Electromagnetic wave absorbing sheet

Abstract

To provide an electromagnetic wave absorption sheet that can impart crime prevention properties to patterned glass used for window glass, etc.SOLUTION: An electromagnetic wave absorption sheet 10 includes an electromagnetic wave absorption layer 20, a spacer layer 30, a reflective layer 40, and an adhesive layer 50, and the electromagnetic wave absorption layer 20, the spacer layer 30, the reflective layer 40, and the adhesive layer 50 are laminated in this order, and the adhesive layer 50 has a thickness of 10 μm or more and 100 μm or less, an adhesive force to a glass substrate of 7 N / 25 mm or more, and a total thickness of the constituent layers other than the adhesive layer 50 of 300 μm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In order to impart heat ray shielding properties and electromagnetic wave absorbing properties to window glass, it has been considered to attach a transparent film having the above properties to the window glass. Known examples of heat ray shielding films include those containing heat ray absorbing metal compound microparticles, which have an average particle size of 10 to 100 nm, a heat ray shielding coefficient of 0.70 or less, a visible light reflectance of 10% or more, and a visible light transmittance of 55% or more (see, for example, Patent Document 1). Known examples of transparent electromagnetic wave shielding films include those consisting of a laminate of a transparent substrate, a high refractive index transparent conductive layer of 0.1 Ω / □ to 10 Ω / □, and a metal thin film layer, and having electromagnetic shielding properties of 40 dB or more in the frequency band of 30 MHz to 10,000 MHz (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-217515 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-116646 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the heat ray shielding film of Patent Document 1 and the transparent electromagnetic wave shielding film of Patent Document 2 have the problem that they cannot provide security to window glass.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide an electromagnetic wave absorbing sheet that can impart crime prevention properties to patterned glass used for window glass and the like. [Means for solving the problem]

[0006] The present invention provides the following electromagnetic wave absorbing sheet. [1] An electromagnetic wave absorbing layer, a spacer layer, a reflective layer, and an adhesive layer, the electromagnetic wave absorbing layer, the spacer layer, the reflective layer, and the adhesive layer are laminated in this order; The adhesive layer has a thickness of 10 μm or more and 100 μm or less, and an adhesive strength to a glass substrate of 7 N / 25 mm or more, An electromagnetic wave absorbing sheet, wherein the total thickness of the constituent layers other than the adhesive layer is 300 μm or more.

[0007] [2] The electromagnetic wave absorbing sheet according to [1], wherein the thickness t of the spacer layer satisfies the following formula (1) in relation to the relative permittivity εr' of the spacer layer:

[0008]

number

[0009] [3] The electromagnetic wave absorbing sheet according to [1], wherein a hard coat layer is formed on the outermost surface of the electromagnetic wave absorbing layer.

[0010] [4] The electromagnetic wave-absorbing sheet according to [1], wherein at least one of the spacer layer and the adhesive layer contains at least one selected from an ultraviolet absorber and a metal oxide.

[0011] [5] The electromagnetic wave-absorbing sheet according to any one of [1] to [4], which has a total light transmittance of 40% or more. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an electromagnetic wave absorbing sheet that can impart crime prevention properties to patterned glass used for window glass and the like. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a plane along the thickness of an electromagnetic wave absorbing member according to an embodiment of the present invention; [Figure 2] 1 is a top view showing an example of an electromagnetic wave absorbing layer constituting an electromagnetic wave absorbing member according to an embodiment of the present invention. [Figure 3] 1 is a top view showing an example of a first electromagnetic wave absorbing pattern of an electromagnetic wave absorbing layer constituting an electromagnetic wave absorbing member according to one embodiment of the present invention. [Figure 4] 3 is a top view showing an example of a second electromagnetic wave absorbing pattern of an electromagnetic wave absorbing layer constituting an electromagnetic wave absorbing member according to one embodiment of the present invention. FIG. [Figure 5] 10 is a top view showing an example of a third electromagnetic wave absorbing pattern of an electromagnetic wave absorbing layer constituting an electromagnetic wave absorbing member according to one embodiment of the present invention. FIG. [Figure 6] FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the electromagnetic wave absorbing sheet of the present invention will be described. It should be noted that the present embodiment is specifically described to provide a better understanding of the gist of the electromagnetic wave absorbing sheet of the present invention, and does not limit the present invention unless otherwise specified.

[0015] In this specification, the term "electromagnetic wave absorbing pattern" refers to an object that is a collection of geometrically shaped units and that selectively absorbs electromagnetic waves of a certain frequency. The "electromagnetic wave absorbing pattern" can be said to have the same function as a so-called antenna. In this specification, "electromagnetic waves in the millimeter wave range" refers to electromagnetic waves with a wavelength of 1 mm to 10 mm. "Electromagnetic waves in the millimeter wave range" can also be said to be electromagnetic waves with a frequency of 30 GHz to 300 GHz. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0016] FIG. 1 is a cross-sectional view of a plane along the thickness direction, schematically illustrating an electromagnetic wave absorbing sheet according to one embodiment of the present invention. 1, the electromagnetic wave absorbing sheet 10 of this embodiment includes an electromagnetic wave absorbing layer 20, a spacer layer 30, a reflective layer 40, and an adhesive layer (first adhesive layer) 50. The electromagnetic wave absorbing layer 20, the spacer layer 30, the reflective layer 40, and the adhesive layer 50 are laminated in this order. The electromagnetic wave absorbing sheet 10 of this embodiment is attached, for example, to one surface 200a of a patterned glass 200. The electromagnetic wave absorbing sheet 10 of this embodiment is attached to the indoor-side surface or the outdoor-side surface of the patterned glass 200.

[0017] The reflective layer 40 is disposed on the other surface (rear 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.

[0018] The electromagnetic wave absorbing layer 20 may be a single layer, or may include a substrate 21 and an electromagnetic wave absorbing pattern 22 formed on the substrate 21 as shown in FIG. When the electromagnetic wave absorbing layer 20 is a single layer, the electromagnetic wave absorbing layer 20 is made of the same material as the electromagnetic wave absorbing pattern 22 described later.

[0019] The electromagnetic wave absorbing sheet 10 of this embodiment may have a second adhesive layer 80 between the electromagnetic wave absorbing layer 20 and the spacer layer 30 to bond them together. The electromagnetic wave absorbing sheet 10 of this embodiment may also have a third adhesive layer 90 between the spacer layer 30 and the reflective layer 40 to bond them together. When the electromagnetic wave absorbing sheet 10 of this embodiment has the second adhesive layer 80 and the third adhesive layer 90, the electromagnetic wave absorbing layer 20, the second adhesive layer 80, the spacer layer 30, the third adhesive layer 90, the reflective layer 40, and the adhesive layer 50 (first adhesive layer) are laminated in this order.

[0020] "Electromagnetic wave absorbing layer" The electromagnetic wave absorbing layer 20 is made of a frequency selective surface (FSS), which is a surface that can block only electromagnetic waves of a specific frequency by forming a continuous structure of a shape smaller than the wavelength using a conductive material or the like.

[0021] Fig. 2 is a top view showing an example of an electromagnetic wave absorbing layer in this embodiment. As shown in Fig. 2, the electromagnetic wave absorbing layer 20 is an electromagnetic wave absorbing film having a flat substrate 21 and an electromagnetic wave absorbing pattern 22 formed on one surface 21a of the substrate 21. The electromagnetic wave absorbing pattern 22 consists of a first electromagnetic wave absorbing pattern 71, a second electromagnetic wave absorbing pattern 72, and a third electromagnetic wave absorbing pattern 73.

[0022] (First electromagnetic wave absorption pattern) FIG. 3( a ) is a top view showing the first electromagnetic wave absorbing pattern 71 . 3(a), the first electromagnetic wave absorbing pattern 71 is made up of a plurality of first units u1, each of which is a geometrical figure. In other words, the first electromagnetic wave absorbing pattern 71 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 electromagnetic wave absorbing pattern 71 may be, for example, a thin line pattern of an FSS element.

[0023] In the first electromagnetic wave absorbing pattern 71, 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(a). It can also be said that the first electromagnetic wave absorbing pattern 71 has a plurality of first arrays R1. The first electromagnetic wave absorbing pattern 71 can be configured by forming a plurality of first arrays R1 on the substrate 21 at predetermined intervals along the direction indicated by the double-headed arrow P. The spacing between the multiple first arrays R1 is not particularly limited, and the spacing between the first arrays R1 may be regular or irregular.

[0024] FIG. 3(b) is a top view showing the first unit u1. FIG. 3(b) is a top view showing a first unit u1 that constitutes the first electromagnetic wave absorbing pattern 71. As shown in FIG. As shown in FIG. 3(b), the first unit u1 has a cross shape that is symmetrical in both 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 and a straight line portion parallel to the y-axis direction in FIG. 3(b). Linear 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, respectively, so as to be perpendicular to each straight line portion.

[0025] By adjusting the length L1 of the first unit u1 in the x-axis direction and the length W1 of each of the four ends T1 in the x-axis direction, the electromagnetic wave absorption characteristics of the first unit u1 functioning as a single antenna can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction.

[0026] However, the shape of the first unit is not limited to a cross shape, and is not particularly limited as long as the frequency value at which the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71 shows a maximum value is A [GHz]. For example, the shape of the graphic that is the first unit may be a circle, an annular shape, a straight line, a square shape, a polygonal shape, an H-shape, a Y-shape, a V-shape, or the like.

[0027] In the electromagnetic wave absorbing layer 20, 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. 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.

[0028] The first electromagnetic wave absorbing pattern 71 selectively absorbs electromagnetic waves with a frequency of A [GHz]. The frequency value A [GHz] is the frequency value at which the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71 shows a maximum value in the range of 20 GHz to 110 GHz. The frequency value A [GHz] at which the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71 exhibits a maximum value can be identified by, for example, the following method X or method Y.

[0029] Method X: Electromagnetic waves are irradiated onto a standard film described below while varying the frequency within the range of 20 GHz to 110 GHz, and the frequency of the electromagnetic waves at which the amount of electromagnetic waves absorbed by the standard film reaches its maximum is defined as A [GHz]. Method Y: From an electromagnetic-wave-absorbing film having a substrate and multiple electromagnetic-wave-absorbing patterns formed on the substrate, the electromagnetic-wave-absorbing pattern is removed from the substrate so that only a single electromagnetic-wave-absorbing pattern remains. Next, the film having only the single electromagnetic-wave-absorbing pattern is irradiated with electromagnetic waves while changing the frequency within a range of 20 GHz to 110 GHz, and the frequency of the electromagnetic waves when the amount of electromagnetic waves absorbed by the film is maximum is defined as A [GHz].

[0030] The standard film has a flat standard substrate and a standard pattern formed on the standard substrate. 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 explained in detail in the explanation of the substrate 21 below.

[0031] The standard pattern consists of only a plurality of standard units that are identical in shape. In the case of a standard film, it can be said that a standard pattern consisting of only one type of figure that is identical in shape is formed on a standard substrate. The standard pattern can be formed by the fine line pattern of a normal FSS element. Usually, the standard pattern is the same electromagnetic wave absorbing pattern as the first electromagnetic wave absorbing pattern 71. In the standard pattern, the shapes of the multiple standard units are not particularly limited as long as they are identical to one another. Examples of the shapes of the standard units include circles, rings, lines, squares, polygons, crosses, H-shapes, Y-shapes, and V-shapes. Usually, the shape of the standard unit is identical to that of the first unit u1.

[0032] In a standard film, multiple standard units are arranged on a standard substrate so that the distance between the edges of the figure is 1 mm. For example, if the figure of the standard unit is a cross, the intersection of the cross is the center of the figure, and the edges of the figure are the parts farthest from the center along each of the directions of the two straight lines that make up the cross.

[0033] The material of the standard unit that constitutes the standard pattern is not particularly limited, as long as it is such that when electromagnetic waves are irradiated onto the standard film while changing the frequency within the range of 20 GHz to 110 GHz, the amount of electromagnetic waves absorbed by the standard film can reach a maximum value. The material details of the standard unit can be the same as those of the first unit.

[0034] The amount of electromagnetic waves absorbed by a standard film can be calculated using the following formula (1). Absorption amount = input signal - reflection characteristic (S11) - transmission characteristic (S21) (1) The input signal is a measure of the intensity of the electromagnetic wave at the source when the standard film is irradiated with the electromagnetic wave. The reflection characteristic (S11) is an index of the intensity of the electromagnetic wave reflected by the standard film when the standard film is irradiated with electromagnetic waves from an irradiation source. The reflection characteristic (S11) can be measured, for example, by the free-space method using a vector network analyzer. The transmission characteristic (S21) is an index of the intensity of the electromagnetic wave that passes through the standard film when the standard film is irradiated with the electromagnetic wave from the irradiation source. The transmission characteristic (S21) can be measured, for example, by the free space method using a vector network analyzer.

[0035] The frequency A [GHz] can be determined, for example, by the following method. First, the standard film is irradiated with electromagnetic waves while changing the frequency within the range of 20 GHz to 110 GHz, and the amount of electromagnetic waves absorbed by the standard film is calculated using the above formula (1). Next, an absorption spectrum is created by plotting the changed frequency on the horizontal axis and the absorption calculated by the above formula (1) on the vertical axis. Usually, in this absorption spectrum, there is one frequency value on the horizontal axis at which the absorption is maximum. Therefore, the plot shows a single peak where the absorption of the electromagnetic wave is at its maximum. In this way, the frequency of the electromagnetic wave at which the absorption of the electromagnetic wave is maximum can be determined as A [GHz].

[0036] In method X, if the value of frequency A can be predicted in advance, the frequency of the electromagnetic waves irradiated onto the standard film may be changed within a range narrower than 20 GHz to 110 GHz. For example, the frequency of the electromagnetic waves irradiated onto the standard film may be changed within a range of 50 GHz to 110 GHz.

[0037] The first electromagnetic wave absorbing pattern 71 absorbs electromagnetic waves having a frequency of A [GHz] specified by the above-mentioned method X. In the electromagnetic wave absorbing layer 20 of 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. When the frequency value A is within the above range, the electromagnetic wave absorbing layer 110 can absorb electromagnetic waves in the millimeter wave region, and is easily applicable to automobile parts, road peripheral members, building exterior wall related materials, windows, communication devices, radio telescopes, etc.

[0038] In Method Y, the amount of electromagnetic waves absorbed by a film can be measured in the same way as in Method X. That is, the film is irradiated with electromagnetic waves while changing the frequency within the range of 20 to 110 [GHz], and the amount of electromagnetic waves absorbed by the film is calculated using the above formula (1). Next, an absorption spectrum is created by plotting frequency on the horizontal axis and the absorption calculated by the above formula (1) on the vertical axis. Usually, in this absorption spectrum, there is one frequency value on the horizontal axis at which the absorption is maximum. Therefore, the plot shows a single peak where the absorption of the electromagnetic wave is at a local maximum. In this way, the frequency of the electromagnetic wave at which the absorption of the electromagnetic wave is maximum can be determined as A [GHz].

[0039] The material of the first unit u1 is not particularly limited as long as it can adjust the absorption characteristics to the desired frequency. Examples of the material of the first unit include thin metal wires, conductive thin films, and conductive paste deposits. Examples of metal materials 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.

[0040] 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 the 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 one another. 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 influence of the surrounding environment and improving the precision of the frequency band of the electromagnetic waves that are absorbed during manufacturing.

[0041] (Second electromagnetic wave absorption pattern) FIG. 4( a ) is a top view showing the second electromagnetic wave absorbing pattern 72 . 4(a), the second electromagnetic wave absorbing pattern 72 is composed of a plurality of second units u2. Each of the second units u2 is a geometric figure. In other words, the second electromagnetic wave absorbing pattern 72 can be said to be an aggregate of the second units u2, which are geometric figures. Each of the second units u2 functions as an antenna. The second electromagnetic wave absorbing pattern 72 may be, for example, a thin line pattern of an FSS element.

[0042] In the second electromagnetic wave absorbing pattern 72, a second array R2 is formed in which a plurality of second units u2 are arranged along the direction indicated by the double-headed arrow P in Fig. 4(a). It can also be said that the second electromagnetic wave absorbing pattern 72 has a plurality of second arrays R2. The second electromagnetic wave absorbing pattern 72 can be configured by forming the second arrays R2 on the substrate 21 at predetermined intervals along the direction indicated by the double-headed arrow P. The spacing between the multiple second arrays R2 is not particularly limited, and the spacing between the second arrays R2 may be regular or irregular.

[0043] FIG. 4(b) is a top view showing the second unit u2. As shown in Figure 4(b), the second unit u2 has a cross shape that is symmetrical in both the vertical and horizontal directions. Specifically, the second unit u2 has one cross portion S2 and four end portions T2. The cross portion S2 is composed of a straight line portion parallel to the x-axis direction and a straight line portion parallel to the y-axis direction in Figure 4(b). Linear end portions T2 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, respectively, so as to be perpendicular to each straight line portion.

[0044] In the electromagnetic wave absorbing layer 20, the length L2 of the second unit u2 in the x-axis direction is shorter than the length L1 of the first unit u1 in the x-axis direction. In addition, the length W2 of each of the four ends T2 in the x-axis direction or the y-axis direction is shorter than the length W1 of each of the four ends T1 of the first unit u1. By adjusting the length L2 of the second unit u2 in the x-axis direction and the length W2 of each of the four ends T2 in the x-axis direction, the electromagnetic wave absorption characteristics of the second unit u2 functioning as a single antenna can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction.

[0045] In the electromagnetic wave absorbing layer 20, the shapes of the plurality of second units u2 are the same as each other. However, the shapes of the plurality of second units u2 do not have to be the same as each other. In another example of the present invention, the shapes of the plurality of second units may be the same as each other or different as long as the absorption characteristics can be adjusted to the target frequency.

[0046] The second electromagnetic wave absorbing pattern 72 selectively absorbs electromagnetic waves having a frequency B [GHz] that satisfies the following formula (2). The frequency value B [GHz] is the frequency value at which the amount of electromagnetic waves absorbed by the second electromagnetic wave absorbing pattern 72 reaches a maximum. The frequency value B [GHz] satisfies the following formula (2). 1.037×A≦B≦1.30×A...Equation (2)

[0047] As shown in the above formula (2), the second electromagnetic wave absorbing pattern 72 absorbs electromagnetic waves with frequencies of 1.037×A [GHz] to 1.30×A [GHz]. The second electromagnetic wave absorbing pattern 72 preferably absorbs electromagnetic waves with frequencies of 1.17×A [GHz] to 1.30×A [GHz]. Since the second electromagnetic wave absorbing pattern 72 absorbs electromagnetic waves with frequencies of 1.037×A [GHz] or higher, in the frequency band higher than A [GHz], the peak of the amount of electromagnetic waves absorbed by the second electromagnetic wave absorbing pattern 72 fully overlaps with the peak of the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71. As a result, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorbing film is expanded to the frequency band higher than A [GHz], compared to a film having the first electromagnetic wave absorbing pattern 71 alone. Since the second electromagnetic wave absorbing pattern 72 absorbs electromagnetic waves with a frequency of 1.30×A [GHz] or less, in the frequency band higher than A [GHz], there is a small difference in frequency between the peak of the amount of electromagnetic waves absorbed by the second electromagnetic wave absorbing pattern 72 and the peak of the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71. As a result, a single peak is formed at which the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorbing film reaches a local maximum value. As described above, the second electromagnetic wave absorbing pattern 72 absorbs electromagnetic waves with frequencies of 1.037×A [GHz] to 1.30×A [GHz], and therefore the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorbing film is extended to the higher frequency band.

[0048] However, the shape of the second unit is not limited to a cross shape. The shape of the second unit is not particularly limited as long as the absorption characteristics can be adjusted to the target frequency. For example, the shape of the figure that is the second unit can be a circle, an annular shape, a linear shape, a square shape, a polygonal shape, an H-shape, a Y-shape, a V-shape, etc.

[0049] The material of the second unit constituting the second electromagnetic wave absorbing pattern 72 is not particularly limited as long as it can absorb electromagnetic waves of B [GHz], and is not particularly limited as long as the absorption 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.

[0050] The distance between the ends of the figure that is the second unit u2 is not particularly limited as long as the absorption characteristics can be adjusted to the desired frequency. For example, the intervals between the ends of the figures that are the second units u2 may all be the same or may be different from one another. However, it is preferable that the intervals between the ends of the figures that are the second units u2 are the same from one another, because this makes it easier to design an electromagnetic-wave-absorbing film that is less susceptible to the influence of the surrounding environment and improves the precision of the frequency band of the electromagnetic waves that are absorbed during production.

[0051] (Third electromagnetic wave absorption pattern) FIG. 5( a ) is a top view showing the third electromagnetic wave absorbing pattern 73 . 5(a), the third electromagnetic wave absorbing pattern 73 is composed of a plurality of third units u3. Each of the third units u3 is a geometric figure. In other words, the third electromagnetic wave absorbing pattern 73 can be said to be an aggregate of the third units u3, which are geometric figures. Each of the third units u3 functions as an antenna. The third electromagnetic wave absorbing pattern 73 may be, for example, a thin line pattern of an FSS element.

[0052] In the third electromagnetic wave absorbing pattern 73, a third array R3 is formed in which a plurality of third units u3 are arranged along the direction indicated by the double-headed arrow P in Fig. 5(a). It can also be said that the third electromagnetic wave absorbing pattern 73 has a plurality of third arrays R3. The third electromagnetic wave absorbing pattern 73 can be configured by forming the third arrays R3 on the substrate 21 at predetermined intervals along the direction indicated by the double-headed arrow P. The spacing between the multiple third sequences R3 is not particularly limited, and the spacing between the third sequences R3 may be regular or irregular.

[0053] FIG. 5(b) is a top view showing the third unit u3. As shown in Figure 5(b), the third unit u3 has a cross shape that is symmetrical in both the vertical and horizontal directions. Specifically, the third unit u3 has one cross portion S3 and four end portions T3. The cross portion S3 is composed of a straight line portion parallel to the x-axis direction and a straight line portion parallel to the y-axis direction in Figure 5(b). Linear end portions T3 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, respectively, so as to be perpendicular to each straight line portion.

[0054] In the electromagnetic wave absorbing layer 20, the length L3 of the third unit u3 in the x-axis direction is longer than the length L1 of the first unit u1 in the x-axis direction. In addition, the length W3 of each of the four ends T3 in the x-axis direction or the y-axis direction is longer than the length W1 of each of the four ends T1 of the first unit u1. By adjusting the length L3 of the third unit u3 in the x-axis direction and the length W3 of each of the four ends T3 in the x-axis direction, the electromagnetic wave absorption characteristics of the third unit u3 functioning as a single antenna can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction.

[0055] In the electromagnetic wave absorbing layer 20, the shapes of the multiple third units u3 are the same. However, the shapes of the multiple third units u3 do not have to be the same. In another example of the present invention, the shapes of the multiple third units may be the same or different as long as the absorption characteristics can be adjusted to a target frequency.

[0056] The third electromagnetic wave absorbing pattern 73 selectively absorbs electromagnetic waves with a frequency of C [GHz] that satisfies the following formula (3). The frequency value C [GHz] is the frequency value at which the amount of electromagnetic waves absorbed by the third electromagnetic wave absorbing pattern 73 reaches a maximum. The frequency value C [GHz] satisfies the following formula (3). 0.60×A≦C≦0.963×A...Equation (3)

[0057] As shown in the above formula (3), the third electromagnetic wave absorbing pattern 73 absorbs electromagnetic waves with frequencies of 0.60×A [GHz] to 0.963×A [GHz]. It is preferable that the third electromagnetic wave absorbing pattern 73 absorbs electromagnetic waves with frequencies of 0.60×A [GHz] to 0.83×A [GHz]. Since the third electromagnetic wave absorbing pattern 73 absorbs electromagnetic waves with frequencies of 0.60×A [GHz] or higher, in the frequency band lower than A [GHz], there is a small difference in frequency between the peak of the amount of electromagnetic waves absorbed by the third electromagnetic wave absorbing pattern 73 and the peak of the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71. As a result, a single peak is formed at which the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorbing layer 20 reaches a local maximum value. Since the third electromagnetic wave absorbing pattern 73 absorbs electromagnetic waves with frequencies of 0.963×A [GHz] or less, in the frequency band lower than A [GHz], the peak of the amount of electromagnetic waves absorbed by the third electromagnetic wave absorbing pattern 73 fully overlaps with the peak of the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71. As a result, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorbing film is expanded to the frequency band lower than A [GHz], compared to a film having the first electromagnetic wave absorbing pattern 71 alone. As described above, since the third electromagnetic wave absorbing pattern 73 absorbs electromagnetic waves with frequencies of 0.60×A [GHz] to 0.963×A [GHz], the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorbing layer 20 is extended to the lower frequency band.

[0058] However, the shape of the third unit u3 is not limited to a cross shape. The shape of the third unit u3 is not particularly limited as long as the absorption characteristics can be adjusted to the target frequency. For example, the shape of the figure that is the third unit may be a circle, an annular shape, a linear shape, a square shape, a polygonal shape, an H-shape, a Y-shape, a V-shape, etc.

[0059] The material of the third unit u3 constituting the third electromagnetic wave absorbing pattern 73 is not particularly limited as long as it can absorb electromagnetic waves of C [GHz], and is not particularly limited as long as the absorption 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.

[0060] The distance between the ends of the figure that is the third unit u3 is not particularly limited as long as the absorption characteristics can be adjusted to the desired frequency. For example, the intervals between the ends of the figures that are the third units u3 may all be the same or may be different from one another. However, it is preferable that the intervals between the ends of the figures that are the third units u3 are the same from one another, because this makes it easier to design an electromagnetic-wave-absorbing film that is less susceptible to the influence of the surrounding environment and improves the precision of the frequency band of the electromagnetic waves that are absorbed during production.

[0061] In the electromagnetic-wave absorbing layer 20 shown in Fig. 2, the first array R1, the second array R2, and the third array R3 are arranged adjacent to each other along the direction indicated by the double-headed arrow P. Since the first array R1, the second array R2, and the third array R3 are arranged adjacent to each other on the substrate 21, the frequency band of the electromagnetic waves selectively absorbed by the second electromagnetic-wave absorbing pattern 72 and the frequency band of the electromagnetic waves selectively absorbed by the third electromagnetic-wave absorbing pattern 73 overlap with each other, based on the frequency value A [GHz] of the peak position of the electromagnetic waves selectively absorbed by the first electromagnetic-wave absorbing pattern 71. As a result, the absorption range of the electromagnetic waves absorbed by the entire electromagnetic-wave absorbing layer 20 is easily expanded toward both the high-frequency side and the low-frequency side, based on the frequency value A [GHz] of the peak position.

[0062] 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, as shown in FIG. 2, may be the same as or different from each other. The distance d1 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm. The distance d2 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm. The distance d3 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm. When the distances d1, d2, and d3 are each within the above numerical ranges, the absorption range of electromagnetic waves absorbed by the entire electromagnetic wave absorbing layer 20 is likely to be further expanded based on the frequency value A [GHz] at the peak position.

[0063] In the electromagnetic wave absorbing layer 20, the first unit u1, the second unit u2, and the third unit u3 have the same shape. However, the shapes of the first unit u1, the second unit u2, and the third unit u3 do not have to be the same. 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.

[0064] The electromagnetic wave absorption layer 20 may have a plurality of second electromagnetic wave absorption patterns 72. For example, in addition to the second electromagnetic wave absorption pattern 72, the electromagnetic wave absorption layer 20 may further have the following electromagnetic wave absorption pattern 72a and electromagnetic wave absorption pattern 72b. Electromagnetic wave absorption pattern 72a: An electromagnetic wave absorption pattern in which the value of the frequency at which the absorption amount of the absorbed electromagnetic wave shows a maximum value is D [GHz] satisfying the following formula (4). Electromagnetic wave absorption pattern 72b: An electromagnetic wave absorption pattern in which the value of the frequency at which the absorption amount of the absorbed electromagnetic wave shows a maximum value is E [GHz] satisfying the following formula (5). 1.037×A ≦ D < 1.09×A ··· Formula (4) 1.09×A ≦ E < 1.17×A ··· Formula (5) In the above formula (4) and the above formula (5), A is the frequency [GHz] specified by the above method X or method Y.

[0065] When the electromagnetic wave absorption layer 20 further has the electromagnetic wave absorption pattern 72a and the electromagnetic wave absorption pattern 72b in addition to the second electromagnetic wave absorption pattern 72, the value of the frequency at which the absorption amount of the electromagnetic wave absorbed by the second electromagnetic wave absorption pattern 72 shows a maximum value is preferably 1.17×A [GHz] to 1.30×A [GHz]. In this case, the effect of expanding the high-frequency side of the frequency band of the electromagnetic wave that can be absorbed by the entire electromagnetic wave absorption layer 20 is more remarkable, and the effect of the present invention can be obtained more remarkably.

[0066] The electromagnetic wave absorption layer 20 may have a plurality of third electromagnetic wave absorption patterns. For example, in addition to the third electromagnetic wave absorption pattern 73, the electromagnetic wave absorption layer 20 may further have the following electromagnetic wave absorption pattern 73a and electromagnetic wave absorption pattern 73b. Electromagnetic wave absorption pattern 73a: An electromagnetic wave absorption pattern in which the value of the frequency at which the absorption amount of the absorbed electromagnetic wave shows a maximum value is F [GHz] satisfying the following formula (6). Electromagnetic wave absorption pattern 73b: An electromagnetic wave absorption pattern in which the value of the frequency at which the absorption amount of the absorbed electromagnetic wave shows a maximum value is G [GHz] satisfying the following formula (7). 0.91×A < F ≦ 0.963×A ··· Formula (6) 0.83×A < G ≤ 0.91×A ··· Equation (7) In the following Equation (6) and Equation (7), A is the frequency [GHz] specified by the above-mentioned Method X or Method Y.

[0067] When the electromagnetic wave absorption layer 20 further has an electromagnetic wave absorption pattern 73a and an electromagnetic wave absorption pattern 73b in addition to the third electromagnetic wave absorption pattern 73, the value of the frequency at which the absorption amount of the electromagnetic wave absorbed by the third electromagnetic wave absorption pattern 73 shows a maximum value is preferably 0.60×A [GHz] to 0.83×A [GHz]. In this case, the effect of expanding the low-frequency side of the frequency band of the electromagnetic wave that can be absorbed by the entire electromagnetic wave absorption layer 20 is more remarkable, and the effect of the present invention can be obtained more remarkably.

[0068] FIG. 6 is a cross-sectional view taken along the line VIII-VIII of the electromagnetic wave absorption layer 20 in FIG. 2. The base material 21 has two surfaces 21a and 21b facing each other. And on one surface 21a of the base material 21, a first electromagnetic wave absorption pattern 71, a second electromagnetic wave absorption pattern 72, and a third electromagnetic wave absorption pattern 73 are formed. As shown in FIG. 6, a plurality of first units u1, a plurality of second units u2, and a plurality of third units u3 are provided on one surface 21a of the base material 21, respectively.

[0069] The base material 21 is not particularly limited as long as it is in a flat plate shape and can form a first electromagnetic wave absorption pattern 71, a second electromagnetic wave absorption pattern 72, and a third electromagnetic wave absorption pattern 73 on one surface 21a. The base material 71 may have a single-layer structure or a multi-layer structure.

[0070] The thickness K of the base material 21 may be, for example, 5 μm to 500 μm, 15 μm to 200 μm, or 25 μm to 100 μm. The thickness H1 of the first electromagnetic wave absorption pattern 71, the thickness H2 of the second electromagnetic wave absorption pattern 72, and the thickness H3 of the third electromagnetic wave absorption pattern 73 are not particularly limited. The thicknesses H1, H2, and H3 can be arbitrarily changed according to the desired characteristics. Also, the thicknesses H1, H2, and H3 may be the same as each other or different from each other. The thicknesses H1, H2, and H3 may be, for example, 1 μm to 100 μm, 5 μm to 50 μm, or 10 μm to 30 μm. The thicker the thicknesses H1, H2, and H3, the better the electromagnetic wave absorption, but the higher the manufacturing costs. Taking this into consideration, the thicknesses H1, H2, and H3 may be set.

[0071] The material of the substrate 21 can be appropriately selected depending on the application of the electromagnetic wave absorbing sheet 10 . For example, the substrate 21 may be made of a transparent material in order to provide transparency to the electromagnetic wave absorbing sheet 10. Alternatively, the substrate 21 may be made of a flexible material in order to provide conformability to curved surfaces of the electromagnetic wave absorbing sheet 10. The surface of the substrate 21 may be smoothed in order to improve the transparency and three-dimensional formability of the electromagnetic wave absorbing sheet 10.

[0072] For example, the base material 21 can be made of resin. The resin may be a thermoplastic resin or a thermosetting resin. However, when the three-dimensional formability of the electromagnetic wave absorbing sheet 10 is taken into consideration, the base material 21 preferably contains a thermoplastic resin. Examples of thermoplastic resins include polyolefin resins, polyester 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. Specific examples of polyolefin resins include polypropylene, polyethylene, etc. Specific examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.

[0073] Examples of thermosetting resins that can be used include epoxy resin compositions, resin compositions that cure by urethane reaction, and resin compositions that cure by radical polymerization reaction. These may be used alone or in combination of two or more.

[0074] In consideration of further improving the electromagnetic wave absorption performance of the electromagnetic wave absorbing sheet 10, the thickness, permittivity, electrical conductivity and magnetic permeability of the substrate 21 can be set as appropriate. When the electrical characteristics of the electromagnetic waves to be absorbed are taken into consideration, the base material 21 may be a layer with a high dielectric constant. If the base material 21 is a layer with a high dielectric constant, the thickness of the electromagnetic wave absorbing sheet 10 can be made relatively thin.

[0075] The electromagnetic wave absorbing layer 20 can be produced, for example, by the following method. First, a substrate 21 is prepared. Next, a first electromagnetic wave absorbing pattern 71, a second electromagnetic wave absorbing pattern 72, and a third electromagnetic wave absorbing pattern 73 are formed on one surface 21a of the substrate 21. Here, when the first electromagnetic wave absorbing pattern 71 is formed, it is formed so that the frequency value at which the amount of electromagnetic waves absorbed by the first electromagnetic wave absorbing pattern 71 shows a maximum value is A [GHz]. When the second electromagnetic wave absorbing pattern 72 is formed, it is formed so that the frequency value at which the amount of electromagnetic waves absorbed by the second electromagnetic wave absorbing pattern 72 shows a maximum value is B [GHz]. The third electromagnetic wave absorbing pattern 73 is formed so that the frequency at which the amount of electromagnetic waves absorbed by the third electromagnetic wave absorbing pattern 73 exhibits a maximum value is C [GHz]. There is no particular limitation on the order in which the first electromagnetic wave absorbing pattern 71, the second electromagnetic wave absorbing pattern 72, and the third electromagnetic wave absorbing pattern 73 are formed. The first electromagnetic wave absorbing pattern 71, the second electromagnetic wave absorbing pattern 72, and the third electromagnetic wave absorbing pattern 73 may be formed in the same process, or may be formed in separate processes.

[0076] The method for forming each electromagnetic wave absorbing pattern is not particularly limited as long as it can form a predetermined frequency. Examples of the method for forming each electromagnetic wave absorbing pattern include the following methods. A printing method in which each electromagnetic wave absorbing pattern is printed on one surface 21a of the substrate 21 using a conductive paste. A developing method for developing each electromagnetic wave absorbing pattern on one surface 21a of the substrate 21. A method in which a metal thin film is provided on one surface 21a of the substrate 21 by sputtering, vacuum deposition, or lamination of metal foil, and a pattern of the metal thin film is formed on one surface 21a of the substrate 21 by photolithography. A method in which a metal wire is disposed on one surface 21a of a substrate 21.

[0077] In the printing method, each electromagnetic wave absorbing pattern is printed on one surface 21a of the base material 21 to form each of the units u1, u2, and u3, which are figures. The printing method is not particularly limited. Examples include screen printing, gravure printing, and inkjet printing. The conductive paste used for printing may be, for example, a paste-like composition containing at least one selected from the group consisting of metal particles, carbon nanoparticles, and carbon fibers, and a binder resin component. The metal particles may be particles of metals such as copper, silver, nickel, and aluminum. Examples of the binder resin component include thermoplastic resins such as polyester resin, (meth)acrylic resin, polystyrene resin, and polyamide resin, and thermosetting resins such as epoxy resin, amino resin, and polyimide resin, although the metal particles and binder resin component are not limited to these examples. The conductive paste may further contain a black pigment such as carbon black. When the conductive paste further contains a black pigment, the metallic luster of the metal powder that constitutes the printed electromagnetic wave absorbing pattern can be suppressed, and reflection of external light can be reduced.

[0078] In the developing method, an electromagnetic wave absorbing pattern is developed on one surface 21a of the base material 21 to form the units u1, u2, and u3 which are figures. There are two development methods: a negative development method in which the developed product appears in the exposed areas that are not covered by the exposure mask, and a positive development method in which the developed product appears in the unexposed areas that are covered by the exposure mask. That is, in a negative development method, each unit u1, u2, u3 is formed as the developed product in the opposite shape to the exposure mask. On the other hand, in a positive development method, each unit u1, u2, u3 is formed as the developed product in the same shape as the exposure mask. Silver is usually used as the metal used in the developed product.

[0079] An example of a method for forming an electromagnetic wave absorbing pattern by photolithography is as follows. First, a resist is applied to one surface 21a of the substrate 21, followed by heat treatment, and then the solvent is removed from the resist. Next, the resist is exposed to light with a desired pattern and developed to form a layer made of the resist pattern. Next, a vapor-deposited film is formed over the entire surface of the substrate and the layer made of the resist pattern, and a resist remover is used to simultaneously remove the layer made of the resist pattern and the vapor-deposited film on top of it. This allows an electromagnetic wave absorbing pattern to be formed on the surface of the substrate. As another example, a metal thin film is provided on one surface 21a of the substrate 21, and a resist is applied to part of the surface of the metal thin film, followed by heat treatment. Next, the metal thin film is removed from the part where the resist is not applied by etching. Thereafter, the resist is removed as necessary, and an electromagnetic wave absorbing pattern is formed. A metal plating layer (not shown) may be further provided on the surface of each of the units u1, u2, and u3 that make up each electromagnetic wave absorbing pattern.

[0080] Specific examples of metals constituting the metal wire include the same metals as those described above as the materials for the units u1, u2, and u3. In addition, the metal wire may be plated with tin, zinc, silver, nickel, chromium, a nickel-chromium alloy, solder, or the like, or may have a surface coated with a carbon material, a polymer, or the like. Examples of carbon materials that may coat the surface of the metal wire include amorphous carbon such as carbon black, activated carbon, hard carbon, soft carbon, mesoporous carbon, and carbon fiber; graphite; fullerene; graphene; and carbon nanotubes.

[0081] "Spacer layer" The spacer layer 30 is provided on the other surface 21 b of the substrate 21 of the electromagnetic wave absorbing layer 20 . The spacer layer 30 has two surfaces 30a and 30b. One surface 30a of the spacer layer 30 is in contact with the other surface 21b of the substrate 21. A reflective layer 40 is provided on the other surface 30b of the spacer layer 30. The spacer layer 30 may have a single layer structure or a multi-layer structure.

[0082] The material of the spacer layer 30 can be selected appropriately depending on the application of the partition. For example, the spacer layer 30 may be made of a transparent material to provide transparency to the partition. Alternatively, the spacer layer 30 may be made of a flexible material to provide conformability to the curved surface of the partition. Examples of flexible materials include plastic film, rubber, paper, cloth, nonwoven fabric, foam, rubber sheet, etc. Among these, foam is preferred in order to make the electromagnetic wave absorbing sheet 10 lightweight. Specific examples of resins that can be used to form the plastic film include the same thermoplastic resins as those described above for the substrate 21. The foam may be, for example, a foam sheet obtained by foaming the resin constituting the plastic film and forming it into a sheet. Specific examples of foam sheets include polyethylene foam, polypropylene foam, and polyurethane foam.

[0083] When the wavelength shortening effect of the spacer layer 30 is taken into consideration, the thickness of the spacer layer 30 is appropriately changed in accordance with the wavelength of the electromagnetic wave to be absorbed and the relative dielectric constant of the spacer layer 30 . When the wavelength shortening effect of the spacer layer 30 is taken into consideration, it is preferable that the thickness of the spacer layer 30 in the z-axis direction satisfies the following formula (8). (thickness of spacer layer 30 in the z-axis direction)=(λ)×(¼) / (ε) 1 / 2 ...Equation (8) In the above formula (8), λ is the wavelength of the incident electromagnetic wave, and ε is the relative dielectric constant of the spacer layer 30. The thickness of the spacer layer 30 in the z-axis direction may be adjusted appropriately to improve absorption characteristics. For example, it can be changed within a range of 0.1 to 3.0 times the thickness of the spacer layer 30 in the z-axis direction obtained by formula (8).

[0084] When the relationship between the thickness of the spacer layer 30 in the z-axis direction and the wavelength λ satisfies the above formula (8), the electromagnetic-wave absorbing sheet 10 has a so-called λ / 4 structure, which further increases the maximum absorption amount of electromagnetic waves by the electromagnetic-wave absorbing sheet 10. The thickness of the spacer layer 30 can be set appropriately depending on the wavelength λ of the electromagnetic wave to be absorbed. The thickness of the spacer layer 30 may be, for example, 25 μm to 5000 μm, 50 μm to 4500 μm, or 100 μm to 4000 μm. The spacer layer 30 may be made of a material with a high dielectric constant. If the spacer layer 30 is a layer with a high dielectric constant, the thickness of the spacer layer 30 can be made relatively thin. When the dielectric constant of the spacer layer 30 is taken into consideration, the spacer layer 30 preferably contains at least one material selected from the group consisting of barium titanate, titanium oxide, and strontium titanate.

[0085] By increasing the dielectric constant of the spacer layer 30, it is possible to reduce the thickness of the spacer layer 30. This allows the electromagnetic wave absorbing sheet 10 to be made lighter.

[0086] The two surfaces 30a, 30b of the spacer layer 30 are preferably adhesive. This allows the electromagnetic wave absorbing layer 20 and the reflective layer 40 to be bonded to the two surfaces 30a, 30b, respectively. For example, by employing a multilayer structure in which the two surfaces 30a, 30b are adhesive layers containing an adhesive, the two surfaces 30a, 30b can be made adhesive. Details and preferred embodiments of the adhesive layer can be the same as those described for the adhesive layer in the base material 21.

[0087] In the electromagnetic wave absorbing sheet 10 of the present embodiment, it is preferable that the thickness t of the spacer layer 30 and the relative dielectric constant εr′ of the spacer layer 30 satisfy the following formula (1):

[0088]

number

[0089] By satisfying the above formula (1), the electromagnetic wave absorbing sheet 10 can absorb radio waves in the 79 GHz band.

[0090] The relative dielectric constant εr' of the spacer layer 30 can be measured by, for example, the free space method.

[0091] "Reflective layer" The reflective layer 40 has two surfaces 40a and 40b. The surface 40a of the reflective layer 40 is in contact with the other surface 30b of the spacer layer 30. The reflective layer 40 is not particularly limited in form as long as it can reflect electromagnetic waves that arrive at the surface of the electromagnetic wave absorbing sheet 10 and pass through the electromagnetic wave absorbing sheet 10. A portion of the electromagnetic waves that arrive at the electromagnetic wave absorbing sheet 10 is reflected by or absorbed by the electromagnetic wave absorbing layer 20. On the other hand, electromagnetic waves that are not reflected or absorbed by the electromagnetic wave absorbing layer 20 pass through the electromagnetic wave absorbing layer 20. The electromagnetic waves that have passed through the electromagnetic wave absorbing layer 20 are reflected by the reflective layer 40 toward the electromagnetic wave absorbing layer 20. For example, if the reflective layer 40 has conductivity in the planar direction of the two faces 40a, 40b, it can reflect electromagnetic waves that have passed through the electromagnetic wave absorbing layer 20. Specifically, a resin film such as polyethylene terephthalate to which a metal foil such as copper foil or a metal plate such as a copper plate is attached may be used as the reflective layer 40. 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. Among these, a metal plate is preferred in terms of high conductivity.

[0092] Considering the reflective properties of the reflective layer 40, metal wires, conductive threads, twisted yarns containing metal wires and conductive threads, or a conductive thin film may be provided on the other surface 40b of the reflective layer 40. The conductive thin film can be provided on the surface 40b by, for example, a printing method such as screen printing, gravure printing, or inkjet printing; a sputtering method or vacuum deposition; or photolithography.

[0093] "Adhesive layer" The adhesive layer 50 has two surfaces 50a and 50b. One surface 50a of the adhesive layer 50 is in contact with the other surface 40b of the reflective layer 40. The other surface 50b of the adhesive layer 50 is attached to one surface 200a of the patterned glass 200. The patterned glass 200 is assumed to be window glass installed in a building, a vehicle, or the like.

[0094] When the adhesive layer 50 has a thickness equal to or greater than a predetermined value, it exerts sufficient adhesive strength and exhibits excellent glass shatter prevention and durability. Furthermore, when the adhesive layer 50 has a thickness equal to or less than a predetermined value, the surface smoothness of the adhesive layer 50 can be maintained. From this perspective, the thickness of the adhesive layer 50 is 10 μm or more and 100 μm or less, and preferably 20 μm or more and 60 μm or less. Furthermore, as described above, a second adhesive layer 80 may be provided between the electromagnetic wave absorbing layer 20 and the spacer layer 30, and a third adhesive layer 90 may be provided between the spacer layer 30 and the reflective layer 40. In this case, it is preferable that the second adhesive layer 80 and the third adhesive layer 90 are similar to the adhesive layer 50 in terms of productivity, cost, and the like. In this case, from the viewpoint that the adhesive layer 50 and other adhesive layers do not affect the electromagnetic wave design of the electromagnetic wave absorbing layer 20 and the spacer layer 30, it is preferable that the thickness of the second adhesive layer 80 and the third adhesive layer 90 be the same as that of the adhesive layer 50, more preferably 40 μm or less, and even more preferably 30 μm or less.

[0095] The adhesive layer 50 is not restricted by the dielectric constant. On the other hand, as described above, when a second adhesive layer 80 is provided between the electromagnetic wave absorbing layer 20 and the spacer layer 30, and a third adhesive layer 90 is provided between the spacer layer 30 and the reflective layer 40, and when the second adhesive layer 80 and the third adhesive layer 90 are similar to the adhesive layer 50, the dielectric constant of the adhesive layer 50 is 1 to 10, preferably 1.5 to 6, and more preferably 2 to 4. When the dielectric constant of the adhesive layer 50 is equal to or greater than the lower limit, it is easy to achieve compatibility with adhesive strength. When the dielectric constant of the adhesive layer 50 is equal to or less than the upper limit, it can be made to have no effect on the electromagnetic wave control of the electromagnetic wave absorbing layer 20 or the spacer layer 30.

[0096] The relative dielectric constant of the adhesive layer 50 can be measured in the same manner as the relative dielectric constant of the spacer layer 30 .

[0097] The adhesive strength of the adhesive layer 50 to a glass substrate is 7 N / 25 mm or more, preferably 12 N / 25 mm or more, more preferably 17 N / 25 mm or more, and particularly preferably 20 N / 25 mm or more. When the adhesive strength of the adhesive layer 50 is 7 N / 25 mm or more, the adhesive layer 50 can hold the glass and prevent it from shattering when the figured glass breaks. Furthermore, the adhesive strength of the adhesive layer 50 to a glass substrate is preferably 100 N / 25 mm or less, more preferably 40 N / 25 mm or less. When the adhesive strength of the adhesive layer 50 is 100 N / 25 mm or less, the adhesive layer 50 can be easily repositioned during application. The adhesive strength of the adhesive layer 50 can be controlled, for example, by the composition of the adhesive constituting the adhesive composition used to form the adhesive layer, the glass transition temperature, the amount of crosslinking agent in the adhesive composition, etc. If the adhesive composition does not contain a highly polar monomer, the adhesive strength tends to be low, the adhesive strength tends to be higher as the glass transition temperature (Tg) is lower, and the adhesive strength tends to be higher as the amount of crosslinker in the adhesive composition is reduced.

[0098] Furthermore, when a second adhesive layer 80 is provided between the electromagnetic wave absorbing layer 20 and the spacer layer 30, and a third adhesive layer 90 is provided between the spacer layer 30 and the reflective layer 40, the adhesive strength of the second adhesive layer 80 and the third adhesive layer 90 to the electromagnetic wave absorbing layer (the surface opposite to the surface on which the electromagnetic wave absorbing pattern is formed) 20, to the spacer layer 30, and to the reflective layer 40 preferably falls within the following ranges. By falling within these ranges, it becomes easy to design the relative permittivity within the above range, and the resulting electromagnetic wave absorbing sheet 10 can be made to have excellent durability. From this viewpoint, the adhesive strength to the electromagnetic wave absorbing layer 20, the spacer layer 30, and the reflective layer 40 is preferably 7 N / 25 mm or more and 100 N / 25 mm or less, more preferably 12 N / 25 mm or more and 60 N / 25 mm or less, and particularly preferably 18 N / 25 mm or more and 40 N / 25 mm or less.

[0099] The adhesive strength of the adhesive layer 50 can be measured according to JIS Z0237:2000.

[0100] The adhesive layer 50, the second adhesive layer 80, and the third adhesive layer 90 are formed using an adhesive composition. The adhesive used in the adhesive composition is not particularly limited, and acrylic adhesives, rubber adhesives, silicone adhesives, urethane adhesives, polyester adhesives, etc. may be used. The above adhesives may be used alone or in combination of two or more.

[0101] From the viewpoint of adhesive reliability, acrylic adhesives are particularly suitable for use as the adhesive. The acrylic copolymer constituting the acrylic adhesive is formed by using a (meth)acrylic acid alkyl ester as the main monomer component, and, as necessary, a monomer copolymerizable with the (meth)acrylic acid alkyl ester (copolymerizable monomer). Here, the main component refers to 50% by mass or more (up to 100% by mass) of the monomer, preferably 65% ​​by mass or more, and more preferably 85% by mass or more.

[0102] The alkyl group of the (meth)acrylic acid alkyl ester may be any of a linear, branched, or cyclic alkyl group, and is preferably an alkyl group having 1 to 24 carbon atoms, and more preferably an alkyl group having 1 to 18 carbon atoms.

[0103] Specific examples of (meth)acrylic acid alkyl esters (alkyl(meth)acrylates) include, but are not limited to, methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, tert-butyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, tert-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, decyl(meth)acrylate, isodecyl(meth)acrylate, dodecyl(meth)acrylate, tridecyl(meth)acrylate, stearyl(meth)acrylate, isostearyl(meth)acrylate, cyclohexyl(meth)acrylate, and 4-n-butylcyclohexyl(meth)acrylate. These alkyl (meth)acrylates may be used alone or in combination of two or more.

[0104] The molecular weight of the acrylic copolymer is not particularly limited, but a weight-average molecular weight (Mw) of 400,000 or more is preferred. A weight-average molecular weight of 400,000 or more of the acrylic copolymer improves the cohesive strength of the adhesive. The larger the weight-average molecular weight of the acrylic copolymer, the better, but for manufacturing reasons, it is usually 2,000,000 or less. The weight-average molecular weight of the acrylic copolymer is more preferably 600,000 to 1,500,000, and even more preferably 700,000 to 1,200,000. In this specification, the weight-average molecular weight (Mw) is measured by gel permeation chromatography (GPC) as a standard polystyrene-equivalent molecular weight. Specifically, values ​​measured under the following measurement conditions are used.

[0105] <Measurement conditions> GPC measurement equipment: Tosoh HLC-8220 GPC GPC columns (passed in the following order): Tosoh Corporation TSK guard column HXL-H TSK gel GMHXL TSK gel GMHXL TSK gel G2000HXL Measurement solvent: tetrahydrofuran ·Measurement temperature: 40℃

[0106] The method for producing the acrylic copolymer is not particularly limited, and conventionally known methods such as solution polymerization using a polymerization initiator, emulsion polymerization, suspension polymerization, and bulk polymerization can be used. In addition to methods initiating polymerization using a polymerization initiator, methods initiating polymerization by irradiation with electron beams, ultraviolet rays, etc. can also be used. Among these, solution polymerization using a polymerization initiator is preferred because it facilitates molecular weight control and minimizes impurities. For example, the copolymer can be obtained by using ethyl acetate, toluene, methyl ethyl ketone, or the like as a solvent, adding preferably 0.01 to 0.50 parts by mass of the polymerization initiator per 100 parts by mass of the total amount of monomers, and reacting under a nitrogen atmosphere at a reaction temperature of, for example, 60 to 90°C for 3 to 10 hours.

[0107] The pressure-sensitive adhesive composition preferably further contains a crosslinking agent in addition to the pressure-sensitive adhesive (preferably an acrylic pressure-sensitive adhesive). Crosslinking can prevent the pressure-sensitive adhesive layer from spilling out.

[0108] As the crosslinking agent, known crosslinking agents can be used, including, but not limited to, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents.

[0109] Examples of isocyanate-based crosslinking agents include aliphatic diisocyanates such as hexamethylene diisocyanate (HDI); aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, and diphenylmethane diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate; and isocyanate derivatives such as adducts of diisocyanate compounds and polyol compounds such as trimethylolpropane, and biurets and isocyanurates of diisocyanate compounds.

[0110] Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

[0111] Examples of the metal chelate crosslinking agent include acetylacetonate complexes of metals such as aluminum, titanium, nickel, chromium, iron, zinc, cobalt, manganese, and zirconium.

[0112] These crosslinking agents can be used alone or in combination of two or more.

[0113] From the viewpoint of easily obtaining an adhesive layer having the desired physical properties of the present invention, the crosslinking agent is preferably an isocyanate-based compound.

[0114] The content of the crosslinking agent in the pressure-sensitive adhesive composition is preferably at least 0.1 parts by mass, more preferably at least 0.5 parts by mass, per 100 parts by mass of the pressure-sensitive adhesive. The content of the crosslinking agent in the pressure-sensitive adhesive composition is preferably at most 5.0 parts by mass, more preferably at most 4.0 parts by mass, and even more preferably at most 3.75 parts by mass, per 100 parts by mass of the pressure-sensitive adhesive. When the content of the crosslinking agent is within the above range, the degree of crosslinking is kept appropriate, and it is easy to control the properties of the resulting pressure-sensitive adhesive layer within desired ranges.

[0115] The PSA composition may further contain other conventionally known additives, such as colorants such as dyes and pigments, antioxidants such as anilides and phenols, light stabilizers, tackifiers such as rosin and rosin esters, fillers such as smectite, kaolin, talc, mica, and calcium carbonate, flame retardants, hydrolysis inhibitors, heat stabilizers, lubricants, antistatic agents, plasticizers, curing accelerators, and reaction inhibitors.

[0116] The method for forming the adhesive layer 50, the second adhesive layer 80, and the third adhesive layer 90 is not particularly limited. For example, the adhesive layer can be formed by applying an adhesive composition to a release liner and then drying it. The method for applying the adhesive composition is not particularly limited. For example, the adhesive composition can be applied using a known application device such as a roll coater, knife coater, air knife coater, bar coater, blade coater, slot die coater, lip coater, or gravure coater. After applying the adhesive composition to the release liner, the adhesive layer is formed by drying. The drying conditions are not particularly limited. For example, drying is performed at 60°C to 150°C for 10 to 60 seconds. The adhesive layer formed on the release liner is transferred to the other surface 40b of the reflective layer 40, forming the adhesive layer 50 on the other surface 40b of the reflective layer 40.

[0117] In the electromagnetic wave-absorbing sheet 10 of this embodiment, at least one of the spacer layer 30, the adhesive layer 50, the adhesive layer 80, and the adhesive layer 90 preferably contains at least one selected from an ultraviolet absorber and a metal oxide. From the viewpoint of achieving both light resistance and the original function of the layer, the ultraviolet absorber or metal oxide is preferably contained in any one of these layers in an amount of from 0.01% to 30% by mass, more preferably from 0.1% to 15% by mass, and particularly preferably from 1% to 10% by mass.

[0118] Examples of ultraviolet absorbers include benzophenone-based, benzotriazole-based, and triazine-based ones. Examples of metal oxides include titanium oxide, zinc oxide, and zirconium oxide. At least one of the spacer layer 30 and the adhesive layer 50 contains at least one selected from an ultraviolet absorber and a metal oxide, thereby improving the ultraviolet shielding properties of the electromagnetic wave-absorbing sheet 10.

[0119] "Hard coat layer" The electromagnetic wave absorbing sheet 10 of this embodiment may include a hard coat layer 100 formed on the outermost surface of the electromagnetic wave absorbing layer 20 , that is, on one surface (front surface) 20 a of the electromagnetic wave absorbing layer 20 . The hard coat layer 100 is not particularly limited as long as it can protect the electromagnetic wave absorbing layer 20 .

[0120] The thickness of the hard coat layer 100 is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 20 μm or less, and even more preferably 2 μm or more and 10 μm or less. When the thickness of the hard coat layer 100 is equal to or more than the above lower limit, sufficient scratch resistance can be exhibited. When the thickness of the hard coat layer 100 is equal to or less than the above upper limit, seepage of the composition constituting the hard coat layer 100 from the side surfaces can be suppressed, and flexibility can be imparted to the electromagnetic wave-absorbing sheet 10.

[0121] The electromagnetic wave-absorbing sheet 10 of this embodiment preferably has a total light transmittance of 40% or more, more preferably 50% or more, and even more preferably 54% or more. If the electromagnetic wave-absorbing sheet 10 has a total light transmittance of 40% or more, the transparency of window glass or the like can be ensured even when the electromagnetic wave-absorbing sheet 10 is attached to window glass or the like.

[0122] The total light transmittance of the electromagnetic wave-absorbing sheet 10 can be measured in accordance with JIS K7361-1:1997.

[0123] In the electromagnetic wave absorbing sheet 10 of this embodiment, the total thickness of the constituent layers other than the adhesive layer 50, i.e., the thickness obtained by subtracting the thickness of the adhesive layer 50 from the total thickness of the electromagnetic wave absorbing sheet 10, is 300 μm or more, preferably 600 μm or more, and more preferably 755 μm or more. When the total thickness of the constituent layers other than the adhesive layer 50 is equal to or greater than the above-mentioned lower limit, excellent electromagnetic wave absorption properties are easily achieved. There is no particular upper limit, but from the viewpoint of excellent total light transmittance, it is preferably 3000 μm or less, more preferably 1000 μm or less, particularly preferably 900 μm or less, and most preferably 800 μm or less.

[0124] Furthermore, from the viewpoint of achieving excellent electromagnetic wave absorption, the total thickness of the second adhesive layer 80 and the third adhesive layer 90 is preferably 20 to 200 μm, more preferably 28 to 100 μm, and even more preferably 38 to 50 μm.

[0125] [Method of manufacturing electromagnetic wave absorbing member] The electromagnetic wave absorbing sheet 10 can be produced, for example, by the following method. An electromagnetic wave absorbing layer 20 is prepared, having an electromagnetic wave absorbing pattern 22 formed on one side thereof. If necessary, a hard coat layer can be provided on the side opposite to the side on which the electromagnetic wave absorbing pattern is formed. Next, the second adhesive layer 80 is attached to the surface of the electromagnetic wave absorbing layer 20 on which the electromagnetic wave absorbing pattern 22 is formed, and is laminated on the spacer layer 30. In this way, a laminate A consisting of the electromagnetic wave absorbing layer 20 / second adhesive layer 80 / spacer layer 30 is obtained. Furthermore, using a third adhesive layer 90 and a first adhesive layer 50 each having a release layer, the third adhesive layer 90 and the adhesive layer 50 are attached to each surface of the reflective layer 40. This results in a laminate B consisting of release film / third adhesive layer 90 / reflective layer 40 / first adhesive layer 50 / release film. Next, the release film on the third adhesive layer 70 side of the laminate B is peeled off, and the exposed third adhesive layer 90 and the exposed surface of the spacer layer of the laminate A are laminated together. This makes it possible to obtain an electromagnetic wave absorbing sheet having the hard coat layer / electromagnetic wave absorbing layer 20 / second adhesive layer 80 / spacer layer 30 / third adhesive layer 90 / reflective layer 40 / first adhesive layer 50 / release film in that order. The adhesive layers may all be the same as the adhesive layer 50, or may be different adhesive layers. [Example]

[0126] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0127] [Example 1] Copper was vapor-deposited onto a substrate made of a 50 μm thick PET film (product name: PET50A4160, manufactured by Toyobo Co., Ltd.) to form a copper thin film. Thereafter, the copper thin film was patterned into an electromagnetic wave absorbing pattern by photolithography to form an electromagnetic wave absorbing pattern as shown in Figure 2, thereby obtaining an electromagnetic wave absorbing layer having an electromagnetic wave absorbing pattern. The thickness of the electromagnetic wave absorbing pattern was set to 20 μm. A multifunctional acrylate resin, Opstar Z7530 (manufactured by Arakawa Chemical Industries, Ltd.), was applied to the surface of the substrate opposite to the surface on which the electromagnetic wave absorbing pattern was formed, and coated to a thickness of 2 μm using a Meyer bar. After drying, the coating was irradiated with UV light to form a hard coat layer. Additionally, an acrylic copolymer with a weight-average molecular weight of 800,000 was prepared, 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. 1 part by mass (solids equivalent) of an isocyanate-based crosslinking agent and 8 parts by mass of Tinuvin 477 as an ultraviolet absorber were added to 100 parts by mass (solids equivalent) of the acrylic copolymer, and the mixture was diluted with ethyl acetate to prepare an acrylic pressure-sensitive adhesive solution. The acrylic adhesive solution was then applied to a release film, dried at 90°C for 1 minute, and cured at room temperature for 1 week to obtain an adhesive layer with a thickness of 20 µm. Three adhesive layers were prepared. The first adhesive layer was attached to the surface on which the electromagnetic wave absorbing pattern was formed, and then the release film on the adhesive layer was peeled off, followed by laminating the adhesive layer on the spacer layer. The spacer layer was made of a sheet of pellet resin EV560 (εr′ = 2.3) manufactured by Mitsui Dow Polychemicals Co., Ltd., which was pressed at 200°C for 10 minutes using a hydraulic heating press (Tester Sangyo Co., Ltd., SA-302) to a thickness of 625 μm. Next, a reflective layer was formed by laminating a film (50 μm thick) manufactured by MADICO, RLW 300 SPS 80 PS SR, with a second adhesive layer and a third adhesive layer covering both sides. In other words, a laminate consisting of release film / adhesive layer / reflective layer / adhesive layer / release film was obtained. One of the release films was then peeled off, and the exposed adhesive layer was laminated on the side opposite the electromagnetic wave absorbing pattern of the spacer layer. This resulted in an electromagnetic wave absorbing sheet (total thickness 787 μm excluding the release film) consisting of a hard coat layer (thickness 2 μm) / substrate / electromagnetic wave absorbing pattern / adhesive layer (thickness 20 μm) / spacer layer (thickness 625 μm) / adhesive layer (thickness 20 μm) / reflective layer (thickness 50 μm) / adhesive layer (thickness 20 μm) / release film.

[0128] [Example 2] The electromagnetic wave absorbing sheet of Example 2 was produced in the same manner as Example 1, except that the thickness of the adhesive layer between the spacer layer and the reflective layer, and between the reflective layer and the release film was changed to 10 μm.

[0129] [Example 3] An electromagnetic wave-absorbing sheet of Example 3 was produced in the same manner as in Example 1, except that no hard coat layer was provided and the thickness of the adhesive layer was changed to 40 μm.

[0130] [Comparative Example 1] An electromagnetic wave absorbing sheet of Comparative Example 1 was produced in the same manner as in Example 1, except that no hard coat layer was provided, the thickness of the adhesive layer between the spacer layer and the reflective layer and between the reflective layer and the release film was changed to 5 μm, and the adhesive layer did not contain an ultraviolet absorber.

[0131] Comparative Example 2 An electromagnetic wave absorbing sheet of Comparative Example 2 was produced in the same manner as in Example 1, except that no hard coat layer was provided, the thickness of the spacer layer was 100 μm, the thickness of the adhesive layer between the spacer layer and the reflective layer and between the reflective layer and the release film was 10 μm, and the adhesive layer did not contain an ultraviolet absorber.

[0132] Comparative Example 3 An electromagnetic wave absorbing sheet of Comparative Example 3 was produced in the same manner as in Example 1, except that the adhesive in the adhesive layer between the spacer layer and the reflective layer, and between the reflective layer and the release film was changed to a silicone-based adhesive, and the adhesive layer did not contain an ultraviolet absorber.

[0133] [evaluation] The electromagnetic wave absorbing sheets of Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated as follows. The results are shown in Table 1.

[0134] "Measurement of the thickness of adhesive layers and electromagnetic wave absorbing sheets" The thickness of the adhesive layer and the total thickness of the electromagnetic wave absorbing sheet were measured using a constant pressure thickness measuring instrument (PG-20J) manufactured by Teclock Corporation.

[0135] "Measurement of total light transmittance of electromagnetic wave absorbing sheet" The total light transmittance of the electromagnetic wave absorbing sheet was measured using a haze meter (product name: NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000.

[0136] "Measurement of ultraviolet transmittance of electromagnetic wave absorbing sheet" The ultraviolet transmittance of the electromagnetic wave absorbing sheet was measured using a UV-vis (UV-3600) manufactured by Shimadzu Corporation, and the average value was calculated.

[0137] "Measurement of the relative permittivity of the spacer layer and adhesive layer" The relative dielectric constants of the spacer layer and the adhesive layer were measured using a dielectric constant measuring device (40 GHz TE mode) manufactured by AET Corporation and a network analyzer (MS46122B) manufactured by Anritsu Corporation.

[0138] "Measurement of adhesive strength of adhesive layer" The electromagnetic wave absorbing sheets obtained in the Examples and Comparative Examples were cut to a width of 25 mm and a length of 100 mm, the release film was peeled off, and the sheets were attached to either 1) the PET film used to prepare the electromagnetic wave absorbing layer, 2) the spacer layer prepared in Example 1, 3) the reflective layer used in Example 1, or 4) a soda-lime glass plate to prepare samples for measuring adhesive strength corresponding to Table 1. The samples were left to stand for 24 hours in an environment of 23°C and 50% RH, and then the protective sheet was peeled off using a tensile tester at a peel angle of 180° and a peel rate of 300 mm / min, and the adhesive strength of the adhesive layer was measured. Note that measurement conditions other than those mentioned above were in accordance with JIS Z0237:2009.

[0139] "Durability test" The adhesive strength measurement sample was left in an environment of 85° C. and 85% RH for 240 hours, and then the adhesive strength was measured in the same manner.

[0140] "Glass shatterproof test" (Glass shatterproof performance test (burglary prevention test)) A sample measuring 900±5 mm in width and 100±5 mm in length was attached to a 5 mm thick glass plate and left to stand in an environmental chamber at a temperature of 23±2°C and a humidity of 50±5% for more than 30 days. A polished steel ball with a diameter of 100±0.2 mm and a mass of 4.11±0.06 kg was dropped onto a PG-film-coated glass plate from a height of 3000±50 mm to evaluate its shatterproofness. The sample was then left in an environment of 85°C and 85% RH for 240 hours, and its shatterproofness (after durability) was evaluated in the same manner as above.

[0141] "Evaluation of radio wave absorption" Using the free-space S-parameter method, the reflection characteristics (S11) of radio waves were measured in the band from 60 GHz to 90 GHz, and the amount of absorption was calculated using the following formula to determine the radio wave absorption characteristics. Absorption amount = Input signal - Reflection characteristic (S11) The radio wave characteristics were evaluated according to the following criteria.

[0142] "Evaluation of character visibility" The visibility of letters was evaluated at a distance of 1 m from the glass through an electromagnetic wave absorbing sheet attached to the glass.

[0143] "Lightfastness evaluation" The release film was peeled off from the electromagnetic wave absorbing sheets obtained in the examples and comparative examples, and the sheets were attached to a 1 mm thick alkali-free glass plate to prepare measurement samples. The samples were placed in a light resistance tester (manufactured by Suga Test Instruments, product name "Ultraviolet Fade Meter U48", light source: carbon arc lamp) and irradiated with ultraviolet light (illuminance: 500 mW / m2) from the glass plate side for 500 hours. In this test, if any of the layers in the electromagnetic wave absorbing sheet showed coloration, the sheet was evaluated as "×", and if no change was observed, the sheet was evaluated as "◯".

[0144] [Table 1]

[0145] From the results shown in Table 1, it was found that the electromagnetic wave absorbing sheets of Examples 1 to 3 have excellent security and radio wave absorption properties because the thickness of the adhesive layer is 10 μm or more and 100 μm or less, the adhesive strength of the adhesive layer to the glass substrate is 7 N / 25 mm or more, and the total thickness of the constituent layers other than the first adhesive layer is 300 μm or more. On the other hand, the electromagnetic wave absorbing sheet of Comparative Example 1 was found to have poor security and radio wave absorption properties because the adhesive layer had a thickness of 5 μm. The electromagnetic wave absorbing sheet of Comparative Example 2 was found to have poor radio wave absorption properties because the total thickness of the constituent layers other than the first adhesive layer was 230 μm. The electromagnetic wave absorbing sheet of Comparative Example 3 was found to have poor security and radio wave absorption properties because the adhesive strength of the adhesive layer to the glass substrate was 5 N / 25 mm. [Industrial Applicability]

[0146] The electromagnetic wave absorbing member of the present invention can be suitably used for aiming partitions used in the aiming of automobiles. [Explanation of symbols]

[0147] 10 Electromagnetic wave absorbing sheet 20 Electromagnetic wave absorbing layer 21 Base material 22 Electromagnetic wave absorption pattern 30 spacer layer 40 reflective layer 50 Adhesive layer (1st adhesive layer) 71 First electromagnetic wave absorption pattern 72 Second electromagnetic wave absorption pattern 73 Third Electromagnetic Wave Absorption Pattern 80 Second adhesive layer 90 Third adhesive layer 200 Patterned Glass

Claims

1. The electromagnetic wave absorbing layer, the spacer layer, the reflective layer, and the adhesive layer are included. the electromagnetic wave absorbing layer, the spacer layer, the reflective layer, and the adhesive layer are laminated in this order; The adhesive layer has a thickness of 10 μm or more and 100 μm or less, An electromagnetic wave absorbing sheet having a total thickness of constituent layers other than the adhesive layer of 300 μm or more, The electromagnetic wave absorbing sheet has an adhesive strength to a glass substrate of 7 N / 25 mm or more when the electromagnetic wave absorbing sheet is attached to the glass substrate at the adhesive layer.

2. 2. The electromagnetic wave absorbing sheet according to claim 1, wherein the thickness t of the spacer layer satisfies the following formula (1) in relation to the relative dielectric constant εr' of the spacer layer: [Equation 1]

3. 2. The electromagnetic wave absorbing sheet according to claim 1, further comprising a hard coat layer formed on the outermost surface of the electromagnetic wave absorbing layer.

4. 2. The electromagnetic wave-absorbing sheet according to claim 1, wherein at least one of the spacer layer and the adhesive layer contains at least one selected from an ultraviolet absorber and a metal oxide.

5. 5. The electromagnetic wave-absorbing sheet according to claim 1, which has a total light transmittance of 40% or more.

6. An electromagnetic wave absorbing sheet described in any one of claims 1 to 4, wherein the adhesive layer attaches the electromagnetic wave absorbing sheet to plate glass.

7. An electromagnetic wave absorbing sheet described in any one of claims 1 to 4, wherein the reflective layer is formed by bonding a conductive material selected from the group consisting of metal foil, transparent conductive film, and mesh sheet to a resin film.

8. An electromagnetic wave absorbing sheet described in any one of claims 1 to 4, wherein the electromagnetic wave absorbing sheet is a sheet for preventing glass from shattering.

Images