JP4847553B2 - Powder magnetic core and manufacturing method thereof - Google Patents

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. When the dust core is used in an alternating magnetic field, an energy loss called iron loss (Pc) occurs. This iron loss can be expressed by the following [Formula 1] relationship. Among these, the iron loss is represented by the sum of hysteresis loss (Ph) and eddy current loss (Pe). The hysteresis loss is proportional to the operating frequency, and the 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.
[Equation 1]
Pc = Ph + Pe, Ph = Kh × f, Pe = Ke × f ² ... Formula 1
Kh: Hysteresis loss coefficient, Ke: Eddy current loss coefficient, f: Frequency

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. By reducing the coercive force, the initial permeability can be improved and the hysteresis loss can be reduced. Eddy current loss is inversely proportional to the specific resistance of the core, as shown in [Equation 2].
[Equation 2]
Ke = k1Bm ² t ² / ρ ... Formula 2
k1: coefficient, Bm: magnetic flux density, t: particle diameter (thickness in the case of plate material), ρ: specific resistance

  As a method of manufacturing such a high-density molded powder magnetic core, a method using iron powder subjected to phosphate treatment as a base material (for example, see Patent Document 1), or a magnetism mainly containing iron. A method in which a phosphate-based first insulating layer and a second insulating layer made of a silicone resin are provided as an insulating coating on the powder (see, for example, Patent Document 2), or a soft magnetic powder surface containing no resin There is known a method (for example, refer to Patent Document 3) in which the surface of the insulating layer is subjected to an insulating coating treatment.

JP 2000-504785 A JP 2006-5173 A JP 2003-332116 A

  However, although a high density molded powder magnetic core has a high magnetic flux density, many distortions are generated in the particles of the soft magnetic powder during molding. This distortion increases the coercivity of the dust core and increases hysteresis loss. Therefore, an annealing operation for the purpose of distortion removal is performed. In the soft magnetic powder containing iron as a main component, a high annealing temperature of 500 ° C. or higher is required to remove this strain. However, when the annealing temperature is increased, dielectric breakdown between the powder particles occurs, the core resistivity increases, eddy current loss increases, and a sufficient effect cannot be obtained.

  For example, in the invention described in Patent Document 1, when the annealing temperature is increased to 500 ° C. or higher in the phosphate-based insulation treatment, dielectric breakdown occurs, so that an eddy current loss increases and a sufficient effect is obtained. There was a problem that was not possible.

  Moreover, in invention of patent document 2, although the heat-resistant temperature shall be 500 degreeC or more, in order to evaluate the insulation between powder, it evaluates with a specific resistance. The heat resistant temperature of 500 ° C. or higher means that the specific resistance is 100 μΩm or higher after the powder magnetic core is annealed at 500 ° C. for 30 minutes. The heat-resistant temperature is 600 ° C. or higher when the powder core is annealed at 600 ° C. for 30 minutes and the specific resistance is 10 μΩm or higher. The calculated eddy current loss is 10 times larger at 600 ° C. In Reference 2, a low frequency such as 400 Hz or 800 Hz is not a big problem, but at a high frequency of 20 kHz as examined in this patent, a specific resistance at 600 ° C. of 10 μΩm or more causes dielectric breakdown. It becomes evaluation that it is.

  Furthermore, in the invention of Patent Document 3, the insulating layer and the insulating powder are specified, and the average particle size of the insulating powder is 0.1 to 10 μm. As this effect, even if the heat treatment temperature after molding is 500 to 900 ° C., compression molding strain remaining in the soft magnetic powder can be released without destroying the insulating layer.

When this result is examined in detail, as shown in Table 5, eddy current loss is evaluated at 15 kHz and 50 mT, and there is no change from 400 ° C. to 900 ° C. On the other hand, the specific resistance is 941 μΩm at 500 ° C., 640 μΩm at 600 ° C., 310 μΩm at 700 ° C., 150 μΩm at 800 ° C., 100 μΩm at 900 ° C. and 500 μC at 900 ° C. At 700 degrees Celsius, it is drastically reduced to 33% at 800 and 11% at 900. The eddy current loss is proportional to the square of the magnetic flux density according to [Equation 2]. That is, in the case of 50 mT as described in Patent Document 3, the influence does not appear so much, but in the case of a high magnetic flux density such as 150 mT, the ratio of iron loss increases, and the specific resistance is greatly reduced. affect.

The present invention has been made in order to solve the above-described problems. The purpose of the present invention is to increase the annealing temperature by covering the surface of the soft magnetic powder with an inorganic insulating powder having a specific surface area of 100 to 300 m ² / g. Thus, it is an object of the present invention to provide a dust core having a low hysteresis loss and a method for manufacturing the same, in which eddy current loss is constant (does not increase) even at high frequency and high magnetic flux density.

Based on the above object, the dust core of the present invention is a mixture of a soft magnetic powder mainly composed of iron and an inorganic insulating powder, and the mixture is coated with a binding insulating resin, and then a binding insulating A soft magnetic powder obtained by mixing a resin and a lubricating resin are mixed, and the mixture is pressure-molded to produce a molded body, and the molded body is annealed. The specific surface area is 100 to 300 m ² / g.

  For the purpose of reducing hysteresis loss, annealing is performed at a temperature of 550 ° C. or higher and below the temperature at which the soft magnetic powder starts to be sintered, a silicone resin is used as a binder resin, or an insulating binder resin is used. In order to reduce the addition amount, a phosphate coating is applied to the soft magnetic powder, or at least one of magnesia powder, alumina powder, silica powder, titania powder and zirconia powder is used as the insulating powder. A dust core in which hysteresis loss is reduced by mixing is also an embodiment of the present invention.

According to the present invention as described above, the inorganic insulating powder is formed on the surface of the soft magnetic powder by mixing the soft magnetic powder mainly composed of iron and the inorganic insulating powder having a specific surface area of 100 to 300 m ² / g. As a result, the eddy current loss is constant even at high frequency and high magnetic flux density, and the hysteresis loss can be reduced. Thereby, a low loss powder magnetic core and its manufacturing method can be provided.

The graph which showed the relationship between the specific surface area of the inorganic insulating powder used by this invention, and the shape of particle | grains. The graph which showed the relationship between the specific surface area of an inorganic insulating powder and the iron loss in the 1st characteristic comparison of the Example of this invention. The graph which showed the relationship between the addition amount of MgO powder and the iron loss in the 2nd characteristic comparison of the Example of this invention. Graph showing the Al ₂ O ₃ powder added amount and the iron loss of the relationship between the second characteristic comparison of Examples of the present invention. The graph which showed the relationship between the inorganic insulating powder and the density in the 2nd characteristic comparison of the Example of this invention. The graph which showed the relationship between the addition amount of an inorganic insulating powder and the eddy current loss in the 3rd characteristic comparison of the Example of this invention. The graph which showed the relationship between the annealing temperature and the iron loss in the 4th characteristic comparison of the Example of this invention. The graph which showed the relationship between the addition amount and density of the powder with respect to the soft-magnetic powder in the 4th characteristic comparison of the Example of this invention. The graph which showed the relationship between the addition amount and density of the powder with respect to the soft-magnetic powder in the 4th characteristic comparison of the Example of this invention.

[1. Manufacturing process]
The manufacturing method of the powder magnetic core of the present embodiment includes the following steps.
(1) A phosphate coating process for applying a phosphate coating to the soft magnetic powder (step 1).
(2) The 1st mixing process (step 2) which mixes an inorganic insulating powder with respect to the soft magnetic powder which passed through the phosphate film processing process.
(3) A coating process (step 3) in which the mixture that has undergone the first mixing process is coated with a binding insulating resin.
(4) A second mixing step (step 4) in which a lubricant is mixed with the mixture coated with the binding insulating resin.
(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) Phosphate treatment step In the phosphate treatment step, a phosphate coating treatment is performed on the soft magnetic powder that is an atomized powder of pure iron. The method of the phosphate coating treatment may be the same as that of the conventional invention. By applying a phosphate coating to the soft magnetic powder, a phosphate compound film can be formed on the surface of the soft magnetic powder. The phosphate compound film is a dense crystalline phosphate film, and has heat resistance, poor electrical conductivity, and vitrification properties. Furthermore, the dense crystalline film has adhesiveness, and the inorganic insulating powder mixed in the first mixing step described later is easily bound to the surface of the soft magnetic powder. Thereby, even with a small amount of inorganic insulating powder, a strong insulating layer can be provided around the soft magnetic powder, so that annealing treatment can be performed at a high temperature. As a result, it is possible to remove the processing strain removal during atomized powder production of atomized powder produced by water atomizing method, gas atomizing method, water gas atomizing method as soft magnetic powder, so the effect of reducing hysteresis loss of dust core Can be obtained.

(2) 1st mixing process In a 1st mixing process, the atomized powder of the pure iron which passed through the phosphate film processing process, and inorganic insulating powder (specific surface area has preferable 100-300 m < ² > / g) are mixed. By mixing the inorganic insulating powder, the surface of the soft magnetic powder can be uniformly covered with a film of the inorganic insulating powder. This film of inorganic insulating powder makes it possible to provide a strong insulating layer between the soft magnetic powders, so that annealing can be performed at a high temperature. Thereby, hysteresis loss can be reduced significantly.

  The inorganic insulating powder is preferably at least one of magnesia powder, alumina powder, silica powder, titania powder, and zirconia powder, which is an inorganic insulating powder having a melting point of 1000 ° C. or higher. The inorganic insulating powder having a melting point of 1000 ° C. or higher is used as a material for the powder magnetic core by sintering the inorganic insulating powder by heat applied in the annealing process for the purpose of removing the strain caused by the pressure applied during the molding described later. This is to prevent it from becoming unusable.

The addition amount of the inorganic insulating powder is 0.5 to 2.0 wt% with respect to the soft magnetic powder. If it is less than this, insulation performance cannot fully be exhibited, and eddy current loss increases remarkably at high annealing temperatures. On the other hand, if it exceeds this, the insulation performance can be exhibited, but there is a problem that the molding density becomes low (less than 7.24 g / cm ³ ) and the magnetic characteristics other than the eddy current loss are lowered.

(3) Coating step The coating step of coating the mixture that has passed through the mixing step with a binding insulating resin comprises a mixture having undergone the mixing step and a binding property of 0.2 to 3.0 wt% with respect to the soft magnetic powder. The resin is mixed and dried by heating. 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, as the binder resin, a silicone resin or a methylphenyl silicone adhesive can be used. The appropriate amount of methylphenyl silicone resin added is 0.1 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.

  Furthermore, the soft magnetic powder may be treated with an organic metal coupling agent (such as a silane coupling agent) of 0.1 to 0.5 wt% of the soft magnetic powder. This organometallic coupling agent is used to reduce the amount of the binder resin. For example, when 0.1 to 0.5 wt% of a silane coupling agent is used as the organic coupling agent, a silicone resin can be used as the binder resin. At this time, the usage amount of the silicone resin can be reduced to 0.125 to 0.75 wt%. Further, the binding resin added here acts as a binder at the time of molding.

(4) 2nd mixing process In the 2nd mixing process which mixes a lubrication agent with the mixture which passed through the said covering process, 0.2-0.7 wt% with respect to the mixture which coat | covered binder insulating resin, and the said soft-magnetic powder % Lubricant. 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. Further, the lubricant can be put in two portions of the first mixing step and the second mixing step. In this case, the addition amount of the lubricating resin is set to 0.1 to 0.8 wt% with respect to the soft magnetic powder by combining the first mixing step and the second mixing step.

(4) Molding step In the molding step, a molded body is formed by pressure molding the soft magnetism covered with the binder as described above. At this time, the 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, and in the present invention, about 1500 MPa is preferable.

(5) Annealing process In the annealing process, the insulating film covered with soft magnetic powder at 550 ° C. or higher is destroyed in the N ₂ gas or N ₂ + H ₂ gas non-oxidizing atmosphere. A powder magnetic core is produced by performing an annealing process below the temperature. The reason why the annealing process is performed at a temperature lower than the temperature at which the insulating film is broken is to release the distortion in the molding process and to prevent the insulating film coated around the soft magnetic powder from being broken by the heat during the annealing process. is there. On the other hand, if the annealing temperature is raised too much, the insulating film coated with the soft magnetic powder is broken, and the eddy current loss is greatly increased due to the deterioration of the insulating performance. This causes a problem that the magnetic characteristics are deteriorated.

When heat treatment is performed, when the temperature at the time of temperature rise is about 350 ° C., the methyl group directly bonded to the Si group is thermally decomposed. Thereafter, it remains as a silica (SiO ₂ ) layer on the surface of the soft magnetic powder, which becomes a strong binder and insulating film. By performing the heat treatment of the powder magnetic core, a dense and strong silica layer is formed. Therefore, even if the heat treatment is performed at a high temperature, the insulating property does not deteriorate, and hysteresis loss due to oxidation does not increase. Further, by performing heat treatment, the methyl group does not remain as carbon due to thermal decomposition, so that the mechanical strength can be improved.

[2. Shape of inorganic insulating powder]
The inorganic insulating powder used for the manufacturing method of the powder magnetic core of the present embodiment has a specific surface area of 100 to 300 m ² / g. The specific surface area is an index indicating the shape of the powder, and the relationship between the specific surface area (S) and the particle shape (D) can be expressed by Equation [3] when the particles are assumed to be spherical. FIG. 1 is a graph showing the relationship between the specific surface area (S) and the particle shape (D) of the inorganic insulating powder used in the present invention.
[Formula 3]
S = 6 / (Dρ) [Equation 3]
ρ: Density

In FIG. 1, when the specific surface area is 100 to 300 m ² / g, it can be seen that the calculated value when the inorganic insulating powder is assumed to be spherical and the actually measured value are different. The calculated value and the actually measured value are different because the surface of the inorganic insulating powder has irregularities. In particular, in the case of 160 m ² / g, it can be seen that the calculated value and the actually measured value are greatly different. This is because when the specific surface area is 160 m ² / g, the inside of the inorganic insulating powder is porous, and the specific surface area becomes large due to the presence of voids inside. Further, the composition of the inorganic insulating powder is desirably at least one of magnesia powder, alumina powder, silica powder, titania powder, and zirconia powder having a melting point of 1000 ° C. or higher. Thereby, even when the heat treatment temperature during the heat treatment step is increased, it is possible to prevent the insulation performance from being lowered and the eddy current loss from being lowered.

Examples 1 to 17 of the present invention will be described below with reference to Tables 1 to 4.
[2. Measurement item]
As measurement items, magnetic permeability, maximum magnetic flux density, and DC superposition characteristics 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 (Pc) was measured under the conditions of 20 kHz and maximum magnetic flux density Bm = 0.15T. And hysteresis loss (Ph) and eddy current loss (Pe) were calculated from the iron loss. This calculation was performed by calculating the hysteresis loss coefficient (Kh) and the eddy current loss coefficient (Ke) of the iron loss frequency curve by the least square method using Equation 1.

[2. First characteristic comparison (comparison of specific surface area of inorganic insulating powder)]
In the second characteristic comparison, the specific surface areas of the inorganic insulating powders added to the pure atomized water atomized powder having a particle size of 75 μm or less were compared. Table 2 is a table showing the type, specific surface area, addition amount, and heat treatment temperature during the heat treatment step of the inorganic insulating powder added to the pure atomized water atomized powder in this example. In this table, as magnetic characteristics, density, magnetic permeability, and iron loss (core loss) per unit deposition (Pc, Ph, Pe) were measured.

The sample used for this characteristic comparison was produced as follows.
In Example 2, after subjecting pure iron water atomized powder to a phosphate coating treatment, MgO having a specific surface area of 160 m ² / g as inorganic insulating powder was 1.0 wt% with respect to pure iron water atomized powder, Mix in a pot mill for 12 hours. In Example 6, after subjecting pure iron water atomized powder to a phosphate coating treatment, Al ₂ O ₃ as an inorganic insulating powder was mixed with 1.0 wt% of pure iron water atomized powder in a pot mill for 12 hours. did. In Example 8, a pure iron water atomized powder was subjected to a phosphate coating treatment, and then SiO ₂ was mixed as an inorganic insulating powder in an amount of 1.0 wt% with respect to the pure iron water atomized powder in a pot mill for 12 hours.

In Comparative Examples 1 and 2, was subjected to a phosphate coating treatment water atomized powder of pure iron, the specific surface area as an inorganic insulating powder of MgO of 34m 2 / ^g or 8m 2 ^{/ g} in water atomized powder of pure iron After adding 1.0 wt%, the mixture was mixed in a pot mill for 12 hours.

A silane coupling agent is mixed with 0.1 wt% of these, a silicone resin is further mixed with 0.3 wt%, heat-dried at 180 ° C for 2 hours, and a zinc stearate 0.4 wt% is mixed as a lubricant. did. Further, it is pressure-molded at a pressure of 1500 MPa to produce a ring-shaped molded body having an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 5 mm, and 600 in a non-oxidizing atmosphere (N ₂ 90% + H ₂ 10%) A heat treatment was performed at 2 ° C. for 2 hours to prepare a dust core.

In Table 1, the inorganic insulating powder 1.0 wt% preferred using MgO Example 2 and item A of Comparative Examples 1 and 2, the inorganic insulating powder item Example 6 using the SiO ₂ of 1.0 wt% to B In addition, 1.0 wt% SiO ₂ Example 8 was set as item C in the inorganic insulating powder. Table 1 shows the relationship between the types of inorganic insulating powder added to pure iron water atomized powder, specific surface area and addition amount, heat treatment temperature, density, permeability at 20 kHz, and core loss for these items A to C. It is a table. FIG. 2 is a graph showing the relationship between the specific surface area of the inorganic insulating powder added to the water atomized powder of pure iron and the core loss.

As can be seen from Table 1, in Examples 2,6,8 specific surface area was added an inorganic insulating insulating powder 100 to 300 m ² / g, a specific surface area of the inorganic insulating powder ^34m 2 / g and ^8m 2 / g Since the eddy current loss (Pe) is significantly reduced as compared with the added Comparative Examples 1 and 2, it can be seen that the iron loss (Pc) is reduced. In particular, when Example 6 is compared with Comparative Examples 1 and 2, when the specific surface area of the inorganic insulating powder is made smaller than 100 ² / g, the permeability increases, but the eddy current loss (Pe) increases significantly. Therefore, it can be seen that the iron loss (Pc) is increased.

Further, FIG. 2 shows that the effect of reducing the eddy current loss (Pe) is exhibited as the specific surface area of the inorganic insulating powder added to the soft magnetic powder is increased. In particular, when the specific surface area is 100 m ² / g or more, an increase in eddy current loss (Pe) is suppressed, and the effect is sufficiently exhibited. On the other hand, it can be seen that the hysteresis loss (Ph) is constant regardless of the specific surface area of the inorganic insulating powder to be added.

As described above, by adding the inorganic insulating powder having a specific surface area of 100 to 300 m ² / g to the soft magnetic powder, an insulating layer made of the inorganic insulating powder can be formed on the surface of the soft magnetic powder. With this insulating layer, the annealing temperature can be increased and hysteresis loss can be reduced. As a result, it is possible to provide a dust core having a constant eddy current loss even at a high frequency and a high magnetic flux density, and a manufacturing method thereof.

[3. Second characteristic comparison (comparison of added amount of inorganic insulating powder)]
In the second characteristic comparison, the amount of the inorganic insulating powder added to the pure atomized water atomized powder having a particle size of 75 μm or less was compared. Table 2 is a table showing the type, specific surface area, and addition amount of the inorganic insulating powder added to the water atomized powder of pure iron in this example. In this table, as magnetic characteristics, density, magnetic permeability, and iron loss (core loss) per unit volume (Pc, Ph, Pe) were measured.

The sample used for this characteristic comparison was produced as follows.
In Examples 1 to 3, after subjecting pure iron water atomized powder to phosphate coating treatment, MgO having a specific surface area of 160 m ² / g as inorganic insulating powder was 0.50 with respect to pure iron water atomized powder. ˜2.00 wt%, mixed in a pot mill for 12 hours. In Examples 4 to 7, after applying a phosphate coating to pure iron water atomized powder, Al ₂ O ₃ having a specific surface area of 100 m ² as an inorganic insulating powder was set to 0.000 on pure iron water atomized powder. 50 to 2.00 wt% was mixed in a pot mill for 12 hours.
In Comparative Example 3, a phosphate coating treatment was applied to water atomized powder of pure iron. In Comparative Example 4, after subjecting pure iron water atomized powder to phosphate coating treatment, MgO having a specific surface area of 160 m ² / g as inorganic insulating powder was 0.25 wt% with respect to pure iron water atomized powder, Mix in a pot mill for 12 hours. In Comparative Example 5, after pure iron water atomized powder was subjected to a phosphate coating treatment, Al ₂ O ₃ having a specific surface area of 100 m ² / g as an inorganic insulating powder was reduced to 0. 0 with respect to pure iron water atomized powder. 25 wt% was mixed in a pot mill for 12 hours.

A silane coupling agent is mixed with 0.1 wt% of these, a silicone resin is further mixed with 0.3 wt%, heat-dried at 180 ° C for 2 hours, and a zinc stearate 0.4 wt% is mixed as a lubricant. did. Further, it is pressure-molded at a pressure of 1500 MPa to produce a ring-shaped molded body having an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 5 mm, and 600 in a non-oxidizing atmosphere (N ₂ 90% + H ₂ 10%) A heat treatment was performed at 2 ° C. for 2 hours to prepare a dust core.

Table 2 shows the types of inorganic insulating powder added to pure iron water atomized powder, specific surface area and addition amount, heat treatment temperature, density, magnetic permeability at 20 kHz, and core loss for Examples 1 to 7 and Comparative Examples 3 to 5. It is the table | surface shown about the relationship. 3 shows a case where MgO powder is added as an inorganic insulating powder to pure iron water atomized powder. FIG. 4 shows a case where Al ₂ O ₃ powder is added as an inorganic insulating powder to water atomized powder of pure iron. FIG. 5 is a diagram showing the relationship between the amount of each inorganic insulating powder added and the iron loss. FIG. 5 is a diagram showing the relationship between the amount of inorganic insulating powder added and the density of the dust core.

As can be seen from Table 2, Examples 1 to 7 and Comparative Examples 4 and 5 in which the inorganic insulating powder was added to the water atomized powder of pure iron were compared with Comparative Example 3 in which the inorganic insulating powder was not added. It can be seen that although the magnetic permeability is lowered, the hysteresis loss (Ph) and the eddy current loss (Pe) are greatly reduced. Further, Examples 1 to 3 in which 0.50 to 2.00 wt% of MgO powder was added as an inorganic insulating powder with respect to water atomized powder of pure iron were compared with Comparative Example 4 in which 0.25 wt% of MgO powder was added. In Examples 1 to 3 in which the added amount of MgO powder is 0.50 wt% or more, the density and permeability are reduced, but the eddy current loss (Pe) is greatly reduced. It can be seen that the loss (Pc) is reduced. Similarly, in Examples 4 to 7 and Comparative Example 5 in which Al ₂ O ₃ powder was added as an inorganic insulating powder to pure iron water atomized powder, Al ₂ O ₃ powder was changed to 0.50 to 2 In Examples 4 to 7 in which 0.000 wt% was added, the density and permeability were lower than in Comparative Example 5 in which 0.25 wt% of Al ₂ O ₃ powder was added, but eddy current loss (Pe) was significantly increased. It can be seen that the iron loss (Pc) is reduced.

3 and 4 show that the effect of reducing the eddy current loss (Pe) is exhibited by adding inorganic insulating powder to both MgO powder and Al ₂ O ₃ powder. In particular, when the inorganic insulating powder is added by 0.5 wt% or more, the effect is sufficiently exhibited. On the other hand, it can be seen that the hysteresis loss (Ph) is constant regardless of the amount of inorganic insulating powder added.

Further, from FIG. 5, when Al ₂ O ₃ powder and MgO powder are added as inorganic insulating powder to pure iron water atomized powder, the density of the dust core decreases as inorganic insulating powder is added. You can see that When the density of the dust core is reduced, the DC superposition characteristics of the dust core are affected. Therefore, when an appropriate amount or more of the inorganic insulating powder is added, the DC superposition characteristics of the dust core are deteriorated.

As described above, by adding 0.50 to 2.00 wt% of the inorganic insulating powder having a specific surface area of 100 to 300 m ² / g to the water atomized powder of pure iron, the surface of the soft magnetic powder is made of the inorganic insulating powder. An insulating layer is formed. With this insulating layer, the annealing temperature can be increased and hysteresis loss can be reduced. As a result, it is possible to provide a dust core having a constant eddy current loss even at a high frequency and a high magnetic flux density, and a manufacturing method thereof.

[4. Third characteristic comparison (comparison of presence or absence of phosphate coating treatment)]
In the third characteristic comparison, the presence / absence of the phosphate coating treatment on the water atomized powder of pure iron having a particle size of 75 μm or less was compared. Table 3 is a table showing the type, specific surface area, and addition amount of the inorganic insulating powder added to the water atomized powder of pure iron in this example. In this table, as magnetic characteristics, density, magnetic permeability, and iron loss (core loss) per unit deposition (Pc, Ph, Pe) were measured.

In this characteristic comparison, the samples of Examples 1 to 3 and Comparative Examples 3 and 4 used in the characteristic comparison and a sample newly prepared as follows were used.
In Examples 9 to 12, Al ₂ O ₃ as an inorganic insulating powder was added to the pure iron water atomized powder not subjected to the phosphate coating treatment, and 0.50 to 2.00 wt.% With respect to the pure iron water atomized powder. % Was mixed in a pot mill for 12 hours.
In Comparative Example 6, pure iron water atomized powder that was not subjected to phosphate coating treatment, Al ₂ O ₃ as an inorganic insulating powder, and 0.25 wt% with respect to pure iron water atomized powder in a pot mill for 12 hours Mixed.
These were mixed with 0.1 wt% of a silane coupling agent, 0.3 wt% of a silicone resin, further dried by heating at 180 ° C. for 2 hours, and mixed with 0.4 wt% of zinc stearate as a lubricant. .

Next, Examples 9 to 12 and Comparative Example 6 were pressure-molded at a pressure of 1500 MPa at room temperature to produce a ring-shaped molded body having an outer diameter of 16 mm, an inner diameter of 11 mm, and a height of 11 mm, and a non-oxidizing atmosphere. Heat treatment was performed at 600 ° C. for 2 hours in the middle (N ₂ 90% + H ₂ 10%) to produce a dust core.

Table 3 shows the types, specific surface area, added amount, density, and permeability at 20 kHz of the inorganic insulating powder added to the pure atomized water atomized powder for Examples 1 to 3 and 9 to 12 and Comparative Examples 3 and 4 and 6. It is the table | surface shown about the relationship with a magnetic permeability and a core loss. FIG. 6 is a diagram showing the relationship between the amount of inorganic insulating powder added and eddy current loss for items G and H.

  As can be seen from Table 3, in Examples 9 to 12 and Comparative Example 6 in which the inorganic insulating powder was added to the water atomized powder of pure iron not subjected to the phosphate coating treatment, the results of the second characteristic comparison and Similarly, in Examples 9 to 12 to which 0.50 to 2.00 wt% of the inorganic insulating powder was added, the density and the magnetic permeability were lower than those in Comparative Example 6 to which 0.25 wt% of the inorganic insulating powder was added. However, since the eddy current loss (Pe) is greatly reduced, it can be seen that the iron loss (Pc) is reduced. On the other hand, in Examples 1 to 3 and Comparative Examples 3 and 4 in which the phosphate coating treatment was performed on the water atomized powder of pure iron, Examples 9 to 12 and Comparative Example 6 in which the phosphate coating treatment was not performed. In comparison, it can be seen that eddy current loss is reduced when the same amount of inorganic insulating powder is added.

  Similarly, as can be seen from FIG. 6, the eddy current loss (Pe) is reduced by applying the phosphoric acid coating to the pure iron water atomized powder as compared with the case where the phosphoric acid coating is not applied. As a result, the iron loss (Pc) decreases. On the other hand, even when the phosphoric acid coating treatment is performed, if the inorganic insulating powder is less than 0.50 wt%, the effect of the inorganic insulating powder cannot be sufficiently exhibited, and the eddy current loss (Pe) increases. It cannot be prevented.

  As described above, a phosphate compound film can be formed on the surface of the soft magnetic powder by performing the phosphoric acid coating process on the pure iron water atomized powder. This phosphate film facilitates the binding of the inorganic insulating powder. Thereby, even with a small amount of inorganic insulating powder, a strong insulating layer can be provided on the surface of the soft magnetic powder.

[5. Fourth characteristic comparison (comparison of annealing temperature during annealing process)]
In 4th characteristic comparison, the annealing temperature in the annealing process which anneals the molded object which passed through the shaping | molding process was compared. Table 4 is a table showing the type, specific surface area, and addition amount of the inorganic insulating powder added to the water atomized powder of pure iron in this example. In this table, as magnetic characteristics, density, magnetic permeability, and iron loss (core loss) per unit volume (Pc, Ph, Pe) were measured.

The sample used for this characteristic comparison was produced as follows.
In Examples 13-19, after subjecting pure iron water atomized powder to phosphoric acid coating treatment as items I, Al ₂ O ₃ was added as inorganic insulating powder, and 0.50 wt% with respect to pure iron water atomized powder. Mix in a pot mill for 12 hours.
In Comparative Examples 11 to 13, as an item J, a phosphoric acid coating treatment was performed on water atomized powder of pure iron.
In the examples and comparative examples of items I and J, 0.1 wt% of the silane coupling agent is mixed, 0.3 wt% of the silicone resin is further mixed, and heat drying is performed at 180 ° C. for 2 hours, and stearic acid is used as a lubricant. Zinc 0.4 wt% was mixed.

  In Comparative Examples 15 to 17, as an item K, pure iron water-atomized powder was subjected to a phosphoric acid coating treatment and then mixed with 0.4 wt% zinc stearate as a lubricant.

Examples and Comparative Examples of Items I to K are pressure-molded at a pressure of 1500 MPa at room temperature to produce a ring-shaped molded body having an outer diameter of 16 mm, an inner diameter of 11 mm, and a height of 11 mm in a non-oxidizing atmosphere ( N ₂ 90% + H ₂ 10%) at 400 to 650 ° C. for 2 hours to produce a dust core.

Table 4 shows the relationship between the types of inorganic insulating powder, specific surface area, added amount, density, magnetic permeability at 20 kHz, and core loss for the examples and comparative examples of items I to K. It is the table shown. 7 to 9 are diagrams showing the relationship between the added amount of the inorganic insulating powder and the eddy current loss (Pe) for the examples of items I to K and the comparative example.

  As can be seen from Table 4, in items 13 to 19 of Examples 13 to 19 in which the inorganic insulating powder was added to the water atomized powder of pure iron, the items J and K of Comparative Examples 11 to 16 in which the inorganic insulating powder was not added. In comparison, in item I, it can be seen that the eddy current loss does not increase significantly even when the annealing temperature exceeds 550 ° C. On the other hand, in item J, eddy current loss increases when the annealing temperature exceeds 550 ° C., and in item K, eddy current loss increases when it exceeds 500 ° C.

  From FIG. 7, it can be seen that the iron loss gradually decreases as the annealing temperature is increased, and that the iron loss greatly increases at 500 ° C. for item K and 550 ° C. for item J. On the other hand, even if the item I, annealing temperature is 650 ° C., it can be seen that there is no significant increase in iron loss. From FIG. 8, it can be seen that when the annealing temperature is increased, eddy current loss increases significantly at 500 ° C. for item K and 550 ° C. for item J. On the other hand, in item I, it can be seen that there is no significant increase in eddy current loss even when the annealing temperature is 650 ° C. From FIG. 9, it can be seen that the hysteresis loss gradually decreases as the annealing temperature is increased, and that the hysteresis loss significantly increases at 500 ° C. for item K and 550 ° C. for item J. On the other hand, in item I, it can be seen that there is no significant increase in hysteresis loss even when the annealing temperature is 650 ° C.

  From the above, it can be seen that by adding the inorganic insulating powder to the pure atomized water atomized powder, the insulating layer is not destroyed even when the annealing temperature exceeds 550 ° C. Since the water atomized powder of pure iron does not come into contact with each other in the molded dust core by the insulating layer, sufficient insulation performance can be exhibited. Therefore, a powder magnetic core with reduced hysteresis loss (Pe) can be produced by removing strain inside the soft magnetic powder by annealing at a high temperature.

[6. Other Embodiments]
The present invention is not limited to the embodiment described above. Other embodiments such as the following are also included. The soft magnetic powder used in the above examples is not limited to an average particle size of 75 μm, and may have an average particle size in the range of 30 to 100 μm. If the average particle size is larger than this range, eddy current loss may occur. On the other hand, if the average particle size is smaller than this range, the hysteresis loss due to density reduction increases.

Claims (12)

Mixing soft magnetic powder mainly composed of iron and inorganic insulating powder,
The mixture is coated with a binding insulating resin, and then the soft magnetic powder obtained by mixing the binding insulating resin and the lubricating resin are mixed,
In the powder magnetic core formed by pressure-molding the mixture to produce a molded body and annealing the molded body,
The powder magnetic core according to claim 1, wherein the inorganic insulating powder has a specific surface area of 100 to 300 m ² / g.   2. The dust core according to claim 1, wherein the added amount of the inorganic insulating powder is 0.5 to 2.0% of the soft magnetic powder.   The dust core according to claim 1 or 2, wherein the inorganic insulating powder is at least one of magnesia powder, alumina powder, silica powder, titania powder and zirconia powder.   The dust core according to any one of claims 1 to 3, wherein the soft magnetic powder is produced by a water atomizing method, a gas atomizing method, or a water gas atomizing method.   5. The dust core according to claim 1, wherein the compact is annealed at a temperature of 550 ° C. or higher and a temperature at which the soft magnetic powder starts sintering.   The dust core according to any one of claims 1 to 5, wherein a phosphate coating is applied to the soft magnetic powder before mixing the soft magnetic powder and the inorganic insulating powder. . A mixing step of mixing the inorganic insulating powder with the soft magnetic powder;
A coating step of coating the mixture that has undergone the mixing step with a binding insulating resin;
A second mixing step of mixing a lubricant with the mixture coated with the binding insulating resin;
A molding process for producing a molded body by subjecting the mixture that has undergone the second mixing process to pressure molding; and
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 method for producing a dust core, wherein the inorganic insulating powder has a specific surface area of 100 to 300 m ² / g.   The method for producing a dust core according to claim 7, wherein the amount of the inorganic insulating powder added is 0.5 to 2.0% of the soft magnetic powder.   The pressure according to claim 7 or 8, wherein the insulating powder used in the mixing step is at least one of magnesia powder, alumina powder, silica powder, titania powder and zirconia powder. Manufacturing method of a powder magnetic core.   The method for manufacturing a dust core according to any one of claims 7 to 9, wherein an addition amount of the inorganic insulating powder is 0.5 to 2.0% of the soft magnetic powder.   The method for producing a dust core according to any one of claims 7 to 10, wherein the soft magnetic powder is produced by a water atomizing method, a gas atomizing method, or a water gas atomizing method.   The phosphate coating step of applying a phosphate coating to the soft magnetic powder before the mixing step of mixing the soft magnetic powder and the inorganic insulating powder. The manufacturing method of the powder magnetic core of any one of Claims 1.

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