JPH11298187A - Noise suppression sheet excellent in electromagnetic wave absorbing characteristic of ghz band - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent radio wave absorbing characteristic in high frequency band, reduce thickness and improve noise suppression effect, by dispersing nanocrystal soft magnetic powder in polymer binder. SOLUTION: After amorphous alloy powder is previously formed by using an atomization method, a cavitaion method, etc., the amorphous alloy powder is thermally treated in inert gas atmosphere at 500-600 deg.C for several hours and nanocrystallized. Structure of this powder has fine nanocrystal grains whose mean grain diameter is at most 50 nm, and soft magnetic property is ensured by this nanocrystal structure. The obtained powder is thermally treated in an oxidizing atmosphere or held in organic solvent, and insulating cover film is formed on the surface of powder by a drying method, silane coupling treatment, a microcapsulizing method, etc. Polymer binder is necessary for dispersing and holding nanocrystal soft magnetic powder and also executes function which insulates spaces between soft magnetic powder, for improving radio wave absorbing effect in GHz band. It is preferable that adding parts of nanocrystal soft magnetic alloy powder to polymer binder is 100-1500 phr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise suppression sheet used in a high frequency band such as a GHz band to cope with electromagnetic interference caused by interference of unnecessary electromagnetic noise.

[0002]

2. Description of the Related Art In recent years, the drive frequency of various digital electronic devices, such as personal computers, has been rapidly increasing with the downsizing and higher performance, and devices utilizing such high frequencies have become increasingly popular. There is a tendency to expand. Above all, the spread of satellite broadcasting, mobile communication equipment, car navigation equipment and the like using microwave band radio waves is remarkable. As a result, electromagnetic environment problems caused by unnecessary electromagnetic noise generated by these devices have become more serious.
Attempts have been made to use various noise suppression products.

Among them, an electromagnetic wave shield made of a conductive material such as a metal has a problem of secondary adverse effects due to reflected noise. Are increasing. Known electromagnetic wave absorbers include ferrite tiles produced by sintering ferrite powder, and sheet-like materials in which soft magnetic powder such as ferrite powder or carbonyl iron powder is mixed with resin. It is widely used for radar, false image prevention, and other unnecessary radiation prevention.

[0004]

SUMMARY OF THE INVENTION Ferrite tiles
The applicable frequency band is MHz, which is not suitable for use in the GHz band. In addition, it is difficult to apply to a small electronic device because it is thick, about 5 to 10 mm, and lacks flexibility. A radio wave absorber obtained by combining ferrite powder with a resin is flexible and can be used in a high frequency band of several GHz or more, but has a problem that the sheet is thick like a ferrite tile. On the other hand, a radio wave absorber obtained by mixing a metal magnetic powder such as carbonyl iron powder with a resin can be made as thin as several mm.
There is a problem limited to use in a frequency band of 0 GHz or more. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a noise suppression sheet which is excellent in radio wave absorption characteristics of 1 to 10 GHz, thin and excellent in noise suppression effect.

[0005]

Means for Solving the Problems The present inventors diligently studied the relationship between various soft magnetic alloy powders and radio wave absorption characteristics at high frequencies, and found that a sheet in which nanocrystalline soft magnetic powder was dispersed in a polymer binder was made of a material such as ferrite. Excellent radio wave absorption characteristics can be obtained in the GHz band that cannot be obtained with conventional radio wave absorbers,
In addition, the inventors have found that the thickness can be reduced, and have reached the present invention. That is, the present invention is a noise suppression sheet having excellent radio wave absorption characteristics in the GHz band, characterized in that nanocrystalline soft magnetic powder is dispersed in a polymer binder.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The nanocrystalline soft magnetic powder according to the present invention is a powder having fine nanocrystalline grains having an average particle diameter of 50 nm or less in its structure. The nanocrystalline structure secures soft magnetism. is there. As a specific composition, Fe-Cu-Nb-Si- described in Japanese Patent Publication No.
A B-based alloy or the like can be used, but the composition is not particularly limited as long as the main component is Fe and soft magnetic properties are ensured by a nanocrystalline structure.

The nanocrystalline soft magnetic powder is prepared by preparing an amorphous alloy powder in advance by an atomizing method or a cavitation method, and then sintering the powder in an inert gas atmosphere.
It can be manufactured by heat-treating at 0 to 600 ° C. for several hours to nanocrystallize. Further, after the amorphous ribbon produced by the single-roll method, the twin-roll method or the like is embrittled at a temperature of 400 to 500 ° C., it is pulverized by various ball mills to a predetermined particle size, and finally produced by a method of nanocrystallizing. You can also. The obtained powder is subjected to a heat treatment in an oxidizing atmosphere or a method of drying after holding in an organic solvent, and further, an insulating film is formed on the surface of the powder by a silane coupling treatment or a method of microencapsulation.
The radio wave absorption characteristics in the band can also be improved.

[0008] The polymer binder referred to in the present invention is necessary for dispersing and holding the nanocrystalline soft magnetic powder.
It also has the function of insulating between soft magnetic powders to obtain a radio wave absorption effect in the band. As a polymer binder,
For example, polyethylene, polyester, polyurethane,
Chloroprene rubber, silicone rubber, or a copolymer thereof can be used. Further, depending on the type of the polymer binder, a crosslinking agent may be added as needed. The average particle size of the powder is preferably from 5 to 300 μm.
When the particle size is small, the influence of the demagnetizing field becomes
The magnetic permeability in the band deteriorates, and good absorption characteristics cannot be obtained. Conversely, when the particle size is large, the dielectric constant is significantly increased, and the insulation of the sheet is deteriorated, so that the radio wave absorption effect is reduced.

The number of parts of the nanocrystalline soft magnetic alloy powder added to the polymer binder is preferably 100 to 1500 phr. This is because if the number of added parts is small, the frequency at which good absorption characteristics can be obtained is 10 GHz or more, and if the number of added parts is large, flexibility is impaired. Here, the unit ph of the number of added parts
r is the weight ratio of the amount of powder added to the polymer 100. (For example, this unit is used in Osamu Hashimoto, Introduction to Radio Wave Absorbers, Morikita Publishing, p. 32, 1997.) Further, an adhesive layer can be formed on the sheet surface as necessary. This facilitates attachment to the electronic device.

[0010]

EXAMPLES (Example 1) Fe was formed by high-pressure water atomization.
An amorphous alloy powder having a composition of _73.5 Cu ₁ Nb ₃ Si _13.5 B ₉ (at%) having an average particle diameter of 25 μm was prepared, and this amorphous alloy powder was heated at 550 ° C. in a nitrogen gas atmosphere.
For 1 hour to obtain a nanocrystalline soft magnetic alloy powder having a fine structure with a crystal grain size of 10 nm. Next, after dissolving the polyester resin in toluene, a nanocrystalline alloy powder (added to 500 phr) and an isocyanate compound as a cross-linking agent are blended and heat-treated at 120 ° C. for 40 minutes to obtain a noise suppression sheet having a thickness of 1 mm. Was.

From the obtained sheet, an outer diameter of 7 mm and an inner diameter of 3 m
A sample having a donut shape of m was placed in a coaxial tube, and a reflector was applied to the back surface of the noise suppression sheet by the S-parameter method using a network analyzer.
The return loss at GHz was measured. Table 1 shows the measurement results. The same evaluation was performed on a sheet using a ferrite powder and a carbonyl iron powder conventionally used as a comparative example. It means that the larger the return loss, the more effective the noise absorption effect. However, it can be seen that the noise suppression sheet of the present invention exhibits a thin and practical level of absorption characteristics in the GHz microwave band.

[0012]

[Table 1]

(Example 2) Fe ₇₄ Cu was produced by a single roll method.
20 μm thick having a composition of ₁ Nb ₃ Si ₁₆ B ₇ (at%)
m amorphous alloy ribbon was prepared, and the amorphous alloy ribbon was embrittled at 450 ° C. for 1 hour in an Ar gas atmosphere. Then, the ribbon was pulverized with a vibrating ball mill to produce powders having different average particle diameters. . After that, 5 times in an Ar gas atmosphere.
Heat treatment was performed at 30 ° C. for 1 hour to obtain a nanocrystalline soft magnetic alloy powder having a fine structure with a particle size of 15 nm. Next, after dissolving the urethane resin in toluene, the nanocrystalline alloy powder (50
0 phr) and 30 m at 130 ° C.
In the heat treatment, a noise suppression sheet having a thickness of 1 mm was obtained.

From the obtained sheet, an outer diameter of 7 mm and an inner diameter of 3 m
A sample having a m-shaped donut shape was taken, placed in a coaxial tube, and measured for relative permeability and relative permittivity at 1 GHz by a network analyzer. Note that both the relative permittivity and the relative magnetic permeability are parameters that greatly affect the noise absorption characteristics. Table 2 shows the measurement results. It can be seen that the noise suppression sheet of the present invention becomes a sheet excellent in both dielectric properties and magnetic permeability properties by using a nanocrystalline alloy powder having an average particle size of 5 to 300 μm.

[0015]

[Table 2]

Example 3 A noise suppression sheet was obtained in the same manner as in Example 1. At this time, a sheet having a thickness of 2 mm was prepared by changing the number of added portions of the nanocrystalline soft magnetic powder. A donut-shaped sample having an outer diameter of 7 mm and an inner diameter of 3 mm was sampled from the obtained sheet, placed in a coaxial tube, and subjected to S-parameter method using a network analyzer to determine the maximum return loss and return loss. The frequency was measured. Further, the presence or absence of cracks when the sheet was bent at 90 ° was examined. Table 3 shows the measurement results. The noise suppression sheet of the present invention
It can be seen that when the number of added parts is 100 to 1500 phr, the composition is flexible and exhibits excellent absorption characteristics in a microwave band of 1 to 10 GHz.

[0017]

[Table 3]

[0018]

According to the present invention, it is possible to obtain a noise suppression sheet having excellent noise absorption characteristics especially at 1 to 10 GHz, and therefore a great effect can be expected as a noise countermeasure for mobile communication.

Claims (3)

[Claims] 1. A noise suppression sheet having excellent radio wave absorption characteristics in the GHz band, characterized in that nanocrystalline soft magnetic powder is dispersed in a polymer binder. 2. The nanocrystalline soft magnetic powder having an average particle size of 5 to 3
2. The GH according to claim 1, wherein the GH is 00 μm.
Noise suppression sheet with excellent z-band radio wave absorption characteristics. 3. The noise suppression sheet according to claim 1, wherein the number of parts of the nanocrystalline soft magnetic powder added to the polymer binder is 100 to 1500 phr.