JP4696347B2 - R-Fe-B permanent magnet electroplating method - Google Patents
R-Fe-B permanent magnet electroplating method Download PDFInfo
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- JP4696347B2 JP4696347B2 JP2000297044A JP2000297044A JP4696347B2 JP 4696347 B2 JP4696347 B2 JP 4696347B2 JP 2000297044 A JP2000297044 A JP 2000297044A JP 2000297044 A JP2000297044 A JP 2000297044A JP 4696347 B2 JP4696347 B2 JP 4696347B2
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- 238000000034 method Methods 0.000 title claims description 54
- 238000009713 electroplating Methods 0.000 title claims description 50
- 238000007747 plating Methods 0.000 claims description 175
- 238000005260 corrosion Methods 0.000 claims description 48
- 230000007797 corrosion Effects 0.000 claims description 48
- 230000015572 biosynthetic process Effects 0.000 claims description 23
- 239000013078 crystal Substances 0.000 claims description 5
- 239000010408 film Substances 0.000 description 126
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 17
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 16
- 239000001257 hydrogen Substances 0.000 description 16
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- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 4
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- 230000000694 effects Effects 0.000 description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 4
- 239000010409 thin film Substances 0.000 description 4
- 229910021645 metal ion Inorganic materials 0.000 description 3
- 229910001172 neodymium magnet Inorganic materials 0.000 description 3
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- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
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- 229910052804 chromium Inorganic materials 0.000 description 1
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- MPTQRFCYZCXJFQ-UHFFFAOYSA-L copper(II) chloride dihydrate Chemical compound O.O.[Cl-].[Cl-].[Cu+2] MPTQRFCYZCXJFQ-UHFFFAOYSA-L 0.000 description 1
- JZCCFEFSEZPSOG-UHFFFAOYSA-L copper(II) sulfate pentahydrate Chemical compound O.O.O.O.O.[Cu+2].[O-]S([O-])(=O)=O JZCCFEFSEZPSOG-UHFFFAOYSA-L 0.000 description 1
- DOBRDRYODQBAMW-UHFFFAOYSA-N copper(i) cyanide Chemical compound [Cu+].N#[C-] DOBRDRYODQBAMW-UHFFFAOYSA-N 0.000 description 1
- 230000005347 demagnetization Effects 0.000 description 1
- XPPKVPWEQAFLFU-UHFFFAOYSA-J diphosphate(4-) Chemical compound [O-]P([O-])(=O)OP([O-])([O-])=O XPPKVPWEQAFLFU-UHFFFAOYSA-J 0.000 description 1
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- 229940081974 saccharin Drugs 0.000 description 1
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- YWYZEGXAUVWDED-UHFFFAOYSA-N triammonium citrate Chemical compound [NH4+].[NH4+].[NH4+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O YWYZEGXAUVWDED-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
- H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
- H01F10/12—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys
- H01F10/126—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys containing rare earth metals
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/14—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying magnetic films to substrates
- H01F41/16—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying magnetic films to substrates the magnetic material being applied in the form of particles, e.g. by serigraphy, to form thick magnetic films or precursors therefor
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Hard Magnetic Materials (AREA)
- Manufacturing Cores, Coils, And Magnets (AREA)
- Electroplating Methods And Accessories (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、薄膜でも優れた耐食性を示すめっき被膜を表面に有するＲ−Ｆｅ−Ｂ系永久磁石を安定に量産することができる電気めっき方法に関する。
【０００２】
【従来の技術】
Ｎｄ−Ｆｅ−Ｂ系永久磁石に代表されるＲ−Ｆｅ−Ｂ系永久磁石は、高い磁気特性を有しており、今日様々な分野で使用されている。該磁石は、大気中で酸化腐食されやすい金属種（特にＲ）を含む。それ故、表面処理を行わずに使用した場合には、わずかな酸やアルカリや水分などの影響によって表面から腐食が進行して錆が発生し、それに伴って、磁気特性の劣化やばらつきを招くことになる。さらに、磁気回路などの装置に組み込んだ磁石に錆が発生した場合、錆が飛散して周辺部品を汚染する恐れがある。これらの問題点を回避するために、従来から、該磁石に要求される耐食性を付与すべく電気めっきを行うことで、耐食性被膜としてのめっき被膜をその表面に形成することが行われている。
電気めっきを行うに際しては、大量処理が可能との観点から、バレル式電気めっき法が広く採用されている。
【０００３】
【発明が解決しようとする課題】
バレル式電気めっき法は、被処理物である磁石とメディア（スチールボールなど）をバレル内に多数個収容し、該バレルをめっき浴中に浸漬し、バレルを回転させて内部の磁石とメディアを攪拌させながらバレルの電極からメディアを介して磁石に通電し、磁石の表面にめっき被膜を形成するものであり、量産性の点において優れた方法であることは上記の通りである。
ところで、近年、磁石が使用される部品の小型化が進んでおり、これに伴って、磁石の表面処理についても薄膜化などの対応に迫られている。しかしながら、バレル式電気めっき法で薄膜のめっき被膜を形成した場合、磁石間での耐食性のバラツキが大きく、すぐに発錆する磁石が少なからず見受けられるという問題があった。
そこで本発明は、薄膜でも優れた耐食性を示すめっき被膜を表面に有するＲ−Ｆｅ−Ｂ系永久磁石を安定に量産することができる電気めっき方法を提供することを目的とする。
【０００４】
【課題を解決するための手段】
本発明者は、バレル式電気めっき法で薄膜のめっき被膜を形成した場合、なぜ上記のような問題が生じるのか分析することで、以下の知見を得た。
（１）まず、バレル式電気めっき法で被膜が形成された磁石のうち、耐食性に劣る磁石の被膜にはピンホールが数多く存在しており、これが磁石間での耐食性のバラツキの原因になっている。
（２）バレル内では磁石とメディアがいわば集合体として存在するので、集合体の外側に存在する磁石は通電が良好でめっきされやすいが、内部に存在する磁石はめっき液に浸漬された状態で存在するに過ぎず腐食されやすい状態にある。もちろん磁石とメディアは攪拌されてはいるが、形成するめっき被膜が薄膜になるほど、磁石が単にめっき液に浸漬された状態におかれている影響が大きくなり、これがめっき被膜のピンホールの原因になる。さらに、いったん磁石が腐食すると、めっきがされている間にその腐食部分にめっき液が残存してしまい、被膜が形成された後も内部に残存しためっき液が磁石の腐食を進行させる。
（３）特に、Ｎｄ−Ｆｅ−Ｂ系永久磁石の焼結磁石のように主相（Ｎｄ２Ｆｅ１４Ｂ相）と主相より卑な腐食電位を有する粒界相（Ｎｄ−ｒｉｃｈ相）の複数の結晶相で構成されている磁石においては、粒界相は本質的に腐食電位が非常に卑な相であるのに加えて、主相との腐食電位差が大きいため、めっき液によって容易に腐食され、これが均一なめっき被膜の形成を阻害し、ピンホール発生の原因となる。そして、このような磁石の腐食は、耐食性向上を目的とした多層めっきを行う場合においてもその耐食性に大きく影響を及ぼす。
（４）Ｎｄ−Ｆｅ−Ｂ系永久磁石は、特に粒界相がめっき時に発生する水素を吸蔵することにより、磁気特性の劣化やめっき被膜との密着性の低下を引き起こす傾向が強い。そのため、めっきを行うに際しては、水素発生を抑制するために電流密度を低くする必要がある。バレル式電気めっき法の場合、バレル内の金属イオン濃度は小さくなる傾向にあるので、水素がより発生しやすく、また、集合体の内部に発生した水素は、その場所に滞留しやすいことから、水素発生を極力抑制するためには、電流密度をより低い値に設定する必要がある。そのため、平均成膜速度は自ずと遅くなってしまい、磁石がめっき液に浸漬された状態で存在する時間が長くなり、磁石の腐食をより促進させてしまう。
（５）また、（２）に記載したように、通電が良好な磁石は集合体の外側に存在するものに限られており、設定した電流密度に対する実際の個々の磁石における電流密度にはバラツキがある。設定した電流密度以上の電流密度がかかっている部分では水素が多量に発生して（４）に記載したような問題を引き起こすので、量産時には、電流密度はそのバラツキを加味して設定しなければならず、その値は自ずと低いものになってしまう。その結果、めっき液による磁石の腐食に起因する耐食性のバラツキが助長される。
（６）さらに、メディアの存在により、集合体の外側に存在する磁石の数量は制限されるので、磁石の腐食や形成される被膜におけるピンホールの発生をより引き起こす傾向にある。磁石の腐食を極力抑制するための手段としては、バレルの回転速度を上げることによりバレル内部の磁石とメディアの攪拌効率を上げる方法が考えられるが、この方法を採った場合、磁石同士の衝突や磁石とメディアとの衝突が頻繁に起こったり、強い衝撃力で起こったりし、その結果、磁石に多数の割れや欠けを発生させてしまうので好ましくない。
（７）そして、このような磁石の腐食によって、めっき液中にＮｄやＦｅなどの磁石を構成する金属成分が溶出する。例えばＮｉめっきを行った場合、溶出した金属成分のうち、Ｆｅは電流密度が小さい状態ではＮｉと共析して耐食性に劣る被膜を形成してしまう。Ｎｄはイオン吸着現象によりＮｉの安定な析出を阻害し、被膜の密着不良を引き起こす。バレル電気めっき法においては、上記のように個々の磁石に対する通電状態にバラツキがあるため、電流密度は低い値に設定しなければならず、それではこのような耐食性に劣る被膜の析出を抑制することは困難である。従って、量産時においては、良質で均一な被膜形成が困難であり、ロット間での品質のバラツキを引き起こす。
【０００５】
本発明者は、上記の知見に基づいて種々の検討を重ねた結果、薄膜でも優れた耐食性を示すめっき被膜を表面に有する希土類系永久磁石を安定に量産するためには、バレル式電気めっき法を採用せず、かつ、めっき初期の段階で速やかにめっき被膜を形成することが重要であることに思い至った。
本発明は、上記のような経緯のもとになされたものであり、本発明の電気めっき方法は、請求項１記載の通り、主相と主相より卑な腐食電位を有する粒界相の複数の結晶相からなるＲ−Ｆｅ−Ｂ系永久磁石を複数個同時に電気めっきする方法において、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から膜厚が０．５μｍのめっき被膜を磁石表面に形成するまでは０．２μｍ／分以上の平均成膜速度で成膜し、膜厚が０．５μｍ以上になった以降に電流密度をそれ以前の電流密度よりも小さくすることで平均成膜速度を変更して成膜することを特徴とする。
また、請求項２記載の電気めっき方法は、請求項１記載の電気めっき方法において、電流密度が２０Ａ／ｄｍ２以下の条件で成膜することを特徴とする。
また、請求項３記載の電気めっき方法は、請求項１または２記載の電気めっき方法において、めっきがＮｉめっき、ＺｎめっきおよびＣｕめっきから選ばれるいずれかであることを特徴とする。
また、請求項４記載の電気めっき方法は、請求項１乃至３のいずれかに記載の電気めっき方法において、めっき被膜の膜厚を１μｍ〜２５μｍとすることを特徴とする。
また、本発明の表面にめっき被膜を有するＲ−Ｆｅ−Ｂ系永久磁石は、請求項５記載の通り、請求項１乃至４のいずれかに記載の電気めっき方法により得られたことを特徴とする。
【０００６】
【発明の実施の形態】
本発明の電気めっき方法は、主相と主相より卑な腐食電位を有する粒界相の複数の結晶相からなるＲ−Ｆｅ−Ｂ系永久磁石を複数個同時に電気めっきする方法において、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から膜厚が０．５μｍのめっき被膜を磁石表面に形成するまでは０．１μｍ／分以上の平均成膜速度で成膜することを特徴とするものである。
即ち、本発明の電気めっき方法においては、複数の磁石が集合体を形成しないように参集させることなく磁石同士が離間する状態にせしめ、かつ、めっき初期の平均成膜速度をある一定値以上にすることにより、磁石をめっき液に浸漬した後、均一なめっき被膜を全ての磁石に速やかに形成することで、バレル式電気めっき法が有する種々の問題点、即ち、磁石の腐食とそれに起因するピンホールの発生、水素吸蔵による磁石の磁気特性の劣化やめっき被膜との密着性の低下を解消することができる。
【０００７】
本発明の電気めっき方法においては、個々の磁石を、磁石同士が離間する状態にせしめることが重要な要件となる。個々の磁石をこの状態にせしめることにより、設定した電流密度を全ての磁石に対して均一にかけることができるので、高電流密度の設定のもとでも水素発生を抑制することができ、水素が発生しても磁石の磁気特性に及ぼす影響や磁石とめっき被膜との密着性に及ぼす影響を極力回避することができる。従って、電流密度を高くしてめっき被膜の平均成膜速度を上げることが可能となり、磁石の腐食が始まるまでにその表面に対して均一なめっき被膜を速やかに形成することができる。
【０００８】
ここで、「離間する状態」とは、個々の磁石が互いに接触する可能性が排除された状態を意味する。このような状態は、例えば、ラック式電気めっき法、即ち、被処理物である磁石を支持するとともに磁石にめっき電流を供給する導電性支持部材を多数備えるめっき治具を使用し、各支持部材に磁石をそれぞれ独立して支持させ、めっき液中で支持部材を介して磁石に直接通電することにより磁石表面にめっき被膜を形成する方法を採用することにより実現化することができる。
【０００９】
ラック式電気めっき法に採用される治具には様々な態様のものがあるが、磁石に支持跡（接点跡）を残さない機構を備えた治具を使用することが望ましい。このような治具としては、例えば、磁石を支持するとともに磁石にめっき電流を供給する導電性支持部材の磁石の支持位置が、磁石と部材との関係において相対的に変化する機構を備えた治具が挙げられる。このような治具の具体例として、特願平１１−９１５８５号明細書に記載の治具を図１に示す。
【００１０】
図１は、磁石を支持する部材の少なくとも１つの部材を一定周期で他の部材に交替させ、交替した部材が磁石を支持することにより、磁石の支持位置が変化するように、磁石を支持する部材を配置した治具である。即ち、この治具は、内側磁石支持部材４−ａ、４−ｂと外側磁石支持部材５−ａ、５−ｂを有している。両部材は金属製であり、内側磁石支持部材は金属製の支持枠１に、外側磁石支持部材は金属製の支持枠２に取り付けられている。両部材と両支持枠は必要に応じて所望する個所に絶縁被膜が被覆される。支持枠１と支持枠２は磁石を支持している部材にのみめっき電流が供給されるようにするための切替装置７に接続されている。かかる切替装置７により、部材や支持枠の不必要なめっき太りが抑制される。支持枠２には、絶縁体８を介して電動式アクチュエータ６が取り付けられており、外側磁石支持部材５−ａ、５−ｂが一定周期で矢示のように上下移動するようになっている。電動式アクチュエータ６と切替装置７の作動は制御部９にて制御されている。図１は、磁石３を外側磁石支持部材５−ａ、５−ｂが支持し、切替装置７によって、該部材にのみめっき電流が供給されている状態を示している。電動式アクチュエータ６によって外側磁石支持部材を下降させると、磁石は内側磁石支持部材４−ａ、４−ｂに交替して支持され、切替装置７によって該部材にのみめっき電流が供給されるようになる。このように磁石３を支持する部材を一定周期で内側磁石支持部材４−ａ、４−ｂと外側磁石支持部材５−ａ、５−ｂとで交替させることにより、部材が支持する磁石の支持位置が固定化されないので、支持跡のないめっき被膜を磁石表面に形成することができる。
【００１１】
特願平１１−９１５８５号明細書に記載の治具以外の、磁石に支持跡を残さない機構を備えた好適な治具としては、リング状磁石のめっきに好適な治具として、磁石を回転させながらめっきすることにより、支持位置を移動させることができる機構を備えた治具が挙げられる。このような治具の具体例としては、特願平１１−２９０５７１号明細書に記載の、円筒形状の内周面を有するリング状磁石を内周面側から支持するとともに磁石に回転動作を与える導電性支持部材を設け、磁石を支持部材に押圧する加負荷部材を設けた治具、特願２０００−１７４５３７号明細書に記載の、リング状磁石の中空部に挿入配置される陽極と、磁石をその中心軸線を中心に回転させるとともに磁石にめっき電流を供給するための導電性支持部材を有する治具、特願２０００−２６９９８６号明細書に記載の、回転軸を中心に公転動作を行う導電性支持部材を設け、この支持部材は円筒形状の内周面を有するリング状磁石を内周面側から回動自在に支持する治具などが挙げられる。また、特願平１１−２６５４００号明細書や特願２０００−２１３４２７号明細書に記載されているような、多数の籠状区画室を備えた導電性支持部材の各区画室に磁石を１個ずつ収容し、支持部材を回転させながらめっきを行う治具や、特願２０００−６４２３７号明細書に記載の、複数の導電性ローラ上で磁石を搬送させながらめっきを行う装置も好適に使用される。
【００１２】
次に、本発明の電気めっき方法においては、めっき開始から膜厚が０．５μｍのめっき被膜を磁石表面に形成するまでは０．１μｍ／分以上の平均成膜速度で成膜することが重要な要件となる。個々の磁石を、磁石同士が離間する状態にせしめても、膜厚が０．５μｍのめっき被膜をめっき開始から５分以内に磁石表面に形成しなければ、めっき液中で磁石の腐食が始まり、被膜中にピンホールを発生させたり、めっき液を劣化させたりする要因となる。
【００１３】
本発明におけるめっきは、どのようなめっきであってもよいが、磁石表面との優れた密着性が得られる被膜であり、しかも低コストにて成膜できる点からは、Ｎｉめっき、Ｚｎめっき、Ｃｕめっきが望ましい。このようなめっきを、めっき開始から膜厚が０．５μｍのめっき被膜を磁石表面に形成するまでは０．１μｍ／分以上、望ましくは０．２μｍ／分以上の平均成膜速度で行う。このような速度は、個々の磁石を、磁石同士が離間する状態にせしめることにより、各磁石に対して電流密度を均等にかけることが可能となる結果、電流密度を適正値に設定することにより達成することができる。バレル式電気めっき法においてこのような平均成膜速度にて成膜しようとしても、個々の磁石における電流密度にはバラツキがあるため、上記したような種々の問題が発生してしまい、全ての磁石に対してその表面に均一な被膜を形成することはできない。
【００１４】
０．１μｍ／分以上の平均成膜速度は、通常、２価の金属イオンを用いるＮｉめっき、Ｚｎめっき、Ｃｕめっきを行う場合は電流密度を０．５Ａ／ｄｍ２以上に設定することで、また、シアン化銅などの１価のＣｕイオンを用いるＣｕめっきを行う場合は電流密度を０．２５Ａ／ｄｍ２以上に設定することで達成することができるが、電流密度は２０Ａ／ｄｍ２以下に設定して成膜することが望ましい。電流密度をこの値を超えて設定した場合、水素発生の問題が顕在化し、磁石の水素吸蔵による特性劣化やめっき被膜との密着性の低下を引き起こす恐れがあるからである。電流密度を２０Ａ／ｄｍ２以下に設定して成膜することにより、磁石表面の水素量を１００ｐｐｍ以下、望ましくは５０ｐｐｍ以下に抑制することが可能となる。
【００１５】
磁石表面に形成されるめっき被膜の最終的な膜厚は、望ましくは１μｍ以上とする。平均成膜速度は、めっき開始当所からの０．１μｍ／分以上の平均成膜速度を固定して維持してもよいし、ある時点で変更してもよい。本発明の電気めっき方法によって磁石表面に形成することのできるめっき被膜の膜厚の上限は特段制限されるものではないが、本発明の電気めっき方法は、磁石自体の小型化に基づく要請から、２５μｍ以下、望ましくは２０μｍ以下、より望ましくは１０μｍ以下の膜厚のめっき被膜を有するＲ−Ｆｅ−Ｂ系永久磁石を安定に量産するのに適している。近年、より薄膜かつ高耐食性を示すめっき被膜を簡易なプロセスで安定して量産することが要求されているが、本発明の電気めっき方法は、このような時代のニーズに応えることのできる方法である。
【００１６】
本発明に使用されるめっき液は特段限定されるものではなく、これまでに市販や提案されている各種のめっき液を使用することができるが、水素発生を極力抑制するという観点からは電析効率が９０％以上の特性を有するめっき液を使用することが望ましい。また、一般に低ｐＨのめっき液を使用した場合、磁石を構成する金属成分の溶出に伴い、めっき被膜中にピンホールが発生したり、めっき液が劣化したりする恐れがあり、高ｐＨのめっき液を使用した場合、磁石表面に水酸化物が析出して均一なめっき被膜が形成されない恐れがある。従って、めっき液はｐＨが５〜１３のものを使用することが望ましく、ｐＨが６〜１２のものを使用することがより望ましい。
【００１７】
磁石の腐食の大きな要因となるめっき液中の塩素イオン濃度は２０ｇ／Ｌ以下に調整することが望ましく、１０ｇ／Ｌ以下に調整することがより望ましい。この観点から、ＺｎめっきやＣｕめっきを行う場合、塩素イオンを含まないシアン化浴やピロリン酸浴などの錯化剤を用いたアルカリ浴を使用することが望ましい。特にＣｕめっきを行う場合には、このようなアルカリ浴を使用することで、磁石表面における磁石を構成する金属成分であるＲやＦｅとＣｕとの置換反応を抑制することができる点においても望ましい。
【００１８】
めっき液は、磁石表面に対して金属イオンの供給を確実に行って平均成膜速度を維持するとともに、水素発生を極力抑制するために、また、水素が発生しても速やかに磁石表面から発生した水素を排除するために攪拌することが望ましい。また、磁石の全表面に対して均一なめっき被膜が形成されるように、個々の磁石に対して異なる少なくとも２方向に陽極を設けることが望ましい。
【００１９】
本発明に適用されるＲ−Ｆｅ−Ｂ系永久磁石における希土類元素（Ｒ）は、Ｎｄ、Ｐｒ、Ｄｙ、Ｈｏ、Ｔｂ、Ｓｍのうち少なくとも１種、あるいはさらに、Ｌａ、Ｃｅ、Ｇｄ、Ｅｒ、Ｅｕ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙのうち少なくとも１種を含むものが望ましい。
また、通常はＲのうち１種をもって足りるが、実用上は２種以上の混合物（ミッシュメタルやジジムなど）を入手上の便宜などの理由によって使用することもできる。
さらに、Ａｌ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｂｉ、Ｎｂ、Ｔａ、Ｍｏ、Ｗ、Ｓｂ、Ｇｅ、Ｓｎ、Ｚｒ、Ｎｉ、Ｓｉ、Ｚｎ、Ｈｆ、Ｇａのうち少なくとも１種を添加することで、保磁力や減磁曲線の角型性の改善、製造性の改善、低価格化を図ることが可能となる。また、Ｆｅの一部をＣｏで置換することによって、得られる磁石の磁気特性を損なうことなしに温度特性を改善することができる。
【００２０】
本発明の電気めっき方法によって磁石表面に形成されためっき被膜の上に、同種のめっき被膜や異種のめっき被膜を積層形成してもよいし、化成処理被膜などの別種の被膜を積層形成してもよい。このような構成を採用することによって、本発明の電気めっき方法によって形成されためっき被膜の特性を増強・補完したり、更なる機能性を付与したりすることができる。このような多層被膜を形成する場合でも、本発明の電気めっき方法によって形成されためっき被膜は、その効力を十分に示し、全体としての膜厚（総膜厚）が薄くても優れた耐食性を発揮する。なお、このような総膜厚としては、１μｍ〜２５μｍが望ましい。
【００２１】
【実施例】
本発明を以下の実施例によってさらに詳細に説明するが、本発明は以下の記載に何ら限定されるものではない。
【００２２】
（１）使用するＲ−Ｆｅ−Ｂ系永久磁石：
例えば、米国特許４７７０７２３号公報や米国特許４７９２３６８号公報に記載されているようにして、公知の鋳造インゴットを粉砕し、微粉砕後に成形、焼結、熱処理、表面加工を行うことによって得られた１４Ｎｄ−７９Ｆｅ−６Ｂ−１Ｃｏ組成の縦１５ｍｍ×横２５ｍｍ×高さ７ｍｍ寸法の焼結磁石を使用した。
【００２３】
（２）使用するめっき治具：
（イ）本発明の電気めっき方法に好適に使用されるめっき治具として図１に示す機構を備え、１００個の磁石を同時に処理することができる治具（横１０列×縦１０列配置）を使用した（以下ラック治具と略称する）。
（ロ）バレル式電気めっき法に使用される、断面が１辺１５０ｍｍの正六角形で長さが３００ｍｍのプラスチック製の一般的なバレル治具に磁石１００個と直径２ｍｍのスチールボール２ｋｇを投入し、５ｒｐｍの回転速度で回転させて使用した。
【００２４】
（３）めっきの前処理：
特開平６−５７４８０号公報に記載の方法に準じて行った。即ち、めっき治具に磁石をセットした後、これを硝酸ナトリウム０．２ｍｏｌ／Ｌ、硫酸１．５ｖｏｌ％からなる液温３０℃の処理液に４分間浸漬した後、直ちに１μＳ／ｃｍ以下のイオン交換水で３０秒超音波洗浄し、その後速やかにめっきを開始した。
【００２５】
実施例Ａ：Ｎｉめっき（その１）
硫酸ニッケル・６水和物２５０ｇ／Ｌ、塩化ニッケル・６水和物４５ｇ／Ｌ、ホウ酸３０ｇ／Ｌからなり、炭酸ニッケルでｐＨ５．５に調整した液温５０℃のめっき浴を使用し、表１に示す（ａ）めっき開始から５分後までに設定した電流密度、（ｂ）その間の平均成膜速度（ｎ＝１０の実測値：蛍光Ｘ線膜厚計ＳＦＴ−７０００（セイコー電子社製）を使用。以下同じ。）、（ｃ）めっき開始から５分後以降に設定した電流密度にて膜厚が１０μｍのＮｉめっき被膜を磁石表面に形成した。
形成されためっき被膜の平均膜厚（ｎ＝１０の実測値：蛍光Ｘ線膜厚計ＳＦＴ−７０００（セイコー電子社製）を使用。以下同じ。）とプレッシャー・クッカー・テスト（１２０℃×１００％ＲＨ×２気圧×７２時間）による耐食性評価結果を表１に示す。表１から、ラック治具を使用して、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から５分間は０．１μｍ／分以上の平均成膜速度で成膜したことで、優れた耐食性を示すめっき被膜を表面に有する磁石を安定に量産することができることがわかった。また、実施例２で得られた表面にめっき被膜を有する磁石のうちの１個について、めっき被膜を磁石から剥離し、磁石表面の水素量をグロー放電発光分析（ＧＤＳ：ＧＤＬＳ−５０１７：島津製作所社製）で測定した結果、４２ｐｐｍと非常に少ないものであった。
【００２６】
【表１】
実施例Ｂ：Ｎｉめっき（その２）
硫酸ニッケル・６水和物１３０ｇ／Ｌ、クエン酸アンモニウム３０ｇ／Ｌ、ホウ酸１５ｇ／Ｌ、塩化アンモニウム８ｇ／Ｌ、サッカリン８ｇ／Ｌからなり、アンモニア水でｐＨ６．５に調整した液温５０℃のめっき浴を使用し、表２に示す（ａ）めっき開始から５分後までに設定した電流密度、（ｂ）その間の平均成膜速度（ｎ＝１０の実測値）、（ｃ）めっき開始から５分後以降に設定した電流密度にて膜厚が１０μｍのＮｉめっき被膜を磁石表面に形成した。
形成されためっき被膜の平均膜厚（ｎ＝１０の実測値）とプレッシャー・クッカー・テスト（１２０℃×１００％ＲＨ×２気圧×７２時間）による耐食性評価結果を表２に示す。表２から、ラック治具を使用して、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から５分間は０．１μｍ／分以上の平均成膜速度で成膜したことで、優れた耐食性を示すめっき被膜を表面に有する磁石を安定に量産することができることがわかった。
【００２８】
【表２】
実施例Ｃ：２層Ｎｉめっき
工程１：実施例Ｂで使用しためっき浴と同じめっき浴を使用し、表３に示す（ａ）めっき開始から５分後までに設定した電流密度、（ｂ）その間の平均成膜速度（ｎ＝１０の実測値）、（ｃ）めっき開始から５分後以降に設定した電流密度にて膜厚が４μｍのＮｉめっき被膜を磁石表面に形成した。形成されためっき被膜の平均膜厚（ｎ＝１０の実測値）を表３に示す。
【００３０】
【表３】
工程２：硫酸ニッケル・６水和物２４０ｇ／Ｌ、塩化ニッケル・６水和物４５ｇ／Ｌ、ホウ酸３０ｇ／Ｌ、１，５−ナフタレンジスルホン酸ナトリウム８ｇ／Ｌ、ゼラチン０．０１ｇ／Ｌからなり、ｐＨ４．２の液温５０℃のめっき浴を使用し、電流密度０．７Ａ／ｄｍ２にて膜厚が１６μｍのＮｉめっき被膜を工程１で形成されたＮｉめっき被膜表面に形成した。
工程１と工程２で形成されためっき被膜の合計平均膜厚（ｎ＝１０の実測値）と中性塩水噴霧試験（５％ＮａＣｌ×３５℃×１６８時間）による耐食性評価結果を表４に示す。表４から、工程１において、ラック治具を使用して、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から５分間は０．１μｍ／分以上の平均成膜速度で成膜したことで、多層めっきを行った場合においても、その効果が発揮されることがわかった。
【００３２】
【表４】
実施例Ｄ：量産時におけるめっき液の劣化の影響
実施例Ａの条件でのＮｉめっきを１つのめっき浴を使用して繰り返し行った際の５０回目の結果を表５に示す。また、実施例Ｂの条件でのＮｉめっきを１つのめっき浴を使用して繰り返し行った際の５０回目の結果を表６に示す。表５と表６から、本発明の電気めっき方法は、磁石を構成する金属成分の溶出に伴うめっき液の劣化を効果的に抑制し、１つのめっき浴を５０回繰り返して使用しても優れた耐食性を示すめっき被膜を表面に有する磁石を安定に量産することができること、その効果はｐＨ６以上の方が優れることがわかった。
【００３４】
【表５】
【表６】
実施例Ｅ：Ｚｎめっき
塩化亜鉛７０ｇ／Ｌ、塩化カリウム２００ｇ／Ｌ、ホウ酸２５ｇ／Ｌからなり、ｐＨ５．８の液温２５℃のめっき浴を使用し、表７に示す（ａ）めっき開始から５分後までに設定した電流密度、（ｂ）その間の平均成膜速度（ｎ＝１０の実測値）、（ｃ）めっき開始から５分後以降に設定した電流密度にて膜厚が１５μｍのＺｎめっき被膜を磁石表面に形成した。
形成されためっき被膜の平均膜厚（ｎ＝１０の実測値）とプレッシャー・クッカー・テスト（１２０℃×１００％ＲＨ×２気圧×７２時間）による耐食性評価結果を表７に示す。表７から、ラック治具を使用して、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から５分間は０．１μｍ／分以上の平均成膜速度で成膜したことで、優れた耐食性を示すめっき被膜を表面に有する磁石を安定に量産することができることがわかった。
【００３７】
【表７】
実施例Ｆ：Ｃｕめっき
硫酸銅・５水和物２２０ｇ／Ｌ、硫酸５０ｇ／Ｌ、塩化銅・２水和物１２０ｍｇ／Ｌからなり、ｐＨ０〜２の液温２５℃のめっき浴を使用し、表８に示す（ａ）めっき開始から５分後までに設定した電流密度、（ｂ）その間の平均成膜速度（ｎ＝１０の実測値）、（ｃ）めっき開始から５分後以降に設定した電流密度にて膜厚が１０μｍのＣｕめっき被膜を磁石表面に形成した。
形成されためっき被膜の平均膜厚（ｎ＝１０の実測値）とプレッシャー・クッカー・テスト（１２０℃×１００％ＲＨ×２気圧×７２時間）による耐食性評価結果を表８に示す。表８から、ラック治具を使用して、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から５分間は０．１μｍ／分以上の平均成膜速度で成膜したことで、優れた耐食性を示すめっき被膜を表面に有する磁石を安定に量産することができることがわかった。
【００３９】
【表８】
【発明の効果】
本発明の電気めっき方法によれば、主相と主相より卑な腐食電位を有する粒界相の複数の結晶相からなるＲ−Ｆｅ−Ｂ系永久磁石を複数個同時に電気めっきする方法において、個々の磁石を、磁石同士が離間する状態にせしめ、かつ、めっき開始から膜厚が０．５μｍのめっき被膜を磁石表面に形成するまでは０．１μｍ／分以上の平均成膜速度で成膜することにより、磁石をめっき液に浸漬した後、均一なめっき被膜を全ての磁石に速やかに形成することで、バレル式電気めっき法が有する種々の問題点、即ち、磁石の腐食とそれに起因するピンホールの発生、水素吸蔵による磁石の磁気特性の劣化やめっき被膜との密着性の低下を解消し、薄膜でも優れた耐食性を示すめっき被膜を表面に有するＲ−Ｆｅ−Ｂ系永久磁石を安定に量産することができる。
【図面の簡単な説明】
【図１】 本発明の電気めっき方法に好適に使用されるめっき治具の概略図である。
【符号の説明】
１、２ 支持枠
３ 磁石
４−ａ、４−ｂ 内側磁石支持部材
５−ａ、５−ｂ 外側磁石支持部材
６ 電動式アクチュエータ
７ 切替装置
８ 絶縁体
９ 制御部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroplating method capable of stably mass-producing an R—Fe—B permanent magnet having a plating film having excellent corrosion resistance even on a thin film.
[0002]
[Prior art]
R-Fe-B permanent magnets represented by Nd-Fe-B permanent magnets have high magnetic properties and are used in various fields today. The magnet contains a metal species (particularly R) that is susceptible to oxidative corrosion in the atmosphere. Therefore, when used without surface treatment, corrosion progresses from the surface due to the influence of slight acid, alkali, moisture, etc., and rust is generated, resulting in deterioration and dispersion of magnetic properties. It will be. Furthermore, when rust is generated in a magnet incorporated in a device such as a magnetic circuit, the rust may be scattered and contaminate peripheral components. In order to avoid these problems, conventionally, a plating film as a corrosion-resistant film has been formed on the surface thereof by performing electroplating to give the magnet the required corrosion resistance.
In performing electroplating, a barrel-type electroplating method is widely adopted from the viewpoint that a large amount of processing is possible.
[0003]
[Problems to be solved by the invention]
In the barrel type electroplating method, a large number of magnets and media (steel balls, etc.), which are objects to be processed, are accommodated in a barrel, the barrel is immersed in a plating bath, and the barrel is rotated to dispose the magnet and media inside. While stirring, the magnet is energized from the electrode of the barrel through the medium to form a plating film on the surface of the magnet, and as described above, this is an excellent method in terms of mass productivity.
By the way, in recent years, miniaturization of parts in which magnets are used has progressed, and accordingly, surface treatment of magnets is also required to be made thin. However, when a thin plating film is formed by a barrel-type electroplating method, there is a large variation in corrosion resistance between the magnets, and there is a problem that not a few magnets rust immediately.
Accordingly, an object of the present invention is to provide an electroplating method capable of stably mass-producing an R—Fe—B permanent magnet having a plating film having excellent corrosion resistance even on a thin film.
[0004]
[Means for Solving the Problems]
The present inventor has obtained the following knowledge by analyzing why the above-described problems occur when a thin plating film is formed by a barrel-type electroplating method.
(1) First, among the magnets formed by the barrel-type electroplating method, there are many pinholes in the magnet coating that is inferior in corrosion resistance, which causes variations in the corrosion resistance between the magnets. Yes.
(2) Since magnets and media exist in a so-called aggregate in the barrel, the magnet existing outside the aggregate is well energized and easily plated, but the magnet present inside is immersed in the plating solution. It just exists and is susceptible to corrosion. Of course, the magnet and the media are agitated, but the thinner the plating film to be formed, the greater the influence that the magnet is simply immersed in the plating solution, which causes pinholes in the plating film. Become. Furthermore, once the magnet is corroded, the plating solution remains in the corroded portion during plating, and the plating solution remaining inside after the coating is formed advances the corrosion of the magnet.
(3) In particular, the main phase (Nd—Nd—Fe—B permanent magnet as in the sintered magnet) 2 Fe 14 B phase) and a magnet composed of a plurality of crystal phases of a grain boundary phase (Nd-rich phase) having a lower corrosion potential than the main phase, the grain boundary phase has essentially a very low corrosion potential. In addition to being a phase, the difference in corrosion potential from the main phase is large, so that it is easily corroded by the plating solution, which inhibits the formation of a uniform plating film and causes pinholes. Such corrosion of the magnet greatly affects the corrosion resistance even when performing multilayer plating for the purpose of improving the corrosion resistance.
(4) Nd—Fe—B permanent magnets have a strong tendency to cause deterioration of magnetic properties and a decrease in adhesion to a plating film, particularly when the grain boundary phase occludes hydrogen generated during plating. Therefore, when performing plating, it is necessary to reduce the current density in order to suppress hydrogen generation. In the case of the barrel type electroplating method, the metal ion concentration in the barrel tends to be small, so hydrogen is more likely to be generated, and the hydrogen generated inside the assembly is likely to stay in that place, In order to suppress hydrogen generation as much as possible, it is necessary to set the current density to a lower value. For this reason, the average film formation rate naturally becomes slow, the time during which the magnet is immersed in the plating solution becomes long, and the corrosion of the magnet is further promoted.
(5) In addition, as described in (2), magnets with good energization are limited to those that exist outside the assembly, and the actual current density of individual magnets with respect to the set current density varies. There is. In areas where a current density higher than the set current density is applied, a large amount of hydrogen is generated, causing problems such as those described in (4). For mass production, the current density must be set in consideration of the variation. Rather, the value is naturally low. As a result, variation in corrosion resistance due to corrosion of the magnet by the plating solution is promoted.
(6) Further, since the number of magnets existing outside the aggregate is limited due to the presence of the media, it tends to cause more corrosion of the magnets and generation of pinholes in the formed coating. As a means for suppressing the corrosion of the magnet as much as possible, a method of increasing the stirring efficiency of the magnet and the medium inside the barrel by increasing the rotation speed of the barrel can be considered. The collision between the magnet and the media frequently occurs or with a strong impact force, and as a result, many cracks and chips are generated in the magnet, which is not preferable.
(7) Then, due to such corrosion of the magnet, metal components such as Nd and Fe are eluted in the plating solution. For example, when Ni plating is performed, among the eluted metal components, Fe co-deposits with Ni in a state where the current density is low, and forms a film having poor corrosion resistance. Nd inhibits stable precipitation of Ni by an ion adsorption phenomenon, and causes poor adhesion of the film. In the barrel electroplating method, since there is a variation in the energization state for each magnet as described above, the current density must be set to a low value, and this suppresses the deposition of such a coating having poor corrosion resistance. It is difficult. Therefore, in mass production, it is difficult to form a high-quality uniform film, which causes variations in quality between lots.
[0005]
As a result of repeating various studies based on the above knowledge, the present inventor has developed a barrel-type electroplating method in order to stably mass-produce a rare earth-based permanent magnet having a plating film exhibiting excellent corrosion resistance even on a thin film. It was thought that it is important to form a plating film promptly at the initial stage of plating without adopting the above.
The present invention has been made based on the above-mentioned circumstances, and the electroplating method of the present invention comprises a main phase and a grain boundary phase having a lower corrosion potential than the main phase as described in claim 1. In the method of simultaneously electroplating a plurality of R—Fe—B permanent magnets composed of a plurality of crystal phases, each magnet is brought into a state in which the magnets are separated from each other, and the film thickness is 0.5 μm from the start of plating. Until the plating film is formed on the magnet surface 0.2 μm / min Deposition at the average deposition rate above Then, after the film thickness reaches 0.5 μm or more, the average film formation rate is changed by making the current density smaller than the previous current density. It is characterized by doing.
The electroplating method according to
The electroplating method according to
The electroplating method according to
In addition, an R—Fe—B permanent magnet having a plating film on the surface of the present invention is obtained by the electroplating method according to any one of claims 1 to 4 as described in
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The electroplating method of the present invention is a method of simultaneously electroplating a plurality of R-Fe-B permanent magnets composed of a main phase and a plurality of crystal phases of a grain boundary phase having a lower corrosion potential than the main phase. The magnet is placed in a state where the magnets are separated from each other, and the film is formed at an average film formation rate of 0.1 μm / min or more from the start of plating until a plating film having a film thickness of 0.5 μm is formed on the magnet surface. It is characterized by.
That is, in the electroplating method of the present invention, the magnets are separated from each other without causing a plurality of magnets to gather so as not to form an aggregate, and the average film formation rate at the initial stage of plating is set to a certain value or more. By immersing the magnet in the plating solution, a uniform plating film is quickly formed on all the magnets, thereby causing various problems with the barrel-type electroplating method, that is, corrosion of the magnet and its cause. It is possible to eliminate the deterioration of the magnetic properties of the magnet due to the generation of pinholes and hydrogen occlusion and the decrease in adhesion to the plating film.
[0007]
In the electroplating method of the present invention, it is an important requirement that the individual magnets be separated from each other. By letting the individual magnets in this state, the set current density can be applied uniformly to all the magnets, so that hydrogen generation can be suppressed even under a high current density setting. Even if it occurs, the influence on the magnetic properties of the magnet and the influence on the adhesion between the magnet and the plating film can be avoided as much as possible. Therefore, the current density can be increased to increase the average deposition rate of the plating film, and a uniform plating film can be rapidly formed on the surface of the magnet before corrosion starts.
[0008]
Here, the “separated state” means a state in which the possibility that individual magnets come into contact with each other is excluded. Such a state can be achieved, for example, by using a rack-type electroplating method, that is, using a plating jig provided with a large number of conductive support members that support a magnet to be processed and supply a plating current to the magnet. This can be realized by adopting a method of forming a plating film on the surface of a magnet by supporting the magnets independently and applying current directly to the magnet through a support member in a plating solution.
[0009]
There are various types of jigs employed in the rack-type electroplating method, but it is desirable to use a jig having a mechanism that does not leave a support trace (contact trace) on the magnet. As such a jig, for example, a jig provided with a mechanism for supporting a magnet and supplying a plating current to the magnet with a relative change in the support position of the magnet relative to the relationship between the magnet and the member. Tools. As a specific example of such a jig, a jig described in the specification of Japanese Patent Application No. 11-91585 is shown in FIG.
[0010]
FIG. 1 shows that a magnet is supported such that the support position of the magnet is changed by replacing at least one member that supports the magnet with another member at a constant period and supporting the magnet by the replaced member. It is the jig | tool which has arrange | positioned the member. That is, this jig has inner magnet support members 4-a and 4-b and outer magnet support members 5-a and 5-b. Both members are made of metal, the inner magnet support member is attached to the metal support frame 1, and the outer magnet support member is attached to the
[0011]
Other than the jig described in Japanese Patent Application No. 11-91585, as a suitable jig having a mechanism that does not leave a support trace on the magnet, the magnet is rotated as a jig suitable for plating a ring-shaped magnet. The jig provided with the mechanism which can move a support position is mentioned by plating, carrying out. As a specific example of such a jig, a ring-shaped magnet having a cylindrical inner peripheral surface described in Japanese Patent Application No. 11-290571 is supported from the inner peripheral surface side, and the magnet is rotated. A jig provided with a conductive support member and a load member that presses the magnet against the support member, an anode inserted in the hollow portion of the ring-shaped magnet described in Japanese Patent Application No. 2000-174537, and a magnet A jig having a conductive support member for rotating a metal plate around its central axis and supplying a plating current to the magnet, as described in Japanese Patent Application No. 2000-269986. The support member includes a jig that supports a ring-shaped magnet having a cylindrical inner peripheral surface so as to be rotatable from the inner peripheral surface side. Further, one magnet is provided in each compartment of the conductive support member having a large number of bowl-shaped compartments as described in Japanese Patent Application No. 11-265400 and Japanese Patent Application No. 2000-213427. A jig for plating while accommodating and rotating the support member and an apparatus for plating while conveying magnets on a plurality of conductive rollers described in Japanese Patent Application No. 2000-64237 are also preferably used. .
[0012]
Next, in the electroplating method of the present invention, it is important to form a film at an average film formation speed of 0.1 μm / min or more from the start of plating until a plating film having a film thickness of 0.5 μm is formed on the magnet surface. Requirements. Even if the individual magnets are separated from each other, if a plating film with a film thickness of 0.5 μm is not formed on the surface of the magnet within 5 minutes from the start of plating, corrosion of the magnet begins in the plating solution. , Pinholes are generated in the coating, and the plating solution is deteriorated.
[0013]
The plating in the present invention may be any plating, but is a film that provides excellent adhesion to the magnet surface, and from the point that it can be formed at low cost, Ni plating, Zn plating, Cu plating is desirable. Such plating is performed at an average film formation rate of 0.1 μm / min or more, preferably 0.2 μm / min or more from the start of plating until a 0.5 μm-thick plating film is formed on the magnet surface. Such a speed can be obtained by setting the current density to an appropriate value as a result of making the individual magnets in a state where the magnets are separated from each other, thereby making it possible to apply the current density evenly to each magnet. Can be achieved. Even if it is going to form a film at such an average film formation speed in the barrel type electroplating method, there are variations in the current density of individual magnets, which causes various problems as described above. However, a uniform film cannot be formed on the surface.
[0014]
The average film formation rate of 0.1 μm / min or more is usually 0.5 A / dm when the current density is Ni plating, Zn plating, or Cu plating using divalent metal ions. 2 By setting the above, when performing Cu plating using monovalent Cu ions such as copper cyanide, the current density is 0.25 A / dm. 2 This can be achieved by setting the above, but the current density is 20 A / dm. 2 It is desirable to form a film with the following settings. This is because when the current density is set to exceed this value, the problem of hydrogen generation becomes obvious, which may cause deterioration of characteristics due to hydrogen occlusion of the magnet and deterioration of adhesion to the plating film. Current density is 20 A / dm 2 By forming the film with the following setting, the amount of hydrogen on the magnet surface can be suppressed to 100 ppm or less, desirably 50 ppm or less.
[0015]
The final film thickness of the plating film formed on the magnet surface is desirably 1 μm or more. The average film formation rate may be fixed and maintained at an average film formation rate of 0.1 μm / min or more from the start of plating, or may be changed at a certain time. Although the upper limit of the thickness of the plating film that can be formed on the magnet surface by the electroplating method of the present invention is not particularly limited, the electroplating method of the present invention is based on a request based on the downsizing of the magnet itself, It is suitable for stably mass-producing R—Fe—B permanent magnets having a plating film with a thickness of 25 μm or less, desirably 20 μm or less, and more desirably 10 μm or less. In recent years, there has been a demand for stable and mass production of a plating film showing a thinner film and higher corrosion resistance by a simple process, but the electroplating method of the present invention is a method that can meet the needs of such times. is there.
[0016]
The plating solution used in the present invention is not particularly limited, and various commercially available and proposed plating solutions can be used. From the viewpoint of suppressing hydrogen generation as much as possible, electrodeposition is performed. It is desirable to use a plating solution having a characteristic that the efficiency is 90% or more. In general, when a low pH plating solution is used, pinholes may occur in the plating film or the plating solution may deteriorate due to the elution of the metal components constituting the magnet. When the liquid is used, there is a fear that a uniform plating film may not be formed due to the precipitation of hydroxide on the magnet surface. Therefore, it is desirable to use a plating solution having a pH of 5 to 13, and more desirably a pH of 6 to 12.
[0017]
The chlorine ion concentration in the plating solution, which is a major factor for magnet corrosion, is preferably adjusted to 20 g / L or less, and more preferably adjusted to 10 g / L or less. From this point of view, when performing Zn plating or Cu plating, it is desirable to use an alkali bath using a complexing agent such as a cyanide bath or a pyrophosphate bath that does not contain chlorine ions. In particular, when performing Cu plating, it is also desirable in that the substitution reaction between R and Fe, which are metal components constituting the magnet on the magnet surface, can be suppressed by using such an alkaline bath. .
[0018]
The plating solution reliably supplies metal ions to the magnet surface to maintain the average film formation rate and suppresses hydrogen generation as much as possible. It is desirable to stir in order to eliminate the hydrogen. Further, it is desirable to provide anodes in at least two different directions for each magnet so that a uniform plating film is formed on the entire surface of the magnet.
[0019]
The rare earth element (R) in the R—Fe—B permanent magnet applied to the present invention is at least one of Nd, Pr, Dy, Ho, Tb, and Sm, or further La, Ce, Gd, Er, It is desirable to include at least one of Eu, Tm, Yb, Lu, and Y.
Usually, one type of R is sufficient, but in practice, a mixture of two or more types (such as misch metal and didymium) may be used for reasons of convenience.
Furthermore, by adding at least one of Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni, Si, Zn, Hf, and Ga, It becomes possible to improve the squareness of the coercive force and the demagnetization curve, improve the manufacturability, and reduce the price. Further, by replacing part of Fe with Co, the temperature characteristics can be improved without impairing the magnetic characteristics of the obtained magnet.
[0020]
On the plating film formed on the magnet surface by the electroplating method of the present invention, the same kind of plating film or a different kind of plating film may be laminated, or another kind of film such as a chemical conversion treatment film may be laminated. Also good. By employ | adopting such a structure, the characteristic of the plating film formed by the electroplating method of this invention can be strengthened and complemented, or the further functionality can be provided. Even when such a multilayer coating is formed, the plated coating formed by the electroplating method of the present invention exhibits its effectiveness sufficiently, and exhibits excellent corrosion resistance even if the overall film thickness (total film thickness) is small. Demonstrate. In addition, as such a total film thickness, 1 micrometer-25 micrometers are desirable.
[0021]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following description.
[0022]
(1) R-Fe-B permanent magnet used:
For example, as described in U.S. Pat. No. 4,770,723 and U.S. Pat. No. 4,792,368, a known cast ingot is pulverized and finely pulverized, followed by molding, sintering, heat treatment, and surface processing to obtain 14Nd. A sintered magnet having a length of 15 mm × width of 25 mm × height of 7 mm and having a composition of −79Fe-6B-1Co was used.
[0023]
(2) Plating jig used:
(A) A jig that is equipped with the mechanism shown in FIG. 1 as a plating jig suitably used in the electroplating method of the present invention and can process 100 magnets simultaneously (10 rows x 10 rows). (Hereinafter abbreviated as rack jig).
(B) Throw 100 magnets and 2 kg of steel balls with a diameter of 2 mm into a general plastic barrel jig with a cross section of 150 mm and a length of 300 mm, which is used for barrel-type electroplating. It was used by rotating at a rotation speed of 5 rpm.
[0024]
(3) Pretreatment of plating:
This was performed according to the method described in JP-A-6-57480. That is, after setting a magnet on a plating jig, this was immersed in a treatment solution of sodium nitrate 0.2 mol / L and sulfuric acid 1.5 vol% for 4 minutes, and then immediately ionized at 1 μS / cm or less. After ultrasonic cleaning with replacement water for 30 seconds, plating was started immediately.
[0025]
Example A: Ni plating (part 1)
It consists of nickel sulfate hexahydrate 250 g / L, nickel chloride hexahydrate 45 g / L, boric acid 30 g / L, and uses a plating bath with a liquid temperature of 50 ° C. adjusted to pH 5.5 with nickel carbonate, (A) Current density set from 5 minutes after the start of plating shown in Table 1, (b) Average film formation rate during that time (actual value of n = 10: fluorescent X-ray film thickness meter SFT-7000 (Seiko Electronics Co., Ltd.) The same applies hereinafter.), (C) A Ni plating film having a thickness of 10 μm was formed on the magnet surface at a current density set after 5 minutes from the start of plating.
Average film thickness of the formed plating film (actual value of n = 10: use fluorescent X-ray film thickness meter SFT-7000 (manufactured by Seiko Denshi); the same applies hereinafter) and pressure cooker test (120 ° C. × 100 Table 1 shows the results of evaluation of corrosion resistance according to% RH × 2 atm × 72 hours. From Table 1, using a rack jig, each magnet was placed in a state where the magnets were separated from each other, and the film was formed at an average film formation rate of 0.1 μm / min or more for 5 minutes from the start of plating. Thus, it has been found that magnets having a plating film having excellent corrosion resistance on the surface can be stably mass-produced. Moreover, about one of the magnets having a plating film on the surface obtained in Example 2, the plating film was peeled off from the magnet, and the amount of hydrogen on the magnet surface was determined by glow discharge emission analysis (GDS: GDLS-5017: Shimadzu Corporation). As a result of measurement by the company), it was very low as 42 ppm.
[0026]
[Table 1]
Example B: Ni plating (2)
Nickel sulfate hexahydrate 130g / L, ammonium citrate 30g / L, boric acid 15g / L, ammonium chloride 8g / L, saccharin 8g / L, adjusted to pH 6.5 with aqueous ammonia at 50 ° C Table 2 shows (a) the current density set up to 5 minutes after the start of plating, (b) the average deposition rate (measured value of n = 10) during that time, and (c) the start of plating. After that, a Ni plating film having a film thickness of 10 μm was formed on the magnet surface at a current density set after 5 minutes.
Table 2 shows the average film thickness (measured value of n = 10) of the formed plating film and the corrosion resistance evaluation results by the pressure cooker test (120 ° C. × 100% RH × 2 atm × 72 hours). From Table 2, using a rack jig, individual magnets were separated from each other, and the film was formed at an average film formation rate of 0.1 μm / min or more for 5 minutes from the start of plating. Thus, it has been found that magnets having a plating film having excellent corrosion resistance on the surface can be stably mass-produced.
[0028]
[Table 2]
Example C: Two-layer Ni plating
Step 1: Using the same plating bath as that used in Example B, (a) current density set up to 5 minutes after the start of plating shown in Table 3, (b) average film formation rate (n = Actual measurement value of 10), (c) A Ni plating film having a film thickness of 4 μm was formed on the magnet surface at a current density set after 5 minutes from the start of plating. Table 3 shows the average film thickness (measured value of n = 10) of the formed plating film.
[0030]
[Table 3]
Step 2: From nickel sulfate hexahydrate 240 g / L, nickel chloride hexahydrate 45 g / L, boric acid 30 g / L, sodium 1,5-naphthalenedisulfonate 8 g / L, gelatin 0.01 g / L Using a plating bath with a pH of 4.2 and a liquid temperature of 50 ° C., a current density of 0.7 A / dm 2 A Ni plating film having a thickness of 16 μm was formed on the surface of the Ni plating film formed in step 1.
Table 4 shows the total average film thickness (measured value of n = 10) of the plating films formed in Step 1 and
[0032]
[Table 4]
Example D: Effect of plating solution deterioration during mass production
Table 5 shows the results of the 50th time when Ni plating under the conditions of Example A was repeated using one plating bath. Table 5 shows the results of the 50th time when Ni plating under the conditions of Example B was repeated using one plating bath. From Tables 5 and 6, the electroplating method of the present invention effectively suppresses the deterioration of the plating solution accompanying the elution of the metal components constituting the magnet, and is excellent even when one plating bath is used repeatedly 50 times. It has been found that a magnet having a plating film exhibiting corrosion resistance on its surface can be stably mass-produced, and that the effect is superior at pH 6 or higher.
[0034]
[Table 5]
[Table 6]
Example E: Zn plating
It consists of 70 g / L of zinc chloride, 200 g / L of potassium chloride, and 25 g / L of boric acid. Using a plating bath with a pH of 5.8 and a liquid temperature of 25 ° C., shown in Table 7 (a) 5 minutes after the start of plating Set current density, (b) average film formation rate (measured value of n = 10), (c) magnetized Zn plating film with a film thickness of 15 μm at current density set after 5 minutes from the start of plating Formed on the surface.
Table 7 shows the corrosion resistance evaluation results by the average film thickness (actual value of n = 10) of the formed plating film and the pressure cooker test (120 ° C. × 100% RH × 2 atm × 72 hours). From Table 7, using a rack jig, each magnet was placed in a state where the magnets were separated from each other, and the film was formed at an average film formation speed of 0.1 μm / min or more for 5 minutes from the start of plating. Thus, it has been found that magnets having a plating film having excellent corrosion resistance on the surface can be stably mass-produced.
[0037]
[Table 7]
Example F: Cu plating
It consists of copper sulfate pentahydrate 220 g / L, sulfuric acid 50 g / L, copper chloride dihydrate 120 mg / L, and uses a plating bath with a liquid temperature of 25 ° C. having a pH of 0 to 2 and shown in Table 8 (a ) Current density set up to 5 minutes after the start of plating, (b) Average film formation rate during that time (actual value of n = 10), (c) Film with current density set after 5 minutes from the start of plating A Cu plating film having a thickness of 10 μm was formed on the magnet surface.
Table 8 shows the average film thickness (measured value of n = 10) of the formed plating film and the corrosion resistance evaluation results by the pressure cooker test (120 ° C. × 100% RH × 2 atm × 72 hours). From Table 8, using a rack jig, individual magnets were separated from each other, and the film was formed at an average film formation rate of 0.1 μm / min or more for 5 minutes from the start of plating. Thus, it has been found that magnets having a plating film having excellent corrosion resistance on the surface can be stably mass-produced.
[0039]
[Table 8]
【The invention's effect】
According to the electroplating method of the present invention, in the method of simultaneously electroplating a plurality of R-Fe-B permanent magnets composed of a main phase and a plurality of crystal phases of a grain boundary phase having a lower corrosion potential than the main phase, Each magnet is brought into a state where the magnets are separated from each other, and the film is formed at an average film formation speed of 0.1 μm / min or more from the start of plating until a plating film having a film thickness of 0.5 μm is formed on the magnet surface. By immersing the magnet in the plating solution, a uniform plating film is quickly formed on all the magnets, thereby causing various problems with the barrel-type electroplating method, that is, corrosion of the magnet and its cause. R-Fe-B permanent magnets that have a plating film with excellent corrosion resistance even on a thin film can be stabilized by eliminating pinholes and deterioration of the magnetic properties of the magnet due to hydrogen occlusion and lowering of adhesion to the plating film. Mass production You can.
[Brief description of the drawings]
FIG. 1 is a schematic view of a plating jig suitably used in the electroplating method of the present invention.
[Explanation of symbols]
1, 2 Support frame
3 Magnet
4-a, 4-b Inner magnet support member
5-a, 5-b outer magnet support member
6 Electric actuator
7 Switching device
8 Insulator
9 Control unit
Claims (5)
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| US7462403B2 (en) | 2003-06-27 | 2008-12-09 | Tdk Corporation | R-T-B system permanent magnet |
| CN100588752C (en) * | 2004-08-10 | 2010-02-10 | 日立金属株式会社 | Method for producing rare earth element based permanent magnet having copper plating film on surface thereof |
| JP4650275B2 (en) * | 2004-08-10 | 2011-03-16 | 日立金属株式会社 | Rare earth permanent magnet with copper plating film on the surface |
| JP2008251648A (en) * | 2007-03-29 | 2008-10-16 | Hitachi Metals Ltd | MANUFACTURING METHOD OF R-Fe-B-BASED PERMANENT MAGNET |
| JP5090781B2 (en) * | 2007-04-27 | 2012-12-05 | 株式会社ソフテム | Permanent magnet anticorrosion method |
| JP5012942B2 (en) * | 2010-03-26 | 2012-08-29 | Ｔｄｋ株式会社 | Rare earth sintered magnet, manufacturing method thereof, and rotating machine |
| CN103125005B (en) * | 2010-09-30 | 2016-02-10 | 日立金属株式会社 | The method of electro-coppering tunicle is formed on the surface of rare earth element permanent magnet |
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| JPH01304713A (en) * | 1988-06-02 | 1989-12-08 | Shin Etsu Chem Co Ltd | Manufacture of corrosion-resistant rare earth magnet |
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| JPH04287302A (en) * | 1991-03-15 | 1992-10-12 | Tdk Corp | Permanent magnet and its manufacture |
| JP3126215B2 (en) * | 1992-04-23 | 2001-01-22 | 信越化学工業株式会社 | Manufacturing method of corrosion resistant rare earth permanent magnet |
| JP3232037B2 (en) * | 1998-01-19 | 2001-11-26 | 住友特殊金属株式会社 | High corrosion resistance R-Fe-B bonded magnet with excellent crushing strength |
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