JP2017069550A - Powder-compact magnetic core, and coil part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a powder-compact magnetic core which enables the cutting of use of an expensive material in quantity, and having a requisite magnetic property; and a coil part with such a powder-compact magnetic core.SOLUTION: A powder-compact magnetic core having soft magnetic powder comprises: bare iron powder without insulative coating; and a powdery lubricant having a melting point of 120°C or higher. In the soft magnetic powder, the content of the bare iron powder is over 45 mass%. In the powder-compact magnetic core, the content of the lubricant is 0.05-0.5 mass%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a dust core and a coil component.

  Patent Document 1 discloses a dust core mainly composed of coated iron powder having an insulating coating and containing a very small amount of an aliphatic lubricant. This powder magnetic core can be obtained by heat-pressing a compression molded body that has been demolded after pressurizing and compressing a mixed powder of coated iron powder and an aliphatic lubricant.

Japanese Patent Laying-Open No. 2015-70077

  Cost reduction is desired for powder magnetic cores used for coil parts and the like. From the viewpoint of reducing the cost of dust cores, it is possible to reduce the amount of coated iron powder that is a constituent material of the dust core, and use cheap bare iron powder that does not have an insulation coating instead of coated iron powder. It is desired.

  As described in Patent Document 1, the conventional dust core uses coated iron powder to increase the electrical resistance of the dust core by insulating coating and reduce core loss such as eddy current loss. When bare iron powder is used in place of the coated iron powder, the iron particles constituting the bare iron powder are combined with each other to form a large conduction portion, which tends to increase eddy current and increase core loss. In particular, in the dust core, the permeability increases as the size of the iron powder constituting it increases. However, if the size of the bare iron powder is large, the core loss tends to increase further.

  Accordingly, an object of the present invention is to provide a dust core that can reduce the amount of expensive materials used and that has necessary magnetic properties. Another object is to provide a coil component including a dust core that can reduce the amount of expensive material used and has the necessary magnetic properties.

The dust core according to the present disclosure is:
A dust core having soft magnetic powder,
Bare iron powder without insulation coating,
A powdery lubricant having a melting point of 120 ° C. or higher,
The content of the bare iron powder in the soft magnetic powder is more than 45% by mass,
The content of the lubricant in the dust core is 0.05% by mass or more and 0.5% by mass or less.

The coil component according to the present disclosure is:
A coil component comprising a coil and a magnetic core,
At least a part of the magnetic core includes the dust core according to the present disclosure.

  The dust core and the coil component described above can reduce the amount of expensive materials used and have necessary magnetic properties.

It is explanatory drawing which shows typically the structure | tissue of the powder magnetic core of embodiment. It is explanatory drawing which shows typically the powder magnetic core of embodiment. FIG. 2 is a schematic configuration diagram illustrating a coil component according to the first embodiment. FIG. 6 is a schematic configuration diagram showing a coil component according to a second embodiment. FIG. 6 is a schematic configuration diagram illustrating a coil component according to a third embodiment.

[Description of Embodiment of the Present Invention]
The inventors of the present invention have made various studies using bare iron powder that does not have an insulating coating in order to manufacture a dust core that can reduce the amount of expensive material used and that has necessary magnetic properties. As a result, by adding a powdery lubricant with a high melting point, even if the content of bare iron powder is large, the lubricant will be interposed between the bare iron powder, and the increase in core loss is suppressed, And the knowledge that the powder magnetic core which has a favorable magnetic characteristic was obtained was acquired. First, the contents of the embodiment of the present invention will be listed and described.

(1) A powder magnetic core according to an embodiment of the present invention includes:
A dust core having soft magnetic powder,
Bare iron powder without insulation coating,
A powdery lubricant having a melting point of 120 ° C. or higher,
The content of the bare iron powder in the soft magnetic powder is more than 45% by mass,
The content of the lubricant in the dust core is 0.05% by mass or more and 0.5% by mass or less.

  In the above-mentioned dust core, bare iron powder is contained in the soft magnetic powder in an amount of more than 45% by mass, and the amount of coated iron powder provided with an insulating coating can be reduced by the amount of the bare iron powder content. . Since bare iron powder is less expensive than coated iron powder, the above-mentioned dust core having a bare iron powder content of more than 45% by mass is excellent in economic efficiency. The above powder magnetic core has a powdery lubricant having a melting point of 120 ° C. or higher added at a specific content, and this lubricant serves as an insulating material between the bare iron powders. It is possible to suppress an increase in eddy current due to the generation of a conductive portion by combining iron particles constituting the powder, and it is possible to suppress an increase in core loss. Since the melting point of the lubricant is a high melting point of 120 ° C. or higher, it is possible to suppress the dissolution and liquefaction of the lubricant even at high temperatures in the production conditions and usage conditions of the powder magnetic core, and to stabilize the space between the bare iron powders. Can be insulated. In addition, since the lubricant is in a powder form, an insulating material exists between the iron particles in the form of dots, and an insulating material exists in the form of a film between the iron particles like the coated iron powder. Compared with the case, the magnetic flux easily passes, and good magnetic permeability can be secured.

(2) As an example of the above powder magnetic core,
The dust core has a long piece,
In the transverse section or longitudinal section of the long piece, the bare iron powder is a flat shape having a minor axis and a major axis, and when the minor axis direction is a compression direction,
The said long piece has a form which has the narrow part whose length of the direction orthogonal to both the longitudinal direction and the said compression direction is 80 times or less of the average particle diameter of the said bare iron powder.

  One of the indicators for discriminating the compression direction of the dust core is to look at the elongation direction of bare iron powder (iron particles) existing in the cross section of the dust core. Since the powder magnetic core compresses and compresses the raw material powder, each iron particle constituting the raw material powder is crushed in the compression direction (plastically deformed), typically in a direction orthogonal to the compression direction. It becomes an elongated shape. That is, when the bare iron powder has a flat shape having a minor axis and a major axis, it can be expected that the minor axis direction is the compression direction. If it does so, the direction orthogonal to both the longitudinal direction and compression direction of a long piece turns into the major axis direction which bare iron powder extended. In the powder magnetic core, the long piece has a narrow portion whose length in the direction orthogonal to both the longitudinal direction and the compression direction is 80 times or less the average particle diameter of the bare iron powder.

  The powder magnetic core having the above shape and size is easy to further suppress an increase in core loss for the following two reasons. First, the short diameter direction of the bare iron powder tends to increase the grain boundary between the iron particles, and the lubricant is interposed between the iron particles, so that eddy currents hardly flow. Second, the major axis direction of bare iron powder tends to reduce the grain boundary between each iron particle, and eddy current tends to flow, but if the longitudinal direction of the long piece is the magnetic flux direction, it is long. Since the length of the long piece (powder magnetic core) along the major axis direction of the bare iron powder other than the lengthwise direction of the scale piece is small, the length in which the eddy current flows is small. From the above, the powder magnetic core can easily suppress an increase in core loss by adjusting the length of the bare iron powder along the major axis direction.

(3) As an example of the above powder magnetic core,
Examples of the lubricant include a form containing a metal stearate.

  As a lubricant having a melting point of 120 ° C. or higher, a metal stearate can be suitably used. By including a stearic acid metal salt as a lubricant, at the time of demolding from the mold, it is possible to reduce the friction (friction) between the molded body and the mold, and the demoldability is excellent.

(4) As an example of the above powder magnetic core,
The bare iron powder has an average particle size of 40 μm or more and 100 μm or less,
The form whose particle | grain ratio is 200 mass% or less among the constituent particles of the said bare iron powder is mentioned.

  Bare iron powder has an average particle size of 100 μm or less, and the proportion of particles having a particle size of constituent particles (iron particles) of 200 μm or more is 10% by mass or less, which is large even when iron particles are bonded to each other. It is easy to suppress an increase in eddy current due to the occurrence of a conductive portion, and it is easy to suppress an increase in core loss. On the other hand, when the average particle size of the bare iron powder is 40 μm or more, it is easy to handle the bare iron powder in the manufacturing process, and the compressibility is excellent.

(5) As an example of the above powder magnetic core,
Furthermore, it comprises a coated iron powder with an insulating coating,
The form whose content of the said covering iron powder in the said soft-magnetic powder is 30 mass% or more and less than 55 mass% is mentioned.

  When the dust core has the coated iron powder, the coated iron powder exists between the bare iron powders. Therefore, since the insulation coating of the coated iron powder exists around the constituent particles of the bare iron powder, it is easy to suppress contact between the constituent particles of the bare iron powder, the increase in eddy current can be suppressed, and the core loss is increased. It is easy to suppress. When the content of the coated iron powder in the soft magnetic powder is 30% by mass or more, the insulation is excellent due to the intervening insulating coating, and the increase in core loss is easily suppressed. On the other hand, when the content of the coated iron powder in the soft magnetic powder is 55% by mass or less, the content of the bare iron powder can be relatively increased, and the content of the expensive coated iron powder can be reduced.

(6) As an example of the above powder magnetic core,
Examples of the bare iron powder include a form in which the oxygen content is less than 0.1 mass% and the total content of phosphorus, chromium, manganese, nickel, and copper is less than 0.2 mass%.

  The bare iron powder has an oxygen content of less than 0.1% by mass (including 0% by mass) and a total content of phosphorus, chromium, manganese, nickel, and copper of less than 0.2% by mass (0 Hysteresis loss can be reduced because there are few impurities inside bare iron powder. In particular, when heat treatment is not performed after compression in the manufacturing process of the powder magnetic core, hysteresis loss can be effectively reduced by using bare iron powder with less impurities. Furthermore, since bare iron powder with few impurities is excellent in a deformability, the powder magnetic core of the outstanding permeability can be obtained by filling between bare iron powders without a gap.

(7) The coil component according to the embodiment of the present invention is
A coil component comprising a coil and a magnetic core,
At least a part of the magnetic core includes the dust core according to any one of (1) to (6).

  Said coil components can reduce the usage-amount of expensive covering iron powder, can suppress the increase in core loss, and have favorable magnetic permeability.

(8) As an example of the above coil component,
The dust core has a long piece,
In the cross section of the long piece, the bare iron powder is a flat shape having a short diameter and a long diameter,
The said long piece has the form arrange | positioned so that the longitudinal direction may turn into the direction along the magnetic flux direction accompanying the excitation of the said coil.

  Depending on the compression direction of the dust core, it is easy to ensure good magnetic permeability by arranging the dust core so that its longitudinal direction is along the magnetic flux. The fact that the bare iron powder has a flat shape having a short diameter and a long diameter in the cross section of the dust core means that the long diameter of the bare iron powder is along the longitudinal direction of the dust core. The major axis direction of bare iron powder is that the grain boundary between the bare iron powder constituent particles (iron particles) is reduced, and magnetic flux easily passes. Therefore, the major axis of the bare iron powder is along the longitudinal direction of the dust core. Thus, good magnetic permeability can be secured.

[Details of the embodiment of the present invention]
Details of the embodiment of the present invention will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included. The same code | symbol in a figure shows the same name thing.

[Dust core]
The powder magnetic core 1 of the embodiment is a molded body having soft magnetic powder, and contains a relatively large amount of bare iron powder 20 composed of iron particles not provided with an insulating coating as shown in FIG. The dust core 1 further includes a lubricant 30. The dust core 1 also includes a coated iron powder 10 composed of coated iron particles in which the outer periphery of the iron particles 12 is covered with an insulating coating 14. Typically, the powder magnetic core 1 is formed by compressing the raw material powder P so that the powder particles constituting the powders 10 and 20 are plastically deformed and meshed with each other via the lubricant 30. Is retained. Hereinafter, each configuration will be described in detail.

・ Nude iron powder (iron particles)
.. Composition One feature of the dust core 1 of the embodiment is that the magnetic component is pure iron. By making the iron particles pure iron, the dust core 1 has high magnetic permeability and saturation magnetic flux density. Further, by making the iron particles pure iron, the powder magnetic core 1 is excellent in plastic deformability of the raw material powder P, is easy to mold, is excellent in manufacturability, is easily densified, and is easy to improve magnetic characteristics (especially magnetic permeability). The powder particles are sufficiently meshed with each other through the lubricant 30 and have an effect that the mechanical strength is excellent. Further, by using pure iron as the iron particles, it is cheaper than an iron alloy and is excellent in economic efficiency. In the dust core 1 of the embodiment, the bare iron powder 20 which is an essential component and the iron particles 12 of the coated iron powder 10 which is an optional component are both pure iron.

  One feature of the bare iron powder 20 is that the amount of impurities is small. 99 mass% or more of pure iron constituting the iron particles of the bare iron powder 20 is Fe, and the remainder is inevitable impurities. The smaller the inevitable impurities in pure iron, the lower the hysteresis loss. The bare iron powder 20 has an oxygen (O) content of less than 0.1% by mass, and the total of phosphorus (P), chromium (Cr), manganese (Mn), nickel (Ni), and copper (Cu). The content is preferably less than 0.2% by mass. If it is this range, it will be easy to reduce the hysteresis loss resulting from inclusion of an impurity, and it will be easy to improve magnetic permeability. The smaller the element content, the better. The O content is preferably 0.08% by mass or less, more preferably 0.07% by mass or less, and particularly preferably 0.06% by mass or less. The total content of P, Cr, Mn, Ni and Cu is preferably 0.18% by mass or less, more preferably 0.17% by mass or less, and particularly preferably 0.16% by mass or less.

  For example, the content of impurities may be comprehensively determined by performing thermal analysis, infrared spectroscopy, or the like in addition to high frequency inductively coupled plasma (ICP) emission spectroscopy. These analyzes are performed only on the bare iron powder 20. Even when the dust core 1 includes the coated iron powder 10, since the heat treatment is not performed after the molding process in the manufacturing process of the dust core, the dust core 1 is pulverized to form the bare iron powder 20 and the coated iron powder 10. It is easy to take out, for example, it is possible to determine the bare iron powder 20 by performing energy dispersive X-ray spectroscopy (EDX) on the surface of the powder taken out using an electron microscope and examining the presence or absence of coating. it can.

  The composition of the bare iron powder 20, the composition of the coated iron powder 10, and the composition of the lubricant 30 in the powder magnetic core 1 are not subjected to heat treatment after compression in the manufacturing process, so that the raw material powder P (coated iron powder 100, bare iron powder) 200, substantially the composition of the lubricant 300).

.. Content One of the characteristics is that the content of the bare iron powder 20 in the soft magnetic powder is more than 45% by mass. When the content of the bare iron powder 20 is more than 45% by mass, the amount of the coated iron powder 10 described later can be relatively reduced. As the content of the bare iron powder 20 increases, the amount of the coated iron powder 10 used can be relatively reduced, and the cost can be reduced. The content of the bare iron powder 20 in the soft magnetic powder can be 50% by mass or more, further 60% by mass or more, 65% by mass or more, 70% by mass or more, 80% by mass or more, and particularly 100% by mass. However, as the content of the bare iron powder 20 increases, eddy current loss (core loss) due to the coupling between the iron particles constituting the bare iron powder 20 tends to increase. Therefore, it is important to secure insulation between the iron particles (details will be described later). When the content of the bare iron powder 20 is less than 100% by mass, the balance of the soft magnetic powder is the coated iron powder 10 described later. The mass of the soft magnetic powder of the dust core 1 is a value obtained by dividing the mass of the lubricant 30 described later from the mass of the dust core 1 (the total mass of the lubricant and additives when other additives are included). To do.

.. Size The bare iron powder 20 is characterized by containing relatively small iron particles. Specifically, the average particle diameter of the bare iron powder 20 is preferably 40 μm or more and 100 μm or less. When the average particle diameter of the bare iron powder 20 is 100 μm or less, an increase in eddy current due to the generation of a large conduction portion can be suppressed even when the iron particles are combined, and an increase in core loss can be suppressed. Moreover, since the lubricant 30 described later is easily interposed between the bare iron powders 20 and the insulating property can be enhanced by the lubricant 30, an increase in core loss can be suppressed. The average particle diameter of the bare iron powder 20 can be 95 μm or less, more preferably 90 μm or less, and particularly 85 μm or less.

  When the average particle size of the bare iron powder 20 is 40 μm or more, it is easy to handle the bare iron powder 200 in the manufacturing process, and it has excellent fluidity and excellent deformability. Therefore, it is easy to increase the strength by deformation, and it is excellent in manufacturability. Moreover, since it is excellent in compressibility, it is easy to raise the density of the powder magnetic core 1, and it is excellent also in magnetic characteristics, such as a magnetic permeability. The average particle diameter of the bare iron powder 20 can be 50 μm or more, more preferably 60 μm or more, and particularly preferably 70 μm or more.

  The bare iron powder 20 preferably has too few powder particles. Specifically, it is preferable that the ratio of the iron particles constituting the bare iron powder 20 having a particle diameter of 200 μm or more is 10% by mass or less, with the bare iron powder 20 being 100% by mass. Further, in the bare iron powder 20, the ratio of iron particles having a particle size of 180 μm or more is preferably 10% by mass or less, and particularly the ratio of iron particles having a particle size of 150 μm or more is preferably 10% by mass or less. The dust core 1 having a small number of iron particles that are too large can suppress an increase in eddy current due to the presence of coarse particles and suppress an increase in core loss. From this point, the ratio of the iron particles having a particle size of 200 μm or more (preferably 180 μm or more, 150 μm or more) in the bare iron powder 20 in the dust core 1 is 5 mass% or less, and further 3 mass% or less, 2 It is preferable that it is not more than 1% by mass, particularly not substantially present. The powder magnetic core 1 having a small number of powder particles that are too large typically uses the bare iron powder 200 having a small particle size of 200 μm or more (preferably 180 μm or more, preferably 150 μm or more) as the raw material powder P. Can be manufactured. Since such a bare iron powder 200 has a narrow particle size distribution, it is easy to uniformly move the bare iron powder 200 and compress the raw material powder P in the mold during the manufacturing process.

Lubricant The powder magnetic core 1 according to the embodiment includes a powdery lubricant 30 having a high melting point. The lubricant 30 in the powder magnetic core 1 is mainly interposed between the bare iron powders 20 described above to insulate the iron particles constituting the bare iron powders 20 (for example, a volume specific resistance of 1 kΩ · cm Above). It also has a function of reducing friction between the powder particles constituting the raw material powder P in the manufacturing process, friction between the molded body and the mold during demolding, and the like.

-Composition The lubricant 30 has a melting point of 120 ° C or higher. Since the lubricant 30 has a high melting point of 120 ° C. or higher, the lubricant 30 can be prevented from being dissolved and liquefied even at a high temperature in the production conditions and use conditions of the powder magnetic core 1. It can exist in a powder form between the iron particles. Therefore, each iron particle can be insulated stably. Since the lubricant 30 is in the form of powder and is present between the iron particles, an insulating material is present in the form of dots between the iron particles, and between the iron particles as in the coated iron powder 10 described later. Compared with the case where an insulating material is present in the form of a film, it is easier for magnetic flux to pass through, and good magnetic permeability can be ensured.

  As the lubricant 30 having a melting point of 120 ° C. or higher, for example, a stearic acid metal salt can be used. Specific examples of the metal stearate include zinc stearate (melting point: about 120 ° C. to 125 ° C.), lithium stearate (melting point: about 210 ° C. to about 220 ° C.), and the like. When the metal salt of stearic acid is contained as the lubricant 30, one or more kinds can be included.

  The lubricant 30 can further contain a fatty acid amide. The fatty acid amide typically has a melting point of about 70 ° C to 150 ° C, and more preferably about 90 ° C to 120 ° C. By including a fatty acid amide having a relatively low melting point as the lubricant 30, the fatty acid amide that has been dissolved and liquefied is easily arranged uniformly between the powders. Therefore, in addition to being excellent in compressibility and demoldability, in addition to the powdery high melting point lubricant, the insulation can be further improved. Specific fatty acid amides include stearic acid amide (melting point of about 100 ° C.), palmitic acid amide, and the like.

  When the lubricant 30 contains a plurality of types of lubricants, it is preferable that the content ratio of the metal stearate is higher. This is because the metal stearate has a high melting point, so that it can be suppressed from being dissolved and liquefied, and is easily present in powder form between the iron particles of the bare iron powder 20. In the case where a plurality of types of lubricants are contained, the total content of the lubricant is 100% by mass, and the content of the stearic acid metal salt is 25% by mass or more and 100% by mass or less. The components of the lubricant 300 in the raw material powder P may be adjusted so that the lubricant 30 in the dust core 1 becomes a specific component.

.. Content One content is that the content of the lubricant 30 in the dust core 1 is 0.05% by mass or more and 0.5% by mass or less. When the content of the lubricant 30 is 0.05% by mass or more, it can be sufficiently interposed between the iron particles of the bare iron powder 20. Therefore, it is possible to suppress an increase in eddy current due to a combination of iron particles and the generation of a conductive portion, and it is possible to suppress an increase in core loss. The content of the lubricant 30 in the dust core 1 can be 0.1% by mass or more, and further 0.2% by mass or more. The content of the lubricant 30 is substantially correlated with the content of the bare iron powder 20. For example, when the content of the bare iron powder 20 is increased, the number of insulating portions between the iron particles is increased. Therefore, by increasing the content of the lubricant 30, an increase in core loss can be suppressed. On the other hand, when the content of the bare iron powder 20 is small, the number of insulating portions between the iron particles is reduced. Therefore, by reducing the content of the lubricant 30, a decrease in the ratio of the soft magnetic powder of the dust core 1 is suppressed. it can.

  When the content of the lubricant 30 in the dust core 1 is 0.5% by mass or less, a decrease in the ratio of the soft magnetic powder due to an excess of the lubricant 30 can be suppressed, and a decrease in magnetic characteristics can be suppressed. For example, when the content ratio of the bare iron powder 20 in the soft magnetic powder is 100% by mass (the total amount of the soft magnetic powder is the bare iron powder 20), the content of the lubricant 30 in the dust core 1 is the upper limit of 0.00. It is mentioned that it is 5 mass%. The content of the lubricant 30 in the dust core 1 can be 0.45% by mass or less, and further 0.40% by mass or less.

.. Size The lubricant 30 exists as a powder. If a powdery material is used as the lubricant 300 of the raw material powder P, the lubricant 30 may exist in a powder form even after compression molding. The lubricant 30 is preferably smaller than the bare iron powder 20. Specifically, the average particle size of the lubricant 30 is preferably 1 μm or more and 50 μm or less. When the average particle diameter of the lubricant 30 is 1 μm or more, the iron particles of the bare iron powder 20 can be sufficiently insulated. Moreover, it is easy to handle the lubricant 30 during the manufacturing process.

  When the average particle diameter of the lubricant 30 is 50 μm or less, the lubricant 30 is easily interposed between the iron particles, and is easily disposed substantially uniformly around the iron particles. Since the lubricant 30 is substantially uniformly disposed around each iron particle, it is easy to suppress an increase in core loss. The average particle diameter of the lubricant 30 can be set to 40 μm or less, and further to 30 μm or less.

  The lubricant 30 is deformed at the time of compression molding and exists in an arbitrary shape along the iron particles of the bare iron powder 20 or the coated iron particles of the coated iron powder 10 described later, or is divided into smaller powders. Or may be combined with other particles of lubricant to form a larger powder.

-Coated iron powder The coated iron powder 10 is comprised from the coated iron particle by which the outer periphery of the iron particle 12 similar to the iron particle of the bare iron powder 20 mentioned above was covered by the insulation coating 14. FIG. The insulating coating 14 mainly functions as an insulating material that prevents direct contact between the iron particles 12 and increases the electrical resistance of the dust core 1. As long as the insulation coating 14 can insulate between the iron particles 12 or between the iron particles 12 and the iron particles of the bare iron powder 20, the entire surface of the iron particles 12 may not be covered, and a part of the iron particles 12 is exposed. The existence state is allowed.

  The constituent material of the insulating coating 14 can take various insulating materials. For example, a compound containing a metal element or a compound containing a nonmetallic element can be given. The former includes one or more metal elements selected from Fe, Al, Ca, Mn, Zn, Mg, V, Cr, Y, Ba, Sr, and rare earth elements (excluding Y), oxygen, nitrogen, And one or more compounds selected from carbon (for example, metal oxides, metal nitrides, metal carbides), zirconium compounds, aluminum compounds, and the like. Examples of the latter include phosphorus compounds and silicon compounds. Other examples include metal phosphate compounds (typically iron phosphate, manganese phosphate, zinc phosphate, calcium phosphate, etc.), metal salt compounds such as borate metal salt compounds, silicate metal salt compounds, and titanate metal salt compounds. The powder magnetic core 1 including the metal phosphate compound as the insulating coating 14 has the insulating coating 14 in an excellent manner and has excellent insulating properties, and has low eddy current loss and consequently low core loss. Since the metal phosphate compound is excellent in deformability, when the coated iron powder 100 provided with the insulating coating 140 of the metal phosphate compound is used as the raw material powder P, the metal phosphate compound follows the deformation of the iron particles 120 during molding. This is because it easily deforms and is not easily damaged, and has high adhesion to iron, so that it is difficult to drop off from the surface of the iron particles 120 during molding or the like. On the other hand, phosphorus contained in the metal phosphate compound diffuses into the iron particles 12, which may increase core loss. Therefore, it is considered that the content of phosphorus contained in the entire powder magnetic core 1 is preferably 1000 mass ppm or less, and more preferably 600 mass ppm or less. The components of the iron particles 120, the components of the insulating coating 140, and the thickness may be adjusted so that the phosphorus amount becomes a desired value.

  Examples of other constituent materials of the insulating coating 14 include various resins and higher fatty acid salts. Specific examples of the resin include polyamide resins and silicone resins. Examples of polyamide resins include nylon 6 and nylon 66.

  As for the thickness of the insulation coating 14, 10 nm or more and 1 micrometer or less are mentioned, for example. If the thickness is 10 nm or more, good insulation between the iron particles (between the iron particles 12 of the coated iron powder 10 and between the iron particles 12 and the iron particles of the bare iron powder 20) can be secured satisfactorily. If the said thickness is 1 micrometer or less, there are few insulation coatings 14, the fall of the ratio of the magnetic component in the dust core 1 can be suppressed, and it is easy to raise a magnetic permeability. A more preferable thickness is 20 nm or more and 100 nm or less. The thickness of the insulating coating 14 in the dust core 1 depends on the composition of the film obtained by composition analysis (analyzer using transmission electron microscope and energy dispersive X-ray spectroscopy (TEM-EDX)), and inductively coupled plasma. Considering the amount of element obtained by the mass spectrometer (ICP-MS), the equivalent thickness is derived, and further, the insulation coating 14 is directly observed by the TEM photograph, and the order of the equivalent thickness derived earlier is appropriate. The average thickness is determined by confirming that the value is correct. The thickness of the insulating coating 14 generally maintains the thickness of the insulating coating 140 of the raw material powder P.

-Content The content of the coated iron powder 10 in the soft magnetic powder is 30% by mass or more and less than 55% by mass. When the content of the coated iron powder in the soft magnetic powder is 30% by mass or more, the insulation is excellent due to the presence of the insulating coating 14, and an increase in core loss is easily suppressed. The content of the coated iron powder 10 in the soft magnetic powder can be 35% by mass or more, and further 40% by mass or more. On the other hand, when the content of the coated iron powder in the soft magnetic powder is less than 55% by mass, the content of the bare iron powder can be relatively increased, and the content of the coated iron powder can be reduced. Therefore, the content of the coated iron powder 10 in the soft magnetic powder can be 50% by mass or less, and further 45% by mass or less.

-Size The coated iron powder 10 includes relatively large powder particles. Since the coated iron powder 10 is large, the dust core 1 can sufficiently secure a magnetic path and have high magnetic permeability. Specifically, the average particle diameter of the coated iron powder 10 is preferably 150 μm or more and 400 μm or less. When the average particle size of the coated iron powder 10 is 150 μm or more, it is easy to reduce the core loss in addition to the high magnetic permeability. The average particle diameter of the coated iron powder 10 can be 180 μm or more, and further 200 μm or more.

  When the average particle diameter of the coated iron powder 10 is 400 μm or less, it is difficult to increase the eddy current loss generated in the iron particles 12 due to the increase in the diameter of the iron particles 12, and the core loss can be reduced. The average particle diameter of the coated iron powder 10 can be 350 μm or less, and further 300 μm or less.

-Other inclusions The powder magnetic core 1 can contain resin etc. as another additive. Specifically, polyacetal (POM), polyamide (PA), polycarbonate (PC), polybutylene terephthalate (PBT), modified polyphenylene ether (m-PPE), polyphenylene sulfide (PPS), polyether ether ketone (PEEK) Engineering plastics such as polyetherimide (PEI). The content of the additive is preferably more than 0 and 0.5% by mass or less, with the dust core 1 being 100% by mass. By including a resin or the like within this range, the moldability and shape retention can be improved, and a decrease in the proportion of the magnetic component due to the inclusion of the resin can be prevented. In particular, the polyamide-based resin can function as an insulating material that insulates the iron particles of the bare iron powder 20. The polyamide-based resin may be in the form of a powder between the powder particles as in the case of the lubricant 30 or in the form of the insulating coating 14 of the coated iron powder 10. In the case of powder, resin powder may be mixed with the raw material powder P.

-Shape The powder magnetic core 1 of the embodiment can take various shapes by using various shapes of molds. Typically, a columnar body having two opposing surfaces as end faces and a cylindrical body having through holes penetrating both end faces are exemplified. More specifically, a cylinder, a cylinder, a ring (thickness is thin), a rectangular column such as a rectangular parallelepiped, a square cylinder whose end face is a frame shape, and the like can be given. In addition, the outer shape such as a shape having one or a plurality of steps or a shape including one or a plurality of flange portions at the end portion may be an irregular columnar body or cylindrical body having an uneven shape.

  As a specific shape, the powder magnetic core 1 may have a long piece 1L (FIG. 2). As this long piece 1L, the ratio L / W of the length L to the width W is 10 or more. That is, the dust core 1 has an elongated shape. The long piece 1L has a flat shape in which the iron particles constituting the bare iron powder 20 have a short diameter and a long diameter in the transverse section or the longitudinal section. By observing the iron particles, the compression direction of the long piece 1L (the dust core 1) can be determined. Since the powder magnetic core 1 compresses and compresses the raw material powder P, each powder particle constituting the raw material powder P is crushed (plastically deformed) in the compression direction, and is typically orthogonal to the compression direction. It becomes the shape extended in the direction. Therefore, when the iron particles have a flat shape having a minor axis and a major axis, the minor axis direction (direction orthogonal to the extending direction) can be expected to be the compression direction.

  In the long piece 1L shown in FIG. 2, the bare iron powder 20 has a shape in which each iron particle extends in the transverse direction having a short diameter and a long diameter (enlarged view shown on the lower side of FIG. 2). Here is an example. That is, the long piece 1L shown in FIG. 2 is a compression molded body compressed in the vertical direction. Therefore, in the long piece 1L, each iron particle has a substantially circular shape (enlarged view shown in the upper side of FIG. 2) having the above-mentioned major axis in a cut surface (horizontal cross section) along the upper and lower surfaces. That is, each iron particle of the bare iron powder 20 has a major axis in the length L direction and the width W direction of the long piece 1L, and a minor axis in the height H direction.

  The dust core 1 preferably has an elongated shape in which the longitudinal direction of the long piece 1L is a direction orthogonal to the compression direction. When the dust core 1 is a coil component to be described later, it is preferable that the long piece 1L is arranged so that the longitudinal direction thereof is in the direction along the direction of magnetic flux accompanying excitation of the coil. The major axis direction of the iron particles constituting the bare iron powder 20 is easy to pass magnetic flux because there are few grain boundaries between the iron particles. Therefore, a better magnetic permeability can be ensured by the long magnetic flux direction.

  Moreover, it is preferable that the powder magnetic core 1 has a narrow part with a short length W in a direction orthogonal to both the longitudinal direction and the compression direction of the long piece 1L. The length W of the narrow portion is not more than 80 times the average particle size of the bare iron powder 20. Since the iron particles constituting the bare iron powder 20 have a flat shape, the average particle diameter of the bare iron powder 20 is the equivalent circle diameter of each area. In the major axis direction of the iron particles, there is a problem that eddy currents easily flow because there are few grain boundaries between the iron particles, but an increase in core loss can be suppressed because the length of the eddy currents flowing is small. In the minor axis direction of the iron particles, grain boundaries between the iron particles tend to increase, and the lubricant 30 is interposed between the iron particles, so that the eddy current hardly flows.

  In addition, the compression direction of the long piece 1L (the dust core 1) may be a direction along the longitudinal direction (the direction of the length L in FIG. 2). In this case, the iron particles constituting the bare iron powder 20 have a short diameter in the longitudinal direction of the long piece 1L and a long diameter in a direction orthogonal to the longitudinal direction. Therefore, the powder magnetic core 1 has a length in the direction orthogonal to the compression direction (for example, at least one of the width W and height H in FIG. It is preferable that it is less than 2 times.

  As one of the indexes for determining the compression direction of the dust core 1, there is an outer shape in addition to the extending direction of the bare iron powder 20 (iron particles). Since the dust core 1 is typically a molded body using a uniaxial mold, its outer shape is limited to a shape that can be extracted from the mold. For example, in the case of a dust core having a through hole (such as the core piece 10f in FIG. 3), the axial direction of the through hole can be expected to be the compression direction. Furthermore, as one of the indexes for determining the compression direction of the powder magnetic core 1, for example, the presence or absence of a sliding contact mark can be mentioned. When the molded body is extracted from the die on the contact surface with the die that forms the outer peripheral surface of the dust core 1 or the contact surface with the rod that forms the inner peripheral surface of the dust core when there is a through hole, When the rod is withdrawn, the molded body and the die or the rod are in sliding contact, and a sliding contact mark may remain. That is, it can be expected that the surface having the sliding contact mark is a surface formed by a die or a rod, and the surface having no sliding contact mark is an end surface formed by a punch. Then, it can be expected that the direction orthogonal to the pair of end faces opposed to each other is the compression direction.

- An example of a dust core 1 density embodiment include those having a density satisfies the 7.3 g / cm ³ or more 7.7 g / cm ³ or less. If the density is 7.3 g / cm ³ or more, the relative density ((apparent density / true density) × 100. The true density = the density of the pure iron powder) is 92% or more, the magnetic permeability is high, and the strength is high. Excellent. Since the magnetic permeability and strength increase as the density increases, the density of the dust core 1 preferably satisfies 7.35 g / cm ³ or more, and more preferably 7.4 g / cm ³ or more. On the other hand, if the density of the powder magnetic core 1 is 7.7 g / cm ³ or less, it is manufactured at a relatively low molding pressure, and when the coated iron powder is contained, damage to the insulating coating during molding is reduced. Even so, the core loss can be reduced. Thus, the density of the dust core 1, 7.65 g / cm ³ or less, it is possible to further 7.6 g / cm ³ or less.

-Characteristics When the dust core 1 of the embodiment is assembled into a coil to form a coil component, the powder magnetic core 1 has magnetic characteristics necessary for the coil component. For example, the AC magnetic permeability of the dust core 1 is 350 or more, further 400 or more, particularly 420 or more when the measurement condition is 1.0 T / 1 kHz. Further, the core loss is 300 W / kg or less, further 280 W / kg or less, particularly 250 W / kg or less.

[Coil parts]
The dust core 1 of the embodiment can be used as a constituent member of a magnetic path. For example, in a coil component including a coil formed by spirally winding a winding and a magnetic core in which the coil is arranged to form a magnetic path, the dust core 1 can be used for at least a part of the magnetic core. . 3-5 shows an example of a coil component. In the figure, the same reference numerals indicate the same names.

  A coil component 1A according to the first embodiment shown in FIG. 3 includes, as a magnetic core 10A, a frame-shaped core piece 10f having a through hole 10h, an I-shaped core piece 10i disposed inside the core piece 10f, Is provided. The frame shape may be a square frame shape or a rectangular frame shape. The magnetic core 10A is combined such that each end face of the I-shaped core piece 10i faces two opposing inner faces of the frame-like core piece 10f, as shown by a two-dot chain line in the left diagram of FIG. Constructs a closed magnetic circuit. In this example, a gap G is provided between one end face of the I-shaped core piece 10i and the frame-shaped core piece 10f, and the coil C is fitted on the outer periphery of the I-shaped core piece 10i. Show.

  A part of the magnetic core 10A, for example, a frame-shaped core piece 10f on which the coil C is not disposed can be used as the dust core 1 of the embodiment. That is, the frame-shaped core piece 10f has four square bar pieces. Each of the four square bar pieces corresponds to the long piece 1L of the dust core 1. In the frame-shaped core piece 10f, the axial direction of the through hole 10h is the compression direction, and thus the major axis direction of the iron particles constituting the bare iron powder 20 is arranged along the magnetic flux direction. Therefore, since the magnetic flux easily passes through the frame-shaped core piece 10f, a good magnetic permeability can be ensured. The frame-shaped core piece 10f has a relatively small length in the direction orthogonal to both the longitudinal direction and the compression direction (the length extending from the inner surface to the outer surface of the frame-shaped core piece 10f) (bare iron powder 20 It is preferable that the average particle size is 80 times or less. By doing so, an increase in core loss can also be suppressed. The I-shaped core piece 10i may be formed of a coated iron powder as in the past (bare iron powder may be contained in a range of more than 0% by mass and 45% by mass or less) as a dust core. preferable. Of course, the I-shaped core piece 10i may be the dust core 1 of the embodiment.

  A coil component 1B according to the second embodiment illustrated in FIG. 4 includes an I-shaped core piece 10i and a U-shaped core piece 10p as the magnetic core 10B. This magnetic core 10B is an O-shaped magnetic core that constitutes a frame-shaped closed magnetic path by combining both core pieces 10i and 10p (the left diagram in FIG. 4). Here, an example is shown in which a gap G is provided between both core pieces 10i and 10p, and a coil C is arranged on the I-shaped core piece 10i. In this example, it is preferable that the U-shaped core piece 10p be the dust core 1 of the embodiment. Of course, the I-shaped core piece 10i may be the dust core 1 of the embodiment.

  A coil component 1C of the third embodiment shown in FIG. 5 includes four I-shaped core pieces 10i to 10i as the magnetic core 10C. The magnetic core 10C is an O-shaped magnetic core that constitutes a frame-like closed magnetic path by combining these four core pieces 10i to 10i (the left diagram in FIG. 5). Here, a gap G is formed between the two core pieces 10i, 10i arranged in parallel in the left-right direction in FIG. 5 and another core piece 10i that connects the ends of the two core pieces 10i, 10i. An example is shown in which coils C and C are respectively disposed on the two core pieces 10i and 10i arranged in parallel. As in the coil component 1B of the second embodiment, only one of the core pieces 10i can include the coil C. In this example, it is preferable that the I-shaped core piece 10 i in which the coil C is not disposed is the dust core 1 of the embodiment. Of course, all the I-shaped core pieces 10i may be used as the dust core 1 of the embodiment.

  The shapes of the magnetic cores 10A to 10C and the core pieces 10i, 10f, and 10p shown in FIGS. 3 to 5 are examples, and can be appropriately changed to known shapes. For example, the shape etc. which have the curved surface which rounded the corner | angular part are mentioned. In addition, it is not a simple shape as shown in FIG. 3 to FIG. 5, but an outer shape with irregularities such as a shape having one or a plurality of steps, a shape having one or a plurality of flange portions at the end, and the like. It can be an irregular solid having The number of core pieces provided in the coil component can be appropriately changed, and FIGS. 3 to 5 are examples.

  As for the winding wire constituting the coil C, a covered wire having an insulating layer on the outer periphery of the conductor can be mentioned. Examples of the conductor include a wire made of a conductive material such as copper, copper alloy, aluminum, and aluminum alloy. Examples of the wire include a round wire having a circular cross section and a rectangular wire having a rectangular cross section. Examples of the constituent material of the insulating layer include enamel, tetrafluoroethylene-hexafluoropropylene copolymer (FEP) resin, polytetrafluoroethylene (PTFE) resin, and silicone rubber. Known windings can be used. The number of coils C provided in the coil component can be changed as appropriate, and FIGS. 3 to 5 are merely examples.

  The gap G can be appropriately provided so as to obtain desired magnetic characteristics. For example, it can be set as the form which is not provided with the gap G. The gap G can be an air gap in addition to a form using a gap material made of a nonmagnetic material.

[Production method of dust core]
The powder magnetic core 1 of the embodiment can be manufactured by a manufacturing method that includes, for example, the following preparation process and a molding process, and does not perform heat treatment after the molding process (FIG. 1).

-Preparation process In a preparation process, the bare iron powder 200 and the lubricant 300 are prepared. The bare iron powder 200 is a powder having an average particle size of 40 μm or more and 100 μm or less, and a ratio of iron particles having a particle size of 200 μm or more is 10% by mass or less. The lubricant 300 is a powder having an average particle diameter of 1 μm or more and 50 μm or less and a melting point of 120 ° C. or more (for example, metal stearate). When the powder magnetic core 1 including the coated iron powder 10 is manufactured, the coated iron powder 100 having an average particle diameter of 150 μm or more and 400 μm or less and a ratio of powder particles having a particle diameter of 75 μm or less is 10% by mass or less. prepare.

  In the manufacturing method described above, since heat treatment is not performed after molding, the constituent components of the obtained molded body (dust core 1) substantially maintain the constituent components of the raw material powder P as described above. In addition, although the raw material powder P is slightly deformed by molding, the size and the mixing ratio of the powder particles constituting the powder magnetic core 1 depend on the size and the mixing ratio of the powder particles included in the raw material powder P and are generally maintained. Tend to. Therefore, detailed description of the component, size, blending ratio, etc. of the raw material powder P is omitted. The matters described regarding the coated iron powder 10, the lubricant 30, and the bare iron powder 20 included in the dust core 1 can be applied to the coated iron powder 100, the lubricant 300, and the bare iron powder 200 included in the raw material powder P, respectively. Other matters are described below.

  The pure iron powder used for the bare iron powder 200 and the coated iron powder 100 can be produced by a known method such as an atomizing method such as a gas atomizing method or a water atomizing method. For forming the insulating coating 140 of the coated iron powder 100, for example, chemical conversion treatment such as phosphate chemical conversion treatment, spraying of a solvent, sol-gel treatment using a precursor, or the like can be used. When forming a coating of a silicone organic compound, wet coating using an organic solvent, direct coating using a mixer, or the like can be used. As the coated iron powder 100, commercially available coated iron powder can be used. The size of the bare iron powder 200 and the size of the coated iron powder 100 are adjusted by pulverizing the pure iron powder, or the bare iron powder 200 and the coated iron powder 100 are classified by a sieving method or the like. You can adjust it.

  About the bare iron powder 200 and the covering iron powder 100 in the raw material powder P, the size and the mass ratio of the specific particle size can be measured by using a commercially available particle size measuring device. As a simple measurement, the mass ratio of the specific particle size is classified using a sieve and the mass of the selected powder particles having the specific particle size is measured.

  For mixing the raw material powder P, an appropriate mixer such as a V-type mixer or a double cone mixer can be used. This mixing is preferably performed to such an extent that the insulating coating 140 of the coated iron powder 100 is not damaged.

-Molding process In the molding process, the raw material powder P prepared in the preparation process is filled in a mold and compressed by pressure to produce a dust core 1.

  The mold typically includes a die having a die having a through hole and a pair of punches for compressing and compressing the raw material powder P. Specifically, a bottomed cylindrical shape is formed by a part of the inner peripheral surface of the die and one surface of one punch (the surface facing the other punch), and the raw material powder P is placed in the space in the bottomed cylindrical shape. Fill and press and compress with both punches to form the desired shape. The molded body extracted from the die is the dust core 1. When manufacturing a cylindrical or annular powder magnetic core (such as the core piece 10f in FIG. 3) having a through hole, the through hole of the molded body is formed by being inserted into the through hole of the die as a mold. A thing provided with a rod should be used. When molding a shaped body having a step, a pair of punches each divided into a plurality of punches can be used. A known configuration can be used as the configuration of the mold.

  The molding pressure can be, for example, less than 1200 MPa, further 1000 MPa or less, and further 800 MPa or less. Since the raw material powder P is excellent in compressive deformability as described above, densification and densification can be achieved by setting the molding pressure to 500 MPa or more, further 550 MPa or more, and further 600 MPa or more.

Molding can be performed in a state in which the mold is heated to some extent (the processing heat resulting from continuous molding may be sufficient). In this case, the moldability of the coated iron powder 100 or the bare iron powder 200 can be improved, or the lubricant 300 can be softened to some extent to facilitate flow, thereby improving the compression moldability. Therefore, the molding pressure can be further reduced. When the mold is heated, the mold temperature is, for example, (T _M / 2) ° C. or more and less than T _M ° C. when the melting point of the lubricant is T _M. For example, the melting point _{T M} is if 120 ° C. to 200 DEG ° C., include about 60 ° C. to 100 ° C.. If it is this range, it is excellent in a moldability, and it can suppress that the lubricant 300 melt | dissolves and liquefies, and the lubricant 30 of the powder magnetic core 1 can be interposed between the bare iron powder 20 in a powder form. .

  The mold can be held at a lower temperature (for example, room temperature or lower) using a water cooling device or the like. In this case, it is easy to obtain a molded body having excellent dimensional accuracy.

  The atmosphere at the time of molding includes, for example, an air atmosphere. Bare iron powder 200 is in contact with lubricant 300, so that oxidation of the iron component can be considerably prevented even in an atmosphere containing oxygen. The atmosphere is excellent in workability because it is easy to control.

  In the mold, a release coating can be applied to a region in contact with the raw material powder P and the molded body. The release coating is selected from, for example, DLC, TiN, TiC, CrN, and Ti-XN (where X is at least one element selected from C, Al, Cr, Mo, and W). There is at least one kind. For forming the release coating, a known physical vapor deposition method, chemical vapor deposition method, arc method or the like can be used, and in particular, a sputtering method can be suitably used. By performing the release coating, it is possible to further improve the demoldability.

[Use]
The dust core 1 of the embodiment can be used for a magnetic core of various coil components (for example, a reactor, a transformer, a motor, a choke coil, an antenna, a fuel injector, an ignition coil, etc.). The coil components 1A, 1B, and 1C of the embodiment can be used for a reactor, a transformer, a motor, a choke coil, an antenna, a fuel injector, an ignition coil, and the like.

[Test Example 1]
A dust core formed by compression-molding a mixed powder containing bare iron powder was produced, and the permeability and core loss of each obtained dust core were examined.

・ Sample No. 1-1 to 1-6
As a raw material powder of each sample, a mixed powder containing bare iron powder and a lubricant is used. Sample No. Samples other than 1-4 further contain coated iron powder as a raw material powder. Bare iron powder is a collection of iron particles composed of pure iron (Fe is 99% by mass or more and the balance is inevitable impurities). This bare iron powder was classified. The average particle diameter (μm) of the bare iron powder and the ratio (mass%) of particles in which the iron particles constituting the bare iron powder were 200 μm or more were measured. The ratio of the iron particles having a specific particle diameter indicates the ratio of each particle size when the total weight of the iron particles before classification is 100% by mass. The particle size distribution was measured using a commercially available laser diffraction / scattering particle size / particle size distribution measuring apparatus. The average particle size of the bare iron powder is measured with the above particle size distribution measuring apparatus, and the particle size at which the integrated weight (mass) is 50%, that is, 50% particle size (mass). As a result, the average particle size of the bare iron powder was 73 μm, and the ratio of the particles having iron particles of 200 μm or more was 1% by mass or less.

  The coated iron powder is a coating provided with an insulating coating (average thickness of about 20 nm to 100 nm) made of iron phosphate around iron particles made of pure iron (99% by mass or more of Fe, the remainder being inevitable impurities). A collection of iron particles. The coated iron powder was classified in the same manner as the bare iron powder described above, and the average particle diameter (μm) and the ratio (mass%) of particles having a particle diameter of 75 μm or less constituting the coated iron powder were measured. As a result, the average particle size of the coated iron powder was 240 μm, and the proportion of particles having a particle size of 75 μm or less was 7% by mass or less.

  The blending ratio of the bare iron powder and the coated iron powder is the content shown in Table 1 for the bare iron powder and the coated iron powder when the total amount of both powders (the total amount of the soft magnetic powder) is 100% by mass. .

  As the lubricant, powder of zinc stearate (melting point: 120 ° C. to 125 ° C.) was used. The content of zinc stearate was shown in Table 1 when the raw material powder (the total of the soft magnetic powder and the lubricant) was 100% by mass. Sample No. Samples other than 4 contained a powder of stearamide (melting point: about 100 ° C.) in addition to zinc stearate. The content of stearamide was shown in Table 1 when the raw material powder (the total of the soft magnetic powder and the lubricant) was 100% by mass. The average particle size of each lubricant was measured with a particle size distribution measuring device in the same manner as the bare iron powder described above. As a result, zinc stearate (commercial product) had an average particle size of 30 μm, and stearic acid amide (commercial product) had an average particle size of 45 μm.

The mold was filled with the mixed powder and pressurized and compressed to form a prismatic shaped body (see FIG. 2). Sample No. 1-1 to 1-4 were compressed along the height H direction so as to form a molded body having a length L of 30 mm, a width W of 3 mm, and a height H of 5 mm. Sample No. 1-5 compressed along the length L direction so that it might become a molded object of length L: 30mm, width W: 3mm, and height H: 5mm. Sample No. 1-6 compressed along the height H direction so that it might become a molded object of length L: 30mm, width W: 7.3mm, and height H: 5mm. The molding conditions were an atmospheric atmosphere, a molding pressure was selected from 686 MPa to 882 MPa ( ⁷ ton / cm ² to 9 ton / cm ² ), and a mold temperature was selected from 50 ° C. to 60 ° C. The obtained molded body was not subjected to heat treatment.

・ Sample No. 1-11
This is a sample using a mixed powder containing coated iron powder and a lubricant and not containing bare iron powder as raw material powder. That is, the total soft magnetic powder is the coated iron powder. The lubricant contains 0.3% by mass of stearamide and does not contain a high melting point lubricant. For other conditions, sample no. It is the same as 1-1.

・ Sample No. 1-12, 1-13
It is a sample using a mixed powder containing bare iron powder, coated iron powder and a lubricant as raw material powder. The blending ratio of the bare iron powder and the coated iron powder was the content shown in Table 1 when the total amount of both powders (the total amount of the soft magnetic powder) was 100% by mass. The lubricant contains 0.3% by mass of stearamide and does not contain a high melting point lubricant. For other conditions, sample no. It is the same as 1-1.

  The prepared sample No. For the molded bodies (dust cores) 1-1 to 1-6 and 1-11 to 1-13, the amount of lubricant was measured as follows. Each of the compacts is pulverized by a pulverizer (atmosphere), and 1 g of the powder having the same size as that of the raw material is weighed. A liquid mixture obtained by adding acetone to 1 g of the weighed powder is obtained. From this mixed solution, a lubricant (here, zinc stearate, stearamide) is dissolved and recovered by ultrasonic extraction. The recovered lubricant was qualitatively and quantitatively analyzed by gas chromatography. That is, the lubricant amount x (g) per 1 g of the pulverized powder is obtained, and the mass ratio of the lubricant to the mass of the molded body ((xx) / y) × using the mass y (g) of the molded body. 100 was determined. This amount of lubricant is a ratio which makes a molded object 100 mass%. As a result, each of the molded bodies contained a lubricant (zinc stearate or stearamide) having a content equivalent to that of the raw material powder.

  Sample No. Four compacts (powder magnetic cores) 1-1 to 1-6 and 1-11 to 1-13 are combined into a square frame (a shape equivalent to the frame-shaped core piece 10f shown in FIG. 3). An I-shaped core piece is placed inside the frame-shaped member, and the same winding is wound around the I-shaped core piece to produce a measurement member (coil component) (see coil component 1A in FIG. 3). ). Using the produced measurement member and AC-BH curve tracer, when the excitation magnetic flux density Bm is 1T and the measurement frequency is 1 kHz, the AC permeability of the sample is obtained from the slope of the AC-BH curve, and the vortex of the sample Current loss (eddy loss) and hysteresis loss (his loss) were determined. The core loss, which is the sum of eddy loss and hiss loss, is defined as core loss. The measurement results are also shown in Table 1.

  “Compression direction / magnetic flux direction” in Table 1 indicates the relationship between the compression direction and the magnetic flux direction. When the compression direction and the magnetic flux direction are orthogonal to each other, it is “orthogonal”. Are in the same direction, it is “parallel”. “Width / particle diameter” in Table 1 is a value obtained by dividing the width W (see FIG. 2) of the powder magnetic core by the average particle diameter of the bare iron powder. The average particle diameter of the bare iron powder is determined by measuring the short diameter and the long diameter of the iron particles constituting the bare iron powder present in the transverse section or the longitudinal section of the dust core, and taking the equivalent circle diameter of the area of the iron particles.

  As shown in Table 1, Sample No. containing a relatively large amount of bare iron powder. In each of the dust cores 1-1 to 1-6, the magnetic permeability is 350 or more, the core loss is 300 W / kg or less, and all soft magnetic powders are composed of coated iron powder. It was found to be equivalent to 1-11. That is, even if bare iron powder without an insulating coating is used instead of coated iron powder as a soft magnetic powder, a dust core having necessary magnetic properties by containing a high melting point lubricant as a lubricant I understood that I can do it. This is because the high melting point lubricant is contained, and even when the powder core is manufactured or used at high temperatures, the lubricant does not dissolve and liquefy, and is interposed between the bare iron powders. This is probably because the iron powder is insulated. For example, Sample No. containing a high melting point lubricant. Sample No. 1-2 which does not contain a high melting point lubricant. Compared with 1-13, the magnetic permeability is high and the core loss is also reduced. Sample No. In No. 1-13, since no lubricant is interposed as an insulating material between the bare iron powders, the iron particles constituting the bare iron powders are combined to produce a conductive portion, which is thought to increase the eddy current. .

  In particular, Sample No. in which the compression direction of the dust core and the direction of magnetic flux accompanying excitation of the coil are orthogonal. It can be seen that 1-1 to 1-4 and 1-6 tend to have high magnetic permeability. This is presumably because the major axis direction of the iron particles constituting the bare iron powder has few grain boundaries between the iron particles, but the major axis direction is parallel to the magnetic flux direction, so that the magnetic flux easily passes.

[Test Example 2]
The permeability and core loss due to the difference in the content of impurities contained in the bare iron powder were investigated.

・ Sample No. 2-1 to 2-4
Bare iron powder containing impurities shown in Table 2 was prepared. These impurities are O, P, Cr, Mn, Ni, and Cu. The blending ratio of the bare iron powder and the coated iron powder is as follows: when the total amount of both powders (the total amount of the soft magnetic powder) is 100 mass%, the naked iron powder is 50 mass% and the coated iron powder is 50 mass%. did. The content of the lubricant was set to zinc stearate: 0.2% by mass and stearamide: 0.1% by mass when the raw material powder (total of soft magnetic powder and lubricant) was 100% by mass. . Other conditions (powder particle size, coated iron powder insulation coating thickness, molding conditions, etc.) are as follows. It was the same as 1-1.

  Sample No. Samples Nos. 2-1 to 2-4 (powder magnetic cores) of Sample No. In combination with the same shape as 1-1, a measurement member (coil part) was prepared. The magnetic permeability and core loss were measured as in 1-1. The results are also shown in Table 2.

  As shown in Table 2, it can be seen that the dust core with fewer bare iron powder impurities has higher magnetic permeability and smaller core loss. In particular, Sample No. in which the O content is 0.10% by mass or less and the total content of P, Cr, Mn, Ni, Cu is 0.20% by mass or less. As for 2-3 and 2-4, it turns out that magnetic permeability is 450 or more and core loss is 215 W / kg or less, and it is very high magnetic permeability and low core loss. This is presumably because the bare iron powder has a small impurity content, so that the bare iron powder is easily deformed, the filling property is improved, and the hysteresis loss is reduced.

DESCRIPTION OF SYMBOLS 1 Powder magnetic core 1L Long piece 10 Coated iron powder 12 Iron particle 14 Insulation coating 20 Bare iron powder 30 Lubricant P Raw material powder 100 Coated iron powder 120 Iron particle 140 Insulation coating 200 Bare iron powder 300 Lubricant 1A, 1B, 1C Coil parts 10A, 10B, 10C Magnetic core 10i I-shaped core piece 10f Frame-shaped core piece 10p U-shaped core piece 10h Through hole G gap C Coil

Claims (8)

A dust core having soft magnetic powder,
Bare iron powder without insulation coating,
A powdery lubricant having a melting point of 120 ° C. or higher,
The content of the bare iron powder in the soft magnetic powder is more than 45% by mass,
The powder magnetic core whose content of the said lubricant in the said powder magnetic core is 0.05 mass% or more and 0.5 mass% or less. The dust core has a long piece,
In the transverse section or longitudinal section of the long piece, the bare iron powder is a flat shape having a minor axis and a major axis, and when the minor axis direction is a compression direction,
The said long piece has the narrow part whose length of the direction orthogonal to both the longitudinal direction and the said compression direction has a narrow part which is 80 times or less of the average particle diameter of the said bare iron powder. core.   The powder magnetic core according to claim 1, wherein the lubricant contains a stearic acid metal salt. The bare iron powder is
The average particle size is 40 μm or more and 100 μm or less,
The dust core according to any one of claims 1 to 3, wherein a ratio of particles having a particle diameter of 200 µm or more among the constituent particles of the bare iron powder is 10 mass% or less. Furthermore, it comprises a coated iron powder with an insulating coating,
The dust core according to any one of claims 1 to 4, wherein a content of the coated iron powder in the soft magnetic powder is 30% by mass or more and less than 55% by mass.   6. The bare iron powder has an oxygen content of less than 0.1% by mass and a total content of phosphorus, chromium, manganese, nickel, and copper of less than 0.2% by mass. The dust core according to any one of the above. A coil component comprising a coil and a magnetic core,
A coil component comprising the dust core according to any one of claims 1 to 6 in at least a part of the magnetic core. The dust core has a long piece,
In the cross section of the long piece, the bare iron powder is a flat shape having a short diameter and a long diameter,
The coil component according to claim 7, wherein the long piece is disposed such that a longitudinal direction thereof is a direction along a magnetic flux direction accompanying excitation of the coil.

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