JP2008195970A - Composite magnetic material, powder magnetic core and magnetic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite magnetic material which has superior direct-current-superimposition characteristics and provides superior magnetic properties through a high-frequency power; a powder magnetic core using the same; and a magnetic element using the same. <P>SOLUTION: A powder of a magnetic metal material has a composition containing 6 to 7 wt.% Si, 5 wt.% or less (including 0 wt.%) Cr, with respect to the total magnetic metal material and the balance Fe with unavoidable impurities; has a saturated magnetic flux density of 1.2 T or more at ordinary temperature; and has a specific resistance of 0.8 μΩm or more. The composite magnetic material is obtained by the steps of: annealing the powder of the magnetic metal material; and mixing an insulative binding agent of 1 to 10 wt.% with respect to the powder of the magnetic metal material into the powder. The powder magnetic core or the magnetic element is produced by using the composite magnetic material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite magnetic material for an inductance component such as a choke coil and an inductor, a dust core and a magnetic element using the same.

  In recent years, power inductors are required to handle large currents as the power supply voltage decreases. In particular, electronic devices are becoming smaller and power supplies have higher frequencies, and magnetic materials and high-performance magnetic elements that can cope with them have been demanded. Conventionally, a ferrite is often used in a magnetic core such as an inductor used in a high frequency band. Since ferrite is cheaper than metal magnetic material powder, it has been used in many choke coils and noise filters as a magnetic element material that has changed to metal magnetic material powder, which has been the mainstream until now. In response to recent demands for small size and large current, metal magnetic material powder having a high saturation magnetic flux density has been used as a magnetic element magnetic core again. In particular, the powder magnetic core of the metal magnetic material powder has attracted attention as a magnetic element corresponding to higher frequency of electronic parts in recent years because the characteristics are stable even in a high frequency band.

  Patent Document 1 proposes a composite magnetic material composed of soft magnetic alloy powder and an insulating binder. In this method, heat treatment is performed at a temperature of 500 to 1000 ° C. in a nitrogen atmosphere after the metal magnetic powder before adding the insulating binder or pressure molding as a composite magnetic material. According to the above literature, before the pressure-formed body is annealed at a temperature of 700 to 1000 ° C. in a non-oxidizing atmosphere, heat treatment is performed at a temperature of 500 to 1000 ° C. in the nitrogen atmosphere. Magnetic properties can be obtained. As a result, it is necessary to perform heat treatment twice at a high temperature, and it is necessary to perform annealing at 700 to 1000 ° C. in a non-oxidizing atmosphere after the composite magnetic material is pressure-molded. In addition to the increase, in a magnetic element formed by compacting a composite magnetic material so as to include an air-core coil composed of a conductor whose surface is coated, there is a risk that the conductor covering is thermally decomposed and rarely short-circuited This is a highly reliable method.

  Patent Document 2 proposes a composite magnetic material comprising a soft magnetic alloy powder and an insulating binder and its magnetic element. According to this document, after forming a dust magnetic element using a composite magnetic material composed of a metal magnetic material powder and an insulating binder, the insulating binder is cured at a low temperature of 80 ° C. or higher in air. By performing a heat treatment for oxidizing the metal magnetic material, a magnetic element having excellent corrosion resistance and excellent magnetic characteristics can be produced. In general, it is desirable to perform annealing to alleviate the strain of the metal magnetic material because the iron loss, particularly hysteresis loss, is reduced by reducing the strain in the material. However, in the above document, the metal magnetic material powder is annealed. Not.

  In order to reduce the influence of strain in a metal magnetic material, it is desirable to use a magnetic material powder having a magnetostriction constant of about 0, such as PC permalloy in which the send material or nickel is about 80% by weight. However, although PC permalloy with nickel of around 80% by weight is a low magnetic loss and high permeability material, it cannot obtain excellent DC superposition characteristics because of its low saturation magnetic flux density. In addition, there is a problem that the volume resistivity is low and the magnetic loss at high frequency is increased, which is not suitable as a dust core used at high frequency. Moreover, since expensive nickel is contained in an amount of about 80% by weight, there is a problem that the material cost becomes high in terms of component composition.

  Patent Document 3 proposes a sendust powder for a metal composite core. Good characteristics with low coercive force and low magnetic loss are obtained. However, it is difficult to use Sendust powder because the saturation flux density of Sendust is 1.1 T or less and the magnetic element that requires excellent DC superposition characteristics has a low saturation flux density.

JP 2003-243215 A JP 2003-160847 A JP 2003-68513 A

  In general, a metal magnetic material made of an Fe-based alloy needs to be annealed at a temperature of at least 600 ° C. to 700 ° C. in order to relieve strain remaining in the material. Therefore, it is preferable that the powder magnetic core made of the metal magnetic material powder is annealed at a temperature of 600 ° C. to 700 ° C. or more after the forming process. However, in the composite magnetic material, there is a problem that the insulating binder to be mixed is thermally decomposed, and it is difficult to perform annealing to relieve strain after molding. In addition, in a magnetic element in which an air-core coil composed of a conductive wire whose surface is coated and a composite magnetic material are integrally formed, the coating of the conductor of the built-in air-core coil is thermally decomposed, and there is a high risk of causing a short circuit. Therefore, it is difficult to anneal the magnetic element. Due to such problems, many composite magnetic materials and magnetic elements made of composite magnetic materials cannot be annealed after molding, and magnetic elements made of composite magnetic materials have good characteristics without annealing the composite magnetic material. It is necessary to study the powder and method of magnetic material to be used.

  In this situation, an object of the present invention is to provide a composite magnetic material that is excellent in direct current superposition characteristics and has excellent magnetic characteristics at high frequencies, and a dust core and a magnetic element using the same.

  As the power supply voltage is lowered, a magnetic element that is required to handle a large current is required to cope with a higher frequency of electronic components. Therefore, a composite magnetic material required for a magnetic element is also required to be a magnetic material having excellent magnetic properties at high frequencies.

  Since a magnetic element having excellent DC superposition characteristics can be obtained as the saturation magnetic flux density of the magnetic material is higher, the magnetic material preferably has a saturation magnetic flux density of 1.2 T or more. Moreover, since the iron loss reduction at a high frequency can be achieved when the volume specific resistance is large, the magnetic material preferably has a volume specific resistance of 0.8 μΩm or more. However, a metal magnetic material made of an Fe-based alloy has a tendency that the saturation magnetic flux density tends to decrease as the volume specific resistance increases, so the balance between the saturation magnetic flux density and the volume specific resistance must be taken into consideration.

  The powder that is molded is preferably a metal magnetic material powder that is excellent in molding processability and that provides excellent magnetic properties with a dust core. In addition, the composite magnetic material that cannot be annealed to relieve strain and the metal magnetic material powder used in the magnetic element using the composite magnetic material are preferably magnetic material powders that provide good magnetic properties after compacting, A powder of a magnetic material having a magnetostriction constant that is hardly affected by strain and near zero is more preferable.

  By annealing the metal magnetic material powder in a non-oxidizing atmosphere at a temperature of 600 ° C. or higher and 800 ° C. or lower before mixing with the insulating binder, strain in the metal magnetic material powder can be alleviated. In general, a metal magnetic material made of an Fe-based alloy is annealed at a temperature of about ½ of the melting point, so that the strain is relaxed. Therefore, it is desirable to heat-treat at least 600 ° C. However, in the composite magnetic material obtained by mixing the metal magnetic material powder and the insulating binder, annealing the composite magnetic material is difficult because the insulating binder is thermally decomposed when annealed at 600 ° C. or higher. is there. Moreover, when annealing the powder of the metal magnetic material before forming the composite magnetic material, there is a problem that the powder is sintered when annealed at a temperature of 900 ° C. or higher.

  In order to reduce the iron loss of a magnetic element at high frequency, it is necessary to reduce eddy current loss. In order to reduce the eddy current loss at high frequencies, it is effective to reduce the particle size of the metal magnetic material or increase the specific resistance of the metal magnetic material. As the particle size is smaller, the effect of suppressing the eddy current loss is expected. When the particle size exceeds 50 μm, the eddy current loss increases, and the powder shape tends to be deformed. On the contrary, if the particle size is less than 1 μm, there is a problem that the effective permeability of the molded body does not increase and the powder yield is deteriorated, and the metal powder particle size is suitably from 1 μm to 50 μm.

  The insulating binder is not a problem as long as it is a thermosetting resin material such as a phenol resin, an epoxy resin, or a silicone resin. When the mixing amount of the insulating binder is less than 1% by weight with respect to the metal magnetic material powder, the binding force between the metal magnetic material powders is weak, and when it exceeds 10% by weight, the powder filling rate of the magnetic core decreases, and the magnetic element magnetic properties are reduced. Since the characteristics are deteriorated, the amount of the insulating binder mixed is preferably 1 wt% or more and 10 wt% or less with respect to the metal magnetic material powder (100 wt%).

  In addition, these composite magnetic material powders consisting of thermosetting resin and metal magnetic material powder can be obtained by heat-curing the insulating binder in an inert gas during or after pressure molding of the powder magnetic core. It is desirable to manufacture a magnetic element.

  In summary, the composite magnetic material of the present invention is a composite formed by mixing a metal magnetic material powder and 1 to 10% by weight of an insulating binder expressed as a ratio to the total weight of the powder. In the magnetic material, the metal magnetic material powder has a Si content of 6 wt% to 7 wt%, a Cr content of 5 wt% or less (including 0 wt%), the balance being Fe and inevitable with respect to the total weight of the powder. It is characterized in that it is annealed at a temperature of 600 ° C. or higher and 800 ° C. or lower in a non-oxidizing atmosphere before mixing with the insulating binder. The metal magnetic material has a saturation magnetic flux density of 1.2 T or more and a volume resistivity of 0.8 μΩm or more. The metal magnetic material powder has an average particle size of 1 μm or more and 50 μm or less.

  The dust core of the present invention is characterized by using the composite magnetic material.

  The magnetic element according to the present invention is characterized in that the composite magnetic material is compacted so as to include an air-core coil made of a conductive wire whose surface is coated.

  According to the present invention, it is possible to provide a composite magnetic material having a high saturation magnetic flux density and excellent magnetic characteristics even at high frequencies. The composite magnetic material has excellent DC superposition characteristics and excellent magnetic characteristics even at high frequencies. Can be provided. In addition, it is possible to obtain a magnetic element with excellent characteristics by winding the powder magnetic core, and furthermore, an air-core coil composed of a surface-coated lead wire and composite magnetism that has characteristics effective even at high frequencies. It is possible to provide a small magnetic element in which materials are integrally formed.

  An embodiment of the present invention will be described.

(Embodiment 1) First, a magnetic element according to the present invention and a magnetic core used therefor will be described. FIG. 1 shows an example of a dust core shape, FIG. 1 (a) is a perspective view of an E-type core, FIG. 1 (b) is a perspective view of a cylindrical or toroidal core, and FIG. It is a perspective view. FIG. 2 shows an example of a magnetic element, FIG. 2 (a) is a perspective view showing an inductance part by an EI type core, FIG. 2 (b) is a perspective view showing an integrally formed type inductance part, 21 is a magnetic core, 22 is a perspective view. Is a winding part, 23 is an integral mold core, and 24 is a winding part.

  Next, a composite magnetic material used for such a magnetic core will be described.

  First, metal magnetic materials were selected. A typical soft magnetic material and an Fe—Cr alloy-based magnetic material were produced by the water atomization method, and the saturation magnetic flux density at room temperature and the volume resistivity were compared. The results are shown in Table 1.

  ○ when the saturation magnetic flux density at room temperature is 1.2T or more, ○ when it is less than 1.2T, ○ when the volume resistivity is 0.8μΩm or more, and × when it is less than 0.8μΩm. . It can be seen that pure iron and 1 to 3% silicon steel composition have high saturation magnetic flux density but low volume resistivity. Sendust has a high volume resistivity but a low saturation magnetic flux density, and PC permalloy has a low saturation magnetic flux density and a volume resistivity.

  FIG. 3 shows changes in saturation magnetic flux density Bs due to Cr components in Fe and Fe—Si alloys, and FIG. 4 shows changes in volume resistivity ρ due to Cr components in Fe and Fe—Si alloys. Note that Fe-3Si and Fe-6.5Si contain 3 wt% and 6.5 wt% Si, respectively. From this data, it is effective to increase the amount of Si and Cr in order to increase the volume resistivity ρ, but there is also a problem that the saturation magnetic flux density Bs decreases conversely. It is necessary to select materials considering both.

  The material selected as described above, that is, Si—Cr having a component composition of 6 to 7% by weight, 5% by weight or less (including 0% by weight) of Cr, and the balance of Fe and inevitable impurities. The composite magnetic material of the present invention can be obtained using a -Fe alloy.

  Sample No. in Table 1 A metal powder corresponding to 4 to 13 (mainly a component composition with a saturation magnetic flux density at room temperature of 1.2 T or more and a volume resistivity of 0.8 μΩm or more) was prepared by a water atomization method, and a ring A dust core with a shape was prepared. The average particle size of each powder was adjusted to a range of about 10 to 12 μm. A thermosetting epoxy resin was used as the insulating binder, and an amount of 5% by weight with respect to these powders was mixed and kneaded. The granulated composite magnetic powder was then sized with a sieve to 500 μm or less. The composite magnetic powder was mixed with 0.5% by weight of zinc stearate and filled in a press mold having an outer diameter of 14 mm and an inner diameter of 10 mm, and the dust ring core was press-molded. Thereafter, heat treatment was performed at 150 ° C. in a nitrogen atmosphere to thermally cure the insulating binder, and a powdered ring core with a powder space factor of 75% was produced. At this time, as for the powder of each metal magnetic material, prepare one that is not annealed before mixing the insulating binder and one that is annealed at 700 ° C. in an argon atmosphere. Each dust ring core was produced.

  Table 2 shows an example of the effective magnetic permeability and iron loss of the powder ring core produced as described above at a frequency of 300 kHz. In addition, in the powder of the metal magnetic material, the one that has been subjected to the above annealing has a higher effective magnetic permeability as a dust ring core, and as a result, the effect of improving the characteristics by annealing the powder of the metal magnetic material is seen. ○ is displayed. Similarly, in the metal magnetic material powder, the above-mentioned annealing has a lower iron loss as a dust ring core, and as a result, the iron loss reduction effect by annealing the metal magnetic material powder was seen. Is displayed as ○.

  Saturation magnetic flux density is 1.2 T or more, volume resistivity is 0.8 μΩm or more, Si is 6 wt% or more and 7 wt% or less, Cr is 5 wt% or less (including 0 wt%), the balance is Fe and inevitable A composite magnetic material obtained by mixing a metal magnetic material powder composed of various impurities and an insulating binder has good characteristics. Sample No. The powder annealing effect of 13 Sendust is recognized, but since the saturation magnetic flux density does not reach 1.2T, it is not practical.

  In addition, the press element of the present embodiment is also excellent in press formability with respect to a magnetic element as shown in FIG. 2B in which an air-core coil made of a conductive wire coated with a surface and a composite magnetic material are integrally formed. As well as excellent magnetic properties.

(Embodiment 2)
In Table 1, sample no. A powder of a metal magnetic material having a component composition composed of 6.5% by weight of Si corresponding to 4 and the balance of Fe and inevitable impurities was prepared by a water atomization method. The powder was classified into particle sizes to obtain a powder having an average particle size of 10.47 μm, and then a ring-shaped dust core was produced. A thermosetting epoxy resin was used as the insulating binder, and an amount of 5% by weight with respect to this powder was mixed and kneaded. The granulated composite magnetic powder was then sized with a sieve to 500 μm or less. The composite magnetic powder was mixed with 0.5% by weight of zinc stearate and filled into a press mold having an outer diameter of φ14 mm and an inner diameter of φ10 mm, and the dust ring core was press-molded. Thereafter, heat treatment was performed at 150 ° C. in a nitrogen atmosphere to thermally cure the insulating binder, and a powdered ring core having a powder space factor of 75% was produced. At this time, the powder of the metal magnetic material is annealed in an argon atmosphere which is a non-oxidizing atmosphere at a temperature of 400 ° C. to 900 ° C. without annealing before mixing the insulating binder. Each powdered ring core was prepared under the above conditions. Table 3 shows an example of the iron loss of the frequency: 300 kHz of the powdered ring core produced as described above.

  In the case of annealing at 900 ° C., the powder was sintered and was not evaluated. Compared with the iron loss of the dust ring core by the unannealed powder, the iron loss of the powder ring core annealed at a temperature of 600 ° C to 800 ° C is lower, and the iron loss reduction effect of the dust core by annealing is seen It is done.

(Embodiment 3)
In Table 1, sample no. A powder of a metallic magnetic material having a component composition consisting of 7% by weight of Si corresponding to 8 and 2% by weight of Cr and the balance of Fe and inevitable impurities was prepared by a water atomization method. The powder was classified into particle sizes to obtain a powder having an average particle size of 10.01 μm, and then a ring-shaped dust core was produced. A thermosetting phenol resin was used as the insulating binder, and an amount of 4% by weight with respect to these powders was mixed and kneaded. The granulated composite magnetic powder was then sized with a sieve to 500 μm or less. The composite magnetic powder was mixed with 0.5% by weight of zinc stearate and filled in a press mold having an outer diameter of 14 mm and an inner diameter of 10 mm, and the dust ring core was press-molded. Thereafter, heat treatment was performed at 150 ° C. in a nitrogen atmosphere to thermally cure the insulating binder, and a powdered ring core having a powder space factor of 70% was produced. At this time, the powder of the metal magnetic material is prepared by annealing at 750 ° C. in an argon atmosphere before mixing the insulating binder, and each powdered ring core is manufactured under the above conditions. did. Table 4 shows an example of the effective magnetic permeability and eddy current loss of the powder ring core produced as described above at a frequency of 300 kHz.

  Thus, the smaller the average particle size of the metal magnetic material powder, the lower the effective magnetic permeability, and the larger the average particle size, the larger the eddy current loss. Practically, in a powder of a metal magnetic material having an average particle diameter of 1 μm or more and 50 μm or less, a low-loss powder magnetic core can be obtained without impairing the effective magnetic permeability.

The figure which shows an example of a powder magnetic core shape. 1A is a perspective view of an E-type core, FIG. 1B is a perspective view of a cylindrical or toroidal core, and FIG. 1C is a perspective view of a hooked core. The figure which shows an example of a magnetic element. FIG. 2A is a perspective view showing an inductance component using an EI type core, and FIG. 2B is a perspective view showing an integrally molded type inductance component. The figure which shows the change of the saturation magnetic flux density by Cr component in Fe and Fe-Si alloy. The figure which shows the change of the specific resistance by Cr component in Fe and Fe-Si alloy.

Explanation of symbols

21 Magnetic core 22 Winding part 23 Integrated molding magnetic core 24 Winding part

Claims (5)

  In a composite magnetic material obtained by mixing a metal magnetic material powder and an insulating binder in an amount of 1 wt% or more and 10 wt% or less expressed as a ratio to the total weight of the powder, the metal magnetic material powder is the powder Having a component composition comprising Si of 6 wt% or more and 7 wt% or less, Cr of 5 wt% or less (including 0 wt%), and the balance of Fe and inevitable impurities with respect to the total weight of A composite magnetic material characterized by being annealed at a temperature of 600 ° C. or higher and 800 ° C. or lower in a non-oxidizing atmosphere before mixing with a binder.   2. The composite magnetic material according to claim 1, wherein the metal magnetic material has a saturation magnetic flux density at room temperature of 1.2 T or more and a volume resistivity of 0.8 μΩm or more.   3. The composite magnetic material according to claim 1, wherein an average particle diameter of the metal magnetic material powder is 1 μm or more and 50 μm or less.   A powder magnetic core comprising the composite magnetic material according to claim 1.   A magnetic element obtained by compacting the composite magnetic material according to any one of claims 1 to 3 so as to include an air-core coil comprising a conducting wire whose surface is coated.

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