Electromagnetic noise suppression sheet, production method for same, and communication cable and electronic device using electromagnetic noise suppression sheet

Abstract

This electromagnetic noise suppression sheet is characterized by being formed by layering a magnetic layer and a base material, the magnetic layer including a magnetic material and a resin, and the base material including a metal layer that is on the outer surface side of the base material. The electromagnetic noise suppression sheet is also characterized in that, when surface roughness is defined as arithmetic average height Sa, the surface roughness Sa1 on the outer surface side of the magnetic layer and the surface roughness Sa2 on the outer surface side of the metal layer satisfy expressions (1) and (2).　(1) 1.9 μm≤Sa1≤5.0 μm. (2) 2.0 μm≤Sa2≤4.0 μm.

Description

Electromagnetic Noise Suppression Sheet, Method for Manufacturing the Same, Communication Cable Using the Electromagnetic Noise Suppression Sheet, and Electronic Device

[0001] This application relates to an electromagnetic noise suppression sheet that absorbs magnetic field noise and electromagnetic waves in the MHz to GHz bands.

[0002] With the development of wireless communication technologies represented by mobile phones, various devices and sensors are being wirelessly connected to networks. Also, in the medical field, from the perspective of infection prevention, the cordlessization of devices is progressing, and medical devices are starting to be wirelessly connected. These communications require relatively high-speed and large-capacity over short distances and use high frequencies. With the increase in the number of devices using such high frequencies, the risk of malfunctions and interference with the used electromagnetic waves due to electromagnetic noise generated from the devices is increasing in electronic devices and communications. Furthermore, in recent years, the installation of millimeter-wave radars for the purpose of preventing automobile collision accidents has also started. Malfunctions in these devices in the medical and automotive fields affect human lives, so there must be no malfunction. Therefore, there is an increasing need to apply an electromagnetic noise suppression sheet as a countermeasure against electromagnetic noise generated by devices and the malfunctions caused by the interference therefrom, so-called EMC (Electromagnetic Compatibility), to circuit elements and transmission lines that transmit and receive electromagnetic waves in the MHz to GHz bands.

[0003] By providing the electromagnetic noise suppression sheet to society, among the 17 goals of the Sustainable Development Goals (SDGs) established by the United Nations, it can contribute to the achievement of Goal 3 (Ensure healthy lives and promote well-being for all people of all ages), Goal 9 (Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation), and Goal 12 (Ensure sustainable consumption and production patterns).

[0004] In this context, Patent Document 1 proposes using a laminate comprising a magnetic material layer containing magnetic powder and binder resin, and a polymer compound film layer, as a magnetic sheet that suppresses the transmission of electromagnetic waves. In Patent Document 1, the laminate is manufactured by applying a magnetic powder dispersion (magnetic layer forming coating) onto a polymer compound film layer which serves as a base material, drying it, and then performing pressure molding (calendar treatment). This pressure molding reduces air bubbles (voids) in the magnetic material layer and increases the magnetic permeability of the magnetic material layer.

[0005] On the other hand, when the magnetic layer is subjected to pressure treatment, the surface smoothness of the magnetic layer increases. When the manufactured magnetic sheet is wound up and stored, the number of true contact points increases at the contact surface of the magnetic sheet during winding, that is, at the contact surface between the smooth magnetic layer surface and the originally smooth polymer compound film layer (substrate). Since adhesion due to intermolecular forces occurs at the true contact points, interlayer adhesion (blocking) between sheets is more likely to occur, which makes it difficult to unwind the sheet.

[0006] Furthermore, prior art documents related to the electromagnetic noise suppression sheet of the present application include Patent Documents 2 and 3. Patent Document 2 discloses a sheet for electronic components having an electromagnetic wave absorbing and heat dissipation layer containing magnetic powder, thermally conductive powder, and resin, and a conductive sealing layer laminated on the electromagnetic wave absorbing and heat dissipation layer. Patent Document 3 discloses a magnetic shielding material comprising a magnetic layer containing a magnetic material and a conductive layer containing a conductive material.

[0007] Japanese Patent Publication No. 2016-36965, Japanese Patent Publication No. 2002-198686, Japanese Patent Publication No. 2020-88045

[0008] This invention solves the above problem and provides an electromagnetic noise suppression sheet that is less prone to blocking even when wound up and stored after manufacturing.

[0009] The electromagnetic noise suppression sheet of the present invention comprises a magnetic layer and a substrate laminated together, wherein the magnetic layer includes a magnetic material and a resin, the substrate includes a metal layer, the metal layer is arranged on the outer surface side of the substrate, and the surface roughness is defined by the arithmetic mean height Sa, and if the surface roughness on the outer surface side of the magnetic layer is Sa1 and the surface roughness on the outer surface side of the metal layer is Sa2, then the following relational expressions (1) and (2) hold: 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2)

[0010] The communication cable of the present invention is characterized by including the electromagnetic noise suppression sheet of the present invention.

[0011] The electronic device of the present invention is characterized by including the electromagnetic noise suppression sheet of the present invention.

[0012] The present invention relates to a method for manufacturing an electromagnetic noise suppression sheet, comprising: a first step of mixing a magnetic material, a resin, and a solvent to produce a magnetic layer forming coating; a second step of applying the magnetic layer forming coating to a substrate and drying it to produce a magnetic layer / substrate laminated sheet; and a third step of pressurizing and heating the magnetic layer / substrate laminated sheet, wherein the substrate includes a metal layer, and the metal layer is positioned on the side of the substrate opposite to the side to which the magnetic layer forming coating is applied, and at the end of the third step, if the surface roughness is defined by the arithmetic mean height Sa, and the surface roughness of the outer side of the magnetic layer is Sa1 and the surface roughness of the outer side of the metal layer is Sa2, then the following relational expressions (1) and (2) hold: (1) 1.9 μm ≤ Sa1 ≤ 5.0 μm (2) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2)

[0013] According to this invention, by adjusting the surface roughness of the outer surface of the magnetic layer and the surface roughness of the outer surface of the base layer, it is possible to provide an electromagnetic noise suppression sheet that is less prone to blocking even when wound up and stored after manufacturing.

[0014] Figure 1 is a schematic cross-sectional view showing an electromagnetic noise suppression sheet before pressurized heating treatment. Figure 2 is a schematic cross-sectional view showing an electromagnetic noise suppression sheet after pressurized heating treatment. Figure 3 is a schematic cross-sectional view showing an example of an electromagnetic noise suppression sheet according to the embodiment. Figure 4 is a schematic cross-sectional view showing another example of an electromagnetic noise suppression sheet according to the embodiment. Figure 5 is a schematic cross-sectional view showing an example of a coaxial cable according to the embodiment.

[0015] (Electromagnetic Noise Suppression Sheet) An embodiment of the electromagnetic noise suppression sheet of the present invention will now be described. The electromagnetic noise suppression sheet of this embodiment is constructed by laminating a magnetic layer and a substrate, the magnetic layer includes a magnetic material and a resin, the substrate includes a metal layer, the metal layer is arranged on the outer surface side of the substrate, the surface roughness is defined by the arithmetic mean height Sa, and if the surface roughness on the outer surface side of the magnetic layer is Sa1 and the surface roughness on the outer surface side of the metal layer is Sa2, then the following relational expressions (1) and (2) hold true. 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2)

[0016] Generally, in electromagnetic noise suppression sheets consisting of a laminate of a magnetic layer and a substrate, pressure and heat treatment is performed to increase the magnetic permeability of the magnetic layer. As a result, the packing of the magnetic material contained in the magnetic layer is improved and the magnetic permeability is increased, but at the same time the surface smoothness of the magnetic layer is also increased. When the manufactured electromagnetic noise suppression sheet is wound up and stored, interlayer adhesion (blocking) is likely to occur at the contact surface between the surface of the magnetic layer, which has become smoother, and the surface of the film substrate, which is normally formed to be smooth from the beginning. If blocking occurs, the sheet may not be able to be unwound after being wound up, or even if it can be unwound, a part of the magnetic layer may adhere to the substrate and peel off.

[0017] Therefore, the inventors investigated a sheet configuration that could suppress blocking between the magnetic layer and the substrate even when subjected to pressurized heat treatment. They found that by forming the outer surface of the substrate with a metal layer, blocking between the magnetic layer and the substrate laminated on the magnetic layer could be suppressed even when calendered. The reason for this will be explained with reference to the drawings.

[0018] Figure 1 is a schematic cross-sectional view showing the electromagnetic noise suppression sheet before pressurized heat treatment, and Figure 2 is a schematic cross-sectional view showing the electromagnetic noise suppression sheet after pressurized heat treatment. In Figure 1, the electromagnetic noise suppression sheet 1 before pressurized heat treatment has a magnetic layer 3 placed on a base material 2, and the base material 2 is composed of a metal layer 2a and a resin layer 2b, with the metal layer 2a placed on the outer surface side of the base material 2. The outer surface side of the magnetic layer 3 in Figure 1 is formed rough due to the protrusion of magnetic particles contained in the magnetic layer 3. On the other hand, the outer surface side of the base material 2 is formed smoothly with the metal layer 2a exposed. When pressurized heat treatment is performed in the state of Figure 1, as shown in Figure 2, the magnetic particles contained in the magnetic layer 3 can be pressed into the magnetic layer, and the protrusion of the magnetic particles can be suppressed to some extent, so the outer surface side of the magnetic layer 3 after pressurized heat treatment in Figure 2 becomes flatter than in Figure 1. On the other hand, since it is not possible to pressurize all of the protrusions of magnetic particles contained in the magnetic layer 3, a certain degree of roughness remains on the outer surface side of the magnetic layer 3, and the outer surface of the magnetic layer 3 in Figure 2 has a surface roughness (Sa1).

[0019] Furthermore, when the magnetic particles are pressed into the magnetic layer by the above pressurized heating treatment, the magnetic particles protrude from the inner surface of the magnetic layer 3 towards the substrate side, causing irregularities on the substrate surface. Irregularities are also created on the outer surface of the metal layer 2a on the outer surface of the substrate, and the outer surface of the metal layer 2a in Figure 2 will have a surface roughness (Sa2).

[0020] Even if the electromagnetic noise suppression sheet 1 is rolled up and stored after pressurized and heat-treated in this state, the outer surface of the magnetic layer 3 and the outer surface of the metal layer 2a each have a certain surface roughness, so blocking between sheets can be suppressed.

[0021] Based on the above findings, further investigation revealed that in the electromagnetic noise suppression sheet of the present invention, blocking between sheets can be suppressed even when subjected to pressurized heat treatment by setting the surface roughness Sa1 of the outer surface of the magnetic layer and the surface roughness Sa2 of the outer surface of the metal layer such that the following relationships (1) and (2) hold: 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2)

[0022] On the other hand, if Sa1 is less than 1.9 μm, and Sa2 is less than 2.0 μm, blocking cannot be suppressed, making it impossible to unwind the sheet, or even if it can be unwound, a part of the magnetic layer may adhere to the substrate and peel off. Furthermore, it was found that if Sa1 is greater than 5.0 μm, and Sa2 is greater than 4.0 μm, air is more likely to enter between the magnetic layer and the metal layer when winding the electromagnetic noise suppression sheet, making it easier for the sheet to be misaligned during winding.

[0023] Furthermore, it was found that the electromagnetic noise suppression sheet of this invention can also suppress blocking between the magnetic layer and the substrate laminated on the magnetic layer by satisfying the following relation (3): 1.0 ≤ Sa1 / Sa2 ≤ 1.9 (3)

[0024] Based on the above, the electromagnetic noise suppression sheet of the present invention can suppress blocking between sheets (between the magnetic layer and the substrate laminated on the magnetic layer) and can improve the characteristic of being able to wind the sheet without winding misalignment (hereinafter referred to as winding neatness).

[0025] In Figures 1 and 2, a composite substrate consisting of a metal layer and a resin layer was used as the base material for the electromagnetic noise suppression sheet, but the same effect can be achieved even if only the metal layer is used as the base material.

[0026] However, by having a substrate that is a laminate of a resin layer and a metal layer, and a magnetic layer on the surface of the resin layer, it is possible to suppress electromagnetic noise and improve the adhesion between the magnetic layer and the substrate.

[0027] Furthermore, in the electromagnetic noise suppression sheet of this embodiment, it is preferable to set the thickness of the metal layer to 5 μm or more and 15 μm or less. If the thickness of the metal layer is less than 5 μm, the shielding performance against electrical noise will decrease, and if the thickness exceeds 15 μm, the thickness of the metal layer will be too large, which may reduce the processability of the electromagnetic noise suppression sheet and make it difficult to wind up the sheet.

[0028] The thickness of the magnetic layer is preferably 10 μm or more and 60 μm or less. If the thickness of the magnetic layer is less than 10 μm, the shielding performance against magnetic noise will decrease, and if the thickness exceeds 60 μm, the flexibility of the magnetic layer will decrease, which may make it difficult to control the surface roughness Sa1 on the outer surface of the magnetic layer and the surface roughness Sa2 on the outer surface of the metal layer by the aforementioned pressurized heat treatment. In addition, the overall thickness of the electromagnetic noise suppression sheet will increase, which may make winding difficult.

[0029] The volume content of the magnetic material in the magnetic layer is preferably 20% by volume or more and 60% by volume or less. If the volume content is less than 20% by volume, the shielding performance against magnetic noise will decrease, and if the volume content is more than 60% by volume, the flexibility of the magnetic layer will decrease, which may make it difficult to control the surface roughness Sa1 on the outer surface of the magnetic layer and the surface roughness Sa2 on the outer surface of the metal layer by the aforementioned calendering treatment.

[0030] The average particle size D of the magnetic material is preferably 3 μm or more and 50 μm or less. If the average particle size D is less than 3 μm, the shielding performance against magnetic noise will decrease, and if the average particle size D is greater than 50 μm, even if the aforementioned pressurized heat treatment is performed, the surface roughness Sa1 on the outer side of the magnetic layer may exceed 5.0 μm, and the surface roughness Sa2 on the outer side of the metal layer may also exceed 4.0 μm, making it easier for air to enter between the magnetic layer and the metal layer, which can easily cause misalignment of the sheet during winding.

[0031] It is preferable that the following relationship (4) holds between the surface roughness Sa1 on the outer surface of the magnetic layer and the average particle diameter D (μm) of the magnetic material: 0.05 ≤ Sa1 / D ≤ 0.8 (4)

[0032] Sa1 / D is a parameter that represents the surface roughness of the magnetic layer based on the average particle size of the magnetic material. Within the above range, in terms of creating irregularities on the substrate side of the electromagnetic noise suppression sheet, it becomes easier to press the protruding magnetic particles into the magnetic layer by pressurized heat treatment. As a result, the arithmetic mean height Sa1 of the magnetic layer can be easily adjusted to a value appropriate for achieving both winding neatness and blocking resistance. The above range is preferably within the range of 0.05 ≤ Sa1 / D ≤ 0.8, and more preferably 0.08 ≤ Sa1 / D ≤ 0.75.

[0033] The electromagnetic noise suppression sheet of this embodiment will now be described based on the drawings. The electromagnetic noise suppression sheet of this embodiment is constructed by laminating a magnetic layer and a base material. Figure 3 is a schematic cross-sectional view showing an example of the electromagnetic noise suppression sheet of this embodiment. In Figure 3, the electromagnetic noise suppression sheet 10 comprises a base material 11 consisting only of a metal layer and a magnetic layer 12 laminated on the base material 11. In Figure 3, the electromagnetic noise suppression sheet 10 is composed of a base material 11 and a magnetic layer 12, but an adhesive layer may also be placed on either of the outer surfaces.

[0034] Figure 4 is a schematic cross-sectional view showing another example of the electromagnetic noise suppression sheet of this embodiment. In Figure 4, the electromagnetic noise suppression sheet 20 comprises a base material 21 and a magnetic layer 22 laminated on the base material 21. The base material 21 is composed of a metal layer 21a and a resin layer 21b. In Figure 4, the electromagnetic noise suppression sheet 20 is composed of a base material 21 and a magnetic layer 22, but an adhesive layer may also be placed on either of the outer surfaces.

[0035] In both Figure 3 and Figure 4, the surface roughness Sa1 on the outer surface of the magnetic layer and the surface roughness Sa2 on the outer surface of the metal layer are set within the ranges of the following relational expressions (1) and (2), however, the actual representation of the surface roughness on the drawings is omitted in Figures 3 and 4. 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2)

[0036] If the combination of Sa1 and Sa2 ranges described above is suitable, the winding performance of the electromagnetic noise suppression sheet will be improved, and interlayer adhesion (blocking) will not occur when stored in a stacked state. On the other hand, if Sa1 and Sa2 are smaller than the above ranges, the sheet surface will be too smooth, resulting in a larger contact area between layers, which will make interlayer adhesion (blocking) more likely to occur. Also, if Sa1 and Sa2 are larger than the above ranges, the sheet surface will be too rough, making it easier for air to be trapped during winding, which will reduce the winding performance.

[0037] Furthermore, when the ratio of Sa1 to Sa2 is in the range of 1.0 ≤ Sa1 / Sa2 ≤ 1.9, the surface roughness of the outer surface of the magnetic layer and the surface roughness of the outer surface of the metal layer are in an appropriate combination, resulting in good winding stability and blocking resistance.

[0038] Furthermore, the ratio of the thickness of the metal layer to the average particle diameter D (μm) of the magnetic material (thickness of the metal layer / D) is preferably 0.2 to 2.0, and more preferably 0.22 to 2.0. This ensures sufficient press-fitting of the magnetic material into the metal layer by pressurized heat treatment, making it easier to adjust the surface roughness Sa2 of the metal layer to within the range of 2.0 μm ≤ Sa2 ≤ 4.0 μm. As a result, the outer surface of the metal layer has a constant surface roughness, resulting in good winding stability and blocking resistance.

[0039] Preferably, the following relationship (5) holds between the surface roughness Sa2 of the outer surface of the metal layer and the average particle diameter D (μm) of the magnetic material: 0.05 ≤ Sa2 / D ≤ 0.7 (5)

[0040] Within the above range, the outer surface of the metal layer has a certain surface roughness, resulting in good winding stability and resistance to blocking. Within the above range, winding stability and resistance to blocking are more preferably exhibited within the range of 0.05 ≤ Sa² / D ≤ 0.61.

[0041] The overall thickness of the electromagnetic noise suppression sheet of this embodiment is preferably 10 to 85 μm, more preferably 20 to 60 μm. If the overall thickness of the electromagnetic noise suppression sheet is too thin, the thickness of the magnetic layer will also be thin, resulting in a decrease in the shielding performance of magnetic noise and a decrease in the strength of the entire sheet. On the other hand, if the overall thickness of the electromagnetic noise suppression sheet is too thick, the flexibility will decrease, making it difficult to wrap around cables and connectors for use.

[0042] Next, each component of the electromagnetic noise suppression sheet of this embodiment will be described.

[0043] <Substrate> The substrate used in the electromagnetic noise suppression sheet of this embodiment serves as a base for forming the magnetic layer. The substrate includes a metal layer, and the thickness of the metal layer is set, for example, to be 5 μm or more and 15 μm or less, and the metal layer is disposed on the outer surface side of the substrate. Also, the substrate can be composed only of the metal layer. Further, the substrate can be composed of a metal layer and a resin layer, and in that case, the resin layer is disposed on the inner surface side of the substrate.

[0044] Since the electromagnetic noise suppression sheet of this embodiment includes a metal layer, it can impart electric field shielding performance to the electromagnetic noise suppression sheet, and can suppress not only magnetic noise but also electric noise. Hereinafter, the components of the substrate will be described.

[0045] [Metal layer] The type of metal constituting the metal layer is not particularly limited as long as it has a certain degree of flexibility and can reflect the surface roughness of the magnetic layer surface to the outer surface side of the metal layer by pressure heat treatment. However, aluminum, copper, permalloy, etc. are preferable. Among aluminum, soft aluminum, and among copper, rolled copper are more preferable because they have high conductivity, are inexpensive, are easy to process into thin films, and have excellent flexibility. In addition to conductivity, permalloy has a high magnetic focusing effect in the kHz region and can also obtain the effect as a magnetic shield.

[0046] As described above, the thickness of the metal layer is set, for example, to be 5 μm or more and 15 μm or less.

[0047] As the above metal layer, it can be used alone as a metal foil, or it can also be formed as a metal thin film by vapor deposition or sputtering on the resin layer that constitutes the base material described later and used.

[0048] [Resin layer] As the resin layer that constitutes the above base material, any material can be used as long as it has flexibility and can ensure adhesion to the magnetic layer. Usually, a resin film is used. Examples of the resin that constitutes the above resin layer include polyolefin resins (such as polyethylene and polypropylene), polyester resins (such as polyethylene terephthalate: PET, polyethylene naphthalate: PEN, polybutylene terephthalate: PBT, polybutylene naphthalate: PBN, etc.), polyimide resins, polyamide resins, ethylene-vinyl acetate copolymers, ionomer resins, ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylate copolymers, ethylene-butene copolymers, ethylene-hexene copolymers, polyurethane resins, polyether ketone resins, polyether resins, polyether sulfone resins, polystyrene resins (such as polystyrene), polyvinyl chloride resins, polyvinylidene chloride resins, polyvinyl alcohol resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate copolymers, polycarbonate resins, fluorine resins, silicone resins, cellulose resins, and cross-linked products of these resins. Among these, polyethylene terephthalate (PET) is more preferable in terms of mechanical properties and price. These resins can be used alone or in combination of two or more. In addition, the above resin may have a functional group as necessary. Also, a functional monomer or a modifying monomer may be grafted onto the resin material.

[0049] The surface of the above resin layer may be subjected to a known surface treatment to improve adhesion to the adjacent magnetic layer. Specific examples of the above surface treatment include, for example, corona discharge treatment, ozone exposure treatment, high-voltage electric shock exposure treatment, ionizing radiation treatment, etc. Also, coating treatment with an undercoat agent (such as silicone treatment), primer treatment, mat treatment, cross-linking treatment, etc. may be applied to the above resin layer.

[0050] The resin layer may be a single layer or a laminate of two or more layers. Furthermore, known additives such as fillers, flame retardants, degradation inhibitors, antistatic agents, softeners, and plasticizers may be added to the resin layer as needed.

[0051] The thickness of the resin layer is not particularly limited, but is preferably 5 to 20 μm, and more preferably 10 to 15 μm. If the thickness of the resin layer is within the above range, both strength and flexibility can be achieved in the electromagnetic noise suppression sheet of this embodiment.

[0052] The above substrate can also be used as a metal-resin composite film by laminating the above metal layer and the above resin layer.

[0053] <Magnetic Layer> The magnetic layer used in the electromagnetic noise suppression sheet of this embodiment functions as an electromagnetic noise suppression layer and contains a magnetic material and a resin. As mentioned above, the thickness of the magnetic layer is preferably 10 μm or more and 60 μm or less. The constituent materials of the magnetic layer will be described below.

[0054] [Magnetic Material] As the above magnetic material, soft magnetic materials and hard magnetic materials can be used, but it is preferable to use soft magnetic materials. Soft magnetic materials have a high initial magnetic permeability and can exhibit magnetic noise shielding performance even when included in a small amount in the magnetic layer, so they can exhibit electromagnetic noise suppression effect even when the magnetic layer is a thin film.

[0055] Examples of the soft magnetic materials mentioned above include iron, carbonyl iron powder, silicon iron, permalloy, FeAlSi alloy, permendur, soft ferrite, ferritic stainless steel, electromagnetic stainless steel, amorphous magnetic alloy, and nanocrystal magnetic alloy. However, carbonyl iron powder represented by Fe(CO)5 is particularly preferred as a soft magnetic material. This is because carbonyl iron powder can exhibit electromagnetic wave absorption performance (electromagnetic noise suppression effect) even in relatively high frequency ranges such as the GHz band.

[0056] Examples of the hard magnetic materials mentioned above include hard ferrite (ferrite magnets), alnico magnets, samarium cobalt magnets, neodymium magnets, samarium iron nitrogen magnets, and epsilon-type iron oxide.

[0057] The magnetic material described above is usually provided as a spherical or flattened powder, and its average particle size D is preferably 3 μm to 50 μm, and more preferably 3 μm to 20 μm, as described above. The average particle size D can be measured using a laser diffraction scattering particle size distribution analyzer. However, the magnetic material powder may also be granular (irregular shape), needle-shaped, etc.

[0058] As mentioned above, the volume content of the magnetic material contained in the magnetic layer is preferably 20% by volume or more and 60% by volume or less.

[0059] [Resin] The resin used in the magnetic layer functions as a binder that holds and fixes the magnetic material and adheres it to the substrate. Preferably, the resin includes an amorphous resin (A) with a glass transition temperature of -50°C to 0°C and an amorphous resin (B) with a glass transition temperature of 10°C or higher. Amorphous resins have high solubility in water and other solvents and excellent dispersibility of magnetic materials (magnetic powder). Therefore, by dispersing magnetic powder in a resin dissolved in water or other solvents, and then coating and drying it on the substrate to an arbitrary thickness, it is possible to form a magnetic layer into a sheet.

[0060] As the amorphous resin (A), amorphous polyester, amorphous polyurethane, amorphous acrylic, etc., having a glass transition temperature of -50°C to 0°C can be used, and as the amorphous resin (B), amorphous polyester, amorphous polyurethane, amorphous acrylic, etc., having a glass transition temperature of 10°C or higher can be used. Among these, amorphous polyester (a) with a glass transition temperature of -50°C to 0°C is particularly preferred as amorphous resin (A), and amorphous polyester (b) with a glass transition temperature of 10°C or higher is particularly preferred as amorphous resin (B). Among amorphous resins, amorphous polyester has excellent solubility and flexibility and is suitable for manufacturing sheet-like magnetic layers.

[0061] From the above viewpoint, the content ratio of amorphous polyester (a) and amorphous polyester (b) is preferably (a):(b) = 95:5 to 35:65 by mass ratio, and more preferably (a):(b) = 90:10 to 50:50. The content ratio of amorphous polyester (a) and (b) can be estimated to some extent from the intensity of the two glass transition temperature peaks detected by measuring the glass transition temperature of the magnetic layer. The glass transition temperature can be measured by differential scanning calorimeter (DSC).

[0062] Examples of the amorphous polyesters (a) and (b) mentioned above include "Byron" (registered trademark) manufactured by Toyobo Co., Ltd., "Pluscoat" (registered trademark) manufactured by Go-O Chemical Co., Ltd., "Nichigo Polyester" (registered trademark) manufactured by Mitsubishi Chemical Corporation, and "Almatex" (registered trademark) manufactured by Mitsui Chemicals, Inc. Because these have excellent solubility in water and organic solvents, they can be used by dissolving them in water or organic solvents in any proportion.

[0063] Furthermore, it is preferable that at least one of the amorphous polyester (a) and the amorphous polyester (b) includes a crosslinked portion formed by amide bonds. This further improves the adhesion of the magnetic layer to the substrate. Typically, the amorphous polyesters (a) and (b) have carboxyl groups at least at their molecular ends, and carboxyl groups can be optionally added to their molecular chains. Therefore, by using a crosslinking agent, a crosslinked portion formed by amide bonds can be formed.

[0064] Next, the electromagnetic noise suppression characteristics of the electromagnetic noise suppression sheet of this embodiment will be described. The electromagnetic noise suppression sheet of this embodiment can reduce the mutual decoupling ratio (Rde) in the frequency range of 100 MHz to 6 GHz to -20 dB or less. The mutual decoupling ratio (Rde) indicates the effect of suppressing electromagnetic noise transmission between two circuit boards, and the smaller the value of the mutual decoupling ratio (Rde), the greater the electromagnetic noise suppression effect of the electromagnetic noise suppression sheet.

[0065] The decoupling ratio (Rde) of the electromagnetic noise suppression sheet was measured in accordance with IEC 62333. Specifically, the decoupling ratio was measured using an Anritsu Corporation vector network analyzer "MS46122B-043" and a Keycom Corporation loop antenna "IT-IB-6B," connected with a Junko Co., Ltd. coaxial cable "MWX051-03000KFSKMS / B" (3m).

[0066] The vector network analyzer was pre-calibrated using SOLT (Short-Open-Load-Thru) and measured using Keycom's analysis software "DMP-002041020-09 measurement program". The frequency range was 0.1 GHz to 6 GHz, and measurement points were set up with 401 logarithmic scaling points. First, the electromagnetic wave transmission attenuation (S21R) was measured without placing an electromagnetic noise suppression sheet between the loop antennas. Then, the electromagnetic wave transmission attenuation (S21M) was measured with a 50 mm x 50 mm electromagnetic noise suppression sheet placed between the loop antennas, and the mutual decoupling ratio (Rde) was calculated using the following formula (1).

[0067] Formula (1):

[0068] (Method for Manufacturing an Electromagnetic Noise Suppression Sheet) An embodiment of the method for manufacturing an electromagnetic noise suppression sheet of the present invention will be described. The method for manufacturing an electromagnetic noise suppression sheet of the present invention of this embodiment is a method for manufacturing the electromagnetic noise suppression sheet of the present invention as described above, and comprises: a first step of mixing a magnetic material, a resin, and a solvent to produce a coating for forming a magnetic layer; a second step of applying the coating for forming a magnetic layer to a substrate and drying it to produce a magnetic layer / substrate laminated sheet; and a third step of pressurizing and heating the magnetic layer / substrate laminated sheet, wherein the substrate includes a metal layer, and in the substrate, the metal layer is arranged on the side opposite to the side to which the coating for forming a magnetic layer is applied, and at the end of the third step, if the surface roughness is defined by the arithmetic mean height Sa, and the surface roughness on the outer side of the magnetic layer is Sa1 and the surface roughness on the outer side of the metal layer is Sa2, then the following relational expressions (1) and (2) hold true. 1.9μm≦Sa1≦5.0μm (1) 2.0μm≦Sa2≦4.0μm (2)

[0069] <Paint for forming a magnetic layer> The above-mentioned paint for forming a magnetic layer can be made by mixing a magnetic material, a resin, and a solvent.

[0070] The magnetic material and resin described above are the same as those that constitute the magnetic layer of the electromagnetic noise suppression sheet in the embodiment of the present invention described above.

[0071] Examples of solvents that can be used include water, ethyl alcohol, methyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, ethylene glycol, propylene glycol, methyl ethyl ketone, ethyl acetate, toluene, and the like.

[0072] The content of the above solvent is not particularly limited, but it should be 50.0% by mass or more and 99.5% by mass or less, relative to the total mass of the magnetic layer forming coating.

[0073] The above-mentioned coating for forming a magnetic layer may further contain surface modifiers, defoamers, thickeners, etc.

[0074] <Formation of Magnetic Layer> As a method for applying the above-mentioned magnetic layer-forming coating onto the substrate, for example, coating methods such as bar coating, reverse coating, gravure coating, microgravure® coating, die coating, dipping, spin coating, slit coating, and spray coating can be used.

[0075] The drying after coating as described above can be carried out under conditions that allow the solvent component of the magnetic layer-forming coating to evaporate, and is preferably done at 80 to 150°C for 3 to 30 minutes. If solvent remains in the magnetic layer, the strength tends to be inferior. Drying methods include, for example, hot air drying, heating drying, vacuum drying, and natural drying.

[0076] The above pressurized heat treatment can be carried out using metal rolls or resin rolls. Furthermore, when forming the magnetic layer on a single sheet, the pressurized heat treatment can be performed by press working. In the pressurized heat treatment, it is preferable to carry it out at a temperature above the glass transition temperature (Tg) of the resin used for the formed magnetic layer, and more preferably at a temperature 20°C or higher than Tg. The pressure for the pressurized heat treatment is preferably 250 kg / cm or higher in the case of calendering using metal rolls or resin rolls. In the case of press working, it is preferably 200 kg / cm. 2 The above pressure is preferable. The calendering and pressing processes may be performed multiple times.

[0077] As explained above using Figures 1 and 2, the above pressurized heating treatment allows the following relationships to be satisfied at the end of the third step, where Sa1 is the surface roughness of the outer surface of the magnetic layer and Sa2 is the surface roughness of the outer surface of the metal layer: (1) and (2) below. 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2)

[0078] (Communication Cable) An embodiment of the communication cable of the present invention will now be described. The communication cable of this embodiment is characterized by comprising the electromagnetic noise suppression sheet of the embodiment of the present invention described above. The communication cable of this embodiment includes coaxial cables, twisted pair cables, multi-core cables, etc. In particular, coaxial cables are used for high-frequency transmission and are used for video cable applications.

[0079] The following describes a coaxial cable, which is one of the communication cables in this embodiment, based on the drawings. In the coaxial cable described below, the electromagnetic noise suppression sheet of this application is used as the electromagnetic noise suppression layer of the coaxial cable.

[0080] Figure 5 is a schematic cross-sectional view showing an example of a coaxial cable. The coaxial cable 30 comprises an internal conductor 31, an insulating layer 32, a metal foil 33, a metal braid 34, an electromagnetic noise suppression layer 35, and an outer covering layer 36. The electromagnetic noise suppression layer 35 uses the electromagnetic noise suppression sheet of the present invention described above, and is composed of a base layer 35a and a magnetic layer 35b arranged on one side of the base layer 35a.

[0081] In Figure 5, the magnetic layer 35b of the electromagnetic noise suppression layer 35 is positioned on the axial side, but the base material layer 35a may also be positioned on the axial side.

[0082] The electromagnetic noise suppression layer 35 of the coaxial cable 30 can be formed by wrapping the electromagnetic noise suppression sheet of this invention around the outer surface of a linear conductor consisting of an internal conductor 31, an insulating layer 32, a metal foil 33, and a metal braid 34. This allows for a thinner electromagnetic noise suppression layer and shorter processing time.

[0083] (Electronic Device) An embodiment of the electronic device of the present invention will now be described. The electronic device of this embodiment is characterized by comprising the electromagnetic noise suppression sheet of the embodiment of the present invention described above. This makes it possible to use the electromagnetic noise suppression sheet of the present invention as an electromagnetic noise suppression member of the electronic device. Specifically, in the electronic device of this embodiment, for example, the electromagnetic noise suppression sheet of the present invention is placed on the uneven surfaces and corners of electronic equipment that emits electromagnetic noise or electronic equipment that is to be protected from electromagnetic noise. Furthermore, the electromagnetic noise suppression sheet of the present invention can also be used as a substitute for ferrite cores used in cables for electronic equipment.

[0084] The present application will be described in detail below using examples. However, the present application is not limited to the following examples. Unless otherwise specified, "parts" below means "parts by mass".

[0085] (Example 1) <Preparation of magnetic layer forming paint> A magnetic layer forming paint was prepared by mixing and dispersing the following components. (1) Soft magnetic material (flattened carbonyl iron powder manufactured by Tenichi Co., Ltd., product name "RPZ", Fe content: 99.0% by mass, average particle size: 15 μm): 33.7 parts (2) Amorphous polyester (a) (water-soluble polyester resin solution, manufactured by Goyo Chemical Co., Ltd., product name "Pluscoat Z-3310", resin Tg: -20℃, solids concentration: 25.0% by mass, solvent: water): 27.2 parts (3) Amorphous polyester (b) (water-soluble polyester resin solution, manufactured by Goyo Chemical Co., Ltd., product name "Pluscoat Z-730", resin Tg: 43℃, solids concentration: 25.0% by mass, solvent: water): 11.7 parts (4) Crosslinking agent (oxazoline group-containing polymer, manufactured by Nippon Shokubai Co., Ltd., product name "Epocross WS500", solids concentration: 40.0% by mass, solvent: water): 4.0 parts (5) Solvent (n-propyl alcohol): 13.5 parts (6) Pure water: 10.0 parts

[0086] In the above-mentioned coating for forming a magnetic layer, the content ratio of amorphous polyesters (a) and (b) was (a):(b) = 70:30 in terms of solid content mass ratio, and the volume content of the soft magnetic material relative to the total solid content of the above-mentioned coating for forming a magnetic layer was 39%.

[0087] <Formation of Magnetic Layer> Next, an aluminum foil / PET composite film (manufactured by Daido Chemical Co., Ltd., product name "Alpet #1012"), which was made by laminating a 10 μm thick aluminum foil and a 12 μm thick PET film, was used as a base material. The above-mentioned magnetic layer forming coating was applied to the PET surface of the base material using a comma direct application method so that the thickness of the magnetic layer after calendering would be 40 μm, and it was dried at 100°C. Subsequently, the electromagnetic noise suppression sheet of Example 1 was produced by calendering the raw material roll with a metal roll in a calendering device at a temperature of 80°C and a linear pressure of 300 kg / cm, thereby forming a magnetic layer on the PET surface.

[0088] (Example 2) An electromagnetic noise suppression sheet of Example 2 was prepared in the same manner as in Example 1, except that the soft magnetic material was changed to spherical carbonyl iron powder manufactured by Tenichi Co., Ltd. (product name "YW3", Fe content: 97.5% by mass, average particle size: 5 μm), and the volume content of the soft magnetic material relative to the total solid content of the coating for forming the magnetic layer was changed to 56%.

[0089] (Example 3) An electromagnetic noise suppression sheet of Example 3 was prepared in the same manner as in Example 1, except that the soft magnetic material was changed to flat Fe-Si-Al alloy powder manufactured by Sanyo Special Steel Co., Ltd. (product name "FME3D-AH", average particle size: 45 μm), and the volume content of the soft magnetic material relative to the total solid content of the coating for forming the magnetic layer was changed to 35%.

[0090] (Example 4) An electromagnetic noise suppression sheet for Example 4 was prepared in the same manner as in Example 1, except that the thickness of the aluminum foil base material was changed to 5 μm.

[0091] (Example 5) An electromagnetic noise suppression sheet for Example 5 was prepared in the same manner as in Example 1, except that the thickness of the aluminum foil base material was changed to 15 μm.

[0092] (Example 6) An electromagnetic noise suppression sheet of Example 6 was prepared in the same manner as in Example 1, except that the thickness of the magnetic layer was changed to 10 μm and the volume content of the soft magnetic material relative to the total solid content of the coating for forming the magnetic layer was changed to 21%.

[0093] (Example 7) An electromagnetic noise suppression sheet for Example 7 was prepared in the same manner as in Example 1, except that the calendering conditions were changed to a temperature of 80°C and a linear pressure of 100 kg / cm.

[0094] (Comparative Example 1) An electromagnetic noise suppression sheet of Comparative Example 1 was prepared in the same manner as in Example 1, except that calendering was not performed in the magnetic layer formation process.

[0095] (Comparative Example 2) An electromagnetic noise suppression sheet for Comparative Example 2 was prepared in the same manner as in Example 2, except that calendering was not performed in the magnetic layer formation process.

[0096] (Comparative Example 3) An electromagnetic noise suppression sheet of Comparative Example 3 was prepared in the same manner as in Example 3, except that calendering was not performed in the magnetic layer formation process.

[0097] (Comparative Example 4) An electromagnetic noise suppression sheet for Comparative Example 4 was prepared in the same manner as in Example 1, except that the thickness of the aluminum foil base material was changed to 1 μm and the thickness of the magnetic layer was changed to 10 μm.

[0098] (Comparative Example 5) An electromagnetic noise suppression sheet for Comparative Example 5 was prepared in the same manner as in Example 1, except that the thickness of the aluminum foil base material was changed to 20 μm.

[0099] (Comparative Example 6) An electromagnetic noise suppression sheet for Comparative Example 6 was prepared in the same manner as in Example 1, except that the aluminum side of the aluminum foil / PET composite film used in Example 1 was sandblasted to a surface roughness Sa of 4 μm.

[0100] The electromagnetic noise suppression sheets of Examples 1 to 7 and Comparative Examples 1 to 6 were subjected to the following measurements, and the results are shown in Tables 1 and 2.

[0101] <Surface Roughness (Arithmetic Mean Height Sa)> The surface roughness Sa1 of the outer magnetic layer and the surface roughness Sa2 of the outer metal layer of the fabricated electromagnetic noise suppression sheet were measured at a magnification of 50x using a KEYENCE digital microscope "VHX-X1" (product name), a high-resolution head "VHX-7100" (product name), and a high-resolution low-magnification objective lens "VHX-E20" (product name). In addition, the VHX application from KEYENCE was used as the application.

[0102] The above measurements were performed by observing the measurement surface from directly above while tension was applied to the fabricated electromagnetic noise suppression sheet, and creating a depth composite image. For shape correction, "sphere / cylindrical correction (correction strength 1)" was applied, and an arbitrary range of 3000 μm × 3000 μm was specified, and the arithmetic mean height Sa was calculated as an index of surface roughness.

[0103] <Winding Neatness> A 100m length of electromagnetic noise suppression sheet, slit to 8mm width, was wound onto a polycarbonate hub with an inner diameter of 3 inches, an outer diameter of 3.2 inches, and a width of 12mm, under a winding tension of 50g, to create a winding sample. This winding sample was stored for 48 hours in a temperature and humidity environment of 40°C and 70% humidity, with the hub of the winding sample in a horizontal position. The vertical winding misalignment of the sheet in the winding sample was observed, and the winding neatness was evaluated according to the following criteria: Evaluation A (Good): Winding misalignment from the initial winding position is within 1mm. Evaluation B (Poor): Winding misalignment from the initial winding position exceeds 1mm.

[0104] <Blocking Resistance> A 100m length of electromagnetic noise suppression sheet, slit to 8mm width, was wound onto a polycarbonate hub with an inner diameter of 3 inches, an outer diameter of 3.2 inches, and a width of 12mm, under a winding tension of 50g. This wound sample was stored for 48 hours in a temperature and humidity environment of 40°C and 70% humidity. Afterward, the sheet was unwound from the wound sample under an unwinding tension of 50g, and the presence or absence of adhesion between sheets was observed. Blocking resistance was evaluated according to the following criteria: Evaluation A (Good): No adhesion between sheets was observed. Evaluation B (Poor): Adhesion between sheets was observed.

[0105] <Magnetic Noise Suppression Effect> The magnetic noise suppression effect of the fabricated electromagnetic noise suppression sheet was evaluated by measuring the mutual decoupling ratio (Rde) using the measurement method described above. The smaller the value of the mutual decoupling ratio (Rde), the greater the electromagnetic noise suppression effect of the electromagnetic noise suppression sheet.

[0106] The results described above, along with the configuration of the fabricated electromagnetic noise suppression sheet, are shown in Tables 1 and 2.

[0107]

[0108]

[0109] Tables 1 and 2 show that the electromagnetic noise suppression sheets of Examples 1 to 7 yielded good results in terms of winding ability and blocking resistance, and demonstrated a sufficient magnetic noise suppression effect. On the other hand, the electromagnetic noise suppression sheets of Comparative Examples 1 to 6 were inferior in at least one of the following: winding ability or blocking resistance, and Comparative Example 4 also showed inferior magnetic noise suppression effect.

[0110] With respect to embodiments of the present application including the above-described examples 1 to 7, the following additional embodiments are further disclosed. (Additional Embodiment 1) An electromagnetic noise suppression sheet comprising a magnetic layer and a substrate laminated together, wherein the magnetic layer comprises a magnetic material and a resin, the substrate comprises a metal layer, the metal layer is disposed on the outer surface side of the substrate, and the surface roughness is defined by the arithmetic mean height Sa, and if the surface roughness on the outer surface side of the magnetic layer is Sa1 and the surface roughness on the outer surface side of the metal layer is Sa2, then the following relational expressions (1) and (2) hold true. (1) 1.9 μm ≤ Sa1 ≤ 5.0 μm (2) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2) (Additional Embodiment 2) The electromagnetic noise suppression sheet according to Additional Embodiment 1, wherein the thickness of the metal layer is 5 μm or more and 15 μm or less. (Appendix Form 3) An electromagnetic noise suppression sheet comprising a magnetic layer and a substrate laminated together, wherein the magnetic layer comprises a magnetic material and a resin, the substrate comprises a metal layer, the thickness of the metal layer is 5 μm or more and 15 μm or less, the metal layer is arranged on the outer surface side of the substrate, and the surface roughness is defined by the arithmetic mean height Sa, with Sa1 being the surface roughness on the outer surface side of the magnetic layer and Sa2 being the surface roughness on the outer surface side of the metal layer, characterized in that the following relational expressions (1) and (2) hold true. 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2) (Appendix Form 4) An electromagnetic noise suppression sheet according to any of the appendix forms 1 to 3, wherein the following relational expression (3) holds true. 1.0 ≤ Sa1 / Sa2 ≤ 1.9 (3) (Appendix 5) The electromagnetic noise suppression sheet according to any one of appendix forms 1 to 4, wherein the substrate further comprises a resin layer, and the resin layer is located on the inner surface side of the substrate. (Appendix 6) The electromagnetic noise suppression sheet according to any one of appendix forms 1 to 5, wherein the thickness of the magnetic layer is 10 μm or more and 60 μm or less. (Appendix 7) The electromagnetic noise suppression sheet according to any one of appendix forms 1 to 6, wherein the volume content of the magnetic material contained in the magnetic layer is 20 volume% or more and 60 volume% or less. (Appendix 8) The electromagnetic noise suppression sheet according to any one of appendix forms 1 to 7, wherein the following relational expression (4) holds true, given that Sa1 is the surface roughness on the outer surface side of the magnetic layer and D (μm) is the average particle diameter of the magnetic material.0.05 ≤ Sa1 / D ≤ 0.8 (4) (Appendix 9) An electromagnetic noise suppression sheet according to any of appendix forms 1 to 8, wherein the average particle diameter D of the magnetic material is 3 μm or more and 50 μm or less. (Appendix 10) An electromagnetic noise suppression sheet according to any of appendix forms 1 to 9, wherein the magnetic material includes a soft magnetic material. (Appendix 11) An electromagnetic noise suppression sheet according to appendix form 10, wherein the soft magnetic material is carbonyl iron powder. (Appendix 12) An electromagnetic noise suppression sheet according to any of appendix forms 1 to 11, wherein the mutual decoupling rate (Rde) in the frequency range of 100 MHz to 6 GHz is -20 dB or less. (Appendix 13) A communication cable characterized by including an electromagnetic noise suppression sheet according to any of appendix forms 1 to 12. (Appendix 14) An electronic device characterized by including an electromagnetic noise suppression sheet according to any of appendix forms 1 to 12. (Appendix Form 15) A method for manufacturing an electromagnetic noise suppression sheet according to any of the appendix forms 1 to 12, comprising: a first step of mixing a magnetic material, a resin, and a solvent to produce a coating for forming a magnetic layer; a second step of applying the coating for forming a magnetic layer to a substrate and drying it to produce a magnetic layer / substrate laminated sheet; and a third step of pressurizing and heating the magnetic layer / substrate laminated sheet, wherein the substrate includes a metal layer, the metal layer is arranged on the side of the substrate opposite to the side to which the coating for forming a magnetic layer is applied, and at the end of the third step, if the surface roughness is defined by the arithmetic mean height Sa, and the surface roughness on the outer side of the magnetic layer is Sa1 and the surface roughness on the outer side of the metal layer is Sa2, then the following relational expressions (1) and (2) hold true, characterized in that the method for manufacturing an electromagnetic noise suppression sheet. 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2) (Appendix 16) A method for manufacturing an electromagnetic noise suppression sheet according to appendix 15, wherein the solvent contained in the magnetic layer forming coating is at least one selected from water and a water-soluble solvent.

[0111] This application can also be implemented in forms other than those described above. The embodiments disclosed herein are examples and are not limiting. The scope of this application shall be interpreted in accordance with the claims attached, which take precedence over the description in the above specification, and all modifications within the scope equivalent to the claims shall be included in the claims.

[0112] 1, 10, 20 Electromagnetic noise suppression sheet 2, 11, 21 Base material 2a, 21a Metal layer 2b, 21b Resin layer 3, 12, 22 Magnetic layer 30 Coaxial cable 31 Internal conductor 32 Insulating layer 33 Metal foil 34 Metal braided body 35 Electromagnetic noise suppression layer 35a Base material layer 35b Magnetic layer 36 outer coating layer

Claims

1. An electromagnetic noise suppression sheet comprising a magnetic layer and a substrate laminated together, wherein the magnetic layer comprises a magnetic material and a resin, the substrate comprises a metal layer, the metal layer is disposed on the outer surface side of the substrate, and the surface roughness is defined by the arithmetic mean height Sa, with Sa1 being the surface roughness on the outer surface side of the magnetic layer and Sa2 being the surface roughness on the outer surface side of the metal layer, such that the following relational expressions (1) and (2) hold: 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2) 2. The electromagnetic noise suppression sheet according to claim 1, wherein the thickness of the metal layer is 5 μm or more and 15 μm or less.

3. An electromagnetic noise suppression sheet comprising a magnetic layer and a substrate laminated together, wherein the magnetic layer comprises a magnetic material and a resin, the substrate comprises a metal layer, the thickness of the metal layer is 5 μm or more and 15 μm or less, the metal layer is arranged on the outer surface side of the substrate, and the surface roughness is defined by the arithmetic mean height Sa, with Sa1 being the surface roughness on the outer surface side of the magnetic layer and Sa2 being the surface roughness on the outer surface side of the metal layer, such that the following relational expressions (1) and (2) hold: 1.9 μm ≤ Sa1 ≤ 5.0 μm (1) 2.0 μm ≤ Sa2 ≤ 4.0 μm (2) 4. An electromagnetic noise suppression sheet according to any one of claims 1 to 3, such that the following relation (3) holds: 1.0 ≤ Sa1 / Sa2 ≤ 1.9 (3) 5. The electromagnetic noise suppression sheet according to any one of claims 1 to 4, wherein the substrate further comprises a resin layer, and the resin layer is disposed on the inner surface side of the substrate.

6. The electromagnetic noise suppression sheet according to any one of claims 1 to 5, wherein the thickness of the magnetic layer is 10 μm or more and 60 μm or less.

7. The electromagnetic noise suppression sheet according to any one of claims 1 to 6, wherein the volume content of the magnetic material contained in the magnetic layer is 20 volume% or more and 60 volume% or less.

8. An electromagnetic noise suppression sheet according to any one of claims 1 to 7, wherein the following relation (4) holds true, where Sa1 is the surface roughness of the outer surface of the magnetic layer and D (μm) is the average particle diameter of the magnetic material: 0.05 ≤ Sa1 / D ≤ 0.8 (4) 9. The electromagnetic noise suppression sheet according to any one of claims 1 to 8, wherein the average particle diameter D of the magnetic material is 3 μm or more and 50 μm or less.

10. The electromagnetic noise suppression sheet according to any one of claims 1 to 9, wherein the magnetic material includes a soft magnetic material.

11. The electromagnetic noise suppression sheet according to claim 10, wherein the soft magnetic material is carbonyl iron powder.

12. An electromagnetic noise suppression sheet according to any one of claims 1 to 11, wherein the mutual decoupling ratio (Rde) in the frequency range of 100 MHz to 6 GHz is -20 dB or less.

13. A communication cable characterized by including an electromagnetic noise suppression sheet according to any one of claims 1 to 12.

14. An electronic device characterized by including an electromagnetic noise suppression sheet according to any one of claims 1 to 12.

15. A method for manufacturing an electromagnetic noise suppression sheet according to any one of claims 1 to 12, comprising: a first step of mixing a magnetic material, a resin, and a solvent to produce a coating for forming a magnetic layer; a second step of applying the coating for forming a magnetic layer to a substrate and drying it to produce a laminated magnetic layer / substrate sheet; and a third step of pressurizing and heating the laminated magnetic layer / substrate sheet, wherein the substrate includes a metal layer, the metal layer is arranged on the side of the substrate opposite to the side to which the coating for forming the magnetic layer is applied, and at the end of the third step, if the surface roughness is defined by the arithmetic mean height Sa, and the surface roughness on the outer side of the magnetic layer is Sa1 and the surface roughness on the outer side of the metal layer is Sa2, then the following relational expressions (1) and (2) hold true.

16. The method for manufacturing an electromagnetic noise suppression sheet according to claim 15, wherein the solvent contained in the magnetic layer forming paint is at least one selected from water and a water-soluble solvent.

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