JP2018142596A - Powder magnetic core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further decrease the amount of a binder component for use in the formation of a powder magnetic core to improve relative density of magnetic powder.SOLUTION: A powder magnetic core includes first metal magnetic powder whose NIT value is 10% or more and 30% or less and second metal magnetic powder whose NIT value is more than 30% and 90% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a dust core, and more particularly to a dust core having a high filling rate of metal magnetic powder.

 In recent years, miniaturization of coil parts such as inductors, choke coils, transformers, etc. and motors has been demanded. Therefore, a metal magnetic material that has a higher saturation magnetic flux density than ferrite and can maintain DC superposition characteristics up to a high magnetic field. Became widely used. Most metal magnetic materials use Fe-based amorphous alloy magnetic powder with high magnetic permeability. The Fe-based amorphous alloy magnetic powder is generally hard and hardly deformed. For this reason, compression molding is difficult with Fe-based amorphous alloy magnetic powder alone, and a powder magnetic core (core) is obtained by mixing with an appropriate amount of binder and compression molding.

 In the dust core, the particles of the metal magnetic powder are bound together by a binder, thereby realizing insulation between the metal magnetic powder and maintaining the magnetic core shape. On the other hand, when the amount of the binder is excessive, the relative ratio of the magnetic powder is lowered, and the magnetic permeability of the dust core is inevitably lowered. For this reason, a technique for filling the powder magnetic core with magnetic powder at a high density has been proposed.

 Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2004-197218), Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2004-363466) and Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2010-118486) describe a mixture of amorphous soft magnetic powder and crystalline soft magnetic powder. It has been proposed to improve the filling rate of magnetic powder by using powder. Since the crystalline magnetic powder has a lower hardness than the amorphous magnetic powder, the filling rate can be improved and the magnetic permeability can be increased by plastically deforming the crystalline soft magnetic powder during compression molding.

 Patent Document 4 (Japanese Patent Laid-Open No. 2014-103265) describes using magnetic powders having different Vickers hardness (high Hv and low Hv).

 That is, in Patent Documents 1 to 4, magnetic powders having different hardnesses are used in combination, low hardness magnetic powders are deformed by pressure during compression molding, and gaps between high hardness magnetic powders are filled, thereby filling magnetic powders. The degree is improved.

JP2004-197218 JP2004-363466 JP2010-118486 JP 2014-103265

  In Patent Documents 1 to 4, although the filling degree of the magnetic powder is improved, it has been difficult to maintain the shape of the green compact without using a binder component. This is supported by the fact that the binder component is used in combination in Examples of Patent Documents 1 to 4. Therefore, the present invention provides a technology that further reduces the amount of binder component used, improves the relative density of magnetic powder in the magnetic core, and ultimately enables compacting without using the binder component. It is an object.

  The inventors of the present invention have continually studied to improve the filling rate of the metal magnetic powder constituting the powder magnetic core, and the hardness of the magnetic powder is one of the indicators of its deformability, but the shape maintainability is improved. I thought that it was not reflected. That is, even if the hardness is low and the deformation is easy, if the original shape is restored after the pressure is released, the filling property between the magnetic powders is lowered, and cracks may occur in the dust core.

 In view of the plastic deformation of the magnetic powder and the importance of maintaining the shape after the deformation, the present inventors conduct a material search and use a combination of magnetic powder that satisfies a specific parameter (the NIT value described later). As a result, it was found that high-filling of magnetic powder was possible, and that powder magnetism excellent in shape retention was obtained, and the present invention was completed.

That is, the present invention includes the following gist.
(1) A dust core including a first metal magnetic powder having an NIT value of 10% to 30% and a second metal magnetic powder having an NIT value of more than 30% and 90% or less.
(2) 30 to 50 parts by mass of the first metal magnetic powder and 70 to 50 parts by mass of the second metal magnetic powder per 100 parts by mass in total of the first metal magnetic powder and the second metal magnetic powder ( The dust core according to 1).
(3) The dust core according to (1) or (2), wherein the content of the resin component with respect to the total mass of the dust core is 2% by mass or less.
(4) The dust core according to any one of (1) to (3), wherein a difference between the NIT value of the first metal magnetic powder and the NIT value of the second metal magnetic powder is 60% or less.
(5) The dust core according to (4), wherein a difference between the NIT value of the first metal magnetic powder and the NIT value of the second metal magnetic powder is 50% or less.
(6) The dust core according to any one of (1) to (5), wherein the first metal magnetic powder and the second metal magnetic powder are both Fe-based soft magnetic powder.
(7) The dust core according to any one of (1) to (6), wherein one or both of the first metal magnetic powder and the second metal magnetic powder have an insulating coating.

 In the present invention, at least two metal magnetic powders having different NIT values are used in combination. The first metal magnetic powder has a low NIT value, is easily deformed, and maintains the shape after deformation. One second metal magnetic powder has a high NIT value, is relatively hard, and has low deformability. For this reason, the space between the second metal magnetic powders is filled with the first metal magnetic powder during the compacting, and the state is maintained. As a result, the filling rate of the metal magnetic powder is improved, and a dust core having excellent shape retention is obtained.

 According to the present invention, since the first metal magnetic powder functions as a binder, the amount of resin-based binder used can be reduced, and ultimately a dust core can be obtained without using a resin-based binder. it can.

FIG. 1 shows a typical example of a load-displacement curve obtained by the nanoindentation method.

  Hereinafter, the present invention will be described based on specific embodiments, but various modifications are allowed without departing from the gist of the present invention.

(Dust core)
The dust core according to the present embodiment includes two kinds of metal magnetic powders. An organic binder component may be included in the dust core, but according to the present invention, the amount of resin binder used can be reduced, and ultimately a dust core can be obtained without using a resin binder. You can also. An insulating coating may be formed on one or both of the metal magnetic powders.

  Such a dust core is preferably used as a magnetic core of a coil-type electronic component. For example, it may be a coil-type electronic component in which an air-core coil around which a wire is wound is embedded in a dust core having a predetermined shape, or a wire may be wound on a surface of a dust core having a predetermined shape. It may be a coil-type electronic component that is wound only. Examples of the shape of the magnetic core around which the wire is wound include FT type, ET type, EI type, UU type, EE type, EER type, UI type, drum type, toroidal type, pot type, and cup type. it can.

(Metal magnetic powder)
The metal magnetic powder in this embodiment contains the 1st metal magnetic powder whose NIT value is 10% or more and 30% or less, and the 2nd metal magnetic powder whose NIT value exceeds 30% and is 90% or less. The NIT value is a characteristic value evaluated by the Nano-IndenTation (nanoindentation) method, and is a parameter value that reflects plastic deformability and shape retention.

  In the nanoindentation method, a diamond pyramid indenter is pushed into the surface of the sample placed on the base of the measuring device to a certain load (press-fit), and then the load until the indenter is removed (unloaded) (P ) And displacement (press-fit depth h) (press-fit (load) -unload curve). FIG. 1 shows a typical load-displacement curve obtained by the nanoindentation method.

 The indentation (load) curve reflects the elastic-plastic deformation behavior of the material, and the unloading curve is obtained by the elastic recovery behavior. The area (α) surrounded by the load curve, the unload curve and the horizontal axis is the energy Ep consumed for plastic deformation. In addition, an area (β) surrounded by a perpendicular drawn from the maximum load point of the load curve to the horizontal axis (pressing depth h) and the unloading curve is energy Ee absorbed by elastic deformation.

In the present embodiment, the ratio (percentage) of the area (α) to the area (α + β) surrounded by the perpendicular drawn from the maximum load point of the load curve to the horizontal axis (press-in depth h), the load curve, and the horizontal axis. Defined as NIT value.
NIT value = 100α / (α + β)

  A low NIT value indicates that the amount of energy required for plastic deformation is small and is easily deformed, and that the energy absorbed by elastic deformation is large, and thus the shape after deformation is maintained. On the other hand, a high NIT value indicates that the energy required for plastic deformation is large and is difficult to deform, and that the energy absorbed by elastic deformation is small, so that the shape is restored even when deformed. doing.

 The NIT value of the first metal magnetic powder is 10% or more and 30% or less, preferably 12 to 28%, more preferably 15 to 25%. The NIT value of the second metal magnetic powder is more than 30% and not more than 90%, preferably 50 to 88%, more preferably 59 to 86%. When the NIT value of the first metal magnetic powder and the second metal magnetic powder is in the above range, the gap between the second metal magnetic powder is filled with the first metal magnetic powder during the compacting, and the state is maintained. To do. As a result, the filling rate of the metal magnetic powder is improved, and a dust core having excellent shape retention is obtained. If the NIT value of the first metal magnetic powder is less than 10%, the material may be too soft and the molded body may be deformed after compacting. If the NIT value of the first metal magnetic powder exceeds 30%, it is as hard as the second metal magnetic powder, so that it becomes difficult to deform and may not be molded. Moreover, even if it can shape | mold, a molded object may not maintain a shape. If the NIT value of the second metal magnetic powder is 30% or less, the shape of the formed body may not be maintained because it is as soft as the first metal magnetic powder. Moreover, when the NIT value of the second metal magnetic powder exceeds 90%, molding becomes difficult, and the shape may not be maintained even if it can be molded.

 If the difference between the NIT value of the first metal magnetic powder and the NIT value of the second metal magnetic powder is too large, the core loss of the obtained dust core may increase. Therefore, the difference between the NIT value of the first metal magnetic powder and the NIT value of the second metal magnetic powder is preferably 60% or less, and more preferably 50% or less.

  The first metal magnetic powder and the second metal magnetic powder are not particularly limited, but are preferably soft magnetic particles and may be Fe-based soft magnetic particles. Specifically, Fe-based magnetic particles include pure iron, Fe-based alloy, Fe-Si-based alloy, Fe-Al-based alloy, Fe-Ni-based alloy, Fe-Si-Al-based alloy, Fe-Co-based alloy, Examples include Fe—Ni—Si—Co based alloys, Fe based amorphous alloys, Fe based nanocrystalline alloys, and the like, and pure iron or Fe—Si based alloys are more preferable.

 In the Fe—Si based alloy which is a preferable metal magnetic powder, the total content of Fe and Si is 80% by weight or more. Further, the ratio of Fe and Si is not particularly limited. However, when the weight ratio is Si / Fe = 0/100 to 10/90, the saturation magnetic charge is preferably increased.

 There are no particular restrictions on the method for producing the metal magnetic powder, but various powdering methods such as an atomizing method (for example, a water atomizing method, a gas atomizing method, a high-speed rotating water stream atomizing method, etc.), a reduction method, a carbonyl method, a pulverizing method, etc. Manufactured by.

 The first metal magnetic powder and the second metal magnetic powder may be the same material or different materials as long as the NIT value is in the above range. The NIT value can be controlled by the material of the magnetic powder, the type and amount of impurities added to the magnetic powder, and the heat treatment conditions of the magnetic powder. For example, the NIT value increases by adding carbon to Fe-based magnetic powder and heat-treating it at 1000 ° C. or higher. As a non-limiting example, 0.5% by mass of carbon is added to an Fe-based magnetic powder having an NIT value of 18%, heated to 1200 ° C., and rapidly cooled to increase the NIT value to about 35%. Similarly, 0.2% by mass of carbon is added to an Fe-based magnetic powder having a NIT value of 15%, heated to 1100 ° C., and rapidly cooled to increase the NIT value to about 23%. In general, the Fe-based magnetic powder tends to have a lower NIT value as the purity is higher, and the Fe-based magnetic powder having a purity of 99.9% has an NIT value of about 10%. Also, since the NIT value of crystalline magnetic powder is generally small and the NIT value of amorphous magnetic powder tends to be large, the magnetic powder having a desired NIT value should be selected in consideration of the crystallinity of the magnetic powder. In addition, magnetic powder having a desired NIT value can be obtained by crystallization treatment or non-crystallization treatment of the magnetic powder.

 An insulating film may be formed on one or both of the first metal magnetic powder and the second metal magnetic powder.

  Examples of the constituent material of the insulating coating include magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, phosphate such as cadmium phosphate, silicate (water glass) such as sodium silicate, soda lime Inorganic coatings such as glass, borosilicate glass, lead glass, aluminosilicate glass, borate glass, and sulfate glass are preferably used. Since the inorganic coating is particularly excellent in insulation, the Joule loss due to the induced current can be particularly suppressed. Further, by providing the insulating coating, it is possible to particularly improve the insulation between the particles composed of the metal material.

  The thickness of the insulating coating is preferably 5 to 100 nm, more preferably 5 to 50 nm, and particularly preferably 10 to 30 nm. If the thickness of the insulating coating is too thin, sufficient corrosion resistance cannot be obtained, and if it is too thick, the interval between the metal magnetic materials is widened, and the permeability μ as the dust core may be lowered.

 The size and shape of the first metal magnetic powder and the second metal magnetic powder constituting the powder magnetic core according to the present embodiment are not particularly limited. Since the first metal magnetic powder has deformability and fills the gaps between the second metal magnetic powders, a high filling rate is achieved regardless of the shape of the first metal magnetic powder and the second metal magnetic powder. it can. Therefore, the shape of the first metal magnetic powder and the second metal magnetic powder is not particularly limited. For example, a spherical shape, an elliptical shape, a cylindrical shape, a polygonal column, a needle shape or a rod shape, a plate shape, a disc shape, and a flake Examples include shapes, scale shapes, and irregular shapes. In addition, since the first metal magnetic powder has deformability and fills the gaps between the second metal magnetic powders, the first metal magnetic powder may have a relatively small particle size than the second metal magnetic powder. preferable. Although not limited in any way, the equivalent circle diameter of the first metal magnetic powder is preferably 10 to 30 μm, more preferably 15 to 25 μm, and the equivalent circle diameter of the second metal magnetic powder is preferably 30 to 60 μm. More preferably, it exists in the range of 40-50 micrometers.

 The mixing ratio of the first metal magnetic powder and the second metal magnetic powder in the dust core is not particularly limited. The second metal magnetic powder having a high NIT value is generally amorphous and preferably has a high magnetic permeability as compared with crystalline magnetic powder. Therefore, the blending amount of the first metal magnetic powder is preferably 30 to 50 parts by mass, more preferably 35 to 45 parts by mass per 100 parts by mass in total of the first metal magnetic powder and the second metal magnetic powder. The amount of the second metal magnetic powder is preferably in the range of 70 to 50 parts by mass, more preferably 65 to 55 parts by mass.

 The first metal magnetic powder is easily deformed and has a property of maintaining the shape after deformation. One second metal magnetic powder is relatively hard and has low deformability. For this reason, the space between the second metal magnetic powders is filled with the first metal magnetic powder during the compacting, and the state is maintained. As a result, the filling rate of the metal magnetic powder is improved, and a dust core having excellent shape retention is obtained. And since the 1st metal magnetic powder fulfill | performs the function as a binder, the usage-amount of a resin-type binder can be reduced, and a powder magnetic core can also be obtained ultimately without using a resin-type binder.

 Therefore, in the dust core according to the present embodiment, the content of the resin component with respect to the total mass of the dust core can be 2% by mass or less, and in a preferred embodiment, it can be 1% by mass or less. Furthermore, you may obtain a compacting body, without mix | blending a binder.

  In addition, as resin which comprises the binder which may be used, well-known resin can be used. Specifically, various organic polymer resins, silicone resins, phenol resins, epoxy resins and the like are exemplified.

(Production method of dust core)
A method for producing the dust core is not particularly limited, and a known method can be adopted. First, 1st metal magnetic powder, 2nd metal magnetic powder, and a binder are mixed as needed, and mixed powder is obtained. Moreover, it is good also considering the obtained mixed powder as granulated powder as needed. Then, the mixed powder or granulated powder is filled into a mold and compression molded to obtain a molded body having the shape of a magnetic body (a powder magnetic core) to be produced. By subjecting the obtained molded body to a heat treatment, a powder magnetic core having a predetermined shape to which metal magnetic powder is fixed is obtained. There is no restriction | limiting in particular in the conditions of a thermosetting process, For example, heat processing is performed at 150-220 degreeC for 1 to 10 hours. Moreover, there is no restriction | limiting in particular in the atmosphere at the time of heat processing, You may heat-process in air | atmosphere. A coil-type electronic component such as an inductor is obtained by winding a wire around the obtained dust core a predetermined number of times.

  Moreover, the above-mentioned mixed powder or granulated powder and an air-core coil formed by winding a wire a predetermined number of times are filled in a mold and compression molded to obtain a molded body in which the coil is embedded. Also good. By performing heat treatment on the obtained molded body, a powder magnetic core having a predetermined shape in which a coil is embedded is obtained. Since such a dust core has a coil embedded therein, it functions as a coil-type electronic component such as an inductor.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment at all, You may modify | change in various aspects within the scope of the present invention.

EXAMPLES Hereinafter, although an invention is demonstrated in detail using an Example, this invention is not limited to these Examples.
In the following, the NIT value was measured as follows.

<NIT value measurement>
The NIT value of the metal magnetic powder was measured using an ultra-fine indentation hardness tester (ENT-1100a, manufactured by Elionix Co., Ltd.) as a nanoindentation measuring apparatus. Polishing was performed so that the surface of the metal magnetic powder was flat. Polishing was performed with polishing paper, then buffed (6 μm), and further buffed (1 μm). In addition, since accurate measurement cannot be performed if the powder is too small, a relatively large powder is used from each metal magnetic powder. Depending on the type of magnetic powder to be measured, a highly reliable measurement value can be obtained by using a powder of about 50 to 100 μm.

After pressing (injecting) a diamond pyramid indenter into the surface of the sample placed on the base of the measuring device to a load of 1,000,000 μN (press-in), the load (P) and displacement (injection) until the indenter is removed (unloading) The relationship (depth (load) -unloading curve) of depth h) was measured. The area surrounded by the load curve and unloading curve and the horizontal axis (α), the vertical line drawn from the maximum load point of the load curve to the horizontal axis (press-in depth h), the area surrounded by the load curve and the horizontal axis ( NIT value was calculated from (α + β) based on the following formula.
NIT (%) = 100α / (α + β)
The following table summarizes the NIT value, equivalent circle diameter, and shape of each metal magnetic powder used. In the table below, Ex represents an example and CEx represents a comparative example.

Example 1
As the first metal magnetic powder, an Fe-based magnetic powder having a NIT value of 16% and an equivalent circle diameter of 20 μm was prepared (magnetic powder 1A). In addition, an elliptical amorphous magnetic powder having a NIT value of 59% and a circle-equivalent diameter of 45 μm was prepared as the second metal magnetic powder (magnetic powder 2A).

  40 parts by mass of magnetic powder 1A and 60 parts by mass of magnetic powder 2A were mixed. The mixed powder was filled in a toroidal mold having an outer diameter of 17.5 mm and an inner diameter of 11.0 mm, and pressed with a molding pressure of 980 MPa to obtain a molded body of a dust core. The molded body weight was 5 g. The formed powder magnetic core was heat-cured in the atmosphere at 200 ° C. for 5 hours to obtain a powder magnetic core.

(Example 2)
As the first metal magnetic powder, an FeNiSiCo-based magnetic powder having a NIT value of 25% and an equivalent circle diameter of 23 μm was prepared (magnetic powder 1B). Moreover, spherical amorphous magnetic powder having a NIT value of 65% and an equivalent circle diameter of 47 μm was prepared as the second metal magnetic powder (magnetic powder 2B).

  40 parts by mass of magnetic powder 1B and 60 parts by mass of magnetic powder 2B were mixed, and a dust core was obtained in the same manner as in Example 1.

(Example 3)
Magnetic powder 1B was prepared as the first metal magnetic powder. Further, as the second metal magnetic powder, a piece-like amorphous magnetic powder having a NIT value of 65% and an equivalent circle diameter of 40 μm was prepared (magnetic powder 2C).

  40 parts by mass of magnetic powder 1B and 60 parts by mass of magnetic powder 2C were mixed, and a dust core was obtained in the same manner as in Example 1.

(Example 4)
Magnetic powder 1A was prepared as the first metal magnetic powder. Further, an elliptical amorphous magnetic powder having a NIT value of 70% and an equivalent circle diameter of 42 μm was prepared as the second metal magnetic powder (magnetic powder 2D).

  40 parts by mass of magnetic powder 1A and 60 parts by mass of magnetic powder 2D were mixed, and a dust core was obtained in the same manner as in Example 1.

(Example 5)
Magnetic powder 1B was prepared as the first metal magnetic powder. Moreover, magnetic powder 2A was prepared as the second metal magnetic powder. Moreover, the epoxy resin which is a thermosetting resin and the imide resin which is a hardening | curing agent were prepared as a binder (henceforth "binder" is described).

  40 parts by mass of magnetic powder 1B, 60 parts by mass of magnetic powder 2A, and 2% by mass of binder based on the total weight of the magnetic powder were mixed, and a dust core was obtained in the same manner as in Example 1.

(Example 6)
Magnetic powder 1A was prepared as the first metal magnetic powder. In addition, an amorphous amorphous magnetic powder having an NIT value of 63% and an equivalent circle diameter of 50 μm was prepared as the second metal magnetic powder (magnetic powder 2E).

  40 parts by mass of magnetic powder 1A and 60 parts by mass of magnetic powder 2E were mixed, and a dust core was obtained in the same manner as in Example 1.

(Example 7)
Magnetic powder 1B was prepared as the first metal magnetic powder. Further, as the second metal magnetic powder, an elliptical amorphous magnetic powder having a NIT value of 86% and an equivalent circle diameter of 36 μm was prepared (magnetic powder 2F).

  40 parts by mass of magnetic powder 1B, 60 parts by mass of magnetic powder 2F, and 1% by mass of a binder were mixed, and a dust core was obtained in the same manner as in Example 1.

(Example 8)
Magnetic powder 1A was prepared as the first metal magnetic powder. Moreover, magnetic powder 2A was prepared as the second metal magnetic powder.

  30 parts by mass of magnetic powder 1A and 70 parts by mass of magnetic powder 2A were mixed, and a dust core was obtained in the same manner as in Example 1.

Example 9
Magnetic powder 1A was prepared as the first metal magnetic powder. Moreover, magnetic powder 2A was prepared as the second metal magnetic powder.

  50 parts by mass of magnetic powder 1A and 50 parts by mass of magnetic powder 2A were mixed, and a dust core was obtained in the same manner as in Example 1.

(Example 10)
Magnetic powder 1A was prepared as the first metal magnetic powder. Moreover, magnetic powder 2A was prepared as the second metal magnetic powder. In addition, an amorphous amorphous magnetic powder having an NIT value of 63% and an equivalent circle diameter of 40 μm was prepared (magnetic powder 3A).

  40 parts by mass of magnetic powder 1A, 60 parts by mass of magnetic powder 2A, and 10 parts by mass of magnetic powder 3A were mixed, and a dust core was obtained in the same manner as in Example 1.

(Comparative Example 1)
In Comparative Example 1, two types of second metal magnetic powder having an NIT value exceeding 30% were used.
Magnetic powder 2A was prepared as the second metal magnetic powder. Separately, an irregularly shaped Fe-2Si magnetic powder having a NIT value of 33% and an equivalent circle diameter of 20 μm was prepared (magnetic powder 2G).

  40 parts by mass of magnetic powder 2G and 60 parts by mass of magnetic powder 2A were mixed, and a dust core was obtained in the same manner as in Example 1.

(Comparative Example 2)
Magnetic powders 2B and 2G were prepared as second metal magnetic powders.

  40 parts by mass of magnetic powder 2G and 60 parts by mass of magnetic powder 2B were mixed, and a dust core was obtained in the same manner as in Example 1.

(Comparative Example 3)
Using only the magnetic powder 2A, compacting was performed in the same manner as in Example 1. However, the shape retention was poor and the magnetic core shape could not be maintained.

(Comparative Example 4)
Using only the magnetic powder 2C, compacting was performed in the same manner as in Example 1. However, the shape retention was poor and the magnetic core shape could not be maintained.

(Comparative Example 5)
In Comparative Example 5, two kinds of second metal magnetic powders having NIT values exceeding 30% were used.
Magnetic powder 2A was prepared as the second metal magnetic powder. Separately, an elliptical amorphous magnetic powder having a NIT value of 65% and an equivalent circle diameter of 40 μm was prepared (magnetic powder 2H).

  Although 40 parts by mass of magnetic powder 2A and 60 parts by mass of magnetic powder 2H were mixed and compacted in the same manner as in Example 1, the shape retention was poor and the magnetic core shape could not be maintained.

(Comparative Example 6)
3% by mass of binder was mixed with magnetic powder 2H, and a dust core was obtained in the same manner as in Example 1.

(Comparative Example 7)
In Comparative Example 7, in place of the first metal magnetic powder (magnetic powder 1A) of Example 1, a pure Fe-based magnetic powder (magnetic powder 3B) having a NIT value of 5% and an equivalent circle diameter of 15 μm was used. Although compacting was performed in the same manner as in Example 1, the shape retention was poor and the magnetic core shape could not be maintained.

(Comparative Example 8)
In Comparative Example 8, in place of the second metal magnetic powder (magnetic powder 2A) of Example 1, a fragmented amorphous magnetic powder (magnetic powder 3C) having a NIT value of 95% and an equivalent circle diameter of 45 μm was used. Although compacting was performed in the same manner as in Example 1, the shape retention was poor and the magnetic core shape could not be maintained.

(Comparative Example 9)
A dust core was obtained in the same manner as in Example 1 by using only the magnetic powder 1A.

The following evaluation was performed about each dust core created above.
<Shape retention>
The created dust core is observed visually and with a magnifying glass. Observe the core for breaks, cracks, and cracks to check for any abnormalities. The case where there was no abnormality was defined as “good”, and although there was a slight abnormality, “good” was indicated when the core shape could be maintained, and “bad” when the core shape could not be maintained. In addition, when the shape retention property is poor, the following relative density, magnetic permeability, and core loss are not measured.

<Relative density>
The density of the obtained dust core is calculated from its size and mass, and the space density (relative density) is calculated by dividing the calculated density of the dust core by the true density calculated from the mass ratio of the magnetic powder. Was calculated.

<Permeability>
The initial magnetic permeability of the obtained dust core was measured. The initial permeability was measured with an LCR meter (HP Corporation LCR428A) with a wire wound around a dust core and a winding number of 12 turns.

<Core loss>
On the obtained toroidal core sample, the primary winding and the secondary winding were wound with primary 20 times and secondary 14 times each, and the power loss Pcv at 2 MHz, 10 mT, and 23 ° C. was measured (unit: kW / m). ³ ). The measurement was performed using a BH analyzer (SY-8232 manufactured by Iwasaki Tsushinki Co., Ltd.).
The above results are summarized in the table below.

  From the above, by using a combination of the first metal magnetic powder having a NIT value of 10% or more and 30% or less and the second metal magnetic powder having a NIT value of more than 30% but not more than 90%, It can be seen that a dust core having high density and magnetic permeability can be obtained. When the first metal magnetic powder is not used, sufficient shape retention cannot be obtained, and the shape of the magnetic core cannot be maintained (Comparative Examples 3, 4, and 5), or a magnetic core having a low relative density can be obtained (Comparison). Examples 1, 2). Even when the first metal magnetic powder is not used, the magnetic core can be formed by blending the binder, but the relative density decreases and the magnetic permeability decreases (Comparative Example 6). The shape of the magnetic core could not be maintained even when a metal magnetic powder having an excessively low NIT value was used instead of the first metal magnetic powder (Comparative Example 7). Even if metal magnetic powder having an excessively high NIT value was used in place of the second metal magnetic powder, the shape of the magnetic core could not be maintained (Comparative Example 8). Further, when the second metal magnetic powder was not used, the magnetic permeability did not increase and the shape retention was not sufficient (Comparative Example 9).

Claims (7)

  A dust core including a first metal magnetic powder having an NIT value of 10% to 30% and a second metal magnetic powder having an NIT value of more than 30% and 90% or less.  The first metal magnetic powder is contained in a ratio of 30 to 50 parts by mass and the second metal magnetic powder is contained in a ratio of 70 to 50 parts by mass per 100 parts by mass in total of the first metal magnetic powder and the second metal magnetic powder. The dust core described.  The dust core according to claim 1 or 2, wherein the content of the resin component with respect to the total mass of the dust core is 2 mass% or less.  The powder magnetic core according to any one of claims 1 to 3, wherein a difference between the NIT value of the first metal magnetic powder and the NIT value of the second metal magnetic powder is 60% or less.  The powder magnetic core according to claim 4, wherein the difference between the NIT value of the first metal magnetic powder and the NIT value of the second metal magnetic powder is 50% or less.   The dust core according to any one of claims 1 to 5, wherein both the first metal magnetic powder and the second metal magnetic powder are Fe-based soft magnetic powders.   The dust core according to any one of claims 1 to 6, wherein one or both of the first metal magnetic powder and the second metal magnetic powder have an insulating coating.

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