JP2007180469A - Magnetic powder for radio wave absorber, its production process and radio wave absorber - Google Patents
Magnetic powder for radio wave absorber, its production process and radio wave absorber Download PDFInfo
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Abstract
Description
本発明は、１ＧＨｚ以上の高周波帯域で使用する電波吸収体に適したＺ型六方晶フェライトの粉体、およびその製造法、並びにその粉体を使用した電波吸収体に関する。 The present invention relates to a Z-type hexagonal ferrite powder suitable for a radio wave absorber used in a high frequency band of 1 GHz or more, a method for producing the same, and a radio wave absorber using the powder.
近年、情報通信技術の高度化に伴い、ＧＨｚ帯域の電波が種々の用途で使用されるようになってきた。例えば、携帯電話、無線ＬＡＮ、衛星放送、高度道路交通システム、ノンストップ自動料金徴収システム（ＥＴＣ）、自動車走行支援システム（ＡＨＳ）などが挙げられる。このように高周波域での電波利用形態が多様化すると、電子部品同士の干渉による故障、誤動作、機能不全などが懸念され、その対策が重要となってくる。その１つとして、電波吸収体を用いて不要な電波を吸収し、電波の反射および侵入を防ぐ方法が有効である。昨今、ＧＨｚ帯域用の電波吸収体は需要が増大しつつある。 In recent years, with the advancement of information communication technology, radio waves in the GHz band have been used for various purposes. For example, a mobile phone, wireless LAN, satellite broadcasting, intelligent road transportation system, non-stop automatic toll collection system (ETC), automobile driving support system (AHS), and the like can be given. Thus, when radio wave usage forms in a high frequency range are diversified, there is a concern about failure, malfunction, malfunction or the like due to interference between electronic components, and countermeasures are important. As one of them, a method of absorbing unnecessary radio waves using a radio wave absorber and preventing reflection and intrusion of radio waves is effective. Recently, the demand for radio wave absorbers for the GHz band is increasing.
従来、高周波帯域用の電波吸収体には、主としてフェライト等の酸化物系磁性材料が多く用いられている。フェライトの中でも、ＭＨｚ帯域では主としてスピネル系のものが使用されるが、ＧＨｚ以上の高周波帯域において優れた特性を発揮するものとしてＺ型六方晶フェライトが有望視されている。 Conventionally, oxide-based magnetic materials such as ferrite are often used for radio wave absorbers for high frequency bands. Among ferrites, spinel type is mainly used in the MHz band, but Z-type hexagonal ferrite is promising as a material that exhibits excellent characteristics in a high frequency band of GHz or higher.
スピネル型フェライトでは、Ｓｎｏｅｋの限界を破ることができないため、１ＧＨｚを超える高周波帯域での使用が難しい。
これに対し、Ｚ型六方晶フェライトは１ＧＨｚ以上での電波吸収特性が期待される。しかし、従来のＺ型六方晶フェライトの粉体では、十分に高い複素透磁率（虚数部μ''）を有する電波吸収体を得ることが必ずしも容易ではなく、電波吸収性能を一層顕著に改善する技術の確立が望まれている。
Since spinel ferrite cannot break the limit of Snoek, it is difficult to use in a high frequency band exceeding 1 GHz.
On the other hand, Z-type hexagonal ferrite is expected to have radio wave absorption characteristics at 1 GHz or higher. However, with a conventional Z-type hexagonal ferrite powder, it is not always easy to obtain a radio wave absorber having a sufficiently high complex permeability (imaginary part μ ″), and the radio wave absorption performance is significantly improved. Establishment of technology is desired.
複素透磁率の虚数部μ''を高めるには、使用する磁性粉体の粒子形状を、より薄い板状の形状にすることが効果的であると考えられる。Ｚ型六方晶フェライトは、立方晶の構造を有するスピネル型フェライトと比べると、その結晶構造上、粉砕などにより板状の粒子を得ることは容易である。しかし、μ''を十分に向上できるに足るだけの薄い板状粒子を得ることは難しい。 In order to increase the imaginary part μ ″ of the complex permeability, it is considered effective to make the particle shape of the magnetic powder to be used a thinner plate shape. Compared with spinel type ferrite having a cubic structure, Z-type hexagonal ferrite can easily obtain plate-like particles by pulverization or the like due to its crystal structure. However, it is difficult to obtain thin plate-like particles sufficient to sufficiently improve μ ″.
本発明はこのような現状に鑑み、薄い板状のＺ型六方晶フェライトの粒子を製造するための効率的な手法を開発し、１ＧＨｚ以上の高周波帯域における電波吸収性能の改善を図ることを目的とする。 In view of such a current situation, the present invention has developed an efficient method for producing thin plate-like Z-type hexagonal ferrite particles and aims to improve the radio wave absorption performance in a high frequency band of 1 GHz or more. And
発明者らは詳細な研究の結果、フラックス成分である金属塩化物を原料中に配合すると、薄い板状のＺ型六方晶フェライトの粉体を得る上で極めて有効であることを見出した。また、焼成体を粉砕する際に、粒子に負担をかけすぎると、薄い板状のＺ型六方晶フェライト粉体を得ることが却って難しくなることを突き止めた。そして、種々検討の結果、平均アスペクト比が４以上の粉体においてＧＨｚ帯域での電波吸収性能に大きな改善効果が見られることがわかった。本発明はこのような知見に基づいて完成したものである。 As a result of detailed studies, the inventors have found that when a metal chloride, which is a flux component, is blended in a raw material, it is extremely effective in obtaining a thin plate-like Z-type hexagonal ferrite powder. Further, it was found that it is difficult to obtain a thin plate-like Z-type hexagonal ferrite powder if the particles are overburdened when the sintered body is pulverized. As a result of various studies, it has been found that a large improvement effect is seen in the radio wave absorption performance in the GHz band in the powder having an average aspect ratio of 4 or more. The present invention has been completed based on such findings.
すなわち本発明では、下記Ａ成分、下記Ｍ成分およびＦｅと、酸素で構成され、Ｍ成分とＦｅのモル比を、Ｍ成分：Ｆｅ＝ｘ：２４とするとき、１.２≦ｘ≦２.５が成立する組成のＺ型六方晶フェライトの粉体であって、当該粉体を構成する前記Ｚ型六方晶フェライト粒子の平均アスペクト比が４以上である電波吸収体用磁性粉体が提供される。
ただし、Ａ成分はアルカリ土類金属元素およびＰｂの１種以上、Ｍ成分は２価のＦｅを除く金属元素の１種以上からなる。
That is, in the present invention, it is composed of the following A component, the following M component and Fe, and oxygen, and when the molar ratio of the M component to Fe is M component: Fe = x: 24, 1.2 ≦ x ≦ 2. A Z-type hexagonal ferrite powder having a composition satisfying 5 is provided, wherein the Z-type hexagonal ferrite particles constituting the powder have an average aspect ratio of 4 or more. The
However, A component consists of 1 or more types of an alkaline-earth metal element and Pb, and M component consists of 1 or more types of metal elements except bivalent Fe.
このＺ型六方晶フェライトは、組成式Ａ3Ｍ2Ｆｅ24Ｏ41（例えばＢａ3Ｃｏ2Ｆｅ24Ｏ41）で表されるＺ型六方晶フェライトと同様の結晶構造を有し、そのことはＸ線回折により確認することができる。ただし、Ｍ成分とＦｅのモル比は必ずしも２：２４になっている必要はなく、Ｍ成分：Ｆｅ＝ｘ：２４とするとき、１.２≦ｘ≦２.５の範囲で変動しうる。また、Ａ成分とＦｅのモル比も厳密に３：２４であるとは限らず多少の変動が許容される。同様にＦｅとＯ（酸素）のモル比も厳密に２４：４１であるとは限らず多少の変動が許容される。ただし、上記のとおり組成式Ａ3Ｍ2Ｆｅ24Ｏ41で表されるＺ型六方晶フェライトと同様の結晶構造をもつ。 This Z-type hexagonal ferrite has the same crystal structure as that of the Z-type hexagonal ferrite represented by the composition formula A 3 M 2 Fe 24 O 41 (for example, Ba 3 Co 2 Fe 24 O 41 ). It can be confirmed by X-ray diffraction. However, the molar ratio of the M component to Fe does not necessarily have to be 2:24. When the M component: Fe = x: 24, the molar ratio may vary within the range of 1.2 ≦ x ≦ 2.5. Further, the molar ratio of the component A and Fe is not strictly 3:24, and some variation is allowed. Similarly, the molar ratio of Fe to O (oxygen) is not strictly 24:41, and some variation is allowed. However, as described above, it has the same crystal structure as that of the Z-type hexagonal ferrite represented by the composition formula A 3 M 2 Fe 24 O 41 .
前記Ａ成分は例えばＳｒ、Ｂａ、ＣａおよびＰｂの１種以上である。また、前記Ｍ成分は例えば２価のＣｏ、Ｎｉ、Ｚｎ、Ｃｕ、Ｍｇ、Ｆｅ、Ｍｎおよび「１価のＬｉと３価のＦｅの組み合わせ」の１種以上である。「１価のＬｉと３価のＦｅの組み合わせ」は、１価のＬｉと３価のＦｅが１：１の原子比で含まれる場合である。この場合、例えばＭ成分として１価のＬｉと３価のＦｅを１：１の原子比で含み、さらに上記２価の金属の１種以上を含むことによってＭ成分を構成することができる。Ｍ成分に含まれる３価のＦｅは、前記のモル比「Ｍ成分：Ｆｅ＝ｘ：２４」においてＭ成分も元素として扱われる。 The A component is, for example, one or more of Sr, Ba, Ca, and Pb. The M component is, for example, one or more of divalent Co, Ni, Zn, Cu, Mg, Fe, Mn, and “a combination of monovalent Li and trivalent Fe”. The “combination of monovalent Li and trivalent Fe” is a case where monovalent Li and trivalent Fe are contained at an atomic ratio of 1: 1. In this case, for example, the M component can be configured by containing monovalent Li and trivalent Fe in a 1: 1 atomic ratio as the M component, and further including one or more of the above divalent metals. The trivalent Fe contained in the M component is also treated as an element in the molar ratio “M component: Fe = x: 24”.
より具体的なＺ型六方晶フェライトの構成として、以下のものが挙げられる。
［１］前記Ａ成分がＢａからなり、前記Ｍ成分がＮｉおよびＺｎからなるもの。
［２］前記Ａ成分がＢａからなり、前記Ｍ成分がＣｏからなるもの。
［３］前記Ａ成分がＢａからなり、前記Ｍ成分がＣｏおよびＺｎからなるもの。
The following is mentioned as a more specific structure of Z-type hexagonal ferrite.
[1] The A component is made of Ba, and the M component is made of Ni and Zn.
[2] The A component is made of Ba and the M component is made of Co.
[3] The A component is made of Ba, and the M component is made of Co and Zn.
本発明の磁性粉体には、Ｚ型六方晶フェライト相の他、製造段階で不可避的に混入しうる不純物相の存在が許容される。 In addition to the Z-type hexagonal ferrite phase, the magnetic powder of the present invention allows the presence of an impurity phase that can be inevitably mixed in the production stage.
アスペクト比は粒子の長軸径と短軸径（板状体の厚さ）の比である。平均アスペクト比は個々の粒子について測定されるアスペクト比の値を平均したものであるが、これは、後述の方法により当該粉末粒子の中から任意に選んだ５０個以上の粒子についてアスペクト比を測定し、その値を平均することによって求めることができる。 The aspect ratio is the ratio of the major axis diameter to the minor axis diameter (plate thickness) of the particles. The average aspect ratio is the average of the aspect ratio values measured for individual particles. This is the measurement of the aspect ratio for 50 or more particles arbitrarily selected from the powder particles by the method described later. And it can obtain | require by averaging the value.
このような磁性粉末の製造法として、成分調整された原料の混合・造粒物を焼成して上記Ｚ型六方晶フェライトを生成させ、その焼成体を粉砕して粉体を得るに際し、原料に金属塩化物を配合すること、および焼成体の粉砕では平均アスペクト比４以上が維持される軽度の粉砕を行うことを特徴とする電波吸収体用磁性粉体の製造法が提供される。特に、焼成体の粉砕はハンマーミルによる衝撃粉砕により、あるいはハンマーミルによる衝撃粉砕と湿式粉砕とにより、平均アスペクト比４以上に調整する手法が採用できる。
上記金属塩化物としては例えばＢａＣｌ2、ＳｒＣｌ2の１種以上を採用することができる。上記金属塩化物がＢａＣｌ2の場合、当該ＢａＣｌ2を除く配合原料（主原料）１００質量部に対し、ＢａＣｌ2の配合量を１〜１０質量部となるように調整することができる。
As a method of producing such a magnetic powder, the mixed and granulated product of raw materials adjusted in ingredients is fired to produce the Z-type hexagonal ferrite, and the fired body is pulverized to obtain a powder. There is provided a method for producing a magnetic powder for a radio wave absorber, characterized in that a metal chloride is blended, and the pulverization of the fired body is performed with a mild pulverization maintaining an average aspect ratio of 4 or more. Particularly, the pulverization of the fired body may be performed by adjusting the average aspect ratio to 4 or more by impact pulverization using a hammer mill, or by impact pulverization using a hammer mill and wet pulverization.
As the metal chloride, for example, one or more of BaCl 2 and SrCl 2 can be employed. The metal case of chloride of BaCl 2, with respect to mixed material (main raw material) 100 parts by weight, excluding the BaCl 2, it is possible to adjust the amount of BaCl 2 so that 1 to 10 parts by weight.
ここで、「成分調整された原料」とは、上記組成式のＺ型六方晶フェライトが合成されるように原料物質を配合して、Ａ成分、Ｍ成分、およびＦｅのモル比が調整されているものを意味する。ハンマーミルは、脆性材料にハンマーによる衝撃を加えることにより当該脆性材料を破砕するタイプの粉砕機である。湿式粉砕は、被粉砕材料を液体中に懸濁させ、スラリーの状態で機械的に粉砕する手法である。 Here, the “component-adjusted raw material” means that the raw material is blended so that the Z-type hexagonal ferrite of the above composition formula is synthesized, and the molar ratio of the A component, the M component, and Fe is adjusted. Means what A hammer mill is a type of pulverizer that crushes a brittle material by applying impact to the brittle material with a hammer. The wet pulverization is a technique in which a material to be pulverized is suspended in a liquid and mechanically pulverized in a slurry state.
また本発明では、前記のＺ型六方晶フェライトで構成される粉体を用いた電波吸収体が提供される。特に、Ｚ型六方晶フェライトの粉体は高分子基材中に混ぜ込んだ電波吸収体が提供される。 The present invention also provides a radio wave absorber using a powder composed of the Z-type hexagonal ferrite. In particular, a radio wave absorber in which a Z-type hexagonal ferrite powder is mixed in a polymer base material is provided.
本発明によれば、従来、安定して製造することが困難であった薄い板状のＺ型六方晶フェライト粒子からなる粉体が提供された。この粉体を用いた電波吸収体では、１ＧＨｚ以上の高周波領域において複素透磁率の虚数部μ''を顕著に向上させることができ、従来の製法で得られた同じ組成のＺ型六方晶フェライトと比較すると、より薄い肉厚の電波吸収体において、同等以上の電波吸収性能を得ることができる。すなわち、電波吸収体シートの薄肉化が可能になる。 According to the present invention, there has been provided a powder composed of thin plate-like Z-type hexagonal ferrite particles that has been difficult to manufacture stably. In the radio wave absorber using this powder, the imaginary part μ ″ of the complex permeability can be remarkably improved in a high frequency region of 1 GHz or higher, and the Z-type hexagonal ferrite of the same composition obtained by the conventional manufacturing method. Compared with, a thinner and thicker wave absorber can obtain equal or better radio wave absorption performance. That is, it is possible to reduce the thickness of the radio wave absorber sheet.
〔組成〕
本発明では、Ａ成分、Ｍ成分およびＦｅと、酸素で構成され、Ｍ成分とＦｅのモル比を、Ｍ成分：Ｆｅ＝ｘ：２４とするとき、１.２≦ｘ≦２.５が成立する組成のＺ型六方晶フェライトを採用する。Ａ成分、Ｍ成分については上述のとおりである。
〔composition〕
In the present invention, it is composed of A component, M component, Fe, and oxygen, and when the molar ratio of M component to Fe is M component: Fe = x: 24, 1.2 ≦ x ≦ 2.5 is established. Z-type hexagonal ferrite having the composition is adopted. The A component and the M component are as described above.
〔粒子形状〕
Ｚ型六方晶フェライト粉体を構成する粒子は、その形状ができるだけ「薄い板状」であることが、電波吸収体において１ＧＨｚ以上での複素透磁率の虚数部μ''を向上させるうえで有効である。発明者らの詳細な検討の結果、平均アスペクト比が４以上の粉体を使用することによって、同じ減衰量を得るために必要な電波吸収体の肉厚が大幅に低減される。すなわち電波吸収体シートの顕著な薄肉化が可能になる。平均アスペクト比５以上が一層好ましい。あまりアスペクト比が大きくなると、高分子基材中への分散性が低下する等の不都合が生じやすくなるので、平均アスペクト比は２０以下の範囲とすればよい。通常、平均アスペクト比１５以下の範囲で良好な結果が得られる。なお、長軸径による平均粒径は２〜５０μｍの範囲が好ましく、３〜２０μｍが一層好ましい。
(Particle shape)
It is effective for improving the imaginary part μ '' of the complex permeability at 1 GHz or more in the radio wave absorber that the shape of the Z-type hexagonal ferrite powder is as thin as possible. It is. As a result of detailed investigations by the inventors, the use of powder having an average aspect ratio of 4 or more greatly reduces the thickness of the radio wave absorber necessary for obtaining the same attenuation. That is, the wave absorber sheet can be significantly thinned. An average aspect ratio of 5 or more is more preferable. If the aspect ratio becomes too large, inconveniences such as a decrease in dispersibility in the polymer base material tend to occur, so the average aspect ratio may be in the range of 20 or less. In general, good results are obtained when the average aspect ratio is 15 or less. In addition, the average particle diameter by a major axis diameter has the preferable range of 2-50 micrometers, and 3-20 micrometers is still more preferable.
上記平均アスペクト比は以下のような方法で求めることができる。すなわち、ＦＥ−ＳＥＭ（電界放射型走査電子顕微鏡）を用いて粉体中のランダムに選んだ粒子について、試料ステージを回転・傾動させて、粒子の長軸が観察方向に対して垂直となる画像、および短軸（厚さ方向）が観察方向 に対して垂直となる画像を採取し、それらの画像から、それぞれ当該粒子の長軸径および短軸径（厚さ）を測定し、長軸径／短軸径の値をその粒子のアスペクト比とする。そして、ランダムに選んだ５０個以上の粒子についてのアスペクト比を算術平均することにより、当該粉体の平均アスペクト比を求める。 The average aspect ratio can be obtained by the following method. That is, for a randomly selected particle in powder using an FE-SEM (field emission scanning electron microscope), the sample stage is rotated and tilted so that the long axis of the particle is perpendicular to the observation direction. And images with the minor axis (thickness direction) perpendicular to the observation direction, and from these images, the major axis diameter and minor axis diameter (thickness) of the particles are measured, respectively. / The value of the minor axis diameter is defined as the aspect ratio of the particle. Then, the average aspect ratio of the powder is obtained by arithmetically averaging the aspect ratios of 50 or more randomly selected particles.
〔製造法〕
本発明のＺ型六方晶フェライトからなる粉体は、焼成過程までは従来一般的なソフトフェライトの製造法に準じて行うことができる。すなわち、Ａ成分、Ｍ成分、Ｆｅが所定の割合で含まれるように金属酸化物や金属塩（例えば炭酸塩）などの原料を配合し、混合、造粒したのち、これを焼成することにより前記組成のＺ型六方晶フェライトを合成することができる。焼成温度は概ね１２００〜１３００℃、焼成雰囲気は大気、焼成時間は１〜４ｈ程度とすればよい。
[Production method]
The powder comprising the Z-type hexagonal ferrite of the present invention can be carried out in accordance with a conventional method for producing soft ferrite until the firing process. That is, by mixing raw materials such as metal oxide and metal salt (for example, carbonate) so that A component, M component, and Fe are included in a predetermined ratio, mixing, granulating, and then firing the above, Z-type hexagonal ferrite having a composition can be synthesized. The firing temperature is approximately 1200 to 1300 ° C., the firing atmosphere is air, and the firing time is about 1 to 4 hours.
ただし、その原料として、金属塩化物を配合することが極めて有効である。発明者らの研究によれば、金属塩化物はフラックス成分として働くとともに、焼成過程において六方晶構造の結晶が成長する際、六方晶のａ軸およびｂ軸方向の粒成長が活発化すると考えられる。すなわち焼成段階で従来よりａ軸（またはｂ軸）とｃ軸との長さの比が一層大きい結晶粒が得られるものと考えられる。このような相対的に薄い形状の結晶粒からなる焼成体の構造が、粉砕時においてアスペクト比の大きい粒子の形成に大きく寄与していると推察される。
金属塩化物としては例えばＢａＣｌ2、ＳｒＣｌ2を挙げることができる。これらは単独で配合することもできるし、複合で配合することもできる。金属塩化物としてＢａＣｌ2を単独で配合する場合、その配合量は、当該ＢａＣｌ2を除く配合原料全体に対する質量比で概ね１〜１０質量％の範囲で調整することが好ましい。３質量％以下でも効果がある。Ａ成分にＢａを含む組成のＺ型六方晶フェライトを作る場合は、このＢａＣｌ2以外の主原料でＡ成分のＢａを賄うように秤量すればよい。
However, it is very effective to mix metal chloride as the raw material. According to the studies by the inventors, metal chloride acts as a flux component, and when hexagonal crystals grow in the firing process, it is considered that grain growth in the hexagonal a-axis and b-axis directions is activated. . That is, it is considered that crystal grains having a larger ratio of the length of the a-axis (or b-axis) and the c-axis than in the past can be obtained in the firing stage. It is inferred that such a structure of a fired body composed of relatively thin crystal grains greatly contributes to the formation of particles having a large aspect ratio during pulverization.
Examples of the metal chloride include BaCl 2 and SrCl 2 . These can be blended singly or in combination. When BaCl 2 is blended alone as a metal chloride, the blending amount is preferably adjusted within a range of approximately 1 to 10% by mass with respect to the entire blending raw material excluding the BaCl 2 . Even if it is 3% by mass or less, it is effective. When making a Z-type hexagonal ferrite having a composition containing Ba in the A component, the main raw material other than the BaCl 2 may be weighed to cover the A component Ba.
通常のソフトフェライトの製造においては、焼成後に、焼成体を粉砕して所定の粒度を有する粉体が製造されている。本発明の磁性粉体を得る場合も、焼成体を粉砕することが必要である。ただし、粉砕において粒子にあまり大きな負荷を与えると、アスペクト比が低下することがわかった。したがって、本発明の磁性粉体を得るためには、過度な粉砕を行わないようにすることが有効である。具体的には、焼成体をハンマーミルによる衝撃粉砕に供することにより平均アスペクト比を４以上に調整するか、あるいは焼成体をハンマーミルによる衝撃粉砕と湿式粉砕に供することにより平均アスペクト比を４以上に調整する手法が採用できる。上述のように原料に金属塩化物を配合して得た焼成体は相対的に薄い板状の結晶粒をもつ構造を有しており、この形状をなるべく崩さないように、上記のような粉砕方法により平均アスペクト比の大きい粉体を得ることができるものと推察される。
なお、湿式粉砕にはアトライター、遊星ボールミル等の粉砕機が使用できる。
In normal soft ferrite production, after firing, the fired body is pulverized to produce a powder having a predetermined particle size. Even when obtaining the magnetic powder of the present invention, it is necessary to grind the fired body. However, it was found that if the particle was subjected to a very large load during grinding, the aspect ratio decreased. Therefore, in order to obtain the magnetic powder of the present invention, it is effective not to perform excessive pulverization. Specifically, the average aspect ratio is adjusted to 4 or more by subjecting the fired body to impact grinding with a hammer mill, or the average aspect ratio is 4 or more by subjecting the fired body to impact grinding and wet grinding with a hammer mill. It is possible to adopt a method of adjusting to As described above, the fired body obtained by blending the metal chloride with the raw material has a structure having relatively thin plate-like crystal grains, and the above-mentioned pulverization is performed so as not to break this shape as much as possible. It is presumed that a powder having a large average aspect ratio can be obtained by this method.
For wet pulverization, a pulverizer such as an attritor or a planetary ball mill can be used.
〔電波吸収体〕
得られたＺ型六方晶フェライトの粉体は、高分子基材とともに混練することにより電波吸収体素材（混練物）が得られる。混練物中におけるＺ型六方晶フェライト粉体の配合量は６０質量％以上とすることが好ましい。ただし９５質量％を超えると高分子基材との混練が難しくなる。Ｚ型六方晶フェライト粉体の混合割合は８０〜９５質量％とすることがより好ましく、８５〜９５質量％が一層好ましい。
[Radio wave absorber]
The obtained Z-type hexagonal ferrite powder is kneaded with a polymer base material to obtain a radio wave absorber material (kneaded material). The blending amount of the Z-type hexagonal ferrite powder in the kneaded product is preferably 60% by mass or more. However, if it exceeds 95% by mass, kneading with the polymer substrate becomes difficult. The mixing ratio of the Z-type hexagonal ferrite powder is more preferably 80 to 95% by mass, and still more preferably 85 to 95% by mass.
高分子基材としては、使用環境に応じて、耐熱性、難燃性、耐久性、機械的強度、電気的特性を満足する各種のものが使用できる。例えば、樹脂（ナイロン等）、ゲル（シリコーンゲル等）、熱可塑性エラストマー、ゴムなどから適切なものを選択すれば良い。また２種以上の高分子化合物をブレンドして基材としてもよい。 As the polymer substrate, various materials satisfying heat resistance, flame retardancy, durability, mechanical strength, and electrical characteristics can be used depending on the use environment. For example, an appropriate material may be selected from resin (nylon or the like), gel (silicone gel or the like), thermoplastic elastomer, rubber or the like. Two or more polymer compounds may be blended to form a base material.
高分子基材との相溶性や分散性を改善するために、Ｚ型六方晶フェライト粉体には予め表面処理剤（シランカップリング剤、チタネートカップリング剤等）による表面処理を施すことができる。また、Ｚ型六方晶フェライト粉体と高分子基材との混合に際し、可塑剤、補強剤、耐熱向上剤、熱伝導性充填剤、粘着剤などの各種添加剤を添加することができる。 In order to improve the compatibility and dispersibility with the polymer base material, the Z-type hexagonal ferrite powder can be subjected to surface treatment with a surface treatment agent (such as a silane coupling agent or a titanate coupling agent) in advance. . In addition, when the Z-type hexagonal ferrite powder and the polymer base material are mixed, various additives such as a plasticizer, a reinforcing agent, a heat resistance improver, a heat conductive filler, and an adhesive can be added.
上記電波吸収体素材（混練物）を圧延により所定のシート厚に成形することで電波吸収体が得られる。また、圧延の代わりに混練物を射出成形することにより所望の電波吸収体形状に成形することもできる。あるいは、Ｚ型六方晶フェライト粉体を直接塗料中に分散させて、基体表面に塗布することにより、塗膜としての電波吸収体を形成することもできる。 A radio wave absorber can be obtained by forming the above radio wave absorber material (kneaded material) into a predetermined sheet thickness by rolling. Moreover, it can also shape | mold into a desired electromagnetic wave absorber shape by carrying out injection molding of the kneaded material instead of rolling. Alternatively, the electromagnetic wave absorber as a coating film can be formed by dispersing the Z-type hexagonal ferrite powder directly in the coating material and applying it to the surface of the substrate.
各実施例および比較例において、下記の工程Ａ〜ＣのいずれかによりＺ型六方晶フェライトの磁性粉末を製造した。
［工程Ａ］秤量→混合→造粒→乾燥→焼成→粗粉砕（ハンマーミル）→湿式粉砕
［工程Ｂ］秤量→混合→造粒→乾燥→焼成→粗粉砕（ハンマーミル）
［工程Ｃ］秤量→混合→造粒→乾燥→焼成→粗粉砕（ハンマーミル）→乾式粉砕
In each example and comparative example, magnetic powder of Z-type hexagonal ferrite was produced by any of the following steps A to C.
[Step A] Weighing → Mixing → Granulation → Drying → Firing → Rough grinding (hammer mill) → Wet grinding [Step B] Weighing → Mixing → Granulation → Drying → Firing → Rough grinding (Hammermill)
[Step C] Weighing → Mixing → Granulation → Drying → Firing → Coarse grinding (hammer mill) → Dry grinding
〔実施例１〕
原料としてＢａＣＯ3、ＮｉＯ、ＺｎＯ、α−Ｆｅ2Ｏ3と、フラックス機能を有するＢａＣｌ2を用い、ＢａＣｌ2を除く上記原料を表１に示す組成（実施例１ではモル比で、Ｂａ：Ｎｉ：Ｚｎ：Ｆｅ＝３：１：１：２）に対応する量比で秤量した。ＢａＣｌ2の配合量（原料全体に占める質量割合）は表１に示すとおりとした（実施例１では２.７質量％）。秤量された原料粉を用いて工程Ａにより粉体を作製した。具体的には、原料粉をハイスピードミキサーで混合したのち、更に振動ミルにより乾式法で混合強化する方法で混合した。得られた混合粉をペレット状に造粒成形し、この成形体をローラーハース型電気炉に装入し、大気中で表１に示す焼成温度で２ｈ保持することにより焼成した。得られた焼成品をハンマーミルで粗粉砕し、更にアトライター（溶媒：水）で５ｍｉｎ湿式粉砕することにより、磁性粉体を得た。
[Example 1]
Using BaCO 3 , NiO, ZnO, α-Fe 2 O 3 and BaCl 2 having a flux function as raw materials, the above raw materials excluding BaCl 2 are shown in Table 1 (in the molar ratio of Ba: Ni in Example 1). : Zn: Fe = 3: 1: 1: 2). The blending amount of BaCl 2 (mass ratio in the entire raw material) was as shown in Table 1 (2.7 mass% in Example 1). A powder was prepared by Step A using the weighed raw material powder. Specifically, the raw material powders were mixed by a high speed mixer and then mixed by a method of strengthening mixing by a dry method using a vibration mill. The obtained mixed powder was granulated and formed into pellets, and the formed body was placed in a roller hearth type electric furnace and fired in the air by holding at the firing temperature shown in Table 1 for 2 hours. The obtained fired product was roughly pulverized with a hammer mill, and further wet pulverized with an attritor (solvent: water) for 5 minutes to obtain a magnetic powder.
Ｘ線回折の結果、この磁性粉体はＺ型六方晶フェライトであることが確認された（以下の実施例、比較例において同様）。図１２に実施例１のＺ型六方晶フェライトについてのＸ線回折パターンを例示する。ここで、Ｘ線回折の測定条件は、管球：コバルト管球、Ｇｏｎｉｏｍｅｔｅｒ：Ｕｌｔｉｍａ＋水平ゴニオメータＩ型、Ａｔｔａｃｈｍｅｎｔ：ＡＳＣ−４３（縦型）、Ｍｏｎｏｃｈｒｏｍｅｔｅｒ：全自動モノクロメータ、ＳｃａｎｎｉｎｇＭｏｄｅ：２θ／θ、ＳｃａｎｎｉｎｇＴｙｐｅ：ＣＯＮＴＩＮＵＯＵＳ、Ｘ−Ｒａｙ：４０ｋＶ／３０ｍＡ、発散スリット：１／２ｄｅｇ.、散乱スリット：１／２ｄｅｇ.、受光スリット：０.１５ｍｍ、測定範囲：３０°〜７０°である。 As a result of X-ray diffraction, it was confirmed that the magnetic powder was Z-type hexagonal ferrite (the same applies to the following examples and comparative examples). FIG. 12 illustrates an X-ray diffraction pattern of the Z-type hexagonal ferrite of Example 1. Here, the measurement conditions of X-ray diffraction are as follows: tube: cobalt tube, Goniometer: Ultimate + horizontal goniometer type I, Attachment: ASC-43 (vertical type), Monochromator: fully automatic monochromator, Scanning Mode: 2θ / θ, ScanningType : CONTINUOUS, X-Ray: 40 kV / 30 mA, divergence slit: 1/2 deg., Scattering slit: 1/2 deg., Light receiving slit: 0.15 mm, measurement range: 30 ° to 70 °.
また、この磁性粉体について、ＦＥ−ＳＥＭ（（株）日立ハイテクノロジーズ製、電界放射型走査電子顕微鏡 Ｓ−４７００型）を用いて倍率２０００倍で前述の方法によりランダムに選んだ５０個の粒子の長軸径と短軸径を測定し、平均アスペクト比を求めた。その結果を表１に示してある（以下の実施例、比較例において同様）。 Moreover, about this magnetic powder, 50 particles randomly selected by the above-described method at a magnification of 2000 using an FE-SEM (manufactured by Hitachi High-Technologies Corporation, field emission scanning electron microscope S-4700 type). The major axis diameter and the minor axis diameter were measured, and the average aspect ratio was determined. The results are shown in Table 1 (the same applies to the following examples and comparative examples).
上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）の含有量が表１に示す割合（実施例１では８５質量％）となるように、当該粉体と高分子基材を混練して電波吸収体素材（混練物）を作製した。高分子基材としては合成ゴム（ＪＳＲ（日本合成ゴム）製、Ｎ２１５ＳＬ）を使用した。この電波吸収体素材を圧延ロールにより厚さ２.０ｍｍに圧延し、電波吸収体シートを得た。
このシートを後述の電波吸収特性の測定に供した。
The powder and the polymer group were adjusted so that the content of the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite) became the ratio shown in Table 1 (85% by mass in Example 1). The material was kneaded to prepare a radio wave absorber material (kneaded material). Synthetic rubber (JSR (Nippon Synthetic Rubber), N215SL) was used as the polymer substrate. The radio wave absorber material was rolled to a thickness of 2.0 mm with a rolling roll to obtain a radio wave absorber sheet.
This sheet was subjected to the measurement of the radio wave absorption characteristics described later.
〔実施例２、５〕
原料としてＢａＣＯ3、Ｃｏ3Ｏ4、α−Ｆｅ2Ｏ3と、フラックス機能を有するＢａＣｌ2を用い、ＢａＣｌ2を除く上記原料を表１に示す組成に対応する量比で秤量した。ＢａＣｌ2の配合量は表１に示すとおりとした。秤量された原料粉を用いて工程Ａにより実施例１と同様の条件で粉体を作製し、得られた粉体について実施例１と同様の方法で平均アスペクト比を求めた。上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）を用いて、磁性粉体の含有量が表１に示す割合となるように実施例１と同様の方法で電波吸収体シートを作製し、このシートを後述の電波吸収特性の測定に供した。
[Examples 2 and 5]
BaCO 3 , Co 3 O 4 , α-Fe 2 O 3 and BaCl 2 having a flux function were used as raw materials, and the above raw materials excluding BaCl 2 were weighed in a quantitative ratio corresponding to the composition shown in Table 1. The amount of BaCl 2 was as shown in Table 1. Using the weighed raw material powder, a powder was prepared in the same manner as in Example 1 by Step A, and the average aspect ratio of the obtained powder was determined in the same manner as in Example 1. Using the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite), radio wave absorption was performed in the same manner as in Example 1 so that the content of the magnetic powder became the ratio shown in Table 1. A body sheet was prepared, and this sheet was subjected to measurement of radio wave absorption characteristics described later.
〔実施例３、８、９、１１〕
原料粉として、ＢａＣＯ3、Ｃｏ3Ｏ4、ＺｎＯ、α−Ｆｅ2Ｏ3と、フラックス機能を有するＢａＣｌ2を用い、ＢａＣｌ2を除く上記原料を表１に示す組成に対応する量比で秤量した。ＢａＣｌ2の配合量は表１に示すとおりとした。秤量された原料粉を用いて工程Ｂにより、実施例１の粗粉砕までの工程と同様の条件にて粉体を作製し、得られた粉体について実施例１と同様の方法で平均アスペクト比を求めた。上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）を用いて、磁性粉体の含有量が表１に示す割合となるように実施例１と同様の方法で電波吸収体シートを作製し、このシートを後述の電波吸収特性の測定に供した。
[Examples 3, 8, 9, and 11]
BaCO 3 , Co 3 O 4 , ZnO, α-Fe 2 O 3 and BaCl 2 having a flux function are used as raw material powder, and the above raw materials excluding BaCl 2 are weighed in a quantitative ratio corresponding to the composition shown in Table 1. did. The amount of BaCl 2 was as shown in Table 1. Using the weighed raw material powder, a powder was produced by the process B under the same conditions as in the process up to the coarse pulverization in Example 1, and the average aspect ratio of the obtained powder was determined in the same manner as in Example 1. Asked. Using the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite), radio wave absorption was performed in the same manner as in Example 1 so that the content of the magnetic powder became the ratio shown in Table 1. A body sheet was prepared, and this sheet was subjected to measurement of radio wave absorption characteristics described later.
〔実施例４〕
実施例３と同じ組成となるように原料を秤量し、工程Ａにより実施例１と同様の条件にて粉体を作製し、得られた粉体について実施例１と同様の方法で平均アスペクト比を求めた。上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）を用いて、磁性粉体の含有量が表１に示す割合となるように実施例１と同様の方法で電波吸収体シートを作製し、このシートを後述の電波吸収特性の測定に供した。
Example 4
The raw materials were weighed so as to have the same composition as in Example 3, and a powder was prepared in the same manner as in Example 1 by Step A. The average aspect ratio of the obtained powder was determined in the same manner as in Example 1. Asked. Using the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite), radio wave absorption was performed in the same manner as in Example 1 so that the content of the magnetic powder became the ratio shown in Table 1. A body sheet was prepared, and this sheet was subjected to measurement of radio wave absorption characteristics described later.
〔実施例６、７、１０、比較例４〕
原料としてＢａＣＯ3、Ｃｏ3Ｏ4、α−Ｆｅ2Ｏ3と、フラックス機能を有するＢａＣｌ2を用い、ＢａＣｌ2を除く上記原料を表１に示す組成に対応する量比で秤量した。ＢａＣｌ2の配合量は表１に示すとおりとした。秤量された原料粉を用いて工程Ｂにより実施例３と同様の条件で粉体を作製し、得られた粉体について実施例１と同様の方法で平均アスペクト比を求めた。上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）を用いて、磁性粉体の含有量が表１に示す割合となるように実施例１と同様の方法で電波吸収体シートを作製し、このシートを後述の電波吸収特性の測定に供した。
[Examples 6, 7, and 10, Comparative Example 4]
BaCO 3 , Co 3 O 4 , α-Fe 2 O 3 and BaCl 2 having a flux function were used as raw materials, and the above raw materials excluding BaCl 2 were weighed in a quantitative ratio corresponding to the composition shown in Table 1. The amount of BaCl 2 was as shown in Table 1. Using the weighed raw material powder, a powder was produced in the same manner as in Example 3 in Step B, and the average aspect ratio of the obtained powder was determined in the same manner as in Example 1. Using the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite), radio wave absorption was performed in the same manner as in Example 1 so that the content of the magnetic powder became the ratio shown in Table 1. A body sheet was prepared, and this sheet was subjected to measurement of radio wave absorption characteristics described later.
〔比較例１〕
実施例１と同じ組成となるように原料を秤量し、工程Ａにより実施例１と同様の条件にて粉体を作製した。ただし、原料にはフラックス機能を有するＢａＣｌ2を配合しなかった。得られた粉体について実施例１と同様の方法で平均アスペクト比を求めた。上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）を用いて、磁性粉体の含有量が表１に示す割合となるように実施例１と同様の方法で電波吸収体シートを作製し、このシートを後述の電波吸収特性の測定に供した。
[Comparative Example 1]
The raw materials were weighed so as to have the same composition as in Example 1, and powders were produced in the same manner as in Example 1 by Step A. However, BaCl 2 having a flux function was not blended in the raw material. The average aspect ratio of the obtained powder was determined in the same manner as in Example 1. Using the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite), radio wave absorption was performed in the same manner as in Example 1 so that the content of the magnetic powder became the ratio shown in Table 1. A body sheet was prepared, and this sheet was subjected to measurement of radio wave absorption characteristics described later.
〔比較例２〕
実施例２と同じ組成となるように原料を秤量し、工程Ｃにより粉体を作製した。ただし、原料にはフラックス機能を有するＢａＣｌ2を配合しなかった。工程Ｃでは、焼成までは実施例１（工程Ａ）と共通条件であるが、その後、焼成品をハンマーミルで粗粉砕したのち、さらに村上精機工作所製、３Ｌ−ＶＭ（型式はユーラスバイブレーターＫＥＣ−８−４）を用いて８ｍｉｎ乾式粉砕することにより粉砕工程を終了して、磁性粉体を得た。得られた粉体について実施例１と同様の方法で平均アスペクト比を求めた。上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）を用いて、磁性粉体の含有量が表１に示す割合となるように実施例１と同様の方法で電波吸収体シートを作製し、このシートを後述の電波吸収特性の測定に供した。
[Comparative Example 2]
The raw materials were weighed so as to have the same composition as in Example 2, and a powder was produced in Step C. However, BaCl 2 having a flux function was not blended in the raw material. In Step C, the conditions up to firing are the same as those in Example 1 (Step A). After that, the fired product is roughly pulverized with a hammer mill, and then 3L-VM (model is Eurus Vibrator KEC) manufactured by Murakami Seiki Kogakusho. Using -8-4), the pulverization step was completed by dry pulverization for 8 minutes to obtain a magnetic powder. The average aspect ratio of the obtained powder was determined in the same manner as in Example 1. Using the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite), radio wave absorption was performed in the same manner as in Example 1 so that the content of the magnetic powder became the ratio shown in Table 1. A body sheet was prepared, and this sheet was subjected to measurement of radio wave absorption characteristics described later.
〔比較例３〕
実施例３と同じ組成となるように原料を秤量し、工程Ｃにより粉体を作製した。ただし、原料にはフラックス機能を有するＢａＣｌ2を配合しなかった。工程Ｃの製造条件は、焼成温度を１２９０℃にしたこと以外、比較例２と同様とした。得られた粉体について実施例１と同様の方法で平均アスペクト比を求めた。上記粉砕後の磁性粉体（Ｚ型六方晶フェライトで構成される粉体）を用いて、磁性粉体の含有量が表１に示す割合となるように実施例１と同様の方法で電波吸収体シートを作製し、このシートを後述の電波吸収特性の測定に供した。
[Comparative Example 3]
The raw materials were weighed so as to have the same composition as in Example 3, and a powder was produced in Step C. However, BaCl 2 having a flux function was not blended in the raw material. The manufacturing conditions in Step C were the same as those in Comparative Example 2 except that the firing temperature was 1290 ° C. The average aspect ratio of the obtained powder was determined in the same manner as in Example 1. Using the pulverized magnetic powder (powder composed of Z-type hexagonal ferrite), radio wave absorption was performed in the same manner as in Example 1 so that the content of the magnetic powder became the ratio shown in Table 1. A body sheet was prepared, and this sheet was subjected to measurement of radio wave absorption characteristics described later.
〔電波吸収特性の評価〕
得られた電波吸収体シートについてＳパラメーター法により電波吸収特性を調べた。シートから切り出した小片を外径７ｍｍ、内径３ｍｍの円筒状測定ピースに成形し、これをφ７ｍｍ×φ３.０４ｍｍの同軸管に挿入し、同軸管の端をショートホルダーで短絡し、ネットワークアナライザー（ヒュレットパッカード社製、ＨＰ８７２０Ｄ）を用いて１〜２０ＧＨｚにおける反射・透過係数（Ｓパラメーター）を測定した。
[Evaluation of radio wave absorption characteristics]
The obtained radio wave absorber sheet was examined for radio wave absorption characteristics by the S parameter method. A small piece cut out from the sheet is formed into a cylindrical measuring piece having an outer diameter of 7 mm and an inner diameter of 3 mm, inserted into a φ7 mm × φ3.04 mm coaxial tube, and the end of the coaxial tube is short-circuited with a short holder. The reflection / transmission coefficient (S parameter) at 1 to 20 GHz was measured using HP 8720D manufactured by Ret Packard.
図１〜８、１４〜２０に、各実施例、比較例のシートについて測定した複素透磁率の実数部μ'と虚数部μ''の周波数依存性を示す。Ｚ型六方晶フェライトの組成が同じであれば、複素透磁率の虚数部μ''が最も向上する周波数域もほぼ同じになる。しかし、実施例のものは、比較例のものよりμ''の極大値が大きく向上している（図１と図５の対比、図２と図６の対比、図３、４と図７の対比）。 1 to 8 and 14 to 20 show the frequency dependence of the real part μ ′ and the imaginary part μ ″ of the complex permeability measured for the sheets of the examples and comparative examples. If the composition of the Z-type hexagonal ferrite is the same, the frequency range in which the imaginary part μ ″ of the complex permeability is most improved is almost the same. However, in the example, the maximum value of μ ″ is greatly improved as compared with the comparative example (the comparison between FIGS. 1 and 5, the comparison between FIGS. 2 and 6, the comparison between FIGS. 3, 4 and 7). Contrast).
μ''が極大となる付近の周波数（実施例１、比較例１では１５ＧＨｚ、実施例２、比較例２では４ＧＨｚ、実施例３、４、８〜１１、比較例３では２.５ＧＨｚ、実施例５〜７、１０、比較例４では３ＧＨｚ）について、上記のＳパラメーターを基に、電波吸収体シートのシート厚（ｍｍ）と電波の減衰量（ｄＢ）の関係をシミュレートした。その結果を図９〜１１、１３に示す。縦軸の減衰量は、上記測定で得られた反射量（Ｓ１１）を用い、試料をホルダーに装入した場合の反射量から、試料を装入しない場合の反射量を引いた値（反射減衰量）である。 The frequency near the maximum of μ ″ (Example 1, Comparative Example 1 is 15 GHz, Example 2, Comparative Example 2 is 4 GHz, Examples 3, 4, 8 to 11 and Comparative Example 3 is 2.5 GHz. For Examples 5 to 7, 10 and 3 GHz in Comparative Example 4, the relationship between the sheet thickness (mm) of the radio wave absorber sheet and the radio wave attenuation (dB) was simulated based on the S parameter. The results are shown in FIGS. The amount of attenuation on the vertical axis is the value obtained by subtracting the amount of reflection when the sample is not loaded from the amount of reflection when the sample is loaded in the holder, using the amount of reflection (S11) obtained in the above measurement (reflection attenuation). Amount).
表１に各例における組成、製造条件、粉体の長軸径による平均粒径、短軸径による平均粒径、平均アスペクト比、電波吸収体シートにおける粉体含有量、およびシミュレーション結果をまとめて示した。 Table 1 summarizes the composition, production conditions, average particle diameter by the major axis diameter, average particle diameter by the minor axis diameter, average aspect ratio, powder content in the radio wave absorber sheet, and simulation results in each example. Indicated.
表１中、シミュレーション結果の「シート厚」は、図９〜１１、１３のそれぞれのデータを基に、同じ減衰量（「評価減衰量」という）を得るのに必要なシート厚を表示したものである。 In Table 1, “Sheet Thickness” as a simulation result is a sheet thickness necessary for obtaining the same attenuation amount (referred to as “evaluation attenuation amount”) based on the data of FIGS. 9 to 11 and 13. It is.
比較例１は原料にフラックスとして機能するＢａＣｌ2を配合しなかったことにより実施例１の粉体より平均アスペクト比が大幅に小さかった。１５ＧＨｚ域で減衰量２０ｄＢ以上を得るのに必要なシート厚は、実施例１で１.３ｍｍであるのに対し、比較例１では１.６ｍｍを要する。 In Comparative Example 1, the average aspect ratio was significantly smaller than that of the powder of Example 1 because BaCl 2 functioning as a flux was not added to the raw material. The sheet thickness required to obtain an attenuation of 20 dB or more in the 15 GHz region is 1.3 mm in Example 1, but 1.6 mm in Comparative Example 1.
比較例２は原料にＢａＣｌ2を配合しなかったこと、および粉体に対する負荷の大きい乾式粉砕で仕上げたことにより、実施例２よりも粉体の平均アスペクト比が大幅に小さくなった。４ＧＨｚ域で減衰量１５ｄＢ以上を得るのに必要なシート厚は、実施例２で２.７ｍｍであるのに対し、比較例２では４.２ｍｍを要する。 In Comparative Example 2, the average aspect ratio of the powder was significantly smaller than that of Example 2 because BaCl 2 was not blended in the raw material and finished by dry pulverization with a large load on the powder. The sheet thickness required to obtain an attenuation of 15 dB or more in the 4 GHz region is 2.7 mm in Example 2, while 4.2 mm is required in Comparative Example 2.
比較例３も原料にＢａＣｌ2を配合しなかったこと、および粉体に対する負荷の大きい乾式粉砕で仕上げたことにより、実施例３、４よりも粉体の平均アスペクト比が大幅に小さくなった。２.５ＧＨｚ域で減衰量１５ｄＢ以上を得るのに必要なシート厚は、実施例３で２.８ｍｍ、実施例４で２.９ｍｍであるのに対し、比較例３では４.１ｍｍを要する。 In Comparative Example 3 as well, the average aspect ratio of the powder was significantly smaller than that of Examples 3 and 4 because BaCl 2 was not blended in the raw material and was finished by dry pulverization with a large load on the powder. The sheet thickness required to obtain an attenuation of 15 dB or more in the 2.5 GHz region is 2.8 mm in Example 3 and 2.9 mm in Example 4, whereas 4.1 mm is required in Comparative Example 3.
比較例４は、ＢａＣｌ2を配合し、工程Ｂにより粉体を製造したが、Ｍ成分のモル比（ｘ）が小さすぎたことにより粉体の平均アスペクト比を４以上とすることができなかった。その結果、実施例５、６、７、１０と比べ３ＧＨｚ域での減衰量が小さくなり、減衰量２０ｄＢ以上が得られるシート厚は存在しなかった。 In Comparative Example 4, BaCl 2 was blended and a powder was produced by Step B. However, the average aspect ratio of the powder could not be 4 or more because the molar ratio (x) of the M component was too small. It was. As a result, the amount of attenuation in the 3 GHz region was smaller than in Examples 5, 6, 7, and 10, and there was no sheet thickness that yielded an attenuation of 20 dB or more.
これに対し、本発明例である各実施例の粉体は平均アスペクト比が４以上を満足し、例えば１５ＧＨｚ域においてシート厚１.５ｍｍ以下で減衰量２０ｄＢ以上が得られる粉体、４ＧＨｚ域においてシート厚３ｍｍ以下で減衰量１５ｄＢ以上が得られる粉体、２.５ＧＨｚ域においてシート厚３ｍｍ以下あるいは３.５ｍｍ以下で減衰量１５ｄＢ以上が得られる粉体、３ＧＨｚ域においてシート厚３ｍｍ以下あるいは３.５ｍｍ以下で減衰量２０ｄＢ以上が得られる粉体を実現することができ、実用性の高い電波吸収体を構築することが可能になる。 On the other hand, the powder of each example which is an example of the present invention satisfies an average aspect ratio of 4 or more, for example, a powder capable of obtaining an attenuation of 20 dB or more at a sheet thickness of 1.5 mm or less in a 15 GHz region, in a 4 GHz region. Powder with an attenuation of 15 dB or more when the sheet thickness is 3 mm or less, Powder with an attenuation of 15 dB or more when the sheet thickness is 3 mm or less or 3.5 mm or less in the 2.5 GHz region, or Sheet thickness of 3 mm or less or 3 in the 3 GHz region. A powder capable of obtaining an attenuation of 20 dB or more at 5 mm or less can be realized, and a highly practical radio wave absorber can be constructed.
Claims (12)
ただし、Ａ成分はアルカリ土類金属元素およびＰｂの１種以上、Ｍ成分は２価のＦｅを除く金属元素の１種以上からなる。 A composition comprising the following A component, the following M component, Fe, and oxygen, and satisfying 1.2 ≦ x ≦ 2.5 when the molar ratio of the M component to Fe is M component: Fe = x: 24 A Z-type hexagonal ferrite powder, wherein the Z-type hexagonal ferrite particles constituting the powder have an average aspect ratio of 4 or more.
However, A component consists of 1 or more types of an alkaline-earth metal element and Pb, and M component consists of 1 or more types of metal elements except bivalent Fe.
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| JP2016086112A (en) * | 2014-10-28 | 2016-05-19 | Tdk株式会社 | Hexagonal ferrite composite magnetic material, and high-frequency magnetic part arranged by use thereof |
| JPWO2020230680A1 (en) * | 2019-05-14 | 2020-11-19 |
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| WO2012060583A3 (en) * | 2010-11-01 | 2012-06-28 | (주)소노비젼 | Co2z type ferrite for high-frequency applications, a production method for the same and an antenna using the same |
| JP2016086112A (en) * | 2014-10-28 | 2016-05-19 | Tdk株式会社 | Hexagonal ferrite composite magnetic material, and high-frequency magnetic part arranged by use thereof |
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