JP2000252113A - Platy soft magnetic ferrite particles and powder and soft magnetic ferrite particle composition using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a soft magnetic ferrite particle composite which has a high real part in permeability in low frequency band and can absorb electromagnetic waves over a wide band in high frequency band, by forming the soft magnetic ferrite particles and powder used for forming the composite in platy shapes and specifying the composition of the particles and powder. SOLUTION: The composition of soft magnetic ferrite particles and powder satisfies a formula, MgaCubZncFedO4 (where, 0.3<=a<=0.5, 0<=b<=0.2, 0.4<=c<=0.6, 1.8<=d<=2.2). The mean surface diameter and aspect ratio of the platy soft magnetic ferrite particles are respectively adjusted to about 0.5-50 μm and about 1.2-50, respectively. The content of the platy soft magnetic ferrite particles and powder in a soft magnetic ferrite particle composite is adjusted to about 75-92 wt.%. In the soft magnetic ferrite particle composite, in addition, an additive, such as carbon particles and power, SiC particles and powder, etc., are mixed and scattered. Therefore, the composite has a high rear part in permeability in the low frequency band and can absorb electromagnetic waves over a wide band in the high frequency band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate-like soft magnetic ferrite particle powder and a soft magnetic ferrite particle composite using the same, and more particularly, to a high relative magnetic permeability real part in a low frequency band. The present invention relates to a plate-like soft magnetic ferrite particle powder capable of providing a soft magnetic ferrite particle composite capable of absorbing electromagnetic waves over a wide band in a high frequency band, and a soft magnetic ferrite particle composite using the particle powder.

[0002]

2. Description of the Related Art Conventionally, a soft magnetic ferrite particle composite in which granular soft magnetic ferrite particle powder is mixed and dispersed in a matrix material such as a resin has a high real part of relative permeability at an appropriate frequency and a magnetic loss. As shown, it has been used in a wide variety of applications such as coil cores, radio wave absorbing materials, and noise absorbing materials. In particular, a composite mixed with a resin is widely used because it has better workability and flexibility than a sintered body, and has a high insulating property with an appropriate composition. Recently, a sheet-like soft magnetic ferrite particle composite has been used for reducing electromagnetic waves radiated from an electronic component by attaching the composite to the inner surface of a housing for housing the electronic component.

In recent years, electronic equipment has been reduced in size and weight, and as a material used for the soft magnetic ferrite particle composite, a real part of relative permeability shows a higher value in a low frequency band around 100 kHz. The body is required. In addition, with the rise of the clock frequency of personal computers and the spread of wireless LANs, malfunctions of devices due to unnecessary electromagnetic waves radiated in a high frequency band around 1 GHz have become a problem. In order to solve this, a soft magnetic ferrite particle composite having broadband electromagnetic wave absorption characteristics and noise absorption characteristics near 1 GHz is desired.

In response to these demands, Japanese Patent Application Laid-Open No.
902 and JP-A-60-91699 describe that the larger the ratio of the diameter and the thickness of the plate-like ferrite, the higher the effective magnetic permeability, and accordingly the natural resonance frequency shifts to a lower frequency. It has been shown that a soft magnetic ferrite particle composite in which a plate-like soft magnetic ferrite particle powder is oriented and mixed and dispersed may satisfy the above requirements.
However, the real part of the relative permeability in the low frequency band of the soft magnetic ferrite particle composite described in these publications is about 5, which is the same as that of the composite using the conventional granular soft magnetic ferrite particle powder. It is smaller than the real part of the relative permeability. There is no description that electromagnetic waves are absorbed over a wide band around 1 GHz.

On the other hand, JP-A-49-47899 and JP-A-62-3021 disclose a plate-like soft magnetic ferrite particle powder as a raw material of an anisotropic ferrite sintered body and a method for producing the same. Japanese Patent Application Laid-Open No. 5-45527 discloses a plate-like soft magnetic ferrite particle powder by a flux method and a method for producing the same. There is no description about the characteristics.

[0006]

As described above, if the shape of the soft magnetic ferrite particles is made into a plate shape, the soft magnetic ferrite particle composite using the same exhibits a high value of the real part of the relative magnetic permeability. The potential is recognized, but not actually realized. This is because the composition of the plate-shaped soft magnetic ferrite particle powder having a high relative magnetic permeability and the production method thereof has not been established. Accordingly, the present invention provides a plate-shaped soft magnetic ferrite particle powder capable of providing a soft magnetic ferrite particle composite that has a high relative real part in a low frequency band and absorbs electromagnetic waves over a wide band in a high frequency band. An object of the present invention is to provide a soft magnetic ferrite particle composite using the same.

[0007]

Since the soft magnetic ferrite particles have a spinel type crystal structure, the particles usually have a granular or irregular shape reflecting the crystal structure. Therefore, in order to obtain plate-like soft magnetic ferrite particles, it is necessary to consider selection of raw materials, firing conditions, and the like. For example, when a plate-like α-Fe ₂ O ₃ is used as a source of Fe, if the firing temperature is high, the plate-like properties of the generated particles are destroyed. Ferrite particles having soft magnetism cannot be obtained. Therefore, in order to obtain a plate-like soft magnetic ferrite particle powder, it is necessary to select the type of cation constituting the ferrite and its composition so as to exhibit soft magnetism even at a low firing temperature.

As a result of intensive studies based on the above findings, the present inventors have found that a plate-like soft magnetic ferrite particle powder composed of a specific cation and having a specific composition achieves the above object. Invented the invention. That is, claim 1 of the present invention has a plate-like shape and a composition of Mg _a Cu _b Zn _c
Fe _d O ₄ (however, 0.3 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.2, 0.4 ≤ c
.Ltoreq.0.6, 1.8.ltoreq.d.ltoreq.2.2).

In a preferred embodiment, the average plate surface diameter is 0.5 to 50 μm and the aspect ratio is 1.2 to 50.
The soft magnetic ferrite particle powder according to claim 1, wherein

In a third aspect of the present invention, the soft magnetic ferrite particle powder according to the first or second aspect is contained in a matrix in an amount of 75 to 50%.
A soft magnetic ferrite particle composite characterized by being mixed and dispersed at a ratio of 92% by weight.

According to a fourth aspect of the present invention, there is provided the soft magnetic ferrite particle composite according to the third aspect, wherein the real part of the relative magnetic permeability at a frequency of 100 kHz is 18 to 30.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the present invention, a plate-like α-Fe ₂ O ₃ is used as a supply source of the Fe element. In addition, as a supply source of the Mg, Cu, and Zn elements, oxides, hydroxides, oxalates, carbonates, and the like containing these elements can be used. In addition, a plate-like α-Fe ₂
O ₃ can be obtained by a hydrothermal reaction using an autoclave. After mixing these raw materials, firing is performed at a temperature of 1200 ° C. or less. Firing at a temperature exceeding 1200 ° C. is not preferable because the plate-like property of the particles is lost. A more preferable firing temperature is 1100 ° C. or lower. The lower limit of the firing temperature is 800 ° C. from the viewpoint of sufficient reactivity. The firing time is usually about 1 to 10 hours.

The composition of the plate-like soft magnetic ferrite particles according to the present invention is Mg _a Cu _b Zn _c Fe _d O ₄ (provided that 0.3 ≦ a ≦ 0.5
, 0 ≦ b ≦ 0.2, 0.4 ≦ c ≦ 0.6, 1.8 ≦ d ≦ 2.2). Outside these ranges, the real part of the relative magnetic permeability becomes small, and it becomes impossible to absorb electromagnetic waves over a wide band. More preferred composition is 0.35 ≦ a ≦ 0.45, 0 ≦ b ≦
0.15, 0.45 ≦ c ≦ 0.55, 1.9 ≦ d ≦ 2.1.

The average plate surface diameter of the plate-shaped soft magnetic ferrite particles according to the present invention is preferably 0.5 to 50 μm in consideration of the kneading property into the matrix. If it is less than 0.5 μm, it will be difficult to knead, and if it exceeds 50 μm, the particles will be broken during kneading, the real part of the relative magnetic permeability will be small, and it will not be possible to absorb electromagnetic waves over a wide band. A more preferred average plate surface diameter is 0.5 to 20 μm.

The aspect ratio of the tabular soft magnetic ferrite particles according to the present invention is preferably from 1.2 to 50. The aspect ratio in the present invention is defined by the ratio of the average plate surface diameter to the average thickness of the particles. When the aspect ratio is less than 1.2, the shape becomes substantially granular, so that the real part of the relative magnetic permeability becomes small and the electromagnetic wave over a wide band tends to be unable to be absorbed. On the other hand, if the aspect ratio exceeds 50, the particles are broken during kneading,
As the real part of the relative magnetic permeability decreases, it tends to be impossible to absorb electromagnetic waves over a wide band. A more preferred aspect ratio is 2 to 25.

The obtained plate-like soft magnetic ferrite particles are mixed and dispersed in a matrix to form a composite. Specifically, for example, a plate-shaped soft magnetic ferrite particle powder is mixed and dispersed in a matrix such as a resin, and then extruded with a biaxial hot roll maintained at an appropriate temperature to form a plate-shaped soft magnetic ferrite particle in the matrix. A soft magnetic ferrite particle composite in which magnetic ferrite particles are oriented can be obtained. However,
The method for orienting the particles is not limited to this, and a known method can be selected. The matrix is not particularly limited as long as it is used in the conventional soft magnetic ferrite particle composite, and may be selected from rubber, vinyl chloride resin, ethylene-vinyl acetate copolymer resin, polyamide (nylon) resin, and the like. Can be selected. Further, using a building material such as cement as a matrix, a wall material or the like containing a plate-like soft magnetic ferrite particle powder can be obtained.

The content of the plate-like soft magnetic ferrite particle powder in the soft magnetic ferrite particle composite is preferably 75 to 92% by weight. If the content is less than 75% by weight, the real part of the relative magnetic permeability becomes small, and it becomes impossible to absorb electromagnetic waves over a wide band. On the other hand, if it exceeds 92% by weight, it becomes difficult to mix the plate-like soft magnetic ferrite particles into the matrix. More preferably, it is 82 to 92% by weight.

The soft magnetic ferrite particle composite according to the present invention contains carbon particles for the purpose of controlling the dielectric constant and conductivity, improving the kneading property into resin and the flexibility of the composite. Known additives such as powder and SiC particles can be mixed and dispersed together with the plate-like soft magnetic ferrite particles.

[0019]

Table 2 shows a comparison between the frequency and the relative permeability (μ'-jμ ") of the soft magnetic ferrite particle composite according to the present invention and a conventional ferrite particle composite.
The plate-like soft magnetic ferrite particles according to the present invention (1)
(Combustion at 000 ° C.) is mixed and dispersed in a resin to show the real part (μ ′) and the imaginary part (μ ″) of the relative magnetic permeability.
In Comparative Example 1, the real part (μ ′) and the imaginary part (μ ″) of the relative magnetic permeability of a composite obtained by mixing and dispersing conventional granular Ni—Zn—Cu-based ferrite particle powder (fired at 1300 ° C.) in a resin are described. )
Is shown. Further, in Comparative Example 2, the conventional plate-like Ni-Zn-
The real part (μ ′) and the imaginary part (μ ″) of the relative magnetic permeability of a composite obtained by mixing and dispersing Cu-based ferrite particle powder (fired at 1000 ° C.) in a resin are shown. All amounts are 84.0% by weight.

As can be seen from Example 1 in Table 2, the real part (μ ') of the relative magnetic permeability of the soft magnetic ferrite particle composite according to the present invention shows 20.9 at 100 kHz, while Comparative Example 1 shows. Therefore, the soft magnetic ferrite particle powder of the present invention having a specific composition has a real part of a relative magnetic permeability that is extremely large, with the shape being plate-like. It turns out that it is high.

Although the reason why the real part of the relative magnetic permeability is increased by making the shape plate-shaped and having a specific composition as in the present invention is not clear, it is considered as follows. First, it is considered that the cause of the difference in the real part of the relative magnetic permeability due to the difference in shape is that the resonance frequency decreases due to the plate shape. It is considered that the difference in the real part of the relative magnetic permeability due to the difference in the composition is due to the difference in crystallinity due to the difference in the firing temperature. That is, it is necessary to fire at a low temperature of 1200 ° C. or less, more preferably at a temperature of 1100 ° C. or less, in order to maintain the tabularity of the particles formed after firing. In the composition of the present invention, ferrite particles having good crystallinity can be obtained at a temperature of 1200 ° C. or less. However, in a composition outside the scope of the present invention, ferrite particles having good crystallinity can be obtained at a low temperature of 1200 ° C. or less. No (Comparative Example 2). Therefore, if the firing temperature is set to 1200 ° C. or higher in order to obtain ferrite particles having good crystallinity, plate-like soft magnetic ferrite particles cannot be obtained because the plate-like property is lost (Comparative Example 1). For the above reasons, the conventional plate-like Ni-
It is considered that the real part of the relative magnetic permeability of the composite obtained by mixing and dispersing the Zn-Cu-based ferrite particle powder in the resin is low.

Table 3 shows radio wave absorption characteristics when each of the composites shown in Table 2 is backed with a metal. The thickness of each composite was adjusted so that the maximum absorption was -20 dB.
Example 1 shows the absorption characteristics of a composite in which the plate-like soft magnetic ferrite particles according to the present invention were mixed and dispersed in a resin, and the thickness of the composite was 8.5 mm. Comparative Example 1 shows the absorption characteristics of a composite obtained by mixing and dispersing conventional granular Ni—Zn—Cu-based ferrite particles in a resin, and the thickness of the composite is 10.5 mm. Comparative Example 2 shows the absorption characteristics of a composite obtained by mixing and dispersing conventional plate-like Ni-Zn-Cu-based ferrite particles in a resin, and the thickness of the composite was 13.5 mm. As can be seen from Table 3, the soft magnetic ferrite particle composite according to the present invention has a thinner bandwidth and a wider bandwidth 2 than Comparative Examples 1 and 2, assuming that the bandwidth exhibiting absorption of −10 dB or more is a measure of the radio wave absorption characteristics. .50
GHz is shown. The cause is, as described above, the relative permeability of the soft magnetic ferrite particle composite according to the present invention,
It is considered that both the real part and the imaginary part are larger than the conventional ferrite composite.

[0023]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which do not limit the scope of the present invention. The particle shape, average plate surface diameter, and aspect ratio in the following Examples and Comparative Examples were observed with a scanning electron microscope. To identify the product phase, X
A line diffractometer RAD-2A (manufactured by Rigaku Corporation) was used.

The relative magnetic permeability of the composite at 1 MHz or lower was calculated from the value obtained by measuring the impedance with an impedance analyzer HP4192A (manufactured by Hewlett-Packard Japan Co., Ltd.) after winding a coil around a sample molded in a ring shape. . The relative magnetic permeability of the composite at 1 MHz or higher can be determined by inserting a ring-shaped sample into a coaxial tube and then using a network analyzer HP8753C.
(Hewlett-Packard Co., Ltd.) by measuring the reflection coefficient S ₁₁ and the transmission coefficient S _21, was calculated from these values.

The radio wave absorption characteristic is determined by inserting a ring-shaped sample into a coaxial tube having one end short-circuited with a metal plate so as to be in close contact with the metal plate, and then using a network analyzer HP8.
753C (Nippon Hewlett-Packard Co., Ltd.)
Was evaluated using a reflection coefficient S ₁₁ measured by. The thickness of the composite was adjusted so that the maximum absorption was -20 dB, and the bandwidth showing absorption of -10 dB or more was used as a measure of the radio wave absorption characteristics.

Example 1 Plate-like α-Fe ₂ O ₃ , amorphous Mg (OH) ₂ , CuO and ZnO were weighed so that the composition became Mg _0.41 Cu _0.10 Zn _0.51 Fe _1.98 O _4, and wet After mixing with an attritor for 1 hour, the mixture was filtered and dried. Then, the mixed powder was dried at 1000 ° C. in air for 3 hours.
Fired for hours. The shape of the obtained soft magnetic ferrite particles was plate-like, the average plate surface diameter was 3.3 μm, and the aspect ratio was 5.3. According to X-ray diffraction, the crystal structure was a spinel type.

The obtained plate-like soft magnetic ferrite particles and ethylene-vinyl acetate copolymer resin were mixed so that the ratio of the plate-like soft magnetic ferrite particles was 84.0% by weight, and the mixture was formed using a plast mill. And kneaded at a temperature of 80 ° C. The obtained kneaded material was heated to 60 ° C. using a biaxial hot roll.
At a temperature of. This was punched out into a ring shape having an outer diameter of 38 mm and an inner diameter of 17 mm using a mold to obtain a sample for measuring relative magnetic permeability and radio wave absorption characteristics. Table 2 shows the relative permeability at each frequency of the relative permeability of the obtained ring-shaped sample.
The real part at 100 kHz was 20.9. Further, as shown in Table 3, the radio wave absorption characteristics of the composite sample having a thickness of 8.5 mm were as follows.
It showed -20 dB at GHz, and the bandwidth showing absorption of -10 dB or more was 2.50 GHz.

Examples 2 to 5 Composition of plate-shaped soft magnetic ferrite particle powder, firing temperature, firing time, average plate diameter, aspect ratio, content of plate-shaped soft magnetic ferrite particle powder in composite, and A plate-like soft magnetic ferrite particle powder and a soft magnetic ferrite particle composite using the same were prepared in the same manner as in Example 1 except that the thickness of the composite was variously changed. The manufacturing conditions are shown in Table 1, and various characteristics are shown in Tables 2 and 3.

COMPARATIVE EXAMPLE 1 Amorphous α-Fe ₂ O ₃ , NiO, ZnO, and CuO were composed of Ni _0.28 Zn
_After weighing _0.67 Cu _0.08 Fe _1.97 O ₄ and mixing with a wet attritor for 1 hour, the mixture was filtered and dried. afterwards,
This mixed powder was fired in the air at 1300 ° C. for 2 hours.
The fired particle powder was pulverized by a wet ball mill, and then filtered and dried. The shape of the obtained soft magnetic ferrite particle powder was granular, and the crystal structure was a spinel type according to X-ray diffraction. A ring-shaped composite sample was prepared from the granular soft magnetic ferrite particles in the same manner as in Example 1, and the relative magnetic permeability and radio wave absorption characteristics were measured. The measurement results of the relative magnetic permeability are shown in Table 2, and the real part at 100 kHz is 9.
The value was as low as 1. Further, as shown in Table 3, the radio wave absorption characteristics of the composite sample having a thickness of 13.5 mm showed -20 dB at a center frequency of 1.36 GHz, and at that time, -10 dB.
The bandwidth showing the absorption of dB or more was a narrow bandwidth of 1.60 GHz.

Comparative Example 2 Plate-like α-Fe_TwoO_ThreeAmorphous NiO, ZnO, CuO
_0.20Zn_0.62Cu_0.22Fe _1.96O_FourWeighed so that
After mixing with an attritor for 1 hour, the mixture was filtered and dried. So
Then, the mixed powder is fired in the air at 1000 ° C. for 5 hours.
did. The shape of the obtained soft magnetic ferrite particle powder is plate-like
With an average plate surface diameter of 3.5 μm and an aspect ratio of 5.8.
there were. According to X-ray diffraction, the crystal structure is spinel type.
Met. The plate-like ferrite particles were prepared in the same manner as in Example 1.
A ring-shaped composite sample is prepared by the same method as above, and the relative permeability and
The radio wave absorption characteristics were measured. Table 2 shows the measurement results of the relative magnetic permeability.
As shown, the real part at 100 kHz is as low as 4.3.
Value. In addition, a composite specimen having a thickness of 13.5 mm was used.
As shown in Table 3, the radio wave absorption characteristics of the material have a center frequency of 1.
Shows -20dB at 78GHz, then -10dB or more
Is a narrow bandwidth of 1.78 GHz.
Was.

Comparative Example 3 A plate-like ferrite particle powder was prepared in the same manner as in Example 1 except that the composition was Mg _0.28 Cu _0.04 Zn _0.70 Fe _1.98 O ₄ and the firing temperature was 950 ° C. The shape of the obtained ferrite particle powder was plate-like, with an average plate surface diameter of 9.8 and an aspect ratio of 15.7. According to X-ray diffraction, the crystal structure was a spinel type. A ring-shaped composite sample was prepared from the plate-like ferrite particle powder in the same manner as in Example 1, and the relative magnetic permeability and the radio wave absorption characteristics were measured. The measurement results of the relative magnetic permeability are shown in Table 2, and the real part at 100 kHz was a low value of 7.3. In addition, the thickness is 12.0 mm
As shown in Table 3, the radio wave absorption characteristics of the composite sample
It showed -20 dB at a center frequency of 1.48 GHz, and the bandwidth showing absorption of -10 dB or more was a narrow bandwidth of 1.72 GHz.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

As described above, the soft magnetic ferrite particle composite in which the plate-like soft magnetic ferrite particles according to the present invention are mixed and dispersed in a matrix has a high real part of relative permeability in a low frequency band. Because it can absorb electromagnetic waves over a wide band in the high frequency band, and has excellent workability and high flexibility, it should be used for a wide range of applications such as coil cores, radio wave absorbing materials, and noise absorbing materials. Can be.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G002 AA06 AD02 AE02 5E041 AB14 AB19 BB04 CA10 HB17 NN02 NN06 NN14 5E321 BB33 BB53 GG05 GG07 GG11 5J020 BD02 EA02 EA08 EA10

Claims (4)

[Claims] 1. A plate-like shape having a composition of Mg _a Cu _b Zn _c
Fe _d O ₄ (however, 0.3 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.2, 0.4 ≦ c
≦ 0.6, 1.8 ≦ d ≦ 2.2) soft magnetic ferrite particles. 2. The soft magnetic ferrite particle powder according to claim 1, wherein the average plate surface diameter is 0.5 to 50 μm and the aspect ratio is 1.2 to 50. 3. A soft magnetic ferrite particle composite comprising the soft magnetic ferrite particle powder according to claim 1 and 2 mixed and dispersed in a matrix at a ratio of 75 to 92% by weight. 4. The soft magnetic ferrite particle composite according to claim 3, wherein the real part of the relative magnetic permeability at a frequency of 100 kHz is 18 to 30.