Granulated powder, magnetic molded body, and inductor

Abstract

Provided is a granulated powder that has a highly stable fill weight repeatability for a molded body mold and is capable of increasing the density of a molded body produced by heating and pressurization inside the mold.　This granulated powder has large particles and small particles, wherein there is a difference of -1.68 or less between the value obtained by dividing the D90 particle size of the granulated powder by the D10 particle size of the granulated powder, and the value obtained by dividing the D90 particle size of the large particles by the D10 particle size of the large particles.

Description

Granulated powder, magnetic compact, and inductor

[0001] The present invention relates to a granulated powder, a magnetic molded body, and an inductor.

[0002] Patent Document 1 discloses composite particles including first particles made of a soft magnetic metal material and second particles adhered to the first particles so as to cover 70% or more of the surface of the first particles. The composite particles described in Patent Document 1 can reliably bind the first particles and the second particles, so that when the composite particles are compressed to form a powder magnetic core, the first particles and the second particles can be uniformly distributed, resulting in a powder magnetic core with a high packing ratio and high magnetic permeability.

[0003] JP 2014-103265 A

[0004] The density of a magnetic core produced by filling a mold with granulated powder and then hot-press molding it can depend on the fluidity of the granulated powder.

[0005] An object of the present invention is to provide a granulated powder, a magnetic molded body, and an inductor that can improve the fluidity of the granulated powder and thereby improve the density of a molded body produced by heating and pressurizing in a molding die.

[0006] This specification includes the entire content of Japanese Patent Application No. 2024-101265, filed on June 24, 2024. One aspect of the present invention is a granulated powder having large particles and small particles, in which the difference between the D90 particle size of the granulated powder divided by the D10 particle size of the granulated powder and the D90 particle size of the large particles divided by the D10 particle size of the large particles is −1.68 or less.

[0007] According to the present invention, it is possible to provide a granulated powder, a magnetic molded body, and an inductor that can improve the density of a molded body produced by heating and pressurizing in a molding die by improving the fluidity of the granulated powder.

[0008] FIG. 1 is a perspective view of an inductor according to an embodiment of the present invention, viewed from the top side. FIG. 2 is a perspective view of the inductor, viewed from the bottom side. FIG. 3 is a see-through perspective view showing the internal configuration of the inductor. FIG. 4 is a diagram showing a manufacturing process of the inductor. FIG. 5 is a schematic view showing the configuration of granulated particles contained in granulated powder. FIG. 6 is a schematic view showing an example of stress measurement results.

[0009] In a magnetic core produced by filling a die with granulated powder and then hot-pressing and molding it, the filling rate of the granulated powder in the die depends on the properties of the granulated powder.

[0010] The inventors have conducted extensive research into the properties and state that granulated powder should have, particularly from the perspective of improving the density of a molded body produced by heating and pressurizing in a molding die, and have arrived at the present invention.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] [1. Inductor] First, an example of the configuration and manufacturing process of an inductor manufactured using granulated powder as a magnetic core raw material will be described. [1.1. Inductor Configuration] An inductor manufactured using granulated powder as a magnetic core raw material is, for example, a chip inductor manufactured in a substantially hexahedral shape. FIGS. 1, 2, and 3 are diagrams showing the overall configuration of an inductor 1 according to one embodiment. FIG. 1 is a perspective view of the inductor 1 viewed from the top surface 12 side, and FIG. 2 is a perspective view of the inductor 1 viewed from the bottom surface 10 side. The inductor 1 of this embodiment is configured as a surface-mount electronic component and includes an element body 2 having a substantially rectangular parallelepiped shape, which is one embodiment of a substantially hexahedral shape, and a pair of external electrodes 4 provided on the surface of the element body 2.

[0013] Hereinafter, in the element body 2, the first main surface facing the mounting substrate (not shown) during mounting is defined as the bottom surface 10, the second main surface opposite the bottom surface 10 is defined as the top surface 12, a pair of third main surfaces perpendicular to the bottom surface 10 are defined as end surfaces 14, and a pair of fourth main surfaces perpendicular to the bottom surface 10 and the pair of end surfaces 14 are defined as side surfaces 16. As shown in FIG. 1 , the distance from the bottom surface 10 to the top surface 12 is defined as the thickness T of the element body 2, the distance between the pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between the pair of end surfaces 14 is defined as the length L of the element body 2. Furthermore, the direction of the thickness T is defined as the thickness direction DT, the direction of the width W is defined as the width direction DW, and the direction of the length distance is defined as the length direction DL. The size of the inductor is, for example, the length L dimension is 2.0 mm, the width W dimension is 1.2 mm, and the thickness T dimension is 0.9 mm.

[0014] 3 is a perspective view showing the internal structure of the inductor. The element body 2 includes a coil conductor 20 and a substantially hexahedral core 30 in which the coil conductor 20 is embedded, and is configured as a molded inductor in which the coil conductor 20 is sealed in the core 30.

[0015] The core 30 is a molded body obtained by compressing and molding granulated powder containing metal magnetic particles and resin into a substantially hexahedral shape by applying pressure and heat while the coil conductor 20 is contained therein.

[0016] The metal magnetic particles include particles of two particle sizes: first metal magnetic particles that are large particles with a relatively large average particle size, and second metal magnetic particles that are small particles with a relatively small average particle size. As a result, during compression molding, the second metal magnetic particles, which are small particles, enter between the first metal magnetic particles, which are large particles, together with the resin, thereby increasing the density of the metal magnetic particles in the core 30 and increasing the magnetic permeability.

[0017] The particle diameters of the first and second metal magnetic particles will be described in detail below.

[0018] The first metal magnetic particles and the second metal magnetic particles are both particles having a metal particle and an insulating film covering the surface thereof. By covering the metal particle with the insulating film, the insulation resistance and the withstand voltage are increased.

[0019] The first and second metal magnetic particles may be made of Fe (pure iron) or Fe alloys, for example. Examples of Fe alloys include alloys containing Fe and Ni, alloys containing Fe and Co, alloys containing Fe and Si, alloys containing Fe, Si and Cr, alloys containing Fe, Si and Al, alloys containing Fe, Si, B and C, alloys containing Fe, Si, B and Cr, and alloys containing Fe, P, Cr, Si, B, Nb and C.

[0020] The composition of the first metal magnetic particles and the composition of the second metal magnetic particles may be the same or different. The insulating film formed on the surfaces of the first metal magnetic particles and the second metal magnetic particles may be, for example, one or more insulating films selected from the group consisting of inorganic glass films, organic-inorganic hybrid films, and inorganic insulating films formed by the sol-gel reaction of metal alkoxides.

[0021] In this embodiment, the first metal magnetic particles are made of Fe-Si-B-C amorphous alloy powder, and the second metal magnetic particles are made of pure iron coated with glass by a sol-gel method.

[0022] The resin material in the granulated powder is preferably a thermosetting resin, for example, a thermosetting epoxy resin.

[0023] The granulated powder will be further described below.

[0024] As shown in Fig. 3, the coil conductor 20 includes a winding portion 22 around which a conductor wire is wound, and a pair of lead-out portions 24 that are drawn out from the winding portion 22 and at least partially exposed from the element body 2. The coil conductor 20 is composed of a conductor wire and a coating layer formed on the surface of the conductor wire. The conductor wire is a strip-shaped conductor wire made of copper and having a rectangular cross section (so-called flat conductor wire). Note that the coil conductor 20 does not necessarily have to be wound, and may be linear, meandering, or the like.

[0025] The winding portion 22 of the coil conductor 20 is formed by spirally winding a strip-shaped conductor wire (hereinafter simply referred to as a conductor wire) such that both ends are drawn out to the outer periphery and connected to each other at the inner periphery. Inside the element body 2, the coil conductor 20 is embedded in the core 30 with the central axis of the winding portion 22 oriented along the thickness direction DT of the element body 2. The lead-out portions 24 are drawn out from the winding portion 22 to each of a pair of end faces 14, with one main surface exposed from the element body 2 and the other main surface embedded in the element body 2. The one main surface of the lead-out portion 24 exposed from the element body 2 is electrically connected to the external electrode 4.

[0026] The pair of external electrodes 4 are so-called L-shaped electrodes, consisting of L-shaped members extending from each of the end faces 14 of the element body 2 to the bottom face 10. Each of the external electrodes 4 is connected to the lead-out portion 24 of the coil conductor 20 at the end face 14, and the portion 4A (FIG. 2) extending to the bottom face 10 is electrically connected to wiring on the circuit board by appropriate mounting means such as solder. Note that the external electrodes 4 are not limited to the L-shaped electrodes described above, and may have a so-called five-sided electrode structure or may be bottom electrodes.

[0027] An insulating film, or element protection layer, is formed on the surface of the element 2 excluding the area of ​​the external electrodes 4. The element protection layer can be made of, for example, epoxy resin, phenoxy resin, or novolac resin, and can contain metal oxide fine particles as a filler. In this embodiment, the element protection layer contains a filler of silicon dioxide, which becomes metal oxide fine particles, and an epoxy resin. In addition to the above materials, the element protection layer can also be made of resins such as urethane, acrylic, polyimide, polyimide amide, or polyamide, or glass or an oxide film.

[0028] Inductors with such a configuration can improve DC bias characteristics by using a soft magnetic material as the metallic magnetic particles, and are therefore used as electronic components in electric circuits through which large currents flow, as choke coils in DC-DC converter circuits and power supply circuits, and as electronic components in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, medical and industrial machinery, etc. However, the uses of inductors are not limited to these, and they can also be used, for example, in tuning circuits, filter circuits, rectifying and smoothing circuits, etc.

[0029] [1.2. Manufacturing Process of Inductor] The inductor 1 can be manufactured, for example, as follows. Fig. 4 is a diagram showing the manufacturing process of the inductor 1. The manufacturing process of the inductor 1 can include a granulation process (S1), a preform formation process (S2), a coil conductor formation process (S3), an element molding process (S4), a barrel polishing process (S5), a surface treatment process (S6), and an external electrode formation process (S7).

[0030] The granulation step (S1) is a step of granulating a mixed powder obtained by mixing metal magnetic particles and resin, which are raw materials for the core 30, to obtain granulated powder. The granulation step (S1) will be described in detail later.

[0031] The preform formation step (S2) is a step of forming a preform called a tablet. The preform is formed by placing the granulated powder, which is the material of the element body 2, in a mold and pressurizing it to form a solid form that is easy to handle. In this embodiment, as an example, two types of tablets are formed: a first tablet having an E-shaped cross section with a groove into which the coil conductor 20 fits, and a second tablet having an I-shaped (plate-like) cross section that covers the groove of the first tablet.

[0032] The coil conductor forming step (S3) is a step of forming the coil conductor 20 from a conductive wire. The coil conductor 20 is formed by winding the conductive wire into a shape having, for example, an alpha-winding winding portion 22 and a pair of lead-out portions 24. As described above, the coil conductor 20 does not necessarily have to be wound, and may be linear, meandering, or the like.

[0033] In the element molding step (S4), the first tablet, the coil conductor 20, and the second tablet are set in a molding die, and while heated, pressure is applied in the overlapping direction of the first tablet and the second tablet to harden them, integrating the first tablet, the coil conductor, and the second tablet, thereby molding the element 2 in which the coil conductor 20 is enclosed in the core 30.

[0034] In the barrel polishing step (S4), a plurality of element bodies 2 are loaded into a drum, and the drum is rotated so as not to apply excessively strong impacts. A coating liquid that will form an element body protective layer is sprayed onto the element bodies 2. This rounds the corners of the element bodies 2 and applies the coating liquid to the element bodies 2. The element bodies 2 with the coating liquid applied are then removed from the drum and heat-treated, thereby forming an element body protective layer on the surface of the element bodies 2.

[0035] The formation of the element body protective layer is not limited to the above, and can be performed by various methods, such as by providing a separate process from the barrel polishing process (S4) and spraying a coating liquid onto the element body 2, dipping the element body 2 into the coating liquid, supplying the coating liquid onto the surface of the element body 2 via a dispenser, and / or printing a coating material onto the surface of the element body 2 using various printing methods.

[0036] The surface treatment step (S5) is a step of modifying the surface of the planned electrode area by irradiating the planned electrode area on the surface of the core 30 with laser light. Here, the planned electrode area refers to the area on the surface of the core 30 where the external electrode 4 is to be formed, including the area where the lead-out portion 24 is exposed. Specifically, by irradiating the laser light, the element body protective layer on the surface of the core 30 and the coating layer on the lead-out portion 24 of the coil conductor 20 are removed within the planned electrode area, the resin on the surface of the core 30 is removed, and the insulating film on the surface of the metal magnetic particles exposed from the core 30 is removed. As a result, the exposed area of ​​the metal of the metal magnetic particles per unit area of ​​the surface of the core 30 is larger in the planned electrode area of ​​the surface of the core 30 than in other surface areas of the core 30.

[0037] In the external electrode formation step (S7), the external electrodes 4 are formed at the intended electrode locations on the core 30. Specifically, first, a Cu plating layer is formed by electrolytic plating at the intended electrode locations on the core 30. Subsequently, a Ni plating layer and a Sn plating layer can be formed by electrolytic plating on the Cu plating layer.

[0038] [2. Granulated Powder] Next, the granulated powder used to form core 30, which is the magnetic core of inductor 1, will be described. As described above, in a magnetic core produced by filling a mold with granulated powder and then hot-pressing, the filling rate of the granulated powder in the mold depends on the properties of the granulated powder. As conditions required of the granulated powder, it is particularly important that the filling rate of the granulated powder filled in the mold is high and that the density of the magnetic core produced from the granulated powder is high (i.e., that the density of the metal magnetic particles is high).

[0039] The inventors have thoroughly investigated the properties and state that granulated powder should have from the above perspectives, and have found that when the D90 particle size / D10 particle size (the value obtained by dividing the D90 particle size by the D10 particle size) of the granulated powder is set to a predetermined value, the slipperiness of the granulated powder, as described below, is improved. This improves the fluidity of the granulated powder when heated and pressurized, enabling the magnetic core to be densified. The larger the D90 particle size / D10 particle size ratio, the larger the D90 particle size relative to the D10 particle size, resulting in a relatively broad particle size distribution. On the other hand, as the D90 particle size / D10 particle size ratio decreases and approaches 1, the smaller the D90 particle size relative to the D10 particle size, resulting in a relatively sharp particle size distribution.

[0040] Hereinafter, embodiments and examples of granulated powder that enable improvement in the shape stability and high density of the magnetic core will be described.

[0041] [2.1. Granulated Powder Embodiment] According to this embodiment, the difference between the D90 particle size / D10 particle size of the granulated powder and the D90 particle size / D10 particle size of the first metal magnetic particles alone is -2.00 or less. More preferably, the difference between the D90 particle size / D10 particle size of the granulated powder and the D90 particle size / D10 particle size of the first metal magnetic particles alone is -1.68 or less.

[0042] These preferred particle sizes allow the second metal magnetic particles to adhere well to the periphery of the first metal magnetic particles, thereby improving the fluidity of the granulated powder. Note that the adhesion of the second metal magnetic particles refers to the arrangement and number of the second metal magnetic particles attached to the periphery of the first metal magnetic particles.

[0043] [2.2. Granulated Powder Manufacturing Method] Next, a method for manufacturing granulated powder according to this embodiment will be described. The granulated powder manufacturing method described below can be carried out, for example, in the granulation step (S1) shown in the manufacturing process of FIG. 4.

[0044] The granulated powder is produced by an agitation granulation method or a tumbling fluidized bed granulation method.

[0045] The agitation granulation method is a method in which a powder of raw metal magnetic particles is placed into a granulation container using an agitation granulator, and the main shaft and granulation shaft are rotated horizontally to agitate and mix the first metal magnetic particles and the second metal magnetic particles, while adding a resin solution that is a solution of a thermosetting resin, causing them to agglomerate into spherical granulated powder.

[0046] The tumbling fluidization granulation method is a method in which a powder of metal magnetic particles is placed in a roughly cylindrical fluidized bed vessel using a tumbling fluidization granulator, and the powder is fluidized in the vessel by rotating the stirring blades while blowing in a gas (e.g., nitrogen) from an air outlet at the bottom, and in this state, a resin solution is sprayed onto the fluidized powder from a spray nozzle at the top, causing it to agglomerate into spherical granulated powder.

[0047] As an example, the configuration of the metal magnetic particles and the composition of the resin solution are as follows. The powder of metal magnetic particles includes first metal magnetic particles, which are large particles, and second metal magnetic particles, which are small particles. The first metal magnetic particles are an Fe-Si-B-C alloy and have a D50 particle size of 28.25 μm. The second metal magnetic particles are pure iron coated with glass by a sol-gel method and have a D50 particle size of 2.07 μm. The weight ratio of the first metal magnetic particles to the second metal magnetic particles in the powder of metal magnetic particles is 90-60:10-40 (first metal magnetic particles:second metal magnetic particles) in both the stirring granulation method and the rolling fluidized bed granulation method, and more preferably 65:35 (first metal magnetic particles:second metal magnetic particles).

[0048] The resin solution contains a thermosetting resin (epoxy resin) as a base resin and an epoxy resin curing agent as a curing agent, and a diluent solvent (methyl ethyl ketone). The diluent solvent is not limited to methyl ethyl ketone, but may be any solvent capable of diluting the base resin and curing agent. Other diluent solvents include ethanol, methanol, acetone, methyl isobutyl ketone, ethyl acetate, isobutyl acetate, toluene, xylene, tetrahydrofuran, normal hexane, and cyclohexane.

[0049] Furthermore, the granulation step (S1) includes a sieving process for separating the particle size of the granulated powder obtained by the stirring granulation method or the tumbling fluidized bed granulation method. The sieving process can also be called a classification process.

[0050] The sieving process is a process described below. A sieve with 106 μm openings is set on the upper side and a sieve with 53 μm openings is set on the lower side, and the resulting granulated powder is placed on the upper sieve with 106 μm openings and shaken in a sieve shaker for 5 minutes. Subsequently, a first process is performed in which only the granulated powder remaining on the lower sieve with 53 μm openings is removed and placed on the upper sieve with 106 μm openings and shaken in a sieve shaker for 5 minutes. The first process is repeated three times, and only the granulated powder remaining on the sieve with 53 μm openings is used to proceed to the next preform molding process (S2).

[0051] By performing this sieving process, it is possible to remove granulated powders with particle sizes that are too large and those with particle sizes that are too small. It is presumed that granulated powders with particle sizes that are too large are caused, for example, by agglomeration of first metal magnetic particles with relatively large particle sizes, or by excessive adhesion of second metal magnetic particles to the first metal magnetic particles, resulting in poor adhesion of the second metal magnetic particles to the first metal magnetic particles. It is presumed that granulated powders with particle sizes that are too small are caused by agglomeration of second metal magnetic particles with relatively small particle sizes that do not sufficiently adhere to the first metal magnetic particles, resulting in poor adhesion of the second metal magnetic particles to the first metal magnetic particles. Furthermore, this sieving process has the advantage of being able to change the properties of the granulated powder after granulation, which is difficult to do with stirring granulation, tumbling fluidized bed granulation, or other known granulation methods.

[0052] FIG. 5 is a schematic diagram showing the configuration of granulated particles 40 of the granulated powder according to the present embodiment. Granulated particles 40 contained in the granulated powder are particles granulated from metal magnetic particles and a predetermined weight ratio of a base agent and a curing agent to form a thermosetting resin, and include metal magnetic particles 41 and a thermosetting resin 42. Metal magnetic particles 41 include first metal magnetic particles 41a and second metal magnetic particles 41b having different particle sizes. The average particle size of second metal magnetic particles 41b is smaller than the average particle size of first metal magnetic particles 41a. As shown in FIG. 5, second metal magnetic particles 41b are attached to the periphery of first metal magnetic particles 41a.

[0053] [2.3. Granulated Powder Examples] Granulated powders were obtained by the rolling granulation method and rolling fluidized bed granulation method described in the granulation step (S2). Furthermore, each of the obtained granulated powders was subjected to a sieve treatment. A total of six types of granulated powders obtained by the above two treatments and the first metal magnetic particles, which are one of the raw materials of the granulated powders, were evaluated.

[0054] The evaluation targets are listed below. The first is the first metal magnetic particles alone, designated Comparative Example 1. The second is granulated powder produced by the agitation granulation method and not subjected to sieving, designated Comparative Example 2. The third is granulated powder produced by the agitation granulation method and remaining on a sieve with 53 μm openings in the sieving process, designated Example 1. The fourth is granulated powder produced by the agitation granulation method, passed through a sieve with 53 μm openings in the sieving process, and dropped to the bottom inside the sieve shaker, designated Comparative Example 3. The fifth is granulated powder produced by the tumbling fluidized bed granulation method and not subjected to sieving, designated Comparative Example 4. The sixth is granulated powder produced by the tumbling fluidized bed granulation method and remaining on a sieve with 53 μm openings in the sieving process, designated Example 2. The seventh example is a granulated powder produced by the tumbling fluidized bed granulation method, passed through a sieve with 53 μm openings in the sieving process, and dropped to the bottom inside the sieve shaker, and is designated as Comparative Example 5.

[0055]

[0056] Table 1 shows the evaluation results.

[0057] (Particle size) The particle size distributions of the D10 particle size, D50 particle size, and D90 particle size of each type of evaluation object were measured using a particle size distribution analyzer (Malvern Instruments Mastersizer 3000) by a laser diffraction scattering method in accordance with JIS Z 8825.

[0058] The D90 particle size / D10 particle size ratio was calculated by dividing the D90 particle size ratio by the D10 particle size ratio for each type of evaluation object. The D90 particle size / D10 particle size ratio of Comparative Example 1, i.e., the D90 particle size / D10 particle size ratio of the relatively large first metal magnetic particles, 5.08, was defined as α, and the D90 particle size / D10 particle size - α ratio for each type of evaluation object was calculated.

[0059] D90 particle size / D10 particle size - α corresponds to the difference between the D90 particle size / D10 particle size of the granulated powder and the D90 particle size / D10 particle size of the first metal magnetic particles alone.

[0060] The particle size distribution of the object to be evaluated can also be measured using the following methods. One method involves obtaining a powder by dissolving the resin contained in the granulated powder in a solvent (e.g., methyl ethyl ketone, acetone, carbon tetrachloride, etc.) or by thermally decomposing it by heating, and then measuring the particle size of the powder to obtain the particle size distribution. Another method involves observing the cross-sections of multiple granulated powders and calculating the circle-equivalent diameter of the granulated powder particles. Specifically, a heaped pile of about 1 g of granulated powder is subjected to a process such as thermal curing to prevent the resin contained in the granulated powder from dissolving into the resin used to expose the cross-section and changing its shape. The resin is then embedded in the resin to expose the cross-section, and the cross-section is then observed to obtain a volume-based particle size distribution using the circle-equivalent diameter. Among the peaks of the particle size distribution obtained by the above two methods, particles falling into the first particle size distribution with the largest particle diameter peak are designated as first metal magnetic particles, and the D90 particle size / D10 particle size value of the large particles is determined from the first particle size distribution. If the particle size distributions of the first metal magnetic particles and the second metal magnetic particles overlap and it is difficult to determine the value of the first particle size distribution with the maximum peak, the first metal magnetic particles and the second metal magnetic particles are each assumed to be normally distributed, and the two peaks are separated using either a Gaussian function, a Voigt function, or a Lorentz function, and the particle with the larger maximum peak value is determined to be the first metal magnetic particle.

[0061] (Slipperiness) The slipperiness of each type of evaluation object was evaluated. The method for measuring slipperiness is described below.

[0062] Slipperiness can be measured in accordance with JIS-Z 8835. More specifically, slipperiness can be measured using a direct-acting lower cell type single shear tester (NS-S500 powder bed shear force measuring device manufactured by Nano Seeds Co., Ltd.) according to the following procedure. The inner diameters of the upper and lower cells are both set to 15 mm, and the gap (micro gap) between the upper and lower cells is set to 0.2 mm. Before adding the powder, an upper mortar is placed in the upper and lower cells to set the zero point so that the thickness of the powder layer can be measured using a laser sensor. 10 g of powder sample is uniformly filled into this upper and lower divided cell, and the upper mortar is gently placed in place. A 150 N indentation load is applied using the vertical servo motor. The position of the load cell of the vertical servo motor is fixed at the point when the 150 N indentation load is applied using the vertical servo motor. The indentation speed is set to 0.2 mm / sec. Horizontal sliding begins 100 seconds after the position of the load cell of the vertical servo motor is fixed. In other words, the sliding start delay is set to 100 seconds. After sliding begins with the horizontal servo motor, pressure is measured every 0.1 seconds. The sliding speed is set to 5 μm / second. Continuous measurements are taken at N = 50 or more points for each sample while the horizontal servo motor is operating, and measurements are stopped when the coefficient of variation (CV value) of the measured values ​​falls below 0.4%. The final thickness of the consolidated powder layer (final powder layer thickness) is measured using a laser sensor. This measurement yields data such as that shown in Figure 6. In the graph in Figure 6, the stress on the vertical axis represents the measured bottom load (the load applied to the load cell on the bottom side), with (a) representing the time the vertical servo motor is operating, (b) representing the maximum indentation load, (c) representing the indentation load at the start of sliding, and (d) representing the time the horizontal servo motor is operating.

[0063] Stress relaxation rate [%] = 100 × (maximum indentation load [N] - lateral sliding indentation load [N]) / maximum indentation load [N] (1) Slipperiness [% / mm] = stress relaxation rate [%] / (final powder layer thickness [mm]) (2)

[0064] The slipperiness can be calculated using the above formulas (1) and (2) based on the values ​​of the maximum indentation load (the value detected by the load cell on the bottom side), the indentation load at the start of lateral sliding, and the final powder layer thickness obtained by the measurement.

[0065] As shown in Table 1, it was confirmed that the granulated powder produced by the agitation granulation method had greater slipperiness in Example 1, which was subjected to sieving, than in Comparative Example 2, which was not subjected to sieving, and Comparative Example 3, which was removed by sieving.

[0066] Here, the granulated powder corresponding to Comparative Example 2, which is produced by the stirring granulation method and has a slipperiness greater than that of the granulated powder that has not been subjected to sieving, is presumed to have better fluidity than the granulated powder produced only by the normal stirring granulation method.

[0067] When the relationship between D90 particle size / D10 particle size - α and slipperiness for each of Comparative Example 2, Example 1, and Comparative Example 3 is approximated by a quadratic function, the approximate formula calculates that D90 particle size / D10 particle size - α is -1.54 when the slipperiness is 2.74. Note that in the approximation using slipperiness as a quadratic function, D90 particle size / D10 particle size - α is the independent variable, and it is presumed that the smaller the D90 particle size / D10 particle size - α, the better the slipperiness actually is, so the solution with the smaller value of D90 particle size / D10 particle size - α when the slipperiness is 2.74 is adopted.

[0068] Furthermore, as shown in Table 1, it was confirmed that the slipperiness of Example 2, which was subjected to sieving, was greater than that of Comparative Example 4, which was not subjected to sieving, and Comparative Example 5, which was removed by sieving, in the granulated powder produced by the tumbling fluidized granulation method.

[0069] From the above results, it is presumed that the granulated powder produced by the stirring granulation method corresponding to Comparative Example 4, which has a greater slipperiness than the granulated powder that has not been subjected to sieving, has better fluidity than the granulated powder produced only by the normal tumbling fluidization granulation method.

[0070] When the relationship between D90 particle size / D10 particle size - α and slipperiness for each of Comparative Example 4, Example 2, and Comparative Example 5 is approximated by a quadratic function, it is calculated that D90 particle size / D10 particle size - α is -1.81 when the slipperiness is 2.86.

[0071] From the above, it is estimated that the threshold value of the value of D90 particle size / D10 particle size - α, at which the slipperiness of the granulated powder is increased and the flowability is improved compared to when sieving is not performed, whether using agitation granulation or tumbling fluidization granulation, is -1.68, which is the arithmetic mean value of -1.54 and -1.81.

[0072] Thus, it is confirmed that granulated powder having a D90 particle size / D10 particle size - α of -1.68 or less has good slip properties and therefore good fluidity.

[0073] The reason why the relationship between D90 particle size / D10 particle size - α and the slipperiness is approximated by a quadratic function, more specifically, the relationship between D90 particle size / D10 particle size - α and the slipperiness has an extreme value, is presumed to be as follows: That is, the granulated powder that has passed through a sieve with a mesh size of 53 μm is expected to contain a large amount of agglomerated second metal magnetic particles that did not adhere to the first metal magnetic particles.

[0074] It should be noted that all of the above-described embodiments and examples are merely examples of one aspect of the present invention, and can be modified and applied as desired without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the horizontal, vertical, and other directions, various numerical values, shapes, and materials in the above-described embodiments include a range that provides the same action and effect as those directions, numerical values, shapes, and materials (so-called equivalent ranges).

[0075] 3. Configurations Supported by the Above-described Embodiments and Examples The above-described embodiments and examples support the following configurations.

[0076] (Configuration 1) A granulated powder having large particles and small particles, wherein the difference between the D90 particle size of the granulated powder divided by the D10 particle size of the granulated powder and the D90 particle size of the large particles divided by the D10 particle size of the large particles is −1.68 or less. According to Configuration 1, by improving the flowability of the granulated powder, it is possible to improve the density of a molded body produced by heating and pressurizing in a molding die.

[0077] (Configuration 2) The granulated powder according to Configuration 1, wherein the difference between the D90 particle size of the granulated powder divided by the D10 particle size of the granulated powder and the D90 particle size of the large particles divided by the D10 particle size of the large particles is −2.00 or less. According to Configuration 2, the flowability of the granulated powder is further improved compared to Configuration 1, thereby making it possible to improve the density of a molded body produced by heating and pressurizing in a molding die.

[0078] (Configuration 3) The granulated powder according to Configuration 1 or 2, wherein the large particles are metallic magnetic materials. According to Configuration 3, the granulated powder exhibits favorable magnetic properties.

[0079] (Configuration 4) The granulated powder according to any one of Configurations 1 to 3, wherein the small particles are metallic magnetic materials. According to Configuration 4, the granulated powder exhibits favorable magnetic properties.

[0080] (Configuration 5) A magnetic compact using the granulated powder according to any one of Configurations 1 to 4. Configuration 5 provides the same functions and effects as those described above.

[0081] (Configuration 6) An inductor using the magnetic molded body according to Configuration 5. Configuration 6 provides the same functions and effects as those described above.

[0082] 1...inductor, 2...element body, 4...external electrode, 10...bottom surface, 12...top surface, 14...end surface, 16...side surface, 20...coil conductor, 22...winding portion, 24...lead portion, 30...core.

Claims

1. A granulated powder having large particles and small particles, wherein the difference between the D90 particle size of the granulated powder divided by the D10 particle size of the granulated powder and the D90 particle size of the large particles divided by the D10 particle size of the large particles is -1.68 or less.

2. The granulated powder according to claim 1, wherein the difference between the value obtained by dividing the D90 particle size of the granulated powder by the D10 particle size of the granulated powder and the value obtained by dividing the D90 particle size of the large particles by the D10 particle size of the large particles is -2.00 or less.

3. The granulated powder according to claim 1 or 2, wherein the large particles are metallic magnetic particles.

4. The granulated powder according to any one of claims 1 to 3, wherein the small particles are metallic magnetic materials.

5. A magnetic compact made using the granulated powder according to any one of claims 1 to 4.

6. An inductor using the magnetic molding according to claim 5.

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