Mixed powder

Abstract

Provided is a mixed powder demonstrating both excellent extractability and compressibility at the time of molding. This mixed powder includes an iron-based soft magnetic powder, an insulating layer formed on a surface of particles forming the iron-based soft magnetic powder, and a lubricant. The lubricant contains an organic lubricant and an inorganic layered compound.

Description

mixed powder

[0001] The present invention relates to a powder mixture.

[0002] Conventionally, magnetic cores used in motors, transformers, etc. have been made by laminating electromagnetic steel sheets, but in recent years, dust cores have been attracting attention.

[0003] When magnetic steel sheets are used as the material, the magnetic core is formed by lamination, which limits the degree of freedom in shape. On the other hand, dust cores are made by pressure-molding soft magnetic particles with an insulating layer. The shape can be changed by changing the mold, allowing for greater freedom in shape than with magnetic steel sheets. Furthermore, while the desired shape is mainly obtained using techniques such as punching when magnetic steel sheets are used as the material, dust cores can be obtained by press molding, improving yield. Furthermore, by forming dust cores with the particles that make up the soft magnetic powder insulated from each other by an insulating layer, eddy current loss can be suppressed compared to magnetic cores manufactured by laminating magnetic steel sheets, enabling higher efficiency in motors, transformers, and the like.

[0004] When manufacturing dust cores, soft magnetic powders are mixed with lubricants as needed. Lubricants provide lubrication when the mixed powder (compressed powder) compacted in a die is removed (ejected) from the die. Generally, powder compacts are ejected from a die by pushing with a punch, which generates significant frictional resistance due to friction between the compact and the die surface. However, adding a lubricant reduces the friction between the compact and the die surface, allowing the compact to be ejected with less energy. Because lubricants generally have a lower density than soft magnetic powders, adding a lubricant to achieve the required ejectability tends to reduce the density of the resulting compact (green density). However, to achieve the desired performance as a magnetic core, it is necessary to increase the density of the dust core. Against this background, mixed powders containing soft magnetic powders and lubricants have been studied to achieve both ejectability and compressibility.

[0005] In Patent Document 1, in addition to an organic lubricant, a bismuth-based fine particle compound having a Mohs hardness of less than 3.5 is added as a fine particle, soft inorganic substance.

[0006] Special Publication No. 2013-505563

[0007] According to the technology proposed in Patent Document 1, certain improvements in compressibility and ejection properties are observed, but further improvements in performance are required.

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide a mixed powder that has both excellent compressibility and ejectability during molding.

[0009] The present invention has been made to solve the above problems, and the gist of the present invention is as follows.

[0010] 1. A mixed powder comprising an iron-based soft magnetic powder, an insulating layer formed on the surface of particles constituting the iron-based soft magnetic powder, and a lubricant, wherein the lubricant comprises an organic lubricant and an inorganic layered compound.

[0011] 2. The mixed powder according to 1 above, wherein S defined by the following formula (1) is greater than 0 and not greater than 0.50: Here, n is the number of lubricants, a ｉ is the content of each lubricant expressed in parts by mass relative to 100 parts by mass of the iron-based soft magnetic powder and the insulating layer, ρ ｉ is g / cm ３ is the density of each of the lubricants expressed in

[0012] 3. The mixed powder according to 1 or 2 above, wherein the insulating layer has, from the surface of the particle toward the outside, a first coating layer containing condensed aluminum phosphate and a second coating layer containing a silicone resin, in this order.

[0013] 4. The mixed powder according to any one of 1 to 3 above, wherein the inorganic layered compound is at least one selected from the group consisting of tungsten disulfide, molybdenum disulfide, hexagonal boron nitride, talc, mica, and graphite.

[0014] 5. The mixed powder according to 4 above, wherein the inorganic layered compound is hexagonal boron nitride.

[0015] 6. The volume resistivity of the inorganic layer compound is 1.0×10 ６5. The mixed powder according to any one of 1 to 4, having a specific resistance of Ω cm or more.

[0016] According to the present invention, a mixed powder having both excellent compressibility and ejectability during molding can be provided.

[0017] Hereinafter, a method for carrying out the present invention will be specifically described. Note that the following description shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto. In the following description, the iron-based powder refers to a powder containing 50 mass % or more of Fe.

[0018] [Mixed Powder] The mixed powder of the present invention contains an iron-based soft magnetic powder, an insulating layer formed on the surface of particles constituting the iron-based soft magnetic powder, and a lubricant. The mixed powder is suitable for use in dust cores. The mixed powder may be an iron-based mixed powder or a soft magnetic mixed powder. The mixed powder may be a mixed powder consisting of an iron-based soft magnetic powder, an insulating layer formed on the surface of particles constituting the iron-based soft magnetic powder, and a lubricant.

[0019] (Iron-based soft magnetic powder) As the iron-based soft magnetic powder, for example, iron powder or iron-based alloy powder can be used, but iron powder is preferred because it has good compressibility during compaction and is easy to increase density. Here, "iron powder" refers to a powder consisting of Fe and unavoidable impurities, and is generally referred to as "pure iron powder" in this technical field. Furthermore, "iron-based alloy powder" refers to an alloy powder containing 50 mass% or more of Fe.

[0020] The iron-based soft magnetic powder is preferably an atomized powder. Powders obtained by oxide reduction and electrolytic deposition have low apparent densities, and even if additional processing such as crushing is performed to increase the apparent density, sufficient apparent density cannot be achieved. Therefore, from the viewpoint of improving the green density, the iron-based soft magnetic powder is preferably a powder produced by atomization (atomized powder). The atomization method is a method of pulverizing a molten metal and cooling it to solidify it. Any of water atomization, gas atomization, and centrifugal atomization can be used. The water atomization method is a method of pulverizing a molten metal by spraying water onto it, while the gas atomization method is a method of pulverizing a molten metal by spraying gas onto it. The pulverization may be performed by spraying both water and gas. The centrifugal atomization method is a method of pulverizing a molten metal by utilizing centrifugal force due to rotation. Powders obtained by two or more of these methods may be combined. That is, the iron-based soft magnetic powder may be at least one selected from the group consisting of gas atomized powder, water atomized powder, and centrifugal atomized powder. When water atomization is used, the particles have many irregularities on their surfaces, which makes them more likely to become entangled, and when compacted into a powder core, this improves the strength of the powder core. Water atomization is also inexpensive. Therefore, water-atomized powder is preferred from the standpoint of the strength and cost of the resulting powder core. Water-atomized iron powder is even more preferred. In contrast, gas atomization allows for relatively large-scale production, so gas-atomized powder is preferred from the standpoint of mass production.

[0021] The apparent density of the iron-based soft magnetic powder is not limited, but from the viewpoint of easily producing a high-density dust core, it is preferably 2.8 Mg / m ３ The upper limit of the apparent density is not particularly limited, but is usually 5.0 Mg / m ３ It can be as follows:

[0022] The average particle size of the iron-based soft magnetic powder is not particularly limited, but is preferably 10 μm or more, more preferably 60 μm or more, from the viewpoint of improving fluidity and facilitating filling into a mold in the production of a dust core. On the other hand, for the same reason, the average particle size is preferably 200 μm or less. Here, the average particle size is the volume-based median diameter D measured by laser diffraction. ５０ is used.

[0023] (Insulating Layer) The mixed powder of the present invention has an insulating layer formed on the surface of the particles constituting the iron-based soft magnetic powder. The insulating layer ensures insulation between particles and can suppress short circuits between particles.

[0024] Any coating can be used as the insulating layer. The insulating layer may be a single-layer coating or a multilayer coating consisting of two or more layers. The multilayer coating may be a multilayer coating consisting of the same type of coating or a multilayer coating consisting of different types of coatings.

[0025] As the insulating layer, for example, one or both of an inorganic insulating layer and an organic insulating layer can be used.

[0026] The inorganic insulating layer can use either or both of an amorphous material and a crystalline material as the inorganic insulating material. Examples of the amorphous material include metal phosphates and metal borates. The metal phosphate is not particularly limited, but condensed aluminum phosphate is preferred from the viewpoint of more easily ensuring insulation between particles. Examples of the crystalline material include metal oxides and SiO ２ Examples of the metal oxide include MgO, forsterite, talc, and Al. ２ O ３ The inorganic insulating layer is a layer containing the inorganic insulating material, and is preferably made of the inorganic insulating material.

[0027] Condensed aluminum phosphates include aluminum dihydrogen tripolyphosphate, aluminum metaphosphate, and mixtures thereof, all of which can be obtained by heating aluminum monophosphate to cause a dehydration reaction. Among these, aluminum dihydrogen tripolyphosphate is preferred from the viewpoint of forming an insulating layer with high adhesion due to its high reactivity with iron. The hydration state of aluminum dihydrogen tripolyphosphate is not limited, and examples thereof include the dihydrate (AIH ２ P ３ O １０ ・2H ２ In this specification, aluminum dihydrogen tripolyphosphate may be referred to as aluminum tripolyphosphate.

[0028] The organic insulating layer is a layer containing an organic resin, and is preferably made of an organic resin. Silicone resin is preferably used as the organic resin. Silicone resin forms Si—O bonds with excellent heat resistance when heat treated, so that excellent insulating properties can be maintained even when the compact is subjected to a high-temperature (e.g., 600° C.) stress relief heat treatment during production of the dust core.

[0029] Examples of silicone resins include resin-based silicone resins, such as silicone resins containing 60 mol% or more of T units (trifunctional siloxane units). Among these, silicone resins in which 50 mol% or more of the functional groups on the Si are methyl groups are preferred, such as methylphenyl silicone resins (KR-255, KR-311, KR-300, etc., manufactured by Shin-Etsu Chemical Co., Ltd.), and methyl silicone resins (KR-251, KR-400, KR-220L, KR-220LP, KR-242A, KR-240, KR-500, KC-89, manufactured by Shin-Etsu Chemical Co., Ltd., and SILRES (registered trademark) MKPOWDER, etc., manufactured by Wacker Asahi Kasei Silicones Co., Ltd.). SR2400 and Trefil R-910 manufactured by Dow Corning Toray Co., Ltd. can also be used. The silicone resin is not particularly limited, and powder and / or flake silicone resins can be used. The silicone resin used is preferably one that is softened by heat.

[0030] Furthermore, from the viewpoint of ensuring insulation, the content of the insulating layer is preferably 0.20 parts by mass or more per 100 parts by mass of the iron-based soft magnetic powder and the insulating layer combined. On the other hand, if the amount of coating is excessively large, the magnetic flux density may decrease, impairing the function as an iron core, and the density of the iron core may also decrease. Therefore, the content of the insulating layer is preferably 2.00 parts by mass or less, and more preferably 1.00 parts by mass or less, per 100 parts by mass of the iron-based soft magnetic powder and the insulating layer combined.

[0031] In a preferred embodiment of the present invention, the insulating layer comprises, from the surface of the particle toward the outside, a first coating layer containing condensed aluminum phosphate and a second coating layer containing a silicone resin, in this order. That is, the powder on which the insulating layer is formed preferably comprises, from the inside, the iron-based soft magnetic powder, the first coating layer, and the second coating layer, in this order. It is more preferable that the insulating layer is composed of the first coating layer and the second coating layer.

[0032] Since the first coating layer is less likely to be destroyed during compaction of the mixed powder, the presence of the first coating layer makes it easier to ensure insulation between particles. The content of the first coating layer is preferably 0.10 parts by mass or more, and more preferably 0.15 parts by mass or more, per 100 parts by mass of the iron-based soft magnetic powder and the insulating layer. On the other hand, in order to further improve the resistivity of the produced dust core, the content of the first coating layer is preferably 0.50 parts by mass or less, and more preferably 0.30 parts by mass or less, per 100 parts by mass of the iron-based soft magnetic powder and the insulating layer.

[0033] The content of condensed aluminum phosphate in the first coating layer is not limited and may be, for example, 50% by mass or more. However, the content is preferably 99% by mass or more, and the first coating layer is more preferably made of condensed aluminum phosphate. The first coating layer is preferably a coating layer using condensed aluminum phosphate.

[0034] The presence of the second coating layer improves the flexibility of the insulating layer, making it less likely that the insulating layer will be broken due to particle deformation during compaction. To further improve the flexibility of the insulating layer, the content of the second coating layer is preferably 0.10 parts by mass or more per 100 parts by mass of the iron-based soft magnetic powder and the insulating layer. On the other hand, to further improve the resistivity of the produced dust core, the content of the second coating layer is preferably 1.50 parts by mass or less, more preferably 0.60 parts by mass or less, and even more preferably 0.30 parts by mass or less per 100 parts by mass of the iron-based soft magnetic powder and the insulating layer.

[0035] The content of the silicone resin in the second coating layer is not limited and may be, for example, 50% by mass or more. However, the content is preferably 99% by mass or more, and the second coating layer is more preferably made of a silicone resin. The second coating layer is preferably a coating layer using a silicone resin.

[0036] (Lubricant) The mixed powder of the present invention contains a lubricant to improve ejection properties during compaction. Hereinafter, the content (parts by mass) of the lubricant is expressed with the total of the iron-based soft magnetic powder and the insulating layer being 100 parts by mass. To ensure better lubrication, the mixed powder preferably contains 0.10 parts by mass or more of the lubricant, more preferably 0.15 parts by mass or more, and even more preferably 0.20 parts by mass or more. To further improve the green density, the mixed powder preferably contains 1.05 parts by mass or less of the lubricant, more preferably 0.80 parts by mass or less. While the insulating layer is formed in the form of a layer on the surface of the particles constituting the iron-based soft magnetic powder, the lubricant is usually present in a free state.

[0037] Regarding the lubricant, S, as defined by the above formula (1), is preferably greater than 0 and less than 0.50. When S is 0.50 or less, the content of low-density lubricant in the mixed powder is small, resulting in a higher theoretical density of the mixed powder. This further improves the compressibility of the mixed powder, making it possible to obtain a green density close to that obtained when a die-lubricated compaction method is used. To further improve compressibility, S is more preferably 0.23 or less. On the other hand, to further improve ejection properties, S is more preferably greater than 0.13.

[0038] The lubricant includes an organic lubricant. The organic lubricant can be one or more selected from the group consisting of fatty acid amides, metal soaps, fatty acids, liquid lubricants, and thermoplastic resins. Examples of fatty acid amides include monoamides and bisamides. A fatty acid amide having one amide group and one amide bond in total is called a monoamide, while a fatty acid amide having two amide groups in total is called a bisamide. Examples of monoamides include stearic acid amide (SA) and erucic acid amide. Examples of bisamides include ethylene bisstearic acid amide (EBS). Examples of metal soaps include zinc stearate, manganese stearate, and lithium stearate. Examples of fatty acids include oleic acid and stearic acid. Examples of liquid lubricants include phosphate esters, polyol esters, mineral oils, and polyglycols. Examples of thermoplastic resins include polyamides, polyethylene, and polyacetals.

[0039] To further improve the ejection property, the content of the organic lubricant is preferably 0.07 parts by mass or more, more preferably 0.10 parts by mass or more, while to further increase the green density, the content of the organic lubricant is preferably 0.80 parts by mass or less, more preferably 0.50 parts by mass or less.

[0040] The lubricant also includes an inorganic layered compound. An inorganic layered compound is an inorganic compound having a layered structure in which unit layers composed of atoms bonded by strong bonds such as covalent or ionic bonds are stacked by weak van der Waals forces. Inorganic lubricants such as inorganic layered compounds have a higher density than organic lubricants, so mixing them does not reduce the green density. Additionally, because they have a layered structure, they are easily sheared when a load is applied, so when used as a lubricant, they can reduce frictional forces and improve ejection properties during molding. In particular, they are highly effective in reducing kinetic frictional forces. Therefore, from the perspective of compressibility and ejection properties during molding, the lubricant includes an inorganic layered compound.

[0041] The layered structure may be, for example, a sandwich structure. A sandwich structure has a structure in which a slippery surface and a non-slippery surface are laminated. Therefore, by using an inorganic layered compound having a sandwich structure, a smaller frictional force can be realized, and the extraction property can be further improved.

[0042] Examples of the inorganic layered compound include tungsten disulfide (WS ２ ), molybdenum disulfide (MoS ２ ), hexagonal boron nitride (BN), graphite, graphite fluoride, phyllosilicates, etc. Examples of phyllosilicates include talc and mica. Two or more materials may be used as the inorganic layered compound. The inorganic layered compound is preferably at least one selected from the group consisting of tungsten disulfide, molybdenum disulfide, hexagonal boron nitride, talc, mica, and graphite. Furthermore, from the viewpoint of further reducing the coefficient of friction between the insulating layer and the mold and further improving ejection properties during molding, it is more preferable that the inorganic layered compound be hexagonal boron nitride. Here, hexagonal boron nitride is particularly effective in reducing the coefficient of friction between the silicone resin and the mold. Therefore, from the viewpoint of further improving ejection properties during molding, it is even more preferable that the inorganic layered compound be hexagonal boron nitride and the insulating layer have a coating layer containing a silicone resin.

[0043] In order to further increase the compact density, the density of the inorganic layered compound is 2.0 g / cm ３ The density of the inorganic layered compound is preferably 4.0 g / cm or more. ３ may be less than 4.0 g / cm ３ Here, when two or more kinds of inorganic layer compounds are used, the average density is the density of the inorganic layer compounds. For example, when the density ρ Ａ 70 parts by mass of inorganic layer compound A, density ρ Ｂ When 30 parts by mass of the inorganic layer compound B is contained, the average density ρ ＡＢ is the density of the inorganic layered compound. ＡＢ = 1 / {(0.7 / ρ Ａ ) + (0.3 / ρ Ｂ )} The density is 4.0 g / cm ３ Examples of the inorganic layered compounds include molybdenum disulfide and tungsten disulfide. ３ 4.0g / cm or more ３ Examples of the inorganic layered compound of less than 1000 kJ / cm include graphite, hexagonal boron nitride, talc, mica, etc. That is, the inorganic layered compound may be at least one selected from the group consisting of hexagonal boron nitride, talc, mica, and graphite.

[0044] The volume resistivity of the inorganic layered compound is not particularly limited. However, it is preferable that the inorganic layered compound has high insulating properties. Unlike organic lubricants, inorganic lubricants do not decompose during the heat treatment process, so they remain in the molded body after the heat treatment. Therefore, depending on the substance, the function of the insulating coating may be hindered. On the other hand, if the inorganic layered compound has insulating properties, it is expected to have the effect of supporting the function of the insulating coating. Therefore, the volume resistivity of the inorganic layered compound is set to 1.0 × 10 ６ Ω cm or more is preferable, and 1.0 × 10 ９ The upper limit of the volume resistivity of the inorganic layer compound is not particularly limited, but it is, for example, 1.0×10 １８The volume resistivity may be Ω cm or less. Here, the volume resistivity is measured by measuring the resistance value when a load is applied to the inorganic layered compound using a universal testing machine. Specifically, it is measured by the method described in the examples.

[0045] In order to further improve ejection properties during molding, the content of the inorganic layer compound is preferably 0.03 parts by mass or more, more preferably 0.05 parts by mass or more. In addition, in order to further improve ejection properties during molding, the density of the inorganic layer compound is preferably 4.0 g / cm ３ In the case of the above, the content is more preferably 0.15 parts by mass or more, and even more preferably 0.25 parts by mass or more. On the other hand, in order to further increase the compressibility while ensuring the ejection property, the density of the inorganic layered compound is 4.0 g / cm ３ When the content is less than 0.25 parts by mass or less, the content is preferably 0.25 parts by mass or less, and more preferably 0.15 parts by mass or less.

[0046] The lubricant may be composed of an organic lubricant and an inorganic layered compound. However, in addition to the organic lubricant and the inorganic layered compound, one or more other inorganic lubricants may be used as the lubricant. Examples of inorganic lubricants other than the inorganic layered compound include zinc oxide (ZnO), bismuth oxide (BiO), and the like. ２ O ３ ), iron sulfide (FeS), bismuth sulfide (Bi ２ S ３ However, it is preferable that the mixed powder does not contain any inorganic lubricant other than the inorganic layer compound. In other words, it is preferable that the inorganic lubricant contained in the mixed powder is made of the inorganic layer compound.

[0047] [Method for Producing Mixed Powder] Next, a method for producing the mixed powder according to one embodiment of the present invention will be described. Note that the following description shows one example of the production method, and the present invention is not limited to the following description.

[0048] The mixed powder can be produced by forming an insulating layer on the surface of the particles constituting the iron-based soft magnetic powder, and then mixing in a lubricant.

[0049] The insulating layer can be formed by a method such as a wet method or a dry method, without any particular limitation. The wet method is a method of mixing the material to be used for the insulating layer with the iron-based soft magnetic powder using a solvent such as water or an organic solvent. On the other hand, the dry method is a method of mixing the material to be used for the insulating layer with the iron-based soft magnetic powder without using a solvent. The mixing can be performed using a mixer, which may be, for example, a rotary blade type mixer. The rotary blade may be, for example, a stirring blade provided at the bottom of a mixing container. Examples of rotary blade type mixers include the FM Mixer series (manufactured by Nippon Coke) and the High Speed ​​Mixer series (manufactured by EarthTechnica).

[0050] Below, we will explain in detail the case where the insulating layer has, from the surface of the particle toward the outside, a first coating layer made of condensed aluminum phosphate and a second coating layer made of silicone resin, in that order.

[0051] (First Coating Layer) First, a first coating layer made of condensed aluminum phosphate is formed on the iron-based soft magnetic powder. The first coating layer can be formed, for example, by a dry method, specifically by mixing the iron-based soft magnetic powder and the condensed aluminum phosphate powder, preferably by heating and mixing. Using a dry method avoids the problem of oxidation of the iron-based soft magnetic powder and is advantageous in terms of equipment and workability, as it does not require the steps of dissolving the powder in a solvent and drying the solvent. Furthermore, heating and mixing can achieve excellent adhesion of the first coating layer to the surface of the iron-based soft magnetic powder. This is presumably due to a reaction occurring at the interface between the condensed aluminum phosphate coating and the iron-based soft magnetic powder.

[0052] The average particle size of the condensed aluminum phosphate powder is not limited, but if the average particle size is 1 μm or more and 10 μm or less, sufficient fluidity can be ensured to improve workability, and the first coating layer can be easily formed uniformly as a continuous film. The average particle size may be 1 μm or more, and preferably 1.5 μm or more. On the other hand, the smaller the average particle size, the larger the specific surface area, and therefore the improved coverage. Therefore, the average particle size is preferably 10 μm or less, more preferably 7.5 μm or less, and even more preferably 5 μm or less. The average particle size is determined by the volume-based median diameter D measured by laser diffraction. ５０ is.

[0053] The above-mentioned mixer can be used for the mixing. The rotation speed of the mixer is not particularly limited, but in order to efficiently form the first coating layer and make the first coating layer a continuous film, it is preferably 100 rpm or more, more preferably 200 rpm or more. On the other hand, excessively high-speed stirring may cause plastic deformation of the iron-based soft magnetic powder, resulting in a decrease in compressibility during pressure molding and an increase in hysteresis loss. Therefore, the rotation speed is preferably 1000 rpm or less, more preferably 800 rpm or less.

[0054] The maximum temperature reached during mixing is not particularly limited. However, in order to facilitate the formation of the first coating layer and improve the adhesion of the first coating layer, the maximum temperature is preferably 130°C or higher, more preferably 150°C or higher. On the other hand, high temperatures may cause deterioration of the condensed aluminum phosphate and a decrease in crystallinity, and oxidation of the iron-based soft magnetic powder may reduce the density of the dust core. Therefore, the maximum temperature is preferably 200°C or lower. Note that the temperature referred to here refers to the temperature of the powder during mixing. When a rotating blade mixer is used, it refers to the temperature indicated by a thermocouple protruding from the wall of the stirring tank to a degree that does not come into contact with the rotating blades. The thermocouple is installed in a position where it is buried in the stationary powder layer in the stirring tank when the mixer is stationary. The maximum temperature reached during mixing refers to the highest temperature of the powder during mixing, and can be the highest temperature among the temperatures of the powder containing the iron-based soft magnetic powder and the condensed aluminum phosphate powder measured by the thermocouple. The temperature during mixing may be controlled by heating or cooling. For example, the temperature during mixing may be controlled by providing a heating / cooling jacket on the mixing tank of the mixer and heating or cooling the powder in the mixing tank from outside the mixer. For the heating, one or both of steam and hot water may be used, and for the cooling, a refrigerant such as cold water may be used. The temperature during mixing may also be controlled by utilizing the heat generated by mixing (heat of mixing). To prevent oxidation of the iron-based soft magnetic powder, the mixing is preferably carried out in an inert gas atmosphere, for example, a nitrogen atmosphere.

[0055] After the mixing, in terms of suppressing oxidation and subsequent handling, it is preferable to cool the powder having the first coating layer to 80° C. or less. The lower limit of the temperature of the powder after cooling is not particularly limited, and may be, for example, room temperature or higher, 0° C. or higher, or 30° C. or higher.

[0056] (Second coating layer) Next, a second coating layer made of silicone resin is formed on the powder obtained by the above method. The second coating layer can be formed by, for example, a wet method using an organic solvent or a dry method without using a solvent. The dry method is preferred because it does not require any safety measures associated with the use of organic solvents and is advantageous in terms of cost, equipment, and workability.

[0057] In the case of a wet method, the silicone resin can be attached by kneading a solution in which the silicone resin is dissolved in an organic solvent with the powder obtained by the above-mentioned method and drying. Examples of the organic solvent include petroleum-based organic solvents such as alcohols, xylene, and toluene. The solids concentration of the silicone resin in the solution can be 1 to 10% by mass. Drying can be carried out in the atmosphere. The drying temperature can be a temperature at which the organic solvent used volatilizes and below the curing temperature of the silicone resin. The types and mixing ratios of the silicone resins to be mixed are as described above. In the case of a wet method, it is preferable to use at least one silicone resin selected from the group consisting of SR2400 manufactured by Toray Dow Corning Co., Ltd., KR-311, and LR-220L manufactured by Shin-Etsu Chemical Co., Ltd.

[0058] In the dry method, the silicone resin can be attached by mixing a silicone resin powder with the powder having the first coating layer obtained by the above-mentioned method. The above-mentioned mixer can be used for the mixing. Furthermore, the mixing may be performed subsequently using the mixer used for forming the first coating layer. The rotation speed of the mixer is not particularly limited, but to efficiently form the second coating layer, 100 rpm or more is preferred, and 200 rpm or more is more preferred. On the other hand, excessively high-speed stirring may cause plastic deformation of the iron-based soft magnetic powder, resulting in reduced compressibility during pressure molding and increased hysteresis loss. Therefore, the rotation speed is preferably 2000 rpm or less, and more preferably 1500 rpm or less. The temperature during mixing is not particularly limited, but it is recommended to set it to 80°C or higher to soften the silicone resin and further improve the adhesion of the second coating layer. To increase the temperature during mixing and utilize the heat storage of the powder layer to reduce production costs, mixing with the silicone resin is preferably performed during cooling after forming the first coating layer. The type and mixing ratio of the silicone resin to be mixed are as described above. In the case of the dry method, it is preferable to use, as the silicone resin, at least one selected from the group consisting of SILRES (registered trademark) MKPOWDER manufactured by Asahi Kasei Wacker Silicone Co., Ltd., Trefil R-910 manufactured by Toray Dow Corning Co., Ltd., and KR-220LP manufactured by Shin-Etsu Chemical Co., Ltd.

[0059] After the silicone resin is applied by a wet or dry method, heat treatment may be performed to increase the hardness of the applied silicone resin. The heat treatment temperature may be, for example, 150° C. or higher and 250° C. or lower. The heat treatment may be performed in air or in an inert gas atmosphere (e.g., a nitrogen atmosphere).

[0060] After the insulating layer is formed as described above, a lubricant is further mixed in. For example, the lubricant may be added to the iron-based soft magnetic powder on which the insulating layer has been formed by the above-described method, and then mixed. The above-described mixer may be used for mixing. Alternatively, the mixer used to form the insulating layer may be used to perform mixing without removing the powder. The type and amount of lubricant to be added are as described above.

[0061] [Dust Core] Next, a method for producing a dust core using the mixed powder of the present invention will be described. Note that the following description shows one example of the production method, and the present invention is not limited to the following description.

[0062] (Pressure Molding) The mixed powder is charged into a die and pressure molded to the desired dimensions and shape. Furthermore, the pressure molding method is not particularly limited, and any of the usual molding methods, such as room temperature molding and die lubrication molding, can be used. Die lubrication molding is a method that can improve ejection properties by applying a lubricant to the die wall surface and then performing pressure molding. Suitable lubricants to be applied to the wall surface include metal soaps such as lithium stearate, zinc stearate, and calcium stearate, and waxes such as fatty acid amides. The molding pressure is determined appropriately depending on the application, but increasing the molding pressure can increase the density of the resulting dust core, so it is preferably 10 t / cm. ２ More preferably, 15 t / cm ２ That's all.

[0063] (Strain relief heat treatment) After the pressure molding, a heat treatment (strain relief heat treatment) is carried out for the purpose of reducing hysteresis loss by strain relief and improving the strength of the compact. The heat treatment temperature is not particularly limited. The holding time of the heat treatment is also not particularly limited, but is preferably 5 to 120 minutes. A stage of holding the temperature at a constant temperature during temperature increase or decrease during the heat treatment may be provided. The atmosphere for the heat treatment is not particularly limited, and may be, for example, air, an inert atmosphere, a reducing atmosphere, or a vacuum. The dew point of the atmosphere is not particularly limited, and may be determined appropriately depending on the application.

[0064] The present invention will be specifically described below based on examples.

[0065] (Test 1) As an iron-based soft magnetic powder, an apparent density of 3.0 Mg / m ３Water-atomized pure iron powder (JIP304AS manufactured by JFE Steel Corporation) with a median diameter of 100 μm was used. First, the iron-based soft magnetic powder and aluminum dihydrogen triphosphate dihydrate powder (K-FRESH #100P manufactured by Teika Corporation, average particle diameter approximately 5 μm) were heated and mixed to form a coating layer made of aluminum tripolyphosphate. 1.5 kg of the iron-based soft magnetic powder was used, and 0.2 parts by mass of the aluminum dihydrogen triphosphate dihydrate powder was mixed with 100 parts by mass of the iron-based soft magnetic powder. A high-speed mixer (LFS-GS-2J model manufactured by Earth Technica (formerly Fukae Powtec Co., Ltd.)) was used for mixing. The atmosphere in the stirring tank was nitrogen, and the rotating blades were rotated at 500 rpm while stirring for 20 minutes. The maximum temperature of the powder during mixing was controlled to 170°C.

[0066] Next, silicone resin powder (KR-220LP manufactured by Shin-Etsu Chemical Co., Ltd.) was further added to the powder in the stirring tank and mixed, thereby forming a coating layer made of silicone resin on the outside of the coating layer made of aluminum tripolyphosphate. After the heating and mixing, the rotation speed of the rotating blade was maintained at 500 rpm, and the addition was carried out when the temperature of the powder had dropped to 150°C. The amount added was 0.2 parts by mass per 100 parts by mass of the iron-based soft magnetic powder. Stirring was continued until the temperature of the powder had dropped to 60°C.

[0067] Next, organic lubricants and inorganic lubricants of the types and amounts shown in Table 1 were further added to the powder in the stirring tank, and the mixture was mixed for 5 minutes at a rotating blade speed of 500 rpm, and the powder was then removed from the stirring tank. Here, the amounts added in Table 1 are shown in parts by mass when the total mass of the iron-based soft magnetic powder and insulating layer is 100 parts by mass. The density of each lubricant used is shown in Table 2.

[0068] A green compact was produced using the mixed powder obtained by the above procedure, and the density (green density) of the green compact and the ejection energy when the green compact was ejected from a die were measured. The green compact was produced by filling 75 g of the mixed powder into a die having a diameter of 25 mm and compacting at 80°C to form a cylindrical green compact. The pressure during the compacting was 980 MPa. The green density was calculated from the dimensions and mass of the obtained green compact. In addition, the ejection energy was calculated from the integral of the ejection load and the travel distance when the green compact was ejected.

[0069] The evaluation results are also shown in Table 1. Powders that satisfied the requirements of the present invention had high green density and low ejection energy. On the other hand, the mixed powders of Comparative Examples 1 to 7 did not contain any inorganic layered compound, and therefore had low green density or high ejection energy. In addition, when a powder consisting of an iron-based soft magnetic powder and an insulating layer was obtained without adding a lubricant in the above procedure, and this powder was molded by a die lubrication molding method (lubricant: lithium stearate) to produce a green compact, the green density was 7.60 g / cm ３ It was.

[0070]

[0071]

[0072] (Test 2) The powders of Comparative Example 2 and Invention Examples 1 to 6 in Test 1 were compacted using a die lubrication compaction method at a compaction pressure of 980 MPa to prepare ring-shaped test specimens with an outer diameter of 38 mm, an inner diameter of 25 mm, and a height of 6 mm. The prepared test specimens were heat-treated in nitrogen at 600°C for 45 minutes. The obtained iron cores were subjected to measurement of resistivity using a four-terminal method and evaluation of magnetic flux density. The results are shown in Table 3. Furthermore, the volume resistivity of each inorganic layered compound was measured according to the method for measuring electrical resistivity specified in JIS K 1469, and the results are shown in Table 4. The volume resistivity was measured under a pressure of 250 N. All test specimens had a resistivity of 100 μΩm or more, demonstrating sufficient insulation. Furthermore, a 1.0×10 ６The test pieces made from the powders of Examples 3 to 5, which used inorganic layered compounds having volume resistivities of Ω·cm or more, had resistivities of 1000 μΩm or more, and had superior insulating properties.

[0073]

[0074]

Claims

1. Iron-based soft magnetic powder and An insulating layer formed on the surface of the particles constituting the iron-based soft magnetic powder, A mixed powder containing a lubricant, The lubricant is a mixed powder containing an organic lubricant and an inorganic layered compound.

2. The mixed powder according to claim 1, wherein S, as defined by the following formula (1), is greater than 0 and less than or equal to 0.

50. [Math 1] Here, n is the number of lubricants, a ｉ The content of each lubricant is expressed in parts by mass relative to 100 parts by mass of the total of the iron-based soft magnetic powder and the insulating layer, ρ ｉ g / cm ３ This represents the density of each of the aforementioned lubricants.

3. The mixed powder according to claim 1, wherein the insulating layer has, in this order, a first coating layer containing condensed aluminum phosphate and a second coating layer containing a silicone resin, extending outward from the surface of the particles.

4. The mixed powder according to claim 2, wherein the insulating layer has, in this order, a first coating layer containing condensed aluminum phosphate and a second coating layer containing a silicone resin, extending outward from the surface of the particles.

5. The mixed powder according to any one of claims 1 to 4, wherein the inorganic layered compound is at least one selected from the group consisting of tungsten disulfide, molybdenum disulfide, hexagonal boron nitride, talc, mica, and graphite.

6. The mixed powder according to claim 5, wherein the inorganic layered compound is hexagonal boron nitride.

7. The volume resistivity of the inorganic layered compound is 1.0 × 10⁻⁶. ６ A mixed powder according to any one of claims 1 to 4, wherein the density is Ω·cm or greater.

8. The mixed powder according to claim 5, wherein the volume resistivity of the inorganic layered compound is 1.0 × 10⁶ Ω·cm or more.

Images