powder compact

Abstract

To provide green compact having low core loss in a high frequency band and excellent DC superposition characteristics.SOLUTION: Green compact 10 includes a plurality of metal particles 20 and an inclusion 50 interposed between the metal particles 20. The metal particles 20 are made of a soft magnetic alloy of a FeSiAl system and have a flat shape when viewed in a predetermined direction (a vertical direction in FIG. 2). One or more of predetermined holes 22 are formed in one or more metal particles 20. The predetermined hole 22 penetrates the metal particles 20 in a predetermined direction. A maximum width of the predetermined hole 22 in a predetermined plane orthogonal to the predetermined direction is equal to or larger than a depth of the predetermined hole 22 in the predetermined direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a powder compact having a plurality of metal particles and inclusions interposed between the metal particles. [Background technology]

[0002] For example, Patent Document 1 discloses this type of powder compact.

[0003] Patent Document 1 discloses a soft magnetic molded body (compressed powder body) in which flat-shaped soft magnetic metal powder is bound with a binder component (inclusions). The compressed powder body of Patent Document 1 has good magnetic properties such as low core loss at frequencies of about 1 MHz, and can be used as magnetic parts such as inductors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-175047 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for magnetic components with even lower core loss at higher frequencies. In addition, there is a demand for magnetic components with good DC bias characteristics. That is, there is a demand for green compacts that can be used as magnetic components with such magnetic characteristics.

[0006] Therefore, an object of the present invention is to provide a powder compact having low core loss in the high frequency band and good DC bias characteristics. [Means for solving the problem]

[0007] The present invention provides a first powder compact, A powder compact comprising a plurality of metal particles and inclusions interposed between the metal particles, the metal particles are made of a FeSiAl-based soft magnetic alloy and have a flat shape when viewed along a predetermined direction, one or more predetermined holes are formed in the one or more metal particles, the predetermined hole penetrates the metal particle in the predetermined direction, The maximum width of the predetermined hole in a predetermined plane perpendicular to the predetermined direction is equal to or greater than the thickness of the metal particle in the predetermined direction. A powder compact is provided.

[0008] Further, the present invention provides a first powder compact as the second powder compact, The thickness of the metal particles in which the predetermined holes are formed is 0.5 μm or more and 5 μm or less. A powder compact is provided.

[0009] Furthermore, the present invention provides a third powder compact, which is the first or second powder compact, The maximum width of the predetermined hole is 1 μm or more and 5 μm or less. A powder compact is provided.

[0010] Furthermore, the present invention provides a fourth powder compact, which is any one of the first to third powder compacts, The predetermined hole is a cavity. A powder compact is provided.

[0011] Furthermore, the present invention provides a fifth powder compact, which is any one of the first to fourth powder compacts, Both ends of the predetermined hole in the predetermined direction are covered by a part of the inclusion. A powder compact is provided.

[0012] Furthermore, the present invention provides a sixth powder compact, which is any one of the first to fifth powder compacts, The inclusions have silicon oxide as a main component or are glass. A powder compact is provided. [Effects of the Invention]

[0013] The powder compact of the present invention is formed by bonding flat metal particles having predetermined pores (through holes) of a predetermined size together with inclusions. By forming through holes in the flat metal particles, the core loss of the powder compact can be reduced in high frequency bands of several MHz or more. In addition, the DC bias characteristics of the powder compact can be improved. That is, according to the present invention, a powder compact having low core loss and good DC bias characteristics in high frequency bands can be provided. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an example of a powder compact according to an embodiment of the present invention; [Figure 2] 2 is an image showing a portion of the example of the powder compact of FIG. 1 along line II-II. [Figure 3] 3 is an image of the metal particles included in the example of FIG. 2 taken with an electron microscope at an applied voltage of 5 kV. [Figure 4] This is an image of the metal particle in Figure 3 taken with an electron microscope at an applied voltage of 15 kV. [Figure 5] 5(A) is a top view schematically showing the metal particle of FIG. 3. The outline of the predetermined hole hidden by the oxide film is drawn with a dashed line. 5(B) is a side view showing the metal particle of FIG. 5(A). [Figure 6] FIG. 6 is a top view illustrating the magnetic properties of the metal particles of FIG. 5. [Figure 7] FIG. 6 is a diagram showing the DC superposition characteristics of the metal particles of FIG. 5. [Figure 8] 6A to 6C are diagrams showing a process of forming predetermined holes in the metal particles of FIG. 5. [Figure 9] FIG. 1 is a diagram showing core losses according to an example of the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Referring to FIG. 1 , a powder compact 10 according to an embodiment of the present invention is a powder magnetic core. The powder magnetic core of this embodiment has a toroidal shape. More specifically, the powder compact 10 has a circular ring shape in a horizontal plane (XY plane). That is, a central hole 12 is formed in the powder compact 10. The central hole 12 has a circular shape in the horizontal plane and penetrates the powder compact 10 in a predetermined direction perpendicular to the horizontal plane. In this embodiment, the predetermined direction is the up-down direction, or Z direction. In this embodiment, up is the +Z direction, and down is the −Z direction. However, terms indicating positional relationships such as “horizontal,” “up,” and “down” do not indicate absolute positional relationships with respect to the ground, but merely indicate relative positional relationships in the drawing.

[0016] As described above, the powder compact 10 of this embodiment is a toroidal-shaped magnetic core. However, the present invention is not limited to this and can be applied to various magnetic parts other than magnetic cores. For example, the powder compact 10 of the present invention may be a magnetic sheet. Furthermore, the shape of the powder compact 10 of the present invention is not particularly limited.

[0017] Referring to FIG. 2, the powder compact 10 includes a plurality of metal particles 20 and inclusions 50 interposed between the metal particles 20. As will be described later, the powder compact 10 of this embodiment is formed by subjecting a mixture of a thermosetting binder (hereinafter simply referred to as "binder") containing an inorganic substance and the metal particles 20 to a heat treatment. The inclusions 50 of this embodiment are formed from the binder during the heat treatment. The inclusions 50 have pores (voids) of various shapes formed therein.

[0018] The powder compact 10 of this embodiment is formed from metal particles 20, inclusions 50, and voids. Specifically, the powder compact 10 of this embodiment contains 60 volume % or more of metal particles 20, 4 volume % or more and 30 volume % or less of inclusions 50, and 10 volume % or more and 30 volume % or less of voids. The powder compact 10 contains a sufficient number of metal particles 20 and has the magnetic properties required for a magnetic core. However, the present invention is not limited thereto. For example, the volume ratio of the metal particles 20 to the powder compact 10 is not particularly limited as long as the powder compact 10 has the magnetic properties required for the application. Furthermore, the powder compact 10 may contain other substances in addition to the metal particles 20 and inclusions 50.

[0019] 2 to 4, each of the metal particles 20 has a flat shape when viewed in a predetermined direction (vertical direction). In the powder compact 10, each of the metal particles 20 is oriented parallel to a horizontal plane. That is, the axis of easy magnetization of the powder compact 10 extends in a direction parallel to the horizontal plane. This reduces the demagnetizing factor in the direction parallel to the horizontal plane, thereby increasing the relative permeability of the powder compact 10. More specifically, the powder compact 10 of this embodiment has a relative permeability of 60 or more and 150 or less when no magnetic field is applied.

[0020] The inclusions 50 are partially aggregated in a particle-like form and spread out in a planar form along both surfaces (upper and lower surfaces) of the metal particles 20. That is, the inclusions 50 are present throughout the entire powder compact 10 and bind the metal particles 20 together.

[0021] Each of the metal particles 20 is made of a FeSiAl-based soft magnetic alloy (Sendust). That is, each of the metal particles 20 contains Fe, Si, and Al as primary elements. Each of the metal particles 20 may contain other elements in addition to Fe, Si, and Al. From the viewpoint of obtaining the magnetic properties required for a magnetic component, the metal particles 20 must contain primarily Fe. The Fe ratio in the metal particles 20 is preferably 70% by weight or more and 95% by weight or less, the Si ratio is preferably 3% by weight or more and 18% by weight or less, and the Al ratio is preferably 1% by weight or more and 12% by weight or less. However, the present invention is not limited thereto, and the Si ratio and the Al ratio in the metal particles 20 are not particularly limited as long as the green compact 10 has the required magnetic properties.

[0022] Some of the metal particles 20 contained in the powder compact 10 have one or more predetermined holes 22 formed therein that satisfy the conditions described below. In other words, one or more metal particles 20 have one or more predetermined holes 22 formed therein. The metal particles 20 having the predetermined holes 22 formed therein have a structure schematically shown in FIG. 5. The illustrated metal particles 20 have an elliptical shape in a horizontal plane and a constant size (thickness TP) in a predetermined direction (up and down direction). In addition, the illustrated metal particles 20 extend completely parallel to the horizontal plane. However, the present invention is not limited to this. For example, the shape of an actual metal particle 20 in a horizontal plane is irregular. Furthermore, the thickness TP of an actual metal particle 20 varies slightly depending on the location. Furthermore, the metal particles 20 may extend approximately parallel to the horizontal plane while being curved in a predetermined direction.

[0023] Referring to FIG. 5 , each of the predetermined holes 22 penetrates the metal particle 20 in a predetermined direction (vertical direction). Each of the illustrated predetermined holes 22 has a pentagonal shape in a horizontal plane and has a constant horizontal cross section regardless of its position in the predetermined direction. Furthermore, each of the illustrated predetermined holes 22 penetrates the metal particle 20 straight along the predetermined direction. However, the present invention is not limited to this. For example, the shape of each of the predetermined holes 22 in a horizontal plane may be rectangular, trapezoidal, or triangular. The horizontal cross section of each of the predetermined holes 22 may vary slightly depending on its position in the predetermined direction. Each of the predetermined holes 22 may penetrate the metal particle 20 in a direction oblique to the predetermined direction, or may penetrate the metal particle 20 in a curved manner.

[0024] Each of the predetermined holes 22 has a relatively large size in a horizontal plane. Specifically, the maximum width LM of the predetermined hole 22 in a predetermined plane (i.e., a horizontal plane) perpendicular to the predetermined direction (up-down direction) is equal to or greater than the thickness TP of the metal particle 20 in the predetermined direction. In other words, the predetermined hole 22 is a through-hole formed in the metal particle 20 that satisfies the above-mentioned size conditions. The metal particle 20 may have formed therein thin holes or recesses other than the predetermined holes 22 that satisfy these conditions. Such thin holes or recesses are likely to be formed, for example, in the peripheral portion of the metal particle 20.

[0025] The maximum width LM of the predetermined hole 22 is the distance between the two most distant points on the horizontal cross sections when observing various horizontal cross sections of the predetermined hole 22. That is, the maximum width LM of the predetermined hole 22 is the maximum distance between two points on the upper end of the predetermined hole 22, the maximum distance between two points on the lower end of the predetermined hole 22, or the maximum distance between two points on the middle part of the predetermined hole 22 in a predetermined direction (up and down direction).

[0026] Strictly speaking, the thickness TP of the metal particle 20 is the maximum value of the size in the predetermined direction (vertical direction) of the portion of the metal particle 20 surrounding the predetermined hole 22. However, the thickness of the metal particle 20 does not vary significantly except for the peripheral portion. In particular, the thickness of the metal particle 20 in a narrow region such as the periphery of the predetermined hole 22 can be considered to be almost constant. In other words, the thickness TP can be considered to be the same as the size (depth DP) of the predetermined hole 22 in the predetermined direction.

[0027] Each of the predetermined holes 22 in this embodiment is open to the outside of the metal particle 20 at both ends (upper and lower ends) in a predetermined direction (vertical direction). However, both surfaces (upper and lower surfaces) in the predetermined direction of the illustrated metal particle 20 are covered with a thin oxide film 26. The oxide film 26 is a portion of the inclusion 50 that extends in a planar shape along both surfaces of the metal particle 20. In other words, the oxide film 26 is a part of the inclusion 50, and blocks the opening of the predetermined hole 22.

[0028] The oxide film 26 is part of the inclusions 50 that cover both sides of the metal particles 20 during the manufacturing process of the powder compact 10. In this embodiment, the upper and lower ends of each of the predetermined holes 22 are basically completely covered by the oxide film 26. That is, both ends of each of the predetermined holes 22 in a predetermined direction (vertical direction) are covered by a portion of the inclusions 50. However, the thickness of the oxide film 26 is extremely thin, about 10 to 100 nm. Referring to FIG. 3, when the applied voltage of the electron microscope is low, about 5 kV, the predetermined holes 22 are covered by the oxide film 26 except for the portions where the oxide film 26 was peeled off during delamination for observation. On the other hand, referring to FIG. 4, when the applied voltage of the electron microscope is high, about 15 kV, the predetermined holes 22 covered by the oxide film 26 can be observed.

[0029] 5, according to this embodiment, each of the predetermined holes 22 is a closed space covered with the oxide film 26. However, the present invention is not limited to this. Each of the predetermined holes 22 may be partially covered with the oxide film 26, or may not be covered with the oxide film 26 at all.

[0030] In this embodiment, each of the predetermined holes 22 is hollow. That is, no tangible substance such as the inclusions 50 exists inside each of the predetermined holes 22. However, the present invention is not limited to this. For example, each of the predetermined holes 22 may be filled with a portion of the inclusions 50.

[0031] 6, it can be considered that the predetermined holes 22 divide one flat metal particle 20 into a plurality of spherical virtual particles 70 (fine spherical particles). According to this consideration, the metal particle 20 having the predetermined holes 22 formed therein should have intermediate magnetic properties between the magnetic properties of a conventional flat particle (flat particle) and the magnetic properties of a conventional fine spherical particle. This consideration can be verified as follows.

[0032] Referring to Figure 7, conventional flat particles have high inductance when no magnetic field is applied, but the inductance deteriorates rapidly when a magnetic field is applied. Conventional fine spherical particles have low inductance when no magnetic field is applied, but the inductance hardly deteriorates when a magnetic field is applied. In other words, conventional fine spherical particles have extremely good DC bias characteristics compared to conventional flat particles.

[0033] On the other hand, referring to Figure 7 together with Figure 6, the flat particles of this embodiment (i.e., metal particles 20 with predetermined holes 22 formed therein) have a lower inductance than conventional flat particles when no magnetic field is applied, but a higher inductance than conventional fine spherical particles. In addition, the inductance of the flat particles of this embodiment does not deteriorate significantly even when a magnetic field is applied. Such DC bias characteristics cannot be obtained by mixing conventional flat particles with conventional fine spherical particles.

[0034] The verification results shown in Figure 7 suggest that the above considerations are correct. Specifically, by forming predetermined holes 22 in flat-shaped metal particles 20, the magnetic domain structure changes from that of conventional flat particles to that of a plate-like structure containing a high density of fine spherical particles. As a result, DC bias characteristics intermediate between those of conventional flat particles and those of conventional fine spherical particles are obtained. Furthermore, referring to Example 1 in Figure 9, the refinement of the magnetic domain structure reduces core loss in the high-frequency band of 1 MHz to 10 MHz.

[0035] Summarizing the above explanation with reference to FIGS. 2 to 4, the powder compact 10 of this embodiment is formed by bonding flat metal particles 20 having predetermined pores 22 (through holes) of a predetermined size together with inclusions 50. By forming through holes in the flat metal particles 20, it is possible to reduce the core loss of the powder compact 10 in a high frequency band of several MHz or more. In addition, it is possible to improve the DC bias characteristics of the powder compact 10. That is, according to this embodiment, it is possible to provide a powder compact 10 that has low core loss and good DC bias characteristics in a high frequency band.

[0036] If the metal particles 20 having one or more predetermined holes 22 formed therein are defined as "predetermined metal particles 20," then the metal particles 20 contained in the powder compact 10 may all be predetermined metal particles 20, or only a portion of the metal particles 20 may be predetermined metal particles 20. According to this embodiment, the ratio of the predetermined metal particles 20 to all the metal particles 20 contained in the powder compact 10 is about 5%. By including this amount of predetermined metal particles 20 in the powder compact 10, it is possible to provide a powder compact 10 having low core loss in the high frequency band and good DC superposition characteristics. 。 However, the present invention is not limited to this, and it is sufficient that the ratio of the predetermined metal particles 20 to all the metal particles 20 contained in the powder compact 10 is 5% or more. More specifically, it is sufficient that the ratio of the predetermined metal particles 20 to the metal particles 20 observed within a field of view of 60 × 45 μm in an SEM (scanning electron microscope) photograph taken at 2000 times magnification of the cross section of the powder compact 10 is 5% or more.

[0037] An example of a method for producing the powder compact 10 will be described below with reference to FIG.

[0038] First, flat soft magnetic metal powder is prepared by flattening spherical soft magnetic metal powder (material powder) made of, for example, an FeSiAl alloy using a ball mill.

[0039] Next, a mixture consisting of material powder, solvent, thickener, and binder is prepared. The solvent and thickener can be, for example, ethanol and polyacrylic acid ester, respectively. The binder can be, for example, methyl silicone resin. The mixture is thoroughly mixed to prepare a homogeneous slurry. More specifically, for example, the mixture is placed in a container with a diameter of 150 mm and a liquid surface depth of 150 mm. A homogeneous slurry can be prepared by stirring the mixture in the container, for example, with a rotating blade with a diameter of 100 mm, at a relatively high rotation speed (for example, 250 revolutions per minute) for a relatively long period of time (for example, 5 hours).

[0040] Next, the slurry is applied onto a substrate. For example, a doctor blade method can be used as the application method. For example, a PET (polyethylene terephthalate) film can be used as the substrate. The applied slurry is heated to volatilize the solvent, thereby producing a sheet-like preform, which is the material for the powder compact 10. The preform is not made of a brittle material, so it can be pressure-molded. In the preform, each of the metal particles 20 is oriented parallel to a horizontal plane.

[0041] Next, the preform is punched out to produce the required number of sheets of the required size. Next, the sheets are stacked in a predetermined direction (vertical direction) and compressed by applying pressure in the predetermined direction to produce a pressed molded body. For example, a mold is used to perform two pressings, room temperature pressing and hot pressing, to produce a pressed molded body. In the pressed molded body, the metal particles 20 are close to each other in the predetermined direction. Two metal particles 20 that are close to each other vertically extend parallel to each other in the predetermined direction, sandwiching the binder therebetween.

[0042] Next, the pressed molded body is heat-treated at a high temperature. For example, the heat treatment is performed in air at a maximum holding temperature of 850°C. The heat treatment hardens the binder and decomposes and removes the organic components of the binder. More specifically, the methyl-based silicone resin undergoes dehydration condensation, and the methyl groups are thermally decomposed to form silica, primarily composed of silicon oxide (SiO2) and containing traces of Fe and Al. The formed silica acts as inclusions 50, binding the metal particles 20 together and filling the spaces between the metal particles 20.

[0043] The powder compact 10 of this embodiment can be manufactured by the above steps.

[0044] 8, as a result of pressurization in a predetermined direction (vertical direction), the metal particles 20 stacked one above the other extend parallel to each other at a distance DS of 0.5 μm or less in the predetermined direction. In addition, during the process of heating the pressed molded body to a high temperature such as 850°C, the inclusions 50 (silica) formed from the binder fill the gap between the two metal particles 20 stacked one above the other, leaving almost no gaps. In other words, silicon oxide, which is the main component of the inclusions 50, contacts the metal particles 20 over the entire surfaces (top and bottom) of the metal particles 20. When the pressed molded body is maintained at a high temperature such as 850°C, the metal particles 20 and the inclusions 50 are arranged as described above.

[0045] Among the elements contained in the metal particles 20, Al is more easily oxidized than other contained elements or other elements such as Cr. While the pressed compact is maintained at a high temperature, such as 850°C, the Al contained in the metal particles 20 diffuses to both surfaces of the metal particles 20 and is selectively oxidized, forming an Al oxide film primarily composed of Al. Furthermore, the Al diffuses through both surfaces of the metal particles 20 and into the inclusions 50 (see the dashed arrows in Figure 8). As a result of this diffusion, predetermined holes 22 are formed in the metal particles 20. In this embodiment, the predetermined holes 22 are believed to be formed as described above. However, it is believed that Fe also diffuses through the Al oxide film and forms an Fe oxide film outside the Al oxide film. In other words, the Fe element is also believed to contribute to the formation of the predetermined holes 22 to some extent.

[0046] As can be understood from the above explanation, in order to form the predetermined holes 22 in the metal particles 20, the holding temperature during the heat treatment of the pressed molded body needs to be high enough to cause diffusion of elements. On the other hand, if the holding temperature is too high, the metal particles 20 may be directly bonded to each other, which may result in insufficient insulation between the metal particles 20. More specifically, the holding temperature in this embodiment needs to be about 850°C.

[0047] By making the metal particles 20 flat, elements inside the metal particles 20 can more easily diffuse to the surface. In other words, in order to form the predetermined holes 22, the metal particles 20 are preferably flat particles. More specifically, the aspect ratio of the metal particles 20 (the maximum width along the surface of the metal particles 20 divided by the average thickness of the metal particles 20) is preferably 10 or more, and more preferably 20 or more. However, if the aspect ratio is too large, the metal particles 20 are more likely to be damaged when producing the green compact 10. Therefore, the aspect ratio of the metal particles 20 is preferably 50 or less, and more preferably 40 or less. That is, according to this embodiment, the aspect ratio of the metal particles 20 in which the predetermined holes 22 are formed is preferably 10 or more and 50 or less, and more preferably 20 or more and 40 or less.

[0048] If the metal particles 20 are thick, it is difficult to form the predetermined holes 22. In other words, in order to form the predetermined holes 22, it is preferable to make the metal particles 20 thin. More specifically, the thickness TP of the metal particles 20 is preferably 5 μm or less. On the other hand, in order to prevent damage to the metal particles 20 when manufacturing the powder compact 10, the metal particles 20 need to be made thick to a certain extent. In particular, if the metal particles 20 are excessively pulverized and the thickness TP is less than 0.5 μm, it is difficult to increase the density of the powder compact 10. In addition, the specific surface area of ​​the metal particles 20 increases (they become bulky), making molding difficult. Therefore, the thickness TP of the metal particles 20 is preferably 0.5 μm or more. That is, according to this embodiment, the thickness TP of the metal particles 20 in which the predetermined holes 22 are formed is preferably 0.5 μm or more and 5 μm or less.

[0049] Referring to FIG. 8 together with FIGS. 5 and 6, in order to form the magnetic domain structure of the above-described flat plate-like structure, when the metal grains 20 are viewed in a predetermined direction (vertical direction), the total area of ​​the predetermined holes 22 is preferably 1% or more of the area of ​​the metal grains 20. Furthermore, in order to sufficiently refine the magnetic domain structure, the maximum width LM of the predetermined holes 22 is preferably 1 μm or more. However, if the maximum width LM of the predetermined holes 22 exceeds 5 μm, the Al, Fe, and Si elements diffused into the inclusions 50 between the metal grains 20 may become a source of electrons and holes, potentially reducing the insulation between the metal grains 20. Therefore, the maximum width LM of the predetermined holes 22 is preferably 1 μm or more and 5 μm or less.

[0050] Referring to FIG. 8 , it is believed that inclusions 50 that come into contact with the surfaces of metal particles 20 and absorb diffused elements are necessary to form the predetermined holes 22. The inclusions 50 of this embodiment contain silicon oxide as a primary component and are presumed to absorb the diffused elements of metal particles 20 made of a FeSiAl-based soft magnetic alloy. Specifically, it is presumed that Si contained in silicon oxide primarily contributes to the formation of the predetermined holes 22 through the absorption of the diffused elements. However, the present invention is not limited thereto. For example, the inclusions 50 may contain, as a primary element, one or more of P, B, Bi, alkali metals (Li, Na, K), and alkaline earth metals (Mg, Ca, Sr, Ba) instead of or in addition to Si. These elements promote the formation of the predetermined holes 22.

[0051] For example, instead of or in addition to a methyl-based silicone resin, a glass frit containing one or more of P, B, Bi, alkali metals (Li, Na, K), and alkaline earth metals (Mg, Ca, Sr, Ba) may be used as the binder for forming the inclusions 50. More specifically, a Bi2O3-B2O3-based glass frit or a P2O5-R2O-Al2O3-based glass frit (where R is one or more elements selected from the group consisting of Li, Na, and K) may be used. These glass frits melt during heat treatment and then form glass. Furthermore, adding a material containing an alkali metal can lower the glass transition point and firing temperature, improving the fluidity of the glass. Furthermore, adding a material containing an alkaline earth metal can stabilize the chemical durability and amorphization of the glass.

[0052] To summarize the above explanation, the inclusions 50 of this embodiment preferably contain silicon oxide as a main component or are glass. That is, the binder of this embodiment preferably contains at least one of a thermosetting resin containing Si and glass frit. By increasing the proportion of glass frit mixed in the binder, the holding temperature during heat treatment can be reduced to about 600°C. As a result, the maximum holding temperature during heat treatment can be set to 600°C or higher and 900°C or lower.

[0053] When glass frit is contained in the binder, if the particle size of the glass frit is large, the density of the metal particles 20 in the slurry decreases, which is not preferable. When glass frit is contained in the binder, it is preferable to pulverize the glass frit to make it finer so that the particle size (D50) is about 0.95 μm.

[0054] According to this embodiment, after producing a thin sheet, multiple sheets are stacked and pressed. However, the present invention is not limited to this. For example, the material powder may be coated with a binder, granulated, and then filled into a mold and pressed. However, producing a thin sheet makes it easier for the material powder to be oriented along a horizontal plane and for the binder to be filled uniformly. As a result, the predetermined holes 22 are more easily formed in the metal particles 20. Therefore, unless there is a specific reason, the manufacturing method of this embodiment is preferred. [Example]

[0055] The powder compact of the present invention will be described in more detail below with reference to Examples 1 to 19 and Comparative Examples 1 and 2. First, the manufacturing methods of Example 1, Comparative Example 1 and Comparative Example 2 will be described.

[0056] (Preparation of material powders of Example 1 and Comparative Examples 1 and 2) Approximately spherical powder made of an FeSiAl alloy was flattened to produce the material powders of Example 1 and Comparative Example 1. Furthermore, approximately spherical powder made of an FeSiCr alloy was flattened to produce the material powder of Comparative Example 2. The material powders of Example 1 and Comparative Example 1 had an average powder length of 50 μm and an average aspect ratio of 29. The material powder of Comparative Example 2 had an average powder length of 16 μm and an average aspect ratio of 32.

[0057] (Preparation of Slurry in Example 1 and Comparative Examples 1 and 2) Slurries were prepared using the material powders of Example 1 and Comparative Examples 1 and 2. Specifically, a mixture was prepared by mixing the material powders, a solvent, a thickener, and a binder. The mixture was stirred to prepare a homogeneous slurry. Ethanol was used as the solvent. Polyacrylic ester was used as the thickener. Methyl silicone resin was used as the binder.

[0058] (Production of preforms of Example 1 and Comparative Examples 1 and 2) Preforms were prepared from the slurries of Example 1 and Comparative Examples 1 and 2. Specifically, the slurries were applied onto a PET film using a doctor blade method. The film was then dried at a temperature of approximately 70°C in a drying oven. The solvent was removed by drying to prepare preforms. The thickness of the prepared preforms was 200 μm.

[0059] (Production of molded bodies of Example 1 and Comparative Examples 1 and 2) The preforms of Example 1 and Comparative Examples 1 and 2 were each cut using a die to obtain a plurality of square sheets measuring 65 mm in width and 65 mm in length. For each of Example 1 and Comparative Examples 1 and 2, a predetermined number of sheets were stacked to produce a laminate. The produced laminate was cut into 6 t / cm using a die. 2 The laminate after room temperature pressing was pressed at a pressure of 80 kgf / cm. 2The molded body was hot-pressed at a temperature of 170°C under a pressure of 1.2 mm to produce a molded body plate with a thickness of 1.2 mm. The molded body plate thus produced was machined using a milling machine to produce the molded bodies of Example 1 and Comparative Examples 1 and 2. Each of the molded bodies had a toroidal shape with an outer diameter of 13 mm and an inner diameter of 8 mm.

[0060] (Production of dust cores of Example 1 and Comparative Examples 1 and 2) The molded bodies of Example 1 and Comparative Examples 1 and 2 were subjected to heat treatment in the atmosphere to produce dust cores of Example 1 and Comparative Examples 1 and 2. In the heat treatment, the binder removal time was 7 hours, and the temperature rise time was 2.5 hours. After the molded bodies of Example 1 and Comparative Example 2 were heated, they were held at a maximum holding temperature of 850°C (maximum holding temperature) for 1.5 hours. On the other hand, after the molded body of Comparative Example 1 was heated, it was held at a maximum holding temperature of 650°C (maximum holding temperature) for 1.5 hours.

[0061] The dust cores of Example 1 and Comparative Examples 1 and 2 prepared as described above were cut along a vertical plane, and the thickness of the metal particles inside the cores and the presence or absence of predetermined holes in the metal particles were observed. The observation results are shown in Table 1.

[0062] [Table 1]

[0063] Referring to Table 1, with the dust core of Example 1, holding at a high temperature of 850°C resulted in the formation of numerous predetermined pores in the flat particles (metal particles) made of an FeSiAl alloy. On the other hand, with the dust core of Comparative Example 1, holding at a relatively low temperature of 650°C resulted in no predetermined pores being formed in the metal particles. Specifically, although thin pores were formed around the peripheries of the metal particles, relatively large pores that satisfied the size requirements for the predetermined pores were not formed. Furthermore, with the dust core of Comparative Example 2, even when held at a high temperature of 850°C, no predetermined pores were formed in the flat particles (metal particles) made of an FeSiCr alloy. These results demonstrate that the composition containing Al element and the holding temperature are important for the formation of predetermined pores.

[0064] The core loss and DC bias characteristics were measured for the dust cores of Example 1 and Comparative Examples 1 and 2. The measurement results are shown in Table 2 and FIG.

[0065] [Table 2]

[0066] 9, in Example 1, the flat metal particles have predetermined holes formed therein, so that the metal particles function as flat plate-like structures containing a high density of virtual spherical particles. That is, the magnetic domains in each flat particle are refined, and the core loss in the high frequency band of 1 MHz to 10 MHz is lower than that of the flat particles of Comparative Examples 1 and 2, which do not have predetermined holes.

[0067] Referring to Table 2, H70 indicates the strength of the magnetic field at which the relative magnetic permeability is reduced by 30% compared to the relative magnetic permeability (initial magnetic permeability: μ′0) when no magnetic field is applied. μ′0 × H70 is the value obtained by multiplying the initial magnetic permeability by H70, and it can be determined that the larger this value, the better the DC bias characteristics. According to Comparative Example 1, high inductance is obtained by producing a dust core using flat particles, but the inductance rapidly deteriorates when a magnetic field is applied. On the other hand, according to Example 1, the above-mentioned flat particle structure achieves DC bias characteristics intermediate between those of flat particles and spherical particles. As a result, the dust core of Example 1 is less likely to deteriorate in magnetic permeability when a magnetic field is applied, compared to the dust cores of Comparative Examples 1 and 2.

[0068] To summarize the above considerations, by maintaining a molded body made using flat particles of an FeSiAl alloy at a high temperature during heat treatment, a dust core can be obtained that has low core loss in the high frequency band and good DC bias characteristics.

[0069] The metal particles 20 of Example 1 contained 83 wt % Fe, 12 wt % Si, and 5 wt % Al. 、Powder magnetic cores were manufactured using various FeSiAl alloys with different weight ratios in the same manner as in Example 1. As a result, effects similar to those in Example 1 were obtained when the Fe ratio was at least 70% by weight or more and 95% by weight or less, the Si ratio was 3% by weight or more and 18% by weight or less, and the Al ratio was 1% by weight or more and 12% by weight or less.

[0070] (Production of dust cores of Examples 2 to 19) Only the maximum holding temperature during heat treatment of the molded body of Example 1 was changed in increments of 50°C within a range of 600°C to 950°C, thereby producing the dust cores of Examples 2 to 5. Furthermore, part or all of the binder of Example 1 was replaced with a Bi2O3-B2O3-based glass frit, and further, the maximum holding temperature during heat treatment of the molded body was changed in increments of 50°C within a range of 600°C to 950°C, thereby producing the dust cores of Examples 6 to 17. The volume ratio of the glass frit in the binder of each Example is shown in the "Mixing Ratio" column in Table 3. Furthermore, the entire binder of Example 1 was replaced with a P2O5-R2O-Al2O3-based glass frit (where R is one or more elements selected from the group consisting of Li, Na, and K), and further, the maximum holding temperature during heat treatment of the molded body was changed in increments of 50°C within a range of 600°C to 950°C, thereby producing the dust cores of Examples 18 and 19.

[0071] The magnetic properties such as relative permeability were measured for the dust cores of Examples 2 to 19. The measurement results are shown in Table 3.

[0072] [Table 3]

[0073] With reference to Examples 2 to 5 in Table 3, when only a methyl-based silicone resin was used as the binder, the desired pores were not formed at a maximum holding temperature of 700°C or lower. Furthermore, although the desired pores were formed at a maximum holding temperature of 950°C, the resistivity was so low that a usable dust core could not be produced. With reference to Examples 6 to 17 in Table 3, as the proportion of Bi2O3-B2O3-based glass frit in the binder increased, the maximum holding temperature required to form the desired pores gradually decreased from 700°C to 650°C. Meanwhile, the maximum holding temperature required to obtain the required magnetic properties, such as resistivity, also gradually decreased from 900°C to 650°C. With reference to Examples 18 and 19 in Table 3, when the entire binder was replaced with a P2O5-R2O-Al2O3-based glass frit, the maximum holding temperature required to form the desired pores and obtain the required magnetic properties was 600°C or 650°C. From the above measurement results, the maximum holding temperature required to manufacture the dust core of the present invention is 600°C or higher and 900°C or lower. [Explanation of symbols]

[0074] 10 Powder Compacts 12 Center hole 20 metal particles 22 Predetermined hole 26 Oxide film 50 inclusions 70 Virtual Particles

Claims

1. A powder compact comprising a plurality of metal particles and inclusions interposed between the metal particles, the metal particles are made of an FeSiAl-based soft magnetic alloy and have a flat shape when viewed along a predetermined direction, one or more predetermined holes are formed in the one or more metal particles, the predetermined hole penetrates the metal particle in the predetermined direction, a maximum width of the predetermined hole in a predetermined plane perpendicular to the predetermined direction is equal to or greater than a thickness of the metal particle in the predetermined direction; The inclusions have silicon oxide as a main component or are glass. Powder compact.

2. The powder compact according to claim 1, The thickness of the metal particles in which the predetermined holes are formed is 0.5 μm or more and 5 μm or less. Powder compact.

3. The powder compact according to claim 1 or 2, The maximum width of the predetermined hole is 1 μm or more and 5 μm or less. Powder compact.

4. The powder compact according to any one of claims 1 to 3, The predetermined hole is a cavity. Powder compact.

5. The powder compact according to any one of claims 1 to 4, Both ends of the predetermined hole in the predetermined direction are covered by a part of the inclusion. Powder compact.

Images