Soft-magnetic metal magnetic powder, inductor, and method for manufacturing soft-magnetic metal magnetic powder

Abstract

Provided are: a soft-magnetic metal magnetic powder in which the volume resistivity and slipperiness of an insulating film that covers each soft-magnetic metal particle are further improved; an inductor; and a method for manufacturing a soft-magnetic metal magnetic powder. A soft-magnetic metal powder 20 according to the present disclosure comprises: soft-magnetic metal particles 21; and an insulation coating 22 that covers each of the soft-magnetic metal particles 21. The content of sulfur contained in the insulation coating 22 is, over the entire insulation coating, 350-1390 ppm.

Description

Soft magnetic metal powder, inductor, and method for manufacturing soft magnetic metal powder

[0001] The present disclosure relates to a soft magnetic metal powder, an inductor, and a method for manufacturing the soft magnetic metal powder.

[0002] Electronic components such as inductors are widely used in the power supply circuits of various electronic devices. These electronic components include a coil and a magnetic core placed inside the coil. In recent years, soft magnetic metal powder has been widely used as a magnetic core material instead of conventional ferrite. Compared to ferrite, soft magnetic metal powder has a higher saturation magnetization (saturation magnetic flux density) and excellent DC bias characteristics (large DC bias allowable current), making it suitable for miniaturizing electronic components (magnetic cores).

[0003] When soft magnetic metal powder is used in a magnetic core, eddy currents are likely to occur within the magnetic core due to electrical conduction between the soft magnetic metal particles contained in the soft magnetic metal powder. In other words, when soft magnetic metal powder is used in a magnetic core, eddy current loss is likely to occur. As a result, there is a risk that the efficiency of the power supply circuit will decrease due to eddy current loss and the power consumption of electronic devices will increase. Therefore, it is necessary to reduce eddy current loss, and to do so, the insulating coating of the soft magnetic metal particles requires a high volume resistivity.

[0004] Furthermore, to achieve high withstand voltage, it is necessary to pack the soft magnetic metal particles at a high density by reducing the gaps between them. This allows a large amount of soft magnetic metal powder to support high voltage. High-density packing requires high slippage of the insulating coating that covers the soft magnetic metal particles.

[0005] As explained above, in order to reduce eddy current loss and obtain high withstand voltage characteristics, high volume resistivity and good slip properties of the insulating coating of the soft magnetic metal particles are required.

[0006] Patent Documents 1 to 5 disclose magnetic metal powders in which an insulating coating covering soft magnetic metal particles (for example, pure iron powder) contains phosphorus.

[0007] JP 2009-120915 A JP 2018-120966 A JP 2022-169638 A JP 2022-174132 A JP 10-154613 A

[0008] The insulating coatings that coat the soft magnetic metal particles described in Patent Documents 1 to 5 contain phosphorus, which is hygroscopic. Therefore, when the phosphorus in the insulating coating absorbs moisture, the corrosion rate of the soft magnetic metal particles increases, accelerating the oxidation of the soft magnetic metal particles and increasing the surface roughness of the soft magnetic metal particles. When soft magnetic metal particles with rough surfaces are coated with an insulating coating, the interfacial resistance between the soft magnetic metal particles and the insulating coating is affected, resulting in a decrease in the resistivity of the insulating coating. Furthermore, the surface roughness of the insulating coating that covers the rough-surfaced soft magnetic metal particles also increases, resulting in a decrease in the slipperiness of the soft magnetic metal powder (powder in which soft magnetic metal particles are coated with an insulating coating). This results in a decrease in the packing ability of the soft magnetic metal powder when producing a dust core, and a decrease in the withstand voltage characteristics.

[0009] In view of these points, the present disclosure aims to provide a soft magnetic metal magnetic powder, an inductor, and a method for manufacturing soft magnetic metal magnetic powder in which the volume resistivity and slipperiness of the insulating coating that covers the soft magnetic metal particles are further improved.

[0010] The soft magnetic metal powder according to the present disclosure comprises soft magnetic metal particles and an insulating coating that covers the soft magnetic metal particles, and the insulating coating contains sulfur in an amount of 350 ppm or more and 1390 ppm or less based on the entire insulating coating.

[0011] An inductor according to the present disclosure includes an element body including the soft magnetic metal powder described above, and a coil provided within the element body.

[0012] The method for producing soft magnetic metal powder according to the present disclosure includes a preparation step of preparing soft magnetic metal particles, and a coating step of surface treating the soft magnetic metal particles with an aqueous solution containing sulfur and coating the soft magnetic metal particles with an insulating coating containing sulfur in an amount of 350 ppm or more and 1390 ppm or less based on the total amount of the insulating coating.

[0013] According to the present disclosure, it is possible to provide a soft magnetic metal powder, an inductor, and a method for manufacturing the soft magnetic metal powder, in which the volume resistivity and slipperiness of the insulating coating that coats the soft magnetic metal particles are further improved.

[0014] FIG. 1 is a perspective view of an inductor according to the present disclosure. FIG. 2 is an exploded perspective view of one embodiment of an inductor according to the present disclosure. FIG. 3 is a cross-sectional view of the region defined by the dashed line in FIG. 2, as viewed in the direction of the arrows along line III-III. FIG. 4 is a perspective view of another embodiment of an inductor according to the present disclosure. FIG. 5 is a manufacturing flow illustrating the manufacturing process of the soft magnetic metal powder according to the present disclosure. FIG. 6 is a STEM-EDX mapping image of the soft magnetic metal powder. FIG. 7 is a table showing the results of a demonstration test. FIG. 8 is a table showing the results of a demonstration test.

[0015] The soft magnetic metal powder, inductor, and method for manufacturing the soft magnetic metal powder according to the present disclosure will be described in detail below. While the description will refer to the drawings as necessary, the contents shown in the drawings are merely schematic and illustrative for the purpose of understanding the present disclosure, and the appearance and dimensional ratios may differ from the actual products.

[0016] FIG. 1 is a perspective view of an inductor of the present disclosure, FIG. 2 is an exploded perspective view of one embodiment of the inductor of the present disclosure, FIG. 3 is a cross-sectional view taken along the arrow III-III in the area bounded by the dashed line in FIG. 2, FIG. 4 is a perspective view of another embodiment of the inductor of the present disclosure, and FIG. 5 is a manufacturing flow chart illustrating the manufacturing process of the soft magnetic metal powder of the present disclosure.

[0017] <Description of Soft Magnetic Metal Powder According to the Present Disclosure> First, the soft magnetic metal powder according to the present disclosure will be described. The soft magnetic metal powder 20 includes soft magnetic metal particles 21 and insulating coatings 22 that coat the soft magnetic metal particles 21 (see FIG. 3 ).

[0018] An example of the soft magnetic metal particles 21 is nickel. Such a soft magnetic metal material can have a suitable magnetic permeability when used in an inductor. The soft magnetic metal particles 21 may be an Fe—Ni-based alloy (permalloy), an Fe—Si—Cr (chromium)-based alloy, an Fe—Si—Al (aluminum)-based alloy, an Fe—Si—B (boron)-P (phosphorus)-Cu (copper)-C (carbon)-based alloy, an Fe—Si—B—Nb (niobium)-Cu-based alloy, an alloy containing Ni, or Fe. The soft magnetic metal particles 21 containing Fe and Si may contain impurities such as Cr, Mn (manganese), Cu, Ni (nickel), P, S (sulfur), or Co (cobalt) that are not intended during manufacturing. The soft magnetic metal particles 21 may be contained in a magnetic paste, as will be described in detail in the description of the manufacturing method. The resin component contained in the magnetic paste may disappear by heat treatment, or may remain.

[0019] The insulating coating 22 has insulating properties. In this specification, "insulating" means that the volume resistivity is 1 MΩcm or more. The insulating coating 22 contains sulfur in an amount of 350 ppm or more and 1390 ppm or less based on the entire insulating coating. More specifically, the insulating coating 22 contains Si, O, and S elements.

[0020] The ion content in the insulating coating 22 can be measured by oxygen-flow combustion-infrared absorption spectroscopy. The "oxygen-flow combustion-infrared absorption spectroscopy" used in this specification refers to a method using an analyzer (Horiba, Ltd., Model No. EMIA-920V2 / FA) to combust a sample (soft magnetic metal powder) in an oxygen carrier with a combustion improver in a high-frequency induction heating furnace. The carbon in the sample is converted to carbon dioxide (CO), carbon monoxide (CO), sulfur to sulfur dioxide (SO), and hydrogen to water (HO). The water (HO) is then removed using a dehydrating agent, and the CO, CO, and SO present in the oxygen carrier are detected using an infrared detector. Note that the measurement of ion content is not limited to the above method. For example, the insulating coating on the surface of the soft magnetic metal powder may be locally analyzed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The oxygen flow combustion-infrared absorption method can be affected by the materials contained in the soft magnetic metal particles, but laser ablation ICP mass spectrometry (an analysis method using, for example, an Agilent 7500 Series ICP-MS manufactured by Agilent Technologies) irradiates the insulating coating on the surface of the soft magnetic metal powder with laser light, using the energy to evaporate and atomize the insulating coating and measure the elements contained in the insulating coating, making it possible to measure microscopic areas and the outermost layer by controlling the laser light.

[0021] In the soft magnetic metal powder 20 of the present disclosure, the insulating coating 22 contains sulfur in an amount of 350 ppm to 1390 ppm based on the entire insulating coating. Sulfur is poorly soluble in water and does not react easily with moisture in the atmosphere, which reduces corrosion of the surfaces of the soft magnetic metal particles 21 due to reaction between the soft magnetic metal powder and moisture and increases the volume resistivity of the soft magnetic metal particles and the insulating coating. Furthermore, because corrosion of the surfaces of the soft magnetic metal particles 21 is reduced, surface roughness is reduced, and the lubricity of the soft magnetic metal powder 20 can be improved.

[0022] Furthermore, as will be described in detail in the examples below, there is an appropriate range for the sulfur content. Specifically, if the sulfur content is lower than the specified amount, the soft magnetic metal particles will be affected by moisture in the air and will not be sufficiently inhibited from oxidizing. Furthermore, if the sulfur content is higher than the specified amount, the surrounding sulfur will form disulfide bonds, causing swelling in response to moisture in the air. Therefore, the appropriate range for the sulfur content is 350 ppm to 1390 ppm based on the entire insulating coating. Within this optimal sulfur content range, the sulfur at the interface between the insulating coating 22 and the soft magnetic metal particles 21 also acts as an electron nucleophile and therefore has electron-withdrawing properties. The terminal functional group of organosilane (silane coupling agent) is a methyl group, which has electron-donating properties. Due to strong electrostatic interaction, organosilane is appropriately adsorbed to the surface of the soft magnetic metal particles 21, thereby improving the lubricity of the soft magnetic metal powder 20.

[0023] In a preferred embodiment of the insulating coating 22, the phosphorus content of the insulating coating 22 is 0 ppm or more and 780 ppm or less based on the entire insulating coating. A lower phosphorus content in the insulating coating 22 is preferable because it suppresses reaction with moisture in the atmosphere, but since the soft magnetic metal powder 20 of the present disclosure contains sulfur, a phosphorus content of 0 ppm or more and 780 ppm or less based on the entire insulating coating may be tolerated. Even with such a soft magnetic metal powder 20, appropriate volume resistivity and lubricity can be achieved, as will be described in detail in the examples below.

[0024] The preferred average particle size of the soft magnetic metal powder 20 may be 1 μm or more and 30 μm or less. The average particle size of the soft magnetic metal powder 20 can be measured using the procedure described below. An inductor sample is cut to obtain a cross section. Specifically, the sample cross section is obtained by cutting the sample through the winding axis of the coil of the element body, perpendicular to the mounting surface and end surface of the element body. Multiple (e.g., five) regions (e.g., 130 μm × 100 μm) of the obtained cross section are photographed using an SEM. The obtained SEM images are analyzed using image analysis software (e.g., image analysis software "Win R00F" (manufactured by Mitani Shoji Co., Ltd.)) to determine the circle-equivalent diameter of the soft magnetic metal powder. The average value of the obtained circle-equivalent diameters is defined as the average particle size of the soft magnetic metal powder. Note that the "average particle size" used in this specification may refer to the average particle size D50 (particle size corresponding to a cumulative percentage of 50% on a volume basis).

[0025] <Method for manufacturing soft magnetic metal powder according to the present disclosure> Next, the method for manufacturing soft magnetic metal powder according to the present disclosure will be described with reference to Fig. 5. The method for manufacturing soft magnetic metal powder according to the present disclosure includes a preparation step of preparing soft magnetic metal particles, and a coating step of surface treating the soft magnetic metal particles with a sulfur-containing aqueous solution and coating the soft magnetic metal particles with an insulating coating containing 350 ppm to 1390 ppm of sulfur based on the entire insulating coating. The method will be described below with reference to the manufacturing flow shown in Fig. 5.

[0026] Preparation step of preparing soft magnetic metal particles: First, a metal salt aqueous solution containing soft magnetic metal particles is prepared. As an example, a metal salt aqueous solution containing nickel may be prepared. Next, a reducing agent solution that causes a reduction reaction in the metal salt aqueous solution containing the soft magnetic metal particles is prepared. Then, the metal salt aqueous solution and the reducing agent solution are mixed together to cause a reduction precipitation reaction. This produces a slurry-like reaction liquid containing the soft magnetic metal particles.

[0027] Coating step: An aqueous solution containing a sulfur coating agent is added to the obtained slurry-like reaction liquid containing the soft magnetic metal particles, and the soft magnetic metal particles and the aqueous solution are mixed to attach the sulfur component to the surface of the soft magnetic metal particles, thereby subjecting the soft magnetic metal particles to surface treatment. After that, solid-liquid separation treatment is performed and the resulting mixture is dried, thereby obtaining soft magnetic metal particles surface-treated with sulfur.

[0028] Next, a slurry for forming the insulating coating 22 that covers the soft magnetic metal particles is prepared. The slurry is prepared by dissolving a metal alkoxide containing Si (e.g., tetraethyl orthosilicate) in an alcohol solution having OH groups (e.g., isopropanol). That is, a solution containing a compound having Si atoms and a compound having OH groups is prepared. Note that a phosphate ester-type anionic surfactant (aqueous solution containing phosphorus) may be added to the solution to contain phosphorus in a range of 0 ppm to 780 ppm based on the total amount of the insulating coating.

[0029] Sulfur-surface-treated soft magnetic metal particles are added to the slurry that constitutes the insulating coating 22. The solution reacts in an alkaline environment to generate silanol groups. The alcohol solution containing OH groups is not limited to isopropanol; for example, ethanol may be used. The Si-containing metal alkoxide is not limited to tetraethyl orthosilicate; for example, tetramethoxysilane may be used.

[0030] After the soft magnetic metal particles are coated with an insulating film by the above reaction, the soft magnetic metal powder of the present disclosure is obtained by solid-liquid separation by suction filtration or the like and drying. Note that the product may be subjected to treatment such as washing (e.g., acetone washing) before solid-liquid separation. Furthermore, pressure filtration such as using a filter press or centrifugal filtration may be performed instead of the above-mentioned suction filtration.

[0031] As described above, according to the method for producing soft magnetic metal powder disclosed herein, the insulating coating can contain sulfur in an amount of 350 ppm to 1390 ppm based on the entire insulating coating. Therefore, the sulfur content can reduce corrosion of the soft magnetic metal particle surface due to a reaction between the soft magnetic metal powder and moisture, and increase the volume resistivity of the soft magnetic metal particle and the insulating coating. Furthermore, because corrosion of the soft magnetic metal particle surface is reduced, surface roughness can be reduced, improving the lubricity of the soft magnetic metal powder.

[0032] <Description of Inductor of the Present Disclosure> Next, the inductor of the present disclosure will be described with reference to Figures 1 to 4. The inductor of the present disclosure includes an element body 10 including the soft magnetic metal powder described above, and a coil provided within the element body 10.

[0033] The inductor of the present disclosure may be an inductor configured by laminating a plurality of base layers G1 to G8, each having a coil conductor CD and a magnetic layer ML, as shown in Fig. 2 (hereinafter referred to as inductor 1A of the first embodiment), or an inductor configured by winding a conductor wire as shown in Fig. 4 (hereinafter referred to as inductor 1B of the second embodiment). In the following explanation, the inductor of the first embodiment will be described first, followed by the inductor of the second embodiment.

[0034] Description of the Inductor of the First Embodiment The element body 10 has, for example, a rectangular parallelepiped shape or a substantially rectangular parallelepiped shape having six sides. The element body 10 may have rounded corners and ridges. A corner is a portion where three sides of the element body 10 intersect, and a ridge is a portion where two sides of the element body 10 intersect.

[0035] 1, the length direction, width direction, and height direction of the inductor 1A and the element body 10 are shown as L direction, W direction, and T direction, respectively. The length direction L, width direction W, and height direction T are perpendicular to each other. The mounting surface of the inductor 1A is, for example, a surface (LW surface) parallel to the length direction L and width direction W.

[0036] 1 has a first main surface 11 and a second main surface 12 that face each other in a height direction T, a first end surface 13 and a second end surface 14 that are perpendicular to the height direction T and face each other in a length direction L, and a first side surface 15 and a second side surface 16 that face each other in a width direction W that is perpendicular to the length direction L and the height direction T. In the example shown in FIG. 1 , the first main surface 11 of the element body 10 corresponds to the mounting surface (bottom surface) of the element body 10. Note that the second main surface 12 may also be the mounting surface of the element body 10.

[0037] The element body 10 has a laminated structure in which a plurality of element body layers, each having a magnetic layer ML and a coil conductor CD formed thereon, are stacked in a stacking direction (for example, height direction T). In this embodiment, the element body 10 is constructed by stacking element body layers G1 to G8 as shown in FIG. 2. A coil is then constructed by stacking a plurality of coil conductors CD. By constructing a coil by stacking coil conductors CD, it is possible to make it smaller than the coil C of the second embodiment described below. Note that the boundaries between the layers in the laminated structure of the element body 10 disappear. Furthermore, each of the element body layers G1 to G8 may be constructed by stacking a plurality of identical patterns.

[0038] A coil formed by stacking multiple coil conductors CD is provided within the element body 10. In the example shown in FIG. 2, two coils (a first coil and a second coil) are provided within the element body 10 along the stacking direction. More specifically, the first coil is formed by the coil conductors CD of element body layers G4 and G5, and the second coil is formed by the coil conductors CD of element body layers G2 and G3. The inductor 1A of the first embodiment is not limited to this example, and may have, for example, three or more coils provided along the stacking direction. Furthermore, a coil array may be formed by arranging multiple coils side by side within the element body 10 in a direction intersecting the stacking direction (direction L in FIG. 1).

[0039] External electrodes E are provided on the mounting surface (first main surface 11) of the element body 10. In the example shown in Fig. 2, the external electrodes E include a first external electrode E1 and a second external electrode E2 connected to the respective ends of the first coil, and a third external electrode E3 and a fourth external electrode E4 connected to the respective ends of the second coil. Two external electrodes are provided for each coil. Therefore, if the number of coils is three, the number of external electrodes may be six.

[0040] The through-hole conductors TH may be used to connect the coil and the external electrodes E. That is, the first through-hole conductors TH1 to TH4 may be provided corresponding to the first external electrode E1 to the fourth external electrode E4. The first through-hole conductors TH1 to TH4 may extend along the stacking direction.

[0041] The inductor of the present disclosure uses the above-described soft magnetic metal powder 20 in the manufacture of the element body 10. Therefore, according to the inductor of the present disclosure, the insulating coating 22 can contain sulfur at a content of 350 ppm to 1390 ppm based on the entire insulating coating. Therefore, the contained sulfur can reduce corrosion of the surfaces of the soft magnetic metal particles 21 due to a reaction between the soft magnetic metal powder 20 and moisture, and can increase the volume resistivity of the soft magnetic metal particles 21 and the insulating coating 22. Furthermore, because corrosion of the surfaces of the soft magnetic metal particles 21 is reduced, surface roughness is reduced, and the lubricity of the soft magnetic metal powder 20 can be improved.

[0042] An example of a method for identifying the insulating coatings 22 of the soft magnetic metal particles 21 from the inductor of the present disclosure is as follows: (1) A cross section is prepared by cutting the element body 10 in the thickness direction along the length of the element body 10 from the mounting surface side of the element body 10 at a position passing through the winding axis of the coil C. (2) This cross section is photographed at 1000x magnification using an SEM and / or EDX at the winding axis portion of the coil C so that the soft magnetic metal powder 20 is included in the field of view, and the materials of the soft magnetic metal particles 21 and the insulating coatings 22 can be identified.

[0043] Furthermore, in the inductor 1A of the first embodiment, the magnetic layers ML and the coil conductors CD are stacked and sintered to form the element body 10, and therefore there are portions within the element body 10 where the insulating coatings 22 of the soft magnetic metal powder particles 20 are bonded together (see FIG. 3). Furthermore, after the magnetic layers ML and the coil conductors CD are stacked and sintered, resin is impregnated between the soft magnetic metal powder particles 20. Therefore, by bonding the insulating coatings 22 of the soft magnetic metal powder particles 20 together, the rigidity of the element body 10 can be increased compared to when the soft magnetic metal powder particles are simply in contact with each other.

[0044] Description of Inductor of Second Embodiment Next, an inductor 1B of a second embodiment will be described with reference to Fig. 4. Note that the description of the configuration common to the inductor 1A of the first embodiment will be omitted as appropriate.

[0045] In the inductor 1B of the second embodiment, a coil C is formed by winding a conductor wire, and the coil C is embedded inside the element body 10.

[0046] The conductor wire is preferably made of a rectangular wire, which has the effect of allowing the wires to be wound densely without gaps between them and reducing DC resistance. However, the conductor wire is not limited to this example, and for example, a round wire or the like may also be used.

[0047] The conductor is preferably made of a metal wire (e.g., copper wire) coated with an insulating material such as resin, which, in combination with a resin (e.g., epoxy resin) contained in the element body 10 (described later), allows the coil C to be firmly molded within the element body 10.

[0048] The element body 10 further contains a resin in addition to the soft magnetic metal powder 20 described above. The resin is contained in the element body 10 and cured, causing the soft magnetic metal powder particles 20 to come into contact with each other. The resin may be, for example, a thermosetting epoxy resin and / or a phenoxy resin. The resin content may be 2 wt % or more and 3.5 wt % or less, more preferably 2.7 wt % or more and 3.0 wt % or less, based on the total weight of the soft magnetic metal powder 20 and the resin.

[0049] In the element body 10 of the inductor 1B of the second embodiment, the soft magnetic metal powder 20 may be composed of a first magnetic powder and a second magnetic powder having a smaller average particle size than the first magnetic powder. With this configuration, the second magnetic powder having a smaller average particle size than the first magnetic powder fills the gaps between the first magnetic powder particles, thereby improving the filling rate of the soft magnetic metal powder in the element body 10.

[0050] The soft magnetic metal powder 20 as the first magnetic powder may have an average particle size of 20 μm to 30 μm, more preferably 21.4 μm to 27.4 μm, while the second magnetic powder may have an average particle size of 1 μm to 10 μm, more preferably 1.5 μm to 1.8 μm.

[0051] The first magnetic powder is an alloy containing nickel, and may have an oxide film.

[0052] The second magnetic powder is carbonyl iron powder. The second magnetic powder may have an oxide film. The second magnetic powder may be composed of the same material as the first magnetic powder, or may be composed of a different material. The first magnetic powder and the second magnetic powder may be coated with the insulating coating 22 to form the soft magnetic metal powder, or both may be coated with the insulating coating 22 to form the soft magnetic metal powder. By forming the soft magnetic metal powder by coating at least one of the first magnetic powder and the second magnetic powder with different average particle sizes, the sliding property between the first magnetic powder and the second magnetic powder can be improved, thereby further increasing the filling rate of the soft magnetic metal powder in the base body 10.

[0053] Furthermore, based on the total weight of the first and second magnetic powders, the first magnetic powder may be 70 wt % to 85 wt %, preferably 70 wt % to 80 wt %, and the second magnetic powder may be 15 wt % to 30 wt %, preferably 20 wt % to 30 wt %.

[0054] The soft magnetic metal powders of the present disclosure were subjected to a verification test, which will be described in detail below. Specifically, the soft magnetic metal powders of Examples 1 to 8 and Comparative Examples 1 to 3 were produced.

[0055] Example 1 (Step 1) 20 g of nickel sulfate hexahydrate (Fujifilm / Wako Pure Chemical Industries) was weighed as a metal salt, 1.52 mg of copper sulfate pentahydrate (Fujifilm / Wako Pure Chemical Industries) was weighed as a precious metal catalyst, 7 g of L-arginine (Tokyo Chemical Industry) was weighed as a basic amino acid, and 24 g of trisodium citrate dihydrate was weighed and dissolved in pure water to prepare a metal salt aqueous solution. (Step 2) 65 g of 60% hydrazine hydrate (Otsuka Chemical) and 57 g of sodium hydroxide (Tosoh) as a pH adjuster were weighed and dissolved in 280 mL of pure water to prepare a reducing agent solution. (Step 3) The metal salt aqueous solution and reducing agent solution were each heated to a liquid temperature of 60°C, and then the two solutions were stirred and mixed to form a mixed solution, and the reduction precipitation reaction was initiated. The pH of the mixed solution at the start of the precipitation reaction was 13. After 2-3 minutes from the start of the reaction, the reaction solution changed due to nucleation caused by the action of the precious metal catalyst. However, the reduction reaction was continued for another 2 hours with continued stirring to obtain nickel precipitate powder. (Step 4) The reaction solution containing the obtained nickel precipitate powder was in a slurry state. To this nickel precipitate powder slurry, an aqueous solution containing 14 mg of thiomalic acid (Tokyo Chemical Industry) dissolved as a sulfur coating agent was added to perform a surface treatment on the nickel precipitate powder. After surface treatment, the nickel precipitate powder was subjected to solid-liquid separation using pure water and dried in a vacuum dryer set at 150°C to obtain sulfur-surface-treated nickel powder. (Step 5) 50 g of the sulfur-surface-treated nickel powder was added to a mixed solvent of 20.5 g of isopropanol (Kanto Chemical Industry) and 20.5 g of 9% ammonia water (Daisei Chemical Industry). Next, 0.58 g of Plysurf AL (Dai-ichi Kogyo Seiyaku) and 5.98 mL of tetraethyl orthosilicate (TEOS, Kanto Chemical) were added and stirred for 30 minutes. (Step 6) After stirring in Step 5, 660 μL of TEOS and 680 μL of organosilane (Shin-Etsu Silicones) were added and stirred for 1 hour. (Step 7) After stirring in Step 6, the nickel powder slurry was subjected to solid-liquid separation by suction filtration, and the powder surface was washed with acetone (Nacalai Tesque). The mixture was then air-dried overnight to obtain soft magnetic metal powder containing sulfur in the insulating silica coating.

[0056] Example 2 In (Step 4) of Example 1, the amount of thiomalic acid was changed to 7 mg, and other steps were carried out in the same manner as in Example 1 to produce soft magnetic metal powder.

[0057] Example 3 In (step 4) of Example 1, the amount of thiomalic acid was changed to 6 mg, and other steps were carried out in the same manner as in Example 1 to produce soft magnetic metal powder.

[0058] Example 4 In (step 4) of Example 1, thiomalic acid was used in an amount of 7 mg. In addition, in (step 5) of Example 1, Plysurf AL was used in an amount of 0.60 g. Other than this, a soft magnetic metal powder was produced through the same steps as in Example 1.

[0059] Example 5 In (step 4) of Example 1, the amount of thiomalic acid was changed to 28 mg, and other steps were carried out in the same manner as in Example 1 to produce soft magnetic metal powder.

[0060] Example 6 In (Step 4) of Example 1, the amount of thiomalic acid was changed to 29 mg, and other steps were carried out in the same manner as in Example 1 to produce soft magnetic metal powder.

[0061] Example 7 In (step 5) of Example 1, the amount of Plysurf AL was changed to 0.29 g, and other steps were carried out in the same manner as in Example 1 to produce soft magnetic metal powder.

[0062] Example 8 In step 5 of Example 1, 0.29 g of polyvinylpyrrolidone (Pitzcol K-30, Dai-ichi Kogyo Seiyaku) was added instead of Plysurf AL. A soft magnetic metal powder was produced through the same steps as in Example 1.

[0063] Comparative Example 1 Steps 1 to 4 of Example 1 were carried out, but steps 5 and 6 were not carried out. In other words, metal magnetic particles without an insulating coating were produced.

[0064] Comparative Example 2 In (Step 4) of Example 1, the amount of thiomalic acid was changed to 56 mg, and other steps were carried out in the same manner as in Example 1 to produce a soft magnetic metal powder.

[0065] Comparative Example 3 In (step 4) of Example 1, thiomalic acid was used in an amount of 30 mg, and in (step 5) of Example 1, Plysurf AL was used in an amount of 1.16 g. Except for this, a soft magnetic metal powder was produced through the same steps as in Example 1.

[0066] The soft magnetic metal powders of Examples 1 to 8 and Comparative Examples 1 to 3 were subjected to the following verification tests.

[0067] (Demonstration Test 1: STEM-EDX Measurement) STEM-EDX measurement was performed on the soft magnetic metal powder of Example 1. Figure 6 shows an image captured by STEM. From Figure 6, it can be seen that nickel is present in the soft magnetic metal particle portion, and oxygen, silicon, and sulfur elements are present on the outer surface of the soft magnetic metal particles. Note that in the oxygen element mapping, silicon element mapping, and sulfur element mapping of Figure 6, oxygen, silicon, and sulfur elements appear to be present in the soft magnetic metal particle portion as well, but this is due to adhesions that adhere to the cross section of the nickel portion due to trimming when forming the cross section of the nickel portion, appearing as noise. Therefore, oxygen, silicon, and sulfur elements are substantially absent from the soft magnetic metal particle portion.

[0068] (Demonstration Test 2: Measurement of Sulfur Content) The sulfur content of the soft magnetic metal powders of Examples 1 to 8 and Comparative Examples 1 to 3 was measured. The sulfur content was measured using an analytical device (Horiba, Ltd., Model No. EMIA-920V2 / FA) by the above-mentioned "oxygen flow combustion-infrared absorption method." Note that in this disclosure, the sulfur content was measured by the "oxygen flow combustion-infrared absorption method." However, when using the LA-ICP-MS (laser ablation ICP-MS) analytical method, an Agilent 7500 from Agilent Technologies may be used to irradiate a laser onto the insulating coating present on the surface of the soft magnetic metal powder, vaporizing and atomizing the insulating coating with the energy, and then measuring the sulfur contained in the insulating coating.

[0069] 7, the soft magnetic metal powders of Examples 1 to 8 contained 350 ppm or more and 1390 ppm or less of elemental sulfur in the insulating coatings. On the other hand, the contents of elemental sulfur in Comparative Examples 1 to 3 were outside the above-mentioned range.

[0070] (Demonstration Test 3: Measurement of Phosphorus Content) The phosphorus content of the soft magnetic metal powders of Examples 1 to 8 and Comparative Examples 1 to 3 was measured. The phosphorus content was measured using an ICP-AES analyzer (an ICP optical emission spectroscopy apparatus (iCAP6300 radial, Thermo Fisher Scientific) and an atomic absorption spectroscopy apparatus (iCE3300, Thermo Fisher Scientific)). In the present disclosure, the phosphorus content was measured by ICP-AES analysis. However, when using LA-ICP-MS (laser ablation ICP mass spectrometry), an Agilent 7500 (Agilent Technologies) may be used to irradiate a laser onto the insulating coating present on the surface of the soft magnetic metal powder, vaporize and atomize the insulating coating with the energy, and then measure the sulfur contained in the insulating coating.

[0071] 7, the soft magnetic metal powders of Examples 1 to 8 contained phosphorus in the insulating coatings at a content of 0 ppm to 780 ppm. On the other hand, the phosphorus content of Comparative Example 3 was outside the above-mentioned range.

[0072] (Demonstration Test 4: Measurement of Corrosion Current Density) The corrosion current density was measured at room temperature using an electrochemical system (Hokuto Denko, Model No. HZ-5000). To prepare the measurement sample for measuring the corrosion current density, the soft magnetic metal powders of Examples 1 to 8 and Comparative Examples 1 to 3 and carbon paste were mixed with a spatula in a mass ratio of 2:1 to prepare a carbon paste working electrode. A 3% by mass NaCl aqueous solution was added to a glass cell, and the aforementioned carbon paste working electrode, Ag / AgCl electrode, and Pt counter electrode were inserted to prepare a three-electrode cell. The corrosion current density was then calculated using the Tafel extrapolation method.

[0073] The measurement results of the corrosion current density are shown in Figure 7. In the results of Figure 7, the smaller the "corrosion current density" value, the more surface corrosion is suppressed. The soft magnetic metal powders of Examples 1 to 8 had lower corrosion current densities than the soft magnetic metal powders of Comparative Examples 1 to 3. Therefore, the soft magnetic metal powders of Examples 1 to 8 were found to have appropriately suppressed surface corrosion.

[0074] (Demonstration test 5: Measurement of volume resistivity) The volume resistivity of soft magnetic metal powder was measured using a powder resistance instrument (manufactured by Mitsubishi Chemical Analytech, model number: Hiresta UX MCP-HT800). For the measurement, the soft magnetic metal powder was placed in a dedicated jig, and the pressure conditions were changed in 4 kN steps, and the volume resistivity was measured from 4 kN to 20 kN. The measurement results in Figure 7 correspond to the data at a load of 20 kN.

[0075] The results of measuring the volume resistivity are shown in Figure 7. Note that in the results of Figure 7, the larger the "volume resistivity" value, the higher the insulating properties provided by the insulating coating. The soft magnetic metal powders of Examples 1 to 8 had higher volume resistivities than the soft magnetic metal powders of Comparative Examples 1 to 3. Therefore, the soft magnetic metal powders of Examples 1 to 8 had higher insulating properties than the soft magnetic metal powders of Comparative Examples 1 to 3.

[0076] (Demonstration Test 6: Slippage Packing Coefficient) The slippage of nickel powder was evaluated using a powder bed shear force measuring device (NS-S500, Nano Seeds). The measurement conditions were an indentation load of 150 N, a powder tray of 15 mm, and a tray gap of 0.2 mm.

[0077] The measurement results of the slippage filling coefficient are shown in Figure 7. Note that in the results of Figure 7, the "slippage filling coefficient" indicates that the larger the numerical value, the greater the slippage. The soft magnetic metal powders of Examples 1 to 8 had higher slippage filling coefficients than the soft magnetic metal powders of Comparative Examples 1 to 3.

[0078] Next, a demonstration test on an inductor using the soft magnetic metal powder of the present disclosure will be described in detail. Specifically, powder magnetic cores for use in the inductors described in Examples 9 to 16 and Comparative Example 4 below were manufactured.

[0079] Example 9 (Step 1) The soft magnetic metal powder described in Example 1 above was mixed with a solution of epoxy resin (thermosetting resin), imide resin (curing agent), and acetone, and the acetone was evaporated to obtain granules. The total mass of the epoxy resin and imide resin was 3 mass% by powder weight ratio. (Step 2) The granules were sized using a stainless steel sieve. The mesh size of the stainless steel sieve was 180 μm. A molded body was obtained by molding the granules using a toroidal mold. The inner diameter of the mold was 6.5 mm, and the outer diameter of the mold was 11 mm. The molding pressure was 3.0 t / cm. 2 The molded body was heated at 180°C for 1 hour to harden the epoxy resin, thereby obtaining a toroidal powder magnetic core.

[0080] Example 10 A dust core was produced through the same steps as in Example 9, except that the soft magnetic metal powder described in Example 2 was used in (Step 1) of Example 9.

[0081] Example 11 A dust core was produced through the same steps as in Example 9, except that the soft magnetic metal powder described in Example 3 was used in (Step 1) of Example 9.

[0082] Example 12 A dust core was produced through the same steps as in Example 9, except that the soft magnetic metal powder described in Example 4 was used in (Step 1) of Example 9.

[0083] Example 13 A dust core was produced through the same steps as in Example 9, except that in (step 1) of Example 6, the soft magnetic metal powder described in Example 5 was used.

[0084] Example 14 A dust core was produced through the same steps as in Example 9, except that the soft magnetic metal powder described in Example 6 was used in (Step 1) of Example 9.

[0085] Example 15 A powder magnetic core was produced through the same steps as in Example 9, except that the soft magnetic metal powder described in Example 7 was used in (step 1) of Example 9. Example 16 A powder magnetic core was produced through the same steps as in Example 9, except that the soft magnetic metal powder described in Example 8 was used in (step 1) of Example 9.

[0086] Comparative Example 4 A dust core was produced through the same steps as in Example 9, except that the soft magnetic metal powder described in Comparative Example 1 was used in (Step 1) of Example 9.

[0087] (Demonstration Test 7: Withstand Voltage Measurement) A voltage was applied to the powder core using a digital ultra-high resistance / microcurrent meter (model number: R8340A, manufacturer: ADC). The current in the powder core was continuously measured while the voltage was continuously increased. The withstand voltage of the powder core was defined as the voltage when the current in the powder core reached 1 mA.

[0088] The measurement results of the withstand voltage are shown in Figure 8. Note that in the results of Figure 8, a larger "withstand voltage" value indicates that the material can withstand a higher voltage. The soft magnetic metal powders of Examples 1 to 8 had higher withstand voltages than the soft magnetic metal powders of Comparative Examples 1 to 3. Therefore, the powder cores of Examples 9 to 16 had better withstand voltage characteristics than the powder core of Comparative Example 4.

[0089] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. The technical scope of the present disclosure also includes all modifications within the scope and meaning equivalent to the claims.

[0090] The soft magnetic metal powder, inductor, and soft magnetic metal powder disclosed herein are as follows: <1> A soft magnetic metal powder comprising soft magnetic metal particles and an insulating coating covering the soft magnetic metal particles, wherein the insulating coating contains 350 ppm to 1390 ppm of sulfur based on the entire insulating coating. <2> The soft magnetic metal powder according to <1>, wherein the insulating coating contains 0 ppm to 780 ppm of phosphorus based on the entire insulating coating. <3> The soft magnetic metal powder according to <1> or <2>, wherein the soft magnetic metal particles are nickel or an alloy containing nickel. <4> An inductor comprising an element body comprising the soft magnetic metal powder according to any one of <1> to <3>, and a coil provided within the element body. <5> The inductor according to <4>, wherein the coil is configured by stacking multiple conductor layers. <6> The inductor according to <4>, wherein the coil is configured by a wound conductor wire. <7> The inductor according to any one of <4> to <6>, wherein the element body comprises first magnetic particles and second magnetic particles having an average particle size smaller than that of the first magnetic particles, and at least one of the first magnetic particles and the second magnetic particles is the soft magnetic metal particle. <8> A method for producing soft magnetic metal powder, comprising: a surface treatment step of adding an aqueous solution containing sulfur to the soft magnetic metal particles, mixing the soft magnetic metal particles with the aqueous solution, and drying the mixture to adhere a sulfur component to the surfaces of the soft magnetic metal particles; and a coating step of coating the soft magnetic metal particles with an insulating coating by mixing the soft magnetic metal particles with an insulating coating material solution and drying the mixture to obtain a soft magnetic metal powder having an insulating coating formed on the surfaces of the soft magnetic metal particles, the insulating coating containing 350 ppm to 1390 ppm of sulfur based on the entire insulating coating. <9> The method for producing soft magnetic metal powder according to <8>, wherein the coating step further comprises adding an aqueous solution containing phosphorus to the insulating film to contain phosphorus, thereby obtaining soft magnetic metal powder having an insulating coating formed on the surface of the soft magnetic metal particles, the insulating coating containing phosphorus in a content of 0 ppm to 780 ppm based on the entire insulating coating. <10> The method for producing soft magnetic metal powder according to claim <8> or <9>, wherein the soft magnetic metal particles prepared in the preparation step contain nickel element.

[0091] The soft magnetic metal powder, inductor, and method for producing soft magnetic metal powder of the present disclosure can be suitably used as electronic components having improved volume resistivity and slipperiness of the insulating coating that coats the soft magnetic metal particles.

[0092] 1, 1A, 1B Inductor 10 Body 11 First main surface 12 Second main surface 13 First end surface 14 Second end surface 15 First side surface 16 Second side surface 20 Soft magnetic metal powder 21 Soft magnetic metal particle 22 Insulating coating C Coil CD Coil conductor E External electrode E1 to E4 First external electrode to fourth external electrode G1 to G6 Body layer ML Magnetic layer TH Through-hole conductor TH1 to TH4 First through-hole conductor to fourth through-hole conductor

Claims

1. A soft magnetic metal powder comprising soft magnetic metal particles and an insulating coating covering the soft magnetic metal particles, wherein the insulating coating contains 350 ppm to 1390 ppm of sulfur based on the entire insulating coating.

2. The soft magnetic metal powder according to claim 1, wherein the insulating coating contains phosphorus in an amount of 0 ppm to 780 ppm based on the entire insulating coating.

3. The soft magnetic metal powder according to claim 1 or 2, wherein the soft magnetic metal particles are nickel or an alloy containing nickel element.

4. An inductor comprising: an element body comprising the soft magnetic metal powder according to any one of claims 1 to 3; and a coil provided within the element body.

5. The inductor according to claim 4, wherein the coil is constructed by laminating a plurality of conductor layers.

6. The inductor of claim 4, wherein the coil is constructed from wound conductive wire.

7. An inductor according to any one of claims 4 to 6, wherein the element body comprises first magnetic particles and second magnetic particles having an average particle size smaller than that of the first magnetic particles, and at least one of the first magnetic particles and the second magnetic particles is a soft magnetic metal particle.

8. A method for producing soft magnetic metal powder, comprising: a surface treatment of soft magnetic metal particles by adding an aqueous solution containing sulfur to soft magnetic metal particles, mixing the soft magnetic metal particles with the aqueous solution, and drying the particles to adhere sulfur components to the surfaces of the soft magnetic metal particles; and a coating process of coating the soft magnetic metal particles with an insulating coating by mixing the soft magnetic metal particles with an insulating coating material solution and drying the resulting soft magnetic metal powder having an insulating coating formed on the surface of the soft magnetic metal particles, the insulating coating containing sulfur in an amount of 350 ppm to 1390 ppm based on the entire insulating coating.

9. A method for producing soft magnetic metal powder as described in claim 8, wherein the coating step further includes adding an aqueous solution containing phosphorus to the insulating coating material solution to cause the insulating coating to contain phosphorus, thereby obtaining soft magnetic metal powder in which an insulating coating containing phosphorus in a content of 0 ppm to 780 ppm based on the entire insulating coating is formed on the surfaces of the soft magnetic metal particles.

10. The method for producing soft magnetic metal powder according to claim 8 or 9, wherein the soft magnetic metal particles are nickel or an alloy containing nickel element.

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