JP2003298279A - Electromagnetic wave absorption sheet and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorption sheet having a superior shielding characteristic (electromagnetic wave absorption characteristic) without changing materials of a sheet of a matrix and metal powders. <P>SOLUTION: The electromagnetic wave absorption sheet includes a sheet body formed of an insulating material and multiple metal flakes or metal powders buried in the sheet body. A real part (ε') of a dielectric constant in a frequency region which is not more than 1 GHz is not less than 350. The method includes a material sheet forming process for mixing the multiple metal flakes of metal powders formed of a soft magnetic metal or alloy in the insulating material by a rate of 20 to 70 vol.% and forming a material sheet and a press process for pressing the material sheet along the thickness direction and forming the sheet body by prescribed thickness. The real part (ε') of the dielectric constant in the frequency region which is not more than 1 GHz becomes not less than 350. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has excellent shielding properties.
The present invention relates to an electromagnetic wave absorbing sheet having (electromagnetic wave absorbing characteristics) and a method for manufacturing the same.

[0002]

2. Description of the Related Art As an electromagnetic wave absorbing sheet for absorbing a high frequency electromagnetic wave, a sheet obtained by burying soft magnetic metal powder in a matrix rubber sheet or resin sheet and rolling it is used. The electromagnetic wave absorbing sheet in such a form is designed based on the return loss, which is an index of electromagnetic wave absorbing characteristics. Among them, the absorption peaks shown by the electromagnetic wave absorbing sheet are dielectric constant (ε), magnetic permeability (μ), and sheet thickness.
It is proportional to (t) and inversely proportional to the wavelength (λ). The following methods are available to improve the electromagnetic wave absorption characteristics.

For example, by adding additives such as carbon together with soft magnetic metal powder to a resin sheet or the like, the dielectric constant (ε)
There is a way to improve. However, when an additive such as carbon is added, the addition amount of the metal powder is reduced, so that the dielectric constant (ε) is rather reduced. Alternatively, there is also a method of improving the dielectric constant (ε) by changing the material such as the metal powder or the resin sheet and the compounding amount thereof. However, for example, when the material of the resin sheet is changed, the heat resistance and the like change, which limits the applications to which it should be applied. On the other hand, if the material of the metal powder or the amount of the metal powder is changed, the magnetic permeability (μ) changes greatly, so that there is a problem that the application is also limited.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the problems in the prior art as described above, and has excellent shielding characteristics without changing the materials of the matrix sheet and the metal powder.
An object is to provide an electromagnetic wave absorbing sheet having (electromagnetic wave absorbing characteristics) and a method for producing the same.

[0005]

In order to solve the above-mentioned problems, the present invention has been made with the idea of increasing the dielectric constant of a resin sheet in which metal powder or metal flakes are embedded. That is, an electromagnetic wave absorbing sheet (Claim 1) of the present invention includes a sheet body made of an insulating material and a large number of metal flakes or metal powders embedded in the sheet body, and has a dielectric property in a frequency range of 1 GHz or less. The real part (ε ′) of the ratio is 350 or more.
According to this, the real part of the dielectric constant in the above frequency region
Since (ε ') is 350 or more, higher shielding properties can be exhibited as compared with, for example, the conventional electromagnetic wave absorbing sheet formed by roll forming. If the real part (ε ′) is less than 350,
Such a range was excluded because the shielding property may not be improved. The permittivity (ε) is the real part (ε ′) and the imaginary part (ε ″).
And the real part in the frequency range of 1 GHz or less.
(ε ') dominates the action of the shielding property. In addition, the insulating material forming the sheet body includes rubber, resin, or a composite material containing these. Further, atomized powder is used for the metal powder, and flattened atomized powder is used for the metal flakes.

Further, according to the present invention, the imaginary part (ε ″) of the dielectric constant in the frequency region of 1 GHz or less is 70 or more,
An electromagnetic wave absorbing sheet (claim 2) is also included. According to this, the real part (ε ′) of the dielectric constant in the frequency region is 35
Since the imaginary part (ε ″) is 0 or more and the imaginary part (ε ″) is 70 or more, the high shielding property can be more reliably exhibited. When the imaginary part (ε ″) is less than 70, the shielding property may not be improved. , Such range was excluded. The imaginary part (ε ″) is calculated by multiplying the value obtained by multiplying the imaginary number (i) by the real part (ε ′) to calculate the dielectric constant (ε) at the frequency.

Further, in the present invention, the metal flakes or the metal powders are made of soft magnetic Fe, Ni, Co or an alloy based on any of these, and
An electromagnetic wave absorbing sheet (claim 3) embedded at a rate of 20 to 70 vol% with respect to the sheet body is also included. According to this, since the metal flakes and the like are evenly dispersed and embedded in both the thickness direction and the plane direction of the sheet body, it is possible to surely achieve the above-mentioned high shielding property on the entire surface of the sheet. Becomes If the ratio of metal flakes is less than 20 vol%, several tens of GHz
Since it becomes an electromagnetic wave absorber in the band, the dielectric constant (ε, ε ′, ε ″) below 1 GHz does not improve so much, while
If the above ratio exceeds 70 vol%, the insulating material becomes too small to form a sheet (sheeting), so these ranges were excluded.

On the other hand, in the method for producing an electromagnetic wave absorbing sheet of the present invention (claim 4), a large number of metal flakes or metal powders made of a soft magnetic metal or alloy is used as an insulating material in an amount of 20 to 70 vo.
and a flat sheet forming step of forming a flat flat sheet by mixing at a ratio of 1%, and a pressing step of pressing the raw sheet along its thickness direction to form a sheet body having a predetermined thickness. The real part (ε ') of the dielectric constant in the frequency region of 1 GHz or less is 350 or more. According to this, by press-forming the raw sheet, the distribution ratio of the metal flakes in the thickness direction of the sheet body obtained is easier to disperse and has a uniform distribution density as compared with the case of the conventional roll-forming. Become. As a result, the real part (ε ') of the dielectric constant in the above frequency range
It is possible to reliably manufacture an electromagnetic wave absorbing sheet having a value of 350 or more. In addition, the above-mentioned manufacturing method includes a method in which the imaginary part (ε ″) of the dielectric constant (ε) in the obtained electromagnetic wave absorbing sheet is 70 or more. When the mixing ratio of metal flakes is less than 20 vol%, Since it becomes an electromagnetic wave absorber in the several tens GHz band, it becomes difficult to obtain an electromagnetic wave absorption sheet having the above dielectric constant at 1 GHz or less.
If the above ratio exceeds 70 vol%, the amount of insulating material becomes too small, and sheeting by the above press cannot be performed. In order to prevent these, the above ranges are excluded.

Further, in the present invention, the method for producing an electromagnetic wave absorbing sheet, wherein the pressing step presses the raw sheet at a temperature of 50 ° C. or more and a pressure of 49 N / mm ² or more for 1 minute or more ( Claim 5) is also included. According to this, since it is possible to reliably embed metal flakes or the like in the obtained sheet main body with a uniform distribution density, it is possible to reliably manufacture the electromagnetic wave absorbing sheet having the above-mentioned characteristics of the dielectric constant (ε ′). You can The heating temperature of the raw sheet is 50
If the temperature is below ℃, the pressure required during pressing will be too high.
The range is excluded. Also, the press pressure is 4
If it is less than 9 N / mm ² and the pressing time is at least one of less than 1 minute, it becomes difficult to uniformly distribute the metal flakes in the molded sheet body, so these ranges were excluded.

Furthermore, the present invention also includes a method for manufacturing an electromagnetic wave absorbing sheet (claim 6), wherein the pressing step comprises pressing a plurality of the elementary sheets in the thickness direction thereof in a laminated state. According to this, it becomes possible to efficiently manufacture the electromagnetic wave absorbing sheet having the characteristic of the dielectric constant (ε ') in which the metal flakes are uniformly embedded in the sheet body.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments for carrying out the present invention will be described. Soft magnetic Fe, Ni, or Co or an alloy based on any of them is formed into a metal powder having an average particle diameter of several tens of μm by a water atomizing method or a gas atomizing method. The flat metal flakes are obtained by charging the metal powder in a known wet attritor and stirring it together with hard spheres. Such metal flakes are classified into a particle size distribution having a length of 20 to 30 μm or more and a thickness of about 10 μm or less. The metal powder may be mixed with the insulating material described below while being classified. Next, the metal flakes or metal powders are added to 20 to
70% by volume is mixed with liquid rubber or resin (insulating material), and the resulting mixture is dipped in a solvent such as toluene, and then thinly spread on the surface of the Si sheet from the bottom of the dipping tank and dried. . As a result, the thickness is about 0.1
A raw sheet having a thickness of mm and made of an insulating material in which the metal flakes or the metal powder are embedded is obtained (raw sheet forming step).

Then, while heating the above-mentioned raw sheet at 50 ° C. or higher, it is placed and restrained on a die of a press (not shown). Then, the punch of the press is pressed (pressed) against the exposed surface of the raw sheet for 1 minute with a pressure of 49 N / mm ² (corresponding to 5 kg / mm ² ) or more. In addition, the pressing (pressing) by the punch may be performed at a time while a plurality of raw sheets are constrained on the die. As a result, the thickness is about 0.0
It is possible to obtain an electromagnetic wave shielding sheet composed of a sheet body of 4 to about 6 mm made of the insulating material and the metal flakes or metal powder embedded in the sheet body with a substantially uniform distribution density. When the real part (ε ′) and the imaginary part (ε ″) of the dielectric constant in the frequency range of 1 GHz or less are measured for the electromagnetic wave shielding sheet using a known network analyzer, the real part (ε ′) is 350 or more. And the imaginary part
(ε ″) is at least 70. Therefore, in the frequency range of 1 GHz or less, it is possible to obtain an electromagnetic wave absorbing sheet having higher shielding properties than the conventional shielding sheet formed by rolling.

[0013]

EXAMPLES Now, specific examples of the present invention will be described.
This will be described together with a comparative example. A soft magnetic alloy of Fe-80 wt% Ni was made into a metal powder having an average particle size of 10 μm by a water atomizing method, and the metal powder was charged into a wet attritor and stirred with hard spheres to produce flat metal flakes. Obtained. The metal flakes were sieved to classify them into a range of 20 to 30 μm or more in length and about 10 μm or less in thickness. The metal flakes after the classification were mixed with liquid chlorinated polyethylene (insulating material, hereinafter referred to as CPE) at 55 vol%. 7 mixture of toluene
After being dipped in the (solvent), it was thinly spread on the surface of the Si sheet from the bottom of the dipping tank and dried. As a result, seven types of raw sheets made of CPE (insulating material) having the dimensions shown in Table 1 and having the metal flakes embedded therein were obtained (raw sheet forming step).

Next, among the seven types of base sheets, four types of base sheets were pressed by the press pressure, temperature and time shown in Table 1 to obtain Examples 1 to 4. The pressing process performed in Examples 1 to 4 is 50 to
Using an n press, an aluminum plate is placed on the die, and as shown in Table 1, only one sheet or a plurality of raw sheets are stacked and restrained, and further, the aluminum sheet is placed thereon. In the mounted state, the punch was pressed with the pressing pressure shown in Table 1 while heating at 120 ° C. Of the rest
Comparative example 1 is a raw sheet that has not been processed or treated as it is.
And Further, with respect to the remaining two types of raw sheets, a rolling process in which one raw sheet or five raw sheets stacked in the thickness direction are inserted between opposing rolls (not shown),
The steps were individually performed according to the number of passes shown in Table 1. The sheets thus obtained were designated as Comparative Examples 2 and 3.

[0015]

[Table 1]

The dimensions of the electromagnetic wave absorbing sheets of Examples 1 to 4 obtained by the pressing are shown in Table 2. Table 2 also shows the dimensions of the electromagnetic wave absorbing sheets of Comparative Examples 2 and 3 obtained by the rolling. The raw sheet of Comparative Example 1 was used as it was as the electromagnetic wave absorbing sheet of Comparative Example 1, and the dimensions are shown in Table 2. Next, one electromagnetic wave absorption sheet is extracted for each example, and using a known network analyzer, the real part (ε ′) and imaginary part (ε) of the dielectric constant in the frequency region of 0.1 to 3.0 GHz are extracted. ″) Was measured. At the same time,
The real part (μ ′) and the imaginary part (μ ″) of the magnetic permeability (μ) in the sheet of each example were measured. Of these, the real part (ε ′) and the imaginary part (ε) of the dielectric constant at 1 GHz of each example were measured. ″) And 10 MHz
The real part (μ ′) and imaginary part (μ ″) of permeability (μ) in
And are shown in Table 2. Also, the real part of the dielectric constant in each example
The graph of Fig. 1 shows the measurement result of (ε ′) as a whole, and the imaginary part of the permittivity
The measurement results of the entire (ε ″) are shown in the graph of FIG.

[0017]

[Table 2]

According to the graph of FIG. 1, in the electromagnetic wave absorbing sheets of Examples 1 to 4, the real part (ε ') of the dielectric constant was 350 or more over the entire frequency range of 0.1 to 1.0 GHz. . It is presumed that, in each of the sheets of Examples 1 to 4, the gas in the sheet was released by pressing, the density of the metal flakes was increased, and the orientation thereof was improved. In contrast, the untreated electromagnetic wave absorbing sheet in Comparative Example 1 has a real part of the dielectric constant.
(ε ′) remained at a level of about 330 to 270, and in the rolled sheets of Comparative Examples 2 and 3, the real part (ε ′) of the dielectric constant was 2.
On the contrary, it fell to a level below 00. This is Comparative Example 1
The density of the metal flakes is the same as that of the bare sheet, and in Comparative Examples 2 and 3, it is presumed that strain was applied to the metal flakes when rolling these bare sheets. Further, according to the graph of FIG. 2, the electromagnetic wave absorbing sheets of Examples 1 to 4 had an imaginary part (ε ″) of the dielectric constant of 70 or more over the entire frequency range of 0.1 to 1.0 GHz. On the other hand, in the sheet of Comparative Example 1, the imaginary part of the dielectric constant (ε ″) remained at the level of 50 to 63, and in the electromagnetic wave absorbing sheets of Comparative Examples 2 and 3, the imaginary part of the dielectric constant (ε ″) was found. On the contrary, it fell to a level below 30. These reasons are the same as above.

Therefore, according to the sheets of Examples 1 to 4,
Since the permittivity (ε), which is the sum of the real part (ε ′) and the imaginary part (ε ″ (multiplying the imaginary number i)), is remarkably improved, it is possible to improve the electromagnetic wave shielding property accordingly. The above results indicate that, in the electromagnetic wave absorbing sheets of Examples 1 to 4, since the raw sheet was subjected to the pressing step, the entire cross section of the raw sheet was compressed and included in the thickness direction. It is presumed that this is due to the reliable discharge of air bubbles and the uniform distribution density of the metal flakes etc. in the obtained sheet body. It can be easily understood that the effect that the excellent shielding property can be exhibited is supported.
It is also apparent from Examples 2 to 4 that an electromagnetic wave absorbing sheet having the above-described actions and effects can be efficiently produced by stacking a plurality of elementary sheets and pressing them simultaneously. It should be noted that Examples 1 to 4 are all improved in comparison with Comparative Example 1 in the real part (μ ′) of magnetic permeability, and Examples 1 and 2 are Comparative Examples in the imaginary part (μ ″) of magnetic permeability. It was better than 1.

The present invention is not limited to the forms and examples described above. The insulating material that forms the sheet body is not limited to the CPE, but synthetic rubber such as chloroprene rubber, polybutadiene rubber, polyisoprene rubber, ethylene propylene rubber, butadiene acrylonitri rubber, isobutylene isoprene rubber, styrene butadiene rubber, or polyamide. System, phenol system, epoxy system,
Various synthetic resins such as polyester-based, acrylic-based, polyvinyl acetate, polystyrene and polyurethane can also be applied. Alternatively, it is also possible to use the above-mentioned rubber-based and resin-based composite materials, or rubber-rubber-based or resin-resin-based composite materials. Further, the metal flakes or metal powders are not limited to the permalloy-based Fe-Ni-based alloys, but may be Fe-Ni-Co-based alloys (for example, Kovar), Fe.
-Cr-Ni system stainless steel, Fe-10-18wt%
Cr stainless steel, Fe—Cr—Al alloy, Fe—Cr—Si alloy, or the like may be applied. Further, the pressing step may be performed as upset forging. The present invention can be variously modified without departing from the spirit thereof.

[0021]

According to the electromagnetic wave absorbing sheet of the present invention (claim 1), it is possible to exhibit excellent shielding characteristics (electromagnetic wave absorbing characteristics) due to its high dielectric constant. Further, according to the electromagnetic wave absorbing sheet of the second aspect, it is possible to more surely exhibit excellent shielding characteristics. On the other hand, according to the method for producing an electromagnetic wave absorbing sheet of the present invention (claim 4), it is possible to reliably produce a sheet having the above characteristics. Further, according to the manufacturing method of the fifth aspect, it becomes possible to more reliably manufacture the electromagnetic wave absorbing sheet having the above characteristics. Furthermore, according to the manufacturing method of claim 6, the electromagnetic wave absorbing sheet having the above characteristics can be efficiently manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing a real part (ε ′) of a dielectric constant in a predetermined frequency range of each sheet of Examples and Comparative Examples.

FIG. 2 is a graph showing an imaginary part (ε ″) of a dielectric constant in a predetermined frequency range of each sheet of the example and the comparative example.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Atsushi Kametani             Daido Special, 10 Ryugucho, Minato-ku, Nagoya City, Aichi Prefecture             Special Steel Co., Ltd., Tsukiji Factory F-term (reference) 5E321 BB21 BB33 BB53 GG11

Claims (6)

[Claims] 1. A real part (ε ′) of a dielectric constant in a frequency region of 1 GHz or less, which includes a sheet body made of an insulating material and a large number of metal flakes or metal powders embedded in the sheet body.
Is 350 or more, The electromagnetic wave absorption sheet characterized by the above-mentioned. 2. The electromagnetic wave absorbing sheet according to claim 1, wherein the imaginary part (ε ″) of the dielectric constant in the frequency range of 1 GHz or less is 70 or more. 3. The metal flakes or metal powders are made of soft magnetic Fe, Ni, Co or an alloy based on any of them, and are embedded at a ratio of 20 to 70 vol% with respect to the sheet body. The electromagnetic wave absorption sheet according to claim 1 or 2, wherein 4. A base sheet forming step of forming a flat base sheet by mixing a large number of metal flakes or metal powders made of a soft magnetic metal or alloy in an insulating material at a ratio of 5 to 55 vol%, and the base sheet. Pressing step along the thickness direction to form a sheet body having a predetermined thickness, and the real part (ε ') of the dielectric constant in the frequency region of 1 GHz or less.
Is 350 or more, The manufacturing method of the electromagnetic wave absorption sheet characterized by the above-mentioned. 5. In the pressing step, the raw sheet is heated to 50 ° C.
1 at the above temperature and with a pressure of 49 N / mm ² or more
Pressing for more than a minute, The manufacturing method of the electromagnetic wave absorption sheet of Claim 4 characterized by the above-mentioned. 6. The method of manufacturing an electromagnetic wave absorbing sheet according to claim 4, wherein in the pressing step, a plurality of the elementary sheets are laminated and pressed in the thickness direction thereof.