WO2025197678A1 - Electromagnetic noise suppression film, and electromagnetic noise suppression sheet, communication cable, and electronic device that use said electromagnetic noise suppression film - Google Patents

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

This application relates to an electromagnetic noise suppression film that absorbs electromagnetic waves in the GHz band.

With the advancement of wireless communication technology, exemplified by mobile phones, a variety of devices and sensors are now wirelessly connected to networks. Furthermore, in the medical field, cordless devices are becoming more 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 use high frequencies. With the increase in devices using such high frequencies, there is an increasing 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. Furthermore, in recent years, millimeter-wave radar has begun to be installed in vehicles with the aim of preventing automobile collisions. Malfunctions in these medical and automotive devices can have an impact on human lives, so 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 in devices and the resulting interference, a so-called EMC (Electromagnetic Compatibility) countermeasure.

Generally, the transmission attenuation rate in the microstrip line method, which is an indicator of the electromagnetic noise suppression performance of an electromagnetic noise suppression film that uses a magnetic material, increases as the imaginary part of the magnetic permeability of the electromagnetic noise suppression film increases, improving electromagnetic noise suppression performance. However, the magnetic permeability of typical iron oxide magnetic materials used as electromagnetic wave absorbing materials in electromagnetic noise suppression films remains almost constant up to a certain frequency as the frequency is gradually increased. It then increases as the frequency increases, reaching a maximum value at a specific frequency of several GHz, after which it decreases almost inversely proportional to the frequency, eventually reaching a point where the real part of the magnetic permeability is 1 and the imaginary part is 0. The frequency at which this permeability decreases is the limit frequency (limit frequency) at which the magnetic material can be used practically, and is known as the Snake limit.

Here, the greater the anisotropic magnetic field, the higher the limiting frequency. Therefore, conventionally, the shape of the magnetic material was made closer to a sphere, eliminating the shape magnetic anisotropy of the magnetic material and increasing the anisotropic magnetic field of the magnetic 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.

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. Therefore, while using spherical magnetic material as an electromagnetic noise absorption material in an electromagnetic noise suppression film widens the practical frequency range, it also leads to a decrease in the imaginary part of the magnetic permeability of the electromagnetic noise suppression film, resulting in a problem of reduced electromagnetic wave noise suppression performance.

Japanese Patent Application Laid-Open No. 2000-138492 Japanese Patent Application Laid-Open No. 2005-340318

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

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 containing spherical carbonyl iron with a particle size of 4 μm or less and having a thickness of 1 mm, which has been calendered. Patent Document 2 discloses an electromagnetic wave absorber containing approximately spherical carbonyl iron with an average particle size of 1 to 10 μm and having a thickness of 1 to 3 mm, which has been calendered.

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 is characterized in that when an external magnetic field of 10 kOe is applied in the in-plane direction of the magnetic layer, where _M10t is the magnetization per unit area in the in-plane direction of the magnetic layer, the transmission attenuation rate relative to the magnetization per unit area measured by a microstrip line method at 28 GHz for the magnetization _M10t is 3 dB· ^cm2 /emu or more.

The electromagnetic noise suppression sheet of the present application is characterized by including a substrate and the electromagnetic noise suppression film of the present application.

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

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

According to this application, even when spherical soft magnetic materials are used, it is possible to provide a magnetic noise suppression film that has a high electromagnetic wave absorption rate relative to the amount of magnetization per unit area of the electromagnetic noise suppression layer (magnetic layer).

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 illustrating 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 the embodiment.

(Electromagnetic noise suppression film)
An embodiment of an electromagnetic noise suppression film of the present invention will be described below. The electromagnetic noise suppression film of this embodiment includes a magnetic layer containing spherical soft magnetic material and a binder, and is characterized in that when a magnetic field of 10 kOe is applied externally in the in-plane direction of the magnetic layer, where _M10t is the magnetization per unit area in the in-plane direction of the magnetic layer, the transmission attenuation rate relative to the magnetization per unit area, _M10t , measured by a microstrip line method at 28 GHz, is 3 dB· ^cm2 /emu or more.

The electromagnetic noise suppression film of the present application uses spherical soft magnetic material as the electromagnetic wave absorbing material. As mentioned above, this increases the anisotropy magnetic field of the magnetic material, shifting the threshold frequency to the higher frequency side and widening 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. For this reason, using spherical soft magnetic material as the electromagnetic wave absorbing material in an electromagnetic noise suppression film poses the problem of reduced electromagnetic noise suppression performance due to the decrease in the imaginary part of the magnetic permeability of the electromagnetic noise suppression film.

In the electromagnetic noise suppression film of the present application, the magnetic layer is made thinner to solve the above problems. 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.

In other words, it is generally known that in the magnetic layer manufacturing process, if a thin-film magnetic layer is formed using fine-particle magnetic material, and then calendaring is performed to pack the magnetic fine particles more densely, the magnetic permeability of the magnetic layer improves. This is because calendaring packs the magnetic fine particles more densely, reducing the spacing between the magnetic fine particles in the magnetic layer and increasing the magnetic interaction between each magnetic fine particle. When a magnetic field is applied from the outside in this state, the magnetic interaction between the magnetic fine particles cancels out part of the demagnetizing field generated in each magnetic fine particle, and another 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, improving the magnetic permeability of the magnetic layer. This effect of improving permeability due to the demagnetizing field is particularly significant when a soft magnetic material is used.

Therefore, the inventors conducted extensive research, conceiving that even if a magnetic layer is formed using a soft magnetic material whose magnetic permeability has been reduced by spheroidizing the magnetic material, calendaring the magnetic layer would result in a higher packing density of the spherical magnetic microparticles compared to conventional non-spherical magnetic microparticles, and the spherical magnetic microparticles in the magnetic layer would be spaced closer together, thereby further improving the magnetic permeability of the magnetic layer.As a result, it was found that a good amount of electromagnetic wave absorption can be achieved by setting 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 microparticles in the magnetic layer, to 3 dB· ^cm2 /emu or more, and by setting the transmission attenuation rate relative to the amount of magnetization per unit area within a specific range.In other words, the present application is characterized by not simply specifying a range for the transmission attenuation rate of the electromagnetic noise suppression film, but by setting the transmission attenuation rate relative to the amount of magnetization per unit area, which is related to the packing density of the spherical magnetic material, within a specific range.

Furthermore, it was found that by setting the thickness of the magnetic layer to between 5 μm and 60 μm, the magnetic anisotropy in the in-plane direction of the magnetic layer can be increased. Here, for example, to set the thickness of the magnetic layer to between 5 μm and 60 μm, it is preferable that the particle diameter of the spherical soft magnetic material is less than 60 μm and 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 microparticles of this particle diameter, the spherical soft magnetic microparticles are more densely packed by calendaring, which increases the magnetic interaction between the spherical soft magnetic microparticles and further improves the magnetic permeability of the magnetic layer.

From the above investigations, it has been confirmed that in the electromagnetic noise suppression film of this embodiment, when an external magnetic field of 10 kOe is applied in the in-plane direction of the magnetic layer, if the magnetization per unit area in the in-plane direction _of the magnetic layer is _M10t , the transmission attenuation rate for the magnetization per unit area measured by the microstrip line method at 28 GHz for the magnetization M10t can be made 3 dB· ^cm2 /emu or more.

Next, the inventors investigated whether it would be possible to specify, from another perspective, the electromagnetic noise suppression film of this embodiment, which is capable of achieving a transmission attenuation rate of 3 dB·cm ₂ /emu or more relative to the magnetization per unit area of the magnetic layer when an external magnetic field of 10 kOe is applied in the in-plane direction of the magnetic layer, as measured by a microstrip line method at ²⁸ GHz for the magnetization M _10t . In this embodiment, to achieve an electromagnetic noise suppression film with a transmission attenuation rate of 3 dB·cm ² /emu or more relative to the magnetization per unit area, factors such as the type of spherical magnetic particles used, particle diameter, packing rate, and packing amount are intricately related. For example, the particle diameter varies depending on the type of spherical magnetic particles, which may affect the packing rate and packing amount. Furthermore, if the particle diameter of the spherical magnetic particles is small, the particles tend to aggregate easily, and therefore the packing rate and packing amount may not necessarily be improved. For this reason, it is thought that it would be simpler to specify the electromagnetic noise suppression film of this embodiment by other, more definite characteristics rather than by these factors.

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 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 , and 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 and the magnetization per unit area in the in-plane direction of the magnetic layer _{is M10t} , the transmission attenuation rate for the magnetization per unit area measured by the microstrip line method at 28 GHz for the magnetization M10t can be 3 dB· ^cm2 /emu or more.

In the electromagnetic noise suppression film of this embodiment, the ratio _M8t1 / _M8t2 being 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.

<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.

Next, we will explain the materials that make up the magnetic layer.

[Magnetic material]
The magnetic material used is a spherical soft magnetic material, which is defined herein as a soft magnetic material having a ratio of the maximum particle size to the minimum particle size of the magnetic particles (minimum particle size/maximum particle size) of 0.8 to 1.

The above soft magnetic materials have high initial magnetic permeability and can exhibit electromagnetic wave absorption properties even when contained in small amounts in the magnetic layer, so they can exhibit electromagnetic noise suppression effects even when the magnetic layer is made thin.

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 alloys, and nanocrystalline magnetic alloys. However, carbonyl iron, which contains 97.5% or more by mass of iron (Fe), is particularly preferred as a soft magnetic material. This is because carbonyl iron can exhibit electromagnetic wave absorption performance (electromagnetic noise suppression effect) even in relatively high frequency ranges such as the GHz band.

The average particle size of the spherical soft magnetic material is preferably 0.1 to 50 μm, and more preferably 1 to 20 μm. If the particle size of the magnetic material is too small, the particles are prone to secondary aggregation, making 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 is prone to settling when made into a paint, 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.

The volume content of the spherical soft magnetic material contained in the magnetic layer is preferably 30 to 80%, and 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, and if it exceeds 80%, the proportion of binder in the magnetic layer decreases, and the strength of the magnetic layer tends to decrease.

[Binder]
The binder preferably contains 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 for magnetic materials (magnetic powder). Therefore, by dispersing magnetic powder in a resin dissolved in water or other solvent, applying the resin to a desired thickness on a substrate, and drying it, it is possible to form a magnetic layer into a film.

Using an amorphous resin (A) with a glass transition temperature of -50°C to 0°C can impart flexibility to the magnetic layer and improve adhesion of the magnetic layer to the substrate. However, using only amorphous resin (A) can easily cause tackiness in the magnetic layer, which can lead to adjacent magnetic layers or the magnetic layer sticking to the substrate when the magnetic film is stacked or wound into a roll. On the other hand, using only amorphous resin (B) with a glass transition temperature of 10°C or higher will make the surface of the magnetic layer hard and less likely to stick, but when the magnetic layer is laminated on a substrate, adhesion to the substrate may decrease and the magnetic layer may crack when wound. For this reason, it is preferable to use a combination of the above amorphous resins (A) and (B) as the binder in this embodiment.

The upper limit of the glass transition temperature of amorphous resin (B) with 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) with 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.

The amorphous resin (A) can be an amorphous polyester, amorphous polyurethane, amorphous acrylic, or the like, with a glass transition temperature of -50°C to 0°C, while the amorphous resin (B) can be an amorphous polyester, amorphous polyurethane, amorphous acrylic, or the like, with a glass transition temperature of 10°C or higher. Among these, amorphous resin (A) is preferably an amorphous polyester (a) with a glass transition temperature of -50°C to 0°C, and amorphous resin (B) is preferably an amorphous polyester (b) with a glass transition temperature of 10°C or higher. Among amorphous resins, amorphous polyesters have excellent solubility and flexibility, making them suitable for producing film-like magnetic layers.

From the above perspective, the content ratio of the amorphous polyester (a) and 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).

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 dissolved in water or organic solvents in any ratio for use.

Furthermore, it is preferable that at least one of the amorphous polyester (a) and the amorphous polyester (b) contains crosslinked portions crosslinked 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 the molecular terminals, and carboxyl groups can be optionally added to the molecular chains. Therefore, by using a crosslinking agent, crosslinked portions crosslinked by amide bonds can be formed.

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

<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 made -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.

<Method for measuring the characteristics of electromagnetic noise suppression film>
[Transmission attenuation rate relative to magnetization amount per unit area]
The transmission attenuation rate of the electromagnetic noise suppression film was measured by the microstrip line method (compliant with IEC 62333-1 and IEC 62333-2). 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.

The vector network analyzer was previously calibrated using SOLT (Short-Open-Load-Thru) and measurements were performed 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 divided by the magnetization per unit area (unit: emu/ ^cm2 ) to calculate the transmission attenuation rate relative to the magnetization per unit area (Rtp-S). 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), with 0.1 GHz being the first point.

Formula (1):

[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.

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

The above-mentioned magnetization amount was measured for a cylindrical sample in two 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) as shown in Figure 1. The magnetization amount at each measurement point was then divided by ^0.16πcm2 , which is the area of the measurement sample in the in-plane direction, to calculate the magnetization amount per unit area.

In this specification, the magnetization amount per unit area in the in-plane direction when an external magnetic field of ₁₀ kOe is applied is denoted as M10t, the magnetization amount 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 _M8t1 , and the magnetization amount 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 M8t2.

(Electromagnetic noise suppression sheet)
An embodiment of an electromagnetic noise suppression sheet according to the present invention will now be described. The electromagnetic noise suppression sheet according to this embodiment is characterized by comprising a substrate and the electromagnetic noise suppression film (magnetic layer) according to the above-described embodiment of the present invention.

The electromagnetic noise suppression sheet of this embodiment includes a substrate, which improves the strength of the entire sheet. Furthermore, because the electromagnetic noise suppression sheet of this embodiment includes the electromagnetic noise suppression film (magnetic layer) of the present embodiment, when an external magnetic field of 10 kOe is applied in the in-plane direction of the magnetic layer, where _M10t is the magnetization per unit area in the in-plane direction of the magnetic layer, the transmission attenuation rate relative to the magnetization per unit area, _M10t , measured by the microstrip line method at 28 GHz, can be 3 dB· ^cm2 /emu or more.

<Base material>
The substrate serves as 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.

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 a primer (such as silicone treatment), a primer treatment, a matte treatment, a crosslinking treatment, etc.

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

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.

The substrate may be any material that is flexible and can ensure adhesion to the magnetic layer. Therefore, instead of the resin film, a metal layer such as metal foil, which will be described later, may be used as the substrate. A composite film made by laminating a resin film and metal foil may also be used as the substrate.

<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.

The type of metal that makes up 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 are highly conductive, inexpensive, easy to process into thin films, and have excellent flexibility. Furthermore, permalloy is not only conductive, but also has a high magnetic collecting effect in the kHz range, making it effective as a magnetic shield.

There are no particular restrictions on the thickness of the metal layer, but if it is too thick, flexibility will decrease, so it is usually set in the range of 0.1 to 30 μm.

As the metal layer, metal foil can be used alone, but it can also be used by forming a thin metal film on the aforementioned substrate (resin film) using vapor deposition or sputtering methods.

<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 saturates 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.

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 an electromagnetic noise suppression sheet of this embodiment. In FIG. 3, the electromagnetic noise suppression sheet 10 comprises 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.

FIG. 4 is a schematic cross-sectional view showing another example of an electromagnetic noise suppression sheet according to this embodiment. In FIG. 4, the electromagnetic noise suppression sheet 20 comprises a substrate 11, a metal layer 13 disposed on the substrate 11, and a magnetic layer 12 disposed on the metal layer 13. In FIG. 4, the electromagnetic noise suppression sheet 20 has a three-layer structure consisting of the substrate 11, the magnetic layer 12, and the metal layer 13, but 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. In FIG. 4, the metal layer 13 is disposed between the substrate 11 and the magnetic layer 12, but it may also be disposed on the outer surface of the magnetic layer 12.

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 magnetic layer will also be thin, reducing its electromagnetic wave absorption performance and the strength of the entire sheet. On the other hand, if the overall thickness of the electromagnetic noise suppression sheet is too thick, its flexibility will be reduced, making it difficult to wrap around a cable or connector for use.

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

(Method for manufacturing an electromagnetic noise suppression sheet)
An embodiment of a method for manufacturing an electromagnetic noise suppression sheet according to the present invention will now be described. The method for manufacturing an electromagnetic noise suppression sheet according to the present invention 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.

<Paint for forming magnetic layer>
The magnetic layer-forming paint can be prepared by mixing spherical soft magnetic material, a binder, and a solvent.

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

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.

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.

The magnetic layer-forming paint may further contain surface conditioners, antifoaming agents, thickeners, etc.

<Formation of magnetic layer>
Examples of methods that can be used to apply 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.

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

The above-mentioned calendering can be carried out using metal rolls or resin rolls. Furthermore, when forming the magnetic layer on a sheet, calendering can be carried out by pressing. Calendering is preferably carried out at a temperature above the glass transition temperature of the formed magnetic layer, and calendering can be carried out multiple times.

(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.

Below, a coaxial cable, which is one type of communication cable according to this embodiment, will be described with reference to the drawings. In the coaxial cable described below, the electromagnetic noise suppression sheet of the present application is used as the electromagnetic noise suppression layer of the coaxial cable.

Figure 5 is a schematic cross-sectional view showing an example of a coaxial cable. The coaxial cable 30 comprises 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 application described above, and is composed of a base layer 35a and a magnetic layer 35b arranged on one side of the base layer 35a.

In Figure 5, the magnetic layer 35b of the magnetic sheath layer 35 is positioned on the axial center side, but the substrate layer 35a may also be positioned on the axial center side.

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

(Electronic equipment)
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.

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 mean "parts by mass."

Example 1
<Preparation of paint for forming magnetic layer>
The following components were mixed and dispersed to prepare a coating material 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 "PLASCOAT 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 "PLASCOAT Z-730", Tg: 43 ° C., solid content: 25.0% by mass, solvent: water): 8.3 parts (4) Crosslinking agent (O Xazoline group-containing polymer, manufactured by 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

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

<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 in a calendaring device having a metal roll at a temperature of 50° C. and a linear pressure of 50 kg/cm, thereby producing an electromagnetic noise suppression sheet of Example 1 in which a magnetic layer was formed on one main surface.

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.

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.

(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.

(Comparative Example 2)
An electromagnetic noise suppression sheet of Comparative Example 2 was produced in the same manner as in Example 1, except that Fe—Si—Cr spherical iron powder (Fe _88.8 Si _6.2 Cr _5.0 , Fe content: 87.0 mass %) was used as the soft magnetic material instead of the spherical carbonyl iron powder (product name "YW-5") and the thickness of the magnetic layer was changed to 100 μm.

(Comparative Example 3)
An electromagnetic noise suppression sheet of Comparative Example 3 was produced in the same manner as in Example 1, except that, as the soft magnetic material, Fe—Si—Cr spherical iron powder (Fe _88.8 Si _6.2 Cr _5.0 , Fe content: 87.0 mass %) was used instead of spherical carbonyl iron powder (product name "YW-5") and the thickness of the magnetic layer was changed to 30 μm.

For the electromagnetic noise suppression sheets of Examples 1 to 3 and Comparative Examples 1 to 3, the transmission attenuation rate per unit area (Rtp-S), M ₈ t1/M 8 t2, and the average value of the return loss (S11) at measurement frequencies of 10 GHz to 30 GHz were measured using the above-mentioned measurement method with respect to the magnetization amount M ₁₀ t, measured by the microstrip line method at ₂₈ GHz.

The above results are shown in Table 1, along with the magnetic material and thickness of the magnetic layer of the electromagnetic noise suppression sheet produced.

Table 1 shows that the electromagnetic noise suppression sheets of Examples 1 to 3 were able to achieve a transmission attenuation ratio (Rtp-S) of 3 dB·cm ² /emu or more relative to the magnetization per unit area (M ₁₀ t) measured by the microstrip line method at 28 GHz, indicating a higher electromagnetic wave absorption rate relative to the magnetization per unit area of the magnetic layer 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 M ₈ t1/M ₈ t2 ratio of 1.35 or more, indicating that the in-plane magnetic anisotropy of the magnetic layer was greater than the magnetic anisotropy 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 frequencies between 10 GHz and 30 GHz, indicating low reflection.

The following additional embodiments are disclosed regarding the embodiments of the present application including the above-described Examples 1 to 3.
(Additional Embodiment 1) An electromagnetic noise suppression film including a magnetic layer,
the magnetic layer includes spherical soft magnetic material and a binder,
An electromagnetic noise suppression film _{characterized in that, when an external magnetic field of 10 kOe is applied in the in-plane direction of the magnetic layer, the transmission attenuation rate relative to the magnetization per unit area in the in-plane direction of the magnetic layer, M10t ,} measured by a microstrip line method at 28 GHz, is 3 dB· ^cm2 /emu or more, where M10t is the magnetization per unit area in the in-plane direction of the magnetic layer.
(Additional Form 2) An electromagnetic noise suppression film according to Additional Form 1, in which the ratio M8t1/M8t2 is 1.35 or greater, where _M8t1 is the amount of magnetization per unit area in the in-plane direction when an external magnetic field of 10 kOe is applied to the magnetic layer in the in-plane direction and then the external magnetic field is changed to 8 kOe, and _M8t2 is the amount of magnetization per unit area in the perpendicular direction when an external magnetic field of ₁₀ kOe is applied to the magnetic layer in the perpendicular direction and then the external magnetic field is changed to ₈ kOe.
(Additional Form 3) The electromagnetic noise suppression film according to Additional Form 1 or 2, wherein the spherical soft magnetic particles are spherical carbonyl iron.
(Additional Form 4) The electromagnetic noise suppression film according to Additional Form 3, wherein the carbonyl iron contains 97.5 mass % or more of iron.
(Additional Form 5) The 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) The electromagnetic noise suppression film according to any one of Additional Forms 1 to 5, wherein the magnetic layer has a thickness of 5 μm or more and less than 60 μm.
(Additional Form 7) The electromagnetic noise suppression film according to any one of Additional Forms 1 to 5, wherein the magnetic layer has a thickness of 10 μm or more and 30 μm or less.
(Additional Form 8) The electromagnetic noise suppression film according to any one of Additional Forms 1 to 7, 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 value of the return loss is −20 dB or less.
(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) The 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 including 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.

This application may be implemented in forms other than those described above. The embodiments disclosed in this application are merely examples and are not intended to be limiting. The scope of this 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 included within the scope of the claims.

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 (13)

An electromagnetic noise suppression film including a magnetic layer,
the magnetic layer includes spherical soft magnetic material and a binder,
An electromagnetic noise suppression film _{characterized in that, when an external magnetic field of 10 kOe is applied in the in-plane direction of the magnetic layer, the transmission attenuation rate relative to the magnetization per unit area in the in-plane direction of the magnetic layer, M10t ,} measured by a microstrip line method at 28 GHz, is 3 dB· ^cm2 /emu or more, where M10t is the magnetization per unit area in the in-plane direction of the magnetic layer. 2. The electromagnetic noise suppression film according to claim 1, wherein the ratio M8t1/M8t2 is 1.35 or greater, where _M8t1 is the amount of magnetization per unit area in the in-plane direction when an external magnetic field of 10 kOe is applied to the magnetic layer in the in-plane direction and then the external magnetic field is changed to 8 kOe, and _M8t2 is the amount of magnetization per unit area in the perpendicular direction when an external magnetic field of ₁₀ kOe is applied to the magnetic layer in the perpendicular direction and then the external magnetic field is changed to ₈ kOe. The electromagnetic noise suppression film according to claim 1, wherein the spherical soft magnetic material is spherical carbonyl iron. The electromagnetic noise suppression film according to claim 3, wherein the carbonyl iron contains 97.5 mass% or more of iron. 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%. 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. 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. The electromagnetic noise suppression film according to claim 1, wherein when the return loss is measured using the microstrip line method at a measurement frequency range of 10 GHz to 30 GHz, the average return loss is -20 dB or less. An electromagnetic noise suppression sheet comprising a substrate and the electromagnetic noise suppression film described in any one of claims 1 to 8. The electromagnetic noise suppression sheet according to claim 9, wherein the substrate is a resin film. The electromagnetic noise suppression sheet according to claim 9, further comprising a metal layer. A communication cable comprising the electromagnetic noise suppression film described in any one of claims 1 to 8. An electronic device comprising the electromagnetic noise suppression film described in any one of claims 1 to 8.