Near-field noise suppression sheet

Abstract

Provided is a near-field noise suppression sheet having excellent noise suppression performance in a high frequency band. This near-field noise suppression sheet is characterized by: including a base material, flat alloy powder supported in the base material, and one or more additives dispersed in the base material; and satisfying all of predetermined requirements (i), (ii), and (iii).

Description

Near-field noise suppression sheet

[0001] The present invention relates to a near-field noise suppression sheet.

[0002] As communications become more advanced, electronic devices using the GHz band are becoming more widespread. While conventional mobile communications have used frequency bands of around several hundred MHz, fifth-generation mobile communications systems (5G) are expected to use higher frequency bands, specifically bands of several GHz to several tens of GHz. In addition, as electronic devices become lighter, thinner, shorter, and smaller, the space available in their internal structures is becoming less, making electromagnetic interference problems in electrical and electronic circuits even more serious. Given this background, there is a demand for near-field noise suppression sheets that are effective in the MHz to GHz bands.

[0003] A typical noise suppression sheet contains flat soft magnetic powder supported in an organic substrate, and converts noise into heat through magnetic loss in the soft magnetic powder. The noise suppression performance of the noise suppression sheet depends on the properties of the soft magnetic powder contained in the noise suppression sheet.

[0004] As a near-field noise suppression sheet, for example, Patent Document 1 discloses a noise suppression sheet made by dispersing flat soft magnetic alloy powder with an oxide layer formed on the surface in a binder.

[0005] Japanese Patent Application Laid-Open No. 2005-281783

[0006] One index of noise suppression performance for a near-field noise suppression sheet is the internal decoupling ratio (Rda). This internal decoupling ratio (Rda) can be measured based on the IEC 62333-2 standard, and is expressed in dB. FIG. 3 shows an outline of the measurement results of the internal decoupling ratio (Rda) of an exemplary near-field noise suppression sheet. In FIG. 3, the negative direction of the vertical axis corresponds to the amount of noise absorption. As shown in FIG. 3, Rda usually has a peak in the negative direction at a specific frequency, and at this frequency (peak frequency), a particularly strong noise suppression effect is exhibited.

[0007] Here, it is known that the peak frequency of Rda depends on the thickness of the noise suppression sheet. That is, it is known that the thicker the noise suppression sheet, the more the Rda peak shifts to the lower frequency side. In other words, in anticipation of the fifth generation mobile communication system (5G), the Rda peak appears in a higher frequency band, and therefore, in order to obtain a noise suppression effect in a higher frequency band, it can be thought that the thickness of the noise suppression sheet should be reduced. However, since it is necessary to maintain the shape of the sheet, there is a limit to how much the sheet thickness can be reduced.

[0008] It has been suggested that the properties of the soft magnetic powder (material and various processing conditions) may also affect the peak frequency of Rda, but this has not yet been identified. Also, Fe-Si-Al alloy powder, which is a type of soft magnetic powder, is known to exhibit high magnetic permeability, but magnetic permeability is merely a physical property value and is not an index that directly represents noise suppression performance.

[0009] In light of the above, it is important to use soft magnetic powder while adjusting the Rda peak to a target frequency band, particularly a high frequency band (for example, 1 GHz or more and 10 GHz or less), and a means for achieving this is required to be established.

[0010] Therefore, an object of the present invention is to provide a near-field noise suppression sheet that has excellent noise suppression performance in the high frequency band.

[0011] The present inventors focused on Fe—Si—Al alloy powder as a soft magnetic powder and conducted extensive research to solve the above-mentioned problems. As a result, they first discovered that when flat Fe—Si—Al alloy powder is used, the peak frequency of Rda of the noise suppression sheet is affected by the orientation characteristics of the alloy powder. Then, as a result of further research, they discovered that by optimizing the composition of such flat soft magnetic powder, and by having peaks not only in the (400) plane of Fe—Si—Al but also in the (111) and (422) planes, and by achieving predetermined orientation characteristics, Rda peaks can be produced in higher frequency bands, and therefore noise suppression effects can be obtained in higher frequency bands.

[0012] The present invention has been made based on the above findings. That is, the gist and configuration of the present invention are as follows.

[0013] [1] A near-field noise suppression sheet including a substrate, flat alloy powder supported in the substrate, and one or more additives dispersed in the substrate, the near-field noise suppression sheet satisfying the following requirements (i), (ii), and (iii): (i): The flat alloy powder contains, by mass %, Fe １００－ｘ－ｙ Si ｘ Al ｙ (ii) In the X-ray diffraction of the near-field noise suppression sheet, a peak for the (400) plane, a peak for the (422) plane, and a peak for the (111) plane of Fe—Si—Al are present, and the peak intensity P （４００） , (422) plane peak intensity P （４２２） , and the peak intensity P of the (111) plane （１１１） is expressed by the following formula (a) and the following formula (b): P （４００） >P （４２２） ...(a) P （４００） >P （１１１） (iii): When the internal decoupling ratio Rda is measured at frequencies from 0.1 to 6 GHz in accordance with IEC 62333-2 on a test piece of the near-field noise suppression sheet having a size of 100 mm × 50 mm and a thickness t (mm), the peak frequency f (GHz) of Rda and the thickness t (mm) satisfy the following relationship: f ≧ −0.45ln(t) + 0.1 (A).

[0014] [2] In the X-ray diffraction, the peak intensity P of the (400) plane of Fe—Si—Al （４００） The peak intensity P of the (422) plane when （４２２） The near-field noise suppression sheet according to [1], wherein the ratio is 40 or more and 85 or less.

[0015] [3] In the X-ray diffraction, the peak intensity P of the (400) plane of Fe—Si—Al （４００）The peak intensity P of the (111) plane when （１１１） The near-field noise suppression sheet according to [1] or [2], wherein the ratio is 30 or more and 90 or less.

[0016] [4] The near-field noise suppression sheet according to any one of [1] to [3], wherein the additive comprises an aromatic amine-based antiaging agent, and the content of the aromatic amine-based antiaging agent is 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the flat alloy powder.

[0017] [5] The near-field noise suppression sheet according to any one of [1] to [4], wherein the additive comprises a silane coupling agent, and the amount of the silane coupling agent is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the flat alloy powder.

[0018] [6] The near-field noise suppression sheet according to any one of [1] to [5], wherein the additive contains a non-halogenated flame retardant in an amount of 20 parts by mass or less per 100 parts by mass of the flat alloy powder.

[0019] [7] The near-field noise suppression sheet according to any one of [1] to [6], which has a thickness of 0.050 mm or more and less than 0.500 mm.

[0020] [8] The near-field noise suppression sheet according to any one of [1] to [7], wherein the filling amount of the flat alloy powder is 25 vol % or more and 55 vol % or less.

[0021] [9] The near-field noise suppression sheet according to any one of [1] to [8], wherein the average particle size of the flat alloy powder is 30 μm or more and 80 μm or less.

[0022] According to the present invention, it is possible to provide a near-field noise suppression sheet that has excellent noise suppression performance in the high frequency band.

[0023] 1 is a plot of the thickness t (mm) and peak frequency f (GHz) of the sheets in the examples and comparative examples, and is a schematic diagram of the measurement results of the internal decoupling ratio (Rda) of an exemplary near-field noise suppression sheet.

[0024] Hereinafter, embodiments of the present invention will be described. However, the description is intended to exemplify the present invention and is not intended to limit the present invention in any way.

[0025] (Near-field noise suppression sheet) A near-field noise suppression sheet according to one embodiment of the present invention (hereinafter sometimes referred to as "the sheet of this embodiment") is a near-field noise suppression sheet including a substrate, flat alloy powder carried in the substrate, and one or more additives dispersed in the substrate, and is characterized in that it satisfies all of the following requirements (i), (ii), and (iii): (i): The flat alloy powder contains, by mass %, Fe １００－ｘ－ｙ Si ｘ Al ｙ (ii) In the X-ray diffraction of the near-field noise suppression sheet, a peak for the (400) plane, a peak for the (422) plane, and a peak for the (111) plane of Fe—Si—Al are present, and the peak intensity P （４００） , (422) plane peak intensity P （４２２） , and the peak intensity P of the (111) plane （１１１） is expressed by the following formula (a) and the following formula (b): P （４００） >P （４２２） ...(a) P （４００） >P （１１１） (iii): When the internal decoupling ratio Rda is measured at frequencies of 0.1 to 6 GHz in accordance with the IEC 62333-2 standard for a test piece of the near-field noise suppression sheet having a size of 100 mm × 50 mm and a thickness t (mm), the peak frequency f (GHz) of Rda and the thickness t (mm) satisfy the following relationship: f≧−0.45ln(t)+0.1 (A).

[0026] The sheet of this embodiment uses a flat Fe-Si-Al alloy powder with predetermined characteristics, and by providing peaks in the (111) and (422) planes of the Fe-Si-Al and by providing predetermined orientation characteristics, the resonant frequency changes and Rda peaks appear in a higher frequency band. Therefore, it is believed that the sheet of this embodiment can achieve noise suppression effects in a higher frequency band than conventional noise suppression sheets of the same thickness.

[0027] In the sheet of this embodiment, Fe powder with high saturation magnetization is used as the flat soft magnetic powder, and Fe—Si—Al alloy powder is used, to which Si and Al are added in order to minimize the magnetic anisotropy, and is supported in the substrate. More specifically, the flat alloy powder used in this embodiment contains, by mass %, Fe １００－ｘ－ｙ Si ｘ Al ｙ (where 12.2≦x+y≦17.8, 8.0≦x≦11.2, 4.2≦y≦6.6) (requirement (i)). That is, the flat Fe—Si—Al alloy powder used in this embodiment has a composition in which the Si content is 8.0 mass% or more and 11.2 mass% or less, the Al content is 4.2 mass% or more and 6.6 mass% or less, and the Fe content is 82.2 mass% or more and 87.8 mass% or less. If the composition of the alloy powder used is outside the above ranges, there is a risk that the desired peak intensity ratio in X-ray diffraction cannot be obtained.

[0028] The flat alloy powder used in this embodiment preferably has an average particle size of 30 μm or more and 80 μm or less. An average particle size of 80 μm or less makes it easier to obtain a flat, smooth alloy powder and to obtain a desired peak intensity ratio in X-ray diffraction. Furthermore, an average particle size of 80 μm or less prevents excessive contact between the alloy powder particles in the substrate, maintaining insulation and preventing a decrease in the surface resistance of the noise suppression sheet. A low surface resistance of the noise suppression sheet not only increases the risk of short circuits in electronic and electrical circuits, but also makes it easier for noise radio waves to be reflected on the surface of the noise suppression sheet, thereby reducing the noise suppression effect. In particular, when an alloy powder with a relatively high Fe content is used, as in this embodiment, the electrical resistance of the alloy powder itself is low, resulting in a significant decrease in surface resistance. In contrast, if the average particle size of the flat alloy powder is 80 μm or less, the surface area does not become excessively large, and the surface resistance of the resulting noise suppression sheet can be maintained at a predetermined value or higher (e.g., 1.0 × 10 ５ Ω / □ or more). On the other hand, the lower limit of the average particle size of the flat alloy powder is preferably 30 μm or more in order to reduce the effect of the demagnetizing field of the alloy powder and shift the peak frequency to a higher frequency. From the same viewpoint, the average particle size of the flat alloy powder is more preferably 40 μm or more, and more preferably 70 μm or less. In this specification, the average particle size of the flat alloy powder can be measured using a particle size distribution measuring instrument. The average particle size of the flat alloy powder can also be measured from the manufactured noise suppression sheet. In this case, the average particle size is defined as the average value of the longitudinal lengths of 20 or more random alloy powder particles in an image of the cross section of the noise suppression sheet observed with a scanning electron microscope.

[0029] The thickness of the flat alloy powder used in this embodiment is not particularly limited, but is, for example, 1 μm or less. The lower limit of the thickness of the flat alloy powder is not particularly limited, but can be 0.1 μm or more, because the flattening process saturates even if the flattening process time is extended and the flattening process for a long time reduces productivity.

[0030] In the sheet of this embodiment, X-ray diffraction shows peaks in the Fe-Si-Al (400), (422), and (111) planes (requirement (ii)). In this specification, "peaks" refers to a baseline being taken from the X-ray diffraction measurement results, and when the peak intensity of the highest peak based on this baseline is set to 100, an intensity of 1 or more is confirmed and the half-width is 2θ = 5° or less. In this specification, the X-ray diffraction measurement range is wide, from 2θ = 10° to 100°. Furthermore, in order to increase the accuracy of the measurement values, the scanning speed is slowed to 1° / min or less, the sampling interval is set to 0.01° or less, and measurements are continuously performed at a constant speed.

[0031] Furthermore, in X-ray diffraction, the sheet of this embodiment has a peak intensity P （４００） , (422) plane peak intensity P （４２２） , and the peak intensity P of the (111) plane （１１１） is expressed by the following formula (a) and the following formula (b): P （４００） >P （４２２） ...(a) P （４００） >P （１１１） ...(b) (Requirement (ii)). In other words, the sheet of this embodiment has a peak intensity P （４００） Peak intensity P （４２２） The ratio (P （４２２） / P （４００） ) is less than 1.00, and the peak intensity P （４００） Peak intensity P （１１１） The ratio (P （１１１） / P （４００） ) is less than 1.00. In this case, the peak intensity of the internal decoupling ratio Rda itself becomes sufficiently large, and the noise suppression effect itself can be further improved.

[0032] In the sheet of this embodiment, the peak intensity P （４００） The peak intensity P of the (422) plane when （４２２） It is preferable that the ratio of the peak intensity P （４００）Peak intensity P （４２２） The ratio (P （４２２） / P （４００） ) is preferably 0.40 or more and 0.85 or less. If the ratio is 40 or more, the decrease in the resonant frequency is suppressed, and the peak of the internal decoupling factor Rda can be shifted to a higher frequency band. Furthermore, if the ratio is 85 or less, the peak intensity of the internal decoupling factor Rda itself becomes sufficiently large, and thus the noise suppression effect itself can be further enhanced. Furthermore, if the ratio is 40 or more and 85 or less, the orientation characteristics become more desirable, and it becomes easier to satisfy the requirement (iii) described below. From the same viewpoint, the peak intensity P （４００） The peak intensity P of the (422) plane when （４２２） The ratio is more preferably 45 or more and more preferably 70 or less.

[0033] In the sheet of this embodiment, the peak intensity P （４００） The peak intensity P of the (111) plane when （１１１） It is preferable that the ratio of the peak intensity P （４００） Peak intensity P （１１１） The ratio (P （１１１） / P （４００） ) is preferably 0.30 or more and 0.90 or less. If the ratio is 30 or more, the decrease in the resonant frequency is suppressed, and the peak of the internal decoupling factor Rda can be shifted to a higher frequency band. Furthermore, if the ratio is 90 or less, the peak intensity of the internal decoupling factor Rda itself becomes sufficiently large, and as a result, the noise suppression effect itself can be further enhanced. Furthermore, if the ratio is 30 or more and 90 or less, the orientation characteristics become more desirable, and it becomes easier to satisfy the requirement (iii) described below. From the same viewpoint, the peak intensity P （４００） The peak intensity P of the (111) plane when （１１１） The ratio is more preferably 40 or more and more preferably 65 or less.

[0034] The above-mentioned characteristics of the peak of the Fe—Si—Al (400) plane, the peak of the (422) plane, and the peak of the (111) plane may be related to the conditions of each material used in the sheet of this embodiment, the conditions of the sheet forming, etc. Specific examples of such conditions include the composition, shape, and size of the alloy powder used in the sheet; the filling amount of the alloy powder in the sheet; the magnetic field environment during sheet forming; the forming speed during sheet forming; and the viscosity of the slurry when the sheet is formed by a coating method using a slurry.

[0035] When the internal decoupling ratio Rda of the sheet of this embodiment is measured at frequencies of 0.1 to 6 GHz based on the IEC 62333-2 standard using a test piece having a size of 100 mm x 50 mm and a thickness t (mm), the peak frequency f (GHz) of Rda and the thickness t (mm) satisfy the following relationship (requirement (iii)): f≧−0.45ln(t)+0.1 (A) where ln is the natural logarithm, and ｅ is synonymous with.

[0036] Requirement (iii) is normalized by the peak frequency f as a function of the sheet thickness t, and is formulated based on extensive study to demonstrate that even if the sheet has a certain thickness, the Rda peak is in a relatively high frequency band. The sheet of this embodiment, which satisfies requirement (iii), is novel compared to conventional noise suppression sheets of the same thickness. Furthermore, requirement (iii) is more easily satisfied when the sheet of this embodiment has desired orientation characteristics, particularly when the conditions of the materials used in the sheet and the conditions for forming the sheet are combined.

[0037] Furthermore, the sheet of this embodiment preferably satisfies the relationship of the following formula (B): f≦−0.95ln(t)+0.25 (B) In this case, the desired performance as a noise suppression sheet can be fully exhibited.

[0038] Furthermore, the sheet of this embodiment preferably satisfies the following formula (C): f≧−0.50ln(t)+0.1 (C).

[0039] The sheet of this embodiment includes a substrate. This substrate is typically made of an organic material, particularly a rubber and / or resin organic material, and functions as a binder in the sheet. In accordance with environmental regulations such as the RoHS Directive, this organic material preferably does not contain halogen elements. Furthermore, since near-field noise suppression sheets are also required to have flexibility, heat resistance, and durability, the organic material is preferably at least one or more rubber materials selected from the group consisting of silicone rubber, acrylic rubber, nitrile rubber, and butyl rubber. Alternatively, a resin material such as epoxy can also be used as the organic material.

[0040] The sheet of the present embodiment contains one or more additives dispersed in the substrate, such as an antioxidant, a silane coupling agent, a flame retardant, a plasticizer, etc.

[0041] Examples of the antiaging agent include aromatic amine-based antiaging agents. These antiaging agents can prevent deterioration and deformation of the substrate, such as a resin, due to oxidation or environmental changes, and improve the oxidation resistance of the noise suppression sheet. If the substrate, such as a resin, deteriorates or deforms, the orientation of the flat alloy powder dispersed in the noise suppression sheet becomes disordered, causing a change in the resonant frequency, which may result in a shift of the peak of the internal decoupling ratio Rda to a lower frequency or a decrease in the noise absorption capacity. To more fully avoid such situations, the sheet of this embodiment may contain an aromatic amine-based antiaging agent as an additive.

[0042] Examples of the aromatic amine-based antioxidant include 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N'-di-2-naphthyl-p-phenylenediamine, phenyl-α-naphthylamine, phenyl-β-naphthylamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-β-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, and N-phenyl-N'-isopropyl-p-phenylenediamine. These aromatic amine-based antioxidants may be used alone or in combination of two or more. Furthermore, from the viewpoint of efficiently preventing deterioration and deformation, the content of the aromatic amine-based antioxidant in the sheet of this embodiment is preferably 0.5 parts by mass to 10 parts by mass based on 100 parts by mass of the flat alloy powder.

[0043] The silane coupling agent can further improve the dispersibility of the flat alloy powder in the noise suppression sheet. Poor dispersibility of the flat alloy powder may result in the formation of many voids and bubbles within the sheet during sheet formation. Such voids and bubbles may cause the noise suppression sheet to expand or deform when exposed to a high-temperature environment. Expansion or deformation of the noise suppression sheet disrupts the orientation of the flat alloy powder dispersed within the noise suppression sheet, changing the resonant frequency. This may shift the peak of the internal decoupling ratio Rda to a lower frequency or reduce the noise absorption capacity. To more fully avoid such situations, the sheet of this embodiment may contain a silane coupling agent as an additive.

[0044] Examples of the silane coupling agent include 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane. These silane coupling agents may be used alone or in combination of two or more. Furthermore, from the viewpoint of efficiently preventing expansion and deformation, the content of the silane coupling agent in the sheet of this embodiment is preferably 1 part by mass to 10 parts by mass per 100 parts by mass of the flat alloy powder.

[0045] The flame retardant can improve the flame retardancy of the noise suppression sheet. Therefore, the sheet of this embodiment may contain a flame retardant as an additive. The flame retardant is preferably one that does not contain halogen elements, i.e., a non-halogen flame retardant, similar to the organic material of the substrate. Examples of the non-halogen flame retardant include aluminum hydroxide, magnesium hydroxide, zinc borate, and melamine cyanelate. Furthermore, red phosphorus can also be used as a non-halogen flame retardant if there are no limitations on the usage environment. These non-halogen flame retardants may be used alone or in combination of two or more. When the sheet of this embodiment contains a non-halogen flame retardant, the content of the non-halogen flame retardant may be, for example, 20 parts by mass or less per 100 parts by mass of the flat alloy powder.

[0046] The plasticizer can increase the flexibility of the noise suppression sheet, so the sheet of this embodiment may contain a plasticizer as an additive.

[0047] In the sheet of this embodiment, the filling amount of the flat alloy powder is preferably 25 vol% or more and 55 vol% or less. If the filling amount is in the range of 25 vol% or more and 55 vol% or less, the orientation characteristics become more desirable, and the desired noise suppression effect can be further enhanced. Note that if the filling amount is excessively small, this may affect the viscosity of the slurry and, in turn, the ease with which the flat alloy powder is oriented during magnetic field compaction. Also, if the filling amount is excessively large, this may affect the viscosity of the slurry and, in turn, the ease with which the flat alloy powder is oriented during magnetic field compaction. Furthermore, if the filling amount is 55 vol% or less, the flexibility of the noise suppression sheet is maintained well, and an excessive decrease in surface resistance (for example, 1.0 × 10 ５ From the same viewpoint, the filling amount of the flat alloy powder is more preferably 30 vol % or more, and more preferably 50 vol % or less.

[0048] The filling amount of the flat alloy powder is defined as follows. First, a cross section of the noise suppression sheet cut in a direction perpendicular to the in-plane direction of the sheet is observed with a scanning electron microscope to obtain an observation image. This observation image is used to separate the flat alloy powder from the substrate by binarizing the colors of the images relating to the flat alloy powder and the substrate. After separation is complete, the area ratio of the flat alloy powder is determined, and this is defined as the "filling amount" of the flat alloy powder. Note that the binarization process can be appropriately set so that the boundary between the flat alloy powder and the substrate is clear. Similarly, when one or more types of additives other than the flat alloy powder are present, separation is performed by multi-level processing, and the "filling amount (additive amount)" of each can be determined by determining the area ratios of the flat alloy powder and the additives.

[0049] The thickness of the sheet of this embodiment is not particularly limited, but can be, for example, 0.050 mm or more and less than 0.500 mm.

[0050] The density of the sheet of this embodiment is not particularly limited, but is, for example, 3.0 g / cm ３ 3.8g / cm or more ３ It can be as follows:

[0051] The surface resistance of the sheet of this embodiment is not particularly limited, but is, for example, 1.0×10 ５ It is preferably Ω / □ or more.

[0052] Next, a method for manufacturing the near-field noise suppression sheet of this embodiment will be described. There are no particular restrictions on the method for manufacturing the sheet of this embodiment. As an example, a method for manufacturing the near-field noise suppression sheet includes the following steps: １００－ｘ－ｙ Si ｘ Al ｙ (where 12.2≦x+y≦17.8, 8.0≦x≦11.2, 4.2≦y≦6.6), a processing step of wet-flattening the Fe—Si—Al alloy powder to obtain a flat alloy powder, a mixing step of mixing the flat alloy powder with a base material made of an organic material and an additive to obtain a mixture, and a molding step of molding the mixture into a sheet in a magnetic field environment (magnetic field molding) to obtain a near-field noise suppression sheet. By this manufacturing method, the sheet of the present embodiment described above can be manufactured.

[0053] The method for the above processing step (flattening method) can be any known or arbitrary mechanical processing such as an attritor or a bead mill. Furthermore, a solvent such as isopropyl alcohol (IPA) can be used for wet flattening. The flat alloy powder obtained in the above processing step can be adjusted to a desired average particle size by sieving or the like.

[0054] The method for the forming step (method for forming into a sheet) is not particularly limited, and any known or arbitrary method can be used, such as a coating method, a rolling method, etc. Here, the coating method is taken as an example, and the specific procedures for the mixing step and forming step when the coating method is adopted will be described.

[0055] In the mixing step, a flat alloy powder, a base material made of an organic material, an additive, and an organic solvent are mixed and stirred at a predetermined blending ratio to obtain a slurry. Next, in the compacting step, the slurry is coated with a doctor blade and molded into a sheet. During compacting, a magnetic field is applied to the coated slurry (i.e., magnetic field compaction) to adjust the horizontal orientation of the flat alloy powder. A method for applying a magnetic field to the coated slurry includes, for example, placing a permanent magnet or an electromagnet facing each other.

[0056] When a permanent magnet is used, the magnetic flux density of the permanent magnet is preferably 50 to 300 mT. When an electromagnet is used, it is preferable to set a current value that results in a magnetic flux density equivalent to 50 to 300 mT. In this case, if the magnetic flux density is less than 50 mT, there is a risk that the flat alloy powder will not be sufficiently horizontally oriented. On the other hand, if the magnetic flux density is greater than 300 mT, there is a risk that the flat alloy powder will be attracted to the permanent magnet or electromagnet, resulting in poor coating.

[0057] When the flat alloy powder is retained by the magnetic field, it is preferable to adjust the coating conditions appropriately. Examples of such coating conditions include the coating speed (molding speed) and the slurry viscosity. Specifically, the coating speed (molding speed) is preferably 0.1 m / s or more and 10 m / s or less. Furthermore, the slurry viscosity is preferably 1,000 cP or more and 30,000 cP or less. If the coating speed (molding speed) is less than 0.1 m / s or the slurry viscosity is less than 1,000 cP, retention due to the magnetic field may occur, resulting in poor coating. Furthermore, if the coating speed (molding speed) exceeds 10 m / s, the time during which the flat alloy powder is affected by the magnetic field is shortened, which may result in insufficient orientation of the flat alloy powder. Furthermore, if the slurry viscosity exceeds 30,000 cP, the movement of the flat alloy powder within the organic material as the substrate is restricted, which may result in insufficient orientation of the flat alloy powder. From the same viewpoint, the slurry viscosity is more preferably 3,000 cP or more, and more preferably less than 10,000 cP.

[0058] If the flat alloy powder dispersed in the slurry is not properly oriented, the peak intensity of the (400) plane will decrease, and the peak intensity of the (111) plane and the (422) plane will increase relatively, affecting the resonant frequency. Therefore, care must be taken with the magnetic field compaction conditions.

[0059] The sheet obtained in the molding step may be pressed while heated to a temperature above the softening point of the organic material (for example, about 60 to 150°C) in order to increase the degree of horizontal orientation and density of the flat alloy powder.

[0060] The near-field noise suppression sheet of this embodiment has been described above, but the present disclosure is not limited to the above embodiment and can be modified as appropriate.

[0061] The present invention will be described in more detail below with reference to examples. However, these examples are intended to illustrate the present invention and are not intended to limit the present invention in any way.

[0062] Example 1: As a raw material, Fe—Si—Al alloy powder having an Fe content of 84.8 mass%, a Si content of 9.65 mass%, an Al content of 5.55 mass%, and an average particle size of 8.62 μm was used. This raw material was wet flattened using IPA (isopropyl alcohol) as a solvent to a thickness of 1 μm or less, resulting in a flat alloy powder (Fe—Si—Al alloy powder) with an average particle size of 59.2 μm. Next, this flat alloy powder was dried in an oven at 80°C in air, and then heat-treated to remove stress during flattening. Next, the flat alloy powder was added to acrylic rubber as a base material and toluene as an organic solvent in an amount that would result in the final target filling amount, and the mixture was kneaded using a ball mill to produce a slurry. In addition, 1.0 parts by mass of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine as an antioxidant and 5.0 parts by mass of 3-acryloxypropyltrimethoxysilane as a silane coupling agent were added to this slurry relative to 100 parts by mass of the flat alloy powder. After sufficient kneading, the slurry was vacuum degassed, and the organic solvent was volatilized until the slurry viscosity reached 9,000 cP. Next, the slurry was formed into a sheet using a doctor blade in a magnetic field (magnetic field molding), and the flat alloy powder was oriented. At this time, the magnetic flux density of the magnet used during magnetic field molding was 100 mT, and the molding speed was 1.0 m / s. Subsequently, the slurry was pressed at 150 °C to further increase density and produce a sheet. The filling amount of the flat alloy powder in the pressed sheet was 42 vol%.

[0063] (Example 2) A sheet was produced under the same conditions as in Example 1, except that the organic solvent was evaporated until the slurry viscosity reached 10,000 cP, and flat alloy powder was added in an amount such that the filling amount of flat alloy powder in the sheet was 54 vol%.

[0064] Example 3 A sheet was produced under the same conditions as in Example 1, except that the organic solvent was evaporated until the slurry viscosity reached 8,000 cP and the molding speed during magnetic field molding was set to 0.1 m / s.

[0065] (Example 4) A sheet was produced under the same conditions as in Example 2, except that flat alloy powder was added in an amount such that the filling amount of the flat alloy powder in the sheet was 26 vol%, and the magnetic flux density of the magnet used during magnetic field molding was 300 mT and the molding speed was 5.0 m / s.

[0066] Example 5: As a raw material, Fe—Si—Al alloy powder having an Fe content of 85.05 mass%, an Si content of 9.42 mass%, an Al content of 5.53 mass%, and an average particle size of 9.13 μm was used. This raw material was wet flattened using IPA as a solvent to a thickness of 1 μm or less to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 67.3 μm. Next, a sheet was produced under the same conditions as in Example 1, except that this flat alloy powder was used and the organic solvent was evaporated until the slurry viscosity reached 8,500 cP.

[0067] (Example 6) A sheet was produced under the same conditions as in Example 5, except that the organic solvent was volatilized until the slurry viscosity reached 3,000 cP and the magnetic flux density of the magnet used during magnetic field molding was 150 mT.

[0068] (Example 7) A sheet was produced under the same conditions as in Example 5, except that the organic solvent was volatilized until the slurry viscosity reached 8,000 cP, and the magnetic flux density of the magnet used during magnetic field molding was 300 mT and the molding speed was 5.0 m / s.

[0069] (Example 8) A sheet was produced under the same conditions as in Example 5, except that the organic solvent was evaporated until the slurry viscosity reached 8,000 cP, and flat alloy powder was added in an amount such that the filling amount of flat alloy powder in the sheet was 26 vol%.

[0070] (Example 9) A sheet was produced under the same conditions as in Example 5, except that flat alloy powder was added in an amount such that the filling amount of the flat alloy powder in the sheet was 54 vol%, the molding speed during magnetic field molding was 10.0 m / s, and the organic solvent was evaporated until the slurry viscosity reached 10,000 cP.

[0071] (Example 10) As a raw material, Fe—Si—Al alloy powder having an Fe content of 84.0 mass%, an Si content of 10.86 mass%, an Al content of 5.14 mass%, and an average particle size of 9.54 μm was used. This raw material was wet flattened using IPA as a solvent to a thickness of 1 μm or less to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 36.4 μm. Next, a sheet was produced under the same conditions as in Example 1, except that this flat alloy powder was used, the organic solvent was volatilized until the slurry viscosity reached 30,000 cP, and the magnetic flux density of the magnet used during magnetic field molding was 50 mT.

[0072] (Comparative Example 1) As a raw material, an Fe—Si—Al alloy powder having an Fe content of 78.39 mass%, an Si content of 16.00 mass%, an Al content of 5.61 mass%, and an average particle size of 8.87 μm was used. This raw material was wet flattened using IPA as a solvent to a thickness of 1 μm or less to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 57.4 μm. Next, a sheet was produced under the same conditions as in Example 1, except that this flat alloy powder was used and the organic solvent was evaporated until the slurry viscosity reached 10,000 cP.

[0073] (Comparative Example 2) As a raw material, Fe—Si—Al alloy powder having an Fe content of 75.48 mass%, an Si content of 15.60 mass%, and an Al content of 8.92 mass% was used. This raw material was wet flattened using IPA as a solvent to a thickness of 1 μm or less to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 57.4 μm. Next, a sheet was produced under the same conditions as in Comparative Example 1, except that this flat alloy powder was used and the flat alloy powder was added in an amount such that the filling amount of the flat alloy powder in the sheet was 15 vol%.

[0074] (Comparative Example 3) As a raw material, an Fe—Si—Al alloy powder having an Fe content of 87.68 mass%, an Si content of 10.23 mass%, an Al content of 2.09 mass%, and an average particle size of 8.96 μm was used. This raw material was wet flattened using IPA as a solvent to a thickness of 1 μm or less to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 63.9 μm. Next, a sheet was produced under the same conditions as in Comparative Example 2, except that this flat alloy powder was used.

[0075] Comparative Example 4: The flat alloy powder of Example 1 was sieved to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 101.5 μm. A sheet was then produced under the same conditions as Example 1, except that this flat alloy powder was used, the flat alloy powder was added in an amount such that the filling amount of the flat alloy powder in the sheet was 15 vol%, the organic solvent was volatilized until the slurry viscosity reached 50,000 cP, and the forming speed during magnetic field forming was 10.0 m / s.

[0076] Comparative Example 5: The flat alloy powder of Example 1 was sieved to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 62.6 μm. Next, a sheet was produced under the same conditions as Example 1, except that this flat alloy powder was used, the organic solvent was volatilized until the slurry viscosity reached 10,000 cP, and the magnetic flux density of the magnet used during magnetic field compaction was 30 mT and the compaction speed was 10.0 m / s.

[0077] Comparative Example 6 A sheet was produced under the same conditions as in Comparative Example 4, except that the organic solvent was evaporated until the slurry viscosity reached 35,000 cP and the molding speed during magnetic field molding was set to 1.0 m / s.

[0078] Comparative Example 7 A sheet was produced under the same conditions as in Comparative Example 6, except that the flat alloy powder was added in an amount such that the filling amount of the flat alloy powder in the sheet was 80 vol %.

[0079] (Comparative Example 8) A sheet was produced under the same conditions as in Example 1, except that flat alloy powder was added in an amount such that the filling amount of the flat alloy powder in the sheet was 80 vol%, the organic solvent was volatilized until the slurry viscosity reached 50,000 cP, and the magnetic flux density of the magnet used during magnetic field molding was 300 mT.

[0080] Comparative Example 9: The flat alloy powder of Example 1 was sieved to obtain a flat alloy powder (Fe—Si—Al alloy powder) having an average particle size of 19.2 μm. Next, a sheet was produced under the same conditions as Example 1, except that this flat alloy powder was used, the organic solvent was volatilized until the slurry viscosity reached 10,000 cP, and the magnetic flux density of the magnet used during magnetic field compaction was 10 mT and the compaction speed was 10.0 m / s.

[0081] (Comparative Example 10) A sheet was produced under the same conditions as in Comparative Example 9, except that the organic solvent was volatilized until the slurry viscosity reached 50,000 cP, and the magnetic flux density of the magnet used during magnetic field molding was 30 mT and the molding speed was 1.0 m / s.

[0082] Next, the sheets obtained in each example were subjected to the following measurements and evaluations.

[0083] <X-ray diffraction> The measurement sample was cut into a rectangular shape from each example sheet, and the surface direction of the sample was used as the measurement target. X-ray diffraction measurements were performed using an X-ray diffractometer (Rigaku Corporation, "Smart-Lab") with a focused optical system. The measurement range was 2θ = 10° to 100°, the scanning speed was 1° / min or less, and the sampling interval was 0.01° or less, with continuous measurements being performed at a constant speed. From the X-ray diffraction measurement results, it was confirmed whether or not peaks were present in the (111) plane, (400) plane, and (422) plane. Furthermore, when peaks were present in the (111) plane, (400) plane, and (422) plane, the peak intensity P （４００） The peak intensity P of the (111) plane when （１１１） The ratio (P （１１１） / P （４００） Similarly, the peak intensity P （４００）The peak intensity P of the (422) plane when （４２２） The ratio (P （４２２） / P （４００） The results are shown in Table 1. For reference, the results of X-ray diffraction measurements of the sheets of Example 1 and Comparative Example 9 are shown in FIG.

[0084] <Surface Resistance> The surface resistance of each example sheet was measured using a resistance meter ("Hiresta-UX MCP-HT800" manufactured by Mitsubishi Analytech Co., Ltd.) with a double ring probe. The results are shown in Table 1.

[0085] <Peak Frequency f of Rda> For each example sheet having a thickness t (mm) shown in Table 1, a test piece measuring 100 mm x 50 mm was prepared, and the internal decoupling ratio Rda of each test piece was measured at frequencies of 0.1 to 6 GHz in accordance with the IEC 62333-2 standard. In a plot with frequency on the horizontal axis and internal decoupling ratio Rda on the vertical axis, the frequency (peak frequency f (GHz)) at which Rda peaked in the negative direction was read. Furthermore, for each example, it was confirmed whether the peak frequency f (GHz) and thickness t (mm) satisfied the above-mentioned formula (A). These results are shown in Table 1. For reference, FIG. 2 shows a plot of the sheet thickness t (mm) and peak frequency f (GHz) for each example, along with the boundary line of formula (A).

[0086]

[0087] From Table 1 and FIG. 2, it can be seen that the sheets of the examples according to the near-field noise suppression sheet of the present invention, taking into consideration the thickness t, have peaks of Rda in a relatively high frequency band, and therefore can achieve noise suppression effects in the high frequency band.

[0088] According to the present invention, it is possible to provide a near-field noise suppression sheet that has excellent noise suppression performance in the high frequency band.

Claims

1. A noise suppression sheet for near-field, comprising a base material, flattened alloy powder supported in the base material, and one or more additives dispersed in the base material, satisfying the following requirements (i), (ii), and (iii): (i): The flattened alloy powder has a composition represented by mass% as Fe １００－ｘ－ｙ Si ｘ Al ｙ (where 12.2 ≦ x + y ≦ 17.8, 8.0 ≦ x ≦ 11.2, 4.2 ≦ y ≦ 6.6). (ii): In the X-ray diffraction of the noise suppression sheet for near-field, the peaks of the (400) plane, (422) plane, and (111) plane of Fe-Si-Al exist, and the peak intensity P （４００） of the (400) plane, the peak intensity P （４２２） of the (422) plane, and the peak intensity P （１１１） of the (111) plane of Fe-Si-Al satisfy the following formulas (a) and (b): P （４００） > P （４２２） ... (a) P （４００） > P （１１１） ... (b). (iii): For a test piece with the noise suppression sheet for near-field having a size of 100 mm × 50 mm and a thickness t (mm), when measuring the internal decoupling ratio Rda at a frequency of 0.1 to 6 GHz based on the IEC62333-2 standard, the peak frequency f (GHz) of Rda and the thickness t (mm) satisfy the following formula (A): f ≧ -0.45 ln(t) + 0.1... (A). A noise suppression sheet for near-field, characterized by satisfying all of the above.

2. In the X-ray diffraction, the peak intensity P of the (400) plane of Fe—Si—Al （４００） is set to 100, and the peak intensity P （４２２） of the (422) plane satisfies 40 or more and 85 or less. The noise suppression sheet for near-field according to claim 1.

3. In the X-ray diffraction, the peak intensity P of the (400) plane of Fe—Si—Al （４００） is set to 100, and the ratio of the peak intensity P （１１１） of the (111) plane is 30 or more and 90 or less. The noise suppression sheet for the vicinity field according to claim 1 or 2.

4. The noise suppression sheet for near-field includes an aromatic amine-based antioxidant as the additive, and the content of the aromatic amine-based antioxidant is 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the flat alloy powder. The noise suppression sheet for near-field according to any one of claims 1 to 3.

5. The noise suppression sheet for near-field includes a silane coupling agent as the additive, and the content of the silane coupling agent is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the flat alloy powder. The noise suppression sheet for near-field according to any one of claims 1 to 4.

6. The noise suppression sheet for near-field includes a non-halogen-based flame retardant as the additive, and the content of the non-halogen-based flame retardant is 20 parts by mass or less with respect to 100 parts by mass of the flat alloy powder. The noise suppression sheet for near-field according to any one of claims 1 to 5.

7. The thickness is 0.050 mm or more and less than 0.500 mm. The noise suppression sheet for near-field according to any one of claims 1 to 6.

8. The filling amount of the flat alloy powder is 25 vol% or more and 55 vol% or less. The noise suppression sheet for near-field according to any one of claims 1 to 7.

9. The average particle diameter of the flat alloy powder is 30 μm or more and 80 μm or less. The noise suppression sheet for near-field according to any one of claims 1 to 8.

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