JP4124395B2 - Electromagnetic wave absorber - Google Patents
Electromagnetic wave absorber Download PDFInfo
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- JP4124395B2 JP4124395B2 JP2000039013A JP2000039013A JP4124395B2 JP 4124395 B2 JP4124395 B2 JP 4124395B2 JP 2000039013 A JP2000039013 A JP 2000039013A JP 2000039013 A JP2000039013 A JP 2000039013A JP 4124395 B2 JP4124395 B2 JP 4124395B2
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- Prior art keywords
- electromagnetic wave
- boron
- wave absorber
- carbon black
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Description
【０００１】
【発明の属する技術分野】
本発明は、電磁波吸収体に関する。
【０００２】
【従来の技術】
近年、電子機器の普及に伴い、電子機器等から発生する電磁波によって信号が乱され、障害が多発している。電磁波吸収体は、この電磁波を吸収し電磁波障害による電子機器等への妨害を除去するものである。従って、電磁波吸収体が備えなければならない特性は、複雑形状の電子機器等であっても容易にそれを覆うことができること、電磁波を透過させないこと、電磁波が交錯する空間で妨害となる電磁波を除去することである。これに加えて、軽量化、薄肉化が可能であれば更に望ましい。
【０００３】
従来は、テレビゴースト対策やレーダー偽像対策等の目的で、カーボンブラックを含有してなるポリエチレン等のポリオレフィン系成形体を電磁波吸収体として使用されている。この電磁波吸収体は、カーボンブラックのかわりに金属フレークや金属繊維等の金属材料又はカーボン繊維を用いたものと比較し、軽量かつ電子機器の被覆性に優れ、かつ安価である利点がある。
【０００４】
【発明が解決しようとする課題】
しかしながら、カーボンブラックのなかで高導電性を発現するものは、高比表面積を有するケッチェンブラック、高比表面積と高ストラクチャーを有するアセチレンブラック等であるが、これらを用いても上記金属材料を用いた場合に比較し、電磁波吸収特性が小さく更なる改善が望まれている。
【０００５】
本発明は、上記に鑑みてなされたものであり、その目的は、電磁波吸収特性に優れ、吸収体の厚みが薄く、軽量化でき、複雑形状の電子機器であっても容易にそれを被覆することができる電磁波吸収体を提供することである。
【０００６】
【課題を解決するための手段】
すなわち、本発明は、ＪＩＳ Ｋ １４６９による電気抵抗率が０．１Ωｃｍ以下であるホウ素固溶のカーボンブラックを含有したポリオレフィン系成形体からなることを特徴とする電磁波吸収体である。
【０００７】
【発明の実施の形態】
以下、更に詳しく本発明について説明する
【０００８】
本発明で使用されるホウ素固溶のカーボンブラックは、特願平１１ー８６６６１号公報に記載のように、炭化水素の熱分解反応時及び／又は燃焼反応時にホウ素源を存在させることにより製造することができる。本発明においては、その原粉をそのままポリオレフィンに配合しても良いが、樹脂への均一分散性の点から、それを０．１〜２ｍｍ程度に造粒してから配合することが好ましい。カーボンブラック原粉の造粒には、イオン交換水を湿潤剤として用いることが望ましく、その詳細は特公平１−５８２２７号公報に記載されている。
【０００９】
本発明において、ホウ素固溶のカーボンブラックのＪＩＳ Ｋ １４６９による電気抵抗率が０．１Ωｃｍを超えると、導電性付与効果が劣り、電磁波吸収能力は向上しない。
【００１０】
本発明で使用される樹脂はポリオレフィン系であり、ポリエチレン、ポリプロピレンを代表例としてあげることができる。これらの市販品を何ら不都合なく用いることができる。
【００１１】
ポリオレフィン系樹脂とホウ素固溶のカーボンブラックとの好適な割合は、電磁波周波数によって異なる。低周波数域では、カーボンブラックの割合が少なく、高周波数域では多くすることが望ましい。具体的には、質量基準で、ポリオレフィン系樹脂１００部あたり、低周波数領域では５〜１０部、 高周波数領域では８０〜１００部である。
【００１２】
本発明の電磁波吸収体は、ポリオレフィン系樹脂とホウ素固溶のカーボンブラックとを混合し、押し出し成形等によって所望形状に成形することによって製造することができる。形状の一例を示すと、薄片板状である。
【００１３】
【実施例】
以下、実施例と比較例をあげて更に具体的に本発明を説明する。
【００１４】
実施例１、２ 比較例１、２
低密度ポリエチレン（三井化学社製商品名「４０３Ｐ」）１００質量部と、ホウ素固溶量及び電気抵抗率が種々異なるカーボンブラックとを表１に示す割合（質量部）とを配合し、内容積６０ｍｌの混練試験機（東洋精機製作所製「ラボプラストグラフＲ−６０」）で、ブレード回転数３０ｒｐｍ、温度１６０℃で１０分間混練した。
【００１５】
得られた樹脂混練物を加熱プレス機にて温度１６０℃、圧力９．８ＭＰａで１０分間プレスし、２００×２００×５ｍｍのシートを成形した。更に、機械研削を行い、表１の厚みに仕上げ、電磁波吸収体とした。
【００１６】
カーボンブラックのホウ素固溶量、電気抵抗率、沃素吸着量、ＤＢＰ吸収量、樹脂混練物のメルトフローインデックス（ＭＦＩ）、及び電磁波吸収体の電波吸収特性を以下に従い測定した。それらの結果を表１に示す。
【００１７】
（１）ホウ素固溶量：以下に従って測定された全ホウ素量から可溶ホウ素量を差し引くことによって求めた。
【００１８】
全ホウ素量は、カーボンブラック０．５ｇを白金皿に取り、１．５％Ｃａ（ＯＨ）2溶液２０ｍｌ、アセトン５ｍｌを加え、超音波洗浄機で１時間分散させる。それをサンドバスで乾固させた後、電気炉を用い、酸素気流中、８００℃で３時間かけて灰化させる。次いで、ＨＣｌ（１＋１）溶液１０ｍｌを加えサンドバス中で加熱して溶出させる。溶出液を１００ｍｌに定容し、ＩＣＰ−ＡＥＳでホウ素量を定量し、カーボンブラック中の全ホウ素量とする。
【００１９】
可溶ホウ素量は、カーボンブラック１ｇを石英ガラス製三角フラスコに取り、水１００ｍｌとアセトン１ｍｌを加える。それをウォーターバス上で２４時間還留させ、０．８μｍメンブランフィルターで濾過する。炉液のホウ素量をＩＣＰ−ＡＥＳで定量し、カーボンブラック中の可溶ホウ素量とする。
全ホウ素量より可溶ホウ素量を差し引き固溶ホウ素量を算出した。
【００２０】
（２）電気抵抗率：ＪＩＳ Ｋ １４６９に従って測定した。
（３）沃素吸着量：ＪＩＳ Ｋ １４７４に従って測定した。
（４）ＤＢＰ吸収量：ＪＩＳ Ｋ ６２１７に準じて測定した。
【００２１】
（５）樹脂混練物のＭＦＩ（メルトフローインデックス）：混練物の一部をカッターで微砕化し、流動性測定機（東洋精機製作所製「メルトインデクサーＡ−１１１」）で２００℃の加熱下、５ｋｇの加重下にて内径２ｍｍのノズルから流れる１０分間当たりのコンパウンド質量を測定した。
（６）電波吸収特性は、２００×２００ｍｍで表１に示す厚みのシートを用い、自由空間法（橋本 修著 「電磁波吸収体入門」 森北出版 １９９７．１０．１６発行 第４．２．１項、第９．４項）により測定した。測定周波数は８〜１２ＧＨｚ域で実施した。
【００２２】
【表１】
【発明の効果】
本発明の電磁波吸収体は、電磁波吸収特性に優れており、しかも吸収体厚みを薄く、軽く、かつ柔軟化できる。従って、本発明の電磁波吸収体は、電磁波を発生する電子機器等の形状が複雑であっても、それを容易に覆うことができるので、電磁波障害を著しく軽減することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic wave absorber.
[0002]
[Prior art]
In recent years, with the widespread use of electronic devices, signals are disturbed by electromagnetic waves generated from electronic devices and the like, resulting in frequent failures. The electromagnetic wave absorber absorbs this electromagnetic wave and removes interference with electronic equipment due to electromagnetic interference. Therefore, the characteristics that the electromagnetic wave absorber must have are that it can easily cover even complex electronic devices, etc., does not transmit electromagnetic waves, and removes electromagnetic waves that interfere with electromagnetic waves. It is to be. In addition to this, it is more desirable if the weight and thickness can be reduced.
[0003]
Conventionally, polyolefin molded articles such as polyethylene containing carbon black have been used as electromagnetic wave absorbers for the purpose of TV ghost countermeasures and radar false image countermeasures. This electromagnetic wave absorber has an advantage that it is light in weight, excellent in the coverage of electronic devices, and inexpensive compared to a material using metal materials such as metal flakes and metal fibers or carbon fibers instead of carbon black.
[0004]
[Problems to be solved by the invention]
However, carbon black that exhibits high conductivity is ketjen black having a high specific surface area, acetylene black having a high specific surface area and a high structure. Compared with the case where it had, the electromagnetic wave absorption characteristic is small, and the further improvement is desired.
[0005]
The present invention has been made in view of the above, and the object thereof is excellent in electromagnetic wave absorption characteristics, the thickness of the absorber is thin, the weight can be reduced, and even an electronic device having a complicated shape can be easily covered. It is to provide an electromagnetic wave absorber that can be used.
[0006]
[Means for Solving the Problems]
That is, the present invention is an electromagnetic wave absorber comprising a polyolefin-based molded body containing boron solid solution carbon black having an electrical resistivity of 0.1 Ωcm or less according to JIS K 1469.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The boron solid solution carbon black used in the present invention is produced by the presence of a boron source during the thermal decomposition reaction and / or combustion reaction of hydrocarbons as described in Japanese Patent Application No. 11-86661. be able to. In the present invention, the raw powder may be blended with the polyolefin as it is, but from the viewpoint of uniform dispersibility in the resin, it is preferably blended after granulating it to about 0.1 to 2 mm. For granulation of the carbon black raw powder, it is desirable to use ion-exchanged water as a wetting agent, and details thereof are described in JP-B-1-58227.
[0009]
In the present invention, when the electrical resistivity of boron solid solution carbon black according to JIS K 1469 exceeds 0.1 Ωcm, the conductivity imparting effect is inferior, and the electromagnetic wave absorbing ability is not improved.
[0010]
The resin used in the present invention is a polyolefin, and polyethylene and polypropylene can be given as typical examples. These commercially available products can be used without any inconvenience.
[0011]
A suitable ratio between the polyolefin resin and the boron-soluble carbon black varies depending on the electromagnetic wave frequency. It is desirable that the ratio of carbon black is small in the low frequency range and increased in the high frequency range. Specifically, it is 5 to 10 parts in the low frequency region and 80 to 100 parts in the high frequency region per 100 parts of the polyolefin-based resin on a mass basis.
[0012]
The electromagnetic wave absorber of the present invention can be produced by mixing a polyolefin-based resin and boron solid-soluble carbon black and molding the mixture into a desired shape by extrusion molding or the like. An example of the shape is a thin plate shape.
[0013]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
[0014]
Examples 1 and 2 Comparative Examples 1 and 2
100 parts by mass of low-density polyethylene (trade name “403P” manufactured by Mitsui Chemicals, Inc.) and carbon black having different amounts of boron solid solution and different electrical resistivity are blended in the proportions (parts by mass) shown in Table 1, and the internal volume The mixture was kneaded with a 60 ml kneading tester (“Lab Plastograph R-60” manufactured by Toyo Seiki Seisakusho) at a blade rotation speed of 30 rpm and a temperature of 160 ° C. for 10 minutes.
[0015]
The obtained resin kneaded product was pressed with a hot press machine at a temperature of 160 ° C. and a pressure of 9.8 MPa for 10 minutes to form a 200 × 200 × 5 mm sheet. Furthermore, mechanical grinding was performed to finish the thickness shown in Table 1 to obtain an electromagnetic wave absorber.
[0016]
The amount of boron dissolved in carbon black, electrical resistivity, iodine adsorption, DBP absorption, melt flow index (MFI) of the resin kneaded product, and radio wave absorption characteristics of the electromagnetic wave absorber were measured as follows. The results are shown in Table 1.
[0017]
(1) Boron solid solution amount: It was determined by subtracting the soluble boron amount from the total boron amount measured according to the following.
[0018]
For the total boron content, 0.5 g of carbon black is placed in a platinum dish, 20 ml of 1.5% Ca (OH) 2 solution and 5 ml of acetone are added, and dispersed for 1 hour with an ultrasonic cleaner. After drying it in a sand bath, it is incinerated for 3 hours at 800 ° C. in an oxygen stream using an electric furnace. Subsequently, 10 ml of HCl (1 + 1) solution is added and heated in a sand bath to elute. The eluate is made up to a volume of 100 ml, and the amount of boron is quantified by ICP-AES to obtain the total amount of boron in carbon black.
[0019]
For the amount of soluble boron, 1 g of carbon black is placed in a quartz glass Erlenmeyer flask, and 100 ml of water and 1 ml of acetone are added. It is allowed to return for 24 hours on a water bath and filtered through a 0.8 μm membrane filter. The amount of boron in the furnace liquid is quantified by ICP-AES to obtain the amount of soluble boron in carbon black.
The amount of solid boron was calculated by subtracting the amount of soluble boron from the total amount of boron.
[0020]
(2) Electrical resistivity: measured in accordance with JIS K 1469.
(3) Iodine adsorption amount: measured in accordance with JIS K 1474.
(4) DBP absorption: Measured according to JIS K 6217.
[0021]
(5) MFI (melt flow index) of resin kneaded material: A part of the kneaded material is pulverized with a cutter, and heated at 200 ° C. with a fluidity measuring device (“Melt Indexer A-111” manufactured by Toyo Seiki Seisakusho). The compound mass per 10 minutes flowing from a nozzle with an inner diameter of 2 mm under a load of 5 kg was measured.
(6) The electromagnetic wave absorption characteristics are 200 × 200 mm with the thickness shown in Table 1. Free space method (Osamu Hashimoto, “Introduction to electromagnetic wave absorbers” published by Morikita Publishing, 1997. 10.16, Section 4.2.1 , Section 9.4). The measurement frequency was 8 to 12 GHz.
[0022]
[Table 1]
【The invention's effect】
The electromagnetic wave absorber of the present invention is excellent in electromagnetic wave absorption characteristics, and the thickness of the absorber is thin, light and flexible. Therefore, the electromagnetic wave absorber of the present invention can easily cover even if the shape of an electronic device or the like that generates an electromagnetic wave is complicated, and can significantly reduce electromagnetic interference.
Claims (1)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000039013A JP4124395B2 (en) | 2000-02-17 | 2000-02-17 | Electromagnetic wave absorber |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000039013A JP4124395B2 (en) | 2000-02-17 | 2000-02-17 | Electromagnetic wave absorber |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2001230587A JP2001230587A (en) | 2001-08-24 |
| JP4124395B2 true JP4124395B2 (en) | 2008-07-23 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2000039013A Expired - Fee Related JP4124395B2 (en) | 2000-02-17 | 2000-02-17 | Electromagnetic wave absorber |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4124395B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006003924A1 (en) * | 2004-06-30 | 2006-01-12 | Denki Kagaku Kogyo Kabushiki Kaisha | Electromagnetic wave absorbent |
| EP4271157A4 (en) | 2020-12-25 | 2024-06-12 | Nitto Denko Corporation | Radio wave scattering body, and member for attenuating radio waves comprising radio wave scattering body |
-
2000
- 2000-02-17 JP JP2000039013A patent/JP4124395B2/en not_active Expired - Fee Related
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| Publication number | Publication date |
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| JP2001230587A (en) | 2001-08-24 |
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