METHOD FOR PRODUCING METAL POWDER FOR CORE, ... AND METHOD FOR PRODUCING CORE

Abstract

To provide a method for producing metal powder for cores with excellent weather resistance.SOLUTION: A method for producing metal powder for cores includes a first step (step S1) for mixing a rust inhibitor diluted with a low polar solvent with metal powder, and coating the surface of metal powder with the rust inhibitor, and a second step (step S2) for mixing a binder diluted with a high polar solvent with the metal powder coated with the rust inhibitor to granulate the mixture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, inductors have been used in a variety of electronic circuits. In general, the characteristics of an inductor are significantly affected by the core (magnetic core) that makes up the inductor. One of the parameters that indicates inductor characteristics is DCR (direct current resistance). The lower the DCR, the better the inductor characteristics, but achieving a low DCR requires a core with high magnetic permeability (high μ material). Patent Document 1 discloses technology related to a powder compact with high magnetic permeability and excellent strength, and a method for manufacturing the powder compact. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-120678 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, pure iron powder is a material that exhibits high magnetic permeability. Using pure iron powder to form a core can achieve a low DCR for the inductor. However, metal powders such as pure iron powder are prone to rust and have weather resistance issues.

[0005] In view of the above problems, an object of the present invention is to provide a method for producing a metal powder for a core having excellent weather resistance, a metal powder for a core, and a core. [Means for solving the problem]

[0006] A method for producing a core metal powder according to one embodiment of the present invention comprises a first step of mixing a metal powder with a rust inhibitor diluted with a low-polarity solvent and coating the surface of the metal powder with the rust inhibitor, and a second step of mixing a binder diluted with a high-polarity solvent with the metal powder coated with the rust inhibitor and granulating the mixture.

[0007] A core metal powder according to one embodiment of the present invention includes a metal powder coated with a rust inhibitor and a binder, and the mass of the rust inhibitor relative to the metal powder is 0.3 mass % or more and 1.0 mass % or less.

[0008] A core according to one aspect of the present invention is a core formed using the above-described core metal powder. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for producing a metal powder for a core, a metal powder for a core, and a core having excellent weather resistance. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flowchart showing a method for manufacturing a core metal powder according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating a core metal powder according to an embodiment. [Figure 3] FIG. 2 is a cross-sectional view illustrating a core metal powder according to an embodiment. [Figure 4] 1 is a table showing the results of a molding-time bleeding test and a water immersion test when the amount of rust inhibitor added is changed. [Figure 5] This is a table showing various characteristics of inductors (products) and ring cores with and without rust inhibitors. [Figure 6] 1 is a graph showing magnetic properties and the like with and without a rust inhibitor. [Figure 7] 1 is a table showing the weather resistance of core metal powders when the manufacturing method of the core metal powder, the main component of the rust inhibitor, and the diluent of the rust inhibitor are changed. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described. Fig. 1 is a flowchart showing a method for producing a core metal powder according to an embodiment. As shown in Fig. 1, the method for producing a core metal powder according to this embodiment includes the following two steps.

[0012] (1) A first step (step S1) involves mixing a rust inhibitor diluted with a low-polarity solvent with metal powder, and coating the surface of the metal powder with the rust inhibitor. (2) A second process (step S2) involves mixing and granulating a binder diluted with a highly polar solvent and metal powder coated with a rust inhibitor. Here, a low-polarity solvent is a solvent whose Hansen solubility parameter (HSP) δH (a solubility parameter related to intermolecular hydrogen bonding) is less than 20. A high-polarity solvent is a solvent whose δH is 20 or more.

[0013] In this embodiment, the metal powder is typically a soft magnetic metal powder. For example, pure iron powder, Fe-Si-Al alloys, Fe-Si alloys, Fe-Al alloys, etc. can be used as the metal powder. These materials are merely examples, and other materials may also be used as the metal powder in this embodiment. The surface of the metal powder may be covered with an insulating layer. The particle size (median diameter D50) of the metal powder is, for example, 2 μm or more and 150 μm or less, preferably 10 μm or more and 80 μm or less.

[0014] In this embodiment, the rust inhibitor is used to prevent the metal powder from rusting. For example, an oil-soluble rust inhibitor that dissolves in a low-polarity solvent can be used as the rust inhibitor. In particular, in this embodiment, it is preferable to use a rust inhibitor that dissolves in a low-polarity solvent but is difficult to dissolve in a high-polarity solvent. As an example, the rust inhibitor can be made of oxidized paraffin, fatty acid, naphthenic acid, abietic acid, dimer acid, alkenyl succinic acid, petroleum sulfonic acid, and salts thereof. Note that these materials are only examples, and materials other than these may also be used as the rust inhibitor in this embodiment.

[0015] In this embodiment, the low-polarity solvent is used to dilute the rust inhibitor. In other words, the low-polarity solvent is used as an organic solvent that dilutes the rust inhibitor. For example, alcohols having 10 to 25 carbon atoms may be used as the low-polarity solvent. As an example, toluene, mineral spirits, or a mixture of toluene and isopropyl alcohol (IPA) (for example, a mixture ratio of 1:1) may be used as the low-polarity solvent.

[0016] In this embodiment, the highly polar solvent is used to dilute the binder. For example, alcohols having 1 to 9 carbon atoms may be used as the highly polar solvent. For example, methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, and 2-methyl-2-propanol may be used as the highly polar solvent.

[0017] In this embodiment, the binder is used to bind the metal powder together and granulate it. For example, organic binders such as polyvinyl alcohol (PVA), polyvinylpyrrolidone, and epoxy resin can be used as the binder.

[0018] In this embodiment, as shown in step S1 of FIG. 1, the rust inhibitor diluted with a low-polarity solvent is mixed with a metal powder, thereby coating the surface of the metal powder with the rust inhibitor. For example, the rust inhibitor and the low-polarity solvent are placed in a granulator (e.g., a stirring / mixing granulator) and mixed at a predetermined rotation speed. Then, the metal powder is placed in the granulator, and the rust inhibitor diluted with the low-polarity solvent and the metal powder are mixed. Then, by mixing at a predetermined rotation speed until a predetermined target moisture content (e.g., 0.1%) is reached, the surface of the metal powder can be coated with the rust inhibitor.

[0019] Fig. 2 is a cross-sectional view for explaining the metal powder according to this embodiment, showing the metal powder coated with a rust inhibitor produced by the process shown in step S1 of Fig. 1. As shown in Fig. 2, the surface of the metal powder 11 is coated with a rust inhibitor 12. If the surface of the metal powder 11 is covered with an insulating layer (not shown), the surface of the insulating layer is coated with the rust inhibitor 12.

[0020] In this embodiment, as shown in step S2 of Fig. 1, a binder diluted with a highly polar solvent and metal powder coated with a rust inhibitor in step S1 are mixed and granulated. For example, the binder diluted with a highly polar solvent is added to a granulator containing metal powder coated with a rust inhibitor, and the mixture is mixed and granulated at a predetermined rotation speed. This allows the formation of metal powder aggregates in which a predetermined number of metal powder particles are aggregated together.

[0021] Fig. 3 is a cross-sectional view illustrating the core metal powder according to this embodiment, showing the core metal powder (granulated powder) produced by the process shown in step S2 of Fig. 1. As shown in Fig. 3, the core metal powder 10 is composed of an aggregate of a plurality of metal powder particles 11 coated with a rust inhibitor 12. That is, by mixing and granulating the metal powder 11 coated with the rust inhibitor 12 with a binder 15 diluted with a highly polar solvent, a metal powder aggregate (core metal powder 10) can be formed in which a predetermined number of metal powder particles 11 are bound together by the binder 15.

[0022] In this embodiment, the mass of the rust inhibitor relative to the metal powder is 0.3% by mass to 1.0% by mass, preferably 0.6% by mass to 1.0% by mass, and more preferably 0.6% by mass to 0.75% by mass. Here, "mass % of rust inhibitor relative to metal powder" refers to the ratio (mass %) of the rust inhibitor to the metal powder mixed in step S1, and the amount of rust inhibitor is the amount of rust inhibitor before dilution with the low-polarity solvent, i.e., the net amount of rust inhibitor excluding the low-polarity solvent.

[0023] In this embodiment, a core (magnetic core) for an inductor is formed using a core metal powder. When forming the core, the core metal powder (metal powder after granulation) is placed in a mold and compressed under a predetermined load. The compact is then fired at a predetermined temperature to form the core. Alternatively, the core may be formed by warm compacting the core metal powder.

[0024] As described above, the method for producing a core metal powder according to this embodiment includes the following steps: (1) A first step (step S1) of mixing a rust inhibitor diluted with a low-polarity solvent with a metal powder and coating the surface of the metal powder with the rust inhibitor; (2) A second step (step S2) of mixing and granulating the binder diluted with a highly polar solvent and the metal powder coated with the rust inhibitor.

[0025] As described above, in this embodiment, in step S1, the rust inhibitor is diluted with a low-polarity solvent and mixed with the metal powder, and the rust inhibitor (including the low-polarity solvent) is coated on the surface of the metal powder. Furthermore, in step S2, the metal powder coated with the rust inhibitor is mixed with a binder and granulated. In this embodiment, a binder diluted with a high-polarity solvent is used, which prevents the rust inhibitor on the surface of the metal powder from dissolving in the binder diluted with the high-polarity solvent. In other words, in this embodiment, the rust inhibitor dissolves in a low-polarity solvent and is less soluble in a high-polarity solvent, which prevents the rust inhibitor on the surface of the metal powder from dissolving in the binder diluted with the high-polarity solvent. Therefore, the rust inhibitor can be maintained coated on the surface of the metal powder.

[0026] Furthermore, when producing a core, metal powder is placed in a mold and compression-molded under a predetermined load, but the pressure applied to the metal powder at this time could damage the rust inhibitor coated on the surface of the metal powder. In contrast, in this embodiment, the rust inhibitor can be kept coated on the surface of the metal powder when producing the metal powder for the core, so that damage to the rust inhibitor coated on the surface of the metal powder can be suppressed when the metal powder is compression-molded.

[0027] Therefore, the invention according to this embodiment can provide a method for producing a core metal powder, a core metal powder, and a core that are excellent in weather resistance. [Example]

[0028] Examples of the present invention will be described below.

[0029] (Examples 1 to 7, Comparative Example 1) As an example, a sample was prepared using the following method. First, 150 g of a rust inhibitor (oxidized paraffin) was diluted with 1,250 g of toluene to prepare a rust inhibitor solution. Also, 25,000 g of pure iron powder was prepared. The prepared rust inhibitor solution and metal powder were then placed in a stirring / mixing granulator and mixed at 130 rpm for 60 minutes, coating the surface of the metal powder with the rust inhibitor.

[0030] Next, 840 g of binder (PVA) was diluted with 1500 g of methanol to prepare a binder solution. The binder solution was then added to the stirring / mixing granulator containing the stirred metal powder, and mixed and granulated at 130 rpm for 40 minutes.

[0031] In this example, samples (Examples 1 to 7) were prepared in which the amount of rust inhibitor added to the metal powder was 0.3%, 0.5%, 0.6%, 0.7%, 0.75%, 0.8%, and 1.0%. The amount of rust inhibitor added was adjusted by changing the amount of rust inhibitor solution added to the stirring / mixing granulator. In addition, a sample without added rust inhibitor was prepared as Comparative Example 1.

[0032] The metal powder for the core (hereinafter referred to as granulated powder) prepared by the above method was placed in a mold and granulated at a rate of 2.5 t / cm 2 The presence or absence of seepage of the rust inhibitor when compression molded at a pressure of 1000 kJ / cm was confirmed.

[0033] The granulated powder prepared by the above method was placed in a mold and warm-molded to form a core. The warm-molding conditions were a mold temperature of 80°C and a molding pressure of 2.5 t / cm. 2 The formed core was then submerged in water, and the time until rust was observed was measured (submersion test).

[0034] The table in Figure 4 shows the results of the exudation during molding and the submersion test when the amount of rust inhibitor added was changed. As shown in the table in Figure 4, no exudation of the rust inhibitor was observed in Examples 1 to 5, where the amount of rust inhibitor added was 0.3%, 0.5%, 0.6%, 0.7%, and 0.75%, and in Comparative Example 1. On the other hand, exudation of the rust inhibitor was observed in Examples 6 and 7, where the amount of rust inhibitor added was 0.8% and 1.0%.

[0035] As shown in the table in Figure 4, in Comparative Example 1, where no rust inhibitor was added, the time to confirm rust was 9 hours after submersion, while in Example 1, where the amount of rust inhibitor added was 0.3%, the time to confirm rust was 14 hours after submersion. This confirms that adding a rust inhibitor has a rust-inhibiting effect. Furthermore, as the amount of rust inhibitor added increased, the time to confirm rust became longer. This confirms that the greater the amount of rust inhibitor added, the greater the rust-inhibiting effect.

[0036] From the results of Figure 4, in the present invention, a rust-inhibiting effect was obtained by adding 0.3% or more and 1.0% or less of the rust inhibitor to the metal powder. Furthermore, by adding 0.3% or more and 0.75% or less of the rust inhibitor to the metal powder, a rust-inhibiting effect was obtained while suppressing the seepage of the rust inhibitor during compression molding. In particular, by adding 0.6% or more and 0.75% or less of the rust inhibitor to the metal powder, a high rust-inhibiting effect was obtained while suppressing the seepage of the rust inhibitor during compression molding.

[0037] Next, metal powders containing anti-rust agents (Examples 3 and 4) and metal powders containing no anti-rust agents (Comparative Example 1) were used to form inductors (products) and ring cores, and their various characteristics were compared. The inductors (products) were formed by warm compaction under the above-mentioned conditions. The ring cores were formed at 8 t / cm 2 It was formed by cold forming at a pressure of 1000 kJ / cm.

[0038] The table in Figure 5 shows various characteristics of the inductors (products) and ring cores formed from the metal powders of Comparative Example 1, Example 3, and Example 4. The table in Figure 5 shows the inductance (L) of the inductor, the DC superimposed rated current (Isat), and the resistance value (IR) when 100 V is applied between the coil core. The table in Figure 5 also shows the saturation magnetic flux density (Pcv), density, and strength of the ring core.

[0039] As shown in the table in Figure 5, the inductors according to Examples 3 and 4, to which a rust inhibitor was added, did not show any deterioration in their characteristics compared to the inductor according to Comparative Example 1, to which no rust inhibitor was added. Focusing on the inductance (L) of the inductor, the inductance (L) increased by 3% in Example 3 compared to Comparative Example 1, and by 4% in Example 4 compared to Comparative Example 1. This is thought to be because the density of the inductor increased due to the addition of the rust inhibitor (oxidized paraffin).

[0040] 6, the magnetic properties of Comparative Example 1 (no rust inhibitor), Example 3 (0.6% added), and Example 4 (0.7% added) were almost the same. Therefore, it was found that adding a rust inhibitor had almost no effect on the magnetic properties of the inductor.

[0041] As shown in the table in Figure 5, the ring cores of Examples 3 and 4, to which a rust inhibitor was added, did not show any deterioration in their properties compared to the ring core of Comparative Example 1, to which no rust inhibitor was added. Focusing on the strength of the ring core, Example 3 showed a 20% increase in strength compared to Comparative Example 1, and Example 4 showed a 29% increase in strength compared to Comparative Example 1. This is thought to be because the addition of the rust inhibitor (oxidized paraffin) allowed the rust inhibitor to function as a lubricant, thereby increasing the strength of the ring core.

[0042] Next, to investigate the effects of differences in the manufacturing process and main components of the rust inhibitor, the following four samples were prepared (see Figure 7).

[0043] (Comparative Example 2) The rust inhibitor, whose main component is an organic acid amine salt, methanol as a diluent, binder, and metal powder were placed in a stirring mixer and granulator and mixed at 130 rpm for 60 minutes to produce granulated powder. This method of adding and mixing all materials at the same time is referred to as the simultaneous mixing method.

[0044] (Comparative Example 3) A rust inhibitor whose main component is an organic acid amine salt, methanol as a diluent, and metal powder were placed in a stirring / mixing granulator and mixed at 130 rpm for 60 minutes, coating the metal powder surface with the rust inhibitor (corresponding to step S1). Then, a binder diluted with methanol was prepared, and the binder solution was placed in the stirring / mixing granulator containing the mixed metal powder. The binder solution was mixed at 130 rpm for 40 minutes to granulate (step S2). This two-step mixing method (see Figure 1) is referred to as the separate mixing method.

[0045] Comparative Example 4 A rust inhibitor containing oxidized paraffin as its main component, toluene as a diluent, a binder, and metal powder were placed in a stirring / mixing granulator and mixed at 130 rpm for 60 minutes to produce granulated powder.

[0046] Example 8 A rust inhibitor containing oxidized paraffin as its main component, toluene as a diluent, and metal powder were placed in a stirring / mixing granulator and mixed at 130 rpm for 60 minutes to coat the surface of the metal powder with the rust inhibitor (corresponding to step S1). After that, a binder diluted with methanol was prepared, and the binder solution was placed in the stirring / mixing granulator containing the mixed metal powder, and mixed at 130 rpm for 40 minutes to granulate (step S2).

[0047] The granulated powders according to Comparative Examples 2 to 4 and Example 8 prepared by the above-mentioned methods were placed in a mold and warm-molded to form cores. The formed cores were then submerged in water, and the time until rust was observed was measured (water immersion test).

[0048] As shown in Figure 7, the rust prevention effect was shorter than 24 hours in Comparative Examples 2 to 4. On the other hand, the rust prevention effect in Example 8 was 48 to 50 hours, which was better than that of Comparative Examples 2 to 4. Therefore, by using the separation and mixing method, it was possible to produce a core metal powder with excellent weather resistance.

[0049] The present invention has been described above in accordance with the above-mentioned embodiment, but the present invention is not limited to the configuration of the above-mentioned embodiment, and naturally includes various modifications, alterations, and combinations that a person skilled in the art can make within the scope of the invention as defined in the claims of this application. [Explanation of symbols]

[0050] 10 Metal powder for core 11 Metal powder 12 Rust inhibitor 15 Binder

Claims

1. a first step of mixing a metal powder with a rust inhibitor diluted with a low-polarity solvent and coating the surface of the metal powder with the rust inhibitor; a second step of mixing and granulating a binder diluted with a highly polar solvent and the metal powder coated with the rust inhibitor, the low-polarity solvent is at least one selected from the group consisting of alcohols having 10 to 25 carbon atoms, toluene, mineral spirits, and a mixture of toluene and isopropyl alcohol (IPA); The highly polar solvent is at least one selected from the group consisting of alcohols having 1 to 9 carbon atoms. Manufacturing method of metal powder for core.

2. The method for producing a core metal powder according to claim 1 , wherein a mass of the rust inhibitor relative to the metal powder is 0.3 mass % or more and 1.0 mass % or less.

3. The method for producing a core metal powder according to claim 1 , wherein a mass of the rust inhibitor relative to the metal powder is 0.6 mass % or more and 1.0 mass % or less.

4. The method for producing a core metal powder according to any one of claims 1 to 3, wherein the rust inhibitor is an oil-soluble rust inhibitor that dissolves in a low-polarity solvent.

5. 5. The method for producing a core metal powder according to claim 4, wherein the rust inhibitor is at least one selected from the group consisting of oxidized paraffin, fatty acid, naphthenic acid, abietic acid, dimer acid, alkenyl succinic acid, petroleum sulfonic acid, and salts thereof.

6. 6. The method for producing a core metal powder according to claim 1, wherein the highly polar solvent is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, and 2-methyl-2-propanol.

7. The method for producing a core metal powder according to any one of claims 1 to 6, wherein the surface of the metal powder is covered with an insulating layer, and the surface of the insulating layer is coated with the rust inhibitor.

8. 8. The method for producing a core metal powder according to claim 1, wherein the metal powder is at least one selected from the group consisting of pure iron powder, an Fe—Si—Al alloy, an Fe—Si alloy, and an Fe—Al alloy.

9. a metal powder coated with a rust inhibitor and a binder; The mass of the rust inhibitor relative to the metal powder is 0.3 mass% or more and 1.0 mass% or less, the rust inhibitor is soluble in a low-polarity solvent, and the binder is soluble in a high-polarity solvent; the low-polarity solvent is at least one selected from the group consisting of alcohols having 10 to 25 carbon atoms, toluene, mineral spirits, and a mixture of toluene and isopropyl alcohol (IPA); The highly polar solvent is at least one selected from the group consisting of alcohols having 1 to 9 carbon atoms. Metal powder for cores.

10. The core metal powder according to claim 9 is placed in a mold, and a predetermined load is applied to the core metal powder to perform compression molding to form a molded body; The compact after compression molding is fired at a predetermined temperature. Core manufacturing method.

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