JP5555945B2 - Powder magnetic core and manufacturing method thereof - Google Patents

Description

  The present invention relates to a dust core and a method for manufacturing the same.

  In recent years, so-called low pollution vehicles such as fuel cell vehicles, electric vehicles, and hybrid vehicles have been developed. In particular, hybrid vehicles are becoming increasingly popular in Japan and overseas. For such a hybrid vehicle, in recent years, in order to improve the output of the electric motor, it is desired to increase the voltage for driving the electric motor, and the hybrid having a booster circuit that boosts the voltage of the mounted battery. Automobiles are in practical use. The booster circuit is provided with a reactor including a core (magnetic core) and a coil wound around the core.

  In general, the core material for the reactor includes a silicon steel plate, amorphous ribbon, oxide ferrite, and the like, and the core is manufactured by laminating plate materials, compacting, compacting and the like. In order to improve the direct current superimposition characteristics, an appropriate air gap (gap) is provided in the magnetic path of the core to adjust the apparent permeability.

  In addition, as a material for the core, there is a dust core produced by compression-molding soft magnetic metal powder such as iron. Compared with a laminated magnetic core made of an electromagnetic steel plate or the like, the dust core has a good material yield at the time of production and can reduce the material cost. In addition, it is possible to improve the characteristics by optimizing the magnetic core shape with a high degree of freedom in shape. Furthermore, eddy current loss (iron loss) can be achieved by mixing insulating materials such as organic resins and inorganic powders with metal powder, or by forming an insulating layer on the surface of the metal powder to increase the insulation between the metal powders. ) Can be significantly reduced, and excellent magnetic properties can be obtained particularly in the high frequency range. For these reasons, in recent years, dust cores have attracted attention as soft magnetic cores used in rotating electrical machines, transformers, reactors, choke coils and the like that are required to be downsized and highly efficient.

  As a method of manufacturing a dust core, there is a method in which a mixed powder obtained by adding a thermosetting resin powder to a soft magnetic powder having an inorganic insulating film formed on the surface thereof is compression-molded, and the powder is subjected to a resin curing treatment (patent) Literature 1 etc.). In recent years, there has been a demand for further reduction in iron loss of the powder magnetic core, and in order to reduce hysteresis loss, it is possible to reduce the hysteresis loss by applying heat treatment to the powder magnetic core to alleviate distortion caused by powder molding. (Patent Document 2 etc.).

Japanese Patent Laid-Open No. 9-320830 JP 2000-235925 A

  However, in recent years, with an increase in the output of motors and the like, cores such as reactors are required to be used at a magnetic flux density of 1.0 T or more under a high magnetic field of 10,000 A / m. In ordinary cores, the magnetic flux density is saturated under a high magnetic field, and the differential permeability, which is the slope of the tangent line of the magnetization curve, decreases, but the core for a reactor used in a high magnetic field is also differentiated on the high magnetic field side. It is required that the magnetic permeability does not decrease, that is, the constant magnetic permeability is excellent. Although the magnetic cores such as insulating materials and pores are dispersed in the dust core, the constant permeability under high magnetic fields is excellent, but the constant permeability under high magnetic fields is still insufficient. Absent.

  The constant magnetic permeability of the dust core and the iron loss may be in a trade-off relationship. For example, a dust core in which a resin is added as an insulator has a low maximum magnetic permeability and an excellent constant magnetic permeability under a high magnetic field. However, when heat treatment is performed on a powder magnetic core to which a resin is added as an insulator, if the heat treatment temperature is too high, the resin deteriorates and decomposes, resulting in deterioration of insulation. Therefore, the heat treatment temperature is lower than the heat-resistant temperature of the resin (about 300 ° C.), the distortion removal is incomplete, the hysteresis loss cannot be sufficiently reduced, and the iron loss becomes high.

  On the other hand, if a dust core is made of only iron-based soft magnetic powder with a phosphate-based insulating layer formed on its surface without the addition of resin, heat treatment of the dust core at a high temperature is possible. We can hope for damage. In this case, the higher the heat treatment temperature, the greater the magnetic permeability under a high magnetic field with respect to the maximum magnetic permeability, thereby degrading the constant magnetic permeability. In order to apply a core with poor magnetic permeability to the reactor, it is necessary to design a thicker gap, increase the number of gaps, etc. Increase in the size of the reactor and the size of the reactor, which is not preferable for applications such as in-vehicle use where fuel efficiency requirements and mounting space are limited.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a dust core capable of ensuring constant magnetic permeability characteristics in a high magnetic field and reducing iron loss, and a method for manufacturing the same.

  The dust core of the present invention is a dust core having an insulating layer containing a particulate metal oxide between metal powders, and the insulating layer contains Ca, P, O, Si and C as elements. The insulating layer preferably contains calcium phosphate and silicon oxide.

  In this case, the insulating layer contains particulate metal oxide, calcium phosphate and silicon oxide, and the insulating layer is formed so as to surround the metal powder while firmly bonding to the metal powder. For this reason, the powder magnetic core which suppressed the iron loss without impairing a constant magnetic permeability characteristic is obtained. As a method for improving the constant magnetic permeability characteristic, there is a method of adding a metal oxide powder serving as a filler to a coated metal powder provided with an insulating layer containing a phosphate. In this case, there is a disadvantage that the density of the dust core is reduced due to the presence of the filler. On the other hand, since the dust core of the present invention can form a dust core only from the coated metal powder provided with the composite insulating layer containing the metal oxide, a high-strength dust core can be provided. Increasing the strength of the dust core expands the application range from the viewpoint of in-vehicle components.

  The particle diameter of the metal oxide is preferably 10 nm or more and 350 nm or less. As the metal oxide having a larger particle diameter is used, the insulating property is better, and as the metal oxide having a smaller particle diameter is used, the strength and the density of the molded body tend to be higher. In addition, metal oxides having different particle diameters can be used in combination in terms of improving the coverage of the surface of the metal powder and making the metal oxide layer denser. When fine metal oxide fine particles are mixed between relatively large metal oxides deposited on the surface of the metal powder, a high-density insulator can be formed. In addition, it is difficult to form a uniform film on the convex portions / curved portions on the surface of the metal powder with a metal oxide having a particle diameter of 100 nm or more. For convex portions and curved portions where it is difficult to form a film with a metal oxide, the uniformity of the film can be improved by using a metal oxide having a particle diameter of less than 100 nm, more preferably 50 nm or less.

  The dust core preferably has a specific resistance of 10,000 μΩcm or more. The specific resistance is preferably 15000 to 20000 μΩcm, particularly preferably 20000 μΩcm. In a dust core having a specific resistance of less than 10,000 μΩcm, eddy current loss (intergranular eddy current loss) tends to increase remarkably under an alternating current of 5 kHz or higher.

The dust core preferably has an iron loss at 0.1 T of 5 kHz of 70 kW / m ³ or less and a maximum magnetic permeability μmax of 60 to 150. Or, the iron loss at 0.1 T and 10 kHz is 150 kW / m ³ or less, and the maximum magnetic permeability μmax is 60 to 150, or the iron loss at 0.1 T and 20 kHz is 400 kW / m ³ or less, And it is preferable that the maximum magnetic permeability μmax is 60 to 150.

  The manufacturing method of a powder magnetic core forms an insulating layer on the surface of a metal powder by reacting an aqueous solution containing calcium ions and phosphate ions with a metal powder mainly composed of iron in the presence of a metal oxide. A step of contacting the organometallic compound with the coated metal powder on which the insulating layer is formed, and arranging the organosilicon compound on the surface or inside of the insulating layer to produce the coated metal powder; And pressurizing at 1480 MPa and heating at 600 ° C. or higher. When the coated metal powder is heat-treated at a high temperature of 600 ° C. or higher, the resulting iron core can be reduced in iron loss.

During the production of the dust core, heating is preferably performed in an H ₂ or N ₂ atmosphere. Thus, by heating in inert gas atmosphere, the insulation of the powder magnetic core to manufacture increases. The reason for this is not necessarily clear, but the inventors believe that the siloxane bond (—Si—O—Si—) derived from the organosilicon compound is broken by heating and then changed to a silanol group. Guess.

  ADVANTAGE OF THE INVENTION According to this invention, the dust core which aimed at reduction of an iron loss, and its manufacturing method can be provided, maintaining a constant magnetic permeability characteristic.

It is a schematic diagram for demonstrating the cross-section of a powder magnetic core. It is a SEM photograph of the powder magnetic core obtained in Example 1, and the result of the element mapping of EDX of Fe in the powder magnetic core. It is the result of the element mapping by EDX of the powder magnetic core obtained in Example 1. FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted. In addition, the dimension of each figure has the part exaggerated for description, and does not necessarily correspond with an actual dimension ratio.

  FIG. 1 is a schematic diagram for explaining a cross-sectional structure of a dust core. As shown in FIG. 1, the dust core 10 in the present embodiment includes a plurality of metal powders 1 and an insulating layer 2 existing between the metal powders 1. The insulating layer 2 includes, in addition to the particulate metal oxide 3, silicon oxide and calcium phosphate (not shown), pores 4 remaining when the coated metal powder is molded by pressurization and heating.

  The coated metal powder for producing the dust core 10 is a coated metal powder comprising a metal powder mainly composed of iron and an insulating layer made of calcium phosphate and a metal oxide formed on the surface of the metal powder, An organosilicon compound is present on the surface or inside. For this reason, when manufacturing the dust core by heating and pressurizing the coated metal powder to form the dust core, the insulating layer 2 is formed so as to cover the metal powder 1 while being firmly bonded to the metal powder 1. As a result, since the insulating property of the dust core 10 is ensured, it is possible to suppress iron loss while ensuring constant magnetic permeability characteristics.

  Here, in the present embodiment, the one made of calcium phosphate and metal oxide formed on the surface of the metal powder is referred to as an “insulating layer”, and the insulating layer containing an organosilicon compound on the surface or inside thereof is referred to as “organosilicon-treated insulation”. Called “layer”. In addition, it is ideal that the insulating layer is originally formed with powder particles such as calcium phosphate contained in the insulating layer. However, in practice, a layer may be formed in a state in which several particles are hardened. Even in such a state, there is no problem in characteristics.

  The calcium phosphate layer functions as a binder for fixing the metal oxide to the metal particles. However, since the crystal structure of calcium phosphate is hard, there is a possibility that the calcium phosphate layer on the surface of the metal powder 1 is damaged by the pressing process in the molding process. Therefore, when the calcium phosphate layer is damaged, the metal oxide 3 layer has a function of repairing the calcium phosphate layer by the metal particles being digged in by the pressure of the press treatment.

  The organosilicon-treated insulating layer plays a role of preventing the metal oxide 3 particles from falling off from an insulating layer made of only inorganic materials. A silicone resin suitable as the organosilicon compound is an organic insulating material having excellent heat resistance. For this reason, by providing on the surface of the metal powder, heat treatment can be performed at a high temperature of about 600 ° C., and the iron core of the obtained dust core can be reduced. In the coated metal powder provided with the insulating layer made only of phosphate, the heat treatment temperature was limited to about 500 to 550 ° C. In addition, since the silicone resin can form a film having excellent smoothness, the insulating film does not fall off or break due to the pressure of the press treatment, and a good dust core can be obtained. Hereinafter, each component is described in order.

  The coated metal powder has the above-described configuration, but preferably has ferromagnetism and a high saturation magnetic flux density. Therefore, first as the metal powder used in the present invention, soft magnetism such as iron powder, silicon steel powder, sendust powder, amorphous powder, permendur powder, soft ferrite powder, amorphous magnetic alloy powder, nanocrystal magnetic alloy powder and permalloy powder. Materials are mentioned. These can be used alone or in admixture of two or more. Among them, iron powder is preferable because it is strong in magnetism and can be obtained at low cost. The composition of the metal powder is not particularly limited, but pure iron powder, Fe-Si powder and the like are typical. The invention according to the present embodiment is effective in pure iron powder, particularly water atomized powder having a distorted shape, but can be applied to the above-described metal powders mainly composed of iron. Such metal powder generally has 0 to 10% by mass of Si and 100% by mass of the total mass of the metal powder, and the balance is Fe and Al, Ni, Co, etc. added for the purpose of improving magnetic properties. The modification element and unavoidable impurities.

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

  When iron powder is employed as the metal powder, pure iron powder is particularly preferable in terms of excellent saturation magnetic flux density, magnetic permeability, and compressibility. Examples of such pure iron powder include atomized iron powder, reduced iron powder, electrolytic iron powder, and the like. For example, 300NH manufactured by Kobe Steel, JIP-MG270H and JIP-304AS manufactured by JFE Steel Corporation. Atomized pure iron powder (trade name: ABC100.30) manufactured by Höganäs.

  The manufacturing method of metal powder is not ask | required. Either pulverized powder or atomized powder may be used, and the atomized powder may be any of water atomized powder, gas atomized powder, and gas water atomized powder. At present, water atomized powder has the highest availability 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, but it is difficult to form a uniform insulating layer and high resistivity is difficult to obtain. On the other hand, the gas atomized powder is a pseudo-spherical powder having a substantially spherical shape. Since the shape of each particle is substantially spherical, when soft magnetic powder is pressure-molded, the aggressiveness between the powder particles is reduced, the breakdown of the insulating layer is suppressed, and the powder with high specific resistance A magnetic core is easily obtained stably.

  Moreover, since gas atomized powder consists of substantially spherical particles, its surface area is smaller than water atomized powder having a distorted particle shape. For this reason, even if the total amount of fine particles constituting the organosilicon-treated insulating layer is the same, a thicker insulating layer can be formed using gas atomized powder, and eddy current loss can be more easily reduced. Conversely, if an insulating layer having the same film thickness is provided, the total amount of the organic silicon-treated insulating layer 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).

  As the metal powder, a metal powder that has been subjected to phosphoric acid treatment for the purpose of preventing oxidation can also be used. Oxidation of the surface of the metal powder can be prevented by using the metal powder that has been subjected to such treatment in advance. The phosphoric acid treatment can be performed by the method described in, for example, JP-A-7-245209, JP-A-2000-504785, and JP-A-2005-213621, and is commercially available as a metal powder subjected to phosphoric acid treatment. May be used.

  There is no restriction | limiting in particular in the particle size of metal powder, It can determine suitably with the use of a powder magnetic core, and a required characteristic, Generally, it can select from the range of 1 micrometer-300 micrometers. If the particle size is 1 μm or more, the powder core tends to be formed easily, and if it is 300 μm or less, the eddy current of the powder core can be suppressed from increasing, and calcium phosphate tends to be easily formed. is there. The average particle diameter (calculated by a sieving method) is preferably 50 to 250 μm. There is no restriction | limiting in the shape of metal powder, You may use the spherical and lump-shaped thing, and the flat powder which carried out the flat process by the well-known manufacturing method or machining.

  Next, the organosilicon treatment insulating layer will be described. The thickness of the organic silicon-treated insulating layer is preferably 10 to 1000 nm, more preferably 50 to 300 nm. If the film thickness of the organosilicon-treated insulating layer 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 thickness of the organosilicon-treated insulating layer is excessive, the magnetic properties of the dust core are reduced. Hereinafter, each structure of calcium phosphate, a metal oxide, and a silicon oxide is demonstrated in order.

  Calcium phosphate covering the surface of the metal powder mainly has a function as an insulating film of the metal powder. Moreover, the metal oxide mentioned later can also be formed in the metal powder surface by forming calcium phosphate. From such a viewpoint, it is preferable that the calcium phosphate has a coating structure that covers the surface of the metal powder in a layered manner. The insulating coating with calcium phosphate can be formed of any powder as long as it is a metal powder.

  As for the degree of coating of the metal powder with calcium phosphate, some metal powder may be exposed, but the higher the coverage, the higher the specific resistance value (insulation index) of the dust core during molding. In addition, metal oxides and alkoxysilanes which will be described later are liable to adhere, and as a result, the bending strength is improved. Specifically, it is preferable that 90% or more of the surface of the metal powder is coated with two or more kinds of inorganic substances including calcium phosphate and metal oxide, more preferably 95% or more, and the whole (approximately 100%). %) Is more preferable.

  The thickness of the insulating coating made of calcium phosphate is preferably 10 nm to 1000 nm, and more preferably 20 to 500 nm. If the thickness is 10 nm or more, there is a tendency to obtain an insulating effect, and if it is 1000 nm or less, there is no significant reduction in the density of the molded body.

  The amount of calcium phosphate formed on the surface of the metal powder is preferably 0.1 to 1.5 parts by mass and more preferably 0.4 to 0.8 parts by mass with respect to 100 parts by mass of the metal powder. preferable. If it is 0.1 mass part or more, the improvement of insulation (specific resistance) and the adhesion effect | action of the metal oxide mentioned later are obtained. If it is 1.5 mass parts or less, there exists a tendency which can prevent that a molded object density falls when it is set as a powder magnetic core. The mass of calcium phosphate can be determined by measuring the mass increase of the obtained coated metal powder.

As calcium phosphate, primary calcium phosphate {Ca (H ₂ PO ₄ ) ₂ · 0 to 1H ₂ O}, dibasic calcium phosphate (CaHPO ₄ ), dibasic calcium phosphate (anhydrous) {CaHPO 4 · 2H ₂ O}, tribasic calcium phosphate { 3Ca ₃ (PO ₄ ) ₂ · Ca (OH) ₂ }, tricalcium phosphate {Ca ₃ (PO ₄ ) ₂ }, α-type tricalcium phosphate {α-Ca ₃ (PO ₄ ) ₂ }, β-type phosphorus Tricalcium phosphate {β-Ca ₃ (PO ₄ ) ₂ }, hydroxyapatite {Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ }, tetracalcium phosphate {Ca ₄ (PO ₄ ) ₂ O}, calcium pyrophosphate (Ca ₂ P ₂ O ₇ ), calcium pyrophosphate dihydrogen (CaH ₂ P ₂ O ₇ ), and the like. Of these, hydroxyapatite having excellent heat resistance is preferable. The heat-resistant temperature of hydroxyapatite is 1000 ° C. or higher. When used as an insulating layer of coated metal powder, heat treatment can be performed at a high temperature of about 600 ° C., and the iron core of the resulting dust core can be reduced. . The hydroxyapatite, OH in the structure ^- for having a group, metal oxide, is excellent in reactivity with the alkoxysilane.

Hydroxyapatite is a form of calcium phosphate and is represented by the chemical formula: Ca ₁₀ (PO _{4) 6} (OH) ₂ . In the hydroxyapatite shown in the present embodiment, a part of the structure may be replaced with another element. When hydroxyapatite is precipitated as calcium phosphate, the stoichiometric composition formula of the resulting hydroxyapatite is Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , but most of it has an apatite structure and can be maintained. As long as it is a non-stoichiometric composition such as Ca-deficient hydroxyapatite. That is, in the present invention, non-stoichiometric materials such as Ca-deficient hydroxyapatite and hydroxyapatite are considered. Specifically, hydroxyapatite is theoretically formed at a molar ratio of Ca / P = 1.66, but Ca / P may be 1.4 to 1.8.

Hydroxyapatite may substitute some of the ions in the structure with other elements within a range that does not impair the properties. An apatite compound typified by hydroxyapatite is a composition represented by the following general formula (I), and there are various combinations of compounds by substituting M ²⁺ , ZO ₄ ⁻ , and X ⁻ . X ^- is OH ^- is particularly referred to as a hydroxy apatite the case is.
M ₁₀ (ZO ₄ ) ₆ X ₂ (I)

In the general formula (I), a metal ion capable of substituting calcium is ^{inserted at} the position of the atom M ²⁺ that gives a cation. Specifically, sodium, magnesium, potassium, aluminum, scandium, titanium, chromium, manganese, Iron, cobalt, nickel, zinc, strontium, yttrium, zirconium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, barium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, Examples include ions such as dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, platinum, gold, mercury, thallium, lead, and bismuth. Further, PO ₄ ³⁻ , CO ₃ ²⁻ , CrO ₄ ³⁻ , AsO ₄ ³⁻ , VO ₄ ³⁻ , UO ₄ ³⁻ , SO ₄ ²⁻ , SiO ₄ ⁴⁻ , GeO are positioned at ZO ₄ ^−. ₄ ^4- etc. OH ⁻ , halide ions (F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ ), BO ₂ ⁻ , CO ₃ ²⁻ , O ^{2−, and the} like enter the X ⁻ position. The number of ions substituted for M ²⁺ , ZO ₄ ⁻ , and X ⁻ may be one or two or more.

Here, X is preferably OH ⁻ and F ⁻ . In the case of OH ⁻ , it is preferable in terms of excellent application property to metal powder due to increase in hydrophilicity, and in the case of F ⁻ , it is preferable in terms of excellent strength. That is, hydroxyapatite: Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ or fluoroapatite: Ca ₁₀ (PO ₄ ) _{6 in} terms of excellent insulation, heat resistance, and mechanical properties when a dust core is formed. it is particularly preferable to use F _2.

As for the degree of substitution of each component with other elements, when calcium is substituted with other atoms, the degree of substitution (number of moles of other atoms to be substituted / number of moles of calcium) is preferably 30% or less. Similarly, when the phosphate ion is substituted, the degree of substitution is preferably 30% or less, but the hydroxyl group may be substituted with other atoms by 100%. Calcium phosphate is obtained by reacting a solution containing calcium ions (in the case of containing atoms other than calcium, ions of atoms M that give cations other than calcium described later) with an aqueous solution containing phosphate ions. When an ion of an atom M described later is reacted instead of the calcium ion, calcium phosphate (apatite compound or the like) in which the position of the atom M ²⁺ giving a cation is substituted with the M ion in the general formula (I) Is obtained.

  To deposit the phosphate compound on the surface of the metal powder, first put an aqueous solution and metal powder containing calcium ions and adjusted to pH in an alkaline environment in a metal, plastic, glass or other container, and then add phosphate ions. The aqueous solution containing is added, pH in the aqueous solution after mixing is adjusted to 7 or more, and Ca / P is adjusted to a desired ratio. After adjusting the aqueous solution, it is preferable to mix while crushing the aqueous solution and the metal powder in the aqueous solution. In this case, the addition order may be changed, an aqueous solution containing phosphate ions and metal powder may be added, and an aqueous solution containing calcium ions may be added later. Further, an aqueous solution containing phosphate ions, metal powder, and calcium ions may be simultaneously added.

  The calcium ion is not particularly limited as long as it is derived from a calcium compound. Specifically, for example, calcium ion sources include calcium salts of inorganic bases such as calcium hydroxide, calcium salts of inorganic acids such as calcium nitrate, calcium salts of organic acids such as calcium acetate, calcium salts of organic bases, etc. Can be mentioned. Examples of the phosphoric acid source include phosphoric acid, phosphates such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, and condensed phosphoric acids such as pyrophosphoric acid (diphosphoric acid) and metaphosphoric acid. Any of these phosphate compounds that can be precipitated by reacting a salt (nitrate, acetate, carbonate, sulfate, chloride, hydroxide) that gives phosphate and calcium ions in an aqueous solution. A phosphoric acid compound may also be used. Further, in view of the impurities to be mixed in, it is particularly preferable to deposit using an ammonium phosphate salt.

  The reaction solution for forming calcium phosphate on the surface of the metal powder is preferably a neutral region to a basic region. Thereby, the oxidation of the metal powder surface can be prevented, and hydroxyapatite can be particularly formed in the calcium phosphate. In consideration of the solubility product of calcium phosphates, the reaction solution at the time of formation is preferably pH 7 or more, more preferably 8 to 11, and further preferably 10 to 11. Hydroxyapatite is dissolved in the acidic region, and calcium phosphate other than hydroxyapatite is precipitated or mixed in the neutral region. In the acidic region, depending on the type of the metal powder, it may be oxidized and partially converted into an oxide to cause rust and discoloration. Therefore, it is necessary to accurately adjust the pH of the reaction solution using a base such as ammonia water, sodium hydroxide, or potassium hydroxide.

  The said crushing means unraveling the part which the metal powder aggregated using the shearing force being applied to the metal powder by friction or collision between the metal powders during stirring. As a method of mixing an aqueous solution containing metal powder while crushing metal powder, it can be wet-stirred (mixed) such as planetary mixer, ball mill, bead mill, jet mill, mix rotor, evaporator, ultrasonic dispersion, etc. Anything can be used. In particular, it is preferable to adjust the number of rotations with a mix rotor or the like and perform stirring according to the sample. Among metal powders, iron powder for powder magnetic cores is manufactured by an atomizing method, has a relatively wide particle size distribution, and shows coarse agglomerated iron powder and agglomeration between iron powders. Coarse powder mixing can also cause a decrease in magnetic properties and compact density, so by performing such agitation, metal powder is coated with calcium phosphate while preventing magnetic properties and compact density from decreasing. It becomes possible.

  As the stirring speed, the optimal rotation speed varies depending on the volume of the container to be used, the mass and apparent volume of the metal powder to be used, and the volume of the aqueous solution. For example, the volume of the container is 1000 cm3, the metal powder to be used is 300 g, and the aqueous solution. When the volume is 120 to 130% of the apparent volume of the metal powder, 30 to 300 rpm is preferable, and 40 to 100 rpm is more preferable. At this time, with the rotation of the container, it is necessary for the metal powder to flow moderately on the inner wall of the container, and if it is 300 rpm or more, the metal powder does not flow and sticks to the inner wall and rotates, resulting in There is no efficient stirring. On the other hand, if it is less than 30 rpm, the rotation of the container is too slow, and the weight of the metal powder causes a state of staying constant at the position of the bottom of the container (the lowest position during stirring), and stirring is not performed at all.

  The reaction temperature during the formation of calcium phosphate on the metal powder surface is not particularly problematic even at room temperature, but the reaction can be promoted by increasing the temperature, and the time required for the formation can be shortened. As reaction temperature, it is preferable that it is 50 degreeC or more, and it is more preferable that it is 70 degreeC or more.

  The reaction time during the formation of calcium phosphate on the metal powder surface varies depending on the concentration of the aqueous solution containing calcium ions and the aqueous solution containing phosphate ions. The concentration of the solution containing each ion is preferably in the range of 0.003 to 1.0M. The concentration of the solution containing each ion is preferably in the range of 0.001 to 2.0M, and more preferably in the range of 0.1 to 1.0M. In this case, the reaction time is preferably 1 to 10 hours, and more preferably 2 to 5 hours. When it is 2.0 M or more, metals tend to aggregate together, and low density when formed into a molded product becomes a problem. On the other hand, when it is 0.01M or less, the reaction time becomes longer than necessary, and it becomes difficult to uniformly coat the metal powder depending on the selected material. Moreover, when reaction time is short, for example, about 1 to 10 minutes, the production | generation of the target calcium phosphate is inadequate on the metal powder surface, and a yield fall and lack of insulation (specific resistance) are caused.

  The amount of the aqueous solution at the time of formation of calcium phosphate on the surface of the metal powder is required to be an amount that allows the metal powder to flow efficiently with the rotation of the container, and is preferably 100 to 200% of the apparent volume of the metal powder to be used. 140% is more preferable, and 120 to 130% is most preferable.

  Next, the metal oxide will be described. The metal oxide according to the present embodiment forms a metal oxide on the surface of the metal powder by adding the metal oxide to the aqueous solution when or after forming calcium phosphate on the surface of the metal powder in water. The metal oxide may be formed on either the metal powder surface or calcium phosphate. A high specific resistance can be obtained by forming a uniform insulating layer of an inorganic material using the above-described calcium phosphate and metal oxide.

  The metal oxide may be in powder form, but is preferably in slurry form. That is, it is preferable that the metal oxide is dispersed without being aggregated in a solvent (water or an organic solvent). In the step of forming the metal oxide on the surface of the metal powder, the metal oxide is added during or after the formation of calcium phosphate. This means that the coating of the metal powder with calcium phosphate is performed using water as a solvent, and thus the dropping procedure of the metal oxide is not particularly limited. When metal oxide is added at the time of formation, calcium phosphate and metal oxide are mixed, and the distribution of calcium phosphate and metal oxide is uniform throughout the iron powder, and a dense layer is formed. On the other hand, when a metal oxide is added after the calcium phosphate layer is formed, a fine metal oxide film is formed on the surface of the calcium phosphate layer. In particular, the effect as a cushioning material is further enhanced because the metal oxide is concentrated on the uneven surface portion where cracks are likely to occur when the molded body is produced.

  Examples of the metal oxide include aluminum oxide, titanium oxide, cerium oxide, yttrium oxide, zinc oxide, silicon oxide, tin oxide, copper oxide, holmium oxide, bismuth oxide, cobalt oxide, and indium oxide. These metal oxides can be used alone or in combination of two or more, and may be charged as powder, but a form like a slurry is preferable. A more uniform fine particle film can be formed by dispersing the target metal oxide powder in an appropriate solvent (water or organic solvent).

  The method for dispersing the metal oxide is not particularly limited, and specific examples include a pulverizing method using an apparatus such as a bead mill and a jet mill, and ultrasonic dispersion. Moreover, you may use the product currently sold as a slurry as it is. There are various shapes such as a spherical shape and a dharma shape, but there is no particular limitation. Specific slurry products include NanoTek Slurry series manufactured by CI Kasei Co., Ltd., Quartron PL series and SP series manufactured by Fuso Chemical Industry Co., Ltd., Snowtex Series (colloidal silica, organosol) manufactured by Nissan Chemical Industries, Ltd., alumina sol, Examples include Nano Youth and Admafine of Admatechs Co., Ltd.

  Various particle sizes of the metal oxide can be used, but a particle size of submicron or less is preferable for film forming properties. The (average) particle diameter of these metal oxides can be measured using instrumental analysis such as dynamic light scattering or laser diffraction. In addition, the fine metal oxide formed on the calcium phosphate surface can be directly observed and measured using an electron microscope such as SEM or an optical microscope. When directly observing, for example, 10 pieces of the metal oxide particles are arbitrarily selected from one scanning electron micrograph, and 10 measured values are obtained, and the total of the measured values is 10. The “average value” divided is called the particle size. Hereinafter, only the particle diameter is described.

  The particle diameter of the metal oxide is preferably from 10 nm to 350 nm in terms of (average) particle diameter. As the metal oxide having a larger particle diameter is used, the insulating property is better, and as the metal oxide having a smaller particle diameter is used, the strength and the density of the molded body tend to be higher. In addition, metal oxides having different particle diameters can be used in combination in terms of improving the coverage of the surface of the metal powder and making the metal oxide layer denser. When fine metal oxide fine particles are mixed between relatively large metal oxides deposited on the surface of the metal powder, a high-density insulator can be formed. In addition, it is difficult to form a uniform film on the convex portions / curved portions on the surface of the metal powder with a metal oxide having a particle diameter of 100 nm or more. For convex portions and curved portions where it is difficult to form a film with a metal oxide, the uniformity of the film can be improved by using a metal oxide having a particle diameter of less than 100 nm, more preferably 50 nm or less.

  The solvent for dispersing the metal oxide is not particularly limited, and specifically, alcohol solvents such as methanol, ethanol and isopropyl alcohol, ketone solvents such as acetone and methyl ethyl ketone, and toluene are representative. And aromatic solvents. There is no problem even if water is used.

  In addition, it is preferable that the addition amount of a metal oxide shall be 0.05-2.0 mass parts with respect to 100 mass parts of metal powder to be used. If the addition amount is 0.05 parts by mass or more, the metal oxide can be uniformly coated on the metal powder, and there is a tendency that an effect of improving insulation (specific resistance) is obtained. On the other hand, if it is 2.0 parts by mass or less, there is a tendency that when the powder magnetic core is made, the density of the molded body can be prevented from being lowered and the bending strength of the obtained powder magnetic core can be prevented from being lowered.

  Next, the organosilicon compound will be described. Examples of the organosilicon compound include alkoxysilane, a reaction product thereof, and a silicone resin, and a silicone resin is more preferable. As the silicone resin, those containing at least one of the following compounds (1), (2) and (3) are preferable. (1) A polyorganosiloxane composed of a bifunctional siloxane unit (D unit) (for example, polydimethylsiloxane, polymethylphenylsiloxane) (2) a monofunctional siloxane unit (M unit), a trifunctional siloxane unit (T unit) and a polyorganosiloxane composed of at least one of tetrafunctional siloxane units (Q unit) (for example, MQ resin composed of M unit and Q unit) and bifunctional siloxane unit (D unit) A mixture with a polyorganosiloxane (for example, polydimethylsiloxane, polymethylphenylsiloxane) (this mixture may be sticky at room temperature or may be sticky when heated) ) (3) Monofunctional siloxane unit (M unit), trifunctional siloxane unit (T unit) and tetrafunctional A polyorganosiloxane composed of at least one siloxane unit (Q unit) and a bifunctional siloxane unit (D unit, for example, dimethylsiloxane unit, methylphenylsiloxane unit) (the number of D units is M units, T units). The polyorganosiloxane is preferably an organosiloxane composed of at least one of T units and Q units and D units.

  The silicone resin is preferably a curable (particularly thermosetting) silicone resin. This silicone resin film not only functions as an insulating film that covers the surface of the inorganic insulator, but also functions as a binder that bonds the constituent particles. Although the transformation temperature at which the silicone resin gels varies depending on the type of silicone resin, it cannot be specified unconditionally, but is about 150 to 300 ° C. By heating to this temperature, the silicone resin adhering to the particle surface of the soft magnetic powder becomes a hard silicone resin film. In this silicone resin coating, siloxane bonds progress with an increase in temperature, and therefore, by performing a high-temperature heat treatment such as annealing, partial crosslinking is changed to overall crosslinking, and the coating strength is improved. In addition, since this silicone resin film is excellent in heat resistance, it is not destroyed even if high temperature heating such as annealing is performed on the compacted powder magnetic core, and the above crosslinking further proceeds, so that the particles of the powder for the magnetic core The bond between them is strengthened.

  Silicone resins are roughly classified into a heat-curing 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 number of functional groups of the silane compound of the silicone resin is 1 to a maximum of four. Although there is no restriction | limiting in the number of functional groups of the silicone resin used by this invention, A crosslinking density becomes high by using the silicone which has a 3 or 4 functional silane compound, and is preferable.

  The type of silicone resin varies depending on the application, such as resin-based, silane compound-based, rubber-based silicone, silicone powder, organically modified silicone oil, or composites thereof. In the present invention, any silicone resin may be used. However, a resin-based silicone resin for coating, that is, a straight silicone resin composed only of silicone or a modifying silicone resin composed of silicone and an organic polymer (alkyd, polyester, epoxy, acrylic, etc.) is used. From the viewpoints of heat resistance, weather resistance, moisture resistance, electrical insulation, and simplicity in coating.

  As the silicone resin, a methylphenyl silicone resin in which a functional group on Si is a methyl group or a phenyl group is generally used. It is more preferable to have many phenyl groups because they tend to have excellent heat resistance. In addition, about the ratio and functionality of the methyl group of a silicone resin, and a phenyl group, it can analyze by FT-IR etc. Examples of the silicone resin used in the present invention include SH805, SH806A, SH840, SH997, SR620, SR2306, SR2309, SR2310, SR2316, DC12577, SR2400, SR2402, SR2404, SR2405, SR2406, manufactured by Toray Dow Corning Co., Ltd. SR2410, SR2411, SR2416, SR2420, SR2107, SR2115, SR2145, SH6018, DC6-230, DC3037, DC3074, QP8-5314, 217-Flake Resin, YR3370, YR3286, TSR194R, TSR125R, manufactured by Momentive Performance KR251, KR255, KR114A, KR112 manufactured by Chemical Industry Co., Ltd. R2610B, KR2621-1, KR230B, KR220, KR220L, KR285, K295, KR300, KR2019, KR2706, KR165, KR166, KR169, KR2038, KR221, KR155, KR240, KR101-10, R21, KR11, KR120, KR11 KR211, KR212, KR216, KR213, KR217, KR9218, SA-4, KR206, KR5206, ES1001N, ES1002T, ES1004, KR9706, KR5203, KR5221, X-52-1435, and the like. Silicone resins other than those listed here may be used. Moreover, you may use the silicone resin which modified these substances or these raw material substances. Furthermore, you may use the silicone resin which mixed 2 or more types of silicone resins from which a kind, molecular weight, and a functional group differ in a suitable ratio.

  The adhesion amount of the silicone resin coating is preferably adjusted to be 0.01 to 0.8% by mass with respect to the metal powder. When the content is less than 0.01% by mass, the insulation is inferior and the electrical resistance is lowered. On the other hand, if it is added in an amount of more than 0.8% by mass, the powder after heat drying tends to be lumpy, and it is difficult to achieve a high density of the molded body produced using such a damped powder, and the film is formed during molding. , The eddy current loss is likely to be insufficiently reduced.

  The silicone resin film can be formed by dissolving the silicone resin in alcohols, ketones, petroleum organic solvents such as toluene, xylene, etc., and mixing this solution with iron powder to volatilize the organic solvent. it can. The film forming conditions are not particularly limited, but the resin solution prepared so that the solid content is 0.5 to 5.0% by mass is added to 100 parts by mass of the magnetic powder coated with the insulating particles. On the other hand, about 0.5 to 10 parts by mass may be added, mixed and dried. If the amount is less than 0.5 parts by mass, mixing may take time, and the coating film may be non-uniform. On the other hand, when the amount exceeds 10 parts by mass, the amount of the solution is so large that it may take a long time to dry or may be insufficiently dried. The resin solution may be appropriately heated.

  The thickness of the silicone resin film greatly affects the decrease in magnetic flux density. Therefore, 10 to 500 nm is preferable. A more preferable thickness is 20 to 200 nm. The total thickness of the inorganic insulator and the silicone resin film is preferably 100 nm to 1500 nm.

  In the drying step of the silicone resin, it is desirable that the organic solvent be sufficiently evaporated by heating at a temperature at which the used organic solvent volatilizes and below the curing temperature of the silicone resin. The specific drying temperature is a temperature equal to or higher than the boiling point of each organic solvent. For example, as a specific example of drying when a solvent such as ketones is used, the drying temperature is 10 to 60 at 100 to 250 ° C. It is good to heat-dry for 1 minute, More preferably, it is suitable to heat-dry at 120-200 degreeC for 10 to 30 minutes.

  The drying step is aimed at pre-curing the silicone resin as well as drying the resin film (removing the solvent). When the powder coated with silicone resin is vacuum-dried, the surface is sticky and has poor handling properties. Therefore, by performing preliminary curing as necessary, it is possible to secure the flowability of the magnetic powder during molding and to suppress the occurrence of cracks in the molded body. As a specific method, the magnetic powder on which the silicone resin film is formed is heated in the vicinity of the curing temperature of the silicone resin for a short time. The difference between this pre-curing and curing is that, in the pre-curing, the powders can be easily crushed without completely solidifying, whereas in the high-temperature heat treatment process (annealing) performed after the molding of the powder. The resin is cured and the powders are bonded and solidified to improve the strength of the molded body.

  As described above, after pre-curing the silicone resin, it is pulverized to obtain a powder having excellent fluidity when filling the mold. If it is not pre-cured, for example, powders may adhere to each other during warm molding, and it may be difficult to charge the mold in a short time. In practical operation, the improvement in handling properties is very significant, and it has been found that the specific resistance of the obtained dust core is improved by pre-curing. Although this reason is not clear, it is thought that it may be because the adhesiveness with the iron powder at the time of curing increases. Further, if necessary, a sieve having an opening of about 300 to 500 μm may be passed for the purpose of removing aggregated lumps after drying.

(Manufacture of dust core)
The dust core can be obtained by a manufacturing method including a step of pressurizing and heating the above-described coated metal powder. Here, the method for producing a powder magnetic core may include a step of mixing a lubricant with the coated metal powder as necessary, and pressurizing and heating it. That is, the dust core may be obtained by mixing a coated metal powder with a lubricant as necessary, and pressurizing and heating it. The lubricant can also be used after being dispersed in an appropriate dispersion medium to form a dispersion, which is applied to the inner wall surface of the die (the wall surface in contact with the punch) and dried.

  The produced coated metal powder is formed into a compact called a dust core through a filling process in which the core powder is largely filled into a molding die and a molding process in which the powder metal powder is pressed. Press molding of powdered magnetic core coated metal powder (including the above mixed powder) filled into a molding die is performed by mixing an internal lubricant or the like into the powder regardless of whether it is cold, warm or hot. It may be performed by a typical molding method. However, from the viewpoint of improving the magnetic characteristics by increasing the density, it is more preferable to employ the mold lubrication warm pressing method described below. As a result, even if the molding pressure is increased, no galling occurs between the inner surface of the molding die and the coated metal powder, and the release pressure is not excessive, and a reduction in mold life can be suppressed. And it becomes possible to mass-produce high-density powder magnetic cores not at the test level but at the industrial level.

  As the lubricant, metal soap such as zinc stearate, calcium stearate and lithium stearate, long chain hydrocarbons such as wax, silicone oil and the like can be used.

  The degree of pressurization in the molding step is preferably 980 to 1480 MPa from the viewpoint of mold life and productivity.

  When the coated metal powder is pressure-molded, residual stress and residual strain are generated inside. In order to remove this, it is preferable to perform a heat treatment step (annealing) in which the molded body is heated and slowly cooled. Thereby, hysteresis loss is reduced. In addition, a good dust core such as followability to an alternating magnetic field can be obtained. The residual strain removed in the annealing step may be strain accumulated in the metal powder before the forming step.

  Residual strain and the like are effectively removed as the heat treatment temperature increases. Even the heat-resistant organosilicon-treated insulating layer causes at least partial destruction. Therefore, it is preferable to determine the heat treatment temperature in consideration of the heat resistance of the organosilicon-treated insulating layer. For example, when the heat treatment temperature is 600 to 800 ° C., it is possible to achieve both the removal of residual strain and the protection of the organosilicon treatment insulating layer. The heating time is 1 to 300 minutes, preferably 10 to 60 minutes, in view of the effect and economy.

The atmosphere during the heat treatment is preferably a non-oxidizing atmosphere. For example, a vacuum atmosphere or an inert gas (H ₂ , N ₂ , Ar) atmosphere. The reason why the heat treatment process is performed in a non-oxidizing atmosphere is to prevent the powder magnetic core and the magnetic powder constituting the powder core from being excessively oxidized and deteriorating the magnetic characteristics and electrical characteristics. Specifically, there is a case where FeO is generated or an Fe ₂ SiO ₄ layer is generated.

  The dust core produced using the above-described coated metal powder can be used for various electromagnetic devices such as motors (particularly cores and yokes), actuators, reactor cores, transformers, induction heaters (IH), speakers, and the like. . In particular, this dust core can reduce hysteresis loss due to annealing or the like with a high magnetic flux density, and can be applied to devices used in a relatively low frequency range.

  In order to describe the present invention in more detail, the following examples will be described. In addition, this invention is not limited to this Example.

[Production of coated metal powder]
Example 1
1 kg of iron powder (Heganes AB, ABC100.30) classified to a maximum particle size of 75 μm or less is put into 300 ml of water, and 6 g of calcium phosphate shown in Table 1 is added while stirring, and iron is obtained by stirring at 100 rpm × 30 minutes. Calcium phosphate was adhered to the powder surface (formation of the first layer).
Next, as a step of attaching the metal oxide, colloidal silica (water-dispersed slurry) shown in Table 1 was added as SiO ₂ to 8 g, and stirring was continued for 30 minutes to form (second layer formation).
Here, after the drying treatment was once performed, the mixture was kneaded with a silicone resin (manufactured by Shin-Etsu Silicone: KR311) and dried to obtain a coated metal powder provided with an organosilicon treatment insulating layer. In addition, as a prior art, only the phosphoric acid coating process was performed to the same iron powder, and the phosphoric acid coating process powder which was produced by drying and the commercially available insulation processing powder (made by Höganäs AB) were prepared.

(Example 2)
The SiO ₂ used for the second layer in Example 1, except that the particle size was changed to SiO ₂ of 125nm was manufactured coated metal powder in the same manner as in Example 1.

(Example 3)
A coated metal powder was produced in the same manner as in Example 1 except that SiO ₂ used for the second layer in Example 1 was changed to Al ₂ O ₃ .

(Example 4)
A coated metal powder was produced in the same manner as in Example 1 except that SiO ₂ used for the second layer in Example 1 was changed to TiO ₂ .

(Example 5)
A coated metal powder was produced in the same manner as in Example 1 except that SiO ₂ used for the second layer in Example 1 was changed to Zr ₂ O ₂ .

(Example 6)
A coated metal powder was produced in the same manner as in Example 1 except that SiO ₂ used in the second layer in Example 1 was changed to Y ₂ O ₃ .

(Example 7)
Similar to Example 1 except that the hydroxyapatite (Ca (PO ₄ ) ₆ (OH) ₂ ) used in the first layer in Example 1 was changed to monocalcium phosphate (Ca (H ₂ PO ₄ ) ₂ ). The coated metal powder was prepared by the method described above.

(Example 8)
Coated metal powder in the same manner as in Example 1 except that hydroxyapatite (Ca (PO ₄ ) ₆ (OH) ₂ ) used in the first layer in Example 1 was changed to dicalcium phosphate (CaHPO ₄ ). Was made.

Example 9
Example 1 except that the hydroxyapatite (Ca (PO ₄ ) ₆ (OH) ₂ ) used in the first layer in Example 1 was changed to β-type tricalcium phosphate (Ca ₃ (PO ₄ ) ₂ ). A coated metal powder was prepared in the same manner.

(Example 10)
A coated metal powder was produced in the same manner as in Example 1 except that the silicone resin used in the third layer in Example 1 (manufactured by Shin-Etsu Chemical Co., Ltd .: KR311 was changed to Momentive Performance Co., Ltd .: YR3286).

(Example 11)
A coated metal powder was prepared in the same manner as in Example 1 except that the silicone resin used in the third layer in Example 1 (Shin-Etsu Chemical Co., Ltd .: KR311 was changed to Momentive Performance Co., Ltd .: TSR194) was used. .

(Example 12)
A method of synthesizing the calcium phosphate layer, which is the first layer, in a wet process was studied.
14.2 g of calcium nitrate tetrahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) and 4.15 ammonium dihydrogen phosphate were dissolved in 150 g of pure water. Next, 1 kg of iron powder having a maximum particle diameter of 75 μm or less (Heganes AB, ABC100), the calcium nitrate aqueous solution and the ammonium dihydrogen phosphate aqueous solution are put into a plastic container, and aqueous ammonia is gradually added dropwise. The pH of was adjusted to 9 to precipitate hydroxyapatite. After the ammonia water was dropped, the container was immediately sealed and stirred for 30 minutes at a rotation speed of 100 rpm to form hydroxyapatite on the iron powder surface.
Next, as a step of attaching the metal oxide, colloidal silica (water-dispersed slurry) having a particle diameter of 60 nm was added as SiO ₂ to 8 g, and stirred again at a rotation speed of 100 rpm for 30 minutes.
The obtained coated iron powder was filtered and dried, and then kneaded with a silicone resin (manufactured by Shin-Etsu Silicone: KR311).

(Example 13)
In Example 12, a coated metal powder was produced in the same manner as in Example 12 except that SiO ₂ having a particle diameter of 125 nm was used instead of SiO ₂ having a particle diameter of 60 nm used for the second layer.

(Comparative Example 1)
In Example 1, a coated metal powder in which only hydroxyapatite was formed on the surface of the metal powder in the first layer was produced.

(Comparative Example 2)
In Example 1, a coated metal powder consisting only of hydroxyapatite in the first layer and SiO _{2 in} the second layer was produced.

(Comparative Example 3)
Only the phosphoric acid coating treatment was performed on the iron powder (Heganes AB, ABC100.30) classified to a maximum particle size of 75 μm or less, and dried to prepare a coated metal powder.

(Comparative Example 4)
Commercially available “Somaloy110i1P” manufactured by Höganäs was prepared.

[Method for producing specimen for bending test]
15 g of the obtained magnetic core powder was weighed and coated with lithium stearate dispersed in alcohol in a 12 mm × 34 mm molding die, and the magnetic core powder and the molding die were heated to 130 ° C. It was filled in the molding die, a molding pressure 980~1480MPa at 2000kN Amsler universal testing machine bending test piece density 7.3Mg ^{/ m 3} ~7.35Mg ^/ m 3 of (12 × 34 × 5mm) Several were produced.
The density was measured using the Archimedes method calculated from the dry weight and the weight in water.

[Heating process]
The produced ring molded body and the bending test piece were heat-treated at a temperature of 650 ° C. for 30 minutes in a N ₂ atmosphere at a temperature rising rate of 10 ° C./min in an atmosphere adjustment induction heating furnace. After heating for 30 minutes, it was cooled by furnace cooling to obtain a dust core.

[Iron loss measurement]
Iron loss indicates energy loss due to excitation magnetic flux density and frequency, and the lower the loss, the higher the efficiency of the material.
The iron loss measurement was evaluated using SY-8232 manufactured by Iwadori Measurement. After measuring the inner diameter, outer diameter, overall length, and weight of the dust core, an insulating paper was wound around the surface of the dust core, and then detection and excitation windings were applied. The number of windings of the detection copper wire was 20 turns, and the number of windings of the exciting copper wire was 60 turns, which was used as a test piece.
The excitation magnetic flux density was constant at 0.1 T, the frequencies were 5 kHz, 10 kHz, and 20 kHz, and the iron loss was measured for each.

[Maximum relative permeability measurement]
The maximum relative permeability measurement was evaluated using a BH analyzer manufactured by Riken Denshi. After measuring the inner diameter, outer diameter, overall length, and weight of the dust core, an insulating paper was wound around the surface of the dust core, and then detection and excitation windings were applied. The detection copper wire was φ0.26 mm and was wound for 20 turns, and the excitation copper wire was φ0.5 mm and was wound for 200 turns to obtain a ring test piece.

  The maximum value of the magnetizing force H was 10000 A / m, the magnetizing force was changed, the relative permeability was measured from the change of the magnetic flux density B, and the maximum value was taken as the maximum relative permeability.

[Folding strength]
The bending test was based on JIS-Z-2248, and a three-point bending test was performed using a precision universal testing machine (Autograph). The distance between the fulcrums was 25.4 mm, the pressing speed was 0.5 mm / min, and the bending strength was determined from the maximum test force.

[Resistivity]
The specific resistance value of the powder magnetic core obtained by using the magnetic core powder was measured with a four-end needle measuring instrument on the press surface of the ring molded body after the annealing. At that time, in order to eliminate the influence of the lubricant remaining on the surface layer portion during molding and annealing, the press surface was polished with No. 400-600 polishing paper, and after removing the residue on the surface layer portion, the specific resistance was measured. .

[LI characteristics]
The LI characteristic is a method for evaluating the inductance (L) when the superimposed current (I) is applied under an alternating current, and the inductance value under the added current with respect to the non-superimposed (0 A) inductance value. The lower the drop, the better.
Since the inductance value also varies depending on the core shape, core weight, and number of windings of copper wire, the evaluation is φ20 × φ30 × 5 mm, 14.5 g constant, the copper wire is φ1.0 mm, and evaluation is performed with 20 turns. did.
The evaluation uses an LCR meter LM-2101B manufactured by Kuniyo Denki, the frequency is 10 kHz, the applied current is increased by 1 A every 50 mSec from no overlap (0 A), the maximum applied current is 30 A, and the inductance at each applied current is measured. did. The drop rate of the inductance value at 30 A with respect to the inductance value when there was no superposition at that time was evaluated.

[Energy dispersive X-ray analysis (EDX analysis)]

  Using an ion milling device (manufactured by Hitachi High-Technologies Corporation: E-3500), the end of the molded body is cross-section polished under the conditions of an acceleration voltage of 6 kV, a discharge voltage of 4 kV, and a swing speed of 1 (no unit). An EDX element mapping analysis of the cross section was performed using an analyzer (INCA Energy 350, manufactured by Oxford Instruments Co., Ltd.) under the conditions of acceleration voltage: 15 kV, vapor deposition material: Pt—Pd, and material tilt angle: 0 ° C.

  Table 1 shows the evaluation results of the iron loss, the maximum magnetic permeability, the bending strength, the specific resistance, and the LI characteristics of the dust cores of Examples 1 to 13 and Comparative Examples 1 to 4. Moreover, the EDX analysis result of the powder magnetic core obtained in Example 1 is shown in FIG. Fig.2 (a) is a SEM image of the powder magnetic core obtained in Example 1, (b) is a FeEDX analysis result. FIG. 3 shows the results of EDX analysis of Ca, O, P, and Si.

Samples in which the second layer (metal oxide) is colloidal silica (SiO ₂ ) and samples in which the metal oxide is Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Y ₂ O ₃ were subjected to normal phosphoric acid coating treatment. Compared with the coated metal powder, the iron loss shows a good value, which is a characteristic value equivalent to that obtained by applying a commercially available insulation coating. The maximum permeability μmax of the sample of the example is a value lower than that of the insulation-treated product with a phosphate coating or a commercially available product. For this reason, it is expected that the change in permeability with respect to the magnetic field is also reduced.

From the viewpoint of the strength of the obtained powder magnetic core, the powder magnetic core provided with the organosilicon-treated insulating layer shows a good strength value, and is equivalent to the coated metal powder coated with phosphate and commercially available powder. .
Moreover, since the specific resistance of the dust core provided with the organic silicon treatment insulating layer is higher than that of the conventional technique and the comparative example, stable iron loss in a high frequency region can be obtained.

  In addition, as shown in FIG. 3, it was confirmed that Ca, P, O, and Si were present as elements in the insulating layer 2 of the dust core of Example 1.

DESCRIPTION OF SYMBOLS 1 ... Metal powder, 2 ... Insulating layer, 3 ... Metal oxide, 10 ... Powder magnetic core.

Claims (3)

A dust core formed by pressurizing and heating a coated metal powder,
The coated metal powder, a metal powder containing iron as a main component, the surface of the metal powder, an insulating layer comprising a layer of layers and particulate metal oxides-phosphate calcium in this order, the surface of the insulating layer anda silicone resin coating covering the,
The dust core includes the insulating layer between the metal powder, the insulating layer may include Ca, P, Si and C as the element, wherein the silicone resin coating, Ri thickness 10nm~500nm der,
0.1 T, and the iron loss at 20kHz is 400 kW / ^{m 3} or less, and the maximum magnetic permeability mu _m is 60 to 150, a dust core.   2. The dust core according to claim 1, wherein an average particle diameter of the particulate metal oxide is greater than 10 nm and less than or equal to 350 nm. The powder magnetic core according to claim 1 or 2, wherein the specific resistance is 10,000 µΩcm or more.