.

[0012] Solution for solving the problem

[0013] This invention provides an electromagnetic wave absorber comprising a resistive layer, a reflector, and a dielectric layer.

[0014] The resistive layer comprises multiple layers of carbon nanotubes and has a resistivity of less than 1.5 Ω·cm;

[0015] The reflector reflects electromagnetic waves;

[0016] The dielectric layer is disposed between the resistive layer and the reflector in the thickness direction of the resistive layer.

[0017] In addition, the present invention provides a laminated body for an electromagnetic wave absorber.

[0018] It has a resistive layer and a dielectric layer.

[0019] The resistive layer comprises multiple layers of carbon nanotubes and has a resistivity of less than 1.5 Ω·cm;

[0020] The resistive layer overlaps with the dielectric layer.

[0021] The effects of the invention

[0022] The aforementioned electromagnetic wave absorber and the resistive layer of the electromagnetic wave absorber laminate are advantageous from the viewpoint of high tensile strength and high durability in high temperature and high humidity environments. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view showing an example of the electromagnetic wave absorber of the present invention.

[0024] Figure 2 This is a cross-sectional view showing another example of the electromagnetic wave absorber of the present invention.

[0025] Figure 3 This is a cross-sectional view showing another example of the electromagnetic wave absorber of the present invention.

[0026] Figure 4 This is a cross-sectional view showing another example of the electromagnetic wave absorber of the present invention.

[0027] Figure 5 This is a cross-sectional view showing another example of the electromagnetic wave absorber of the present invention.

[0028] Figure 6 This is a cross-sectional view showing an example of a laminated body for absorbing electromagnetic waves according to the present invention.

[0029] Figure 7 This is a field emission transmission electron microscope (FE-TEM) image of the cross-section of the resistive layer of the electromagnetic wave absorber in Example 1.

[0030] Figure 8 This is an FE-TEM image of the resistive layer of the electromagnetic wave absorber in Example 3.

[0031] Figure 9 This is an FE-TEM image of the resistive layer of the electromagnetic wave absorber in Example 5. Detailed Implementation

[0032] The embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to the following embodiments.

[0033] like Figure 1 As shown, the electromagnetic wave absorber 1a includes a resistive layer 10, a reflector 30, and a dielectric layer 20. The resistive layer 10 comprises multiple layers of carbon nanotubes 11. Furthermore, the resistive layer 10 has a resistivity of 1.5 Ω·cm or less. The reflector 30 reflects electromagnetic waves. The dielectric layer 20 is disposed between the resistive layer 10 and the reflector 30 in the thickness direction of the resistive layer 10.

[0034] The electromagnetic wave absorber 1a is, for example, a λ / 4 type electromagnetic wave absorber. The electromagnetic wave absorber 1a is designed such that when an electromagnetic wave of wavelength λ0, which is the target wavelength for absorption, is incident on the electromagnetic wave absorber 1a, the electromagnetic wave reflected from the surface of the resistive layer 10 (surface reflection) interferes with the electromagnetic wave reflected from the reflector 30 (back reflection). The electromagnetic wave absorber 1a can absorb electromagnetic waves, for example, millimeter waves or submillimeter waves of a specific frequency band.

[0035] The resistive layer 10 comprises multiple layers of carbon nanotubes 11, resulting in a resistivity of 1.5 Ω·cm or less, thus exhibiting high tensile strength. For example, even when the resistive layer 10 is stretched, its resistance and other properties are unlikely to change. It is believed that even when the resistive layer 10 is stretched, the resistance of the multiple carbon nanotubes 11 themselves is unlikely to change. Furthermore, the reason for the high tensile strength of the resistive layer 10 lies in the contact state between the multiple carbon nanotubes 11. The diameter (fiber diameter) of the multiple carbon nanotubes 11 is relatively small for fibrous carbon materials. Therefore, it is believed that in the resistive layer 10, the multiple carbon nanotubes 11 are in contact while being intertwined in a linear fashion. If the resistive layer 10 comprises multiple layers of carbon nanotubes 11, resulting in a resistivity of 1.5 Ω·cm or less, it is believed that even when the resistive layer 10 is stretched, the contact state of the multiple carbon nanotubes 11 being intertwined in a linear fashion is easily maintained. As a result, the resistive layer 10 exhibits high tensile strength.

[0036] In the resistive layer, other fibrous carbon materials such as carbon nanofibers can be considered instead of multilayer carbon nanotubes. However, it is believed that carbon nanofibers, with a fiber diameter larger than that of multilayer carbon nanotubes (e.g., exceeding 70 nm), are difficult to intertwine into a linear structure within the resistive layer. Therefore, the contact between carbon nanofibers tends to become point-like, and the contact between them is easily weakened. Consequently, it is considered that when a resistive layer containing carbon nanofibers is stretched, the carbon nanofibers are highly likely to separate, making it difficult to improve the tensile strength of the resistive layer.

[0037] By incorporating multiple layers of carbon nanotubes 11 into the resistive layer 10, the resistive layer 10 readily exhibits high durability in high-temperature and high-humidity environments. For example, even when the resistive layer 10 is placed in a high-temperature and high-humidity environment, its resistance and other properties are unlikely to change. The multiple layers of carbon nanotubes 11 are considered to have a multilayer structure; therefore, even if the outermost layer of the multiple layers of carbon nanotubes 11 undergoes chemical degradation, damaging the bonding between carbon atoms, in a high-temperature and high-humidity environment, the physical state of the inner layers is easily maintained. Thus, the conductivity of the multiple layers of carbon nanotubes 11 is easily maintained in high-temperature and high-humidity environments. As a result, the resistive layer 10 is considered to readily exhibit high durability in high-temperature and high-humidity environments. On the other hand, in a resistive layer, for example, when a single-layer carbon nanotube is used instead of a multiple-layer carbon nanotube, the surface of the single-layer carbon nanotube undergoes chemical degradation in a high-temperature and high-humidity environment, thereby reducing the conductivity of the single-layer carbon nanotube. For example, in a high-temperature and high-humidity environment, the surface of the single-layer carbon nanotube undergoes chemical degradation, and there is a possibility that the conjugated system structure will be disrupted, leading to a decrease in the conductivity of the resistive layer.

[0038] In this specification, the term "high temperature and high humidity environment" is not limited to a specific environment. For example, a high temperature and high humidity environment is one with a temperature of 60°C to 120°C and a relative humidity of 60% or higher. An example of a high temperature and high humidity environment is one with a temperature of 85°C and a relative humidity of 85%.

[0039] The resistivity of the resistive layer 10 can be less than 1.4 Ω·cm, less than 1.3 Ω·cm, or less than 1.2 Ω·cm. The lower limit of the resistivity of the resistive layer 10 is not limited to a specific value. The resistivity of the resistive layer 10 can be greater than or equal to 0.001 Ω·cm, greater than or equal to 0.005 Ω·cm, greater than or equal to 0.01 Ω·cm, or greater than or equal to 0.02 Ω·cm.

[0040] The diameter of the multilayer carbon nanotubes 11 is not limited to a specific value. For example, the diameter of the multilayer carbon nanotubes 11 is 70 nm or less. As a result, the multilayer carbon nanotubes 11 in the resistive layer 10 can easily be wrapped around each other in a wire-like manner while in contact, and the resistive layer 10 can easily exhibit high tensile strength.

[0041] The diameter of the multilayer carbon nanotubes 11 can be less than 60 nm, less than 50 nm, less than 40 nm, or less than 30 nm. The diameter of the multilayer carbon nanotubes 11 can, for example, be greater than 3 nm, greater than 5 nm, or greater than 7 nm. The diameter of the multilayer carbon nanotubes 11 can be determined, for example, by observing a sample using a field emission transmission electron microscope (FET), wherein the sample is prepared using a microsampling method with a focused ion beam (FIB) processing device for observing the cross-section of the resistive layer 10. Alternatively, the diameter of the multilayer carbon nanotubes 11 in the resistive layer 10 can be determined based on technical data such as catalogs related to electromagnetic absorbers or their materials.

[0042] As long as the resistivity of the resistive layer 10 is below 1.5 Ω·cm, the content of the multilayer carbon nanotubes 11 in the resistive layer 10 is not limited to a specific value. For example, its content is 3% or more by mass. Therefore, it is believed that even if the resistive layer 10 is stretched, the multilayer carbon nanotubes 11 can more reliably maintain a state where they are intertwined and in contact with each other. As a result, the resistive layer 10 exhibits higher tensile strength more reliably.

[0043] The content of multilayer carbon nanotubes 11 in the resistive layer, based on a mass basis, can be 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, or 60% or more. The content of multilayer carbon nanotubes 11 in the resistive layer, based on a mass basis, can be, for example, less than 90%, less than 85%, or less than 80%.

[0044] like Figure 1 As shown, the resistive layer 10 further includes, for example, an adhesive 12. The adhesive 12 bonds the multilayer carbon nanotubes 11 together. The adhesive 12 comprises, for example, at least one selected from the group consisting of polyurethane, polyacrylate, epoxy resin, and polyester. Therefore, even when the resistive layer 10 is stretched, it is easier and more reliable to maintain the multilayer carbon nanotubes 11 in contact while they are intertwined in a linear shape. As a result, the resistive layer 10 exhibits more reliable high tensile strength.

[0045] The resistive layer 10, for example, does not contain aliphatic cellulose esters. In this way, even if the resistive layer 10 does not contain aliphatic cellulose esters, the resistive layer as an electromagnetic wave absorber still has the desired characteristics.

[0046] The resistance R of the resistance layer 10 after the tensile test tThe resistance R0 of the resistance layer 10 before the tensile test is not limited to a specific relationship. It should be noted that the tensile test is performed, for example, by applying tensile stress to the resistance layer 10 in a direction perpendicular to its thickness direction to induce a strain of 10%. Resistance R t The resistance R0 satisfies, for example, 100 × {(R t The relationship is / R0)-1}≤15. In this way, the resistive layer 10 has high tensile strength, and even if the resistive layer 10 is stretched, the resistance of the resistive layer 10 is difficult to change.

[0047] In resistive layer 10, 100×{(R t The value of / R0)-1} is preferably 10 or less, more preferably 5 or less.

[0048] The thin-film resistance R of resistive layer 10 after high temperature and high humidity environmental testing H The thin-film resistance R of resistive layer 10 before high temperature and high humidity environment test i Not limited to a specific relationship. It should be noted that high temperature and high humidity environment tests are conducted, for example, by maintaining the environment of the resistive layer 10 at 85°C and 85% relative humidity for 24 hours. Thin-layer resistivity R H and thin film resistance R i For example, satisfying 100×{(R) H / R i The relationship is 100 × {(R) - 1} ≤ 15. H / R i The value of )-1} is preferably 10 or less, more preferably 5 or less, and may also be 0.05 or less.

[0049] As long as the electromagnetic wave absorber 1a can absorb the desired electromagnetic wave, the thin-film resistance of the resistive layer 10 is not limited to a specified value. For example, the thin-film resistance of the resistive layer 10 can be 200Ω / □ to 600Ω / □. The thin-film resistance of the resistive layer 10 can be 220Ω / □ to 550Ω / □, or 240Ω / □ to 500Ω / □.

[0050] The thickness of the resistive layer 10 is not limited to a specific thickness. The thickness of the resistive layer 10 may be, for example, 75 μm or less, 60 μm or less, 50 μm or less, or 40 μm or less. The thickness of the resistive layer 10 may be, for example, 0.5 μm or more.

[0051] The reflector 30 is not particularly limited as long as it can reflect the electromagnetic waves of the absorbing object. The reflector 30 may be formed in a layered shape, for example. In this case, the reflector 30 has a thin-layer resistance lower than that of the resistive layer 10. The reflector 30 may also have a shape other than a layered shape. For example, the housing or structural component of a specified device may also function as the reflector 30.

[0052] The reflector 30 may contain conductive materials such as metals, alloys, metal oxides, and carbon materials. The reflector 30 may contain at least one material selected from the group consisting of aluminum, copper, iron, aluminum alloys, copper alloys, and iron alloys, or it may contain transparent conductive materials such as indium tin oxide.

[0053] The relative permittivity of the dielectric layer 20 is not limited to a specific value, as long as it can absorb the desired electromagnetic waves from the electromagnetic wave absorber 1a. For example, the dielectric layer 20 may have a relative permittivity of 2.0 to 20.0. In this case, the thickness of the dielectric layer 20 can be easily adjusted, and the electromagnetic wave absorption performance of the electromagnetic wave absorber 1a can be easily adjusted. For example, the relative permittivity of the dielectric layer 20 may be the relative permittivity at 10 GHz measured using the cavity resonance method.

[0054] The dielectric layer 20 is formed, for example, from a specified polymer. The dielectric layer 20 comprises, for example, at least one polymer selected from the group consisting of ethylene vinyl acetate copolymer, vinyl chloride resin, polyurethane resin, acrylic resin, acrylic polyurethane resin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, and cyclic olefin polymers. In this case, the thickness of the dielectric layer 20 can be easily adjusted, and the manufacturing cost of the electromagnetic wave absorber 1a can be kept low. The dielectric layer 20 can be manufactured, for example, by hot pressing a specified resin composition.

[0055] The dielectric layer 20 can be formed as a single layer or as multiple layers made of the same or different materials. When the dielectric layer 20 has n layers (n being an integer greater than or equal to 2), the relative permittivity of the dielectric layer 20 is determined, for example, by measuring the relative permittivity ε of each layer. i (i is an integer from 1 to n). Next, the relative permittivity ε of each layer was measured. i Multiply by the thickness t of the layer i ε is calculated as a proportion of the overall thickness T of the dielectric layer 20. i ×(t i / T). ε relative to all layers i ×(t i By adding the dielectric constants of the dielectric layer 20 ( / T), the relative permittivity of the dielectric layer 20 can be determined.

[0056] like Figure 1As shown, the dielectric layer 20 includes, for example, a first layer 21 and a second layer 35. The first layer 21 is disposed between the resistive layer 10 and the second layer 35. The first layer 21 includes, for example, at least one polymer selected from the group consisting of ethylene vinyl acetate copolymer, vinyl chloride resin, polyurethane resin, acrylic resin, acrylic polyurethane resin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, and cyclic olefin polymers.

[0057] In the electromagnetic wave absorber 1a, the second layer 35, for example, supports a layered reflector 30. In this case, the layered reflector 30 is, for example, a metal foil or an alloy foil. The layered reflector 30 can also be fabricated on the second layer 35 by methods such as sputtering, ion plating, or coating (e.g., rod coating). The second layer 35 is disposed in the electromagnetic wave absorber 1a closer to the resistive layer 10 than the layered reflector 30, forming part of the dielectric layer 20. The second layer 35 contains, for example, an organic polymer. The organic polymer is not limited to a specific polymer, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic resin (PMMA), polycarbonate (PC), polyimide (PI), or cyclic olefin polymer (COP). Among these, PET is ideally the organic polymer contained in the second layer 35 from the viewpoint of a good balance of heat resistance, dimensional stability, and manufacturing cost.

[0058] The second layer 35 has a thickness of, for example, 5 to 150 μm, ideally 5 to 100 μm. This results in low bending stiffness of the second layer 35 and, in the case of forming a layered reflector 30, suppresses the occurrence or deformation of wrinkles in the second layer 35. It should be noted that the second layer 35 can also be omitted.

[0059] like Figure 1 As shown, the electromagnetic wave absorber 1a also includes, for example, a support layer 15. The support layer 15 contains an organic polymer and supports the resistive layer 10. In this case, the resistive layer 10 is protected by the support layer 15, and the electromagnetic wave absorber 1a easily exhibits high durability. Furthermore, the thickness of the resistive layer 10 can be easily and uniformly adjusted by the support layer 15.

[0060] The organic polymer contained in the support layer 15 is not limited to a specific polymer, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic resin (PMMA), polycarbonate (PC), polyimide (PI), or cyclic olefin polymer (COP). However, from the viewpoint of a good balance between heat resistance, dimensional stability, and manufacturing cost, PET is ideally the organic polymer contained in the second layer 35.

[0061] Electron wave absorber 1a can also be like Figure 2 and 3 Modifications are made as shown for radio wave absorbers 1b and 1c. Except where specifically stated, radio wave absorbers 1b and 1c are constructed in the same manner as radio wave absorber 1a. The constituent elements of radio wave absorbers 1b and 1c, corresponding to those of radio wave absorber 1a, are marked with the same reference numerals, and detailed descriptions are omitted. The description of radio wave absorber 1a applies to radio wave absorbers 1b and 1c, provided it does not contradict the technical specifications.

[0062] In the electromagnetic wave absorbers 1b and 1c, the support layer 15 is disposed closer to the reflector 30 than the resistive layer 10 in the thickness direction. In this case, the support layer 15 can form part of the dielectric layer 20.

[0063] Furthermore, in the electromagnetic wave absorber 1c, the layered reflector 30 is positioned closer to the resistive layer 10 than the second layer 35 in the thickness direction of the resistive layer 10. In this case, the layered reflector 30 is easily protected by the second layer 35, and the electromagnetic wave absorber 1c tends to have high durability.

[0064] In the electromagnetic wave absorbers 1a to 1c, the first layer 21 can also be composed of multiple layers. Specifically, as shown in... Figure 1 and Figure 3 As shown, when the first layer 21 is in contact with at least one of the resistive layer 10 and the layered reflector 30, the first layer 21 may be composed of multiple layers.

[0065] The first layer 21 may or may not be adhesive. If the first layer 21 is adhesive, the adhesive layer may be disposed in contact with at least one of the two main surfaces of the first layer 21, or it may not be disposed in contact with the two main surfaces. If the first layer 21 is not adhesive, it is ideal to be disposed in contact with both main surfaces of the first layer 21. It should be noted that, as with electromagnetic absorbers 1b and 1c, when the dielectric layer 20 includes a support layer 15, even if the support layer 15 is not adhesive, the adhesive layer may not be disposed in contact with the two main surfaces of the support layer 15. In this case, the adhesive layer may be disposed in contact with one main surface of the support layer 15. As with electromagnetic absorbers 1a and 1b, when the dielectric layer 20 includes a second layer 35, even if the second layer 35 is not adhesive, the adhesive layer may not be disposed in contact with the two main surfaces of the second layer 35. The adhesive layer may be disposed in contact with at least one main surface of the second layer 35.

[0066] Electron wave absorber 1a can also be like Figure 4 and Figure 5Modifications are made as shown for radio wave absorbers 1d and 1e. Except where specifically stated, radio wave absorbers 1d and 1e are constructed in the same manner as radio wave absorber 1a. The constituent elements of radio wave absorbers 1d and 1e corresponding to those of radio wave absorber 1a are marked with the same reference numerals, and detailed descriptions are omitted. The description of radio wave absorber 1a applies to radio wave absorbers 1d and 1e, provided it does not contradict the technical specifications.

[0067] like Figure 4 As shown, the electromagnetic wave absorber 1d also includes an adhesive layer 40a. In the electromagnetic wave absorber 1d, the reflector 30 is disposed between the dielectric layer 20 and the adhesive layer 40a in the thickness direction of the resistive layer 10. The adhesive layer 40a can be in contact with the reflector 30, or it can be separated from the reflector 30 in the thickness direction of the adhesive layer 40a. For example, in the thickness direction of the adhesive layer 40a, other layers such as a support layer for supporting the reflector 30 can also be disposed between the adhesive layer 40a and the reflector 30. In this case, the components contained in the adhesive layer 40a are less likely to come into contact with the reflector 30, and the reflector 30 is less likely to deteriorate.

[0068] For example, by bringing the adhesive layer 40a into contact with a specified article and pressing the electromagnetic wave absorber 1d, the electromagnetic wave absorber 1d can be adhered to the article. Thus, an article with an electromagnetic wave absorber can be obtained.

[0069] The adhesive layer 40a may include, for example, a rubber-based adhesive, an acrylic adhesive, a silicone-based adhesive, or a polyurethane-based adhesive. The electromagnetic wave absorber 1d may also include a release film (not shown). In this case, the release film covers the adhesive layer 40a. The release film is typically a thin film that maintains the adhesive strength of the adhesive layer 40a when covering it and can be easily peeled off from the adhesive layer 40a. The release film is, for example, a film made of polyester resin such as PET. By peeling off the release film, the adhesive layer 40a is exposed, allowing the electromagnetic wave absorber 1d to be attached to an article.

[0070] In an electromagnetic wave absorber, the dielectric layer 20 can also have adhesive properties to the reflector 30. For example, as... Figure 5 As shown, in the electromagnetic wave absorber 1e, the dielectric layer 20 has multiple layers including an adhesive layer 40b. The adhesive layer 40b is in contact with the reflector 30. The adhesive layer 40b includes, for example, a rubber-based adhesive, an acrylic adhesive, a silicone adhesive, or a polyurethane adhesive. The adhesive layer 40b is disposed, for example, between the first layer 21 and the reflector 30 in the thickness direction of the resistive layer 10.

[0071] like Figure 5As shown, the dielectric layer 20 further includes an adhesive layer 40c. The adhesive layer 40c is in contact with the resistive layer 10, for example. The adhesive layer 40c comprises, for example, a rubber-based adhesive, an acrylic adhesive, a silicone-based adhesive, or a polyurethane-based adhesive. The adhesive layer 40c is disposed, for example, between the first layer 21 and the resistive layer 10.

[0072] like Figure 6 As shown, a laminate 1f for electromagnetic wave absorbers can also be provided. Except as otherwise specified, the laminate 1f for electromagnetic wave absorbers is constructed in the same manner as the electromagnetic wave absorber 1a. The constituent elements of the electromagnetic wave absorber 1f, which correspond to those of the electromagnetic wave absorber 1a, are marked with the same reference numerals, and detailed descriptions are omitted.

[0073] like Figure 6 As shown, the electromagnetic wave absorber laminate 1f includes a resistive layer 10 and a dielectric layer 20. The resistive layer 10 overlaps with the dielectric layer 20. For example, an electromagnetic wave absorber can be manufactured by mounting the electromagnetic wave absorber laminate 1f onto the component in such a way that the dielectric layer 20 is located between the surface of the component reflecting electromagnetic waves and the resistive layer 10.

[0074] Example

[0075] The present invention will be described in more detail below through examples. However, the present invention is not limited to the following examples. First, the evaluation methods related to the examples and comparative examples will be described.

[0076] [Observation using an electron microscope]

[0077] Using a Hitachi High-Tech FB2000 focused ion beam processing observation apparatus, cross-sectional observation samples of the resistive layers in the thin films with resistive layers of each example and comparative example were prepared. Then, the cross-sectional observation samples were observed using a JEM-2800 field emission transmission electron microscope (FET) manufactured by Nippon Electron. FE-TEM images of the cross-sections of the resistive layers in the thin films with resistive layers of Examples 1, 3, and 5 are shown below. Figure 7 , 8 9. Furthermore, using a Hitachi High-Tech S-4800 scanning electron microscope, cross-sections of the thin films with resistive layers in each embodiment and each comparative example were observed, and the thickness of the resistive layer in each embodiment and each comparative example was measured. The results are shown in Table 1.

[0078] [Resistivity and Thin Film Resistance]

[0079] Using the NC-80LINE non-contact resistance measuring apparatus manufactured by Napson Corporation, the thin-film resistance of the resistive layer in the thin films with resistive layers in each embodiment and comparative example was measured by the eddy current method according to Japanese Industrial Standard JIS Z 2316. The resistivity of the resistive layer was determined by calculating the product of the thickness of the resistive layer measured as described above and the thin-film resistance of the resistive layer measured as described above.

[0080] [Radio wave absorption performance]

[0081] Referring to JIS R 1679:2007, using a vector network analyzer manufactured by ANRITSU CORPORATION, radio waves with frequencies of 60–90 GHz were incident at an incident angle of 0° onto samples of each embodiment and comparative example fixed on a sample holder, and the reflection attenuation |S| at each frequency was determined according to the following formula (1). In formula (1), P0 is the power of the transmitted radio wave when the radio wave is incident on the test object at a specified incident angle, P... i This represents the power of the received radio wave under this condition. It should be noted that, instead of the samples in the embodiments and comparative examples, an aluminum plate was fixed to a sample holder. The reflection attenuation |S| when the radio wave is incident on the plate at an incident angle of 0° was considered to be 0 dB, and the reflection attenuation |S| for each sample was determined. The plate has a surface area of ​​30 cm² and a thickness of 5 mm. The maximum value of the reflection attenuation |S| was determined for each sample. The results are shown in Table 1.

[0082] S[dB]=10×log|P i / P0| Equation (1)

[0083] [Tension Test]

[0084] Strips with a length of 50 mm and a width of 10 mm were cut from the resistive films of each embodiment and comparative example to prepare test pieces for tensile testing. Next, the test pieces were mounted on the chucks of a tensile testing machine. Then, tensile stress was applied along the length of the test piece at a tensile speed of 50 μm / s until the strain of the test piece reached 10%. The initial distance between the chucks was adjusted to 20 mm. Before and after the tensile test, probes of a digital multimeter were mounted on the test pieces to measure the resistance R0 of the resistive layer before the tensile test and the resistance R after the tensile test. t The 100×{(R) calculated based on the measurement results t The values ​​of / R0)-1} are shown in Table 1.

[0085] [High Temperature and High Humidity Environment Test]

[0086] Test pieces for high-temperature and high-humidity environment testing were prepared using samples from the examples and comparative examples. These test pieces were placed at 85°C and 85% relative humidity for 24 hours. Before and after the high-temperature and high-humidity environment test, the reflective film was peeled off from the test piece inside a glove box at -40°C, and the thin-film resistance R of the resistive layer before the high-temperature and high-humidity environment test was measured. i The thin-film resistance R of the resistive layer after high temperature and high humidity environment test H Thin-film resistance R i and thin film resistance R H The measurements were performed using a non-contact resistance measuring device, NC-80MA, manufactured by Napson Corporation. Based on the measurement results, 100 × {(R} was calculated. H / R i The values ​​of )-1} are shown in Table 1.

[0087] <Example 1>

[0088] A coating solution was prepared by mixing a multilayer carbon nanotube (CNT) dispersion MWNT INK manufactured by Meijo Nano Carbon Co., Ltd., and a polyurethane-based binder HUX-401 manufactured by ADEKA Co., Ltd., and stirring at 500 rpm for 5 minutes. The multilayer carbon nanotubes contained in the multilayer CNT dispersion MWNT INK had a diameter of approximately 10 nm. The amount of multilayer CNT dispersion MWNT INK added was adjusted so that the content of multilayer CNTs in the solid component of the coating solution was 5% by mass. It should be noted that this content can be regarded as the content of multilayer CNTs in the resistive layer. The coating solution was coated on one main side of a PET film to form a coating film. Then, the coating film was dried using a warm air at 90°C for 3 minutes, and then the environment of the coating film was maintained at 120°C for 15 minutes to dry the coating film, forming the resistive layer of Example 1. The film with a resistive layer of Example 1 was thus prepared. The coating film formation conditions were adjusted to achieve a thickness of 31 μm for the resistive layer. Next, an acrylic resin having a relative permittivity of 2.6 was molded to a thickness of 560 μm to obtain acrylic resin layer A. Additionally, a reflective film with an aluminum layer disposed between a pair of PET layers was obtained. In the reflective film, one PET layer has a thickness of 25 μm, and the other PET layer has a thickness of 9 μm. Furthermore, the aluminum layer of the reflective film has a thickness of 7 μm. The resistive film of Example 1 was overlapped onto acrylic resin layer A such that the resistive layer of the resistive film of Example 1 was in contact with one main surface of acrylic resin layer A. Then, the reflective film was overlapped onto acrylic resin layer A such that the 25 μm thick PET layer of the reflective film was in contact with the other main surface of acrylic resin layer A. Thus, the sample of Example 1 was obtained.

[0089] <Example 2>

[0090] Except as described below, the resistive film of Example 2 was prepared in the same manner as in Example 1. In the preparation of the coating liquid, the amount of MWNT INK added to the multilayer CNT dispersion was adjusted so that the content of multilayer CNTs in the solid component of the coating liquid was 9% by mass. Furthermore, the coating film formation conditions were adjusted to achieve a resistive layer thickness of 12 μm. The sample of Example 2 was prepared in the same manner as in Example 1, except that the resistive film of Example 2 was used instead of the resistive film of Example 1.

[0091] <Example 3>

[0092] Except for the points described below, the resistive film of Example 3 was prepared in the same manner as in Example 1. In the preparation of the coating liquid, the amount of MWNT INK added to the multilayer CNT dispersion was adjusted so that the content of multilayer CNTs in the solid component of the coating liquid was 13% by mass. Furthermore, the coating film formation conditions were adjusted to achieve a resistive layer thickness of 6.5 μm. The sample of Example 3 was prepared in the same manner as in Example 1, except that the resistive film of Example 3 was used instead of the resistive film of Example 1.

[0093] <Example 4>

[0094] Except for the points described below, the resistive film of Example 4 was prepared in the same manner as in Example 1. In the preparation of the coating liquid, the amount of MWNT INK added to the multilayer CNT dispersion was adjusted so that the content of multilayer CNTs in the solid component of the coating liquid was 49% by mass. Furthermore, the coating film formation conditions were adjusted to achieve a resistive layer thickness of 2 μm. The sample of Example 4 was prepared in the same manner as in Example 1, except that the resistive film of Example 4 was used instead of the resistive film of Example 1.

[0095] <Example 5>

[0096] Except for the points described below, the resistive film of Example 5 was prepared in the same manner as in Example 1. In the preparation of the coating liquid, the amount of MWNT INK added to the multilayer CNT dispersion was adjusted so that the content of multilayer CNTs in the solid component of the coating liquid was 65% by mass. Furthermore, the coating film formation conditions were adjusted to achieve a resistive layer thickness of 1 μm. The sample of Example 5 was prepared in the same manner as in Example 1, except that the resistive film of Example 5 was used instead of the resistive film of Example 1.

[0097] <Comparative Example 1>

[0098] Except as described below, the resistive film of Comparative Example 1 was prepared in the same manner as in Example 1. In the preparation of the coating liquid, the amount of MWNT INK added to the multilayer CNT dispersion was adjusted so that the content of multilayer CNTs in the solid component of the coating liquid was 1% by mass. Furthermore, the coating film formation conditions were adjusted to achieve a resistive layer thickness of 61 μm. The sample of Comparative Example 1 was prepared in the same manner as in Example 1, except that the resistive film of Comparative Example 1 was used instead of the resistive film of Example 1.

[0099] <Comparative Example 2>

[0100] Except as described below, the resistive film of Comparative Example 2 was prepared in the same manner as in Example 1. In the preparation of the coating liquid, instead of the multilayer CNT dispersion MWNT INK, the single-layer CNT dispersion TB002M manufactured by KJ Special Paper Co., Ltd. was used, and the coating film formation conditions were adjusted to ensure that the thickness of the resistive layer was less than 0.2 μm. The sample of Comparative Example 2 was prepared in the same manner as in Example 1, except that the resistive film of Comparative Example 2 was used instead of the resistive film of Example 1.

[0101] As shown in Table 1, the samples of each embodiment and each comparative example have a maximum value of the specified reflection attenuation |S| and have specified electromagnetic wave absorption performance. In the resistive layer of each embodiment, 100×{(R t The value of / R0)-1} and 100×{(R H / R i The value of 100×{(R)-1} is small. Therefore, it can be understood that the resistive layer of each embodiment has high tensile strength and high durability in high temperature and high humidity environments. On the other hand, in Comparative Example 1, 100×{(R)-1} is small. t The value of 100 × {(R0)-1} is high, making it difficult to conclude that the resistive layer of Comparative Example 1 has high tensile strength. Furthermore, in Comparative Example 2, 100 × {(R0)-1} H / R i The value of )-1} is high, so it is difficult to say that the resistive layer of Comparative Example 2 has high durability in high temperature and high humidity environments.

[0102] [Table 1]

[0103]

Claims

1. An electromagnetic wave absorber comprising a resistive layer, a reflector, and a dielectric layer. The resistive layer comprises multiple layers of carbon nanotubes and has a resistivity of less than 0.57 Ω·cm; The reflector reflects electromagnetic waves; The dielectric layer is disposed between the resistive layer and the reflector in the thickness direction of the resistive layer. The resistance of the resistive layer is 200Ω / □~600Ω / □.

2. The electromagnetic wave absorber according to claim 1, wherein, The multilayer carbon nanotubes have a diameter of less than 70 nm.

3. The electromagnetic wave absorber according to claim 1, wherein, The resistive layer contains an adhesive that bonds the multilayer carbon nanotubes together. The adhesive comprises at least one selected from the group consisting of polyurethane, polyacrylate, epoxy resin and polyester.

4. The electromagnetic wave absorber according to claim 1, wherein, The resistive layer does not contain aliphatic cellulose esters.

5. The electromagnetic wave absorber according to claim 1, wherein, The resistance R of the resistive layer after undergoing a tensile test in which a tensile stress of 10% is applied to the resistive layer in a direction perpendicular to the thickness direction of the resistive layer is obtained. t The resistance R0 of the resistance layer before the tensile test satisfies 100 × {(R... t The relationship is: / R0)-1}≤15.

6. The electromagnetic wave absorber according to claim 1, further comprising a support layer containing an organic polymer and supporting the resistive layer.

7. The electromagnetic wave absorber according to claim 1, wherein, The content of the multilayer carbon nanotubes in the resistive layer is 3% or more by mass.

8. A laminate for an electromagnetic wave absorber, comprising a resistive layer and a dielectric layer, The resistive layer comprises multiple layers of carbon nanotubes and has a resistivity of less than 0.57 Ω·cm; The sheet resistance of the resistive layer is 200Ω / □~600Ω / □. The resistive layer overlaps with the dielectric layer.

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