Electromagnetic noise suppression film, and electromagnetic noise suppression sheet, communication cable, and electronic device that use said electromagnetic noise suppression film

Abstract

An electromagnetic noise suppression film according to the present application includes a magnetic layer, and the magnetic layer includes a spherical soft magnetic body and a binder. When a magnetic field of 10 kOe is applied from the outside in an in-plane direction of the magnetic layer, and the magnetization amount per unit area in the in-plane direction of the magnetic layer is defined as M10t, the transmission attenuation rate with respect to the magnetization amount M10t per unit area, as measured by a microstrip line method at 28 GHz, is at least 3 dB•cm2 / emu. An electromagnetic noise suppression sheet according to the present application comprises a substrate and the electromagnetic noise suppression film according to the present application.

Description

Electromagnetic noise suppression film, and electromagnetic noise suppression sheet, communication cable, and electronic device using said electromagnetic noise suppression film

[0001] The present application relates to an electromagnetic noise suppression film that absorbs electromagnetic waves in the GHz band.

[0002] With the advancement of wireless communication technologies, typified by mobile phones, various devices and sensors are now wirelessly connected to networks. Furthermore, in the medical field, cordless devices are becoming increasingly common to prevent infection, and medical devices are beginning to connect wirelessly. These communications require high speed and large capacity over relatively short distances, and therefore use high frequencies. With the increase in devices using such high frequencies, the risk of malfunctions in electronic devices and communications due to malfunctions caused by electromagnetic noise generated by the devices and interference with the electromagnetic waves used is increasing. Furthermore, in recent years, millimeter-wave radar has begun to be installed in vehicles to prevent automobile collisions. Since malfunctions in these medical and automotive devices could affect human lives, malfunctions must be avoided. Therefore, there is a growing need to apply electromagnetic noise suppression films to circuit elements and transmission lines that emit and receive electromagnetic waves in the GHz band to prevent malfunctions caused by electromagnetic noise and the resulting interference in devices, a so-called EMC (Electromagnetic Compatibility) measure.

[0003] Generally, the transmission attenuation rate in the microstrip line method, which is an index of the electromagnetic noise suppression performance of an electromagnetic noise suppression film using a magnetic material, increases as the imaginary part of the magnetic permeability of the electromagnetic noise suppression film increases, thereby improving the electromagnetic noise suppression performance. However, the magnetic permeability of a typical iron oxide magnetic material used as an electromagnetic wave absorbing material in an electromagnetic noise suppression film remains almost constant up to a certain frequency as the frequency is gradually increased, and then increases as the frequency increases, reaching a maximum value at a specific frequency of several GHz. Thereafter, the magnetic permeability decreases almost inversely proportional to the frequency, and eventually the real part of the magnetic permeability becomes 1 and the imaginary part becomes 0. The frequency at which the magnetic permeability decreases is the limit frequency (limit frequency) at which the magnetic material can be used practically, and is called the snake's limit.

[0004] Here, the greater the anisotropic magnetic field, the higher the limiting frequency. Therefore, conventionally, the shape of the magnetic material has been made closer to a sphere, thereby eliminating the shape magnetic anisotropy of the magnetic material, increasing the anisotropic magnetic field of the magnetic material particles, shifting the limiting frequency toward higher frequencies, and expanding the frequency range in which the magnetic material can be used toward the high-frequency band.

[0005] However, reducing the shape magnetic anisotropy by making the shape of the magnetic material closer to a sphere leads to a decrease in the imaginary part of the magnetic permeability of the magnetic material, and therefore, although using a spherical magnetic material as an electromagnetic noise absorption material in an electromagnetic noise suppression film widens the practical frequency range, it leads to a decrease in the imaginary part of the magnetic permeability of the electromagnetic noise suppression film, resulting in a problem of decreased electromagnetic wave noise suppression performance.

[0006] JP 2000-138492 A JP 2005-340318 A

[0007] The present application solves the above problem by providing a magnetic noise suppression film that has a high electromagnetic wave absorption capacity relative to the amount of magnetization per unit area of ​​the electromagnetic noise suppression layer (magnetic layer) even when using spherical soft magnetic materials.

[0008] Prior art documents related to the electromagnetic noise suppression sheet of the present application include Patent Document 1 and Patent Document 2. Patent Document 1 discloses an electromagnetic wave absorber having a thickness of 1 mm and containing spherical carbonyl iron with a particle size of 4 μm or less, and which has been subjected to a calendering process. Patent Document 2 discloses an electromagnetic wave absorber having a thickness of 1 to 3 mm and containing substantially spherical carbonyl iron with an average particle size of 1 to 10 μm.

[0009] The electromagnetic noise suppression film of the present application includes a magnetic layer, the magnetic layer including spherical soft magnetic material and a binder, and when a magnetic field of 10 kOe is applied from the outside in the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M 10 t, the magnetization amount M 10 The transmission attenuation rate for the amount of magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 / emu or more.

[0010] The electromagnetic noise suppression sheet of the present invention is characterized by including a substrate and the electromagnetic noise suppression film of the present invention.

[0011] The communication cable of the present application is characterized by including the electromagnetic noise suppression film or the electromagnetic noise suppression sheet of the present application.

[0012] The electronic device of the present application is characterized by including the electromagnetic noise suppression film or the electromagnetic noise suppression sheet of the present application.

[0013] According to the present invention, even when spherical soft magnetic materials are used, it is possible to provide a magnetic noise suppression film having a high electromagnetic wave absorption amount relative to the amount of magnetization per unit area of ​​the electromagnetic noise suppression layer (magnetic layer).

[0014] Fig. 1 is a schematic side view showing a cylindrical measurement sample for measuring magnetic properties. Fig. 2 is a diagram showing an example of a hysteresis curve obtained by measuring magnetic properties. Fig. 3 is a schematic cross-sectional view showing an example of an electromagnetic noise suppression sheet according to an embodiment. Fig. 4 is a schematic cross-sectional view showing another example of an electromagnetic noise suppression sheet according to an embodiment. Fig. 5 is a schematic cross-sectional view showing an example of a coaxial cable, which is one of the communication cables according to an embodiment.

[0015] (Electromagnetic Noise Suppression Film) An embodiment of an electromagnetic noise suppression film of the present invention will be described. The electromagnetic noise suppression film of this embodiment includes a magnetic layer, and the magnetic layer contains spherical soft magnetic material and a binder. When a magnetic field of 10 kOe is applied externally in the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M 10 t, the magnetization amount M 10 The transmission attenuation rate for the amount of magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 / emu or more.

[0016] The electromagnetic noise suppression film of the present application uses a spherical soft magnetic material as the electromagnetic wave absorbing material. As described above, this increases the anisotropy magnetic field of the magnetic material, shifts the threshold frequency to the higher frequency side, and widens the frequency range in which the soft magnetic material can be used toward the higher frequency band. On the other hand, reducing the shape magnetic anisotropy by making the shape of the soft magnetic material closer to a sphere leads to a decrease in the imaginary part of the magnetic permeability of the magnetic material. Therefore, when a spherical soft magnetic material is used as the electromagnetic wave absorbing material in an electromagnetic noise suppression film, the decrease in the imaginary part of the magnetic permeability of the electromagnetic noise suppression film causes a problem of decreased electromagnetic noise suppression performance.

[0017] In the electromagnetic noise suppression film of the present invention, in order to solve the above problems, the magnetic layer is made thinner. This makes it possible to increase the electromagnetic wave absorption capacity of the electromagnetic noise suppression film even when a soft magnetic material with reduced magnetic permeability due to being spherical is used as the electromagnetic wave absorbing material. The reason for this is explained below.

[0018] That is, in the general manufacturing process of a magnetic layer, after forming a thin-film magnetic layer using fine-particle magnetic material, it is known that the magnetic permeability of the magnetic layer is improved by performing a calendering process to pack the magnetic fine particles closely together. This is because the packing of the magnetic fine particles by calendering reduces the spacing between the magnetic fine particles in the magnetic layer, increasing the magnetic interaction between each magnetic fine particle. When a magnetic field is applied from the outside under such conditions, the magnetic interaction between the magnetic fine particles cancels out part of the demagnetizing field generated in each magnetic fine particle, and the other part of the demagnetizing field acts in the direction of the applied magnetic field, resulting in a positive effect on the magnetic layer as a whole in the direction of the applied magnetic field, thereby improving the magnetic permeability of the magnetic layer. This effect of improving the magnetic permeability due to the demagnetizing field is particularly significant when a soft magnetic material is used.

[0019] Therefore, the inventors of the present invention have conducted extensive research, thinking that even if a magnetic layer is formed using a soft magnetic material whose magnetic permeability has been reduced by spheroidizing the magnetic material, if the magnetic layer is subjected to a calendering process, the spherical magnetic particles can be packed more densely than conventional non-spherical magnetic particles, the intervals between the spherical magnetic particles in the magnetic layer can be made closer, and the magnetic permeability of the magnetic layer can be further improved. As a result, they have found that the transmission attenuation rate measured by the microstrip line method at a specific frequency relative to the amount of magnetization per unit area in the in-plane direction of the magnetic layer, which indicates the degree of packing of the magnetic particles in the magnetic layer, can be reduced to 3 dB cm. 2 / emu or more and setting the transmission attenuation rate relative to the amount of magnetization per unit area within a specific range. That is, the present application is characterized by not simply specifying the range of the transmission attenuation rate of the electromagnetic noise suppression film, but setting the transmission attenuation rate relative to the amount of magnetization per unit area, which is related to the packing of the spherical magnetic particles, within a specific range.

[0020] Furthermore, it has been found that the in-plane magnetic anisotropy of the magnetic layer can be increased by setting the thickness of the magnetic layer to 5 μm or more and less than 60 μm. Here, for example, in order to set the thickness of the magnetic layer to 5 μm or more and less than 60 μm, it is preferable that the particle diameter of the spherical soft magnetic material is less than 60 μm and is equal to or less than the thickness of the magnetic layer. It is thought that when the magnetic layer is formed using spherical soft magnetic fine particles with such particle diameters, the spherical soft magnetic fine particles are more densely packed by the calendaring process, the magnetic interaction between the spherical soft magnetic fine particles is more significant, and the magnetic permeability of the magnetic layer is further improved.

[0021] From the above investigation, it has been found that in the electromagnetic noise suppression film of this embodiment, when a magnetic field of 10 kOe is applied from the outside in the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M 10 t, the magnetization amount M 10 The transmission attenuation rate for the magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 It was confirmed that it is possible to increase it to / emu or more.

[0022] Next, the inventors have determined that when a magnetic field of 10 kOe is applied externally to the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M 10 t, the magnetization amount M 10 The transmission attenuation rate for the magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 The electromagnetic noise suppression film of this embodiment, which was able to achieve a transmission attenuation rate of 3 dB cm / emu or more, was examined from another perspective. 2 To achieve an electromagnetic noise suppression film with a capacitance of 1 / emu or more, factors such as the type of spherical magnetic material used, particle diameter, packing rate, and packing amount are intricately related. For example, the particle diameter varies depending on the type of spherical magnetic material, which may affect the packing rate and packing amount. Furthermore, if the particle diameter of the spherical magnetic material is small, the particles tend to aggregate, so the packing rate and packing amount do not necessarily improve. For this reason, it was considered simpler to specify the electromagnetic noise suppression film of this embodiment by other, more specific characteristics rather than by these factors.

[0023] As a result of this investigation, it was found that when an external magnetic field of 10 kOe is applied to the in-plane direction of the magnetic layer and then the external magnetic field is changed to 8 kOe, the amount of magnetization per unit area in the in-plane direction is M8t1, and when an external magnetic field of 10 kOe is applied to the perpendicular direction of the magnetic layer and then the external magnetic field is changed to 8 kOe, the amount of magnetization per unit area in the perpendicular direction is M8t2. If the ratio M8t1 / M8t2 is 1.35 or more, in the electromagnetic noise suppression film of this embodiment, when an external magnetic field of 10 kOe is applied to the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M8t1. 10 t, the magnetization amount M 10 The transmission attenuation rate for the magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 It was found that it is possible to do more than / emu.

[0024] In the electromagnetic noise suppression film of this embodiment, a ratio M8t1 / M8t2 of 1.35 or more means that the magnetic anisotropy in the in-plane direction of the magnetic layer is greater than the magnetic anisotropy in the perpendicular direction. Therefore, it can be seen that the transmission attenuation rate relative to the amount of magnetization per unit area in the microstrip line method, which is an index of the electromagnetic noise suppression performance of an electromagnetic noise suppression film, is related to the magnitude of the magnetic anisotropy in the in-plane direction of the magnetic layer. This is thought to be because, even if the magnetic layer is formed using a magnetic material with reduced permeability due to spheroidization, increasing the magnetic anisotropy in the in-plane direction of the magnetic layer relatively improves the magnetic permeability of the magnetic layer, thereby increasing the electromagnetic wave absorption capacity of the electromagnetic noise suppression film.

[0025] <Magnetic Layer> The magnetic layer used in the electromagnetic noise suppression film of this embodiment will be described below. The magnetic layer of the electromagnetic noise suppression film of this embodiment functions as an electromagnetic noise suppression layer and contains spherical soft magnetic material and a binder. As mentioned above, the thickness of the magnetic layer can be set to less than 60 μm, but if it is too thin, the electromagnetic wave absorption performance will decrease, so it is preferably set to 5 μm or more. That is, the thickness of the magnetic layer is preferably set to 5 μm or more and less than 60 μm, and more preferably 10 μm or more and 30 μm or less.

[0026] Next, the materials constituting the magnetic layer will be described.

[0027] [Magnetic Material] The magnetic material used is a spherical soft magnetic material. Here, the spherical soft magnetic material is defined herein as a soft magnetic material in which the ratio of the maximum particle diameter to the minimum particle diameter of the magnetic particles (minimum particle diameter / maximum particle diameter) is 0.8 or more and 1 or less.

[0028] The soft magnetic material has a high initial magnetic permeability and can exhibit electromagnetic wave absorption performance even when contained in a small amount in the magnetic layer, so that electromagnetic noise suppression effects can be exhibited even when the magnetic layer is thin.

[0029] Examples of the soft magnetic material include iron, carbonyl iron, silicon iron, permalloy, sendust, permendur, soft ferrite, ferritic stainless steel, electromagnetic stainless steel, amorphous magnetic alloy, nanocrystalline magnetic alloy, etc., but carbonyl iron containing 97.5 mass % or more of iron (Fe) is particularly preferred as the soft magnetic material, because carbonyl iron can exhibit electromagnetic wave absorption performance (electromagnetic noise suppression effect) even in a relatively high frequency range such as the GHz band.

[0030] The average particle size of the spherical soft magnetic material is preferably 0.1 to 50 μm, more preferably 1 to 20 μm. If the particle size of the magnetic material is too small, the particles tend to undergo secondary aggregation, which makes it difficult to obtain a uniform coating film (magnetic layer). On the other hand, if the particle size is too large, the soft magnetic material tends to settle when used as a coating material, making it difficult to obtain a uniform coating film. The average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer.

[0031] The volume content of the spherical soft magnetic material contained in the magnetic layer is preferably 30 to 80%, more preferably 40 to 70%. If the volume content is below 30%, the electromagnetic wave absorption performance (electromagnetic noise suppression effect) of the magnetic layer tends to be insufficient, while if it exceeds 80%, the proportion of the binder in the magnetic layer decreases, and the strength of the magnetic layer tends to decrease.

[0032] [Binder] The binder preferably contains an amorphous resin (A) having a glass transition temperature of −50° C. to 0° C. and an amorphous resin (B) having a glass transition temperature of 10° C. or higher. Amorphous resins have high solubility in water and other solvents and excellent dispersibility for magnetic materials (magnetic powder). Therefore, by dispersing magnetic powder in a resin dissolved in water or other solvent, applying the resin to a substrate at a desired thickness, and drying it, it is possible to form a magnetic layer into a film.

[0033] By using an amorphous resin (A) with a glass transition temperature of -50°C to 0°C, flexibility can be imparted to the magnetic layer, and adhesion of the magnetic layer to the substrate can be improved. However, if only the amorphous resin (A) is used, the magnetic layer is likely to become tacky (sticky), and when the magnetic film is stacked or wound into a roll, adjacent magnetic layers or the magnetic layer and the substrate may stick together. On the other hand, if only the amorphous resin (B) with a glass transition temperature of 10°C or higher is used, the surface of the magnetic layer will be hard and less likely to stick, but when the magnetic layer is laminated with the substrate, adhesion to the substrate may be reduced or the magnetic layer may crack when wound and used. For this reason, it is preferable to use the above-mentioned amorphous resins (A) and (B) in combination as the binder of this embodiment.

[0034] The upper limit of the glass transition temperature of the amorphous resin (B) having a glass transition temperature of 10° C. or higher is preferably 100° C., and more preferably 80° C. If the glass transition temperature is higher than this upper limit, even if an amorphous resin (A) having a glass transition temperature of −50° C. to 0° C. is used in combination, the surface of the magnetic layer is likely to harden, which may reduce adhesion between the magnetic layer and the substrate, or make the magnetic layer more susceptible to cracking when attached to an uneven or curved surface or when folded during wrapping.

[0035] 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. Of these, amorphous resin (A) is preferably amorphous polyester (a) having a glass transition temperature of -50°C to 0°C, and amorphous resin (B) is preferably amorphous polyester (b) having a glass transition temperature of 10°C or higher. Of the amorphous resins, amorphous polyester has excellent solubility and flexibility and is suitable for producing a film-like magnetic layer.

[0036] From the above viewpoints, the content ratio of the amorphous polyester (a) to the amorphous polyester (b) is preferably (a):(b)=95:5 to 35:65 by mass. The content ratio of the amorphous polyesters (a) and (b) can be estimated to some extent from the intensities 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 using a differential scanning calorimeter (DSC).

[0037] Examples of the amorphous polyesters (a) and (b) include "Vylon" (registered trademark) manufactured by Toyobo Co., Ltd., "Pluscoat" (registered trademark) manufactured by Goo Chemical Co., Ltd., "Nichigo Polyester" (registered trademark) manufactured by Mitsubishi Chemical Corporation, and "Alumatex" (registered trademark) manufactured by Mitsui Chemicals, Inc. These have excellent solubility in water and organic solvents and can be used by dissolving them in water or organic solvents at any ratio.

[0038] Preferably, at least one of the amorphous polyester (a) and the amorphous polyester (b) contains a crosslinked portion crosslinked by an amide bond. 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 the molecular terminals, and carboxyl groups can be optionally added to the molecular chains. Therefore, by using a crosslinking agent, a crosslinked portion crosslinked by an amide bond can be formed.

[0039] Next, further characteristics of the electromagnetic noise suppression film of this embodiment will be described.

[0040] <Return Loss> When the return loss of the electromagnetic noise suppression film of this embodiment is measured by a microstrip line method in a measurement frequency range of 10 GHz to 30 GHz, the average return loss can be −20 dB or less. That is, the return loss, which is the absolute value of the −dB value, can be increased, and reflection can be reduced. This is because the magnetic layer of the electromagnetic noise suppression film of this embodiment uses spherical magnetic particles as the electromagnetic wave absorbing material, and spherical magnetic particles have smaller reflection characteristics than non-spherical magnetic particles. This allows the transmission attenuation rate of the electromagnetic noise suppression film of this embodiment to be improved.

[0041] <Method for measuring characteristics of electromagnetic noise suppression film> [Transmission attenuation rate relative to amount of magnetization per unit area] The transmission attenuation rate of the electromagnetic noise suppression film was measured by the microstrip line method (compliant with IEC62333-1 and IEC62333-2). Specifically, the transmission attenuation rate was measured by connecting a vector network analyzer "MS46122B-043" manufactured by Anritsu Corporation and a microstrip line "TF-30A test fixture" manufactured by Keycom Co., Ltd. with a coaxial cable "MWX051-03000KFSKMS / B" (3 m) manufactured by Junkosha Co., Ltd.

[0042] The vector network analyzer was previously 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 30 GHz, and measurement points were set using 401-point linear scaling. A 30 mm x 30 mm electromagnetic noise suppression film was placed on the microstrip line, and the electromagnetic wave reflection attenuation (S11M) and electromagnetic wave transmission attenuation (S21M) were measured with a load applied by a 150 g PTFE block. The transmission attenuation rate (Rtp) was calculated using the following formula (1), and the calculated Rtp was converted into the magnetization per unit area (unit: emu / cm). 2 The transmission attenuation rate (Rtp-S) for the amount of magnetization per unit area was calculated by dividing the return loss by 0.1 GHz. The average return loss from 10 GHz to 30 GHz was calculated as the average value from 10 GHz (the 134th point) to 30 GHz (the 401st point), assuming that 0.1 GHz was the first point.

[0043] Formula (1):

[0044] [Magnetic Properties] The hysteresis curve of the electromagnetic noise suppression film was determined using a vibrating sample magnetometer "VSM-P7" manufactured by Toei Kogyo Co., Ltd. Specifically, the electromagnetic noise suppression film was cut into a circular piece with a diameter of 8 mm to prepare a cut sample, and 10 of these cut samples were stacked together to prepare a cylindrical measurement sample, as shown in FIG.

[0045] The plot mode for the data from the vibrating sample magnetometer was a magnetic field applied of -10 kOe to 10 kOe, and as shown in Figure 2, a magnetic field in the positive direction of up to 10 kOe was applied to the magnetic layer until magnetization in the positive direction (point A) was reached. After that, a magnetic field in the opposite direction to the positive direction (direction 1a in Figure 2) of 10 kOe to -10 kOe was applied until magnetization in the opposite direction (point B) was reached, and the magnetization amount (unit: emu) was calculated using 316-point linear scaling using "VSM-P7 analysis software" manufactured by Toei Kogyo Co., Ltd.

[0046] The magnetization amount was measured for a cylindrical sample in two different magnetic field application directions, in-plane and perpendicular, where the external magnetic field was applied in the stacking direction as shown in Figure 1, and perpendicular to the stacking direction (in-plane direction of the cylindrical sample). After that, the magnetization amount at each measurement point was calculated based on the area of ​​the sample in the in-plane direction, 0.16π cm. 2 The magnetization per unit area was calculated by dividing the value by .

[0047] In this specification, the amount of magnetization per unit area in the in-plane direction when an external magnetic field of 10 kOe is applied is defined as M 10 Furthermore, the amount of magnetization per unit area in the in-plane direction when an external magnetic field of 10 kOe is applied and then changed to 8 kOe is denoted as Mt1, and the amount of magnetization per unit area in the perpendicular direction when an external magnetic field of 10 kOe is applied and then changed to 8 kOe is denoted as Mt2.

[0048] (Electromagnetic noise suppression sheet) An embodiment of the electromagnetic noise suppression sheet of the present invention will be described. The electromagnetic noise suppression sheet of this embodiment is characterized by including a substrate and the electromagnetic noise suppression film (magnetic layer) of the above-described embodiment of the present invention.

[0049] The electromagnetic noise suppression sheet of this embodiment includes a substrate, which improves the strength of the entire sheet. Also, since the electromagnetic noise suppression sheet of this embodiment includes the electromagnetic noise suppression film (magnetic layer) of the embodiment of the present application, when a magnetic field of 10 kOe is applied externally in the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M 10 If t, the magnetization amount M10 The transmission attenuation rate for the magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 It can be / emu or higher.

[0050] <Substrate> The substrate is a base on which the magnetic layer is formed. Any material may be used as the substrate as long as it is flexible and can ensure adhesion to the magnetic layer, and a resin film is usually used. Examples of resins constituting the substrate include polyolefin resins (polyethylene, polypropylene, etc.), polyester resins (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)acrylic acid ester copolymers, ethylene-butene copolymers, ethylene-hexene copolymers, polyurethane resins, polyether ketone resins, polyether resins, polyethersulfone resins, polystyrene resins (polystyrene, etc.), polyvinyl chloride resins, polyvinylidene chloride resins, polyvinyl alcohol resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate copolymers, polycarbonate resins, fluorine-based resins, silicone resins, cellulose resins, and substrates made from constituent materials such as crosslinked bodies of these resins. Among these, polyethylene terephthalate (PET) is more preferred in terms of mechanical properties and cost. These resin materials can be used alone or in combination. The resin materials may have functional groups, if necessary. Functional monomers or modifying monomers may be grafted onto the resin materials.

[0051] The surface of the substrate may be subjected to a known surface treatment to improve adhesion to the adjacent magnetic layer. Specific examples of such surface treatments include corona discharge treatment, ozone exposure treatment, high-voltage shock exposure treatment, and ionizing radiation treatment. The substrate may also be subjected to a coating treatment with an undercoat agent (such as silicone treatment), a primer treatment, a matte treatment, a crosslinking treatment, or the like.

[0052] The substrate may be in the form of a single layer or a laminate of two or more layers. If necessary, known auxiliary agents such as fillers, flame retardants, antidegradants, antistatic agents, softeners, and plasticizers may be added to the substrate.

[0053] The thickness of the substrate is not particularly limited, but is preferably 5 to 20 μm, and more preferably 10 to 15 μm. If the thickness of the substrate is within this range, the electromagnetic noise suppression sheet of this embodiment can achieve both strength and flexibility.

[0054] The substrate may be any material that is flexible and can ensure adhesion to the magnetic layer, and therefore a metal layer such as a metal foil, which will be described later, may be used as the substrate instead of the resin film. Also, a composite film formed by laminating a resin film and a metal foil may be used as the substrate.

[0055] <Metal Layer> When a resin film is used as the substrate, the electromagnetic noise suppression sheet of this embodiment can further include a metal layer. By providing a metal layer on the electromagnetic noise suppression sheet of this embodiment, the electromagnetic noise suppression sheet can be endowed with electric field shielding performance, and can suppress not only magnetic noise but also electrical noise.

[0056] The type of metal constituting the metal layer is not particularly limited as long as it has flexibility and adhesion to the magnetic layer, but aluminum, copper, permalloy, etc. are preferred. Aluminum and copper have high conductivity, are inexpensive, can be easily processed into thin films, and have excellent flexibility. Furthermore, permalloy has high conductivity and a high magnetic collecting effect in the kHz range, and can be used as a magnetic shield.

[0057] The thickness of the metal layer is not particularly limited, but if it is too thick, flexibility decreases, so it is usually set in the range of 0.1 to 30 μm.

[0058] As the metal layer, a metal foil can be used alone, but a metal thin film can also be formed on the above-mentioned substrate (resin film) by vapor deposition or sputtering.

[0059] <Adhesive Layer> The electromagnetic noise suppression sheet of this embodiment can further include an adhesive layer. When an adhesive layer is provided on the electromagnetic noise suppression sheet of this embodiment, the thickness of the adhesive layer is preferably 10 to 50 μm, more preferably 15 to 35 μm. If the thickness is less than 10 μm, sufficient adhesive strength may not be obtained. If the thickness exceeds 50 μm, the adhesive effect of the adhesive layer becomes saturated and the overall thickness of the electromagnetic noise suppression sheet increases, reducing the flexibility of the electromagnetic noise suppression sheet, reducing its ability to conform when attached to electronic components, and making it difficult to wrap around wiring, etc.

[0060] Next, the electromagnetic noise suppression sheet of this embodiment will be described with reference to the drawings. Fig. 3 is a schematic cross-sectional view showing an example of the electromagnetic noise suppression sheet of this embodiment. In Fig. 3, the electromagnetic noise suppression sheet 10 includes a substrate 11 and a magnetic layer 12 disposed on the substrate 11. In Fig. 3, the electromagnetic noise suppression sheet 10 has a two-layer structure consisting of the substrate 11 and the magnetic layer 12, but it may also have a three-layer structure by further disposing an adhesive layer on either the substrate 11 side or the magnetic layer 12 side.

[0061] Fig. 4 is a schematic cross-sectional view showing another example of an electromagnetic noise suppression sheet according to this embodiment. In Fig. 4, an electromagnetic noise suppression sheet 20 includes a substrate 11, a metal layer 13 disposed on the substrate 11, and a magnetic layer 12 disposed on the metal layer 13. While the electromagnetic noise suppression sheet 20 in Fig. 4 has a three-layer structure consisting of the substrate 11, the magnetic layer 12, and the metal layer 13, it may also have a four-layer structure by further disposing an adhesive layer on either the substrate 11 side or the magnetic layer 12 side. While the metal layer 13 is disposed between the substrate 11 and the magnetic layer 12 in Fig. 4, it may also be disposed on the outer surface of the magnetic layer 12.

[0062] The overall thickness of the electromagnetic noise suppression sheet of this embodiment is preferably 10 to 85 μm, and 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 reduced electromagnetic wave absorption performance and a reduced 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 be reduced, making it difficult to wrap around a cable or connector for use.

[0063] The electromagnetic noise suppression film and electromagnetic noise suppression sheet of this embodiment may be used as is in the form of a film or sheet, or may be processed into a tape for use. When the film or sheet is processed into a tape, the width can be appropriately set depending on the application. When the film or sheet is processed into a tape, the tape-like electromagnetic noise suppression film or electromagnetic noise suppression sheet can be rolled up and stored, for example.

[0064] (Method for manufacturing an electromagnetic noise suppression sheet) An embodiment of the method for manufacturing an electromagnetic noise suppression sheet of the present application will be described. The method for manufacturing an electromagnetic noise suppression sheet of this embodiment is a method for manufacturing the electromagnetic noise suppression sheet of the present application described above, and includes the steps of mixing spherical soft magnetic material and a binder together with a solvent to prepare a coating material for forming a magnetic layer, applying the coating material for forming a magnetic layer to a substrate and drying it to form a magnetic layer, and calendering the formed magnetic layer.

[0065] <Magnetic Layer Forming Paint> The magnetic layer forming paint can be prepared by mixing spherical soft magnetic material, a binder, and a solvent.

[0066] The spherical soft magnetic particles and the binder can be the same as those constituting the magnetic layer of the electromagnetic noise suppression film of the above-described embodiment of the present application.

[0067] Examples of the solvent that can be used include water, ethyl alcohol, methyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, ethylene glycol, and propylene glycol.

[0068] The content of the solvent is not particularly limited, but may be 50.0% by mass or more and 99.5% by mass or less relative to the total mass of the coating material for forming the magnetic layer.

[0069] The coating material for forming the magnetic layer may further contain a surface conditioner, an antifoaming agent, a thickener, and the like.

[0070] <Formation of Magnetic Layer> Examples of a method for applying the magnetic layer-forming coating material onto a substrate include bar coating, reverse coating, gravure coating, microgravure (registered trademark) coating, die coating, dipping, spin coating, slit coating, and spray coating.

[0071] The drying after application is preferably carried out at 80 to 150°C for 3 to 30 minutes under conditions that allow the solvent component of the magnetic layer-forming coating material to evaporate. If the solvent remains in the magnetic layer, the strength tends to decrease. Drying methods include, for example, hot air drying, heat drying, vacuum drying, and natural drying.

[0072] The calendering can be carried out using a metal roll or a resin roll. When forming the magnetic layer on a sheet, the calendering can be carried out by pressing. The calendering is preferably carried out at a temperature equal to or higher than the glass transition temperature of the formed magnetic layer, and the calendering may be carried out multiple times.

[0073] (Communication Cable) An embodiment of a communication cable of the present application will be described. The communication cable of this embodiment is characterized by including the electromagnetic noise suppression film or electromagnetic noise suppression sheet of the above-described embodiment of the present application. The communication cable of this embodiment includes a coaxial cable, a twisted pair cable, a multi-core cable, and the like. In particular, a coaxial cable is used for high-frequency transmission and is used as a video cable.

[0074] A coaxial cable, which is one of the communication cables of the present embodiment, will be described below with reference to the drawings. In the coaxial cable described below, the electromagnetic noise suppression sheet of the present application is used as an electromagnetic noise suppression layer of the coaxial cable.

[0075] 5 is a schematic cross-sectional view showing an example of a coaxial cable. The coaxial cable 30 includes an inner conductor 31, an insulating layer 32, a metal foil 33, a metal braid 34, a magnetic sheath layer 35, and an outer coating layer 36. The magnetic sheath layer 35 uses the electromagnetic noise suppression sheet of the present invention and is composed of a base layer 35a and a magnetic layer 35b disposed on one side of the base layer 35a.

[0076] In FIG. 5, the magnetic layer 35b of the magnetic sheath layer 35 is disposed on the axial center side, but the base layer 35a may also be disposed on the axial center side.

[0077] The magnetic sheath layer 35 of the coaxial cable 30 can be formed by wrapping the electromagnetic noise suppression sheet of the present invention around the outer surface of a linear conductor consisting of the inner conductor 31, the insulating layer 32, the metal foil 33, and the metal braid 34. This allows the thickness of the magnetic sheath layer to be thin, and also shortens the processing time.

[0078] (Electronic Device) An embodiment of an electronic device of the present application will be described. The electronic device of this embodiment is characterized by including the electromagnetic noise suppression film or electromagnetic noise suppression sheet of the above-described embodiment of the present application. As a result, the electromagnetic noise suppression film or electromagnetic noise suppression sheet of the present application can be used as an electromagnetic noise suppression member for the electronic device. Specifically, the electronic device of this embodiment is, for example, an electronic device in which the electromagnetic noise suppression film or electromagnetic noise suppression sheet of the present application is disposed on an uneven surface or corner of an electronic device that emits electromagnetic noise or an electronic device from which electromagnetic noise should be prevented. The electromagnetic noise suppression sheet of the present application can also be used as a substitute for a ferrite core used in a cable for an electronic device.

[0079] 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" in the following means "parts by mass."

[0080] Example 1 Preparation of Paint for Forming Magnetic Layer The following components were mixed and dispersed to prepare a paint for forming a magnetic layer. (1) Soft magnetic material (Tenichi Co., Ltd. spherical carbonyl iron powder, trade name "YW-5", Fe content: 97.5% by mass): 42.2 parts (2) Amorphous polyester (a) (water-soluble polyester resin solution, GOO Chemical Co., Ltd., trade name "Plus Coat Z-3310", Tg: -20 ° C., solid content: 25.0% by mass, solvent: water): 12.5 parts (3) Amorphous polyester (b) (water-soluble polyester resin solution, GOO Chemical Co., Ltd., trade name "Plus Coat Z-730", Tg: 43 ° C., solid content: 25.0% by mass, solvent: water): 8.3 parts (4) Crosslinking agent (oxazoline group-containing polymer, Nippon Shokubai Co., Ltd., trade name "Epocross WS500", solid content: 40.0% by mass, solvent: water): 3.0 parts (5) Antifoaming agent (silicon-free polymer, manufactured by BYK-Chemie, trade name “BKY-012”, solid content: 100.0% by mass): 0.2 parts (6) Thickener (synthetic layered silicate synthetic hectorite for aqueous systems, manufactured by BYK-Chemie, trade name “LAPONITERD”, solid content: 100.0% by mass): 1.2 parts (7) Solvent (n-propyl alcohol): 10.0 parts (8) Pure water: 22.6 parts

[0081] In the magnetic layer forming paint, the content ratio of the amorphous polyesters (a) and (b) was (a):(b) = 60:40 in terms of solid mass ratio, and the volume content of the soft magnetic material relative to the total solid content of the magnetic layer forming paint was 50.0%.

[0082] <Formation of Magnetic Layer> Next, a 12 μm-thick PET film (manufactured by Toyobo Co., Ltd., product name "Ester Film E5100") was used as a substrate, and the above-described magnetic layer-forming paint was comma-directly applied to one main surface of the substrate so that the magnetic layer would have a thickness of 10 μm after calendaring, and then dried at 100° C. Thereafter, the original roll was subjected to calendaring at a temperature of 50° C. and a linear pressure of 50 kg / cm using a calendaring device having a metal roll, thereby producing an electromagnetic noise suppression sheet of Example 1 having a magnetic layer formed on one main surface.

[0083] Example 2 An electromagnetic noise suppression sheet of Example 2 was produced in the same manner as Example 1, except that the thickness of the magnetic layer was changed to 30 μm.

[0084] Example 3 An electromagnetic noise suppression sheet of Example 3 was produced in the same manner as Example 1, except that the thickness of the magnetic layer was changed to 50 μm.

[0085] Comparative Example 1 An electromagnetic noise suppression sheet of Comparative Example 1 was produced in the same manner as in Example 1, except that the thickness of the magnetic layer was changed to 60 μm.

[0086] (Comparative Example 2) As a soft magnetic material, instead of spherical carbonyl iron powder (product name "YW-5"), Fe-Si-Cr spherical iron powder (Fe 88.8 Si 6.2 Cr 5.0 An electromagnetic noise suppression sheet of Comparative Example 2 was produced in the same manner as in Example 1, except that a magnetic layer having a thickness of 100 μm was used, and the Fe content was 87.0 mass %.

[0087] (Comparative Example 3) As a soft magnetic material, instead of spherical carbonyl iron powder (product name "YW-5"), Fe-Si-Cr spherical iron powder (Fe 88.8 Si 6.2 Cr 5.0 An electromagnetic noise suppression sheet of Comparative Example 3 was produced in the same manner as in Example 1, except that a magnetic layer having a thickness of 30 μm was used, and the Fe content was 87.0 mass %.

[0088] For the electromagnetic noise suppression sheets of Examples 1 to 3 and Comparative Examples 1 to 3, the magnetization amount M 10 The transmission attenuation rate (Rtp-S), M8t1 / M8t2, and the average value of the return loss (S11) at measurement frequencies of 10 GHz to 30 GHz were measured using the microstrip line method at 28 GHz.

[0089] The above results are shown in Table 1 together with the magnetic material and thickness of the magnetic layer of the electromagnetic noise suppression sheet that was produced.

[0090]

[0091] As can be seen from Table 1, in the electromagnetic noise suppression sheets of Examples 1 to 3, the magnetization amount M 10 The transmission attenuation rate (Rtp-S) relative to the amount of magnetization per unit area measured by the microstrip line method at 28 GHz was 3 dB cm 2 / emu or more, which indicates that the electromagnetic wave absorption amount relative to the amount of magnetization per unit area of ​​the magnetic layer is higher than that of the electromagnetic noise suppression sheets of Comparative Examples 1 to 3. Furthermore, the electromagnetic noise suppression sheets of Examples 1 to 3 were able to achieve an M8t1 / M8t2 ratio of 1.35 or more, which indicates that the magnetic anisotropy in the in-plane direction of the magnetic layer was greater than that in the perpendicular direction, compared to the electromagnetic noise suppression sheets of Comparative Examples 1 to 3. Furthermore, the electromagnetic noise suppression sheets of Examples 1 to 3 were able to achieve an average return loss of -20 dB or less when measured by the microstrip line method at a measurement frequency range of 10 GHz to 30 GHz, indicating that they had little reflection.

[0092] The following additional embodiments are disclosed in relation to the embodiments of the present application including the above Examples 1 to 3. (Additional Embodiment 1) An electromagnetic noise suppression film including a magnetic layer, wherein the magnetic layer includes spherical soft magnetic material and a binder, and when a magnetic field of 10 kOe is applied externally in the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M 10 t, the magnetization amount M 10 The transmission attenuation rate for the amount of magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 / emu or more. (Additional Form 2) The electromagnetic noise suppression film according to Additional Form 1, in which, when an external magnetic field of 10 kOe is applied to the in-plane direction of the magnetic layer and then the external magnetic field is changed to 8 kOe, the magnetization per unit area in the in-plane direction is M8t1, and when an external magnetic field of 10 kOe is applied to the perpendicular direction of the magnetic layer and then the external magnetic field is changed to 8 kOe, the magnetization per unit area in the perpendicular direction is M8t2, the ratio M8t1 / M8t2 is 1.35 or more. (Additional Form 3) The electromagnetic noise suppression film according to Additional Form 1 or 2, in which the spherical soft magnetic particles are spherical carbonyl iron. (Additional Form 4) The electromagnetic noise suppression film according to Additional Form 3, in which the carbonyl iron contains 97.5 mass % or more of iron. (Additional Form 5) An electromagnetic noise suppression film according to any one of Additional Forms 1 to 4, wherein the volume content of the spherical soft magnetic material contained in the magnetic layer is 30 to 80%. (Additional Form 6) An electromagnetic noise suppression film according to any one of Additional Forms 1 to 5, wherein the thickness of the magnetic layer is 5 μm or more and less than 60 μm. (Additional Form 7) An electromagnetic noise suppression film according to any one of Additional Forms 1 to 5, wherein the thickness of the magnetic layer is 10 μm or more and 30 μm or less. (Additional Form 8) An electromagnetic noise suppression film according to any one of Additional Forms 1 to 7, wherein the average return loss is −20 dB or less when the return loss is measured by a microstrip line method at a measurement frequency range of 10 GHz to 30 GHz. (Additional Form 9) An electromagnetic noise suppression sheet comprising a substrate and the electromagnetic noise suppression film according to any one of Additional Forms 1 to 8. (Additional Form 10) An electromagnetic noise suppression sheet according to Additional Form 9, wherein the substrate is a resin film. (Additional Form 11) The electromagnetic noise suppression sheet according to Additional Form 9 or 10, further comprising a metal layer. (Additional Form 12) A communication cable comprising the electromagnetic noise suppression film according to any one of Additional Forms 1 to 8 or the electromagnetic noise suppression sheet according to any one of Additional Forms 9 to 11. (Additional Form 13) An electronic device comprising the electromagnetic noise suppression film according to any one of Additional Forms 1 to 8 or the electromagnetic noise suppression sheet according to any one of Additional Forms 9 to 11.

[0093] The present application may be implemented in other forms than those described above. The embodiments disclosed in the present application are merely examples and are not intended to be limiting. The scope of the present application shall be interpreted in accordance with the appended claims rather than the above description, and all modifications within the scope of the claims are intended to be embraced within the scope of the claims.

[0094] REFERENCE SIGNS LIST 10, 20 Electromagnetic noise suppression sheet 11 Substrate 12 Magnetic layer 13 Metal layer 30 Coaxial cable 31 Inner conductor 32 Insulating layer 33 Metal foil 34 Metal braid 35 Magnetic sheath layer 35a Substrate layer 35b Magnetic layer 36 Outer coating layer

Claims

1. An electromagnetic noise suppression film including a magnetic layer, wherein the magnetic layer includes spherical soft magnetic material and a binder, and when a magnetic field of 10 kOe is applied externally in the in-plane direction of the magnetic layer, the amount of magnetization per unit area in the in-plane direction of the magnetic layer is M 10 t, the magnetization amount M 10 The transmission attenuation rate for the amount of magnetization per unit area measured by the microstrip line method at 28 GHz is 3 dB cm 2 / emu or more.

2. The electromagnetic noise suppression film according to claim 1, wherein when an external magnetic field of 10 kOe is applied to the in-plane direction of the magnetic layer and then the external magnetic field is changed to 8 kOe, the amount of magnetization per unit area in the in-plane direction is M8t1, and when an external magnetic field of 10 kOe is applied to the perpendicular direction of the magnetic layer and then the external magnetic field is changed to 8 kOe, the amount of magnetization per unit area in the perpendicular direction is M8t2, and the ratio M8t1 / M8t2 is 1.35 or more.

3. The electromagnetic noise suppression film according to claim 1, wherein the spherical soft magnetic material is spherical carbonyl iron.

4. The electromagnetic noise suppression film according to claim 3, wherein the carbonyl iron contains 97.5 mass % or more of iron.

5. The electromagnetic noise suppression film according to claim 1, wherein the volume content of the spherical soft magnetic material contained in the magnetic layer is 30 to 80%.

6. The electromagnetic noise suppression film according to claim 1, wherein the thickness of the magnetic layer is 5 μm or more and less than 60 μm.

7. The electromagnetic noise suppression film according to claim 1, wherein the thickness of the magnetic layer is 10 μm or more and 30 μm or less.

8. The electromagnetic noise suppression film according to claim 1, wherein when the return loss is measured by a microstrip line method in a measurement frequency range of 10 GHz to 30 GHz, the average return loss is −20 dB or less.

9. An electromagnetic noise suppression sheet comprising a substrate and the electromagnetic noise suppression film according to any one of claims 1 to 8.

10. The electromagnetic noise suppression sheet according to claim 9, wherein the substrate is a resin film.

11. The electromagnetic noise suppression sheet according to claim 9, further comprising a metal layer.

12. A communication cable comprising the electromagnetic noise suppression film according to any one of claims 1 to 8.

13. An electronic device comprising the electromagnetic noise suppression film according to any one of claims 1 to 8.

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