JP2006128216A - Composite magnetic particles and composite magnetic parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite magnetic material capable of achieving both high magnetic permeability and low eddy current loss in a high frequency region.
A composite magnetic particle in which metal magnetic particles are coated with an oxide magnetic material coating, wherein the metal magnetic particles are made of a Ni-Fe-Mo alloy, and the composite A composite magnetic component, wherein a magnetic particle powder is molded and then heat-treated.
[Selection] Figure 1

Description

  The present invention relates to composite magnetic particles and composite magnetic parts produced using the composite magnetic particles. More specifically, the present invention relates to a composite magnetic material that can be used for magnetic parts such as a transformer and a reactor mounted on a switching power supply and the like and can achieve both high magnetic permeability and low eddy current loss in a high frequency region.

  In recent years, various electronic devices have been required to be smaller and lighter and to have lower power consumption. In connection with this, the request | requirement with respect to a highly efficient and small switching power supply as a power supply mounted in an electronic device is increasing. In particular, switching power supplies used in small information devices such as notebook computers and mobile phones, thin CRTs, and flat panel displays are strongly required to be small and thin. In conventional switching power supplies, the main components such as transformers and reactors occupy a large volume. To reduce the size and thickness of switching power supplies, the volume of these magnetic parts must be reduced. It was essential to scale down.

  Conventionally, metal magnetic materials such as Sendust and Permalloy, and oxide magnetic materials such as ferrite have been used for such magnetic parts. Metallic magnetic materials generally have a high saturation magnetic flux density but have a low electrical resistivity, so that eddy current loss increases particularly in a high frequency region. Since switching power supplies tend to be highly efficient and miniaturized by driving the circuit at high frequency, it is difficult to use metal magnetic materials for magnetic parts for switching power supplies due to the effects of the above eddy current loss. is there. On the other hand, an oxide magnetic material typified by ferrite has a higher electrical resistivity than a metal magnetic material, and therefore, eddy current loss that occurs even in a high frequency region is small. However, when a transformer or reactor is used for power applications such as a switching power supply, an alternating current is often applied in a state where a direct current is superimposed on a coil, and generally the saturation magnetic flux density of ferrite is higher than that of a metal magnetic material. Since it is small, when a DC magnetic field is applied, it is magnetically saturated and the magnetic permeability is significantly reduced. Thus, it has been difficult to satisfy both high frequency driving and miniaturization required for the magnetic components of the switching power supply, regardless of which material is used.

Therefore, as a magnetic material having the advantages of both a metal magnetic material and an oxide magnetic material, a film of an oxide magnetic material having a high electrical resistivity is formed on the surface of a metal magnetic material having a high saturation magnetic flux density and a high magnetic permeability. Magnetic materials have been proposed (see Patent Document 1). Further, the surface of the metallic magnetic material consisting of 1~10μm particles _M-Fe x _{O 4} (where, M = Ni, Mn, Zn , x ≦ 2) coated with a metal oxide magnetic material of the spinel composition represented by A high-density sintered magnetic material is proposed (see Patent Document 2). Furthermore, a ferromagnetic fine particle powder of a metal or intermetallic compound having a ferrite layer coating formed by ultrasonic excitation ferrite plating on the surface is compression-molded, and a magnetic field is generated between the ferromagnetic particles via the ferrite layer. There is also proposed a composite magnetic material characterized in that the material is formed (see Patent Document 3).

JP-A-53-091397 JP 56-038402 A WO03 / 015109 pamphlet

  Metallic magnetic particles coated with an oxide magnetic material (ferrite or the like) film can obtain a high magnetic permeability by heat treatment after compression molding. This is because an interface layer magnetically coupled is formed by element diffusion between the oxide magnetic material coating and the metal magnetic particles. However, it has been found that a high proportion of Fe in the metal magnetic particles has a negative effect on the magnetic permeability obtained when heat treatment is performed after compression molding. It has been found that this is caused by the decomposition of the ferrite coating because the element diffusion between the oxide magnetic material coating such as ferrite and the metal magnetic particles proceeds excessively.

  Therefore, the present invention provides an oxide magnetic material such as ferrite due to excessive element diffusion by forming an interface layer magnetically coupled by element diffusion between the oxide magnetic material film and the metal magnetic particles in the heat treatment. It is an object of the present invention to provide composite magnetic particles or composite magnetic materials that can achieve both high magnetic permeability and low eddy current loss in a high frequency region by preventing the decomposition of the coating.

  In order to solve the above problems, the composite magnetic particle according to the first embodiment of the present invention is a composite magnetic particle in which the metal magnetic particle is coated with an oxide magnetic material coating, wherein the material of the metal magnetic particle is Ni- It is an Fe—Mo alloy.

  The composite magnetic component according to the second embodiment of the present invention is characterized in that the composite magnetic particle powder is molded and then heat-treated.

  The composite magnetic material obtained by the composite magnetic particles of the present invention can prevent the oxide magnetic material coating such as ferrite from being decomposed, and also increases the electrical resistivity of the metal magnetic particles by adding Mo itself, so that it can be used in a high frequency region. It is possible to achieve both high magnetic permeability and low eddy current loss.

  1 In the first embodiment of the present invention, in the composite magnetic particle in which the metal magnetic particle is coated with an oxide magnetic material film, the material of the metal magnetic particle is a Ni—Fe—Mo alloy. A composite magnetic particle is provided.

(1) The metal magnetic particles of the present invention are particles made of an alloy having soft magnetic properties and are Ni-Fe-Mo alloys.

  The Mo ratio in the Ni-Fe-Mo alloy prevents the formation of nonmagnetic iron oxides such as FeO in the interface layer during heat treatment or the decomposition of the oxide magnetic material coating, and the electric resistance of the metal magnetic particles. From the viewpoint of increasing the rate, it is preferably 3% by weight or more, more preferably more than 5% by weight, particularly preferably 6% by weight or more, and preferably 15% by weight from the viewpoint of suppressing a decrease in magnetic permeability of the metal magnetic particles. % Or less, and particularly preferably 10% by weight or less. Here, the Mo ratio means the Mo content (% by weight) in the metal magnetic particles.

  In addition, the average particle size of the metal magnetic particles (50% particle size: measured with a laser diffraction / scattering type particle size distribution analyzer) is easy to handle, has good packing density during molding, and good permeability characteristics. In view of the above, it is preferably 1 μm or more, more preferably 5 μm or more, and from the viewpoint of suppressing the occurrence of loss due to eddy currents at high frequencies, preferably 100 μm or less, more preferably 25 μm or less, and even more preferably 15 μm or less. is there.

  Further, the metal magnetic particles may contain other optional components as long as the effects of the present invention are not impaired.

  Further, the metal magnetic particles can be obtained, for example, by adding Mo to a Ni—Fe alloy. Specifically, the metal magnetic particles are known to those skilled in the art such as a metal magnetic material pulverization method, a water atomization method, and a gas atomization method. It can be produced by any known method. However, from the viewpoint of particle shape stability and mass productivity, it is preferable to use a water atomization method, which is a method of instantly pulverizing and rapidly solidifying molten metal using high-pressure water to produce metal powder.

(2) The oxide magnetic material of the present invention refers to an oxide having soft magnetic properties, and is preferably a ferrite from the viewpoint of having a high magnetic permeability, particularly Ni-Zn ferrite for high frequency applications. Is more preferably used.

  The film thickness of the oxide magnetic material coating is preferably in the range of 10 to 200 nm, more preferably in the range of 25 to 100 nm, from the viewpoint of being able to cope with high frequencies and obtaining high magnetic permeability.

  Moreover, as a method of forming the coating of the oxide magnetic material, for example, an ultrasonic excitation ferrite plating method described in Patent Document 3 can be used.

  2 In a second embodiment of the present invention, there is provided a composite magnetic part, wherein the composite magnetic particle powder is molded and then heat-treated.

(1) In forming the composite magnetic particle powder, the composite magnetic particle produced as described above is formed into a desired magnetic core shape by pressing to form a green compact. For example, the composite magnetic particles can be filled in a cemented carbide mold and formed into a ring shape by uniaxial pressing.

(2) Next, the green compact is heat-treated.

  The heat treatment temperature is preferably 500 ° C. or higher, more preferably 650 ° C. or higher, from the viewpoint of preventing the magnetic permeability from being reduced by forming the interface layer, and the excessive amount of Fe from the oxide magnetic material coating such as ferrite. From the viewpoint of preventing nonmagnetic iron oxides such as FeO from being generated in the interface layer due to diffusion and preventing the magnetic permeability from decreasing, the temperature is preferably 900 ° C. or lower, more preferably 750 ° C. or lower. In addition, the heat treatment time is preferably 1 second or more for the sample to be 500 ° C. or more from the viewpoint of sufficiently heating the inside of the green compact and suppressing the decrease in magnetic permeability, such as ferrite From the viewpoint of preventing non-magnetic iron oxide such as FeO from forming in the interface layer due to excessive diffusion of Fe from the oxide magnetic material film, the sample becomes 500 ° C. or higher. The time is preferably within 10 minutes, more preferably within 3 minutes.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(Examples 1-5, Comparative Example 1)
As the metal magnetic particles, various Ni—Fe—Mo alloy particles having an average particle diameter of 8 μm prepared by a water atomization method were prepared. Here, the Mo ratio was 0 to 20% by weight, and the Fe ratio was 40% by weight.

Next, a ferrite film that is an oxide magnetic material is formed on the surface of the metal magnetic particles. The coating with this ferrite film was performed by the ultrasonic excitation ferrite plating method described in Patent Document 3. Specifically, the metal magnetic particles were transferred into a glass plating reaction vessel containing pure water, and 19.5 kHz ultrasonic waves were applied. In this reaction vessel, a metal ion solution (H ₂ O: 500 ml, FeCl ₂ · 4H ₂ O: 7.95 g, NiCl ₂ · 6H ₂ O: 2.38 g, ZnCl ₂ : 1.36 g, MnCl ₂ · 4H ₂ O: 0.026 g) and an oxidizing agent solution (H ₂ O: 500 ml, NaNO ₂ : 1.00 g) were respectively supplied at a constant rate, and the pH was kept at 10.0 by appropriately dropping ammonia water. After this plating treatment was performed for 30 minutes, the particles were classified and dried to form composite magnetic particles in which Ni—Fe—Mo alloy particles having an average particle diameter of 8 μm were coated with a ferrite film of about 50 nm.

The above composite magnetic particles are filled into a cemented carbide mold and formed into a ring core shape having an inner diameter of 3 mmφ, an outer diameter of 8 mmφ, and a height of about 3 mm by uniaxial pressing of 980 MPa (10 ton weight / cm ² ). Produced.

  The heat treatment was performed at a relatively rapid temperature rise and fall as follows. In particular, at a temperature of 500 ° C. or higher, the temperature was increased at a rate of 100 ° C./min or higher, and held at a temperature range of 600 ° C. to 900 ° C. for 1 second to 10 seconds. Further, the temperature was lowered at a rate of 100 ° C./min or higher until the temperature reached 500 ° C. or lower.

An inductor was produced by winding a conductor wire coated with insulation on the ring-type green compact after the heat treatment, and the relative permeability μ _s at a frequency of 1 MHz was measured using an AC BH analyzer. For reference, the relative permeability at a frequency of 100 kHz was also measured. The results are shown in Table 1.

  From Table 1, it can be seen that Examples 1-4 of the present invention have a high relative permeability of 100 or more at a high frequency of 1 MHz as well as a frequency of 100 kHz. Further, even when the Mo ratio is 20% by weight, it can be seen that the relative permeability at 1 MHz is improved as compared with Comparative Example 1. On the other hand, Comparative Example 1 that does not contain Mo shows a high relative permeability at a frequency of 100 kHz, but the relative permeability at a high frequency of 1 MHz is insufficient.

  As is apparent from the results, the composition of the metal magnetic particles is a Ni—Fe—Mo alloy, more preferably, the Mo ratio of the alloy particles is 3 wt% or more and 15 wt% or less. It can be seen that a high relative permeability can be obtained even in the high frequency region. This is considered to be because Mo in the metal magnetic particles during the heat treatment suppressed the progress of element diffusion more than necessary between the ferrite coating and the metal magnetic particles. For this reason, the element between the ferrite coating and the metal magnetic particles It is considered that the magnetically coupled interface layer can be formed by diffusion and the decomposition of ferrite can be prevented.

  Moreover, in FIG. 1, the XRD (X-ray diffraction) pattern 11 of the compacting body of Example 1 and the XRD of the compacting body to which Mo obtained in Comparative Example 1 is not added are compared for comparison. Pattern 12 is shown. As is apparent from this result, it can be seen that the formation of nonmagnetic iron oxides such as FeO is suppressed by using a Ni-Fe-Mo alloy as the composition of the metal magnetic particles.

  By using the composite magnetic material of the present invention, it is possible to produce a high-functional, small, and thin magnetic component for a switching power source such as a notebook personal computer, a small portable device, and a thin display.

It is an XRD pattern of the compacting body obtained in Example 1 and Comparative Example 1.

Explanation of symbols

11 XRD pattern of the green compact obtained in Example 1 12 XRD pattern of the green compact obtained in Comparative Example 1

Claims (5)

  A composite magnetic particle in which metal magnetic particles are covered with an oxide magnetic material coating, wherein the material of the metal magnetic particles is a Ni-Fe-Mo alloy.   2. The composite magnetic particle according to claim 1, wherein the Mo ratio in the metal magnetic particle is 3 wt% or more and 15 wt% or less.   The composite magnetic particle according to claim 1, wherein the magnetic oxide material is ferrite.   The composite magnetic particle according to claim 3, wherein the ferrite is Ni—Zn ferrite.   A composite magnetic part, wherein the composite magnetic particle powder according to claim 1 is molded and then heat-treated.

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