Flat metal powder based on iron (FE) and method for producing same

Abstract

Provided are a flat metal powder based on iron (Fe) having excellent powder properties and excellent magnetic properties and a method for producing the flat metal powder based on iron (Fe). This flat metal powder based on iron (Fe) includes flat metal particles including at least iron (Fe) as a magnetic metal. The flat metal particles each have, provided to the surface, an insulating coat layer comprising an inorganic oxide as a main component. The flat metal powder has an average particle diameter of 0.2-3 μm, an average aspect ratio of 2-15, and a particle diameter CV value (coefficient of variation), as obtained in accordance with equation (1), of 25% or less.

Description

Iron (Fe)-based flat metal powder and its manufacturing method

[0001] The present invention relates to an iron (Fe)-based flat metal powder and a method for producing the same.

[0002] Soft magnetic materials are used in magnetic components such as inductors and magnetic sheets for noise suppression in various electronic devices. Iron-nickel alloys known as permalloys are soft magnetic materials with high magnetic permeability, and materials such as 78 permalloy (permalloy A) and 45 permalloy are known. Of these, 78 permalloy is an iron-nickel alloy with a nickel content of approximately 78.5% by mass and is characterized by high magnetic permeability. 45 permalloy is an iron-nickel alloy with a nickel content of 45% by mass and is characterized by a high saturation magnetic flux density despite a slightly low magnetic permeability. In addition to these high-permeability iron-nickel alloys (permalloys), an iron-cobalt alloy known as permendur is also known. Permendur is an iron-cobalt alloy with a cobalt content of approximately 50% by mass and is characterized by a high saturation magnetic flux density. Soft magnetic materials such as permalloy and permendur are used according to their magnetic properties and applications.

[0003] In recent years, mobile devices such as laptops and smartphones have rapidly become smaller and more powerful. Therefore, soft magnetic metal powders used in magnetic components and magnetic sheets are required to have not only smaller particle sizes but also improved magnetic properties. Specifically, high saturation magnetic flux density and high magnetic permeability (especially in the high-frequency range) are required.

[0004] As an effort to improve the magnetic properties (saturation magnetic flux density, magnetic permeability, etc.) of soft magnetic metal powder, Patent Documents 1 to 3 propose soft magnetic flat metal powders with insulating coatings. The technologies proposed here involve pulverizing and flattening spherical soft magnetic metal powder raw materials using a media agitation mill, followed by coating with an inorganic material, or forming an insulating coating such as an oxide film at temperatures of approximately 500 to 900°C. The insulating coating formed on the surface of the soft magnetic flat metal particles is intended to improve interparticle insulation, suppress eddy currents, and increase magnetic permeability at high frequencies. However, these methods flatten large soft magnetic metal powders with an average particle size of 20 μm or more produced by atomization, and therefore do not address the need for smaller particle size (miniaturization).

[0005] Known methods for producing fine soft magnetic metal powder with an average particle size of several microns or less include dry methods such as a gas-phase reduction method in which a metal halide in a gas phase is reduced with hydrogen, and wet methods in which a metal salt is reduced in a solution with a reducing agent.

[0006] As a document disclosing such a technique, for example, Patent Document 4 describes that Ni-Fe alloy powder used as a material for noise filters, choke coils, inductors, etc. is produced by a vapor phase reduction method with an average particle size of 0.1 to 1 μm (paragraphs

[0001] ,

[0012] and

[0014] of Patent Document 4). ２ and FeCl ３ The method discloses that the mixture is heated, and the vaporized chloride is brought into contact with hydrogen gas to cause a reduction reaction, thereby producing a Ni—Fe alloy fine powder having an average particle size of 0.23 μm (Patent Document 4, paragraph

[0016] ).

[0007] Patent Document 5 describes an Fe-Ni alloy powder used as a material for electronic components such as choke coils and inductors, in which oxides of Fe and Ni are reduced in a reducing gas to produce an alloy powder having an average particle size of 0.1 to 5 μm (claim 1 of Patent Document 5).

[0008] On the other hand, it has been proposed to produce finer nickel-iron alloy powders using wet processes. For example, Patent Document 6 discloses a method for producing nickel-iron alloy nanoparticles, which comprises adding a reducing agent such as hydrazine to an aqueous solution containing a nickel salt and an iron salt, and simultaneously reducing the nickel ions and iron ions contained in the aqueous solution to produce nickel-iron alloy nanoparticles (claims 1 to 6 of Patent Document 6). This production method is said to enable efficient production of nickel-iron alloy nanoparticles with an average primary particle size of 200 nm or less, which are suitable as a filler for imparting magnetic properties, on an industrial scale at low production cost (paragraph

[0015] of Patent Document 6).

[0009] Patent Document 7 discloses a method for producing an iron-nickel alloy powder by crystallizing an iron-nickel alloy powder or an iron-nickel-cobalt alloy powder by a reduction reaction in a reaction solution containing an iron salt, a nickel salt, and optionally a cobalt salt, a nucleating agent, a complexing agent, an alkali hydroxide, hydrazine (a reducing agent), and water (claims 1 and 7 of Patent Document 7). This production method is said to produce alloy powder with an average particle size of 0.10 μm to 0.60 μm and a narrow particle size distribution, which can be used for various electronic components such as noise filters, choke coils, inductors, and radio wave absorbers (paragraphs

[0161] and

[0162] of Patent Document 7).

[0010] JP 2006-179901 A JP 2007-214425 A JP 2020-61530 A JP 2003-193160 A JP 2012-197474 A JP 2008-024961 A WO2022 / 080487 A

[0011] Although soft magnetic flat metal powders and methods for producing them have been proposed, these are primarily aimed at large particle size metal powders with particle sizes of 20 μm or more. Fine metal powders with particle sizes of 0.1 to several μm and methods for producing them have also been disclosed, but fine flat metal powders in which the fine metal powders are uniformly flattened and methods for producing them have not been clarified.

[0012] The present inventors have conducted research in light of the above-described conventional situation. As a result, they have found that forming an insulating coating layer mainly composed of an inorganic oxide on the surface of fine iron (Fe)-based metal powder particles with a narrow particle size distribution, followed by mechanical pulverization using a pulverization medium to flatten the particles, can promote uniform flattening while preventing particle coalescence and coarsening. They have also found that the iron-based flat metal powder obtained by this method is fine and has a narrow particle size distribution, and therefore has excellent powder properties and magnetic properties.

[0013] The present invention was completed based on such findings, and an object of the present invention is to provide an iron-based flat metal powder having excellent powder properties and magnetic properties, and a method for producing the same.

[0014] The present invention encompasses the following aspects (a) to (m). In this specification, the expression "to" includes both the numerical values ​​of the two ends. That is, "X to Y" is synonymous with "X or more and Y or less." In addition, in this specification, any combination of suitable aspects can be adopted as long as technical consistency can be achieved. For example, one of the suitable numerical ranges can be combined with the other.

[0015] (a) An iron (Fe)-based flat metal powder having flat metal particles containing at least iron (Fe) as a magnetic metal, wherein the flat metal particles have an insulating coating layer on their surfaces containing an inorganic oxide as a main component, and the flat metal powder has an average particle size of 0.2 μm or more and 3 μm or less, an average aspect ratio of 2 or more and 15 or less, and a particle size CV value (coefficient of variation) calculated according to the following formula (1) is 25% or less.

[0016] (b) The iron (Fe)-based flat metal powder of (a) above, wherein the iron (Fe) content of the flat metal powder is 30 mol% or more and 100 mol% or less.

[0017] (c) The iron (Fe)-based flat metal powder of (a) or (b) above, wherein the flat metal powder further contains at least one of nickel (Ni) and cobalt (Co) as a magnetic metal.

[0018] (d) The flat metal powder is an iron (Fe)-based flat metal powder of (c) above, in which the amount of iron (Fe) is 30 mol% or more and less than 100 mol%, and the total amount of nickel (Ni) and cobalt (Co) is more than 0 mol% and 70 mol% or less.

[0019] (e) The insulating coating layer is made of silicon dioxide (SiO ２ The iron (Fe)-based flat metal powder according to any one of (a) to (d) above, containing as an inorganic oxide.

[0020] (f) Any of the iron (Fe)-based flat metal powders (a) to (e) above, wherein the saturation magnetic flux density of the flat metal powder is 1.0 T (tesla) or more.

[0021] (g) A method for producing iron (Fe)-based flat metal powder, the method comprising the following steps: a step of preparing iron (Fe)-based non-flat metal powder having non-flat metal particles containing at least iron (Fe) as a magnetic metal, an average particle size of 0.1 μm or more and 3 μm or less, and a particle size CV value (coefficient of variation) calculated according to the following formula (2) of 25% or less; a step of applying an insulating coating treatment to the non-flat metal powder to form an insulating coating layer containing inorganic oxides as its main component on the surface of the non-flat metal particles; and a step of applying a flattening treatment to the non-flat metal powder that has been subjected to the insulating coating treatment to flatten the non-flat metal particles having the insulating coating layer, wherein the flattening treatment is a mechanical crushing treatment using a crushing medium.

[0022] (h) The manufacturing method of (g) above, wherein the amount of iron (Fe) in the flat metal powder is 30 mol% or more and 100 mol% or less.

[0023] (i) The manufacturing method of (g) or (h) above, wherein the flat metal powder further contains at least one of nickel (Ni) and cobalt (Co) as a magnetic metal.

[0024] (j) The manufacturing method of (i) above, wherein the flat metal powder has an iron (Fe) content of 30 mol% or more but less than 100 mol%, and a total amount of nickel (Ni) and cobalt (Co) of more than 0 mol% but not more than 70 mol%.

[0025] (k) Any of the manufacturing methods (g) to (j) above, wherein the insulating coating treatment is a treatment to form an insulating coating layer containing an inorganic oxide as a main component by hydrolysis and dehydration condensation polymerization of an alkoxide compound.

[0026] (l) The alkoxide compound contains silicon alkoxide (alkyl silicate), and the insulating coating layer contains silicon dioxide (SiO ２ ) as an inorganic oxide.

[0027] (m) The manufacturing method according to any one of (g) to (l) above, wherein the mechanical pulverization treatment is a treatment using at least one pulverization device selected from the group consisting of a paint shaker, a bead mill, an attritor, and a planetary mill.

[0028] According to the present invention, there are provided iron-based flat metal powders having excellent powder properties and magnetic properties, and a method for producing the same.

[0029] 1 is a schematic diagram showing the particle shape of the flat metal powder of this embodiment (top view of the plate surface (flat surface) (a), cross-sectional view perpendicular to the plate surface (flat surface) (b)). FIG. 2 is a process diagram used to explain the method for manufacturing flat metal powder. FIG. 3 shows an SEM image of metal powder (Example 1) having an insulating coating layer (before flattening treatment (a), after flattening treatment (b)). FIG. 4 shows an SEM image of metal powder (Comparative Example 1) not having an insulating coating layer (before flattening treatment (a), after flattening treatment (b)).

[0030] Specific embodiments of the present invention (hereinafter referred to as "present embodiments") are described below. However, the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention. Furthermore, in this specification, any combination of preferred aspects can be adopted as long as technical consistency can be achieved. For example, one preferred numerical range and another preferred numerical range can be combined arbitrarily.

[0031] <<1. Iron-based flat metal powder>> The iron (Fe)-based flat metal powder of this embodiment has flat metal particles. The flat metal particles contain at least iron (Fe) as a magnetic metal and further have an insulating coating layer on the surface containing an inorganic oxide as a main component. The flat metal powder also has an average particle size of 0.2 μm or more and 3 μm or less, an average aspect ratio of 2 or more and 15 or less, and a particle size CV value (coefficient of variation) calculated according to the following formula (1) of 25% or less.

[0032]

[0033] The iron (Fe)-based flat metal powder of this embodiment (hereinafter sometimes simply referred to as "flat metal powder") has flat metal particles. That is, it mainly contains flat metal particles. Flat metal particles are metal particles having a flat shape in which the thickness dimension is smaller than the particle size. The shape of a flat metal particle is represented by the major axis, minor axis, and thickness, as shown schematically in Figures 1(a) and 1(b). Figure 1(a) is a top view showing the flat surface of a flat metal particle, and Figure 1(b) is a cross-sectional view showing a particle cross section perpendicular to the flat surface. The major axis is the longest dimension on the flat surface of the flat metal particle, and the minor axis is the shortest dimension on the flat surface. The particle size of a flat metal particle is calculated as the average value of the major axis and minor axis. The thickness is the particle dimension along the direction perpendicular to the flat surface.

[0034] The flat metal powder may contain particles other than flat metal particles, such as spherical particles, acicular particles, or irregularly shaped particles. However, in order to maximize the effects of the flat metal particles, a higher proportion of flat metal particles is preferable. The proportion of flat metal particles may be, for example, 30% by mass or more, 50% by mass or more, or 70% by mass or more.

[0035] The flat metal powder and the flat metal particles contained therein contain at least iron (Fe), a magnetic metal. The amount of iron contained in the flat metal powder is not limited. The amount of iron may be 30 mol% or more and 100 mol% or less, or 50 mol% or more and 90 mol% or less. The flat metal powder may further contain at least one of nickel (Ni) and cobalt (Co) as a magnetic metal. When the flat metal powder contains nickel or cobalt, the amount of iron may be 30 mol% or more and less than 100 mol%, and the total amount of nickel and cobalt may be more than 0 mol% and 70 mol% or less. However, the total amount of magnetic metals (iron, nickel, and cobalt) is 100 mol% or less. Because the flat metal powder contains magnetic metals such as iron, it has a high saturation magnetic flux density and excellent magnetic properties. In this specification, magnetic metal refers to a metal that exhibits ferromagnetism (ferromagnetic metal) and is a general term for Fe, Ni, and Co. Furthermore, non-magnetic metal refers to a metal other than ferromagnetic metals.

[0036] The flat metal powder may contain additional components other than magnetic metals (Fe, Ni, Co). Examples of such additional components include non-magnetic metals such as copper (Cu), chromium (Cr), and aluminum (Al), or semi-metals such as silicon (Si) and boron (B). However, to maximize the effects of the magnetic metals, it is preferable to keep the content of additional components other than magnetic metals to a minimum. The content of components other than magnetic metals may be 10% by mass or less, 5% by mass or less, 1% by mass or less, or even 0% by mass.

[0037] In addition, the flat metal powder may contain impurities (unavoidable impurities) that are inevitably mixed in during production. Such inevitable impurities include oxygen (O), carbon (C), chlorine (Cl), sulfur (S), and alkaline components (Na, K, etc.). Because inevitable impurities may cause deterioration of the properties of the flat metal powder, it is preferable to minimize their amount. Among the inevitable impurities, the oxygen (O) contained in the oxide film formed on the surface of the flat metal powder is preferably 5% by mass or less, more preferably 3% by mass or less. On the other hand, carbon (C), chlorine (Cl), sulfur (S), and alkaline components (Na, K, etc.) are each preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. The flat metal powder may have a composition containing a magnetic metal, with the remainder consisting of inevitable impurities.

[0038] The flat metal powder may or may not be an alloy powder. That is, if the flat metal powder contains magnetic metals other than iron (Ni, Co), non-magnetic metals (Cu, Cr, Al, etc.), semi-metals (Si, B, etc.), and / or non-metals, the flat metal powder may be an alloy powder. On the other hand, if the flat metal powder contains only iron, the flat metal powder is composed of a single metal. In this specification, the term "alloy" is a concept that includes crystals such as solid solutions and eutectics, and intermetallic compounds.

[0039] The flat metal powder of this embodiment is characterized by the size of its constituent particles. Specifically, the average particle size of the flat metal powder is 0.2 μm or more and 3 μm or less. Here, the average particle size is determined by averaging the particle sizes of the flat metal particles contained in the flat metal powder on a number basis. By appropriately increasing the average particle size, it is possible to suppress deterioration of magnetic properties due to surface oxidation and a decrease in coercivity due to an increase in surface area. Furthermore, by appropriately decreasing the average particle size, it is possible to reduce eddy current loss, which is a problem when the flat metal powder is used in applications such as inductors, thereby enabling the miniaturization of magnetic components. The average particle size is not limited, but is more preferably 0.3 μm or more and 2 μm or less, and even more preferably 0.3 μm or more and 1 μm or less.

[0040] The average particle size is determined by microscopic observation of the flat metal powder. Specifically, the flat metal powder is observed using a microscope such as an electron microscope to obtain a microscopic image. In the microscopic image, particles whose major and minor axes of the flat surface can be measured, as shown in Figure 1 (a), are focused on, and their major and minor axes are determined, and their average value is calculated as the particle size. The same procedure is performed for multiple particles to determine the particle size distribution on a number basis, and the average value is calculated to determine the average particle size of the flat metal powder.

[0041] The flat metal powder of this embodiment is also characterized by the shape of the particles contained therein. Specifically, the average aspect ratio of the flat metal powder is 2 or more and 15 or less. Here, the average aspect ratio is an index representing the degree of flatness of the particles contained in the flat metal powder, and is calculated according to the following formula (3). In the following formula (3), the average thickness is calculated by averaging the thickness of each particle on a number basis for the multiple metal particles that make up the flat metal powder.

[0042]

[0043] By limiting the average aspect ratio to the above range (2 or more and 15 or less), it is possible to improve the magnetic properties of the flat metal powder, such as the magnetic permeability. On the other hand, if the average aspect ratio is less than 2, the above effect becomes insufficient. Furthermore, if the average aspect ratio exceeds 15, there is a problem that the flattening treatment is too excessive, resulting in destruction of the insulating coating layer on the surface of the flat metal particles. The average aspect ratio is preferably 2 or more and 15 or less, and more preferably 3 or more and 10 or less.

[0044] The average aspect ratio is determined by microscopic observation of the flat metal powder. Specifically, an observation sample is prepared by embedding the flat metal powder in a resin such as epoxy resin. At this time, it is desirable to apply force to the flat metal powder to orient each particle contained in the flat metal powder. Next, the observation sample is observed using a microscope such as an electron microscope to obtain a microscopic image. In the microscopic image, particles whose particle thickness (particle dimension perpendicular to the flat surface) can be measured, as shown in Figure 1(b), are focused on and their thickness is determined. The same procedure is performed for multiple particles, and the thickness of each particle is averaged on a number basis to determine the average thickness of the flat metal powder. The average particle size and average thickness of the flat metal powder are then used to determine the average aspect ratio according to the above formula (3).

[0045] The flat metal powder of this embodiment is also characterized by the degree of particle size variation of the particles that make it up. Specifically, the particle size CV value (coefficient of variation) of the flat metal powder is 25% or less. Here, the particle size CV value is an index of particle size variation, and the smaller the value, the narrower (sharper) the particle size distribution. By keeping the particle size CV value small, excessively coarse particles and excessively fine particles are reduced. Therefore, when the flat metal powder is applied to inductors, etc., it is possible to prevent an increase in eddy current loss while maintaining excellent magnetic properties. The particle size CV value is more preferably 20% or less, and even more preferably 15% or less. The lower limit of the particle size CV value is not particularly limited. For example, it can be 1% or more, or 5% or more.

[0046] The particle size CV value is determined by microscopic observation of the flat metal powder. Specifically, the particle size distribution on a number basis is determined for multiple particles whose major and minor axes of the flat surfaces can be measured using the method described above. The average value (average particle size) and standard deviation are then determined from this particle size distribution, and the particle size CV value is calculated according to the following formula (1).

[0047]

[0048] In the flat metal powder of this embodiment, the flat metal particles contained therein have an insulating coating layer on their surface, the insulating coating layer containing inorganic oxides as its main component. By providing an insulating coating layer made of inorganic oxides with high electrical resistance on the particle surface, the electrical insulation between particles is improved. This makes it possible to reduce eddy currents flowing between particles and the losses caused by them. Furthermore, combined with the effects of the manufacturing method, it is possible to effectively prevent the inclusion of coarse flat particles.

[0049] The material of the insulating coating layer is not limited as long as it is an inorganic oxide. However, silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), and titanium dioxide (TiO ２ ) is preferable. In particular, silicon dioxide (SiO ２ Therefore, it is preferable that the insulating coating layer contains silicon dioxide as an inorganic oxide.

[0050] The thickness of the insulating coating layer is not limited to a specific value, as it depends on the required level of insulation. In other words, a thickness of 1 nm to 30 nm is preferable, 2 nm to 25 nm is more preferable, and 3 nm to 20 nm is even more preferable. If the thickness is excessively thick, the insulating properties will saturate, while the content of soft magnetic components will decrease, resulting in deterioration of magnetic properties such as saturation magnetic flux density. If the thickness is within the above range, the insulating function of the insulating coating layer can be fully exhibited while maintaining properties such as magnetic properties.

[0051] The compact resistivity of the flat metal powder is 10 ６ Preferably, Ω·cm or more, ７ Ω·cm or more is more preferable. By providing an insulating coating layer, the insulating properties of the metal powder are significantly improved. For example, the compact resistivity (applied pressure: 64 MPa) of iron-nickel alloy powder without an insulating coating layer is usually 0.1 Ω·cm or less. In contrast, when silicon dioxide (SiO ２), the green resistivity is increased to 10 ６ The resistivity of the compact is improved to Ω cm or more. Metal powder with improved insulation can reduce eddy currents and the losses associated with them. The compact resistivity is the resistivity measured for a flat metal powder compact obtained by press molding under an applied pressure of 64 MPa.

[0052] The saturation magnetic flux density of the flat metal powder is preferably 1.0 T (tesla) or more, more preferably 1.5 T (tesla) or more, even more preferably 1.8 T or more, and particularly preferably 2.0 T or more. Increasing the saturation magnetic flux density of the flat metal powder can improve the performance of magnetic components. There is no particular upper limit to the saturation magnetic flux density. For example, it can be set to 3.0 T or less. A low coercive force of the flat metal powder is preferable, but if the average particle diameter is reduced to, for example, about 0.2 μm, the coercive force increases due to the increased surface area. Therefore, it is desirable to appropriately set the average particle diameter of the flat metal powder, taking into account the balance with the coercive force.

[0053] The iron (Fe)-based flat metal powder of this embodiment is composed of fine flat particles with an insulating coating layer mainly composed of an inorganic oxide formed on the particle surface, and is characterized by a narrow particle size distribution. Therefore, it is suitable for applications such as magnetic parts such as inductors and magnetic sheets for noise suppression in various electronic devices in electronic devices, which are rapidly becoming smaller and more powerful.

[0054] <<Method for Manufacturing Iron-Based Flat Metal Powder>> This embodiment also relates to a method for manufacturing iron (Fe)-based flat metal powder. This iron-based flat metal powder contains at least iron as a magnetic metal. This manufacturing method includes the following steps: preparing iron (Fe)-based flat metal powder having flat metal particles containing at least iron (Fe) as a magnetic metal, an average particle size of 0.1 μm to 3 μm, and a particle size CV value (coefficient of variation) calculated according to the following formula (2) of 25% or less (raw material powder preparation step); applying an insulating coating treatment to the flat metal powder to form an insulating coating layer containing inorganic oxides as a main component on the surface of the flat metal particles (insulating coating step); and applying a flattening treatment to the insulating coated flat metal powder to flatten the flat metal particles having the insulating coating layer (flattening step). The flattening treatment is a mechanical grinding treatment using a grinding medium.

[0055]

[0056] The method for producing flat metal powder of this embodiment includes at least a raw material powder preparation process, an insulation coating process, and a flattening process. If necessary, a process for performing a crushing process (crushing process) may be provided after the insulation coating process or the flattening process. Furthermore, a process for performing a high-temperature heat treatment (high-temperature heat treatment process) may be provided after the flattening process. An example of the process in the production method of this embodiment is shown schematically in FIG. 2. While FIG. 2 shows the crushing process and high-temperature heat treatment, these processes may be provided as needed and are not essential. Furthermore, when the crushing process and / or high-temperature heat treatment are performed, there are no restrictions on the order in which these processes are performed. Details of each process are described below.

[0057] <Raw material powder preparation process> In the raw material powder preparation process, iron (Fe)-based non-flattened metal powder is prepared as raw material powder to be subjected to the subsequent insulating coating process and flattening process. The non-flattened metal powder has non-flattened metal particles containing at least iron (Fe) as a magnetic metal. That is, it mainly contains non-flattened metal particles. Furthermore, the non-flattened metal powder has an average particle size of 0.1 μm or more and 3 μm or less, and a particle size CV value (coefficient of variation) calculated according to the above formula (2) is 25% or less.

[0058] The composition of the raw material powder (unflattened metal powder) is not particularly limited as long as it satisfies the above-mentioned particle size and particle size distribution. The composition may be appropriately selected depending on the application, taking into consideration magnetic properties such as saturation magnetic flux density, coercive force, and magnetic permeability. Examples of compositions include, but are not limited to, Fe-based, Fe-Ni-based, Fe-Co-based, Fe-Ni-Co-based, Fe-Si-based, Fe-Al-Si-based, Fe-Cr-Si-based, and Fe-B-Si-based.

[0059] The raw material powder satisfying the above-described particle size and particle size distribution may be prepared by a dry method such as a gas phase reduction method or a wet method in which a metal salt is reduced in a solution. Alternatively, a commercially available product may be used. As an example of raw material powder production, the production of alloy powder (iron-nickel alloy powder, iron-nickel-cobalt alloy powder, etc.) by a wet method disclosed in Patent Document 7 will be described below.

[0060] In the manufacturing method disclosed in Patent Document 7, a crystallized powder containing a magnetic metal is crystallized by a reduction reaction in a reaction solution containing a magnetic metal source (iron salt, nickel salt, and optionally a cobalt salt), a nucleating agent, a complexing agent, a pH adjuster (alkali hydroxide), a reducing agent (hydrazine), and water, to produce an alloy powder (iron-nickel alloy powder, iron-nickel-cobalt alloy powder, etc.). However, the raw material powder of this embodiment is not limited to iron-nickel alloy powder or iron-nickel-cobalt alloy powder. Needless to say, it may also include alloy powders that do not contain nickel, metal powders that do not contain nickel, or the like.

[0061] (a) Magnetic Metal Source The magnetic metal source (iron salt, nickel salt, and optionally cobalt salt) is a raw material for the magnetic metal component contained in the alloy powder, and is not particularly limited as long as it is water-soluble. Examples of water-soluble iron salts include iron chloride, iron sulfate, iron nitrate, and mixtures thereof, each containing divalent and / or trivalent iron ions, and preferably ferrous chloride (FeCl ２ ), ferrous sulfate (FeSO ４ ), and ferrous nitrate (Fe(NO ３ ) ２ The water-soluble nickel salt is preferably at least one selected from the group consisting of nickel chloride (NiCl ２ ), nickel sulfate (NiSO ４ ), and nickel nitrate (Ni(NO３ ) ２ The water-soluble cobalt salt is preferably at least one selected from the group consisting of cobalt chloride (CoCl ２ ), cobalt sulfate (CoSO ４ ), and cobalt nitrate (Co(NO ３ ) ２ ) is at least one selected from the group consisting of

[0062] (b) Nucleating Agent: The nucleating agent is a water-soluble salt of a metal nobler than nickel. This nucleating agent (a water-soluble salt of a metal nobler than nickel) is preferentially reduced in the reaction solution during crystallization to generate initial nuclei, which then promote the precipitation of the crystallized powder. Therefore, by adjusting the amount of nucleating agent added, it is possible to control the particle size of the crystallized powder. For example, by increasing the amount of nucleating agent added, the crystallized powder can be made finer.

[0063] The nucleating agent is not particularly limited as long as it is a water-soluble salt of a metal more noble than nickel, but is preferably at least one selected from the group consisting of copper salts, palladium salts, and platinum salts. Copper (Cu), palladium (Pd), and platinum (Pt) are particularly effective as nucleating agents due to their strong noble nature and low ionization tendency. Examples of water-soluble copper salts include copper sulfate, and examples of water-soluble palladium salts include sodium palladium(II) chloride, ammonium palladium(II) chloride, palladium(II) nitrate, and palladium(II) sulfate. Water-soluble palladium salts are particularly suitable as nucleating agents, and their use allows for even finer control of the particle size of the crystallized powder (alloy powder).

[0064] (c) Complexing Agent: The complexing agent is at least one selected from the group consisting of hydroxycarboxylic acids, salts of hydroxycarboxylic acids, and derivatives of hydroxycarboxylic acids, and functions as a reduction reaction accelerator, a spheroidization accelerator, and a surface smoothing agent during crystallization. The use of this complexing agent (e.g., hydroxycarboxylic acid) allows the magnetic metal component to dissolve in large amounts in the reaction solution as complex ions (e.g., Fe complex ions, Ni complex ions, Co complex ions). The presence of such complex ions increases the reduction reaction rate, suppresses localized uneven distribution of the magnetic metal component, and enables the reaction system to be homogenized. The complexing agent also has the effect of changing the complex stability balance of multiple magnetic metal ions in the reaction solution. Therefore, the presence of the complexing agent favorably shifts the balance between the nucleation rate and the particle growth rate during the magnetic metal reduction reaction, resulting in improved powder properties (particle size, particle size distribution, sphericity, and particle surface properties) of the resulting alloy powder. A suitable complexing agent is tartaric acid ((CH(OH)COOH) ２ ) and citric acid (C(OH)(CH ２ COOH) ２ COOH) or salts thereof.

[0065] (d) Reducing Agent The reducing agent is hydrazine (N ２ H ４ , molecular weight: 32.05). Hydrazine has a strong reducing power, especially in a strong alkaline solution, and therefore has the effect of reducing magnetic metal ions and complex ions in the reaction solution during crystallization. Hydrazine also has the advantage that by-products from the reduction reaction are unlikely to be generated in the reaction solution and are unlikely to be mixed into the crystallized powder. For this reason, for example, a boron hydride compound (NaBH ４ This can prevent problems with impurities such as boron (B) being mixed into the alloy powder, which tend to occur when using other alloys.

[0066] Hydrazine includes anhydrous hydrazine and hydrazine hydrate (N ２ H ４ ・H ２ 0, molecular weight: 50.06), either of which may be used.

[0067] (e) pH Adjuster The pH adjuster is an alkali hydroxide, which has the effect of strengthening the reduction reaction of hydrazine, which is a reducing agent. The higher the pH of the reaction solution, the stronger the reducing power of hydrazine. Therefore, using an alkali hydroxide as a pH adjuster promotes the reduction reaction of magnetic metal ions and complex ions in the reaction solution and the resulting precipitation of crystallized powder. The type of alkali hydroxide is not particularly limited. However, in terms of availability and price, it is preferable that the pH adjuster contains at least one selected from sodium hydroxide (NaOH) and potassium hydroxide (KOH).

[0068] (f) Other Additives If necessary, the reaction liquid may further contain an amine compound which is at least one of alkyleneamine and alkyleneamine derivative.

[0069] The amine compound has the effect of promoting the reduction reaction in the subsequent crystallization step. That is, the amine compound functions as a complexing agent and acts to reduce the magnetic metal ions (Fe ２＋ , Ni ２＋ , Co ２＋ It has the function of complexing Fe, Ni, Co, etc., to form complex ions (Fe complex ions, Ni complex ions, Co complex ions, etc.). It is believed that the presence of complex ions in the reaction solution further promotes the reduction reaction.

[0070] Furthermore, amine compounds have the effect of suppressing the self-decomposition of hydrazine, which is a reducing agent. That is, when a crystallized powder of magnetic metals precipitates in the reaction solution, nickel (Ni) among these magnetic metals (Fe, Ni, Co) is particularly likely to act as a catalyst. This can lead to the decomposition of hydrazine. This is called the self-decomposition of hydrazine. This decomposition reaction occurs as shown in the following formula (4): ２ H ４ ) is nitrogen (N ２ ) and ammonia (NH ３ This type of self-decomposition is undesirable because it reduces the total amount of hydrazine, which is the reducing agent.

[0071]

[0072] Adding an amine compound such as an alkyleneamine or an alkyleneamine derivative to the reaction solution makes it possible to more effectively suppress the self-decomposition of hydrazine (reducing agent).

[0073] A specific example of an alkyleneamine is ethylenediamine (abbreviation: EDA) (H ２ NC ２ H ４ NH ２ ), diethylenetriamine (abbreviation: DETA) (H ２ NC ２ H ４ NHC ２ H ４ NH ２ ), triethylenetetramine (abbreviation: TETA) (H ２ N (C ２ H ４ NH) ２ C ２ H ４ NH ２ ), tetraethylenepentamine (abbreviation: TEPA) (H ２ N (C ２ H ４ NH) ３ C ２ H ４ NH ２ ), pentaethylenehexamine (abbreviation: PEHA) (H ２ N (C ２ H ４ NH) ４ C ２ H ４ NH ２ ), propylenediamine (also known as 1,2-diaminopropane, 1,2-propanediamine) (abbreviation: PDA) (CH ３ CH(NH ２ ) CH ２ NH ２ ) and one or more selected from the group consisting of. Specific examples of alkyleneamine derivatives include tris(2-aminoethyl)amine (abbreviation: TAEA) (N(C ２ H ４ NH ２ ) ３ ), N-(2-aminoethyl)ethanolamine (also known as 2-(2-aminoethylamino)ethanol (abbreviation: AEEA) (H ２ NC２ H ４ NHC ２ H ４ OH), N-(2-aminoethyl)propanolamine (also known as 2-(2-aminoethylamino)propanol (abbreviated as AEPA) (H ２ NC ２ H ４ NHC ３ H ６ OH), L (or D, DL)-2,3-diaminopropionic acid (also known as 3-amino-L (or D, DL)-alanine) (abbreviated as DAPA) (H ２ NCH ２ CH(NH)COOH), ethylenediamine-N,N'-diacetic acid (also known as ethylene-N,N'-diglycine) (abbreviation: EDDA) (HOOCCH ２ NHC ２ H ４ NHCH ２ COOH), 1,2-cyclohexanediamine (also known as 1,2-diaminocyclohexane) (abbreviation: CHDA) (H ２ NC ６ H １０ NH ２ These alkyleneamines and alkyleneamine derivatives are water-soluble, and among them, ethylenediamine having the following structural formula (A) and diethylenetriamine having the following structural formula (B) are preferred because they have a relatively strong inhibitory effect on the self-decomposition of hydrazine, and are easily available and inexpensive.

[0074]

[0075]

[0076] In the crystallization process, a reaction solution containing the above-mentioned (a) magnetic metal source, (b) nucleating agent, (c) complexing agent, (d) reducing agent, (e) pH adjuster, and optionally (f) other additives (such as amine compounds), and water is prepared, and a magnetic metal-containing crystallized powder is crystallized in this reaction solution by a reduction reaction. To reduce the amount of impurities in the resulting alloy powder, it is preferable to use high-purity water for the preparation of the reaction solution. Specifically, pure water with a conductivity of 1 μS / cm or less or ultrapure water with a conductivity of 0.06 μS / cm or less is preferred, with inexpensive and readily available pure water being particularly preferred. The term "crystallization reaction" here refers to a reaction that occurs during the crystallization process. While the term primarily refers to a reduction reaction by hydrazine (such as the formula (7) described below), it also includes the self-decomposition reaction of hydrazine (the formula (4) described above). Therefore, the term "crystallization reaction" is used in a broader sense than a reduction reaction.

[0077] Specific procedures for preparing a reaction solution for crystallization include, for example, heating at least one of a plurality of solutions, such as a metal salt raw material solution containing (a) a magnetic metal source, (b) a nucleating agent, and (c) a complexing agent, or a reducing agent solution containing (d) a reducing agent and (e) a pH adjuster, followed by mixing these solutions by agitation or other methods to prepare a reaction solution. The reaction solution is heated and stirred in a reaction vessel while maintaining a predetermined temperature, and the crystallization reaction proceeds under these conditions. Stirring and mixing can be performed using a stirring device equipped with stirring blades or the like. Heating can be performed using a conventional method, such as placing the reaction vessel (reaction vessel) in a water bath, or using a steam-jacketed reaction vessel or a heater-equipped reaction vessel. The reaction vessel (reaction vessel) and the stirring blades used to stir the reaction solution must be made of inert materials that minimize nucleation on their surfaces when in contact with the reaction solution, in order to avoid interfering with the function of the nucleating agent. Excellent strength and thermal conductivity are also required. To satisfy these requirements, for example, a metal container (such as a Teflon (registered trademark) coated stainless steel container) or a stirring blade (such as a Teflon (registered trademark) coated stainless steel stirring blade) coated with a fluororesin (such as PTFE or PFA) is suitable.

[0078] When an amine compound is added, for example, the amine compound may be added to at least one of the metal salt raw material solution and the reducing agent solution, or the amine compound may be added after mixing these solutions.

[0079] When the reaction solution is prepared, a reduction reaction occurs in this reaction solution. That is, in the presence of a pH adjuster (alkali hydroxide) and a nucleating agent (a salt of a metal nobler than nickel), ions and complex ions of the magnetic metal source are reduced by a reducing agent (hydrazine), thereby forming a crystallized powder containing the magnetic metal.

[0080] The reduction reaction in the crystallization step will be explained using a reaction formula. The reduction reaction of iron (Fe), nickel (Ni), and cobalt (Co) is a two-electron reaction as shown in the following formula (5). On the other hand, the reduction reaction of hydrazine (N ２ H ４ The reaction of (1) is a four-electron reaction as shown in the following formula (6).

[0081]

[0082] Magnetic metal sulfates (FeSO ４ , NiSO ４ , CoSO ４ When Fe, Ni, Co are used as the magnetic metal source and sodium hydroxide (NaOH) is used as the pH adjuster, as shown in the following formula (7), first, the sulfate of the magnetic metal and sodium hydroxide undergo a neutralization reaction to produce hydroxide ((Fe, Ni, Co)(OH) ２ Then, this hydroxide ((Fe, Ni, Co)(OH) ２ These magnetic metals (Fe, Ni, Co, etc.) are reduced by the action of a reducing agent (hydrazine) to form a crystallized powder. To reduce 1 mole of magnetic metal (Fe, Ni, Co), 0.5 moles of reducing agent (hydrazine) are required. As can be seen from the above formula (6), the higher the alkalinity (pH), the stronger the reducing power of hydrazine. Therefore, sodium hydroxide, which is used as a pH adjuster, also has the effect of accelerating the reduction reaction by hydrazine.

[0083]

[0084] In the reduction reaction of the above formula (7), the reduction of the ions (or hydroxides) of each magnetic metal element (Fe, Ni, Co) proceeds to some extent simultaneously due to co-reduction. Here, co-reduction refers to the phenomenon in which the reduction reaction of one element occurs concomitantly with the reduction reaction of another element. However, as mentioned above, iron ions (or iron hydroxide) are less easily reduced than nickel ions (or nickel hydroxide) and cobalt ions (or cobalt hydroxide). Therefore, toward the end of the crystallization reaction, nickel ions (or nickel hydroxide) and cobalt ions (or cobalt hydroxide) tend to be consumed and disappear in the reduction reaction in the reaction solution, while iron ions (or iron hydroxide) tend to remain. This tendency is particularly pronounced when the iron content is high (e.g., when the iron content of the alloy powder exceeds 60 mol%). When this phenomenon occurs, not only does it take a long time to complete the crystallization reaction (reduction reaction), but also a gradient structure with a non-uniform composition tends to form within the particles. When a gradient structure is formed, the particle center of the resulting alloy powder has a nickel-rich or cobalt-rich composition, and the composition becomes iron-rich closer to the particle surface.

[0085] To promote the progress of the reduction reaction during crystallization, the temperature of the reaction solution (reaction temperature) is preferably 60°C or higher and 99°C or lower, more preferably 70°C or higher and 95°C or lower, and even more preferably 80°C or higher and 90°C or lower. If possible, one of the metal salt raw material solution and the reducing agent solution is preheated (e.g., heated to 70-95°C), while the other solution is not preheated (e.g., kept at 25°C). These solutions are then added and mixed, and the reaction solution is heated to a predetermined temperature (e.g., 55°C) slightly lower than the reaction temperature immediately after preparation, and thereafter the reaction solution is continuously heated and maintained at the reaction temperature. This is because the initial nuclei are generated immediately after preparation of the reaction solution. Lowering the temperature of the reaction solution at this time allows nuclei to be generated more uniformly, resulting in a crystallized powder with a sharper particle size distribution.

[0086] The crystallized powder can be recovered from the reaction solution after crystallization has been completed by a known method. For example, a separation device such as a Denver filter, a filter press, a centrifuge, or a decanter can be used to separate the crystallized powder from the reaction solution. The crystallized powder can be washed during or after solid-liquid separation. The washing can be carried out using a washing liquid. High-purity pure water with a conductivity of 1 μS / cm or less can be used as the washing liquid. The washed crystallized powder can be dried. The drying can be carried out using a general-purpose drying device such as an atmospheric dryer, a hot air dryer, an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer at a temperature of 40° C. to 150° C., preferably 50° C. to 120° C.

[0087] Note that crystallized powders dried in a sealed container of an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer have particle surfaces that are not highly oxidized. Therefore, if the dried crystallized powder is immediately removed from the dryer into the atmosphere, the particle surfaces will rapidly oxidize, and the heat generated by the oxidation reaction may cause the crystallized powder to burn. Therefore, it is desirable to subject crystallized powders that are not highly oxidized after drying to a gradual oxidation treatment, which involves forming a thin oxide film on the particle surfaces to stabilize them. Crystallized powders that have been subjected to the gradual oxidation treatment are resistant to oxidation and stable, so there is no risk of heat generation or combustion even when left in the atmosphere. A specific procedure for the gradual oxidation treatment is to lower the temperature of the crystallized powder that has been heated and dried in a sealed container to about room temperature to 40°C, and then supply a gas with a low oxygen concentration into the sealed container to slowly oxidize the particle surfaces of the crystallized powder. By slowly oxidizing the particle surfaces, a thin oxide film is formed on the particle surfaces. The sealed container can be an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer. Examples of gases with a low oxygen concentration include nitrogen gas and argon gas containing 0.1 to 2% by volume of oxygen.

[0088] According to the method (wet method) disclosed in Patent Document 7, it is possible to obtain alloy powder having an average particle size of about 0.1 μm to 0.6 μm and a narrow particle size distribution with a coefficient of variation (CV value) of about 25% or less, and this alloy powder can be used as raw material powder (unflattened metal powder).

[0089] <Insulation Coating Process> In the insulation coating process, the prepared non-flat metal powder (raw material powder) is subjected to an insulation coating process to form an insulation coating layer containing an inorganic oxide as a primary component on the surface of the non-flat metal particles. By providing an insulation coating layer made of an inorganic oxide with high electrical resistance on the particle surface, electrical insulation between particles is improved. Furthermore, in the flattening process described below, if multiple particles contained in the metal powder are flattened while still agglomerated and combined, coarse flat particles may be formed. By providing an insulation coating layer, the formation of such coarse flat particles can be prevented. The oxide coating formed on the particle surface of the alloy powder by the aforementioned gradual oxidation process is extremely thin, and therefore has little effect on electrical insulation and suppression of coarse flat particles. In contrast, applying an insulation coating process to the metal powder can fully reduce eddy currents flowing between particles and suppress the formation of coarse flat particles.

[0090] The insulating coating process can be performed, for example, by the following procedure. First, a non-flat metal powder (raw material powder) is dispersed in a mixed solvent containing water and an organic solvent, and an alkoxide compound is added to and mixed with the mixed solvent to prepare a slurry. Next, the alkoxide compound is hydrolyzed and subjected to dehydration condensation polymerization in the resulting slurry to form an insulating coating layer on the particle surfaces of the non-flat metal powder. Note that the hydrolysis reaction of the alkoxide compound in a mixed solvent containing water and an organic solvent proceeds very slowly if left untreated, so a small amount of a hydrolysis catalyst such as an acid or base (alkali) is generally added to promote the reaction. In this embodiment, it is also preferable to add a base catalyst (alkali catalyst).

[0091] Thereafter, a cake of the non-flat metal powder on which the insulating coating layer has been formed is recovered from the slurry by solid-liquid separation, and the recovered cake is dried to recover the non-flat metal powder (insulation-coated metal powder) on which the insulating coating layer made of a high-resistivity inorganic oxide has been formed. Furthermore, the separated and dried insulation-coated metal powder may be subjected to a heat treatment, if necessary.

[0092] As the alkoxide compound used to prepare the slurry in the insulating coating treatment, a compound capable of forming an inorganic oxide by hydrolysis and dehydration polycondensation is selected. Specifically, a compound having as its main component at least one selected from the group consisting of silicon alkoxide (alkyl silicate), aluminum alkoxide (alkyl aluminate), zirconium alkoxide (alkyl zirconate), and titanium alkoxide (alkyl titanate) is preferred, and among these, a compound having as its main component silicon alkoxide (alkyl silicate) is particularly preferred. Therefore, the alkoxide compound contains silicon alkoxide (alkyl silicate), and the insulating coating layer contains silicon dioxide (SiO ２ It is preferable that the alkoxide compound contains, as an inorganic oxide, a small amount of a component (e.g., boron alkoxide) that is incorporated into the insulating coating layer by hydrolysis or the like when the alkoxide compound is hydrolyzed and subjected to dehydration polycondensation to form the insulating coating layer may be added to the alkoxide compound, if necessary.

[0093] Specific examples of silicon alkoxides (alkyl silicates) include tetramethoxysilane (also known as tetramethyl orthosilicate, silicon tetramethoxide) (abbreviation: TMOS) (Si(OCH ３ ) ４ ), tetraethoxysilane (also known as tetraethyl orthosilicate, silicon tetraethoxide) (abbreviation: TEOS) (Si(OC ２ H ５ ) ４ ), tetrapropoxysilane (also known as tetrapropyl orthosilicate, silicon tetrapropoxide) (Si(OC ３ H ７ ) ４ , tetrabutoxysilane (also known as tetrabutyl orthosilicate and silicon tetrabutoxide) (Si(OC ４ H ９ ) ４and the like. Alternatively, alkoxides in which the alkoxyl group of these alkoxides has been substituted with another alkoxyl group may be used, or commercially available alkyl silicates as silicate oligomers that have already been polymerized to a tetramer or pentamer (for example, Erusilicate 40 (trade name), Erusilicate 48 (trade name), Methylsilicate 51 (trade name), etc., manufactured by Colcoat Co., Ltd.) may be used. Among these, tetraethoxysilane (TEOS) is preferred because it is less harmful, easily available, and inexpensive.

[0094] Specific examples of aluminum alkoxides (alkylaluminates) include aluminum trimethoxide (Al(OCH ３ ) ３ ), aluminum triethoxide (Al(OC ２ H ５ ) ３ ), aluminum triisopropoxide (Al(O-iso-C ３ H ７ ) ３ ), aluminum tri-n-butoxide (Al(O-n-C ４ H ９ ) ３ ), aluminum tri-sec-butoxide (Al(O-s-C ４ H ９ ) ３ ), and aluminum tri-tert-butoxide (Al(Ot-C ４ H ９ ) ３ ) and the like.

[0095] Specific examples of zirconium alkoxides (alkyl zirconates) include zirconium tetraethoxide (Zr(OC ２ H ５ ) ４ ), zirconium tetra-n-propoxide (Zr(O-n-C ３ H ７ ) ４ ), zirconium tetraisopropoxide (Zr(O-iso-C ３ H ７ ) ４), zirconium tetra-n-butoxide (Zr(O-n-C ４ H ９ ) ４ ), zirconium tetra-tert-butoxide (Zr(O-t-C ４ H ９ ) ４ ), and zirconium tetraisobutoxide (Zr(O-iso-C ４ H ９ ) ４ ) and the like.

[0096] Specific examples of titanium alkoxides (alkyl titanates) include titanium tetramethoxide (Ti(OCH ３ ) ４ ), titanium tetraethoxide (Ti(OC ２ H ５ ) ４ ), titanium tetraisopropoxide (Ti(O-iso-C ３ H ７ ) ４ ), titanium tetraisobutoxide (Ti(O-iso-C ４ H ９ ) ４ ), titanium tetra-n-butoxide (Ti(O-n-C ４ H ９ ) ４ ), titanium tetra-tert-butoxide (Ti(O-t-C ４ H ９ ) ４ ), and titanium tetra-sec-butoxide (Ti(O-s-C ４ H ９ ) ４ ) and the like.

[0097] Other alkoxide compounds include boron trimethoxide (B(OCH ３ ) ３ ), borontriethoxide (B(OC ２ H ５ ) ３ ), boron tri-tert-butoxide (B(O-t-C ４ H ９ ) ３and the like.

[0098] The organic solvent used to prepare the slurry in the insulating coating process is preferably one that can form a mixed solvent with water and that dries easily. That is, it is preferable that the solvent has high compatibility with water and a relatively low boiling point (approximately 60°C to 90°C). In addition, it is preferable that the solvent is highly safe, easy to handle, readily available, and inexpensive. Considering these factors, denatured alcohol, whose main component is ethyl alcohol, is preferable.

[0099] The hydrolysis reaction and dehydration condensation polymerization reaction in the insulating coating treatment were carried out using silicon alkoxide (Si(OR) ４ , R: alkyl group) will be explained using a reaction formula.

[0100] In the hydrolysis reaction, ammonia (NH ３ In the presence of a base catalyst (alkali catalyst) such as OH, silicon atoms (Si) react with nucleophilic hydroxy ions (OH) as shown in the following formula (8): － Upon direct attack from the silicon atom, one of the alkoxy groups (-OR) is first hydrolyzed. This reduces the charge on the silicon atom, and the nucleophilic hydroxyl ion (OH － As a result, all four alkoxy groups (-OR) are hydrolyzed and converted into silanol groups (Si-OH) as shown in the following formula (9). In this way, when a base catalyst (alkali catalyst) is used, all alkoxy groups (-OR) in the hydrolyzed silicon alkoxide molecule are hydrolyzed, so the completely hydrolyzed molecule (Si(OH) ４ ) and completely unhydrolyzed molecules (Si(OR) ４ ) coexist in the slurry.

[0101]

[0102] On the other hand, nitric acid (HNO ３ In the presence of an acid catalyst such as , protons (H ＋) by protonation of the alkoxy group (-OR), the silicon atom (Si) becomes water (H ２ Therefore, first one of the alkoxy groups (-OR) is hydrolyzed and converted into a silanol group (Si-OH). Although the details are omitted here, when this happens, the charge on the silicon atom and the charge on the oxygen atom (O) decrease, so the proton (H ＋ ) are less susceptible to attack. Therefore, the next hydrolysis does not occur immediately, and the alkoxy groups (-OR) of other unhydrolyzed silicon alkoxide molecules are more susceptible to hydrolysis. In this way, when an acid catalyst is used, the hydrolysis of the alkoxy groups (-OR) proceeds evenly in all silicon alkoxide molecules, as shown in the following formula (11). Therefore, there are no completely hydrolyzed molecules or molecules that are not hydrolyzed at all, and the molecules that are evenly hydrolyzed (Si(OH) Ｘ (OR) ４－Ｘ ; 0<x<4) occurs in the slurry.

[0103]

[0104] The dehydration polycondensation reaction is a reaction in which the formation of siloxane bonds (Si—O—Si) progresses due to the dehydration polycondensation reaction of silanol groups (Si—OH) between hydrolyzed silicon alkoxide molecules, as shown in the following formula (12). When this dehydration polycondensation reaction progresses to completion, silicon dioxide (SiO ２ ) is generated.

[0105]

[0106] In summary, when the hydrolysis and dehydration polycondensation of silicon alkoxide are completed, silicon dioxide (SiO ２ ) and alcohol. For example, tetraethoxysilane (TEOS: Si(OR) ４ , R:C ２ H ５ ) is used, silicon dioxide (SiO ２ ) and ethyl alcohol (C ２ H ５ OH) is produced.

[0107]

[0108] The above formula (14) is valid regardless of whether a base catalyst (alkali catalyst) or an acid catalyst is used as long as silicon alkoxide is hydrolyzed. However, silicon dioxide (SiO ２ The morphology of the resulting polyisocyanate is greatly affected by the state of hydrolysis by the above-mentioned hydrolysis catalyst.

[0109] Silicon alkoxide molecules (Si(OH)) homogeneously hydrolyzed by acid catalyst Ｘ (OR) ４－Ｘ ; 0<x<4), unhydrolyzed alkoxy groups (—OR) exist within the molecule. Therefore, as intermolecular dehydration condensation polymerization of silanol groups (Si—OH) progresses, hydrolysis polymers polymerized into linear or branched linear shapes are produced. When this occurs in the slurry during the insulating coating treatment, hydrolysis polymers of silicon alkoxide are produced on the particle surfaces of the metal powder, which consist of iron oxide (FeO), nickel oxide (NiO), or cobalt oxide (CoO). However, because these polymerize into linear or branched linear shapes, they are difficult to densify in the slurry solvent, making it difficult to form a dense insulating coating layer.

[0110] On the other hand, when a base catalyst (alkali catalyst) is used, the completely hydrolyzed molecule (Si(OH) ４ ) are present. Therefore, when the dehydration condensation polymerization of silanol groups (Si-OH) between molecules progresses, dense hydrolysis polymers that have been polymerized into a block are produced. Therefore, even in the solvent of the slurry used in the insulating coating treatment, dense hydrolysis polymers of silicon alkoxide are produced on the particle surfaces of the metal powder particles made of iron oxide (FeO), nickel oxide (NiO), or cobalt oxide (CoO), and as a result, a dense insulating coating layer can be formed. Note that when a base catalyst (alkali catalyst) is used, completely unhydrolyzed molecules (Si(OR) ４However, as will be described later, unhydrolyzed molecules and particulate silicon alkoxide hydrolysis polymers (silica sol) with very small molecular weights that remain in the slurry without being consumed in the insulating coating process are removed from the system along with the filtrate during filtration and cleaning in the insulating coating process. Therefore, they do not affect the insulating coating process.

[0111] For the above reasons, the hydrolysis of the alkoxide compound in the insulating coating treatment is preferably carried out using a base catalyst (alkali catalyst) rather than an acid catalyst. In this respect, the preferred catalyst differs from that used when coating is performed by applying a solvent to a substrate. That is, when used as a binder in a coating liquid that is applied to a substrate and the solvent is dried, rather than coating the particle surface in a solvent, linear or branched linear polymers produced by the acid catalyst described above are preferred.

[0112] With regard to the timing of hydrolysis of the alkoxide compound in the insulating coating process, we have previously described a mode in which the metal powder and alkoxide compound are homogeneously mixed in a slurry and then hydrolyzed using a hydrolysis catalyst. However, this embodiment is not limited to this timing of hydrolysis. For example, it is possible to prepare an inorganic oxide sol (silica sol in the case of silicon alkoxide) by pre-hydrolyzing the alkoxide compound using a hydrolysis catalyst, and then mix this inorganic oxide sol with the metal powder to form a slurry. If the average molecular weight of the inorganic oxide sol is small, approximately 500 to 5,000, the timing of hydrolysis of the alkoxide compound has almost no effect. This is because the iron oxide (FeO), nickel oxide (NiO), or cobalt oxide (CoO) on the metal powder surface bonds with the hydrolysis groups of the inorganic oxide sol (silanol groups (Si—OH) in the case of silicon alkoxide), covering the metal powder particle surfaces with small metal oxide sol particles, which then polymerizes among the sol particles.

[0113] In the insulating coating process, from the viewpoint of forming a uniform insulating coating layer, it is preferable to subject a slurry containing metal powder (unflattened metal powder), water, an organic solvent, an alkoxide compound, and a hydrolysis catalyst to agitation using a stirring blade of a stirrer or agitation by rotating a container using a dedicated roller. The processing time and temperature of the insulating coating process vary depending on the type of alkoxide compound used and the required thickness of the insulating coating layer. For example, methoxide compounds generally have a higher hydrolysis rate than ethoxide compounds. Therefore, the processing time and temperature need only be set appropriately and are not particularly limited. For example, the processing time may be several hours to one week, and the processing temperature may be room temperature to 60°C. At a high processing temperature of approximately 40°C to 60°C, the processing speed can be increased to several times that at room temperature.

[0114] The metal powder on which the insulating coating layer is formed by hydrolysis and dehydration polycondensation of the alkoxide compound is recovered as a cake-like metal powder by solid-liquid separation. Solid-liquid separation can be performed using a known separation device such as a Denver filter, filter press, centrifuge, or decanter. If necessary, the metal powder can be washed during solid-liquid separation. For washing, a cleaning solution such as water, an organic solvent such as a relatively low-boiling alcohol, or a mixture thereof can be used. As mentioned above, if there is any alkoxide compound or its hydrolyzed polymer (unhydrolyzed molecules or inorganic oxide sol with a small molecular weight) remaining in the slurry without being consumed by the insulating coating, these are discharged and removed from the system together with the filtrate and washing waste liquid during solid-liquid separation and washing.

[0115] The cake-like metal powder obtained after solid-liquid separation is dried and, if necessary, heated to recover a metal powder (insulation-coated metal powder) bearing an insulating coating layer made of a high-resistance inorganic oxide. The drying method is not particularly limited as long as excessive oxidation during drying can be suppressed. However, it is preferable to use a drying device such as an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer. Drying may be carried out at a temperature of, for example, 40°C or higher and 150°C or lower. The higher the drying temperature, the more the dehydration condensation polymerization of the alkoxide hydrolysis polymer constituting the insulating coating layer progresses, resulting in a harder, denser, and more insulating inorganic oxide. If further improvement is desired, a heat treatment at above 150°C and up to 450°C may be performed in an inert gas atmosphere, a reducing gas atmosphere, or a vacuum. Since the insulating coating layer has already been formed, a gradual oxidation treatment is generally not required after drying.

[0116] <Flattening Process> In the flattening process, the non-flat metal powder that has been subjected to an insulating coating process is subjected to a flattening process to flatten the non-flat metal particles having an insulating coating layer. Flat metal powder is obtained by the flattening process. The flattening process is a mechanical pulverization process using a grinding medium. The mechanical pulverization process (flattening process) processes the particles into a flat shape while preventing particle coalescence and coarsening, thereby imparting shape anisotropy to the particles. Examples of mechanical pulverization processes using a grinding medium include, but are not limited to, processes using at least one grinding device consisting of a paint shaker, a bead mill, an attritor, and a planetary mill.

[0117] The specific procedure for the flattening process is to move a slurry made by mixing water, an organic solvent, or a mixture of these with unflattened metal powder (insulation-coated metal powder) on which an insulating coating layer has been formed, together with beads or balls as grinding media at high speed. During this process, the kinetic energy of the grinding media is transmitted to the insulation-coated metal powder, causing the powder to flatten.

[0118] Preferred materials for the grinding media include glass such as quartz, alumina, and ceramics such as zirconia. Among these, zirconia, which has a high specific gravity of approximately 6 and excellent wear resistance, is preferred, and partially stabilized zirconia such as yttria-stabilized zirconia (YSZ) is particularly preferred. The size of the grinding media depends on the particle size and hardness of the insulation-coated metal powder, its concentration in the slurry (slurry concentration), the grinding processing device, and other factors, but a diameter of 0.05 mm or more and 0.5 mm or less is preferred, and a diameter of 0.1 mm or more and 0.3 mm or less is more preferred. If the diameter is less than 0.05 mm, the kinetic energy of the grinding media is too small, making flattening difficult to proceed, and handling and separation of the grinding media from the slurry are also difficult. Furthermore, if the diameter exceeds 0.5 mm, the kinetic energy of the grinding media is too large, and the number of grinding media is reduced. Therefore, kinetic energy is transferred more locally to the insulation-coated metal powder, resulting in uneven flattening, with some particles being overly flattened and others being insufficiently flattened.

[0119] The slurry concentration, depending on the average particle size of the insulation-coated metal powder, is preferably 15% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 50% by mass or less. If the slurry concentration is less than 15% by mass, not only will the amount of flattened metal powder obtained decrease, resulting in lower productivity, but the number of particles in the insulation-coated metal powder will also decrease. Therefore, the kinetic energy of the grinding medium is locally concentrated on some metal particles, making it more likely that excessively flattened particles will result. Furthermore, if the slurry concentration exceeds 60% by mass, the specific gravity of the slurry increases, reducing the difference in specific gravity between the slurry and the grinding medium. Therefore, the kinetic energy of the grinding medium, which is proportional to the difference in specific gravity between the slurry and the grinding medium, decreases, making flattening less likely to proceed. Furthermore, particularly when the average particle size of the insulation-coated metal powder is small, the increased viscosity of the slurry reduces fluidity, making the flattening process itself difficult.

[0120] After the flattening treatment, the grinding media are separated from the slurry containing the flat metal powder using a mesh or centrifugal force, and the separated and recovered slurry is subjected to solid-liquid separation to recover the treated product. The cake-like treated product obtained by solid-liquid separation is dried and, if necessary, heated to finally become flat metal powder. For solid-liquid separation, known separation devices such as a Denver filter, filter press, centrifuge, or decanter may be used. Furthermore, for drying and heating, it is preferable to use a dryer or heater that can be used in an inert gas atmosphere, a reducing gas atmosphere, or a vacuum atmosphere.

[0121] In the manufacturing method of this embodiment, additional processes such as a high-temperature heat treatment process and a crushing process, which will be described below, may be performed after the flattening process. The crushing process may be performed after the insulation coating process. That is, the insulation-coated iron-based metal powder may be subjected to the crushing process.

[0122] <High-Temperature Heat Treatment Step> If necessary, a high-temperature heat treatment step may be performed after the flattening step, in which the flat metal powder is subjected to high-temperature heat treatment. In this step, the recovered flat metal powder may be dried and then subjected to high-temperature heat treatment. Alternatively, the recovered flat metal powder may be subjected to high-temperature heat treatment directly without drying. The high-temperature heat treatment may be performed in an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere at a temperature greater than 150°C and less than 400°C, preferably greater than 200°C and less than 350°C. High-temperature heat treatment can promote the diffusion of heterogeneous elements, such as Fe, Ni, and Co, within the Fe—Ni—Co alloy flat particles, thereby improving the compositional uniformity within the particles. It can also alleviate the strain within the particles caused by the flattening process, improving magnetic properties such as coercivity.

[0123] <Crushing Process> If necessary, a crushing process may be performed on the insulation-coated metal powder before the flattening process and / or the flattened metal powder after the flattening process. In the insulation coating process, an insulation coating may be applied to the agglomerated particles. In other words, the insulation-coated metal powder obtained through the insulation coating process may contain coarse agglomerated particles. As mentioned above, the flattening process flattens the particles while preventing particle coalescence and coarsening. If the insulation-coated metal powder before the flattening process is crushed, more uniform flattening can be expected. Crushing can be performed by dry crushing using a device such as a spiral jet or counter jet mill, wet crushing such as high-pressure fluid impingement crushing, or other general-purpose crushing methods. Dry powder such as the insulation-coated metal powder recovered in the insulation coating process can be directly subjected to dry crushing. Slurries recovered after insulation coating or immediately before the flattening process can be subjected to wet crushing. These methods utilize the collision energy of metal particles to break down agglomerated particles.

[0124] In this way, the iron (Fe)-based flat metal powder of this embodiment can be obtained. The manufacturing method of this embodiment is characterized in that an insulating coating layer mainly composed of an inorganic oxide is formed on a fine iron-based metal powder with a narrow (sharp) particle size distribution, and then a flattening process such as a mechanical crushing process using a crushing medium is performed. This makes it possible to obtain a fine flat metal powder with excellent insulating properties and a narrow particle size distribution.

[0125] To the best of the inventor's knowledge, there is no known method for easily and inexpensively producing fine iron-based flat metal powder with such excellent properties and a narrow particle size distribution. For example, Patent Documents 1 to 3 describe producing soft magnetic flat metal powder with an insulating coating by pulverization using a media agitation mill, but the flattened powder is a coarse soft magnetic alloy powder with an average particle size of 20 μm or more produced by an atomization method. Therefore, the flat metal powder produced by these methods has an average particle size exceeding 20 μm and a wide particle size distribution. Therefore, the demand for fine flat metal powder with a uniform particle size is not met.

[0126] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples.

[0127] (1) Evaluation of Iron-Based Flat Metal Powders Iron-based flat metal powders were prepared in Examples 1 and 2 and Comparative Example 1, and the obtained flat metal powders were evaluated for various properties as follows.

[0128] <Composition Analysis> X-ray diffraction (XRD) measurements were carried out using an X-ray diffractometer, and the obtained XRD data was used to confirm whether alloying had occurred in the flat metal powder.

[0129] <Analysis of Metal Impurities> The impurity content in the flat metal powder was analyzed. The oxygen content was measured by an inert gas fusion method using an oxygen analyzer (TC436, manufactured by LECO Corporation), and the carbon content and sulfur content were measured by a combustion method using a carbon-sulfur analyzer (CS600, manufactured by LECO Corporation). The chlorine content was measured using an X-ray fluorescence analyzer (Magix, manufactured by Spectris Inc.), and the silicon content and sodium content were measured using an ICP optical emission spectrometer (5100, manufactured by Agilent Technologies Inc.).

[0130] <Powder Properties (Average Particle Size, Average Aspect Ratio, Particle Size CV Value)> The flat metal powder was observed using a scanning electron microscope (SEM) to evaluate the powder properties (average particle size, average aspect ratio, particle size CV value) of the flat metal powder. Specifically, the flat metal powder was observed using a scanning electron microscope (JEOL Ltd., JSM-7100F) to obtain an SEM image. The observation was performed at a magnification of 5,000 to 80,000 times. The obtained SEM image was then subjected to image analysis to determine the particle size (average value of the major and minor axes) of multiple (several hundred) flat metal particles. The obtained particle sizes were then averaged on a number basis to determine the average particle size and the standard deviation, and the particle size CV value (coefficient of variation) was calculated according to the following formula (1).

[0131]

[0132] In addition, the cross section of the resin in which the flat metal powder was embedded was similarly observed using an SEM, and the obtained cross-sectional SEM image was analyzed to determine the thickness of multiple (several hundred) flat metal particles, and the obtained thicknesses were averaged on a number basis to determine the average thickness. Next, the average aspect ratio was calculated from the obtained average particle diameter and average thickness according to the following formula (3).

[0133]

[0134] <Magnetic Properties (Saturation Magnetic Flux Density, Coercive Force)> The saturation magnetic flux density and coercive force of the soft magnetic powder (flat metal powder) were evaluated. The saturation magnetic flux density (Bs) (T: Tesla) was calculated from the B-H curve (magnetic hysteresis curve) obtained by measurement using a vibrating sample magnetometer (VSM). The coercive force (Hc) was measured using an automatic coercive force meter (K-HC1000, manufactured by Tohoku Special Steel Co., Ltd.).

[0135] (2) Preparation of iron-based flat metal powder [Example 1] In Example 1, an iron-based flat metal powder (iron-nickel-cobalt flat alloy powder) containing 70 mol% iron (Fe), 10 mol% nickel (Ni), and 20 mol% cobalt (Co) was prepared according to the procedure shown in Fig. 2. In Example 1, a crushing process was performed as an additional process between the insulating coating process and the flattening process, and a high-temperature heat treatment was performed as an additional process after the flattening process.

[0136] <Raw material powder preparation step> The raw material, unflattened metal powder (iron-nickel-cobalt alloy powder), was prepared by the wet method described above. Specifically, a metal salt raw material solution (liquid temperature: 25°C) containing (a) a magnetic metal source, (b) a nucleating agent, and (c) a complexing agent was mixed with a reducing agent solution (liquid temperature: 85°C) containing (d) a reducing agent and (e) a pH adjuster to prepare a reaction solution, and (f) an amine compound solution was added dropwise to the reaction solution to allow the crystallization reaction to proceed.

[0137] In this case, the water-soluble iron salt is ferrous sulfate heptahydrate (FeSO ４ ・7H ２ O, molecular weight: 278.05, reagent manufactured by Wako Pure Chemical Industries, Ltd.) as a water-soluble nickel salt; ４ ・6H ２O, molecular weight: 262.85, reagent manufactured by Wako Pure Chemical Industries, Ltd.), and cobalt sulfate heptahydrate (CoSO ) was used as a water-soluble cobalt salt. ４ ・7H ２ O, molecular weight: 281.103, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was used. The nucleating agent was ammonium palladium (II) chloride (also known as ammonium tetrachloropalladate (II)) ((NH ４ ) ２ PdCl ４ , molecular weight: 284.31, reagent manufactured by Wako Pure Chemical Industries, Ltd.) as a complexing agent, and trisodium citrate dihydrate (Na ３ (C ３ H ５ O (COO) ３ ) 2H ２ The reducing agent used was commercially available industrial grade 60% by mass hydrazine hydrate (manufactured by Otsuka-MGC Chemical Co., Ltd.), and the pH adjuster used was sodium hydroxide (NaOH, molecular weight: 40.0, reagent manufactured by Wako Pure Chemical Industries, Ltd.). The 60% by mass hydrazine hydrate was obtained by the method described above. ２ H ４ ・H ２ The amine compound is ethylenediamine (EDA; H ２ NC ２ H ４ NH ２ , molecular weight: 60.1, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was used.

[0138] The metal salt raw material solution was prepared by dissolving 343.0 g of ferrous sulfate heptahydrate (a water-soluble iron salt), 46.3 g of nickel sulfate hexahydrate (a water-soluble nickel salt), 99.1 g of cobalt sulfate heptahydrate (a water-soluble cobalt salt), 100.2 μg of palladium (II) chloride ammonium (nucleating agent), and 187.6 g of trisodium citrate dihydrate (a complexing agent) in 1000 mL of pure water. In this case, in the resulting metal salt raw material solution, the amount of palladium (Pd) relative to the total amount of magnetic metals (Fe, Ni, and Co) was 0.40 ppm by mass (0.21 mol ppm), and the amount of trisodium citrate relative to the total amount of magnetic metals (Fe, Ni, and Co) was 0.362 (36.2 mol%) in molar ratio.

[0139] The reducing agent solution was prepared by dissolving and mixing 499 g of sodium hydroxide (pH adjuster) and 215 g of 60 mass % hydrazine hydrate (reducing agent) in 1221 mL of pure water. In the reaction solution prepared by crystallization, the molar ratio of the amount of hydrazine to the total amount of magnetic metals (Fe, Ni, and Co) was 1.46, and the molar ratio of the amount of sodium hydroxide to the total amount of magnetic metals (Fe, Ni, and Co) was 7.07.

[0140] The amine compound solution was prepared by uniformly mixing 1.06 g of ethylenediamine (amine compound) and 18 mL of pure water. In the reaction solution prepared by crystallization, the molar ratio of the amount of ethylenediamine to the total amount of magnetic metals (Fe, Ni, and Co) was 0.01 (1.0 mol%).

[0141] Details of the crystallization (preparation of the reaction solution and the crystallization reaction) are as follows. First, the prepared metal salt raw material solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring blade placed in a water bath and heated with stirring to a liquid temperature of 85°C. Subsequently, the metal salt raw material solution at a liquid temperature of 25°C was added to the reducing agent solution heated in the water bath and mixed for 10 seconds to obtain a reaction solution at a liquid temperature of 67°C. The concentration of magnetic metals (Fe, Ni, and Co) in the reaction solution was 34.8 g / L. This initiated the reduction reaction (crystallization reaction) at a liquid temperature of 67°C. The temperature of the reaction solution continued to rise by heating in the water bath after the start of the reaction, and was maintained at 85°C for 10 minutes after the start of the reaction (reaction temperature 85°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The color immediately after the start of the reaction turned dark green because the reaction according to the above formula (7) progressed and iron hydroxide (Fe(OH) ２ ) and nickel hydroxide (Ni(OH) ２ ) and cobalt hydroxide (Co(OH) ２ The color changed to dark gray a few minutes after the start of the reaction, probably due to the generation of nuclei by the action of the nucleating agent (palladium salt).

[0142] The reduction reaction was carried out by adding the amine compound solution dropwise to the reaction solution over a period of 10 minutes, from 3 minutes to 13 minutes after the start of the reaction, when the color of the reaction solution changed to dark gray. As a result, an iron-based alloy powder (iron-nickel-cobalt alloy powder) precipitated in the reaction solution. At this time, the color of the reaction solution was black, but within 40 minutes after the start of the reaction, the supernatant liquid of the reaction solution became transparent. It is believed that the reduction reaction of the above formula (7) was completed, and all of the iron, nickel, and cobalt components in the reaction solution were reduced to metallic iron, metallic nickel, and metallic cobalt. After the reaction was completed, the reaction solution was a slurry containing iron-based alloy powder (iron-nickel-cobalt alloy powder).

[0143] The slurry-like reaction solution obtained by crystallization was subjected to filtration, washing, and solid-liquid separation to recover a cake-like iron-nickel-cobalt alloy powder. Filtration and washing were performed using pure water with a conductivity of 1 μS / cm until the conductivity of the filtrate filtered from the slurry reached 10 μS / cm or less. The recovered cake-like alloy powder was dried in a vacuum dryer set at 50°C. The dried alloy powder was then cooled to 35°C in a vacuum, after which nitrogen gas containing 1.0% by volume of oxygen was supplied to the alloy powder for gradual oxidation. In this way, an iron-based alloy powder (iron-nickel-cobalt alloy powder) was obtained. The obtained alloy powder was composed of spherical particles with smooth surfaces. The particle size distribution was sharp (CV value: 9.8%), and the average particle size was 0.23 μm.

[0144] <Insulation Coating Step (including Crushing as Additional Treatment)> 50.0 g of the obtained iron-based metal powder (iron-nickel-cobalt alloy powder) was placed in a sealed polypropylene container, and 7.0 g of pure water and ethyl alcohol (C ２ H ５ The metal powder was dispersed in a mixed solvent of water and ethyl alcohol to which 50.0 g of a silicon alkoxide (tetraethoxysilane (also known as tetraethyl orthosilicate, tetraethyl silicate) (abbreviation: TEOS) (Si(OC ２ H ５ ) ４9.8 g of 28 to 30 mass % ammonia water (NH 3 ), molecular weight: 208.33, reagent manufactured by Wako Pure Chemical Industries, Ltd., was added and mixed thoroughly, and 2.4 g of 1 mass % ammonia water was added as a base catalyst (alkali catalyst) for hydrolysis of silicon alkoxide with stirring to obtain a uniform slurry. ３ , molecular weight: 17.03, reagent manufactured by Wako Pure Chemical Industries, Ltd.) diluted with pure water. The metal powder, water, ethyl alcohol, tetraethoxysilane, and 1% by mass ammonia water were all at room temperature, and addition and mixing were all carried out at room temperature.

[0145] A slurry containing metal powder, water, ethyl alcohol, tetraethoxysilane, and ammonia was kept at 40°C for 2 days in a rotating polypropylene sealed container, and hydrolysis and dehydration polycondensation of tetraethoxysilane were carried out while stirring the slurry. This resulted in the formation of an insulating coating layer on the surface of the metal powder particles. This insulating coating layer was composed mostly of silicon dioxide (SiO ), although it contained a small amount of hydrolysis polymer of tetraethoxysilane (silanol groups (Si—OH)). ２ ) was the main component.

[0146] The slurry was then subjected to filtration, washing, and solid-liquid separation to recover a cake-like metal powder. Filtration and washing were performed first using ethanol containing 50% by mass of pure water, and then using ethanol. The hydrolysis polymer of tetraethoxysilane remaining in the insulating coating on the metal particle surface is a particle (silica sol) with a very small molecular weight, and is removed together with the filtrate during filtration and washing. Therefore, it does not remain in the recovered cake-like metal powder.

[0147] The collected cake-like metal powder was dried in a vacuum dryer at 50°C, and then heat-treated in vacuum at 150°C for 2 hours. This heat treatment caused the hydrolysis polymer of tetraethoxysilane that constituted the insulating coating layer to undergo further dehydration condensation polymerization, resulting in harder and denser silicon dioxide (SiO ２ ) and the insulating properties of the insulating coating layer were further improved. By this insulating coating treatment, highly resistive silicon dioxide (SiO ２As a result, a metal powder (insulation-coated metal powder) having an insulating coating layer made of the above-mentioned tantalum phosphate was obtained.

[0148] The obtained insulation-coated metal powder was subjected to a spiral jet crushing process, a dry crushing method, using an ultra-small jet mill (Japan Pneumatic Co., Ltd., JKE-30) at a crushing gas pressure of 0.5 MPa. The loose agglomerations of insulation-coated metal particles that occurred during the insulation coating process were crushed by the spiral jet crushing process. The insulation-coated metal powder after the crushing process was composed of spherical particles with smooth surfaces. The particle size distribution was sharp (CV value: 10.1%), and the average particle size was 0.25 μm. The thickness of the insulation coating layer was estimated to be approximately 0.010 μm (10 nm). Furthermore, the insulation coating process significantly increased the electrical resistivity of the metal powder. Specifically, the compact resistivity of the metal powder before the insulation coating process (applied pressure: 64 MPa) was 0.04 Ω·cm, while the compact resistivity of the insulation-coated metal powder after the crushing process exceeded the measurement range (>10 ７ Ω·cm).

[0149] <Flattening Process (Including High-Temperature Heat Treatment as an Additional Treatment)> One part by weight of the crushed insulation-coated metal powder was dispersed in four parts by weight of a mixed solvent of pure water and ethyl alcohol to obtain a slurry with a concentration of 20% by mass. In the mixed solvent, the ratio of pure water to ethyl alcohol was 1:1 by mass. Next, 20 parts by weight of zirconia beads (YTZ balls φ0.2, manufactured by Nikkato Corporation) with a diameter of 0.2 mm were added as a grinding medium to the obtained slurry, and flattening was performed for 100 minutes using a planetary mill (rotating / revolving mixer ARE-250, manufactured by Thinky Corporation) under conditions of a revolution of 2000 rpm and a rotation of 800 rpm.

[0150] The grinding media were removed using a nylon mesh (mesh size: 77 μm) to recover a slurry containing flat metal powder. After the grinding media were removed, the slurry was allowed to stand and then decanted to remove the supernatant mixture of pure water and ethyl alcohol. Further solid-liquid separation (filtration) was performed to obtain a cake-like flat metal powder.

[0151] The resulting cake-like flat metal powder was dried in a vacuum dryer at 50°C and then subjected to a high-temperature heat treatment in a vacuum at 200°C for two hours. This high-temperature heat treatment alleviates the distortion induced in the particles during the flattening process, which is expected to improve magnetic properties such as coercivity. This flattening process resulted in an iron-based flat metal powder (iron-nickel-cobalt flat alloy powder) with an insulating coating layer formed on it. The resulting flat metal powder was composed of flat particles primarily consisting of circular and elliptical shapes. The particle size distribution was relatively sharp (particle size CV value 13.2%), and the average particle size was 0.35 μm. The average aspect ratio was 3.9.

[0152] [Example 2] In Example 2, in the flattening process, 1 part by weight of the crushed insulation-coated metal powder was dispersed in 3 parts by weight of a mixed solvent of pure water and ethyl alcohol to obtain a slurry with a slurry concentration of 25% by mass. The ratio of pure water to ethyl alcohol in the mixed solvent was 1:1 by mass. Next, 16 parts by weight of zirconia beads (YTZ balls φ0.1, manufactured by Nikkato Corporation) with a diameter of 0.1 mm were added as a grinding medium to the obtained slurry, and a flattening process was performed for 150 minutes using a planetary mill (rotation-revolution mixer ARE-250, manufactured by Thinky Corporation) under conditions of 2000 rpm revolution and 800 rpm rotation. Otherwise, an iron-based flat metal powder (iron-nickel-cobalt flat metal powder) was produced in the same manner as in Example 1. The obtained flat metal powder was composed of flat particles mainly consisting of circular or elliptical shapes. The particle size distribution was relatively sharp (particle size CV value 11.1%), the average particle size was 0.32 μm, and the average aspect ratio was 3.0.

[0153] [Comparative Example 1] In Comparative Example 1, the raw material metal powder (iron-nickel-cobalt alloy powder) was subjected to crushing and flattening without being subjected to an insulating coating treatment. Iron-based flat metal powder (iron-nickel-cobalt flat alloy powder) was produced in the same manner as in Example 1, except that crushing was not performed. The obtained flat metal powder was composed of flat particles, mainly consisting of amorphous particles, mixed with circular and elliptical particles. The particle size distribution was wide (particle size CV value 28.3%), and the average particle size was 0.64 μm. The average aspect ratio was 8.6.

[0154] The manufacturing conditions of the flat metal powders of Examples 1 and 2 and Comparative Example 1 are summarized in Table 1 below.

[0155]

[0156] (3) Summary of Evaluation Results The evaluation results obtained for Example 1, Example 2, and Comparative Example 1 are summarized in Table 2 below. SEM images (a) of the metal powder (alloy powder) before flattening treatment and (b) of the flattened metal powder after flattening treatment in Example 1 and Comparative Example 1 are shown in Figures 3 and 4, respectively.

[0157] Examples 1, 2, and Comparative Example 1 are all examples in which flattening was performed using a planetary mill (rotating / revolving mixer) equipped with zirconia beads (grinding media) with a diameter of 0.1 mm to 0.2 mm. The iron-based flat metal powders obtained in Examples 1 and 2, in which the metal powder was subjected to an insulating coating treatment, had fine average particle sizes of 0.32 μm to 0.35 m. Furthermore, it was found that the particle size CV value was small and the particle size distribution was relatively sharp.

[0158] In contrast, in Comparative Example 1, in which the metal powder was flattened without being subjected to an insulating coating, coarse, flat particles were observed in the metal powder, in which multiple particles were aggregated and combined to form flat particles. Furthermore, the obtained flat metal powder contained coarse particles, resulting in a large average particle size and a broad particle size distribution. While the insulating coating is thought to improve the electrical insulation of this flat metal powder, it also contained coarse, flat particles and had an uneven particle size distribution. Therefore, it is not suitable for use.

[0159]

[0160] From the above results, it can be seen that this embodiment provides an iron-based flat metal powder having excellent powder properties and magnetic properties, and a method for producing the same.

Claims

1. An iron (Fe)-based flat metal powder having flat metal particles containing at least iron (Fe) as a magnetic metal, wherein the flat metal particles have an insulating coating layer on their surface containing an inorganic oxide as a primary component, and the flat metal powder has an average particle size of 0.2 μm or more and 3 μm or less, an average aspect ratio of 2 or more and 15 or less, and a particle size CV value (coefficient of variation) calculated according to the following formula (1) is 25% or less.

2. The iron (Fe)-based flat metal powder according to claim 1, wherein the iron (Fe) content of the flat metal powder is 30 mol % or more and 100 mol % or less.

3. The iron (Fe)-based flat metal powder according to claim 1, wherein the flat metal powder further contains at least one of nickel (Ni) and cobalt (Co) as a magnetic metal.

4. The iron (Fe)-based flat metal powder according to claim 3, wherein the flat metal powder has an iron (Fe) content of 30 mol% or more and less than 100 mol%, and a total amount of nickel (Ni) and cobalt (Co) of more than 0 mol% and not more than 70 mol%.

5. The insulating coating layer is made of silicon dioxide (SiO ２ 3. The iron (Fe)-based flat metal powder according to claim 1 or 2, comprising as an inorganic oxide.

6. The iron (Fe)-based flat metal powder according to claim 1 or 2, wherein the flat metal powder has a saturation magnetic flux density of 1.0 T (tesla) or more.

7. A method for producing iron (Fe)-based flat metal powder, the method comprising the following steps: a step of preparing iron (Fe)-based non-flat metal powder having non-flat metal particles containing at least iron (Fe) as a magnetic metal, with an average particle size of 0.1 μm or more and 3 μm or less, and with a particle size CV value (coefficient of variation) calculated according to the following formula (2) of 25% or less; a step of applying an insulating coating treatment to the non-flat metal powder to form an insulating coating layer containing inorganic oxides as a main component on the surface of the non-flat metal particles; and a step of applying a flattening treatment to the non-flat metal powder that has been subjected to the insulating coating treatment to flatten the non-flat metal particles having the insulating coating layer, wherein the flattening treatment is a mechanical crushing treatment using a crushing medium.

8. The manufacturing method according to claim 7, wherein the amount of iron (Fe) in the flat metal powder is 30 mol % or more and 100 mol % or less.

9. The manufacturing method according to claim 7, wherein the flat metal powder further contains at least one of nickel (Ni) and cobalt (Co) as a magnetic metal.

10. The manufacturing method described in claim 9, wherein the flat metal powder has an iron (Fe) content of 30 mol% or more and less than 100 mol%, and a total amount of nickel (Ni) and cobalt (Co) of more than 0 mol% and not more than 70 mol%.

11. The manufacturing method according to claim 7 or 8, wherein the insulating coating treatment is a treatment for forming an insulating coating layer containing an inorganic oxide as a main component by hydrolysis and dehydration condensation polymerization of an alkoxide compound.

12. The alkoxide compound contains silicon alkoxide (alkyl silicate), and the insulating coating layer contains silicon dioxide (SiO ２ 12. The method according to claim 11, wherein the inorganic oxide is 13. The manufacturing method according to claim 7 or 8, wherein the mechanical crushing treatment is a treatment using at least one crushing device selected from the group consisting of a paint shaker, a bead mill, an attritor, and a planetary mill.

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