Method for producing dust core and dust core

Abstract

To provide a method for producing a dust core that maintains excellent insulating quality even when held under high temperatures for a long time.SOLUTION: A method for producing a dust core includes: an insulation coating step (step 2) of forming an insulation layer on a surface of soft magnetic powder to prepare insulation coating powder; a granulation step (step 3) of mixing the insulation coating powder, a thermosetting resin and an organic solvent to prepare granulated powder; and a pressurizing step (step 4) of filling the granulated powder within a mold to pressure mold the granulated particles within the mold. The soft magnetic powder has an oxide layer on a surface thereof. The soft magnetic powder has a BET specific surface area of 0.35 m2 / g or less. The insulation layer comprises at least one selected from phosphate and silicate.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing a powder magnetic core and a powder magnetic core. [Background technology]

[0002] Patent Document 1 discloses a powder magnetic core manufactured using composite particles having a core portion (soft magnetic powder) made of a soft magnetic material and a coating layer made of an insulating material that coats the surface of the core portion. The powder magnetic core of Patent Document 1 is manufactured by mixing composite particles, a binder, and an organic solvent, drying the resulting mixture to obtain a dried mass, pulverizing this dried mass to form a granulated powder, and pressurizing and molding the granulated powder to obtain a molded body, which is then heated to harden the binder in the molded body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-232223 Summary of the Invention [Problem to be solved by the invention]

[0004] When a powder magnetic core such as that of Patent Document 1 is used in on-board equipment of an electric vehicle, it is required to maintain excellent insulation properties even when kept at high temperatures for a long period of time, taking into consideration the usage environment.

[0005] Therefore, an object of the present invention is to provide a method for producing a powder magnetic core that maintains excellent insulation properties even when held at high temperatures for long periods of time, and to provide a powder magnetic core produced by the method. [Means for solving the problem]

[0006] The present invention provides a first method for producing a powder magnetic core, comprising: an insulating coating step of forming an insulating layer on the surface of the soft magnetic powder to produce an insulating coated powder; a granulation step of mixing the insulating coating powder, a thermosetting resin, and an organic solvent to prepare a granulated powder; and a pressurizing step of filling a mold with the granulated powder and pressurizing and molding the granulated powder in the mold. A method for producing a powder magnetic core, comprising: the soft magnetic powder has an oxide layer on its surface, The BET specific surface area of ​​the soft magnetic powder is 0.35 m 2 / g or less, The insulating layer is made of one or more selected from phosphates and silicates. A method for producing a powder magnetic core is provided.

[0007] The present invention also provides a method for producing a second powder magnetic core, which is the same as the method for producing the first powder magnetic core, and includes the steps of: The soft magnetic powder contains 2000 ppm or less of oxygen. A method for producing a powder magnetic core is provided.

[0008] The present invention also provides a third method for producing a powder magnetic core, which is the method for producing the first powder magnetic core, comprising: The soft magnetic powder contains at least one of 3% by weight to 6% by weight of Si and 3% by weight to 6% by weight of Cr. A method for producing a powder magnetic core is provided.

[0009] The present invention also provides a fourth method for producing a powder magnetic core, which is the first method for producing a powder magnetic core, comprising: the insulating layer and the oxide layer constitute a complex oxide layer, The composite oxide layer has a thickness of 10 nm or more and 100 nm or less. A method for producing a powder magnetic core is provided.

[0010] The present invention also provides a first powder magnetic core, A powder magnetic core containing soft magnetic powder, The specific resistance of the powder magnetic core was 10 8 Ωcm or more, The average aspect ratio of the particles of the soft magnetic powder, as determined from a scanning electron microscope (SEM) image of a cross section of the powder core, is less than 1.5. A powder magnetic core is provided.

[0011] The present invention also provides a second powder magnetic core, A powder magnetic core containing soft magnetic powder, The specific resistance of the powder magnetic core was 10 8 Ωcm or more, When the cross-sectional area of ​​the particles of the soft magnetic powder obtained from a scanning electron microscope (SEM) image of the cut surface of the powder core is S and the circumferential length of the particles of the soft magnetic powder is L, the range in which the cumulative distribution (%) of the circularity A given by the following formula is 10% or more is 0.70 to 1.00. A=2 / L·(π·S) 1 / 2 A powder magnetic core is provided.

[0012] The present invention also provides a third powder magnetic core, which is the first powder magnetic core, the soft magnetic powder is made of an Fe-Si-Cr alloy, The Fe-Si-Cr alloy contains 3% by weight or more and 6% by weight or less of Si and 3% by weight or more and 6% by weight or less of Cr. A powder magnetic core is provided.

[0013] The present invention also provides a fourth powder magnetic core, which is the first or second powder magnetic core, the powder magnetic core contains an insulating coating powder, The insulating coating powder has an insulating layer on a surface thereof, the insulating coating powder contains the soft magnetic powder, the soft magnetic powder has an oxide layer on its surface, the insulating layer and the oxide layer constitute a complex oxide layer, The complex oxide layer contains one or more elements selected from P, Si, Zn, Fe, Al, Ti, and B. A powder magnetic core is provided.

[0014] The present invention also provides a fifth powder magnetic core, which is the fourth powder magnetic core, The composite oxide layer has a thickness of 10 nm or more and 100 nm or less. A powder magnetic core is provided. [Effects of the Invention]

[0015] The soft magnetic powder used in the method for producing a powder magnetic core of the present invention has a BET specific surface area of ​​0.35 m 2 / g or less. As a result, in a powder magnetic core manufactured by the method for manufacturing a powder magnetic core of the present invention, the soft magnetic powder particles have high sphericity, allowing a thick insulating layer to be formed on the soft magnetic powder with a small amount of insulating material. The insulating coating powder particles are appropriately spaced, reducing the number of contact points between the insulating coating powder particles, resulting in a high resistivity value at the initial stage of manufacture. Furthermore, in a powder magnetic core manufactured by the method for manufacturing a powder magnetic core of the present invention, the soft magnetic powder particles have high sphericity, reducing the contact area between the insulating coating powder and the thermosetting resin binder. This suppresses deterioration of the thermosetting resin due to metal ions diffused from the soft magnetic powder, allowing the powder magnetic core to maintain a high resistivity value over a long period of time. In other words, the method for manufacturing a powder magnetic core of the present invention provides a powder magnetic core that maintains excellent insulation even when held at high temperatures for a long period of time.

[0016] Furthermore, the powder magnetic core of the present invention has a specific resistance of 10 even after being held in an environment of 180°C for 1000 hours. 8 In other words, the dust core of the present invention maintains excellent insulation properties even when kept at high temperatures for a long period of time. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a powder magnetic core according to an embodiment of the present invention; [Figure 2]FIG. 1 is a diagram showing granulated powder according to an embodiment of the present invention. [Figure 3] 2 is a flowchart showing the manufacturing process of the powder magnetic core of FIG. 1. [Figure 4] 1 is a scanning electron microscope (SEM) image showing an example of a cross section of a powder magnetic core according to an example of the present invention. [Figure 5] 10 is an SEM image showing another example of a cut surface of a powder magnetic core according to an example of the present invention. [Figure 6] 1 is an SEM image showing an example of a cut surface of a powder magnetic core of a comparative example. [Figure 7] 10 is an SEM image showing another example of a cut surface of a powder magnetic core of a comparative example. [Figure 8] 1 is a histogram and cumulative distribution diagram of the circularity of particles of soft magnetic powder in a powder magnetic core according to an embodiment of the present invention. [Figure 9] 1 is a histogram and cumulative distribution diagram of the circularity of particles of soft magnetic powder in a powder magnetic core of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0018] (powder magnetic core) 1, a powder magnetic core 100 according to an embodiment of the present invention is a composite magnetic body in which insulating coating powder 300 is dispersed within a cured thermosetting resin 500. That is, the powder magnetic core 100 contains the insulating coating powder 300.

[0019] (insulating coating powder) Referring to FIG. 1, insulating coating powder 300 of this embodiment has an insulating layer 310 on its surface.

[0020] (insulating layer) 1, insulating layer 310 of the present embodiment is made of one or more materials selected from phosphates and silicates. That is, insulating layer 310 may be made of phosphate, silicate, or a combination of phosphate and silicate.

[0021] 1, the insulating coating powder 300 contains the soft magnetic powder 200. That is, the dust core 100 contains the soft magnetic powder 200. An insulating layer 310 is formed on the surface of the soft magnetic powder 200.

[0022] (Soft magnetic powder) The average aspect ratio of the particles of the soft magnetic powder 200 of this embodiment is less than 1.5. The average aspect ratio of the particles of this soft magnetic powder 200 was determined by calculating the aspect ratio of each of 50 or more particles randomly extracted from a scanning electron microscope (SEM) image of the cross section of the powder core 100, and averaging the aspect ratios of the calculated particles.

[0023] The range in which the cumulative distribution (%) of the circularity A of the particles of the soft magnetic powder 200 of this embodiment is 10% or more is 0.70 to 1.00. That is, the 10% cumulative value in the cumulative distribution of the circularity A of the particles of the soft magnetic powder 200 of this embodiment is in the range of 0.70 to 1.00. Furthermore, the range in which the cumulative distribution (%) of the circularity A of the particles of the soft magnetic powder 200 of this embodiment is 10% or more is preferably 0.85 to 1.00. That is, the 10% cumulative value in the cumulative distribution of the circularity A of the particles of the soft magnetic powder 200 of this embodiment is preferably in the range of 0.85 to 1.00. The range in which the cumulative distribution (%) of the circularity A of the particles of this soft magnetic powder 200 is 10% or more was determined based on the 10% cumulative value in the number-based cumulative distribution of the circularity A of the calculated multiple particles, by calculating the circularity A using the following formula for each of 50 or more particles randomly extracted from a scanning electron microscope (SEM) image of the cross section of the powder core 100 from the circumferential length L and cross-sectional area S of the particle obtained from the SEM image. Note that this circularity A is 1, which is the maximum value, when the particles are truly spherical. A=2 / L·(π·S) 1 / 2

[0024] The soft magnetic powder 200 of this embodiment is an Fe-based soft magnetic alloy powder containing Fe as a primary element. Specifically, the soft magnetic powder 200 of this embodiment is made of an Fe-Si-Cr alloy. Here, the Fe-Si-Cr alloy contains 3% by weight to 6% by weight of Si and 3% by weight to 6% by weight of Cr. That is, the soft magnetic powder 200 contains 3% by weight to 6% by weight of Si and 3% by weight to 6% by weight of Cr. However, the present invention is not limited thereto, and the soft magnetic powder 200 may contain at least one of 3% by weight to 6% by weight of Si and 3% by weight to 6% by weight of Cr.

[0025] When the soft magnetic powder 200 contains 3% by weight or more of Si, oxidation of the soft magnetic powder 200 and thermal decomposition of the cured thermosetting resin 500 in the powder core 100 containing the soft magnetic powder 200 are suppressed, and the magnetostriction and coercive force of the soft magnetic powder 200 are reduced, thereby reducing the core loss of the powder core 100 containing the soft magnetic powder 200. For this reason, the Si content in the soft magnetic powder 200 is preferably 3% by weight or more.

[0026] When the soft magnetic powder 200 contains 6% by weight or more of Si, the proportion of Fe in the soft magnetic powder 200 decreases, thereby reducing the saturation magnetic flux density Bs of the soft magnetic powder 200, and the powder core 100 using such soft magnetic powder 200 becomes easily magnetically saturated at a large current. Furthermore, when the soft magnetic powder 200 contains 6% by weight or more of Si, the hardness of the soft magnetic powder 200 itself increases, which deteriorates compression moldability and reduces the density of the soft magnetic powder 200 contained in the powder core 100, making the powder core 100 more likely to become magnetically saturated and also reducing the magnetic core strength of the powder core 100. For this reason, the amount of Si contained in the soft magnetic powder 200 is preferably 6% by weight or less.

[0027] When the soft magnetic powder 200 contains 3% by weight or more of Cr, it is possible to suppress oxidation of the soft magnetic powder 200 and reduce the oxygen concentration of the soft magnetic powder 200. For this reason, the Cr content of the soft magnetic powder 200 is preferably 3% by weight or more.

[0028] When the soft magnetic powder 200 contains 6% by weight or more of Cr, the proportion of Fe in the soft magnetic powder 200 decreases, resulting in a decrease in the saturation magnetic flux density Bs of the soft magnetic powder 200. For this reason, the Cr content in the soft magnetic powder 200 is preferably 6% by weight or less.

[0029] The soft magnetic powder 200 of this embodiment has an oxide layer 210 on the surface thereof. The oxide layer 210 is covered with an insulating layer 310.

[0030] Referring to Fig. 1, the insulating layer 310 and the oxide layer 210 constitute a complex oxide layer 350. The complex oxide layer 350 of this embodiment has a thickness of 10 nm or more and 100 nm or less. The complex oxide layer 350 contains one or more elements selected from P, Si, Zn, Fe, Al, Ti, and B. The complex oxide layer 350 has a thickness of 10 nm or more and 100 nm or less.

[0031] Generally, the oxygen contained in soft magnetic powder originates from the oxide layer on the surface. That is, the thicker the oxide layer, the higher the oxygen concentration in the soft magnetic powder, and the thinner the oxide layer, the lower the oxygen concentration in the soft magnetic powder. Furthermore, if the soft magnetic powder contains a large amount of powder that is close to spherical, the specific surface area decreases, and the area of ​​the oxide layer on the powder surface also decreases, resulting in a lower oxygen concentration in the soft magnetic powder. Furthermore, the oxide layer of the soft magnetic powder depends on the composition of the soft magnetic powder. For example, if there is little Si or Cr in the molten alloy (described below), oxidation occurs more easily during production of the soft magnetic powder, and the oxide layer on the powder surface also increases.

[0032] On the other hand, the soft magnetic powder 200 of this embodiment has fewer irregularly shaped particles that deviate from a spherical shape. That is, because the specific surface area of ​​the soft magnetic powder 200 of this embodiment is small, the oxygen concentration contained in the soft magnetic powder 200 is 2000 ppm or less. Therefore, even when an insulating layer 310 is formed on the particles of the soft magnetic powder 200, a sufficient thickness can be ensured, and when such soft magnetic powder 200 is used to manufacture a powder core 100, sufficient spacing can be ensured between the particles of the insulating coating powder 300. As a result, the powder core 100 containing the soft magnetic powder 200 of this embodiment is less likely to decrease in resistivity even when held at high temperatures for a long period of time.

[0033] Furthermore, when the oxygen concentration of the soft magnetic powder 200 is 1500 ppm or less, the number of irregularly shaped particles deviating from a spherical shape in the soft magnetic powder 200 is further reduced, and the specific surface area is further reduced. This ensures that even when an insulating layer 310 is formed on the particles of the soft magnetic powder 200, a sufficient thickness can be ensured. Furthermore, when a powder core 100 is manufactured using such soft magnetic powder 200, the spacing between the particles of the insulating coating powder 300 can be further ensured. That is, a powder core 100 containing soft magnetic powder 200 with an oxygen concentration of 1500 ppm is less likely to experience a further decrease in resistivity even when held at high temperatures for a long period of time. Therefore, it is preferable that the soft magnetic powder 200 contain 1500 ppm or less oxygen.

[0034] Taking the above into consideration, in order to further reduce the oxygen concentration in the soft magnetic powder 200, the Si concentration in the soft magnetic powder 200 is more preferably 3% by weight or more, and the Cr concentration in the soft magnetic powder 200 is more preferably 4% by weight or more.

[0035] Generally, for soft magnetic powders of the same particle size, the smaller the BET specific surface area, the less uneven the particle surface of the soft magnetic powder and the higher the sphericity. Furthermore, when insulating the particle surface of soft magnetic powder, the smaller the BET specific surface area, the thicker the insulating layer can be formed with a smaller amount of insulating material. Furthermore, when a powder core is produced by binding insulating coated powder with a thermosetting resin, the spacing between the insulating coated powder particles can be maintained appropriately, reducing the number of contact points between the insulating coated powder particles, thereby improving the insulation resistance of the powder core. From this perspective, the BET specific surface area of ​​the soft magnetic powder 200 of this embodiment is 0.35 m 2 / g or less. The BET specific surface area of ​​the soft magnetic powder 200 of this embodiment is 0.25 m 2 / g or less. The BET specific surface area of ​​the soft magnetic powder 200 of this embodiment is a value measured by the BET method.

[0036] Generally, in soft magnetic powders, the median diameter D 50 When the value is reduced, not only do eddy current loss and iron loss decrease, but also spacing between particles of the soft magnetic powder is more easily ensured, improving the DC bias characteristics of the dust core containing the soft magnetic powder.

[0037] On the other hand, the median diameter D of the soft magnetic powder 200 of this embodiment 50 The median diameter D of the soft magnetic powder 200 is 9 μm or more and 15 μm or less. As a result, the dust core 100 manufactured using the soft magnetic powder 200 of this embodiment can have a good balance of high magnetic permeability, low iron loss, high high frequency characteristics, and high DC bias characteristics. 50 The median diameter D in this embodiment is preferably 9 μm or more and 12 μm or less. 50 is a measurement value obtained by the laser diffraction / scattering method.

[0038] A method for manufacturing the powder magnetic core 100 of this embodiment will be described below.

[0039] 2 and 3, the method for manufacturing the dust core 100 of this embodiment includes a soft magnetic powder manufacturing process (step 1) for manufacturing the soft magnetic powder 200, an insulating coating process (step 2) for forming an insulating layer 310 on the surface of the soft magnetic powder 200 to manufacture the insulating coating powder 300, a granulation process (step 3) for mixing the insulating coating powder 300, a thermosetting resin 400, and an organic solvent (not shown) to manufacture the granulated powder 600, and a pressurizing process (step 4) for filling the granulated powder 600 into a mold and pressurizing the granulated powder 600 in the mold.

[0040] (Soft magnetic powder process) In this step, an atomization method such as water atomization or gas atomization is used to produce the soft magnetic powder 200. The soft magnetic powder 200 produced in this manner is composed of a plurality of substantially spherical particles.

[0041] Specifically, in the soft magnetic powder process (step 1), first, raw materials are prepared. Next, the raw materials are weighed to have a predetermined composition and melted to produce a molten alloy. Next, the molten alloy is discharged from a nozzle and broken into alloy droplets using high-pressure gas or water, thereby producing fine soft magnetic powder 200.

[0042] In this soft magnetic powder process (step 1), fluids used to break up the molten alloy include high-pressure water and high-pressure inert gases such as argon and nitrogen. According to the water atomization method using high-pressure water, the soft magnetic powder 200 of this embodiment having a fine particle size can be easily obtained. On the other hand, the gas atomization method using high-pressure inert gas has inferior breaking power and cooling capacity compared to the water atomization method. Therefore, the alloy droplets immediately after breaking up may be rapidly cooled by contacting them with a high-speed cooling fluid or solid, or the alloy droplets may be re-broken up to further refine them. When a liquid is used for cooling, for example, water or oil may be used. When a solid is used for cooling, for example, a rotating copper roll or a rotating aluminum plate may be used. However, the cooling liquid and solid are not limited to these, and various materials may be used.

[0043] (insulation coating process) In this process, an insulating layer 310 is formed on the surface of the soft magnetic powder 200, thereby producing the insulating coated powder 300. That is, the insulating coated powder 300 of this embodiment is obtained by forming the insulating layer 310 on the surface of the soft magnetic powder 200. Here, the insulating layer 310 is formed by a method of compounding the soft magnetic powder 200 and an insulating material through a mechanochemical reaction, or a method of immersing the soft magnetic powder 200 in a solution in which the insulating material is diluted with a solvent such as methanol, and then volatilizing the solvent. Here, examples of insulating materials include glass powders such as phosphate glass, borate glass, and silicate glass, phosphates, borates, chromates, metal oxides (silica, alumina, magnesia, etc.), metal alkoxides (tetraethoxysilane, etc.), inorganic phosphoric acid, and inorganic polymers (polysilane, polygermane, polystannane, polysiloxane, polysilsesquioxane, polysilazane, polyborazylene, polyphosphazene, etc.). The coating amount (solid content) of the insulating material was set to 1% by weight relative to 200 of the soft magnetic powder.

[0044] (granulation process) Referring to FIG. 2, in this process, insulating coating powder 300, thermosetting resin 400, and an organic solvent are mixed to produce granulated powder 600. Specifically, insulating coating powder 300 is mixed with thermosetting resin 400, which has good insulating properties, and an organic solvent such as methanol, and the organic solvent is then evaporated to obtain granulated powder 600. Examples of thermosetting resin 400 include silicone, epoxy, phenol, melamine, polyurethane, polyimide, and polyamide-imide. A silane coupling agent may be used together with thermosetting resin 400 to improve insulating properties and binding properties. The amount of thermosetting resin 400 is generally preferably about 1.0 to 10 wt%, and, considering insulating properties and filling rate, about 2.0 to 6.0 wt% is preferable. However, the amount of thermosetting resin 400 may be appropriately determined taking into account the powder particle size, applicable frequency, application, etc.

[0045] (Pressure process) In this step, granulated powder 600 is filled into a mold, and granulated powder 600 in the mold is pressure-molded to obtain a compact. When granulated powder 600 is pressure-molded, a powder softer than soft magnetic powder 200 according to this embodiment, such as Fe, FeSi, FeSiCr, FeSiAl, FeNi, or carbonyl iron powder, may be mixed in to improve packing properties. Furthermore, instead of or together with the above soft powder, any soft magnetic powder having a particle size different from that of soft magnetic powder 200 according to this embodiment may be mixed.

[0046] The molded body is then subjected to a heat treatment under predetermined heat treatment conditions, which hardens the thermosetting resin 400 to produce the powder magnetic core 100.

[0047] Hereinafter, the embodiment of the present invention will be described in more detail with reference to several examples.

[0048] (Examples 1 to 3 and Comparative Examples 1 to 3) As raw materials for the soft magnetic powders 200 of Examples 1 to 3 and the soft magnetic powders of Comparative Examples 1 to 3 listed in Table 1 below, industrially pure iron, ferrosilicon, and ferrochrome were prepared. The raw materials were weighed to obtain a predetermined alloy composition, and melted by high-frequency melting in an argon atmosphere to prepare a molten alloy. Next, the prepared molten alloy was quenched by water atomization to prepare the soft magnetic powders 200 of Examples 1 to 3 and the soft magnetic powders of Comparative Examples 1 to 3.

[0049] The median diameter D 50 The median diameter D 50 The specific surface area was measured by the laser diffraction / scattering method. The BET specific surface area was measured by the BET method. The oxygen concentration was measured using an oxygen / nitrogen analyzer. The results of these measurements are shown in Table 1.

[0050] [Table 1]

[0051] From Table 1, the median diameter D 50 is 10 to 12 μm, and the median diameter D 50 On the other hand, it was found from Table 1 that the median diameter D50 of Comparative Examples 1 to 3 was 10 μm.

[0052] From Table 1, the BET specific surface areas of Examples 1 to 3 are 0.18 to 0.31 m 2 / g, and the BET specific surface area of ​​Examples 1 to 3 is 0.35 m 2 On the other hand, it was found from Table 1 that the BET specific surface areas of Comparative Examples 1 to 3 were 0.36 to 0.62 m 2 / g, and the BET specific surface area of ​​Comparative Examples 1 to 3 was 0.35 m 2 It was found to exceed / g.

[0053] It can be seen from Table 1 that the oxygen concentrations in Examples 1 to 3 were 1400 to 2000 ppm, and 2000 ppm or less in Examples 1 to 3. On the other hand, it can be seen from Table 1 that the oxygen concentrations in Comparative Examples 1 to 3 were 2200 to 3800 ppm.

[0054] The soft magnetic powders 200 according to Examples 1 to 3 produced by the above method were used to produce the dust cores 100 according to Examples 1 to 3 by the following method.

[0055] First, 1.0 wt% of phosphate-based inorganic powder was mixed with the soft magnetic powder 200 in terms of solid content, and an insulating layer 310 was formed by a mechanochemical reaction to produce insulating coating powder 300. Next, insulating coating powder 300, thermosetting resin (epoxy resin) 400, and ethanol were mixed so that the solid content ratio of thermosetting resin 400 to insulating coating powder 300 was 5.0 wt%, and after volatilizing the ethanol, the mixture was sieved using a stainless steel sieve with 500 μm openings to obtain granulated powder 600. Thereafter, this granulated powder 600 was filled into a mold and molded under a molding pressure of 5 t / cm. 2This produced a ring-shaped molded body with an outer diameter of 13 mm, an inner diameter of 8 mm, and a height of 5 mm. Finally, the obtained ring-shaped molded body was heated and held at 150°C for two hours or more in a thermostatic chamber to harden the thermosetting resin 400, and then air-cooled to room temperature to produce the powder magnetic cores 100 of Examples 1 to 3.

[0056] Furthermore, dust cores according to Comparative Examples 1 to 3 were produced using the soft magnetic powders of Comparative Examples 1 to 3 in the same manner as above.

[0057] The powder magnetic core 100 produced in Example 1 was cut and then processed using a cross-section polisher (CP), and an SEM image was taken of the processed cut surface. The aspect ratio and circularity A of each of 50 or more particles randomly selected from the SEM image were calculated, and the ranges in which the average aspect ratio and cumulative distribution (%) of circularity A for the calculated particles were 10% or more were obtained. Additionally, using a method similar to that described above, the ranges in which the average aspect ratio and cumulative distribution (%) of circularity A for particles in the soft magnetic powder constituting the powder magnetic core in Comparative Example 1 were 10% or more were obtained.

[0058] 4 and 5 show SEM images obtained from the powder core 100 of Example 1. Using the above method, the average aspect ratio of the particles in the soft magnetic powder 200 constituting the powder core 100 according to Example 1 was calculated to be 1.25. This revealed that the average aspect ratio of the particles of the soft magnetic powder 200 obtained from a scanning electron microscope (SEM) image of the cross section of the powder core 100 was less than 1.5.

[0059] Furthermore, the circularity A of the particles in the soft magnetic powder 200 constituting the dust core 100 according to Example 1 was calculated using the method described above, and a histogram was obtained. The results are shown in Table 2 and FIG.

[0060] [Table 2]

[0061] From the above results, it was found that the range in which the cumulative distribution (%) of the circularity A of particles in the soft magnetic powder 200 constituting the powder core 100 according to Example 1 is 10% or more is 0.85 or more. This shows that the range in which the cumulative distribution (%) of the circularity A of particles in the soft magnetic powder 200 obtained from a scanning electron microscope (SEM) image of a cross section of the powder core 100 is 10% or more is included in 0.70 to 1.00.

[0062] 6 and 7 show SEM images taken from the powder magnetic core of Comparative Example 1. Using the above method, the average aspect ratio of the particles in the soft magnetic powder constituting the powder magnetic core of Comparative Example 1 was calculated to be 1.57. This revealed that the average aspect ratio of the particles of the soft magnetic powder determined from the scanning electron microscope (SEM) image of the cross section of the powder magnetic core of Comparative Example 1 exceeded 1.5.

[0063] Furthermore, the circularity A of the particles in the soft magnetic powder constituting the dust core according to Comparative Example 1 was calculated using the method described above, and a histogram was obtained. The results are shown in Table 3 and FIG.

[0064] [Table 3]

[0065] The above results revealed that the range in which the cumulative distribution (%) of the circularity A of particles in the soft magnetic powder constituting the powder magnetic core according to Comparative Example 1 is 10% or more is 0.68 or more. This revealed that part of the range in which the cumulative distribution (%) of the circularity A of particles in the soft magnetic powder, obtained from a scanning electron microscope (SEM) image of the cut surface of the powder magnetic core according to Comparative Example 1, is 10% or more is outside the range of 0.70 to 1.00.

[0066] The insulation resistance of the powder magnetic cores 100 of Examples 1 to 3 after being held in an environment of 180°C for a predetermined time was measured using a high resistance meter by applying a voltage of 100 V to electrodes with a diameter of 1 mm on the top and bottom surfaces of the powder magnetic cores 100. 2) and length (0.5 cm) were used to calculate the resistivity. Similarly, the insulation resistance was measured and the resistivity was calculated for the powder magnetic cores of Comparative Examples 1 to 3. The results are shown in Table 4.

[0067] [Table 4]

[0068] From Table 4, the resistivity of Examples 1 to 3 after 1 hour of heating was 4.7*10 12 ~3.4*10 13 That is, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 180°C for 1 hour. 12 It was also clear from Table 4 that the resistivity of Comparative Examples 1 to 3 after heating for 1 hour was 6.5*10 9 ~2.1*10 12 It was found that the resistivity values ​​of Examples 1 to 3 were greater than the resistivity values ​​of Comparative Examples 1 to 3 at a heating time of 1 hour.

[0069] In addition, the resistivity of Examples 1 to 3 after 16 hours of heating was 2.0*10 10 ~1.4*10 13 That is, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 180°C for 16 hours. 10 Furthermore, it was found from Table 4 that the resistivity of Comparative Examples 1 to 3 after 16 hours of heating was 1.7*10 9 ~1.5*10 10 That is, it was found that the resistivity values ​​of Examples 1 to 3 were greater than the resistivity values ​​of Comparative Examples 1 to 3 even after being held in an environment of 180°C for 16 hours.

[0070] In addition, the resistivity of Examples 1 to 3 after 100 hours of heating was 3.1*10 9 ~6.5*10 11 That is, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 180°C for 100 hours. 9Furthermore, it was found from Table 4 that the resistivity of Comparative Examples 1 to 3 after 100 hours of heating was 2.0*10 7 ~6.3*10 8 That is, it was found that the resistivity values ​​of Examples 1 to 3 were greater than the resistivity values ​​of Comparative Examples 1 to 3 even after being held in an environment of 180°C for 100 hours.

[0071] In addition, the resistivity of Examples 1 to 3 after 300 hours of heating was 3.1*10 8 ~1.7*10 10 In other words, the resistivity of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 180°C for 300 hours. 8 Furthermore, it was found from Table 4 that the resistivity of Comparative Examples 1 to 3 after heating for 300 hours was 1.0*10 6 ~6.0*10 7 That is, it was found that the resistivity values ​​of Examples 1 to 3 were greater than the resistivity values ​​of Comparative Examples 1 to 3 even after being held in an environment of 180°C for 300 hours.

[0072] In addition, the resistivity of Examples 1 to 3 after 500 hours of heating was 2.5*10 8 ~1.0*10 10 In other words, the resistivity of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 180°C for 500 hours. 8 Furthermore, it was found from Table 4 that the resistivity of Comparative Examples 1 to 3 after 500 hours of heating was 8.1*10 5 ~3.5*10 7 That is, it was found that the resistivity values ​​of Examples 1 to 3 were greater than the resistivity values ​​of Comparative Examples 1 to 3 even after being held in an environment of 180°C for 500 hours.

[0073] Furthermore, from Table 4, the resistivity of Examples 1 to 3 at a heating time of 1000 hours was 2.0*10 8 ~4.6*10 9 In other words, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 180°C for 1000 hours.8 Furthermore, it was found from Table 4 that the resistivity of Comparative Examples 1 to 3 after 1000 hours of heating was 6.1*10 5 ~3.0*10 7 It was found that the resistivity was Ωcm. That is, even after being held in an environment of 180°C for 1000 hours, the resistivity values ​​of Examples 1 to 3 were found to be greater than the resistivity values ​​of Comparative Examples 1 to 3. In other words, it was found that the powder core 100 of the present embodiment maintained excellent insulation properties even when held in an environment of 180°C for a long period of time, compared to the powder cores of the comparative examples.

[0074] The insulation resistance of the powder magnetic core 100 of Example 1 after being held in an environment of 200°C for a predetermined time was measured using a high-resistance meter by applying a voltage of 100 V to the top and bottom surfaces of the powder magnetic core 100 with electrodes having a diameter of 1 mm, and the resistivity was calculated using the cross-sectional area (0.825 cm) and length (0.5 cm). Similarly, the insulation resistance of the powder magnetic cores of Comparative Examples 1 and 2 was also measured, and the resistivity was calculated. The results are shown in Table 5.

[0075] [Table 5]

[0076] From Table 5, the resistivity of Example 1 after 1 hour of heating is 2.5*10 13 In other words, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 200°C for 1 hour. 13 Furthermore, it was found from Table 5 that the resistivity of Comparative Examples 1 and 2 after heating for 1 hour was 9.5*10 9 Ωcm, 4.6*10 10 That is, it was found that the resistivity of Example 1 was greater than the resistivity of Comparative Examples 1 and 2 even after being held in an environment of 200°C for 1 hour.

[0077] Furthermore, from Table 5, the resistivity of Example 1 after 16 hours of heating was 3.8*10 11 That is, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 200°C for 16 hours.11 Furthermore, it was found from Table 5 that the resistivity of Comparative Examples 1 and 2 after 16 hours of heating was 6.5*10 8 Ωcm,6.5*10 7 That is, it was found that the resistivity value of Example 1 was greater than the resistivity values ​​of Comparative Examples 1 and 2 even after being held in an environment of 200°C for 16 hours.

[0078] In addition, from Table 5, the resistivity of Example 1 after 100 hours of heating was 1.1*10 10 That is, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 200°C for 100 hours. 10 Furthermore, it was found from Table 5 that the resistivity of Comparative Examples 1 and 2 after 100 hours of heating was 2.4*10 7 Ωcm, 1.2*10 7 That is, it was found that the resistivity of Example 1 was greater than the resistivity of Comparative Examples 1 and 2 even after being held in an environment of 200° C. for 100 hours.

[0079] Furthermore, from Table 5, the resistivity of Example 1 after 300 hours of heating was 1.7*10 9 That is, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 200°C for 300 hours. 9 Furthermore, it was found from Table 5 that the resistivity of Comparative Examples 1 and 2 after 300 hours of heating was 1.8*10 7 Ωcm, 2.6*10 6 That is, it was found that the resistivity value of Example 1 was greater than the resistivity values ​​of Comparative Examples 1 and 2 even after being held in an environment of 200°C for 300 hours.

[0080] Furthermore, from Table 5, the resistivity of Example 1 after 500 hours of heating was 8.4*10 8 That is, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 200°C for 500 hours. 8Furthermore, it was found from Table 5 that the resistivity of Comparative Examples 1 and 2 after 500 hours of heating was 1.5*10 7 Ωcm, 2.6*10 6 That is, it was found that the resistivity value of Example 1 was greater than the resistivity values ​​of Comparative Examples 1 and 2 even after being held in an environment of 200°C for 500 hours.

[0081] Furthermore, from Table 5, the resistivity of Example 1 after 1000 hours of heating was 8.4*10 8 In other words, the specific resistance of the powder magnetic core 100 was 10 Ωcm even after being held in an environment of 200°C for 1000 hours. 8 Furthermore, it was found from Table 5 that the resistivity of Comparative Examples 1 and 2 after 1000 hours of heating was 1.7*10 7 ,2.4*10 6 It was found that the resistivity was Ωcm. That is, even after being held in an environment of 200°C for 1000 hours, the resistivity value of Example 1 was found to be greater than the resistivity values ​​of Comparative Examples 1 and 2. In other words, it was found that the powder core 100 of the present embodiment maintained excellent insulation properties compared to the powder cores of the comparative examples, even when held in an environment of 200°C, which is a higher temperature, for a long period of time.

[0082] Although the best mode for carrying out the present invention has been described, it will be apparent to those skilled in the art that modifications can be made to the present invention without departing from the spirit of the present invention, and such modifications are within the scope of the present invention. [Explanation of symbols]

[0083] 100 powder magnetic core 200 Soft magnetic powder 210 Oxide layer 300 Insulation Coating Powder 310 Insulating layer 350 Complex oxide layer 400 Thermosetting resin 500 Thermosetting resin 600 Granulated powder

Claims

1. an insulating coating step of forming an insulating layer on the surface of the soft magnetic powder to produce an insulating coated powder; a granulation step of mixing the insulating coating powder, a thermosetting resin, and an organic solvent to prepare a granulated powder; and a pressurizing step of filling a mold with the granulated powder and pressurizing and molding the granulated powder in the mold. A method for producing a powder magnetic core, comprising: the soft magnetic powder has an oxide layer on its surface, The BET specific surface area of ​​the soft magnetic powder is 0.35 m ２ / g or less, The insulating layer is made of one or more selected from phosphates and silicates. A method for manufacturing a powder magnetic core.

2. A method for producing a powder magnetic core according to claim 1, The soft magnetic powder contains 2000 ppm or less of oxygen. A method for manufacturing a powder magnetic core.

3. A method for producing a powder magnetic core according to claim 1, The soft magnetic powder contains at least one of 3% by weight to 6% by weight of Si and 3% by weight to 6% by weight of Cr. A method for manufacturing a powder magnetic core.

4. A method for producing a powder magnetic core according to claim 1, the insulating layer and the oxide layer constitute a complex oxide layer, The composite oxide layer has a thickness of 10 nm or more and 100 nm or less. A method for manufacturing a powder magnetic core.

5. A powder magnetic core containing soft magnetic powder, The specific resistance of the powder magnetic core was 10 even after being held in an environment of 180°C for 1000 hours. ８ Ωcm or more, The average aspect ratio of the particles of the soft magnetic powder, as determined from a scanning electron microscope (SEM) image of a cross section of the powder magnetic core, is less than 1.

5. Powder magnetic core.

6. A powder magnetic core containing soft magnetic powder, The specific resistance of the powder magnetic core was 10 even after being held in an environment of 180°C for 1000 hours. ８ Ωcm or more, When the cross-sectional area of ​​the particles of the soft magnetic powder obtained from a scanning electron microscope (SEM) image of the cut surface of the powder core is S and the circumferential length of the particles of the soft magnetic powder is L, the range in which the cumulative distribution (%) of the circularity A given by the following formula is 10% or more is 0.70 to 1.

00. A=2 / L・(π・S) 1／２ Powder magnetic core.

7. 6. The powder magnetic core according to claim 5, the soft magnetic powder is made of an Fe—Si—Cr alloy, The Fe-Si-Cr alloy contains 3% by weight or more and 6% by weight or less of Si and 3% by weight or more and 6% by weight or less of Cr. Powder magnetic core.

8. 7. The powder magnetic core according to claim 5 or 6, the powder magnetic core contains an insulating coating powder, The insulating coating powder has an insulating layer on a surface thereof, the insulating coating powder contains the soft magnetic powder, the soft magnetic powder has an oxide layer on its surface, the insulating layer and the oxide layer constitute a complex oxide layer, The complex oxide layer contains one or more elements selected from the group consisting of P, Si, Zn, Fe, Al, Ti, and B. Powder magnetic core.

9. The powder magnetic core according to claim 8, The composite oxide layer has a thickness of 10 nm or more and 100 nm or less. Powder magnetic core.

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