JP2006024869A - Dust core and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance dust core suitable for using in a low-frequency range. <P>SOLUTION: In the dust core obtained by pressurizing and forming powder for a magnetic core obtained by coating magnetic powder consisting mainly of Fe with an insulating coat, the magnetic powder contains Si of ≤1.5 %mass, its volume mean particle diameter is 80 to 300 μm, its density ratio is ≥96%, and the dust core is used in an alternate magnetic field of a 100 to 2,000 Hz frequency. When the dust core is used in a frequency range like this, the dust core shows a low iron loss equal to or lower and high magnetic flux density equal to or higher than those of an electromagnetic steel board used conventionally. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dust core having low loss and excellent magnetic properties, and a method for manufacturing the same.

  There are many products that use electromagnetism around us, such as transformers, motors, generators, speakers, induction heaters, and various actuators. Many of these products use an alternating magnetic field. In order to efficiently obtain a large alternating magnetic field locally, a magnetic core (soft magnet) is usually provided in the alternating magnetic field.

  Due to the nature of such a magnetic core, first, it is required that a large magnetic flux density be obtained in an alternating magnetic field. Next, when used in an alternating magnetic field, it is required that the high frequency loss (hereinafter simply referred to as “iron loss”) regardless of the material of the magnetic core is reduced. The iron loss includes eddy current loss, hysteresis loss, and residual loss. The main problems are eddy current loss and hysteresis loss. Furthermore, it is also important that the coercive force is small so that the magnetic core can follow the alternating magnetic field and quickly reach a high magnetic flux density. By reducing the coercive force, it is possible to improve the (initial) magnetic permeability and reduce the hysteresis loss.

  However, it is not easy to simultaneously achieve high magnetic flux density, low eddy current loss and low hysteresis loss. When a thin silicon steel plate is laminated as well as a simple iron ingot, eddy current loss and hysteresis loss increase even if a high magnetic flux density is obtained.

  Recently, dust cores having high magnetic properties and low loss, which are obtained by press-molding magnetic powder (magnetic core powder) coated with an insulating coating, are being developed (Patent Documents 1 and 2). In order to further reduce the iron loss of the dust core, magnetic powders and insulating coatings having various forms and compositions have been developed (Patent Documents 3 to 14).

JP 2000-504785 gazette JP 2003-297624 A JP 2003-297624 A JP 2001-85211 A JP 2003-303711 A Japanese Patent No. 2710152 JP 2000-30924 A JP 11-54314 A JP 2002-43113 A JP 2002-141213 A Japanese Patent Publication No. 7-15124 JP 2003-272909 A JP 2003-105403 A JP 2001-102207 A

  However, even though there are individual proposals regarding magnetic powder and insulating coatings, when it comes to dust cores used in the low frequency range where the operating frequency range is several kHz or less, the overall magnetic characteristics are improved and the iron loss is reduced. Until now, there has never been a reduction in both dimensions.

  Conventionally, as described in Patent Documents 7, 10, 12, 13, 14 and the like, as a reactor for use in a high frequency range where the operating frequency is about 20 to 100 kHz, a high magnetic flux density and a low magnetic core are used. Most of them tried to lose. In order to reduce the iron loss of the dust core used in such a high frequency range, it has been important to reduce the eddy current loss that increases in proportion to the square of the frequency.

  On the other hand, in order to reduce the iron loss of the dust core used in the low frequency range, it is important to reduce the hysteresis loss that increases in proportion to the frequency. Even if a conventional dust core developed on the premise of use in a high frequency range is applied to a dust core used in a low frequency range as it is, preferable characteristics cannot be obtained.

  The present invention has been made in view of such circumstances, and on the premise that it is used in a relatively low frequency range, a high magnetic property (high magnetic flux density) and a low loss dust core and its manufacture It aims to provide a method.

  As a result of extensive research and trial and error, the present inventor has conducted a trial and error, and as a result, a magnetic powder suitable for increasing the magnetic flux density and reducing the loss of a dust core used in a low frequency range has been developed. The inventors have newly found out the particle form, composition, etc., and completed the present invention.

(Dust core)
That is, the powder magnetic core of the present invention is a powder magnetic core obtained by press-molding a magnetic core powder in which a magnetic powder mainly composed of iron (Fe) is coated with an insulating film.
The magnetic powder contains 1.5% by mass or less of silicon (Si), has a volume average particle size of 80 to 300 μm, and a bulk density (ρ) of the dust core with respect to a true density (ρ ₀ ) of the magnetic powder. The density ratio (ρ / ρ ₀ :%) is a ratio of 96% or more and is used in an alternating magnetic field having a frequency of 100 to 2000 Hz.

  The dust core of the present invention has not only excellent magnetic properties but also very low iron loss when used in an alternating magnetic field in a relatively low frequency range of 100 to 2000 Hz. The reason why the powder magnetic core of the present invention exhibits such excellent characteristics is not necessarily clear, but it is considered as follows.

  First, the magnetic powder constituting the dust core of the present invention is mainly composed of Fe exhibiting ferromagnetism and has a small content of paramagnetic Si. Furthermore, the density ratio of the dust core is as high as 96% or higher. It is considered that the dust core of the present invention has developed excellent magnetic properties by the fusion of both.

  Next, since the magnetic powder constituting the powder magnetic core of the present invention has a relatively large particle size, the coercive force of the magnetic powder is reduced. As a result, the hysteresis loss of the dust core can be reduced. For example, when the magnetic powder is atomized powder, if the particle size is large, the crystal particle size is usually large, and the domain wall is easily moved when magnetized, thereby further reducing the coercive force and thus reducing the hysteresis loss.

  Note that the increase in the particle size of the magnetic powder decreases the volume specific resistance value (hereinafter simply referred to as “specific resistance” as appropriate), and causes an increase in eddy current loss. However, since the dust core of the present invention is premised on the use in the low frequency region described above, its influence on the entire iron loss is small. That is, according to the dust core of the present invention, by setting the particle size of the magnetic powder within the above-described range, the hysteresis loss is greatly reduced, and as a result, the iron loss is sufficiently reduced as a whole.

(Production method of dust core)
The present invention can be grasped not only as the powder magnetic core but also as a manufacturing method thereof.
That is, the present invention fills a mold with a magnetic core powder in which a magnetic powder having Fe as a main component, Si of 1.5% by mass or less and a volume average particle size of 80 to 300 μm is coated with an insulating coating. It is good also as the manufacturing method of the powder magnetic core which consists of a process and the shaping | molding process which press-molds the powder for magnetic cores in this metal mold | die, and obtains the powder magnetic core of this invention mentioned above.

  Next, the present invention will be described in more detail with reference to embodiments. It should be noted that the contents described in this specification, including the following embodiments, are applicable not only to the dust core of the present invention but also to the manufacturing method thereof.

(1) Magnetic powder The magnetic powder which concerns on this invention consists of a powder which contains Fe as a main component and contains Si 1.5 mass% or less. Si is an element that increases the electrical resistivity of the powder particles. A powder magnetic core made of magnetic powder containing Si has a high specific resistance and reduces eddy current loss. However, when the Si content increases, the magnetic properties (magnetic flux density) of the dust core are likely to decrease. Therefore, in the present invention, the magnetic flux density of the dust core is increased by suppressing the Si content in the magnetic powder. Here, in the case of the present invention, even if the Si content in the magnetic powder is reduced, the magnetic powder itself is covered with the insulating coating, so that the eddy current loss of the dust core does not increase rapidly. Furthermore, the eddy current loss increases in proportion to the square (f ² ) of the frequency (f) of the alternating magnetic field. However, in the case of the dust core of the present invention, the operating frequency range is low, so the eddy current loss itself is the whole. In the first place, the ratio of the total iron loss is low.

  The Si content in the magnetic powder is 1.5% by mass or less, 1.2% by mass or less, 1.0% by mass or less, 0.8% by mass or 0.5% by mass with respect to 100% by mass of the entire magnetic powder. Is preferable. From the viewpoint of enhancing the magnetic properties of the dust core, the magnetic powder is preferably pure iron powder having a purity of 99.5% or more, 99.7% or more, and further 99.8% or more. The magnetic powder may be composed of Si, the balance being Fe and inevitable impurities, and may contain a magnetic property improving element or an iron loss reducing element as appropriate. Examples of such elements include aluminum (Al), nickel (Ni), and cobalt (Co).

  The magnetic powder of the present invention comprises particles having a volume average particle size of 80 to 300 μm. Thereby, the hysteresis loss can be greatly reduced while suppressing the eddy current loss of the dust core used in the low frequency range. If the volume average particle size is too small, it is difficult to reduce the hysteresis loss. On the other hand, an excessive volume average particle size is not preferable because the specific resistance value decreases and eddy current loss increases. The lower limit of the volume average particle diameter is preferably 100 μm, 120 μm, or 150 μm. The upper limit of the volume average particle diameter is preferably 280 μm, 250 μm, or even 200 μm.

The volume average particle diameter referred to in this specification is an average value (Σd ₀ / N) of volume particle diameters (d ₀ ) determined for each of a predetermined number (N = 100) of constituent particles. The volume particle size (d ₀ ) is defined as the diameter of a solid sphere having the same mass as the mass (m) per constituent particle. That is, d ₀ = (3m / 4πρ ₀ ) ^1/3 . Here, ρ ₀ is the true density obtained from the composition of the magnetic powder.

  The particle shape of the magnetic powder is not particularly limited, but it is preferably composed of flat particles having a substantially oval shape with an average thickness of 20 to 100 μm, further 20 to 50 μm. This is because the use of magnetic powder made of flat particles can suppress the generation of eddy currents with respect to the magnetic flux flowing in the longitudinal direction of the flat powder of the powder magnetic core, thereby further reducing eddy current loss.

The thickness (h ₀ ) of the flat particles is obtained from the average ((h ₁ + h ₂ ) / 2) of the maximum thickness (h ₁ ) and the minimum thickness (h ₂ ), and the average thickness is a predetermined number (N = 100) of flatness. It is obtained as an average value (Σh ₀ / N) of the thickness (h ₀ ) obtained for each particle.

The flat particles can be produced, for example, by crushing substantially spherical powder particles by rolling, forging, or the like. When the powder particles having the above volume average particle size are formed into a substantially oval shape having an average thickness of 20 to 100 μm, the two-dimensional average particle size is about 80 to 1500 μm. The two-dimensional average particle diameter is a two-dimensional particle diameter (d ′ ₀ = (d ′ ₁ ) that is an average value of the major axis (d ′ ₁ ) and the minor axis (d ′ ₂ ) for each of a predetermined number (N) of the constituent particles. + D ′ ₂ ) / 2) and the average value (Σd ′ ₀ / N) of the predetermined number (N). The major axis is the longest diameter of the constituent particles, and the minor axis is the length measured in the direction perpendicular to the major axis direction through the midpoint of the major axis. The measurement surface of the two-dimensional particle diameter is a plane orthogonal to the thickness direction of the flat particles.

Magnetic powder, the surface area in which the specific surface area per unit mass of constituent particles average specific surface area on average 5x10 ^-3 m ² / g or less and more preferably is not more than 3x10 ^-3 m ² / g. When the average specific surface area becomes excessive, the total amount of the insulating coating covering the surface of the constituent particles increases with respect to the film thickness, which causes a decrease in the magnetic properties of the dust core. If the total amount of the insulating coating is considered constant, the film thickness becomes relatively thin. As a result, the specific resistance of the dust core is reduced, leading to an increase in eddy current loss. In any case, an increase in the average specific surface area is not preferable.

The average specific surface area as used herein is an average value of specific surface areas determined for a predetermined number (N = 100) of constituent particles. The specific surface area is determined by (ΣS ₀ ′) / N. Here, S ₀ ′ = S / (V · ρ) = 4πr ² / (4πr ³ ρ / 3) = 3 / (ρ · r), r: powder radius, ρ: powder constant.

  The closer the shape of the constituent particles of the magnetic powder is to a sphere, the smaller the surface area per unit mass. An example of such magnetic powder is atomized powder. In particular, water gas atomized powder having a low cooling rate and further gas atomized powder are preferred because water-atomized powder having a low cooling rate can be obtained as particles having a nearly spherical shape.

  The magnetic powder preferably has an average crystal grain size of the constituent particles of 50 μm or more, further 200 μm or more. The larger the crystal grain size of the constituent particles, the easier the movement of the domain wall and the lower the coercive force, so it is easier to reduce the hysteresis loss. The average crystal grain size here is an average value of crystal grain sizes obtained for a predetermined number (N = 100) of constituent particles. The crystal grain size per each constituent particle was obtained from image analysis of all phase observation.

  The crystal grain size of the constituent particles of the magnetic powder is larger as the crystal grows more easily. Taking atomized powder as an example, water gas atomized powder having a low cooling rate and gas atomized powder are more preferable than water atomized powder having a large cooling rate. From both the specific surface area and the crystal grain size described above, it is very preferable that the magnetic powder is made of gas atomized powder.

  In addition, even if magnetic powder consists of gas atomized powder, magnetic powder does not necessarily need to be the form at the time of the gas atomization. In other words, the magnetic powder may be a powder made of the above-described flat particles obtained by rolling a gas atomized powder. By subjecting the gas atomized powder to a rolling process or the like, the specific surface area of the constituent particles can be slightly increased as compared with the gas atomized powder before the process. However, the specific surface area of the constituent particles made of gas atomized powder is much smaller than that of water atomized powder whose particle surface is distorted.

  Furthermore, considering the case of high-pressure molding of magnetic powder, it is preferable to use smooth particles having a surface shape such as gas atomized powder, in addition to the above-mentioned reasons, because eddy current loss and hysteresis loss can be further reduced. . This is because, when the magnetic powder is pressed, if the surface of the constituent particles is smooth, the aggression between the particles in contact with each other decreases. For example, it is possible to avoid a situation in which a projection or the like of a certain particle pierces another adjacent particle and the insulating coating formed on the surface of each particle is destroyed. As a result, it is easy to obtain the originally planned specific resistance, and it is easy to reduce the eddy current loss of the dust core.

  When the surface of the constituent particles is smooth, it is possible to suppress large strain and stress from being applied only to a part of the constituent particles, so that the increase in coercive force and hysteresis loss due to residual strain and residual stress is reduced. Such a situation is the same even when the magnetic powder is composed of the above-described flat particles.

  If an example of the manufacturing method of the atomized powder mentioned above is shown, gas atomized powder will be obtained by the gas spray atomization method which sprays gas to the molten metal flow of a predetermined composition, and is atomized. Water atomized powder is obtained by a water spray atomization method in which water is sprayed on the molten metal stream to atomize it.

  Of course, a powder other than the atomized powder described above may be used as the magnetic powder. For example, pulverized powder obtained by pulverizing an alloy ingot with a ball mill or the like may be used. When pulverized powder is used, the crystal grain size can be increased by subsequent heat treatment (for example, heat treatment at 800 ° C. or higher in an inert atmosphere (N 2 gas, Ar gas, etc.), or rolling treatment. For example, it is possible to obtain a powder composed of flat particles having a relatively smooth surface shape.

(2) Insulating coating The insulating coating covering the surface of the magnetic powder increases the specific resistance of the dust core and reduces its eddy current loss. The thicker the insulation coating, the greater the specific resistance of the dust core. However, if the insulating coating is too thick, the magnetic flux density of the dust core will decrease. From the viewpoint of ensuring the magnetic flux density and specific resistance of the dust core, the film thickness is preferably 10 to 100 nm, more preferably 10 to 50 nm. In terms of the mass ratio, the insulating coating is preferably 0.1 to 0.3 mass% when the entire dust core is 100 mass%. In terms of volume%, the insulating coating is preferably 1 to 3% by volume, and more preferably 1.5 to 2.5% by volume, when the entire powder magnetic core is 100% by volume. Needless to say, it is ideal that the insulating coating is originally formed for each of the powder particles. However, in practice, naturally, an insulating film may be formed around several particles in a solid state, and such a state is also assumed by the present invention.

  The insulating coating includes an oxide coating, a phosphate coating, and a resin coating (a coating made of silicone resin, amide resin, imide resin, phenol resin, etc.). Any of the insulating coatings of the present invention may be used, but in view of heat resistance, an oxide coating or a phosphate coating is preferable.

As the oxide film, in addition to a typical SiO ₂ film, an Al ₂ O ₃ film, a TiO ₂ film, ZrO ₂ , a composite oxide insulating film thereof (FeSiO ₃ , FeAl ₂ O ₄ , NiFe ₂ O _4, etc.) Coating). When the magnetic powder contains 0.3 to 1.5 mass% of Si, the SiO ₂ film can also be formed by surface oxidation of the magnetic powder. However, in order to reliably provide a predetermined amount of the SiO ₂ coating on the surface of the magnetic powder, it is preferable to use a silicone resin.

The silicone resin is a synthetic resin having a siloxane bond. The silicone resin film itself functions as a binder or an insulating film. However, when it is heated at a high temperature (700 to 900 ° C.), it changes to a SiO ₂ film excellent in heat resistance. The heating of the silicone resin is preferably performed after the powder magnetic core is formed. By heating after molding, together with the formation of the SiO ₂ film, residual strain or residual stress in the powder compact (magnetic powder) introduced during molding is removed, and a dust core with less coercive force and hysteresis loss is obtained. It is because it is obtained.

By the way, in order to form the SiO ₂ film directly and stably on the surface of the magnetic powder, it is better that the magnetic powder contains 0.8 mass% or more of Si. The reason is not clear, but it seems that the silicone resin is easily chemically adsorbed to Si atoms on the surface of the magnetic powder.

On the other hand, when the Si content in the magnetic powder is low (when the magnetic powder is pure iron powder, for example), the SiO ₂ coating directly coated on the surface of the magnetic powder is durable (not only deteriorated over time but also destroyed during molding) Durability) is not necessarily sufficient. Here, the case where the amount of Si is small is specifically a case where the amount of Si is 0.8% by mass or less, further 0.5% by mass or less when the entire magnetic powder is 100% by mass.

In order to stably form a silicone resin film (or SiO ₂ film) on the surface of the magnetic powder, the present inventor has newly proposed that it is preferable to provide a phosphate film on the surface of the magnetic powder as the base treatment. I found it. Therefore, the insulating coating of the present invention has a first insulating layer made of a phosphate coating and a second insulating made of a silicone resin covering the first insulating layer when the amount of Si in the magnetic powder is 0.8% or less. It is preferable that it is formed of layers.

  The insulating film composed of the first insulating layer and the second insulating layer is very excellent in heat resistance. Even when the powder magnetic core made of magnetic powder coated with this insulating coating is annealed at a high temperature of 400 ° C. or higher, 450 ° C. or higher, or even 500 ° C. or higher, the insulating coating is completely Will not be destroyed. That is, the dust core exhibits a sufficient specific resistance even after annealing. Such heat resistance of the insulating coating is very important even in a dust core used in a relatively low frequency region as in the present invention. Even if the powder core is annealed to remove residual strain and residual stress accumulated inside it, and the hysteresis loss of the powder core is reduced, the insulation film is greatly destroyed during the annealing. This is because, if the specific resistance decreases rapidly, the iron loss increases even though the powder magnetic core is used in a low frequency range. Therefore, it is preferable that the heat resistance of the insulating coating is higher even in the case of a dust core used in a relatively low frequency region as in the present invention. If the heat resistance of the insulating coating is high, annealing can be performed at a higher temperature while suppressing a decrease in specific resistance. This is because residual strain and the like accumulated inside the dust core are more easily removed, and hysteresis loss can be further reduced.

Furthermore, the present inventor has newly developed an insulating film having excellent heat resistance, in which oxide particles are combined with the first insulating layer and the second insulating layer. The following can be considered as a method of combining oxide particles. One is a case where the second insulating layer is formed of a composite insulating layer in which oxide particles are dispersed in the silicone resin. The other is a case where a third insulating layer mainly composed of oxide particles is further provided on the second insulating layer formed of the silicone resin coating alone or a composite insulating layer thereof. However, in any case, what is important is that the specific resistance of the powder magnetic core is stably maintained even after heating, and the eddy current loss is suppressed, not the structure or form of the insulating coating itself. . As an actual problem, since the film thickness of the insulating film covering the surface of the magnetic powder of about 100 μm is very thin, about 100 nm, it is difficult to clearly specify the structure of the insulating film. In addition, when the powder magnetic core immediately after molding is annealed or used in a high-temperature atmosphere, it is easily expected that the form of the insulating coating covering the magnetic powder will greatly change from the initial state. . From this point of view, the structure and form of the insulating coating itself are not meaningful, and as a result, an insulating coating that can ensure a sufficient specific resistance is sufficient.
The first insulating layer, the second insulating layer, the third insulating layer, and the oxide particles described above will be described in more detail.

(A) 1st insulating layer The phosphate film which is a 1st insulating layer does not ask | require the kind. For example, as disclosed in Patent Document 1, the first insulating layer may be a phosphate coating formed by bringing a magnetic powder into contact with a predetermined concentration of phosphoric acid to form iron phosphate on the surface of the magnetic powder. Further, an Mg— (Fe) —B—P—O-based insulating layer as described in Patent Document 6 may be used.

  However, the present inventors have newly developed a phosphate coating that is more excellent in heat resistance, unlike these phosphate coatings. Then, it has been confirmed that when this phosphate coating is used as the first insulating layer and the above-described second insulating layer and further the third insulating layer are formed thereon, an insulating coating having extremely excellent heat resistance can be obtained. . This first insulating layer has a 6-coordinate ion radius defined by Shannon (R, D) and at least 0.073 nm defined by Shannon (R, D) and at least a first element group consisting of phosphorus (P) and oxygen (O) 2 And a second element capable of generating a cation higher than the valence. The first insulating layer may contain Fe dissolved from the magnetic powder. Further, a borophosphate coating containing boron (B) (in this specification, such a coating is also included in the “phosphate coating”) is more excellent in heat resistance than a simple phosphate coating.

By the way, the first insulating layer in this case is considered to be an amorphous phosphate glass coating. Therefore, it is preferable to appropriately extract and select the second element according to the Zacca Raisen rule, which is a rule relating to a network forming body (network forming ion) and a network modifying body (network modifying ion) constituting the glass. An amorphous glassy insulating layer composed of a network-forming body composed of a first element group and a network-modified body that is a second element having a large ionic radius is difficult to crystallize, increases in viscosity, and sinters. -Aggregation hardly occurs. The reason why the cation of the second element is divalent or higher is that monovalent cations (for example, Na ⁺ , K ⁺ ) are easy to react with water, and it is preferable that they do not exist in consideration of long-term stability. It is. The reason why Shannon's ionic radius is used as the ionic radius of the second element is that it is currently most widely used. Among them, the reason why the six-coordinate ionic radius is used is that the ionic radius differs depending on the number of coordination, and thus the comparison target is clarified. And when this inventor examined various elements, when the ion radius of the 2nd element was 0.073 nm or more, it discovered that the coating film expressed the outstanding heat resistance. On the contrary, if the ion radius is less than 0.073 nm, the heat resistance is at the conventional level, and the heat resistance cannot be improved. The ionic radius is more preferably 0.075 nm or more, and further preferably 0.080 nm or more. In addition, the upper limit of the ion radius is preferably 0.170 nm or less in consideration of handleability and the like.

  Specific examples of such a second element include an alkaline earth metal element and a rare earth element (RE). Alkaline earth metal elements include beryllium (Be), Mg, Ca, Sr, barium (Ba), and radium (Ra), but Be and Mg have a six-coordinate ion radius of less than 0.073 nm. Will be excluded. In consideration of handleability, safety, environmental friendliness, etc., Ca or Sr is preferable as the second element from the alkaline earth metal element. The rare earth elements include scandium (Sc), Y, lanthanoid elements, and actinoid elements. Similarly, Y is preferable in consideration of handling properties and the like. Other elements that can be the second element include lanthanoids (La to Lu) and bismuth (Bi). The ionic radii of each of these elements are shown in Table 6 together with the valence for reference. Needless to say, these second elements may be not only one kind of element but also a plurality of kinds of elements. Thus, an insulating film (first insulating layer) excellent in heat resistance constituting the first layer of the present invention was obtained.

(B) Second insulating layer The second insulating layer is formed on the first insulating layer and is made of silicone resin. Due to the presence of the second insulating layer, an insulating coating of the present invention that exhibits higher heat resistance than the first insulating layer alone was obtained. Although the detailed mechanism at which this excellent effect is manifested is unknown at present, the heat resistance is not improved by mere duplication of the insulating layer, but the insulating film has a synergistic effect between the first insulating layer and the second insulating layer. It is thought that the heat resistance was further improved.

  The silicone resin is preferably contained in a proportion of 0.05 to 0.8% by mass, further 0.1 to 0.3% by mass, based on 100% by mass of the entire magnetic powder. This is because if the amount of silicone resin is too small, the effect of improving the heat resistance of the insulating coating is small, and if the amount of silicone resin is excessive, the magnetic flux density of the dust core is reduced, which is not preferable. The amount of the silicone resin is substantially the same even when the oxide particles described later are included, but the ratio may be slightly varied depending on the presence or absence of the oxide particles.

  Silicone resin refers to a polyorganosiloxane containing a monofunctional (M unit), bifunctional (D unit), trifunctional (T unit), or tetrafunctional (Q unit) siloxane unit in the molecule. . This silicone resin is characterized in that it has a higher crosslink density than silicone oil or silicone rubber, and is hard when cured. Silicone resins are roughly classified into straight silicone resins whose components are composed solely of silicone and silicone-modified organic resins that are copolymers of silicone components and organic resins. The silicone resins used in the present invention are any of them. But it ’s okay.

  Straight silicone resins are broadly classified into MQ resins and DT resins, and any of them may be used. Examples of the silicone-modified organic resin include alkyd modification, epoxy modification, polyester modification, acrylic modification, and phenol modification.

  Silicone resins include a type that cures by heating (heat curing type) and a type that cures even at room temperature (room temperature curing type). The curing mechanism of thermosetting silicone resin is roughly divided into dehydration condensation reaction, addition reaction, peroxide reaction, etc., and the curing mechanism of room temperature curable silicone resin is based on deoxime reaction and dealcoholization reaction. There is something. Any of these may be used for the silicone resin used in the present invention.

  Specific examples of such silicone resins include, for example, SH 805, SH 806A, SH 840, SH 997, SR 620, SR 2306, SR 2309, SR 2310, SR 2316, DC12577, SR2400, manufactured by Toray Dow Corning Silicone. SR2402, SR2404, SR2405, SR2406, SR2410, SR2411, SR2416, SR2420, SR2107, SR2115, SR2145, SH6018, DC-2230, DC3037, QP8-5314, and the like. Also available from Shin-Etsu Chemical Co., Ltd. , KR101-10, KR120, KR105, KR271, KR282, KR311, KR211, KR212, KR216, KR213, KR217, KR9218, SA-4, KR206, ES1001N, ES1002T, ES1004, KR9706, KR5203, KR5221 and so on. Of course, silicone resins other than these brands may be used.

  The silicone resin used in the present invention may be a finely divided silicone resin dispersed in a solvent to form a colloidal shape, or may be a silicone resin obtained by modifying the raw material. Furthermore, you may use the silicone resin which mixed the 2 or more types of silicone resin from which a kind, molecular weight, and a functional group differ in a suitable ratio.

  By the way, in the case of the second insulating layer in which oxide particles are dispersed in such a silicone resin, as described above, the heat resistance of the insulating coating is further improved. The reason for this is not necessarily clear, but it can be considered as follows.

As a result of various experiments conducted by the present inventor, the treatment liquid obtained by adding fine oxide particles (SiO ₂ ) to the silicone resin solution has higher fluidity than the silicone resin solution alone. When the treatment liquid to which the oxide particles are added is used, the second insulating layer can be easily formed on the surface of the magnetic powder on which the first insulating layer is formed. This is considered to have contributed to the uniformity of the second insulating layer formed on the first insulating layer, and consequently the uniformity of the insulating film. Here, the uniformity of the insulating coating is required because, for example, when the coating state by the insulating coating is non-uniform, the thin film portion is preferentially attacked, and the magnetic powder particles are This is because direct contact, further sintering, and the like occur, and the specific resistance value of the dust core decreases.

  In addition, the oxide particles are very excellent in heat resistance (high temperature insulation). It is considered that the oxide particles are present uniformly on the surface of the magnetic powder, are interposed between the constituent particles, and their direct contact is actively suppressed, and the heat resistance of the insulating coating of the present invention is further increased. It is done.

As long as the oxide which comprises this oxide particle has high insulation and heat resistance, the kind will not ask | require. Examples of such oxides include SiO ₂ , Al ₂ O ₃ , ZrO ₂ , MgO, and composite oxide spinels and garnets. In view of availability, cost, etc., the oxide particles are preferably one or more oxides of Si, Zr, Mg, or Al. The oxide particles may be oxides of alloys of two or more metals. A colloidal oxide may be used.

  The average particle diameter of the oxide particles is preferably 100 nm or less, more preferably 70 nm or less. On the other hand, considering the manufacturability and availability of the oxide particles, the lower limit of the particle size is preferably 50 nm, more preferably 30 nm. In particular, the particle size ratio (d / D) between the volume average particle size (D) of the magnetic powder and the particle size (d) of the oxide particles is 1/10 to 1/100000, or 1/100 to 1/10000. Preferably there is.

  The mixing ratio of the oxide particles to the silicone resin (oxide particles / silicone resin) is preferably 0.1 to 10, and more preferably 0.3 to 3 by weight.

  In addition, let the average particle diameter of the oxide particle said by this invention be the number average particle diameter of the fixed direction diameter observed with the microscope.

(C) 3rd insulating layer It is suitable when the 3rd insulating layer mainly consisting of the oxide particle mentioned above is formed on the 2nd insulating layer.

The second insulating layer which is the lower layer of the third insulating layer may be an insulating layer made of only a silicone resin, or a composite insulating layer in which oxide particles are dispersed in the silicone resin. In this case, the reason why the heat resistance of the insulating coating of the present invention is improved is not necessarily clear, but at present, it is considered to be almost the same as the reason described above.
As a method for forming the third insulating layer mainly composed of oxide particles on the second insulating layer, mechanical mixing, a method of adding oxide particles in advance to various coating solutions, and the like are conceivable.

  By the way, when considering the powder for the magnetic core, regardless of whether the oxide particles are mixed in the second insulating layer or dispersed on the second insulating layer, the oxide particles are 100% by mass as a whole, It is preferable that it is contained at a ratio of 0.05 to 0.5 mass%, further 0.08 to 0.3 mass%. This is because if the amount of oxide particles is too small, the effect of improving the heat resistance of the insulating coating is small, and if the amount of oxide particles is excessive, the magnetic flux density of the dust core is reduced, which is not preferable. The amount of silicone resin at this time is as described above.

  The insulating coating of this invention should just have the 1st insulating layer and the 2nd insulating layer which were mentioned above at the time of a coating | cover. Furthermore, from the stage of coating, both layers may be integrated as a whole to form a single insulating film as a whole. In any case, the insulating coating does not necessarily have to maintain the initial coating state. The insulating coating may be one in which the first insulating layer and the second insulating layer are changed, altered, or transformed by subsequent heating or the like. The dust core obtained as such a product is also included in the scope of the present invention.

  Note that the above-described insulating coating is not necessarily premised on the case where it is exposed to a high temperature state by annealing or the like. It may be a case where it is used in an unheated state or at room temperature. In that case, needless to say, the insulating coating of the present invention stably exhibits a very high insulating property (high resistance value).

(3) Formation method of insulating coating (manufacturing method of magnetic core powder)
The insulating coating is formed on the surface of the magnetic powder by an appropriate method according to the type. For example, in the case of a silicone resin coating, it is formed by adding a silicone resin solution to magnetic powder and stirring, kneading, or the like. Thereby, the magnetic core powder in which the surface of the magnetic powder is coated with the silicone resin is obtained. In the case of the SiO ₂ coating, the magnetic powder coated with the silicone resin is formed by heating at high temperature. In addition, an oxide film can be formed on the surface of the magnetic powder itself by oxidizing it in an appropriate oxidizing atmosphere. Such a method for forming an insulating film is well known in the art. Below, the formation method of the insulating film which consists of a 1st insulating layer mentioned above, a 2nd insulating layer, and also a 3rd insulating layer is demonstrated.

  This insulating film forming method (even if considered as a magnetic core powder manufacturing method) basically comprises a first insulating layer forming step and a second insulating layer forming step. Of course, when the insulating film includes the third insulating layer, a third insulating layer forming step of forming the third insulating layer on the second insulating layer of the magnetic powder is provided.

(A) First insulating layer forming step The first insulating layer forming step includes a contact step in which the first coating treatment liquid is brought into contact with the magnetic powder, and a drying step in which the magnetic powder is subsequently dried.

  First, the first coating treatment liquid is a solution containing phosphoric acid and the second element referred to in the present invention. This is not limited to an aqueous solution, but may be a solution using an organic solvent such as ethanol, methanol, isopropyl alcohol, acetone, glycerin or the like. In any case, the first coating treatment liquid is prepared by mixing phosphoric acid in these solvents and dissolving a compound or salt of an alkaline earth metal element or a rare earth element. In addition, surfactants effective for improving wettability with magnetic powder (for example, Fe powder) and forming a uniform film, rust preventive agent for preventing oxidation of magnetic powder (for example, Fe powder), etc. May be appropriately added thereto.

  The contact process includes various methods (processes) such as a solution spraying method (spraying process) in which the first coating treatment liquid is sprayed on the material to be treated and a solution immersion method (immersion process) in which the first coating treatment liquid is immersed in the first coating treatment liquid. Can be done. The solution spraying method and the solution dipping method can be processed in large quantities, and are industrially effective methods. The method is not limited to these methods, and a thin and uniform insulating film may be formed on the surface of the material to be processed using an electrochemical reaction, such as plating. In this case, since the surface of the material to be treated coated with the insulating coating is electrically insulated, the uncovered surface portion (exposed portion) naturally reacts preferentially with the first coating treatment liquid. To do. As a result, the surface of the material to be treated (magnetic powder) is sequentially coated, and the entire surface of the material to be treated is uniformly coated without pinholes.

  By changing the concentration of the first coating treatment liquid used in this contact step, it is possible to adjust the film thickness of the insulating coating to be formed. When the concentration of the first coating treatment liquid is increased, a thick insulating film is obtained, and when the concentration is reduced, a thin insulating film is obtained. Of course, it may be formed by overlapping thin films to form a thick insulating film as a whole. Further, the contact time between the material to be treated and the first coating treatment liquid may also affect the film thickness. However, in reality, the reaction time between the two may be short, and once the surface of the material to be treated is coated, the change in film thickness is small even if the contact time is increased.

  The drying process is a process of diverging excess first coating treatment liquid and its solvent adhering to the material to be treated. This drying step may be natural drying as well as heat drying. However, heat drying (heat drying step) is preferable in order to stably and quickly fix the insulating coating on the surface of the material to be processed. The heating temperature is preferably about 80 to 350 ° C., and the heating time is preferably about 10 to 180 minutes. The heating atmosphere may be vacuum degassing, nitrogen, or air.

(B) Second insulating layer forming step The second insulating layer forming step is a step of forming a second insulating layer made of silicone resin on the first insulating layer of the material to be processed. At this time, in order to uniformly form the second insulating layer, it is preferable to use a second coating treatment liquid in which a silicone resin is dissolved or dispersed in a solvent or the like. Examples of such solvents include alcohol solvents such as ethanol and methanol, ketone solvents such as acetone and methyl ethyl ketone, and aromatic solvents such as benzene, toluene, xylene, phenol, and benzoic acid. , Petroleum solvents such as ligroin and kerosene. In particular, an aromatic solvent that easily dissolves the silicone resin is preferable. If the silicone resin is soluble or dispersible, water may be used as a solvent. The concentration of the treatment liquid (second coating treatment liquid) in which a silicone resin is dissolved in a solvent may be determined in consideration of ease of construction, drying time, and the like.

  The second insulating layer forming step also includes a contact step in which the second coating treatment liquid is brought into contact with the magnetic powder on which the first insulating layer is formed, and then a drying step in which it is dried. This is the same as the forming process. The contents of the contact process and the drying process are substantially the same. However, when a volatile solvent (such as ethanol) is used as the solvent for the silicone resin, the solvent will spontaneously volatilize and the drying process will be substantially completed, without needing to dry by heating. . In the case where oxide particles are mixed in the second insulating layer, the oxide particles may be added together with the silicone resin in a solvent and stirred and mixed.

(C) Third insulating layer forming step The third insulating layer forming step is a step of forming a third insulating layer made of oxide particles on the second insulating layer of the material to be processed.

  The third insulating layer forming step also includes the contact step of bringing the third coating treatment liquid into contact with the magnetic powder on which the second insulating layer is formed, and the subsequent drying step of drying the first insulating layer. This is the same as the forming step and the second insulating layer forming step. In addition, the contents of the contacting step and the drying step can be substantially the same as those cases.

(4) Manufacturing Method of Dust Core A manufacturing method of a dust core includes a filling step of filling the above-described magnetic core powder into a molding die (simply referred to as “mold”), and filling the filled magnetic core powder. It basically consists of a molding process for pressure molding. This molding process may be performed in a magnetic field or in a non-magnetic field, but in any case, it greatly affects the magnetic properties of the dust core. In particular, the molding pressure greatly affects the increase in the density of the dust core and the accompanying increase in the magnetic flux density of the dust core. However, when the molding pressure is increased, galling is likely to occur between the inner surface of the mold and the magnetic core powder, the pressure is excessively increased, and the mold life is extremely reduced. For this reason, in the conventional molding method, it was actually difficult to increase the molding pressure.

  The present inventor has established an epoch-making warm high-pressure molding method and has solved these problems. In this warm high-pressure molding method, the filling step is a step of filling a metal mold coated with a higher fatty acid-based lubricant with a magnetic core powder, and the molding step is performed between the magnetic core powder and the inner surface of the mold. This is a warm high pressure forming process in which a metal soap film is formed.

  For example, when the magnetic powder is a powder containing Fe as a main component and the higher fatty acid-based lubricant is lithium stearate, the outer surface of the dust core in contact with the inner surface of the mold has excellent lubricity. A metal soap film made of iron stearate is formed. The presence of this iron stearate film does not cause galling or the like, and the dust core is taken out from the mold with a very low pressure. In addition, the life of the mold can be extended.

Next, this manufacturing method will be described in more detail.
(A) Filling step In the filling step, it is necessary to apply a higher fatty acid-based lubricant to the inner surface of the mold (application step).
The higher fatty acid lubricant to be applied is preferably a metal salt of a higher fatty acid in addition to the higher fatty acid itself. Examples of the higher fatty acid metal salts include lithium salts, calcium salts, and zinc salts. In particular, lithium stearate, calcium stearate, and zinc stearate are preferable. In addition, barium stearate, lithium palmitate, lithium oleate, calcium palmitate, calcium oleate, and the like can also be used.

  This coating step is preferably a step of spraying a higher fatty acid lubricant dispersed in water or an aqueous solution into a heated mold.

  When the higher fatty acid lubricant is dispersed in water or the like, it becomes easy to uniformly spray the higher fatty acid lubricant on the inner surface of the mold. Furthermore, when it is sprayed into a heated mold, the moisture quickly evaporates, and the higher fatty acid-based lubricant can be uniformly attached to the inner surface of the mold. The heating temperature of the mold at that time needs to take into consideration the temperature of the molding process described later, but it is sufficient to heat it to 100 ° C. or higher, for example. However, in order to form a uniform film of a higher fatty acid-based lubricant, it is preferable that the heating temperature be lower than the melting point of the higher fatty acid-based lubricant. For example, when lithium stearate is used as the higher fatty acid-based lubricant, the heating temperature is preferably less than 220 ° C.

  When the higher fatty acid-based lubricant is dispersed in water or the like, when the total weight of the aqueous solution is 100% by mass, the higher fatty acid-based lubricant is 0.1 to 5% by mass, If it is contained at a ratio of 2% by mass, a uniform lubricating film is preferably formed on the inner surface of the mold.

  Further, when the higher fatty acid-based lubricant is dispersed in water or the like, if the surfactant is added to the water, the higher fatty acid-based lubricant can be uniformly dispersed. Examples of such surfactants include alkylphenol surfactants, polyoxyethylene nonylphenyl ether (EO) 6, polyoxyethylene nonyl phenyl ether (EO) 10, anionic nonionic surfactants, and boric acid. Ester-based Emulbon T-80 or the like can be used. Two or more of these may be used in combination. For example, when lithium stearate is used as a higher fatty acid-based lubricant, three types of polyoxyethylene nonylphenyl ether (EO) 6, polyoxyethylene nonylphenyl ether (EO) 10 and borate ester Emulbon T-80 are available. It is preferable to use a surfactant at the same time. This is because the dispersibility of lithium stearate in water or the like is further activated when added in combination as compared with the case of adding only one of them.

  In order to obtain an aqueous solution of a higher fatty acid-based lubricant having a viscosity suitable for spraying, when the total amount of the aqueous solution is 100% by volume, the ratio of the surfactant is preferably 1.5 to 15% by volume.

In addition, a small amount of an antifoaming agent (for example, a silicon-based antifoaming agent) may be added. This is because when the foaming of the aqueous solution is severe, it is difficult to form a uniform higher fatty acid-based lubricant film on the inner surface of the mold when sprayed. The addition ratio of the antifoaming agent may be, for example, about 0.1 to 1% by volume when the total volume of the aqueous solution is 100% by volume.
The higher fatty acid-based lubricant particles dispersed in water or the like preferably have a maximum particle size of less than 30 μm.

When the maximum particle size is 30 μm or more, the higher fatty acid-based lubricant particles are likely to precipitate in the aqueous solution, and it becomes difficult to uniformly apply the higher fatty acid-based lubricant to the inner surface of the mold.
Application of the aqueous solution in which the higher fatty acid-based lubricant is dispersed can be performed using, for example, a spray gun for painting, an electrostatic gun, or the like.

  In addition, as a result of investigating the relationship between the coating amount of the higher fatty acid-based lubricant and the extraction pressure of the powder molded body, the present inventor has found that the higher fatty acid-based lubricant has a film thickness of about 0.5 to 1.5 μm. It has been found that it is preferable to apply a lubricant to the inner surface of the mold.

(B) Molding process Although details are not clear, it is considered that the above-mentioned metal soap film is generated by a mechanochemical reaction in this process.

  That is, by the reaction, the magnetic core powder (particularly, the insulating coating) and the higher fatty acid-based lubricant are chemically bonded, and the metal soap coating (for example, the higher fatty acid iron salt coating) is formed into the magnetic core powder. Formed on the surface. This metal soap film is firmly bonded to the surface of the powder molded body and exhibits a lubricating performance far superior to the higher fatty acid-based lubricant adhered to the inner surface of the mold. As a result, it is considered that the frictional force between the contact surfaces of the inner surface of the mold and the outer surface of the powder molded body is remarkably reduced, and high pressure molding is possible.

  Each particle of the magnetic core powder is coated with an insulating film, but an element that promotes the formation of a metal soap film in the insulating film (for example, Fe, which is the main component of the magnetic powder, or the second element referred to in the present invention). ) As a main component, it is considered that a metal salt film of higher fatty acid (metal soap film) is formed based on them.

  “Warm” in the molding process means that the molding process is performed under an appropriate heating condition according to each situation. However, in order to promote the reaction between the magnetic core powder and the higher fatty acid-based lubricant, it is generally preferable that the molding temperature is 100 ° C. or higher. Moreover, in order to prevent destruction of the insulating coating and alteration of the higher fatty acid-based lubricant, it is generally preferable that the molding temperature is 200 ° C. or lower. And it is more suitable when molding temperature shall be 120-180 degreeC.

  The degree of "pressurization" in the molding process is also appropriately determined according to the desired properties of the powder magnetic core, the magnetic core powder, the insulating coating, the type of the higher fatty acid-based lubricant, the mold material, the inner surface properties, etc. However, when this production method is used, molding can be performed under a high pressure exceeding the conventional molding pressure. For this reason, for example, the molding pressure can be set to 700 MPa or more, 785 MPa or more, 1000 MPa or more, or 2000 MPa. The higher the molding pressure, the higher the density magnetic core. However, in consideration of the life and productivity of the mold, the molding pressure is preferably 2000 MPa or less, more preferably 1500 MPa or less.

  In addition, when this inventor used this warm high-pressure shaping | molding method, it has confirmed by experiment that a shaping | molding pressure is about 600 Mpa, and the extraction pressure becomes the maximum, and if it exceeds it, it will rather fall. And even when the molding pressure was changed in the range of 900 to 2000 MPa, the extraction pressure was maintained at a very low value of about 5 MPa. This also shows how the metal soap film formed by the warm high pressure forming method, which is one of the production methods of the present invention, is excellent in lubricity. It can be seen that this warm high-pressure forming method is optimal as a method for manufacturing a dust core that requires high density by high-pressure forming. Such a phenomenon can occur not only when lithium stearate is used as the higher fatty acid-based lubricant but also when calcium stearate or zinc stearate is used.

(C) Heating process, annealing process It is suitable for the manufacturing method of the powder magnetic core of this invention to be further equipped with the heating process or annealing temperature which heats the powder compact obtained after the said shaping | molding process. The heating temperature and heating time of the heating process and annealing temperature may be appropriately selected according to the specifications of the dust core. In this respect, there is no essential difference between the heating process and the annealing temperature, but both have different purposes.

The heating step is a step for heating the powder molded body obtained after the molding step to make the silicone resin coating a SiO ₂ coating when the insulating coating is a silicone resin coating. On the other hand, the annealing process is a process for removing strain (residual strain) and stress (residual stress) accumulated in the powder molded body obtained after the molding process for the purpose of reducing coercive force and hysteresis loss. . However, the heating process may also serve as the annealing temperature by appropriately selecting the heating temperature, the heating time, and the heating atmosphere, and the annealing process may also serve as the heating process.

  In addition, the insulating film having a multilayer structure including the first insulating layer made of a phosphate film and the second insulating layer made of a silicone resin that covers the first insulating layer is remarkably excellent in heat resistance as described above. It is preferable to perform an annealing step on the powder compact provided with this insulating film, since hysteresis loss is sufficiently reduced while suppressing reduction in eddy current loss. The composition of the magnetic powder on which this insulating film is formed is not particularly limited, but as described above, it is particularly effective when the amount of Si in the magnetic powder is pure iron powder of 0.8% or less.

  In the heating / annealing step, heating is preferably performed at 300 to 900 ° C., further 500 to 700 ° C. for 0.1 to 10 hours, and further 0.5 to 2.0 hours. The atmosphere at this time is preferably an inert atmosphere. Again, the insulating coating can change at least partially from its original state by performing such a heating or annealing step. However, even the dust core after such a heating step or annealing step is the dust core of the present invention.

(5) Powder magnetic core The powder magnetic core of the present invention is obtained by molding the above-described magnetic core powder at a high density, and the ratio of the bulk density (ρ) of the powder magnetic core to the true density (ρ ₀ ) of the magnetic powder. The density ratio (ρ / ρ ₀ ) is 96% or more. Such a high-density dust core generates a very high magnetic flux density. This is equivalent to or better than conventional electromagnetic steel sheets used for high performance motors and the like. The higher the density ratio is 97% or more, 98% or more, and 99% or more, it is preferable because a higher magnetic flux density can be obtained. Further, the magnetic powder constituting the dust core of the present invention has a relatively small amount of Si. Accordingly, the dust core of the present invention exhibits a higher magnetic flux density compared to a dust core using a general magnetic powder such as Fe-3% Si.

  In the present invention, the magnetic properties of the dust core are indirectly indicated by the density ratio. For example, the magnetic properties of the dust core are directly measured by the magnetic flux density when placed in a magnetic field of a specific strength. You may specify. In addition, although there is a magnetic permeability as an index for indicating the magnetic characteristics of the dust core, the magnetic permeability is not constant as understood from a general BH curve. The magnetic properties of the dust core are evaluated by the density.

The specific magnetic field may be appropriately selected from 1 to 20 kA / m. For example, 2 kA / m, 5 kA / m, 8 kA / m, 10 kA / m, 16 kA / m, 20 kA / m, and the like. The magnetic flux density generated when the dust core is placed in these magnetic fields can be expressed as B _2k , B _5k , B _8k , B _10k , B _16k , B _20k, etc., respectively, and the dust core of the present invention can be evaluated. . In the case of the dust core of the present invention, for example, B _20k ≧ 1.7T, 1.8T, 1.9T or even 2.0T, B _10k ≧ 1.5T, 1.6T, 1.7T or 1.8T. High magnetic flux density is demonstrated.

  Note that if the saturation magnetization Ms is small, a large magnetic flux density cannot be obtained in a high magnetic field. However, in the dust core of the present invention, for example, the saturation magnetization Ms ≧ 1.9T in a 1.6 MA / m magnetic field. Since it is 2.0 T or more, a stable high magnetic flux density can be obtained even in a high magnetic field.

  Further, there is a coercive force as an index of the magnetic characteristics of the dust core. The smaller the coercive force, the better the followability of the dust core to the AC magnetic field, and the smaller the hysteresis loss. In the case of the dust core of the present invention, the coercive force bHc can be 150 A / m or less, 130 A / m or less, or even 100 A / m or less. The coercive force bHc in this specification is defined as a value measured from a magnetization curve at a maximum magnetic field of 2 kA / m.

  Incidentally, the coercive force of the dust core tends to decrease as the amount of Si in the magnetic powder increases. From this viewpoint, the amount of Si in the magnetic powder according to the present invention is preferably 0.8 to 1.5% by mass.

  Next, electrical characteristics (that is, specific resistance) of the dust core will be described. The specific resistance is, in principle, an eigenvalue for each dust core that does not depend on the shape, and if the dust core has the same shape, the larger the specific resistance, the more the eddy current loss can be reduced. The specific resistance varies depending on the type of insulating film, the amount of insulating film (film thickness), the presence or absence of annealing, etc., but if the specific resistance is 50 μΩm or more, 100 μΩm or more, 300 μΩm or more, or even 1000 μΩm or more, sufficient eddy current loss Can be reduced.

  Note that the relationship between the specific resistance of the dust core and the magnetic flux density varies depending on the amount of the insulating coating on the entire dust core. Specifically, as the amount of insulating coating increases, the specific resistance increases and the magnetic flux density decreases. On the contrary, if the amount of the insulating coating is reduced, the specific resistance is decreased and the magnetic flux density is increased. This tendency is basically the same even with an annealed powder magnetic core. By using the above-described insulating coating excellent in durability, heat resistance and the like and reducing the amount of use, a dust core excellent in both magnetic characteristics and electrical characteristics can be obtained.

  The mechanical properties (particularly strength) of the dust core are also important when considering actual use. Unlike the cast product and the sintered product, the dust core is mainly mechanically bonded by the plastic deformation of the constituent particles covered with the insulating film, and its strength is not high. However, since the density ratio of the present invention is as high as 96% or higher, it has practically sufficient strength. For example, a high strength of 50 MPa or more, further 100 MPa or more is exhibited at a four-point bending strength σ. The four-point bending strength σ is not defined in JIS, but can be obtained by a green compact test method.

(6) Use of dust core The dust core of the present invention can be used for various electromagnetic devices such as motors, actuators, transformers, induction heaters (IH), speakers, reactors, and the like. Especially, it is preferable when it is used for the electromagnetic equipment which operate | moves in a low frequency region, such as 2000 Hz or less (for example, 100-2000 Hz). When used in such a low frequency range, the dust core of the present invention exhibits high magnetic properties while remarkably suppressing iron loss. As an electromagnetic device used in such a low frequency range, there are an electric motor (motor) and a generator. That is, the dust core of the present invention is preferably an iron core constituting a field or armature of an electric motor or generator. In particular, the dust core of the present invention is suitable for a drive motor that requires low loss and high output (high magnetic flux density). Such a driving motor is used in, for example, a hybrid vehicle or an electric vehicle. An example of the iron loss of the dust core of the present invention will be given. When the dust core of the present invention is used in an alternating magnetic field having a working frequency of 800 Hz and a magnetic flux density of 1.0 T, the iron loss is as small as 55 W / kg or less, 53 W / kg or less, or 38 W / kg or less. This iron loss is much smaller than that of a conventional dust core and is equal to or less than that of a high performance electrical steel sheet (20JNEH1200 (manufactured by JFE Steel)) used in a motor. Among the above iron losses, the hysteresis loss is sufficiently small, 37 W / kg or less, 34 W / kg or less, and further 32 W / kg or less. Of course, among the iron losses, the eddy current loss is 21 W / kg or less, 16 W / kg or less, and further 6 W / kg or less.

The present invention will be described more specifically with reference to examples.
(First embodiment)
(1) Formation of insulating coating (manufacture of magnetic core powder)
As the raw material powder (magnetic powder), a commercially available atomized powder having a composition of pure Fe (purity: 99.8%, ABC100.30 manufactured by Höganäs), Fe-1% Si and Fe-3% Si was prepared. The unit is mass% (hereinafter the same). The trade names and manufacturers of each powder are as follows.

  The volume average particle diameter of each powder was 80 μm of pure iron powder, 80 μm of Fe-1% Si powder, and 80 μm of Fe-3% Si powder.

  Each of these powders was coated with a silicone resin film (insulating film) as follows.

A coating treatment solution in which a commercially available silicone resin (“SR-2400” manufactured by Toray Dow Corning Silicone Co., Ltd.) was dissolved in 5 times the organic solvent (toluene) was prepared. After this coating treatment liquid was added to the magnetic powder, mixing and stirring were performed, and then they were dried at 150 ° C. for 2 hours. Thus, a magnetic powder (magnetic core powder) whose surface was coated with a silicone resin coating was obtained. The coating treatment solution was added so that the amount of the silicone resin was 0.2% by mass with respect to 100% by mass of the magnetic powder. In addition, since the mass% of this silicone resin is very small, the above ratio hardly changes even when the entire powder (or dust core) for magnetic core after coating is considered to be 100 mass% (the same applies hereinafter). Incidentally, the silicone resin decomposes when heated to 750 ° C., and forms an oxide film (insulating film) of SiO _{2 on} the surface of the magnetic powder.

(2) Manufacture of dust cores By applying a die-lubricating warm high pressure molding method to each core powder, a ring shape (outer diameter: φ39 mm × inner diameter φ30 mm × thickness 5 mm) and plate shape (5 mm × 10 mm × 55 mm) ) 2 types of test pieces were produced. This ring-shaped test piece is for evaluating magnetic properties, and the plate-shaped test piece is for evaluating electric resistance. No internal lubricant, resin binder, or the like was used at the time of molding each test piece (dust core).

  Specifically, the die lubrication warm high pressure molding method was performed as follows.

(A) A cemented carbide mold having a cavity corresponding to each test piece shape was prepared. This mold was preheated to 150 ° C. with a band heater. Further, the inner peripheral surface of this mold was previously subjected to TiN coating treatment, and the surface roughness was set to 0.4Z.

Lithium stearate dispersed in an aqueous solution was uniformly applied to the inner peripheral surface of the heated mold with a spray gun at a rate of about 10 cm ³ / min (application process). The aqueous solution used here is obtained by adding a surfactant and an antifoaming agent to water. As the surfactant, polyoxyethylene nonylphenyl ether (EO) 6, (EO) 10 and boric acid ester Emulbon T-80 were used, and each was added by 1% by volume with respect to the entire aqueous solution (100% by volume). did. As the antifoaming agent, FS Antifoam 80 was used and 0.2% by volume was added to the entire aqueous solution (100% by volume).

Further, lithium stearate having a melting point of about 225 ° C. and a particle size of 20 μm was used. The dispersion amount was 25 g with respect to 100 cm ^{3 of the} aqueous solution. Then, this was further refined with a ball mill type pulverizer (Teflon-coated steel balls: 100 hours), and the obtained stock solution was diluted 20 times to give an aqueous solution having a final concentration of 1%, which was used in the coating step.

(B) A magnetic core powder that had been heated to 150 ° C., the same temperature as that of which the lithium stearate was coated on the inner surface was filled (filling step).

(C) While maintaining the mold at 150 ° C., the core powder filled in the mold was basically warm-pressed at a molding pressure of 1568 MPa (molding step).
In this warm high-pressure molding, none of the magnetic core powders galling with the mold, and the powder molded body could be taken out from the mold with a low depressurization of about 5 MPa.

(D) Each obtained powder compact was subjected to heat treatment (annealing treatment) at 750 ° C. for 30 minutes in a nitrogen atmosphere (heating step or annealing step). As a result, the silicone resin film becomes a SiO ₂ film, and strain and stress remaining in the powder molded body are removed.

(Second embodiment)
The above-described Fe-1% Si magnetic powder (volume average particle size: 80 μm) was coated with a silicone resin coating (insulating coating) in the same manner as in the first example. However, the amount of the silicone resin was 0.1% by mass, 0.2% by mass and 0.5% by mass with respect to 100% by mass of the magnetic powder. Thus, three kinds of magnetic core powders having different amounts of insulating coating were obtained.

  Each of the obtained magnetic core powders was subjected to warm high pressure molding similar to that of the first example, and the obtained powder compacts were subjected to the heat treatment described above (750 ° C. × 30 minutes in a nitrogen atmosphere). did.

(Third embodiment)
Fe-1% Si magnetic powder classified into 8 stages by a sieving method was prepared. Specifically, (a) 45-63 μm (b) 63-74 μm, (c) 74-105 μm, (d) 105-150 μm, (e) 150-212 μm, (f) 212-250 μm, (g) 250- 300, (h) 300-355 μm. In terms of the volume average particle diameter of the present invention, (a) 50 to 60 μm (b) 65 to 70 μm, (c) 80 to 100 μm, (d) 120 to 140 μm, (e) 170 to 190 μm, ( f) 220-240 μm, (g) 270-290 μm, (h) 320-340 μm. The Fe-1% Si magnetic powder used is an atomized powder similar to that of the first embodiment.

A silicone resin film was formed on each of these magnetic powders in the same manner as in the first example. The amount of the silicone resin was 0.2% by mass with respect to 100% by mass of the magnetic powder. Thus, eight kinds of magnetic core powders having different particle diameters were obtained.
Each of the obtained magnetic core powders was subjected to warm high pressure molding similar to that of the first example, and the obtained powder compacts were subjected to the heat treatment described above (750 ° C. × 30 minutes in a nitrogen atmosphere). did.

(Fourth embodiment)
Fe-1% Si magnetic powder classified into 11 stages by a sieving method was prepared. These classifications are the 8-stage classifications shown in the third embodiment. The Fe-1% Si magnetic powder used is an atomized powder similar to that of the first embodiment.

  These various powders were each rolled with a small rolling mill (DBR-50S (manufactured by Daito Seisakusho)) so that the thicknesses were 0.05 mm and 0.1 mm (flat processing step). In this way, oblate flat particles having different particle sizes or thicknesses were obtained. The classification before rolling can be divided into 8 stages, and the thickness after rolling can be divided into 2 stages. Therefore, 22 kinds of magnetic powders were obtained in total.

A silicone resin film was formed on each of these magnetic powders in the same manner as in the first example. The amount of the silicone resin was 0.2% by mass with respect to 100% by mass of the magnetic powder.
Each of the obtained magnetic core powders was subjected to warm high pressure molding similar to that of the first example, and the obtained powder compacts were subjected to the heat treatment described above (750 ° C. × 30 minutes in a nitrogen atmosphere). did.

(5th Example)
(1) Manufacture of powder for magnetic cores Two types of pure iron powder commercially available as magnetic powders were facilitated. One is water atomized powder (KIP-304AS from Kawasaki Steel), and the other is gas atomized powder (manufactured by Sanyo Special Steel). These powders were not used for classification and used as received. The particle size was 100-200 μm. This is 130 to 170 μm in terms of the volume average particle size of the present invention.

(A) The first insulating layer was coated on the magnetic powder by the following method.
Commercially available reagents SrCO ₃ (alkaline earth metal oxide): 11 g, boric acid (H ₃ BO ₃ ): 3 g, phosphoric acid (H ₃ PO ₄ ): 19 g, 200 ml of ions The solution was added to the exchanged water and dissolved by stirring to obtain a coating solution (first coating treatment solution). These mixing ratios are Sr: B: P = 1.5: 1: 4 in molar ratio.

  20 ml of the coating solution was dropped onto 100 g of each magnetic powder placed in a 100 ml beaker (first contact step). This was put into an electric furnace and dried by heating in the atmosphere at 200 ° C. for 30 minutes (first drying step). Thus, the first insulating layer (Sr—B—P—O-based insulating layer, strontium phosphate-based glassy insulating layer) was fixed and formed on the surface of the magnetic powder (first insulating layer forming step). In addition, the ratio of this 1st insulating layer was 3 mass% in the case of water atomized powder, and 2 mass% in the case of gas atomized powder with respect to the whole magnetic powder (100 mass%) before a process.

(B) The coating process of the second insulating layer onto the magnetic powder on which the first insulating layer was formed (hereinafter simply referred to as “first magnetic powder”) was performed by the following method.
A silicone resin solution (SR2400 manufactured by Toray Dow Corning Co., Ltd.) and silica (SiO ₂ ) particles (manufactured by Admatechs Co., Ltd., particle size 50 nm) as oxide particles were prepared. The silicone resin solution (SR2400) is obtained by dissolving a silicone resin at a ratio of 50% by mass in toluene as a solvent.

A second insulating layer (or third insulating layer) was formed on the first magnetic powder as follows.
When forming the second insulating layer made of silicone resin, add 50 g of each first magnetic powder into a 100 ml beaker, and add the silicone resin solution from above to the silicone resin amount so that the amount of silicone resin is as shown in Table 2 (Second contact step). Moreover, when forming the composite insulating layer of the silicone resin and the silica particles, the silicone resin solution was further added, and then the silica particles were added so as to have the ratio shown in Table 2 (second contact step).

  In each beaker to which the first magnetic powder and various proportions of the silicone resin solution and the like were added, 30 ml of ethanol was added and stirred for 30 minutes in an atmosphere of 60 ° C. or more to completely volatilize the ethanol (first 2 contact process).

  Thus, on the magnetic powder on which the first insulating layer composed of the Sr—B—P—O-based insulating layer is formed, the second insulating layer composed of the silicone resin or the second insulating layer composed of the silicone resin and the silica particles (composite insulation). Layer) was formed (second insulating layer forming step). Thus, various magnetic core powders coated with the first insulating layer and the second insulating layer were obtained.

(2) Manufacture of dust core Using these respective core powders, warm high pressure molding similar to that of the first example was performed. The obtained powder compact was appropriately subjected to annealing in the air at an annealing temperature of 500 ° C. or 600 ° C. and an annealing time of 30 minutes. Some test pieces were annealed at an annealing temperature of 650 ° C. in an antioxidant atmosphere (Ar gas atmosphere).

(Measurement)
(1) Specific resistance was measured using a plate-shaped test piece. The specific resistance was measured by a four-terminal method using a micro-ohm meter (manufacturer: Hewlett-Packard (HP), model number: 34420A) (hereinafter the same).

(2) Using a ring-shaped test piece and a plate-like test piece, their magnetic properties and density were measured.
Among the magnetic characteristics, the static magnetic field characteristics were measured with a direct current magnetic flux meter (manufacturer: Toei Kogyo, model number: MODEL-TRF). The AC magnetic field characteristics were measured with an AC BH curve tracer (manufacturer: Iwasaki Tsushinki Co., Ltd., model number: SY-8232). The AC magnetic field characteristics in each table are obtained by measuring the iron loss when the dust core is placed in a magnetic field of 1.0 T at 400 Hz or 800 Hz. In the table, Ph is hysteresis loss, Pe is eddy current loss, Pc is iron loss (Pe + Ph), and Pcm is weight specific iron loss.

The magnetic flux density in the static magnetic field indicates the magnetic flux density that can be obtained when the magnetic field strength is sequentially changed to 2, 5, 8, 10, 16, 20 kA / m. In each table, they are shown as B _2k , B _5k , B _8k , B _10k , B _16k , and B _20k , respectively. The μm in the table is the maximum magnetic permeability. In this specification, the coercive force bHc is a value measured from a magnetization curve at a maximum magnetic field of 2 kA / m. The density was measured by the Archimedes method.

  The results thus obtained are also shown in Tables 1 to 4 and Tables 5A and 5B. Table 1 shows the results of the first example, Table 2 shows the results of the second example, Table 3 shows the results of the third example, Table 4 shows the results of the fourth example, and Tables 5A and 5B show the results. The result of 5th Example is shown, respectively.

(Evaluation)
(1) First Example As can be seen from the results shown in Table 1, as the amount of Si in the magnetic powder increases, the coercive force bHc decreases and the hysteresis loss Ph also decreases. Further, as the amount of Si in the magnetic powder increases, the specific resistance increases and the eddy current loss Pe also decreases. Therefore, the iron loss is smaller as the test piece has a larger amount of Si in the magnetic powder. On the other hand, as the amount of Si increases, the magnetic flux density decreases as a whole. Therefore, in order to achieve a high balance between low iron loss and high magnetic flux density, it is preferable that Si is contained in the magnetic powder by about 1% by mass (1.5% by mass or less).

  Note that when pure iron powder is used as the magnetic powder, the specific resistance and eddy current loss of the test piece are relatively large because the insulating coating was easily broken, decomposed, or lost during molding or heating. I think. In other words, it seems that the stability of the silicone resin film covering the surface of the pure iron powder was weak.

(2) Second Example As can be seen from the results shown in Table 2, as the amount of silicone resin increases, the specific resistance increases and the eddy current loss Pe decreases. At this time, the coercive force bHc and the hysteresis loss Ph are substantially constant values. As a result, the iron loss decreases as the amount of silicone resin increases. On the other hand, as the amount of silicone resin increases, the magnetic flux density decreases as a whole. Therefore, in order to achieve a high balance between low iron loss and high magnetic flux density, the amount of the silicone resin is preferably 0.1 to 0.3% by mass.

(3) Third Example As can be seen from the results shown in Table 3, as the particle size of the magnetic powder increases, the eddy current loss increases and the hysteresis loss decreases. When the frequency was 800 Hz with an AC magnetic field of 1.0 T, the iron loss, which is the sum of eddy current loss and hysteresis loss, was a stable low value when the particle size of the magnetic powder was 80 to 300 μm. This is shown in FIG.

(4) Fourth Example As can be seen from the results shown in Table 4, when magnetic powder composed of flat particles (thickness 0.05 mm) was used, eddy current loss was greatly reduced. The decreasing rate was more remarkable as the particle size of the magnetic powder was larger. Iron loss showed a similar trend. Conversely, it can be said that the hysteresis loss itself hardly changed depending on the shape of the constituent particles of the powder. This is shown superimposed on FIG.

  The influence of the particle shape and composition of the magnetic powder on the relationship between the particle size and eddy current loss is shown in FIG. It was found that the eddy current loss becomes smaller as the magnetic powder is made of flat particles and the thickness is smaller.

(5) Fifth Example As can be seen from the results shown in Tables 5A and 5B, in the case of a dust core having an insulating coating having a multilayer structure, the specific resistance was as large as more than 100 μΩm even after annealing at 500 ° C. It has been found that if magnetic powder coated with this insulating film is used, even if the magnetic powder is pure iron powder, not only hysteresis loss but also eddy current loss can be reduced at the same time. That is, it was found that a dust core having a low iron loss can be obtained.

  In particular, the specific resistance of the test piece when the insulating coating contains silica particles showed a sufficiently high value not only after annealing at 500 ° C. but also after annealing at 600 ° C.

  Comparing the case where the AC frequency is 400 Hz and the case where the frequency is 800 Hz, when the frequency is low (400 Hz), the effect of hysteresis loss is larger, and the reduction rate of iron loss due to the annealing temperature rise (500 ° C → 600 ° C) Was also big.

  The test piece made of gas atomized powder generally had a larger specific resistance than the test piece made of water atomized powder, although the amount of the first insulating layer was small. Therefore, it has been found that if a gas atomized powder is used, a dust core having a low magnetic loss and a high magnetic flux density can be obtained while reducing the amount of insulating coating.

(6) Others Additional comments will be made on the relationship between crystal grain size and coercive force. Pure Fe magnetic powder and Fe-1Si magnetic powder were heat-treated at 900 ° C. and 1250 ° C., respectively, and the relationship between crystal grain size and coercive force was investigated. The result is shown in FIG.

  Each crystal grain size is an average value of crystal grain sizes obtained for a predetermined number (N = 100) of constituent particles.

  As is clear from FIG. 3, the coercive force decreased as the crystal grain size increased. Therefore, hysteresis loss can be further reduced by using magnetic powder having a large crystal grain size (for example, gas atomized powder having a relatively low cooling rate). However, when the crystal grain size exceeds 200 μm, the decrease in coercive force approaches a saturated state. Considering eddy current loss, it is preferable to use magnetic powder having a crystal grain size of 50 to 250 μm.

  Although the case where the AC frequency is 800 Hz has been described so far, the same applies to other frequencies (2000 Hz or less).

It is a graph which shows the relationship between the particle size of a magnetic powder, and an iron loss. It is a graph which shows the relationship between the particle size of magnetic powder, and eddy current loss. It is a graph which shows the relationship between the crystal grain diameter of magnetic powder, and a coercive force.

Claims (20)

In a powder magnetic core formed by press-molding a magnetic core powder in which a magnetic powder mainly composed of iron (Fe) is coated with an insulating coating,
The magnetic powder contains 1.5% by mass or less of silicon (Si), has a volume average particle size of 80 to 300 μm,
The density ratio (ρ / ρ ₀ :%), which is the ratio of the bulk density (ρ) of the dust core to the true density (ρ ₀ ) of the magnetic powder, is 96% or more,
A dust core characterized by being used in an alternating magnetic field having a frequency of 100 to 2000 Hz. The dust core according to claim 1, wherein a magnetic flux density B _20k generated in a magnetic field of 20 kA / m is 1.7 T or more.   2. The dust core according to claim 1, wherein the magnetic powder is formed of flat particles having a substantially oval shape with an average thickness of 20 to 100 μm. ^2. The dust core according to claim 1, wherein the magnetic powder has an average specific surface area of 5 × 10 ⁻³ m ² / g or less, which is obtained by averaging a specific surface area that is a surface area per unit mass of the constituent particles.   The powder magnetic core according to claim 1, wherein the magnetic powder has an average crystal grain size of constituent particles of 50 μm or more.   The powder magnetic core according to claim 1, wherein the magnetic powder is a gas atomized powder. The dust core according to claim 1, wherein the insulating coating is a silicone resin coating or a silicon dioxide (SiO ₂ ) coating. The magnetic powder is pure iron powder having Si of 0.8% or less,
2. The dust core according to claim 1, wherein the insulating coating includes a first insulating layer made of a phosphate coating and a second insulating layer made of a silicone resin that covers the first insulating layer.   The dust core according to claim 8, wherein the second insulating layer is a composite insulating layer in which oxide particles are dispersed in the silicone resin.   The dust core according to claim 8, further comprising a third insulating layer provided on the second insulating layer and mainly made of oxide particles.   The dust core according to claim 9 or 10, wherein the oxide particles have an average particle diameter of 10 to 100 nm.   2. The dust core according to claim 1, wherein the insulating coating is 0.1 to 0.3 mass% when the entire powder magnetic core is 100 mass%. The coercive force is 150 A / m or less,
The dust core according to claim 1, wherein the volume resistivity value is 20 μΩm or more.   2. The dust core according to claim 1, which is an iron core constituting a field or armature of an electric motor or a generator.   The dust core according to claim 14, wherein the electric motor is for a hybrid vehicle or an electric vehicle. (Production method of dust core)
A filling step of filling a mold with a magnetic core powder in which a magnetic powder having Fe as a main component and Si of 1.5% by mass or less and a volume average particle size of 80 to 300 μm is coated with an insulating coating;
A molding step of pressure molding the magnetic core powder in the mold,
A method for producing a dust core, wherein the dust core according to claim 1 is obtained. The filling step is a step of filling the magnetic core powder into the mold coated with a higher fatty acid-based lubricant on the inner surface,
The method of manufacturing a dust core according to claim 16, wherein the forming step is a warm high-pressure forming step of forming a metal soap film between the magnetic core powder and the inner surface of the mold. The insulating coating is a silicone resin coating,
Moreover, method for producing a dust core according to claim 16, comprising a heating step of the silicone resin coating film and SiO ₂ film by heating the powder compact obtained after the molding process. The magnetic powder is pure iron powder having Si of 0.8% or less,
The insulating coating consists of a first insulating layer made of a phosphate coating and a second insulating layer made of a silicone resin that covers the first insulating layer,
Furthermore, the manufacturing method of the powder magnetic core of Claim 16 provided with the annealing process which anneals the powder compact obtained after the said shaping | molding process.   A dust core obtained by the method for producing a dust core according to claim 18.

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