JP2004281710A

JP2004281710A - Method for manufacturing magnetic anisotropic rare earth-based bonded magnet

Info

Publication number: JP2004281710A
Application number: JP2003071051A
Authority: JP
Inventors: Takeshi Nishiuchi; 武司西内
Original assignee: Neomax Co Ltd
Current assignee: Proterial Ltd
Priority date: 2003-03-14
Filing date: 2003-03-14
Publication date: 2004-10-07
Anticipated expiration: 2023-03-14
Also published as: JP4374874B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetic anisotropic rare earth-based bond magnet which is excellent in oxidation resistance and has high magnetic characteristics. <P>SOLUTION: As a method for forming an inorganic coat on the surface of the powder of the magnetic anisotropic rare earth-based bond magnet, inorganic material which is housed in a melting and evaporating part and which becomes the forming source of the inorganic coat is irradiated with a discharge plasma flow generated by the orthogonal magnetic field discharge of a double pressure gradient inside a vacuum treatment chamber to heat and evaporate the inorganic material to ionize for ion plating to form the inorganic coat on the surface of vibrated and/or agitated magnet powder. The method for manufacturing the magnetic anisotropic rare earth-based bonded magnet comprises a process for obtaining the magnet powder whose surface is coated with the inorganic coat 0.05μm to 2μm thick by the method of forming the inorganic coat, a process for preparing a compound for bonded magnet by mixing the obtained magnet powder coated with a metal coat and a resin binder, and a process for heat-molding the prepared compound in a prescribed shape while orienting it in a magnetic field. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、耐酸化性に優れるとともに高い磁気特性を有する磁気的異方性希土類系ボンド磁石の新規な製造方法に関する。
【０００２】
【従来の技術】
Ｎｄ−Ｆｅ−Ｂ系磁石粉末に代表されるＲ−Ｆｅ−Ｂ系磁石粉末などの希土類系磁石粉末を、バインダとして熱可塑性樹脂や熱硬化性樹脂などを用いて所定形状に加熱成形することで製造される希土類系ボンド磁石は、樹脂バインダを含有しているために希土類系焼結磁石に比較すれば磁気特性が低くなるものの、フェライト磁石などに比べればなお十分に高い磁気特性を有しており、また、複雑形状や薄肉形状の磁石やラジアル異方性磁石を容易に得ることができるといった希土類系焼結磁石にはない特徴を持っている。従って、希土類系ボンド磁石は、特にスピンドルモータやステッピングモータなどの小型モータに多く用いられ、近年、その需要が増加している。
中でも、例えば、所定の組成を有する希土類系磁石合金を水素中で加熱して水素を吸蔵させた後、脱水素処理し、次いで冷却してから粉砕することによって得られる、ＨＤＤＲ（Ｈｙｄｒｏｇｅｎａｔｉｏｎ−Ｄｉｓｐｒｏｐｏｒｔｉｏｎａｔｉｏｎ−Ｄｅｓｏｒｐｔｉｏｎ−Ｒｅｃｏｍｂｉｎａｔｉｏｎ）磁石粉末（特公平６−８２５７５号公報参照）などの磁気的異方性磁石粉末を用いて所定形状に加熱成形した磁気的異方性希土類系ボンド磁石は、高い磁気特性を有することから、これまで磁気的等方性希土類系ボンド磁石などが用いられていた製品への応用展開に注目が高まっている。
しかしながら、磁気的異方性希土類系ボンド磁石は高い磁気特性を有する反面、ボンド磁石を構成する磁石粉末の組成の大半をＲやＦｅが占めることから、腐食や酸化を起しやすいという問題がある。特に、ＨＤＤＲ磁石粉末は、酸化による磁気特性の低下が顕著な磁石粉末であり、ＨＤＤＲ磁石粉末と樹脂バインダを混練してボンド磁石用コンパウンドを調製し、調製されたコンパウンドを用いて磁界中で配向させながら射出成形などにより所定形状に加熱成形してボンド磁石を製造した場合、コンパウンド調製時や加熱成形時の高温環境下（通常１５０℃以上であり場合によっては２５０℃を超えることもある）において、ＨＤＤＲ磁石粉末が酸化することで高い磁気特性を有するボンド磁石が得られない場合がある。
【０００３】
以上のような問題を解決する方法としては、下記の特許文献１にて提案されているような、蒸着、スパッタリング、めっきなどにより、磁気的異方性を有するＲ−Ｆｅ−Ｂ系磁石合金の粉砕粉末の表面に金属被膜を形成し、金属被膜で表面被覆された磁石粉末を用いて希土類系ボンド磁石を製造する方法がある。この特許文献には、この方法の効果として磁石粉末の耐酸化性の向上が記載されており、また、磁石粉末の表面に金属被膜を形成した後、３００℃〜１０００℃の範囲で熱処理を施すことで、磁石粉末と金属被膜との密着性の向上を図ることができるとともに、被膜を構成する金属の磁石粉末への拡散による磁気特性の向上を図ることができるとされ、その実施例１では、磁石粉末の表面に蒸着によりアルミニウム被膜を形成し、次いで９００℃で１時間と６００℃で１時間の２段熱処理を施している。
下記の特許文献１に記載された方法は注目に値するものである。しかしながら、ＨＤＤＲ磁石粉末などのような、平均結晶粒径が１μｍ以下の微細な結晶粒を有する磁石粉末に対してこの特許文献に記載された方法に従ってその表面にアルミニウム被膜を形成し、９００℃や６００℃という高温での熱処理を施すと、磁石粉末の微細な結晶粒が粗大化することで磁気特性が低下するという問題がある。また、このような問題とともに、アルミニウム被膜が軟化や溶融することで磁石粉末の凝集が起こるという問題がある。ＨＤＤＲ磁石粉末のような磁気的異方性希土類系磁石粉末が凝集した場合、凝集体に含まれる磁石粉末の容易磁化方向はランダムであるので、このような凝集体と樹脂バインダを混練してボンド磁石用コンパウンドを調製し、調製されたコンパウンドを用いて磁界中で配向させながら射出成形などにより所定形状に加熱成形してボンド磁石としても、磁石粉末の容易磁化方向を磁界方向に十分に配向させることができないことで、高い磁気特性（特に減磁曲線の角型性）が得られない。また、磁石粉末と樹脂バインダを十分に混練できないことで、ボンド磁石として十分な成形性や機械的強度が得られない。もちろん、凝集体を解砕してもよいが、このような処理を行うと、磁石粉末の表面からのアルミニウム被膜の剥離が多少なりとも起こるので、ボンド磁石中における磁石粉末の酸化を防止するという本来的な目的を達することができなくなるという問題がある。また、アルミニウム被膜で表面被覆された磁石粉末に対して９００℃や６００℃という高温での熱処理を施した場合、磁石粉末へのアルミニウムの拡散が必要以上に起こることで磁気特性の低下を招くという問題がある。従って、下記の特許文献１に記載された方法では、耐酸化性に優れるとともに高い磁気特性を有する磁気的異方性希土類系ボンド磁石を製造することはできないと言わざるを得ない。
【０００４】
【特許文献１】
特開平３−２１７００３号公報
【０００５】
【発明が解決しようとする課題】
そこで本発明は、耐酸化性に優れるとともに高い磁気特性を有する磁気的異方性希土類系ボンド磁石の新規な製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者は上記の点に鑑みて種々の検討を行った結果、気相成長法によって磁気的異方性希土類系磁石粉末の表面に無機質被膜を形成するに際し、無機質被膜の形成源となる無機質材料の蒸発方法と被膜形成方法の最適化を図るとともに、無機質被膜の膜厚の適正化を図ることで、樹脂バインダと混練してボンド磁石用コンパウンドを調製し、調製されたコンパウンドを用いて磁界中で配向させながら射出成形などにより所定形状に加熱成形する際、容易磁化方向を磁界方向に十分に配向させることができる無機質被膜被覆磁石粉末を得ることができ、この無機質被膜被覆磁石粉末を用いることで、耐酸化性に優れるとともに高い磁気特性を有する磁気的異方性希土類系ボンド磁石を製造することができることを知見した。
【０００７】
上記の知見に基づいてなされた本発明の磁気的異方性希土類系ボンド磁石の製造方法は、請求項１記載の通り、磁気的異方性希土類系磁石粉末の表面に無機質被膜を形成する方法として、真空処理室の内部にて、二重圧力勾配型直交磁場放電により発生させた放電プラズマ流を、溶融蒸発部に収容した無機質被膜の形成源となる無機質材料に照射することで無機質材料を加熱蒸発させてイオン化し、イオンプレーティングを行うことにより、振動および／または攪拌させた磁石粉末の表面に無機質被膜を形成する方法を採用し、この方法で膜厚が０．０５μｍ〜２μｍの無機質被膜で表面被覆された磁石粉末を得る工程、得られた無機質被膜被覆磁石粉末と樹脂バインダを混練してボンド磁石用コンパウンドを調製する工程、調製されたコンパウンドを用いて磁界中で配向させながら所定形状に加熱成形する工程を含むことを特徴とする。
また、請求項２記載の製造方法は、請求項１記載の製造方法において、イオンプレーティングを行う際の真空処理室の内部のバックグラウンド真空度を１×１０^−３Ｐａ以下とすることを特徴とする。
また、請求項３記載の製造方法は、請求項１または２記載の製造方法において、無機質被膜が金属被膜であることを特徴とする。
また、請求項４記載の製造方法は、請求項３記載の製造方法において、金属被膜がアルミニウム被膜であることを特徴とする。
また、請求項５記載の製造方法は、請求項１記載の製造方法において、無機質被膜被覆磁石粉末中における無機質被膜の体積比率を３％以下とすることを特徴とする。
また、請求項６記載の製造方法は、請求項１乃至５のいずれかに記載の製造方法において、樹脂バインダが熱可塑性樹脂であることを特徴とする。
また、請求項７記載の製造方法は、請求項１乃至６のいずれかに記載の製造方法において、所定形状への加熱成形を射出成形、押出成形、ロール成形から選ばれるいずれか一つの方法で行うことを特徴とする。
また、請求項８記載の製造方法は、請求項１乃至７のいずれかに記載の製造方法において、磁気的異方性希土類系磁石粉末の平均粒径が５０μｍ〜１５０μｍであることを特徴とする。
また、請求項９記載の製造方法は、請求項８記載の製造方法において、磁気的異方性希土類系磁石粉末の平均結晶粒径が１μｍ以下であることを特徴とする。
また、請求項１０記載の製造方法は、請求項８または９記載の製造方法において、磁気的異方性希土類系磁石粉末がＨＤＤＲ磁石粉末であることを特徴とする。
また、本発明の磁気的異方性希土類系ボンド磁石は、請求項１１記載の通り、請求項１記載の製造方法によって製造されてなることを特徴とする。
また、本発明の無機質被膜被覆磁石粉末の製造方法は、請求項１２記載の通り、磁気的異方性希土類系磁石粉末の表面に無機質被膜を形成する方法として、真空処理室の内部にて、二重圧力勾配型直交磁場放電により発生させた放電プラズマ流を、溶融蒸発部に収容した無機質被膜の形成源となる無機質材料に照射することで無機質材料を加熱蒸発させてイオン化し、イオンプレーティングを行うことにより、振動および／または攪拌させた磁石粉末の表面に無機質被膜を形成する方法を採用し、この方法で膜厚が０．０５μｍ〜２μｍの無機質被膜で表面被覆された磁石粉末を得る工程を含むことを特徴とする。
また、本発明の無機質被膜被覆磁石粉末は、請求項１３記載の通り、請求項１２記載の製造方法によって製造されてなることを特徴とする。
また、本発明のボンド磁石用コンパウンドの製造方法は、請求項１４記載の通り、磁気的異方性希土類系磁石粉末の表面に無機質被膜を形成する方法として、真空処理室の内部にて、二重圧力勾配型直交磁場放電により発生させた放電プラズマ流を、溶融蒸発部に収容した無機質被膜の形成源となる無機質材料に照射することで無機質材料を加熱蒸発させてイオン化し、イオンプレーティングを行うことにより、振動および／または攪拌させた磁石粉末の表面に無機質被膜を形成する方法を採用し、この方法で膜厚が０．０５μｍ〜２μｍの無機質被膜で表面被覆された磁石粉末を得る工程、得られた無機質被膜被覆磁石粉末と樹脂バインダを混練してボンド磁石用コンパウンドを調製する工程を含むことを特徴とする。
また、本発明のボンド磁石用コンパウンドは、請求項１５記載の通り、請求項１４記載の製造方法によって製造されてなることを特徴とする。
【０００８】
【発明の実施の形態】
本発明の磁気的異方性希土類系ボンド磁石の製造方法においては、まず、磁気的異方性希土類系磁石粉末の表面に無機質被膜を形成する方法として、真空処理室の内部にて、二重圧力勾配型直交磁場放電により発生させた放電プラズマ流を、溶融蒸発部に収容した無機質被膜の形成源となる無機質材料に照射することで無機質材料を加熱蒸発させてイオン化し、イオンプレーティングを行うことにより、振動および／または攪拌させた磁石粉末の表面に無機質被膜を形成する方法を採用し、この方法で膜厚が０．０５μｍ〜２μｍの無機質被膜で表面被覆された磁石粉末を得る第１工程を行う。
【０００９】
二重圧力勾配型直交磁場放電（Ｄｏｕｂｌｅ−Ｐｒｅｓｓｕｒｅ−Ｇｒａｄｉｅｎｔ−ＴｙｐｅＰＩＧＤｉｓｃｈａｒｇｅ）が二重の圧力勾配型放電とＰＩＧ放電を組み合わせた放電方式であることは当業者にとって自明である（浦本上進，「真空」，第３７巻，第１０号，１９９４，ｐ８３３−８３８を必要ならば参照のこと）。本発明においては、この放電方式で発生させた放電プラズマ流が極めて高いプラズマ密度を有することに着目し、この放電プラズマ流を無機質被膜の形成源となる無機質材料に照射し、無機質材料の加熱蒸発とイオン化を効率的に行うことにした。また、気相成長法による被膜形成方法としてイオンプレーティングを行うことにより、高い被膜形成効率で密着性に優れた無機質被膜を磁気的異方性希土類系磁石粉末の表面に形成することにした。これにより、短時間で優れた特性を有する無機質被膜を所望する膜厚で磁石粉末の表面に形成することができるので、生産性の向上を図ることができる他、加熱された溶融蒸発部からの輻射熱などによる、磁石粉末の微細な結晶粒の粗大化の問題や、無機質被膜としてアルミニウム被膜などの比較的低い融点を有する金属被膜を用いた場合における金属被膜の軟化や溶融に起因する磁石粉末の凝集の問題を回避することができるので、磁気特性の低下を未然に防止することができる。
【００１０】
この第１工程は、例えば、図１にその模式的正面を示したイオンプレーティング装置を用いて実施することができる。
図１において、真空処理室１の内部上面には、無機質被膜の形成源となる無機質材料２を収容した溶融蒸発部３がターゲットとして配置されており、溶融蒸発部３の下方には、図略の手段により上下左右に振動させることが可能な磁気的異方性希土類系磁石粉末Ｘを収容するための粉体保持容器４が配置されている。符号３０は、溶融蒸発部３に収容された無機質材料２から生成したイオン粒子の降下領域である。
真空処理室１の内部下面には排気口５が設けられ、この排気口５を介して排気手段としての真空ポンプ６により、真空処理室１の内部を真空排気するようになっている。真空ポンプ６は、真空処理室１の内部の真空度を少なくとも１×１０^−３Ｐａ未満に真空化できる性能を有するものが望ましい。真空処理室１の左側面には、例えば、アルゴン、ヘリウム、水素などのキャリアガスを真空処理室１の内部に導入するためのキャリアガス導入口７が開口しており、キャリアガス導入口７に連通するキャリアガス導入経路８に放電プラズマ流発生装置としてのプラズマガン９が配置されている。このプラズマガン９は、陰極１０、筒状第１中間電極１１、筒状第２中間電極１２、補助陽極筒１３、補助陽極リング１４を、キャリアガスの流れ方向に沿って順次に備えている。陰極１０としては、プラズマ発生用に適したＴａ−ＬａＢ_６複合陰極などを用いることが望ましい。
符号１５は、プラズマガン９における補助陽極領域（補助陽極筒１３と補助陽極リング１４）を通過する放電プラズマ流Ｆを収束させるための空芯の電磁コイルである。符号１６は、補助陽極リング１４を抜けた放電プラズマ流Ｆを真空処理室１の内部上面に配置された溶融蒸発部３の方向に偏向させるための磁場手段としての永久磁石である。符号１７は、筒状第１中間電極１１、筒状第２中間電極１２、補助陽極筒１３、補助陽極リング１４及び溶融蒸発部３と、陰極１０との間の電位差を段階的に増大させるための放電電源である。符号１８は、真空処理室１の内部上面に設けられ、イオン粒子と反応させるための、酸素、窒素、アセチレンなどの反応ガスや、真空処理室１の内部での易酸化性の無機質材料や無機質被膜の酸化を抑制するための、水素などの還元性ガスとアルゴンなどの不活性ガスとの混合ガスを導入するガス導入口である。
陰極１０からの放電プラズマ流Ｆは、筒状第１中間電極１１、筒状第２中間電極１２、補助陽極筒１３、補助陽極リング１４を順次に抜けて、キャリアガス導入口７を通して真空処理室１の内部に導入される。プラズマガン９における補助陽極領域には、放電プラズマ流Ｆに平行な強磁場（例えば３００〜５００ガウス）がかかっており、電子は多数回のマグネトロン運動と中性粒子との多数回の衝突の後に陽極としての補助陽極リング１４の中央まで到達できる。補助陽極リング１４を抜けた放電プラズマ流Ｆは、真空処理室１の内部には適当な磁場があるので、陽極としての溶融蒸発部３に照射されることになる。
放電プラズマ流Ｆは、プラズマガン９に導入するキャリアガス量と真空処理室１の内部の排気速度を調節することで、陰極領域を１０Ｐａ〜１００Ｐａに、中間電極領域−補助陽極領域を０．１Ｐａ〜１０Ｐａに、真空処理室の内部を１×１０^−２Ｐａ〜０．１Ｐａに維持することにより、二重の圧力勾配の存在下で直流放電が行われて発生させられる。溶融蒸発部３は、例えば、Ｍｏ，Ｗ，Ｃまたはセラミックなどの耐熱材料で構成される。溶融蒸発部３の底面が無機質被膜の形成源となる無機質材料２の蒸発面３ａとなっており、この蒸発面３ａには多数の微小な蒸発孔３ｂが形成されている。溶融蒸発部３に収容された無機質材料２は、微小な蒸発孔３ｂを通して溶融蒸発部３の外部に臨むことになるが、微小な蒸発孔３ｂは、溶融した無機質材料２の落下を防止しつつその蒸気化を促すことのできる孔径に設定されている。具体的には微小な蒸発孔３ｂの孔径としては、０．１ｍｍ〜数ｍｍ程度が望ましい。
磁気的異方性希土類系磁石粉末Ｘは、粉体保持容器４に収容され、この粉体保持容器４を矢示の如く上下左右に振動させることで磁石粉末Ｘを振動および／または攪拌させる一方、以上の二重圧力勾配型直交磁場放電により発生させた放電プラズマ流Ｆを、溶融蒸発部３に収容した無機質被膜の形成源となる無機質材料２に照射することで無機質材料２を加熱蒸発させてイオン化し、イオンプレーティングを行う。溶融蒸発部３を磁石粉末Ｘの上方に配置し、溶融蒸発部３に収容された無機質材料２から生成したイオン粒子を重力降下させて磁石粉末Ｘに被着させることにより、高い被膜形成効率で、かつ、均一に磁石粉末Ｘの表面に無機質被膜を形成することができる。磁石粉末Ｘの表面に無機質被膜を形成するための具体的処理条件は、磁石粉末Ｘの処理量や所望する無機質被膜の種類や膜厚などに応じて適宜決定される。
【００１１】
イオンプレーティングを行う際の真空処理室１の内部のバックグラウンド真空度は、１×１０^−３Ｐａ以下とすることが望ましい。１×１０^−３Ｐａを超えると、無機質被膜の形成源となる無機質材料として易酸化性のアルミニウムなどの金属材料を用いた場合、良質の金属被膜が形成できなかったり、磁石粉末の表面における無機質被膜の成長が柱状に起こることで形成された無機質被膜の表面の凹凸が顕著になり、樹脂バインダと混練してボンド磁石用コンパウンドを調製し、調製されたコンパウンドを用いて磁界中で配向させながら射出成形などにより所定形状に加熱成形する際、無機質被膜の表面の凹凸が障害となって、容易磁化方向を磁界方向に十分に配向させることができなかったりすることで、耐酸化性に優れるとともに高い磁気特性を有する磁気的異方性希土類系ボンド磁石を製造することができない恐れがあるからである。
【００１２】
耐酸化性被膜としての無機質被膜としては、磁気的異方性希土類系磁石粉末に耐酸化性を付与することができるものであれば特段制限されるものではないが、磁石粉末との密着性に優れる点において金属被膜が好適である。中でも、既出のアルミニウム被膜の他、Ｚｎ，Ｉｎ，Ｓｎ，Ｂｉなどの被膜のような比較的低い融点を有する金属被膜は、高い被膜形成効率で磁石粉末の表面に形成することができ、加熱された溶融蒸発部からの輻射熱などの影響を最小限に抑えることができる点において望ましい金属被膜である。とりわけ、アルミニウム被膜は、磁石粉末との密着性に極めて優れる点において望ましい。耐酸化性被膜としての無機質被膜としては、以上のような比較的低い融点を有する金属被膜の他、Ｓｉ，Ｔｉ，Ｖ，Ｃｒ，Ｍｎ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｒ，Ａｇ，Ｔａなどの被膜や、金属酸化物や金属窒化物や金属炭化物の被膜などが挙げられる。
【００１３】
本発明において、磁気的異方性希土類系磁石粉末の表面に形成する無機質被膜の膜厚を０．０５μｍ〜２μｍと規定するのは、無機質被膜の膜厚が０．０５μｍ未満であると、磁石粉末に十分な耐酸化性を付与することができずに、コンパウンド調製時や加熱成形時の高温環境下において、磁石粉末が酸化することで高い磁気特性を有するボンド磁石を製造することができない恐れがある一方、無機質被膜の膜厚が２μｍを超えると、無機質被膜被覆磁石粉末中における磁石粉末の有効体積が小さくなり、ボンド磁石とした際に高い磁気特性を確保することができなくなる恐れや、無機質被膜の表面の凹凸が顕著になり、樹脂バインダと混練してボンド磁石用コンパウンドを調製し、調製されたコンパウンドを用いて磁界中で配向させながら射出成形などにより所定形状に加熱成形する際、無機質被膜の表面の凹凸が障害となって、容易磁化方向を磁界方向に十分に配向させることができないことで、高い磁気特性を有するボンド磁石を製造することができない恐れがあるからである。なお、磁石粉末の表面に形成する無機質被膜の膜厚は、望ましくは０．１μｍ〜１μｍである。
【００１４】
膜厚が０．０５μｍ〜２μｍの無機質被膜で表面被覆された磁気的異方性希土類系磁石粉末（無機質被膜被覆磁石粉末）中における無機質被膜の体積比率は３％以下とすることが望ましく、１％以下とすることがより望ましい。３体積％を超えると、無機質被膜被覆磁石粉末中における磁石粉末の有効体積が小さくなり、ボンド磁石とした際に高い磁気特性を確保することができなくなる恐れがあるからである。
【００１５】
次に、第２工程として、以上のようにして得られた金属被膜被覆磁石粉末と樹脂バインダを混練してボンド磁石用コンパウンドを調製する工程を行う。この工程は、自体公知の方法で行えばよい。コンパウンドは、無機質被膜被覆磁石粉末を９０質量％〜９６質量％含有してなることが望ましい。無機質被膜被覆磁石粉末の含有割合が９０質量％未満であると、高い磁気特性を有するボンド磁石を製造することができなくなる恐れがある一方、無機質被膜被覆磁石粉末の含有割合が９６質量％を超えると、樹脂バインダが少なすぎて優れた流動性を有するコンパウンドが得られないことで、射出成形や押出成形やロール成形などが困難になる恐れがあるからである。
【００１６】
樹脂バインダとしては、エポキシ樹脂、フェノール樹脂、メラミン樹脂などの熱硬化性樹脂、ポリアミド（ナイロン６６やナイロン６やナイロン１２など）、ポリエチレン、ポリプロピレン、ポリ塩化ビニル、ポリエステル、ポリフェニレンサルファイドなどの熱可塑性樹脂、ゴムやエストラマ、これらの変性体や共重合体や混合物（例えば、熱硬化性樹脂（エポキシ樹脂など）に熱可塑性樹脂の粉末を分散させたもの：Ｆ．Ｙａｍａｓｈｉｔａ，ＡｐｐｌｉｃａｔｉｏｎｓｏｆＲａｒｅ−ＥａｒｔｈＭａｇｎｅｔｓｔｏｔｈｅＳｍａｌｌｍｏｔｏｒｉｎｄｕｓｔｒｙ，ｐｐ．１００−１１１，Ｐｒｏｃｅｅｄｉｎｇｓｏｆｔｈｅｓｅｖｅｎｔｅｅｎｔｈｉｎｔｅｒｎａｔｉｏｎａｌｗｏｒｋｓｈｏｐ，ＲａｒｅＥａｒｔｈＭａｇｎｅｔｓａｎｄＴｈｅｉｒＡｐｐｌｉｃａｔｉｏｎｓ，Ａｕｇｕｓｔ１８−２２，２００２，Ｎｅｗａｒｋ，Ｄｅｌａｗａｒｅ，ＵＳＡ，ＥｄｉｔｅｄｂｙＧ．Ｃ．ＨａｄｊｉｐａｎａｙｉｓａｎｄＭ．Ｊ．Ｂｏｎｄｅｒ，ＲｉｎｔｏｎＰｒｅｓｓを参照）などを用いることができるが、例えば、射出成形におけるスプルーのリサイクルなどの観点からは熱可塑性樹脂を用いることが望ましい（融点が２５０℃以上のものを用いることがより望ましい）。コンパウンドを調製する際には、カップリング剤や潤滑剤や硬化剤などの添加剤をその目的に応じて通常用いられる添加量にて添加してもよい。
【００１７】
最後に、第３工程として、以上のようにして調製されたコンパウンドを用いて磁界中で配向させながら所定形状に加熱成形する工程を行うことで磁気的異方性希土類系ボンド磁石を得る。この工程は、自体公知の条件下にて磁界中で配向させながら射出成形や押出成形やロール成形などで行えばよい。なお、磁気的異方性希土類系ボンド磁石は脱磁が困難であるので、磁気的異方性希土類系ボンド磁石は、それが適用される部品に直接磁界中で配向させながら加熱成形するようにしてもよい。
【００１８】
本発明は、とりわけ平均粒径が５０μｍ〜１５０μｍである磁気的異方性希土類系磁石粉末を用いて磁気的異方性希土類系ボンド磁石を製造する際にその効果を発揮する。平均粒径が５０μｍ未満であると、十分な耐酸化性を磁石粉末に付与することができるに足る膜厚の無機質被膜を磁石粉末の表面に形成した場合、無機質被膜被覆磁石粉末中における磁石粉末の有効体積が小さくなり、ボンド磁石とした際に高い磁気特性を確保することができなくなる恐れがある一方、平均粒径が１５０μｍを超えると、樹脂バインダと混練してボンド磁石用コンパウンドを調製しても、流動性や磁界中での配向性に優れたコンパウンドが得られず、射出成形や押出成形やロール成形などにより所定形状に加熱成形することが困難になる恐れがあるからである。
【００１９】
本発明が適用される磁気的異方性希土類系磁石粉末としては、既出のＨＤＤＲ磁石粉末が挙げられる。本発明によりＨＤＤＲ磁石粉末を用いてボンド磁石を製造すれば、平均結晶粒径が１μｍ以下の微細な結晶粒を粗大化させることもなく、耐酸化性に優れるとともに高い磁気特性を有するボンド磁石を得ることができる。平均粒径が５０μｍ〜１５０μｍであるＨＤＤＲ磁石粉末は、所定の組成を有する希土類系磁石合金を水素中で加熱して水素を吸蔵させた後、脱水素処理し、次いで冷却してから所望する平均粒径になるように粉砕することによって得ることができる。また、所定の組成を有する希土類系磁石合金を所望する平均粒径になるように粉砕してから、水素中で加熱して水素を吸蔵させた後、脱水素処理し、次いで冷却することによって得ることもできる。
なお、本発明が適用される磁気的異方性希土類系磁石粉末はＨＤＤＲ磁石粉末に限定されるものではなく、例えば、急冷合金法によって得られた合金粉をホットプレスなどにより低温で焼結し、さらに温間据え込み加工によって磁気的異方性を付与したバルク状磁石体を粉砕する温間加工・粉砕法や、急冷合金法によって得られた合金粉をそのまま金属製容器に充填封入し、温間圧延などの塑性加工によって磁気的異方性を付与する方法などによって得られる磁気的異方性希土類系磁石粉末であってもよい。
【００２０】
なお、本発明により製造される磁気的異方性希土類系ボンド磁石に、耐食性を付与することなどを目的として、その表面に樹脂塗装被膜や電気めっき被膜や化成処理被膜などの各種被膜を単層形成や積層形成してもよいことはいうまでもない。
【００２１】
【実施例】
以下、本発明を実施例によってさらに詳細に説明するが、本発明はこれに限定して解釈されるものではない。なお、以下の実施例は、高周波溶解によって組成がＮｄ：１２．４原子％，Ｆｅ：６４．９原子％，Ｃｕ：０．１原子％，Ｃｏ：１６．１原子％，Ｇａ：０．２原子％，Ｚｒ：０．１原子％，Ｂ：６．２原子％の鋳隗を作製し、アルゴンガス雰囲気中で１１００℃×２４時間焼鈍したものを酸素濃度０．５％以下のアルゴンガス雰囲気中で粉砕して平均粒径１００μｍの合金粉末としてからこれを０．１５ＭＰａの水素ガス加圧雰囲気中で８７０℃×３時間の水素化熱処理を行い、その後、減圧（１ｋＰａ）アルゴンガス流気中で８５０℃×１時間の脱水素処理を行ってから冷却して製造したＨＤＤＲ磁石粉末（平均結晶粒径８５０ｎｍ：磁石粒子の破面の走査型電子顕微鏡観察による）を用いて行った。
【００２２】
Ａ：アルミニウム被膜で表面被覆されたＨＤＤＲ磁石粉末の製造とその特性
図１に示すイオンプレーティング装置を用いてＨＤＤＲ磁石粉末の表面にアルミニウム被膜を形成した。アルミニウム被膜の形成源としては純アルミニウムを用いた。
内径５００ｍｍの粉体保持容器にＨＤＤＲ磁石粉末を１００ｇ収容した後、真空処理室の内部のバックグラウンド真空度が１×１０^−４Ｐａ以下になるまで真空排気した。
続いて、プラズマガンに導入するアルゴンガス（キャリアガス）量と真空処理室の内部の排気速度を調節することで、陰極領域を約４０Ｐａに、中間電極領域−補助陽極領域を約１．３Ｐａに、真空処理室の内部を４×１０^−２Ｐａに維持した。
その後、粉体保持容器を上下左右に振動させることにより、ＨＤＤＲ磁石粉末を振動および／または攪拌させながら、プラズマガンによって直流放電電流１００Ａ、放電電圧７０Ｖの条件で二重圧力勾配型直交磁場放電を起こして放電プラズマ流を発生させ、発生させた放電プラズマ流を、溶融蒸発部に収容したアルミニウム被膜の形成源としての純アルミニウムに照射することでアルミニウムを加熱蒸発させてイオン化し、５種類の処理時間でイオンプレーティングを行うことにより、表１に示す５種類の膜厚のアルミニウム被膜で表面被覆されたＨＤＤＲ磁石粉末（サンプル２〜サンプル６）を作製した（サンプル１は未処理のＨＤＤＲ磁石粉末）。
サンプル２〜サンプル６を光学顕微鏡にて観察したところ、磁石粉末の凝集体は見当たらず、個々の磁石粒子がアルミニウム被膜によって均一に表面被覆されていた。なお、ＨＤＤＲ磁石粉末の表面に形成されたアルミニウム被膜の膜厚は、サンプルを乳鉢で軽く粉砕することによって生じた磁石粒子の破面を、走査型電子顕微鏡（ＳＥＭ）で観察することにより求めた。また、サンプル２〜サンプル６について、サンプル中におけるアルミニウム被膜の体積比率を、ＩＣＰ発光分析によって求めたアルミニウムの質量比率、未処理のＨＤＤＲ磁石粉末（サンプル１）の密度（７．６ｇ／ｃｍ^３）、アルミニウムの密度（２．７ｇ／ｃｍ^３）から算出した。結果を表１に示す。
サンプル１〜サンプル６に対して、２００℃×１時間の大気中放置試験を行い、試験前後の各サンプルの磁気特性（ＢＨ）_ｍａｘを振動試料型磁力計（ＶＳＭ）で測定するとともにその低下率を算出した。結果を表１に示す。表１から明らかなように、ＨＤＤＲ磁石粉末の表面に形成されたアルミニウム被膜の膜厚が厚くなるにつれて、耐酸化性が向上することで磁気特性の低下が抑制された。
【００２３】
Ｂ：アルミニウム被膜で表面被覆されたＨＤＤＲ磁石粉末を用いたボンド磁石の製造
サンプル１〜サンプル６について、サンプル：９２質量％、ナイロン１２樹脂：６．７質量％、チタネート系カップリング剤（味の素ファインテクノ社製：ＫＲ−ＴＴＳ）：０．７５質量％、ステアリン酸アミド：０．５５質量％を混合し、ラボプラストミルを用いて回転数８０ｒｐｍ、混練温度２３０℃、混練時間１０分の条件で混練してボンド磁石用コンパウンドを調製した。調製されたコンパウンドを粉砕した後、磁界中射出成形機を用い、射出温度２７０℃、配向磁場８００ｋＡ／ｍ（試料の高さ方向）、金型温度８０℃の条件にて、直径１０ｍｍ×高さ７ｍｍの円柱状ボンド磁石を作製した。
得られた円柱状ボンド磁石の磁気特性をＢＨトレーサにより評価した。結果を表１に示す。なお、Ｂ_ｒ／Ｊ_１．２は、配向度を示す指標で、磁場１．２ＭＡ／ｍにおける磁化Ｊの値で残留磁束密度Ｂ_ｒを除したものであり、数値が１に近いほど配向性に優れることを示す。
表１から明らかなように、サンプル２〜サンプル５を用いて作製されたボンド磁石は、高い磁気特性を有するものであった。中でも、サンプル２〜サンプル４を用いて作製されたボンド磁石は、ＨＤＤＲ磁石粉末の表面に形成したアルミニウム被膜の膜厚が１μｍ以下であることで、優れた配向性を示すものであった。とりわけ、サンプル２とサンプル３を用いて作製されたボンド磁石は、サンプル中におけるアルミニウム被膜の体積比率を３％以下としたことにより、極めて高い磁気特性を有するものであった。
一方、サンプル１は、アルミニウム被膜が表面に形成されていない未処理のＨＤＤＲ磁石粉末であることから、耐酸化性が不十分であり、コンパウンド調製時や加熱成形時の高温環境下において酸化されることで、高い磁気特性を有するボンド磁石を作製することができなかった。また、サンプル６は、ＨＤＤＲ磁石粉末に対して十分な耐酸化性を付与するものであったが、ＨＤＤＲ磁石粉末の表面に形成されたアルミニウム被膜の膜厚が厚すぎたことで、磁気特性が低かったことに加え、容易磁化方向を磁界方向に十分に配向させることができなかったことから、高い磁気特性を有するボンド磁石を作製することができなかった。
【００２４】
【表１】

【００２５】
【発明の効果】
本発明によれば、耐酸化性に優れるとともに高い磁気特性を有する磁気的異方性希土類系ボンド磁石の新規な製造方法が提供される。
【図面の簡単な説明】
【図１】本発明の製造方法を実施するためのイオンプレーティング装置の一例の模式的正面図である。
【符号の説明】
１真空処理室
２無機質材料
３溶融蒸発部
４粉体保持容器
５排気口
６真空ポンプ
７キャリアガス導入口
８キャリアガス導入経路
９プラズマガン
１０陰極
１１筒状第１中間電極
１２筒状第２中間電極
１３補助陽極筒
１４補助陽極リング
１５電磁コイル
１６永久磁石
１７放電電源
１８ガス導入口
３０イオン粒子の降下領域
Ｆ放電プラズマ流
Ｘ磁気的異方性希土類系磁石粉末[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel method for producing a magnetically anisotropic rare earth-based bonded magnet having excellent oxidation resistance and high magnetic properties.
[0002]
[Prior art]
A rare-earth magnet powder such as an R-Fe-B magnet powder represented by an Nd-Fe-B magnet powder is heat-molded into a predetermined shape using a thermoplastic resin or a thermosetting resin as a binder. Although the manufactured rare-earth bonded magnets have lower magnetic properties than rare-earth sintered magnets because they contain a resin binder, they still have sufficiently higher magnetic properties than ferrite magnets and the like. In addition, it has features that rare earth sintered magnets do not have, such as a magnet having a complicated shape, a thin shape, and a radial anisotropic magnet can be easily obtained. Therefore, rare earth-based bonded magnets are often used for small motors such as spindle motors and stepping motors, and the demand for them is increasing in recent years.
Above all, for example, a rare earth magnet alloy having a predetermined composition is heated in hydrogen to occlude hydrogen, dehydrogenated, then cooled, and then pulverized to obtain a HDDR (Hydrogenation-Dissolution Portion). A magnetically anisotropic rare earth-based bonded magnet that is heat-formed into a predetermined shape using a magnetically anisotropic magnet powder such as a Desorption-Recombination magnet powder (see Japanese Patent Publication No. 6-82575) has high magnetic properties. For this reason, attention has been paid to application development to products in which magnetic isotropic rare earth-based bonded magnets and the like have been used.
However, although the magnetically anisotropic rare earth-based bonded magnet has high magnetic properties, R and Fe occupy most of the composition of the magnet powder constituting the bonded magnet, and thus have a problem that corrosion and oxidation are likely to occur. . In particular, the HDDR magnet powder is a magnet powder whose magnetic properties are significantly reduced due to oxidation. The HDDR magnet powder is kneaded with a resin binder to prepare a compound for a bond magnet, and the prepared compound is oriented in a magnetic field using the prepared compound. When a bonded magnet is manufactured by heat molding into a predetermined shape by injection molding or the like, in a high temperature environment during compound preparation or heat molding (normally 150 ° C. or higher, sometimes exceeding 250 ° C. in some cases) In some cases, a bonded magnet having high magnetic properties cannot be obtained due to oxidation of the HDDR magnet powder.
[0003]
As a method for solving the above-mentioned problems, as proposed in Patent Document 1 below, by vapor deposition, sputtering, plating, or the like, an R-Fe-B-based magnet alloy having magnetic anisotropy is used. There is a method in which a metal coating is formed on the surface of the pulverized powder, and a rare-earth bonded magnet is manufactured using the magnet powder coated with the metal coating. This patent document describes an improvement in the oxidation resistance of the magnet powder as an effect of this method. Further, after forming a metal film on the surface of the magnet powder, heat treatment is performed at a temperature in the range of 300 ° C. to 1000 ° C. By this, it is said that the adhesion between the magnet powder and the metal coating can be improved, and the magnetic properties can be improved by diffusing the metal constituting the coating into the magnet powder. An aluminum film is formed on the surface of the magnet powder by vapor deposition, and then subjected to a two-stage heat treatment at 900 ° C. for 1 hour and at 600 ° C. for 1 hour.
The method described in Patent Document 1 below is noteworthy. However, an aluminum coating is formed on the surface of a magnet powder having a fine crystal grain having an average crystal grain size of 1 μm or less, such as an HDDR magnet powder, according to the method described in this patent document. When heat treatment is performed at a high temperature of 600 ° C., there is a problem that the magnetic properties are deteriorated due to coarsening of fine crystal grains of the magnet powder. In addition to such a problem, there is a problem that the aluminum powder is softened or melted to cause aggregation of the magnet powder. When magnetically anisotropic rare earth magnet powder such as HDDR magnet powder is aggregated, the easy magnetization direction of the magnet powder contained in the aggregate is random. A compound for magnets is prepared, and the prepared compound is oriented in a magnetic field while being heat-molded into a predetermined shape by injection molding or the like, so that even a bonded magnet can sufficiently orient the magnet powder in the magnetic field direction. Because of this, high magnetic properties (especially squareness of the demagnetization curve) cannot be obtained. Further, since the magnet powder and the resin binder cannot be sufficiently kneaded, sufficient moldability and mechanical strength as a bonded magnet cannot be obtained. Of course, agglomerates may be crushed, but if such treatment is performed, peeling of the aluminum coating from the surface of the magnet powder occurs more or less, so that oxidation of the magnet powder in the bonded magnet is prevented. There is a problem that the essential purpose cannot be achieved. In addition, when heat treatment is performed at a high temperature of 900 ° C. or 600 ° C. on a magnet powder whose surface is coated with an aluminum film, diffusion of aluminum into the magnet powder occurs more than necessary, resulting in deterioration of magnetic properties. There's a problem. Therefore, it cannot be said that the method described in Patent Document 1 below cannot manufacture a magnetically anisotropic rare earth-based bonded magnet having excellent oxidation resistance and high magnetic properties.
[0004]
[Patent Document 1]
JP-A-3-217003
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a novel method for producing a magnetically anisotropic rare earth-based bonded magnet having excellent oxidation resistance and high magnetic properties.
[0006]
[Means for Solving the Problems]
The present inventor has conducted various studies in view of the above points, and found that when forming an inorganic film on the surface of a magnetically anisotropic rare earth magnet powder by a vapor phase growth method, an inorganic material serving as a source of the inorganic film is formed. By optimizing the material evaporation method and film formation method, and optimizing the thickness of the inorganic film, kneading with a resin binder to prepare a compound for bond magnets, and using the prepared compound for magnetic field When heat-forming into a predetermined shape by injection molding or the like while orienting in a magnet, it is possible to obtain an inorganic-coated magnet powder capable of sufficiently orienting the easy magnetization direction to the magnetic field direction. Thus, it has been found that a magnetically anisotropic rare earth-based bonded magnet having excellent oxidation resistance and high magnetic properties can be manufactured.
[0007]
The method for producing a magnetically anisotropic rare earth-based bonded magnet according to the present invention based on the above-mentioned findings provides a method for forming an inorganic coating on the surface of a magnetically anisotropic rare earth-based magnet powder as described in claim 1. As the inside of the vacuum processing chamber, the inorganic material is irradiated with the discharge plasma flow generated by the double pressure gradient type orthogonal magnetic field discharge to the inorganic material serving as the formation source of the inorganic coating housed in the melting and evaporating section, and thereby the inorganic material is irradiated. A method of forming an inorganic coating on the surface of a vibrated and / or agitated magnet powder by ionizing by heating and evaporating and ion-plating the inorganic powder having a thickness of 0.05 μm to 2 μm by this method is adopted. A step of obtaining a magnet powder coated on the surface with a coating, a step of kneading the obtained inorganic-coated magnet powder and a resin binder to prepare a compound for a bonded magnet, The method includes a step of heat-forming into a predetermined shape while orienting in a magnetic field using a window.
According to a second aspect of the present invention, in the manufacturing method according to the first aspect, the background vacuum inside the vacuum processing chamber at the time of performing the ion plating is 1 × 10 5. ^-3 Pa or less.
Further, a manufacturing method according to claim 3 is characterized in that, in the manufacturing method according to claim 1 or 2, the inorganic coating is a metal coating.
A manufacturing method according to a fourth aspect is characterized in that, in the manufacturing method according to the third aspect, the metal film is an aluminum film.
The manufacturing method according to a fifth aspect is characterized in that, in the manufacturing method according to the first aspect, the volume ratio of the inorganic coating in the inorganic coating-coated magnet powder is 3% or less.
According to a sixth aspect of the present invention, there is provided the manufacturing method according to any one of the first to fifth aspects, wherein the resin binder is a thermoplastic resin.
The manufacturing method according to claim 7 is the manufacturing method according to any one of claims 1 to 6, wherein the heat molding into a predetermined shape is performed by any one method selected from injection molding, extrusion molding, and roll molding. It is characterized by performing.
The manufacturing method according to claim 8 is characterized in that, in the manufacturing method according to any one of claims 1 to 7, the average particle diameter of the magnetically anisotropic rare earth magnet powder is 50 μm to 150 μm. .
According to a ninth aspect of the present invention, in the manufacturing method of the eighth aspect, the average crystal grain size of the magnetically anisotropic rare earth magnet powder is 1 μm or less.
A tenth aspect of the present invention is the manufacturing method according to the eighth or ninth aspect, wherein the magnetically anisotropic rare earth magnet powder is an HDDR magnet powder.
Further, the magnetically anisotropic rare earth bonded magnet of the present invention is produced by the production method of claim 1 as described in claim 11.
Further, the method for producing an inorganic coating-coated magnet powder of the present invention, as described in claim 12, as a method of forming an inorganic coating on the surface of the magnetically anisotropic rare earth magnet powder, inside a vacuum processing chamber, By irradiating the discharge plasma flow generated by the double pressure gradient type orthogonal magnetic field discharge to the inorganic material serving as the source of the inorganic film accommodated in the melting and evaporating section, the inorganic material is heated and evaporated to be ionized, and ion plating is performed. To form an inorganic coating on the surface of the vibrated and / or agitated magnet powder, thereby obtaining a magnet powder surface-coated with an inorganic coating having a thickness of 0.05 μm to 2 μm by this method. It is characterized by including a step.
According to a thirteenth aspect of the present invention, there is provided a magnet powder coated with an inorganic film, which is manufactured by the manufacturing method according to the twelfth aspect.
Further, the method for producing a compound for a bonded magnet according to the present invention is a method for forming an inorganic coating on the surface of a magnetically anisotropic rare earth magnet powder as described in claim 14 in a vacuum processing chamber. By irradiating a discharge plasma flow generated by a heavy pressure gradient type orthogonal magnetic field discharge to an inorganic material serving as a formation source of an inorganic film housed in a melting and evaporating section, the inorganic material is heated and evaporated to be ionized, and ion plating is performed. A method of forming an inorganic coating on the surface of the vibrated and / or agitated magnet powder by performing the method, and obtaining a magnet powder surface-coated with the inorganic coating having a thickness of 0.05 μm to 2 μm by this method. And a step of kneading the obtained inorganic-coated magnet powder and a resin binder to prepare a compound for a bonded magnet.
According to a fifteenth aspect of the present invention, a compound for a bonded magnet is manufactured by the manufacturing method of the fourteenth aspect.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
In the method for producing a magnetic anisotropic rare earth-based bonded magnet of the present invention, first, as a method of forming an inorganic coating on the surface of a magnetic anisotropic rare earth-based magnet powder, By irradiating a discharge plasma flow generated by a pressure gradient type orthogonal magnetic field discharge to an inorganic material serving as a formation source of an inorganic film housed in a melting and evaporating section, the inorganic material is heated and evaporated to be ionized, and ion plating is performed. Thereby, a method of forming an inorganic coating on the surface of the vibrated and / or agitated magnet powder is adopted, and this method is used to obtain a magnet powder surface-coated with an inorganic coating having a thickness of 0.05 μm to 2 μm. Perform the process.
[0009]
It is obvious for those skilled in the art that the double-pressure-gradient orthogonal magnetic field discharge (Double-Pressure-Gradient-Type PIG Discharge) is a discharge method in which the double pressure gradient-type discharge and the PIG discharge are combined (Uramoto J. Susumu) , "Vacuum", Vol. 37, No. 10, 1994, pp. 833-838 if necessary). In the present invention, attention is paid to the fact that the discharge plasma flow generated by this discharge method has an extremely high plasma density, and this discharge plasma flow is irradiated to an inorganic material serving as a source for forming an inorganic film, and the inorganic material is heated and evaporated. And I decided to perform ionization efficiently. In addition, by performing ion plating as a method of forming a film by a vapor phase growth method, an inorganic film having high film formation efficiency and excellent adhesion is formed on the surface of the magnetically anisotropic rare earth magnet powder. With this, an inorganic coating having excellent properties can be formed on the surface of the magnet powder in a desired thickness in a short time, so that productivity can be improved, and in addition, the heat generated from the heated melt evaporation portion can be improved. Due to radiant heat, etc., the problem of coarsening of fine crystal grains of the magnet powder, and the use of a metal coating having a relatively low melting point such as an aluminum coating as an inorganic coating, the softening or melting of the metal coating due to the softening and melting of the metal coating. Since the problem of agglomeration can be avoided, a decrease in magnetic properties can be prevented.
[0010]
This first step can be performed, for example, using an ion plating apparatus whose schematic front is shown in FIG.
In FIG. 1, a melting and evaporating section 3 containing an inorganic material 2 serving as a source for forming an inorganic film is disposed as a target on the inner upper surface of a vacuum processing chamber 1. The powder holding container 4 for storing the magnetically anisotropic rare earth magnet powder X, which can be vibrated up, down, left and right by the means, is disposed. Reference numeral 30 denotes a falling region of ion particles generated from the inorganic material 2 accommodated in the melting and evaporating unit 3.
An exhaust port 5 is provided on the inner lower surface of the vacuum processing chamber 1, and the inside of the vacuum processing chamber 1 is evacuated through the exhaust port 5 by a vacuum pump 6 as an exhaust unit. The vacuum pump 6 reduces the degree of vacuum inside the vacuum processing chamber 1 to at least 1 × 10 ^-3 It is desirable that the material has a performance capable of vacuuming to less than Pa. On the left side of the vacuum processing chamber 1, a carrier gas inlet 7 for introducing a carrier gas such as argon, helium, or hydrogen into the vacuum processing chamber 1 is opened. A plasma gun 9 as a discharge plasma flow generator is arranged in the communicating carrier gas introduction path 8. The plasma gun 9 includes a cathode 10, a cylindrical first intermediate electrode 11, a cylindrical second intermediate electrode 12, an auxiliary anode cylinder 13, and an auxiliary anode ring 14, which are sequentially provided along the carrier gas flow direction. As the cathode 10, Ta-LaB suitable for plasma generation ₆ It is desirable to use a composite cathode or the like.
Reference numeral 15 denotes an air-core electromagnetic coil for converging the discharge plasma flow F passing through the auxiliary anode region (the auxiliary anode cylinder 13 and the auxiliary anode ring 14) in the plasma gun 9. Reference numeral 16 denotes a permanent magnet as a magnetic field means for deflecting the discharge plasma flow F having passed through the auxiliary anode ring 14 toward the melting and evaporating unit 3 disposed on the upper surface inside the vacuum processing chamber 1. Reference numeral 17 is for gradually increasing the potential difference between the cathode 10 and the first cylindrical intermediate electrode 11, the second cylindrical intermediate electrode 12, the auxiliary anode cylinder 13, the auxiliary anode ring 14 and the melting and evaporating section 3. Discharge power supply. Reference numeral 18 denotes a reaction gas such as oxygen, nitrogen, or acetylene, which is provided on the upper surface inside the vacuum processing chamber 1 and reacts with ion particles, and an easily oxidizable inorganic material or inorganic material inside the vacuum processing chamber 1. A gas inlet for introducing a mixed gas of a reducing gas such as hydrogen and an inert gas such as argon for suppressing the oxidation of the film.
The discharge plasma flow F from the cathode 10 passes through the cylindrical first intermediate electrode 11, the cylindrical second intermediate electrode 12, the auxiliary anode cylinder 13, and the auxiliary anode ring 14 in order, and passes through the carrier gas inlet 7 to the vacuum processing chamber. 1 is introduced inside. In the auxiliary anode region of the plasma gun 9, a strong magnetic field (for example, 300 to 500 Gauss) is applied in parallel to the discharge plasma flow F, and electrons travel after many times of magnetron motion and many times of collisions with neutral particles. It can reach the center of the auxiliary anode ring 14 as an anode. The discharge plasma flow F that has passed through the auxiliary anode ring 14 has an appropriate magnetic field inside the vacuum processing chamber 1, so that the discharge plasma flow F is applied to the melt evaporation section 3 as an anode.
By adjusting the amount of carrier gas introduced into the plasma gun 9 and the evacuation speed inside the vacuum processing chamber 1, the discharge plasma flow F is adjusted to 10 Pa to 100 Pa in the cathode region and 0.1 Pa in the intermediate electrode region-auxiliary anode region. 1 × 10 Pa to 10 Pa ^-2 By maintaining the pressure between Pa and 0.1 Pa, a direct current discharge is performed and generated in the presence of a double pressure gradient. The melting and evaporating section 3 is made of, for example, a heat-resistant material such as Mo, W, C, or ceramic. The bottom surface of the melt evaporation section 3 is an evaporation surface 3a of the inorganic material 2 which is a source of forming the inorganic film, and a large number of minute evaporation holes 3b are formed in the evaporation surface 3a. The inorganic material 2 accommodated in the melting and evaporating section 3 faces the outside of the melting and evaporating section 3 through the minute evaporating holes 3b. The minute evaporating holes 3b prevent the molten inorganic material 2 from dropping. The hole diameter is set so as to promote the vaporization. Specifically, the diameter of the minute evaporation holes 3b is desirably about 0.1 mm to several mm.
The magnetically anisotropic rare earth magnet powder X is contained in a powder holding container 4, and the powder holding container 4 is vibrated up and down and left and right as indicated by arrows to vibrate and / or stir the magnetic powder X. The inorganic material 2 is heated and evaporated by irradiating a discharge plasma flow F generated by the above-described double pressure gradient type orthogonal magnetic field discharge to the inorganic material 2 serving as a formation source of the inorganic film accommodated in the melting and evaporating section 3. To perform ion plating. The melting and evaporating unit 3 is disposed above the magnet powder X, and the ion particles generated from the inorganic material 2 accommodated in the melting and evaporating unit 3 are caused to fall by gravity and adhere to the magnet powder X, thereby achieving high film formation efficiency. In addition, an inorganic coating can be uniformly formed on the surface of the magnet powder X. Specific processing conditions for forming the inorganic coating on the surface of the magnet powder X are appropriately determined according to the processing amount of the magnet powder X and the type and thickness of the desired inorganic coating.
[0011]
The background vacuum inside the vacuum processing chamber 1 when performing ion plating is 1 × 10 ^-3 It is desirable to set it to Pa or less. 1 × 10 ^-3 If it exceeds Pa, when a metal material such as aluminum which is easily oxidizable is used as an inorganic material as a source of the formation of the inorganic coating, a good quality metal coating cannot be formed, or the growth of the inorganic coating on the surface of the magnet powder is columnar. The unevenness of the surface of the formed inorganic film becomes remarkable due to the occurrence of, the compound is kneaded with a resin binder to prepare a compound for a bonded magnet, and the prepared compound is oriented in a magnetic field using a predetermined method such as injection molding. When heat-formed into a shape, the unevenness of the surface of the inorganic coating becomes an obstacle, making it difficult to easily orient the magnetization direction in the direction of the magnetic field. This is because there is a possibility that a magnetically anisotropic rare earth-based bonded magnet cannot be manufactured.
[0012]
The inorganic coating as the oxidation-resistant coating is not particularly limited as long as it can provide oxidation resistance to the magnetically anisotropic rare-earth magnet powder, but the adhesion to the magnet powder is not limited. Metal coatings are preferred in that they are excellent. Among them, a metal coating having a relatively low melting point, such as a coating of Zn, In, Sn, Bi, etc., other than the above-mentioned aluminum coating, can be formed on the surface of the magnet powder with high coating formation efficiency, and is heated. This is a desirable metal coating in that the influence of radiant heat from the melted evaporator can be minimized. In particular, an aluminum coating is desirable in that it has extremely excellent adhesion to magnet powder. As the inorganic coating as the oxidation-resistant coating, a coating of Si, Ti, V, Cr, Mn, Co, Ni, Cu, Zr, Ag, Ta, etc., in addition to the metal coating having a relatively low melting point as described above. And films of metal oxides, metal nitrides, and metal carbides.
[0013]
In the present invention, the thickness of the inorganic coating formed on the surface of the magnetic anisotropic rare earth magnet powder is defined to be 0.05 μm to 2 μm when the thickness of the inorganic coating is less than 0.05 μm. Insufficient oxidation resistance cannot be imparted to the powder, and the magnet powder may be oxidized in a high-temperature environment during compound preparation or heat molding, making it impossible to produce a bonded magnet having high magnetic properties. On the other hand, when the thickness of the inorganic coating exceeds 2 μm, the effective volume of the magnet powder in the inorganic coating-coated magnet powder becomes small, and it may become impossible to secure high magnetic properties when the bonded magnet is used. The unevenness of the surface of the inorganic coating becomes remarkable, and it is kneaded with a resin binder to prepare a compound for a bonded magnet, and is oriented while being oriented in a magnetic field using the prepared compound. When performing heat molding to a predetermined shape by molding or the like, unevenness on the surface of the inorganic coating becomes an obstacle, and it is not possible to sufficiently orient the magnetization direction in the direction of the magnetic field, thereby producing a bonded magnet having high magnetic properties. This is because they may not be able to do so. The thickness of the inorganic coating formed on the surface of the magnet powder is desirably 0.1 μm to 1 μm.
[0014]
The volume ratio of the inorganic coating in the magnetically anisotropic rare earth magnet powder (inorganic coating-coated magnet powder) whose surface is coated with an inorganic coating having a thickness of 0.05 μm to 2 μm is desirably 3% or less. % Is more desirable. If the content exceeds 3% by volume, the effective volume of the magnet powder in the inorganic-coated magnet powder becomes small, and it may not be possible to secure high magnetic properties when a bonded magnet is used.
[0015]
Next, as the second step, a step of kneading the metal-coated magnet powder obtained as described above and a resin binder to prepare a compound for a bonded magnet is performed. This step may be performed by a method known per se. The compound desirably contains 90% to 96% by mass of the inorganic-coated magnet powder. If the content of the inorganic coating-coated magnet powder is less than 90% by mass, a bonded magnet having high magnetic properties may not be able to be produced, while the content of the inorganic coating-coated magnet powder exceeds 96% by mass. This is because the amount of the resin binder is too small to obtain a compound having excellent fluidity, which may make injection molding, extrusion molding, roll molding, and the like difficult.
[0016]
Examples of the resin binder include thermosetting resins such as epoxy resin, phenol resin, and melamine resin, and thermoplastic resins such as polyamide (nylon 66, nylon 6, and nylon 12), polyethylene, polypropylene, polyvinyl chloride, polyester, and polyphenylene sulfide. , Rubber and elastomers, modified products, copolymers and mixtures thereof (for example, thermoplastic resin powder dispersed in a thermosetting resin (epoxy resin, etc.): F. Yamashita, Applications of Rare-Earth Magnets to the Small motor industry, pp. 100-111, Proceedings of the seventeenth international workshop, Rare Earth Ma. gnets and Their Applications, August 18-22, 2002, Newark, Delaware, USA, Edited by GC, Hadipanyais and MJ Bonder, Rinton Press, etc. From the viewpoint of sprue recycling, it is desirable to use a thermoplastic resin (it is more desirable to use one having a melting point of 250 ° C. or higher). When preparing the compound, additives such as a coupling agent, a lubricant and a curing agent may be added in an amount generally used depending on the purpose.
[0017]
Finally, as a third step, a magnetically anisotropic rare earth bonded magnet is obtained by performing a step of heat-forming into a predetermined shape while orienting in a magnetic field using the compound prepared as described above. This step may be performed by injection molding, extrusion molding, roll molding or the like while orienting in a magnetic field under conditions known per se. Since magnetically anisotropic rare-earth bonded magnets are difficult to demagnetize, magnetically anisotropic rare-earth bonded magnets should be heated and molded while directly orienting the parts to which they are applied in a magnetic field. You may.
[0018]
The present invention exerts its effects particularly when a magnetically anisotropic rare earth-based bonded magnet is produced using a magnetically anisotropic rare earth-based magnet powder having an average particle diameter of 50 µm to 150 µm. When the average particle size is less than 50 μm, when an inorganic coating having a thickness sufficient to give sufficient oxidation resistance to the magnet powder is formed on the surface of the magnet powder, the magnetic powder in the inorganic coating-coated magnet powder may be used. When the average particle diameter exceeds 150 μm, the compound for a bonded magnet is prepared by kneading with a resin binder. However, a compound excellent in fluidity and orientation in a magnetic field cannot be obtained, and it may be difficult to heat-mold into a predetermined shape by injection molding, extrusion molding, roll molding, or the like.
[0019]
Examples of the magnetically anisotropic rare earth magnet powder to which the present invention is applied include the above-mentioned HDDR magnet powder. When a bonded magnet is manufactured using the HDDR magnet powder according to the present invention, a bonded magnet having excellent oxidation resistance and high magnetic properties can be obtained without coarsening fine crystal grains having an average crystal grain size of 1 μm or less. Obtainable. HDDR magnet powder having an average particle size of 50 μm to 150 μm is obtained by heating a rare earth magnet alloy having a predetermined composition in hydrogen to occlude hydrogen, performing dehydrogenation treatment, and then cooling to obtain a desired average value. It can be obtained by grinding to a particle size. Further, a rare-earth magnet alloy having a predetermined composition is pulverized so as to have a desired average particle size, heated in hydrogen to absorb hydrogen, dehydrogenated, and then cooled. You can also.
The magnetic anisotropic rare earth magnet powder to which the present invention is applied is not limited to HDDR magnet powder. For example, an alloy powder obtained by a quenching alloy method is sintered at a low temperature by a hot press or the like. In addition, the alloy powder obtained by the warm working / pulverizing method of pulverizing the bulk magnet body imparted with magnetic anisotropy by warm upsetting or the quenching alloy method is directly filled in a metal container and sealed. A magnetically anisotropic rare earth magnet powder obtained by a method of imparting magnetic anisotropy by plastic working such as warm rolling may be used.
[0020]
For the purpose of imparting corrosion resistance to the magnetically anisotropic rare earth-based bonded magnet produced by the present invention, a single layer of various coatings such as a resin coating, an electroplating coating, or a chemical conversion coating is applied on the surface thereof. Needless to say, they may be formed or laminated.
[0021]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention should not be construed as being limited thereto. In the following examples, the composition was Nd: 12.4 at%, Fe: 64.9 at%, Cu: 0.1 at%, Co: 16.1 at%, Ga: 0.2 by high frequency melting. Atomic%, Zr: 0.1 atomic%, B: 6.2 atomic%, prepared and annealed at 1100 ° C. for 24 hours in an argon gas atmosphere, an argon gas atmosphere having an oxygen concentration of 0.5% or less And then subjected to a hydrogenation heat treatment at 870 ° C. for 3 hours in a hydrogen gas pressurized atmosphere of 0.15 MPa, and then in a reduced pressure (1 kPa) argon gas stream. 850 ° C. × 1 hour, followed by cooling, and using an HDDR magnet powder (average crystal grain size: 850 nm: observation of the fracture surface of the magnet particles by a scanning electron microscope).
[0022]
A: Production and properties of HDDR magnet powder surface-coated with aluminum coating
An aluminum coating was formed on the surface of the HDDR magnet powder using the ion plating apparatus shown in FIG. Pure aluminum was used as the source of the aluminum film.
After storing 100 g of HDDR magnet powder in a powder holding container having an inner diameter of 500 mm, the degree of background vacuum inside the vacuum processing chamber is 1 × 10 ^-4 Evacuation was performed until the pressure became Pa or less.
Subsequently, by adjusting the amount of argon gas (carrier gas) introduced into the plasma gun and the evacuation speed inside the vacuum processing chamber, the cathode area was set to about 40 Pa, and the intermediate electrode area-auxiliary anode area was set to about 1.3 Pa. 4 × 10 inside the vacuum processing chamber ^-2 Pa was maintained.
Then, by vibrating and / or stirring the HDDR magnet powder by vibrating the powder holding container up, down, left and right, a double pressure gradient type orthogonal magnetic field discharge is performed by a plasma gun under the conditions of a DC discharge current of 100 A and a discharge voltage of 70 V. The discharge plasma flow is generated by irradiating the generated discharge plasma flow to pure aluminum as a source for forming an aluminum film accommodated in the melting and evaporating section, thereby heating and evaporating the aluminum to ionize it, thereby performing five types of treatments. By performing ion plating for a time, HDDR magnet powders (Samples 2 to 6) whose surfaces were coated with aluminum coatings having five different film thicknesses as shown in Table 1 were produced (Sample 1 is an untreated HDDR magnet powder). ).
When the samples 2 to 6 were observed with an optical microscope, no aggregates of the magnet powder were found, and the individual magnet particles were uniformly covered with the aluminum film. The thickness of the aluminum film formed on the surface of the HDDR magnet powder was determined by observing the fracture surface of magnet particles generated by crushing the sample lightly in a mortar with a scanning electron microscope (SEM). . For Samples 2 to 6, the volume ratio of the aluminum coating in the sample was determined by the mass ratio of aluminum determined by ICP emission spectrometry, and the density of the untreated HDDR magnet powder (Sample 1) (7.6 g / cm). ³ ), Density of aluminum (2.7 g / cm ³ ). Table 1 shows the results.
Samples 1 to 6 were subjected to a standing test in the air at 200 ° C. for 1 hour, and the magnetic properties (BH) of each sample before and after the test _max Was measured with a vibrating sample magnetometer (VSM) and the rate of decrease was calculated. Table 1 shows the results. As is evident from Table 1, as the thickness of the aluminum coating formed on the surface of the HDDR magnet powder increases, the oxidation resistance improves and the deterioration of the magnetic properties is suppressed.
[0023]
B: Production of bonded magnet using HDDR magnet powder surface-coated with aluminum coating
About Samples 1 to 6, sample: 92% by mass, nylon 12 resin: 6.7% by mass, titanate-based coupling agent (KR-TTS, manufactured by Ajinomoto Fine Techno Co.): 0.75% by mass, stearamide: 0.55% by mass was mixed and kneaded using a Labo Plastmill under the conditions of a rotation speed of 80 rpm, a kneading temperature of 230 ° C. and a kneading time of 10 minutes to prepare a compound for a bonded magnet. After pulverizing the prepared compound, using an injection molding machine in a magnetic field, the injection temperature is 270 ° C., the orientation magnetic field is 800 kA / m (in the height direction of the sample), the mold temperature is 80 ° C., and the diameter is 10 mm × height. A 7 mm cylindrical bonded magnet was produced.
The magnetic properties of the obtained cylindrical bonded magnet were evaluated with a BH tracer. Table 1 shows the results. Note that B _r / J _1.2 Is an index indicating the degree of orientation, and is a value of magnetization J at a magnetic field of 1.2 MA / m, and is a residual magnetic flux density B _r And the closer the value is to 1, the better the orientation.
As is clear from Table 1, the bonded magnets manufactured using Samples 2 to 5 had high magnetic properties. Above all, the bonded magnets manufactured using Samples 2 to 4 exhibited excellent orientation because the thickness of the aluminum coating formed on the surface of the HDDR magnet powder was 1 μm or less. In particular, the bonded magnets manufactured using Samples 2 and 3 had extremely high magnetic properties because the volume ratio of the aluminum coating in the samples was 3% or less.
On the other hand, since Sample 1 is an untreated HDDR magnet powder having no aluminum film formed on the surface, it has insufficient oxidation resistance and is oxidized in a high temperature environment during compound preparation or heat molding. As a result, a bonded magnet having high magnetic properties could not be manufactured. Sample 6 imparts sufficient oxidation resistance to the HDDR magnet powder. However, since the aluminum coating formed on the surface of the HDDR magnet powder was too thick, the magnetic characteristics were poor. In addition to being low, it was not possible to sufficiently orient the magnetization direction in the direction of the magnetic field, so that a bonded magnet having high magnetic properties could not be produced.
[0024]
[Table 1]

[0025]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the novel manufacturing method of the magnetically anisotropic rare earth-based bonded magnet which is excellent in oxidation resistance and has high magnetic characteristics is provided.
[Brief description of the drawings]
FIG. 1 is a schematic front view of an example of an ion plating apparatus for performing a manufacturing method of the present invention.
[Explanation of symbols]
1 vacuum processing chamber
2 Inorganic materials
3 Melt evaporation section
4 Powder holding container
5 Exhaust port
6 vacuum pump
7 Carrier gas inlet
8 Carrier gas introduction route
9 Plasma gun
10 Cathode
11 cylindrical first intermediate electrode
12 cylindrical second intermediate electrode
13 Auxiliary anode tube
14 Auxiliary anode ring
15 Electromagnetic coil
16 permanent magnet
17 Discharge power supply
18 Gas inlet
30 Ion particle descent region
F Discharge plasma flow
X Magnetic anisotropic rare earth magnet powder

Claims

As a method of forming an inorganic coating on the surface of a magnetically anisotropic rare earth magnet powder, a discharge plasma flow generated by a double pressure gradient type orthogonal magnetic field discharge in a vacuum processing chamber is housed in a melt evaporation section. By irradiating the inorganic material serving as a source of the formed inorganic film with heat to evaporate and ionize the inorganic material and performing ion plating, the inorganic film is formed on the surface of the vibrated and / or stirred magnet powder. A step of obtaining a magnet powder surface-coated with an inorganic coating having a thickness of 0.05 μm to 2 μm by this method, kneading the obtained inorganic coating magnet powder and a resin binder to form a compound for a bonded magnet. A magnetically anisotropic rare earth characterized by comprising a step of preparing, and a step of heat-forming into a predetermined shape while orienting in a magnetic field using the prepared compound. Manufacturing method of similar type bonded magnet.

2. The method according to claim 1, wherein the background vacuum inside the vacuum processing chamber when performing ion plating is 1 × 10 ⁻³ Pa or less.

3. The method according to claim 1, wherein the inorganic coating is a metal coating.

The method according to claim 3, wherein the metal coating is an aluminum coating.

2. The method according to claim 1, wherein the volume ratio of the inorganic coating in the inorganic coating-coated magnet powder is 3% or less.

The method according to any one of claims 1 to 5, wherein the resin binder is a thermoplastic resin.

The method according to any one of claims 1 to 6, wherein the heat molding into a predetermined shape is performed by any one method selected from injection molding, extrusion molding, and roll molding.

The method according to any one of claims 1 to 7, wherein the magnetically anisotropic rare earth magnet powder has an average particle size of 50 µm to 150 µm.

9. The method according to claim 8, wherein the average crystal grain size of the magnetically anisotropic rare earth magnet powder is 1 [mu] m or less.

10. The method according to claim 8, wherein the magnetically anisotropic rare earth magnet powder is an HDDR magnet powder.

A magnetically anisotropic rare-earth bonded magnet manufactured by the manufacturing method according to claim 1.

As a method of forming an inorganic coating on the surface of a magnetically anisotropic rare earth magnet powder, a discharge plasma flow generated by a double pressure gradient type orthogonal magnetic field discharge in a vacuum processing chamber is housed in a melt evaporation section. By irradiating the inorganic material serving as a source of the formed inorganic film with heat to evaporate and ionize the inorganic material and performing ion plating, the inorganic film is formed on the surface of the vibrated and / or stirred magnet powder. A method for producing a magnet powder coated with an inorganic coating, comprising a step of obtaining a magnet powder coated with an inorganic coating having a thickness of 0.05 μm to 2 μm by this method.

An inorganic coating-coated magnet powder produced by the production method according to claim 12.

As a method of forming an inorganic coating on the surface of a magnetically anisotropic rare earth magnet powder, a discharge plasma flow generated by a double pressure gradient type orthogonal magnetic field discharge in a vacuum processing chamber is housed in a melt evaporation section. By irradiating the inorganic material serving as a source of the formed inorganic film with heat to evaporate and ionize the inorganic material and performing ion plating, the inorganic film is formed on the surface of the vibrated and / or stirred magnet powder. A step of obtaining a magnet powder surface-coated with an inorganic coating having a thickness of 0.05 μm to 2 μm by this method, kneading the obtained inorganic coating magnet powder and a resin binder to form a compound for a bonded magnet. A method for producing a compound for a bonded magnet, comprising a step of preparing.

A compound for a bonded magnet manufactured by the manufacturing method according to claim 14.