JP7778079B2 - Electromagnetic wave control sheet - Google Patents

Description

The present invention relates to an electromagnetic wave control sheet.
This application claims priority based on Japanese Patent Application No. 2020-165243, filed on September 30, 2020, the contents of which are incorporated herein by reference.

Electromagnetic wave control sheets that selectively absorb electromagnetic waves of a predetermined frequency are known. For example, electromagnetic wave control sheets include a first frequency selective shielding layer and a second frequency selective shielding layer. In such electromagnetic wave control sheets, the fine line patterns of FSS (Frequency Selective Surface) elements formed in the first frequency selective shielding layer and the second frequency selective shielding layer allow each layer to absorb electromagnetic waves of a predetermined frequency, and as a whole, selectively block electromagnetic waves of two different frequencies.

There has been a demand for an electromagnetic wave control sheet that can be attached to curved surfaces using TOM (Three Dimension Overlay Method) molding, a molding method that enhances the design and functionality of various three-dimensional objects by laminating a special film onto the surface.
Patent Document 1 describes an electromagnetic wave shielding film used to cover irregularities of 500 μm, which has a storage modulus at 150° C. of 2.0×10 ⁵ MPa to 2.0×10 ⁸ MPa.
Patent Document 2 describes the values of Young's modulus and relative dielectric constant for an electromagnetic wave absorber that can be attached to a non-flat surface.

JP 2014-57041 A Japanese Patent Application Laid-Open No. 2019-4002

The electromagnetic wave shielding film described in Patent Document 1 has a problem in that it has poor formability due to its high storage modulus.
Patent Document 2 does not disclose the storage modulus or glass transition temperature of the electromagnetic wave absorber, and therefore there is a problem in that the electromagnetic wave absorber described in Patent Document 2 has poor moldability.

The present invention has been made in consideration of the above circumstances, and aims to provide an electromagnetic wave control sheet that can be molded into a three-dimensional shape by TOM molding at around 120°C, and further, an electromagnetic wave control sheet that can be attached to an article with a curved surface at the same time as the sheet is molded.

The present invention provides the following electromagnetic wave control sheet.
[1] An electromagnetic wave control sheet comprising a dielectric layer and a conductive pattern provided on the dielectric layer, wherein the length of a long side of the conductive pattern is 2 mm or less, the glass transition temperature of the dielectric layer is 30°C to 120°C, and the storage modulus of the dielectric layer at 120°C is 1.0 x ^10-2 MPa to 1.0 x ¹⁰³ MPa.
[2] The electromagnetic wave control sheet according to [1], which has a base layer including a reflective layer disposed on the back surface side of the dielectric layer, and the conductive pattern is provided on the base layer.
[3] The electromagnetic wave control sheet according to [2], wherein the base layer is made of polyurethane or polyester.
[4] The electromagnetic wave control sheet according to any one of [1] to [3], wherein the conductive patterns are composed of a first conductive pattern, a second conductive pattern, and a third conductive pattern, and the frequency at which the amount of electromagnetic wave absorption by the first conductive pattern shows a maximum value in a range of 20 GHz to 110 GHz is A [GHz], the frequency at which the amount of electromagnetic wave absorption by the second conductive pattern shows a maximum value is B [GHz] that satisfies the following formula (1), and the frequency at which the amount of electromagnetic wave absorption by the third conductive 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 ≦ 0.933 × A (2)
[5] The electromagnetic wave control sheet according to [4], wherein the first conductive pattern has a plurality of first arrays in which a plurality of first units having the same shape are arranged, the second conductive pattern has a plurality of second arrays in which a plurality of second units having the same shape are arranged, and the third conductive pattern has a plurality of third arrays in which a plurality of third units having the same shape are arranged, and the first arrays, the second arrays, and the third arrays are arranged on the base material so as to be adjacent to each other.

The present invention provides an electromagnetic wave control sheet that can be molded into a three-dimensional shape by TOM molding at around 120°C, and further provides an electromagnetic wave control sheet that can be attached to an article with a curved surface at the same time as the sheet is molded.

1 is a cross-sectional view of an electromagnetic wave control sheet according to an embodiment of the present invention, taken along the thickness direction of an electromagnetic wave absorber. 1 is a cross-sectional view of an electromagnetic wave control sheet according to an embodiment of the present invention, taken along the thickness direction of an electromagnetic wave absorber. FIG. 2 is a top view showing an example of a conductive pattern that constitutes an electromagnetic wave control sheet according to an embodiment of the present invention. FIG. 2 is a top view showing an example of a first conductive pattern that constitutes an electromagnetic wave control sheet according to an embodiment of the present invention. FIG. 2 is a top view showing an example of a first unit of a first conductive pattern that constitutes an electromagnetic wave control sheet according to an embodiment of the present invention. FIG. 4 is a top view showing an example of a second conductive pattern that constitutes an electromagnetic wave control sheet according to an embodiment of the present invention. FIG. 10 is a top view showing an example of a second unit of a second conductive pattern that constitutes an electromagnetic wave control sheet according to an embodiment of the present invention. FIG. 10 is a top view showing an example of a third conductive pattern constituting the electromagnetic wave control sheet according to one embodiment of the present invention. FIG. 10 is a top view showing an example of a third unit of a third conductive pattern that constitutes an electromagnetic wave control sheet according to an embodiment of the present invention. FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG.

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

[Electromagnetic wave control sheet]
An embodiment of the present invention will be described below. In the drawings used in the following description, for the sake of convenience, essential parts may be shown enlarged to make the features of the present invention easier to understand, and the dimensional ratios of the components may not necessarily be the same as those in reality.
The electromagnetic wave control sheet of the present invention comprises a dielectric layer and a conductive pattern provided on the dielectric layer. The dielectric layer in the present invention is made of a dielectric material having a given dielectric constant. The dielectric layer may be composed of only a substrate layer, or may be composed of a substrate layer and a spacer layer, and refers to a dielectric material provided between the conductive pattern and the reflective layer. Furthermore, the support constituting the reflective layer described below may be used as the dielectric layer. The electromagnetic wave control sheet of the present invention may have one dielectric layer or two or more dielectric layers.

1 and 2 are cross-sectional views of an electromagnetic wave control sheet according to an embodiment of the present invention, taken along the thickness direction of the electromagnetic wave control sheet. Fig. 1 shows a case where the dielectric layer is a single layer, and Fig. 2 shows a case where the dielectric layer is a two-layer.
1, the electromagnetic wave control sheet 10 according to this embodiment includes a base layer 20 and a conductive pattern 30. The base layer 20 is a dielectric layer (first dielectric layer).
2, the electromagnetic wave control sheet 10 according to this embodiment may include a reflective layer 40 and a spacer layer 50. The spacer layer 50 is a dielectric layer (second dielectric layer).

The conductive pattern 30 is arranged on one side (surface) 20a of the substrate layer 20.

"Base material layer"
The substrate layer 20 is a dielectric layer. The glass transition temperature of the substrate layer 20 is 30°C to 120°C, preferably 40°C to 100°C, and more preferably 50°C to 80°C. If the glass transition temperature of the substrate layer 20 is below the lower limit, the handling properties of the electromagnetic wave control sheet will be reduced. If the glass transition temperature of the substrate layer 20 exceeds the upper limit, the adhesive strength of the adhesive layer may be reduced due to a thermal load.

The glass transition temperature of the substrate layer 20 is measured using a dynamic mechanical analysis (DMA) device.

The storage modulus of the base layer 20 at 120°C is 1.0×10 ^-2 MPa to 1.0×10 ³ MPa, preferably 1.0×10 ^-1 MPa to 7.5×10 ² MPa, and more preferably 1.0 MPa to 5.0×10 ² MPa. If the storage modulus of the base layer 20 at 120°C is less than the above lower limit, the handling properties of the electromagnetic wave control sheet will be reduced. If the storage modulus of the base layer 20 at 120°C exceeds the above upper limit, the TOM formability will be poor.

The storage modulus of the base layer 20 is measured using a dynamic mechanical analysis (DMA) device.

The base layer 20 is not particularly limited as long as it satisfies the above glass transition temperature and storage modulus, but is preferably made of polyester, polyurethane, polymethyl methacrylate resin (PMMA), or polyvinyl chloride resin (PVC).
Specific examples of polyurethane include thermoplastic urethane.

The thickness of the base layer 20 is preferably 1 μm to 125 μm, more preferably 10 μm to 100 μm, and even more preferably 25 μm to 75 μm.

The thickness of the substrate layer 20 is measured using a digital indicator manufactured by TECLOCK.

In consideration of further improving the electromagnetic wave absorption performance of the electromagnetic wave control sheet 10, the thickness, permittivity, and magnetic permeability of the base layer 20 can be set as appropriate.
When the electrical characteristics of the electromagnetic waves to be absorbed are taken into consideration, the base layer 20 may be a layer with a high dielectric constant. If the base layer 20 is a layer with a high dielectric constant, the thickness of the electromagnetic wave control sheet 10 can be made relatively thin.

The other surface (rear surface) 20b of the base layer 20 may be adhesive so that the electromagnetic wave control sheet 10 can be attached to the surface of various articles. When the other surface 20b of the base layer 20 is adhesive, a release film may be provided to cover the surface 20b. The release film is removed when the electromagnetic wave control sheet 10 is used. Covering the adhesive surface with the release film improves handling during distribution.
For example, by employing a multilayer structure in which the other surface 20b of the base material layer 20 is an adhesive layer containing an adhesive, the other surface 20b of the base material layer 20 can be made adhesive.

Examples of such adhesives include heat-sealing adhesives that bond by heat, adhesives that become adhesive when moistened, pressure-sensitive adhesives (adhesives) that bond by pressure, etc. Among these, adhesives (pressure-sensitive adhesives) are preferred from the viewpoint of simplicity.
Specific examples of the pressure-sensitive adhesive include acrylic pressure-sensitive adhesives, urethane pressure-sensitive adhesives, rubber pressure-sensitive adhesives, polyester pressure-sensitive adhesives, silicone pressure-sensitive adhesives, polyvinyl ether pressure-sensitive adhesives, etc. Among these, at least one selected from the group consisting of acrylic pressure-sensitive adhesives, urethane pressure-sensitive adhesives, and rubber pressure-sensitive adhesives is preferred, and acrylic pressure-sensitive adhesives are more preferred.

Examples of the acrylic adhesive include the following acrylic polymers.
An acrylic polymer (1) containing a structural unit derived from an alkyl(meth)acrylate having a linear alkyl group or a branched alkyl group (i.e., a polymer obtained by polymerizing at least an alkyl(meth)acrylate as a monomer).
An acrylic polymer (2) containing a structural unit derived from a (meth)acrylate having a cyclic structure (i.e., 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.

The acrylic pressure-sensitive adhesive is preferably the following acrylic copolymer (Q).
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').

From the viewpoint of improving adhesive properties, the number of carbon atoms in the chain alkyl group contained in the monomer component (q1') is preferably 1 to 12, more preferably 4 to 8, and even more preferably 4 to 6. 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, lauryl (meth)acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate. Of 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. Among these, hydroxy group-containing monomers and carboxy 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, 4-hydroxybutyl (meth)acrylate, etc. Among these, 2-hydroxyethyl (meth)acrylate is preferred.
Specific examples of the carboxy group-containing monomer include (meth)acrylic acid, maleic acid, fumaric acid, and itaconic acid, with (meth)acrylic acid being preferred.
Specific examples of epoxy group-containing monomers include glycidyl (meth)acrylate.
Specific examples of amino group-containing monomers include diaminoethyl (meth)acrylate.
Specific examples of cyano group-containing monomers include acrylonitrile.
These may be used alone or in combination of two or more.

Examples of the monomer component (q3') include (meth)acrylates having a cyclic structure such as cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, imide (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), relative to 100% by mass of all structural units in the acrylic copolymer (Q), 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.
The content of the structural unit (q2), relative to 100% by mass of all structural units in the acrylic copolymer (Q), is preferably 0.1% by mass to 50% by mass, more preferably 0.5% by mass to 40% by mass, even more preferably 1.0% by mass to 30% by mass, and particularly preferably 1.5% by mass to 20% by mass.
The content of the structural unit (q3) is preferably 0 to 40% by mass, more preferably 0 to 30% by mass, even more preferably 0 to 25% by mass, and particularly preferably 0 to 20% by mass, relative to 100% by mass of all structural units in the acrylic copolymer (Q).

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

For the purpose of improving impact resistance, the adhesive layer may be made of a material that is cured by energy rays such as ultraviolet rays, visible energy rays, infrared rays, electron beams, etc. In this case, the adhesive layer contains an energy ray-curable component.
When the energy ray is ultraviolet light, examples of the energy ray-curable component include 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, tetramethylolmethane tetra(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 oligomer, epoxy-modified (meth)acrylate, and polyether (meth)acrylate.
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 in combination, as the photopolymerization initiator increases the curing speed.
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-hydroxycyclohexyl phenyl ketone, benzyl diphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, 2-chloroanthraquinone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-benzothiazole-N,N-diethyldithiocarbamate, and oligo{2-hydroxy-2-methyl-1-[4-(1-propenyl)phenyl]propanone}.

Conductive pattern
Fig. 3 is a top view showing an example of an electromagnetic wave control sheet of this embodiment. As shown in Fig. 3, the electromagnetic wave control sheet 10 has a flat substrate layer 20 and a conductive pattern 30 formed on one surface 20a of the substrate layer 20. The conductive pattern 30 is made up of a first conductive pattern 31, a second conductive pattern 32, and a third conductive pattern 33.

(First Conductive Pattern)
FIG. 4 is a top view showing the first conductive pattern 31. As shown in FIG.
4, the first conductive pattern 31 is made up of a plurality of first units u1, each of which is a geometrical figure.
In other words, the first conductive pattern 31 can be said to be an aggregate of first units u1, which are geometric figures.
Each of the first units u1 functions as an antenna. The first conductive pattern 31 may be, for example, a thin line pattern of an FSS element.

In the first conductive pattern 31, a plurality of first arrays R1 are formed, each of which has a plurality of first units u1 arranged along the direction indicated by the double-headed arrow P in Fig. 4. It can also be said that the first conductive pattern 31 has a plurality of first arrays R1. The first conductive pattern 31 can be configured by forming a plurality of first arrays R1 on the base layer 20 at predetermined intervals along the direction indicated by the double-headed arrow P.
The intervals between the plurality of first arrays R1 are not particularly limited, and the intervals between the 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 a first unit u1 constituting the first conductive pattern 31. As shown in FIG.
As shown in Figure 5, the first unit u1 has a cross shape that is symmetrical in both the vertical and horizontal directions. Specifically, the first unit u1 has one cross portion S1 and four end portions T1. The cross portion S1 is composed of a straight line portion parallel to the x-axis direction and a straight line portion parallel to the y-axis direction in Figure 5. Linear end portions T1 contact both ends of the straight line portion parallel to the x-axis direction and both ends of the straight line portion parallel to the y-axis direction, respectively, so as to be perpendicular to each straight line portion.

By adjusting the x-axis length L1 of the first unit u1 and the x-axis length W1 of each of the four ends T1, the electromagnetic wave absorption characteristics of the first unit u1, which functions as a single antenna, can be adjusted. The electromagnetic wave absorption characteristics can be adjusted in the same way in the y-axis direction.

Here, the length L1 of the first unit u1 in the x-axis direction is defined as the length of the long side of the first unit u1. The length L1 of the first unit u1 in the x-axis direction is 2 mm or less, and preferably 1.5 mm or less. If the length L1 of the first unit u1 in the x-axis direction exceeds the above upper limit, the absorption performance at the desired frequency will decrease, and there is a possibility that the conductive pattern will break during TOM molding.

However, the shape of the first unit is not limited to a cross shape, as long as the frequency value at which the amount of electromagnetic waves absorbed by first conductive pattern 31 reaches a maximum value is A [GHz].
For example, the shape of the graphic that is the first unit may be a circle, an annular shape, a straight line, a square, a polygon, an H-shape, a Y-shape, a V-shape, or the like.

In the conductive pattern 30, the shapes of the multiple first units u1 are identical to each other. However, the shapes of the multiple first units u1 do not have to be identical figures to each other. In other examples of the present invention, the shapes of the multiple first units may be identical to each other or different, as long as the effects of the present invention can be obtained.

The first conductive pattern 31 selectively absorbs electromagnetic waves having a frequency of A [GHz]. The frequency value A [GHz] is the frequency value at which the amount of electromagnetic waves absorbed by the first conductive pattern 31 reaches 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 conductive pattern 31 reaches a maximum value can be determined by, for example, the following method X or method Y.

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

The standard film has a standard base layer that is flat and a standard pattern formed on the standard base layer.
The details of the standard substrate layer can be the same as those of the substrate layer 20. Therefore, the details of the standard substrate layer will be described in detail in the description of the substrate layer 20 below.

The standard pattern consists of only a plurality of standard units that are identical in shape. In the standard film, it can be said that a standard pattern consisting of only one type of figure that is identical in shape is formed on a standard substrate layer. The standard pattern can be formed by the fine line pattern of a normal FSS element. Usually, the standard pattern is the same electromagnetic wave absorbing pattern as the first conductive pattern 31.
In the standard pattern, the shapes of the multiple standard units are not particularly limited as long as they are identical to one another. Examples of the shapes of the standard units include a circle, an annular shape, a linear shape, a square shape, a polygonal shape, a cross shape, an H-shape, a Y-shape, a V-shape, etc. Usually, the shape of the standard unit is identical to that of the first unit u1.

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

The material of the standard unit that constitutes the standard pattern is not particularly limited, as long as it is such that when the standard film is irradiated with electromagnetic waves whose frequency is varied within the range of 20 GHz to 110 GHz, the amount of electromagnetic waves absorbed by the standard film can reach a maximum value.
The 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 using 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 standard film is irradiated with the electromagnetic wave.
The reflection characteristic (S11) is an index of the intensity of the electromagnetic wave reflected by the standard film when the standard film is irradiated with the electromagnetic wave from the irradiation source. The reflection characteristic (S11) can be measured by the 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.

The frequency A [GHz] can be determined, for example, by the following method.
First, the standard film is irradiated with electromagnetic waves while changing the frequency within the range of 20 GHz to 110 GHz, and the amount of electromagnetic waves absorbed by the standard film is calculated using the above formula (3).
Next, an absorption spectrum is created by plotting the changed frequency on the horizontal axis and the absorption calculated by the above formula (3) on the vertical axis. Typically, in this absorption spectrum, there is one frequency value on the horizontal axis at which the absorption is maximum. Therefore, the plot shows a single peak where the absorption of the electromagnetic wave is at its maximum. In this way, the frequency of the electromagnetic wave at which the absorption of the electromagnetic wave is maximum can be determined as A [GHz].

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

The first conductive pattern 31 absorbs electromagnetic waves having a frequency of A [GHz] as determined by the above-described method X.
In the conductive pattern 30 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 this range, the conductive pattern 30 can absorb electromagnetic waves in the millimeter wave region, making it easier to apply to automobile parts, road peripheral components, building exterior wall related materials, windows, communication devices, radio telescopes, etc.

In Method Y, the amount of electromagnetic waves absorbed by a film can be measured in the same way as in Method X. That is, the film is irradiated with electromagnetic waves while changing the frequency within the range of 20 to 110 GHz, and the amount of electromagnetic waves absorbed by the film is calculated using the above formula (3).
Next, an absorption spectrum is created by plotting frequency on the horizontal axis and the absorption calculated by the above formula (3) on the vertical axis. Typically, in this absorption spectrum, there is one frequency value on the horizontal axis at which the absorption is maximum. Therefore, the plot shows a single peak where the absorption of the electromagnetic wave is at a local maximum. In this way, the frequency of the electromagnetic wave at which the absorption of the electromagnetic wave is maximum can be determined as A [GHz].

The material of the first unit u1 is not particularly limited as long as it is within a range that allows absorption of electromagnetic waves.
Examples of the material of the first unit include thin metal wires, conductive thin films, and conductive paste deposits.
Examples of the metal material include copper, aluminum, tungsten, iron, molybdenum, nickel, titanium, silver, gold, and alloys containing two or more of these metals (for example, steels such as stainless steel and carbon steel, brass, phosphor bronze, zirconium-copper alloy, beryllium copper, iron-nickel, nichrome, nickel-titanium, Kanthal, Hastelloy, rhenium-tungsten, etc.).
Examples of materials for the conductive thin film include metal particles, carbon nanoparticles, and carbon fibers.

The distance between the ends of the graphic form of the first unit u1 is not particularly limited as long as it is within a range in which electromagnetic wave absorption is obtained.
For example, the distances between the ends of the figures that are the first units u1 may all be the same or may be different from one another. However, it is preferable that the distances between the ends of the figures that are the first units u1 be the same from the viewpoint of making it easier to design an electromagnetic wave control sheet that is less susceptible to the influence of the surrounding environment and improving the precision of the frequency band of the electromagnetic waves that are absorbed during manufacturing.

(Second Conductive Pattern)
FIG. 6 is a top view showing the second conductive pattern 32. As shown in FIG.
6, the second conductive pattern 32 is composed of a plurality of second units u2. Each of the second units u2 is a geometric figure. In other words, the second conductive pattern 32 can be said to be an aggregate of the second units u2, which are geometric figures.
Each of the second units u2 functions as an antenna. The second conductive pattern 32 may be, for example, a thin line pattern of an FSS element.

In the second conductive pattern 32, 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. 6. It can also be said that the second conductive pattern 32 has a plurality of second arrays R2. The second conductive pattern 32 can be configured by forming the second arrays R2 on the base layer 20 at predetermined intervals along the direction indicated by the double-headed arrow P.
The intervals between the plurality of second arrays R2 are not particularly limited, and 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 Figure 7, the second unit u2 has a cross shape that is symmetrical in both the vertical and horizontal directions. Specifically, the second unit u2 has one cross portion S2 and four end portions T2. The cross portion S2 is composed of a straight line portion parallel to the x-axis direction and a straight line portion parallel to the y-axis direction in Figure 7. Linear end portions T2 contact both ends of the straight line portion parallel to the x-axis direction and both ends of the straight line portion parallel to the y-axis direction, respectively, so as to be perpendicular to each straight line portion.

In the conductive pattern 30, the length L2 of the second unit u2 in the x-axis direction is shorter than the length L1 of the first unit u1 in the x-axis direction. In addition, the length W2 of each of the four ends T2 in the x-axis direction or the y-axis direction is shorter than the length W1 of each of the four ends T1 of the first unit u1.
By adjusting the length L2 of the second unit u2 in the x-axis direction and the length W2 of each of the four ends T2 in the x-axis direction, the electromagnetic wave absorption characteristics of the second unit u2 functioning as a single antenna can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction.

Here, the length L2 of the second unit u2 in the x-axis direction is defined as the length of the long side of the second unit u2. The length L2 of the second unit u2 in the x-axis direction is 2 mm or less, and preferably 1.2 mm or less. If the length L2 of the second unit u2 in the x-axis direction exceeds the above upper limit, the absorption performance at the desired frequency will decrease.

In the conductive pattern 30, the shapes of the multiple second units u2 are identical to each other. However, the shapes of the multiple second units u2 do not have to be identical figures to each other. In other examples of the present invention, the shapes of the multiple second units may be identical to each other or different, as long as the effects of the present invention can be obtained.

The second conductive pattern 32 selectively absorbs electromagnetic waves having a frequency of B [GHz] that satisfies the following formula (1). The frequency value B [GHz] is the frequency value at which the amount of electromagnetic waves absorbed by the second conductive pattern 32 reaches a maximum. The frequency value B [GHz] satisfies the following formula (1).
1.037×A≦B≦1.30×A...Formula (1)

As shown in the above formula (1), the second conductive pattern 32 absorbs electromagnetic waves with a frequency of 1.037×A [GHz] to 1.30×A [GHz]. It is preferable that the second conductive pattern 32 absorbs electromagnetic waves with a frequency of 1.17×A [GHz] to 1.30×A [GHz].
Because the second conductive pattern 32 absorbs electromagnetic waves with frequencies of 1.037×A [GHz] or higher, the peak of the amount of electromagnetic waves absorbed by the second conductive pattern 32 and the peak of the amount of electromagnetic waves absorbed by the first conductive pattern 31 fully overlap in the frequency band higher than A [GHz]. As a result, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave control sheet is expanded to a frequency band higher than A [GHz], compared to a film having the first conductive pattern 31 alone.
Because the second conductive pattern 32 absorbs electromagnetic waves with a frequency of 1.30×A [GHz] or less, in the frequency band higher than A [GHz], the difference in frequency between the peak of the amount of electromagnetic waves absorbed by the second conductive pattern 32 and the peak of the amount of electromagnetic waves absorbed by the first conductive pattern 31 becomes small. As a result, a single peak is formed at which the amount of electromagnetic waves absorbed by the entire electromagnetic wave control sheet reaches a local maximum value.
As described above, the second conductive pattern 32 absorbs electromagnetic waves with frequencies of 1.037×A [GHz] to 1.30×A [GHz], and therefore the amount of electromagnetic waves absorbed by the entire electromagnetic wave control sheet is extended to the higher frequency band.

However, the shape of the second unit is not limited to a cross. There are no particular limitations on the shape of the second unit as long as it is within a range that allows for electromagnetic wave absorption. For example, the shape of the figure that is the second unit may be a circle, annular, linear, square, polygonal, H-shaped, Y-shaped, V-shaped, etc.

The material of the second unit constituting the second conductive pattern 32 is not particularly limited as long as it can absorb electromagnetic waves of B [GHz], and is not particularly limited as long as it is within a range in which electromagnetic wave absorption can be obtained.
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 graphic form of the second unit u2 is not particularly limited as long as it is within a range in which electromagnetic wave absorption is obtained.
For example, the distances between the ends of the figures that are the second units u2 may all be the same or may be different from one another. However, it is preferable that the distances 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 control sheet that is less susceptible to the influence of the surrounding environment and improving the precision of the frequency band of the electromagnetic waves that are absorbed during manufacturing.

(Third Conductive Pattern)
FIG. 8 is a top view showing the third conductive pattern 33. As shown in FIG.
8, the third conductive pattern 33 is composed of a plurality of third units u3. Each of the third units u3 is a geometric figure. In other words, the third conductive pattern 33 can be said to be an aggregate of the third units u3, which are geometric figures.
Each of the third units u3 functions as an antenna. The third conductive pattern 33 may be, for example, a thin line pattern of an FSS element.

In the third conductive pattern 33, 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. 8. It can also be said that the third conductive pattern 33 has a plurality of third arrays R3. The third conductive pattern 33 can be configured by forming the third arrays R3 on the base material layer 20 at predetermined intervals along the direction indicated by the double-headed arrow P.
The intervals between the plurality of third arrays R3 are not particularly limited, and may be regular or irregular.

FIG. 9 is a top view showing the third unit u3.
As shown in Figure 9, the third unit u3 has a cross shape that is symmetrical in both the vertical and horizontal directions. Specifically, the third unit u3 has one cross portion S3 and four end portions T3. The cross portion S3 is composed of a straight line portion parallel to the x-axis direction and a straight line portion parallel to the y-axis direction in Figure 9. Linear end portions T3 contact both ends of the straight line portion parallel to the x-axis direction and both ends of the straight line portion parallel to the y-axis direction, respectively, so as to be perpendicular to each straight line portion.

In the conductive pattern 30, the length L3 of the third unit u3 in the x-axis direction is longer than the length L1 of the first unit u1 in the x-axis direction. In addition, the length W3 of each of the four ends T3 in the x-axis direction or the y-axis direction is longer than the length W1 of each of the four ends T1 of the first unit u1.
By adjusting the length L3 of the third unit u3 in the x-axis direction and the length W3 of each of the four ends T3 in the x-axis direction, the electromagnetic wave absorption characteristics of the third unit u3 functioning as a single antenna can be adjusted. Similarly, the electromagnetic wave absorption characteristics can be adjusted in the y-axis direction.

Here, the length L3 of the third unit u3 in the x-axis direction is defined as the length of the long side of the third unit u3. The length L3 of the third unit u3 in the x-axis direction is 2 mm or less, and preferably 1.8 mm or less. If the length L3 of the third unit u3 in the x-axis direction exceeds the above upper limit, the absorption performance of the desired frequency will decrease.

In the conductive pattern 30, the shapes of the multiple third units u3 are identical to each other. However, the shapes of the multiple third units u3 do not have to be identical figures to each other. In other examples of the present invention, the shapes of the multiple third units may be identical to each other or different, as long as the effects of the present invention can be obtained.

The third conductive pattern 33 selectively absorbs electromagnetic waves having a frequency of C [GHz] that satisfies the following formula (2). The frequency value C [GHz] is the frequency value at which the amount of electromagnetic waves absorbed by the third conductive pattern 33 reaches a maximum. The frequency value C [GHz] satisfies the following formula (2).
0.60×A≦C≦0.933×A...Formula (2)

As shown in the above formula (2), the third conductive pattern 33 absorbs electromagnetic waves with a frequency of 0.60×A [GHz] to 0.933×A [GHz]. Preferably, the third conductive pattern 33 absorbs electromagnetic waves with a frequency of 0.60×A [GHz] to 0.83×A [GHz].
Because the third conductive pattern 33 absorbs electromagnetic waves with frequencies of 0.60×A [GHz] or higher, the difference in frequency between the peak of the amount of electromagnetic waves absorbed by the third conductive pattern 33 and the peak of the amount of electromagnetic waves absorbed by the first conductive pattern 31 becomes small in the frequency band lower than A [GHz]. As a result, a single peak is formed at which the amount of electromagnetic waves absorbed by the entire conductive pattern 30 reaches a local maximum value.
Because the third conductive pattern 33 absorbs electromagnetic waves with frequencies of 0.933×A [GHz] or less, in the frequency band lower than A [GHz], the peak of the amount of electromagnetic waves absorbed by the third conductive pattern 33 and the peak of the amount of electromagnetic waves absorbed by the first conductive pattern 31 fully overlap. As a result, the frequency band of electromagnetic waves that can be absorbed by the entire electromagnetic wave control sheet is expanded to a frequency band lower than A [GHz], compared to a film having the first conductive pattern 31 alone.
As described above, the third conductive pattern 3 absorbs electromagnetic waves with frequencies between 0.60×A [GHz] and 0.933×A [GHz], and therefore the amount of electromagnetic waves absorbed by the entire conductive pattern 30 is extended to the lower frequency band.

However, the shape of the third unit u3 is not limited to a cross shape. There are no particular limitations on the shape of the third unit u3, as long as it is within a range that allows for electromagnetic wave absorption. For example, the shape of the figure that is the third unit may be a circle, annular, linear, rectangular, polygonal, H-shaped, Y-shaped, V-shaped, etc.

The material of the third unit u3 constituting the third conductive pattern 33 is not particularly limited as long as it is capable of absorbing electromagnetic waves of C [GHz], and is not particularly limited as long as it is within a range in which electromagnetic wave absorption can be obtained.
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 it is within a range that allows electromagnetic wave absorption.
For example, the distances between the ends of the figures that are the third units u3 may all be the same or may be different from one another. However, it is preferable that the distances 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 control sheet that is less susceptible to the influence of the surrounding environment and improving the accuracy of the frequency band of the electromagnetic waves that are absorbed during manufacturing.

3, the first array R1, the second array R2, and the third array R3 are arranged adjacent to each other along the direction indicated by the double-headed arrow P. Because the first array R1, the second array R2, and the third array R3 are arranged adjacent to each other on the base layer 20, the frequency band of the electromagnetic waves selectively absorbed by the second conductive pattern 32 and the frequency band of the electromagnetic waves selectively absorbed by the third conductive pattern 33 overlap, based on the frequency value A [GHz] of the peak position of the electromagnetic waves selectively absorbed by the first conductive pattern 31. As a result, the absorption range of the electromagnetic waves absorbed by the entire conductive pattern 30 is likely to be expanded toward both the high-frequency side and the low-frequency side, based on the frequency value A [GHz] of 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 d3 between the third unit u3 and the first unit u1, which are shown in FIG. 3, may be the same as or different from each other.
The distance d1 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm.
The distance d2 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm.
The distance d3 may be, for example, 0.2 mm to 4 mm, 0.3 mm to 2 mm, or 0.5 mm to 1 mm.
When the distances d1, d2, and d3 are each within the above-mentioned numerical ranges, the absorption range of electromagnetic waves absorbed by the entire conductive pattern 30 is likely to be further expanded based on the frequency value A [GHz] at the peak position.

In the conductive pattern 30, the shapes of the first unit u1, the second unit u2, and the third unit u3 are identical to one another. However, the shapes of the first unit u1, the second unit u2, and the third unit u3 do not have to be identical to one another. That is, in another example of the present invention, the shapes of the first unit u1, the second unit u2, and the third unit u3 may be identical to one another or may be different.

The conductive pattern 30 may have a plurality of second conductive patterns 32. For example, in addition to the second conductive pattern 2, the conductive pattern 30 may further have the following conductive pattern 32a and conductive pattern 32b.
Electromagnetic wave absorbing pattern 32a: A conductive pattern in which the frequency value at which the amount of electromagnetic wave absorption shows a maximum value is D [GHz] that satisfies the following formula (4).
Electromagnetic wave absorbing pattern 32b: A conductive pattern in which the frequency value at which the amount of electromagnetic wave absorption 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 formulas (4) and (5), A is the frequency [GHz] specified by the above method X or method Y.

When the conductive pattern 30 further includes conductive pattern 32a and conductive pattern 32b in addition to the second conductive pattern 32, the frequency at which the amount of electromagnetic wave absorption by the second conductive pattern 32 reaches a maximum is preferably 1.17 x A [GHz] to 1.30 x A [GHz]. In this case, the effect of expanding the frequency band of electromagnetic waves that can be absorbed by the entire conductive pattern 30 toward higher frequencies is even more pronounced, resulting in even more pronounced electromagnetic wave absorption.

The conductive pattern 30 may have a plurality of third conductive patterns. For example, the conductive pattern 30 may further have the following conductive pattern 33a and conductive pattern 33b in addition to the third conductive pattern 33.
Conductive pattern 33a: A conductive pattern in which the frequency value at which the amount of electromagnetic wave absorption is maximized is F [GHz] that satisfies the following formula (6).
Conductive pattern 33b: A conductive pattern in which the frequency value at which the amount of electromagnetic wave absorption shows a maximum value is G [GHz] that satisfies the following formula (7).
0.91×A<F≦0.933×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 the above-mentioned method X or method Y.

When the conductive pattern 30 further includes conductive patterns 33a and 33b in addition to the third conductive pattern 33, the frequency at which the amount of electromagnetic wave absorption by the third conductive pattern 33 reaches a maximum is preferably 0.60 x A [GHz] to 0.83 x A [GHz]. In this case, the effect of extending the frequency band of electromagnetic waves that can be absorbed by the entire conductive pattern 30 toward the lower frequency side is even more pronounced, resulting in even more pronounced electromagnetic wave absorption.

FIG. 10 is a cross-sectional view of the electromagnetic wave control sheet 10 taken along line VIII-VIII of FIG.
The base layer 20 has two surfaces 20a and 20b facing each other. A first conductive pattern 31, a second conductive pattern 32, and a third conductive pattern 33 are formed on one surface 20a of the base layer 20. 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 20a of the base layer 20.

There are no particular limitations on the thickness H1 of the first conductive pattern 31, the thickness H2 of the second conductive pattern 32, and the thickness H3 of the third conductive pattern 33. The thicknesses H1, H2, and H3 can be changed as desired depending on the desired characteristics. Furthermore, the thicknesses H1, H2, and H3 may be the same as or different from one another.
The thicknesses H1, H2, and H3 may be, for example, 1 μm to 100 μm, 5 μm to 50 μm, or 10 μm to 30 μm. The thicker the thicknesses H1, H2, and H3, the better the electromagnetic wave absorption, but the higher the manufacturing costs. Taking this into consideration, the thicknesses H1, H2, and H3 may be set.

The electromagnetic wave control sheet 10 can be produced, for example, by the following method.
First, the base layer 20 is prepared. Next, the first conductive pattern 31, the second conductive pattern 32, and the third conductive pattern 33 are formed on one surface 20a of the base layer 20.
Here, when the first conductive pattern 31 is formed, it is formed so that the frequency value at which the amount of electromagnetic waves absorbed by the first conductive pattern 31 shows a maximum value is A [GHz].
The second conductive pattern 32 is formed so that the frequency at which the amount of electromagnetic waves absorbed by the second conductive pattern 32 reaches a maximum value is B [GHz].
The third conductive pattern 33 is formed so that the frequency at which the amount of electromagnetic waves absorbed by the third conductive pattern 33 reaches a maximum value is C [GHz].
There is no particular limitation on the order in which the first conductive pattern 31, the second conductive pattern 32, and the third conductive pattern 33 are formed. The first conductive pattern 31, the second conductive pattern 32, and the third conductive pattern 33 may be formed in the same process, or may be formed in separate processes.

The method for forming each conductive pattern is not particularly limited as long as it is possible to form a predetermined frequency. Examples of the method for forming each conductive pattern include the following methods.
A printing method in which each conductive pattern is printed on one surface 20a of the base layer 20 using a conductive paste.
A developing method for developing each conductive pattern on one surface 20a of the base material layer 20.
A method in which a metal thin film is provided on one surface 20a of the base layer 20 by sputtering, vacuum deposition, or lamination of metal foil, and a pattern of the metal thin film is formed on one surface 20a of the base layer 20 by photolithography.
A method in which metal wires are arranged on one surface 20a of the base layer 20.

In the printing method, each conductive pattern is printed on one surface 20a of the base layer 20 to form each of the units u1, u2, and u3, which are figures. The printing method is not particularly limited. Examples include screen printing, gravure printing, and inkjet printing.
The conductive paste used for printing may be, for example, a paste-like composition containing at least one selected from the group consisting of metal particles, carbon nanoparticles, and carbon fibers, and a binder resin component. The metal particles may be particles of metals such as copper, silver, nickel, and aluminum.
Examples of the binder resin component include thermoplastic resins such as polyester resins, (meth)acrylic resins, polystyrene resins, and polyamide resins, and thermosetting resins such as epoxy resins, amino resins, and polyimide resins, but the metal particles and binder resin component are not limited to these examples.
The conductive paste may further contain a black pigment such as carbon black, which can suppress the metallic luster of the metal powder that constitutes the printed conductive pattern and reduce reflection of external light.

In the developing method, a conductive pattern is developed on one surface 20a of the base layer 20 to form the units u1, u2, and u3, which are figures.
There are two types of development methods: a negative development method in which a developed product appears in the exposed areas that are not covered by the exposure mask, and a positive development method in which a developed product appears in the unexposed areas that are covered by the exposure mask. That is, in the negative development method, each unit u1, u2, u3 is formed as a developed product in the opposite shape to the exposure mask. On the other hand, in the positive development method, each unit u1, u2, u3 is formed as a developed product in the same shape as the exposure mask. Silver is usually used as the metal used in the developed product.

An example of a method for forming a conductive pattern by photolithography is as follows.
First, a resist is applied to one surface 20a of the base layer 20, followed by heat treatment, 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 base layer 20 and the layer consisting of the resist pattern, and the layer consisting of the resist pattern and the vapor-deposited film thereon are simultaneously removed using a resist remover. This allows a conductive pattern to be formed on the surface of the base layer 20.
As another example, a metal thin film is provided on the base layer 20, a resist is applied to a portion of the surface of the metal thin film, and the resulting film is subjected to a heat treatment. Next, the metal thin film is removed from the portion not coated with the resist by an etching process. Thereafter, the resist is removed as necessary to form the electromagnetic wave absorbing pattern. A metal plating layer (not shown) may be further provided on the surface of each of the units u1, u2, and u3 that make up each electromagnetic wave absorbing pattern.

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

As described above, in the electromagnetic wave control sheet 10 of this embodiment, the dielectric layer may be composed of a base layer and a spacer layer.
2, the electromagnetic wave control sheet 10 according to the present embodiment may include a base layer 20, a conductive pattern 30, and a spacer layer 50. Furthermore, as shown in FIG. 2, the electromagnetic wave control sheet 10 according to the present embodiment may include a reflective layer 40.
The reflective layer 40 is disposed on the other surface 20b side of the base layer 20. The spacer layer 50 is disposed between the base layer 20 and the reflective layer 40. That is, the base layer 20 and the reflective layer 40 are stacked with the spacer layer 50 interposed therebetween.

"Reflective layer"
The reflective layer 40 has two surfaces 40 a and 40 b. The surface 40 a of the reflective layer 40 is in contact with the other surface 50 b of the spacer layer 50 .
The reflective layer 40 is not particularly limited in form as long as it can reflect electromagnetic waves that arrive at the surface of the electromagnetic wave control sheet 10 and that have passed through the electromagnetic wave control sheet 10. A portion of the electromagnetic waves that arrive at the electromagnetic wave control sheet 10 is reflected by or absorbed by the conductive pattern 30. On the other hand, electromagnetic waves that are not reflected or absorbed by the conductive pattern 30 pass through the conductive pattern 30. The electromagnetic waves that have passed through the conductive pattern 30 are reflected by the reflective layer 40 toward the conductive pattern 30.
For example, if the reflective layer 40 has conductivity in the surface direction of the two surfaces 40a, 40b, it can reflect electromagnetic waves that have passed through the conductive pattern 30. Specifically, a metal foil such as copper foil may be attached to a support made of a resin film such as polyethylene terephthalate, and the reflective layer 40 may be formed on the support. Alternatively, the reflective layer 40 may be laminated directly on the spacer layer 50. Instead of the metal foil, a conductive film such as ITO, or a mesh sheet made of metal wires, may be used.
The support for the reflective layer 40 can also be used as a dielectric layer.

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

If the spacer layer 50 is formed on a conductive object such as a metal, the conductive object such as a metal will serve as the reflective layer 40, and the reflective layer 40 can be omitted.

For the purpose of applying the electromagnetic wave control sheet 10 to the surfaces of various articles, the other surface 40b of the reflective layer 40 may be made adhesive. When the other surface 40b of the reflective layer 40 is made adhesive, a release film may be provided to cover the surface 40b.
The adhesive used may be the same as that used to make the other surface 20b of the base material layer 20 adhesive.

"Spacer layer"
The spacer layer 50 is a dielectric layer and is provided on the other surface 20 b of the base layer 20 .
The spacer layer 50 has two surfaces 50a and 50b. The surface 50a of the spacer layer 50 is in contact with the other surface 20b of the base layer 20. The reflective layer 40 is provided on the other surface 50b of the spacer layer 50.
The spacer layer 50 may have a single layer structure or a multi-layer structure.

The material of the spacer layer 50 can be selected appropriately depending on the application of the electromagnetic wave control sheet 10. For example, the spacer layer 50 may be made of a transparent material in order to provide transparency to the electromagnetic wave absorbing film electromagnetic wave control sheet 10. Alternatively, the spacer layer 50 may be made of a flexible material in order to provide the electromagnetic wave control sheet 10 with the ability to conform to a curved surface.
Examples of flexible materials include plastic films, rubber, paper, cloth, nonwoven fabric, foam sheets, rubber sheets, etc. Among these, foam sheets are preferred in terms of their ability to conform to the curved surface of the electromagnetic wave control sheet 10.
Specific examples of resins that can be used to form the plastic film include the same thermoplastic resins as those described above for the base layer 20 .
The foamed sheet may be, for example, a foamed sheet formed by foaming the resin constituting the plastic film and forming it into a sheet. Specific examples of foamed sheets include polyethylene foam, polypropylene foam, and polyurethane foam. Examples of polyethylene foam include low-density polyethylene foam and high-density polyethylene foam.

The glass transition temperature of the spacer layer 50 is preferably 30°C to 120°C, more preferably 40°C to 100°C, and even more preferably 50°C to 80°C. If the glass transition temperature of the spacer layer 50 is above the lower limit above, the handling properties of the electromagnetic wave control sheet will be poor. If the glass transition temperature of the spacer layer 50 is below the upper limit above, the adhesive strength of the adhesive layer may be reduced due to thermal load.

The glass transition temperature of the spacer layer 50 is measured in the same manner as the glass transition temperature of the substrate layer 20.

The storage modulus of the spacer layer 50 at 120°C is preferably 1.0×10 ^-2 MPa to 1.0×10 ³ MPa, more preferably 1.0×10 ^-1 MPa to 7.5×10 ² MPa, and even more preferably 1.0 MPa to 5.0×10 ² MPa. If the storage modulus of the spacer layer 50 at 120°C is equal to or greater than the lower limit, the handling properties of the electromagnetic wave control sheet will be poor. If the storage modulus of the spacer layer 50 at 120°C is equal to or less than the upper limit, the TOM formability will be poor.

The storage modulus of the spacer layer 50 is measured in the same manner as the storage modulus of the base layer 20.

When the wavelength shortening effect of the spacer layer 50 is taken into consideration, the thickness of the spacer layer 50 is appropriately changed in accordance with the wavelength of the electromagnetic wave to be absorbed and the relative dielectric constant of the spacer layer 50 .
When the wavelength shortening effect of the spacer layer 50 is taken into consideration, it is preferable that the thickness of the spacer layer 50 in the z-axis direction satisfies the following formula (8).
(Thickness of the spacer layer 50 in the z-axis direction)=(λ)×(¼)/(ε)½ (Equation (8))
In the above formula (8), λ is the wavelength of the incident electromagnetic wave, and ε is the relative dielectric constant of the spacer layer 50. The thickness of the spacer layer 40 in the z-axis direction may be adjusted appropriately to improve absorption characteristics. For example, it can be changed within a range of 0.1 to 3.0 times the thickness of the spacer layer 40 in the z-axis direction obtained by formula (8).

When the relationship between the thickness of the spacer layer 50 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 50 can be set appropriately depending on the wavelength λ of the electromagnetic wave to be absorbed. The thickness of the spacer layer 50 may be, for example, 25 μm to 5000 μm, 50 μm to 4500 μm, or 100 μm to 4000 μm.
The spacer layer 50 may be made of a material with a high dielectric constant. If the spacer layer 50 is a layer with a high dielectric constant, the thickness of the spacer layer 50 can be made relatively thin.
When the dielectric constant of the spacer layer 50 is taken into consideration, the spacer layer 50 preferably contains at least one material selected from the group consisting of barium titanate, titanium oxide, and strontium titanate.

The spacer layer 50 preferably includes at least one selected from the group consisting of a plastic film, a foam sheet, and a rubber sheet, and more preferably includes a foam sheet among these. When the spacer layer 50 is at least one selected from the group consisting of a plastic film, a foam sheet, and a rubber sheet, the ability of the electromagnetic wave control sheet 10 to conform to a curved surface is improved.
The spacer layer 50 may have a single-layer structure made of a single sheet, or a multi-layer structure made of a laminate of multiple sheets. The material and structure of the sheets constituting the spacer layer 50 can be selected appropriately depending on the application of the electromagnetic wave absorbing sheet.

The two surfaces 50a, 50b of the spacer layer 50 are preferably adhesive. This allows the base layer 20 and the reflective layer 40 to be bonded to each of the two surfaces 50a, 50b. For example, by employing a multilayer structure in which the two surfaces 50a, 50b are adhesive layers containing an adhesive, the two surfaces 50a, 50b can be made adhesive.
The details and preferred aspects of the adhesive layer can be the same as those described for the adhesive layer in the base material layer 20.

When the electromagnetic wave control sheet 10 includes the reflective layer 40 and the spacer layer 50, the electromagnetic wave absorber 10 can be manufactured by, for example, the following method.
The adhesive composition is applied to the release-treated surface of a release film, and the resulting coating is dried to form an adhesive layer, which is then laminated to the release-treated surface of another release film to obtain an adhesive sheet.
Next, one side of the release film of the adhesive sheet is peeled off, and one side of the exposed adhesive sheet is attached to the other side 20b of the base material layer 20 in the laminate (electromagnetic wave control sheet 10) consisting of the base material layer 20 and the conductive pattern 30 prepared as described above.

Next, the other side of the release film of the adhesive sheet is peeled off, and a material to become the spacer layer 50 is attached to the other surface of the exposed adhesive sheet.
Next, in the same manner as in the case of the spacer layer 50, the material that will become the reflective layer 40 is attached to the other surface 50b of the spacer layer 50 via the adhesive sheet.
By the above method, the electromagnetic wave control sheet 10 is obtained.

As described above, the electromagnetic wave control sheet 10 of this embodiment includes the base layer 20 as a dielectric layer, or the base layer 20 and the spacer layer 50, and a conductive pattern provided on the dielectric layer, wherein the length of the long side of the conductive pattern 30 is 2 mm or less, the glass transition temperature of the dielectric layer is 30°C to 120°C, and the storage modulus of the dielectric layer at 120°C is 1.0 x 10 ^-2 MPa to 1.0 x 10 ³ MPa. Therefore, the electromagnetic wave control sheet 10 of this embodiment can be formed three-dimensionally by TOM molding at around 120°C, and therefore can be attached to an adherend having a curved surface. Furthermore, the sheet can be attached to an article having a curved surface at the same time as it is formed.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1]
A 75 μm thick PMMA sheet (PMMA sheet, manufactured by Mitsubishi Chemical Corporation, product name: ACRYPLEN™ HBS010) was used as a substrate, with a 35 μm thick adhesive applied to one side of the sheet. A conductive pattern with a long side length of 2 mm or less, as shown in FIG. 3, was formed on the side opposite the adhesive. Copper was used as the material for the conductive pattern. The thickness of each conductive pattern was 18 μm.
Furthermore, a spacer layer was laminated on the surface of the substrate opposite to the surface on which the conductive pattern was formed, via the adhesive side of an adhesive PMMA sheet. The spacer layer was a foamed sheet (low-density polyethylene foam, manufactured by Inoac Corporation, product name: VR3003B, thickness: 3 mm).
Next, another adhesive support was prepared, and a reflective layer made of copper and having a thickness of 100 nm was formed by PVD on the surface of the support opposite to the adhesive surface.
Next, the adhesive surface of the reflective layer was attached to the surface of the spacer layer opposite to the substrate, thereby obtaining an electromagnetic wave control sheet of Example 1.
In Example 1, the dielectric layer is the substrate, the spacer layer, and the support for the reflective layer.

[Example 2]
An electromagnetic wave control sheet of Example 2 was obtained in the same manner as in Example 1, except that a foam sheet (high-density polyethylene foam, manufactured by Inoac Corporation, product name: B-150, thickness: 3 mm) was used as the spacer layer.
In Example 2, the dielectric layer is the substrate, the spacer layer, and the support for the reflective layer.

[Example 3]
An electromagnetic wave control sheet of Example 3 was obtained in the same manner as in Example 1, except that the spacer layer and the reflective layer were not provided.
In Example 3, the dielectric layer is composed of only the substrate.

[Comparative Example 1]
An electromagnetic wave control sheet of Comparative Example 1 was obtained in the same manner as in Example 1, except that a foam sheet manufactured by Inoac Corporation (low-density polyethylene foam, manufactured by Inoac Corporation, product name: LD-45, thickness: 3 mm) was used as the spacer layer.
In Comparative Example 1, the dielectric layer is composed of a substrate and a spacer layer.

[Comparative Example 2]
An electromagnetic wave control sheet of Comparative Example 2 was obtained in the same manner as in Example 1, except that a rubber sheet (product name: MS-760N-N, manufactured by Shin-Nihon Radio Wave Absorber Co., Ltd.) was used as the substrate and the spacer layer and the reflective layer were not provided.
In Comparative Example 2, the dielectric layer is composed of only the substrate.

[evaluation]
"Measurement of storage modulus and glass transition temperature"
The storage modulus and glass transition temperature at 120° C. of the substrate, spacer layer and reflective layer of the electromagnetic wave control sheets of Examples 1 to 3 and Comparative Examples 1 and 2 were measured.
The storage modulus and glass transition temperature were measured using a Dynamic Mechanical Analysis (DMA) device (trade name: DMA242E, manufactured by NETZSCH).
The measurement conditions were as follows:
Measurement was carried out at a frequency of 10 Hz while the temperature was increased from room temperature (30° C.) to 120° C. at a rate of 5° C./min.
The size of the sample was 15 mm x 5 mm.
The tension applied to the sample was 3.5N.
The results are shown in Table 1.

"TOM moldability test"
The electromagnetic wave control sheets of Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to a TOM moldability test using a TOM molding machine manufactured by SIBE AUTOMATION.
A hemisphere with a radius of 40 mm was used as a mold, and the electromagnetic wave control sheet was visually evaluated for moldability when tested at 120°C. If molding was possible without any defects in appearance, it was evaluated as "○", and if molding was not possible and the electromagnetic wave control sheet had defects in appearance such as wrinkles or tears, it was evaluated as "×". The results are shown in Table 1.

From the results shown in Table 1, the electromagnetic wave control sheet of Example 1 has a storage modulus of 115.8 MPa and a glass transition temperature of 114°C for the substrate and the support of the reflective layer, and a storage modulus of 2.93 MPa and a glass transition temperature of 89°C for the spacer layer. The electromagnetic wave control sheet of Example 2 has a storage modulus of 115.8 MPa and a glass transition temperature of 114°C for the substrate and the support of the reflective layer, and a storage modulus of 3.29 MPa and a glass transition temperature of 100°C for the spacer layer. It was confirmed that Examples 1 and 2 have excellent TOM formability at 120°C. Such excellent TOM formability enables attachment to the surface of an article having a three-dimensional shape. In contrast, it was confirmed that the electromagnetic wave control sheet of Comparative Example 1, in which the storage modulus of 115.8 MPa and the glass transition temperature of 114°C for the substrate and the support of the reflective layer and the storage modulus of 3.5 MPa and the glass transition temperature of 127°C for the spacer layer, has poor TOM formability at 120°C.
From the results shown in Table 1, it was confirmed that the electromagnetic wave control sheets of Examples 1 to 3, in which the storage modulus of the substrate and the support of the reflective layer was 115.8 MPa and the glass transition temperature was 114° C., had excellent TOM formability at 120° C. In contrast, it was confirmed that the electromagnetic wave control sheet of Comparative Example 2, in which the storage modulus of the substrate was 18.4 MPa and the glass transition temperature was 137° C., had poor TOM formability at 120° C.

The electromagnetic wave control sheet of the present invention can be used in automobile parts, road-related components, building exterior wall-related materials, windows, communication equipment, radio telescopes, etc.

10 electromagnetic wave control sheet 20 base layer 30 conductive pattern 31 first conductive pattern 32 second conductive pattern 33 third conductive pattern 40 reflective layer 50 spacer layer

Claims (4)

a dielectric layer; and a conductive pattern provided on the dielectric layer;
the dielectric layer has a substrate layer,
the conductive pattern is provided on the base layer;
the substrate layer is made of polymethyl methacrylate resin,
The length of the long side of the conductive pattern is 2 mm or less,
The glass transition temperature of the dielectric layer is 30°C to 120°C.
The electromagnetic wave control sheet, wherein the dielectric layer has a storage modulus at 120° C. of 1.0×10 ⁻² MPa to 1.0×10 ³ MPa. the electromagnetic wave control sheet includes a reflective layer disposed on the back surface side of the base material layer via a spacer layer ,
The electromagnetic wave control sheet according to claim 1 , wherein the dielectric layer is composed of the base layer and the spacer layer . the conductive pattern includes a first conductive pattern, a second conductive pattern, and a third conductive pattern;
the frequency at which the amount of electromagnetic waves absorbed by the first conductive pattern shows a maximum value in a range of 20 GHz to 110 GHz is A [GHz];
a frequency at which the amount of electromagnetic waves absorbed by the second conductive pattern exhibits a maximum value is B [GHz], which satisfies the following formula (1):
3. The electromagnetic wave control sheet according to claim 1 , wherein the frequency at which the amount of electromagnetic waves absorbed by the third conductive pattern exhibits a maximum value is C [GHz], which satisfies the following formula (2):
1.037 × A ≦ B ≦ 1.30 × A (1)
0.60 × A ≦ C ≦ 0.933 × A (2) the first conductive pattern has a plurality of first arrays in which a plurality of first units each having the same shape are arranged;
the second conductive pattern has a plurality of second arrays in which a plurality of second units having the same shape are arranged,
the third conductive pattern has a plurality of third arrays in which a plurality of third units each having the same shape are arranged,
The electromagnetic wave control sheet according to claim 3 , wherein the first array, the second array, and the third array are arranged on the base layer so as to be adjacent to each other.