JP2010245459A - Dust core, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core having excellent press-molded ring strength and magnetic characteristics even if low-pressure molding is performed at the room temperature. <P>SOLUTION: In a first mixing step, soft magnetic powder consisting principally of iron and inorganic insulating powder are mixed for six hours using a mixing machine. The mixture obtained in the first mixing step is subjected to a heat treatment in a non-oxidizing atmosphere of 1,000°C to a temperature equal to or lower than the temperature at which the soft magnetic powder begins to be sintered. The mixture obtained in the mixing step and a 0.2 to 3.0 wt.% binding resin for the soft magnetic powder are mixed, and heated to be dried. In a second mixing step wherein a lubricating resin is mixed with the mixture after a coating step, the lubricating resin is mixed with the mixture coated with the binding resin. In a molding step, the soft magnetic powder coated with the binder is pressed to form a molding. In an annealing step, the molding is annealed in the non-oxidizing atmosphere. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dust core made of soft magnetic powder and a method for producing the same.

  A choke coil is used as an electronic device for a control power source such as an OA device, a solar power generation system, an automobile, or an uninterruptible power supply, and a ferrite magnetic core or a dust core is used as its core. Among these, the ferrite core has a defect that the saturation magnetic flux density is small. On the other hand, a dust core produced by molding metal powder has a higher saturation magnetic flux density than soft magnetic ferrite, and thus has excellent DC superposition characteristics.

  The powder magnetic core is required to have a magnetic characteristic capable of obtaining a large magnetic flux density with a small applied magnetic field and a magnetic characteristic that an energy loss due to a change in the magnetic flux density is small due to demands such as improvement of energy exchange efficiency and low heat generation. The energy loss includes what is called iron loss that occurs when a dust core is used in an alternating magnetic field. This iron loss is represented by the sum of hysteresis loss, eddy current loss, and abnormal eddy current loss. Particularly problematic are hysteresis loss and eddy current loss. Hysteresis loss is proportional to the operating frequency, and eddy current loss is proportional to the square of the operating frequency. Therefore, the hysteresis loss is dominant in the low frequency region, and the eddy current loss is dominant in the high frequency region. The dust core is required to have magnetic characteristics that reduce the occurrence of this iron loss.

  In order to reduce the hysteresis loss of the dust core, the domain wall can be easily moved. To that end, the coercive force of the soft magnetic powder particles can be reduced. Therefore, pure iron having a small coercive force has been widely used as soft magnetic powder particles. For example, using pure iron as the soft magnetic powder and reducing the mass loss ratio of impurities to the soft magnetic powder to 120 ppm or less (see, for example, Patent Document 1), pure iron as the soft magnetic powder. A method of reducing hysteresis loss by using the amount of manganese contained in the soft magnetic powder to 0.013% by mass or less is known (for example, see Patent Document 2). In addition, a method for heat-treating soft magnetic powder before forming an insulating coating is known.

  Also known is a method of reducing hysteresis loss by performing a heat treatment on the soft magnetic powder before forming the insulating coating. According to this method, domain wall movement is facilitated by removing strain existing in soft magnetic particles, removing defects such as crystal grain boundaries, and growing (expanding) crystal particles in soft magnetic powder particles, thereby reducing coercive force. Can be lowered. For example, a soft magnetic powder containing iron as a main component, containing 2 to 5% by mass of Si, having an average particle size of 30 to 70 μm, and an average aspect ratio of 1 to 3 is 800 ° C. or higher in an inert atmosphere. The heat treatment is performed to increase the crystal particles in the powder particles, reduce the coercive force, and reduce hysteresis loss (for example, see Patent Document 3), or mix metal particles and spacer particles. In addition, a method of preventing metal particles from being sintered and solidified by separating the metal particles from each other is known (see, for example, Patent Document 4).

JP 2005-15914 A JP 2007-59656 A JP 2004-288893 A JP 2005-336513 A

  However, in the inventions of Patent Documents 1 and 2, it is necessary to perform heat treatment at a low temperature so that the insulating coating on the surface of the soft magnetic powder is not thermally decomposed in the annealing of the molded body after pressure molding, which effectively reduces hysteresis loss. There is a problem that cannot be reduced.

  Further, in the invention of Patent Document 3, when the soft magnetic particles are pure iron, the soft magnetic particles are sintered and solidified. Therefore, the soft magnetic particles need to be mechanically pulverized. There is a problem that new distortion occurs. In the invention of Patent Document 4, it is necessary to separate the metal particles and the spacer particles after the heat treatment, which is not convenient. Further, since magnets are used for separation, there are problems such as magnetization of metal particles.

  The present invention has been made in order to solve the above-described problems, and its purpose is to provide a convenient method that effectively suppresses hysteresis loss without being sintered and hardened during heat treatment of the soft magnetic powder. It is to provide a dust core that can be reduced and a method for manufacturing the same.

  In order to achieve the above object, the dust core of the present invention comprises a mixture of soft magnetic powder and inorganic insulating powder, heat treatment of the mixture, and heat treated soft magnetic powder and inorganic insulating powder. Covered with a binder insulating resin, mixed with a lubricating resin, and the mixture is pressure-molded to produce a molded product, and the molded product is annealed. And In particular, the inorganic insulating powder is a powder having a melting point of 1500 ° C. or higher, a heat treatment temperature of 1000 ° C. or higher, and a heat treatment in a non-oxidizing atmosphere at a temperature lower than the temperature at which the soft magnetic powder starts sintering. It is characterized by that.

Note that Al ₂ O ₃ (melting point: 2046 ° C.), MgO (melting point: 2800 ° C.) or the like is used as the inorganic insulating powder, or heat treatment is performed in a reducing atmosphere such as a hydrogen atmosphere, an inert atmosphere, or a vacuum atmosphere as a non-oxidizing atmosphere. The powder magnetic core and the manufacturing method thereof are also an embodiment of the present invention.

  According to the present invention, when the inorganic insulating fine powder having a melting point of 1500 ° C. or more is uniformly dispersed, the soft magnetic powder particles can be separated from each other during the heat treatment of the powder, and the soft magnetic powder particles are sintered. And can be prevented from solidifying.

The flowchart which shows the manufacturing method of the powder magnetic core of an Example. The graph which showed the relationship between relative permeability (micro | micron | mu) / micro 0 and an applied magnetic field (kA / m).

[1. Manufacturing process]
The method for manufacturing a dust core according to the present invention includes the following steps as shown in FIG.
(1) A first mixing step (step 1) in which an inorganic insulating powder is mixed with a soft magnetic powder.
(2) A heat treatment step (step 2) in which heat treatment is performed on the mixture that has undergone the first mixing step.
(3) A coating process (step 3) in which the soft magnetic powder and the inorganic insulating powder that have undergone the heat treatment process are coated with a binding insulating resin.
(4) A second mixing step (step 4) in which the soft magnetic powder coated with the binding insulating resin is mixed with the lubricating resin with respect to the inorganic insulating powder.
(5) A molding step (step 5) in which the mixture that has undergone the second mixing step is pressure-molded to produce a molded body.
(6) An annealing process (step 6) of annealing the molded body that has undergone the molding process.
Hereafter, each process is demonstrated concretely.

(1) First mixing step In the first mixing step, soft magnetic powder mainly composed of iron and inorganic insulating powder are mixed for 6 hours using a mixer (V-type mixer). In this soft magnetic powder, the silicon component produced by the gas atomization method, the water gas atomization method, and the water atomization method is 0.0 to 1.0 wt% of the soft magnetic powder and 1.0 to 6.5 wt% with respect to the soft magnetic powder. % Soft magnetic powder. The silicon component of the soft magnetic powder is preferably 6.5 wt% or less with respect to the soft magnetic powder, and if it exceeds this, the moldability is poor, and the density of the powder magnetic core is lowered and the magnetic properties are lowered. To do.

  Moreover, the addition amount of the inorganic insulating powder is 0.25 to 1.0 wt% with respect to the soft magnetic powder in the case of soft magnetic powder having a silicon component of 0.0 to 1.0 wt%. In the case of a soft magnetic powder having a silicon component of 1.0 to 6.8 wt%, the content is 0.05 to 0.5 wt% with respect to the soft magnetic powder. If it is less than these, sufficient effects cannot be obtained, and if it is increased, it causes an increase in hysteresis loss due to a decrease in density, a decrease in maximum magnetic flux density, and a decrease in magnetic permeability. On the other hand, the average particle diameter of the inorganic insulating powder is 7 to 400 nm in the case of soft magnetic powder having a silicon component of 0.0 to 1.0 wt%. In addition, in the case of a soft magnetic powder having a silicon component of 1.0 to 6.8 wt%, the thickness is set to 7 to 760 nm. Production of inorganic insulating powders having a particle size smaller than these is difficult, and if it is larger than this, gaps are formed between the soft magnetic powders, the density is lowered, and the magnetic permeability, core loss, and direct current superposition characteristics are deteriorated.

Furthermore, the specific surface area of the inorganic insulating powder is 34 to 300 m ² / g. An inorganic insulating powder having a specific surface area smaller than this is difficult to produce, and if it is larger than this, a gap is generated between the soft magnetic powders, the density is lowered, and the magnetic permeability, core loss, and direct current superposition characteristics are deteriorated. In addition, as the inorganic insulating material, Al ₂ O ₃ , MgO, zirconia oxide, and titania powder, which are powders having a melting point of 1500 ° C. or more, can be used.

(2) Heat treatment process The mixture which passed through the said 1st mixing process is heat-processed in 1000 degreeC or more and the temperature below the temperature which a soft magnetic powder starts sintering. The non-oxidizing atmosphere may be a reducing atmosphere such as a hydrogen atmosphere, an inert atmosphere, or a vacuum atmosphere. That is, it is preferably not an oxidizing atmosphere.

  In addition, by performing heat treatment at a temperature of 1000 ° C. or higher, the domain wall can be obtained by removing strain existing in the soft magnetic powder, removing defects such as crystal grain boundaries, and growing (enlarging) crystal grains in the soft magnetic powder particles. The movement becomes easy, the coercive force can be reduced, and the hysteresis loss can be reduced. Further, when heat treatment is performed at a temperature at which the soft magnetic powder sinters, the soft magnetic powder sinters and hardens, which makes it impossible to use as a material for the dust core.

(3) Coating process The coating process in which the mixture that has undergone the mixing process is coated with a binding insulating resin has a binding property of 0.2 to 3.0 wt% with respect to the mixture that has undergone the mixing process and the soft magnetic powder. The resin is mixed and heat-dried. That is, the heat-resistant insulating film is formed on the surface of the soft magnetic powder by the binding resin with respect to the mixture that has undergone the mixing step. Here, a methylphenyl silicone adhesive can be used as the binder resin. The appropriate amount of methylphenyl silicone resin added is 0.2 to 2.0 wt% with respect to the soft magnetic powder. If it is less than the appropriate amount, the strength of the molded body is insufficient and cracks occur. On the other hand, if the amount is larger than the appropriate amount, there arises a problem that the maximum magnetic flux density is decreased due to the decrease in density and the magnetic characteristics are decreased due to an increase in hysteresis loss.

  Further, the soft magnetic metal powder may be treated with 0.1 to 1.0 wt% of an organometallic coupling agent (such as a silane coupling agent) with respect to the soft magnetic powder. This organometallic coupling agent is used to reduce the amount of the binder resin. The binder resin added here acts as a binder during molding.

(4) Second mixing step In the second mixing step of mixing the lubricating resin with the mixture that has undergone the coating step, the lubricating resin is mixed with the first mixture coated with the binder resin. Here, as the lubricant, a wax such as stearic acid, stearate, stearic acid soap, or ethylene bisstearamide can be used. By adding these, it is possible to improve the slippage between the granulated powders, so that the density during mixing can be improved and the molding density can be increased. Furthermore, it is possible to prevent the powder from sticking to the mold. The amount of the lubricating resin to be mixed is 0.1 to 0.8 wt% with respect to the soft magnetic powder. If it is less than this, a sufficient effect cannot be obtained, and if it is more than this, there arises a problem that the maximum magnetic flux density is reduced due to density reduction and the magnetic characteristics are lowered due to increase in hysteresis loss.

(5) Molding step In the molding step, a molded body is formed by pressure molding the soft magnetism coated with the binder as described above. At this time, the pressure-dried binding insulating resin acts as a binder during molding. The pressure at the time of molding may be the same as that of the conventional invention. In the present invention, about 1600 MPa is preferable.

(6) In the annealing step annealing process, dust by performing relative to said shaped body at a _{N 2} gas or _N 2 + _{H 2} gas non-oxidizing atmosphere, an annealing treatment (600 to 800 ° C. are preferred) A magnetic core is produced. This is because if the annealing temperature is raised too much, the magnetic characteristics deteriorate due to the deterioration of the insulation performance, and in particular, the eddy current loss greatly increases, thereby suppressing the iron loss from increasing.

  At this time, the binding insulating resin is thermally decomposed when it reaches a certain temperature during the annealing process. By performing the heat treatment of the dust core in a nitrogen atmosphere, the binding insulating resin becomes a film covering the surface of the soft magnetic powder. Therefore, even if heat treatment is performed at a high temperature, the insulation does not deteriorate and hysteresis loss due to oxidation does not increase. It also serves to improve mechanical strength.

[2. Measurement item]
As measurement items, permeability, maximum magnetic flux density, and direct current superimposition are measured by the following method. The magnetic permeability was calculated from the inductance at 20 kHz and 0.5 V by applying a primary winding (20 turns) to the produced dust core and using an impedance analyzer (Agilent Technology: 4294A).

  The core loss is obtained by applying a primary winding (20 turns) and a secondary winding (3 turns) to the dust core, and using a BH analyzer (Iwatori Measurement Co., Ltd .: SY-8232), which is a magnetic measurement instrument, Iron loss (core loss) was measured under the conditions of 20 kHz and maximum magnetic flux density Bm = 0.15T. This calculation was performed by calculating the number of hysteresis loss systems and the number of eddy current systems by the following equation, using the following three formulas, and the frequency of iron loss by the least square method.

[Equation 1]
Pc = Kh × f + Ke × f ²
Ph = Kh × f
Pe = Ke × f ²
Pc: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss

[3. Example in which soft magnetic powder having silicon component of 1.0 to 6.8 wt% is used]
Examples 1 to 33 of the present invention will be described below with reference to Tables 1 to 7. These Examples 1 to 33 are examples in which soft magnetic powder having a silicon component of 1.0 to 6.8 wt% is used.

[3-1. First characteristic comparison (comparison of temperature of inorganic insulating powder and heat treatment process)]
In the first characteristic comparison, the inorganic insulating powder added to the soft magnetic powder was compared with the temperature during the heat treatment step. Tables 1 to 4 are tables showing the types of inorganic insulating substances added to the soft magnetic powder and the temperatures of the heat treatment process as comparative examples and examples. The average particle size of each inorganic insulating material is 7 nm for SiO ₂ (specific surface area 300 m ² / g), 13 nm for Al ₂ O ₃ (specific surface area 100 m ² / g), and 50 nm for MgO (specific surface area 34 m ² / g). is there.

In Examples 1 to ₃ , 0.05 to 0.25 wt% of Al ₂ O ₃ is added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 63 μm or less and having a particle size of 63 μm or less and manufactured using a gas atomization method. .
In Example 4, 0.1 wt% of MgO is added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 63 μm or less and having a particle size of 63 μm or less and having a particle size of 63 μm or less.
In Comparative Example 1, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 63 μm or less and having a silicon component of 1.0 wt% produced by the gas atomization method.
In Comparative Examples 2 to 4, 0.05 to 0.25 wt% of SiO ₂ is added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 63 μm or less and having a particle size of 63 μm or less, which is produced by a gas atomization method.
Thereafter, these samples are heat-treated in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 950 ° C. to 1150 ° C.

Table 1 shows the relationship between soft magnetic powder, inorganic insulating powder type and addition amount, first heat treatment temperature, and whether or not the inorganic insulating powder is sintered for Examples 1 to 4 and Comparative Examples 1 to 4. It is. In the table, ○ indicates that the inorganic insulating powder can be used as it is without sintering, Δ indicates that re-pulverization is necessary, and × indicates that pulverization is impossible.

In Examples 5 to 8, 0.01 to 0.1 wt% of Al ₂ O ₃ was added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 75 μm or less produced by a water gas atomizing method and having a particle size of 2.8 wt%. To do.
In Comparative Example 5, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less and produced by the water gas atomization method.
In Comparative Examples 6 to 8, 0.05 to 0.2 wt% of SiO ₂ is added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less manufactured by a water gas atomizing method.
Thereafter, these samples are heat-treated in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 950 ° C. to 1150 ° C.

Table 2 shows the relationship between the soft magnetic powder and the types and addition amounts of the inorganic insulating powder, the first heat treatment temperature, and whether the inorganic insulating powder is sintered for Examples 5 to 8 and Comparative Examples 5 to 8. It is. O, Δ, and X in the table are the same as those in Table 1.

In Examples 9 to 12, 0.01 to 0.1 wt% of Al ₂ O ₃ was added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 75 μm or less prepared by a water atomization method and having a particle size of 75 μm or less. To do.
In Comparative Example 9, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less and having a particle size of 75 μm or less.
In Comparative Examples 10 and 11, the Fe-Si alloy powder of the following silicon components 3.0 wt% particle size 75μm was prepared by water atomization, as the inorganic insulating powder, adding SiO ₂ 0.05~0.1wt%.
Thereafter, these samples are heat-treated in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 950 ° C. to 1150 ° C.

Table 3 shows the relationship between the soft magnetic powder, the type and addition amount of the inorganic insulating powder, the first heat treatment temperature, and whether the inorganic insulating powder is sintered for Examples 9 to 12 and Comparative Examples 9 to 11. It is. O, Δ, and X in the table are the same as those in Table 1.

In Examples 13 to 16, 0.01 to 0.1 wt% of Al ₂ O ₃ was added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 75 μm or less produced by a water atomization method and having a particle size of 75 μm or less. To do.
In Comparative Example 12, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less, which is prepared by the water atomization method.
In Comparative Example 13, 0.05 wt% of SiO ₂ is added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less prepared by a water atomization method.
Thereafter, these samples are heat-treated in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 950 ° C. to 1150 ° C.

Table 4 is a table showing the relationship between soft magnetic powder, inorganic insulating powder type and addition amount, first heat treatment temperature and whether the inorganic insulating powder is sintered for Examples 13 to 16 and Comparative Examples 12 and 13. It is. O, Δ, and X in the table are the same as those in Table 1.

As can be seen from Tables 1 to 4 above, in Comparative Examples 1 to 13, when heat treatment exceeding 1000 ° C. is performed, the powders are solidified. This is because, when the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 63 to 75 μm or less as the soft magnetic powder and the inorganic insulating fine powder being SiO ₂ (melting point). This is because the powders coagulate when using (1500 ° C.). On the other hand, inorganic insulating fine powders such as Al ₂ O ₃ (melting point 2046 ° C.) and MgO (melting point 2800 ° C.) prevent soft magnetic powder particles from being sintered and hardened in a powder heat treatment at 1000 ° C. or higher. I can do it.

  That is, by using an inorganic insulating powder having a high melting point, heat treatment at a high temperature is possible in a conventional heat treatment method such as a box furnace or a tunnel furnace, and the degree of freedom in selecting the furnace is increased. Furthermore, in order to prevent solidification of the powders, heat treatment at a higher temperature becomes possible by using a rotary kiln that is a method of rotating the powders to shorten the time of contact between the powders and preventing solidification.

[3-2. Second characteristic comparison (comparison of added amount of inorganic insulating material)]
In the second characteristic comparison, the amount of inorganic insulating material added to the soft magnetic powder was compared. Table 5 is a table showing the types and components of inorganic insulating materials added to the soft magnetic powder as comparative examples and examples. The average particle size of each inorganic insulating material is 7 nm for SiO ₂ (specific surface area 300 m ² / g), 13 nm for Al ₂ O ₃ (specific surface area 100 m ² / g) and 640 nm, (specific surface area 130 m ² / g), MgO Are 49 nm (specific surface area 34 m ² / g) and 230 nm (specific surface area 160 m ² / g).

The sample used for this characteristic comparison was produced as follows.
In Examples 17 to 19, 13 nm (specific surface area 100 m ² / g) of Al ₂ O ₃ was added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 63 μm or less and having a particle size of 63 μm or less, produced by a gas atomization method. Add 0.5-0.25 wt%.
In Examples 20 to 22, Fe-Si alloy powder having a particle size of 63 μm or less and having a particle size of 63 μm or less and Fe-Si alloy powder of 49 nm (specific surface area 34 m ² / g) as MgO of 0.1 nm was used as the inorganic insulating powder. Add ~ 0.50 wt%.
In Comparative Example 14, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 63 μm or less and having a silicon component of 1.0 wt% produced by the gas atomization method.
In Comparative Example 15, 7 nm (specific surface area: 300 m ² / g) of SiO ₂ as an inorganic insulating powder was added to 0.25 wt% as an inorganic insulating powder with a 1.0 wt% silicon component having a particle size of 63 μm or less produced by a gas atomization method. Added.
Thereafter, these samples are heat-treated in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 950 ° C. to 1150 ° C. Then, 0.1% by mass of the silane coupling agent and 0.5% by weight of the silicone resin were mixed in this order and dried by heating (180 ° C. for 2 hours). Then, 0.4% by weight of zinc stearate was added as a lubricant. Mixed (V-type mixer — 2 hours).

These samples were pressure-molded at a pressure of 1500 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 5 mm. These powder magnetic cores were annealed at 675 ° C. for 2 hours in a nitrogen atmosphere (N ₂ + H ₂ ).

In Examples 23 to 26, a Fe-Si alloy powder having a particle size of 75 µm or less and having a particle size of 75 µm or less prepared by a water gas atomization method was used as an inorganic insulating powder, and 13 nm (specific surface area 100 m ² / g) of Al ₂ O _3. Is added in an amount of 0.01 to 0.50 wt%.
In Comparative Example 16, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less and produced by the water gas atomizing method.
In Comparative Examples 17 and 18, Fe-Si alloy powder having a particle size of 75 μm or less prepared by a water gas atomization method and containing 2.8 wt% of SiO— ₂ of 7 nm (specific surface area 300 m ² / g) as an inorganic insulating powder is 0. Add 0.05 to 0.10 wt%.
Thereafter, these samples are heat-treated in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 950 ° C. to 1150 ° C. Then, 0.1% by mass of the silane coupling agent and 0.2% by weight of the silicone resin were mixed in this order and dried by heating (180 ° C. for 2 hours). Then, 0.4% by weight of zinc stearate was added as a lubricant. Mixed (V-type mixer — 2 hours).

These samples were pressure-molded at a pressure of 1500 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 5 mm. And these powder magnetic cores were annealed at 575-675 ° C. for 2 hours in a nitrogen atmosphere (N ₂ + H ₂ ).

Table 5 shows the relationship between soft magnetic powder, inorganic insulating powder type and addition amount, first heat treatment temperature, magnetic permeability, and iron loss per unit volume (core loss) for Examples 17 to 31 and Comparative Examples 14 to 19. It is the table | surface shown about.

As can be seen from Table 5, in the soft magnetic powder produced by the gas atomization method with Si of 1.0 wt%, the inorganic insulating powder was added in Examples 17 to 22 in which Al ₂ O ₃ and MgO were added as the inorganic insulator. Hysteresis loss (Ph) at 20 kHz is lower than Comparative Example 14 that is not performed and Comparative Example 15 in which SiO ₂ is added as an inorganic insulating material. Thereby, it turns out that the magnetic characteristic in the whole is improving. In Examples 17-22, when the addition amount of an inorganic insulating powder increases, it turns out that a density falls as an addition amount increases. Moreover, in Examples 17-19, since the heat processing temperature can be raised by increasing the addition amount of an inorganic insulating powder, the hysteresis loss (Ph) falls and the whole magnetic characteristic is improving. On the other hand, in Examples 20 to 22, it can be seen that as the amount of the inorganic insulating powder added increases, the density decreases and the hysteresis loss (Ph) increases, so that the overall magnetic characteristics are deteriorated.

Moreover, in the soft magnetic powder produced by the water gas atomization method with Si of 2.8%, in Examples 23 to 26 in which Al ₂ O ₃ was added as an inorganic insulator, Comparative Example 16 in which no inorganic insulating powder was added. The hysteresis loss (Ph) at 20 kHz is lower than that. As a result, it can be seen that the overall magnetic properties are improved. In Examples 23 to 26, it can be seen that as the amount of inorganic insulating powder increases, the density decreases as the amount added increases. In comparison between Comparative Examples 17 and 18 and Examples 24 and 25, Examples 24 and 25 in which Al ₂ O ₃ was added as an inorganic insulating material were compared to Comparative Examples 17 and 18 in which SiO ₂ was added as an inorganic insulating material. However, since the heat treatment can be performed at a high temperature, the hysteresis loss (Ph) is reduced. However, in Example 26, the hysteresis loss (Ph) is higher than in Comparative Examples 4 and 5. This is because even when SiO ₂ is used as an inorganic insulating material, if the amount of SiO ₂ added is a certain amount or more, the heat treatment temperature is close to the melting point and the powders are solidified to be ground, This is because a dust core can be produced (see Tables 1 to 4).

From the above, it can be seen that Al ₂ O ₃ and MgO having a melting point exceeding 1500 ° C. are suitable for the kind of the inorganic insulating powder in the case where the inorganic insulating powder is mixed with the soft magnetic powder and the heat treatment exceeding 1000 ° C. is performed. The amount of inorganic insulating powder added is preferably 0.05 to 0.5 wt% with respect to the soft magnetic powder. If it is less than this, a sufficient effect cannot be obtained, and if it exceeds 0.5 wt%, it causes an increase in hysteresis loss due to a decrease in density, a decrease in maximum magnetic flux density, and a decrease in magnetic permeability.

[3-3. Third characteristic comparison (comparison of particle size of inorganic insulating materials)]
In the third characteristic comparison, the particle sizes of the inorganic insulating materials added to the soft magnetic powder were compared. Table 6 is a table showing the types and components of inorganic insulating materials added to the soft magnetic powder as comparative examples and examples. The average particle diameter of each inorganic insulating material is 13 nm (specific surface area 100 m ² / g) and 640 nm for Al ₂ O ₃ (specific surface area 130 m ² / g), 49 nm (specific surface area 34 m ² / g) and 230 nm for MgO (specific surface area 130 m ² / g). Specific surface area of 160 m ² / g).

The sample used for this characteristic comparison was produced as follows.
In Examples 27 to 30, a Fe-Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less prepared by a water atomization method was used as an inorganic insulating powder at 13 nm (specific surface area 100 m ² / g) and 640 nm, (ratio 0.10 to 0.50 wt% of Al ₂ O ₃ having a surface area of 130 m ² / g) is added. In Example 31, 230 nm (specific surface area 160 m ² / g) of MgO was added as the inorganic insulating powder.
In Comparative Example 19, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 75 μm or less and 3.5 wt% silicon component produced by the water atomization method.
Thereafter, heat treatment is performed on these samples in a reducing atmosphere of hydrogen at 1100 ° C. in 25% (the remaining 75% is nitrogen). Then, 0.1% by mass of the silane coupling agent and 0.8% by weight of the silicone resin were mixed in this order and dried by heating (180 ° C. for 2 hours). Then, 0.4% by weight of zinc stearate was added as a lubricant. Mixed (V-type mixer — 2 hours).

These were pressure-molded at a pressure of 1500 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 5 mm. And these powder magnetic cores were annealed at 675 ° C. for 2 hours in a nitrogen atmosphere (N ₂ + H ₂ ).

Table 6 shows the relationship between soft magnetic powder, inorganic insulating powder type and addition amount, first heat treatment temperature, magnetic permeability, and iron loss per unit volume (core loss) for Examples 27 to 31 and Comparative Example 19. It is a table.

As can be seen from Table 6, in the soft magnetic powder produced by the gas atomization method with Si of 3.5 wt%, Al of 13 nm (specific surface area 100 m ² / g) and 640 nm (specific surface area 130 m ² / g) is used as the inorganic insulator. _In Examples 17 to 22 in which 2O ₃ and 230 nm (specific surface area 160 m ² / g) were added, the hysteresis loss (Ph) at 20 kHz was lower than that in Comparative Example 19 in which no inorganic insulating powder was added. ing. Thereby, it turns out that the magnetic characteristic in the whole is improving. In Examples 27-30, when the addition amount of an inorganic insulating powder increases, it turns out that a density falls as an addition amount increases. Further, when Examples 28 and 29 using Al ₂ O ₃ inorganic insulating powders of 13 nm (specific surface area 100 m ² / g) and 640 nm (specific surface area 130 m ² / g) are compared, the amount of inorganic insulating powder added is At the same time, it can be seen that the density of Example 28 having a small particle diameter increases.

From the above, when the inorganic insulating powder is mixed with the soft magnetic powder and the heat treatment exceeding 1000 ° C. is performed, the average particle diameter of the inorganic insulating powder is preferably 7 to 640 nm. Inorganic insulating powders with particle sizes smaller than this are difficult to produce, and if larger than this, gaps occur between soft magnetic powders, density decreases, magnetic permeability, iron loss per unit volume (core loss) In addition, the DC superimposition characteristic is deteriorated. Furthermore, the specific surface area of the inorganic insulating powder is 34 to 300 m ² / g. An inorganic insulating powder having a specific surface area smaller than this is difficult to produce, and if it is larger than this, a gap occurs between soft magnetic powders, the density decreases, magnetic permeability, iron loss per unit volume (core loss) In addition, the DC superimposition characteristic is deteriorated.

[3-4. Fourth characteristic comparison (comparison of Si component of soft magnetic powder)]
In the fourth characteristic comparison, the content of the Si component in the soft magnetic powder was compared. Table 7 is a table showing the Si component content of the soft magnetic powders used as comparative examples and examples. The average particle size of each inorganic insulating material is 7 nm for SiO ₂ (specific surface area 300 m ² / g), 13 nm for Al ₂ O ₃ (specific surface area 100 m ² / g), and 50 nm for MgO (specific surface area 34 m ² / g). is there.

The sample used for this characteristic comparison was produced as follows.
In Example 32, 0.10 wt% of Al ₂ O ₃ is added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less produced by a water gas atomizing method.
In Comparative Example 20, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less produced by the water gas atomization method.
Thereafter, heat treatment is performed on these samples in a reducing atmosphere of hydrogen at 1100 ° C. in 25% (the remaining 75% is nitrogen). Then, 0.1% by mass of the silane coupling agent and 0.8% by weight of the silicone resin were mixed in this order and dried by heating (180 ° C. for 2 hours). Then, 0.4% by weight of zinc stearate was added as a lubricant. Mixed (V-type mixer — 2 hours).

In Example 33, 0.10 wt% of Al ₂ O ₃ is added as an inorganic insulating powder to an Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less produced by a water atomization method. Thereafter, heat treatment is performed in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 1100 ° C.
In Comparative Example 21, the inorganic insulating powder is not added to the Fe—Si alloy powder having a particle size of 75 μm or less and having a particle size of 75 μm or less, which is produced by the water atomization method.
Thereafter, heat treatment is performed on these samples in a reducing atmosphere of hydrogen at 1100 ° C. in 25% (the remaining 75% is nitrogen). Then, 0.1% by mass of the silane coupling agent and 0.8% by weight of the silicone resin were mixed in this order and dried by heating (180 ° C. for 2 hours). Then, 0.4% by weight of zinc stearate was added as a lubricant. Mixed (V-type mixer — 2 hours).

These were pressure-molded at a pressure of 1500 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 5 mm. And these powder magnetic cores were annealed at 675 ° C. for 2 hours in a nitrogen atmosphere (N ₂ + H ₂ ).

Table 7 shows Examples 18, 27, 32 and 33 and Comparative Examples 14 and 19 to 21. Types and addition amounts of soft magnetic powder and inorganic insulating powder, first heat treatment temperature, magnetic permeability, and iron loss per unit volume. It is the table | surface shown about the relationship with (core loss).

As can be seen from Table 7, in Examples 18, 27, 32, and 33, in which 0.10 wt% of Al ₂ O ₃ was added as an inorganic insulator to the soft magnetic powder, and heat treatment was performed at 1100 ° C. On the other hand, in the comparative example to which no inorganic insulating powder was added, the hysteresis loss (Ph) at 20 kHz was lower in Examples 18, 27, 32, and 33, so that the overall magnetic characteristics were improved. You can see that On the other hand, comparing Examples 18, 27, 32, and 33, it can be seen that the density decreases as the Si ratio is increased.

  From the above, it is desirable that the Si ratio of the inorganic insulating fine powder is 1.0 to 6.5%. That is, when the Si ratio of the inorganic insulating fine powder exceeds 6.5%, the moldability is poor, the density of the dust core is lowered, and the magnetic properties are lowered.

[4. Example in which soft magnetic powder having silicon component of 0.0 to 1.0 wt% is used]
Examples 34 to 56 of the present invention will be described below with reference to Tables 8 to 11. In Examples 34 to 56, soft magnetic powder having a silicon component of 0.0 to 1.0 wt% is used.

[4-1. Fifth characteristic comparison (comparison of temperature of inorganic insulating powder and heat treatment process)]
In the fifth characteristic comparison, the inorganic insulating powder added to the soft magnetic powder was compared with the temperature during the heat treatment step. Table 8 is a table showing the types and components of inorganic insulating materials added to the soft magnetic powder as comparative examples and examples. The average particle size of each inorganic insulating material is as follows: SiO ₂ is 7 nm (specific surface area 300 m ² / g), Al ₂ O ₃ is 13 to 1000 nm (specific surface area ₃ to 100 m ² / g), and MgO is 50 to 2000 nm (specific surface area). 1-34 m < ² > / g).

In Examples 34 to 38, 0.25 to 0.75 wt% of Al ₂ O ₃ is added as an inorganic insulating powder to a soft magnetic powder having a particle size of 63 μm or less prepared by a water atomization method and containing 0 wt%.
In Examples 37 and 38, 0.50 to 0.75 wt% of MgO is added as an inorganic insulating powder to a soft magnetic powder having a particle size of 63 μm or less and having a particle size of 63 μm or less produced by a water atomization method.
In Comparative Example 22, 0.52 to 0.75 wt% of SiO ₂ is added as an inorganic insulating powder to a soft magnetic powder having a particle size of 63 μm or less and having a particle size of 63 μm or less produced by a water atomization method.

Table 8 shows the relationship between the first heat treatment temperature and whether the inorganic insulating powder is sintered when the powders of Examples 34 to 38 and Comparative Example 22 are heat-treated in a reducing atmosphere containing 25% hydrogen. It is the table | surface shown about. ◎ in the table can be used as it is without being sintered, ◯ can be used just by lightly loosening, △ needs to be crushed, and × shows a state where pulverization is impossible.

From Table 8, in Comparative Example 22 using SiO ₂ as the inorganic insulating powder, the heat treatment at 900 ° C. does not sinter the inorganic insulating powder, but when the heat treatment exceeding 950 ° C. is performed, the powders are It turns out that it solidifies. On the other hand, in Examples 34 to 38 using Al ₂ O ₃ and MgO powder as the inorganic insulating powder, it can be seen that the inorganic insulating powder can be used as it is without being sintered even in the heat treatment at 1000 ° C.

In Examples 39 to 41 and Comparative Example 23, after applying a flattening process to a soft magnetic powder having a particle size of 106 μm or less produced by a water atomization method and having a particle size of 106 μm or less, Al ₂ O ₃ having a diameter of 13 to 1000 nm is added in an amount of 0.50 to 0.75 wt%.
In Examples 42 to 45 and Comparative Example 24, after applying a flattening process to a soft magnetic powder having a particle size of 106 μm or less and having a particle size of 106 μm or less produced by a water atomization method, 0.50 to 0.75 wt% of MgO having a diameter of 13 to 1000 nm is added.
In Examples 46 to 49 and Comparative Example 24, after applying a flattening treatment to a soft magnetic powder having a particle size of 106 μm or less and having a particle size of 106 μm or less produced by a water atomization method, 0.50 to 0.75 wt% of MgO having a diameter of 13 to 1000 nm is added.

Table 9 shows whether or not the first heat treatment temperature and the inorganic insulating powder sinter when the powders of Examples 39 to 49 and Comparative Examples 23 to 25 were heat-treated in a reducing atmosphere containing 25% hydrogen. It is the table | surface shown about the relationship. ◎ in the table can be used as it is without being sintered, ◯ can be used just by lightly loosening, △ needs to be crushed, and × shows a state where pulverization is impossible.

From Table 9, from Examples 39 to 41 and Comparative Example 23 using Al ₂ O ₃ as the inorganic insulating powder, the inorganic insulating powder is not sintered even if heat treatment is performed at 1150 ° C. when the particle size is 300 nm. It can be seen that when the particle diameter exceeds 1000 ° C. when the particle diameter is 1000 nm, the powders are solidified. Further, from Examples 42 to 45 and Comparative Example 24 in which MgO was used as the inorganic insulating powder and the addition amount of the inorganic insulating powder was 0.50 wt%, heat treatment was performed at 1000 ° C. when the particle diameter was 400 nm. Although the inorganic insulating powder is not sintered, it can be seen that when the particle diameter is 1000 nm, the powder solidifies when the temperature exceeds 950 ° C. Furthermore, from Examples 46 to 49 and Comparative Example 25 in which MgO was used as the inorganic insulating powder and the addition amount of the inorganic insulating powder was 0.75 wt%, even when heat treatment was performed at 1000 ° C. when the particle diameter was 400 nm. Although the inorganic insulating powder is not sintered, it can be seen that when the particle diameter is 2000 nm, the temperature at which the powder solidifies becomes lower than when the particle diameter is 400 nm.

Further, when Al ₂ O ₃ and MgO are used as the inorganic insulating powder, it can be seen that when the particle diameter is 50 nm or less, the inorganic insulating powder is hardly sintered even when the temperature is highest.

In Examples 50 and 51, a soft magnetic powder having a particle size of 75 μm or less and having a particle size of 75 μm or less produced by a water gas atomizing method was added with 0.25 to 0.005 Al ₂ O ₃ having a particle diameter of 13 nm as an inorganic insulating powder. Add 50 wt%.

Table 10 shows the relationship between the first heat treatment temperature and whether the inorganic insulating powder sinters when the powders of Examples 50 and 51 are heat-treated in a reducing atmosphere containing 25% hydrogen. It is. ◎ in the table can be used as it is without being sintered, ◯ can be used just by lightly loosening, △ needs to be crushed, and × shows a state where pulverization is impossible.

From Table 10, in Example 51 in which Al ₂ O ₃ was used as the inorganic insulating powder and the soft magnetic powder was flattened, the powders were solidified compared to Example 50 in which the flattening treatment was not performed. It turns out that the temperature which will do becomes high.

In Examples 52 and 53, a soft magnetic powder having a particle size of 63 μm or less and having a particle size of 63 μm or less and having a particle size of 63 μm or less of Al ₂ O ₃ having a particle diameter of 13 nm was added to 0.25 to 0. 5 as an inorganic insulating powder. Add 50 wt%.
In Examples 54 and 55, 0.25 to 0.50 wt% of MgO having a particle diameter of 50 nm was added as an inorganic insulating powder to a soft magnetic powder having a particle size of 63 μm or less and having a particle size of 63 μm or less produced by a water gas atomization method. To do.
In Comparative Example 26, 0.25 wt% of SiO ₂ is added as an inorganic insulating powder to a soft magnetic powder having a particle size of 63 μm or less and having a particle size of 63 μm or less and having a silicon component of 1.0 wt%.

Table 11 shows the relationship between the first heat treatment temperature and whether the inorganic insulating powder is sintered when the powders of Examples 52 to 55 and Comparative Example 26 are heat-treated in a reducing atmosphere containing 25% hydrogen. It is the table | surface shown about. ◎ in the table can be used as it is without being sintered, ◯ can be used just by lightly loosening, △ needs to be crushed, and × shows a state where pulverization is impossible.

From Table 11, in Examples 52-55 and Comparative Example 26 using a silicon component of 1.0 wt% having a particle size of 63 μm or less prepared by a water gas atomization method as a soft magnetic powder, SiO ₂ was used as an inorganic insulating powder. In Comparative Example 26, it can be seen that the heat treatment at 900 ° C. does not sinter the inorganic insulating powder, but when the heat treatment exceeding 950 ° C. is performed, the powders solidify. On the other hand, in Examples 34 to 38 using Al ₂ O ₃ and MgO powder as the inorganic insulating powder, it can be seen that the inorganic insulating powder can be used as it is without being sintered even in the heat treatment at 1150 ° C.

As can be seen from Tables 8 to 11 above, even when the silicon component of the soft magnetic powder is 0.0 to 1.0, when SiO ₂ (melting point 1500 ° C.) is used as the inorganic insulating powder, 1000 ° C. When the heat treatment exceeding is performed, the powders are solidified. In contrast, inorganic insulating fine powders such as Al ₂ O ₃ (melting point: 2046 ° C.) and MgO (melting point: 2800 ° C.) have a tendency that the soft magnetic powder particles sinter and harden during powder heat treatment at 1000 ° C. or higher. Can be deterred.

Even when Al ₂ O ₃ , MgO is used as the inorganic insulating powder, if the particle diameter exceeds 400 nm, the effect of suppressing the soft magnetic powder particles from being sintered and solidified becomes low. This is because when the powder magnetic core is manufactured, if the particle diameter of the inorganic insulating powder exceeds 400 nm, a gap is generated between the soft magnetic powders, and the density is lowered.

  That is, by using an inorganic insulating powder having a high melting point, heat treatment at a high temperature is possible in a conventional heat treatment method such as a box furnace or a tunnel furnace, and the degree of freedom in selecting the furnace is increased. Furthermore, in order to prevent solidification of the powders, heat treatment at a higher temperature becomes possible by using a rotary kiln that is a method of rotating the powders to shorten the time of contact between the powders and preventing solidification.

[5-2. Sixth characteristic comparison (comparison of added amount and type of inorganic insulating powder)]
In the sixth characteristic comparison, the amount and type of inorganic insulating powder added to the soft magnetic powder were compared. Table 12 is a table showing the types and components of inorganic insulating materials added to the soft magnetic powder as comparative examples and examples. The average particle size of each inorganic insulating material is as follows: SiO ₂ is 7 nm (specific surface area 300 m ² / g), Al ₂ O ₃ is 13 to 300 nm (specific surface area 100 m ² / g), and MgO is 50 to 400 nm (specific surface area 34 m ² / G).

The sample used for this characteristic comparison was produced as follows.
In Examples 56 to 59 and Comparative Example 27, soft magnetic powder having a particle size of 63 μm or less and having a silicon component of 0.0 wt% produced by a water atomization method was used.
In Examples 56 and 57, 0.5 to 0.75 wt% of 13 nm (specific surface area 100 m ² / g) of Al ₂ O ₃ is added to the soft magnetic powder as an inorganic insulating powder.
In Examples 58 and 59, 0.75 to 1.00 wt% of 50 nm (specific surface area 34 m ² / g) MgO is added to the soft magnetic powder as an inorganic insulating powder.
In Comparative Example 27, no inorganic insulating powder is added to the soft magnetic powder.
Thereafter, heat treatment is performed on the samples of Examples 56 to 59 in a reducing atmosphere of 1050 ° C. to 1100 ° C. of hydrogen 25% (the remaining 75% is nitrogen).

In Examples 60 to 65 and Comparative Example 28, the degree of circularity is 0.761, the degree of unevenness is 0.942, and the aspect ratio is 0.061% for the soft magnetic powder having a particle size of 106 μm or less and produced by the water atomization method. The soft magnetic powder which performed the planarization process which will be set to 1.450 was used.
In Examples 60 to 62, 0.5 to 0.75 wt% of Al ₂ O ₃ having a thickness of 13 to 300 nm (specific surface area of 100 m ² / g) is added to the soft magnetic powder as an inorganic insulating powder.
In Examples 63 to 65, 0.50 wt% of 50 to 400 nm (specific surface area 34 m ² / g) of MgO is added to the soft magnetic powder as an inorganic insulating powder.
In Comparative Example 28, no inorganic insulating powder is added to the soft magnetic powder.
Thereafter, heat treatment is performed on the samples of Examples 60 to 65 in a reducing atmosphere of 1050 ° C. to 1100 ° C. of 25% hydrogen (the remaining 75% is nitrogen).

In Example 66 and Comparative Example 29, soft magnetic powder having a particle size of 63 μm or less and having a silicon component of 0.0 wt% produced by a water gas atomization method was used.
In Example 66, 0.50 wt% of Al ₂ O ₃ having a thickness of 13 nm (specific surface area 100 m ² / g) is added to the soft magnetic powder as an inorganic insulating powder.
In Comparative Example 29, no inorganic insulating powder is added to the soft magnetic powder.
Thereafter, the sample of Example 66 is heat-treated in a reducing atmosphere of 1100 ° C. of hydrogen 25% (the remaining 75% is nitrogen).

In Examples 67 to 69 and Comparative Examples 30 and 31, soft magnetic powder having a particle size of 63 μm or less and having a silicon component of 1.0 wt% produced by a gas atomization method was used.
In Example 67, 0.25 wt% of Al ₂ O ₃ having a thickness of 13 nm (specific surface area: 100 m ² / g) is added to the soft magnetic powder as an inorganic insulating powder.
In Examples 68 and 69, 0.25 to 0.50 wt% of 50 nm (specific surface area 34 m ² / g) of MgO is added to the soft magnetic powder as an inorganic insulating powder.
In Comparative Example 30, no inorganic insulating powder is added to the soft magnetic powder.
In Comparative Example 31, 0.25 wt% of SiO ₂ having a thickness of 7 nm (specific surface area 300 m ² / g) is added as the inorganic insulating powder.
Thereafter, the samples of Examples 56 to 59 and Comparative Example 31 are heat treated in a reducing atmosphere of 25% hydrogen (the remaining 75% is nitrogen) at 950 ° C. to 1150 ° C.

  The samples of Examples 56 to 69 and Comparative Examples 27 to 31 were mixed and heated in the order of 0.1 to 0.5 mass% of the silane coupling agent and 0.4 to 0.6 wt% of the silicone resin. After drying (180 ° C. for 2 hours), 0.4% by weight of zinc stearate as a lubricant was added and mixed (V-type mixer—2 hours). Then, it pressure-molded with the pressure of 1500 MPa, and produced the powder magnetic core which makes | forms the ring shape of outer diameter 16mm, internal diameter 8mm, and height 5mm. And these powder magnetic cores were annealed at 675 ° C. for 2 hours.

Table 12 shows the relationship among soft magnetic powder, inorganic insulating powder type and addition amount, first heat treatment temperature, magnetic permeability, and iron loss per unit volume (core loss) for Examples 56 to 69 and Comparative Examples 27 to 31. It is the table | surface shown about.

As can be seen from Table 12, in addition to the water atomizing method and the water atomizing method, a planarization treatment, a soft magnetic powder produced by the water gas atomizing method and the gas atomizing method, and an example in which Al ₂ O ₃ and MgO were added as inorganic insulating powders In the case of 56 to 69, the hysteresis loss (Ph) at 20 kHz is significantly lower than those of Comparative Examples 27 to 30 in which the inorganic insulating powder is not added. Thereby, an iron loss (core loss) will fall and a magnetic characteristic will improve. Moreover, it turns out that a density falls as the addition amount of an inorganic insulating powder increases.
Further, when Comparative Example 30 and Comparative Example 31 were compared, SiO ₂ O ₃ and MgO were added as inorganic insulating powders.

From the above, when the inorganic insulating powder is mixed with the soft magnetic powder having a silicon component of 0.0 to 1.0 wt% and the heat treatment exceeding 1000 ° C. is performed, the kind of the inorganic insulating powder is Al ₂ having a melting point exceeding 1500 ° C. It can be seen that O ₃ and MgO are suitable. Further, the amount of the inorganic insulating powder added is preferably 0.25 to 1.0 wt% with respect to the soft magnetic powder. If it is less than this, a sufficient effect cannot be obtained, and if it exceeds 1.0 wt%, it causes an increase in hysteresis loss due to a decrease in density, a decrease in maximum magnetic flux density, and a decrease in permeability.

[5-3. Seventh characteristic comparison (comparison of DC superposition characteristics)]
In the seventh characteristic comparison, direct current superposition characteristics were compared in the presence or absence of a flattening treatment to a soft magnetic powder having a silicon component of 1.0 wt%. In FIG. 2, μ is a permeability that is normalized when the DC bias magnetic field is H (A / m) and μ 0 that is a relative permeability when the DC bias magnetic field is 0 (A / m). It is the figure which showed the relationship between the relative permeability (micro | micron | mu) 0 which is magnetic permeability, and an applied magnetic field (kA / m).

  From FIG. 2, it can be seen that the relative permeability in the applied magnetic field is superior in the example in which the flattening process is performed compared to the comparative example in which the flattening process is not performed on the soft magnetic powder. By performing a planarization process on the soft magnetic powder, it is possible to remove surface irregularities and make the powder shape close to a sphere. For this reason, it is possible to produce a dust core having a high density even at a low pressure. It can be seen that the dust core has a characteristic that the DC superposition characteristic is excellent when the density is high, and the DC superposition characteristic is improved by increasing the density of the dust core. As described above, by performing the flattening process, not only a low-loss dust core can be provided, but also a dust core having high density and excellent direct current superposition characteristics can be provided.

Claims (22)

Mix soft magnetic powder and inorganic insulating powder, heat-treat the mixture,
The heat-treated soft magnetic powder and the inorganic insulating powder are coated with a binder insulating resin, and the mixture is mixed with a lubricating resin, and the mixture is pressure-molded to produce a molded body. In the dust core formed by annealing the molded body,
The inorganic insulating powder has a melting point of 1500 ° C. or higher,
A dust core produced by performing heat treatment on the soft magnetic powder and the inorganic insulating powder in a non-oxidizing atmosphere at 1000 ° C. or more and below the temperature at which the soft magnetic powder starts sintering. .   2. The dust core according to claim 1, wherein a silicon component of the soft magnetic powder is 1 to 6.8 wt%. _3. The dust core according to claim 1, wherein the inorganic insulating powder is Al ₂ O ₃ or MgO powder, and an addition amount is 0.05 to 0.5 wt%.   The powder magnetic core according to claim 1, wherein the inorganic insulating powder has an average particle size of 7 to 640 nm. The powder magnetic core according to claim 1, wherein the inorganic insulating powder has a specific surface area of 34 to 300 m ² / g.   The addition amount of the inorganic insulating powder is 0.05 to 0.2 wt%, the first heat treatment temperature is 1100 ° C. or more and the soft magnetic powder is less than the temperature at which the sintering starts, and the soft magnetic powder is 2.8 to It is 6.5 wt%, The powder magnetic core of any one of Claims 1-5 characterized by the above-mentioned.   2. The dust core according to claim 1, wherein a silicon component of the soft magnetic powder is 0 to 1.0 wt%. The dust core according to claim 7, wherein the inorganic insulating powder is Al ₂ O ₃ or MgO powder, and the addition amount is 0.25 to 1.0 wt%.   The dust core according to claim 7 or 8, wherein the inorganic insulating powder has an average particle size of 7 to 400 nm.   The dust core according to any one of claims 1 to 9, wherein the soft magnetic powder is produced by a water atomizing method, a gas atomizing method, or a water gas atomizing method.   11. The dust core according to claim 10, wherein when the soft magnetic powder is produced by a water atomizing method, the powder produced by the water atomizing method is obtained by performing a flattening process. A first mixing step of mixing the inorganic insulating powder with the soft magnetic powder;
A heat treatment step of performing a heat treatment on the mixture that has undergone the first mixing step;
A coating step of covering the soft magnetic powder and the inorganic insulating powder that have undergone the heat treatment step with a binding insulating resin;
A mixture obtained by mixing the soft insulating powder coated with the binding insulating resin with the inorganic insulating powder and the lubricating resin with the inorganic insulating powder is subjected to pressure molding treatment to produce a molded body. Molding process;
In the manufacturing method of the powder magnetic core having an annealing step of annealing the molded body that has undergone the molding step,
The inorganic insulating powder has a melting point of 1500 ° C. or higher,
The method for producing a powder magnetic core, wherein the heat treatment for the soft magnetic powder and the inorganic insulating powder is performed in a non-oxidizing atmosphere at a temperature of 1000 ° C. or higher and a temperature at which the soft magnetic powder starts sintering.   The method for producing a dust core according to claim 12, wherein a silicon component of the soft magnetic powder is 1 to 6.8 wt%. Wherein the inorganic insulating _powder, in Al 2 _{O 3} or MgO powder, method for producing a dust core according to claim 12 or claim 13, wherein the addition amount is 0.05 to 0.5%.   The method for producing a dust core according to any one of claims 12 to 14, wherein an average particle size of the inorganic insulating powder is 7 to 640 nm. The specific surface area of the said inorganic insulating powder is 34-300 m < ² > / g, The manufacturing method of the powder magnetic core of any one of Claims 12-15 characterized by the above-mentioned.   The addition amount of the inorganic insulating powder is 0.05 to 0.2 wt%, the first heat treatment temperature is 1100 ° C. or more and the soft magnetic powder is less than the temperature at which the sintering starts, and the soft magnetic powder is 2.8 to It is 6.5 wt%, The manufacturing method of the powder magnetic core of any one of Claims 12-16 characterized by the above-mentioned.   The method for producing a dust core according to claim 12, wherein a silicon component of the soft magnetic powder is 0 to 1.0 wt%. Wherein the inorganic insulating _powder, in Al 2 _{O 3} or MgO powder, method for producing a dust core according to claim 18, the amount of addition is characterized in that it is a 0.25~1.0wt%.   20. The method for manufacturing a dust core according to claim 18, wherein the inorganic insulating powder has an average particle size of 7 to 400 nm.   The method for producing a dust core according to any one of claims 12 to 20, wherein the soft magnetic powder is produced by a water atomizing method, a gas atomizing method, or a water gas atomizing method.   The method for producing a dust core according to claim 21, wherein when the soft magnetic powder is produced by a water atomizing method, the powder produced by the water atomizing method is flattened.

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