Manufacturing method of powder magnetic core

Abstract

To provide a manufacturing method of powder magnetic core capable of effectively reducing the friction force that is generated between the metal magnetic powder and the molding die.SOLUTION: The manufacturing method of powder magnetic core includes: a first step of applying metal soap 110, which is liquid at 25°C, to the inner surface 102s of a pressure molding die 100; and a second step of obtaining a molded body by pressurized molding granulated powder 10A that includes a metal magnetic powder composed of a plurality of metal magnetic particles and a binder that binds the plurality of metal magnetic particles together using the pressure molding die 100 coated with the metal soap 110.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a powder magnetic core. [Background technology]

[0002] Conventionally, oxide magnetic materials such as ferrite and metal magnetic materials have been used as magnetic materials for the magnetic cores of inductors and transformers. Magnetic cores using these magnetic materials include, for example, powder magnetic cores formed by compacting metal magnetic powder. Such powder magnetic cores have a high saturation magnetic flux density and are advantageous for miniaturizing components such as inductors and transformers. Generally, powder magnetic cores are formed by pressure-molding a mixture of metal magnetic powder and resin using a molding die.

[0003] In the manufacture of powder magnetic cores, increasing the pressure during compaction is an effective way to improve the magnetic properties of the powder magnetic core. However, using high pressure during compaction can easily cause a phenomenon known as "galling" on the mold surface. "Galling" is a phenomenon in which the mold surface is scraped away. Galling on the mold surface can cause scratches on the surface of the powder magnetic core, reducing the quality of the powder magnetic core. Furthermore, high pressure compaction increases the ejection pressure of the powder magnetic core compact, making it difficult to remove the compact.

[0004] In order to suppress galling and reduce ejection pressure, Patent Document 1 discloses a method for producing a powder magnetic core by warm-pressing an iron-based magnetic powder using a molding die whose inner surface is coated with a higher fatty acid-based lubricant. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2002 / 058085 Summary of the Invention [Problem to be solved by the invention]

[0006] The occurrence of the galling and the increase in ejection pressure are partly due to the increased frictional force generated between the metal magnetic powder and the molding die caused by the high pressure molding. Therefore, in the production of powder magnetic cores, a method is required to effectively reduce the frictional force generated between the metal magnetic powder and the molding die. [Means for solving the problem]

[0007] A method for manufacturing a powder magnetic core according to one embodiment of the present disclosure includes a first step of applying a metal soap that is liquid at 25°C to the inner surface of a pressure molding die, and a second step of using the pressure molding die to which the metal soap has been applied to pressure mold a granulated powder that includes a metal magnetic powder composed of a plurality of metal magnetic particles and a binder that binds the plurality of metal magnetic particles together to obtain a molded body. [Effects of the Invention]

[0008] According to the present disclosure, the frictional force generated between the metal magnetic powder and the molding die can be effectively reduced in the production of a powder magnetic core. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view showing the configuration of an electrical component including a powder magnetic core according to an embodiment. [Figure 2] FIG. 2 is a diagram schematically showing a cross section of a powder magnetic core according to an embodiment. [Figure 3] FIG. 3 is a schematic perspective view showing the configuration of an electrical component including a powder magnetic core according to a modified example of the embodiment. [Figure 4] FIG. 4 is an exploded perspective view showing the configuration of an electrical component including a powder magnetic core according to a modified example of the embodiment. [Figure 5] FIG. 5 is a diagram schematically showing a cross section of a powder magnetic core according to a modified example of the embodiment. [Figure 6] FIG. 6 is a flowchart showing a method for manufacturing a powder magnetic core according to the embodiment and the modified example of the embodiment. [Figure 7]FIG. 7 is a schematic diagram for explaining application of a metal soap to a pressure molding die. [Figure 8] FIG. 8 is a schematic diagram for explaining pressure molding of granulated powder using a pressure molding die. [Figure 9] FIG. 9 is a schematic diagram showing the outline of the powder bed shear force measuring device used to measure the friction coefficient. [Figure 10] FIG. 10 is a diagram showing the measurement results of the friction coefficient in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be specifically described with reference to the drawings.

[0011] Note that the embodiments described below each illustrate a specific example of the present disclosure. The numerical values, shapes, materials, components, component placement positions, connection configurations, steps (processes), and order of steps (processes) shown in the following embodiments are examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not described in independent claims are described as optional components.

[0012] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0013] Furthermore, in this specification, terms indicating the relationship between elements, such as parallel or perpendicular, terms indicating the shape of elements, such as rectangle or rectangular parallelepiped, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0014] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the number or order of components unless otherwise specified, but are used to avoid confusion between similar components and to distinguish between components.

[0015] (Embodiment) Hereinafter, a powder magnetic core according to an embodiment and an electrical component using the powder magnetic core will be described.

[0016] [composition] First, the configuration of an electrical component using a powder magnetic core according to an embodiment will be described with reference to FIGS.

[0017] Fig. 1 is a schematic perspective view showing the configuration of an electrical component 1 including a powder magnetic core 10 according to an embodiment. Fig. 1 shows the general shape of the powder magnetic core 10, which will be described later, and also shows a see-through view of the interior of the powder magnetic core 10. For example, components such as a coil member 40 that are hidden by being embedded in the powder magnetic core 10 are shown with dashed lines, indicating that they can be seen through the powder magnetic core 10.

[0018] As shown in FIG. 1, the electrical component 1 includes a powder magnetic core 10, a coil member 40, a first terminal member 25, and a second terminal member .

[0019] As an example, the electrical component 1 is a rectangular parallelepiped inductor, and the approximate outer shape is determined by the shape of the powder core 10. The powder core 10 can be formed into any shape by pressure molding. In other words, the electrical component 1 can be formed into any shape depending on the shape of the powder core 10 during pressure molding. Therefore, the shape of the powder core is not limited to a rectangular parallelepiped, and other shapes are also possible.

[0020] The electrical component 1 is a passive element that stores electrical energy flowing between the first terminal member 25 and the second terminal member 35 as magnetic energy using the coil member 40. In this embodiment, the electrical component 1 will be described as one example of use of the powder magnetic core 10, but the powder magnetic core 10 can simply be used as a magnetic material, and the use example is not limited to the electrical component 1 according to this embodiment.

[0021] The powder magnetic core 10 has rectangular opposing surfaces on which the first terminal member 25 and the second terminal member 35 are respectively formed, and has a substantially square prism shape in which the four sides of each opposing surface are connected by a top surface, a bottom surface, and two side surfaces. In this embodiment, the powder magnetic core 10 has a rectangular shape with bottom and top surfaces measuring, for example, about 14.0 mm x 12.5 mm, and the distance from the bottom surface to the top surface is about 8.0 mm.

[0022] 2 is a diagram schematically showing a cross section of the powder magnetic core 10. FIG. 2 is an enlarged view of a portion of the cross section of the powder magnetic core 10.

[0023] As shown in FIG. 2, the powder magnetic core 10 has a metal magnetic powder 15 made up of a plurality of metal magnetic particles, and a binder 16 that binds the plurality of metal magnetic particles of the metal magnetic powder 15 together.

[0024] Metal magnetic powders such as Fe-Si-Al, Fe-Si, Fe-Si-Cr, Fe-Si-Cr-B, or Fe-Si-Cr-BC are used as the metal magnetic powder 15. Metal magnetic powder 15 has a higher saturation magnetic flux density than magnetic powders such as ferrite, and is therefore useful for use under large currents.

[0025] For example, when using an Fe-Si-Al-based metal magnetic powder, the composition elements are Si with a content of 8 wt% to 12 wt%, Al with a content of 4 wt% to 6 wt%, and the remaining composition elements are Fe and unavoidable impurities. Here, examples of unavoidable impurities include Mn, Ni, P, S, and C. By setting the contents of the composition elements that make up the metal magnetic powder 15 within the above composition ranges, high magnetic permeability and low coercive force can be obtained.

[0026] For example, when using an Fe-Si based metal magnetic powder, the composition elements are Si with a content of 1 wt% to 8 wt%, with the remaining composition elements being Fe and unavoidable impurities, which are the same as those described above.

[0027] For example, when using an Fe-Si-Cr based metal magnetic powder, the composition elements are Si with a content of 1 wt% to 8 wt%, Cr with a content of 2 wt% to 8 wt%, and the remaining composition elements are Fe and unavoidable impurities, which are the same as those described above.

[0028] For example, when using an Fe-Si-Cr-B based metal magnetic powder, the composition elements are Si with a content of 1 wt% to 8 wt%, Cr with a content of 2 wt% to 8 wt%, B with a content of 1 wt% to 8 wt%, and the remaining composition elements are Fe and unavoidable impurities, which are the same as those described above.

[0029] For example, when using an Fe-Si-Cr-BC based metal magnetic powder, the composition elements are Si with a content of 1 wt% to 8 wt%, Cr with a content of 2 wt% to 8 wt%, B with a content of 1 wt% to 8 wt%, C with a content of 0.01 wt% to 1 wt%, and the remaining composition elements are Fe and unavoidable impurities, such as Mn, Ni, P, and S.

[0030] The role of Si in the composition elements of the above-mentioned metal magnetic powder 15 is to reduce magnetic anisotropy and magnetostriction constant, increase electrical resistance, and reduce eddy current loss. By making the Si content in the composition elements 1 wt% or more, it is possible to obtain an improvement effect on soft magnetic properties, and by making it 8 wt% or less, it is possible to suppress a decrease in saturation magnetization and thus a decrease in DC bias characteristics.

[0031] Furthermore, the effect of improving weather resistance can be imparted by including Cr in the metal magnetic powder 15. By making the Cr content in the composition elements 2 wt% or more, the weather resistance improvement effect can be obtained, and by making it 8 wt% or less, the deterioration of soft magnetic properties can be suppressed.

[0032] The method for producing the metal magnetic powder 15 according to this embodiment is not particularly limited, and various atomization methods and various pulverization methods can be used.

[0033] The median diameter D50 of these metal magnetic powders 15 is, for example, 1.0 μm or more and 35 μm or less. In order to alleviate electric field concentration between particles, insulating properties can be ensured by making the median diameter D50 of the metal magnetic powder 15 small. Furthermore, by setting the median diameter D50 to the above value, a high filling rate and easy handling can be ensured. Furthermore, by setting the median diameter D50 of the metal magnetic powder 15 to 35 μm or less, core loss, particularly eddy current loss, can be reduced in the high frequency range. Furthermore, the metal magnetic powder 15 may be a powder obtained by mixing two or more types of powders with different median diameters D50. The median diameter D50 of the metal magnetic powder 15 is the particle diameter measured by a particle size distribution analyzer using a laser diffraction scattering method, counting particles from the smallest to the largest, and the cumulative value reaches 50% of the total.

[0034] The binder 16 is provided so as to cover the periphery of the metal magnetic particles of the metal magnetic powder 15. The binder 16 is located between the metal magnetic particles of the metal magnetic powder 15. The binder 16 is an insulating resin material containing resin as a main component. The binder 16 may further contain a material other than resin, and may further contain, for example, at least one of a metal soap, a coupling agent, and insulating particles (for example, inorganic particles such as talc).

[0035] The resin is, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenol resin, silicone resin, and polyimide resin. The resin may be a thermoplastic resin. Examples of thermoplastic resins include acrylic resin, polyethylene, polypropylene, and polystyrene. The binder 16 may contain multiple types of resins.

[0036] A metal soap that is liquid at 25°C may be adhered to the surface 10s of the powder core 10. As will be described in detail below, the metal soap that is liquid at 25°C and adhered to the surface 10s of the powder core 10 is applied to the inner surface of a molding die during the manufacture of the powder core 10. When the metal soap is adhered to the surface 10s of the powder core 10, the concentration of the metal element contained in the metal soap on the surface 10s of the powder core 10 will be higher than the concentration of the metal element at the center of the powder core 10. The concentration of the metal element is measured using, for example, an energy dispersive X-ray (EDX) spectrometer.

[0037] Continuing with reference to FIG. 1, the coil member 40, the first terminal member 25, and the second terminal member 35 will be described.

[0038] The coil member 40 is wound with a long conductor wire coated with an insulating film (winding portion), and both ends of the wire are connected to the first terminal member 25 and the second terminal member 35, respectively (lead portions 20 and 30). In this embodiment, a round conductor wire with a cross-sectional diameter of approximately 0.65 mm is used as the conductor wire. There are no particular limitations on the thickness or shape of the conductor wire. As long as the thickness allows for winding and other processes, round conductor wires and flat conductor wires with rectangular cross sections can be appropriately selected and used. The winding portion is embedded near the center of the powder core 10. In the lead portions 20 and 30, each end of the conductor wire extends continuously from the winding portion to the opposing surfaces and protrudes outside the powder core 10. Here, portions of the lead portions are flattened and bent to fit along the opposing surfaces and the bottom surface. The insulating film coating is removed from the extended portions, allowing for electrical connection to the outside.

[0039] The first terminal member 25 and the second terminal member 35 are made of a conductive plate such as phosphor bronze or copper. Each of the first terminal member 25 and the second terminal member 35 has a recess near the center along the opposing surface and is configured to recess into the powder core 10. The lead portions 20 and 30 are disposed outside this recess. The lead portion 20 and the first terminal member 25 are electrically connected. The lead portion 30 and the second terminal member 35 are electrically connected. The lead portions 20 and 30 are connected to the first terminal member 25 and the second terminal member 35 by resistance welding or the like. The first terminal member 25 and the second terminal member 35 are bent so as to be inserted toward the inside of the powder core 10, and the first terminal member 25 and the second terminal member 35 are fixed to the powder core 10 with the bent portions inserted into the powder core 10.

[0040] Additionally, the first terminal member 25 and the second terminal member 35 are bent together with the lead portions 20 and 30 so as to fit along the bottom surface of the powder magnetic core 10. As a result, the lead portions 20 and 30 are held by the first terminal member 25 and the second terminal member 35 and routed around the bottom underside of the electrical component 1. In other words, the lead portions 20 and 30 can be directly connected to lands (not shown) of a mounting board or the like on which the electrical component 1 is mounted.

[0041] The first terminal member 25 and the second terminal member 35 are not essential components. If the lead portions 20 and 30 have the strength to maintain their shape independently, the first terminal member 25 and the second terminal member 35 do not have to be provided.

[0042] [Variations] Next, the configuration of an electrical component using a powder magnetic core according to a modified example of the embodiment will be described with reference to Figures 3 to 5. In the following description of the modified example, differences from the embodiment will be mainly described, and descriptions of commonalities will be omitted or simplified.

[0043] Fig. 3 is a schematic perspective view showing the configuration of an electric component 2 including a powder magnetic core 12 according to this modified example. Fig. 4 is an exploded perspective view showing the configuration of an electric component 2 including a powder magnetic core 12 according to this modified example.

[0044] The electrical component 2 according to this modification is composed of a magnetic core (dust core) formed of a powder magnetic core 12 and a coil portion disposed inside the magnetic core. The electrical component 2 is, for example, an inductor. In this modification, the electrical component 2 will be described as one example of use of the powder magnetic core 12, but the powder magnetic core 12 can be used simply as a magnetic material, and the use example is not limited to the electrical component 2 according to this modification.

[0045] 3 and 4, the electrical component 2 includes two powder magnetic cores 12, a coil member 13, and two coil supports 14. The two powder magnetic cores 12, which are two split magnetic cores, form a magnetic core, and the coil member 13 and the two coil supports 14 form a coil portion.

[0046] The powder magnetic core 12 includes a base 12a and a cylindrical core 12b formed on one surface of the base 12a. Walls 12c standing upright from the edge of the base 12a are formed on two opposing sides of the four sides that make up the base 12a. The core 12b and the wall 12c are at the same height from the one surface of the base 12a. Each of the two powder magnetic cores 12 is a powder magnetic core formed by pressure-molding a magnetic material into a predetermined shape.

[0047] The two powder magnetic cores 12 are arranged so that their core portions 12b and wall portions 12c abut against each other. At this time, the coil member 13 is arranged so as to surround the periphery of the core portion 12b. The coil member 13 is incorporated into the powder magnetic core 12 via a coil support member 14. The coil member 13 is a long conductor that is wound around the coil support member 14 and coated with an insulating film.

[0048] 4, the two coil supports 14 each include an annular base portion 14a and a cylindrical portion 14b. The core portion 12b of the powder magnetic core 12 is disposed inside the cylindrical portion 14b, and the coil member 13 is disposed on the outer periphery of the cylindrical portion 14b.

[0049] 5 is a diagram schematically showing a cross section of the powder magnetic core 12. FIG. 5 is an enlarged view of a portion of the cross section of the powder magnetic core 12.

[0050] 5, the powder magnetic core 12 includes a metal magnetic powder 15 made up of a plurality of metal magnetic particles, and an insulating material 18. In the powder magnetic core 12, the metal magnetic powder 15 is compacted, and a film of insulating material 18 is formed on the surface of each metal magnetic particle of the metal magnetic powder 15. The insulating material 18 covering the surfaces of adjacent metal magnetic particles of the metal magnetic powder 15 is bonded to each other. In other words, the insulating material 18 is disposed between each metal magnetic particle of the metal magnetic powder 15, and the metal magnetic particles of the metal magnetic powder 15 are insulated from each other.

[0051] The insulating material 18 is formed so as to cover the surface of the metal magnetic powder 15, and adjacent metal magnetic particles of the metal magnetic powder 15 are insulated by the insulating material 18. The insulating material 18 contains, for example, a residue after degreasing of the binder 16 used in manufacturing the dust core 12 described below.

[0052] Furthermore, a metal soap that is liquid at 25° C. may be adhered to the surface 12s of the powder core 12. As will be described in detail later, the metal soap that is liquid at 25° C. and adhered to the surface 12s of the powder core 12 is applied to the inner surface of a molding die during the production of the powder core 12.

[0053] [Manufacturing method] Next, an example of a method for manufacturing the above-mentioned powder magnetic cores 10 and 12 will be described.

[0054] FIG. 6 is a flowchart showing a method for manufacturing the powder magnetic cores 10 and 12 according to the embodiment and the modified example of the embodiment.

[0055] As shown in Fig. 6, in the method for producing the powder magnetic cores 10 and 12, first, metal magnetic substance powder 15 and a material contained in binder 16 are mixed to produce a granular granulated powder containing metal magnetic substance powder 15 and binder 16 that binds together the multiple metal magnetic substance particles that make up metal magnetic substance powder 15 (step S10). For example, the granulated powder is produced by mixing metal magnetic substance powder 15 with a resin. At this time, materials other than the resin may be further mixed in as necessary. The granulated powder may also be classified to obtain granulated powder with particle sizes aligned within a predetermined range.

[0056] Furthermore, when mixing the metal magnetic powder 15 with the material contained in the binder 16, a solvent may be further added and mixed. If a solvent is added, after mixing, the mixture is evaporated by heating at a temperature of, for example, 65°C or higher and 150°C or lower, and the solvent is removed from the mixture. Examples of the solvent that can be used include toluene, xylene, ethanol, isopropyl alcohol, acetone, and methyl ethyl ketone.

[0057] In producing the granulated powder, the mixing ratio of the binder 16 to the metal magnetic powder 15 (i.e., the ratio of the added amount of the material contained in the binder 16 to the added amount of the metal magnetic powder 15) is, for example, 1 wt% or more and 10 wt% or less.

[0058] In the manufacturing method of the powder magnetic cores 10 and 12, step S10 may be omitted, and a granular granulated powder containing a pre-prepared metal magnetic powder 15 and a binder 16 that binds together the multiple metal magnetic particles that make up the metal magnetic powder 15 may be prepared.

[0059] Next, the pressure molding die is heated to a temperature higher than room temperature (step S20). Step S20 is an example of the third step. The temperature in step S20 is, for example, 75°C or higher and 120°C or lower. In the example shown in FIG. 6, step S20 is performed before applying the metal soap in step S30 described below. Note that step S20 may be performed at any timing as long as it is before pressure molding of the granulated powder described below. For example, step S20 may be performed in parallel with step S30 described below or after step S30 described below. Also, the pressure molding described below may be performed at room temperature without performing step S20.

[0060] Next, a metal soap that is liquid at 25°C is applied to the inner surface of the pressure molding die (step S30). Step S30 is an example of a first step. Then, using the pressure molding die to which the metal soap has been applied in step S30, the granulated powder obtained in step S10 is pressure molded to obtain a green body (step S40). Step S40 is an example of a second step. In step S40, for example, 2 ton / cm 2 More than 12ton / cm 2 The pressure molding is carried out at the pressure within the following range.

[0061] When manufacturing powder core 10, the compact obtained in step S40 is subjected to a curing treatment by heating as necessary to produce powder core 10. The conditions for the curing treatment are set depending on the type of resin used for binder 16. In step S40, granulated powder may be pressure-molded together with coil member 40.

[0062] When manufacturing the powder magnetic core 12, the compact obtained in step S40 is subjected to a curing treatment by heating as necessary, and then the compact is degreased (step S50). In degreasing, for example, the compact is heated in the atmosphere at a temperature condition of 200°C or higher and 450°C or lower. This removes at least a portion of the resin contained in the compact. Note that degreasing may be performed under a predetermined oxygen partial pressure or in a non-oxidizing atmosphere. Next, the compact degreased in step S50 is annealed (step S60). In the annealing in step S60, the compact is heated at a temperature of 400°C or higher and 1000°C or lower in a non-oxidizing atmosphere such as nitrogen gas. In this way, the powder magnetic core 12 is manufactured.

[0063] Steps S30 and S40 will now be described in detail with reference to Figs. 7 and 8. Fig. 7 is a schematic diagram illustrating application of metal soap 110 to a pressure-molding die 100. Fig. 8 is a schematic diagram illustrating pressure molding of granulated powder 10A using the pressure-molding die 100. Fig. 7 is a cross-sectional view showing how metal soap 110, which is liquid at 25°C, is applied to an inner surface 102s of the pressure-molding die 100. Fig. 8 is a cross-sectional view showing how granulated powder 10A is pressure-molded by the pressure-molding die 100.

[0064] A pressure molding die 100 shown in FIGS. 7 and 8 is a die for pressure molding granulated powder 10A obtained in step S10. In the example shown in FIGS. 7 and 8, pressure molding die 100 has a lower punch 101, a side wall 102, and an upper punch 103. Lower punch 101 and upper punch 103 are columnar die members for pressure molding granulated powder 10A in one axial direction. Side wall 102 is connected to lower punch 101 and extends upward so as to stand along the outer periphery of lower punch 101. Lower punch 101 and side wall 102 form a concave mold, and a molding space 100a surrounded by lower punch 101 and side wall 102 is formed in the concave mold. The concave mold may be a concave mold in which a portion of lower punch 101 and a portion of side wall 102 are integrally formed. Before pressure molding, the top of molding space 100a is open, and granulated powder 10A is charged into molding space 100a. Upper punch 103 is driven toward lower punch 101, whereby granulated powder 10A charged into molding space 100a is pressure molded. Note that the structure of pressure molding die 100 is not particularly limited as long as it can pressure mold granulated powder 10A.

[0065] In step S30, metal soap 110 that is liquid at 25°C is applied to the inner surface 102s of the pressure-molding die 100 that forms the molding space 100a. As a result, a coating film of the metal soap 110 is formed on the inner surface 102s, and the metal soap 110 acts as a lubricant during pressure molding of the granulated powder 10A, thereby reducing the frictional force that occurs between the metal magnetic substance powder 15 and the pressure-molding die 100. In particular, by using metal soap 110 that is liquid at 25°C rather than the metal soap that is solid at 25°C as described in Patent Document 1, the frictional force that occurs between the metal magnetic substance powder 15 and the pressure-molding die 100 can be effectively reduced.

[0066] Specifically, because the metal soap 110 is liquid, there is no need for pre-treatment before application, such as dispersing the metal soap into a liquid and then applying it, as is the case with solid metal soap. Furthermore, the metal soap 110 spreads more evenly over the inner surface 102s than a solid metal soap dispersion, and is more effective in reducing the frictional force generated between the metal magnetic powder 15 and the pressure-molding die 100. Furthermore, unlike solid metal soap, there is no need to heat the metal soap 110 to function as a lubricant, and the frictional force generated between the metal magnetic powder 15 and the pressure-molding die 100 can be reduced even at relatively low temperatures.

[0067] Reducing the frictional force generated between the metal magnetic substance powder 15 and the pressure molding die 100 can, for example, suppress the occurrence of galling in the pressure molding die 100. One cause of galling in the pressure molding die 100 is adhesive wear caused by repeated adhesion and detachment of the metal magnetic substance powder 15 to the pressure molding die 100 due to frictional heat generated by friction between the pressure molding die 100 and the metal magnetic substance powder 15. Therefore, reducing the frictional force generated between the metal magnetic substance powder 15 and the pressure molding die 100 also reduces frictional heat, making adhesive wear less likely to occur, and therefore suppressing the occurrence of galling in the pressure molding die 100.

[0068] Since the metal soap 110 is liquid at 25°C, the melting point of the metal soap 110 is below 25°C. The metal soap 110 is a metal salt of a fatty acid containing a metal element and a fatty acid. The metal element is, for example, Zn, Zr, or Ti. The metal soap 110 has a branch in the hydrocarbon chain of the fatty acid to lower the melting point. The metal soap 110 is produced, for example, by a direct method or a metathesis method. The direct method is a method in which a fatty acid is directly reacted with a metal oxide or metal hydroxide. The metathesis method is a method in which a basic compound is reacted with a fatty acid in an aqueous solution to form a basic compound of the fatty acid, and then a metal salt containing a metal or metalloid is reacted with the basic compound.

[0069] The metal soap 110 may contain, for example, a tetravalent metal element. In the metal soap 110 containing a tetravalent metal element, the valence of the metal element is large, so the metal elements are easily cross-linked, and the metal soaps are easily bonded to each other. This improves the lubricity of the metal soap 110 applied to the inner surface 102s, and can further reduce the frictional force generated between the metal magnetic substance powder 15 and the pressure molding die 100.

[0070] 7 and 8, the metal soap 110 is applied, for example, to at least the inner surface 102s of the side wall 102 among the inner surfaces of the pressure molding die 100. The inner surface 102s of the side wall 102 is a surface along the compression direction of the granulated powder 10A during pressure molding, and therefore friction is likely to occur between the metal magnetic substance powder 15 and the pressure molding die 100. Therefore, by applying the metal soap 110 to the inner surface 102s, it is possible to effectively reduce the frictional force generated between the metal magnetic substance powder 15 and the pressure molding die 100. Note that the metal soap 110 may be applied to the inner surface of the pressure molding die 100 other than the inner surface 102s of the side wall 102, depending on the mold shape, etc.

[0071] There is no particular limitation on the method for applying the metal soap 110. For example, a bar coater such as a non-wire bar coater, or a spray gun such as an air spray gun, an airless spray gun, or an electrostatic spray gun may be used to apply the metal soap 110.

[0072] The thickness of the coating film of the metal soap 110 applied to the inner surface 102s is, for example, 2 μm or more. This allows the metal soap 110 to fully function as a lubricant. Furthermore, the thickness of the coating film of the metal soap 110 applied to the inner surface 102s is, for example, 10 μm or less. This makes it easier to apply the metal soap 110 uniformly and prevents the metal soap 110 from dripping.

[0073] [Evaluation of friction force] The following describes the results of evaluating the effect of reducing frictional force by applying the metal soap 110, which is liquid at 25°C, to the inner surface 102s of the pressure-molding die 100. Specifically, the coefficient of friction between the granulated powder and the substrate (a plate made of the same material as the side wall of the pressure-molding die) was measured by the method described below.

[0074] <Preparation of granulated powder> First, we will explain how to prepare the granulated powder used in the evaluation. A Fe-Si-Cr-BC metal magnetic powder, an isopropyl alcohol solution of silicone resin (concentration 50 wt%), and toluene were mixed, heated to remove the solvent, and then pulverized to prepare granular granulated powder. The amount of silicone resin added relative to the amount of metal magnetic powder added was 2.6 wt%. Note that the amount of silicone resin added is the amount added by weight excluding the solvent.

[0075] <Measurement of friction coefficient> The coefficient of friction between the granulated powder prepared above and a substrate was measured using the methods of Comparative Examples 1 and 2 and Examples 1 to 3 below. The coefficient of friction was measured in accordance with JIS Z 8835:2016 using a powder bed shear force measuring device (NS-S500, manufactured by Nano Seeds Co., Ltd.). FIG. 9 is a schematic diagram showing the general configuration of the powder bed shear force measuring device 200 used to measure the coefficient of friction. The method for measuring the coefficient of friction will be described in detail below with reference to FIG. 9.

[0076] (1) Comparative Example 1 First, substrate 220 formed of an iron-chromium alloy, which is one of the materials used for molding die 100, was prepared. Then, substrate 220 was placed in lower movable cell 201, which has a temperature control function and is movable in the horizontal direction, so that surface 220s of substrate 220 faced upward, and the temperature of substrate 220 was adjusted to a predetermined temperature. Next, upper fixed cell 202, which is a cylindrical frame, was fixed above surface 220s. When fixing upper fixed cell 202, a small gap was provided between upper fixed cell 202 and surface 220s to prevent leakage of granulated powder 10A, so that upper fixed cell 202 and surface 220s did not come into contact with each other. Then, granulated powder 10A was introduced into fixed upper fixed cell 202. After confirming that the temperature of substrate 220 had reached a predetermined temperature, a predetermined vertical load was applied to granulated powder 10A via pressure member 203 by servo cylinder 204. Pressurizing member 203 was held for 100 seconds at a position where a predetermined vertical load was applied to granulated powder 10A (stress relaxation of granulated powder 10A against the vertical load obtained from load cell 211 disposed between servo cylinder 204 and pressurizing member 203 was almost completed). After that, linear actuator 205 pushed substrate 220 together with lower movable cell 201 laterally (in the direction of the hollow arrow in FIG. 9 ) at a speed of 10 μm / s so as to shear at the interface between substrate 220 and granulated powder 10A, and the maximum shear stress and the vertical stress at the maximum shear stress were measured. A load cell 213 disposed below lower movable cell 201 (load cell 213 was disposed between lower movable cell 201 and a horizontally movable base not shown) was used to measure the vertical stress. A load cell 212 disposed between linear actuator 205 and lower movable cell 201 was used to measure the shear stress.

[0077] The above measurements were performed under three load conditions, with predetermined normal loads of 100 N, 200 N, and 300 N. The measurement results under the three load conditions were plotted with the maximum shear stress on the vertical axis and the normal stress at the maximum shear stress on the horizontal axis. The slope of an approximation equation obtained by linearly regressing the plotted measurement results under the three load conditions was then determined as the coefficient of friction. The maximum shear stress is the stress when granulated powder 10A starts moving from a stationary state relative to substrate 220, so the calculated coefficient of friction can also be considered as the static coefficient of friction.

[0078] Furthermore, the coefficient of friction was measured under four predetermined temperature conditions: 25°C (room temperature), 75°C, 90°C, and 120°C.

[0079] (2) Example 1 The friction coefficient was measured in the same manner as in Comparative Example 1, except that a metal soap containing divalent Zn, fatty acid zinc (hereinafter also referred to as "Zn-containing liquid metal soap") that is liquid at 25°C, was applied to the surface 220s of the substrate 220 using a non-wire bar coater under conditions setting the film thickness to 2 to 10 μm, and then the substrate 220 was placed in the lower movable cell 201.

[0080] (3) Example 2 The friction coefficient was measured in the same manner as in Example 1, except that fatty acid titanium (hereinafter also referred to as "Ti-containing liquid metal soap"), which is liquid at 25°C, was used as the metal soap containing tetravalent Ti element.

[0081] (4) Example 3 The friction coefficient was measured in the same manner as in Example 1, except that fatty acid zirconium (hereinafter also referred to as "Zr-containing liquid metal soap"), which is liquid at 25°C, was used as the metal soap containing tetravalent Zr element.

[0082] (5) Comparative Example 2 The friction coefficient was measured in the same manner as in Example 1, except that a fatty acid zinc salt (hereinafter also referred to as "Zn-containing solid metal soap") that is solid at 25°C was used as the metal soap containing divalent Zn element, and a 0.1 wt% isopropyl alcohol solution of the Zn-containing solid metal soap was applied to the surface 220s of the substrate 220.

[0083] <Friction coefficient measurement results> The results of the friction coefficient measured by the above method are shown in Table 1 and Fig. 10. Fig. 10 shows the relationship between the temperature of the substrate 220 and the friction coefficient. In Fig. 10, the vertical axis represents the measurement results of the friction coefficient, and the horizontal axis represents the temperature of the substrate 220.

[0084] [Table 1]

[0085] As shown in Table 1 and FIG. 10 , the coefficient of friction in Comparative Example 2, in which a Zn-containing solid metal soap was applied to the surface 220s of the substrate 220, was not reduced except at temperatures of 120°C, compared with Comparative Example 1, in which no metal soap was applied to the surface 220s of the substrate 220. On the other hand, in Examples 1 to 3, in which a metal soap that was liquid at 25°C was applied to the surface 220s of the substrate 220, the coefficient of friction was lower than that in Comparative Examples 1 and 2 under all temperature conditions. This is likely due to the fact that the metal soap is liquid at 25°C, allowing the metal soap to be uniformly distributed over the surface 220s and functioning as a lubricant even at low temperatures. Because the substrate 220 is made of an iron-chromium alloy used in pressure-molding dies, the measurement results of the friction coefficients in Examples 1 to 3 indicate that applying a metal soap that is liquid at 25°C to the inner surface of the pressure-molding die can effectively reduce the frictional force generated between the metal magnetic powder and the pressure-molding die.

[0086] Furthermore, in Examples 1 to 3, by heating the substrate 220 to 75°C or higher and 120°C or lower, the coefficient of friction can be reduced compared to when the temperature of the substrate 220 is 25°C.

[0087] Furthermore, in Examples 2 and 3, which used a metal soap containing a tetravalent metal element, the friction coefficient was smaller than in Example 1, which used a metal soap containing a divalent metal element. The reason for this is thought to be that the metal elements contained in the metal soap have a large valence, which makes them more likely to be cross-linked, forming a structure in which the metal soaps are easily linked together, thereby improving the lubricity of the metal soap applied to the surface 220s.

[0088] (Other embodiments, etc.) Although the powder magnetic core according to the embodiment of the present disclosure has been described above, the present disclosure is not limited to this embodiment.

[0089] For example, the present disclosure also includes electrical components using the above-described powder magnetic cores. Examples of electrical components include inductance components such as high-frequency reactors, inductors, and transformers. The present disclosure also includes power supply devices equipped with the above-described electrical components.

[0090] Furthermore, the present disclosure is not limited to the above-described embodiments, and various modifications conceivable by those skilled in the art to the present embodiments and configurations constructed by combining components of different embodiments may also be included within the scope of one or more aspects, as long as they do not deviate from the spirit of the present disclosure.

[0091] Below, an example of the method for manufacturing a powder magnetic core according to the present disclosure, which has been described based on the above embodiment, will be shown. The method for manufacturing a powder magnetic core according to the present disclosure is not limited to the following example.

[0092] For example, a method for manufacturing a powder magnetic core according to a first aspect of the present disclosure includes a first step of applying a metal soap that is liquid at 25°C to the inner surface of a pressure molding die, and a second step of using the pressure molding die to which the metal soap has been applied to pressure mold a granulated powder that includes a metal magnetic powder composed of a plurality of metal magnetic particles and a binder that binds the plurality of metal magnetic particles together to obtain a molded body.

[0093] Furthermore, for example, a method for producing a powder magnetic core according to a second aspect of the present disclosure is the method for producing a powder magnetic core according to the first aspect, wherein the metal soap contains Zn, Zr, or Ti.

[0094] Furthermore, for example, a method for producing a powder magnetic core according to a third aspect of the present disclosure is the method for producing a powder magnetic core according to the first or second aspect, wherein the metal soap contains a tetravalent metal element.

[0095] Furthermore, for example, a method for producing a powder magnetic core according to a fourth aspect of the present disclosure is the method for producing a powder magnetic core according to any one of the first to third aspects, and further includes a third step of heating the pressure molding die to 75°C or higher and 120°C or lower before pressure molding the granulated powder. [Industrial Applicability]

[0096] The powder magnetic core according to the present disclosure can be used as a material for the magnetic core of high-frequency inductors, transformers, and the like. [Explanation of symbols]

[0097] 1, 2 Electrical components 10, 12 Powder magnetic core 10A Granulated powder 10s, 12s surface 12a base 12b Core 12c wall 13, 40 Coil member 14 Coil support 14a base 14b Cylindrical part 15 Metal magnetic powder 16 Binder 18 Insulation 20, 30 Lead section 25 First terminal member 35 Second terminal member 100 Pressure molding mold 100a Molding space 101 Lower Punch 102 Side wall 102s inner surface 103 Upper Punch 110 Metal soap

Claims

1. A first step of applying a metal soap that is liquid at 25°C to the inner surface of a pressure molding die; a second step of obtaining a green body by pressure-molding a granulated powder containing a metal magnetic substance powder composed of a plurality of metal magnetic substance particles and a binder that binds the plurality of metal magnetic substance particles together, using the pressure-molding die to which the metal soap has been applied; Including, A method for manufacturing a powder magnetic core.

2. The metal soap contains Zn, Zr, or Ti. A method for producing the powder magnetic core according to claim 1.

3. The metal soap contains a tetravalent metal element. A method for producing the powder magnetic core according to claim 1.

4. Further comprising a third step of heating the pressure molding die to 75°C or higher and 120°C or lower before pressure molding the granulated powder. The method for producing the powder magnetic core according to claim 1 .

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