JP2008277775A - Dust core and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a soft-magnetic metal dust core that can be subjected to high-temperature heat treatment while having low hysteresis loss, high electric resistance, and high strength; and its manufacturing method. <P>SOLUTION: A dust core manufacturing method is configured as follows. An insulating oxide film is formed partially or wholly on the powder surface after immersing soft-magnetic powder mainly composed of Fe into an alkoxide solution. Then, an inorganic binder is mixed. After press-molding, it is subjected to heat treatment at ≥600°C. Preferably, a coating film thickness of the insulating oxide film is formed in the range between ≥10 nm and ≤1 μm while the heat treatment is executed at a temperature in the range between ≥900°C and ≤1,100°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a soft core having high strength, good electrical insulation and low loss when used as a magnetic core for electric and electronic parts such as power chokes, transformers, reactors, and rotating machines used in digital information equipment. The present invention relates to a magnetic metal dust core and a manufacturing method thereof.

  In recent years, with the increase in frequency and current of digital information equipment, inductors using soft magnetic metal powder and noise countermeasure components are attracting attention. In particular, the use of parts used with a drive current of 10-100 A in the 10-100 kHz band is expanding. In the field of electrical components such as a rotating machine core and a transformer core, higher density and smaller size are also demanded. For this reason, the development of soft magnetic metal dust cores used in these electric and electronic parts, particularly soft magnetic powder magnetic cores having excellent magnetic properties in the mid-high frequency region, is underway. A dust core made of soft magnetic metal powder has a higher saturation magnetic flux density than a ferrite core that has been used so far, which is advantageous for downsizing electronic components and increasing current. is there.

  However, the powder magnetic core made of soft magnetic metal powder has a drawback that the eddy current loss is large because the electrical resistivity is lower than that of ferrite. Therefore, when a metal-based powder magnetic core is used as a core, the loss particularly in the middle and high frequency range of several tens of kilohertz or more is greater than that of a ferrite core. In addition, there was a problem of temperature rise due to heat generation of the core, and it was difficult to put it into practical use as an electronic component. Conventionally, as a means for solving this problem, in order to reduce the loss, the surface of the soft magnetic metal powder is made high in resistivity by coating with an insulator such as phosphate as in Patent Document 1, for example. Attempts have been made to suppress the generation of eddy currents. Non-Patent Document 1 proposes a method of increasing the resistance of the powder surface by coating the surface of the metal powder with an oxide such as MgO and reducing eddy current loss. All of these are intended to reduce eddy current loss and core loss by improving the electrical resistance of the powder surface.

  By the way, the iron loss of the entire core is generally represented by the sum of hysteresis loss and eddy current loss. In general, the hysteresis loss changes in proportion to the first power of the frequency, and the eddy current loss changes in proportion to the second power of the frequency. Therefore, reducing the eddy current loss largely in comparison with the contribution of the hysteresis loss in the high frequency region is an effective means for reducing the core loss. On the other hand, not only the eddy current loss but also the contribution from hysteresis loss cannot be ignored for devices used at relatively low and medium frequencies such as motor cores and reactor cores. Therefore, in the low and medium frequency range, reducing not only eddy current loss but also hysteresis loss is effective in reducing core loss.

  The hysteresis loss of a magnetic core is determined by the magnitude of hysteresis when a magnetic field is turned on / off in the core. In order to reduce the hysteresis loss, it is necessary to make the coercive force of the magnetic powder as small as possible. The coercive force of soft magnetic powder reflects the ease of domain wall movement when a magnetic field is applied, and this includes distortion, dislocation, etc. due to plastic deformation generated during the formation of grain boundaries, impurity inclusions, and a dust core. It becomes a factor to prevent. For this reason, in order to obtain a core with low hysteresis loss, in a Fe-based magnetic powder, a low coercive force powder is originally formed at a low pressure and subjected to strain relief annealing at a high temperature of 700 ° C. or higher, preferably 900 ° C. or higher. Is desired.

  However, in the prior art described in Patent Document 1, Non-Patent Document 1, etc., when heat treatment is performed at a high temperature of 800 ° C. or higher, the insulating material coated to suppress the generation of eddy current reacts with the magnetic powder, Insulation film is altered and destroyed due to thermal decomposition, etc., resulting in deterioration of insulation, so heat treatment at high temperature cannot be performed, crystal grain size can be increased, and processing strain can be completely removed. Therefore, there is a problem that hysteresis loss cannot be sufficiently reduced.

In addition, the conventional dust core is formed by adding a few weight percent of a silicon resin or an acrylic resin as a binder to an insulating coated magnetic powder, applying a pressure of 1-2 GPa, press-molding, and then straining at 400-600 ° C. In general, the powder magnetic core is prepared by annealing, but the resin binder is decomposed by heat treatment at 400 ° C. or higher, so that the bonding strength after heat treatment is remarkably lowered. As described above, in order to reduce the core iron loss of the dust core, it is necessary to reduce both hysteresis loss and eddy current loss. For this reason, low coercive magnetic powder and insulation coating technology that can withstand high-temperature heat treatment are required.
Further, in Patent Document 2, an iron-based powder in which a film containing a silicone resin, a metal oxide, and a pigment made of glass or the like is formed on a powder containing Fe as a main component, and sintered at a temperature at which organic matter is decomposed. A dust core obtained by tying is disclosed. As this effect, the point which shows high insulation and high intensity | strength after annealing is described.

JP 2003-282316 A JP 2003-303711 A Gakuji Uozumi et al., Outline of the 2005 Fall Meeting of the Powder and Powder Metallurgy Association (2005), p136

However, the present situation is that a dust core capable of obtaining a high strength with a high electrical resistance capable of withstanding a high-temperature heat treatment with a low hysteresis loss that realizes a low core loss has not yet been obtained.
In order to solve the above problems, an object of the present invention is to provide a soft magnetic metal dust core capable of high-temperature heat treatment, low hysteresis loss, high electrical resistance and high strength, and a method for manufacturing the same.

  The present inventors have found that the above object can be achieved by forming an insulating film on the powder surface by attaching an insulating oxide film to the soft magnetic metal powder and annealing at a high temperature using an inorganic binder. The present invention has been reached.

That is, in the method for producing a soft magnetic metal dust core of the present invention, a soft magnetic powder containing Fe as a main component is immersed in an alkoxide solution to form an insulating oxide film on the powder surface, and then an inorganic binder is mixed. After press molding, heat treatment is performed at 600 ° C. or higher.
It is preferable to form the insulating oxide film with a thickness of 10 nm to 1 μm and to perform the heat treatment at 900 ° C. to 1100 ° C. Only when the thickness of the oxide film is within this range and heat treatment is performed at a temperature in the vicinity of 1000 ° C., the effect of improving the crushing strength can be obtained. The thickness of the insulating oxide film is preferably 0.1 μm or more and 0.9 μm or less, more preferably 0.3 μm or more and 0.8 μm or less. Moreover, preferable heat processing temperature is 950 degreeC or more and 1050 degrees C or less. The molding pressure is preferably 0.6 GPa or more.

Moreover, it is preferable to mix the inorganic binder in an amount of 0.3% by weight to 2.0% by weight with respect to the weight of the soft magnetic powder. A more preferable range of the added amount of the inorganic binder is 0.4 to 1.8% by weight.
The inorganic binder is preferably selected from one or more of colloidal silica, amorphous silica, fused silica, water glass, and silicon emulsion. Further, it is preferable to mix the organic resin binder at 2 wt% or less (excluding 0) and the lubricant at 0.1 wt% or more and 0.5 wt% or less with respect to the weight of the soft magnetic powder.
The alkoxide solution preferably has a concentration of 10 mol / L or more and a pH in the range of 6.0 to 12.0.

According to this manufacturing method, a compact having a crushing strength of 30 MPa or more and an electrical resistivity of 10 ⁴ Ωm or more is obtained in a molded product obtained by subjecting soft magnetic powder containing Fe as a main component to heat treatment after press molding. An insulating oxide film is formed on the whole or part of the surface of the soft magnetic powder. The thickness of the insulating oxide film is preferably 10 nm or more and 1 μm or less. Examples of the soft magnetic powder containing Fe as a main component include Fe powder, Fe-Si powder, Fe-Si-Al powder, Fe-Ni powder, Fe-Si-B powder, and Fe nanocrystal powder. The metal powder can be used.
In the case of Fe-Si powder, Fe-Si-Al powder, and Fe-Ni powder, the amount of Fe is preferably 85 atomic percent or more, and more preferably 90 atomic percent or more. In the case of Fe—Si—B-based powder and Fe-based nanocrystal powder, the amount of Fe is preferably 65 atomic% or more, more preferably 70 atomic% or more, and further preferably 75 atomic% or more.

By the above-described manufacturing method, a powder magnetic core having a crushing strength of 30 MPa or more and an electric resistivity of 10 ⁴ Ωm or more is obtained as a molded body obtained by subjecting soft magnetic powder mainly composed of Fe to heat treatment after press molding. Can do. The crushing strength is a value measured by a crushing strength test method defined in JIS Z 2507.

  The dust core preferably has an insulating oxide film formed on the entire surface or a part thereof, and the thickness of the film is preferably 10 nm or more and 1 μm or less. Further, when the dust core is used in an environment having a frequency of 50 kHz or less, the core loss of the dust core can be reduced by setting the film pressure of the insulating oxide film. Details are described in the Examples.

By using the soft magnetic metal dust core produced according to the present invention, it is possible to set the crushing strength after heat treatment of the dust core (magnetic core) to 30 MPa and the electrical resistivity to 10 ⁴ Ωm or more. Moreover, it is possible to significantly reduce both eddy current loss and hysteresis loss.

  By performing high-temperature annealing, the distortion applied to the soft magnetic metal powder during core forming is sufficiently removed, and the crystal grain size increases, which facilitates domain wall movement within the powder and greatly reduces hysteresis loss. The In addition, since the insulating coating that suppresses the generation of eddy current has heat resistance, it maintains high electrical resistivity without deterioration due to alteration by high-temperature annealing and deterioration of insulation, and suppresses increase in eddy current loss.

  Also, by adding an inorganic Si-based binder that binds to the insulating oxide film at 1000 ° C. or lower, the insulating oxide film reacts during high-temperature annealing to strengthen the bond between the powders, and the dust core after the heat treatment The crushing strength increases.

The soft magnetic powder magnetic core of the present invention and the manufacturing method thereof will be specifically described below. The present invention relates to a powder magnetic core having high strength and high electrical resistivity obtained by attaching an insulating oxide film to the surface of magnetic powder, mixing an inorganic binder, etc., and then heat-treating it at a high temperature and manufacturing the same. Is the method.
The soft magnetic powder used as a raw material is mainly composed of Fe, and specifically, Fe, Fe—Si, Fe—Si—Al, Fe—Ni, and Fe-based nanocrystal powder. As a manufacturing method thereof, any method such as a gas atomizing method, a water atomizing method, and other methods may be used. Moreover, it is effective in any shape such as a spherical shape, a flat shape, and an irregular shape regardless of the shape of the soft magnetic powder. The effect of the present invention can be obtained regardless of the particle size of the soft magnetic powder, but with the same composition, the larger the particle size, the larger one crystal grain can be reduced to reduce the coercive force, so the hysteresis loss is small. Therefore, the loss of the powder magnetic core as a whole tends to be reduced.

The alkoxide solution in the production method of the present invention is a solution obtained by dissolving a metal alkoxide, which is a raw material of an oxide to be deposited, in an alcohol such as IPA or ethanol. Examples of the metal alkoxide include M as a metal element, alkyl such as methoxide M (OCH ₃ ) n, ethoxide M (OC ₂ H ₅ ) n, propoxide M (O · n-, i-C ₃ H ₇ ) n. Use one with a short chain length. The metal element M is at least one element selected from Mg, Al, Si, Ca, Ti, Sr, Ba, Li, Na, K, St, Ge, Bi, Cu, Y, Zr, and Ta. A metal alkoxide may be used individually by 1 type, and may be used in combination of 2 or more type. As an element that forms a stable oxide, Si, Ti, Zr, and Al are particularly preferable. Specifically, tetraethoxysilane or tetramethoxysilane which is an alkoxide solution of Si, or titanium alkoxide which is an alkoxide solution of Ti is preferable.

The metal alkoxide solution may contain ceramic particles such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), and magnesia (MgO). However, if these contents are large, the magnetic properties of the powder magnetic core deteriorate. Therefore, it is necessary to select and use as appropriate.
Further, an insulating viscous substance may be added to the metal alkoxide solution. The insulating viscous substance is added together with the ceramic particles to prevent its precipitation and uniformly disperse in the metal alkoxide solution. As a result, an effect that the insulating property of the soft magnetic powder is improved can be obtained. As the insulating viscous substance, any of a synthetic viscous substance, a semi-synthetic viscous substance, a natural viscous substance, and the like can be used as appropriate. As the synthetic viscous material, any of a cation system, an anion system, and a nonionic system can be used. As the semisynthetic viscous material, for example, methylcellulose which is a cellulose dielectric system viscous material can be used. As the natural viscous substance, either plant mucilage or animal mucilage can be used, such as gum arabic or gelatin.

These alkoxide solutions and the raw material soft magnetic powder are mixed. At the time of mixing, if the concentration of the alkoxide solution is extremely small, the insulating oxide film adhering to the surface of the metal powder is not sufficient, so that the effect of the present invention cannot be obtained. Therefore, the concentration of the alkoxide solution needs to be 10 mol / L or more. There is no upper limit to the concentration, but if the concentration is too high, the amount discarded without adhering to the raw soft magnetic powder increases, which causes a problem in manufacturing cost. In order to deposit a more uniform and dense oxide, in reality, it is desirably about 5 mol / L or less, and in order to prevent the film thickness from increasing excessively, it is desirably about 2 mol / L or less.
Further, the time for mixing the alkoxide solution and the raw soft magnetic powder is preferably 30 minutes or longer because if the time is too short, the reaction hardly proceeds and the insulating oxide film cannot be deposited. There is no upper limit on the treatment time, but when the reaction reaches equilibrium, no further adhesion can be expected, so there is no effect. Therefore, practically, a range of 30 minutes to 5 hours is preferable.
In addition, the form and speed | rate of reaction of the alkoxide solution mentioned above change with pH. For this purpose, it is more desirable that the pH is from pH 6 to pH 12, preferably from pH 8.3 to pH 11. A pH of 6 or less is not preferable because Fe elution occurs in the solution from the raw magnetic powder. On the other hand, if the pH is 11 or more, the adhesion amount becomes excessive and the film thickness increases excessively, which adversely affects the characteristics.

The insulating oxide film does not necessarily have to cover the entire surface of the magnetic powder. Even if there is no insulating oxide film in part due to the shape, composition, surface state, manufacturing conditions, etc. of the raw soft magnetic powder, sufficient effects of insulation and high strength can be obtained.
Further, when the thickness of the insulating oxide film exceeds 1 μm, the proportion of the metal powder component in the dust core becomes low, and a high magnetic flux density cannot be obtained. Therefore, the thickness of the insulating oxide film is preferably 1 μm or less. On the other hand, if the thickness is too thin, the effect of suppressing electrical conduction is lost and an increase in eddy current loss is caused, so a thickness of 10 nm or more is necessary. In addition, as described above, the crushing strength is improved by performing heat treatment particularly at a thickness of 0.1 μm or more and 0.9 μm or less and at a temperature in the vicinity of 1000 ° C. Details will be described in Examples.

  After removing the soft magnetic powder from the alkoxide solution, the powder is dried. When heat treatment is performed after molding, there is an effect of preventing a decrease in density due to evaporation of a solvent or water remaining in the metal powder. The drying process is general and may be performed in the atmosphere, in a vacuum, or in an inert atmosphere, and may be performed at a temperature at which the solvent or water evaporates (50 ° C. to 300 ° C.) for 30 minutes to 10 hours.

An inorganic binder, an organic resin binder, and a lubricant are mixed in the soft magnetic powder produced by the above process. These are added for the purpose of improving the strength of the dust core after heat treatment, the strength of the dust core at the time of molding, and the moldability.
The addition amount of the inorganic binder is preferably in the range of 0.3 to 2.0%. By performing high-temperature heat treatment in the presence of an insulating oxide film and an inorganic binder on the surface of the adjacent magnetic powder, the crushing strength of the dust core is improved. In either case, sufficient effects cannot be obtained with only one of them. When an inorganic binder is not added, the bond formation between the insulating oxide films on the surface of the magnetic powder is insufficient. On the other hand, the insulation between powders cannot be obtained only with the inorganic binder. As an insulation treatment, there is a method of mixing an insulating filler such as kaolin. In this case, since the insulating filler is only attached to the surface of the magnetic powder and does not form a bond, the magnetic powder can be added even if an inorganic binder is added. It does not lead to strengthening the bond between them. Therefore, as shown in the manufacturing method of the present invention, it is considered that both the insulating oxide film and the inorganic binder bonded to the surface of the magnetic powder are necessary for obtaining a high-strength powder magnetic core. In addition, when there is too much addition amount, the density of a powder magnetic core will decrease and it will become impossible to obtain a high saturation magnetic flux density, and the improvement effect of a crushing strength will not be acquired. Therefore, it is desirable that the amount added does not exceed 2%. As the inorganic binder, an inorganic Si-based binder is preferable.

As the organic resin binder, an acrylic emulsion in which an acrylic resin is dispersed in water is suitable. Necessary for maintaining the strength of the dust core during molding. It escapes from the dust core by sublimation and thermal decomposition during heat treatment. If the added amount is large, the density is reduced as in the case of amorphous silica, and a binder remains in the dust core during heat treatment, which may adversely affect the crushing strength and magnetic characteristics. Therefore, the addition amount is desirably 2% or less.
The lubricant added to improve moldability is a higher fatty acid lubricant, stearic acid and its lithium, sodium, potassium, calcium, magnesium and zinc salts. Zinc stearate is preferred in terms of price and characteristics. Addition amount is 0.1-0.5%. If it is less than 0.1%, it is difficult to pull out from the mold. May cause adverse effects on the crushing strength and magnetic properties.

  After the soft magnetic powder produced by the above process is molded, heat treatment is performed at 600 ° C. or higher. This makes it possible to perform strain relief annealing at a high temperature by making the heat treatment step for producing the soft magnetic metal powder of the present invention the same as the strain relief annealing step for the core. In order to increase the strength of the dust core, high temperature heat treatment at 800 ° C. or higher is more preferable, and in order to obtain a dust core with low hysteresis loss, high temperature heat treatment at 900 ° C. or higher is more preferable. The heat treatment time may be about 30 minutes to 2 hours. The heat treatment atmosphere is preferably a non-oxidizing atmosphere.

(Example 1-9)
500 g of a soft magnetic raw material powder having a composition of Fe-6.5% Si and an average particle size of 80 μm was mixed with 100 mL of tetraalkoxysilane (Kanto Chemical) / IPA solution, and stirred for 3 hours using a propeller stirrer. Thereafter, the soft magnetic powder and the tetraalkoxysilane / IPA solution were separated and dried at 100 ° C. for 1 hour. The obtained soft magnetic powder was mixed with 0.5 wt% colloidal silica (Nissan Chemical Industries) and 1.5 wt% acrylic emulsion (Showa High Polymer), stirred and dried, and further mixed with 0.3 wt% zinc stearate. The soft magnetic powder thus obtained was compression-molded at 1200 MPa at room temperature to prepare a ring sample having an outer diameter of 14 mm, an inner diameter of 8 mm, and a height of 4.5 mm, and this was heat-treated at 800 ° C. for 2 hours in nitrogen gas. went.
(Comparative Example 1-4)
The same raw material powder as in Example 1 was mixed with 1.2 wt% colloidal silica, 1.5 wt% acrylic emulsion, and 0.3 wt% zinc stearate in the same manner, followed by molding and heat treatment.
(Comparative Example 5-8)
Add 0.5 wt% of kaolin as an insulator to the same raw material powder as in Example 1, mix 1.2 wt% of colloidal silica, 1.5 wt% of acrylic emulsion, and 0.3 wt% of zinc stearate in the same manner, and perform molding and heat treatment. went.
(Comparative Example 9-13)
After the same raw material powder as in Example 1 was treated with the same alkoxide solution as in Example 1, 1.5 wt% of acrylic emulsion and 0.3 wt% of zinc stearate were mixed in the same manner, followed by molding and heat treatment.
The crushing strength and electrical resistivity of the dust core obtained as described above were measured. The crushing strength was calculated from the compression force measured by Shimadzu Autograph (AG-50kNG). The electrical resistivity was measured by a two-terminal method using a digital multimeter (VOAC7521) manufactured by Iwasaki Tsushinki Co., Ltd., by applying a silver paste on the pressed surface of the ring sample. Table 1 shows each powder and its crushing strength and electrical resistivity values.

As shown in Example 1, Comparative Example 1, and Comparative Example 9, in order to show high values for both the crushing strength and the electrical resistivity, the coating treatment with the alkoxide solution and the inorganic silica-based binder are each insufficient. , You can see that both are necessary.
Further, as shown in Comparative Example 5, a relatively high electrical resistivity can be obtained by mixing kaolin as an insulator instead of performing the coating treatment with the alkoxide solution, but the crushing strength becomes a very low value. Silica produced by the alkoxide solution is chemically bonded to the surface of the metal powder, but kaolin is only mixed and is only attached to the surface of the metal powder.

  As shown in Comparative Example 9-13, the crushing strength is low in both cases where the amount of the inorganic binder added is too small or too large. It is considered that when the added amount of the binder is small, there are insufficient bonding sites for connecting the metal powders, and when the added amount is large, the compressibility at the time of molding deteriorates.

  Table 2 shows the relationship between the thickness of the coating, the crushing strength, and the electrical resistivity. The coating thickness was changed by changing the alkoxide concentration of the alkoxide / IPA solution. The thicker the film, the higher the electrical resistivity, and the eddy current loss can be suppressed because the insulation can be ensured. However, when the film thickness exceeds 1 μm, the density of the dust core becomes significantly reduced, so the high magnetic flux density is increased. It cannot be obtained, and the crushing strength also decreases.

The influence of the thickness of the insulating oxide film and the pressure ring strength by the heat treatment temperature after forming was investigated. Except for changing the thickness of the insulating oxide film, the ring sample obtained in the same manner as in Example 1 was placed in nitrogen gas at 800 ° C., 900 ° C., 1000 ° C., 1100 ° C., and 1200 ° C. for 2 hours. Heat treatment was performed. The results are shown in FIG.
When the heat treatment temperature is 1000 ° C., the crushing strength is improved when the thickness of the insulating oxide film is in the range of 0.1 to 1 μm. The heat treatment temperatures of 900 ° C. and 1100 ° C. have a similar tendency, but when the heat treatment temperature is 800 ° C. and 1200 ° C., the crushing strength decreases as the thickness of the insulating acid film increases.
This is presumably because the melting temperature of the amorphous silica is around 800 ° C., so that the strength between the silica is increased and the strength is increased by setting the temperature around 1000 ° C., which is higher than that. When the temperature is further increased to about 1200 ° C., crystallization of silica starts and fine cracks are likely to occur, so that the strength is expected to decrease.
Further, it is considered that the core strength of the green compact is mainly determined by the following three strengths. (1) Strength between metal powder and silica coating, (2) Strength of silica coating, (3) Strength between coated powders. Since the strength of (3) is basically determined by heat treatment, it is not affected by the film thickness, but if the film thickness is thin, the strength of (1) is reduced by the molding press, and if it is thick, the coating itself cracks. Since it is easy, the strength of (2) is considered to be reduced. For this reason, it is presumed that the balance between the two is achieved only under the above specific manufacturing conditions, and the crushing strength is improved.

  The effect of insulating oxide thickness and applied frequency on the core loss was investigated. Table 2 shows the magnetic core loss of the dust core measured under the environment of magnetic field Bm = 50 mT and frequency f = 50 kHz, and the core loss of the dust core measured under environment of magnetic field Bm = 30 mT and frequency f = 1 MHz. . The dust core was manufactured in the same manner as in Example 1 except that the thickness of the insulating oxide film was changed in the range of 0.03 μm to 1.2 μm.

When the dust core is used in a low frequency environment, the insulation loss is impaired and the core loss is increased when the insulating oxide film has a film pressure of 0.03 μm. Further, when the film pressure is 1.2 μm, the magnetic material volume ratio in the magnetic core is lowered, the hysteresis loss is impaired, and the magnetic core loss is similarly increased. On the other hand, when used in an environment with a frequency of 1 MHz, the core loss tends to increase as the film pressure decreases.
When this dust core is used under a low frequency environment of 50 kHz or less, by controlling the film pressure of the insulating oxide film as described above, the magnetic core loss is reduced in addition to the effect of improving the mechanical strength. An effect is also obtained.

It is a figure which shows the relationship between the heat processing temperature, the thickness of an insulating oxide film, and the crushing strength.

Claims (9)

A soft magnetic powder containing Fe as a main component is immersed in an alkoxide solution to form an insulating oxide film on the whole or part of the powder surface, and then mixed with an inorganic binder, press-molded, and then heat treated at 600 ° C. or higher. A method for producing a dust core, comprising: 2. The method of manufacturing a dust core according to claim 1, wherein the insulating oxide film is formed with a thickness of 10 nm to 1 μm, and the heat treatment is performed at 900 ° C. to 1100 ° C. 3. The method for producing a dust core according to claim 1, wherein an inorganic binder is mixed in an amount of 0.3% by weight to 2.0% by weight with respect to the weight of the soft magnetic powder. . The dust core according to any one of claims 1 to 3, wherein the inorganic binder is selected from one or more of colloidal silica, amorphous silica, fused silica, water glass, and silicon emulsion. Production method. The organic resin binder is mixed in an amount of 2 wt% or less (excluding 0) and the lubricant is mixed in an amount of 0.1 wt% or more and 0.5 wt% or less based on the weight of the soft magnetic powder. The manufacturing method of the powder magnetic core of 1-4. A compact core obtained by subjecting a soft magnetic powder containing Fe as a main component to a heat treatment after press molding and having a crushing strength of 30 MPa or more and an electric resistivity of 10 ⁴ Ωm or more. The dust core according to claim 6, wherein an insulating oxide film is formed on all or part of the surface of the magnetic powder in the dust core. The dust core according to claim 6 or 7, wherein a thickness of the insulating oxide film is 10 nm or more and 1 µm or less. 9. The dust core according to claim 6, wherein the dust core is used in an environment having a frequency of 50 kHz or less.

Images