Powder 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 compressed 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 has become larger in 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 compressed powder compact 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 compressed powder core and an inductor having good DC superposition characteristics.

Means for Solving the Problems

[0006] The compressed powder core according to one aspect of the present disclosure is a compressed 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 magnetic permeability when the magnetic flux density generated by a direct current is 0.5 T. B=0.5T When this is the case, μ B=0.5T / μ B=0T has a value of 0.65 or more.

[0007] The inductor according to one aspect of the present disclosure includes the above-described compressed powder core and coil.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a compressed powder core and an inductor having good DC superposition characteristics.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0010] <Inductor> 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 compacted powder cores 10_1, 10_2 and a coil 13. The compacted powder core 10_1 has a cavity penetrating the central portion in the vertical direction and is arranged so as to surround the outside of the coil 13. The compacted powder 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 compacted powder core 10_2 in the recess of the coil 13 and then press-fitting the compacted powder core 10_1 from above. Thereby, the inductor 1 in which the coil 13 is surrounded by the compacted powder cores 10_1, 10_2 can be formed. In this specification, the compacted powder cores 10_1, 10_2 are also collectively referred to as the compacted powder core 10. Further, the configuration of the inductor 1 shown in FIG. 1 is an example, and the compacted powder core 10 according to the present embodiment may be used for an inductor having a configuration other than that shown in FIG. 1. Hereinafter, the compacted powder core according to the present embodiment will be described in detail.

[0012] <Compacted Powder Core> The compacted powder core according to the present embodiment is a compacted powder core in which magnetic powder is bound via a binder layer. In the present embodiment, the compacted powder 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 In this case, the value of μ B=0.5T / μ B=0T is 0.65 or more. Here, μ B=0.5T / μ B=0TThe value is a value indicating the DC superposition characteristic. Note that the value of the DC superposition characteristic, that is, μ B=0.5T / μ B=0T The method for obtaining the value will be described later.

[0013] The magnetic powder used in the compressed powder core according to this embodiment is a soft magnetic powder containing iron element. 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, which is a value measured using the laser diffraction / scattering method.

[0014] In this embodiment, metallic glass powder can be used as the magnetic powder. For example, as the metallic glass powder, amorphous metallic glass powder produced by the atomization method can be used. For example, Fe-P-B alloy, Fe-B-P-Nb-Cr alloy, Fe-Si-B alloy, Fe-Si-B-P alloy, Fe-Si-B-P-Cr alloy, Fe-Si-B-P-C alloy can be used, and by powdering by the atomization method, metallic glass powder having a glass transition point can be formed. Particularly in this embodiment, it is preferable to use an Fe-B-P-Nb-Cr-based material. Note that the metallic glass powder obtained by the atomization method is not limited to these, and amorphous powder having no glass transition point can also be used.

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

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

[0017] In this embodiment, the closer the particle shape of the magnetic powder is to spherical, the more preferable it is. When the sphericity of the particles is low, protrusions are generated on the particle surface, and when a molding pressure is applied, stress from the surrounding particles concentrates on the protrusions and the coating is broken, and sufficient insulation cannot be maintained. As a result, the magnetic properties (particularly loss) of the obtained compacted magnetic core may deteriorate. Note that the sphericity of the particles can be controlled within a suitable range by adjusting the production conditions of the magnetic powder, for example, in the case of the water atomization method, the amount and water pressure of the high-pressure water jet used for atomization, the temperature and supply rate of the molten raw material, and the like. Specific production conditions vary depending on the composition of the magnetic powder to be produced and the desired productivity.

[0018] In the compacted magnetic core according to this embodiment, the binder layer has a function of binding the magnetic powders together. The binder layer contains a low melting point glass and a resin material. In this embodiment, the total amount of the low melting point glass and the resin material is less than 10% by volume with respect to the magnetic powder of the compacted magnetic core. As the low melting point glass, 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, telluride-based, and the like can be used. In particular, in this embodiment, it is preferable to use a phosphate-based or tin phosphate-based low melting point glass. Further, the volume ratio of the low melting point glass to the magnetic powder is 0.5% by volume or more and 6% by volume or less, preferably 1.25% by volume or more and 3% by volume or less.

[0019] Further, as the resin material contained in the binder layer, at least one selected from the group consisting of a phenol resin, a polyimide resin, an epoxy resin, and an acrylic resin can be used. Also, 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 permeability of the compacted magnetic core when the magnetic flux density generated by a direct current is 0 T is μ B=0T and the permeability when the magnetic flux density generated by a direct current is 0.5 T is μ B=0.5T When this is the case, the value of μ B=0.5T / μ B=0T is 0.65 or more, preferably 0.8 or more.

[0021] Also, in the compacted magnetic core according to this embodiment, the volume filling rate of the magnetic powder (that is, the volume content of the magnetic powder) is 88% by volume or more, preferably 90% by volume or more. In the compacted magnetic core according to this embodiment, since the volume filling rate of the magnetic powder is high in this way, good DC superposition characteristics are exhibited.

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

[0023] <Manufacturing method of compacted magnetic core> Next, the manufacturing method of the compacted magnetic core according to this embodiment will be described. FIG. 2 is a flowchart for explaining the manufacturing method of the compacted magnetic core according to this embodiment. FIG. 3 is a schematic diagram for explaining the manufacturing method of the compacted magnetic core according to this embodiment.

[0024] As shown in Fig. 2, when manufacturing a compacted magnetic core, first, magnetic powder is prepared (step S1). As the magnetic powder, the above-described magnetic powder can be used. It is preferable to use a magnetic material that softens at 400°C or higher (a material that easily deforms during hot forming). For example, after vacuum melting the raw material of the magnetic powder, amorphous magnetic powder can be obtained by simultaneously performing powdering and rapid cooling using the water atomization method. The magnetic powder thus obtained may be classified as necessary to remove abnormally coarsened powder.

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

[0026] For example, 1000 g of magnetic powder and 10 g of low-melting-point glass powder are mixed, and the magnetic powder is coated with the low-melting-point glass using the mechanofusion method. Thereby, the volume ratio of the coated low-melting-point glass to the magnetic powder can be made 0.5% by volume or more and 6% by volume or less.

[0027] Next, a resin material is coated on the magnetic powder coated with the low-melting-point glass and granulated (step S3). As the resin material, the resin materials described above can be used. As the resin material, it is preferable to use a material that softens at about 100°C and functions as an insulating material and a binder after hot forming. Also, as the resin material, it is preferable to use a material that is difficult to decompose during hot forming (at high temperatures). When coating (granulating) the resin material, a rolling granulation method, a spray drying method, or the like can be used. Specifically, a resin layer can be formed on the low-melting-point glass of the magnetic powder by mixing and drying the resin material dissolved in an organic solvent and the magnetic powder coated with the low-melting-point glass.

[0028] The left figure of Fig. 3 shows the magnetic powder 20 after granulation. As shown in Fig. 3, in the magnetic powder 20 after granulation, a low-melting-point glass 31 is coated on the magnetic powder 21, and a resin material 32 is further coated on 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 magnetic powder after granulation is preformed (step S4). For example, in preforming, the magnetic powder after granulation is put into a mold and pressurized (for example, 500 kgf / cm at room temperature 2 ), and then, the green compact is heated and cured at a predetermined temperature (for example, 100°C to 150°C) without pressure. When the resin material used is a thermosetting resin, the intermediate molded body is molded using the curing of the resin during heating. When the resin material used is a thermoplastic resin, the intermediate molded body is molded by the softening of the resin during heating and the solidification during cooling.

[0030] That is, as shown in the central figure of Fig. 3, when preformed, the magnetic powder 21 (coated with the low-melting-point glass 31) is bound through the outermost resin material 32 to form an intermediate molded body 25. Note that since the low-melting-point glass does not soften at the preforming temperature (for example, 150°C), it does not exhibit binding properties or fluidity. Note that the preforming step (step S4) may be omitted.

[0031] Next, the intermediate compact after pre-forming (when step S4 is omitted, the magnetic powder after granulation) is hot-formed (step S5). Hot-forming is carried out by heating while applying pressure with the intermediate compact after pre-forming (or the magnetic powder after granulation) placed in a mold. The heating temperature at this time is set as follows, for example.

[0032] When the magnetic powder used is a metallic glass powder, the temperature during hot-forming is set to be equal to or higher than the higher of the softening temperature of the low-melting glass and the glass transition temperature of the magnetic powder, and equal to or lower than the crystallization temperature of the magnetic powder. By setting the hot-forming temperature to be equal to or higher than the glass transition temperature of the magnetic powder, plastic deformation of the magnetic powder becomes more likely to occur, so a high filling rate of the magnetic powder can be obtained. Also, by setting the hot-forming temperature to be equal to or higher than the softening temperature of the low-melting glass, the low-melting glass coated on the magnetic powder follows the deformation of the magnetic powder and can well coat the surface of the magnetic powder, so the iron loss can be reduced. For example, it is 450°C or higher and 500°C or lower.

[0033] When the magnetic powder used is nanocrystalline powder, the temperature during hot forming is set to be not lower than the higher of the softening temperature of the low melting point glass and the first crystallization temperature of the magnetic powder, and not higher than the second crystallization temperature of the magnetic powder. By setting the hot forming temperature around the first crystallization temperature, when the α-Fe phase crystallizes, plastic deformation of the magnetic powder is more likely to occur, so a high filling rate of the magnetic powder can be obtained. Also, by setting the hot forming temperature to be not lower than the softening temperature of the low melting point glass, the low melting point glass coated on the magnetic powder can follow the deformation of the magnetic powder and can well coat the surface of the magnetic powder, so the iron loss can be reduced. For example, it is 400°C or higher and 500°C or lower. Also, in this embodiment, it is preferably not lower 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 a magnetic material with an amorphous structure is heat-treated, crystallization occurs two or more times. The temperature at which crystallization starts first is the first crystallization temperature, and then the temperature at which crystallization starts is the second crystallization temperature. More specifically, the magnetic powder has at least two exothermic peaks indicating crystallization in the heating process of the DSC curve obtained by differential scanning calorimetry (DSC). Among the said exothermic peaks, the exothermic peak on the lowest temperature side 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 or the like crystallize.

[0034] When the magnetic powder used is crystalline powder, the temperature during hot forming is set to be not lower than the softening temperature of the low melting point glass. By setting the hot forming temperature to be not lower than the softening temperature of the low melting point glass, due to the dynamic recovery of the magnetic powder, plastic deformation of the magnetic powder is more likely to occur, so a high filling rate of the magnetic powder can be obtained. Also, by setting the hot forming temperature to be not lower than the softening temperature of the low melting point glass, the low melting point glass coated on the magnetic powder can follow the deformation of the magnetic powder and can well coat the surface of the magnetic powder, so the iron loss can be reduced. For example, it is 400°C or higher and 600°C or lower.

[0035] In this embodiment, it is preferable to set the heating temperature within the above-mentioned temperature range and to set the temperature condition such that the iron loss value of the compacted magnetic core is low.

[0036] Also, the pressure during hot forming is, for example, 5 to 10 ton·f / cm 2 is set. If the pressure is too low, the filling rate of the formed body (compacted magnetic core) will be low, and the iron loss of the compacted magnetic core will increase. Conversely, if the pressure is too high, the mold will wear severely, which is not preferable in terms of cost. Therefore, it is preferable to set the pressure within the above-mentioned range.

[0037] Also, 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 transmitted to the inside of the formed body, and deformation due to softening of the magnetic powder cannot be obtained sufficiently, so the filling rate of the formed body will be low, and the iron loss of the compacted magnetic core will increase. Conversely, if the forming time is too long, thermal decomposition of the resin material used for the binder layer will progress, so the effect of suppressing the fluidity of the low melting point glass will be low, and the iron loss of the compacted magnetic core will increase. Therefore, the hot forming time may be set within a range that is preferably cost-effective by sufficiently transmitting heat to the inside of the formed body, completing the deformation due to softening of the magnetic powder, and suppressing thermal decomposition of the resin material used for the binder layer. It is preferable to set the forming time within the above-mentioned range.

[0038] For example, the hot forming conditions can be a hot forming temperature of 480 °C, a hot forming pressure of 8 ton·f / cm 2 , and a hot forming time of 10 seconds.

[0039] As shown in the right figure of FIG. 3, in the formed body (compacted magnetic core) 10 after hot forming, the magnetic powders 21 are bonded to each other via a binder layer 22 containing a low melting point glass and a resin material. In this embodiment, the volume ratio of the magnetic powder contained in the compacted 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] <Method for Obtaining DC Superposition Characteristics> Next, a method for obtaining the DC superposition characteristics of the dust core according to the present embodiment will be described. FIG. 4 is a flowchart for explaining the method for obtaining the DC superposition characteristics of the dust core according to the present embodiment. FIGS. 5 to 10 are graphs for explaining the method for obtaining the DC superposition characteristics of the dust core according to the present embodiment. Note that the graphs shown in FIGS. 5 to 10 correspond to the graphs when obtaining the DC superposition characteristics of Example 1.

[0042] As shown in FIG. 4, when obtaining the DC superposition characteristics of the dust core, first, an L-I curve is measured using a toroidal core with windings (step S11). For measuring the L-I curve, for example, a DC superposition tester can be used. For example, a DC current is superimposed on a sine wave of 1 MHz and an amplitude of 10 mA for measurement. FIG. 5 shows an example of the measurement result of the L-I curve.

[0043] Next, the L-I curve measured in step S11 is converted into a μ r -H curve (step S12). The following formula is used for the conversion. FIG. 6 shows the graph after converting the L-I curve into a μ r -H curve. Note that the toroidal core is regarded as an annular solenoid with a substantially closed magnetic circuit.

[0044]

Equation

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

[0046] Next, the μ r -H curve obtained in step S12 is approximated by an approximate formula (step S13). Specifically, μ rApproximate it with the polynomial shown below as a function of H. Fig. 7 shows an example approximated with a fifth-degree polynomial. Note that the values of a to f shown in Fig. 7 correspond to the values obtained in Example 1 described later. Also, in this embodiment, an approximation formula other than the fifth-degree polynomial may be used.

[0047]

Number

[0048] Next, as shown in the following formula, integrate the function of μ r (H) indefinitely to obtain the relationship between B and H (B-H curve) (step S14). Fig. 8 shows the graph of the obtained B-H curve. Note that in this embodiment, since a soft magnetic material with not very large residual magnetization is used, it can be calculated with B = 0 when H = 0 (integration constant C = 0).

[0049]

Number

[0050] Next, using the results of step S13 and step S14, obtain the relationship between μ r and B (step S15). Fig. 9 is a graph showing the relationship between μ r and B.

[0051] Then, convert the relative permeability μ r in step S15 to a relative value with respect to B = 0 T, and obtain the relative permeability when Bdc = 0.5 T (step S16). Specifically, as shown in Fig. 10, taking the relative permeability μ r at B = 0 obtained in step S15 as 100%, convert the relative permeability μ r to a relative value. Then, obtain the value of the relative permeability when the direct current magnetic flux density Bdc = 0.5 T.

[0052] In this embodiment, the value of the relative permeability when Bdc = 0.5T obtained in this way is used as a value indicating the DC superposition characteristic. Note that the value of the relative permeability when Bdc = 0.5T is the permeability μ B=0T when the magnetic flux density generated by the DC current is 0T, and the permeability μ B=0.5T when the magnetic flux density generated by the DC current is 0.5T. The value of μ B=0.5T / μ B=0T corresponds to "the value".

[0053] In this embodiment, the permeability of the compacted powder core when the magnetic flux density generated by the DC current is 0T is μ B=0T and the permeability when the magnetic flux density generated by the DC current is 0.5T is μ B=0.5T . When μ B=0.5T / μ B=0T is 0.65 or more, preferably 0.8 or more. Therefore, a compacted powder core and an inductor with good DC superposition characteristics can be provided.

Example

[0054] Next, examples will be described.

[0055] <Example 1> Using the above-described method for manufacturing a compacted powder core (see FIG. 2), a sample according to Example 1 was produced. The shape of the compacted powder core according to Example 1 was 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. As the magnetic powder, an Fe-Si-B-P-Cu-Cr-based powder, which is a nanocrystalline powder with a particle size of 11 μm (median diameter D50), was used. Next, the magnetic powder and the low-melting-point glass powder were mixed, and the low-melting-point glass was coated on the magnetic powder using the mechanofusion method. A phosphate-based glass was used as the low-melting-point glass. At this time, 2.5% by volume of the low-melting-point glass was mixed with the magnetic powder.

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

[0057] Next, the granulated magnetic powder was put into a mold and pressed under the condition of 500 kgf / cm 2 . After that, the green compact was heated and cured at a temperature of 150 °C without pressure to perform preliminary forming. Then, the intermediate formed body after preliminary forming was hot formed while being placed in a mold. The conditions for hot forming were a forming temperature of 470 °C, a pressing pressure of 8 tonf / cm 2 , and a pressing time of 30 seconds.

[0058] <Example 2> As a sample according to Example 2, a sample using an Fe-B-P-Cu-based powder, which is a nanocrystalline powder with a particle size of 14 μm (median diameter D50), as the magnetic powder was prepared. Also, in Example 2, the condition for hot forming was a forming temperature of 455 °C. Otherwise, it was the same as in Example 1.

[0059] <Example 3> As a sample according to Example 3, a sample using a metallic glass powder as the magnetic powder was prepared. For the metallic glass powder, an Fe-B-P-Nb-Cr-based powder with a particle size of 9 μm (median diameter D50) was used. Also, in Example 3, the condition for hot forming was a forming temperature of 490 °C. Otherwise, it was the same as in Example 1.

[0060] <Example 4> As a sample according to Example 4, a sample using pure iron as the magnetic powder was prepared. For the raw material of pure iron, carbonyl iron powder with a particle size of 8 μm (median diameter D50) was used. Otherwise, it was the same as in Example 1.

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

[0062] <Comparative Example 1> As a sample according to Comparative Example 1, a sample using nanocrystalline powder as the magnetic powder was prepared. As the nanocrystalline powder, an Fe-Si-B-P-Cu-Cr-based powder with a particle size of 11 μm (median diameter D50) was used. Also, in Comparative Example 1, by mixing 20% by volume of the resin material with respect to the magnetic powder, the magnetic powder coated with the low-melting glass was coated with the resin material and granulated. Further, the molding conditions were cold molding (molding temperature: 25°C). Otherwise, it was the same as in Example 1.

[0063] <Comparative Example 2> As a sample according to Comparative Example 2, a sample using an Fe-Si-based alloy as the magnetic powder was prepared. As the Fe-Si-based alloy, an Fe-5.5Si powder with a particle size of 10 μm (median diameter D50) was used. Also, in Comparative Example 2, by mixing 20% by volume of the resin material with respect to the magnetic powder, the magnetic powder coated with the low-melting glass was coated with the resin material and granulated. Further, the molding conditions were cold molding (molding temperature: 25°C). Otherwise, it was the same as in Example 1.

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

[0065] The filling rate of the magnetic powder was determined by comparing the volume of the magnetic powder contained in the magnetic core with the volume of the entire magnetic core measured by the Archimedes method. The volume of the magnetic powder contained in the magnetic core was obtained by subtracting the weight of the low-melting glass added as a binder and the weight of the remaining resin material from the total weight of the magnetic core to obtain the weight of the magnetic powder contained in the magnetic 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 a toroidal-shaped compacted powder core using the two-coil method with a B-H analyzer (manufactured by Iwasaki Telecom Co., Ltd.). The measurement conditions were a sinusoidal excitation condition of 1 MHz and 50 mT. The DC superposition characteristic (μ B=0.5T / μ B=0T ) was determined using the above method (see Figure 4). Hereinafter, as an example, the measurement of the DC superposition characteristic (μ B=0.5T / μ B=0T ) of the sample according to Example 1 will be specifically described.

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

[0068] Thereafter, the measured L-I curve was converted into a μ r -H curve (step S12 in Figure 4). The following formula was used for the conversion.

[0069]

Equation

[0070] Note that μ r is the relative magnetic permeability, μ0 is the magnetic permeability of vacuum (N / A 2 ), L is the measured inductance (H), l is the effective magnetic path length (m), s is the effective cross-sectional area (m 2 ), and n is the number of turns of the coil. In this measurement, each parameter was set as follows. Also, Figure 6 shows a graph after converting the L-I curve into a μ r -H curve. 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 μ-H curve after conversion was approximated by an approximate formula (step S13 in FIG. 4). Specifically, μ r was approximated by the following polynomial as a function of H. r

[0072]

Equation

[0073] FIG. 7 shows the result approximated by a fifth-degree polynomial. The values of the constants of the polynomial are 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, the function of μ r (H) was integrated indefinitely to obtain the relationship between B and H (B-H curve) (step S14 in FIG. 4). FIG. 8 shows the graph of the obtained B-H curve.

[0075]

Equation

[0076] The values of the constants of the above polynomial are as follows. In this example, since a soft magnetic material with not too large residual magnetization is used, it was calculated 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 step S13 and step S14, the relationship between μ and B with respect to H was obtained, and further the relationship between μ and B was obtained (step S15 in FIG. 4). FIG. 9 is a graph showing the relationship between μ and B. r and the relationship between μ and B. r (step S15 in FIG. 4). FIG. 9 is a graph showing the relationship between μ and B. r and B is shown.

[0078] Then, the relative permeability μ in step S15 r was converted to a relative value with respect to B = 0 T, and the relative permeability at Bdc = 0.5 T was obtained (step S16 in FIG. 4). Specifically, as shown in FIG. 10, the relative permeability μ at B = 0 T obtained in step S15 r was set to 1, and the relative permeability μ r was converted to a relative value. Then, the value of the relative permeability at the direct current magnetic flux density Bdc = 0.5 T was obtained.

[0079] In this embodiment, the value of the relative permeability at Bdc = 0.5 T obtained in this way (corresponding to the value of μ B=0.5T / μ B=0T was used as a value indicating the direct current superposition characteristic. The direct current superposition characteristics were obtained for other embodiments and comparative examples using the same method.

[0080] <Measurement Results> The measurement results of Examples 1 to 5 and Comparative Examples 1 to 2 are shown in Table 1. Also, the measurement results of the direct current superposition characteristics of Examples 1 to 5 and Comparative Examples 1 to 2, that is, the relationship between the relative permeability (μ) with respect to the direct current magnetic flux density Bdc (T), are shown in FIG. 11.

[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 characteristics (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 characteristics (μ B=0.5T / μ B=0T ) were 0.87 and 0.97, respectively, and 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 that 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 in each Bm increased as the frequency increased. Also, the iron loss values increased as the Bm value increased.

[0091] As described above, the present invention has been described in accordance with the above embodiments. However, the present invention is not limited only to the configurations of the above embodiments, and of course includes various modifications, corrections, and combinations that can be made by those skilled in the art within the scope of the invention of the claims of the present patent application.

Explanation of Signs

[0092] 1 Inductor 10, 10_1, 10_2 Compressed powder core 13 Coil 20 Magnetic powder after granulation 21 Magnetic powder 22 Binder layer 25 Intermediate compact 31 Low melting point glass 32 Resin material

Claims

1. A compacted powder magnetic core in which magnetic powder is bonded via a binder layer, Let μ be the magnetic permeability when the magnetic flux density generated by the direct current is 0 T. Ｂ＝０Ｔ Let μ be the magnetic permeability when the magnetic flux density generated by the direct current is 0.5 T. Ｂ＝０．５Ｔ In the case where Ｂ＝０．５Ｔ / μ Ｂ＝０Ｔ the value of is 0.65 or more. Compacted powder magnetic core.

2. said μ Ｂ＝０．５Ｔ / μ Ｂ＝０Ｔ The dust core according to claim 1, wherein the value of Ｂ＝０．５Ｔ / Ｂ＝０Ｔ is 0.8 or more.

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

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

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

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

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

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

9. The compacted powder magnetic core according to claim 7, wherein the resin material is at least one selected from the group consisting of a phenol resin, a polyimide resin, an epoxy resin, and an acrylic resin.

10. An inductor comprising the compacted powder magnetic core according to claim 1 or 2 and a coil.

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