Soft magnetic flat powder and magnetic member

Abstract

The purpose of the present invention is to provide a soft magnetic flat powder with which it is possible to obtain a magnetic sheet having excellent noise suppression performance, and to provide a soft magnetic flat powder comprising a plurality of flat particles, the material of which is an Fe-Si-Al alloy containing 0.010 mass% or more and 0.050 mass% or less of C.

Description

Technical Field

[0001] This specification relates to a powder in which the shape of constituent particles is flat and which has soft magnetism, that is, soft magnetic flat powder. In addition, this specification relates to a magnetic member including a matrix and soft magnetic flat powder dispersed in the matrix. Background Art

[0002] Electronic devices such as personal computers and mobile phones have circuits. Radio wave noise radiated from electronic components mounted on the circuits causes radio wave interference between the electronic components and other electronic components, and radio wave interference between the electronic circuits and other electronic circuits. The radio wave interference causes malfunction of the electronic devices. For the purpose of suppressing the malfunction, a magnetic sheet (electromagnetic wave absorption sheet) is inserted into the electronic device. The magnetic sheet converts electromagnetic waves into magnetic force. By this magnetic sheet, noise can be suppressed.

[0003] A magnetic sheet containing soft magnetic flat powder is disclosed in Japanese Unexamined Patent Application Publication No. 2017-118114. The material of the powder is an Fe-Si-Al alloy. The average aspect ratio of the powder is large. The powder can contribute to high electromagnetic wave absorption performance of the magnetic sheet.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-118114 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] Miniaturization and high performance of electronic devices are in progress. For circuit components in an electronic device, the requirements for miniaturization and high performance are also increased. In miniaturized and high-performance devices, the density of electronic components mounted on the circuit is high. Therefore, radio wave noise radiated from the electronic components easily causes radio wave interference between the electronic components and radio wave interference between the electronic circuits. Therefore, a magnetic member capable of further suppressing noise is required.

[0009] An object of this specification is to provide a soft magnetic flat powder capable of obtaining a magnetic member having excellent noise suppression performance. In addition, an object of this specification is to provide a magnetic member having excellent noise suppression performance.

[0010] Means for Solving the Problems

[0011] The soft magnetic flat powder disclosed in this specification includes a plurality of flat particles. The material of these flat particles is an Fe-Si-Al-based alloy containing 0.010 mass% or more and 0.050 mass% or less of C.

[0012] Preferably, the median diameter D50 of the soft magnetic flat powder on a volume basis is 20.0 μm or more and 90.0 μm or less.

[0013] Preferably, the tapped density TD of the soft magnetic flat powder is 1.25 g / cm 3 or less.

[0014] Preferably, the coercive force of the soft magnetic flat powder when a magnetic field is applied in the longitudinal direction of the flat particles is 400 A / m or less.

[0015] The magnetic member disclosed in this specification has a matrix based on a polymer and soft magnetic flat powder dispersed in the matrix. The soft magnetic flat powder includes a plurality of flat particles. The material of these flat particles is an Fe—Si—Al alloy containing 0.01% by mass or more and 0.05% by mass or less of C.

[0016] Advantageous Effects of Invention

[0017] The soft magnetic flat powder disclosed in this specification has a small coercive force. The magnetic member containing the powder has a large magnetic permeability. The magnetic member has excellent noise suppression performance. Description of Drawings

[0018] Figure 1 is a schematic cross-sectional view showing a part of the magnetic member according to one embodiment.

[0019] Figure 2 is for showing Figure 1 an enlarged view of the flat particles included in the magnetic member. Detailed Description of the Invention

[0020] Hereinafter, preferred embodiments will be described in detail with appropriate reference to the drawings.

[0021] [Magnetic Sheet]

[0022] Figure 1 A magnetic sheet 2 (an example of a magnetic member) is shown. The magnetic sheet 2 has a matrix 4 and soft magnetic flat powder dispersed in the matrix 4. The matrix 4 is a polymer composition. Typical base materials of the polymer composition are rubber or resin. The soft magnetic flat powder is an aggregate of a plurality of flat particles 6.

[0023] In the manufacture of the magnetic sheet 2, the soft magnetic flat powder is kneaded with various chemical reagents in a base polymer to obtain a polymer composition. The kneading can be performed by a known method. For example, kneading can be performed using a closed kneader, an open mill, or the like. Examples of the chemical reagents include processing aids such as lubricating materials and binders.

[0024] Next, the magnetic sheet 2 is formed from the obtained polymer composition. The forming can be carried out by known methods. Forming can be performed by a pressing method, an injection molding method, an extrusion molding method, a calendering method, etc.

[0025] The shape of the magnetic member is not limited to a sheet shape. Shapes such as a ring shape, a cubic shape, a rectangular parallelepiped shape, a cylindrical shape, etc. can be adopted. In addition, the soft magnetic flat powder of the present embodiment is also suitable for magnetic members having a complex shape.

[0026] [Shape of particles]

[0027] Figure 2 The cross-section of a flat particle 6 is shown. In Figure 1 the symbol L1 represents the length of the major axis of the flat particle 6, and the symbol T1 represents the thickness of the flat particle 6. The length L1 is greater than the thickness T1. In other words, the shape of the flat particle 6 is flat.

[0028] The flat particle 6 has shape anisotropy. This anisotropy can contribute to the high real part permeability μ' of the magnetic sheet 2. Moreover, in the magnetic sheet 2 containing the flat particles 6 with a small thickness T1, eddy current loss is suppressed, so relaxation of the real part permeability μ' is difficult to occur. The magnetic sheet 2 containing the flat particles 6 can sufficiently shield noise.

[0029] [Material of particles]

[0030] The material of the flat particle 6 is a Fe-Si-Al alloy containing C. The Fe-Si-Al alloy can have an ordered lattice of the D03 structure. Therefore, in the Fe-Si-Al alloy, a low magnetostriction constant and a low magnetocrystalline anisotropy constant can be achieved at the same time. The soft magnetic flat powder formed of the Fe-Si-Al alloy can achieve a high real part permeability μ'. Hereinafter, the functions of each element will be described in detail.

[0031] [C (carbon)]

[0032] C is the most important additive element in the soft magnetic flat powder of the present embodiment. C is added in a trace amount to the Fe-Si-Al alloy. C contributes to the large median diameter D50 of the soft magnetic flat powder, so that a large aspect ratio of the flat particle 6 can be achieved. The permeability of the magnetic sheet 2 containing the flat particles 6 with a large aspect ratio is large. The reason why C contributes to the large median diameter D50 is presumably that a part of the D03 structure of the Fe-Si-Al alloy is changed to other structures due to C.

[0033] In soft magnetic flat powder made of Fe-Si-Al-based alloy, a large median diameter D50 can be achieved by changing the Si content rate or the Al content rate. However, changing the Si content rate and changing the Al content rate will cause an increase in the magnetostriction constant and the magnetocrystalline anisotropy constant. In the present embodiment, a large median diameter D50 is achieved by adding a small amount of C. Adding a small amount of C will not significantly increase the magnetostriction constant of the Fe-Si-Al-based alloy. Adding a small amount of C will not significantly increase the magnetocrystalline anisotropy constant of the Fe-Si-Al-based alloy. In other words, by adding a small amount of C, a large median diameter D50 can be achieved with almost no damage to the electromagnetic properties of the Fe-Si-Al-based alloy.

[0034] In addition, C preferentially adsorbs oxygen in the alloy. The formation of Fe oxide, Si oxide, and Al oxide is suppressed in the alloy containing C. In this alloy, the pinning effect caused by these oxides is suppressed. In other words, C suppresses the coercive force of the soft magnetic flat powder and can contribute to the high permeability of the magnetic sheet 2.

[0035] From the viewpoint of high permeability, the C content rate is preferably 0.010 mass% or more, more preferably 0.015 mass% or more, and particularly preferably 0.020 mass% or more. From the viewpoint of high permeability, the C content rate is preferably 0.050 mass% or less, more preferably 0.045 mass% or less, and particularly preferably 0.040 mass% or less.

[0036] [Silicon (Si)]

[0037] Si contributes to a large resistivity and can reduce eddy current loss. Si also contributes to high permeability. Si contributes to noise suppression. From this viewpoint, the Si content rate is preferably 3.0 mass% or more, more preferably 4.0 mass% or more, and particularly preferably 5.0 mass% or more. Excessive Si will cause a decrease in permeability due to a decrease in saturation magnetic flux density. From the viewpoint of high permeability, the Si content rate is preferably 12.0 mass% or less, more preferably 11.0 mass% or less, and particularly preferably 10.0 mass% or more.

[0038] [Aluminum (Al)]

[0039] Al contributes to a large resistivity and can reduce eddy current loss. Al also contributes to high permeability. From this viewpoint, the Al content rate is preferably 2.0 mass% or more, more preferably 2.5 mass% or more, and particularly preferably 3.0 mass% or more. Excessive Al will cause a decrease in permeability due to a decrease in saturation magnetic flux density. From the viewpoint of high permeability, the Al content rate is preferably 10.0 mass% or less, more preferably 9.0 mass% or less, and particularly preferably 8.0 mass% or more.

[0040] [Iron (Fe)]

[0041] Fe is the base material of the alloy. Fe has strong magnetism. Fe contributes to the magnetic properties of the soft magnetic flat powder.

[0042] [Preferred composition]

[0043] The Fe-Si-Al alloy particularly suitable for the magnetic sheet 2 contains:

[0044] Si: 3.0 mass% or more and 12.0 mass% or less;

[0045] Al: 2.0 mass% or more and 10.0 mass% or less; and

[0046] C: 0.010 mass% or more and 0.050 mass% or less.

[0047] The balance is Fe and unavoidable impurities. Preferably, regardless of the respective content rates of Si, Al, and C, the balance is Fe and unavoidable impurities.

[0048] [Median diameter D50]

[0049] The length L1 of the particles with a large median diameter D50 (refer to Figure 2 ) is greater than the length L1 of the particles with a thickness T1 equal to the thickness T1 of the particles and a small median diameter D50. In other words, in the flat processing to obtain a specified thickness T1, the particles with a large median diameter D50 contribute to a large aspect ratio. From the viewpoint of achieving a large aspect ratio, the median diameter D50 of the soft magnetic flat powder is preferably 20.0 μm or more, more preferably 30.0 μm or more, and particularly preferably 40.0 μm or more. From the viewpoint of the smoothness of the surface of the magnetic sheet 2, the median diameter D50 of the soft magnetic flat powder is preferably 90.0 μm or less, more preferably 80.0 μm or less, and particularly preferably 70.0 μm or less.

[0050] The median diameter D50 is calculated on a volume basis. The median diameter D50 is the diameter of the flat particles 6 at the point on the cumulative curve where the cumulative reaches 50% when the total volume of the soft magnetic flat powder is set to 100%. The median diameter D50 can be measured by the laser diffraction / scattering method. Specifically, the median diameter D50 can be measured, for example, by the laser diffraction / scattering type particle size distribution measuring device "Microtrac MT3000" of Nikkiso Co., Ltd. The soft magnetic flat powder and pure water flow into the unit of the device together, and based on the light scattering information of each flat particle 6 constituting the soft magnetic flat powder, the median diameter D50 is detected.

[0051] [Aspect ratio]

[0052] As described above, the shape of the flat particle 6 is flat. The flat particle 6 has shape anisotropy. This anisotropy increases the real part permeability μ' of the magnetic member. From the viewpoint of high permeability, the average aspect ratio of the soft magnetic flat powder is preferably 1.5 or more, more preferably 5.0 or more, and particularly preferably 8.0 or more. The average aspect ratio is preferably 100 or less.

[0053] In the measurement of the aspect ratio, a specimen capable of observing the thickness of the flat particle 6 is used. In this specimen, a plurality of flat particles 6 are embedded in resin. The specimen is polished, and the polished surface is observed using a scanning electron microscope (SEM). The magnification of the image during observation is 1000 times. In the analysis of this image, the image data of the flat particle 6 is binarized. When the binarized image approximates an ellipse, the ratio of the length of the major axis of the ellipse to the length of the minor axis is the aspect ratio of the flat particle 6. The arithmetic mean of the aspect ratios of all the flat particles 6 obtained in four fields of view is calculated to obtain the average aspect ratio of the soft magnetic flat powder.

[0054] [Tap density TD]

[0055] The tap density TD of the soft magnetic flat powder is preferably 1.25 g / cm 3 or less. A magnetic sheet 2 with a smooth surface can be obtained from the soft magnetic flat powder having a tap density TD in this range. From this viewpoint, the tap density TD is more preferably 1.00 g / cm 3 or less, and particularly preferably 0.90 g / cm 3 or less. The lower limit value of the tap density TD is preferably 0.3 g / cm 3 or more.

[0056] In the measurement of the tap density TD, approximately 20 g of the soft magnetic flat powder is filled into a graduated cylinder with a volume of 100 cm 3 . The measurement conditions are as described below.

[0057] Drop height: 10 mm

[0058] Number of taps: 200

[0059] [Coercive force Hc]

[0060] The coercive force Hc is the intensity of the external magnetic field required to return a magnetized magnet to an unmagnetized state. When a magnetic field is applied in the length direction of the flat particle 6, the coercive force Hc of the soft magnetic flat powder is preferably 400 A / m or less. The soft magnetic flat powder having a coercive force Hc in this range can achieve a high real part permeability μ'. From this viewpoint, the coercive force Hc is more preferably 300 A / m or less, and particularly preferably 200 A / m or less.

[0061] The coercive force Hc can be measured, for example, using the coercive force meter "HC-1031" of the Electronic Magnetics Industry. In the measurement, the soft magnetic flat powder is filled in a resin container and magnetized in the diameter direction of the container. The maximum applied magnetic field is 239 kA / m.

[0062] [Method for manufacturing powder]

[0063] The soft magnetic flat powder of the present embodiment is obtained by performing flat processing on raw material powder. The raw material powder can be obtained by gas atomization method, water atomization method, disk atomization method, pulverization method, etc. Gas atomization method and disk atomization method are preferred.

[0064] In the gas atomization method, the raw material metal is heated and melted to obtain molten metal. The molten metal flows out from the nozzle. Gas (argon, nitrogen, etc.) is blown onto the molten metal. By the energy of this gas, the molten metal is pulverized into droplets and cooled while falling. The droplets solidify to form particles. In this gas atomization method, since the molten metal is instantaneously dropletized and cooled at the same time, a uniform fine structure can be obtained. Moreover, since droplets are continuously formed, the compositional difference between particles is extremely small.

[0065] In the disk atomization method, the raw material metal is heated and melted to obtain molten metal. The molten metal flows out from the nozzle. The molten metal falls onto a disk rotating at high speed. The molten metal is quenched and solidified to obtain powder.

[0066] Typical flat processing is performed by a grinder. The flat processing can be performed dry or wet. In the wet flat processing, an appropriate amount of organic solvent is used. Various organic solvents can be used for this wet processing. Organic solvents that can inhibit the oxidation of particles are preferred.

[0067] Heat treatment is performed on the powder after flat processing as needed. From the viewpoint of high permeability, the preferred heat treatment temperature is 500 °C or higher and 900 °C or lower. The heat treatment time is appropriately adjusted according to the processing amount of the powder, productivity, etc. Heat treatment in a vacuum or an inert gas is preferred. Heat treatment can be performed on the raw material powder before flat processing as needed.

[0068] Classification can be performed on the powder. Classification can be performed on the powder before flat processing, on the powder after flat processing, or on the powder after heat treatment.

[0069] Examples

[0070] Hereinafter, the effects of the soft magnetic flat powder of the examples are clarified, but the scope disclosed in this specification should not be construed in a limiting manner based on the description of the examples.

[0071] [Example 1]

[0072] Raw material powder is obtained through gas atomization and classification. The material of the raw material powder analyzed by an ICP (Inductive Coupled Plasma) optical emission spectrometer is an Fe-9Si-6Al alloy containing 0.011% by mass of C. 500 g of the raw material powder is put into a grinder together with a naphthenic solvent. The material of the medium is high-carbon chromium bearing steel (SUJ2). The diameter of this medium is 4.8 mm. Through this grinder, flat processing is performed on the raw material powder. Heat treatment is performed on this powder to obtain the soft magnetic flat powder of Example 1. The conditions of the heat treatment are as described below.

[0073] Temperature: 800 °C

[0074] Holding time: 1 hour

[0075] Cooling method: Slow cooling

[0076] The median diameter D50 of this soft magnetic flat powder is 52.6 μm, and the tapped density TD is 0.77 g / cm 3 , and the coercive force Hc is 133 A / m.

[0077] [Examples 2-4 and Comparative Examples 1 and 2]

[0078] Make the C content of the raw material powder as shown in Tables 1 and 2 below. Except for this, in the same manner as in Example 1, powders of Examples 2-4 and Comparative Examples 1 and 2 are obtained.

[0079] [Comparative Examples 3 and 4]

[0080] Make the composition of the raw material powder as shown in Table 2 below. Except for this, in the same manner as in Example 1, powders of Comparative Examples 3 and 4 are obtained.

[0081] [Measurement of permeability]

[0082] The flat powder is kneaded with an acrylic resin to obtain a slurry. This slurry is supplied to a doctor blade method to obtain a sheet. Pressing processing is performed on this sheet under the conditions of a temperature of 60 °C and a pressure of 50 MPa to obtain a magnetic sheet. The volume filling rate of the flat powder in this magnetic sheet is about 35%. The complex permeability of this magnetic sheet is measured using an impedance analyzer (product name "E4991B" of Keysight Technology). The measurement is performed in the range of 1 MHz or more and 1 GHz or less, and the average value of the real part permeability μ' in the range of 2 MHz or more and 5 MHz is obtained. The results are shown in Tables 1 and 2 below.

[0083] [Table 1]

[0084]

[0085] [Table 2]

[0086]

[0087] As can be seen from Tables 1 and 2, the soft magnetic flat powder of each example can contribute to a large real part permeability μ' of the magnetic member. Based on these evaluation results, the superiority of the soft magnetic flat powder of each example is obvious.

[0088] Industrial Applicability

[0089] The soft magnetic flat powder described above is suitable for various magnetic members.

[0090] Explanation of Reference Numerals

[0091] 2 ··· magnetic sheet

[0092] 4 ··· substrate

[0093] 6 ··· flat particle

Claims

1. A soft magnetic flat powder comprising a plurality of flat particles made of an Fe-Si-Al alloy containing 0.010% by mass or more and 0.050% by mass or less of C.

2. The soft magnetic flat powder according to claim 1, wherein the median diameter D50 on a volume basis is 20.0 μm or more and 90.0 μm or less.

3. The soft magnetic flat powder according to claim 1 or 2, wherein The tapped density TD is 1.25 g / cm 3 or less.

4. The soft magnetic flat powder according to claim 1 or 2, wherein the coercive force of the powder when a magnetic field is applied in the longitudinal direction of the flat particles is 400 A / m or less.

5. A magnetic member comprising: a matrix with a polymer as a base material, and soft magnetic flat powder dispersed in the matrix, the soft magnetic flat powder comprising a plurality of flat particles, the flat particles being made of an Fe-Si-Al alloy containing 0.01% by mass or more and 0.05% by mass or less of C.

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