Compacted magnetic core and inductor

Abstract

To provide a powder magnetic core and an inductor with good DC superimposition characteristics.SOLUTION: In a powder magnetic core according to an embodiment of the present disclosure, magnetic powder is bonded through a binder layer. Defining the magnetic permeability at a magnetic flux density of 0T, generated by a direct current, as μB=0T, and the magnetic permeability at a magnetic flux density of 0.5T, generated by a direct current, as μB=0.5T, the value of μB=0.5T / μB=0T is 0.65 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a compacted powder core and an inductor.

Background Art

[0002] In recent years, inductors have been used in various electronic devices. Particularly in electronic devices such as personal computers, as the power consumption increases, the supply power is increasing in large current. Therefore, an inductor used in an electronic device such as a personal computer is required to exhibit high inductance characteristics even when a large current flows. Patent Document 1 discloses a method for manufacturing a compacted body of an amorphous soft magnetic alloy having little decrease in magnetic permeability in a high frequency region.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, an inductor used in an electronic device such as a personal computer is required to exhibit high inductance characteristics even when a large current flows. That is, an inductor having little decrease in magnetic permeability even when a large current flows, in other words, an inductor having good DC superposition characteristics is required.

[0005] In view of the above problems, an object of the present disclosure is to provide a compacted powder core and an inductor having good DC superposition characteristics.

Means for Solving the Problems

[0006] A compacted powder core according to an aspect of the present disclosure is a compacted powder core in which magnetic powder is bound via a binder layer, and the magnetic permeability when the magnetic flux density generated by a direct current is 0 T is μ B=0TLet μ be the permeability when the magnetic flux density produced by a direct current is 0.5T. B=0.5T In that case, μ B=0.5T / μ B=0T The value is 0.65 or greater.

[0007] An inductor according to one aspect of the present disclosure comprises the above-described powder core and coil. [Effects of the Invention]

[0008] This disclosure makes it possible to provide a powdered magnetic core and an inductor with good DC superposition characteristics. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing an example of an inductor according to an embodiment. [Figure 2] This is a flowchart illustrating the method for manufacturing a compacted magnetic core according to the embodiment. [Figure 3] This is a schematic diagram illustrating the method for manufacturing a powdered magnetic core according to an embodiment. [Figure 4] This is a flowchart illustrating how to determine the DC superposition characteristics of a compacted magnetic core according to the embodiment. [Figure 5] This graph illustrates how to determine the DC superposition characteristics of the compacted magnetic core according to the embodiment (corresponding to step S11). [Figure 6] This graph illustrates how to determine the DC superposition characteristics of the compacted magnetic core according to the embodiment (corresponding to step S12). [Figure 7] This graph illustrates how to determine the DC superposition characteristics of the compacted magnetic core according to the embodiment (corresponding to step S13). [Figure 8] This graph illustrates how to determine the DC superposition characteristics of the compacted magnetic core according to the embodiment (corresponding to step S14). [Figure 9] This graph illustrates how to determine the DC superposition characteristics of the compacted magnetic core according to the embodiment (corresponding to step S15). [Figure 10]A graph for explaining how to obtain the DC superposition characteristics of the powder compact magnetic core according to the embodiment (corresponding to step S16). [Figure 11] A graph showing the DC superposition characteristics of the powder compact magnetic core according to the example.

Mode for Carrying Out the Invention

[0010] <Inductor>[[ID=X12]] FIG. 1 is a perspective view showing an example of an inductor according to the embodiment. As shown in FIG. 1, the inductor 1 according to the present embodiment includes powder compact magnetic cores 10_1, 10_2 and a coil 13. The powder compact magnetic core 10_1 has a cavity penetrating in the vertical direction at the central portion and is arranged so as to surround the outside of the coil 13. The powder compact magnetic core 10_2 is provided inside the coil 13 and is arranged in the recess of the U-shaped cross-section coil 13.

[0011] For example, the inductor 1 shown in FIG. 1 can be formed by arranging the powder compact magnetic core 10_2 in the recess of the coil 13 and then press-fitting the powder compact magnetic core 10_1 from above. Thereby, an inductor 1 in which the coil 13 is surrounded by the powder compact magnetic cores 10_1, 10_2 can be formed. In this specification, the powder compact magnetic cores 10_1, 10_2 are also collectively referred to as the powder compact magnetic core 10. Further, the configuration of the inductor 1 shown in FIG. 1 is an example, and the powder compact magnetic core 10 according to the present embodiment may be used for an inductor having a configuration other than FIG. 1. Hereinafter, the powder compact magnetic core according to the present embodiment will be described in detail.

[0012] <Powder Compact Magnetic Core> The powder compact magnetic core according to the present embodiment is a powder compact magnetic core in which magnetic powder is bound via a binder layer. In the present embodiment, the powder compact magnetic core has a magnetic permeability μ when the magnetic flux density generated by a direct current is 0 T, B=0T and a magnetic permeability μ when the magnetic flux density generated by a direct current is 0.5 T. B=0.5T When set as, μ B=0.5T / μ B=0T the value of is 0.65 or more. Here, μ​​​The value of represents the DC superposition characteristic. Note that the value of the DC superposition characteristic, i.e., μ B=0.5T / μ B=0T The method for determining the value will be explained later.

[0013] The magnetic powder used in the compacted magnetic core according to this embodiment is a soft magnetic powder containing iron. For example, the particle size of the magnetic powder is 2 μm or more and 25 μm or less, preferably 5 μm or more and 15 μm or less. In this embodiment, the particle size is the median diameter D50 and is a value measured using the laser diffraction and scattering method.

[0014] In this embodiment, metallic glass powder can be used as the magnetic powder. For example, amorphous metallic glass powder produced by the atomization method can be used as the metallic glass powder. For example, Fe-PB alloy, Fe-BP-Nb-Cr alloy, Fe-Si-B alloy, Fe-Si-BP alloy, Fe-Si-BP-Cr alloy, and Fe-Si-BPC alloy can be used, and by atomizing them into powder, metallic glass powder having a glass transition temperature can be formed. In particular, in this embodiment, it is preferable to use Fe-BP-Nb-Cr based materials. However, the metallic glass powder obtained by the atomization method is not limited to these, and amorphous powder without a glass transition temperature can also be used.

[0015] Furthermore, in this embodiment, for example, nanocrystalline powder may be used as the magnetic powder. For example, nanocrystalline powder produced by atomization may be used as the nanocrystalline powder. For example, by atomizing Fe-Si-BPC-Cu, Fe-Si-B-Cu-Cr, Fe-Si-BP-Cu-Cr, Fe-BPC-Cu, Fe-Si-BP-Cu, Fe-BP-Cu, and Fe-Si-B-Nb-Cu materials, nanocrystalline powder having at least two exothermic peaks indicating crystallization during the heat treatment process of the magnetic powder can be formed. The nanocrystalline powder used is not particularly limited, but for example, it is preferable to use Fe-Si-BP-Cu-Cr material.

[0016] In this embodiment, crystalline powder may be used as the magnetic powder. For example, crystalline powder produced by the carbonylation method or atomization method can be used. For example, carbonyl iron, Fe-Si alloy, Fe-Si-Cr alloy, and Fe-Si-Ai alloy can be used, and crystalline powder can be formed by pulverizing them by the carbonylation method or atomization method. In particular, in this embodiment, it is preferable to use carbonyl iron or Fe-Si based materials.

[0017] In this embodiment, the closer the particle shape of the magnetic powder is to spherical, the more preferable it is. If the sphericity of the particles is low, protrusions will form on the particle surface, and when molding pressure is applied, stress from surrounding particles will concentrate on these protrusions, causing the coating to break down and the insulation not to be sufficiently maintained. As a result, the magnetic properties (especially losses) of the resulting compacted magnetic core may deteriorate. The sphericity of the particles can be controlled to a suitable range by adjusting the manufacturing conditions of the magnetic powder, for example, in the water atomization method, the amount and pressure of the high-pressure water jet used for atomization, the temperature of the molten raw material, and the supply rate. The specific manufacturing conditions will vary depending on the composition of the magnetic powder to be manufactured and the desired productivity.

[0018] In the compacted magnetic core according to this embodiment, the binder layer has the function of binding magnetic powders together. The binder layer contains low-melting-point glass and a resin material. In this embodiment, the total amount of low-melting-point glass and resin material is less than 10 volume percent relative to the magnetic powder of the compacted magnetic core. The low-melting-point glass can be phosphate-based, tin-phosphate-based, borate-based, silicate-based, borosilicate-based, barium silicate-based, bismuth oxide-based, germanate-based, vanadate-based, aluminophosphate-based, arsenate-based, and telluride-based glass. In particular, in this embodiment, it is preferable to use phosphate-based or tin-phosphate-based low-melting-point glass. Furthermore, the volume ratio of low-melting-point glass to magnetic powder is 0.5 volume percent or more and 6 volume percent or less, preferably 1.25 volume percent or more and 3 volume percent or less.

[0019] Furthermore, at least one resin material selected from the group consisting of phenolic resin, polyimide resin, epoxy resin, and acrylic resin can be used as the resin material included in the binder layer. In addition, the volume ratio of the resin material to the magnetic powder is 0.5% by volume or more and 9% by volume or less, preferably 1% by volume or more and 5% by volume or less.

[0020] In this embodiment, the magnetic core has a permeability of μ when the magnetic flux density generated by a DC current is 0T. B=0T Let μ be the permeability when the magnetic flux density produced by a direct current is 0.5T. B=0.5T In that case, μ B=0.5T / μ B=0T The value of is 0.65 or higher, preferably 0.8 or higher.

[0021] Furthermore, in the compacted magnetic core according to this embodiment, the volume packing ratio of the magnetic powder (i.e., the volume content of the magnetic powder) is 88 volume% or more, preferably 90 volume% or more. In the compacted magnetic core according to this embodiment, because the volume packing ratio of the magnetic powder is high, good DC superposition characteristics are observed.

[0022] Furthermore, in this embodiment, the iron loss of the compacted magnetic core at 1 MHz and 50 mT is 4500 kW / m 3 The following is preferably 1500 kW / m 3 The following is the result. Therefore, it is possible to realize a powder magnetic core with low iron loss while exhibiting good DC superposition characteristics.

[0023] <Manufacturing method for compressed porcelain core> Next, the method for manufacturing a powdered magnetic core according to this embodiment will be described. Figure 2 is a flowchart illustrating the method for manufacturing a powdered magnetic core according to this embodiment. Figure 3 is a schematic diagram illustrating the method for manufacturing a powdered magnetic core according to this embodiment.

[0024] As shown in Figure 2, when manufacturing compacted magnetic cores, first, magnetic powder is prepared (step S1). The magnetic powder described above can be used. Preferably, the magnetic powder is a magnetic material that softens at 400°C or higher (a material that deforms easily during hot forming). For example, amorphous magnetic powder can be obtained by vacuum melting the raw materials for the magnetic powder and then simultaneously performing pulverization and rapid cooling using the water atomization method. The magnetic powder obtained in this way may be classified as needed to remove abnormally coarse powder.

[0025] Next, the magnetic powder is coated with low-melting-point glass (step S2). It is preferable to use a low-melting-point glass that softens at 400°C or higher, that is, a material that softens during hot forming and acts as an insulator and binder after hot forming. For example, phosphate-based glass can be used as the low-melting-point glass. When coating the magnetic powder with low-melting-point glass, wet thin-film fabrication methods such as mechanofusion or sol-gel methods, or dry thin-film fabrication methods such as sputtering can be used. For example, in the mechanofusion method, a layer of low-melting-point glass can be formed on the surface of the magnetic powder by mixing the magnetic powder and low-melting-point glass powder while applying strong mechanical energy.

[0026] For example, 1000g of magnetic powder and 10g of low-melting-point glass powder are mixed, and the magnetic powder is coated with the low-melting-point glass using a mechanofusion method. This makes it possible to set the volume ratio of the coated low-melting-point glass to the magnetic powder to between 0.5% and 6% by volume.

[0027] Next, the magnetic powder coated with low-melting-point glass is coated with a resin material and granulated (Step S3). The resin material can be any of the resin materials mentioned above. Preferably, the resin material is one that softens at around 100°C and acts as an insulating material and binder after hot forming. It is also preferable to use a resin material that does not decompose easily during hot forming (at high temperatures). When coating (granulating) with the resin material, methods such as rolling granulation or spray drying can be used. Specifically, a resin layer can be formed on the low-melting-point glass of the magnetic powder by mixing a resin material dissolved in an organic solvent with the magnetic powder coated with low-melting-point glass and drying the mixture.

[0028] The left panel of Figure 3 shows the magnetic powder 20 after granulation. As shown in Figure 3, the magnetic powder 20 after granulation has a low-melting-point glass 31 coated on top of the magnetic powder 21, and a resin material 32 further coated on top of the low-melting-point glass 31. For example, the diameter of the magnetic powder 21 is 11 μm, the thickness of the low-melting-point glass 31 is 20 nm, and the thickness of the resin material is 20 nm.

[0029] Next, the granulated magnetic powder is pre-formed (step S4). For example, pre-formation involves placing the granulated magnetic powder into a mold and pressurizing it (for example, 500 kgf / cm² at room temperature). 2 ), and then the compacted powder can be heated and cured at a predetermined temperature (e.g., 100°C to 150°C) without pressurization. If the resin material used is a thermosetting resin, the intermediate molded body is formed by the curing of the resin during heating. If the resin material used is a thermoplastic resin, the intermediate molded body is formed by the softening of the resin during heating and the solidification during cooling.

[0030] In other words, as shown in the center diagram of Figure 3, when pre-molding is performed, the magnetic powder 21 (coated with low-melting-point glass 31) adheres to the outermost resin material 32 to form an intermediate molded body 25. Note that the low-melting-point glass does not soften at the pre-molding temperature (e.g., 150°C), so it does not exhibit bonding properties or fluidity. The pre-molding step (step S4) may be omitted.

[0031] Next, the pre-formed intermediate molded body (or granulated magnetic powder if step S4 is omitted) is hot-formed (step S5). Hot forming is carried out by heating the pre-formed intermediate molded body (or granulated magnetic powder) in the mold while applying pressure. The heating temperature at this time is set as follows, for example.

[0032] When using metallic glass powder as the magnetic powder, the temperature during hot forming should be set to be above the higher of the softening temperature of the low-melting-point glass and the glass transition temperature of the magnetic powder, and below the crystallization temperature of the magnetic powder. Setting the hot forming temperature above the glass transition temperature of the magnetic powder makes plastic deformation of the magnetic powder more likely, thus achieving a high packing density of the magnetic powder. Furthermore, by setting the hot forming temperature above the softening temperature of the low-melting-point glass, the low-melting-point glass coated on the magnetic powder follows the deformation of the magnetic powder, allowing for good coating of the magnetic powder surface and thus reducing iron loss. One example is a temperature between 450°C and 500°C.

[0033] When nanocrystalline magnetic powder is used, the temperature during hot forming is set to be higher than the higher of the softening temperature of the low-melting-point glass and the first crystallization temperature of the magnetic powder, and lower than the second crystallization temperature of the magnetic powder. By setting the hot forming temperature to around the first crystallization temperature, the α-Fe phase crystallizes and plastic deformation of the magnetic powder becomes more likely, resulting in a high packing density of the magnetic powder. Furthermore, by setting the hot forming temperature to be higher than the softening temperature of the low-melting-point glass, the low-melting-point glass coated on the magnetic powder follows the deformation of the magnetic powder and can properly coat the surface of the magnetic powder, thereby reducing iron loss. For example, the temperature is 400°C to 500°C. In this embodiment, it is preferable that the temperature is higher than the higher of the softening temperature of the low-melting-point glass and the first crystallization temperature of the magnetic powder + 40°C. Here, the first crystallization temperature and the second crystallization temperature are as follows. That is, when an amorphous magnetic material is heat-treated, crystallization occurs two or more times. The temperature at which crystallization first begins is the first crystallization temperature, and the temperature at which crystallization begins thereafter is the second crystallization temperature. More specifically, magnetic powders have at least two exothermic peaks indicating crystallization in the heating process of the DSC curve obtained by differential scanning calorimetry (DSC). Of these exothermic peaks, the lowest temperature exothermic peak is the first crystallization temperature at which the α-Fe phase crystallizes, and the next exothermic peak is the second crystallization temperature at which borides and other substances crystallize.

[0034] When using crystalline magnetic powder, the hot forming temperature should be set above the softening temperature of the low-melting-point glass. By setting the hot forming temperature above the softening temperature of the low-melting-point glass, the dynamic recovery of the magnetic powder makes plastic deformation of the magnetic powder more likely, resulting in a higher packing density of the magnetic powder. Furthermore, by setting the hot forming temperature above the softening temperature of the low-melting-point glass, the low-melting-point glass coated on the magnetic powder follows the deformation of the magnetic powder, allowing for good coating of the magnetic powder surface and thus reducing iron loss. One example is a temperature between 400°C and 600°C.

[0035] In this embodiment, it is preferable to set the heating temperature within the above-mentioned temperature range and to use temperature conditions that result in a low iron loss value for the compacted magnetic core.

[0036] Furthermore, the pressure used during hot forming is, for example, 5-10 ton·f / cm². 2 Therefore, if the pressure is too low, the filling rate of the molded body (powdered magnetic core) will be low, and the iron loss of the powdered magnetic core will increase. Conversely, if the pressure is too high, the mold will wear out quickly, which is undesirable from a cost perspective. For this reason, it is preferable to set the pressure within the range described above.

[0037] Furthermore, the hot forming time is preferably in the range of 5 to 60 seconds, and more preferably 30 seconds or less. If the forming time is too short, heat will not be sufficiently transferred to the interior of the molded body, and deformation due to the softening of the magnetic powder will not be sufficiently obtained, resulting in a low filling rate of the molded body and increased iron loss of the compacted magnetic core. Conversely, if the forming time is too long, the thermal decomposition of the resin material used in the binder layer will progress, reducing the effect of suppressing the fluidity of the low-melting-point glass and increasing iron loss of the compacted magnetic core. Therefore, the hot forming time should be set within a range that is cost-effective while ensuring sufficient heat is transferred to the interior of the molded body, completing the deformation due to the softening of the magnetic powder, and suppressing the thermal decomposition of the resin material used in the binder layer. It is preferable to set the forming time within the range described above.

[0038] For example, the conditions for hot forming are: hot forming temperature: 480°C, hot forming pressure: 8 ton·f / cm². 2 The hot forming time can be set to 10 seconds.

[0039] As shown in the right-hand figure of Figure 3, in the molded body (powdered magnetic core) 10 after hot forming, the magnetic powders 21 are bound together via a binder layer 22 containing low-melting-point glass and resin material. In this embodiment, the volume percentage of magnetic powder contained in the powdered magnetic core 10 is 88% by volume or more, preferably 90% by volume or more.

[0040] By using the manufacturing method described above, the compacted magnetic core according to this embodiment can be manufactured.

[0041] <How to determine DC superposition characteristics> Next, the method for determining the DC superposition characteristics of the compacted magnetic core according to this embodiment will be explained. Figure 4 is a flowchart illustrating the method for determining the DC superposition characteristics of the compacted magnetic core according to this embodiment. Figures 5 to 10 are graphs illustrating the method for determining the DC superposition characteristics of the compacted magnetic core according to this embodiment. Note that the graphs shown in Figures 5 to 10 correspond to the graphs obtained when determining the DC superposition characteristics of Example 1.

[0042] As shown in Figure 4, when determining the DC superposition characteristics of a powdered magnetic core, first, the LI curve is measured using a toroidal core with a winding (step S11). For measuring the LI curve, a DC superposition tester can be used, for example. For example, the measurement is performed by superimposing a DC current on a sine wave with a frequency of 1 MHz and an amplitude of 10 mA. Figure 5 shows an example of the measurement results of the LI curve.

[0043] Next, the LI curve measured in step S11 is μ r - Convert to an H curve (Step S12). The following equation is used for the conversion. Figure 6 shows the LI curve as μ r The graph after converting to an H-curve is shown. Note that the toroidal core is considered to be essentially a closed magnetic circuit annular solenoid.

[0044]

number

[0045] Here, μ r μ0 is the relative permeability, and μ0 is the permeability of vacuum (N / A). 2 ), L is the measured inductance (H), l is the effective magnetic path length (m), and s is the effective cross-sectional area (m²). 2 ), where n is the number of turns in the coil.

[0046] Next, the μ obtained in step S12 r -Approximate the H curve with an approximation formula (step S13). Specifically, μ rWe approximate this as a function of H with the polynomial shown below. Figure 7 shows an example of approximation with a 5th-degree polynomial. The values ​​a to f shown in Figure 7 correspond to the values ​​obtained in Example 1, which will be described later. In this embodiment, an approximation formula other than a 5th-degree polynomial may also be used.

[0047]

number

[0048] Next, as shown in the following formula, μ r The function of (H) is indefinitely integrated to find the relationship between B and H (BH curve) (Step S14). Figure 8 shows the graph of the obtained BH curve. In this embodiment, a soft magnetic material with relatively low remanent magnetization is used, so when H=0, B=0 (integration constant C=0) can be used for the calculation.

[0049]

number

[0050] Next, using the results of steps S13 and S14, μ r Find the relationship between and B (Step S15). Figure 9 shows μ r This graph shows the relationship between B and [another element].

[0051] Then, the relative permeability μ in step S15 r Convert this to a relative value with respect to B=0T and find the relative permeability when Bdc=0.5T (Step S16). Specifically, as shown in Figure 10, the relative permeability μ at B=0T obtained in Step S15 is... r Relative permeability μ, with μ set to 100% r Convert the values ​​to relative values. Then, find the value of the relative permeability when the DC magnetic flux density Bdc = 0.5T.

[0052] In this embodiment, the relative permeability value obtained in this manner when Bdc = 0.5T is used as the value indicating the DC superposition characteristics. Note that the relative permeability value when Bdc = 0.5T is the permeability when the magnetic flux density generated by the DC current is 0T as described above. B=0T Let μ be the permeability when the magnetic flux density produced by a direct current is 0.5T. B=0.5T μ in this case B=0.5T / μ B=0T This corresponds to the value of "

[0053] In this embodiment, the magnetic core has a permeability of μ when the magnetic flux density generated by a DC current is 0T. B=0T Let μ be the permeability when the magnetic flux density produced by a direct current is 0.5T. B=0.5T In that case, μ B=0.5T / μ B=0T The value of is 0.65 or higher, preferably 0.8 or higher. Therefore, it is possible to provide a powdered magnetic core and an inductor with good DC superposition characteristics. [Examples]

[0054] Next, we will describe some examples.

[0055] <Example 1> A sample according to Example 1 was prepared using the manufacturing method of the compacted magnetic core described above (see Figure 2). The compacted magnetic core according to Example 1 had a toroidal shape with an outer diameter of 13 mm, an inner diameter of 8 mm, and a height of 3 mm. Specifically, first, magnetic powder was prepared. For the magnetic powder, an Fe-Si-BP-Cu-Cr system powder, which is a nanocrystalline powder with a particle size of 11 μm (median diameter D50), was used. Next, the magnetic powder and low-melting-point glass powder were mixed, and the magnetic powder was coated with low-melting-point glass using the mechanofusion method. A phosphate-based glass was used as the low-melting-point glass. At this time, 2.5 volume% of the low-melting-point glass was mixed with the magnetic powder.

[0056] Subsequently, the magnetic powder coated with low-melting-point glass was granulated by coating it with a resin material. Phenolic resin was used as the resin material, and 2.5 volume% of the resin material was mixed with the magnetic powder.

[0057] Next, the granulated magnetic powder is placed into the mold and subjected to a pressure of 500 kgf / cm². 2 After pressurizing under the specified conditions, the compacted powder was pre-formed by heating and curing it at 150°C without further pressure. Subsequently, the pre-formed intermediate molded body was hot-formed while placed in a mold. The hot-forming conditions were a molding temperature of 470°C and a pressurizing pressure of 8 tonf / cm². 2 The pressurization time was set to 30 seconds.

[0058] <Example 2> For Example 2, a sample was prepared using Fe-BP-Cu-based powder, which is a nanocrystalline powder with a particle size of 14 μm (median diameter D50), as the magnetic powder. In Example 2, the hot forming conditions were set to a forming temperature of 455°C. All other conditions were the same as in Example 1.

[0059] <Example 3> For Example 3, a sample was prepared using metallic glass powder as the magnetic powder. The metallic glass powder used was an Fe-BP-Nb-Cr powder with a particle size of 9 μm (median diameter D50). In Example 3, the hot forming conditions were set to a forming temperature of 490°C. Other than this, the conditions were the same as in Example 1.

[0060] <Example 4> As a sample for Example 4, a sample was prepared using pure iron as the magnetic powder. Carbonyl iron powder with a particle size of 8 μm (median diameter D50) was used as the raw material for the pure iron. Other than this, the procedure was the same as in Example 1.

[0061] <Example 5> For Example 5, a sample was prepared using an Fe-Si alloy as the magnetic powder. Fe-3.5Si powder with a particle size of 10 μm (median diameter D50) was used as the Fe-Si alloy. Other than this, the procedure was the same as in Example 1.

[0062] <Comparative Example 1> For Comparative Example 1, a sample was prepared using nanocrystalline powder as the magnetic powder. The nanocrystalline powder used was an Fe-Si-BP-Cu-Cr system powder with a particle size of 11 μm (median diameter D50). In Comparative Example 1, 20 volume% of resin material was mixed with the magnetic powder to coat the magnetic powder with low-melting-point glass, thereby granulating the resin material. The molding conditions were cold molding (molding temperature: 25°C). Other than this, the conditions were the same as in Example 1.

[0063] <Comparative Example 2> For Comparative Example 2, a sample was prepared using an Fe-Si alloy as the magnetic powder. Fe-5.5Si powder with a particle size of 10 μm (median diameter D50) was used as the Fe-Si alloy. In Comparative Example 2, 20% by volume of resin material was mixed with the magnetic powder to coat the resin material onto the magnetic powder coated with low-melting-point glass, thereby granulation. The molding conditions were cold forming (molding temperature: 25°C). Other than these, the conditions were the same as in Example 1.

[0064] <Sample Measurement> For the samples prepared in Examples 1-5 and Comparative Examples 1-2 as described above, the packing density of the magnetic powder (volume %), the saturation magnetic flux density Bs(T) of the compacted magnetic core, the initial permeability, and the DC superposition characteristics (μ) were measured. B=0.5T / μ B=0T ), and the iron loss was measured.

[0065] The packing density of the magnetic powder was determined by comparing the volume of magnetic powder contained in the core with the total volume of the core measured by the Archimedes method. The volume of magnetic powder contained in the core was determined by subtracting the weight of the low-melting-point glass added as a binder and the remaining resin material from the total weight of the core to find the weight of the magnetic powder contained in the core, and then dividing the weight of the magnetic powder by the true density of the magnetic powder.

[0066] The magnetic permeability was determined using an impedance analyzer at a frequency of 1 MHz, and the iron loss was determined by measuring the toroidal powder core using a BH analyzer (manufactured by Iwasaki Communication Equipment Co., Ltd.) with the two-coil method. The measurement conditions were a sinusoidal excitation of 1 MHz and 50 mT. DC superposition characteristics (μ B=0.5T / μ B=0T The DC superposition characteristics (μ) of the sample according to Example 1 were determined using the method described above (see Figure 4). Below, as an example, the DC superposition characteristics (μ) of the sample according to Example 1 are shown. B=0.5T / μ B=0T I will explain the measurement of ) in detail.

[0067] <Measurement of DC superposition characteristics> A toroidal core (outer diameter 13 mm, inner diameter 8 mm, height 3 mm) was fabricated according to Example 1 as described above, and a winding was applied to it. The number of turns was set to 32. Then, using a DC superposition tester (manufactured by Axis Net Co., Ltd.), a DC current was superimposed on a sine wave with a measurement frequency of 1 MHz and an amplitude of 10 mA, and the LI curve of the toroidal core was measured (step S11 in Figure 4). Figure 5 shows the measurement results of the LI curve of the sample according to Example 1.

[0068] Subsequently, the measured LI curve was μ r - The curve was converted to an H-curve (step S12 in Figure 4). The following equation was used for the conversion.

[0069]

number

[0070] Note that μ r μ0 is the relative permeability, and μ0 is the permeability of vacuum (N / A). 2 ), L is the measured inductance (H), l is the effective magnetic path length (m), and s is the effective cross-sectional area (m²). 2 ), where n is the number of turns in the coil. In this measurement, each parameter was set as follows. Also, in Figure 6, the LI curve is shown as μ r -The graph after converting to an H-curve is shown. μ0 = 1.26 × 10 -6 (N / A 2 ) l = 3.30 × 10 -2 (m) s = 7.47 × 10 -6 (m 2 ) n=32

[0071] Next, the converted μ r -The H curve was approximated by an approximation formula (step S13 in Figure 4). Specifically, μ r We approximated it as a function of H with the polynomial shown below.

[0072]

number

[0073] Figure 7 shows the result of approximating with a fifth-degree polynomial. The values ​​of the constants in the polynomial were as follows. a = -1.50 × 10 -18 b = 4.41 × 10 -14 c = -3.52 × 10 -10 d = -4.96 × 10 -8 e = 1.39 × 10 -3 f = 1.18 × 10 2

[0074] Next, as shown in the following formula, μ r The function (H) was indefinitely integrated to find the relationship between H and B (the BH curve) (step S14 in Figure 4). Figure 8 shows the graph of the obtained BH curve.

[0075]

number

[0076] The values ​​of the constants in the above polynomial were as follows. In this embodiment, since a soft magnetic material with relatively low remanent magnetization was used, the calculation was performed with B=0 (integration constant C=0) when H=0. a / 6 = -2.49 × 10 -19 b / 5 = 8.82 × 10 -15 c / 4 = -8.81 × 10 -11 d / 3 = -1.65 × 10 -8 e / 2 = 6.95 × 10 -4 f = 1.18 × 10 2

[0077] Next, using the results of steps S13 and S14, we determine the μ for H. r Find the relationship between and B, and further μ r The relationship between and B was determined (step S15 in Figure 4). Figure 9 shows μ r This graph shows the relationship between B and [another element].

[0078] Then, the relative permeability μ in step S15 r The relative permeability was calculated by converting it to a relative value with respect to B=0T, and determining the relative permeability when Bdc=0.5T (step S16 in Figure 4). Specifically, as shown in Figure 10, the relative permeability μ at B=0T obtained in step S15 was calculated. r Taking μ as 1, relative permeability μ r The values ​​were converted to relative values. Then, the relative permeability value was calculated when the DC magnetic flux density Bdc = 0.5T.

[0079] In this embodiment, the relative permeability value (μ) obtained when Bdc = 0.5T is used in this manner. B=0.5T / μ B=0T The value corresponding to ( ) was used as the value indicating the DC superposition characteristics. The DC superposition characteristics were determined for other examples and comparative examples using the same method.

[0080] <Measurement results> Table 1 shows the measurement results for Examples 1-5 and Comparative Examples 1-2. Figure 11 shows the measurement results of the DC superposition characteristics for Examples 1-5 and Comparative Examples 1-2, that is, the relationship between the relative permeability (μ) and the DC magnetic flux density Bdc(T).

[0081] [Table 1]

[0082] As shown in Table 1 and Figure 11, in Examples 1 to 5, the value of the DC superposition characteristic (μ B=0.5T / μ B=0T ) was 0.65 or more. On the other hand, in Comparative Examples 1 and 2, the values of the DC superposition characteristic (μ B=0.5T / μ B=0T ) were 0.59 and 0.63, respectively. Therefore, in Examples 1 to 5, the value of the DC superposition characteristic (μ B=0.5T / μ B=0T ) was a good value. In particular, in Examples 1 and 2, the values of the DC superposition characteristic (μ B=0.5T / μ B=0T ) were 0.87 and 0.97, respectively, which were very good values.

[0083] Also, focusing on the iron loss (iron loss measured at 1 MHz and 50 mT), in Examples 1 to 4, the value of the iron loss was 4500 or less, showing good values in both the DC superposition characteristic and the iron loss. In particular, in Examples 1 to 3, the value of the iron loss was 1500 or less, showing good values. Also, focusing on the filling rate, in the case of hot forming, the filling rate was higher than in the case of cold forming.

[0084] <Iron Loss under Each Measurement Condition> For the samples according to Examples 1 to 5 and Comparative Examples 1 and 2, the iron loss under each measurement condition was measured. Specifically, the iron loss at each Bm when the frequency conditions were 500 kHz, 800 kHz, 1 MHz, and 2 MHz was measured.

[0085] The measurement results of the iron loss measured at frequencies of 500 kHz, 800 kHz, 1 MHz, and 2 MHz are shown in Tables 2 to 5, respectively.

[0086]

Table 2

[0087]

Table 3

[0088] [Table 4]

[0089] [Table 5]

[0090] As shown in Tables 2 to 5, the iron loss values ​​for each Bm increased with increasing frequency. Furthermore, the iron loss values ​​also increased with increasing Bm.

[0091] Although the present invention has been described above in accordance with the above embodiments, the present invention is not limited to the configuration of the above embodiments, and of course includes various modifications, alterations, and combinations that can be made by a person skilled in the art within the scope of the claims of the present patent application. [Explanation of Symbols]

[0092] 1 Inductor 10, 10_1, 10_2 Powder magnetic core 13 coils 20. Magnetic powder after granulation 21 Magnetic powder 22 Binder Layers 25 Intermediate molded body 31 Low melting point glass 32 Resin materials

Claims

1. A compacted magnetic core in which magnetic powder is bound via a binder layer, To measure the DC superposition characteristics of the aforementioned powder core, a toroidal core with an outer diameter of 13 mm, an inner diameter of 8 mm, and a height of 3 mm was constructed using the powder core, and a 32-turn winding was applied to the toroidal core. When the DC superposition characteristics were measured, the permeability when the magnetic flux density generated by the DC current was 0 T was measured as μ Ｂ＝０Ｔ Let μ be the permeability when the magnetic flux density produced by a direct current is 0.5T. Ｂ＝０．５Ｔ In that case, μ Ｂ＝０．５Ｔ / μ Ｂ＝０Ｔ The value is 0.65 or higher. Powder magnetic core.

2. Said μ Ｂ＝０．５Ｔ / μ Ｂ＝０Ｔ The compacted magnetic core according to claim 1, wherein the value of is 0.8 or greater.

3. The powdered magnetic core according to claim 1 or 2, wherein the powdered magnetic core contains 90 volume% or more of magnetic powder.

4. The iron loss of the aforementioned powder core at 1 MHz and 50 mT is 4500 kW / m ３ The compacted magnetic core according to claim 1 or 2, which is as follows:

5. The iron loss of the aforementioned powder core at 1 MHz and 50 mT is 1500 kW / m ３ The compacted magnetic core according to claim 1 or 2, which is as follows:

6. The compacted magnetic core according to claim 1 or 2, wherein the magnetic powder is metallic glass powder or nanocrystalline powder.

7. The compacted magnetic core according to claim 1 or 2, wherein the binder layer comprises a low-melting-point glass and a resin material.

8. The powdered magnetic core according to claim 7, wherein the low-melting-point glass is a phosphate-based or tin-phosphate-based glass.

9. The powdered magnetic core according to claim 7, wherein the resin material is at least one selected from the group consisting of phenolic resin, polyimide resin, epoxy resin, and acrylic resin.

10. An inductor comprising a powdered magnetic core and a coil as described in claim 1 or 2.

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