Electromagnetic wave absorbing member

Abstract

Provided is an electromagnetic wave absorbing member (10) provided with an electromagnetic wave absorbing layer (20), a barrier layer (30), and a reflecting layer (40) laminated in this order, the barrier layer (30) having a relative dielectric constant of 5 or more and the barrier layer (30) having a melting point of 150 DEG C or more.

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave absorbing member.

[0002] This application claims priority based on Japanese Patent Application No. 2022-134106 filed in Japan on August 25, 2022, and the contents are incorporated herein by reference. Background Art

[0003] A sheet-like electromagnetic wave absorbing member that selectively absorbs electromagnetic waves of a specified frequency is known. The electromagnetic wave absorbing member is, for example, a member having a first frequency selective shielding layer and a second frequency selective shielding layer. In this electromagnetic wave absorbing member, each layer absorbs electromagnetic waves of a specified frequency through a fine line pattern of FSS (Frequency Selective Surface) elements formed on the first frequency selective shielding layer and the second frequency selective shielding layer, and selectively shields electromagnetic waves of two different frequencies as a whole.

[0004] When an electromagnetic wave absorbing member is attached to a curved surface depending on the application, it is required to closely adhere to the curved surface.

[0005] Patent document 1 describes an electromagnetic wave absorbing member having the following characteristics (1) and (2) so that it can be easily mounted even on an uneven surface. Characteristic (1): The product of the Young's modulus of the magnetic layer and the thickness of the magnetic layer is 0.1 MPa·mm to 1000 MPa·mm. Characteristic (2): The relative dielectric constant of the magnetic layer is 1 to 10.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-4003 Summary of the invention

[0009] 1. Technical issues to be resolved

[0010] However, the electromagnetic wave absorbing member described in Patent Document 1 has a problem in that the electromagnetic wave absorbing property after the heat resistance test is poorly maintained, although the member has excellent curved surface followability.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electromagnetic wave absorbing member having excellent curved surface followability and maintenance of electromagnetic wave absorbing properties after a heat resistance test.

[0012] (II) Technical solution

[0013] The present invention provides the following electromagnetic wave absorbing member.

[0014] [1] An electromagnetic wave absorbing member comprising an electromagnetic wave absorbing layer, an isolation layer, and a reflecting layer stacked in this order, wherein the isolation layer has a relative dielectric constant of 5 or more and a melting point of 150° C. or more.

[0015] [2] The electromagnetic wave absorbing member according to [1], wherein the thickness of the isolation layer is not less than 200 μm and not more than 450 μm.

[0016] [3] The electromagnetic wave absorbing member according to [1] or [2], wherein the Young's modulus of the isolation layer is 50 MPa or more.

[0017] [4] The electromagnetic wave absorbing member according to any one of [1] to [3], wherein the bending rigidity of the electromagnetic wave absorbing member is 300 N·mm 2 the following.

[0018] (III) Beneficial effects

[0019] According to the present invention, it is possible to provide an electromagnetic wave absorbing member which is excellent in curved surface followability and maintenance of electromagnetic wave absorbing performance after a heat resistance test. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a cross-sectional view schematically showing an electromagnetic wave absorbing member according to an embodiment of the present invention, taken along a thickness direction.

[0021] Figure 2 This is a plan view showing an example of an electromagnetic wave absorbing layer constituting the electromagnetic wave absorbing member according to one embodiment of the present invention.

[0022] Figure 3 It is a schematic diagram showing a method for measuring the bending rigidity of the electromagnetic wave absorbing member according to one embodiment of the present invention. DETAILED DESCRIPTION

[0023] This specific embodiment is specifically described for better understanding of the gist of the electromagnetic wave absorbing member of the present invention. Unless otherwise specified, the present invention is not limited to this specific embodiment.

[0024] In this specification, an "electromagnetic wave absorption pattern" is a collection of geometrical units and refers to an object that selectively absorbs electromagnetic waves of frequencies within a specific range. That is, an "electromagnetic wave absorption pattern" has the same function as a so-called antenna.

[0025] In this specification, "electromagnetic waves in the millimeter wave region" refer to electromagnetic waves with a wavelength of 1 mm to 10 mm. In other words, "electromagnetic waves in the millimeter wave region" refer to electromagnetic waves with a frequency of 30 GHz to 300 GHz.

[0026] In the present specification, "~" indicating a numerical range means that the numerical values ​​described before and after it are included as the lower limit and the upper limit.

[0027] [Electromagnetic wave absorbing member]

[0028] Figure 1 This is a cross-sectional view schematically showing an electromagnetic wave absorbing member according to an embodiment of the present invention, taken along a thickness direction.

[0029] like Figure 1 As shown, the electromagnetic wave absorbing member 10 of the present embodiment includes an electromagnetic wave absorbing layer 20, an isolation layer 30, and a reflecting layer 40. The electromagnetic wave absorbing layer 20, the isolation layer 30, and the reflecting layer 40 are stacked in this order.

[0030] The reflective layer 40 is disposed on the other surface (back surface) 20b side of the electromagnetic wave absorbing layer 20. The spacer layer 30 is disposed between the electromagnetic wave absorbing layer 20 and the reflective layer 40. That is, the electromagnetic wave absorbing layer 20 and the reflective layer 40 are stacked with the spacer layer 30 interposed therebetween.

[0031] The electromagnetic wave absorbing layer 20 may be a single layer or may be Figure 1 The device shown includes a substrate 21 and an electromagnetic wave absorption pattern 22 formed on the substrate 21 .

[0032] When the electromagnetic wave absorption layer 20 is a single layer, the electromagnetic wave absorption layer 20 is made of the same material as that of the electromagnetic wave absorption pattern 22 described later.

[0033] In the electromagnetic wave absorbing member 10 of the present embodiment, the relative dielectric constant of the isolation layer 30 is 5 or more, preferably 7 or more, more preferably 8 or more, and particularly preferably 9 or more. By setting the relative dielectric constant of the isolation layer 30 to 5 or more, the thickness of the isolation layer 30 can be made thin. As a result, the electromagnetic wave absorbing member 10 can have excellent curved surface followability.

[0034] From the viewpoint of preventing the Young's modulus of the isolation layer 30 from becoming too high, the upper limit of the relative dielectric constant of the isolation layer 30 may be 30 or less, 25 or less, 20 or less, or 15 or less.

[0035] The relative dielectric constant of the isolation layer 30 can be measured by the method described in the examples described later.

[0036] In the electromagnetic wave absorbing member 10 of the present embodiment, the melting point of the insulating layer 30 is 150° C. or higher, preferably 160° C. or higher, and more preferably 170° C. or higher. In addition, the melting point of the insulating layer 30 refers to the melting point of the material constituting the insulating layer 30. When the melting point of the insulating layer 30 is lower than the lower limit, the relative dielectric constant of the insulating layer 30 changes after the heat resistance test, and the performance of the insulating layer 30 is reduced. From the perspective of preventing the Young's modulus of the insulating layer 30 from becoming too high, the upper limit of the melting point of the insulating layer 30 may be 400° C. or lower, 300° C. or lower, 240° C. or lower, and further 190° C. or lower.

[0037] The melting point of the isolation layer 30 can be measured by the method described in Examples below.

[0038] In the electromagnetic wave absorbing member 10 of the present embodiment, the thickness of the spacer layer 30 is preferably 200 μm to 450 μm, more preferably 250 μm to 400 μm, and particularly preferably 300 μm to 340 μm. If the thickness of the spacer layer 30 is above the lower limit, it is easy to obtain the spacer layer 30 having a high relative dielectric constant. If the thickness of the spacer layer 30 is below the upper limit, the bending rigidity of the spacer layer 30 is low, and the curved surface followability of the spacer layer 30 is improved.

[0039] When the wavelength shortening effect of the spacer layer 30 is taken into consideration, the thickness of the spacer layer 30 can be appropriately changed according to the wavelength of the electromagnetic wave to be absorbed and the relative dielectric constant of the spacer layer 30 .

[0040] When the wavelength shortening effect of the spacer layer 30 is taken into consideration, it is preferred that the thickness of the spacer layer 30 satisfy the following formula (1).

[0041] (Thickness of the isolation layer 30) = (λ) × (1 / 4) / (ε) 1 / 2 Formula (1)

[0042] In the above formula (1), λ is the wavelength of the transmitted electromagnetic wave, and ε is the relative dielectric constant of the isolation layer 30. The thickness of the isolation layer 30 can be appropriately adjusted according to the absorption characteristics. For example, it can be changed within the range of 0.1 to 3.0 times the thickness of the isolation layer 30 obtained by formula (1).

[0043] When the relationship between the thickness of the isolation layer 30 and the wavelength λ satisfies the above formula (1), the electromagnetic wave absorbing member 10 has a so-called λ / 4 structure. As a result, the maximum value of the amount of electromagnetic wave absorption by the electromagnetic wave absorbing member 10 becomes higher.

[0044] The thickness of the spacer layer 30 can be appropriately set within a range of 200 μm to 450 μm, both inclusive, according to the wavelength λ of the electromagnetic wave to be absorbed.

[0045] The isolation layer 30 may be made of a material with a high dielectric constant. If the isolation layer 30 is a layer with a high dielectric constant, the thickness of the isolation layer 30 can be made relatively thin.

[0046] In consideration of the dielectric constant of the isolation layer 30 , the isolation layer 30 preferably includes at least one selected from the group consisting of barium titanate, titanium oxide, and strontium titanate.

[0047] The thickness of the isolation layer 30 can be measured by a constant pressure thickness gauge manufactured by Teclock.

[0048] The Young's modulus of the isolation layer 30 is preferably 1000 MPa or less, more preferably 600 MPa or less, and further preferably 400 MPa or less. If the Young's modulus of the isolation layer 30 is below the upper limit, the curved surface tracking property is improved. From the perspective of shape retention, the lower limit of the Young's modulus of the isolation layer 30 may be 50 MPa or more, 100 MPa or more, or 200 MPa or more.

[0049] The Young's modulus of the separation layer 30 can be measured in accordance with JIS K7127:1999 "Plastics-Determination of tensile properties-Part 3: Test conditions for films and sheets".

[0050] The electromagnetic wave absorbing member 10 of this embodiment preferably has a bending rigidity of 240 N·mm 2 Below, more preferably 180N·mm 2 Below, more preferably 100 N·mm 2 If the bending rigidity of the electromagnetic wave absorbing member 10 is below the upper limit, the curved surface following property is improved. From the viewpoint of shape maintenance, the lower limit of the bending rigidity of the electromagnetic wave absorbing member 10 may be 10 N·mm 2 Above, 30N·mm is also possible 2 Above, can also be 60N·mm 2 above.

[0051] The bending rigidity of the electromagnetic wave absorbing member 10 can be measured by the method described in the examples to be described later.

[0052] In addition, from the perspective of balancing curved surface tracking properties and electromagnetic wave absorption properties, the total thickness of the electromagnetic wave absorption component 10 of the present embodiment (the total thickness from the outermost surface of the electromagnetic wave absorption layer 20, that is, the surface of the electromagnetic wave absorption pattern 22 (one surface (surface) 20a of the electromagnetic wave absorption layer 20) to the surface (the other surface) 40b of the setting surface side of the reflective layer 40) is preferably 350μm~800μm, more preferably 400μm~600μm, and particularly preferably 450μm~520μm.

[0053] "Electromagnetic wave absorption layer"

[0054] The electromagnetic wave absorbing layer 20 is composed of a frequency selective surface (FSS). The frequency selective surface is formed of a conductive member or the like and has a continuous structure having a shape equal to or smaller than a specific wavelength. The frequency selective surface can shield only electromagnetic waves of a specific frequency.

[0055] Figure 2 FIG. 2 is a top view showing an example of the electromagnetic wave absorbing layer in this embodiment. Figure 2 As shown, the electromagnetic wave absorption layer 20 is an electromagnetic wave absorption film including a flat substrate 21 and an electromagnetic wave absorption pattern 22 formed on one surface 21a of the substrate 21. The electromagnetic wave absorption pattern 22 includes a first electromagnetic wave absorption pattern 51, a second electromagnetic wave absorption pattern 52, and a third electromagnetic wave absorption pattern 53.

[0056] The Young's modulus of the electromagnetic wave absorbing layer 20 is preferably 10 GPa or less, more preferably 7 GPa or less, and further preferably 5 GPa or less. If the Young's modulus of the electromagnetic wave absorbing layer 20 is below the upper limit, the bending rigidity is reduced and the curved surface tracking property is improved. From the perspective of shape retention, the lower limit of the Young's modulus of the electromagnetic wave absorbing layer 20 may be 0.5 GPa or more, 1 GPa or more, or 3 GPa or more.

[0057] The Young's modulus of the electromagnetic wave absorbing layer 20 can be measured in accordance with JIS K7127:1999 "Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets".

[0058] (First electromagnetic wave absorption pattern)

[0059] like Figure 2 As shown, the first electromagnetic wave absorption pattern 51 is composed of a plurality of first units u1. Each of the first units u1 is a geometric shape.

[0060] That is, the first electromagnetic wave absorption pattern 51 can also be said to be an aggregate of first units u1 of geometric figures.

[0061] Each of the first units u1 functions as an antenna. The first electromagnetic wave absorption pattern 51 may be, for example, a thin line pattern of an FSS element.

[0062] In the first electromagnetic wave absorption pattern 51, a plurality of first arrays R1 are formed. The first array R1 is composed of a plurality of first units u1 along Figure 2That is, the first electromagnetic wave absorption pattern 51 includes a plurality of first arrays R1. The first electromagnetic wave absorption pattern 51 can be configured as follows: a plurality of first arrays R1 are formed on the substrate 21 along the direction indicated by the double arrow P at predetermined intervals.

[0063] There is no particular limitation on the intervals between the plurality of first arrays R1. The intervals between the first arrays R1 may be regular or irregular.

[0064] like Figure 2 As shown in FIG. 1 , the shape of the first unit u1 is a cross shape that is symmetrical in both vertical and horizontal directions. Specifically, the first unit u1 includes a cross portion S1 and four end portions T1. The cross portion S1 is composed of Figure 2 The straight line portion parallel to the x-axis direction and the straight line portion parallel to the y-axis direction are formed. Each straight line end T1 is connected to 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 in a manner orthogonal to each straight line portion.

[0065] 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 an antenna can be adjusted. The electromagnetic wave absorption characteristics in the y-axis direction can also be adjusted in the same manner.

[0066] However, the shape of the first unit is not limited to a cross shape, and is not particularly limited as long as the value of the frequency at which the absorption amount of electromagnetic waves absorbed by the first electromagnetic wave absorption pattern 51 shows a local maximum value is A [GHz].

[0067] For example, the shape of the first unit graphic may be a circle, a ring, a straight line, a rectangle, a polygon, an H shape, a Y shape, a V shape, or the like.

[0068] In the electromagnetic wave absorption layer 20, the shapes of the plurality of first units u1 are the same as each other. However, the shapes of the plurality of first units u1 may not be the same as each other. In other embodiments of the present invention, the shapes of the plurality of first units may be the same as each other or different from each other as long as the absorption characteristics can be adjusted for the target frequency.

[0069] The first electromagnetic wave absorption pattern 51 selectively absorbs electromagnetic waves of a frequency of A [GHz]. The frequency value A [GHz] is a value of a frequency when the absorption amount of electromagnetic waves absorbed by the first electromagnetic wave absorption pattern 51 shows a maximum value in the range of 20 GHz to 110 GHz.

[0070] The value A [GHz] of the frequency at which the absorption amount of the electromagnetic wave absorbed by the first electromagnetic wave absorption pattern 51 shows a local maximum value can be determined by, for example, the following method X.

[0071] Method X: While changing the frequency within the range of 20 GHz to 110 GHz, the standard film described below is irradiated with electromagnetic waves, and the frequency of the electromagnetic waves when the absorption amount of the electromagnetic waves absorbed by the standard film reaches a maximum is defined as A [GHz].

[0072] The standard film includes a flat standard substrate and a standard pattern formed on the standard substrate.

[0073] The details of the standard substrate can be the same as those of the substrate 21. Therefore, the details of the standard substrate will be described in detail in the description of the substrate 21 to be described later.

[0074] The standard pattern is composed of a plurality of standard units of graphics having the same shape. That is, in the standard film, a standard pattern composed of only one type of graphics having the same shape is formed on a standard substrate. The standard pattern can be formed by a fine line pattern of a conventional FSS element. Typically, the standard pattern is the same electromagnetic wave absorption pattern as the first electromagnetic wave absorption pattern 51 (having the same shape as the unit u1).

[0075] In the standard film, a plurality of standard units are arranged on a standard substrate in such a way that the interval between the ends of the pattern is 1 mm. For example, when the pattern of the standard unit is a cross, the intersection of the cross is the center of the pattern, and the ends of the pattern are the parts farthest from the center along the directions of the two straight line parts constituting the cross.

[0076] The material of the standard unit constituting the standard pattern is not particularly limited as long as the amount of electromagnetic waves absorbed by the standard film reaches a maximum value when the standard film is irradiated with electromagnetic waves while changing the frequency within the range of 20 GHz to 110 GHz.

[0077] The details of the material of the standard unit can be the same as those of the first unit.

[0078] The amount of electromagnetic waves absorbed by the standard film can be calculated by the following formula (2).

[0079] Absorption amount = input signal - reflection characteristic (S11) - transmission characteristic (S21)...(2)

[0080] The input signal is an index of the intensity of the electromagnetic wave from the irradiation source when the standard film is irradiated with the electromagnetic wave.

[0081] The reflection characteristic (S11) is an index of the intensity of electromagnetic waves reflected by the reference film when the reference film is irradiated with electromagnetic waves from an irradiation source. The reflection characteristic (S11) can be measured by a free space method using a vector network analyzer, for example.

[0082] The transmission characteristic (S21) is an index of the intensity of electromagnetic waves transmitted through the standard film when the standard film is irradiated with electromagnetic waves from an irradiation source. The transmission characteristic (S21) can be measured by a free space method using a vector network analyzer, for example.

[0083] The frequency A [GHz] can be determined by, for example, the following method.

[0084] First, electromagnetic waves are irradiated onto the standard film while changing the frequency within the range of 20 GHz to 110 GHz, and the absorption amount of the electromagnetic waves absorbed by the standard film is calculated from the above formula (2).

[0085] Next, an absorption spectrum is prepared, in which the changing frequency is plotted on the horizontal axis and the absorption amount calculated by the above formula (2) is plotted on the vertical axis. Usually, in the absorption spectrum, there is a value of the frequency at which the absorption amount reaches a maximum value on the horizontal axis. Therefore, in the plotted diagram, a single peak is formed at which the absorption amount of the electromagnetic wave reaches a maximum value. Thus, the frequency of the electromagnetic wave when the absorption amount of the electromagnetic wave reaches a maximum value can be taken as A [GHz].

[0086] In method X, when the value of frequency A can be predicted in advance, the frequency of the electromagnetic wave irradiated to the standard film can be changed within a narrower range than 20 GHz to 110 GHz. For example, the frequency of the electromagnetic wave irradiated to the standard film can be changed within a range of 50 GHz to 110 GHz.

[0087] The first electromagnetic wave absorption pattern 51 absorbs electromagnetic waves having a frequency of A [GHz] determined by the above-described method X.

[0088] For the electromagnetic wave absorbing layer 20 in this embodiment, the frequency value A is preferably 20 GHz to 110 GHz, more preferably 60 GHz to 100 GHz, further preferably 65 GHz to 95 GHz, and particularly preferably 70 GHz to 90 GHz. If the frequency value A is within the numerical range, the electromagnetic wave absorbing layer 20 can absorb electromagnetic waves in the millimeter wave region, and can be easily applied to automotive parts, road peripheral components, building exterior wall related materials, windows, communication equipment, radio telescopes, etc.

[0089] The material of the first unit u1 is not particularly limited as long as the absorption characteristics can be adjusted for the target frequency.

[0090] Examples of the material of the first unit include metal thin wires, conductive films, and conductive paste fixtures.

[0091] Examples of the metal material include copper, aluminum, tungsten, iron, molybdenum, nickel, titanium, silver, gold, or alloys containing two or more of these metals (for example, stainless steel, carbon steel and other steels, brass, phosphor bronze, zirconium-copper alloy, beryllium copper, iron-nickel, nickel-chromium alloy, nickel-titanium, iron-chromium-aluminum alloy (Kanthal), Hastelloy, rhenium-tungsten, etc.).

[0092] Examples of the material of the conductive film include metal particles, carbon nanoparticles, and carbon fibers.

[0093] The interval between the ends of the pattern serving as the first unit u1 is not particularly limited as long as the absorption characteristics can be adjusted for a target frequency.

[0094] For example, the intervals between the ends of the graphics as the first unit u1 may be all the same or different from each other. However, in order to facilitate the design of an electromagnetic wave absorbing film that is not easily affected by the surrounding environment and to improve the accuracy of the frequency band of the absorbed electromagnetic waves during manufacturing, the intervals between the ends of the graphics as the first unit u1 are preferably the same.

[0095] (Second electromagnetic wave absorption pattern)

[0096] like Figure 2 As shown, the second electromagnetic wave absorption pattern 52 is composed of a plurality of second units u2.

[0097] The second electromagnetic wave absorption pattern 52 is formed in the same manner as the first electromagnetic wave absorption pattern 51 .

[0098] The second electromagnetic wave absorption pattern 52 selectively absorbs electromagnetic waves having a frequency of B [GHz] satisfying the following formula (3). The frequency value B [GHz] is the frequency value when the absorption amount of electromagnetic waves absorbed by the second electromagnetic wave absorption pattern 52 shows a maximum value. The frequency value B [GHz] satisfies the following formula (3).

[0099] 1.037×A≤B≤1.30×A···Formula (3)

[0100] As shown in the above formula (3), the second electromagnetic wave absorption pattern 52 absorbs electromagnetic waves with a frequency of 1.037×A[GHz] to 1.30×A[GHz]. The second electromagnetic wave absorption pattern 52 preferably absorbs electromagnetic waves with a frequency of 1.17×A[GHz] to 1.30×A[GHz].

[0101] The second electromagnetic wave absorption pattern 52 absorbs electromagnetic waves with a frequency of 1.037×A [GHz] or more. Therefore, in the frequency band higher than A [GHz], the peak of the electromagnetic wave absorption amount based on the second electromagnetic wave absorption pattern 52 fully overlaps with the peak of the electromagnetic wave absorption amount based on the first electromagnetic wave absorption pattern 51. As a result, the frequency band of electromagnetic waves that can be absorbed by the electromagnetic wave absorption film as a whole is expanded to the frequency band higher than A [GHz] compared to the film having the first electromagnetic wave absorption pattern 51 alone.

[0102] The second electromagnetic wave absorption pattern 52 absorbs electromagnetic waves with a frequency of 1.30×A [GHz] or less. Therefore, in the frequency band higher than A [GHz], the difference in frequency between the peak of the electromagnetic wave absorption amount based on the second electromagnetic wave absorption pattern 52 and the peak of the electromagnetic wave absorption amount based on the first electromagnetic wave absorption pattern 51 becomes smaller. As a result, a single peak is formed at which the absorption amount of electromagnetic waves absorbed by the entire electromagnetic wave absorption film reaches a maximum value.

[0103] In summary, since the second electromagnetic wave absorption pattern 52 absorbs electromagnetic waves with a frequency of 1.037×A [GHz] to 1.30×A [GHz], the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorption film is expanded to a frequency band on the high frequency side.

[0104] The material of the second unit constituting the second electromagnetic wave absorption pattern 52 is not particularly limited as long as it is capable of absorbing electromagnetic waves of B [GHz], and is not particularly limited as long as the absorption characteristics can be adjusted for a target frequency.

[0105] The material of the second unit is the same as that described for the material of the first unit u1.

[0106] (Third electromagnetic wave absorption pattern)

[0107] like Figure 2 As shown, the third electromagnetic wave absorption pattern 53 is composed of a plurality of third units u3.

[0108] The third electromagnetic wave absorption pattern 53 is formed in the same manner as the first electromagnetic wave absorption pattern 51 .

[0109] The third electromagnetic wave absorption pattern 53 selectively absorbs electromagnetic waves having a frequency of C [GHz] satisfying the following formula (4). The frequency value C [GHz] is the frequency value when the absorption amount of electromagnetic waves absorbed by the third electromagnetic wave absorption pattern 53 shows a maximum value. The frequency value C [GHz] satisfies the following formula (4).

[0110] 0.60×A≤C≤0.963×A···Formula (4)

[0111] As shown in the above formula (4), the third electromagnetic wave absorption pattern 53 absorbs electromagnetic waves with a frequency of 0.60×A[GHz] to 0.963×A[GHz]. The third electromagnetic wave absorption pattern 53 preferably absorbs electromagnetic waves with a frequency of 0.60×A[GHz] to 0.83×A[GHz].

[0112] The third electromagnetic wave absorption pattern 53 absorbs electromagnetic waves with a frequency of 0.60×A [GHz] or more. Therefore, in the frequency band lower than A [GHz], the difference in frequency between the peak of the electromagnetic wave absorption amount based on the third electromagnetic wave absorption pattern 53 and the peak of the electromagnetic wave absorption amount based on the first electromagnetic wave absorption pattern 51 becomes smaller. As a result, a single peak is formed at which the absorption amount of electromagnetic waves absorbed by the entire electromagnetic wave absorption layer 20 reaches a maximum value.

[0113] The third electromagnetic wave absorption pattern 53 absorbs electromagnetic waves with a frequency of 0.963×A [GHz] or less. Therefore, in the frequency band below A [GHz], the peak of the absorption amount of electromagnetic waves based on the third electromagnetic wave absorption pattern 53 fully overlaps with the peak of the absorption amount of electromagnetic waves based on the first electromagnetic wave absorption pattern 51. As a result, the frequency band of electromagnetic waves that can be absorbed by the electromagnetic wave absorption film as a whole is expanded to the frequency band on the side below A [GHz] compared to the film having the first electromagnetic wave absorption pattern 51 alone.

[0114] In summary, since the third electromagnetic wave absorption pattern 53 absorbs electromagnetic waves with a frequency of 0.60×A [GHz] to 0.963×A [GHz], the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorption layer 20 is expanded to a frequency band on the low frequency side.

[0115] The material of the third unit u3 constituting the third electromagnetic wave absorption pattern 53 is not particularly limited as long as it is in a form capable of absorbing electromagnetic waves of C [GHz], and is not particularly limited as long as the absorption characteristics can be adjusted for a target frequency.

[0116] The material of the third unit u3 is the same as that described for the material of the first unit u1.

[0117] exist Figure 2In the electromagnetic wave absorption layer 20 shown, the first array R1, the second array R2, and the third array R3 are arranged in a manner adjacent to each other in the direction indicated by the double arrow P. Thus, the first array R1, the second array R2, and the third array R3 are arranged on the substrate 21 in a manner adjacent to each other. Therefore, based on the value A [GHz] of the frequency of the peak position of the electromagnetic wave selectively absorbed by the first electromagnetic wave absorption pattern 51, the frequency band of the electromagnetic wave selectively absorbed by the second electromagnetic wave absorption pattern 52 and the frequency band of the electromagnetic wave selectively absorbed by the third electromagnetic wave absorption pattern 53 overlap. As a result, the absorption region of the electromagnetic wave absorbed by the electromagnetic wave absorption layer 20 as a whole is easily expanded to both the high frequency side and the low frequency side based on the value A [GHz] of the frequency of the peak position.

[0118] Figure 2 The interval d1 between the first unit u1 and the second unit u2, the interval d2 between the second unit u2 and the third unit u3, and the interval d3 between the third unit u3 and the first unit u1 shown in the figure may be the same as or different from each other.

[0119] The interval d1 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm.

[0120] The interval d2 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm.

[0121] The interval d3 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm.

[0122] When the intervals d1 , d2 , and d3 are within the above numerical ranges, the absorption region of electromagnetic waves absorbed by the entire electromagnetic wave absorption layer 20 is more likely to be expanded based on the value A [GHz] of the frequency at the peak position.

[0123] In the electromagnetic wave absorbing layer 20, the shapes of the first unit u1, the second unit u2, and the third unit u3 are the same as each other. However, the shapes of the first unit u1, the second unit u2, and the third unit u3 may not be the same as each other. That is, in other examples of the present invention, the shapes of the first unit u1, the second unit u2, and the third unit u3 may be the same as each other or different from each other.

[0124] The substrate 21 is not particularly limited as long as it is a flat plate and has a form on one surface 21a of which the first electromagnetic wave absorption pattern 51, the second electromagnetic wave absorption pattern 52, and the third electromagnetic wave absorption pattern 53 can be formed. The substrate 21 may have a single-layer structure or a multi-layer structure.

[0125] The thickness of the substrate 21 may be, for example, 5 μm to 500 μm, 15 μm to 200 μm, or 25 μm to 100 μm.

[0126] The thickness of the first electromagnetic wave absorption pattern 51, the thickness of the second electromagnetic wave absorption pattern 52, and the thickness of the third electromagnetic wave absorption pattern 53 are not particularly limited. These thicknesses can be arbitrarily changed according to the required characteristics. In addition, these three thicknesses can be the same as each other or different from each other. Considering productivity, they are preferably the same. In addition, from the perspective of balancing electromagnetic wave absorbency and curved surface tracking, the thickness of the first electromagnetic wave absorption pattern 51, the second electromagnetic wave absorption pattern 52, and the third electromagnetic wave absorption pattern 53 is preferably 0.1μm~300μm, more preferably 1μm~150μm, and particularly preferably 10μm~80μm.

[0127] The material of the base material 21 can be appropriately selected according to the application of the electromagnetic wave absorbing member 10 .

[0128] For example, when the purpose is to make the electromagnetic wave absorbing member 10 transparent, the substrate 21 may be made of a transparent material. In addition, when the purpose is to make the electromagnetic wave absorbing member 10 have the ability to follow a curved surface, the substrate 21 may be made of a flexible material. When the purpose is to improve the transparency and three-dimensional formability of the electromagnetic wave absorbing member 10, the surface of the substrate 21 may be made smooth.

[0129] For example, the base material 21 may be made of a resin. The resin may be a thermoplastic resin or a thermosetting resin. However, in consideration of the three-dimensional moldability of the electromagnetic wave absorbing member 10, the base material 21 preferably includes a thermoplastic resin.

[0130] Examples of the thermoplastic resin include polyolefin resins, polyester resins, polyester-polyether resins, polyacrylic resins, polystyrene resins, polyimide resins, polyimideamide resins, polyamide resins, polyurethane resins, polycarbonate resins, polyarylate resins, melamine resins, epoxy resins, urethane resins, silicone resins, and fluororesins.

[0131] Specific examples of the polyolefin resin include polypropylene, polyethylene, etc. Specific examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.

[0132] The substrate 21 may contain any component within a range that does not impair the effects of the present invention. Examples of the optional component include inorganic fillers, colorants, curing agents, antioxidants, light stabilizers, flame retardants, conductive agents, antistatic agents, plasticizers, and the like.

[0133] The thickness, dielectric constant, electrical conductivity, and magnetic permeability of the base material 21 can be appropriately set in consideration of further improving the electromagnetic wave absorption performance of the electromagnetic wave absorbing member 10 .

[0134] In consideration of the electrical properties of electromagnetic waves to be absorbed, the substrate 21 may be a layer having a high dielectric constant. If the substrate 21 is a layer having a high dielectric constant, the thickness of the electromagnetic wave absorbing member 10 can be made relatively thin.

[0135] The electromagnetic wave absorbing layer 20 can be produced by, for example, the following method.

[0136] First, the substrate 21 is prepared. Next, the first electromagnetic wave absorption pattern 51 , the second electromagnetic wave absorption pattern 52 , and the third electromagnetic wave absorption pattern 53 are formed on one surface 21 a of the substrate 21 .

[0137] When forming each electromagnetic wave absorption pattern, it is formed so that the value of the frequency at which the absorption amount of electromagnetic waves absorbed by each electromagnetic wave absorption pattern shows a local maximum value becomes a predetermined value [GHz].

[0138] The order of forming the electromagnetic wave absorption patterns is not particularly limited. The electromagnetic wave absorption patterns may be formed in the same process or in different processes.

[0139] There is no particular limitation on the method for forming each electromagnetic wave absorption pattern as long as it is a method that can form a predetermined frequency. Examples of the method for forming each electromagnetic wave absorption pattern include the following methods.

[0140] A printing method in which each electromagnetic wave absorption pattern is printed on one surface 21 a of the substrate 21 using a conductive paste.

[0141] A developing method for developing each electromagnetic wave absorption pattern on one surface 21 a of the substrate 21 .

[0142] A method in which a metal thin film is provided on one surface 21 a of the substrate 21 by sputtering, vacuum deposition or lamination of metal foil, and a pattern of the metal thin film is formed on the one surface 21 a of the substrate 21 by photolithography.

[0143] A method of disposing a metal wire on one surface 21 a of a substrate 21 .

[0144] "Isolation layer"

[0145] The isolation layer 30 is provided on the other surface 21 b of the substrate 21 included in the electromagnetic wave absorbing layer 20 .

[0146] The spacer layer 30 has two surfaces, namely, surfaces 30a and 30b. One surface 30a of the spacer layer 30 faces the other surface 21b of the substrate 21. The reflective layer 40 is provided on the other surface 30b of the spacer layer 30.

[0147] The isolation layer 30 may be a single-layer structure or a multi-layer structure.

[0148] The material of the isolation layer 30 can be appropriately selected according to the application. For example, when used for automobile exterior, it is preferable to select a material that has the ability to follow a curved surface and has excellent heat resistance.

[0149] Examples of the flexible material include plastic films, nonwoven fabrics, rubber sheets, etc. Among them, plastic films are preferred because they can be easily kneaded with fillers.

[0150] As a specific example of the resin constituting the plastic film, for example, a resin having a high melting point among the thermoplastic resins described above for the base material 21 can be used.

[0151] The spacer layer 30 may contain a filler. The filler is not particularly limited as long as it has a high dielectric constant, and examples thereof include barium titanate, strontium titanate, calcium titanate, titanium oxide, and the like.

[0152] The content of the filler in the isolation layer 30 is preferably 20% by volume or more and 60% by volume or less, more preferably 25% by volume or more and 50% by volume or less, and particularly preferably 30% by volume or more and 45% by volume or less. If the content of the filler is greater than the upper limit, the isolation layer 30 becomes brittle and sometimes it is difficult to manufacture the isolation layer 30. If the content of the filler is less than the lower limit, the thickness required for the isolation layer 30 to obtain the necessary electromagnetic wave absorptivity becomes too thick, and sometimes it is impossible to obtain curved surface tracking properties.

[0153] It is preferable to provide adhesive layers on two surfaces, namely, surfaces 30a and 30b, of the spacer layer 30. This makes it easy to bond the electromagnetic wave absorbing layer 20 and the reflecting layer 40 to the two surfaces, namely, surfaces 30a and 30b, respectively.

[0154] The details and preferred embodiments of the adhesive layer can be the same as those described for the adhesive layer in the reflective layer described later.

[0155] "Reflection Layer"

[0156] The reflective layer 40 has two surfaces, namely, surfaces 40 a and 40 b . One surface 40 a of the reflective layer 40 faces the other surface 30 b of the spacer layer 30 .

[0157] The reflective layer 40 is not particularly limited as long as it is in a form that can reflect the electromagnetic waves transmitted to the surface of the electromagnetic wave absorbing member 10 and transmitted through the electromagnetic wave absorbing member 10. A portion of the electromagnetic waves transmitted to the electromagnetic wave absorbing member 10 is reflected by the electromagnetic wave absorbing layer 20 or absorbed by the electromagnetic wave absorbing layer 20. On the other hand, the electromagnetic waves that are not reflected or absorbed by the electromagnetic wave absorbing layer 20 transmit the electromagnetic wave absorbing layer 20. The electromagnetic waves that have transmitted the electromagnetic wave absorbing layer 20 are reflected toward the electromagnetic wave absorbing layer 20 at the reflective layer 40.

[0158] For example, as long as the reflective layer 40 is in a form that has conductivity in the direction of either of the two surfaces, namely, the surfaces 40a and 40b, the electromagnetic waves that have passed through the electromagnetic wave absorption layer 20 can be reflected. Specifically, a structure formed by laminating a metal foil such as aluminum foil or copper foil, or a metal plate such as a copper plate, on a resin film such as polyethylene terephthalate can be used as the reflective layer 40. A mesh formed by a transparent conductive film such as ITO (indium tin oxide) or a metal wire, which replaces the metal foil or the metal plate, can also be used. Among them, a metal plate is preferred in terms of the high or low conductivity.

[0159] Considering the reflective properties of the reflective layer 40, metal wires, conductive threads, twisted wires including metal wires and conductive threads, and conductive films may be provided on the other side 40b of the reflective layer 40. The conductive film may be provided on the side 40b by printing methods such as screen printing, gravure printing, and inkjet printing; sputtering or vacuum evaporation; or photolithography.

[0160] The Young's modulus of the reflective layer 40 is preferably 6 GPa or less, more preferably 5.5 GPa or less, and further preferably 5 GPa or less. If the Young's modulus of the reflective layer 40 is below the upper limit, the curved surface tracking property is improved. The lower limit of the Young's modulus of the reflective layer 40 may be 0.5 GPa or more, 1 GPa or more, or 3 GPa or more.

[0161] The Young's modulus of the reflective layer 40 can be measured in accordance with JIS K7127:1999 "Plastics-Determination of tensile properties-Part 3: Test conditions for films and sheets".

[0162] When the spacer layer 30 is formed on a conductive object such as metal, the conductive object such as metal functions as the reflective layer 40. Therefore, the reflective layer 40 can be omitted.

[0163] When the electromagnetic wave absorbing member 10 is applied to the surface of various articles, an adhesive layer may be provided on the other side 40b of the reflecting layer 40. When the adhesive layer is provided on the other side 40b of the reflecting layer 40, a release film may be provided on the side of the adhesive layer opposite to the side in contact with the same side 40b. The release film is removed when the electromagnetic wave absorbing member 10 is used. By covering the adhesive surface with the release film, the operability during distribution becomes good.

[0164] Examples of the adhesive constituting the adhesive layer include heat-seal adhesives that adhere by heat, adhesives that exhibit adhesion by wetting, and pressure-sensitive adhesives (adhesives) that adhere by pressure. Among them, adhesives (pressure-sensitive adhesives) are preferred from the perspective of simplicity.

[0165] Specific examples of the adhesive include acrylic adhesives, urethane adhesives, rubber adhesives, polyester adhesives, silicone adhesives, polyvinyl ether adhesives, etc. Among them, at least one selected from the group consisting of acrylic adhesives, urethane adhesives, and rubber adhesives is preferred, and acrylic adhesives are more preferred.

[0166] Furthermore, the electromagnetic wave absorbing member 10 of the present embodiment may include a protective layer formed on one surface (surface) 20 a of the electromagnetic wave absorbing layer 20 .

[0167] The protective layer is not particularly limited as long as it can protect the electromagnetic wave absorbing layer 20 .

[0168] According to the electromagnetic wave absorbing member 10 of the present embodiment, since the relative dielectric constant of the spacer layer 30 is 5 or more and the melting point of the spacer layer 30 is 150° C. or more, the curved surface following property and the electromagnetic wave absorbing property after the heat resistance test are excellently maintained. If a low melting point resin is used as a resin constituting the spacer layer, the thickness of the spacer layer and the distribution of the filler contained in the spacer layer will change due to the heat resistance test, and the electromagnetic wave absorbing property will decrease.

[0169] The electromagnetic wave absorbing member 10 of this embodiment has excellent shape retention because the Young's modulus of the spacer layer 30 is 50 MPa or more. Here, excellent shape retention means that the film thickness does not change even under thermal or mechanical action, and the electromagnetic wave absorbency does not change.

[0170] Example

[0171] Hereinafter, the present invention will be further specifically described by way of Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0172] [Example 1]

[0173] "Manufacturing of electromagnetic wave absorbing members"

[0174] An electromagnetic wave absorbing member was produced as follows.

[0175] Copper was vapor-deposited on a substrate composed of a PET film (trade name: PET50A4160, manufactured by TOYOBO CO., LTD.) having a thickness of 50 μm to form a copper thin film.

[0176] Then, the copper film is patterned into an electromagnetic wave absorption pattern by photolithography to form a Figure 2 The electromagnetic wave absorption pattern shown was obtained to obtain an electromagnetic wave absorption layer having the electromagnetic wave absorption pattern. The thickness of the electromagnetic wave absorption pattern was set to 20 μm.

[0177] Next, a laboratory mixing extruder (Labo Plastomill) (model: 4C150, manufactured by Toyo Seiki Seisaku-sho, Ltd.) was used to mix the polyester-polyether copolymer as a resin (trade name: P-55B, manufactured by TOYOBO CO., LTD.) and the barium titanate as a filler (trade name: BT-UP2, manufactured by Nippon Chemical Industrial CO., LTD.) at 200°C and 40 rpm for 5 minutes to prepare a mixed material with a barium titanate content of 40 volume%.

[0178] The mixed material was pressed at 200° C. for 3 minutes using a hydraulic heating press (model: SA-302, manufactured by TESTER SANGYO CO., LTD.) to obtain a separation layer with a thickness of 300 μm.

[0179] As the material of the adhesive layer, an acrylic copolymer having a weight average molecular weight of 800,000 formed by 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. To 100 parts by mass (solid content conversion value) of the acrylic copolymer, 1 part by mass (solid content conversion value) of an isocyanate crosslinking agent and 8 parts by mass of an ultraviolet absorber (trade name: Tinuvin 477, manufactured by BASF Japan Ltd.) were added, and diluted with ethyl acetate to prepare an acrylic adhesive solution.

[0180] Next, the acrylic adhesive solution was applied onto a release film, dried at 90° C. for 1 minute, and aged at room temperature for 1 week to obtain an adhesive layer having a thickness of 20 μm.

[0181] Next, the adhesive layer is laminated on one surface of the release layer.

[0182] Next, a 50 μm thick Metalmy TS (a film obtained by vapor-depositing aluminum on a PET film) manufactured by TORAY ADVANCED FILM CO., LTD. was prepared as a reflective layer, and the film was laminated so that the adhesive layer covered both surfaces of the film. That is, a laminate of release film / adhesive layer / reflective layer / adhesive layer / release film was obtained.

[0183] Next, the release film on the aluminum-deposited side of the reflective layer was peeled off, and the adhesive layer exposed on the aluminum-deposited side of the reflective layer was arranged to face the surface of the spacer layer opposite to the surface forming the electromagnetic wave absorbing layer.

[0184] Next, the release film on the electromagnetic wave absorbing layer side of the spacer layer was peeled off, and the exposed adhesive layer was laminated on the surface of the electromagnetic wave absorbing layer opposite to the surface having the electromagnetic wave absorbing pattern formed thereon, thereby obtaining an electromagnetic wave absorbing member with an adhesive layer.

[0185] [Example 2]

[0186] An electromagnetic wave absorbing member with an adhesive layer of Example 2 was obtained in the same manner as in Example 1 except that the content of barium titanate in the mixed material for forming the spacer layer was 35 volume % and the thickness of the spacer layer was 350 μm.

[0187] [Example 3]

[0188] An electromagnetic wave absorbing member with an adhesive layer of Example 3 was obtained in the same manner as in Example 1 except that polyester (manufactured by Bell Polyester Products, Inc.) was used as the resin and the thickness of the separator was set to 360 μm.

[0189] [Example 4]

[0190] An electromagnetic wave absorbing member with an adhesive layer of Example 4 was obtained in the same manner as in Example 1 except that the content of barium titanate in the mixed material for forming the spacer layer was 25 volume % and the thickness of the spacer layer was 425 μm.

[0191] [Comparative Example 1]

[0192] An electromagnetic wave absorbing component with an adhesive layer of Comparative Example 1 was obtained in the same manner as in Example 1, except that the resin constituting the mixed material for making the isolation layer was set to ethylene-vinyl acetate copolymer resin (EVA, manufactured by DOW-MITSUI POLYCHEMICALS CO., LTD.), the content of barium titanate in the mixed material was set to 45 volume %, and the thickness of the isolation layer was set to 300 μm.

[0193] [Comparative Example 2]

[0194] An electromagnetic wave absorbing component with an adhesive layer of Comparative Example 2 was obtained in the same manner as in Example 1, except that the resin constituting the mixed material for making the isolation layer was set to low-density polyethylene (LDPE, manufactured by Japan PolyStyrene Inc.), the content of barium titanate in the mixed material was set to 20 volume %, and the thickness of the isolation layer was set to 470 μm.

[0195] [evaluate]

[0196] The following evaluation was performed on the electromagnetic wave absorbing members of Examples 1 to 4 and Comparative Examples 1 and 2. The results are shown in Table 1.

[0197] "Evaluation of relative dielectric constant"

[0198] The relative dielectric constants of the spacer layers obtained in the examples and comparative examples were measured using a dielectric constant measuring device (40 GHz TE mode) manufactured by AET, INC. and a network analyzer (model: MS46122B) manufactured by ANRITSU CORPORATION.

[0199] "Determination of Young's modulus (tensile modulus)"

[0200] The electromagnetic wave absorption layer, the isolation layer and the reflection layer were cut into test pieces of 15 mm in length and 150 mm in width, and the tensile modulus E was measured according to JIS K7127: 1999 "Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets". Specifically, for the above test pieces, a tensile tester (trade name: Autograph AG-IS 500N, manufactured by Shimadzu Corporation) was used, and the chuck spacing was set to 100 mm, and a tensile test was performed at a speed of 200 mm / min to measure the tensile modulus (MPa) of the electromagnetic wave absorption layer, the isolation layer and the reflection layer.

[0201] "Determination of Melting Point"

[0202] The melting point of the isolation layer was measured using DSC (model: Q2000) manufactured by TA Instruments. The measurement conditions were set as follows.

[0203] Heating conditions: 20℃ / min

[0204] Measuring temperature range: -50℃~250℃

[0205] "Heat resistance evaluation"

[0206] The heat resistance test of the isolation layer was carried out using a high temperature hygrostat (model: PHH-102) manufactured by ESPEC CORP. The temperature of the high temperature hygrostat was set to 120°C, and the isolation layer was placed in the high temperature hygrostat for 240 hours. The relative dielectric constant of the isolation layer after being taken out of the high temperature hygrostat was measured to evaluate the change before and after the test.

[0207] "Evaluation of Surface Following Performance"

[0208] The electromagnetic wave absorbing members were attached to curved surfaces having different diameters, and the curved surface conformability of the electromagnetic wave absorbing members was evaluated.

[0209] The minimum diameter (mm) of the curved surface on which the electromagnetic wave absorbing member can be attached without causing appearance defects such as wrinkles or end lifting was evaluated.

[0210] "Evaluation of bending stiffness"

[0211] use Figure 3 And the following formula (11), the bending rigidity of the electromagnetic wave absorbing member is calculated.

[0212] Will Figure 3 The centroid position of the electromagnetic wave absorbing member in is set to y c , the width of the electromagnetic wave absorbing member is denoted as W. Furthermore, the thicknesses of the electromagnetic wave absorbing layer, the isolation layer, and the reflecting layer are denoted as t1, t2, and t3, respectively, and the heights to the centers of the respective layers are denoted as y1, y2, and y3.

[0213] The respective areas (A1, A2, A3) of the electromagnetic wave absorption layer, the isolation layer, and the reflection layer, the overall area A, and y1, y2, y3 are calculated using the following equations (11) to (17).

[0214] A1=W×t1(11)

[0215] A2=W×t2(12)

[0216] A3=W×t3(13)

[0217] A=A1+A2+A3(14)

[0218] y1=t1 / 2 (15)

[0219] y2=t1+t2 / 2 (16)

[0220] y3=t1+t2+t3 / 2 (17)

[0221] Using the values ​​obtained from equations (11) to (17), the centroid y of the electromagnetic wave absorbing member is calculated by the following equation (18):c .

[0222] y c =(A1y1+A2y2+A3y3) / A (18)

[0223] Here, the moments of inertia I1, I2, I3 and I2 related to the centroid of each layer are calculated by the following equations (20) to (25). c1 ,I c2 ,I c3 .

[0224] I1=(W×t1 3 ) / 12 (20)

[0225] I2=(W×t2 3 ) / 12 (21)

[0226] I3=(W×t3 3 ) / 12 (22)

[0227] I c1 =I1+A1×(y c -y1) 2 (twenty three)

[0228] I c2 =I2+A2×(y c -y2) 2 (twenty four)

[0229] Ic3=I3+A3×(y c -y3) 2 (25)

[0230] The moment of inertia I of the electromagnetic wave absorbing member is calculated by the following formula (26), and the bending rigidity of the electromagnetic wave absorbing member is obtained by the following formula (27).

[0231] I=I c1 +I c2 +I c3 (26)

[0232] Bending stiffness (N·mm 2 )=E(N / mm 2 )×I(mm 4 ) (27)

[0233] "Evaluation of Return Loss"

[0234] The heat resistance test of the electromagnetic wave absorbing member was carried out using a high temperature hygrostat (model: PHH-102) manufactured by ESPEC CORP. The temperature of the high temperature hygrostat was set to 120°C, and the electromagnetic wave absorbing member was placed in the high temperature hygrostat for 240 hours. The return loss of the electromagnetic wave absorbing member after being taken out of the high temperature hygrostat was measured to evaluate the change before and after the test.

[0235] Return loss is measured by the free space method.

[0236] [Table 1]

[0237]

[0238] From the results shown in Table 1, it can be seen that the electromagnetic wave absorbing members of Examples 1 to 4 are excellent in curved surface followability and maintenance of electromagnetic wave absorbency after the heat resistance test.

[0239] However, it is found that the electromagnetic wave absorbing member of Comparative Example 1 is poor in maintaining the electromagnetic wave absorbency after the heat resistance test.

[0240] It is found that the electromagnetic wave absorbing member of Comparative Example 2 is inferior in curved surface followability and maintenance of electromagnetic wave absorbency after the heat resistance test.

[0241] Industrial Applicability

[0242] The electromagnetic wave absorbing member of the present invention can be suitably used as an electromagnetic wave absorbing member for transportation equipment such as automobiles.

[0243] Description of Reference Numerals

[0244] 10: electromagnetic wave absorbing component; 20: electromagnetic wave absorbing layer; 21: substrate; 22: electromagnetic wave absorbing pattern; 30: isolation layer; 40: reflection layer; 51: first electromagnetic wave absorbing pattern; 52: second electromagnetic wave absorbing pattern; 53: third electromagnetic wave absorbing pattern.

Claims

1. An electromagnetic wave absorbing member comprising an electromagnetic wave absorbing layer, an isolation layer, and a reflecting layer stacked in this order, wherein the relative dielectric constant of the isolation layer is 5 or more, and the melting point of the isolation layer is 150° C. or more.

2. The electromagnetic wave absorbing member according to claim 1, in, The thickness of the isolation layer is greater than or equal to 200 μm and less than or equal to 450 μm.

3. The electromagnetic wave absorbing member according to claim 1, in, The Young's modulus of the isolation layer is greater than 50 MPa.

4. The electromagnetic wave absorbing member according to claim 1, in, The bending stiffness of the electromagnetic wave absorbing member is 300 N·mm 2 the following.

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