JP2007273732A - Noise suppressing soft magnetism metal powder and noise suppressing sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a sheet with high noise suppressing effect by increasing permeability of a Fe-Si-Cr alloy. <P>SOLUTION: Noise suppressing soft magnetic metal powder of the present invention comprises: 13 to 28 at% Si; 10 at% or less (not containing 0) Cr; and Fe and inevitable impurities as a remaining part, with a weight average particle diameter D<SB>50</SB>of 30 to 100 μm and with a Vickers hardness of 400 to 800. Further, a noise suppressing sheet of the present invention consists of: noise suppressing soft magnetic metal powder which comprises 13 to 28 at% Si; 10 at% or less (not containing O) Cr; and Fe and inevitable impurities as a remaining part, with the weight average particle diameter D<SB>50</SB>of 30 to 100 μm and with the Vickers hardness of 400 to 800 and consists of a coupling agent for coupling the noise suppressing soft magnetic metal powder. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sheet for suppressing noise generated from a digital device, and more particularly to improvement of magnetic permeability of Fe—Si—Cr alloy powder used in combination with a resin.

Electromagnetic interference (EMI) is increasing as electronic devices such as personal computers and mobile phones are developed with high-speed operation processing and digitalization. In particular, since a digital device may malfunction due to noise, it is important to reduce noise generated from the digital device.
Conventionally, noise is absorbed by a noise filter made of a magnetic material as one means for noise suppression. As a typical magnetic material constituting a noise filter, there is a ferrite material having a spinel crystal structure. In a high frequency band, a material having a higher electric resistance has a smaller eddy current loss and is advantageous for noise absorption. Therefore, a Ni-based ferrite material having a higher electric resistance has been used among the ferrite materials for the high frequency band. However, when the noise is in the gigahertz band, the “Snoek limit” becomes a problem. That is, the upper limit of the noise absorption band of the ferrite material is 1 GHz, and it is difficult to cope with recent high frequency noise. In addition, since the ferrite material is a brittle material, it may be destroyed by dropping, impact, or the like.

  In contrast, a noise suppression sheet in which soft magnetic metal powder is dispersed in resin and rubber has been proposed. For example, a composite magnetic material in which flat Fe—Si—Cr soft magnetic metal powder is oriented and arranged in rubber or resin has been proposed (for example, see Patent Document 1).

Japanese Patent No. 2523388

  In this composite magnetic material, since the base is made of flexible rubber or resin, there is no fear of breakage due to dropping or impact like a ferrite material. That is, the noise suppression sheet is produced by mixing and dispersing soft magnetic metal powder in an insulator matrix such as rubber or plastic and performing press molding / extrusion molding, calendar roll molding, or the like. By selecting the matrix and the processing method, members of various forms such as a sheet shape or a block shape of about 0.1 mm to several mm can be produced. Further, by selecting a matrix and controlling the thickness, flexibility can be imparted, or conversely, rigidity can be increased. Further, by selecting a matrix, use at a high temperature of about 250 ° C. is also possible.

  The noise suppression effect of the noise suppression sheet depends on its magnetic permeability. Recently, with the increase in noise intensity, further improvement in noise suppression effect is desired. Therefore, it is necessary to increase the magnetic permeability of the above-described noise suppression sheet, in other words, the soft magnetic metal powder contained in the noise suppression sheet. The noise suppression effect is roughly classified into a magnetic shielding effect that prevents mutual interference between adjacent circuit boards by shielding magnetism, and a noise absorption effect that absorbs electromagnetic noise energy and converts it into heat. The magnetic permeability at high frequency is expressed as complex permeability μ = μ′−jμ ″ using real part permeability μ ′ and imaginary part permeability μ ″, but the magnetic shielding effect is the real part permeability μ ′. Depending on the magnitude, the noise absorption effect depends on the magnitude of the imaginary part permeability μ ″. Generally, the maximum value of the imaginary part permeability μ ″ increases as the real part permeability μ ′ increases. Therefore, the present invention aims to increase the real part permeability μ ′ of a composite magnetic material using an Fe—Si—Cr alloy as a magnetic material, thereby improving the noise suppression effect.

  The magnetic permeability of the composite magnetic material is increased by using a soft magnetic metal powder having a large particle size and aspect ratio and a small coercive force. There are no particular restrictions on the means for flattening the soft magnetic metal powder, and any means can be used as long as the desired flattening is possible, but a stress is applied to the soft magnetic metal powder to obtain a flat powder. As a method, a method using a medium stirring mill is known. This is a method of flattening by stirring the medium and repeating the collision with the soft magnetic metal powder, but if the powder breaks due to the shearing force due to the collision, the desired aspect ratio and further the particle size is reduced. You can't get it. In the case of an Fe—Si—Cr alloy, the hardness depends on the Si content, and as the content increases, the hardness increases and becomes brittle. With such an Fe—Si—Cr alloy, it is difficult to obtain a flat powder having a large particle size. On the other hand, the coercive force of the Fe—Si—Cr alloy is minimized in the vicinity of Si = 12 at% (6.5 wt%) where the magnetostriction constant becomes zero. However, the Fe-Si-Cr alloy having this composition has a relatively small Vickers hardness, so that a flat powder having a large particle size is easily obtained. However, since the strain associated with the flattening treatment increases, the coercive force cannot be reduced. . Therefore, as a result of investigating the relationship between the hardness, the particle size after the flattening treatment and the coercive force, the present inventors have controlled the hardness within a predetermined range (Hv: Vickers hardness = 400 to 800), It has become possible to sufficiently increase the particle size to 30 μm or more and to further reduce the coercive force.

The present invention is based on the above findings, and has a composition comprising Si: 13 to 28 at%, Cr: 10 at% or less (however, not including 0), balance: Fe and unavoidable impurities, and weight average grains A soft magnetic metal powder for noise suppression, wherein the diameter D ₅₀ is 30 to 100 μm and the Vickers hardness is 400 to 800.
Further, the present invention has a composition comprising Si: 13 to 28 at%, Cr: 10 at% or less (excluding 0), the balance: Fe and unavoidable impurities, and a weight average particle diameter D ₅₀ of 30 to 100 μm. There is also provided a noise suppressing sheet comprising: a noise suppressing soft magnetic metal powder having a Vickers hardness of 400 to 800; and a binder that binds the noise suppressing soft magnetic metal powder.

  As described above, according to the present invention, a sheet having a high noise suppression effect can be produced by increasing the magnetic permeability of the Fe—Si—Cr alloy.

Embodiments of the present invention will be described below.
<Alloy composition>
The noise-suppressing soft magnetic metal powder according to the present invention has a composition of Si: 13 to 28 at%, Cr: 10 at% or less (excluding 0), the balance: Fe and inevitable impurities.
As shown in the examples described later, the hardness of the Fe—Si—Cr alloy depends on the amount of Si, and the hardness increases as the amount of Si increases. When the amount of Si decreases, the hardness decreases and the coercive force increases due to an increase in distortion during the flattening process. On the other hand, when the amount of Si is too large, the saturation magnetization Ms is lowered and hardened, so that the powder is easily broken during the flattening treatment. Therefore, it becomes difficult to obtain a flat powder having a large particle size. Considering the above, the present invention sets the Si amount to 13 to 28 at%. A preferable Si amount is 15 to 25 at%, and a more preferable Si amount is 17 to 23 at%.

In the Fe—Si—Cr alloy of the present invention, Cr can impart corrosion resistance. However, as the amount increases, the saturation magnetization Ms decreases. In the present invention for the purpose of obtaining high magnetic permeability, the Cr content is 10 at% or less (however, 0 is not included). A preferable Cr amount is 0.5 to 5 at%, and a more preferable Cr amount is 0.5 to 3 at%.
In addition to Si and Cr, the Fe—Si—Cr alloy according to the present invention is Fe and inevitable impurities, but the inclusion of various additive elements is not denied.

<Weight average particle diameter _{D 50>}
The noise-suppressing soft magnetic metal powder according to the present invention has a weight average particle diameter D ₅₀ (hereinafter, simply D ₅₀ ) of 30 to 100 μm. When D ₅₀ is smaller than 30 μm, the magnetic permeability is lowered. On the other hand, when D ₅₀ is too large, it is not easy to mix with the binder, it is difficult to produce a noise suppression sheet. Therefore, the upper limit of D ₅₀ is set to 100 μm. The preferable D ₅₀ of the soft magnetic metal powder for noise suppression is 35 to 90 μm, and the more preferable D ₅₀ is 40 to ₅₀ μm. D ₅₀ is the sum of the weights of the particles constituting the noise-suppressing soft magnetic metal powder from the smaller particle diameter, and when this value reaches 50% of the total weight of the noise-suppressing soft magnetic metal powder. It is the particle size (long axis length) of the flat soft magnetic particles. The particle size in this case can be measured by using a light scattering method. For example, while circulating the measurement object, the scattering angle of Franhofer diffraction or My scattering is measured using a laser beam or a halogen lamp as a light source. The distribution is measured.

In the noise-suppressing soft magnetic metal powder of the present invention, a preferable thickness range is 0.1 to 2.0 μm, and a more preferable range is 0.5 to 1.5 μm. When the thickness of the noise-suppressing soft magnetic metal powder is less than 0.1 μm, it is not easy to manufacture and handling becomes difficult. Further, if the thickness of the soft magnetic metal powder for noise suppression exceeds 2.0 μm, it is not preferable because the magnetic characteristics at high frequencies are deteriorated.
Moreover, the soft magnetic metal powder for noise suppression according to the present invention has a preferred aspect ratio (= particle size / thickness) of 10 to 200, and a more preferred range of 20 to 100. When the aspect ratio is 10 or less, the demagnetizing field increases, and the apparent magnetic permeability is reduced only when the noise suppression sheet is used. When the aspect ratio is 200 or more, the filling ratio (= volume of soft magnetic metal powder for noise suppression / noise suppression). The volume of the sheet) decreases and the magnetic permeability decreases.

<Hardness>
The soft magnetic metal powder for noise suppression according to the present invention has a Vickers hardness (Hv) of 400 to 800. When the Vickers hardness (Hv) is less than 400, the distortion accompanying the flattening process increases and the coercive force increases. Further, when the Vickers hardness (Hv) exceeds 800, the alloy tends to break during the brittle becomes flattened, the weight average particle diameter D ₅₀ is difficult to obtain a more flat powder 30 [mu] m. In the present invention, the preferred Vickers hardness (Hv) is 450 to 750, and the more preferred Vickers hardness (Hv) is 500 to 700.

<Raw material alloy powder>
The noise-suppressing soft magnetic metal powder according to the present invention can be obtained by preparing a raw material alloy powder having the above composition and flattening it. The raw material alloy powder may be obtained by pulverizing an ingot, or may be obtained by a molten metal quenching method such as water atomization, gas atomization, or roll quenching method. It is preferable that D50 of raw material alloy powder shall be _5-50 micrometers. D ₅₀ of the material alloy powder is less than 5μm, it is difficult to obtain a 30μm or more D ₅₀ be subjected to flattening treatment. Further, when _{D 50} of the material alloy powder exceeds 50 [mu] m, _{D 50} exceeds easily 100μm by flattening processing. As shown in the examples below, starting alloy weight average particle diameter D ₅₀ of the powder, it is possible to increase the greater the magnetic permeability of noise suppression sheets within the above range. Therefore, the weight average particle diameter D50 of the preferable raw material alloy powder is 15 to _{50 [} mu] m, and the weight average particle diameter D50 of the more preferable raw material alloy powder is 25 to _{50 [} mu] m.

<Flatening treatment>
The raw material alloy powder is flattened. The flattening means is not particularly limited, and any means may be used as long as desired flattening is possible. For example, the flattening treatment can be performed using a medium stirring mill, a rolling ball mill, or the like, but it is particularly preferable to use a medium stirring mill. The medium stirring mill is a stirrer also called a pin type mill, a bead mill, or an agitator ball mill. The flattening treatment is preferably performed wet using an organic solvent such as toluene. The particle size distribution of the soft magnetic metal powder for noise suppression at this time does not necessarily have to be sharp, and may have a distribution of two peaks.

<Heat treatment>
A heat treatment is performed after the flattening treatment. By this heat treatment, the flat noise-suppressing soft magnetic metal powder is dried, and further, distortion caused by flattening is removed. This heat treatment can be performed in the atmosphere or in an inert gas (for example, nitrogen) containing a certain amount (for example, oxygen partial pressure of 1% or less) of oxygen.
The temperature of the heat treatment is a stable temperature of 275 to 450 ° C, more preferably 300 to 400 ° C. The stabilization time is preferably 30 to 180 minutes. This is because the noise-suppressing soft magnetic metal powder made of an Fe—Si—Cr alloy has a higher coercive force Hc of the noise-suppressing soft magnetic metal powder obtained after the heat treatment when the heat treatment is out of the above temperature range. It is preferable to perform the heat treatment in the above temperature range including the temperature at which the coercive force Hc becomes a minimum value.

The above-mentioned stable temperature is preferably varied as appropriate depending on the composition of the soft magnetic metal powder for noise suppression, and is preferably set to an optimum condition. For example, in the Fe _98.5-X Si _X Cr _1.5 alloy, when x = 15, the stable temperature is preferably 325 to 450 ° C., more preferably 350 to 400 ° C. Further, when x = 21, 24, the stable temperature is preferably 275 to 375 ° C., more preferably 300 to 350 ° C. When X = 26, 28, the stable temperature is preferably 300 to 400 ° C, more preferably 325 to 375 ° C.

The noise-suppressing soft magnetic metal powder obtained as described above has a composition of Si: 13 to 28 at%, Cr: 10 at% or less (excluding 0), and the balance: Fe and inevitable impurities. , D ₅₀ is 30 to 100 μm, and Vickers hardness (Hv) is 400 to 800. Using this noise-suppressing soft magnetic metal powder, a noise suppression sheet can be produced as follows.

For example, after kneading a soft magnetic metal powder for noise suppression and a binder, it is formed into a sheet by press molding or extrusion, or the soft magnetic metal powder for noise suppression and a binder are dispersed in an organic solvent. After forming into a predetermined thickness by a blade method, after drying, it is rolled into a sheet by a calendar roll. In this way, a noise suppression sheet having a thickness of 0.05 to 2 mm can be obtained.
The reason why the thickness of the noise suppression sheet is 0.05 to 2 mm is based on the following reason. That is, when the thickness of the noise suppression sheet is thinner than 0.05 mm, sufficient inductance cannot be obtained. On the other hand, if the thickness of the noise suppression sheet exceeds 2 mm, it is because of the constraint that it is difficult to fit in the narrow space inside the housing of the electric device.

It is preferable that the filling rate of the noise suppressing soft magnetic metal powder in the noise suppressing sheet is 60 to 95 wt%. When the filling rate is less than 60 wt%, the noise suppressing effect is insufficient, and when it exceeds 95 wt%, the noise suppressing soft magnetic metal powders cannot be firmly bonded by the binder, and the strength of the noise suppressing sheet is reduced. The filling rate is more preferably 70 to 90 wt%.
As the binder, a known thermoplastic resin, thermosetting resin, ultraviolet curable resin, radiation curable resin, rubber-based material, or the like can be used. Specifically, polyester resin, polyethylene resin, polyvinyl chloride resin, polyvinyl butyral resin, polyurethane resin, cellulose resin, ABS resin, nitrile-butadiene rubber, styrene-butadiene rubber, epoxy resin, phenol resin Amide resin and the like.

  Note that the noise suppression sheet may contain a curing agent, a dispersant, a stabilizer, a coupling agent, and the like in addition to the soft magnetic metal powder for noise suppression and the binder. Moreover, when the noise suppression sheet of the present invention is formed or applied into a required shape, a noise suppression sheet with high directivity can be obtained by applying an orientation magnetic field or mechanically orienting it.

  First, the Vickers hardness (Hv) of Fe—Si—Cr alloys with different compositions was investigated. FIG. 1 shows the Vickers hardness (Hv) of an Fe—Si—Cr alloy alloyed by arc melting. The measurement was performed according to the “Vickers hardness test method (JIS Z 2244)”, 5 points were measured for each composition, and the average value of 3 points excluding the maximum value and the minimum value was plotted. As shown in FIG. 1, it can be seen that the Vickers hardness (Hv) of the Fe—Si—Cr alloy varies depending on the Si amount regardless of the Cr amount, and decreases as the Si amount decreases.

Next, after flattening a Fe—Si—Cr alloy (water atomized powder) having a different amount of Si, the Vickers hardness (Hv) of the soft magnetic metal powder for noise suppression, the ease of flattening, and the coercive force (Hc) ) Was investigated.
A raw material alloy powder having a composition of Fe _98.5-X Si _X Cr _1.5 (at%) was produced by a water atomization method. The particle diameter of the raw material alloy powder was three types: D ₅₀ = 10, 25, and 40 μm. The raw material alloy powder was flattened in a medium stirring mill using toluene as a solvent while changing the treatment time in the range of 0 to 8 hours. It dried after the flattening process and heat-processed. The heat treatment was performed at a temperature (300 to 400 ° C.) at which the coercive force (Hc) was minimized, and the coercive force (Hc) was measured with a vibrating sample magnetometer (VSM) after the heat treatment. However, the Vickers hardness (Hv) was measured by mirror polishing after filling a raw material alloy powder (water atomized powder) with a resin.

Figure 2 shows a flattening process time and flattening treated relationship D ₅₀ of the soft magnetic metal powder for noise suppression. The particle diameter of the raw material alloy powder is D ₅₀ = 10 μm. D ₅₀ is increased by the flattening process. However, if the treatment time is long, crushing occurs beyond flattening, so D ₅₀ shows a peak at a certain time. Further, in the same processing time, the lower the Vickers hardness (Hv), the larger the D ₅₀ of the noise-suppressing soft magnetic metal powder that has been flattened. Therefore, the lower the Vickers hardness (Hv), the easier the flattening. Recognize. _{Incidentally, D 50} is HELOS SYSTEM (Nippon Denshi, dry method) using a light scattering method is 50% particle diameter by.

  FIG. 3 shows the relationship between the flattening time and the coercive force (Hc) of the noise suppressing soft magnetic metal powder after the heat treatment. From FIG. 3, even when the coercive force (Hc) (flattening treatment time 0h: almost no change before and after the heat treatment) for the raw material alloy powder is small, if the Vickers hardness (Hv) is low, the distortion accompanying flattening is large Thus, the coercive force (Hc) after the flattening process is increased. Therefore, it can be seen that it is preferable to use an alloy having high hardness from the viewpoint of coercive force (Hc).

FIG. 4 shows the relationship between Vickers hardness (Hv) and D ₅₀ of the noise-suppressing soft magnetic metal powder when the raw material alloy powder has different particle sizes. The larger the particle size of the raw material alloy powder, the larger the particle size after the flattening treatment can be. It turns out that is difficult to grow.

  FIG. 5 shows the relationship between the Vickers hardness (Hv) and the coercive force (Hc) of the noise-suppressing soft magnetic metal powder when the particle diameters of the raw material alloy powders are different. It can be seen that the higher the Vickers hardness (Hv), the smaller the coercive force (Hc). Moreover, it turns out that a coercive force (Hc) becomes small, so that the particle size of raw material alloy powder is large.

Next, the noise suppression sheet | seat was produced using the soft magnetic metal powder for noise suppression.
The noise suppression sheet was produced by the following procedure. The noise-suppressing soft magnetic metal powder (after heat treatment) and a binder of 15 wt% were mixed using a diluent, and the resulting slurry was applied onto a PET (Poly Ethylene Terephthalate) film and then magnetically oriented. Noise suppression soft magnetic metal powder is obtained by flattening processing time that D ₅₀ becomes the maximum, the magnetic field orientation was performed by passing between the magnets are opposed to the poles. Furthermore, roll rolling was performed to obtain a noise suppression sheet having a thickness of 0.25 mm and a density of 3.5 Mg / m ³ . A toroidal sample having an outer diameter of 18 mm and an inner diameter of 10 mm was prepared from this sheet, and real part permeability μ ′ and imaginary part permeability μ ″ were measured using an impedance analyzer (HP4291A manufactured by Hewlett-Packard Company). The relationship between the Vickers hardness (Hv) of the noise suppressing soft magnetic metal powder and the real part permeability μ ′ of the noise suppressing sheet is shown in Fig. 6. The noise suppressing soft magnetic metal powder has a Vickers hardness (Hv) of 400 to 800. 'it can be seen that increases. in particular, the raw material alloy powder D ₅₀ of 60 or more when the above 30 [mu] m, more 80 or more in the real part permeability mu' Mibu permeability mu when seen can be obtained.

  FIG. 7 shows the frequency characteristics of the real part permeability μ ′ and the imaginary part permeability μ ″, and FIG. 8 shows the relationship between the maximum values of the real part permeability μ ′ and the imaginary part permeability μ ″ at 10 MHz. It can be seen that the maximum value of the imaginary part permeability μ ″ increases as the real part permeability μ ′ increases.

It is a graph which shows the relationship between the amount of Si of the Fe-Si-Cr alloy alloyed by arc melting, and Vickers hardness (Hv). Is a graph showing the relationship between the D ₅₀ of the treated flattening processing time and flattening soft magnetic metal powder. It is a graph which shows the relationship between the flattening time and the coercive force (Hc) of the soft magnetic metal powder after the heat treatment. The particle size of the raw material alloy powder is a graph showing the relationship between the Vickers hardness (Hv) and the noise suppression soft magnetic metal powder D ₅₀ of vary. It is a graph which shows the relationship between the Vickers hardness (Hv) in case the particle size of raw material alloy powder differs, and the coercive force (Hc) of the soft magnetic metal powder for noise suppression. It is a graph which shows the relationship between the Vickers hardness (Hv) of the soft magnetic metal powder for noise suppression, and the real part magnetic permeability (micro | micron | mu) 'of a noise suppression sheet | seat. It is a graph which shows the frequency characteristic of real part magnetic permeability (mu) 'and imaginary part magnetic permeability (mu) "of a noise suppression sheet. It is a graph which shows the relationship of the maximum value of real part magnetic permeability (mu) 'and imaginary part magnetic permeability (mu) "in 10 MHz of a noise suppression sheet | seat.

Claims (2)

Si: 13 to 28 at%, Cr: 10 at% or less (however, not including 0), balance: Fe and a composition consisting of unavoidable impurities,
The weight average particle diameter D ₅₀ is 30-100 μm,
A soft magnetic metal powder for noise suppression having a Vickers hardness of 400 to 800. Si: 13 to 28 at%, Cr: 10 at% or less (however, not including 0), balance: Fe and a composition consisting of unavoidable impurities,
The weight average particle diameter D ₅₀ is 30-100 μm,
Soft magnetic metal powder for noise suppression having a Vickers hardness of 400 to 800,
A binder that binds the soft magnetic metal powder for noise suppression;
A noise-suppressing sheet comprising:

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