Insulating Material-Coated Soft Magnetic Powder, Compressed Powder Core, Electronic Device, and Moving Body

Abstract

Provided are an insulating-coated soft magnetic powder capable of being heat-treated at high temperatures and having a low coercive force and a high insulation resistance value between particles, a compacted magnetic core, a magnetic component, an electronic device, and a moving body. The insulating-coated soft magnetic powder is characterized by having: a core particle having a base portion and an oxide film, the base portion containing a soft magnetic material mainly composed of Fe and containing at least one of Si, Cr, and Al, the oxide film being provided on the surface of the base portion and containing an oxide of at least one of Si, Cr, and Al; and an insulating coating film provided on the surface of the core particle and containing a ceramic, the thickness of the insulating coating film being 5 nm or more and 300 nm or less, and at the interface between the oxide film and the insulating coating film, mutual diffusion occurs between the oxide contained in the oxide film and the ceramic contained in the insulating coating film.

Description

Technical Field

[0001] The present invention relates to an insulating material-coated soft magnetic powder, a compacted powder magnetic core, a magnetic component, an electronic device, and a moving body. Background Art

[0002] Patent Document 1 discloses a soft magnetic particle powder characterized by being a soft magnetic particle powder having an insulating layer on the particle surface, and the insulating layer is composed of oxide fine particles such as aluminum. In addition, the content that the average particle diameter of the oxide fine particles is less than 100 nm is also disclosed. By providing an insulating layer on the surface of the metal particles, even when fired at a high temperature, the resistivity is difficult to decrease, and thus a high-performance compacted powder magnetic core can be obtained.

[0003] Furthermore, in Patent Document 1, as a method for manufacturing such a soft magnetic particle powder, the following method is disclosed: after premixing the metal particle powder and the oxide fine particles, mechanical energy composed of compressive force and shear force is made to act to form an insulating layer on the surface of the metal particles.

[0004] In addition, Patent Document 1 discloses the following content: strain is removed by annealing the soft magnetic particle powder at a high temperature.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-188270.

[0008] When mechanical energy composed of compressive force and shear force acts on the metal particles, the internal strain (stress) of the metal particles increases. As a result, the coercive force of the metal particles becomes high. As a result, there is a problem that the magnetic properties of the soft magnetic particle powder are reduced.

[0009] In addition, although the strain can be reduced by annealing, the coercive force that has become high due to the increase in strain cannot be sufficiently reduced. Moreover, in the insulating layer forming method described in Patent Document 1, the film thickness of the insulating layer easily becomes uneven. Therefore, the insulation of the insulating layer easily becomes insufficient. In addition, when the film thickness of the insulating layer is uneven, the annealing temperature cannot be sufficiently increased, and the annealing effect cannot be sufficiently obtained. Summary of the Invention

[0010] The insulating material-coated soft magnetic powder according to an application example of the present invention is characterized by having:

[0011] A nuclear particle having a base portion and an oxide film, the base portion containing a soft magnetic material mainly composed of Fe and containing at least one of Si, Cr, and Al, the oxide film being provided on the surface of the base portion and containing an oxide of at least one of Si, Cr, and Al; and

[0012] An insulating coating provided on the surface of the nuclear particle and containing a ceramic,

[0013] The thickness of the insulating coating is 5 nm or more and 300 nm or less,

[0014] At the interface between the oxide film and the insulating coating, mutual diffusion occurs between the oxide contained in the oxide film and the ceramic contained in the insulating coating.

[0015] The powder compact magnetic core according to an application example of the present invention is characterized by containing the soft magnetic powder coated with an insulator according to an application example of the present invention.

[0016] The magnetic element according to an application example of the present invention is characterized by including the powder compact magnetic core according to an application example of the present invention.

[0017] The electronic device according to an application example of the present invention is characterized by including the magnetic element according to an application example of the present invention.

[0018] The moving body according to an application example of the present invention is characterized by including the magnetic element according to an application example of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a cross-sectional view schematically showing one particle of the soft magnetic powder coated with an insulator according to an embodiment.

[0020] Figure 2 It is a cross-sectional view schematically showing one particle of the soft magnetic powder coated with an insulator after the coating process.

[0021] Figure 3 It is a top view schematically showing a ring-type coil part.

[0022] Figure 4 It is a perspective three-dimensional view schematically showing a closed magnetic circuit type coil part.

[0023] Figure 5 It is a three-dimensional view showing a mobile personal computer as an electronic device including the magnetic element according to an embodiment.

[0024] Figure 6 It is a top view showing a smart phone as an electronic device including the magnetic element according to an embodiment.

[0025] Figure 7 FIG. 1 is a perspective view of a still digital camera as an electronic device including the magnetic element according to the embodiment.

[0026] Figure 8 FIG. 2 is a perspective view of an automobile as a moving body including the magnetic element according to the embodiment.

[0027] Figure 9 FIG. 3 is an example of an observation image of a transmission electron microscope (TEM) obtained for a cross-section of an insulating-coated soft magnetic powder before heat treatment.

[0028] Figure 10 FIG. 4 is an example of an observation image of a transmission electron microscope obtained for a cross-section of an insulating-coated soft magnetic powder after heat treatment.

[0029] Figure 11 FIG. 5 is a diagram in which Figure 9 the observation image (TEM image), a diagram in which the Si mapping analysis result indicating the concentration of Si atoms is overlapped on the TEM image, a diagram in which the Al mapping analysis result indicating the concentration of Al atoms is overlapped on the TEM image, and a diagram in which the Fe mapping analysis result indicating the concentration of Fe atoms is overlapped on the TEM image are arranged.

[0030] Figure 12 FIG. 6 is a diagram in which Figure 10 the observation image (TEM image), a diagram in which the Si mapping analysis result indicating the concentration of Si atoms is overlapped on the TEM image, a diagram in which the Al mapping analysis result indicating the concentration of Al atoms is overlapped on the TEM image, and a diagram in which the Fe mapping analysis result indicating the concentration of Fe atoms is overlapped on the TEM image are arranged.

[0031] Reference Signs

[0032] 1, insulating-coated soft magnetic particles; 1x, insulating-coated soft magnetic particles; 2, core particles; 2a, base; 2b, oxide film; 3, nanoparticles; 4, insulating coating film; 10, coil part; 11, compacted powder core; 12, wire; 20, coil part; 21, compacted powder core; 22, wire; 100, display unit; 1000, magnetic element; 1100, personal computer; 1102, keyboard; 1104, main body part; 1106, display unit; 1200, smartphone; 1202, operation button; 1204, earpiece; 1206, microphone; 1300, still digital camera; 1302, housing; 1304, light receiving unit; 1306, shutter button; 1308, memory; 1500, automobile. Detailed Embodiment

[0033] Hereinafter, based on the preferred embodiments shown in the drawings, the insulating material-coated soft magnetic powder, powder compact magnetic core, magnetic element, electronic device, and moving body of the present invention will be described in detail.

[0034] 1. Insulating material-coated soft magnetic powder

[0035] First, the insulating material-coated soft magnetic powder according to the embodiment will be described.

[0036] Figure 1 FIG. is a cross-sectional view schematically showing one particle of the insulating material-coated soft magnetic powder according to the embodiment. It should be noted that, in the following description, one particle of the insulating material-coated soft magnetic powder is also referred to as an "insulating material-coated soft magnetic particle".

[0037] Figure 1 The shown insulating material-coated soft magnetic particle 1 has a core particle 2 and an insulating coating film 4 provided on the surface of the core particle 2. Among them, the core particle 2 includes a base portion 2a and an oxide film 2b. The base portion 2a contains a soft magnetic material described later. The oxide film 2b is provided on the surface of the base portion 2a and contains an oxide of an element contained in the soft magnetic material. The insulating coating film 4 is provided on the surface of the core particle 2, contains ceramics, and has insulating properties.

[0038] At the interface between the oxide film 2b and the insulating coating film 4, mutual diffusion occurs between the oxide contained in the oxide film 2b and the ceramics contained in the insulating coating film 4. Due to such mutual diffusion, the adhesion of the insulating coating film 4 to the core particle 2 is improved. As a result, the obtained insulating material-coated soft magnetic particle 1 does not impair the insulation of the insulating coating film 4 even when subjected to heat treatment at a high temperature, and can also suppress sintering. Thus, the insulating material-coated soft magnetic particle 1 has a low coercive force and a high inter-particle insulation resistance value.

[0039] When a plurality of such insulating material-coated soft magnetic particles 1 are aggregated to form a powder compact magnetic core, the inter-particle insulation can be improved. Thereby, the eddy current loss can be reduced in a magnetic element having a powder compact magnetic core. As a result, it helps to realize a magnetic element with less loss (iron loss) in a high frequency band.

[0040] The shape of the insulating material-coated soft magnetic particle 1 is not limited to a substantially spherical shape, and may be, for example, an irregular shape having a plurality of protrusions on the surface. The average particle diameter of the insulating material-coated soft magnetic particle 1 is preferably 1.0 μm or more and 50.0 μm or less, more preferably 2.0 μm or more and 30.0 μm or less, and further preferably 3.0 μm or more and 15.0 μm or less. Thereby, in the powder compact magnetic core manufactured from the insulating material-coated soft magnetic particle 1, the eddy current loss can be reduced and magnetic properties such as magnetic permeability and magnetic flux density can be improved.

[0041] It should be noted that the average particle size in this specification refers to the particle size when the cumulative volume in the volume-based particle size distribution is 50%. This particle size distribution is obtained by the dynamic light scattering method and the laser diffraction method described in JIS Z 8825:2013. Specifically, for example, a particle size distribution meter based on the dynamic light scattering method can be used.

[0042] 1.1. Core particle

[0043] As described above, the core particle 2 includes a base portion 2a and an oxide film 2b.

[0044] 1.1.1. Base portion

[0045] The soft magnetic material contained in the base portion 2a has Fe as the main component and contains at least one of Si, Cr, and Al as a sub-component. In addition, the soft magnetic material may contain any element in addition to the main component and the sub-components.

[0046] Specific examples of the soft magnetic material include, in addition to Fe-Si-based alloys such as silicon steel and Fe-Si-Al-based alloys such as iron-silicon-aluminum alloys, various alloys such as Fe-Si-B-based, Fe-Si-B-C-based, Fe-Si-B-Cr-C-based, Fe-Si-Cr-based, Fe-Cr-Al-based, Fe-Co-Si-B-based, and Fe-Si-B-Nb-based alloys.

[0047] By using the soft magnetic material having such a composition, the insulated soft magnetic particles 1 having high magnetic permeability, magnetic flux density, etc. and low coercive force can be obtained. Further, by using such a soft magnetic material to manufacture the core particle 2, the oxide film 2b can be formed efficiently and uniformly.

[0048] The content rate of Fe in the soft magnetic material is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more in terms of mass ratio. Thereby, the magnetic properties such as the magnetic permeability and magnetic flux density of the insulated soft magnetic particles 1 can be improved.

[0049] The crystallinity of the soft magnetic material is not particularly limited and can be any one of crystalline, amorphous (non-crystalline), and microcrystalline (nanocrystalline). Among them, the soft magnetic material preferably contains amorphous or microcrystalline. By containing these crystalline states, the coercive force becomes smaller, which also helps to reduce the hysteresis loss of the insulated soft magnetic particles 1. It should be noted that materials having different crystallinities may be mixed and present in the soft magnetic material.

[0050] In the base part 2a, the soft magnetic material is the main material, but impurities may also be included in addition to the soft magnetic material. The main material refers to the material that accounts for 50% or more of the base part 2a by mass ratio. The content rate of the soft magnetic material in the base part 2a is preferably 80% by mass or more, more preferably 90% by mass or more. Thereby, the base part 2a exhibits good soft magnetism.

[0051] In the base part 2a, arbitrary additives may be added in addition to the soft magnetic material. As such additives, for example, various metal materials, various non-metal materials, various metal oxide materials, etc. can be cited.

[0052] 1.1.2. Oxide film

[0053] The oxide film 2b of the core particle 2 contains oxides of elements derived from the soft magnetic material contained in the base part 2a. For example, when the soft magnetic material is an Fe-Si-Cr alloy system, the oxide film 2b contains one or more of iron oxide, chromium oxide, and silicon oxide. In addition, when the Fe-Si-Cr alloy system contains other elements in addition to Fe, Cr, and Si as the main elements, the oxide film 2b may also contain oxides of these elements.

[0054] As the oxides contained in the oxide film 2b, it depends on the soft magnetic material used, but examples include iron oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, boron oxide, phosphorus oxide, aluminum oxide, magnesium oxide, calcium oxide, zinc oxide, titanium oxide, vanadium oxide, cerium oxide, etc. The oxide film 2b may contain one or more of them.

[0055] Since the conductivity of these oxides is low, the insulation resistance of the surface of the core particle 2 itself is improved. Therefore, when the insulating material-coated soft magnetic particles 1 are applied to the powder compact magnetic core, based on the insulation of the insulating coating film 4, the eddy current loss can also be reduced due to the oxide film 2b.

[0056] In addition, the oxide film 2b preferably contains a glass-forming component or a glass-stabilizing component. Thereby, an interaction is generated between the oxides contained in the oxide film 2b and the ceramics contained in the insulating coating film 4. As a result, the adhesion of the insulating coating film 4 to the oxide film 2b is promoted. Specifically, vitrification can occur between the glass-forming component or the glass-stabilizing component contained in the oxide film 2b and the ceramics. Thereby, the oxide film 2b and the insulating coating film 4 are firmly adhered. Therefore, the insulating coating film 4 is not easily peeled off from the surface of the core particle 2. As a result, the coating rate and heat resistance of the insulating coating film 4 can be improved.

[0057] In addition, due to the above-mentioned vitrification or other effects, at the interface between the oxide film 2b and the insulating coating film 4, the oxides contained in the oxide film 2b and the ceramics contained in the insulating coating film 4 diffuse into each other. As a result, the integration of the oxide film 2b and the insulating coating film 4 is achieved. As a result, for example, even when the insulator-coated soft magnetic particles 1 are placed in an environment with repeated high and low temperatures, it is not easy to generate a gap between the core particles 2 and the insulating coating film 4. In addition, the intrusion of moisture and the like into the gap is suppressed, and the insulation is maintained. That is, in the insulator-coated soft magnetic particles 1, the resistance to temperature changes is improved.

[0058] Examples of the glass-forming component include silicon oxide, boron oxide, chromium oxide, phosphorus oxide, etc. Examples of the glass-stabilizing component include aluminum oxide, etc. Among them, the oxide film 2b more preferably contains at least one of silicon oxide, aluminum oxide, and chromium oxide.

[0059] It should be noted that the type of the oxide contained in the oxide film 2b can be determined by, for example, X-ray photoelectron spectroscopy.

[0060] The presence or absence of the oxide film 2b in the core particle 2 can be determined based on the concentration distribution of oxygen atoms in the direction from the surface of the core particle 2 toward the center, in other words, in the depth direction of the core particle 2. Specifically, the concentration distribution of oxygen atoms in the depth direction of the core particle 2 is obtained, and the presence or absence of the oxide film 2b can be known from the obtained concentration distribution. It should be noted that in the following description, the concentration of oxygen atoms is also simply referred to as oxygen concentration.

[0061] The above-mentioned concentration distribution can be obtained, for example, by depth direction analysis based on Auger electron spectroscopy combined with sputtering. Specifically, an electron beam is irradiated on the surface of the core particle 2, and Auger electrons are emitted from the surface layer of the core particle 2. Based on the kinetic energy of the Auger electrons, qualitative and quantitative analysis of the atoms present in the surface layer of the core particle 2 is performed. Ions are collided with the surface of the core particle 2 by sputtering, and this operation is repeated while gradually peeling off the atomic layer on the surface of the core particle 2. Then, the time required for sputtering is converted into the thickness of the atomic layer peeled off by sputtering, and thus the relationship between the depth from the surface of the core particle 2 and the composition ratio can be known.

[0062] Here, the position at a depth of 300 nm from the surface of the core particle 2 can be regarded as being deep enough from the surface. Therefore, the oxygen concentration at this position can be regarded as the oxygen concentration in the interior, that is, the base 2a, of the core particle 2. Therefore, the relative amount of the oxygen concentration with respect to the base 2a is calculated based on the distribution of the oxygen concentration in the depth direction from the surface of the core particle 2, and the thickness of the oxide film 2b is determined.

[0063] Specifically, if the oxygen concentration calculated at a certain depth position of the core particle 2 is within the range of ±50% of the oxygen concentration of the base 2a, it is regarded that there is no oxide film 2b at this depth position. In contrast, when the calculated oxygen concentration exceeds +50% of the oxygen concentration of the base 2a, it is regarded that there is an oxide film 2b. By repeating such evaluations, the thickness of the oxide film 2b can be known.

[0064] The thickness of the oxide film 2b in the core particle 2 is preferably 5 nm or more and 200 nm or less, more preferably 10 nm or more and 100 nm or less. Accordingly, the insulation property of the core particle 2 itself is improved. At the same time, since the proportion of the oxide film 2b in the core particle 2 is suppressed, a decrease in the density of the magnetic material in the core particle 2 can be suppressed. In addition, the adhesion strength between the oxide film 2b and the insulating coating film 4 is further improved.

[0065] The core particle 2 can be particles manufactured by any method. As examples of the manufacturing method, various atomization methods such as water atomization method, gas atomization method, and rotating water flow atomization method; reduction method; carbonyl method; pulverization method, etc. can be cited. Among them, for the core particle 2, particles manufactured by the atomization method are preferably used. According to the atomization method, it is possible to efficiently manufacture fine powders with a uniform particle size. In addition, in the water atomization method or the rotating water flow atomization method, since powdering is carried out by the contact of molten metal with water, it is easy to form an oxide film 2b with an appropriate thickness on the surface of the core particle 2.

[0066] The thickness of the oxide film 2b is adjusted according to conditions in the manufacturing process of the core particle 2, such as the cooling rate of the molten metal. Specifically, if the cooling rate is slowed down, the thickness of the oxide film 2b becomes thicker.

[0067] In addition, the oxide film 2b preferably covers the entire surface of the base 2a, but there may be interrupted portions.

[0068] In addition, the particle size of the core particle 2 is adjusted according to the amount of molten metal dropped per unit time, the pressure and flow rate of water as the spray medium, etc. in the manufacturing process of the core particle 2. In addition, in order to adjust the average particle size of the core particle 2, a classification process can also be carried out.

[0069] 1.2. Insulating Coating Film

[0070] The insulating coating film 4 covers at least a part of the surface of the core particle 2 and contains ceramics.

[0071] As the ceramics, for example, boron oxide, aluminum oxide, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, iron oxide, potassium oxide, sodium oxide, calcium oxide, chromium oxide, boron nitride, silicon nitride, silicon carbide, etc. can be cited, and one or more of these can be used.

[0072] Among them, the ceramic preferably contains at least one of alumina, silica, zirconia, boron nitride, and silicon nitride. Since the hardness and melting point of these ceramics are relatively high, the hardness and melting point of the insulating coating film 4 are also increased. Therefore, it is not easy to cause a shape change in the compression load during powder pressing molding, and a decrease in the insulation of the insulating coating film 4 is suppressed. Thus, it is possible to realize the insulating material-coated soft magnetic particles 1 that can be molded under high pressure. In addition, the heat resistance of the insulating coating film 4 is increased. Therefore, even when subjected to heat treatment at a high temperature, the insulation of the insulating coating film 4 is not easily reduced, and sintering and agglomeration are less likely to occur.

[0073] As the ceramic, a ceramic with a relatively high hardness is preferably used. Specifically, the Mohs hardness of the ceramic is preferably 6.0 or more, more preferably 6.5 or more and 9.5 or less. Thereby, when the insulating material-coated soft magnetic particles 1 are subjected to powder pressing molding, it becomes particularly difficult for the insulating coating film 4 to deform. Therefore, even after powder pressing molding, the insulation between particles is not easily reduced, and powder pressing molding under high pressure becomes possible. Powder pressing molding under high pressure helps to improve the magnetic properties of the powder compact magnetic core.

[0074] In addition, ceramics with a Mohs hardness within the above range generally have a high melting point and thus relatively high heat resistance. Therefore, even when subjected to high-temperature heat treatment, thermal deformation is not likely to occur.

[0075] The insulating coating film 4 covers at least a part of the surface of the core particles 2. The thickness of the insulating coating film 4 is 5 nm or more and 300 nm or less, preferably 5 nm or more and 250 nm or less, more preferably 10 nm or more and 200 nm or less. Thereby, the insulation of the insulating coating film 4 and the filling rate of the soft magnetic material in the powder compact magnetic core can be further improved. It should be noted that if the thickness of the insulating coating film 4 is lower than the above lower limit value, the insulation and heat resistance of the insulating coating film 4 become insufficient. On the other hand, if the thickness of the insulating coating film 4 exceeds the above upper limit value, the insulating coating film 4 becomes easily peeled off, or the filling rate of the soft magnetic material during powder pressing decreases.

[0076] The thickness of the insulating coating film 4 is measured, for example, by magnifying and observing the cross section of the insulating material-coated soft magnetic particles 1. Specifically, the insulating material-coated soft magnetic particles 1 are cut by focused ion beam to produce a cross-sectional thin film specimen. Then, the obtained cross-sectional thin film specimen is observed with a scanning transmission electron microscope to measure the thickness of the insulating coating film 4. In addition, through observation, the integrated state of the oxide film 2b and the insulating coating film 4 can also be confirmed.

[0077] In the manufacturing process of the insulating material-coated soft magnetic particles 1, the thickness of the insulating coating film 4 is adjusted according to conditions such as the amount of ceramic attached to the core particles 2, the temperature and time of heat treatment, etc.

[0078] In addition, the insulating coating film 4 may contain the nanoparticles 3 as required. Accordingly, although the nanoparticles 3 are generated due to, for example, the residual raw materials during the manufacturing process of the insulating coating film 4, the insulating coating film 4 may contain the nanoparticles 3. Thereby, it is easy to ensure the thickness of the insulating coating film 4, and thus it is easier to improve the insulation and heat resistance of the insulating coating film 4. It should be noted that even if the nanoparticles 3 are contained, the properties such as the insulation and heat resistance of the insulating coating film 4 will not be reduced. In addition, the insulating coating film 4 does not necessarily have to contain the nanoparticles 3, and the insulating coating film 4 may also not contain the nanoparticles 3. That is to say, during the manufacturing process, the nanoparticles 3 may also melt or sinter and lose the shape of the particles.

[0079] The main material of the nanoparticles 3 is the above-mentioned ceramic. The main material refers to the material that accounts for 50% or more of the nanoparticles 3 by mass ratio. The content rate of the ceramic in the nanoparticles 3 is preferably 80% by mass or more, more preferably 90% by mass or more.

[0080] The average particle diameter of the nanoparticles 3 is preferably 1 nm or more and 500 nm or less, more preferably 5 nm or more and 300 nm or less, and further preferably 8 nm or more and 100 nm or less. If the average particle diameter is like this, even if the insulating coating film 4 contains the nanoparticles 3, it is not easy to reduce the insulation and heat resistance. In addition, it is possible to avoid the situation where the thickness of the insulating coating film 4 becomes too thick.

[0081] The average particle diameter of the nanoparticles 3 is also measured in the same manner as the thickness of the insulating coating film 4.

[0082] The particle diameter of the nanoparticles 3 is 1 / 50000 or more and 1 / 100 or less of the particle diameter of the core particles 2, preferably 1 / 30000 or more and 1 / 300 or less, and more preferably 1 / 10000 or more and 1 / 500 or less.

[0083] By making the particle diameter of the nanoparticles 3 relative to the particle diameter of the core particles 2 within the above range, it is not easy to generate a gap between the nanoparticles 3 and the core particles 2, and the thickness of the insulating coating film 4 can be made relatively thin. Thereby, while ensuring the insulation of the insulating material covering the soft magnetic particles 1, the filling density of the soft magnetic material in the powder compact magnetic core can be further improved.

[0084] 1.3. Other forming materials

[0085] The insulating material-coated soft magnetic particles 1 may contain, in addition to the above-described forming materials, an insulating material other than ceramics. Examples of such materials include glass materials and silicon materials. Among them, examples of the components contained in the glass material include Bi2O3, B2O3, SiO2, Al2O3, ZnO, SnO, P2O5, PbO, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, Gd2O3, Y2O3, La2O3, and Yb2O3, etc., and one or more of them are used.

[0086] Such other forming materials may be contained in the insulating film 4, but in this case, the content is preferably 50% by mass or less of the ceramics, and more preferably 30% by mass or less. Thereby, the insulating property of the insulating film 4 can be further improved.

[0087] As described above, the insulating material-coated soft magnetic powder according to the present embodiment has a core particle 2 and an insulating film 4. The core particle 2 includes a base portion 2a and an oxide film 2b. The base portion 2a contains a soft magnetic material mainly composed of Fe and containing at least one of Si, Cr, and Al. The oxide film 2b is provided on the surface of the base portion 2a and contains an oxide of at least one of Si, Cr, and Al. The insulating film 4 is provided on the surface of the core particle 2 and contains ceramics.

[0088] In addition, the thickness of the insulating film 4 is 5 nm or more and 300 nm or less. Moreover, at the interface between the oxide film 2b and the insulating film 4, the oxide contained in the oxide film 2b and the ceramics contained in the insulating film 4 have undergone mutual diffusion.

[0089] According to such a configuration, an insulating material-coated soft magnetic particle 1 in which an insulating film 4 having an appropriate thickness, high insulating property, and high heat resistance is well adhered to the core particle 2 can be obtained. Such insulating material-coated soft magnetic particles 1 are not easily sintered and the insulating film 4 is not easily deteriorated, so heat treatment at a high temperature can be performed. Therefore, insulating material-coated soft magnetic particles 1 having a low coercive force and a high inter-particle insulation resistance value can be realized.

[0090] In addition, since the insulating film 4 contains ceramics, even if the thickness of the insulating film 4 is thin, the insulating film 4 exhibits a sufficiently large insulation resistance value. Therefore, when the insulating material-coated soft magnetic particles 1 are compacted, the filling rate of the soft magnetic material can be easily increased, and a magnetic element having good magnetic permeability and magnetic flux density can be manufactured.

[0091] In addition, the insulating film 4 may contain nano-particles 3 as insulating particles mainly made of ceramics. By including the nano-particles 3 in the insulating film 4, the thickness can be easily ensured. Thereby, the insulating property and heat resistance of the insulating film 4 can be further improved.

[0092] 1.4. Characteristics of Insulator-Coated Soft Magnetic Powder

[0093] When the specific surface area of the insulator-coated soft magnetic powder is S [m 2 / g], the true density of the core particle 2 is ρ [g / m 3 , and the average particle diameter of the insulator-coated soft magnetic powder is d [m], the insulator-coated soft magnetic powder preferably satisfies the relationship represented by the following formulas (A) and (B):

[0094] S = k{6 / (d·ρ)}……(A)

[0095] 1.0 ≤ k ≤ 3.2……(B)

[0096] The insulator-coated soft magnetic powder with the specific surface area S within the above range has a sufficiently low specific surface area S based on the specific surface area of a spherical particle calculated from the average particle diameter d and the true density ρ of the core particle 2. That is, k included in formula (A) corresponds to the multiple indicating how many times the specific surface area S of the insulator-coated soft magnetic powder is that of the spherical particle. The closer k is to 1.0 times, the smaller the specific surface area S is suppressed. By making this k satisfy the relationship of formula (B), the insulator-coated soft magnetic powder becomes a soft magnetic powder with excellent uniformity of the film thickness of the insulating film 4 and excellent filling property during powder pressing. Therefore, by using the insulator-coated soft magnetic powder, a magnetic element with excellent magnetic properties such as magnetic permeability and magnetic flux density and excellent insulation between particles can be obtained.

[0097] It should be noted that k in formula (B) is preferably set to 1.5 or more and 3.0 or less, more preferably 2.0 or more and 2.9 or less. If the value of k is within the above range, an insulator-coated soft magnetic powder that can achieve the above effects and has excellent manufacturing stability can be realized.

[0098] It should be noted that the specific surface area S of the insulator-coated soft magnetic powder is measured using the BET specific surface area measuring device HM1201-010 manufactured by Mountech Co., Ltd. The amount of the sample is 5 g.

[0099] The coercive force of the insulator-coated soft magnetic powder is preferably 7.0 [Oe] (557 [A / m]) or less, more preferably 1.5 [Oe] (119 [A / m]) or more and 5.0 [Oe] (398 [A / m]) or less. By using the insulator-coated soft magnetic powder with such a small coercive force, a magnetic element that can sufficiently suppress magnetic hysteresis loss even when used in a high-frequency band can be manufactured.

[0100] It should be noted that the coercivity of the soft magnetic powder can be measured by, for example, a magnetization measuring device TM-VSM1230-MHHL manufactured by Tamagawa Seiki Co., Ltd.

[0101] When the soft magnetic powder coated with an insulating material is filled in a container, the volume resistivity, i.e., the resistivity, is preferably 1 MΩ·cm or more, more preferably 5 MΩ·cm or more and 1000 GΩ·cm or less, and still more preferably 10 MΩ or more and 500 GΩ·cm or less.

[0102] When the resistivity is within the above range, the insulation between the particles in the soft magnetic powder coated with an insulating material is ensured, and the amount of additional insulating material used is reduced. Therefore, in the case of using it for a powder compact magnetic core, increasing the content of the soft magnetic powder coated with an insulating material in the powder compact magnetic core can balance the magnetic properties and low loss. Further, the insulation breakdown voltage of the powder compact magnetic core can be increased. The resistivity of the soft magnetic powder coated with an insulating material can be measured in the following order.

[0103] Fill 1 g of the soft magnetic powder coated with an insulating material into a cylinder made of alumina, and arrange electrodes made of brass at both ends of the cylinder. Then, while applying a pressure of 20 kgf between the electrodes at both ends of the cylinder using a digital force gauge, measure the resistance between the electrodes at both ends of the cylinder using a digital multimeter. At this time, also measure the distance between the electrodes at both ends of the cylinder.

[0104] Next, substitute the measured distance between the electrodes during pressurization, the resistance, and the cross-sectional area inside the cylinder into the following formula (C) to calculate the resistivity.

[0105] Resistivity [MΩ·cm] = Resistance [MΩ] × Cross-sectional area inside the cylinder [cm 2 / Distance between the electrodes during pressurization [cm]... (C)

[0106] It should be noted that when the inner diameter of the cylinder is 2r [cm], the cross-sectional area inside the cylinder is equal to πr 2 [cm 2 . The inner diameter of the cylinder is not particularly limited, for example, it is 0.8 cm. In addition, the distance between the electrodes during pressurization is not particularly limited, for example, it is 0.425 cm.

[0107] 2. Manufacturing method of the soft magnetic powder coated with an insulating material

[0108] Next, an example of the manufacturing method of the above-mentioned soft magnetic powder coated with an insulating material will be described.

[0109] The manufacturing method of the soft magnetic powder coated with an insulator includes: a preparation step of preparing core particles 2 and nanoparticle 3; a coating step of attaching the nanoparticle 3 to the surface of the core particles 2; and a heat treatment step of performing heat treatment on the core particles 2 to which the nanoparticle 3 is attached. Hereinafter, each step will be described.

[0110] In the preparation step, the core particles 2 and the nanoparticle 3 as raw materials are prepared.

[0111] In the coating step, the nanoparticle 3 is pressed onto the surface of the core particles 2 using a dry-type mixer or crusher. Examples of the mixer and crusher include various crushers such as a hammer mill, a disk mill, a roll crusher, a ball mill, a planetary mill, and a jet mill; and various friction mixers such as a container vibration type mixer, an Angmill (registered trademark), a high-speed elliptical mixer, a Mix Muller (registered trademark), a Jacobson mill, a MechanoFusion (registered trademark), and a Hybridization (registered trademark); and a rotation-revolution type mixer. The energy during the processing is adjusted to reduce the generation of processing strain of the core particles 2 accompanied by mechanical damage. In order to extremely suppress the processing strain, among the above devices, a container vibration type or a container rotation type grinder or mixer is particularly preferred.

[0112] In the mixer and the mixer, in addition to the raw materials as the objects, a ball medium can also be used. The diameter of the ball medium is not particularly limited, but it is preferably 40 mm or less, more preferably 0.3 mm or more and 10 mm or less, and further preferably 0.5 mm or more and 5. mm or less. By setting the diameter of the ball medium within the above range, the processing strain can be sufficiently suppressed, and the nanoparticle 3 can be efficiently pressed onto the surface of the core particles 2. It should be noted that the use of the ball medium can also be omitted.

[0113] In the case of using a container vibration type device, its vibration frequency is not particularly limited, but it is preferably 10 Hz or more and 100 Hz or less, more preferably 20 Hz or more and 80 Hz or less. Thereby, the raw materials can be effectively resonated.

[0114] The addition amount of the nanoparticle 3 relative to the core particles 2 is preferably 0.1 mass% or more and 5.0 mass% or less, more preferably 0.1 mass% or more and 1.0 mass% or less. Thereby, the insulating coating film 4 with the above thickness can be formed.

[0115] The coating process using the above-described apparatus is a dry coating method, different from wet coating methods using solutions or the like. Therefore, it can be carried out in a dry atmosphere or an inert gas atmosphere, suppressing the inclusion of moisture or the like between the core particles 2 and the nanoparticles 3, and improving the long-term durability of the insulating material-coated soft magnetic particles 1.

[0116] It should be noted that as a pretreatment for the coating process, a surface treatment can be applied to the nanoparticles 3. As the surface treatment, for example, a hydrophobic treatment can be cited. By applying a hydrophobic treatment to the nanoparticles 3, the adsorption of moisture to the nanoparticles 3 can be suppressed. Therefore, the generation of deterioration or the like caused by moisture in the core particles 2 can be suppressed. In addition, by the hydrophobic treatment, the generation of aggregation in the insulating material-coated soft magnetic powder can be further suppressed.

[0117] As the above-mentioned hydrophobic treatment, for example, arylation such as trimethylsilylation and phenylation can be cited. In trimethylsilylation, for example, a trimethylsilylating agent such as trimethylchlorosilane is used. In arylation, for example, an aryl halide is used as the arylating agent.

[0118] Figure 2 It is a cross-sectional view schematically showing one particle of the insulating material-coated soft magnetic powder after the coating process.

[0119] Through the coating process, an insulating material-coated soft magnetic particle 1x before heat treatment is produced as shown in Figure 2 which has nanoparticles 3 attached to the surface of the oxide film 2b in the core particles 2. In the insulating material-coated soft magnetic particle 1x before heat treatment shown in Figure 2 there are nanoparticles 3 embedded in the oxide film 2b and nanoparticles 3 attached to the surface of the oxide film 2b. It should be noted that the state of existence of the nanoparticles 3 with respect to the oxide film 2b is not limited to the above situation. For example, all of the nanoparticles 3 can be embedded in the oxide film 2b, or all of the nanoparticles 3 can be in a state of not being embedded in the oxide film 2b but attached to the surface.

[0120] In the heat treatment process, heat treatment is applied to the insulating material-coated soft magnetic particle 1x before heat treatment. By this heat treatment, the strain remaining in the insulating material-coated soft magnetic particle 1x before heat treatment is removed. Thus, an insulating material-coated soft magnetic particle 1 with a low coercivity can be obtained. It should be noted that by heat treatment, at least a part of the nanoparticles 3 can also be melted or sintered.

[0121] The heating temperature in the heat treatment is not particularly limited, but is preferably 600 °C or higher and 1200 °C or lower, more preferably 900 °C or higher and 1100 °C or lower. The time for applying the heat treatment, that is, the holding time of the heating temperature, is not particularly limited, but is preferably 10 minutes or longer and 10 hours or shorter, more preferably 20 minutes or longer and 6 hours or shorter. By setting the conditions of the heat treatment within the above ranges, compared with the case where the conditions of the heat treatment are outside the above ranges, strain removal and formation of the insulating coating film 4 can be reliably performed in a short time.

[0122] The atmosphere for applying the heat treatment is not particularly limited, and examples include: an oxidizing gas atmosphere containing oxygen and air, a reducing gas atmosphere containing hydrogen and ammonia decomposition gas, an inert gas atmosphere containing nitrogen and argon, a reduced pressure atmosphere obtained by reducing any gas, etc. Among them, a reducing gas atmosphere or an inert gas atmosphere is preferably used, and a reduced pressure atmosphere is more preferably used. According to these atmospheres, while suppressing an increase in the thickness of the oxide film 2b of the nuclear particles 2, heat treatment, that is, annealing treatment, can be applied. Therefore, an insulating material-coated soft magnetic particle 1 having good magnetic properties and a high coating rate of the nuclear particles 2 by the insulating coating film 4 can be obtained.

[0123] The apparatus used for the heat treatment is not particularly limited, as long as the above treatment conditions can be set, and a known electric furnace or the like can be used.

[0124] The insulating material-coated soft magnetic powder is manufactured as described above.

[0125] 3. Powder Compression Core and Magnetic Element

[0126] Next, the powder compression core and magnetic element according to the embodiment will be described.

[0127] The magnetic element according to the embodiment can be applied to various magnetic elements having a magnetic core, such as a choke coil, an inductor, a noise filter, a reactor, a transformer, an electric motor, an actuator, a solenoid valve, a generator, etc. In addition, the powder compression core according to the embodiment can be applied to the magnetic cores of these magnetic elements.

[0128] Hereinafter, as an example of the magnetic element, two types of coil parts will be described as representatives.

[0129] 3.1. Toroidal Type

[0130] First, a toroidal type coil part as an example of the magnetic element according to the embodiment will be described.

[0131] Figure 3 is a top view schematically showing a toroidal type coil part.

[0132] Figure 3The shown coil component 10 has an annular compacted powder magnetic core 11 and a wire 12 wound around the compacted powder magnetic core 11. Such a coil component 10 is generally referred to as a toroidal coil.

[0133] The compacted powder magnetic core 11 is obtained by mixing an insulating coated soft magnetic powder and a binder material according to the embodiment, and then supplying the obtained mixture to a molding die and pressing and molding it. That is, the compacted powder magnetic core 11 is a compacted body containing the insulating coated soft magnetic powder according to the embodiment. The coil component 10 having such a compacted powder magnetic core 11 has low iron loss and high magnetic properties such as magnetic permeability and magnetic flux density. As a result, when the coil component 10 is mounted on an electronic device or the like, the power consumption of the electronic device or the like can be reduced, or high performance and miniaturization can be achieved.

[0134] It should be noted that the binder material can be added as needed or can be omitted.

[0135] As constituent materials of the binder material for manufacturing the compacted powder magnetic core 11, for example, organic materials such as silicone resins, epoxy resins, phenolic resins, polyamide resins, polyimide resins, and polyphenylene sulfide resins can be cited; inorganic materials such as phosphates such as magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, and cadmium phosphate, and silicates such as sodium silicate, etc. can be cited. However, thermosetting polyimide or epoxy resins are particularly preferred. These resin materials are easily cured by heating and have excellent heat resistance. Therefore, the manufacturability and heat resistance of the compacted powder magnetic core 11 can be improved.

[0136] In addition, the ratio of the binder material to the insulating coated soft magnetic powder slightly varies depending on the target magnetic properties, target mechanical properties, allowable eddy current loss, etc. of the compacted powder magnetic core 11 to be produced, but is preferably about 0.5 mass% or more and 5 mass% or less, and more preferably about 1 mass% or more and 3 mass% or less. Thereby, a coil component 10 can be obtained in which the particles of the insulating coated soft magnetic powder are sufficiently bonded to each other and the magnetic properties are excellent.

[0137] Various additives can also be added to the mixture as needed for any purpose.

[0138] As a constituent material of the wire 12, a material with high conductivity can be cited. For example, metal materials containing Cu, Al, Ag, Au, Ni, etc. can be cited. In addition, an insulating film can be provided on the surface of the wire 12 as needed.

[0139] It should be noted that the shape of the compacted powder magnetic core 11 is not limited to Figure 3 the shown annular shape. For example, it can also be a shape in which a part of the ring is missing, or a shape in which the long side direction is linear.

[0140] In addition, the compacted powder magnetic core 11 may also contain, as required, soft magnetic powders and non-magnetic powders other than the insulated soft magnetic powders involved in the above-described embodiments.

[0141] As described above, the coil part 10 as a magnetic element has a compacted powder magnetic core 11 containing the above-described insulated soft magnetic powders. Thus, a coil part 10 with low iron loss and excellent magnetic properties can be achieved.

[0142] 3.2. Closed magnetic circuit type

[0143] Next, a coil part of the closed magnetic circuit type, which is an example of the magnetic element according to the embodiment, will be described.

[0144] Figure 4 is a perspective three-dimensional view schematically showing the coil part of the closed magnetic circuit type.

[0145] Hereinafter, the coil part of the closed magnetic circuit type will be described. However, in the following description, the description will focus on the differences from the coil part of the toroidal type, and the description of the same matters will be omitted.

[0146] As Figure 4 shown, the coil part 20 according to the present embodiment is formed by embedding a wire 22 formed in a coil shape inside a compacted powder magnetic core 21. That is, the coil part 20 as a magnetic element includes a compacted powder magnetic core 21 containing the above-described insulated soft magnetic powders, and the wire 22 is molded by the compacted powder magnetic core 21. This compacted powder magnetic core 21 has the same configuration as the above-described compacted powder magnetic core 11. Thus, a coil part 20 with low iron loss and excellent magnetic properties can be achieved.

[0147] The coil part 20 in such a manner is easily formed to be relatively small. In addition, the coil part 20 has high magnetic properties and low iron loss. As a result, when the coil part 20 is mounted on an electronic device or the like, the power consumption of the electronic device or the like can be reduced, or high performance and miniaturization can be achieved.

[0148] In addition, since the wire 22 is embedded inside the compacted powder magnetic core 21, it is not easy to generate a gap between the wire 22 and the compacted powder magnetic core 21. Therefore, vibration caused by magnetostriction of the compacted powder magnetic core 21 can be suppressed, and noise generated along with the vibration can also be suppressed.

[0149] It should be noted that the compacted powder magnetic core 21 may also contain, as required, soft magnetic powders and non-magnetic powders other than the insulated soft magnetic powders involved in the above-described embodiments.

[0150] 4. Electronic device

[0151] Next, based on Figures 5 - 7An electronic device having a magnetic element according to an embodiment will be described.

[0152] Figure 5 FIG. 1 is a perspective view of a mobile personal computer as an electronic device having a magnetic element according to an embodiment. Figure 5 The illustrated personal computer 1100 includes a main body 1104 including a keyboard 1102 and a display unit 1106 including a display 100. The display unit 1106 is rotatably supported by the main body 1104 via a hinge structure. In such a personal computer 1100, magnetic elements 1000 such as a choke coil, an inductor, and a motor for a switching power supply are built in.

[0153] Figure 6 FIG. 2 is a top view of a smart phone as an electronic device having a magnetic element according to an embodiment. Figure 6 The illustrated smart phone 1200 includes a plurality of operation keys 1202, a receiver 1204, and a microphone 1206. In addition, a display 100 is disposed between the operation keys 1202 and the receiver 1204. In such a smart phone 1200, magnetic elements 1000 such as an inductor, a noise filter, and a motor are built in.

[0154] Figure 7 FIG. 3 is a perspective view of a still digital camera as an electronic device having a magnetic element according to an embodiment. The still digital camera 1300 photoelectrically converts the optical image of a subject using an imaging element such as a CCD (Charge Coupled Device) to generate an imaging signal.

[0155] Figure 7 The illustrated still digital camera 1300 includes a display 100 provided on the back surface of a housing 1302. The display 100 functions as a viewfinder that displays the subject as an electronic image. In addition, a light receiving unit 1304 including an optical lens, a CCD, etc. is provided on the front side of the housing 1302, i.e., the inner side in the figure.

[0156] When the photographer confirms the subject image displayed on the display 100 and presses the shutter button 1306, the imaging signal of the CCD at that moment is transmitted to and stored in a memory 1308. In such a still digital camera 1300, magnetic elements 1000 such as an inductor and a noise filter are also built in.

[0157] As the electronic device according to the embodiment, in addition to Figure 5 the personal computer, Figure 6 the smart phone, Figure 7In addition to static digital cameras, examples include: mobile phones, tablet terminals, clocks, inkjet ejection devices (e.g., inkjet printers), laptop personal computers, televisions, video cameras, video cassette recorders, car navigation devices, pagers, electronic notebooks, electronic dictionaries, calculators, electronic game machines, word processors, workstations, video phones, anti-theft television monitors, electronic binoculars, POS terminals, medical devices (e.g., electronic thermometers, sphygmomanometers, blood glucose meters, electrocardiogram measuring devices, ultrasonic diagnostic devices, electronic endoscopes), fish finders, various measuring devices, measuring instruments (e.g., measuring instruments for vehicles, aircraft, ships), mobile body control devices (e.g., automotive control devices, aircraft control devices, railway vehicle control devices, ship control devices), flight simulators, etc.

[0158] As described above, such an electronic device includes the magnetic element according to the embodiment. Thereby, the effects of the magnetic element such as low coercivity and low iron loss can be enjoyed, and the high performance of the electronic device can be achieved.

[0159] 5. Mobile Body

[0160] Next, based on Figure 8 a mobile body including the magnetic element according to the present embodiment will be described.

[0161] Figure 8 FIG. is a perspective view of an automobile as a mobile body including the magnetic element according to the embodiment.

[0162] A magnetic element 1000 is built in the automobile 1500. Specifically, the magnetic element 1000 is built in various automotive components such as, for example, an automotive navigation system, an anti-lock braking system (ABS), an engine control unit, a battery control unit of a hybrid vehicle or an electric vehicle, an electronic control unit (ECU: electronic control unit) such as a vehicle body attitude control system and an autonomous driving system, a driving motor, a generator, and an air conditioning unit.

[0163] As described above, such a mobile body includes the magnetic element according to the embodiment. Thereby, the effects of the magnetic element such as low coercivity and low iron loss can be enjoyed, and the high performance of the mobile body can be achieved.

[0164] It should be noted that the mobile body according to the present embodiment, in addition to Figure 9 the illustrated automobile, may be, for example, a two-wheeled vehicle, a bicycle, an aircraft, a helicopter, a drone, a ship, a submarine, a railway vehicle, a rocket, a spaceship, etc.

[0165] As described above, the insulating material-coated soft magnetic powder, the compacted powder core, the magnetic component, the electronic device, and the moving body of the present invention have been described based on the preferred embodiments, but the present invention is not limited thereto.

[0166] For example, in the above-described embodiment, as an example of the use of the insulating material-coated soft magnetic powder of the present invention, a compacted powder such as a compacted powder core has been described, but the example of use is not limited thereto, and it may be, for example, a magnetic device such as a magnetic fluid, a magnetic head, or a magnetic shielding sheet.

[0167] In addition, the shapes of the compacted powder core and the magnetic component are not limited to the shapes shown in the drawings, and may be any shape.

[0168] Examples

[0169] Next, specific examples of the present invention will be described.

[0170] 6. Manufacture of insulating material-coated soft magnetic powder

[0171] 6.1. Example 1

[0172] First, as the core particles 2, metal powder of an Fe—Si—Cr-based alloy manufactured by a water atomization method was prepared. This metal powder is an Fe-based alloy powder having Fe as a main component and containing Cr at a ratio of 4.5 mass% and Si at a ratio of 3.5 mass%. It should be noted that the average particle diameter of this metal powder is 10 μm. In addition, this metal powder was analyzed, and as a result, the presence of the oxide film 2b was observed. The oxide film 2b mainly contains silicon oxide.

[0173] On the other hand, alumina powder was prepared as the nanoparticles 3. The average particle diameter of the alumina powder is 15 nm.

[0174] Next, the metal powder and the alumina powder were mixed. The addition amount of the alumina powder with respect to the metal powder was set to 0.30 mass%. The obtained mixture was put into a vibratory ball mill device and vibratorily stirred. The conditions for vibratory stirring are shown in Table 1.

[0175] Next, a part of the insulating material-coated soft magnetic particles 1x before heat treatment was set aside for observation described later, and the remaining part was subjected to heat treatment. The heat treatment was performed using an electric furnace, and the treatment conditions were a heating rate of 5° C. / minute, a heating temperature of 900° C., and a heating time of 1 hour in an argon atmosphere. Then, after the heat treatment was completed, it was cooled to 25° C. Thus, insulating material-coated soft magnetic powder was obtained.

[0176] 6.2. Examples 2 to 17

[0177] An insulating-coated soft magnetic powder was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 1 or Table 2. It should be noted that in Examples 14 to 17, no ball medium was used.

[0178] 6.3. Example 18

[0179] An insulating-coated soft magnetic powder was obtained in the same manner as in Example 1, except that a rotary vane mixer was used instead of the vibratory ball mill used in Example 1, and nanoparticles were attached to the surface of the core particles by mechanical shear energy to form an insulating coating. It should be noted that in Table 2, "mechanical shear" is described as the method for forming the insulating coating.

[0180] 6.4. Comparative Examples 1 to 3

[0181] An insulating-coated soft magnetic powder was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 2.

[0182] 6.5. Comparative Example 4

[0183] A soft magnetic powder was obtained in the same manner as in Example 1, except that the heat treatment was omitted and the manufacturing conditions were changed as shown in Table 2.

[0184] 6.6. Comparative Example 5

[0185] A soft magnetic powder was obtained in the same manner as in Example 1, except that the addition of nanoparticles was changed to none and the manufacturing conditions were changed as shown in Table 2.

[0186] 7. Evaluation of Insulating-Coated Soft Magnetic Powder

[0187] 7.1. Observation of Cross-Section

[0188] First, the cross-sections of the insulating-coated soft magnetic powder before heat treatment and after heat treatment were observed using a scanning transmission electron microscope.

[0189] Figure 9 This is an example of a transmission electron microscope (TEM) observation image of the cross-section of the insulating-coated soft magnetic powder before heat treatment.

[0190] As Figure 9 shown, in the insulating-coated soft magnetic powder (insulating-coated soft magnetic particles 1x) before heat treatment, it was observed that an oxide film 2b existed on the surface of the base 2a of the core particle 2, and nanoparticles 3 existed on the surface of the oxide film 2b.

[0191] Figure 10This is an example of an observation image obtained by a transmission electron microscope of a cross-section of an insulating-coated soft magnetic powder after heat treatment.

[0192] As Figure 10 shown, in the insulating-coated soft magnetic powder (insulating-coated soft magnetic particles 1) after heat treatment, nanoparticles 3 were not observed in the insulating film 4. From this, it can be known that due to heat treatment, the nanoparticles 3 melted or sintered and did not retain the shape of particles. Specifically, in Figure 10 it is the same shade in the area corresponding to the insulating film 4 as compared with Figure 9 , and it can be regarded that there are almost no nanoparticles 3.

[0193] Figure 11 is a figure in which the observation image (TEM image) of Figure 9 and the Si mapping analysis result showing the concentration of Si atoms overlapped on the TEM image, the Al mapping analysis result showing the concentration of Al atoms overlapped on the TEM image, and the Fe mapping analysis result showing the concentration of Fe atoms overlapped on the TEM image are arranged.

[0194] In the Figure 11 TEM image, the vicinity of the surface in the particle cross-section is magnified. Moreover, in Figure 11 a core particle 2 and nanoparticles 3 located on the surface of the core particle 2 are observed, and this core particle 2 has a base 2a and an oxide film 2b located on the surface of the base 2a.

[0195] In addition, from the Figure 11 shown Si mapping analysis result, it can be confirmed that Si segregation occurred in the oxide film 2b. In the Si mapping analysis result, the relatively light-colored area represents the area with a high Si concentration. From this, it is speculated that silicon oxide is contained in a relatively large amount in the oxide film 2b. Further, from the Figure 11 shown Al mapping analysis result, it can be confirmed that Al segregation occurred in the nanoparticles 3. In the Al mapping analysis result, the relatively light-colored area represents the area with a high Al concentration. From this, it is speculated that aluminum oxide is contained in a relatively large amount in the nanoparticles 3. In addition, from the Figure 11 shown Fe mapping analysis result, it can be known that the Fe concentration is high in the base 2a.

[0196] Moreover, in Figure 11 the areas with a high Si concentration and a high Al concentration are exclusive. Therefore, it can be considered that in the insulating-coated soft magnetic powder before heat treatment, the silicon oxide contained in the oxide film 2b and the aluminum oxide contained in the nanoparticles 3 are almost non-mixed and are distributed exclusively.

[0197] Figure 12 is a figure in which Figure 10A figure in which the observed image (TEM image), a figure in which the Si mapping analysis result indicating the concentration of Si atoms is overlapped on the TEM image, a figure in which the Al mapping analysis result indicating the concentration of Al atoms is overlapped on the TEM image, and a figure in which the Fe mapping analysis result indicating the concentration of Fe atoms is overlapped on the TEM image are arranged.

[0198] In Figure 12 the TEM image of, the vicinity of the surface in the particle profile is magnified. Moreover, in Figure 12 , the core particle 2 and the insulating coating film 4 located on the surface of the core particle 2 are observed, and the core particle 2 includes a base portion 2a and an oxide film 2b located on the surface of the base portion 2a.

[0199] In addition, from Figure 12 the Si mapping analysis result shown, a light-colored region extends linearly in a manner corresponding to the oxide film 2b. Therefore, it can be confirmed that Si segregation has occurred in the oxide film 2b. From this, it is speculated that silicon oxide is contained in a relatively large amount in the oxide film 2b. However, the width of this linear region continuously widens in the thickness direction.

[0200] On the other hand, from Figure 12 the Al mapping analysis result shown, it can be confirmed that Al segregation has occurred in the insulating coating film 4. From this, it is speculated that aluminum oxide is contained in a relatively large amount in the insulating coating film 4. Moreover, an overlap of the region where the Si distribution is observed and the region where the Al distribution is observed is observed. Therefore, it is considered that due to the heat treatment, the silicon oxide contained in the oxide film 2b and the aluminum oxide contained in the insulating coating film 4 have mutually diffused.

[0201] In addition, from Figure 12 the Fe mapping analysis result shown, it can be known that the Fe concentration is high in the base portion 2a.

[0202] The above observations were made on the insulating material-coated soft magnetic powder of the example, and the insulating material-coated soft magnetic powder and the soft magnetic powder of the comparative example. Moreover, when mutual diffusion occurred between the oxide contained in the oxide film 2b and the ceramic contained in the insulating coating film 4 at the interface between the oxide film 2b and the insulating coating film 4, it was recorded as "yes" in Tables 1 and 2. In addition, when no mutual diffusion was observed, it was recorded as "no" in Tables 1 and 2.

[0203] In addition, when nanoparticles 3 remained in the insulating coating film 4 after the heat treatment, it was recorded as "yes" in Tables 1 and 2. In addition, when no remaining nanoparticles 3 were found in the insulating coating film 4 after the heat treatment, it was recorded as "no" in Tables 1 and 2.

[0204] 7.2. Coercivity

[0205] For the insulating-coated soft magnetic powder of the examples, the insulating-coated soft magnetic powder and the soft magnetic powder of the comparative examples, the coercive force was measured using the TM-VSM1230-MHHL of the VSM series manufactured by Tamagawa Seiki Co., Ltd. as a magnetization measurement device. Then, the measured coercive force was evaluated according to the following criteria. The evaluation results are shown in Tables 1 and 2. It should be noted that hereinafter, the insulating-coated soft magnetic powder of the examples may sometimes be simply referred to as the powder of the examples, and the insulating-coated soft magnetic powder and the soft magnetic powder of the comparative examples may sometimes be simply referred to as the powder of the comparative examples.

[0206] A: Coercive force is less than 3.0 [Oe]

[0207] B: Coercive force is 3.0 [Oe] or more and less than 3.5 [Oe].

[0208] C: Coercive force is 3.5 [Oe] or more and less than 5.0 [Oe].

[0209] D: Coercive force is 5.0 [Oe] or more and less than 7.0 [Oe].

[0210] E: Coercive force is 7.0 [Oe] or more and less than 10.0 [Oe].

[0211] F: Coercive force is 10.0 [Oe] or more.

[0212] 7.3. Insulation breakdown voltage

[0213] For the powders of the examples and the comparative examples, the insulation breakdown voltage was measured by the following method and the numerical values were recorded in Tables 1 and 2.

[0214] First, 2 g of each of the powders of the examples and the comparative examples was filled into an alumina cylinder with an inner diameter of 8 mm, and electrodes made of brass were arranged at both ends of the cylinder. Thereafter, at an ambient temperature of 25 °C, while applying a pressure of 40 kg / cm 2 between the electrodes at both ends of the cylinder using a digital force gauge, a voltage of 50 V was applied between the electrodes for 2 seconds. At this time, the resistance between the electrodes was measured using a digital multimeter to confirm the occurrence of insulation breakdown.

[0215] Next, the voltage applied between the electrodes was increased to 100 V and maintained for 2 seconds, and the resistance between the electrodes was measured at this time to confirm the occurrence of insulation breakdown.

[0216] Furthermore, while the voltage applied between the electrodes was increased from 150 V by 50 V, the resistance between the electrodes was measured each time to confirm whether insulation breakdown occurred. The voltage was increased by 50 V each time and the resistance was measured until insulation breakdown occurred. It should be noted that the voltage applied between the electrodes was set to a maximum of 1000 V. If insulation breakdown did not occur at 1000 V, the measurement was terminated at 1000 V.

[0217] The above series of operations was repeated three times each time the powder was renewed, and the lowest voltage value that caused insulation breakdown among the three times was taken as the insulation breakdown voltage.

[0218] 7.4. Filling

[0219] The filling rate of the powders of Examples and Comparative Examples was evaluated for filling property, which is an index of moldability during powder compaction. The results are shown in Tables 1 and 2.

[0220] First, the apparent density of the powders of Examples and Comparative Examples was measured. Specifically, the apparent density was measured according to the method for measuring the apparent density of metal powders specified in JIS Z 2504:2012.

[0221] Next, the true density of the powders of Examples and Comparative Examples was measured by constant volume expansion method. It should be noted that the units of apparent density and true density are g / cm 3 .

[0222] Then, the value obtained by dividing the apparent density by the true density was calculated as the filling rate [%], and each filling rate was evaluated as the filling property according to the following criteria.

[0223] A: The filling rate is 40% or more.

[0224] B: The filling rate is 35% or more and less than 40%.

[0225] C: The filling rate is 30% or more and less than 35%.

[0226] D: Filling rate is less than 30%.

[0227] E: The powder was sintered and could not be measured.

[0228] 7.5. Magnetic permeability

[0229] Ring-shaped magnetic cores for choke coils, so-called toroidal cores, were manufactured from the powders of the examples and comparative examples, and the magnetic permeability of the toroidal cores was measured. Specifically, a methyl ethyl ketone solution of an epoxy resin as a binder was added to the powder in an amount of 2.0% by mass based on the solid content. The mixture was mixed and dried to form a block. The block was crushed and then pressed under a molding pressure of 3000 kgf / cm2 It is stamped into an annular shape with an outer diameter of Ф14 mm, an inner diameter of Ф7 mm, and a thickness of 3 mm. Then, it is heated at 150 °C for 30 minutes to make an annular iron core. The permeability at a frequency of 100 kHz of this annular iron core is measured using a 4294A precision impedance analyzer manufactured by Agilent. Each measured permeability is evaluated according to the following evaluation criteria, and the results are recorded in Table 1 and Table 2.

[0230] A: The permeability is 29 or more.

[0231] B: The permeability is 28 or more and less than 29.

[0232] C: The permeability is 27 or more and less than 28.

[0233] D: The permeability is less than 27.

[0234] 7.6. Specific surface area

[0235] For the powders of the examples and comparative examples, the specific surface area S is measured using a BET-type specific surface area measuring device HM1201-010 manufactured by Mountech Co., Ltd.

[0236] Then, when the specific surface area of a spherical particle calculated from the average particle diameter d of the powder and the true density ρ of the core particles is {6 / (d·ρ)}, the multiple k of the specific surface area S with respect to the specific surface area {6 / (d·ρ)} of the spherical particle is calculated. The calculation results are shown in Table 1 and Table 2.

[0237] Table 1

[0238]

[0239] Table 2

[0240]

[0241] It can be clearly seen from Table 1 and Table 2 that the powders of the examples have low coercivity and high inter-particle insulation even when heat-treated at high temperatures compared with the powders of the comparative examples.

[0242] In addition, in the formation of the insulating coating, when a method using a vibratory ball mill is adopted instead of a method accompanied by mechanical shear energy, it is particularly found that the coercivity is easily reduced by heat treatment. In the method accompanied by mechanical shear energy, since the processing strain applied during the film-forming treatment is large, it is considered that the coercivity is not easily reduced by heat treatment. In the case of using a vibratory ball mill, good insulation characteristics are obtained under any conditions of not introducing ball media and different diameters of ball media.

[0243] In addition, the following was confirmed: by means of appropriate heat treatment, interdiffusion occurs between the oxide contained in the oxide film of the core particles and the ceramic contained in the insulating coating film, which can further improve the insulation and reduce the specific surface area of the powder.

[0244] Moreover, the following was confirmed: when the specific surface area of the powder is expressed as a multiple of the specific surface area of spherical particles, by suppressing this multiple to a certain extent, it is possible to improve the packing property while maintaining the insulation between particles.

[0245] It should be noted that iron-silicon-aluminum alloy (Fe-Si-Al alloy) powder was used as the metal powder instead of Fe-Si-Cr alloy powder, and an insulated soft magnetic powder was obtained in the same manner as above. Then, the same evaluation as above was performed on the obtained insulated soft magnetic powder. As a result, an evaluation result showing the same tendency as the case where Fe-Si-Cr alloy powder was used was obtained.

Claims

1. An insulating-coated soft magnetic powder, characterized in that, comprising: a core particle having a base portion and an oxide film, the base portion containing a soft magnetic material mainly composed of Fe and containing at least one of Si, Cr, and Al, the oxide film being provided on the surface of the base portion and containing at least one element of Si, Cr, and Al and being an oxide of an element contained in the base portion; and an insulating coating film provided on the surface of the core particle and containing a ceramic, the addition amount of the insulating coating film with respect to the core particle is 0.1 mass% or more and 0.4 mass% or less, at the interface between the oxide film and the insulating coating film, mutual diffusion occurs between the oxide contained in the oxide film and the ceramic contained in the insulating coating film, the insulating coating film contains nano-particles as insulating particles mainly composed of the ceramic, and at least a part of the nano-particles is melted or sintered, the ceramic contains at least one of alumina, silica, zirconia, boron nitride, and silicon nitride, When the specific surface area of the soft magnetic powder coated with an insulator is S, the true density of the core particles is ρ, and the average particle diameter of the soft magnetic powder coated with an insulator is d, the relationship represented by the following formulas (A) and (B) is satisfied, where the unit of S is m 2 / g, the unit of ρ is g / m 3 , the unit of d is m, S = k[6 / (d·ρ)] …… (A) 1.0 ≤ k ≤ 3.2 …… (B).

2. The soft magnetic powder coated with an insulator according to claim 1, wherein the thickness of the insulating coating film is 5 nm or more and 300 nm or less.

3. The soft magnetic powder coated with an insulator according to claim 1 or 2, wherein the average particle diameter of the soft magnetic powder coated with an insulator is 1.0 μm or more and 50.0 μm or less.

4. The soft magnetic powder coated with an insulator according to claim 1, wherein the coercive force is 7.0 Oe or less.

5. A compacted magnetic core, characterized in that it contains the soft magnetic powder coated with an insulator according to any one of claims 1 to 4.

6. A magnetic component, characterized in that, comprising the compacted magnetic core according to claim 5.

7. An electronic device, characterized in that, comprising the magnetic element according to claim 6.

8. A moving body, characterized in that, comprising the magnetic element according to claim 6.

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