Electromagnetic wave reflection film

Abstract

The present invention provides a transparent and flexible electromagnetic wave reflection film.　This electromagnetic wave reflection film is provided with: a conductive layer that reflects electromagnetic waves in a specific frequency band of 1 GHz to 300 GHz inclusive; a first base material layer that supports the conductive layer; a second base material layer that is disposed on the reverse side of the conductive layer from the first base material layer; and an adhesive layer that bonds the second base material layer to the conductive layer. The thickness (t3) of the first base material layer is 1.0 mm or less, and the ratio (t3 / t1) of the thickness of the first base material layer to the thickness (t1) of the conductive layer is 0.25 to 1.0 × 105 inclusive.

Description

Electromagnetic wave reflective film

[0001] The present invention relates to an electromagnetic wave reflective film.

[0002] Base stations are being deployed in indoor and outdoor spaces to realize a variety of use cases, including automation of manufacturing processes and office work, remote operation, the introduction of AI (artificial intelligence) control and management, and autonomous driving. Indoor and outdoor spaces include factories, plants, office buildings, commercial facilities, medical facilities, event venues, highways, and railway tracks. The fifth-generation mobile communication system (hereinafter referred to as "5G") offers a frequency band below 6 GHz, known as "sub-6," and the 28 GHz band, classified as the millimeter wave band. The next-generation 6G mobile communication standard is expected to expand into the terahertz band. Using these high-frequency bands will expand communication bandwidth, enabling large-volume data transmission with low latency.

[0003] 5G radio waves have a strong tendency to travel in a straight line and are difficult to diffract. On roads, radio waves are blocked by vehicles and structures on the road, and in factories, by machines and product racks on production lines, creating dead zones in various locations. By installing electromagnetic wave reflecting panels in appropriate locations, dead zones can be eliminated. A configuration has been proposed in which electromagnetic wave reflecting devices are placed along at least a portion of a production line (see, for example, Patent Document 1).

[0004] International Publication No. 2021 / 199504

[0005] Metal reflectors made of metal plates such as aluminum and copper are well-known as electromagnetic wave reflective panels. Metal reflectors are generally opaque. When installed on roads, factories, office buildings, etc., they can obstruct visibility. Furthermore, installing metal reflectors on office building windows can not only obstruct natural light but also spoil the building's atmosphere and scenery. Therefore, the use of transparent electromagnetic wave reflective panels using resin or glass substrates has been considered. However, it is difficult to attach rigid transparent electromagnetic wave reflective panels with a certain thickness tightly and without gaps to existing structures. When rigid electromagnetic wave reflective panels are attached to structures with adhesive, air bubbles or air gaps are likely to be trapped between the electromagnetic wave reflective panel and the structure, making them difficult to apply to curved surfaces. An object of the present invention is to provide a transparent and flexible electromagnetic wave reflective film.

[0006] In one embodiment, an electromagnetic wave reflecting film includes: a conductive layer that reflects electromagnetic waves in a predetermined frequency band of 1 GHz or more and 300 GHz or less; a first base layer that supports the conductive layer; a second base layer that is disposed on the conductive layer on the opposite side to the first base layer; and an adhesive layer that adheres the second base layer to the conductive layer, wherein the thickness of the first base layer is 1.0 mm or less, and the ratio of the thickness of the first base layer to the thickness of the conductive layer is 0.25 or more and 1.0 x 10 ６ The following is the result.

[0007] A transparent and flexible electromagnetic wave reflective film is realized.

[0008] Fig. 4 is a schematic diagram showing an application example of an electromagnetic wave reflecting film of an embodiment. Fig. 5 is a schematic diagram showing another application example of an electromagnetic wave reflecting film of an embodiment. Fig. 6 is a schematic diagram showing the layer structure of an electromagnetic wave reflecting film of a first embodiment. Fig. 7 is a schematic diagram showing an application example of the electromagnetic wave reflecting film of Fig. 2 to window glass. Fig. 8 is a schematic diagram showing the layer structure of an electromagnetic wave reflecting film of a second embodiment. Fig. 9 is a schematic diagram showing an application example of the electromagnetic wave reflecting film of Fig. 4 to window glass.

[0009] In an embodiment, a conductive layer that reflects electromagnetic waves in a predetermined frequency band is supported by a transparent, flexible substrate layer, and the surface of the conductive layer is protected by a protective layer via an adhesive layer. By setting the ratio of the thickness t2 of the adhesive layer to the thickness t1 of the conductive layer (t2 / t1) or the ratio of the thickness t3 of the substrate layer to the thickness t1 of the conductive layer (t3 / t1) within an appropriate range, an electromagnetic wave reflective film with a certain degree of reflection characteristics and transparency can be realized.

[0010] The following describes an electromagnetic wave reflecting film according to an embodiment with reference to the drawings. The embodiments described below are examples for embodying the technical concept of the invention, and do not limit the present invention to the following steps or numerical values. In the drawings, components having the same function may be assigned the same reference numerals to avoid redundant description. Partial substitution or combination between different embodiments or configuration examples is possible. The size, positional relationship, etc. of each component shown in each drawing may be exaggerated to facilitate understanding of the invention. When referring to a positional relationship, "above" or "below" refers to above or below the stacking direction or film formation direction, unless otherwise specified, and is not an absolute direction.

[0011] FIG. 1A is a schematic diagram showing an application example of an electromagnetic wave reflective film 10 according to an embodiment. The electromagnetic wave reflective film 10 is applied to the window glass 3 of a window 1 in, for example, a shopping mall or an office building. The electromagnetic wave reflective film 10 may be attached to the entire window glass 3 supported by a window frame 6, or may be attached to a portion of the window glass 3 depending on the incident direction of the electromagnetic waves, the desired reflection direction, and the like. As will be described later, the total light transmittance of the electromagnetic wave reflective film 10 is 70% or more, preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. The absolute value of the return loss of the electromagnetic wave reflective film 10 measured according to JIS R1679 is 1.00 dB or less, preferably 0.50 dB or less. The electromagnetic wave reflective film 10 can efficiently reflect electromagnetic waves in a predetermined frequency band ranging from 1 GHz to 300 GHz without interfering with visibility or scenery. The electromagnetic wave reflecting film 10 can be applied not only to windows in shopping malls and office buildings, but also to safety fences in production lines, soundproof walls on roads, and the like.

[0012] FIG. 1B is a schematic diagram showing another application example of the electromagnetic wave reflective film 10. The electromagnetic wave reflective film 10 can be applied to a structure 2, such as a wall or pillar in a shopping mall or underground shopping mall. Because the entire electromagnetic wave reflective film 10 is flexible, it can be installed along the surface of the structure 2, even if the structure 2 includes a curved surface. The electromagnetic wave reflective film 10 can be applied to any position on the structure 2, depending on the incident direction of the electromagnetic wave and the desired reflection direction. Furthermore, as described above, since the total light reflectivity is 70% or higher, information such as text, still images, and moving images drawn or displayed on the surface of the structure 2 can be presented to the outside. Even when the base station is not within the line of sight (LOS) of the receiving antenna, the electromagnetic wave reflective film 10 can expand the reception area of ​​radio waves in a specified frequency band emitted from the base station.

[0013] 2 is a schematic diagram of the layer structure of an electromagnetic wave reflecting film 10 of a first embodiment. The electromagnetic wave reflecting film 10 has a first base material layer 11, a conductive layer 13 supported on the first base material layer 11, a second base material layer 14 disposed on the side of the conductive layer 13 opposite the first base material layer 11, and an adhesive layer 12 that adheres the second base material layer 14 to the conductive layer 13.

[0014] The first base layer 11 is a transparent, flexible dielectric film having a thickness t3 of 1.00 mm or less, preferably 0.70 mm or less, more preferably 0.50 mm or less, and even more preferably 0.10 mm or less. The flexible film is made of a transparent, heat-resistant, dielectric resin material such as polyethylene terephthalate (PET), polycarbonate (PC), cycloolefin polymer (COP), polyimide (PI), or fluororesin.

[0015] The first base layer 11 functions as a support layer for the conductive layer 13, and can also function as a protective layer that protects the surface 131 of the conductive layer 13 depending on the direction of incidence of electromagnetic waves. For example, when the electromagnetic wave reflective film 10 is attached to a window glass or a structure using the adhesive layer 12 with the second base layer 14 used as a release layer, the first base layer 11 can serve as a protective layer that protects one surface 131 of the conductive layer 13.

[0016] The first base layer 11 is transparent to visible light and also transparent to electromagnetic waves in a predetermined frequency band of 1 GHz or more and 300 GHz or less, and minimizes attenuation of electromagnetic waves in the above frequency band that are incident on the conductive layer 13.

[0017] The conductive layer 13 is formed of a good conductor such as Ag, Cu, Ni, Al, or Pd, or a transparent metal oxide conductor, and may be processed into a periodic pattern, mesh pattern, geometric pattern, or the like. The conductive layer 13 reflects electromagnetic waves in a predetermined frequency band from 1 GHz to 300 GHz. Electromagnetic waves in this range include microwaves, millimeter waves, and submillimeter waves. The conductive layer 13 may be formed as a regular reflecting surface that specularly reflects electromagnetic waves in the above frequency band, or as a metasurface that controls the reflection or diffusion of incident electromagnetic waves. The conductive layer 13 may also have a specular reflecting surface region and a metasurface region.

[0018] When the conductive layer 13 is formed of an indium oxide-based transparent conductive material doped with a metal element such as Sn, Ti, Zn, Zr, Ga, or W, or a metal material with high visible light transmittance such as Ag, the conductive layer 13 may be formed as a solid film on the first substrate layer 11 or as a thin film having a periodic pattern. The conductive layer 13 may also be formed as a mesh pattern of a metal such as SUS, Al, or Cu. When using a metal mesh pattern, it is desirable to set the aperture ratio of the metal mesh to 70% or more so that the total light transmittance is 70% or more. When the conductive layer 13 is formed of Ag or a transparent conductive material, it can be formed on the first substrate layer 11 by sputtering or vacuum deposition at room temperature. When using a metal mesh, a pre-fabricated metal mesh may be placed on the first substrate layer 11, and the adhesive layer 12 may be applied to the metal mesh. Alternatively, a metal mesh pattern may be formed on the first substrate layer 11 by sputtering and etching, for example.

[0019] When the conductive layer 13 is formed by sputtering or vacuum deposition, the thickness "t1" of the conductive layer 13 can be 5 nm or more and 500 nm or less. When a metal mesh is used, the thickness t1 of the conductive layer 13 may be several hundred nm to several hundred μm. The surface resistivity of the conductive layer 13 is 10.0 Ω / □ or less. When a metal mesh is used, the surface resistivity of the conductive layer 13 can be less than 0.1 Ω / □.

[0020] The adhesive layer 12 is a dielectric adhesive layer capable of adhering the second base layer 14 to the other surface 132 of the conductive layer 13, and may be made of a thermoplastic resin such as vinyl acetate resin, acrylic resin, cellulose resin, or silicone resin. Durable and moisture-resistant ethylene-vinyl acetate (EVA) copolymer or cycloolefin polymer (COP) may also be used for the adhesive layer 12. The thickness "t2" of the adhesive layer 12 may be appropriately selected between 10 μm and 750 μm depending on the material of the adhesive layer 12, the thickness and weight of the conductive layer 13 and the first base layer 11, etc.

[0021] The second base material layer 14 may be used as a release layer. Before the electromagnetic wave reflecting film 10 is attached to an object, the second base material layer 14 is attached to the conductive layer 13 by the adhesive layer 12. When attaching the electromagnetic wave reflecting film 10 to a window glass or a structure, the second base material layer 14 may be peeled off and the electromagnetic wave reflecting film 10 may be attached to the object by the adhesive layer 12. The adhesive layer 12 is an adhesive that can be peeled off or reworked.

[0022] 3 is a schematic diagram showing an example of application of the electromagnetic wave reflective film 10 of FIG. 2 to a window glass 3. The electromagnetic wave reflective film 10, from which the second base layer 14 has been peeled off, is attached to the surface of the window glass 3 supported by a window frame 6, by an adhesive layer 12. The electromagnetic wave reflective film 10 may be attached from the indoor 4 side or from the outdoor 5 side. In places where a small wireless base station is installed indoors 4, such as offices and shopping malls, the electromagnetic wave reflective film 10 may be attached from the indoor 4 side. In this case, electromagnetic waves W radiated from the antenna of the base station installed indoors 4 ＥＭis reflected toward the indoor 4 by the conductive layer 13 of the electromagnetic wave reflecting film 10, thereby reducing the blind zone of the indoor 4.

[0023] If the window glass 3 and adhesive layer 12 are transparent to electromagnetic waves in the frequency range of 1 GHz to 300 GHz and the conductive layer 13 has a reflecting function for the frequency band for wireless communication used outdoors 5, the conductive layer 13 arranged on the indoor 4 side also functions as a reflective film for electromagnetic waves incident from outdoors 5. In this case, it is also possible to reduce the blind zone of outdoors 5.

[0024] When the electromagnetic wave reflective film 10 is attached from the outdoor 5 side, the first base layer 11 may have impact resistance or durability so as to function as a protective layer. As the base layer having a protective function, a polycarbonate film, a PET film, a COP film, or the like having a thickness of 0.025 mm or more and 1.0 mm or less may be used. A hard coat layer for ultraviolet protection and scratch prevention may be provided on both or either one of the surfaces of the first base layer 11.

[0025] The dielectric constants and dielectric loss tangents of the first base layer 11 and the adhesive layer 12 are appropriately selected for the entire laminate so that the electromagnetic wave reflecting film 10 achieves the target reflection characteristics. The dielectric constant of the dielectric portion excluding the conductive layer 13 is, for example, 2.0 or more and 3.0 or less, and the dielectric loss tangent is 0.0001 or more and less than 0.1000. Flexible films with a dielectric constant of less than 2.0 are currently difficult to obtain. If the dielectric constant exceeds 3.0, there is a risk of increased loss, particularly at high frequencies. The same is true for the dielectric loss tangent. Flexible films with a dielectric loss tangent of less than 0.0001 are difficult to obtain, and if the dielectric loss tangent is 0.1000 or more, the loss of electrical energy within the electromagnetic wave reflecting film 10 increases.

[0026] A transparent and flexible electromagnetic wave reflecting film 10 can be obtained by using a flexible film first base layer 11 and optimizing the ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13, or the ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13. The optimal ranges for t3 / t1 and t2 / t1 will be described later.

[0027] 4 is a schematic diagram of the layer structure of an electromagnetic wave reflecting film 20 of a second embodiment. The electromagnetic wave reflecting film 20 has a first base material layer 21, a conductive layer 23 supported on the first base material layer 21, a second base material layer 24 disposed on the side of the conductive layer 23 opposite the first base material layer 21, and an adhesive layer 22 that bonds the second base material layer 24 to the conductive layer 23. The electromagnetic wave reflecting film 20 also has a third base material layer 27 attached by a second adhesive layer 26 to a surface 212 of the first base material layer 21 opposite the surface 211 that supports the conductive layer 23.

[0028] The first base layer 21 is a transparent, flexible dielectric film having a thickness t3 of 1.00 mm or less, preferably 0.70 mm or less, more preferably 0.50 mm or less, and even more preferably 0.10 mm or less. As in the first embodiment, the flexible film is made of a transparent, heat-resistant, dielectric resin material such as PET, PC, COP, PI, or fluororesin.

[0029] The first base layer 21 functions as a support layer for the conductive layer 23, and also as an attachment surface to a window glass or a structure. For example, when the electromagnetic wave reflective film 20 is attached to a window glass or a structure by the second adhesive layer 26 using the third base layer 27 as a release layer, the surface 212 of the first base layer 21 becomes the attachment surface to the window glass or the structure.

[0030] The conductive layer 23 is formed of a good conductor such as Ag, Cu, Ni, Al, or Pd, or a transparent metal oxide conductor, and may be processed into a periodic pattern, mesh pattern, geometric pattern, or the like. The conductive layer 23 reflects electromagnetic waves in a predetermined frequency band from 1 GHz to 300 GHz. Electromagnetic waves in this range include microwaves, millimeter waves, and submillimeter waves. The conductive layer 23 may be formed as a regular reflective surface that specularly reflects electromagnetic waves in the above frequency band, or as a metasurface that controls the reflection or diffusion of incident electromagnetic waves. The material, formation method, surface resistivity, thickness "t1," and the like of the conductive layer 23 are the same as those of the conductive layer 13 in the first embodiment.

[0031] The adhesive layer 22 is a dielectric adhesive layer capable of adhering the second base layer 24 to the conductive layer 23, and may be made of a thermoplastic resin such as vinyl acetate resin, acrylic resin, cellulose resin, or silicone resin. Durable and moisture-resistant ethylene-vinyl acetate (EVA) copolymer or cycloolefin polymer (COP) may also be used for the adhesive layer 22. The thickness "t2" of the adhesive layer 22 may be appropriately selected between 10 μm and 750 μm depending on the material of the adhesive layer 22, the thicknesses of the conductive layer 23 and the second base layer 24, and the like.

[0032] The second substrate layer 24 is transparent to visible light and also transparent to electromagnetic waves in a predetermined frequency band of 1 GHz to 300 GHz, minimizing attenuation of electromagnetic waves in the above-mentioned frequency band that are incident on the conductive layer 23. The second substrate layer 24 functions as a protective layer. A hard coat layer for scratch prevention or ultraviolet protection may be applied to both or either one of the surfaces of the second substrate layer 24.

[0033] The third base material layer 27 is used as a release layer. Before the electromagnetic wave reflecting film 20 is attached to an object, the third base material layer 27 is attached to the surface 212 of the first base material layer 21 by the second adhesive layer 26. When the electromagnetic wave reflecting film 20 is attached to a window glass or a structure, the third base material layer 27 may be peeled off and the film may be attached by the second adhesive layer 26.

[0034] 5 is a schematic diagram showing an example of application of the electromagnetic wave reflecting film 20 of FIG. 4 to a window glass 3. The electromagnetic wave reflecting film 20, from which the third base layer 27 has been peeled off, is attached to the surface of the window glass 3 supported by a window frame 6, by means of a second adhesive layer 26. Since the second adhesive layer 26 supports the entire electromagnetic wave reflecting film 20 on the window glass 3, it is desirable that the second adhesive layer 26 is thicker or more adhesive than the adhesive layer 22. The electromagnetic wave reflecting film 20 may be attached from the indoor 4 side or from the outdoor 5 side. When the electromagnetic wave reflecting film 20 is arranged on the indoor 4 side, the electromagnetic waves W incident from the indoor 4 side are reflected by the second adhesive layer 26. ＥＭ is reflected toward the indoor 4 by the conductive layer 23 of the electromagnetic wave reflecting film 20, thereby reducing the blind zone of the indoor 4.

[0035] If the window glass 3, the second adhesive layer 26, and the first base material layer 21 are transparent to electromagnetic waves in the range of 1 GHz to 300 GHz, and the conductive layer 23 has a reflective function for the frequency band for wireless communication used outdoors 5, the conductive layer 23 also functions as a reflective film for electromagnetic waves incident from outdoors 5. In this case, it is possible to reduce the blind zone of outdoors 5.

[0036] When the electromagnetic wave reflective film 20 is attached from the outdoor 5 side, the second base layer 24 may have impact resistance or durability so as to function as a protective layer. A PC film, PET film, COP film, or the like having a thickness of 0.025 mm or more and 1.0 mm or less may be used as the base layer having a protective function. A hard coat layer for ultraviolet protection and scratch prevention may be provided on both or either one of the surfaces of the second base layer 24.

[0037] The dielectric constants and dielectric loss tangents of the first base layer 21, the second base layer 24, the adhesive layer 22, and the second adhesive layer 26 are appropriately selected for the entire laminate so that the electromagnetic wave reflecting film 20 achieves the target reflection characteristics. As in the first embodiment, the dielectric constant of the dielectric portion excluding the conductive layer 23 is, for example, 2.0 or more and 3.0 or less, and the dielectric loss tangent is 0.0001 or more and less than 0.1000. Flexible films with a dielectric constant of less than 2.0 are currently difficult to obtain. If the dielectric constant exceeds 3.0, there is a risk of increased loss, particularly at high frequencies. The same is true for the dielectric loss tangent. Flexible films with a dielectric loss tangent of less than 0.0001 are difficult to obtain, and if the dielectric loss tangent is 0.1000 or more, the loss of electrical energy within the electromagnetic wave reflecting film 20 increases.

[0038] A transparent and flexible electromagnetic wave reflecting film 20 can be obtained by using a flexible film first base material layer 21 and optimizing the ratio (t3 / t1) of the thickness t3 of the first base material layer 21 to the thickness t1 of the conductive layer 23, or the ratio (t2 / t1) of the thickness t2 of the adhesive layer 22 to the thickness t1 of the conductive layer 23. The optimal ranges for t3 / t1 and t2 / t1 will be described later.

[0039] <Characteristic Evaluation> Samples of electromagnetic wave reflective films were prepared and their total light transmittance and return loss were measured as follows. The samples had the same layer structure as the electromagnetic wave reflective film 10 of the first embodiment. The total light transmittance was measured using an ultraviolet-visible-infrared spectrophotometer manufactured by Shimadzu Corporation. The return loss was measured using a method conforming to JIS R1679. Specifically, the return loss was measured when a 28.0 GHz plane wave was incident at an incident angle of 0°. The material and thickness t3 of the first base layer 11, the material and thickness t1 of the conductive layer 13, and the thickness t2 of the adhesive layer 12 were varied. A removable acrylic adhesive was used for the adhesive layer 12. Samples that achieved a total light transmittance of 70% or more and a return loss (absolute value) of 1.0 dB or less were designated as example samples, and samples that did not satisfy either or both of the total light transmittance and return loss were designated as comparative samples. The total light transmittance and return loss were measured in a state including the second base material layer 14, which serves as a peel layer, and the type and thickness of the second base material layer 14 were set to optimize the total light transmittance and return loss for the layer structure of each sample.

[0040] Example 1 Example 1 is Example 1. In Example 1, a PET film measuring 0.5 m in length, 0.5 m in width, and 0.188 mm in thickness (t3) is used as the first base layer 11. A thin Ag film having a thickness (t1) of 0.360 μm (360 nm) is formed on this PET film by room temperature sputtering to form the conductive layer 13. The surface resistivity of this Ag thin film is 1.0 Ω / □. An adhesive having a thickness (t2) of 0.025 mm is applied to the surface of the Ag thin film to form the adhesive layer 12. This adhesive layer 12 bonds a 0.150 mm thick PET film to the conductive layer 13 as the second base layer 14. The sum of the thicknesses of the conductive layer 13, adhesive layer 12, and first base layer 11 (Tsum = t1 + t2 + t3) is 213.4 μm.

[0041] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 5.2×10 ２ The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 6.9×10. The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 1.7×10.－３ The total light transmittance of the sample was 90.4%, and the return loss measured by the method in accordance with JIS R1679 was −0.05 dB. The sample of Example 1 had high transparency and small return loss.

[0042] Example 2 Example 2 is Example 2. In Example 2, a PET film measuring 0.5 m in length, 0.5 m in width, and 0.350 mm in thickness (t3) is used as the first base layer 11. A thin Ag film having a thickness (t1) of 0.050 μm (50 nm) is formed on this PET film by room temperature sputtering to form the conductive layer 13. The surface resistivity of this Ag thin film is 5.0 Ω / □. An adhesive having a thickness (t2) of 0.025 mm is applied to the surface of the Ag thin film to form the adhesive layer 12. A PET film having a thickness of 0.150 mm is bonded to the conductive layer 13 as the second base layer 14 by this adhesive layer 12. The sum of the thicknesses of the conductive layer 13, the adhesive layer 12, and the first base layer 11 (Tsum = t1 + t2 + t3) is 375.1 μm.

[0043] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 7.0×10 ３ The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 5.0×10 ２ The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 1.3×10 －４ The total light transmittance of the sample was 95.3%, and the return loss measured by the method in accordance with JIS R1679 was −0.15 dB. The sample of Example 2 had high transparency and small return loss.

[0044] Example 3 Example 3 is Example 3. In Example 3, a PET film measuring 0.5 m in length, 0.5 m in width, and 0.025 mm in thickness (t3) is used as the first base layer 11. A thin ITO film having a thickness (t1) of 0.500 μm (500 nm) is formed on this PET film by room temperature sputtering to form the conductive layer 13. The surface resistivity of this ITO thin film is 5.0 Ω / □. An adhesive having a thickness (t2) of 0.010 mm is applied to the surface of the ITO thin film to form the adhesive layer 12. This adhesive layer 12 bonds a PET film having a thickness of 0.150 mm to the conductive layer 13 as the second base layer 14. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, adhesive layer 12, and first base layer 11 is 35.5 μm.

[0045] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 5.0×10. The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 2.0×10. The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 1.0×10. －２ The total light transmittance of the sample was 87.0%, and the return loss measured by the method in accordance with JIS R1679 was −0.02 dB. The sample of Example 3 had high transparency and small return loss.

[0046] Example 4 Example 4 is Example 4. In Example 4, a PET film measuring 0.5 m in length, 0.5 m in width, and 0.500 mm in thickness (t3) is used as the first base layer 11. A thin ITO film having a thickness (t1) of 0.005 μm (5 nm) is formed on this PET film by room temperature sputtering to form the conductive layer 13. The surface resistivity of this ITO thin film is 10.0 Ω / □. An adhesive having a thickness (t2) of 0.750 mm is applied to the surface of the ITO thin film to form the adhesive layer 12. This adhesive layer 12 bonds a PET film having a thickness of 0.150 mm to the conductive layer 13 as the second base layer 14. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, adhesive layer 12, and first base layer 11 is 1250.0 μm.

[0047] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 1.0×10５ The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 1.5×10 ５ The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 4.0×10 －６ The total light transmittance of the sample was 85.2%, and the return loss measured by the method in accordance with JIS R1679 was −0.03 dB. The sample of Example 4 had high transparency and small return loss.

[0048] Example 5 Example 5 is Example 5. In Example 5, a PC film having a length of 0.5 m, a width of 0.5 m, and a thickness (t3) of 1.000 mm is used as the first base layer 11. A thin Ag film having a thickness (t1) of 0.010 μm (10 nm) is formed on this PC film by room temperature sputtering to form the conductive layer 13. The surface resistivity of this Ag thin film is 10.0 Ω / □. An adhesive having a thickness (t2) of 0.025 mm is applied to the surface of the Ag thin film to form the adhesive layer 12. This adhesive layer 12 bonds a PC film having a thickness of 0.100 mm to the conductive layer 13 as the second base layer 14. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, the adhesive layer 12, and the first base layer 11 is 1025.0 μm.

[0049] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 1.0×10 ５ The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 2.5×10 ３ The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 1.0×10 －４ The total light transmittance of the sample was 95.3%, and the return loss measured by the method in accordance with JIS R1679 was −0.15 dB. The sample of Example 5 had high transparency and small return loss.

[0050] Example 6 Example 6 is Example 6. In Example 6, a PET film measuring 0.5 m in length, 0.5 m in width, and 1.000 mm in thickness (t3) is used as the first base layer 11. A SUS mesh having a thickness (t1) of 200 μm is placed on this PET film to form the conductive layer 13. The surface resistivity of this SUS mesh is 0.03 Ω / □. An adhesive having a thickness (t2) of 0.200 mm is applied to the surface of the SUS mesh to form the adhesive layer 12. A PET film having a thickness of 0.100 mm is bonded to the conductive layer 13 as the second base layer 14 by this adhesive layer 12. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, the adhesive layer 12, and the first base layer 11 is 1400.0 μm.

[0051] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 5.0. The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 1.0. The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 1.4×10 －１ The total light transmittance of the sample is 72.3%, and the return loss measured by the method in accordance with JIS R1679 is −0.23 dB. The transparency of the sample of Example 6 is within the acceptable range, and the return loss is small.

[0052] Example 7 Example 7 is Example 7. In Example 7, a PET film measuring 0.5 m in length, 0.5 m in width, and 0.025 mm in thickness (t3) is used as the first base layer 11. A SUS mesh having a thickness (t1) of 100 μm is placed on this PET film to form the conductive layer 13. The surface resistivity of this SUS mesh is 0.03 Ω / □. An adhesive having a thickness (t2) of 0.200 mm is applied to the surface of the SUS mesh to form the adhesive layer 12. A PET film having a thickness of 0.100 mm and hard coat layers on both sides is bonded to the conductive layer 13 as the second base layer 14 using this adhesive layer 12. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, adhesive layer 12, and first base layer 11 is 325.0 μm.

[0053] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 2.5×10 -１The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 2.0. The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 3.1×10 －１ The total light transmittance of the sample is 70.3%, and the return loss measured by the method in accordance with JIS R1679 is −0.23 dB. The transparency of the sample of Example 7 is within the acceptable range, and the return loss is small.

[0054] Example 8 Example 8 is Example 8. In Example 8, a double-sided hard-coated PC film measuring 0.7 m in length, 0.7 m in width, and 0.700 mm in thickness (t3) is used as the first substrate layer 11. A thin Ag film having a thickness (t1) of 0.360 μm (360 nm) is formed on this double-sided hard-coated PC film to form the conductive layer 13. The surface resistivity of the conductive layer 13 is 1.0 Ω / □. An adhesive having a thickness (t2) of 0.400 mm is applied to the surface of the Ag thin-film conductive layer 13 to form the adhesive layer 12. A 0.100 mm thick PET film is bonded to the conductive layer 13 as the second substrate layer 14 using this adhesive layer 12. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, the adhesive layer 12, and the first substrate layer 11 is 1100.4 μm.

[0055] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 1.9×10 ３ The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 1.1×10 ３ The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 3.3×10 －４ The total light transmittance of the sample is 75.2%, and the return loss measured by a method in accordance with JIS R1679 is −0.98 dB. The transparency of the sample of Example 8 is within the acceptable range, and the return loss is small.

[0056] Example 9 Example 9 is Comparative Example 1. In Comparative Example 1, a PET film measuring 0.5 m in length, 0.5 m in width, and 0.025 mm in thickness (t3) is used as the first base layer 11. A SUS mesh having a thickness (t1) of 0.200 mm is placed on this PET film to form the conductive layer 13. The surface resistivity of this SUS mesh is 0.01 Ω / □. An adhesive having a thickness (t2) of 0.40 mm is applied to the surface of the SUS mesh to form the adhesive layer 12. A PET film having a thickness of 0.150 mm is bonded to the conductive layer 13 as the second base layer 14 by this adhesive layer 12. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, the adhesive layer 12, and the first base layer 11 is 625.0 μm.

[0057] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 1.3×10 -１ The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 2.0. The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 3.2×10 －１ The total light transmittance of the sample was 85.2%, and the return loss measured by a method conforming to JIS R1679 was -1.02 dB. Although the sample of Example 9 has high transparency, the return loss exceeds the allowable range and therefore cannot be used as a product.

[0058] Example 10 Example 10 is Comparative Example 2. In Comparative Example 2, a PET film measuring 0.5 m in length, 0.5 m in width, and 0.025 mm in thickness (t3) is used as the first base layer 11. A SUS mesh having a thickness (t1) of 0.100 mm is placed on this PET film to form the conductive layer 13. The surface resistivity of this SUS mesh is 0.03 Ω / □. An adhesive having a thickness (t2) of 0.025 mm is applied to the surface of the SUS mesh to form the adhesive layer 12. A PET film having a thickness of 0.150 mm is bonded to the conductive layer 13 as the second base layer 14 by this adhesive layer 12. The total thickness (Tsum = t1 + t2 + t3) of the conductive layer 13, the adhesive layer 12, and the first base layer 11 is 150.0 μm.

[0059] The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is 2.5×10 -１ The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is 2.5×10 -１ The ratio (t1 / Tsum) of the thickness t1 of the conductive layer 13 to Tsum (t1+t2+t3) is 6.6×10 －１ The opening ratio of the metal mesh is 69.5%, the total light transmittance of the sample is 62.3%, and the return loss measured by the measurement method in accordance with JIS R1679 is -0.32 dB. Although the return loss of the sample of Example 10 is small, its transparency is insufficient and it cannot be used as a product.

[0060] Table 1 shows the characteristic parameters and measurement results of the samples of Examples 1 to 10.

[0061] The results of Examples 1 to 10 lead to the following conclusions. (1) In order to provide the electromagnetic wave reflective film with sufficient flexibility, the thickness of the first base layer is preferably 1.0 mm or less. (2) In order to provide sufficient reflective properties, the surface resistivity of the conductive layer is preferably 10.0 Ω / □ or less. (3) From the viewpoint of transparency, the total light transmittance of the electromagnetic wave reflective film is preferably 70% or more. (4) From the viewpoint of reflection efficiency, the return loss (absolute value) of the electromagnetic wave reflective film is preferably 1.00 dB or less. (5) The ratio (t3 / t1) of the thickness t3 of the first base layer 11 to the thickness t1 of the conductive layer 13 is preferably 0.25 or more and 1.0 x 10 ５ If the thickness of the first base layer 11 is insufficient compared to the thickness of the conductive layer 13, the conductive layer 13 cannot be stably supported, and twisting or undulation may occur in the conductive layer 13, resulting in reflection loss. (6) The ratio (t2 / t1) of the thickness t2 of the adhesive layer 12 to the thickness t1 of the conductive layer 13 is preferably 1.0 or more and 1.5×10 or less. ５It is desirable that the thickness of the adhesive layer 12 is not more than that of the conductive layer 13. If the thickness of the adhesive layer 12 is insufficient compared to the thickness of the conductive layer 13, air bubbles may be trapped or generated between the adhesive layer 12 and the object to which the electromagnetic wave reflecting film 10 is applied, or between the adhesive layer 12 and the conductive layer 13, resulting in a decrease in transparency. (7) The electromagnetic wave reflecting film 10 is produced so that the sum Tsum of the thickness t1 of the conductive layer 13, the thickness t2 of the adhesive layer 12, and the thickness t3 of the first base layer 11 is in the range of 30 μm or more and 1500 μm or less, and it is preferable that the ratio of the thickness of the conductive layer 13 to Tsum (t1 / Tsum) is less than 1 / 3.

[0062] By having the above-mentioned structure, a transparent electromagnetic wave reflective film with good reflection properties is realized.

[0063] The above disclosure includes the following configuration: (Item 1) A conductive layer that reflects electromagnetic waves in a predetermined frequency band of 1 GHz or more and 300 GHz or less, a first base material layer that supports the conductive layer, a second base material layer that is disposed on the conductive layer on the opposite side to the first base material layer, and an adhesive layer that adheres the second base material layer to the conductive layer, wherein the thickness of the first base material layer is 1.0 mm or less, and the ratio of the thickness of the first base material layer to the thickness of the conductive layer is 0.25 or more and 1.0 x 10 ５ (Item 2) An electromagnetic wave reflective film, wherein the ratio of the thickness of the adhesive layer to the thickness of the conductive layer is 1.0 or more and 1.5 × 10 or less. ５Item 1. The electromagnetic wave reflective film according to Item 1, wherein the conductive layer has a surface resistivity of 10.0 Ω / □ or less. (Item 3) The electromagnetic wave reflective film according to Item 1 or 2, wherein the conductive layer has a surface resistivity of 10.0 Ω / □ or less. (Item 4) The electromagnetic wave reflective film according to any one of Items 1 to 3, wherein the conductive layer is an Ag thin film or a transparent conductive film of a metal oxide, and wherein the conductive layer has a thickness of 5 nm or more and 1000 nm or less. (Item 5) The electromagnetic wave reflective film according to any one of Items 1 to 3, wherein the conductive layer has a metal mesh, and wherein the opening ratio of the metal mesh is 70% or more. (Item 6) The electromagnetic wave reflective film according to Item 5, wherein the metal mesh has a surface resistivity of less than 1.0 Ω / □. (Item 7) The electromagnetic wave reflective film according to any one of Items 1 to 6, wherein the total thickness of the first base layer, the conductive layer, and the adhesive layer is 30 μm or more and 1500 μm or less, and wherein the ratio of the thickness of the conductive layer to the total thickness is 1 / 3 or less. (Item 8) The electromagnetic wave reflective film according to any one of Items 1 to 7, comprising: a second adhesive layer provided on the surface of the first base material layer opposite the conductive layer; and a third base material layer adhered to the first base material layer by the second adhesive layer. (Item 9) The electromagnetic wave reflective film according to Item 8, wherein the second adhesive layer is thicker or more adhesive than the adhesive layer. (Item 10) The electromagnetic wave reflective film according to any one of Items 1 to 7, wherein a hard coat layer is applied to both or either one of the surfaces of the first base material layer. (Item 11) The electromagnetic wave reflective film according to Item 8 or 9, wherein a hard coat layer is applied to both or either one of the surfaces of the second base material layer.

[0064] This international application claims priority based on Japanese Patent Application No. 2023-190975, filed on November 8, 2023, the entire contents of which are incorporated herein by reference.

[0065] 10, 20 Electromagnetic wave reflecting film 11, 21 First base material layer 12, 22 Adhesive layer 13, 23 Conductive layer 14, 24 Second base material layer 26 Second adhesive layer 27 Third base material layer

Claims

1. A conductive layer that reflects electromagnetic waves in a predetermined frequency band of 1 GHz or more and 300 GHz or less; a first base material layer that supports the conductive layer; a second base material layer that is disposed on the conductive layer on the opposite side to the first base material layer; and an adhesive layer that adheres the second base material layer to the conductive layer, wherein the thickness of the first base material layer is 1.0 mm or less, and the ratio of the thickness of the first base material layer to the thickness of the conductive layer is 0.25 or more and 1.0 x 10 ５ Below is an electromagnetic wave reflective film.

2. The ratio of the thickness of the adhesive layer to the thickness of the conductive layer is 1.0 or more and 1.5 x 10 ５ The electromagnetic wave reflective film according to claim 1 , wherein:

3. The electromagnetic wave reflective film according to claim 1, wherein the surface resistivity of the conductive layer is 10.0 Ω / □ or less.

4. The electromagnetic wave reflective film according to claim 1, wherein the conductive layer is a thin Ag film or a transparent conductive film of a metal oxide, and the thickness of the conductive layer is 5 nm or more and 1000 nm or less.

5. The electromagnetic wave reflective film according to claim 1, wherein the conductive layer has a metal mesh, and the opening ratio of the metal mesh is 70% or more.

6. The electromagnetic wave reflective film according to claim 5, wherein the surface resistivity of the metal mesh is less than 1.0 Ω / □.

7. The electromagnetic wave reflective film according to claim 1, wherein the total thickness of the first base layer, the conductive layer, and the adhesive layer is 30 μm or more and 1500 μm or less, and the ratio of the thickness of the conductive layer to the total thickness is 1 / 3 or less.

8. The electromagnetic wave reflecting film according to claim 1, comprising: a second adhesive layer provided on the surface of the first base material layer opposite the conductive layer; and a third base material layer adhered to the first base material layer by the second adhesive layer.

9. The electromagnetic wave reflecting film according to claim 8, wherein the second adhesive layer is thicker or more adhesive than the first adhesive layer.

10. The electromagnetic wave reflective film according to claim 1, wherein a hard coat layer is applied to both or either one of the surfaces of the first substrate layer.

11. The electromagnetic wave reflective film according to claim 8, wherein a hard coat layer is applied to both or either one of the surfaces of the second substrate layer.