Electromagnetic wave absorber

Abstract

To provide an electromagnetic wave absorber with improved resistance to heat and moisture and bending durability.SOLUTION: An electromagnetic wave absorber includes a gas barrier layer, a resistance layer, and a spacer layer, and the gas barrier layer, the resistance layer, and the spacer layer are laminated in this order, and the thickness of the spacer layer is 1.0 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In order to improve various autonomous driving technologies, electromagnetic wave absorbers are sometimes provided in electromagnetic wave sensors used in autonomous driving to ensure that the sensors function without malfunctioning due to radio interference caused primarily by electromagnetic noise generated by surrounding electronic devices, for example. In this situation, electromagnetic wave absorbers (millimeter wave absorbers, etc.) installed in electromagnetic wave sensors in automobiles, etc., are sometimes required to absorb electromagnetic waves without being affected even in high temperature and high humidity environments, and at the same time to be flexible. Patent Document 1, for example, discloses a dielectric sheet for an electromagnetic wave absorber and an electromagnetic wave absorber, each of which includes a resistive layer, a dielectric layer, and a conductive layer in this order. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-100090 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, although Patent Document 1 discloses a method for suppressing floating (a state in which any layer is locally separated from the substrate and rises up compared to the surrounding area) in the resistive layer or conductive layer that constitutes the electromagnetic wave absorber, it does not consider the bending durability of the electromagnetic wave absorber or the moist heat resistance related to reliability.

[0005] In view of the above, an object of the present invention is to provide an electromagnetic wave absorber having improved resistance to moist heat and bending durability. [Means for solving the problem]

[0006] Means for Solving the Problems The present inventors have conducted intensive research to solve the above problems, and as a result have found that an electromagnetic wave absorber comprising a gas barrier layer, a resistance layer, and a spacer layer, in which a thin gas barrier layer having high gas barrier properties is provided on the resistance layer, and a spacer layer having a specific thickness is used, thereby simultaneously improving the moist heat resistance and bending durability of the electromagnetic wave absorber, and have completed the present invention. That is, the present invention provides the following [1] to [9]. [1] An electromagnetic wave absorber comprising a gas barrier layer, a resistance layer, and a spacer layer, wherein the gas barrier layer, the resistance layer, and the spacer layer are laminated in this order, and the thickness of the spacer layer is 1.0 mm or less. [2] The electromagnetic wave absorber according to the above [1], wherein the spacer layer has a Young's modulus of 50 MPa or more. [3] The electromagnetic wave absorber according to the above [1] or [2], wherein the spacer layer has a relative dielectric constant of 5 or more and less than 100. [4] The electromagnetic wave absorber according to any one of the above [1] to [3], further comprising a reflective layer. [5] The electromagnetic wave absorber according to any one of the above [1] to [4], wherein the spacer layer is in direct contact with the gas barrier layer and the resistance layer. [6] The electromagnetic wave absorber according to any one of the above [1] to [5], wherein the gas barrier layer has at least one layer selected from silicon oxide, silicon nitride, silicon oxynitride, and silicon oxynitride carbide. [7] The electromagnetic wave absorber according to any one of the above [1] to [6], wherein the gas barrier layer has a thickness of 10 to 2000 nm. [8] The electromagnetic wave absorber according to any one of the above [1] to [7], having a thickness of 0.05 to 3.0 mm. [9] An electronic device comprising the electromagnetic wave absorber according to any one of the above [1] to [8]. Effect of the Invention

[0007] According to the present invention, it is possible to provide an electromagnetic wave absorber having improved resistance to moist heat and bending durability. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an example of an electromagnetic wave absorber according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a cross-sectional view showing another example of an electromagnetic wave absorber according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a plan view showing an example of a resistive layer constituting an electromagnetic wave absorber according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Electromagnetic wave absorber] The electromagnetic wave absorber of the present invention includes a gas barrier layer, a resistance layer, and a spacer layer, and is characterized in that the gas barrier layer, the resistance layer, and the spacer layer are laminated in this order, and the thickness of the spacer layer is 1.0 mm or less. The electromagnetic wave absorber of the present invention includes a gas barrier layer, a resistance layer, and a spacer layer, and the gas barrier layer has high gas barrier properties and is thin and is provided on the resistance layer, and the spacer layer has a specific thickness, thereby improving the moisture and heat resistance and bending durability of the electromagnetic wave absorber under high temperature and high humidity conditions.

[0010] In this specification, the term "resistive layer pattern" refers to an object that is a collection of geometrically shaped units and selectively transmits electromagnetic waves of a certain frequency. The "resistive layer pattern" can be said to have the same function as an antenna. In this specification, the term "electromagnetic waves in the millimeter wave region" refers to electromagnetic waves with a wavelength of 1 to 10 mm. The term "electromagnetic waves in the millimeter wave region" can also be said to be electromagnetic waves with a frequency of 30 to 300 GHz.

[0011] In this specification, preferred definitions may be selected arbitrarily, and combinations of preferred definitions may be considered more preferred. In this specification, the expression "XX to YY" means "at least XX and at most YY." In this specification, the lower limit and upper limit described in stages for the preferred numerical range (e.g., range of content, etc.) can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."

[0012] The electromagnetic wave absorber of the present invention will now be described with reference to the drawings.

[0013] FIG. 1 is a cross-sectional view showing an example of an electromagnetic wave absorber according to one embodiment of the present invention. As shown in FIG. 1, the electromagnetic wave absorber 1 of this embodiment has a gas barrier layer 2, a resistance layer 3, a spacer layer 4, and a reflective layer 5.

[0014] FIG. 2 is a cross-sectional view showing the configuration of another example of an electromagnetic wave absorber according to an embodiment of the present invention. As shown in FIG. 2, the electromagnetic wave absorber 11 of this embodiment has a gas barrier layer 2, a resistance layer 3, a spacer layer 4, and a reflective layer 5 laminated on a substrate (P) 7 with an adhesive layer 6 interposed therebetween.

[0015] [Resistance layer] The resistive layer 3 is made of a frequency selective surface (FSS), which 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.

[0016] Fig. 3 is a top view showing an example of a resistive layer in this embodiment. As shown in Fig. 3, the resistive layer 3 has a resistive layer pattern 22 formed on one surface 4a of a flat spacer layer 4. The resistive layer pattern 22 is made up of a first resistive layer pattern 51, a second resistive layer pattern 52, and a third resistive layer pattern 53.

[0017] (First resistive layer pattern) 3, the first resistive layer pattern 51 is composed of a plurality of first units u1. Each of the first units u1 is a geometrical figure. In other words, the first resistive layer pattern 51 can be said to be an aggregate of first units u1 which are geometric figures. Each of the first units u1 functions as an antenna. The first resistive layer pattern 51 may be, for example, a fine line pattern of an FSS element.

[0018] In the first resistive layer pattern 51, a plurality of first arrays R1 are formed, in which a plurality of first units u1 are arranged along the direction indicated by the double-headed arrow P in Fig. 3. It can also be said that the first resistive layer pattern 51 has a plurality of first arrays R1. The first resistive layer pattern 51 can be configured by forming a plurality of first arrays R1 on the spacer layer 4 at predetermined intervals along the direction indicated by the double-headed arrow P. The intervals between the multiple first arrays R1 are not particularly limited, and the intervals between the multiple first arrays R1 may be regular or irregular.

[0019] As shown in Fig. 3, the first unit u1 has a cross shape that is symmetrical in the vertical and horizontal directions. Specifically, the first unit u1 has one cross portion S1 and four end portions T1. The cross portion S1 is composed of a straight line portion parallel to the x-axis direction in Fig. 3 and a straight line portion parallel to the y-axis direction. Straight line end portions T1 contact both ends of the straight line portion parallel to the x-axis direction and both ends of the straight line portion parallel to the y-axis direction so as to be perpendicular to each straight line portion.

[0020] By adjusting the length of the first unit u1 in the x-axis direction and the length of each of the four ends T1 in the x-axis direction, the electromagnetic wave absorption characteristics of the first unit u1 functioning as one antenna can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction.

[0021] However, the shape of the first unit is not limited to a cross shape. The shape of the first unit is not particularly limited as long as the frequency value at which the amount of electromagnetic wave absorbed by the first resistive layer pattern 51 shows a maximum value is A [GHz]. For example, examples of the shape of the figure that is the first unit include a circle, an annular shape, a straight line, a square, a polygon, an H-shape, a Y-shape, a V-shape, and the like.

[0022] In the resistive layer 3, the shapes of the multiple first units u1 are the same. However, the shapes of the multiple first units u1 do not have to be the same figures. In another example of the present invention, the shapes of the multiple first units may be the same or different as long as the absorption characteristics can be adjusted to a target frequency.

[0023] The first resistive layer pattern 51 selectively transmits an electromagnetic wave having a frequency of A [GHz]. The frequency value A [GHz] is the frequency value at which the amount of electromagnetic wave transmitted by the first resistive layer pattern 51 exhibits a maximum value in the range of 20 GHz to 110 GHz.

[0024] In the resistive layer 3 of this embodiment, the frequency value A is preferably 20 to 110 GHz, more preferably 60 to 100 GHz, further preferably 65 to 95 GHz, and particularly preferably 70 to 90 GHz. When the frequency value A is within the above range, the resistive layer 3 can transmit electromagnetic waves in the millimeter wave region, making it easier to apply to automobile parts, road peripheral members, building exterior wall related materials, windows, communication devices, radio telescopes, etc.

[0025] The material of the first unit u1 is not particularly limited as long as the absorption characteristics can be adjusted to a desired frequency. Examples of the material of the first unit include thin metal wires, conductive thin films, and conductive paste deposits. Examples of the metal material 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, rhenium-tungsten, etc.). Examples of materials for the conductive thin film include metal particles, carbon nanoparticles, and carbon fibers.

[0026] The distance between the ends of the figure that is the first unit u1 is not particularly limited as long as the absorption characteristics can be adjusted to a desired frequency. For example, the intervals between the ends of the figures that are the first units u1 may all be the same or may be different from each other. However, it is preferable that the intervals between the ends of the figures that are the first units u1 are the same from the viewpoint of making it easier to design an electromagnetic-wave-absorbing film that is less susceptible to the effects of the surrounding environment and improving the precision of the frequency band of the transmitted electromagnetic waves during manufacturing.

[0027] (Second resistive layer pattern) As shown in FIG. 3, the second resistive layer pattern 52 is composed of a plurality of second units u2. The second resistive layer pattern 52 is formed in the same manner as the first resistive layer pattern 51 .

[0028] The second resistive layer pattern 52 selectively transmits electromagnetic waves having a frequency of B [GHz] that satisfies the following formula (1). The frequency value B [GHz] is the frequency value at which the amount of electromagnetic waves transmitted by the second resistive layer pattern 52 exhibits a maximum value. The frequency value B [GHz] satisfies the following formula (1). 1.037×A≦B≦1.30×A...Equation (1)

[0029] As shown in the above formula (1), the second resistive layer pattern 52 absorbs electromagnetic waves with frequencies of 1.037×A to 1.30×A [GHz]. The second resistive layer pattern 52 preferably absorbs electromagnetic waves with frequencies of 1.17×A to 1.24×A [GHz]. Since the second resistive layer pattern 52 transmits electromagnetic waves with frequencies of 1.037×A [GHz] or more, the peak of the amount of electromagnetic wave transmitted by the second resistive layer pattern 52 and the peak of the amount of electromagnetic wave transmitted by the first resistive layer pattern 51 sufficiently overlap in a frequency band higher than A [GHz]. As a result, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorbing film is expanded to a frequency band higher than A [GHz], compared to a film having only the first resistive layer pattern 51. Since the second resistive layer pattern 52 transmits electromagnetic waves with frequencies of 1.30×A [GHz] or less, in a frequency band higher than A [GHz], the frequency difference between the peak of the amount of electromagnetic wave transmitted by the second resistive layer pattern 52 and the peak of the amount of electromagnetic wave transmitted by the first resistive layer pattern 51 becomes small. As a result, a single peak is formed at which the amount of electromagnetic wave absorbed by the entire electromagnetic wave absorbing film is maximized. As described above, the second resistive layer pattern 52 transmits electromagnetic waves with frequencies of 1.037×A to 1.30×A [GHz], so that the amount of electromagnetic waves absorbed by the entire electromagnetic-wave absorbing film is extended to the higher frequency band.

[0030] The material of the second unit constituting the second resistive layer pattern 52 is not particularly limited as long as it can transmit electromagnetic waves of B [GHz], and is not particularly limited as long as the transmission characteristics can be adjusted to the desired frequency. The material of the second unit is the same as that described for the material of the first unit u1.

[0031] (Third resistive layer pattern) As shown in FIG. 3, the third resistive layer pattern 53 is composed of a plurality of third units u3. The third resistive layer pattern 53 is formed in the same manner as the first resistive layer pattern 51 .

[0032] The third resistive layer pattern 53 selectively transmits electromagnetic waves having a frequency of C [GHz] that satisfies the following formula (2). The frequency value C [GHz] is the frequency value when the amount of electromagnetic waves transmitted by the third resistive layer pattern 53 exhibits a maximum value. The frequency value C [GHz] satisfies the following formula (2). 0.60×A≦C≦0.963×A...Equation (2)

[0033] As shown in the above formula (2), the third resistive layer pattern 53 transmits electromagnetic waves with frequencies of 0.60×A to 0.963×A [GHz]. The third resistive layer pattern 53 preferably transmits electromagnetic waves with frequencies of 0.60×A to 0.83×A [GHz]. Since the third resistive layer pattern 53 transmits electromagnetic waves with frequencies of 0.60×A [GHz] or more, the frequency difference between the peak of the amount of electromagnetic wave transmitted by the third resistive layer pattern 53 and the peak of the amount of electromagnetic wave transmitted by the first resistive layer pattern 51 in a frequency band lower than A [GHz] becomes small. As a result, a single peak is formed where the amount of electromagnetic wave transmitted through the entire resistive layer 3 is a maximum value. Since the third resistive layer pattern 53 transmits electromagnetic waves with frequencies of 0.963×A [GHz] or less, in a frequency band lower than A [GHz], the peak of the amount of electromagnetic wave transmitted by the third resistive layer pattern 53 sufficiently overlaps with the peak of the amount of electromagnetic wave transmitted by the first resistive layer pattern 51. As a result, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorbing film is expanded to a frequency band lower than A [GHz], compared to a film having the first resistive layer pattern 51 alone. As described above, the third resistive layer pattern 53 transmits electromagnetic waves with frequencies of 0.60×A to 0.963×A [GHz], so that the amount of electromagnetic waves transmitted by the entire resistive layer 3 is expanded to the lower frequency band.

[0034] The material of the third unit u3 constituting the third resistive layer pattern 53 is not particularly limited as long as it is capable of absorbing electromagnetic waves of C [GHz], and is not particularly limited as long as the transmission characteristics can be adjusted to the desired frequency. The material of the third unit u3 is the same as that described for the material of the first unit u1.

[0035] In the resistive layer 3 shown in FIG. 3, the first array R1, the second array R2, and the third array R3 are arranged in the direction indicated by the double-headed arrow P so as to be adjacent to each other. In this manner, the first array R1, the second array R2, and the third array R3 are arranged in the spacer layer 4 so as to be adjacent to each other, so that the frequency band of the electromagnetic wave selectively transmitted by the second resistive layer pattern 52 and the frequency band of the electromagnetic wave selectively transmitted by the third resistive layer pattern 53 overlap with each other, based on the frequency value A [GHz] of the peak position of the electromagnetic wave selectively transmitted by the first resistive layer pattern 51. As a result, the transmission range of the electromagnetic wave transmitted by the entire resistive layer 3 is easily expanded to both the high frequency side and the low frequency side, based on the frequency value A [GHz] of the peak position.

[0036] The distance d1 between the first unit u1 and the second unit u2, the distance d2 between the second unit u2 and the third unit u3, and the distance d3 between the third unit u3 and the first unit u1, each shown in FIG. 3, may be the same as or different from each other. The distance d1 may be, for example, 0.2 to 4 mm, 0.3 to 2 mm, or 0.5 to 1 mm. The distance d2 may be, for example, 0.2 to 4 mm, 0.3 to 2 mm, or 0.5 to 1 mm. The distance d3 may be, for example, 0.2 to 4 mm, 0.3 to 2 mm, or 0.5 to 1 mm. When the intervals d1, d2, and d3 are each within the above-mentioned numerical ranges, the transmission range of the electromagnetic wave transmitted through the entire resistive layer 3 tends to be further expanded with the frequency value A [GHz] at the peak position as the reference.

[0037] In the resistive layer 3, the first unit u1, the second unit u2, and the third unit u3 have the same shapes. However, the shapes of the first unit u1, the second unit u2, and the third unit u3 do not have to be the same figures. That is, in another example of the present invention, the shapes of the first unit u1, the second unit u2, and the third unit u3 may be the same or different from each other.

[0038] The thickness of the first resistive layer pattern 51, the second resistive layer pattern 52, and the third resistive layer pattern 53 corresponding to the resistive layer pattern 22 of the resistive layer 3 is not particularly limited. These thicknesses can be changed arbitrarily according to the desired characteristics. Moreover, these three thicknesses may be the same or different from each other, and are preferably the same in consideration of productivity. The thicknesses of the first resistive layer pattern 51, the second resistive layer pattern 52, and the third resistive layer pattern 53 are preferably 0.01 to 300 μm, more preferably 0.04 to 100 μm, and particularly preferably 0.08 to 1 μm, from the viewpoint of achieving both electromagnetic wave absorption properties and bending durability.

[0039] In another aspect of the embodiment of the present invention, the resistance layer 3 may be provided with a base material (Q) between it and the spacer layer 4. The base material (Q) is not particularly limited, but is preferably made of a resin from the viewpoint of flexibility. The resin may be a thermoplastic resin or a thermosetting resin, and preferably contains a thermoplastic resin. Examples of thermoplastic resins include polyolefin resins, polyester resins, polyester-polyether resins, polyacrylic resins, polystyrene resins, polyimide resins, polyurethane resins, epoxy resins, and silicone resins. Specific examples of polyolefin resins include polypropylene and polyethylene. Specific examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. The thickness of the substrate (Q) is not particularly limited, but from the viewpoint of flexibility, it is preferably from 5 to 500 μm, more preferably from 15 to 200 μm, and even more preferably from 25 to 100 μm.

[0040] The resistance layer 3 can be produced, for example, by the following method. First, the spacer layer 4 is prepared. Next, a first resistive layer pattern 51, a second resistive layer pattern 52, and a third resistive layer pattern 53 are formed on one surface 4a of the spacer layer 4. Each resistive layer pattern is formed so that the frequency at which the amount of electromagnetic waves transmitted by each resistive layer pattern exhibits a maximum value is a predetermined value [GHz]. The order in which the respective resistive layer patterns are formed is not particularly limited, and the respective resistive layer patterns may be formed in the same process or in separate processes.

[0041] The method for forming each resistive layer pattern is not particularly limited as long as it can form a predetermined frequency. Examples of the method for forming each resistive layer pattern include the following methods. A printing method in which each resistive layer pattern is printed on one surface 4a of the spacer 4 using a conductive paste. A developing method for developing each resistive layer pattern on one surface 4a of the spacer 4. A method in which a metal thin film is provided on one surface 4a of the spacer layer 4 by sputtering, vacuum deposition or lamination of metal foil, and a pattern of the metal thin film is formed on one surface 4a of the spacer layer 4 by photolithography.

[0042] [Spacer layer] In the electromagnetic wave absorber 11 of this embodiment, the spacer layer 4 has two surfaces. One surface 4a of the spacer layer 4 is in direct contact with the other surface 3b of the resistance layer 3 and the other surface 2b of the gas barrier layer 2, but does not have to be in direct contact with them. A reflective layer 5 laminated on a base material (P) 7 is provided on the other surface 4b of the spacer layer 4 via an adhesive layer 6. The spacer layer 4 may have a single-layer structure or a multi-layer structure.

[0043] In the electromagnetic wave absorber 11 of this embodiment, the thickness of the spacer layer 4 is 1.0 mm or less. The thickness of the spacer layer 4 is preferably 100 to 800 μm, more preferably 1500 to 600 μm, and further preferably 200 to 450 μm. When the thickness of the spacer layer 4 is equal to or more than the lower limit, it is easy to obtain a spacer layer 4 having a high relative dielectric constant. When the thickness of the spacer layer 4 is equal to or less than the upper limit, it is easy to obtain flexibility, and bending durability is improved.

[0044] When the wavelength shortening effect of the spacer layer 4 is taken into consideration, the thickness of the spacer layer 4 is appropriately changed according to the wavelength of the electromagnetic wave to be absorbed and the relative dielectric constant of the spacer layer 4 . When the wavelength shortening effect of the spacer layer 4 is taken into consideration, the thickness of the spacer layer 4 preferably satisfies the following formula (3). (Thickness of spacer layer 4)=(λ)×(1 / 4) / (ε) 1 / 2 ...Equation (3) In the above formula (3), λ is the wavelength of the incident electromagnetic wave, and ε is the relative dielectric constant of the spacer layer 4. The thickness of the spacer layer 4 may be appropriately adjusted for absorption characteristics. For example, it can be changed within a range of 0.1 to 3.0 times the thickness of the spacer layer 4 obtained by formula (3).

[0045] When the relationship between the thickness of the spacer layer 4 and the wavelength λ satisfies the above formula (3), the electromagnetic wave absorber 11 has a so-called λ / 4 structure, whereby the electromagnetic wave absorber 11 absorbs the electromagnetic wave. The spacer layer 4 may be made of a material having a high dielectric constant. When the spacer layer 4 is a layer having a high dielectric constant, the thickness of the spacer layer 4 can be made relatively thin.

[0046] The thickness of the spacer layer 4 can be measured by a constant pressure thickness measuring instrument manufactured by Tecrock Corporation.

[0047] In the electromagnetic wave absorber 11 of this embodiment, the relative dielectric constant of the spacer layer 4 is preferably 5 or more and less than 100, more preferably 7-50, further preferably 8-30, and particularly preferably 9-15. The spacer layer 4 can be thinned by having a relative dielectric constant of 5 or more, which allows the electromagnetic wave absorber 11 to have excellent flexibility. When the relative dielectric constant of the spacer layer 4 is 100 or less, the Young's modulus of the spacer layer 4 can be prevented from becoming too high.

[0048] The relative dielectric constant of the spacer layer 4 can be measured by the method described in the examples below.

[0049] The Young's modulus of the spacer layer 4 is preferably 50 MPa or more, more preferably 80 to 1000 MPa, further preferably 150 to 500 MPa, and particularly preferably 200 to 450 MPa. When the Young's modulus of the spacer layer 4 is equal to or less than the upper limit, the flexibility is easily improved. When the Young's modulus of the spacer layer 4 is equal to or more than the lower limit, the shape retention is easily ensured.

[0050] The Young's modulus of the spacer layer 4 can be measured in accordance with JIS K7127:1999 "Plastics-Test methods for tensile properties-Part 3: Test conditions for films and sheets".

[0051] The material of the spacer layer 4 can be appropriately selected depending on the application. For example, when used for the exterior of an automobile, it is preferable to select a material that has flexibility and excellent heat resistance. Examples of the flexible material include a plastic film, a nonwoven fabric, a rubber sheet, etc. Among these, a plastic film is preferred from the viewpoint of ease of kneading with the filler. As a specific example of the resin constituting the plastic film, for example, one having a high melting point selected from the thermoplastic resins explained for the substrate 21 above can be used.

[0052] The spacer layer 4 may contain a filler. There are no particular limitations on the filler as long as it has a high relative dielectric constant, and examples of the filler include barium titanate, strontium titanate, calcium titanate, and titanium oxide.

[0053] The filler content in the spacer layer 4 is preferably 20 to 60% by volume, more preferably 25 to 50% by volume, and particularly preferably 30 to 45% by volume. When the filler content is equal to or greater than the lower limit, the thickness of the spacer layer 4 required to obtain the required electromagnetic wave absorption can be reduced, and flexibility can be easily obtained. When the filler content is equal to or less than the upper limit, the spacer layer 4 is not embrittled, and is easily manufactured.

[0054] An adhesive layer (for example, adhesive layer 6 in FIG. 2) may be provided on the two surfaces 4a and 4b of the spacer layer 4. This makes it possible to easily attach the resistive layer 3 and the reflective layer 5 to each of the two surfaces 4a and 4b. Details and preferred embodiments of the adhesive layer may be the same as those described below for the adhesive layer.

[0055] [Reflective layer] In the embodiment of the present invention, the electromagnetic wave absorber 11 preferably further includes a reflective layer 5 . The reflective layer 5 has two surfaces. One surface 5a of the reflective layer 5 faces the other surface 4b of the spacer layer 4 via an adhesive layer 6. The other surface 5b of the reflective layer 5 contacts one surface 7a of the base material (P) 7. The reflective layer 5 is not particularly limited in shape as long as it can reflect the electromagnetic waves that arrive at the surface of the electromagnetic wave absorber 11 and transmit through the gas barrier layer 2, the resistive layer 3, the spacer layer 4, and the adhesive layer 6. A part of the electromagnetic waves that arrive at the electromagnetic wave absorber 11 is reflected by or absorbed by the resistive layer 3. On the other hand, the electromagnetic waves that are not reflected or absorbed by the resistive layer 3 transmit through the resistive layer 3. The electromagnetic waves that transmit through the resistive layer 3 are reflected by the reflective layer 5 toward the resistive layer 3. For example, if the reflective layer 5 has conductivity in the surface direction of either of the two faces 5a, 5b, it can reflect the electromagnetic waves transmitted through the resistance layer 3. Specifically, a metal foil such as aluminum foil or copper foil, or a metal plate such as a copper plate, bonded to a base material (P) 7 such as polyethylene terephthalate may be used as the reflective layer 5. Details of the base material (P) 7 may be the same as those of the base material (Q) described above. Instead of the metal foil or metal plate, a transparent conductive film such as ITO, or a mesh sheet formed of metal wires may be used.

[0056] In the electromagnetic wave absorber 11 of this embodiment, the thickness of the reflective layer 5 is not particularly limited, but is preferably 0.01 to 300 μm, more preferably 0.04 to 100 μm, and further preferably 0.08 to 0.9 μm. By making the thickness of the reflective layer 5 equal to or greater than the lower limit, it becomes easier to form a uniform film and to more easily exhibit the reflective properties. By making the thickness equal to or less than the upper limit, it becomes easier to obtain flexibility and to easily suppress the occurrence of cracks, thereby improving the flex durability.

[0057] When the spacer layer 4 is formed on an object having electrical conductivity, such as a metal, the object having electrical conductivity, such as a metal, serves as the reflective layer 5, and therefore the reflective layer 5 can be omitted.

[0058] [Gas barrier layer] The electromagnetic wave absorber 11 of this embodiment includes a gas barrier layer on one surface 3a of the resistance layer 3 (including between the patterns). The gas barrier layer according to the embodiment of the present invention is not particularly limited in terms of material, etc., as long as it has gas barrier properties.

[0059] Preferred examples of the gas barrier layer include silicon oxide, aluminum oxide, magnesium oxide, zinc oxide, indium oxide, tin oxide, silicon nitride, aluminum nitride, titanium nitride, silicon oxynitride, and silicon oxynitride carbide, and from the viewpoint of easily obtaining excellent gas barrier properties at low cost, those containing at least one of silicon oxide, silicon nitride, silicon oxynitride, and silicon oxynitride carbide are more preferred. Note that the gas barrier layer may contain the above-mentioned main components (for example, 60 mass% or more, more preferably 80 mass% or more, and even more preferably 99 mass% or more) and may contain other components. These may be used alone or in combination of two or more. The gas barrier layer may be a single layer or a multilayer.

[0060] From the viewpoints of gas barrier properties and ease of handling, the thickness of the gas barrier layer is preferably in the range of 10 to 2,000 nm, more preferably 20 to 1,000 nm, more preferably 30 to 500 nm, and even more preferably 40 to 400 nm.

[0061] Methods for forming a gas barrier layer include PVD (physical vapor deposition) methods such as vacuum deposition, sputtering, and ion plating, CVD methods such as thermal CVD (chemical vapor deposition), plasma CVD, and photo CVD, and methods in which a coating film is obtained and then modified.

[0062] As a method for obtaining a coating film and performing a modification treatment, a method in which a solution containing a polysilazane-based compound such as organic polysilazane or perhydropolysilazane is applied, dried, and then the modification treatment described below is performed can be mentioned. The polysilazane compounds may be used alone or in combination of two or more.

[0063] The solution may contain other components within the scope of the present invention, such as a curing agent, other polymers, antioxidants, light stabilizers, and flame retardants.

[0064] In the electromagnetic wave absorber 11 according to one embodiment of the present invention, for example, a solution containing a polysilazane compound, and optionally other components, and a solvent, etc., is applied onto a resistance layer, a spacer layer, a substrate, etc. by a known method, the resulting coating film is dried, and a modification treatment, which will be described later, is performed to form a gas barrier layer. The gas barrier layer obtained in this manner has a two-layer laminate structure, for example, of a silicon oxynitride layer (modified region) and a silicon oxide layer (unmodified region, a region oxidized over time by oxygen or water vapor in the air).

[0065] The solution can be applied using a known device such as a spin coater, a knife coater, a gravure coater, or a die coater.

[0066] It is preferable to dry the obtained coating film or heat the coating film in order to improve the gas barrier property of the electromagnetic wave absorber. As the heating and drying method, a conventionally known drying method such as hot air drying, hot roll drying, infrared irradiation, etc. can be adopted. The heating temperature is usually 80 to 150°C, and the heating time is usually several tens of seconds to several tens of minutes. Then, a modification treatment is performed.

[0067] Examples of the modification treatment include ion implantation, vacuum ultraviolet light irradiation, etc. Among these, ion implantation is preferred because it provides high gas barrier performance. In the ion implantation, the amount of ions implanted into the coating film may be appropriately determined according to the intended use of the electromagnetic wave absorber to be formed (required gas barrier properties, transparency, etc.), etc.

[0068] The ions to be implanted include ions of rare gases such as argon, helium, neon, krypton, and xenon; ions of fluorocarbons, hydrogen, nitrogen, oxygen, carbon dioxide, chlorine, fluorine, and sulfur; and the like.

[0069] Among these, at least one ion selected from the group consisting of hydrogen, nitrogen, oxygen, argon, helium, neon, xenon, and krypton is preferred, as it can be more easily injected and results in a gas barrier layer having particularly excellent gas barrier properties.

[0070] The method of injecting ions is not particularly limited, but includes a method of irradiating ions (ion beam) accelerated by an electric field, a method of injecting ions in plasma, etc. Among them, the latter method of injecting plasma ions is preferred because it allows a film with gas barrier properties to be easily obtained.

[0071] As the plasma ion implantation method, (α) a method in which ions present in plasma generated using an external electric field are implanted into a polymer layer, or (β) a method in which ions present in plasma generated only by an electric field due to a negative high voltage pulse applied to the layer without using an external electric field are implanted into the polymer layer.

[0072] In the method (α), the pressure during ion implantation (pressure during plasma ion implantation) is preferably 0.01 to 1 Pa. When the pressure during plasma ion implantation is in this range, ions can be implanted simply, efficiently and uniformly, and the desired gas barrier layer can be efficiently formed.

[0073] The method (β) does not require a high degree of vacuum, is easy to operate, and can significantly reduce the processing time. In addition, the layer can be uniformly processed throughout, and ions in the plasma can be continuously injected into the polymer layer with high energy when a negative high voltage pulse is applied. Furthermore, high-quality ions can be uniformly injected into the polymer layer by simply applying a negative high voltage pulse to the layer, without requiring any other special means such as a high-frequency power source such as radio frequency (hereinafter abbreviated as "RF") or microwave.

[0074] In both of the methods (α) and (β), the pulse width when applying a negative high voltage pulse, i.e., when injecting ions, is preferably 1 to 15 μsec. When the pulse width is in this range, ions can be injected more simply, efficiently, and uniformly.

[0075] The voltage applied when generating plasma is preferably -1 to -50 kV. When ion implantation is performed at an applied voltage of more than -1 kV, the amount of ion implantation (dose) becomes sufficient, and the desired performance is easily obtained. On the other hand, when ion implantation is performed at a voltage of less than -50 kV, charging and coloring of the film are easily prevented.

[0076] A plasma ion implantation device is used to implant ions in the plasma into the polymer layer. Specific examples of plasma ion implantation devices include: (i) a plasma ion implantation device that generates plasma using an external electric field from a high-frequency power source such as microwaves, and applies a high-voltage pulse to attract and inject ions in the plasma; and (ii) a plasma ion implantation device that injects ions in the plasma generated only by the electric field generated by applying a high-voltage pulse, without using an external electric field.

[0077] In the plasma ion implantation devices of (i) and (ii), the high-voltage pulse power supply also serves as the plasma generating means for generating plasma, and therefore no other special means such as a high-frequency power source of RF, microwave or the like is required. By simply applying a negative high-voltage pulse, plasma can be generated, ions in the plasma can be continuously implanted into a polymer layer, and an electromagnetic wave absorber can be mass-produced in which a polymer layer having a portion modified by ion implantation on its surface, i.e., a gas barrier layer, is formed.

[0078] The thickness of the portion into which ions are implanted can be controlled by the type of ion, the applied voltage, the treatment time, and other implantation conditions, and may be determined depending on the thickness of the polymer layer, the intended use of the electromagnetic wave absorber, and the like, but is usually 5 to 1,000 nm.

[0079] The implantation of ions can be confirmed by performing elemental analysis measurement at a depth of about 10 nm from the surface of the polymer layer using X-ray photoelectron spectroscopy (XPS).

[0080] The gas barrier layer having gas barrier properties can be confirmed by the fact that the gas barrier layer has a small water vapor permeability. The water vapor transmission rate of the gas barrier layer at 40°C and a relative humidity of 90% is usually 1.0 g m -2 ·day -1 or less, and more preferably 0.1 g m -2 ·day -1 The water vapor transmission rate can be measured by the method described in the examples below.

[0081] For the purpose of applying the electromagnetic wave absorber 11 to the surfaces of various articles, an adhesive layer may be provided on the other surface 5b of the reflective layer 5. When an adhesive layer is provided on the other surface 5b of the reflective layer 5, a release film may be provided on the surface of the adhesive layer opposite to the side in contact with the other surface 5b of the reflective layer 5. The release film is removed when the electromagnetic wave absorber 11 is used. Covering the adhesive surface with the release film improves handling during distribution.

[0082] (adhesive layer) Examples of adhesives constituting the adhesive layer include heat-seal type adhesives that adhere by heat, adhesives that develop stickiness when moistened, pressure-sensitive adhesives (adhesives) that adhere by pressure, etc. Among these, adhesives (pressure-sensitive adhesives) are preferred from the viewpoint of simplicity. Specific examples of the adhesive include acrylic adhesives, urethane adhesives, rubber adhesives, polyester adhesives, silicone adhesives, polyvinyl ether adhesives, etc. Among these, at least one selected from the group consisting of acrylic adhesives, urethane adhesives, and rubber adhesives is preferred, and acrylic adhesives are more preferred.

[0083] Moreover, the thickness of the electromagnetic wave absorber 11 of this embodiment (sometimes referred to as "total thickness"; the total thickness from the outermost surface of the gas barrier layer 2 (one surface 2a of the gas barrier layer 2) to the other surface 7b of the substrate (P) 7) is preferably 0.05 to 3.0 mm, more preferably 0.1 to 1.0 mm, and particularly preferably 0.3 to 0.5 mm, from the viewpoint of achieving both bending durability and electromagnetic wave absorbency.

[0084] The water vapor transmission rate of the electromagnetic wave absorber 11 of this embodiment before initial bending in an atmosphere of 40°C and relative humidity of 90% is usually 1.0 g m -2 ·day -1 less than 0.1 g m -2 ·day -1 More preferably, it is 1×10 -2 g m -2 ·day -1 or less, and more preferably 1×10-3 g m -2 ·day -1 In addition, after bending (100,000 times at a bending radius of 2 mm under an environment of 20°C and 50 RH%), the water vapor transmission rate at 40°C and a relative humidity of 90% is usually 1.0 g m -2 ·day -1 less than 0.1 g m -2 ·day -1 More preferably, it is 1×10 -2 g m -2 ·day -1 or less, and more preferably 1×10 -3 g m -2 ·day -1 The water vapor transmission rate can be measured by the method described in the Examples below. The ratio of the water vapor transmission rate after the bending test to the initial water vapor transmission rate before bending is preferably 10 or less, more preferably 5 or less, and even more preferably 2 or less. Furthermore, the water vapor transmission rate of the electromagnetic wave absorber 11 of this embodiment after a moist heat resistance test in an atmosphere of 40°C and a relative humidity of 90% is usually 1.0 g m -2 ·day -1 less than 0.1 g m -2 ·day -1 More preferably, it is 1×10 -2 g m -2 ·day -1 or less, and more preferably 1×10 -3 g m -2 ·day -1 The following is the result. Moreover, the electromagnetic wave absorber 11 of this embodiment has an electromagnetic wave absorption rate of usually 80% or more, preferably 90% or more, more preferably 94% or more, and further preferably 97% or more. Furthermore, the electromagnetic wave absorber 11 of this embodiment has an electromagnetic wave absorption rate after a moist heat resistance test of usually 80% or more, preferably 90% or more, more preferably 94% or more, and even more preferably 97% or more.

[0085] [Electronic Devices] The electromagnetic wave absorber according to one embodiment of the present invention is preferably provided in an electronic device. Examples of electronic devices include, from the viewpoint of electromagnetic interference suppression or noise reduction, devices related to millimeter wave radars used in intelligent transport systems (ITS) and automatic driving control systems that communicate information between automobiles, roads, and people. Other examples include devices related to optical transceivers, short-distance wireless transfer technology, next-generation mobile communication systems (5G, 6G), etc. Further examples include electronic devices related to home appliances that require measures against noise caused by electromagnetic interference inside electronic devices, and electronic devices such as smartphones. EXAMPLES

[0086] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0087] The electromagnetic wave absorbers produced in the examples and comparative examples were evaluated as follows.

[0088] [Water vapor transmission rate measurement] The electromagnetic wave absorbers obtained in the examples and comparative examples were 2 The water vapor transmission rate [WVTR (g m )] was measured using a water vapor transmission rate measuring device (MOCON, device name: AQUATRAN (registered trademark) 2) under the conditions of a temperature of 40°C, a relative humidity of 90%, and a gas flow rate of 20 sccm. -2 ·day -1 )] was measured.

[0089] [Measurement of electromagnetic wave absorption rate] The electromagnetic wave absorbers produced in the examples and comparative examples were evaluated for their transmission characteristics by a free space method using a network analyzer (manufactured by Keysight, model name: FS-330) to measure the S11 value (reflection coefficient) at 76 GHz, and the electromagnetic wave absorption rate was calculated from the obtained value using the following formula (4). Electromagnetic wave absorption rate (%) = 100-((10) (S11) / 10 ×100)...Equation (4)

[0090] [Evaluation of bending durability] The bending durability of the electromagnetic wave absorbers produced in the examples and comparative examples was evaluated by repeatedly bending the samples 100,000 times each at bending radii of 2, 3, and 5 mm in an environment of 23°C and 50 RH% using a stretch tester (manufactured by Yuasa Systems Co., Ltd., model name: DLDMLH-FS) with the gas barrier layer side facing outward, and the water vapor transmission rate after the bending test was measured by the method described above. In the bending test, the smaller the bending radius, the more severe the test conditions. In addition, for electromagnetic wave absorbers that do not inherently have flexibility, the bending durability was not evaluated, and the electromagnetic wave absorption rate and water vapor transmission rate were not measured either (Table 1 states "N: Not measured due to lack of flexibility; however, measurements were performed for the evaluation of moist heat resistance).

[0091] [Moisture and heat resistance evaluation] A humidity and moisture resistance test of the electromagnetic wave absorber was carried out using a temperature and humidity chamber (manufactured by Espec Corporation, model name: PHH-102). The temperature of the temperature and humidity chamber was set to 60°C and the relative humidity to 90%, and the electromagnetic wave absorber was placed in the temperature and humidity chamber for 1000 hours. After being removed from the temperature and humidity chamber, the gas barrier property (water vapor transmission rate) and electromagnetic wave absorption rate of the electromagnetic wave absorber were measured.

[0092] [Evaluation of relative dielectric constant] The relative dielectric constant of the spacer layers used in the examples and comparative examples was measured using a dielectric constant measuring device (manufactured by AET, 40 GHz TE mode) and a network analyzer (manufactured by Anritsu, model name: MS46122B).

[0093] [Measurement of Young's modulus (tensile elastic modulus)] The spacer layer used in the examples and comparative examples was cut into a test piece measuring 15 mm long x 150 mm wide, and the tensile modulus E was measured in accordance with JIS K7127:1999 "Plastics - Test methods for tensile properties - Part 3: Test conditions for films and sheets". Specifically, the test piece was subjected to a tensile test at a speed of 200 mm / min using a tensile tester (manufactured by Shimadzu Corporation, product name: Autograph AG-IS 500N) with the chuck distance set to 100 mm, to measure the Young's modulus (tensile modulus E) (MPa) of the spacer layer.

[0094] Example 1 <Preparation of electromagnetic wave absorber> (1) Formation of spacer layer 22 parts by mass of a polyester-polyether copolymer (manufactured by Toyobo Co., Ltd., product name: P-55B) as a resin and 78 parts by mass of barium titanate (manufactured by Nippon Kagaku Co., Ltd., product name: BT-UP2, average particle size: 2 μm) as a filler were kneaded at 200°C and 40 rpm for 5 minutes using a Labo Plastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd., model name: 4C150) to prepare a mixed material with a barium titanate content of 40 volume %. The above mixed material was hot-pressed at 200° C. and 4500 MPa for 3 minutes using a hydraulic hot press machine (manufactured by Tester Sangyo Co., Ltd., model name: SA-302) to obtain a spacer layer having a thickness of 300 μm.

[0095] (2) Formation of a resistive layer A water-washable ink was pattern-printed on one side of the spacer layer (thickness: 100 μm, pattern openings in the shape of a cross; see FIG. 3), and then copper was evaporated on the pattern printing to a thickness of 100 nm to form a copper thin film. The water-washable ink was then washed away with water to remove the copper thin film except for the openings, thereby obtaining a resistive layer (electromagnetic wave absorbing layer) having a resistive layer pattern made of a copper thin film with a thickness of 100 nm as shown in FIG. 3.

[0096] (3) Formation of a reflective layer As a material for the adhesive layer, an acrylic copolymer with a weight average molecular weight of 800,000 consisting of 70% by mass of 2-ethylhexyl acrylate, 29% by mass of n-butyl acrylate, 0.5% by mass of acrylic acid, and 0.5% by mass of 2-hydroxyethyl acrylate was prepared. An acrylic adhesive solution was prepared by adding 1 part by mass (solid content equivalent) of an isocyanate-based crosslinking agent and 8 parts by mass of an ultraviolet absorber (manufactured by BASF Japan, product name: Tinuvin 477) to 100 parts by mass (solid content equivalent) of the acrylic copolymer, and diluting the mixture with ethyl acetate. Next, the above acrylic adhesive solution was applied onto a release film and dried at 90°C for 1 minute. After that, the adhesive layer was cured at room temperature for one week to obtain an adhesive layer having a thickness of 20 μm. Next, a polyethylene terephthalate film (thickness: 50 μm) having an aluminum vapor deposition film (thickness: 100 nm) on one side was prepared as a reflective layer, and the aluminum vapor deposition film side of the film was laminated with the adhesive layer to cover it, thus obtaining a laminate of release film / adhesive layer / aluminum vapor deposition film / polyethylene terephthalate film. Next, the release film was peeled off, and the exposed adhesive layer was laminated on the surface of the spacer layer opposite to the surface that would become the resistive layer, to prepare a precursor of the electromagnetic wave absorber.

[0097] (4) Formation of gas barrier layer A perhydropolysilazane solution (manufactured by DNF, weight average molecular weight: 10,000 g / mol, dispersion solvent: xylene) was applied to the resistive layer pattern surface (including the area between the patterns on the spacer surface) of the electromagnetic wave absorber precursor obtained in (3) using a spin coater, and the resulting coating was dried at 100°C for 2 minutes to form one polysilazane layer. The thickness of the polysilazane layer was 300 nm. Next, using a plasma ion implantation device, plasma ion implantation was performed on the polysilazane layer under the following conditions to modify the surface of the polysilazane layer, thereby forming a gas barrier layer, thereby producing an electromagnetic wave absorber. The plasma ion implantation apparatus and plasma ion implantation conditions used are as follows. (Plasma ion implantation equipment) RF power supply: Model number "RF" 56000, manufactured by JEOL Ltd. High voltage pulse power supply: "PV-3-HSHV-0835", manufactured by Kurita Manufacturing Co., Ltd. (Plasma ion implantation conditions) Plasma generating gas: He Gas flow rate: 100sccm ·Duty ratio: 0.5% Repetition rate: 1000Hz Applied voltage: -8kV ·RF power: Frequency 13.56MHz, applied power 1000W Chamber pressure: 0.2Pa Pulse width: 5μsec Processing time (ion implantation time): 200 seconds

[0098] Example 2 An electromagnetic wave absorber was produced in the same manner as in Example 1, except that the thickness of the gas barrier layer was set to 200 nm.

[0099] Example 3 An electromagnetic wave absorber was produced in the same manner as in Example 1, except that the thickness of the gas barrier layer was set to 100 nm.

[0100] Example 4 An electromagnetic wave absorber was produced in the same manner as in Example 1, except that the thickness of the gas barrier layer was set to 50 nm.

[0101] Example 5 A water-washing ink was pattern-printed (thickness: 100 μm, the opening of the pattern was cross-shaped; see FIG. 3) on one side of a polyethylene terephthalate film (thickness 50 μm) as a substrate, and then copper was evaporated to a thickness of 100 nm on the pattern printing to form a copper thin film. The water-washing ink was then washed with water to remove the copper thin film other than the opening, thereby obtaining a resistance layer (electromagnetic wave absorbing layer) having a resistance layer pattern made of a copper thin film having a thickness of 100 nm as shown in FIG. 3. Next, one side of a 20 μm thick adhesive layer prepared in the same manner as in Example 1 was attached to the surface opposite to the resistance layer side of the polyethylene terephthalate film. Then, the release film on the adhesive layer was peeled off, and a spacer layer having a thickness of 300 μm obtained in the same manner as in Example 1 was attached to the other surface of the exposed adhesive layer. Next, a laminate consisting of a release film / adhesive layer / aluminum vapor deposition film / polyethylene terephthalate film was prepared in the same manner as in Example 1, and the release film was peeled off from the laminate, and the exposed adhesive layer was laminated on the exposed surface side of the spacer layer to produce a precursor of an electromagnetic wave absorber. A gas barrier layer (thickness 50 nm) similar to that in Example 1 was formed on the resistive layer pattern surface (including the space between the patterns on the polyethylene terephthalate film surface), which is the resistive layer of the obtained precursor of an electromagnetic wave absorber, to produce an electromagnetic wave absorber.

[0102] Comparative Example 1 An electromagnetic wave absorber was produced in the same manner as in Example 5, except that a urethane foam material (manufactured by Rogers Inoac Corporation, product name: Poron HH-48, thickness 2 mm) was used as the spacer layer, and a gas barrier layer was not formed on the resistive layer pattern surface (including between the patterns on the polyethylene terephthalate film surface).

[0103] Comparative Example 2 An electromagnetic wave absorber was produced in the same manner as in Example 5, except that the same spacer layer as in Comparative Example 1 (thickness: 2 mm) was used and the thickness of the gas barrier layer was 200 nm.

[0104] Table 1 shows the evaluation results of the water vapor transmission rate, electromagnetic wave absorption rate, bending durability, and moist heat resistance of the electromagnetic wave absorbers produced in Examples 1 to 5 and Comparative Examples 1 and 2, as well as the relative dielectric constant and Young's modulus of the spacer layer.

[0105] [Table 1]

[0106] It can be seen that the electromagnetic wave absorbers of Examples 1 to 5, which include a spacer layer having a specific thickness that satisfies the specifications of the present invention, simultaneously satisfy both moist heat resistance and bending durability, compared to the electromagnetic wave absorbers of Comparative Examples 1 and 2, which do not satisfy the specifications of the spacer layer thickness. [Industrial Applicability]

[0107] The electromagnetic wave absorber of the present invention can be used, for example, as an electromagnetic wave absorber for transportation equipment (equipped with millimeter wave radar) such as automobiles. In particular, since it simultaneously has moist heat resistance and bending durability, it can be suitably used in a highly moist and hot environment, or attached to a curved surface. [Explanation of symbols]

[0108] 1,11: Electromagnetic wave absorber 2: Gas barrier layer 2a: One surface of the gas barrier layer 2 2b: the other surface of the gas barrier layer 2 3: Resistance layer 3a: One surface of the resistive layer 3 3b: The other surface of the resistive layer 3 4: Spacer layer 4a: One surface of the spacer layer 4 4b: the other surface of the spacer layer 4 5: Reflective layer 5a: One surface of the reflective layer 5 5b: the other surface of the reflective layer 5 6: Adhesive layer 7: Base material (P) 7a: One surface of the substrate (P) 7 7b: The other surface of the substrate (P) 7 22: Resistive layer pattern 51: First resistive layer pattern 52: Second resistive layer pattern 53: Third resistive layer pattern

Claims

1. An electromagnetic wave absorber comprising a gas barrier layer, a resistive layer, and a spacer layer, The electromagnetic wave absorber comprises the gas barrier layer, the resistance layer, and the spacer layer laminated in this order, and the spacer layer has a thickness of 1.0 mm or less.

2. 2. The electromagnetic wave absorber according to claim 1, wherein the spacer layer has a Young's modulus of 50 MPa or more.

3. 3. The electromagnetic wave absorber according to claim 1, wherein the spacer layer has a relative dielectric constant of 5 or more and less than 100.

4. The electromagnetic wave absorber according to claim 1 or 2, further comprising a reflective layer.

5. 3. The electromagnetic wave absorber according to claim 1, wherein the spacer layer is in direct contact with the gas barrier layer and the resistance layer.

6. 3. The electromagnetic wave absorber according to claim 1, wherein the gas barrier layer comprises at least one layer selected from silicon oxide, silicon nitride, silicon oxynitride, and silicon oxynitride carbide.

7. 3. The electromagnetic wave absorber according to claim 1, wherein the gas barrier layer has a thickness of 10 to 2000 nm.

8. 3. The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorber has a thickness of 0.05 to 3.0 mm.

9. An electronic device comprising the electromagnetic wave absorber according to claim 1 or 2.

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