Method for producing powder compact, method for producing powder magnetic core, and mixed lubricant

Abstract

To provide a method for producing a green compact by which a lubricant can be easily and uniformly applied to a die, to provide a method for producing a dust core, and to provide a mixed lubricant.SOLUTION: The method for producing a green compact includes a mixed lubricant preparation step of preparing a mixed lubricant by mixing a lubricant with a mixed solution, a mixed lubricant spraying step of spraying the mixed lubricant from a nozzle N to a mold M in a mist form to apply the mixed lubricant to the mold, and a pressure molding step of filling the mold with a soft magnetic powder, pressurizing the soft magnetic powder to produce a green compact, and taking out the green compact from the mold. The lubricant has a D100 particle size of 41 μm or more and 61 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a powder compact by spraying a lubricant onto a die, a method for producing a powder magnetic core, and a mixed lubricant. [Background technology]

[0002] Powder magnetic cores are used as cores for coil components such as reactors. For example, reactors are electromagnetic components that convert electrical energy into magnetic energy and store and release it, and are used in a variety of fields, including drive systems for hybrid vehicles, electric vehicles, and fuel cell vehicles, as well as office equipment, solar power generation systems, and uninterruptible power supplies.

[0003] Powder magnetic cores are made by filling a mold with soft magnetic powder or soft magnetic powder with an insulating layer on its surface, compacting it under pressure to produce a powder compact, and then annealing the compact. Generally, during compaction, a pressure of 10 to 20 ton / cm is applied. 2 High pressure is applied.

[0004] After compaction, when the powder compact is removed from the die, it rubs against the die. The surface of the powder compact that rubs against the die is called the sliding surface. When the powder compact is removed from the die, the sliding surface may be damaged. Damage to the sliding surface may increase eddy current loss and deteriorate magnetic properties. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5778993 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, a method for improving the mold releasability of a powder compact by applying a lubricant to a mold is known. For example, an electrostatic application method is known in which the lubricant is charged and applied to the mold. However, with the electrostatic application method, there is a risk that the charging becomes unstable and the lubricant cannot be applied uniformly to the mold.

[0007] To address this issue, there are methods in which the worker applies the lubricant manually using a brush, etc., or by applying the lubricant to a punch and then moving the punch up and down to apply the lubricant to the wall of the die. However, when applying the lubricant manually, it depends on the skill of the worker, and when using a punch, it depends on the dimensional accuracy of the punch and die, making it difficult to apply the lubricant uniformly to the die.

[0008] The present invention has been proposed to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a powder compact, a method for producing a powder magnetic core, and a mixed lubricant that allow a lubricant to be easily and uniformly applied to a die. [Means for solving the problem]

[0009] In order to achieve the above object, the method for producing a powder compact of the present invention includes a mixed lubricant preparation step of mixing a lubricant into a mixed liquid to prepare a mixed lubricant, a mixed lubricant spraying step of spraying the mixed lubricant in a mist form onto a die and applying the mixed lubricant to the die, and a pressure molding step of filling the die with soft magnetic powder, pressurizing the soft magnetic powder to prepare a powder compact, and removing the powder compact from the die, wherein the lubricant has a particle size distribution D100 of 41 μm or more and 61 μm or less.

[0010] The method for producing a powder magnetic core of the present invention is characterized by including an annealing step of heat-treating the powder compact produced by the above method.

[0011] Furthermore, the mixed lubricant of the present invention is a mixed lubricant that is sprayed in the form of a mist onto a mold for producing a powder compact and applied to the mold, and is characterized by comprising: a lubricant having a particle size distribution D100 of 41 μm or more and 61 μm or less; and a mixed liquid that is mixed with the lubricant. [Effects of the Invention]

[0012] According to the present invention, it is possible to obtain a method for producing a powder compact, a method for producing a powder magnetic core, and a mixed lubricant that allow a lubricant to be easily and uniformly applied to a die. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a perspective view showing the overall configuration of a powder molded body. [Figure 2] FIG. 2 is a schematic diagram showing a state in which the mixed lubricant is sprayed onto a die from a nozzle. [Figure 3] FIG. 2 is a schematic diagram showing a state in which soft magnetic powder is filled into a mold. [Figure 4] 2 is a schematic diagram showing a state in which soft magnetic powder is pressed by a lower punch and an upper punch. FIG. [Figure 5] FIG. 10 is a schematic diagram showing a step of removing the powder compact. [Figure 6] 1 is a graph showing the relationship between the particle size of D100 of a lubricant and the amount of release. DETAILED DESCRIPTION OF THE INVENTION

[0014] "Embodiment" The configurations of a powder compact 1 and a powder magnetic core according to this embodiment will be described with reference to the drawings. Fig. 1 is a perspective view showing the overall configuration of a powder compact 1. Note that the present invention is not limited to the embodiment described below.

[0015] Coil components such as reactors have a core containing a magnetic material. A powder magnetic core is used as the core. A powder magnetic core is produced by filling a mold with soft magnetic powder coated with an insulating material, compacting it under pressure, and then subjecting this powder compact 1 to a heat treatment called annealing.

[0016] As shown in FIG. 1, the powder compact 1 is composed of three legs 11, 12, and 13 and a yoke 14 connecting the three legs 11, 12, and 13. The three legs 11, 12, and 13 are arranged with gaps between them so that their extension directions are parallel. That is, leg 12 is located in the middle, and legs 11 and 13 are located on both sides of leg 12. In this way, the powder magnetic core has a roughly E-shape.

[0017] When the core is provided in a coil component, the tip surfaces 15 of the legs 11, 12, and 13 of the two powder compacts 1 are joined together, thereby forming a ring-shaped core and a closed magnetic circuit.

[0018] The powder compact 1 also has a press surface 16 and a sliding surface 17. The press surface 16 is a surface that is pressed by a punch or the like when producing the powder compact 1. The sliding surface 17 is a surface on which the sliding marks of the punch remain during press forming. In this embodiment, the surface that forms the E-shape is the press surface 16, and the other surfaces, including the tip surfaces 15 of the legs 11, 12, and 13, are the sliding surfaces 17.

[0019] The powder compact 1 contains soft magnetic powder. The soft magnetic powder is mainly composed of iron. Examples of soft magnetic powder that can be used include pure iron powder, iron-based permalloy (Fe-Ni alloy), Si-containing iron alloy (Fe-Si alloy), sendust alloy (Fe-Si-Al alloy), and a mixture of two or more of these powders. Alternatively, amorphous alloy or nanocrystalline alloy powder may be used as the soft magnetic powder. However, it is preferable that the soft magnetic powder contains pure iron, i.e., it is a mixture of pure iron or pure iron with other alloy powder.

[0020] The circularity of the soft magnetic powder is preferably 0.85 or more in terms of the powder's average particle size (median diameter D50). When the circularity of the soft magnetic powder is 0.85 or more, the gaps between the soft magnetic powder particles are reduced, enabling improvements in density and magnetic permeability. It is particularly preferable for the circularity of the soft magnetic powder to be 0.90 or more, which significantly improves density and magnetic permeability. In addition, the average particle size (median diameter D50) of the soft magnetic powder is preferably 1 to 100 μm. Note that multiple powders with different average particle sizes may be used as the soft magnetic powder.

[0021] An insulating layer is formed around the soft magnetic powder. The insulating layer is made of an insulating material. Examples of insulating materials that can be used include silane compounds, silicone resins, and silicone oligomers. The insulating layer may be made of one type or two or more types. When two or more types are used, the insulating layers may be stacked, or a single layer made of a mixture of two or more insulating materials may be used. For example, when using a silane compound and a silicone resin, an insulating layer made of the silane compound may be formed around the soft magnetic powder, and then another insulating layer made of silicone resin may be formed around this insulating layer. Alternatively, a single insulating layer made of a mixture of the silane compound and silicone resin may be formed.

[0022] The silane compound includes a silane compound having no functional group and a silane coupling agent. As the silane compound having no functional group, for example, an alkoxysilane such as an ethoxy-based or methoxy-based silane can be used, with tetraethoxysilane being particularly preferred. As the silane coupling agent, an aminosilane-based, epoxysilane-based, or isocyanurate-based silane coupling agent can be used, with 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate being particularly preferred.

[0023] The amount of the silane compound added is preferably 0.05 wt% or more and 1.0 wt% or less of the soft magnetic powder. By adding the silane compound in this range, the fluidity of the soft magnetic powder can be improved, and the density, magnetic properties, and strength properties of the compacted powder 1 can be improved.

[0024] Silicone resin is a resin with a siloxane bond (Si-O-Si) as its main skeleton. By using silicone resin, an insulating layer with excellent flexibility can be formed. Silicone resins that can be used include methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified, alkyd resin-modified, polyester resin-modified, and rubber-based. Among these, when using methylphenyl-based silicone resin in particular, it is possible to form an insulating layer with little loss on heating and excellent heat resistance.

[0025] The amount of silicone resin added is preferably 0.6 wt% or more and 2.5 wt% relative to the soft magnetic powder. If the amount added is less than 0.6 wt%, it will not function as an insulating layer, and eddy current loss will increase, resulting in reduced magnetic properties. If the amount added is more than 2.5 wt%, the density of the powder compact 1 will decrease.

[0026] Examples of silicone oligomers that can be used include methyl-based and methylphenyl-based oligomers that have an alkoxysilyl group but no reactive functional group, epoxy-based, epoxymethyl-based, mercapto-based, mercaptomethyl-based, acrylic methyl-based, methacrylic methyl-based, and vinylphenyl-based oligomers that have an alkoxysilyl group and a reactive functional group, and alicyclic epoxy-based oligomers that have a reactive functional group instead of an alkoxysilyl group. In particular, the use of methyl-based or methylphenyl-based silicone oligomers allows for the formation of a thick, hard insulating layer. Furthermore, in consideration of the ease of forming an insulating layer, methyl-based and methylphenyl-based oligomers with relatively low viscosity may also be used.

[0027] The amount of silicone oligomer added is preferably 0.1 wt% or more and 2.0 wt% or less of the soft magnetic powder. If the amount added is less than 0.1 wt%, it will not function as an insulating layer, and eddy current loss will increase, resulting in reduced magnetic properties. If the amount added is more than 2.0 wt%, the density of the powder compact 1 will decrease.

[0028] The soft magnetic powder with the insulating layer formed as described above is filled into a die coated with a mixed lubricant and pressure-molded to produce a powder compact 1. This powder compact 1 is then subjected to a heat treatment known as annealing to produce a powder magnetic core.

[0029] Next, the methods for manufacturing the powder compact 1 and the powder magnetic core will be described in detail. The methods for manufacturing the powder compact 1 and the powder magnetic core of this embodiment are characterized in that a mixed lubricant is prepared and sprayed onto a die, thereby uniformly applying the mixed lubricant to the die and improving the releasability of the powder compact 1. The method for manufacturing the powder compact 1 includes (1) an insulating layer forming step, (2) a mixed lubricant preparing step, (3) a mixed lubricant spraying step, and (4) a pressure molding step. After the (4) pressure molding step, the powder magnetic core is manufactured by passing through a (5) annealing step.

[0030] (1) Insulation layer formation process The insulating layer formation process is a process for forming an insulating layer made of an insulating material around the soft magnetic powder. First, an insulating material such as a silane compound, silicone resin, or silicone oligomer is added to the soft magnetic powder and mixed. Then, the mixture is heated and dried to form an insulating layer on the surface of the soft magnetic powder. The heating and drying conditions are, but are not limited to, a temperature of 25°C to 350°C for approximately two hours. The insulating layer formation process may be performed before the pressure molding process.

[0031] (2) Mixed lubricant preparation process The mixed lubricant preparation process involves mixing a lubricant into a liquid mixture to prepare a mixed lubricant to be applied to a mold. The lubricant used has a particle size distribution D100 of 41 μm or more and 61 μm or less.

[0032] As a result of extensive research, the inventors have discovered that a mixed lubricant, prepared by mixing a lubricant into a liquid mixture, can be sprayed in the form of a mist toward a mold, thereby enabling uniform application. Furthermore, they have discovered that by setting the D100 particle size distribution of the lubricant to 41 μm or more and 61 μm or less, the lubricant can be sprayed in the form of a mist in the lubricant spraying step described below, and the mixed lubricant can be easily and uniformly applied to the mold. In other words, if the D100 is less than 41 μm or greater than 61 μm, at least a portion of the mixed lubricant will be applied in a dripping state rather than in the form of a mist, making it impossible to apply the mixed lubricant uniformly to the mold.

[0033] Conventionally, a method for applying mixed lubricants to dies is known, using electrostatic application. In this method, the mixed lubricant is electrically charged before application. In this case, the focus is on D50, which is the central and dominant part of the particle size distribution. This is because it has the greatest impact on electrostatic chargeability. In addition, when applying lubricant by hand with a brush or when applying it to dies using the up and down movement of a punch, the focus is also on D50, which is the central and dominant part of the particle size distribution.

[0034] On the other hand, in this embodiment, the particle size distribution D100 is focused on in order to spray the mixed lubricant in a mist form, and the lubricant is made to have a particle size distribution D100 of 41 μm or more and 61 μm or less, which enables it to be sprayed in a mist form. In other words, if the particle size is less than 41 μm or more than 61 μm, some of the lubricant will drip, making it impossible to apply the mixed lubricant uniformly to the mold, and making it more likely to damage the sliding surface 17. However, if D100 is set to 41 μm or more and 61 μm or less, the lubricant can be applied uniformly to the mold more easily than with electrostatic application methods, manual application methods, or punch up and down movement methods, and the sliding surface 17 can be protected.

[0035] Furthermore, the electrostatic application method requires the installation of a separate charging device and a structure to maintain the charge of the charged mixed lubricant, which increases the size of the device, whereas the spray method simply sprays the lubricant from a nozzle, so the device can be installed without being larger than the electrostatic application method.

[0036] Furthermore, by setting D100 to 41 μm or more and 61 μm or less, the viscosity remains below 10 (Pa·s) even when the solid content of the lubricant is 20% or more. This means that the lubricant concentration in the mixed lubricant is appropriate, and more than 100 mg of mixed lubricant can be sprayed with one push of the nozzle N. This eliminates the need for increased spraying frequency, improving production efficiency. Furthermore, the time from the mixed lubricant spraying process to the compacting process is short, ensuring that the mixed lubricant remains uniformly applied to the mold without dripping. Therefore, the powder compact 1 has good releasability from the mold, effectively preventing damage to the sliding surface 17 of the powder compact 1.

[0037] In particular, it is more preferable that D100 is 42 μm or more and 61 μm or less. By setting it in this range, the amount sprayed in each mixed lubricant spraying step exceeds 200 (mg), increasing the amount that can be sprayed at one time and improving productivity. In addition, the layer of mixed lubricant applied to the mold becomes thicker, further improving mold releasability and preventing damage to the sliding surface 17 of the powder compact 1.

[0038] Furthermore, it is more preferable that the particle size distribution of the lubricant has a D50 of 16 μm or more. By making the D50 16 μm or more, when the mixed lubricant is sprayed, the particle size of the mist particles of the mixed lubricant is stable, and a sufficient amount can be applied to the specified location. In other words, if the D50 is less than 16 μm, the particle size of the sprayed mist particles is small and they will disperse to other locations before reaching the application surface, making it impossible to ensure a sufficient amount of application.

[0039] The viscosity of the mixed lubricant is preferably 8 seconds or more and 10 seconds or less. By setting the viscosity of the mixed lubricant in this range, the mixed lubricant can be applied uniformly to the mold, including the upper part of the mold. In other words, if the viscosity of the mixed lubricant is lower than 8 seconds, there is a risk that the mixed lubricant applied to the upper part of the mold will drip downward.

[0040] Examples of lubricants that can be used include Nissan Electol, ethylene bisstearamide, zinc stearate, calcium stearate, aluminum stearate, sodium stearate, oleic acid monoamide, zinc myristate, zinc laurate, zinc hydroxystearate, aluminum hydroxystearate, zinc montanate, aluminum montanate, and zinc undecylenate. Examples of the mixed liquid that can be used include isopropyl alcohol (IPA), methanol, and ethanol.

[0041] (3) Mixed lubricant spraying process The mixed lubricant spraying process is a process of applying the mixed lubricant to a mold. Figure 2 is a schematic diagram showing the state in which the mixed lubricant is sprayed onto the mold from a nozzle N. As shown in Figure 2, the nozzle N is positioned above the mold M, and sprays the mixed lubricant in a mist form, causing the mixed lubricant to adhere to the surface of the mold. Through the mixed lubricant spraying process, a mixed lubricant layer 2 is formed uniformly on the surface of the mold M.

[0042] In this embodiment, the tip end surface 15 that joins the two powder molded bodies 1 serves as the sliding surface 17. If the tip end surface 15 serves as the sliding surface 17, when the powder molded body 1 produced by pressure molding is removed from the mold M, the surface portion of the insulating layer of the soft magnetic powder that forms the tip end surface 15 on the sliding surface 17 side may be damaged by friction caused by sliding, which may increase eddy current loss.

[0043] Therefore, in the mixed lubricant spraying step, the mixed lubricant is applied to at least the portion of the mold where the tip surfaces 15 of the legs 11, 12, and 13 are formed. In this embodiment, an insulating layer is formed on the surface of the soft magnetic powder. When the powder compact 1 is removed from the mold, there is a risk that the surface layer of the insulating layer of the soft magnetic powder forming the tip surface 15 on the sliding surface 17 side may be damaged due to friction with the mold. If the insulating layer of the tip surface 15 is damaged, eddy currents may flow between adjacent soft magnetic powder particles, increasing eddy current loss. Therefore, by uniformly applying the mixed lubricant to at least the portion of the mold where the tip surfaces 15 of the legs 11, 12, and 13 are formed, the mold releasability of the tip surface 15 is improved. This prevents damage to the insulating layer of the tip surface 15 when the powder compact 1 is removed from the mold, resulting in a powder core with excellent magnetic properties. It is preferable to also apply the mixed lubricant to the mold parts other than the tip end surface 15, which will be the sliding surface 17 of the leg parts 11, 12, 13 and the yoke part .

[0044] The amount of mixed lubricant sprayed from the nozzle N at one time is preferably 100 mg or more. That is, one push of the nozzle N preferably sprays 100 mg or more of the mixed lubricant. Here, one push refers to pushing the nozzle N from the starting position to the terminal position. One push also includes multiple pushes from the starting position to the terminal position, such as pushing from the starting position to an intermediate position and then pushing from that intermediate position to the terminal position twice. In this embodiment, the nozzle N is positioned above the mold where the leg portion 11 is formed, above the mold where the leg portion 12 is formed, and above the mold where the leg portion 13 is formed, and sprays once from each position, so that 100 mg or more of the mixed lubricant is sprayed at each position. Spraying 100 mg or more at one time can improve the releasability of the powder compact 1 from the mold with one push, thereby improving productivity.

[0045] The nozzle diameter of nozzle N is preferably 0.5 mm or less. If the nozzle diameter is greater than 0.5 mm, the particle size of the mist-like particles of the sprayed mixed lubricant will be large, which may cause spots to appear on the coated surface of the mold. Therefore, by setting the nozzle diameter to 0.5 mm or less, the mixed lubricant can be evenly applied to the coated surface of the mold, further improving the releasability of the powder compact 1 from the mold.

[0046] The depth of the mold M is 60 mm or more, for example, 65 mm. In the electrostatic application method, the mixed lubricant is charged and applied, so in the case of a large mold M with a depth of 60 mm or more, the charging becomes unstable and it becomes difficult to apply the mixed lubricant evenly to every corner of the mold. On the other hand, if the spray method is used, the mixed lubricant can be applied evenly to every corner of the mold, even for a large mold M with a depth of 60 mm or more.

[0047] (4) Pressure molding process The pressure molding process is a process for producing a powder compact 1. Fig. 3 is a schematic diagram showing the state in which soft magnetic powder is filled into a die. In the pressure molding process, first, soft magnetic powder 5, around which an insulating layer has been formed in the insulating layer forming process, is filled into the space defined by the lower punch 3 and the die M.

[0048] Fig. 4 is a schematic diagram showing a state in which soft magnetic powder 5 is pressed by a lower punch 3 and an upper punch 4. As shown in Fig. 4, the upper punch 4 presses against the lower punch 3. The pressing force of the upper punch 4 is 5 ton / cm 2 ~20ton / cm 2 The soft magnetic powder 5 is compressed by the upper punch 4 and the lower punch 3 to produce the powder compact 1.

[0049] FIG. 5 is a schematic diagram showing the step of removing the powder compact 1. As shown in FIG. 5, after pressing, the upper punch 4 moves upward. Thereafter, the lower punch 3 moves upward, exposing the powder compact 1 from the die M. At this time, the powder compact 1 slides within the die M, but because the mixed lubricant layer 2 is uniformly formed on the surface of the die M, damage to the powder compact 1 due to sliding is suppressed. The exposed powder compact 1 is then removed from the die M. In this manner, the powder compact 1 is produced.

[0050] (5) Annealing process The annealing process is a process of heat-treating the powder compact 1 produced through the pressure molding process. In the annealing process, heat treatment is performed at a temperature of 600°C or higher and 900°C or lower in a non-oxidizing atmosphere such as nitrogen gas, a mixed gas of nitrogen and hydrogen, or a low-oxygen atmosphere with an oxygen concentration of 0.01%, or in the air. A powder magnetic core is produced through this annealing process. The annealing process removes distortion and residual stress contained in the powder compact 1.

[0051] (Example) The present invention will be described in more detail based on examples, but the present invention is not limited to the following examples. Mixed lubricants of Examples 1 to 5 and Comparative Examples 1 to 3 were prepared.

[0052] In Example 1, a lubricant with a particle size distribution D100 of 41 μm was used. This lubricant was mixed into a mixed liquid. Isopropyl alcohol was used as the mixed liquid. The lubricant was added to the isopropyl alcohol at a solids concentration of 21 wt %. The solids concentration refers to the concentration of the lubricant in the mixed lubricant of isopropyl alcohol and lubricant. To mix, isopropyl alcohol and lubricant were placed in a 1000 ml plastic bottle (a polyethylene bottle-shaped resin container) with the ratio adjusted to a total of 300 g. Then, the container containing the isopropyl alcohol and lubricant was mixed in a pot mill at a rotation speed of 150 rpm for 30 minutes. In this way, the mixed lubricant of Example 1 was prepared.

[0053] Example 2 differs from Example 1 only in the particle size of the lubricant, and other production materials, production methods, and production conditions are the same as those of Example 1. The lubricant used in Example 2 had a D100 in the particle size distribution of 42 μm.

[0054] Example 3 differs from Example 1 only in the particle size of the lubricant, and other production materials, production methods, and production conditions are the same as those of Example 1. Example 3 used a lubricant with a D100 in the particle size distribution of 46 μm.

[0055] Example 4 differs from Example 1 only in the particle size of the lubricant, and other production materials, production method, and production conditions are the same as those of Example 1. In Example 4, a mixed lubricant was produced using a lubricant with a D100 in the particle size distribution of 61 μm.

[0056] In Comparative Example 1, only the particle size of the lubricant was different from that in Example 1, and the other production materials, production method, and production conditions were the same as those in Example 1. In Comparative Example 1, a mixed lubricant was produced using a lubricant whose D100 in the particle size distribution was 25 μm.

[0057] In Comparative Example 2, only the particle size of the lubricant was different from that in Example 1, and the other production materials, production method, and production conditions were the same as those in Example 1. In Comparative Example 2, a mixed lubricant was produced using a lubricant with a D100 in the particle size distribution of 31 μm.

[0058] In Comparative Example 3, only the particle size of the lubricant was different from that in Example 1, and the other production materials, production method, and production conditions were the same as those in Example 1. In Comparative Example 3, a mixed lubricant was produced using a lubricant with a D100 in the particle size distribution of 73 μm.

[0059] In Comparative Example 4, only the particle size of the lubricant was different from that in Example 1, and the other production materials, production method, and production conditions were the same as those in Example 1. In Comparative Example 4, a mixed lubricant was produced using a lubricant with a D100 in the particle size distribution of 78 μm.

[0060] In Comparative Example 5, only the particle size of the lubricant was different from that in Example 1, and the other production materials, production method, and production conditions were the same as those in Example 1. In Comparative Example 5, a mixed lubricant was produced using a lubricant having a D100 in the particle size distribution of 121 μm.

[0061] The viscosity and release amount of the mixed lubricants of Examples 1 to 4 and Comparative Examples 1 to 5 prepared as described above were measured. A viscosity cup (NK-2 type manufactured by Anest Iwata Corporation) was used to measure the viscosity. To measure the viscosity, the container of the viscosity cup was first buried in the mixed lubricant, and the viscosity cup was pulled up from the mixed lubricant, and at the same time, time measurement was started with a stopwatch. The time (sec) until the outflow of the mixed lubricant in the viscosity cup stopped was then measured.

[0062] The amount of mixed lubricant released is the amount of mixed lubricant released from the nozzle with one push. A nozzle (nozzle diameter 0.5 mm) was used to measure the amount of released. With tissue paper placed in a container, one push of the mixed lubricant was released from the nozzle into the container, and the container was immediately covered. The air pressure used to release the mixed lubricant from the nozzle was 0.5 MPa. The amount of released was then measured by subtracting the volume of the mixed lubricant before release from the volume after release.

[0063] The results are shown in Table 1. Also, Figure 6 is a graph showing the relationship between the particle size of D100 of the lubricant and the amount released.

[0064] [Table 1]

[0065] As shown in Table 1 and FIG. 6, it was confirmed that Examples 1 to 4 could be sprayed in a mist form using a nozzle. It was also confirmed that Examples 1 to 4 emitted an amount of 110 mg or more with one push. On the other hand, the viscosity of Comparative Example 1 was as high as 150 sec, and the viscosity of Comparative Example 2 was too high to measure. Therefore, Comparative Examples 1 and 2 could not be sprayed in a mist form using a nozzle, and could not be discharged into a container containing tissue paper. Furthermore, Comparative Examples 3 to 5 could not spray the mixed lubricant in a mist form, and could not be discharged into a container containing tissue paper. Therefore, it was confirmed that the lubricant particle size distribution can be uniformly sprayed using a nozzle when D100 is 41 μm or more and 61 μm or less.

[0066] In particular, Examples 2 to 4 had a release amount of 210 mg or more, which was more than twice that of Example 1. Therefore, it was confirmed that the release amount per push increases when the particle size distribution of the lubricant is such that D100 is 42 μm or more and 61 μm or less.

[0067] Next, mixed lubricants of Comparative Examples 6 and 7 were prepared. Comparative Example 6 differs from Comparative Example 1 only in the solid content concentration of the lubricant, and other preparation materials, preparation method, and preparation conditions, including lubricant D100, are the same as those of Comparative Example 1. In Comparative Example 6, the lubricant was added to isopropyl alcohol so that the solid content concentration of the lubricant was 4 wt%.

[0068] Comparative Example 7 differs from Comparative Example 2 only in the solids concentration of the lubricant, and other preparation materials, preparation methods, and preparation conditions, including lubricant D100, are the same as those of Comparative Example 2. In Comparative Example 7, the lubricant was added to isopropyl alcohol so that the solids concentration of the lubricant was 11 wt%. The viscosity and release amount were measured using the same method and under the same conditions as above.

[0069] The measurement results are shown in Table 2 below.

[0070] [Table 2]

[0071] As shown in Table 2, it was confirmed that by reducing the solid content of the lubricant, the lubricant can be sprayed from a nozzle even if its D100 is less than 41 μm. However, in Comparative Examples 6 and 7, the solid content of the lubricant is lower than in Examples 1 to 4, so the lubricant concentration in the mixed lubricant is low. Therefore, even if it is sprayed in a mist, the effect of improving releasability is low. On the other hand, in Examples 1 to 4, the solid content of the lubricant is 21 wt %, and the lubricant concentration in the mixed lubricant is high, so the effect of improving releasability is fully exerted with one push. From this perspective, it was also confirmed that the particle size distribution of the lubricant should be such that D100 is 41 μm or more and 61 μm or less.

[0072] (Other embodiments) Although the present specification describes an embodiment of the present invention, this embodiment is presented as an example and is not intended to limit the scope of the invention. The above-described embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. The embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

[0073] In the above embodiment, the powder molded body 1 has an E-shape, but the shape of the powder molded body 1 is not limited to this. The powder molded body 1 may have, for example, a U-shape, an I-shape, or a toroidal shape.

[0074] In the above embodiment, the mold is coated with a mixed lubricant. However, a lubricant may also be added to the soft magnetic powder. That is, prior to the (4) pressure molding step, for example, after the (1) insulating layer forming step, a lubricant may be added and mixed with the soft magnetic powder on which the insulating layer has been formed. Examples of lubricants include stearic acid, calcium stearate, lithium stearate, aluminum stearate, zinc stearate, ethylene bisstearamide, ethylene bisstearamide, and ethylene bisstearamide. The amount of lubricant added is preferably about 0.2 wt% to 0.8 wt% of the soft magnetic powder. Adding a lubricant to the soft magnetic powder itself can further improve the releasability of the powder compact 1 from the mold. [Explanation of symbols]

[0075] 1. Powder compact 11, 12, 13 legs 14 York 15 Tip surface 16 Press surface 17 Sliding surface 2 Mixed lubricant layer 3 Lower Punch 4 Upper Punch 5 Soft magnetic powder N nozzle M mold

Claims

1. a mixed lubricant preparation step of mixing a lubricant into a mixed liquid to prepare a mixed lubricant; a mixed lubricant spraying step of spraying the mixed lubricant onto a die in the form of a mist; a pressure molding step of filling the die with soft magnetic powder, pressing the soft magnetic powder to prepare a powder compact, and removing the powder compact from the die; Including, The lubricant has a particle size distribution D100 of 41 μm or more and 61 μm or less; A method for producing a powder compact, characterized by:

2. The lubricant has a particle size distribution D100 of 42 μm or more and 61 μm or less; 2. The method for producing a powder compact according to claim 1,

3. The viscosity of the mixed lubricant is 8 (sec) or more and 10 (sec) or less; 2. The method for producing a powder compact according to claim 1,

4. In the mixed lubricant spraying step, 100 (mg) or more of the mixed lubricant is released in one spray.

2. The method for producing a powder compact according to claim 1,

5. The mixed lubricant spraying step includes spraying the mixed lubricant in the form of a mist using a nozzle, The nozzle has a nozzle diameter of 0.5 mm or less; 2. The method for producing a powder compact according to claim 1,

6. the powder molded body has a plurality of legs and a yoke portion connecting the plurality of legs, the leg portion has a tip end surface that is an end surface opposite to a surface that is connected to the yoke portion, the tip end surface is a sliding surface that rubs against a mold in the pressure molding process, In the mixed lubricant spraying step, the mixed lubricant is sprayed at least on a portion of the die where the tip end surface is to be formed.

2. The method for producing a powder compact according to claim 1,

7. an insulating layer forming step of forming an insulating layer made of an insulating material around the soft magnetic powder in a stage prior to the pressure molding step; The method for producing a powder compact according to claim 6,

8. The method includes an annealing step of heat-treating the powder compact produced by the method of any one of claims 1 to 7. A method for producing a powder magnetic core characterized by the above.

9. A mixed lubricant that is sprayed in a mist form onto a die for producing a powder compact and applied to the die, a lubricant having a particle size distribution D100 of 41 μm or more and 61 μm or less; a mixture liquid to be mixed with the lubricant; To have A mixed lubricant characterized by:

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