JP2012186255A - Dust core and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust core having a high permeability equivalent to or exceeding that of Sendust, and a low iron loss approximate to that of Sendust.SOLUTION: The dust core is composed of coated powder consisting of multiple coated particles, i.e. soft magnetic particles having an insulation coating on the surface, and a shape-retaining material which integrates these coated particles. In the dust core, the soft magnetic particles are composed of mixed particles of Fe-Si-Al alloy particles and Fe-Ni alloy particles, and when the dust core is analyzed by X-ray diffractometry, the next diffraction peak intensity ratio is 0.45 or less. Integrated intensity of 1st peak of FeO/{(integrated intensity of 1st peak of duplicated Fe-Si-Al and Fe-Ni×volume fraction of Fe-Ni occupying the total volume of Fe-Si-Al and Fe-Ni)+integrated intensity of 1st peak of FeNi}.

Description

  The present invention relates to a dust core and a method for manufacturing the same. In particular, the present invention relates to a powder magnetic core having a low coercive force and a low iron loss, and a manufacturing method thereof, mainly composed of Fe-Si-Al alloy powder.

  Inductors such as choke coils are used in circuits that convert energy, such as switching power supplies and DC / DC converters. As a configuration example of an inductor, one having a powder magnetic core obtained by firing a powder compact of soft magnetic powder and a coil formed by winding a winding around the outer periphery of the powder magnetic core is known. .

  This powder magnetic core is prepared, for example, by preparing a soft magnetic powder that is an aggregate of composite magnetic particles in which an insulating film is formed on the surface of the soft magnetic particles, and press-molding the soft magnetic powder into a predetermined shape. It is made by heat-treating the body. According to the dust core obtained by such a method, insulation between soft magnetic particles is ensured by the insulating coating, and low iron loss is realized.

  As a soft magnetic powder as a raw material for such a powder magnetic core, particularly a powder magnetic core used at a frequency of about 100 kHz, there is an Fe—Si—Al alloy powder represented by Sendust. Although Sendust is a material that can achieve low iron loss, it is a material that is extremely hard and difficult to deform, so when formed into a powder magnetic core, there are more voids between the individual particles that make up the powder, and the magnetic permeability And the saturation magnetic flux density tends to be low.

  Therefore, there is a technique described in Patent Document 1 as a technique for improving these. This document discloses a composite magnetic material in which a mixture obtained by mixing a sendust alloy powder having an oxide film and a highly compressible soft magnetic metal powder in a predetermined composition is bonded through a binder. Such a composite magnetic material uses raw material powder in which sendust is mixed with highly compressible metal powder, thereby filling gaps between alloy particles of sendust with highly compressible metal powder rich in deformability, permeability and saturation magnetic flux. It is thought to improve the density. In this document, pure iron and Fe—Si alloy are listed as specific examples of the highly compressible soft magnetic metal powder.

JP-A-6-236808

However, in the composite magnetic material according to Patent Document 1, all of the highly compressible materials mixed with Sendust are materials having a large coercive force, and the magnetic permeability is improved as compared with Sendust. Will increase significantly.
The present invention has been made in view of the above circumstances, and one of its purposes is a dust core having a high magnetic permeability equivalent to or higher than Sendust and having a low iron loss similar to Sendust and its manufacture. And to provide a method.

The present inventors use a Fe-Ni alloy having a high compressibility and a holding power equivalent to Sendust, typically a raw material powder in which Permalloy is mixed with Sendust, thereby achieving high permeability, low coercive force, and low iron. It was investigated to obtain a lossy magnetic core. However, it has been found that when the raw material powder obtained by simply mixing permalloy with Sendust is subjected to the same molding and heat treatment as before, the magnetic permeability can be improved but the iron loss cannot be reduced. As the main cause, as will be understood from the test examples described later, the Fe ₂ O ₃ phase (hereinafter referred to as the Fe ₂ O ₃ phase) on the particle surface of the permalloy when the heat treatment for relaxing the strain on the powder magnetic core was performed. Generation of an oxidized phase) and generation of a FeNi ₃ ordered phase (hereinafter also referred to as a different phase) having a large coercive force in the dust core. Therefore, as a result of various trials and errors, the heat treatment applied to the green compact was devised to suppress the generation of oxidized and foreign phases, and high dust permeability, low coercive force, and low iron loss powder. Obtaining knowledge that a magnetic core can be obtained, the present invention has been completed.

The dust core of the present invention comprises a coating powder comprising a plurality of coated particles having an insulating coating on the surface of soft magnetic particles, and a shape-retaining material that integrates these coated particles. In the dust core, the soft magnetic particles are composed of mixed particles of Fe-Si-Al alloy particles and Fe-Ni alloy particles. When the dust core is analyzed by X-ray diffraction, the following diffraction peak is obtained. The intensity ratio is 0.45 or less.
<< Diffraction peak intensity ratio >>
Integral intensity of 1st peak of Fe ₂ O ₃ / {(Integral intensity of 1st peak overlapping Fe-Si-Al and Fe-Ni x volume of Fe-Ni in total volume of Fe-Si-Al and Fe-Ni Fraction) + integrated intensity of 1st peak of FeNi ₃ }

  According to this configuration, by using a mixed powder of hard Fe-Si-Al alloy powder and relatively soft Fe-Ni alloy powder, Fe-Ni alloy particles are placed in the gaps between Fe-Si-Al alloy particles. Can be obtained, and a dust core with high density and high permeability can be obtained.

Further, by limiting the intensity ratio of the X-ray diffraction peak to the above value, a dust core in which the generation of the Fe ₂ O ₃ phase affecting the coercive force of the dust core is suppressed can be obtained. The oxidation phase tends to occur on the outer periphery of the Fe—Ni alloy particles, and has a linear expansion coefficient different from that of the Fe—Ni alloy. When heat treatment for removing strain (second heat treatment described later) is performed on the compacted body including the Fe-Ni alloy powder in which the oxidation phase is generated, the Fe-Ni alloy is cooled during the cooling process. Since it is stressed and soft, strain (transition) may occur. The generation of the distortion increases the coercive force of the dust core by preventing the domain wall from moving. The coercive force has a strong correlation with the hysteresis loss. When the coercive force is reduced, the iron loss, particularly the hysteresis loss is reduced. In other words, according to the above configuration, the low coercivity, which is the original characteristic of the Fe-Ni alloy powder, can be utilized by using a dust core in which the generation of an oxidation phase that affects the coercive force is suppressed. It is possible to obtain a dust core with reduced iron loss.

Furthermore, according to this configuration, it is possible to dust core deposition of FeNi ₃ ordered phase to increase the coercive force of the powder core is suppressed. The occurrence of this heterogeneous phase itself increases the coercive force of the dust core. Therefore, if generation | occurrence | production of a different phase is suppressed, it can be set as the powder magnetic core of a low iron loss.

  As one form of the powder magnetic core of the present invention, the blended particles are mixed in mass%, Fe—Si—Al alloy particles are 80% to 99%, and Fe—Ni alloy particles are 1% to 20%. There are some.

  According to this structure, it is suitable for obtaining a dust core having high magnetic permeability and low iron loss.

As one form of the powder magnetic core of the present invention, the Fe-Si-Al alloy particles are composed of a material in which the contents (mass%) of Si and Al in the alloy satisfy the following formula: It is done.
Si content + (Al content / 2) ≥ 5% by mass

  Fe-Si-Al alloy particles of this composition are not easily deformed by the pressure during molding, and are suitable for obtaining a high permeability powder core with good moldability by mixing with Fe-Ni alloy particles. Yes.

On the other hand, the manufacturing method of the powder magnetic core of the present invention includes the following steps.
A raw material powder preparation step of preparing a coating powder composed of a plurality of coated particles having an insulating coating on the surface of soft magnetic particles composed of Fe-Si-Al alloy particles, Fe-Ni alloy particles, and mixed particles.
A granulation step in which a molding resin for retaining the molded body is mixed with the coating powder and granulated.
A molding process in which this granulated powder is compression molded to form a compact.
A first heat treatment step of evaporating the binder by heating the green compact to a predetermined temperature in an air atmosphere.
A second heat treatment step for relaxing the distortion of the soft magnetic powder constituting the green compact by heating the compact after the first heat treatment to a predetermined temperature in a non-oxidizing atmosphere and then cooling.
When the atmosphere is changed during the transition from the first heat treatment step to the second heat treatment step, the atmosphere temperature is kept at 500 ° C. or lower until the oxygen concentration in the atmosphere becomes 5000 ppm or less.

  According to the above configuration, when the atmosphere is replaced from the air atmosphere to the non-oxidizing atmosphere, the atmosphere temperature is set to 500 ° C. until the replacement of the atmosphere is almost completed, that is, until the oxygen concentration in the atmosphere becomes 5000 ppm or less. By maintaining below, it is possible to suppress the generation of an oxidized phase that affects the coercive force. Therefore, a dust core with a low iron loss can be obtained.

  As one form of the manufacturing method of this invention, the cooling process in said 2nd heat treatment process makes the temperature range of 500 to 350 degreeC be rapid cooling of 1 degreeC / min or more.

  According to this configuration, it is possible to suppress the generation of a heterogeneous phase having a large coercive force by passing through a temperature range in which the heterogeneous phase is likely to precipitate at an early stage by rapid cooling. Therefore, a dust core with a low iron loss can be obtained.

  As one form of the manufacturing method of this invention, it is mentioned that the heating temperature in said 2nd heat treatment process is 600 degreeC or more and 850 degrees C or less.

  This heating temperature is suitable for obtaining a dust core having a low iron loss. When the lower limit is 600 ° C. or more, the hysteresis loss of the dust core can be effectively reduced. Conversely, by setting the upper limit to 850 ° C. or less, it is possible to suppress the thermal damage of the insulating coating provided in the soft magnetic particles and suppress the increase in eddy current loss.

  The dust core of the present invention is a dust core having high permeability and low iron loss. In addition, according to the method for manufacturing a dust core of the present invention, a dust core having high magnetic permeability and low iron loss can be easily manufactured.

It is explanatory drawing which shows the pattern from which the temperature history of the 1st heat processing and the 2nd heat processing in a test example differs. (A) is a photomicrograph showing the structure of sample No. 1-5 as an example, and (B) is a photomicrograph showing the structure of sample No. 1-3 as a comparative example. It is explanatory drawing which shows how to obtain | require the integrated intensity | strength of a diffraction peak. It is a schematic diagram which shows an example of an X-ray diffraction pattern. It is a graph which shows the temperature history in the cooling process of 2nd heat processing. It is a graph which shows the relationship between 2nd heat processing temperature and loss.

  Embodiments of the present invention will be described below. Here, the manufacturing method of a dust core will be described first, and then the configuration of the dust core will be described.

[Production method of dust core]
The dust core according to the present invention is manufactured through the raw material powder preparation step, the granulation step, the molding step, the first heat treatment step, and the second heat treatment step.

(Raw material powder preparation process)
In this preparation step, Fe—Si—Al alloy particles and Fe—Ni alloy particles are prepared as alloy particles constituting the soft magnetic powder. The individual alloy particles are later formed into a coating powder by forming an insulating coating.

<Fe-Si-Al alloy particles>
The alloy constituting this particle is based on Fe, contains Si and Al, and the remainder is made of impurities. A representative example of the Fe—Si—Al alloy is Sendust. The Si content in the alloy is preferably about 4 to 13% by mass. A more preferable Si content is about 7 to 10% by mass. The content of Al is preferably about 4 to 10% by mass. A more preferable content of Al is 5 to 7% by mass. Among them, it is preferable that {Si content + (Al content / 2)} ≧ 5 mass% is satisfied, and further, this formula satisfies 7 mass% or more, particularly 10 mass% or more. The larger the value of this formula, the more the Fe-Si-Al alloy tends to become harder, and if it is Fe-Si-Al alloy particles of this composition, the Fe-Ni alloy particles are less likely to be deformed by the pressure during molding. By mixing with, a powder core having a high magnetic permeability can be obtained with good moldability.

  The average particle size of the Fe—Si—Al alloy particles is preferably in the range of about 40 to 150 μm. Use of powder having such a particle size is effective in suppressing an increase in eddy current loss when used in a high frequency range of 1 kHz or higher. For suppression of eddy current loss, the smaller the average particle size, the better. A more preferable average particle diameter is about 50 to 80 μm. In addition, the average particle diameter of the Fe—Si—Al alloy particles is preferably 5 times or more the average particle diameter of the Fe—Ni alloy particles described below. With such dimensions, the soft Fe-Ni alloy particles are filled between the hard Fe-Si-Al alloy particles, and a high-density, high-permeability powder magnetic material can be easily formed. In order to realize the close-packed state, it is ideal that the magnification is 7 times, but in reality, deformation of Fe-Ni alloy particles occurs during molding, so it may be about 5 times or more. Conceivable.

<Fe-Ni alloy particles>
The alloy that constitutes the particles is basically based on Fe, contains Ni, and the remainder is composed of impurities. Furthermore, it may contain additional elements such as Cu, Cr, Co, and Mo. A typical example of the Fe—Ni alloy is permalloy. JIS standards include PB permalloy with Ni content of 41-51% by mass, PC permalloy with Ni content of 70-85% by mass and containing additive elements such as Mo, PE permalloy with Ni content of 35-40%, etc. Has been. In this example, an Fe—Ni alloy having a Ni content of 41 to 80% by mass is suitable for Fe—Ni alloy particles. In particular, an Fe—Ni alloy having a Ni content of 41 to 51 mass%, that is, PB permalloy can be suitably used.

<Blending ratio of both alloy particles>
The blending ratio of Fe-Si-Al alloy powder and Fe-Ni alloy powder is mass%, Fe-Si-Al alloy particles are 80% to 99%, Fe-Ni alloy particles are 1% to 20%. It is preferable that When the content of the Fe—Ni alloy particles is 1% by mass or more, the magnetic permeability can be increased as compared with a dust core made of only sendust. On the other hand, by setting the content of Fe—Ni alloy particles to 20% by mass or less, Fe—Ni alloy particles are not excessively increased, and Fe—Ni alloy particles are electrically connected to each other to increase eddy loss. Can be suppressed. The content of Fe—Ni alloy particles is more preferably 2% by mass or more and 15% by mass or less.

<Insulating coating>
The insulating coating includes an inorganic insulating layer made of an inorganic material mainly composed of silicon oxide, for example. The inorganic insulating layer ensures insulation between the soft magnetic powders by covering the outer peripheral surface of the soft magnetic particles. This inorganic insulating layer mainly composed of silicon oxide has high hardness and is not destroyed by the applied pressure when a granulated powder using a coating powder is compressed later to form a molded body, and It is not decomposed by heat when the molded body is fired. The content of silicon oxide in the inorganic insulating layer is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 90% by mass or more. A typical example of such silicon oxide is SiO ₂ , but SiO ₂ may contain at least one of SiO and Si ₂ O ₃ . Examples of the inorganic insulating layer made of an inorganic substance mainly composed of silicon oxide include a film formed by heat-treating a silicone resin in an atmosphere containing oxygen.

  The thickness of the inorganic insulating layer is preferably 20 nm or more and 1 μm or less. By making the said thickness more than a lower limit, while ensuring the insulation between soft-magnetic particles, it can be set as the inorganic insulating layer which has the mechanical strength which is not destroyed by the applied pressure at the time of granulated powder compression. In addition, by setting the thickness to the upper limit value or less, when a dust core is produced from the coating powder, a sufficient amount of soft magnetic particles in the dust core can be secured.

  The insulating coating is formed by mixing and drying the soft magnetic powder and the insulating agent, followed by heat treatment as necessary. The insulating agent is preferably a low molecular silicone resin or a silicate aqueous solution such as water glass. The mixing is preferably performed with a mixer or the like. The blending amount of the insulating agent is preferably selected according to the specific surface area of the soft magnetic particles to be mixed. By determining the blending amount of the insulating agent according to the specific surface area of the soft magnetic particles, coated particles in which an insulating coating having a predetermined thickness is formed on the outer peripheral surface of the soft magnetic particles can be produced. The blending amount of the soft magnetic particles and the insulating agent is, for example, such that the insulating agent is about 0.02 to 1.8% by mass with respect to the mixture of both. The blending amount is more preferably 0.05 to 1.5% by mass, and still more preferably 0.1 to 1.0% by mass.

  In the case where the insulating agent is a silicone resin, it is preferable to perform a heat treatment after the coating to decompose and vitrify the silicone resin. A preferred heat treatment temperature is 400 ° C to 1000 ° C, and a more preferred heat treatment temperature is 600 ° C to 900 ° C. A preferable heat treatment time is about 30 minutes to 2 hours.

  When the insulating agent is an aqueous solution of silicate, it is only necessary to dry at 50 to 100 ° C. after coating. Moreover, you may implement continuously with the granulation of the following process, and handling is simple compared with a silicone resin.

(Granulation process)
The soft magnetic powder is further mixed with a molding resin to form a granulated powder. In this granulated powder, at least a molding resin and a soft magnetic powder are integrated, and if necessary, a baking resin may be further integrated.

<Resin for molding>
The molding resin is a resin for maintaining the shape of the compact when the coating powder is compressed into a green compact, and it is heated from the viewpoint of both the deformability during molding and the mechanical strength of the compact. A plastic resin is preferred. Specific examples of the thermoplastic resin include polyvinyl alcohol, acrylic resin, polyethylene resin and the like in addition to polyvinyl butyral. In particular, an acrylic resin is preferable from the viewpoint of both the deformability during molding and the mechanical strength during shape retention. This molding resin does not substantially remain when vaporized (volatilized) in a first heat treatment step to be described later and formed into a dust core through the heat treatment.

  The molding resin is preferably a resin that vaporizes at 450 ° C. or lower. This is because if the vaporization temperature exceeds 500 ° C., an oxidized phase may be generated in the soft magnetic powder, and it is preferable to complete the vaporization of the molding resin at a temperature sufficiently lower than that. If necessary, a plurality of types of molding resins such as a resin for retaining the coating powder and a resin for ensuring lubricity during molding may be used. Furthermore, the molding resin is preferably not carbonized in the first heat treatment step, and the carbonization temperature of the resin is suitably higher than 450 ° C.

  The mixture of the soft magnetic powder and the binder is preferably mixed so that the total amount of the binder to be added is 0.5 to 3% by mass of the mixture. By setting the resin content above this lower limit, the powder compact or the powder magnetic core can be sufficiently retained. Conversely, by setting the resin content below the upper limit, the amount of resin in the mixture becomes an appropriate amount, and the dust compact The molded body and the powder magnetic core can be densified.

<Resin for baking>
The firing resin comprises a shape-retaining material that retains the coating powder as a ceramic compound when the compacted body obtained by compressing the coating powder is subjected to a second heat treatment to be described later to form a sintered body (powder magnetic core). Become. Typically, a silicone resin is used as the firing resin. The silicone resin is presumed to be an amorphous shape-retaining material containing Si, C, and O in the second heat treatment step. In addition, a sodium silicate binder (water glass) can be used as the firing resin.

(Molding process)
In the molding step, the mixed raw material after the granulation step, that is, granulated powder, is filled in a mold and compressed, and molded into a predetermined shape to obtain a compacted body. The pressure during compression is preferably about 10 to 12 ton / cm ² . By setting the pressure to the lower limit value or more, a high-density molded body can be obtained. Moreover, the damage of the inorganic insulating layer accompanying a deformation | transformation of a soft-magnetic particle can be suppressed because a pressure shall be below an upper limit. This pressurization may be performed at room temperature, but when a thermoplastic resin is used as the molding resin, it is preferably molded at a temperature equal to or higher than the glass transition temperature of the resin. This can improve the density and strength of the molded body.

(First heat treatment process)
The first heat treatment is a heat treatment performed in an air atmosphere in order to vaporize the molding resin. The reason why it is performed in the air atmosphere is that carbonized residue is easily generated when the first heat treatment is performed in a non-oxidizing atmosphere.

  In the first heat treatment, the molding resin is vaporized so as not to be carbonized. The heating temperature is preferably 500 ° C. or lower. If it is 500 degrees C or less, it will be easy to vaporize, without carbonizing molding resin. The holding time at this heating temperature is a time sufficient for vaporizing the molding resin, and a time that is not unnecessarily long. Specifically, it is about 15 minutes to 90 minutes.

  As described above, when a plurality of types of molding resins are used, the first heat treatment may be performed while maintaining a plurality of stages according to the vaporization temperature of each resin. Although it is possible to evaporate all molding resins by heating to a high vaporization temperature at once, among multiple types of molding resins, it is possible to maintain the temperature step by step according to the vaporization temperature of each resin. This is because each resin can be reliably vaporized without being carbonized.

(Second heat treatment process)
The second heat treatment is a heat treatment performed in a non-oxidizing atmosphere in order to relieve strain introduced into the soft magnetic powder during molding of the green compact and reduce hysteresis loss. This heat treatment is performed in a non-oxidizing atmosphere such as a nitrogen atmosphere in order to suppress the generation of an oxidized phase that affects the coercive force.

  The heating temperature is preferably 600 ° C. or higher and 850 ° C. or lower. Hysteresis loss of the dust core can be effectively reduced when the temperature is 600 ° C. or higher. On the contrary, by setting it as 850 degrees C or less, the thermal damage of the insulating film with which a soft-magnetic particle is equipped can be suppressed, and the increase in eddy current loss can be suppressed. A more preferable heating temperature is 700 ° C. or higher and 850 ° C. or lower, and a particularly preferable heating temperature is 700 ° C. or higher and 800 ° C. or lower. The holding time at this heating temperature is preferably 15 minutes or longer and 2 hours or shorter. By setting it to 15 minutes or more, a sufficient distortion removing effect can be achieved. By setting it as 2 hours or less, industrial production efficiency can be improved and thermal damage of the insulating coating can be suppressed. About 30 minutes to 1 hour is practical.

Furthermore, in the cooling process from the heating temperature to the normal temperature in the second heat treatment, it is preferable that the temperature range of 500 ° C. to 350 ° C. is rapidly cooled to 1 ° C./min or more. The FeNi ₃ ordered phase which is a different phase is likely to precipitate in a temperature range of 500 ° C to 350 ° C. Therefore, by rapidly cooling this temperature range and passing in a short time, a low magnetic core powder core with reduced foreign phase can be obtained. The faster the cooling rate, the more the generation of heterogeneous phases can be suppressed. Therefore, a more preferable cooling rate is 3 ° C./min or more, and a particularly preferable cooling rate is 10 ° C./min or more.

(Conditions for changing atmosphere during transition between both heat treatments)
The first heat treatment is performed in an air atmosphere, while the second heat treatment is performed in a non-oxidizing atmosphere. Therefore, the atmosphere in the heat treatment furnace is changed during the transition period between both heat treatments. When the atmosphere is replaced, the atmospheric temperature is maintained at 500 ° C. or lower until the oxygen concentration in the atmosphere becomes 5000 ppm (volume ratio) or lower. This replacement is performed by gradually replacing the atmosphere with nitrogen, but since the second heat treatment temperature is higher than the first heat treatment, if the temperature is raised during the replacement, before the atmosphere is sufficiently replaced with nitrogen, That is, there is a possibility that the high temperature at which an oxidation phase is generated may be reached while the oxygen concentration is high. Conventionally, when vaporization of the molding resin by the first heat treatment is completed, the temperature is raised to the second heat treatment temperature during this transition period, so that it is considered that the generation of the oxidized phase occurred during that time. Therefore, by maintaining the temperature at which the oxygen concentration in the heat treatment furnace is sufficiently low and the oxidation phase is unlikely to occur until the non-oxidizing atmosphere is replaced, the generation of the oxidation phase can be suppressed, and low loss can be achieved. A dust core can be obtained.

[Dust core]
The dust core obtained by the above method includes the above-described coating powder and a shape-retaining material that integrates the coating powder. As described above, the coating powder includes a mixed powder of Fe—Si—Al alloy powder and Fe—Ni alloy powder. On the other hand, the shape-retaining material is a ceramic material in which a firing resin is modified by heat during firing. In this shape-retaining material, it is presumed that the silicone resin added as a firing resin is an amorphous body containing Si, C, and O during the firing process. That is, the powder magnetic core is in a state where the soft magnetic powder is held in the shape-retaining material. In this dust core, the vicinity of the outer surface of the soft magnetic particles is composed of an inorganic insulating layer mainly composed of silicon oxide, but the outside of the inorganic insulating layer has a C content as compared with the inorganic insulating layer. It is considered that the amorphous material contains many materials, that is, Si, C, and O.

When the dust core is analyzed by XRD (X-ray diffraction), the following diffraction peak intensity ratio is 0.45 or less.
Integral intensity of 1st peak of Fe ₂ O ₃ / {(Integral intensity of 1st peak overlapping Fe-Si-Al and Fe-Ni x volume of Fe-Ni in total volume of Fe-Si-Al and Fe-Ni Fraction) + integrated intensity of 1st peak of FeNi ₃ }

  By satisfying this peak intensity ratio, there is little precipitation of an oxidation phase, the increase in coercive force is suppressed, and it can be said that it is a low loss dust core. A more preferable peak intensity ratio is 0.30 or less, and a more preferable peak intensity ratio is 0.20 or less.

  In addition, the magnetic permeability of the dust core is, for example, 65 or more, more preferably 70 or more, still more preferably 75 or more, and particularly preferably 80 or more. When an electromagnetic component is configured by combining the dust core of this example with a coil, the magnetic permeability is preferably low when the current value is large, and the magnetic permeability is preferably high when the current value is small.

[Test Example 1: Magnetic property analysis]
Preparation of coated powder, generation of granulated powder, molding of compacted body, first heat treatment and second heat treatment under the following conditions to produce a powder core test piece, and evaluate the magnetic properties of the test piece did.

<Preparation of sample>
First, a plurality of types of soft magnetic powders having different compositions were prepared. Soft magnetic powder is an aggregate of soft magnetic particles. The composition of each soft magnetic powder is as shown in Table 1 below. Sample No. 1-1 corresponds to Sendust, Sample No. 1-2 corresponds to the conventional example described in Patent Document 1, and Samples No. 1-3 to No. 1-5 correspond to mixed soft magnetic powder of Sendust and Permalloy. In either case, the average particle size of the Fe—Si—Al alloy powder was about 60 μm. On the other hand, the average particle size of the Fe powder in sample No. 1-2 and the Fe—Ni alloy powder in samples No. 1-3 to No. 1-5 was about 10 μm. The soft magnetic particles of any sample have a phosphate coating. Among the soft magnetic powders of these samples, the powders of samples No. 1-2 to No. 1-5 were mixed for 120 minutes with a V-type mixer.

  Next, an aqueous solution containing potassium silicate as a main component is prepared. The concentration of potassium silicate in this aqueous solution was 30% by mass. This aqueous solution and the soft magnetic powder were mixed with a mixer and dried at about 80 ° C. to form an inorganic insulating layer mainly composed of potassium silicate on the surface of the soft magnetic particles. The blending amount of the soft magnetic powder and the aqueous solution was such that the solid content of the aqueous solution was 0.3% by mass with respect to the mixture of both.

  Through the above-described steps, a coated powder that was an aggregate of coated particles in which an inorganic insulating layer mainly composed of silicon oxide was formed on the surface of soft magnetic particles was produced.

  The obtained coating powder was mixed with a molding resin to produce granulated powder. The mixing ratio of the soft magnetic powder and the molding resin in the granulated powder is 100: 1 by mass ratio. Two types of acrylic resins were used as the molding resin.

Next, the granulated powder of each sample is supplied to a mold and compressed to form a molded body. The surface pressure during this pressure molding is 10 ton / cm ² . With this surface pressure, the Fe—Si—Al alloy particles are not substantially deformed during molding.

  And the 1st heat processing and the 2nd heat processing are performed to the obtained compacting body by the temperature history of the pattern 1-the pattern 3 shown in FIG. In the temperature history of each pattern, the heat treatment performed in the air atmosphere is the first heat treatment, and the heat treatment performed in the nitrogen atmosphere is the second heat treatment. In Pattern 1, the temperature is raised even in the process of switching from the first heat treatment to the second heat treatment, and the temperature at the time when the atmosphere is replaced with nitrogen from the atmosphere is about 600 ° C. On the other hand, in pattern 2, the temperature is maintained at 450 ° C. during the atmosphere replacement process, and the temperature rise is started after the atmosphere is replaced with nitrogen from the atmosphere. Further, the pattern 3 is different from the pattern 2 in the cooling process in the second heat treatment. That is, in Pattern 2, the furnace temperature was cooled over 6 hours from the heating temperature (775 ° C) to room temperature, whereas in Pattern 3, the heating temperature (775 ° C) was transferred by transferring the sample from the heating furnace to the cooling furnace. It was rapidly cooled in 10 minutes from room temperature to room temperature. In the cooling furnace, the furnace wall is circulated and cooled by a refrigerant.

  The reason why the holding temperature of the first heat treatment is in two stages in any pattern is that two types of resins having different vaporization temperatures are used as the molding resin and holding is performed at each vaporization temperature. . The holding time at 350 ° C. is 60 minutes, and the holding time at 450 ° C. is 60 minutes. On the other hand, the holding time in the second heat treatment is 60 minutes. It is considered that the molding resin is substantially lost by the second heat treatment. The obtained test piece was ring-shaped and had an outer diameter of 34 mm, an inner diameter of 20 mm, and a thickness of 5 mm.

<Evaluation>
About each sample produced as mentioned above, the magnetic characteristic was measured in the procedure shown next.

  First, a winding was applied to a ring-shaped test piece, and a measurement member for measuring the magnetic properties of the test piece was produced. The magnetic permeability μ (H / m) of this measuring member was measured. (DC / AC-BH tracer (Metron Giken Co., Ltd.) was used for the permeability measurement. Furthermore, this measurement member was excited using a BH / μ analyzer SY-8258 made by Iwatatsu Measurement Co., Ltd. The iron loss W1 / 100k was measured at magnetic flux density Bm: 1kG (= 0.1T) and measurement frequency: 100kHz, and the results are also shown in Table 1. In Table 1, the hysteresis loss is "His loss" and eddy current. The loss is indicated as “vortex loss.” In other test examples described later, the same indication may be displayed.

The iron loss is composed of hysteresis loss and eddy current loss. In this test example, the hysteresis loss and eddy current loss were calculated by fitting the frequency curve of iron loss with the following three formulas using the least square method.
(Iron loss) = (Hysteresis loss) + (Eddy current loss)
(Hysteresis loss) = (Hysteresis loss coefficient) x (Frequency)
(Eddy current loss) = (Eddy current loss coefficient) x (Frequency) ²

  As is clear from the results in Table 1, it can be seen that Sendust of Sample No. 1-1 has a low magnetic loss but a low iron loss.

  Next, in Sample No. 1-2, in which pure iron was added to Sendust, the magnetic permeability was higher than Sendust, but the iron loss was greatly increased.

Sample No. 1-3 uses a soft magnetic powder obtained by adding permalloy to Sendust. Although the permeability is improved compared to Sendust, the iron loss is greatly increased. This is presumably because the temperature was raised in the atmosphere exchange process of both heat treatments, and the Fe ₂ O ₃ phase, which was an oxidation phase, was formed on the outer periphery of the permalloy particles in the process. It is also considered that a relatively large amount of FeNi ₃ ordered phase having a large coercive force was precipitated. This is supported by the results of photographic analysis and X-ray diffraction described later.

  Sample No. 1-4 has a significantly improved permeability compared to Sendust of sample No. 1-1, and the iron loss is relatively close to that of sample 1-1. For sample No.1-4, the soft magnetic powder material is the same as sample No.1-3, but the replacement is completed without raising the temperature in the process of changing the atmosphere from the first heat treatment to the second heat treatment. Hold at 450 ° C until Therefore, it is considered that the generation of an oxidized phase that affects the coercive force is suppressed and the iron loss is reduced. In particular, it can be seen that the hysteresis loss is significantly reduced as compared with Sample No. 3.

Sample No. 1-5 has the same magnetic permeability as sample No. 1-4, and the iron loss is further reduced. This is presumably because the precipitation of FeNi ₃ ordered phase having a large coercive force was suppressed because quenching was performed in the cooling process in the second heat treatment of Sample No. 5.

[Test Example 2: Photo analysis]
Next, Sample Nos. 1-3 and No. 1-5 in Test Example 1 were photographed with an SEM, and the structure of the obtained dust core was evaluated. Each particle component in the photograph was identified by EDS (Energy-dispersive X-ray Spectroscopy). The result is shown in FIG.

Comparing the photograph of sample No.1-5 shown in FIG. 2 (A) with the photograph of sample No.1-3 shown in FIG. 2 (B), the former has few Fe ₂ O ₃ phases and the FeNi ₃ rule It can be seen that there is little phase precipitation. That is, it is considered that the formation of the Fe ₂ O ₃ phase is suppressed by maintaining the temperature at 450 ° C. without increasing the temperature in the process of switching the atmospheres of the first heat treatment and the second heat treatment. Further, it is considered that precipitation of the FeNi ₃ ordered phase is suppressed by quenching in the cooling process of the second heat treatment step.

[Test Example 3: X-ray diffraction]
Next, each sample was analyzed by an X-ray diffraction method to obtain an X-ray diffraction pattern, and the peak intensity of each material was examined. In this test example, X-ray diffraction was performed on three types of samples No. 2-1 to No. 2-3. Sample No. 2-1 (Pattern 3) corresponds to Sample No. 1-5 in Test Example 1, and Sample No. 2-3 (Pattern 1) corresponds to Sample No. 1-3 in Test Example 1. In Sample No. 2-2, in the process of changing the atmosphere from the first heat treatment to the second heat treatment, the temperature increase was started when the oxygen concentration was 5000 ppm. The other temperature history of sample No. 2-2 is the same as that of sample No. 2-1. Further, for Sample No. 2-2, the magnetic permeability and iron loss were examined in the same manner as in Test Example 1.

When the diffraction patterns of the two samples were compared, the first peak of the Fe ₂ O ₃ phase was more noticeable in sample No. 2-1 than in sample No. _2-3 .

Further, the following diffraction intensity ratio was determined from this X-ray diffraction pattern.
Integral intensity of 1st peak of Fe ₂ O ₃ / {(Integral intensity of 1st peak overlapping Fe-Si-Al and Fe-Ni x volume of Fe-Ni in total volume of Fe-Si-Al and Fe-Ni Fraction) + integrated intensity of 1st peak of FeNi ₃ }

The 1st peak of each material is the 1st peak of each material in the JCPDS card. For example, the integrated intensity at the peak of 2θ = X1 is indicated by the area of the hatched portion in FIG. Specifically, it is represented by the following expression using an approximate expression of the peak. The horizontal axis in FIG. 3 represents the background line, and A ₁ and B ₁ in the approximate expression in the figure are constants that are appropriately selected according to the peak curve.
Integral intensity = (area of the portion surrounded by the approximate expression at each peak and y = y _max / 2) + (half-value width x y _max / 2)

  For example, FIG. 4 shows the diffraction pattern of Sample No. 2-3. In this diffraction pattern, each 1st peak of Fe—Si—Al and Fe—Ni (indicated by ○) overlaps each other. Therefore, the integrated intensity of the 1st peak of Fe—Si—Al and Fe—Ni is used with this overlapping peak as one peak. Multiply "(Integral intensity of the 1st peak where Fe-Si-Al and Fe-Ni overlap)" by "Fe-Ni volume fraction of total volume of Fe-Si-Al and Fe-Ni". Thus, the integrated intensity of the 1st peak of Fe-Ni corresponding to the volume fraction of Fe-Ni in the soft magnetic powder is obtained. Table 2 shows the oxygen concentration in the atmosphere and the peak intensity ratio (indicated simply as “peak ratio” in Table 2) when the temperature increase was started when the atmosphere of each sample was changed.

  As is clear from Table 2, when the atmosphere is changed during the transition from the first heat treatment to the second heat treatment, if the oxygen concentration is kept below 500 ° C. until the oxygen concentration becomes 5000 ppm or less, the diffraction peak intensity ratio Is 0.45 or less, and it can be seen that the formation of an oxidized phase is suppressed. As a result, a low iron loss powder magnetic core can be obtained.

[Test Example 4: Cooling conditions for second heat treatment]
Furthermore, the relationship between the cooling rate in the cooling process of the second heat treatment and the magnetic properties of the dust core was investigated. In this test example, four types of samples No. 3-1 to No. 3-4 were prepared by changing the cooling rate, and the magnetic permeability and iron loss were examined in the same manner as in Test Example 1. Sample No. 3-1 corresponds to Sample No. 1-5 in Test Example 1. FIG. 5 shows the temperature history of the cooling process of each sample, and Table 3 shows the results.

As is apparent from Table 3, the iron loss in Sample No. 3-3 and Sample No. 3-4 is 1050 kW / m ³ or more, whereas Sample No. 3-1 and Sample No. 3-2 in the iron loss is a ^three 1010kW / m. Therefore, it can be said that if the cooling rate is a rapid cooling of 1 ° C./min or more, it is effective for suppressing precipitation of the FeNi ₃ ordered phase. Further, FIG. 5 shows that if the temperature range from 500 ° C. to 350 ° C. at which the FeNi ₃ ordered phase is likely to precipitate is cooled early, it is effective in suppressing the precipitation of the FeNi ₃ ordered phase. As long as this temperature range is rapidly cooled, the cooling in other temperature ranges may not be rapid.

[Test Example 5: Relationship between second heat treatment temperature and loss]
Next, the relationship between the heating temperature and loss in the second heat treatment was examined. Samples here are based on Sample No. 1-5 in Test Example 1, and the heating temperature was changed to prepare a total of 6 types of samples. As in Test Example 1, iron loss, eddy current loss, and hysteresis loss were obtained. Asked. The results are shown in FIG.

  As is apparent from FIG. 6, it can be seen that when the heating temperature is 600 ° C. or higher, the hysteresis loss is greatly reduced. On the other hand, when the temperature exceeds 850 ° C., vortex loss increases. Therefore, it can be seen that the iron loss represented by the sum of hysteresis loss and vortex loss can be effectively reduced by performing the second heat treatment at 600 ° C. or higher and 850 ° C. or lower. In particular, the iron loss is remarkably low at 750 ° C. or higher and 800 ° C. or lower.

  In addition, the Example of this invention is not necessarily limited to the Example mentioned above, In the range which does not deviate from the summary of this invention, it can change suitably.

  The dust core of the present invention can be suitably used for a high-frequency choke coil, a high-frequency tuning coil, a bar antenna coil, a power choke coil, a power transformer, a switching power transformer, a reactor, and the like. The method for manufacturing a dust core of the present invention can be suitably used to obtain dust cores used for various inductors.

Claims (6)

A dust core comprising a coating powder composed of a plurality of coated particles having an insulating coating on the surface of soft magnetic particles, and a shape-retaining material that integrates these coated particles,
The soft magnetic particles are composed of mixed particles of Fe-Si-Al alloy particles, Fe-Ni alloy particles,
A dust core having a diffraction peak intensity ratio of 0.45 or less when the dust core is analyzed by an X-ray diffraction method.
Integral intensity of 1st peak of Fe ₂ O ₃ / {(Integral intensity of 1st peak overlapping Fe-Si-Al and Fe-Ni x volume of Fe-Ni in total volume of Fe-Si-Al and Fe-Ni Fraction) + integrated intensity of 1st peak of FeNi ₃ } The mixing of the mixed particles is in mass%,
Fe-Si-Al alloy particles are 80% or more and 99% or less,
2. The dust core according to claim 1, wherein the Fe—Ni alloy particles are 1% or more and 20% or less. 3. The dust core according to claim 1, wherein the Fe—Si—Al alloy particles are made of a material in which the contents of Si and Al in the alloy satisfy the following formula.
{Si content + (Al content / 2)} ≧ 5 mass% A raw material powder preparation step of preparing a coating powder composed of a plurality of coated particles having an insulating coating on the surface of soft magnetic particles composed of mixed particles of Fe-Si-Al alloy particles and Fe-Ni alloy particles;
A granulating step of mixing and granulating a molding resin for retaining the molded body in this coating powder; and
A molding process for compressing and molding this granulated powder into a green compact,
A first heat treatment step of evaporating the binder by heating the green compact to a predetermined temperature in an air atmosphere;
A second heat treatment step for relieving the distortion of the soft magnetic powder constituting the powder compact by heating the compact after the first heat treatment step to a predetermined temperature in a non-oxidizing atmosphere and then cooling it,
When the atmosphere is changed during the transition from the first heat treatment step to the second heat treatment step, the atmospheric temperature is maintained at 500 ° C. or less until the oxygen concentration in the atmosphere becomes 5000 ppm or less. Manufacturing method of a powder magnetic core.   5. The method of manufacturing a dust core according to claim 4, wherein the cooling process in the second heat treatment step is performed by rapidly cooling a temperature range of 500 ° C. to 350 ° C. at 1 ° C./min or more.   6. The method for producing a dust core according to claim 4, wherein the heating temperature in the second heat treatment step is 600 ° C. or higher and 850 ° C. or lower.