JP2024037653A - Electromagnetic wave attenuation film - Google Patents

Abstract

[Problem] The purpose of the present invention is to easily and inexpensively obtain an electromagnetic wave attenuating film that has light transmittance and transparency with little shift in absorption peak frequency and changes in frequency characteristics and angular characteristics over time. . [Solution] The electromagnetic wave attenuation film of the present invention includes a dielectric base material having a front surface and a back surface, and a mesh-like pattern formed of thin conductive thin film wires disposed on both the front surface and the rear surface of the dielectric base material. an electromagnetic wave attenuation base having a mesh-like thin film conductive layer with protruding ends; a support layer disposed on the back surface of the electromagnetic wave attenuation base; and a mesh formed of thin conductive thin film wires disposed on the back surface of the support layer. the mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements. In addition, the conductive elements are arranged periodically, and when the distance in the plane direction of the center of gravity of the front and back conductive elements is l, and the shortest distance from the center of gravity of the conductive element to the edge of the mesh is a, the following formula (1) is obtained. may be satisfied. l≦3.6a…(1) [Selection diagram] Figure 2

Description

The present invention relates to an electromagnetic wave attenuation film capable of capturing incident waves and attenuating reflected waves.

Radio waves with a frequency band of several gigahertz (GHz) are used in mobile communications such as mobile phones, wireless LAN, automated toll collection systems (ETC), and the like.

As a radio wave absorbing sheet that absorbs such radio waves, Non-Patent Document 1 describes a radio wave absorber in which a plurality of metal patterns are periodically arranged in two layers, and circular metal patterns with slightly different diameters are arranged in different layers. A radio wave absorber having absorption characteristics in two bands has been proposed.

IEICE Journal B Vol. J103-B No. 12pp. 684-686

However, when a radio wave absorber is created by providing a conductive element on one side of a base material and using a plurality of layers as an absorbing layer, the laminated film provided with the conductive element may elongate or bend. This may cause a shift in the positional accuracy between the layers, resulting in a shift in the absorption frequency. The absorber proposed in Non-Patent Document 1 has a problem in that dielectric substrates such as FR4 on which a predetermined conductive pattern is formed must be laminated together with high accuracy.
In addition, there is a concern that frequency characteristics and angular characteristics may change due to positional deviation between elements due to aging deterioration of the overlapped portions. In addition, it is not preferable to increase the number of substrates provided with elements from the viewpoint of process and cost.
Furthermore, when a metal plate is formed on the opposite side of the conductive element via a base material as proposed in Non-Patent Document 1, light transmission and transparency cannot be obtained.
The present invention solves these conventional problems, and makes it possible to easily and inexpensively produce an electromagnetic wave attenuating film that has translucency and transparency with little shift in absorption peak frequency and changes in frequency characteristics and angular characteristics over time. The purpose is to obtain.

In order to solve the above problems, one of the typical electromagnetic wave attenuating films of the present invention includes a dielectric base material having a front surface and a back surface, and a conductive thin film disposed on both the front surface and the back surface of the dielectric base material. an electromagnetic wave attenuating substrate having a mesh-like thin film conductive layer having a mesh-like pattern formed of thin wires with protruding ends of the thin wires; a support layer disposed on the back surface of the electromagnetic wave attenuating substrate; and a back surface of the support layer. a mesh-like flat plate inductor formed of thin wires of a conductive thin film arranged in the mesh-like thin film conductive layer, the mesh-like thin film conductive layer being an electromagnetic wave attenuating film including a plurality of mesh-like conductive elements.

According to the present invention, it is possible to easily and inexpensively obtain an electromagnetic wave attenuating film that exhibits little shift in absorption peak frequency and changes in frequency characteristics and angular characteristics over time, and is imparted with translucency and transparency.
Further, according to the present invention, it is possible to attenuate radio waves having a frequency in the millimeter wave band, and to provide a thin electromagnetic wave attenuation film. In addition, by simultaneously forming mesh-like thin film conductive layers with protruding thin wire ends on the front and back sides of a single layer of base material, the positional accuracy of the mesh-like thin film conductive layers placed on the front and back sides can be ensured. , it becomes possible to easily produce an electromagnetic wave attenuation film that has absorption performance at a target frequency.

FIG. 1 is a schematic plan view showing an electromagnetic wave attenuation film according to a first embodiment of the present invention. 2 is a schematic diagram showing a part of a cross section taken along line II in FIG. 1. FIG. FIG. 2 is a cross-sectional view of a mesh-like thin film conductive layer placed on a dielectric base material via an adhesive layer and patterned. FIG. 3 is a schematic diagram showing an example of a plan view shape of a mesh-like conductive element. FIG. 3 is a schematic diagram showing an example of a combination of shapes of mesh-like conductive elements in plan view. 7 is a graph showing the relationship between the dimensions of a mesh-like conductive element and the wavelength of electromagnetic waves to be attenuated. It is a perspective image showing an example of the distance between a front conductive element and a back conductive element. 7A is an image showing a simulation result of electric field strength in a cross section taken along line II in FIG. 7A. It is a perspective image showing another example of the distance between the front conductive element and the back conductive element. 8A is an image showing a simulation result of electric field strength in a cross section taken along line II in FIG. 8A. 7 is a graph showing simulation results of electromagnetic wave attenuation due to changes in the thickness of a conductive element. FIG. 3 is a schematic plan view showing an electromagnetic wave attenuation film according to a second embodiment of the present invention. 11 is a schematic diagram showing a part of a cross section taken along line II-II in FIG. 10. FIG. FIG. 2 is a schematic diagram of an example showing a part of a cross section taken along line II in FIG. 1 when a blackening layer is provided. FIG. 2 is a schematic diagram of another example showing a part of the cross section taken along line II in FIG. 1 when a blackening layer is provided. FIG. 2 is a schematic diagram of another example showing a part of the cross section taken along line II in FIG. 1 when a blackening layer is provided. FIG. 2 is a schematic diagram showing a part of a cross section taken along line II in FIG. 1 when a top coat layer is provided. FIG. 2 is a schematic diagram showing a part of the cross section of the electromagnetic wave attenuating film shown in Examples 1 to 5. 3 is a graph showing electromagnetic wave attenuation characteristics of Example 1. 7 is a graph showing electromagnetic wave attenuation characteristics of Example 2. 3 is a graph showing electromagnetic wave attenuation characteristics of Example 3. 7 is a graph showing electromagnetic wave attenuation characteristics of Example 4. 7 is a graph showing electromagnetic wave attenuation characteristics of Example 5. FIG. 2 is a schematic diagram showing a part of a cross section of an electromagnetic wave attenuation film of Comparative Example 1. 3 is a graph showing electromagnetic wave attenuation characteristics of Comparative Example 1. 7 is a graph showing electromagnetic wave attenuation characteristics of Comparative Example 2. 3 is a graph showing electromagnetic wave attenuation characteristics of Comparative Example 3. 7 is a graph showing electromagnetic wave attenuation characteristics of Comparative Example 4. 7 is a graph showing electromagnetic wave attenuation characteristics of Comparative Example 5.

Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are denoted by the same reference numerals. In addition, the reference numerals may be omitted for the same parts.

In the disclosure of the embodiments, the directions shown in the x-axis, y-axis, and z-axis shown on the drawings may be used to indicate directions. Unless otherwise specified, "plane" means the xy plane, "plan view" means the surface viewed from the z-axis direction, "plan view" means the surface seen from the z-axis direction, and "plan view shape" and "plan shape" ” means the shape of the drawing viewed from the z-axis direction.

In addition, in the disclosure of the embodiments, the "front" of an object means the surface when the object is viewed from the positive side of the z-axis, the "back" means the surface when viewed from the negative side of the z-axis, and the "front" of the object means the surface when viewed from the negative side of the z-axis. '' means the outer surface sandwiched between the front and back surfaces. The term "thickness direction" means the z-axis direction.

Furthermore, in the disclosure of the embodiments, the term "center of gravity" means the center of gravity in a planar shape. However, in the case of a mesh-like plane in which the thin wires forming the mesh have protruding ends, this refers to the plane shape formed by regarding the virtual line segment connecting the protruding ends as the outermost periphery.

[First embodiment]
FIG. 1 is a schematic plan view showing an electromagnetic wave attenuation film 1 according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing a part of a cross section taken along line II in FIG. 1. FIG. 2(a) is a cross section between α and β on line II, for example. FIG. 2(b) is a schematic plan view of the mesh-like thin film conductive layers 30 and 31 (widths of thin lines are omitted).

The electromagnetic wave attenuation film 1 includes a dielectric base material (dielectric layer) 10, a mesh-like thin film conductive layer 30 formed on the front surface 10a of the dielectric base material 10, and a mesh-like thin film conductive layer 30 formed on the back surface 10b of the dielectric base material 10. An electromagnetic wave attenuating base 20 composed of a mesh-like thin film conductive layer 31, a support layer 11 formed on the back side of the mesh-like thin film conductive layer 31 on the back side, and a mesh-like flat plate inductor 50 formed on the back side of the support layer 11. It is equipped with The mesh-like thin film conductive layers 30 and 31 are mesh-like conductor flat plates in which the thin wire ends protrude in a mesh-like pattern formed of thin conductive thin wires (hereinafter also referred to as "conductive thin wires" or "thin wires"). This is the layer of The mesh-like thin film conductive layers 30 and 31 may include a plurality of conductive elements (hereinafter, the thin film conductive layer may also be referred to as a conductive element when considering a specific shape, arrangement, etc.). The mesh-like flat plate inductor 50 is formed of a thin wire of a conductive thin film, and a current is generated near the surface inside the mesh-like flat plate inductor 50 by external magnetic flux. It also has a function of generating a magnetic field near the surface outside the mesh-like flat plate inductor 50 along with the current.
Note that the front surface can be the surface on which electromagnetic waves are incident. The back surface is the surface of the dielectric substrate opposite to the front surface. In the following description of the embodiments, the term "thin film conductive layer (conductive element)" or "flat plate inductor" may be used, but unless otherwise specified, it means a mesh-like structure.
Further, when the electromagnetic wave attenuated by the electromagnetic wave attenuation film has a frequency f that is a single minimum value, this frequency f is defined as the attenuation center frequency f. Further, when the electromagnetic wave attenuated by the electromagnetic wave attenuation film has a plurality of minimum values, the attenuation center frequency is the average value of the plurality of frequencies that is -3 dB from the minimum value with the largest attenuation. The attenuation center wavelength can be determined by dividing the speed of light in the dielectric base material and the support layer by the attenuation center frequency f, which will be described later.
Further, the electromagnetic wave attenuation film 1 may include a top coat layer 200 (described later) for impedance matching with air and for improving the weather resistance of the sheet.

(Electromagnetic wave attenuation base)
As shown in FIG. 2, the electromagnetic wave attenuation base 20 has a structure in which mesh-like thin film conductive layers 30 and 31 are arranged on the front surface 10a and the back surface 10b of the dielectric base material 10.
A typical example of the material constituting the dielectric base material 10 is synthetic resin. The type of synthetic resin is not particularly limited as long as it has sufficient strength, flexibility, and processability as well as insulation properties. This synthetic resin can be a thermoplastic resin. Synthetic resins include, for example, polyesters such as polyethylene terephthalate (PET); polyarylene sulfides such as polyphenylene sulfide; polyolefins such as polyethylene and polypropylene; polyamides, polyimides, polyamideimides, polyethersulfones, polyetheretherketones, polycarbonates, and acrylics. Examples include, but are not limited to, resins and polystyrene. These materials may be used alone, two or more of them may be mixed, or a laminate may be used. Further, the dielectric base material 10 may contain conductive particles, insulating particles, magnetic particles, or a mixture thereof.
In order to form the electromagnetic wave attenuation substrate 20, a mesh-like laminate is formed, in which thin film conductive layers 30 and 31 patterned in a mesh shape are formed on both sides of a dielectric substrate 10, together with an anchor layer and an adhesive layer via an adhesive layer. may also be used.
Further, the dielectric base material 10 has a bending rigidity of 7000 MPa·mm ⁴ or less.

In an embodiment of the present invention, the thickness of the dielectric base material and the support layer can be made sufficiently thin with respect to the wavelength of electromagnetic waves. It is known that when the dielectric base material and the support layer are sufficiently thin with respect to the wavelength of electromagnetic waves, no traveling waves are generated in the dielectric base material and the support layer. "Sufficiently thin" may be less than 1/2 of the wavelength. At less than 1/2 the wavelength, traveling waves are not guided. This is a phenomenon called electromagnetic wave cutoff. Furthermore, it can be made less than 1/10 of the wavelength. Generally, when the difference in the propagation distance of electromagnetic waves is 1/10 of the wavelength or less, no substantial phase difference occurs. In other words, when the distance between the conductive element and the flat inductor is 1/10 or less of the wavelength at the dielectric base material and support layer, the electromagnetic waves re-emitted by the conductive element and the reflected waves from the flat inductor are substantially No phase difference occurs. It is thought that electromagnetic waves are not guided within a sufficiently thin dielectric base material or support layer sandwiched between conductors, and normally electromagnetic waves are cut off when the material becomes thin enough. Electric fields and magnetic fields are not localized in such dielectric base materials and support layers. Note that this wavelength in embodiments of the present invention may be the attenuation center wavelength. Furthermore, unexpectedly, attenuation is obtained even when the dielectric base material and support layer have a wavelength of 1/100 or less. This thickness is on the same level as the unevenness of the highest precision mirror surface, and attenuation is obtained with a structure that has virtually no thickness with respect to the scale of electromagnetic waves.

As a result of various experiments and simulations, the inventors have found that even within a sufficiently thin dielectric base material and support layer, stationary localization of electric and magnetic fields due to electromagnetic waves occurs. The thickness (t) of the dielectric base material 10 can be 5 μm or more and 300 μm or less. Furthermore, the thickness (t) of the dielectric base material 10 can be 5 μm or more and 100 μm or less. This is thinner than 1/2 of the wavelength of the millimeter wave band, and further thinner than 1/10 of the wavelength of the millimeter wave band. Therefore, although the electromagnetic wave attenuation film is a thin film, it is possible to attenuate electromagnetic waves in the millimeter wave band. The thickness (t) of the dielectric base material 10 is constant or variable. Similarly, the thickness (ts) of the support layer 11 can be 5 μm or more and 250 μm or less. Furthermore, it can be made to be 10 μm or more and 200 μm or less. Furthermore, the thickness can be set to 15 μm or more and 150 μm or less.

In an embodiment of the present invention, the electromagnetic wave attenuation substrate 20 may have an adhesive layer 12 between it and the support layer 11. The support layer 11 is a single layer or a multilayer. As the material for the support layer 11, the same material as the dielectric base material 10 can be used. For example, it can be a single substance, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, and silicone resin. Support layer 11 can be an extruded film. The extruded film can be an unstretched film or a stretched film. Further, the support layer can also be formed on the back surface of the electromagnetic wave attenuating substrate 20 by coating. The adhesive layer 12 may be composed of two layers: a molding layer and an anchor layer. Further, an adhesive layer may be provided to improve the adhesion between the adhesive layer 12 and the conductive element. For the adhesive layer 12, molding layer, anchor layer, and adhesive layer, the same materials as those constituting the dielectric base material can be used.

The mesh-like thin film conductive layer 30 formed on the front surface 10a of the dielectric base material 10 and the mesh-like thin film conductive layer 31 formed on the back surface 10b cover the entire front surface 10a, back surface 10b or partially covered. The mesh-like thin film conductive layers 30 and 31 can be formed by forming a layer of conductive material directly on both sides of the dielectric base material 10 by vapor deposition or sputtering, and then patterning it by etching or the like, as shown in FIG. . FIG. 3 is a cross-sectional view of a mesh-like thin film conductive layer arranged on a dielectric base material with an adhesive layer interposed therebetween and patterned. The mesh-like thin film conductive layers 30 and 31 are formed by forming a thin film conductive layer by laminating a conductive material foil to the dielectric base material 10 via the adhesive layer 13, as shown in FIG. 3, and then attaching the conductive material by etching or the like. It can be formed by patterning and arranging. As shown in FIG. 3, even when forming a conductive pattern on the dielectric base material 10 via the adhesive layer 13, the adhesive layer 13 is patterned to have the same dimensions as the conductive pattern. Even if stress is applied to the electromagnetic wave attenuating film on which a conductive pattern is formed by bending it, the stress is divided for each conductive pattern, so there is no misalignment between the conductive patterns formed on the front and back sides of the dielectric. .

The mesh flat plate inductor 50 covers the whole or part of the back surface of the support layer 11. As long as the performance of the electromagnetic wave attenuation film 1 is not significantly impaired, for example, there may be a portion of the periphery of the electromagnetic wave attenuation film 1 that is not covered by the mesh thin film conductive layers 30, 31 or the mesh flat plate inductor 50. It's okay.

The materials of the mesh thin film conductive layers 30, 31 and the mesh flat plate inductor 50 are not particularly limited as long as they have conductivity. From the viewpoint of corrosion resistance and cost, aluminum, copper, silver, gold, platinum, tin, nickel, cobalt, chromium, molybdenum, iron, and alloys thereof are preferred. The mesh thin film conductive layers 30 and 31 and the mesh flat plate inductor 50 can be formed by vacuum deposition on the dielectric base material 10, or by laminating a conductive material foil to the dielectric base material 10 via the adhesive layer 13. It can also be formed by The thickness of the adhesive layer 13 for bonding the conductive material foil to the dielectric can be 10 nm or more and 2000 nm or less. If the thickness is less than 10 nm, the adhesion of the conductive material foil to the dielectric may decrease, and if it exceeds 2000 nm, productivity may decrease. Further, the adhesive layer 13 has a bending rigidity of 7000 MPa·mm ⁴ or less. Furthermore, the ratio of the thicknesses of the mesh-like thin film conductive layers 30 and 31 to the adhesive layer 13 is preferably 1:2.
The mesh plate inductor 50 may be made of a conductive compound.
The thickness (tm) of the mesh-like thin film conductive layers 30 and 31 can be 10 nm or more and 1000 nm or less. If it is less than 10 nm, the ability to attenuate electromagnetic waves may deteriorate. If it exceeds 1000 nm, productivity may decrease.
The mesh flat plate inductor 50 can be made of cast metal, rolled metal plate, metal foil, vapor deposited film, sputtered film, or plating. The thickness of the rolled metal plate can be 0.1 mm or more and 5 mm or less. The thickness of the metal foil can be 5 μm or more and less than 100 μm. When the flat plate inductor 50 is a vapor deposited film, a sputtered film, or a plated film, the thickness can be set to 0.5 μm or more and less than 5 mm. The thickness (tmb) of the mesh flat plate inductor 50 can be 0.5 μm to 5 mm. Furthermore, if the mesh flat plate inductor 50 is cast, the maximum dimension may be 10 mm or more, although the thickness is not specified. Further, the thickness (tmb) of the mesh flat plate inductor 50 can be set to be equal to or greater than the skin depth determined by the attenuation center wavelength. Further, the thickness (tmb) of the mesh-like flat plate inductor 50 can be made thicker than the thickness (tm) of the mesh-like thin film conductive layers 30 and 31.
The mesh thin film conductive layers 30 and 31 and the mesh flat plate inductor 50 may be made of the same metal type. The same metal type may be the same pure metal or an alloy of the same metal (for example, both are aluminum alloys), or the mesh thin film conductive layers 30 and 31 may be pure metal and the mesh flat plate inductor 50 may be the mesh thin film conductive layer 30. It may also be an alloy of metals. Moreover, the materials of the mesh-like thin film conductive layers 30 and 31 and the mesh-like flat plate inductor 50 may be different metal types.
The line width (w) of the thin wire of the conductive material forming the mesh thin film conductive layers 30, 31 and the mesh flat plate inductor 50 and the aperture width (wa) need to be designed in accordance with the desired attenuation center wavelength. The aperture width (wa) of the conductor thin wire that absorbs millimeter wave band can be 1/10 to 1/225 of the wavelength, and the line width (w) can be 30 μm to 500 μm.
It is thought that by forming the thin film conductive layers 30, 31 and the flat plate inductor 50 into a mesh shape, not only light transmission and transparency can be obtained, but also moisture permeability can be obtained. The ability to transmit light and transparency has potential benefits such as being able to provide electromagnetic wave absorbing properties in areas where transparency is required, such as window glass, and while being considerate of the landscape. Furthermore, its moisture permeability makes it highly permeable and easy to handle, even when environmentally friendly water-based adhesives are used to bond wallpaper, etc. is possible.
The mesh-like thin film conductive layers 30 and 31 are characterized by protruding ends of conductive thin wires. Since the ends of the conductive thin wires protrude and there is no conductive thin wire surrounding the outermost periphery, the proportion of the conductor in the dielectric becomes small, making it easier to ensure translucency and transparency.

The shapes of the mesh-like conductive elements 30 and 31 and their combinations will be described. FIG. 4 is a schematic diagram showing an example of the planar shape of a mesh-like conductive element. Polygons include squares, hexagons, crosses, other polygons, circles, and ellipses. The corners of the square, hexagon, cross, and other polygons may be rounded, but are not limited to these shapes. Furthermore, the intersection angle of the mesh of conductive thin wires is not limited to these.
Moreover, FIG. 5 is a schematic diagram showing an example of a combination of planar shapes of mesh-like conductive elements. It may be a combination of different sizes, and may be a single shape or a combination of multiple shapes.

It is thought that the electromagnetic wave attenuation film 1 exhibits a unique mechanism at a specific wavelength due to the above-described configuration.

Electromagnetic waves incident on the electromagnetic wave attenuating film of the present invention behave as follows. Specifically, the electromagnetic field and current generated by the incident wave are considered to be as follows.

First, fluctuations in the magnetic flux of the incident wave transmitted through the mesh-like conductive element induce an alternating current in the mesh-like flat plate inductor 50 that is horizontal to the incident surface of the mesh-like flat plate inductor 50 according to Faraday's law. This alternating current generates a varying magnetic field in the dielectric base material adjacent to the mesh plate inductor 50 according to Ampere's law. Furthermore, the varying magnetic field becomes a magnetic flux that varies with magnetic permeability as a coefficient.

The electric field generated by the varying magnetic flux typically induces a current in a direction that suppresses the magnetic flux according to Henry's law. However, in the case of the configuration of the present application, contrary to expectations, it works in the direction of increasing the current. As a result, a current greater than that induced by the incident wave flows through the mesh-like conductive element. That is, although the area of the mesh-like conductive element is smaller than the area of the mesh-like flat plate inductor 50, it is possible to generate a current comparable to that of the mesh-like flat plate inductor 50.

The direction of the current generated in this conductive element is opposite to that of the mesh flat plate inductor 50. A closed circuit can be formed by the currents flowing in opposite directions in both the mesh-like conductive element and the mesh-like flat plate inductor 50, and the displacement current flowing therebetween. A closed circuit exists only between the mesh-like conductive element and the mesh-like flat plate inductor 50, and if no electric flux is generated horizontally to the electromagnetic wave attenuating film in the space outside the electromagnetic wave attenuating film, reflected waves cannot be generated. Furthermore, the waves reflected by the mesh plate inductor 50 and the electromagnetic waves re-emitted by the current of the conductive element are out of phase by π, so they cancel each other out.

According to the above principle, the reflected waves by the electromagnetic wave attenuation film are attenuated. From an energy perspective, multiple mechanisms are thought to act synergistically, as described below.

The first mechanism is the generation of a periodically oscillating electromagnetic field that is not propagated by the incident wave. First, the mesh-like flat plate inductor 50 induces magnetic flux into an incident wave in the tangential direction of the mesh-like flat plate inductor 50 . The induced magnetic flux causes the mesh-like flat plate inductor 50 to extend in the direction extending from the pair of opposing sides (the outermost thin conductive wires) of the mesh-like thin film conductive layers 30 and 31 (that is, the mesh-like conductive element). An electric field is generated in the vertical direction. Next, when electromagnetic waves are incident on the mesh flat plate inductor, a current is induced near the surface of the mesh flat plate inductor due to the varying magnetic flux. A magnetic field is generated in the dielectric base material 10 and support layer 11 near the surface of the mesh-like flat inductor by the current induced in the mesh-like flat inductor. This electric field and the current of the mesh-like conductive element and the mesh-like flat plate inductor 50 generate a magnetic field between the mesh-like conductive element and the mesh-like flat plate inductor 50 in the same direction as the magnetic flux induced by the mesh-like flat plate inductor 50. Here, the material of the mesh conductive element is metal. The electric field generated within the dielectric base material fluctuates with the same period as the period of the incident wave. Periodic fluctuations in the magnetic field cause periodic fluctuations in the electric field between the mesh thin film conductive layers 30, 31 and the mesh flat plate inductor 50. As a result, a periodically fluctuating electromagnetic field that does not advance is generated between the mesh thin film conductive layers 30, 31 and the mesh flat plate inductor 50. As shown later by current density simulations, the magnetic field in the periodically varying electromagnetic field induces an alternating current in the conductive element. The periodically varying electric field also generates a periodically varying potential in the conductive element. The electromagnetic field does not travel and remains in place, and the induced alternating current causes power loss, resulting in the energy of the electromagnetic field being converted into heat and absorbing electromagnetic waves. Further, it is considered that the alternating current induced in the conductive element re-emits electromagnetic waves from the surface of the conductive element opposite to the surface in contact with the dielectric base material 10 and the support layer 11.
In other words, it is thought that part of the electromagnetic wave energy captured by the electromagnetic wave attenuation film is converted into thermal energy, and the rest is re-emitted. Furthermore, according to the classical electromagnetic theory expressed by Maxwell's equations, etc., the frequency of the induced alternating current is the same as the incident wave, so the frequency of the re-emitted electromagnetic wave is the same as the frequency of the incident wave. It will be the same. As a result, electromagnetic waves with the same frequency as the incident wave are re-emitted. Furthermore, if we consider the oscillating electromagnetic field as a quantum, it is also possible that the quantum loses energy and re-emits electromagnetic waves with lower energy and longer wavelengths. Furthermore, re-emission is thought to include stimulated emission due to incident electromagnetic waves and spontaneous emission. In stimulated emission, it is thought that an electromagnetic wave coherent with a reflected wave in which the incident wave is reflected in the direction of reflection of the incident wave, that is, in the direction of specular reflection, is emitted. Spontaneous emissions are thought to decay over time. Moreover, the spatial distribution of spontaneous emission is considered to be close to Lambertian reflection when the electromagnetic wave attenuation film does not have a diffraction structure, an interference structure, or a refraction structure.
The attenuation center wavelength correlates with the dimension W1 (see FIG. 6, hereinafter sometimes referred to as "width W1") of the mesh conductive elements 30, 31 in the in-plane direction. FIG. 6 is a graph showing the relationship between the dimensions of the mesh conductive element and the wavelength of electromagnetic waves to be attenuated. FIG. 6(a) is a graph showing the relationship between the width W1 (horizontal axis) and the attenuation center frequency (vertical axis), and FIG. 6(b) shows various dimensions used in the simulation. As shown in FIG. 2(b), W1 represents the length from end to end of the mesh conductive element (square), which is twice the length a of the shortest distance from the center of gravity to the end of the mesh. It is.
That is, the wavelength of the electromagnetic waves suitably attenuated by the first mechanism can be changed by changing the dimension W1, and in the electromagnetic wave attenuation film 1, the attenuation of the electromagnetic waves can be set easily and with a high degree of freedom. Therefore, it is possible to easily obtain a configuration that can capture linearly polarized electromagnetic waves in a band of 15 GHz or more and 150 GHz or less.

Periodic fluctuations in the electromagnetic field that do not advance are considered to occur between opposing sides (outermost thin conductive wires) of the mesh-like conductive element in plan view. Therefore, in order for the first mechanism to occur, it is preferable that sides of a certain length face each other. Based on this and the study results by the inventors, a section in the thin film conductive layer having a width W1 of 0.25 mm or more can be used as a conductive element. If a certain conductive element can have a plurality of W1 values, the maximum value among them can be defined as W1 for that conductive element. By setting W1 within the range of about 0.25 mm to 4 mm, it becomes possible to attenuate electromagnetic waves in a band of 15 GHz or more and 150 GHz or less. As shown in FIG. 6, the relationship between the frequency of the electromagnetic wave to be attenuated and the width of the conductive element can be expressed as a straight line on a logarithmic graph. In other words, the frequency of the electromagnetic wave that is attenuated is a power function of the width of the conductive element. The power of the function is approximately -1, and is approximately inversely proportional.
The plurality of conductive elements included in the thin film conductive layer may be arranged in a plurality of types having different dimensions W1. In this case, the attenuation peaks of the respective electromagnetic waves are superimposed, and the electromagnetic waves that can be attenuated can be broadened.

The second mechanism is confinement of the electromagnetic field by the mesh thin film conductive layers 30 and 31 and the mesh flat plate inductor 50. In the electromagnetic wave attenuation film 1 , a dielectric base material 10 and a support layer 11 are sandwiched between mesh-like thin film conductive layers 30 and 31 and a mesh-like flat plate inductor 50 . Therefore, the electric field generated in the dielectric base material 10 and support layer 11 of the electromagnetic wave attenuation film 1 due to the electromagnetic waves is caused by the charge of the conductive elements and the current between the mesh-like thin film conductive layers 30 and 31 containing the conductive elements and the mesh-like flat plate inductor 50. It is confined within the dielectric base material 10 and the support layer 11 between them. That is, the conductive element suppresses the electromagnetic field and confines the electromagnetic field to the dielectric base material 10 and the support layer 11. That is, the conductive element can function as a choke. In other words, the conductive element can be a choke plate that functions as a choke.
It is also believed that magnetic flux is induced by periodic fluctuations in this confined electric field. This causes the oscillating electromagnetic field to accumulate, increasing the energy density of the electromagnetic field. Generally, the higher the energy density, the easier it is to attenuate, so this mechanism attenuates electromagnetic waves efficiently. In addition, in the second mechanism, the higher the dielectric loss tangent of the dielectric base material 10 and the support layer 11, the greater the energy loss of the electromagnetic field accumulated within the dielectric base material. Further, the magnetic field accumulated on the dielectric base material causes a large current in the conductive element, and the electric field accumulated on the dielectric base material produces a large potential difference. A large current and a large potential difference can increase the power loss, which is the product of both. Energy of electromagnetic waves is consumed as power loss, and as a result, electromagnetic waves are attenuated.

The third mechanism is due to power loss in an electric circuit including a capacitor due to the opposing mesh-like thin film conductive layers 30 and 31, the mesh-like flat plate inductor 50, the dielectric base material 10, and the support layer 11 between them. In the electromagnetic wave attenuation film 1 , a dielectric base material 10 and a support layer 11 are sandwiched between mesh-like thin film conductive layers 30 and 31 and a mesh-like flat plate inductor 50 . Therefore, the dielectric base material 10 and the support layer 11 function as a capacitor. Therefore, the electromagnetic waves incident on the dielectric base material 10 and the support layer 11 of the electromagnetic wave attenuation film 1 are attenuated by the electric circuit including the capacitor. The larger the capacitance of a capacitor, the more energy it can store by storing more charge, so the larger the capacitance, the more energy it can handle.
Since the capacitance is inversely proportional to the thickness of the dielectric base material 10 and the support layer 11, from this point of view, it is more preferable that the dielectric base material 10 and the support layer 11 be thinner. Furthermore, since the distance between the mesh thin film conductive layers 30 and 31 and the mesh flat plate inductor 50 is determined by the thickness of the dielectric base material 10 and the support layer 11, the distance between the mesh thin film conductive layers 30 and 31 and the mesh flat plate inductor 50 is The electrical resistance between the two is proportional to the thickness of the dielectric base material 10 and the support layer 11. When the resistance of the dielectric base material 10 and the support layer 11 is small, the leakage current in the dielectric base material 10 and the support layer 11 increases, and the electric circuit including the capacitor of the mesh-like thin film conductive layer 30 and the mesh-like flat plate inductor 50 increases. The current flowing through increases. Therefore, power loss due to leakage current is likely to increase, and electromagnetic wave energy is likely to be absorbed due to power loss. Furthermore, in the electromagnetic wave attenuating film 1 according to the embodiment of the present invention, even if the thickness of the dielectric base material 10 and the support layer 11 at the portion where the conductive element is arranged is changed, the wavelength of the electromagnetic field to be attenuated does not shift. The thickness of the dielectric base material 10 and the support layer 11 can be designed according to the characteristics of the electric circuit including the following.

As explained above, the electromagnetic waves incident on the electromagnetic wave attenuation film 1 generate an electromagnetic field in the dielectric base material 10 and the support layer 11 that are close to the surface of the flat inductor by the first mechanism, and the electromagnetic waves are generated by the second mechanism. The electromagnetic field generated by this is trapped and captured. In this way, the electromagnetic wave attenuation film 1 can capture electromagnetic waves. The captured electromagnetic waves are attenuated by electric field loss and power loss due to the second mechanism, and power loss due to the electric circuit as the third mechanism.

In the electromagnetic wave attenuation film 1 of the first embodiment, as shown in FIG. , including a conductive element. The distance on the same plane between the center of gravity of the conductive element placed on the front side 10a of the dielectric base material 10 and the center of gravity of the conductive element placed on the back side 10b is defined as l, and the shortest distance from the center of gravity of the conductive element to the end of the mesh is By arranging the conductive element at a position that satisfies the following formula (1) where a is the value, it is possible to create an absorber that can provide attenuation at the desired frequency. FIG. 7 is an image showing simulation results of electric field strength regarding an example of the distance between the front conductive element and the back conductive element. FIG. 7A is a perspective image showing an example of the distance between the front conductive element and the back conductive element. FIG. 7B is an image showing a simulation result of electric field strength in a cross section taken along line II in FIG. 7A. When the distance l is placed at a position 2a that satisfies the following formula (1) and electromagnetic waves are incident from the front side, resonance coupling occurs between the front conductive element 30 and the back conductive element 31 as shown in FIG. 7B. It can be seen that a strong electric field is generated. Therefore, it is possible to efficiently attenuate electromagnetic waves. Note that other dimensions are the same as the simulation conditions in FIG. 6.
l≦3.6a…(1)
FIG. 8 is an image showing simulation results of electric field strength regarding another example of the distance between the front conductive element and the back conductive element. FIG. 8A is a perspective image showing another example of the distance between the front conductive element and the back conductive element. FIG. 8B is an image showing a simulation result of electric field strength in a cross section taken along line II in FIG. 8A. If the conductive elements are arranged with a distance l of 4a, it is possible to attenuate electromagnetic waves, but as shown in FIG. 8B, the front conductive elements and the back conductive elements resonate independently, and the front and back conductive elements The resonances of the two are no longer coupled, and the effect of arranging the conductive elements on the front and back surfaces is weakened. Note that other dimensions are the same as the simulation conditions in FIG. 6. Furthermore, when l becomes 3.6a or more and the distance between the front and back conductive elements becomes large, it becomes difficult to attenuate electromagnetic waves at a target frequency.

In the electromagnetic wave attenuation film 1, the role played by the third mechanism is also important. Electromagnetic waves are incident on the front surface 10a of the dielectric base material 10, and an electric field is generated in the dielectric base material 10, and an electric field is also generated on the support layer 11 disposed between the back surface 10b and the mesh-like flat inductor 50, and the electric field is generated below the conductive element. The electromagnetic field is confined to That is, an electromagnetic field with high energy density is generated below the conductive element. The confined electromagnetic field is believed to be attenuated by power loss through the second mechanism and dielectric loss through the third mechanism.

In the prior art, it was thought that by making the resonant conductor thicker than the skin depth, a sufficient alternating current would be generated in the resonant layer, and the electromagnetic waves would be attenuated by the power loss of the alternating current. However, the inventors have discovered that when the thickness of the conductive element becomes less than the skin depth, the attenuation of electromagnetic waves increases.

FIG. 9 is a graph showing simulation results of the attenuation of electromagnetic waves due to changes in the thickness of the conductive element. FIG. 9(a) shows the simulation results, and FIG. 9(b) shows various dimensions used in the simulation. The material of the conductive element is copper. The incident wave was a linearly polarized sine wave, and was incident perpendicularly to the electromagnetic wave attenuation film. In addition, in the simulation, the flat plate inductor was assumed to be a perfect conductor. The electromagnetic wave attenuation property of the electromagnetic wave attenuation film is measured using monostatic RCS based on the case of only a flat plate inductor. Note that the vertical axis indicating the attenuation of electromagnetic waves is expressed in decibels. Monostatic RCS (Radar Cross-Section) is an index representing the ease of detecting a target with a monostatic radar, and can be calculated using the following formula (1). Note that a monostatic radar performs transmission and reception at the same location.

As a result of the simulation, as shown in FIG. 9, large attenuation of electromagnetic waves was observed when the thickness was 30 nm or more. On the contrary, below 30 nm, the attenuation of electromagnetic waves decreases.
Note that when the conductive element is provided with a blackening layer, stable film formation is possible if the combined thickness of the conductive element and the blackening layer is 1000 nm or less.

The phenomenon shown in FIG. 9 has an interesting relationship with skin depth. The skin depth of copper at a frequency of 41 GHz is approximately 326 nm. That is, when the thickness of the conductive element becomes less than the skin depth of the material, the attenuation of electromagnetic waves increases. Further, at less than 1/e ² of the skin depth, the attenuation of electromagnetic waves decreases. This is because if the conductive layer is thicker than the skin depth, sufficient resistance cannot be obtained and the voltage drop necessary for power loss cannot be obtained, and the current is concentrated only near the center of the conductive element, creating a potential difference. It is conceivable that the current in the region decreases. On the other hand, even if the thickness of the conductive layer is less than the skin depth, if it is less than 1/e ² of the skin depth, it is conceivable that sufficient current for power loss cannot be obtained. It goes without saying that power loss is given as the product of current and voltage. In other words, sufficient attenuation of electromagnetic waves can be obtained as long as the following LN function formula (2), which is expressed using the natural logarithm of the value obtained by normalizing the thickness T of the conductive element with the skin depth d, is satisfied. It can be said that it can be done.
-2 ≦ ln(T/d) ≦ 0...(2)
Furthermore, when a metal with low admittance is used for the conductive element, attenuation of electromagnetic waves can be obtained even within the range of formula (3) below. Furthermore, when the area of the conductive element occupies a large proportion of the front surface of the dielectric base material, attenuation of electromagnetic waves can be obtained even within the range of formula (3) below. When this area ratio is large, the ratio of the area of the conductive element to the front surface of the dielectric base material can be 50% or more and 90% or less.
0 < ln(T/d) ≦ 1...(3)
Based on equations (2) and (3), the attenuation of electromagnetic waves can be obtained within the range of equation (4) below.
-2 ≦ ln(T/d) ≦ 1...(4)
Note that in the embodiment of the present invention, this skin depth can be calculated using the attenuation center frequency f. That is, when the attenuation center frequency f is used, the skin depth d is calculated as shown in the following equation (5), as is well known.

Simulation results also showed that attenuation increased when the thickness of the conductive element was thinner than the skin depth. This is because the current generated due to the magnetic flux of the dielectric base material of the conductive element reaches the opposite side of the dielectric base material, and the reflected wave from the dielectric inductor is canceled out by the current. This is thought to be because electromagnetic waves with a phase shift of π are emitted. In addition, as the thickness of the conductive element becomes thinner than the skin depth, the current in the conductive element is regulated, and as a result, a magnetic field is generated not only near the center of the conductive element but also throughout the entire conductive element, and is induced by the generated magnetic field. It is believed that the reflected waves are further attenuated because current is also generated across the conductive element, increasing the emission of electromagnetic waves that cancel out the waves reflected by the dielectric inductor.
Additionally, the electric field in the dielectric substrate between the conductive element and the dielectric inductor attracts the conductive element and the dielectric inductor. If the electric field varies periodically, the attractive force on the conductive element will also vary periodically. Therefore, the electric field in the dielectric substrate between the conductive element and the dielectric inductor causes the conductive element to vibrate. The energy of this vibration is converted into heat and lost. Therefore, it is thought that the mechanics of the electromagnetic field acting on the conductive element also contribute to the attenuation of the electromagnetic waves.
Furthermore, if we consider periodic fluctuations in the electromagnetic field as quanta, we can think of them as a state in which the momentum is zero and the quantum is trapped by the electromagnetic field. In addition, since the thickness of the conductive element is on the order of several hundred nanometers, it is possible that the energy level within the conductive element may be affected.
In this way, the phenomena in the embodiments of the present invention can be interpreted not only as classical electromagnetism but also as classical mechanics or quantum mechanics.
Therefore, when interpreting equation (4), the range is reasonably determined, but it is not a range that is strictly calculated by taking into account all physical phenomena. Therefore, when determining whether a target product falls within the range of the above formula, it is appropriate to consider and interpret the physical phenomena occurring.
Incidentally, in the prior art, there is usually no example of using a conductor that is about skin depth to thinner than skin depth. Therefore, the embodiment of the present invention is considered to be different from the conventional mechanism in the interaction mechanism itself with electromagnetic waves in the millimeter wave band.

[Second embodiment]
A second embodiment of the present invention will be described with reference to FIGS. 10 and 11. The second embodiment differs from the first embodiment in the arrangement of conductive elements. In the following description, components that are common to those already described may be given the same reference numerals and redundant descriptions may be omitted. It is thought that the first, second, and third mechanisms described above are also expressed in the second embodiment.

FIG. 10 is a schematic plan view showing an electromagnetic wave attenuation film according to a second embodiment of the present invention. FIG. 11 is a schematic diagram showing a part of a cross section taken along line II-II in FIG. 10. For example, it is a cross section between α and β on line II-II. Symbols regarding various dimensions are the same as in FIG. 2.
The electromagnetic wave attenuation film 61 includes a dielectric base material 62, a plurality of mesh-like conductive elements 30A and 31A, and a mesh-like flat plate inductor 50. The thickness of the mesh-like conductive elements 30A and 31A can be 1000 nm or less.

The dielectric base material 62 of the second embodiment can be made of the same material and configuration as the dielectric base material 10 of the first embodiment. As shown in FIG. 11, the electromagnetic wave attenuation base 60 has a structure in which mesh-like thin film conductive layers 30A and 31A are arranged on the front surface 62a and the back surface 62b of a dielectric base material 62. In order to form the electromagnetic wave attenuating substrate 60, a laminate in which thin film conductive layers are formed on both sides of a dielectric substrate 62 via an anchor layer and an adhesive layer may be used.

Support layer 11 can be an extruded film. The extruded film can be an unstretched film or a stretched film. Further, the support layer can also be formed on the back surface of the electromagnetic wave attenuating substrate 60 by coating. The support layer has a bending rigidity of 7000 MPa·mm ⁴ or less.

The mesh-like thin film conductive layer 30A formed on the front surface 62a of the dielectric base material 62 and the mesh-like thin film conductive layer 31A formed on the back surface 62b cover the entire front surface 62a, back surface 62b or partially covered. The mesh flat plate inductor 50 covers the whole or part of the back surface of the support layer 11. The mesh flat plate inductor 50 may be covered with the mesh thin film conductive layers 30A, 31A or the mesh flat plate inductor 50, for example, on a part of the periphery of the electromagnetic wave attenuating film 61, as long as the performance of the electromagnetic wave attenuating film 1 is not significantly impaired. There may be parts that are not covered.
Although the mesh flat inductor 50 is provided on the back surface of the support layer 11, an adhesive layer may be provided between the back surface of the support layer 11 and the mesh flat inductor 50. The adhesive layer and the mesh flat plate inductor 50 can be formed from the same material and by the same manufacturing method as in the first embodiment.

The setting of the attenuation in the electromagnetic wave attenuation film 61 of the second embodiment can be controlled by the arrangement positions of the mesh-like conductive elements 30A and 31A arranged on the front surface 62a and the back surface 62b of the dielectric base material 62. The combination of the front and back conductive elements that satisfies the following formula (6), where the distance in the plane direction of the center of gravity of the front and back conductive elements is l, and the shortest distance from the center of gravity of the conductive element to the edge of the mesh is a. By mixing combinations of front and back conductive elements that satisfy the following formula (7), it is possible to create an electromagnetic wave attenuation film 61 having electromagnetic wave attenuation performance at multiple frequencies. The range of combinations is not particularly limited, but for example, when the electromagnetic wave attenuation film is viewed in plan, the combination may be between a predetermined front (back) conductive element and an adjacent back (front) conductive element.
When the relationship between the distance 1 in the plane direction of the center of gravity of the front and back conductive elements and the shortest distance from the center of gravity of the conductive element to the end of the mesh a satisfies the following formula (6), the front and back conductive elements are flat , the capacitance C shown by the following equation (8) increases, and the resonant frequency shifts to a lower frequency range. This allows the front and back conductive elements to overlap in the plane direction and places where they do not overlap on one plane, thereby allowing electromagnetic waves with attenuation at multiple frequencies to be generated without changing the dimensions of the conductive elements. It becomes possible to create attenuating films.
l<2a…(6)
l≧2a…(7)

ω ₀ =1/sqrt(LC)…(8)
ω ₀ : Resonance frequency L: Reactance C: Capacitance

Furthermore, by adjusting the ratio of the combinations in which the front and back conductive elements are stacked in the plane direction and the combinations in which they are not stacked on one plane, and the area ratio in which the front and back conductive elements are stacked in the plane direction. By controlling the frequency at which electromagnetic waves are attenuated, it is possible to create an electromagnetic wave attenuating film that has an attenuation peak that attenuates over a wide range of frequencies or attenuates only a specific frequency among multiple frequencies. The method of calculating the mixing ratio is not particularly limited, but it may be calculated, for example, from the ratio of the number of combinations that satisfy equation (6) and the number of combinations that satisfy equation (7). Note that although adjacent front conductive elements or rear conductive elements may overlap each other, they may be treated as independent conductive elements in calculating the combination.

<Blackening layer>
In embodiments of the present invention, a blackening layer may be provided by performing a blackening treatment around the thin film conductive layer.
FIG. 12 is a schematic diagram of an example showing a part of a cross section taken along line II in FIG. 1 when a blackening layer is provided. As shown in FIG. 12, a blackening layer 32 may be provided on the front surface of the thin film conductive layer 30, a blackening layer 33 may be provided on the side surface of the thin film conductive layer 30, a blackening layer 34 may be provided on the back surface of the thin film conductive layer 31, and a blackening layer 35 may be provided on the side surface.
Further, FIG. 13 is a schematic diagram of another example showing a part of the cross section taken along the line II in FIG. 1 when a blackening layer is provided. As shown in FIG. 13, a blackened layer is formed before forming the thin film conductive layers 30 and 31 on the dielectric base material 10, and then a thin film conductive layer is formed, and the blackened layer and the thin film conductive layer are formed in the same layer by etching or the like. The blackening layers 36 and 37 are provided between the thin film conductive layers 30 and 31 and the dielectric base material 10, and the blackening layer 32 is formed on the front surface of the thin film conductive layer 30, and the blackening layer 33 is formed on the side surface of the thin film conductive layer 30. A blackening layer 34 may be provided on the back surface of the layer 31, and a blackening layer 35 may be provided on the side surface thereof.
Further, FIG. 14 is a schematic diagram of another example showing a part of the cross section taken along the line II in FIG. 1 when a blackening layer is provided. As shown in FIG. 14, before forming the thin film conductive layers 30 and 31 on the dielectric base material 10, a blackening layer is formed via the adhesive layer 13, and then the thin film conductive layer is formed and the adhesive layer is removed by etching or the like. The blackening layer and the thin film conductive layer are patterned to have the same dimensions, and the adhesive layer 13 and the blackening layers 36 and 37 are provided between the thin film conductive layers 30 and 31 and the dielectric base material 10, and the blackening layer 36 and 37 are provided on the front surface of the thin film conductive layer 30. A blackening layer 32, a blackening layer 33 on the side surface, a blackening layer 34 on the back side of the thin film conductive layer 31, and a blackening layer 35 on the side surface may be provided.
The blackening treatment may be performed by performing either a sulfurization blackening treatment or a substitution blackening treatment to form a blackened layer. By forming such a blackened layer on the surface of the conductive element, effects such as suppressing an increase in the resistance value of the conductive element and suppressing metallic luster to improve visibility can be obtained. Alternatively, a conductive element may be formed by providing a blackening layer on the surface of the dielectric base material 10 or by providing a blackening layer via an adhesive layer 13 and then etching a multilayer conductor layer in which thin film layers are laminated. Can be done. By forming such a blackened layer between the dielectric base material and the conductive element, it is possible to improve the adhesion of the conductive element to the dielectric base material. The thickness of the blackening layer is preferably 200 nm or less. If it is 200 nm or more, productivity may decrease. Further, the surface roughness of the blackened layer is Ra 0.5 μm or more.

The mesh-like thin film conductive layer 31 may have a support layer 11 on the surface opposite to the dielectric base material 10 (back surface). The thickness (ts) of the support layer 11 can be 5 μm or more and 250 μm or less. Furthermore, it can be made to be 10 μm or more and 200 μm or less. The support layer 11 is a single layer or a multilayer. As the material for the support layer 11, the same material as the dielectric base material 10 can be used. For example, it can be a single substance, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, and silicone resin. Support layer 11 can be an extruded film. The extruded film can be an unstretched film or a stretched film. Further, the support layer 11 can also be formed on the back surface of the electromagnetic wave attenuating substrate 20 by coating.

The mesh-like thin film conductive layer 30 may have a top coat layer 200 on the surface opposite to the dielectric base material 10 (front surface). FIG. 15 is a schematic diagram showing a part of the cross section taken along line II in FIG. 1 when the top coat layer 200 is provided. The flat inductor 50 may also have a top coat layer 200 on the surface opposite to the dielectric base material 10 (back surface). The thickness (h) of the top coat layer 200 can be 0.1 μm or more and 50 μm or less. Furthermore, it can be made to be 1 μm or more and 5 μm or less. Top coat layer 200 is a single layer or multilayer. The material of the top coat layer 200 can be a single substance, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, and silicone resin. It may also contain insulating particles, magnetic particles, conductive particles, or a mixture thereof. The particles can be inorganic particles. By providing the top coat layer 200, the impedance matches the air through which radio waves propagate, and it becomes possible to effectively attenuate radio waves with respect to the thin film conductive layer. Further, corrosion resistance, chemical resistance, heat resistance, abrasion resistance, impact resistance, etc. can be imparted to the mesh-like thin film conductive layers 30, 31 and the mesh-like flat plate inductor 50. For example, by using crosslinked acrylic resin, crosslinked epoxy resin, polyamide, polyimide, polyamideimide, silicone resin, etc., it is possible to improve heat resistance in addition to improving solvent resistance. Further, by using urethane resin or the like, it is possible to improve the impact resistance, and by using a silicone resin, it is possible to improve the abrasion resistance.

Furthermore, the top coat layer 200 may contain a pigment or the like in order to impart design properties. Examples of the pigments used include organic pigments and inorganic pigments. As the organic pigment, for example, organic pigments such as azo pigments, lake pigments, anthraquinone pigments, phthalocyanine pigments, isoindolinone pigments, and dioxazine pigments can be employed. Examples of inorganic pigments include yellow lead, yellow iron oxide, cadmium yellow, titanium yellow, barium yellow, aureolin, molybdate orange, cadmium red, Bengara, red lead, cinnabar, mars violet, manganese violet, cobalt violet, and cobalt. Blue, cerulean blue, ultramarine, navy blue, emerald green, chrome vermilion, chromium oxide, viridian, iron black, carbon black, etc. can be used. In addition, examples of white pigments such as inorganic pigments include titanium oxide (titanium white, titanium white), zinc oxide (zinc white), basic lead carbonate (lead white), basic lead sulfate, zinc sulfide, lithopone, titanox, etc. can be used. Inorganic pigments in particular have excellent light resistance (fading resistance) and chemical resistance, so they are very suitable from the viewpoint of durability and fastness when it is desired to add design to the top coat layer. .

When the top coat layer 200 is multilayered, it may be separated into a durability-imparting layer and a design-imparting layer. If necessary, a protective layer for protecting the design-imparting layer may be provided on the design-imparting layer. Alternatively, the top coat layer 200 may be formed by providing an adhesive layer or an adhesive layer on the surface in contact with the mesh-like thin film conductive layer 30 and bonding a separately prepared durability imparting layer and a design imparting layer.
When bonding the top coat layer 200 to the electromagnetic wave attenuation film of the present invention, the desired electromagnetic wave attenuation characteristics can be maintained by bonding the top coat layer 200 to the mesh-like thin film conductor layer 30 so that air bubbles etc. do not enter between the layers. I can do it.

When applying the electromagnetic wave attenuation film of the present invention to a building material such as wallpaper, a pattern may be provided on the top coat layer 200 or the design imparting layer in order to impart design. The type of pattern is not particularly limited, and any pattern can be used depending on the purpose of the building material such as wallpaper. For example, wood grain patterns, cork patterns, stone grain patterns, marble patterns, abstract patterns, etc. that are widely used in the field of conventional building materials can be used. Furthermore, for example, if the purpose is simply coloring or color adjustment, a single solid color may be used. Moreover, an uneven pattern may be provided as necessary. The type of pattern of the uneven pattern is not particularly limited, and any pattern can be used depending on the purpose of the building material such as wallpaper. For example, various patterns such as a wood grain pattern, a stone grain pattern, a Japanese paper pattern, a marble pattern, a cloth grain pattern, and a geometric pattern, which are widely used in the field of conventional building materials such as wallpaper, can be employed. Further, a simple matte texture, grain texture, hairline texture, suede texture, etc. can also be used. The method for forming the uneven pattern is not particularly limited, and any method for forming the uneven pattern can be used. For example, a mechanical embossing method using a metal embossing plate can be employed.
In this manner, by imparting design properties, when the electromagnetic wave attenuating film of the present invention is used as a building material, it becomes possible to harmonize the atmosphere of the color and texture with the space.

The inventors' studies have revealed that the attenuation due to the first mechanism changes depending on the admittance (reciprocal of electrical resistance) of the metal constituting the conductive element. Admittance (siemens/m) was 10 million or more, and good attenuation of electromagnetic waves was obtained. Silver is known as a substance with the highest admittance among normal conductors, and its admittance is 61 to 66×10 ⁶ , so the upper limit of admittance is approximately 70 million. A metal having an admittance of 5 million or more and 70 million or less can be used. The metal constituting the conductive element can be ferromagnetic, paramagnetic, diamagnetic, or antiferromagnetic. Examples of ferromagnetic metals are nickel, cobalt, iron or alloys thereof. Examples of paramagnetic metals are aluminum, tin (beta tin) or alloys thereof. Examples of diamagnetic metals are gold, silver, copper, tin (alpha tin), zinc or alloys thereof. An example of a diamagnetic alloy is brass, which is an alloy of copper and zinc. An example of an antiferromagnetic metal is chromium. Good attenuation of electromagnetic waves was demonstrated by these metallic conductive elements.

<Manufacturing method>
An example of a method for manufacturing the electromagnetic wave attenuation film 1 will be described.

Various methods can be considered for obtaining the electromagnetic wave attenuation film of the present invention, but the manufacturing method described below is simple and provides high precision in the arrangement of the thin film conductive layer.

First, a method of manufacturing the electromagnetic wave attenuation base 20 will be explained. For this purpose, mesh-like thin film conductive layers 30 and 31 consisting of a predetermined repeating pattern of conductive elements are simultaneously formed on the front surface 10a and back surface 10b of the dielectric base material 10. The conductive elements may be formed by any method as long as a desired pattern can be obtained, and for example, photolithography can be used. Note that the front surface 10a and the back surface 10b of the dielectric base material 10 may be subjected to either a sulfurization blackening treatment or a substitution blackening treatment in advance to form a blackened layer, if necessary.

Examples of the material of the dielectric base material 10 include polyester such as polyethylene terephthalate (PET); polyarylene sulfide such as polyphenylene sulfide; polyolefin such as polyethylene and polypropylene; polyamide, polyimide, polyamideimide, polyether sulfone, and polyether. Examples include, but are not limited to, ether ketone, polycarbonate, acrylic resin, polystyrene, and the like.

When using the photolithography method, first, a metal film is formed on both the front surface 10a and the back surface 10b of the dielectric base material 10 so as to cover the entire region of the pattern desired to be finally obtained. The metal film may be formed by physical deposition such as vapor deposition or sputtering, or may be formed by pasting metal foil or the like. Alternatively, it can also be formed by plating. Plating can be electrolytic plating or electroless plating. The plating can be copper plating, electroless nickel plating, electrolytic nickel plating, zinc plating, electrolytic chrome plating, or a stack of these. The metal film may be formed on the front surface 10a and the back surface 10b simultaneously or separately. If they are performed separately, the order of formation may be in any order.

Subsequently, a resist layer is formed on the metal film formed on the front surface 10a and back surface 10b of the dielectric base material 10. Although the resist layer may be formed by applying a normal resist solution and drying it, a method using a dry film resist is preferable since there is no fear of liquid dripping due to insufficient drying. The resist layer may be formed on the front side 10a and the back side 10b simultaneously or separately. Similar to the formation of metal films, the order of formation does not matter if they are performed separately.

Next, the front side 10a and the back side 10b of the dielectric base material 10 are simultaneously exposed to light through a material that blocks light in a pattern, such as a photomask. In an embodiment of the present invention, when a photolithography method is employed, "simultaneously forming" refers to performing an exposure process at the same time. The two photomasks on the front side 10a and the back side 10b typically have different pattern shapes and/or positions. If the positions of the two photomasks can be properly controlled during exposure, the positional relationship between the mesh-like thin film conductive layers 30 and 31 will be as designed, and there will be no misalignment after formation or when using the electromagnetic wave attenuation film. Anxiety is minimized.

Thereafter, development is performed using a developer to remove unnecessary portions of the resist layer. Development may be performed on the front side 10a and back side 10b of the dielectric base material 10 at the same time or separately, but if done at the same time, problems may occur due to the developer flowing around to the opposite side. I like it because I don't have to worry about it.

Furthermore, the resist layer is removed and the exposed portions of the metal layer are removed. Removal of the metal layer is generally performed by wet etching, but dry etching or any other method may be used as long as only exposed portions can be selectively removed. The metal layer may be removed simultaneously from the front side 10a and the back side 10b of the dielectric base material 10, or may be removed separately, but if wet etching is used, it is convenient to remove the metal layer at the same time. .

Finally, unnecessary portions are removed and the resist layer remaining on the patterned metal layer, ie, the thin film conductive layers 30 and 31, is removed. The resist layer may also be removed from the front side 10a and the back side 10b of the dielectric base material 10 at the same time or separately, but it is convenient to remove them at the same time. Note that this step can be omitted if there is a design reason why it is more convenient to leave the resist layer on the mesh-like thin film conductive layers 30 and 31.

Note that, as already mentioned, the formation of the thin film conductive layers 30 and 31 on the dielectric base material 10 does not have to be based on photolithography. A printing method, an inkjet method, and any other forming method can be applied. In the present invention, "simultaneously formed" means that when a printing method is used, transfer is performed at the same time, and when an inkjet method is used, deposition is performed at the same time.

Furthermore, in the embodiments of the present invention, the "metal film" does not have to be made of metal. For example, it may be a conductive organic material such as PEDOT/PSS or a conductive oxide such as InGaZnO.

After these steps are completed, the mesh-like thin film conductive layers 30 and 31 may be subjected to either a sulfurization blackening treatment or a substitution blackening treatment to form a blackening layer, if necessary.

Subsequently, the support layer 11 on which the flat plate inductor 50 is formed is prepared. Note that this step is performed after the formation of the mesh-like thin film conductive layers 30 and 31 on the dielectric base material 10 merely for convenience of explanation, and the order may be reversed or both steps may be performed. It goes without saying that there is no problem in proceeding with these in parallel.

The support layer 11 on which the mesh-like flat plate inductor 50 is formed can typically be obtained by laminating the mesh-like flat plate inductor 50 on the support layer 11. As the material for the support layer 11, the same material as the dielectric base material 10 can be used. Then, in the same way as forming a metal film on the dielectric base material 10, a mesh-like flat plate inductor 50, which is a metal mesh film, can be formed on the support layer 11. Alternatively, the mesh-like flat plate inductor 50 may be obtained by bonding a mesh-like casting or metal plate to the support layer 11.

As the material for the support layer 11, the same material as the dielectric base material 10 can be used. The support layer 11 may be made of the same material as the dielectric base material 10, or may be made of a different material.

Further, as the material for the mesh-like flat plate inductor 50, the same material as the mesh-like thin film conductive layers 30 and 31 can be used. The mesh flat plate inductor 50 may be made of the same material as the mesh thin film conductive layers 30 and 31, or may be made of a different material.

The mesh-like flat plate inductor 50 of the support layer 11 has the mesh-like flat plate inductor 50 formed on the back side 10b of the dielectric base material 10 (electromagnetic wave attenuation base 20) on which the mesh-like thin film conductive layers 30 and 31 are formed. The electromagnetic wave attenuating film 1 of the present invention can be obtained by bonding opposite sides together.

Another method for obtaining the electromagnetic wave attenuation film of the present invention is to form the mesh-like thin film conductive layers 30 and 31 on the front surface 10a and the back surface 10b of the dielectric base material 10 at the same time, and then The support layer 11 may be laminated on the support layer 11, and the mesh-like flat plate inductor 50 may be formed on the support layer 11 on the opposite side of the dielectric base material 10.

In the case of providing the top coat layer 200, a dielectric film may be laminated via an adhesive layer, but the method for forming the top coat layer 200 is not limited to this, and a coating method may be used. The coating method may be appropriately selected from methods used in film production. Examples of coating methods include gravure coating, reverse coating, gravure reverse coating, die coating, flow coating, and the like.

[Example]
Each embodiment of the present invention will be further described using examples. FIG. 16 is a schematic diagram showing a part of the cross section of the electromagnetic wave attenuating film shown in Examples 1 to 5. l and l1 are the distances between the centers of gravity of the mesh-like conductive elements on the front and back sides of the dielectric substrate, and a, a1, and a2 (see Figure 2(b)) are the shortest distances from the center of gravity of the mesh-like conductive elements to the ends of the mesh. For example, it is assumed that the mesh-like conductive elements 30 may have different dimensions a and a1, and furthermore, the mesh-like conductive elements 31 may also have different dimensions a2. t is the thickness of the dielectric base material, ts is the thickness of the support layer, tm is the thickness of the mesh conductive element, tmb is the thickness of the mesh flat inductor, and h is the thickness of the top coat layer. In this example, since the mesh conductive elements have the same shape (square shape) and the same dimensions, a, a1, and a2 are equal. wa represents the opening width of the mesh thin film conductive layer and the mesh flat plate inductor, and w represents the line width of the mesh thin film conductive layer and the mesh flat plate inductor.
When the conductive elements of the same shape are uniformly arranged as in the first embodiment shown in FIG. 1, l is equal to l1. On the other hand, when there are conductive elements having different distances from each other as in the second embodiment shown in FIG. 10, l and l1 take different values. Table 1 shows the structures of the electromagnetic wave attenuating films of Examples 1 to 5. Examples 1 to 4 correspond to examples of the first embodiment, and Example 5 corresponds to an example of the second embodiment.

<Manufacturing method>
A common manufacturing method for manufacturing the electromagnetic wave attenuating films according to Examples 1 to 3 will be explained. A 500 nm thick copper layer was formed on both sides of a 50 μm thick PET sheet by sputtering. Then, after cleaning the copper layer, a dry resist film was laminated onto the copper layer on both sides of the PET sheet. After that, both sides are exposed simultaneously through a mesh photomask having a mesh pattern, and then both sides of the acrylic negative resist layer are simultaneously developed with a mixed alkaline aqueous solution of sodium carbonate and sodium bicarbonate to remove unnecessary resist. A portion of the underlying thin film conductive layer was exposed.

Next, both sides of the copper layer partially covered by the resist layer were simultaneously immersed in a ferric chloride solution, and the exposed portions of the copper layer were removed by etching. Thereafter, the remaining resist layer was simultaneously removed from both sides using an alkaline solution to obtain a mesh copper pattern. Next, a blackening treatment was applied to the surface and side surfaces of the copper pattern.

Next, a mesh-like copper pattern was formed on one side of a PET film with a thickness of 100 μm in the same manner as described above to produce a mesh-like flat plate inductor, and then adhesive was applied to the back side of the film having mesh-like copper patterns on both sides. Laminated through layers. The above is the manufacturing procedure of Examples 1 to 3 according to the first embodiment.

A manufacturing method for producing an electromagnetic wave attenuation film according to Example 4 will be explained. A thin film conductive layer was formed on the front and back sides of the dielectric substrate using the same manufacturing procedure as in Examples 1 to 3, and a support layer in which a mesh-like flat plate inductor was formed was formed on the back side of the thin film conductive layer via an adhesive layer. After that, a top coat layer was formed on the front side of the dielectric base material. The top coat layer was formed by the procedure shown below.
The main component is an acrylic resin composition consisting of a mixture of 80 parts by mass of methyl methacrylate monomer and 20 parts by mass of cyclohexyl methacrylate, and the solid content of the acrylic resin composition is 100 parts by mass, and the structure shown in the chemical formula A above is obtained. 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber ("ADK STAB LA-46" manufactured by ADEKA Co., Ltd.) having 6 parts by mass of a benzotriazole-based ultraviolet absorber ("Tinuvin 329" manufactured by Ciba Specialty Chemicals Co., Ltd.) (produced by Specialty Chemicals Co., Ltd.), 3 parts by mass of a hindered amine radical scavenger (Ciba Specialty Chemicals Co., Ltd.) 5 parts by mass of Tinuvin 292 (manufactured by Chemicals Co., Ltd.) was added, and an ethyl acetate solvent was added to adjust the solid content to create a base solution with a solid content of 33 parts by mass, and an ethyl acetate solvent was added to adjust the solid content. A solid content of 75 parts by mass of a hexamethylene diisocyanate type curing agent solution is used, and the ratio of the base solution to the hardener solution is 10:1 (at this time, the ratio of the number of hydroxyl groups in the base solution to the number of isocyanate groups in the hardener solution is 1: 2), and further added ethyl acetate as a solvent component to adjust the solid content to 20 parts by mass, and then applied the coating solution to a thickness of 6 μm after the solvent evaporated. A coat layer was obtained. The above is the manufacturing procedure of Example 4 according to the first embodiment.

A manufacturing method for producing an electromagnetic wave attenuating film according to Example 5 will be explained. Using the same manufacturing procedure as in Examples 1 to 3, the positions of the thin film conductive layers to be formed on the front and back surfaces of the dielectric base material were changed to a combination (l<2a) in which the front and back thin film conductive layers overlap in the plane direction. A thin conductive layer was formed by mixing 50% non-overlapping combinations (l≧2a) in one plane. Next, a support layer was formed on the back side of the thin film conductive layer via an adhesive layer, and then a flat plate inductor was formed on the back side of the support. The above is the manufacturing procedure of Example 5 according to the second embodiment.

<Common evaluation items>
The electromagnetic wave attenuating films according to Examples 1 to 5 manufactured by the above-described manufacturing method were evaluated for bending tests, electromagnetic wave attenuation characteristics, weather resistance, and transmittance.
(bending test)
A bending test was conducted on the electromagnetic wave attenuating films of Examples 1 to 5. Using the electromagnetic wave attenuation film produced in each example, a bending test was performed by sandwiching the sample between a set of two bending R jigs (mandrels), and the position of the conductive element on the test piece was observed with a microscope after the test. The presence or absence of misalignment of the conductive layer was confirmed. The evaluation results are shown in Table 1.

(Electromagnetic wave attenuation characteristics)
The electromagnetic wave absorption characteristics were simulated using the configuration after the bending test. The evaluation results are shown in Table 1. 17 to 21 show graphs of monostatic RCS attenuation for each frequency.
FIG. 17 is a graph showing the electromagnetic wave attenuation characteristics of Example 1. It showed good absorption characteristics of -13 dB at 76 GHz.
FIG. 18 is a graph showing the electromagnetic wave attenuation characteristics of Example 2. It showed good absorption characteristics of -10 dB at 76 GHz.
FIG. 19 is a graph showing the electromagnetic wave attenuation characteristics of Example 3. It showed good absorption characteristics of -12 dB at 73 GHz.
FIG. 20 is a graph showing the electromagnetic wave attenuation characteristics of Example 4. It showed good absorption characteristics of -10 dB at 70 GHz.
FIG. 21 is a graph showing the electromagnetic wave attenuation characteristics of Example 5. It showed good absorption characteristics of -11 dB at 79 GHz and -15 dB at 89 GHz.

(Weatherability)
Furthermore, the produced electromagnetic wave attenuation film was pressure-bonded to a stainless steel plate via an adhesive layer, and after being exposed to the equivalent of 10 years of outdoor exposure using a sunshine weather meter, the surface of the electromagnetic wave attenuation film was wiped with a cotton cloth to form a top coat layer. , or the remaining state of the electromagnetic wave attenuating layer including the electromagnetic wave attenuating substrate, support layer, and flat inductor. The evaluation results are shown in Table 1. If there was no effect on any layer after wiping, it was rated as ○, and if peeling occurred within a range that did not cause any practical problems, it was rated as △.

(transmittance)
Regarding the transmittance, it was calculated as the ratio of the incident intensity and the transmitted intensity when white light was incident on the electromagnetic wave attenuating film, and a film with a transmittance of at least 10% was considered to have passed.

(comprehensive evaluation)
As a result of producing and evaluating the electromagnetic wave attenuating films of Examples 1 to 5, it was found that in the electromagnetic wave attenuating films having thin conductive layers simultaneously formed on the front and back surfaces of the dielectric substrate, misalignment of the thin conductive layer occurred even after the bending test. It was possible to maintain the structure before the test.
Furthermore, the frequency to be absorbed was as designed, and the amount of absorption was -10 dB. As a result of the weather resistance test, it was confirmed that there was no deterioration in either the top coat layer or the electromagnetic wave attenuation layer, and that the formation of the top coat layer in particular improved the weather resistance and provided particularly good characteristics for practical use. Furthermore, the transmittance exceeded the acceptance criteria.

(Test example 1)
A laminated sheet in which a design imparting layer having a wood grain pattern is laminated on the electromagnetic wave attenuation film according to Example 3 on the durability imparting layer is separately prepared, and a laminated sheet is laminated between the electromagnetic wave attenuation film according to Example 3 and the mesh-like thin film conductor layer 30. The top coat layer 200 according to the present invention was obtained by bonding with an adhesive while preventing air bubbles from entering, and the electromagnetic wave attenuation film of Test Example 1 was obtained.
As a result, electromagnetic wave attenuation characteristics comparable to those of Example 3 were obtained. Furthermore, when the electromagnetic wave attenuating film of Test Example 1 was pasted next to a decorative sheet with a wood grain pattern in the room, the electromagnetic wave attenuating film of Test Example 1 did not feel out of place with the decorative sheet with a wood grain pattern, and the entire room was harmonious with the wood grain pattern. It became something that was taken.

(Test example 2)
A laminated sheet in which a design imparting layer having a wood grain pattern is laminated on the electromagnetic wave attenuation film according to Example 5 is separately prepared, and a laminated sheet is laminated between the electromagnetic wave attenuation film according to Example 5 and the mesh-like thin film conductor layer 30. The top coat layer 200 according to the present invention was obtained by bonding with an adhesive while preventing air bubbles from entering, and the electromagnetic wave attenuation film of Test Example 2 was obtained.
As a result, electromagnetic wave attenuation characteristics comparable to those of Example 5 were obtained. Furthermore, when the electromagnetic wave attenuating film of Test Example 2 was pasted next to a decorative sheet with a wood grain pattern in the room, the electromagnetic wave attenuating film of Test Example 2 did not feel out of place with the decorative sheet with a wood grain pattern, and the entire room was harmonious with the wood grain pattern. It became something that was taken.

(Test example 3)
A laminated sheet in which a design imparting layer having a marble pattern on the durability imparting layer is laminated on the electromagnetic wave attenuation film according to Example 3 is separately prepared, and a laminated sheet is laminated between the electromagnetic wave attenuation film according to Example 3 and the mesh-like thin film conductor layer 30. The top coat layer 200 according to the present invention was obtained by bonding with an adhesive while avoiding air bubbles, and the electromagnetic wave attenuation film of Test Example 3 was obtained.
As a result, electromagnetic wave attenuation characteristics comparable to those of Example 3 were obtained. Furthermore, when the electromagnetic wave attenuating film of Test Example 3 was installed next to indoor marble-patterned flooring, the electromagnetic wave-attenuating film of Test Example 3 did not look out of place with the marble-patterned flooring. The sense of luxury was not compromised.

(Test example 4)
A laminated sheet in which a design imparting layer having a marble pattern on the durability imparting layer is laminated on the electromagnetic wave attenuation film according to Example 5 is separately prepared, and a laminated sheet is laminated between the electromagnetic wave attenuation film according to Example 5 and the mesh-like thin film conductor layer 30. The top coat layer 200 according to the present invention was obtained by bonding with an adhesive while preventing air bubbles from entering, and the electromagnetic wave attenuation film of Test Example 4 was obtained.
As a result, the same electromagnetic wave attenuation characteristics as in Example 5 were obtained. Furthermore, when the electromagnetic wave attenuation film of Test Example 4 was installed next to indoor marble-patterned flooring, the electromagnetic wave attenuation film of Test Example 4 did not look out of place with the marble-patterned flooring. The sense of luxury was not compromised.

[Comparative example]
Table 2 shows the structure and evaluation results of the electromagnetic wave attenuation film according to the comparative example. Furthermore, graphs of monostatic RCS attenuation for each frequency are shown in FIGS. 23 to 29.

(Comparative example 1)
The electromagnetic wave attenuation film according to Comparative Example 1 has the structure of a bonded laminate, whereas the structure of the example has a structure in which thin film conductive layers are formed on both the front and back surfaces of the dielectric base material (electromagnetic wave attenuation base material). different from. FIG. 22 is a schematic diagram showing a part of the cross section of the electromagnetic wave attenuation film of Comparative Example 1. Description of the configuration similar to that in FIG. 16 will be omitted. It has a structure in which a laminated upper layer 40 and a laminated lower layer 41 in which a mesh-like thin film conductive layer 30 is formed only on the front surface of a dielectric base material 10 are laminated. Table 2 shows the structure of the electromagnetic wave attenuation film of Comparative Example 1.

<Manufacturing method>
According to Example 1, two sheets of a laminated upper layer 40 and a laminated lower layer 41 were prepared in which the mesh-like thin film conductive layer 30 was disposed only on the front side of the dielectric base material 10. A lower lamination layer 41 was laminated on the back side of the lamination upper layer 40 with an acrylic adhesive layer 12 interposed therebetween. Next, a mesh-like thin copper film is formed on one side of the PET film with a film thickness of 100 μm by etching, and laminated through the adhesive layer 12 to form the support layer 11 and the mesh-like flat plate inductor 50, thereby creating an electromagnetic wave attenuation film by multilayer lamination. It was created.

<Evaluation method/results>
According to Example 1, the bending test, electromagnetic wave attenuation characteristics, weather resistance, and transmittance of the electromagnetic wave attenuation film were evaluated. The evaluation results are shown in Table 2.
After performing a bending test on the electromagnetic wave attenuating film formed by laminating multiple layers in Comparative Example 1, the position of the conductive element on the test piece was observed. As a result, a shift occurred between the film of the laminated upper layer 40 and the film of the laminated lower layer 41, and the upper layer The result was that the placement position of the lower layer mesh-like conductive element 30 was shifted by about 5 mm from before the test.
FIG. 23 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 1. While the target absorption frequency is around 75 GHz in the design value, the absorption peak frequency of the electromagnetic wave absorbing sheet produced by laminating and laminating was 57 GHz, which was a large deviation from the design value.
Regarding weather resistance, when wiped with a cotton cloth, the thin metal layer peeled off, resulting in not so good results.

(Comparative example 2)
In the electromagnetic wave attenuation film according to Comparative Example 2, conductive elements were arranged on the front and back sides of the dielectric 10 to form a support layer, and then a flat plate inductor was formed on the back side of the support layer. In Comparative Example 2, the conductive element and the flat plate inductor are not mesh-shaped.

<Manufacturing method>
A thin film conductive layer was formed on the front and back sides of the dielectric base material, a support layer was formed on the back side of the thin film conductive layer via an adhesive layer, and then a flat plate inductor was formed on the back side of the support layer.

<Evaluation method/results>
According to Example 1, the bending test, electromagnetic wave attenuation characteristics, weather resistance, and transmittance of the electromagnetic wave attenuation film were evaluated. The evaluation results are shown in Table 2.
Regarding the bending test, no displacement of the thin film conductive layer occurred even after the bending test.
FIG. 24 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 2. An absorption amount of -13 dB was obtained at 74 GHz. The transmittance was 0%, and no light transmittance or transparency was obtained.

(Comparative Examples 3, 4, 5)
Comparative Examples 3, 4, and 5 have the same structure as the electromagnetic wave absorbing film according to Example 1, etc., except for some differences in the dimensions of the constituent elements of the electromagnetic wave absorbing film, so the explanation will focus on the differences.
Comparative Example 3 is based on the following equation (1), where l is the distance in the plane direction between the centers of gravity of the conductive elements on the front and back sides of the dielectric base material, and a is the shortest distance from the center of gravity of the conductive elements to the edge of the mesh. It has a structure in which conductive elements are formed with a positional relationship that is not satisfied.
l≦3.6a…(1)
Comparative Example 4 has a structure in which the thickness of the support layer is less than 5 μm.
Comparative Example 5 has a structure in which the opening width (wa) of the mesh of the conductive elements on the front and rear sides of the dielectric base material and the flat plate inductor arranged on the back side of the support layer is larger than 1/10 of the attenuation center wavelength.
Table 2 shows the structures of the electromagnetic wave attenuating films of Comparative Examples 3, 4, and 5.

<Manufacturing method>
A mesh-like thin film conductive layer was formed on the front and back sides of a dielectric base material according to Example 1, and a mesh-like thin copper film was formed on one side of a PET film with a film thickness of 100 μm by etching, and then laminated with an adhesive layer interposed therebetween. A support layer and a mesh-like flat plate inductor were formed.

<Evaluation method/results>
According to Example 1, the bending test, electromagnetic wave attenuation characteristics, weather resistance, and transmittance of the electromagnetic wave attenuation film were evaluated. The evaluation results are shown in Table 2.
Regarding the bending test, in Comparative Examples 3, 4, and 5, no displacement of the thin film conductive layer occurred even after the bending test.
FIG. 25 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 3. Since 1/a was 4.4, which did not satisfy the relationship of equation (1), resonance coupling did not occur between the front and back conductive elements, resulting in an absorption amount that did not reach the target -10 dB.
FIG. 26 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 4. As in Comparative Example 4, when the thickness of the support layer formed on the back side of the conductive element on the back side of the dielectric substrate was 4 μm, which was thinner than 5 μm, the absorption amount did not reach the target -10 dB. . For this reason, the thickness of the support layer is preferably 5 μm (0.005 mm) or more.
Regarding weather resistance, the thin metal layer peeled off when wiped with a cotton cloth, resulting in not-so-good results.
FIG. 27 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 5. As in Comparative Example 5, the opening width of the mesh of the mesh thin film conductive layer formed on the front and back surfaces of the dielectric substrate and the mesh flat plate inductor arranged on the back of the support layer is larger than 1/10 of the attenuation center wavelength. In some cases, the absorption amount did not reach the target of -10 dB. From this, it is desirable that the opening width of the mesh is 1/10 or less of the attenuation center wavelength.

Although each embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and modifications and combinations of the configuration may be made without departing from the gist of the present invention. included. Some changes are illustrated below, but these are not all, and other changes are also possible. Two or more of these changes may be combined as appropriate.

In the first embodiment, the aspects used in the second embodiment, such as the frequency band, the metal type of the conductive element, the blackening layer, and the manufacturing method, can be used as appropriate. The same is true vice versa.

In the present invention, the form of the flat plate inductor is not limited to that formed on the entire back surface.
For example, a plurality of conductive elements may be arranged in the same manner as on the front surface.

In the present invention, the shape of the conductive element is not limited to a square, and can be set to various shapes such as a circle (including an ellipse), a polygon other than a square, various polygons with rounded corners, and an irregular shape.
It is preferable that the total area of the conductive elements occupying the projected area of the front surface is 20% or more.
In this way, electromagnetic waves can be efficiently attenuated.

In the electromagnetic wave attenuation film according to the present invention, there may be a configuration in which the back surface is not provided with a flat plate inductor. For example, if the object to which the back surfaces are to be joined is metal, the second and third mechanisms can be exerted without any problem by the metal surfaces to be joined without a flat plate inductor. In such a case, a bonding layer such as an adhesive layer that can be bonded to the object may be provided on the back surface.

In the electromagnetic wave attenuation film according to the present invention, parameters such as the structural period and the dimensions of the conductive elements do not necessarily have to be completely the same in all parts. For example, in the present invention, even if the above-mentioned parameters vary within the tolerance range (approximately 5% above and below) during the manufacturing process, this is included in "same shape and same size" in the present invention. Further, the "predetermined range of values" can be a regular range of values. This regularity can be a Gaussian distribution, a binomial distribution, a random distribution or pseudo-random distribution with equal frequency within a certain section, or a range of tolerance in the manufacturing process.

In the electromagnetic wave attenuating film according to the present invention, after providing a release layer on the supporting base material, the electromagnetic wave attenuating film of the first embodiment and the second embodiment is provided, and an adhesive/pressure-sensitive adhesive is further provided, and the transfer foil is You can also use it as
By using transfer foil, it is possible to make the film even thinner, and it is also possible to further improve followability, and it is possible to transfer even complex shapes, which increases the scope of application of the electromagnetic wave attenuation film of the present invention. It becomes possible to widen the area.

In the above embodiment, the attenuation of electromagnetic waves is considered, but it is known that a conductor that attenuates specific electromagnetic waves serves as an antenna for receiving radio waves. Therefore, the embodiments described above can also be used as receiving antennas. Furthermore, in the above-described embodiment, since a quantum with zero momentum is captured in a two-dimensional system, it is considered possible to use the conductive element as an element for calculating and recording data in its quantum state.

As mentioned above, the embodiments of the present invention differ from the prior art in the mechanism of interaction with electromagnetic waves, and therefore products that exhibit an equivalent mechanism are those that substantially use the embodiments of the present invention. should be captured.

Possible embodiments of the present invention are described below, but are not limited thereto.
(Aspect 1)
a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back surface of the electromagnetic wave attenuating base; a mesh-like flat plate inductor formed of thin wires of a conductive thin film disposed on the back surface of the support layer;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements.
Electromagnetic wave attenuation film.
(Aspect 2)
a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back surface of the electric and electromagnetic wave attenuating base; a mesh-like flat plate inductor formed of thin wires of a conductive thin film disposed on the back surface of the support layer;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
the conductive elements are arranged periodically;
The following formula (1) is satisfied when the distance in the plane direction of the center of gravity of the conductive elements on the front and back sides of the dielectric substrate is l, and the shortest distance from the center of gravity of the conductive element to the end of the mesh is a,
Electromagnetic wave attenuation film.
l≦3.6a…(1)
(Aspect 3)
a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back surface of the electromagnetic wave attenuating base; a mesh-like flat plate inductor formed of thin wires of a conductive thin film disposed on the back surface of the support layer;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
The mesh-like conductive elements are arranged periodically,
The thickness of the support layer is 0.005 mm or more,
Electromagnetic wave attenuation film.
(Aspect 4)
a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back surface of the electromagnetic wave attenuating base; a mesh-like flat plate inductor formed of thin wires of a conductive thin film disposed on the back surface of the support layer;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
The mesh-like conductive elements are arranged periodically, and when the thickness of the mesh-like conductive elements is T and the skin depth is d, the following formula (4) is satisfied.
Electromagnetic wave attenuation film.
-2 ≦ ln(T/d) ≦ 1...(4)
(Aspect 5)
a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back surface of the electric and electromagnetic wave attenuating base; a mesh-like flat plate inductor formed of thin wires of a conductive thin film disposed on the back surface of the support layer;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
The mesh-like conductive elements are arranged periodically,
When the distance in the plane direction of the center of gravity of the mesh-like conductive elements on the front and back sides of the dielectric substrate is l, and the shortest distance from the center of gravity of the mesh-like conductive element to the end of the mesh is a, the following formula (6) is expressed. Electromagnetic wave attenuation can be achieved at multiple frequencies by mixing the combination of the mesh-shaped conductive elements on the front and rear sides of the dielectric base that satisfies the following equation (7) and the combination of the mesh-shaped conductive elements on the front and rear sides of the dielectric base that satisfies the following formula (7). with performance,
Electromagnetic wave attenuation film.
l<2a...(6)
l≧2a…(7)
(Aspect 6)
The electromagnetic wave attenuating film according to any one of aspects 1 to 5, wherein the mesh-like thin film conductive layer and the mesh-like flat plate inductor are spaced apart in the thickness direction of the dielectric base material or the support layer.
(Aspect 7)
7. The electromagnetic wave attenuation film according to any one of aspects 1 to 6, characterized in that blackening layers are provided on the front and back surfaces of the mesh-like thin film conductive layer disposed on the front surface of the dielectric substrate.
(Aspect 8)
8. The electromagnetic wave attenuation film according to any one of aspects 1 to 7, characterized in that blackening layers are provided on the front and back surfaces of the mesh-like thin film conductive layer disposed on the back surface of the dielectric substrate.
(Aspect 9)
The electromagnetic wave attenuating film according to any one of aspects 1 to 8, further comprising a top coat layer on the front side of the electromagnetic wave attenuating substrate.
(Aspect 10)
The electromagnetic wave attenuation film according to aspect 9, wherein the top coat layer has impedance matching with an air layer through which electromagnetic waves propagate.
(Aspect 11)
11. The electromagnetic wave attenuating film according to any one of aspects 9 or 10, wherein the top coat layer is mainly composed of an acrylic resin composition containing cyclohexyl (meth)acrylate as a monomer component.
(Aspect 12)
The electromagnetic wave attenuating film according to any one of aspects 9 to 11, wherein the top coat layer contains an ultraviolet absorber and an ultraviolet scattering agent in an acrylic resin composition.
(Aspect 13)
The electromagnetic wave attenuating film according to any one of aspects 1 to 12, wherein the mesh-like thin film conductive layer is made of silver, copper, or aluminum.
(Aspect 14)
14. The electromagnetic wave attenuation film according to any one of aspects 1 to 13, wherein the mesh-like thin film conductive layer is configured to be able to capture electromagnetic waves incident from the front side of the dielectric base material.
(Aspect 15)
15. The electromagnetic wave attenuating film according to any one of aspects 1 to 14, wherein the mesh-like conductive element is a planar element and has a pair of opposing sides.
(Aspect 16)
The electromagnetic wave attenuating film according to aspect 15, wherein the length of a pair of opposing sides of the planar element is 0.25 mm or more and 4 mm or less.
(Aspect 17)
The mesh-like thin film conductive layer and the mesh-like flat plate inductor have a thin line width of 30 to 500 μm, and a mesh opening width of 1/10 to 1/225 of the attenuation center wavelength. Electromagnetic wave attenuation film described in .
(Aspect 18)
18. The electromagnetic wave attenuation film according to any one of aspects 1 to 17, wherein the dielectric base material has a thickness that is sufficiently thin with respect to an attenuation center wavelength.
(Aspect 19)
The electromagnetic wave attenuation film according to aspect 18, wherein the thickness of the dielectric base material is less than 1/10 of the attenuation center wavelength.

1, 61 Electromagnetic wave attenuation film 10, 62 Dielectric substrate 10a, 62a Front side 10b, 62b Back side 20, 60 Electromagnetic wave attenuation base 30, 30A, 31, 31A Mesh-like thin film conductive layer, mesh-like conductive element 32, 33, 34, 35, 36, 37 Blackening layer 11 Support layer 12, 13 Adhesive layer 40 Lamination upper layer 41 Lamination lower layer 50 Mesh-like flat plate inductor 200 Top coat layer

In order to solve the above problems, one of the typical electromagnetic wave attenuating films of the present invention includes a dielectric base material having a front surface and a back surface, and a conductive thin film disposed on both the front surface and the back surface of the dielectric base material. an electromagnetic wave attenuating substrate having a mesh-like thin film conductive layer having a mesh-like pattern formed of thin wires with protruding ends of the thin wires; a support layer disposed on the back surface of the electromagnetic wave attenuating substrate; and a back surface of the support layer. a mesh-like flat plate inductor formed of thin wires of a conductive thin film, the mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements, and the mesh-like conductive elements are arranged periodically. , the distance in the plane direction of the center of gravity of the adjacent mesh-like conductive elements on the front and back sides of the dielectric substrate is l, and the shortest distance from the center of gravity of the mesh-like conductive element to the end of the mesh is a, the following formula ( It is an electromagnetic wave attenuation film that satisfies 1) .
l≦3.6a…(1)

Claims (19)

a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back side of the electromagnetic wave attenuating base;
a mesh-like flat plate inductor arranged on the back side of the support layer and formed of thin wires of a conductive thin film;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements.
Electromagnetic wave attenuation film. a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer placed on the back side of the electrical and electromagnetic wave attenuating base;
a mesh-like flat plate inductor arranged on the back side of the support layer and formed of thin wires of a conductive thin film;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
The mesh-like conductive elements are arranged periodically,
When the distance in the plane direction of the center of gravity of the mesh-like conductive elements on the front and back sides of the dielectric substrate is l, and the shortest distance from the center of gravity of the mesh-like conductive element to the end of the mesh is a, the following formula (1) can be calculated. Fulfill,
Electromagnetic wave attenuation film.
l≦3.6a…(1) a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back side of the electromagnetic wave attenuating base;
a mesh-like flat plate inductor arranged on the back side of the support layer and formed of thin wires of a conductive thin film;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
The mesh-like conductive elements are arranged periodically,
The thickness of the support layer is 0.005 mm or more,
Electromagnetic wave attenuation film. a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer disposed on the back side of the electromagnetic wave attenuating base;
a mesh-like flat plate inductor formed of thin wires of a conductive thin film and arranged on the back side of the support layer;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
The mesh-like conductive elements are arranged periodically,
When the thickness of the mesh-like conductive element is T and the skin depth is d, the following formula (4) is satisfied,
Electromagnetic wave attenuation film.
-2 ≦ ln(T/d) ≦ 1...(4) a dielectric base material having a front surface and a back surface; and a mesh-like thin film conductive layer arranged on both the front surface and the back surface of the dielectric base material and having a mesh pattern formed of thin wires of a conductive thin film with ends of the thin wires protruding. an electromagnetic wave attenuating base having;
a support layer placed on the back side of the electrical and electromagnetic wave attenuating base;
a mesh-like flat plate inductor arranged on the back side of the support layer and formed of thin wires of a conductive thin film;
Equipped with
The mesh-like thin film conductive layer includes a plurality of mesh-like conductive elements,
The mesh-like conductive elements are arranged periodically,
When the distance in the plane direction of the center of gravity of the mesh-like conductive elements on the front and back sides of the dielectric substrate is l, and the shortest distance from the center of gravity of the mesh-like conductive element to the end of the mesh is a, the following formula (6) is expressed. Electromagnetic wave attenuation can be achieved at multiple frequencies by mixing the combination of the mesh-shaped conductive elements on the front and rear sides of the dielectric base that satisfies the following equation (7) and the combination of the mesh-shaped conductive elements on the front and rear sides of the dielectric base that satisfies the following formula (7). with performance,
Electromagnetic wave attenuation film.
l<2a...(6)
l≧2a…(7) The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the mesh-like thin film conductive layer and the mesh-like flat plate inductor are spaced apart in the thickness direction of the dielectric base material or the support layer. The electromagnetic wave attenuating film according to any one of claims 1 to 5, further comprising blackening layers on the front and back surfaces of the mesh-like thin film conductive layer disposed on the front surface of the dielectric substrate. The electromagnetic wave attenuation film according to any one of claims 1 to 5, characterized in that blackening layers are provided on the front and back surfaces of the mesh-like thin film conductive layer disposed on the back surface of the dielectric substrate. The electromagnetic wave attenuating film according to any one of claims 1 to 5, further comprising a top coat layer on the front side of the electromagnetic wave attenuating substrate. The electromagnetic wave attenuation film according to claim 9, wherein the top coat layer has impedance matching with an air layer through which electromagnetic waves propagate. 10. The electromagnetic wave attenuation film according to claim 9, wherein the top coat layer is mainly composed of an acrylic resin composition containing cyclohexyl (meth)acrylate as a monomer component. The electromagnetic wave attenuating film according to claim 9, wherein the top coat layer contains an ultraviolet absorber and an ultraviolet scattering agent in an acrylic resin composition. The electromagnetic wave attenuating film according to any one of claims 1 to 5, wherein the mesh-like thin film conductive layer is made of silver, copper, or aluminum. The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the mesh-like thin film conductive layer is configured to be able to capture electromagnetic waves incident from the front side of the dielectric base material. The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the mesh-like conductive element is a planar element and has a pair of opposing sides. The electromagnetic wave attenuation film according to claim 15, wherein the length of a pair of opposing sides of the planar element is 0.25 mm or more and 4 mm or less. The mesh-like thin film conductive layer and the mesh-like flat plate inductor have a thin line width of 30 to 500 μm and a mesh opening width of 1/10 to 1/225 of the attenuation center wavelength, any one of claims 1 to 5. Electromagnetic wave attenuation film described in . The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the dielectric base material has a thickness that is sufficiently thin with respect to an attenuation center wavelength. The electromagnetic wave attenuation film according to claim 18, wherein the thickness of the dielectric base material is less than 1/10 of the attenuation center wavelength.

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