JP2015023036A - Electromagnetic wave absorber and method of manufacturing the same - Google Patents
Electromagnetic wave absorber and method of manufacturing the same Download PDFInfo
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- JP2015023036A JP2015023036A JP2013147203A JP2013147203A JP2015023036A JP 2015023036 A JP2015023036 A JP 2015023036A JP 2013147203 A JP2013147203 A JP 2013147203A JP 2013147203 A JP2013147203 A JP 2013147203A JP 2015023036 A JP2015023036 A JP 2015023036A
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Images
Abstract
Description
本発明は、電磁波吸収体とその製造方法に関するものである。より詳しくは、本発明は、薄く軽量性に優れ、電磁波を広帯域かつ高い吸収度で吸収する電磁波吸収体と、該電磁波吸収体を少工程ながらも簡便かつ高精度に作りうる電磁波吸収体の製造方法に関するものである。 The present invention relates to an electromagnetic wave absorber and a method for producing the same. More specifically, the present invention is an electromagnetic wave absorber that is thin and excellent in light weight, absorbs electromagnetic waves in a wide band and with a high degree of absorption, and an electromagnetic wave absorber that can be easily and accurately produced in a small number of steps. It is about the method.
近年、半導体、エレクトロニクス分野の技術革新により、コンピューターの無線通信や民生用電子機器、すなわち携帯電話やスマートフォン、携帯型ゲーム機等の情報通信機器において、また高速道路通行時などに利用される自動料金収受システム（ＥＴＣ）や車載レーダー装置を用いた安全運転支援システムに代表される高度道路交通システム（ＩＴＳ）、更には、現行の、あるいは将来的に利用される高精細ハイビジョン放送などにおいて、使用される電磁波の高周波化が顕著に進展し、１秒間に１０億回以上振動するいわゆるギガヘルツ（ＧＨｚ）帯電磁波が頻繁に使用されるようになってきた。それに伴い、これら装置・機器が安定に動作するために、あるいはこれら装置・機器を安全に使用するために、反射あるいは予期せぬ方向への発信のために障害となりうる電磁波を吸収する、広帯域ＧＨｚ帯対応の電磁波吸収体の開発が望まれている。 In recent years, due to technological innovations in the semiconductor and electronics fields, automatic charges for wireless communication of computers and consumer electronic devices, that is, information communication devices such as mobile phones, smartphones and portable game machines, and when traveling on highways, etc. Used in intelligent traffic systems (ITS) represented by safe driving support systems using toll collection systems (ETC) and on-vehicle radar devices, and high-definition high-definition broadcasts that are currently or in the future. The so-called gigahertz (GHz) band electromagnetic wave that vibrates more than 1 billion times per second has been used frequently. Along with this, in order for these devices / equipment to operate stably, or to use these devices / equipment safely, broadband GHz that absorbs electromagnetic waves that can be an obstacle for reflection or transmission in unexpected directions The development of an electromagnetic wave absorber that is compatible with the band is desired.
狭域通信で使用されるＧＨｚ帯で機能する、ＥＴＣ装置（起動周波数５．８ＧＨｚ）等の誤作動防止用電波吸収シートの技術が開示されている（例えば特許文献１参照）。該技術は、異方性黒鉛とバインダーを含むペーストを塗工、乾燥させて塗工吸収シートを得て、かかるシートをＸ方向とＹ方向（Ｘ方向を９０度回転させた方向）とに交互に積層して構成することで、電磁波の入射角度に依らず安定した電波吸収性を示す電波吸収シートを作製するものである。しかしながら、用いる異方性黒鉛は数十μｍレベルの粒径を有しており樹脂中の分散性が極めて悪く、薄いシートを作るのは難しく、特に塗布用に用いるのは極めて困難であった。また、異方性黒鉛に由来する粗粒がシート表面に顕在して表面粗度が高くなる傾向にあり、結果として電磁波吸収性能のばらつきが大きく、更には高濃度の異方性黒鉛を含有したシートは脆くて取扱い性や施工性が悪いものであった。 A technology of a radio wave absorption sheet for preventing malfunction such as an ETC device (starting frequency 5.8 GHz) that functions in a GHz band used in narrowband communication is disclosed (for example, see Patent Document 1). The technology applies anisotropic graphite and a binder-containing paste and dries to obtain a coating-absorbing sheet. The sheet alternates in the X direction and the Y direction (the direction in which the X direction is rotated 90 degrees). Thus, a radio wave absorption sheet that exhibits stable radio wave absorptivity regardless of the incident angle of electromagnetic waves is produced. However, the anisotropic graphite used has a particle size on the order of several tens of μm, and the dispersibility in the resin is extremely poor, making it difficult to produce a thin sheet, and particularly difficult to use for coating. In addition, coarse grains derived from anisotropic graphite tend to appear on the sheet surface and the surface roughness tends to be high. As a result, there is a large variation in electromagnetic wave absorption performance, and furthermore, a high concentration of anisotropic graphite is contained. The sheet was brittle and had poor handleability and workability.
また小粒径の天然黒鉛を含む塗工液を塗布乾燥させて形成した誘電体シートを用いた電磁波吸収体の技術が開示されている（例えば、特許文献２参照）。該技術は薄く軽量の誘電体シートを作製するものである。しかしながら、ミクロンレベルの小粒径の天然黒鉛は極めて疎水性でバインダー樹脂との親和性が低く、高い凝集性を示すため、誘電体シートを形成させる塗布乾燥（溶媒除去）工程で、バインダー樹脂から分離して天然黒鉛粒子同士が凝集しやすいこと、また天然黒鉛を含有した樹脂の誘電率は天然黒鉛同士の繋がり（パーコレーション）に依存するため、天然黒鉛の僅かな分散不均一で誘電率が変化しやすい（ばらつきが大きい）ことなどから、結果として一定の誘電特性を有する誘電体シートの作製は非常に難しいものであった。 Moreover, the technique of the electromagnetic wave absorber using the dielectric material sheet formed by apply | coating and drying the coating liquid containing small graphite natural graphite is disclosed (for example, refer patent document 2). This technique produces a thin and lightweight dielectric sheet. However, natural graphite with a small particle size of micron level is extremely hydrophobic, has a low affinity with the binder resin, and exhibits high cohesiveness. Therefore, in the coating and drying (solvent removal) process for forming the dielectric sheet, The natural graphite particles are likely to aggregate together, and the dielectric constant of the resin containing natural graphite depends on the connection (percolation) between the natural graphite, so the dielectric constant changes due to slight dispersion of natural graphite. As a result, it is very difficult to manufacture a dielectric sheet having a certain dielectric property.
最近、従来の黒鉛に代わる新たな炭素材料として、カーボンナノチューブや樹脂材料を炭化焼成して得られるグラファイトシートやグラフェン類等が黒鉛同様の高導電性材料として幅広い用途に活用されつつある。特にグラフェン類については、天然黒鉛よりも薄い、１ミクロン以下の単層グラフェンあるいは多層グラフェン（薄層黒鉛）が、高い導電性と非常に薄い特性を両立するとともに、高強度／高弾性率、高い移動度など多くの優れた特性を有する材料として知られつつあり、新材料として利用すべく研究開発が活発化している。 Recently, graphite sheets, graphenes, and the like obtained by carbonizing and firing carbon nanotubes and resin materials as new carbon materials that replace conventional graphite are being used in a wide range of applications as high-conductivity materials similar to graphite. In particular, for graphenes, single-layer graphene or multilayer graphene (thin-layer graphite) of 1 micron or less, which is thinner than natural graphite, has both high conductivity and very thin properties, and high strength / high elastic modulus and high It is becoming known as a material having many excellent properties such as mobility, and research and development is being actively promoted for use as a new material.
前記課題に対し、電磁波吸収体を構成する際にグラフェン類を用いる試みが幾つかなされている。例えば、剥離薄層化して調製したグラフェン粉をニトリル−ブタジエンゴム（ＮＢＲ）に含有せしめて得た複合体に関する技術が開示されている（例えば、非特許文献１参照）。当該技術においては、黒鉛粉の化学的処理により得た酸化グラフェンを熱処理により還元し、ＮＢＲとともにキシレン中に分散させたのちキュアして複合体を得ており、該複合体の電磁波吸収特性の評価においては、ＧＨｚ帯での吸収特性を有する結果が示されている。しかしながら当該結果は単にＧＨｚ帯での吸収特性を有することを示したのみで、当該技術は狭帯域の電磁波吸収特性を実現するにとどまるものであった。 Several attempts have been made to use graphenes in constructing an electromagnetic wave absorber for the above-mentioned problems. For example, a technique relating to a composite obtained by incorporating graphene powder prepared by peeling and thinning into nitrile-butadiene rubber (NBR) is disclosed (for example, see Non-Patent Document 1). In this technology, graphene oxide obtained by chemical treatment of graphite powder is reduced by heat treatment, dispersed in xylene together with NBR, and then cured to obtain a composite. Evaluation of electromagnetic wave absorption characteristics of the composite Shows the result of absorption characteristics in the GHz band. However, the result merely showed that it has an absorption characteristic in the GHz band, and the technique has only realized an electromagnetic wave absorption characteristic in a narrow band.
本発明者らは前述の課題を解決すべく、薄層黒鉛を利用した電磁波吸収体において、高い電磁波吸収特性を有しながらも、軽量性、物理物性を維持し、また高精度の素材設計が可能で、工業的に高い利用価値を有する、電磁波吸収体を実現するべく鋭意取り組んだものである。 In order to solve the above-mentioned problems, the inventors of the present invention have an electromagnetic wave absorber using thin-layer graphite that has high electromagnetic wave absorption characteristics while maintaining light weight and physical properties, and is capable of designing a highly accurate material. The present inventors have eagerly worked to realize an electromagnetic wave absorber that is possible and has high industrial utility value.
すなわち本発明の目的は、少ない工程で簡便に作製が可能で、薄く軽量性に優れる、広帯域の電磁波を吸収する電磁波吸収体を提供することにある。 That is, an object of the present invention is to provide an electromagnetic wave absorber that absorbs broadband electromagnetic waves that can be easily produced with few steps, is thin and excellent in light weight.
本発明は、上記の課題を解決するため、以下の構成を採用するものである。
（１）平板状の電磁波吸収帯を備える電磁波吸収体であって、前記電磁波吸収帯は、薄層黒鉛を含有するとともに、厚み方向に電磁波吸収性能の不均一性を有するものである、
電磁波吸収体。
（２）前記電磁波吸収帯が、２層以上の電磁波吸収層から構成されるとともに、前記電磁波吸収帯における電磁波吸収性能の不均一性が、吸収対象周波数の相違する２層以上の電磁波吸収層を備えることにより発現するものである、前記（１）に記載の電磁波吸収体。
（３）前記対象吸収周波数の相違は、各電磁波吸収層に含有される薄層黒鉛の酸化度の相違により発現するものである、前記（２）に記載の電磁波吸収体。
（４）前記電磁波吸収帯の電磁波吸収性能の不均一性が、該電磁波吸収帯の厚み方向に、連続的な電磁波吸収性能の変化を有することにより発現するものである、前記（１）に記載の電磁波吸収体。
（５）前記連続的な電磁波吸収性能の変化が、前記電磁波吸収帯の厚み方向の、薄層黒鉛の密度変化により発現するものである、前記（４）に記載の電磁波吸収体。
（６）シート状の形状を有する、（１）〜（５）のいずれかに記載の電磁波吸収体。
（７）前記電磁波吸収帯が、１０％以下の空隙率を有する、前記（１）〜（６）のいずれかに記載の電磁波吸収体。
（８）前記電磁波吸収層が、さらにポリマーを含有する、前記（２）〜（７）のいずれかに記載の電磁波吸収体。
（９）前記電磁波吸収帯が、さらにポリマーを含有する、前記（１）〜（８）のいずれかに記載の電磁波吸収体。
（１０）さらに、電磁波を反射する基板を有し、前記電磁波吸収帯が、前記基板上に設けられている、前記（１）〜（９）のいずれかに記載の電磁波吸収体。
（１１）電磁波吸収性能測定により得られた吸収スペクトルにおいて、１ＧＨｚ以上の周波数帯域で、２５ｄＢ以上の電磁波吸収性能を有する周波数が１ＧＨｚ以上の帯域にわたり連続する、前記（１）〜（１０）のいずれかに記載の電磁波吸収体。
（１２）平板状の電磁波吸収帯を備える電磁波吸収体の製造方法であって、対象吸収周波数が相違する、２層以上の、薄層黒鉛を含有する電磁波吸収層を積層することで、前記電磁波吸収帯を形成するステップを有する電磁波吸収体の製造方法。
（１３）前記対象吸収周波数の相違は、各電磁波吸収層が含有する薄層黒鉛の密度または該薄層黒鉛の酸化度の相違により発現するものである、前記（１２）に記載の電磁波吸収体の製造方法。
（１４）さらに、積層した電磁波吸収層同士を結合させて、厚み方向に連続的な電磁波吸収性能の変化を有する電磁波吸収帯を形成するステップを有する、前記（１２）または（１３）に記載の電磁波吸収体の製造方法。
（１５）前記２層以上の、薄層黒鉛を含有する電磁波吸収層が、熱可塑性ポリマーを含有するものであり、前記電磁波吸収層同士の結合が、前記熱可塑性ポリマーの融点または軟化点温度以上に加熱することによる溶融結合により行われるものである、前記（１４）に記載の電磁波吸収体の製造方法。
（１６）平板状の電磁波吸収帯を備える電磁波吸収体電磁波吸収体の製造方法であって、熱可塑性ポリマーを含有する電磁波吸収帯を１層に形成した後、前記熱可塑性ポリマーの軟化点温度以上の温度で加熱し、電磁波吸収帯の厚み方向に連続的な電磁波吸収性能の変化を付与せしめるステップを有する電磁波吸収体の製造方法。
The present invention employs the following configuration in order to solve the above problems.
(1) An electromagnetic wave absorber comprising a flat electromagnetic wave absorption band, wherein the electromagnetic wave absorption band contains thin-layer graphite and has non-uniformity in electromagnetic wave absorption performance in the thickness direction.
Electromagnetic wave absorber.
(2) The electromagnetic wave absorption band is composed of two or more electromagnetic wave absorption layers, and the non-uniformity of the electromagnetic wave absorption performance in the electromagnetic wave absorption band includes two or more electromagnetic wave absorption layers having different absorption target frequencies. The electromagnetic wave absorber according to (1), which is expressed by providing the electromagnetic wave absorber.
(3) The electromagnetic wave absorber according to (2), wherein the difference in the target absorption frequency is manifested by a difference in the degree of oxidation of the thin graphite contained in each electromagnetic wave absorption layer.
(4) The non-uniformity of the electromagnetic wave absorption performance of the electromagnetic wave absorption band is manifested by having a continuous change in the electromagnetic wave absorption performance in the thickness direction of the electromagnetic wave absorption band. Electromagnetic wave absorber.
(5) The electromagnetic wave absorber according to (4), wherein the continuous change in electromagnetic wave absorption performance is manifested by a change in density of thin-layer graphite in the thickness direction of the electromagnetic wave absorption band.
(6) The electromagnetic wave absorber according to any one of (1) to (5), which has a sheet-like shape.
(7) The electromagnetic wave absorber according to any one of (1) to (6), wherein the electromagnetic wave absorption band has a porosity of 10% or less.
(8) The electromagnetic wave absorber according to any one of (2) to (7), wherein the electromagnetic wave absorption layer further contains a polymer.
(9) The electromagnetic wave absorber according to any one of (1) to (8), wherein the electromagnetic wave absorption band further contains a polymer.
(10) The electromagnetic wave absorber according to any one of (1) to (9), further including a substrate that reflects electromagnetic waves, wherein the electromagnetic wave absorption band is provided on the substrate.
(11) In any of the above (1) to (10), in the absorption spectrum obtained by the electromagnetic wave absorption performance measurement, a frequency having an electromagnetic wave absorption performance of 25 dB or more is continuous over a band of 1 GHz or more in a frequency band of 1 GHz or more. The electromagnetic wave absorber according to crab.
(12) A method for producing an electromagnetic wave absorber having a flat electromagnetic wave absorption band, wherein the electromagnetic wave is laminated by laminating two or more electromagnetic wave absorbing layers containing thin graphite layers having different target absorption frequencies. A method for producing an electromagnetic wave absorber comprising a step of forming an absorption band.
(13) The electromagnetic wave absorber according to (12), wherein the difference in the target absorption frequency is expressed by the difference in density of the thin graphite contained in each electromagnetic wave absorption layer or the degree of oxidation of the thin graphite. Manufacturing method.
(14) The method according to (12) or (13), further including a step of bonding the laminated electromagnetic wave absorption layers to form an electromagnetic wave absorption band having a continuous change in electromagnetic wave absorption performance in the thickness direction. Manufacturing method of electromagnetic wave absorber.
(15) The electromagnetic wave absorbing layer containing two or more layers and containing thin-layer graphite contains a thermoplastic polymer, and a bond between the electromagnetic wave absorbing layers is equal to or higher than a melting point or a softening point temperature of the thermoplastic polymer. The method for producing an electromagnetic wave absorber according to (14), wherein the method is performed by melt bonding by heating to a temperature.
(16) A method for producing an electromagnetic wave absorber comprising a flat electromagnetic wave absorption band, wherein an electromagnetic wave absorption band containing a thermoplastic polymer is formed in one layer, and then the softening point temperature of the thermoplastic polymer or higher. The manufacturing method of the electromagnetic wave absorber which has the step which heats at the temperature of and gives the change of the continuous electromagnetic wave absorption performance to the thickness direction of an electromagnetic wave absorption band.
本発明の電磁波吸収体は、広い帯域での優れた電磁波吸収性能、好ましくは１ＧＨｚ以上の周波数帯において広い帯域幅で２５ｄＢ以上の高い電磁波吸収性能を有するため、近年頻繁に利用されつつあるＧＨｚ帯の電磁波を利用した各種用途に広範に利用しうるものである。また薄層黒鉛の特性に由来し、薄くすることが可能かつ容易で、電磁波吸収体の材料特性が損なわれないため、優れた電磁波吸収体として利用しうる。 The electromagnetic wave absorber of the present invention has an excellent electromagnetic wave absorption performance in a wide band, preferably a high electromagnetic wave absorption performance of 25 dB or more in a wide bandwidth in a frequency band of 1 GHz or higher, and therefore has been frequently used in recent years. It can be widely used for various applications using electromagnetic waves. In addition, it is derived from the characteristics of the thin-layer graphite, can be thinned easily, and the material characteristics of the electromagnetic wave absorber are not impaired.
本発明の電磁波吸収体は、平板状の電磁波吸収帯を有し、該電磁波吸収帯は薄層黒鉛を含有するものである。 The electromagnetic wave absorber of the present invention has a flat electromagnetic wave absorption band, and the electromagnetic wave absorption band contains thin-layer graphite.
まず、薄層黒鉛について説明する。薄層黒鉛は、炭素原子のπ結合により形成される六角形のベンゼン環格子構造が蜂の巣のように平面方向に多数集合したグラフェンシートが、一層単独で存在、あるいは二層以上積層した構造を有している。積層している場合、各層は独立であっても、また層間で共有結合あるいは非共有結合を介して接続されていても良い。 First, thin layer graphite will be described. Thin-layer graphite has a structure in which a number of hexagonal benzene ring lattice structures formed by π bonds of carbon atoms are gathered in the plane direction like a honeycomb, or each layer is a single layer or a stack of two or more layers. doing. In the case of stacking, each layer may be independent, or may be connected between the layers via a covalent bond or a non-covalent bond.
該薄層黒鉛としては、天然黒鉛や人造黒鉛、膨張黒鉛、グラファイトシートなどを原料として物理的および／または化学的な薄層化処理を経て薄層化して得た微粒子や、あるいは気体、液体、固体の中から少なくとも１種選ばれた原料を用いて、物理的および／または化学的合成法により、原子レベルからボトムアップ的に合成された微粒子を用いることが可能である。 As the thin-layer graphite, fine particles obtained by thinning through natural and / or chemical thinning treatment using natural graphite, artificial graphite, expanded graphite, graphite sheet or the like, or gas, liquid, It is possible to use fine particles synthesized bottom-up from the atomic level by a physical and / or chemical synthesis method using at least one raw material selected from solids.
天然黒鉛あるいは人造黒鉛を原料として用いた薄層黒鉛は、次のような物理的および／または化学的な薄層化処理を経て得ることができる。まず物理的な薄層化処理としては各種ミル、すなわち遊星ボールミルや略一次元方向に高速で往復するミキサーミル、石臼のようなディスクミル、高速回転刃と遠心力を利用したローターミルを用いることができる。薄層化処理時には原料単独で処理を行ってもよく、また後述するポリマーや塗布用の混合液を構成する溶媒を共存させて処理を行ってもよく、あるいは該原料とポリマーとからなる複合体をいったん形成した後に該ミルによる処理を行っても良い。 Thin layer graphite using natural graphite or artificial graphite as a raw material can be obtained through the following physical and / or chemical thinning treatment. First, as physical thinning processing, various mills, that is, a planetary ball mill, a mixer mill that reciprocates at a high speed in a substantially one-dimensional direction, a disk mill such as a stone mortar, and a rotor mill that uses centrifugal force with a high-speed rotating blade are used. Can do. During the thinning treatment, the raw material may be treated alone, or the treatment described below may be performed in the presence of a polymer or a solvent constituting the mixed liquid for coating, or a composite comprising the raw material and the polymer. Once formed, the treatment with the mill may be performed.
また物理的な薄層化処理としては、前記ミル以外にも、スクリュー状の軸を１本あるいは２本以上備えた混練機を用いて原料黒鉛とポリマーを共存させて混練し、処理を行うことで薄層黒鉛が得られる。この方法においては、スクリューによる剪断力で原料黒鉛の剥離が促進されるが、特にポリマーが熱可塑性で粘弾性を有する場合には、該粘弾性とスクリューによる剪断効果で効果的に剥離が発現し薄層化が達成できる。混練機に関してはポリマーと薄層黒鉛とを混練した際に薄層黒鉛が効率的に薄層化されつつ混練されるという点で２軸以上の多軸エクストルーダを採用することが好ましい。また薄層黒鉛とポリマーとがより均質に混練される点で、粉体もしくは粉体化された熱可塑性ポリマーを用いることが好ましい。また薄層黒鉛の添加は、多軸エクストルーダに供給する以前の段階で熱可塑性ポリマーと乾式ブレンドしておいても良く、あるいは多軸エクストルーダに配設したサイドフィーダーを用いて溶融した熱可塑性ポリマーと多軸エクストルーダ中にて混合しても良く、混練は窒素やアルゴンなどの不活性ガスを供給した雰囲気中で行うことが好ましい。 As the physical thinning treatment, in addition to the mill, a kneading machine equipped with one or more screw-shaped shafts is used to perform kneading by mixing the raw material graphite and the polymer together. A thin layer graphite is obtained. In this method, exfoliation of the raw graphite is promoted by the shearing force by the screw, but exfoliation is effectively exhibited by the viscoelasticity and the shearing effect by the screw, particularly when the polymer is thermoplastic and has viscoelasticity. Thinning can be achieved. Regarding the kneader, it is preferable to employ a biaxial or more multi-axial extruder in that when the polymer and the thin-layer graphite are kneaded, the thin-layer graphite is kneaded while being efficiently thinned. In addition, it is preferable to use a powder or a pulverized thermoplastic polymer in that the thin layer graphite and the polymer are kneaded more uniformly. In addition, the thin layer graphite may be added by dry blending with a thermoplastic polymer before being supplied to the multiaxial extruder, or a thermoplastic polymer melted by using a side feeder disposed in the multiaxial extruder. Mixing may be performed in a multiaxial extruder, and kneading is preferably performed in an atmosphere supplied with an inert gas such as nitrogen or argon.
上記物理的な薄層化処理として好ましいのは、遊星ボールミルやミキサーミル、スクリュー状の軸を２本以上備えた多軸混練機（多軸エクストルーダ）を用いた処理である。またこれら物理的な薄層化処理を２種以上組み合わせて行うと、効果的な薄層化が達成できるためより好ましく、具体的には、スクリュー状の軸を２本以上備えた多軸混練機を用いて原料の薄層化処理を施しながら熱可塑性ポリマーとあらかじめ複合化させ、その後ローターミルを用いて処理を行うことで薄層化処理を行う処理方法がより好ましい態様として挙げられる。 Preferable as the above-mentioned physical thinning process is a process using a planetary ball mill, a mixer mill, or a multi-axis kneader (multi-axis extruder) having two or more screw-shaped shafts. Further, it is more preferable to carry out a combination of two or more of these physical thinning treatments because effective thinning can be achieved. Specifically, a multi-screw kneader provided with two or more screw-shaped shafts. As a more preferable embodiment, there is a method of performing a thinning treatment by previously combining with a thermoplastic polymer while performing a thinning treatment of the raw material by using and then performing a treatment using a rotor mill.
膨張黒鉛を原料として用いた薄層黒鉛も本発明では採用できるが、膨張黒鉛自体は比表面積が大きくポリマーとの濡れ性や混和性が極めて悪いため、天然黒鉛や人造黒鉛同様に前述のミルや混練機を用いた物理的な薄層化処理を採用して薄層化することで初めて用いうる。ここで膨張黒鉛については、酸処理黒鉛の高温高速熱処理で黒鉛層間が広げられて形成されたものであって、該酸処理黒鉛は黒鉛を酸性物質および酸化剤を含む溶液中に浸漬して黒鉛層間化合物を生成した後、洗浄・乾燥して得たもので、高温高速熱処理により数百倍に膨張して膨張黒鉛が得られるものである。高温高速熱処理は、５００℃以上の高温炉に入れて行う方法、あるいはマイクロ波により急速加熱する方法が採用でき、特にマイクロ波による急速加熱は膨張率が大きく好ましい方法である。なお、膨張黒鉛は薄層化処理を考慮すると、膨張黒鉛のシート化物など成型したものを適用する場合、薄層化の効率や効果が劣る場合がある。そして好ましい物理的な薄層化処理としては、遊星ボールミル中で乾式で膨張黒鉛のみを存在させて薄層化処理を行う、あるいはミキサーミル中で膨張黒鉛と溶媒とプレポリマーとを共存させて薄層化処理を行う、あるいはスクリュー状の軸を２本以上備えた多軸混練機を用いて熱可塑性ポリマーと混練複合化しながら剪断力で薄層化処理を行う方法、の各方法である。 Although thin-layer graphite using expanded graphite as a raw material can also be used in the present invention, expanded graphite itself has a large specific surface area and is extremely poor in wettability and miscibility with polymers. It can be used for the first time by adopting a physical thinning process using a kneader. Here, the expanded graphite is formed by expanding the graphite layer by high-temperature high-speed heat treatment of acid-treated graphite. The acid-treated graphite is obtained by immersing graphite in a solution containing an acidic substance and an oxidizing agent. After the intercalation compound is formed, it is obtained by washing and drying, and expands several hundred times by high-temperature rapid heat treatment to obtain expanded graphite. For the high-temperature rapid heat treatment, a method in which the heat treatment is performed in a high-temperature furnace at 500 ° C. or higher, or a rapid heating method using microwaves can be adopted. In consideration of the thinning treatment of expanded graphite, the efficiency and effect of thinning may be inferior when applying a molded product such as a sheet of expanded graphite. As a preferable physical thinning treatment, the thinning treatment is performed in a planetary ball mill in the dry type in the presence of only expanded graphite, or in the mixer mill, the expanded graphite, solvent and prepolymer coexist. Each method includes a layering treatment or a method in which a thinning treatment is performed with a shearing force while kneading and compounding with a thermoplastic polymer using a multi-screw kneader equipped with two or more screw-shaped shafts.
グラファイトシートを原料として用いた薄層黒鉛も本発明では採用できる。グラファイトシートはフィルム状の樹脂を非常に高温の不活性雰囲気で不融化した後に焼成することで作製され、樹脂の種類としては、ポリアクリロニトリル、セルロース系樹脂、ポリアミド系樹脂、ポリイミド系樹脂やフェノール系樹脂、ピッチ系樹脂などがよく用いられ、通常１０００℃以下の温度で不融化した後、３５００℃以下の温度で焼成処理して得られる。該グラファイトシートはあらかじめナイフミルやクラッシュミルなどで粗粒片化した後に前述のミルや混練機を用いた物理的な薄層化処理を行うことで薄層黒鉛となすことができる。この時、グラファイトシートの厚みは、粗粒片化および薄層化処理が効率よくなされるように一定の厚みを持つことが好ましく、１０ｎｍ〜５００μｍの範囲であることが特に好ましい。 Thin-layer graphite using a graphite sheet as a raw material can also be used in the present invention. Graphite sheets are made by incinerating a film-like resin in a very high temperature inert atmosphere and then firing it. The types of resin are polyacrylonitrile, cellulose resin, polyamide resin, polyimide resin and phenolic resin. Resins, pitch-based resins, and the like are often used, and are usually obtained by infusibilizing at a temperature of 1000 ° C. or lower and then firing at a temperature of 3500 ° C. or lower. The graphite sheet can be made into a thin-layer graphite by carrying out a physical thinning process using the above-mentioned mill or kneader after coarsely pulverizing with a knife mill or a crush mill. At this time, the thickness of the graphite sheet preferably has a constant thickness so that coarse grain sizing and thinning can be efficiently performed, and particularly preferably in the range of 10 nm to 500 μm.
化学的な薄層化処理としては、有機合成手法あるいはプラズマやマイクロ波などの高エネルギー印加手法を用いることができ、これら手法によって前述の天然黒鉛や人造黒鉛、膨張黒鉛、グラファイトシートなどの黒鉛系原料に官能基を付加させ、原料を構成するグラフェンシート層間が広がり剥離する作用を利用して薄層化処理がなされる。有機合成手法としては、数多くの手法が知られており、代表的な手法としては、濃硝酸中で塩素酸カリウムを酸化剤として用いて黒鉛を酸化した後に水で処理するＢｒｏｄｉｅ法、硝酸と硫酸の混合溶液に黒鉛を投入し塩素酸カリウムで酸化処理を行うＳｔａｕｄｅｎｍａｉｅｒ法、硫酸ナトリウムを含む冷却した濃硫酸中に黒鉛を投入して均質になるまで撹拌した後、過マンガン酸カリウムを投入して酸化するＨｕｍｍｅｒｓ法、あるいはこれら手法を改良した黒鉛原料を用いた化学的な分散液調製法が好適に用いられる。これら手法の中で特に天然黒鉛あるいは膨張黒鉛を原料として用いたＨｕｍｍｅｒｓ法あるいは改良されたＨｕｍｍｅｒｓ法は、反応が最も穏やかで薄層化が効率よく進行し、また後述する酸化度についても制御が行いやすく、工業的利用の点で好ましい手法である。反応後、得られた反応液を遠心分離あるいは濾過により不要な金属化合物、金属イオン、酸系イオンなどを除去することで、薄層黒鉛が分散された水系分散液が得られ、分散媒である水を除去することで薄層黒鉛の粉体が得られる。 As the chemical thinning treatment, an organic synthesis method or a high energy application method such as plasma or microwave can be used. By these methods, graphite systems such as the above-mentioned natural graphite, artificial graphite, expanded graphite, and graphite sheet are used. A thinning process is performed by adding a functional group to the raw material and utilizing the action of spreading and peeling between the graphene sheet layers constituting the raw material. Many methods are known as organic synthesis methods. Typical methods include Brodie method in which graphite is oxidized using potassium chlorate as an oxidizing agent in concentrated nitric acid and then treated with water, nitric acid and sulfuric acid. The Staudenmeier method, in which graphite is added to the mixed solution of the above and oxidized with potassium chlorate, after stirring in homogeneously cooled concentrated sulfuric acid containing sodium sulfate and stirring until homogeneous, potassium permanganate is added. The Hummers method for oxidation or a chemical dispersion preparation method using a graphite raw material improved by these methods is preferably used. Among these methods, the Hummers method or the modified Hummers method using natural graphite or expanded graphite as a raw material, in particular, has the mildest reaction and the thinning proceeds efficiently, and the degree of oxidation described later is also controlled. It is easy and preferable in terms of industrial use. After the reaction, the obtained reaction liquid is centrifuged or filtered to remove unnecessary metal compounds, metal ions, acid ions, etc., thereby obtaining an aqueous dispersion in which thin-layer graphite is dispersed, which is a dispersion medium. By removing water, a thin-layer graphite powder can be obtained.
またプラズマやマイクロ波などの高エネルギー印加手法によっても化学的な薄層化処理を好ましく行うことができる。プラズマについては大気圧プラズマや低圧プラズマを用いることができ、マイクロ波を含め、気体中あるいは液体中で処理を行うことができる。雰囲気の気体を二酸化炭素やアンモニア、酸素、窒素など、置換あるいは割合を変更する、あるいは液中であれば分散媒の種類に応じて、これら手法により処理を行うことで黒鉛系原料に所望の官能基を付与しうる。 Also, a chemical thinning process can be preferably performed by a high energy application method such as plasma or microwave. As the plasma, atmospheric pressure plasma or low pressure plasma can be used, and treatment can be performed in a gas or a liquid including a microwave. Replace the atmosphere gas with carbon dioxide, ammonia, oxygen, nitrogen, etc., or change the ratio, or if it is in the liquid, depending on the type of dispersion medium, these methods can be used to treat the graphite raw material with the desired functionality. A group may be imparted.
当該化学的な薄層化処理によって、薄層黒鉛には酸素原子由来の官能基、すなわち水酸基（−ＯＨ)、カルボキシル基（−ＣＯＯＨ）、エステル（−Ｃ（＝Ｏ）−Ｏ−）、エーテル（−Ｃ−Ｏ−Ｃ−）、ケトン（−Ｃ（＝Ｏ）−）などを有する。これにより電磁波吸収帯および／または電磁波吸収層を構成するポリマーまたはプレポリマーとの親和性が向上して、また薄層化が達成されることで結果としてポリマーに分散されやすくなる。ただし官能基を過度に有することで薄層黒鉛が本来有している導電性や移動度などの特性が低下することがある。 By the chemical thinning treatment, the thin graphite layer has functional groups derived from oxygen atoms, that is, hydroxyl groups (—OH), carboxyl groups (—COOH), esters (—C (═O) —O—), ethers. (—C—O—C—), ketone (—C (═O) —) and the like. Thereby, the affinity with the polymer or prepolymer constituting the electromagnetic wave absorption band and / or the electromagnetic wave absorption layer is improved, and as a result of achieving a thin layer, it is easily dispersed in the polymer. However, if the functional group is excessively contained, characteristics such as conductivity and mobility inherent in the thin-layer graphite may be deteriorated.
またこれら化学的な薄層化処理の一環として、さらに還元処理を経て、付加された官能基を制御し、ポリマーとの親和性や電磁波吸収性能を制御することができる。該還元では付加した官能基の一部の酸素原子が失われることで、薄層黒鉛の導電性が向上する。ここで還元処理としては、水素化ホウ素ナトリウム（ＮａＢＨ4）やヒドラジン（Ｎ2Ｈ4）などの還元剤による化学的還元、レーザー光やフラッシュ光、紫外線、マイクロ波などの光源や電磁波による熱還元、あるいは不活性雰囲気中、１００℃以上の加熱による加熱還元など、多種多様な方法を採用することが出来る。ただし薄層黒鉛の分散液の状態で還元処理を行うと、均一分散していた薄層黒鉛同士が相互作用で凝集することもあるため、必要に応じて凝集を阻害する分散剤が用いられても良い。また還元によって薄層黒鉛のポリマーへの親和性が低下することがある。 Further, as a part of these chemical thinning treatments, the functional group added can be controlled through further reduction treatment, and the affinity with the polymer and the electromagnetic wave absorption performance can be controlled. In the reduction, some of the oxygen atoms of the added functional group are lost, so that the conductivity of the thin-layer graphite is improved. Here, the reduction treatment includes chemical reduction with a reducing agent such as sodium borohydride (NaBH 4 ) and hydrazine (N 2 H 4 ), thermal reduction with a light source such as laser light, flash light, ultraviolet light, and microwaves, and electromagnetic waves. Alternatively, various methods such as heat reduction by heating at 100 ° C. or higher in an inert atmosphere can be employed. However, when the reduction treatment is performed in the state of a thin-layer graphite dispersion, the uniformly dispersed thin-layer graphite may agglomerate due to interaction, so a dispersant that inhibits aggregation is used as necessary. Also good. In addition, the affinity of the thin-layer graphite for the polymer may be reduced by the reduction.
上記化学的な薄層化処理として好ましいのは、天然黒鉛あるいは膨張黒鉛を原料として用いたＨｕｍｍｅｒｓ法あるいは改良されたＨｕｍｍｅｒｓ法による有機合成手法である。またこれら化学的な薄層化処理を２種以上組み合わせて行うと、効果的な薄層化が達成できるためより好ましく、具体的には、天然黒鉛あるいは膨張黒鉛を空気中でマイクロ波処理した後に、Ｈｕｍｍｅｒｓ法あるいは改良されたＨｕｍｍｅｒｓ法により処理を行うことで薄層化処理を行う処理方法がより好ましい態様として挙げられる。 Preferable as the chemical thinning treatment is an organic synthesis method using a Hummers method or an improved Hummers method using natural graphite or expanded graphite as a raw material. Further, it is more preferable to perform a combination of two or more of these chemical thinning treatments because effective thinning can be achieved. Specifically, after natural graphite or expanded graphite is subjected to microwave treatment in air, A treatment method in which a thinning process is performed by performing a treatment by the Hummers method or an improved Hummers method is mentioned as a more preferable embodiment.
そして上記物理的な薄層化処理と化学的な薄層化処理は組み合わせて用いることでより効果的な薄層化が達成できるため好ましい。具体的には、天然黒鉛あるいは膨張黒鉛を遊星ボールミルで物理的に薄層化処理を行った後、Ｈｕｍｍｅｒｓ法あるいは改良されたＨｕｍｍｅｒｓ法により処理を行うことで薄層化処理を行う処理方法が特に好ましい組み合わせの態様として挙げられる。 The physical thinning treatment and the chemical thinning treatment are preferably used in combination because more effective thinning can be achieved. Specifically, there is a processing method in which natural graphite or expanded graphite is physically thinned with a planetary ball mill, and then thinned by a treatment using the Hummers method or an improved Hummers method. It is mentioned as an aspect of a preferable combination.
本発明の電磁波吸収体に用いられる薄層黒鉛の平均厚みは、電磁波吸収性能や後述するポリマー（またはプレポリマー）との混和性あるいは薄層黒鉛とポリマー（またはプレポリマー）とを含有する混合液の塗布性が阻害されない範囲で、薄ければ薄いほど良い。薄層黒鉛の平均厚みは０．３ｎｍ〜２００ｎｍであることが好ましく、薄層黒鉛が平面状の形態を維持しやすい点で、０．６ｎｍ〜１００ｎｍであることがより好ましく、１．０ｎｍ〜５０ｎｍであることが特に好ましく、１．０ｎｍ〜２５ｎｍであることが最も好ましい。そして薄層黒鉛はグラフェンシートが積層したものであることから、これらを満たす薄層黒鉛を構成するグラフェンの層数としては、層数が１〜６００であることが好ましく、薄層黒鉛が平面状の形態を維持しやすい点で、２〜３００であることが好ましく、３〜１５０であることが特に好ましく、３〜７５であることが最も好ましい。薄層黒鉛の平均厚みは後述するＢ．項に記載のとおり、透過型電子顕微鏡で測定することができる。 The average thickness of the thin-layer graphite used in the electromagnetic wave absorber of the present invention is a mixed solution containing electromagnetic wave absorption performance, miscibility with the polymer (or prepolymer) described later, or thin-layer graphite and polymer (or prepolymer). As long as the coating property is not hindered, the thinner the better. The average thickness of the thin-layer graphite is preferably 0.3 nm to 200 nm, more preferably 0.6 nm to 100 nm, and more preferably 1.0 nm to 50 nm in that the thin-layer graphite easily maintains a planar shape. It is particularly preferable that the thickness is 1.0 nm to 25 nm. And since the thin graphite is a laminate of graphene sheets, the number of graphene layers constituting the thin graphite satisfying these is preferably 1 to 600, and the thin graphite is planar. It is preferable that it is 2-300 by the point which is easy to maintain this form, It is especially preferable that it is 3-150, It is most preferable that it is 3-75. The average thickness of the thin graphite is B. described later. As described in the section, it can be measured with a transmission electron microscope.
本発明の電磁波吸収体に用いられる薄層黒鉛の平均大きさは、電磁波吸収性能やポリマー（またはプレポリマー）との混和性あるいは薄層黒鉛とポリマー（またはプレポリマー）とを含有する混合液の塗布性が阻害されない範囲であればよく、該平均大きさは０．０２〜１０μｍであることが好ましく、０．０５〜５μｍであることがより好ましく、０．１〜２μｍであることが特に好ましい。ここで該薄層黒鉛の平均大きさは後述するＥ．項に記載の方法で解析できる。 The average size of the thin-layer graphite used in the electromagnetic wave absorber of the present invention is the electromagnetic wave absorption performance, miscibility with the polymer (or prepolymer), or the mixed liquid containing the thin-layer graphite and the polymer (or prepolymer). It is sufficient that the coating properties are not hindered, and the average size is preferably 0.02 to 10 μm, more preferably 0.05 to 5 μm, and particularly preferably 0.1 to 2 μm. . Here, the average size of the thin graphite is E. It can be analyzed by the method described in the section.
電磁波吸収帯における薄層黒鉛の量は、目的とする電磁波吸収帯の誘電率に応じて適宜決定することができるが、電磁波吸収帯が適切な、すなわち複素誘電率で表される誘電率の実部が１〜５０、虚部が０．２５〜１０の誘電特性を持つという点で、電磁波吸収帯中、あるいは各電磁波吸収層中で５〜３０体積％の含有量であることが好ましく、８〜２５体積％であることがより好ましい。 The amount of thin-layer graphite in the electromagnetic wave absorption band can be appropriately determined according to the dielectric constant of the target electromagnetic wave absorption band, but the electromagnetic wave absorption band is appropriate, that is, the actual dielectric constant expressed by the complex dielectric constant. The content is preferably 5 to 30% by volume in the electromagnetic wave absorption band or in each electromagnetic wave absorption layer in that the part has a dielectric property of 1 to 50 and the imaginary part has a dielectric property of 0.25 to 10. More preferably, it is -25 volume%.
また、本発明の電磁波吸収体における電磁波吸収帯は、薄層黒鉛を電磁波吸収材として用いることにより、空隙率を大幅に低下させることが可能である。詳しいことは明らかになっていないが、薄層黒鉛の有する薄さとポリマー（またはプレポリマー）との親和性を具有することにより塗布あるいは成型時の流動性ないし変形追従性に優れるためと考えられる。そして本発明における電磁波吸収帯は、機械的強度を向上させる観点から、空隙率が１０％以下であることが好ましく、５％以下であることが好ましく、空隙率が２％以下であることが特に好ましい。ここで電磁波吸収帯の空隙率は後述するＦ．項に記載の方法で求められる。 Moreover, the electromagnetic wave absorption band in the electromagnetic wave absorber of the present invention can significantly reduce the porosity by using thin-layer graphite as an electromagnetic wave absorber. Although details have not been clarified, it is considered that by having an affinity between the thin layer graphite and the polymer (or prepolymer), it is excellent in fluidity or deformation followability during coating or molding. And from the viewpoint of improving mechanical strength, the electromagnetic wave absorption band in the present invention preferably has a porosity of 10% or less, preferably 5% or less, and particularly preferably has a porosity of 2% or less. preferable. Here, the porosity of the electromagnetic wave absorption band is F. It is calculated | required by the method of description.
薄層黒鉛は、酸素原子に由来する一定の酸化度を有する。本発明における酸化度とは、薄層黒鉛における酸素原子の原子組成百分率（アトミックパーセント、単位として「ａｔ％」を用いる。）であり、後述するＤ．項に記載の方法で平均酸化度として算出できる。通常、天然黒鉛で２〜３ａｔ％、人造黒鉛でもわずかながら（１ａｔ％未満）、それぞれ酸化度を有する。 Thin graphite has a certain degree of oxidation derived from oxygen atoms. The degree of oxidation in the present invention is the atomic composition percentage of oxygen atoms in the thin-layer graphite (atomic percent, “at%” is used as a unit). The average degree of oxidation can be calculated by the method described in the item. Usually, natural graphite has a degree of oxidation of 2 to 3 at%, and artificial graphite has a slight degree (less than 1 at%).
前述の物理的および／または化学的な処理を経て得た薄層黒鉛は、空気中の酸素ないし添加された試薬等から酸素原子を含む官能基が付加されて、原料黒鉛に比べて酸化度が増加する傾向にある。そして該酸化度は高いほど前述の親和性や分散性が向上しうるが、一方で酸化度が高いと電磁波吸収性能に関係のある導電性や誘電特性が低下することもあるため、平均酸化度は５〜３０ａｔ％であることが好ましい。 The thin-layer graphite obtained through the above-mentioned physical and / or chemical treatment is added with a functional group containing oxygen atoms from oxygen in the air or added reagent, etc., and has a degree of oxidation as compared with the raw graphite. It tends to increase. The higher the degree of oxidation, the better the above-mentioned affinity and dispersibility. On the other hand, the higher the degree of oxidation, the lower the conductivity and dielectric properties related to electromagnetic wave absorption performance. Is preferably 5 to 30 at%.
そして電磁波吸収体の設計においてより薄くかつ高い吸収性能（吸収量）を持ちうるという点で薄層黒鉛の平均酸化度は５〜２５ａｔ％であることが特に好ましい。 The average oxidation degree of the thin-layer graphite is particularly preferably 5 to 25 at% in that the electromagnetic wave absorber can be thinner and have higher absorption performance (absorption amount).
なお本発明の薄層黒鉛は、電磁波吸収性能を阻害しない範囲において、炭素原子や酸素原子、水素原子以外の異元素、例えばホウ素（Ｂ）や窒素（Ｎ）、硫黄（Ｓ）、ナトリウム（Ｎａ）、カリウム（Ｋ）、などを５ａｔ％以下の原子組成百分率で含まれても良い。これら異元素の解析は後述するＤ．項に記載の方法により算出することができる。 The thin-layer graphite of the present invention is a different element other than carbon atoms, oxygen atoms and hydrogen atoms, such as boron (B), nitrogen (N), sulfur (S), sodium (Na ), Potassium (K), and the like may be included at an atomic composition percentage of 5 at% or less. The analysis of these different elements will be described in D. It can be calculated by the method described in the item.
本発明の電磁波吸収体の電磁波吸収帯ないし電磁波吸収層に含有される薄層黒鉛は、１種類を単独で用いても良く、あるいは複数種を用いても良い。後述するように、電磁波吸収帯を２層以上の複数層で構成する場合、あるいは２層以上の電磁波吸収層を積層した後に層同士を結合させて厚み方向に連続的な電磁波吸収性能の変化を有する電磁波吸収帯を構成する場合、各電磁波吸収層の電磁波吸収特性を薄層黒鉛の種類を変更することで種々設計することができるため、電磁波吸収体全体としては複数種の薄層黒鉛を用いるのが好ましい。該薄層黒鉛の種類を変更する場合、前述の薄層黒鉛の平均厚みや平均大きさを変更しうるが、特に平均酸化度を変更することで、容易に電磁波吸収層の電磁波吸収特性を変更・制御することができる。そのため、平均酸化度の異なる複数の薄層黒鉛を用いることは、例えば厚さやポリマーの要求仕様があらかじめ定められている電磁波吸収体を設計しようとする場合に非常に有効である。 The thin-layer graphite contained in the electromagnetic wave absorption band or the electromagnetic wave absorption layer of the electromagnetic wave absorber of the present invention may be used alone or in combination. As will be described later, when the electromagnetic wave absorption band is composed of two or more layers, or after laminating two or more electromagnetic wave absorption layers, the layers are combined to change the continuous electromagnetic wave absorption performance in the thickness direction. When configuring the electromagnetic wave absorption band, the electromagnetic wave absorption characteristics of each electromagnetic wave absorption layer can be designed in various ways by changing the type of thin layer graphite. Therefore, multiple types of thin layer graphite are used as the entire electromagnetic wave absorber. Is preferred. When changing the type of the thin-layer graphite, the average thickness and average size of the above-mentioned thin-layer graphite can be changed, but the electromagnetic wave absorption characteristics of the electromagnetic wave absorption layer can be easily changed by changing the average oxidation degree.・ It can be controlled. For this reason, the use of a plurality of thin-layer graphites having different average degrees of oxidation is very effective, for example, when designing an electromagnetic wave absorber having predetermined thickness and polymer requirements.
本発明の電磁波吸収体は、平板状の電磁波吸収帯を備え、この電磁波吸収帯は、薄層黒鉛を含有し、その厚み方向に電磁波吸収性能の不均一性を有するものである。電磁波吸収帯が平板状であることで、面内均一性に優れた吸収性能を発現しうる。また、非常に薄い層においても高い電磁波吸収性能を発揮する薄層黒鉛の特性を生かすという観点からも、平板状とする意義が大きい。ここで、「平板状」とは、扁平形状であることにより厚み方向が観念できる形状であれば特に形状は限定されず、電磁波吸収体全体の設計に応じて適宜設計することが可能である。 The electromagnetic wave absorber of the present invention includes a flat electromagnetic wave absorption band, and this electromagnetic wave absorption band contains thin-layer graphite and has non-uniformity of electromagnetic wave absorption performance in the thickness direction. Absorption performance excellent in in-plane uniformity can be expressed because the electromagnetic wave absorption band is flat. Further, from the viewpoint of taking advantage of the properties of thin-layer graphite that exhibits high electromagnetic wave absorption performance even in a very thin layer, it is significant to make it flat. Here, the “flat plate shape” is not particularly limited as long as it has a flat shape and can be thought of in the thickness direction, and can be appropriately designed according to the design of the entire electromagnetic wave absorber.
そして、壁等の垂直な平面に貼付する場合に自重により剥離しないこと、厚みにより嵩張らないこと、また製造時や設置施工時の取扱い性が容易であること等から、電磁波吸収帯の厚みは１５ｍｍ以下であることが好ましく、１０ｍｍ以下がより好ましく、５ｍｍ以下が特に好ましく、２ｍｍ以下が最も好ましい。 And when sticking on a vertical plane such as a wall, the thickness of the electromagnetic wave absorption band is 15 mm because it does not peel off due to its own weight, it is not bulky due to its thickness, and it is easy to handle at the time of manufacturing and installation. Is preferably 10 mm or less, more preferably 5 mm or less, and most preferably 2 mm or less.
また、本発明の電磁波吸収体は、全体としてもシート状の形状を有することが好ましい。ここで、「シート状の形状を有する」とは、電磁波吸収体が扁平形状であり、電磁波吸収体の扁平面方向における最も幅の狭い部分が、厚みの３倍以上の長さを持つ形状を有することをいう。また、電磁波吸収体の適用用途が広がる点、および、ロールツーロールプロセス（ロール状に巻かれた基材への連続的な製造プロセス）での製造が可能になる点からは、可撓性を有し、巻き取り可能なシート状であることが特に好ましい。 Moreover, it is preferable that the electromagnetic wave absorber of this invention has a sheet-like shape as a whole. Here, “having a sheet-like shape” means that the electromagnetic wave absorber has a flat shape, and the narrowest portion in the flat surface direction of the electromagnetic wave absorber has a length of three times or more the thickness. It means having. In addition, from the point that the application application of the electromagnetic wave absorber is widened and the roll-to-roll process (continuous manufacturing process to a substrate wound in a roll shape) becomes possible, flexibility is improved. It is particularly preferable that it is in the form of a sheet that can be wound and wound.
また本発明における平板状の電磁波吸収帯は、層の厚み方向に電磁波吸収性能の不均一性を有する。このような不均一性を有することにより、１つの電磁波吸収体に広い波長域に渡る電磁波を吸収しうる特性を付与することができる。 The flat electromagnetic wave absorption band in the present invention has non-uniformity in electromagnetic wave absorption performance in the thickness direction of the layer. By having such non-uniformity, it is possible to impart a characteristic capable of absorbing electromagnetic waves over a wide wavelength range to one electromagnetic wave absorber.
電磁波吸収帯は、厚み方向に電磁波吸収性能の不均一性を有し、対象とする電磁波の帯域に吸収特性を有する限りにおいて、１層の電磁波吸収層で形成されても良く、２層以上の電磁波吸収層から構成されても良いが、対象とする電磁波の帯域に応じた設計の容易さや、製造の簡便さの観点から、２層以上の電磁波吸収層から構成されることが好ましい。２層以上の電磁波吸収層から電磁波吸収帯を構成する場合、吸収対象周波数の相違する２層以上の電磁波吸収層を備えるよう構成することが好ましい。この場合、電磁波吸収帯の厚み方向の電磁波吸収性能の不均一性は、吸収対象周波数の相違する２層以上の電磁波吸収層を備えることにより発現することになる。 The electromagnetic wave absorption band may be formed of one electromagnetic wave absorption layer as long as it has non-uniformity of electromagnetic wave absorption performance in the thickness direction and has absorption characteristics in the target electromagnetic wave band. Although it may be composed of an electromagnetic wave absorbing layer, it is preferably composed of two or more electromagnetic wave absorbing layers from the viewpoint of ease of design according to the target electromagnetic wave band and ease of production. When an electromagnetic wave absorption band is formed from two or more electromagnetic wave absorption layers, it is preferable to include two or more electromagnetic wave absorption layers having different absorption target frequencies. In this case, the non-uniformity of the electromagnetic wave absorption performance in the thickness direction of the electromagnetic wave absorption band is expressed by providing two or more electromagnetic wave absorption layers having different absorption target frequencies.
本発明において、２層以上の電磁波吸収層は、製造する電磁波吸収体が目的とする吸収周波数帯、あるいは厚みなどの要求特性に応じて選択することができる。電磁波吸収性能の不均一性を発現させるためには、少なくとも１層の電磁波吸収層が、その他のいずれかの層と異なる吸収対象周波数を有するものであることが必要である。これを満たす限り、電磁波吸収帯は互いに同一の吸収対象周波数を有する複数の電磁波吸収層を有していてもよいが、全ての層が互いに異なる吸収対象周波数を有する電磁波吸収層によって構成されていることが好ましい。また、積層する電磁波吸収層の数もまた、電磁波吸収体の要求特性により適宜決定される事項であり、何ら限定されるものではないが、広帯域での電磁波吸収性能を担保する観点からは３層以上であることが好ましく、４層以上であることがより好ましい。また薄さと軽量性を担保し、設計を容易にする観点からは、１０層以下であることが好ましく、６層以下であることがより好ましい。本明細書において、吸収対象周波数とは、各電磁波吸収層が１０ｄＢ以上の電磁波吸収性能を発揮する周波数帯域をいう。 In the present invention, two or more electromagnetic wave absorbing layers can be selected according to required characteristics such as an intended absorption frequency band or thickness of an electromagnetic wave absorber to be manufactured. In order to develop non-uniformity of the electromagnetic wave absorption performance, it is necessary that at least one electromagnetic wave absorption layer has a frequency to be absorbed different from any of the other layers. As long as this is satisfied, the electromagnetic wave absorption band may have a plurality of electromagnetic wave absorption layers having the same absorption target frequency, but all layers are configured by electromagnetic wave absorption layers having different absorption target frequencies. It is preferable. Further, the number of electromagnetic wave absorbing layers to be laminated is also a matter appropriately determined according to the required characteristics of the electromagnetic wave absorber, and is not limited at all. However, from the viewpoint of ensuring the electromagnetic wave absorbing performance in a wide band, three layers are used. It is preferable that the number is 4 or more. Further, from the viewpoint of ensuring the thinness and light weight and facilitating the design, it is preferably 10 layers or less, and more preferably 6 layers or less. In this specification, the frequency to be absorbed refers to a frequency band in which each electromagnetic wave absorbing layer exhibits an electromagnetic wave absorbing performance of 10 dB or more.
図１は、本発明の電磁波吸収体の一実施態様を示す模式図である。図１に示すように、例えば、電磁波吸収体６は、電磁波を反射する基板１の上に、電磁波吸収帯５を設けることにより形成することができる。この電磁波吸収帯５は、３層の電磁波吸収層２，３，４を積層させて構成することができる。電磁波吸収層２，３，４は、それぞれの吸収対象周波数が互いに相違するとよい。
FIG. 1 is a schematic view showing an embodiment of the electromagnetic wave absorber of the present invention. As shown in FIG. 1, for example, the
本発明の電磁波吸収帯は薄層黒鉛を含有するものであるため、各電磁波吸収層のうち少なくとも１層は薄層黒鉛を含有する必要がある。この限りにおいて、電磁波吸収帯は薄層黒鉛を含まない電磁波吸収層を有していてもよいが、電磁波吸収体全体としての薄さと軽量性を担保する観点からは、全ての電磁波吸収層が薄層黒鉛を含有するものであることが好ましい。薄層黒鉛を含まない電磁波吸収層としては、例えば、メガヘルツ（ＭＨｚ）以下の長波長電磁波を吸収する磁性層や、表面コートとしての機能を兼ねうるあるいは低誘電率層として機能しうるポリマーのみの層等が挙げられる。 Since the electromagnetic wave absorption band of the present invention contains thin-layer graphite, at least one of the electromagnetic wave absorption layers needs to contain thin-layer graphite. As long as this is the case, the electromagnetic wave absorption band may have an electromagnetic wave absorption layer that does not contain thin graphite, but from the viewpoint of ensuring the thinness and light weight of the entire electromagnetic wave absorber, all the electromagnetic wave absorption layers are thin. It is preferable that it contains layer graphite. Examples of the electromagnetic wave absorbing layer that does not contain thin graphite include, for example, a magnetic layer that absorbs long-wavelength electromagnetic waves of megahertz (MHz) or less, and only a polymer that can function as a surface coat or function as a low dielectric constant layer. Layer and the like.
電磁波吸収層は、薄層黒鉛の濃度を変える、含有する薄層黒鉛の酸化度を変える、含有するポリマーの種類を変える、厚みを変える等の様々な方法により、その吸収対象周波数を調整することができる。吸収対象周波数の相違する２層以上の電磁波吸収層により不均一性を形成する場合、どのような手段により吸収対象周波数を調整したものを用いてもよいが、設計する電磁波吸収体の厚みや比重の制限に依らずに適用できるという点で、含有する薄層黒鉛の酸化度が相違する複数の電磁波吸収層を用いることが好ましい。 The electromagnetic wave absorption layer can adjust the frequency of absorption by various methods such as changing the concentration of thin graphite, changing the degree of oxidation of the thin graphite contained, changing the type of polymer contained, and changing the thickness. Can do. When non-uniformity is formed by two or more electromagnetic wave absorption layers having different absorption target frequencies, the absorption target frequency adjusted by any means may be used, but the thickness and specific gravity of the electromagnetic wave absorber to be designed It is preferable to use a plurality of electromagnetic wave absorbing layers having different degrees of oxidation of the thin-layer graphite contained in that it can be applied without depending on the restrictions.
これら２層以上の電磁波吸収層を形成する方法は特に制限はなく、接着、溶着等により積層することができるが、電磁波吸収の設計の観点からは、接着剤を用いず、熱可塑性ポリマーからなる電磁波吸収層同士の熱接着を行うことが好ましい。 The method for forming these two or more electromagnetic wave absorbing layers is not particularly limited and can be laminated by adhesion, welding, etc., but from the viewpoint of electromagnetic wave absorption design, it is made of a thermoplastic polymer without using an adhesive. It is preferable to perform thermal bonding between the electromagnetic wave absorbing layers.
また、薄層黒鉛と、ポリマーまたは重合前のモノマーやプレポリマーなどの前駆体を含む混合液を、基材上に順次塗布して電磁波吸収層を形成する方法も、好ましい方法として挙げられる。この方法は、工程数が少なくかつ簡便な手法であり、また接着剤を用いないために設計が容易で設計自由度も高い。また異なる電磁波吸収特性を有する電磁波吸収層を積層する場合にも、設計する順に塗布・積層するだけでよく、適当な溶媒を選択することで電磁波吸収層の層間の結合も容易であるため、優れた手法である。 In addition, a method of forming an electromagnetic wave absorbing layer by sequentially applying a thin layer graphite and a mixed solution containing a polymer or a precursor such as a prepolymerized monomer or prepolymer on a substrate is also mentioned as a preferable method. This method is a simple method with a small number of steps, and since it does not use an adhesive, it is easy to design and has a high degree of design freedom. In addition, even when laminating electromagnetic wave absorbing layers having different electromagnetic wave absorbing properties, it is only necessary to apply and laminate in the order of design, and it is easy to bond between the layers of the electromagnetic wave absorbing layer by selecting an appropriate solvent. Method.
ここで、基材としては、樹脂基材、織物や編み物、不織布などの繊維基材、金属やセラミック等の無機基材、黒鉛平板基材等が挙げられるが、後述する、電磁波を反射する基板であることが好ましい。すなわち、電磁波を反射する基板上に電磁波吸収層を形成するための混合液を順次塗布・積層することで、簡易な工程で本発明の電磁波吸収体を製造することが可能である。 Here, examples of the base material include resin base materials, fiber base materials such as woven fabrics, knitted fabrics, and non-woven fabrics, inorganic base materials such as metals and ceramics, graphite flat plate base materials, and the like. It is preferable that That is, the electromagnetic wave absorber of the present invention can be produced by a simple process by sequentially applying and laminating a mixed solution for forming an electromagnetic wave absorbing layer on a substrate that reflects electromagnetic waves.
より具体的には、薄層黒鉛と溶媒可溶性ポリマーと溶媒とを混合して、または熱硬化性ポリマーや光硬化性ポリマーの場合は硬化するモノマーないしプレポリマーと薄層黒鉛とを混合して、混合液を調製する。ここで、混合手法としては超音波ホモジナイザー、遊星ボールミル、ミキサーミルなどを用いることができる。そして、調製して得た混合液を電磁波を反射する基材上に塗布したのち、溶媒を乾燥させることで塗膜を形成する。ここで塗布直後の塗膜の厚みは０．１〜２００μｍであることが好ましい。この厚みとなるように塗工装置で塗膜を形成した後、膜の厚みや使用する樹脂、溶媒により異なるものの、好ましくは８０〜１５０℃の雰囲気下、１〜３０分加熱乾燥して、好ましくは３５μｍ以下の厚みの電磁波吸収層を得る。乾燥後の厚みを大きくする場合には、重ね塗りを行うことが好ましい。 More specifically, a thin layer graphite, a solvent-soluble polymer, and a solvent are mixed, or in the case of a thermosetting polymer or a photocurable polymer, a curing monomer or prepolymer and a thin layer graphite are mixed, Prepare a mixture. Here, as a mixing method, an ultrasonic homogenizer, a planetary ball mill, a mixer mill, or the like can be used. And after apply | coating the liquid mixture obtained by preparing on the base material which reflects electromagnetic waves, a coating film is formed by drying a solvent. Here, the thickness of the coating film immediately after coating is preferably 0.1 to 200 μm. After forming a coating film with a coating device to have this thickness, although it varies depending on the thickness of the film, the resin used, and the solvent, it is preferably heated and dried in an atmosphere of 80 to 150 ° C. for 1 to 30 minutes, Obtains an electromagnetic wave absorbing layer having a thickness of 35 μm or less. In order to increase the thickness after drying, it is preferable to perform overcoating.
また、適切な溶媒、例えばエタノール、メタノール、イソプロパノール、テトラヒドロフラン、クロロホルム、塩化メチレン、トルエン、ベンゼン、キシレン、ｎ−ヘキサン、ジオキサン、Ｎ−メチル−２−ピロリドン、ジメチルスルホキシド、ジメチルフォルムアミド、ジメチルアセトアミド、等を選択することで、前層の表面をわずかに溶解ないし活性化することで次に塗布する層と結合させることができる。ここで塗布には塗工装置を用いることができ、ダイコーター、バーコーター、アプリケーター、スプレーコーター、スピンコーター、インクジェットコーター等を好適に採用できる。 Also suitable solvents such as ethanol, methanol, isopropanol, tetrahydrofuran, chloroform, methylene chloride, toluene, benzene, xylene, n-hexane, dioxane, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, By selecting etc., the surface of the previous layer can be slightly dissolved or activated to be combined with the next layer to be applied. Here, a coating apparatus can be used for the application, and a die coater, a bar coater, an applicator, a spray coater, a spin coater, an inkjet coater, or the like can be suitably employed.
また本発明の電磁波吸収体における電磁波吸収帯の厚み方向の電磁波吸収性能の不均一性は、該電磁波吸収帯が、その厚み方向に連続的な電磁波吸収性能の変化を有することにより発現するものであってもよい。この場合、電磁波吸収帯は実質的に１層であるが、無限の層からなる電磁波吸収帯と同意であるとも言え、その電磁波吸収特性は、前述の２層以上電磁波吸収層を設けてなる電磁波吸収帯と類似する。すなわち、電磁波吸収帯が実質的に１層からなる態様においては、「電磁波吸収層」は「電磁波吸収帯」と同意である。 The non-uniformity of the electromagnetic wave absorption performance in the thickness direction of the electromagnetic wave absorption band in the electromagnetic wave absorber of the present invention is manifested by the electromagnetic wave absorption band having a continuous change in the electromagnetic wave absorption performance in the thickness direction. There may be. In this case, the electromagnetic wave absorption band is substantially one layer, but it can be said that it is the same as the electromagnetic wave absorption band consisting of an infinite layer, and the electromagnetic wave absorption characteristic is an electromagnetic wave formed by providing the above two or more electromagnetic wave absorption layers. Similar to absorption band. That is, in an aspect in which the electromagnetic wave absorption band is substantially composed of one layer, the “electromagnetic wave absorption layer” is the same as the “electromagnetic wave absorption band”.
該厚み方向に連続的な電磁波吸収性能の変化を設ける方法は種々あり、２種以上の薄層黒鉛の含有割合を連続的に変化させる方法や、ポリマーの含有割合を連続的に変化させる方法、薄層黒鉛の含有割合を厚み方向に連続的に変化させる（すなわち、厚み方向に薄層黒鉛の密度変化をつける）方法などがあるが、電磁波吸収性能の調整が容易であることから、薄層黒鉛の密度変化により連続的に電磁波吸収性能を変化させる方法が好ましい。 There are various methods for providing a continuous change in electromagnetic wave absorption performance in the thickness direction, a method for continuously changing the content ratio of two or more types of thin-layer graphite, a method for continuously changing the content ratio of the polymer, There is a method of continuously changing the content ratio of the thin-layer graphite in the thickness direction (that is, changing the density of the thin-layer graphite in the thickness direction). A method of continuously changing the electromagnetic wave absorption performance by changing the density of graphite is preferable.
この場合、電磁波吸収帯が有する電磁波吸収性能の変化は、必ずしも電磁波吸収帯の一面から他面へと向かう単調関数的な変化である必要はないが、電磁波の反射を抑制し、より効率的な吸収特性を有する設計のため、電磁波吸収性能が単調関数的に変化するものであることが好ましい。すなわち、電磁波吸収帯は、厚み方向に連続的な電磁波吸収性能の勾配を有していることが好ましい。 In this case, the change in the electromagnetic wave absorption performance of the electromagnetic wave absorption band does not necessarily have to be a monotonic function change from one side of the electromagnetic wave absorption band to the other side, but the reflection of the electromagnetic wave is suppressed and more efficient. Because of the design having absorption characteristics, it is preferable that the electromagnetic wave absorption performance changes monotonically. That is, it is preferable that the electromagnetic wave absorption band has a continuous gradient of electromagnetic wave absorption performance in the thickness direction.
さらに、電磁波吸収効率を向上させる観点からは、電磁波入射面から他面に向かうにつれ、複素誘電率の実部の値が序々に高くなるよう設計することが好ましい。 Furthermore, from the viewpoint of improving electromagnetic wave absorption efficiency, it is preferable to design so that the value of the real part of the complex dielectric constant gradually increases from the electromagnetic wave incident surface toward the other surface.
薄層黒鉛の密度勾配により電磁波吸収性能の変化を担保する場合においては、電磁波入射面から他面に向かうにつれて薄層黒鉛密度が高くなる密度勾配を設けることが好ましい。 In the case where the change in electromagnetic wave absorption performance is ensured by the density gradient of the thin-layer graphite, it is preferable to provide a density gradient in which the density of the thin-layer graphite increases from the electromagnetic wave incident surface toward the other surface.
厚み方向に連続的な電磁波吸収性能の変化を付与する方法は特に限定されないが、例えば、互いに異なる吸収対象周波数を有する、熱可塑性ポリマーを含有する電磁波吸収層を複数層積層し、その後、該熱可塑性ポリマーの融点または軟化点温度以上に短時間加熱溶融したのち、冷却する方法を用いることができる。 The method for imparting a continuous change in electromagnetic wave absorption performance in the thickness direction is not particularly limited.For example, a plurality of electromagnetic wave absorption layers containing thermoplastic polymers having different absorption target frequencies are laminated, and then the heat A method of cooling after heating and melting for a short time above the melting point or softening point temperature of the plastic polymer can be used.
また、１層に形成した熱可塑性ポリマーを含有する電磁波吸収帯を、該熱可塑性ポリマーの融点または軟化点温度以上の温度で必要時間加熱することによっても、電磁波吸収帯に連続的な電磁波吸収性能の変化を付与せしめることが可能である。これは、熱可塑性ポリマーを溶融することで、熱対流により比重の小さいポリマーが上部へ、比重の大きな薄層黒鉛が下部へ、それぞれ徐々に移動し、上部と下部とで密度勾配が形成されることによる。 In addition, the electromagnetic wave absorption band containing the thermoplastic polymer formed in one layer is also heated to a temperature equal to or higher than the melting point or softening point temperature of the thermoplastic polymer for a necessary time, so that the electromagnetic wave absorption performance continuous to the electromagnetic wave absorption band is obtained. It is possible to give this change. This is because by melting the thermoplastic polymer, the polymer with a low specific gravity moves gradually toward the top and the thin-layer graphite with a high specific gravity moves toward the bottom due to thermal convection, and a density gradient is formed between the top and the bottom. It depends.
ここでポリマーの融点は下記Ｇ．項に、また軟化点温度は下記Ｈ．項に記載の方法にてそれぞれ測定される。また加熱時間は６０分以内であることが好ましく、３０分以内であることがより好ましい。但し十分な連続構造形成時間をとるという点で、５分以上であることが好ましい。また、薄層黒鉛の濃度あるいは酸化度が序列を持って異なる複数の分散液を塗布・乾燥を繰り返しながら電磁波吸収層を積層することによって連続して変化させる方法や、溶媒可溶性ポリマーあるいはプレポリマーの場合は薄層黒鉛とポリマーとの比重差を利用して、薄層黒鉛をポリマー溶液あるいはプレポリマー中に分散させた分散液を、長時間かけて薄層黒鉛とこれらポリマー溶液あるいはプレポリマーとの比重差を利用して薄層黒鉛を沈降させながら固化する方法、厚み方向に連続して含有する混合液を複数、好ましくは３種以上用意し、混合割合を連続的に変えるように塗布積層する方法によっても、厚み方向に薄層黒鉛含有量の密度勾配を有する電磁波吸収帯を形成することができる。 Here, the melting point of the polymer is G. The softening point temperature is H. Each is measured by the method described in the paragraph. The heating time is preferably 60 minutes or less, and more preferably 30 minutes or less. However, it is preferably 5 minutes or more from the viewpoint of taking a sufficient continuous structure formation time. In addition, a method of continuously changing a plurality of dispersions having different concentrations or oxidation degrees of the thin-layer graphite by laminating an electromagnetic wave absorption layer while repeatedly applying and drying, a solvent-soluble polymer or a prepolymer In some cases, using the difference in specific gravity between the thin-layer graphite and the polymer, a dispersion in which the thin-layer graphite is dispersed in the polymer solution or prepolymer is used over a long period of time. A method of solidifying the thin-layer graphite while precipitating using the specific gravity difference, and preparing a plurality of, preferably three or more, mixed liquids continuously in the thickness direction, and coating and laminating so as to continuously change the mixing ratio Also by the method, an electromagnetic wave absorption band having a density gradient of the thin graphite content in the thickness direction can be formed.
所望の特性を発現せしめるべく前述の薄層黒鉛を電磁波吸収体において保持するには様々な材料、例えば蝋やワックス、アスファルト、セメント等、薄層黒鉛を含有せしめた後に固化しうる、多くの材料があるものの、加熱や溶媒に溶解せしめるなどの手法で薄層黒鉛を含有したままでも優れた賦型性を有する点から、本発明の電磁波吸収体における電磁波吸収帯および／または電磁波吸収層はポリマーを含有することが好ましい。 Many materials that can be solidified after containing thin layer graphite such as wax, wax, asphalt, cement, etc. to hold the above thin layer graphite in the electromagnetic wave absorber in order to develop desired properties. However, the electromagnetic wave absorption band and / or electromagnetic wave absorption layer in the electromagnetic wave absorber of the present invention is a polymer because it has excellent moldability even when it contains thin-layer graphite by a method such as heating or dissolving in a solvent. It is preferable to contain.
該ポリマーは、特に限定されず、後述する工程や使用環境で求められる耐久性に応じて、熱可塑性ポリマー、溶媒可溶性ポリマー、熱硬化性ポリマー、光硬化性ポリマーを使い分けることができる。加熱によって容易に所望の形状、形態を付与しうる点で、熱可塑性ポリマーを用いることが好ましい。また塗布および簡便な後処理によって非常に薄い形状にしうる点で溶媒可溶性ポリマーと熱硬化性ポリマーが好ましい。 The polymer is not particularly limited, and a thermoplastic polymer, a solvent-soluble polymer, a thermosetting polymer, and a photocurable polymer can be properly used depending on the durability required in the process and use environment described below. It is preferable to use a thermoplastic polymer in that a desired shape and form can be easily imparted by heating. In addition, a solvent-soluble polymer and a thermosetting polymer are preferable because they can be formed into a very thin shape by coating and simple post-treatment.
熱可塑性ポリマーは、後述するような薄層黒鉛との溶融混練によって混合されて電磁波吸収層を好適に形成しうる。熱可塑性ポリマーとしては、具体的には、例えば、ポリエステル系ポリマー、ポリアミド系ポリマー、ポリイミド系ポリマー、ポリオレフィン系ポリマーやその他ビニル基の付加重合により合成されるビニル系ポリマー、フッ素系ポリマー、セルロース系ポリマー、シリコーン系ポリマー、芳香族あるいは脂肪族ケトン系ポリマー、天然ゴムや合成ゴムなどのエラストマー、その他多種多様なエンジニアリングプラスチックなどを挙げることができる。より具体的には、ポリオレフィン系ポリマーやビニル系ポリマーとしては、ポリエチレン、ポリプロピレン、ポリブチレン、ポリメチルペンテン、ポリスチレン、ポリアクリル酸、ポリメタクリル酸、ポリメタクリル酸メチル、ポリアクリロニトリル、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、ポリ塩化ビニリデン、ポリシアン化ビニリデン、ポリビニルアルコールなどが挙げられる。これらは単一モノマーの重合によるポリマーであっても良いし、あるいは薄層黒鉛の分散性を損ねない範囲において、複数のモノマーの重合により形成される共重合ポリマーであっても良い。 The thermoplastic polymer can be suitably mixed by melt-kneading with thin-layer graphite as will be described later to suitably form an electromagnetic wave absorbing layer. Specific examples of the thermoplastic polymer include polyester polymers, polyamide polymers, polyimide polymers, polyolefin polymers, and other vinyl polymers synthesized by addition polymerization of vinyl groups, fluorine polymers, and cellulose polymers. And silicone polymers, aromatic or aliphatic ketone polymers, elastomers such as natural rubber and synthetic rubber, and various other engineering plastics. More specifically, examples of polyolefin polymers and vinyl polymers include polyethylene, polypropylene, polybutylene, polymethylpentene, polystyrene, polyacrylic acid, polymethacrylic acid, polymethyl methacrylate, polyacrylonitrile, polytetrafluoroethylene, polyfluoroethylene. And vinylidene chloride, polyvinylidene chloride, polycyanide vinylidene, and polyvinyl alcohol. These may be a polymer obtained by polymerization of a single monomer, or may be a copolymer formed by polymerization of a plurality of monomers as long as the dispersibility of the thin-layer graphite is not impaired.
熱可塑性ポリマーとしては重縮合型のポリマーも好適に用いられる。重縮合型のポリマーとして、ポリアミド系ポリマーが好適に用いられ、具体的にはナイロン６、ナイロン７、ナイロン９、ナイロン１１、ナイロン１２、ナイロン６，６、ナイロン４，６、ナイロン６，９、ナイロン６，１２、ナイロン５，７およびナイロン５，６が例示される。その他、本発明の趣旨を損ねない範囲で他の芳香族、脂肪族、脂環族ジカルボン酸と芳香族、脂肪族、脂環族ジアミン成分が用いられたポリアミド系ポリマー、あるいは芳香族、脂肪族、脂環族などの１つの化合物がカルボン酸とアミノ基を両方有したアミノカルボン酸化合物が単独で用いられたポリアミド系ポリマーでもよい。
A polycondensation type polymer is also preferably used as the thermoplastic polymer. As the polycondensation type polymer, a polyamide polymer is preferably used. Specifically,
また重縮合型ポリマーとしては、ポリエステル系ポリマーも好適に用いられる。具体的には、ジカルボン酸とジオールからなるポリエチレンテレフタレート、ポリプロピレンテレフタレート（ポリトリメチレンテレフタレートとも言う）、ポリブチレンテレフタレート（ポリテトラメチレンテレフタレートとも言う）、ポリエチレンナフタレートおよびポリシクロヘキサンジメタノールテレフタレート、あるいは芳香族ヒドロキシカルボン酸を主成分とする溶融液晶性を有する液晶ポリエステルなどが挙げられる。またポリエステル系ポリマーとしては、ヒドロキシカルボン酸を単独モノマーとするポリエステルも挙げることができ、該ポリ（ヒドロキシカルボン酸）としては、例えばポリ乳酸、ポリ（３−ヒドロキシプロピオネート）、ポリ（３−ヒドロキシブチレート）、ポリ（３−ヒドロキシブチレートバリレート）等を好適なものとしてあげることができる。そして、これらポリエステル系ポリマーには、本発明の趣旨を損ねない範囲で他の成分が共重合されていても良く、例えばジカルボン酸化合物として、テレフタル酸、イソフタル酸、ナフタレンジカルボン酸、ジフェニルジカルボン酸、アントラセンジカルボン酸、フェナントレンジカルボン酸、ジフェニルエーテルジカルボン酸、ジフェノキシエタンジカルボン酸、ジフェニルエタンジカルボン酸、アジピン酸、セバシン酸、１，４−シクロヘキサンジカルボン酸、５−ナトリウムスルホイソフタル酸、５−テトラブチルホスホニウムイソフタル酸、アゼライン酸、ドデカンジオン酸、ヘキサヒドロテレフタル酸、といった芳香族、脂肪族、脂環族ジカルボン酸およびそれらのアルキル、アルコキシ、アリル、アリール、アミノ、イミノ、ハロゲン化物などの誘導体、付加体、構造異性体および光学異性体を挙げることができる。またジオール化合物を共重合せしめることもでき、エチレングリコール、プロピレングリコール、ブチレングリコール、ペンタンジオール、ヘキサンジオール、１，４−シクロヘキサンジメタノール、ネオペンチルグリコール、ハイドロキノン、レゾルシン、ジヒドロキシビフェニル、ナフタレンジオール、アントラセンジオール、フェナントレンジオール、２，２−ビス（４−ヒドロキシフェニル）プロパン、４，４´−ジヒドロキシジフェニルエーテル、ビスフェノールＳ、といった芳香族、脂肪族、脂環族ジオール化合物およびそれらのアルキル、アルコキシ、アリル、アリール、アミノ、イミノ、ハロゲン化物などの誘導体、付加体、構造異性体および光学異性体を挙げることができる。これら共重合するジカルボン酸化合物あるいはジオール化合物は、１種を単独で用いても良いし、または発明の趣旨を損ねない範囲で２種以上を組み合わせて用いても良い。 As the polycondensation polymer, a polyester polymer is also preferably used. Specifically, polyethylene terephthalate consisting of dicarboxylic acid and diol, polypropylene terephthalate (also called polytrimethylene terephthalate), polybutylene terephthalate (also called polytetramethylene terephthalate), polyethylene naphthalate and polycyclohexanedimethanol terephthalate, or aromatic Examples thereof include liquid crystal polyester having a melt liquid crystallinity mainly composed of hydroxycarboxylic acid. Examples of the polyester-based polymer also include polyesters having hydroxycarboxylic acid as a single monomer. Examples of the poly (hydroxycarboxylic acid) include polylactic acid, poly (3-hydroxypropionate), and poly (3- Hydroxybutyrate), poly (3-hydroxybutyrate valerate) and the like can be mentioned as suitable ones. These polyester-based polymers may be copolymerized with other components within a range that does not impair the spirit of the present invention. For example, as a dicarboxylic acid compound, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, Anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenylethane dicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium isophthalic acid Aromatic, aliphatic, alicyclic dicarboxylic acids such as acids, azelaic acid, dodecanedioic acid, hexahydroterephthalic acid and their alkyl, alkoxy, allyl, aryl, amino, imino, Derivatives such as androgenic compound, adduct include a structure and optical isomers. Diol compounds can also be copolymerized, such as ethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol, neopentylglycol, hydroquinone, resorcin, dihydroxybiphenyl, naphthalenediol, anthracenediol. Aromatic, aliphatic and alicyclic diol compounds such as phenanthrenediol, 2,2-bis (4-hydroxyphenyl) propane, 4,4'-dihydroxydiphenyl ether, bisphenol S, and their alkyl, alkoxy, allyl, aryl , Amino, imino and halide derivatives, adducts, structural isomers and optical isomers. One of these dicarboxylic acid compounds or diol compounds to be copolymerized may be used alone, or two or more of them may be used in combination as long as the gist of the invention is not impaired.
その他に本発明における熱可塑性ポリマーとしては、ポリカーボネート系ポリマー、ポリイミド系ポリマー、ポリエーテル系ポリマー、ポリフェニレンスルフィド系ポリマー、ポリエーテルエーテルケトン系ポリマー、ポリエーテルケトンケトン系ポリマー、脂肪族ポリケトンなどのポリマーの他、熱可塑性セルロース系ポリマーや、熱可塑性のキチン、キトサンおよびそれらの誘導体など、天然高分子由来のポリマーなども挙げられる。 In addition, examples of the thermoplastic polymer in the present invention include polycarbonate polymers, polyimide polymers, polyether polymers, polyphenylene sulfide polymers, polyether ether ketone polymers, polyether ketone ketone polymers, and aliphatic polyketones. Other examples include thermoplastic cellulosic polymers and polymers derived from natural polymers such as thermoplastic chitin, chitosan and derivatives thereof.
これら熱可塑性ポリマーの中で、本発明の電磁波吸収体における電磁波吸収帯および／または電磁波吸収層として耐候性や成型性、賦型性に優れることから、融点または軟化点が１５０℃以上のポリエステル系ポリマー、ポリアミド系ポリマー、ポリオレフィン系ポリマーが好ましく、高濃度の薄層黒鉛を含有させた場合でも軽量性に優れることから、特に融点または軟化点が１５０℃以上のポリオレフィン系ポリマー、融点または軟化点が２００℃以上のポリエステル系ポリマーおよびポリアミド系ポリマーより選択される１または２以上のポリマーからなることが好ましい。ここで融点とは下記実施例のＧ．項に記載の方法にて測定されるピーク温度を指す。また軟化点は下記実施例のＨ．項に記載の方法にて測定される。 Among these thermoplastic polymers, a polyester system having a melting point or softening point of 150 ° C. or higher because of excellent weather resistance, moldability and formability as an electromagnetic wave absorption band and / or electromagnetic wave absorption layer in the electromagnetic wave absorber of the present invention. Polymers, polyamide-based polymers, and polyolefin-based polymers are preferable, and even when a high-concentration thin-layer graphite is contained, they are excellent in lightness. It is preferably composed of one or more polymers selected from polyester polymers and polyamide polymers at 200 ° C. or higher. Here, the melting point is G. in the following examples. It refers to the peak temperature measured by the method described in the section. The softening point is H. It is measured by the method described in the item.
上記の熱可塑性ポリマーの溶融粘度は、特に制限されるものではなく、ポリマーを含有する電磁波吸収層の成型加工温度で、剪断速度が１０ｓｅｃ-1の溶融粘度が１０〜１０，０００［Ｐａ・秒］のポリマーが通常用いられ、好ましくは３０〜５，０００［Ｐａ・秒］である。また、該熱可塑性ポリマーの融点または軟化点温度以上の温度で必要時間加熱することによって連続帯を形成する場合は、やや粘度が低い方がより好ましいため３０〜５００［Ｐａ・秒］である。ここで溶融粘度とは溶融粘度測定装置、例えば（株）東洋精機社製キャピログラフ１Ｂを用いて、好ましくは窒素雰囲気下、ノズル（ノズル長１０ｍｍ，ノズル内径１ｍｍ〕を用いて、剪断速度１０ｓｅｃ-1で測定し、５回測定した値の平均値を溶融粘度の測定値とすることで採用できる。なお測定時間が過度に長いと熱可塑性ポリマーの劣化が見られる場合があるため、試料の劣化を防ぐために好ましくは５回の測定を３０分以内で完了するのがよい。
The melt viscosity of the thermoplastic polymer is not particularly limited, and the melt viscosity of the electromagnetic wave absorbing layer containing the polymer is 10 to 10,000 [Pa · sec] at a shear rate of 10 sec −1. ] Is usually used, and preferably 30 to 5,000 [Pa · sec]. Moreover, when a continuous band is formed by heating for a required time at a temperature equal to or higher than the melting point or softening point temperature of the thermoplastic polymer, the viscosity is preferably 30 to 500 [Pa · sec] because the lower viscosity is more preferable. Here, the melt viscosity is a melt viscosity measuring apparatus, for example, Capillograph 1B manufactured by Toyo Seiki Co., Ltd., preferably using a nozzle (nozzle length 10 mm, nozzle
本発明の電磁波吸収体における電磁波吸収層は、溶媒可溶性ポリマーに少なくとも１種の薄層黒鉛を含有せしめた後、後述するような塗布あるいは型に入れて溶媒を除去することで形成することができる。また熱硬化性ポリマーや光硬化性ポリマーを用いる場合は、これらのモノマーないしプレポリマーに、必要に応じて溶媒を用いて、更に少なくとも１種の薄層黒鉛を含有せしめた後、熱や紫外線等の光照射により固化させることで形成することができる。これら溶媒可溶性ポリマー、熱硬化性ポリマー、光硬化性ポリマーの好ましいものとしては、二液混合エポキシ樹脂、ポリメタクリル酸メチル、ポリフッ化ビニリデンあるいはフッ化ビニリデンモノマー、ポリビニルアルコール、ポリビニルブチラール、ポリ塩化ビニルを挙げることができ、薄層黒鉛の分散性が良いことと、塗工程の容易さからポリビニルブチラールが最も好ましい。なお溶媒可溶性ポリマーについては、好ましい溶媒として、Ｎ，Ｎ−ジメチルホルムアミド（ＤＭＦ）、ジメチルスルホキシド（ＤＭＳＯ）、Ｎ−メチル−２−ピロリドン（ＮＭＰ）、ジメチルアセトアミド、イソプロパノール（ＩＰＡ）、テトラヒドロフラン（ＴＨＦ）、エタノール、アセトン、メチルエチルケトン（ＭＥＫ）、メチルイソブチルケトン（ＭＩＢＫ）を用いることができ、特にＩＰＡ、ＤＭＦ、ＮＭＰが好ましい。これら溶媒は１種類を単独で用いても良く、発明の趣旨を損ねない範囲で、薄層黒鉛の分散性を向上させるなど目的や必要に応じて２種類以上を混用してもよい。 The electromagnetic wave absorbing layer in the electromagnetic wave absorber of the present invention can be formed by adding at least one kind of thin graphite to a solvent-soluble polymer and then putting it in a coating or mold as described later and removing the solvent. . In the case of using a thermosetting polymer or a photocurable polymer, these monomers or prepolymers are further added with at least one kind of thin-layer graphite using a solvent as necessary, and then heat, ultraviolet rays, etc. It can be formed by solidifying by light irradiation. Preferred examples of these solvent-soluble polymers, thermosetting polymers and photocurable polymers include two-component mixed epoxy resins, polymethyl methacrylate, polyvinylidene fluoride or vinylidene fluoride monomers, polyvinyl alcohol, polyvinyl butyral, and polyvinyl chloride. Polyvinyl butyral is the most preferable because of the good dispersibility of the thin-layer graphite and the ease of the coating process. For solvent-soluble polymers, preferred solvents are N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), dimethylacetamide, isopropanol (IPA), tetrahydrofuran (THF). , Ethanol, acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) can be used, and IPA, DMF, and NMP are particularly preferable. One kind of these solvents may be used alone, or two or more kinds may be used as needed for the purpose and necessity, for example, to improve the dispersibility of the thin-layer graphite within a range not impairing the gist of the invention.
本発明の電磁波吸収帯または電磁波吸収層には、上記の中から選ばれるポリマーのうち１種類を単独で用いても良く、また発明の趣旨を損ねない範囲において複数種のポリマーを併用しても良い。 In the electromagnetic wave absorption band or electromagnetic wave absorption layer of the present invention, one of the polymers selected from the above may be used alone, or a plurality of types of polymers may be used in combination as long as the spirit of the invention is not impaired. good.
また、本発明の電磁波吸収帯における電磁波吸収層は、発明の趣旨を損ねない範囲において、必要に応じて、薄層黒鉛を均一に分散せしめる分散剤を含むことができる。具体的には、芳香族エーテル型、カルボン酸エステル型、アクリル酸エステル型、リン酸エステル型、スルホン酸エステル型、脂肪酸エステル型、ウレタン型、フッ素型、アミノアマイド型、アクリルアマイド型などの非イオン系界面活性剤、ボスホニウム含有ポリマーなどの陽イオン界面活性剤、カルボン酸型、リン酸型、スルホン酸型、ヒドロキシ脂肪酸型、脂肪酸アマイド型などの陰イオン系界面活性剤が用いられる。中でも、前述あるいは後述の塗布による電磁波吸収層の形成において、低粘度の塗工液中での薄層黒鉛の分散性が安定化する観点から、リン酸エステル型界面活性剤が好ましい。 Moreover, the electromagnetic wave absorption layer in the electromagnetic wave absorption band of the present invention can contain a dispersing agent for uniformly dispersing the thin-layer graphite, if necessary, within a range not impairing the gist of the invention. Specifically, non-aromatic ether type, carboxylic acid ester type, acrylic acid ester type, phosphoric acid ester type, sulfonic acid ester type, fatty acid ester type, urethane type, fluorine type, amino amide type, acrylic amide type, etc. Cationic surfactants such as ionic surfactants and phosphonium-containing polymers, and anionic surfactants such as carboxylic acid type, phosphoric acid type, sulfonic acid type, hydroxy fatty acid type, and fatty acid amide type are used. Of these, phosphate ester type surfactants are preferred from the viewpoint of stabilizing the dispersibility of the thin-layer graphite in the low-viscosity coating solution in the formation of the electromagnetic wave absorbing layer by the coating described above or below.
本発明の電磁波吸収帯または電磁波吸収層は、本発明で目的とする電磁波吸収性能を損ねない範囲において、薄層黒鉛やポリマー以外の難燃剤、滑剤、酸化防止剤、結晶核剤、末端基封止剤等の添加剤や、粒子状や棒状、繊維状の金属微粒子やファーネスブラック、ケッチェンブラックあるいはアセチレンブラック、カーボンナノチューブ等の炭素系微粒子を少量含有しても良い。 The electromagnetic wave absorption band or electromagnetic wave absorption layer of the present invention is a flame retardant other than thin-layer graphite or polymer, lubricant, antioxidant, crystal nucleating agent, end-group-sealing as long as the target electromagnetic wave absorption performance is not impaired in the present invention. A small amount of additives such as a stopper, particulate metal, rod-like, fibrous metal fine particles, furnace black, ketjen black, acetylene black, carbon nanotubes or the like may be contained.
本発明の電磁波吸収体は、電磁波入射面の他面側に電磁波を反射する基板を設けたものであることが好ましい。すなわち、本発明の電磁波吸収体は、電磁波入射面から、電磁波吸収帯、電磁波を反射する基板、の順に積層された構造を有することが好ましい。このように構成することで、電磁波吸収体に入射する電磁波を基板で反射させ、電磁波を電磁波吸収帯中で往復させることができ、更に電磁波を効率的に吸収することが可能となる。 The electromagnetic wave absorber of the present invention is preferably one in which a substrate that reflects electromagnetic waves is provided on the other side of the electromagnetic wave incident surface. That is, the electromagnetic wave absorber of the present invention preferably has a structure in which an electromagnetic wave absorption band and a substrate that reflects electromagnetic waves are laminated in this order from the electromagnetic wave incident surface. By comprising in this way, the electromagnetic wave which injects into an electromagnetic wave absorber can be reflected with a board | substrate, an electromagnetic wave can be reciprocated in an electromagnetic wave absorption band, and also it becomes possible to absorb electromagnetic waves efficiently.
電磁波を反射する基板としては、導電性の高い素材であることが好ましく、金属からなる板やシート、箔、あるいはメッキが好適に用いられる。電磁波吸収体自体を薄くすることで軽量性に優れることから、金属からなる電磁波を反射する基板の厚さは薄い方が好ましい。 The substrate that reflects electromagnetic waves is preferably a highly conductive material, and a metal plate, sheet, foil, or plating is preferably used. Since the electromagnetic wave absorber itself is excellent in light weight, the thickness of the substrate that reflects the electromagnetic wave made of metal is preferably thin.
電磁波吸収体を薄くするためには、基板も薄い方が好ましいため、該基板の厚さとしては５００μｍ以下であることが好ましく、１００μｍ以下であることがより好ましく、１０μｍ以下であることが特に好ましい。また該基板は薄い方が好ましいものの、十分な電磁波反射性を有する必要があることから、厚さ５０ｎｍ以上であることが好ましく、１００ｎｍ以上であることがより好ましく、２００ｎｍ以上であることが特に好ましい。 In order to reduce the thickness of the electromagnetic wave absorber, it is preferable that the substrate is also thin. Therefore, the thickness of the substrate is preferably 500 μm or less, more preferably 100 μm or less, and particularly preferably 10 μm or less. . Further, although the substrate is preferably thin, it is necessary to have sufficient electromagnetic wave reflectivity. Therefore, the thickness is preferably 50 nm or more, more preferably 100 nm or more, and particularly preferably 200 nm or more. .
このように、電磁波を反射する基板は薄いことが好ましいことから、膜、箔、あるいはメッキで形成されることがより好ましい。特にメッキは、非常に薄い薄膜状の基板を形成でき、かつ接着剤が不要で設計された電磁波吸収性能の再現性に優れることから特に好ましく、真空蒸着やスパッタリング、イオンプレーティングなどの真空メッキ法により形成される薄膜が電磁波を反射する基板であることが最も好ましい。 Thus, since it is preferable that the board | substrate which reflects electromagnetic waves is thin, forming with a film | membrane, foil, or plating is more preferable. In particular, plating is particularly preferable because it can form a very thin thin-film substrate and is excellent in reproducibility of electromagnetic wave absorption performance designed without the need for an adhesive. Vacuum plating methods such as vacuum deposition, sputtering, and ion plating Most preferably, the thin film formed by is a substrate that reflects electromagnetic waves.
基板に用いられうる金属の種類として具体的には、アルミニウム（Ａｌ）、クロム（Ｃｒ）、ニッケル（Ｎｉ）、銅（Ｃｕ）、亜鉛（Ｚｎ）、モリブデン（Ｍｏ）、銀（Ａｇ）、インジウム（Ｉｎ）、スズ（Ｓｎ）、タングステン（Ｗ）、白金(Ｐｔ）、金(Ａｕ）が好ましいものとして挙げられる。これらの金属は、単体で用いられてもよく、あるいは電磁波を反射する機能を有する限り、これらの金属の化合物、すなわち、酸化物、窒化物、炭化物、硫黄化物等の金属化合物として用いられてもよく、あるいは複数種類の金属から構成されてなる金属化合物として用いられてもよい。 Specific examples of metals that can be used for the substrate include aluminum (Al), chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), molybdenum (Mo), silver (Ag), and indium. (In), tin (Sn), tungsten (W), platinum (Pt), and gold (Au) are preferable. These metals may be used alone or as a compound of these metals, that is, as a metal compound such as an oxide, a nitride, a carbide, or a sulfide as long as it has a function of reflecting electromagnetic waves. Alternatively, it may be used as a metal compound composed of a plurality of types of metals.
ここで複数種類の金属を併用する場合は、例えば一種類目の金属あるいは金属化合物を用いて薄膜（基板）を形成した後に二種類目以上の金属あるいは金属化合物を上から薄膜形成させて積層してもよいし、あるいは複数種の金属あるいは金属化合物を同時に存在させて薄膜形成させても良い。そして高々三種類の金属を含んでなることが好ましい。 When using multiple types of metals here, for example, after forming a thin film (substrate) using the first type of metal or metal compound, the second or more types of metal or metal compound are formed into a thin film from above and laminated. Alternatively, a thin film may be formed by simultaneously presenting a plurality of kinds of metals or metal compounds. And it is preferable to contain at most three kinds of metals.
これらの中で工程および時間が少なくて済む点で一種類の金属であることがより好ましい。なお一種類の金属であることが好ましいものの、０．１％未満の割合の金属成分は、該基板として形成された金属種の数に含まない。そして特にこれら金属の中でメッキ性（薄膜形成性）が良好であるため好ましいのはアルミニウム、ニッケル、銅、亜鉛、銀、スズ、金あるいはこれらの化合物であり、アルミニウム、銅、銀、金が入手容易性の点で特に好ましい。 Among these, it is more preferable to use one kind of metal in that the process and time are reduced. In addition, although it is preferable that it is one type of metal, the metal component of a ratio of less than 0.1% is not included in the number of metal species formed as the substrate. Among these metals, aluminum, nickel, copper, zinc, silver, tin, gold, or a compound thereof is preferable because of good plating properties (thin film formation), and aluminum, copper, silver, and gold are preferable. It is particularly preferable in terms of availability.
また電磁波を反射する基板は、上記金属以外でもよく、高導電性の炭素材料が好適に用いられ、炭素繊維織物やグラファイトシートなどが好適に用いられる。特にグラファイトシートは前述したように樹脂フィルムの焼成処理により製造され、極めて電磁波の反射性能が優れている。またグラファイトシートの他の種類としては、微小グラファイトが多数敷き詰められて積層されてなるシートであっても良い。微小グラファイトを多数敷き詰めて積層するには幾つかの手法があり、粉体となした微小グラファイトを平板上に吹き付けて、あるいは溶媒中に分散させた分散液を噴霧法あるいはスピンコート法などにより塗布した後、分散液の溶媒が蒸発・消失することで平板上に敷き詰められ積層されて得られる。該微小グラファイトからなるシートはプレスなどの方法により、緻密かつ非常に薄い基板となりうる。 The substrate that reflects electromagnetic waves may be other than the above metal, and a highly conductive carbon material is preferably used, and a carbon fiber fabric, a graphite sheet, or the like is preferably used. In particular, a graphite sheet is produced by baking a resin film as described above, and has extremely excellent electromagnetic wave reflection performance. Another type of graphite sheet may be a sheet in which a large number of fine graphites are spread and laminated. There are several methods for laminating and laminating a large number of fine graphite, and spraying fine graphite powder on a flat plate or applying a dispersion dispersed in a solvent by spraying or spin coating After that, the solvent of the dispersion liquid is evaporated and disappeared to be spread and laminated on a flat plate. The sheet made of fine graphite can be a dense and very thin substrate by a method such as pressing.
そしてこれら電磁波を反射する基板としては、真空メッキ法により形成される金属薄膜、樹脂フィルムの焼成処理により製造されるグラファイトシートまたは微小グラファイトが多数敷き詰められて積層されてなるシートが特に好ましい。 And as a board | substrate which reflects these electromagnetic waves, the sheet | seat formed by laminating | stacking many metal sheets formed by the vacuum plating method, the graphite sheet manufactured by the baking process of a resin film, or many fine graphites is laminated | stacked.
本発明の電磁波吸収体は、発明の趣旨を損ねない範囲で他の層を設けても良い。具体的には保護層などの耐久性や耐候性を補佐する層、あるいは強度などの物理物性を補佐する層を設けても良い。 The electromagnetic wave absorber of the present invention may be provided with other layers as long as the spirit of the invention is not impaired. Specifically, a layer for assisting durability and weather resistance such as a protective layer, or a layer for assisting physical properties such as strength may be provided.
本発明は、前述の通り、任意の周波数帯域に電磁波吸収特性を有する電磁波吸収体とすることができるものであり、目的とする周波数帯域は特に限定されない。しかし、ＧＨｚ帯に吸収対象周波数帯を有する電磁波吸収体は、これまで十分な性能のものが得られておらず、本発明の効果をひときわ発揮することができるものと考えられる。このような観点からは、電磁波吸収性能測定により得られた吸収スペクトルにおいて、１ＧＨｚ以上の周波数帯域で、２５ｄＢ以上の電磁波吸収性能を有する周波数が、１ＧＨｚ以上の帯域にわたり連続することが好ましい。また、２５ｄＢ以上の電磁波吸収性能を有する周波数が２ＧＨｚ以上の帯域にわたり連続することが好ましく、５ＧＨｚ以上の帯域にわたり連続することがより好ましく、１０ＧＨｚ以上の帯域にわたり連続することが特に好ましく、３０ＧＨｚ以上の帯域にわたり連続することが最も好ましい。 As described above, the present invention can be an electromagnetic wave absorber having electromagnetic wave absorption characteristics in an arbitrary frequency band, and the target frequency band is not particularly limited. However, an electromagnetic wave absorber having a frequency band to be absorbed in the GHz band has not been obtained with sufficient performance so far, and it is considered that the effect of the present invention can be exhibited remarkably. From such a viewpoint, in the absorption spectrum obtained by the electromagnetic wave absorption performance measurement, it is preferable that a frequency having an electromagnetic wave absorption performance of 25 dB or more is continuous over a band of 1 GHz or more in a frequency band of 1 GHz or more. Further, the frequency having an electromagnetic wave absorption performance of 25 dB or more is preferably continuous over a band of 2 GHz or more, more preferably continuous over a band of 5 GHz or more, particularly preferably continuous over a band of 10 GHz or more, and 30 GHz or more. Most preferably it is continuous over a zone.
以下、実施例により本発明を具体的かつより詳細に説明するが、本発明はこれらの実施例のみに制限されるものではない。なお実施例中の部は特に具体的な記載のない限り重量部を意味する。実施例中の物性値は、下記の方法によって測定した。 EXAMPLES Hereinafter, although an Example demonstrates this invention concretely and in detail, this invention is not restrict | limited only to these Examples. In the examples, “parts” means “parts by weight” unless otherwise specified. The physical property values in the examples were measured by the following methods.
Ａ．電磁波吸収層の厚みおよび電磁波吸収体の総厚みの測定
株式会社テクロック製ＳＭ−１２５を用いて、無作為に抽出した１０個の試料の、任意の厚み１０点を測定して、その平均した値を電磁波吸収層の厚みとして得た。
A. Measurement of the thickness of the electromagnetic wave absorbing layer and the total thickness of the electromagnetic wave absorber Using SM-125 manufactured by TECKLOCK Co., Ltd., randomly measuring 10 samples, measuring 10 arbitrary thicknesses, and averaging the values Was obtained as the thickness of the electromagnetic wave absorbing layer.
Ｂ．薄層黒鉛の平均厚みの測定方法
試料は、ポリマー中に分散された薄層黒鉛をそのまま、あるいは粉体状の薄層黒鉛であればあらかじめエポキシ樹脂中に包埋して使用した。各試料は、窒素雰囲気下８０℃で乾燥した後、ＦＥＩ社製Ｓｔｒａｔａ ＤＢ２３５を用いて加速電圧３０ｋＶで集束イオンビーム法により試料薄膜を作製して、株式会社日立ハイテクノロジーズ社製透過電子顕微鏡Ｈ−９０００ＵＨＲ ＩＩＩを用い、加速電圧３００ｋＶで、薄層黒鉛厚みが５０ｎｍ未満であれば２００万倍で、５０ｎｍ以上５００ｎｍ未満であれば２０万倍で、５００ｎｍ以上５μｍ未満であれば２万倍でそれぞれ観察して、１つの画面に存在する薄層黒鉛を無作為に３０個抽出して各薄層黒鉛１つのドメインの最大厚みを測定し、１００μｍ以上離れた異なる３点の厚みの平均値で薄層黒鉛の平均厚みとした。
B. Method for Measuring Average Thickness of Thin-Layer Graphite As a sample, thin-layer graphite dispersed in a polymer is used as it is or, if it is powdery thin-layer graphite, it is embedded in an epoxy resin in advance. Each sample was dried at 80 ° C. in a nitrogen atmosphere, and then a sample thin film was prepared by a focused ion beam method at an acceleration voltage of 30 kV using Strata DB235 manufactured by FEI, and a transmission electron microscope H- manufactured by Hitachi High-Technologies Corporation. Using 9000 UHR III, observed at an acceleration voltage of 300 kV and a thin graphite thickness of 2 million times if the thickness of the thin graphite is less than 50 nm, 200,000 times if it is 50 nm or more and less than 500 nm, and 20,000 times if it is 500 nm or more and less than 5 μm. Then, 30 thin-layer graphites present on one screen are randomly extracted and the maximum thickness of one domain of each thin-layer graphite is measured, and the average value of the thickness of three different points separated by 100 μm or more The average thickness of graphite was used.
Ｃ．誘電率および電磁波吸収性能の測定方法
（誘電率測定）
アジレントテクノロジー（株）製ネットワークアナライザ８７２２Ｄおよび関東電子（株）製の材料定数測定ソフト８５０７１を用いて測定した。
C. Measuring method of dielectric constant and electromagnetic wave absorption performance (dielectric constant measurement)
Measurement was performed using a network analyzer 8722D manufactured by Agilent Technologies, Inc. and material constant measurement software 85071 manufactured by Kanto Electronics Co., Ltd.
試料調製は、１〜１８ＧＨｚの測定においては内径３．０４ｍｍ、外形７．０ｍｍの円盤で内側に穴のあるドーナツ型、１８ＧＨｚ〜５０ＧＨｚ以上は、外径寸法１０．７ｍｍ×４．３ｍｍ×４．３ｍｍ〜５．７ｍｍ×２．８５ｍｍ×２．８５ｍｍの直方体型にそれぞれ削り出し加工して、計測に供した。また５０ＧＨｚ以上の周波数では、ホーンアンテナの中央に直径５０．２ｍｍの試料を金属リングで設置固定して、フリースペース型Ｓパラメータ法により、ＳパラメータのＳ１１、Ｓ２１を測定し反射係数と透過係数を算出し、そこから、複素誘電率の実部と虚部を算出した。 The sample preparation is a donut shape with an inner diameter of 3.04 mm and an outer diameter of 7.0 mm in the measurement of 1 to 18 GHz, and an inner diameter of 10.7 mm × 4.3 mm × 4. Each piece was cut into a rectangular parallelepiped shape of 3 mm to 5.7 mm × 2.85 mm × 2.85 mm and used for measurement. At a frequency of 50 GHz or more, a sample having a diameter of 50.2 mm is placed and fixed at the center of the horn antenna with a metal ring, and S parameters S11 and S21 are measured by a free space type S parameter method to obtain a reflection coefficient and a transmission coefficient. The real part and the imaginary part of the complex dielectric constant were calculated therefrom.
（電磁波吸収性能測定）
試料は上述した誘電率測定用の試料と同様に、各周波数によって必要な試料形状に加工したのち、電磁波を反射する基板がある場合はそのまま、電磁波を反射する基板が無い電磁波吸収層のみの場合には反射材としてＳＵＳ板を試料の裏面に重ねて、それぞれ試料を固定した。測定はアジレントテクノロジー（株）製ネットワークアナライザ８７２２Ｄを用いて、Ｓパラメータ法により、試料への入射波と反射波の測定結果から、１〜１００ＧＨｚの範囲で周波数を変化せた電磁波を照射させ、電磁波吸収量を算出した。
(Electromagnetic wave absorption performance measurement)
In the same way as the dielectric constant measurement sample described above, after processing into the required sample shape according to each frequency, if there is a substrate that reflects electromagnetic waves, the sample is just an electromagnetic wave absorbing layer without a substrate that reflects electromagnetic waves In this example, a SUS plate as a reflecting material was stacked on the back surface of the sample, and the samples were fixed respectively. The measurement is performed by irradiating an electromagnetic wave whose frequency is changed in the range of 1 to 100 GHz from the measurement result of the incident wave and the reflected wave on the sample by the S parameter method using a network analyzer 8722D manufactured by Agilent Technologies. Absorption was calculated.
周波数に対する電磁波吸収量のプロットから、電磁波吸収量が最大値を示した周波数を求め、「電磁波吸性能最大ピーク周波数」とした。また１ＧＨｚ以上の連続する帯域幅で２５ｄＢ以上の電磁波吸収性能が測定された電磁波の帯域幅を「２５ｄＢ以上の吸収量の連続する帯域幅」として求めた。 From the plot of the electromagnetic wave absorption amount against the frequency, the frequency at which the electromagnetic wave absorption amount showed the maximum value was determined and was defined as “the maximum peak frequency of electromagnetic wave absorption performance”. Further, the bandwidth of the electromagnetic wave in which the electromagnetic wave absorption performance of 25 dB or more was measured with a continuous bandwidth of 1 GHz or more was determined as “continuous bandwidth of the absorption amount of 25 dB or more”.
Ｄ．薄層黒鉛の平均酸化度の評価および異元素の解析方法
解析する試料は、窒素雰囲気下８０℃で乾燥した後、用いた。株式会社堀場製作所製エネルギー分散型Ｘ線検出器（ＥＤＸ）Ｘ−Ｍａｘ ＳＩＬＩＣＯＮ ＤＲＩＦＴ Ｘ−ＲＡＹ ＤＥＴＥＣＴＯＲが付属した、株式会社日立ハイテクノロジーズ社製走査電子顕微鏡ＳＵ８０２０を用い、加速電圧１ｋＶ、倍率１００倍で、観察視野が全て薄層黒鉛となるように観察しながら、各種原子の原子組成百分率（ａｔｏｍｉｃ（ａｔ）％）を解析した。酸化度については、酸素原子のａｔ％について視野が全く重ならない別視野１０か所について解析し、酸化度の平均値を求めて、当該試料の平均酸化度とした。また炭素原子や酸素原子、水素原子以外の異元素の有無についても、同一解析において、０．０５ａｔ％を測定限界として、０．０５ａｔ％未満であれば、無しと判断した。
D. Evaluation of average oxidation degree of thin-layer graphite and analysis method of foreign elements Samples to be analyzed were used after drying at 80 ° C. in a nitrogen atmosphere. Using a scanning electron microscope SU8020 manufactured by Hitachi High-Technologies Corporation, with an energy dispersive X-ray detector (EDX) X-Max SILICON DRIVE X-RAY DETECTOR manufactured by HORIBA, Ltd., at an acceleration voltage of 1 kV and a magnification of 100 times The atomic composition percentage (atomic (at)%) of various atoms was analyzed while observing so that the observation field of view was all thin-layer graphite. The degree of oxidation was analyzed for 10 different visual fields where the visual field did not overlap at all with respect to at% of oxygen atoms, and the average value of the degree of oxidation was obtained to obtain the average degree of oxidation of the sample. Further, regarding the presence or absence of foreign elements other than carbon atoms, oxygen atoms, and hydrogen atoms, in the same analysis, 0.05 at% was set as a measurement limit, and it was determined to be absent if it was less than 0.05 at%.
Ｅ．薄層黒鉛の平均大きさの解析方法
解析する試料は、あらかじめ薄層黒鉛の分散液をスピンコート法で清浄なガラス基板上に塗布した後、窒素雰囲気下８０℃で乾燥して調製した後、解析に供した。株式会社島津製作所製ＳＦＴ−３５００を用い、まずレーザー顕微鏡モードで観察視野が１００μｍ×１３０μｍ程度の倍率で観察し、高さ（厚さ）が０．１μｍ以上の粒子に対して粒子幅を測定した。厚さが０．１μｍ未満の粒子については、プローブ顕微鏡モードにおいて、観察視野が３０μｍ×３０μｍのダイナミックモードでマッピング観察し、各薄層黒鉛粒子の最大幅を測定した。そして平均大きさについては、レーザー顕微鏡モードのみ、あるいはプローブ顕微鏡モードのみ、各々別々で評価し、観察視野内の任意の薄層黒鉛粒子５０個の粒子最大幅を測定し、更に１ｍｍ以上異なる５か所の観察視野において同様に最大粒子幅を測定してその平均値を算出し、薄層黒鉛の平均大きさとして得た。
E. Analytical method of the average size of the thin layer graphite After the sample to be analyzed was prepared by applying a thin layer graphite dispersion liquid on a clean glass substrate by spin coating in advance and then drying at 80 ° C. in a nitrogen atmosphere, It used for analysis. Using SFT-3500 manufactured by Shimadzu Corporation, the observation field was first observed in a laser microscope mode at a magnification of about 100 μm × 130 μm, and the particle width was measured for particles having a height (thickness) of 0.1 μm or more. . For the particles having a thickness of less than 0.1 μm, in the probe microscope mode, mapping observation was performed in a dynamic mode with an observation field of view of 30 μm × 30 μm, and the maximum width of each thin-layer graphite particle was measured. The average size is evaluated separately for only the laser microscope mode or only for the probe microscope mode, and the maximum width of 50 arbitrary thin-layer graphite particles in the observation field is measured. Similarly, the maximum particle width was measured in the observation field of view, and the average value was calculated to obtain the average size of the thin-layer graphite.
Ｆ．空隙率の評価方法
作製した試料の重量と体積の実測値から算出した嵩密度を、試料を構成する複数の材料の密度を各材料の体積含有率で加重平均して算出した試料の真密度で除し、空隙率＝［１−（嵩密度／真密度）］×１００（％）の式から、空隙率を算出した。尚、電磁波吸収層が基材上に設けられる場合の重量と体積の実測は、基材の重量と体積を差し引くことで算出した。体積の実測は、試料が直方体に近似できる場合は各辺の長さを実測し、近似できない場合は水中に浸漬して増加した水の体積を測定することで行った。
F. Porosity evaluation method The bulk density calculated from the measured values of the weight and volume of the prepared sample is the true density of the sample calculated by weighted averaging the density of multiple materials that make up the sample with the volume content of each material. The porosity was calculated from the equation: porosity = [1- (bulk density / true density)] × 100 (%). In addition, the actual measurement of the weight and volume when the electromagnetic wave absorbing layer is provided on the substrate was calculated by subtracting the weight and volume of the substrate. The actual measurement of the volume was performed by measuring the length of each side when the sample can be approximated to a rectangular parallelepiped, and measuring the volume of water increased by being immersed in water when the sample cannot be approximated.
Ｇ．ポリマーの融点（Ｔｍ）の測定
パーキンエルマー社製示差走査熱量分析装置（ＤＳＣ−２）を用いて試料１０ｍｇで、昇温速度１６℃／分で熱可塑性ポリマーの融点（Ｔｍ）を測定した。Ｔｍの定義は、一旦昇温速度１６℃／分で測定した際に観測される吸熱ピーク温度（Ｔｍ１）の観測後、約（Ｔｍ１＋２０）℃の温度で５分間保持した後、室温まで急冷し、（急冷時間および室温保持時間を合わせて５分間保持）、再度１６℃／分の昇温条件で測定した際に、結晶の融解温度として観測される吸熱ピーク温度をＴｍとした。
G. Measurement of Polymer Melting Point (Tm) The melting point (Tm) of a thermoplastic polymer was measured with a 10 mg sample at a heating rate of 16 ° C./min using a differential scanning calorimeter (DSC-2) manufactured by PerkinElmer. The definition of Tm is, after observing the endothermic peak temperature (Tm1) observed once measured at a heating rate of 16 ° C./min, holding at a temperature of about (Tm1 + 20) ° C. for 5 minutes, and then rapidly cooling to room temperature. (The quenching time and the room temperature holding time were combined and held for 5 minutes), and the endothermic peak temperature observed as the melting temperature of the crystal when measured again at a temperature rising condition of 16 ° C./min was defined as Tm.
Ｈ．ポリマーの軟化点温度（Ｔｓ）の測定
測定対象のポリマーを用いて厚さ５ｍｍ、縦横共に５ｃｍの板状試料を作製し、シリコンオイル中でオイル温度を１２０℃／時間の昇温速度で昇温させながら、断面積１ｍｍ2の針で試験荷重５０Ｎの荷重で試料に当て、侵入深さが１ｍｍになった温度を熱可塑性ポリマーの軟化点温度（Ｔｓ）とした。
H. Measurement of the softening point temperature (Ts) of the polymer Using the polymer to be measured, a plate-like sample having a thickness of 5 mm and a length and width of 5 cm was prepared, and the oil temperature was increased in silicon oil at a rate of 120 ° C / hour. The temperature at which the penetration depth reached 1 mm was defined as the softening point temperature (Ts) of the thermoplastic polymer by applying a test load of 50 N with a needle having a cross-sectional area of 1 mm 2 .
［製造例１］（物理的および化学的に薄層化処理した薄層黒鉛の製造方法）
原料として平均大きさ１００μｍの天然黒鉛１０ｇを株式会社レッチェ製遊星ボールミルＰＭ１００を用いて、公転回転数４００ｒｐｍ、公自転比１：−２、で６時間処理することで、平均大きさ４．３μｍの物理的に薄層化処理した天然黒鉛を得た。その後、氷冷した４００部の９８％硫酸を撹拌しながら、前述の物理的に薄層化処理した天然黒鉛１２部、純度９９％以上の硝酸ナトリウム４部を加え、更に純度９９．３％以上の過マンガン酸カリウム１５部を少しずつ添加して加えたのち、２０℃で４時間反応させた。反応物は４６０部の純水で氷冷しながら希釈した後１５分間強撹拌し、更に６８０部の純水で希釈しながら３０分間強撹拌したのち、濃度３０％の過酸化水素水６０部を添加して更に１０分間強撹拌して反応を停止した。
[Production Example 1] (Method for producing physically and chemically thinned graphite)
By processing 10 g of natural graphite having an average size of 100 μm as a raw material for 6 hours at a revolution speed of 400 rpm and a rotation ratio of 1: -2 using a planetary ball mill PM100 manufactured by Lecce Co., Ltd., an average size of 4.3 μm is obtained. Naturally thinned natural graphite was obtained. Then, while stirring 400 parts of ice-cooled 98% sulfuric acid, 12 parts of the above-mentioned physically thinned natural graphite and 4 parts of sodium nitrate having a purity of 99% or more were added, and the purity was 99.3% or more. After adding 15 parts of potassium permanganate little by little, the mixture was reacted at 20 ° C. for 4 hours. The reaction product was diluted with 460 parts of pure water while cooling with ice, and then vigorously stirred for 15 minutes. Further, the mixture was vigorously stirred for 30 minutes while diluted with 680 parts of pure water, and then 60 parts of hydrogen peroxide solution having a concentration of 30% was added. The reaction was stopped by vigorous stirring for 10 minutes after the addition.
得られた混合物は株式会社久保田製作所製高速冷却遠心機７７８０ＩＩを用いて、重力の２０００倍（２０００×ｇ）に相当する遠心力で遠心分離を行った。遠心分離後に上澄み液を除去して試料を得たのち、得られた試料に対して除去した上澄み液と同量の純水を添加し、遠心分離操作で５０００×ｇの遠心力で３０分間かけて分離して固体を得た後、更に同様に純水を用いてｐＨが３以上となるまで純水での洗浄と２００００×ｇでの遠心分離処理を繰り返して、凍結乾燥して、化学的に薄層化処理した薄層黒鉛Ａを得た。該薄層黒鉛は平均大きさ１．１μｍ、平均厚みは２．３ｎｍ、酸化度は２１ａｔ％であった。またＣ、Ｏ、Ｈ以外の元素は測定限界未満であった。 The obtained mixture was centrifuged with a centrifugal force equivalent to 2000 times gravity (2000 × g) using a high-speed cooling centrifuge 7780II manufactured by Kubota Corporation. After centrifuging, the supernatant is removed to obtain a sample, and then the same amount of pure water as that of the removed supernatant is added to the obtained sample, followed by centrifugation at a centrifugal force of 5000 × g for 30 minutes. In the same manner, the solid is obtained by repeated washing with pure water and centrifugation at 20000 × g using pure water until the pH becomes 3 or more, and freeze-drying and chemical treatment. A thin layer graphite A was obtained. The thin graphite had an average size of 1.1 μm, an average thickness of 2.3 nm, and an oxidation degree of 21 at%. Moreover, elements other than C, O, and H were less than the measurement limit.
［製造例２］（物理処理による薄層黒鉛の製造方法）
黒鉛（ＸＧｓｃｉｅｎｃｅ社製、タイプＭ−５）３．０ｇを株式会社レッチェ製ミキサーミルＭＭ１００の容量５０ｍｌのＳＵＳ容器に入れ、直径１０ｍｍのＳＵＳボールを入れて、１０分撹拌と２分静置を６回繰り返し、薄層黒鉛の平均大きさが４．９μｍ、平均厚み８．３ｎｍ、酸化度１０．７ａｔ％である薄層黒鉛Ｂを得た。また黒鉛（ＸＧｓｃｉｅｎｃｅ社製、タイプＣ−７５０）３．０ｇをＫＥＹＥＮＣＥ社製ハイブリッドミキサーＨＭ５００を用いて、公転２０００ｒｐｍ、自転８００ｒｐｍで６０分処理することにより、薄層黒鉛の平均大きさが１．９μｍ、平均厚さ４．５ｎｍ、酸化度７．１ａｔ％の薄層黒鉛Ｃを得た。薄層黒鉛Ｂ、ＣともにＣ、Ｏ、Ｈ以外の異種元素は測定限界未満であった。
[Production Example 2] (Method for producing thin-layer graphite by physical treatment)
Graphite (manufactured by XGscience, type M-5) (3.0 g) is placed in a 50 ml capacity SUS container of a mixer mill MM100 manufactured by Lecce Co., Ltd., a 10 mm diameter SUS ball is placed, stirred for 10 minutes and allowed to stand for 2 minutes. Repeatedly, thin-layer graphite B having an average size of thin-layer graphite of 4.9 μm, an average thickness of 8.3 nm, and an oxidation degree of 10.7 at% was obtained. In addition, 3.0 g of graphite (manufactured by XGscience, type C-750) is treated with a hybrid mixer HM500 manufactured by KEYENCE for 60 minutes at a revolution of 2000 rpm and a rotation of 800 rpm, so that the average size of the thin-layer graphite is 1.9 μm. A thin-layer graphite C having an average thickness of 4.5 nm and an oxidation degree of 7.1 at% was obtained. In both the thin-layer graphites B and C, different elements other than C, O and H were less than the measurement limit.
［実施例１］
製造例２で得た薄層黒鉛Ｃを１．１５ｇと溶媒可溶性ポリマーとしてポリビニルブチラール（軟化点温度１８１℃、以下、ＰＶＢ）３．２５ｇをＮ−メチル−２−ピロリドン（以下、ＮＭＰ）１１．７ｍｌ中に分散させた混合液とを、株式会社レッチェミキサーミルＭＭ１００の容量５０ｍｌのＳＵＳ容器に入れ、直径５ｍｍのＳＵＳボール１０個入れて、４５分処理し、薄層黒鉛混合分散液Ｃ（ＰＶＢに対する薄層黒鉛含有量：１５体積％；薄層黒鉛Ｃの比重２．０、ＰＶＢの比重１．０として算出）を得た。また同様の方法により、製造例２で得た薄層黒鉛Ｂを０．７２ｇ、また０．３４ｇ（それぞれＰＶＢは３．２５ｇ）をそれぞれ用いて、薄層黒鉛混合分散液Ｂ１（ＰＶＢに対する薄層黒鉛含有量：１０体積％；薄層黒鉛Ｂの比重２．０として算出）、およびＢ２（ＰＶＢに対する薄層黒鉛含有量：５体積％）をそれぞれ得た。
[Example 1]
1.15 g of the thin-layer graphite C obtained in Production Example 2 and 3.25 g of polyvinyl butyral (softening temperature 181 ° C., hereinafter, PVB) as a solvent-soluble polymer are added to N-methyl-2-pyrrolidone (hereinafter, NMP) 11. The mixed liquid dispersed in 7 ml is put into a 50 ml SUS container of Lecce Mixer Mill MM100, 10 SUS balls having a diameter of 5 mm, treated for 45 minutes, and mixed with a thin layer graphite mixed dispersion C (PVB Content of thin layer graphite: 15% by volume; calculated as specific gravity of thin layer graphite C 2.0 and specific gravity of PVB 1.0). Further, by the same method, 0.72 g and 0.34 g (each PVB is 3.25 g) of the thin-layer graphite B obtained in Production Example 2 are used, respectively, and the thin-layer graphite mixed dispersion B1 (thin layer with respect to PVB) is used. Graphite content: 10% by volume; calculated as specific gravity of thin layer graphite B of 2.0) and B2 (thin layer graphite content with respect to PVB: 5% by volume) were obtained.
電磁波吸収体を得る際に、前記得られた混合分散液Ｃ、Ｂ１、Ｂ２を用いて、福田金属箔粉社製３３μｍ厚の圧延銅箔（基板）上に、コーティングテスター社製マルチアプリケーターを用いて塗布した。マルチアプリケーターは乾燥後の厚みが３０ないし４０μｍとなるように、クリアランスを調節し、塗工速度は５０ｍｍ／分で動かした。そして各層に必要な厚みとなるように複数回塗布と乾燥を繰り返して、各層を形成した。すなわち、混合分散液Ｃを用いた塗布および乾燥を５回繰り返し、基板上に乾燥後の厚みが１５０μｍになるようにア層を形成した。次にア層の上に、混合分散液Ｂ１を用いた塗布および乾燥を１０回繰り返し、乾燥後の厚みが３００μｍになるようにイ層を積層した。次いでイ層の上に、混合分散液Ｂ２を用いた塗布および乾燥を１４回繰り返し、乾燥後の厚みが７００μｍになるようにウ層を積層して、電磁波吸収層の厚み１１４１μｍ、電磁波吸収体としての総厚み１１７４μｍとなるシート状の電磁波吸収体を得た。なお各層を塗布積層する間の乾燥は１３０℃で３０分間、窒素雰囲気下で行った。電磁波吸収性能を測定したところ、２５０ＧＨｚおよび２９０ＧＨｚに大きな吸収ピークを有する、２５ｄＢ以上の吸収量が連続する帯域幅が８０ＧＨｚもの広帯域に対応する電磁波吸収体が得られた。該電磁波吸収体は表面が極めて平滑なシート状の電磁波吸収体であり、電磁波吸収層に空隙は全く見られなかった。 When obtaining an electromagnetic wave absorber, a multi-applicator manufactured by Coating Tester Co., Ltd. is used on a 33 μm-thick rolled copper foil (substrate) manufactured by Fukuda Metal Foil Powder Co., Ltd. using the obtained mixed dispersions C, B1, B2. And applied. The clearance of the multi-applicator was adjusted so that the thickness after drying was 30 to 40 μm, and the coating speed was moved at 50 mm / min. And each layer was formed by repeating application | coating and drying several times so that it might become thickness required for each layer. That is, coating and drying using the mixed dispersion C were repeated 5 times, and an a layer was formed on the substrate so that the thickness after drying was 150 μm. Next, coating and drying using the mixed dispersion B1 were repeated 10 times on the layer A, and the layer A was laminated so that the thickness after drying was 300 μm. Next, coating and drying using the mixed dispersion B2 are repeated 14 times on the layer A, and the layer U is laminated so that the thickness after drying becomes 700 μm, and the electromagnetic wave absorbing layer has a thickness of 1141 μm and an electromagnetic wave absorber. A sheet-like electromagnetic wave absorber having a total thickness of 1174 μm was obtained. In addition, the drying during coating and laminating each layer was performed at 130 ° C. for 30 minutes in a nitrogen atmosphere. When the electromagnetic wave absorption performance was measured, an electromagnetic wave absorber having a large absorption peak at 250 GHz and 290 GHz and a bandwidth with a continuous bandwidth of 25 dB or more corresponding to a wide band of 80 GHz was obtained. The electromagnetic wave absorber was a sheet-like electromagnetic wave absorber having an extremely smooth surface, and no void was found in the electromagnetic wave absorbing layer.
［実施例２］
熱可塑性ポリマーとして日本ポリプロ株式会社製ポリプロピレン（タイプ ノバテックＰＰ ＭＡ３、融点１６２℃、以下ＰＰ）を用いて、このペレットを５０℃１０時間真空乾燥した後、２軸エクストルーダを用いて、溶融したＰＰに窒素雰囲気下で製造例１において得られた薄層黒鉛Ａと製造例２で得られた薄層黒鉛Ｃをそれぞれ３０体積％、１８体積％となるように添加／混練した後、吐出されたガットを水道水で冷却したのちカッターで切断して混練ペレットＡ，混練ペレットＣを得た。混練ペレットを５０℃１０時間真空乾燥した後、１９０℃の加熱プレスで混練ペレットＡを使ったものは５．０ｍｍ(Ａ層）、混練ペレットＣを使ったものは２．５ｍｍ（Ｃ層）の厚さにプレスしてシート状の電磁波吸収層を得た。そして該シート状の電磁波吸収層を５０℃１０時間真空乾燥した後、これらを重ねて、ＳＵＳ平板上で１７０℃で５分間加熱して結合して平板状の電磁波吸収帯を得た。該シート状の電磁波吸収帯に、混練ペレットＣを用いたシートの面にマグネトロンＲＦスパッタ装置を用いて、銅からなる厚み０．５μｍの電磁波を反射する基材層を設けて、総厚み７５００．５μｍの表面が極めて平滑な電磁波吸収体を得た。電磁波吸収性能を測定したところ、３２ＧＨｚ、５０ＧＨｚ、６９ＧＨｚに大きな吸収ピークを有する、２２ＧＨｚ以上１００ＧＨｚの周波数帯（測定上限が１００ＧＨｚ）で２５ｄＢ以上の吸収量が連続する帯域幅が７８ＧＨｚ以上の広帯域に対応する電磁波吸収体が得られた。
[Example 2]
Using a polypropylene (type Novatec PP MA3, melting point 162 ° C., hereinafter referred to as PP) manufactured by Nippon Polypro Co., Ltd. as a thermoplastic polymer, the pellets were vacuum-dried at 50 ° C. for 10 hours, and then melted into PP using a biaxial extruder. After adding / kneading the thin-layer graphite A obtained in Production Example 1 and the thin-layer graphite C obtained in Production Example 2 to 30% by volume and 18% by volume, respectively, in a nitrogen atmosphere, the discharged gut After cooling with tap water, it was cut with a cutter to obtain kneaded pellets A and C. After the kneaded pellets were vacuum-dried at 50 ° C. for 10 hours, the one using the kneaded pellets A with a 190 ° C. hot press was 5.0 mm (A layer), and the one using the kneaded pellets C was 2.5 mm (C layer). The sheet was pressed to a thickness to obtain a sheet-like electromagnetic wave absorbing layer. The sheet-like electromagnetic wave absorbing layer was vacuum-dried at 50 ° C. for 10 hours, and then stacked, and heated and bonded on a SUS flat plate at 170 ° C. for 5 minutes to obtain a flat electromagnetic wave absorbing band. In the sheet-like electromagnetic wave absorption band, a base layer that reflects an electromagnetic wave having a thickness of 0.5 μm made of copper is provided on the surface of the sheet using the kneaded pellets C using a magnetron RF sputtering apparatus, and the total thickness is 7500. An electromagnetic wave absorber having an extremely smooth surface of 5 μm was obtained. When the electromagnetic wave absorption performance is measured, it has a large absorption peak at 32 GHz, 50 GHz, and 69 GHz, and supports a wide band with an absorption amount of 25 dB or more in a frequency band of 22 GHz or more and 100 GHz (measurement upper limit is 100 GHz) of 78 GHz or more. An electromagnetic wave absorber was obtained.
［実施例３］
熱可塑性ポリマーとして実施例２のＰＰを用いて、このペレットを５０℃１０時間真空乾燥した後、２軸エクストルーダを用いて、溶融したＰＰに窒素雰囲気下で製造例２において得られた薄層黒鉛Ｂを１５体積％となるように添加／混練した後、吐出されたガットを水道水で冷却したのちカッターで切断して混練ペレットＢを得た。該混練ペレットＢを５０℃１０時間真空乾燥した後、１９０℃の加熱プレスで１．０ｍｍの厚さにプレスしながら３０分保持して、厚み方向に薄層黒鉛の濃度が連続的に変化している（上部から下部に徐々に薄層黒鉛の濃度が高くなり、密度勾配が形成されている）シート状の電磁波吸収帯を得た。該電磁波吸収帯のプレス時に下面だった面にマグネトロンＲＦスパッタ装置を用いて、銅からなる厚み０．５μｍの電磁波を反射する基材層を設けて、総厚み１０００．５μｍの表面が極めて平滑な電磁波吸収体を得た。電磁波吸収性能を測定したところ、２４ＧＨｚ、４２ＧＨｚ、５８ＧＨｚに大きな吸収ピークを有する、２１ＧＨｚ以上１００ＧＨｚの周波数帯（測定上限が１００ＧＨｚ）で２５ｄＢ以上の吸収量が連続する帯域幅が７９ＧＨｚ以上の広帯域に対応する電磁波吸収体が得られた。
[Example 3]
Using the PP of Example 2 as the thermoplastic polymer, the pellets were vacuum-dried at 50 ° C. for 10 hours, and then the thin-layer graphite obtained in Production Example 2 was melted into the melted PP under a nitrogen atmosphere using a biaxial extruder. After adding / kneading B to 15% by volume, the discharged gut was cooled with tap water and then cut with a cutter to obtain kneaded pellets B. The kneaded pellets B were vacuum dried at 50 ° C. for 10 hours, and then held for 30 minutes while being pressed to a thickness of 1.0 mm with a heating press at 190 ° C., and the concentration of the thin graphite layer continuously changed in the thickness direction. A sheet-like electromagnetic wave absorption band was obtained (the density of the thin-layer graphite gradually increased from the upper part to the lower part, forming a density gradient). Using a magnetron RF sputtering apparatus on the surface that was the lower surface during pressing of the electromagnetic wave absorption band, a base material layer made of copper that reflects electromagnetic waves having a thickness of 0.5 μm is provided, and the surface having a total thickness of 1000.5 μm is extremely smooth. An electromagnetic wave absorber was obtained. When the electromagnetic wave absorption performance is measured, it has a large absorption peak at 24 GHz, 42 GHz, and 58 GHz, and it corresponds to a wide band of 79 GHz or more with a continuous bandwidth of 25 dB or more in a frequency band of 21 GHz or more and 100 GHz (upper limit of measurement is 100 GHz). An electromagnetic wave absorber was obtained.
［比較例１］
黒鉛（ＸＧｓｃｉｅｎｃｅ社製、タイプＭ−５）を１．１５ｇとポリビニルブチラール（以下、ＰＶＢ）３．２５ｇをＮ−メチル−２−ピロリドン（以下、ＮＭＰ）１１．７ｍｌ中に分散させた混合液とをヒールッシャー製超音波ホモジナイザー（タイプＵＰ４００Ｓ−Ｔ）で、６０Ｗ，１時間処理し、薄層黒鉛混合分散液（樹脂に対する薄層黒鉛含有量：１０体積％）を得た。該分散液を実施例１と同様の方法により銅箔上に塗布したところ、塗布斑が頻発し、表面がざらざらかつ部分的に凹凸を有する膜厚均質性の劣る電磁波吸収体を得た。電磁波吸収層内部には多数の空隙が見られた。また電磁波吸収性能も低いものであった。
[Comparative Example 1]
A mixed liquid in which 1.15 g of graphite (XGscience, type M-5) and 3.25 g of polyvinyl butyral (hereinafter referred to as PVB) are dispersed in 11.7 ml of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) Was treated with a Heelscher ultrasonic homogenizer (type UP400S-T) at 60 W for 1 hour to obtain a thin-layer graphite mixed dispersion (thin-layer graphite content with respect to resin: 10% by volume). When the dispersion was applied onto a copper foil by the same method as in Example 1, an application of frequent application spots, an electromagnetic wave absorber having poor surface uniformity with rough surfaces and irregularities was obtained. Many voids were observed inside the electromagnetic wave absorbing layer. The electromagnetic wave absorption performance was also low.
［比較例２］
参考例１で得た薄層黒鉛Ａを１．１５ｇとポリビニルブチラール（以下、ＰＶＢ）３．２５ｇをＮ−メチル−２−ピロリドン（以下、ＮＭＰ）１１．７ｍｌ中に分散させた混合液とを、株式会社レッチェミキサーミルＭＭ１００の容量５０ｍｌのＳＵＳ容器に入れ、直径５ｍｍのＳＵＳボール１０個入れて、４５分処理し、薄層黒鉛分散液Ａ（ＰＶＢに対する薄層黒鉛含有量：１５体積％；薄層黒鉛Ａの比重２．０、ＰＶＢの比重１．０として算出）を得た。得られた薄層黒鉛分散液Ａを福田金属箔粉社製３３μｍ厚の圧延銅箔（基盤）上に、コーティングテスター社製マルチアプリケーターを用いて塗布した。マルチアプリケーターは乾燥後の厚みが３０ないし４０μｍとなるように、クリアランスを調節し、塗工速度は５０ｍｍ／分で動かした。これにより厚み３４μｍの電磁波吸収帯を有するシート状の電磁波吸収体を得た。電磁波吸収層に空隙は全く見られなかったが２５ｄＢ以上の電磁波吸収量を示す連続する帯域幅が０．９ＧＨｚ分であり電磁波吸収帯域が狭いものであった。
[Comparative Example 2]
1.15 g of the thin-layer graphite A obtained in Reference Example 1 and a mixed liquid in which 3.25 g of polyvinyl butyral (hereinafter referred to as PVB) was dispersed in 11.7 ml of N-methyl-2-pyrrolidone (hereinafter referred to as NMP). , Put into a 50 ml capacity SUS container of Lecce Mixer Mill MM100, put 10 SUS balls with a diameter of 5 mm, treat for 45 minutes, and thin layer graphite dispersion A (thin layer graphite content with respect to PVB: 15% by volume; The specific gravity of thin layer graphite A was calculated as 2.0 and the specific gravity of PVB was calculated as 1.0. The obtained thin-layer graphite dispersion A was applied onto a 33 μm-thick rolled copper foil (substrate) manufactured by Fukuda Metal Foil Powder Co., Ltd. using a multi-applicator manufactured by Coating Tester. The clearance of the multi-applicator was adjusted so that the thickness after drying was 30 to 40 μm, and the coating speed was moved at 50 mm / min. As a result, a sheet-like electromagnetic wave absorber having an electromagnetic wave absorption band with a thickness of 34 μm was obtained. Although no gap was found in the electromagnetic wave absorption layer, the continuous bandwidth showing an electromagnetic wave absorption amount of 25 dB or more was 0.9 GHz, and the electromagnetic wave absorption band was narrow.
［比較例３］
実施例３において１９０℃の加熱プレスを行ってシート状の電磁波吸収帯を得る際に、３分保持した以外は実施例３と同様の手法により厚み１．０ｍｍの電磁波吸収帯を有する電磁波吸収体を得た。該電磁波吸収帯は厚み方向に均質な薄層黒鉛分散構造を１層形成するのみで、電磁波吸収層に空隙は全く見られなかったが２５ｄＢ以上の電磁波吸収量を示す連続する帯域幅が０．９ＧＨｚ分であり電磁波吸収帯域が狭いものであった。
[Comparative Example 3]
An electromagnetic wave absorber having an electromagnetic wave absorption band having a thickness of 1.0 mm in the same manner as in Example 3 except that the sheet-like electromagnetic wave absorption band was obtained by performing a heat press at 190 ° C. in Example 3 and held for 3 minutes. Got. The electromagnetic wave absorption band only forms one layer of a thin graphite dispersed structure that is homogeneous in the thickness direction, and no void was found in the electromagnetic wave absorption layer, but the continuous bandwidth showing an electromagnetic wave absorption amount of 25 dB or more is 0. The band was 9 GHz and the electromagnetic wave absorption band was narrow.
本発明の電磁波吸収体は、現在あるいは将来的に、情報量の多いＧＨｚ帯電磁波向けの障害となりうる不要電磁波を高性能で吸収する電磁波吸収体として、コンピューターの無線通信や携帯電話等の情報通信機器分野、自動料金収受システム（ＥＴＣ）や車載レーダーに代表される高度道路交通システム（ＩＴＳ）、高精細ハイビジョン放送など幅広い用途において優れた性能や機能を十分に発現しうる。 The electromagnetic wave absorber of the present invention is an electromagnetic wave absorber that absorbs unnecessary electromagnetic waves with high performance that can be a hindrance for GHz band electromagnetic waves with a large amount of information now or in the future. Excellent performance and functions can be fully expressed in a wide range of applications such as equipment fields, automatic toll collection systems (ETC), intelligent road traffic systems (ITS) represented by in-vehicle radar, and high-definition high-definition broadcasting.
１：電磁波を反射する基板
２〜４：電磁波吸収層
５：電磁波吸収帯
６：電磁波吸収体
1: Substrate 2-4 for reflecting electromagnetic waves: Electromagnetic wave absorption layer 5: Electromagnetic wave absorption band 6: Electromagnetic wave absorber
本発明は、上記の課題を解決するため、以下の構成を採用するものである。
（１）平板状の電磁波吸収帯を備える電磁波吸収体であって、前記電磁波吸収帯は、薄層黒鉛を含有するとともに、厚み方向に電磁波吸収性能の不均一性を有するものである、
電磁波吸収体。
（２）前記電磁波吸収帯が、２層以上の電磁波吸収層から構成されるとともに、前記電磁波吸収帯における電磁波吸収性能の不均一性が、吸収対象周波数の相違する２層以上の電磁波吸収層を備えることにより発現するものである、前記（１）に記載の電磁波吸収体。
（３）前記対象吸収周波数の相違は、各電磁波吸収層に含有される薄層黒鉛の酸化度の相違により発現するものである、前記（２）に記載の電磁波吸収体。
（４）前記電磁波吸収帯の電磁波吸収性能の不均一性が、該電磁波吸収帯の厚み方向に、連続的な電磁波吸収性能の変化を有することにより発現するものである、前記（１）に記載の電磁波吸収体。
（５）前記連続的な電磁波吸収性能の変化が、前記電磁波吸収帯の厚み方向の、薄層黒鉛の密度変化により発現するものである、前記（４）に記載の電磁波吸収体。
（６）シート状の形状を有する、（１）〜（５）のいずれかに記載の電磁波吸収体。
（７）前記電磁波吸収帯が、１０％以下の空隙率を有する、前記（１）〜（６）のいずれかに記載の電磁波吸収体。
（８）前記電磁波吸収層が、さらにポリマーを含有する、前記（２）〜（７）のいずれかに記載の電磁波吸収体。
（９）前記電磁波吸収帯が、さらにポリマーを含有する、前記（１）〜（８）のいずれかに記載の電磁波吸収体。
（１０）さらに、電磁波を反射する基板を有し、前記電磁波吸収帯が、前記基板上に設けられている、前記（１）〜（９）のいずれかに記載の電磁波吸収体。
（１１）電磁波吸収性能測定により得られた吸収スペクトルにおいて、１ＧＨｚ以上の周波数帯域で、２５ｄＢ以上の電磁波吸収性能を有する周波数が１ＧＨｚ以上の帯域にわたり連続する、前記（１）〜（１０）のいずれかに記載の電磁波吸収体。
（１２）平板状の電磁波吸収帯を備える電磁波吸収体の製造方法であって、対象吸収周波数が相違する、２層以上の、薄層黒鉛を含有する電磁波吸収層を積層することで、前記電磁波吸収帯を形成するステップを有する電磁波吸収体の製造方法。
（１３）前記対象吸収周波数の相違は、各電磁波吸収層が含有する薄層黒鉛の密度または該薄層黒鉛の酸化度の相違により発現するものである、前記（１２）に記載の電磁波吸収体の製造方法。
（１４）さらに、積層した電磁波吸収層同士を結合させて、厚み方向に連続的な電磁波吸収性能の変化を有する電磁波吸収帯を形成するステップを有する、前記（１２）または（１３）に記載の電磁波吸収体の製造方法。
（１５）前記２層以上の、薄層黒鉛を含有する電磁波吸収層が、熱可塑性ポリマーを含有するものであり、前記電磁波吸収層同士の結合が、前記熱可塑性ポリマーの融点または軟化点温度以上に加熱することによる溶融結合により行われるものである、前記（１４）に記載の電磁波吸収体の製造方法。
（１６）平板状の電磁波吸収帯を備える電磁波吸収体の製造方法であって、熱可塑性ポリマーを含有する電磁波吸収帯を１層に形成した後、前記熱可塑性ポリマーの軟化点温度以上の温度で加熱し、電磁波吸収帯の厚み方向に連続的な電磁波吸収性能の変化を付与せしめるステップを有する電磁波吸収体の製造方法。
The present invention employs the following configuration in order to solve the above problems.
(1) An electromagnetic wave absorber comprising a flat electromagnetic wave absorption band, wherein the electromagnetic wave absorption band contains thin-layer graphite and has non-uniformity in electromagnetic wave absorption performance in the thickness direction.
Electromagnetic wave absorber.
(2) The electromagnetic wave absorption band is composed of two or more electromagnetic wave absorption layers, and the non-uniformity of the electromagnetic wave absorption performance in the electromagnetic wave absorption band includes two or more electromagnetic wave absorption layers having different absorption target frequencies. The electromagnetic wave absorber according to (1), which is expressed by providing the electromagnetic wave absorber.
(3) The electromagnetic wave absorber according to (2), wherein the difference in the target absorption frequency is manifested by a difference in the degree of oxidation of the thin graphite contained in each electromagnetic wave absorption layer.
(4) The non-uniformity of the electromagnetic wave absorption performance of the electromagnetic wave absorption band is manifested by having a continuous change in the electromagnetic wave absorption performance in the thickness direction of the electromagnetic wave absorption band. Electromagnetic wave absorber.
(5) The electromagnetic wave absorber according to (4), wherein the continuous change in electromagnetic wave absorption performance is manifested by a change in density of thin-layer graphite in the thickness direction of the electromagnetic wave absorption band.
(6) The electromagnetic wave absorber according to any one of (1) to (5), which has a sheet-like shape.
(7) The electromagnetic wave absorber according to any one of (1) to (6), wherein the electromagnetic wave absorption band has a porosity of 10% or less.
(8) The electromagnetic wave absorber according to any one of (2) to (7), wherein the electromagnetic wave absorption layer further contains a polymer.
(9) The electromagnetic wave absorber according to any one of (1) to (8), wherein the electromagnetic wave absorption band further contains a polymer.
(10) The electromagnetic wave absorber according to any one of (1) to (9), further including a substrate that reflects electromagnetic waves, wherein the electromagnetic wave absorption band is provided on the substrate.
(11) In any of the above (1) to (10), in the absorption spectrum obtained by the electromagnetic wave absorption performance measurement, a frequency having an electromagnetic wave absorption performance of 25 dB or more is continuous over a band of 1 GHz or more in a frequency band of 1 GHz or more. The electromagnetic wave absorber according to crab.
(12) A method for producing an electromagnetic wave absorber having a flat electromagnetic wave absorption band, wherein the electromagnetic wave is laminated by laminating two or more electromagnetic wave absorbing layers containing thin graphite layers having different target absorption frequencies. A method for producing an electromagnetic wave absorber comprising a step of forming an absorption band.
(13) The electromagnetic wave absorber according to (12), wherein the difference in the target absorption frequency is expressed by the difference in density of the thin graphite contained in each electromagnetic wave absorption layer or the degree of oxidation of the thin graphite. Manufacturing method.
(14) The method according to (12) or (13), further including a step of bonding the laminated electromagnetic wave absorption layers to form an electromagnetic wave absorption band having a continuous change in electromagnetic wave absorption performance in the thickness direction. Manufacturing method of electromagnetic wave absorber.
(15) The electromagnetic wave absorbing layer containing two or more layers and containing thin-layer graphite contains a thermoplastic polymer, and a bond between the electromagnetic wave absorbing layers is equal to or higher than a melting point or a softening point temperature of the thermoplastic polymer. The method for producing an electromagnetic wave absorber according to (14), wherein the method is performed by melt bonding by heating to a temperature.
(16) In the method of the electromagnetic wave absorber comprising a plate-shaped electromagnetic wave absorption band, the electromagnetic wave absorption band containing a thermoplastic polymer after forming the first layer, with the thermoplastic softening point temperature or higher of the polymer A method for producing an electromagnetic wave absorber, comprising a step of heating and imparting a continuous change in electromagnetic wave absorption performance in the thickness direction of the electromagnetic wave absorption band.
Claims (16)
前記電磁波吸収帯は、薄層黒鉛を含有するとともに、厚み方向に電磁波吸収性能の不均一性を有するものである、
電磁波吸収体。 An electromagnetic wave absorber comprising a flat electromagnetic wave absorption band,
The electromagnetic wave absorption band contains thin-layer graphite and has non-uniformity of electromagnetic wave absorption performance in the thickness direction.
Electromagnetic wave absorber.
前記電磁波吸収帯における電磁波吸収性能の不均一性が、吸収対象周波数の相違する２層以上の電磁波吸収層を備えることにより発現するものである、
請求項１に記載の電磁波吸収体。 The electromagnetic wave absorption band is composed of two or more electromagnetic wave absorption layers,
The non-uniformity of the electromagnetic wave absorption performance in the electromagnetic wave absorption band is manifested by including two or more electromagnetic wave absorption layers having different absorption target frequencies.
The electromagnetic wave absorber according to claim 1.
請求項２に記載の電磁波吸収体。 The difference in the target absorption frequency is expressed by the difference in the degree of oxidation of the thin-layer graphite contained in each electromagnetic wave absorption layer.
The electromagnetic wave absorber according to claim 2.
請求項１に記載の電磁波吸収体。 Non-uniformity of the electromagnetic wave absorption performance of the electromagnetic wave absorption band is manifested by having a continuous change in electromagnetic wave absorption performance in the thickness direction of the electromagnetic wave absorption band.
The electromagnetic wave absorber according to claim 1.
請求項１〜６のいずれかに記載の電磁波吸収体。 The electromagnetic wave absorption band has a porosity of 10% or less,
The electromagnetic wave absorber in any one of Claims 1-6.
前記電磁波吸収帯が、前記基板上に設けられている、
請求項１〜９のいずれかに記載の電磁波吸収体。 Furthermore, it has a substrate that reflects electromagnetic waves,
The electromagnetic wave absorption band is provided on the substrate;
The electromagnetic wave absorber in any one of Claims 1-9.
対象吸収周波数が相違する、２層以上の、薄層黒鉛を含有する電磁波吸収層を積層することで、前記電磁波吸収帯を形成するステップを有する
電磁波吸収体の製造方法。 An electromagnetic wave absorber manufacturing method comprising a flat electromagnetic wave absorption band,
The manufacturing method of the electromagnetic wave absorber which has the step which forms the said electromagnetic wave absorption zone | band by laminating | stacking the electromagnetic wave absorption layer containing the thin layer graphite of two or more layers from which object absorption frequency differs.
請求項１２に記載の電磁波吸収体の製造方法。 The difference in the target absorption frequency is manifested by the difference in the density of the thin-layer graphite contained in each electromagnetic wave absorption layer or the degree of oxidation of the thin-layer graphite.
The manufacturing method of the electromagnetic wave absorber of Claim 12.
前記電磁波吸収層同士の結合が、前記熱可塑性ポリマーの融点または軟化点温度以上に加熱することによる溶融結合により行われるものである、
請求項１４に記載の電磁波吸収体の製造方法。 The electromagnetic wave absorbing layer containing two or more layers and a thin layer graphite contains a thermoplastic polymer,
Bonding between the electromagnetic wave absorption layers is performed by melt bonding by heating above the melting point or softening point temperature of the thermoplastic polymer.
The manufacturing method of the electromagnetic wave absorber of Claim 14.
熱可塑性ポリマーを含有する電磁波吸収帯を１層に形成した後、前記熱可塑性ポリマーの軟化点温度以上の温度で加熱し、電磁波吸収帯の厚み方向に連続的な電磁波吸収性能の変化を付与せしめるステップを有する
電磁波吸収体の製造方法。 An electromagnetic wave absorber comprising a flat electromagnetic wave absorption band, a method for producing an electromagnetic wave absorber,
After forming an electromagnetic wave absorption band containing a thermoplastic polymer in one layer, it is heated at a temperature equal to or higher than the softening point temperature of the thermoplastic polymer to give a continuous change in electromagnetic wave absorption performance in the thickness direction of the electromagnetic wave absorption band. The manufacturing method of the electromagnetic wave absorber which has a step.
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| WO2018124131A1 (en) * | 2016-12-27 | 2018-07-05 | 関西ペイント株式会社 | Millimeter-wave-band electromagnetic wave absorption sheet and millimeter-wave-band electromagnetic wave absorption method |
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| JP2020038879A (en) * | 2018-09-03 | 2020-03-12 | リンテック株式会社 | Electromagnetic wave absorbing film and electromagnetic wave absorbing sheet |
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| CN114534701A (en) * | 2022-02-17 | 2022-05-27 | 成都飞机工业（集团）有限责任公司 | Impregnation liquid, impregnation liquid preparation method and honeycomb material |
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