JP7334835B2 - Soft magnetic compositions, cores, and coil-type electronic components - Google Patents

Description

The present invention relates to soft magnetic compositions, cores, and coil-type electronic components.

A metal magnetic material has the advantage of obtaining a high saturation magnetic flux density compared to ferrite. Fe--Si--Al based alloys, Fe--Si--Cr based alloys, and the like are known as such metal magnetic bodies.

Patent Document 1 proposes a coil-type electronic component using a magnetic material containing chromium, aluminum, and silicon and having improved magnetic permeability.

Examples of coil-type electronic components include inductors, EMC coils, and transformers.

In recent years, there has been a demand for further reduction in core loss of magnetic materials used in these coil-type electronic components.

JP 2011-249774 A

An object of the present invention is to provide a soft magnetic composition, a core and a coil-type electronic component that can achieve a low core loss.

In order to achieve the above object, the soft magnetic composition according to the present invention is
Having a plurality of soft magnetic alloy particles,
The soft magnetic alloy particles contain an element M and iron,
The element M has a stronger ionization tendency than silicon,
When the maximum value of the mass ratio of silicon to the element M in the region between the soft magnetic alloy grains is (Si/M) _MAX ,
The (Si/M) _MAX satisfies 1≦(Si/M) _MAX ≦10.

In the soft magnetic composition according to the present invention, the soft magnetic alloy particles contain the element M, and (Si / M) _MAX satisfies 1 ≤ (Si / M) _MAX ≤ 10, so that the core loss can be reduced. .

Preferably, an amorphous layer is present at the (Si/M) _MAX location.

The presence of the amorphous layer at the (Si/M) _MAX location can reduce the core loss.

Preferably, the element M is continuously present in a predetermined range including the (Si/M) _MAX point,
The predetermined range is a range of 50% or more of the distance between the adjacent soft magnetic alloy grains.

Core loss can be reduced by the continuous presence of the element M in a predetermined range including the (Si/M) _MAX point.

Further, a core according to the present invention is composed of any one of the soft magnetic compositions described above.

Preferably, a coating layer is formed on at least part of the surface of the core.

A coil electronic component according to the present invention has the above core. Examples of coil-type electronic components include, but are not limited to, electronic components such as inductors, EMC coils, and transformers. In particular, it is suitable for miniaturized coil-type electronic components that can be surface-mounted on a circuit board.

FIG. 1 is a core according to one embodiment of the present invention. 2 is an enlarged cross-sectional view of the core shown in FIG. 1. FIG. FIG. 3 is an enlarged cross-sectional view of the main part of the core showing observation points when EDS analysis is performed. FIG. 4 is a selected area diffraction pattern of a crystal lattice. FIG. 5 is a selected area diffraction pattern of an amorphous layer. FIG. 6 shows the results of EDS analysis of Example 4 according to the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on embodiments shown in the drawings.

The core of the coil-shaped electronic component according to the present embodiment is a core (powder core) molded by powder compaction. Powder compacting is a method of obtaining a compact by filling a mold of a pressing machine with a material containing soft magnetic alloy powder and applying pressure under a predetermined pressure for compression molding.

As the shape of the core (magnetic core) according to the present embodiment, in addition to the toroidal type shown in FIG. A mold, a cup type, etc. can be exemplified. A desired coil-type electronic component can be obtained by winding a single or multiple wires around this core.

A core for a coil-type electronic component according to this embodiment is composed of a soft magnetic composition.

The soft magnetic composition according to this embodiment has a plurality of soft magnetic alloy particles 21 and 22 as shown in FIG. Further, in the present embodiment, the regions from one soft magnetic alloy grain 21 to the other soft magnetic alloy grain 22 are defined as regions 30 and 31 between the soft magnetic alloy grains.

The soft magnetic alloy particles 21 and 22 according to this embodiment contain the element M and iron (Fe). Although not particularly limited, the soft magnetic alloy particles 21 and 22 according to this embodiment may additionally contain silicon (Si), carbon (C), or zinc (Zn).

The element M has a stronger ionization tendency than silicon (Si). Also, the element M tends to form oxide films on the surfaces of the soft magnetic alloy particles 21 and 22 . Examples of the element M include chromium (Cr), aluminum (Al), magnesium (Mg), titanium (Ti), zirconium (Zr), manganese (Mn), and zinc (Zn). From the viewpoint of forming a uniform oxide film, chromium (Cr) or aluminum (Al) is preferable. Also, the element M is not limited to one type, and a plurality of elements may be used.

For example, when the element M is chromium (Cr), the soft magnetic alloy particles 21 and 22 according to the present embodiment contain 1 to 9% by mass of chromium (Cr) in terms of Cr, and 0 to 9 mass% of silicon (Si) in terms of Si. It contains 9% by mass, and the balance is composed of iron (Fe).

Further, in the soft magnetic alloy particles 21 and 22 according to the present embodiment, for example, when the element M is aluminum (Al), aluminum (Al) is 1 to 9% by mass in terms of Al, and silicon (Si) is in terms of Si. It contains 0 to 14% by mass, and the balance is composed of iron (Fe).

The content of chromium (Cr) in the soft magnetic alloy particles 21 and 22 according to this embodiment is preferably 1 to 9% by mass in terms of Cr. This makes it easier to keep (Si/M) _MAX within a predetermined range. From the above point of view, the content of chromium (Cr) in the soft magnetic alloy particles 21 and 22 is more preferably 3 to 7% by mass in terms of Cr.

The content of aluminum (Al) in the soft magnetic alloy particles 21 and 22 according to the present embodiment is preferably 1 to 9% by mass in terms of Al. This makes it easier to keep (Si/M) _MAX within a predetermined range. From the above point of view, the content of aluminum (Al) in the soft magnetic alloy particles 21 and 22 is more preferably 3 to 7% by mass in terms of Al.

The content of silicon (Si) in the soft magnetic alloy particles 21 and 22 according to the present embodiment is preferably 0 to 9% by mass, more preferably 2 to 8.5% by mass in terms of Si.

The balance of the soft magnetic alloy particles 21 and 22 according to the present embodiment may be composed only of iron (Fe).

The soft magnetic composition according to this embodiment may contain components such as carbon (C) and zinc (Zn) in addition to the constituent components of the soft magnetic alloy particles 21 and 22 .

The content of carbon (C) in the soft magnetic composition according to the present embodiment is preferably less than 0.05% by mass, more preferably 0.01 to 0.04% by mass.

The content of zinc (Zn) in the soft magnetic composition according to this embodiment is preferably 0.004 to 0.2% by mass, more preferably 0.01 to 0.2% by mass.

The soft magnetic composition according to this embodiment may contain unavoidable impurities in addition to the above components.

The average crystal grain size of the soft magnetic alloy grains 21 and 22 according to this embodiment is preferably 4 to 60 μm. By setting the average crystal grain size within the above range, the thickness of the core can be easily reduced.

Below, "the mass of silicon (Si), element M or iron (Fe) relative to the total mass of silicon (Si), element M and iron (Fe) in regions 30 and 31 between soft magnetic alloy particles 21 and 22 "ratio" is defined as "mass ratio of three elements".

In addition, below, "oxygen (O), silicon ( Si), the element M, or iron (Fe) shall be referred to as the “mass ratio of the four elements”.

In this embodiment, the amorphous layer exists at (Si/M) _MAX . This makes it possible to obtain a soft magnetic composition capable of achieving low core loss.

From the above point of view, the regions 30, 31 between the soft magnetic alloy grains 21, 22 preferably contain an amorphous layer of Si--M oxide or Si--M composite oxide.

The Si—M oxide is an oxide mainly composed of silicon (Si), element M and oxygen (O). Further, the Si—M composite oxide is an oxide containing silicon (Si), element M and oxygen (O), and further containing elements other than these three components (Si, M and O).

Elements other than the three components (Si, elements M and O) contained in the Si—M composite oxide include vanadium (V), nickel (Ni) and copper (Cu).

The Si—M oxide contains elements other than silicon (Si), the element M and oxygen (O) in a total amount of 0.5% with respect to 100% by mass of the total mass of silicon (Si), the element M and oxygen (O). It contains less than 1% by mass.

Elements other than the three components (Si, elements M and O) contained in the Si—M oxide include vanadium (V), nickel (Ni) and copper (Cu).

In this embodiment, the regions 30 and 31 between the soft magnetic alloy grains 21 and 22 are considered to contain silicon (Si) not derived from the elements contained in the soft magnetic alloy grains 21 and 22 . Silicon (Si) not derived from elements contained in the soft magnetic alloy particles 21 and 22 is not particularly limited, but is considered to be derived from, for example, silicon (Si) contained in the silicone resin used as the binder.

In this embodiment, when the maximum value of the mass ratio of silicon (Si) to the element M in the regions 30 and 31 between the soft magnetic alloy grains 21 and 22 is (Si/M) _MAX , (Si/M) _MAX satisfies 1≦(Si/M) _MAX ≦10. This makes it possible to obtain a soft magnetic composition capable of achieving low core loss.

The Si—M oxide or Si—M composite oxide, which is an amorphous layer present in the regions 30 and 31 between the soft magnetic alloy grains 21 and 22, is the region between the soft magnetic alloy grains 21 and 22 due to its randomness. This tends to contribute to the reduction of eddy current loss crossing 30 and 31 . Therefore, when (Si/M) _MAX is within a predetermined range and the Si—M oxide or Si—M composite oxide, which is an amorphous layer, is present at the location of (Si/M) _MAX , the eddy current Loss is reduced, and core loss tends to be lower.

In this embodiment, the method for calculating (Si/M) _MAX is not particularly limited, but a specific method will be shown below.

First, the soft magnetic alloy grains 21 and 22 and the regions 30 and 31 between the soft magnetic alloy grains 21 and 22 are distinguished by observing the cross section of the core using a scanning transmission electron microscope (STEM). Specifically, a cross section of the core is photographed by STEM to obtain a bright field (BF) image. In the bright-field image, regions existing between the soft magnetic alloy grains 21 and 22 and having a contrast different from that of the soft magnetic alloy grains 21 and 22 are defined as the soft magnetic alloy grains 21 and 22 are defined as regions 30 and 31 between . The determination as to whether or not there is a different contrast may be made visually, or may be determined using software or the like that performs image processing.

Regarding the composition of the regions 30 and 31 between the soft magnetic alloy grains 21 and 22, as shown in FIG. EDS analysis is performed. FIG. 6 shows the results of the EDS analysis of this embodiment. The first vertical axis in FIG. 6 indicates the mass ratio of three elements, the second vertical axis indicates the Si/M mass ratio, and the horizontal axis indicates the distance from the starting point. Here, the “starting point” is an arbitrary point within the soft magnetic alloy grains 21 .

In FIG. 6, the mass ratio of the three elements of silicon (Si) is indicated by a solid line, the mass ratio of the three elements of chromium (Cr) is indicated by a dotted line, and the mass ratio of the three elements of iron (Fe) is indicated by a dashed line. , and the Si/M mass ratio is indicated by a two-dot chain line.

In FIG. 6, the mass ratio of the three elements of iron (Fe) is almost constant around 95 wt % in the interval from 0 to 0.35 μm from the starting point. This section is one soft magnetic alloy grain 21 .

In FIG. 6, the mass ratio of the three elements of iron (Fe) decreases in the interval of 0.35 μm to 0.66 μm from the starting point, becomes almost constant around 0 wt %, and then increases. This section is a region 31 between the soft magnetic alloy grains 21,22.

Then, in FIG. 6, the mass ratio of the three elements of iron (Fe) is almost constant in the vicinity of 95 to 98 wt % again in the interval of 0.66 μm to 1.0 μm from the starting point. This section is the other soft magnetic alloy grain 22 .

Then, (Si/M) _MAX in the region 31 between the soft magnetic alloy grains 21 and 22 is determined based on the obtained numerical value.

Although not particularly limited, in the present embodiment, the four-element mass ratio of oxygen (O) at the same position is 8 to 65% by mass, the four-element mass ratio of silicon (Si) is 8 to 65% by mass, and When the mass ratio of the four elements of the element M is 8 to 65% by mass, the position is determined to be Si--M oxide or Si--M composite oxide.

In addition, the mapping image of oxygen (O), the mapping image of silicon (Si), and the mapping image of element M are compared to determine if oxygen (O), silicon (Si), and element M are present at the same position. For example, it can be determined that the position is Si--M oxide or Si--M composite oxide.

In this embodiment, the method for determining whether an amorphous layer exists in the regions 30 and 31 between the soft magnetic alloy grains 21 and 22 is not particularly limited. may be determined by analyzing the selected area diffraction pattern (SADP) of the reciprocal lattice space. In the selected area diffraction pattern, when the crystal structure is regular, diffraction spots reflecting the crystal structure are observed as shown in FIG. On the other hand, in the case of an amorphous layer that does not have a regular crystal structure, as shown in FIG. 5, concentric circles centered on the central spot are observed. Also, in the case of the amorphous layer, no clear diffraction spots other than the central spot are observed.

In the present embodiment, as shown in FIG. 6, it is preferable that the element M exists continuously in a predetermined range including the (Si/M) _MAX point. This makes it possible to obtain a soft magnetic composition capable of achieving low core loss.

From the above point of view, it is preferable that silicon (Si) is continuous in a predetermined range including the (Si/M) _MAX point.

Here, the predetermined range is preferably a range of 50% or more of the distance between the adjacent soft magnetic alloy grains 21,22.

Note that the element M is continuous in a predetermined range means that the mass ratio of the three elements of the element M is preferably 8% by mass or more, more preferably 10% by mass or more in the predetermined range. say.

Further, silicon (Si) is continuous in a predetermined range means that the mass ratio of the three elements of silicon (Si) is preferably 5% by mass or more, more preferably 8% by mass or more in the predetermined range. It means that

The predetermined range of length is preferably 0.01 to 0.4 μm, more preferably 0.01 to 0.1 μm.

A coating layer may be formed on at least part of the surface of the core according to the present embodiment. This can further reduce the core loss of the core.

The material of the coating layer is not particularly limited, and examples thereof include glass compositions, SiO ₂ , B ₂ O ₃ , ZrO ₂ and resins. In addition, the coating layer may be composed of a plurality of materials, or may have a laminated structure composed of a plurality of layers.

The coating layer is formed, for example, on at least part of the surface of the core. The ratio of the coating layer to the surface area of the core (coverage) is preferably 50 to 100%. The higher the coverage, the greater the role of the protective layer for preventing chipping of the core. From the above viewpoint, the coverage is more preferably 90 to 100%.

Next, an example of the manufacturing method of the core according to this embodiment will be described.
The core of the present embodiment can be produced by firing a compact containing soft magnetic alloy powder and a binder (binder resin). A preferred method for manufacturing the core of this embodiment will be described in detail below.

Preferably, the manufacturing method according to the present embodiment is
A step of mixing a soft magnetic alloy powder and a binder to obtain a mixture;
drying the mixture to form a granulated powder;
a step of molding the mixture or granulated powder into the shape of the core to be produced to obtain a molded body;
and obtaining a core by heating the obtained compact.

Also, a coating layer may be formed on the core.

The core obtained by the manufacturing method according to the present embodiment is composed of the soft magnetic composition according to the present embodiment.

As the soft magnetic alloy powder, alloy particles containing 1 to 9% by mass of chromium (Cr) in terms of Cr, 0 to 9% by mass of silicon (Si) in terms of Si, and the balance being iron (Fe). Those containing can be used.

The shape of the soft magnetic alloy powder is not particularly limited, but from the viewpoint of maintaining the inductance up to a high magnetic field region, it is preferably spherical or ellipsoidal. Among these, an ellipsoidal shape is desirable from the viewpoint of increasing the strength of the core.

Also, the average particle size of the soft magnetic alloy powder is preferably 3 to 80 μm. When the average particle size of the soft magnetic alloy powder is within the above range, the magnetic permeability is improved, eddy current loss is less likely to occur, and abnormal loss tends to be reduced. Moreover, handling becomes easy. From the above viewpoint, it is more preferable that the average particle size of the soft magnetic alloy powder is 5 to 20 μm.

The soft magnetic alloy powder can be obtained by a method similar to a known soft magnetic alloy powder preparation method. At this time, the gas atomization method, the water atomization method, the rotating disk method, or the like can be used for the preparation. Among these methods, the water atomization method is preferred because it facilitates production of soft magnetic alloy powder having desired magnetic properties.

As the binder, one containing a silicone resin is used. By using the silicone resin as the binder, the regions 30, 31 between the soft magnetic alloy particles 21, 22 effectively contain silicon (Si) not derived from the elements contained in the soft magnetic alloy particles 21, 22. be As a result, amorphous layers are easily formed in the regions 30 and 31 between the soft magnetic alloy grains 21 and 22 .

It should be noted that other binders may be included as long as the effects of the present invention are not impaired. Other binders include, for example, various organic polymer resins, phenolic resins, epoxy resins and water glass.

As the binder, silicone resin can be used alone or in combination with other binders. Since it is preferable to limit the content of carbon (C) in the soft magnetic composition to less than 0.05% by mass, it is preferable to mainly use a silicone resin as the binder. By setting the content of carbon (C) in the soft magnetic composition within the above range, the strength of the resulting core can be improved.

The amount of the binder added varies depending on the required properties of the core, but preferably 0.2 to 10% by mass can be added with respect to 100% by mass of the soft magnetic alloy powder. Amorphous layers are easily formed in the regions 30 and 31 between the soft magnetic alloy grains 21 and 22 when the amount of the binder added is within the above range. From the above point of view, the amount of the binder added is more preferably 0.5 to 6% by mass with respect to 100% by mass of the soft magnetic alloy powder.

The amount of the silicone resin to be added is preferably 0.2 to 8% by mass with respect to 100% by mass of the soft magnetic alloy powder. When the amount of the silicone resin added is within the above range, an amorphous layer is easily formed in the regions 30 and 31 between the soft magnetic alloy particles 21 and 22 . From the above point of view, the amount of the silicone resin to be added is more preferably 0.5 to 5% by mass with respect to 100% by mass of the soft magnetic alloy powder.

In addition, an organic solvent may be added to the mixture or granulated powder as necessary within a range that does not impair the effects of the present invention.

The organic solvent is not particularly limited as long as it can dissolve the binder, and examples thereof include various solvents such as toluene, isopropyl alcohol, acetone, methyl ethyl ketone, chloroform, and ethyl acetate.

In addition, various additives, lubricants, plasticizers, thixotropic agents, etc. may be added to the mixture or granulated powder, if necessary, as long as the effects of the present invention are not impaired.

Lubricants include, for example, aluminum stearate, barium stearate, magnesium stearate, calcium stearate, zinc stearate and strontium stearate. These are used individually by 1 type or in combination of 2 or more types. Among these, it is preferable to use zinc stearate as the lubricant from the viewpoint of so-called small springback.

When a lubricant is used, the amount added is preferably 0.1 to 0.9% by mass with respect to 100% by mass of the soft magnetic alloy powder.

In particular, when zinc stearate is used as a lubricant, the content of zinc (Zn) in the resulting soft magnetic composition is in the range of 0.004 to 0.2% by mass. Adjusting is preferred. This tends to lead to better core strength.

Although the method for obtaining the mixture is not particularly limited, it can be obtained by mixing a soft magnetic alloy powder, a binder and an organic solvent by a conventionally known method. Various additives may be added as necessary.

For mixing, for example, a mixer such as a pressure kneader, an atalitor, a vibration mill, a ball mill, or a V mixer, or a granulator such as a fluidized granulator or a tumbling granulator can be used.

The temperature and time for the mixing treatment are preferably room temperature and about 1 to 30 minutes.

The method for obtaining the granulated powder is not particularly limited, and it can be obtained by drying the mixture by a known method.

The drying temperature and time are preferably room temperature to about 200° C. for 1 to 60 minutes.

A lubricant can be added to the granulated powder as necessary. After adding the lubricant to the granulated powder, it is desirable to mix for 1 to 60 minutes.

The method for obtaining the molded body is not particularly limited. A molding die having a cavity of a desired shape is used by a known method, the cavity is filled with a mixture or granulated powder, and the molding temperature is set at a predetermined temperature. It is preferred to compression mold the mixture at a molding pressure of .

The molding conditions for compression molding are not particularly limited, and may be appropriately determined according to the shape and size of the soft magnetic alloy powder, the shape, size and density of the dust core, and the like. For example, the maximum pressure is normally about 100 to 1000 MPa, preferably about 400 to 800 MPa, and the maximum pressure is maintained for about 0.5 seconds to 1 minute.

In the manufacturing method according to this embodiment, since the binder contains the silicone resin, an amorphous layer is easily formed in the regions 30, 31 between the soft magnetic alloy particles 21, 22 forming the core.

The molding temperature is not particularly limited, but usually room temperature to about 200°C is preferable. This increases the density of the compact and improves the performance of the resulting core.

Next, the molded body obtained after molding is sintered to obtain a core (sintering step).

The holding temperature in the firing step is not particularly limited, but is usually preferably about 600 to 900°C. This makes it easier to keep (Si/M) _MAX within a predetermined range. From the above point of view, the holding temperature during firing is preferably 700 to 850°C.

The heating rate in the firing step is not particularly limited, but it is preferable to reach the holding temperature in a short period of time after the start of heating. By heating in such a short time, (Si/M) _MAX can be easily set within a predetermined range.

The above heating method in the firing step is not particularly limited, but for example, a thin, small-area container with good heat transfer is prepared, and a small number (1 to 10) of molded bodies are placed in this container, sufficiently separated. put it on Specifically, adjacent compacts are placed with a distance of 10 to 100 mm. Next, there is a method of directly putting the molded product together with the container into a furnace that has reached the holding temperature. In addition, there is also a method in which a heating body that has reached the holding temperature is sandwiched from above and below the molded body and placed in the furnace as it is.

The atmosphere of the firing step is not particularly limited, and may be performed in an oxygen-containing atmosphere. Here, the oxygen-containing atmosphere is not particularly limited, but includes an air atmosphere (usually containing 20.95% oxygen), or a mixed atmosphere with an inert gas such as argon or nitrogen. be done. Alternatively, it may be carried out under an inert gas such as argon or nitrogen.

The retention time of the firing step is not particularly limited, and is, for example, 10 minutes to 5 hours.

Next, on the surface of the obtained core, a coating layer before heat treatment comprising a glass composition, a binder resin and the like is formed as necessary.

After the heat treatment, a coating layer is formed on the surface of the core.

The core thus obtained can be used as a magnetic core.

(Si/M) _MAX according to the present embodiment is the composition of the soft magnetic alloy powder, the type or amount of binder added in the core manufacturing method, other additive components, the heating rate in the firing process, and the holding temperature. Alternatively, it can be controlled by the atmosphere or the like.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to such embodiments, and can of course be embodied in various modes within the scope of the gist of the present invention. .

For example, in the above-described embodiments, the core (powder core) is produced by compacting the mixture or the granulated powder, but the core is produced by sheet-forming and laminating the mixture. good too. In addition to dry molding, a molded body may be obtained by wet molding, extrusion molding, or the like.

In the above-described embodiments, a silicone resin is used as a binder in order to form a layer containing silicon (Si) at the grain boundaries of the soft magnetic composition. Silicon (Si)-containing components such as silica particles may also be used.

In the above-described embodiment, a toroidal core composed of a soft magnetic composition is shown. In addition, the soft magnetic composition of this embodiment may constitute a core in which a coil is embedded. can. The core in which the coil is embedded is specifically a core that surrounds the coil and contains a soft magnetic composition and a resin.

In addition, the application of the core according to the present embodiment is not particularly limited, and for example, it can be suitably used as the core of various electronic parts such as coil-type electronic parts, switching power supplies, DC-DC converters, transformers, and choke coils. .

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Example 1)
[Preparation of soft magnetic alloy powder]
Ingots, chunks, or shots of iron (Fe), chromium (Cr), and silicon (Si) were prepared. Next, they were mixed so as to have a composition of 4% by mass of chromium (Cr), 5% by mass of silicon (Si) and the balance iron (Fe), and placed in a crucible placed in a water atomizer. Next, in an inert atmosphere, the crucible was heated to 1600° C. or higher by high-frequency induction using a work coil provided outside the crucible, and the ingot, chunk or shot in the crucible was melted and mixed to obtain a melt.

Next, the melt in the crucible is ejected from a nozzle provided in the crucible, and at the same time, the ejected melt is quenched by colliding with a high-pressure (50 MPa) water flow to obtain a soft magnetic material composed of Fe-Si-Cr-based particles. An alloy powder (average particle size: 11 μm) was produced.

As a result of composition analysis of the obtained soft magnetic alloy powder by fluorescent X-ray spectroscopy, it was confirmed that the composition coincided with the charged composition.

[Preparation of core]
4% by mass of a silicone resin (SR2414LV manufactured by Dow Corning Toray Silicone Co., Ltd.) was added to 100% by mass of the soft magnetic alloy powder obtained, and the mixture was mixed for 30 minutes at room temperature using a pressure kneader. The mixture was then dried in air at 150° C. for 20 minutes. Zinc stearate (manufactured by Nitto Kasei Co., Ltd.: zinc stearate) was added as a lubricant to the dried soft magnetic alloy powder, and mixed for 10 minutes with a V mixer. The amount of zinc stearate added was 0.5% by mass with respect to 100% by mass of the soft magnetic alloy powder.

Subsequently, the obtained mixture was molded into a toroidal sample having an outer diameter of 20 mm, an inner diameter of 10 mm, and a thickness of 5 mm to prepare a molded body. In addition, the molding pressure was 600 MPa.

A heating body that has reached the holding temperature was sandwiched from above and below the molded body and placed in a furnace. In addition, in Tables 1 and 2, when the temperature of the compact is raised by such a method, it is described as "Short-time temperature rise" in the column of "Firing conditions". A core was obtained by firing the compact at a holding temperature of 650° C. for 60 minutes in the atmosphere.

(Examples 2 to 5 and Comparative Examples 3 and 4)
A core was obtained in the same manner as in Example 1, except that the holding temperature of the molded body was changed as shown in Table 1.

(Comparative Examples 1 and 2)
In Comparative Example 1, the compact was placed in a furnace and heated to the holding temperature over 6 hours, and in Comparative Example 2, the compact was placed in the furnace and heated to the holding temperature over 2 hours. The core was obtained in the same manner as In Comparative Examples 1 and 2, the heating body was not sandwiched from above and below the molded body.

(Examples 11 to 15 and Comparative Examples 13 and 14)
Using Al alone instead of Cr alone, it is mixed so as to have a composition of 91% by mass of iron (Fe), 5% by mass of aluminum (Al), and 4% by mass of silicon (Si) to obtain an Fe—Si—Al system A soft magnetic alloy powder composed of particles (average particle size: 9 μm) was prepared, and a core was obtained in the same manner as in Example 1 except that the holding temperature of the compact was changed as shown in Table 2.

(Comparative Examples 11 and 12)
In Comparative Example 11, the compact was placed in a furnace and heated to the holding temperature over 6 hours, and in Comparative Example 12, the compact was placed in the furnace and heated to the holding temperature over 2 hours. The core was obtained in the same manner as In Comparative Examples 11 and 12, the heating body was not sandwiched from above and below the molded body.

[Various evaluations]

<Confirmation of (Si/M) _MAX >
The cross section of the core was observed with a scanning transmission electron microscope (STEM) to distinguish between "soft magnetic alloy grains" and "regions between soft magnetic alloy grains".

Next, as shown in FIG. 3, EDS analysis was performed on an arbitrarily selected observation line X using an EDS apparatus with sufficiently high resolution attached to the STEM. (Si/M) _MAX was obtained based on the obtained numerical value. Results are shown in Tables 1 and 2. In particular, the results of Example 4 are shown in FIG. In FIG. 6, the first vertical axis indicates the mass ratio of three elements, the second vertical axis indicates the Si/M mass ratio, and the horizontal axis indicates the distance from the starting point.

<Confirmation of amorphous layer>
The presence of the amorphous layer was determined by analyzing the selected area diffraction pattern (SADP) of the reciprocal lattice space in a scanning transmission electron microscope (TEM).

<Core Loss>
A toroidal dust core sample was wrapped with 10 turns of copper wire and measured for core loss using an LCR meter (Hewlett-Packard 4284A). The measurement conditions were a measurement frequency of 1 MHz, a measurement temperature of 23° C., and a measurement level of 0.4 A/m. Results are shown in Tables 1 and 2.

From STEM observation and EDS analysis, Examples 1 to 5 in which (Si/M) _MAX is more than 0.5 and less than 10.6, Comparative Examples 1 to 3 in which (Si/M) _MAX is 10.6 or more and It was confirmed that the core loss was lower than that of Comparative Example 4 in which (Si/M) _MAX was 0.5.

From TEM observation, it was confirmed that Examples 1 to 4 had an amorphous layer at the (Si/M) _MAX location. In Comparative Example 4, since the holding temperature was high, the soft magnetic alloy particles were partially melted and alloyed, and an amorphous layer was not formed at the (Si/M) _MAX location.

From STEM observation and EDS analysis, Examples 11 to 15 having a (Si/M) _MAX of more than 0.7 and less than 14.0, Comparative Examples 11 to 13 having a (Si/M) _MAX of 14.0 or more and It was confirmed that the core loss was lower than that of Comparative Example 14 in which (Si/M) _MAX was 0.7.

From TEM observation, it was confirmed that Examples 11 to 14 had an amorphous layer at the (Si/M) _MAX location. In Comparative Example 14, since the holding temperature was high, the soft magnetic alloy particles were partially melted and alloyed, and no amorphous layer was formed.

From FIG. 6, it was confirmed that silicon (Si) and chromium (Cr) were continuously present in a predetermined range including the (Si/M) _MAX portion of Example 4.

In addition, for Example 4, it was confirmed by the following method whether or not silicon (Si) not derived from the elements contained in the soft magnetic alloy particles was contained in the regions between the soft magnetic alloy particles of the core. .

In FIG. 6 (Example 4), most of chromium (Cr) exists in the regions between the soft magnetic alloy grains and is hardly contained in the soft magnetic alloy grains. On the other hand, iron (Fe) is mostly present in the soft magnetic alloy grains and hardly contained in the regions between the soft magnetic alloy grains.

Therefore, it is considered that chromium (Cr) in the soft magnetic alloy powder migrated to the regions between the soft magnetic alloy particles and iron (Fe) in the soft magnetic alloy powder remained in the soft magnetic alloy particles during the core manufacturing process.

For this reason, the mass ratio of iron (Fe) and silicon (Si) in the raw materials of the soft magnetic alloy powder and the mass ratio of iron (Fe) and silicon (Si) in the soft magnetic alloy particles in FIG. If they match, it can be said that the raw material silicon (Si) of the soft magnetic alloy powder became the silicon (Si) of the soft magnetic alloy particles. As a result, it can be said that the silicon (Si) present in the regions between the soft magnetic alloy particles is not silicon (Si) derived from the raw material of the soft magnetic alloy powder, but silicon (Si) derived from the silicone resin.

Then, as a result of calculation, the mass ratio of iron (Fe) and silicon (Si) in the raw material of the soft magnetic alloy powder and the mass ratio of iron (Fe) and silicon (Si) in the soft magnetic alloy particle part of FIG. were generally consistent. Therefore, it can be said that the silicon (Si) present in the regions between the soft magnetic alloy particles is not silicon (Si) derived from the raw material of the soft magnetic alloy powder, but silicon (Si) derived from the silicone resin.

A core composed of the soft magnetic composition according to the present invention can achieve low core loss.

21, 22... Soft magnetic alloy grains 30, 31... Regions between soft magnetic alloy grains

Claims (5)

Having a plurality of soft magnetic alloy particles,
The soft magnetic alloy particles contain an element M and iron,
The element M has a stronger ionization tendency than silicon,
When the maximum value of the mass ratio of silicon to the element M in the region between the soft magnetic alloy grains is (Si/M) _MAX ,
The (Si/M) _MAX satisfies 1 ≤ (Si/M) _MAX ≤ 10,
The element M is continuously present in a predetermined range including the (Si/M) _MAX point,
The soft magnetic composition, wherein the predetermined range is a range of 50% or more of the distance between the adjacent soft magnetic alloy grains. 2. The soft magnetic composition according to claim 1, wherein an amorphous layer is present at the (Si/M) _MAX location. A core composed of the soft magnetic composition according to claim 1 or 2. 4. The core according to claim 3, wherein a coating layer is formed on at least part of the surface of said core. A coil-type electronic component comprising the core according to claim 3 or 4.

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