JPH10107541A - Composite magnetic body, its manufacture and electromagnetic interference suppressing body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin composite magnetic body with an excellent high frequency permeability characteristic and a high electromagnetic interference suppression effect. SOLUTION: Soft magnetic powder 2 each particle of which is processed to be flat and an organic binder 3 are kneaded with a solvent and the mixture is painted and dried to obtain a composite magnetic body 1. In this case, in order that a ratio of Hdd /Hdc a ratio of a demagnetizing field Hdd in a direction of a magnetization difficult axis to a demagnetizing field Hdc in a direction of a magnetization easy axis when the composite magnetic body is formed in a cube, is 4 or over, a shear stress is exerted in the painting direction in the stage of the painting above or before the drying. Or a magnetic field may be applied in a planer direction in place of exertion of the shear stress. Or the compound may be formed into a sheet by using the roll mill method without the use of painting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite magnetic material having excellent complex magnetic permeability characteristics in a high frequency range and an electromagnetic wave absorber as one application example thereof, and more particularly to a problem in a high frequency electronic circuit / device. The present invention relates to a composite magnetic material having an excellent complex magnetic permeability characteristic effective for suppressing electromagnetic interference, a method for producing the same, and an electromagnetic interference suppressor.

[0002]

2. Description of the Related Art In recent years, electronic devices using high frequencies such as digital electronic devices have become widespread. In particular, mobile communication devices using a quasi-microwave band have been remarkably spread.
In mobile communication devices represented by such mobile phones,
There is a high demand for miniaturization and weight reduction, and high-density mounting of electronic components is the biggest technical issue. In such a dense mounting, electronic components, printed wiring, wiring between modules, and the like are extremely close to each other. Furthermore,
Since the signal processing speed has also been increased, interference between lines due to electrostatic coupling and / or electromagnetic coupling has increased, and interference due to radiated noise has occurred. I have.

Conventionally, measures against such a so-called electromagnetic interference have been taken mainly by providing a conductor shield.

[0004]

However, since the conductor shield is a countermeasure against electromagnetic interference utilizing the reflection of electromagnetic waves caused by impedance mismatch with the space, even if the shielding effect is obtained, it is possible to prevent the unnecessary shielding from unnecessary radiation sources. There is a disadvantage that electromagnetic coupling due to reflection of light is promoted. To solve that shortcoming,
As a secondary countermeasure against electromagnetic interference, it is effective to suppress unnecessary radiation using the magnetic loss of the magnetic material, that is, the imaginary part magnetic permeability μ ″.

That is, unnecessary radiation can be suppressed by disposing a magnetic material having a large magnetic loss between the shield and the unnecessary radiation source.

Here, the thickness d of the magnetic material is inversely proportional to μ ″ in a frequency band satisfying the relationship of μ ″> μ ′, so that the thickness d is thin in order to meet the above-mentioned demand for downsizing and weight reduction of electronic devices. In order to obtain an electromagnetic interference suppressor, that is, a composite including a shield and an absorber, a magnetic material having a large imaginary part permeability μ ”is required.

In order to increase the magnetic loss, that is, the imaginary part magnetic permeability μ ″, it is necessary to increase the real part magnetic permeability μ ′. To this end, it is necessary to reduce the demagnetizing field of the composite magnetic body. Here, the magnitude of the demagnetizing field of the composite magnetic material is determined by the demagnetizing factor N _d of the flat soft magnetic powder.
And the manner in which the flat soft magnetic powder is arranged in the composite magnetic body, and the filling amount of the soft magnetic powder, etc., and the flat soft magnetic powder is moved in the in-plane direction of the composite magnetic body. It is reduced by aligning with a high degree of orientation. Therefore, how to arrange soft magnetic powders having a flat shape in the same direction is a problem for improving the size of μ ″, and the degree of orientation, that is, the arrangement of the soft magnetic powders is quantitatively determined. The introduction of effective parameters for grasping is also industrially important.

Accordingly, an object of the present invention is to provide a composite magnetic material having a further improved degree of orientation and, as a result, excellent magnetic loss characteristics, and to introduce a parameter which is a measure of the degree of orientation of a magnetic powder. I do.

[0009]

According to the present invention, there is provided a composite magnetic material obtained by dispersing a soft magnetic powder having shape anisotropy in an organic binder. A composite magnetic material is obtained in which the ratio H _dd / H _de of the demagnetizing field H _{dd in the} axial direction to the demagnetizing field H _{de in the} easy axis direction is 4 or more.

As the soft magnetic powder having the shape anisotropy, a powder having a flat powder particle is convenient.

According to the present invention, there is further provided a method for producing a composite magnetic material comprising kneading a soft magnetic material powder having shape anisotropy and an organic binder together with a solvent, coating and kneading the mixture.
The ratio H _dd / H between the demagnetizing field H _{dd in the} hard axis direction and the demagnetizing field H _{de in the} easy axis direction when the composite magnetic body is formed as a cube.
_{In order for de to} be 4 or more, a shear stress is applied in the coating direction during the coating or before drying.

Instead of applying a shear stress, an external magnetic field may be applied in the direction of the coating surface during the coating or before drying.

Alternatively, when the kneaded material is roll-rolled regardless of coating and drying, the demagnetizing field H _{dd in the} hard axis direction and the demagnetizing field in the easy axis direction when the composite magnetic body is formed into a cube. the ratio H _dd / H _de with H _de may also be present a 4 or higher.

Further, according to the present invention, it is possible to obtain an electromagnetic interference suppressor using the composite magnetic material as a material and having an excellent effect of suppressing electromagnetic interference.

[0015]

The present inventors have paid attention to the fact that the high-frequency magnetic permeability of the soft magnetic material strongly depends on the magnitude of the demagnetizing field. By calculating the ratio H _dd / H _de of the demagnetizing field H _dd and the demagnetizing field H _{de in the} easy axis direction, the filling rate of the magnetic powder in the composite magnetic material sample and the demagnetizing coefficient of the powder itself change. In this case, it has been found that excellent magnetic permeability characteristics can be obtained by making it possible to grasp the effective magnitude of the demagnetizing field and setting the ratio to 4 or more when the sample shape is a cube. The control of the ratio H _dd / H _de can be performed by the method of manufacturing a composite magnetic material as described above.

Here, the "diamagnetic field" Hd will be described with reference to FIG.

The composite magnetic material sample is marked and processed into a cubic shape so that the orientation direction of the magnetic particles can be recognized.
Using a VSM (vibrating magnetometer) for this cubic sample, each MH in the orientation direction (easy axis direction of magnetization) and the direction perpendicular to the orientation direction (hard axis direction) of the magnetic particles was measured.
Find a curve (magnetization curve). The MH curve is shown in FIG.
A straight line (shown by a dotted line in FIG. 1) passing through the origin is drawn in parallel with the linear region of the obtained MH curve, and the magnetic field corresponding to the intersection of this straight line and the Ms line (saturated magnetization line) is referred to as " Magnetic field "H
d.

The demagnetizing field in the “easy axis direction” is represented by H _de , and the demagnetizing field in the “hard axis direction” is represented by H _dd .

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a metal soft magnetic material such as an iron aluminum silicon alloy (Sendust), an iron nickel alloy (Permalloy), or an amorphous alloy having a high high-frequency magnetic permeability is used as a raw material. I can do it.

In the present invention, crushing these raw materials, it was flattened by stretching and tearing process or the like, flat and its thickness as well as to equal to or less than the skin depth, to the demagnetization factor N _d of the powder to about 1 It is necessary to make the aspect ratio of the soft magnetic material material approximately 10 or more. Here, the skin depth δ is given by the following equation.

Δ = (ρ / πμf) ^{1/2 In the above} equation, ρ represents specific resistance, μ represents magnetic permeability, and f represents frequency. Here, the value differs depending on the target frequency, but one of the simplest means to obtain the desired skin depth and aspect ratio is to specify the average particle size of the starting crude material powder. Typical milling means that can be used for the milling, stretching and tearing operations include a ball mill, an attritor, a pin mill, and the like. The thickness and aspect ratio of the soft magnetic material powder satisfying the above conditions can be obtained. There is no limitation on the crushing means as long as it is possible, but it is necessary to set the processing means and the processing conditions in consideration of the magnitude of the residual strain caused by the stretching / tearing, which is closely related to the effect of the present invention.

The soft magnetic material may have a magnetostriction constant λ of zero, a positive material, or a negative material. However, when a positive raw material magnetic material is used, the soft magnetic material is shaped by stretching and tearing. Along with the occurrence of magnetic anisotropy, a strain magnetic anisotropy (magnetoelastic effect) due to residual strain occurs, and the directions of the two become the same. Therefore, the magnetostriction constant λ
The value of the anisotropic magnetic field becomes larger and the magnetic resonance frequency becomes higher as compared with the case where the raw material having zero is used. By the way, since the residual strain caused by the flattening process is reduced by performing an appropriate annealing process,
In the composite magnetic material using the raw material powder subjected to the annealing treatment after the flattening treatment, magnetic resonance appears at a frequency fr corresponding to the annealing treatment conditions. This magnetic resonance frequency fr is lower than that of the composite magnetic material using the magnetic powder that has not been subjected to the annealing treatment, and is higher than that of the composite magnetic material using the magnetic powder having the zero magnetostriction constant λ. By doing so, it is possible to arbitrarily set the magnetic resonance frequency within the range.

On the other hand, when a raw material magnetic material having a negative magnetostriction constant λ is used, the direction of the strain magnetic anisotropy (magnetoelastic effect) caused by the residual strain is orthogonal to the direction of the shape magnetic anisotropy. As a result, the anisotropic magnetic field becomes smaller, and the magnetic resonance frequency becomes lower than that of a raw material having zero magnetostriction constant.

As described above, by combining the shape anisotropy, the sign of the magnetostriction constant λ, and the annealing conditions, the magnetic resonance frequency fr can be greatly varied.

Further, in order to electrically insulate the individual magnetic powders in the composite magnetic body and to secure the insulating properties of the composite magnetic body even in a state where the magnetic powder is highly filled, the soft magnetic powder is A dielectric layer must be formed on the surface. This dielectric layer is obtained as an oxide layer of a metal constituting the powder by oxidizing the surface of the metal magnetic powder. For example, in the case of iron aluminum silicon alloy (Sendust), it is presumed that it is mainly AlO _x and SiO _x . As an example of a means for oxidizing the surface of the metal powder, particularly for powders having a relatively small size and high activity, the oxygen partial pressure is controlled in a hydrocarbon organic solvent or in an inert gas atmosphere. Oxidation by a slow acid method in a liquid phase or a slow acid method in a gas phase, in which a mixed gas of nitrogen and oxygen is introduced, is preferred in terms of controllability, stability, and safety.

It is to be noted that either the slow acid treatment for surface oxidation or the annealing treatment for reducing residual strain described above may be performed first, or may be performed in the same step. It is.

The organic binder used as one component of the composite magnetic material of the present invention includes polyester resin, polyethylene resin, polyvinyl chloride resin, polyvinyl butyral resin, polyurethane resin, cellulose resin,
Examples include BS resin, nitrile-butadiene rubber, styrene-butadiene rubber, epoxy resin, phenol resin, amide resin, imide resin, and copolymers thereof.

One method for obtaining a composite magnetic material from the kneaded and dispersed magnetic material mixture is to coat the magnetic material mixture on a support and to dry it. During the coating, a shearing stress is applied by using a doctor blade device (applicator) having a gap equal to or smaller than the size of the magnetic powder, or by pulling the support before drying. Thereby, the ratio H _dd between the demagnetizing field H _{dd in the} hard axis direction and the demagnetizing field H _{de in the} easy axis direction when the manufactured composite magnetic body is formed into a cube.
/ H _de can be 4 or more, and a composite magnetic material having excellent high-frequency magnetic permeability can be obtained.

In order to set the ratio H _dd / H _de to 4 or more, a method of applying a magnetic field instead of applying the shearing force may be employed.

Alternatively, the kneaded and dispersed magnetic material may be directly formed into a sheet by roll rolling without using a coating method. By this roll rolling, a ratio H _dd / H _de of 4 or more can be realized.

In order to explain the structure of the composite magnetic material of the present invention, its cross section is schematically shown in FIG. Referring to FIG.
The composite magnetic body 1 is obtained by mixing the flat soft magnetic particles 2 with an organic binder 3.
Are dispersed and bound in a layer of Reference numeral 4 denotes a support, which may be an insulating plate or a metal plate, which may be used as needed, or may not be used.

An embodiment will be described below.

[0033]

EXAMPLE A plurality of iron-aluminum-silicon alloy powders prepared by a water atomizing method were prepared, pulverized, stretched and torn under various conditions using an attritor and a pin mill. Then, the mixture was stirred for 8 hours while introducing a nitrogen-oxygen mixed gas having an oxygen partial pressure of 35%, and gradually acidified in a liquid phase, to obtain a plurality of powder samples. As a result of surface analysis of the powder obtained here, formation of a metal oxide was clearly confirmed, and the presence of an oxide film on the surface of the sample powder was recognized.

The pulverized, stretched and torn iron-silicon alloy powder was dried under reduced pressure, and then dried at an oxygen partial pressure of 20%.
Metal oxides are also detected on the surface of the sample that has undergone gas phase deoxidation in a nitrogen-oxygen mixed gas atmosphere, and at least the surface of the oxidized soft magnetic material powder that can be used for the composite magnetic material of the present invention is obtained. It was confirmed that it can be prepared by a slow acid method in a liquid phase or a slow acid method in a gas phase.

The following composite magnetic material samples were obtained using these sample powders.

[Sample 1] A soft magnetic paste having the following composition was prepared, formed into a film on a support by a doctor blade method, and a shearing force was applied by applying a pulling force in a coating direction. This was subjected to hot pressing, and then cured at 85 ° C. for 24 hours to obtain Sample 1.

When the obtained sample 1 was analyzed using a scanning electron microscope, the particle arrangement direction was in the in-plane direction of the sample film.

Flat soft magnetic material (Fe-Al-Si alloy) fine powder A: 95 parts by weight Average particle size: φ20 μm × 0.3 μm ^t Magnetostriction size: +0.72 Annealing treatment: None Polyurethane resin ··· 8 parts by weight Curing agent (isocyanate compound) ··· 2 parts by weight Solvent (mixture of cyclohexanone and toluene) ··· 40 parts by weight [Sample 2] A soft magnetic paste having the following composition is prepared and mixed. A film was formed on a support by a doctor blade method. After applying an in-plane magnetic field thereto, curing was performed at 85 ° C. for 24 hours to obtain a sample 2.

When the obtained sample 2 was analyzed using a scanning electron microscope, the particle arrangement direction was in the in-plane direction of the sample film.

Flat soft magnetic material (Fe—Al—Si alloy) fine powder B: 95 parts by weight Average particle size: φ20 μm × 0.3 μm ^t Magnetostriction size: +0.72 Annealing treatment: 650 ° C. × 2 hr Polyurethane resin 8 parts by weight Hardener (isocyanate compound) 2 parts by weight Solvent (mixture of cyclohexanone and toluene) 40 parts by weight [Sample 3] A soft magnetic paste having the following composition is prepared. This was formed on a support by a doctor blade method. After subjecting this to hot pressing, it was cured at 85 ° C. for 24 hours to obtain Sample 3.

When the obtained sample 3 was analyzed using a scanning electron microscope, it was found that the particle arrangement direction was the in-plane direction of the sample film.

Flat soft magnetic material (Fe—Ni alloy) fine powder C: 95 parts by weight Average particle size: φ30 μm × 0.4 μm ^t Magnetostriction size: −1.03 Annealing treatment: None Polyurethane resin 8 parts by weight Curing agent (isocyanate compound) 2 parts by weight Solvent (mixture of cyclohexanone and toluene) 40 parts by weight [Sample 4] A soft magnetic material having the following composition is prepared and mixed on a mixing roll. , And formed into a sheet by roll rolling to obtain Sample 4.

When the obtained sample 4 was analyzed using a scanning electron microscope, it was found that the particle arrangement direction was the in-plane direction of the sample film.

Flat soft magnetic material (Fe—Al—Si alloy) fine powder A: 60 parts by weight Average particle size: φ20 μm × 0.3 μm ^t Magnetostriction size: +0.72 Annealing treatment: None Flat soft Magnetic substance (Fe-Al-Si alloy) fine powder B: 35 parts by weight Average particle diameter: φ20 μm × 0.3 μm ^t Magnetostriction size: +0.72 Annealing treatment: 650 ° C. × 2 hr Polyurethane resin ・ ・ ・ 8 parts curing agent (isocyanate compound).. for 2 parts by weight solvent (mixture of cyclohexanone and toluene) ..... 40 parts by weight or more of the sample, was determined for H _dd and H _de,
The sample was processed into a toroidal shape, a one-turn coil was wound around the sample, a high-frequency current was passed through the coil, the impedance was measured, and the magnetic permeability was determined. Magnetic permeability showed good high frequency characteristics.

[0045]

As described above, according to the present invention, in a composite magnetic material comprising a soft magnetic material powder and an organic binder,
The soft magnetic material powder is formed into a flat shape having magnetic anisotropy, and in the method of manufacturing the composite magnetic material, by applying a shear stress in the coating direction at the time of coating or before drying, or in-plane. By applying a magnetic field in the direction, the ratio H _dd / H _de of the demagnetizing field H _{dd in the} hard axis direction to the demagnetizing field H _{de in the} easy axis direction when the composite magnetic body is formed into a cube is 4 or more. By doing so, a composite magnetic body having excellent high-frequency magnetic permeability characteristics can be obtained.

Further, according to the present invention, in a composite magnetic material comprising a soft magnetic material powder and an organic binder, the soft magnetic material powder is formed into a flat shape having magnetic anisotropy, and a method for producing the composite magnetic material is provided. In this case, the composite magnetic body is formed into a sheet by a roll rolling method, so that the ratio H of the demagnetizing field H _{dd in the} hard axis direction and the demagnetizing field H _{de in the} easy axis direction when the composite magnetic body is formed into a cube. _{By making dd} / H _de 4 or more,
A composite magnetic material having excellent high-frequency magnetic permeability characteristics can be obtained.

Therefore, a thin electromagnetic interference suppressor effective for excellent electromagnetic interference suppression can be obtained by using the composite magnetic material.

It should be noted that the composite magnetic body and the electromagnetic wave interference / interference suppressor of the present invention can easily be given flexibility as can be seen from the constituent elements thereof, and can cope with complicated shapes and have strict requirements. Capable of meeting vibration and shock requirements.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a “diamagnetic field” used in the description of the present invention.

FIG. 2 is a diagram schematically showing a cross section of a composite magnetic body of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Composite magnetic substance 2 Flat soft magnetic substance powder particle 3 Organic binder 4 Support

Claims (7)

[Claims] 1. A composite magnetic material obtained by dispersing a soft magnetic material powder having shape anisotropy in an organic binder, wherein when a cubic material is formed, a demagnetizing field H _{dd in a} hard axis direction and a magnetization easy A composite magnetic material having a ratio H _dd / H _de to the demagnetizing field H _{de in the} axial direction of 4 or more. 2. The composite magnetic material according to claim 1, wherein the particles of the soft magnetic material powder having shape anisotropy are flat. 3. A method for producing a composite magnetic material, comprising kneading a soft magnetic material powder having shape anisotropy and an organic binder together with a solvent, coating and kneading the mixture and drying the composite magnetic material with a cube. In order to make the ratio H _dd / H _de of the demagnetizing field H _{dd in the} hard axis direction and the demagnetizing field H _{de in the} easy axis direction at the time of formation to be 4 or more, it is necessary to carry out the coating at the time of coating or before drying. A method for producing a composite magnetic material, comprising applying a shear stress in a coating direction in a step. 4. A method for producing a composite magnetic body, comprising kneading a soft magnetic substance powder having shape anisotropy and an organic binder together with a solvent, coating and kneading the mixture, and forming the composite magnetic substance into a cube. In order to make the ratio H _dd / H _de of the demagnetizing field H _{dd in the} hard axis direction and the demagnetizing field H _{de in the} easy axis direction at the time of formation to be 4 or more, it is necessary to carry out the coating at the time of coating or before drying. A method for producing a composite magnetic body, comprising applying an external magnetic field in the direction of a coating surface in a step. 5. A soft magnetic material powder having shape anisotropy and an organic binder are kneaded together with a solvent, and this is roll-rolled to form a cubic body of the composite magnetic body in the direction of hard axis. A method of manufacturing a composite magnetic body, comprising manufacturing a composite magnetic body having a ratio H _dd / H _de of 4 or more between a demagnetizing field H _dd and a demagnetizing field H _{de in an} easy axis direction. 6. The method of manufacturing a composite magnetic material according to claim 3, wherein the soft magnetic material powder having the shape anisotropy is crushed, stretched, and torn flat particles. A method for producing a composite magnetic material, comprising: 7. An electromagnetic interference suppressor made of the composite magnetic material according to claim 1.