Soft magnetic metal powder, powder magnetic core, and inductor

Abstract

A soft magnetic metal powder includes coated particles having soft magnetic metal particles (1) and a coating layer (2) coating the surface of the soft magnetic metal particles (1), the coating layer (2) including at least one compound selected from the group consisting of molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, glimmer, and kaolin.

Description

Technical Field

[0001] This invention relates to soft magnetic metal powder, pressed magnetic core, and inductor. Background Technology

[0002] Electronic components such as inductors use pressed powder cores manufactured by pressing soft magnetic metal powder. As a pressed powder core, a pressed powder core formed by pressing a powder consisting of soft magnetic metal powder and an insulating film covering the powder has been proposed.

[0003] For example, Patent Document 1 describes a soft magnetic material comprising a plurality of composite magnetic particles and a particulate lubricant added in a proportion of 0.001% to 0.01% by mass relative to the plurality of composite magnetic particles. The plurality of composite magnetic particles have metallic magnetic particles and an insulating film surrounding the surface of the metallic magnetic particles and comprising at least one of a metal phosphate salt and an oxide. The particulate lubricant has an average particle size of 2.0 μm or less and comprises at least one of a metal soap and an inorganic lubricant having a hexagonal crystal structure.

[0004] Patent Document 2 describes a soft magnetic metal powder comprising a plurality of soft magnetic metal particles containing Fe. The powder is characterized in that the surface of the soft magnetic metal particles is covered by a coating portion, the coating portion having a first coating portion and a second coating portion sequentially from the surface of the soft magnetic metal particles outward, the first coating portion containing one or more elements selected from Cu, W, Mo and Cr, and the second coating portion containing P.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 4325950

[0008] Patent Document 2: Japanese Patent No. 6504289 Summary of the Invention

[0009] Regarding the soft magnetic material described in Patent Document 1, the surface of the metal magnetic particles is surrounded by an insulating film containing at least one of a metal phosphate salt and an oxide film. However, the metal phosphate salt and the oxide film have poor flexibility, and therefore there are the following risks: they cannot follow the deformation of the metal magnetic particles during pressure molding and break, and the metal magnetic particles conduct to each other, increasing magnetic loss.

[0010] The soft magnetic metal powder described in Patent Document 2 uses metals such as Cu, W, Mo, and Cr as the first coating and oxides such as phosphorus pentoxide as the second coating. However, there are risks: the soft magnetic metal particles cannot be insulated from each other in the first coating made of metal. In addition, the second coating containing P breaks during pressure molding, and the soft magnetic metal particles become conductive to each other, increasing magnetic loss.

[0011] This invention addresses the aforementioned problems and aims to provide a soft magnetic metal powder capable of producing a pressed powder core with low magnetic loss. Furthermore, it aims to provide a pressed powder core with low magnetic loss. Finally, it aims to provide an inductor incorporating the aforementioned pressed powder core.

[0012] The soft magnetic metal powder of the present invention comprises coated particles having soft magnetic metal particles and a coating layer covering the surface of the soft magnetic metal particles, the coating layer comprising at least one compound selected from molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, pyrophyllite and kaolin.

[0013] The pressed powder magnetic core of the present invention has soft magnetic metal particles and an interface layer existing between the soft magnetic metal particles. The interface layer contains at least one compound selected from molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, pyrophyllite and kaolin, and has a molding density of 85% or more.

[0014] The inductor of the present invention comprises the above-described pressed powder core.

[0015] According to the present invention, a soft magnetic metal powder capable of producing a pressed powder core with low magnetic loss can be provided. Furthermore, according to the present invention, a pressed powder core with low magnetic loss and an inductor incorporating the pressed powder core can be provided. Attached Figure Description

[0016] Figure 1 This is a cross-sectional schematic diagram showing an example of the coated particles constituting the soft magnetic metal powder of the present invention.

[0017] Figure 2 This is a cross-sectional schematic diagram of the chamber of the coating device used to manufacture the soft magnetic metal powder of the present invention.

[0018] Figure 3 This is a cross-sectional schematic diagram illustrating an example of the internal structure of the pressed powder magnetic core of the present invention.

[0019] Figure 4 This is a perspective view schematically illustrating an example of an inductor according to the present invention.

[0020] Figure 5A is a bright-field image obtained by taking a cross-section of the coated particles constituting the soft magnetic metal powder obtained in Example 1 using a scanning transmission electron microscope. Figure 5 B is a mapping image of the Fe element. Figure 5 C is a mapping image of the Mo element. Figure 5 D is a mapping image of elements S. Figure 5 E is a mapping image of element O.

[0021] Figure 6 This table shows the SEM images, Fe mapping images, Mo mapping images, and Bi mapping images obtained by observing the cross-sections of the pressed powder magnetic cores obtained in Examples 6-10 and Comparative Example 2 using a scanning electron microscope. Detailed Implementation

[0022] The following describes the soft magnetic metal powder, pressed magnetic core, and inductor of the present invention.

[0023] However, the present invention is not limited to the following configurations, and can be appropriately modified and applied without changing the spirit of the invention. It should be noted that combining two or more of the preferred configurations of the invention described below also constitutes the present invention.

[0024] The soft magnetic metal powder of the present invention comprises coated particles having soft magnetic metal particles and a coating layer covering the surface of the soft magnetic metal particles. Figure 1 A cross-sectional schematic diagram showing an example of the coated particles constituting the soft magnetic metal powder of the present invention. For example... Figure 1 As shown, the aforementioned coated particles consist of soft magnetic metal particles 1 and a coating layer 2 covering their surfaces.

[0025] The soft magnetic metal constituting the aforementioned soft magnetic metal particles is not particularly limited as long as it is a metallic material exhibiting soft magnetism; it can be crystalline or amorphous. For example, metallic materials with Fe as the main component are preferred. Specifically, pure iron-based soft magnetic materials (electromagnetic soft iron), Fe-based alloys, Fe-Si alloys, Fe-Ni alloys, Fe-Al alloys, Fe-Si-Al alloys, Fe-Si-Cr alloys, Fe-Ni-Si-Co alloys, Fe-based amorphous alloys, or Fe-based nanocrystalline alloys are more preferred. Examples of Fe-based amorphous alloys include Fe-Si-B and Fe-Si-B-Cr-C alloys. Examples of Fe-based nanocrystalline alloys include Fe-B, Fe-Si-B-Cu, Fe-Si-B-Cu-Cr, Fe-Si-B-C-Cu, Fe-Si-B-P-C-Cu, Fe-Si-B-P-C-Cu, Fe-Si-B-P-C-Cu-Sn, Fe-Si-B-Nb, and Fe-Si-B-Nb-Cu. From the viewpoint of improving magnetic permeability, the aforementioned soft magnetic metals are preferably Fe-based amorphous alloys or Fe-based nanocrystalline alloys, and more preferably Fe-based amorphous alloys. Furthermore, Fe-based amorphous alloys include metallic glasses. Metallic glasses have a composition in which a glass transition is clearly observed in amorphous alloys. One or more of the aforementioned soft magnetic metals can be used.

[0026] The average particle size of the aforementioned soft magnetic metal particles is preferably 1 μm to 30 μm, more preferably 1 μm to 20 μm, and even more preferably 1 μm to 10 μm. The average particle size can be measured using a laser diffraction-scattering particle size distribution measuring device. By achieving an average particle size within the above range, both formability and magnetic properties can be improved. Alternatively, two or more soft magnetic metal powders with average particle sizes within the above range but different average particle sizes can be appropriately mixed and used. By mixing powders with different average particle sizes, smaller particles can enter the gaps between larger particles, further improving formability.

[0027] The coating layer contains at least one compound selected from molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, pyrophyllite and kaolin (hereinafter also referred to as "compound (1)").

[0028] The coating layer described above can be a single layer consisting of only one layer containing compound (1), or it can be a multilayer consisting of two or more layers containing compound (1). In the case of a multilayer coating layer, the type of compound (1) can be different in each layer, for example, it can include a first layer consisting of molybdenum disulfide and a second layer consisting of boron nitride. In the case of a multilayer coating layer, the number of coating layers is not particularly limited, but it can be, for example, 10 layers or less, or three layers or less. In addition, the coating layer described above can include a mixed layer containing two or more compounds (1), for example, a layer containing one compound (1) can contain both molybdenum disulfide and molybdenum oxide, or it can contain molybdenum disulfide, molybdenum oxide and boron nitride.

[0029] The coating may contain impurities contained in the compounds. Especially when the compounds are minerals such as mica, talc, pyrophyllite, or kaolinite, impurities are sometimes contained within the minerals themselves.

[0030] Mica is composed of X2Y 4－6 Z8O 20 (OH,F)4 [where X is one or more selected from K, Na, Ca, Ba, Rb and Cs, Y is one or more selected from Al, Mg, Fe, Mn, Cr, Ti and Li, and Z is one or more selected from Al, Fe and Ti] represents a layered compound.

[0031] Talc is composed of Mg3Si4O 10 (OH)2 represents a layered compound.

[0032] Pyrophyllite is composed of Al2Si4O 10 (OH)2 represents a layered compound.

[0033] Kaolin is composed of Al4Si4O 10 (OH)8 represents a layered compound.

[0034] The compound (1) is selected from at least one of molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, pyrophyllite, and kaolin. Since the compound (1) is a layered compound, it functions as a mold lubricant, promoting particle movement and rearrangement during molding and increasing molding density. In addition, by including the layered compound, the elastic strain applied to the soft magnetic metal particles can be reduced, and the increase in hysteresis loss can be suppressed. Therefore, it is possible to form a high-density, high-frequency permeability core with improved resistance and low magnetic loss. From the viewpoint of further improving lubricity during molding and further reducing the magnetic loss of the obtained powder core, the compound (1) is preferably a compound having a hexagonal layered crystal structure, more preferably at least one of molybdenum disulfide, molybdenum oxide, and boron nitride, and even more preferably molybdenum disulfide.

[0035] The coating layer may be a layer consisting solely of the aforementioned compound (1), or it may be a layer containing substances other than the aforementioned compound (1). However, it is preferable to contain 50% by mass or more of the aforementioned compound (1), more preferably 75% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly even more preferably 99% by mass or more, and most preferably substantially consisting solely of the aforementioned compound (1). Examples of substances other than the aforementioned compound (1) include polyimide and glass (preferably glass with a softening point of 300°C or higher and a crystallization point of 600°C or lower).

[0036] The average thickness of the coating layer is not particularly limited, but from the viewpoint of improving lubricity during molding and obtaining a powder core with excellent frequency characteristics of magnetic permeability and low loss, an average thickness of 1 nm to 200 nm is preferred. More preferably, it is 5 nm or more, even more preferably 10 nm or more, further preferably 100 nm or less, even more preferably 50 nm or less, even more preferably 40 nm or less, and particularly preferably 30 nm or less.

[0037] The average thickness of the coating layer of the soft magnetic metal powder is determined as follows: After measuring the average particle size of the soft magnetic metal powder using a laser diffraction-scattering particle size distribution measuring device, coated particles with a particle size greater than 20% larger than the average particle size are removed by sieving. A sample is prepared for observing the cross-section of the coated particles after sieving. The cross-sections of multiple coated particles with an apparent particle size of ±20% of the above-determined average particle size are observed using a transmission electron microscope or a scanning electron microscope. The thickness of the coating layer is measured and averaged.

[0038] For the aforementioned coated particles, the coating layer can be in direct contact with the surface of the soft magnetic metal particles. Alternatively, a layer other than the coating layer can be present on the inner side (soft magnetic metal particle side) of the coating layer, or on the outer side (opposite to the soft magnetic metal particles) of the coating layer. Since this improves lubrication during molding and the molding density of the resulting powder core, it is preferable to have the coating layer on the outermost layer.

[0039] Preferably, the coated particles do not contain a layer containing phosphorus atoms on the outside of the soft magnetic metal particles. Specific forms in which the coated particles do not contain a layer containing phosphorus atoms include: (1) a form consisting only of the soft magnetic metal particles and the coating layer that does not contain phosphorus atoms; (2) a form consisting only of the soft magnetic metal particles, the coating layer that does not contain phosphorus atoms, and one or more layers that do not contain phosphorus atoms (hereinafter also referred to as "phosphorus-free layers") that are different from the coating layer, with the phosphorus-free layers existing inside the coating layer; (3) a form consisting only of the soft magnetic metal particles, the coating layer that does not contain phosphorus atoms, and one or more layers that do not contain phosphorus atoms, with the phosphorus-free layers existing outside the coating layer; and (4) a form consisting only of the soft magnetic metal particles, the coating layer that does not contain phosphorus atoms, and one or more layers that do not contain phosphorus atoms, with the phosphorus-free layers existing on both the inside and outside sides of the coating layer.

[0040] The average particle size of the coated particles is preferably 1 μm to 30 μm, more preferably 1 μm to 20 μm, and even more preferably 1 μm to 10 μm. The average particle size can be measured using a laser diffraction-scattering particle size distribution measuring device. By setting the average particle size within the above range, excellent formability and magnetic properties can be achieved.

[0041] In the soft magnetic metal powder of the present invention, since the permeability of the obtained pressed magnetic core can be improved, the proportion of soft magnetic metal particles is preferably 90% by mass or more. The above proportion is preferably 95% by mass or more, more preferably 97% by mass or more, and from the viewpoint of improving the resistivity of the powder, it is preferably 99.9% by mass or less, more preferably 99.5% by mass or less.

[0042] In the soft magnetic metal powder of the present invention, from the viewpoint of improving the resistivity of the powder, the proportion of compound (1) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. In addition, since the permeability of the obtained pressed powder magnetic core can be improved, the proportion of compound (1) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0043] In the soft magnetic metal powder of the present invention, the coating layer preferably covers the soft magnetic metal particles at a rate of 95% or more, more preferably at 98% or more, and even more preferably at 100%. The coating rate can be calculated, for example, by: (1) analyzing the constituent elements of the powder surface by X-ray photoelectron spectroscopy (XPS) and calculating the ratio of the amount of the constituent elements of the coating layer to the amount of the constituent elements of the soft magnetic metal particles; or (2) obtaining an elemental mapping image of the surface of the soft magnetic metal particles by energy dispersive X-ray analysis (EDX) or wavelength dispersive X-ray analysis (WDX) and calculating the ratio of the area of ​​the constituent elements of the coating layer detected inside the outline of the soft magnetic metal particles to the area of ​​the soft magnetic metal particles; or (3) embedding and grinding the soft magnetic metal particles in resin to prepare a sample for observing the particle cross-section by transmission electron microscopy (TEM), obtaining an EDX image of the particle cross-section, and calculating the ratio of the outline length of the constituent elements of the coating layer to the outline length of the soft magnetic metal particles.

[0044] The soft magnetic metal powder of the present invention can be obtained by adding soft magnetic metal particles and the above-mentioned compound (1) into a container and mixing them while applying mechanical impact energy, more preferably while applying impact, compression and shear energy. For example, the soft magnetic metal powder of the present invention can be obtained by applying energy of 6 MJ / kg or more during the mixing process.

[0045] As a coating device capable of mixing while applying mechanical impact energy, as described above, examples include... Figure 2 The coating apparatus 11 is shown. The coating apparatus 11 has a cylindrical chamber 12, and is configured such that a blade 13 rotates within the chamber 12 as indicated by arrow 14. A workpiece 15 (soft magnetic metal particles and compound (1)) is placed into the chamber 12, and in this state, the workpiece 15 is processed by the blade 13 rotating at a speed of, for example, 4000 to 6000 rpm. As a coating apparatus as described above, examples include the powder processing apparatus (NOBILTA) manufactured by Hosokawa Micron Corporation. In addition, as a device capable of mixing while applying mechanical impact force, examples include planetary mills.

[0046] Since the soft magnetic metal powder of this invention can improve the volume resistivity of the pressed magnetic core and reduce magnetic loss, the powder resistivity at room temperature (approximately 25°C) and under pressure of 64 MPa is preferably 1.0 × 10⁻⁶. 3 Ω·cm or higher. More preferably, the resistivity of the above-mentioned powder is 1.0 × 10⁻⁶. 4 Ω·cm or higher, more preferably 1.0×10 5 Ω·cm or higher. The soft magnetic metal powder of the present invention can achieve the above-mentioned powder resistivity by having a coating layer containing compound (1).

[0047] The soft magnetic metal powder of the present invention is suitable for use as a material for pressed magnetic cores.

[0048] The pressed powder magnetic core of the present invention comprises soft magnetic metal particles and an interface layer existing at the interfaces between the soft magnetic metal particles. This interface layer contains at least one compound selected from molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, pyrophyllite, and kaolin (1), and has a molding density of 85% or higher. By having the above-described structure, the pressed powder magnetic core of the present invention can maintain a high volume resistivity, and its permeability hardly decreases with increasing frequency. Furthermore, it exhibits low loss when a magnetic field is applied. The pressed powder magnetic core of the present invention can be obtained by pressing the soft magnetic metal powder of the present invention into powder and then performing heat treatment as needed. The pressing conditions can employ conventionally known methods. Figure 3 This is a cross-sectional schematic diagram illustrating an example of the internal structure of the pressed powder magnetic core of the present invention. For example... Figure 3 As shown, the pressed powder magnetic core of the present invention has soft magnetic metal particles 1 and an interface layer 3 existing at the interface 4 between the soft magnetic metal particles 1.

[0049] The molding density of the pressed magnetic core of the present invention is 85% or higher. Since it can improve magnetic permeability, the molding density is preferably 90% or higher, more preferably 93% or higher. By pressing the soft magnetic metal powder of the present invention into powder, the molding density can be within the above range. A higher molding density is better; there is no upper limit, but it can be, for example, 100% or 99%. Furthermore, the molding density can be from 89.40% to 96.60%.

[0050] In the pressed powder magnetic core of the present invention, by using the soft magnetic metal powder of the present invention as the material and the compound (1) coating the surface of the soft magnetic metal particles as a lubricant, a high molding density can be achieved. For example, even without forming a coating layer such as molybdenum disulfide, if only plastic deformation and high density are achieved, it can be achieved by hot forming under high pressure exceeding 1000 MPa in room temperature molding. However, in this case, a high volume resistivity cannot be achieved. Since the layer containing the compound (1) can withstand high temperatures exceeding 400°C and pressures of hundreds of MPa, a high volume resistivity can be maintained after hot forming, and the increase in initial permeability and the deterioration of frequency characteristics can be suppressed.

[0051] The average thickness of the aforementioned interface layer is preferably 1 nm to 300 nm. More preferably, it is 5 nm or more, even more preferably 10 nm or more, further preferably 200 nm or less, even more preferably 100 nm or less, even more preferably 50 nm or less, particularly more preferably 40 nm or less, and particularly preferably 30 nm or less. By achieving the thickness within the above range, a powder-pressed magnetic core with high permeability and resistance and low loss can be obtained.

[0052] It should be noted that when two or more layers are stacked, each containing at least one compound selected from molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, pyrophyllite and kaolin (1), the average thickness of the aforementioned interface layers is the sum of these layers.

[0053] In the pressed powder magnetic core of the present invention, preferably, the soft magnetic metal particles are in direct contact with the interface layer. The soft magnetic metal particles and the interface layer may be in direct contact at least partially, or there may be portions where the soft magnetic metal particles and the interface layer are not in direct contact.

[0054] In the pressed powder magnetic core of the present invention, the coating rate of the above-mentioned compound (1) on the soft magnetic metal particles is preferably 95% or more, more preferably 98% or more, and even more preferably 100%. The above coating rate can be calculated by using EDX analysis and WDX analysis and observing the cross-section of the pressed powder magnetic core to obtain a mapping image of the constituent elements of the soft magnetic metal particles and the constituent elements of the coating layer, and calculating the ratio of the perimeter of the coating layer to the perimeter of the outline portion of the metal particles.

[0055] The pressed powder magnetic core of the present invention preferably has a bonding material at the grain boundaries of the soft magnetic metal particles. By having the aforementioned bonding material at the grain boundaries, the pressed powder magnetic core exhibits excellent mechanical strength. In this specification, "grain boundaries of soft magnetic metal particles" refers to the boundaries between adjacent soft magnetic metal particles, encompassing both the interfaces between the soft magnetic metal particles and the gaps existing between them. Figure 3 As shown, the pressed powder core has soft magnetic metal particles 1 and an interface layer 3 existing at the interface 4 between the soft magnetic metal particles 1, but gaps 5 also exist between the soft magnetic metal particles 1. The bonding material can exist at the above interface or in the above gap.

[0056] There are no particular limitations on the aforementioned bonding material. For example, glass is preferred, and various glass materials such as Si-B system, Si-B-alkali metal system, Si-B-Zn system, V-Te system, Sn-P-Zn system, and water glass can be cited.

[0057] The glass used as the binder is preferably a glass containing at least one of bismuth, boron, vanadium, tin, and zinc. The content of bismuth, boron, vanadium, tin, and zinc is not particularly limited, and glass containing known binders such as bismuth and boron can be used.

[0058] The content of the above-mentioned binder material is preferably 1 to 10 parts by mass relative to 100 parts by mass of soft magnetic metal particles, and more preferably 1 to 5 parts by mass.

[0059] In the pressed powder magnetic core of the present invention, it is preferable that the interface layer and the bonding material are in direct contact. This form is formed when the soft magnetic metal powder of the present invention does not have other layers outside the coating layer, that is, the coating layer is the outermost layer.

[0060] From the viewpoint that the pressed magnetic core of the present invention can improve magnetic permeability and reduce losses, the area of ​​soft magnetic metal particles is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. By pressing the soft magnetic metal powder of the present invention into powder, the area of ​​soft magnetic metal particles can be made to be within the above range. The upper limit of the above area is not particularly limited, but the above area can be 99% or less, or 98% or less.

[0061] From the viewpoint that the pressed powder magnetic core of the present invention can further reduce magnetic loss, the volume resistivity is preferably 20 Ω·cm or more, more preferably 25 Ω·cm or more, even more preferably 100 Ω·cm or more, and particularly preferably 500 Ω·cm or more. A high volume resistivity is preferred, and there is no upper limit, but for example, the upper limit could be 1 × 10⁻⁶. 5 Ω·cm. By pressing the soft magnetic metal powder of the present invention into powder, the volume resistivity can be made into the range described above.

[0062] In the pressed powder magnetic core of the present invention, the initial permeability at 100 kHz is preferably 30 or more. More preferably, it is 40 or more, and even more preferably, it is 50 or more. The upper limit of the above-mentioned initial permeability is not limited, but it can be, for example, 1000 or less. By pressing the soft magnetic metal powder of the present invention into powder, the above-mentioned initial permeability can be made to be within the above-mentioned range.

[0063] Furthermore, in the pressed powder magnetic core of the present invention, the initial permeability at 100 MHz is preferably 30 or more. More preferably, it is 40 or more, and even more preferably, it is 50 or more. The upper limit of the above-mentioned initial permeability is not limited, but it can be, for example, 1000 or less. By pressing the soft magnetic metal powder of the present invention into powder, the above-mentioned initial permeability can be made to be within the above-mentioned range.

[0064] In the powder-pressed magnetic core of the present invention, the ratio of initial permeability at 100 MHz to initial permeability at 100 kHz is preferably 0.1 or higher. More preferably, it is 0.5 or higher, and even more preferably, it is 0.8 or higher. By achieving the above range, a powder-pressed magnetic core with excellent frequency characteristics can be manufactured.

[0065] In the pressed powder magnetic core of the present invention, the loss when a magnetic field of 0.1T and 50kHz is applied is preferably 1000kW / m. 3 The following is preferred. More preferably, it is 500kW / m². 3 The following is a further preferred value: 400kW / m 3 The following is particularly preferred: 300kW / m 3 The following applies. Lower losses are better; there is no fixed lower limit, but for example, a lower limit of 1 W / m² is acceptable. 3 It can also be 1kW / m 3 .

[0066] The pressed magnetic core of the present invention can be obtained by pressing the soft magnetic metal powder of the present invention into powder and then heat-treating it as needed. The pressing conditions are not particularly limited and can be appropriately determined according to the type of soft magnetic metal particles and compound (1).

[0067] The pressed powder magnetic core of the present invention can be used in inductors, various coils, reactors, motors, transformers, DC-DC converters, AC-DC converters, etc.

[0068] The inductor of the present invention comprises the pressed powder core of the present invention as described above. Preferably, the inductor of the present invention comprises the pressed powder core of the present invention and a winding disposed around the pressed powder core.

[0069] The inductor of the present invention, except for having the pressed powder core of the present invention, can have the same structure as conventionally known inductors and can be manufactured by the same manufacturing method. The inductor of the present invention can be used for conventionally known applications.

[0070] Figure 4 This is a three-dimensional diagram schematically representing an example of an inductor. Figure 4 The inductor 100 shown includes the pressed powder core 110 of the present invention and a primary winding 120 and a secondary winding 130 wound around the pressed powder core 110. Figure 4 In the inductor 100 shown, a primary winding 120 and a secondary winding 130 are wound on a double-wire plywood core 110 having a ring-shaped ring shape.

[0071] The structure of an inductor is not limited to Figure 4 The inductor 100 shown has the following structure. For example, a winding can be wound on a calibrated powder core having a ring shape. Alternatively, it can have a structure that includes the calibrated powder core of the present invention and a winding embedded in the calibrated powder core.

[0072] The inductor of the present invention has a high space filling rate of soft magnetic metal particles in the pressed powder core, thus becoming a coil with high permeability and high saturation magnetic flux density.

[0073] Example

[0074] The following describes in more detail embodiments of the soft magnetic metal powder, pressed magnetic core, and inductor of the present invention. It should be noted that the present invention is not limited to these embodiments.

[0075] In the examples and comparative examples, the evaluation was carried out as follows.

[0076] [Average thickness of the coating layer for soft magnetic metal powder]

[0077] After measuring the average particle size using a laser diffraction-scattering particle size and particle size distribution measuring device, coated particles with a particle size greater than 20% larger than the average particle size are removed by sieving. Next, a sample is prepared for observing the cross-section of the sieved coated particles. For example, after resin encapsulation of powder, mechanical grinding, ion grinding, cross-section polishing, or focused ion beam (FIB) can be used. At this time, the diameter (apparent particle size) of the particles appearing in the cross-section observation sample is smaller than the particle size when the particles are scraped shallowly, and close to the particle size when the particles are scraped in a manner that crosses the vicinity of their center. Furthermore, the observed coating thickness (apparent thickness) is thicker than the actual thickness when the particles are scraped shallowly, and close to the actual thickness when the particles are scraped in a manner that crosses the vicinity of their center. Then, using a transmission electron microscope or a scanning electron microscope, the cross-sections of 10 or more coated particles with an apparent particle size within ±20% of the measured average particle size are observed, and the coating thickness is measured and averaged to determine the coating thickness.

[0078] For example, when the average particle size of the coated particles is 5 μm, a sieve is applied to the powder that passes through particles with a particle size of 6 μm or less. A cross-sectional observation sample is prepared using the powder obtained from the sieve, and further measurements are taken only for particles with an apparent particle size of 4 μm to 6 μm. The apparent thickness of the coating layer observed in this way falls within the range from the actual coating layer thickness to +25%.

[0079] [Calculate the amount of coating material to be added and the thickness of the coating based on the target thickness of the coating of soft magnetic metal powder]

[0080] The specific surface area (SSA) of soft magnetic metal powders can be determined using specific gravity ρ1 and d. 50 Calculated as

[0081] SSA=6 / (ρ1d 50 ).

[0082] When the specific gravity of the coating material is set as ρ2 and the target thickness is set as t, the addition rate w (mass%) of the coating material to be added is calculated as follows:

[0083] w=6tρ2 / ρ1d 50 ×100.

[0084] On the other hand, when obtaining a soft magnetic metal powder with a certain coating, in order to deduce the thickness t of the coating, it can be calculated as follows:

[0085] t = w / (ρ2×SSA×100).

[0086] Here, in the method for calculating w, ρ2, and SSA of the obtained soft magnetic metal powder, firstly, only the coated soft magnetic metal particles with a high specific gravity are extracted from the soft magnetic metal powder to remove the coating material without coated soft magnetic metal particles. This can be done by exposing the soft magnetic metal powder to a magnetic field, or by mixing the soft magnetic metal powder into a liquid and then centrifuging it, or by blowing air from below into the powder layer to create a flow state and separating it based on the specific gravity difference. Next, the composition of the soft magnetic metal particles and the coating material are analyzed separately. Composition analysis can be performed using inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), fluorescence X-ray analysis (XRF), etc. In addition, if the coating is crystalline, the composition of the coating can also be determined by powder X-ray diffraction (XRD). Based on the composition analysis results, the specific gravity ρ1, ρ2 of the soft magnetic metal particles and the coating material, and the addition rate w of the coating material are calculated. On the other hand, the average particle size d was measured using a laser diffraction-scattering particle size distribution measuring device. 50 , can be made by d 50 The specific surface area SSA of the soft magnetic metal powder is calculated from the value of ρ1.

[0087] [Average thickness of the interface layer in powder-pressed magnetic cores]

[0088] The following methods are used to prepare cross-sectional specimens for observing pressed powder magnetic cores. These specimens are prepared by resin embedding and mechanical grinding of fragments obtained from cutting, fracturing, or crushing pressed powder magnetic cores. Alternatively, they are prepared by grinding the cross-sectional portion of the fragments using methods such as ion milling, cross-section polishing, or focused ion beam (FIB). The prepared cross-sectional specimens are then observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). When using a SEM, the soft magnetic metal particle portion and the interface layer portion can be distinguished by obtaining reflected electron images. Alternatively, the distribution of the constituent elements of the soft magnetic metal particles (e.g., Fe) and the interface layer (e.g., Mo) can be differentiated by analyzing the distribution of the constituent elements of the soft magnetic metal particles and the interface layer using WDX analysis. Similarly, when using a TEM, the distribution of the constituent elements of the soft magnetic metal particles and the interface layer can be differentiated by analyzing the distribution of the constituent elements of the soft magnetic metal particles and the interface layer using EDX analysis. Furthermore, the crystal structure of the soft magnetic metal particles and the interface coating (crystalline or amorphous, and in the case of crystalline structures, different crystal structures) can be used to observe the lattice image at high magnification. For example, when the soft magnetic metal particles are amorphous and the coating layer is crystalline, the thickness of the interface is obtained as the thickness of the region where lattice fringes are visible. The average thickness of the interface layer can be calculated by measuring the thickness of the portion of the interface layer distribution at multiple points, for example, 10 points, using these methods and calculating the average value. Here, the measurement sites of the interface are selected sequentially at 10 points in the observed image, starting from the location where the soft magnetic metal particles are closest to each other.

[0089] [Powder resistivity at room temperature (approximately 25°C) and under pressure of 64 MPa (upper limit of 10 MΩcm)]

[0090] The volume resistivity was measured using the MCP-PD51 powder resistivity measuring unit manufactured by Mitsubishi Chemical Analytech Co., Ltd., under a pressure of 64 MPa.

[0091] [Elemental composition of powder surface]

[0092] The results were obtained using XPS (X-ray photoelectron spectroscopy) analysis with a PHI-5000 VersaProbe manufactured by ULVAC-PHI, Inc.

[0093] [Molding density of pressed powder magnetic cores]

[0094] Use vernier calipers to measure the outer diameter φo and inner diameter φi of the powder-pressed magnetic core at three points each, and calculate the average value. Use a micrometer to measure the thickness t of the magnetic core at four points, calculate the average value, and use the following formula to calculate the volume Vc of the powder-pressed magnetic core.

[0095]

[0096] The weight m of the sample is determined by an electronic balance. The weight ratio and weight of each component are calculated from the mixing ratio of the soft magnetic metal powder, the coating material (molybdenum disulfide, etc.) and the binder. The porosity n is calculated using the density of each component by the following formula.

[0097]

[0098] m1 is the weight of the soft magnetic metal powder, m2 is the weight of the coating material, m3 is the weight of the binder material, ρ1 is the density of the soft magnetic metal powder, ρ2 is the density of the coating material, and ρ3 is the density of the binder material.

[0099] The molding density is calculated as 100 - n (porosity).

[0100] [The percentage of soft magnetic metal particles in the pressed powder core]

[0101] V used in the calculation of molding density c Given m1 and ρ1, calculate the area ratio as {(m1 / ρ1)} / V. c .

[0102] [Volume resistivity of pressed powder core]

[0103] Indium gallium (InGa) alloy is coated on both the upper and lower surfaces of the powder-pressed magnetic core to form electrode surfaces. The powder-pressed magnetic core is clamped with two Kelvin clips and connected to a digital multimeter. There are no particular limitations on the digital multimeter as long as it can perform four-terminal resistance measurements. In addition to a digital multimeter, a constant voltage power supply and a ohmmeter can also be used in combination. The resistance value R obtained through measurement is given by the following formula:

[0104]

[0105] (where φ) o φ is the outer diameter of the pressed powder magnetic core. i The electrode area S (where S is the inner diameter of the powder-pressed magnetic core) and the thickness t of the powder-pressed magnetic core are used to calculate the volume resistivity ρ as follows:

[0106] ρ=R×(S / t).

[0107] [Initial permeability at 100kHz and 100MHz, and loss when a magnetic field of 0.1T and 50kHz is applied]

[0108] The initial permeability of the pressed powder core was determined using a Keysight Technologies E4991A impedance analyzer and a 16454A magnetic material testing fixture.

[0109] The magnetic field loss of the pressed powder cores obtained in the examples and comparative examples was measured using a BH analyzer SY8218 manufactured by Iwatsu Communications Co., Ltd. It should be noted that the diameter of the copper wire wound on the pressed powder core was 0.26 mm. Furthermore, both the primary winding used for excitation and the secondary winding used for detection had 30 turns each, and double-wire winding was implemented.

[0110] Example 1

[0111] Prepare soft magnetic metal powder (manufactured by EPSON ATMIX Corporation, AW2-PF.8F, average particle size 5μm, specific gravity 7.1g / cm³). 3 (and molybdenum disulfide (MoS2) powder (manufactured by DAIZOCORPORATION, average particle size 0.45 μm, specific gravity 5.08 g / cm³)) and molybdenum disulfide (MoS2) powder (DAIZOCORPORATION, average particle size 0.45 μm, specific gravity 5.08 g / cm³) 3 Based on the specific gravity and average particle size of each powder, the powder was weighed at a mass ratio (MoS2 addition of 2.0 wt.%) with a target MoS2 coating thickness of 25 nm. 70 g of the weighed powder was introduced into a powder processing apparatus (manufactured by Hosokawa Micron Corporation, NOBILTA MINI (NOB-MINI)) and processed at 6000 rpm for 30 minutes to obtain MoS2-coated soft magnetic metal powder. Under the above conditions, the total energy applied to the powder was approximately 8 MJ / kg.

[0112] For the coated soft magnetic metal powder, the resistivity of the powder was measured under a pressure of 64 MPa at room temperature. The results are shown in Table 1. The resistivity of the powder under pressure when coated with MoS2 at a target of 25 nm was 445 kΩcm. Furthermore, the results of a semi-quantitative analysis of the elemental composition and amount on the particle surface of the same powder by XPS (X-ray photoelectron spectroscopy) are shown in Table 2. In the XPS analysis results, C and O are attributed to atmospheric CO2 adsorbed on the particle surface. The Fe content was below the detection limit, confirming that only Mo and S, along with a portion of O, are distributed at a depth of several nm from the powder particle surface. That is, it can be said that the surface of the soft magnetic metal particles is coated with Mo sulfides having a MoS2 structure and Mo oxides having a MoO3 structure, with a coating rate of 100% or as close to 100%. Furthermore, bright-field images of the cross-section obtained by resin embedding and cross-sectional grinding of the same powder followed by FIB (converging ion beam) processing and STEM (scanning transmission electron microscopy), as well as mapping images of the constituent elements determined by EDX (energy-dispersive X-ray diffraction), are shown below. Figure 5 As shown. By Figure 5It can be seen that the surface of the soft magnetic metal particles is uniformly covered by a compound film composed of Mo sulfide with a MoS2 structure and Mo oxide with a MoO3 structure. The average thickness of the coating layer of the coated soft magnetic metal powder was measured and found to be 28 nm.

[0113] As mentioned above, the resistivity of coated soft magnetic metal powder under pressure is 445 kΩcm, a high resistance that uncoated soft magnetic metal powder cannot achieve. This is believed to be because, as... Figure 5 As shown in the STEM-EDX images and XPS analysis in Table 2, MoS2 is thinly and uniformly coated on the surface of soft magnetic metal particles, thereby suppressing the conductivity between the soft magnetic metal particles. The high resistance maintained even under pressure is because MoS2 has strong covalent bonds along the a and b axes of the crystal lattice, and weak van der Waals bonds along the c axis. Therefore, when subjected to external pressure or friction, the parts with van der Waals bonds slide (called interlayer sliding) without causing overall rupture, thus leaving the film intact along its thickness direction.

[0114] Examples 2-5

[0115] Using the same method as in Example 1, MoS2 was mixed with soft magnetic metal powder in proportions equal to the target thicknesses shown in Table 1 (the MoS2 addition amounts were 0.5 wt.%, 1.0 wt.%, 4.0 wt.%, and 8.0 wt.%, respectively, for target thicknesses of 6, 13, 50, and 100 nm). The resistivity of the coated soft magnetic metal powder was measured under a pressure of 64 MPa. The results are shown in Table 1.

[0116] In addition, the average thickness of the coating layer of each soft magnetic metal powder treated with coating in Examples 2, 3, 4 and 5 was measured, and the average thicknesses were 8.8 nm, 10.4 nm, 36.2 nm and 66.5 nm, respectively.

[0117] Comparative Example 1

[0118] The resistivity of a soft magnetic metal powder (manufactured by EPSON ATMIX Corporation, AW2-PF.8F, average particle size 5 μm) without MoS2 coating was measured under a pressure of 64 MPa. The results are shown in Table 1.

[0119] As can be seen from the comparison of powder resistivity shown in Table 1, even with a small amount of MoS2 that is mixed and treated to form a film of only 6 nm, the powder resistivity of soft magnetic metal powder can be significantly improved.

[0120] [Table 1]

[0121]

[0122] [Table 2]

[0123]

[0124] Example 6

[0125] Compared to the coated soft magnetic metal powder prepared in Example 1, glass powder (manufactured by AGC Inc., ASF1096 (glass containing Bi and B)) used as the binder in thermoforming was weighed at a weight ratio of coated soft magnetic metal powder to binder material of 98:2, and further mixed and granulated simultaneously with acrylic binder and toluene. The resulting granulated powder was introduced into a superhard mold and placed in a pressure firing furnace. Under a N2 atmosphere, it was heated at 445°C while applying a pressure of 650 MPa to form a ring-shaped pressed magnetic core. The heating rate was set to 25°C / min, and the holding time was set to 2 minutes and 30 seconds. Cooling was performed naturally, and depressurization was carried out 1 minute after the start of cooling. In this thermoforming, the acrylic binder does not affect the bonding of the magnetic core due to volatilization. Furthermore, in order to remove the strain applied during molding, the pressed magnetic core was placed in a box furnace and heat-treated at 435°C for 1 hour under an atmospheric atmosphere. An inductor is formed by winding copper wire onto a pressed powder magnetic core.

[0126] Table 3 shows the target thickness of the MoS2 film, the molding density (100 – porosity) of the powder-pressed magnetic core, the occupancy of the soft magnetic metal particles, the volume resistivity, the initial permeability of the powder-pressed magnetic core at 100 kHz and 100 MHz, and the loss when a magnetic field of 0.1 T at 50 kHz is applied. The molding density of the powder-pressed magnetic core is as high as 94.60%, and the occupancy of the soft magnetic metal particles also exceeds 90%. The volume resistivity is 975 Ω·cm, confirming that it can be maintained at a high level. In addition, the initial permeability at 100 kHz and 100 MHz is 62 and 60, respectively, showing almost no decay with increasing frequency. The loss when a magnetic field of 0.1 T at 50 kHz is as low as 144.3 kW / m. 3 The cross-sectional SEM (scanning electron microscope) image and WDX (wavelength dispersive X-ray diffraction)-based elemental mapping image of the pressed powder core are shown below. Figure 6 The average thickness of the interface layer in the pressed powder core is 83 nm. This average thickness is thicker than the average thickness of 28 nm of the coating layer of the soft magnetic metal particles after the coating layer has been formed. However, this is because the coating layers of two adjacent particles are bonded together, and the coating appears thicker because the center of the metal particles is not ground out.

[0127] The high molding density is due to the simultaneous heating and pressurization during molding, which promotes the plastic deformation of the soft magnetic metal powder. This allows the surface of the soft magnetic metal powder to be coated with a layered compound (molybdenum disulfide), acting as an internal lubricant. For example... Figure 6 As shown, because the molybdenum disulfide layers are distributed seamlessly at the grain boundaries between the soft magnetic metal powders, the metal particles are not electrically connected to each other. Therefore, in addition to suppressing the increase in initial permeability and the deterioration of frequency characteristics, a power output of 144.3 kW / m² can be achieved. 3 Low loss.

[0128] Furthermore, the Bi in the glass composition is not distributed as a film at the grain boundaries between the metal particles, but rather in the interstitial regions where there are no metal particles. That is, in this embodiment, only MoS2 is coated with metal particles in a film-like manner.

[0129] It should be noted that in the above embodiments, the inductor is formed by thermoforming the pressed powder core and then winding copper wire. However, it is also possible to thermoform both magnetic powder and copper wire in a mold, forming an inductor-embedded element in which a molded body of soft magnetic particles surrounds the entire copper wire. Furthermore, while the above embodiments show a toroidal pressed powder core, it is also possible to form a rod-magnet-shaped core by inserting copper wire into the inductor, which is wound into a spring shape.

[0130] Furthermore, in the above embodiments, the metal particles coated with MoS2 are granulated and put into a mold for thermoforming. However, the pressed powder magnetic core can also be formed by mixing the MoS2 coated metal particles with an adhesive and an organic solvent, molding them into sheets, punching them, stacking them, and then compressing them in a heated environment.

[0131] Examples 7-10

[0132] Using the coated soft magnetic metal powders prepared in Examples 2-5, pressed powder magnetic cores were fabricated in the same manner as in Example 6. Table 3 shows the target thickness of the MoS2 film, the forming density (100 – porosity) of the pressed powder magnetic core, the occupancy of the soft magnetic metal particles, the volume resistivity, the initial permeability of the pressed powder magnetic core at 100 kHz and 100 MHz, and the loss when a magnetic field of 0.1 T·50 kHz is applied in each example.

[0133] Comparative Example 2

[0134] Using the powder used in Comparative Example 1, pressed powder magnetic cores were fabricated in the same manner as in Example 6. The target thickness of the MoS2 film, the molding density of the pressed powder magnetic core (100 - porosity), the occupancy of the soft magnetic metal particles, the volume resistivity, the initial permeability of the pressed powder magnetic core at 100 kHz and 100 MHz, and the loss when a magnetic field of 0.1 T·50 kHz is applied are shown in Table 3.

[0135] As shown in Table 3, in Examples 9 and 10, where the target thickness of the MoS2 coating is thick, the forming density of the pressed magnetic core tends to be higher, while in Examples 6-8, where the target thickness is thinner, the occupancy of soft magnetic metal particles tends to be higher. This is because, in the examples with thicker MoS2 coatings, the forming density is easier to increase due to better lubricity, but the amount of MoS2 occupying the core also increases relatively, thus reducing the occupancy of soft magnetic metal particles. In the examples with thinner MoS2 coatings, the forming density is not easily increased, but the amount of MoS2 is less, thus increasing the occupancy of soft magnetic metal particles. Similar to Examples 1-5 regarding powder, even with a target amount of only 6 nm, a high volume resistivity of tens to thousands of Ω·cm can be achieved when using soft magnetic metal powder coated with MoS2. Through this effect, losses can also be reduced to 200 kW / m. 3 On the other hand, in the pressed magnetic core using uncoated MoS2 soft magnetic metal powder (Comparative Example 2), a short circuit occurred, making it impossible to measure the resistance. Furthermore, the loss also increased significantly to 1689 kW / m. 3 .

[0136]

[0137] Examples 11 and 12

[0138] The additives shown in Table 4 were mixed with the soft magnetic metal powder in the same manner as in Example 1, to achieve a target thickness of 50 nm. Talc was manufactured by Sigma-Aldrich (average particle size 10 μm) and added at 2.2 wt.%. Mica was manufactured by YAMAGUCHI MICA CO.,LTD. (average particle size 5 μm) and added at 2.4 wt.%.

[0139] [Table 4]

[0140]

[0141] As shown in Table 4, the addition of talc and mica can significantly improve the resistivity of coated soft magnetic metal powders obtained in the same way as MoS2.

[0142] Talc, mica, and pyrophyllite and kaolin not used in the above embodiments have the following structure: they consist of layers composed of silicates (SiO4) and the like, connected by strong bonds formed by covalent and ionic bonds in a plane perpendicular to the c-axis, with these layers overlapping each other by weak van der Waals bonds. Therefore, like MoS2, they can be used as solid lubricants with heat resistance and insulation properties.

[0143] Example 13

[0144] Boron nitride (BN) was mixed with soft magnetic metal powder in the same manner as in Example 1, to achieve a target thickness of 50 nm (1.8 wt.%). The boron nitride (BN) was manufactured by High Purity Chemical Research Institute, Ltd. (average particle size 10 μm). Using the obtained powder, pressed magnetic cores were fabricated in the same manner as in Example 6. Table 5 shows the types of additives used in each example and the losses when applied at 0.1 T and 50 kHz.

[0145] Examples 14 and 15

[0146] Using the powders prepared in Examples 11 and 12, pressed powder magnetic cores were fabricated in the same manner as in Example 6. The types of additives used in each example and the losses when a magnetic field of 0.1T and 50kHz was applied are shown in Table 5.

[0147]

[0148] As shown in Table 5, it can be seen that the losses of Examples 13 to 15 are lower than those of Comparative Example 2 (a magnetic core made without adding high-resistivity materials such as MoS2).

[0149] Symbol Explanation

[0150] 1. Soft magnetic metal particles

[0151] 2. Covering layer

[0152] 3 Interface Layer

[0153] 4. Interface

[0154] 5 gaps

[0155] 6. Grain boundaries

[0156] 11 covered device

[0157] 12 chambers

[0158] 13 blades

[0159] 14 arrows

[0160] 15. Items to be processed

[0161] 100 Inductors (Magnetic Application Components)

[0162] 110 Powder-pressed magnetic core

[0163] 120 primary winding

[0164] 130 secondary winding

Claims

1. A pressed powder magnetic core, comprising soft magnetic metal particles and an interface layer existing at the interfaces between the soft magnetic metal particles. The interface layer covers the surface of the soft magnetic metal particles, and adjacent interface layers are in contact with each other. The interface layer contains more than 50% by mass of at least one compound selected from molybdenum disulfide, molybdenum oxide, mica, talc, pyrophyllite, and kaolin. The molding density is above 85%. The average thickness of the interface layer is 1 nm to 300 nm. The soft magnetic metal particles are in direct contact with the interface layer.

2. The pressed powder magnetic core according to claim 1, wherein, The molding density is 89.40%–96.60%.

3. The pressed powder magnetic core according to claim 1 or 2, wherein, The volume resistivity is above 20 Ω·cm.

4. The pressed powder magnetic core according to claim 1 or 2, wherein, The grain boundaries between the soft magnetic metal particles have a binding material.

5. The pressed powder magnetic core according to claim 4, wherein, The adhesive material is glass.

6. The pressed powder magnetic core according to claim 5, wherein, The glass of the bonding material contains at least one of bismuth, boron, vanadium, tin, and zinc.

7. The pressed powder magnetic core according to claim 4, wherein, The interface layer is in direct contact with the adhesive material.

8. The pressed powder magnetic core according to claim 1 or 2, wherein, The loss is 1000 kW / m when a magnetic field of 0.1 T and 50 kHz is applied. 3 the following.

9. An inductor comprising a pressed powder core as described in any one of claims 1 to 8.

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