Near-field noise suppression sheet and manufacturing method thereof

Abstract

An object of the present invention is to provide a near-field noise suppression sheet having an imaginary magnetic permeability μ" of 2.0 or greater at 10 GHz, exhibiting excellent noise suppression performance in a frequency band exceeding 10 GHz, and having sufficient flexibility. The near-field noise suppression sheet of the present invention comprises a substrate composed of an organic material and flat Fe powder supported on the substrate, wherein the Fe powder has an Fe content of 95 mass% or greater, a thickness of 1 μm or less, and a powder diameter of 20 μm or less, and the filling amount of the Fe powder relative to the substrate is 40 vol% or greater and 70 vol% or less, and the half-value width of the peak of the bcc (200) plane of Fe detected by powder X-ray diffraction is 0.4 or greater.

Description

Technical Field

[0001] The present invention relates to a near-field noise suppression sheet and a method for manufacturing the same. Background Art

[0002] With the rapid development of communications, electronic devices using the GHz band have become popular. For example, in previous mobile communications, frequency bands ranging from several hundred MHz to around 3 GHz have been used. However, in the fifth-generation mobile system (5G), the use of submillimeter wave bands with higher frequencies is being considered. In addition, as electronic devices become thinner and shorter, the space available in the internal structure is becoming less, and the electromagnetic interference problem in electrical and electronic circuits is becoming more serious. Against this background, there is a demand for noise suppression sheets for the near field that are thin and effective in frequency bands exceeding 10 GHz.

[0003] A typical noise suppression sheet has a flat soft magnetic powder loaded on a base material made of an organic substance, and converts noise into heat through the magnetic loss of the soft magnetic powder. The noise suppression performance of the noise suppression sheet depends on the magnetic permeability of the soft magnetic powder contained in the noise suppression sheet. Usually, the magnetic permeability is expressed as a complex magnetic permeability μ = μ'-jμ" using the real magnetic permeability μ' and the imaginary magnetic permeability μ", where μ' represents the scale of noise absorption and μ" represents the scale of noise conversion into heat. In the case of a noise suppression sheet that utilizes magnetic loss, μ" becomes particularly important. In other words, it is particularly important to distribute μ" in the frequency band of the radio wave noise to be suppressed. In order to obtain a near-field noise suppression sheet that is effective also in the frequency band exceeding 10 GHz, it is desired that μ" at 10 GHz is 2.0 or more.

[0004] As noise suppression sheets for the GHz band, Patent Documents 1 and 2 disclose noise suppression sheets using a flat magnetic material containing more than 80 mass % of Fe.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6280157;

[0008] Patent Document 2: Japanese Patent No. 6633037.

[0009] However, the noise suppression sheets described in Patent Documents 1 and 2 have an imaginary magnetic permeability μ" of less than 2 at 10 GHz, and cannot function in a frequency band exceeding 10 GHz.

[0010] Since the product of magnetic permeability and frequency depends on the saturation magnetization of the magnetic material, using a magnetic material with a higher saturation magnetization can achieve higher frequencies if the magnetic permeability is constant. Since Fe has a high saturation magnetization, increasing the Fe content in noise suppression sheets has been considered to achieve noise suppression sheets targeting the GHz band. However, excessively high Fe content reduces the sheet's flexibility, making it less durable for practical use. Summary of the Invention

[0011] The present invention has been made in view of this situation, and an object of the present invention is to provide a near-field noise suppression sheet having an imaginary magnetic permeability μ" of 2.0 or greater at 10 GHz, exhibiting excellent noise suppression performance even in a frequency band exceeding 10 GHz, and having sufficient flexibility.

[0012] Solutions for solving problems

[0013] In order to solve the above-mentioned problems, the inventors have repeatedly conducted in-depth research and obtained the following insights. Spherical Fe powder with an Fe content of 95 mass% or more and an average particle size of 2 μm or more and 8 μm or less is flattened so that its thickness is 1 μm or less and the powder diameter is 20 μm or less. The flattening is carried out in a wet manner, and no heat treatment of 200°C or more is performed during the drying of the powder after processing. By treating in this way, the magnetic anisotropy in the Fe powder can be improved. By filling the flat Fe powder prepared in this way with 40 vol% or more and 70 vol% or less in the base material, a near-field noise suppression sheet can be provided which has an imaginary magnetic permeability μ" of 2.0 or more at 10 GHz, exhibits excellent noise suppression performance in the frequency band exceeding 10 GHz, and has sufficient flexibility.

[0014] The present invention has been completed based on the above findings. Specifically, the main contents of the present invention are as follows.

[0015] [1] A near-field noise suppression sheet comprising a substrate composed of an organic material and flat Fe powder supported on the substrate.

[0016] The Fe powder has an Fe content of 95 mass% or more, a thickness of 1 μm or less, and a powder diameter of 20 μm or less.

[0017] The filling amount of Fe powder relative to the above-mentioned base material is 40 vol% or more and 70 vol% or less,

[0018] The half-value width of the peak of the bcc (200) plane of Fe detected by powder X-ray diffraction is 0.4 or more.

[0019] [2] The near-field noise suppression sheet according to [1] above, wherein the imaginary magnetic permeability μ" at 10 GHz is 2.0 or greater.

[0020] [3] The near-field noise suppression sheet according to [1], wherein the surface resistance of the near-field noise suppression sheet is 10 5 Ω / □ or more.

[0021] [4] The near-field noise suppression sheet according to [2], wherein the surface resistance of the near-field noise suppression sheet is 10 5 Ω / □ or more.

[0022] [5] The near-field noise suppression sheet according to [1] or [2] above, wherein the Fe powder is obtained by flattening carbonyl iron powder.

[0023] [6] The near-field noise suppression sheet according to [1] or [2], further comprising a flame retardant composed of at least one of a nitrogen-based compound and a hydroxide-based compound.

[0024] [7] The near-field noise suppression sheet according to [4] above, further comprising a flame retardant composed of at least one of a nitrogen-based compound and a hydroxide-based compound.

[0025] [8] The near-field noise suppression sheet according to [1] or [2], wherein the thickness of the near-field noise suppression sheet is not less than 25 μm and not more than 1200 μm.

[0026] [9] The near-field noise suppression sheet according to [4] or [7] above, wherein the thickness of the near-field noise suppression sheet is greater than or equal to 25 μm and less than or equal to 1200 μm.

[0027]

[10] A method for manufacturing a near-field noise suppression sheet, the method comprising:

[0028] A raw material Fe powder having an Fe content of 95 mass% or more and an average particle size of 2 μm or more and 8 μm or less is flattened by wet processing to obtain a flat Fe powder having a thickness of 1 μm or less and a powder diameter of 20 μm or less.

[0029] The flat Fe powder is mixed with a base material composed of an organic matter to obtain a mixture.

[0030] The mixture is formed into a sheet to obtain a near-field noise suppression sheet.

[0031] However, the flat Fe powder after the flattening process is not subjected to a heat treatment at 200° C. or higher.

[0032]

[11] The method for manufacturing a near-field noise suppression sheet according to

[10] above, wherein the raw material Fe powder is carbonyl iron powder.

[0033] Effects of the Invention

[0034] According to the present invention, a near-field noise suppression sheet can be provided that has an imaginary magnetic permeability μ" of 2.0 or more at 10 GHz, exhibits excellent noise suppression performance even in a frequency band exceeding 10 GHz, and has sufficient flexibility. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present invention will be described. In addition, in this specification, a numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0036] The near-field noise suppression sheet of this embodiment includes a base material made of an organic substance and flat Fe powder supported on the base material.

[0037] The Fe powder has an Fe content of 95 mass% or more, a thickness of 1 μm or less, and a powder diameter of 20 μm or less.

[0038] The filling amount of Fe powder relative to the above-mentioned base material is 40 vol% or more and 70 vol% or less,

[0039] The half-value width of the peak of the bcc (200) plane of Fe detected by powder X-ray diffraction is 0.4 or more.

[0040] The near-field noise suppression sheet contains Fe powder with high saturation magnetization as a magnetic loss material. Since saturation magnetization depends on Fe concentration, the Fe powder preferably has a high Fe content. The Fe content of the Fe powder is 95 mass% or greater. The Fe content of the Fe powder is preferably 97 mass% or greater, and more preferably 99 mass% or greater. The upper limit of the Fe content of the Fe powder is not particularly limited and may be 100%.

[0041] The thickness of the flat Fe powder is 1 μm or less. When the thickness of the flat Fe powder is greater than 1 μm, the distribution of the imaginary magnetic permeability μ" cannot be in the GHz band, and the distribution width of the imaginary magnetic permeability μ" also becomes narrow. Therefore, a near-field noise suppression sheet having an imaginary magnetic permeability μ" of 2.0 or more at 10 GHz cannot be obtained. The thickness of the flat Fe powder is preferably 0.7 μm or less, more preferably 0.5 μm or less. The lower limit of the thickness of the flat Fe powder is not particularly limited, but can be 0.1 μm or more from the viewpoint that the processing will gradually tend to saturation even if the flat processing time is extended, and that long-term flat processing will reduce productivity.

[0042] The powder diameter of the flat Fe powder is 20 μm or less. In addition, the "powder diameter" here is defined as the length in the long side direction of the Fe powder in the observation image of the cross section of the noise suppression sheet observed through a scanning electron microscope. When the diameter of the flat Fe powder is greater than 20 μm, it is difficult to obtain a smooth flat Fe powder, and the surface area of ​​the flat Fe powder also becomes larger. Therefore, the contact between the Fe powders in the substrate increases, it is difficult to maintain insulation, and the surface resistance of the noise suppression sheet becomes lower. When the surface resistance of the noise suppression sheet is low, not only the risk of short circuit in the electronic / electrical circuit increases, but also the noise electromagnetic wave is easily reflected on the surface of the noise suppression sheet, and the noise suppression effect is reduced. In particular, when Fe powder with a high Fe content is used as in the present invention, the reduction in surface resistance is particularly significant. The reason is that since the Fe powder does not contain a large amount of semi-metallic elements such as Si and C, the resistance of the Fe powder itself is low. If the flat Fe powder has a powder diameter of 20 μm or less, the surface area of ​​the Fe powder will not become too large, and a sheet with a surface resistance of 10 5 A near-field noise suppression sheet having a surface resistance of Ω / □ or greater. The lower limit of the powder diameter of the flat Fe powder is not particularly limited, but the powder diameter is preferably greater than 5 μm to reduce the influence of the powder's demagnetization field.

[0043] In addition, the thickness and powder diameter of the flat Fe powder are calculated as follows: the cross-section of the near-field noise suppression sheet is observed using a scanning electron microscope, and the average value of the thickness and powder diameter of any 20 or more Fe powders in the observation image is calculated and used as the thickness and powder diameter of the flat Fe powder.

[0044] The filling amount of Fe powder relative to the base material is 40 vol% or more and 70 vol% or less. If the filling amount of flat Fe powder is less than 40 vol%, the desired magnetic permeability cannot be obtained. If the filling amount is more than 70 vol%, the flexibility of the noise suppression sheet is reduced and the surface resistance of 10 5 Ω / □ or more. The filling amount of Fe powder relative to the substrate is preferably 50 vol% or more. In addition, the filling amount of Fe powder relative to the substrate is preferably 60 vol% or less.

[0045] Flat Fe powder can be obtained by flattening raw Fe powder. The details of flattening will be described later.

[0046] The half width of the peak of the bcc (200) plane of Fe detected in the powder X-ray diffraction is 0.4 or more. By improving the magnetic anisotropy of the flat Fe powder, the distribution of the imaginary magnetic permeability μ" can be effectively extended to the submillimeter wave band. In the present invention, the raw material Fe powder is flattened to produce crystalline distortion, resulting in an increase in the magnetic anisotropy of the processed flat Fe powder. In order to confirm the crystalline distortion of the Fe powder in the noise suppression sheet, the half width of the peak (near 2θ=65°) of the bcc (200) plane of Fe detected in the powder X-ray diffraction (Cu-Kα) on the surface or inside of the noise suppression sheet is determined. In this embodiment, the half width of the peak of the bcc (200) plane of Fe is made to be 0.4 or more in order to make the imaginary magnetic permeability μ" at 10 GHz be 2.0 or more. The half width of the peak of the bcc (200) plane of Fe detected in the powder X-ray diffraction is preferably 0.45 or more. The upper limit of the half width of the peak of the bcc (200) plane of Fe detected in the powder X-ray diffraction is not particularly limited, but when the flattening time is extended, the processing gradually tends to saturation, and therefore the magnetic anisotropy of the powder gradually tends to saturation, and the magnetic anisotropy of the powder is prevented from becoming larger, the magnetic permeability is prevented from decreasing, and the imaginary magnetic permeability μ" at 10 GHz is more preferably prevented. The half width of the peak of the bcc (200) plane of Fe detected in the powder X-ray diffraction is measured as follows. The surface direction of the rectangular measurement sample cut out from the noise suppression sheet is used as the measurement direction. The measurement is carried out on a fixed plane using a focusing optical system. Since the peak of the bcc (200) plane of Fe appears near 2θ=65°, the wider 2θ=50°~80° is used as the measurement range, and continuous measurement is performed at a fixed speed. At this time, in order to improve the accuracy of the measured value, the scanning speed is reduced to less than 1° / minute, and the sampling interval is reduced to less than 0.01°. In the diffraction peak near 2θ=65° detected by this measurement, the peak width at half the maximum peak intensity value after subtracting the background is defined as the half width. As a measuring device, an X-ray diffraction device made by Rigaku: Smart-Lab is used.

[0047] As the organic material constituting the substrate, based on environmental regulations such as the RoHS directive, it is preferably an organic material that does not contain halogen elements. Because near-field noise suppression sheets require not only flexibility but also heat resistance and durability, the organic material is preferably a rubber-based material selected from at least one of silicone rubber, acrylic rubber, nitrile rubber, and butyl rubber, or a mixture thereof. Resin materials such as epoxy resin can also be used as the organic material. In addition, to improve the flexibility of the near-field noise suppression sheet, a plasticizer can be added as needed.

[0048] In order to improve the flame retardancy of the near-field noise suppression sheet, a flame retardant can also be added. As a flame retardant, a flame retardant that does not contain halogen elements like organic matter is preferred. Specifically, it can be selected from: nitrogen compounds such as melamine cyanurate; and one or more hydroxide compounds such as aluminum hydroxide and magnesium hydroxide. In addition, if there is no restriction on the use environment, red phosphorus can also be used as one of the flame retardants. It is preferred that the average particle size of the flame retardant in the final near-field noise suppression sheet is 10 μm or less. It is more preferred that the average particle size of the flame retardant in the near-field noise suppression sheet is 0.2 μm or more and 6 μm or less. The flame retardant is dispersed between the flat Fe powders. If the average particle size of the flame retardant is 10 μm or less, the flame retardant does not reduce the orientation degree of the Fe powder in the in-plane direction of the noise suppression sheet and a more preferred noise suppression effect can be obtained. In addition, if the average particle size of the flame retardant is 0.2 μm or more, high flame retardancy can be maintained. The amount of the flame retardant filled in the base material is preferably 10 vol% or more and preferably 30 vol% or less.

[0049] According to the present embodiment, a near-field noise suppression sheet having an imaginary permeability μ" value of 2.0 or more at 10 GHz can be provided. The imaginary permeability μ" value of the near-field noise suppression sheet at 10 GHz is preferably 3 or more, more preferably 4.5. In addition, there is no particular upper limit on the value of the imaginary permeability μ" of the near-field noise suppression sheet at 10 GHz. When the imaginary permeability μ" value at 10 GHz is at the upper limit, the filling amount of the flat Fe powder will be further increased. In order to better ensure the insulation of the flat powder through the base material to make the surface resistance better and to make the flexibility of the near-field noise suppression sheet better, the imaginary permeability μ" value of the near-field noise suppression sheet at 10 GHz is preferably 4.5 or less. Here, the method for measuring the imaginary permeability μ" value of the near-field noise suppression sheet at 10 GHz is as follows. A ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3 mm was cut out from the near-field noise suppression sheet. This sample was inserted into a coaxial tube sample holder, and the imaginary magnetic permeability μ" at 10 GHz was measured by the S-parameter method using a network analyzer P5008A manufactured by Keysight Technologies.

[0050] The surface resistance of the near field noise suppression sheet is preferably 10 5 Ω / □ or more. Here, the surface resistance of the near-field noise suppression sheet was measured using a resistance meter: Hiresta-UXMCP-HT800 manufactured by Mitsubishi Analytech, using a double-loop probe.

[0051] The thickness of the near-field noise suppression sheet is not particularly limited, but in one example, it can be 25 μm or more and 1200 μm or less.

[0052] Next, a method for manufacturing the near-field noise suppression sheet of this embodiment is described. The method for manufacturing the near-field noise suppression sheet of this embodiment includes:

[0053] A raw material Fe powder having an Fe content of 95 mass% or more and an average particle size of 2 μm or more and 8 μm or less is flattened by wet processing to obtain a flat Fe powder having a thickness of 1 μm or less and a powder diameter of 20 μm or less.

[0054] The flat Fe powder is mixed with a base material composed of an organic matter to obtain a mixture.

[0055] The mixture is formed into a sheet to obtain a near-field noise suppression sheet.

[0056] However, the flat Fe powder after the flattening process is not subjected to a heat treatment at 200° C. or higher.

[0057] First, a raw material Fe powder having an Fe content of 95 mass% or more and an average particle size of 2 μm to 8 μm is flattened to a thickness of 1 μm or less and a powder diameter of 20 μm or less, thereby producing a flat Fe powder. The flattening method can be any known or arbitrary mechanical process such as an attritor or a bead mill.

[0058] The Fe powder after flattening is not subjected to a heat treatment of 200°C or above. Here, “the Fe powder after flattening is not subjected to a heat treatment of 200°C or above” means that not only the Fe powder itself is not subjected to a heat treatment of 200°C or above, but also the mixture of the Fe powder after flattening and the base material, and the near-field noise suppression sheet obtained by molding the mixture are not subjected to a heat treatment of 200°C or above. This is because when a heat treatment of 200°C or above is applied, the crystalline distortion generated by the flattening is reduced due to the annealing effect, and the magnetic anisotropy in the Fe powder cannot be improved. Therefore, when the Fe powder after flattening is dried by heat treatment, the drying temperature is set to below 200°C. In addition, flattening can be performed in either a dry or wet manner, but in the case of a dry method, in order to prevent oxidation of the powder during processing, the processing chamber must be kept in an inert environment, which is not suitable for industrial mass production. Therefore, flattening is preferably performed in a wet manner using isopropyl alcohol (IPA) or the like as a solvent.

[0059] As the raw material Fe powder before flattening, one with an average particle size of 2 μm to 8 μm is used. An example of a raw material that meets this requirement is carbonyl iron. Carbonyl iron is a small-particle spherical powder synthesized through a chemical process. Industrially, carbonyl iron with an Fe content of 95 mass% or more and an average particle size of 2 μm to 8 μm can also be produced. Carbonyl iron powder comes in two types: hard powder and soft powder obtained by reduction annealing the hard powder. Either type can be used. From the perspective of flattening processability, soft powder, which has a soft mechanical strength, is preferred.

[0060] As raw material Fe powder, in addition to carboxyl iron powder, atomized powder with an Fe content of 95 mass% or more and an average particle size of 2 μm or more and 8 μm or less can also be used as raw material Fe powder. However, since it is difficult to efficiently produce powder with an average particle size of less than 10 μm by the atomization method, the average particle size is adjusted to 2 μm or more and 8 μm or less by classification. In addition, in atomized powder with an average particle size greater than 10 μm, it is difficult to obtain a flat Fe powder with a thickness of less than 1 μm and a powder diameter of less than 30 μm by flattening. Although this can be achieved through long-term flattening and subsequent classification, productivity is reduced and powder cost is increased. In addition, the wear of the medium during flattening also becomes severe, medium impurities are mixed into the powder, and the durability of the medium is also reduced.

[0061] The flat Fe powder after flattening can also be subjected to annealing in an inert environment, coating to improve the powder's insulation, heat treatment, and coupling agent treatment to improve the bonding between the powder and the organic binder. In this case, the heat treatment temperature should be below 200°C to prevent annealing of the Fe powder.

[0062] Next, the flat Fe powder is mixed with a base material composed of an organic matter to obtain a mixture. Next, the mixture is formed into a sheet to obtain a noise suppression sheet. As a forming method, a known or arbitrary method such as a coating method and a calendering method can be used. Here, an example of using a coating method as a forming method is described. Flat Fe powder, an organic matter, an organic solvent, and an arbitrary flame retardant are adjusted to a specified mixing ratio and mixed and stirred to prepare a slurry. The slurry is formed into a sheet by a scraper and dried. At this time, in the final noise suppression sheet, the flat Fe powder is added in such a manner that the filling amount becomes greater than 40 vol% and less than 70 vol%.

[0063] To increase the horizontal orientation and density of the flat Fe powder, the noise suppression sheet is then preferably pressed while heated to a temperature above the softening point of the organic material (e.g., approximately 60-150°C). While varying depending on the manufacturing conditions, the thickness of the sheet obtained by the coating method is approximately 25-500 μm. When producing a noise suppression sheet with a thickness greater than 500-1200 μm, the desired thickness can be achieved by stacking the coated sheets and subjecting them to the aforementioned pressing process.

[0064] As mentioned above, the near-field noise suppression sheet and the manufacturing method thereof of the present invention have been described. However, the present invention is not limited to the above-described embodiment, and appropriate changes can be made within the scope of the claims.

[0065] Example

[0066] (Example 1)

[0067] Using IPA as a solvent, a spherical carbonyl iron powder as a soft powder with an iron content of 97.5 mass% and an average particle size of 3.5 μm was flattened in a wet process to a thickness of less than 1 μm to obtain a flat Fe powder. After the flat Fe powder was dried in an oven at 80°C in the atmosphere, it was heat-treated at 150°C for 1 hour in the atmosphere to form an insulating oxide film on the surface of the powder. Next, acrylic rubber was used as a substrate and toluene was used as an organic solvent. The powder was formed into a sheet by a scraper and dried. Thereafter, a sheet with a thickness of 100 μm was produced by pressing at 120°C. In addition, the filling rate of the flat Fe powder was 40 vol%.

[0068] (Example 2)

[0069] A sheet having a thickness of 100 μm was prepared under the same conditions as in Example 1 except that the filling rate of the flat Fe powder was 50 vol %.

[0070] (Example 3)

[0071] A sheet having a thickness of 100 μm was prepared under the same conditions as in Example 1 except that the filling rate of the flat Fe powder was set to 60 vol %.

[0072] (Example 4)

[0073] A sheet having a thickness of 100 μm was prepared under the same conditions as in Example 1 except that the filling rate of the flat Fe powder was set to 70 vol %.

[0074] (Comparative Example 1)

[0075] A sheet having a thickness of 100 μm was prepared under the same conditions as in Example 1 except that the filling rate of the flat Fe powder was set to 35 vol %.

[0076] (Comparative Example 2)

[0077] A sheet having a thickness of 100 μm was prepared under the same conditions as in Example 1 except that the filling rate of the flat Fe powder was 75 vol %.

[0078] (Comparative Example 3)

[0079] In Example 1, the flat Fe powder after heat treatment was annealed in Ar at 600° C. for 5 hours. A sheet having a thickness of 100 μm was produced under the same conditions as in Example 1 except that the annealing treatment was performed.

[0080] (Comparative Example 4)

[0081] In Example 1, a sheet having a thickness of 100 μm was produced under the same conditions as in Example 1 except that the thickness of the powder after flattening was set to be greater than 1 μm.

[0082] (Example 5)

[0083] Spherical carbonyl iron powder, a soft powder with an Fe content of 96.7 mass% and an average particle size of 4.1 μm, was flattened to a thickness of 1 μm or less. Using acrylic rubber as the base material, melamine cyanurate as the flame retardant, and toluene as the organic solvent, the sheet was formed using a doctor blade and dried. Subsequently, the sheet was pressed at 150°C to a thickness of 100 μm. The filling ratio of the flat Fe powder was 40 vol%, and the filling ratio of the flame retardant was 30 vol%.

[0084] The thickness of the Fe powder, the powder diameter, the half width of the peak of the bcc (200) plane of Fe detected in the powder X-ray diffraction, the value of the imaginary magnetic permeability μ" at 10 GHz, and the surface resistance of each noise suppression sheet manufactured according to the above method were measured. In addition, the results of each noise suppression sheet are shown in Table 1. In Examples 1, 2, 3, 4, and 5, the half width of the peak of the bcc (200) plane of Fe detected in the powder X-ray diffraction (Cu-Kα) on the surface of the noise suppression sheet was greater than 0.4, and μ" at 10 GHz was greater than 2.0. In Comparative Example 1, since the filling amount of the flat Fe powder was too small, the powder orientation degree in the horizontal direction became poor, and μ" at 10 GHz was less than 2.0. In Comparative Example 2, since the filling amount of the flat Fe powder was too much, it was difficult to ensure the insulation of the flat Fe powder by the acrylic rubber, and the surface resistance was less than 10 5Ω / □, and cracks were generated when the sheet was bent, resulting in a lack of flexibility. In Comparative Example 3, the magnetic anisotropy of the flat Fe powder was alleviated by annealing, and the half-width of the (200) peak on the sheet surface in the powder X-ray diffraction was less than 0.4, and μ" at 10 GHz was less than 2. In Comparative Example 4, the flatness of the powder was insufficient, and the magnetic anisotropy of the flat Fe powder was also reduced, and the half-width of the (200) peak on the sheet surface in the powder X-ray diffraction was less than 0.4, and μ" at 10 GHz was less than 2.0.

[0085] [Table 1]

[0086]

[0087] Industrial applicability

[0088] The near-field noise suppression sheet of the present invention can be incorporated into electronic devices and can particularly effectively absorb radio waves generated within these electronic devices.

Claims

1. A near-field noise suppression sheet comprising a substrate composed of an organic substance and flat Fe powder supported on the substrate. The Fe powder has an Fe content of 95 mass% or more, a thickness of 1 μm or less, and a powder diameter of 20 μm or less. The filling amount of Fe powder relative to the substrate is 40 vol% or more and 70 vol% or less, The half-value width of the peak of the bcc (200) plane of Fe detected by powder X-ray diffraction is 0.4 or more.

2. The near-field noise suppression sheet according to claim 1, wherein The value of the imaginary magnetic permeability μ" at 10 GHz is 2.0 or more.

3. The near-field noise suppression sheet according to claim 1, wherein The surface resistance of the near field noise suppression sheet is 10 5 Ω / □ or more.

4. The near-field noise suppression sheet according to claim 2, wherein The surface resistance of the near field noise suppression sheet is 10 5 Ω / □ or more.

5. The near-field noise suppression sheet according to claim 1 or 2, wherein: The Fe powder is obtained by flattening carbonyl iron powder. 6 . The near-field noise suppression sheet according to claim 1 , further comprising a flame retardant composed of at least one of a nitrogen-based compound and a hydroxide-based compound. 7 . The near-field noise suppression sheet according to claim 4 , further comprising a flame retardant composed of at least one of a nitrogen-based compound and a hydroxide-based compound.

8. The near-field noise suppression sheet according to claim 1 or 2, wherein: The near-field noise suppression sheet has a thickness of 25 μm or more and 1200 μm or less.

9. The near-field noise suppression sheet according to claim 4 or 7, wherein: The near-field noise suppression sheet has a thickness of 25 μm or more and 1200 μm or less.

10. A method for manufacturing a near-field noise suppression sheet, the method comprising: A raw material Fe powder having an Fe content of 95 mass% or more and an average particle size of 2 μm or more and 8 μm or less is flattened by wet processing to obtain a flat Fe powder having a thickness of 1 μm or less and a powder diameter of 20 μm or less. The flat Fe powder is mixed with a base material composed of an organic matter to obtain a mixture, The mixture is formed into a sheet to obtain a near-field noise suppression sheet. However, the flat Fe powder after the flattening process is not subjected to a heat treatment at 200° C. or higher.

11. The method for manufacturing a near-field noise suppression sheet according to claim 10, wherein: The raw material Fe powder is carbonyl iron powder.

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