【０００１】
【発明の属する技術分野】
本発明は熱収縮型希土類磁石の製造方法およびその永久磁石型モ−タに関する。更に詳しくは磁気的に等方性から異方性に至る希土類磁石に熱収縮機能を付与することにより、当該磁石、非磁性から磁性に至る支持部材、或いは回転軸と低熱機械的負荷によって一体化するもので、高寸法精度と高（ＢＨ）ｍａｘ（最大エネルギ−積）の薄肉環状磁石を搭載した永久磁石型モ−タを提供することができる。したがって、本熱収縮型希土類磁石を応用した永久磁石型モ−タは出力数〜数十Ｗ級のＯＡ、ＡＶ、家電、空調機器の駆動源として利用される表面磁石型同期モ−タ、および永久磁石型ステップモ−タなどの高出力化・高効率化に寄与することができる。
【０００２】
【従来の技術】
ＯＡ、ＡＶ、家電、空調機器等に搭載されるモ−タは機器の小型軽量化への対応とともに、省電力化の努力がなされてきた。しかし、家庭や工場、事務所の電力消費（約９０００億ｋＷｈ／９６年度）の内訳をみると、何れもモ−タによる電力消費が多く、全体でも５０％を超えると推定される。昨今、地球温暖化防止、オゾン層保護など地球環境保全のうえで、更なる高効率モ−タの開発と普及が求められている。モ−タの高効率化には損失削減または高出力化が必要である。高出力化の鍵の一つは磁石であり、磁石素材の性能を如何にモ−タ性能に反映させるかが重要である。ところで、個々のモ−タに応用するために必要な磁石の具備すべき条件は、▲１▼空隙に必要な静磁界を与え得る磁気特性、▲２▼非可逆減磁に代表される安定性、▲３▼求める形状に応じられる形状任意性、▲４▼原料の資源確保から実装に至るまでの総合的な経済性の４点において、最も高い整合性を獲得しなければならない。一般にモ−タ効率と小型化とは相反する関係にあり、数百Ｗ以下の比較的小型の磁石モ−タでは、磁石とモ−タづくりとの融合を進展させる必要がある。
【０００３】
上記、小型モ−タに広く使われるボンド磁石に関して、非特許文献１：広沢、富澤らの“Ｒｅｃｅｎｔ Ｐｒｏｇｒｅｓｓ ｉｎ Ｒｅｓｅａｒｃｈ ａｎｄＤｅｖｅｌｏｐｍｅｎｔ Ｒｅｌａｔｅｄ ｔｏ Ｂｏｎｄｅｄ Ｒａｒｅ−Ｅｒａｔｈ Ｐｅｒｍａｎｅｎｔ Ｍａｇｎｅｔｓ”日本応用磁気学会誌，Ｖｏｌ．２１，Ｎｏ．４−１，ｐｐ．１６１〜１６７（１９９７）が端的に解説している。磁石粉末を結合剤で固めたボンド磁石では磁石粉末、結合剤、成形加工がそれぞれ等しく重要である。したがって、引用文献に基づく図１を用いてボンド磁石作製における３大要素技術、すなわち磁石粉末、結合剤、成形加工の連携を説明する。
【０００４】
先ず、磁石粉末▲１▼としてはフェライト系▲１▼−ａ、アルニコ系▲１▼−ｂ、希土類系▲１▼−ｃ、結合剤システム▲２▼としてはフレキシブル系（ゴム、熱可塑性エラストマ−）▲２▼−ａ、堅い熱可塑性樹脂▲２▼−ｂ、堅い熱硬化性樹脂▲２▼−ｃ、加工方法▲３▼としてはカレンダ−リング▲３▼−ａ、押出成形▲３▼−ｂ、射出成形▲３▼−ｃ、圧縮成形▲３▼−ｄがある。そして、それらの連携は図中の実線で示すように整理される。例えば、希土類系磁石粉末▲１▼−ｃは結合剤システム▲２▼としてフレキシブル系（ゴム、熱可塑性エラストマ−）▲２▼−ａ、堅い熱可塑性樹脂▲２▼−ｂ、堅い熱硬化性樹脂▲２▼−ｃ、また、成形加工方法▲３▼としてカレンダ−リング▲３▼−ａ、押出成形▲３▼−ｂ、射出成形▲３▼−ｃ、圧縮成形▲３▼−ｄというように▲２▼と▲３▼の全ての要素と連携している。しかし、圧縮成形▲３▼−ｄと希土類系磁石粉末▲１▼−ｃとの連携では、結合剤システム▲２▼の要素が、例えばエポキシ樹脂のような堅い熱硬化性樹脂▲２▼−ｄとの関係に限られるのが現状である。
【０００５】
上記、ボンド磁石作製における３大要素技術、すなわち希土類系磁石粉末▲１▼−ｃ、結合剤▲２▼、成形加工▲３▼との連携とモ−タの高性能化の関係としては、例えば非特許文献２：Ｆ．Ｙａｍａｓｈｉｔａ，Ｙ．Ｓａｓａｋｉ，Ｈ．Ｆｕｋｕｎａｇａ，“Ｉｓｏｔｒｏｐｉｃ Ｎｄ−Ｆｅ−Ｂ Ｔｈｉｎ Ａｒｃ−ｓｈａｐｅｄ Ｂｏｎｄｅｄ Ｍａｇｎｅｔｓ ｆｏｒ Ｓｍａｌｌ ＤＣ ＭｏｔｏｒｓＰｒｅｐａｒｅｄ ｂｙ Ｐｏｗｄｅｒ Ｃｏｍｐａｃｔｉｎｇ Ｐｒｅｓｓｗｉｔｈ Ｍｅｔａｌ Ｉｏｎ−ｉｍｐｌａｎｔｅｄ Ｐｕｎｃｈｅｓ”，日本応用磁気学会誌，Ｖｏｌ．２５，Ｎｏ．４−２，ｐｐ．６８３〜６８６（２００１）の記載のように、最大厚さ０．９ｍｍの薄肉円弧状磁石の作製において、希土類系磁石粉末▲３▼−ｄ／堅い熱可塑性樹脂▲２▼−ｂ／押出成形▲３▼−ｂとの連携から、希土類系磁石粉末▲３▼−ｄ／堅い熱硬化性樹脂▲２▼−ｃ／圧縮成形▲３▼−ｃへの連携に変更することで、出力２００ｍＷ級の永久磁石界磁型小型ＤＣモ−タの最大効率を８％改善している。このことは、希土類系磁石粉末が全く同であっても、他の連携要素との組換えにより効率的な小型モ−タが提供できることを示唆している。
【０００６】
本発明者らによる、効率的な小型モ−タへの提案は、例えば特許文献１：特公平６−８７６３４号公報を引用することができる。すなわち、電機子鉄心と対向した空隙に強力な静磁界をつくるため、磁気的に等方性のＲ−Ｆｅ−Ｂ（ＲはＮｄ／Ｐｒ）希土類系磁石粉末▲１▼−ｃと堅いエポキシ樹脂▲２▼−ｃとを圧縮成形▲３▼−ｄした外径２５ｍｍ以下、密度５Ｍｇ／ｍ３以上の環状ボンド磁石を多極着磁した構成の永久磁石型モ−タである。磁気的に異方性の希土類系磁石粉末▲１▼−ｃは小径化に伴っての配向度が低下するために、結合剤システムとして堅い熱可塑性樹脂▲２▼−ｂで射出成形▲３▼−ｃしたり、堅い熱硬化性樹脂▲２▼−ｃで圧縮成形▲３▼−ｄする連携に拘らず、ラジアル異方性磁石は小径化に伴って配向度が低下するため、半径方向の磁気特性が低下する。したがって、ラジアル異方性磁石を使ったモ−タは小径化に伴った磁石の半径方向の磁気特性低下に連動したモ−他の機械出力低下を免れなかった。すなわち、小型化に伴って次第に効率的でないモ−タとなってしまう欠点があった。しかしながら、磁気的に等方性の希土類磁石粉末であれば環状磁石の径に依存することなく、例えば磁気的に等方性Ｎｄ２Ｆｅ１４Ｂ系希土類磁石粉末を圧縮成形することで最大エネルギ−積（ＢＨ）ｍａｘ８０ｋＪ／ｍ３に達する。この値は、フェライト系フレキシブル磁石の（ＢＨ）ｍａｘ１２ｋＪ／ｍ３のおよそ６．７倍である。その結果、この種の磁石は小型モ−タの高出力化、低消費電流化に効果を奏し、電子機器分野を主体に、所謂効率的な小型モ−タとして認知された。例えば、フェライト系磁石粉末▲１▼−ａ／フレキシブル系（ゴム、熱可塑性エラストマ−）▲２▼−ａ／カレンダ−リング▲３▼−ａ、または押出成形▲３▼−ｂという連携のもとで製造された厚さ１．５５ｍｍ、幅７．２ｍｍのシ−ト状磁石を帯状に切断し、カ−リングして内径２２．５ｍｍの回転子枠の周壁内面に固着した小型モ−タの起動トルク１．５ｍＮ−ｍに対し、磁気的に等方性のＮｄ２Ｆｅ１４Ｂ系希土類磁石粉末▲１▼−ｃと堅いエポキシ樹脂▲２▼−ｃとを圧縮成形▲３▼−ｄした外径２２．５ｍｍ、厚さ１．１０ｍｍ、高さ９．４ｍｍ、密度５．８Ｍｇ／ｍ３の磁石を使った永久磁石型モ−タの起動トルクは１３倍の２０ｍＮ−ｍに達する。
【０００７】
ところで、ＰＭ型ステップモ−タや同期モ−タに用いられるロ−タ表面に磁石を配置した構造の磁石ロ−タを対象とし、磁石とモ−タづくりとの融合を図った従来技術として、磁気的に等方性のＮｄ２Ｆｅ１４Ｂ系希土類磁石粉末▲１▼−ｃと液体エポキシオリゴマ−を内包したカプセルを含む堅いエポキシ樹脂▲２▼−ｃとのコンパウンドを鉄心の外周側面で圧縮成形▲３▼−ｄした鉄心一体型グリ−ンコンパクトを加熱硬化する鉄心一体型磁石が非特許文献３：Ｍ．Ｗａｄａ，Ｆ．Ｙａｍａｓｈｉｔａ，“Ｎｄ−Ｆｅ−Ｂ Ｒｅｓｉｎ Ｂｏｎｄｅｄ Ｍａｇｎｅｔ ｔｏ ｔｈｅ Ｂｒｕｓｈ−ｌｅｓｓ Ｍｏｔｏｒ ｆｏｒ Ｈｏｍｅ Ａｐｐｌｉａｎｃｅ Ｕｓｅ”，Ｐｒｏｃ．１０ｔｈ Ｉｎｔ．Ｗｏｒｋｓｈｏｐ ｏｎＲａｒｅ−Ｅａｒｔｈ Ｍａｇｎｅｔｓ ａｎｄ Ｔｈｅｉｒ Ａｐｐｌｉｃａｔｉｏｎｓ（ＩＩ），ｐｐ．９１〜１０１（１９８９）に記載されている。図２は上記引例に記載されている鉄心一体型磁石のグリ−ンコンパクトを粉末成形で作製する工程図である。ただし、図中Ａは充填工程、Ｂは圧縮工程、Ｃは離型工程、Ｄは加熱処理工程であり、１１は積層鉄心、１２はコンパウンド、１３はダイ、１４は下コア、１５は下パンチ、１６はフィ−ダカップ、１７は上パンチ、１８は上コア、１９は磁石圧粉体、２０はグリ−ンコンパクトに含まれるエポキシ樹脂を加熱硬化した鉄心一体型磁石である。この磁石は回転軸を鉄心に圧入して磁石ロ−タとなる。先ず、図中の工程に従って通常８〜１０ｔｏｎ／ｃｍ２でコンパウンドを圧縮する。その後、型から離型すると通常０．６５〜０．７０％のスプリングバックがある。しかし、この技術は磁石のスプリングバックを抑えて鉄心と磁石とを接着レスとし、磁石ロ−タとしての機械強度と寸法精度を確保した鉄心一体型磁石としている。
【０００８】
図３は上記、磁気的に等方性のＮｄ２Ｆｅ１４Ｂ系希土類磁石粉末▲１▼−ｃの含有量が９５ｗｔ．％のコンパウンドを圧縮して、外径４８ｍｍ積厚１１ｍｍの鉄心外周面に厚さ１ｍｍの鉄心一体型磁石の磁石と鉄心との境界部分の断面図を示す。磁石１と鉄心２とが接着層または空隙なく一体化していることが了解される。
【０００９】
図４は、上記外径４８ｍｍ積厚１１ｍｍの鉄心外周に厚さ１ｍｍの環状磁石を配置した鉄心一体型磁石において、磁気的に等方性のＮｄ２Ｆｅ１４Ｂ系希土類磁石粉末▲１▼−ｃの含有量に対するスプリングバック、および鉄心一体型磁石の磁石と鉄心間の接合強さ（せん断力）の関係を示す特性図である。図のように磁石粉末を９５ｗｔ．％以下（エポキシ樹脂を５ｗｔ．％以上）とすることでスプリングバックを通常の１／１０以下の０．０７％以下に抑制し、その結果として磁石と鉄心との接合力を得ている。
【００１０】
以下に、従来の技術の説明にて示した特許文献及び非特許文献を記載する。
【００１１】
【特許文献１】
特公平６−８７６３４号公報
【非特許文献１】
広沢、富澤らの“Ｒｅｃｅｎｔ Ｐｒｏｇｒｅｓｓ ｉｎ Ｒｅｓｅａｒｃｈ ａｎｄ Ｄｅｖｅｌｏｐｍｅｎｔ Ｒｅｌａｔｅｄ ｔｏ Ｂｏｎｄｅｄ Ｒａｒｅ−Ｅｒａｔｈ Ｐｅｒｍａｎｅｎｔ Ｍａｇｎｅｔｓ”日本応用磁気学会誌，Ｖｏｌ．２１，Ｎｏ．４−１，ｐｐ．１６１〜１６７（１９９７）
【非特許文献２】
Ｆ．Ｙａｍａｓｈｉｔａ，Ｙ．Ｓａｓａｋｉ，Ｈ．Ｆｕｋｕｎａｇａ，“Ｉｓｏｔｒｏｐｉｃ Ｎｄ−Ｆｅ−Ｂ Ｔｈｉｎ Ａｒｃ−ｓｈａｐｅｄ Ｂｏｎｄｅｄ Ｍａｇｎｅｔｓ ｆｏｒ Ｓｍａｌｌ ＤＣ Ｍｏｔｏｒｓ Ｐｒｅｐａｒｅｄ ｂｙ Ｐｏｗｄｅｒ Ｃｏｍｐａｃｔｉｎｇ Ｐｒｅｓｓ ｗｉｔｈＭｅｔａｌ Ｉｏｎ−ｉｍｐｌａｎｔｅｄ Ｐｕｎｃｈｅｓ”，日本応用磁気学会誌，Ｖｏｌ．２５，Ｎｏ．４−２，ｐｐ．６８３〜６８６（２００１）
【非特許文献３】
Ｍ．Ｗａｄａ，Ｆ．Ｙａｍａｓｈｉｔａ，“Ｎｄ−Ｆｅ−Ｂ Ｒｅｓｉｎ Ｂｏｎｄｅｄ Ｍａｇｎｅｔ ｔｏ ｔｈｅ Ｂｒｕｓｈ−ｌｅｓｓ Ｍｏｔｏｒ ｆｏｒ Ｈｏｍｅ Ａｐｐｌｉａｎｃｅ Ｕｓｅ”，Ｐｒｏｃ．１０ｔｈ Ｉｎｔ．Ｗｏｒｋｓｈｏｐ ｏｎ Ｒａｒｅ−Ｅａｒｔｈ Ｍａｇｎｅｔｓａｎｄ Ｔｈｅｉｒ Ａｐｐｌｉｃａｔｉｏｎｓ（ＩＩ），ｐｐ．９１〜１０１（１９８９）
【００１２】
【発明が解決しようとする課題】
しかしながら、上記のような磁石のスプリングバックを０．０７％以下に抑制し、高いせん断強さの鉄心一体型磁石を作製するには磁石に含まれるエポキシ樹脂の割合を５％以上に設定する必要がある。
【００１３】
図５は上記磁石の密度と磁気特性の関係を示す特性図である。図のように、磁石の残留磁化Ｉｒや（ＢＨ）ｍａｘは当該磁石の密度に依存する。例えば、エポキシ樹脂の含有量を１．５ｗｔ．％とした合金組成Ｎｄ１２Ｆｅ７７Ｃｏ５Ｂ６の磁気的に等方性のＮｄ２Ｆｅ１４Ｂ系希土類磁石粉末▲１▼−ｃとのコンパウンドを９８０ＭＰａで圧縮し、その磁石圧粉体のエポキシ樹脂を加熱硬化して作製した磁石は密度６．１Ｍｇ／ｍ３、４ＭＡ／ｍのパルス磁界で磁化した後の（ＢＨ）ｍａｘは８３ｋＪ／ｍ３が得られる。これに対し、鉄心一体型磁石の作製に最低限必要なエポキシ樹脂の割合５ｗｔ．％とし、同じ合金組成Ｎｄ１２Ｆｅ７７Ｃｏ５Ｂ６の磁石粉末コンパウンドを９８０ＭＰａで圧縮し、グリ−ンコンパクトに含まれるエポキシ樹脂を加熱硬化して作製した磁石は５．４〜５．５Ｍｇ／ｍ３以上の密度が得られない。したがって、４ＭＡ／ｍのパルス磁界で磁化した後の（ＢＨ）ｍａｘは５８ｋＪ／ｍ３と、密度６．１Ｍｇ／ｍ３の磁石に比べて同一磁石粉末を使用しているにも拘らず（ＢＨ）ｍａｘが概３０％減少する。したがって、上記技術に準じた方法で鉄心一体型磁石を作製すると磁石の（ＢＨ）ｍａｘの減少が避けられず、この意味から磁石粉末の本来の性能をモ−タ性能に十分反映できないという課題があった。
【００１４】
図６は永久磁石型モ−タなどに用いられる代表的な磁石ロ−タの外観を示す。ただし、図中１は例えば磁気的に等方性のＮｄ２Ｆｅ１４Ｂ系希土類磁石粉末▲１▼−ｃと堅いエポキシ樹脂▲２▼−ｃとのコンパウンドを９８０ＭＰａで圧縮成形▲３▼−ｄし、エポキシ樹脂▲２▼−ｃを加熱硬化して作製した環状磁石、２は回転軸、３は成形材料である。この磁石ロ−タの作製は環状の磁石１とともに回転軸２を成形型キャビティに装填し、それらの間隙にＰＢＴ（ポリブチレンテレフタレ−ト），ＰＥＴ（ポリエチレンテレフタレ−ト）などの高分子材料をマトリクスとしたガラス繊維強化成形材料３を、例えば２２０〜２８０℃、１０００〜１２００ＭＰａという高温高圧下で射出充填し、金型内で冷却・固化することにより磁石と回転軸とを当該成形材料によって固定し、磁石ロ−タとしていた。この場合、磁石密度は６．１Ｍｇ／ｍ３、４ＭＡ／ｍのパルス磁界で磁化した後の（ＢＨ）ｍａｘは８３ｋＪ／ｍ３と高性能な磁石となる。しかしながら、薄肉形状の磁石を金型内に装填すると、磁石は成形材料と一体化する際の熱機械的負荷に耐えることができない。したがって、磁石ロ−タ作製における歩留まりを確保するために、（１）磁石に含まれるエポキシ樹脂の増量、または、（２）磁石を厚肉化せざるを得ず、磁石粉末を必要以上に消費する割に、磁石粉末のもつ本来の磁気性能をモ−タ性能に十分反映できないという課題があった。
【００１５】
以上、磁気的に等方性の希土類系磁石粉末▲１▼−ｃと堅いエポキシ樹脂のような熱硬化性樹脂▲２▼−ｃとともに圧縮成形▲３▼−ｄした磁石、それらを利用した小型モ−タを主対象とし、より効率的な永久磁石型モ−タと、それに伴う磁石の製造方法を提供することが本発明の目的である。
【００１６】
【課題を解決するための手段】
本発明は、図１のボンド磁石製造における３大要素技術において▲１▼磁石粉末を希土類磁石粉末、▲２▼結合剤を熱硬化性樹脂組成物、▲３▼成形加工法を圧縮成形、圧延、および熱処理とする新規な熱収縮型希土類磁石の製造方法、並びにそれを利用した新規な高性能永久小型磁石型モ−タ▲４▼の提供を目的とする。
【００１７】
（作用）
更に詳しくは、希土類磁石粉末と熱硬化性樹脂組成物とのコンパウンドを圧縮成形した環状グリ−ンコンパクトの結合剤成分を熱硬化して磁石とし、当該磁石を圧延し、然るのち熱収縮せしめる熱収縮型希土類磁石の製造方法。或いは希土類磁石粉末と熱硬化性樹脂組成物とのコンパウンドを圧縮成形したグリ−ンシ−トを環状に形成し、結合剤成分を熱硬化してシ−ト磁石とし、然るのち当該シ−ト磁石を圧延し、熱収縮せしめる熱収縮型希土類磁石の製造方法。更には、希土類磁石粉末と熱硬化性樹脂組成物とのコンパウンドを圧縮成形したグリ−ンシ−トの結合剤成分を熱硬化してシ−ト磁石とし、当該シ−ト磁石を環状に形成し、圧延し、然るのち熱収縮する熱収縮型希土類磁石の製造方法が基本となる。
【００１８】
上記のような熱収縮型希土類磁石の製造方法では飽和磁化１．３Ｔ以上のＦｅ，Ｆｅ−Ｎｉ，Ｆｅ−Ｃｏ，Ｆｅ−Ｓｉ，Ｆｅ−Ｎ，Ｆｅ−Ｂの群から選ばれる１種または２種以上と熱硬化性樹脂組成物、および必要に応じて適宜加える添加剤とで構成したコンパウンドを圧縮成形した軟磁性体との複合体であっても差し支えない。
【００１９】
図７は本発明に係る熱収縮型希土類磁石とそれを応用した永久磁石型モ−タのロ−タの構成図である。図において、１は磁石で、極数は４で代表している。２は磁性、或いは非磁性支持部材、３は熱収縮型希土類磁石との複合体を形成する熱収縮型軟磁性部材、４は回転軸である。
【００２０】
本発明に係る上記熱収縮型希土類磁石１を熱収縮せしめる際に、圧延した環状磁石１を環状非磁性支持部材２に挿入し、然るのち熱処理する非磁性支持部材一体、熱収縮型希土類磁石［図７（ａ）］の製造方法、並びに前記多極着磁した非磁性支持部材一体、熱収縮型希土類磁石［図７（ａ）］をロ−タとしたＰＭ型ステッピングモ−タ。圧延した軟磁性体３との複合環状磁石１を環状非磁性支持部材に挿入し、然るのち熱処理する非磁性支持部材一体、軟磁性複合熱収縮型希土類磁石［図７（ｂ）］の製造方法、並びに前記多極着磁した非磁性支持部材一体、軟磁性複合熱収縮型希土類磁石［図７（ｂ）］をロ−タとした永久磁石型モ−タ。圧延した環状磁石１を環状磁性支持部材２に挿入し、然るのち熱処理する磁性支持部材一体、熱収縮型希土類磁石［図７（ａ）］の製造方法、並びに前記多極着磁した磁性支持部材一体、熱収縮型希土類磁石［図７（ａ）］をロ−タとした永久磁石型モ−タ。圧延した環状磁石１を回転軸４に挿入し、然るのち熱処理する回転軸一体、熱収縮型希土類磁石［図７（ｃ）］の製造方法、並びに前記多極着磁した回転軸一体、熱収縮型希土類磁石［図７（ｃ）］をロ−タとした永久磁石型モ−タを挙げることができる。なお、環状磁石は図７（ａ），（ｂ），（ｃ）］のように均質である必要はなく、不等肉厚［図７（ｄ）］であったり、不等幅［図７（ｅ）］とし、ステ−タ鉄心との空隙磁束密度分布を正弦波状に近づけるようにすることもできる。
【００２１】
次に、本発明で言う結合剤は、少なくとも融点以下での熱圧着機能と熱硬化性官能基を有する粉末状樹脂成分を有し、コンパウンドが、１種または２種以上の粘着剤によって希土類磁石粉末と他の結合剤成分を物理的に統合する結合剤で構成される。更に詳しくは、結合剤を構成する熱硬化性樹脂組成物が、少なくとも室温で固体のエポキシオリゴマ−と室温で粘着性を付与した熱圧着性ポリアミドまたは／およびポリアミドイミド粉末、および必要に応じて適宜加える粉末状潜在性エポキシ硬化剤、滑剤から構成される。希土類磁石粉末は、平均膜厚が０．１μｍ以下の室温で固体のエポキシオリゴマ−で表面被覆することが望ましい。また、その平均膜厚は０．１μｍ以下とする。これは、異方性の希土類磁石粉末同士の２次凝集による配向度の低下を防ぐために重要である。更に、希土類磁石粉末へのエポキシオリゴマ−の被覆方法としては、先ず、当該エポキシオリゴマ−を有機溶媒に溶解し、その後、希土類磁石粉末と湿式混合し、溶媒を除去した当該塊状混合物を解砕する。
【００２２】
上記、本発明で言うエポキシオリゴマ−とは１分子中に少なくとも２個以上のオキシラン環を有する化合物で、室温で固体、且つアセトンなどの有機溶媒に易溶である必要がある。エポキシオリゴマ−として好ましくは、分子鎖内にオキシラン環を有する下記化学構造で表せる軟化温度７０℃以上、エポキシ当量２３５以下のノボラック型エポキシオリゴマ−を挙げることができる。
【００２３】
次に、上記エポキシオリゴマ−と架橋する粉末エポキシ硬化剤とはジシアンジアミドおよびその誘導体、カルボン酸ジヒドラジド、ジアミノマレオニトリルおよびその誘導体のヒドラジドの群より選ばれた１種または２種以上などを挙げることができる。これ等は一般に有機溶媒に難溶の高融点化合物であるが、粒子径を数ないし数十μｍに調整したものが好ましい。なお、ジシアンジアミド誘導体としては、例えばｏ−トリルビグアニド、α−２・５−ジメチルビクアニド、α−ω−ジフェニルビグアニド，５−ヒドロキシブチル−１−ビグアニド、フェニルビグアニド、α−，ω−ジメチルビクアニドなどがある。更に、カルボン酸ジヒドラジドとしてはコハク酸ヒドラジド、アジピン酸ヒドラジド、イソフタル酸ヒドラジド，ｐ−アキシ安息香酸ヒドラジドなどがある。これらの硬化剤はコンパウンドに乾式混合によって添加することが望ましい。なお、コンパウンドの成形型への移着を防ぐには、成形型の設定温度よりも高融点の高級脂肪酸、高級脂肪酸アミド、高級脂肪酸金属石鹸類から選ばれる１種または２種以上を０．２ｗｔ．％以下コンパウンドに乾式混合によって添加することが望ましい
本発明に係る熱収縮型希土類磁石は希土類磁石粉末の含有量が９２ｗｔ．％から９８ｗｔ．％の範囲とし、このようなコンパウンドの圧縮成形は圧力３９０ＭＰａ以上、温度５０℃以上とすることで、高密度グリ−ンコンバクトを作製することができる。グリ−ンコンバクトは環状もしくはシ−ト状とし、シ−ト状の場合には当該グリ−ンコンパクトの端面を接合して環状としたのちに熱硬化しても差し支えない。
【００２４】
本発明に係る圧延は図８（ａ）（ｂ）のような等速ロ−ルにより行う。ただし、図中１は圧延ロ−ル、２は本発明に係る希土類磁石を示している。図において、圧延率を３〜１２％とすると、例えば熱収縮率３〜７％の熱収縮型希土類磁石に調整することができる。なお、熱収縮温度は当該磁石の使用温度上限以上とすると、その後の実使用での高温暴露における磁石の寸法安定性を確保することができる。一方磁気的に異方性の希土類磁石粉末を含む圧延後の厚さを１ｍｍ以下、圧延率を１５％以下とすると圧延における配向の低下を抑制した熱収縮型希土類磁石を提供することができる。
【００２５】
次に、磁気的に等方性の希土類磁石粉末としてはスピニングカップアトマイゼ−ションによって準備されたＮｄ２Ｆｅ１４Ｂ系球状粉末（Ｂ．Ｈ．Ｒａｂｉｎ，Ｂ．Ｍ．Ｍａ、”Ｒｅｃｅｎｔ Ｄｅｖｅｌｏｐｍｅｎｔｓ ｉｎ ＮｄＦｅＢＰｏｗｄｅｒ” １２０ｔｈ Ｔｏｐｉｃａｌ Ｓｙｍｐｏｓｉｕｍ ｏｆ ｔｈｅ Ｍａｇｎｅｔｉｃ Ｓｏｃｉｅｔｙ ｏｆ Ｊａｐａｎ ２３，２００１）．メルトスピニング（Ｊ．Ｊ．Ｃｒｏａｔ，Ｊ．Ｆ．Ｈｅｒｂｓｔ，Ｒ．Ｗ．Ｌｅｅ ａｎｄ Ｆ．Ｅ．Ｐｉｎｋｅｒｔｏｎ，Ｊ．Ａｐｐｌ．Ｐｈｙｓ．，５５，２０７８，１９８４）によって準備されたＮｄ２Ｆｅ１４Ｂ系フレ−ク状粉末（Ｒ．Ｗ．Ｌｅｅ ａｎｄ Ｊ．Ｊ．Ｃｒｏａｔ，ＵＳ−Ｐａｔｅｎｔ ４，９０２，３６１．１９９０）、αＦｅ／Ｎｄ２Ｆｅ１４Ｂ系フレ−ク状粉末、Ｆｅ３Ｂ／Ｎｄ２Ｆｅ１４Ｂ系フレ−ク状粉末、Ｓｍ２Ｆｅ１７Ｎ３系フレ−ク状粉末、αＦｅ／Ｓｍ２Ｆｅ１７Ｎ３系フレ−ク状粉末、などを挙げることができる。
【００２６】
次に、磁気的に異方性の希土類磁石粉末としては熱間据込加工（Ｄｉｅ−Ｕｐ−Ｓｅｔｔｉｎｇ）によるＮｄ２Ｆｅ１４Ｂ系塊状粉末（例えば、Ｍ．Ｄｏｓｅｒ，Ｖ．Ｐａｎｃｈａｎａｔｈａｎ；”Ｐｕｌｖｅｒｉｚｉｎｇ ａｎｉｓｏｔｒｏｐｉｃ ｒａｐｉｄｌｙ ｓｏｌｉｄｉｆｉｅｄ Ｎｄ−Ｆｅ−Ｂ ｍａｔｅｒｉａｌｓ ｆｏｒ ｂｏｎｄｅｄ ｍａｇｎｅｔ”；Ｊ．Ａｐｐｌ．Ｐｈｙｓ．７０（１０），１５，１９９３）。ＨＤＤＲ処理（水素分解／再結合）によって準備された磁気的に異方性のＮｄ２Ｆｅ１４Ｂ系塊状粉末、すなわち、Ｎｄ−Ｆｅ（Ｃｏ）−Ｂ系合金のＮｄ２（Ｆｅ，Ｃｏ）１４Ｂ相の水素化（Ｈｙｄｒｏｇｅｎａｔｉｏｎ，Ｎｄ２［Ｆｅ，Ｃｏ］１４ＢＨｘ），６５０〜１０００℃での相分解（Ｄｅｃｏｍｐｏｓｉｔｉｏｎ，ＮｄＨ２＋Ｆｅ＋Ｆｅ２Ｂ）、脱水素（Ｄｅｓｏｒｐｓｉｏｎ）、再結合（Ｒｅｃｏｍｂｉｎａｔｉｏｎ）するＨＤＤＲ処理（Ｔ．Ｔａｋｅｓｈｉｔａ ａｎｄ Ｒ．Ｎａｋａｙａｍａ：Ｐｒｏｃ．ｏｆ ｔｈｅ １０ｔｈ ＲＥ Ｍａｇｎｅｔｓ ａｎｄ Ｔｈｅｉｒ Ａｐｐｌｉｃａｔｉｏｎｓ，Ｋｙｏｔｏ，Ｖｏｌ．１，５５１ １９８９）で作製した磁気的に異方性の希土類磁石粉末である。前記粉末の表面を予め光分解したＺｎなど不活性化処理した粉末など（例えば、Ｋ．Ｍａｃｈｉｄａ，Ｋ．Ｎｏｇｕｃｈｉ，Ｍ．Ｎｕｓｈｉｍｕｒａ，Ｙ．Ｈａｍａｇｕｃｈｉ，Ｇ．Ａｄａｃｈｉ，Ｐｒｏｃ．９ｔｈ Ｉｎｔ．Ｗｏｒｋｓｈｏｐ ｏｎ Ｒａｒｅ−Ｅａｒｔｈ Ｍａｇｎｅｔｓ ａｎｄＴｔｈｅｉｒ Ａｐｐｌｉｃａｔｉｏｎｓ，Ｓｅｎｄａｉ，Ｊａｐａｎ，ＩＩ，８４５ ２０００，或いは、Ｋ．Ｍａｃｈｉｄａ，Ｙ．Ｈａｍａｇｕｃｈｉ，Ｋ．Ｎｏｇｕｃｈｉ，Ｇ．Ａｄａｃｈｉ，Ｄｉｇｅｓｔｓ ｏｆ ｔｈｅ ２５ｔｈ Ａｎｎｕａｌ ｃｏｎｆｅｒｅｎｃｅ ｏｎ Ｍａｇｎｅｔｃｓｉｎ Ｊａｐａｎ，２８ａＣ−６ ２００１）を挙げることができる。一方、磁気的に異方性の希土類磁石粉末としてはＲＤ（酸化還元）処理によって準備されたＳｍ２Ｆｅ１７Ｎ３系微粉末、前記粉末表面を予め不活性化処理した粉末を挙げることもできる。
【００２７】
上記、希土類系磁石粉末は単独でも、或いは２種以上の混合系であっても差し支えない。なお、本発明に係る熱収縮型希土類磁石の４ＭＡ／ｍパルス着磁後の室温における最大エネルギ−積（ＢＨ）ｍａｘは８０ｋＪ／ｍ３以上、とくに１３０ｋＪ／ｍ３以上であることが望ましい。
【００２８】
【発明の実施の形態】
以下、本発明を実施例により更に詳しく説明する。ただし、本発明は実施例によって限定されるものではない。
【００２９】
（実施例の説明１、材料）
本実施例では磁気的に等方性のスピニングカップガスアトマイゼ−ションによって準備されたＮｄ２Ｆｅ１４Ｂ系球状磁石粉末（Ｎｄ１３．３Ｆｅ６２．５Ｂ６．８Ｇａ０．３Ｚｒ０．１）ｐｏｗｄｅｒ−Ａ，ＨＤＤＲ処理（水素分解／再結合）によって準備された磁気的に異方性のＨＤＤＲ−Ｎｄ２Ｆｅ１４Ｂ系磁石粉末（Ｎｄ１２．３Ｄｙ０．３Ｆｅ６４．７Ｃｏ１２．３Ｂ６．０Ｇａ０．６Ｚｒ０．１）ｐｏｗｄｅｒ−Ｂを使用した。
【００３０】
また、結合剤の構成成分としては室温で固体のノボラック型エポキシオリゴマ−、粒子径１５μｍ以下の粉末状潜在性エポキシ硬化剤、粘着剤を含み予め１００μｍ以下に冷凍粉砕したポリアミド粉末、並びに粒子径１０μｍ以下の滑剤が、この実施例で使用された。なお、ノボラック型エポキシオリゴマ（化１）、１，２−ドデカン酸エステル１ｍｏｌと、アクリル酸エステル２ｍｏｌの付加反応生成物にヒドラジンを反応させて得られる平均粒子径３０〜５０μｍの酸ヒドラジド粉末状潜在性エポキシ硬化剤（化２）の化学構造は以下の通りである。
【００３１】
【化１】
【００３２】
（ＮＨ２ＮＨＣＯＣＨ２ＣＨ２）２Ｎ（ＣＨ２）１１ＣＯＮＨＮＨ２・・（化２）
【００３３】
（実施例の説明２、製造プロセス）
本発明は磁気的に等方性のスピニングカップガスアトマイゼ−ションによって準備されたＮｄ２Ｆｅ１４Ｂ系球状磁石粉末（Ｎｄ１３．３Ｆｅ６２．５Ｂ６．８Ｇａ０．３Ｚｒ０．１）ｐｏｗｄｅｒ−Ａをベ−スとして、要求される磁気特性に合わせて磁気的に異方性のＨＤＤＲ−Ｎｄ２Ｆｅ１４Ｂ系磁石粉末ｐｏｗｄｅｒ−Ｂのような希土類磁石粉末の１種または２種以上から様々な特性と形態の熱収縮型希土類磁石を作製し、効率的な小型モ−タに適用するためになされた。図９は本発明にかかる異方性熱収縮型希土類磁石の製造プロセスの要部を示す模式図である。とくに、ｐｏｗｄｅｒ−Ｂのような磁気的に異方性磁石粉末を含む本発明に掛かる熱収縮型希土類磁石は、図９に示すように磁化の前後に磁石をマンドレルなどに巻付けて環状に形成することによってラジアル磁界配向の小径化に伴う配向度の低下、すなわち磁気特性低下という困難を克服する。
【００３４】
図９において、（ａ−１）はｐｏｗｄｅｒ−Ｂのような磁気的に異方性磁石粉末を含むコンパウンドをアキシャル磁界中で配向しながら圧縮成形して得たグリ−ンコンパクトの結合剤成分を熱硬化したシ−ト磁石１を示している。また、（ａ−２）はシ−ト磁石１を拡大した模式図、（ａ−３）は異方性磁石粉末の模式図である。磁気的に異方性の粒子はＲＤ−Ｓｍ２Ｆｅ１７Ｎ３系のような単磁区粒子モデルやＨＤＤＲ−Ｎｄ２Ｆｅ１４Ｂ系のような多結晶集合型粒子モデルがあるが、（ａ−３）１ｂは、それらの異方性磁石粉末を表し、（ａ−３）１ｃは、それらの粉末の磁化容易軸を表している。多結晶集合型粒子モデルでは粉末中にたくさんの磁化容易軸１ｃが存在するが、その方向は（ａ−３）のように、ほぼ一定方向に揃っている。図９、（ｂ−１）は配向したシ−ト磁石１または（ｃ−１）のようにシ−ト磁石１を圧延した磁石１１をマンドレル４に巻付けている様子を表している。このとき、磁石１または１１中で配向した異方性磁石粉末１ｂは（ｂ−２）のように磁化容易軸１ｃの配向方向をラジアル方向に変えながらマンドレル４に巻付けられる。なお、磁石１をマンドレル４に巻付けた場合は、環状に形成したのち、（ｃ−２）のように圧延した磁石１１とする必要がある。圧延した環状磁石１１は（ｄ−１）に示すように非磁性から磁性に至る支持部材６、或いは回転軸７に直接挿入し、加熱すると、磁石１１は（ｄ−１）５のような方向に熱収縮を起こし、本発明にかかる熱収縮型希土類磁石１１１となる。
【００３５】
一方、図１０は本発明にかかる等方性熱収縮型希土類磁石の製造プロセスの要部を示す模式図である。Ｐｏｗｄｅｒ−Ａのように磁気的に等方性の希土類磁石粉末の場合には、図１０（ａ−１）のように予め環状のグリ−ンコンパクトを成形し、当該結合剤成分を熱硬化して環状磁石１を作製する。次に、図１０（ｃ−２）のように圧延した磁石１１を作製し、最後に図１０（ｄ−１）のように非磁性から磁性に至る支持部材６、或いは回転軸７に直接挿入し、加熱すると、磁石１１は図１０（ｄ−１）５のような方向に熱収縮を起こし、本発明にかかる熱収縮型希土類磁石１１１となる。
【００３６】
以上のように本発明にかかる異方性から等方性の熱収縮型希土類磁石は回転軸を含む他の支持部材と組合わせて、当該磁石の熱収縮によってそれらと一体化させることができる。
【００３７】
（実施例の説明３、磁石の作製）
先ず、ヘンシェル・ミキサ−に所定量の希土類磁石粉末ｐｏｗｄｅｒ−Ａ，−Ｂを５ｋｇ投入し、前記粉末を４８０ｒ／ｍｉｎで攪拌しながら、室温で固体のエポキシオリゴマ−の５０％アセトン溶液５０ｇを滴下した。攪拌を続けるとおよそ５ｍｉｎで乾燥したエポキシオリゴマ−を被覆した希土類磁石粉末が得られた。続いて、前記エポキシオリゴマ−を表面被覆した希土類磁石粉末に対し、２〜７ｗｔ．％の粘着剤２０％含有ポリアミド粒子、粉末状潜在性エポキシ硬化剤剤、および滑剤（粒子径１０μｍ以下のステアリン酸カルシウム）を添加し、コンパウンドとした。スピニングカップガスアトマイゼ−ションによって準備されたＮｄ２Ｆｅ１４Ｂ系磁石粉末ｐｏｗｄｅｒ−Ａから作製したコンパウンドの平均粒子径は約５５μｍ、磁気的に異方性のＨＤＤＲ−Ｎｄ２Ｆｅ１４Ｂ系塊状磁石粉末ｐｏｗｄｅｒ−Ｂから作製したコンパウンドの平均粒子径は約８５μｍであり、何れも３０〜４０ｓｅｃ／５０ｇ（ＪＩＳ Ｚ−２５１１）の粉末流動性を示した。
【００３８】
磁気的に異方性のＨＤＤＲ−Ｎｄ２Ｆｅ１４Ｂ系磁石粉末ｐｏｗｄｅｒ−Ｂから作製したコンパウンドを圧縮してグリ−ンコンパクトを作製する際には当該異方性希土類磁石粉末を配向させるために１．２ＭＡ／ｍ以上の磁界を印加した。コンパウンドの平均粒子径は、それらの希土類磁石粉末の平均粒子径とほぼ等しく調整しているため、それぞれの磁石粉末は配向磁界によって、独立して自由に回転できる。また、配向磁界はアキシャル方向で、環状磁石のようなラジアル方向ではないため配向度が高く、磁石粉末本来の磁気特性を磁石性能として引出せる。また、配向度を高めるために、キャビティは６０℃程度に加熱し、結合剤成分が熱軟化した状態が好ましい。また、圧縮圧力は０．５ＧＰａ以上でグリ−ンコンパクトの密度は飽和する傾向を示す。このため、本実施例の圧縮圧力は０．５ＧＰａとした。
【００３９】
次に、上記グリ−ンコンパクトの結合剤成分の熱硬化は粉末状潜在性エポキシ硬化剤やポリアミド粉末がエポキシオリゴマ−に溶解することによって引き起こされると推察される。本実施例のグリ−ンコンパクトの機械的強度上昇は１２０℃以上の加熱によって観測される。しかし、結合剤成分を充分に硬化するために、本実施例での硬化条件は１８０℃−２０ｍｉｎとして本発明にかかる磁石を作製した。
【００４０】
（実施例の説明４、熱収縮率の制御）
本発明にかかる磁石の熱収縮性の付与は図９（ｃ−１）、（ｃ−２）、図１０（ｃ−２）に示す圧延による。また、熱収縮率は圧延率によって制御することができる。図１１はスピニングカップガスアトマイゼ−ションによって準備されたＮｄ２Ｆｅ１４Ｂ系球状磁石粉末ｐｏｗｄｅｒ−Ａから作製した環状磁石の圧延率と熱収縮率との関係を示す特性図である。ただし、圧延前の磁石１の直径は１９．９２〜１９．９５ｍｍ、圧延後の磁石１１の直径は２１．０６〜２４．９９ｍｍ、熱収縮後の磁石１１１の直径は２０．４８〜２３．０６ｍｍである。なお、ここでの熱収縮は１２０℃、５ｍｉｎの熱処理であり、図９，１０の（ｄ−１）に示す支持部材５や回転軸６とは組合わせていない。図から明らかなように、圧延後の磁石１１と熱収縮後の磁石１１１とは強い相関性があり、熱収縮率をＤｏ、圧延率をＲとすれば、Ｄｏ＝３．５８９６Ｌｎ（Ｒ）−１．９３９９なる関係が成立する。たとえば、圧延率を４〜１２％とすると１２０℃、５ｍｉｎの熱処理で環状磁石は直径で３〜７％熱収縮することになる。この熱収縮率は圧延率との関係は結合剤量２〜７％の範囲で同様の結果を示した。したがって、このように、熱収縮率は圧延率で制御することができる。
なお、上記の本発明にかかる熱収縮型希土類磁石は熱収縮温度以下であれば、高温で長期間暴露されても寸法変化を殆ど起こさない利点がある。
【００４１】
図１２は圧延前の磁石１と熱収縮した磁石１１１の仕上がり経の比率を圧延率に対して示した特性図である。この仕上がり経の比率と圧延率の両者にも強い相関性があり、もとの磁石１に対する熱収縮磁石１１１の仕上がり経の比率Ｄ１は圧延率Ｒに対してＤ１＝１．１０３４Ｒ−０．８９１１なる関係が成り立つ。したがって、本発明にかかる熱収縮型希土類磁石の仕上がり経は圧延率で制御することができる。なお、熱収縮せしめた本発明にかかる磁石は、熱収縮温度以下での高温長時間暴露で継時的な収縮は認められず、よい寸法安定性を示した。
【００４２】
（実施例の説明５、磁気特性）
本発明にかかる熱収縮型希土類磁石を４ＭＡ／ｍでバルス磁化したときの代表的な減磁曲線を図１３に示す。ただし、図中１は磁気的に異方性のＨＤＤＲ−Ｎｄ２Ｆｅ１４Ｂ系磁石粉末ｐｏｗｄｅｒ−Ｂから作製した異方性磁石１１１、図中２はスピニングカップガスアトマイゼ−ションによって準備されたＮｄ２Ｆｅ１４Ｂ系磁石粉末ｐｏｗｄｅｒ−Ａから作製した等方性磁石１１１である。等方性磁石１１１の減磁曲線は図１３の２で示されるように、その（ＢＨ）ｍａｘは４０ｋＪ／ｍ３に過ぎないが、異方性磁石の減磁曲線１は１４０ｋＪ／ｍ３に達する。このことは、ｐｏｗｄｅｒ−Ａとｐｏｗｄｅｒ−Ｂとの混合によって、少なくとも減磁曲線１，２の中間域の磁石が準備できる。
【００４３】
図１４は図１３の１で示した１４０ｋＪ／ｍ３の異方性磁石の圧延率に対する磁束の低下率を示す特性図である。ただし、図中１は圧延前の磁石１の厚さが１ｍｍ、２は圧延前の磁石１の厚さが２．５ｍｍの場合を示している。図から明らかなように、圧延による磁石粉末の配向の乱れは異方性磁石の磁気特性の劣化を招く、しかしながら、圧延率に対する磁束の低下率は磁石１の厚さに依存し、磁石１の厚さを１ｍｍ程度に設定すると圧延率約１２％まで、磁束の低下を引き起こさない。圧延率１２％ならば本発明にかかる熱収縮磁石１１１の収縮率は直径で７％程度と設定でき、高磁気性能を維持した環状磁石ロ−タが低熱機械的負荷で作製できることが了解される。
【００４４】
（実施例の説明６、寸法精度）
図１５は本発明にかかる熱収縮型希土類磁石を適用した磁石ロ−タの斜視外観図である。ただし、図中１は熱収縮型希土類磁石、２は回転軸、３は非磁性支持部材であり、磁石ロ−タの直径は３０．１ｍｍ、長さは１８．８ｍｍである。また、磁石の厚さは１ｍｍである。たとえば、等方性のＮｄ２Ｆｅ１４Ｂ系希土類磁石粉末▲１▼−ｃと堅いエポキシ樹脂▲２▼−ｃとのコンパウンドを９８０ＭＰａで圧縮成形▲３▼−ｄし、エポキシ樹脂▲２▼−ｃを加熱硬化して作製する従来の環状磁石と同等の（ＢＨ）ｍａｘを有する８０ｋＪ／ｍ３の熱収縮型希土類磁石を準備することができ、しかも本発明にかかる磁石は支持部材に挿入し、回転軸と組合わせて熱収縮によって図１５のような磁石ロ−タとすることができる。熱収縮は、例えば１２０℃、５ｍｉｎでよい。なお、図６に示した従来の磁石ロ−タのように、ＰＢＴ（ポリブチレンテレフタレ−ト），ＰＥＴ（ポリエチレンテレフタレ−ト）などの高分子材料をマトリクスとしたガラス繊維強化成形材料を、例えば２２０〜２８０℃、１０００〜１２００ＭＰａという高温高圧下で射出するという製造プロセスでは、環状磁石に熱機械的負荷がかかるため、磁石厚さを例えば１．８ｍｍ以上に設定する必要があった。また、回転軸基準での磁石ロ−タの外周振れを抑制することは、この種の永久磁石型モ−タにとっては極めて重要な課題のひとつであるが、従来の方法では磁石外周振れは約５０μｍ、最大では１００μｍに達するものもあった。この磁石外周振れが大きい原因としては環状磁石の機械的強度や寸法精度の変動、射出成形における熱機械的負荷の変動などが起因すると考えられる。しかしながら、本発明にかかる熱収縮型希土類磁石を適用した図１５の磁石ロ−タでは図１６に示すように、磁石ロ−タの外周振れは磁石と支持部材の同軸度にのみ依存する。すなわち、従来の磁石ロ−タのように環状磁石の機械的強度や寸法精度の変動、射出成形における熱機械的負荷の変動などが存在しないため、軸と支持部材との同軸度を例えば２０μｍ以下とすれば、全ての磁石ロ−タの外周振れを３０μｍ以下に仕上げることもできる。
【００４５】
なお、本発明にかかる熱収縮型希土類磁石を磁性支持部材に適用すれば、図２で示したような（ＢＨ）ｍａｘの減少が避けられなかった鉄心一体型磁石に対しても、磁石の（ＢＨ）ｍａｘを減少させることなく、低熱機械的負荷で鉄心一体型磁石を作製することができる。
【００４６】
【発明の効果】
希土類磁石粉末と結合剤とのコンパウンドを圧縮してグリ−ンコンパクトを作製し、結合剤成分を熱硬化して作成する従来の磁石はスプリングバックに起因する膨張が避けられなかった。スプリングバックを抑制するには結合剤成分を増量する必要があり、磁石の磁気性能の低下は免れない。本発明はかかる不具合を解消する全く新規な熱収縮型希土類磁石の製造方法を開示したものである。また、本発明にかかる熱収縮型希土類磁石を適用すると磁石ロ−タを製造する際の熱機械的負荷が大幅に削減されるため、磁石の密度による磁気特性の低下、磁石肉厚を増すことなく、高い寸法精度の磁石ロ−タと、それを用いた永久磁石型モ−タを製造することができる。
【図面の簡単な説明】
【図１】ボンド磁石作製における３大要素技術、すなわち磁石粉末、結合剤、成形加工連携を示す概念図
【図２】鉄心一体型磁石のグリ−ンコンパクト作製する工程図
【図３】従来技術の磁石と鉄心との境界部分の断面図
【図４】従来技術のスプリングバック、せん断力の関係を示す特性図
【図５】磁石の密度と磁気特性の関係を示す特性図
【図６】永久磁石型ロ−タに使用される回転子の外観図
【図７】本発明に係る熱収縮型希土類磁石とそれを応用した永久磁石型モ−タのロ−タの構成図
【図８】本発明に係る等速ロ−ル圧延を示す模式図
【図９】本発明にかかる異方性熱収縮型希土類磁石の製造プロセスの要部模式図
【図１０】本発明にかかる等方性熱収縮型希土類磁石の製造プロセスの要部模式図
【図１１】環状磁石の圧延率と熱収縮率との関係を示す特性図
【図１２】熱収縮型希土類磁石の仕上がり径と圧延率の関係を示す特性図
【図１３】熱収縮型希土類磁石の減磁曲線を示す特性図
【図１４】異方性熱収縮型希土類磁石の圧延率に対する磁束の低下率を示す特性図
【図１５】実施例におけるモータのロータの外観斜視図
【図１６】磁石と支持部材の同軸度に対する磁石ロ−タの外周振れの程度を示す特性図
【符号の説明】
▲１▼ 磁石粉末
▲１▼−ａ フェライト系磁石粉末
▲１▼−ｂ アルニコ系磁石粉末
▲１▼−ｃ 希土類系磁石粉末
▲２▼ 結合剤
▲２▼−ａ フレキシブルな結合剤（ゴム、熱可塑性エラストマ−）
▲２▼−ｂ 堅い熱可塑性樹脂結合剤
▲２▼−ｃ 堅い熱硬化性樹脂結合剤
▲３▼ 成形加工
▲３▼−ａ カレンダ−リング
▲３▼−ｂ 押出成形
▲３▼−ｃ 射出成形
▲３▼−ｄ 圧縮成形[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a heat shrinkable rare earth magnet and a permanent magnet type motor thereof. More specifically, by imparting a heat-shrinking function to a rare-earth magnet that is magnetically isotropic to anisotropic, it is integrated with the magnet, a support member that is non-magnetic to magnetic, or a rotating shaft with a low thermo-mechanical load. High dimensional accuracy and high (BH) max It is possible to provide a permanent magnet type motor equipped with a thin annular magnet having a maximum energy product. Therefore, a permanent magnet type motor to which the present heat shrinkable rare earth magnet is applied is a surface magnet type synchronous motor used as a drive source for OA, AV, home appliances, air conditioners and the like having an output of several to several tens of watts, and This can contribute to higher output and higher efficiency of a permanent magnet type step motor and the like.
[0002]
[Prior art]
For motors mounted on OA, AV, home appliances, air conditioners, etc., efforts have been made to reduce the size and weight of the devices and to save power. However, looking at the breakdown of the power consumption of households, factories, and offices (approximately 900 billion kWh / 1996), it is estimated that all of them consume a large amount of power by motors, and that the total consumption exceeds 50%. In recent years, there has been a demand for the development and spread of higher-efficiency motors for global environmental protection such as prevention of global warming and protection of the ozone layer. To increase the efficiency of the motor, it is necessary to reduce the loss or increase the output. One of the keys to high output is a magnet, and it is important how the performance of the magnet material is reflected in the motor performance. By the way, the conditions required for the magnet to be applied to each motor are as follows: (1) magnetic characteristics capable of providing a required static magnetic field in the air gap; and (2) stability represented by irreversible demagnetization. (3) The highest consistency must be obtained in terms of the shape arbitrariness according to the desired shape, and (4) the overall economic efficiency from securing the resources of the raw materials to mounting. Generally, motor efficiency and miniaturization are in opposition to each other, and for a relatively small magnet motor of several hundred watts or less, it is necessary to advance the integration of magnets and motor fabrication.
[0003]
Non-Patent Document 1: "Recent Progress in Research and Development Related to Bonded Rare-Erath Permanent Magnets" by Hirosawa and Tomizawa, Journal of the Japan Society of Applied Magnetics, Vol. 21, No. 4-1 pp. 161 to 167 (1997) provide a brief explanation. In a bonded magnet in which magnet powder is solidified with a binder, the magnet powder, the binder, and the forming process are equally important. Therefore, the three major element technologies in the production of the bonded magnet, that is, the cooperation of the magnet powder, the binder, and the molding process will be described with reference to FIG. 1 based on the cited document.
[0004]
First, ferrite-based (1) -a, alnico-based (1) -b, and rare-earth-based (1) -c as magnet powder (1), and flexible (rubber, thermoplastic elastomer) as binder system (2). ) (2) -a, hard thermoplastic resin (2) -b, hard thermosetting resin (2) -c, processing method (3) as calendar ring (3) -a, extrusion molding (3)- b, injection molding (3) -c, and compression molding (3) -d. Then, their cooperation is arranged as shown by a solid line in the figure. For example, rare earth magnet powder (1) -c is used as a binder system (2) as a flexible system (rubber, thermoplastic elastomer) (2) -a, hard thermoplastic resin (2) -b, hard thermosetting resin. {Circle around (2)}-c, and as molding method {circle around (3)}, calendar ring {3} -a, extrusion molding {3} -b, injection molding {3} -c, compression molding {3} -d and so on. It cooperates with all the elements of (2) and (3). However, in the cooperation between the compression molding {circle around (3)}-d and the rare earth magnet powder {circle around (1)}-c, the elements of the binder system {circle around (2)} are made of a hard thermosetting resin {circle around (2)}-d such as an epoxy resin. At present, it is limited to the relationship.
[0005]
The relationship between the above three major element technologies in the production of the bonded magnet, namely, the cooperation with the rare earth magnet powder (1) -c, the binder (2), and the molding (3), and the improvement of the motor performance are as follows. Non-Patent Document 2: F. Yamashita, Y .; Sasaki, H .; Fukunaga, "Isotropic Nd-Fe-B Thin Arc-shaped Bonded Magnets for Small DC Motors Prepared by Power Pressing Pressing Metals International Press-Metal. 25, no. 4-2, pp. As described in 683 to 686 (2001), in the production of a thin arc-shaped magnet having a maximum thickness of 0.9 mm, rare earth magnet powder {3} -d / hard thermoplastic resin {2} -b / extrusion molding { By changing from linking with 3 ▼ -b to linking with rare earth magnet powder {3} -d / hard thermosetting resin {2} -c / compression molding {3} -c, output of 200mW class The maximum efficiency of the permanent magnet field type small DC motor is improved by 8%. This suggests that even if the rare earth magnet powder is exactly the same, an efficient small motor can be provided by recombination with other linking elements.
[0006]
The proposal by the present inventors to an efficient small motor can be cited, for example, in Japanese Patent Application Laid-Open No. Hei 6-87634. That is, in order to create a strong static magnetic field in the gap facing the armature core, a magnetically isotropic R-Fe-B (R is Nd / Pr) rare earth magnet powder (1) -c and a hard epoxy resin (2) -c is compression molded. (3) -d is an outer diameter of 25 mm or less and a density of 5 Mg / m. 3 This is a permanent magnet motor having a configuration in which the above-described annular bond magnet is multipolarly magnetized. The magnetically anisotropic rare-earth magnet powder (1) -c is injection-molded with a rigid thermoplastic resin (2) -b as a binder system because the degree of orientation decreases as the diameter decreases. Irrespective of the cooperation of -c or compression molding with hard thermosetting resin (2) -c (3) -d, the degree of orientation of radial anisotropic magnet decreases as the diameter becomes smaller, Magnetic properties deteriorate. Therefore, the motor using the radial anisotropic magnet was inevitably reduced in the mechanical output of other motors in conjunction with the reduction in the magnetic properties in the radial direction of the magnet accompanying the reduction in diameter. In other words, there is a disadvantage that the motor becomes less efficient as the size becomes smaller. However, magnetically isotropic rare-earth magnet powders are not dependent on the diameter of the annular magnet, and are, for example, magnetically isotropic Nd. 2 Fe 14 Maximum energy product (BH) by compression molding B-based rare earth magnet powder max 80kJ / m 3 Reach This value is (BH) of the ferrite flexible magnet. max 12kJ / m 3 Is about 6.7 times. As a result, this type of magnet is effective in increasing the output and reducing the current consumption of a small motor, and has been recognized as a so-called efficient small motor mainly in the field of electronic devices. For example, under the cooperation of ferrite magnet powder (1) -a / flexible (rubber, thermoplastic elastomer) (2) -a / calender ring (3) -a, or extrusion molding (3) -b. Of a 1.55 mm thick, 7.2 mm wide sheet-shaped magnet manufactured in the above, cut into strips, curled, and fixed to the inner surface of the peripheral wall of a rotor frame having an inner diameter of 22.5 mm. Magnetically isotropic Nd for starting torque 1.5 mN-m 2 Fe 14 B-type rare earth magnet powder (1) -c and hard epoxy resin (2) -c are compression-molded (3) -d. The outer diameter is 22.5 mm, the thickness is 1.10 mm, the height is 9.4 mm, and the density is 5. 8Mg / m 3 The starting torque of the permanent magnet type motor using the above magnet reaches 13 times 20 mN-m.
[0007]
By the way, as a conventional technology for a magnet rotor having a structure in which a magnet is arranged on a rotor surface used for a PM type stepping motor or a synchronous motor, and a magnet is combined with a motor, Magnetically isotropic Nd 2 Fe 14 A compound of B-based rare earth magnet powder (1) -c and a hard epoxy resin (2) -c containing a capsule containing a liquid epoxy oligomer, compression-molded on the outer peripheral surface of the iron core (3) -d. Non-Patent Document 3: M.-M. Wada, F .; Yamashita, "Nd-Fe-B Resin Bonded Magnet to the Brush-less Motor for Home Appliance Use", Proc. 10th Int. Works on Rare-Earth Magnets and Their Applications (II), pp. 91-101 (1989). FIG. 2 is a process diagram for producing the green compact of the iron core-integrated magnet described in the above-mentioned reference by powder molding. In the drawing, A is a filling step, B is a compression step, C is a release step, D is a heat treatment step, 11 is a laminated core, 12 is a compound, 13 is a die, 14 is a lower core, and 15 is a lower punch. , 16 is a feeder cup, 17 is an upper punch, 18 is an upper core, 19 is a magnet compact, and 20 is a core-integrated magnet obtained by heating and curing an epoxy resin contained in a green compact. This magnet serves as a magnet rotor with its rotating shaft pressed into the iron core. First, usually 8 to 10 ton / cm according to the steps in the drawing. 2 Compress the compound with. Thereafter, when the mold is released from the mold, there is usually a springback of 0.65 to 0.70%. However, this technique suppresses the springback of the magnet so that the iron core and the magnet are not bonded to each other, and is an iron core integrated magnet that secures mechanical strength and dimensional accuracy as a magnet rotor.
[0008]
FIG. 3 shows the magnetically isotropic Nd 2 Fe 14 When the content of the B-based rare earth magnet powder (1) -c is 95 wt. % Of the compound is compressed, and a sectional view of a boundary portion between the magnet and the core of the 1 mm-thick core-integrated magnet is shown on the outer peripheral surface of the iron core having an outer diameter of 48 mm and a thickness of 11 mm. It is understood that the magnet 1 and the iron core 2 are integrated without an adhesive layer or a gap.
[0009]
FIG. 4 shows a magnetically isotropic Nd in a core-integrated magnet in which an annular magnet having a thickness of 1 mm is arranged on the outer periphery of a core having a thickness of 48 mm and an outer diameter of 48 mm. 2 Fe 14 FIG. 4 is a characteristic diagram showing a relationship between a content of a B-based rare earth magnet powder {circle around (1)}-c and a bonding strength (shearing force) between a magnet and an iron core of an iron core integrated magnet. As shown in FIG. % (Epoxy resin is 5 wt.% Or more), the springback is suppressed to 1/10 or less of 0.07% or less, and as a result, the joining force between the magnet and the iron core is obtained.
[0010]
Hereinafter, patent documents and non-patent documents described in the description of the related art will be described.
[0011]
[Patent Document 1]
Japanese Patent Publication No. Hei 6-87634
[Non-patent document 1]
Hirosawa, Tomizawa et al., "Recent Progress in Research and Development Related to Bonded Rare-Erath Permanent Magnets", Journal of the Japan Society of Applied Magnetics, Vol. 21, No. 4-1 pp. 161-167 (1997)
[Non-patent document 2]
F. Yamashita, Y .; Sasaki, H .; Fukunaga, "Isotropic Nd-Fe-B Thin Arc-shaped Bonded Magnets for Small DC Motors Prepared by Powder, Pressing, Pressing, Metals, Pressing, Metals, Pressing, Metals, Pressing, Metals, Press, Metals, Press, Metals, Press, Metals, Press, Metals, Press, Metals, Press, Metals. 25, no. 4-2, pp. 683-686 (2001)
[Non-Patent Document 3]
M. Wada, F .; Yamashita, "Nd-Fe-B Resin Bonded Magnet to the Brush-less Motor for Home Appliance Use", Proc. 10th Int. Works on Rare-Earth Magnetsand Their Applications (II), pp. 91-101 (1989)
[0012]
[Problems to be solved by the invention]
However, in order to suppress the above-mentioned springback of the magnet to 0.07% or less and to produce an iron core integrated magnet having high shear strength, it is necessary to set the proportion of epoxy resin contained in the magnet to 5% or more. There is.
[0013]
FIG. 5 is a characteristic diagram showing the relationship between the magnet density and the magnetic characteristics. As shown in the figure, the residual magnetization Ir of the magnet and (BH) max Depends on the density of the magnet. For example, when the content of the epoxy resin is 1.5 wt. % Nd alloy composition 12 Fe 77 Co 5 B 6 Magnetically isotropic Nd 2 Fe 14 The magnet produced by compressing the compound with the B-based rare earth magnet powder (1) -c at 980 MPa and heat-curing the epoxy resin of the magnet compact is 6.1 Mg / m2 in density. 3 (BH) after being magnetized by a pulse magnetic field of 4 MA / m max Is 83 kJ / m 3 Is obtained. On the other hand, the ratio of the epoxy resin, which is the minimum required for producing the core-integrated magnet, is 5 wt. % And the same alloy composition Nd 12 Fe 77 Co 5 B 6 Magnet powder compound was compressed at 980 MPa, and the epoxy resin contained in the green compact was heat-cured to produce a magnet of 5.4 to 5.5 Mg / m. 3 The above density cannot be obtained. Therefore, (BH) after being magnetized with a pulse magnetic field of 4 MA / m max Is 58 kJ / m 3 And a density of 6.1 Mg / m 3 Despite using the same magnet powder as compared to the magnet (BH) max Is reduced by approximately 30%. Therefore, when an iron core-integrated magnet is manufactured by a method according to the above technology, the magnet (BH) max In this sense, there is a problem that the original performance of the magnet powder cannot be sufficiently reflected in the motor performance.
[0014]
FIG. 6 shows the appearance of a typical magnet rotor used for a permanent magnet type motor or the like. However, in the figure, 1 is, for example, magnetically isotropic Nd 2 Fe 14 An annular magnet produced by compression molding a compound of B-based rare earth magnet powder (1) -c and hard epoxy resin (2) -c at 980 MPa (3) -d, and heat-curing the epoxy resin (2) -c. Reference numeral 2 denotes a rotating shaft, and reference numeral 3 denotes a molding material. To manufacture this magnet rotor, a rotating shaft 2 is loaded into a mold cavity together with an annular magnet 1, and a polymer such as PBT (polybutylene terephthalate) or PET (polyethylene terephthalate) is filled in a gap therebetween. The glass fiber reinforced molding material 3 having the material as a matrix is injected and filled under a high temperature and a high pressure of, for example, 220 to 280 ° C. and 1000 to 1200 MPa, and cooled and solidified in a mold so that the magnet and the rotating shaft are combined with the molding material. And a magnet rotor. In this case, the magnet density is 6.1 Mg / m 3 (BH) after being magnetized by a pulse magnetic field of 4 MA / m max Is 83 kJ / m 3 And become a high-performance magnet. However, when a thin-walled magnet is loaded into a mold, the magnet cannot withstand the thermomechanical load when integrated with the molding material. Therefore, in order to secure the yield in the manufacture of the magnet rotor, (1) the amount of epoxy resin contained in the magnet must be increased, or (2) the magnet must be thickened, and the magnet powder is consumed more than necessary. However, there is a problem that the original magnetic performance of the magnet powder cannot be sufficiently reflected in the motor performance.
[0015]
As described above, magnets which are compression-molded with magnetically isotropic rare earth magnet powder {circle around (1)}-c and thermosetting resin such as hard epoxy resin {circle around (2)}-c, and {3} -d are small magnets using them. SUMMARY OF THE INVENTION It is an object of the present invention to provide a more efficient permanent magnet type motor mainly for a motor and a method for manufacturing a magnet therewith.
[0016]
[Means for Solving the Problems]
The present invention relates to three major element technologies in the production of the bonded magnet shown in FIG. 1; (1) a magnet powder as a rare earth magnet powder, (2) a binder as a thermosetting resin composition, and (3) a compression molding and rolling method. It is an object of the present invention to provide a novel heat-shrinkable rare earth magnet manufacturing method for heat treatment and heat treatment, and a new high-performance permanent small magnet type motor (4) using the same.
[0017]
(Action)
More specifically, a binder component of an annular green compact obtained by compression molding a compound of a rare earth magnet powder and a thermosetting resin composition is thermoset to form a magnet, and the magnet is rolled and then thermally contracted. A method for manufacturing a heat shrinkable rare earth magnet. Alternatively, a green sheet obtained by compression molding a compound of a rare earth magnet powder and a thermosetting resin composition is formed into an annular shape, and the binder component is thermoset to form a sheet magnet, and then the sheet is formed. A method for producing a heat-shrinkable rare earth magnet in which a magnet is rolled and heat-shrinked. Furthermore, a binder component of a green sheet obtained by compression-molding a compound of the rare earth magnet powder and the thermosetting resin composition is heat-cured to form a sheet magnet, and the sheet magnet is formed into a ring shape. The method is based on a method for producing a heat-shrinkable rare-earth magnet which is rolled and then heat-shrinked.
[0018]
In the method for manufacturing a heat-shrinkable rare-earth magnet as described above, one or two selected from the group consisting of Fe, Fe-Ni, Fe-Co, Fe-Si, Fe-N, and Fe-B having a saturation magnetization of 1.3 T or more. The compound may be a composite of a soft magnetic material obtained by compression-molding a compound composed of at least one kind, a thermosetting resin composition, and an additive appropriately added as necessary.
[0019]
FIG. 7 is a block diagram of a heat shrinkable rare earth magnet according to the present invention and a rotor of a permanent magnet type motor to which the magnet is applied. In the figure, 1 is a magnet and the number of poles is represented by four. Reference numeral 2 denotes a magnetic or non-magnetic support member, 3 denotes a heat-shrinkable soft magnetic member forming a composite with a heat-shrinkable rare earth magnet, and 4 denotes a rotating shaft.
[0020]
When the heat-shrinkable rare-earth magnet 1 according to the present invention is thermally shrunk, the rolled annular magnet 1 is inserted into the annular non-magnetic support member 2 and then heat-treated. 7 (a)] and a PM type stepping motor using the multi-polarized non-magnetic support member integrated with a heat shrinkable rare earth magnet [FIG. 7 (a)] as a rotor. Production of a soft magnetic composite heat-shrinkable rare earth magnet [FIG. 7 (b)] with the non-magnetic support member integrated with the rolled composite magnetic magnet 1 with the soft magnetic material 3 inserted into the annular non-magnetic support member and then heat-treated. A method and a permanent magnet motor using the multi-polar magnetized non-magnetic support member integrated with a soft magnetic composite heat shrinkable rare earth magnet [FIG. 7 (b)] as a rotor. The rolled annular magnet 1 is inserted into the annular magnetic support member 2 and then heat-treated. The magnetic support member is integrated, a method of manufacturing a heat-shrinkable rare earth magnet [FIG. 7 (a)], and the multipolar magnetized magnetic support. A permanent magnet type motor using a member integrated, heat shrinkable rare earth magnet [FIG. 7 (a)] as a rotor. A method of manufacturing a heat-shrinkable rare earth magnet [FIG. 7 (c)] by inserting the rolled annular magnet 1 into the rotating shaft 4 and then heat-treating the heat-shrinkable rare earth magnet [FIG. A permanent magnet motor using a shrinkable rare earth magnet [FIG. 7 (c)] as a rotor can be given. The annular magnet does not need to be uniform as shown in FIGS. 7A, 7B, and 7C, but has an unequal wall thickness [FIG. 7D] or an unequal width [FIG. (E)], and the magnetic flux density distribution in the air gap with the stator core may be approximated to a sine wave shape.
[0021]
Next, the binder referred to in the present invention has at least a thermocompression bonding function at a melting point or lower and a powdery resin component having a thermosetting functional group, and the compound is made of one or more kinds of pressure-sensitive adhesives. Consists of a binder that physically integrates the powder and other binder components. More specifically, the thermosetting resin composition constituting the binder is a thermocompression-bondable polyamide or / and a polyamideimide powder provided with an epoxy oligomer which is solid at least at room temperature and an adhesive at room temperature, and if necessary, It is composed of a powdery latent epoxy curing agent and a lubricant to be added. The rare earth magnet powder is desirably coated on the surface with a solid epoxy oligomer having a mean film thickness of 0.1 μm or less at room temperature. Further, the average film thickness is set to 0.1 μm or less. This is important in order to prevent a decrease in the degree of orientation due to secondary aggregation of the anisotropic rare earth magnet powders. Further, as a method for coating the rare earth magnet powder with the epoxy oligomer, first, the epoxy oligomer is dissolved in an organic solvent, and then the wet mixture is mixed with the rare earth magnet powder to disintegrate the bulk mixture from which the solvent has been removed. .
[0022]
The epoxy oligomer referred to in the present invention is a compound having at least two or more oxirane rings in one molecule, and needs to be solid at room temperature and easily soluble in an organic solvent such as acetone. A preferred epoxy oligomer is a novolak-type epoxy oligomer having a softening temperature of 70 ° C. or more and an epoxy equivalent of 235 or less represented by the following chemical structure having an oxirane ring in the molecular chain.
[0023]
Next, the powder epoxy curing agent that crosslinks with the epoxy oligomer includes one or more selected from the group consisting of dicyandiamide and derivatives thereof, carboxylic acid dihydrazide, diaminomaleonitrile and hydrazides of derivatives thereof, and the like. it can. These are generally high-melting compounds that are hardly soluble in organic solvents, but those whose particle diameter is adjusted to several to several tens of μm are preferred. The dicyandiamide derivatives include, for example, o-tolylbiguanide, α-2,5-dimethylbiquanide, α-ω-diphenylbiguanide, 5-hydroxybutyl-1-biguanide, phenylbiguanide, α-, ω-dimethylbiquanide There are anides and the like. Further, examples of the carboxylic acid dihydrazide include succinic hydrazide, adipic hydrazide, isophthalic hydrazide, p-hydroxybenzoic hydrazide and the like. These curing agents are desirably added to the compound by dry mixing. In order to prevent the compound from being transferred to the molding die, one or more selected from higher fatty acids, higher fatty acid amides, and higher fatty acid metal soaps having a melting point higher than the set temperature of the molding die are 0.2 wt. . % Should be added to the compound by dry mixing
The heat shrinkable rare earth magnet according to the present invention has a rare earth magnet powder content of 92 wt. % To 98 wt. %, And the compression molding of such a compound is performed at a pressure of 390 MPa or more and a temperature of 50 ° C. or more, whereby a high-density green compact can be produced. The green compact may be annular or sheet-like. In the case of the sheet compact, the end faces of the green compact may be joined to form a ring, and then heat-cured.
[0024]
The rolling according to the present invention is performed by a constant velocity roll as shown in FIGS. In the drawings, reference numeral 1 denotes a rolling roll, and 2 denotes a rare earth magnet according to the present invention. In the drawing, if the rolling ratio is 3 to 12%, it can be adjusted to a heat shrinkable rare earth magnet having a heat shrinkage of 3 to 7%, for example. When the heat shrinkage temperature is equal to or higher than the upper limit of the operating temperature of the magnet, the dimensional stability of the magnet during the subsequent high temperature exposure in actual use can be secured. On the other hand, when the thickness after rolling including the magnetically anisotropic rare-earth magnet powder is 1 mm or less and the rolling ratio is 15% or less, a heat-shrinkable rare-earth magnet can be provided in which a reduction in orientation during rolling is suppressed.
[0025]
Next, Nd prepared by spinning cup atomization was used as the magnetically isotropic rare earth magnet powder. 2 Fe 14 B-type spherical powder (BH Rabin, BM Ma, "Recent Developments in NdFeBP Powder" 120th Topical Symposium of the Magnetic Society of Japan 23, 2001). Nd prepared by melt spinning (JJ Croat, JF Herbst, RW Lee and FE Pinkerton, J. Appl. Phys., 55, 2078, 1984). 2 Fe 14 B-type flake powder (RW Lee and JJ Croat, US-Patent 4,902, 361.1990), αFe / Nd 2 Fe 14 B-type flake powder, Fe 3 B / Nd 2 Fe 14 B-type flake powder, Sm 2 Fe 17 N 3 Flake powder, αFe / Sm 2 Fe 17 N 3 Flake powder.
[0026]
Next, as the magnetically anisotropic rare earth magnet powder, Nd by hot upsetting (Die-Up-Setting) is used. 2 Fe 14 B-based bulk powder (for example, M. Doser, V. Panchanathan; "Pulverizing anisotropic rapidly solidified Nd-Fe-B materials for bonded magnetnet"; J. Appl. Magnetically anisotropic Nd prepared by HDDR treatment (hydrogen decomposition / recombination) 2 Fe 14 B-based bulk powder, that is, Nd of Nd-Fe (Co) -B-based alloy 2 (Fe, Co) 14 Hydrogenation of phase B ( H hydrogenation, Nd 2 [Fe, Co] 14 BHx), phase decomposition at 650-1000 ° C ( D ecomposition, NdH 2 + Fe + Fe 2 B), dehydrogenation ( D esorpsion), recombination ( R HDDR processing (T. Takeshita and R. Nakayama: Proc. of the 10) th RE Magnets and Their Applications, Kyoto, Vol. 1,551 1989). A powder in which the surface of the powder has been deactivated, such as Zn, which has been photolyzed in advance (eg, K. Machida, K. Noguchi, M. Nushimura, Y. Hamaguchi, G. Adachi, Proc. 9th Int. Works on Rare- Earth Magnets and Ttheir Applications, Sendai, Japan, II, 845 2000, or K. Machida, Y. Hamaguchi, K. Noguchi, G. Adachi, Digests of the 25th. th Annual Conference on Magnetcsin Japan, 28aC-6 2001). On the other hand, as the magnetically anisotropic rare earth magnet powder, Sm prepared by RD (oxidation-reduction) treatment is used. 2 Fe 17 N 3 System fine powder and powder obtained by previously inactivating the powder surface can also be used.
[0027]
The rare earth magnet powder described above may be used alone or in a mixture of two or more. The maximum energy product (BH) at room temperature of the heat shrinkable rare earth magnet according to the present invention after 4 MA / m pulse magnetization. max Is 80 kJ / m 3 Above, especially 130 kJ / m 3 It is desirable that this is the case.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited by the examples.
[0029]
(Description of Example 1, Materials)
In this embodiment, Nd prepared by magnetically isotropic spinning cup gas atomization 2 Fe 14 B type spherical magnet powder (Nd 13.3 Fe 62.5 B 6.8 Ga 0.3 Zr 0.1 ) Powder-A, magnetically anisotropic HDDR-Nd prepared by HDDR treatment (hydrogen decomposition / recombination) 2 Fe 14 B-based magnet powder (Nd 12.3 Dy 0.3 Fe 64.7 Co 12.3 B 6.0 Ga 0.6 Zr 0.1 ) Powder-B was used.
[0030]
The components of the binder include a novolak-type epoxy oligomer which is solid at room temperature, a powdery latent epoxy curing agent having a particle diameter of 15 μm or less, a polyamide powder containing an adhesive and previously freeze-ground to 100 μm or less, and a particle diameter of 10 μm The following lubricants were used in this example. The novolak-type epoxy oligomer (Chemical Formula 1), an acid hydrazide powder having an average particle diameter of 30 to 50 μm obtained by reacting hydrazine with an addition reaction product of 1 mol of 1,2-dodecanoic acid ester and 2 mol of acrylate ester. The chemical structure of the epoxy curing agent (formula 2) is as follows.
[0031]
Embedded image
[0032]
(NH 2 NHCOCH 2 CH 2 ) 2 N (CH 2 ) 11 CONHNH 2 .. (Chemical 2)
[0033]
(Description of Example 2, Manufacturing Process)
The present invention relates to Nd prepared by magnetically isotropic spinning cup gas atomization. 2 Fe 14 B type spherical magnet powder (Nd 13.3 Fe 62.5 B 6.8 Ga 0.3 Zr 0.1 ) HDDR-Nd which is magnetically anisotropic in accordance with required magnetic characteristics based on powder-A. 2 Fe 14 It was made to produce heat-shrinkable rare-earth magnets of various characteristics and forms from one or more rare-earth magnet powders such as powder B-based magnet powder powder-B and to apply them to efficient small motors. . FIG. 9 is a schematic view showing a main part of a manufacturing process of the anisotropic heat shrinkable rare earth magnet according to the present invention. In particular, the heat-shrinkable rare earth magnet according to the present invention containing magnetically anisotropic magnet powder such as powder-B is formed in a ring shape by winding the magnet around a mandrel or the like before and after magnetization as shown in FIG. By doing so, it is possible to overcome the difficulty of lowering the degree of orientation due to the reduction in the radial magnetic field orientation, that is, lowering the magnetic properties.
[0034]
In FIG. 9, (a-1) shows a binder component of a green compact obtained by compression-molding a compound containing magnetically anisotropic magnet powder such as powder-B while orienting it in an axial magnetic field. 1 shows a thermoset sheet magnet 1. (A-2) is an enlarged schematic diagram of the sheet magnet 1, and (a-3) is a schematic diagram of an anisotropic magnet powder. Magnetically anisotropic particles are RD-Sm 2 Fe 17 N 3 Domain model and HDDR-Nd 2 Fe 14 There are polycrystalline aggregated particle models such as those of the B type, where (a-3) 1b represents those anisotropic magnet powders, and (a-3) 1c represents the easy axis of magnetization of those powders. ing. In the polycrystalline aggregate type particle model, many easy axes of magnetization 1c exist in the powder, but their directions are aligned in a substantially constant direction as shown in (a-3). FIG. 9 (b-1) shows a state in which the oriented sheet magnet 1 or the magnet 11 obtained by rolling the sheet magnet 1 as in (c-1) is wound around the mandrel 4. At this time, the anisotropic magnet powder 1b oriented in the magnet 1 or 11 is wound around the mandrel 4 while changing the orientation direction of the easy axis 1c to the radial direction as shown in (b-2). When the magnet 1 is wound around the mandrel 4, it is necessary to form the magnet 11 into an annular shape and then roll it as shown in (c-2). As shown in (d-1), the rolled annular magnet 11 is directly inserted into the support member 6 which changes from non-magnetic to magnetic, or the rotating shaft 7, and when heated, the magnet 11 moves in the direction as shown in (d-1) 5. The heat shrinkage occurs in the heat shrinkable rare earth magnet 111 according to the present invention.
[0035]
On the other hand, FIG. 10 is a schematic view showing a main part of a manufacturing process of the isotropic heat shrinkable rare earth magnet according to the present invention. In the case of magnetically isotropic rare earth magnet powder such as Powder-A, an annular green compact is previously formed as shown in FIG. 10 (a-1), and the binder component is thermally cured. Thus, an annular magnet 1 is manufactured. Next, as shown in FIG. 10 (c-2), the rolled magnet 11 is manufactured, and finally, as shown in FIG. 10 (d-1), the magnet 11 is directly inserted into the support member 6 from non-magnetic to magnetic or the rotating shaft 7. Then, when heated, the magnet 11 undergoes thermal contraction in the direction as shown in FIG. 10 (d-1) 5, and becomes the heat-shrinkable rare-earth magnet 111 according to the present invention.
[0036]
As described above, the anisotropic heat-shrinkable rare-earth magnet according to the present invention can be combined with other support members including the rotating shaft by heat shrinkage of the magnet in combination with the other support members.
[0037]
(Explanation 3 of Example, Production of Magnet)
First, 5 kg of a predetermined amount of rare earth magnet powders powder-A, -B is put into a Henschel mixer, and 50 g of a 50% acetone solution of a solid epoxy oligomer at room temperature is dropped while stirring the powder at 480 r / min. did. When the stirring was continued, a rare earth magnet powder coated with the epoxy oligomer dried in about 5 minutes was obtained. Subsequently, 2 to 7 wt.% Of the rare earth magnet powder coated with the epoxy oligomer was applied. % Of a polyamide particle containing 20% of an adhesive, a powdery latent epoxy curing agent, and a lubricant (calcium stearate having a particle diameter of 10 μm or less) were added to obtain a compound. Nd prepared by spinning cup gas atomization 2 Fe 14 The compound prepared from the B-based magnet powder powder-A has an average particle size of about 55 μm, and has a magnetically anisotropic HDDR-Nd. 2 Fe 14 The compound produced from the B-type bulk magnet powder powder-B had an average particle size of about 85 μm, and all exhibited powder flowability of 30 to 40 sec / 50 g (JIS Z-2511).
[0038]
HDDR-Nd magnetically anisotropic 2 Fe 14 When compressing the compound produced from the B-based magnet powder powder-B to produce a green compact, a magnetic field of 1.2 MA / m or more was applied to orient the anisotropic rare earth magnet powder. Since the average particle size of the compound is adjusted to be approximately equal to the average particle size of the rare earth magnet powder, each magnet powder can be freely rotated independently by the orientation magnetic field. Further, since the orientation magnetic field is in the axial direction and not in the radial direction as in an annular magnet, the orientation magnetic field has a high degree of orientation, and the original magnetic properties of the magnet powder can be derived as magnet performance. In order to increase the degree of orientation, it is preferable that the cavity is heated to about 60 ° C. and the binder component is thermally softened. When the compression pressure is 0.5 GPa or more, the density of the green compact tends to be saturated. For this reason, the compression pressure in this example was set to 0.5 GPa.
[0039]
Next, it is presumed that the thermal curing of the binder component of the green compact is caused by the dissolution of the powdery latent epoxy curing agent and the polyamide powder in the epoxy oligomer. The increase in mechanical strength of the green compact of this embodiment is observed by heating at 120 ° C. or higher. However, in order to sufficiently cure the binder component, the magnets according to the present invention were manufactured under the curing conditions of 180 ° C. for 20 minutes in this example.
[0040]
(Description of Example 4, Control of Heat Shrinkage)
The heat shrinkability of the magnet according to the present invention is provided by rolling shown in FIGS. 9 (c-1), 9 (c-2) and 10 (c-2). Further, the heat shrinkage can be controlled by the rolling reduction. FIG. 11 shows Nd prepared by spinning cup gas atomization. 2 Fe 14 FIG. 4 is a characteristic diagram showing a relationship between a rolling ratio and a heat shrinkage ratio of an annular magnet produced from B-type spherical magnet powder powder-A. However, the diameter of the magnet 1 before rolling is 19.92 to 19.95 mm, the diameter of the magnet 11 after rolling is 21.06 to 24.99 mm, and the diameter of the magnet 111 after heat shrinking is 20.48 to 23.06 mm. It is. Note that the heat shrinkage here is a heat treatment at 120 ° C. for 5 minutes, and is not combined with the support member 5 and the rotating shaft 6 shown in (d-1) of FIGS. As is clear from the figure, there is a strong correlation between the magnet 11 after rolling and the magnet 111 after heat shrinking. If the heat shrinkage rate is Do and the rolling rate is R, Do = 3.5896 Ln (R) − The relationship of 1.3993 is established. For example, assuming that the rolling reduction is 4 to 12%, the heat treatment at 120 ° C. for 5 minutes causes the ring magnet to thermally contract by 3 to 7% in diameter. The relationship between the heat shrinkage and the rolling reduction showed the same result when the amount of the binder was in the range of 2 to 7%. Therefore, in this way, the heat shrinkage can be controlled by the rolling reduction.
The heat-shrinkable rare-earth magnet according to the present invention has an advantage that almost no dimensional change occurs even when exposed to a high temperature for a long period of time, provided that the heat-shrinkable rare-earth magnet is at or below the heat shrinkage temperature.
[0041]
FIG. 12 is a characteristic diagram showing the ratio of the finished diameter of the magnet 1 before rolling and the magnet 111 which has been thermally contracted to the rolling ratio. There is also a strong correlation between the ratio of the finished warp and the rolling reduction, and the ratio D of the finished warp of the heat-shrinkable magnet 111 to the original magnet 1 is D 1 Is D for rolling rate R 1 = 1.103R-0.8911 is established. Therefore, the finishing diameter of the heat shrinkable rare earth magnet according to the present invention can be controlled by the rolling reduction. The heat-shrinkable magnet according to the present invention did not show continuous shrinkage when exposed to a high temperature for a long time at a heat shrinkage temperature or lower, and showed good dimensional stability.
[0042]
(Explanation 5 of embodiment, magnetic characteristics)
FIG. 13 shows a typical demagnetization curve when the heat shrinkable rare earth magnet according to the present invention is pulsed at 4 MA / m. However, in the figure, 1 is a magnetically anisotropic HDDR-Nd. 2 Fe 14 Anisotropic magnet 111 made from B-based magnet powder powder-B, 2 in the figure is Nd prepared by spinning cup gas atomization 2 Fe 14 This is an isotropic magnet 111 manufactured from B-based magnet powder powder-A. The demagnetization curve of the isotropic magnet 111 is shown by (BH) in FIG. max Is 40 kJ / m 3 But the demagnetization curve 1 of the anisotropic magnet is 140 kJ / m 3 Reach This means that by mixing powder-A and powder-B, at least a magnet in the middle region of the demagnetization curves 1 and 2 can be prepared.
[0043]
FIG. 14 shows 140 kJ / m shown in 1 of FIG. 3 FIG. 4 is a characteristic diagram showing a reduction rate of a magnetic flux with respect to a rolling rate of the anisotropic magnet of FIG. In the drawing, reference numeral 1 denotes a case where the thickness of the magnet 1 before rolling is 1 mm, and 2 denotes a case where the thickness of the magnet 1 before rolling is 2.5 mm. As is apparent from the drawing, the disorder of the orientation of the magnet powder due to the rolling causes deterioration of the magnetic properties of the anisotropic magnet. However, the rate of decrease of the magnetic flux with respect to the rolling rate depends on the thickness of the magnet 1, When the thickness is set to about 1 mm, the magnetic flux does not decrease until the rolling reduction reaches about 12%. If the rolling ratio is 12%, the contraction ratio of the heat-shrinkable magnet 111 according to the present invention can be set to about 7% in diameter, and it is understood that an annular magnet rotor maintaining high magnetic performance can be manufactured with low thermomechanical load. .
[0044]
(Description of Example 6, Dimensional Accuracy)
FIG. 15 is a perspective external view of a magnet rotor to which the heat shrinkable rare earth magnet according to the present invention is applied. In the drawing, 1 is a heat shrinkable rare earth magnet, 2 is a rotating shaft, 3 is a non-magnetic support member, and the magnet rotor has a diameter of 30.1 mm and a length of 18.8 mm. The thickness of the magnet is 1 mm. For example, isotropic Nd 2 Fe 14 A conventional compound made by compression molding a compound of B-based rare earth magnet powder (1) -c and hard epoxy resin (2) -c at 980 MPa (3) -d and heat-curing the epoxy resin (2) -c Same as annular magnet (BH) max 80 kJ / m with 3 The magnet according to the present invention can be inserted into a support member and combined with a rotating shaft to form a magnet rotor as shown in FIG. 15 by heat shrinkage. The heat shrinkage may be, for example, 120 ° C. for 5 minutes. As in the conventional magnet rotor shown in FIG. 6, a glass fiber reinforced molding material in which a polymer material such as PBT (polybutylene terephthalate) or PET (polyethylene terephthalate) is used as a matrix is used. For example, in a manufacturing process in which injection is performed at a high temperature and a high pressure of, for example, 220 to 280 ° C. and 1000 to 1200 MPa, a thermomechanical load is applied to the ring magnet, and therefore, it is necessary to set the magnet thickness to, for example, 1.8 mm or more. In addition, it is one of the extremely important issues for this type of permanent magnet type motor to suppress the outer peripheral runout of the magnet rotor on the basis of the rotation axis. Some reached 50 μm, up to 100 μm. It is considered that the cause of the large magnet runout is caused by a change in mechanical strength and dimensional accuracy of the annular magnet, a change in thermomechanical load in injection molding, and the like. However, in the magnet rotor of FIG. 15 to which the heat shrinkable rare earth magnet according to the present invention is applied, as shown in FIG. 16, the outer peripheral runout of the magnet rotor depends only on the coaxiality between the magnet and the support member. That is, since there is no fluctuation in the mechanical strength and dimensional accuracy of the annular magnet and fluctuation in the thermomechanical load in injection molding as in the conventional magnet rotor, the coaxiality between the shaft and the supporting member is, for example, 20 μm or less. In this case, it is possible to finish the outer peripheral runout of all the magnet rotors to 30 μm or less.
[0045]
When the heat-shrinkable rare earth magnet according to the present invention is applied to a magnetic support member, (BH) as shown in FIG. max (BH) of iron-integrated magnets, for which reduction of max The core-integrated magnet can be manufactured with low thermomechanical load without reducing the temperature.
[0046]
【The invention's effect】
Conventional magnets made by compressing a compound of a rare earth magnet powder and a binder to produce a green compact and thermally curing the binder component inevitably undergo expansion due to springback. In order to suppress springback, it is necessary to increase the amount of the binder component, and the magnetic performance of the magnet is inevitably reduced. The present invention discloses a completely novel heat shrinkable rare earth magnet manufacturing method which solves such a problem. Further, when the heat shrinkable rare earth magnet according to the present invention is applied, the thermomechanical load in manufacturing the magnet rotor is greatly reduced, so that the magnetic properties are reduced due to the density of the magnet and the magnet thickness is increased. In addition, it is possible to manufacture a magnet rotor having high dimensional accuracy and a permanent magnet type motor using the same.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing three major element technologies in the production of a bonded magnet, namely, magnet powder, a binder, and molding and processing cooperation.
FIG. 2 is a process diagram for producing a green compact of an iron core integrated magnet.
FIG. 3 is a cross-sectional view of a boundary portion between a magnet and an iron core according to the related art.
FIG. 4 is a characteristic diagram showing a relationship between a springback and a shear force according to the related art.
FIG. 5 is a characteristic diagram showing a relationship between magnet density and magnetic characteristics.
FIG. 6 is an external view of a rotor used for a permanent magnet rotor.
FIG. 7 is a configuration diagram of a rotor of a heat-shrinkable rare earth magnet according to the present invention and a permanent magnet type motor using the same.
FIG. 8 is a schematic view showing constant velocity roll rolling according to the present invention.
FIG. 9 is a schematic diagram of a main part of a manufacturing process of the anisotropic heat shrinkable rare earth magnet according to the present invention.
FIG. 10 is a schematic diagram of a main part of a manufacturing process of an isotropic heat shrinkable rare earth magnet according to the present invention.
FIG. 11 is a characteristic diagram showing a relationship between a rolling reduction and a heat shrinkage of an annular magnet.
FIG. 12 is a characteristic diagram showing a relationship between a finished diameter of a heat shrinkable rare earth magnet and a rolling reduction.
FIG. 13 is a characteristic diagram showing a demagnetization curve of a heat shrinkable rare earth magnet.
FIG. 14 is a characteristic diagram showing a reduction rate of magnetic flux with respect to a rolling rate of an anisotropic heat shrinkable rare earth magnet.
FIG. 15 is an external perspective view of a rotor of a motor according to the embodiment.
FIG. 16 is a characteristic diagram showing the degree of run-out of the outer periphery of the magnet rotor with respect to the coaxiality of the magnet and the support member.
[Explanation of symbols]
▲ 1 ▼ Magnet powder
(1) -a Ferrite magnet powder
(1) -b Alnico magnet powder
(1) -c Rare earth magnet powder
(2) Binder
(2) -a Flexible binder (rubber, thermoplastic elastomer)
(2) -b Hard thermoplastic resin binder
(2) -c Hard thermosetting resin binder
▲ 3 ▼ Forming
(3) -a Calendar ring
(3) -b Extrusion molding
(3) -c Injection molding
(3) -d Compression molding
