JP4002534B2

JP4002534B2 - High corrosion-resistant coated steel sheet with excellent paint film adhesion and sharpness and low environmental impact

Info

Publication number: JP4002534B2
Application number: JP2003121688A
Authority: JP
Inventors: 和彦本田; 英利畑中
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2003-02-03
Filing date: 2003-04-25
Publication date: 2007-11-07
Anticipated expiration: 2023-04-25
Also published as: JP2004292943A

Description

【０００１】
【発明の属する技術分野】
本発明は、塗装鋼板に係わり、更に詳しくは環境負荷の大きいとされるクロムを含まずに優れた塗膜密着性と耐食性を有し、種々の用途、例えば家電用や建材用鋼板として適用できる塗装鋼板に関するものである。
【０００２】
【従来の技術】
塗装金属板は、金属板を先に成形加工して複雑な形状物とした後に塗装を加える方式に比べ、塗装工程が合理化できる、品質が均一になる、塗料の消費量が節約される等の利点があることから、これまで多く使用されており、今後とも使用量は増加すると考えられる。
【０００３】
一般に塗装金属板は、冷延鋼板、亜鉛めっき系鋼板、その他の金属板に予め塗装をした後、任意の形状に成形加工して最終の用途に供するものであり、例えば、冷蔵庫、洗濯機、電子レンジなどの家電製品、自動販売機、事務機器、自動車、エアコン室外機などの金属製品に用いられている。
【０００４】
こうした塗装鋼板の耐食性を向上させることを目的として本発明者らは、塗装溶融Ｚｎ−Ａｌ−Ｍｇ−Ｓｉめっき鋼板を提案した（特許文献１）。また、本発明者らは、この溶融Ｚｎ−Ａｌ−Ｍｇ−Ｓｉめっき鋼板にＣａ、Ｂｅ、Ｔｉ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｒ、Ｍｎの１種又は２種以上を添加することにより、更に耐食性が優れた塗装鋼板が得られることを明らかにした（特許文献２）。
【０００５】
これらはいずれも、耐食性に優れるめっき鋼板の上にクロメート処理と呼ばれる耐食性と密着性に優れる下地処理を施し、その上に耐食性に優れるクロム系防錆顔料を含む下塗り層を有し、更にその上に着色された上塗り層を有する構造をとっている。
【０００６】
こうしたクロメート処理及びクロム系防錆顔料から溶出する可能性のある６価のクロムは環境負荷が大きな物質であるため、本発明者らは、環境負荷の小さい塗装溶融Ｚｎ−Ａｌ−Ｍｇ−Ｓｉめっき鋼板を提案した（特許文献３及び４）。
【０００７】
また、溶融Ｚｎ−Ａｌ−Ｍｇめっき鋼板にＴｉ、Ｂ、Ｓｉを添加することにより表面外観が良好になることが開示されている（例えば、特許文献５）。
【０００８】
【特許文献１】
特許第３１７９４４６号公報
【特許文献２】
特開２０００−６４０６１号公報
【特許文献３】
特許第３０９０２０７号公報
【特許文献４】
特許第３１２４２６６号公報
【特許文献５】
特開２００１−２９５０１５号公報
【０００９】
【発明が解決しようとする課題】
Ｚｎ−Ｍｇ−Ａｌの三元系合金は３質量％Ｍｇ−４質量％Ａｌ−９３質量％Ｚｎに三元共晶点を持ち、それよりＡｌ濃度が高い場合、初晶としてＡｌ相が晶出する。
【００１０】
溶融めっき時のめっき凝固速度が十分に確保されている場合、Ａｌ相が大きく成長しないうちにめっきが凝固するため表面平滑性は問題とならないが、めっき凝固速度が小さい場合、このＡｌ相が先に大きく成長することによってめっき表面に凸凹が形成され、表面平滑性が劣化するという問題点を有している。
【００１１】
このため、このような表面平滑性が低い鋼板で塗装鋼板を製造した場合、０．２〜１００μｍ程度の厚さの比較的薄い塗膜ではめっき表面の凸凹を完全には隠蔽できず、塗装鋼板の鮮映性が劣化するという問題点を有している。
【００１２】
しかし、前記特許特許文献１〜４に開示される技術では、塗装鋼板の鮮映性が劣化するという問題は考慮されていない。
【００１３】
また、前記特許文献５に開示される技術では、表面外観を劣化させるＺｎ₁₁Ｍｇ₂相の生成・成長を抑制する目的としてＴｉとＢを添加しているが、表面平滑性や塗装後の鮮映性が劣化するという問題は考慮されておらず、金属間化合物についても言及されていない。
【００１４】
そこで、本発明は、上記問題点に鑑みなされたものであり、４質量％を超えるような高Ａｌ濃度の場合でも十分鮮映性が優れ、環境負荷の小さい高耐食性塗装鋼板を提供することを目的としている。
【００１５】
【課題を解決するための手段】
本発明者らは、鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板の開発について鋭意研究を重ねた結果、鋼板の表面に添加元素の添加量を最適化した亜鉛系めっきを形成した後、下地処理としてクロメート処理の代わりにタンニン又はタンニン酸系処理を施し、その上にクロム系防錆顔料の代わりにクロムフリー防錆顔料を有する塗膜を施すことで、塗装密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板を得られることを知見した。
【００１６】
即ち、本発明は上記知見に基いて完成したもので、本発明の要旨は以下のとおりである。
【００１７】
（１）鋼板の片面又は両面に、Ａｌ：４〜１０質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、その上に固形分として水性樹脂１００質量部、タンニン又はタンニン酸０．２〜５０質量部を含有する皮膜層を下地処理層として有し、上層として０．２〜１００μｍ厚の有機被膜層を有することを特徴とする鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００１８】
（２）鋼板の片面又は両面に、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、その上に固形分として水性樹脂１００質量部、タンニン又はタンニン酸０．２〜５０質量部を含有する皮膜層を下地処理層として有し、上層として０．２〜１００μｍ厚の有機被膜層を有することを特徴とする塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００１９】
（３）鋼板の片面又は両面に、Ａｌ：４〜１０質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、その上に固形分として水性樹脂１００質量部、タンニン又はタンニン酸０．２〜５０質量部を含有する皮膜層を下地処理層として有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ₂Ｍｇの三元共晶組織〕の素地中に〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕及び〔Ｚｎ相〕の１種又は２種以上が混在した金属組織を有し、且つ、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕及び〔Ｚｎ相〕の１種又は２種以上の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００２０】
（４）鋼板の片面又は両面に、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、その上に固形分として水性樹脂１００質量部、タンニン又はタンニン酸０．２〜５０質量部を含有する皮膜層を下地処理層として有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ₂Ｍｇの三元共晶組織〕の素地中に〔Ｍｇ₂Ｓｉ相〕、〔Ａｌ相〕及び〔Ｚｎ₂Ｍｇ相〕が混在した金属組織を有し、且つ、〔Ａｌ相〕と〔Ｚｎ₂Ｍｇ相〕の１種又は２種の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２１】
（５）鋼板の片面又は両面に、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、その上に固形分として水性樹脂１００質量部、タンニン又はタンニン酸０．２〜５０質量部を含有する皮膜層を下地処理層として有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ₂Ｍｇの三元共晶組織〕の素地中に〔Ｍｇ₂Ｓｉ相〕、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕及び〔Ｚｎ相〕が混在した金属組織を有し、且つ、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕及び〔Ｚｎ相〕の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２２】
（６）鋼板の片面又は両面に、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、その上に固形分として水性樹脂１００質量部、タンニン又はタンニン酸０．２〜５０質量部を含有する皮膜層を下地処理層として有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ₂Ｍｇの三元共晶組織〕の素地中に〔Ｍｇ₂Ｓｉ相〕、〔Ａｌ相〕及び〔Ｚｎ相〕が混在した金属組織を有し、且つ、〔Ａｌ相〕と〔Ｚｎ相〕の１種又は２種の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２３】
（７）前記（３）乃至（６）のいずれかに記載のＴｉ−Ａｌ系金属間化合物が、ＴｉＡｌ₃であることを特徴とする塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２４】
（８）前記（３）乃至（６）のいずれかに記載のＴｉ−Ａｌ系金属間化合物が、Ｔｉ（Ａｌ_1-XＳｉ_X）₃（但し、Ｘ＝０〜０．５である）であることを特徴とする塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２５】
（９）めっき層中の〔Ａｌ相〕の中に含有されるＴｉ−Ａｌ系金属間化合物が、Ｚｎ−Ａｌの共析反応によって析出したＺｎ相中に存在することを特徴とする前記（３）乃至（８）のいずれかに記載の塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２６】
（１０）めっき層中の〔Ａｌ相〕の樹枝状晶の大きさが５００μｍ以下であることを特徴とする前記（１）乃至（９）のいずれかに記載の塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２７】
（１１）下地処理層の皮膜層に固形分として、微粒シリカ１０〜５００質量部を更に含有することを特徴とする、前記（１）乃至（１０）のいずれかに記載の塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２８】
（１２）有機被膜が、熱硬化型の樹脂塗膜であることを特徴とする前記（１）乃至（１１）のいずれかに記載の塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００２９】
（１３）有機皮膜層が防錆顔料を含む下塗り層と着色された上塗り層からなる前記（１）乃至（１２）のいずれかに記載の塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００３０】
（１４）防錆顔料がケイ酸イオン、リン酸イオン、バナジン酸イオン、モリブデン酸イオンのうち一種類以上を放出するものであることを特徴とする前記（１３）に記載の塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００３１】
（１５）下地処理層の乾燥後の付着量が１０〜３０００ｍｇ／ｍ²であることを特徴とする前記（１）乃至（１４）のいずれかに記載の塗膜密着性と鮮映性に優れ環境負荷の小さい高耐食性塗装鋼板。
【００３２】
【発明の実施形態】
以下に本発明を詳細に説明する。
【００３３】
本発明において、塗装鋼板とは、鋼板上に亜鉛系めっき層とタンニン又はタンニン酸系処理、及び有機皮膜からなる層を順次付与したものである。本発明の下地鋼板としては、熱延鋼板、冷延鋼板共に使用でき、鋼種もＡｌキルド鋼、Ｔｉ、Ｎｂ等を添加した極低炭素鋼板、及び、これらにＰ、Ｓｉ、Ｍｎ等の強化元素を添加した高強度鋼、ステンレス鋼等種々のものが適用できる。
【００３４】
下層の亜鉛系めっき層は、Ａｌ：４〜１０質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、残部がＺｎ及び不可避不純物からなるめっき層か、或いは、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下、残部がＺｎ及び不可避不純物からなるめっき層である。
【００３５】
Ｚｎ−Ａｌ−Ｍｇ−Ｔｉ系めっき層においてＡｌの含有量を４〜１０質量％に限定した理由は、Ａｌの含有量が１０質量％を超えるとめっき密着性の低下が見られるため、Ｓｉを添加していないめっき層中のＡｌの含有量は１０質量％以下にする必要があるためである。また、４質量％未満では初晶としてＡｌ相が晶出しないため、平滑性低下の問題がないためである。
【００３６】
従って、本発明における高耐食性塗装鋼板においては、特にＡｌ濃度が１０質量％を超えるような高濃度の場合には、めっき密着性を確保するために、めっき層中にＳｉを添加することが必須である。
【００３７】
一方、Ｚｎ−Ａｌ−Ｍｇ−Ｔｉ−Ｓｉ系めっき層において、Ａｌの含有量を４〜２２質量％に限定した理由は、４質量％未満では初晶としてＡｌ相が晶出しないため、平滑性低下の問題がないためであり、２２質量％を超えると耐食性を向上させる効果が飽和するためである。
【００３８】
Ｓｉの含有量を０．５質量％以下（但し、０質量％を除く）に限定した理由は、Ｓｉは密着性を向上させる効果があるが、０．５質量％を超えると密着性を向上させる効果が飽和するからである。望ましくは０．００００１〜０．５質量％である、更に望ましくは０．０００１〜０．５質量％である。
【００３９】
Ｓｉの添加はＡｌの含有量が１０質量％を超えるめっき層には必須であるが、Ａｌの含有量が１０％以下のめっき層においてもめっき密着性向上に効果が大きいため、加工が厳しい部材に使用する等、高いめっき密着性を必要とする場合にはＳｉを添加することが有効である。また、Ｓｉ添加によりめっき層の凝固組織中に〔Ｍｇ₂Ｓｉ相〕が晶出する。この〔Ｍｇ₂Ｓｉ相〕は加工部耐食性向上に効果があるため、Ｓｉの添加量を多くし、めっき層の凝固組織中に〔Ｍｇ₂Ｓｉ相〕が混在した金属組織を作製することがより望ましい。
【００４０】
Ｍｇの含有量を１〜５質量％に限定した理由は、１質量％未満では耐食性を向上させる効果が不十分であるためであり、５質量％を超えるとめっき層が脆くなって密着性が低下するためである。Ｔｉの含有量を０．１質量％以下（０質量％は除く）に限定した理由は、ＴｉはＴｉ−Ａｌ系金属間化合物を晶出させ、鮮映性を向上させる効果があるが、０．１質量％を超えるとめっき後の外観が粗雑になり、外観不良が発生する。また、Ｔｉ−Ａｌ系金属間化合物がめっき表面に濃化し表面平滑性を低下させる。望ましくは０．００００１〜０．１質量％である。更に望ましくは０．００００１〜０．０１質量％未満である。
【００４１】
本めっき層は、〔Ａｌ／Ｚｎ／Ｚｎ₂Ｍｇの三元共晶組織〕の素地中に〔Ｚｎ相〕、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｍｇ₂Ｓｉ相〕、Ｔｉ−Ａｌ系金属間化合物の１つ以上を含む金属組織ができる。
【００４２】
ここで、〔Ａｌ／Ｚｎ／Ｚｎ₂Ｍｇの三元共晶組織〕とは、Ａｌ相と、Ｚｎ相と金属間化合物Ｚｎ₂Ｍｇ相との三元共晶組織であり、この三元共晶組織を形成しているＡｌ相は例えばＡｌ−Ｚｎ−Ｍｇの三元系平衡状態図における高温での「Ａｌ″相」（Ｚｎ相を固溶するＡｌ固溶体であり、少量のＭｇを含む）に相当するものである。この高温でのＡｌ″相は常温では通常は微細なＡｌ相と微細なＺｎ相に分離して現れる。また、該三元共晶組織中のＺｎ相は少量のＡｌを固溶し、場合によっては更に少量のＭｇを固溶したＺｎ固溶体である。該三元共晶組織中のＺｎ₂Ｍｇ相は、Ｚｎ−Ｍｇの二元系平衡状態図のＺｎ：約８４質量％の付近に存在する金属間化合物相である。状態図で見る限りそれぞれの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられるがその量は通常の分析では明確に区別できないため、この３つの相からなる三元共晶組織を本明細書では〔Ａｌ／Ｚｎ／Ｚｎ₂Ｍｇの三元共晶組織〕と表す。
【００４３】
また、〔Ａｌ相〕とは、前記の三元共晶組織の素地中に明瞭な境界をもって島状に見える相であり、これは例えばＡｌ−Ｚｎ−Ｍｇの三元系平衡状態図における高温での「Ａｌ″相」（Ｚｎ相を固溶するＡｌ固溶体であり，少量のＭｇを含む）に相当するものである。この高温でのＡｌ″相はめっき浴のＡｌやＭｇ濃度に応じて固溶するＺｎ量やＭｇ量が相違する。この高温でのＡｌ″相は常温では通常は微細なＡｌ相と微細なＺｎ相に分離するが、常温で見られる島状の形状は高温でのＡｌ゛相の形骸を留めたものであると見てよい。状態図で見る限りこの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられるが通常の分析では明確に区別できないため、この高温でのＡｌ″相に由来し、且つ、形状的にはＡｌ″相の形骸を留めている相を本明細書では〔Ａｌ相〕と呼ぶ。この〔Ａｌ相〕は前記の三元共晶組織を形成しているＡｌ相とは顕微鏡観察において明瞭に区別できる。
【００４４】
また、〔Ｚｎ相〕とは、前記の三元共晶組織の素地中に明瞭な境界をもって島状に見える相であり、実際には少量のＡｌさらには少量のＭｇを固溶していることもある。状態図で見る限りこの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられる。この〔Ｚｎ相〕は前記の三元共晶組織を形成しているＺｎ相とは顕微鏡観察において明瞭に区別できる。
【００４５】
また、〔Ｚｎ₂Ｍｇ相〕とは、前記の三元共晶組織の素地中に明瞭な境界をもって島状に見える相であり、実際には少量のＡｌを固溶していることもある。状態図で見る限りこの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられる。この〔Ｚｎ₂Ｍｇ相〕は前記の三元共晶組織を形成しているＺｎ₂Ｍｇ相とは顕微鏡観察において明瞭に区別できる。
【００４６】
また、〔Ｍｇ₂Ｓｉ相〕とは、めっき層の凝固組織中に明瞭な境界をもって島状に見える相である。状態図で見る限りＺｎ、Ａｌ、Ｔｉは固溶していないか、固溶していても極微量であると考えられる。この〔Ｍｇ₂Ｓｉ相〕はめっき中では顕微鏡観察において明瞭に区別できる。
【００４７】
また、Ｔｉ−Ａｌ系金属間化合物とは、めっき層の凝固組織中に明瞭な境界をもって島状に見える相である。状態図で見る限りＴｉＡｌ₃であると考えられるが、分析するとＳｉが観察されることから、Ｓｉを固溶したＴｉＡｌ₃又はＡｌの一部がＳｉに置き換わったＴｉ（Ａｌ_1-XＳｉ_X）₃（但し、Ｘ＝０〜０．５である）であると考えられる。
【００４８】
本発明の溶融めっき鋼材において、このＴｉ−Ａｌ系金属間化合物は、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｚｎ相〕の中に存在することを特徴とする。Ｔｉ−Ａｌ系金属間化合物の含有形態を〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｚｎ相〕の中に限定した理由は、それ以外の位置に存在するＴｉ−Ａｌ系金属間化合物では、鮮映性を向上させることができないためである。〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｚｎ相〕の中に存在するＴｉ−Ａｌ系金属間化合物が鮮映性を向上させる理由は、Ｔｉ−Ａｌ系金属間化合物が、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｚｎ相〕の核となることでこれらの結晶の晶出を促進させ、微細で多数の組織とするためであると考えられる。即ち、結晶が微細になるとめっき層表面の凹凸が抑制され、めっき表面が平滑になり、比較的薄い塗膜でもめっき表面の凸凹を隠蔽できるようになり、塗装鋼板の鮮映性が向上すると考えられる。
【００４９】
この効果は、特に〔Ａｌ相〕において顕著である。〔Ａｌ相〕の樹枝状晶の大きさを５００μｍ以下に制御することにより、表面が平滑になり、摩擦係数が低下する。望ましくは４００μｍ以下である。更に望ましくは３００μｍ以下である。
【００５０】
本発明者等が多数のめっき中の金属組織を調査した結果、大部分の金属組織の中から大きさ数μｍの金属間化合物が観察された。〔Ａｌ相〕中に存在する金属間化合物の一例を図１に示す。図１の上段の図（ａ）は、本発明におけるめっき鋼材のめっき層の顕微鏡写真（倍率１０００倍）であり、該写真中の各組織の分布状態を図示したものが下段の図（ｂ）である。この図からも判るように、本発明におけるめっき鋼材のめっき層の顕微鏡写真によって明確に各組織を特定することができる。
【００５１】
図１ではＡｌ−Ｚｎ−Ｍｇの三元系平衡状態図における高温での「Ａｌ″相」に相当するものの中にＴｉ−Ａｌ系金属間化合物が観察される。この高温でのＡｌ″相は、Ａｌ−Ｚｎの二元系平衡状態図における２７７℃で起こる共析反応により、常温では通常は微細なＡｌ相と微細なＺｎ相に分離して現れる。ここで亜共析反応の場合、高温で晶出したＡｌ″相は、Ａｌ−Ｚｎ−Ｍｇの三元系平衡状態図における三元共晶温度からＺｎ相の析出を開始し、Ａｌ−Ｚｎの二元系平衡状態図における共析反応に相当する温度で残ったＡｌ″相が微細なＡｌ相と微細なＺｎ相の共析組織となる。
【００５２】
図２の上段の図（ａ）は、図１（ａ）のＡｌ″相を拡大した顕微鏡写真（倍率３５００倍）であり、該写真中の各組織の分布状態を図示したものが下段の図（ｂ）である。Ａｌ″相を詳細に観察すると、析出したＺｎ相がＡｌ″相の外側とＴｉ−Ａｌ系金属間化合物の周りに存在することが観察される。
本発明において金属間化合物の大きさは特に限定しないが、発明者らが観察したものは、大きさ１０μｍ以下であった。また、めっき組織中の金属間化合物の存在割合も特に限定しないが、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｚｎ相〕のどれかに１割以上存在することが望ましい。
【００５３】
本発明において、めっき鋼板の製造方法については特に限定するところはなく、通常の無酸化炉方式の溶融めっき法が適用できる。
【００５４】
金属間化合物の添加方法については特に限定するところはなく、金属間化合物の微粉末を浴中に混濁させる方法や、金属間化合物を浴に溶解させる方法等が適用できるが、無酸化炉方式の溶融めっき法を使用した連続ライン等で製造する場合、めっき浴中にＴｉを溶解させる方法が適当である。めっき浴中にＴｉを溶解させる方法としては、Ｔｉ−Ｚｎ系金属間化合物を添加する方法が低温、短時間で溶解可能なため効率的である。添加するＴｉ−Ｚｎ系金属間化合物としては、Ｚｎ₁₅Ｔｉ、Ｚｎ₁₀Ｔｉ、Ｚｎ₅Ｔｉ、Ｚｎ₃Ｔｉ、Ｚｎ₂Ｔｉ、ＺｎＴｉ等がある。こうした金属間化合物を単独或いはＺｎ、Ｚｎ−Ａｌ、Ｚｎ−Ａｌ−Ｍｇ合金中に混合させてめっき浴に添加すると、溶解したＴｉがめっき中にＴｉ−Ａｌ系金属間化合物として晶出し、表面平滑性と成形性を向上させる。
【００５５】
めっきの付着量については特に制約は設けないが、耐食性の観点から１０ｇ／ｍ²以上、加工性の観点から３５０ｇ／ｍ²以下で有ることが望ましい。
【００５６】
亜鉛めっき層中には、これ以外にＦｅ、Ｓｂ、Ｐｂ、Ｓｎを単独或いは複合で０．５質量％以内含有してもよい。また、Ｃａ、Ｂｅ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｒ、Ｍｎ、Ｐ、Ｂ、Ｎｂ、Ｂｉや３族元素を合計で０．５質量％以下含有しても本発明の効果を損なわず、その量によっては更に耐食性が改善される等好ましい場合もある。
【００５７】
本発明の塗装鋼板に用いる下地処理層は、水性樹脂をベースとしてタンニン又はタンニン酸を含むことを特徴としている。この下地処理層とＺｎ−Ｍｇ−Ａｌ−Ｔｉ系合金めっき層、或いは、Ｚｎ−Ｍｇ−Ａｌ−Ｓｉ−Ｔｉ系合金めっき層を組み合わせることにより相乗的に塗装密着性と加工部の耐食性が向上する。
【００５８】
本下地処理層のタンニン又はタンニン酸の役割は、めっき層と強固に反応して密着することと、一方で水性樹脂とも密着することにある。タンニン又はタンニン酸と密着した水性樹脂はその上に塗装される樹脂と強固に密着し、その結果としてめっき鋼板と塗膜が従来から使用されてきたクロメート処理を使用せずとも強固に密着するようになったものと考えられる。また、タンニンやタンニン酸そのものが水性樹脂を仲立ちとせずにめっき鋼板と塗膜の結合に関与している部分も存在するものと考えられる。
【００５９】
下地処理層の水性樹脂としては、水溶性樹脂のほか、本来水不溶性でありながらエマルジョンやサスペンジョンのように水中に微分散された状態になりうる樹脂を含めて言う。このような水性樹脂として使用できるものは、例えば、ポリオレフィン系樹脂、アクリルオレフィン系樹脂、ポリウレタン系樹脂、ポリカーボネート系樹脂、エポキシ系樹脂、ポリエステル系樹脂、アルキド系樹脂、フェノール系樹脂、その他の熱硬化型樹脂が挙げられ、架橋可能な樹脂が望ましい。特に好ましい樹脂は、アクリルオレフィン系樹脂、ポリウレタン系樹脂、及び、両者の混合樹脂である。これらの水性樹脂の２種類以上を混合或いは重合して使用しても良い。
【００６０】
タンニンやタンニン酸は、水性樹脂の存在下で、Ｚｎ−Ｍｇ−Ａｌ−Ｔｉ系合金めっき、或いは、Ｚｎ−Ｍｇ−Ａｌ−Ｓｉ−Ｔｉ系合金めっきと塗膜の両者と強固に結合し、塗膜の密着性を飛躍的に向上させ、ひいては加工部の耐食性を向上させる。タンニン又はタンニン酸としては加水分解できるタンニンでも縮合タンニンでもよく、これらの一部が分解されたものでも良い。タンニン及びタンニン酸は、ハマメタタンニン、五倍子タンニン、没食子タンニン、ミロバロンのタンニン、ジビジビのタンニン、アルガロビラのタンニン、バロニアのタンニン、カテキンなど特に限定するものではなく、市販のもの、例えば「タンニン酸：ＡＬ」（富士化学工業製）などを使用することができる。
【００６１】
タンニン及びタンニン酸の含有量は樹脂１００質量部に対して、タンニン又はタンニン酸０．２〜５０質量部がよい。タンニン又はタンニン酸の含有量が０．２質量部未満ではこれらを添加した効果が見られず、塗膜密着性や加工部の耐食性が不十分である。一方、５０質量部を超えると逆に耐食性が低下したり、処理液を長期間貯蔵しておくとゲル化したりして問題がある。
【００６２】
更に微粒シリカを添加すると耐擦り傷性、塗膜密着性、耐食性が向上する。本発明において微粒シリカとは、微細な粒径をもつために水中に分散させた場合に安定に水分散状態を維持でき、半永久的に沈降が認められないような特色を有するシリカを総称していうものである。このような微粒シリカとしては、ナトリウムなどの不純物が少なく、弱アルカリ系のものであれば、特に限定されない。例えば、「スノーテックスＮ」（日産化学工業社製）、「アデライトＡＴ−２０Ｎ」（旭電化工業社製）などの市販のシリカなどを用いることができる。
【００６３】
微粒シリカの含有量は固形分換算で、水性樹脂１００質量部に対して１０〜５００質量部であることが好ましい。１０質量部未満では添加した効果が少なく、５００質量部を超えると耐食性向上の効果が飽和して不経済である。
【００６４】
また、必要に応じて界面活性剤、防錆抑制剤、発泡剤、顔料などを添加しても良い。更に密着性を向上させるために、エッチング性フッ化物を添加してもよい。エッチング性フッ化物としては、例えば、フッ化亜鉛四水和物、ヘキサフルオロケイ酸亜鉛六水和物などを使用することができる。同じく、密着性を向上させる目的でシランカップリング剤を添加しても良い。シランカップリング剤としては、例えば、γ−（２−アミノエチル）アミノプロピルトリメトキシシラン、γ−（２−アミノエチル）アミノプロピルメチルジメトキシシラン、アミノシラン、γ−メタクリロキシプロピルトリメトキシシラン、Ｎ−β−（Ｎ−ビニルベンジルアミノエチル）−γ−アミノプロピルトリメトキシシラン、γ−グリシドキシプロピルトリメトキシシラン、γ−メルカプトプロピルトリメトキシシラン、メチルトリメトキシシラン、ビニルトリメトキシシラン、オクタデシルジメチル〔３−（トリメトキシシリル）プロピル〕アンモニウムクロライド、γ−クロロプロピルメチルジメトキシシラン、γ−メルカプトプロピルメチルジメトキシシラン、メチルトリクロロシラン、ジメチルジクロロシラン、トリメチルクロロシランなどを挙げることができる。
【００６５】
下地処理層の塗布方法は特別限定するものではなく、一般に公知の塗装方法、例えば、ロールコート、エアースプレー、エアーレススプレー、浸漬などが適用できる。塗布後の乾燥・焼き付けは、樹脂の重合反応や硬化反応を考慮して、熱風炉、誘導加熱炉、近赤外線炉、等公知の方法或いはこれらを組み合わせた方法で行えばよい。また、使用する水性樹脂の種類によっては紫外線や電子線などによって硬化させることもできる。或いは強制乾燥を用いずに自然乾燥してもよいし、Ｚｎ−Ｍｇ−Ａｌ−Ｔｉ系合金めっき鋼板、或いは、Ｚｎ−Ｍｇ−Ａｌ−Ｓｉ−Ｔｉ系合金めっき鋼板を予め加熱しておいて、その上に塗布して自然乾燥してもよい。
【００６６】
下地処理層の乾燥後の付着量は１０〜３０００ｍｇ／ｍ²が好適である。１０ｍｇ／ｍ²未満では密着性が劣り加工部の耐食性が不十分である。一方、３０００ｍｇ／ｍ²を超えると不経済であるばかりか加工性も低下して耐食性も劣るようになる。
【００６７】
本発明の塗装鋼板は下地処理したＺｎ−Ｍｇ−Ａｌ−Ｔｉ系合金めっき鋼板、或いは、Ｚｎ−Ｍｇ−Ａｌ−Ｓｉ−Ｔｉ系合金めっき鋼板の上に有機被覆層を有することを特徴としている。有機被覆としてはポリオレフィン樹脂、アクリル樹脂、ウレタン樹脂、エポキシ樹脂、ポリエステル樹脂、塩化ビニル樹脂、フッ素系樹脂、ブチラール樹脂、ポリカーボネート樹脂、フェノール樹脂などである。これらの混合物や共重合物も使用できる。また、これらにイソシアネート樹脂、アミノ樹脂、シランカップリング剤或いはチタンカップリング剤等を補助成分として併用することができる。本発明によるプレコート鋼板は加工後に補修をされずにそのまま使用されるケースが多いので、厳しい加工が施される用途では、ポリエステル樹脂をメラミンで架橋する樹脂系、ポリエステル樹脂をウレタン樹脂（イソシアネート、イソシアネート樹脂）で架橋する樹脂系、塩化ビニル樹脂系、フッ素樹脂系（溶剤可溶型、アクリル樹脂との分散混合型）が望ましい。
【００６８】
次に塗装鋼板の上層の有機被膜としては、ポリエステル樹脂、アミノ樹脂、エポキシ樹脂、アクリル樹脂、ウレタン樹脂、フッ素樹脂等が例として挙げられ、特に限定されるものではないが、特に加工が厳しい製品に使用する場合、熱硬化型の樹脂塗膜が最も好ましい。熱硬化型の樹脂塗膜としては、エポキシポリエステル塗料、ポリエステル塗料、メラミンポリエステル塗料、ウレタンポリエステル塗料等のポリエステル系塗料や、アクリル塗料が挙げられる。
【００６９】
ポリエステル樹脂の酸成分の一部を脂肪酸に置き換えたアルキッド樹脂や、油で変性しないオイルフリーアルキッド樹脂に、メラミン樹脂やポリイソシアネート樹脂を硬化剤として併用したポリエステル系の塗料、及び各種架橋剤と組み合わせたアクリル塗料は、他の塗料に比べて加工性が良いため、厳しい加工の後にも塗膜に亀裂などが発生しないためである。
【００７０】
膜厚は、０．２〜１００μｍが適正である。膜厚を０．２μｍ以上とした理由は、膜厚が０．２μｍ未満では耐食性が確保できないためである。また、膜厚を１００μｍ以下とした理由は、膜厚が１００μｍを超えるとコスト面から不利になるためである。望ましくは、５０μｍ以下である。有機被膜層は、単層でも複層でもかまわない。
【００７１】
なお、本発明の方法に使用される有機被膜には、必要に応じて、可塑剤、酸化防止剤、熱安定剤、無機粒子、顔料、有機潤滑などの添加剤を配合させる。
【００７２】
有機被覆層は公知の方法で下地処理層の上に塗装される。例えば、ロールコーター、カーテンコーター、静電塗装、スプレー塗装、浸漬塗装などである。その後、熱風、誘導加熱、近赤外、遠赤外、などの加熱によって乾燥・硬化される。有機被覆層の樹脂が電子線や紫外線で硬化するものであれば、これらの照射によって硬化される。これらの併用であってもよい。
【００７３】
本発明の塗装鋼板で化成処理層と着色された有機層の間に、必要に応じて防錆顔料を添加した皮膜層を下塗り層として有することができる。この下塗り層は主に耐食性の向上を目的とするが、その他に成形加工性、耐薬品性なども考慮して設計される。下塗り層を構成する樹脂としては、一般に公知の樹脂、例えば、ポリエステル樹脂、ウレタン樹脂、アクリル樹脂、エポキシ樹脂、メラミン樹脂などをそのまま、或いは、組み合わせて使用できる。防錆顔料としては一般に公知のもの、例えば、（１）リン酸亜鉛、リン酸鉄、リン酸アルミニウム、亜リン酸亜鉛、等のリン酸系防錆顔料、（２）モリブデン酸カルシウム、モリブデン酸アルミニウム、モリブデン酸バリウム、等のモリブデン酸系防錆顔料、（３）酸化バナジウムなどのバナジウム系防錆顔料、（４）カルシウムシリケートなどのシリケート系顔料、（５）水分散シリカ、ヒュームドシリカ、等の微粒シリカなどを用いることができる。これらの防錆顔料は、それぞれリン酸イオン、モリブデン酸イオン、バナジン酸イオン、ケイ酸イオンを放出する。
【００７４】
防錆顔料の添加量は皮膜の固形分基準に１〜４０質量％がよい。１質量％より少ないと耐食性の改良が十分でなく、４０質量％を超えると加工性が低下して、加工時に有機被膜層の脱落が起こり、耐食性も劣るようになる。
【００７５】
防錆顔料を含む下塗り層の塗布は一般に公知の方法でできる。例えば、ロールコート、カーテンコート、エアースプレー、エアーレススプレー、浸漬、刷毛塗り、バーコートなどである。その後、熱風、誘導加熱、近赤外、遠赤外、などの加熱によって乾燥・硬化される。有機被覆層の樹脂が電子線や紫外線で硬化するものであればこれらの照射によって硬化される。これらの併用であってもよい。
【００７６】
【実施例】
以下、実施例により本発明を具体的に説明する。
【００７７】
（実施例１）
まず、厚さ０．８５ｍｍの冷延鋼板を準備し、これに４００〜６００℃で浴中の添加元素量を変化させためっき浴で３秒溶融めっきを行い、Ｎ₂ワイピングでめっき付着量を片面１４０ｇ／ｍ²に調整し、冷却速度１０℃／ｓ以下で冷却した。得られためっき鋼板のめっき組成を表１に示す。また、めっき鋼板を断面からＳＥＭで観察し、めっき層の金属組織を観察した結果を同じく表１に示す。Ｔｉ−Ａｌ系金属間化合物は、めっき鋼板を１０度傾斜で研磨した後、ＥＰＭＡで観察し、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｚｎ相〕の中に存在するものを観察した。
【００７８】
めっき層中の〔Ａｌ相〕の樹枝状晶の大きさは、めっき鋼板の表面をＣＭＡでマッピングし、得られたＡｌのマッピングを使用して樹脂状晶の長径を測定した。測定は、５×５ｃｍの範囲を行い、大きいものから順に５つの樹脂状晶の長径を測定し、その平均値を〔Ａｌ相〕の樹枝状晶の大きさとして使用した。
【００７９】
次に、脱脂剤として日本パーカライジング（株）製ＦＣ−３６４Ｓを使用し、２質量％、６０℃、１０秒間浸漬し、その後、水洗、乾燥の工程で脱脂処理を行った。次いで、アクリルオレフィン樹脂１００質量部に対しタンニン酸２．５質量部、シリカ３０質量部含有させた下地処理材を塗布し、熱風乾燥炉で乾燥して付着量２００ｍｇ／ｍ²とした。乾燥時の到達板温は１５０℃とした。タンニン酸としては「タンニン酸ＡＬ」富士化学工業（株）製を使用した。シリカとしては「スノーテックスＮ」（日産化学工業製）を使用した。
【００８０】
その上に、下塗り塗装として日本ペイント製Ｐ６４１プライマー塗料（ポリエステル樹脂系）の防錆顔料を表１に記載した防錆顔料（亜リン酸亜鉛、カルシウムシリケート、バナジン酸／リン酸混合系、モリブデン酸系）に変更したものをバーコーターで塗布し、熱風乾燥炉で最高到達板温が２２０℃となる条件で焼き付けて膜厚を５μｍになるように調整した。下塗り塗装の上に、上塗り塗装として、日本ペイント製ＦＬ１００ＨＱ（ポリエステル樹脂系）をバーコーターで塗布し、熱風乾燥炉で到達板温が２２０℃となる条件で焼き付けて膜厚を１５μｍに調整した。
【００８１】
以上のようにして作製した塗装鋼板に対して３Ｔ折り曲げ加工（原板を３枚はさんだ状態で１８０°の折り曲げ加工）を施し、加工部の塗膜密着性試験と耐食性試験を行った。塗膜密着性試験は、加工部に粘着テープを貼り付け、これを勢い良く剥離したときの粘着テープへの塗膜の付着状況で評価した。評点は、試験した長さに対する付着した塗膜の長さの割合に基づき、０％以上２％未満を５、２％以上５％未満を４、付着量が５％以上３０％を３、３０％以上８０％未満を２、８０％以上を１、として評点４以上を合格とした。一方、耐食性の試験は、塩水噴霧（５％ＮａＣｌ、３５℃、２ｈｒ）→乾燥（６０℃、３０％ＲＨ、４ｈｒ）→湿潤（５０℃、９５％ＲＨ、２ｈｒ）からなるサイクル腐食試験を１２０サイクル行い、サイクル腐食試験後に加工部の赤錆発生面積率を目視で観察した。評点は、赤錆５％未満を５、赤錆５％以上１０％未満を４、赤錆１０％以上２０％未満を３、２０％以上３０％未満を２、３０％以上を１、として評点３以上を合格とした。
【００８２】
鮮映性は携帯用鮮明度光沢度計（ＰＧＤ計）での鮮映性測定値（Ｇｄ値）を測定した。鮮映性は、Ｇｄ値が０．６以上のものを合格、Ｇｄ値が０．６未満のものを不合格とした。
【００８３】
評価結果を表１に示す。番号１８は、Ｔｉ−Ａｌ系金属間化合物を含有しないため、Ａｌ相が成長し、鮮映性が不合格となった。番号１９は、Ｔｉの含有量が多すぎたため、Ｔｉ−Ａｌ系金属間化合物が表面に濃化し、鮮映性が不合格となった。番号２０は、Ｍｇ、Ａｌ、Ｓｉ、Ｔｉが本発明の範囲外であるため、耐食性が不合格となった。これら以外はいずれも良好な塗膜密着性、鮮映性、耐食性を示した。
【００８４】
【表１】

【００８５】
（実施例２）
まず、厚さ０．８５ｍｍの冷延鋼板を準備し、これに４００〜６００℃で浴中の添加元素量を変化させためっき浴で３秒溶融めっきを行い、Ｎ₂ワイピングでめっき付着量を片面１４０ｇ／ｍ²に調整し、冷却速度１０℃／ｓ以下で冷却した。得られためっき鋼板のめっき組成を表２に示す。また、めっき鋼板を断面からＳＥＭで観察し、めっき層の金属組織を観察した結果を同じく表２に示す。
【００８６】
Ｔｉ−Ａｌ系金属間化合物は、めっき鋼板を１０度傾斜で研磨した後、ＥＰＭＡで観察し、〔Ａｌ相〕、〔Ｚｎ₂Ｍｇ相〕、〔Ｚｎ相〕の中に存在するものを観察した。
【００８７】
めっき層中の〔Ａｌ相〕の樹枝状晶の大きさは、めっき鋼板の表面をＣＭＡでマッピングし、得られたＡｌのマッピングを使用して樹脂状晶の長径を測定した。測定は、５×５ｃｍの範囲を行い、大きいものから順に５つの樹脂状晶の長径を測定し、その平均値を〔Ａｌ相〕の樹枝状晶の大きさとして使用した。
【００８８】
次に、脱脂剤として日本パーカライジング（株）製ＦＣ−３６４Ｓを使用し、２質量％、６０℃、１０秒間浸漬し、その後、水洗、乾燥の工程で脱脂処理を行った。次いで、アクリルオレフィン樹脂１００質量部に対しタンニン酸２．５質量部、シリカ３０質量部含有させた下地処理材を塗布し、熱風乾燥炉で乾燥して付着量２００ｍｇ／ｍ²とした。乾燥時の到達板温は１５０℃とした。タンニン酸としては「タンニン酸ＡＬ」富士化学工業（株）製を使用した。シリカとしては「スノーテックスＮ」（日産化学工業製）を使用した。
【００８９】
塗装は、エポキシポリエステル塗料、ポリエステル塗料、メラミンポリエステル塗料、ウレタンポリエステル塗料、アクリル塗料をそれぞれバーコーターで塗装し、熱風乾燥炉で焼き付けて表２に示す膜厚に調整した。
【００９０】
鮮映性は携帯用鮮明度光沢度計（ＰＧＤ計）での鮮映性測定値（Ｇｄ値）を測定した。鮮映性は、Ｇｄ値が０．６以上のものを合格、Ｇｄ値が０．６未満のものを不合格とした。
【００９１】
塗膜密着性は、ＪＩＳＢ−７７２９に準ずるエリクセン試験機を使用して７ｍｍ押し出した加工部に粘着テープを貼り付け、これを勢い良く剥離したときの押し出し部の外観を目視で判定した。目視で評価しにくい場合には、メチルバイオレットの３％アセトン溶液で染色し、染色された部分には被膜が存在し、染色されていない部分には被膜が存在しないとして密着性を評価した。評点は、剥離面積２％未満を５、２％以上２０％未満を４、２０％以上５０％を３、５０％以上８０％未満を２、８０％以上を１、として評点４以上を合格とした。
【００９２】
耐食性は、ＪＩＳＢ−７７２９に準ずるエリクセン試験機を使用して７ｍｍ押し出した加工部をＪＩＳＺ−２３７１に準ずる塩水噴霧試験で７２ｈｒ試験し、白錆が発生しなかったものを合格、白錆が発生したものを不合格とした。
【００９３】
評価結果を表２に示す。番号２９は、塗膜厚が本発明の範囲外であるため、耐食性が不合格となった。これら以外はいずれも良好な塗膜密着性、鮮映性、耐食性を示した。
【００９４】
【表２】

【００９５】
（実施例３）
まず、厚さ０．８５ｍｍの冷延鋼板を準備し、これに４５０℃のＺｎ−Ｍｇ−Ａｌ−Ｓｉ−Ｔｉめっき浴で３秒溶融めっきを行い、Ｎ₂ワイピングでめっき付着量を片面１４０ｇ／ｍ²に調整し、冷却速度１０℃／ｓ以下で冷却した。得られためっき鋼板のめっき層中組成は、Ｍｇ３％、Ａｌ１１％、Ｓｉ０．２％、Ｔｉ０．００９％であった。
【００９６】
めっき鋼板は、脱脂剤として日本パーカライジング（株）製ＦＣ−３６４Ｓを使用し、２質量％、６０℃、１０秒間浸漬し、その後、水洗、乾燥の工程で脱脂処理を行った。次いで、表３に示す組成の下地処理材を塗布し熱風乾燥炉で乾燥した。乾燥時の到達板温は１５０℃とした。タンニン酸としては「タンニン酸ＡＬ」富士化学工業（株）製、「ＢＲＥＷＴＡＮ」（オムニケム社製）、ＴＡＮＡＬ１（オムニケム社製）を使用した。シリカとしては「スノーテックスＮ、表中ではＳＴ−Ｎと記載」（日産化学工業製）を使用した。
【００９７】
なお、比較材の鋼板は、塗布型のクロメート処理液に浸漬して、クロメート処理を行った。クロメート皮膜の付着量はＣｒ換算量で５０ｍｇ／ｍ²とした。
【００９８】
次に、下塗り塗装として日本ペイント製Ｐ６４１プライマー塗料（ポリエステル樹脂系、表中の樹脂種はポリエステルとした）、日本ペイント製Ｐ１０８プライマー（エポキシ樹脂系、表中の樹脂種はエポキシとした）、日本ペイント製Ｐ３０４プライマー（ウレタン樹脂系、表中の樹脂種はウレタンとした）の防錆顔料を表２に記載した防錆顔料（亜リン酸亜鉛、カルシウムシリケート、バナジン酸／リン酸混合系、モリブデン酸系）に変更したものをバーコーターで塗布し、熱風乾燥炉で最高到達板温が２２０℃となる条件で焼き付けて膜厚を５μｍになるように調整した。下塗り塗装の上に、上塗り塗装として、日本ペイント製ＦＬ１００ＨＱ（ポリエステル樹脂系）をバーコーターで塗布し、熱風乾燥炉で到達板温が２２０℃となる条件で焼き付けて膜厚を１５μｍに調整した。
【００９９】
以上のようにして作製した塗装鋼板に対して３Ｔ折り曲げ加工（原板を３枚はさんだ状態で１８０°の折り曲げ加工）を施し、加工部の塗膜密着性試験と耐食性試験を行った。塗膜密着性試験は、加工部に粘着テープを貼り付け、これを勢い良く剥離したときの粘着テープへの塗膜の付着状況で評価した。評点は、試験した長さに対する付着した塗膜の長さの割合に基づき、０％以上２％未満を５、２％以上５％未満を４、付着量が５％以上３０％を３、３０％以上８０％未満を２、８０％以上を１、として評点４以上を合格とした。一方、耐食性の試験は、塩水噴霧（５％ＮａＣｌ、３５℃、２ｈｒ）→乾燥（６０℃、３０％ＲＨ、４ｈｒ）→湿潤（５０℃、９５％ＲＨ、２ｈｒ）からなるサイクル腐食試験を１２０サイクル行った。サイクル腐食試験後に加工部の赤錆発生面積率を目視で観察した。評点は、赤錆５％未満を５、赤錆５％以上１０％未満を４、赤錆１０％以上２０％未満を３、２０％以上３０％未満を２、３０％以上を１、として評点３以上を合格とした。
【０１００】
鮮映性は携帯用鮮明度光沢度計（ＰＧＤ計）での鮮映性測定値（Ｇｄ値）を測定した。鮮映性は、Ｇｄ値が０．６以上のものを合格、Ｇｄ値が０．６未満のものを不合格とした。
【０１０１】
評価結果を表３に示す。番号１５、１７はタンニン酸の含有量が本発明の範囲外であるため、加工部耐食性が不合格となった。番号１６、１８は下地処理層の付着量が本発明の範囲外であるため、加工部耐食性が不合格となった。番号２７、２８は下地処理層にクロメート処理を使用しているため環境負荷が大きく不合格となった。これら以外はいずれも良好な塗膜密着性、鮮映性、耐食性を示した。
【０１０２】
【表３】

【０１０３】
（実施例４）
まず、厚さ０．８５ｍｍの冷延鋼板を準備し、これに５２０℃で浴中の添加元素量を変化させためっき浴で３秒溶融めっきを行い、Ｎ₂ワイピングでめっき付着量を片面１４０ｇ／ｍ²に調整し、冷却速度１０℃／ｓ以下で冷却した。得られためっき鋼板のめっき組成を表４に示す。また、めっき鋼板を断面からＳＥＭで観察し、めっき層の金属組織を観察した結果を同じく表４に示す。
【０１０４】
Ｔｉ−Ａｌ系金属間化合物は、めっき鋼板を１０度傾斜で研磨した後、ＥＰＭＡで観察し、〔Ａｌ相〕、〔Ｚｎ₂ Ｍｇ相〕、〔Ｚｎ相〕の中に存在するものを観察した。また、〔Ａｌ相〕の中に存在するＴｉ−Ａｌ系金属間化合物については、ＥＰＭＡで観察し、Ｚｎ−Ａｌの共析反応によって析出したＺｎ相中への存在有無を観察した。更にＴｉ−Ａｌ系金属間化合物のＥＰＭＡ観察を行い、Ｔｉ−Ａｌ系金属間化合物のＳｉ含有有無を観察した。
【０１０５】
次に、脱脂剤として日本パーカライジング（株）製ＦＣ−３６４Ｓを使用し、２質量％、６０℃、１０秒間浸漬し、その後、水洗、乾燥の工程で脱脂処理を行った。次いで、アクリルオレフィン樹脂１００質量部に対しタンニン酸２．５質量部、シリカ３０質量部含有させた下地処理材を塗布し、熱風乾燥炉で乾燥して付着量２００ｍｇ／ｍ²とした。乾燥時の到達板温は１５０℃とした。タンニン酸としては「タンニン酸ＡＬ」富士化学工業（株）製を使用した。シリカとしては「スノーテックスＮ」（日産化学工業製）を使用した。
【０１０６】
その上に、プライマーとしてエポキシポリエステル塗料をバーコーターで塗装し、熱風乾燥炉で焼き付けて膜厚を５μｍに調整した。トップコートは、ポリエステル塗料をバーコーターで塗装し、熱風乾燥炉で焼き付けて膜厚を２０μｍに調整した。
【０１０７】
密着性は、デュポン衝撃試験後の塗装めっき鋼板に粘着テープを貼り、その後引き剥がし、めっき及び塗膜が剥離しなかった場合を○、めっき又は塗膜の剥離が１０％未満の場合を△、めっき又は塗膜が１０％以上剥離した場合を×とした。デュポン試験は先端に１／２インチの丸みを持つ撃ち型を使用し、１ｋｇの重りを１ｍの高さから落下させて行った。
【０１０８】
加工後耐食性の評価は、３Ｔ折り曲げ加工（原板を３枚はさんだ状態で１８０°の折り曲げ加工）を施したサンプルの折り曲げ部について、ＣＣＴ１２０サイクル後の赤錆発生状況を以下に示す評点づけで判定した。ＣＣＴは、ＳＳＴ２ｈｒ→乾燥４ｈｒ→湿潤２ｈｒを１サイクルとした。評点は３以上を合格とした。
５：５％未満
４：５％以上１０％未満
３：１０％以上２０％未満
２：２０％以上３０％未満
１：３０％以上
評価結果を表４に示す。番号２はＡｌとＳｉの添加量が本発明の範囲外であるため密着性が不合格となった。これら以外はいずれも、密着性、加工後耐食性が良好な結果となった。特にＳｉを添加しためっき鋼板は良好な密着性と加工後耐食性を示した。
【０１０９】
【表４】

【０１１０】
【発明の効果】
以上述べてきたように，本発明により，高Ａｌ濃度の場合でも十分鮮映性が優れ，環境負荷の大きなクロムを含有せずに，加工部の耐食性に優れる塗装鋼板を製造することが可能となり，工業上極めて優れた効果を奏することができる。
【図面の簡単な説明】
【図１】（ａ）は、本発明のめっき鋼材のめっき層についての図面代用顕微鏡写真（倍率１０００倍）であり、（ｂ）は写真中の各組織の分布状態を示す図である。
【図２】（ａ）は、図１の「Ａｌ″相」を拡大した図面代用顕微鏡写真（倍率３５００倍）であり、（ｂ）は写真中の各組織の分布状態を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a coated steel sheet, and more specifically, has excellent coating film adhesion and corrosion resistance without containing chromium, which is said to have a large environmental load, and can be applied as a steel sheet for various uses such as home appliances and building materials. It relates to painted steel sheets.
[0002]
[Prior art]
Compared with the method in which a metal plate is first formed into a complex shape and then applied to a painted metal plate, the painting process can be streamlined, the quality is uniform, and the consumption of paint is saved. Since there are advantages, it has been used a lot so far, and the amount used will continue to increase.
[0003]
In general, a coated metal plate is a cold-rolled steel plate, a galvanized steel plate, and other metal plates that are pre-coated, and then molded into an arbitrary shape for use in the final use. For example, a refrigerator, a washing machine, Used in metal products such as household appliances such as microwave ovens, vending machines, office equipment, automobiles, and air conditioner outdoor units.
[0004]
In order to improve the corrosion resistance of such a coated steel sheet, the present inventors have proposed a coated molten Zn—Al—Mg—Si plated steel sheet (Patent Document 1). In addition, the inventors further added corrosion resistance by adding one or more of Ca, Be, Ti, Cu, Ni, Co, Cr, and Mn to the molten Zn—Al—Mg—Si plated steel sheet. It was clarified that a coated steel sheet excellent in the above can be obtained (Patent Document 2).
[0005]
Each of these has a surface treatment that is excellent in corrosion resistance and adhesion called chromate treatment on a plated steel sheet that is excellent in corrosion resistance, and has an undercoat layer containing a chromium-based rust preventive pigment that is excellent in corrosion resistance. It has a structure having a colored overcoat layer.
[0006]
Since hexavalent chromium that may be eluted from the chromate treatment and chromium-based anticorrosive pigment is a substance with a large environmental load, the present inventors have applied the coating molten Zn—Al—Mg—Si plating with a small environmental load. A steel plate was proposed (Patent Documents 3 and 4).
[0007]
Further, it is disclosed that the surface appearance is improved by adding Ti, B, and Si to a molten Zn—Al—Mg plated steel sheet (for example, Patent Document 5).
[0008]
[Patent Document 1]
Japanese Patent No. 3179446
[Patent Document 2]
JP 2000-64061 A
[Patent Document 3]
Japanese Patent No. 3090207
[Patent Document 4]
Japanese Patent No. 312266
[Patent Document 5]
JP 2001-295015 A
[0009]
[Problems to be solved by the invention]
A Zn-Mg-Al ternary alloy has a ternary eutectic point in 3 mass% Mg-4 mass% Al-93 mass% Zn, and when the Al concentration is higher than that, an Al phase is crystallized as the primary crystal. To do.
[0010]
If the plating solidification rate at the time of hot dipping is sufficiently secured, the surface smoothness will not be a problem because the plating solidifies before the Al phase grows greatly, but if the plating solidification rate is low, this Al phase However, there is a problem that unevenness is formed on the plating surface and the surface smoothness deteriorates.
[0011]
For this reason, when a coated steel sheet is produced with such a steel sheet having low surface smoothness, the unevenness of the plating surface cannot be completely hidden by a relatively thin coating film having a thickness of about 0.2 to 100 μm. There is a problem that the sharpness of the image deteriorates.
[0012]
However, the techniques disclosed in Patent Documents 1 to 4 do not consider the problem that the sharpness of the coated steel sheet deteriorates.
[0013]
In the technique disclosed in Patent Document 5, Zn that deteriorates the surface appearance is used.₁₁Mg₂Ti and B are added for the purpose of suppressing phase formation / growth, but the problem of deterioration of surface smoothness and sharpness after coating is not considered, and intermetallic compounds are also mentioned. Absent.
[0014]
Therefore, the present invention has been made in view of the above problems, and provides a highly corrosion-resistant coated steel sheet that is excellent in sharpness even in the case of a high Al concentration exceeding 4% by mass and has a small environmental load. It is aimed.
[0015]
[Means for Solving the Problems]
As a result of earnest research on the development of a highly corrosion-resistant coated steel sheet with excellent visibility and low environmental impact, the present inventors have formed a zinc-based plating that optimizes the additive element addition amount on the surface of the steel sheet, Applying tannin or tannic acid-based treatment instead of chromate treatment as a base treatment, and coating with chromium-free rust-preventive pigment instead of chromium-based rust-preventive pigment to improve paint adhesion and clarity It was found that a highly corrosion-resistant coated steel sheet with excellent environmental impact can be obtained.
[0016]
That is, the present invention has been completed based on the above findings, and the gist of the present invention is as follows.
[0017]
(1) A zinc-based plating layer containing Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less on the one surface or both surfaces of a steel plate, with the balance being zinc and inevitable impurities And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer, and an organic layer having a thickness of 0.2 to 100 μm as an upper layer A highly corrosion-resistant coated steel sheet with excellent image clarity and low environmental impact, characterized by having a coating layer.
[0018]
(2) On one side or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and It has a zinc-based plating layer made of inevitable impurities, and has a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer on the upper layer. A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness and having a small environmental load, characterized by having an organic coating layer having a thickness of 0.2 to 100 μm.
[0019]
(3) A zinc-based plating layer containing Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less on the one surface or both surfaces of the steel plate, the balance being zinc and inevitable impurities And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer, and an organic layer having a thickness of 0.2 to 100 μm as an upper layer Zinc-based plating layer of coated steel sheet with coating layer is [Al / Zn / Zn₂[Al phase], [Zn] in the base of Mg ternary eutectic structure₂It has a metal structure in which one or more of [Mg phase] and [Zn phase] are mixed, and [Al phase], [Zn phase]₂A highly corrosion-resistant coated steel sheet having excellent sharpness, comprising a Ti—Al intermetallic compound in one or more of [Mg phase] and [Zn phase].
[0020]
(4) On one side or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and It has a zinc-based plating layer made of inevitable impurities, and has a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer on the upper layer. As a zinc-based plating layer of a coated steel plate having an organic coating layer having a thickness of 0.2 to 100 μm [Al / Zn / Zn₂[Mg ternary eutectic structure] [Mg₂[Si phase], [Al phase] and [Zn]₂[Mg phase] has a mixed metal structure, and [Al phase] and [Zn phase]₂A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness, and having a low environmental impact, characterized by containing a Ti—Al intermetallic compound in one or two of the [Mg phase].
[0021]
(5) On one side or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and It has a zinc-based plating layer made of inevitable impurities, and has a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer on the upper layer. As a zinc-based plating layer of a coated steel plate having an organic coating layer having a thickness of 0.2 to 100 μm [Al / Zn / Zn₂[Mg ternary eutectic structure] [Mg₂Si phase], Al phase, Zn₂It has a metal structure in which [Mg phase] and [Zn phase] are mixed, and [Al phase], [Zn phase]₂A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness and having a low environmental impact, characterized by containing a Ti—Al intermetallic compound in [Mg phase] and [Zn phase].
[0022]
(6) On one or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and It has a zinc-based plating layer made of inevitable impurities, and has a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer on the upper layer. As a zinc-based plating layer of a coated steel plate having an organic coating layer having a thickness of 0.2 to 100 μm [Al / Zn / Zn₂[Mg ternary eutectic structure] [Mg₂[Si phase], [Al phase] and [Zn phase] have a mixed metal structure, and Ti-Al intermetallic compound is included in one or two of [Al phase] and [Zn phase]. A highly corrosion-resistant coated steel sheet with excellent paint film adhesion and sharpness that has a low environmental impact.
[0023]
(7) The Ti—Al intermetallic compound according to any one of (3) to (6) is TiAl._ThreeA highly corrosion-resistant coated steel sheet with excellent paint film adhesion and sharpness that has a low environmental impact.
[0024]
(8) The Ti—Al-based intermetallic compound according to any one of (3) to (6) is Ti (Al_1-XSi_X)_Three(However, X = 0 to 0.5) A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness, and having a small environmental load.
[0025]
(9) The Ti-Al intermetallic compound contained in the [Al phase] in the plating layer is present in the Zn phase precipitated by Zn-Al eutectoid reaction (3) ) A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness as defined in any one of (8) to (8) and having a low environmental impact.
[0026]
(10) The coating film adhesion and sharpness according to any one of (1) to (9) above, wherein the size of the [Al phase] dendrite in the plating layer is 500 μm or less. High corrosion resistance coated steel sheet with excellent environmental impact and low environmental impact.
[0027]
(11) The coating film adhesion according to any one of (1) to (10) above, further containing 10 to 500 parts by mass of fine silica as a solid content in the coating layer of the ground treatment layer High corrosion-resistant coated steel sheet with excellent image clarity and low environmental impact.
[0028]
(12) The organic coating film is a thermosetting resin coating film, and is excellent in coating film adhesion and sharpness according to any one of the above (1) to (11) and having a low environmental impact. Corrosion resistant coated steel sheet.
[0029]
(13) The organic coating layer is composed of an undercoat layer containing a rust preventive pigment and a colored topcoat layer, and has excellent coating film adhesion and sharpness according to any one of the above (1) to (12), and has a small environmental load. High corrosion resistance coated steel sheet.
[0030]
(14) The rust preventive pigment is characterized in that it releases one or more of silicate ion, phosphate ion, vanadate ion and molybdate ion.13)High corrosion-resistant coated steel sheet with excellent coating adhesion and sharpness, and low environmental impact.
[0031]
(15) Adhesion amount after drying of the ground treatment layer is 10 to 3000 mg / m²The highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness as defined in any one of (1) to (14) and having a small environmental load.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0033]
In the present invention, the coated steel sheet is obtained by sequentially providing a zinc-based plating layer, a tannin or tannic acid-based treatment, and a layer made of an organic film on the steel sheet. As the base steel sheet of the present invention, both hot-rolled steel sheets and cold-rolled steel sheets can be used, and the steel grades are ultra-low carbon steel sheets to which Al killed steel, Ti, Nb, etc. are added, and strengthening elements such as P, Si, Mn, etc. Various materials such as high-strength steel and stainless steel to which is added can be applied.
[0034]
The lower zinc-based plating layer is Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, and the balance is Zn and inevitable impurities, or Al: 4 ˜22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, the balance being a plating layer made of Zn and inevitable impurities.
[0035]
The reason why the content of Al is limited to 4 to 10% by mass in the Zn-Al-Mg-Ti-based plating layer is that when the Al content exceeds 10% by mass, a decrease in plating adhesion is observed. This is because the Al content in the plating layer not added needs to be 10% by mass or less. In addition, when the amount is less than 4% by mass, the Al phase does not crystallize as the primary crystal, and there is no problem of reduced smoothness.
[0036]
Accordingly, in the highly corrosion-resistant coated steel sheet according to the present invention, it is essential to add Si to the plating layer in order to ensure plating adhesion, particularly when the Al concentration exceeds 10% by mass. It is.
[0037]
On the other hand, in the Zn-Al-Mg-Ti-Si-based plating layer, the reason why the Al content is limited to 4 to 22% by mass is that the Al phase does not crystallize as a primary crystal when the content is less than 4% by mass, so that smoothness is achieved. This is because there is no problem of reduction, and when it exceeds 22% by mass, the effect of improving the corrosion resistance is saturated.
[0038]
The reason for limiting the Si content to 0.5% by mass or less (excluding 0% by mass) is that Si has the effect of improving the adhesion, but if it exceeds 0.5% by mass, the adhesion is improved. This is because the effect to be saturated is saturated. Desirably, it is 0.00001-0.5 mass%, More desirably, it is 0.0001-0.5 mass%.
[0039]
The addition of Si is essential for plating layers with an Al content of more than 10% by mass. However, even in plating layers with an Al content of 10% or less, the effect of improving plating adhesion is great, so the processing is severe. It is effective to add Si when high plating adhesion is required. Further, by adding Si, [Mg₂Si phase] crystallizes out. This [Mg₂Since the Si phase is effective in improving the corrosion resistance of the processed part, the amount of Si added is increased, and [Mg]₂It is more desirable to produce a metal structure in which the [Si phase] is mixed.
[0040]
The reason why the content of Mg is limited to 1 to 5% by mass is that if it is less than 1% by mass, the effect of improving the corrosion resistance is insufficient, and if it exceeds 5% by mass, the plating layer becomes brittle and adhesion is improved. It is because it falls. The reason why the content of Ti is limited to 0.1% by mass or less (excluding 0% by mass) is that Ti has the effect of crystallizing a Ti—Al intermetallic compound and improving the sharpness, but 0 When the amount exceeds 1% by mass, the appearance after plating becomes rough, resulting in poor appearance. In addition, the Ti—Al intermetallic compound is concentrated on the plating surface to reduce the surface smoothness. Desirably, it is 0.00001-0.1 mass%. More desirably, it is 0.00001-0.01 mass%.
[0041]
This plating layer is made of [Al / Zn / Zn₂[Zn phase], [Al phase], [Zn phase] in the Mg ternary eutectic structure₂Mg phase], [Mg₂Si phase], a metal structure containing one or more of Ti—Al intermetallic compounds is formed.
[0042]
Here, [Al / Zn / Zn₂Mg ternary eutectic structure] means Al phase, Zn phase and intermetallic compound Zn₂This is a ternary eutectic structure with Mg phase, and the Al phase forming this ternary eutectic structure is, for example, an “Al ″ phase” (Zn at high temperature in an Al—Zn—Mg ternary equilibrium diagram. It is an Al solid solution that solidly dissolves the phase and contains a small amount of Mg). The Al ″ phase at high temperature usually appears separated into a fine Al phase and a fine Zn phase at room temperature. The Zn phase in the ternary eutectic structure dissolves a small amount of Al, and in some cases Is a Zn solid solution in which a small amount of Mg is solid-solved.Zn in the ternary eutectic structure₂The Mg phase is an intermetallic compound phase existing in the vicinity of Zn: about 84 mass% in the Zn-Mg binary equilibrium diagram. As far as seen in the phase diagram, Si and Ti are not dissolved in each phase, or even if they are dissolved, it is considered that the amount is extremely small, but the amount cannot be clearly distinguished by ordinary analysis. In this specification, a ternary eutectic structure consisting of two phases is referred to as [Al / Zn / Zn₂Mg ternary eutectic structure].
[0043]
In addition, the [Al phase] is a phase that looks like an island with a clear boundary in the ternary eutectic structure, which is, for example, at a high temperature in an Al—Zn—Mg ternary equilibrium diagram. "Al" phase "(Al solid solution in which Zn phase is dissolved, and contains a small amount of Mg). The Al ″ phase at this high temperature differs in the amount of Zn and Mg dissolved depending on the Al and Mg concentrations in the plating bath. The Al ″ phase at this high temperature is usually fine Al phase and fine Zn at room temperature. Although it separates into phases, it can be seen that the island-like shape seen at room temperature is the one that retains the shape of the Al ′ phase at high temperature. As can be seen from the phase diagram, Si and Ti are not dissolved in this phase, or even if they are dissolved, they are considered to be extremely small, but they cannot be clearly distinguished by ordinary analysis. A phase that is derived from a phase and that retains the shape of an Al ″ phase in shape is referred to as an “Al phase” in this specification. This [Al phase] can be clearly distinguished from the Al phase forming the ternary eutectic structure by microscopic observation.
[0044]
In addition, the [Zn phase] is a phase that looks like an island with a clear boundary in the ternary eutectic structure, and actually contains a small amount of Al and a small amount of Mg as a solid solution. There is also. As far as the phase diagram is concerned, it is considered that Si and Ti are not dissolved in this phase, or even if they are dissolved in a very small amount. This [Zn phase] can be clearly distinguished from the Zn phase forming the ternary eutectic structure by microscopic observation.
[0045]
[Zn₂The “Mg phase” is a phase that looks like an island with a clear boundary in the substrate of the ternary eutectic structure, and a small amount of Al may actually be dissolved. As far as the phase diagram is concerned, it is considered that Si and Ti are not dissolved in this phase, or even if they are dissolved in a very small amount. This [Zn₂Mg phase] is Zn forming the ternary eutectic structure.₂It can be clearly distinguished from the Mg phase by microscopic observation.
[0046]
[Mg₂The “Si phase” is a phase that looks like an island with a clear boundary in the solidified structure of the plating layer. As can be seen from the phase diagram, Zn, Al, and Ti are not dissolved or are considered to be extremely small even if they are dissolved. This [Mg₂The Si phase] can be clearly distinguished by microscopic observation during plating.
[0047]
Further, the Ti—Al intermetallic compound is a phase that looks like an island with a clear boundary in the solidified structure of the plating layer. As far as the phase diagram is concerned, TiAl_ThreeAlthough Si is observed when analyzed, TiAl is a solid solution of Si._ThreeOr Ti (Al in which a part of Al is replaced by Si (Al_1-XSi_X)_Three(However, X = 0 to 0.5).
[0048]
In the hot-dip galvanized steel material of the present invention, this Ti-Al intermetallic compound includes [Al phase], [Zn₂It exists in [Mg phase] and [Zn phase]. The content of Ti-Al intermetallic compound is changed to [Al phase], [Zn₂The reason for limiting to [Mg phase] and [Zn phase] is that the vividness cannot be improved with the Ti—Al intermetallic compounds present at other positions. [Al phase], [Zn₂The reason why the Ti—Al intermetallic compound existing in the [Mg phase] and [Zn phase] improves the sharpness is that the Ti—Al intermetallic compound is the [Al phase], [Zn phase].₂It is thought that this is because the crystallization of these crystals is promoted by becoming a nucleus of [Mg phase] and [Zn phase], and a fine and numerous structure is formed. That is, when the crystal becomes finer, unevenness on the surface of the plating layer is suppressed, the plating surface becomes smooth, and unevenness on the plating surface can be concealed even with a relatively thin coating film, which improves the clarity of the coated steel sheet. It is done.
[0049]
This effect is particularly remarkable in the [Al phase]. By controlling the size of the [Al phase] dendrites to 500 μm or less, the surface becomes smooth and the friction coefficient decreases. Desirably, it is 400 micrometers or less. More desirably, it is 300 μm or less.
[0050]
As a result of the inventors investigating a number of metal structures in plating, an intermetallic compound having a size of several μm was observed from most of the metal structures. An example of an intermetallic compound present in the [Al phase] is shown in FIG. The upper diagram (a) in FIG. 1 is a micrograph (magnification 1000 times) of the plating layer of the plated steel material in the present invention, and the lower diagram (b) illustrates the distribution state of each structure in the photograph. It is. As can be seen from this figure, each structure can be clearly identified by a micrograph of the plated layer of the plated steel material in the present invention.
[0051]
In FIG. 1, Ti—Al intermetallic compounds are observed in the one corresponding to the “Al ″ phase” at a high temperature in the Al—Zn—Mg ternary equilibrium diagram. This Al ″ phase at high temperature usually appears separated into a fine Al phase and a fine Zn phase at room temperature by a eutectoid reaction occurring at 277 ° C. in the binary equilibrium diagram of Al—Zn. In the hypoeutectoid reaction, the Al ″ phase crystallized at a high temperature starts to precipitate the Zn phase from the ternary eutectic temperature in the Al—Zn—Mg ternary equilibrium diagram, and the Al—Zn binary. The Al ″ phase remaining at the temperature corresponding to the eutectoid reaction in the system equilibrium diagram shows the eutectoid structure of the fine Al phase and the fine Zn phase.
[0052]
The upper diagram (a) of FIG. 2 is a micrograph (magnification of 3500 times) of the Al ″ phase of FIG. 1 (a), and the lower diagram shows the distribution state of each tissue in the photograph. (B) When the Al ″ phase is observed in detail, it is observed that the deposited Zn phase exists outside the Al ″ phase and around the Ti—Al intermetallic compound.
In the present invention, the size of the intermetallic compound is not particularly limited, but what the inventors have observed is a size of 10 μm or less. Further, the proportion of the intermetallic compound in the plating structure is not particularly limited, but [Al phase], [Zn₂It is desirable that 10% or more of [Mg phase] and [Zn phase] exist.
[0053]
In the present invention, the method for producing a plated steel sheet is not particularly limited, and a normal non-oxidizing furnace type hot dipping method can be applied.
[0054]
The method for adding the intermetallic compound is not particularly limited, and a method of turbidizing the fine powder of the intermetallic compound in the bath or a method of dissolving the intermetallic compound in the bath can be applied. When manufacturing with a continuous line using a hot dipping method, a method of dissolving Ti in the plating bath is suitable. As a method of dissolving Ti in the plating bath, a method of adding a Ti—Zn-based intermetallic compound is efficient because it can be dissolved at a low temperature in a short time. As the Ti—Zn-based intermetallic compound to be added, Zn₁₅Ti, Zn_TenTi, Zn_FiveTi, Zn_ThreeTi, Zn₂There are Ti, ZnTi, and the like. When these intermetallic compounds are added alone or mixed in a Zn, Zn-Al, Zn-Al-Mg alloy and added to the plating bath, the dissolved Ti crystallizes as a Ti-Al intermetallic compound during plating, and the surface is smoothed. Improve moldability and moldability.
[0055]
There are no particular restrictions on the amount of plating applied, but 10 g / m from the viewpoint of corrosion resistance.²From the viewpoint of workability, 350 g / m²It is desirable that
[0056]
In addition to this, the galvanized layer may contain Fe, Sb, Pb and Sn alone or in combination within 0.5% by mass. Further, even if Ca, Be, Cu, Ni, Co, Cr, Mn, P, B, Nb, Bi or a group 3 element is contained in a total amount of 0.5% by mass or less, the effect of the present invention is not impaired, and the amount thereof Depending on the case, the corrosion resistance may be further improved.
[0057]
The base treatment layer used for the coated steel sheet of the present invention is characterized by containing tannin or tannic acid based on an aqueous resin. By combining this base treatment layer and a Zn-Mg-Al-Ti alloy plating layer or a Zn-Mg-Al-Si-Ti alloy plating layer, the coating adhesion and the corrosion resistance of the processed part are improved synergistically. .
[0058]
The role of tannin or tannic acid in the ground treatment layer is to react firmly with and adhere to the plating layer, and to adhere to the aqueous resin. Aqueous resin in close contact with tannin or tannic acid adheres firmly to the resin to be coated on it, and as a result, the plated steel sheet and the coating film adhere firmly without using the chromate treatment conventionally used. It is thought that it became. In addition, it is considered that there is a portion where tannin or tannic acid itself is involved in the bonding between the plated steel sheet and the coating film without interposing the aqueous resin.
[0059]
The water-based resin for the base treatment layer includes, in addition to water-soluble resins, resins that are essentially water-insoluble but can be finely dispersed in water, such as emulsions and suspensions. Examples of such water-based resins that can be used include polyolefin resins, acrylic olefin resins, polyurethane resins, polycarbonate resins, epoxy resins, polyester resins, alkyd resins, phenol resins, and other thermosetting resins. Type resin, and a crosslinkable resin is desirable. Particularly preferred resins are acrylic olefin resins, polyurethane resins, and mixed resins thereof. Two or more of these aqueous resins may be mixed or polymerized for use.
[0060]
Tannin and tannic acid are strongly bonded to both the Zn-Mg-Al-Ti alloy plating or the Zn-Mg-Al-Si-Ti alloy plating and the coating film in the presence of an aqueous resin. The adhesion of the film is drastically improved, and as a result, the corrosion resistance of the processed part is improved. The tannin or tannic acid may be hydrolyzable tannin or condensed tannin, or a part of them may be decomposed. Tannin and tannic acid are not particularly limited, such as Hamametatannin, pentaploid tannin, gallic tannin, milobaron tannin, dibibi tannin, argaroviran tannin, valonia tannin, catechin, etc., for example, “tannic acid: AL "(manufactured by Fuji Chemical Industry Co., Ltd.) can be used.
[0061]
The content of tannin and tannic acid is preferably 0.2 to 50 parts by mass of tannin or tannic acid with respect to 100 parts by mass of the resin. If the content of tannin or tannic acid is less than 0.2 parts by mass, the effect of adding these is not observed, and the coating film adhesion and the corrosion resistance of the processed part are insufficient. On the other hand, when the amount exceeds 50 parts by mass, the corrosion resistance is lowered, and when the treatment liquid is stored for a long period of time, gelation occurs.
[0062]
Further, when fine silica is added, the scratch resistance, coating film adhesion and corrosion resistance are improved. In the present invention, the fine silica is a general term for silica having such a characteristic that when dispersed in water since it has a fine particle diameter, it can stably maintain a water-dispersed state, and no semi-permanent settling is observed. Is. Such fine silica is not particularly limited as long as it has few impurities such as sodium and is weakly alkaline. For example, commercially available silica such as “Snowtex N” (manufactured by Nissan Chemical Industries, Ltd.) and “Adelite AT-20N” (manufactured by Asahi Denka Kogyo Co., Ltd.) can be used.
[0063]
The content of fine silica is preferably 10 to 500 parts by mass with respect to 100 parts by mass of the aqueous resin in terms of solid content. If it is less than 10 parts by mass, the added effect is small, and if it exceeds 500 parts by mass, the effect of improving corrosion resistance is saturated, which is uneconomical.
[0064]
Moreover, you may add surfactant, an antirust inhibitor, a foaming agent, a pigment, etc. as needed. Further, in order to improve the adhesion, an etching fluoride may be added. As the etching fluoride, for example, zinc fluoride tetrahydrate, zinc hexafluorosilicate hexahydrate and the like can be used. Similarly, a silane coupling agent may be added for the purpose of improving adhesion. Examples of the silane coupling agent include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, aminosilane, γ-methacryloxypropyltrimethoxysilane, N- β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl [ 3- (trimethoxysilyl) propyl] ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchloro Or the like can be given a run.
[0065]
The method for applying the ground treatment layer is not particularly limited, and generally known coating methods such as roll coating, air spray, airless spray, and immersion can be applied. The drying and baking after coating may be performed by a known method such as a hot air furnace, an induction heating furnace, a near infrared furnace, or a combination of these in consideration of the polymerization reaction and curing reaction of the resin. Further, depending on the type of aqueous resin to be used, it can be cured by ultraviolet rays or electron beams. Alternatively, it may be naturally dried without using forced drying, or a Zn-Mg-Al-Ti alloy-plated steel sheet or a Zn-Mg-Al-Si-Ti alloy-plated steel sheet is heated in advance, You may apply | coat on it and dry naturally.
[0066]
The amount of adhesion of the ground treatment layer after drying is 10 to 3000 mg / m.²Is preferred. 10 mg / m²If it is less than 1, the adhesion is inferior and the corrosion resistance of the processed part is insufficient. On the other hand, 3000mg / m²Exceeding this is not only economical, but also deteriorates workability and deteriorates corrosion resistance.
[0067]
The coated steel sheet of the present invention is characterized by having an organic coating layer on a Zn-Mg-Al-Ti alloy-plated steel sheet or a Zn-Mg-Al-Si-Ti alloy-plated steel sheet that has been subjected to a base treatment. Examples of the organic coating include polyolefin resin, acrylic resin, urethane resin, epoxy resin, polyester resin, vinyl chloride resin, fluorine resin, butyral resin, polycarbonate resin, and phenol resin. Mixtures and copolymers of these can also be used. Moreover, an isocyanate resin, an amino resin, a silane coupling agent, a titanium coupling agent, or the like can be used in combination as an auxiliary component. Since the precoated steel sheet according to the present invention is often used as it is without being repaired after processing, in applications where severe processing is performed, a resin system in which a polyester resin is crosslinked with melamine, a polyester resin is a urethane resin (isocyanate, isocyanate) Resin), vinyl chloride resin, and fluororesin (solvent soluble type, dispersion mixed type with acrylic resin) are desirable.
[0068]
Next, examples of the organic coating on the upper layer of the coated steel sheet include polyester resins, amino resins, epoxy resins, acrylic resins, urethane resins, fluororesins, etc., and are not particularly limited. When used in a thermosetting resin coating, the thermosetting resin coating is most preferable. Examples of the thermosetting resin coating include polyester-based paints such as epoxy polyester paints, polyester paints, melamine polyester paints, urethane polyester paints, and acrylic paints.
[0069]
Combined with alkyd resins in which part of the acid component of the polyester resin is replaced with fatty acids, and oil-free alkyd resins that are not modified with oil, polyester-based paints combined with melamine resins or polyisocyanate resins as curing agents, and various crosslinking agents This is because the acrylic paint has better processability than other paints, so that the coating film does not crack after severe processing.
[0070]
The appropriate film thickness is 0.2 to 100 μm. The reason why the film thickness is 0.2 μm or more is that the corrosion resistance cannot be secured if the film thickness is less than 0.2 μm. The reason why the film thickness is 100 μm or less is that when the film thickness exceeds 100 μm, it is disadvantageous in terms of cost. Desirably, it is 50 μm or less. The organic coating layer may be a single layer or multiple layers.
[0071]
In addition, additives, such as a plasticizer, antioxidant, a heat stabilizer, an inorganic particle, a pigment, organic lubrication, are mix | blended with the organic film used for the method of this invention as needed.
[0072]
The organic coating layer is coated on the base treatment layer by a known method. For example, roll coater, curtain coater, electrostatic coating, spray coating, dip coating, and the like. Thereafter, it is dried and cured by heating with hot air, induction heating, near infrared, far infrared, or the like. If the resin of the organic coating layer is hardened by electron beam or ultraviolet light, it is hardened by these irradiations. These combinations may be used.
[0073]
Between the chemical conversion treatment layer and the colored organic layer of the coated steel sheet of the present invention, a coating layer to which a rust preventive pigment is added as necessary can be provided as an undercoat layer. This subbing layer is mainly intended to improve corrosion resistance, but is also designed in consideration of molding processability and chemical resistance. As the resin constituting the undercoat layer, generally known resins, for example, polyester resins, urethane resins, acrylic resins, epoxy resins, melamine resins and the like can be used as they are or in combination. As the anti-rust pigment, generally known ones, for example,(1)Phosphate anticorrosive pigments such as zinc phosphate, iron phosphate, aluminum phosphate, zinc phosphite,(2)Molybdate antirust pigments such as calcium molybdate, aluminum molybdate, barium molybdate,(3)Vanadium rust preventive pigments such as vanadium oxide,(4)Silicate pigments such as calcium silicate,(5)Fine silica such as water-dispersed silica and fumed silica can be used.These rust preventive pigments release phosphate ions, molybdate ions, vanadate ions, and silicate ions, respectively.
[0074]
The addition amount of the rust preventive pigment is preferably 1 to 40% by mass based on the solid content of the film. If the amount is less than 1% by mass, the corrosion resistance is not sufficiently improved. If the amount exceeds 40% by mass, the workability is lowered, the organic coating layer is dropped during processing, and the corrosion resistance is deteriorated.
[0075]
In general, the undercoat layer containing the rust preventive pigment can be applied by a known method. For example, roll coating, curtain coating, air spray, airless spray, dipping, brush coating, bar coating, and the like. Thereafter, it is dried and cured by heating with hot air, induction heating, near infrared, far infrared, or the like. If the resin of the organic coating layer is hardened by an electron beam or ultraviolet rays, it is cured by these irradiations. These combinations may be used.
[0076]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
[0077]
Example 1
First, a cold rolled steel sheet having a thickness of 0.85 mm was prepared, and this was subjected to hot dip plating for 3 seconds in a plating bath in which the amount of additive elements in the bath was changed at 400 to 600 ° C., and N₂Wiping reduces plating adhesion on one side 140g / m²And cooled at a cooling rate of 10 ° C./s or less. Table 1 shows the plating composition of the obtained plated steel sheet. Moreover, the result of having observed the plated steel plate from the cross section by SEM and observing the metal structure of a plating layer is similarly shown in Table 1. Ti-Al intermetallic compounds are obtained by polishing a plated steel sheet with a 10 degree inclination and then observing with EPMA, [Al phase], [Zn₂Those present in [Mg phase] and [Zn phase] were observed.
[0078]
The size of the [Al phase] dendrites in the plating layer was determined by mapping the surface of the plated steel plate with CMA and measuring the major axis of the resinous crystals using the resulting Al mapping. The measurement was performed in a range of 5 × 5 cm, the major diameters of five resinous crystals were measured in order from the largest, and the average value was used as the size of the [Al phase] dendrites.
[0079]
Next, FC-364S manufactured by Nihon Parkerizing Co., Ltd. was used as a degreasing agent, soaked at 2% by mass, 60 ° C. for 10 seconds, and then degreased in water washing and drying steps. Next, a base treatment material containing 2.5 parts by mass of tannic acid and 30 parts by mass of silica is applied to 100 parts by mass of the acrylic olefin resin, and dried in a hot air drying furnace to deposit 200 mg / m.²It was. The ultimate plate temperature during drying was 150 ° C. As the tannic acid, “tannic acid AL” manufactured by Fuji Chemical Industry Co., Ltd. was used. As the silica, “Snowtex N” (manufactured by Nissan Chemical Industries) was used.
[0080]
Furthermore, as an undercoat, the antirust pigments of P641 primer paint (polyester resin system) made by Nippon Paint are listed in Table 1. Antirust pigments (zinc phosphite, calcium silicate, vanadic acid / phosphoric acid mixed system, molybdic acid) What was changed to the system) was applied with a bar coater, and baked in a hot air drying furnace under the condition that the maximum plate temperature reached 220 ° C., and the film thickness was adjusted to 5 μm. On the undercoat, as a topcoat, FL100HQ (polyester resin system) manufactured by Nippon Paint was applied with a bar coater, and baked in a hot air drying furnace under the condition that the ultimate plate temperature was 220 ° C., and the film thickness was adjusted to 15 μm.
[0081]
The coated steel plate produced as described above was subjected to 3T bending (180 ° bending with three original plates sandwiched), and a coating film adhesion test and a corrosion resistance test were performed on the processed part. The coating film adhesion test was evaluated based on the state of adhesion of the coating film to the adhesive tape when a pressure-sensitive adhesive tape was applied to the processed part and peeled off vigorously. The score is based on the ratio of the length of the coated film to the length tested, 0% to less than 2%, 5 to 2% to less than 5%, 4 to 5% to 30%, 3 to 30%. % Or more and less than 80% was 2, 2, 80% or more was 1, and a score of 4 or more was considered acceptable. On the other hand, the corrosion resistance test is a cyclic corrosion test consisting of salt spray (5% NaCl, 35 ° C., 2 hr) → dry (60 ° C., 30% RH, 4 hr) → wet (50 ° C., 95% RH, 2 hr). The cycle was performed, and after the cycle corrosion test, the red rust generation area ratio of the processed part was visually observed. The score is 5 for red rust less than 5%, 4 for red rust 5% to less than 10%, 3 for red rust 10% to less than 20%, 2 for 20% to less than 30%, and 1 for 30% or more. Passed.
[0082]
The sharpness was determined by measuring the sharpness measurement value (Gd value) with a portable sharpness gloss meter (PGD meter). As for the sharpness, a Gd value of 0.6 or more was accepted, and a Gd value of less than 0.6 was rejected.
[0083]
The evaluation results are shown in Table 1. No. 18 did not contain a Ti—Al intermetallic compound, so the Al phase grew and the sharpness was rejected. In No. 19, since the Ti content was too large, the Ti—Al intermetallic compound was concentrated on the surface, and the sharpness was not acceptable. In No. 20, since Mg, Al, Si, and Ti were outside the scope of the present invention, the corrosion resistance was rejected. Except for these, all showed good coating film adhesion, sharpness, and corrosion resistance.
[0084]
[Table 1]

[0085]
(Example 2)
First, a cold rolled steel sheet having a thickness of 0.85 mm was prepared, and this was subjected to hot dip plating for 3 seconds in a plating bath in which the amount of additive elements in the bath was changed at 400 to 600 ° C., and N₂Wiping reduces plating adhesion on one side 140g / m²And cooled at a cooling rate of 10 ° C./s or less. Table 2 shows the plating composition of the obtained plated steel sheet. Moreover, the result of having observed the plated steel plate by SEM from the cross section and observing the metal structure of a plating layer is similarly shown in Table 2.
[0086]
Ti-Al intermetallic compounds are obtained by polishing a plated steel sheet with a 10 degree inclination and then observing with EPMA, [Al phase], [Zn₂Those present in [Mg phase] and [Zn phase] were observed.
[0087]
The size of the [Al phase] dendrites in the plating layer was determined by mapping the surface of the plated steel plate with CMA and measuring the major axis of the resinous crystals using the resulting Al mapping. The measurement was performed in a range of 5 × 5 cm, the major diameters of five resinous crystals were measured in order from the largest, and the average value was used as the size of the [Al phase] dendrites.
[0088]
Next, FC-364S manufactured by Nihon Parkerizing Co., Ltd. was used as a degreasing agent, soaked at 2% by mass, 60 ° C. for 10 seconds, and then degreased in water washing and drying steps. Next, a base treatment material containing 2.5 parts by mass of tannic acid and 30 parts by mass of silica is applied to 100 parts by mass of the acrylic olefin resin, and dried in a hot air drying furnace to deposit 200 mg / m.²It was. The ultimate plate temperature during drying was 150 ° C. As the tannic acid, “tannic acid AL” manufactured by Fuji Chemical Industry Co., Ltd. was used. As the silica, “Snowtex N” (manufactured by Nissan Chemical Industries) was used.
[0089]
For coating, epoxy polyester paint, polyester paint, melamine polyester paint, urethane polyester paint, and acrylic paint were each coated with a bar coater, baked in a hot air drying furnace, and adjusted to the film thickness shown in Table 2.
[0090]
The sharpness was determined by measuring the sharpness measurement value (Gd value) with a portable sharpness gloss meter (PGD meter). As for the sharpness, a Gd value of 0.6 or more was accepted, and a Gd value of less than 0.6 was rejected.
[0091]
The adhesiveness of the coating film was determined by visual observation of the appearance of the extruded part when an adhesive tape was applied to a processed part extruded 7 mm using an Erichsen tester according to JIS B-7729 and peeled off vigorously. When it was difficult to evaluate visually, it was dyed with a 3% acetone solution of methyl violet, and the adhesion was evaluated on the assumption that a film was present in the stained part and no film was present in the unstained part. The score is 5 when the peeled area is less than 2%, 4 when 2 or more but less than 20%, 3 when 20% or more but 50%, 2 when 50% or more but less than 80%, and 1 when 80% or more. did.
[0092]
Corrosion resistance was tested for 72 hours in a salt spray test according to JIS Z-2371 using a Erichsen tester according to JIS B-7729, which was extruded 7 mm. What was generated was rejected.
[0093]
The evaluation results are shown in Table 2. In No. 29, the coating thickness was out of the range of the present invention, so that the corrosion resistance was unacceptable. Except for these, all showed good coating film adhesion, sharpness, and corrosion resistance.
[0094]
[Table 2]

[0095]
(Example 3)
First, a cold rolled steel sheet having a thickness of 0.85 mm was prepared, and this was hot-plated for 3 seconds in a 450 ° C. Zn—Mg—Al—Si—Ti plating bath, and N₂Wiping reduces plating adhesion on one side 140g / m²And cooled at a cooling rate of 10 ° C./s or less. The composition in the plated layer of the obtained plated steel sheet was Mg 3%, Al 11%, Si 0.2%, Ti 0.009%.
[0096]
The plated steel sheet used FC-364S manufactured by Nippon Parkerizing Co., Ltd. as a degreasing agent, was immersed in 2% by mass at 60 ° C. for 10 seconds, and then degreased in the steps of washing with water and drying. Next, a base treatment material having the composition shown in Table 3 was applied and dried in a hot air drying furnace. The ultimate plate temperature during drying was 150 ° C. As the tannic acid, “tannic acid AL” manufactured by Fuji Chemical Industry Co., Ltd., “BREWTAN” (manufactured by Omnichem), and TANAL1 (manufactured by Omnichem) were used. As the silica, “Snowtex N, described as ST-N in the table” (manufactured by Nissan Chemical Industries) was used.
[0097]
The comparative steel plate was immersed in a coating type chromate treatment solution and chromated. The amount of chromate film deposited is 50 mg / m in terms of Cr.²It was.
[0098]
Next, P641 primer paint made by Nippon Paint (polyester resin system, resin type in the table is polyester), P108 primer made by Nippon Paint (epoxy resin system, resin type in the table is epoxy), Japan Rust preventive pigments (zinc phosphite, calcium silicate, vanadic acid / phosphoric acid mixed system, molybdenum) listed in Table 2 as anticorrosive pigments for paint P304 primer (urethane resin type, resin type in the table is urethane) What was changed to (acid type) was applied with a bar coater, and baked in a hot air drying furnace under the condition that the maximum temperature reached 220 ° C., and the film thickness was adjusted to 5 μm. On the undercoat, as a topcoat, FL100HQ (polyester resin system) manufactured by Nippon Paint was applied with a bar coater, and baked in a hot air drying furnace under the condition that the ultimate plate temperature was 220 ° C., and the film thickness was adjusted to 15 μm.
[0099]
The coated steel plate produced as described above was subjected to 3T bending (180 ° bending with three original plates sandwiched), and a coating film adhesion test and a corrosion resistance test were performed on the processed part. The coating film adhesion test was evaluated based on the state of adhesion of the coating film to the adhesive tape when a pressure-sensitive adhesive tape was applied to the processed part and peeled off vigorously. The score is based on the ratio of the length of the coated film to the length tested, 0% to less than 2%, 5 to 2% to less than 5%, 4 to 5% to 30%, 3 to 30%. % Or more and less than 80% was 2, 2, 80% or more was 1, and a score of 4 or more was considered acceptable. On the other hand, the corrosion resistance test is a cyclic corrosion test consisting of salt spray (5% NaCl, 35 ° C., 2 hr) → dry (60 ° C., 30% RH, 4 hr) → wet (50 ° C., 95% RH, 2 hr). Cycled. After the cycle corrosion test, the red rust generation area ratio of the processed part was visually observed. The score is 5 for red rust less than 5%, 4 for red rust 5% to less than 10%, 3 for red rust 10% to less than 20%, 2 for 20% to less than 30%, and 1 for 30% or more. Passed.
[0100]
The sharpness was determined by measuring the sharpness measurement value (Gd value) with a portable sharpness gloss meter (PGD meter). As for the sharpness, a Gd value of 0.6 or more was accepted, and a Gd value of less than 0.6 was rejected.
[0101]
The evaluation results are shown in Table 3. In Nos. 15 and 17, since the content of tannic acid was outside the range of the present invention, the corrosion resistance of the processed part was rejected. In Nos. 16 and 18, since the adhesion amount of the ground treatment layer was outside the range of the present invention, the corrosion resistance of the processed part was rejected. In Nos. 27 and 28, since the chromate treatment was used for the base treatment layer, the environmental load was greatly rejected. Except for these, all showed good coating film adhesion, sharpness, and corrosion resistance.
[0102]
[Table 3]

[0103]
Example 4
First, a cold rolled steel sheet having a thickness of 0.85 mm was prepared, and this was subjected to hot dipping for 3 seconds in a plating bath in which the amount of additive elements in the bath was changed at 520 ° C., and N₂Wiping reduces plating adhesion on one side 140g / m²And cooled at a cooling rate of 10 ° C./s or less. Table 4 shows the plating composition of the obtained plated steel sheet. Moreover, the result of having observed the plated steel plate by SEM from the cross section and observing the metal structure of a plating layer is similarly shown in Table 4.
[0104]
Ti-Al intermetallic compounds are obtained by polishing a plated steel sheet with a 10 degree inclination and then observing with EPMA, [Al phase], [Zn₂ Those present in [Mg phase] and [Zn phase] were observed. Moreover, about the Ti-Al type intermetallic compound which exists in [Al phase], it observed by EPMA and the presence or absence in the Zn phase which precipitated by the eutectoid reaction of Zn-Al was observed. Further, EPMA observation of the Ti—Al intermetallic compound was performed, and the presence or absence of Si contained in the Ti—Al intermetallic compound was observed.
[0105]
Next, FC-364S manufactured by Nihon Parkerizing Co., Ltd. was used as a degreasing agent, soaked at 2% by mass, 60 ° C. for 10 seconds, and then degreased in water washing and drying steps. Next, a base treatment material containing 2.5 parts by mass of tannic acid and 30 parts by mass of silica is applied to 100 parts by mass of the acrylic olefin resin, and dried in a hot air drying furnace to deposit 200 mg / m.²It was. The ultimate plate temperature during drying was 150 ° C. As the tannic acid, “tannic acid AL” manufactured by Fuji Chemical Industry Co., Ltd. was used. As the silica, “Snowtex N” (manufactured by Nissan Chemical Industries) was used.
[0106]
On top of that, an epoxy polyester paint was applied as a primer with a bar coater and baked in a hot air drying furnace to adjust the film thickness to 5 μm. The top coat was coated with a polyester paint with a bar coater and baked in a hot air drying furnace to adjust the film thickness to 20 μm.
[0107]
Adhesion is a case where the adhesive tape is applied to the coated plated steel sheet after the DuPont impact test, and then peeled off. The case where the plating and the coating film are not peeled off, the case where the plating or the coating film peeling is less than 10%, The case where plating or a coating film peeled 10% or more was set as x. The DuPont test was conducted by using a shooting type having a 1/2 inch roundness at the tip and dropping a 1 kg weight from a height of 1 m.
[0108]
Corrosion resistance after processing was evaluated by the following rating of the occurrence of red rust on the bent part of the sample that had been subjected to 3T bending processing (180 ° bending processing with three original sheets sandwiched). . For CCT, one cycle was SST2hr → dry 4hr → wet 2hr. A score of 3 or more was accepted.
5: Less than 5%
4: 5% or more and less than 10%
3: 10% or more and less than 20%
2: 20% or more and less than 30%
1: 30% or more
The evaluation results are shown in Table 4. In No. 2, since the addition amount of Al and Si was outside the range of the present invention, the adhesion was rejected. Other than these, good adhesion and post-processing corrosion resistance were obtained. In particular, the plated steel sheet to which Si was added exhibited good adhesion and post-processing corrosion resistance.
[0109]
[Table 4]

[0110]
【The invention's effect】
As described above, according to the present invention, it is possible to produce a coated steel sheet that has excellent sharpness even in the case of high Al concentration and does not contain chromium with a large environmental load, and has excellent corrosion resistance of the processed part. , Industrially excellent effects can be achieved.
[Brief description of the drawings]
FIG. 1A is a drawing-substituting photomicrograph (magnification 1000 times) of a plated layer of a plated steel material of the present invention, and FIG. 1B is a diagram showing a distribution state of each structure in the photograph.
2A is a drawing-substituting micrograph (magnification of 3500 times) in which the “Al ″ phase” of FIG. 1 is enlarged, and FIG. 2B is a diagram showing a distribution state of each tissue in the photograph.

Claims

On one side or both sides of the steel sheet, there is a zinc-based plating layer containing Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, with the balance being zinc and inevitable impurities. And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer, and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer. A highly corrosion-resistant coated steel sheet with excellent image clarity and low environmental impact.

On one or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and inevitable impurities And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer. A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness, having a 2 to 100 μm-thick organic coating layer, and having a low environmental impact.

On one side or both sides of the steel sheet, there is a zinc-based plating layer containing Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, with the balance being zinc and inevitable impurities. And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer, and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer. 1 or 2 types of [Al phase], [Zn ₂ Mg phase] and [Zn phase] in the base of [Al / Zn / Zn ₂ Mg ternary eutectic structure] with the zinc-based plating layer of the coated steel plate having The above has a mixed metal structure and contains a Ti—Al intermetallic compound in one or more of [Al phase], [Zn ₂ Mg phase] and [Zn phase]. A highly corrosion-resistant coated steel sheet with excellent image clarity.

On one or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and inevitable impurities And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer. A zinc-based plating layer of a coated steel sheet having an organic coating layer having a thickness of 2 to 100 μm is in a [Al / Zn / Zn ₂ Mg ternary eutectic structure] substrate [Mg ₂ Si phase], [Al phase] and [ has a metal structure Zn ₂ Mg phase] are mixed, and a feature in that it contains Ti-Al system intermetallic compound in one or the [Al phase] [Zn ₂ Mg phase] High corrosion-resistant coated steel sheet with excellent coating film adhesion and sharpness and low environmental impact.

On one or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and inevitable impurities And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer. A zinc-based plating layer of a coated steel sheet having an organic coating layer having a thickness of 2 to 100 μm is in a [Al / Zn / Zn ₂ Mg ternary eutectic structure] substrate [Mg ₂ Si phase], [Al phase], [ [Zn ₂ Mg phase] and [Zn phase] have a mixed metal structure, and [Al phase], [Zn ₂ Mg phase] and [Zn phase] contain a Ti-Al intermetallic compound. High corrosion resistance coating with excellent coating adhesion and sharpness and low environmental impact Plate.

On one or both sides of the steel sheet, Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and inevitable impurities And a coating layer containing 100 parts by weight of an aqueous resin as a solid content and 0.2 to 50 parts by weight of tannin or tannic acid as a base treatment layer. A zinc-based plating layer of a coated steel sheet having an organic coating layer having a thickness of 2 to 100 μm is in a [Al / Zn / Zn ₂ Mg ternary eutectic structure] substrate [Mg ₂ Si phase], [Al phase] and [ A coating structure characterized by having a metal structure mixed with [Zn phase] and containing a Ti-Al intermetallic compound in one or two of [Al phase] and [Zn phase] Highly corrosion-resistant coated steel plate with excellent environmental properties and sharpness and low environmental impact.

A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness, having a low environmental load, wherein the Ti—Al intermetallic compound according to claim 3 is TiAl ₃ .

The Ti—Al-based intermetallic compound according to claim 3 is Ti (Al _1-X Si _x ) ₃ (where X = 0 to 0.5). High corrosion-resistant coated steel sheet with excellent coating adhesion and sharpness, and low environmental impact.

9. The Ti—Al-based intermetallic compound contained in the [Al phase] in the plating layer is present in a Zn phase precipitated by a Zn—Al eutectoid reaction. A highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness as described in any one and having a low environmental impact.

The size of the [Al phase] dendrites in the plating layer is 500 μm or less, and has excellent coating film adhesion and sharpness and low environmental impact. High corrosion resistance coated steel sheet.

The coating layer according to any one of claims 1 to 10, wherein the coating layer of the ground treatment layer further contains 10 to 500 parts by mass of fine silica as a solid content. High corrosion resistance coated steel sheet with low load.

12. The highly corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness and low environmental impact, according to claim 1, wherein the organic coating is a thermosetting resin coating.

The high corrosion-resistant coated steel sheet having excellent coating film adhesion and sharpness and low environmental load, according to any one of claims 1 to 12, wherein the organic coating layer comprises an undercoat layer containing a rust preventive pigment and a colored overcoat layer.

Anticorrosive pigments silicate ions, phosphate ions, vanadate ions, the coating adhesion and sharpness according to claim 13, characterized in that to release one or more of the molybdate ion High corrosion-resistant coated steel sheet with excellent environmental impact.

The adhesion amount after drying of the ground treatment layer is 10 to 3000 mg / m ^2. High corrosion resistance with excellent coating film adhesion and sharpness and low environmental impact according to any one of claims 1 to 14. Painted steel sheet.