Powder magnetic core, inductor, and method for manufacturing powder magnetic core

Abstract

The invention provides a dust core capable of improving the reliability of an inductor. A dust core (1) according to one aspect of the present invention is a dust core (1) in which a magnetic powder (11) is bonded by an insulating layer (12). The insulating layer (12) contains a phosphoric acid insulating material (13), a resin material (15), and a calcium-containing moisture absorption inhibitor (14). For example, the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor (14) to phosphorus contained in the phosphoric acid insulating material (13) is 0.10 or more.

Description

Technical Field

[0001] The present invention relates to a powder magnetic core, an inductor, and a method for manufacturing the powder magnetic core. Background Art

[0002] In recent years, inductors have been used in a variety of electronic devices. Therefore, improving the reliability of inductors is crucial to enhancing the reliability of electronic devices. Patent Document 1 discloses a method for producing a compacted amorphous soft magnetic alloy with minimal drop in magnetic permeability in the high-frequency range.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 10-212503. Summary of the Invention

[0006] Problems to be solved by the invention

[0007] As mentioned above, inductors are used in a variety of electronic devices. These devices are expected to be used in a variety of environments. Therefore, to improve the reliability of these electronic devices, it is necessary to use inductors that do not degrade their characteristics under various conditions—in other words, highly reliable inductors.

[0008] In view of the above problems, an object of the present invention is to provide a dust core, an inductor, and a method for manufacturing the dust core, which can improve the reliability of the inductor.

[0009] Solutions for solving problems

[0010] A powder magnetic core according to one aspect of the present invention is formed by bonding magnetic powder via an insulating layer. The insulating layer includes a phosphate-based insulating material, a resin material, and a moisture absorption inhibitor containing calcium.

[0011] An inductor according to one aspect of the present invention includes the above-described powder magnetic core and a coil.

[0012] A method for manufacturing a powder magnetic core according to one aspect of the present invention includes: a process of coating a phosphoric acid-based insulating material on the surface of a magnetic powder; a process of coating the coated magnetic powder with a calcium-containing moisture absorption inhibitor; a process of adding a resin material to the magnetic powder coated with the moisture absorption inhibitor and granulating the powder; and a process of molding and thermally curing the granulated magnetic powder.

[0013] Another aspect of the present invention provides a method for manufacturing a powder magnetic core, including: a step of coating a phosphoric acid-based insulating material on the surface of a magnetic powder; a step of adding a calcium-containing moisture absorption inhibitor and a resin material to the coated magnetic powder and granulating the powder; and a step of molding and thermally curing the granulated magnetic powder.

[0014] Effects of the Invention

[0015] According to the present invention, a dust core capable of improving the reliability of an inductor, an inductor, and a method for manufacturing the dust core can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram for explaining the first aspect of the dust core according to the embodiment.

[0017] Figure 2 It is a schematic diagram for explaining the second aspect of the dust core according to the embodiment.

[0018] Figure 3 This is a flowchart for explaining the method for manufacturing the dust core according to the first aspect.

[0019] Figure 4 This is a flowchart for explaining the method for manufacturing the dust core according to the second aspect.

[0020] Figure 5 This is a graph showing the relationship between Ca / P and weight increase rate when calcium carbonate is coated on magnetic powder.

[0021] Figure 6 This is a graph showing the relationship between Ca / P and the weight increase rate when calcium carbonate is added to magnetic powder. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments will be described.

[0023] The dust core of this embodiment is made by bonding magnetic powder via an insulating layer. The insulating layer contains a phosphate-based insulating material, a resin material, and a calcium-containing moisture absorption inhibitor. This structure of the dust core of this embodiment enables the realization of a dust core that improves the reliability of the inductor. Furthermore, the inductor of this embodiment can be constructed using the aforementioned dust core and coil. The dust core of this embodiment is described in detail below.

[0024] Figure 1 1 is a schematic diagram for explaining the first aspect of the powder magnetic core of this embodiment, and is an enlarged schematic diagram of a portion of the powder magnetic core. Figure 1As shown, the dust core 1_1 of the first embodiment is a dust core formed by bonding magnetic powder 11 via an insulating layer 12_1. The insulating layer 12_1 includes a phosphate-based insulating material 13, a resin material 15, and a moisture absorption inhibitor 14 containing calcium.

[0025] In the compressed magnetic powder core 1_1 of the first aspect, the surface of the magnetic powder 11 is coated with a phosphoric acid-based insulating material 13, and its surface is further coated with a moisture absorption inhibitor 14. The magnetic powder 11 coated with the phosphoric acid-based insulating material 13 and the moisture absorption inhibitor 14 is then bonded using a resin material 15. Furthermore, in the compressed magnetic powder core 1_1 of the first aspect, the moisture absorption inhibitor 14 is not only coated on the surface of the magnetic powder 11, but the moisture absorption inhibitor 14 may also be contained in the resin material 15.

[0026] Figure 2 1 is a schematic diagram for explaining the second aspect of the powder magnetic core of this embodiment, and is an enlarged schematic diagram of a portion of the powder magnetic core. Figure 2 As shown, the powder core 1_2 of the second embodiment is a powder core formed by bonding magnetic powder 11 via an insulating layer 12_2. The insulating layer 12_2 includes a phosphate-based insulating material 13, a resin material 15, and a moisture absorption inhibitor 14 containing calcium.

[0027] In the second aspect of the compressed magnetic core 1_2, the surface of the magnetic powder 11 is coated with a phosphoric acid-based insulating material 13. The magnetic powder 11 coated with the phosphoric acid-based insulating material 13 is then bonded using a resin material 15 containing a moisture absorption inhibitor 14. In other words, in the second aspect of the compressed magnetic core 1_2, the moisture absorption inhibitor 14 is dispersed in the resin material 15.

[0028] In the dust core 1_1 of the first embodiment and the dust core 1_2 of the second embodiment, the insulating layers 12_1 and 12_2 contain a moisture absorption inhibitor 14. This prevents the dust cores 1_1 and 1_2 from absorbing moisture. Specifically, the calcium contained in the moisture absorption inhibitor 14 prevents the phosphorus contained in the dust cores 1_1 and 1_2 from absorbing moisture from the atmosphere. This improves the reliability of the inductor. It should be noted that, hereinafter, the dust core 1_1 of the first embodiment and the dust core 1_2 of the second embodiment will be collectively referred to as the dust core 1 of the embodiment. Furthermore, the insulating layers 12_1 and 12_2 will be collectively referred to as the insulating layer 12.

[0029] Soft magnetic powder can be appropriately selected and used from materials exhibiting soft magnetism. From the perspective of magnetic properties, iron-containing materials are preferred, which can be simple iron or alloys containing iron and other elements. As soft magnetic powder, preferably, iron alloy powders such as carbonyl iron, Fe-Si alloy, Fe-Ni alloy, Fe-Si-Cr alloy, Fe-Si-Al alloy, Fe-based amorphous alloy powder containing at least Fe-B, and Fe-based nanocrystalline alloy containing at least Fe-BP-Cu are included. Here, the above-mentioned Fe-based amorphous alloy refers to an amorphous alloy that does not have a crystalline structure in the Fe-based alloy. In addition, the Fe-based nanocrystalline alloy refers to an alloy in which the above-mentioned Fe-based amorphous alloy is heat-treated and fine α-Fe crystals are precipitated in the amorphous phase. Soft magnetic powder can be used alone or in combination of two or more.

[0030] In this embodiment, the closer the particle shape of the magnetic powder 11 is to a sphere, the more preferred it is. If the sphericity of the particles is low, protrusions will appear on the surface of the particles. When the molding pressure is applied, the stress from the surrounding particles will be concentrated on the protrusions, causing the coating to be destroyed and the insulation to be unable to be fully maintained. As a result, the magnetic properties (especially the loss) of the obtained pressed powder core will sometimes deteriorate. In addition, the sphericity of the particles can be controlled within a suitable range by adjusting the manufacturing conditions of the magnetic powder. For example, in the water atomization method, it can be controlled within a suitable range by adjusting the water volume and / or water pressure of the high-pressure water jet used for atomization, the temperature and supply rate of the molten raw material, etc. The specific manufacturing conditions will vary depending on the composition of the magnetic powder to be manufactured and the desired productivity. For example, the particle size of the magnetic powder 11 can be greater than 5 μm and less than 30 μm (median particle size D50).

[0031] Phosphate-based insulating material 13 is an insulating material containing phosphate, and phosphate-based glass, for example, can be used. In other words, phosphate-based insulating material 13 used in this embodiment is a low-melting-point glass containing phosphate. Because phosphate-based insulating material 13 is flexible, it can be coated on the surface of magnetic powder 11 using an insulation treatment, such as a mechanochemical method, to form a high-performance insulating film on the surface of magnetic powder 11. The thickness of phosphate-based insulating material 13 coated on magnetic powder 11 is preferably from 10 nm to 100 nm, and more preferably from 10 nm to 60 nm.

[0032] The moisture absorption inhibitor 14 is a calcium-containing moisture absorption inhibitor, and calcium carbonate can be used, for example. The moisture absorption inhibitor 14 has the function of inhibiting moisture absorption by the dust core 1. In this embodiment, the moisture absorption inhibitor 14 can be made of any material that can inhibit moisture absorption by the dust core 1.

[0033] The resin material 15 is, for example, a thermosetting resin. For example, at least one selected from silicone resin, phenolic resin, polyimide resin, epoxy resin, and acrylic resin can be used as the resin material 15 .

[0034] In this embodiment, the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor 14 to phosphorus contained in the phosphate-based insulating material 13 can be 0.10 or greater, preferably 0.29 or greater, more preferably 0.44 or greater, and even more preferably 0.69 or greater. By setting the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor 14 to phosphorus contained in the phosphate-based insulating material 13 within this range, moisture absorption by the dust core 1 can be effectively suppressed, thereby improving the reliability of the inductor.

[0035] Furthermore, in this embodiment, the volume ratio of moisture absorption inhibitor 14 to phosphate-based insulating material 13 is 7% or greater, preferably 20% or greater, more preferably 30%, and even more preferably 50% or greater. By setting the volume ratio of moisture absorption inhibitor 14 to phosphate-based insulating material 13 within this range, moisture absorption by dust core 1 can be effectively suppressed, thereby improving the reliability of the inductor.

[0036] In the dust core 1 of this embodiment, a phosphoric acid-based insulating material 13 is used to coat the surface of the magnetic powder 11. Since the phosphoric acid-based insulating material 13 is soft, coating the surface of the magnetic powder 11 with the phosphoric acid-based insulating material 13 allows for the formation of a high-performance insulating film on the surface of the magnetic powder 11. However, due to the high hygroscopicity of the phosphoric acid-based insulating material 13, there is a problem: when the dust core is exposed to high temperature and high humidity, the dust core absorbs moisture from the air, resulting in a decrease in the durability of the dust core and, consequently, in the reliability of the inductor. Specifically, when the dust core absorbs moisture from the air, the moisture contained in the dust core expands when the dust core is heated, potentially causing the dust core to crack. Consequently, there is a problem of reduced reliability of the inductor due to the decreased properties of the dust core.

[0037] Therefore, in this embodiment, the insulating layer 12 of the dust core 1 contains a moisture absorption inhibitor 14. By including the moisture absorption inhibitor 14 in the insulating layer 12, the dust core 1 (phosphate-based insulating material 13) can be prevented from absorbing moisture, thereby improving the reliability of the inductor.

[0038] Next, the method for manufacturing the powder magnetic core of this embodiment will be described. Figure 3 The flowchart shown in FIG. 1 illustrates the powder magnetic core 1_1 according to the first embodiment (see FIG. Figure 1 ) manufacturing method.

[0039] like Figure 3As shown, when manufacturing the pressed powder core 1_1 of the first aspect, first, prepare the magnetic powder 11 (step S1). The above-mentioned magnetic powder can be used as the magnetic powder 11. Next, a phosphate-based insulating material 13 is coated on the magnetic powder 11 (step S2). For example, phosphate-based glass can be used as the phosphate-based insulating material 13. The method of coating the phosphate-based insulating material 13 on the magnetic powder 11 can be appropriately selected from, for example, a powder mixing method, a mechanochemical method, an impregnation method, a sol-gel method, a CVD method, a PVD method, or various well-known methods other than the above. From the perspective of ensuring insulation resistance and suppressing oxidation of the resin cured product, the average thickness of the phosphate-based insulating material 13 is preferably 10 to 100 nm, and more preferably 10 to 60 nm.

[0040] Next, a moisture absorption inhibitor 14 is applied to the magnetic powder 11 coated with the phosphate-based insulating material 13 (step S3). For example, calcium carbonate can be used as the moisture absorption inhibitor 14. When applying the moisture absorption inhibitor 14 to the magnetic powder 11, a method can be appropriately selected from a powder mixing method, a mechanochemical method, an impregnation method, a sol-gel method, a CVD method, a PVD method, or various other known methods. For example, the moisture absorption inhibitor 14 can be dispersed in a binder and adhered to the surface of the magnetic powder 11 while drying.

[0041] Next, a resin material 15 is added to the magnetic powder 11 coated with the moisture absorption inhibitor 14 and granulated (step S4). The above-mentioned resin material can be used as the resin material 15. The resin material 15 preferably uses a material that softens at around 100°C and acts as an insulating material or a bonding material after thermal curing. When coating (granulating) the resin material, a rolling granulation method, a spray drying method, etc. can be used. Specifically, a resin layer containing the resin material 15 can be formed on the surface of the magnetic powder 11 coated with the moisture absorption inhibitor 14 by mixing a resin material dissolved in an organic solvent with the magnetic powder 11 coated with the moisture absorption inhibitor 14 and drying it.

[0042] In the present embodiment, there may be a portion of the magnetic powder that is not coated with the resin material 15. In the present embodiment, it is preferable to use a thermosetting resin as the resin material 15.

[0043] Next, the granulated magnetic powder is molded (step S5). For example, the molding can be performed by putting the granulated magnetic powder into a mold and applying pressure.

[0044] Next, the molded body is thermally cured (step S6). For example, the molded body is heated at 150°C to 250°C for 2 hours to thermally cure the resin material (binder). In addition, in this embodiment, the granulated magnetic powder can be pre-molded, and the pre-molded intermediate body can be hot-pressed. Hot-pressing can be performed by placing the pre-molded intermediate body in a mold while applying pressure and heating.

[0045] The powder magnetic core 1_1 of the first aspect can be manufactured by the manufacturing method described above (see Figure 1 When manufacturing the dust core 1_1 of the first aspect, the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor 14 to phosphorus contained in the phosphate-based insulating material 13 can be set to 0.10% or more, preferably 0.29 or more, more preferably 0.44 or more, and even more preferably 0.69 or more.

[0046] Next, use Figure 4 The flowchart shown in FIG. 1 illustrates the powder magnetic core 1_2 of the second embodiment (see FIG. 2 ). Figure 2 ) manufacturing method.

[0047] like Figure 4 As shown, when manufacturing the pressed powder core 1_2 of the second aspect, first prepare the magnetic powder 11 (step S11). The above-mentioned magnetic powder can be used as the magnetic powder 11. Next, a phosphate-based insulating material 13 is coated on the magnetic powder 11 (step S12). For example, phosphate-based glass can be used as the phosphate-based insulating material 13. The method of coating the phosphate-based insulating material 13 on the magnetic powder 11 can be appropriately selected from, for example, a powder mixing method, a mechanochemical method, an impregnation method, a sol-gel method, a CVD method, a PVD method, or various well-known methods other than the above. From the perspective of ensuring insulation resistance and suppressing oxidation of the resin cured product, the average thickness of the phosphate-based insulating material 13 is preferably 10 to 100 nm, and more preferably 10 to 60 nm.

[0048] Next, a moisture absorption inhibitor 14 and a resin material 15 are added to the magnetic powder 11 coated with the phosphoric acid-based insulating material 13 and granulation is performed (step S13). For example, calcium carbonate can be used as the moisture absorption inhibitor 14. The above-mentioned resin material can be used as the resin material 15. The resin material 15 preferably uses a material that softens at around 100°C and acts as an insulating material or a bonding material after thermal curing. When coating (granulating) the moisture absorption inhibitor 14 and the resin material 15, a rolling granulation method, a spray drying method, etc. can be used. Specifically, an organic solvent, a moisture absorption inhibitor 14, and a resin material 15 can be mixed with the magnetic powder 11 coated with the phosphoric acid-based insulating material 13 and dried, thereby forming a resin layer containing the moisture absorption inhibitor 14 and the resin material 15 on the surface of the magnetic powder 11 coated with the phosphoric acid-based insulating material 13.

[0049] In the present embodiment, there may be a portion of the magnetic powder that is not coated with the moisture absorption inhibitor 14 and the resin material 15. In the present embodiment, it is preferable to use a thermosetting resin as the resin material 15.

[0050] Next, the granulated magnetic powder is molded (step S14). For example, the molding can be performed by putting the granulated magnetic powder into a mold and applying pressure.

[0051] Next, the formed body is thermally cured (step S15). For example, the formed body is heated at 150°C to 250°C for 2 hours to thermally cure the resin material (binder). In addition, in this embodiment, the granulated magnetic powder can be preformed, and the preformed intermediate body can be hot-pressed. Hot-pressing can be performed by placing the preformed intermediate body in a mold while applying pressure and heating it.

[0052] By using the manufacturing method described above, the powder magnetic core 1_2 of the second aspect can be manufactured (see Figure 2 When manufacturing the dust core 1_2 of the second aspect, the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor 14 to phosphorus contained in the phosphate-based insulating material 13 can be set to 0.10% or more, preferably 0.29 or more, more preferably 0.44 or more, and even more preferably 0.69 or more.

[0053] The weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor 14 to phosphorus contained in the phosphate-based insulating material 13 can be determined, for example, by performing a composition analysis of the powder core 1. For example, the composition of the entire powder core 1 can be analyzed using energy dispersive X-ray spectroscopy (EDS). In this case, if the magnetic powder 11 contains phosphorus, the amount of phosphorus contained in the magnetic powder 11 can be determined in advance, and then the amount of phosphorus contained in the magnetic powder 11 can be subtracted from the amount of phosphorus contained in the entire powder core 1 to determine the amount of phosphorus contained in the phosphate-based insulating material 13. Alternatively, the amount of phosphorus contained in the phosphate-based insulating material 13 as a raw material can be determined in advance, and the weight ratio of calcium to phosphorus (Ca / P) can be determined by calculation.

[0054] Alternatively, the amount of the carbon dioxide can be determined by observing the powder core 1 using a scanning electron microscope (SEM) and analyzing calcium contained in the moisture absorption inhibitor 14 and phosphorus contained in the phosphate-based insulating material 13 using EDS.

[0055] Example

[0056] Next, examples will be described.

[0057] Experiment 1

[0058] (Sample production)

[0059] In order to confirm the effect of the moisture absorption inhibitor (calcium carbonate), the following experiment was conducted.

[0060] use Figure 4 The method for manufacturing a powdered magnetic core 1_2 according to the second aspect shown in the figure was used to produce a powdered magnetic core of sample 1-1. Specifically, magnetic powder was first prepared. The magnetic powder used was a powder of an Fe-Si-Cr alloy with a particle size of 10 μm (median particle size D50). Next, the magnetic powder was mixed with a phosphate-based insulating material A, and the phosphate-based insulating material A was coated on the magnetic powder using a mechanochemical method. The phosphate-based insulating material A used was a material having the composition shown in sample 2-1 in Table 2.

[0061] Next, a moisture absorption inhibitor (calcium carbonate) and a resin material were added to the magnetic powder coated with the phosphate-based insulating material A, and granulation was performed. Silicone resin was used as the resin material. The volume ratios of the phosphate-based insulating material A, calcium carbonate, and resin material were 2.0 vol%, 2.0 vol%, and 32.0 vol%, respectively (see Table 1). The volume ratios of the phosphate-based insulating material A, calcium carbonate, and resin material are relative to the volume of the magnetic powder.

[0062] Next, the granulated magnetic powder was placed in a mold and pressed to form a compact. The compact was then heated at 200° C. for 2 hours for thermal curing.

[0063] Using the method described above, a powder magnetic core of Sample 1-1 was produced. Sample 1-2 was also produced, adding mica instead of calcium carbonate. Sample 1-3 was also produced, adding talc instead of calcium carbonate. Finally, Sample 1-4 was produced, without calcium carbonate or other additives. It should be noted that the production methods for Samples 1-2 through 1-4 were identical to those for Sample 1-1, except for the changes in additives.

[0064] (Environmental testing)

[0065] The following environmental tests were performed on each of the produced samples.

[0066] First, the weight of each sample was measured before environmental testing. The samples were then placed in an environment with a temperature of 85°C and a humidity of 85% for one week for environmental testing. The weight of each sample after environmental testing was then measured. Table 1 shows the weight gain of Samples 1-1 to 1-4 after environmental testing.

[0067] As shown in Table 1, the weight gain rate of sample 1-1 to which calcium carbonate was added after the environmental test was 0%. On the other hand, the weight gain rate of sample 1-2 to which mica was added instead of calcium carbonate after the environmental test was 0.14%. In addition, the weight gain rate of sample 1-3 to which talc was added instead of calcium carbonate after the environmental test was 0.13%. In addition, the weight gain rate of sample 1-4 to which no additive was added after the environmental test was 0.32%. This shows that in samples 1-2 to 1-4, the powder core absorbed moisture during the environmental test, resulting in an increase in weight. On the other hand, the weight gain rate of sample 1-1 to which calcium carbonate was added after the environmental test was 0%, which can suppress the absorption of moisture by the powder core. Therefore, it can be seen that by adding calcium carbonate as an additive, the absorption of moisture by the powder core can be suppressed.

[0068] [Table 1]

[0069] [Table 1]

[0070]

[0071] Experiment 2

[0072] Next, in order to confirm the effect of the moisture absorption inhibitor (calcium carbonate) due to the difference in the phosphate-based insulating material, the following experiment was conducted.

[0073] (Sample production)

[0074] First, 1.0 g of phosphate-based insulating material A and phosphate-based insulating material B were prepared respectively. The compositions of phosphate-based insulating material A and phosphate-based insulating material B were analyzed using EDS, and the results were the compositions shown in Table 2. Then, phosphate-based insulating material A was used as sample 2-1. At this time, two types of samples were prepared: a sample with calcium carbonate added and a sample without calcium carbonate added. In the sample with calcium carbonate added, the volume ratio of phosphate-based insulating material A to calcium carbonate was 1:1. These samples were recorded as sample 2-1 (containing calcium carbonate) and sample 2-1 (not containing calcium carbonate).

[0075] In addition, phosphate-based insulating material B was designated as Sample 2-2. Two types of samples were prepared: one with calcium carbonate added and one without. In the sample with calcium carbonate added, the volume ratio of phosphate-based insulating material B to calcium carbonate was set at 1:1. These samples were designated Sample 2-2 (with calcium carbonate) and Sample 2-2 (without calcium carbonate).

[0076] Each sample was then placed in a Petri dish and dried at 125°C. The dish containing each sample was then weighed (the weight at this time was recorded as Weight A). The Petri dish containing each sample and a separate Petri dish containing water were then placed in the same container and sealed. After 300 hours, the Petri dish containing each sample was weighed again (the weight at this time was recorded as Weight B). The weight gain rate of each sample was calculated using the following formula.

[0077] Weight increase rate (%) = {(weight B - weight A) / weight A} × 100

[0078] The weight rate of increase tried to achieve by the above method is shown in Table 2. As shown in Table 2, in sample 2-1 (not containing calcium carbonate), the weight rate of increase illustrates high value, and in sample 2-1 (containing calcium carbonate), the weight rate of increase illustrates low value. As can be seen, the sample 2-1 (containing calcium carbonate) that has added calcium carbonate can suppress absorption moisture. In addition, in sample 2-2 (not containing calcium carbonate), the weight rate of increase illustrates high value, and in sample 2-2 (containing calcium carbonate), the weight rate of increase illustrates low value. As can be seen, the sample 2-2 (containing calcium carbonate) that has added calcium carbonate can suppress absorption moisture.

[0079] According to the experimental results of Experiment 2, in both the phosphate-based insulating material A and the phosphate-based insulating material B, the effect of suppressing moisture absorption by adding calcium carbonate was confirmed.

[0080] [Table 2]

[0081] [Table 2]

[0082]

[0083] Experiment 3

[0084] (Sample production)

[0085] use Figure 3 The method for manufacturing a dust core 1_1 according to the first aspect was used to produce dust cores of Samples 3-1 and 3-4. Specifically, magnetic powder was first prepared. The magnetic powder used was an Fe-Si-Cr alloy powder with a particle size of 10 μm (median particle size D50). Next, the magnetic powder was mixed with a phosphate-based insulating material A, and the phosphate-based insulating material A was coated onto the magnetic powder using a mechanochemical method.

[0086] Afterwards, a moisture absorption inhibitor (calcium carbonate) was applied to the magnetic powder coated with the phosphate-based insulating material A. A resin material was then added to the magnetic powder coated with the phosphate-based insulating material A and calcium carbonate, and granulated. Silicone resin was used as the resin material. The amounts of phosphate-based insulating material A, calcium carbonate, magnetic powder, and resin material used in Samples 3-1 and 3-4 were as shown in Table 3.

[0087] The volume ratios of the phosphate-based insulating material A and calcium carbonate shown in Table 3 are the volume ratios relative to the magnetic powder. Specifically, the volume ratio (vol%) of the phosphate-based insulating material A is the volume ratio of the phosphate-based insulating material A relative to the magnetic powder. Furthermore, the volume ratio (vol%) of the calcium carbonate is the volume ratio of the calcium carbonate relative to the magnetic powder. The weights (g) of the magnetic powder, phosphate-based insulating material A, calcium carbonate, and resin material shown in Table 3 represent the amounts of each material contained in a 2.5g dust core.

[0088] Next, the granulated magnetic powder is put into a mold and heated at 5000 kgf / cm 2 The molded body was then heated at 200° C. for 2 hours for thermal curing.

[0089] Using the method described above, powder cores of Samples 3-1 to 3-4 were produced. Sample 3-1 is a sample to which no calcium carbonate was added. Sample 3-2 is a sample in which the volume ratio of calcium carbonate to the phosphate-based insulating material A is 0.10, and the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 0.14. Sample 3-3 is a sample in which the volume ratio of calcium carbonate to the phosphate-based insulating material A is 0.50, and the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 0.69. Sample 3-4 is a sample in which the volume ratio of calcium carbonate to the phosphate-based insulating material A is 0.75, and the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 1.03.

[0090] (Environmental testing)

[0091] The following environmental tests were performed on each of the produced samples.

[0092] First, the weight of each sample before the environmental test was measured. After that, the environmental test was carried out by placing the samples in an environment with a temperature of 85°C and a humidity of 85% for one week. Then, the weight of each sample after the environmental test was measured. Table 3 shows the weight increase rate of Samples 3-1 to 3-4 after the environmental test. In addition, Figure 5 The graph shows the relationship between Ca / P and weight gain rate.

[0093] As shown in Table 3, Figure 5 As shown, the weight gain rate after environmental testing for sample 3-1, which did not contain calcium carbonate, was 0.31%. Furthermore, the weight gains after environmental testing for samples 3-2 and 3-4, which contained calcium carbonate, were 0.15%, 0.01%, and -0.01%, respectively. These results indicate that the greater the amount of calcium carbonate added, the lower the weight gain rate after environmental testing.

[0094] [Table 3]

[0095] [Table 3]

[0096]

[0097] Experiment 4

[0098] (Sample production)

[0099] use Figure 4 The method for manufacturing the dust core 1_2 according to the second aspect shown in the figure was used to produce dust cores of Samples 4-1 to 4-5. Specifically, magnetic powder was first prepared. The magnetic powder used was Fe-Si-Cr alloy powder with a particle size of 10 μm (median particle size D50). Next, the magnetic powder was mixed with a phosphate-based insulating material A, and the phosphate-based insulating material A was coated onto the magnetic powder using a mechanochemical method.

[0100] A moisture absorption inhibitor (calcium carbonate) and a resin material were then added to the magnetic powder coated with the phosphoric acid-based insulating material A, and granulation was performed. Silicone resin was used as the resin material. The amounts of phosphoric acid-based insulating material A, calcium carbonate, magnetic powder, and resin material used in Samples 4-1 and 4-5 were as shown in Table 4.

[0101] The volume ratios of the phosphate-based insulating material A and calcium carbonate shown in Table 4 are the volume ratios relative to the magnetic powder. The weights (g) of the magnetic powder, phosphate-based insulating material A, calcium carbonate, and resin material shown in Table 4 represent the amounts of each material contained in a 2.5 g powder magnetic core.

[0102] Next, the granulated magnetic powder is put into a mold and heated at 5000 kgf / cm 2 The molded body was then heated at 200° C. for 2 hours for thermal curing.

[0103] Using the method described above, powder cores of Samples 4-1 to 4-5 were produced. Sample 4-1 is a sample to which no calcium carbonate was added. Sample 4-2 is a sample in which the volume ratio of calcium carbonate to the phosphate-based insulating material A is 0.07, and the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 0.10. Sample 4-3 is a sample in which the volume ratio of calcium carbonate to the phosphate-based insulating material A is 0.20, and the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 0.29. Sample 4-4 is a sample in which the volume ratio of calcium carbonate to the phosphate-based insulating material A is 0.30, and the weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 0.44. Sample 4-5 has a volume ratio of calcium carbonate to phosphate-based insulating material A of 0.68, and a weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material of 0.97.

[0104] (Environmental testing)

[0105] The following environmental tests were performed on each of the produced samples.

[0106] First, the weight of each sample before the environmental test was measured. After that, the environmental test was carried out by placing the samples in an environment with a temperature of 85°C and a humidity of 85% for 1 week. Then, the weight of each sample after the environmental test was measured. Table 4 shows the weight increase rate of samples 4-1 to 4-5 after the environmental test. In addition, Figure 6 The graph shows the relationship between Ca / P and weight gain rate.

[0107] As shown in Table 4, Figure 6 As shown, the weight gain rate after environmental testing for sample 4-1, which did not contain calcium carbonate, was 0.31%. Furthermore, the weight gains after environmental testing for samples 4-2 to 4-5, which contained calcium carbonate, were 0.22%, 0.10%, 0.02%, and -0.03%, respectively. These results indicate that the greater the amount of calcium carbonate added, the lower the weight gain rate after environmental testing.

[0108] [Table 4]

[0109] [Table 4]

[0110]

[0111] The present invention has been described above in conjunction with the above-mentioned embodiments, but the present invention is not limited to the configuration of the above-mentioned embodiments, but also includes various deformations, modifications and combinations that can be achieved by those skilled in the art within the scope of the invention of the claims of the patent application.

[0112] This application claims the benefit of priority based on Japanese patent application No. 2023-20052, filed on February 13, 2023, the entire contents of which are incorporated herein by reference.

[0113] Description of Reference Numerals

[0114] 1, 1_1, 1_2: pressed powder core;

[0115] 11: magnetic powder;

[0116] 12, 12_1, 12_2: insulation layer;

[0117] 13: Phosphoric acid insulating material;

[0118] 14: Moisture absorption inhibitor;

[0119] 15: Resin material.

Claims

1. A powder core, which is made of magnetic powder bonded by an insulating layer. The insulating layer includes a phosphate-based insulating material, a resin material, and a moisture absorption inhibitor containing calcium.

2. The powder magnetic core according to claim 1, wherein A weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 0.10 or more.

3. The powder magnetic core according to claim 1, wherein A weight ratio (Ca / P) of calcium contained in the moisture absorption inhibitor to phosphorus contained in the phosphate-based insulating material is 0.44 or more.

4. The powder magnetic core according to any one of claims 1 to 3, wherein The calcium-containing moisture absorption inhibitor is calcium carbonate.

5. The powder magnetic core according to any one of claims 1 to 3, wherein The phosphate-based insulating material is phosphate-based glass.

6. The powder magnetic core according to any one of claims 1 to 3, wherein The resin material is a thermosetting resin.

7. The powder magnetic core according to any one of claims 1 to 3, wherein The volume ratio of the moisture absorption inhibitor to the phosphate-based insulating material is 7% or more.

8. The powder magnetic core according to any one of claims 1 to 3, wherein The surface of the magnetic powder is coated with the phosphoric acid-based insulating material, The phosphoric acid-based insulating material coating the magnetic powder has a thickness of 10 nm to 100 nm. 9 . An inductor comprising the powder magnetic core according to claim 1 and a coil.

10. A method for manufacturing a powder magnetic core, comprising: The process of coating the surface of the magnetic powder with a phosphoric acid-based insulating material; A step of coating the coated magnetic powder with a moisture absorption inhibitor containing calcium; a step of adding a resin material to the magnetic powder coated with a moisture absorption inhibitor and granulating the magnetic powder; and The granulated magnetic powder is subjected to a process of molding and thermally curing.

11. A method for manufacturing a powder magnetic core, comprising: The process of coating the surface of the magnetic powder with a phosphoric acid-based insulating material; A step of adding a calcium-containing moisture absorption inhibitor and a resin material to the coated magnetic powder and granulating the powder; and The granulated magnetic powder is subjected to a process of molding and thermally curing.

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