JP3822704B2

JP3822704B2 - Manufacturing method of steel sheet for welding can excellent in weldability, corrosion resistance, appearance and adhesion

Info

Publication number: JP3822704B2
Application number: JP07677597A
Authority: JP
Inventors: 茂平野; 信介浜口; 亨千々木
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1997-03-28
Filing date: 1997-03-28
Publication date: 2006-09-20
Anticipated expiration: 2017-03-28
Also published as: JPH10265968A

Description

【０００１】
【発明の属する技術分野】
本発明は、製缶素材として、特にシーム溶接性、耐食性、外観性、塗料及びフィルム密着性に優れた溶接缶用鋼板の製造方法に関するものである。
【０００２】
【従来の技術】
近年、ワイヤーシーム抵抗溶接法による溶接缶の製缶技術が急速に進展し、飲料缶分野での実用化が急速に進展してきた。この種の溶接缶に使用される缶用鋼板は、電気めっきによりＦｅ−Ｎｉ合金めっきを行った後、Ｓｎめっきを行い、更に溶錫処理し、クロメート処理を行うシーム溶接性に優れた製缶用表面処理鋼板の製造方法（特開昭６０−２０８４９４号公報）、あるいは、Ｆｅ−Ｎｉ合金を施した後、Ｓｎめっき、クロメート処理することにより塗料密着性、溶接性に優れたシーム溶接缶用表面処理鋼板の製造方法（特開昭６０−１３０９８号公報）により作製される。確かにこのような発明による製造方法は、溶接性、耐食性、塗料密着性を備えた溶接缶用表面処理鋼板を提供するものである。
更に、これらの容器用表面処理鋼板を用いて、缶内面には耐食性を確保するための塗装焼き付けが行われ、缶外面には多色刷り印刷が行われる。この後、ワイヤーシーム溶接法により製缶が行われて、実用に供されている。
【０００３】
【発明が解決しようとする課題】
近年では、より一層の製缶技術の進歩と製缶コストダウンが相俟って、製缶工程の大幅な生産性向上を狙って、塗装・印刷の代わりに、缶内面かつ／または外面に有機フィルムをラミネートした材料が使用されるようになった。
ところが、缶内面かつ／または外面に有機フィルムをラミネートする材料として、上記に述べた容器用表面処理鋼板を適用した場合、溶接部近傍で塗料やフィルム密着性不良が発生する。これは、上記の容器用表面処理鋼板は、めっき層に合金化していない金属Ｓｎを含有しているため、溶接余熱によりＳｎ融点以上に温度上昇される溶接部近傍は、めっき層が溶融する。この時、めっき層上の塗料やフィルムは溶融した液体金属Ｓｎ上にいわば浮かんでいる様な状態になるため、塗料やフィルム密着性が極めて低くなり、冷却風による塗料やフィルム剥離や塗料やフィルムの内部応力による塗料やフィルム収縮が起こり易くなり、塗料やフィルムの剥離が生じる。
【０００４】
【課題を解決するための手段】
塗料及びフィルム密着不良を回避するためには、金属Ｓｎのめっき量を少なくし、金属Ｓｎの被覆率を低下させれば、確かに塗料及びフィルム密着性は向上する。しかし、Ｓｎめっき量が減少すれば、溶接缶用鋼板として具備すべき特性である溶接性や耐食性が劣化するため、フィルム密着性、溶接性、外観性、塗料密着性を全て満足する溶接缶用材料の製造は困難であった。
本発明者等は、これらの問題点に対して、外観性、塗料及びフィルム密着性、溶接性、塗料密着性を全て満足する溶接缶用材料として、Ｓｎが球状化し、金属Ｓｎの存在しないフィルム密着性の優れたＦｅ−ＮｉまたはＦｅ−Ｎｉ−Ｓｎ合金めっき層が露出するめっき構造を有する鋼板が、溶接熱影響部のようなＳｎの融点を超える箇所でも、優れた密着性を確保することが出来ることを見出した。更に、その製造において経済的に優れた製造方法として、本発明者等は、硫酸系あるいは硫酸−塩酸系のめっき浴からのＦｅ−Ｎｉ合金めっきのめっき条件とＳｎの球状化について鋭意検討した結果、上記の球状化Ｓｎめっき層を、工業的に効率良く製造できる事を見い出した。
【０００５】
以下に本発明の本質について説明する。
先ず、Ｆｅ−Ｎｉ合金めっき上でのＳｎの球状化現象は、以下の様に考えられる。硫酸系あるいは硫酸−塩酸系でのＦｅ−Ｎｉ合金めっきは、いわゆる水酸化鉄の発生を伴う異常共析型のめっきであると言われている。Ｆｅ−Ｎｉ合金めっき上には水酸化鉄が生成しており、この水酸化鉄上にＳｎめっきが行われ、溶融溶錫処理が行われる。溶融したＳｎは下地の水酸化鉄との濡れ性が低いため、はじき現象を生じ、Ｓｎの球状化が進むと考えられる。
従って、Ｓｎの球状化は、水酸化鉄の量と均一被覆性依存すると考えられる。即ち、水酸化鉄量が多いほど、また、均一に存在するほど、Ｓｎの球状化が進行しやすくなると考えられる。
【０００６】
本発明者等は、この水酸化鉄の均一被覆性が、Ｆｅ−Ｎｉ合金めっきの低電流密度めっきによって促進され、水酸化鉄の付着量は、高電流密度めっきによって促進されることを発見し、更に、２回以上Ｆｅ−Ｎｉ合金めっきを行う場合、始めに、低電流密度でめっきを行い、その後、高電流密度でめっきを行うことにより、より一層の高効率で、球状化Ｓｎの生成に必要な水酸化鉄を付着させることを知見した。これは、始めに行う低電流密度Ｆｅ−Ｎｉ合金めっきにより水酸化鉄の微小な核が均一に分散生成し、続いて行われる高電流密度Ｆｅ−Ｎｉ合金めっきで、この核を中心に水酸化鉄が付着するため、１回だけのＦｅ−Ｎｉ合金めっき法に比べて均一かつ所定量の水酸化鉄を効率良く生成できると考えられる。
【０００７】
即ち本発明は、
（１）鋼板の表面にＮｉめっき量で２〜２００ｍｇ／ｍ²、Ｎｉ含有率５〜５５％のＦｅ−Ｎｉ合金めっきを、０．０５〜４０Ａ／ｄｍ²の電流密度で２回以上行うことで達成し、この際全めっき回数の内の２回のめっきを比較して、前段のめっき電流密度を後段のめっき電流密度より低電流密度とする組み合わせを少なくとも一組有し、次いで、４００〜２５００ｍｇ／ｍ²錫めっきを行い、溶融溶錫処理により形成した面積被覆率４０〜９８％の球状Ｓｎめっき層を有するようにしたことを特徴とする溶接性、耐食性、外観性及び密着性に優れた溶接缶用鋼板の製造方法。
【０００８】
（２）鋼板の表面にＮｉめっき量で２〜２００ｍｇ／ｍ²、Ｎｉ含有率５〜５５％のＦｅ−Ｎｉ合金めっきを、０．０５〜４０Ａ／ｄｍ²の電流密度で２回以上行うことで達成し、この際全めっき回数の内の２回のめっきを比較して、前段のめっき電流密度を後段のめっき電流密度より低電流密度とする組み合わせを少なくとも一組有し、次いで、４００〜２５００ｍｇ／ｍ²錫めっきを行い、溶融溶錫処理により形成した面積被覆率８０％を越えて９８％以下の球状Ｓｎめっき層を有するようにしたことを特徴とする溶接性、耐食性、外観性及び密着性に優れた溶接缶用鋼板の製造方法。
【０００９】
（３）Ｆｅ−Ｎｉ合金めっきを２回以上行うめっき方法において、前段のめっき電流密度が０．０５〜４Ａ／ｄｍ²であることを特徴とする前記（１）または（２）に記載の溶接性、耐食性、外観性及び密着性に優れた溶接缶用鋼板の製造方法。
（４）最表層にＣｒ換算量で２〜４０ｍｇ／ｍ²のクロメート被覆層を形成したことを特徴とする前記（１）〜（３）のいずれかに記載の溶接性、耐食性、外観性及び密着性に優れた溶接缶用鋼板の製造方法にある。
【００１０】
【発明の実施の形態】
以下に本発明の作用である溶接性、耐食性、外観性、塗料及びフィルム密着性優れた溶接缶用鋼板の製造方法について詳細に説明する。
本発明においてめっき原板は特に規制されるものではなく、通常、容器材料として使用される鋼板を用いる。めっき原板の製造法、材質なども特に規制されるものではなく、通常の鋼片製造工程から熱間圧延、酸先、冷間圧延、焼鈍、調質等の工程を経て製造される。更に、このめっき原板は必要とされる缶体強度および板厚に応じて冷間圧延後、焼鈍を行ってから再冷間圧延（即ち２ＣＲ法）する工程で製造してもよい。
【００１１】
上記のめっき原板に、めっきを行う場合、通常、めっき原板表面を清浄化するため前処理として脱脂、酸洗が行われるが、それらの方法は特に規制するものでは無く、例えば、１０％苛性ソーダ中で脱脂した後、５％硫酸溶液中で酸洗を行えばよい。脱脂、酸洗に引き続き、Ｆｅ−Ｎｉ合金めっきが行われる。Ｆｅ−Ｎｉ合金めっき層を付与する目的は、耐食性と溶接性の両特性の確保である。
【００１２】
Ｎｉは高耐食金属のため、Ｎｉをめっきする事により、めっき層の耐食性を向上させることが出来る。Ｎｉによるめっき層の耐食性向上効果は、片面当たりのＮｉめっき量２ｍｇ／ｍ²以上から発現する。従って、Ｎｉめっき量は２ｍｇ／ｍ²以上必要である。Ｎｉめっき量が多くなる程、めっき層の耐食性向上効果は増加するが、ＮｉはＳｎと極めて合金化し易い金属のため、Ｎｉめっき量が多くなると上層のＳｎとの合金化が製缶工程で進行し、工業的に効率よく溶接するために必要な、合金化していないＳｎが十分に確保されない。従って、Ｎｉめっき量は、２００ｍｇ／ｍ²以下にする必要がある。
【００１３】
また、耐食性と溶接性の両特性を確保するためには、Ｆｅ−Ｎｉ合金めっき層中のＮｉ含有率は以下の様に規定される。Ｎｉ含有率が低すぎるとＮｉの表面濃度が低くなり表面から進行する腐食を防ぐ事が困難になるため、Ｆｅ−Ｎｉ合金めっき層中のＮｉ含有率は５％以上必要である。また、Ｎｉ含有率が５５％を越えると、Ｎｉの表面濃度が高くなりすぎＳｎとの合金化が進行し易くなり、Ｆｅ−Ｎｉ合金めっき層中のＮｉ含有率は５５％以下にする必要がある。
【００１４】
従って、実用上、耐食性と溶接性を確保するために必要なＦｅ−Ｎｉ合金めっきに於けるＮｉめっき量は鋼板片面当たり５０〜２００ｍｇ／ｍ²、Ｆｅ−Ｎｉめっき層中のＮｉ含有率は５〜５５％にする必要がある。
上記のＦｅ−Ｎｉ合金めっきを行うために使用されるＦｅ−Ｎｉ合金めっき浴は、硫酸系あるいは硫酸−塩酸系の一般に知られている異常共析型のＦｅ−Ｎｉ合金めっきを生じるめっき浴を用いればよい。しかし、前述の如く、溶融溶錫時に球状Ｓｎめっきを工業的に効率よく形成させるには、Ｆｅ−Ｎｉめっき条件を以下の様にする必要がある。
【００１５】
Ｆｅ−Ｎｉ合金めっきを行うときの電流密度は、片面当り０．０５Ａ／ｄｍ²以上必要である。これは、Ｆｅ−Ｎｉ合金めっきの電流密度が、０．０５Ａ／ｄｍ²未満であると異常共析型の電析が行われず、水酸化鉄も付着しないため、溶融溶錫処理時にＳｎが弾かず、その結果、必要な密着性が確保できなくなる。従って、Ｆｅ−Ｎｉ合金めっきの電流密度は、０．０５Ａ／ｄｍ²以上にする必要がある。一方、Ｆｅ−Ｎｉ合金めっきの電流密度は、高くなる程、水酸化鉄の付着量が増加するが、水酸化鉄の均一付着が損なわれるため、めっき電流密度は４０Ａ／ｄｍ²以下にする必要がある。
【００１６】
ところが、工業的経済的な観点では、Ｆｅ−Ｎｉ合金めっきの電流密度が低い場合、所定のＮｉめっき量あるいはＳｎ球状化に必要な十分な水酸化鉄を確保できないため、比較的長時間のＦｅ−Ｎｉ合金めっき処理が必要になり、また、Ｆｅ−Ｎｉ合金めっきの電流密度が高い場合、Ｓｎ球状化に必要な十分被覆した水酸化鉄を確保できないため、やはり比較的長時間のＦｅ−Ｎｉ合金めっき処理が必要になる。この様な場合、高速処理が必要とされる連続ストリップラインでは、２回、３回あるいは４回以上に渡りＦｅ−Ｎｉ合金めっきを行う必要があるが、前述の如く、始めに、低電流密度Ｆｅ−Ｎｉ合金めっきを行い、続いて、高電流密度Ｆｅ−Ｎｉ合金めっきを行えば、効率良く、Ｆｅ−Ｎｉ合金めっきを行うことが出来る。
【００１７】
本法の効果を効果的に得るためには、始めに行われるＦｅ−Ｎｉ合金めっきの電流密度は、０．０５〜４Ａ／ｄｍ²にする必要がある。電流密度が、０．０５Ａ／ｄｍ²未満であると異常共析型の電析が行われず、水酸化鉄も付着しないため、始めに行われるＦｅ−Ｎｉ合金めっきの電流密度は、０．０５Ａ／ｄｍ²以上にする必要がある。この低電流密度Ｆｅ−Ｎｉ合金めっきの目的は、微小水酸化鉄核の均一分散生成にあることから、めっき電流密度は、４Ａ／ｄｍ²以下にする必要がある。
【００１８】
また、Ｆｅ−Ｎｉ合金めっきを２回以上行う場合には、１回以上の低電流密度Ｆｅ−Ｎｉ合金めっきと１回以上高電流密度Ｆｅ−Ｎｉ合金めっきを、少なくとも１回の低電流密度Ｆｅ−Ｎｉ合金めっきを高電流密度Ｆｅ−Ｎｉ合金めっきの前に行うという条件で、行えばよく、その各々の回数については、本発明の本質に関するものではない。Ｆｅ−Ｎｉ合金めっきの後、Ｓｎめっきが行われる。ここで言うＳｎめっきとは、金属Ｓｎと不可避的不純物からなる。Ｓｎめっきは、前述したように溶接性確保するために行われるが、工業的に効率良く溶接を行うには、Ｓｎのめっき量を４００ｍｇ／ｍ²以上にする必要がある。Ｓｎめっき量が増加すると、溶接性の向上効果は増加するが、めっき量が２５００ｍｇ／ｍ²を越えると、溶接性の向上効果が飽和するため、経済的には２５００ｍｇ／ｍ²以下で良い。このＳｎめっき方法については特に規制する物ではなく、例えば、通常の電気めっきにより行うことが出来る。
【００１９】
Ｓｎめっきの後、溶融溶錫処理が行われる。溶融溶錫処理に於いては、Ｓｎの融点を超える加熱処理が行えれば良く、例えば、通電加熱、誘導加熱、炉内加熱などの方法を使用すればよい。この溶融溶錫処理により、異常析出により形成された上層に水酸化物を有するＦｅ−Ｎｉ合金めっきの前述の効果から、めっきされたＳｎが球状化し、密着性の優れためっき層構造が形成される。この時の、Ｓｎの面積占有率は、４０〜９８％にする必要がある。これは、面積占有率が４０％未満であると外観に優れたＳｎの面積率が少なすぎるため、外観性が劣化する。従って、Ｓｎの面積占有率は４０％以上必要である。
【００２０】
また、より優れた外観性を発揮するためには、外観性に優れたＳｎの面積被覆率を高くすれば良く、その為には、Ｓｎの面積占有率が好ましくは８０％を越えればよい。一方、鋼板の外観性はＳｎの面積占有率が増加するほど向上するが、面積占有率が９８％を越えると、フィルムの密着性が劣化するため、Ｓｎの面積占有率は９８％以下にする必要がある。引き続き、溶融溶錫処理の後、フィルム密着性、耐食性（アンダーカッティングコロージョンの防止）を目的としてクロメート皮膜が付与される。ここで言うクロメート皮膜とは、水和酸化クロム単一の皮膜、即ち本来のクロメート皮膜といま一つは下層に金属クロム層、上層に水和酸化クロム層の二層よりなる被膜の二つの場合を指している。水和酸化クロム層には、後述するめっき助剤である硫酸イオンやフッ素イオンなどを含む場合がある。フィルム密着性や耐食性は、この水和酸化クロムの官能基とラミネートされるフィルムの官能基が強固な化学的な結合を行うことによって確保される。
【００２１】
しかし、水和酸化クロム被膜は電気的に絶縁体のため電気抵抗が非常に高く、金属クロムも融点が高くかつ電気抵抗も高いので、両者とも溶接性を劣化せしめるマイナス要因である。そのため、良好なフィルム密着性、耐食性と実用的に溶接性を劣化せしめない適正なクロメート皮膜付着量が非常に重要となる。従って、クロメート皮膜付着量は金属クロム換算で片面当たり２〜４０ｍｇ／ｍ²が選定される。即ち、クロメート皮膜付着量が２ｍｇ／ｍ²未満では、フィルム密着性の向上、アンダーカテッィングコロージョンの防止に効果が得られないので、２ｍｇ／ｍ²以上の付着量が望ましい。一方、クロメート皮膜付着量が４０ｍｇ／ｍ²を越えると接触抵抗が著しく増加し、局部的な発熱による散りが発生し易くなり溶接性が劣化する。そのためクロメート皮膜付着量は４０ｍｇ／ｍ²以下に規制される。
【００２２】
クロメート処理方法は、各種のクロム酸のナトリウム塩、カリウム塩、アンモニウム塩の水溶液による浸漬処理、スプレー処理、電解処理などいずれの方法で行っても良いが、特に陰極電解処理が優れている。とりわけ、クロム酸にめっき助剤として硫酸イオン、フッ化物イオン（錯イオンを含む）あるいはそれらの混合物を添加した水溶液中での陰極電解処理が最も優れている。
【００２３】
【実施例】
以下に本発明の実施例及び比較例について述べ、その結果を各々表１に示す。冷間圧延もしくは焼鈍後の２回圧延により、所定の板厚に調整しためっき原板を５％苛性ソーダ中で電解脱脂し、水洗後１０％硫酸中で電解酸洗し、表面活性後表面処理を行った。このめっき原板に、
（１）に示す条件でＦｅ−Ｎｉ合金めっきを行った後、（２）に示す条件で錫めっきを行い、引き続き（３）−（Ａ）〜（Ｂ）に示す条件で加熱処理を行い、引き続き（４）−（Ａ）〜（Ｃ）に示す処理浴でクロメート皮膜を生成させたものを作製した。
【００２４】
（１）Ｆｅ−Ｎｉ合金めっき条件
Ｎｉイオン：２５ｇ／ｌ、Ｆｅイオン：５０ｇ／ｌ、硫酸イオン：１５ｇ／ｌ、塩素イオン：１０ｇ／ｌ、ホウ酸：２０ｇ／ｌを有する３５℃のめっき浴中に試験片を浸漬し、０．０５〜４０Ａ／ｄｍ²で電解することによりＦｅ−Ｎｉ合金めっき層を形成させる。電解時間及びめっき回数は、めっき量等に応じて適当に調整する。
（２）錫めっき条件
錫イオン：１５ｇ／ｌ、フェノールスルホン酸イオン：１５ｇ／ｌ、光沢添加剤：１．２ｇ／ｌを有する４０℃のめっき浴中に（１）で作製した試験片を浸漬し、８Ａ／ｄｍ²で電解することにより錫めっきを行う。電解時間は、めっき量に応じて調整する。
【００２５】
（３）加熱処理条件
（Ａ）加熱炉法
４００℃雰囲気の加熱炉に（２）で作製した錫めっき鋼板を５〜３０ｓｅｃ入れ、錫を溶融させ取り出し、直ちに冷却する。
（Ｂ）通電加熱法
（２）で作製した錫めっき鋼板に交流を通電し、鋼板電気抵抗により発熱させ、錫を溶融させ、直ちに冷却する。
（Ｃ）誘導加熱法
（２）で作製した錫めっき鋼板を誘導加熱により発熱させ、錫を溶融させ、直ちに冷却する。
【００２６】
（４）クロメート処理条件
以下のめっき組成の浴中に（３）で作製した試験片を浸漬し電解する。電解時間は、めっき量に応じて調整する。
（Ａ）酸化クロム１００ｇ／ｌ、硫酸イオン０．６ｇ／ｌ
めっき条件２０〜６０℃、５〜８０Ａ／ｄｍ²
（Ｂ）重クロム酸ソーダ１５〜４５ｇ／ｌ
めっき条件３０〜５０℃、１０〜４０Ａ／ｄｍ²
（Ｃ）クロム酸８０ｇ／ｌ、硫酸イオン０．０５ｇ／ｌ、ケイフッ化ソーダ
２．５ｇ／ｌ、フッ化アンモン０．５ｇ／ｌ、
めっき条件１５〜７５℃、１０〜８５Ａ／ｄｍ²
【００２７】
上記処理材について、以下に示す（Ａ）〜（Ｅ）の各項目について実施し、その性能を評価した。
（Ａ）シーム溶接性
試験片は高温短時間での塗装焼付け条件を想定して３２０℃まで２３ｓｅｃで昇温する条件で焼付けを行い、以下の溶接条件でシーム溶接性を評価した。ラップ代０．５ｍｍ、加圧力４５ｋｇｆ、溶接ワイヤースピード８０ｍ／ｍｉｎの条件で、電流を変更して溶接を実施し、十分な溶接強度が得られる最小電流値と散りなどの溶接欠陥が目立ち始める最大電流値からなる適正電流範囲の広さから総合的に判断し、４段階（◎：非常に広い、○：広い、△：実用上問題なし、×：狭い）で評価した。
【００２８】
（Ｂ）塗料密着性
試験片の缶内面側に相当する面にエポキシフェノール系塗料を５５ｍｇ／ｄｍ²塗布し、更に缶外面に相当する面にクリヤーラッカーを４０ｍｇ／ｄｍ²塗布し、２９０℃まで１５ｓｅｃの焼き付け条件で乾燥硬化した。引き続き、各々の面に１ｍｍ間隔でスクラッチを入れ、約１００個の碁盤目を作製し、速やかにテープ剥離し、その剥離状況を観察し、４段階（◎：全く剥離無し、○：極僅かな剥離有り、△：僅かな剥離有り、×：大部分で剥離）で塗料密着性を評価した。
【００２９】
（Ｃ）フィルム密着性評価試験
試験片に厚さ１５μｍのＰＥＴ（ポリエチレンテレフタレート）系フィルムをラミネートした後、地鉄に達するまでクロスカットを入れ、速やかに２４０℃に加熱し、クロスカット中央部に５ｋｇ／ｃｍ²の空気ガスを垂直に吹きつけ、４段階（◎：全く剥離無し、○：極僅かな剥離有り、△：僅かな剥離有り、×：大部分で剥離）でフィルムの剥離状況を評価した。
【００３０】
（Ｄ）ＵＣＣ（アンダーカッティングコロージョン）評価テスト
試験片の缶内面に相当する面の耐食性を評価するため、缶内面側に相当する面に厚さ１５μｍのＰＥＴ（ポリエチレンテレフタレート）系フィルムをラミネートした。その後、地鉄に達するまでクロスカットを入れ、１．５％クエン酸−１．５％食塩混合液からなる試験液中に大気開放下５５℃×４日間浸漬した。試験終了後、速やかにスクラッチ部および平面部をテープで剥離して、スクラッチ部近傍の腐食状況、スクラッチ部のピッティング状況および平面部のフィルム剥離状況を４段階（◎：剥離が無く腐食も認められない、○：極僅かな剥離が有るが腐食は認められない、△：僅かな剥離が有り微小な腐食が認められる、×：大部分で剥離し激しい腐食が認められる）で判断して総合的に評価した。
【００３１】
（Ｅ）外観性評価テスト
缶外面側に相当する面に、ホワイト印刷を行った厚さ１５μｍのＰＥＴ（ポリエチレンテレフタレート）系フィルムをラミネートし、色調の明るさを４段階（◎：非常に明るい、○：やや明るい、△：明るい、×：暗い）で評価した。
表１に示すように、本発明により製造された溶接缶用鋼板は、優れた溶接性、外観性、塗料密着性及びフィルム密着性、耐食性を有することが明らかになった。
【００３２】
【表１】

【００３３】
【発明の効果】
以上述べたように、本発明により、製缶素材として、特にシーム溶接性、耐食性、外観性、塗料及びフィルム密着性に優れた溶接缶用鋼板を経済的に製造する事が出来る極めて工業上優れた効果を奏するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a steel sheet for a welding can that is particularly excellent in seam weldability, corrosion resistance, appearance, paint and film adhesion as a can-making material.
[0002]
[Prior art]
In recent years, welding can manufacturing technology using wire seam resistance welding has been rapidly advanced, and practical application in the beverage can field has been rapidly progressing. The steel plate for cans used in this type of welded can is a can-making machine with excellent seam weldability in which Fe-Ni alloy plating is performed by electroplating, followed by Sn plating, further tin treatment, and chromate treatment. For surface treated steel sheets (Japanese Patent Laid-Open No. 60-208494), or for seam welded cans with excellent paint adhesion and weldability by applying Sn-plating and chromate treatment after applying Fe-Ni alloy It is produced by a method for producing a surface-treated steel sheet (Japanese Patent Laid-Open No. 60-13098). Certainly, the manufacturing method according to the present invention provides a surface-treated steel sheet for a welding can having weldability, corrosion resistance, and paint adhesion.
Furthermore, using these surface-treated steel sheets for containers, paint baking is performed on the inner surface of the can to ensure corrosion resistance, and multicolor printing is performed on the outer surface of the can. Thereafter, the can is made by a wire seam welding method and put into practical use.
[0003]
[Problems to be solved by the invention]
In recent years, combined with further advancement in can manufacturing technology and reduction in can manufacturing costs, aiming at significant productivity improvement in the can manufacturing process, instead of painting and printing, organic can inner and / or outer surface Film laminated materials have been used.
However, when the above-described surface-treated steel sheet for containers is applied as a material for laminating an organic film on the inner surface and / or outer surface of the can, paint and film adhesion defects occur in the vicinity of the weld. This is because the above-mentioned surface-treated steel sheet for containers contains metal Sn that is not alloyed in the plating layer, so that the plating layer is melted in the vicinity of the weld where the temperature is raised to the Sn melting point or more by the residual heat of welding. At this time, since the paint or film on the plating layer is in a state of floating on the molten liquid metal Sn, the adhesion of the paint or film becomes extremely low, and the paint or film is peeled off by the cooling air or the paint or film. The paint or film shrinks easily due to the internal stress, and the paint or film peels off.
[0004]
[Means for Solving the Problems]
In order to avoid poor paint and film adhesion, if the amount of metal Sn plating is reduced and the coverage of metal Sn is lowered, the paint and film adhesion is certainly improved. However, if the Sn plating amount decreases, the weldability and corrosion resistance, which should be provided as a steel plate for welded cans, deteriorate, so that for welded cans that satisfy all film adhesion, weldability, appearance, and paint adhesion. The production of the material has been difficult.
In order to solve these problems, the inventors of the present invention have developed a welding can material that satisfies all of the appearance, paint and film adhesion, weldability, and paint adhesion. To ensure excellent adhesion even when the steel sheet having a plating structure with an exposed Fe—Ni or Fe—Ni—Sn alloy plating layer with excellent adhesion exceeds the melting point of Sn, such as a weld heat affected zone. I found out that I can do it. Furthermore, as an economically superior production method in the production, the present inventors have conducted extensive studies on the plating conditions of Fe—Ni alloy plating from a sulfuric acid-based or sulfuric acid-hydrochloric acid-based plating bath and Sn spheroidization. The inventors have found that the above-described spheroidized Sn plating layer can be produced industrially and efficiently.
[0005]
The essence of the present invention will be described below.
First, the spheroidization phenomenon of Sn on the Fe—Ni alloy plating is considered as follows. It is said that the Fe-Ni alloy plating in the sulfuric acid system or sulfuric acid-hydrochloric acid system is an abnormal eutectoid type plating accompanied by generation of so-called iron hydroxide. Iron hydroxide is generated on the Fe—Ni alloy plating, Sn plating is performed on the iron hydroxide, and molten tin treatment is performed. Since the melted Sn has low wettability with the underlying iron hydroxide, it is considered that a rebound phenomenon occurs and Sn spheroidization proceeds.
Therefore, Sn spheroidization is considered to depend on the amount of iron hydroxide and uniform coverage. That is, it is considered that Sn spheroidization progresses more easily as the amount of iron hydroxide is larger and evenly present.
[0006]
The present inventors have found that this uniform coverage of iron hydroxide is promoted by low current density plating of Fe—Ni alloy plating, and the amount of iron hydroxide deposited is promoted by high current density plating. Furthermore, when performing Fe-Ni alloy plating two or more times, first, plating is performed at a low current density, and then plating is performed at a high current density, thereby generating spheroidized Sn with higher efficiency. It was found that the iron hydroxide necessary for adhesion was deposited. This is because fine nuclei of iron hydroxide are uniformly dispersed and formed by the low current density Fe—Ni alloy plating performed first, and the subsequent high current density Fe—Ni alloy plating performs the hydroxylation around the nuclei. Since iron adheres, it is considered that a uniform and predetermined amount of iron hydroxide can be efficiently generated as compared with the one-time Fe—Ni alloy plating method.
[0007]
That is, the present invention
(1) Fe-Ni alloy plating with a Ni plating amount of ² to 200 mg / m ² and a Ni content of 5 to 55% is performed twice or more at a current density of 0.05 to 40 A / dm ^{2 on} the surface of the steel sheet. In this case, at least one combination in which the plating current density of the former stage is lower than the plating current density of the latter stage is compared by comparing two platings out of the total number of plating times, and then 400- performed 2500 mg / m ² of tin plating, excellent weldability, corrosion resistance, appearance and adhesiveness, characterized in that it has to have a spherical Sn plating layer of the area coverage from 40 to 98% formed by melting溶錫treatment A method of manufacturing a steel plate for a welded can.
[0008]
( 2 ) Fe-Ni alloy plating with a Ni plating amount of ² to 200 mg / m ² and a Ni content of 5 to 55% is performed twice or more at a current density of 0.05 to 40 A / dm ^{2 on} the surface of the steel sheet. In this case, at least one combination in which the plating current density of the former stage is lower than the plating current density of the latter stage is compared by comparing two platings out of the total number of plating times, and then 400- Welding, corrosion resistance, appearance, characterized by having a spherical Sn plating layer with an area coverage of 80% and less than 98% formed by performing 2500 mg / m ² tin plating A method for producing a steel sheet for welding cans with excellent adhesion.
[0009]
( 3 ) In the plating method in which the Fe—Ni alloy plating is performed twice or more , the plating current density in the previous stage is 0.05 to 4 A / dm ² , and the welding according to (1) or (2), For producing steel plate for welding can excellent in heat resistance, corrosion resistance, appearance and adhesion.
( 4 ) The weldability, corrosion resistance, appearance, and appearance according to any one of (1) to ( 3) above, wherein a chromate coating layer of ² to 40 mg / m ^{2 in} terms of Cr is formed on the outermost layer. It exists in the manufacturing method of the steel plate for welding cans excellent in adhesiveness.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Below, the manufacturing method of the steel plate for welding cans which is the effect | action of this invention and was excellent in the weldability, corrosion resistance, external appearance property, a coating material, and film adhesiveness is demonstrated in detail.
In the present invention, the plating original plate is not particularly limited, and a steel plate used as a container material is usually used. There are no particular restrictions on the production method, material, and the like of the plating original plate, and the plate is manufactured through normal steel slab manufacturing processes such as hot rolling, acid tip, cold rolling, annealing, and tempering. Further, the plating original plate may be manufactured in a step of performing cold rolling (ie, 2CR method) after performing cold rolling and annealing after depending on the required strength of the can body and the plate thickness.
[0011]
When plating is performed on the above-described plating base plate, usually, degreasing and pickling are performed as pretreatment to clean the plating base plate surface, but these methods are not particularly restricted, for example, in 10% caustic soda After degreasing, the pickling may be performed in a 5% sulfuric acid solution. Subsequent to degreasing and pickling, Fe—Ni alloy plating is performed. The purpose of providing the Fe—Ni alloy plating layer is to secure both characteristics of corrosion resistance and weldability.
[0012]
Since Ni is a highly corrosion-resistant metal, the corrosion resistance of the plating layer can be improved by plating Ni. The effect of improving the corrosion resistance of the plating layer by Ni is manifested from a Ni plating amount of 2 mg / m ² or more per side. Therefore, the Ni plating amount needs to be ² mg / m ² or more. The effect of improving the corrosion resistance of the plating layer increases as the Ni plating amount increases, but since Ni is a metal that is extremely easy to alloy with Sn, alloying with the upper Sn layer proceeds in the can manufacturing process as the Ni plating amount increases. However, Sn which is not alloyed necessary for industrially efficient welding is not sufficiently secured. Therefore, the Ni plating amount needs to be 200 mg / m ² or less.
[0013]
Moreover, in order to ensure both the corrosion resistance and the weldability, the Ni content in the Fe—Ni alloy plating layer is defined as follows. If the Ni content is too low, the surface concentration of Ni becomes low and it is difficult to prevent corrosion that proceeds from the surface. Therefore, the Ni content in the Fe—Ni alloy plating layer needs to be 5% or more. If the Ni content exceeds 55%, the surface concentration of Ni becomes too high, and alloying with Sn tends to proceed, and the Ni content in the Fe—Ni alloy plating layer needs to be 55% or less. is there.
[0014]
Therefore, practically, the Ni plating amount in the Fe—Ni alloy plating necessary for ensuring corrosion resistance and weldability is 50 to 200 mg / m ² per one side of the steel sheet, and the Ni content in the Fe—Ni plating layer is 5 Need to be ~ 55%.
The Fe-Ni alloy plating bath used for performing the above-described Fe-Ni alloy plating is a plating bath that produces a commonly known abnormal eutectoid Fe-Ni alloy plating of sulfuric acid type or sulfuric acid-hydrochloric acid type. Use it. However, as described above, in order to form spherical Sn plating industrially efficiently at the time of molten tin, it is necessary to set the Fe-Ni plating conditions as follows.
[0015]
The current density when performing Fe—Ni alloy plating needs to be 0.05 A / dm ² or more per side. This is because when the current density of the Fe—Ni alloy plating is less than 0.05 A / dm ² , abnormal eutectoid type electrodeposition is not performed and iron hydroxide does not adhere, so that Sn is not elastic during the molten tin treatment. However, as a result, necessary adhesion cannot be secured. Therefore, the current density of the Fe—Ni alloy plating needs to be 0.05 A / dm ² or more. On the other hand, as the current density of Fe—Ni alloy plating increases, the amount of iron hydroxide adhesion increases, but the uniform adhesion of iron hydroxide is impaired, so the plating current density must be 40 A / dm ² or less. There is.
[0016]
However, from an industrial and economic point of view, when the current density of Fe—Ni alloy plating is low, a sufficient amount of iron hydroxide necessary for a predetermined Ni plating amount or Sn spheroidization cannot be secured. -Ni alloy plating treatment is required, and when the current density of Fe-Ni alloy plating is high, sufficient coated iron hydroxide necessary for Sn spheroidization cannot be secured. An alloy plating process is required. In such a case, in a continuous strip line that requires high-speed processing, it is necessary to perform Fe-Ni alloy plating twice, three times, or four times or more. If Fe—Ni alloy plating is performed, followed by high current density Fe—Ni alloy plating, the Fe—Ni alloy plating can be performed efficiently.
[0017]
In order to effectively obtain the effect of this method, the current density of the Fe—Ni alloy plating performed first must be 0.05 to 4 A / dm ² . If the current density is less than 0.05 A / dm ² , abnormal eutectoid type electrodeposition is not performed and iron hydroxide does not adhere, so the current density of the first Fe—Ni alloy plating is 0.05 A. / Dm ² or more is necessary. Since the purpose of this low current density Fe—Ni alloy plating is to uniformly disperse fine iron hydroxide nuclei, the plating current density needs to be 4 A / dm ² or less.
[0018]
When Fe-Ni alloy plating is performed twice or more, at least one low current density Fe-Ni alloy plating and one or more high current density Fe-Ni alloy platings are performed at least once. -Ni alloy plating may be performed under the condition that it is performed before high current density Fe-Ni alloy plating, and the number of each is not related to the essence of the present invention. After the Fe—Ni alloy plating, Sn plating is performed. Sn plating mentioned here consists of metal Sn and inevitable impurities. As described above, Sn plating is performed to ensure weldability. However, in order to perform welding efficiently industrially, the Sn plating amount needs to be 400 mg / m ² or more. When the amount of Sn plating increases, the effect of improving weldability increases. However, when the amount of plating exceeds 2500 mg / m ² , the effect of improving weldability is saturated, so economically it may be 2500 mg / m ² or less. The Sn plating method is not particularly restricted, and can be performed, for example, by ordinary electroplating.
[0019]
After Sn plating, molten tin treatment is performed. In the molten tin treatment, it is only necessary to perform a heat treatment exceeding the melting point of Sn. For example, methods such as energization heating, induction heating, and furnace heating may be used. Due to the molten tin treatment, the plated Sn is spheroidized and a plating layer structure with excellent adhesion is formed due to the above-described effect of the Fe—Ni alloy plating having hydroxide on the upper layer formed by abnormal precipitation. The At this time, the Sn area occupation ratio needs to be 40 to 98%. This is because when the area occupancy is less than 40%, the area ratio of Sn having an excellent appearance is too small, and the appearance is deteriorated. Accordingly, the area occupation ratio of Sn needs to be 40% or more.
[0020]
Further, in order to exhibit a more excellent appearance, it is only necessary to increase the area coverage of Sn, which is excellent in appearance, and for this purpose, the area occupancy of Sn should preferably exceed 80%. On the other hand, the appearance of the steel sheet improves as the Sn area occupancy increases. However, if the area occupancy exceeds 98%, the adhesion of the film deteriorates, so the Sn area occupancy is 98% or less. There is a need. Subsequently, after the molten tin treatment, a chromate film is applied for the purpose of film adhesion and corrosion resistance (prevention of undercutting corrosion). The chromate film referred to here is a single film of hydrated chromium oxide, that is, the original chromate film and another one of two films: a metal chromium layer on the lower layer and a hydrated chromium oxide layer on the upper layer. Pointing. The hydrated chromium oxide layer may contain sulfate ions or fluorine ions which are plating aids described later. Film adhesion and corrosion resistance are ensured by a strong chemical bond between the functional group of the hydrated chromium oxide and the functional group of the laminated film.
[0021]
However, since the hydrated chromium oxide film is an electrical insulator, the electrical resistance is very high, and the metallic chromium has a high melting point and high electrical resistance, both of which are negative factors that degrade the weldability. Therefore, it is very important to have good film adhesion, corrosion resistance, and an appropriate amount of chromate film that does not practically degrade weldability. Therefore, 2-40 mg / m ² per side is selected as the amount of chromate film adhesion in terms of metallic chromium. In other words, if the chromate film adhesion amount is less than 2 mg / m ² , the effect of improving the film adhesion and preventing the under-catching corrosion cannot be obtained, so an adhesion amount of ² mg / m ² or more is desirable. On the other hand, if the amount of chromate film deposited exceeds 40 mg / m ² , the contact resistance is remarkably increased, and scattering due to local heat generation is likely to occur, resulting in poor weldability. Therefore, the amount of chromate film adhesion is regulated to 40 mg / m ² or less.
[0022]
The chromate treatment method may be performed by any method such as immersion treatment with various sodium salts, potassium salts, and ammonium salts of chromic acid, spray treatment, electrolytic treatment, etc., but cathodic electrolytic treatment is particularly excellent. In particular, cathodic electrolysis in an aqueous solution in which sulfate ions, fluoride ions (including complex ions) or a mixture thereof is added as a plating aid to chromic acid is most excellent.
[0023]
【Example】
Examples of the present invention and comparative examples are described below, and the results are shown in Table 1, respectively. Cold-rolled or twice-rolled after annealing, the plating plate adjusted to the specified plate thickness is electrolytically degreased in 5% caustic soda, then washed with water, electrolytically pickled in 10% sulfuric acid, and surface treatment is performed after surface activation. It was. On this plating plate,
After performing Fe—Ni alloy plating under the conditions shown in (1), tin plating is performed under the conditions shown in (2), and subsequently heat treatment is performed under the conditions shown in (3)-(A) to (B). Then, what produced the chromate film | membrane with the processing bath shown to (4)-(A)-(C) was produced.
[0024]
(1) Fe—Ni alloy plating conditions 35 ° C. plating bath having Ni ions: 25 g / l, Fe ions: 50 g / l, sulfate ions: 15 g / l, chlorine ions: 10 g / l, boric acid: 20 g / l A test piece is immersed therein and electrolyzed at 0.05 to 40 A / dm ² to form a Fe—Ni alloy plating layer. The electrolysis time and the number of times of plating are appropriately adjusted according to the amount of plating.
(2) Tin plating conditions The test piece prepared in (1) was immersed in a 40 ° C. plating bath having tin ion: 15 g / l, phenol sulfonate ion: 15 g / l, and gloss additive: 1.2 g / l. Then, tin plating is performed by electrolysis at 8 A / dm ² . The electrolysis time is adjusted according to the amount of plating.
[0025]
(3) Heat treatment conditions (A) Heating furnace method The tin-plated steel sheet prepared in (2) is placed in a heating furnace at 400 ° C. for 5 to 30 seconds, the tin is melted and taken out, and immediately cooled.
(B) An alternating current is applied to the tin-plated steel sheet produced by the electric heating method (2), heat is generated by the electric resistance of the steel sheet, the tin is melted, and immediately cooled.
(C) The tin-plated steel sheet produced by the induction heating method (2) is heated by induction heating to melt tin, and immediately cooled.
[0026]
(4) Chromate treatment conditions The test piece prepared in (3) is immersed in a bath having a plating composition or less and electrolyzed. The electrolysis time is adjusted according to the amount of plating.
(A) Chromium oxide 100 g / l, sulfate ion 0.6 g / l
Plating conditions 20-60 ° C., 5-80 A / dm ²
(B) Sodium dichromate 15-45 g / l
Plating conditions 30-50 ° C., 10-40 A / dm ²
(C) Chromic acid 80 g / l, sulfate ion 0.05 g / l, sodium silicofluoride 2.5 g / l, ammonium fluoride 0.5 g / l,
Plating conditions 15-75 ° C., 10-85 A / dm ²
[0027]
About the said processing material, it implemented about each item of (A)-(E) shown below, and evaluated the performance.
(A) The seam weldability test piece was baked under the condition that the temperature was raised to 320 ° C. in 23 seconds assuming the coating baking condition in a short time at high temperature, and the seam weldability was evaluated under the following welding conditions. Welding is performed by changing the current under the conditions of a lapping margin of 0.5 mm, a pressing force of 45 kgf, and a welding wire speed of 80 m / min. Judging comprehensively from the width of the appropriate current range consisting of current values, evaluation was made in four stages (◎: very wide, ○: wide, Δ: no practical problem, ×: narrow).
[0028]
(B) an epoxy-phenolic paint 55 mg / dm ² was applied to a surface corresponding to the can inner surface side of the paint adhesion test piece, further a clear lacquer 40 mg / dm ² was applied to a surface corresponding to the can outer surface, to 290 ° C. It was dried and cured under baking conditions of 15 sec. Subsequently, scratches were placed on each surface at intervals of 1 mm, and approximately 100 grids were prepared. The tape was peeled off quickly, and the peeling situation was observed. Four steps (◎: no peeling, ○: very slight) Paint adhesion was evaluated by peeling, Δ: slight peeling, ×: peeling in most cases.
[0029]
(C) Film adhesion evaluation test After laminating a 15 μm thick PET (polyethylene terephthalate) film on a test piece, a crosscut is made until it reaches the ground iron, and it is quickly heated to 240 ° C. in the center of the crosscut. blowing air gas 5 kg / cm ² perpendicularly, four steps (◎: completely no peeling, ○: There negligible peeling, △: slight peeling, ×: most with release) the release status of the film evaluated.
[0030]
(D) UCC (Under Cutting Corrosion) Evaluation In order to evaluate the corrosion resistance of the surface corresponding to the inner surface of the can of the test specimen, a PET (polyethylene terephthalate) film having a thickness of 15 μm was laminated on the surface corresponding to the inner surface of the can. Then, the crosscut was put in until it reached the ground iron, and it was immersed in the test liquid which consists of a 1.5% citric acid-1.5% sodium chloride mixed solution at 55 degreeC x 4 days in open air. After the test is completed, the scratch part and the flat part are peeled off immediately with tape, and the corrosion situation near the scratch part, the pitting situation of the scratch part and the film peeling situation of the flat part are classified into four levels (◎: no peeling and corrosion is recognized) No, ○: There is very little peeling but no corrosion is observed, △: There is slight peeling and minute corrosion is observed, ×: Most parts are peeled and severe corrosion is recognized) Evaluated.
[0031]
(E) Appearance evaluation test A white-printed PET (polyethylene terephthalate) film with a thickness of 15 μm is laminated on the surface corresponding to the outer surface side of the test can, and the brightness of the color tone is 4 levels (◎: very bright, ○: Slightly bright, Δ: bright, ×: dark).
As shown in Table 1, it was revealed that the steel sheet for welding cans produced according to the present invention has excellent weldability, appearance, paint adhesion, film adhesion, and corrosion resistance.
[0032]
[Table 1]

[0033]
【The invention's effect】
As described above, according to the present invention, as a can-making material, it is possible to economically produce a steel sheet for a welding can that is particularly excellent in seam weldability, corrosion resistance, appearance, paint and film adhesion. It is effective.

Claims

The Fe-Ni alloy plating of Ni plating amount on the surface of 2 to 200 mg / m ^2, Ni content of 5 to 55% of the steel sheet, and achieved by performing two or more times at a current density of 0.05~40A / dm ² In this case, at least one combination in which the plating current density in the previous stage is lower than the plating current density in the subsequent stage by comparing two platings out of the total number of plating times, and then 400 to 2500 mg / m ² Welding can excellent in weldability, corrosion resistance, appearance and adhesion, characterized by having a spherical Sn plating layer with an area coverage of 40-98% formed by molten tin treatment after tin plating Steel plate manufacturing method.

Achieve Fe-Ni alloy plating of 2 to 200 mg / m ^2, Ni content 5-55%, in line Ukoto more than once at a current density of 0.05~40A / dm ² of Ni coating weight on the surface of the steel sheet In this case, at least one combination in which the plating current density in the previous stage is lower than the plating current density in the subsequent stage by comparing two platings out of the total number of plating times, and then 400 to 2500 mg / performed m ² tin plating, weldability, characterized in that it has to have a spherical Sn plating layer 98% or less than 80% area coverage formed by melt溶錫treatment, corrosion resistance, appearance and adhesiveness The manufacturing method of the steel plate for welding cans excellent in.

In the plating method of performing Fe-Ni alloy plating more than once, weldability according to claim 1 or 2, wherein the plating current density of the pre-stage is characterized by a 0.05~4A / dm ^2, corrosion resistance, appearance and A method for producing a steel sheet for welding cans with excellent adhesion.

The weld having excellent weldability, corrosion resistance, appearance, and adhesion according to any one of claims 1 to 3, wherein a chromate coating layer of ² to 40 mg / m ^{2 in} terms of Cr is formed on the outermost layer. Manufacturing method of steel plate for cans.