JP2010114407A - Mixed ferrite powder, method for manufacturing the same, and radio-wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ferrite powder that ensures a prescribed attenuation amount in a prescribed frequency band when manufacturing a radio-wave absorbing sheet and a method for manufacturing the same, and a radio-wave absorbing sheet. <P>SOLUTION: Mixed ferrite powder is configured as follows. The size of each peak particle size of mixed ferrite powder, in which two or more of ferrite powders are mixed, is set as P. When the largest peak particle size is set as P<SB>max</SB>and the smallest peak particle size as P<SB>min</SB>, they meet P<SB>max</SB>/P<SB>min</SB>≥1.5. Each radio-wave absorber is manufactured from each of the two or more of ferrite powders constituting the mixed ferrite powder. A frequency showing the maximum value of an imaginary part μ" of a complex permeability is set as f. When the highest frequency in the frequencies f of the two or more of radio-wave absorbers is set as f<SB>max</SB>and the lowest frequency as f<SB>min</SB>, they meet f<SB>max</SB>/f<SB>min</SB>≤1.3. When the largest maximum value in the maximum values of the respective imaginary parts μ" of each complex permeability is set as μ"<SB>max</SB>and the smallest maximum value as μ"<SB>min</SB>, they meet μ"<SB>max</SB>/μ"<SB>min</SB>≤1.5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a mixed ferrite powder suitable for a radio wave absorber used in a high frequency band of 1 GHz or more, a manufacturing method thereof, and a radio wave absorber using the mixed ferrite powder.

In recent years, with the advancement of information communication technology, radio waves in the GHz band have been used for various purposes. For example, mobile phones, wireless LANs, satellite broadcasting, intelligent road transportation systems, non-stop automatic toll collection systems (ETC), automobile driving support systems (AHS), and the like. Thus, when radio wave usage forms in a high frequency range are diversified, there is a concern about failure, malfunction, malfunction or the like due to interference between electronic components, and countermeasures are important. As one of countermeasures, a method of absorbing unnecessary radio waves using a radio wave absorber and preventing reflection and intrusion of radio waves is effective. For this reason, the demand for radio wave absorbers for the GHz band is increasing.

  Conventionally, oxide-based magnetic materials such as ferrite are often used for radio wave absorbers for high frequency bands. Among ferrites, spinel type is mainly used in the MHz band. And as what exhibits the outstanding characteristic in the high frequency band above GHz band, this applicant is Z-type hexagonal ferrite (patent document 1), Y-type hexagonal ferrite (patent document 2), M-type hexagonal ferrite. (Patent Document 3) is disclosed.

On the other hand, in the field of ferrite powders for magnets, the present applicant has 15 to 40% by weight of fine powder having an average particle size of 0.30 to 0.50 μm and the remainder of the coarse powder having an average particle size of 1.0 to 2.50 μm. The melt flow rate was 0.9 to 1.5 μm and the powder pH was 7 to 10 and the ferrite flow rate was 93% by weight according to the following MFR measurement method. Discloses a magnetoplumbite type ferrite powder having a particle size of 7 g / 10 min or more (Patent Document 4).

JP 2007-180469 A JP 2008-66364 A JP 2006-137653 A Japanese Patent No. 3257936

However, since the spinel type ferrite described above cannot break the limit of Snoek, it is difficult to use in a high frequency band exceeding 1 GHz.
On the other hand, Z-type hexagonal ferrite powder (may be simply referred to as “Z-type ferrite powder” in the present invention) and Y-type hexagonal ferrite powder (hereinafter simply referred to as “Y-type ferrite powder” in the present invention). M-type hexagonal ferrite powder (sometimes simply referred to as “M-type ferrite powder” in the present invention) is expected to have radio wave absorption characteristics at 1 GHz or higher. However, with conventional Z-type hexagonal ferrite powder, Y-type hexagonal ferrite powder, and M-type hexagonal ferrite powder, it is not easy to obtain a radio wave absorber having a sufficiently high attenuation in a predetermined frequency band. .

Here, the present inventors considered that it is effective to make the particle shape of the magnetic powder to be used thinner to increase the attenuation rate in a predetermined frequency band. Therefore, attempts were made to improve the radio wave absorption performance by making Z-type ferrite powder crystals, Y-type ferrite powder crystals, and M-type hexagonal ferrite powder crystals into thin plates.
However, the crystals of the Z-type, Y-type and M-type ferrite have a sharp particle size distribution and thus have poor packing properties, making it difficult to obtain the expected improvement.

Next, the present inventors apply the technique of Patent Document 4, divide the same type of ferrite powder, and further pulverize one of the divided ferrite powders, thereby having two different types of average particle diameters. The powder was manufactured and mixed to improve the fluidity and orientation, and the compression density of the ferrite powder in the radio wave absorber was increased to improve the radio wave absorption performance.
However, when the present inventors applied the technique of Patent Document 4 to magnetic powder for radio wave absorbers, in order to create fine powder, the size of the powder was reduced by pulverization. I found out that

Therefore, this time, by controlling the firing conditions of the ferrite powder, etc., we tried to produce two or more different kinds of ferrite powder having different average particle diameters, and mixed them to improve the fluidity and orientation. . And by improving the said fluidity | liquidity and orientation, the compression density of ferrite powder was raised in the electromagnetic wave absorber, and the improvement of the electromagnetic wave absorber was tried.
However, when the particle size of the ferrite powder is changed by controlling the firing conditions and the like, it has now been found that the frequency of the radio wave at which the ferrite powder exhibits radio wave absorption characteristics also changes.

  The present invention has been made under the above-mentioned circumstances, and the problem to be solved is to use, for example, a radio wave absorption sheet using the ferrite powder while having the same powder characteristics as the conventional ferrite powder. It is to provide a mixed ferrite powder capable of obtaining a predetermined attenuation in a predetermined frequency band, a manufacturing method thereof, and a radio wave absorbing sheet using the mixed ferrite powder when manufactured.

As a result of the inventors conducting research to solve the above-mentioned problems, it is possible to change the pulverization conditions, firing conditions, etc., in the same composition ferrite powder, and not to produce powders having different particle sizes but peaks. Using each of two or more different types of ferrite powders having different particle sizes and two or more different types of ferrite powders having different peak particle sizes, and a polymer base material, A radio wave absorber having a ferrite powder concentration of 90% by mass is manufactured, and in each of the radio wave absorbers, the frequency indicating the maximum value of the imaginary part μ ″ of the complex permeability is set to f, and the two or more types of radio wave absorbers are absorbed. Of the body frequencies f, where f _{max is} the highest frequency and f _min is the lowest frequency, f _max / f _min ≦ 1.3, and each of the two or more types of radio wave absorbers Imaginary part μ '' of complex permeability Of Daine, 2 having the largest ones mu _{'when' max,} the smallest mu _{'was' min,} that μ _{'' max} / μ '' is a _min ≦ 1.5, approximate magnetic properties More than one type of ferrite powder of different composition is mixed. And the radio wave absorber containing the mixed ferrite powder obtained the epoch-making knowledge that the electromagnetic wave absorption characteristics can be improved at the target frequency, and the present invention was completed.

  In the present invention, the “peak particle size” of the ferrite powder means that when the particle size distribution curve of the ferrite powder is drawn on a graph in which the horizontal axis represents the particle size and the vertical axis represents the frequency (number of particles). In the distribution curve, it is a particle diameter showing the maximum value (peak) of the frequency, and corresponds to a so-called “mode diameter”. The “peak particle size” can be determined by measuring the particle size distribution curve of the ferrite powder using a laser diffraction particle size distribution measuring apparatus.

That is, the first invention for solving the problem is:
A mixed ferrite powder in which two or more kinds of ferrite powders are mixed,
The peak particle size of each of the two or more ferrite powders constituting the mixed ferrite powder is P, and the largest peak particle size of the two or more ferrite powders is P _max , When the smallest peak particle size is P _min , P _max / P _min ≧ 1.5,
And using each of 2 or more types of ferrite powders which constitute the mixed ferrite powder, and a polymer substrate, a radio wave absorber in which each ferrite powder concentration is 90% by mass is prepared, In the radio wave absorber, the frequency indicating the maximum value of the imaginary part μ ″ of the complex permeability is assumed to be f, and among the frequencies f of the two or more types of radio wave absorbers, the highest frequency is f _max and the lowest frequency is f. _{When min} , f _max / f _min ≦ 1.3, and the largest value among the maximum values of the imaginary part μ ″ of the respective complex magnetic permeability of the two or more types of radio wave absorbers The mixed ferrite powder is characterized in that μ ″ _max / μ ″ _min ≦ 1.5 when μ ″ _{max is} the smallest and μ ″ _min .

The second invention is
The two or more types of ferrite powders are Z-type hexagonal ferrite powder and Y-type hexagonal ferrite powder, which is a mixed ferrite powder according to the first invention.

The third invention is
The mixed ferrite powder according to the first aspect, wherein the two or more types of ferrite powders are Z-type hexagonal ferrite powder and M-type hexagonal ferrite powder.

The fourth invention is:
A method for producing a mixed ferrite powder comprising mixing two or more types of ferrite powder to produce a mixed ferrite powder,
The peak particle size of each of the two or more types of ferrite powders is P, and among the peak particle sizes of the two or more types of ferrite powders, the largest peak particle size is P _max and the smallest peak particle size is When P _min , P _max / P _min ≧ 1.5,
In addition, using each of the two or more types of ferrite powders and the polymer base material, a radio wave absorber having a ferrite powder concentration of 90% by mass is prepared. When the frequency indicating the maximum value of the imaginary part μ ″ of the magnetic permeability is f, and the highest frequency among the frequencies f of the two or more types of wave absorbers is f _max , and the lowest frequency is f _min , f _max / f _min ≦ 1.3, and among the maximum values of the imaginary part μ ″ of each of the two or more types of electromagnetic wave absorbers, the largest one is μ ″ _max , the most Mixing characterized in that mixed ferrite powder is produced by mixing two or more kinds of ferrite powders, where μ '' _max / μ '' _min ≦ 1.5, where μ ″ _min is a small one This is a method for producing ferrite powder.

The fifth invention is:
The method for producing a mixed ferrite powder according to the fourth aspect of the invention, wherein a Z-type hexagonal ferrite powder and a Y-type hexagonal ferrite powder are used as the two or more types of ferrite powders.

The sixth invention is:
The method for producing a mixed ferrite powder according to the fourth aspect of the invention, wherein Z-type hexagonal ferrite powder and M-type hexagonal ferrite powder are used as the two or more types of ferrite powders.

The seventh invention
A radio wave absorber comprising the mixed ferrite powder according to any one of the first to third inventions.

  The radio wave absorption sheet using the mixed ferrite powder according to the present invention achieves an attenuation of 20 dB, for example, in the 2.4 GHz band and the 9.58 GHz band, compared to the radio wave absorption sheet using the conventional mixed ferrite powder. In the required film thickness, a reduction of 10% or more was realized.

3 is a production flow diagram of mixed ferrite powder according to Example 1. FIG. It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on Example 1 (ZY type | mold mixing). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 2 (ZY type mixing). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on Example 3 (ZY type | mold mixing). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 4 (ZY type mixing). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on Example 5 (ZY type | mold mixing). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 1 (Z type). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 1 (Y type). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Comparative Example 1 (fine Z type). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex magnetic permeability of the radio wave absorber sheet according to Comparative Example 2 (Strong Z type). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on the comparative example 3 (Z fine Z type | mold mixing). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on the comparative example 4 (Z strong / micro Z type mixing). It is a graph which shows the result of having simulated the influence of the sheet thickness which has on the attenuation amount in 2.4 GHz from the material constant of the electromagnetic wave absorption sheet which concerns on Examples 1-5 and Comparative Examples 1-4. 4 is an X-ray diffraction measurement result of ferrite powder according to Example 3. 3 is an X-ray diffraction measurement result of a ferrite powder according to Comparative Example 1. It is an X-ray-diffraction measurement result of the ferrite powder concerning the comparative example 2. FIG. 10 is a production flow diagram of mixed ferrite powder according to Example 6. 6 is a production flow diagram of mixed ferrite powder according to Comparative Example 5. FIG. It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 6 (Z fine M type mixing). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 7 (Z fine M type mixing). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on Example 8 (Z fine M type | mold mixing). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 6 (Z-type). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Example 6 (fine M type). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on the comparative example 5 (M fine M type | mold mixing). It is a graph which shows the frequency dependence of the real part μ 'and the imaginary part μ' 'in the complex permeability of the radio wave absorber sheet according to Comparative Example 5 (M type). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on the comparative example 6 (M fine M type | mold mixing). It is a graph which shows the frequency dependence of the real part (mu) 'and imaginary part (mu)' 'in the complex magnetic permeability of the electromagnetic wave absorber sheet which concerns on the comparative example 7 (M fine M type | mold mixing). It is a graph which shows the result of having simulated the influence of the sheet thickness which acts on the attenuation amount in 9.5 GHz from the material constant of the electromagnetic wave absorption sheet which concerns on Examples 6-8 and Comparative Examples 5-7. It is a graph which shows the relationship between the X-ray intensity of Y type ferrite, and the compounding ratio of Y type ferrite.

The ferrite powder according to the present invention is a ferrite powder obtained by mixing two or more types of ferrite powder selected from Z-type ferrite, Y-type ferrite, M-type ferrite, W-type ferrite and the like. And in 2 or more types of ferrite powder which comprises the said mixed ferrite powder, the peak particle size ( _Pmax ) of the ferrite powder with the largest peak particle size and the peak particle size (P with the ferrite powder with the smallest peak particle size) _min )) ( _Pmax / _Pmin ) is 1.5 or more, preferably 2.0 or more.

Furthermore, it is important that the mixed ferrite powder according to the present invention is a mixture of two or more ferrite powders having similar magnetic properties.
Specifically, using each of two or more ferrite powders constituting the mixed ferrite powder and a polymer base material, a radio wave absorber having a ferrite powder concentration of 90% by mass is prepared. In each of the radio wave absorbers, f is a frequency indicating the maximum value of the imaginary part μ ″ of the complex magnetic permeability, and the highest frequency among the frequencies f of the two or more radio wave absorbers is f _max and the lowest. When the frequency is f _min , f _max / f _min ≦ 1.3, and among the maximum values of the imaginary part μ ″ of the respective complex magnetic permeability of the two or more types of radio wave absorbers, It is preferable that μ ″ _max / μ ″ _min ≦ 1.5, where μ ″ _{max is} the largest and μ ″ _min is the smallest.

Conventionally, ferrite powder of the same composition was used, and the difference in particle size was created by changing the firing and pulverization levels to improve the compression density. In this conventional method, although the compression density can be improved, the ferrite powder that becomes the fine ferrite powder is excessively pulverized, so that the aspect ratio becomes small. As a result, in the radio wave absorber using the ferrite powder according to the conventional technique, the radio wave absorption characteristics are deteriorated.
Therefore, this time, by controlling the firing conditions of the ferrite powder of the same composition, etc., the ferrite powder of the same composition having two or more different average particle diameters is manufactured, and the fluidity and orientation are mixed by mixing them. Tried to raise. However, if the particle size of the ferrite powder is changed by controlling the firing conditions, etc., the frequency of the radio wave that the ferrite powder exhibits radio wave absorption characteristics will also change, and radio waves in the target frequency band will be changed. Absorption characteristics were degraded.

On the other hand, the ferrite powder according to the present invention having the above-described configuration is intended to improve the compression density due to the difference in the peak particle size between two or more types of ferrite powder. That is, pulverization is not performed in order to obtain a ferrite powder having a small particle diameter to be a fine ferrite powder.
Further, by selecting ferrite powders having similar radio wave absorption characteristics as the two or more types of ferrite powders, the radio wave absorber using the mixed ferrite powder according to the present invention has improved radio wave absorption characteristics. Is.

Due to the improvement of the radio wave absorption characteristics, for example, when a radio wave absorption sheet is used as the radio wave absorber, the radio wave absorption sheet can be made thin. Further, the thinning of the radio wave absorbing sheet enables further weight reduction and miniaturization of the electronic device, which greatly contributes to the industry.

Examples of the two or more types of ferrite powders described above include Z-type ferrite (general formula: A ₃ Me ₂ Fe ₂₄ O ₄₁ ), Y-type ferrite (general formula: A ₂ Me ₂ Fe ₁₂ O ₂₂ ), and M-type. Ferrite (general formula: AFe ₁₂ O ₁₉ ), W-type ferrite (general formula: AMe ₂ Fe ₁₆ O ₂₇ ), where A is, for example, one or more of Sr, Ba, Ca and Pb. For example, it is at least one selected from divalent Co, Ni, Zn, Cu, Mg, Fe, Mn, and a combination of monovalent Li and trivalent Fe. Including a trivalent element such as Al or a tetravalent or divalent element such as Ti and Co).

  Here, the combination of two or more of Z-type, Y-type, M-type, and W-type ferrite powders is suitable for application in the 2-76 GHz band, preferably in the 2-40 GHz band, more preferably in the 2-20 GHz band. Yes.

  In addition, when combining a ferrite powder with a large peak particle size and a ferrite powder with a small peak particle size, from the viewpoint of filling properties, the blending of “weight of ferrite powder with a large peak particle size: weight of ferrite powder with a small peak particle size” The ratio is 95: 5 to 45:55, preferably 90:10 to 50:50.

  Here, for example, the blending ratio of “the weight of the ferrite powder having a large peak particle diameter: the weight of the ferrite powder having a small peak particle diameter” can also be confirmed by X-ray diffraction measurement. Specifically, the strength ratio of the mixed ferrite powder is calculated from the peak intensity ratio of 2θ that appears most strongly from the ferrite powder of each composition, and “weight of ferrite powder having a large peak particle diameter: weight of ferrite powder having a small peak particle diameter” It is possible to determine the blending ratio of

Specifically, X-ray diffraction measurement is performed on each ferrite powder before mixing, and each 2θ that gives the strongest peak intensity is obtained. And X-ray intensity | strength: a in 2 (theta) with the strongest peak intensity | strength of the ferrite powder which wants to obtain | require a mixture ratio is measured. Similarly, the X-ray intensity at 2θ having the strongest peak intensity: b, c,.
From the values of a, b, c,..., XRD peak intensity ratio = a / (a + b + c +...)
And the blending ratio of each composition can be determined from the XRD peak intensity ratio.

Note that 2θ, which has the highest peak intensity, may differ from 2θ, which has the highest peak intensity in the JCPDS card. This is considered to be because the peak intensity of the plate-like surface is strongly observed because the ferrite powder has a plate-like particle shape.
In addition to the above-described X-ray diffraction, the mixed ferrite powder is analyzed by various analyzes such as SEM, SEM-EDS, etc., for example, the blending ratio of “ferrite powder weight having a large peak particle diameter: ferrite powder weight having a small peak particle diameter”. Can be confirmed.

The manufacturing method of each ferrite powder may be a known method. However, although the aggregated particles are dispersed and pulverized with respect to each of the ferrite powders, the pulverization is not performed.
In the present invention, “pulverization” refers to an operation of crushing crystal particles themselves, and “dispersion” refers to secondary particles in which primary particles are aggregated into primary particles without crushing the crystal particles themselves. This is an operation of dispersing, and “pulverization” is an operation of unraveling the powder solidified by an operation such as drying into the original powder.

Hereinafter, the present invention will be specifically described with reference to examples.
First, a method and apparatus for measuring physical properties of a sample used in the examples will be described.

<Specific surface area>
The specific surface area (SSA) of the ferrite powder was measured using a monosorb manufactured by Yuasa Ionics Co., Ltd. based on the BET method.

<Compression density>
The ferrite powder was compressed at a pressure of 1 ton / cm ³ after filling 10 g of ferrite powder into a cylindrical mold having an inner diameter of 2.54 cmφ. The density of the ferrite powder at this time was measured as a compression density.

<Particle size distribution>
The particle size distribution of the ferrite powder is determined by using a laser diffraction particle size distribution measuring device (HELOS & RODOS, manufactured by Nippon Laser Co., Ltd.) under the conditions of focal length = 20 mm, dispersion pressure 5.0 bar, suction pressure 130 mbar. The diameter was measured.
In the particle size distribution, D16, D50, and D84 are cumulative particle size distributions at a volume of 16%, 50%, and 84%, respectively, -0.3μ, −0.52μ, −1μ, + 5μ, “+8.6 μm” means the ratio of particles having a particle size of 0.3 μm under, a particle size of 0.52 μm under, a particle size of 1 μm under, a particle size of 5 μm upper, and a particle size of 8 μm upper.

<Magnetic properties>
The magnetic properties of the ferrite powder were measured for σs (emu / g), σr (emu / g), Hc (Oe), and SQ using VSM (manufactured by Toei Industry Co., Ltd., VSM-P7).

<X-ray measurement>
The measurement conditions of the X-ray diffraction of the ferrite powder are as follows: tube: cobalt tube, Goniometer: Ultimate + horizontal goniometer type I, Attachment: ASC-43 (vertical type), Monochromator: fully automatic monochromator, Scanning Mode: 2θ / θ, ScanningType: CONTINUOUS, X-Ray: 40 kV / 30 mA, diverging slit: 1/2 deg. , Scattering slit: 1/2 deg. , Receiving slit: 0.15 mm, measurement range: 30 ° to 70 °.

<Method for evaluating radio wave absorption characteristics of radio wave absorber>
A small piece cut out from the obtained radio wave absorber (sheet) was molded into a cylindrical measurement piece having an outer diameter of 7 mm and an inner diameter of 3 mm. The measurement piece is inserted into a φ7 mm × φ3.04 mm coaxial tube, the end of the coaxial tube is short-circuited with a short holder, and reflected / transmitted at 1 to 20 GHz using a network analyzer (HP8720D, manufactured by Hewlett-Packard Company). The coefficient (S parameter) was measured.
As will be described later, the measurement result showed that the value of μ ″ peaked in the GHz band. In general, in a radio wave absorber using a magnetic loss material, the complex relative permeability μ ″ indicating magnetic loss is high in a target radio wave absorption frequency band. Therefore, the measurement result of μ ″ was used as a parameter when performing radio wave absorption simulation.

[Example 1]
The production of the mixed ferrite powder according to Example 1 will be described with reference to the production flow shown in FIG.
(Ferrite powder with large peak particle size: Production of Z-type ferrite)
BaCO ₃ , Co ₃ O ₄ , ZnO, α-Fe ₂ O ₃ and BaCl ₂ were used as raw materials.
The raw materials excluding BaCl ₂ were weighed (1) at a molar ratio corresponding to (Ba: Co: Zn: Fe = 3: 1: 0.5: 24) to obtain a blended raw material. To 100 parts by mass of this blended raw material, 2.7 parts by mass of the BaCl ₂ was added.
The blended raw material powder to which BaCl ₂ was added and weighed was mixed (2) with a high-speed mixer, and further mixed by a method of strengthening (3) by a dry method using a vibration mill.
The obtained mixed powder is granulated (4), shaped into pellets and dried (5). This compact was fed into a roller hearth electric furnace and fired (6) by holding it at 1250 ° C. for 2 hours in the air.
The fired product thus obtained was dispersed (7) with a hammer mill, and further subjected to wet dispersion (8) for 5 minutes with attritor (AT) (solvent: water) for pulverization, followed by dehydration and drying (9). The dehydrated and dried product was crushed (10) with a hammer mill to obtain Z-type ferrite powder.

  Table 1 shows measurement results of the obtained Z-type ferrite powder, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 2 shows measurement results of magnetic properties.

(Ferrite powder with small peak particle size: manufacture of Y-type ferrite)
BaCO ₃ , ZnO, α-Fe ₂ O ₃ and BaCl ₂ were used as raw materials. Then, the raw materials excluding the BaCl ₂ were weighed (11) at a molar ratio corresponding to (Ba: Zn: Fe = 2: 1.6: 12). The BaCl ₂ was added in an amount of 2.7 parts by mass with respect to 100 parts by mass of the other blended raw materials.
The weighed raw material powders were mixed (12) with a high-speed mixer, and further mixed by a dry mill method (13) with a vibration mill.
The obtained mixed powder was granulated (14), formed into pellets, and dried (15). This compact was fed into a roller hearth electric furnace and fired (16) by holding it at 1200 ° C. for 2 hours in the air. The obtained fired product was dispersed (17) with a hammer mill, then wet dispersed (18) with an attritor (AT) (solvent: water) for 5 minutes, and dehydrated and dried (19). The dehydrated and dried fired product was crushed (20) with a hammer mill to obtain a Y-type ferrite powder.

  Table 1 shows measurement results of the obtained Y-type ferrite powder, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 2 shows magnetic property measurement results.

(Production of mixed ferrite powder)
From Table 1, in the obtained Z-type ferrite powder and Y-type ferrite powder, the peak particle sizes are Z-type ferrite powder 14.4 μm and Y-type ferrite powder 3.0 μm. Therefore, among the peak particle sizes of the two or more ferrite powders, the largest peak particle size is P _max = 14.4 μm, and the smallest peak particle size is P _min = 3.0 μm. The ratio P _max / P _min = 4.8.
Similarly, from Table 2, the frequency 2.56 GHz indicating the maximum value of the imaginary part μ ″ of the largest complex permeability and the frequency 2.22 GHz indicating the maximum value of the imaginary part μ ″ of the smallest complex permeability are The ratio f _max / f _min is 1.15, the value of μ ″ is 3.98 indicating the maximum value of the imaginary part μ ″ of the largest complex permeability, and the imaginary part μ ′ of the smallest complex permeability. The ratio μ ″ _max / μ ″ _min to the value 3.86 of μ ″ indicating the maximum value of 'was 1.03.
Here, the Z-type ferrite powder (90 wt%) obtained above and the Y-type ferrite powder (10 wt%) are weighed and dried using a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-10 type). The mixed ferrite powder according to Example 1 was obtained by mixing (21) to obtain a mixed ferrite powder.

  Table 1 shows measurement results of the blended ferrite powder according to Example 1, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 2 shows measurement results of magnetic properties. For convenience of explanation, the measurement results are also shown in Tables 9 and 10. The measurement results of the XRD peak intensity ratio are shown in Table 3.

(Manufacture of electromagnetic wave absorber)
Next, a radio wave absorber (sheet) containing the mixed ferrite powder according to Example 1 was manufactured, and radio wave absorption characteristics were measured. This will be specifically described below.
The ferrite powder and polymer base material are kneaded for 10 minutes in total for a total of 10 minutes so that the obtained mixed ferrite content is 90% by mass, and a radio wave absorber material (kneading) Product). In addition, as the polymer material, a synthetic rubber (manufactured by JSR (Japan Synthetic Rubber), N215SL) was used.
The produced radio wave absorber material was rolled to a thickness of 2.0 mm by a rolling roll to obtain a radio wave absorber (sheet) containing the mixed ferrite powder according to Example 1.

The radio wave absorber (sheet) containing the mixed ferrite powder according to Example 1 was evaluated for radio wave absorption characteristics, and the maximum value of the imaginary part μ ″ of the complex permeability of the radio wave absorber and the maximum of the μ ″ The frequency which shows a value and the simulation result of electromagnetic wave absorption were calculated | required.
The wave absorption characteristic evaluation results are shown in FIG. FIG. 2 is a graph in which the vertical axis represents the magnetic permeability μ, the horizontal axis represents the logarithm of the frequency, and the real part μ ′ of the complex permeability is plotted with a thin solid line and the imaginary part μ ″ is plotted with a thick solid line.

  2, the maximum value of the imaginary part μ ″ of the complex permeability of the radio wave absorber using the mixed ferrite powder according to Example 1 is 4.24, and the frequency indicating the maximum value of μ ″ is It was found to be 2.2 GHz. The values are shown in Table 2.

Furthermore, FIG. 13 shows the result of simulating the influence of the sheet thickness on the attenuation amount at 2.4 GHz from the ferrite content and material constant of the radio wave absorption sheet according to Example 1.
FIG. 13 is a graph in which the vertical axis represents the attenuation rate (dB) exhibited by the radio wave absorbing sheet with respect to 2.4 GHz electromagnetic waves, and the horizontal axis represents the sheet thickness (mm) of the radio wave absorbing sheet. At 2.4 GHz, the relationship between the sheet thickness (mm) of the radio wave absorber sheet and the attenuation (dB) of radio waves is simulated based on the S parameter. In FIG. 13, the amount of reflection on the vertical axis is the reflection amount (S11) obtained by the above measurement. The reflection amount (S11) is a value (reflection attenuation amount) obtained by subtracting the reflection amount when the sample is not loaded from the reflection amount when the sample is loaded in the holder.

In FIG. 13, the thick solid line, which is the simulation result of the radio wave absorber (sheet) containing the mixed ferrite powder, has a sheet thickness in a range where the attenuation factor is less than −20 dB, and the sheet thickness that the radio wave absorption sheet according to Example 1 should take. Thought. Then, in the case of the electromagnetic wave absorption sheet according to Example 1, it was found that the sheet thickness should be 3.2 mm or more. The values are shown in Table 2. The measurement results are also shown in Table 10 for convenience of explanation.
The attenuation rate of −20 dB was considered as a criterion for determining the sheet thickness that the radio wave absorption sheet according to Example 1 should adopt. If the attenuation is −20 dB or less in the radio wave absorption sheet, it is sufficiently used as the radio wave absorber. Because it is considered possible.

Here, the radio wave absorption characteristics of the single Z-type ferrite powder and the Y-type ferrite powder used for producing the mixed ferrite powder according to Example 1 will be described.
Specifically, similarly to the mixed ferrite powder, a radio wave absorber (sheet) was manufactured using a single Z-type ferrite powder and a single Y-type ferrite powder, and the same measurement was performed.
FIG. 7 shows the results of evaluating the radio wave absorption characteristics of the Z-type ferrite powder, and FIG. 8 shows the results of evaluating the radio wave absorption characteristics of the Y-type ferrite powder (FIGS. 7 and 8 and FIGS. 3 to 6 and 9 described later). -12 and FIGS. 19-27 are the same graphs as FIG.
From FIG. 7, as described above, it was found that the maximum value of μ ″ of the Z-type ferrite powder was 3.98, and the frequency indicating the maximum value of μ ″ was 2.22 GHz. It was also found that the maximum value of μ ″ of the Y-type ferrite powder was 3.86, and the frequency indicating the maximum value of μ ″ was 2.56 GHz.

Further, FIG. 13 shows the results of simulating the influence of the sheet thickness on the attenuation amount at 2.4 GHz from the ferrite content and material constant of the electromagnetic wave absorbing sheet for the Z-type ferrite powder and the Y-type ferrite powder. However, the Z-type ferrite powder is indicated by a thin solid line, and the Y-type ferrite powder is indicated by an elongated broken line.
From FIG. 13, it was found that in the case of a radio wave absorber (sheet) containing Z-type ferrite powder alone, the sheet thickness needs to be 3.5 mm or more. Similarly, in the case of a radio wave absorber (sheet) containing Y-type ferrite powder alone, it has been found that the sheet thickness needs to be 3.6 mm or more. The values are shown in Table 2.

[Examples 2 to 5]
Z-type ferrite powder and Y-type ferrite powder were produced in the same manner as in Example 1.
The produced Z-type ferrite powder and Y-type ferrite powder were weighed and blended in the proportions shown in Table 9, and mixed with a sample mill to obtain mixed ferrite powders according to Examples 2 to 5.
Table 9 shows measurement results of blended ferrite powders according to Examples 2 to 5, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 10 shows measurement results of magnetic properties. It was.
Furthermore, the X-ray-diffraction measurement result of the mixed ferrite powder which concerns on Example 3 was shown in FIG.

  Using the mixed ferrite powder according to Examples 2 to 5, radio wave absorbers (sheets) including the mixed ferrite powder according to Examples 2 to 5 were manufactured by the same operation as in Example 1. The radio wave absorption of the radio wave absorber (sheet) according to Examples 2 to 5 was measured.

The results of Example 2 are shown in FIG. 3, the results of Example 3 are shown in FIG. 4, the results of Example 4 are shown in FIG. 5, and the results of Example 5 are shown in FIG.
3 that the maximum value of μ ″ of the ferrite powder according to Example 2 is 4.38, and the frequency indicating the maximum value of μ ″ is 2.07 GHz. Similarly, it was found that the maximum value of μ ″ of the ferrite powder according to Example 3 is 4.49, and the frequency indicating the maximum value of μ ″ is 2.03 GHz. Similarly, it was found that the maximum value of μ ″ of the ferrite powder according to Example 4 is 4.35, and the frequency indicating the maximum value of μ ″ is 2.07 GHz. Similarly, it was found that the maximum value of μ ″ of the ferrite powder according to Example 5 was 4.26, and the frequency indicating the maximum value of μ ″ was 2.14 GHz. The values are shown in Table 10.

FIG. 13 shows the result of simulating the influence of the sheet thickness on the attenuation at 2.4 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Examples 2 to 5.
At this time, in FIG. 13, the simulation result of the radio wave absorber (sheet) according to the second embodiment is shown by a thick broken line, and the simulation result of the radio wave absorber (sheet) according to the third embodiment is shown by a thick and short broken line. The simulation result of the radio wave absorber (sheet) according to FIG. 6 is plotted with a thick one-dot chain line, and the simulation result of the radio wave absorber (sheet) according to Example 5 is plotted with a thick two-dot chain line.

  From FIG. 13, in order to obtain an attenuation of −20 dB or less, in the case of the radio wave absorber (sheet) according to Examples 2, 4, and 5, the sheet thickness may be 3.2 mm or more. In the case of the absorber (sheet), it has been found that the sheet thickness should be 3.1 mm or more. The values are shown in Table 10.

Further, in the mixed ferrite powders according to Examples 1 to 5, the blending ratio of the Z-type ferrite and the Y-type ferrite, the X-ray intensity at 2θ having the strongest peak intensity of the Z-type ferrite, and the highest peak intensity of the Y-type ferrite Table 4 shows the value of the XRD peak intensity ratio obtained from the strong X-ray intensity at 2θ, and FIG. 29 shows the relationship between the X-ray intensity of the Y-type ferrite and the blending ratio of the Y-type ferrite. FIG. 29 shows the XRD peak intensity ratio obtained from the X-ray intensity at 2θ, the strongest peak intensity of Y-type ferrite on the vertical axis, and the blending ratio of Y-type ferrite on the horizontal axis. It is the graph which plotted the data of the mixed ferrite powder which concerns. From Table 4, FIG. 29, and Table 3 described above, it can be seen that if the XRD peak intensity ratio obtained from the X-ray intensity at 2θ, which has the strongest peak intensity of Y-type ferrite, is known, the blending ratio of Y-type ferrite can be determined. .

Example 6
The production of the mixed ferrite powder according to Example 6 will be described with reference to the production flow shown in FIG.

(Ferrite powder with large peak particle size: Production of Z-type ferrite)
BaCO ₃ , Co ₃ O ₄ , ZnO, α-Fe ₂ O ₃ and BaCl ₂ were used as raw materials. The raw materials excluding BaCl ₂ were weighed (1) in a molar ratio corresponding to (Ba: Co: Zn: Fe = 3: 0.18: 1.62: 24) to obtain a blended raw material. The BaCl ₂ was added in an amount of 2.7 parts by mass with respect to 100 parts by mass of the other blended raw materials.
The weighed raw material powders were mixed (2) with a high speed mixer, and further mixed by a method of strengthening mixing (3) by a dry method using a vibration mill.
The obtained mixed powder is granulated (4), shaped into pellets and dried (5). This compact was fed into a roller hearth electric furnace and fired (6) by holding it at 1250 ° C. for 2 hours in the air.
The obtained fired product was dispersed (7) with a hammer mill, and further subjected to wet dispersion (8) for 5 minutes with an attritor (solvent: water), followed by dehydration and drying (9). The dehydrated and dried fired product was crushed (10) with a hammer mill to obtain a Z-type ferrite powder.

  Table 5 shows measurement results of the obtained Z-type ferrite powder, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 6 shows measurement results of magnetic properties.

(Ferrite powder with small peak particle size: Production of (fine) M-type ferrite powder with small peak particle size)
BaCO ₃ , Co ₃ O ₄ , ZnO, TiO ₂ and α-Fe ₂ O ₃ were used as raw materials. The raw materials were weighed (11) at a molar ratio corresponding to (Ba: Co: Zn: Ti: Fe = 2: 0.625: 0.625: 1.25: 9.5).
The weighed raw material powders were mixed (12) with a high-speed mixer, and further mixed by a dry mill method (13) with a vibration mill.
The obtained mixed powder is granulated (14) and formed into pellets and dried (15). This compact was fed into a roller hearth electric furnace and fired (16) by holding at 1220 ° C. for 2 hr in the atmosphere.
The obtained fired product was coarsely pulverized (17) with a hammer mill, and further subjected to wet pulverization (18) with an attritor (solvent: water) for 5 minutes for degreasing, followed by dehydration and drying (19). The dehydrated and dried fired product was crushed (20) with a hammer mill to obtain a (fine) M-type ferrite powder having a small peak particle size according to Example 6.

  Table 5 shows the measurement results of the blending of the (fine) M-type ferrite powder having a small peak particle size, the specific surface area (SSA), the compression density (CD), the particle size distribution, and the peak particle size according to Example 6. The measurement results are shown in Table 6. For convenience of explanation, the measurement results are also shown in Tables 9 and 10.

(Production of mixed ferrite powder)
From Table 5, the obtained Z-type ferrite powder and the small (fine) M-type ferrite powder having a small peak particle size have a peak particle size of 8.0 μm and the small (fine) M-type having a small peak particle size. The ferrite powder is 1.8 μm. Accordingly, among the peak particle sizes of the two or more types of ferrite powders, the largest peak particle size is P _max = 8.0 μm, and the smallest peak particle size is P _min = 1.8 μm. The ratio P _max / P _min = 4.4.
Similarly, from Table 6, a frequency of 10.56 GHz indicating the maximum value of the imaginary part μ ″ of the largest complex permeability and a frequency of 9.85 GHz indicating the maximum value of the imaginary part μ ″ of the smallest complex permeability are The ratio f _max / f _min is 1.07, the value of μ ″ 1.13 indicating the maximum value of the imaginary part μ ″ of the largest complex permeability, and the imaginary part μ ′ of the smallest complex permeability The ratio μ ″ _max / μ ″ _min with the value of μ ″ indicating the maximum value of “1.03” was 1.10.
Here, the Z-type ferrite powder (90 wt%) obtained above and the (fine) M-type ferrite powder (10 wt%) with a small peak particle size are weighed and dry-mixed (21) with a sample mill. Thus, mixed ferrite powder according to Example 6 was obtained.

  Table 5 shows measurement results of the blended ferrite powder according to Example 6, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 6 shows measurement results of magnetic properties.

(Manufacture of electromagnetic wave absorber)
Using the mixed ferrite powder according to Example 6, a radio wave absorber (sheet) according to Example 6 was produced by the same operation as in Example 1. The radio wave absorption characteristics of the radio wave absorber (sheet) using the mixed ferrite powder according to Example 6 were measured.

FIG. 19 shows the maximum value of the imaginary part μ ″ of the complex permeability of the radio wave absorber using the mixed ferrite powder according to Example 6, the frequency indicating the maximum value of μ ″, and the electromagnetic wave absorption simulation results. .
From FIG. 19, the maximum value of the imaginary part μ ″ of the complex permeability of the radio wave absorber using the mixed ferrite powder according to Example 6 is 1.13, and the frequency indicating the maximum value of μ ″ is It was found to be 9.85 GHz. The values are shown in Table 6.

Furthermore, the result of simulating the influence of the sheet thickness on the attenuation at 9.5 GHz from the ferrite content and material constant of the radio wave absorption sheet according to Example 6 is shown in FIG.
FIG. 28 is a graph in which the vertical axis represents the attenuation rate (dB) of the electromagnetic wave absorbing sheet with respect to 9.5 GHz electromagnetic waves, and the horizontal axis represents the thickness (mm) of the electromagnetic wave absorbing sheet. At 9.5 GHz, the relationship between the sheet thickness (mm) of the radio wave absorber sheet and the radio wave attenuation (dB) is simulated based on the S parameter. In FIG. 28, the amount of reflection on the vertical axis is the reflection amount (S11) obtained by the above measurement. The reflection amount (S11) is a value (reflection attenuation amount) obtained by subtracting the reflection amount when the sample is not loaded from the reflection amount when the sample is loaded in the holder.

In FIG. 28, the thick solid line, which is the simulation result of the radio wave absorber (sheet) containing the mixed ferrite powder according to Example 6, has a sheet thickness in a range lower than −20 dB, and the radio wave absorber sheet according to Example 6 It was considered as the sheet thickness to be taken. Then, in the case of the electromagnetic wave absorption sheet according to Example 6, it was found that the sheet thickness should be 1.6 mm or more. The values are shown in Table 6. The measurement results are also shown in Table 10 for convenience of explanation.
The attenuation rate of −20 dB was considered as a criterion for determining the sheet thickness that the radio wave absorption sheet according to Example 6 should adopt. If the attenuation is −20 dB or less in the radio wave absorption sheet, it is sufficiently used as the radio wave absorber. Because it is considered possible.

Hereinafter, the radio wave absorption characteristics of the single Z-type ferrite powder and the (fine) M-type ferrite powder having a small peak particle size, which were used for producing the mixed ferrite powder according to Example 6, were also measured.
Specifically, similarly to the mixed ferrite powder, a radio wave absorber (sheet) is manufactured using a single Z-type ferrite powder and a single (fine) M-type ferrite powder having a small peak particle diameter, and the same measurement is performed. Went.
FIG. 22 shows the results of evaluating the radio wave absorption characteristics of the Z-type ferrite powder, and FIG. 23 shows the results of evaluating the radio wave absorption characteristics of the (fine) M-type ferrite powder having a small peak particle size.
From FIG. 22, it was found that the maximum value of μ ″ of the Z-type ferrite powder was 1.13, and the frequency indicating the maximum value of μ ″ was 9.85 GHz. It was also found that the maximum value of μ ″ of the (fine) M-type ferrite powder having a small peak particle size was 1.03, and the frequency indicating the maximum value of μ ″ was 10.56 GHz. Therefore, μ ″ _max / μ ″ _min = 1.10 and f _max / f _min = 1.07. The values are shown in Table 6.

Furthermore, for Z-type ferrite powder and (fine) M-type ferrite powder having a small peak particle size, the effect of sheet thickness on the attenuation at 9.5 GHz was simulated from the ferrite content and material constant of the electromagnetic wave absorbing sheet. The results are shown in FIG. However, the Z-type ferrite powder is indicated by a thin solid line, and the (fine) M-type ferrite powder having a small peak particle size is indicated by an elongated broken line.
From FIG. 28, it was found that in the case of a radio wave absorber (sheet) containing Z-type ferrite powder alone, the sheet thickness needs to be 1.8 mm or more. Similarly, it was found that in the case of a radio wave absorber (sheet) containing only (fine) M-type ferrite powder having a small peak particle size, the sheet thickness is required to be 1.9 mm or more. The values are shown in Table 6.

[Examples 7 and 8]
In the same manner as in Example 6, a Z-type ferrite powder and a (fine) M-type ferrite powder having a small peak particle size were produced.
The prepared Z-type ferrite powder and the (fine) M-type ferrite powder having a small peak particle size are weighed and blended in the proportions shown in Table 9, and mixed in a sample mill to obtain the mixed ferrite powder according to Examples 7 and 8. Obtained.
Table 9 shows the measurement results of the specific surface area (SSA), compression density (CD), particle size distribution, peak particle size, and magnetic properties of the mixed ferrite powders according to Examples 7 and 8.

  Using the mixed ferrite powder according to Examples 7 and 8, radio wave absorbers (sheets) containing the mixed ferrite powder according to Examples 7 and 8 were produced by the same operation as in Example 1. The radio wave absorption of the radio wave absorbers (sheets) according to Examples 7 and 8 was measured.

The results of Example 7 are shown in FIG. 20, and the results of Example 8 are shown in FIG.
From FIG. 20, it was found that the maximum value of μ ″ of the ferrite powder according to Example 7 was 1.14, and the frequency indicating the maximum value of μ ″ was 9.78 GHz. Similarly, it was found that the maximum value of μ ″ of the ferrite powder according to Example 8 was 1.12 and the frequency indicating the maximum value of μ ″ was 9.78 GHz. The values are shown in Table 10.

FIG. 28 shows the result of simulating the influence of the sheet thickness on the attenuation at 9.5 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Examples 7 and 8.
In FIG. 28, the simulation result of the radio wave absorber (sheet) according to Example 7 is plotted by a thick broken line, and the simulation result of the radio wave absorber (sheet) according to Example 8 is plotted by a thick broken line.

  From FIG. 28, in order to obtain an attenuation of −20 dB or less, in the case of the radio wave absorber (sheet) according to Examples 7 and 8, it was found that the sheet thickness should be 1.6 mm or more. The values are shown in Table 10.

[Comparative Example 1]
Only the Z-type ferrite powder was produced by the same operation as in Example 1.
The Z-type ferrite powder was pulverized with a centrifugal ball mill (EBM) for 20 minutes to obtain a ferrite powder according to Comparative Example 1. Hereinafter, it is referred to as “ground (fine) Z-type ferrite powder”.

Table 9 shows the measurement results of the blending, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size of the pulverized (fine) Z-type ferrite powder according to Comparative Example 1, and the magnetic property measurement results. Is shown in Table 10.
Furthermore, the X-ray-diffraction measurement result of the pulverized (fine) Z-type ferrite powder according to Comparative Example 1 is shown in FIG.

(Manufacture of electromagnetic wave absorber)
Using only the pulverized (fine) Z-type ferrite powder according to Comparative Example 1, a radio wave absorber (sheet) according to Comparative Example 1 was produced in the same manner as in Example 1. The radio wave absorber (sheet) according to Comparative Example 1 was subjected to radio wave absorption measurement.
A radio wave absorber (sheet) according to Comparative Example 1 was manufactured. The radio wave absorption characteristics of the radio wave absorber (sheet) according to Comparative Example 1 were measured.

The result of Comparative Example 1 is shown in FIG.
From FIG. 9, it was found that the maximum value of μ ″ of the ferrite powder according to Comparative Example 1 was 2.43, and the frequency indicating the maximum value of μ ″ was 2.56 GHz. The values are shown in Table 10.

  FIG. 13 shows data as a result of simulating the influence of the sheet thickness on the attenuation at 2.4 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Comparative Example 1.

  In FIG. 13, the simulation result of the radio wave absorber (sheet) according to Comparative Example 1 is plotted with a thin broken line. Then, in the case of the electromagnetic wave absorber (sheet) according to Comparative Example 1, it has been found that the sheet thickness is required to be 4.7 mm or more. The results are shown in Table 10.

[Comparative Example 2]
Only the Z-type ferrite powder was produced by the same operation as in Example 1.
The Z-type ferrite powder was pulverized with a centrifugal ball mill (EBM) for 40 minutes to obtain a ferrite powder according to Comparative Example 2. Hereinafter, it is referred to as “strongly pulverized (strong) Z-type ferrite powder”.

Table 9 shows the measurement results of the composition, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size of the strongly pulverized (strong) Z-type ferrite powder according to Comparative Example 2. The measurement results are shown in Table 10.
Furthermore, the X-ray-diffraction measurement result of the strongly ground (strong) Z-type ferrite powder according to Comparative Example 2 is shown in FIG.

(Manufacture of electromagnetic wave absorber)
A radio wave absorber (sheet) according to Comparative Example 2 was manufactured by the same operation as Example 1 using only the strongly pulverized (strong) Z-type ferrite powder according to Comparative Example 2. The radio wave absorption characteristics of the radio wave absorber (sheet) according to Comparative Example 2 were measured.

The result of Comparative Example 2 is shown in FIG.
10 that the maximum value of μ ″ of the ferrite powder according to Comparative Example 2 is 1.68, and the frequency indicating the maximum value of μ ″ is 3.66 Hz. The values are shown in Table 10.

  FIG. 13 shows data obtained as a result of simulating the influence of the sheet thickness on the attenuation at 2.4 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Comparative Example 2.

  In FIG. 13, the simulation result of the radio wave absorber (sheet) according to Comparative Example 2 is plotted with a thin one-dot chain line. Then, in the case of the electromagnetic wave absorber (sheet) according to Comparative Example 2, it was found that the attenuation rate did not reach −20 dB. The results are shown in Table 10.

[Comparative Example 3]
A Z-type ferrite powder was produced in the same manner as in Example 1.
In order to bring a part of the Z-type ferrite powder close to the peak particle diameter of the Y-type ferrite powder, it was pulverized for 20 minutes using a centrifugal ball mill (EBM), and the same pulverized (fine) Z-type as in Comparative Example 1 was used. Ferrite powder was obtained.

  30% by weight of the pulverized (fine) Z-type ferrite powder obtained above and 70% by weight of the Z-type ferrite powder according to Example 1 were weighed and mixed in a sample mill to obtain a mixed powder. Comparative Example 3 To obtain a mixed ferrite powder.

  Table 9 shows the measurement results of the blended ferrite powder according to Comparative Example 3, the specific surface area (SSA), the compression density (CD), the particle size distribution, and the peak particle size, and Table 10 shows the measurement results of the magnetic properties.

(Manufacture of electromagnetic wave absorber)
Using the mixed ferrite powder according to Comparative Example 3, a radio wave absorber (sheet) according to Comparative Example 3 was produced in the same manner as in Example 1. The radio wave absorption characteristics of the radio wave absorber (sheet) according to Comparative Example 3 were measured.

The results of Comparative Example 3 are shown in FIG.
From FIG. 11, it was found that the maximum value of μ ″ of the ferrite powder according to Comparative Example 3 was 3.84, and the frequency indicating the maximum value of μ ″ was 2.12 GHz. The values are shown in Table 10.

  FIG. 13 shows the result of simulating the influence of the sheet thickness on the attenuation at 2.4 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Comparative Example 3.

  In FIG. 13, the simulation result of the radio wave absorber (sheet) according to Comparative Example 3 is plotted with a thin two-dot chain line. Then, in the case of the electromagnetic wave absorber (sheet) according to Comparative Example 3, it has been found that the sheet thickness is required to be 3.5 mm or more. The results are shown in Table 10.

[Comparative Example 4]
A Z-type ferrite powder was produced in the same manner as in Example 1.
In order to bring a part of the Z-type ferrite powder close to the peak particle diameter of the Y-type ferrite powder, it was pulverized for 40 minutes using a centrifugal ball mill (EBM), and was crushed as strongly as in Comparative Example 2 (strong). Z-type ferrite powder was obtained.

  30 wt% of the strongly pulverized (strong) Z-type ferrite powder obtained above and 70 wt% of the Z-type ferrite powder according to Example 1 were weighed and mixed in a sample mill to obtain a mixed powder. A mixed ferrite powder according to Example 4 was obtained.

  Table 9 shows the measurement results of the blended ferrite powder according to Comparative Example 4, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 10 shows the measurement results of magnetic properties.

  Using the mixed ferrite powder according to Comparative Example 4, a radio wave absorber (sheet) according to Comparative Example 4 was produced by the same operation as in Example 1. The radio wave absorption characteristics of the radio wave absorber (sheet) according to Comparative Example 4 were measured.

The result of Comparative Example 4 is shown in FIG.
From FIG. 12, it was found that the maximum value of μ ″ of the ferrite powder according to Comparative Example 4 is 3.68, and the frequency indicating the maximum value of μ ″ is 2.07 GHz. The values are shown in Table 10.

  FIG. 13 shows the result of simulating the influence of the sheet thickness on the attenuation at 2.4 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Comparative Example 4.

  In FIG. 13, the simulation result of the radio wave absorption sheet according to Comparative Example 4 is plotted with a thin broken line. Then, in the case of the radio wave absorber (sheet) according to Comparative Example 4, it was found that the sheet thickness is required to be 3.6 mm or more. The results are shown in Table 10.

[Comparative Example 5]
The production of the mixed ferrite powder according to Comparative Example 5 will be described with reference to the production flow shown in FIG.

(Ferrite powder with large peak particle size: production of M-type ferrite)
BaCO ₃ , Co ₃ O ₄ , ZnO, TiO ₂ , α-Fe ₂ O ₃ and BaCl ₂ were used as raw materials. Then, the raw materials excluding the BaCl ₂ are weighed in a molar ratio corresponding to (Ba: Co: Zn: Ti: Fe = 2: 0.625: 0.625: 1.25: 9.5). (1) Then blended. The BaCl _2, to the other mixed material 100 parts by weight, was added 2.7 parts by weight.
The raw material powder weighed and blended was mixed (2) with a high speed mixer, and further mixed by a method of mixing and strengthening (3) by a dry method using a vibration mill.
The obtained mixed powder was granulated (4) and formed into pellets, and dried (5).
This compact was fed into a roller hearth electric furnace and fired (6) by holding it at 1250 ° C. for 2 hours in the air.
The obtained fired product was dispersed (7) with a hammer mill, wet dispersed (8) for 5 minutes with an attritor (solvent: water), pulverized, and then dehydrated and dried (9). The dehydrated and dried fired product was crushed (10) with a hammer mill to obtain an M-type ferrite powder having a large peak particle size.

Formulation of M type ferrite powder with large peak particle size, specific surface area (SSA), compression density (CD)
Table 7 shows the measurement results of particle size distribution and peak particle size, and Table 8 shows the measurement results of magnetic properties. For convenience of explanation, the measurement results are also shown in Tables 9 and 10.

(Manufacture of electromagnetic wave absorber)
From Table 7, the obtained M-type ferrite powder having a large peak particle size and the (fine) M-type ferrite powder having a small peak particle size have a peak particle size of 4.5 μm. The (fine) M-type ferrite powder having a small peak particle size is 1.8 μm. Accordingly, among the peak particle sizes of the two or more types of ferrite powders, the largest peak particle size is P _max = 8.0 μm, and the smallest peak particle size is P _min = 4.5 μm. The ratio P _max / P _min = 2.5.
Similarly, from Table 8, the frequency indicating the maximum value of the imaginary part μ ″ of the largest complex permeability and the frequency of 8.64 GHz indicating the maximum value of the imaginary part μ ″ of the smallest complex permeability are The ratio f _max / f _min is 1.22, the value of μ ″ 1.64 indicating the maximum value of the imaginary part μ ″ of the largest complex permeability and the imaginary part μ ′ of the smallest complex permeability The ratio μ ″ _max / μ ″ _min to the value 1.03 of μ ″ indicating the maximum value of 'was 1.60.
Here, 90 wt% of the M-type ferrite powder having a large peak particle diameter obtained above and 10 wt% of the fine M-type ferrite powder according to Example 6 were weighed and mixed with a sample mill to obtain a mixed powder. A mixed ferrite powder according to Comparative Example 5 was obtained.
Using the mixed ferrite powder according to Comparative Example 5, a radio wave absorber (sheet) according to Comparative Example 5 was produced in the same manner as in Example 1. The radio wave absorption characteristics of the radio wave absorber (sheet) according to Comparative Example 5 were measured.

The result of Comparative Example 5 is shown in FIG.
From FIG. 24, it was found that the maximum value of μ ″ of the ferrite powder according to Comparative Example 5 was 1.53, and the frequency indicating the maximum value of μ ″ was 8.64 GHz. The values are shown in Table 10.

The radio wave absorber (sheet) according to Comparative Example 5 was subjected to the radio wave absorption measurement described later.
FIG. 28 shows the result of simulating the influence of the sheet thickness on the attenuation at 9.5 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Comparative Example 5.

  In FIG. 28, the simulation result of the radio wave absorption sheet according to Comparative Example 5 is plotted with a thin two-dot chain line. Then, in the case of the radio wave absorber (sheet) according to Comparative Example 5, it was found that the attenuation rate did not reach −20 dB. The results are shown in Table 8. The measurement results are also shown in Table 10 for convenience of explanation.

Hereinafter, the radio wave absorption characteristics were also measured for the M-type ferrite powder having a large peak particle size, which was used for producing the mixed ferrite powder according to Comparative Example 5.
Specifically, similarly to the mixed ferrite powder, a radio wave absorber (sheet) was manufactured using M-type ferrite powder having a large peak particle size, and the same measurement was performed.
FIG. 25 shows the evaluation results of the radio wave absorption characteristics of the M-type ferrite powder having a large peak particle size.
FIG. 25 reveals that the maximum value of μ ″ of the M-type ferrite powder having a large peak particle size is 1.64, and the frequency indicating the maximum value of μ ″ is 8.64 GHz. Further, as described above, the maximum value of μ ″ of the (fine) M-type ferrite powder having a small peak particle size is 1.03, and the frequency indicating the maximum value of μ ″ is 10.56 GHz. There was found. Therefore, μ ″ _max / μ ″ _min = 1.60 and f _max / f _min = 1.22. The values are shown in Table 8.

Furthermore, FIG. 28 shows the result of simulating the influence of the sheet thickness on the attenuation at 9.5 GHz from the ferrite content and material constant of the electromagnetic wave absorbing sheet for M-type ferrite powder having a large peak particle size. However, the M-type ferrite powder having a large peak particle size is indicated by a thick one-dot chain line.
From FIG. 28, it was found that the attenuation rate did not reach −20 dB in the case of a radio wave absorber (sheet) containing M-type ferrite powder having a large peak particle size alone. The results are shown in Table 8.

[Comparative Examples 6 and 7]
An M-type ferrite powder was produced by the same operation as in Comparative Example 5, and a (fine) M-type ferrite powder having a small peak particle size was produced by the same operation as in Example 6.
The prepared M-type ferrite powder and (fine) M-type ferrite powder were weighed and blended in the proportions shown in Table 9, and sample mill mixed to obtain ferrite powders according to Comparative Examples 6 and 7.
Table 9 shows measurement results of mixed ferrite powders according to Comparative Examples 6 and 7, specific surface area (SSA), compression density (CD), particle size distribution, and peak particle size, and Table 10 shows measurement results of magnetic properties. It was.

  Using the mixed ferrite powder according to Comparative Examples 6 and 7, radio wave absorbers (sheets) containing the mixed ferrite powder according to Comparative Examples 6 and 7 were manufactured by the same operation as in Example 1. The radio wave absorption characteristics of the radio wave absorbers (sheets) according to Comparative Examples 6 and 7 were measured.

The result of Comparative Example 6 is shown in FIG.
From FIG. 26, it was found that the maximum value of μ ″ of the ferrite powder according to Comparative Example 6 was 1.33, and the frequency indicating the maximum value of μ ″ was 8.64 GHz. The values are shown in Table 10.
The result of Comparative Example 7 is shown in FIG.
From FIG. 27, it was found that the maximum value of μ ″ of the ferrite powder according to Comparative Example 7 was 1.11 and the frequency indicating the maximum value of μ ″ was 8.78 GHz. The values are shown in Table 10.

FIG. 28 shows a simulation result of the influence of the sheet thickness on the attenuation at 9.5 GHz from the ferrite content and material constant of the radio wave absorber (sheet) according to Comparative Examples 6 and 7.
In FIG. 28, the simulation result of the radio wave absorber (sheet) according to Comparative Example 6 is plotted with a thin broken line, and the simulation result of the radio wave absorber (sheet) according to Comparative Example 7 is plotted with a thin one-dot chain line.

From Table 2 and FIG. 28, it was found that in the case of the radio wave absorber (sheet) according to Comparative Example 6, the attenuation rate did not reach −20 dB.
In the case of the radio wave absorber (sheet) according to Comparative Example 7, it was found that the sheet thickness is required to be 1.9 mm or more in order to obtain an attenuation of −20 dB or less. The results are shown in Table 10.

[Summary]
From the results shown in Table 9, the specific surface area (SSA), compression density (CD), magnetic properties measured by VSM, and particle size distribution data of the ferrite powders according to Examples 1 to 8 are variously manufactured according to the conventional technology. It was found that the ferrite powders according to Comparative Examples 1 to 7 produced by the method are within the range of the data.
From this, it was found that the ferrite powder according to Examples 1 to 8 can be handled with the same operation technique and equipment as the ferrite powder according to the prior art.

On the other hand, from the results shown in Table 10, the radio wave absorption characteristics of the radio wave absorber sheets manufactured from the ferrite powders according to Examples 1 to 8 are the same as those of the radio wave absorber sheets manufactured from the ferrite powders according to Comparative Examples 1 to 7. It was found to be superior to the absorption characteristics.
Specifically, in the 2.4 GHz band, when the ferrite powder concentrations of the radio wave absorber sheets according to Examples 1 to 5 and Comparative Examples 1 to 4 are all the same of 90%, they relate to Examples 1 to 5. The μ ″ of the radio wave absorber sheet was in the range of 4.24 to 4.49, whereas the μ ″ of the radio wave absorber sheet according to Comparative Examples 1 to 4 was 1.68 to 3.84. Stayed. Example 1
The frequency indicating the maximum value of μ ″ of the radio wave absorber sheet according to 5 to 5 was 2.03 to 2.20 GHz, whereas the maximum of μ ″ of the radio wave absorber sheet according to Comparative Examples 1 to 4 was used. The frequency showing the value was 2.07 to 3.66 GHz.

On the other hand, from the simulation results shown in FIG. 13, the radio wave absorber sheet according to Examples 1 to 5 can secure a specified attenuation with a thickness of 3.1 to 3.2 mm in the 2.4 GHz band. There was found. On the other hand, in the case of the radio wave absorber sheet according to Comparative Examples 1 to 4, it has been found that the specified attenuation cannot be secured without a thickness of 3.5 to 4.7 mm. Furthermore, it was also found that the radio wave absorber sheet according to Comparative Example 2 cannot secure a specified attenuation. That is, as the result of Comparative Example 4 shows, after additionally pulverizing the coarse Z-type ferrite powder to have the same peak particle size as the fine Y-type ferrite powder, the additional Even when the pulverized Z-type ferrite powder and the normal coarse Z-type ferrite powder were mixed, the wave absorption characteristics of the obtained absorber sheet were inferior to those of the examples.

On the other hand, in the 9.5 GHz band, when the ferrite powder concentrations of the radio wave absorber sheets according to Examples 6 to 8 and Comparative Examples 5 to 7 are all 90%, the radio wave absorbers according to Examples 6 to 8 The μ ″ of the sheet was in the range of 1.12 to 1.14, whereas the μ ″ of the radio wave absorber sheets according to Comparative Examples 1 to 4 was 1.11 to 1.53. And while the frequency which shows the maximum value of μ ″ of the radio wave absorber sheets according to Examples 6 to 8 was 9.78 to 9.85 GHz, the radio wave absorber sheets according to Comparative Examples 1 to 4 The frequency showing the maximum value of μ ″ remained at 8.64 to 8.78 GHz.

  On the other hand, from the simulation results shown in FIG. 28, it was found that the radio wave absorber sheets according to Examples 6 to 8 can ensure a specified attenuation with a thickness of 1.6 mm in the 9.5 GHz band. On the other hand, in the radio wave absorber sheet according to Comparative Example 7, it has been found that the specified attenuation cannot be secured unless the thickness is 1.9 mm. Furthermore, it was also found that the radio wave absorber sheets according to Comparative Examples 5 and 6 cannot secure a specified attenuation. That is, as the results of Comparative Examples 5 to 7 show, the M-type ferrite powder having a large peak particle size obtained by changing the firing conditions and the like, and the (fine) M-type ferrite powder having a small peak particle size are obtained. Even if they were mixed, the wave absorption characteristics of the obtained absorber sheet were inferior to those of the examples.

Claims (7)

A mixed ferrite powder in which two or more kinds of ferrite powders are mixed,
The peak particle size of each of the two or more ferrite powders constituting the mixed ferrite powder is P, and the largest peak particle size of the two or more ferrite powders is P _max , When the smallest peak particle size is P _min , P _max / P _min ≧ 1.5,
And using each of 2 or more types of ferrite powders which constitute the mixed ferrite powder, and a polymer substrate, a radio wave absorber in which each ferrite powder concentration is 90% by mass is prepared, In the radio wave absorber, the frequency indicating the maximum value of the imaginary part μ ″ of the complex permeability is assumed to be f, and among the frequencies f of the two or more types of radio wave absorbers, the highest frequency is f _max and the lowest frequency is f. _{When min} , f _max / f _min ≦ 1.3, and the largest value among the maximum values of the imaginary part μ ″ of the respective complex magnetic permeability of the two or more types of radio wave absorbers μ _{'' max,} the smallest mu 'when _{the' min, μ '' max /} μ '' mixing ferrite powder, which is a _min ≦ 1.5.   2. The mixed ferrite powder according to claim 1, wherein the two or more types of ferrite powders are a Z-type hexagonal ferrite powder and a Y-type hexagonal ferrite powder.   2. The mixed ferrite powder according to claim 1, wherein the two or more types of ferrite powders are Z-type hexagonal ferrite powder and M-type hexagonal ferrite powder. A method for producing a mixed ferrite powder comprising mixing two or more types of ferrite powder to produce a mixed ferrite powder,
The peak particle size of each of the two or more types of ferrite powders is P, and among the peak particle sizes of the two or more types of ferrite powders, the largest peak particle size is P _max and the smallest peak particle size is When P _min , P _max / P _min ≧ 1.5,
In addition, using each of the two or more types of ferrite powders and the polymer base material, a radio wave absorber having a ferrite powder concentration of 90% by mass is prepared. When the frequency indicating the maximum value of the imaginary part μ ″ of the magnetic permeability is f, and the highest frequency among the frequencies f of the two or more types of wave absorbers is f _max , and the lowest frequency is f _min , f _max / f _min ≦ 1.3, and among the maximum values of the imaginary part μ ″ of each of the two or more types of electromagnetic wave absorbers, the largest one is μ ″ _max , the most Mixing characterized in that mixed ferrite powder is produced by mixing two or more kinds of ferrite powders, where μ '' _max / μ '' _min ≦ 1.5, where μ ″ _min is a small one Ferrite powder manufacturing method.   The method for producing a mixed ferrite powder according to claim 4, wherein a Z-type hexagonal ferrite powder and a Y-type hexagonal ferrite powder are used as the two or more kinds of ferrite powders.   The method for producing a mixed ferrite powder according to claim 4, wherein Z-type hexagonal ferrite powder and M-type hexagonal ferrite powder are used as the two or more types of ferrite powder.   A radio wave absorber comprising the mixed ferrite powder according to claim 1.

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