JP2009259939A - Powder magnetic core and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder magnetic core superior not only in high density but also in strength. <P>SOLUTION: The powder magnetic core is obtained by heating green compact obtained by pressurizing and forming mixed powder where a powder magnetic core in which a coupling layer formed of silane coupling agent is installed on a particle surface of soft magnetic powder coated with an insulated coat, and silicone resin powder are mixed in a warm state where resin powder is softened. Since a gap formed between particles of magnetic core powder is filled with a small amount of silicone resin and is thermally cured in the powder magnetic core. Thus, higher density and higher strength are realized compared to a conventional one. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a dust core not only having high density and high specific resistance but also excellent in strength and a method for producing 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.

  This magnetic core is required to have a high magnetic flux density in an alternating magnetic field and to have low high-frequency loss (hereinafter simply referred to as “iron loss” regardless of the material of the magnetic core) when used in an alternating magnetic field. It is done. In order to achieve both high magnetic flux density (magnetic characteristics) and low loss (electrical characteristics), a powder magnetic core is used that is formed by press-molding soft magnetic powder (magnetic core powder) with an insulating coating on the particle surface. It is done.

Most recently, not only improving the performance of a dust core, but also improving mechanical properties such as the practical strength of the dust core has become an important issue. Therefore, for example, the following Patent Document 1 proposes a powder magnetic core in which pure iron powder whose particle surface is coated with an insulating film made of silica is further coated with a silicone resin layer and heated to improve the strength. is doing. Further, in Patent Document 2 below, although not intended to strengthen the bond between the particles of the magnetic powder, a coupling agent is added to the magnetic powder coated with an insulating film, and a dust core that aims to protect the insulating film is formed. is suggesting.
JP 2006-233295 A JP 2006-134958 A

  However, the dust cores proposed in the above-mentioned patent documents are all single-sided, and can satisfy all of the magnetic characteristics, electrical characteristics, and mechanical characteristics required for the dust core at a high level. Not like that.

  The present invention has been made in view of such circumstances, and it is possible to improve the magnetic characteristics by increasing the density and the electrical characteristics by securing the volume specific resistance value (hereinafter simply referred to as “specific resistance”). An object of the present invention is to provide a dust core and a method for manufacturing the same, which can further improve mechanical properties by increasing strength.

  As a result of extensive research and trial and error, the present inventor has conducted a trial and error process, and after pre-processing the magnetic core powder with a silane coupling agent, the mixed powder of the magnetic core powder and the resin powder is warmed. It has been found that a powder magnetic core obtained by heat-treating a green compact obtained by pressure forming has a significantly improved strength while improving the density. And by developing this result, the present inventor has completed various inventions described below.

<Dust core>

(1) The powder magnetic core of the present invention is formed by pressure-molding a mixed powder obtained by mixing a magnetic core powder made of a soft magnetic powder whose particle surface is coated with an insulating film and a resin powder made of a thermosetting silicone resin. A powder magnetic core obtained by heating the powder compact in a high temperature state where the silicone resin is cured,
The magnetic core powder further has a coupling layer made of a silane coupling agent on the particle surface coated with the insulating film, and the green compact is a warm state in which the mixed powder is softened by the resin powder. It is obtained by pressure molding and is characterized by high density, high specific resistance and high strength.

(2) The dust core of the present invention is excellent not only in magnetic characteristics such as magnetic flux density and electrical characteristics such as specific resistance, but also in mechanical characteristics such as strength. The detailed mechanism by which the dust core of the present invention can express not only high magnetic flux density and low specific resistance but also high strength is not necessarily clear. At present, it is considered as follows.

  The magnetic core powder constituting the dust core of the present invention is not only the surface of the soft magnetic powder particles coated with an insulating film, but also a coupling layer made of a silane coupling agent on the particle surface. Have. Next, a mixed powder obtained by mixing the magnetic core powder and a resin powder made of a small amount of silicone resin is pressed and formed into a green compact in a state where the resin powder is softened (that is, in a warm state).

  When the magnetic core powder is pressure-molded in this warm state (hereinafter referred to as “warm pressure molding” as appropriate), the softened silicone resin tends to plastically flow, and the gaps between the particles of the magnetic core powder ( It is possible to invade or enter the triple point. Here, there is a coupling layer made of a silane coupling agent on the particle surface of the magnetic core powder of the present invention. For this reason, the softened silicone resin is very easily wetted with the magnetic core powder particles, and is much easier to enter or flow into the gaps between the magnetic core powder particles than before. As a result, even a small gap between particles formed by high-pressure molding of the magnetic core powder is highly filled with the silicone resin. When this green compact is heat-treated, the magnetic core powder particles are thermally cured by a very small amount of silicone resin existing between the particles without impairing the density of the green compact, and become (quasi) chemically strong. It is thought that it will become united.

Such a detailed mechanism is basically a corner. In short, the powder magnetic core of the present invention is not only thermally deformed when its constituent particles are pressure-molded, but also entangled and mechanically coupled. It is considered that the silicone resin is bonded evenly and strongly evenly, and the strength of the two is synergistic and the strength is increased.
The absolute value of the strength of the powder magnetic core of the present invention itself may vary depending on the molding pressure of the magnetic core powder, the amount of resin powder to be blended, the degree of heat treatment of the green compact, etc. The crushing strength to be indexed can be 70 MPa or more, 80 MPa or more, or even 100 MPa or more.

(3) By the way, the resin powder is not basically mixed with the magnetic core powder in order to insulate the particle surface of the soft magnetic powder. Of course, even if the particle surface of the soft magnetic powder may be insulated as a result, the soft magnetic powder is separately pre-insulated. Therefore, such an insulating coating is originally intended by the present invention. Absent.
Thus, since the resin powder is added not for forming an insulating film of soft magnetic powder but for strengthening the bond between particles, the blending amount thereof may be small. In particular, when high-density molding is performed to a level close to the true density of the soft magnetic powder, the amount of silicone resin remaining in the green compact or the dust core is very small. And since the resin powder is small in this way, the density of the green compact becomes high and a dust core with a high magnetic flux density can be obtained.

  Of course, the amount of the silicone resin finally remaining and the (bulk) density of the powder magnetic core may vary somewhat depending on the amount of the resin powder to be blended and the pressure applied during molding. However, in general, the amount of resin powder is large in order to insulate the particle surface of the soft magnetic powder, and the coating is hardened to prevent cracking of the film during pressure molding. There are voids between the particles. On the other hand, according to the present invention, it is possible to achieve high density and high magnetic flux density of the dust core while achieving the above-described bond reinforcement by the silicone resin added to the gaps between the constituent particles.

  Based on these matters, for example, the blending amount (addition amount) of the resin powder is preferably 0.05 to 0.5% by mass when the entire green compact is 100% by mass. The lower limit may be 0.1% by mass. The upper limit may be 0.4 mass%, 0.3 mass% or even 0.2 mass%. If the blending amount is too small, the gaps between the particles of the magnetic core powder are not always sufficiently filled with the silicone resin, and high strength cannot be expected. If the blending amount is excessive, the density of the powder magnetic core is lowered and a high magnetic flux density cannot be expected.

  Further, in the dust core, for example, a density ratio (ρ / ρ0:%) which is a ratio of a bulk density (ρ) of the dust core to a true density (ρ0) of the soft magnetic powder is 98% or more, 99% or more. Furthermore, it is preferable when it becomes 99.5 mass%. If the density ratio is too small, the magnetic flux density is lowered, which is not preferable. The density of the dust core can be evaluated by methods other than this density ratio, but as a relatively easy evaluation, the density ratio as described above was used.

(4) By the way, it is preferable that the insulating film covering the particle surface of the magnetic core powder is an insulating film containing silicon (Si). In other words, the magnetic core powder is preferably made of a soft magnetic powder coated with such an insulating film. Specific examples thereof include a silicone resin film obtained by condensation polymerization of a silicone resin, and a Si oxide (silica: SiO2) film. The silica film may be one obtained by transforming a silicone resin for forming an insulating film. When the soft magnetic powder is Fe-Si powder, the powder may be formed on the particle surface by hydrogen reduction treatment.

In any case, since such a Si-based film is compatible with a coupling layer made of a silane coupling agent, the softened silicone resin is coated on the particle surface with the Si-based film. It exhibits higher wettability with the magnetic core powder.
By improving the wettability as described above, as described above, the softened silicone resin densely fills the gaps between the particles of the magnetic core powder, and a high-strength powder magnetic core in which the constituent particles are firmly bonded is obtained. Be able to.

  However, the improvement of the wettability of the softened silicone resin with respect to the magnetic core powder does not only contribute to the improvement of the strength of the powder magnetic core. That is, it is considered that the improvement in wettability has the effect that the softened silicone resin also promotes the slip between the particles of the magnetic core powder and suppresses the breakdown of the insulating film during pressure molding.

<Method of manufacturing a dust core>
The present invention can be grasped not only as a powder magnetic core as described above but also as a method for manufacturing a powder magnetic core.
(1) That is, the present invention provides a contact step of bringing a silane coupling agent into contact with a particle surface of a magnetic core powder made of a soft magnetic powder whose particle surface is coated with an insulating film, and a magnetic core powder after the contact step. A mixing step of mixing a resin powder comprising a thermosetting silicone resin, a molding step of pressure-molding the mixed powder after the mixing step in a warm state in which the resin powder is softened, and a pressure after the molding step The method may be a method for producing a powder magnetic core, characterized in that it comprises a heating step of heating the powder in a high temperature state where the silicone resin is cured, and a powder magnetic core having high density and excellent specific resistance and strength is obtained. .

(2) Further, the molding step includes a warm heating step in which the mixed powder filled in a mold is heated to the warm state, and the resin core is softened by the warm heating step. It may consist of the pressurization process which press-molds the powder for use. The warm heating process and the pressurizing process may proceed independently and both processes may proceed in parallel.

(3) The heating step basically cures the silicone resin that fills the gaps between the particles of the magnetic core powder. However, it is preferable that this heating step also serves as an annealing step for removing residual strain or residual stress generated in the particles of the magnetic core powder after the forming step. Thereby, the high intensity | strength of a powder magnetic core and the reduction of a hysteresis loss can be achieved efficiently.

  Incidentally, although the annealing temperature can be as high as 400 ° C., 600 ° C., and even 750 ° C., the heat-curable silicone resin according to the present invention originally has a high heat resistance temperature, and even if such high temperature annealing is performed, the magnetic core The bonding between the particles of the powder for use is less likely to deteriorate.

<Others>
(1) The form of the “dust core” as used in this specification is not limited. That is, the powder magnetic core may be a material or a bulk shape that is appropriately subjected to machining or the like, or may be a final shape or a structural member close thereto.
Further, the present invention is characterized in that the surface of the soft magnetic powder particles is coated with an insulating film, and a coupling layer is further provided on the surface. This is schematically shown in FIG.

  Of course, an actual insulating film or coupling layer is not always uniform. In the dust core obtained by the heat treatment, the coupling layer may be fused with the insulating film or the silicone resin, which may make it difficult to analyze. Furthermore, the distinction between an insulating film and a heat-cured silicone resin may be difficult to analyze. Therefore, the above-described expression according to the present invention is merely a product-by-process structure specification to facilitate understanding of the dust core of the present invention.

  Therefore, it is included in the present invention as long as it is a dust core having the same meaning as the present invention even if it is a dust core whose distinction is not clear such as an insulating film, a coupling layer, or a heat-cured silicone resin by actual analysis. I refuse to be.

(2) The magnetic core powder is composed of soft magnetic powder and an insulating film formed on the particle surface. The composition of the soft magnetic powder is not particularly limited, but pure iron powder, Fe-Si powder, and the like are typical. For example, when the total amount of the soft magnetic powder is 100% by mass, it is preferable that 0.5 to 3% by mass of Si, with the balance being Fe and modifying elements and / or inevitable impurities.

  Here, the “modified element” is an element effective for improving the characteristics of the dust core in terms of magnetic characteristics, electrical characteristics, mechanical characteristics, and the like. The type of property to be improved is not limited, and the type and combination of elements are not limited. Examples of such elements include Al, Ni, Co and the like other than Si. Incidentally, the content of such a modifying element is usually a relatively small amount so as not to cause a decrease in magnetic properties.

  “Inevitable impurities” include impurities contained in the raw material of soft magnetic powder (such as molten metal), impurities mixed in during powder formation, and the like, and are elements that are difficult to remove due to cost or technical reasons. Examples of the soft magnetic powder according to the present invention include C, S, Cr, P, and Mn. Naturally, since the kind and composition of the basic elements (Fe, Co, Ni, Si, etc.) are important in the soft magnetic powder, the ratio of the modifying elements and inevitable impurities is not particularly limited.

(3) Unless otherwise specified, “x to y” in this specification includes the lower limit x and the upper limit y. Further, the lower limit and the upper limit described in the present specification can be arbitrarily combined to constitute a range such as “ab”.

The present invention will be described in more detail with reference to embodiments of the invention.
In addition, the content demonstrated by this specification including the following embodiment is applicable not only to the powder magnetic core which concerns on this invention but its manufacturing method suitably. Which embodiment is the best depends on the target, required performance, and the like.

<Magnetic core powder>
(1) Soft magnetic powder

  The magnetic core powder is composed of a soft magnetic powder whose particle surface is coated with an insulating film. First, this soft magnetic powder usually contains a ferromagnetic element such as a group 8 transition element (Fe, Co, Ni, etc.) as a main component. Among them, those based on Fe are preferable from the viewpoint of handleability, availability, cost, and the like.

  An Fe—Si alloy powder containing Si as a main component is often used as a raw material powder for a dust core. This is because Si increases the electrical resistivity of the powder particles, improves the specific resistance of the dust core, and reduces eddy current loss.

  For example, when the entire soft magnetic powder is 100% by mass, the lower limit of Si is preferably 0.2% by mass, further 0.8% by mass, and the upper limit of Si is preferably 4% by mass, further 3% by mass. If there is too little Si, there is no effect, and if there is too much Si, the magnetic properties (magnetic flux density) of the dust core may be lowered, and the moldability of the soft magnetic powder may be lowered. In addition, when Si is contained in the particles of the soft magnetic powder, the bondability with the silicone resin film covering the particles is improved, and an insulating film that is difficult to peel is easily formed.

  Of course, the soft magnetic powder has a purity of 99.5% or more, 99.7% or more, and 99.8% or more of pure iron from the viewpoint of improving magnetic properties and moldability according to the use of the dust core. Powder may be used. Furthermore, the iron-based soft magnetic powder contains 5-30% by mass of Co and 0.3-4% by mass of Si or Al when the total soft magnetic powder is 100% by mass in addition to the above-described Si. But it ’s okay.

  The soft magnetic powder may be a mixed powder obtained by mixing a plurality of powders. For example, a mixed powder of pure iron powder and Fe-49Co-2V (permendur) powder, pure iron powder and Fe-3Si powder, sendust (Fe-9Si-6Al) powder and pure iron powder, or the like may be used.

  In order to increase the density of the dust core, it is preferable that the soft magnetic powder has a particle size of 20 to 300 μm, 45 to 250 μm, or 80 to 150 μm. If the particle size of the soft magnetic powder is excessive, it is difficult to reduce the eddy current loss, and if the particle size is excessively small, it is difficult to reduce the hysteresis loss. The soft magnetic powder can be easily classified by a sieving method or the like.

  The method for producing the soft magnetic powder is not limited. Either pulverized powder or atomized powder may be used. The atomized powder may be any of water atomized powder, gas atomized powder, and gas water atomized powder. Currently, water atomized powder is the most available and low cost. Since the water atomized powder has an irregular particle shape, it is easy to improve the mechanical strength of the green compact obtained by pressure molding.

  On the other hand, the gas atomized powder is a pseudo-spherical powder in which the particles are substantially spherical. Since the shape of each particle is substantially spherical, when soft magnetic powder is pressed, the aggressiveness between the powder particles is reduced, the destruction of the insulating film is suppressed, and the powder with high specific resistance A magnetic core is easily obtained stably.

  Moreover, since the gas atomized powder consists of substantially spherical particles, its surface area is smaller than that of a water atomized powder having a distorted particle shape. For this reason, even if the total amount of the insulating film is the same, a thicker insulating film can be formed by using gas atomized powder, and eddy current loss can be more easily reduced. On the contrary, if an insulating film having the same film thickness is provided, the total amount of the insulating film can be reduced, and the magnetic flux density of the dust core can be increased. Furthermore, since the gas atomized powder has a large crystal grain size in the powder particles, the coercive force is reduced and it is easy to reduce the hysteresis loss. Therefore, by using a pseudo-spherical powder such as a gas atomized powder, it is easy to achieve both improvement in magnetic characteristics and reduction in iron loss. Of course, the soft magnetic powder may be powder other than atomized powder, for example, pulverized powder obtained by pulverizing an alloy ingot with a ball mill or the like. Such a pulverized powder can be increased in crystal grain size by heat treatment (for example, heated to 800 ° C. or higher in an inert atmosphere).

(2) Insulating film The film thickness of the insulating film is preferably 10 to 200 nm, more preferably 10 to 100 nm.
When the film thickness of the insulating film is too small, the specific resistance of the dust core becomes small and the iron loss cannot be reduced sufficiently. On the other hand, if the film thickness of the insulating film is excessive, the magnetic characteristics of the dust core are deteriorated. In addition, it is ideal that the insulating film is originally formed for each powder particle. However, in practice, an insulating film may be formed around several particles in a hardened state, and even such a state is within the assumed range of the present invention.

(3) Silicone resin The silicone resin of the present invention is a thermosetting type. This may function as an insulating film that covers the surface of the constituent particles, but mainly functions as a strong binder that binds the constituent particles.
Since the softening temperature and curing temperature of the silicone resin vary depending on the type of the silicone resin, it cannot be generally specified. For example, the softening of the silicone resin starts from about 75 to 150 ° C., and the curing of the silicone resin starts from about 200 to 300 ° C. By heating to the curing temperature, the silicone resin in contact with the surface of the soft magnetic powder particles becomes a hard silicone resin film. This thermosetting silicone resin softens initially as the temperature rises, but transforms from sol to gel as the siloxane bond progresses. Furthermore, when high-temperature heat treatment such as annealing is performed, the partial cross-linking is changed to the overall cross-linking, and the resin is strongly cured.

  Incidentally, silicone resins are generally roughly classified into a heat curable type that condenses and cures by heat and a room temperature curable type that cures at room temperature. In the former, functional groups react by applying heat and siloxane bonds occur to cause cross-linking and condensation / curing occurs. On the other hand, in the latter, functional groups react at room temperature by a hydrolysis reaction, and a siloxane bond occurs, so that crosslinking proceeds and condensation / curing occurs. The silicone resin used in the present invention is the former thermosetting type.

The number of functional groups of the silane compound of the silicone resin is 1 to a maximum of four. There is no restriction | limiting in the functional group number of the silicone resin used by this invention. However, it is preferable to use a silicone resin having 3 or 4 functional silane compounds because the crosslinking density is increased.
There are various types of silicone resins depending on applications such as resin-based, silane compound-based, rubber-based silicone, silicone powder, organically modified silicone oil, or composites thereof. In the present invention, a powdery silicone resin is mainly used, but it can also be combined with other silicone resins. In the present invention, the silicone resin mixed with the magnetic core powder is in the form of a powder. However, a silicone resin solution in which a silicone resin is dissolved or dispersed in advance in a solvent is brought into contact with the magnetic core powder to obtain a particle surface of the magnetic core powder. A silicone resin may be adhered to the substrate.

Specific examples of the silicone resin used in the present invention include YR3370 manufactured by Momentive Performance Materials.
Further, KR220L manufactured by Shin-Etsu Chemical Co., Ltd. can be mentioned. Of course, silicone resins other than these brands may be used. Furthermore, in this invention, 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.

(4) Silane Coupling Agent In the present invention, since the silicone resin is used as a binder for bonding the particles of the magnetic core powder, the silane interposed between the silicone resin and the particles in order to achieve adhesion between the particles. The presence of a coupling layer made of a coupling agent is important.

  Examples of the coupling agent used in the present invention include KBM-303, KBM-403, KBE-402, KBE-403, KBM-602, KBM-603, KBM-903, and KBE-903 (manufactured by Shin-Etsu Chemical Co., Ltd.). is there. By processing the magnetic core powder using a solution in which such a silane coupling agent is dissolved or dispersed in a solvent, a coupling layer can be formed on the surface of the magnetic core powder in advance. As the solvent, water, an organic solvent, or the like can be used. The solution is preferably, for example, 5 to 15 (% by mass), further 8 to 12 (% by mass) with respect to the entire aqueous solution.

  When the inventor investigated the strength of the powder magnetic core using various silane coupling agents, the use of a silane coupling agent exhibiting strong basicity (for example, a silane coupling agent having an amino group) is higher. A strong dust core could be obtained. This is presumably because the amino group silane coupling agent acts as a catalyst for the sol-gel reaction of the silicone resin and accelerates the curing of the silicone resin.

<Dust core>
The powder magnetic core of the present invention is obtained by heat-treating a powder compact obtained by press-molding the above-mentioned powder for magnetic core and a small amount of silicone resin into a desired shape.
(1) Pressure molding method The green compact is usually a filling step in which a magnetic core powder is filled in a molding die (simply referred to as “mold”), and the magnetic core powder in the die is pressure molded. The molding step is performed. In the present invention, the pressure molding method of the magnetic core powder is not limited, but in order to obtain a compact with a high density and a high magnetic flux density, a mold lubrication warm high pressure molding method capable of ultra-high pressure molding is used. preferable. This mold lubrication warm high pressure molding method includes a filling step of filling a mold in which a higher fatty acid-based lubricant is coated on the inner surface with the magnetic core powder, and a higher fatty acid system between the magnetic core powder and the inner surface of the mold. It consists of a molding temperature at which a metal soap film separate from the lubricant is formed and a warm high-pressure molding process in which the metal soap film is pressure-molded at the molding pressure. Details of the mold lubrication warm high pressure molding method are described in many publications such as Japanese Patent Publication No. 3309970 and Japanese Patent No. 4024705. According to this mold lubrication warm high-pressure molding method, it is possible to easily obtain a high-density green compact while extending the mold life. The compacting process may be performed in a magnetic field or in a non-magnetic field.

  Here, the original intention is different between “warm” in the mold lubrication warm high-pressure molding method and “warm” for softening the silicone resin powder. The former is for the production of a metal soap film different from the higher fatty acid-based lubricant, and the latter is for softening the silicone resin powder. However, by making both “warm” states common, a high-density and high-strength powder magnetic core can be efficiently produced. Specifically, it is more preferable that the warm state is 70 ° C. or higher, 200 ° C. or lower, 100 to 180 ° C., 110 to 150 ° C., or 120 to 140 ° C.

(2) Heat treatment (heating process)
The silicone resin softened by warm pressure molding by the heat treatment of the present invention undergoes a sol-gel reaction, and further undergoes a condensation polymerization reaction to be thermally cured. Thereby, the silicone resin filled between the particles of the magnetic core powder firmly binds the particles of the magnetic core powder, and a high-strength powder magnetic core can be obtained. The heating temperature, the heating time, and the heating atmosphere are not limited as long as the thermosetting of the silicone resin proceeds.

  However, as described above, in order to reduce the coercive force and hysteresis loss of the powder magnetic core, it is preferable to anneal the powder compact for the purpose of removing residual strain and residual stress in the powder compact. Therefore, it is preferable that the heating process also serves as an annealing process. This heating temperature depends on the composition of the soft magnetic powder, but is about 400 to 800 ° C., further about 500 to 800 ° C. If the soft magnetic powder is Fe-based powder, the heating temperature is preferably about 500 to 700 ° C. The heating time is preferably about 0.2 to 3 hours, more preferably about 0.5 to 1.0 hours. Since the annealing process is heated at a relatively high temperature, the atmosphere is preferably an inert atmosphere.

  When the gelled silicone resin film is heated at a high temperature exceeding its heat resistance temperature, the silicone resin film can be somewhat altered. However, even in such a case, since the insulating film made of silica or the like and the silicone resin have high heat resistance, the specific resistance of the powder magnetic core is rarely lowered.

(3) Specific resistance of the powder magnetic core The powder magnetic core of the present invention may have any density, specific resistance, strength, etc. as absolute values, but it is naturally preferable that it has a high density, high specific resistance, and high strength. Since the density and strength are as described above, the specific resistance is added here.

  The specific resistance is an eigenvalue for each dust core that is basically independent of the shape. If the powder magnetic core has the same shape, the eddy current loss can be reduced as the specific resistance increases. This specific resistance is affected by the type of insulating film, the amount of insulating film (film thickness), the presence or absence of annealing, etc., but the specific resistance is 100 μΩm or more, 500 μΩm or more, 1000 μΩm, 5000 μΩm or more, or even 10,000 μΩm or more. And preferred.

(4) 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. Specifically, it is preferably used for an iron core (steering core or rotor core) constituting a field or armature of an electric motor or generator. Among these, the dust core of the present invention is suitable as an iron core for a drive motor that requires low loss and high output (high magnetic flux density). Incidentally, such a drive motor is used in, for example, an automobile.

The present invention will be described more specifically with reference to examples.
<Manufacture of dust core>
(1) Manufacture of magnetic core powder Commercially available atomized powder (particle size: 212 to 150 μm) having a composition of Fe-1% Si (mass%) was prepared as a raw material powder (soft magnetic powder).

  This soft magnetic powder was subjected to hydrogen reduction treatment at a concentration of 900 to 950 ° C. to obtain a powder for a magnetic core whose particle surface was coated with an insulating film made of a silica film (insulating coating step).

  The magnetic core powder was contacted with an amino group silane coupling agent (S-330 manufactured by Chisso Corporation) mixed with water and then dried to form a coupling layer (coupling layer) on the particle surface of the magnetic core powder. (Contact process). The aqueous solution of the silane coupling agent used here is a mixture of water and an amino group silane coupling agent in a ratio of 10: 1.

(2) Press forming Magnetic core powder provided with this coupling layer and silicone resin powder (Momentive Performance Materials, "YR3370": resin powder) were mixed to obtain a mixed powder (mixing step) ). The compounding quantity of the silicone resin powder at this time was 0.2 mass% with respect to the whole mixed powder.

  This mixed powder was filled into the mold cavity (filling step). At this time, the mold was held at 120 to 130 ° C. for 0.5 minutes (warm heating step). It pressure-molded at 1568 MPa with this warm state (pressurization process). In addition, during this pressure molding, excess softened silicone resin can be discharged to the outside through the gaps in the mold, but in this example, such discharge hardly occurred. Thus, a test piece (compact) having a ring shape (outer diameter: φ39 mm × inner diameter φ30 mm × thickness 5 mm) was manufactured (molding step).

  Incidentally, this pressure molding used the above-described mold lubrication warm high pressure molding method in which no internal lubricant, binder or the like other than the above resin powder was used. Specifically, this mold lubrication warm high pressure molding method was performed as follows.

(I) A cemented carbide mold having a cavity corresponding to each test piece shape was prepared. This mold was previously heated to 130 ° 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 (1%) 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. 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. 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 for the above application.

  (Ii) The above-described magnetic core powder was filled into the mold cavity in which the lithium stearate was coated on the inner surface (filling step).

  (Iii) While maintaining the mold at 120 to 130 ° C., the core powder filled in the mold was warm-pressed basically at a molding pressure of 1568 MPa (pressurization process, molding process). . In this warm high pressure molding, none of the powders for magnetic cores were galling with the mold, and the green compact could be taken out from the mold with a low pressure.

(3) Heat treatment This compact was subjected to a heat treatment at 750 ° C. for 1 hour in a nitrogen atmosphere at a flow rate of 8 liters / minute using a variable atmosphere sintering furnace to obtain a test piece A1 (dust core) ( Heating process or annealing process).

<Manufacture of other test pieces>
In addition to the above test pieces, the following test pieces were produced by changing the conditions.
(1) Presence or absence of resin powder or silane coupling agent (i) Powder magnetic core (test pieces C1 to C1) in which the silane coupling agent was not brought into contact with the magnetic core powder
C3), (ii) a powder magnetic core (test piece D1 and D2) in which neither the resin powder was mixed nor contacted with the silane coupling agent, and (iii) a powder magnetic core (test piece E1) made of only soft magnetic powder, It was produced by adjusting the molding pressure as appropriate.

(2) Types of silane coupling agents
(i) a powder magnetic core (test pieces A1 to A5) using the amino group silane coupling agent,
(ii) A powder magnetic core (test pieces B1 to B5) using an epoxy group silane coupling agent (KBM403 manufactured by Shin-Etsu Chemical Co., Ltd.) instead of this silane coupling agent is produced by appropriately adjusting the molding pressure. did. In addition, regarding the manufacture of these test pieces, the conditions that are not specified are basically the same as the manufacturing conditions of the test piece A1 described above.

<Measurement of test piece>
Using each ring-shaped test piece, the crushing strength was measured by a method according to JISZ 2507. The specific resistance was measured by a 4-terminal method using a digital multimeter (manufacturer: ADC, Inc., model number: R6581). The density of each test piece (bulk density of the dust core) was measured by the Archimedes method. The true density of the soft magnetic powder used for calculating the density ratio was 7.68 g / cm 3.

  Table 1 shows the measurement results of these test pieces. Furthermore, based on the results shown in Table 1, the correlation between the density and the crushing strength regarding the test pieces A1, C1 to C3, D1, D2, and E1 is shown in FIG. Moreover, the correlation with the density and crushing strength regarding test piece A1-A5 and B1-B5 was shown in FIG.

<Evaluation of various test pieces>
(1) First, from Table 1 and FIG. 2, the test piece A1 according to the present invention is improved in both density and crushing strength compared to other test pieces that were not treated with the silane coupling agent. I understand. Thereby, it was confirmed that the dust core according to the present invention is excellent not only in magnetic properties but also in mechanical properties.

(2) In the dust core using any of the amino group silane coupling agent and the epoxy group silane coupling agent, the density and the crushing strength are improved as compared with the dust core not using the silane coupling agent. . In particular, looking at the overall trend, it was confirmed that a dust core using an amino group silane coupling agent was more likely to have higher strength and higher density than an epoxy group silane coupling agent.

It is the schematic diagram which showed notionally the particle | grains of the powder for magnetic cores which comprises the powder magnetic core of this invention. It is a correlation diagram of the density and crushing strength of each test piece. It is a correlation diagram of the density and crushing strength of the test piece from which the used silane coupling agent differs.

Claims (8)

The silicone resin cures the green compact obtained by press-molding a mixed powder obtained by mixing a magnetic core powder composed of a soft magnetic powder whose particle surface is coated with an insulating film and a resin powder composed of a thermosetting silicone resin. A dust core obtained by heating in a high temperature state,
The magnetic core powder further has a coupling layer made of a silane coupling agent on the particle surface covered with the insulating film,
The green compact is obtained by pressure-molding the mixed powder in a warm state where the resin powder is softened,
A dust core characterized by high density, high specific resistance and high strength.   The dust core according to claim 1, wherein the insulating film is an insulating film containing silicon (Si).   The powder magnetic core according to claim 1 or 2, wherein the silicone resin is 0.05 to 0.5 mass% when the entire green compact is 100 mass%.   The powder dust according to claim 1 or 3, wherein a density ratio (ρ / ρ0:%), which is a ratio of a bulk density (ρ) of the dust core to a true density (ρ0) of the soft magnetic powder, is 98% or more. core.   The dust core according to claim 1 or 4, wherein the green ring strength is 70 MPa or more. A contact step in which a silane coupling agent is brought into contact with the particle surface of the magnetic core powder composed of a soft magnetic powder whose particle surface is coated with an insulating film;
A mixing step of mixing the magnetic core powder after the contact step and a resin powder comprising a thermosetting silicone resin;
A molding step of pressure-molding the mixed powder after the mixing step in a warm state in which the resin powder is softened;
A heating step of heating the green compact after the molding step in a high temperature state where the silicone resin is cured,
A method for producing a dust core, wherein a dust core having high density and excellent specific resistance and strength is obtained. The molding step is a warm heating step of heating the mixed powder filled in a mold to the warm state;
The method for producing a powder magnetic core according to claim 6, further comprising a pressing step of pressing the magnetic core powder in a state where the resin powder is softened by the warm heating step.   The method of manufacturing a dust core according to claim 6 or 7, wherein the heating step is an annealing step for annealing to remove residual strain or residual stress generated in the particles of the magnetic core powder after the forming step.

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