JP7457621B2 - Electromagnetic wave absorber - Google Patents

Description

The present invention relates to an electromagnetic wave absorber.

Electromagnetic wave absorbers that selectively absorb electromagnetic waves of a predetermined frequency are known. The electromagnetic wave absorber, for example, comprises a first frequency selective shielding layer and a second frequency selective shielding layer. In such electromagnetic wave absorbers, the fine line patterns of frequency selective surface (FSS) elements formed on the first frequency selective shielding layer and the second frequency selective shielding layer cause each layer to absorb electromagnetic waves of a predetermined frequency, and as a whole, selectively shield electromagnetic waves of two different frequencies.

Patent document 1 describes an electromagnetic wave shielding material that has a reflective layer having a number of antenna elements arranged on the same plane, and a spacer layer made of a dielectric material sandwiched between two reflective layers, with the reflective layer and the spacer layer being bonded via an adhesive layer.

Japanese Patent Application Publication No. 2009-105387

Patent Document 1 does not describe the material of the adhesive layer. However, considering the dielectric constant of commonly used acrylic adhesives, there is a high possibility that the frequency characteristics of the electromagnetic wave shielding material will change significantly by using the adhesive for bonding.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electromagnetic wave absorber that suppresses changes in frequency characteristics.

The present invention provides the following electromagnetic wave absorber.
[1] An electromagnetic wave absorbing layer, a reflective layer disposed on the back side of the electromagnetic wave absorbing layer, a spacer layer disposed between the electromagnetic wave absorbing layer and the reflective layer, and an electromagnetic wave absorbing layer formed on the surface of the electromagnetic wave absorbing layer. an electromagnetic wave absorbing layer, the electromagnetic wave absorbing layer comprising a frequency selective surface, and the protective layer comprising a cured product of a composition containing a modified polyolefin resin and a polyphenylene ether resin having a reactive group body.
[2] The electromagnetic wave absorber according to [1], wherein the content of the modified polyolefin resin in the protective layer is more than 50% by mass based on the total amount of the protective layer.
[3] The electromagnetic wave absorber according to [1] or [2], wherein the reactive group of the polyphenylene ether resin contains an ethylenically unsaturated bond.
[4] The electromagnetic wave absorber according to any one of [1] to [3], wherein the composition contains at least one compound having an alicyclic skeleton and a cyclic ether group.
[5] At least one of the compounds having an alicyclic skeleton and a cyclic ether group is a compound that is liquid at 25°C, and the content of the compound that is liquid at 25°C is 10% by mass in the total amount of the composition. The electromagnetic wave absorber according to [4] below.
[6] The electromagnetic wave absorber according to any one of [1] to [5], wherein the protective layer has a thickness of 1 μm to 500 μm.
[7] The electromagnetic wave absorber according to any one of [1] to [6], wherein the electromagnetic wave absorbing layer includes a base material and an electromagnetic wave absorbing pattern provided on the base material.
[8] The electromagnetic wave absorption pattern includes a first electromagnetic wave absorption pattern, a second electromagnetic wave absorption pattern, and a third electromagnetic wave absorption pattern, and the amount of electromagnetic waves absorbed by the first electromagnetic wave absorption pattern is 20 GHz or more. The frequency that shows a maximum value in the range of 110 GHz is A [GHz], and the frequency that shows the maximum value of the amount of electromagnetic wave absorbed by the second electromagnetic wave absorption pattern satisfies the following formula (1). GHz], and the frequency at which the amount of electromagnetic waves absorbed by the third electromagnetic wave absorption pattern reaches a maximum value is C[GHz] that satisfies the following formula (2), the electromagnetic wave absorption according to [7] body.
1.037×A≦B≦1.30×A...(1)
0.60×A≦C≦0.963×A...(2)
[9] The first electromagnetic wave absorption pattern has a plurality of first arrays in which a plurality of first units having the same shape are arranged, and the second electromagnetic wave absorption pattern has a shape The third electromagnetic wave absorption pattern has a plurality of second arrays in which a plurality of second units having the same shape are arranged, and the third electromagnetic wave absorption pattern has a plurality of third units having the same shape. [8], wherein the base material has a plurality of third arrays, and the first array, the second array, and the third array are arranged on the base material so that they are adjacent to each other. electromagnetic wave absorber.

According to the present invention, it is possible to provide an electromagnetic wave absorber in which changes in frequency characteristics are suppressed.

1 is a cross-sectional view of a surface along the thickness of the electromagnetic wave absorber, schematically showing an electromagnetic wave absorber according to an embodiment of the present invention. 1 is a cross-sectional view of a surface along the thickness of the electromagnetic wave absorber, schematically showing an electromagnetic wave absorber according to an embodiment of the present invention. FIG. 2 is a top view showing an example of an electromagnetic wave absorbing layer that constitutes an electromagnetic wave absorber according to an embodiment of the present invention. It is a top view showing an example of the 1st electromagnetic wave absorption pattern which constitutes the electromagnetic wave absorber concerning one embodiment of the present invention. It is a top view showing an example of the 1st unit of the 1st electromagnetic wave absorption pattern which constitutes the electromagnetic wave absorber concerning one embodiment of the present invention. It is a top view showing an example of the 2nd electromagnetic wave absorption pattern which constitutes the electromagnetic wave absorber concerning one embodiment of the present invention. It is a top view showing an example of the 2nd unit of the 2nd electromagnetic wave absorption pattern which constitutes the electromagnetic wave absorber concerning one embodiment of the present invention. It is a top view which shows an example of the 3rd electromagnetic wave absorption pattern which comprises the electromagnetic wave absorber based on one embodiment of this invention. 11 is a top view showing an example of a third unit of a third electromagnetic wave absorbing pattern constituting an electromagnetic wave absorber according to one embodiment of the present invention. FIG. FIG. 8 is a cross-sectional view taken along line VIII-VIII of FIG. FIG. 13 is a diagram showing the results of measuring the return loss of an electromagnetic wave absorber of a reference example. FIG. 13 is a diagram showing the results of measuring the return loss of an electromagnetic wave absorber according to an embodiment of the present invention. It is a figure which shows the result of measuring the return loss of the electromagnetic wave absorber of a comparative example.

In this specification, the term "electromagnetic wave absorbing pattern" refers to an object that is a collection of geometrically shaped units and selectively absorbs electromagnetic waves of a certain frequency. The "electromagnetic wave absorbing pattern" can be said to have the same function as an antenna.
In this specification, the term "electromagnetic waves in the millimeter wave region" refers to electromagnetic waves with a wavelength of 1 mm to 15 mm. The term "electromagnetic waves in the millimeter wave region" can also be said to be electromagnetic waves with a frequency of 20 GHz to 300 GHz.
In this specification, the use of "to" indicating a range of values means that the values before and after it are included as the lower and upper limits.

[Electromagnetic wave absorber]
An embodiment to which the present invention is applied will be described below. In the drawings used in the following explanation, important parts may be shown enlarged for convenience in order to make it easier to understand the features of the present invention, and the dimensional ratios of each component are the same as the actual values. Not necessarily.
The electromagnetic wave absorber of the present invention comprises an electromagnetic wave absorbing layer, a reflective layer placed on the back side of the electromagnetic wave absorbing layer, a spacer layer placed between the electromagnetic wave absorbing layer and the reflective layer, and a spacer layer formed on the surface of the electromagnetic wave absorbing layer. and a protective layer.

1 and 2 are schematic cross-sectional views of an electromagnetic wave absorber according to one embodiment of the present invention taken along the thickness direction of the electromagnetic wave absorber.
As shown in FIG. 1, an electromagnetic wave absorber 10 according to this embodiment includes an electromagnetic wave absorbing layer 20, a reflective layer 30, a spacer layer 40, and a protective layer 50.

The reflective layer 30 is arranged on the other surface (back surface) 20b side of the electromagnetic wave absorbing layer 20. Spacer layer 40 is arranged between electromagnetic wave absorbing layer 20 and reflective layer 30. That is, the electromagnetic wave absorbing layer 20 and the reflective layer 30 are laminated with the spacer layer 40 interposed therebetween. The protective layer 50 is formed on one side (surface) 20a of the electromagnetic wave absorbing layer 20.

"Electromagnetic wave absorption layer"
The electromagnetic wave absorbing layer 20 consists of a frequency selective surface. A frequency selective surface is a surface that can block only electromagnetic waves of a specific frequency by forming a continuous structure with a shape smaller than the wavelength using a conductive wire or the like.
The electromagnetic wave absorbing layer 20 may be a single layer as shown in FIG. 1, or may include a base material 21 and an electromagnetic wave absorbing pattern 22 formed on the base material 21 as shown in FIG.
When the electromagnetic wave absorption layer 20 is a single layer, it is made of the same material as the electromagnetic wave absorption pattern 22 described later.

FIG. 3 is a top view showing an example of the electromagnetic wave absorption layer in this embodiment. As shown in FIG. 3, the electromagnetic wave absorbing layer 20 is an electromagnetic wave absorbing film having a flat base material 21 and an electromagnetic wave absorbing pattern 22 formed on one surface 21a of the base material 21. The electromagnetic wave absorption pattern 22 includes a first electromagnetic wave absorption pattern 61, a second electromagnetic wave absorption pattern 62, and a third electromagnetic wave absorption pattern 63.

(First electromagnetic wave absorption pattern)
FIG. 4 is a top view showing the first electromagnetic wave absorption pattern 61. As shown in FIG.
As shown in FIG. 4, the first electromagnetic wave absorption pattern 61 is composed of a plurality of first units u1. Each of the first units u1 is a geometric figure.
In other words, the first electromagnetic wave absorption pattern 61 can be said to be a collection of first units u1 that are geometric figures.
Each of the first units u1 functions as one antenna. The first electromagnetic wave absorption pattern 61 may be, for example, a thin line pattern of an FSS element.

In the first electromagnetic wave absorbing pattern 61, 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. 4. It can also be said that the first electromagnetic wave absorbing pattern 61 has a plurality of first arrays R1. The first electromagnetic wave absorbing pattern 61 can be configured by forming a plurality of first arrays R1 on the substrate 20 at predetermined intervals along the direction indicated by the double-headed arrow P.
The intervals between the multiple first arrays R1 are not particularly limited, and the intervals between the multiple first arrays R1 may be regular or irregular.

FIG. 5 is a top view showing the first unit u1.
FIG. 5 is a top view showing the first unit u1 that constitutes the first electromagnetic wave absorption pattern 61.
As shown in FIG. 5, the shape of the first unit u1 is a cross shape that is vertically and horizontally symmetrical. 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. Each straight end portion T1 is in contact with each of both ends of the straight line portion parallel to the x-axis direction and both ends of the straight line portion parallel to the y-axis direction so as to be orthogonal to each straight line portion.

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 waves generated by the first unit u1 functioning as one antenna can be adjusted. Absorption properties can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction as well.

However, the shape of the first unit is not limited to a cross shape. The shape of the first unit is not particularly limited as long as the frequency value at which the amount of electromagnetic waves absorbed by the first electromagnetic wave absorption pattern 61 has a maximum value is A [GHz].
For example, the shape of the figure that is the first unit includes a circular shape, an annular shape, a linear shape, a square shape, a polygonal shape, an H-shape, a Y-shape, a V-shape, and the like.

In the electromagnetic wave absorption layer 20, the shapes of the plurality of first units u1 are the same. However, the shapes of the plurality of first units u1 do not have to be the same figure. In other examples of the present invention, the shapes of the plurality of first units may be the same or different as long as the absorption characteristics can be adjusted to a target frequency.

The first electromagnetic wave absorption pattern 61 selectively absorbs electromagnetic waves having a frequency of A [GHz]. The frequency value A [GHz] is the frequency value when the amount of electromagnetic waves absorbed by the first electromagnetic wave absorption pattern 61 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 absorption pattern 61 has a maximum value can be specified by, for example, method X and method Y below.

method shall be.
Method Y: From an electromagnetic wave absorbing film having a base material and a plurality of electromagnetic wave absorbing patterns formed on the base material, the electromagnetic wave absorbing pattern is removed from the base material so that only a single electromagnetic wave absorbing pattern remains. Next, a film having only a single electromagnetic wave absorption pattern is irradiated with electromagnetic waves while changing the frequency within the range of 20 GHz to 110 GHz, and the frequency of the electromagnetic waves when the amount of electromagnetic wave absorption of the film reaches the maximum value is determined as A. [GHz].

The standard film has a flat standard base material and a standard pattern formed on the standard base material.
The details of the standard base material can be the same as those of the base material 21. Therefore, details of the standard base material will be explained in detail in the description of the base material 21 described later.

The standard pattern consists only of a plurality of standard units having the same shape. In the standard film, it can be said that a standard pattern consisting of only one type of figure having the same shape is formed on the standard base material. The standard pattern can be formed by a fine line pattern of a normal FSS element. Usually, the standard pattern is the same electromagnetic wave absorption pattern as the first electromagnetic wave absorption pattern 61.
In the standard pattern, the shapes of the plurality of standard units are not particularly limited as long as they are the same figures. Examples of the shape of the figure which is a standard unit include a circular shape, an annular shape, a linear shape, a square shape, a polygonal shape, a cross shape, an H shape, a Y shape, a V shape, and the like. Usually, the shape of the standard unit is the same as the first unit u1.

In the standard film, a plurality of standard units are arranged on a standard base material such that the distance between the edges of the figures is 1 mm. For example, if the standard unit figure is a cross, the intersection of the crosses is the center of the figure, and the edge of the figure is the farthest distance from the center along each of the two straight line parts that make up the cross. This is the part where

The material of the standard units constituting the standard pattern must be in a manner that allows the amount of electromagnetic waves absorbed by the standard film to take the maximum value when the standard film is irradiated with electromagnetic waves while changing the frequency within the range of 20 GHz to 110 GHz. However, there are no particular limitations.
The details of the material of the standard unit can be the same as those of the first unit.

The amount of electromagnetic waves absorbed by the standard film can be calculated by the following formula (3).
Absorption amount=input signal−reflection characteristic (S11)−transmission characteristic (S21) (3)
The input signal is a measure of the intensity of the electromagnetic wave at the source when the electromagnetic wave is irradiated onto a standard film.
The reflection characteristic (S11) is an index of the intensity of an electromagnetic wave reflected by a standard film when the standard film is irradiated with an electromagnetic wave from an irradiation source. The reflection characteristic (S11) can be measured by a free space method using, for example, a vector network analyzer.
The transmission characteristic (S21) is an index of the intensity of electromagnetic waves transmitted through a standard film when the standard film is irradiated with electromagnetic waves from an irradiation source. The transmission characteristic (S21) can be measured, for example, by a free space method using a vector network analyzer.

For example, the frequency A [GHz] can be specified by the following method.
First, a 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 equation (3).
Next, an absorption spectrum diagram is created in which the changed frequency is plotted on the horizontal axis and the absorption amount calculated by the above equation (3) is plotted on the vertical axis. Usually, in this absorption spectrum diagram, there is one frequency value on the horizontal axis where the amount of absorption is the maximum value. Therefore, a single peak is formed in the plot where the amount of electromagnetic wave absorption reaches its maximum value. In this way, the frequency of electromagnetic waves when the amount of absorption of electromagnetic waves takes the maximum value can be set to A [GHz].

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

The first electromagnetic wave absorbing pattern 61 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 50 GHz to 110 GHz, more preferably 60 GHz to 100 GHz, even more preferably 65 GHz to 95 GHz, and particularly preferably 70 GHz to 90 GHz. When the frequency value A is within the above numerical range, the electromagnetic wave absorbing layer 20 can absorb electromagnetic waves in the millimeter wave region, and can be easily applied to automobile parts, road peripheral members, building exterior wall related materials, windows, communication devices, radio telescopes, etc.

In method Y, similarly to method X, the amount of electromagnetic waves absorbed by the film can be measured. 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 equation (3).
Next, an absorption spectrum diagram is created in which the frequency is plotted on the horizontal axis and the absorption amount calculated by the above equation (3) is plotted on the vertical axis. Usually, in this absorption spectrum diagram, there is one frequency value on the horizontal axis where the amount of absorption is the maximum value. Therefore, a single peak is formed in the plot where the amount of electromagnetic wave absorption reaches its maximum value. In this way, the frequency of electromagnetic waves when the amount of absorption of electromagnetic waves takes the maximum value can be set to A [GHz].

The material of the first unit u1 is not particularly limited as long as its absorption characteristics can be adjusted to the desired frequency.
Examples of the material of the first unit include a thin metal wire, a conductive thin film, and a fixed conductive paste.
Metal materials include copper, aluminum, tungsten, iron, molybdenum, nickel, titanium, silver, gold, or alloys containing two or more of these metals (for example, stainless steel, steel such as carbon steel, brass, phosphor bronze, zirconium copper alloy, beryllium copper, iron nickel, nichrome, nickel titanium, kanthal, hastelloy, rhenium tungsten, etc.).
Examples of the material for the conductive thin film include metal particles, carbon nanoparticles, and carbon fibers.

The interval between the ends of the figure, which 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 distances between the ends of the figures that are the first unit u1 may be the same or different. However, since it becomes easier to design an electromagnetic wave absorption film that is less affected by the surrounding environment, and the accuracy of the frequency band of the electromagnetic waves to be absorbed improves during manufacturing, the distance between the edges of the figure, which is the first unit u1, is , are preferably identical to each other.

(Second electromagnetic wave absorption pattern)
FIG. 6 is a top view showing the second electromagnetic wave absorption pattern 62.
As shown in FIG. 6, the second electromagnetic wave absorption pattern 62 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 absorption pattern 62 can be said to be an aggregate of second units u2 that are geometric figures.
Each of the second units u2 functions as one antenna. The second electromagnetic wave absorption pattern 62 may be, for example, a thin line pattern of an FSS element.

In the second electromagnetic wave absorption pattern 62, 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. It can also be said that the second electromagnetic wave absorption pattern 62 has a plurality of second arrays R2. The second electromagnetic wave absorption pattern 62 can be constructed by forming the second array R2 on the base material 21 at predetermined intervals along the direction indicated by the double-headed arrow P.
The interval between the plurality of second arrays R2 is not particularly limited. The intervals between the second arrays R2 may be regular or irregular.

FIG. 7 is a top view showing the second unit u2.
As shown in FIG. 7, the shape of the second unit u2 is a cross shape that is vertically and horizontally symmetrical. 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 FIG. Each straight end T2 is in contact with each of both ends of the straight line portion parallel to the x-axis direction and both ends of the straight line portion parallel to the y-axis direction so as to be orthogonal to each straight line portion.

In the electromagnetic wave absorption 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 waves generated by the second unit u2 functioning as one antenna can be adjusted. Absorption properties can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction as well.

In the electromagnetic wave absorption layer 20, the shapes of the plurality of second units u2 are the same. However, the shapes of the plurality of second units u2 do not have to be the same figure. In other examples of the present invention, the shapes of the plurality of second units may be the same or different as long as the absorption characteristics can be adjusted to the desired frequency.

The second electromagnetic wave absorption pattern 62 selectively absorbs electromagnetic waves whose frequency is B [GHz] that satisfies the following formula (1). The frequency value B [GHz] is the frequency value when the amount of electromagnetic waves absorbed by the second electromagnetic wave absorption pattern 62 shows a maximum value. The frequency value B [GHz] satisfies the following formula (1).
1.037×A≦B≦1.30×A...Formula (1)

As shown in the above equation (1), the second electromagnetic wave absorption pattern 62 absorbs electromagnetic waves having a frequency of 1.037×A [GHz] to 1.30×A [GHz]. The second electromagnetic wave absorption pattern 62 preferably absorbs electromagnetic waves having a frequency of 1.17×A [GHz] to 1.30×A [GHz].
Since the second electromagnetic wave absorption pattern 62 absorbs electromagnetic waves with a frequency of 1.037×A [GHz] or higher, the amount of electromagnetic waves absorbed by the second electromagnetic wave absorption pattern 62 in a frequency band higher than A [GHz] is The peak and the peak of the amount of electromagnetic wave absorbed by the first electromagnetic wave absorption pattern 61 sufficiently overlap. As a result, compared to a film having only the first electromagnetic wave absorption pattern 61, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorption film is expanded to a frequency band higher than A [GHz].
Since the second electromagnetic wave absorption pattern 62 absorbs electromagnetic waves with a frequency of 1.30×A [GHz] or less, the amount of electromagnetic waves absorbed by the second electromagnetic wave absorption pattern 62 in a frequency band higher than A [GHz] is The difference in frequency between the peak and the peak of the amount of electromagnetic waves absorbed by the first electromagnetic wave absorption pattern 61 becomes smaller. As a result, a single peak is formed in which the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorbing film becomes a maximum value.
From the above, since the second electromagnetic wave absorption pattern 62 absorbs electromagnetic waves with a frequency of 1.037×A [GHz] to 1.30×A [GHz], the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorption film is is extended to the higher frequency band.

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 desired frequency. For example, the shape of the figure that is the second unit includes a circular shape, an annular shape, a linear shape, a rectangular shape, a polygonal shape, an H-shape, a Y-shape, a V-shape, and the like.

The material of the second unit constituting the second electromagnetic wave absorption pattern 62 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. Not done.
The material of the second unit is the same as that described for the material of the first unit u1.

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 a 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 each other. However, it is preferable that the intervals between the ends of the figures that are the second units u2 are the same from the viewpoint of making it easier to design an electromagnetic-wave-absorbing film that is less susceptible to the effects of the surrounding environment and improving the precision of the frequency band of the electromagnetic waves to be absorbed during manufacturing.

(Third electromagnetic wave absorption pattern)
FIG. 8 is a top view showing the third electromagnetic wave absorption pattern 63.
As shown in FIG. 8, the third electromagnetic wave absorption pattern 63 is composed of a plurality of third units u3. Each of the third units u3 is a geometric figure. That is, it can be said that the third electromagnetic wave absorption pattern 63 is an aggregate of third units u3 that are geometric figures.
Each of the third units u3 functions as one antenna. The third electromagnetic wave absorption pattern 63 may be, for example, a thin line pattern of an FSS element.

In the third electromagnetic wave absorption pattern 63, 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. It can also be said that the third electromagnetic wave absorption pattern 63 has a plurality of third arrays R3. The third electromagnetic wave absorption pattern 63 can be constructed by forming the third array R3 on the base material 21 at predetermined intervals along the direction indicated by the double-headed arrow P.
The spacing between the plurality of third arrays R3 is not particularly limited. The intervals between the third arrays R3 may be regular or irregular.

FIG. 9 is a top view showing the third unit u3.
As shown in FIG. 9, the shape of the third unit u3 is a cross shape that is vertically and horizontally symmetrical. 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 FIG. Each straight end T3 is in contact with each of both ends of the straight line portion parallel to the x-axis direction and both ends of the straight line portion parallel to the y-axis direction so as to be orthogonal to each straight line portion.

In the electromagnetic wave absorption 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 waves generated by the third unit u3 functioning as one antenna can be adjusted. Absorption properties can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction as well.

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 figures. 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 the desired frequency.

The third electromagnetic wave absorption pattern 63 selectively absorbs electromagnetic waves whose frequency is C [GHz] that satisfies the following formula (2). The frequency value C [GHz] is the frequency value when the amount of electromagnetic waves absorbed by the third electromagnetic wave absorption pattern 63 shows a maximum value. The frequency value C [GHz] satisfies the following formula (2).
0.60×A≦C≦0.963×A...Formula (2)

As shown in the above equation (2), the third electromagnetic wave absorption pattern 63 absorbs electromagnetic waves having a frequency of 0.60×A [GHz] to 0.963×A [GHz]. The third electromagnetic wave absorption pattern 63 preferably absorbs electromagnetic waves having a frequency of 0.60×A [GHz] to 0.83×A [GHz].
Since the third electromagnetic wave absorption pattern 63 absorbs electromagnetic waves with a frequency of 0.60×A [GHz] or higher, the amount of electromagnetic waves absorbed by the third electromagnetic wave absorption pattern 63 in the frequency band lower than A [GHz] is The difference in frequency between the peak and the peak of the amount of electromagnetic waves absorbed by the first electromagnetic wave absorption pattern 61 becomes smaller. As a result, a single peak is formed in which the amount of electromagnetic waves absorbed by the entire electromagnetic wave absorbing layer 20 becomes a maximum value.
Since the third electromagnetic wave absorption pattern 63 absorbs electromagnetic waves with a frequency of 0.963×A [GHz] or less, the amount of electromagnetic waves absorbed by the third electromagnetic wave absorption pattern 63 in the frequency band lower than A [GHz] is The peak and the peak of the amount of electromagnetic wave absorbed by the first electromagnetic wave absorption pattern 61 sufficiently overlap. As a result, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorbing film is expanded to a frequency band lower than A [GHz] compared to a film having only the first electromagnetic wave absorbing pattern 61.
From the above, since the third electromagnetic wave absorption pattern 3 absorbs electromagnetic waves with a frequency of 0.60 × A [GHz] to 0.963 × A [GHz], the absorption of electromagnetic waves absorbed by the entire electromagnetic wave absorption layer 20 The amount is extended to the lower frequency band.

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 a desired frequency. For example, the shape of the figure that is the third unit includes a circular shape, an annular shape, a linear shape, a rectangular shape, a polygonal shape, an H-shape, a Y-shape, a V-shape, and the like.

The material of the third unit u3 constituting the third electromagnetic wave absorption pattern 63 is not particularly limited as long as it is capable of absorbing C [GHz] electromagnetic waves. Not limited.
The material of the third unit u3 is the same as that described for the material of the first unit u1.

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 a 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 each other. However, it is preferable that the intervals between the ends of the figures that are the third units u3 are the same from the viewpoint of making it easier to design an electromagnetic-wave-absorbing film that is less susceptible to the effects of the surrounding environment and improving the precision of the frequency band of the electromagnetic waves to be absorbed during manufacturing.

In the electromagnetic wave absorption layer 20 shown in FIG. 3, a first array R1, a second array R2, and a third array R3 are arranged along the direction indicated by a double arrow P so as to be adjacent to each other. In this way, since the first array R1, the second array R2, and the third array R3 are arranged on the base material 21 so as to be adjacent to each other, the first electromagnetic wave absorption pattern 61 selectively absorbs The frequency band of electromagnetic waves selectively absorbed by the second electromagnetic wave absorption pattern 62 and the electromagnetic waves selectively absorbed by the third electromagnetic wave absorption pattern 63 based on the frequency value A [GHz] of the peak position of the electromagnetic waves Both frequency bands overlap. As a result, the absorption range of electromagnetic waves absorbed by the entire electromagnetic wave absorption layer 20 is likely to be expanded to both the high frequency side and the low frequency side with respect to the frequency value A [GHz] at the peak position.

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 between the third unit u3 and the first unit u1 shown in FIG. 3, respectively. The distance d3 may be the same or different.
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 distance d1, distance d2, and distance d3 are each within the above numerical range, the absorption range of electromagnetic waves absorbed by the entire electromagnetic wave absorption layer 20 is likely to be further expanded with respect to the frequency value A [GHz] at the peak position. Become.

In the electromagnetic wave absorption layer 20, the shapes of the first unit u1, the second unit u2, and the third unit u3 are the same. However, the shapes of the first unit u1, the second unit u2, and the third unit u3 do not have to be the same figure. That is, in other examples of the present invention, the shapes of the first unit u1, the second unit u2, and the third unit u3 may be the same or different.

The electromagnetic wave absorption layer 20 may have a plurality of second electromagnetic wave absorption patterns 62. For example, in addition to the second electromagnetic wave absorption pattern 2, the electromagnetic wave absorption layer 20 may further include an electromagnetic wave absorption pattern 62a and an electromagnetic wave absorption pattern 62b described below.
Electromagnetic wave absorption pattern 62a: An electromagnetic wave absorption pattern in which the frequency value at which the absorbed amount of electromagnetic waves shows a maximum value is D [GHz] that satisfies the following formula (4).
Electromagnetic wave absorption pattern 62b: An electromagnetic wave absorption pattern in which the frequency value at which the amount of absorbed electromagnetic waves shows a maximum value is E [GHz] that satisfies 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.

When the electromagnetic wave absorption layer 20 further includes an electromagnetic wave absorption pattern 62a and an electromagnetic wave absorption pattern 62b in addition to the second electromagnetic wave absorption pattern 62, the amount of electromagnetic wave absorbed by the second electromagnetic wave absorption pattern 62 has a maximum value. The value of the frequency indicating this is preferably 1.17×A [GHz] to 1.30×A [GHz]. In this case, the effect of expanding the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorption layer 20 toward the higher frequency side is even more remarkable, and the effects of the present invention can be obtained even more noticeably.

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 63, the electromagnetic wave absorption layer 20 may further include an electromagnetic wave absorption pattern 63a and an electromagnetic wave absorption pattern 63b described below.
Electromagnetic wave absorption pattern 63a: An electromagnetic wave absorption pattern in which the frequency value at which the amount of absorbed electromagnetic waves shows a maximum value is F [GHz] that satisfies the following formula (6).
Electromagnetic wave absorption pattern 63b: An electromagnetic wave absorption pattern in which the frequency value at which the absorbed amount of electromagnetic waves shows a maximum value is G [GHz] that satisfies the following formula (7).
0.91×A<F≦0.963×A...Formula (6)
0.83×A<G≦0.91×A...Formula (7)
In the following formulas (6) and (7), A is the frequency [GHz] specified by method X or method Y described above.

When the electromagnetic wave absorption layer 20 further includes an electromagnetic wave absorption pattern 63a and an electromagnetic wave absorption pattern 63b in addition to the third electromagnetic wave absorption pattern 63, the amount of electromagnetic wave absorbed by the third electromagnetic wave absorption pattern 63 reaches a maximum value. The value of the frequency shown is preferably 0.60×A [GHz] to 0.83×A [GHz]. In this case, the effect of extending the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave absorbing layer 20 to the lower frequency side is even more remarkable, and the effects of the present invention can be obtained even more noticeably.

FIG. 10 is a cross-sectional view taken along line VIII-VIII of the electromagnetic wave absorbing layer 20 in FIG.
The base material 21 has two surfaces 21a and 21b facing each other. A first electromagnetic wave absorption pattern 61, a second electromagnetic wave absorption pattern 62, and a third electromagnetic wave absorption pattern 63 are formed on one surface 21a of the base material 21. As shown in FIG. 10, 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.

The base material 21 is not particularly limited as long as it is flat and has a form in which the first electromagnetic wave absorption pattern 61, the second electromagnetic wave absorption pattern 62, and the third electromagnetic wave absorption pattern 63 can be formed on one surface 21a. Not done. The base material 21 may have a single layer structure or a multilayer structure.

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 61, the thickness H2 of the second electromagnetic wave absorption pattern 62, and the thickness H3 of the third electromagnetic wave absorption pattern 63 are not particularly limited. Thickness H1, thickness H2, and thickness H3 can be arbitrarily changed according to desired characteristics. Further, the thickness H1, the thickness H2, and the thickness H3 may be the same or different.
The thickness H1, the thickness H2, and the thickness H3 may be, for example, 1 μm to 100 μm, 5 μm to 50 μm, or 10 μm to 30 μm. The thicker each of the thickness H1, the thickness H2, and the thickness H3, the better the electromagnetic wave absorbability, but the higher the manufacturing cost. Taking this point into consideration, each of the thicknesses H1, H2, and H3 may be set.

The material of the base material 21 can be selected as appropriate depending on the use of the electromagnetic wave absorber 10.
For example, in order to provide the electromagnetic wave absorber 10 with transparency, the base material 21 may be made of a transparent material. In addition, the base material 21 may be made of a flexible material for the purpose of providing followability to the curved surface of the electromagnetic wave absorber 10. For the purpose of improving the transparency and three-dimensional formability of the electromagnetic wave absorber 10, the surface of the base material 21 may be made smooth.

For example, the base material 21 can be made of resin. The resin may be a thermoplastic resin or a thermosetting resin. However, when considering the three-dimensional formability of the electromagnetic wave absorber 10, it is preferable that the base material 21 contains a thermoplastic resin.
Examples of thermoplastic resins include polyolefin resins, polyester resins, polyacrylic resins, polystyrene resins, polyimide resins, polyimide amide resins, polyamide resins, polyurethane resins, polycarbonate resins, polyarylate resins, melamine resins, epoxy resins, urethane resins, Examples include silicone resin and fluororesin.
Specific examples of polyolefin resins include polypropylene, polyethylene, and the like. Specific examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like.

As the thermosetting resin, for example, an epoxy resin composition, a resin composition that is cured by a urethane reaction, or a resin composition that is cured by a radical polymerization reaction can be used. These may be used alone or in combination of two or more.
The epoxy resin composition is a composition containing an epoxy resin and a curing agent. Specific examples of epoxy resins include polyfunctional epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, dicyclopentadiene epoxy resins, and the like.
Specific examples of the curing agent include amine compounds, phenolic curing agents, and the like.
Examples of the resin composition that is cured by a urethane reaction include a resin composition containing a (meth)acrylic polyol and a polyisocyanate compound.

Examples of resin compositions that can be cured by radical polymerization include (meth)acrylic resins and unsaturated polyesters having radically polymerizable groups in side chains.
The (meth)acrylic resin includes a polymer of vinyl monomers having a reactive group, and a monomer having a group capable of reacting with a reactive group derived from a vinyl monomer and having a radically polymerizable group. Resins obtained by reacting with epoxy resins include epoxy acrylates having (meth)acrylic groups obtained by reacting (meth)acrylic acid or the like at the ends of epoxy resins.
Specific examples of vinyl monomers having reactive groups include acrylic monomers such as hydroxy (meth)acrylate and glycidyl (meth)acrylate.
Specific examples of monomers that have a group that can react with a reactive group derived from a vinyl monomer and also have a radically polymerizable group include (meth)acrylic acid, isocyanate group-containing (meth)acrylate, etc. can be mentioned.
Examples of the unsaturated polyester include unsaturated polyesters obtained by condensing a carboxylic acid (such as fumaric acid) having an unsaturated group with a diol.
The base material 21 may contain optional components within a range that does not impair the effects of the present invention. Examples of optional components include inorganic fillers, colorants, curing agents, anti-aging agents, light stabilizers, flame retardants, conductive agents, antistatic agents, and plasticizers.

Examples of the inorganic filler include metal particles, metal oxide particles, metal hydroxide particles, metal nitride particles, and the like. More specifically, silver particles, copper particles, aluminum particles, nickel particles, zinc oxide particles, aluminum oxide particles, aluminum nitride particles, silicon oxide particles, magnesium oxide particles, aluminum nitride particles, titanium particles, boron nitride particles, nitride Examples include silicon particles, silicon carbide particles, diamond particles, graphite particles, carbon nanotube particles, metal silicon particles, carbon fiber particles, fullerene particles, and glass particles.
Specific examples of colorants include inorganic pigments, organic pigments, dyes, and the like. These may be used alone or in combination of two or more.

In consideration of further improving the electromagnetic wave absorbing performance of the electromagnetic wave absorber 10, the thickness, dielectric constant, electrical conductivity, and magnetic permeability of the substrate 21 can be appropriately set.
When the electrical characteristics of the electromagnetic waves to be absorbed are taken into consideration, the base material 21 may be a layer having a high dielectric constant. When the base material 21 is a layer having a high dielectric constant, the thickness of the electromagnetic wave absorber 10 can be made relatively thin.

The electromagnetic wave absorbing layer 20 can be produced, for example, by the following method.
First, the base material 21 is prepared. Next, the first electromagnetic wave absorbing pattern 61, the second electromagnetic wave absorbing pattern 62, and the third electromagnetic wave absorbing pattern 63 are formed on one surface 21a of the base material 21.
Here, when the first electromagnetic wave absorbing pattern 61 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 61 shows a maximum value is A [GHz].
The second electromagnetic wave absorbing pattern 62 is formed so that the frequency at which the amount of electromagnetic waves absorbed by the second electromagnetic wave absorbing pattern 62 exhibits a maximum value is B [GHz].
The third electromagnetic wave absorbing pattern 63 is formed so that the frequency at which the amount of electromagnetic waves absorbed by the third electromagnetic wave absorbing pattern 63 exhibits a maximum value is C [GHz].
There is no particular limitation on the order of forming the first electromagnetic wave absorbing pattern 61, the second electromagnetic wave absorbing pattern 62, and the third electromagnetic wave absorbing pattern 63. The first electromagnetic wave absorbing pattern 61, the second electromagnetic wave absorbing pattern 62, and the third electromagnetic wave absorbing pattern 63 may be formed in the same process, or may be formed in separate processes.

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

In the printing method, each electromagnetic wave absorption pattern is printed on one surface 21a of the base material 21 to form each unit u1, u2, u3 which is a figure. The printing method is not particularly limited. Examples include methods such as screen printing, gravure printing, and inkjet printing.
Examples of the conductive paste used for printing include a paste-like composition containing at least one member selected from the group consisting of metal particles, carbon nanoparticles, and carbon fibers and a binder resin component. Examples of the metal particles include particles of metals such as copper, silver, nickel, and aluminum.
Examples of the binder resin component include thermoplastic resins such as polyester resins, (meth)acrylic resins, polystyrene resins, and polyamide resins; thermosetting resins such as epoxy resins, amino resins, and polyimide resins. However, the metal particles and the 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 constituting the printed electromagnetic wave absorption pattern can be suppressed, and the reflection of external light can be suppressed.

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

An example of a method for forming an electromagnetic wave absorption pattern using photolithography includes the following method.
First, a resist is applied to the surface of the base material 21, heat treated, and then the solvent is removed from the resist. Next, a desired pattern is exposed to light on the resist, and the resist pattern is developed to form a layer consisting of the resist pattern. Next, a vapor deposited film is formed over the entire surface of the layer made of the base material and the resist pattern, and a resist stripping agent is used to simultaneously remove the layer made of the resist pattern and the vapor deposited film placed thereon. Thereby, an electromagnetic wave absorption pattern can be formed on the surface of the base material.
As another example, a metal thin film is provided on the base material 21, a resist is applied to a part of the surface of the metal thin film, and heat treatment is performed. Next, the portions of the metal thin film to which the resist is not applied are removed by etching. Thereafter, the resist is removed as necessary to form an electromagnetic wave absorption pattern. A metal plating layer (not shown) may be further provided on the surface of each unit u1, u2, u3 constituting each electromagnetic wave absorption pattern.

Specific examples of the metal 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, nickel-chromium alloy, solder, etc., and may have its surface coated with a carbon material, polymer, etc. Examples of the carbon material that coats the surface of the metal wire include carbon black, activated carbon, hard carbon, soft carbon, mesoporous carbon, amorphous carbon such as carbon fiber, graphite, fullerene, graphene, and carbon nanotubes.

"Reflective layer"
The reflective layer 30 has two surfaces 30a and 30b. One surface 30a of the reflective layer 30 is in contact with the other surface 40b of the spacer layer 40.
The reflective layer 30 is not particularly limited as long as it can reflect electromagnetic waves that have come onto the surface of the electromagnetic wave absorber 10 and passed through the electromagnetic wave absorber 10 . A part of the electromagnetic waves that come to the electromagnetic wave absorber 10 is reflected by the electromagnetic wave absorbing layer 20 or absorbed by the electromagnetic wave absorbing layer 20 . On the other hand, electromagnetic waves that are neither reflected nor absorbed by the electromagnetic wave absorption layer 20 are transmitted through the electromagnetic wave absorption layer 20. The electromagnetic waves that have passed through the electromagnetic wave absorbing layer 20 are reflected by the reflective layer 30 toward the electromagnetic wave absorbing layer 20 .
For example, if the reflective layer 30 is conductive in the plane direction of the two surfaces 30a and 30b, the electromagnetic waves transmitted through the electromagnetic wave absorbing layer 20 can be reflected. Specifically, a resin film such as polyethylene terephthalate and a metal foil such as copper foil bonded together may be used as the reflective layer 30. Instead of metal foil, a mesh sheet formed of a conductive film such as ITO, metal wire, etc. may be used.

In consideration of the reflective properties of the reflective layer 30, a metal wire, a conductive thread, a twisted yarn containing a metal wire and a conductive thread, or a conductive thin film may be provided on the other surface 30b of the reflective layer 30. The conductive thin film can be provided on the surface 30b by, for example, a printing method such as screen printing, gravure printing, or inkjet method; sputtering method or vacuum deposition; or photolithography.

When the spacer layer 40 is formed of a conductive object such as a metal, the reflective layer 30 can be omitted because the conductive object such as a metal plays the role of the reflective layer 30.

For the purpose of applying the electromagnetic wave absorber 10 to the surfaces of various articles, the other surface 30b of the reflective layer 30 may be made adhesive. When the other surface 30b of the reflective layer 30 is adhesive, a release film may be provided to cover the surface 30b. The release film is removed when the electromagnetic wave absorber 10 is used. The release film covers the adhesive surface, making it easier to handle during distribution.
For example, by adopting a multilayer structure in which the other surface 30b of the reflective layer 30 is an adhesive layer containing an adhesive, the other surface 30b of the reflective layer 30 can be made adhesive.

Examples of the adhesive include a heat-seal type adhesive that adheres by heat; an adhesive that exhibits stickiness by wetting; a pressure-sensitive adhesive (adhesive) that adheres by pressure; and the like. Among these, pressure-sensitive adhesives (pressure-sensitive adhesives) are preferred from the viewpoint of simplicity.
Specific examples of the adhesive include acrylic adhesives, urethane adhesives, rubber adhesives, polyester adhesives, silicone adhesives, polyvinyl ether adhesives, and the like. Among these, at least one selected from the group consisting of acrylic adhesives, urethane adhesives, and rubber adhesives is preferred, and acrylic adhesives are more preferred.

Examples of the acrylic pressure-sensitive adhesive include the following acrylic polymers.
Acrylic polymer (1) containing a structural unit derived from an alkyl (meth)acrylate having a linear alkyl group or a branched alkyl group (that is, by polymerizing at least an alkyl (meth)acrylate as a monomer) (obtained polymer).
An acrylic polymer (2) containing a structural unit derived from a (meth)acrylate having a cyclic structure (that is, a polymer obtained by polymerizing at least a (meth)acrylate having a cyclic structure).
The acrylic polymer may be a homopolymer or a copolymer. When the acrylic polymer is a copolymer, the form of copolymerization is not particularly limited. The acrylic copolymer may be a block copolymer, a random copolymer, or a graft copolymer.

As the acrylic pressure-sensitive adhesive, the following acrylic copolymer (Q) is preferred.
Acrylic copolymer (Q): A copolymer containing a structural unit (q1) derived from an alkyl (meth)acrylate having a chain alkyl group having 1 to 20 carbon atoms (hereinafter referred to as "monomer component (q1')") and a structural unit (q2) derived from a functional group-containing monomer (hereinafter referred to as "monomer component (q2')").
The acrylic copolymer (Q) may further include a structural unit (q3) other than the structural unit (q1) and the structural unit (q2). The structural unit (q3) is a structural unit derived from a monomer component (q3') other than the monomer component (q1') and the monomer component (q2').

The number of carbon atoms in the chain alkyl group of the monomer component (q1') is preferably from 1 to 12, more preferably from 4 to 8, even more preferably from 4 to 6, from the viewpoint of improving adhesive properties. Specific examples of the monomer component (q1') include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, Examples include lauryl (meth)acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate. Among these, butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, and butyl (meth)acrylate is more preferred.
These may be used alone or in combination of two or more.

Examples of the monomer component (q2') include hydroxy group-containing monomers, carboxy group-containing monomers, epoxy group-containing monomers, amino group-containing monomers, cyano group-containing monomers, keto group-containing monomers, alkoxysilyl group-containing monomers, etc. Can be mentioned. Among these, hydroxy group-containing monomers and carboxyl group-containing monomers are preferred.
Specific examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Examples include hydroxybutyl (meth)acrylate. Among these, 2-hydroxyethyl (meth)acrylate is preferred.
Specific examples of the carboxyl group-containing monomer include (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, etc., with (meth)acrylic acid being preferred.
Specific examples of the epoxy group-containing monomer include glycidyl (meth)acrylate and the like.
Specific examples of the amino group-containing monomer include diaminoethyl (meth)acrylate and the like.
Specific examples of the cyano group-containing monomer include acrylonitrile and the like.
These may be used alone or in combination of two or more.

Examples of the monomer component (q3') include cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclo Examples include (meth)acrylates having a cyclic structure such as pentenyloxyethyl (meth)acrylate, imido(meth)acrylate, and acryloylmorpholine; vinyl acetate; and styrene.
These may be used alone or in combination of two or more.

The content of the structural unit (q1) is preferably 50% by mass to 99.5% by mass, more preferably 55% by mass to 99% by mass, even more preferably 60% by mass to 97% by mass, and particularly preferably 65% by mass to 95% by mass, based on 100% by mass of all structural units of the acrylic copolymer (Q).
The content of the structural unit (q2) is preferably 0.1 to 50% by mass, more preferably 0.5 to 40% by mass, even more preferably 1.0 to 30% by mass, and particularly preferably 1.5 to 20% by mass, based on 100% by mass of all structural units of the acrylic copolymer (Q).
The content of the structural unit (q3) is preferably from 0 to 40 mass%, more preferably from 0 to 30 mass%, even more preferably from 0 to 25 mass%, and particularly preferably from 0 to 20 mass%, based on 100 mass% of all structural units of the acrylic copolymer (Q).

The acrylic copolymer may be crosslinked with a crosslinking agent. Examples of the crosslinking agent include epoxy crosslinking agents, isocyanate crosslinking agents, aziridine crosslinking agents, metal chelate crosslinking agents, and the like. When crosslinking an acrylic copolymer, a functional group derived from the monomer component (q2') can be used as a crosslinking point that reacts with a crosslinking agent.

For the purpose of improving impact resistance, etc., the adhesive layer may be made of a material that is cured by energy rays such as ultraviolet rays, visible energy rays, infrared rays, and electron beams. In this case, the adhesive layer contains an energy ray-curable component.
Examples of the energy ray-curable component include, when the energy ray is ultraviolet rays, compounds having two or more ultraviolet polymerizable functional groups in one molecule. Specific examples of compounds having two or more ultraviolet polymerizable functional groups in one molecule include trimethylolpropane tri(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, Tetramethylolmethanetetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, caprolactone modified dipentaerythritol hexa(meth)acrylate, 1. 4-Butylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, dicyclopentadiene dimethoxy di(meth)acrylate, polyethylene glycol di(meth)acrylate, oligoester(meth)acrylate, urethane(meth)acrylate ) acrylate oligomers, epoxy-modified (meth)acrylates, polyether (meth)acrylates, and the like.
These may be used alone or in combination of two or more.

When the adhesive layer is energy ray curable, it is preferable to use a photopolymerization initiator together. The photoinitiator increases the curing rate.
Specific examples of the photopolymerization initiator include benzophenone, acetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin benzoic acid, benzoin methyl benzoate, benzoin dimethyl ketal, 2,4 -Diethylthioxanthone, 1-hydroxycyclohexylphenylketone, benzyldiphenylsulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, 2-chloroanthraquinone, 2,4,6-trimethylbenzoyldiphenylphos Examples include fin oxide, 2-benzothiazole-N,N-diethyldithiocarbamate, and oligo{2-hydroxy-2-methyl-1-[4-(1-propenyl)phenyl]propanone}.

"Spacer layer"
The spacer layer 40 is provided on the other surface 21b of the base material 21 that the electromagnetic wave absorption layer 20 has.
Spacer layer 40 has two surfaces 40a and 40b. One surface 40a of the spacer layer 40 is in contact with the other surface 21b of the base material 21. The reflective layer 30 is provided on the other surface 40b of the spacer layer 40.
The spacer layer 40 may have a single layer structure or a multilayer structure.

The material of the spacer layer 40 can be appropriately selected depending on the use of the electromagnetic wave absorbing film. For example, the spacer layer 40 may be made of a transparent material for the purpose of providing transparency to the electromagnetic wave absorbing film. Alternatively, the spacer layer 40 may be made of a flexible material for the purpose of providing followability to the curved surface of the electromagnetic wave absorbing film.
Examples of flexible materials include plastic films, rubber, paper, cloth, nonwoven fabrics, foam sheets, rubber sheets, and the like. Among these, foam sheets are preferred from the viewpoint of conformability to the curved surface of the electromagnetic wave absorber 10.
As a specific example of the resin constituting the plastic film, the same thermoplastic resin as described for the above-mentioned base material 21 can be used, for example.
As the foamed sheet, for example, a foamed sheet formed into a sheet shape by foaming the resin constituting the plastic film can be used. Specific examples of foam sheets include polyethylene foam, polypropylene foam, polyurethane foam, and the like.

When considering the wavelength shortening effect of the spacer layer 40, the thickness of the spacer layer 40 is appropriately changed according to the wavelength of the electromagnetic wave to be absorbed and the dielectric constant of the spacer layer 40.
When considering the wavelength shortening effect of the spacer layer 40, the thickness of the spacer layer 40 in the z-axis direction preferably satisfies the following formula (8).
(Thickness of spacer layer 40 in z-axis direction) = (λ) x (1/4)/(ε) ^1/2 ...Equation (8)
In the above formula (8), λ is the wavelength of the incoming electromagnetic wave, and ε is the relative dielectric constant of the spacer layer 40. The thickness of the spacer layer 40 in the z-axis direction may be adjusted as appropriate for absorption characteristics. For example, it can be changed within a range of 0.1 to 3.0 times the thickness in the z-axis direction of the spacer layer 40 obtained by equation (8).

When the relationship between the thickness of the spacer layer 40 in the z-axis direction and the wavelength λ satisfies the above formula (8), the electromagnetic wave absorber 10 has a so-called λ/4 structure, which further increases the maximum absorption amount of electromagnetic waves by the electromagnetic wave absorber 10.
The thickness of the spacer layer 40 can be appropriately set depending on the wavelength λ of the electromagnetic wave to be absorbed. The thickness of the spacer layer 40 may be, for example, 25 μm to 5000 μm, 50 μm to 4500 μm, or 100 μm to 4000 μm.
The spacer layer 40 may be made of a material with a high dielectric constant. If the spacer layer 40 is a layer with a high dielectric constant, the thickness of the spacer layer 40 can be made relatively thin.
When the dielectric constant of the spacer layer 40 is taken into consideration, the spacer layer 40 preferably contains at least one material selected from the group consisting of barium titanate, titanium oxide, and strontium titanate.

It is preferable that the spacer layer 40 contains at least one kind selected from the group consisting of a plastic film, a foam sheet, and a rubber sheet, and among these, it is more preferable that the spacer layer 40 contains a foam sheet. When the spacer layer 40 is made of at least one kind selected from the group consisting of a plastic film, a foam sheet, and a rubber sheet, the ability to follow the curved surface of the electromagnetic wave absorber 10 is improved.
The spacer layer 40 may have a single layer structure made of a single sheet or a multilayer structure made of a laminate of a plurality of sheets. The material and structure of the sheet constituting the spacer layer 40 can be selected as appropriate depending on the use of the electromagnetic wave absorbing sheet.

The two surfaces 40a, 40b of the spacer layer 40 are preferably adhesive. Thereby, the electromagnetic wave absorbing layer 10 and the reflective layer 30 can be bonded to each of the two surfaces 40a and 40b. For example, by employing a multilayer structure in which the two surfaces 40a, 40b are adhesive layers containing an adhesive, the two surfaces 40a, 40b can be made adhesive.
The details and preferred embodiments of the adhesive layer can be the same as those described for the adhesive layer in the base material 21.

"Protective layer"
The protective layer 50 is provided on one surface 20a of the electromagnetic wave absorbing layer 20. When the electromagnetic wave absorption layer 20 has the base material 21 and the electromagnetic wave absorption pattern 22, the protective layer 50 is provided on one surface 21a of the base material 21 so as to cover the electromagnetic wave absorption layer 20.
The protective layer 50 is not particularly limited as long as it can protect the electromagnetic wave absorbing layer 20.

The thickness of the protective layer 50 is preferably 1 μm to 500 μm, more preferably 3 μm to 100 μm, and even more preferably 5 μm to 50 μm. When the thickness of the protective layer 50 is equal to or greater than the above lower limit, it can adequately conform to and protect the irregularities of the electromagnetic wave absorbing layer. When the thickness of the protective layer 50 is equal to or less than the above upper limit, the composition constituting the protective layer is prevented from seeping out from the sides, and flexibility can be imparted to the electromagnetic wave absorber.

The protective layer 50 is composed of a cured product of a composition containing a modified polyolefin resin and a polyphenylene ether resin having a reactive group. By making a cured product of this composition, a protective layer with low dielectric properties can be obtained, and changes in frequency characteristics can be suppressed.

Examples of the modified polyolefin resin include, but are not particularly limited to, acid-modified polyolefin resins, silane-modified polyolefin resins, and the like. Acid-modified polyolefin resins are preferred because they have excellent adhesive strength.

The content of the modified polyolefin resin in the protective layer 50 is preferably more than 50% by mass, more preferably 55% by mass or more, and even more preferably 60% by mass or more, based on the total amount of the protective layer 50. The upper limit of the content of the modified polyolefin resin in the protective layer 50 may be 90% by mass or less, or 80% by mass or less based on the total amount of the protective layer 50. If the content of the modified polyolefin resin is below the above lower limit, the protective layer 50 will have high dielectric properties, and the reflection loss of the electromagnetic wave absorber will increase.

The polyphenylene ether resin having a reactive group is not particularly limited, but a polyphenylene ether resin in which the reactive group contains an ethylenically unsaturated bond is preferable. Specific examples of the reactive group of the polyphenylene ether resin having a reactive group containing a group containing an ethylenically unsaturated bond include a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a cyclopentenyl group, a vinylbenzyl group, and a vinylnaphthyl group. Examples include groups. The reactive group is more preferably a vinylbenzyl group because a composition having lower dielectric properties can be easily obtained.

The content of polyphenylene ether resin having reactive groups in the protective layer 50 is preferably 1% by mass to 50% by mass, and more preferably 10% by mass to 50% by mass, of the total amount of the protective layer 50. If the content of polyphenylene ether resin having reactive groups is equal to or greater than the lower limit, the glass transition temperature after curing is high, and the resistance to high temperature and high humidity is high. If the content of polyphenylene ether resin having reactive groups is equal to or less than the upper limit, the adhesive strength is low, and the protective layer 50 may peel off from the electromagnetic wave absorbing layer 20.

The composition preferably further contains at least one compound having an alicyclic skeleton and a cyclic ether group. The compound having an alicyclic skeleton and a cyclic ether group is not particularly limited, but examples thereof include polyglycidyl ethers of polyhydric alcohols having at least one alicyclic structure, and cycloalkene oxide compounds such as cyclohexene oxide and cyclopentene oxide-containing compounds obtained by epoxidizing cyclohexene or cyclopentene ring-containing compounds with an oxidizing agent. Among these, from the viewpoint of being able to impart high adhesive strength, it is preferable that the compound having an alicyclic skeleton and a cyclic ether group is a compound that is liquid at 25°C.

The content of the compound having an alicyclic skeleton and a cyclic ether group is preferably 1% by mass or more, more preferably 2% by mass to 15% by mass, based on the total amount of the protective layer 50 in the total amount of the composition. preferable. If the content of the compound having an alicyclic skeleton and a cyclic ether group is below the above upper limit, the adhesive strength will decrease, and the protective layer 50 may peel off from the electromagnetic wave absorbing layer 20.

The composition may further contain a curing agent. It is preferable that the composition contains a curing agent because the curing reaction proceeds more efficiently.
The curing agent is not particularly limited as long as it starts a curing reaction. Since it has excellent stability over time and productivity, a curing agent that initiates a curing reaction by heating is preferably used.
Examples of the curing agent that initiates the curing reaction by heating include thermal cationic polymerization initiators and other heat-reactive curing agents.

[Method of manufacturing electromagnetic wave absorber]
The electromagnetic wave absorber 10 can be manufactured, for example, by the following method.
A composition is prepared that includes a modified polyolefin resin and a polyphenylene ether resin having reactive groups.
The composition can be obtained by adding the modified polyolefin resin and the polyphenylene ether resin having a reactive group to a solvent, stirring and mixing them to dissolve the resins in the solvent.
The composition may contain various additives, such as a silane coupling agent and a curing agent, in addition to the modified polyolefin resin and the polyphenylene ether resin having a reactive group, as necessary.
The curing agent is not particularly limited as long as it initiates a curing reaction. As the curing agent, one that initiates a curing reaction by heating is preferably used because of its excellent stability over time and productivity. By including a curing agent, the curing reaction of the composition proceeds more efficiently, which is preferable. As the curing agent that initiates a curing reaction by heating, a thermal cationic polymerization initiator or other thermally reactive curing agent can be mentioned.
As the silane coupling agent, known silane coupling agents can be used, among which, an organosilicon compound having at least one alkoxysilyl group in the molecule is preferred.
The solvent is not particularly limited as long as it can dissolve the modified polyolefin resin and the polyphenylene ether resin having a reactive group, and examples thereof include aromatic hydrocarbon solvents such as benzene and toluene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as n-pentane, n-hexane and n-heptane; and alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane and methylcyclohexane.

The above composition is applied to one side 20a of the electromagnetic wave absorbing layer 20 produced as described above, and the resulting coating film is heated and cured to form a protective layer 50 on the electromagnetic wave absorbing layer 20. .
The method of applying the composition is not particularly limited. Examples of the coating method include methods using printing methods such as screen printing, gravure printing, and inkjet printing.

The above-mentioned composition is applied onto the release-treated surface of the release film, and the resulting coating film is dried to form an adhesive layer. The release-treated surface of another release film is bonded onto this adhesive layer to obtain an adhesive sheet.
Next, one side of the release film of the adhesive sheet is peeled off, and the exposed one side of the adhesive sheet is attached to the other side 20b of the electromagnetic wave absorbing layer 20.

Next, the other side of the release film of the adhesive sheet is peeled off, and a material that will become the spacer layer 40 is attached to the other exposed surface of the adhesive sheet.
Next, as in the case of the spacer layer 40, the material that will become the reflective layer 30 is attached to the other surface 40b of the spacer layer 40 via the adhesive sheet.
By the above method, electromagnetic wave absorption 10 is obtained.

As explained above, in the electromagnetic wave absorber 10 of this embodiment, the electromagnetic wave absorbing layer 20, the reflective layer 30 disposed on the back surface 20b side of the electromagnetic wave absorbing layer 20, the electromagnetic wave absorbing layer 20 and the reflective layer 30, The electromagnetic wave absorbing layer 20 includes a spacer layer 40 disposed between the layers, and a protective layer 50 formed on the surface 20a of the electromagnetic wave absorbing layer 20. The electromagnetic wave absorbing layer 20 is made of a frequency selective surface, and the protective layer 50 is made of It is composed of a cured product of a composition containing a polyphenylene ether resin having a reactive group. Therefore, in the electromagnetic wave absorber 10 of this embodiment, the change in frequency characteristics is small due to the protective layer 50 provided to protect the electromagnetic wave absorbing layer 20.
In the electromagnetic wave absorber 10 of this embodiment, the electromagnetic wave absorbing layer 20 includes a base material 21 and an electromagnetic wave absorbing pattern 22 provided on the base material 21, and the electromagnetic wave absorbing pattern 22 includes a first electromagnetic wave absorbing pattern 61. , the second electromagnetic wave absorption pattern 62 and the third electromagnetic wave absorption pattern 63, it is possible to support a wide frequency band.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example]
A first electromagnetic wave absorption pattern, a second electromagnetic wave absorption pattern, and a third electromagnetic wave absorption pattern as shown in FIG. An absorbent film was produced.
The shapes of the first electromagnetic wave absorption pattern, the second electromagnetic wave absorption pattern, and the third electromagnetic wave absorption pattern were cross-shaped as shown in FIGS. 5, 7, and 9, respectively. The thicknesses of the first electromagnetic wave absorption pattern, the second electromagnetic wave absorption pattern, and the third electromagnetic wave absorption pattern were all 18 μm. Furthermore, copper was used as the material for the first electromagnetic wave absorption pattern, the second electromagnetic wave absorption pattern, and the third electromagnetic wave absorption pattern.
100 parts by mass of modified polyolefin resin (trade name: UNISTOL H-200, manufactured by Mitsui Chemicals), 50 parts by mass of polyphenylene ether resin (trade name: OPE-2St 1,200, manufactured by Mitsubishi Gas Chemical Co., Ltd.), containing cyclic ether group 3 parts by mass of compound (product name: YX8000, manufactured by Mitsubishi Chemical Corporation), 0.15 parts by mass of curing agent (product name: SAN-AID SI-B3, manufactured by Sanshin Chemical Co., Ltd.), and silane coupling agent (product name: KBM- 4803, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in toluene to prepare an adhesive composition.
The above adhesive composition is applied to one side of the electromagnetic wave absorbing film so as to cover the electromagnetic wave absorbing pattern, and the resulting coating film is heated at 160 ° C. for 1 hour to cure, and on the electromagnetic wave absorbing film, A protective layer was formed to cover the electromagnetic wave absorption pattern.
The above adhesive composition was applied onto the release-treated surface of a release film (first release film, trade name: SP-PET752150, manufactured by Lintec), and the resulting coating film was dried at 100°C for 2 minutes to determine the thickness. formed an adhesive layer with a thickness of 15 μm. On this adhesive layer, the release-treated side of another release film (second release film, trade name: SP-PET381130, manufactured by Lintec Corporation) was laminated to obtain an adhesive sheet.
The first release film of the adhesive sheet was peeled off, and one side of the exposed adhesive sheet was attached to the other side of the electromagnetic wave absorbing film.
The second release film of the adhesive sheet was peeled off, and a urethane foam material (trade name: Poron HH-48, thickness 2 mm, manufactured by Rogers INOAC Corporation) was attached as a spacer layer to the other surface of the exposed adhesive sheet. .
Next, electrolytic copper foil (trade name: CF-V9S-SV, thickness 18 μm, Fukuda Metals Co., Ltd. (manufactured by Powder Industry Co., Ltd.) was attached.
Through the above steps, the electromagnetic wave absorber of the example was obtained.

[Comparative Example]
Instead of forming a protective layer using the above adhesive composition, a film with adhesive (product name: PET25PL Thin, thickness 43 μm, substrate: PET film, substrate thickness: 25 μm, adhesive: acrylic adhesive, manufactured by Lintec Corporation) was used as the protective layer. The film with adhesive was attached to one side of the electromagnetic wave absorbing film so as to cover the electromagnetic wave absorbing pattern, thereby forming a protective layer 50.
Except for this, the electromagnetic wave absorber of the comparative example was obtained in the same manner as in the example.

[evaluation]
"Evaluation of electromagnetic wave absorption"
For the electromagnetic wave absorbers obtained in the examples and comparative examples, the electromagnetic wave reflection characteristics (S11) were obtained using the free space method using a vector network analyzer in the band of 75 GHz to 85 GHz, and this was calculated as reflection attenuation (absorption). Evaluated as quantity. For example, in the case of total reflection, it is 0 dB with no attenuation, and in the case of partial reflection, it is -10 dB with 90% attenuation, and -20 dB with 99% attenuation.
Note that an electromagnetic wave absorber produced in the same manner as in the example except that no protective layer was provided was used as a reference example.
The results are shown in Table 1 and FIGS. 11 to 13. FIG. 11 is a diagram showing the results of measuring the return loss of the electromagnetic wave absorber of the reference example. FIG. 12 is a diagram showing the results of measuring the return loss of the electromagnetic wave absorber of the example. FIG. 13 is a diagram showing the results of measuring the return loss of the electromagnetic wave absorber of the comparative example.

From the results shown in Table 1 and FIGS. 11 to 13, the electromagnetic wave absorber of the example had a slight shift in the frequency peak and the return loss was almost the same as that of the electromagnetic wave absorber of the reference example. . That is, although the electromagnetic wave absorber of the example had a protective layer, it was confirmed that the change in frequency characteristics was small compared to the electromagnetic wave absorber of the reference example.
On the other hand, the electromagnetic wave absorber of the comparative example had a large frequency peak shift and a small amount of return loss compared to the electromagnetic wave absorber of the reference example. That is, it was confirmed that the electromagnetic wave absorber of the comparative example had a larger change in frequency characteristics than the electromagnetic wave absorber of the reference example because the PET film was provided as a protective layer.

The electromagnetic wave absorber of the present invention can be used for automobile parts, road peripheral members, building exterior wall related materials, windows, communication equipment, radio telescopes, and the like.

10 Electromagnetic wave absorber 20 Electromagnetic wave absorbing layer 21 Base material 22 Electromagnetic wave absorbing pattern 30 Reflective layer 40 Spacer layer 50 Protective layer 61 First electromagnetic wave absorbing pattern 62 Second electromagnetic wave absorbing pattern 63 Third electromagnetic wave absorbing pattern

Claims (9)

an electromagnetic wave absorption layer;
a reflective layer disposed on the back side of the electromagnetic wave absorbing layer;
a spacer layer disposed between the electromagnetic wave absorbing layer and the reflective layer;
a protective layer formed on the surface of the electromagnetic wave absorbing layer,
the electromagnetic wave absorbing layer comprises a frequency selective surface;
The protective layer is an electromagnetic wave absorber made of a cured product of a composition containing a modified polyolefin resin and a polyphenylene ether resin having a reactive group. The electromagnetic wave absorber according to claim 1, wherein the content of the modified polyolefin resin in the protective layer is more than 50% by mass based on the total amount of the protective layer. The electromagnetic wave absorber according to claim 1 or 2, wherein the reactive group of the polyphenylene ether resin contains an ethylenically unsaturated bond. The electromagnetic wave absorber according to any one of claims 1 to 3, wherein the composition contains a compound having at least one alicyclic skeleton and a cyclic ether group. At least one of the compounds having an alicyclic skeleton and a cyclic ether group is a compound that is liquid at 25°C, and the content of the compound that is liquid at 25°C is 10% by mass or less in the total amount of the composition. , The electromagnetic wave absorber according to claim 4. The electromagnetic wave absorber according to any one of claims 1 to 5, wherein the protective layer has a thickness of 1 μm to 500 μm. The electromagnetic wave absorber according to any one of claims 1 to 6, wherein the electromagnetic wave absorbing layer includes a substrate and an electromagnetic wave absorbing pattern provided on the substrate. The electromagnetic wave absorption pattern includes a first electromagnetic wave absorption pattern, a second electromagnetic wave absorption pattern, and a third electromagnetic wave absorption pattern,
The frequency at which the amount of electromagnetic wave absorbed by the first electromagnetic wave absorption pattern has a maximum value in the range of 20 GHz to 110 GHz is A [GHz],
The frequency at which the amount of electromagnetic waves absorbed by the second electromagnetic wave absorption pattern has a maximum value is B [GHz] that satisfies the following formula (1),
The electromagnetic wave absorber according to claim 7, wherein the frequency at which the amount of electromagnetic wave absorbed by the third electromagnetic wave absorption pattern shows a maximum value is C [GHz] that satisfies the following formula (2).
1.037×A≦B≦1.30×A...(1)
0.60×A≦C≦0.963×A...(2) The first electromagnetic wave absorption pattern has a plurality of first arrays in which a plurality of first units having the same shape are arranged,
The second electromagnetic wave absorption pattern has a plurality of second arrays in which a plurality of second units having the same shape are arranged,
The third electromagnetic wave absorption pattern has a plurality of third arrays in which a plurality of third units having the same shape are arranged,
The electromagnetic wave absorber according to claim 8, wherein the first array, the second array, and the third array are arranged on the base material so that they are adjacent to each other.

Images