JPH11354973A - Electromagnetic wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display the radio wave absorbing power at the mega/giga frequency band, without using classified powders by specifying the content of an Fe-base flat nano-crystal soft magnetic powder in a bond resin and the imaginary part of the complex permeability. SOLUTION: The compsn. of a nano-crystal soft magnetic powder contains Fe as a main component which reveals a superior soft magnetic characteristic and the imaginary part μ" of the complex permeability is large. Part of Fe may be substituted by a kind of elements M such as Co and/or Ni, a mother alloy is dissolved in the atmospheric air, the melt at 1500 deg.C is atomized by the high pressure water atomizing method to make a powder of amorphous alloy Fe72.5 Cu1 Nb3 Si13.5 B9 (atm.%) of 40 μm in mean grain size and 1 μm thick, and the powder is heat treated in an N gas atmosphere at 500 deg.C for 1 hr. to obtain a nano-crystal soft magnetic powder having a fine structure of 10 nm in crystal grain size. The real part μ' of the complex permeability of a radio wave absorber sheet exceeds 1 from 1 MHz to 1 GHz and its imaginary part μ" rises abruptly from 10 MHz to several GHz, superior in radio wave absorption characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for suppressing electromagnetic interference caused by interference of unwanted electromagnetic noise.
The present invention relates to an electromagnetic wave absorber having a large radio wave absorption effect in a wide frequency band from a Hz band to a GHz band.

[0002]

2. Description of the Related Art In recent years, the drive frequency has been rapidly increasing along with the miniaturization and high performance of various digital and analog electronic devices such as personal computers and mobile communications. The spread of equipment is on the rise. Above all, satellite communication, mobile communication equipment, and car navigation equipment using microwave band radio waves have been remarkably popularized. As a result, electromagnetic environment problems due to electromagnetic noise generated by these devices have become more serious.

[0003] Methods of suppressing electromagnetic wave interference can be roughly classified into a method of reflecting electromagnetic waves and a method of absorbing electromagnetic waves. The method of reflecting electromagnetic waves is to block electromagnetic waves entering a device to be protected by reflecting the electromagnetic waves with a shielding material. As such a shielding material, a conductive material having high conductivity, such as an aluminum plate, a copper plate, or a conductive plastic, is suitable. However, in the method of reflecting electromagnetic waves, secondary obstacles due to the reflected electromagnetic waves are not a little generated.

On the other hand, a method of absorbing electromagnetic waves mainly involves absorbing electromagnetic waves with an absorbing material and converting the electromagnetic waves into heat energy. This method is effective as a drastic noise countermeasure method. As such an absorbing material, a magnetic material having a large magnetic loss is required, and for example, ferrite or the like is used.

Recently, as a material having a large electromagnetic wave absorbing effect, a composite of a flat Fe-Si-Al alloy powder and a polymer has been proposed. Eikichi Yoshida et al. Permeability and electromagnetic interference suppression effect '' (Tokin Technical
Review, November 1996, No. 23, p. 93).

[0006] According to this, an attritor (media stirring type pulverization) is used by using an alloy powder of 9.8 wt.% Si-6 wt.% Al-bal.Fe having a Fe concentration reduced from the center composition of Sendust by water atomization. ) To obtain a flat powder. After removing the fine powder of 400 mesh or less (32 μm or less) by classifying the powder, 650 ° C.
For 2 hours. After mixing the flat powder and the polymer, kneading with an organic solvent, and forming a slurry,
The sample was obtained by repeating coating and drying by the doctor blade method. According to the relationship between the imaginary part μ ″ of the complex magnetic permeability indicating the electromagnetic wave absorbing ability of this sample and the frequency, the frequency is 1 MHz to 1 MHz.
Μ ″ in the GHz band exceeds 10.

[0007]

However, in the above-described method, in order to obtain an electromagnetic wave absorbing effect, fine powder among the flat powder obtained by grinding Sendust powder with an attritor is used. There is a problem that it is necessary to perform a classification process for removing, and the productivity is lowered.

[0008] It is an object of the present invention to provide an electromagnetic wave absorber capable of exhibiting an excellent radio wave absorbing ability particularly at 30 MHz to 1 GHz without using a specially classified powder.

[0009]

Means for Solving the Problems The present invention is based on the finding that a nanocrystalline soft magnetic material obtained as a powder is excellent in radio wave absorption characteristics over a wide band by being combined with a resin. It is completed.

That is, the electromagnetic wave absorber of the present invention is made of Fe
The base flat nanocrystalline soft magnetic powder is contained in the resin to which it is bound in an amount of 50 to 1000 phr, the imaginary part μ ″ of the complex magnetic permeability is 1.5 or more at a frequency of 10 MHz, and 30 MHz to 1 GHz. The frequency is 4 or more.

[0011] The radio wave absorption capacity is calculated by changing the magnetic permeability to the complex magnetic permeability μ =
The imaginary part μ ", which is the magnetic loss term when expressed as μ'-jμ"
Can be evaluated by: That is, a larger μ ″ means a higher ability to convert electromagnetic waves (noise) into thermal energy and absorb it. The imaginary part μ ″ of the complex magnetic permeability according to the present invention is a low frequency of 10 MHz. Is 1.5 or more, and at a high frequency of 30 MHz to 1 GHz, 4
The above-mentioned excellent radio wave absorbing ability can be realized.

Here, it is preferable that the flat nanocrystalline soft magnetic material powder is contained in the resin in an amount of 100 to 700 phr. The flat nanocrystalline soft magnetic powder had a thickness of 3 μm or less and an average particle size of 20 μm.
It is preferably from 50 μm to 50 μm.

The Fe-based flat nanocrystalline soft magnetic powder used in the present invention will be described below.

An Fe-based nanocrystalline soft magnetic material is disclosed in
No. 4393
0% is in the nano order, that is, less than 1000 nm bcc-Fe
It is a material composed of crystal grains with a structure.

It is essential that the magnetic powder used in the present invention has a flat shape. The ratio of the major axis to the thickness of the flat powder is referred to as the aspect ratio (major axis / thickness). Here, the aspect ratio of the flat powder is desirably 20 or more. By making the powder flat, the anisotropic magnetic field of the powder becomes large and the electromagnetic wave absorbing ability can be enhanced up to a high frequency region.

The reason why the average particle size of the flat powder is set to 20 to 50 μm is that if the average particle size is less than 20 μm, the demagnetizing field of the powder becomes large, the magnetic permeability μ becomes small, and the imaginary part μ ″ becomes small. And the dielectric constant .epsilon. Becomes large, and the absorption characteristics deteriorate.

In the present invention, the flat nanocrystalline soft magnetic powder is mixed in the resin in an amount of 50 to 1000 phr, preferably 1 to 100 phr.
00-700 phr. As the resin used here, a resin having properties suitable for the use of the electromagnetic wave absorber of the present invention can be selected. When the electromagnetic wave absorber is made into a plate shape or injection molded, it has a resin suitable for doctor blade method, calendar roll method, injection molding method, for example, polyolefin such as polyethylene and polypropylene, vinyl resin, and acetic acid group. Resins, copolymers thereof, and polyesters such as polyethylene terephthalate. When applied to a calender roll method or a pressure molding method, nylon, synthetic rubber, or the like can be used.

A crosslinking agent can be added depending on the type of the polymer. However, the important property as a resin is
The purpose is to hold the flat nanocrystalline soft magnetic powder and prevent its oxidation, and to electrically insulate the powder particles.

It is important to electrically insulate between the powder particles in order to sufficiently exhibit the radio wave absorption characteristics. When the insulation between the powder particles is deteriorated, the particles exhibit properties like a conductive sheet and reflect electromagnetic waves. This happens when,
The radio wave absorption characteristics will be inferior.

The flat nanocrystalline soft magnetic powder is mixed in a resin with 5
0-1000 phr, preferably 100-700 phr
r, where phr is parts per hund
An abbreviation for red rubber, which is the amount of powder added to 100 parts by weight of a polymer expressed as a weight ratio. If the addition amount of the magnetic powder is less than 50 phr, the imaginary part μ ″ of the complex magnetic permeability at 10 MHz becomes extremely small, so that the electromagnetic wave absorption characteristics at low frequencies deteriorate. The addition of the magnetic powder increases the μ ″. Is getting bigger, but 10
If it exceeds 00 phr, the insulation between the magnetic powders deteriorates,
The dielectric constant ε becomes too large, the balance between the magnetic permeability and the dielectric constant is broken, and the radio wave absorption characteristics deteriorate. At a preferred addition amount of 100 to 700 phr, μ ″ is 10 MH
z is also sufficiently high, and kneading at the time of production becomes easy.

[0021]

BEST MODE _FOR CARRYING OUT THE INVENTION The nanocrystalline soft magnetic powder used in the present invention basically has the general formula: (Fe _1-a M _a ) _100-xyzuvw Cu _x Si _y B _z M ′ _u M ″ _v
X _w (atomic%) where M is Co and / or Ni, M ′ is Nb, W, T
At least one element selected from the group consisting of a, Zr, Hf, Ti and Mo, M ″ is V, Cr, Mn, Al, a white metal element, Sc, Y, a rare earth element, Au, Zn, Re. X is at least one element selected from the group consisting of C, Ge, P, Ga, Sb,
At least one element selected from the group consisting of In, Be, As, a, x, y, z, u, v, and w are each 0 ≤ a ≤ 0.50 ≤ x ≤ 30 ≤ y ≤ 30 0 ≤ satisfying z ≦ 250.1 ≦ u ≦ 300 ≦ v ≦ 100 ≦ w ≦ 10 and 0 ≦ y + z ≦ 35, and at least 50% of the structure is composed of fine grains. And the average crystal grain size of the crystal grains is 50 nm or less.

The reason for limiting the composition of the nanocrystalline soft magnetic powder will be described.

(1) Fe and M (Co and / or Ni) Fe is a main component of the soft magnetic powder, and fine crystal grains having an average crystal grain size of 50 nm or less are mainly composed of α-Fe. It is considered that Si and B are dissolved in solid solution.
By using Fe as a main component, excellent soft magnetic characteristics are exhibited, and the imaginary part μ ″ of the complex magnetic permeability is increased.
And / or Ni. Although the content a of M 2 is 0 ≦ a ≦ 0.5. , Preferably 0 ≦ a ≦ 0.3. If a exceeds 0.3, the soft magnetic properties may deteriorate. (2) Cu Cu is an essential element, and its content x is in the range of 0.1 to 3 atomic%. If it is less than 0.1 atomic%, there is almost no effect of improving the magnetic permeability μ by addition of Cu, while if it is more than 3 atomic%, the magnetic permeability μ becomes worse than that without the addition, which is not preferable. Particularly preferred Cu content x is 0.5 to
2 atomic%, and the magnetic permeability μ is particularly good in this range.

It is considered that the crystal grain refinement occurs due to the large number of crystal nuclei and the difficulty in growing the crystal grains due to the addition of Cu, but this action is caused by Nb, W, Ta, Zr, Hf, Ti and
It is thought to be particularly marked by the presence of Mo.

When Nb, W, Ta, Zr, Hf, Ti and Mo are not present, the crystal grains are not very fine and μ is low.
Nb and Mo are particularly effective, but among these, Nb
In particular, the crystal grains are made finer, resulting in high magnetic permeability.

(3) Si and B Si and B are effective in turning the alloy into an amorphous phase when the alloy is rapidly quenched. In order to grow a nanocrystal, it is obtained by forming fine crystal grains by heat treatment after being made amorphous once. Si and B content y and
For z, y is 30 atom% or less, z is 25 atom% or less, and y + z is 35
If it is not less than atomic%, the magnetic permeability μ becomes extremely low.

(4) M '(Nb, W, Ta, Zr, Hf, Ti and Mo) At least one element M' selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo Refines crystal grains precipitated by complex addition with Cu. M ′ content u is 0.1
If it is less than 0.1 atomic%, the effect of grain refinement is insufficient, and if it exceeds 30 atomic%, the magnetic permeability μ is remarkably reduced. Preferred M 'content u is from 2 to 8 atoms
%. Note that Nb is most preferable as M '. (5) M ″ (V, Cr, Mn, Al, white metal element, Sc, Y, rare earth element, Au, Zn, Re) These elements improve corrosion resistance, improve magnetic characteristics, and reduce magnetostriction. The content is at most 10 atomic%, and when the content exceeds 10 atomic%, the magnetic properties are remarkably deteriorated, and a particularly preferable content is 8 atomic% or less. Of the elements Ru, Rh,
Pd, Os, Ir, Pt, Au, Cr and V improve corrosion resistance and abrasion resistance in particular.

(6) X (C, Ge, P, Ga, Sb, In, Be, A
s) These elements are effective elements for amorphization, and
When added together with i and B, it has the effect of promoting the formation of an amorphous phase and increasing the magnetostriction and Curie temperature.
At least one of these elements can be contained at 10 atomic% or less. This nanocrystalline soft magnetic powder can be manufactured as follows. That is, the molten alloy having the above-described composition is rapidly quenched to obtain an amorphous alloy powder, and the powder is finely flattened. Then, the powder is heated to a temperature higher than the crystallization temperature, and a heat treatment is performed so that at least 50% of the structure has an average grain size of 50 nm or less.

As the ultra-quenching method, a water atomizing method is suitable. A very thin flake can be obtained by the water atomizing method, and the surface thereof has an irregular shape with irregularities, is sufficiently cooled, and is easily crushed in shape.

In this way, a thickness of 3 μm or less is obtained,
A flat nanocrystalline soft magnetic powder having an average particle size of 20 to 50 μm is obtained. This soft magnetic material powder is mixed with 50 to 1
By mixing with a resin so as to contain 000 phr, the electromagnetic wave absorber of the present invention is produced.

[0031]

EXAMPLES (Example 1) After melting a mother alloy in the air,
1500 ° C molten iron is pressurized by high pressure water atomization _73.5Cu₁N
b_ThreeSi_13.5B₉(Atomic%) average particle size 40μ
m, an amorphous alloy powder having a thickness of 1 μm was prepared.
Amorphous alloy powder at 550 ° C in nitrogen gas atmosphere
Heat treated for a long time to have a fine structure with a crystal grain size of 10 nm
A nanocrystalline soft magnetic powder was obtained.

After dissolving the saturated polyester resin in toluene, this nanocrystalline soft magnetic powder is added to 200 phr, and a crosslinking agent (isocyanate compound) is blended. The mixture was heated for 30 minutes to be urethane to obtain an electromagnetic wave absorber (sheet).

When the complex magnetic permeability of the electromagnetic wave absorbing sheet was measured with a network analyzer made by Hewlett-Packard, the real part μ ′ of the complex magnetic permeability as shown in FIG. 1 was obtained.
Imaginary part μ ”.

As is clear from FIG. 1, the real part μ ′ of the complex magnetic permeability is more than about 10 from 1 MHz to 1 GHz. The imaginary part μ ”rises steeply,
At 10 MHz, it exceeds 2 and from 30 HMHz to 10
The value is almost 5 toward 0 MHz, and gradually increases from that, and exceeds 10 at 1 GHz. That is,
It can be seen that the radio wave absorption characteristics are excellent from 10 MHz to several GHz.

Example 2 Using the nanocrystalline soft magnetic powder obtained in Example 1, the amount of the soft magnetic powder added was 50 to
An electromagnetic wave absorber (sheet) was prepared by changing to 500 phr. The imaginary part μ "of the complex magnetic permeability of this electromagnetic wave absorbing sheet
Is set to 10M as shown in FIG.
Hz is 1.5 or more, and 30M
The frequency was 4 or more at a frequency of 1 Hz to 1 GHz.

As shown in this example, when the addition amount of the nanocrystalline soft magnetic material powder is increased, the imaginary part μ ″ is increased to exhibit excellent radio wave absorption characteristics.

[0037]

The electromagnetic wave absorber of the present invention has excellent radio wave absorption characteristics in a wide frequency band from a low frequency to a high frequency, particularly in a low frequency of 30 MHz or less, and is effective in preventing electromagnetic wave interference against unnecessary electromagnetic noise in a wide frequency band. It is extremely effective for reduction.

[Brief description of the drawings]

FIG. 1 is a graph showing the value of the complex magnetic permeability of the electromagnetic wave absorber of the present invention with respect to frequency.

FIG. 2 is a diagram showing the value of the imaginary part of the complex magnetic permeability when the content of the nanocrystalline soft magnetic material powder in the electromagnetic wave absorber of the present invention is changed, using frequency as a parameter.

Claims (3)

[Claims] 1. An Fe-based flat nanocrystalline soft magnetic powder is contained in a resin to which it is bound in an amount of 50 to 1000 phr, and the imaginary part μ ″ of the complex magnetic permeability is 1.5 or more at a frequency of 10 MHz. An electromagnetic wave absorber having a frequency of 4 or more at a frequency of 30 MHz to 1 GHz. 2. The electromagnetic wave absorber according to claim 1, wherein the resin contains 100 to 700 phr of Fe-based flat nanocrystalline soft magnetic powder. 3. The thickness of the Fe-based flat nanocrystalline soft magnetic powder is 3 μm or less, and the average of the particle diameter is 20 to 50 μm.
3. The electromagnetic wave absorber according to claim 1, wherein m is m.