Method for manufacturing dust core

Abstract

To provide a method for manufacturing a dust core capable of reducing iron loss.SOLUTION: A method for manufacturing a dust core includes: an insulating coating layer-forming step of covering a surface of a soft magnetic powder with an insulating coating layer containing a silicone resin; a molded body-producing step of producing a compacted molded body by pressing the soft magnetic powder covered with the insulating coating layer; and a heat treatment step of annealing the compacted molded body. The heat treatment step includes: a heating step of raising the temperature to a predetermined temperature; and a constant-temperature step of maintaining the predetermined temperature. In the heating step, the hydrogen concentration is controlled to 5.0% or more and 15.0% or less in a temperature range of 400°C or more and 640°C or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing a powder magnetic core made of soft magnetic powder coated with an insulating coating layer containing a silicone resin. [Background technology]

[0002] Coil components such as reactors are used in a variety of applications, including office equipment, solar power generation systems, automobiles, and uninterruptible power supplies. For example, a reactor is an electromagnetic component that converts electrical energy into magnetic energy and stores and releases it. A reactor primarily comprises a core and a coil. The coil is wound around the core. When power is supplied to the coil, it generates magnetic flux. The core is ring-shaped. The core serves as a magnetic path through which the magnetic flux generated by the coil flows.

[0003] Powder magnetic cores are sometimes used as reactor cores. Powder magnetic cores are manufactured by first compressing soft magnetic powder coated with an insulating coating layer made of an insulating material such as silicone resin to produce a powder compact. Pressure molding introduces strain into the soft magnetic powder. Therefore, the powder compact is subjected to a heat treatment called annealing to remove the strain.

[0004] Due to demands for improved energy exchange efficiency and low heat generation, powder magnetic cores are required to have magnetic properties that minimize energy loss when magnetic flux density changes. Specifically, the magnetic property related to energy loss is iron loss (Pcv). Iron loss (Pcv) is expressed as the sum of hysteresis loss (Phv) and eddy current loss (Pev). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-030925 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been an increasing demand for smaller and higher performance coil components. This has led to demands for improved magnetic properties in the powder magnetic cores that make up these coil components, and there is a growing demand for powder magnetic cores with low iron loss.

[0007] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a powder magnetic core that can reduce iron loss. [Means for solving the problem]

[0008] As a result of extensive research, the inventors discovered that during heat treatment to remove strain within soft magnetic powder, the amount of methane gas generated increases sharply in the temperature range of 400°C to 640°C. It is believed that this methane gas is generated when the silicone resin reacts with hydrogen during heat treatment. Further research led to the discovery that iron loss can be reduced by controlling the hydrogen concentration in this temperature range of 400°C to 640°C.

[0009] The present invention has been made based on the above findings, and the method for producing a powder magnetic core of the present invention includes an insulating coating layer forming step of coating the surface of a soft magnetic powder with an insulating coating layer containing a silicone resin, a compact production step of pressing the soft magnetic powder coated with the insulating coating layer to produce a powder compact, and a heat treatment step of annealing the powder compact, wherein the heat treatment step includes a temperature rise step of raising the temperature to a predetermined temperature and a constant temperature step of maintaining the temperature at the predetermined temperature, and the hydrogen concentration in the temperature rise step is controlled to be 5.0% or more and 15.0% or less at least in the temperature range of 400°C or more and 640°C or less. [Effects of the Invention]

[0010] According to the present invention, a method for producing a powder magnetic core capable of reducing iron loss can be obtained. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a graph showing the relationship between the temperature inside the furnace and the amount of methane gas generated. [Figure 2] 1 is a graph showing the relationship between hydrogen concentration and iron loss Pcv. [Figure 3] 1 is a graph showing the relationship between hydrogen concentration and eddy current loss Pev. [Figure 4] 1 is a graph showing the relationship between hydrogen concentration and hysteresis loss Phv. [Figure 5] 1 is a graph comparing the carbon amount and specific resistance values of Example 1 and Comparative Example 1. [Figure 6] 1 is a graph comparing the specific resistance values of Example 3 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Embodiment) The configuration of the powder magnetic core of this embodiment will be described below, but the present invention is not limited to the embodiment described below.

[0013] Coil components such as reactors have a core containing a magnetic material. Powder magnetic cores are used as the core. Powder magnetic cores are produced by filling a powder for powder magnetic cores, which is made by coating soft magnetic powder with an insulating material, into a mold, pressuring the powder to produce a powder compact, and then subjecting the powder compact to a heat treatment called annealing.

[0014] The soft magnetic powder is mainly composed of iron. Examples of soft magnetic powders that can be used include pure iron powder, iron-based permalloy (Fe-Ni alloy), Si-containing iron alloy (Fe-Si alloy), Sendust alloy (Fe-Si-Al alloy), and a mixture of two or more of these powders. Amorphous alloys and nanocrystalline alloy powders may also be used as soft magnetic powders. However, it is preferable that the soft magnetic powder contains pure iron, i.e., pure iron or a mixture of pure iron and other alloy powders.

[0015] The Fe-Si-Al alloy powder contains, for example, about 7 wt% to 11 wt% of Si and about 4 wt% to 8 wt% of Al relative to Fe. The Fe-Si-Al alloy powder may also contain, for example, about 1 wt% to 3 wt% of Ni relative to Fe. Furthermore, the Fe-Si-Al alloy powder may also contain Co, Cr, or Mn.

[0016] The Si-containing iron alloy may contain Co, Al, Cr, or Mn. When using permalloy (Fe-Ni alloy), the ratio of Fe to Ni is preferably 50:50 or 25:75, but other ratios are also acceptable. For example, Fe-80Ni, Fe-36Ni, Fe-78Ni, or Fe-47Ni may be used. In addition to Fe and Ni, Si, Cr, Mo, Cu, Nb, Ta, etc. may also be contained. Examples of Fe-Si alloy powder include Fe-3.5% Si alloy powder and Fe-6.5% Si alloy powder, but the ratio of Si to Fe may be other than 3.5% or 6.5%. Pure iron powder contains 99% or more Fe.

[0017] The soft magnetic powder may be produced by a pulverization method or an atomization method, which may be any of water atomization, gas atomization, and water gas atomization.

[0018] The circularity of the soft magnetic powder is preferably 0.85 or more in terms of the powder's average particle size (median diameter D50). When the circularity of the soft magnetic powder is 0.85 or more, the gaps between the soft magnetic powder particles are reduced, allowing for improvements in density and magnetic permeability. It is particularly preferable for the circularity of the soft magnetic powder to be 0.90 or more, which significantly improves density and magnetic permeability. In addition, the average particle size (median diameter D50) of the soft magnetic powder is preferably 1 to 100 μm.

[0019] An insulating coating layer is formed on the surface of the soft magnetic powder. The insulating coating layer is made of an insulating material. An example of the insulating material is silicone resin. The insulating coating layer may be made of silicone resin alone, or may contain other insulating materials in addition to silicone resin.

[0020] Examples of silicone resins include silicone resins and silicone oligomers. Silicone resins are resins that have a siloxane bond (Si-O-Si) as their main skeleton. By using silicone resins, it is possible to form insulating coating layers with excellent flexibility. Examples of silicone resins that can be used include methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified, alkyd resin-modified, polyester resin-modified, and rubber-based.

[0021] Examples of silicone oligomers that can be used include methyl-based and methylphenyl-based ones that have an alkoxysilyl group but no reactive functional group, epoxy-based, epoxymethyl-based, mercapto-based, mercaptomethyl-based, acrylic methyl-based, methacrylic methyl-based, and vinylphenyl-based ones that have an alkoxysilyl group and a reactive functional group, and alicyclic epoxy-based ones that have a reactive functional group instead of an alkoxysilyl group.

[0022] The amount of silicone resin added is preferably 0.3 wt% or more and 2.0 wt% or less of the soft magnetic powder. If the amount added is less than 0.3 wt%, the insulating coating layer will not function, and eddy current loss will increase, resulting in reduced magnetic properties. If the amount added is more than 2.0 wt%, the density of the powder magnetic core will decrease.

[0023] A silane coupling agent may also be added as an insulating material constituting the insulating coating layer. The amount of silane coupling agent added is preferably 0.05 wt% or more and 3.0 wt% or less based on the soft magnetic powder. By adding the silane coupling agent in this range, the fluidity of the soft magnetic powder can be improved, and the density, magnetic properties, and strength properties of the compacted powder core can be improved.

[0024] As the silane coupling agent, aminosilane-based, epoxysilane-based, and isocyanurate-based silane coupling agents can be used, and particularly, tetraethoxysilane, diphenyldimethylsilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate are preferred. As the silane coupling agent, one type may be used, or two or more types may be mixed and used.

[0025] The soft magnetic powder having the insulating coating layer formed thereon is subjected to pressure molding to produce a powder compact, which is then subjected to a heat treatment known as annealing to produce a powder magnetic core.

[0026] Next, a method for producing a powder magnetic core will be described in detail. The method for producing a powder magnetic core includes (1) an insulating coating layer forming step, (2) a lubricant adding step, (3) a compact producing step, and (4) a heat treatment step.

[0027] (1) Insulation coating layer formation process The insulating coating layer formation process is a process in which an insulating coating layer made of an insulating material is formed around the soft magnetic powder. An insulating material such as silicone resin is added to the soft magnetic powder and mixed, and then the mixture is heated and dried to form an insulating coating layer on the surface of the soft magnetic powder. The heating and drying conditions are, but are not limited to, a temperature of 25°C to 350°C for about two hours.

[0028] Furthermore, when a silane coupling agent is added as an insulating material, the insulating coating layer may be a mixed layer in which the silane coupling agent and silicone resin are mixed, or a layer of the silane coupling agent and a layer of the silicone resin may be laminated. For example, when the insulating coating layer is laminated in the order of a layer of the silane coupling agent and a layer of the silicone resin, the silane coupling agent is first added to and mixed with the soft magnetic powder, and the mixture is heated and dried. Then, the silicone resin is added to and mixed with the soft magnetic powder on which the layer of the silane coupling agent has been formed, and the mixture is heated and dried, and a layer of the silicone resin is formed on the surface of the layer of the silane coupling agent.

[0029] Water may be added in the insulating coating layer formation process. Examples of water include water and ethanol. Water can be added after the insulating material is mixed with the soft magnetic powder, or at the initial stage of drying the insulating material. Water can be added by dispersing it in a mist or spray form, or by dripping it as fine droplets. Adding water improves the hydrolysis and condensation reactions required for silane coupling agents, etc., and improves the strength of the core.

[0030] (2) Lubricant addition process After the insulating coating layer formation process, the process moves to the lubricant addition process. In this process, a lubricant is added to the soft magnetic powder on which the insulating coating layer has been formed. By adding a lubricant, the soft magnetic powder particles can slide more smoothly against each other, thereby increasing the density of the compact. Furthermore, it is possible to reduce the upper punch ejection pressure during compaction and prevent the occurrence of vertical streaks on the wall surface of the powder core due to contact between the die and the soft magnetic powder.

[0031] Examples of lubricants include, but are not limited to, stearic acid, calcium stearate, lithium stearate, aluminum stearate, zinc stearate, ethylene bisstearamide, ethylene bisstearamide, and ethylene bisstearate amide.

[0032] The amount of lubricant added is preferably about 0.2 wt% to 0.8 wt% of the soft magnetic powder. By setting the amount in this range, it is possible to further improve the sliding between the soft magnetic powder particles. The lubricant may be added twice, before and after the insulating coating layer forming step.

[0033] (3) Molded body production process After the lubricant addition step, the compact production step is carried out. In the compact production step, the soft magnetic powder on which the insulating coating layer has been formed is pressure-molded to produce a green compact. First, the soft magnetic powder on which the insulating coating layer has been formed is filled into a mold, and then the powder is pressed under a pressure of 5 ton / cm. 2 ~20ton / cm 2 In this way, a powder compact is produced.

[0034] The molding pressure is 10 ton / cm 2 It is preferable that the molding pressure is 10 ton / cm or less. If the molding pressure is too high, the insulating coating layer may be destroyed. If the insulating coating layer is destroyed, the reduction reaction of the silicone resin may be accelerated in the heat treatment step described below, and the insulating performance of the insulating coating layer may be deteriorated. Therefore, it is preferable that the molding pressure is 10 ton / cm or less. 2 By doing the following, an insulating coating layer having good insulating properties can be formed.

[0035] (4) Heat treatment process After the compact preparation step, a heat treatment step is performed. The heat treatment step is a step of annealing the powder compact prepared in the compact preparation step to remove distortion in the soft magnetic powder. The heat treatment step includes a (4-1) temperature increase step and a (4-2) constant temperature step.

[0036] (4-1) Heating process The temperature-raising step is a step of raising the temperature to a predetermined temperature, which is carried out in the constant temperature step. In the temperature-raising step, first, the powder compact is placed in an annealing facility such as a furnace. Then, the temperature in the annealing facility is raised to a predetermined temperature.

[0037] Here, in the temperature rising process, the hydrogen concentration is controlled to be 5.0% or more and 15.0% or less in the temperature range of 400° C. or more and 640° C. or less. For example, in a mixed gas of nitrogen and hydrogen, the hydrogen concentration in the temperature range of 400° C. or more and 640° C. or less is controlled to be 5.0% or more and 15.0% or less.

[0038] If the predetermined temperature in the constant temperature step described below is lower than 640°C, it is sufficient to control the hydrogen concentration from 400°C or higher up to the predetermined temperature. For example, if the predetermined temperature in the constant temperature step is 600°C, it is sufficient to control the hydrogen concentration in the temperature range of 400°C or higher and 600°C or lower.

[0039] In the temperature-raising step, it is not necessary to control the hydrogen concentration to be 5.0% or more and 15.0% or less except in the temperature range of 400°C or more and 640°C or less. That is, in the temperature range up to 400°C and in the temperature range above 640°C, the step may be carried out in an atmosphere with a hydrogen concentration of less than 5.0% or more than 15.0%, such as a nitrogen gas atmosphere or a non-oxidizing atmosphere such as a low-oxygen atmosphere of about 0.01%. However, the temperature-raising step may be carried out while controlling the hydrogen concentration to be 5.0% or more and 15.0% or less in all temperature ranges.

[0040] In particular, it is preferable to control the hydrogen concentration to 5.0% or more and 15.0% or less in the temperature range from the beginning of the heating process to 400°C. That is, it is preferable to control the hydrogen concentration in the temperature range from the beginning of the heating process to 640°C. It is believed that the lubricant reacts with hydrogen and decomposes before 400°C, when the insulating coating layer begins to decompose, and therefore the insulating coating layer can be decomposed without leaving any lubricant residue. Therefore, controlling the hydrogen concentration to 5.0% or more and 15.0% or less in the temperature range from 400°C to 640°C is more effective in forming a good insulating coating layer. Furthermore, productivity is improved because the temperature can be continued to be increased without changing the gas flowing into the furnace once 400°C is reached.

[0041] As a result of extensive research, the inventors of the present invention discovered that a large amount of methane gas is generated during the heating process once the temperature exceeds 400°C. While this is speculation and not limited to this mechanism, it is believed that this generation is due to a reaction between hydrogen and the silicone resin that constitutes the insulating coating layer. As the amount of methane gas generated increases, the amount of silicone resin that constitutes the insulating coating layer decreases, weakening the insulating performance of the insulating coating layer and leading to increased eddy current loss. Furthermore, it is speculated that the amount of methane gas generated peaks between approximately 550°C and 600°C, and after passing the peak, the amount of methane gas generated rapidly decreases. Above 640°C, the amount of methane gas generated is significantly reduced. Therefore, by controlling the hydrogen concentration in the temperature range of 400°C to 640°C, the amount of methane gas generated can be suppressed and a good insulating coating layer can be formed on the surface of the soft magnetic powder.

[0042] As described above, the amount of methane gas generated peaks in the range from about 550°C to 600°C, and then rapidly decreases. Therefore, in order to suppress the amount of methane gas generated and form a good insulating coating layer on the surface of the soft magnetic powder, it is preferable to control the hydrogen concentration in the temperature range from 400°C to 600°C, which exceeds the temperature at which the amount of methane gas generated peaks. Furthermore, by controlling the hydrogen concentration in this temperature-raising process so that it is 5.0% to 15.0% in the temperature range from 400°C to 640°C, preferably from 400°C to 600°C, hysteresis loss can also be reduced. Controlling the hydrogen concentration in this temperature-raising process in this way can reduce iron loss.

[0043] In particular, it is preferable to control the hydrogen concentration to 5.0% or more and 10.0% or less in the temperature range of 400° C. or more and 640° C. or less, preferably 400° C. or more and 600° C. or less. By controlling the temperature rise process in this way, a higher loss reduction effect can be obtained.

[0044] Furthermore, during the temperature rise process, it is particularly preferable to control the hydrogen concentration to 5.0% to 15.0%, or 5.0% to 10.0%, in the temperature range of 425°C or higher and 600°C, which exceeds the temperature at which the amount of methane gas generated reaches its peak. The amount of methane gas generated increases sharply once the temperature exceeds 425°C during the temperature rise process. Therefore, by controlling the hydrogen concentration between 425°C and 600°C, eddy current loss can be more effectively reduced.

[0045] (4-2) Constant temperature process In the temperature-raising step, once the temperature has been raised to a predetermined temperature, the process moves to a constant-temperature step, in which the temperature is kept constant and the powder compact is heat-treated.

[0046] The constant temperature process is carried out in a non-oxidizing atmosphere such as a nitrogen gas atmosphere, a hydrogen gas atmosphere, a mixed gas atmosphere of nitrogen and hydrogen, or a low-oxygen atmosphere of about 0.01%. In the constant temperature process, the powder compact is heat-treated at a constant temperature of 600°C or higher but lower than the temperature at which the insulating coating layer formed around the soft magnetic powder is destroyed (for example, 900°C). The heat treatment time is, but is not limited to, for example, one hour or less. A powder magnetic core is produced through this constant temperature process.

[0047] (effect) As described above, the method for producing a powder magnetic core according to this embodiment includes an insulating coating layer forming step of coating the surface of a soft magnetic powder with an insulating coating layer containing a silicone resin, a compact fabrication step of compressing the soft magnetic powder coated with the insulating coating layer to produce a powder compact, and a heat treatment step of annealing the powder compact. The heat treatment step includes a temperature increase step of increasing the temperature to a predetermined temperature and a constant temperature step of maintaining the temperature at that temperature. The temperature increase step is carried out in a temperature range of at least 400°C to 640°C, with the hydrogen concentration controlled to be between 5.0% and 15.0%.

[0048] This suppresses the reaction between silicone resin and hydrogen in the temperature range of 400°C to 640°C, where the reaction between silicone resin and hydrogen is activated. This suppresses the amount of methane gas generated, allowing the insulating coating layer to be formed without deteriorating its insulating function, thereby reducing eddy current loss. Hysteresis loss is also reduced, leading to reduced iron loss. Furthermore, suppressing the amount of methane gas generated allows for the production of dust cores in an environmentally friendly manner.

[0049] In particular, in the temperature-raising process, the hydrogen concentration is controlled to be between 5.0% and 10.0% at least in the temperature range of 400° C. to 600° C. This makes it possible to further suppress the reaction between the silicone resin and hydrogen, and the effect of reducing eddy current loss is significantly achieved.

[0050] The soft magnetic powder contains pure iron, which can reduce hysteresis loss.

[0051] (Example) The present invention will be described in more detail based on examples, but the present invention is not limited to the following examples. Powder magnetic cores of Examples 1 to 3 and Comparative Examples 1 and 2 were produced.

[0052] The soft magnetic powder used in the dust core of Example 1 was pure iron powder produced by water atomization. The pure iron powder had an average particle size of 44 μm. An insulating coating layer was formed on this pure iron powder.

[0053] Silicone resin and a silane coupling agent were used as the insulating material. Methylphenyl silicone resin was used as the silicone resin. 1.8 wt% of the silicone resin was added to the pure iron powder. 0.5 wt% of the silane coupling agent was added to the pure iron powder. After adding the silicone resin and silane coupling agent, they were mixed. Then, 0.5 wt% of water was added to the pure iron powder and mixed. After adding the water and mixing, the mixture was heated and dried. The drying temperature was 180°C and the drying time was 2 hours. This resulted in pure iron powder with an insulating coating layer formed on it.

[0054] After heating and drying, the pure iron powder was passed through a sieve with 500 μm openings to break down agglomerates. A lubricant was then added and mixed. Zinc stearate was used as the lubricant. The lubricant was added at 0.45 wt% relative to the pure iron powder.

[0055] After adding and mixing the lubricant, the lubricated pure iron powder was filled into a die and pressed to produce a toroidal powder compact with an outer diameter of 20.85 mm, an inner diameter of 12.4 mm, and a height of 5.0 mm. The pressure for pressing was 10.0 ton / cm. 2 So I went.

[0056] Finally, the powder compact was subjected to a heat treatment. First, the powder compact was placed in a furnace (heating furnace: tubular furnace KTF1100°C series (manufactured by JTEKT Thermo Systems Corporation)) and heated to 640°C. The temperature increase in Example 1 was carried out in a mixed gas atmosphere with a hydrogen concentration of 5% and a nitrogen concentration of 95%. The temperature increase in Example 1 was carried out in this mixed gas atmosphere from the beginning until the temperature reached 640°C. The flow rate of the mixed gas was 3 L / min.

[0057] After the temperature reached 640°C in the temperature-raising step, the powder compact was annealed for 50 minutes while the furnace temperature was maintained at 640°C. This constant temperature step was carried out in a mixed gas atmosphere with a hydrogen concentration of 5% and a nitrogen concentration of 95%, just like the temperature-raising step. In this way, the powder magnetic core of Example 1 was produced.

[0058] Examples 2 and 3 differ only in the hydrogen concentration of the atmosphere in the temperature-raising step when heat-treating the powder compact, but otherwise use the same materials, manufacturing method, and conditions as Example 1. In Example 2, the powder compact was heat-treated (both in the temperature-raising step and the constant-temperature step) in a mixed gas atmosphere with a hydrogen concentration of 10% and a nitrogen concentration of 90%. In Example 3, the powder compact was heat-treated (both in the temperature-raising step and the constant-temperature step) in a mixed gas atmosphere with a hydrogen concentration of 15% and a nitrogen concentration of 85%.

[0059] Comparative Examples 1 and 2 differ only in the hydrogen concentration of the atmosphere in the temperature-raising step when heat-treating the powder compact, but otherwise use the same materials, manufacturing method, and conditions as Example 1. Comparative Example 1 was performed in a nitrogen gas atmosphere with a hydrogen concentration of 0%, i.e., a nitrogen concentration of 100%, during the temperature-raising step and constant-temperature step. Comparative Example 2 was performed in a mixed gas atmosphere with a hydrogen concentration of 50% and a nitrogen concentration of 50%, during the temperature-raising step and constant-temperature step.

[0060] The amount of methane gas (CH4) generated was measured for the powder magnetic cores prepared as described above in Examples 1 to 3 and Comparative Examples 1 and 2. The amount of methane gas generated was measured using a gas analyzer (gas chromatograph Agilent 490 Micro GC (manufactured by GL Sciences Inc.)). The measurement conditions were an analysis range of 10 ppm to 100% and an analysis speed of 2 min / cycle.

[0061] The results are shown in Figure 1. In the graph shown in Figure 1, the horizontal axis represents time (min), the scale on the right side of the vertical axis represents the furnace temperature (heat treatment temperature), and the scale on the left side represents the amount of methane gas generated. In addition, the thick solid line in Figure 1 represents the furnace temperature during heat treatment, the dashed-dotted line represents the amount of methane gas generated in Example 1 with a hydrogen concentration of 5%, the dashed-two-dotted line represents the amount of methane gas generated in Example 2 with a hydrogen concentration of 10%, the long dashed line represents the amount of methane gas generated in Example 3 with a hydrogen concentration of 15%, the short dashed line represents the amount of methane gas generated in Comparative Example 1 with a hydrogen concentration of 0%, and the thin solid line represents the amount of methane gas generated in Comparative Example 2 with a hydrogen concentration of 50%.

[0062] As shown in Figure 1, it was confirmed that the amount of methane gas generated exceeded 100 ppm when the temperature exceeded 400°C during the temperature increase process. This is presumably due to the start of a reaction between the silicone resin formed as the insulating coating layer and hydrogen. In particular, it was confirmed that the amount of methane gas generated increased sharply when the temperature exceeded 425°C.

[0063] On the other hand, the amount of methane gas generated peaks in the range from around 550°C to below 600°C, and once the peak is exceeded, the amount of methane gas generated drops sharply. Therefore, it was confirmed that in the temperature rising process, the reaction between silicone resin and hydrogen can be suppressed in the temperature range of 400°C to 600°C, and a good insulating coating layer can be formed.

[0064] Note that methane gas is also generated within the dotted line in the graph of FIG. 1 (100 min to 250 min). However, the generation of methane gas within this range is thought to be due to a reaction between hydrogen and the carbon component contained in the lubricant. Therefore, the generation of methane gas within this range does not affect the formation of the insulating material layer. Methane gas is also generated in Comparative Example 1, which has a hydrogen concentration of 0%, but this is thought to be due to the addition of water.

[0065] Next, the hysteresis loss, eddy current loss, and iron loss of the dust cores of Examples 1 to 3 and Comparative Examples 1 and 2 were measured.

[0066] Iron loss was measured by winding 30 turns of φ0.45 mm copper wire around the powder magnetic core as the primary winding and 30 turns as the secondary winding. Then, using a BH analyzer (Iwatsu Measurement Co., Ltd.: SY-8219), a magnetic measuring instrument, the hysteresis loss Phv, eddy current loss Pev, and iron loss Pcv (kW / m) were measured under the measurement conditions of a frequency of 20 kHz and a maximum magnetic flux density Bm of 200 mT. 3 ) was measured.

[0067] This measurement was carried out by calculating the hysteresis loss coefficient and eddy current loss coefficient from the iron loss frequency curve using the following equations (1) to (3) by the least squares method. Pcv = Kh×f + Ke×f 2 ··(1) Ph = Kh × f (2) Pe = Ke × f 2 (3) Pcv: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: frequency Ph: Hysteresis loss Pe: Eddy current loss

[0068] The measurement results are shown in Table 1. Table 1 also shows the total amount of methane gas generated from the time the heat treatment temperature reached 400°C or higher until 470 minutes, when the amount of methane gas generated stabilized (the point at which the change in the amount of gas generated stabilized at about 5 ppm). Figure 2 shows a graph illustrating the results of hydrogen concentration and iron loss Pcv. Figure 3 shows a graph illustrating the results of hydrogen concentration and eddy current loss Pev. Figure 4 shows a graph illustrating the results of hydrogen concentration and hysteresis loss Phv. Figures 2 and 3 also show the total amount of methane gas.

[0069] [Table 1]

[0070] As shown in Table 1 and FIG. 2, Examples 1 to 3, in which the hydrogen concentration was 5% or more and 15% or less, had reduced iron loss compared to Comparative Examples 1 and 2. In particular, Examples 1 and 2, in which the hydrogen concentration was 5% or more and 10% or less, had an iron loss of 1240 (kW / m 3 ), and it was confirmed that the values were significantly reduced compared to Example 3 and Comparative Examples 1 and 2.

[0071] As a factor for this, as shown in Table 1 and FIG. 3, the eddy current loss in Examples 1 to 3 was 600 (kW / m 3 ), which is a good value. In addition, for Examples 1 and 2, the eddy current loss was 100 (kW / m) lower than that of Comparative Example 1, which had a hydrogen concentration of 0%. 3 On the other hand, the eddy current loss of Comparative Example 2, in which the hydrogen concentration was 50%, was 1300 (kW / m 3 ) and is increasing rapidly.

[0072] Considering these results and Figure 1, it appears that if the hydrogen concentration is set to 5% or more and 15% or less in the temperature range of 400°C or more and 640°C or less during the heating process, the reaction between the silicone resin and hydrogen can be suppressed, allowing for the formation of a high-quality insulating coating layer and reducing eddy current loss.

[0073] Furthermore, the hysteresis loss in Examples 1 to 3 was reduced compared to Comparative Examples 1 and 2. This confirmed that the hysteresis loss was reduced by setting the hydrogen concentration in the range of 5% or more and 15% or less.

[0074] Next, the carbon content and resistivity of the powder magnetic cores of Example 1 and Comparative Example 1 were measured. The powder magnetic cores of Example 1 and Comparative Example 1 differed only in shape from the above-mentioned examples, but were otherwise produced by the same method and under the same conditions as those of Example 1 and Comparative Example 1. That is, for the powder magnetic core of Example 1, the powder compact was heat-treated at a hydrogen concentration of 5%, and for the powder magnetic core of Comparative Example 1, the powder compact was heat-treated at a hydrogen concentration of 0% (100% nitrogen gas). For Example 1 and Comparative Example 1, U-shaped powder magnetic cores measuring 73.4 mm in the longitudinal direction, 27.8 mm in the lateral direction, and 23.4 mm in height were produced.

[0075] The carbon content was measured by crushing the powder magnetic cores produced through the temperature-raising and constant-temperature processes and measuring the residual carbon content using a carbon / sulfur analyzer (EMIA-Pro, manufactured by Horiba, Ltd.).

[0076] The resistivity was measured using a resistivity meter (Loresta-GX MCP-T700 (manufactured by Nitto Seiko Analytech Co., Ltd.)) by the four-terminal method.

[0077] The measurement results are shown in the following Table 2. Fig. 5 shows a graph comparing the carbon amount and resistivity values of Example 1 and Comparative Example 1. In Fig. 5, the resistivity values are shown as a bar graph, and the carbon amount is shown as a line graph.

[0078] [Table 2]

[0079] 5, Example 1 has a lower residual carbon concentration than Comparative Example 1. Furthermore, the specific resistance value of Example 1 is significantly higher than that of Comparative Example 1, confirming that Example 1 has good insulating performance.

[0080] This is presumably because hydrogen contributes to the decomposition of the lubricant. The decomposition of the lubricant begins in the temperature range (100°C to 250°C) before 400°C, at which point decomposition of the insulating coating layer begins. The presence of hydrogen at this time accelerates the decomposition of the lubricant, and in Example 1, it appears that the decomposition of the insulating coating layer occurs without any lubricant residue remaining.

[0081] On the other hand, in Comparative Example 1, the lubricant was not completely decomposed, and lubricant residue remained when the decomposition of the insulating coating layer began, which is presumably why the influence of the lubricant residue deteriorated the insulation performance. As a result, although the amount of methane gas generated in Comparative Example 1 was less than that in Example 1, the eddy current loss was presumably more than twice that of Example 1. From the above, it is believed that by controlling the hydrogen concentration even in the temperature range from the beginning to 400°C in the temperature rise process, the effect of controlling the hydrogen concentration to 5% to 15% in the temperature range of 400°C to 640°C can be further enhanced.

[0082] Furthermore, the resistivity values of the powder magnetic cores of Example 3 and Comparative Example 2 were measured. The powder magnetic cores of Example 3 and Comparative Example 2 were produced by the same method and under the same conditions as Example 3 and Comparative Example 2, except that they differed only in shape from the above-mentioned examples. That is, for the powder magnetic core of Example 3, the powder compact was heat-treated at a hydrogen concentration of 15%, and for the powder magnetic core of Comparative Example 2, the powder compact was heat-treated at a hydrogen concentration of 50%. For Example 3 and Comparative Example 2, U-shaped powder magnetic cores with the above dimensions were produced. The resistivity values were measured in the same manner as above.

[0083] The measurement results are shown in the following Table 3. Also, a graph comparing the resistivity values of Example 3 and Comparative Example 2 is shown in FIG.

[0084] [Table 3]

[0085] As shown in Table 3 and Fig. 6, the resistivity value of Example 3 is significantly higher than that of Comparative Example 2. As shown in Table 1, the amounts of methane gas generated are approximately the same in Example 3 and Comparative Example 2. This is thought to be because the amount of methane gas generated reaches a maximum and saturates at a hydrogen concentration of 15%, so there is no significant change in the amount of methane gas generated even when the hydrogen concentration exceeds 15%.

[0086] However, it is presumed that the high hydrogen concentration in Comparative Example 2 caused the reaction between the silicone resin in the insulating coating layer and hydrogen to proceed quickly, which accelerated the breakdown of the insulating coating layer and resulted in a significant decrease in resistivity. As a result, although the amount of methane gas generated was the same in Example 3 and Comparative Example 2, the eddy current loss in Example 3 was less than half that of Comparative Example 2, demonstrating a significant effect in reducing eddy current loss. Based on the above, in the temperature range of 400°C to 640°C, where the insulating coating layer decomposes, if the hydrogen concentration is too high, a good insulating coating layer cannot be formed. However, by controlling the hydrogen concentration to 5% to 15%, it is possible to form an insulating coating layer with excellent insulating performance, reduce eddy current loss, and, as a result, reduce iron loss.

[0087] (Other embodiments) Although the present specification describes an embodiment of the present invention, this embodiment is presented as an example and is not intended to limit the scope of the invention. The above-described embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. The embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

Claims

1. an insulating coating layer forming step of coating the surface of the soft magnetic powder with an insulating coating layer containing a silicone resin; a compact manufacturing step of pressurizing the soft magnetic powder coated with the insulating coating layer to manufacture a powder compact; a heat treatment step of annealing the powder compact; Including, The heat treatment step includes: a temperature raising step of raising the temperature to a predetermined temperature; a constant temperature step of maintaining the predetermined temperature; Including, In the temperature-raising step, the hydrogen concentration is controlled to be 5.0% or more and 15.0% or less in a temperature range of at least 400°C or more and 640°C or less. A method for producing a powder magnetic core, comprising:

2. In the temperature-raising step, the hydrogen concentration is controlled to be 5.0% or more and 10.0% or less in a temperature range of at least 400°C or more and 600°C or less. The method for producing a powder magnetic core according to claim 1,

3. the soft magnetic powder contains pure iron; 3. The method for producing a powder magnetic core according to claim 1 or 2,

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