JP2003142871A - Adhesive electromagnetic wave absorber and its application method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorber wherein a soft magnetic metal powder is dispersed in a matrix and can be more easily applied than a common-use sheet, and to provide its advantageous application method. SOLUTION: While a material having adhesiveness, especially an acrylic resin or a rubber-based adhesive agent, is used as a matrix, this electromagnetic absorber can be directly adhered to an applicable part of an electronic device, or an enclosure thereof. It may be molded like a sheet having a specified thickness or be made to have adhesiveness. In addition, it is made to have plasticity together with adhesiveness, and it may be applied into a recessed part, or be extended over an application surface and adhered thereto.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electromagnetic wave absorber obtained by dispersing soft magnetic metal powder in a matrix material, and can be easily applied to a place where electromagnetic wave absorption is required. The present invention relates to a device that can be conveniently applied to a place where it was difficult to apply the product.

[0002]

2. Description of the Related Art As a material for shielding electromagnetic waves in various electronic devices, a composite material in which a powder of soft magnetic metal is dispersed in a matrix of rubber or plastic is formed into a sheet or other arbitrary shape. Electromagnetic wave absorbers are used. As the soft magnetic metal powder,
Atomized powders such as sendust, permalloy, and Fe-Cr-Al alloy are used. As a matrix material for forming a sheet, a chlorinated polyethylene rubber is preferably used because of its good moldability and a certain level of flame retardancy. If heat resistance is required, acrylic rubber is selected.

In such an electromagnetic wave absorption sheet, 3G
Those applied to the frequency band of Hz or less are often manufactured by using, as the soft magnetic metal powder, flat powder obtained by flattening spray powder by an attritor treatment or the like, so-called flake powder. The shape of the powder affects not only the thickness of the sheet but also the frequency characteristics of the electromagnetic wave absorbing sheet, particularly the peak absorption frequency. If flat powder is used and its flat surface is oriented along the surface of the sheet, the magnetic permeability of the sheet can be increased, and thus the sheet can be thin. On the other hand, the absorption performance of the electromagnetic wave absorption sheet is generally higher when using spherical powder than when using flat powder. In recent years, the frequency of electronic devices has increased, and it has become necessary to absorb electromagnetic waves at frequencies higher than 3 GHz.

The sheet-shaped electromagnetic wave absorber is easy to use because its frequency characteristics and absorption performance are clear. However, in using it, it is necessary to adhere a sheet cut to an appropriate size to the surface to be applied with an adhesive or the like. This work is often complicated, and if the application surface is subdivided or there are many, it is particularly laborious and increases the manufacturing cost of the electronic device. There is a strong demand for miniaturization of electronic devices, and in response to this, the mounting area is reduced and the distance between boards is shortened.Therefore, there is no space to apply a sheet between surface-mounted boards or parts on boards. Sometimes you can't get it.

Sheets are also difficult to apply to curved surfaces and recesses. If it is applied in the form of paint, it can be easily applied to curved surfaces and recesses, but it must be applied many times to obtain the required film thickness, and it is necessary to ensure a constant thickness. It is not a very practical means because it is troublesome. Increasing the frequency of electronic devices means that the wavelength of the electromagnetic waves used is shortened, and then the electromagnetic waves leak from short wiring and narrow gaps in the housing. But in such places,
It is difficult to use a sheet-shaped electromagnetic wave absorber.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is, as one solution to such a problem, an electromagnetic wave absorber that is easier to apply than a conventional sheet-like one, and an advantageous application method thereof. To provide.

[0007]

The electromagnetic wave absorber of the present invention that achieves the above-mentioned object is an electromagnetic wave absorber obtained by dispersing a powder of a soft magnetic metal in a matrix material of an organic substance, and has adhesiveness as a matrix. It is an electromagnetic wave absorber that is used by directly adhering it to a component that requires electromagnetic wave absorption or by adhering it to a housing by using the material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The term "adhesion" as used herein includes, in addition to the ordinary meaning of "adhesion", those that are only adhered at the time of application and then become adhered. Therefore, the following aspects are typical of the electromagnetic wave absorber of the present invention. -A sheet having a predetermined thickness, which is sticky and is used by sticking it on the application surface, and-A matrix material which has stickiness and plasticity and has a recess Those that are used by filling in or pushing on the surface to be applied and sticking.

As the soft magnetic metal powder, any powder can be used, but commonly used PC permalloy, Fe-Cr alloy, Fe-Si alloy, Fe-Si-Al alloy, Fe.
Powders of —Co based alloys and Fe—Ni based alloys are preferable.
As will be seen in the examples described later, the frequency characteristics of the electromagnetic wave absorber as a product are slightly different depending on the alloy composition of the soft magnetic metal used, and therefore it may be selected according to the application.

A flake-like powder is obtained by atomizing the molten metal of these metals by spraying with water or gas and flattening the powder with an attritor. In the present invention, "flatness" is used as a word representing the degree of flattening. The flatness is determined by observing the flat powder with a SEM (scanning electron microscope) from the surface direction to measure the major axis and the minor axis, and taking the average value of these as the average diameter, embedding the powder in the resin and polishing the surface. Is observed with an optical microscope, the maximum thickness and the minimum thickness of the flat powder are measured, and their average value is taken as the average thickness. Flatness = average diameter / average thickness is a value obtained.

The soft magnetic metal powder produced by the above-mentioned molten metal spraying method usually has a flatness of 1.5 or less and a substantially spherical shape. When using flat powder, the flatness is 4
The above are effective, and 15 or more are preferable. At present, noise electromagnetic waves, which are a problem in electronic devices, are in the frequency region of several hundred MHz to several GHz, and the center frequency of absorption is located in this region by using the soft magnetic metal powder in a flattened state. be able to. The flat powder is also easy to enhance the absorption performance by orienting the flat surface so as to be parallel to the application surface.

The amount of the soft magnetic metal powder to be filled in the electromagnetic wave absorber is preferably 20 to 70% by weight of the entire electromagnetic wave absorber. If the amount of the soft magnetic metal powder is small, the electromagnetic wave absorbing performance is insufficient, while if the amount is large, the adhesive force of the synthetic resin of the matrix is impaired. Two
The range of 0 to 70% by weight is a range in which the two can be harmonized. The decrease in the adhesive strength with the increase of the filling amount means that the adhesive strength can be controlled by appropriately selecting the filling ratio from a different viewpoint, and the electromagnetic wave absorber is required depending on the place and direction of use. Since the adhesive strength varies depending on the situation, the filling ratio of the soft magnetic metal powder should be determined so as to realize the adhesive strength according to such a situation.

As the matrix material, any synthetic resin or rubber which gives the above-mentioned meaning of tackiness can be arbitrarily used. However, the acrylic synthetic resin has a relatively high heat resistance, and the temperature easily rises. It is preferable when applied to electronic parts. In addition, natural rubber or synthetic rubber adhesives are also suitable. When mixing the soft magnetic metal powder and the synthetic resin, a volatile organic solvent may be used. This is because the organic solvent lowers the viscosity of the synthetic resin, increases the apparent volume, facilitates mixing, and then volatilizes to provide a high filling rate. In the present invention, a high filling rate of 70% by volume, which cannot be realized with a rolled sheet, is possible.

[0014]

Examples and Comparative Examples [Example 1] Fe-Si-Al
The water-sprayed powder of the alloy was flattened with an attritor for 24 hours. In the treatment, a hydrocarbon organic solvent was used as a dispersion medium, and zinc stearate was added as a lubricant in an amount of 1% by weight of the powder. The obtained flat powder was placed in a heat treatment furnace and heat-treated at 700 ° C. for 1 hour in an argon atmosphere to eliminate the strain remaining in the powder. Then, this powder was mixed with an acrylic resin so that the proportion of the powder in the mixture was 10, 20, 50, 70 or 80% by volume.

The adhesive strength when each mixture was applied as an electromagnetic wave absorber was evaluated by measuring the 180-degree peel strength according to the method specified in JIS Z1525. Specifically, the mixture is applied to a stainless steel plate with a thickness of 100 μm using a coater, and a width of 25 mm is applied on the stainless steel plate.
A 25 μm-thick polyester film was attached, one end was peeled off together with the film, and the film was pulled at 180 °, that is, in the opposite direction at a speed of 300 mm / min. The strength at this time is defined as "peeling adhesive force f (gf / 25 mm)". The relationship between powder content and adhesive strength is shown in Table 1 below.

[0016]

The adhesive force measured by the above measuring method is about 4
If it is 00 (gf / 25mm), it is said to be useful as an adhesive, and if the powder content is up to 70% by volume,
It was found that the electromagnetic wave absorber had sufficient adhesive force.

As a scale showing the performance of each electromagnetic wave absorber,
The return loss was measured. A metal rod having a diameter of 3 mm was inserted into a metal tube having an inner diameter of 7 mm so that the axes thereof coincided, and one end was closed with a metal plate. A donut type electromagnetic wave absorber obtained by molding each of the above mixtures into a sheet having a thickness of 1.0 mm and punching it into a donut type having an outer diameter of 3 mm and an inner diameter of 3 mm was inserted into the bottom of the coaxial tube until it contacted the metal plate. did. The return end represented by RL = -20logS11 was calculated by connecting the open end of the coaxial tube to a network analyzer and measuring S11 at one port in the frequency range up to 20 GHz.

FIG. 1 shows frequency characteristics of return loss for powder contents of 20, 50 and 70% by volume.
The graph in FIG. 1 shows that increasing the powder content shifts the peak absorption frequency to the lower side and the maximum absorption is higher.

[Example 2] Fe-13Cr was used as a soft magnetic metal.
Under the same conditions as in Example 1, except that the alloy was changed to an attritor treatment time of 6 hours, flat powder production, mixing with an acrylic resin, measurement of adhesive force, sheet molding, and measurement of return loss were performed. I did. The 180 degree peel strength is shown in Table 2 below.

[0021]

20 G of the electromagnetic wave absorber obtained in this example
FIG. 2 shows frequency characteristics of return loss in the frequency range up to Hz. The graph of FIG. 2 is the same as that of Example 1 with respect to the tendency that the increase of the powder content shifts the peak absorption frequency to the lower side and the maximum absorption amount becomes larger, but the peak absorption frequency is higher than that of Example 1. It is on the high frequency side, and it is shown that the characteristics of the electromagnetic wave absorber using the soft magnetic metal are different when the kind of the soft magnetic metal is different.

[Example 3] Fe-Si-Al of Example 1
The alloy powder or the Fe—Cr alloy powder of Example 2 was used, and the matrix material was changed to a rubber adhesive to manufacture an electromagnetic wave absorber having a powder content of 50% by volume. For these, the 20 GHz return loss was measured by the method described above. The frequency characteristic is shown in FIG.

[0024]

The electromagnetic wave absorber of the present invention may be formed into a sheet shape, or may be used as a paint in an indefinite shape, and since it has an adhesive property by itself, it has a conventional sheet shape. Unlike objects, it can be applied to desired electronic devices and housings without the help of another adhesive. If sandwiched between the substrates, the substrates can be joined together. If it is an irregular shape, it is possible to wrap the part you want to shield with this electromagnetic parallel absorber, you can inject it into the gap between parts, or you can close the gap of the housing, so electronic equipment It is possible to cope with the current situation where noise electromagnetic waves are moving to the higher frequency side with the higher frequency.

What is noteworthy about this electromagnetic wave absorber is that
In the conventional rolled sheet, the content of the soft magnetic metal powder is limited to about 50% by volume, but according to the present invention, it can be increased to about 70% by volume. With this advancement, the range of control of the peak absorption frequency is expanded, and the degree of freedom in design is increased. An increase in the powder filling amount leads to an increase in absorption performance, so that a more advantageous electromagnetic wave absorber is realized in this respect as well.

[Brief description of drawings]

FIG. 1 is data of Example 1 of the present invention, which is 20 GHz of an electromagnetic wave absorber obtained by dispersing flattened powder of a soft magnetic metal (Fe—Si—Al alloy) in an acrylic resin matrix. A graph showing frequency characteristics of return loss up to.

FIG. 2 shows data of Example 2 of the present invention, which is obtained by dispersing a flattened powder of a soft magnetic metal (Fe—Cr alloy) in an acrylic resin matrix,
The graph which shows the frequency characteristic of return loss up to 0 GHz.

FIG. 3 is data of Example 3 of the present invention, obtained by dispersing flattened powder of a soft magnetic metal (Fe—Si—Al alloy or Fe—Cr alloy) in a matrix of a rubber adhesive. The graph which shows the frequency characteristic of the return loss up to 20 GHz of the electromagnetic wave absorber.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Suzuki             Daido Special, 10 Ryugucho, Minato-ku, Nagoya City, Aichi Prefecture             Special Steel Co., Ltd., Tsukiji Factory (72) Inventor Shinichiro Yahagi             Daido Special, 10 Ryugucho, Minato-ku, Nagoya City, Aichi Prefecture             Special Steel Co., Ltd., Tsukiji Factory F-term (reference) 5E040 AA01 AA11 AA14 CA13                 5E041 AA02 AA04 AA05 AA07 CA10                 5E321 BB32 BB53 CC16 GG11

Claims (8)

[Claims] 1. An electromagnetic wave absorber comprising a soft magnetic metal powder dispersed in an organic matrix material, wherein a material having adhesiveness is used as a matrix,
An electromagnetic wave absorber that is used by directly adhering to parts that require electromagnetic wave absorption or by adhering it to the housing. 2. The soft magnetic metal powder is used as an electromagnetic wave absorber.
The electromagnetic wave absorber according to claim 1, which occupies 0 to 70% by weight. 3. The electromagnetic wave absorber according to claim 1, which is formed into a sheet having a predetermined thickness, and the sheet has an adhesive property. 4. The matrix material, which has adhesiveness and plasticity, is used by being filled in a recess or by being pushed and spread on a surface to be applied for adhesion.
Electromagnetic wave absorber. 5. The electromagnetic wave absorber according to claim 1, wherein a powder of Fe—Si alloy, Fe—Si—Al alloy, Fe—Co alloy or Fe—Ni alloy is used as the soft magnetic metal powder. 6. The electromagnetic wave absorber according to claim 1, wherein a flat powder is used as the soft magnetic metal powder, and the flat surface of the powder is oriented substantially parallel to the sheet surface or the application surface. 7. The electromagnetic wave absorber according to claim 1, wherein an acrylic synthetic resin is used as the matrix material. 8. An electromagnetic wave absorber using a flat powder as a soft magnetic metal powder is applied by pushing and spreading it on the surface to be applied so that the flat surface of the powder becomes parallel to the application surface. A method for applying an electromagnetic wave absorber that is adhered in an oriented state.