JP2005353686A - Radio wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio wave absorber which has a flame retardancy and is environmentally friendly. <P>SOLUTION: The radio wave absorber contains an organic matrix and soft-magnetic powder dispersed in the organic matrix. The soft-magnetic powder consists of an alloy containing at least iron (Fe), silicon (Si), and chromium (Cr), and the content of Si within the alloy is 5 wt.% to 15 wt.%. The organic matrix does not contain any halogen. It is preferred that the electric wave absorber contains a flame retarder which is preferably a metal hydroxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radio wave absorber used for attenuating noise caused by electromagnetic waves in an electronic device.

  In recent years, electronic devices using a high frequency typified by digital electronic devices have been spreading. These electronic devices are required to be smaller and have higher performance, and various electronic components are mounted at high density. As described above, the electronic components and printed wirings mounted at a high density are extremely close to each other, and there is a problem that interference and interference due to electromagnetic noise generated from these electronic components and the like occur.

  As a method of reducing such electromagnetic wave noise in a small space in the equipment, an electromagnetic wave absorber formed by mixing a mixed composition in which an organic matrix is mixed with soft magnetic powder into a sheet shape is placed around an electromagnetic wave generation source. It is known to place and absorb or attenuate generated electromagnetic waves.

  On the other hand, members used in electronic equipment must have a so-called flame retardant property, which is difficult to burn even if ignited due to electric leakage, etc., from the viewpoint of device safety. The absorber is also required to have flame retardancy.

In response to this requirement, in order to impart flame retardancy to the radio wave absorber, an organic matrix containing halogen has generally been used as the base material of the radio wave absorber. For example, Patent Document 1 and Patent Document 2 are formed by molding a mixed composition in which a chlorinated polyethylene having self-extinguishing properties is used as an organic matrix and soft magnetic powder is mixed with the organic matrix into a sheet shape. An electromagnetic wave absorber is disclosed.
JP-A-11-26977 JP 2002-158488 A

  However, in the electromagnetic wave absorbers of Patent Document 1 and Patent Document 2, halogens such as chlorine in chlorinated polyethylene used as an organic matrix generate substances that have a serious adverse effect on the environment, such as dioxin, when incinerated. obtain. Therefore, the use of such a halogen-containing member is strictly regulated from the viewpoint of environmental load.

  Accordingly, an object of the present invention is to provide a radio wave absorber that has flame retardancy and does not generate harmful substances such as dioxin during incineration, that is, is environmentally friendly. More specifically, an object is to provide a radio wave absorber having flame retardancy using a non-halogen material as an organic matrix.

  In order to solve the above problems, the invention according to claim 1 is an electromagnetic wave absorber including an organic matrix and a soft magnetic powder dispersed in the organic matrix, wherein the soft magnetic powder is: It is made of an alloy containing at least iron, silicon, and chromium, the content of silicon in the alloy is 5 wt% to 15 wt%, and the gist is that the organic matrix is non-halogen.

  The gist of the invention described in claim 2 is that, in the radio wave absorber according to claim 1, the blending ratio of the soft magnetic powder in the radio wave absorber is 15 vol% to 35 vol%.

The gist of the invention described in claim 3 is the radio wave absorber according to claim 1 or 2, wherein the radio wave absorber further contains a flame retardant.
The gist of the invention described in claim 4 is the radio wave absorber according to any one of claims 1 to 3, wherein the flame retardant is a metal hydroxide having crystal water.

  According to the invention of claim 1, in the radio wave absorber, by using an alloy powder containing at least iron, silicon, and chromium as the soft magnetic powder, and having a silicon content in a specific range, The flame retardancy of the radio wave absorber can be improved. In addition, since the organic matrix is non-halogen, an environment-friendly radio wave absorber can be obtained.

According to the second aspect of the present invention, a radio wave absorber having excellent radio wave absorption characteristics and flame retardancy can be obtained.
According to the third aspect of the present invention, a radio wave absorber that is more excellent in flame retardancy can be obtained.

  According to invention of Claim 4, while being excellent in a flame retardance, an environmentally friendly electromagnetic wave absorber is obtained.

  The radio wave absorber of the present invention is formed from a mixed composition containing an organic matrix and soft magnetic powder dispersed in the organic matrix. In the radio wave absorber, the organic matrix is made of a non-halogen material that does not substantially contain halogen. The soft magnetic powder is made of an alloy containing at least iron (Fe), silicon (Si), and chromium (Cr), and the Si content in the alloy is 5 wt% to 15 wt%. As described above, the radio wave absorber of the present invention is an alloy containing at least iron, silicon, and chromium as the soft magnetic powder, and using the alloy powder having a silicon content in a specific range. Even in the case where an organic matrix containing no halogen is used as the base material, the flame retardancy is improved as compared with the prior art. In recent years, a policy for suppressing the use of a halogen-containing material has been promoted due to the influence of an environmental load, and the radio wave absorber of the present invention corresponds to such a policy.

  In one embodiment of the present invention, the radio wave absorber preferably further includes a flame retardant in addition to the organic matrix and the soft magnetic powder. As described above, in the radio wave absorber, in addition to the soft magnetic powder described above, a flame retardant can be further enhanced by adding a flame retardant to the organic matrix. In such an electromagnetic wave absorber, excellent flame retardancy equivalent to the UL94V-0 grade defined in the UL standard established by the United States Writers Laboratories Inc. can be obtained. .

  Moreover, in one Embodiment of this invention, the above electromagnetic wave absorbers are shape | molded in the sheet form. Such a sheet-like electromagnetic wave absorber can be disposed in a limited space in the electronic device, thereby effectively reducing electromagnetic wave noise.

Hereinafter, each component of the present invention will be described in detail.
<Soft magnetic powder>
The soft magnetic powder used for the radio wave absorber of the present invention comprises an alloy containing at least iron (Fe), silicon (Si), and chromium (Cr), that is, a powder of Fe—Si—Cr magnetic stainless steel. . The content of silicon (Si) in the Fe—Si—Cr magnetic stainless steel powder is 5 wt% to 15 wt%. Even in the case of using an organic matrix that does not contain a halogen by blending Fe-Si-Cr magnetic stainless steel powder containing Si in such a range as a soft magnetic powder in a radio wave absorber, conventionally, High flame retardancy can be obtained. When the content of Si in the Fe—Si—Cr magnetic stainless steel powder is less than 5 wt%, sufficient flame retardancy cannot be imparted to the radio wave absorber, and when it exceeds 15 wt%, radio wave absorption performance is obtained. Since it worsens, it is not preferable.

The Fe—Si—Cr magnetic stainless steel may contain other elements such as nickel (Ni) in some amount in addition to iron, silicon, and chromium.
The particles of the Fe—Si—Cr magnetic stainless steel powder have a flat shape, and the flatness is preferably 15 or more. Moreover, it is preferable that the average particle diameter of a Fe-Si-Cr type | system | group magnetic stainless steel powder is 10 micrometers-40 micrometers, More preferably, they are 20 micrometers-30 micrometers. This average particle diameter is the average of the diameters of one particle, that is, a value obtained by (major axis + minor axis) / 2. Flatness is the average particle diameter divided by the maximum particle thickness of the particle. Value. Since the magnetic stainless steel powder has such flatness and average particle size in such a range, the magnetic stainless steel powder exhibits a high value of magnetic permeability that causes attenuation of electromagnetic waves. Even when the radio wave absorber is formed in a thin sheet shape, in order to obtain excellent radio wave absorption characteristics, it is necessary to increase the attenuation of the electromagnetic wave in the radio wave absorber. For this purpose, the soft magnetic powder used in the radio wave absorber of the present invention exhibits a high value of magnetic permeability that causes electromagnetic wave attenuation in the frequency band (several MHz to several tens GHz) of electronic equipment. By selecting magnetic stainless steel powder, the radio wave absorber obtained has excellent radio wave absorption characteristics.

  The blending ratio of the soft magnetic powder in the radio wave absorber is preferably 15 vol% to 35 vol%. If the blending ratio of the soft magnetic powder is less than 15 vol%, sufficient radio wave absorption performance cannot be obtained. On the other hand, when the blending ratio of the soft magnetic powder exceeds 35 vol%, the handling property and molding processability of the mixed composition composed of the soft magnetic powder and the organic matrix are deteriorated, which is not preferable.

<Organic matrix>
In the radio wave absorber of the present invention, a non-halogen (containing no halogen) organic matrix that does not generate a harmful substance such as dioxin at the time of combustion can be used by using the soft magnetic powder described above. Such a non-halogen organic matrix has various performance specifications such as mechanical strength, heat resistance, electrical characteristics, and durability, dispersibility of soft magnetic powder in the organic matrix, and molding processability of a mixed composition thereof. Etc. can be selected in consideration. Examples of non-halogen organic matrices include halogen-free gels, thermoplastic and thermosetting resins or rubbers, thermoplastic elastomers, etc., but there are no particular limitations on the composition, curing mode, and the like. However, particularly preferable examples include styrene-based thermoplastic elastomers excellent in heat resistance and vinyl acetate excellent in processability. The component of the organic matrix is not limited to any one type, and two or more types may be mixed and used.

<Flame Retardant>
The flame retardant generally refers to a substance having a function of making the flammable substance difficult to burn by adding or reacting with a flammable material such as plastic. The flame retardant used in the radio wave absorber of the present invention preferably does not contain a halogen. For example, phosphates, red phosphoruss, metal oxides, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, Examples thereof include silicone-based and triazine-based flame retardants. Among these, metal hydroxides that do not generate harmful substances during combustion are particularly preferable. The metal hydroxide is a flame retardant containing crystal water in the crystal and providing a cooling effect when water is evaporated by a dissociation reaction of the crystal water. Therefore, by using a metal oxide as a flame retardant, it is possible to obtain a radio wave absorber that is more environmentally friendly. The blending amount of such metal hydroxide in the radio wave absorber depends on the type of the organic matrix to be used. For example, as shown later in the examples, when a styrene thermoplastic elastomer is used as the organic matrix, In the radio wave absorber, the compounding amount of the metal oxide is preferably 10 to 30 vol%. When the compounding amount of the metal oxide is 10 vol% or less, it is difficult to obtain the effect of improving flame retardancy, and when the compounding amount of the metal oxide is 30 vol% or more, the ratio of the soft magnetic powder in the radio wave absorber is Therefore, it may be difficult to obtain radio wave absorption performance.

  The radio wave absorber of the present invention may contain other additives in addition to the soft magnetic powder, the organic matrix, and the flame retardant. As such an additive, for example, a plasticizer, an adhesive, a reinforcing agent, a colorant, a heat resistance improver, and the like can be considered.

<Manufacturing method>
The radio wave absorber of the present invention is manufactured by molding a mixed composition in which an organic matrix and an Fe-Si-Cr magnetic stainless steel powder and optionally a flame retardant and other additives are mixed into a desired shape. Can do. Examples of such molding methods include a bar coater method, a doctor blade method, an extrusion molding method using a T-die, a calendar molding method, and a pressure press molding method.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

(Examples 1-3)
As organic matrix, 100 parts by weight of styrene-based thermoplastic elastomer (manufactured by Asahi Kasei Co., Ltd., styrene / ethylene / butylene ratio = 20% by weight / 80% by weight), and Si content shown in Table 2 as soft magnetic powder 350 parts by weight of each Fe—Si—Cr-based magnetic stainless steel powder containing 100 parts by weight of aluminum hydroxide as a flame retardant was mixed. The mixture was mixed and stirred while heating using a kneader to obtain a uniform mixed composition. The content of silicon (Si) in each Fe—Si—Cr magnetic stainless steel powder is as shown in Table 2. These Fe—Si—Cr magnetic stainless steel powders were flat with a flatness of 18, an average particle diameter of 25 μm, and a true specific gravity of 7.2. The mixed composition was filled in a cavity of a mold and pressed with a hot press machine to produce a sheet-like electromagnetic wave absorber having a thickness of 1 mm. In addition, the mixture ratio of each Fe-Si-Cr type | system | group magnetic stainless steel powder in each obtained electromagnetic wave absorber was 25 vol%.

(Examples 4 and 5)
The same and the same as that used in Examples 1 to 3, except that Fe-Si-Cr magnetic stainless steel powder having a Si content of 10 wt% is used as the soft magnetic powder in the amount shown in Table 3. Each blend composition was prepared using a quantity of styrenic thermoplastic elastomer (organic matrix) and aluminum hydroxide (flame retardant). The Fe—Si—Cr magnetic stainless steel powder was flat with a flatness of 18, an average particle size of 25 μm, and a true specific gravity of 7.2. Each of the obtained mixed compositions was molded by the same method as in Examples 1 to 3 to produce a sheet-shaped radio wave absorber having a thickness of 1 mm. Table 3 shows the blending ratio of the Fe—Si—Cr magnetic stainless steel powder in each of the obtained wave absorbers.

About each electromagnetic wave absorber obtained in Examples 1-5, the electromagnetic wave absorption characteristic and the flame retardance were evaluated.
Radio wave absorption characteristics : The reflection coefficient and transmission coefficient of each radio wave absorber were measured using a network analyzer (“8515B” manufactured by Agilent Technologies, Inc.). From those coefficients,
The return loss of the radio wave absorber when the electromagnetic wave was incident from the front surface of the sheet-like radio wave absorber and the back surface was short-circuited to the conductor was determined. FIG. 1 is a graph showing the return loss of each wave absorber with respect to frequency.

Flame retardance : In accordance with UL94V, which defines the flammability of plastic materials in the UL (Under Writers Laboratories Inc) standard, which is a US safety standard, each radio wave absorber is subjected to a combustion test using the apparatus shown in FIG. ,evaluated.

  A test piece 1 (length 127 mm × width 12.7 mm × thickness 1.0 mm) of each wave absorber supported by the clamp 4 is placed on a flame 2 a of a burner 2 (caliber: 10 mm, length: about 10 cm) for 10 seconds. After the indirect flame, each test piece records the burning time away from the flame 2a. When each test piece 1 is extinguished, the flame 2a is again indirectly flamed for 10 seconds, separated from the flame 2a, and the burning time of each test piece is recorded. Furthermore, the fire type holding time (growing time) after the second flame contact and the presence or absence of dripping material that ignites the absorbent cotton 3 disposed below the test piece 1 are recorded. The above operation was performed as a set of 5 times for each test piece. The obtained results were compared with the criteria shown in Table 1 below to determine the flame retardant grade of each radio wave absorber.

実施例１〜５の電波吸収体の電波吸収特性および難燃性の評価結果を表２および表３にまとめた。

Tables 2 and 3 summarize the evaluation results of the radio wave absorption characteristics and flame retardancy of the radio wave absorbers of Examples 1 to 5.

図１から分かるように、実施例１〜５の電波吸収体は、いずれも優れた電波吸収特性を示した。また、これらの電波吸収体は、表２および表３に示したようにＵＬ９４Ｖ−０相当の高い難燃性を有した。

As can be seen from FIG. 1, the radio wave absorbers of Examples 1 to 5 all showed excellent radio wave absorption characteristics. Further, as shown in Tables 2 and 3, these radio wave absorbers had high flame retardancy equivalent to UL94V-0.

(Comparative Example 1)
As shown in Table 2, the soft magnetic powder used in Examples 1 to 3 except that 350 parts by weight of Fe—Si—Cr magnetic stainless steel powder having a Si content of 3 wt% was used. A mixed composition was prepared using the same and the same amount of styrenic thermoplastic elastomer (organic matrix) and aluminum hydroxide (flame retardant). The Fe—Si—Cr magnetic stainless steel powder was flat with a flatness of 18, an average particle size of 25 μm, and a true specific gravity of 7.2. The obtained mixed composition was molded by the same method as in Examples 1 to 3 to produce a sheet-like electromagnetic wave absorber having a thickness of 1 mm. The mixing ratio of the Fe—Si—Cr magnetic stainless steel powder in the obtained radio wave absorber was 25 vol%.

  About the electromagnetic wave absorber obtained by the comparative example 1, when the flame retardance was evaluated similarly to Examples 1-5, the flame retardance of this electromagnetic wave absorber was UL94V-1 grade. Therefore, the flame retardancy of the radio wave absorber of Comparative Example 1 using the Fe—Si—Cr-based magnetic stainless steel powder having a Si content of less than 5% is inferior to that of Examples 1 to 5. I understand.

(Comparative Example 2)
As shown in Table 2, the soft magnetic powder used in Examples 1 to 3 except that 350 parts by weight of Fe—Si—Cr magnetic stainless steel powder having a Si content of 17 wt% was used. A mixed composition was prepared using the same and the same amount of styrenic thermoplastic elastomer (organic matrix) and aluminum hydroxide (flame retardant). The Fe—Si—Cr magnetic stainless steel powder was flat with a flatness of 18, an average particle size of 25 μm, and a true specific gravity of 7.2. The obtained mixed composition was molded by the same method as in Examples 1 to 3 to produce a sheet-like electromagnetic wave absorber having a thickness of 1 mm. The blending ratio of the Fe—Si—Cr magnetic stainless steel powder in the obtained radio wave absorber was 25 vol%.

  About the obtained electromagnetic wave absorber, the electromagnetic wave absorption characteristic was measured like Examples 1-5. The results are shown in FIG. 1 and Table 2. As can be seen from FIG. 1 and Table 2, the electromagnetic wave absorber of Comparative Example 2 using the Fe—Si—Cr magnetic stainless steel powder having a Si content of 15 wt% or more has a practically required 3 GHz. The return loss at the following frequencies was insufficient.

(Comparative Example 3)
As shown in Table 2, the same and the same amount of styrenic thermoplastic as used in Examples 1 to 3 except that 350 parts by weight of Fe—Al—Si based magnetic alloy powder was used as the soft magnetic powder. A mixed composition was prepared using an elastomer (organic matrix) and aluminum hydroxide (a flame retardant). This Fe—Al—Si based magnetic alloy powder had a flat shape with a flatness of 15, an average particle size of 25 μm, and a true specific gravity of 6.8. The obtained mixed composition was molded by the same method as in Examples 1 to 3 to produce a sheet-like electromagnetic wave absorber having a thickness of 1 mm.

  About the electromagnetic wave absorber obtained by the comparative example 3, when the flame retardance was evaluated similarly to Examples 1-5, the flame retardance of this electromagnetic wave absorber was UL94V-1 grade. Therefore, it turns out that the flame retardance of the electromagnetic wave absorber of the comparative example 3 which used the Fe-Al-Si type magnetic alloy powder as a soft-magnetic-material powder is inferior compared with Examples 1-5. This is presumably because the magnetic alloy powder contains aluminum (Al) that is easy to burn.

(Comparative Example 4)
As shown in Table 3, the soft magnetic powder used in Examples 1 to 3 except that 110 parts by weight of Fe-Si-Cr magnetic stainless steel powder having a Si content of 10 wt% was used. A mixed composition was prepared using the same and the same amount of styrenic thermoplastic elastomer (organic matrix) and aluminum hydroxide (flame retardant). The Fe—Si—Cr magnetic stainless steel powder was flat with a flatness of 18, an average particle size of 25 μm, and a true specific gravity of 7.2. The obtained mixed composition was molded by the same method as in Examples 1 to 3 to produce a sheet-like electromagnetic wave absorber having a thickness of 1 mm. Fe in the obtained wave absorber
The blending ratio of the —Si—Cr magnetic stainless steel powder was 10 vol%.

  About the obtained electromagnetic wave absorber, the electromagnetic wave absorption characteristic was measured like Examples 1-5. The results are shown in FIG. As can be seen from FIG. 1, in the radio wave absorber of Comparative Example 4 in which the blending ratio of the Fe—Si—Cr magnetic stainless steel powder in the radio wave absorber is a low value of 10 vol%, sufficient radio wave absorption characteristics are obtained. I could not.

(Comparative Example 5)
As shown in Table 3, the soft magnetic powder used in Examples 1 to 3 except that 700 parts by weight of Fe-Si-Cr magnetic stainless steel powder having a Si content of 10 wt% was used. A mixed composition was prepared using the same and the same amount of styrenic thermoplastic elastomer (organic matrix) and aluminum hydroxide (flame retardant). The Fe—Si—Cr magnetic stainless steel powder was flat with a flatness of 18, an average particle size of 25 μm, and a true specific gravity of 7.2. The blending ratio of the Fe—Si—Cr magnetic stainless steel powder in the mixed composition was 40 vol%. About the obtained mixed composition, preparation of the sheet-like electromagnetic wave absorber which has a thickness of 1 mm was tried by shape | molding by the method similar to Examples 1-3. However, the handleability and molding processability of the mixed composition were poor, and a radio wave absorber could not be produced.

The technical idea grasped from the above embodiment will be described below.
The radio wave absorber according to any one of claims 1 to 4, wherein the organic matrix is a styrene thermoplastic elastomer.
The radio wave absorber according to any one of claims 1 to 4, wherein the radio wave absorber is formed into a sheet shape.
The radio wave absorber according to claim 4, wherein the metal oxide is aluminum hydroxide.

The graph which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorber of the Example and comparative example of this invention. The figure which shows the apparatus which evaluates a flame retardance.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Test piece, 2 ... Burner, 3 ... Absorbent cotton, 4 ... Clamp.

Claims (4)

In an electromagnetic wave absorber containing an organic matrix and a soft magnetic powder dispersed in the organic matrix,
The soft magnetic powder is made of an alloy containing at least iron (Fe), silicon (Si), and chromium (Cr), and the silicon content in the alloy is 5 wt% to 15 wt%,
The electromagnetic wave absorber, wherein the organic matrix is non-halogen.   2. The radio wave absorber according to claim 1, wherein a blending ratio of the soft magnetic material powder in the radio wave absorber is 15 vol% to 35 vol%.   The radio wave absorber according to claim 1, wherein the radio wave absorber further contains a flame retardant.   The radio wave absorber according to any one of claims 1 to 3, wherein the flame retardant is a metal hydroxide having crystal water.

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