Magnetic body, method for manufacturing the same, coil component, and circuit board

Abstract

The present invention relates to a magnetic material, a method for manufacturing the same, a coil component, and a circuit board. The magnetic material of the present invention is composed of particles of a soft magnetic alloy bonded to each other through an oxide layer. The soft magnetic alloy is an alloy containing 1% by mass to 5.5% by mass of Si, a total of 0.2% by mass to 4% by mass of Cr and Al, or Cr, or Al as constituent elements, with the balance being Fe and inevitable impurities. The oxide layer contains at least one of Cr and Al in addition to Si, and Si has the highest content by mass among Fe, Si, Cr, and Al. The present invention can provide a magnetic material having a high magnetic permeability.

Description

Technical Field

[0001] The present invention relates to a magnetic material, a method for manufacturing the same, a coil component using the magnetic material, and a circuit board loaded with the coil component. Background Art

[0002] In recent years, in coil components for passing a large current or the like, in addition to miniaturization, a large current capacity has been required. In order to achieve a large current capacity, it is necessary to use a magnetic material that is not easily magnetically saturated with respect to the current. Therefore, as the magnetic material, an iron-based metallic magnetic material is used instead of a ferrite-based material.

[0003] Generally, a magnetic material for a core of a coil component is manufactured from a powdery soft magnetic material. Regarding the powdery soft magnetic metal material, since the insulating resistance of each particle constituting the powder is low, in order to impart insulation, the surfaces of the particles constituting it are often covered with an insulating film for use.

[0004] For example, in Patent Document 1, it is reported that: Fe-1% Si atomized alloy particles are mixed with water vapor in nitrogen to form an atmosphere of a very low oxygen concentration with a relative humidity of 100% (room temperature), and an oxidation reaction is carried out at 450°C for 2 hours. As a result, a SiO2 oxide film with a film thickness of 5 nm is formed on the particle surface.

[0005] In addition, when manufacturing a magnetic material from a soft magnetic metal powder, after forming the soft magnetic metal powder into a specified shape, in order to bond the particles to each other to improve the strength, or in order to form an insulating film on the particle surface or grow the formed insulating film to electrically insulate the particles, the molded body is sometimes heat-treated.

[0006] For example, in Patent Document 1, it is reported that: after an oxidation reaction is carried out by maintaining a specified time at 450°C in an atmosphere gas with a relative humidity of 100% formed by mixing water vapor with a humidifier in a nitrogen-5% hydrogen mixed gas for a molded body of a soft magnetic alloy powder having a SiO2 film formed on the particle surface, a treatment of raising the temperature to 880°C and maintaining a specified time is then carried out.

[0007] In addition, in Patent Document 2, it is reported that: a molded body of a soft magnetic alloy powder coated on the particle surface with a treatment liquid containing titanium alkoxides and silicon alkoxides is heat-treated at 850°C in an argon atmosphere.

[0008] Moreover, in Patent Document 3, it is reported that: a molded body of an Fe-Si-Cr-based soft magnetic alloy powder having an Si compound disposed on the surface is heat-treated at 700°C for 1 hour in the atmosphere.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Laid-Open No. 2006-49625

[0012] Patent Document 2: Japanese Patent Laid-Open No. 2018-182040

[0013] Patent Document 3: Japanese Patent Laid-Open No. 2015-126047 Summary of the Invention

[0014] Technical Problem to be Solved by the Invention

[0015] As a method for obtaining a magnetic material having excellent magnetic properties such as permeability, a method of increasing the filling rate of a soft magnetic material in the magnetic material can be cited. However, when a metal is used as the soft magnetic material, as described above, it is necessary to form an insulating film to electrically insulate between the particles of the soft magnetic metal, so the filling rate of the soft magnetic metal in the volume amount of the insulating film decreases. Particularly when the electrical insulation of the insulating film is low, it is necessary to form it thicker, so the distance between the metal particles becomes larger, and there is a problem of deterioration of magnetic properties.

[0016] As a method for obtaining a magnetic material having excellent magnetic properties such as permeability, a method of increasing the Fe content ratio in the magnetic material is known. However, for a soft magnetic metal having a high Fe content ratio, there is a problem that the magnetic properties deteriorate due to oxidation of Fe in the atmosphere.

[0017] Then, an object of the present invention is to solve the above problems and provide a magnetic material having a high permeability.

[0018] Technical Solution for Solving the Technical Problem

[0019] The inventors of the present invention conducted various studies to solve the above problems, and found that by making the soft magnetic alloy constituting the magnetic material have a specific composition with a large amount of Fe, and binding the particles of the alloy to each other through an oxide layer having a specific composition, the above problems can be solved, and thus the present invention was completed.

[0020] That is, to solve the above technical problem, a first embodiment of the present invention is a magnetic material in which particles of a soft magnetic alloy are bonded to each other through an oxide layer, characterized in that: the soft magnetic alloy is an alloy containing 1% by mass to 5.5% by mass of Si, a total of 0.2% by mass to 4% by mass of Cr and Al, or Cr, or Al as constituent elements, and the balance is Fe and inevitable impurities, and the oxide layer contains at least one of Cr and Al in addition to Si, and Si has the largest content based on mass among Fe, Si, Cr, and Al.

[0021] Further, a second embodiment of the present invention is a method for manufacturing a magnetic material, which includes: a step of preparing soft magnetic alloy powder, wherein the soft magnetic alloy powder contains 1 mass% to 5.5 mass% of Si, a total of 0.2 mass% to 4 mass% of Cr and Al, or Cr, or Al as constituent elements, with the balance being Fe and inevitable impurities, and the content of Si is more than the total of Cr, or Al, or Cr and Al; a step of shaping the soft magnetic alloy powder to obtain a shaped body; and a step of heat-treating the shaped body in an atmosphere with an oxygen concentration of 10 ppm to 800 ppm at a temperature of 500°C to 900°C to form an oxide layer on the surface of the soft magnetic alloy particles, and binding the soft magnetic alloy particles to each other through the oxide layer.

[0022] Further, a third embodiment of the present invention is a coil component formed by winding a conductor around the above magnetic material, and a fourth embodiment of the present invention is a circuit board loaded with the coil component.

[0023] Advantages of the Invention

[0024] According to the present invention, a magnetic material with high magnetic permeability can be provided. Description of the Drawings

[0025] Figure 1 It is a schematic diagram showing the structural confirmation result of the oxide layer of a scanning transmission electron microscope (STEM) of the magnetic material of Example 1.

[0026] Figure 2 It is along Figure 1 The line analysis result of A-A' in

[0027] Description of Reference Numerals

[0028] 1 Soft magnetic alloy particles

[0029] 2 Oxide layer

[0030] 21 Si-rich region

[0031] A-A' Site where line analysis was performed Detailed Embodiments

[0032] Hereinafter, with reference to the drawings, the structure and effects of the present invention will be described in conjunction with the technical idea. However, the mechanism of action includes speculation, and its correctness does not limit the present invention. In addition, among the constituent elements of the following embodiments, the constituent elements not described in the independent claims representing the most general concept are described as optional constituent elements. Further, the description of a numerical range (a description connecting two numerical values with "~") means that the numerical values described as the lower limit and the upper limit are also included.

[0033] (Magnetic Material)

[0034] The magnetic material according to the first embodiment of the present invention (hereinafter sometimes simply referred to as "the first embodiment") is characterized in that particles of a soft magnetic alloy are bonded to each other through an oxide layer. The soft magnetic alloy is an alloy containing 1 mass% to 5.5 mass% of Si, a total of 0.2 mass% to 4 mass% of Cr and Al, or Cr, or Al as constituent elements, with the balance being Fe and inevitable impurities. The inevitable impurities include oxygen, hydrogen, nitrogen, and inevitable metallic element impurities. The oxide layer contains at least one of Cr and Al in addition to Si, and Si has the highest content by mass among Fe, Si, Cr, and Al.

[0035] The soft magnetic alloy of the first embodiment contains 1 mass% to 5.5 mass% of Si.

[0036] The soft magnetic alloy contains 1 mass% or more of Si, whereby the resistance becomes high and a decrease in magnetic properties due to eddy currents can be suppressed. The content of Si is preferably 1.5 mass% or more, more preferably 2 mass% or more. On the other hand, the content of Si is 5.5 mass% or less, whereby the content of Fe becomes more, and the magnetic permeability of the magnetic material becomes high. The content of Si is preferably 5 mass% or less, more preferably 4.5 mass% or less.

[0037] In addition, the soft magnetic alloy of the first embodiment contains a total of 0.2 mass% to 4 mass% of Cr and Al, or Cr, or Al.

[0038] The soft magnetic alloy contains a total of 0.2 mass% or more of Cr and Al, or Cr, or Al, whereby the oxidation resistance is excellent. On the other hand, the content of Cr, or Al, or Cr and Al in total is 4 mass% or less, whereby segregation of these elements can be suppressed, and the content of Fe becomes more, and the magnetic permeability of the magnetic material becomes high. In order to obtain a higher magnetic permeability, the total content of Cr, or Al, or Cr and Al is preferably 2 mass% or less.

[0039] When the soft magnetic alloy contains Cr, from the viewpoint of obtaining more excellent oxidation resistance, its content is preferably 0.5 mass% or more.

[0040] When the soft magnetic alloy contains Al, from the viewpoint of suppressing its segregation, its content is preferably 1 mass% or less.

[0041] The content of Fe in the soft magnetic alloy of the first embodiment has a great influence on the magnetic permeability of the magnetic material, so it is preferably as much as possible within the range where desired insulation and oxidation resistance can be obtained. The preferred content of Fe is 94 mass% or more, more preferably 95 mass% or more, and further preferably 96 mass% or more.

[0042] In the first embodiment, the particles of the soft magnetic alloy having the above composition contain at least one of Cr and Al in addition to Si, and are bonded by an oxide layer containing the most Si in terms of mass among Fe, Si, Cr, and Al.

[0043] The oxide layer contains at least one of Cr and Al in addition to Si, whereby the movement speed of oxygen in the layer is reduced, and it is possible to suppress the reduction of magnetic properties caused by oxygen reaching the soft magnetic alloy particles and oxidizing Fe.

[0044] In addition, since the oxide layer contains the most Si in terms of mass among Fe, Si, Cr, and Al, it has excellent electrical insulation. In addition, it is preferable that the contents of Fe, Cr, and Al in the oxide layer are less than that of Si, because this means that the diffusion flux from the soft magnetic alloy particles to the oxide layer during the manufacture of the magnetic material is small, and an oxide layer with a small thickness can be obtained. Moreover, it is preferable that the content of Fe in the oxide phase is small, because this means that the content of Fe in the corresponding amount of the soft magnetic alloy is large.

[0045] In this way, in the first embodiment, the particles of the soft magnetic alloy containing a large amount of Fe are separated from each other by an oxide film with a small oxygen movement speed, excellent insulation, and a small thickness, whereby a high permeability can be stably obtained.

[0046] The above oxide layer preferably has a Si-rich region containing more than three times the amount of Si of the element having the second highest content in terms of mass among Fe, Cr, and Al, and the Si-rich region is in contact with the above soft magnetic alloy. Since the oxide layer has such a structure, its electrical insulation is more excellent. Preferably, in the above Si-rich region, there is a part where the Si content based on mass is more than five times that of the element having the second highest content, and more preferably, there is a part where the ratio is more than ten times.

[0047] Here, the composition of the soft magnetic alloy of the magnetic material and the structure of the oxide layer are confirmed by the following process.

[0048] First, after taking out a thin film sample with a thickness of 50 nm to 100 nm from the central part of the inductor core using a focused ion beam device (FIB), immediately use a scanning transmission electron microscope (STEM) equipped with a annular dark field detector and an energy dispersive X-ray spectroscopy (EDS) detector to obtain a composition image of the oxide layer by STEM-EDS method. The measurement conditions of STEM-EDS are that the acceleration voltage is 200 kV, the electron beam diameter is 1.0 nm, and the measurement time is set so that the integrated value of the signal intensity in the range of 6.22 keV to 6.58 keV at each point of the soft magnetic alloy particle part is 25 counts or more. Moreover, the signal intensity of the OKα ray is relative to the signal intensity of the FeKα ray (I FeKα ) and the signal intensity of the CrKα line (ICrKα ) and the total ratio (I AlKα ) of the signal intensity of AlKα rays (I OKα / (I FeKα +I CrKα +I AlKα )) is 0.5 or more is defined as the oxide layer, and the region where this value is less than 0.5 is defined as the soft magnetic alloy.

[0049] The composition of the soft magnetic alloy is determined by performing line analysis in the radial direction from the oxide layer side on the particles of the soft magnetic alloy using STEM-EDS method to measure the distributions of Fe, Si, Cr, and Al, and calculating the average value of the content of each element for the first three measurement points where the variation in the content of each element is within ±1 mass%. In addition, when the composition of the soft magnetic alloy powder used for manufacturing the magnetic body is known, the known composition can be used as the composition of the soft magnetic alloy.

[0050] The structure of the oxide layer is confirmed by performing line analysis using STEM-EDS along a line segment from one soft magnetic alloy particle through the oxide layer to another soft magnetic alloy particle for any part in the oxide layer that binds the soft magnetic alloy particles to measure the distribution of each element.

[0051] (Method for manufacturing a magnetic body)

[0052] The method for manufacturing a magnetic body according to the second embodiment of the present invention (hereinafter sometimes simply referred to as "the second embodiment") includes: a step of preparing a soft magnetic alloy powder containing, as constituent elements, 1 mass% to 5.5 mass% of Si, a total of 0.2 mass% to 4 mass% of Cr and Al, or Cr, or Al, with the balance being Fe and inevitable impurities, the inevitable impurities including oxygen, hydrogen, nitrogen, and inevitable metal element impurities, and the content of Si being more than the total of Cr, or Al, or Cr and Al; a step of molding the soft magnetic alloy powder to obtain a molded body; and a step of heat-treating the molded body in an atmosphere with an oxygen concentration of 10 ppm to 800 ppm at a temperature of 500°C to 900°C to form an oxide layer on the surface of the particles of the soft magnetic alloy and binding the particles of the soft magnetic alloy to each other through the oxide layer.

[0053] The soft magnetic alloy powder used in the second embodiment contains 1 mass% to 5.5 mass% of Si as a constituent element.

[0054] By using soft magnetic alloy powder containing 1% by mass or more of Si, an oxide layer with excellent electrical insulation can be formed by the heat treatment described later. The content of Si is preferably 1.5% by mass or more, more preferably 2% by mass or more. On the other hand, the content of Si in the soft magnetic alloy powder is 5.5% by mass or less, so that the content of Fe in the alloy increases and the permeability of the obtained magnetic body becomes high. The content of Si is preferably 5% by mass or less, more preferably 4.5% by mass or less.

[0055] In addition, the soft magnetic alloy powder used in the second embodiment contains a total of 0.2% by mass to 4% by mass of Cr and Al, or Cr, or Al.

[0056] By using soft magnetic alloy powder containing a total of 0.2% by mass or more of Cr and Al, or Cr, or Al, oxidation of Fe during the manufacturing process of the magnetic body can be prevented, and a magnetic body with high permeability can be obtained. On the other hand, the total content of Cr, or Al, or Cr and Al is 4% by mass or less, whereby segregation of these elements during the manufacturing process can be suppressed, and the content of Fe increases, and the permeability of the magnetic body becomes high. In order to obtain a higher permeability, the total content of Cr, or Al, or Cr and Al is preferably 2% by mass or less.

[0057] When the soft magnetic alloy powder contains Cr, from the viewpoint of obtaining more excellent oxidation resistance, its content is preferably 0.5% by mass or more.

[0058] When the soft magnetic alloy powder contains Al, from the viewpoint of suppressing its segregation, its content is preferably 1% by mass or less.

[0059] The content of Fe in the soft magnetic alloy powder used in the second embodiment has a great influence on the permeability of the obtained magnetic body, so it is preferably as much as possible within the range where the desired insulation and oxidation resistance can be obtained. The preferred content of Fe is 94% by mass or more, more preferably 95% by mass or more, and further preferably 96% by mass or more.

[0060] In the soft magnetic alloy powder used in the second embodiment, the content of Si is more than the total of Cr, or Al, or Cr and Al.

[0061] Since the content of Si is more than the total of Cr, or Al, or Cr and Al, an oxide layer with Si enrichment, high insulation, and thin thickness can be formed on the surface of the alloy particles by the heat treatment described later, and a magnetic body with high permeability can be obtained.

[0062] The particle size of the soft magnetic alloy powder used in the second embodiment is not particularly limited. For example, the average particle size (median diameter (D 50)) is 0.5 μm to 30 μm. The average particle diameter is preferably 1 μm to 10 μm. This average particle diameter can be measured, for example, using a particle size distribution measuring device that utilizes the laser diffraction / scattering method.

[0063] In the second embodiment, before molding the soft magnetic alloy powder, the alloy powder can be heat-treated at a temperature of 600 °C or higher in an atmosphere with an oxygen concentration of 5 ppm to 500 ppm. By this heat treatment, a smooth oxide film with few irregularities is formed on the surface of the particles constituting the soft magnetic alloy powder, and the filling rate can be increased by improving the moldability. In addition, a magnetic body with excellent electrical insulation can be obtained.

[0064] For the above-mentioned oxide film, the ratio of the mass of Si on the outermost surface to the total mass of Cr, or Al, or Cr and Al (Si / (Cr + Al)) is preferably 1 to 10. When the above ratio is 1 or more, the film becomes a smoother film with even fewer minute irregularities. On the other hand, when the above ratio is 10 or less, excessive oxidation can be suppressed, and even if the oxide film is thin, the stability of the film is further improved. The above ratio is preferably 8 or less, and more preferably 6 or less. Thus, even when heat treatment is applied, its surface state can be maintained.

[0065] Here, the ratio of the mass of Si on the outermost surface of the oxide film to the total mass of Cr, or Al, or Cr and Al (Si / (Cr + Al)) is measured by the following method. Using an X-ray photoelectron spectroscopy analyzer (PHI Quantera II manufactured by ULVAC-PHI, Inc.), the content ratios (atomic %) of iron (Fe), silicon (Si), oxygen (O), chromium (Cr), and aluminum (Al) on the surface of the soft magnetic alloy particles formed with the oxide film are measured. The measurement conditions are to use monochromatized AlKα rays as the X-ray source, and the detection area is set to Then, the mass ratios (mass %) of each element are calculated from the obtained results, and based on this, the ratio of the mass of Si to the total mass of Cr, or Al, or Cr and Al is calculated.

[0066] In the second embodiment, it is preferable that by the heat treatment before molding, the mass ratio of Si on the outermost surface of the oxide film is 5 times or more that of the soft magnetic alloy part, and the mass ratio of Cr or Al on the outermost surface of the oxide film is 3 times or more that of the soft magnetic alloy part. By adopting such mass ratios, more excellent fluidity can be obtained.

[0067] In addition, in the second embodiment, it is preferable to perform the heat treatment before molding so that the Si, Cr, and Al concentrations in mass % on the outermost surface of each particle constituting the soft magnetic alloy powder before this heat treatment are set to [Si处理前 , [Cr 处理前 , and [Al 处理前 , when the concentrations of Si, Cr, and Al, expressed in mass%, on the outermost surface of each particle of the heat-treated soft magnetic alloy powder are respectively designated as [Si 处理后 , [Cr 处理后 , and [Al 处理后 , it becomes {([Cr 处理后 + [Al 处理后 ) / ([Cr 处理前 + [Al 处理前 )} > ([Si 处理后 / [Si 处理前 ), that is, by heat treatment, the increase ratio of the total of Cr, or Al, or Cr and Al on the outermost surface of the particle is larger than the increase ratio of Si. By performing heat treatment as described above, soft magnetic alloy powder having an oxide film with higher stability can be obtained.

[0068] Here, the values of the above [Si 处理后 , [Cr 处理后 , and [Al 处理后 are the results obtained by analyzing the outermost surface of the oxide film through the above X-ray photoelectron spectroscopy apparatus for the soft magnetic alloy powder that has undergone heat treatment before molding. The values of the above [Si 处理前 , [Cr 处理前 , and [Al 处理前 are the values obtained by changing the measurement sample to the soft magnetic alloy particles before heat treatment in this analysis.

[0069] In the second embodiment, it is preferable to form soft magnetic alloy powder in which the relationship between the specific surface area S (m 2 / g) and the average particle diameter D 50 (μm) satisfies the following formula (1) through the above heat treatment before molding.

[0070] (Formula 1)

[0071] log S ≤ -0.98 log D 50 + 0.34 (1)

[0072] This formula is based on the common logarithm of the specific surface area S (m 2 / g) and the average particle diameter D 50is derived from the empirical rule that the common logarithm of (μm) forms a straight line relationship. The specific surface area value of the powder is affected by the particle size of the particles in addition to the unevenness of the particle surface. Therefore, it cannot be said that powders with a small specific surface area value are composed of smooth particles with less surface unevenness. Thus, in the second embodiment, by the above formula (1), the influence of the surface state of the particles on the specific surface area is separated from the influence of the particle size on the specific surface area, and the soft magnetic alloy powder with a small specific surface area due to the former influence is regarded as a soft magnetic alloy powder with a smooth surface with less unevenness. By making the relationship between S and D 50 satisfy the above formula (1), a powder with better fluidity is obtained.

[0073] By increasing the proportion of Si present in the oxide film on the particle surface and reducing the unevenness on the surface of the oxide film, the specific surface area S (m 2 / g) can be made smaller. An oxide film with less surface unevenness can maintain insulation with a thinner film thickness, so it is preferred. As described above, the proportion of Si present in the oxide film on the particle surface can be increased by increasing the Si composition ratio of the soft magnetic alloy powder or lowering the heat treatment temperature. Specifically, the relationship between the specific surface area S (m 2 / g) and the average particle size D 50 (μm) more preferably satisfies the following formula (2), and more preferably satisfies the following formula (3).

[0074] (Formula 2)

[0075] log S ≤ -0.98 log D 50 + 0.30 (2)

[0076] (Formula 3)

[0077] log S ≤ -0.98 log D 50 + 0.25 (3)

[0078] Here, the specific surface area S is measured and calculated by the nitrogen adsorption method using a fully automatic specific surface area measuring device (Macsorb manufactured by Mountec Co., Ltd.). First, after degassing the measurement sample in a heater, the measurement sample adsorbs and desorbs nitrogen, and thus the amount of adsorbed nitrogen is measured. Then, the monolayer adsorption amount is calculated by the BET one-point method based on the obtained amount of adsorbed nitrogen, and based on this value, the surface area of the sample is derived using the area occupied by one nitrogen molecule and the value of Avogadro's constant. Finally, the specific surface area S of the powder is obtained by dividing the surface area of the obtained sample by the mass of the sample.

[0079] In addition, the average particle size D 50Measurement and calculation were performed using a particle size distribution measuring device (LA-950 manufactured by Horiba, Ltd.) that utilizes the laser diffraction / scattering method. First, water as a dispersant was added to a wet flow cell, and the powder that had been sufficiently pulverized in advance was introduced into the flow cell at a concentration that could obtain an appropriate detection signal to measure the particle size distribution. Next, the median diameter of the obtained particle size distribution was calculated, and this value was used as the average particle diameter D 50 .

[0080] In the second embodiment, in the case of performing the heat treatment before the above-mentioned molding, it is preferable that the thickness of the oxide film formed thereby is 10 nm to 50 nm. By making the thickness of the oxide film 10 nm or more, it is possible to cover the minute irregularities of the alloy part and form a smooth surface. In addition, high insulation can be obtained. The thickness of the oxide film is more preferably 20 nm or more. By adopting such a method, the ratio of Si on the surface of the oxide film can be further increased. Further, when forming a magnetic body, even in the case where defects of the oxide film are generated due to compression molding by applying pressure, the insulation can be maintained. On the other hand, by making the thickness of the oxide film 50 nm or less, it is possible to suppress the reduction in the smoothness of the particle surface due to non-uniform film thickness. In addition, when forming a magnetic body, a high magnetic permeability can be obtained. The thickness of the oxide film is more preferably 40 nm or less.

[0081] Here, the thickness of the oxide film was calculated by observing the cross section of the magnetic particles constituting the soft magnetic alloy powder with a scanning transmission electron microscope (STEM) (JEM-2100F manufactured by JEOL Ltd.), measuring the thickness of the oxide film identified based on the difference in contrast (brightness) according to the compositional difference from the alloy part inside the particles at 10 positions of different particles at a magnification of 500,000 times, and obtaining the average value.

[0082] In the second embodiment, the above-mentioned soft magnetic alloy powder is formed into a prescribed shape to obtain a molded body.

[0083] The molding method is not particularly limited. For example, a method may be cited in which the soft magnetic alloy powder and a resin are mixed and supplied to a molding die such as a metal mold, and after being pressed by stamping or the like, the resin is cured.

[0084] In this case, the resin mixed with the soft magnetic alloy powder is not particularly limited as long as it can bond the particles of the soft magnetic alloy powder to each other for molding and shape retention, and can be volatilized without leaving carbon or the like by the degreasing treatment. As an example, acrylic resins, butyral resins, and ethylene resins having a decomposition temperature of 500°C or lower can be cited. In addition, lubricants represented by stearic acid or its salts, phosphoric acid or its salts, and boric acid and its salts may be used together with the resin or in place of the resin.

[0085] The addition amount of the resin or lubricant may be appropriately determined in consideration of formability, shape retention property, etc. For example, it can be 0.1 to 5 mass with respect to 100 mass of the soft magnetic alloy powder.

[0086] When a resin is mixed in obtaining the molded body, it is preferable to perform degreasing before heat treatment. The degreasing temperature is set according to the decomposition temperature of the resin used, and is roughly about 200°C to 500°C. In addition, in order to prevent oxidation of the soft magnetic alloy, the degreasing atmosphere is preferably superheated steam.

[0087] In the second embodiment, the above-mentioned molded body is heat-treated in an atmosphere with an oxygen concentration of 10 ppm to 800 ppm.

[0088] By making the oxygen concentration in the heat treatment atmosphere within the above range, an oxide layer containing at least one of Cr and Al in addition to Si and enriched with Si can be formed on the surface of the soft magnetic alloy particles with an appropriate thickness. The above oxygen concentration is preferably 100 ppm or more, and more preferably 200 ppm or more.

[0089] When the oxygen concentration in the heat treatment atmosphere is too low, for short-time heat treatment, the formation of the oxide layer becomes insufficient and the insulation property decreases. For long-time heat treatment, the oxide layer becomes too thick due to the diffusion of Fe or Cr or Al into the oxide layer, resulting in a decrease in permeability. On the other hand, when the oxygen concentration in the heat treatment atmosphere is too high, the content of Fe or Cr or Al in the oxide layer becomes too much, and the insulation property of the oxide layer decreases.

[0090] In addition, in the second embodiment, the above heat treatment is performed at a temperature of 500°C to 900°C.

[0091] By making the heat treatment temperature within the above range, an oxide layer containing at least one of Cr and Al in addition to Si and enriched with Si can be formed on the surface of the soft magnetic alloy particles with an appropriate thickness. The temperature of the above heat treatment is preferably 550°C or more, and more preferably 600°C or more. In addition, the temperature of the above heat treatment is preferably 850°C or less, and more preferably 800°C or less.

[0092] Regarding the heat treatment time of the second embodiment, as long as an oxide layer containing at least one of Cr and Al in addition to Si and enriched with Si is formed on the surface of the soft magnetic alloy particles and the soft magnetic alloy particles can be bonded to each other through the oxide layer, there is no particular limitation. However, from the viewpoint of forming a sufficient thickness of the oxide layer, it is preferably 30 minutes or more, and more preferably 1 hour or more. On the other hand, from the viewpoint of finishing the heat treatment in a short time to improve productivity, it is preferable to make the heat treatment time 5 hours or less, and more preferably 3 hours or less.

[0093] The heat treatment of the second embodiment can be batch processing or flow processing. As an example of flow processing, a method can be cited in which a plurality of heat-resistant trays on which the above-mentioned molded body is placed are intermittently or continuously introduced into a tunnel furnace and passed through a region maintained at a specified atmosphere and temperature for a specified time.

[0094] (Coil component)

[0095] The coil component of the third embodiment of the present invention (hereinafter sometimes simply referred to as "the third embodiment") is constituted by winding a conductor around the magnetic body of the above-mentioned first embodiment.

[0096] The shape and size of the magnetic body and the material and shape of the conductor are not particularly limited and can be appropriately determined according to the required characteristics.

[0097] In the third embodiment, a magnetic body having a high magnetic permeability is used as the magnetic body, so that a coil component having excellent characteristics is obtained. In addition, since the element volume required to obtain the same characteristics can be reduced, a small-sized coil component is obtained.

[0098] (Circuit board)

[0099] The circuit board of the fourth embodiment of the present invention (hereinafter sometimes simply referred to as "the fourth embodiment") is a circuit board on which the coil component of the third embodiment is mounted.

[0100] The structure of the circuit board and the like are not limited, and any structure corresponding to the purpose may be adopted.

[0101] The fourth embodiment can achieve high performance and miniaturization by using the coil component of the third embodiment.

[0102] (Examples)

[0103] The present invention will be described more specifically below by way of examples, but the present invention is not limited to these examples.

[0104] (Example 1)

[0105] (Production of magnetic body)

[0106] First, a soft magnetic alloy powder having a composition of Fe—3.5Si—1.5Cr (the numerical values represent mass percentages) and an average particle diameter of 4.0 μm was prepared. Next, the soft magnetic alloy powder was stirred and mixed with 1.2 mass% of an acrylic-based binder to prepare a molding material. Next, the molding material was put into a mold having a molding space corresponding to an annular space with an outer diameter of 8 mm and an inner diameter of 4 mm, and at 8 t / cm 2Uniaxial pressing was performed under the pressure of

[0107] to obtain a formed body with a thickness of 1.3 mm. Subsequently, the obtained formed body was placed in an oven at 150 °C for 1 hour to cure the binder, and then heated to 300 °C using a superheated steam furnace, and the binder was removed by thermal decomposition. Finally, heat treatment was performed at 800 °C for 1 hour in an atmosphere with an oxygen concentration of 800 ppm using a quartz furnace to obtain an annular magnetic body. 2 In addition, the above-mentioned forming material was put into a mold having a circular plate-shaped forming space with an inner diameter of 7 mm, and uniaxial pressing was performed under the pressure of 8 t / cm

[0108] (Confirmation of the structure of the oxide layer)

[0109] For the above-mentioned circular plate-shaped magnetic body, the structure of the oxide layer was confirmed by the above method. The schematic diagram showing the structure of the oxide layer observed by STEM is shown in Figure 1 , and the line analysis result along the line segment A-A' in Figure 2 is shown in Figure 1 .

[0110] According to Figure 2 , it can be seen that the oxide layer 2 contains Fe and Cr in addition to Si. In addition, throughout almost the entire range of the oxide layer 2, the element with the highest content is Si. Therefore, it can be known that among Fe, Si, Cr, and Al, the element with the highest content in the oxide layer 2 is Si. Moreover, in the oxide layer 2, a Si-rich region 21 with a particularly high Si content was confirmed at the boundary portion with the soft magnetic alloy particles 1, and a portion where the Si content was about 5 times that of Fe, which is the second highest in content, was found in this region.

[0111] (Measurement of the magnetic permeability of the magnetic body)

[0112] Twenty turns of polyurethane-coated copper wire with a diameter of 0.3 mm were wound around the above-mentioned annular iron core in a coil shape to make an evaluation sample.

[0113] For the obtained evaluation sample, a relative magnetic permeability measurement was performed at a frequency of 10 MHz using an LCR meter (4285A manufactured by Agilent Technologies) as a measurement device. The obtained relative magnetic permeability was 22.

[0114] (Evaluation of the insulation of the magnetic body)

[0115] The insulation of the magnetic body was evaluated by volume resistivity and dielectric breakdown voltage.

[0116] An Au film was formed on the entire surfaces of both sides of the above-mentioned disc-shaped magnetic body by sputtering to prepare a sample for evaluation.

[0117] For the obtained sample for evaluation, the volume resistivity was measured based on JIS-K6911. The Au films formed on both sides of the sample were used as electrodes, and a voltage was applied between the electrodes so that the electric field strength became 60 V / cm to measure the resistance value, and the volume resistivity was calculated from this resistance value. The volume resistivity of the sample for evaluation was 0.2 MΩ·cm.

[0118] In addition, the dielectric breakdown voltage of the obtained sample for evaluation was measured by using the Au films formed on both sides of the sample as electrodes and applying a voltage between the electrodes to measure the current value. The applied voltage was gradually increased to measure the current value, and the electric field strength calculated from the voltage at which the current density calculated from this current value was 0.01 A / cm 2 was taken as the breakdown voltage. The dielectric breakdown voltage of the sample for evaluation was 0.0018 MV / cm.

[0119] (Example 2)

[0120] For the soft magnetic alloy powder, a magnetic body of Example 2 was obtained in the same manner as in Example 1 except for the following treatment.

[0121] First, the soft magnetic alloy powder was put into a zirconia container and placed in a vacuum heat treatment furnace.

[0122] Next, after evacuating the furnace to make the oxygen concentration 100 ppm, it was heated to 700 °C at a heating rate of 5 °C / min, held for 1 hour for heat treatment, and then the furnace was cooled to room temperature to obtain the soft magnetic alloy powder.

[0123] The structure of the oxide layer of the obtained magnetic body was confirmed in the same manner as in Example 1, and the same result as the magnetic body of Example 1 was obtained. In the boundary part of the oxide layer with the soft magnetic alloy particles, a region with a particularly high Si content was confirmed, and a part where the Si content was about 12 times that of Fe with the second highest content was found.

[0124] In addition, the characteristics of the obtained magnetic body were evaluated in the same manner as in Example 1. The relative magnetic permeability was 25, the volume resistivity was 103 MΩ·cm, and the dielectric breakdown voltage was 0.0047 MV / cm.

[0125] (Example 3)

[0126] A magnetic body of Example 3 was obtained in the same manner as in Example 1 except for using soft magnetic alloy powder with an average particle size of 2.2 μm.

[0127] The structure of the oxide layer of the obtained magnetic material was confirmed in the same manner as in Example 1, and it was found to have the same structure as the magnetic material of Example 1.

[0128] In addition, the relative magnetic permeability and volume resistivity of the obtained magnetic material were evaluated in the same manner as in Example 1. The relative magnetic permeability was 16, and the volume resistivity was 0.5 MΩ·cm.

[0129] (Evaluation of the Packing Property of the Magnetic Material)

[0130] In this example, in addition to the above evaluations, the packing property of the soft magnetic alloy particles in the magnetic material was evaluated using the filling rate of the disc-shaped sample and the density ratio of the flange portion to the shaft portion of the drum core-shaped sample.

[0131] The disc-shaped sample was fabricated in the same manner as the disc-shaped sample of Example 1.

[0132] For the obtained disc-shaped sample, the outer diameter and thickness were measured to calculate the volume (measured volume). In addition, for the soft magnetic alloy powder used in the production of the disc-shaped sample, the true density was measured by the pycnometer method, and the volume (ideal volume) of the magnetic material formed by the soft magnetic alloy powder with a filling rate of 100% by volume was calculated by dividing the mass of the above disc-shaped sample by this true density value. Then, the filling rate was calculated by dividing the above measured volume by this ideal volume. The obtained filling rate was 78.8% by volume.

[0133] The drum core-shaped sample was fabricated in the same process as the disc-shaped sample, except that the mold for molding was changed to a mold having a space for shaft portion molding and a space for flange portion molding, and a drum core-shaped sample with a shaft portion size of 1.6 mm × 1.0 mm × 1.0 mm and a flange portion thickness of 0.25 mm was obtained.

[0134] The density ratio of the flange portion to the shaft portion of the obtained drum core-shaped sample was calculated by collecting measurement samples from the shaft portion and the flange portion of the sample respectively, measuring the volume of each sample by the constant volume expansion method, measuring the mass of each sample, calculating the density of each part based on these measurement values, and taking the ratio. In this sample, the flange portion and the shaft portion are made of the same material, so the density ratio is equivalent to the ratio of the filling rate. The obtained density ratio was 0.90.

[0135] (Example 4)

[0136] For the soft magnetic alloy powder, a magnetic material of Example 4 was obtained in the same manner as in Example 3, except for the following treatment.

[0137] First, the soft magnetic alloy powder was placed in a zirconia container and arranged in a vacuum heat treatment furnace.

[0138] Next, after exhausting the inside of the furnace to make the oxygen concentration 10 ppm, the temperature was raised to 700 °C at a heating rate of 5 °C / min, and heat treatment was performed for 1 hour, and then the furnace was cooled to room temperature to obtain soft magnetic alloy powder.

[0139] For the soft magnetic alloy powder subjected to this treatment, the thickness of the oxide film formed on the particle surface was confirmed by the above method to be 30 nm.

[0140] The structure of the oxide layer of the obtained magnetic body was confirmed by the same method as in Example 1, and it was found that it had the same structure as the magnetic body of Example 2.

[0141] In addition, the relative magnetic permeability and volume resistivity of the obtained magnetic body were evaluated by the same method as in Example 1. The relative magnetic permeability was 22, and the volume resistivity was 100 MΩ·cm.

[0142] The fillability of the soft magnetic alloy particles of the magnetic body was evaluated by the same method as in Example 3. The filling rate was 80.5 vol%, and the density ratio was 0.93.

[0143] (Comparative Example 1)

[0144] A magnetic body of Comparative Example 1 was obtained in the same manner as in Example 1, except that the heat treatment atmosphere at 800 °C for 1 hour was air.

[0145] The structure of the oxide layer of the obtained magnetic body was confirmed by the same method as in Example 1. The oxide layer contained Fe and Cr in addition to Si, and Si was the most abundant at the boundary with the soft magnetic alloy particles, but Cr was the most abundant in the inner region, and overall, the content of Cr was the highest.

[0146] In addition, the relative magnetic permeability and volume resistivity of the obtained magnetic body were evaluated by the same method as in Example 1. The relative magnetic permeability was 14, and the volume resistivity was 0.07 MΩ·cm.

[0147] The characteristics of the magnetic bodies of the examples and comparative examples measured were summarized in Table 1.

[0148] Table 1

[0149]

[0150] - indicates not measured

[0151] From the comparison between Examples 1 to 4 and Comparative Example 1, it can be said that the oxide layer that binds soft magnetic alloy particles to each other contains at least one of Cr and Al in addition to Si, and among Fe, Si, Cr, and Al, the magnetic material with the highest Si content by mass shows a high relative magnetic permeability. This is because the thickness of the above oxide layer is small and the filling rate of the soft magnetic alloy becomes high.

[0152] In addition, from the comparison between Example 1 and Example 2, and the comparison between Example 3 and Example 4, it can be said that by heat-treating the soft magnetic alloy powder in a low-oxygen atmosphere, a magnetic material with more excellent electrical insulation can be obtained. This is because the content of Si in the Si-rich region at the boundary part of the oxide layer and the soft magnetic alloy particles is particularly high.

[0153] Moreover, from the comparison between Example 3 and Example 4, it can be said that by heat-treating the soft magnetic alloy powder in a low-oxygen atmosphere, a magnetic material with a high filling rate of soft magnetic alloy particles can be obtained. This is because, through heat treatment, a smooth oxide film with few irregularities is formed on the surface of the soft magnetic alloy powder.

[0154] Industrial applicability

[0155] According to the present invention, a magnetic material with a high magnetic permeability can be provided. From the aspect that a coil component with excellent characteristics can be obtained by using this magnetic material, and from the aspect that the volume of the component required to obtain the same characteristics can be reduced so that the coil component can be miniaturized, the present invention is useful for these aspects. In addition, according to a preferred embodiment of the present invention, a magnetic material with high insulation can be provided. By using this magnetic material, a coil component that can handle a large current can be obtained, and the present invention is useful for this aspect.

Claims

1. A magnetic body, which is formed by binding particles of a soft magnetic alloy to each other through an oxide layer, and is characterized in that: The soft magnetic alloy is an alloy containing 1% by mass to 5.5% by mass of Si, a total of 0.2% by mass to 4% by mass of Cr and Al, or Cr, or Al as constituent elements, with the balance being Fe and inevitable impurities, and the content of Si is more than the total of Cr, or Al, or Cr and Al; The oxide layer contains at least one of Cr and Al in addition to Si, and among Fe, Si, Cr, and Al, Si has the highest content by mass.

2. The magnetic body according to claim 1, characterized in that: The content of Cr in the soft magnetic alloy is 0.5% by mass or more.

3. The magnetic body according to claim 1 or 2, characterized in that: The content of Al in the soft magnetic alloy is 1% by mass or less.

4. The magnetic body according to claim 1 or 2, characterized in that: The oxide layer has a Si-rich region, and the oxide layer contacts the soft magnetic alloy in this Si-rich region, wherein the Si-rich region contains Si that is 3 times or more the content of the element among Fe, Cr, and Al that has the second-highest content by mass after Si.

5. A method for manufacturing a magnetic body, characterized in that, Comprising: A step of preparing soft magnetic alloy powder, wherein the soft magnetic alloy powder contains 1% by mass to 5.5% by mass of Si, a total of 0.2% by mass to 4% by mass of Cr and Al, or Cr, or Al as constituent elements, with the balance being Fe and inevitable impurities, and the content of Si is more than the total of Cr, or Al, or Cr and Al; A step of molding the soft magnetic alloy powder to obtain a molded body; And A step of heat-treating the molded body in an atmosphere with an oxygen concentration of 10 ppm to 800 ppm at a temperature of 500 °C to 900 °C to form an oxide layer on the surface of the particles of the soft magnetic alloy, and binding the particles of the soft magnetic alloy to each other through the oxide layer.

6. The method for manufacturing a magnetic body according to claim 5, characterized in that: The content of Cr in the soft magnetic alloy powder is 0.5% by mass or more.

7. The method for manufacturing a magnetic body according to claim 5 or 6, characterized in that: The content of Al in the soft magnetic alloy is 1% by mass or less.

8. The method for manufacturing a magnetic body according to claim 5 or 6, characterized in that: Before the molding, it further includes a step of heat-treating the alloy powder in an atmosphere with an oxygen concentration of 5 ppm to 500 ppm at a temperature of 600 °C or higher.

9. A coil component, characterized in that: It is formed by winding a conductor around the magnetic body according to any one of claims 1 to 4.

10. A circuit board, characterized in that: It is loaded with the coil component according to claim 9.

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