JP2021082717A - Method for manufacturing powder magnetic core obtained by connecting soft magnetic powders with friction bonding of aluminum oxide fine particles by insulating soft magnetic powder with aggregate of aluminum oxide powders - Google Patents

Abstract

To provide a method for manufacturing a powder magnetic core having performance more excellent than a conventional powder magnetic core and having mechanical strength similar to the conventional powder magnetic core, enabling the manufacture of a powder magnetic core at more inexpensive cost with no constraint in the shape and size of the powder magnetic core to be manufactured.SOLUTION: A method for manufacturing a powder magnetic core fills an aggregate of soft magnetic powders covered with aggregates aluminum oxide powders 2, compresses the aggregate of the soft magnetic powders by a press machine, aluminum oxide powders 2 brought into contact with the surfaces of the soft magnetic powders are connected to the surfaces of the soft magnetic powders with frictional heat, the aluminum oxide powders 2 in contact with one another are also connected at contact parts with frictional heat, the soft magnetic powders are connected by connecting the aluminum oxide powders, and a powder magnetic core formed of the connected soft magnetic powders is manufactured in a metal mold. Granular fine particles 2 of aluminum oxide uniformly fill gaps of flat atomized iron powders 1 overlapping flat surfaces on each other.SELECTED DRAWING: Figure 1

Description

In the present invention, a collection of fine crystals of an aluminum compound that precipitates aluminum oxide by thermal decomposition is precipitated in an organic compound, the organic compound is adhered to the surface of a soft magnetic powder made of a metal or an alloy, and the organic compound is further formed. After vaporization, the aluminum compound is thermally decomposed to precipitate a collection of aluminum oxide fine particles on the surface of the soft magnetic powder. After that, the mold is filled with a collection of soft magnetic powders, and the soft magnetic powders are collected and compressed by a press machine. When the repulsive force received by the press machine continues to increase, the compression by the press machine is stopped. As a result, the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat, and the aluminum oxide fine particles are bonded to each other by frictional heat, so that the soft magnetic powders are bonded to each other and consist of a collection of the soft magnetic powders. This is a method for manufacturing a dust core in which a compression molded body is manufactured in a mold. In this manufacturing method, the compression by the press is stopped immediately before the soft magnetic powder is compressed, so that the soft magnetic powder is not plastically deformed. Therefore, no processing strain is generated in the soft magnetic powder, and an annealing treatment for restoring the holding power of the soft magnetic powder after the formation of the compression molded product becomes unnecessary.

The dust core is made by filling a mold with a collection of soft magnetic powder whose surface has been insulated and compressing it, and then annealing the compression molded product to remove the processing strain of the soft magnetic powder generated during compression. , Restores the holding power of soft magnetic powder and manufactures a dust core. Such a dust core is used as a magnetic core that constitutes a stator and a rotor in a motor, and a magnetic core that constitutes a reactor, a noise filter, a choke coil, and the like in a power supply circuit. All of these electric products are general-purpose products, and it is required that the manufacturing cost of the dust core is low.
The eddy current of the soft magnetic powder whose surface is insulated is confined inside the soft magnetic powder when operating in an alternating magnetic field. That is, the eddy current includes an eddy current flowing in the soft magnetic powder and an eddy current flowing in the gap between the soft magnetic powders, and when the surface of the soft magnetic powder is insulated with an insulator, the insulating property of the insulator is improved. The higher the value, the lower the eddy current of the latter. Since the eddy current loss is proportional to the square of the frequency of the alternating magnetic field, the higher the frequency, the greater the effect of reducing the eddy current loss. This eddy current loss becomes an energy loss during electromagnetic conversion of the dust core, and the dust core generates heat due to the energy loss. Therefore, by insulating the surface of the soft magnetic powder, the heat generation of the dust core is reduced.
Further, when the soft magnetic powder is compressed, the soft magnetic powder is plastically deformed, and the plastic deformation causes processing strain in the soft magnetic powder, increasing the holding power of the soft magnetic powder. As a result, the hysteresis loss of the soft magnetic powder increases, and the hysteresis loss becomes an energy loss during electromagnetic conversion of the dust core, and the dust core generates heat due to the energy loss. Therefore, the compression molded body is annealed to restore the holding power of the soft magnetic powder, and the heat generation of the dust core made of the compression molded body is reduced. As described above, the energy loss at the time of electromagnetic conversion of the dust core is composed of an eddy current loss and a hysteresis loss, and both are collectively referred to as an iron loss of the dust core. Since the dust core generates heat due to this iron loss, a treatment for insulating the soft magnetic powder and a treatment for annealing the compression molded product are required.
By the way, the larger the magnetic permeability of the soft magnetic powder, the easier it is for the soft magnetic powder to be magnetized, and the more magnetic energy is easily taken into the dust core. Further, the larger the saturation magnetic flux density of the magnetized soft magnetic powder, the larger the magnetic energy of the dust core. However, there is no soft magnetic powder having a large magnetic permeability and a large saturation magnetic flux density, and the relative sizes are compared. On the other hand, most of the dust cores are used at an operating frequency of 1-500 kHz and an operating magnetic flux density of 0.3-1.3 Tesla. Therefore, a dust core suitable for electric appliances is used according to the saturation magnetic flux density in the operating frequency region of the dust core. On the other hand, the performance of the dust core depends on the frequency characteristics of the magnetic permeability of the soft magnetic powder and the saturation magnetic flux density of the soft magnetic powder. A method for producing a dust core that can be used as a raw material is preferable.
For example, a soft magnetic material made of a cobalt-based amorphous material has a large magnetic permeability, but the saturation magnetic flux density has a small value close to that of Mn / Zn-based ferrite. On the other hand, the soft magnetic material made of iron-based amorphous has a high saturation magnetic flux density but a low magnetic permeability. Iron powder is a soft magnetic powder made of the cheapest metal or alloy, and has the highest saturation magnetic flux density among the soft magnetic powders, but the lowest magnetic permeability. Further, among the nickel-iron alloys of permalloy, the alloy having a composition of Ni77% by mass, Fe14% by mass, Cu5% by mass, and Mo4% by mass has the highest magnetic permeability among the permalloys, but has a magnetic permeability. The saturated magnetic flux density has an intermediate value of the soft magnetic material. Sendust (an alloy consisting of Fe 9.6% by mass, Si 5.6% by mass, and others made of Al, which is a registered trademark of Tohoku University), which has the highest magnetic permeability among iron, silicone, and aluminum alloys, has a magnetic permeability and saturation. Both the magnetic flux density and the magnetic flux density have intermediate values of the soft magnetic material. The cheapest soft magnetic material, Mn / Zn-based ferrite, has a large magnetic permeability but the lowest saturation magnetic flux density.
In addition to these soft magnetic materials, new materials are being developed consisting of thin bands made by quenching amorphous alloys. For example, an amorphous alloy strip in which iron is the main component, silicone and boron are added, and a small amount of copper and niobium are added, and a high-temperature solution having these compositions is rapidly cooled at a rate of 1 million ° C./sec. Has been developed. This amorphous quenching thin band is a material in which both the magnetic permeability and the saturation magnetic flux density are relatively large (see Patent Document 1). Further, a thin band made of an amorphous alloy having a magnetic permeability value close to that of Sendust and a saturation magnetic flux density value close to that of silicon steel has been developed. This material is a material composed of an alloy in which silicon, boron, phosphorus, and copper are added to high-concentration iron (see Patent Document 2).
On the other hand, among the soft magnetic materials, Mn-Zn-based ferrite and Ni-Zn-based ferrite are brittle materials that do not have ductility and malleability and are vulnerable to impact, and form a magnetic core with a sintered body. The volume resistivity at the Mn · Zn ferrite is 1 × 10 ³ Ω · cm, with an insulator of Ni-Zn ferrite is composed of 1 × 10 ⁶ Ω · cm, the eddy current flowing in the sintered body small .. All other soft magnetic materials are conductive metals or alloys, and the eddy current flowing inside the soft magnetic powder is large, insulates the soft magnetic powder, and traps the eddy current inside the soft magnetic powder. Further, the metal or alloy has ductility and malleability, and is plastically deformed by compressive stress. Therefore, the surface of the soft magnetic powder made of metal or alloy is insulated, and the collection of soft magnetic powder made of metal or alloy whose surface is insulated is compressed in the mold, and the plastically deformed soft magnetic powder is entangled with each other. Provides mechanical strength to the compression die and forms a dust core. The dust core in the present invention uses a soft magnetic powder made of a metal or an alloy in order to compress a collection of soft magnetic powder in a mold.

As described above, in the production of the powder magnetic core, a collection of soft magnetic powder whose surface is insulated is filled in a mold, and the collection of soft magnetic powder is simply compressed in the mold to be plastically deformed. By entwining magnetic powders with each other, a dust core with a certain mechanical strength is manufactured in a mold. That is, when a collection of soft magnetic powders is simply compressed, the soft magnetic powders are plastically deformed, voids are formed by the plastic deformation, and the soft magnetic powders are rearranged so as to fill the voids. The rearrangement of the soft magnetic powder is completed with a relatively small compression pressure, but as the compression pressure increases, the plastic deformation of the soft magnetic powder progresses, the voids in the collection of the soft magnetic powder are reduced, and the compression density is increased. The magnetic energy of the magnetized dust core increases according to the compression density of the dust core. On the other hand, since the soft magnetic powder has a constant particle size distribution, in a collection of soft magnetic powders, when the soft magnetic powders having different particle sizes are adjacent to each other and the soft magnetic powders having different particle sizes are plastically deformed at the same time, the plastic deformation occurs. The soft magnetic powders are entangled with each other, and the soft magnetic powders are entangled with each other, so that the soft magnetic powders are bonded to each other and the dust core is mechanically strong. Therefore, the dust core is composed of soft magnetic powder in which a collection of soft magnetic powder is simply compressed and plastic deformation is advanced. However, as the plastic deformation of the soft magnetic powder progresses, the processing strain of the soft magnetic powder increases, which increases the holding power of the soft magnetic powder, and the hysteresis loss increases in accordance with the increase in the holding power. The magnetic core generates heat. This hysteresis loss is larger than the eddy current loss in the soft magnetic powder. Therefore, depending on the progress of plastic deformation, the compression molded product is annealed at 500-800 ° C. to remove the processing strain of the soft magnetic powder and return the holding power of the soft magnetic powder to the original value. On the other hand, the higher the hardness of the soft magnetic powder and the smaller the voids in the gathering of the soft magnetic powder, the larger the compression pressure is required, the processing strain of the soft magnetic powder increases, and the temperature of strain relief annealing increases. .. Therefore, the restoration of the holding power of the soft magnetic powder depends on the heat resistance of the material that insulates the soft magnetic powder. For example, in a powder magnetic core in which soft magnetic powder is insulated with a synthetic resin having low heat resistance, there is almost no effect of restoring the holding power because the heat treatment also serves as resin curing at around 200 ° C.
On the other hand, if the soft magnetic powder is insulated with an inorganic material having high heat resistance and the temperature of the strain removing annealing is raised, the processing cost and the annealing cost for insulating the soft magnetic powder increase. As described above, the strain-removing annealing treatment affects the iron loss performance of the dust core and the manufacturing cost of the dust core. Therefore, if the dust core does not require strain removing and annealing, an inexpensive dust core with little iron loss can be manufactured.
For example, atomized iron powder has a Vickers hardness of 75-87 HV, which is the lowest hardness among soft magnetic powders, and the compression density of the compression molded product is close to 90% of the iron density. The annealing temperature for restoring the holding power is as low as 500-600 ° C. However, the saturation magnetic flux density of atomized iron powder drops sharply at frequencies exceeding 1 kHz.
On the other hand, Sendust (registered trademark of Tohoku University) performs magnetic annealing up to 1100 ° C., which also serves as a treatment for removing impurities, but has a high Vickers hardness of 410-480 HV. On the other hand, the saturation magnetic flux density does not decrease in a relatively low frequency region exceeding 1 kHz like iron powder. However, the annealing temperature for restoring the holding power is as high as 600-700 ° C., and the processing cost for insulating the sendust and the annealing cost increase.
Further, the thin band made of an amorphous alloy has a higher hardness because it is rapidly cooled at a rate of 100,000 to 1,000,000 ° C./sec. For example, the Vickers hardness of the above-mentioned amorphous alloy strip containing iron as a main component and silicone and boron is as high as 720 HV, and the hardness does not decrease significantly even by annealing. Therefore, the annealing temperature at which the holding power is restored is higher than that of Sendust, and the processing cost and annealing cost for insulating the amorphous alloy are further higher than those of Sendust.
Therefore, when the powder magnetic core is manufactured, if the soft magnetic powder is not plastically deformed, processing strain does not occur, and strain removal annealing becomes unnecessary. Moreover, the hysteresis loss of the soft magnetic powder does not increase. However, in order to realize the mechanical strength of the compression molded product and to increase the compression density of the compression molded product, means other than the plastic deformation of the soft magnetic powder are required. Therefore, first, it is necessary to advance the arrangement of the soft magnetic powders in the collection of soft magnetic powders to create a collection of soft magnetic powders accumulated at high density. Further, if the soft magnetic powder can be coated with an insulator having high insulating properties, the eddy current flowing in the gap between the soft magnetic powders can be reduced. Secondly, when compressing a collection of soft magnetic powders covered with an insulator, the insulators covering the soft magnetic powders are bonded to each other, and when the insulators are bonded to each other, the soft magnetic powders are bonded to each other. A compression molded body can be formed. Further, if the insulator is fine particles, an extremely large number of fine particles are bonded to each other, so that the compression molded product has a certain mechanical strength. This eliminates the need to plastically deform the soft magnetic powder. Therefore, regardless of the hardness of the soft magnetic powder, the surface of the soft magnetic powder was insulated with fine particles having high insulating properties, and the collection of the soft magnetic powder was rearranged and accumulated at high density, and the soft magnetic powder was compressed. At that time, if the fine particles are bonded to each other and the soft magnetic powders are bonded to each other by joining the fine particles to each other, it becomes an epoch-making method for producing a powder magnetic core with less iron loss and an inexpensive powder magnetic core.
Therefore, in the new method for producing the dust core, firstly, all the soft magnetic powders are used regardless of the hardness of the soft magnetic powders, and secondly, the soft magnetic powders are insulated with fine particles having high insulating properties. Thirdly, the collection of soft magnetic powders is accumulated at high density, and fourthly, when the collection of soft magnetic powders is compressed, the fine particles are bonded to each other, and the soft magnetic powders are bonded to each other by joining the fine particles. This is a method for manufacturing a dust core with two characteristics. So far, there is no method for producing such an epoch-making powder magnetic core.

Japanese Unexamined Patent Publication No. 2001-300697 Japanese Unexamined Patent Publication No. 2016-094651

Sanyo Special Steel Technical Report, Vol. 7 (2000) No. 1, pages 29-34 Powder and Metallurgy, Vol. 47, No. 7, pp. 711-716 Kawasaki Steel Technical Report, 33 (2001) 4, pages 184-187 Powder and Metallurgy, Vol. 32, No. 7, Pages 9-13 Kobe Steel Technical Report, Vol. 48, No. 3 (1998), pages 25-28 Kobe Steel Technical Report, Vol. 50, No. 3 (2000), page 38 Kobe Steel Technical Report, Vol. 60, No. 2 (2010), page 82 42nd Annual Meeting of the Magnetic Society of Japan (2018), 13aC-3

Here, we will summarize the issues in realizing a new method for manufacturing a dust core.
As described above, firstly, the soft magnetic powder is insulated with highly insulating fine particles, secondly, the collection of the soft magnetic powder is accumulated at a high density, and thirdly, when the collection of the soft magnetic powder is compressed. If the fine particles are bonded to each other and the soft magnetic powders are bonded to each other by the bonding of the fine particles. Fourth, if the powder magnetic core can be produced using all the soft magnetic powders regardless of the hardness of the soft magnetic powders, the conventional method. Compared to the dust core, firstly, the eddy current loss is smaller, secondly, the saturation magnetic flux density is higher, thirdly, there is no increase in hysteresis loss, and fourthly, the magnetic characteristics of the soft magnetic powder are reflected in the inexpensive powder. Magnetic core can be manufactured. Therefore, the new manufacturing method needs to meet the following four requirements.
The first requirement is to evenly cover the soft magnetic powder with a collection of highly insulating fine particles.
The second requirement is to rearrange the collection of soft magnetic powders so that the collections of soft magnetic powders have a high accumulation density and the surfaces of the soft magnetic powders overlap each other. That is, an arrangement in which the soft magnetic powder having a relatively small particle size enters the gap between the collections of the soft magnetic powder is advanced, and then the surfaces of the soft magnetic powder are overlapped with each other. Further, the soft magnetic powder in which the surfaces of the soft magnetic powder overlap each other is covered with a collection of fine particles. Also, the weight of all the fine particles should be less than 1% of the weight of the soft magnetic powder aggregate. When such a collection of soft magnetic powder having a high accumulation density is compressed, the density of the compact compact becomes close to the density of the soft magnetic powder. As a result, when the dust core is magnetized, the magnetic energy of the magnetized dust core is large. On the other hand, since the surface direction of the soft magnetic powder is the axial direction in which the soft magnetic powder is easily magnetized, when all the soft magnetic powders are superposed on each other, the magnetic permeability of the dust core increases and it becomes easy to be magnetized. As a result, the magnetic energy taken into the dust core, which is easily magnetized, is large.
The third requirement relates to the conditions for producing a compression molded article. That is, when an insulatingly coated soft magnetic powder collection is filled in a mold and the soft magnetic powder collection is compressed by a press, first, the insulatingly coated soft magnetic powder collection is formed into a mold shape. Will be done. Secondly, the fine particles covering the soft magnetic powder continuously move to fill the voids of the gathering of the soft magnetic powder, and the continuous movement of the fine particles also moves the adjacent soft magnetic powder to promote rearrangement, and the soft magnetic powder The degree of integration is further increased. Thirdly, when the fine particles cannot move, the fine particles come into contact with each other, frictional heat is generated at the contact portion, and the fine particles are joined by the frictional heat. Further, by joining the fine particles to each other, the soft magnetic powders are bonded to each other, and a dust core composed of a collection of the soft magnetic powders is produced in the mold. Fourth, when the fine particles come into contact with each other and are bonded by frictional heat, the repulsive force received by the press continuously increases, and at this point, the compression by the press is stopped. As a result, the compression is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed. Therefore, the hysteresis loss of the dust core does not increase.
Fourth, all the soft magnetic powders are used regardless of the hardness of the soft magnetic powders, and the powder magnetic core is produced by satisfying the above three requirements.
The requirements of the treatment method of the soft magnetic powder and the requirements of the fine particles that realize the above four requirements will be examined.
The first requirement is to increase the degree of integration of the soft magnetic powder. That is, the collection of soft magnetic powders is repeatedly moved in the liquid in three directions of front and back, left and right, and up and down to advance the arrangement of the soft magnetic powders in the liquid and increase the accumulation density of the collections of soft magnetic powders. That is, since the soft magnetic powders do not come into direct contact with each other in the liquid, the soft magnetic powders easily move. Therefore, when the collection of soft magnetic powder is repeatedly moved in the liquid in three directions of front and back, left and right, and up and down, the arrangement is relative to the arrangement in which the soft magnetic powder having a relatively small particle size enters the gap between the collection of soft magnetic powder. The arrangement in which the soft magnetic powder having a small particle size moves above the collection of the soft magnetic powder advances. Finally, when the collection of soft magnetic powders is moved in the vertical direction, the surfaces of the soft magnetic powders overlap each other.
The second requirement concerns fine particles. The fine particles have high insulating properties, high heat resistance, higher hardness than the soft magnetic powder, and the size is three orders of magnitude smaller than the average particle size of the soft magnetic powder and two orders of magnitude smaller than the thickness of the soft magnetic powder. The weight of all particles should be less than 1% of the weight of the aggregate of soft magnetic powders. The soft magnetic powder is covered with fine particles having these properties, and the collection of the soft magnetic powder is compressed. When the fine particles receive compressive stress, they move continuously, and the fine particles fill the voids between the soft magnetic powders. Further, when the fine particles continue to move, the adjacent soft magnetic powder moves and rearrangement proceeds, further increasing the degree of accumulation of the soft magnetic powder. Further, when the fine particles cannot move, the fine particles come into contact with each other, frictional heat is generated at the contact portion, and the fine particles are bonded to each other by the frictional heat. The soft magnetic powder is bonded by joining the fine particles to each other, and a dust core composed of a collection of the soft magnetic powder is produced in the mold. On the other hand, when the fine particles come into contact with each other and are bonded by frictional heat, the number of fine particles is extremely large, so that the repulsive force received by the press continuously increases, and at this point, the compression by the press is stopped. As a result, the compression is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed.
That is, the soft magnetic powder is evenly covered with a collection of fine particles having the above-mentioned properties, the collection of the soft magnetic powder is filled in a mold, and the collection of the soft magnetic powder is compressed by a press. At this time, first, a collection of soft magnetic powder covered with a collection of fine particles is formed into a mold shape. Second, the fine particles continuously move to fill the voids in the collection of soft magnetic powders. Third, the soft magnetic powder adjacent to the fine particles also moves and rearranges, increasing the degree of accumulation of the soft magnetic powder. Fourth, when there are no voids through which the fine particles can move, the fine particles come into contact with each other. Since the fine particles have high heat resistance and are hard, the fine particles are not destroyed by contact, excessive frictional heat is generated at the part where the fine particles come into contact with each other, and the contact part is cleaned after the foreign matter or impurities in the contact part are vaporized. The fine particles are firmly bonded to each other by frictional heat. In addition, the fine particles that come into contact with the surface of the soft magnetic powder generate excessive frictional heat at the part that comes into contact with the surface of the soft magnetic powder, and after the foreign matter or impurities in the contact portion are vaporized, the soft magnetic powder is cleaned. Firmly joins the contact part with frictional heat. Fifth, when the reaction in which the fine particles are bonded by frictional heat and the reaction in which the fine particles are bonded to the surface of the soft magnetic powder by frictional heat occur, the number of fine particles is extremely large, so that the repulsive force against the pressurizing pressure is generated. It continues to occur on the press and at this point the compression by the press is stopped. As a result, the pressurizing pressure is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed.
The third requirement is to manufacture a dust core using all soft magnetic powders.
By the way, in the conventional method for producing a dust core, a collection of soft magnetic powders is simply compressed to promote plastic deformation of the soft magnetic powders, whereby the plastically deformed soft magnetic powders are entangled with each other and compressed. The molded body has the necessary mechanical strength. Therefore, when the soft magnetic powders are a collection of soft magnetic powders having a high degree of integration in which the surfaces of the soft magnetic powders overlap each other and the collection of the soft magnetic powders is compressed, the soft magnetic powders do not become entangled with each other. Therefore, in the conventional method for producing a dust core, it is not necessary to increase the degree of integration of the soft magnetic powder, and the aggregate of the soft magnetic powder is simply compressed. On the other hand, in the new method for producing a dust core, the soft magnetic powders that overlap each other are bonded to each other by joining the fine particles. Since the number of fine particles is extremely large, the dust core has a certain mechanical strength due to the bonding of the fine particles by frictional heat.
Therefore, the above three requirements are reflected in the new powder magnetic core manufacturing method, and the manufactured dust core has higher saturation magnetic flux density and magnetic permeability than the conventional dust core, and has less eddy current loss. Ideal pressure if there is no increase in hysteresis loss, the dust core has a certain mechanical strength, an inexpensive powder core can be manufactured, and there are no restrictions on the shape and size of the powder core to be manufactured. It becomes a manufacturing method of powder magnetic core. Further, if all the soft magnetic powders can be used regardless of the hardness, a powder magnetic core reflecting the magnetic characteristics of the soft magnetic powder can be formed. In particular, since the frequency characteristic of magnetic permeability differs depending on the material of the soft magnetic powder, it is possible to manufacture a dust core that is easily magnetized and easily takes in magnetic energy even in a high frequency band. There are some problems in realizing this ideal manufacturing method, and these problems are the problems to be solved by the present invention. The problems of the present invention will be described below.
The first issue is to use all soft magnetic powders as raw materials, process the collection of soft magnetic powders in a liquid, advance the arrangement of the soft magnetic powders, and make the soft magnetic powders with high accumulation density and overlapping surfaces. Create a gathering in liquid. The second problem is that the fine particles have higher hardness than the soft magnetic powder, excellent insulation, high heat resistance, and the size is 3 orders of magnitude smaller than the average particle size of the soft magnetic powder and 2 orders of magnitude smaller than the thickness of the soft magnetic powder. Is deposited on the surface of the soft magnetic powder. The third task is to compress a collection of soft magnetic powders covered with a collection of fine particles, bond the fine particles in contact with each other by frictional heat, and bond the soft magnetic powders to each other by joining the fine particles. The fourth problem is that the soft magnetic powder does not plastically deform when the collection of the soft magnetic powder is compressed. The fifth problem is a manufacturing method in which simple treatments are continuously carried out in the steps from the treatment of the soft magnetic powder in the liquid to the formation of the dust core. The sixth problem is that there are no restrictions on the shape and size of the dust core. As a result, it has superior performance to the conventional dust core, has mechanical strength similar to that of the conventional dust core, can be manufactured at a lower cost, and has the shape and size of the manufactured dust core. There are no restrictions. An object of the present invention is to realize a method for producing a dust core that simultaneously solves six problems.

The manufacturing method for producing a dust core is to fill a mold with a collection of soft magnetic powder covered with a collection of aluminum oxide fine particles, compress the collection of soft magnetic powder with a press machine, and use it as a surface of the soft magnetic powder. The aluminum oxide fine particles in contact are bonded to the surface of the soft magnetic powder by frictional heat, and the aluminum oxide fine particles in contact with each other are bonded by frictional heat at the contact site, and the soft aluminum oxide fine particles are bonded to each other by frictional heat. This is a method for producing a dust core in which magnetic powders are bonded to each other and a dust core composed of a collection of the bonded soft magnetic powders is produced in the mold.
A collection of fine crystals of an aluminum compound that precipitates aluminum oxide by thermal decomposition attaches the organic compound precipitated in the organic compound to the surface of the soft magnetic powder, and the surfaces of the soft magnetic powder are brought together via the organic compound. The aluminum oxide fine particles precipitate an aluminum compound that precipitates aluminum oxide fine particles by thermal decomposition, which is the first step of forming an overlapping collection of soft magnetic powders on the bottom surface of the mixer as the shape of the bottom surface. The number of moles precipitated as a weight less than 1/100 of a collection of soft magnetic powders is dispersed in methanol to prepare a methanol dispersion of the aluminum compound, and the first property of dissolving or mixing in methanol and viscosity. An organic compound having a second property higher than the viscosity of methanol and a third property having a boiling point higher than the boiling point of methanol and lower than the thermal decomposition temperature of the aluminum compound is mixed with the methanol dispersion. A mixer having a heating function is placed on a vibration table, the mixer is filled with a collection of the mixture and soft magnetic powder, and the mixer is rotated and rotated. It is shaken to disperse the collection of the soft magnetic powder in the mixed liquid, and further, a vibrator repeatedly generates vibrations in three directions of up and down, left and right, and front and back, and finally generates vibrations in the up and down direction. The vibration generated by the vibrating machine is transmitted to the mixer via the vibrating table, and the collection of the soft magnetic powder in the mixer is repeatedly moved in the mixed solution in the vibration direction to repeatedly move the mixed solution in the vibrating direction. In the process, the arrangement of the soft magnetic powder is advanced, and then the surfaces of the soft magnetic powder are overlapped with each other via the mixed liquid, and a collection of the soft magnetic powder having the shape of the bottom surface is formed on the bottom surface of the mixer. After that, the temperature of the mixer is raised to the boiling point of methanol, whereby a collection of fine crystals of the aluminum compound is deposited all at once in the organic compound, and the organic compound adheres to the soft magnetic powder. Then, in the first step, a collection of the soft magnetic powders in which the surfaces of the soft magnetic powders are overlapped with each other via the organic compound is formed on the bottom surface of the mixer as the shape of the bottom surface.
A collection of aluminum oxide fine particles is deposited on the surface of the soft magnetic powder, the collection of the soft magnetic powder is compressed in a mold, and the aluminum oxide fine particles in contact with the surface of the soft magnetic powder are the surface of the soft magnetic powder. The aluminum oxide fine particles that are in contact with each other are bonded by frictional heat at the contact site, and the soft magnetic powders are bonded to each other by the bonding of the aluminum oxide fine particles, and the bonded soft magnetic powder is bonded to each other. A second step in which a dust core composed of a collection of powder is manufactured in the mold, the mold is filled with the collection of soft magnetic powder prepared in the first step, and the mold is filled with the mold. The temperature is raised to a temperature at which the aluminum compound thermally decomposes, whereby the organic compound is first vaporized, then the fine crystals of the aluminum compound are thermally decomposed, and the surface of the soft magnetic powder is covered with fine aluminum oxide fine particles. The aggregates are deposited all at once, and the aggregates of the aluminum oxide fine particles cover the soft magnetic powder. Then, a continuously increasing pressurizing pressure is applied to the aggregates of the soft magnetic powder by the press machine, and the press machine performs. When the repulsive force received continues to increase, the pressurizing pressure exerted by the press machine is stopped, whereby the collection of the soft magnetic powder is first formed into the shape of the mold, and then the oxidation. When the aluminum fine particles continuously move to fill the voids in the collection of the soft magnetic powder and the aluminum oxide fine particles cannot move, the aluminum oxide fine particles in contact with the surface of the soft magnetic powder become the surface of the soft magnetic powder. The aluminum oxide fine particles that are in contact with each other are bonded by frictional heat at the contact site, and the soft magnetic powders are bonded to each other by the bonding of the aluminum oxide fine particles, and the bonded soft magnetic powder is bonded to each other. A dust core composed of a collection of powder is composed of a second step in which the powder magnetic core is manufactured in the mold.
The two steps are carried out in succession. The mold is filled with a collection of soft magnetic powder covered with a collection of aluminum oxide fine particles, the collection of soft magnetic powder is compressed by a press machine, and the surface of the soft magnetic powder is pressed. The aluminum oxide fine particles in contact with the soft magnetic powder are bonded to the surface of the soft magnetic powder by frictional heat, and the aluminum oxide fine particles in contact with each other are bonded by frictional heat at the contact site, and the aluminum oxide fine particles are bonded to each other. A method for producing a dust core in which soft magnetic powders are bonded to each other and a dust core composed of a collection of the bonded soft magnetic powders is produced in the mold.

In the present invention, vibrations in three directions are repeatedly applied to a collection of soft magnetic powders in a liquid, and finally, vibrations in a vertical direction are applied to advance the arrangement of the soft magnetic powders in the liquid, and then the soft magnetic powders. Overlay the faces. Next, a collection of granular aluminum oxide fine particles having a size of 40-60 nm, which is three orders of magnitude smaller than the average particle size of the soft magnetic powder and two orders of magnitude smaller than the thickness of the soft magnetic powder, is deposited on the surface of the soft magnetic powder. .. Further, the mold is filled with the aggregate of soft magnetic powder, the aggregate of soft magnetic powder is compressed by the press, and when the repulsive force received by the press continues to increase, the compression by the press is stopped. As a result, the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat, the soft magnetic powder is insulated, and the aluminum oxide fine particles are bonded to each other by frictional heat, whereby the soft magnetic powders are bonded to each other. Then, a dust core composed of a collection of the soft magnetic powders is produced in the mold. The dust core has the necessary mechanical strength because an extremely large number of aluminum oxide fine particles are firmly bonded to each other by frictional heat. Further, when the repulsive force received by the press machine is continuously increased, the compression by the press machine is stopped, so that the compression of the soft magnetic powder is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is plastic. Does not deform. Therefore, the strain removing and annealing treatment of the dust core manufactured in the mold becomes unnecessary. Further, since the soft magnetic powder is not plastically deformed, all the soft magnetic powders can be used as raw materials for the dust core regardless of the hardness of the soft magnetic powders.
By the way, the aluminum oxide Al ₂ O ₃ covering the surface of the soft magnetic powder brings the following excellent properties to the dust core. First, aluminum oxide is an excellent insulator, ^{with a large volume resistivity of 10 15} Ω · cm, a high breakdown voltage of 15 kV / mm, and no frequency dependence of insulation. Therefore, the eddy current loss of the dust core is small even in the high frequency region. Secondly, the melting point of aluminum oxide is as high as 2072 ° C., the heat resistance is superior to that of soft magnetic powder, and the heat resistance is superior to that of conventional dust core. In addition, excessive frictional heat is generated at a portion where the fine particles come into contact with each other, and the frictional heat causes the fine particles to join each other. Thirdly, aluminum oxide has a large Mohs hardness of 9, which is the second hardest substance after diamond, and is harder than all soft magnetic powders, and all soft magnetic powders can be used for dust cores. Further, when the aluminum oxide fine particles are stressed, they continuously move so as to fill the voids. When there are no movable voids, the fine particles come into contact with each other and frictional stress is generated at the contact portion, but the fine particles are not destroyed. Fourth, aluminum oxide is less susceptible to acids and alkalis, has better chemical resistance than soft magnetic powder, and has better chemical resistance than conventional dust cores. The density of aluminum oxide is 3.95 g / cm ³ , which is half the density of iron.
Here, a manufacturing method for manufacturing the dust core of the present invention will be described. The manufacturing method for manufacturing the dust core comprises the following seven steps.
An aluminum compound having these three properties, which is inexpensive as a raw material, precipitates aluminum oxide by a simple treatment of thermal decomposition, and has a low thermal decomposition temperature of about 300 ° C., was used as a raw material for aluminum oxide. On the other hand, in order to cover the soft magnetic powder with a collection of aluminum oxide fine particles, the first step is to disperse the aluminum compound in methanol and liquid-phase the aluminum compound.
In order to cover the soft magnetic powder with a collection of aluminum oxide fine particles, it is necessary to attach a methanol dispersion of an aluminum compound to the surface of the soft magnetic powder. Therefore, in the second step, the first property of dissolving or mixing in methanol, the second property of having a viscosity higher than that of methanol, the boiling point of which is higher than the boiling point of methanol, and the thermal decomposition temperature of the aluminum compound. An organic compound having a lower third property is mixed with a methanol dispersion to prepare a mixed solution.
In the third step, the mixture and the collection of soft magnetic powder are filled in a mixer arranged on a vibration table, and the mixer is rotated and rocked, and the aluminum compound is mixed with methanol and an organic compound. The mixture is uniformly dispersed in the mixture of the above, and a mixture in which the soft magnetic powder is uniformly dispersed in this mixture is prepared. Therefore, the mixture adheres to the soft magnetic powder due to the viscosity of the mixture.
In the fourth step, the vibration generated by the exciter is transmitted to the mixer via the exciter, and the entire mixture is vibrated. At this time, the soft magnetic powder is a powder having a constant aspect ratio, which is the ratio of the area to the thickness, and the density of the soft magnetic powder is close to 10 times the density of the mixed liquid, so that the soft magnetic powder is a surface. Moves upward in the mixture in the vibration direction. Further, since the soft magnetic powder having a relatively small particle size has a smaller mass, the soft magnetic powder having a smaller particle size has a larger amount of movement in the mixed solution. Therefore, when vibrations in three directions of front-back, left-right, and up-down are repeatedly applied to the entire mixture, the soft magnetic powder repeatedly moves in the three directions in the mixture. At this time, for the soft magnetic powder having a relatively small particle size, the arrangement that enters the voids of the soft magnetic powder collection and the arrangement that moves above the soft magnetic powder collection progress, and the degree of accumulation of the soft magnetic powder collection Will increase. Finally, when vibration in the vertical direction is applied, the soft magnetic powders are overlapped with each other via the mixed liquid with the surface facing upward. As a result, a collection of soft magnetic powders having a high degree of integration in which the surfaces of the soft magnetic powders overlap each other is formed on the bottom surface of the mixer as the shape of the bottom surface. The vibration acceleration applied to the mixture depends on the amount of soft magnetic powder to be filled, but since the viscosity of the mixed solution is low and the density of the soft magnetic powder is as high as 10 times the density of the mixed solution, it is 0.2-0. It is about 4G. This solves the first problem described in paragraph 6.
The fifth step raises the temperature of the mixer to the boiling point of methanol. At this time, fine crystals of the aluminum compound are deposited all at once in the organic compound, the organic compound adheres to the soft magnetic powder, and a collection of soft magnetic powder in which the surfaces of the soft magnetic powder overlap each other via the organic compound is formed. , It is formed on the bottom surface of the mixer as the shape of the bottom surface. The vaporized methanol is recovered by a recovery machine and reused.
In the sixth step, a collection of soft magnetic powders is transferred from the mixer to a mold, and the temperature of the mold is raised to a temperature at which the aluminum compound is thermally decomposed. At this time, the organic compound is first vaporized, then the fine crystals of the aluminum compound are thermally decomposed, and a collection of aluminum oxide fine particles is deposited all at once on the surface of the soft magnetic powder. Is covered. The aluminum oxide precipitated by the thermal decomposition of the aluminum compound is granular fine particles having a size of 40-60 nm, which is 3 orders of magnitude smaller than the average particle size of the soft magnetic powder and 2 orders of magnitude smaller than the thickness of the soft magnetic powder. This solves the second problem described in paragraph 6. The vaporized organic compound is recovered and reused.
In the seventh step, the pressurizing pressure continuously increased by the press is applied to the collection of soft magnetic powder, and the compression is stopped when the repulsive force received by the press continues to increase. That is, when the pressurizing pressure is applied to the soft magnetic powder, the aluminum oxide fine particles are not bonded to each other, and the aluminum oxide fine particles are not bonded to the soft magnetic powder. It is molded into the shape of a mold. After that, when the pressurizing pressure increases, voids are present in the collection of the soft magnetic powder, so that the aluminum oxide fine particles continuously move so as to fill the voids. Further, with the continuous movement of the aluminum oxide fine particles, the adjacent soft magnetic powder also moves, and the degree of accumulation of the soft magnetic powder is further increased. Further, when the pressurizing pressure is increased, there are no voids through which the aluminum oxide fine particles can move, the aluminum oxide fine particles come into contact with each other, excessive frictional heat is generated at the contact portion, and the aluminum oxide fine particles are joined by the frictional heat. At this time, since aluminum oxide is hard and has a high melting point, the fine particles are not destroyed even by friction between the fine particles. By joining the aluminum oxide fine particles to each other, the soft magnetic powders are bonded to each other. Similarly, when the aluminum oxide fine particles that come into contact with the surface of the soft magnetic powder cannot move, excessive frictional heat is generated at the contact portion, and the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by the frictional heat. As a result, a dust core in which the soft magnetic powders are bonded to each other through the bonding of the aluminum oxide fine particles is produced in the mold. On the other hand, when the reaction in which the aluminum oxide fine particles are bonded to each other by frictional heat and the reaction in which the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat occur, the number of aluminum oxide fine particles is extremely large. A larger pressurizing pressure is required to cause the reaction, and the repulsive force received by the press machine continues to increase. At this point, that is, immediately after the bonding of the aluminum oxide fine particles due to frictional heat occurs, the compression by the press is stopped. Therefore, the pressurizing pressure is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed. This solves the third and fourth issues described in paragraph 6. Further, there are no restrictions on the size and shape of the mold for filling the collection of soft magnetic powder. This solves the sixth problem described in paragraph 6.
The method for producing a dust core, which comprises the seven steps described above, is a method in which simple treatments are continuously performed. This solves the fifth problem described in paragraph 6. As a result, all the problems to be solved by the present invention described in paragraph 6 have been solved.
The dust core produced by the above-mentioned production method has the following effects.
First, since the filling rate of the soft magnetic powder in the dust core is high, the saturation magnetic flux density of the powder magnetic core approaches the saturation magnetic flux density of the soft magnetic powder. Therefore, the magnetic energy of the magnetized dust core is large. That is, the arrangement of the soft magnetic powder was advanced, and a collection of soft magnetic powder having a high degree of integration was formed in the mixer in which the surfaces of the soft magnetic powder were overlapped with each other via the mixed liquid. Further, the soft magnetic powder covered with the aluminum oxide fine particles was formed into a collection of soft magnetic powder having a high degree of integration in which the surfaces of the soft magnetic powder overlap each other. When this collection of soft magnetic powder is compressed by a press machine, all the soft magnetic powders overlap each other, so that compressive stress is applied to all the surfaces of the soft magnetic powder, and the gaps between all the surfaces become narrower. .. Further, when compressive stress is applied to all the surfaces of the soft magnetic powder, if there is a slight void in the gap between the adjacent soft magnetic powders in the direction perpendicular to the surface, the soft magnetic powder can move. The soft magnetic powder moves slightly in the surface direction so as to fill the surface, and the gap between adjacent soft magnetic powders in the direction perpendicular to the surface is also narrowed. As a result, the compression density of the compression molded product approaches the density of the soft magnetic powder. Therefore, the saturation magnetic flux density of the dust core approaches the saturation magnetic flux density of the soft magnetic powder. Further, since the aggregate of the soft magnetic powder is mixed with the dispersion liquid in which the aluminum compound is dispersed in the mixed liquid of methanol and the organic compound, there are no restrictions on the shape, size, and particle size distribution of the soft magnetic powder used as a raw material.
Second, it eliminates the need for strain relief annealing. Therefore, the holding force of the soft magnetic powder constituting the dust core does not change, and the hysteresis loss in the dust core does not increase. Further, since the soft magnetic powder is not plastically deformed, all the soft magnetic powders can be used as raw materials regardless of the hardness. That is, in the conventional method for producing a dust core, the higher the hardness of the soft magnetic powder, the higher the pressurizing pressure for forming the compression molded body. As a result, the plastic deformation of the soft magnetic powder progresses, the processing strain of the soft magnetic powder increases, the annealing temperature of the compression molded product rises, and it becomes difficult to restore the holding power of the soft magnetic powder. Alternatively, the annealing cost increases. Therefore, the effect of eliminating the need for strain removal annealing is great. That is, when the aluminum oxide fine particles cannot move when the collection of the soft magnetic powder is compressed, the aluminum oxide fine particles come into contact with each other, and the aluminum oxide fine particles are bonded to each other by frictional heat. Further, the aluminum oxide fine particles come into contact with the surface of the soft magnetic powder, and a reaction occurs in which the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat. When this friction reaction occurs, the number of aluminum oxide fine particles is extremely large, so that the repulsive force received by the press continuously increases, and at this point, that is, immediately after the friction reaction occurs, compression by the press machine occurs. To stop. Therefore, just before the soft magnetic powder is compressed, the pressurizing pressure on the soft magnetic powder is stopped, the soft magnetic powder does not undergo plastic deformation, and the holding power of the soft magnetic powder does not increase. Further, since the soft magnetic powder is not plastically deformed, all the soft magnetic powders can be used as raw materials for the dust core regardless of the hardness of the soft magnetic powders. As a result, the strain removing and annealing treatment becomes unnecessary, and the manufacturing cost of the dust core can be reduced.
That is, in the conventional method for producing a dust core, an excessive pressure is applied to the soft magnetic powder to promote the plastic deformation of the soft magnetic powder, and the voids of the collection of the soft magnetic powder are filled with the plastically deformed soft magnetic powder. , Plastically deformed soft magnetic powders are entangled with each other. As a result, the compression density of the compression compact approached the density of the soft magnetic powder, and the mechanical strength required for the dust core was generated. Therefore, as the hardness of the soft magnetic powder increases, the pressurizing pressure is increased to plastically deform the soft magnetic powder. On the other hand, in this production method, the fine particles of aluminum oxide fill the voids of the collection of soft magnetic powder having a high accumulation density, and the aluminum oxide fine particles are bonded to each other by frictional heat, and the aluminum oxide fine particles are bonded to each other. The soft magnetic powders were bonded to each other. Therefore, it is not necessary to plastically deform the soft magnetic powder.
Third, the soft magnetic powder is insulated by an insulator having extremely high insulation resistance, and the eddy current loss is smaller than that of the conventional dust core. That is, the aluminum oxide precipitated by the thermal decomposition of the aluminum compound is granular fine particles having a size of 40 to 60 nm, and the aggregates of the granular fine particles are laminated to insulate the soft magnetic powder. Since the aluminum oxide fine particles are granular, the volume is smaller than that of the aluminum oxide fine particles, but there are many pores adjacent to the aluminum oxide fine particles, which are close to the number of the aluminum oxide fine particles. These pores are occupied by air exceeding ^{10 17} Ω · cm, which has a volume resistivity two orders of magnitude higher than that of aluminum oxide. Therefore, the insulating resistance formed by the aggregate of the laminated aluminum oxide fine particles is such that the resistor made of aluminum oxide fine particles and the resistor made of air are connected in series to form an insulating resistance. Furthermore, the number of aluminum oxide fine particles and pores is extremely large. Therefore, the insulation resistance for insulating the soft magnetic powder is three orders of magnitude higher than the insulation resistance formed by ^{the bulk aluminum oxide based on the volume resistivity of 10 15 Ω · cm.} As a result, the soft magnetic powder, a volume resistivity than the powder magnetic core obtained by insulated with a polymeric material consisting of 10 ¹⁴ -10 ¹⁵ Ω · cm, insulation increases 3 orders of magnitude. In addition, the frequency dependence of the insulation resistance of both aluminum oxide and air is small. Therefore, the eddy current loss of the dust core is extremely small even in the high frequency region. As a result, the imaginary portion of the complex magnetic permeability of the dust core increases, and the dust core is easily magnetized.
Fourth, all the soft magnetic powders are aligned in the plane direction, and all the soft magnetic powders are overlapped and bonded to each other through a collection of aluminum oxide fine particles. The plane direction is the axial direction in which the soft magnetic powder is easily magnetized, and the dust core in which all the soft magnetic powders are aligned in the plane direction is easily magnetized and the magnetic permeability increases. Therefore, the dust core is easily magnetized and easily takes in magnetic energy.
Fifth, the soft magnetic powder is insulated by an inexpensive means. That is, the raw material of aluminum oxide is an inexpensive aluminum compound, and the organic compound is also a general-purpose industrial chemical. Further, since aluminum oxide fine particles are produced by thermal decomposition at a temperature of about 300 ° C. in the air atmosphere, the soft magnetic powder is insulated by using an inexpensive raw material and at an inexpensive processing cost.
Sixth, the manufacturing method for manufacturing the dust core is a manufacturing method in which a simple process consisting of seven steps is continuously carried out as described above. In addition, strain removal annealing is not required. As a result, the dust core can be manufactured at a low manufacturing cost.
Seventh, there are no restrictions on the shape and size of the dust core to be manufactured. That is, since there are no restrictions on the size and shape of the mold for filling the collection of soft magnetic powder, there are no restrictions on the shape and size of the dust core.
Eighth, a dust core having a mechanical strength close to that of a conventional dust core is manufactured. That is, aluminum oxide fine particles are frictionally bonded to all surfaces of the soft magnetic powder, and all the aluminum oxide fine particles that are in contact are frictionally bonded to each other. Since the amount is extremely large, mechanical strength close to that of macro-bonding due to plastic deformation of conventional soft magnetic powder can be obtained. That is, frictional heat is generated when an extremely large number of aluminum oxide fine particles bite into the surface of the soft magnetic powder, all foreign substances existing at the contact portion between the two are vaporized, and after the contact portion is cleaned, the aluminum oxide fine particles are generated. It is firmly bonded to the surface of soft magnetic powder by frictional heat. Further, when an extremely large number of aluminum oxide fine particles come into contact with each other, frictional heat is generated in the contact portion, all foreign substances existing in the contact portion are vaporized, and after the contact portion is cleaned, the aluminum oxide fine particles are in frictional heat. Firmly join with. Therefore, it is not necessary to plastically deform the soft magnetic powder.
As described above, according to the present manufacturing method, the saturation magnetic flux density, the insulating property, and the magnetic permeability are increased, the eddy current loss is small, and the hysteresis loss is not increased as compared with the conventional dust core. Can be manufactured. As a result, the powder magnetic core has superior performance to the conventional powder magnetic core, and the powder magnetic core can be manufactured at a lower cost than the conventional powder magnetic core.

In the method for producing an ester core in which the dust core described in paragraph 7 is produced in a mold, the soft magnetic powder described in paragraph 7 is a soft magnetic flat powder having a flat shape, and is described in paragraph 7. The aluminum compound is aluminum benzoate or aluminum naphthenate, and the organic compound described in paragraph 7 is any ester consisting of carboxylic acid vinyl esters, acrylic acid esters, methacrylic acid esters, glycols, etc. It is a liquid monomer composed of one kind of organic compound belonging to any of glycol ethers or a styrene monomer, and the dust core described in paragraph 7 is produced in a mold using these substances. A method for producing a dust core in which a dust core is produced in a mold, which is produced according to the manufacturing method of the above.

That is, in the method for producing a dust core described in paragraph 7, a flat powder having a flat shape is used as the soft magnetic powder, vibrations in three directions are repeatedly applied to the collection of the flat powder in the mixed solution, and finally, in the vertical direction. Add vibration. At this time, regardless of the hardness of the flat powder, the flat powder moves in three directions in the mixed solution with the flat surface facing up, and the flat powder having a relatively small particle size has the flat surface facing up. The arrangement that enters the voids of the collection and the arrangement that moves above the collection of flat powders advance, and then the flat surfaces of the flat powders overlap each other. As a result, a collection of flat powder having a high degree of accumulation and a small volume of voids is formed on the bottom surface of the mixer as the shape of the bottom surface. Since the gap between the overlapping flat surfaces of the soft magnetic powder is narrower than that of the non-flat powder, the degree of accumulation of the flat powder is increased regardless of the hardness of the soft magnetic powder. After that, a collection of aluminum oxide fine particles is deposited in the gaps between the flat surfaces, and when a pressure is applied, the aluminum oxide fine particles continuously move to fill the narrow gaps between the overlapping flat surfaces, and aluminum oxide. When the fine particles cannot move, the aluminum oxide fine particles are bonded to each other by frictional heat, and a dust core is manufactured in the mold. Also, the weight of all the aluminum oxide fine particles is less than 1% of the weight of the aggregate of soft magnetic powder. Therefore, the density of the dust core approaches the density of the soft magnetic powder, and the saturation magnetic flux density of the powder magnetic core approaches the saturation magnetic flux density of the soft magnetic powder.
On the other hand, when the soft magnetic powder is flattened in the plane direction, which is the axial direction for easy magnetization, the demagnetizing field coefficient becomes small, and the larger the flatness, the higher the magnetic permeability of the flat powder, and the more easily it is magnetized. Therefore, when the dust core is manufactured using the flat powder, all the flat powders are overlapped with each other and are bonded together in the flat plane direction which is the easy axial direction of magnetization, and the dust core is more easily magnetized. .. As a result, the magnetic permeability of the dust core is increased, and a powder magnetic core having a saturation magnetic flux density close to the saturation magnetic flux density of the flat powder is formed in the mold. This dust core is easily magnetized regardless of the hardness of the soft magnetic powder, and the captured magnetic energy is large. The flattening treatment of the soft magnetic powder does not depend on the long-time batch processing by the ball mill, but by the attritor treatment by the media stirring type mill, the flattening powder can be continuously obtained in a short time and manufactured at low cost. Will be done. On the other hand, the processing strain generated by the flattening process is eliminated by magnetic annealing.
Next, a carboxylic acid metal compound that precipitates a metal oxide by thermal decomposition will be described. Among the carboxylic acid metal compounds, there is a carboxylic acid metal compound in which an oxygen ion constituting a carboxyl group serves as a ligand and approaches a metal ion to coordinate bond. In this metal carboxylate compound, the metal ion, which is the largest ion, approaches the oxygen ion and is coordinated, so that the distance between the two is shortened. As a result, the oxygen ion coordinate-bonded to the metal ion has the longest distance from the ion covalently bonded on the opposite side of the metal ion. When the carboxylic acid metal compound having such molecular structural characteristics exceeds the boiling point of the carboxylic acid constituting the carboxylic acid metal compound, the oxygen ion constituting the carboxyl group is covalently bonded to the ion on the opposite side of the metal ion. The bond is first split and decomposed into metal oxides and carboxylic acids. When the temperature is further raised, the carboxylic acid takes away the heat of vaporization and vaporizes, and after the vaporization of the carboxylic acid is completed, the metal oxide precipitates. Among these metal carboxylic acid compounds, as metal carboxylic acid compounds whose thermal decomposition is completed at a relatively low temperature of about 300 ° C., metal acetate compounds, metal caprylate compounds, and metal benzoate compounds are arranged in ascending order of boiling point of carboxylic acid. , There are metal naphthenate compounds. Therefore, the metal acetate compound, the metal caprylic acid compound, the metal benzoate compound, and the metal naphthenate compound are metal compounds that precipitate metal oxides by thermal decomposition at a relatively low temperature.
On the other hand, in the carboxylic acid metal compound in which the carboxylate anion is covalently bonded to the metal ion, the bond portion between the oxygen ion and the metal ion is the longest among the bonds between the ions, so that the metal is precipitated by thermal decomposition.
In the aluminum carboxylate compound that precipitates aluminum oxide by thermal decomposition, aluminum acetate and aluminum caprylate precipitate amorphous alumina by thermal decomposition. Therefore, aluminum benzoate and aluminum naphthenate exist as raw materials for precipitating aluminum oxide by thermal decomposition. The boiling point of benzoic acid is 249 ° C., and aluminum benzoate is thermally decomposed at 310 ° C. in the air atmosphere to precipitate aluminum oxide. Further, the thermal decomposition is completed at 340 ° C., which is higher than the thermal decomposition temperature of aluminum naphthenate, and aluminum oxide is precipitated. Therefore, in the method for producing a dust core described in paragraph 7, aluminum benzoate or aluminum naphthenate is used as the aluminum compound. In the thermal decomposition of the aluminum carboxylate compound, the temperature at which the thermal decomposition is completed is 50-60 ° C. lower in the atmospheric atmosphere than in the nitrogen atmosphere. Therefore, the heat treatment in the atmospheric atmosphere requires less heat treatment cost.
Next, an organic compound having the first property of being dissolved or miscible in methanol, the second property having a viscosity higher than that of methanol, and the third property having a boiling point higher than 65 ° C. and lower than 340 ° C. Used as the organic compound described in the paragraph.
As such an organic compound, one kind of organic compound belonging to any one of carboxylic acid vinyl esters, acrylic acid esters, methacrylic acid esters, glycols, glycol ethers, or styrene. There is a liquid monomer consisting of a monomer. Therefore, in the method for producing a dust core described in paragraph 7, any of these organic compounds is used as the organic compound.
Therefore, soft magnetic flat powder is used as the soft magnetic powder described in paragraph 7, aluminum benzoate or aluminum naphthenate is used as the aluminum compound described in paragraph 7, and vinyl carboxylic acid ester is used as the organic compound described in paragraph 7. , Acrylic acid esters, any ester consisting of methacrylic acid esters, one kind of organic compound belonging to any one of glycols, glycol ethers, or liquid monomer composed of styrene monomer, in paragraph 7. When the dust core is manufactured according to the manufacturing method described, the dust core that is easily magnetized and has a large amount of magnetic energy taken in is manufactured in the mold.

It is explanatory drawing which shows schematicly by enlarging a part of the cut surface of a dust core.

Embodiment 1
The present embodiment relates to an organic compound in the method for producing a dust core described in paragraph 7, and the organic compound has a first property of being soluble or mixed in methanol and a second property of having a viscosity higher than that of methanol. It also has a third property that the boiling point is higher than the boiling point of methanol, 65 ° C, and lower than 340 ° C.
As such an organic compound, one kind of organic compound belonging to any one of carboxylic acid vinyl esters, acrylic acid esters, methacrylic acid esters, glycols, glycol ethers, or styrene. There are liquid monomers composed of monomers.
Carboxylic acid vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pipariate, and octyl. It is a vinyl carboxylate composed of vinyl acetate, vinyl monochloroacetate, vinyl adipate, vinyl crotonate, vinyl benzoate and the like.
For example, vinyl acetate is a low boiling point carboxylic acid vinyl ester, the chemical formula is _{shown by CH 3} COO-CH = CH ₂ , it dissolves in methanol, has a higher viscosity than methanol, and has a boiling point of 72.7 ° C. .. Vinyl acetate is an ester obtained by reacting acetic acid with vinyl alcohol, and is an inexpensive organic compound used as a raw material for the synthesis of polyvinyl acetate. Since vinyl acetate is easily polymerized by light or heat, a small amount of a polymerization inhibitor (also referred to as a polymerization inhibitor) is added.
Further, monochloroacetic acid vinyl acetate has a chemical formula of Cl-CH ₂ COO-CH = CH ₂ , is soluble in methanol, and has a boiling point of 136 ° C. Monochlorovinyl acetate is an inexpensive organic compound used as a cross-linking site for acrylic rubber.
The acrylic acid esters are acrylic acid esters composed of methyl acrylate, ethyl acrylate, butyl acrylate, diethylhexyl acrylate and the like.
For example, acrylates having a low boiling point include methyl acrylate, the chemical formula of which is represented by CH ₂ = CH-COOCH ₃ , which is dissolved in methanol and has a boiling point of 80 ° C. Methyl acrylate is an inexpensive organic compound used as a raw material for acrylic resins. Since methyl acrylate is a substance that easily polymerizes, a small amount of stabilizer is added.
Furthermore, butyl acrylate has a chemical formula of CH ₂ = CH-COOC ₄ H ₉ , is soluble in methanol, and has a boiling point of 148 ° C. Butyl acrylate is an ester obtained by reacting acrylic acid with n-butanol, and is an inexpensive organic compound used as a raw material for fiber treatment agents, adhesives, paints, synthetic resins, acrylic rubbers, and emulsions. Methyl acrylate is a substance that easily polymerizes, and a small amount of stabilizer is added.
The methacrylic acid esters are methacrylic acid esters composed of ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, alkyl methacrylate, tridecyl methacrylate, stearyl methacrylate and the like. ..
For example, ethyl methacrylate is one of the methacrylic acid esters having a low boiling point, the chemical formula is represented by H ₂ C = C (CH ₃ ) COOC ₂ H ₅ , and it is dissolved in methanol and has a boiling point of 117 ° C. Ethyl methacrylate is an inexpensive organic compound used as a raw material for pigments, paints, adhesives, fiber treatment agents, molding materials, and dental materials. In addition, ethyl methacrylate is a substance that is easily polymerized, and a trace amount of stabilizer is added.
Further, n-butyl methacrylate has a chemical formula of CH ₂ C (CH ₃ ) COO (CH ₂ ) ₃ CH ₃ and is dissolved in methanol and has a boiling point of 163.5 ° C. N-Butyl methacrylate is an inexpensive organic compound used as a raw material for paints, dispersants, and fiber treatment agents. Since n-butyl methacrylate is easily polymerized by light or heat, a small amount of polymerization inhibitor is added.
In addition, glycols are a kind of alcohol, and are compounds having a structure in which one hydroxy group is substituted for each of two carbon atoms of a chain aliphatic hydrocarbon. Ethylene glycol is one of the glycols having a low boiling point, and its chemical formula is represented by C ₂ H ₄ (OH) ₂ , which is miscible with methanol and has a boiling point of 197.3 ° C. Ethylene glycol is an inexpensive organic compound widely used as a solvent, antifreeze, synthetic raw material and the like.
Further, diethylene glycol having a chemical formula of O (CH ₂ CH ₂ OH) ₂ is miscible with methanol and has a boiling point of 244.3 ° C. In addition to antifreeze, diethylene glycol is an inexpensive organic compound used in brake fluids, lubricants, inks, fabric softeners, fabric softeners, cork plasticizers, adhesives, paper, packaging materials, paints, etc. is there.
Propylene glycol having a chemical formula of CH ₃ CHOHCH ₂ OH is miscible with methanol and has a boiling point of 188.2 ° C. Propylene glycol is used as a moisturizer, lubricant, emulsifier, antifreeze, intermediate material for plastics, solvent, etc., and also has excellent moisturizing and antifungal properties, so it improves the quality of pharmaceuticals, cosmetics, noodles, rice balls, etc. It is an inexpensive organic compound used in a wide range such as agents.
Further, dipropylene glycol has a chemical formula of [CH ₃ CH (OH) CH ₂ ] ₂ O, is miscible with methanol, and has a boiling point of 232.2 ° C. Dipropylene glycol is an inexpensive organic compound used as an intermediate raw material for polyester resins, hydraulic oils for hydraulic equipment, antifreeze liquids, raw materials for printing inks, and the like.
Further, tripropylene glycol has a chemical formula of [CH ₃ CH (OH) CH ₂ ] ₂ O, is miscible with methanol, and has a boiling point of 265 ° C. Tripropylene glycol is used as a raw material for lubricating oils and cutting oils, raw materials for polyurethane / acrylic ester intermediates, paint / ink solvents, antifreezes, feed additives, intermediate raw materials for polyester resins, solvents for water-soluble oils, etc. It is an inexpensive organic compound.
Further, glycol ethers have both an ether group and a hydroxyl group in one molecule, and are water, many organic solvents, and a solvent having high resin solubility, and most glycol ethers are dissolved in methanol. There are the following three types of glycol ethers. Ethylene glycol-based ether and propylene glycol-based ether are inexpensive materials used in paints, inks, dyes, photocopying liquids, cleaning agents, electrolytes, soluble oils, hydraulic oils, brake liquids, refrigerants, antifreeze agents, etc. Organic compound. Further, the dialkyl glycol is an inexpensive organic compound used in a reaction solvent, a separation extractant, a polymerization solvent, a decomposition prevention and stabilizer, an electrolytic solution of a battery or a capacitor, and the like.
For example, ethylene glycol-based ether having a low boiling point includes ethylene glycol monomethyl ether, which has a chemical formula of CH ₃ O- (CH ₂ CH ₂ O) -H, is dissolved in methanol, and has a boiling point of 124.5 ° C. .. Ethylene glycol monoisopropyl ether has a chemical formula of (CH ₃ ) ₂ CHO- (CH ₂ CH ₂ O) -H, is dissolved in methanol, and has a boiling point of 141.8 ° C.
Further, among ethylene glycol-based ethers having a high boiling point, there is triethylene glycol monobutyl ether, the chemical formula of which is C ₄ H ₉ O- (CH ₂ CH ₂ O) _3- H, which is dissolved in methanol and has a boiling point of 271. It is 2 ° C. The chemical formula of diethylene glycol mono2-ethylhexyl ether is represented by C ₂ H _5- C ₄ H ₉ CHCH ₂ O- (CH ₂ CH ₂ O) _2- H, which is dissolved in methanol and has a boiling point of 272 ° C. ..
Further, propylene glycol monomethyl ether having a low boiling point includes propylene glycol monomethyl ether, which has a chemical formula of CH _3- CH ₃ O- (CH ₂ CHO) _2- H, is dissolved in methanol, and has a boiling point of 121 ° C. ..
Moreover, the high boiling point of propylene glycol ether, there is tripropylene glycol monobutyl ether, chemical formula _CH 3 _-C 4 _H 9 _- shown in (CH 2 _CHO) 3 -H, dissolved in methanol, boiling point 274 ° C. Is.
Further, a dialkyl glycol having a low boiling point includes ethylene glycol dimethyl ether, which has a chemical formula of CH ₃ O- (CH ₂ CHO) -CH ₃ , is dissolved in methanol, and has a boiling point of 85.2 ° C.
In addition, diethylene glycol dibutyl ether, which has a high boiling point, has a chemical formula of C ₄ H ₉ O- (CH ₂ CH ₂ O) _2- C ₄ H ₉ , which is dissolved in methanol and has a boiling point of 274 ° C. is there.
Further, the styrene monomer is _{a liquid monomer having a chemical formula of C 6} H ₅ CH = CH ₂ , miscible with methanol, and having a boiling point of 145 ° C. Styrene monomer is an inexpensive organic compound that can be used as a raw material for synthetic resin materials such as expanded polystyrene, acrylonitrile / styrene, acrylonitrile / butadiene / styrene, and unsaturated polyester, including polystyrene. Since the styrene monomer is easily polymerized, a small amount of a polymerization inhibitor is added.
As described above, the above-mentioned three properties of an organic compound belonging to any one of carboxylic acid vinyl esters, acrylic acid esters, and methacrylic acid esters, glycols, and glycol ethers. There is an organic compound that also has. Further, the styrene monomer has the above-mentioned three properties. Therefore, these organic compounds are used as organic compounds in the method for producing a dust core described in paragraph 7.

Embodiment 2
The present embodiment relates to a soft magnetic powder used as a raw material for a dust core. The soft magnetic powder is selected from the operating frequency range of the electric product on which the dust core is mounted and the magnitude of the magnetic flux density of the dust core in this frequency range. On the other hand, in order to increase the saturation magnetic flux density of the dust core, it is necessary to increase the filling rate of the soft magnetic powder in the dust core. In order to increase the filling rate of the soft magnetic powder, it is necessary to apply a large pressurizing pressure to the collection of the soft magnetic powder to promote the plastic deformation of the soft magnetic powder. Therefore, since the hardness of many soft magnetic powders is high, the soft magnetic powders are annealed in advance to reduce the hardness of the soft magnetic powders. Further, since the holding power of the soft magnetic powder that has undergone plastic deformation increases, the holding power of the soft magnetic powder is restored by magnetic annealing of the dust core, and the iron loss of the powder magnetic core is reduced.
The dust core constituting the stator and rotor in the motor has a low operating frequency but a high saturation magnetic flux density. For such applications, pure iron powder having the highest saturation magnetic flux density among soft magnetic powders is used. On the contrary, the dust core constituting the reactor, noise filter, choke coil, etc. in the power supply circuit has a high operating frequency but a low saturation magnetic flux density. Fe—Si alloy powder, Fe—Si—Al alloy powder, and Fe—Ni alloy powder are used for such applications. Amorphous alloy powders have a wide variety of magnetic properties and have individual properties depending on the composition of the alloy, so they are not discussed here.
Pure iron powder has a saturation magnetic flux density of 2.2 tesla, which is the highest saturation magnetic flux density among soft magnetic powders, and has a relatively low hardness. Pure iron powder that has been hydrogen-tanned is easily plastically deformed. The packing density in the dust core is high, and the saturation magnetic flux density of the dust core is further increased. Therefore, it is used for the dust core that constitutes the stator and rotor of a motor that requires magnetic energy. For example, atomized iron powder having a Vickers hardness of 75-87 HV has the lowest hardness among soft magnetic powders, and the compression density of a compression molded product using hydrogen-annealed atomized iron powder is 90% of the iron density. Close to. On the other hand, the Vickers hardness of the reduced iron powder is 160-210 HV, which is more than twice the hardness of the atomized iron powder, but it is easily plastically deformed because it is a porous body having many voids. However, in the production of the dust core, the hardness is lowered by hydrogen annealing. On the other hand, pure iron powder has the lowest magnetic permeability among soft magnetic powders, and has the disadvantage that magnetic energy is difficult to be taken into the dust core. In addition, the holding force is as large as 80 A / m, and the hysteresis loss is large. Furthermore, it is a conductor having a volume resistivity of 1 × ^{10-5 Ω · cm.}
On the other hand, when iron contains silicon, the magnetic permeability increases, but when the silicon content exceeds 5% by mass, it becomes extremely brittle, and most Fe-Si alloys have a silicon content of less than 5% by mass. is there. Further, when silicon is contained in iron, the electric resistance increases, but the volume resistivity of the Fe—Si alloy of 3% by mass is 5 × 10 ⁻⁵ Ω · cm, which is conductive. The holding force of the 3% by mass Fe—Si alloy is as large as 65 A / m and the hysteresis loss is large, but the saturation magnetic flux density is as high as 1.3 Tesla. Further, the Vickers hardness is 180-205 HV, and the hardness is lowered by annealing to be used as a raw material for a dust core. In this way, the magnetic properties of the Fe-Si alloy are similar to those of reduced iron powder, but they are less likely to corrode than the reduced iron powder. Used for powder core.
Further, permalloy, which is an Fe—Ni alloy containing nickel in iron, has a significantly higher magnetic permeability than iron, but a small saturation magnetic flux density. Further, the higher the nickel content, the higher the price, and the nickel content is suppressed to 50% by mass or less. Further, magnetic annealing is performed at 1100 ° C. in a hydrogen atmosphere for about 3 hours to remove impurities and adjust the magnetic characteristics of permalloy. Here, nickel represents the properties of permalloy in an amount of 45% by mass. The DC magnetic characteristics are that the initial magnetic permeability is 3000, the saturation magnetic flux density is 1.4 Tesla, the holding force is 16 A / m, and the saturation magnetic flux density is smaller than that of pure iron powder, but larger than other soft magnetic powders. .. Further, the AC magnetic characteristics are permalloy with a plate thickness of 0.1 mm, an effective magnetic permeability at 1 kHz is 3000, and an effective magnetic permeability at 3 kHz is 2500. In addition, the physical properties are that the density is 8.25 g / cm ^3, which is about 5% higher than iron, the volume resistivity is 5 × ^10-5 Ω · cm, which is conductive, and the magnetic curry point is 420 ° C, which is 350 than iron. It is low in ° C. and has a Rockwell hardness of 60-90 HRB (corresponding to a Vickers hardness of 110-190 HV). Therefore, permalloy is used for trans cores, motor cores, and iron cores for relays because it has excellent alternating current permeability characteristics and saturation magnetic flux density.
Further, the Fe—Si—Al alloy obtained by adding silicon and aluminum to iron has high hardness and is brittle, so that it is easily powdered. In particular, Fe-10 wt% Si-6 a composition of mass% Al sendust (Tohoku University R), permeability tends to be large magnetization 1.2 × 10 ^5, the holding force 0.1 A / m Because it is small, the hysteresis loss is small, and the saturation magnetic flux density is 1 Tesla, which is close to Permalloy. Further, it is a conductor having a volume resistivity of 8 × ^{10-5 Ω · cm.} On the other hand, the Vickers hardness is as high as 410 HV, and the hardness is lowered by annealing, but the filling rate is not as high as that of pure iron powder. Further, when a dust core made of sendust is used at 80-120 ° C., the iron loss increases from room temperature, the heat generated by the iron loss further increases the iron loss, and there is a risk of thermal runaway in a high output transformer. there were. However, recently, it has been found that the composition of Fe-8.8 mass% Si-6.0 mass% Al reduces the iron loss and makes the temperature coefficient of the iron loss negative (Non-Patent Document 1). reference).
Further, among the electromagnetic stainless steels in which chromium, aluminum and molybdenum are added to iron, the electromagnetic stainless steel composed of Fe-13 mass% Cr-0.2 mass% Al-1 mass% Mo has a large magnetic permeability, but The holding force is as large as 85 A / m and the hysteresis loss is large. On the other hand, the magnetic flux density is 1.35 Tesla, which is comparable to Permalloy. The Rockwell hardness is 70 HRB (corresponding to 130 HV in Vickers hardness), which is harder than atomized iron powder and softer than reduced iron powder. It also has excellent corrosion resistance. For this reason, electromagnetic stainless steel is used for solenoid valves of automobiles because it has excellent responsiveness to a pulsed magnetic field. Further, it is a conductor having a volume resistivity of 6.5 × ^{10-5 Ω · cm.}
The characteristics of the soft magnetic powder having a typical composition have been described above for various types of soft magnetic powder. Since all of the soft magnetic powders are conductors, it is necessary to insulate the soft magnetic powders. If the soft magnetic powder is insulated with a collection of aluminum oxide fine particles having high heat resistance and insulating properties in the present invention, the eddy current loss is remarkably reduced. Further, annealing can be performed at a temperature exceeding 800 ° C., and the hysteresis loss of the dust core can be reduced. Further, in order to bring the density of the dust core close to the density of the soft magnetic powder, the hardness of the soft magnetic powder is lowered by annealing in advance. Therefore, the effect of superimposing the soft magnetic powders having an increased degree of integration in the present invention on the surfaces, compressing the collection of the soft magnetic powders, and producing the powder magnetic core without plastically deforming the soft magnetics is great.

Embodiment 3
This embodiment is an embodiment of a dust core prepared by using atomized iron powder and reduced iron powder, which are the cheapest materials among soft magnetic powders, and is described in Non-Patent Document 2. In addition, the superiority of the method for producing the dust core of the present invention will be described from the two types of dust core embodiments. The Vickers hardness of the atomized iron powder used in Non-Patent Document 2 is 100, and the Vickers hardness of the reduced iron powder is 60, both of which are lower in hardness than the iron powder used as an abrasive or the like. Therefore, it is considered that the hardness of the produced iron powder was further reduced by hydrogen annealing.
The initial magnetic permeability of iron powder changes depending on the manufacturing conditions of iron powder, and the initial magnetic permeability changes depending on the impurity concentration of silicon and manganese. The reduced iron powder used in Non-Patent Document 2 has a silicon concentration of 0.05% by mass and a manganese concentration of 0.25% by mass. On the other hand, the atomized iron powder used in Non-Patent Document 2 has a low silicon concentration of 0.01% by mass and a low manganese concentration of 0.04% by mass. Therefore, the initial magnetic permeability of the reduced iron powder is larger than that of the atomized iron powder.
In the production of the dust core, 0.75% by mass of epoxy resin as an insulating material and 0.5% by mass of zinc stearate as a lubricating material are added to both iron powders, and there are two types, 490 MPa and 686 MPa. Pressurized pressure was applied to form a ring shape having an outer diameter of 38 mm, an inner diameter of 25 mm, and a thickness of 6.2 mm. After that, the green compact was heat-treated at 180 ° C. in the air to cure the epoxy resin, and a fine powder magnetic core was produced. Zinc stearate has a melting point of 140 ° C. and liquefies when the epoxy resin is polymerized, and exhibits a function as a lubricant.
The epoxy resin has a volume resistivity of 10 ¹⁵ Ω · cm, which is excellent in insulating properties, but has a heat resistance lower than 200 ° C. In addition, zinc stearate is thermally decomposed at 420 ° C. to become toxic carbon monoxide, carbon dioxide, zinc oxide gas and solid particles. Therefore, the produced dust core has a heat resistance lower than 200 ° C. and cannot be annealed to restore the holding power. Further, due to the magnitude of the pressurizing pressure, the composition pieces of both iron powders are advanced. However, since there is no annealing effect in the heat treatment at 180 ° C., the hysteresis loss of the dust core is large.
The powder magnetic core made of reduced iron powder to which a pressurized pressure of 490 MPa is applied has a density of 6.74 g / cm ³ , a filling rate of 85.8%, and a DC initial magnetic permeability of 71.1. .. The powder magnetic core made of reduced iron powder to which a pressurized pressure of 686 MPa is applied has a density of 6.95 g / cm ³ , a filling rate of 88.4%, and a DC initial magnetic permeability of 75.7. .. On the other hand, the powder magnetic core made of atomized iron powder to which a pressurizing pressure of 490 MPa is applied has a density of 6.87 g / cm ³ , a filling rate of 87.4%, and a DC initial magnetic permeability of 64. .2. The powder magnetic core made of atomized iron powder to which a pressurizing pressure of 686 MPa is applied has a density of 7.06 g / cm ³ , a filling rate of 89.8%, and a DC initial magnetic permeability of 68.7. ..
The initial magnetic permeability of the alternating current of the dust core made of reduced iron powder is 74 at 10 kHz, and the initial magnetic permeability gradually decreases as the frequency increases, and the decrease rate increases from around 300 kHz. On the other hand, the AC initial permeability of the dust core made of atomized iron powder is the frequency characteristic of the AC initial permeability of the powder magnetic core of the reduced iron powder, and the initial permeability is moved downward by 10. Is shown.
Further, regarding the consolidation behavior of the iron powder when the two types of iron powder are pressurized, the rate at which the porosity decreases with respect to the pressurizing pressure shows the same characteristics in the two types of iron powder. The decrease in porosity depends on the plastic deformation and rearrangement of the iron powder. In the two types of iron powder, the rearrangement of the iron powder is completed at a pressure of 100 MPa, and the plastic deformation is started from a pressure pressure of around 50 MPa. Therefore, at a pressure up to about 50 MPa, the voids are reduced by the rearrangement of the iron powder, at a pressure up to 100 MPa, the voids are reduced by the rearrangement of the iron powder and the plastic deformation of the iron powder, and at a pressure of 100 MPa or more, the voids are reduced. The voids are reduced by the plastic deformation of the iron powder. Therefore, in the powder magnetic core manufactured by applying a pressurizing pressure of 490 MPa, the plastic deformation of the iron powder is sufficiently advanced. Therefore, the hysteresis loss of the dust core is increasing.
Here, the measurement results of two types of dust cores will be examined.
First, the compression density of the compression molded product is higher in the atomized iron powder for the same pressure. However, the difference in compression density is only 2%. On the other hand, the Vickers hardness of the reduced iron powder used is 0.6 times that of the atomized iron powder used, and it is easily plastically deformed. However, both iron powders start to be plastically deformed from a pressure of about 50 MPa, and at a pressure of 490 MPa, both iron powders are sufficiently plastically deformed. Therefore, the difference in the hardness of the iron powder has a small effect on the difference in the compression density. On the other hand, the reduced iron powder is a porous body having many voids and is easily crushed by a pressurizing pressure, but the porosity of the plastically deformed iron powder is high. Therefore, it is considered that the difference in compression density is due to the high porosity of the reduced iron powder after plastic deformation.
Second, the initial magnetic permeability of direct current in reduced iron powder is as much as 10% higher than the initial magnetic permeability of direct current in atomized iron powder. Further, the initial magnetic permeability of alternating current from 10 kHz to 1 MHz is 15% higher in the powder magnetic core made of reduced iron powder than in the powder magnetic core made of atomized iron powder. As described above, the reduced iron powder has a high initial magnetic permeability because of the high impurity concentration of silicon and manganese. Furthermore, the initial magnetic permeability increased due to the flattening effect of the reduced iron powder. That is, the atomized iron powder has an irregular contour and is isotropically deformed when pressed. On the other hand, the reduced iron powder also has an irregular contour, but since it is a porous body, the reduced iron powder is easily crushed in the pressurizing direction and easily deformed in the direction perpendicular to the pressurizing direction. That is, the reduced iron powder is deformed in the plane direction, which is the easy axial direction of magnetization, the demagnetizing field coefficient is reduced, and the initial magnetic permeability of the reduced iron powder is increased. This phenomenon is similar to the phenomenon in which the magnetic permeability increases when the soft magnetic powder is flattened.
Thirdly, since the plastic deformation of the two types of iron powder starts from around 50 MPa, the plastic deformation of the two types of iron powder progresses at a pressurizing pressure of 490 MPa, and the iron powder with increased holding power is used as the powder. A magnetic core is formed. However, the heat treatment of the dust core is 180 ° C., which is the curing treatment temperature of the epoxy resin. Therefore, the heat treatment at 180 ° C. does not have an annealing effect that restores the holding power. In addition, the contours of the two types of iron powder are irregular and do not have shape anisotropy. A pressurizing pressure of 490 MPa is required to compress such an aggregate of iron powder and realize the mechanical strength required for a compression molded product. Due to this pressurizing pressure, the plastic deformation of the iron powder progresses, and the entanglement of the iron powder realizes the mechanical strength required for the compression molded body. However, the hysteresis loss of the dust core increases.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, if the iron powder is insulated by a collection of aluminum oxide fine particles, the heat resistance is higher than that of the iron powder, so that strain-removing annealing becomes possible and the holding power of the iron powder is restored. In addition, a collection of aluminum oxide fine particles fills the gaps between the iron powders and the voids of the reduced iron powder, increasing the compression density, and the aluminum oxide fine particles that fill the gaps and voids are joined by frictional heat to form a dust powder. Contributes to the realization of mechanical strength as a magnetic core. Further, since the aluminum oxide fine particles in which the gaps and voids of the iron powder are bonded by frictional heat are filled, the eddy current flowing through the gaps between the iron powders is reduced.
Secondly, even if the iron powder has an irregular shape, if the collection of iron powder is made into a collection of iron powder that overlaps with each other and the collection of iron powder is compressed, the gap between the iron powder that overlaps with each other narrows. , The compression density increases. Further, since all the iron powders are overlapped with each other and the easy axial direction of magnetization is the plane direction, the dust core is easily magnetized and the initial magnetic permeability of the iron powder is increased.
Thirdly, if the pressurizing pressure is stopped before the iron powder is plastically deformed and the iron powders are bonded to each other through the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase, and the pressure is also increased. The powder core has the required mechanical strength.
As a result, in the powder magnetic core produced by using the atomized iron powder and the reduced iron powder according to the method for producing the powder magnetic core of the present invention, the initial magnetic permeability is increased, the eddy current loss is reduced, and the hysteresis loss is not increased.

Embodiment 4
This embodiment is an embodiment for comparing the performance of a powder magnetic core produced by using reduced iron powder and a powder magnetic core produced by using flat reduced iron powder, and is described in Non-Patent Document 3. .. In addition, the superiority of the method for producing the dust core of the present invention will be described from the two types of dust core embodiments.
Epoxy resin as an insulating material is added as 1% by mass to both iron powders, zinc stearate as a lubricating material is added as 0.1% by mass, and pressurizing pressures of 490 MPa and 686 MPa are applied, and the outer diameter is 38 mm. The powder was formed into a ring shape having an inner diameter of 25 mm and a thickness of 6.2 mm, and then the powder compact was heat-treated at 180 ° C. in the air for 30 minutes to cure the epoxy resin to produce a powder compact core. Even if the heat treatment is performed at 180 ° C. for 30 minutes, the holding power of the reduced iron powder cannot be restored, and the hysteresis loss in the dust core is large.
In the powder magnetic core manufactured at a pressure of 490 MPa, the flat reduced iron powder has a compression density of 6.93 g / cm ³ , a filling rate of 88.0%, and a DC initial magnetic permeability of 94.9. On the other hand, in the reduced iron powder, the compression density is 6.74 g / cm ³ , the filling rate is 85.7%, and the initial magnetic permeability of direct current is 72.1. Further, in the powder magnetic core manufactured at a pressure of 686 MPa, the flat reduced iron powder has a compression density of 7.09 g / cm ³ , a filling rate of 90.0%, and a DC initial magnetic permeability of 99.1. .. On the other hand, in the reduced iron powder, the compression density is 6.97 g / cm ³ , the filling rate is 88.5%, and the initial magnetic permeability of direct current is 78.1. In all of the reduced iron powders, when the compressive stress is increased, the compressive density and the initial magnetic permeability of direct current increase.
Further, the powder magnetic core compressed with a pressure of 686 MPa has an initial magnetic permeability of AC at 10-200 kHz, the initial magnetic permeability of the powder magnetic core of flat reduced iron powder is 100, and the initial magnetic permeability of the powder magnetic core of the reduced iron powder. The initial magnetic permeability is 80, and the initial magnetic permeability is increased by 20%. At 200 kHz-1 MHz, the higher the frequency, the smaller the difference in initial magnetic permeability.
The iron loss at a magnetic flux density of 50 mT is smaller than the iron loss of the powder magnetic core using flat reduced iron powder, and the difference between the two increases as the frequency increases. spread. That is, although both iron powders are insulated with the same substance and the same mass number, the iron loss is smaller in the powder magnetic core using flat reduced iron powder.
Here, the measurement results of two types of dust cores will be examined.
First, the gap between the flat-reduced iron powders in the compression molded product using the flat-reduced iron powder was relatively narrower than that in the case of using the reduced iron powder, and the compression density was increased. However, the difference in compression density is only 2-3%. Further, the ratio of the filling rate in the powder magnetic core manufactured at a pressure of 686 MPa to the filling rate in the powder magnetic core manufactured at a pressure of 490 MPa is the powder using flat reduced iron powder. It is 1.023 in the magnetic core, while it is 1.033 in the powder magnetic core using the reduced iron powder. If all the flattened reduced iron powders are overlapped with each other, the difference in the powder density is wider than 2 to 3%, and the filling rate ratio when the flattened reduced iron powders are used is 1.023. Become bigger. Therefore, the flat reduced iron powder that overlaps the flat surfaces remains in a part. On the other hand, when all the flattened iron powders overlap each other on the flat surfaces, there is a problem that the mechanical strength required for the powder magnetic core cannot be realized. Therefore, a collection of flattened iron powder was simply compressed.
Second, in the powder magnetic core using flat reduced iron powder, the initial magnetic permeability of DC increases by 31% at a pressurizing pressure of 490 MPa and pressurizes 686 MPa compared to the powder magnetic core using reduced iron powder. The pressure increased by 27%. Further, in the powder magnetic core prepared at a pressurized pressure of 686 MPa, the initial magnetic permeability increased by 20% at a frequency of 10-200 kHz. That is, when a pressurized pressure is applied to the flat-reduced iron powder, the flat-reduced iron powder is crushed, the flat-reduced iron powder having a certain ratio is deformed in the flat-plane direction, and the flatness is increased. Since this flat plane direction is the axial direction for easy magnetization, the initial magnetic permeability increased due to the flattening effect. Therefore, a difference in the initial magnetic permeability appeared between the powder magnetic core using the flat reduced iron powder and the powder magnetic core using the reduced iron powder.
Thirdly, the result of iron loss in the dust core is that the shape of the reduced iron powder is irregular and the shape of the flat reduced iron powder is flattened in the plane direction. That is, the gap between the flat-reduced iron powders in the compression-molded body made of the flat-reduced iron powder was narrowed, and the compression density was increased. When the gap between the flat reduced iron powders becomes narrower, the insulation between adjacent flat reduced iron powders becomes higher, the eddy current flowing through the gap between the flat reduced iron powders decreases, and the powder magnetic core using the flat reduced iron powders becomes smaller. The eddy current loss of the powder was smaller than the eddy current loss of the dust core using reduced iron powder.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, it is a collection of aluminum oxide fine particles whose heat resistance is higher than that of reduced iron powder. If the reduced iron powder is insulated, strain relief annealing becomes possible, the holding power is restored, and the hysteresis loss of the dust core is reduced. Decrease. In addition, a collection of aluminum oxide fine particles whose size is three orders of magnitude smaller than that of the epoxy resin pellets fills the gaps between the reduced iron powders and the voids of the reduced iron powders, and the compression density increases. Further, the aluminum oxide fine particles that fill the gaps and voids are bonded to each other by frictional heat, and the mechanical strength as a dust core is realized. This eliminates the need for plastic deformation of the reduced iron powder and the flat reduced iron powder, and the hysteresis loss of the dust core is small.
Secondly, even if the reduced iron powder has an irregular shape, if the reduced iron powder is made into a highly integrated iron powder group in which the surfaces are overlapped with each other and the reduced iron powder group is compressed, all the reduced iron powder is obtained. The gap between the reduced iron powders that overlap each other is narrowed, and the compression density is increased. In the flat-reduced iron powder, a collection of flat-reduced iron powder in which flat surfaces overlap each other is compressed, so that the compression density is further increased. Further, since all the reduced iron powders or all the flat reduced iron powders are aligned in the direction of the flat surface, the initial magnetic permeability of the dust core is further increased. Further, the gap between the reduced iron powders or the gap between the flat reduced iron powders becomes narrower, and the narrowed gap is filled with aluminum oxide fine particles having high insulating properties, and the eddy current flowing through the gap is further reduced. As a result, the initial magnetic permeability increases.
Third, if the pressurizing pressure is stopped before both iron powders are plastically deformed and both iron powders are bonded to each other through the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase. Also, the dust core has the required mechanical strength.
As a result, the powder magnetic core produced by using the reduced iron powder and the flat reduced iron powder according to the method for producing the powder magnetic core of the present invention has an increased initial magnetic permeability, a reduced eddy current loss, and a non-increased hysteresis loss. ..

Embodiment 5
This embodiment is an embodiment of a dust core produced by using atomized iron powder, and is described in Non-Patent Document 4. Moreover, the superiority of the method for producing the dust core of the present invention will be described from the embodiment of the dust core.
0.5% by weight of epoxy resin powder is added to atomized iron powder, and four types of pressurizing pressure consisting of 196-686 MPa are applied with a floating die type mold, and the outer diameter is 38 mm, the inner diameter is 25 mm, and the height is 25 mm. Was formed into a 6.5 mm ring, and then cured at 150 ° C. for 1 hour to produce four dust cores. Note that curing at 150 ° C. does not have an annealing effect that restores the holding power of atomized iron powder.
The powder magnetic core formed with a pressurized pressure of 196 MPa has a filling rate of 76% and a DC initial magnetic permeability of 49. The powder magnetic core formed with a pressurized pressure of 294 MPa has a filling rate of 81% and a DC initial magnetic permeability of 60. The powder magnetic core formed at a pressure of 490 MPa has a filling rate of 87% and a DC initial magnetic permeability of 72. The powder magnetic core formed with a pressurizing pressure of 686 MPa has a filling rate of 91% and a DC initial magnetic permeability of 78.
On the other hand, the powder magnetic core made of atomized iron powder described in Non-Patent Document 2 has a filling rate of 87.4% and a DC initial magnetic permeability of 64.2. Met. The packing rate of the dust core to which a pressurizing pressure of 686 MPa was applied was 89.8%, and the initial magnetic permeability of direct current was 68.7. Compared with the powder magnetic core described in Non-Patent Document 4, at the same pressurizing pressure, the filling rate value is close, but the direct current magnetic permeability is small. The reason for this depends on the concentration of impurities. The concentration of silicon in Non-Patent Document 2 is 0.01% by mass, and the concentration of manganese is 0.04% by mass. On the other hand, in Non-Patent Document 4, the concentration of silicon is as high as 0.029% by mass and the concentration of manganese is as high as 0.069% by mass. The atomized iron powder of Non-Patent Document 4 has a high initial magnetic permeability because of the high concentration of silicon and manganese.
Further, the atomized iron powder used for the dust core described in Non-Patent Document 2 has a smaller particle size than the atomized iron powder used for the powder magnetic core described in Non-Patent Document 4. For example, in the atomized iron powder described in Non-Patent Document 2, there is no atomized iron powder having a particle size larger than 180 μm. In addition, atomized iron powder having a particle size of 45 μm or less accounts for 23%. On the other hand, the atomized iron powder described in Non-Patent Document 4 contains 11.2% for atomized iron powder having a particle size of 200-250 μm and 20.1% for atomized iron powder having a particle size of 250-325 μm. Atomized iron powder having a particle size of 325 μm or more accounts for 23.2%. In addition, only 0.1% of atomized iron powder has a particle size of 80 μm or less.
Further, as the pressurizing pressure is increased, the values of the real part and the imaginary part of the complex magnetic permeability gradually increase, and the frequency at which the values of the real part and the imaginary part of the complex magnetic permeability start to decrease gradually becomes low. The result of shifting to the side is shown. At a pressurizing pressure of 294 MPa, the real part has a value of 80 up to around 500 kHz. Further, as the frequency increases from 500 kHz, the real part gradually decreases. On the other hand, the imaginary part of the complex magnetic permeability gradually increases from around 60 kHz, has a peak value of 20 in the frequency region exceeding 1 MHz, and overlaps the real part at a frequency exceeding 200 MHz.
Here, the measurement result of the dust core will be examined.
First, consider the results of compression density. It is expected that the smaller the particle size of the atomized iron powder used for the dust core, the higher the compression density. The atomized iron powder used in Non-Patent Document 2 has a clearly smaller particle size than the atomized iron powder used in Non-Patent Document 4. Although there is a clear difference in the size of the particle size, there is almost no difference in the packing rate of the dust core. On the other hand, the atomized iron powder starts plastic deformation from a pressurizing pressure of around 50 MPa, and at a pressurized pressure of 490 MPa, the plastic deformation of the atomized iron powder progresses considerably. Therefore, the plastic deformation of the iron powder progressed, and the filling rate of the iron powder did not change despite the difference in the particle size distribution of the iron powder. That is, the atomized iron powder was compressed with a pressurizing pressure of about 490 MPa in order to obtain the mechanical strength required for the powder magnetic core. However, the iron powder with advanced plastic deformation has an increased holding force of the iron powder and an increased hysteresis loss. Furthermore, the holding power of iron powder cannot be restored by curing at 150 ° C. for 1 hour.
Second, the results of complex magnetic permeability will be examined. Like the reduced iron powder, the atomized iron powder has an irregular contour, but is not a porous body like the reduced iron powder. Increasing the pressure to pressurize a collection of insulated atomized iron powder narrows the gap between the atomized iron powder, reduces the eddy current flowing through the gap, and reduces the eddy current loss. As a result, the values of the real part and the imaginary part of the complex magnetic permeability increased as the pressurizing pressure was increased. Further, although the atomized iron powder is not a porous body, the flattening of the atomized iron powder progresses as the pressurizing pressure is increased, and the flattening ratio increases. As a result, the values of the real part and the imaginary part of the complex magnetic permeability increased. That is, the proportion of the atomized iron powder deformed in the plane direction, which is the easy axial direction of magnetization, increased, the flatness increased, and the values of the real part and the imaginary part of the complex magnetic permeability of the atomized iron powder increased.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, the dust core was composed of atomized iron powder with advanced plastic deformation. As a result, the holding force of the atomized iron powder increases according to the progress of plastic deformation, and the hysteresis loss increases as the holding force increases. In order to restore the holding power of the atomized iron powder, annealing in a hydrogen atmosphere higher than 500 ° C. is required, and the material for insulating the atomized iron powder needs to have a heat resistance higher than 500 ° C. If the atomized iron powder is insulated with the aluminum oxide fine particles in the present invention, the heat resistance is higher than that of the atomized iron powder, so that strain relief annealing becomes possible, the holding power is restored, and the hysteresis of the dust core is restored. Loss is reduced.
Secondly, if the insulating material is composed of the aluminum oxide fine particles in the present invention, the size of the fine particles is three orders of magnitude smaller than that of the epoxy resin pellets, so that the gap between the atomized iron powders is further narrowed, and the narrowed gap is insulated. Is filled with high aluminum oxide fine particles, and the eddy current flowing through the gap is further reduced. As a result, the values of the real part and the imaginary part of the complex magnetic permeability are further increased. In addition, the compression density also increases, and the saturation magnetic flux density of the dust core increases.
Thirdly, in the method for producing a dust core of the present invention, a collection of atomized iron powder is made into a collection of atomized iron powder having a high degree of integration and overlapping on each other, and the collection of atomized iron powder is compressed. Therefore, the surfaces overlap each other and are compressed, the gaps between the atomized iron powders are narrowed, and the narrowed gaps are filled with aluminum oxide fine particles having high insulating properties. As a result, the eddy current flowing through the gap is further reduced, and the values of the real part and the imaginary part of the complex magnetic permeability are further increased.
Fourth, if the pressurizing pressure is stopped before the atomized iron powder is plastically deformed and the atomized iron powder is bonded to each other through the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase, and the hysteresis loss does not increase. The dust core has the required mechanical strength.
As a result, the powder magnetic core produced by using atomized iron powder according to the method for producing a powder magnetic core of the present invention has an increased initial magnetic permeability, a reduced eddy current loss, and no hysteresis loss.

Embodiment 6
This embodiment is an embodiment of a dust core produced by using flat atomized iron powder, and is described in Non-Patent Document 5. Moreover, the superiority of the method for producing the dust core of the present invention will be described from the embodiment of the dust core.
A ring with an outer diameter of 36 mm, an inner diameter of 24 mm, and a thickness of 5 mm, using flat atomized iron powder and flat atomized iron powder insulated with three types of insulating materials, all under a pressure of 490 MPa. Four types of dust cores consisting of shapes were manufactured. For the first insulated flat atomized iron powder, synthetic resin was added to the iron powder in an amount of 0.8% by weight. The second insulated flat atomized iron powder was obtained by mixing an aqueous solution of phosphoric acid, boric acid and magnesium oxide with the flat atomized iron powder, and then drying the powder. For the third insulated flat atomized iron powder, 0.8% by weight of synthetic resin was further added to the second insulated flat atomized iron powder, and the iron powder was insulated by a double insulating layer.
The phosphoric acid used to insulate the flat atomized iron powder has a melting point of 42.35 ° C., and changes to _{phosphoric acid H 4} P ₂ O _{7 at 200 ° C. and metaphosphoric acid (HPO 3} ) _n at 300 ° C. or higher. To do. Further, boric acid _{changes to metaboric acid HBO 2} at 100 ° C., tetraboric acid H ₂ B ₄ O ₇ at 140 ° C., and glassy boric acid B ₂ O ₃ at 300 ° C. On the other hand, magnesium oxide has a melting point of 2852 ° C. and is excellent in heat resistance. Further, since the four types of dust cores are manufactured by applying a pressurizing pressure of 490 MPa to a collection of flat atomized iron powder, the atomized iron powder starts plastic deformation from a pressurizing pressure of around 50 MPa. The plastic deformation of the flat atomized iron powder constituting the four types of dust cores is progressing. On the other hand, due to the heat resistance of magnesium oxide, it is possible to perform hydrogen annealing of the dust core at a temperature higher than 500 ° C. However, since hydrogen annealing of the four types of dust cores is not performed, the hysteresis loss of the four types of dust cores is large.
First, the result of compression density will be described. The powder magnetic core made of flat atomized iron powder has a density of 7.10 g / cm ³ and a filling rate of 90%. This filling rate is 3% higher than that of the powder magnetic core produced by using the atomized iron powder described in Non-Patent Document 4 and applying the same pressurizing pressure of 490 MPa. As a result, the flattening effect of atomized iron powder was reflected in the increase in compression density. Further, the filling rate is higher than that of the powder magnetic core produced by applying the same pressurizing pressure of 490 MPa using the flattened reduced iron powder described in Non-Patent Document 3. As a result, the temperature at which the flat atomized iron powder was hydrogen-annealed was higher than the hydrogen annealing temperature of the flat reduced iron powder described in Non-Patent Document 3, and the hardness of the flat atomized iron powder was lower than the hardness of the flat reduced iron powder. It seems that it depends. Further, the density of the dust core made of the first insulated iron powder is 6.90 g / cm ³ , and the density of the powder magnetic core made of the second insulated iron powder is 7.04 g / cm. ^3, and the density of the dust core fabricated by iron powder and the third insulated is 6.83 g / cm ^3.
Next, the results of the specific resistances of the four types of dust cores will be described. As for the effect of insulation by the insulating material, the first insulating material has no insulating effect, the second insulating material has a slight insulating effect, and the third insulating material has an insulating effect.
Further, the results of the eddy current loss of the four types of dust cores will be described. The eddy current loss is large in the order of the dust core made of only iron powder, the powder magnetic core made of the first insulator, the powder magnetic core made of the third insulator, and the powder magnetic core made of the second insulator. Although the difference in eddy current loss between the dust core made of the third insulator and the dust core made of the second insulator is small, the dust core made of only iron powder and the first insulator The difference in eddy current loss is large compared to the powder magnetic core made of.
Here, the result of the dust core will be examined.
First, consider the results of compression density. The densities of the three types of powder magnetic cores obtained by insulating flat atomized iron powder are lower than the densities of the powder magnetic cores made only of iron powder. That is, the insulator does not sufficiently fill the gap formed by the plastically deformed flat atomized iron powder. The contour of the flat atomized iron powder is irregular, because all the flat atomized iron powders do not overlap each other, and because the flat atomized iron powder consists of powders of various sizes, compression molding is performed when pressed. Many voids are formed in the body. On the other hand, since each of the three types of insulating materials has a certain size, the voids cannot be filled and the compression density is lowered. In addition, the decrease in the density of the dust core made of the second insulated iron powder is due to the pressure made of the first insulated iron powder and the third insulated iron powder. It is smaller than the decrease in compression density with the powder core. The reason for this is that the crushed resin pellets are larger than the particle size of the magnesium oxide powder, and the crushed resin pellets are an obstacle to filling the voids.
Second, the result of resistivity is examined. The first insulator is made by adding synthetic resin to iron powder in an amount of 0.8% by weight, and since the synthetic resin pellets have a certain size, the crushed synthetic resin pellets are flat atomized iron powder. The insulating effect could not be obtained because some of the flat atomized iron powders were in direct contact with each other without filling the gaps between them. On the other hand, when the flat atomized iron powder covered with the double insulating layer is compressed, the magnesium oxide powder, which has a higher hardness than the synthetic resin pellets, comes into contact with the synthetic resin pellets and makes the synthetic resin pellets finer. The fine pieces of synthetic resin pellets, which are smaller than the first insulator, and the magnesium oxide powder enter the gaps between the flat atomized iron powders. Due to the high insulation between the two, insulation has progressed.
Third, the results of eddy current loss will be examined. Similar to the result of compression density, the dust core made of the first insulator does not fill the gap between the flat atomized iron powders because the resin pellets are large, and some of the flat atomized iron powders do not fill the gap between the flat atomized iron powders. Direct contact resulted in an eddy current loss close to that of a dust core consisting only of iron powder. On the other hand, the dust core made of the third insulator and the powder magnetic core made of the second ^{insulator have high insulating properties with a volume resistivity of 2 × 10 16} Ω · cm and an average particle size. The 1.3 μm magnesium oxide powder and the fine pieces of synthetic resin pellets were present in the gaps between the iron powders, and the eddy current loss was reduced.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, from the above-mentioned compression density results, the smaller the size of the insulator that insulates the flat atomized iron powder, the more the gaps between the atomized iron powders are filled with the insulator, and the decrease in the compression density is suppressed. It was. Therefore, since the size of the aluminum oxide fine particles having an average particle size of 40 to 60 nm in the present invention is two orders of magnitude smaller than that of magnesium oxide powder having an average particle size of 1.3 μm, a decrease in compression density can be suppressed. In addition, the gap between the flat atomized iron powders is surely insulated, and the eddy current flowing through the gap is reduced. As a result, the values of the real part and the imaginary part of the complex magnetic permeability increase.
Secondly, if the flat atomized iron powder is insulated by a collection of granular aluminum oxide fine particles having a size of 40 to 60 nm as in the present invention, the gaps between the flat atomized iron powders are filled with the aluminum oxide fine particles. As the compression density increases, the insulation resistance of the gaps increases significantly due to the enormous number of granular aluminum oxide fine particles and pores. As a result, the eddy current flowing through the gap is significantly reduced, and the eddy current loss of the dust core is reduced. In addition, the values of the real part and the imaginary part of the complex magnetic permeability increase according to the degree of decrease in the eddy current loss.
Thirdly, by compressing a collection of flat atomized iron powders that overlap each other as in the present invention, the gap between the flat atomized iron powders is surely insulated, the eddy current flowing through the gap is reduced, and the eddy current flowing through the gap is reduced. , The compression density increases. Further, since all the flat atomized iron powders are overlapped with each other and aligned in the plane direction which is the easy axial direction of magnetization, the dust core is easily magnetized and the magnetic permeability of the dust core is increased.
Fourth, as in the present invention, if the pressurizing pressure is stopped before the flat atomized iron powder is plastically deformed and the flat atomized iron powders are bonded to each other through the bonding of the aluminum oxide fine particles, the powder magnetic core The hysteresis loss does not increase, and the dust core has the required mechanical strength.
As a result, in the powder magnetic core produced by using the flat atomized iron powder according to the method for producing the powder magnetic core of the present invention, the initial magnetic permeability is increased, the eddy current loss is reduced, and the hysteresis loss is not increased.

The embodiment of four kinds of dust cores produced by using atomized iron powder, flat atomized iron powder, reduced iron powder and flat reduced iron powder has been described. Since the dust core of the embodiment insulates the iron powder with an insulating material having low heat resistance, hydrogen annealing of the iron powder is impossible. In addition, since the dust core was formed by the iron powder that had undergone plastic deformation, the hysteresis loss of the dust core increased. Further, the heat treatment temperature is as low as 180 ° C., and there is no annealing effect of the plastically deformed iron powder. The powder magnetic core produced by the method for producing a powder magnetic core of the present invention has advantages over such a powder magnetic core in the following two points.
First, the surface of the iron powder was insulated with a collection of fine particles of aluminum oxide. This brings about the following four effects. First, the melting point of aluminum oxide is higher than the melting point of iron powder, and the heat resistance of the dust core becomes the heat resistance of iron powder. This enables hydrogen annealing of the dust core, restores the holding power of the iron powder, and reduces the hysteresis loss of the dust core. Secondly, aluminum oxide is granular fine particles having a size of 40-60 nm, and when a collection of iron powder covered with fine particles of aluminum oxide is compressed, the aluminum oxide fine particles move to fill the voids of the collection of iron powder. Further, the aluminum oxide fine particles are bonded to each other by frictional heat at the contact portion, and the powder magnetic core has the necessary mechanical strength in the bonding of the extremely large number of aluminum oxide fine particles. Thirdly, aluminum oxide is an excellent insulator, and an extremely large number of aluminum oxide fine particles and resistors between the pores fill the gaps between the iron powders, and the insulation resistance of the gaps is significantly increased. As a result, the eddy current flowing in the gap between the iron powders is remarkably reduced, the AC magnetic permeability of the dust core is increased, and the dust core is easily magnetized in the corresponding frequency band. Fourth, aluminum oxide is the hardest substance next to diamond, and because it has an extremely high melting point, when aluminum oxide fine particles come into contact with each other, the fine particles are not destroyed and excessive frictional heat is generated at the contact part, causing the fine particles to come into contact with each other. Joins with frictional heat. Since there are an extremely large number of aluminum oxide fine particles in the collection of iron powder to be compressed, the repulsive force for compressing the collection of iron powder increases when the aluminum oxide fine particles are joined to each other, and the compression is stopped at this point. be able to. As a result, the iron powder is not plastically deformed, and the hysteresis loss of the dust core does not increase.
The second is to perform a treatment on a collection of iron powder to form a collection of iron powder in which the surfaces of the iron powder overlap each other. This brings about the following three effects. First, the gap between the iron powders is narrowed, which increases the compression density of the compression compact and the saturation magnetic flux density of the dust core. Second, the narrowed gaps between the iron powders are filled with a collection of aluminum oxide fine particles, the eddy current flowing in the gaps between the iron powders is reduced, and the eddy current loss of the dust core is reduced. As a result, the initial magnetic permeability of alternating current increases, and the dust core is likely to be magnetized in the corresponding frequency band. Third, when a collection of iron powder with overlapping surfaces is compressed, the iron powder is deformed in the axial direction of easy magnetization perpendicular to the surface, so the initial magnetic permeability of alternating current increases, and the dust core in the corresponding frequency band. Is easily magnetized.

Here, the complex magnetic permeability of the soft magnetic material will be described. When the dust core is wound and alternating current is applied to excite the dust core, a hysteresis loss due to the soft magnetic material constituting the dust core occurs. When the configuration of the dust core is shown by an electric circuit, the impedance is represented by R + jωL because the winding forms the L component and the dust core forms the R component. Applying this relationship to magnetic permeability, magnetic permeability is expressed by Equation 1. At this time, μ ′ represents the inductance component in the real part of the complex magnetic permeability, and μ ″ represents the resistance component in the imaginary part of the complex magnetic permeability.
(Equation 1) μ = μ ′ −jμ ″
On the other hand, when a high-frequency alternating current is passed through the dust core, the magnetic permeability of the soft magnetic material cannot be followed by the magnetic flux density B with the change of the magnetic field H, and a phase delay occurs. At this time, the L component (μ ′) decreases and the R component (μ ″) increases. This case was described by the behavior of complex magnetic permeability in the flat powder described above.
The relationship between the magnetic permeability and the complex magnetic permeability at B = μH, which is the definition of the magnetic permeability μ expressed by the relationship between the magnetic field strength H and the magnetic flux density B, is given by Equation 2. Therefore, if at least one of the real part μ'and the imaginary part μ'is increased, the magnetic permeability μ will increase. By increasing the magnetic permeability μ, the dust core is easily magnetized, and magnetic energy based on the product of the saturation magnetic flux density and the applied magnetic field is taken into the dust core.
(Equation 2) μ = {(μ ′) ² + (μ ″) ² } ^1/2

Example 1
In this embodiment, flat atomized iron powder obtained by flattening atomized iron powder is insulated by a collection of fine particles of aluminum oxide, and the insulated flat atomized iron powder collection is compressed in a mold to form a dust core. Is an embodiment of manufacturing in a mold.
As the flat atomized iron powder, 290PC-2 of Kobe Steel, Ltd. was used. This flat iron powder is obtained by flattening atomized iron powder (300M of Kobe Steel, Ltd.). The impurity concentration of atomized iron powder (300M) was 0.01% by weight for silicon and 0.19% by weight for manganese (according to Non-Patent Document 6), which was described in Non-Patent Document 2 described above. The concentration of manganese is higher than the concentration of impurities in atomized iron powder. Therefore, the initial magnetic permeability of atomized iron powder (300M) is slightly higher.
Further, as a raw material for aluminum oxide, aluminum benzoate Al (C ₆ H ₅ COO) ₃ (for example, a product of Mitsuwa Chemical Co., Ltd.) was used. Further, as the organic compound, diethylene glycol (for example, a product of Junsei Chemical Co., Ltd.) having a boiling point of 244 ° C. and a viscosity of 25 ° C. of 30 mPas, which is close to 50 times the viscosity of methanol, was used. Further, as a mixer, a device (for example, rocking mixer RMH-HT manufactured by Aichi Electric Co., Ltd.), which has a built-in heater by far infrared rays and simultaneously performs diffusion mixing by rotation and moving mixing by shaking, is used for further mixing. A vibration exciter was installed at the bottom of the machine.
31 g (corresponding to 0.08 mol) of aluminum benzoate was dispersed in 1 liter of methanol, and 200 cc of diethylene glycol was mixed with this methanol dispersion to prepare a mixed solution. Therefore, the viscosity of the mixture is close to 10 times the viscosity of methanol. Next, the mixer was placed on a vibration table, the mixed solution and 1 kg of flat atomized iron powder were charged into the mixer, and mixing and rocking were repeated by the mixer to prepare a mixture. Therefore, the volume occupied by methanol in the mixture is eight times the volume occupied by flat atomized iron powder. Further, when 31 g of aluminum benzoate is thermally decomposed, 8 g of aluminum oxide is precipitated, and the ratio of the weight of aluminum oxide to the weight of flat atomized iron powder corresponds to 0.008. Next, vibration acceleration consisting of 0.3G in three directions of front-back, left-right, and up-down is repeatedly generated by the exciter, and the vibration is transmitted to the mixture in the mixer via the exciter, and finally, from 0.3G. A vertical vibrational acceleration was applied to the mixture. Further, the temperature of the mixer was raised to 65 ° C., which is the boiling point of methanol, and methanol was vaporized. The vaporized methanol is recovered and reused. After that, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled in a mold. The mold has a shape in which a ring-shaped molded body having an outer diameter of 40 mm, an inner diameter of 25 mm, and a thickness of 6 mm is formed.
Next, the mold was heated to 310 ° C. at a heating rate of 20 ° C./min and held for 1 minute. This first vaporized diethylene glycol and then pyrolyzed aluminum benzoate. The vaporized diethylene glycol is recovered and reused. After that, a pressurizing pressure increasing at a rate of 10 MPa / min is generated by the press machine, the pressurizing pressure is applied to the mixture in the die, and compression is performed when the repulsive force received by the press machine continuously increases. It stopped and the dust core was manufactured in the mold. After that, the dust core was taken out from the mold.
Next, the performance of the prepared dust core was measured. This result is compared with the two types of dust cores described in Non-Patent Document 5. The first powder magnetic core is a ring-shaped powder magnetic core produced by applying a pressurizing pressure of 490 MPa to flat atomized iron powder (290PC-2). The second powder magnetic core insulates the surface of flat atomized iron powder (290PC-2) with phosphoric acid, boric acid, and magnesium oxide, and further adds 0.8% by weight of synthetic resin to provide two types of insulators. It is a powder magnetic core formed by forming a collection of flat atomized iron powder insulated with (1) at a pressurizing pressure of 490 MPa.
First, the weight of the dust core was measured, and the density of the dust core was determined from the volume of the dust core. The density was 7.3 g / cm ³ . On the other hand, the density of the first dust core described in Non-Patent Document 5 is 7.1 g / cm ³ , and the compression density of the second dust core is 6.84 g / cm ³ . The density of the prepared dust core is higher than the density of the two types of dust core described in Non-Patent Document 5. The reason for this is that by superimposing all the flat atomized iron powders on each other, the gap between the flat atomized iron powders is narrowed, and the aluminum oxide fine particles fill the voids of the flat atomized iron powders. It depends on the effect and the effect that the accumulation degree of the flat atomized iron powder is increased with the movement of the aluminum oxide fine particles.
Furthermore, the specific resistance of the dust core was measured. A copper plate was attached to both planes of the dust core via a conductive paste, and the copper plate was pressurized to measure the specific resistance. The specific resistance of the prepared dust core was 38 Ω · cm. On the other hand, the specific resistance of the second dust core described in Non-Patent Document 5 is 21 Ω · cm. The specific resistance of the prepared dust core is higher than the specific resistance of the second powder magnetic core described in Non-Patent Document 5. The reason for this is that the surfaces of the flat atomized iron powders that overlap each other are covered by the aggregates of aluminum oxide fine particles and pores that have extremely high insulation resistance, and the aggregates of the flat atomized iron powders are compressed so that the flat atoms are stacked. This is because the small overlapping gaps are filled with the aggregates of the aluminum oxide fine particles and the vacancies, and the voids of the adjacent flat atomized iron powders are filled with the aggregates of the aluminum oxide fine particles and the vacancies.
Next, the eddy current loss of the prepared dust core was determined using the products SY-8218 / SY-8218 of Iwatsu Electric Co., Ltd., which is a BH analyzer. The eddy current loss at a magnetic flux density of 50 mT was 1 kW / m ³ at 10 kHz and 100 kW / m ³ at 100 kHz. This value is 1/8 of the eddy current loss of the second dust core described in Non-Patent Document 5. The reason for this is that the collection of aluminum oxide fine particles and pores, which have extremely high insulation resistance, fills the small gaps where the flat surfaces overlap, and also fills the voids of the adjacent flat atomized iron powder, and flat atomized iron. This is due to the decrease in eddy currents flowing through the gaps between the powders.
Furthermore, in the magnetic material measurement system, Model No. of Keycom Co., Ltd. The frequency characteristic of magnetic permeability was measured using per. In a magnetic field of 8 A / m, the initial magnetic permeability of the prepared dust core was 80 up to around 10 kHz and 65 around 100 kHz. On the other hand, the initial magnetic permeability of the first dust core described in Non-Patent Document 5 is 82 up to around 10 kHz and 68 at around 100 kHz in a magnetic field of 8 A / m. The initial magnetic permeability of the second dust core has a value of 65 at around 10 kHz and a value of 63 at around 100 kHz in a magnetic field of 8 A / m. The initial magnetic permeability of the dust core is larger than the initial magnetic permeability of the two types of dust core described in Non-Patent Document 5. The reason for this is that the effect of aligning all the flat atomized iron powders in the flat plane direction, which is the axial direction for easy magnetization, and the collection of aluminum oxide fine particles and pores, which have extremely high insulation resistance, are slightly overlapped with each other. This is due to the fact that the gaps between the flat atomized iron powders are filled, and the voids of the adjacent flat atomized iron powders are filled, and the eddy current flowing through the gaps between the flat atomized iron powders is reduced.
Further, the iron loss of the powder magnetic core prepared under the measurement conditions of the exciting magnetic flux density of 1 T and the exciting frequency of 100-800 Hz was measured by a simple iron loss measuring instrument of Toei Kogyo Co., Ltd. The iron loss was 6 W / kg at 100 Hz, 13 W / kg at 200 Hz, 28 W / kg at 400 Hz, and 56 W / kg at 800 Hz.
On the other hand, in Non-Patent Document 7, atomized iron powder (300NH of Kobe Steel Works) is insulated with a two-layer coating of a phosphoric acid-based inorganic insulating film and a silicone resin, and this powder is heated to 130 ° C. to lubricate the mold. A dust core is described in which a ring-shaped dust core is formed at 1176 MPa by the method and then magnetically annealed at 500 ° C. for 30 minutes in a nitrogen atmosphere. The annealing temperature is limited to 550 ° C by the heat resistance of the insulator. According to Non-Patent Document 7, the compression density is 7.61 g / cm ³ and the filling rate reaches 97% because the pressurizing pressure is as high as 1176 MPa. On the other hand, the atomized iron powder pressurized at 1176 MPa is sufficiently plastically deformed. Therefore, in the magnetic annealing at 500 ° C., the reduction of the hysteresis loss of the dust core is limited to a part. Further, the iron loss of the dust core under the measurement conditions where the exciting magnetic flux density is 1.5T and the exciting frequency is 200-700Hz is 5W / kg at 50Hz, 12W / kg at 100Hz, and 23W / kg at 200Hz. It is 50 W / kg at 400 Hz and 100 W / kg at 700 Hz.
The iron loss of the produced dust core is about 1/2 of that of the dust core described in Non-Patent Document 7. The reason for this is that in the produced dust core, the eddy current flowing through the gaps between the flat atomized iron powders is smaller than the eddy currents flowing through the gaps between the atomized iron powders described in Non-Patent Document 7, and the flat atomized iron powders. Is not plastically deformed, and the holding power of the flat atomized iron powder is not increased.
Next, the prepared dust core was dropped from a height of 2 m onto the floor surface, but the dust core was not destroyed. Therefore, the prepared dust core has the required mechanical strength. The reason for this is that a large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Furthermore, the produced dust core was observed and analyzed. The produced dust core was cut in two in the thickness direction, and the cut surface was observed with an electron microscope. As the electron microscope, an extremely low acceleration voltage SEM manufactured by JFE Techno Research Co., Ltd. was used. This device is capable of observing with an extremely low acceleration voltage from 100 volts, and has a feature that the sample can be directly observed without forming a conductive film on the sample.
First, the secondary electron beam between 900 and 1000 V of the backscattered electron beam was taken out and image-processed, and the cut surface was observed. Flat atomized iron powder overlapped with each other on the flat surfaces, and granular fine particles having a size of 40-60 nm formed 13-17 layers and laminated to evenly fill the gaps where the flat surfaces overlapped with each other. Next, the energy of the characteristic X-ray and its intensity were image-processed, and the types of elements constituting the granular fine particles and their distribution states were analyzed. Both aluminum atoms and oxygen atoms were uniformly dispersed, and no particular uneven distribution was observed. Therefore, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps between the flat atomized iron powders overlapping the flat surfaces. FIG. 1 schematically shows a state in which a part of the cut surface is enlarged. 1 is flat atomized iron powder, and 2 is fine particles of aluminum oxide.
As described above, the powder magnetic core prepared using the flat atomized iron powder has a higher compression density and increased insulation resistance than the powder magnetic core prepared by the conventional manufacturing method using the flat atomized iron powder. The eddy current loss was small, the initial magnetic permeability was increased, the holding power of the flat atomized iron powder was not increased, and the required mechanical strength was obtained.

Example 2
In this embodiment, the flat reduced iron powder obtained by flattening the reduced iron powder is insulated by a collection of fine particles of aluminum oxide, and the insulated collection of flat reduced iron powder is compressed in a mold to form a dust core. Is an embodiment of manufacturing in a mold.
MG150D manufactured by JFE Steel Corporation was used as the flattened reduced iron powder. This flat-reduced iron powder is a flattened reduced iron powder (MG270H of JFE Steel Corporation), and is the flat-reduced iron powder described in Non-Patent Document 3.
Further, as in Example 1, aluminum benzoate was used as a raw material for aluminum oxide, diethylene glycol was used as an organic compound, the same device was used as a mixer, and a vibration exciter was installed in the lower part of the mixer.
Further, in the same manner as in Example 1, 31 g of aluminum benzoate was dispersed in 1 liter of methanol, and 200 cc of diethylene glycol was mixed with this methanol dispersion to prepare a mixed solution. Next, the mixer was placed on a vibration table, the mixed solution and 1 kg of flattened iron powder were charged into the mixer, and mixing and rocking were repeated by the mixer to prepare a mixture. Next, the vibration acceleration in the three directions of front-back, left-right, and up-down consisting of 0.3 G was repeatedly generated by the exciter, and finally, the vibration acceleration in the up-down direction consisting of 0.3 G was added to the mixture. Further, the temperature of the mixer was raised to 65 ° C. to vaporize methanol. After that, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled in the same mold as in Example 1.
Next, in the same manner as in Example 1, the temperature of the mold was raised to 310 ° C. and held for 1 minute. After that, as in Example 1, a pressurizing pressure increasing at a rate of 10 MPa / min is generated by the press machine, and the pressurizing pressure is applied to the mixture in the die, and the repulsive force received by the press machine continues. When the pressure increased, compression was stopped and a dust core was manufactured in the mold. After that, the dust core was taken out from the mold.
Next, the performance of the prepared dust core was measured. This result is compared with the dust core described in Non-Patent Document 3. MG150D was used as the flattened iron powder for both powder magnetic cores.
First, the weight of the dust core was measured, and the density of the dust core was determined from the volume of the dust core. The density was 7.2 g / cm ³ . On the other hand, the density of the dust core described in Non-Patent Document 3 is 6.93 g / cm ³ . The reason why the density of the prepared dust core is higher than the density of the dust core described in Non-Patent Document 3 is that all the flat reduced iron powders are superposed on each other in the same way as in Example 1. The effect of narrowing the gap between the flat-reduced iron powders, the effect of the aluminum oxide fine particles filling the voids in the collection of flat-reduced iron powders, and the degree of accumulation of the flat-reduced iron powders due to the movement of the aluminum oxide fine particles. Depends on the increased effect. Further, in the dust core described in Non-Patent Document 3, since the flat reduced iron powder is a porous body, the cured epoxy resin cannot fill the voids of all the flat reduced iron powder, and the dust core cannot be filled. The density of the powder has decreased.
Next, the initial magnetic permeability at direct current was measured using a BH analyzer manufactured by Denshi Kogaku Kogyo Co., Ltd. The initial magnetic permeability of the prepared dust core at direct current was 100. On the other hand, the initial magnetic permeability of the dust core described in Non-Patent Document 3 at direct current is 94.9.
Moreover, the initial magnetic permeability in alternating current was measured using the apparatus of Example 1. The produced dust core was 100 up to around 200 kHz, gradually decreased above 200 kHz, and was 67 at 1 MHz. On the other hand, the powder magnetic core described in Non-Patent Document 3 was 94.9 up to around 200 kHz, gradually decreased above 200 kHz, and was 63 at 1 MHz.
The reason why the initial magnetic permeability of the prepared dust core is higher than the initial magnetic permeability described in Non-Patent Document 3 is that, as in Example 1, all the flat reduced iron powders are all flattened in the axial direction for easy magnetization. The effect of aligning the directions and the collection of aluminum oxide fine particles and pores with extremely high insulation resistance fill the small gaps where the flat surfaces overlap, and also fill the voids of the adjacent flat reduced iron powder. This is due to the decrease in the eddy current flowing through the gaps between the flattened iron powders.
Further, using the apparatus of Example 1, the iron loss of the dust core was measured under the measurement conditions where the exciting magnetic flux density was 50 mT and the exciting frequency was 20-100 kHz. The iron loss of the produced dust core is about 1/2 of the iron loss of the dust core described in Non-Patent Document 3 at 20 kHz, and the iron loss of the dust core described in Non-Patent Document 3 at 50 kHz. It was about 1/4, which was about 1/5 of the iron loss of the dust core described in Non-Patent Document 3 at 100 kHz. The iron loss described in Non-Patent Document 3 is that the pressure for pressurizing the aggregate of flat reduced iron powder is 686 MPa instead of 490 MPa.
As for the result of iron loss, as compared with the result of Example 1, the higher the frequency, the larger the difference from the iron loss of the dust core described in Non-Patent Document 3. The reason for this is that the epoxy resin that insulates the flat-reduced iron powder described in Non-Patent Document 3 does not fill the gaps between the flat-reduced iron powders, and some of the flat-reduced iron powders come into direct contact with each other, so that the flat-reduced iron powders come into direct contact with each other. This is due to the vortex current loss flowing through the gaps between the powders. That is, when all the flat-reduced iron powders overlap each other on the flat surfaces, the mechanical strength required for the powder magnetic core cannot be realized, so that the aggregate of the flat-reduced iron powders is simply compressed. As a result, some flattened iron powders come into direct contact with each other. As a result, since the eddy current loss is proportional to the square of the frequency, the higher the frequency, the greater the eddy current loss of the dust core described in Non-Patent Document 3. Further, since the iron loss at 20 kHz is about 1/2 of the iron loss of the dust core described in Non-Patent Document 3, the hysteresis loss of the flat reduced iron powder increases when the powder magnetic core is manufactured. It depends on the effect that was not there. That is, the powder magnetic core described in Non-Patent Document 3 is heat-treated at 180 ° C. for 30 minutes, but at 180 ° C., the processing strain of the flat reduced iron powder that has undergone plastic deformation at a pressurizing pressure of 686 MPa is This cannot be eliminated, and the hysteresis loss of the dust core is increasing due to the increase in the holding power of the flattened iron powder.
Next, as in Example 1, the dust core was dropped from a height of 2 m onto the floor surface, but the dust core was not destroyed. Therefore, the dust core has the required mechanical strength. The reason for this is that a large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Further, in the same manner as in Example 1, the produced dust core was cut in two in the thickness direction, and the cut surface was observed with an electron microscope. Similar to Example 1, the flat-reduced iron powders overlapped with each other, and granular aluminum oxide fine particles having a size of 40-60 nm were laminated to evenly fill the gaps where the flats overlapped with each other. The cut surface is similar to FIG. 1 and is not shown.
As described above, the powder magnetic core prepared using the flat reduced iron powder has a higher compression density and increased insulation resistance than the powder magnetic core prepared by the conventional manufacturing method using the flat reduced iron powder. The eddy current loss was small, the initial magnetic permeability was increased, the holding power of the flat atomized iron powder was not increased, and the required mechanical strength was obtained.

Example 3
In this embodiment, flat sendust powder is used as a flat soft magnetic powder having high hardness, the flat sendust powder is insulated by a collection of fine particles of aluminum oxide, and the insulated collection of flat sendust powder is compressed in a mold. This is an example of manufacturing a dust core in a mold.
For the flattened sendust powder (a product of Tokin Corporation), water atomized sendust powder was flattened, and then annealed in an argon gas atmosphere at 650 ° C. for 2 hours to remove the strain due to the flattening. The average major axis is 40 μm, the average thickness is 1.5 μm, the thickness is thinner than the above-mentioned flat iron powder, and the flatness is high. The flat sendust powder has a high hardness, and in order to plastically deform the flat sendust powder, a pressurizing pressure larger than the pressurizing pressure for plastically deforming the flat iron powder is applied. This increases the hysteresis loss of the dust core.
Further, as in Example 1, aluminum benzoate was used as a raw material for aluminum oxide, diethylene glycol was used as an organic compound, the same device was used as a mixer, and a vibration exciter was installed in the lower part of the mixer.
Further, in the same manner as in Example 1, 31 g of aluminum benzoate was dispersed in 1 liter of methanol, and 200 cc of diethylene glycol was mixed with this methanol dispersion to prepare a mixed solution. Next, the mixer was placed on a vibration table, the mixed solution and 1 kg of flat sendust powder were charged into the mixer, and mixing and shaking were repeated by the mixer to prepare a mixture. Next, the vibration acceleration in the three directions of front-back, left-right, and up-down consisting of 0.3 G was repeatedly generated by the exciter, and finally, the vibration acceleration in the up-down direction consisting of 0.3 G was added to the mixture. Further, the temperature of the mixer was raised to 65 ° C. to vaporize methanol. After that, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled in the same mold as in Example 1.
Next, the performance of the prepared dust core was measured. This result is compared with the powder magnetic core using the flat sendust powder described in Non-Patent Document 8. The powder magnetic core described in Non-Patent Document 8 is obtained by molding a slurry obtained by mixing a silicone resin, a thickener and a solvent with flat powder into a sheet, and press-molding and heat-treating the obtained sheet. Was applied to produce a dust core. Silicone resin has excellent insulating properties like epoxy resin, but its heat resistance is lower than 250 ° C., and the holding power of flat sendust powder cannot be restored by heat treatment, resulting in hysteresis loss in the dust core. large.
First, the weight of the dust core was measured, and the filling rate of the dust core was determined from the volume of the dust core. The filling rate was 82% by weight. On the other hand, the filling rate of the dust core described in Non-Patent Document 8 is 70% by weight. The large difference in filling rate is due to the following reasons.
Looking at the cross-sectional photograph of the dust core published in Non-Patent Document 8, many voids are formed. Further, most of the voids are formed above and below the flat sendust powder having a relatively large particle size. Therefore, when the slurry was formed into a sheet, voids were formed in the sheet, and then the sheet was pressure-molded, so that the voids were further expanded. As a result, the filling rate of the dust core became low. In other words, since the aggregates of flat sendust powder are not rearranged just by molding into a sheet, the degree of accumulation of the aggregates of flat sendust powder is low, and voids are formed above and below the flat sendust powder having a relatively large particle size. Cheap. Further, in the cross-sectional photograph of the dust core, most of the flat sendust powders are deformed so as to undulate with the flat surface in the vertical direction. In other words, the flat sentust powder has a high hardness, and a large pressurizing pressure is applied when the dust core is manufactured, the flat sentust powder is sufficiently plastically deformed, and the plastically deformed flat sentust powder is entangled to form a machine of the dust core. Target strength is generated. Therefore, since a large pressure was applied to the collection of the flat sendust powder in which the voids were formed and compressed, most of the flat sendust powder was deformed so as to undulate with the flat surface in the vertical direction. This further expanded the voids. On the other hand, the heat resistance of the insulating material is lower than 250 ° C., and the holding power of the flat sentust powder cannot be restored by the heat treatment of the dust core, and the hysteresis loss of the dust core described in Non-Patent Document 8 is large. On the other hand, if all the flat soft magnetic powders are aligned in the flat plane direction as in Example 3, the plastically deformed flat sendust powders are less likely to be entangled, so that the mechanical strength required for the dust core cannot be realized.
On the other hand, in the powder magnetic core of Example 3, vibrations in three directions were repeatedly applied to the mixture of the aggregate of flat sendust powder and the mixed solution, and finally vibrations in the vertical direction were applied. For this reason, the arrangement in which the flat sendust powder having a relatively small particle size enters the voids of the flat sendust powder collection and the arrangement in which the flat sendust powder moves above the flat sendust powder collection progresses with the flat surface facing up, and the flat sendust The degree of accumulation of powder collection increases. Finally, when vibration is applied in the vertical direction, all the flat sendust powders are overlapped with each other with their faces facing up. As a result, the filling rate of the dust core of Example 3 was increased.
Next, the complex magnetic permeability at alternating current was measured using the apparatus of Example 1. The produced dust core had a value of 400 up to about 10 MHz in the real part, gradually decreased when it exceeded 10 MHz, decreased to a value of 210 in the vicinity of 300 MHz, and overlapped with the imaginary part. The imaginary part increased from around 3 MHz, reached a peak value of 210 around 300 MHz, and gradually decreased from around 300 MHz. Incidentally, the conductivity of the sendust is the 1.25 × ¹⁰ 6 S / m, the thickness of the epidermis of sendust of relative permeability 400 in 10 MHz, the 2.25 micrometers. This value corresponds to a value obtained by laminating aluminum oxide fine particles having a thickness of 50 nm in 7 to 8 layers on an average thickness of 1.5 μm of flat sendust powder to insulate them. Therefore, in Example 3, since all the flat sendust powders insulated by the collection of aluminum oxide fine particles are superposed on the flat surfaces, the reduced eddy current flows through the gaps between the flat surfaces having high insulating properties. Further, by reducing the eddy current, the imaginary part of the complex magnetic permeability increased. In addition, since all the flat sendust powders were aligned in the flat plane direction, which is the axial direction for easy magnetization, the real part of the complex magnetic permeability had a constant value.
On the other hand, the dust core published in Non-Patent Document 8 has a value of 280 up to around 5 MHz, gradually decreases above 5 MHz, decreases to a value of 130 near 500 MHz, and overlaps with the imaginary part. It was. The imaginary part increased from around 2 MHz, increased to a value of 130 near 500 MHz, and overlapped with the real part. That is, in the dust core published in Non-Patent Document 8, as described above, many voids are formed, and most of the flat sendust powder is deformed so as to undulate with the flat surface in the vertical direction. There is. Further, the silicone resin, the thickener and the solvent added to the flat sendust powder are adsorbed on the flat sendust powder with an adhesive force according to the concentration of the thickener. After the heat treatment, the silicone resin is cured and the thickener and the solvent are volatilized. Therefore, in the portion where the larger void is formed, when the flat sendust powder is deformed like a swell, a part of the insulator is peeled off from the flat sendust powder, and the flat sendust powders come into direct contact with each other. As a result, an eddy current flows in the gap between the flat sendust powders. As a result, the value of the imaginary part of the complex magnetic permeability of the dust core published in Non-Patent Document 8 was 0.6 times the value of the imaginary part of the complex magnetic permeability of the powder magnetic core in Example 3. Further, the dust core described in Non-Patent Document 8 was deformed so that all the flat sendust powders were undulating, and many voids were formed in the gaps between the flat sendust powders. On the other hand, in the powder magnetic core in Example 3, all the flat sendust powders are aligned in the flat plane direction, which is the axial direction for easy magnetization, so that the actual value of the complex magnetic permeability is published in Non-Patent Document 8. It was 1.4 times the value of the real part of the complex magnetic permeability of the dust core.
Next, as in Example 1, the dust core was dropped from a height of 2 m onto the floor surface, but the dust core was not destroyed. Therefore, the dust core has the required mechanical strength. The reason for this is that a large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Further, in the same manner as in Example 1, the produced dust core was cut in two in the thickness direction, and the cut surface was observed with an electron microscope. Similar to Example 1, flat sendust powder overlapped with each other, and granular aluminum oxide fine particles having a size of 40-60 nm were laminated to evenly fill the gaps where the flat surfaces overlapped with each other. The cut surface is similar to FIG. 1 and is not shown.
Similar to Example 1, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps of the flat sendust powders overlapping the flat surfaces.
As described above, the dust core prepared by using the flat sendust powder has a higher compression density, the insulation resistance is increased, and the eddy current is higher than that of the powder magnetic core prepared by the conventional manufacturing method using the flat sendust powder. The loss was small, the initial magnetic permeability was increased, the holding power of the flat atomized iron powder was not increased, and the required mechanical strength was obtained.

The performance of the dust core in the above three examples was compared with the performance of the dust core prepared by the conventional manufacturing method. The powder magnetic core in the examples is superior to the powder magnetic core produced by the conventional manufacturing method in the following items.
First, the density of the dust core in the examples is higher than the density of the dust core produced by the conventional manufacturing method. The reason for this is that all the flat soft magnetic powders are superposed on each other, narrowing the gaps between the flat soft magnetic powders, and the aluminum oxide fine particles fill the voids of the collection of the flat soft magnetic powders, and further flatten. This is because the aluminum oxide fine particles move when the collection of the soft magnetic powder is compressed, and the degree of accumulation of the flat soft magnetic powder further increases with the movement of the fine particles. As a result, the saturation magnetic flux density of the dust core in the examples becomes higher than the saturation magnetic flux density of the dust core produced by the conventional manufacturing method, and the magnetic energy of the magnetized dust core is large.
Secondly, the magnetic permeability of the dust core in the examples had a value higher than the magnetic permeability of the powder magnetic core prepared by the conventional manufacturing method. The reason for this is that all the flat soft magnetic powders are aligned in the flat plane direction, which is the axial direction for easy magnetization, and the collection of aluminum oxide fine particles having extremely high insulation resistance and fine pores is formed between the flat soft magnetic powders. This is due to the fact that the gap is filled and the eddy current flowing through the gap is reduced. As a result, the dust core in the examples is more likely to be magnetized than the dust core produced by the conventional manufacturing method.
Third, the iron loss of the dust core in the examples is less than the iron loss of the dust core produced by the conventional manufacturing method. The reason for this is that the flat soft magnetic powder is not plastically deformed during the production of the dust core, so that the hysteresis loss of the flat soft magnetic powder does not increase and the eddy current flowing through the gap between the flat soft magnetic powders decreases. It depends on what you did. As a result, the dust core in the examples is less likely to generate heat than the powder core produced by the conventional manufacturing method. That is, the dust core in the examples provided mechanical strength to the dust core by friction-welding an extremely large number of aluminum oxide fine particles to each other. On the other hand, in the powder magnetic core in the conventional manufacturing method, the flat soft magnetic powder is sufficiently plastically deformed, and the plastically deformed flat soft magnetic powder is entangled with each other to give the powder magnetic core mechanical strength. Further, since the powder magnetic core in the conventional manufacturing method insulates the flat soft magnetic powder with an insulator having low heat resistance, the powder magnetic core is magnetically annealed to restore the holding power of the plastically deformed flat soft magnetic powder. I can't.
As described above, in the method for producing a dust core in the present invention, firstly, all soft magnetic powders are used regardless of the hardness of the soft magnetic powders, and secondly, aluminum oxide fine particles having high insulating properties are used. The soft magnetic powder is insulated by the collection of soft magnetic powder, thirdly, the collection of soft magnetic powder is accumulated at high density so that the surfaces overlap each other, and fourth, when the collection of soft magnetic powder is compressed, the aluminum oxide fine particles are separated from each other. This is an epoch-making method for producing a dust core, in which soft magnetic powders are bonded to each other by bonding by frictional heat and bonding of frictional heat between aluminum oxide fine particles.

1 Flat atomized iron powder 2 Fine particles of aluminum oxide

In the present invention, a collection of fine crystals of an aluminum compound that precipitates aluminum oxide by thermal decomposition is precipitated in an organic compound, the organic compound is adhered to the surface of a soft magnetic powder made of a metal or an alloy, and the organic compound is further formed. After vaporization, the aluminum compound is thermally decomposed to precipitate a collection of aluminum oxide fine particles on the surface of the soft magnetic powder. After that, the mold is filled with a collection of soft magnetic powders, and the soft magnetic powders are collected and compressed by a press machine. When the repulsive force received by the press machine continues to increase, the compression by the press machine is stopped. As a result, the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat, and the aluminum oxide fine particles are bonded to each other by frictional heat, so that the soft magnetic powders are bonded to each other and consist of a collection of the soft magnetic powders. This is a method for manufacturing a dust core in which a compression molded body is manufactured in a mold. In this manufacturing method, the compression by the press is stopped immediately before the soft magnetic powder is compressed, so that the soft magnetic powder is not plastically deformed. Therefore, no processing strain is generated in the soft magnetic powder, and an annealing treatment for restoring the holding power of the soft magnetic powder after the formation of the compression molded product becomes unnecessary.

The dust core is made by filling a mold with a collection of soft magnetic powder whose surface has been insulated and compressing it, and then annealing the compression molded product to remove the processing strain of the soft magnetic powder generated during compression. , Restores the holding power of soft magnetic powder and manufactures a dust core. Such a dust core is used as a magnetic core that constitutes a stator and a rotor in a motor, and a magnetic core that constitutes a reactor, a noise filter, a choke coil, and the like in a power supply circuit. All of these electric products are general-purpose products, and it is required that the manufacturing cost of the dust core is low.
The eddy current of the soft magnetic powder whose surface is insulated is confined inside the soft magnetic powder when operating in an alternating magnetic field. That is, the eddy current includes an eddy current flowing in the soft magnetic powder and an eddy current flowing in the gap between the soft magnetic powders, and when the surface of the soft magnetic powder is insulated with an insulator, the insulating property of the insulator is improved. The higher the value, the lower the eddy current of the latter. Since the eddy current loss is proportional to the square of the frequency of the alternating magnetic field, the higher the frequency, the greater the effect of reducing the eddy current loss. This eddy current loss becomes an energy loss during electromagnetic conversion, and the dust core generates heat due to this energy loss. Therefore, by insulating the surface of the soft magnetic powder, the heat generation of the dust core is reduced.
Further, when the soft magnetic powder is compressed, the soft magnetic powder is plastically deformed, and the holding force is increased due to the processing strain of the soft magnetic powder. As a result, the hysteresis loss of the soft magnetic powder increases, and this hysteresis loss becomes an energy loss during electromagnetic conversion, and the dust magnetic core generates heat due to this energy loss. Therefore, the compression molded body is annealed to restore the holding power of the soft magnetic powder, and the heat generation of the dust core made of the compression molded body is reduced. As described above, the energy loss during electromagnetic conversion consists of an eddy current loss and a hysteresis loss, and both are collectively referred to as an iron loss of the dust core. Since the dust core generates heat due to this iron loss, a treatment for insulating the soft magnetic powder and a treatment for annealing the compression molded product are required.
By the way, the larger the magnetic permeability of the soft magnetic powder, the easier it is for the soft magnetic powder to be magnetized, and the more magnetic energy is easily taken into the dust core. Further, the larger the saturation magnetic flux density of the soft magnetic powder, the larger the magnetic energy of the magnetized dust core. However, there is no soft magnetic powder having a large magnetic permeability and a large saturation magnetic flux density, and the relative sizes are compared. On the other hand, most of the dust cores are used at an operating frequency of 1-500 kHz and an operating magnetic flux density of 0.3-1.3 Tesla. Therefore, a dust core suitable for electric appliances is used according to the saturation magnetic flux density in the operating frequency region of the dust core. On the other hand, the performance of the dust core depends on the frequency characteristics of the magnetic permeability of the soft magnetic powder and the saturation magnetic flux density of the soft magnetic powder. A method for producing a dust core that can be used as a raw material is preferable.
For example, a soft magnetic material made of a cobalt-based amorphous material has a large magnetic permeability, but the saturation magnetic flux density has a small value close to that of Mn / Zn-based ferrite. On the other hand, the soft magnetic material made of iron-based amorphous has a high saturation magnetic flux density but a low magnetic permeability. In addition, iron powder has the highest saturation magnetic flux density among soft magnetic materials, but has the lowest magnetic permeability. Further, among the nickel-iron alloys of permalloy, the alloy having a composition of Ni77% by mass, Fe14% by mass, Cu5% by mass, and Mo4% by mass has the highest magnetic permeability among the permalloys, but has a magnetic permeability. The saturated magnetic flux density has an intermediate value of the soft magnetic material. Sendust (an alloy consisting of Fe 9.6% by mass, Si 5.6% by mass, and others made of Al, which is a registered trademark of Tohoku University), which has the highest magnetic permeability among iron, silicone, and aluminum alloys, has a magnetic permeability and saturation. Both the magnetic flux density and the magnetic flux density have intermediate values of the soft magnetic material. The cheapest material, Mn / Zn-based ferrite, has a large magnetic permeability but the lowest saturation magnetic flux density.
In addition to these soft magnetic materials, new materials for thin bands obtained by quenching amorphous alloys are being developed. For example, an amorphous alloy strip in which iron is the main component, silicone and boron are added, and a small amount of copper and niobium are added, and a high-temperature solution having these compositions is rapidly cooled at a rate of 1 million ° C./sec. Has been developed. This amorphous quenching thin band is a material in which both the magnetic permeability and the saturation magnetic flux density are relatively large (see Patent Document 1). Further, a thin band made of an amorphous alloy having a magnetic permeability value close to that of Sendust and a saturation magnetic flux density value close to that of silicon steel has been developed. This material is a material composed of an alloy in which silicon, boron, phosphorus, and copper are added to high-concentration iron (see Patent Document 2).
On the other hand, among the soft magnetic materials, Mn—Zn-based ferrite and Ni—Zn-based ferrite are brittle materials that do not have ductility and malleability and are vulnerable to impact, so a magnetic core is formed from the sintered body. On the other hand, volume resistivity, Mn · Zn ferrites with 1 × 10 ³ Ω · cm, an insulator Ni-Zn ferrite is composed of 1 × 10 ⁶ Ω · cm. Therefore, the eddy current flowing in the sintered body is small. All other soft magnetic materials are conductive metals or alloys, and the eddy current flowing inside the soft magnetic powder is large, insulates the soft magnetic powder, and traps the eddy current inside the soft magnetic powder. Further, the metal or alloy has ductility and malleability, and is elastically deformed and plastically deformed by compressive stress. Therefore, the surface of the soft magnetic powder made of metal or alloy is insulated, and the collection of soft magnetic powder made of metal or alloy whose surface is insulated is compressed in the mold, and the plastically deformed soft magnetic powder is entangled with each other. Provides mechanical strength to the compression die and forms a dust core. The dust core in the present invention uses a soft magnetic powder made of a metal or an alloy in order to compress a collection of soft magnetic powder in a mold.

As described above, in the production of the dust core, a collection of soft magnetic powder whose surface is insulated is filled in a mold, and the collection of soft magnetic powder is simply compressed in the mold to be plastically deformed. A powder magnetic core having a certain mechanical strength is manufactured in a mold by entanglement of magnetic powders. That is, when the collection of soft magnetic powder is simply compressed, the phenomenon that the soft magnetic powder is plastically deformed and the gap is formed by the plastic deformation of the soft magnetic powder, and the soft magnetic powder is rearranged so as to fill the gap. A phenomenon occurs. The rearrangement of the soft magnetic powder is completed with a relatively small compression pressure, but as the compression pressure increases, the plastic deformation of the soft magnetic powder progresses, the voids in the collection of the soft magnetic powder are reduced, and the compression density is increased. This increases the magnetic energy of the magnetized dust core. Further, since the collection of soft magnetic powders has a constant particle size distribution, the soft magnetic powders having different particle sizes are plastically deformed at the same time, and the soft magnetic powders having different plastically deformed particle sizes are adjacent to each other. Is entangled and the soft magnetic powders are entangled with each other, so that the soft magnetic powders are bonded to each other and the mechanical strength of the dust core is realized. Therefore, the dust core is composed of the soft magnetic powder in which the aggregate of the soft magnetic powder is simply compressed and the plastic deformation is advanced. However, as the plastic deformation of the soft magnetic powder progresses, the processing strain of the soft magnetic powder increases, which increases the holding power of the soft magnetic powder and increases the hysteresis loss of the soft magnetic powder. As a result, the dust core generates heat. This hysteresis loss is larger than the eddy current loss in the soft magnetic powder. Therefore, it is necessary to anneal the compression molded product at 500-800 ° C. in a reducing atmosphere to remove the processing strain of the soft magnetic powder and return the holding power of the soft magnetic powder to the original value according to the progress of plastic deformation. There is. On the other hand, the higher the hardness of the soft magnetic powder and the smaller the voids in the gathering of the soft magnetic powder, the larger the compression pressure is required, the processing strain of the soft magnetic powder increases, and the temperature of strain relief annealing increases. .. Therefore, in order to return the holding power of the soft magnetic powder to the original value, it is necessary to insulate the soft magnetic powder with an insulating substance made of an inorganic material having high heat resistance. Therefore, the restoration of the holding power of the soft magnetic powder depends on the heat resistance of the material that insulates the soft magnetic powder. For example, in a powder magnetic core in which soft magnetic powder is insulated with a synthetic resin having low heat resistance, there is almost no effect of restoring the holding power because the heat treatment also serves as resin curing at around 200 ° C.
On the other hand, if the soft magnetic powder is insulated with an inorganic material having high heat resistance and the temperature of the strain removing annealing is raised, the processing cost and the annealing cost for insulating the soft magnetic powder increase. In this way, the strain-removing annealing process greatly affects the performance and manufacturing cost of the dust core. Therefore, if the method for producing a dust core that does not require strain removing and annealing, a powder core with a small hysteresis loss can be produced, and an inexpensive dust core can be produced.
For example, atomized iron powder has a Vickers hardness of 75-87 HV, which is the lowest hardness among soft magnetic powders, and the compression density of the compression molded product is close to 90% of the iron density. The annealing temperature for restoring the holding power is as low as 500-600 ° C. However, the saturation magnetic flux density of atomized iron powder drops sharply at frequencies exceeding 1 kHz.
On the other hand, Sendust (registered trademark of Tohoku University) performs magnetic annealing up to 1100 ° C., which also serves as a treatment for removing impurities, but has a high Vickers hardness of 410-480 HV. On the other hand, the saturation magnetic flux density does not decrease in a relatively low frequency band exceeding 1 kHz like iron powder. However, the annealing temperature for restoring the holding power is as high as 600-700 ° C., and the processing cost for insulating the sendust and the annealing cost increase.
Further, the thin band made of an amorphous alloy has a higher hardness because it is rapidly cooled at a rate of 100,000 to 1,000,000 ° C./sec. For example, the Vickers hardness of the above-mentioned amorphous alloy strip containing iron as a main component and silicone and boron is as high as 720 HV, and the hardness does not decrease significantly even by annealing. Therefore, the annealing temperature at which the holding power is restored is higher than that of Sendust, and the processing cost and annealing cost for insulating the amorphous alloy are further higher than those of Sendust.
Therefore, when the powder magnetic core is manufactured, if the soft magnetic powder is not plastically deformed, processing strain does not occur and strain removal annealing becomes unnecessary. Moreover, the hysteresis loss of the soft magnetic powder does not increase. However, in order to realize the mechanical strength of the compression molded product and to increase the compression density of the compression molded product, means other than the plastic deformation of the soft magnetic powder are required. Therefore, first, it is necessary to advance the arrangement of the soft magnetic powders and create a collection of soft magnetic powders accumulated at high density. Further, if the soft magnetic powder can be coated with an insulator having high insulating properties, the eddy current flowing in the gap between the soft magnetic powders can be reduced. Secondly, when compressing a collection of soft magnetic powders covered with an insulator, the insulators covering the soft magnetic powders are bonded to each other, and when the insulators are bonded to each other, the soft magnetic powders are bonded to each other. A compression molded body can be formed. This eliminates the need to plastically deform the soft magnetic powder. Therefore, regardless of the hardness of the soft magnetic powder, the surface of the soft magnetic powder is insulated with an insulator having high insulating properties, and the collection of the soft magnetic powder is rearranged and accumulated at high density, and the soft magnetic powder is compressed. In this case, if the insulators are joined together and the soft magnetic powders are joined together by joining the insulators, it will be an epoch-making method for manufacturing a powder magnetic core with less iron loss and an inexpensive powder magnetic core. Become.
Therefore, in the new method for producing the dust core, firstly, all the soft magnetic powders are used regardless of the hardness of the soft magnetic powders, and secondly, the soft magnetic powders are insulated with a highly insulating substance. Thirdly, when the collection of soft magnetic powders is accumulated at high density, and fourthly, when the collection of soft magnetic powders is compressed, the insulators are bonded to each other, and when the insulators are bonded to each other, the soft magnetic powders are bonded to each other. This is a method for producing a dust core having these four characteristics. So far, there is no method for producing such an epoch-making powder magnetic core.

Japanese Unexamined Patent Publication No. 2001-300697 Japanese Unexamined Patent Publication No. 2016-094651

Sanyo Special Steel Technical Report, Vol. 7 (2000) No. 1, pages 29-34 Powder and Metallurgy, Vol. 47, No. 7, pp. 711-716 Kawasaki Steel Technical Report, 33 (2001) 4, pages 184-187 Powder and Metallurgy, Vol. 32, No. 7, Pages 9-13 Kobe Steel Technical Report, Vol. 48, No. 3 (1998), pages 25-28 Kobe Steel Technical Report, Vol. 50, No. 3 (2000), page 38 Kobe Steel Technical Report, Vol. 60, No. 2 (2010), page 82 42nd Annual Meeting of the Magnetic Society of Japan (2018), 13aC-3

Here, we will summarize the issues in realizing a new method for manufacturing a dust core.
As described above, firstly, when the soft magnetic powder is insulated with a highly insulating substance, secondly, the collection of the soft magnetic powder is accumulated at a high density, and thirdly, when the collection of the soft magnetic powder is compressed. If the insulators are bonded to each other and the soft magnetic powders are bonded to each other by the bonding between the insulators. Fourth, if the powder magnetic core can be produced using all the soft magnetic powders regardless of the hardness of the soft magnetic powders, Compared to the conventional dust core, firstly, the eddy current loss is smaller, secondly, the saturation magnetic flux density is higher, thirdly, there is no increase in hysteresis loss, and fourthly, the powder that reflects the magnetic characteristics of the soft magnetic powder. Magnetic core can be manufactured. Therefore, the new manufacturing method needs to meet the following four requirements.
The first requirement is to evenly cover the soft magnetic powder with a highly insulating substance.
The second requirement is to rearrange the collection of soft magnetic powders so that the collections of soft magnetic powders have a high accumulation density and the surfaces of the soft magnetic powders overlap each other. That is, an arrangement in which the soft magnetic powder having a relatively small particle size enters the gap between the collections of the soft magnetic powder is advanced, and then the surfaces of the soft magnetic powder are overlapped with each other. Further, the surface of the soft magnetic powder in which the surfaces of the soft magnetic powder overlap each other is covered with an insulating material. Also, the weight of the insulator is made lower than 1% of the weight of the soft magnetic powder. When such a collection of soft magnetic powder having a high accumulation density is compressed, the density of the compact compact becomes close to the density of the soft magnetic powder. As a result, when the dust core is magnetized, the magnetic energy of the magnetized dust core is large. On the other hand, since the surface direction of the soft magnetic powder is the axial direction in which the soft magnetic powder is easily magnetized, when all the soft magnetic powders are superposed on each other, the magnetic permeability of the dust core increases and it becomes easy to be magnetized. As a result, the magnetic energy of the dust core that is easily magnetized is large.
The third requirement relates to the conditions for producing a compression molded article. That is, when an insulatingly coated soft magnetic powder collection is filled in a mold and the soft magnetic powder collection is compressed by a press, first, the insulatingly coated soft magnetic powder collection is formed into a mold shape. Will be done. Secondly, the insulating material covering the soft magnetic powder continuously moves to fill the voids of the gathering of the soft magnetic powder, and the continuous movement of the insulating material also moves the adjacent soft magnetic powder to promote rearrangement and soften. The degree of accumulation of magnetic powder is further increased. Thirdly, when the insulators cannot move, the insulators come into contact with each other, frictional heat is generated at the contact portion, and the insulators are joined by the frictional heat. Further, by joining the insulators to each other, the soft magnetic powders are bonded to each other, and a dust core composed of a collection of the soft magnetic powders is produced in the mold. Fourth, when the insulators come into contact with each other and are bonded by frictional heat, the repulsive force received by the press continuously increases, and at this point, the compression by the press is stopped. As a result, the compression is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed. Therefore, the hysteresis loss of the dust core does not increase.
Fourth, all the soft magnetic powders are used regardless of the hardness of the soft magnetic powders, and the powder magnetic core is produced by satisfying the above three requirements.
The treatment method of soft magnetic powder and the conditions related to the insulator that realize the above four requirements will be examined.
The first condition is to increase the degree of accumulation of the soft magnetic powder. That is, the collection of soft magnetic powders is repeatedly moved in the liquid in three directions of front and back, left and right, and up and down to advance the arrangement of the soft magnetic powders in the liquid and increase the accumulation density of the collections of soft magnetic powders. That is, since the soft magnetic powders do not come into direct contact with each other in the liquid, the soft magnetic powders easily move. Therefore, when the collection of soft magnetic powder is repeatedly moved in the liquid in three directions of front and back, left and right, and up and down, the arrangement is relative to the arrangement in which the soft magnetic powder having a relatively small particle size enters the gap between the collection of soft magnetic powder. The arrangement in which the soft magnetic powder having a small particle size moves above the collection of the soft magnetic powder advances. Finally, when the collection of soft magnetic powders is moved in the vertical direction, the surfaces of the soft magnetic powders overlap each other.
The second condition concerns insulation. The insulator is fine particles having high insulating properties, high heat resistance, higher hardness than the soft magnetic powder, and a size three orders of magnitude smaller than the average particle size of the soft magnetic powder and two orders of magnitude smaller than the thickness of the soft magnetic powder. The weight of the aggregate of fine particles should be less than 1% of the weight of the aggregate of soft magnetic powder. The soft magnetic powder is covered with fine particles having these properties, and the collection of the soft magnetic powder is compressed. When the fine particles receive compressive stress, they move continuously, and the fine particles fill the voids between the soft magnetic powders. Further, when the fine particles continue to move, the adjacent soft magnetic powder moves and rearrangement proceeds, further increasing the degree of accumulation of the soft magnetic powder. Further, when the fine particles cannot move, the fine particles come into contact with each other, frictional heat is generated at the contact portion, and the fine particles are bonded to each other by the frictional heat. The soft magnetic powder is bonded by joining the fine particles to each other, and a dust core composed of a collection of the soft magnetic powder is produced in the mold. On the other hand, when the fine particles come into contact with each other and are bonded by frictional heat, the number of fine particles is extremely large, so that the repulsive force received by the press continuously increases, and at this point, the compression by the press is stopped. As a result, the compression is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed.
That is, the soft magnetic powder is evenly covered with a collection of fine particles having the above-mentioned properties, the collection of the soft magnetic powder is filled in a mold, and the collection of the soft magnetic powder is compressed by a press. At this time, first, a collection of soft magnetic powder covered with a collection of fine particles is formed into a mold shape. Second, the fine particles continuously move to fill the voids in the collection of soft magnetic powders. Third, the soft magnetic powder adjacent to the fine particles also moves and rearranges, increasing the degree of accumulation of the soft magnetic powder. Fourth, when there are no voids through which the fine particles can move, the fine particles come into contact with each other. Since the fine particles have high heat resistance and are hard, the fine particles are not destroyed by contact, excessive frictional heat is generated at the part where the fine particles come into contact with each other, and the contact part is cleaned after the foreign matter or impurities in the contact part are vaporized. The fine particles are firmly bonded to each other by frictional heat. In addition, the fine particles that come into contact with the surface of the soft magnetic powder generate excessive frictional heat at the part that comes into contact with the surface of the soft magnetic powder, and after the foreign matter or impurities in the contact portion are vaporized, the soft magnetic powder is cleaned. Firmly joins the contact part with frictional heat. Fifth, when the reaction in which the fine particles are bonded by frictional heat and the reaction in which the fine particles are bonded to the surface of the soft magnetic powder by frictional heat occur, the number of fine particles is extremely large, so that the repulsive force against the pressurizing pressure is generated. It continues to occur on the press and at this point the compression by the press is stopped. As a result, the pressurizing pressure is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed.
The third condition is to produce a dust core using all soft magnetic powders.
By the way, in the conventional method for producing a dust core, a collection of soft magnetic powders is simply compressed to promote plastic deformation of the soft magnetic powders, whereby the plastically deformed soft magnetic powders are entangled with each other and compressed. The molded body has the necessary mechanical strength. Therefore, if the surfaces of the soft magnetic powders are overlapped with each other to form a collection of soft magnetic powders having a high degree of integration and the collection of soft magnetic powders is compressed, the soft magnetic powders will not be entangled with each other. Therefore, in the conventional method for producing a dust core, it is not necessary to increase the degree of integration of the soft magnetic powder, and the aggregate of the soft magnetic powder is simply compressed. On the other hand, in the new method for producing a dust core, the soft magnetic powders that overlap each other are bonded to each other by joining the fine particles. Since the number of fine particles is extremely large, the dust core has a certain mechanical strength due to the bonding of the fine particles by frictional heat.
Therefore, the above three conditions are reflected in the new powder magnetic core manufacturing method, and the manufactured dust core has higher saturation magnetic flux density and magnetic permeability than the conventional dust core, and less eddy current loss. Ideal if there is no increase in hysteresis loss, the dust core has a certain mechanical strength, an inexpensive powder core can be manufactured, and there are no restrictions on the shape and size of the powder core to be manufactured. This is a method for manufacturing a dust core. Further, if all the soft magnetic powders can be used regardless of the hardness, a powder magnetic core reflecting the magnetic characteristics of the soft magnetic powder can be formed. In particular, since the frequency characteristic of magnetic permeability differs depending on the material of the soft magnetic powder, it is possible to manufacture a dust core that is easily magnetized and easily takes in magnetic energy even in a high frequency band. There are some problems in realizing this ideal manufacturing method, and these problems are the problems to be solved by the present invention. The problems of the present invention will be described below.
The first issue is to use all soft magnetic powders as raw materials, process the collection of soft magnetic powders in a liquid, advance the arrangement of the soft magnetic powders, and make the soft magnetic powders with high accumulation density and overlapping surfaces. Create a gathering in liquid. The second problem is that the fine particles have higher hardness than the soft magnetic powder, excellent insulation, high heat resistance, and the size is 3 orders of magnitude smaller than the average particle size of the soft magnetic powder and 2 orders of magnitude smaller than the thickness of the soft magnetic powder. Is deposited on the surface of the soft magnetic powder. The third task is to compress a collection of soft magnetic powders covered with a collection of fine particles, bond the fine particles in contact with each other by frictional heat, and bond the soft magnetic powders to each other by joining the fine particles. The fourth problem is that the soft magnetic powder does not plastically deform when the collection of the soft magnetic powder is compressed. The fifth problem is a manufacturing method in which simple treatments are continuously carried out in the steps from the treatment of the soft magnetic powder in the liquid to the formation of the dust core. The sixth problem is that there are no restrictions on the shape and size of the dust core. As a result, it has superior performance to the conventional dust core, has mechanical strength similar to that of the conventional dust core, can be manufactured at a lower cost, and has the shape and size of the manufactured dust core. There are no restrictions. An object of the present invention is to realize a method for producing a dust core that simultaneously solves six problems.

The collection of soft magnetic powder covered with a collection of acid aluminum particles and compression method of the soft magnetic powder each other consists of a collection of the soft magnetic powder bound dust core at the junction between the aluminum oxide particles Is
The aluminum compound to deposit fine particles of aluminum oxide by thermal decomposition, the weight of the aluminum oxide particles are precipitated, the aluminum compound is precipitated as less weight than 1/100 of the weight of the collection of soft magnetic powder dispersed in methanol, the The first property of preparing a methanol dispersion of an aluminum compound and dissolving or mixing it in methanol, the second property of having a viscosity higher than that of methanol, and the heat of the aluminum compound having a boiling point higher than that of methanol and having a boiling point higher than that of methanol. An organic compound having a third property lower than the decomposition temperature is mixed with the methanol dispersion to prepare a mixed solution. After that, a mixer equipped with a heating function is placed on the vibration table. The mixer is filled with a collection of the mixed solution and the soft magnetic powder, and the mixer is rotated and rocked to disperse the collection of the soft magnetic powder in the mixed liquid. Vibrations in three directions, left and right and front and back, are repeatedly generated, and finally, vibrations in the vertical direction are generated, and the vibrations caused by the exciter are transmitted to the mixer via the exciter, and the said in the mixer. The collection of the soft magnetic powder is repeatedly moved in the mixed solution in the vibration direction, the arrangement of the soft magnetic powder is advanced in the mixed solution, and finally the vibration in the vertical direction is applied to obtain the soft magnetic powder. The surfaces overlap with each other via the mixed solution, and a collection of the soft magnetic powder having the shape of the bottom surface is formed on the bottom surface of the mixer. After that, the temperature of the mixer is raised to the boiling point of methanol. As a result, a collection of fine crystals of the aluminum compound was precipitated all at once in the organic compound, the organic compound in which the fine crystals of the aluminum compound were precipitated adhered to the soft magnetic powder, and the fine crystals of the aluminum compound were precipitated. In the first step, a collection of soft magnetic powders in which the surfaces of the soft magnetic powders are overlapped with each other via an organic compound is formed on the bottom surface of the mixer as the shape of the bottom surface.
Filling the collection of soft magnetic powder that was created in the previous SL first step in a mold, the aluminum compound mold is heated to thermally decompose the temperature, whereby, first, the organic compound is vaporized Next, the fine crystals of the aluminum compound are thermally decomposed, and a collection of aluminum oxide fine particles is deposited all at once on the surface of the soft magnetic powder, and the collection of the aluminum oxide fine particles covers the soft magnetic powder. A continuously increasing pressurizing pressure is applied by the press machine to the collection of the soft magnetic powder, and when the repulsive force received by the press machine continuously increases, the pressurizing pressure by the press machine is stopped. First, the aggregate of the soft magnetic powder is formed into the shape of the mold, and then the aluminum oxide fine particles continuously move to fill the voids in the aggregate of the soft magnetic powder, and the aluminum oxide fine particles are formed. When the aluminum oxide fine particles that come into contact with the surface of the soft magnetic powder cannot move, the aluminum oxide fine particles that come into contact with the surface of the soft magnetic powder are bonded to the surface of the soft magnetic powder by frictional heat, and the aluminum oxide fine particles that come into contact with each other are brought into contact with each other by frictional heat. This is a second step in which the soft magnetic powders are bonded to each other by joining the aluminum oxide fine particles to each other, and a dust core composed of a collection of the bonded soft magnetic powders is produced in the mold. ,
The two steps by carrying out successively, the dust core formed of a collection of the soft magnetic powder soft magnetic powders to each other is coupled at a junction between the acid aluminum particles are manufacturing, the dust core Production method.

In the present invention, vibrations in three directions are repeatedly applied to a collection of soft magnetic powders in a liquid, and finally, vibrations in a vertical direction are applied to advance the arrangement of the soft magnetic powders in the liquid, and then the soft magnetic powders. Overlay the faces. Next, a collection of granular aluminum oxide fine particles having a size of 40-60 nm, which is three orders of magnitude smaller than the average particle size of the soft magnetic powder and two orders of magnitude smaller than the thickness of the soft magnetic powder, is deposited on the surface of the soft magnetic powder. .. Further, the mold is filled with the aggregate of soft magnetic powder, the aggregate of soft magnetic powder is compressed by the press, and when the repulsive force received by the press continues to increase, the compression by the press is stopped. As a result, the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat, the soft magnetic powder is insulated, and the aluminum oxide fine particles are bonded to each other by frictional heat, whereby the soft magnetic powders are bonded to each other. Then, a dust core composed of a collection of the soft magnetic powders is produced in the mold. The dust core has the necessary mechanical strength because an extremely large number of aluminum oxide fine particles are firmly bonded to each other by frictional heat. Further, when the repulsive force received by the press machine is continuously increased, the compression by the press machine is stopped, so that the compression of the soft magnetic powder is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is plastic. Does not deform. Therefore, the strain removing and annealing treatment of the dust core manufactured in the mold becomes unnecessary. Further, since the soft magnetic powder is not plastically deformed, all the soft magnetic powders can be used as raw materials for the dust core regardless of the hardness of the soft magnetic powders.
By the way, the aluminum oxide Al ₂ O ₃ covering the surface of the soft magnetic powder brings the following excellent properties to the dust core. First, aluminum oxide is an excellent insulator, ^{with a large volume resistivity of 10 15} Ω · cm, a high breakdown voltage of 15 kV / mm, and no frequency dependence of insulation. Therefore, the eddy current loss of the dust core is small even in the high frequency region. Secondly, the melting point of aluminum oxide is as high as 2072 ° C., the heat resistance is superior to that of soft magnetic powder, and the heat resistance is superior to that of conventional dust core. In addition, excessive frictional heat is generated at a portion where the fine particles come into contact with each other, and the frictional heat causes the fine particles to join each other. Thirdly, aluminum oxide has a large Mohs hardness of 9, which is the second hardest substance after diamond, and is harder than all soft magnetic powders, and all soft magnetic powders can be used for dust cores. Further, when the aluminum oxide fine particles are stressed, they continuously move so as to fill the voids. When there are no movable voids, the fine particles come into contact with each other and frictional stress is generated at the contact portion, but the fine particles are not destroyed. Fourth, aluminum oxide is less susceptible to acids and alkalis, has better chemical resistance than soft magnetic powder, and has better chemical resistance than conventional dust cores. The density of aluminum oxide is 3.95 g / cm ³ , which is half the density of iron.
Here, a manufacturing method for manufacturing the dust core of the present invention will be described. The manufacturing method for manufacturing the dust core comprises the following seven steps.
An aluminum compound having these three properties, which is inexpensive as a raw material, precipitates aluminum oxide by a simple treatment of thermal decomposition, and has a low thermal decomposition temperature of about 300 ° C., was used as a raw material for aluminum oxide. On the other hand, in order to cover the soft magnetic powder with a collection of aluminum oxide fine particles, the first step is to disperse the aluminum compound in methanol and liquid-phase the aluminum compound.
In order to cover the soft magnetic powder with a collection of aluminum oxide fine particles, it is necessary to attach a methanol dispersion of an aluminum compound to the surface of the soft magnetic powder. Therefore, in the second step, the first property of dissolving or mixing in methanol, the second property of having a viscosity higher than that of methanol, the boiling point of which is higher than the boiling point of methanol, and the thermal decomposition temperature of the aluminum compound. An organic compound having a lower third property is mixed with a methanol dispersion to prepare a mixed solution.
In the third step, the mixture and the collection of soft magnetic powder are filled in a mixer arranged on a vibration table, and the mixer is rotated and rocked, and the aluminum compound is mixed with methanol and an organic compound. The mixture is uniformly dispersed in the mixture of the above, and a mixture in which the soft magnetic powder is uniformly dispersed in this mixture is prepared. Therefore, the mixture adheres to the soft magnetic powder due to the viscosity of the mixture.
In the fourth step, the vibration generated by the exciter is transmitted to the mixer via the exciter, and the entire mixture is vibrated. At this time, the soft magnetic powder is a powder having a constant aspect ratio, which is the ratio of the area to the thickness, and the density of the soft magnetic powder is close to 10 times the density of the mixed liquid, so that the soft magnetic powder is a surface. Moves upward in the mixture in the vibration direction. Further, since the soft magnetic powder having a relatively small particle size has a smaller mass, the soft magnetic powder having a smaller particle size has a larger amount of movement in the mixed solution. Therefore, when vibrations in three directions of front-back, left-right, and up-down are repeatedly applied to the entire mixture, the soft magnetic powder repeatedly moves in the three directions in the mixture. At this time, for the soft magnetic powder having a relatively small particle size, the arrangement that enters the voids of the soft magnetic powder collection and the arrangement that moves above the soft magnetic powder collection progress, and the degree of accumulation of the soft magnetic powder collection Will increase. Finally, when vibration in the vertical direction is applied, the soft magnetic powders are overlapped with each other via the mixed liquid with the surface facing upward. As a result, a collection of soft magnetic powders having a high degree of integration in which the surfaces of the soft magnetic powders overlap each other is formed on the bottom surface of the mixer as the shape of the bottom surface. The vibration acceleration applied to the mixture depends on the amount of soft magnetic powder to be filled, but since the viscosity of the mixed solution is low and the density of the soft magnetic powder is as high as 10 times the density of the mixed solution, it is 0.2-0. It is about 4G. This solves the first problem described in paragraph 6.
The fifth step raises the temperature of the mixer to the boiling point of methanol. At this time, the fine crystals of the aluminum compound are precipitated all at once in the organic compound, the organic compound in which the fine crystals of the aluminum compound are precipitated adheres to the soft magnetic powder, and the fine crystals of the aluminum compound are precipitated through the organic compound. A collection of soft magnetic powders in which the surfaces of the soft magnetic powders overlap each other is formed on the bottom surface of the mixer as the shape of the bottom surface. The vaporized methanol is recovered by a recovery machine and reused.
In the sixth step, a collection of soft magnetic powders is transferred from the mixer to a mold, and the temperature of the mold is raised to a temperature at which the aluminum compound is thermally decomposed. At this time, the organic compound is first vaporized, then the fine crystals of the aluminum compound are thermally decomposed, and a collection of aluminum oxide fine particles is deposited all at once on the surface of the soft magnetic powder. Is covered. The aluminum oxide precipitated by the thermal decomposition of the aluminum compound is granular fine particles having a size of 40-60 nm, which is 3 orders of magnitude smaller than the average particle size of the soft magnetic powder and 2 orders of magnitude smaller than the thickness of the soft magnetic powder. This solves the second problem described in paragraph 6. The vaporized organic compound is recovered and reused.
In the seventh step, the pressurizing pressure continuously increased by the press is applied to the collection of soft magnetic powder, and the compression is stopped when the repulsive force received by the press continues to increase. That is, when the pressurizing pressure is applied to the soft magnetic powder, the aluminum oxide fine particles are not bonded to each other, and the aluminum oxide fine particles are not bonded to the soft magnetic powder. It is molded into the shape of a mold. After that, when the pressurizing pressure increases, voids are present in the collection of the soft magnetic powder, so that the aluminum oxide fine particles continuously move so as to fill the voids. Further, with the continuous movement of the aluminum oxide fine particles, the adjacent soft magnetic powder also moves, and the degree of accumulation of the soft magnetic powder is further increased. Further, when the pressurizing pressure is increased, there are no voids through which the aluminum oxide fine particles can move, the aluminum oxide fine particles come into contact with each other, excessive frictional heat is generated at the contact portion, and the aluminum oxide fine particles are joined by the frictional heat. At this time, since aluminum oxide is hard and has a high melting point, the fine particles are not destroyed even by friction between the fine particles. By joining the aluminum oxide fine particles to each other, the soft magnetic powders are bonded to each other. Similarly, when the aluminum oxide fine particles that come into contact with the surface of the soft magnetic powder cannot move, excessive frictional heat is generated at the contact portion, and the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by the frictional heat. As a result, a dust core in which the soft magnetic powders are bonded to each other through the bonding of the aluminum oxide fine particles is produced in the mold. On the other hand, when the reaction in which the aluminum oxide fine particles are bonded to each other by frictional heat and the reaction in which the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat occur, the number of aluminum oxide fine particles is extremely large. A larger pressurizing pressure is required to cause the reaction, and the repulsive force received by the press machine continues to increase. At this point, that is, immediately after the bonding of the aluminum oxide fine particles due to frictional heat occurs, the compression by the press is stopped. Therefore, the pressurizing pressure is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed. This solves the third and fourth issues described in paragraph 6. Further, there are no restrictions on the size and shape of the mold for filling the collection of soft magnetic powder. This solves the sixth problem described in paragraph 6.
The method for producing a dust core, which comprises the seven steps described above, is a method in which simple treatments are continuously performed. This solves the fifth problem described in paragraph 6. As a result, all the problems to be solved by the present invention described in paragraph 6 have been solved.
The dust core produced by the above-mentioned production method has the following effects.
First, since the filling rate of the soft magnetic powder in the dust core is high, the saturation magnetic flux density of the powder magnetic core approaches the saturation magnetic flux density of the soft magnetic powder. Therefore, the magnetic energy of the magnetized dust core is large. That is, the arrangement of the soft magnetic powder was advanced, and a collection of soft magnetic powder having a high degree of integration was formed in the mixer in which the surfaces of the soft magnetic powder were overlapped with each other via the mixed liquid. Further, the soft magnetic powder covered with the aluminum oxide fine particles was formed into a collection of soft magnetic powder having a high degree of integration in which the surfaces of the soft magnetic powder overlap each other. When this collection of soft magnetic powder is compressed by a press machine, the compression density of the compression molded product approaches the density of the soft magnetic powder. That is, when the soft magnetic powder collection is compressed by the press machine, the soft magnetic powder collection is first formed into the shape of a mold, and then the aluminum oxide fine particles continuously move to form the soft magnetic powder collection. When the voids are filled and the aluminum oxide fine particles continue to move, the adjacent soft magnetic powder also moves, the soft magnetic powder rearranges, and the degree of accumulation of the soft magnetic powder aggregate increases. Further, when the aluminum oxide fine particles cannot move, the aluminum oxide fine particles come into contact with each other, the aluminum oxide fine particles are bonded to each other by frictional heat, and the soft magnetic powders are bonded to each other by bonding the aluminum oxide fine particles to each other. Further, the weight of the aluminum oxide fine particles is less than 1% of the weight of the aggregate of soft magnetic powder. As a result, the compression density of the compression molded product approaches the density of the soft magnetic powder. Therefore, the saturation magnetic flux density of the dust core approaches the saturation magnetic flux density of the soft magnetic powder. Further, since the aggregate of the soft magnetic powder is mixed with the dispersion liquid in which the aluminum compound is dispersed in the mixed liquid of methanol and the organic compound, there are no restrictions on the shape, size, and particle size distribution of the soft magnetic powder used as a raw material.
Secondly, the strain removing and annealing treatment becomes unnecessary. Therefore, the holding force of the soft magnetic powder constituting the dust core does not change, and the hysteresis loss in the dust core does not increase. Further, since the soft magnetic powder is not plastically deformed, all the soft magnetic powders can be used as raw materials regardless of the hardness. That is, the higher the hardness of the soft magnetic powder, the higher the pressurizing pressure for forming the compression molded product. As a result, the plastic deformation of the soft magnetic powder progresses, the strain of the soft magnetic powder increases, the annealing temperature of the compression molded body rises, and it becomes difficult to restore the holding power of the soft magnetic powder. Alternatively, the annealing cost increases. Therefore, the effect of eliminating the need for strain removing and annealing treatment is great. That is, when the aluminum oxide fine particles cannot move when the collection of the soft magnetic powder is compressed, the aluminum oxide fine particles come into contact with each other, and the aluminum oxide fine particles are bonded to each other by frictional heat. Further, the aluminum oxide fine particles come into contact with the surface of the soft magnetic powder, and a reaction occurs in which the aluminum oxide fine particles are bonded to the surface of the soft magnetic powder by frictional heat. When this friction reaction occurs, the number of aluminum oxide fine particles is extremely large, so that the repulsive force received by the press continuously increases, and at this point, that is, immediately after the friction reaction occurs, compression by the press machine occurs. To stop. Therefore, just before the soft magnetic powder is compressed, the pressurizing pressure on the soft magnetic powder is stopped, the soft magnetic powder does not undergo plastic deformation, and the holding power of the soft magnetic powder does not increase. Further, since the soft magnetic powder is not plastically deformed, all the soft magnetic powders can be used as raw materials for the dust core regardless of the hardness of the soft magnetic powders. As a result, the strain removing and annealing treatment becomes unnecessary, and the manufacturing cost of the dust core can be reduced.
That is, in the conventional method for producing a dust core, an excessive pressure is applied to the soft magnetic powder, the soft magnetic powder having high hardness is sufficiently plastically deformed, and the voids of the collection of the soft magnetic powder are plastically deformed. While filling with powder, plastically deformed soft magnetic powders are entangled with each other. As a result, the compression density of the compression molded product approached the density of the soft magnetic powder, and the mechanical strength required for the compression molded product was generated. On the other hand, in the present production method, the fine particles of aluminum oxide fill the voids of the collection of soft magnetic powder having a high accumulation density, and the aluminum oxide fine particles are bonded to each other by frictional heat, and the aluminum oxide fine particles are bonded to each other. The soft magnetic powders were bonded to each other. Therefore, it is not necessary to plastically deform the soft magnetic powder.
Third, the soft magnetic powder is insulated by an insulator having a larger insulation resistance than the conventional dust core, and the eddy current loss is smaller than that of the conventional dust core. That is, the aluminum oxide precipitated by the thermal decomposition of the aluminum compound is granular fine particles having a size of 40 to 60 nm, and the aggregates of the granular fine particles are laminated to insulate the soft magnetic powder. Since the aluminum oxide fine particles are granular, the volume is smaller than that of the aluminum oxide fine particles, but there are many pores adjacent to the aluminum oxide fine particles, which are close to the number of the aluminum oxide fine particles. These pores are occupied by air exceeding ^{10 17} Ω · cm, which has a volume resistivity two orders of magnitude higher than that of aluminum oxide. Therefore, the insulating resistance formed by the aggregate of the laminated aluminum oxide fine particles is such that the resistor made of aluminum oxide fine particles and the resistor made of air are connected in series to form an insulating resistance. Furthermore, the number of aluminum oxide fine particles and pores is extremely large. Therefore, the insulation resistance for insulating the soft magnetic powder is three orders of magnitude higher than the insulation resistance formed by ^{the bulk aluminum oxide based on the volume resistivity of 10 15 Ω · cm.} As a result, the soft magnetic powder, a volume resistivity than the powder magnetic core obtained by insulated with a polymeric material consisting of 10 ¹⁴ -10 ¹⁵ Ω · cm, insulation increases 3 orders of magnitude. In addition, the frequency dependence of the insulation resistance of both aluminum oxide and air is small. Therefore, the eddy current loss of the dust core is extremely small even in the high frequency region. This increases the imaginary part of the complex magnetic permeability of the dust core.
Fourth, all the soft magnetic powders are aligned in the plane direction, and the soft magnetic powders are overlapped and bonded to each other through a collection of aluminum oxide fine particles. The plane direction of the soft magnetic powder is the axial direction in which the soft magnetic powder is easily magnetized, and the dust core in which all the soft magnetic powders are aligned in the plane direction is easily magnetized and the magnetic permeability increases. Therefore, the dust core is easily magnetized and easily takes in magnetic energy.
Fifth, the soft magnetic powder is insulated by an inexpensive means. That is, the raw material of aluminum oxide is an inexpensive aluminum compound, and the organic compound is also a general-purpose industrial chemical. Further, since aluminum oxide fine particles are produced by thermal decomposition at a temperature of about 300 ° C. in the air atmosphere, the soft magnetic powder is insulated by using an inexpensive raw material and at an inexpensive processing cost.
Sixth, the manufacturing method for manufacturing the dust core is a manufacturing method in which a simple process consisting of seven steps is continuously carried out as described above. In addition, strain removal annealing is not required. As a result, the dust core can be manufactured at a low manufacturing cost.
Seventh, there are no restrictions on the shape and size of the dust core to be manufactured. That is, since there are no restrictions on the size and shape of the mold for filling the collection of soft magnetic powder, there are no restrictions on the shape and size of the dust core.
Eighth, a dust core having a mechanical strength close to that of a conventional dust core is manufactured. That is, aluminum oxide fine particles are frictionally bonded to all surfaces of the soft magnetic powder, and all the aluminum oxide fine particles that are in contact are frictionally bonded to each other. Since the amount is extremely large, mechanical strength close to that of macro-bonding due to plastic deformation of conventional soft magnetic powder can be obtained. That is, frictional heat is generated when an extremely large number of aluminum oxide fine particles bite into the surface of the soft magnetic powder, all foreign substances existing at the contact portion between the two are vaporized, and after the contact portion is cleaned, the aluminum oxide fine particles are generated. It is firmly bonded to the surface of soft magnetic powder by frictional heat. Further, when an extremely large number of aluminum oxide fine particles come into contact with each other, frictional heat is generated in the contact portion, all foreign substances existing in the contact portion are vaporized, and after the contact portion is cleaned, the aluminum oxide fine particles are in frictional heat. Firmly join with. Therefore, it is not necessary to plastically deform the soft magnetic powder.
As described above, according to the present manufacturing method, the saturation magnetic flux density, the insulating property, and the magnetic permeability are increased, the eddy current loss is small, and the hysteresis loss is not increased as compared with the conventional dust core. Can be manufactured. As a result, the powder magnetic core has superior performance to the conventional powder magnetic core, and the powder magnetic core can be manufactured at a lower cost than the conventional powder magnetic core.

In the manufacturing method of the pressure powder magnetic core according to paragraph 7, the soft magnetic powder as described in paragraph 7 is a soft magnetic flat powder consisting of flat shape, the aluminum compound described in 7 paragraph, aluminum benzoate or naphthenate aluminum and organic compounds described 7 paragraph, carboxylic acid vinyl esters, acrylic acid esters, methacrylic acid esters or one of esters composed of, or, glycols, or glycol ethers 1 the type of the organic compound, or a liquid monomer consisting of styrene monomer, using these materials to produce a dust core according to the manufacturing method of the pressure powder magnetic core according to paragraph 7, the manufacturing method of the pressure powder magnetic core.

That is, in the method for producing a dust core described in paragraph 7, a flat powder having a flat shape is used as the soft magnetic powder, vibrations in three directions are repeatedly applied to the collection of the flat powder in the mixed solution, and finally, in the vertical direction. Add vibration. At this time, regardless of the hardness of the flat powder, the flat powder moves in three directions in the mixed solution with the flat surface facing up, and the flat powder having a relatively small particle size has the flat surface facing up. The arrangement that enters the voids of the collection and the arrangement that moves above the collection of flat powders advance, and then the flat surfaces of the flat powders overlap each other. As a result, a collection of flat powder having a high degree of accumulation and a small volume of voids is formed on the bottom surface of the mixer as the shape of the bottom surface. Since the gap between the overlapping flat surfaces of the soft magnetic powder is narrower than that of the non-flat powder, the degree of accumulation of the flat powder is increased regardless of the hardness of the soft magnetic powder. After that, a collection of aluminum oxide fine particles is deposited in the gaps between the flat surfaces, and when a pressure is applied, the aluminum oxide fine particles continuously move to fill the narrow gaps between the overlapping flat surfaces, and aluminum oxide. When the fine particles cannot move, the aluminum oxide fine particles are bonded to each other by frictional heat, and a dust core is manufactured in the mold. Further, the weight of the aluminum oxide fine particles is less than 1% of the weight of the aggregate of soft magnetic powders. Therefore, the density of the dust core approaches the density of the soft magnetic powder, and the saturation magnetic flux density of the powder magnetic core approaches the saturation magnetic flux density of the soft magnetic powder.
On the other hand, when the soft magnetic powder is flattened in the plane direction, which is the axial direction for easy magnetization, the demagnetizing field coefficient becomes small, and the larger the flatness, the higher the magnetic permeability of the flat powder. Therefore, when the dust core is manufactured using the flat powder, all the flat powders overlap each other and are bonded together in the flat plane direction, which is the axial direction for easy magnetization, so that the dust core is easily magnetized. Become. As a result, the magnetic permeability is increased, and a dust core having a saturation magnetic flux density close to the saturation magnetic flux density of the flat powder is formed in the mold. This dust core is easily magnetized regardless of the hardness of the soft magnetic powder, and the captured magnetic energy is large. The flattening treatment of the soft magnetic powder does not depend on the long-time batch processing by the ball mill, but by the attritor treatment by the media stirring type mill, the flattening powder can be continuously obtained in a short time and manufactured at low cost. Will be done. On the other hand, the processing strain generated by the flattening process is eliminated by magnetic annealing.
Next, a carboxylic acid metal compound that precipitates a metal oxide by thermal decomposition will be described. Among the carboxylic acid metal compounds, there is a carboxylic acid metal compound in which an oxygen ion constituting a carboxyl group serves as a ligand and approaches a metal ion to coordinate bond. In this metal carboxylate compound, the metal ion, which is the largest ion, approaches the oxygen ion and is coordinated, so that the distance between the two is shortened. As a result, the oxygen ion coordinate-bonded to the metal ion has the longest distance from the ion covalently bonded on the opposite side of the metal ion. When the carboxylic acid metal compound having such molecular structural characteristics exceeds the boiling point of the carboxylic acid constituting the carboxylic acid metal compound, the oxygen ion constituting the carboxyl group is covalently bonded to the ion on the opposite side of the metal ion. The bond is first split and decomposed into metal oxides and carboxylic acids. When the temperature is further raised, the carboxylic acid takes away the heat of vaporization and vaporizes, and after the vaporization of the carboxylic acid is completed, the metal oxide precipitates. Among these metal carboxylic acid compounds, as metal carboxylic acid compounds whose thermal decomposition is completed at a relatively low temperature of about 300 ° C., metal acetate compounds, metal caprylate compounds, and metal benzoate compounds are arranged in ascending order of boiling point of carboxylic acid. , There are metal naphthenate compounds. Therefore, the metal acetate compound, the metal caprylic acid compound, the metal benzoate compound, and the metal naphthenate compound are metal compounds that precipitate metal oxides by thermal decomposition at a relatively low temperature.
On the other hand, in the carboxylic acid metal compound in which the carboxylate anion is covalently bonded to the metal ion, the bond portion between the oxygen ion and the metal ion is the longest among the bonds between the ions, so that the metal is precipitated by thermal decomposition.
In the aluminum carboxylate compound that precipitates aluminum oxide by thermal decomposition, aluminum acetate and aluminum caprylate precipitate amorphous alumina by thermal decomposition. Therefore, aluminum benzoate and aluminum naphthenate exist as raw materials for precipitating aluminum oxide by thermal decomposition. The boiling point of benzoic acid is 249 ° C., and aluminum benzoate is thermally decomposed at 310 ° C. in the air atmosphere to precipitate aluminum oxide. Further, the thermal decomposition is completed at 340 ° C., which is higher than the thermal decomposition temperature of aluminum naphthenate, and aluminum oxide is precipitated. Therefore, in the method for producing a dust core described in paragraph 7, aluminum benzoate or aluminum naphthenate is used as the aluminum compound. In the thermal decomposition of the aluminum carboxylate compound, the temperature at which the thermal decomposition is completed is 50-60 ° C. lower in the atmospheric atmosphere than in the nitrogen atmosphere. Therefore, the heat treatment in the atmospheric atmosphere requires less heat treatment cost.
Next, an organic compound having the first property of being dissolved or miscible in methanol, the second property having a viscosity higher than that of methanol, and the third property having a boiling point higher than 65 ° C. and lower than 340 ° C. Used as the organic compound described in the paragraph.
As such an organic compound, any one kind of ester consisting of carboxylic acid vinyl esters, acrylic acid esters, and methacrylic acid esters , or any one kind of organic compound of glycols and glycol ethers, or , There is a liquid monomer composed of styrene monomer. Therefore, in the method for producing a dust core described in paragraph 7, any of these organic compounds is used as the organic compound.
Therefore, soft magnetic flat powder is used as the soft magnetic powder described in paragraph 7, aluminum benzoate or aluminum naphthenate is used as the aluminum compound described in paragraph 7, and vinyl carboxylic acid ester is used as the organic compound described in paragraph 7. , Acrylic acid esters, any one kind of esters consisting of methacrylic acid esters, or any one kind of organic compound of glycols, glycol ethers, or liquid monomer made of styrene monomer, 7 When the dust core is manufactured according to the manufacturing method described in the paragraph, the dust core that is easily magnetized and has a large amount of captured magnetic energy is manufactured in the mold.

It is explanatory drawing which shows schematicly by enlarging a part of the cut surface of a dust core.

Embodiment 1
The present embodiment relates to an organic compound in the method for producing a dust core described in paragraph 7, and the organic compound has a first property of being soluble or mixed in methanol and a second property of having a viscosity higher than that of methanol. It also has a third property that the boiling point is higher than the boiling point of methanol, 65 ° C, and lower than 340 ° C.
As such an organic compound, one kind of organic compound belonging to any one of carboxylic acid vinyl esters, acrylic acid esters, methacrylic acid esters, glycols, glycol ethers, or styrene. There are liquid monomers composed of monomers.
Carboxylic acid vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pipariate, and octyl. It is a vinyl carboxylate composed of vinyl acetate, vinyl monochloroacetate, vinyl adipate, vinyl crotonate, vinyl benzoate and the like.
For example, vinyl acetate is a low boiling point carboxylic acid vinyl ester, the chemical formula is _{shown by CH 3} COO-CH = CH ₂ , it dissolves in methanol, has a higher viscosity than methanol, and has a boiling point of 72.7 ° C. .. Vinyl acetate is an ester obtained by reacting acetic acid with vinyl alcohol, and is an inexpensive organic compound used as a raw material for the synthesis of polyvinyl acetate. Since vinyl acetate is easily polymerized by light or heat, a small amount of a polymerization inhibitor (also referred to as a polymerization inhibitor) is added.
Further, monochloroacetic acid vinyl acetate has a chemical formula of Cl-CH ₂ COO-CH = CH ₂ , is soluble in methanol, and has a boiling point of 136 ° C. Monochlorovinyl acetate is an inexpensive organic compound used as a cross-linking site for acrylic rubber.
The acrylic acid esters are acrylic acid esters composed of methyl acrylate, ethyl acrylate, butyl acrylate, diethylhexyl acrylate and the like.
For example, acrylates having a low boiling point include methyl acrylate, the chemical formula of which is represented by CH ₂ = CH-COOCH ₃ , which is dissolved in methanol and has a boiling point of 80 ° C. Methyl acrylate is an inexpensive organic compound used as a raw material for acrylic resins. Since methyl acrylate is a substance that easily polymerizes, a small amount of stabilizer is added.
Furthermore, butyl acrylate has a chemical formula of CH ₂ = CH-COOC ₄ H ₉ , is soluble in methanol, and has a boiling point of 148 ° C. Butyl acrylate is an ester obtained by reacting acrylic acid with n-butanol, and is an inexpensive organic compound used as a raw material for fiber treatment agents, adhesives, paints, synthetic resins, acrylic rubbers, and emulsions. Methyl acrylate is a substance that easily polymerizes, and a small amount of stabilizer is added.
The methacrylic acid esters are methacrylic acid esters composed of ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, alkyl methacrylate, tridecyl methacrylate, stearyl methacrylate and the like. ..
For example, ethyl methacrylate is one of the methacrylic acid esters having a low boiling point, the chemical formula is represented by H ₂ C = C (CH ₃ ) COOC ₂ H ₅ , and it is dissolved in methanol and has a boiling point of 117 ° C. Ethyl methacrylate is an inexpensive organic compound used as a raw material for pigments, paints, adhesives, fiber treatment agents, molding materials, and dental materials. In addition, ethyl methacrylate is a substance that is easily polymerized, and a trace amount of stabilizer is added.
Further, n-butyl methacrylate has a chemical formula of CH ₂ C (CH ₃ ) COO (CH ₂ ) ₃ CH ₃ and is dissolved in methanol and has a boiling point of 163.5 ° C. N-Butyl methacrylate is an inexpensive organic compound used as a raw material for paints, dispersants, and fiber treatment agents. Since n-butyl methacrylate is easily polymerized by light or heat, a small amount of polymerization inhibitor is added.
In addition, glycols are a kind of alcohol, and are compounds having a structure in which one hydroxy group is substituted for each of two carbon atoms of a chain aliphatic hydrocarbon. Ethylene glycol is one of the glycols having a low boiling point, and its chemical formula is represented by C ₂ H ₄ (OH) ₂ , which is miscible with methanol and has a boiling point of 197.3 ° C. Ethylene glycol is an inexpensive organic compound widely used as a solvent, antifreeze, synthetic raw material and the like.
Further, diethylene glycol having a chemical formula of O (CH ₂ CH ₂ OH) ₂ is miscible with methanol and has a boiling point of 244.3 ° C. In addition to antifreeze, diethylene glycol is an inexpensive organic compound used in brake fluids, lubricants, inks, fabric softeners, fabric softeners, cork plasticizers, adhesives, paper, packaging materials, paints, etc. is there.
Propylene glycol having a chemical formula of CH ₃ CHOHCH ₂ OH is miscible with methanol and has a boiling point of 188.2 ° C. Propylene glycol is used as a moisturizer, lubricant, emulsifier, antifreeze, intermediate material for plastics, solvent, etc., and also has excellent moisturizing and antifungal properties, so it improves the quality of pharmaceuticals, cosmetics, noodles, rice balls, etc. It is an inexpensive organic compound used in a wide range such as agents.
Further, dipropylene glycol has a chemical formula of [CH ₃ CH (OH) CH ₂ ] ₂ O, is miscible with methanol, and has a boiling point of 232.2 ° C. Dipropylene glycol is an inexpensive organic compound used as an intermediate raw material for polyester resins, hydraulic oils for hydraulic equipment, antifreeze liquids, raw materials for printing inks, and the like.
Further, tripropylene glycol has a chemical formula of [CH ₃ CH (OH) CH ₂ ] ₂ O, is miscible with methanol, and has a boiling point of 265 ° C. Tripropylene glycol is used as a raw material for lubricating oils and cutting oils, raw materials for polyurethane / acrylic ester intermediates, paint / ink solvents, antifreezes, feed additives, intermediate raw materials for polyester resins, solvents for water-soluble oils, etc. It is an inexpensive organic compound.
Further, glycol ethers have both an ether group and a hydroxyl group in one molecule, and are water, many organic solvents, and a solvent having high resin solubility, and most glycol ethers are dissolved in methanol. There are the following three types of glycol ethers. Ethylene glycol-based ether and propylene glycol-based ether are inexpensive materials used in paints, inks, dyes, photocopying liquids, cleaning agents, electrolytes, soluble oils, hydraulic oils, brake liquids, refrigerants, antifreeze agents, etc. Organic compound. Further, the dialkyl glycol is an inexpensive organic compound used in a reaction solvent, a separation extractant, a polymerization solvent, a decomposition prevention and stabilizer, an electrolytic solution of a battery or a capacitor, and the like.
For example, ethylene glycol-based ether having a low boiling point includes ethylene glycol monomethyl ether, which has a chemical formula of CH ₃ O- (CH ₂ CH ₂ O) -H, is dissolved in methanol, and has a boiling point of 124.5 ° C. .. Ethylene glycol monoisopropyl ether has a chemical formula of (CH ₃ ) ₂ CHO- (CH ₂ CH ₂ O) -H, is dissolved in methanol, and has a boiling point of 141.8 ° C.
Further, among ethylene glycol-based ethers having a high boiling point, there is triethylene glycol monobutyl ether, the chemical formula of which is C ₄ H ₉ O- (CH ₂ CH ₂ O) _3- H, which is dissolved in methanol and has a boiling point of 271. It is 2 ° C. The chemical formula of diethylene glycol mono2-ethylhexyl ether is represented by C ₂ H _5- C ₄ H ₉ CHCH ₂ O- (CH ₂ CH ₂ O) _2- H, which is dissolved in methanol and has a boiling point of 272 ° C. ..
Further, propylene glycol monomethyl ether having a low boiling point includes propylene glycol monomethyl ether, which has a chemical formula of CH _3- CH ₃ O- (CH ₂ CHO) _2- H, is dissolved in methanol, and has a boiling point of 121 ° C. ..
Moreover, the high boiling point of propylene glycol ether, there is tripropylene glycol monobutyl ether, chemical formula _CH 3 _-C 4 _H 9 _- shown in (CH 2 _CHO) 3 -H, dissolved in methanol, boiling point 274 ° C. Is.
Further, a dialkyl glycol having a low boiling point includes ethylene glycol dimethyl ether, which has a chemical formula of CH ₃ O- (CH ₂ CHO) -CH ₃ , is dissolved in methanol, and has a boiling point of 85.2 ° C.
In addition, diethylene glycol dibutyl ether, which has a high boiling point, has a chemical formula of C ₄ H ₉ O- (CH ₂ CH ₂ O) _2- C ₄ H ₉ , which is dissolved in methanol and has a boiling point of 274 ° C. is there.
Further, the styrene monomer is _{a liquid monomer having a chemical formula of C 6} H ₅ CH = CH ₂ , miscible with methanol, and having a boiling point of 145 ° C. Styrene monomer is an inexpensive organic compound that can be used as a raw material for synthetic resin materials such as expanded polystyrene, acrylonitrile / styrene, acrylonitrile / butadiene / styrene, and unsaturated polyester, including polystyrene. Since the styrene monomer is easily polymerized, a small amount of a polymerization inhibitor is added.
As described above, one kind of ester consisting of carboxylic acid vinyl ester, acrylic acid ester, and methacrylic acid ester , or one kind of organic compound belonging to any one of glycols and glycol ethers. In addition, there is an organic compound having the above-mentioned three properties. Further, the styrene monomer has the above-mentioned three properties. Therefore, these organic compounds are used as organic compounds in the method for producing a dust core described in paragraph 7.

Embodiment 2
The present embodiment relates to a soft magnetic powder used as a raw material for a dust core. The soft magnetic powder is selected from the operating frequency range of the electric product on which the dust core is mounted and the magnitude of the magnetic flux density of the dust core in this frequency range. On the other hand, in order to increase the saturation magnetic flux density of the dust core, it is necessary to increase the filling rate of the soft magnetic powder in the dust core. In order to increase the filling rate of the soft magnetic powder, it is necessary to apply a large pressurizing pressure to the collection of the soft magnetic powder to promote the plastic deformation of the soft magnetic powder. Therefore, due to the high hardness of many of the soft magnetic powder, reducing annealing, the hardness of the soft magnetic powder in advance soft magnetic powder. Further, since the holding power of the soft magnetic powder that has undergone plastic deformation increases, the holding power of the soft magnetic powder is restored by magnetic annealing of the dust core, and the iron loss of the powder magnetic core is reduced.
The dust core constituting the stator and rotor in the motor has a low operating frequency but a high saturation magnetic flux density. For such applications, pure iron powder having the highest saturation magnetic flux density among soft magnetic powders is used. On the contrary, the dust core constituting the reactor, noise filter, choke coil, etc. in the power supply circuit has a high operating frequency but a low saturation magnetic flux density. Fe—Si alloy powder, Fe—Si—Al alloy powder, and Fe—Ni alloy powder are used for such applications. Amorphous alloy powders have a wide variety of magnetic properties and have individual properties depending on the composition of the alloy, so they are not discussed here.
Pure iron powder has a saturation magnetic flux density of 2.2 tesla, which is the highest saturation magnetic flux density among soft magnetic powders, and has a relatively low hardness. Pure iron powder that has been hydrogen-tanned is easily plastically deformed. The packing density in the dust core is high, and the saturation magnetic flux density of the dust core is further increased. Therefore, it is used for the dust core that constitutes the stator and rotor of a motor that requires magnetic energy. For example, atomized iron powder having a Vickers hardness of 75-87 HV has the lowest hardness among soft magnetic powders, and the compression density of a compression molded product using hydrogen-annealed atomized iron powder is 90% of the iron density. Close to. On the other hand, the Vickers hardness of the reduced iron powder is 160-210 HV, which is more than twice the hardness of the atomized iron powder, but it is easily plastically deformed because it is a porous body having many voids. However, in the production of the dust core, the hardness is lowered by hydrogen annealing. On the other hand, pure iron powder has the lowest magnetic permeability among soft magnetic powders, and has the disadvantage that magnetic energy is difficult to be taken into the dust core. In addition, the holding force is as large as 80 A / m, and the hysteresis loss is large. Furthermore, it is a conductor having a volume resistivity of 1 × ^{10-5 Ω · cm.}
On the other hand, when iron contains silicon, the magnetic permeability increases, but when the silicon content exceeds 5% by mass, it becomes extremely brittle, and most Fe-Si alloys have a silicon content of less than 5% by mass. is there. Further, when silicon is contained in iron, the electric resistance increases, but the volume resistivity of the Fe—Si alloy of 3% by mass is 5 × 10 ⁻⁵ Ω · cm, which is conductive. The holding force of the 3% by mass Fe—Si alloy is as large as 65 A / m and the hysteresis loss is large, but the saturation magnetic flux density is as high as 1.3 Tesla. Further, the Vickers hardness is 180-205 HV, and the hardness is lowered by annealing to be used as a raw material for a dust core. In this way, the magnetic properties of the Fe-Si alloy are similar to those of reduced iron powder, but they are less likely to corrode than the reduced iron powder. Used for powder core.
Further, permalloy, which is an Fe—Ni alloy containing nickel in iron, has a significantly higher magnetic permeability than iron, but a small saturation magnetic flux density. Further, the higher the nickel content, the higher the price, and the nickel content is suppressed to 50% by mass or less. Further, magnetic annealing is performed at 1100 ° C. in a hydrogen atmosphere for about 3 hours to remove impurities and adjust the magnetic characteristics of permalloy. Here, nickel represents the properties of permalloy in an amount of 45% by mass. The DC magnetic characteristics are that the initial magnetic permeability is 3000, the saturation magnetic flux density is 1.4 Tesla, the holding force is 16 A / m, and the saturation magnetic flux density is smaller than that of pure iron powder, but larger than other soft magnetic powders. .. Further, the AC magnetic characteristics are permalloy with a plate thickness of 0.1 mm, an effective magnetic permeability at 1 kHz is 3000, and an effective magnetic permeability at 3 kHz is 2500. In addition, the physical properties are that the density is 8.25 g / cm ^3, which is about 5% higher than iron, the volume resistivity is 5 × ^10-5 Ω · cm, which is conductive, and the magnetic curry point is 420 ° C, which is 350 than iron. It is low in ° C. and has a Rockwell hardness of 60-90 HRB (corresponding to a Vickers hardness of 110-190 HV). Therefore, permalloy is used for trans cores, motor cores, and iron cores for relays because it has excellent alternating current permeability characteristics and saturation magnetic flux density.
Further, the Fe—Si—Al alloy obtained by adding silicon and aluminum to iron has high hardness and is brittle, so that it is easily powdered. In particular, Fe-10 wt% Si-6 a composition of mass% Al sendust (Tohoku University R), permeability tends to be large magnetization 1.2 × 10 ^5, the holding force 0.1 A / m Because it is small, the hysteresis loss is small, and the saturation magnetic flux density is 1 Tesla, which is close to Permalloy. Further, it is a conductor having a volume resistivity of 8 × ^{10-5 Ω · cm.} On the other hand, the Vickers hardness is as high as 410 HV, and the hardness is lowered by annealing, but the filling rate is not as high as that of pure iron powder. Further, when a dust core made of sendust is used at 80-120 ° C., the iron loss increases from room temperature, the heat generated by the iron loss further increases the iron loss, and there is a risk of thermal runaway in a high output transformer. there were. However, recently, it has been found that the composition of Fe-8.8 mass% Si-6.0 mass% Al reduces the iron loss and makes the temperature coefficient of the iron loss negative (Non-Patent Document 1). reference).
Further, among the electromagnetic stainless steels in which chromium, aluminum and molybdenum are added to iron, the electromagnetic stainless steel composed of Fe-13 mass% Cr-0.2 mass% Al-1 mass% Mo has a large magnetic permeability, but The holding force is as large as 85 A / m and the hysteresis loss is large. On the other hand, the magnetic flux density is 1.35 Tesla, which is comparable to Permalloy. The Rockwell hardness is 70 HRB (corresponding to 130 HV in Vickers hardness), which is harder than atomized iron powder and softer than reduced iron powder. It also has excellent corrosion resistance. For this reason, electromagnetic stainless steel is used for solenoid valves of automobiles because it has excellent responsiveness to a pulsed magnetic field. Further, it is a conductor having a volume resistivity of 6.5 × ^{10-5 Ω · cm.}
The characteristics of the soft magnetic powder having a typical composition have been described above for various types of soft magnetic powder. Since all of the soft magnetic powders are conductors, it is necessary to insulate the soft magnetic powders. If the soft magnetic powder is insulated with a collection of aluminum oxide fine particles having high heat resistance and insulating properties in the present invention, the eddy current loss is remarkably reduced. Further, annealing can be performed at a temperature exceeding 800 ° C., and the hysteresis loss of the dust core can be reduced. Further, in order to bring the density of the dust core close to the density of the soft magnetic powder, the hardness of the soft magnetic powder is lowered by annealing in advance. Therefore, the effect of superimposing the soft magnetic powders having an increased degree of integration in the present invention on the surfaces, compressing the collection of the soft magnetic powders, and producing the powder magnetic core without plastically deforming the soft magnetics is great.

Embodiment 3
This embodiment is an embodiment of a dust core prepared by using atomized iron powder and reduced iron powder, which are the cheapest materials among soft magnetic powders, and is described in Non-Patent Document 2. In addition, the superiority of the method for producing the dust core of the present invention will be described from the two types of dust core embodiments. The Vickers hardness of the atomized iron powder used in Non-Patent Document 2 is 100, and the Vickers hardness of the reduced iron powder is 60, both of which are lower in hardness than the iron powder used as an abrasive or the like. Therefore, it is considered that the hardness of the produced iron powder was further reduced by hydrogen annealing.
The initial magnetic permeability of iron powder changes depending on the manufacturing conditions of iron powder, and the initial magnetic permeability changes depending on the impurity concentration of silicon and manganese. The reduced iron powder used in Non-Patent Document 2 has a silicon concentration of 0.05% by mass and a manganese concentration of 0.25% by mass. On the other hand, the atomized iron powder used in Non-Patent Document 2 has a low silicon concentration of 0.01% by mass and a low manganese concentration of 0.04% by mass. Therefore, the initial magnetic permeability of the reduced iron powder is larger than that of the atomized iron powder.
In the production of the dust core, 0.75% by mass of epoxy resin as an insulating material and 0.5% by mass of zinc stearate as a lubricating material are added to both iron powders, and there are two types, 490 MPa and 686 MPa. Pressurized pressure was applied to form a ring shape having an outer diameter of 38 mm, an inner diameter of 25 mm, and a thickness of 6.2 mm. After that, the green compact was heat-treated at 180 ° C. in the air to cure the epoxy resin, and a fine powder magnetic core was produced. Zinc stearate has a melting point of 140 ° C. and liquefies when the epoxy resin is polymerized, and exhibits a function as a lubricant.
The epoxy resin has a volume resistivity of 10 ¹⁵ Ω · cm, which is excellent in insulating properties, but has a heat resistance lower than 200 ° C. In addition, zinc stearate is thermally decomposed at 420 ° C. to become toxic carbon monoxide, carbon dioxide, zinc oxide gas and solid particles. Therefore, the produced dust core has a heat resistance lower than 200 ° C. and cannot be annealed to restore the holding power. Further, due to the magnitude of the pressurizing pressure, both iron powders are undergoing plastic deformation . However, since there is no annealing effect in the heat treatment at 180 ° C., the hysteresis loss of the dust core is large.
The powder magnetic core made of reduced iron powder to which a pressurized pressure of 490 MPa is applied has a density of 6.74 g / cm ³ , a filling rate of 85.8%, and a DC initial magnetic permeability of 71.1. .. The powder magnetic core made of reduced iron powder to which a pressurized pressure of 686 MPa is applied has a density of 6.95 g / cm ³ , a filling rate of 88.4%, and a DC initial magnetic permeability of 75.7. .. On the other hand, the powder magnetic core made of atomized iron powder to which a pressurizing pressure of 490 MPa is applied has a density of 6.87 g / cm ³ , a filling rate of 87.4%, and a DC initial magnetic permeability of 64. .2. The powder magnetic core made of atomized iron powder to which a pressurizing pressure of 686 MPa is applied has a density of 7.06 g / cm ³ , a filling rate of 89.8%, and a DC initial magnetic permeability of 68.7. ..
The initial magnetic permeability of the alternating current of the dust core made of reduced iron powder is 74 at 10 kHz, and the initial magnetic permeability gradually decreases as the frequency increases, and the decrease rate increases from around 300 kHz. On the other hand, the AC initial permeability of the dust core made of atomized iron powder is the frequency characteristic of the AC initial permeability of the powder magnetic core of the reduced iron powder, and the initial permeability is moved downward by 10. Is shown.
Further, regarding the consolidation behavior of the iron powder when the two types of iron powder are pressurized, the rate at which the porosity decreases with respect to the pressurizing pressure shows the same characteristics in the two types of iron powder. The decrease in porosity depends on the plastic deformation and rearrangement of the iron powder. In the two types of iron powder, the rearrangement of the iron powder is completed at a pressure of 100 MPa, and the plastic deformation is started from a pressure pressure of around 50 MPa. Therefore, at a pressure up to about 50 MPa, the voids are reduced by the rearrangement of the iron powder, at a pressure up to 100 MPa, the voids are reduced by the rearrangement of the iron powder and the plastic deformation of the iron powder, and at a pressure of 100 MPa or more, the voids are reduced. The voids are reduced by the plastic deformation of the iron powder. Therefore, in the powder magnetic core manufactured by applying a pressurizing pressure of 490 MPa, the plastic deformation of the iron powder is sufficiently advanced. Therefore, the hysteresis loss of the dust core is increasing.
Here, the measurement results of two types of dust cores will be examined.
First, the compression density of the compression molded product is higher in the atomized iron powder for the same pressure. However, the difference in compression density is only 2%. On the other hand, the Vickers hardness of the reduced iron powder used is 0.6 times that of the atomized iron powder used, and it is easily plastically deformed. However, both iron powders start to be plastically deformed from a pressure of about 50 MPa, and at a pressure of 490 MPa, both iron powders are sufficiently plastically deformed. Therefore, the difference in the hardness of the iron powder has a small effect on the difference in the compression density. On the other hand, the reduced iron powder is a porous body having many voids and is easily crushed by a pressurizing pressure, but the porosity of the plastically deformed iron powder is high. Therefore, it is considered that the difference in compression density is due to the high porosity of the reduced iron powder after plastic deformation.
Second, the initial magnetic permeability of direct current in reduced iron powder is as much as 10% higher than the initial magnetic permeability of direct current in atomized iron powder. Further, the initial magnetic permeability of alternating current from 10 kHz to 1 MHz is 15% higher in the powder magnetic core made of reduced iron powder than in the powder magnetic core made of atomized iron powder. As described above, the reduced iron powder has a high initial magnetic permeability because of the high impurity concentration of silicon and manganese. Furthermore, the initial magnetic permeability increased due to the flattening effect of the reduced iron powder. That is, the atomized iron powder has an irregular contour and is isotropically deformed when pressed. On the other hand, the reduced iron powder also has an irregular contour, but since it is a porous body, the reduced iron powder is easily crushed in the pressurizing direction and easily deformed in the direction perpendicular to the pressurizing direction. That is, the reduced iron powder is deformed in the plane direction, which is the easy axial direction of magnetization, the demagnetizing field coefficient is reduced, and the initial magnetic permeability of the reduced iron powder is increased. This phenomenon is similar to the phenomenon in which the magnetic permeability increases when the soft magnetic powder is flattened.
Thirdly, since the plastic deformation of the two types of iron powder starts from around 50 MPa, the plastic deformation of the two types of iron powder progresses at a pressurizing pressure of 490 MPa, and the iron powder with increased holding power is used as the powder. A magnetic core is formed. However, the heat treatment of the dust core is 180 ° C., which is the curing treatment temperature of the epoxy resin. Therefore, the heat treatment at 180 ° C. does not have an annealing effect that restores the holding power. In addition, the contours of the two types of iron powder are irregular and do not have shape anisotropy. A pressurizing pressure of 490 MPa is required to compress such an aggregate of iron powder and realize the mechanical strength required for a compression molded product. Due to this pressurizing pressure, the plastic deformation of the iron powder progresses, and the entanglement of the iron powder realizes the mechanical strength required for the compression molded body. However, the hysteresis loss of the dust core increases.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, if the iron powder is insulated by a collection of aluminum oxide fine particles, the heat resistance is higher than that of the iron powder, so that strain-removing annealing becomes possible and the holding power of the iron powder is restored. In addition, a collection of aluminum oxide fine particles fills the gaps between the iron powders and the voids of the reduced iron powder, increasing the compression density, and the aluminum oxide fine particles that fill the gaps and voids are joined by frictional heat to form a dust powder. Contributes to the realization of mechanical strength as a magnetic core. Further, since the aluminum oxide fine particles in which the gaps and voids of the iron powder are bonded by frictional heat are filled, the eddy current flowing through the gaps between the iron powders is reduced.
Secondly, even if the iron powder has an irregular shape, if the collection of iron powder is made into a collection of iron powder that overlaps with each other and the collection of iron powder is compressed, the gap between the iron powder that overlaps with each other narrows. , The compression density increases. Further, since all the iron powders are overlapped with each other and the easy axial direction of magnetization is the plane direction, the dust core is easily magnetized and the initial magnetic permeability of the iron powder is increased.
Thirdly, if the pressurizing pressure is stopped before the iron powder is plastically deformed and the iron powders are bonded to each other through the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase, and the pressure is also increased. The powder core has the required mechanical strength.
As a result, in the powder magnetic core produced by using the atomized iron powder and the reduced iron powder according to the method for producing the powder magnetic core of the present invention, the initial magnetic permeability is increased, the eddy current loss is reduced, and the hysteresis loss is not increased.

Embodiment 4
This embodiment is an embodiment for comparing the performance of a powder magnetic core produced by using reduced iron powder and a powder magnetic core produced by using flat reduced iron powder, and is described in Non-Patent Document 3. .. In addition, the superiority of the method for producing the dust core of the present invention will be described from the two types of dust core embodiments.
Epoxy resin as an insulating material is added as 1% by mass to both iron powders, zinc stearate as a lubricating material is added as 0.1% by mass, and pressurizing pressures of 490 MPa and 686 MPa are applied, and the outer diameter is 38 mm. The powder was formed into a ring shape having an inner diameter of 25 mm and a thickness of 6.2 mm, and then the powder compact was heat-treated at 180 ° C. in the air for 30 minutes to cure the epoxy resin to produce a powder compact core. Even if the heat treatment is performed at 180 ° C. for 30 minutes, the holding power of the reduced iron powder cannot be restored, and the hysteresis loss in the dust core is large.
In the powder magnetic core manufactured at a pressure of 490 MPa, the flat reduced iron powder has a compression density of 6.93 g / cm ³ , a filling rate of 88.0%, and a DC initial magnetic permeability of 94.9. On the other hand, in the reduced iron powder, the compression density is 6.74 g / cm ³ , the filling rate is 85.7%, and the initial magnetic permeability of direct current is 72.1. Further, in the powder magnetic core manufactured at a pressure of 686 MPa, the flat reduced iron powder has a compression density of 7.09 g / cm ³ , a filling rate of 90.0%, and a DC initial magnetic permeability of 99.1. .. On the other hand, in the reduced iron powder, the compression density is 6.97 g / cm ³ , the filling rate is 88.5%, and the initial magnetic permeability of direct current is 78.1. In all of the reduced iron powders, when the compressive stress is increased, the compressive density and the initial magnetic permeability of direct current increase.
Further, the powder magnetic core compressed with a pressure of 686 MPa has an initial magnetic permeability of AC at 10-200 kHz, the initial magnetic permeability of the powder magnetic core of flat reduced iron powder is 100, and the initial magnetic permeability of the powder magnetic core of the reduced iron powder. The initial magnetic permeability is 80, and the initial magnetic permeability is increased by 20%. At 200 kHz-1 MHz, the higher the frequency, the smaller the difference in initial magnetic permeability.
The iron loss at a magnetic flux density of 50 mT is smaller than the iron loss of the powder magnetic core using flat reduced iron powder, and the difference between the two increases as the frequency increases. spread. That is, although both iron powders are insulated with the same substance and the same mass number, the iron loss is smaller in the powder magnetic core using flat reduced iron powder.
Here, the measurement results of two types of dust cores will be examined.
First, the gap between the flat-reduced iron powders in the compression molded product using the flat-reduced iron powder was relatively narrower than that in the case of using the reduced iron powder, and the compression density was increased. However, the difference in compression density is only 2-3%. Further, the ratio of the filling rate in the powder magnetic core manufactured at a pressure of 686 MPa to the filling rate in the powder magnetic core manufactured at a pressure of 490 MPa is the powder using flat reduced iron powder. It is 1.023 in the magnetic core, while it is 1.033 in the powder magnetic core using the reduced iron powder. If all the flattened reduced iron powders are overlapped with each other, the difference in the powder density is wider than 2 to 3%, and the filling rate ratio when the flattened reduced iron powders are used is 1.023. Become bigger. Therefore, the flat reduced iron powder that overlaps the flat surfaces remains in a part. On the other hand, when all the flattened iron powders overlap each other on the flat surfaces, there is a problem that the mechanical strength required for the powder magnetic core cannot be realized. Therefore, a collection of flattened iron powder was simply compressed.
Second, in the powder magnetic core using flat reduced iron powder, the initial magnetic permeability of DC increases by 31% at a pressurizing pressure of 490 MPa and pressurizes 686 MPa compared to the powder magnetic core using reduced iron powder. The pressure increased by 27%. Further, in the powder magnetic core prepared at a pressurized pressure of 686 MPa, the initial magnetic permeability increased by 20% at a frequency of 10-200 kHz. That is, when a pressurized pressure is applied to the flat-reduced iron powder, the flat-reduced iron powder is crushed, the flat-reduced iron powder having a certain ratio is deformed in the flat-plane direction, and the flatness is increased. Since this flat plane direction is the axial direction for easy magnetization, the initial magnetic permeability increased due to the flattening effect. Therefore, a difference in the initial magnetic permeability appeared between the powder magnetic core using the flat reduced iron powder and the powder magnetic core using the reduced iron powder.
Thirdly, the result of iron loss in the dust core is that the shape of the reduced iron powder is irregular and the shape of the flat reduced iron powder is flattened in the plane direction. That is, the gap between the flat-reduced iron powders in the compression-molded body made of the flat-reduced iron powder was narrowed, and the compression density was increased. When the gap between the flat reduced iron powders becomes narrower, the insulation between adjacent flat reduced iron powders becomes higher, the eddy current flowing through the gap between the flat reduced iron powders decreases, and the powder magnetic core using the flat reduced iron powders becomes smaller. The eddy current loss of the powder was smaller than the eddy current loss of the dust core using reduced iron powder.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, it is a collection of aluminum oxide fine particles whose heat resistance is higher than that of reduced iron powder. If the reduced iron powder is insulated, strain relief annealing becomes possible, the holding power is restored, and the hysteresis loss of the dust core is reduced. Decrease. In addition, a collection of aluminum oxide fine particles whose size is three orders of magnitude smaller than that of the epoxy resin pellets fills the gaps between the reduced iron powders and the voids of the reduced iron powders, and the compression density increases. Further, the aluminum oxide fine particles that fill the gaps and voids are bonded to each other by frictional heat, and the mechanical strength as a dust core is realized. This eliminates the need for plastic deformation of the reduced iron powder and the flat reduced iron powder, and the hysteresis loss of the dust core is small.
Secondly, even if the reduced iron powder has an irregular shape, if the reduced iron powder is made into a highly integrated iron powder group in which the surfaces are overlapped with each other and the reduced iron powder group is compressed, all the reduced iron powder is obtained. The gap between the reduced iron powders that overlap each other is narrowed, and the compression density is increased. In the flat-reduced iron powder, a collection of flat-reduced iron powder in which flat surfaces overlap each other is compressed, so that the compression density is further increased. Further, since all the reduced iron powders or all the flat reduced iron powders are aligned in the direction of the flat surface, the initial magnetic permeability of the dust core is further increased. Further, the gap between the reduced iron powders or the gap between the flat reduced iron powders becomes narrower, and the narrowed gap is filled with aluminum oxide fine particles having high insulating properties, and the eddy current flowing through the gap is further reduced. As a result, the initial magnetic permeability increases.
Third, if the pressurizing pressure is stopped before both iron powders are plastically deformed and both iron powders are bonded to each other through the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase. Also, the dust core has the required mechanical strength.
As a result, the powder magnetic core produced by using the reduced iron powder and the flat reduced iron powder according to the method for producing the powder magnetic core of the present invention has an increased initial magnetic permeability, a reduced eddy current loss, and a non-increased hysteresis loss. ..

Embodiment 5
This embodiment is an embodiment of a dust core produced by using atomized iron powder, and is described in Non-Patent Document 4. Moreover, the superiority of the method for producing the dust core of the present invention will be described from the embodiment of the dust core.
0.5% by weight of epoxy resin powder is added to atomized iron powder, and four types of pressurizing pressure consisting of 196-686 MPa are applied with a floating die type mold, and the outer diameter is 38 mm, the inner diameter is 25 mm, and the height is 25 mm. Was formed into a 6.5 mm ring, and then cured at 150 ° C. for 1 hour to produce four dust cores. Note that curing at 150 ° C. does not have an annealing effect that restores the holding power of atomized iron powder.
The powder magnetic core formed with a pressurized pressure of 196 MPa has a filling rate of 76% and a DC initial magnetic permeability of 49. The powder magnetic core formed with a pressurized pressure of 294 MPa has a filling rate of 81% and a DC initial magnetic permeability of 60. The powder magnetic core formed at a pressure of 490 MPa has a filling rate of 87% and a DC initial magnetic permeability of 72. The powder magnetic core formed with a pressurizing pressure of 686 MPa has a filling rate of 91% and a DC initial magnetic permeability of 78.
On the other hand, the powder magnetic core made of atomized iron powder described in Non-Patent Document 2 has a filling rate of 87.4% and a DC initial magnetic permeability of 64.2. Met. The packing rate of the dust core to which a pressurizing pressure of 686 MPa was applied was 89.8%, and the initial magnetic permeability of direct current was 68.7. Compared with the powder magnetic core described in Non-Patent Document 4, at the same pressurizing pressure, the filling rate value is close, but the direct current magnetic permeability is small. The reason for this depends on the concentration of impurities. The concentration of silicon in Non-Patent Document 2 is 0.01% by mass, and the concentration of manganese is 0.04% by mass. On the other hand, in Non-Patent Document 4, the concentration of silicon is as high as 0.029% by mass and the concentration of manganese is as high as 0.069% by mass. The atomized iron powder of Non-Patent Document 4 has a high initial magnetic permeability because of the high concentration of silicon and manganese.
Further, the atomized iron powder used for the dust core described in Non-Patent Document 2 has a smaller particle size than the atomized iron powder used for the powder magnetic core described in Non-Patent Document 4. For example, in the atomized iron powder described in Non-Patent Document 2, there is no atomized iron powder having a particle size larger than 180 μm. In addition, atomized iron powder having a particle size of 45 μm or less accounts for 23%. On the other hand, the atomized iron powder described in Non-Patent Document 4 contains 11.2% for atomized iron powder having a particle size of 200-250 μm and 20.1% for atomized iron powder having a particle size of 250-325 μm. Atomized iron powder having a particle size of 325 μm or more accounts for 23.2%. In addition, only 0.1% of atomized iron powder has a particle size of 80 μm or less.
Further, as the pressurizing pressure is increased, the values of the real part and the imaginary part of the complex magnetic permeability gradually increase, and the frequency at which the values of the real part and the imaginary part of the complex magnetic permeability start to decrease gradually becomes low. The result of shifting to the side is shown. At a pressurizing pressure of 294 MPa, the real part has a value of 80 up to around 500 kHz. Further, as the frequency increases from 500 kHz, the real part gradually decreases. On the other hand, the imaginary part of the complex magnetic permeability gradually increases from around 60 kHz, has a peak value of 20 in the frequency region exceeding 1 MHz, and overlaps the real part at a frequency exceeding 200 MHz.
Here, the measurement result of the dust core will be examined.
First, consider the results of compression density. It is expected that the smaller the particle size of the atomized iron powder used for the dust core, the higher the compression density. The atomized iron powder used in Non-Patent Document 2 has a clearly smaller particle size than the atomized iron powder used in Non-Patent Document 4. Although there is a clear difference in the size of the particle size, there is almost no difference in the packing rate of the dust core. On the other hand, the atomized iron powder starts plastic deformation from a pressurizing pressure of around 50 MPa, and at a pressurized pressure of 490 MPa, the plastic deformation of the atomized iron powder progresses considerably. Therefore, the plastic deformation of the iron powder progressed, and the filling rate of the iron powder did not change despite the difference in the particle size distribution of the iron powder. That is, the atomized iron powder was compressed with a pressurizing pressure of about 490 MPa in order to obtain the mechanical strength required for the powder magnetic core. However, the iron powder with advanced plastic deformation has an increased holding force of the iron powder and an increased hysteresis loss. Furthermore, the holding power of iron powder cannot be restored by curing at 150 ° C. for 1 hour.
Second, the results of complex magnetic permeability will be examined. Like the reduced iron powder, the atomized iron powder has an irregular contour, but is not a porous body like the reduced iron powder. Increasing the pressure to pressurize a collection of insulated atomized iron powder narrows the gap between the atomized iron powder, reduces the eddy current flowing through the gap, and reduces the eddy current loss. As a result, the values of the real part and the imaginary part of the complex magnetic permeability increased as the pressurizing pressure was increased. Further, although the atomized iron powder is not a porous body, the flattening of the atomized iron powder progresses as the pressurizing pressure is increased, and the flattening ratio increases. As a result, the values of the real part and the imaginary part of the complex magnetic permeability increased. That is, the proportion of the atomized iron powder deformed in the plane direction, which is the easy axial direction of magnetization, increased, the flatness increased, and the values of the real part and the imaginary part of the complex magnetic permeability of the atomized iron powder increased.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, the dust core was composed of atomized iron powder with advanced plastic deformation. As a result, the holding force of the atomized iron powder increases according to the progress of plastic deformation, and the hysteresis loss increases as the holding force increases. In order to restore the holding power of the atomized iron powder, annealing in a hydrogen atmosphere higher than 500 ° C. is required, and the material for insulating the atomized iron powder needs to have a heat resistance higher than 500 ° C. If the atomized iron powder is insulated with the aluminum oxide fine particles in the present invention, the heat resistance is higher than that of the atomized iron powder, so that strain relief annealing becomes possible, the holding power is restored, and the hysteresis of the dust core is restored. Loss is reduced.
Secondly, if the insulating material is composed of the aluminum oxide fine particles in the present invention, the size of the fine particles is three orders of magnitude smaller than that of the epoxy resin pellets, so that the gap between the atomized iron powders is further narrowed, and the narrowed gap is insulated. Is filled with high aluminum oxide fine particles, and the eddy current flowing through the gap is further reduced. As a result, the values of the real part and the imaginary part of the complex magnetic permeability are further increased. In addition, the compression density also increases, and the saturation magnetic flux density of the dust core increases.
Thirdly, in the method for producing a dust core of the present invention, a collection of atomized iron powder is made into a collection of atomized iron powder having a high degree of integration and overlapping on each other, and the collection of atomized iron powder is compressed. Therefore, the surfaces overlap each other and are compressed, the gaps between the atomized iron powders are narrowed, and the narrowed gaps are filled with aluminum oxide fine particles having high insulating properties. As a result, the eddy current flowing through the gap is further reduced, and the values of the real part and the imaginary part of the complex magnetic permeability are further increased.
Fourth, if the pressurizing pressure is stopped before the atomized iron powder is plastically deformed and the atomized iron powder is bonded to each other through the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase, and the hysteresis loss does not increase. The dust core has the required mechanical strength.
As a result, the powder magnetic core produced by using atomized iron powder according to the method for producing a powder magnetic core of the present invention has an increased initial magnetic permeability, a reduced eddy current loss, and no hysteresis loss.

Embodiment 6
This embodiment is an embodiment of a dust core produced by using flat atomized iron powder, and is described in Non-Patent Document 5. Moreover, the superiority of the method for producing the dust core of the present invention will be described from the embodiment of the dust core.
A ring with an outer diameter of 36 mm, an inner diameter of 24 mm, and a thickness of 5 mm, using flat atomized iron powder and flat atomized iron powder insulated with three types of insulating materials, all under a pressure of 490 MPa. Four types of dust cores consisting of shapes were manufactured. For the first insulated flat atomized iron powder, synthetic resin was added to the iron powder in an amount of 0.8% by weight. The second insulated flat atomized iron powder was obtained by mixing an aqueous solution of phosphoric acid, boric acid and magnesium oxide with the flat atomized iron powder, and then drying the powder. For the third insulated flat atomized iron powder, 0.8% by weight of synthetic resin was further added to the second insulated flat atomized iron powder, and the iron powder was insulated by a double insulating layer.
The phosphoric acid used to insulate the flat atomized iron powder has a melting point of 42.35 ° C., and changes to _{phosphoric acid H 4} P ₂ O _{7 at 200 ° C. and metaphosphoric acid (HPO 3} ) _n at 300 ° C. or higher. To do. Further, boric acid _{changes to metaboric acid HBO 2} at 100 ° C., tetraboric acid H ₂ B ₄ O ₇ at 140 ° C., and glassy boric acid B ₂ O ₃ at 300 ° C. On the other hand, magnesium oxide has a melting point of 2852 ° C. and is excellent in heat resistance. Further, since the four types of dust cores are manufactured by applying a pressurizing pressure of 490 MPa to a collection of flat atomized iron powder, the atomized iron powder starts plastic deformation from a pressurizing pressure of around 50 MPa. The plastic deformation of the flat atomized iron powder constituting the four types of dust cores is progressing. On the other hand, due to the heat resistance of magnesium oxide, it is possible to perform hydrogen annealing of the dust core at a temperature higher than 500 ° C. However, since hydrogen annealing of the four types of dust cores is not performed, the hysteresis loss of the four types of dust cores is large.
First, the result of compression density will be described. The powder magnetic core made of flat atomized iron powder has a density of 7.10 g / cm ³ and a filling rate of 90%. This filling rate is 3% higher than that of the powder magnetic core produced by using the atomized iron powder described in Non-Patent Document 4 and applying the same pressurizing pressure of 490 MPa. As a result, the flattening effect of atomized iron powder was reflected in the increase in compression density. Further, the filling rate is higher than that of the powder magnetic core produced by applying the same pressurizing pressure of 490 MPa using the flattened reduced iron powder described in Non-Patent Document 3. As a result, the temperature at which the flat atomized iron powder was hydrogen-annealed was higher than the hydrogen annealing temperature of the flat reduced iron powder described in Non-Patent Document 3, and the hardness of the flat atomized iron powder was lower than the hardness of the flat reduced iron powder. It seems that it depends. Further, the density of the dust core made of the first insulated iron powder is 6.90 g / cm ³ , and the density of the powder magnetic core made of the second insulated iron powder is 7.04 g / cm. ^3, and the density of the dust core fabricated by iron powder and the third insulated is 6.83 g / cm ^3.
Next, the results of the specific resistances of the four types of dust cores will be described. As for the effect of insulation by the insulating material, the first insulating material has no insulating effect, the second insulating material has a slight insulating effect, and the third insulating material has an insulating effect.
Further, the results of the eddy current loss of the four types of dust cores will be described. The eddy current loss is large in the order of the dust core made of only iron powder, the powder magnetic core made of the first insulator, the powder magnetic core made of the third insulator, and the powder magnetic core made of the second insulator. Although the difference in eddy current loss between the dust core made of the third insulator and the dust core made of the second insulator is small, the dust core made of only iron powder and the first insulator The difference in eddy current loss is large compared to the powder magnetic core made of.
Here, the result of the dust core will be examined.
First, consider the results of compression density. The densities of the three types of powder magnetic cores obtained by insulating flat atomized iron powder are lower than the densities of the powder magnetic cores made only of iron powder. That is, the insulator does not sufficiently fill the gap formed by the plastically deformed flat atomized iron powder. The contour of the flat atomized iron powder is irregular, because all the flat atomized iron powders do not overlap each other, and because the flat atomized iron powder consists of powders of various sizes, compression molding is performed when pressed. Many voids are formed in the body. On the other hand, since each of the three types of insulating materials has a certain size, the voids cannot be filled and the compression density is lowered. In addition, the decrease in the density of the dust core made of the second insulated iron powder is due to the pressure made of the first insulated iron powder and the third insulated iron powder. It is smaller than the decrease in compression density with the powder core. The reason for this is that the crushed resin pellets are larger than the particle size of the magnesium oxide powder, and the crushed resin pellets are an obstacle to filling the voids.
Second, the result of resistivity is examined. The first insulator is made by adding synthetic resin to iron powder in an amount of 0.8% by weight, and since the synthetic resin pellets have a certain size, the crushed synthetic resin pellets are flat atomized iron powder. The insulating effect could not be obtained because some of the flat atomized iron powders were in direct contact with each other without filling the gaps between them. On the other hand, when the flat atomized iron powder covered with the double insulating layer is compressed, the magnesium oxide powder, which has a higher hardness than the synthetic resin pellets, comes into contact with the synthetic resin pellets and makes the synthetic resin pellets finer. The fine pieces of synthetic resin pellets, which are smaller than the first insulator, and the magnesium oxide powder enter the gaps between the flat atomized iron powders. Due to the high insulation between the two, insulation has progressed.
Third, the results of eddy current loss will be examined. Similar to the result of compression density, the dust core made of the first insulator does not fill the gap between the flat atomized iron powders because the resin pellets are large, and some of the flat atomized iron powders do not fill the gap between the flat atomized iron powders. Direct contact resulted in an eddy current loss close to that of a dust core consisting only of iron powder. On the other hand, the dust core made of the third insulator and the powder magnetic core made of the second ^{insulator have high insulating properties with a volume resistivity of 2 × 10 16} Ω · cm and an average particle size. The 1.3 μm magnesium oxide powder and the fine pieces of synthetic resin pellets were present in the gaps between the iron powders, and the eddy current loss was reduced.
Here, the superiority of the method for producing a dust core of the present invention over the results of two types of dust cores will be described.
First, from the above-mentioned compression density results, the smaller the size of the insulator that insulates the flat atomized iron powder, the more the gaps between the atomized iron powders are filled with the insulator, and the decrease in the compression density is suppressed. It was. Therefore, since the size of the aluminum oxide fine particles having an average particle size of 40 to 60 nm in the present invention is two orders of magnitude smaller than that of magnesium oxide powder having an average particle size of 1.3 μm, a decrease in compression density can be suppressed. In addition, the gap between the flat atomized iron powders is surely insulated, and the eddy current flowing through the gap is reduced. As a result, the values of the real part and the imaginary part of the complex magnetic permeability increase.
Secondly, if the flat atomized iron powder is insulated by a collection of granular aluminum oxide fine particles having a size of 40 to 60 nm as in the present invention, the gaps between the flat atomized iron powders are filled with the aluminum oxide fine particles. As the compression density increases, the insulation resistance of the gaps increases significantly due to the enormous number of granular aluminum oxide fine particles and pores. As a result, the eddy current flowing through the gap is significantly reduced, and the eddy current loss of the dust core is reduced. In addition, the values of the real part and the imaginary part of the complex magnetic permeability increase according to the degree of decrease in the eddy current loss.
Thirdly, by compressing a collection of flat atomized iron powders that overlap each other as in the present invention, the gap between the flat atomized iron powders is surely insulated, the eddy current flowing through the gap is reduced, and the eddy current flowing through the gap is reduced. , The compression density increases. Further, since all the flat atomized iron powders are overlapped with each other and aligned in the plane direction which is the easy axial direction of magnetization, the dust core is easily magnetized and the magnetic permeability of the dust core is increased.
Fourth, as in the present invention, if the pressurizing pressure is stopped before the flat atomized iron powder is plastically deformed and the flat atomized iron powders are bonded to each other through the bonding of the aluminum oxide fine particles, the powder magnetic core The hysteresis loss does not increase, and the dust core has the required mechanical strength.
As a result, in the powder magnetic core produced by using the flat atomized iron powder according to the method for producing the powder magnetic core of the present invention, the initial magnetic permeability is increased, the eddy current loss is reduced, and the hysteresis loss is not increased.

The embodiment of four kinds of dust cores produced by using atomized iron powder, flat atomized iron powder, reduced iron powder and flat reduced iron powder has been described. Since the dust core of the embodiment insulates the iron powder with an insulating material having low heat resistance, hydrogen annealing of the iron powder is impossible. In addition, since the dust core was formed by the iron powder that had undergone plastic deformation, the hysteresis loss of the dust core increased. Further, the heat treatment temperature is as low as 180 ° C., and there is no annealing effect of the plastically deformed iron powder. The powder magnetic core produced by the method for producing a powder magnetic core of the present invention has advantages over such a powder magnetic core in the following two points.
First, the surface of the iron powder was insulated with a collection of fine particles of aluminum oxide. This brings about the following four effects. First, the melting point of aluminum oxide is higher than the melting point of iron powder, and the heat resistance of the dust core becomes the heat resistance of iron powder. This enables hydrogen annealing of the dust core, restores the holding power of the iron powder, and reduces the hysteresis loss of the dust core. Secondly, aluminum oxide is granular fine particles having a size of 40-60 nm, and when a collection of iron powder covered with fine particles of aluminum oxide is compressed, the aluminum oxide fine particles move to fill the voids of the collection of iron powder. Further, the aluminum oxide fine particles are bonded to each other by frictional heat at the contact portion, and the powder magnetic core has the necessary mechanical strength in the bonding of the extremely large number of aluminum oxide fine particles. Thirdly, aluminum oxide is an excellent insulator, and an extremely large number of aluminum oxide fine particles and resistors between the pores fill the gaps between the iron powders, and the insulation resistance of the gaps is significantly increased. As a result, the eddy current flowing in the gap between the iron powders is remarkably reduced, the AC magnetic permeability of the dust core is increased, and the dust core is easily magnetized in the corresponding frequency band. Fourth, aluminum oxide is the hardest substance next to diamond, and because it has an extremely high melting point, when aluminum oxide fine particles come into contact with each other, the fine particles are not destroyed and excessive frictional heat is generated at the contact part, causing the fine particles to come into contact with each other. Joins with frictional heat. Since there are an extremely large number of aluminum oxide fine particles in the collection of iron powder to be compressed, the repulsive force for compressing the collection of iron powder increases when the aluminum oxide fine particles are joined to each other, and the compression is stopped at this point. be able to. As a result, the iron powder is not plastically deformed, and the hysteresis loss of the dust core does not increase.
The second is to perform a treatment on a collection of iron powder to form a collection of iron powder in which the surfaces of the iron powder overlap each other. This brings about the following three effects. First, the gap between the iron powders is narrowed, which increases the compression density of the compression compact and the saturation magnetic flux density of the dust core. Second, the narrowed gaps between the iron powders are filled with a collection of aluminum oxide fine particles, the eddy current flowing in the gaps between the iron powders is reduced, and the eddy current loss of the dust core is reduced. As a result, the initial magnetic permeability of alternating current increases, and the dust core is likely to be magnetized in the corresponding frequency band. Third, when a collection of iron powder with overlapping surfaces is compressed, the iron powder is deformed in the axial direction of easy magnetization perpendicular to the surface, so the initial magnetic permeability of alternating current increases, and the dust core in the corresponding frequency band. Is easily magnetized.

Here, the complex magnetic permeability of the soft magnetic material will be described. When the dust core is wound and alternating current is applied to excite the dust core, a hysteresis loss due to the soft magnetic material constituting the dust core occurs. When the configuration of the dust core is shown by an electric circuit, the impedance is represented by R + jωL because the winding forms the L component and the dust core forms the R component. Applying this relationship to magnetic permeability, magnetic permeability is expressed by Equation 1. At this time, μ ′ represents the inductance component in the real part of the complex magnetic permeability, and μ ″ represents the resistance component in the imaginary part of the complex magnetic permeability.
(Equation 1) μ = μ ′ −jμ ″
On the other hand, when a high-frequency alternating current is passed through the dust core, the magnetic permeability of the soft magnetic material cannot be followed by the magnetic flux density B with the change of the magnetic field H, and a phase delay occurs. At this time, the L component (μ ′) decreases and the R component (μ ″) increases. This case was described by the behavior of complex magnetic permeability in the flat powder described above.
The relationship between the magnetic permeability and the complex magnetic permeability at B = μH, which is the definition of the magnetic permeability μ expressed by the relationship between the magnetic field strength H and the magnetic flux density B, is given by Equation 2. Therefore, if at least one of the real part μ'and the imaginary part μ'is increased, the magnetic permeability μ will increase. By increasing the magnetic permeability μ, the dust core is easily magnetized, and magnetic energy based on the product of the saturation magnetic flux density and the applied magnetic field is taken into the dust core.
(Equation 2) μ = {(μ ′) ² + (μ ″) ² } ^1/2

Example 1
In this embodiment, flat atomized iron powder obtained by flattening atomized iron powder is insulated by a collection of fine particles of aluminum oxide, and the insulated flat atomized iron powder collection is compressed in a mold to form a dust core. Is an embodiment of manufacturing in a mold.
As the flat atomized iron powder, 290PC-2 of Kobe Steel, Ltd. was used. This flat iron powder is obtained by flattening atomized iron powder (300M of Kobe Steel, Ltd.). The impurity concentration of atomized iron powder (300M) was 0.01% by weight for silicon and 0.19% by weight for manganese (according to Non-Patent Document 6), which was described in Non-Patent Document 2 described above. The concentration of manganese is higher than the concentration of impurities in atomized iron powder. Therefore, the initial magnetic permeability of atomized iron powder (300M) is slightly higher.
Further, as a raw material for aluminum oxide, aluminum benzoate Al (C ₆ H ₅ COO) ₃ (for example, a product of Mitsuwa Chemical Co., Ltd.) was used. Further, as the organic compound, diethylene glycol (for example, a product of Junsei Chemical Co., Ltd.) having a boiling point of 244 ° C. and a viscosity of 25 ° C. of 30 mPas, which is close to 50 times the viscosity of methanol, was used. Further, as a mixer, a device (for example, rocking mixer RMH-HT manufactured by Aichi Electric Co., Ltd.), which has a built-in heater by far infrared rays and simultaneously performs diffusion mixing by rotation and moving mixing by shaking, is used for further mixing. A vibration exciter was installed at the bottom of the machine.
31 g (corresponding to 0.08 mol) of aluminum benzoate was dispersed in 1 liter of methanol, and 200 cc of diethylene glycol was mixed with this methanol dispersion to prepare a mixed solution. Therefore, the viscosity of the mixture is close to 10 times the viscosity of methanol. Next, the mixer was placed on a vibration table, the mixed solution and 1 kg of flat atomized iron powder were charged into the mixer, and mixing and rocking were repeated by the mixer to prepare a mixture. Therefore, the volume occupied by methanol in the mixture is eight times the volume occupied by flat atomized iron powder. Further, when 31 g of aluminum benzoate is thermally decomposed, 8 g of aluminum oxide is precipitated, and the ratio of the weight of aluminum oxide to the weight of flat atomized iron powder corresponds to 0.008. Next, vibration acceleration consisting of 0.3G in three directions of front-back, left-right, and up-down is repeatedly generated by the exciter, and the vibration is transmitted to the mixture in the mixer via the exciter, and finally, from 0.3G. A vertical vibrational acceleration was applied to the mixture. Further, the temperature of the mixer was raised to 65 ° C., which is the boiling point of methanol, and methanol was vaporized. The vaporized methanol is recovered and reused. After that, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled in a mold. The mold has a shape in which a ring-shaped molded body having an outer diameter of 40 mm, an inner diameter of 25 mm, and a thickness of 6 mm is formed.
Next, the mold was heated to 310 ° C. at a heating rate of 20 ° C./min and held for 1 minute. This first vaporized diethylene glycol and then pyrolyzed aluminum benzoate. The vaporized diethylene glycol is recovered and reused. After that, a pressurizing pressure increasing at a rate of 10 MPa / min is generated by the press machine, the pressurizing pressure is applied to the mixture in the die, and compression is performed when the repulsive force received by the press machine continuously increases. It stopped and the dust core was manufactured in the mold. After that, the dust core was taken out from the mold.
Next, the performance of the prepared dust core was measured. This result is compared with the two types of dust cores described in Non-Patent Document 5. The first powder magnetic core is a ring-shaped powder magnetic core produced by applying a pressurizing pressure of 490 MPa to flat atomized iron powder (290PC-2). The second powder magnetic core insulates the surface of flat atomized iron powder (290PC-2) with phosphoric acid, boric acid, and magnesium oxide, and further adds 0.8% by weight of synthetic resin to provide two types of insulators. It is a powder magnetic core formed by forming a collection of flat atomized iron powder insulated with (1) at a pressurizing pressure of 490 MPa.
First, the weight of the dust core was measured, and the density of the dust core was determined from the volume of the dust core. The density was 7.3 g / cm ³ . On the other hand, the density of the first dust core described in Non-Patent Document 5 is 7.1 g / cm ³ , and the compression density of the second dust core is 6.84 g / cm ³ . The density of the prepared dust core is higher than the density of the two types of dust core described in Non-Patent Document 5. The reason for this is that by superimposing all the flat atomized iron powders on each other, the gap between the flat atomized iron powders is narrowed, and the aluminum oxide fine particles fill the voids of the flat atomized iron powders. It depends on the effect and the effect that the accumulation degree of the flat atomized iron powder is increased with the movement of the aluminum oxide fine particles.
Furthermore, the specific resistance of the dust core was measured. A copper plate was attached to both planes of the dust core via a conductive paste, and the copper plate was pressurized to measure the specific resistance. The specific resistance of the prepared dust core was 38 Ω · cm. On the other hand, the specific resistance of the second dust core described in Non-Patent Document 5 is 21 Ω · cm. The specific resistance of the prepared dust core is higher than the specific resistance of the second powder magnetic core described in Non-Patent Document 5. The reason for this is that the surfaces of the flat atomized iron powders that overlap each other are covered by the aggregates of aluminum oxide fine particles and pores that have extremely high insulation resistance, and the aggregates of the flat atomized iron powders are compressed so that the flat atoms are stacked. This is because the small overlapping gaps are filled with the aggregates of the aluminum oxide fine particles and the vacancies, and the voids of the adjacent flat atomized iron powders are filled with the aggregates of the aluminum oxide fine particles and the vacancies.
Next, the eddy current loss of the prepared dust core was determined using the products SY-8218 / SY-8218 of Iwatsu Electric Co., Ltd., which is a BH analyzer. The eddy current loss at a magnetic flux density of 50 mT was 1 kW / m ³ at 10 kHz and 100 kW / m ³ at 100 kHz. This value is 1/8 of the eddy current loss of the second dust core described in Non-Patent Document 5. The reason for this is that the collection of aluminum oxide fine particles and pores, which have extremely high insulation resistance, fills the small gaps where the flat surfaces overlap, and also fills the voids of the adjacent flat atomized iron powder, and flat atomized iron. This is due to the decrease in eddy currents flowing through the gaps between the powders.
Furthermore, in the magnetic material measurement system, Model No. of Keycom Co., Ltd. The frequency characteristic of magnetic permeability was measured using per. In a magnetic field of 8 A / m, the initial magnetic permeability of the prepared dust core was 80 up to around 10 kHz and 65 around 100 kHz. On the other hand, the initial magnetic permeability of the first dust core described in Non-Patent Document 5 is 82 up to around 10 kHz and 68 at around 100 kHz in a magnetic field of 8 A / m. The initial magnetic permeability of the second dust core has a value of 65 at around 10 kHz and a value of 63 at around 100 kHz in a magnetic field of 8 A / m. The initial magnetic permeability of the dust core is larger than the initial magnetic permeability of the two types of dust core described in Non-Patent Document 5. The reason for this is that the effect of aligning all the flat atomized iron powders in the flat plane direction, which is the axial direction for easy magnetization, and the collection of aluminum oxide fine particles and pores, which have extremely high insulation resistance, are slightly overlapped with each other. This is due to the fact that the gaps between the flat atomized iron powders are filled, and the voids of the adjacent flat atomized iron powders are filled, and the eddy current flowing through the gaps between the flat atomized iron powders is reduced.
Further, the iron loss of the powder magnetic core prepared under the measurement conditions of the exciting magnetic flux density of 1 T and the exciting frequency of 100-800 Hz was measured by a simple iron loss measuring instrument of Toei Kogyo Co., Ltd. The iron loss was 6 W / kg at 100 Hz, 13 W / kg at 200 Hz, 28 W / kg at 400 Hz, and 56 W / kg at 800 Hz.
On the other hand, in Non-Patent Document 7, atomized iron powder (300NH of Kobe Steel Works) is insulated with a two-layer coating of a phosphoric acid-based inorganic insulating film and a silicone resin, and this powder is heated to 130 ° C. to lubricate the mold. A dust core is described in which a ring-shaped dust core is formed at 1176 MPa by the method and then magnetically annealed at 500 ° C. for 30 minutes in a nitrogen atmosphere. The annealing temperature is limited to 550 ° C by the heat resistance of the insulator. According to Non-Patent Document 7, the compression density is 7.61 g / cm ³ and the filling rate reaches 97% because the pressurizing pressure is as high as 1176 MPa. On the other hand, the atomized iron powder pressurized at 1176 MPa is sufficiently plastically deformed. Therefore, in the magnetic annealing at 500 ° C., the reduction of the hysteresis loss of the dust core is limited to a part. Further, the iron loss of the dust core under the measurement conditions where the exciting magnetic flux density is 1.5T and the exciting frequency is 200-700Hz is 5W / kg at 50Hz, 12W / kg at 100Hz, and 23W / kg at 200Hz. It is 50 W / kg at 400 Hz and 100 W / kg at 700 Hz.
The iron loss of the produced dust core is about 1/2 of that of the dust core described in Non-Patent Document 7. The reason for this is that in the produced dust core, the eddy current flowing through the gaps between the flat atomized iron powders is smaller than the eddy currents flowing through the gaps between the atomized iron powders described in Non-Patent Document 7, and the flat atomized iron powders. Is not plastically deformed, and the holding power of the flat atomized iron powder is not increased.
Next, the prepared dust core was dropped from a height of 2 m onto the floor surface, but the dust core was not destroyed. Therefore, the prepared dust core has the required mechanical strength. The reason for this is that a large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Furthermore, the produced dust core was observed and analyzed. The produced dust core was cut in two in the thickness direction, and the cut surface was observed with an electron microscope. As the electron microscope, an extremely low acceleration voltage SEM manufactured by JFE Techno Research Co., Ltd. was used. This device is capable of observing with an extremely low acceleration voltage from 100 volts, and has a feature that the sample can be directly observed without forming a conductive film on the sample.
First, the secondary electron beam between 900 and 1000 V of the backscattered electron beam was taken out and image-processed, and the cut surface was observed. Flat atomized iron powder overlapped with each other on the flat surfaces, and granular fine particles having a size of 40-60 nm formed 13-17 layers and laminated to evenly fill the gaps where the flat surfaces overlapped with each other. Next, the energy of the characteristic X-ray and its intensity were image-processed, and the types of elements constituting the granular fine particles and their distribution states were analyzed. Both aluminum atoms and oxygen atoms were uniformly dispersed, and no particular uneven distribution was observed. Therefore, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps between the flat atomized iron powders overlapping the flat surfaces. FIG. 1 schematically shows a state in which a part of the cut surface is enlarged. 1 is flat atomized iron powder, and 2 is fine particles of aluminum oxide.
As described above, the powder magnetic core prepared using the flat atomized iron powder has a higher compression density and increased insulation resistance than the powder magnetic core prepared by the conventional manufacturing method using the flat atomized iron powder. The eddy current loss was small, the initial magnetic permeability was increased, the holding power of the flat atomized iron powder was not increased, and the required mechanical strength was obtained.

Example 2
In this embodiment, the flat reduced iron powder obtained by flattening the reduced iron powder is insulated by a collection of fine particles of aluminum oxide, and the insulated collection of flat reduced iron powder is compressed in a mold to form a dust core. Is an embodiment of manufacturing in a mold.
MG150D manufactured by JFE Steel Corporation was used as the flattened reduced iron powder. This flat-reduced iron powder is a flattened reduced iron powder (MG270H of JFE Steel Corporation), and is the flat-reduced iron powder described in Non-Patent Document 3.
Further, as in Example 1, aluminum benzoate was used as a raw material for aluminum oxide, diethylene glycol was used as an organic compound, the same device was used as a mixer, and a vibration exciter was installed in the lower part of the mixer.
Further, in the same manner as in Example 1, 31 g of aluminum benzoate was dispersed in 1 liter of methanol, and 200 cc of diethylene glycol was mixed with this methanol dispersion to prepare a mixed solution. Next, the mixer was placed on a vibration table, the mixed solution and 1 kg of flattened iron powder were charged into the mixer, and mixing and rocking were repeated by the mixer to prepare a mixture. Next, the vibration acceleration in the three directions of front-back, left-right, and up-down consisting of 0.3 G was repeatedly generated by the exciter, and finally, the vibration acceleration in the up-down direction consisting of 0.3 G was added to the mixture. Further, the temperature of the mixer was raised to 65 ° C. to vaporize methanol. After that, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled in the same mold as in Example 1.
Next, in the same manner as in Example 1, the temperature of the mold was raised to 310 ° C. and held for 1 minute. After that, as in Example 1, a pressurizing pressure increasing at a rate of 10 MPa / min is generated by the press machine, and the pressurizing pressure is applied to the mixture in the die, and the repulsive force received by the press machine continues. When the pressure increased, compression was stopped and a dust core was manufactured in the mold. After that, the dust core was taken out from the mold.
Next, the performance of the prepared dust core was measured. This result is compared with the dust core described in Non-Patent Document 3. MG150D was used as the flattened iron powder for both powder magnetic cores.
First, the weight of the dust core was measured, and the density of the dust core was determined from the volume of the dust core. The density was 7.2 g / cm ³ . On the other hand, the density of the dust core described in Non-Patent Document 3 is 6.93 g / cm ³ . The reason why the density of the prepared dust core is higher than the density of the dust core described in Non-Patent Document 3 is that all the flat reduced iron powders are superposed on each other in the same way as in Example 1. The effect of narrowing the gap between the flat-reduced iron powders, the effect of the aluminum oxide fine particles filling the voids in the collection of flat-reduced iron powders, and the degree of accumulation of the flat-reduced iron powders due to the movement of the aluminum oxide fine particles. Depends on the increased effect. Further, in the dust core described in Non-Patent Document 3, since the flat reduced iron powder is a porous body, the cured epoxy resin cannot fill the voids of all the flat reduced iron powder, and the dust core cannot be filled. The density of the powder has decreased.
Next, the initial magnetic permeability at direct current was measured using a BH analyzer manufactured by Denshi Kogaku Kogyo Co., Ltd. The initial magnetic permeability of the prepared dust core at direct current was 100. On the other hand, the initial magnetic permeability of the dust core described in Non-Patent Document 3 at direct current is 94.9.
Moreover, the initial magnetic permeability in alternating current was measured using the apparatus of Example 1. The produced dust core was 100 up to around 200 kHz, gradually decreased above 200 kHz, and was 67 at 1 MHz. On the other hand, the powder magnetic core described in Non-Patent Document 3 was 94.9 up to around 200 kHz, gradually decreased above 200 kHz, and was 63 at 1 MHz.
The reason why the initial magnetic permeability of the prepared dust core is higher than the initial magnetic permeability described in Non-Patent Document 3 is that, as in Example 1, all the flat reduced iron powders are all flattened in the axial direction for easy magnetization. The effect of aligning the directions and the collection of aluminum oxide fine particles and pores with extremely high insulation resistance fill the small gaps where the flat surfaces overlap, and also fill the voids of the adjacent flat reduced iron powder. This is due to the decrease in the eddy current flowing through the gaps between the flattened iron powders.
Further, using the apparatus of Example 1, the iron loss of the dust core was measured under the measurement conditions where the exciting magnetic flux density was 50 mT and the exciting frequency was 20-100 kHz. The iron loss of the produced dust core is about 1/2 of the iron loss of the dust core described in Non-Patent Document 3 at 20 kHz, and the iron loss of the dust core described in Non-Patent Document 3 at 50 kHz. It was about 1/4, which was about 1/5 of the iron loss of the dust core described in Non-Patent Document 3 at 100 kHz. The iron loss described in Non-Patent Document 3 is that the pressure for pressurizing the aggregate of flat reduced iron powder is 686 MPa instead of 490 MPa.
As for the result of iron loss, as compared with the result of Example 1, the higher the frequency, the larger the difference from the iron loss of the dust core described in Non-Patent Document 3. The reason for this is that the epoxy resin that insulates the flat-reduced iron powder described in Non-Patent Document 3 does not fill the gaps between the flat-reduced iron powders, and some of the flat-reduced iron powders come into direct contact with each other, so that the flat-reduced iron powders come into direct contact with each other. This is due to the vortex current loss flowing through the gaps between the powders. That is, when all the flat-reduced iron powders overlap each other on the flat surfaces, the mechanical strength required for the powder magnetic core cannot be realized, so that the aggregate of the flat-reduced iron powders is simply compressed. As a result, some flattened iron powders come into direct contact with each other. As a result, since the eddy current loss is proportional to the square of the frequency, the higher the frequency, the greater the eddy current loss of the dust core described in Non-Patent Document 3. Further, since the iron loss at 20 kHz is about 1/2 of the iron loss of the dust core described in Non-Patent Document 3, the hysteresis loss of the flat reduced iron powder increases when the powder magnetic core is manufactured. It depends on the effect that was not there. That is, the powder magnetic core described in Non-Patent Document 3 is heat-treated at 180 ° C. for 30 minutes, but at 180 ° C., the processing strain of the flat reduced iron powder that has undergone plastic deformation at a pressurizing pressure of 686 MPa is This cannot be eliminated, and the hysteresis loss of the dust core is increasing due to the increase in the holding power of the flattened iron powder.
Next, as in Example 1, the dust core was dropped from a height of 2 m onto the floor surface, but the dust core was not destroyed. Therefore, the dust core has the required mechanical strength. The reason for this is that a large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Further, in the same manner as in Example 1, the produced dust core was cut in two in the thickness direction, and the cut surface was observed with an electron microscope. Similar to Example 1, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps between the flat reduced iron powders overlapping the flat surfaces.
As described above, the powder magnetic core prepared using the flat reduced iron powder has a higher compression density and increased insulation resistance than the powder magnetic core prepared by the conventional manufacturing method using the flat reduced iron powder. The eddy current loss was small, the initial magnetic permeability was increased, the holding power of the flat atomized iron powder was not increased, and the required mechanical strength was obtained.

Example 3
In this embodiment, flat sendust powder is used as a flat soft magnetic powder having high hardness, the flat sendust powder is insulated by a collection of fine particles of aluminum oxide, and the insulated collection of flat sendust powder is compressed in a mold. This is an example of manufacturing a dust core in a mold.
For the flattened sendust powder (a product of Tokin Corporation), water atomized sendust powder was flattened, and then annealed in an argon gas atmosphere at 650 ° C. for 2 hours to remove the strain due to the flattening. The average major axis is 40 μm, the average thickness is 1.5 μm, the thickness is thinner than the above-mentioned flat iron powder, and the flatness is high. The flat sendust powder has a high hardness, and in order to plastically deform the flat sendust powder, a pressurizing pressure larger than the pressurizing pressure for plastically deforming the flat iron powder is applied. This increases the hysteresis loss of the dust core.
Further, as in Example 1, aluminum benzoate was used as a raw material for aluminum oxide, diethylene glycol was used as an organic compound, the same device was used as a mixer, and a vibration exciter was installed in the lower part of the mixer.
Further, in the same manner as in Example 1, 31 g of aluminum benzoate was dispersed in 1 liter of methanol, and 200 cc of diethylene glycol was mixed with this methanol dispersion to prepare a mixed solution. Next, the mixer was placed on a vibration table, the mixed solution and 1 kg of flat sendust powder were charged into the mixer, and mixing and shaking were repeated by the mixer to prepare a mixture. Next, the vibration acceleration in the three directions of front-back, left-right, and up-down consisting of 0.3 G was repeatedly generated by the exciter, and finally, the vibration acceleration in the up-down direction consisting of 0.3 G was added to the mixture. Further, the temperature of the mixer was raised to 65 ° C. to vaporize methanol. After that, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled in the same mold as in Example 1.
Next, the performance of the prepared dust core was measured. This result is compared with the powder magnetic core using the flat sendust powder described in Non-Patent Document 8. The powder magnetic core described in Non-Patent Document 8 is obtained by molding a slurry obtained by mixing a silicone resin, a thickener and a solvent with flat powder into a sheet, and press-molding and heat-treating the obtained sheet. Was applied to produce a dust core. Silicone resin has excellent insulating properties like epoxy resin, but its heat resistance is lower than 250 ° C., and the holding power of flat sendust powder cannot be restored by heat treatment, resulting in hysteresis loss in the dust core. large.
First, the weight of the dust core was measured, and the filling rate of the dust core was determined from the volume of the dust core. The filling rate was 82% by weight. On the other hand, the filling rate of the dust core described in Non-Patent Document 8 is 70% by weight. The large difference in filling rate is due to the following reasons.
Looking at the cross-sectional photograph of the dust core published in Non-Patent Document 8, many voids are formed. Further, most of the voids are formed above and below the flat sendust powder having a relatively large particle size. Therefore, when the slurry was formed into a sheet, voids were formed in the sheet, and then the sheet was pressure-molded, so that the voids were further expanded. As a result, the filling rate of the dust core became low. In other words, since the aggregates of flat sendust powder are not rearranged just by molding into a sheet, the degree of accumulation of the aggregates of flat sendust powder is low, and voids are formed above and below the flat sendust powder having a relatively large particle size. Cheap. Further, in the cross-sectional photograph of the dust core, most of the flat sendust powders are deformed so as to undulate with the flat surface in the vertical direction. In other words, the flat sentust powder has a high hardness, and a large pressurizing pressure is applied when the dust core is manufactured, the flat sentust powder is sufficiently plastically deformed, and the plastically deformed flat sentust powder is entangled to form a machine of the dust core. Target strength is generated. Therefore, since a large pressure was applied to the collection of the flat sendust powder in which the voids were formed and compressed, most of the flat sendust powder was deformed so as to undulate with the flat surface in the vertical direction. This further expanded the voids. On the other hand, the heat resistance of the insulating material is lower than 250 ° C., and the holding power of the flat sentust powder cannot be restored by the heat treatment of the dust core, and the hysteresis loss of the dust core described in Non-Patent Document 8 is large. On the other hand, if all the flat soft magnetic powders are aligned in the flat plane direction as in Example 3, the plastically deformed flat sendust powders are less likely to be entangled, so that the mechanical strength required for the dust core cannot be realized.
On the other hand, in the powder magnetic core of Example 3, vibrations in three directions were repeatedly applied to the mixture of the aggregate of flat sendust powder and the mixed solution, and finally vibrations in the vertical direction were applied. For this reason, the arrangement in which the flat sendust powder having a relatively small particle size enters the voids of the flat sendust powder collection and the arrangement in which the flat sendust powder moves above the flat sendust powder collection progresses with the flat surface facing up, and the flat sendust The degree of accumulation of powder collection increases. Finally, when vibration is applied in the vertical direction, all the flat sendust powders are overlapped with each other with their faces facing up. As a result, the filling rate of the dust core of Example 3 was increased.
Next, the complex magnetic permeability at alternating current was measured using the apparatus of Example 1. The produced dust core had a value of 400 up to about 10 MHz in the real part, gradually decreased when it exceeded 10 MHz, decreased to a value of 210 in the vicinity of 300 MHz, and overlapped with the imaginary part. The imaginary part increased from around 3 MHz, reached a peak value of 210 around 300 MHz, and gradually decreased from around 300 MHz. Incidentally, the conductivity of the sendust is the 1.25 × ¹⁰ 6 S / m, the thickness of the epidermis of sendust of relative permeability 400 in 10 MHz, the 2.25 micrometers. This value corresponds to a value obtained by laminating aluminum oxide fine particles having a thickness of 50 nm in 7 to 8 layers on an average thickness of 1.5 μm of flat sendust powder to insulate them. Therefore, in Example 3, since all the flat sendust powders insulated by the collection of aluminum oxide fine particles are superposed on the flat surfaces, the reduced eddy current flows through the gaps between the flat surfaces having high insulating properties. Further, by reducing the eddy current, the imaginary part of the complex magnetic permeability increased. In addition, since all the flat sendust powders were aligned in the flat plane direction, which is the axial direction for easy magnetization, the real part of the complex magnetic permeability had a constant value.
On the other hand, the dust core published in Non-Patent Document 8 has a value of 280 up to around 5 MHz, gradually decreases above 5 MHz, decreases to a value of 130 near 500 MHz, and overlaps with the imaginary part. It was. The imaginary part increased from around 2 MHz, increased to a value of 130 near 500 MHz, and overlapped with the real part. That is, in the dust core published in Non-Patent Document 8, as described above, many voids are formed, and most of the flat sendust powder is deformed so as to undulate with the flat surface in the vertical direction. There is. Further, the silicone resin, the thickener and the solvent added to the flat sendust powder are adsorbed on the flat sendust powder with an adhesive force according to the concentration of the thickener. After the heat treatment, the silicone resin is cured and the thickener and the solvent are volatilized. Therefore, in the portion where the larger void is formed, when the flat sendust powder is deformed like a swell, a part of the insulator is peeled off from the flat sendust powder, and the flat sendust powders come into direct contact with each other. As a result, an eddy current flows in the gap between the flat sendust powders. As a result, the value of the imaginary part of the complex magnetic permeability of the dust core published in Non-Patent Document 8 was 0.6 times the value of the imaginary part of the complex magnetic permeability of the powder magnetic core in Example 3. Further, the dust core described in Non-Patent Document 8 was deformed so that all the flat sendust powders were undulating, and many voids were formed in the gaps between the flat sendust powders. On the other hand, in the powder magnetic core in Example 3, all the flat sendust powders are aligned in the flat plane direction, which is the axial direction for easy magnetization, so that the actual value of the complex magnetic permeability is published in Non-Patent Document 8. It was 1.4 times the value of the real part of the complex magnetic permeability of the dust core.
Next, as in Example 1, the dust core was dropped from a height of 2 m onto the floor surface, but the dust core was not destroyed. Therefore, the dust core has the required mechanical strength. The reason for this is that a large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Further, in the same manner as in Example 1, the produced dust core was cut in two in the thickness direction, and the cut surface was observed with an electron microscope. Similar to Example 1, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps of the flat sendust powders overlapping the flat surfaces.
As described above, the dust core prepared by using the flat sendust powder has a higher compression density, the insulation resistance is increased, and the eddy current is higher than that of the powder magnetic core prepared by the conventional manufacturing method using the flat sendust powder. The loss was small, the initial magnetic permeability was increased, the holding power of the flat atomized iron powder was not increased, and the required mechanical strength was obtained.

The performance of the dust core in the above three examples was compared with the performance of the dust core prepared by the conventional manufacturing method. The powder magnetic core in the examples is superior to the powder magnetic core produced by the conventional manufacturing method in the following items.
First, the density of the dust core in the examples is higher than the density of the dust core produced by the conventional manufacturing method. The reason for this is that all the flat soft magnetic powders are superposed on each other, narrowing the gaps between the flat soft magnetic powders, and the aluminum oxide fine particles fill the voids of the collection of the flat soft magnetic powders, and further flatten. This is because the aluminum oxide fine particles move when the collection of the soft magnetic powder is compressed, and the degree of accumulation of the flat soft magnetic powder further increases with the movement of the fine particles. As a result, the saturation magnetic flux density of the dust core in the examples becomes higher than the saturation magnetic flux density of the dust core produced by the conventional manufacturing method, and the magnetic energy of the magnetized dust core is large.
Secondly, the magnetic permeability of the dust core in the examples had a value higher than the magnetic permeability of the powder magnetic core prepared by the conventional manufacturing method. The reason for this is that all the flat soft magnetic powders are aligned in the flat plane direction, which is the axial direction for easy magnetization, and the collection of aluminum oxide fine particles having extremely high insulation resistance and fine pores is formed between the flat soft magnetic powders. This is due to the fact that the gap is filled and the eddy current flowing through the gap is reduced. As a result, the dust core in the examples is more likely to be magnetized than the dust core produced by the conventional manufacturing method.
Third, the iron loss of the dust core in the examples is less than the iron loss of the dust core produced by the conventional manufacturing method. The reason for this is that the flat soft magnetic powder is not plastically deformed during the production of the dust core, so that the hysteresis loss of the flat soft magnetic powder does not increase and the eddy current flowing through the gap between the flat soft magnetic powders decreases. It depends on what you did. As a result, the dust core in the examples is less likely to generate heat than the powder core produced by the conventional manufacturing method. That is, the dust core in the examples provided mechanical strength to the dust core by friction-welding an extremely large number of aluminum oxide fine particles to each other. On the other hand, in the powder magnetic core in the conventional manufacturing method, the flat soft magnetic powder is sufficiently plastically deformed, and the plastically deformed flat soft magnetic powder is entangled with each other to give the powder magnetic core mechanical strength. Further, since the powder magnetic core in the conventional manufacturing method insulates the flat soft magnetic powder with an insulator having low heat resistance, the powder magnetic core is magnetically annealed to restore the holding power of the plastically deformed flat soft magnetic powder. I can't.
As described above, in the method for producing a dust core in the present invention, firstly, all soft magnetic powders are used regardless of the hardness of the soft magnetic powders, and secondly, aluminum oxide fine particles having high insulating properties are used. The soft magnetic powder is insulated by the collection of soft magnetic powder, thirdly, the collection of soft magnetic powder is accumulated at high density so that the surfaces overlap each other, and fourth, when the collection of soft magnetic powder is compressed, the aluminum oxide fine particles are separated from each other. This is an epoch-making method for producing a dust core, in which soft magnetic powders are bonded to each other by bonding by frictional heat and bonding of frictional heat between aluminum oxide fine particles.

1 Flat atomized iron powder 2 Fine particles of aluminum oxide

Claims (2)

The manufacturing method for producing a dust core is to fill a mold with a collection of soft magnetic powder covered with a collection of aluminum oxide fine particles, compress the collection of soft magnetic powder with a press machine, and use it as a surface of the soft magnetic powder. The aluminum oxide fine particles in contact are bonded to the surface of the soft magnetic powder by frictional heat, and the aluminum oxide fine particles in contact with each other are bonded by frictional heat at the contact site, and the soft aluminum oxide fine particles are bonded to each other by frictional heat. This is a method for producing a dust core in which magnetic powders are bonded to each other and a dust core composed of a collection of the bonded soft magnetic powders is produced in the mold.
A collection of fine crystals of an aluminum compound that precipitates aluminum oxide by thermal decomposition attaches the organic compound precipitated in the organic compound to the surface of the soft magnetic powder, and the surfaces of the soft magnetic powder are brought together via the organic compound. The aluminum oxide fine particles precipitate an aluminum compound that precipitates aluminum oxide fine particles by thermal decomposition, which is the first step of forming an overlapping collection of soft magnetic powders on the bottom surface of the mixer as the shape of the bottom surface. The number of moles precipitated as a weight less than 1/100 of a collection of soft magnetic powders is dispersed in methanol to prepare a methanol dispersion of the aluminum compound, and the first property of dissolving or mixing in methanol and viscosity. An organic compound having a second property higher than the viscosity of methanol and a third property having a boiling point higher than the boiling point of methanol and lower than the thermal decomposition temperature of the aluminum compound is mixed with the methanol dispersion. A mixer having a heating function is placed on a vibration table, the mixer is filled with a collection of the mixture and soft magnetic powder, and the mixer is rotated and rotated. It is shaken to disperse the collection of the soft magnetic powder in the mixed liquid, and further, a vibrator repeatedly generates vibrations in three directions of up and down, left and right, and front and back, and finally generates vibrations in the up and down direction. The vibration generated by the vibrating machine is transmitted to the mixer via the vibrating table, and the collection of the soft magnetic powder in the mixer is repeatedly moved in the mixed solution in the vibration direction to repeatedly move the mixed solution in the vibrating direction. In the process, the arrangement of the soft magnetic powder is advanced, and then the surfaces of the soft magnetic powder are overlapped with each other via the mixed liquid, and a collection of the soft magnetic powder having the shape of the bottom surface is formed on the bottom surface of the mixer. After that, the temperature of the mixer is raised to the boiling point of methanol, whereby a collection of fine crystals of the aluminum compound is deposited all at once in the organic compound, and the organic compound adheres to the soft magnetic powder. Then, in the first step, a collection of the soft magnetic powders in which the surfaces of the soft magnetic powders are overlapped with each other via the organic compound is formed on the bottom surface of the mixer as the shape of the bottom surface.
A collection of aluminum oxide fine particles is deposited on the surface of the soft magnetic powder, the collection of the soft magnetic powder is compressed in a mold, and the aluminum oxide fine particles in contact with the surface of the soft magnetic powder are the surface of the soft magnetic powder. The aluminum oxide fine particles that are in contact with each other are bonded by frictional heat at the contact site, and the soft magnetic powders are bonded to each other by the bonding of the aluminum oxide fine particles, and the bonded soft magnetic powder is bonded to the aluminum oxide fine particles. A second step in which a dust core composed of a collection of powder is produced in the mold, the mold is filled with the collection of soft magnetic powder prepared in the first step, and the mold is filled with the mold. The temperature is raised to a temperature at which the aluminum compound thermally decomposes, whereby the organic compound is first vaporized, then the fine crystals of the aluminum compound are thermally decomposed, and the surface of the soft magnetic powder is covered with fine aluminum oxide fine particles. The aggregates are deposited all at once, and the aggregates of the aluminum oxide fine particles cover the soft magnetic powder. Then, a continuously increasing compressive stress is applied to the aggregates of the soft magnetic powder by the press machine, and the press machine receives it. When the repulsive force continues to increase, the compressive stress by the press machine is stopped, whereby the collection of the soft magnetic powder is first formed into the shape of the mold, and then the soft magnetic powder is formed. When the aluminum oxide fine particles move to the voids in the gathering and the aluminum oxide fine particles cannot move, the aluminum oxide fine particles that come into contact with the surface of the soft magnetic powder are bonded to the surface of the soft magnetic powder by frictional heat. Further, the aluminum oxide fine particles that are in contact with each other are bonded to each other by frictional heat at the contact portion, and the soft magnetic powders are bonded to each other by the bonding between the aluminum oxide fine particles, and the powder is composed of a collection of the bonded soft magnetic powders. It consists of a second step in which the magnetic core is manufactured in the mold.
The two steps are carried out in succession. The mold is filled with a collection of soft magnetic powder covered with a collection of aluminum oxide fine particles, the collection of soft magnetic powder is compressed by a press machine, and the surface of the soft magnetic powder is pressed. The aluminum oxide fine particles in contact with the soft magnetic powder are bonded to the surface of the soft magnetic powder by frictional heat, and the aluminum oxide fine particles in contact with each other are bonded by frictional heat at the contact site, and the aluminum oxide fine particles are bonded to each other. A method for producing a dust core in which soft magnetic powders are bonded to each other and a dust core composed of a collection of the bonded soft magnetic powders is produced in the mold. The method for producing a dust core in which the dust core is produced in a mold according to claim 1, wherein the soft magnetic powder according to claim 1 is a soft magnetic flat powder having a flat shape. The aluminum compound according to 1 is aluminum benzoate or aluminum naphthenate, and the organic compound according to claim 1 is any ester composed of carboxylic acid vinyl esters, acrylic acid esters, and methacrylic acid esters. , An organic compound belonging to any of glycols and glycol ethers, or a liquid monomer composed of a styrene monomer, and the powder magnetic core according to claim 1 is produced in a mold using these substances. A method for producing a dust core in which a dust core is produced in a mold, which is produced according to a method for producing a dust core.

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