Insulator coated soft magnetic powder

Abstract

The insulating coated soft magnetic powder of the present invention is an insulating coated soft magnetic powder whose surface contains 99.0 wt.% or more iron is coated with an insulating coated oxide. The 50% volume cumulative particle size (D50) of the aforementioned insulating coated soft magnetic powder, as determined by laser diffraction particle size distribution measurement method, is 0.01 μm or more and 2.0 μm or less. The oxygen, carbon and nitrogen contents relative to the total of the aforementioned insulating coated soft magnetic powder are as follows: oxygen: 0.1 wt.% or more and 2.0 wt.% or less, carbon: 0 wt.% or more and 0.2 wt.% or less, nitrogen: 0 wt.% or more and 0.2 wt.% or less. Furthermore, the total oxygen, carbon and nitrogen contents relative to the total of the aforementioned insulating coated soft magnetic powder are 0.1 wt.% or more and 2.0 wt.% or less.

Description

Technical Field

[0001] This invention relates to insulating coated soft magnetic powder. This application asserts priority based on Japanese Application No. 2021-090673, filed on May 28, 2021, and incorporates all the contents of the aforementioned Japanese application. Prior Technology

[0002] In recent years, transformers, current-absorbing coils, and inductors have been used as magnetic components for power supply in the field of electronic devices. These magnetic components have a core and coils arranged as conductors around or inside the core. The core of magnetic components such as inductors can be obtained by compressing soft magnetic powder to form a powder core. Powder cores improve magnetic properties, therefore it is necessary to increase the proportion of magnetic components in the powder core. To increase the proportion of magnetic components in powder cores, methods for manufacturing powder cores have been employed in recent years, using a mixture of multiple soft magnetic powders with different particle sizes. For example, Patent Document 1 discloses a coil electronic component containing magnetic particles with three or more particle size distributions and its manufacturing method.

[0003] In particular, soft magnetic powder with a particle size of several μm or less has been used in the past to replace the insulating portion of pressed powder cores. In this case, if the filling rate of the soft magnetic powder is increased to improve the magnetic composition of the pressed powder core, the contact points between the soft magnetic powder particles increase. However, if the soft magnetic powder particles are in contact with each other, there is a problem that when a voltage is applied to the magnetic components, the loss due to the current flowing through the contacting particles (interparticle eddy current) is large, resulting in increased iron loss in the pressed powder core.

[0004] Therefore, a method is used to reduce iron loss by coating the surface of soft magnetic powder particles with an insulating material, with the insulating coating layer between the particles, thereby cutting off the interparticle eddy currents generated by the pressed magnetic core. Various insulating materials and methods for coating the insulating material have been proposed in the past. For example, Patent Document 2 discloses a method for forming an inorganic insulating layer of low-melting-point glass on the surface of pre-prepared soft magnetic powder using powder coating methods such as mechanical fusion, electroless electroplating, wet methods such as sol-gel, or dry methods such as sputtering. Then, the soft magnetic powder with the inorganic insulating layer is further mixed with resin powder, thereby creating a soft magnetic powder with a surface coating of inorganic insulating layer and resin particle layer. [Previous Technical Documents] [Patent Literature]

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-208002 Patent Document 2: International Publication WO2005 / 015581 Patent Document 3: International Publication WO2018 / 092664 Summary of the Invention

[0006] [The problem the invention aims to solve]

[0007] As mentioned above, for soft magnetic powder used to form pressed magnetic cores, small-particle-size soft magnetic powder with an insulating coating is desirable. Furthermore, in recent years, the requirements for magnetic components with high current have been increasing, and for such components, soft magnetic powder with a higher saturation flux density is preferred. Therefore, the characteristics of small-particle-size soft magnetic powder with an insulating coating also focus on the high saturation flux density of the soft magnetic powder itself. Iron powder has a higher saturation flux density than iron-based alloy powders such as Fe-Si alloys and Fe-Ni alloys, which have been used as soft magnetic powders in the past. Moreover, iron powder is preferably composed of high-purity iron. Therefore, in recent years, there has been a search for small-particle-size powders with high saturation flux density with an insulating coating, especially small-particle-size iron powder with high purity with an insulating coating. However, compared to small-particle-size iron-based alloy powders with an insulating coating, small-particle-size iron powder with high purity with an insulating coating presents a greater manufacturing difficulty.

[0008] For example, as a method for manufacturing insulating coated soft magnetic powder, there is a method of applying an insulating coating to the surface of iron powder that has been pre-made as soft magnetic powder. For example, atomization is a method for manufacturing iron powder as a soft magnetic powder. Atomization uses high-pressure, inert gas or water to atomize a molten liquid above its melting point, thus obtaining particles. However, due to the high viscosity of the molten liquid, it is difficult to atomize the droplets, making it impossible to recover ultrafine particles with a particle size of several μm or less in high yield. Furthermore, while water is more effective than gas for atomization, when manufacturing iron powder, which is highly reactive with oxygen, the iron powder also readily reacts with oxygen derived from water, resulting in iron powder that is oxidized both internally and / or on the surface. Consequently, the purity of the iron in the resulting soft magnetic powder decreases, contributing to a reduction in the magnetic properties of the soft magnetic powder.

[0009] Regarding other methods for manufacturing iron powder as soft magnetic powder, the carbonyl method can be cited. The carbonyl method uses pentacarbonyl iron as raw material, and the processing temperature during iron powder manufacturing is not high, thus easily leading to the presence of carbon and nitrogen. The carbon and nitrogen contained in the iron powder form non-magnetic substances by solid solution with iron, thus contributing to the reduction of the magnetic properties of the resulting soft magnetic powder.

[0010] Therefore, obtaining high-purity iron powder for use as a soft magnetic powder using conventional methods is inherently difficult. Furthermore, even if high-purity iron powder is obtained, its high reactivity with oxygen inevitably leads to the formation of a metal oxide layer on its surface. This metal oxide layer has low insulation properties and is permeable to oxygen; therefore, oxygen from the air easily diffuses through the surface into the interior, reducing the magnetic properties of the soft magnetic powder. Consequently, to improve the insulation and surface stability relative to oxidation, conventional methods, as described above, further coat the oxidized iron powder with an insulating material. However, in this method, the soft magnetic powder manufacturing step and the step of applying an insulating coating to the iron powder surface are separate. Therefore, during the period from powder recovery to the formation of the insulating coating, small-particle-size iron powder becomes easily oxidized. This results in a lack of stability in the quality of the obtained powder, and the heat generated by oxidation poses a risk of heating and fire during the process. To solve this problem, iron powder needs to be treated in an inactive environment to prevent oxidation, but this would incur huge costs.

[0011] On the other hand, spray pyrolysis is a method that simultaneously performs the steps of manufacturing soft magnetic powder and applying an insulating coating to the soft magnetic powder. Patent Document 3 discloses a method that uses spray pyrolysis to simultaneously produce soft magnetic powder and form an insulating film on the surface of the soft magnetic powder, forming a glassy thin film on the surface of the soft magnetic powder. Since the production of soft magnetic powder and the formation of a glassy thin film on the surface of the soft magnetic powder can be performed simultaneously in one step, compared to methods where the steps of manufacturing soft magnetic powder and applying the insulating coating are separate, the oxidation of the soft magnetic powder can be suppressed while an insulating film is formed on the surface of the soft magnetic powder. However, when using spray pyrolysis with a solution of raw materials to produce insulating-coated soft magnetic powder from high-purity iron powder, similar to the atomization method, the iron powder readily reacts with oxygen from the raw material solution, causing oxidation inside and / or on the powder surface. As a result, the purity of iron in the obtained soft magnetic powder decreases, leading to a reduction in the magnetic properties of both the soft magnetic powder and the insulating-coated soft magnetic powder.

[0012] As a result, the insulating coating soft magnetic powder with small particle size requires iron powder with high insulating coating purity. However, in previous methods, oxygen, carbon, or nitrogen can easily enter the iron powder that is a soft magnetic powder, which reduces the purity of iron in the soft magnetic powder and even reduces the magnetic properties of the final insulating coating soft magnetic powder. The present invention addresses the aforementioned problems by providing an insulating coated soft magnetic powder, which is made from iron powder with small particle size and high purity, and has an insulating coated oxide coating on at least a portion of the surface of the soft magnetic powder. [Methods used to solve problems]

[0013] The insulating coated soft magnetic powder of the present invention is an insulating coated soft magnetic powder whose surface contains 99.0 wt.% or more iron is coated with an insulating coated oxide. The 50% volumetric cumulative particle size (D50) of the aforementioned insulating coated soft magnetic powder, determined by laser diffraction particle size distribution measurement, is between 0.01 μm and 2.0 μm. The oxygen, carbon, and nitrogen content of the aforementioned insulating coated soft magnetic powder as a whole is: Oxygen: ≥0.1 wt.% to ≤2.0 wt.%; Carbon: ≥0 wt.% to ≤0.2 wt.%; Nitrogen: ≥0 wt.% to ≤0.2 wt.%; Furthermore, the total content of oxygen, carbon, and nitrogen in the aforementioned insulating coated soft magnetic powder is between 0.1 wt.% and 2.0 wt.%. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an insulating coated soft magnetic powder by forming a soft magnetic powder from iron powder with small particle size and high purity, and to cover at least a portion of the surface of the soft magnetic powder with an insulating coating oxide. Simple Explanation of the Diagram

[0015] none. Implementation

[0016] [The form in which the invention is carried out]

[0017] The insulating coated soft magnetic powder of the present invention is an insulating coated soft magnetic powder with at least a portion of its surface coated with an insulating oxide. The insulating coated soft magnetic powder obtained by the present invention has a small particle size and low content of oxygen, carbon and nitrogen, thus exhibiting a high saturation magnetic flux density. Furthermore, as an insulating coated soft magnetic powder, it has high insulation properties. The insulating coated soft magnetic powder of the present invention contains 99.0 wt.% or more iron. Preferably, it contains 99.2 wt.% or more iron. The iron content in soft magnetic powders can be quantified using high-frequency inductively coupled plasma (ICP) analysis. The soft magnetic powder can be dissolved by acid treatment, and the iron content can be quantified by ICP analysis. Furthermore, if the soft magnetic powder contains carbon / nitrogen, the carbon / nitrogen content obtained from carbon / nitrogen analysis can be calculated as the impurity amount. The iron content in the soft magnetic powder can be obtained by subtracting the carbon / nitrogen content as impurities from the ICP analysis value. Furthermore, soft magnetic powders are not in a powder state, but rather contain magnetic materials (such as pressed magnetic cores), making ICP analysis difficult. Therefore, in such cases, EPMA analysis can be performed on the powder from the cross-section of the magnetic material to quantify the iron content.

[0018] Furthermore, the insulating coated soft magnetic powder of the present invention contains unavoidable impurities, such as Ni, Cr, Co, Mn, S, Zn, Zr, V, Mo, Si, Cu, Nb, etc. These unavoidable impurities may contain less than 1000 ppm, preferably less than 800 ppm, and more preferably less than 500 ppm. When producing high-purity iron powder using conventional methods, impurities, primarily oxygen, carbon, or nitrogen, can enter the soft magnetic powder. Furthermore, after the soft magnetic powder is manufactured but before the insulating coating is formed, the iron purity of the soft magnetic powder decreases due to oxidation of the iron powder and diffusion of oxygen into the powder. In particular, small-particle-size iron powder has a larger specific surface area, making it more susceptible to oxidation, which easily leads to a decrease in iron purity in conventional soft magnetic powders. If the iron purity in the soft magnetic powder decreases, it contributes to a reduction in the magnetic properties of the final insulating-coated soft magnetic powder, and further to a reduction in the magnetic properties of the pressed magnetic core. In contrast, the insulating-coated soft magnetic powder of the present invention is manufactured using the method described later. This allows for the simultaneous formation of an insulating oxide coating layer as an insulating material during the manufacturing of the soft magnetic powder, thereby suppressing the decrease in iron purity caused by impurities in the soft magnetic powder and suppressing the decrease in iron purity caused by oxidation of the soft magnetic powder.

[0019] In the insulating coated soft magnetic powder of the present invention, at least a portion of the surface of the soft magnetic powder is coated with an insulating coating oxide. From the viewpoint of achieving a more uniform coating of the soft magnetic powder, the insulating coating oxide is preferably glassy. When the insulating coating oxide contains glass, the insulating coating oxide as a whole can be amorphous, or it can contain crystalline material. Furthermore, the insulating coating oxide can be a crystalline oxide. High-purity iron powders that are easily oxidized generally form a metal oxide layer such as iron oxide on their surface. Compared to this metal oxide layer, coating soft magnetic powder with an insulating oxide coating can improve the surface stability of the soft magnetic powder. By improving surface stability, the oxidation of the soft magnetic powder over time can be suppressed. Furthermore, coating soft magnetic powder with an insulating oxide coating can improve its insulation properties. By improving the insulation properties of the soft magnetic powder, when applied to magnetic components, an insulating layer can be formed between the contacting soft magnetic powder particles. Therefore, losses caused by current flowing between the soft magnetic powder particles (interparticle eddy currents) can be suppressed, reducing the iron loss of the pressed powder core. Furthermore, in the insulating coated soft magnetic powder of the present invention, it is sufficient for the insulating coating oxide to coat at least a portion of the surface of the soft magnetic powder, but in order to prevent oxidation of the soft magnetic powder, it is preferable that the coating rate of the insulating coating oxide relative to the soft magnetic powder is higher.

[0020] Furthermore, the aforementioned insulating coating oxide preferably contains Si. By including Si, the surface stability of the aforementioned soft magnetic powder can be improved, thereby enhancing the insulation properties of the insulating coated soft magnetic powder. Furthermore, the aforementioned insulating coating oxide preferably further comprises an alkaline earth metal. Specifically, it preferably comprises at least one of Ca and Ba. By including Ca or Ba, the surface stability of the aforementioned soft magnetic powder can be improved, thereby enhancing the insulation properties of the insulating coating soft magnetic powder. Furthermore, the aforementioned insulating oxide coating may further contain Fe as an unavoidable component. By including Fe, the wettability between the surface of the soft magnetic powder and the insulating oxide coating is improved, making it easier to coat the surface of the soft magnetic powder more uniformly. In addition, when the insulating oxide coating is glassy, ​​it is preferably an alkaline earth silicate.

[0021] The 50% volumetric cumulative particle size (D50) of the insulating coated soft magnetic powder determined by the laser diffraction particle size distribution method of the present invention is 0.01 μm or more and 2.0 μm or less. The insulating coated soft magnetic powder of the present invention can also contribute to the high density of troweled magnetic cores. To achieve high density in troweled magnetic cores, the insulating coated soft magnetic powder of the present invention can be used alone or in combination with soft magnetic powders of other particle sizes. Furthermore, by using the D50 of the insulating coated soft magnetic powder of the present invention within this range, eddy current losses generated within the powder can be suppressed. In particular, iron losses in the high-frequency region are mainly caused by eddy current losses; therefore, by using the average particle size (D50) of the insulating coated soft magnetic powder of the present invention within this range, eddy current losses generated within the powder can be suppressed, which is related to the suppression of iron losses. Furthermore, if the average particle size (D 50) of the insulating coated soft magnetic powder of the present invention becomes smaller than 0.01 μm, the amount of the powder added when making the insulating coated soft magnetic powder into a pressed magnetic core will increase, and therefore it is preferable to be 0.01 μm or more.

[0022] Furthermore, the 90% volumetric cumulative particle size (D 90) obtained by the laser diffraction-based particle size distribution measurement method of the insulating coated soft magnetic powder of the present invention is preferably 0.1 μm to 3.5 μm. With a D 90 of 0.1 μm to 3.5 μm, when it is used together with large-particle-size soft magnetic powder to form a pressed powder core, the voids formed by the large-particle-size soft magnetic powder can be efficiently filled, thereby improving the magnetic properties of the resulting pressed powder core. Moreover, by using this range for the D 90 of the insulating coated soft magnetic powder of the present invention, eddy current losses generated within the powder can be suppressed. In particular, conventional methods have made it difficult to obtain insulating coated soft magnetic powders that are made from high-purity iron powder with small D50 and D90. However, by using the manufacturing method described later, it is possible to obtain insulating coated soft magnetic powders that are made from high-purity iron powder with D50 of 0.1 μm or more and D90 of 3.5 μm or less.

[0023] The insulating coated soft magnetic powder of the present invention is preferably spherical. By using a spherical insulating coated soft magnetic powder, the filling performance of the pressed magnetic core can be improved.

[0024] The oxygen content of the insulating coated soft magnetic powder of the present invention is 0.1 wt.% to 2.0 wt.% or less. Although the insulating coating of the insulating oxide is formed on the surface of the soft magnetic powder, the oxygen content of the insulating coated soft magnetic powder as a whole is 0.1 wt.% to 2.0 wt.% or less, meaning that an insulating coating can be formed on the surface of the soft magnetic powder with only a small amount of insulating oxide. This means that the increase in particle size of the insulating coated soft magnetic powder caused by the insulating oxide on the magnetic powder can be suppressed. Furthermore, compared with conventional soft magnetic powders, it is also considered that the oxidation of the soft magnetic powder itself and the diffusion of oxygen into the soft magnetic powder can be suppressed. Furthermore, the carbon content of the insulating coated soft magnetic powder of the present invention is 0 wt.% to 0.2 wt.%. By having a carbon content of 0 wt.% to 0.2 wt.%, the formation of a non-magnetic solid solution composed of carbon and iron can be suppressed, thereby suppressing the reduction of the magnetic properties of the insulating coated soft magnetic powder. Furthermore, the nitrogen content of the insulating coated soft magnetic powder of the present invention is 0 wt.% to 0.2 wt.%. By having a nitrogen content of 0 wt.% to 0.2 wt.%, the formation of a non-magnetic solid solution composed of nitrogen and iron can be suppressed, thereby suppressing the reduction of the magnetic properties of the insulating coated soft magnetic powder.

[0025] Therefore, the oxygen, carbon, and nitrogen content of the insulating coated soft magnetic powder of the present invention is as follows: oxygen: 0.1 wt.% to 2.0 wt.%, carbon: 0 wt.% to 0.2 wt.%, and nitrogen: 0 wt.% to 0.2 wt.%. When manufacturing insulating coated soft magnetic powder using conventional methods, oxygen, carbon, or nitrogen may enter the soft magnetic powder during the process of producing high-purity iron powder; or, after the manufacturing of the soft magnetic powder but before forming the insulating coating, the purity of iron in the soft magnetic powder decreases due to oxidation of the iron powder and diffusion of oxygen into the iron powder. In particular, small-particle-size iron powder has a larger specific surface area and is therefore more susceptible to oxidation, leading to a decrease in the purity of iron in conventional soft magnetic powders. If the purity of iron in the soft magnetic powder decreases, it becomes a cause of a decrease in the magnetic properties of the final insulating coated soft magnetic powder, and further a cause of a decrease in the magnetic properties of the pressed magnetic core. In contrast, the insulating coated soft magnetic powder of the present invention is produced by the method described later, thereby forming a coating layer of insulating oxide as an insulator simultaneously with the production of the soft magnetic powder. Therefore, the content of oxygen, carbon and nitrogen in the final insulating coated soft magnetic powder can be suppressed to: oxygen: 0.1 wt.% to 2.0 wt.%, carbon: 0 wt.% to 0.2 wt.%, and nitrogen: 0 wt.% to 0.2 wt.%.

[0026] Furthermore, the total content of oxygen, carbon, and nitrogen in the insulating coated soft magnetic powder of the present invention is between 0.1 wt.% and 2.0 wt.%. The insulating coated soft magnetic powder of the present invention is produced by the method described later, thereby enabling the formation of a coating layer of insulating oxide as an insulator simultaneously with the production of the soft magnetic powder. Therefore, the total content of oxygen, carbon, and nitrogen in the insulating coated soft magnetic powder of the present invention can be suppressed to between 0.1 wt.% and 2.0 wt.% relative to the total content of the insulating coated soft magnetic powder. By suppressing the total content of oxygen, carbon, and nitrogen in the insulating coated soft magnetic powder to between 0.1 wt.% and 2.0 wt.% relative to the total content of the insulating coated soft magnetic powder, the soft magnetic powder itself can maintain high iron purity while imparting insulation properties through the insulating oxide coating. Therefore, the reduction of the magnetic properties of the insulating coated soft magnetic powder is suppressed, which is related to the improvement of the magnetic properties of the pressed magnetic core.

[0027] Furthermore, depending on the application, it is also permissible to further coat the surface of the insulating coated soft magnetic powder of the present invention with an insulating material. The type of insulating material is not particularly limited, but examples include: inorganic oxides, organic materials, etc. The coating method is also not particularly limited, and commonly used methods can be used for coating.

[0028] Furthermore, the volume resistivity of the molded body formed by molding the insulating coated soft magnetic powder of the present invention under a pressure of 64 MPa is preferably 1.0 × 10⁵ Ωcm or higher. As mentioned above, the insulating coated soft magnetic powder of the present invention has a low oxygen content. Nevertheless, an insulating coating with high insulation properties is formed on the surface of the soft magnetic powder, resulting in a high volume resistivity, which is an indicator of the insulation properties of the insulating coated soft magnetic powder. By forming the molded body of the insulating coated soft magnetic powder under a pressure of 64 MPa with a volume resistivity of 1.0 × 10⁵ Ωcm or higher, the voltage withstand characteristics of the inductor parts can be improved when the insulating coated soft magnetic powder is used to make inductor parts. There is no particular limitation that the volume resistivity of the molded body formed by molding the insulating coated soft magnetic powder under a pressure of 64 MPa is 1.0 × 10⁵ Ωcm or higher, but it can be said to be sufficiently insulating if it is 1.0 × 10¹⁴ Ωcm or lower. The volume resistivity of a molded body formed by pressing insulating coated soft magnetic powder under a pressure of 64 MPa can be measured using a powder resistivity meter. For example, a powder resistivity meter (Mitsubishi Chemical Analysis Technology Co., Ltd.: Loresta GX MCP-T700 resistivity meter) can be used. Under a load of 64 MPa, the powder amount can be adjusted so that the thickness of the pressed powder (molded body) made of soft magnetic powder is 3 to 5 mm, and the powder resistivity (volume resistivity) can be measured using a powder resistivity meter.

[0029] The method for manufacturing insulating coated soft magnetic powder according to an embodiment of the present invention aims to prepare a powder as a starting material powder (hereinafter referred to as "raw material powder") by uniformly mixing a raw material containing iron and a raw material containing an insulating coating oxide forming component. The raw material containing iron is a salt such as nitrate, sulfate, chloride, ammonium salt, phosphate, carboxylate, metal alkoxide, or resin salt. The insulating coating oxide forming component includes the element that forms the insulating coating oxide of the coated soft magnetic powder. The raw material containing the insulating coating oxide forming component is a salt such as silicate, boric acid, phosphoric acid, various silicates, borates, phosphates, and various metal nitrates, sulfates, chlorides, ammonium salts, phosphates, carboxylate, metal alkoxides, or resin salts.

[0030] The method for preparing the raw material powder is not particularly limited, and methods such as spray calcination, flow calcination, spray pyrolysis, hydrothermal method, co-precipitation method, and solid-state method can be used. Alternatively, a raw material powder can be prepared by simply pulverizing and mixing raw materials containing iron components and raw materials containing insulating coating oxide forming components. The raw material powder is preferably mixed with the raw material containing iron and the raw material containing the insulating coating oxide forming component in such a way that the insulating coating oxide forming component, converted from an oxide, is 0.1 to 5.0 wt.% relative to the iron content. In other words, it is preferable to mix the raw material containing iron and the raw material containing the insulating coating oxide forming component in such a way that the oxide of the insulating coating oxide forming component in the raw material containing the insulating coating oxide forming component exists in the form of an oxide, relative to "the iron in the raw material containing iron," is 0.1 to 5.0 wt.%. By mixing in this equal ratio, an insulating film caused by the insulating coating oxide can be formed on the surface of the soft magnetic powder. Furthermore, it is preferable that the volume average particle size of the raw material powder is adjusted to 1.0 μm or less, more preferably 0.9 μm or less, and even more preferably 0.8 μm or less. Previously, it was difficult to thoroughly mix raw materials containing iron components and raw materials containing insulating coating oxide forming components in the form of powder at the aforementioned ratio. However, by mixing the raw material powder with a volume average particle size of 1.0 μm or less, the raw material powder can be thoroughly and uniformly mixed. The prepared raw material powder, along with the reducing agent and carrier gas, is supplied to the reaction vessel through a nozzle. While dispersed in the gas phase, it is heated to a temperature higher than the melting point of iron and the insulating coating oxide forming components, thereby obtaining an insulating coated soft magnetic powder. Furthermore, in the case of a composite oxide containing multiple oxides or a glassy substance, the melting point of the insulating coating oxide forming components refers to the melting point of the composite oxide or glass. At this time, the carrier gas system uses inert gases such as nitrogen and argon, or mixtures thereof. Due to the necessity of environmental control in the reaction vessel, reducing gases such as hydrogen, carbon monoxide, methane, and ammonia may also be used. There are no particular limitations on the nozzle; it can be any shape, including circular, polygonal, or slit-shaped nozzles; nozzles that narrow at the tip; nozzles that narrow halfway through and widen at the opening.

[0031] In this method, it can be assumed that each particle of raw material powder can yield one particle of insulating coated soft magnetic powder, and it is speculated that the following reaction will occur in the reaction vessel. The raw material powder, along with the reducing agent and carrier gas, is supplied to the reaction vessel through a nozzle. While dispersed in the gas phase, it is heated to a temperature higher than the melting points of iron and the insulating oxide-forming component, causing the raw material powder to melt individually within the reaction vessel. The insulating oxide-forming component is discharged from the molten raw material powder, forming a state where molten iron forms the core, surrounded by the molten insulating oxide-forming component. The molten material in the reaction vessel is then directly cooled, yielding soft magnetic powder and an insulating-coated soft magnetic powder with the insulating oxide coating its surface. Because iron is cooled from a molten state, it becomes high-purity iron powder. Furthermore, the molten metal containing the insulating oxide coating, when cooled from a state of molten metal coating iron, becomes a state where the surface of the iron powder is coated with an insulating oxide. In this way, this method can simultaneously form a coating layer of insulating oxide with the iron powder, thus suppressing the oxidation of the iron powder itself while forming an insulating coating layer of insulating oxide. Therefore, by using this method, it is possible to obtain soft magnetic powder with few impurities and an insulating coated soft magnetic powder with an insulating film formed by an insulating coating oxide with high insulation properties. In addition, iron powder with small particle size and high purity has very high activity in its uninsulated state, and there is a risk of calcination or combustion during recycling. However, if this method is used, the highly active iron powder can be recycled in an insulating coated state with an insulating coating oxide, thus also having the advantage of high safety.

[0032] The insulating coated soft magnetic powder obtained by this method, during the raw material powder preparation stage, can not only obtain the insulating coated soft magnetic powder of the present invention by adjusting the amount of insulating coating oxide forming component relative to the iron component, but also obtain an insulating coated soft magnetic powder with the amount of insulating film adjusted. Specifically, an insulating coated soft magnetic powder with an insulating coating oxide content of 0.1 to 20 wt.% relative to the soft magnetic powder can be obtained. In this case, it is also possible to obtain soft magnetic powder containing 99.0 wt.% or more of iron, and insulating coated soft magnetic powder, wherein the insulating coated soft magnetic powder is a soft magnetic powder whose surface is coated with an insulating oxide, and the 50% volumetric cumulative particle size (D50) of the insulating coated soft magnetic powder, as determined by laser diffraction particle size distribution method, is 0.01 μm or more and 2.0 μm or less. At this time, the oxygen content relative to the overall insulating coated soft magnetic powder varies depending on the amount of insulating oxide, but the respective carbon and nitrogen content relative to the overall insulating coated soft magnetic powder can be suppressed to low values ​​such as carbon: 0 wt.% or more and 0.2 wt.% or less, and nitrogen: 0 wt.% or more and 0.2 wt.% or less.

[0033] Furthermore, the insulating coated soft magnetic powder obtained by this method, during the raw material powder preparation stage, by adding raw materials containing iron and alloying components, can not only obtain the insulating coated soft magnetic powder of the present invention, but also an insulating coated soft magnetic powder alloyed with soft magnetic powder. Specifically, it is possible to obtain an insulating coated soft magnetic powder with at least a portion of the surface of an iron-based alloy soft magnetic powder in which the composition of the insulating coated oxide and the alloying component is generally 0.1 to 10 wt.% relative to the overall composition of the soft magnetic powder. For the insulating coated soft magnetic powder made from this iron-based alloy, the above method can also be used to obtain an insulating coated soft magnetic powder with adjusted amount of insulating coated oxide forming component. At this point, a soft magnetic powder of an iron-based alloy containing 90.0 wt.% or more iron, and an insulating-coated soft magnetic powder having at least a portion of its surface coated with an insulating oxide, can be obtained. An insulating-coated soft magnetic powder can be obtained where the 50% volumetric cumulative particle size (D50) determined by laser diffraction particle size distribution method is 0.01 μm to 2.0 μm or less, and the respective carbon and nitrogen contents relative to the total volume of the insulating-coated soft magnetic powder are: carbon: 0 wt.% to 0.2 wt.% and nitrogen: 0 wt.% to 0.2 wt.%; and the mass ratio of the insulating oxide to the soft magnetic powder is 0.1 to 20 wt.%. At this time, by adjusting the amount of insulating coating oxide, an insulating coated soft magnetic powder can also be obtained, wherein the oxygen content relative to the whole insulating coated soft magnetic powder is set to 0.1wt.% to 2.0wt.% and the total content of oxygen, carbon and nitrogen relative to the whole insulating coated soft magnetic powder is 0.1wt.% to 2.0wt.%.

[0034] The insulating coated soft magnetic powder and the method for manufacturing the insulating coated soft magnetic powder according to the embodiments of the present invention are configured as follows. [1] The insulating coated soft magnetic powder of the present invention is an insulating coated soft magnetic powder. It is an insulating coated soft magnetic powder whose surface is coated with an insulating coated oxide to cover at least a portion of a soft magnetic powder containing more than 99.0 wt.% iron. The 50% volumetric cumulative particle size (D50) of the aforementioned insulating coated soft magnetic powder, determined by laser diffraction particle size distribution measurement, is between 0.01 μm and 2.0 μm. The oxygen, carbon, and nitrogen content of the aforementioned insulating coated soft magnetic powder as a whole is: Oxygen: ≥0.1 wt.% to ≤2.0 wt.%; Carbon: ≥0 wt.% to ≤0.2 wt.%; Nitrogen: ≥0 wt.% to ≤0.2 wt.%; Furthermore, the total content of oxygen, carbon, and nitrogen in the aforementioned insulating coated soft magnetic powder is between 0.1 wt.% and 2.0 wt.%. [2] As described in [1] above, the insulating coated soft magnetic powder of the present invention is the aforementioned insulating coated oxide containing glass. [3] As described in [1] above, the insulating coated soft magnetic powder of the present invention is an oxide containing crystalline substances, which is the aforementioned insulating coated oxide. [4] As described in any of [1] to [3] above, the insulating coated soft magnetic powder of the embodiment of the present invention is a molded body formed by molding the aforementioned insulating coated soft magnetic powder under a pressure of 64 MPa, and the volume resistivity is 1.0 × 10 5 Ωcm or more and 1.0 × 10 14 Ωcm or less. [5] As described in any of [1] to [4] above, the insulating coated soft magnetic powder of the embodiment of the present invention has a 90% volume cumulative particle size (D 90) of 0.1 μm or more and 3.5 μm or less as determined by the laser diffraction scattering particle size distribution method of the aforementioned insulating coated soft magnetic powder. [6] As described in any of [1] to [5] above, the insulating coated soft magnetic powder of the embodiment of the present invention is the aforementioned insulating coated oxide containing Si. [7] As described in any of [1] to [6] above, the insulating coated soft magnetic powder of the embodiment of the present invention is the aforementioned insulating coated oxide containing Ca or Ba. [8] As described in any of [1] to [7] above, the insulating coated soft magnetic powder of the embodiment of the present invention is the aforementioned insulating coated oxide containing Fe. [9] As described in any of [2] and [4] to [8] above, the insulating coated soft magnetic powder of the embodiment of the present invention is an alkaline earth silicate containing glassy material in the aforementioned insulating coated oxide.

[10] The method for manufacturing insulating coated soft magnetic powder according to an embodiment of the present invention is a method for manufacturing insulating coated soft magnetic powder. It is a method for manufacturing the insulating coated soft magnetic powder as described above [1]. The process includes steps of preparing raw material powder containing iron and raw materials containing insulating oxide-forming components, and supplying the aforementioned raw material powder, along with a reducing agent and a carrier gas, into a reaction vessel through a nozzle for heating in the gas phase. The aforementioned raw material powder contains, relative to the aforementioned iron content, an insulating coating oxide forming component comprising 0.1 wt.% to 5.0 wt.% of the aforementioned oxide content. The aforementioned heating step involves heating at a temperature higher than the melting point of iron and the aforementioned insulating oxide-forming components.

[11] As described in

[10] above, the method for manufacturing insulating coated soft magnetic powder is an embodiment of the present invention. The volume average particle size of the above-mentioned raw material powder is less than 1.0 μm.

[12] The insulating coated soft magnetic powder of the present invention is an insulating coated soft magnetic powder. It is an insulating coated soft magnetic powder whose surface is coated with an insulating coated oxide to cover at least a portion of a soft magnetic powder containing more than 99.0 wt.% iron. The 50% volumetric cumulative particle size (D50) of the aforementioned insulating coated soft magnetic powder, determined by laser diffraction particle size distribution measurement, is between 0.01 μm and 2.0 μm. The carbon and nitrogen content of the aforementioned insulating coated soft magnetic powder as a whole is as follows: Carbon: ≥0 wt.% to ≤0.2 wt.%; Nitrogen: ≥0 wt.% to ≤0.2 wt.%; The content of the aforementioned insulating coating oxide relative to the aforementioned soft magnetic powder is more than 0.1 wt.% and less than 20 wt.%.

[13] The insulating coated soft magnetic powder of the present invention is an insulating coated soft magnetic powder. It is an insulating coated soft magnetic powder whose surface is coated with an insulating coated oxide to cover at least a portion of a soft magnetic powder containing more than 90.0 wt.% iron. The aforementioned soft magnetic powder comprises iron and alloying components in an amount of 0.1 wt.% to 10 wt.% relative to the total composition of the soft magnetic powder. The 50% volumetric cumulative particle size (D50) of the aforementioned insulating coated soft magnetic powder, determined by laser diffraction particle size distribution measurement, is between 0.01 μm and 2.0 μm. The carbon and nitrogen content of the aforementioned insulating coated soft magnetic powder as a whole is as follows: Carbon: ≥0 wt.% to ≤0.2 wt.%; Nitrogen: ≥0 wt.% to ≤0.2 wt.%; The content of the aforementioned insulating coating oxide relative to the aforementioned soft magnetic powder is more than 0.1 wt.% and less than 20 wt.%.

[14] As described in

[13] above, the insulating coated soft magnetic powder of the embodiment of the present invention is an insulating coated soft magnetic powder. The oxygen content of the aforementioned insulating coated soft magnetic powder is between 0.1 wt.% and 2.0 wt.%. Furthermore, the total content of oxygen, carbon, and nitrogen in the aforementioned insulating coated soft magnetic powder is between 0.1 wt.% and 2.0 wt.%.

[0035] (equivalent) It should be understood that the structures and / or methods described in this specification are shown by way of example, and many variations are possible; therefore, such specific examples or embodiments should not be considered as limiting. A particular procedure or method described in this specification may represent one of many processing methods. Thus, the various actions described and / or recorded can be performed in the order of description and / or recording, or may be omitted. Similarly, the order of the aforementioned methods can be changed. The subject of this disclosure includes all novel and non-obvious combinations and secondary combinations of the various methods, systems and configurations, and other features, functions, behaviors and / or properties disclosed in this specification, as well as all such equivalents. [Example]

[0036] The present invention will now be specifically described by way of examples and comparative examples, but the present invention is not limited thereto. [Preparation of Insulating Coated Soft Magnetic Powder] (Examples 1-10) The raw material solution was prepared using ferric nitrate nonahydrate, tetraethoxysilane (TEOS), barium nitrate, and calcium nitrate tetrahydrate. A raw material solution is prepared by dissolving ferric nitrate nonahydrate, tetraethoxysilane (TEOS), barium nitrate and calcium nitrate tetrahydrate in water to form SiO2, BaO and CaO respectively, with SiO2:BaO:CaO = 48:38:14 and the sum of SiO2, BaO and CaO relative to the iron in ferric nitrate nonahydrate being 1.5 wt.%. The raw material solution was spray-dried to obtain a mixed oxide powder. This mixed oxide powder was further pulverized using an air-jet mill to produce a raw material powder with a volume average particle size of approximately 0.8 μm. This raw material powder, along with a carrier gas at a flow rate of 200 L / min and a reducing agent at a flow rate of 30 g / min of monoethylene glycol, was sprayed into a reactor heated to 1600°C for heat treatment. After thorough cooling, the heat-treated powder was collected using a bag filter as an insulating coated soft magnetic powder. This step was performed in 10 batches, designated as Examples 1 to 10. The resulting insulating coated soft magnetic powder was analyzed as follows.

[0037] [ICP Measurement] 1.0 g of the insulating-coated soft magnetic powder from Examples 1 to 10 was heated at 90°C for 5 hours with a 25 wt.% NaOH aqueous solution, followed by washing with warm water to remove the insulating coating. The soft magnetic powder with the insulating coating removed was dissolved by heating with hydrochloric acid, appropriately diluted, and then quantitatively analyzed for each element using an ICP emission spectrometer (Shimadzu Corporation: ICPS-7510). The iron content in the soft magnetic powder was calculated based on the obtained data. The results are shown in Table 1.

[0038] [Oxygen / Carbon / Nitrogen Content Determination] The oxygen content of the insulating coated soft magnetic powders in Examples 1 to 10 was determined using an oxygen / nitrogen analyzer (manufactured by Horiba Manufacturing Co., Ltd.: EMGA). 10 mg of the insulating coated soft magnetic powder was taken from a combustion crucible, and the crucible was placed in the oxygen / nitrogen analyzer to determine the oxygen / nitrogen content. The oxygen and nitrogen contents calculated from the obtained data are shown in Table 1. The carbon content of the insulating coated soft magnetic powders of Examples 1 to 10 was determined using an instrument (manufactured by Horiba Manufacturing Co., Ltd.: EMIA). 0.3 g of the insulating coated soft magnetic powder was taken into a combustion crucible, which was then placed in the carbon analysis apparatus to determine the carbon content. The carbon content calculated from the obtained data is shown in Table 1. Furthermore, the carbon / nitrogen content of the insulating coated soft magnetic powder measured in this embodiment is treated as the amount of impurities contained in the soft magnetic powder. Based on these values, Table 1 shows the iron content of the insulating coated soft magnetic powder of each embodiment.

[0039] [Particle size distribution determination] The particle size distribution of the insulating coated soft magnetic powders of Examples 1 to 10 was measured. The measurement was performed using a laser particle size distribution measuring device (Horiba Manufacturing Co., Ltd.: LA-960). The obtained values ​​are shown in Table 1.

[0040] [Volume Resistivity] The volume resistivity of the molded body of the insulating coated soft magnetic powder was measured using a powder resistivity meter (Mitsubishi Chemical Analysis Technology Co., Ltd.: Loresta GX MCP-T700 resistivity meter). 5.0 g of the obtained soft magnetic powder was filled into the probe unit of the powder resistivity meter, and pressure was applied at room temperature (25°C). For a cylindrical powder body (molded body) with a diameter of 20 mm, the powder resistivity (volume resistivity) was measured at the time point when a load of 64 MPa was applied. The obtained values ​​are shown in Table 1.

[0041] (Comparative Example 1) For commercially available carbonyl iron powder, the iron content, particle size, oxygen content, carbon content, nitrogen content, and powder resistivity (volume resistivity) in the soft magnetic powder were measured in the same manner as in Examples 1-10. Carbonyl iron powder uses pentacarbonyl iron as raw material, and the processing temperature during iron powder manufacturing is not high; therefore, it is a soft magnetic powder with high carbon and nitrogen content.

[0042] (Comparative Example 2) 2.5 g of the aforementioned commercially available carbonyl iron powder was dispersed in a slurry made of 40 g of isopropanol, and 0.37 g of TEOS was added at a time. After adding TEOS, the mixture was stirred continuously for 5 min to allow the hydrolysis products of TEOS to react with the carbonyl iron powder. Next, 4.5 g of 28 wt.% ammonia water was added to the slurry after the addition of TEOS for 5 min at a rate of 0.1 g / min. After the addition of ammonia water was completed, the slurry was stirred and kept for 1 h to form an insulating oxide coating layer on the surface of the carbonyl iron powder. Then, the slurry was filtered using a pressure filtration device and vacuum dried at 120 °C for 3 h to obtain an insulating coated soft magnetic powder. The obtained insulating coated soft magnetic powder was subjected to particle size, oxygen content, carbon content, nitrogen content, and powder resistivity (volume resistivity) measurements, in the same manner as in Examples 1-10. Carbonyl iron powder uses pentacarbonyl iron as its raw material, and the processing temperature during iron powder manufacturing is not high. Therefore, it is a soft magnetic powder with a high carbon and nitrogen content. Consequently, when carbonyl iron powder is sol-gel coated, the resulting insulating coated soft magnetic powder has high insulation properties, but also a high carbon and nitrogen content. Furthermore, the oxygen content of the insulating coated soft magnetic powder is further increased due to the sol-gel coating process.

[0043] (Comparative Example 3) A raw material solution was prepared by adding / mixing ferric nitrate, TEOS, barium nitrate, calcium nitrate, and ethylene glycol as a reducing agent. The concentration of the metal component in the solution was set at 20 g / L, and the reducing agent was set at 20 wt.% relative to the total solution. This raw material solution was atomized into fine droplets using an ultrasonic nebulizer, and nitrogen gas was supplied as a carrier gas to a ceramic tube heated to 1550°C in an electric furnace. The droplets were heated through the heating zone, and after sufficient cooling, they were collected using a bag filter. The resulting insulating coated soft magnetic powder was subjected to particle size, oxygen content, carbon content, nitrogen content, and powder resistivity (volume resistivity) measurements, in the same manner as in Examples 1-10. The iron content in the soft magnetic powder was calculated, in the same manner as in Examples 1-10, by subtracting the elements and amounts forming the insulating oxide coating layer from the values ​​obtained by ICP emission spectroscopy analysis and carbon / nitrogen content measurement. The insulating coated soft magnetic powder obtained by spray pyrolysis has high insulation properties, but the raw material is a solution, so the resulting insulating coated soft magnetic powder has a high oxygen content.

[0044] [Table 1] Soft magnetic powder Insulation coating Insulating coated soft magnetic powder Iron content / wt.% Insulating coating oxide Constituent elements Particle size distribution Volume conversion Content Volume resistivity (64MPa) / Ω.cm D 50 / μm D 90 / μm oxygen / wt.% carbon / wt.% nitrogen / wt.% Example 1 99.3 Si, Ba, Ca 0.82 1.31 1.28 0.03 0.03 ≥1.0×10⁸ Example 2 99.3 Si, Ba, Ca 1.19 2.45 1.11 0.03 0.03 1.0×10⁶ Example 3 99.3 Si, Ba, Ca 0.91 1.55 1.65 0.04 0.03 2.3×10⁶ Example 4 99.3 Si, Ba, Ca 0.81 1.43 1.42 0.04 0.03 9.2×10⁶ Example 5 99.3 Si, Ba, Ca 0.77 1.32 1.27 0.04 0.03 1.8×10⁷ Example 6 99.3 Si, Ba, Ca 0.72 1.30 1.42 0.05 0.03 1.1×10⁵ Example 7 99.3 Si, Ba, Ca 0.67 1.19 1.41 0.05 0.03 4.2×10⁶ Example 8 99.2 Si, Ba, Ca 0.68 1.13 1.49 0.10 0.03 ≥1.0×10⁸ Example 9 99.2 Si, Ba, Ca 0.75 1.29 1.23 0.09 0.03 ≥1.0×10⁸ Example 10 99.2 Si, Ba, Ca 0.63 1.02 1.50 0.08 0.03 ≥1.0×10⁸ Comparative Example 1 97.5 - 1.37 2.31 0.79 0.95 0.65 2.4×10⁻¹ Comparative Example 2 97.5 Si 1.41 2.47 1.89 1.02 0.66 5.3×10⁵ Comparative Example 3 98.3 Si, Ba, Ca 0.71 1.11 3.20 0.05 0.03 4.0×10⁵

[0045] none

Claims

1. An insulating coated soft magnetic powder, comprising an insulating coated soft magnetic powder having at least a portion of its surface coated with an insulating coated oxide containing 99.0 wt.% or more iron. The 50% volumetric cumulative particle size (D50) of the insulating coated soft magnetic powder determined by laser diffraction particle size distribution method is 0.01 μm to 2.0 μm. The oxygen, carbon and nitrogen contents relative to the total oxygen content of the insulating coated soft magnetic powder are: oxygen: 0.1 wt.% to 2.0 wt.%. Carbon: 0 wt.% to 0.2 wt.%; Nitrogen: 0 wt.% to 0.2 wt.%; Furthermore, the total content of oxygen, carbon and nitrogen relative to the overall soft magnetic powder of the insulating coating is 0.1 wt.% to 2.0 wt.%.

2. The insulating coating soft magnetic powder as claimed in claim 1, wherein, The insulating oxide coating contains glass.

3. The insulating coating soft magnetic powder as described in claim 2, wherein, The insulating oxide contains glassy alkaline earth silicates.

4. The insulating coating soft magnetic powder as claimed in claim 1, wherein, The insulating coating oxide contains crystalline oxides.

5. The insulating coated soft magnetic powder of any one of claims 1 to 4, wherein, The volume resistivity of the molded body formed by molding the insulating coated soft magnetic powder at a pressure of 64 MPa is 1.0 × 10⁵ Ωcm or more and 1.0 × 10¹⁴ Ωcm or less.

6. The insulating coated soft magnetic powder of any one of claims 1 to 4, wherein, The 90% volumetric cumulative particle size (D90) of the insulating coated soft magnetic powder, determined by laser diffraction particle size distribution method, is above 0.1 μm and below 3.5 μm.

7. The insulating coated soft magnetic powder of any one of claims 1 to 4, wherein, The insulating oxide coating contains Si.

8. The insulating coated soft magnetic powder of any one of claims 1 to 4, wherein, The insulating oxide coating contains Ca or Ba.

9. The insulating coated soft magnetic powder of any one of claims 1 to 4, wherein, The insulating oxide coating contains Fe.