Electromagnetic wave absorber

Abstract

To provide a technique advantageous for reuse of an electromagnetic wave absorber.SOLUTION: In an electromagnetic wave absorber in which an electromagnetic wave absorbing layer and an adhesive layer are stacked, the adhesive layer includes a first adhesive layer and a second adhesive layer disposed between the first adhesive layer and the electromagnetic wave absorbing layer and in contact with the first adhesive layer and the electromagnetic wave absorbing layer, and the first adhesive layer has a lower adhesive strength than the second adhesive layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Electromagnetic wave absorbers that absorb electromagnetic waves of a predetermined frequency are known. Patent Document 1 discloses an electromagnetic wave absorber that has an adhesive layer for attaching to a predetermined location. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-056768 Summary of the Invention [Problem to be solved by the invention]

[0004] There may be cases where an electromagnetic wave absorber is used temporarily in an aiming test, etc. When an attempt is made to peel off the electromagnetic wave absorber after use, some of the adhesive may remain on the adherend, or the electromagnetic wave absorber itself may become wrinkled, folded, or curled, making it difficult to reuse the electromagnetic wave absorber.

[0005] An object of the present invention is to provide a technique that is advantageous for reusing electromagnetic wave absorbers. [Means for solving the problem]

[0006] In view of the above problems, an electromagnetic wave absorber according to an embodiment of the present invention is an electromagnetic wave absorber in which an electromagnetic wave absorbing layer and an adhesive layer are laminated together, the adhesive layer including a first adhesive layer and a second adhesive layer disposed between the first adhesive layer and the electromagnetic wave absorbing layer and in contact with the first adhesive layer and the electromagnetic wave absorbing layer, and the first adhesive layer has a weaker adhesive strength than the second adhesive layer. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technique that is advantageous for reusing electromagnetic wave absorbers. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a configuration example of an electromagnetic wave absorber according to an embodiment of the present invention. [Figure 2] 2A and 2B are diagrams showing an example and a comparative example of the electromagnetic wave absorber of FIG. 1; [Figure 3] 2 is a diagram showing an example of the configuration of an electromagnetic wave absorbing layer of the electromagnetic wave absorber of FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0010] An electromagnetic wave absorber according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 3. Hereinafter, in this specification, a "conductor pattern" refers to an object that is an aggregate of geometrically shaped units and that selectively transmits electromagnetic waves of a certain frequency. It can also be said that a "conductor pattern" has the same function as a so-called antenna. In this specification, "electromagnetic waves in the millimeter wave region" refers to electromagnetic waves with a wavelength of 1 mm to 10 mm. "Electromagnetic waves in the millimeter wave region" can also be said to be electromagnetic waves with a frequency of 30 GHz to 300 GHz. In this specification, the symbol "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits.

[0011] 1(a) and 1(b) are cross-sectional views showing an example of the configuration of an electromagnetic wave absorber 100 of this embodiment. The electromagnetic wave absorber 100 includes an electromagnetic wave absorbing layer 110 and an adhesive layer 150 laminated together. The adhesive layer 150 of the electromagnetic wave absorber 100 of this embodiment includes an adhesive layer 152 and an adhesive layer 151 disposed between the adhesive layer 152 and the electromagnetic wave absorbing layer 110 and in contact with the adhesive layer 152 and the electromagnetic wave absorbing layer 110. The adhesive layer 152 has a weaker adhesive strength than the adhesive layer 151. As shown in FIG. 1(a), the electromagnetic wave absorbing layer 110 may include a resistive layer 111, a dielectric layer 112 disposed between the resistive layer 111 and the adhesive layer 151, and a reflective layer 113 disposed between the dielectric layer 112 and the adhesive layer 151. In this case, the dielectric layer 112 may be in contact with the resistive layer 111 and the reflective layer 113, and the reflective layer 113 may be in contact with the dielectric layer 112 and the adhesive layer 151. Alternatively, as shown in FIG. 1( b ), the electromagnetic wave absorbing layer 110 may include the resistive layer 111 and the dielectric layer 112 disposed between the resistive layer 111 and the adhesive layer 151, and may not include a reflective layer. In this case, the dielectric layer 112 may be in contact with the resistive layer 111 and the adhesive layer 151.

[0012] Here, the adhesive layer 150 of this embodiment will be described. Generally, the adhesive layer provided on an electromagnetic wave absorber is often intended to be attached only once, and once attached, it is difficult to reattach it after peeling it off. For example, when an electromagnetic wave absorber is temporarily used in an aiming test or the like and an attempt is made to peel the electromagnetic wave absorber after use, some of the adhesive may remain on the adherend, or the electromagnetic wave absorber itself may become wrinkled, folded, or curled.

[0013] For example, consider the case where an electromagnetic wave absorber having a reflective layer 113 and using a single adhesive layer with relatively strong adhesive force is attached to an adherend 201 such as a metal plate, as shown in FIG. 1(a). In this case, the difference in adhesive force between the reflective layer 113, which is generally made of a metal such as aluminum, and the adhesive layer, and the adhesive force between the adhesive layer and the adherend 201 becomes small. Therefore, when the electromagnetic wave absorber is peeled from the adherend 201, there is a possibility that part of the adhesive layer will remain on the adherend 201 or that cohesive failure will occur. Also, consider the case where the electromagnetic wave absorbing layer 110 does not have a reflective layer 113 as shown in FIG. 1(b), and the adherend 201 is used as the reflective layer, and the dielectric layer 112 and adhesive layer have a λ / 4 structure, as described below. In this case, if an adhesive with strong adhesive force is used, cohesive failure is likely to occur when the electromagnetic wave absorber is peeled from the adherend 201, resulting in a change in the thickness of the adhesive layer. A change in the thickness of the adhesive layer changes the relative dielectric constant of the adhesive layer, which changes the electromagnetic wave absorption characteristics when the electromagnetic wave absorber is reattached. Furthermore, if an adhesive material with low adhesive strength is used, lifting or peeling is likely to occur at the interface between the dielectric layer 112 and the adhesive layer, which also changes the electromagnetic wave absorption characteristics when the electromagnetic wave absorber is reattached.

[0014] Therefore, in this embodiment, the adhesive layer 150 of the electromagnetic wave absorber 100 includes an adhesive layer 152 and an adhesive layer 151 that is disposed between the adhesive layer 152 and the electromagnetic wave absorbing layer 110 and has stronger adhesive strength than the adhesive layer 152. As a result, when the electromagnetic wave absorber 100 is adhered to the adherend 201 so that the adhesive layer 152 is in contact with the adherend 201, the adhesive strength at the interface between the adhesive layer 151 and the electromagnetic wave absorbing layer 110 (the dielectric layer 112 or the reflective layer 113) can be stronger than the adhesive strength at the interface between the adhesive layer 152 and the adherend 201. In this case, the adhesive strength at the interface between the adhesive layer 151 and the adhesive layer 152 may be stronger than the adhesive strength at the interface between the adhesive layer 151 and the electromagnetic wave absorbing layer 110 (the dielectric layer 112 or the reflective layer 113). Similarly, the adhesive strength at the interface between the adhesive layer 151 and the adhesive layer 152 may be stronger than the adhesive strength at the interface between the adhesive layer 152 and the adherend 201. That is, the relationship may be such that the adhesive strength at the interface between the adhesive layer 151 and the adhesive layer 152 > the adhesive strength at the interface between the adhesive layer 151 and the electromagnetic wave absorbing layer 110 (the dielectric layer 112 or the reflective layer 113) > the adhesive strength at the interface between the adhesive layer 152 and the adherend 201. However, without being limited thereto, the adhesive strength at the interface between the adhesive layer 151 and the electromagnetic wave absorbing layer 110 (the dielectric layer 112 or the reflective layer 113) may be stronger than the adhesive strength at the interface between the adhesive layer 151 and the adhesive layer 152. As a result, when the electromagnetic wave absorber 100 attached to the adherend 201 is peeled off from the adherend 201, peeling occurs between the adhesive layer 152 and the adherend 201, but peeling is unlikely to occur between the adhesive layer 151 and the electromagnetic wave absorbing layer 110 (the dielectric layer 112 or the reflective layer 113) and between the adhesive layer 151 and the adhesive layer 152. That is, cohesive failure of the adhesive layer 150 (adhesive layers 151, 152) is unlikely to occur, and an increase in the roughness of the adhesive layer surface when peeled off can be suppressed, enabling re-attachment of the electromagnetic wave absorber 100. Furthermore, even if the dielectric layer 112 and the adhesive layer 150 have a λ / 4 structure, for example, the film thickness of the adhesive layer 150 is unlikely to change, and therefore changes in the electromagnetic wave absorption characteristics of the electromagnetic wave absorber 100 are suppressed.

[0015] Here, examples will be described. First, the adhesive used in the adhesive layers 151 and 152 will be described.

[0016] First, a (meth)acrylic acid ester polymer (A) was prepared as the adhesive layer 152. 94 parts by mass of n-butyl acrylate, 5 parts by mass of 2-phenoxyethyl acrylate, and 1 part by mass of 4-hydroxybutyl acrylate were copolymerized by solution polymerization to prepare the (meth)acrylic acid ester polymer (A). The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described below, and the weight average molecular weight (Mw) was found to be 800,000.

[0017] 100 parts by mass (solid content equivalent, same below) of the (meth)acrylic acid ester polymer (A) obtained in the above-mentioned process and 0.25 parts by mass of trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") as a crosslinking agent (B) were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of an adhesive composition.

[0018] The obtained adhesive composition coating solution was applied to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET752150"), one side of which had been release-treated, using a knife coater. The coating layer was then heat-treated at 90°C for 1 minute to obtain an adhesive layer 152.

[0019] Furthermore, for the adhesive layer 151, 50 parts by mass of an acrylic acid ester copolymer (95% by mass of butyl acrylate units, 2% by mass of acrylic acid units, and 3% by mass of methyl methacrylate units) having a weight average molecular weight of 800,000 was blended with 50 parts by mass of a tackifier (manufactured by Arakawa Chemical Industries, Ltd., product name "Pine Crystal KE-359", rosin ester type, softening point 94°C to 104°C, acid value 10mgKOH / g to 20mgKOH / g) and 1 part by mass of an isocyanate crosslinking agent (manufactured by Toyo Ink Mfg. Co., Ltd., product name "BHS8515"), and the mixture was diluted and mixed with toluene to obtain an adhesive composition having a solids concentration of 20% by mass.

[0020] The obtained pressure-sensitive adhesive composition was applied to a polyethylene terephthalate film having one side treated for release. The release sheet (manufactured by Lintec Corporation, product name "SP-PET381031") After being applied with a knife coater, the adhesive layer 151 was obtained by heat treatment at 100° C. for 4 minutes.

[0021] Next, the surfaces of the adhesive layer 151 and the adhesive layer 152 that were not covered with the release sheet were attached to each other, and then cured for 7 days in an environment of 23°C and 50% RH. As a result, an adhesive layer 150 was formed in which an adhesive layer 151 having a thickness of 20 μm and an adhesive layer 152 having a thickness of 20 μm were laminated. The formed adhesive layer 150 was adhered to the electromagnetic wave absorbing layer 110, and an electromagnetic wave absorber 100 having the configuration shown in FIGS. 1(a) and 1(b) was obtained.

[0022] As shown in FIG. 1(b), an electromagnetic wave absorber 100 in which the dielectric layer 112 and adhesive layer 150 of the electromagnetic wave absorbing layer 110 are in contact with each other was attached to an adherend 201, and adhesive strength was measured. The electromagnetic wave absorbing layer 110 was prepared by preparing a resistive layer 111 having a pattern layer of a 100-nm-thick copper pattern on a 50-μm-thick polyethylene terephthalate (PET) film. An adhesive layer similar to the adhesive layer 152 was laminated on the pattern layer side of the resistive layer 111, and the surface of the adhesive layer opposite the pattern layer was attached to a 2-mm-thick urethane foam sheet (manufactured by Inoac Corporation, product name "PORON HH-48") as the dielectric layer 112, thereby producing the electromagnetic wave absorbing layer 110. A metal plate (SUS404) was used as the adherend 201. The adhesive strength at the interface between the adhesive layer 151 of the adhesive layer 150 and the dielectric layer 112 of the electromagnetic wave absorbing layer 110 was 12.3 N / 25 mm. The adhesive strength at the interface between the adhesive layer 152 of the adhesive layer 150 and the adherend 201 was 9.5 N / 25 mm. The adhesive strength at the interface between the adhesive layer 151 and the adhesive layer 152 was 14.8 N / 25 mm. That is, as described above, the relationship was adhesive strength between the adhesive layer 151 and the adhesive layer 152 (14.8 N / 25 mm) > adhesive strength between the adhesive layer 151 and the dielectric layer 112 of the electromagnetic wave absorbing layer 110 (12.3 N / 25 mm) > adhesive strength between the adhesive layer 152 and the adherend 201 (9.5 N / 25 mm).

[0023] Here, the adhesive strength at the interface between the adhesive layer 151 and the dielectric layer 112 was measured in accordance with JIS Z0237:2022, except that a 100 μm thick PET film was attached to the surface of the adhesive layer 150 facing the adhesive layer 152, the film was cut to a width of 25 mm and a length of 300 mm, a peeling trigger was created in advance at the interface between the adhesive layer 151 and the electromagnetic wave absorbing layer 110, the electromagnetic wave absorbing layer 110 was fixed, and the peeling speed was 0.3 m / min and the peeling angle was 180°. Furthermore, the adhesive strength at the interface between the adhesive layer 152 and the adherend 201 was measured in accordance with JIS Z0237:2022, except that the electromagnetic wave absorber 100 was cut to a width of 25 mm and a length of 300 mm, the exposed surface of the adhesive layer 152 was attached to the adherend 201, the adherend 201 was fixed, and the peeling speed was 0.3 m / min and the peeling angle was 180°. Furthermore, the adhesive strength of the interface between the adhesive layer 151 and the adhesive layer 152 was measured using two samples: Sample A, which was 25 mm wide and 300 mm long and in which only the adhesive layer 151 was laminated on the electromagnetic wave absorbing layer 110; and Sample B, which was 25 mm wide and 300 mm long and in which only the adhesive layer 152 was laminated on a 100 μm thick PET film. The adhesive layers of Sample A and Sample B were attached to each other so that their ends protruded 12 mm from each other. The adhesive strength was then measured in accordance with JIS Z0237:2022, except that the electromagnetic wave absorbing layer 110 side was fixed and the adhesive layer 152 side was peeled off at a peel speed of 0.3 m / min and a peel angle of 180°.

[0024] Here, the adhesive strength at the interface between the adhesive layer 152 and the adherend 201 may be 2 N / 25 mm or more, 4 N / 25 mm or more, or even 6 N / 25 mm or more. The adhesive strength at the interface between the adhesive layer 152 and the adherend 201 may be 20 N / 25 mm or less, 16 N / 25 mm or less, or 11 N / 25 mm or less. If the adhesive strength between the adhesive layer 152 and the adherend 201 is weak, for example, if it is less than 2 N / 25 mm, the electromagnetic wave absorber 100 may peel off or become displaced from the adherend 201. On the other hand, if the adhesive strength between the adhesive layer 152 and the adherend 201 is strong, for example, if it is greater than 20 N / 25 mm, cohesive failure of the adhesive layer 152 may occur when the electromagnetic wave absorber 100 is peeled off from the adherend 201.

[0025] FIG. 2 shows the results of attachment of an example and a comparative example of this embodiment to an adherend 201. Example 1 is an electromagnetic wave absorber 100 having the configuration shown in FIG. 1(b). The row of electromagnetic wave absorbing layers 110 in FIG. 2 indicates the members of the electromagnetic wave absorbing layer 110 to which the adhesive layer 150 (adhesive layer 151 in Example 1) is attached, and in Example 1, this is the dielectric layer 112. By attaching the adhesive layer 152, which has a weaker adhesive strength than the adhesive layer 151, to the adherend 201, when the electromagnetic wave absorber 100 was peeled off from the adherend 201, cohesive failure of the adhesive layer 150 and residue of adhesive on the adherend 201 did not occur. Therefore, re-attachment was possible.

[0026] Furthermore, changes in the electromagnetic wave absorption properties of the electromagnetic wave absorber 100 were examined before and after re-attachment. Specifically, the electromagnetic wave absorber 100 was attached to a metal plate (SUS404) serving as the adherend 201, and electromagnetic wave absorption measurement A was performed. Thereafter, the electromagnetic wave absorber 100 was peeled off from the adherend 201, and the electromagnetic wave absorber was attached again to the metal plate, and electromagnetic wave absorption measurement B was performed. A case in which the decrease in the electromagnetic wave absorption rate in measurement B compared to the electromagnetic wave absorption rate in measurement A was marked "Good", and a case in which the absorption rate decreased by 1% or more was marked "NG". The electromagnetic wave absorption rate was measured by the free space method using a vector network analyzer (manufactured by Keysight, product name "N5222B") to obtain the reflection characteristics (S11) of radio waves at 79 GHz, and the electromagnetic wave absorption rate was calculated according to the following formula (1). Reflectance=10 (S11 / 10) ×100(%) (1)

[0027] As described above, the electromagnetic wave absorber 100 of this example does not suffer from cohesive failure of the adhesive layer 150 or leave any adhesive residue on the adherend 201. Therefore, the change (decrease) in the electromagnetic wave absorption rate was less than 1%.

[0028] Example 2 is an electromagnetic wave absorber 100 having the configuration shown in FIG. 1(a). An adhesive layer 150 (adhesive layer 151) is adhered to a reflective layer 113. In this example, aluminum was used as the reflective layer 113. In Example 2, an adhesive layer 152 having a weaker adhesive strength than the adhesive layer 151 is adhered to an adherend 201. This prevents cohesive failure of the adhesive layer 150 and lifting or peeling at the interface between the adhesive layer 151 and the reflective layer 113 when the electromagnetic wave absorber 100 is peeled from the adherend 201. Therefore, re-attachment was possible. Furthermore, the change (decrease) in the electromagnetic wave absorption rate was less than 1%. The adhesive strength at the interface between the adhesive layer 151 and the reflective layer 113 (electromagnetic wave absorbing layer 110) in this example was greater than the adhesive strength at the interface between the adhesive layer 151 and the dielectric layer 112 (electromagnetic wave absorbing layer 110) in Example 1.

[0029] As comparative examples, electromagnetic wave absorbers were prepared that only included the adhesive layer 151 or the adhesive layer 152. The thickness of the adhesive layer 151 and the adhesive layer 152 was set to 20 μm each.

[0030] Comparative Example 1 is an electromagnetic wave absorber that uses only an adhesive layer 152 having a weaker adhesive strength than the adhesive layer 151, and does not include a reflective layer 113 where the dielectric layer 112 of the electromagnetic wave absorbing layer 110 contacts the adhesive layer 152, as shown in FIG. 1(b). In this case, the adhesive strength at the interface between the adhesive layer 152 and the dielectric layer 112 (urethane foam) was 0.6 N / 25 mm. In addition, the adhesive strength at the interface between the adhesive layer 152 and the adherend 201 (SUS404) was 8.0 N / 25 mm. In the electromagnetic wave absorber of Comparative Example 1, the adhesive strength between the adhesive layer 152 and the dielectric layer 112 was weak, and lifting or peeling occurred at the interface between the dielectric layer 112 and the adhesive layer 152 when the electromagnetic wave absorber was peeled off from the adherend 201. Therefore, re-attachment was not possible. Comparative Example 2 is an electromagnetic wave absorber that uses only an adhesive layer 152 having a weaker adhesive strength than the adhesive layer 151, and in which the reflective layer 113 (aluminum) of the electromagnetic wave absorbing layer 110 is in contact with the adhesive layer 152, as shown in Fig. 1(a). In Comparative Example 2 as well, when the electromagnetic wave absorber was peeled off from the adherend 201, lifting or peeling occurred at the interface between the reflective layer 113 and the adhesive layer 151, and re-attachment was not possible.

[0031] Comparative Example 3 is an electromagnetic wave absorber that uses only the adhesive layer 151 having a stronger adhesive strength than the adhesive layer 152, and does not include the reflective layer 113 where the dielectric layer 112 and adhesive layer 151 of the electromagnetic wave absorbing layer 110 are in contact with each other, as shown in FIG. 1(b). The adhesive strength at the interface between the adhesive layer 151 and the dielectric layer 112 (polyethylene terephthalate) was 14.8 N / 25 mm. The adhesive strength at the interface between the adhesive layer 151 and the adherend 201 (SUS404) was 25.5 N / 25 mm. The electromagnetic wave absorber of Comparative Example 3 had such a strong adhesive strength between the adhesive layer 151 and the adherend 201 that, when the electromagnetic wave absorber was peeled off from the adherend 201, a portion of the adhesive constituting the adhesive layer 151 remained on the adherend 201, and cohesive failure of the adhesive was observed. Therefore, re-attachment was not possible. Comparative Example 4 is an electromagnetic wave absorber that uses only adhesive layer 151 having stronger adhesive strength than adhesive layer 152, and in which reflective layer 113 of electromagnetic wave absorbing layer 110 contacts adhesive layer 151, as shown in Fig. 1(a). In Comparative Example 4 as well, cohesive failure of the adhesive occurred when peeling the electromagnetic wave absorber from adherend 201, and re-adhesion was not possible.

[0032] In this way, the adhesive layer 150 for attaching the electromagnetic wave absorbing layer 110 of the electromagnetic wave absorber 100 to the adherend 201 is formed by laminating the adhesive layer 151 and the adhesive layer 152 having a weaker adhesive strength than the adhesive layer 151, and bonding the adhesive layer 151 to the electromagnetic wave absorbing layer 110. As a result, even when the electromagnetic wave absorber 100 is temporarily used in an aiming test or the like and then peeled off from the adherend 201 after the test, cohesive failure and lifting / peeling of the adhesive layer 150 are suppressed. Furthermore, by suppressing the cohesive failure and lifting / peeling of the adhesive layer 150, changes in the electromagnetic wave absorption characteristics are suppressed. As a result, the electromagnetic wave absorber 100 can be reused.

[0033] The above has mainly described the adhesive layer 150 included in the electromagnetic wave absorber 100 of this embodiment. Below, the configuration of the electromagnetic wave absorbing layer 110 will be described. The resistive layer 111 of the electromagnetic wave absorbing layer 110 may be, for example, a single layer, or may include a base material 121 and a conductor pattern 122 formed on the base material 121, as shown in FIG. 3(a). The resistive layer 111 may have a frequency selective surface (FSS). An FSS is a surface that can block or transmit only electromagnetic waves of a specific frequency by forming a continuous structure with a shape smaller than the wavelength using a conductive material or the like.

[0034] The conductor pattern 122 disposed on the resistive layer 111 is formed on the substrate 121 by, for example, thin metal wires, a conductive thin film, or a conductive paste deposit. Examples of metals include copper, aluminum, tungsten, iron, molybdenum, nickel, titanium, silver, gold, and alloys containing two or more of these metals (for example, steels such as stainless steel and carbon steel, brass, phosphor bronze, zirconium copper alloy, beryllium copper, iron nickel, nichrome, nickel titanium, Kanthal, Hastelloy, and rhenium tungsten).

[0035] Examples of the conductive thin film include metal particles, carbon nanoparticles, carbon fibers, etc. Note that the conductive pattern 122 may be formed using a plurality of materials in order to adjust the transmittance characteristics of the resistance layer 111.

[0036] The base material 121 is a flat plate-like member, and may have a thickness of, for example, 5 μm to 500 μm. The material of the base material 121 can be appropriately selected depending on the application of the electromagnetic wave absorber 100.

[0037] For example, the base material 121 can be made of a resin. The resin may be a thermoplastic resin or a thermosetting resin. When the three-dimensional formability of the electromagnetic wave absorber 100 is taken into consideration, the base material 121 may contain a thermoplastic resin. Examples of the thermoplastic resin include polyolefin resin, polyester resin, polyester-polyether resin, polyacrylic resin, polystyrene resin, polyimide resin, polyimideamide resin, polyamide resin, polyurethane resin, polycarbonate resin, polyarylate resin, melamine resin, epoxy resin, urethane resin, silicone resin, and fluororesin.

[0038] The base material 121 may contain optional components within the scope that does not impair the effects of this embodiment. Examples of optional components include inorganic fillers, colorants, curing agents, antioxidants, light stabilizers, flame retardants, conductive agents, antistatic agents, and plasticizers.

[0039] The dielectric layer 112 is disposed between the resistive layer 111 and the adhesive layer 150. The dielectric layer 112 may have a single-layer structure or a laminated structure. The material used for the dielectric layer 112 can be appropriately selected depending on the application, and examples thereof include plastic film, paper, cloth, nonwoven fabric, rubber sheet, and foam sheet. Among these, a foam sheet may be used for the dielectric layer 112 from the viewpoint of easily increasing the thickness while reducing the weight. As the foam sheet, for example, a foam sheet formed by foaming the resin constituting the above-mentioned plastic film and forming it into a sheet can be used. Specific examples of the foam sheet include polyethylene foam, polypropylene foam, and polyurethane foam.

[0040] Alternatively, a plastic film mixed with a metal filler may be used for the dielectric layer 112. The plastic film may be a thermoplastic resin or a thermosetting resin, but may be the same thermoplastic resin as that used for the above-described substrate 121. Alternatively, the metal filler may be a material with a high dielectric constant, such as barium titanate, strontium titanate, calcium titanate, or titanium oxide.

[0041] When taking into consideration the wavelength shortening effect of the dielectric layer 112, the thickness of the dielectric layer 112 is changed appropriately according to the wavelength of the electromagnetic wave to be absorbed and the relative dielectric constant of the dielectric layer 112. When taking into consideration the wavelength shortening effect of the dielectric layer 112, the thickness of the dielectric layer 112 may satisfy the following formula (2). (thickness of dielectric layer 112)=(λ)×(¼) / (ε) 1 / 2 ···(2) Here, λ is the wavelength of the electromagnetic wave incident on the dielectric layer 112, and ε is the relative dielectric constant of the dielectric layer 112. The thickness of the dielectric layer 112 may be adjusted as appropriate to adjust the absorption characteristics of the electromagnetic wave absorber 100. For example, the thickness of the dielectric layer 112 can be changed within a range of 0.1 to 3.0 times the thickness obtained by formula (2).

[0042] When the relationship between the thickness of the dielectric layer 112 and the wavelength λ satisfies the relationship of formula (1), the electromagnetic wave absorber 100 has a so-called λ / 4 structure. In this case, the phases of the electromagnetic waves that pass through the dielectric layer 112 and are reflected by the reflective layer 113 and the electromagnetic waves that are reflected by the resistive layer 111 are inverted, that is, the phase difference is 180 degrees. This makes it possible to reduce the intensity of the electromagnetic waves reflected from the electromagnetic wave absorber 100.

[0043] 1(b), the electromagnetic wave absorbing layer 110 may not have a reflective layer 113. In that case, the thickness of not only the dielectric layer 112 but also the adhesive layer 150 is appropriately changed in consideration of the λ / 4 structure, according to the wavelength of the electromagnetic wave to be absorbed and the relative dielectric constant of the adhesive layer 150. When the electromagnetic wave absorbing layer 110 does not have a reflective layer 113, the adherend 201 may function as a reflective layer.

[0044] 1(a), when the electromagnetic wave absorbing layer 110 includes a reflective layer 113, the reflective layer 113 reflects electromagnetic waves that arrive at the surface of the electromagnetic wave absorber 100 and pass through the dielectric layer 112. A portion of the electromagnetic waves that arrive at the electromagnetic wave absorber 100 is reflected by or absorbed by the resistive layer 111. On the other hand, electromagnetic waves that are not reflected or absorbed by the resistive layer 111 pass through the resistive layer 111. The electromagnetic waves that pass through the resistive layer 111 are reflected by the reflective layer 113 toward the resistive layer 111.

[0045] For example, reflective layer 113 can reflect electromagnetic waves transmitted through resistive layer 111 as long as it has conductivity in the surface direction of either of the two surfaces facing dielectric layer 112 and adhesive layer 150. Specifically, a resin film such as polyethylene terephthalate to which a metal foil such as aluminum foil or copper foil, or a metal plate such as a copper plate is attached can be used as reflective layer 113. Instead of the metal foil or metal plate, a transparent conductive film such as ITO, or a mesh sheet formed of metal wires, may also be used.

[0046] FIG. 3(b) is a perspective view showing a modified example of the electromagnetic wave absorbing layer 110 shown in FIG. 3(a). In the configuration shown in FIG. 3(a), for example, a conductor pattern 122 is formed on a substrate 121, and the substrate 121 on which the conductor pattern 122 is formed is attached to the dielectric layer 112 using an adhesive layer or the like to produce the electromagnetic wave absorbing layer 110. The conductor pattern 122 may be formed on the surface of the substrate 121 that is to be attached to the dielectric layer 112. Alternatively, as in the configuration shown in FIG. 3(b), the conductor pattern 122 of the resistance layer 111 may be formed directly on the dielectric layer 112. A thin protective layer may be disposed on the resistance layer 111 (the conductor pattern 122). For example, the various materials mentioned above as the material for the substrate 121 can be used for the protective layer. In this case, the protective layer can be made thin because it is not necessary to support (handle) the conductor pattern 122 like the substrate 121 during the manufacturing process of the electromagnetic wave absorber 100. For example, the protective layer can be formed by spray coating with a fluororesin or the like.

[0047] In the configuration shown in Fig. 3(a), when the conductor pattern 122 is formed on the surface of the substrate 121 that is to be bonded to the dielectric layer 112, the surface of the resistive layer 111, i.e., the substrate 121, can be a smooth surface. On the other hand, in the configuration shown in Fig. 3(b), the surface of the resistive layer 111 may have irregularities according to the shape of the conductor pattern 122. Furthermore, in the configuration shown in Fig. 3(b), it is not necessary to provide the substrate 121 as the resistive layer 111. Therefore, an electromagnetic wave absorber 100 that is highly flexible and easy to process can be realized.

[0048] As described above, the electromagnetic wave absorber 100 of this embodiment has a structure in which the adhesive layer 150 is formed by laminating the adhesive layer 151 and the adhesive layer 152 having a weaker adhesive strength than the adhesive layer 151, and the adhesive layer 151 is adhered to the electromagnetic wave absorbing layer 110. As a result, when the electromagnetic wave absorber 100 is peeled off from the adherend 201, the adhesive layer 150 is prevented from remaining on the adherend 201 and the adhesive layer 150 is prevented from lifting or peeling off. Therefore, the adhesive layer 150 can be reattached to the adherend 201 without being damaged. Furthermore, as described above, the suppression of cohesive failure and lifting or peeling off of the adhesive layer 150 suppresses changes in the electromagnetic wave absorption characteristics. As a result, the electromagnetic wave absorber 100 of this embodiment can be reused. After using the electromagnetic wave absorber 100, a release sheet or the like that has been subjected to release treatment with various release agents or the like may be stuck to the surface of the adhesive layer 150 (adhesive layer 152) until the electromagnetic wave absorber 100 is used again. In this way, it is possible to realize an electromagnetic wave absorber 100 that is easy for users to use.

[0049] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0050] 100: electromagnetic wave absorber, 110: electromagnetic wave absorbing layer, 150 to 152: adhesive layers

Claims

1. An electromagnetic wave absorber in which an electromagnetic wave absorbing layer and an adhesive layer are laminated, the adhesive layer includes a first adhesive layer and a second adhesive layer disposed between the first adhesive layer and the electromagnetic wave absorbing layer and in contact with the first adhesive layer and the electromagnetic wave absorbing layer; The electromagnetic wave absorber is characterized in that the first adhesive layer has a weaker adhesive strength than the second adhesive layer.

2. the electromagnetic wave absorber is attached to the adherend so that the first adhesive layer is in contact with the adherend, an adhesive strength at the interface between the first adhesive layer and the second adhesive layer is stronger than an adhesive strength at the interface between the first adhesive layer and the adherend; 2. The electromagnetic wave absorber according to claim 1, wherein the adhesive strength at the interface between the second adhesive layer and the electromagnetic wave absorbing layer is stronger than the adhesive strength at the interface between the first adhesive layer and the adherend.

3. 3. The electromagnetic wave absorber according to claim 2, wherein the adhesive strength at the interface between the first adhesive layer and the second adhesive layer is stronger than the adhesive strength at the interface between the second adhesive layer and the electromagnetic wave absorbing layer.

4. 4. The electromagnetic wave absorber according to claim 2, wherein the adherend includes a metal plate.

5. 2. The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorbing layer includes a resistive layer and a dielectric layer disposed between the resistive layer and the second adhesive layer.

6. 6. The electromagnetic wave absorber according to claim 5, wherein the dielectric layer is in contact with the resistive layer and the second adhesive layer.

7. 7. The electromagnetic wave absorber according to claim 5, wherein the resistive layer comprises a conductive pattern.

Images