JP2010016290A - Ferrous metal magnetic particle, soft magnetic material, powder magnetic core and manufacturing method of them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ferrous metal magnetic particles useful for manufacturing a powder magnetic core in magnetic property and coercive force, wherein iron loss is reduced and influence of impurities, distortion and grain boundary in iron powder is eliminated. <P>SOLUTION: The ferrous metal magnetic particle includes water atomized iron powder containing iron by 99.5 wt.% or more, and a passive film of a metal oxide selected from a group of aluminum oxide, silicon oxide and mixture of them or a composite oxide, which is applied to the surface of the iron powder, and further the iron powder includes oxygen content by 0.01 wt.% or less and carbon content by 0.0010 wt.% or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to iron-based metal magnetic particles used in the production of soft magnetic materials and the use thereof. More specifically, the present invention has a low content of impurities in iron powder and prevents iron powder from being sintered. The present invention relates to an iron-based metal magnetic particle useful for producing a soft magnetic material, a soft magnetic material produced therefrom, and a production method thereof, and a dust core produced from such a soft magnetic material and a production method thereof. The dust core of the present invention can be advantageously used in various products using electromagnetism.

  As is well known, in products using electromagnetics such as transformers, motors, generators, actuators, etc., magnetic cores (soft magnets) are placed in alternating magnetic fields in order to efficiently obtain a large alternating magnetic field locally. It is common to provide in. A magnetic core is usually composed of a plurality of composite metal magnetic particles, which are composed of metal magnetic particles and an insulating film covering the surface thereof, bonded together with an organic binder to produce a soft magnetic material. Manufactured by compression molding. Therefore, such a magnetic core is generally called a “dust core”.

  Various studies have been made in the past to reduce iron loss (electric energy lost when magnetized by alternating current; expressed by the sum of hysteresis loss and eddy current loss) in a dust core. Of iron loss, hysteresis loss is affected by strain, grain boundaries, and impurities in iron powder that hinders domain wall movement, and the reduction of strain, grain boundaries, and impurities as problems is being promoted. However, the problem has not been solved yet. In addition, although the problem about the impurities in iron powder can be solved by using high-purity iron powder, the purity has a large influence on the cost. Therefore, industrially, water atomized iron powder Is currently using a lot. Examples of the water atomized iron powder include pure iron powder, trade name “ABC100.30” (manufactured by Höganäs) and iron powder coated with a phosphate film, and trade name “Somaloy 500” (manufactured by Höganäs).

  In recent years, for example, as described in Patent Document 1, atomized iron powder is subjected to reduction annealing at a temperature of 800 ° C. for 3 hours in an atmosphere of a mixed gas composed of hydrogen and argon, and a metal magnetism containing iron and oxygen. There have been proposed a soft magnetic material including particles and having a proportion of oxygen in the metal magnetic particles of less than 0.05% by mass, and a dust core made therefrom. According to this patent document, the amount of oxygen is reduced to less than 0.05 mass% by annealing, and the coercive force, that is, the hysteresis loss is also reduced.

  Another proposal has been made in Patent Document 2. That is, in this patent document, in order to improve the crystal grain boundary, the metal magnetic particles mainly composed of iron are heated at a temperature of 900 ° C. or higher and lower than the melting point of the metal magnetic particles in a hydrogen atmosphere or an inert gas atmosphere. It is proposed to heat-treat, and at least selected from the group consisting of Al, Si, Y, Zr, Ti, Mg and B prior to the heat-treatment step in order to prevent sintering of the magnetic particles at high temperature It has been proposed to mix spacer particles made of oxides, nitrides or carbides of one or more elements into metal magnetic particles. Patent Document 2 states that the particle diameter of the spacer particles is preferably 0.1 to 2 times the particle diameter of the metal magnetic particles. According to this patent document, metal magnetic particles can be heat-treated without being accompanied by sintering, and the hysteresis loss after the production of the dust core is reduced.

  However, there are still problems to be solved by the methods proposed in these patent documents. For example, in Patent Document 1, it is described that the coercive force can be reduced. However, the value of the coercive force shown is not always sufficient, and from an industrial point of view, it can be stored and processed after processing. There is a problem that oxygen diffuses into the metal magnetic particles in a certain insulating film forming process, and sometimes an iron oxide film is formed, resulting in deterioration of characteristics.

  Further, in the case of Patent Document 2, although it is described that the hysteresis loss is reduced, the value of the hysteresis loss shown is not necessarily sufficient, and is used in the spacer particle or the example described. Among the spacer particles, carbides and nitrides may cause carbon and nitrogen to diffuse into the metal magnetic particles at high temperatures, which may cause deterioration of magnetic properties. In addition, when the hydrogen atmosphere to be applied is particularly high in concentration, the oxide is easily reduced, and when metal elements other than Al and Si diffuse into the metal magnetic particles, it may cause deterioration of magnetic characteristics.

Japanese Patent Laying-Open No. 2005-213621 (Claims, paragraph 0039) JP 2005-336513 A (Claims, paragraphs 0038 to 0042)

  An object of the present invention is to provide a dust core having excellent magnetic properties and coercive force, in which iron loss is reduced and the influence of distortion, grain boundaries and impurities in the iron powder is eliminated, and such a dust core. An object of the present invention is to provide iron-based metal magnetic particles and soft magnetic materials suitable for the production of magnetic cores, and methods for producing them.

  As a result of earnest research to solve the above-mentioned problems, the present inventor used water atomized iron powder, which is pure iron powder, as metal magnetic particles to be used as a starting material when producing a soft magnetic material, and aluminum and The present invention was completed by obtaining the knowledge that it is effective to coat the surface of the iron powder with a passive film made of (or) a silicon oxide.

In one aspect of the present invention, a water atomized iron powder having an iron content of 99.5% by weight or more, an aluminum oxide, a silicon oxide and a mixture thereof applied to the surface of the iron powder, or A passive film of a metal oxide selected from the group consisting of complex oxides,
The iron powder is in an iron-based metal magnetic particle for producing a soft magnetic material having an oxygen content of 0.02% by weight or less and a carbon content of 0.0015% by weight or less.

  In another aspect of the present invention, there is a soft magnetic material including the iron-based metal magnetic particles of the present invention and an insulating film covering the surface of the metal magnetic particles.

  Furthermore, in another aspect of the present invention, there is a dust core made from the soft magnetic material of the present invention.

In addition, the present invention is a method for producing the iron-based magnetic metal particles of the present invention,
Preparing as a starting material water atomized iron powder having an iron content of 99.5% by weight or more and metal oxide particles selected from the group consisting of aluminum oxide, silicon oxide and mixtures or composite oxides thereof And
Mixing the iron powder and the metal oxide particles to prepare an iron-based metal mixture;
Heat-treating the metal mixture at a temperature of 900 ° C. or higher and lower than the melting point of the iron powder in a hydrogen atmosphere having a concentration equal to or higher than the upper limit of explosion
A metal selected from the group consisting of aluminum oxide, silicon oxide, a mixture thereof, or a composite oxide or a passive film of the oxide is formed on the surface by the heat treatment. Separating iron powder from the metal oxide particles;
In the manufacturing method of the iron-type metal magnetic particle containing this.

Further, the present invention is a method for producing the soft magnetic material of the present invention, wherein iron-based metal magnetic particles are produced by the production method of the present invention,
Forming an insulating film on the surface of the iron-based metal powder of the iron-based metal magnetic particles;
A method for producing a soft magnetic material.

Furthermore, the present invention is a method for producing the dust core of the present invention,
Producing ferrous metal magnetic particles by the production method of the present invention;
Forming an insulating film on the surface of the iron-based metal powder of the iron-based metal magnetic particles to produce a soft magnetic material;
Compression-molding the soft magnetic material to form a compression-molded body having a desired shape;
Annealing the compression molded body at an elevated temperature;
In the manufacturing method of the powder magnetic core containing.

  According to the present invention, as will be understood from the following detailed description, the iron loss is reduced, and the effects of distortion, crystal grain boundaries and impurities in the iron powder are eliminated, and the magnetic characteristics and coercive force are reduced. An excellent dust core can be provided. Moreover, according to this invention, the iron-type metal magnetic particle and soft magnetic material which are useful for manufacture of this powder magnetic core can also be provided.

  In addition, according to the present invention, it is possible to provide a method for producing iron-based metal magnetic particles, soft magnetic materials, and dust cores easily and with high reliability and at low cost.

  The iron-based magnetic metal particles, soft magnetic materials, dust cores and methods for producing them according to the present invention can be advantageously implemented in various forms. Hereinafter, although these forms are explained with reference to an accompanying drawing, the present invention is not limited to the form described below.

  The iron-based metal magnetic particles of the present invention have been developed for the purpose of producing a soft magnetic material and a dust core, and are schematically shown in FIG. FIG. 1 (A) shows the entire iron-based metal magnetic particle 5, and FIG. 1 (B) shows an enlarged cross section of the region B in FIG. 1 (A). As shown in the figure, the iron-based metal magnetic particles 5 are composed of water atomized iron powder 1 that is pure iron powder and a metal oxide thin film 2 that covers the surface of the iron powder. The metal oxide thin film 2 is a passive film of a metal oxide such as aluminum oxide or silicon oxide.

  As described above, the iron-based metal magnetic particles of the present invention are composed of water atomized iron powder and a metal oxide passivation film containing aluminum and / or silicon covering the powder. There are the following reasons for this.

  As a premise, the characteristics required for the dust core are high magnetic flux density and low iron loss. Here, the magnetic flux density is determined by the composition of the soft magnetic material (100% of Fe is ideal) and the molding density, and the iron loss is the sum of hysteresis loss and eddy current loss as described above. Hysteresis loss (= coercive force) represents energy loss with respect to a change in magnetic field, and is considered to be caused by impurities, crystal grain size, distortion, and the like of iron powder. In addition, since eddy current loss is caused by eddy current generated by the passage of magnetic flux, it is important to improve the insulation of the dust core. While examining these, the present invention has been found that the coercive force (hysteresis loss) is reduced by paying attention mainly to impurities in the iron powder and reducing it.

  In addition, the basic stance of the present invention is to highly purify iron powder by a technique that can be established industrially in consideration of cost, mass productivity, and the like. Therefore, in the present invention, water atomized iron powder, which is commercially available at low cost, is used instead of powder made of high-purity but very expensive “electrolytic iron” or “gas atomized” iron powder. It is selected and used well. Moreover, although the metal oxide containing aluminum and / or silicon is used, it is because elements other than iron are directly linked to a decrease in magnetic flux density. Furthermore, it has been reported that elements other than aluminum and silicon lead to an increase in coercive force, which is contrary to the object of the present invention.

  In the iron-based metal magnetic particles of the present invention, the water atomized iron powder is pure iron powder and has an iron content of 99.5% by weight or more and a particle size of 100 to 300 μm. Such water atomized iron powder is commercially available, for example, as “ABC100.30” (trade name, average particle size: 80 μm), “300NH” (trade name, average particle size: 80 μm) from Höganäs. .

  Water atomized iron powder has an iron content of 99.5% by weight or more. If the iron content is less than 99.5% by weight, the amount of impurities increases accordingly, the magnetic properties are lowered, and it becomes difficult to ensure the desired magnetic properties.

  Moreover, the water atomized iron powder has a particle size of 100 to 300 μm. In the water atomized iron powder, the smaller the particle size, the more the coercive force is increased, that is, the hysteresis loss and the iron loss are increased. On the other hand, as the particle size increases, although it depends on the operating frequency, eddy currents are likely to be generated, leading to an increase in eddy current loss and an increase in iron loss. Considering such drawbacks, in the present invention, as described above, water atomized iron powder having a particle size of 100 to 300 μm is preferable. For example, when it is assumed that the operating frequency is about 400 MHz, the particle size of the water atomized iron powder is about 100 to 200 μm.

  Further, the water atomized iron powder has an oxygen content of 0.02% by weight or less and a carbon content of 0.0015% by weight or less. Whether the oxygen content exceeds 0.02% by weight or the carbon content exceeds 0.0015% by weight, the contained oxygen and carbon adversely affect the magnetic properties, and the desired magnetic properties can be obtained. Can not.

  In the iron-based metal magnetic particles of the present invention, the surface of water atomized iron powder, which is pure iron powder, is coated with a metal oxide, and at that time, many metals exist as the metal of the metal oxide. In particular, aluminum or silicon is used. The metal oxide is a metal oxide obtained by reacting aluminum or silicon with oxygen. Therefore, the metal oxide thin film is a group consisting of aluminum oxide, silicon oxide and a mixture or composite oxide thereof. A metal oxide passivation film selected from

  The metal oxide passivation film can preferably be roughly divided into two forms. One form is a metal oxide film physically attached to the iron powder, and the other form is a metal oxide diffusion layer that penetrates the surface of the iron powder by diffusion. In any form, the thickness of the metal oxide passivation film is preferably in the range of 1 nm to less than 5 μm.

  It is considered that the metal oxide passivation film has a higher effect of suppressing the oxidation of iron powder as the film thickness is larger. On the other hand, when the thickness of the passive film increases or the contents of aluminum and silicon increase (even if the distribution form of aluminum and silicon is a thin film or diffuses in the elemental state), the hardness of the iron powder Increases, the molding density decreases, and the magnetic flux density decreases. Considering these matters, the thickness of the metal oxide passivation film is usually preferably in the range of 1 nm to less than 5 μm, and more preferably in the range of 10 nm to 1 μm.

  The present invention also provides a soft magnetic material comprising the iron-based metal magnetic particles of the present invention as described above and an insulating film covering the surface of the metal magnetic particles, and a pressure produced from the soft magnetic material. In the powder magnetic core. The dust core of the present invention has a coercive force of 150 A / m or less. The form of the soft magnetic material and the powder magnetic core can be easily understood from the cross-sectional view of FIG.

  FIG. 2 is a cross-sectional view schematically showing the dust core of the present invention. The dust core 10 is a compact of a plurality of soft magnetic metal magnetic particles 5. As described above with reference to FIG. 1, the metal magnetic particle 5 includes a water atomized iron powder 1 that is a pure iron powder and a metal oxide thin film 2 that covers the surface of the iron powder. The water atomized iron powder 1 has a particle size of 100 to 300 μm. In addition, the surface of the metal magnetic particles 5 is covered with an insulating film 3. That is, the soft magnetic material of the present invention is formed by the metal magnetic particles 5 and the insulating coating 3, and the dust core 10 of the present invention is formed from the green compact of the soft magnetic material. In addition, the soft magnetic material of the present invention is a form generally called a composite soft magnetic material.

  The soft magnetic material of the present invention comprises the iron-based metal magnetic particles of the present invention having a passive film on the surface, and an insulating film surrounding the metal magnetic particles. The insulation film covers the metal magnetic particles with the insulation film to increase the electrical resistivity ρ of the resulting dust core when compression molding a soft magnetic material composed of composite magnetic particles of the metal magnetic particles and the insulation film. Further, by increasing the electrical resistivity ρ, it is possible to suppress the eddy current from flowing between the metal magnetic particles and reduce the eddy current loss of the dust core.

  The insulating film can be formed from an insulating material generally used in the production of a dust core by using any film forming method. For example, as the insulating material, a material containing a silicone resin, a metal alkoxide, or a phosphate can be used. For example, when an insulating film is formed from a silicone resin, excellent insulating properties derived from the silicone resin can be achieved with a thin film. Moreover, also when forming an insulating film from the metal oxide containing a phosphate, the coating layer which covers the surface of a metal magnetic particle can be made thinner. Thereby, the magnetic flux density of a composite magnetic particle can be enlarged and a magnetic characteristic can be improved. The insulating film may be used as a single layer, or may be used as two or more layers as necessary.

  Examples of the phosphate used for forming the insulating film include iron phosphate, manganese phosphate, zinc phosphate, calcium phosphate, and aluminum phosphate. Examples of the oxide that can be used include silicon oxide, titanium oxide, aluminum oxide, and zirconium oxide.

  The film thickness of the insulating film can be changed within a wide range. The average film thickness of the insulating film is preferably 0.005 to 20 μm, and more preferably 0.05 to 0.1 μm. By setting the film thickness of the insulating film to 0.005 μm or more, energization due to the tunnel effect can be suppressed. Further, by setting the thickness to 0.05 μm or more, energization due to the tunnel effect can be more effectively suppressed. On the other hand, when the film thickness of the insulating film is 20 μm or less, the insulating film can be prevented from being sheared and destroyed during compression molding. Further, since the ratio of the insulating film in the soft magnetic material does not become too large, it is possible to prevent the magnetic flux density of the dust core obtained by compression molding the soft magnetic material from being significantly reduced. Moreover, the fall of magnetic flux density can further be prevented by making the film thickness of an insulating film into 0.1 micrometer or less. For the formation of the insulating film, a wet coating method using an organic solvent, a dipping method, a direct coating method using a mixer, a spray method, or the like can be used, but the method is not limited to these methods.

  The present invention is in addition to iron-based metal magnetic particles, soft magnetic materials, and dust cores, as well as methods for producing them. The outline of the method of the present invention can be easily understood from the flowchart of the manufacturing process shown in FIG. Note that the flowchart of FIG. 3 is an example, and it is possible to replace processes or add additional processes within the scope of the present invention.

  First, a starting material for producing iron-based metal magnetic particles is prepared. As shown in the figure, the starting material is water atomized iron powder and metal oxide particles containing aluminum or silicon. Optionally, an optional third component may be added to these starting materials. Subsequently, these starting materials are mixed to prepare an iron-based metal mixture.

  Subsequently, the obtained metal mixture is heat-treated at a high temperature in a hydrogen atmosphere. By this heat treatment, an iron powder is formed on the surface of the iron powder, to which a passive film of a metal oxide selected from the group consisting of aluminum oxide, silicon oxide and a mixture or composite oxide is adhered. Is done. This iron powder with a passive film is the iron-based metal magnetic particle of the present invention. The iron-based metal magnetic particles are separated from the metal oxide particles of the raw material that have not adhered, diffused, or permeated therein.

  After producing the iron-based metal magnetic particles of the present invention as described above, an insulating film is formed on the surface of the iron-based metal magnetic particles of the present invention to produce the soft magnetic material of the present invention. The insulation film can be formed according to a conventional method.

  Subsequently, the obtained soft magnetic material is compression-molded and annealed (heat treated) to produce the dust core of the present invention. The compression molding and annealing can be performed according to a conventional method, and if necessary, the compression molding step and the annealing step may be repeated twice or more.

  In one aspect, the present invention is a method for producing the iron-based metal magnetic particles of the present invention. In order to carry out this method, first, it consists of water atomized iron powder having an iron content of 99.5% by weight or more and a particle size of 100 to 300 μm, and aluminum oxide, silicon oxide and a mixture or composite oxide thereof. A metal oxide particle selected from the group is prepared as a starting material. The reason for using these starting materials is as described above.

Next, iron powder and metal oxide particles are mixed to prepare an iron-based metal mixture. The mixing ratio of the iron powder and metal oxide particles is usually in the range of 4: 1 to 1: 1 by weight. For example, water atomized iron powder (Fe) and aluminum oxide (Al ₂ O ₃ ) can be mixed at a weight ratio of 3: 1. As the mixing means, for example, a ball mill (rotating without inserting a ball) or the like can be used.

  After completion of mixing, the obtained iron-based metal mixture is heat-treated. The heat treatment is performed at a temperature of 900 ° C. or higher and lower than the melting point of the iron powder in a hydrogen atmosphere having a concentration higher than the upper limit of explosion. By performing the heat treatment at a temperature of 900 ° C. or higher, the removal of oxygen and carbon can be achieved more effectively. In addition, iron transforms from ferrite to austenite at 911 ° C. as a boundary. Therefore, when the temperature becomes 911 ° C. or higher due to heat treatment, the crystal grain size, which is a cause of hysteresis loss, increases, and the loss factor can be reduced.

Further, the heat treatment is performed in a hydrogen atmosphere having a high concentration exceeding the upper limit of explosion. The main purpose is to discharge oxygen from iron. Since hydrogen has explosive properties, only a low concentration or a high concentration can be used. However, since the higher the concentration of oxygen, the higher the effect, so the present invention uses a high concentration. In addition, for example, in the case of aluminum (Al), it is considered that the reduction is performed only on the high concentration side. Therefore, when the adhesion of Al ₂ O ₃ to the iron powder surface is taken into consideration, the heat treatment is performed in a high concentration hydrogen atmosphere. Must.

  As a result of the heat treatment, a metal selected from the group consisting of aluminum oxide, silicon oxide, a mixture thereof or a composite oxide, called iron-based metal magnetic particles in the present invention, or a passive film of the oxide adheres to the surface. The iron powder that has been caulked is obtained. This iron powder can be separated from the metal oxide particles using conventional separation means. As the separation means, for example, a sieve or the like can be used. Fine metal oxide particles can be sieved by sieving iron powder. Moreover, you may use a magnet together with a sieve. By using a magnet, iron powder that could not be separated by a sieve can be supplementarily separated by attracting it with a magnet.

  The method of the present invention described above may be improved in various ways. For example, the metal oxide used as the starting material preferably has a purity of 99% by weight or more. By using such a pure metal oxide, it is possible to prevent other metal elements from diffusing into the iron powder used together.

The iron powder used as the starting material is preferably D2 <D1, where D1 is the minimum particle size of the iron powder and D2 is the minimum particle size of the metal oxide particles. When the iron powder and the metal oxide satisfy this condition, separation of the obtained iron-based magnetic metal particles from the metal oxide, preferably sieving can be performed more effectively. This condition is also effective in achieving reliable contact between the metal oxide such as Al ₂ O ₃ and the iron powder, thereby preventing sintering, and the metal oxide such as aluminum to the iron powder. Adhesion promotion can be achieved.

  Preferably, in the method of the present invention, the amount of oxygen and the amount of carbon contained in the iron powder used as the starting material are reduced by the heat treatment step. As described above, oxygen can be removed from the iron powder by performing heat treatment in a hydrogen atmosphere at a high temperature. When iron is compared with aluminum and silicon, since aluminum and silicon are more easily oxidized than iron, it is possible to promote the discharge of oxygen inside the iron powder to the outside. Moreover, since carbon is not contained in the atmosphere used here, the carbon in iron powder can also be discharged | emitted outside.

  In another aspect, the present invention resides in a method for producing a soft magnetic material. This method is characterized in that after producing iron-based metal magnetic particles according to the above-described method of the present invention, an insulating film is formed on the surfaces of the iron-based metal magnetic particles. The insulating film can be formed as described above.

In another aspect, the present invention resides in a method for manufacturing a dust core. In this method, after producing iron-based metal magnetic particles according to the above-described method of the present invention, an insulating film is formed on the surface of the iron-based metal magnetic particles to produce a soft magnetic material;
Compression-molding the soft magnetic material to form a compression-molded body having a desired shape;
Annealing the resulting compression molded body at an elevated temperature;
It is characterized by including.

  In the method of the present invention, an insulating film is formed to produce a soft magnetic material, and then the resulting soft magnetic material is compression molded. Here, since it is used as an auxiliary agent at the time of molding, it is preferable that iron-based metal magnetic particles (composite magnetic particles) covered with an insulating film are bonded to each other with a binder. As the binder (binder), an organic binder can be advantageously used as generally used in this technical field. The organic binder can function as a buffer material between the composite magnetic particles in the subsequent compression molding process, and can prevent the insulating coating from being broken by contact between the composite magnetic particles. In addition, the organic binder can be removed from the dust core by combustion or decomposition in an annealing process performed subsequent to the compression process. However, if necessary, an inorganic binder may be used instead of the organic binder.

  The organic binder is not limited to those listed below, but examples thereof include thermoplastic polyimide, thermoplastic polyamide, thermoplastic polyamideimide, polyphenylene sulfide, polyamideimide, polyethersulfone, polyetherimide, and polyetheretherketone. Non-thermoplastic resins such as thermoplastic resin, high molecular weight polyethylene, wholly aromatic polyester, wholly aromatic polyimide, zinc stearate, lithium stearate, calcium stearate, lithium palmitate, calcium palmitate, lithium oleate, calcium oleate And higher fatty acid compounds. These organic binders may be used alone or in combination of two or more.

  When mixing a plurality of composite magnetic particles using a binder, any mixing method can be used. Suitable mixing methods include, for example, mechanical alloying, vibration ball mill, planetary ball mill, mechanofusion, coprecipitation, chemical vapor deposition (CVD), physical vapor deposition (PVD), plating, and sputtering. Method, vapor deposition method, sol-gel method and the like can be used. By this mixing step, a soft magnetic material in which a plurality of composite magnetic particles are bonded to each other with a binder is obtained.

  Here, the ratio of the binder to the soft magnetic material is preferably more than 0 and 1.0% by mass or less. By setting the binder ratio to 1.0% by mass or less, the ratio of the composite magnetic particles in the soft magnetic material can be secured to a certain level or more, and a soft magnetic material having a higher magnetic flux density can be obtained. . The mixing of the binder is not an essential process, and if necessary, a subsequent compression molding process using only the composite magnetic particles may be performed without mixing the binder.

  Subsequently, a compression molding process is performed. For the compression molding process, the soft magnetic material, usually in the form of mixed powder, obtained in the previous process is filled into a mold having a desired shape (for example, ring shape) in the final product. A lubricant may be applied in advance to the inside of the mold. Next, the soft magnetic material filled in the mold is compression-molded at a mold temperature of 100 to 150 ° C. and a pressure of 700 to 1500 MPa, for example. The compression molding can be performed under molding conditions generally used conventionally by using a molding apparatus generally used for manufacturing a dust core. Thereby, mixed powder is compressed and a compression molding body is obtained.

  Subsequently, in order to soften the composite magnetic particles and increase the film strength, and to reset the distortion of the compression molded body generated during compression molding, an annealing process, which may be called heat treatment, is performed as necessary. The annealing process is performed under conditions necessary to reset the strain generated during compression molding, for example, under vacuum at the temperature and time required to achieve it. An annealing process is normally implemented at the temperature which is less than the thermal decomposition temperature of an insulating film from 300 degreeC or more, for example, is implemented at the temperature of 300-910 degreeC. The annealing holding time is usually 1 minute to 10 hours. As described above, the compression molding step and the annealing step may be repeated as necessary. A target dust core can be manufactured through such a series of steps.

  In summary, in the present invention, the metal magnetic particles are particularly limited to pure iron powder in producing metal magnetic particles useful for the production of soft magnetic materials and dust cores. Further, in order to improve the purity of the metal magnetic particles and the grain boundaries, pure iron powder is mixed with metal oxide particles containing one or both of aluminum and silicon. The obtained mixture is heated at 900 ° C. or higher and in an atmosphere having a hydrogen concentration higher than the upper limit of explosion, heat-treated, and then the iron-based iron of the present invention provided with a passive film formed by the heat treatment. The metal magnetic particles are separated from the metal oxide particles used as a raw material.

  In the present invention, since the mixture is heat-treated in a high temperature and high concentration hydrogen atmosphere, oxygen contained in the pure iron powder can be discharged into the atmosphere. Moreover, since carbon is not contained in the hydrogen atmosphere, carbon in the iron powder can be discharged into the atmosphere at the same time.

  In the present invention, it is important that metal oxide particles containing one or both of aluminum and silicon are used in combination with pure iron powder. First, aluminum and silicon have a very small influence on magnetic properties as used in electromagnetic steel sheets and the like, and can contribute to improvement of magnetic properties.

  Furthermore, during the heat treatment, some of the metal oxide particles containing aluminum and silicon are reduced, and one or both of aluminum and silicon adhere to or diffuse on the surface of the pure iron powder. These aluminum and silicon are more likely to be combined with oxygen than iron, and thus easily form a passivated film (“passive film” in the present invention) on the surface of pure iron powder. The formation of the passive film can suppress the oxidation of iron powder that is likely to occur during storage or in a later process.

  Furthermore, in the metal oxide particles containing aluminum and silicon, the smaller the particle size of the particles used, the larger the contact area with the iron powder surface, and more aluminum or silicon adheres to the surface of the pure iron powder. It becomes easy to diffuse. Furthermore, since the particle size of the metal oxide particles is smaller than the substantial minimum particle size of the pure iron powder, the separation process can be performed easily and quickly when separating them by sieving or the like. Then, by adding a separation step using a magnet, almost complete and reliable separation can be achieved.

  By the way, in order to prevent oxidation of iron, there is an example in which aluminum or silicon is added during the preparation of iron powder. In this case, aluminum or silicon penetrates into the iron powder, and as a result, The disadvantage of increased hardness cannot be avoided. As can be appreciated, the application of this technique to the present invention results in an undesirable situation where aluminum or silicon has penetrated into the interior of the metal magnetic particles, resulting in the metal particles becoming too hard, resulting in compaction. When compression molding is performed to manufacture a magnetic core, it is difficult to increase the molding density.

  As described above, the dust core of the present invention is derived from the soft magnetic material used as a starting material, and has a low iron loss (hysteresis loss + eddy current loss) and a high magnetic flux density. Moreover, because of these excellent magnetic properties, the dust core of the present invention can be advantageously used in various products. As an example, it can be advantageously used in various electromagnetic devices using electromagnetism, such as transformers, electric motors, generators, actuators, and the like. The dust core of the present invention is particularly suitable for automotive applications. Examples of automobile applications include fuel injection valves for automobile engines, electromagnetic actuators for driving engine valves, injectors, and the like.

  Subsequently, the present invention will be described with reference to examples thereof. Needless to say, the present invention is not limited to these examples.

Example 1
In this example, the heat treatment atmosphere was identified.

Iron powder heat treatment process:
Commercially available water atomized iron powder (trade name “ABC100.30”, manufactured by Höganäs) was sieved to prepare pure iron powder having a particle size of 100 to 300 μm. Next, 1 kg of the prepared pure iron powder was put into a pot mill together with 300 g of aluminum oxide (Al ₂ O ₃ ) particles having a purity of 99% and a particle diameter of 10 μm, and mixed thoroughly.

The resulting iron-based metal mixture is then placed in an alumina container to determine the heat treatment atmosphere so that the following different atmospheres:
(1) Vacuum atmosphere (2) Mixed gas atmosphere of argon (Ar) and hydrogen (H ₂ ) (H ₂ concentration is 1%)
(3) Hydrogen atmosphere (about 100% hydrogen)
Under heat at 1100 ° C. for 3 hours. The heat treatment apparatus used in this example is a vacuum heat treatment furnace when a vacuum atmosphere is applied, and when a mixed gas atmosphere or hydrogen atmosphere is applied, the heat treatment apparatus having each gas pipe has a predetermined concentration. Gas was supplied so that As a result of the heat treatment, iron-based metal particles (iron powder) made of pure iron powder covered with a passive film of Al ₂ O ₃ were obtained.

Iron powder separation process:
After the heat treatment was completed, the iron powder with a passive film and the Al ₂ O ₃ particles were separated using a sieve having a spread of 75 μm. Furthermore, Al ₂ O ₃ particles remaining between the iron powders were removed using a magnet.

Insulating film formation process:
In order to produce a soft magnetic material, a commercially available silicone resin (trade name “KR220L”, manufactured by Shin-Etsu Chemical Co., Ltd.) in an amount of 0.2% by weight and iron powder with a passive film in an amount of 99.8%, Each prepared. Next, the silicone resin was dissolved in 300 g of isopropyl alcohol (IPA) and sprayed onto iron powder to form an insulating film, and further dried at 200 ° C. for 1 hour. The film thickness of the insulating film was about 100 nm. An iron powder (composite soft magnetic material) with an insulating film was obtained.

Compression molding process:
The composite soft magnetic material obtained in the previous step was filled in a mold (die + core rod). For compression molding, a pressure of 1300 MPa was applied to the mold (upper and lower punches) at a temperature of 130 ° C. with a hydraulic press. A ring-shaped molded body having an outer diameter of 19 mm, an inner diameter of 13 mm, and a thickness of 3 mm was obtained.

Annealing process:
The molded body obtained in the previous step was annealed (heat treated) at a temperature of 600 ° C. for 1 hour in a vacuum furnace. A ring-shaped dust core was obtained. A dust core produced in a vacuum atmosphere was designated as sample B, a dust core produced in a mixed gas atmosphere was designated as sample C, and a dust core produced in a hydrogen atmosphere was designated as sample D.

Further, Al ₂ O ₃ oxide silicon the same amount in place of the particles (SiO ₂₎ using the particle where the above procedure was repeated, equivalent to dust core obtained when using Al ₂ O ₃ particles A ring-shaped dust core was obtained.

  Further, for the purpose of comparison, a ring-shaped dust core was produced according to a conventional method. In this example, only commercially available water atomized iron powder (trade name “ABC100.30”, manufactured by Höganäs) is used as a starting material, and thus the iron powder heat treatment step and the iron powder separation step are omitted from the above-described manufacturing method. And the formation process of the insulating film, the compression molding process, and the annealing process were implemented according to said method. The ring-shaped dust core thus obtained was used as Sample A (control).

[Evaluation of coercive force]
For samples A, B, C and D, coercivity was measured. The coercive force was measured by winding a formed body (annealed) corresponding to each sample and using a DC BH analyzer, and evaluating the coercive force from the obtained measurement results. FIG. 4 is a plot of the obtained measurement results. As can be understood from FIG. 4, only Sample D (a dust core produced in a hydrogen atmosphere) can guarantee the target coercive force of 120 A / m or less.

Example 2
In this example, the heat treatment temperature was determined.

  Although the dust core was produced according to the method described in Example 1, in this example, in order to determine the heat treatment temperature, the iron-based metal mixture was placed in an alumina container, and under a hydrogen atmosphere (about 100% hydrogen). Heat treatment was carried out at different temperatures: 800 ° C., 1000 ° C. or 1100 ° C. for 3 hours. Regarding the obtained ring-shaped dust core, a dust core produced at a heat treatment temperature of 800 ° C. was produced by Sample E, a dust core produced at a heat treatment temperature of 1000 ° C. was produced by Sample F, and a heat treatment temperature of 1100 ° C. The dust core was designated as Sample G. For comparison, the sample A (control) prepared in Example 1 was also used again.

[Evaluation of coercive force]
For samples A, E, F, and G, coercivity was measured according to the method described in Example 1. FIG. 5 is a plot of the obtained measurement results. As understood from FIG. 5, the coercive force reduction effect was insufficient in Sample E (a dust core produced at a heat treatment temperature of 800 ° C.).

Example 3
In this example, changes in the amount of oxygen and the amount of carbon in the iron powder with and without heat treatment were evaluated.

  Although the dust core was produced according to the method described in Example 2, in this example, the iron-based metal mixture was placed in an alumina container, and a different temperature under a hydrogen atmosphere (about 100% hydrogen): 1000 ° C. or 1100 ° C. The heat treatment was carried out for 3 hours. Regarding the obtained ring-shaped dust core, Sample H was a dust core produced at a heat treatment temperature of 1000 ° C., and Sample I was a dust core produced at a heat treatment temperature of 1100 ° C. For comparison, the sample A (control) prepared in Example 1 was also used again.

[Measurement of oxygen content in iron powder]
For samples A, H, and I, the amount of oxygen in the iron powder was measured according to the inert gas dissolution-infrared absorption method, and the measurement results plotted in FIG. 6 were obtained. As understood from FIGS. 5 and 6, the oxygen content needs to be 0.02% or less in order to guarantee the target coercive force of 120 A / m or less.

[Measurement of carbon content in iron powder]
For samples A, H, and I, the amount of carbon in the iron powder was measured according to the combustion-infrared absorption method, and the measurement results plotted in FIG. 7 were obtained. As understood from FIGS. 5 and 7, the carbon content needs to be 0.015% or less in order to guarantee the target coercive force of 120 A / m or less.

Example 4
In this example, the change in the adhesion of aluminum on the iron powder surface with and without heat treatment was evaluated.

A dust core was produced according to the method described in Example 1. As described in Example 1, the heat treatment is performed in different atmospheres as follows:
(1) Vacuum atmosphere (2) Mixed gas atmosphere of argon (Ar) and hydrogen (H ₂ ) (H ₂ concentration is 1%)
(3) Hydrogen atmosphere (about 100% hydrogen)
Carried out at 1100 ° C. for 3 hours. For the obtained ring-shaped dust core, as in Example 1, the dust core produced in a vacuum atmosphere was sample B, the dust core produced in a mixed gas atmosphere was sample C, and in a hydrogen atmosphere The produced dust core was designated as Sample D. For comparison, a dust core was prepared without performing the above heat treatment and used as sample J (control).

[Analysis of iron powder surface]
For samples B, C, D and J, the surface of the iron powder was analyzed by an energy dispersive X-ray fluorescence analyzer (EDX). As a result, in sample J that was not heat-treated, as shown in FIG. 8, although there was a silicon (Si) peak derived from the presence of the insulating film, there was no peak showing adhesion to aluminum (Al). It was. On the other hand, in the samples B, C, and D subjected to the heat treatment, as shown in FIG. 9, there was a peak indicating that Al was adhered to the iron powder surface by the heat treatment only for the sample D produced in a hydrogen atmosphere. In the analysis on the iron powder surface, Al was not detected from a region other than the region having a depth of 1 μm or less from the surface.

Example 5
In this example, it was evaluated how the difference in the particle size of the metal oxide particles affects the production of the dust core.

A dust core was produced according to the method described in Example 1. However, in this example, in the iron powder heat treatment step, the heat treatment conditions are set to a treatment temperature of 1100 ° C., a treatment time of 3 hours, and a hydrogen atmosphere (about 100% hydrogen), and aluminum oxide (Al The particle size of the ₂ O ₃ ) particles was changed from 10 μm to 200 μm and 1 mm.

Subsequent to the iron powder heat treatment process, the iron powder separation process, the insulating film formation process, the molding process, and the annealing process were performed according to Example 1, and when the particle size of the Al ₂ O ₃ particles was 200 μm, sieve classification It became difficult to separate from the iron powder. Moreover, when the particle size of the Al ₂ O ₃ particles was 1 mm, iron powder was partially sintered, making it difficult to use as a raw material. As can be seen from these facts, the particle size of the metal oxide particles is desirably smaller than the particle size of the iron powder.

It is the schematic diagram and partial sectional view which show one preferable form of the iron-type metal magnetic particle by this invention. It is sectional drawing which shows one preferable form of the powder magnetic core by this invention. It is a flow sheet which shows in order the manufacturing process of the iron-type metal magnetic particle by this invention, a soft magnetic material, and a dust core. It is the graph which plotted the result of having measured coercive force about the sample produced by applying different heat processing atmosphere. It is the graph which plotted the result of having measured coercive force about the sample produced by applying different heat processing temperature. It is the graph which plotted the change of the oxygen amount in iron powder by the presence or absence of heat processing. It is the graph which plotted the change of the carbon content in iron powder by the presence or absence of heat processing. It is the graph which showed the result of having analyzed the surface of the iron powder which is not heat-processed by EDX. It is the graph which showed the result of having analyzed the surface of the heat-treated iron powder by EDX.

Explanation of symbols

1 Iron powder 2 Passive film 3 Insulating film 5 Iron-based metal magnetic particles 10

Claims (14)

Water atomized iron powder having an iron content of 99.5% by weight or more, and selected from the group consisting of aluminum oxide, silicon oxide and a mixture or composite oxide applied to the surface of the iron powder Consisting of a passive film of metal oxide,
The iron powder has an oxygen content of 0.02 wt% or less and a carbon content of 0.0015 wt% or less.   The metal magnetic particles according to claim 1, wherein the iron powder has a particle size of 100 to 300 μm.   The passive film is made of a metal oxide film attached to the iron powder or a metal oxide diffusion layer that has penetrated the surface of the iron powder by diffusion, and the thickness thereof ranges from 1 nm to less than 5 μm. The metal magnetic particles according to claim 1, wherein   A soft magnetic material comprising the iron-based metal magnetic particles according to any one of claims 1 to 3 and an insulating film covering a surface of the metal magnetic particles.   A dust core manufactured from the soft magnetic material according to claim 4.   The dust core according to claim 5, which has a coercive force of 150 A / m or less. A method for producing the iron-based metal magnetic particles according to claim 1,
Preparing as a starting material water atomized iron powder having an iron content of 99.5% by weight or more and metal oxide particles selected from the group consisting of aluminum oxide, silicon oxide and mixtures or composite oxides thereof And
Mixing the iron powder and the metal oxide particles to prepare an iron-based metal mixture;
Heat-treating the metal mixture at a temperature of 900 ° C. or higher and lower than the melting point of the iron powder in a hydrogen atmosphere having a concentration equal to or higher than the upper limit of explosion
A metal selected from the group consisting of aluminum oxide, silicon oxide, a mixture thereof, or a composite oxide or a passive film of the oxide is formed on the surface by the heat treatment. Separating iron powder from the metal oxide particles;
The manufacturing method of the iron-type metal magnetic particle containing this.   The said metal oxide is a manufacturing method of Claim 7 whose purity is 99 weight% or more.   The manufacturing method according to claim 7 or 8, wherein D2 <D1, where D1 is a minimum particle diameter of the iron powder and D2 is a minimum particle diameter of the metal oxide particles.   The said iron powder WHEREIN: The manufacturing method of any one of Claims 7-9 by which the quantity of the oxygen contained in it is made to fall by the said heat processing process.   The manufacturing method according to any one of claims 7 to 10, wherein in the iron powder, the amount of carbon contained in the iron powder is reduced by the heat treatment step.   The manufacturing method of any one of Claims 7-11 which performs the said isolation | separation process using a sieve and / or a magnet. A method for producing the soft magnetic material according to claim 4,
Producing iron-based metal magnetic particles by the production method according to any one of claims 7 to 12,
Forming an insulating film on the surface of the iron-based metal magnetic particles;
A method for producing a soft magnetic material, comprising: A method for producing a dust core according to claim 5, comprising:
Producing iron-based metal magnetic particles by the production method according to any one of claims 7 to 12,
Forming an insulating film on the surface of the iron-based metal magnetic particles to produce a soft magnetic material;
Compression-molding the soft magnetic material to form a compression-molded body having a desired shape;
Annealing the compression molded body at an elevated temperature;
A method for producing a powder magnetic core, comprising:

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