JP3567430B2

JP3567430B2 - Painted metal plate with excellent corrosion resistance

Info

Publication number: JP3567430B2
Application number: JP2000192993A
Authority: JP
Inventors: 史城公文; 勝久大崎; 浩圓谷; 和良菅原
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 1999-07-02
Filing date: 2000-06-27
Publication date: 2004-09-22
Anticipated expiration: 2020-06-27
Also published as: JP2001329383A

Description

【０００１】
【発明が属する技術分野】
本発明は、耐食性に優れた塗装金属板に関する。より詳しくは、Ａｌ：４〜１０質量％、Ｍｇ：１〜４質量％及び残部がＺｎ及び不可避的不純物からなるＺｎ−Ａｌ−Ｍｇ系のめっき層あるいはＡｌ：４〜１０質量％、Ｍｇ：１〜４質量％、Ｔｉ：０．００２〜０．１質量％、Ｂ：０．００１〜０．４５質量％及び残部がＺｎ及び不可避的不純物からなるＺｎ−Ａｌ−Ｍｇ（−Ｔｉ−Ｂ）系のめっき層を有する耐食性に優れた塗装金属板に関する。
【０００２】
【従来の技術】
従来から建物の内・外装建材用の金属板として塗装溶融亜鉛めっき鋼板等が使用されている。近年大気汚染が進行し、大気や雨水が硫黄酸化物や窒素酸化物などにより酸性化されてきているために、このような内・外装建材用の金属板の平坦部、切断端面部及び塗膜傷付き部などの塗膜下で亜鉛めっき層の腐食速度が増大し、耐久性が懸念される状況となっている。例えば、平坦部の腐食は、Ｃｌ⁻イオン等の腐食性イオンが塗膜を透過し、亜鉛めっき層の腐食が生じて、体積膨張したＺｎ系の腐食物により塗膜を押し上げられ、その結果外観上、塗膜ふくれとして確認される。
【０００３】
そこで、このように耐食性の点で問題のある従来の溶融亜鉛めっき鋼板に代わって、塗装原板としてより優れた耐食性を有する溶融Ｚｎ−Ａｌ系めっき鋼板を使用する比率が増加する傾向にある。即ち、Ｚｎ−Ａｌ系めっき層におけるＡｌの含有量を増加させると、平坦部や塗膜傷付き部などの耐食性を向上させることができる。しかしながら、塗装溶融Ｚｎ−Ａｌめっき鋼板のＡｌの含有量を増加させると、平坦部や塗膜傷付き部などの耐食性を向上させることはできるが、切断端面部の耐食性については必ずしも満足できるものではない。例えば、塗装溶融Ｚｎ−５５％Ａｌめっき鋼板の切断端面部においては、Ｚｎ−Ａｌめっき層のＺｎ−ｒｉｃｈ相が選択に腐食されて腐食生成物が生じ、この腐食生成物により塗膜が持ち上げられて、エッジクリープと称する塗膜ふくれや塗膜の剥離が生じて、耐食性が低下するという問題がある。
【０００４】
これに対して、塗装溶融Ｚｎ−５５％Ａｌめっき鋼板の切断端面部の耐食性を改善する方法として、例えば、クロム酸ストロンチウム又はクロム酸カルシウムを下塗り塗料の不揮発分に対して３０〜７０質量％配合した塗料を用いて、端面耐食性を向上する方法（特公平２−３６３８４号公報）などが知られている。
【０００５】
しかしながら、この方法で処理された塗装溶融Ｚｎ−５５％Ａｌめっき鋼板において、塩水噴霧試験の評価では従来から使用されている下塗り塗料を用いた同塗装鋼板に比較してある程度の端面耐食性の改善が見出されたが、実使用環境の大気環境下ではその改善効果は、顕著なものではない。更に、この方法で処理された塗装溶融Ｚｎ−５５％Ａｌめっき鋼板は、高温多湿環境下で充分な耐湿性を示さず、また、平坦部でも塗膜ふくれが発生することがある。
また、建築用の内・外装建材用鋼板に加えて、冷蔵庫、洗濯機、電子レンジ等の家電製品、自動販売機、事務機器、自動車、エアコン室外機等に使用されている金属板等も同様にして、高い耐食性が望まれている。
【０００６】
【発明が解決しようとする課題】
即ち、塗装溶融Ｚｎ−Ａｌ系めっき鋼板においては、従来の塗装溶融亜鉛めっき鋼板に比べて平坦部や塗膜傷付き部などの耐食性の改善は見られたが、切断端面部の耐食性が必ずしも満足できるものではなかった。
したがって、本発明の課題は、このような問題を解決し、平坦部や塗膜傷付き部などにおける優れた耐食性と、切断端面部や塗膜傷付き部における優れた耐食性の両方を兼ね備える塗装金属板を提供することである。
【０００７】
【課題を解決するための手段】
本発明者等は、上記課題を解決するために鋭意検討した結果、金属板として特定のＺｎ−Ａｌ−Ｍｇ系のめっき層又はＺｎ−Ａｌ−Ｍｇ（−Ｔｉ−Ｂ）系のめっき層を有する金属板を使用し、その上に化成処理皮膜、下塗り塗膜及び上塗り塗膜を設けると、切断端部における耐食性と、塗膜傷付き部における耐食性がバランスよく優れているという従来技術では二律背反の性質をバランス良く兼ね備えた塗装金属板が得られることを見い出して、本発明を完成するに至った。
【０００８】
即ち、本発明の第一の態様における耐食性に優れた塗装金属板は、Ａｌ：４〜１０質量％、Ｍｇ：１〜４質量％及び残部がＺｎ及び不可避的不純物からなり、〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔初晶Ａｌ相〕又は〔初晶Ａｌ相〕と〔Ｚｎ単相〕が混在した金属組織を有しているめっき層を有する金属板に、前記めっき層の表面に形成された化成処理皮膜、前記化成処理皮膜の表面に形成された下塗り塗膜及び前記下塗り塗膜の上に形成された上塗り塗膜を設けたことを特徴とする。
【０００９】
また、本発明の第二の態様における耐食性に優れた塗装金属板は、Ａｌが４〜１０質量％、Ｍｇが１〜４質量％、Ｔｉが０．００２〜０．１質量％、Ｂが０．００１〜０．４５質量％及び残部がＺｎ及び不可避的不純物からなり、〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔初晶Ａｌ相〕又は〔初晶Ａｌ相〕と〔Ｚｎ単相〕が混在した金属組織を有しているめっき層を有する金属板を基材とし、前記めっき層の表面に形成された化成処理皮膜、前記化成処理皮膜の表面に形成された下塗り塗膜及び前記下塗り塗膜の上に形成された上塗り塗膜を設けてなることを特徴とするものである。
【００１０】
本発明に係るこれらの第一及び第二の態様における耐食性に優れた塗装金属板は、めっき層中にＡｌ及びＭｇを含有しているので金属板の平坦部の耐食性はもとより、塗装金属板の塗膜傷付き部や切断端面部近傍の塗膜下ではめっき層中のＡｌとＭｇが緻密で難溶性の腐食生成物を形成する作用を示し、さらに、この安定な腐食生成物が外部から侵入してくる腐食性イオンを遮蔽する作用を有しているため、塗膜傷付き部，切断端面やその近傍に塗膜ふくれやさびが発生しにくい。
【００１１】
また、前記第一及び第二の態様における耐食性に優れた塗装金属板において、前記化成処理皮膜が従来のクロム系化成処理皮膜でもあるいは非クロム系の化成処理膜でもよい。
クロム化合物は、環境への配慮から鋼材中に含まない方が好ましい態様が増加しつつある。従って、前記化成処理皮膜が非クロム系の化成処理膜とすると、環境への配慮のある耐久性の高い鋼板を提供することが可能となる。
【００１２】
また、前記第一及び第二の態様における耐食性に優れた塗装金属板において、化成処理皮膜の表面に防錆剤としてクロム酸ストロンチウムを不揮発成分に対して１０〜６０質量％配合した塗膜が形成された下塗り塗膜及び前記下塗り塗膜の上に形成された上塗り塗膜が設けられていることを特徴とするものである。
クロム酸ストロンチウムは、非常に優れた防錆効果を発揮する化合物である。本発明の第一及び第二の態様における塗装金属板において、化成処理皮膜の表面に防錆剤としてクロム酸ストロンチウムを使用することによって、特に塗膜傷付き部，切断端面やその近傍に対して優れた防錆効果を発揮する。
【００１３】
また、前記第一及び第二の態様における耐食性に優れた塗装金属板において、化成処理皮膜の表面に非クロム系防錆剤、例えばシリカ−カルシウム系防錆剤を不揮発成分に対して２〜５０質量％配合した塗膜が形成された下塗り塗膜及び前記下塗り塗膜の上に形成された上塗り塗膜が設けられていることを特徴とするものである。
クロム化合物は、環境への配慮から鋼材中に含まない方が好ましい態様が増加しつつある。従って、前記化成処理皮膜が非クロム系の化成処理膜とすると、環境への配慮のある耐久性の高い鋼板を提供することが可能となる。
また、前記第一及び第二の態様における耐食性に優れた塗装金属板において、化成処理皮膜の表面に防錆剤を含まない下塗り塗膜が設けられていることを特徴とするものである。
本発明において、下塗り塗膜に防錆顔料を含まなくとも同様に耐久性の高い金属板が得られる。
【００１４】
また、前記第一及び第二の態様における耐食性に優れた塗装金属板において、前記塗装金属板が、建築用の内・外装建材用鋼板、家電製品、自動販売機、事務機器、自動車又はエアコン室外機用の金属板であることを特徴とするものである。
建築用の内・外装建材用鋼板、家電製品、自動販売機、事務機器、自動車又はエアコン室外機用の金属板、特に鋼板は、高い耐久性を要求されるものである。本発明における塗装金属板を用いることによって、塗膜傷付き部，切断端面やその近傍に塗膜ふくれやさびが発生しにくい製品の製造が可能となる。
【００１５】
【発明の実施の態様】
以下、本発明の実施の態様を詳細に説明する。
本発明において使用される金属板は、Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板であって、本願出願人の特開平１０−２２６８６５公報で開示された溶融Ｚｎ−Ａｌ−Ｍｇ系めっき金属板（第一の態様）又は本願出願人の特開平１０−３０６３５７号公報で開示された溶融Ｚｎ−Ａｌ−Ｍｇ系めっき金属板（第二の態様）である。本発明の第一の態様における溶融Ｚｎ−Ａｌ−Ｍｇ系めっき金属板は、Ａｌ：４〜１０質量％、Ｍｇ：１〜４質量％及び残部がＺｎ及び不可避的不純物からなる溶融Ｚｎ−Ａｌ−Ｍｇめっき層を金属板表面に形成した耐食性に優れた溶融めっき金属板であり、めっき層が〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔初晶Ａｌ相〕又は〔初晶Ａｌ相〕と〔Ｚｎ単相〕が混在した金属組織を有している。
【００１６】
また、本発明の第二の態様における溶融Ｚｎ−Ａｌ−Ｍｇ（−Ｔｉ−Ｂ−）系めっき金属板は、Ａｌ：４〜１０質量％，Ｍｇ：１〜４質量％，Ｔｉ：０．００２〜０．１質量％、Ｂ：０．００１〜０．０４５質量％、残部がＺｎ及び不可避的不純物からなる溶融Ｚｎ−Ａｌ−Ｍｇめっき層を金属板表面に形成した耐食性に優れた溶融めっき金属板であり、めっき層が〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔初晶Ａｌ相〕又は〔初晶Ａｌ相〕と〔Ｚｎ単相〕が混在した金属組織を有している。
【００１７】
これらの第一の態様及び第二の態様における金属板の相違は、めっき層中に所定量のＴｉ及びＢを含有するか否かの点にあり、各々同様の作用効果を示すものである。
これらの第一の態様及び第二の態様における金属板におけるめっき層中のＡｌは、めっき層の耐食性の向上と当該金属板製造時のめっき浴中のドロス発生を抑制する作用を有している。Ａｌ含有量を４〜１０質量％の範囲に特定したのは下記の理由からである。
即ち、Ａｌ含有量が４質量％未満では耐食性の向上効果が十分ではなく、またＭｇ酸化物系のトップドロス発生を抑制する作用が低く、めっき後の表面平滑性が悪く塗装外観を揖ねる原因となる。逆に、Ａｌ含有量が１０質量％を超えると、めっき層と母材鋼板との界面でＦｅ−Ａｌ系合金層の成長が著しくなり、めっき層の加工性及びめっき層の密着牲が低下し、塗装鋼板を加工した場合に大きな塗膜割れ及び塗膜剥離の原因となる。最も好ましいＡｌ含有量は５．０〜７．０質量％である。
【００１８】
金属板のめっき層中のＭｇは、めっき層表面に均一かつ緻密で安定な腐食生成物を生成させて当該めっき層の耐食性を著しく高める作用を有する。Ｍｇ含有量１〜４質量％の範囲に特定したのは下記の理由からである。
即ち、Ｍｇ含有量が１質量％未満では腐食生成物を均一に生成させる作用が十分ではなく、また４質量％を超えてもＭｇによる耐食性向上効果は飽和し、逆にＭｇ酸化物系のトップドロスが発生しやすくなり塗装後の外観を損ねる原因となる。また、Ｍｇ含有量が４質量％を超えるとめっき層の加工性が低下し、塗装鋼板を加工した場合に大きな塗膜割れの原因となる。最も好ましいＭｇ含有量は２．５〜３．５質量％である。
【００１９】
このような量でＡｌ及びＭｇをＺｎ中に含むＺｎ−Ａｌ−Ｍｇの三元組成において、溶融Ｚｎ−Ａｌ−Ｍｇめっき層中にＺｎ_１１Ｍｇ_２系の相が晶出すると、Ｚｎ_１１Ｍｇ_２相は、光沢が高いため目立った模様となり表面外観を悪くするとともに耐食性も悪くなる（前記特開平１０−２２６８６５公報及び特開平１０−３０６３５７号公報参照）。このＺｎ_１１Ｍｇ_２相は、塗装後においても目立った模様となり表面外観を悪くするとともに耐食性も悪くなる。
そのため、本願出願人等が鋭意検討した結果、Ｚｎ_１１Ｍｇ_２相の大きさは溶融めっき浴温と溶融めっき層の速度に依存していることが判った（前記特開平１０−２２６８６５公報参照）。
そのため、本発明の第一の態様において使用する溶融Ｚｎ−Ａｌ−Ｍｇめっき金属板、例えば溶融Ｚｎ−Ａｌ−Ｍｇめっき鋼板の製造において、例えば溶融めっき浴の浴温を融点以上４５０℃以下とし、且つめっき後の冷却速度を１０℃／秒以上に制御すると、前記のＺｎ_１１Ｍｇ_２相は現れず、表面欠陥のない金属組織が得られる。
【００２０】
また、本発明の第二の態様において、金属板のめっき層中のＴｉ及びＢは、前記溶融Ｚｎ−Ａｌ−Ｍｇめっき層中のＺｎ_１１Ｍｇ_２相の生成・成長を抑制する作用を有する（特開平１０−３０６３５７号公報参照）。Ｚｎ_１１Ｍｇ_２相は、光沢が高いため目立った模様となり塗装後の外観を悪くするとともに耐食性も悪くなる。
この場合Ｔｉ含有量が０．００２質量％未満ではＺｎ_１１Ｍｇ_２相の生成・成長抑制効果が十分でなく、０．１質量％を超えるとめっき層中にＴｉ−Ａｌ系の析出物が成長し、めっき層表面に凹凸が生じ塗装後の外観を損ねる原因となるので、Ｔｉ含有量は０．００２〜０．１質量％の範囲内にする必要がある。Ｂ含有量が０．００１質量％未満ではＺｎ_１１Ｍｇ_２相の生成・成長抑制効果が十分でなく、０．０４５質量％を超えるとめっき層中にＴｉ−ＢあるいはＡｌ−Ｂ系の析出物が成長し、めっき層表面に凹凸が生じ、塗装後の外観を損ねる原因となるので、Ｂ含有量は０．００１〜０．０４５質量％の範囲内にする必要がある。
【００２１】
上記のような本発明の第一及び第二の態様における溶融Ｚｎ−Ａｌ−Ｍｇめっき層を有する金属板を使用すると、めっき中に４質量％以上のＡｌを含有していることによりめっき層の腐食速度や抑制され、さらにＭｇを含有していることにより、めっき層の腐食速度がさらに抑制されているので、平坦部の耐食性はもとより、塗装金属板の塗膜傷付き部や切断端面部近傍の塗膜下ではめっき層中のＡｌとＭｇが緻密で難溶性の腐食生成物を形成する作用を示し、さらに、この安定な腐食生成物が外部から侵入してくる腐食性イオンを遮蔽する作用を有しているため、塗膜傷付き部、切断端面やその近傍に塗膜ふくれやさびが発生しにくいという際立った特徴を有する。
【００２２】
本発明の塗装金属板は、従来の塗装金属板と同様に連続塗装ラインを用いて製造される。まず、上記の特定のめっき層を有する金属の表面に化成処理が施される。この際の化成処理皮膜には特に制限はなく、クロメート系皮膜であってもノンクロメート系皮膜であってもよい。例えば、クロメート系皮膜の場合、耐食性、塗膜密着性を確保するため、クロム付着量に関して全Ｃｒ量を５〜１００ｍｇ／ｍ^２にするのが好ましい。さらに、ノンクロメート系皮膜の場合、耐食性、塗膜密着性を確保するため、皮膜量を１０〜１００ｍｇ／ｍ^２にすることが好ましい。
【００２３】
本発明の第一及び第二の態様において、このようにして化成処理膜が形成されたＺｎ−Ａｌ−Ｍｇ−（Ｔｉ−Ｂ）系のめっき層を有する金属板の表面に更に下塗り塗膜を形成するが、この際の下塗り塗膜は、従来の溶融亜鉛めっき鋼板や溶融Ｚｎ−Ａｌめっき鋼板と同様の塗膜厚や塗膜樹脂を用いて同様の方法で形成することができる。
塗膜厚は従来の溶融亜鉛めっき鋼板や溶融Ｚｎ−Ａｌめっき鋼板と同様の３〜７μｍの範囲である。同様にして、塗膜樹脂として、エポキシ系、エポキシ・ウレタン系、アクリル系、ポリエステル系、フェノキシ系樹脂などを使用することができる。更に、下塗り塗料中に防錆顔料として、クロム酸ストロンチウム、クロム酸カルシウム、クロム酸バリウム、クロム酸亜鉛などのクロム酸系防錆顔料や、リン酸アルミニウム、リン酸亜鉛、リン酸カルシウム、炭酸カルシウム、シリカ−カルシウム系などのノンクロメート系の防錆顔料を単独であるいは二種類以上を塗膜樹脂に添加して下塗り塗膜を形成することができる。
【００２４】
例えば、クロム酸系防錆顔料として代表的に使用されるクロム酸ストロンチウムの場合、クロム酸ストロンチウムを不揮発分に対して１０〜６０質量％の範囲が好ましく、より好ましくは２５〜３０質量％である。一般にクロム酸ストロンチウムが１０質量％未満では、従来の溶融亜鉛めっき鋼板や溶融Ｚｎ−Ａｌめっき鋼板よりも優れた耐食性を有するが、重防食用途としては十分な耐食性が得られず、逆に６０質量％を超えても耐食性向上効果は飽和し、塗膜の加工性や塗膜密着性が低下し、塗装金属板を加工した場合に大きな塗膜割れや塗膜剥離の原因となる。
【００２５】
また、非クロメート系防錆顔料として、例えば、多孔質シリカ粒子にカルシウムイオンをイオン交換により結合させた防食抑制剤（以下、シリカ−カルシウム系と称する）の場合、シリカ−カルシウム系防錆顔料を不揮発分に対して２〜５０質量％の範囲で添加することが好ましく、より好ましくは５〜２５質量％である。
また、本発明の別の態様においては、防錆剤を添加しなくともよい場合がある。本発明の構成においては、防錆剤を添加しなくとも十分な耐久性を得られる場合があり、特に非クロメート系の化成処理膜を用いると、クロム不含の塗装金属板となる。
【００２６】
本発明において、下塗り塗膜の上に更に上塗り塗膜が形成されるが、この際の上塗り塗膜についても従来の溶融亜鉛めっき鋼板や溶融Ｚｎ−Ａｌめっき鋼板と同様の塗膜厚や塗膜樹脂を用いて同様の方法で形成することができる。
即ち、上塗り塗膜の樹脂は特に限定はされるものではなく、例えばポリエステル系、ウレタン系、アクリル系、シリコーン変性ポリエステル系、シリコーンアクリル系、ポリ塩化ビニル系及びフッ化ビニリデン系フッ素樹脂などの熱硬化型及び熱可塑型のいずれの塗膜樹脂を使用してもよい。また、顔料を含有して着色されたカラー塗膜であっても、透明なクリアー塗膜であってもよく、必要に応じてこれらの樹脂に無機系及び有機樹脂系の骨材や粉末を添加することができる。さらに、これらの塗膜は、塗料をロールコーターなどで塗装することによってあるいは樹脂フィルムを積層することによって形成することができる。
【００２７】
このようにして、金属板として本発明による特定のＺｎ−Ａｌ−Ｍｇ系めっき層（第一の態様）又はＺｎ−Ａｌ−Ｍｇ（−Ｔｉ−Ｂ）系めっき層を有する金属板を使用し、その上に化成処理膜、下塗り塗膜及び上塗り塗膜を設けると、めっき層中にＡｌ及びＭｇが含有していることにより金属板平坦部の優れた耐食性はもとより、従来技術では不可能であった、めっき金属板の端部の優れた耐食性と塗膜傷付き部の優れた耐食性を有する塗装金属板が得られ、このようにして得られた塗装金属板は、建築用の内・外装建材用金属板、冷蔵庫、洗濯機、電子レンジ等の家電製品、自動販売機、事務機器、自動車、エアコン室外機等の耐食性が要求される部材として好適に使用することが可能となる。
【００２８】
【実施例】
以下、本発明を実施例及び比較例に基づいてより詳細に説明するが、本発明は、これらの実施例に限定されるものではない。
（実施例１〜１８及び比較例１〜８）
表１に示すＺｎ、Ａｌ、Ｍｇ、Ｔｉ及びＢ含有量を有する溶融Ｚｎ−Ａｌ−Ｍｇ系のめっき鋼板及びＺｎ−Ａｌ−Ｍｇ−（Ｔｉ−Ｂ）系のめっき鋼板（板厚：０．４ｍｍ、片面めっき付着量：１２０ｇ／ｍ^２）をゼンジミア方式の連続溶融めっきライン（営業生産機）で製造した。これらのめっき鋼板を表面調整処理を施して、湯洗、水洗により洗浄し、乾燥した。しかる後、塗布型クロメート処理液［日本ペイント株式会社製、商品名；サーフコートＮＲＣ３００ＮＳ］をロールコーターで塗布して、水洗することなく１００℃で乾燥させ、全Ｃｒ量が４０ｍｇ／ｍ^２のクロメート皮膜を形成した。
【００２９】
次いで、このようにして形成したクロメート皮膜の上に、クロム酸ストロンチウムを不揮発分に対して２５質量％を配合し、その他に体質顔料として酸化チタン及びシリカ粉末を配合したエポキシ樹脂の下塗り塗料を乾燥膜厚で５μｍとなるように塗装して、２００℃で乾燥して下塗り塗膜を形成した。このようにして形成された下塗り塗膜の上に、フッ化ビニリデン系フッ素系樹脂の上塗り塗料を乾燥膜厚で２２μｍになるように塗装し、同様に２５０℃で乾燥して上塗り塗膜を形成し、上塗り塗膜としてフッ素樹脂系塗膜を有する本発明の塗装金属板１〜９を作成した（実施例１〜９）。
また、クロメート皮膜の上に、クロム酸ストロンチウムを不揮発分に対して２５質量％を配合し、その他に体質顔料として酸化チタン粉末及びシリカを配合したエポキシ樹脂の下塗り塗料を乾燥膜厚で５μｍになるように塗装して、２１５℃で乾燥後して下塗り塗膜を形成した後、ポリエステル系樹脂の上塗り塗料を乾燥膜厚で１３μｍになるように塗装し、同様に２１５℃で乾燥して上塗り塗膜を形成し、上塗り塗膜としてポリエステル系樹脂塗膜を有する本発明の塗装金属板１０〜１８を作成した（実施例１０〜１８）。
【００３０】
また、比較のために、溶融亜鉛（０．２％Ａｌ）めっき鋼板、溶融Ｚｎ−５％Ａｌめっき鋼板及び溶融Ｚｎ−５５％Ａｌめっき鋼板を使用して同様な塗装を施してフッ素系樹脂系塗膜を有する比較用塗装鋼板１〜３（比較例１〜３）及びポリエステル系樹脂を有する比較用塗装金属板５〜７を作成した（比較例５〜７）。
さらに、溶融Ｚｎ−５５％Ａｌめっき鋼板を用いて、クロム酸ストロンチウムを不揮発分に対して５０質量％を配合した下塗り塗料を塗装して、各々フッ素系樹脂上塗り塗膜及びポリエステル系上塗り塗膜を有する比較用塗装鋼板４及び８を作成した（比較例４及び比較例８）。
【００３１】
このようにして作成された本発明による塗装鋼板及び比較用塗装鋼板に対して、下記の耐食性試験を行った。
（１）促進耐食性試験
塗装鋼板の上下の切断端面及び裏面を塗料で補修し、さらに平坦部の塗膜にカッタ−ナイフで塗膜に傷を入れた試験片を６００サイクルの酸性雨複合腐食試験［１サイクル：▲１▼０．１％ＮａＣｌ腐食液噴霧（温度：３５℃×１時間、ｐＨ：４、硫酸で調整）→▲２▼乾燥（温度：５０℃×４時間）→▲３▼湿潤（温度：５０℃×３時間、相対湿度：９８％）］を行った後、補修していない切断端面から発生した塗膜ふくれ（エッジクリープ）と切断端面の切り口の赤さび発生率を測定した。また、塗膜傷付き部からのさび発生率を測定した。
補修してない切断端面からの塗膜ふくれ幅が０．５ｍｍ以下のものを記号◎、塗膜ふくれ幅が０．６〜１．０ｍｍのものを記号○、塗膜ふくれ幅が１．１〜２．０ｍｍのものを記号△、塗膜ふくれ幅が２．０ｍｍ超のものを記号×で評価した。
次に、赤さびの発生率を、切断面切り口の試験対象部の面積１００に対して、耐食試験でこの部位に生じた赤さびの発生率として求め、切断端面の切り口に赤さびの発生が認められないものを記号◎、５％以下のものを記号○、６〜２０％のものを記号△、２０％超のものを記号×で評価した。
さらに、同様に塗膜傷付き部からさびの発生が認められないものを◎、２５％以下のものを記号○、２６〜５０％のものを記号△、５０％超のものを記号×で評価した。
【００３２】
（２）屋外暴露耐食性試験
塗装鋼板の上下の切断端面及び裏面を塗料で補修した試験片を千葉県市川市の東京湾岸から８００ｍの内陸部の暴露試験場で３年３ヶ月間屋外暴露試験を行った後、補修してない切断端面から発生した塗膜ふくれの幅及び切断端面の切り口の赤さび発生率を測定した。
補修してない切断端面からの塗膜ふくれ幅が０．５ｍｍ以下のものを記号◎、０．６〜１．０ｍｍのものを記号○、１．１〜２．０ｍｍのものを記号△、２．０ｍｍ超のものを記号×で評価した。
また、切断端面の切り口に赤さびの発生が認められないものを記号◎、５％以下のものを記号０．６〜２０％以下のものを記号△、２０％超のものを記号×で評価した。
これらの結果を表１及び表２に示す。
【００３３】
【表１】

【００３４】
【表２】

【００３５】
以上の結果から、本発明の塗装鋼板は、促進耐食性及び暴露耐食性の両方に優れている。特に、本発明の塗装鋼板は、切断端面及び塗装傷付き部の耐食性の両方がバランスよく優れたものであることは特筆すべきである。
また、溶融Ｚｎ−Ａｌ−Ｍｇ系のめっき鋼板を基材として用いた実施例（実施例１〜３及び実施例７〜９）とＺｎ−Ａｌ−Ｍｇ−（Ｔｉ−Ｂ）系のめっき鋼板を基材として用いた実施例（実施例４〜６及び実施例１０〜１２）と同様に優れた効果を奏することが判った。
【００３６】
（実施例１９及び２０、参考例及び比較例１〜１１）
表３に示すＺｎ、Ａｌ、Ｍｇ、Ｔｉ及びＢを含有する溶融Ｚｎ−Ａｌ−Ｍｇ（Ｔｉ−Ｂ）系めっき鋼板と、Ｚｎ、Ａｌ及びＭｇを含有する溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板（板厚：０．４ｍｍ、片面めっき付着量：１２０ｇ／ｍ^２）をゼンジミア方式の連続溶融めっきライン（営業生産機）で製造した。これらのめっき鋼板を表面調整処理を施して、湯洗、水洗により洗浄し、乾燥した。しかる後、このようにして製造された溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板のうち一方は、（イ）塗布型のチタン系非クロム処理を両面に施し、水洗することなく到達板温１００℃で乾燥させ、全皮膜量が７５ｍｇ／ｃｍ^２のチタン系塗布型前処理皮膜を形成した。また、このようにして製造された溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板のうち他方は、（ロ）同様に塗布型クロメート処理を両面に施し、全Ｃｒ量が４０ｍｇ／ｍ^２のクロメート皮膜を形成した。
【００３７】
次いで、このようにして形成した塗装前処理皮膜の上に、体質顔料として酸化チタンとシリカ粉末を含有し、防錆顔料のないエポキシ樹脂の下塗り塗料を乾燥膜厚で５μｍとなるように塗装して、到達板温２１５℃で乾燥焼付けて下塗り塗膜を形成した。このようにして形成された下塗り塗膜の上に、ポリエステル系樹脂の上塗り塗料を乾燥膜厚で１３μｍになるように塗装し、到達板温度２１５℃で乾燥焼付けて上塗り塗膜を形成し、塗装金属板を作製した（実施例１９〜２２）。
【００３８】
一方、比較のため基材として、溶融亜鉛めっき鋼板（０．２％Ａｌ）、溶融Ｚｎ−５％Ａｌめっき鋼板を使用し、実施例と同様な処理及び塗装を施して塗装鋼板を作製した（比較例９、１１、１２、１４及び１５）。また下塗り塗料に非クロム系防錆顔料（シリカ−カルシウム系）を不揮発成分に対して２５質量％配合して塗装し、他の条件は前記と同様の工程で塗装鋼板を作製した（比較例１０、１３及び１６）。さらに、各基材に下塗り塗膜としてのクロム酸ストロンチウムを不揮発成分に対して２５質量％配合して塗装し、他の条件は前記と同様の工程で塗装鋼板を作製した（参考例及び比較例１７〜１９）。
【００３９】
このようにして作製した塗装鋼板について、前述の実施例１〜１８及び比較例１〜８と同様にして耐食性試験を行った。結果を表３に示す。
【００４０】
【表３】

【００４１】
表３の結果から、本発明の塗装鋼板は、下塗り塗料中に防錆顔料を含まずとも、耐食性に優れ、特に切断端面や塗膜損傷部の耐食性に優れることが判る。特に、クロメート皮膜を施さなかった実施例１９及び２０において同等の効果を奏することは特筆すべきことである。
【００４２】
【発明の効果】
以上のように、化成処理皮膜を形成した金属板の表面に下塗り塗膜を形成し、その上に上塗り塗膜とが形成された塗装金属板において、金属板として、Ａｌ：４〜１０質量％、Ｍｇ：１〜４質量％及び残部がＺｎ及び不可避的不純物からなるめっき層又はＡｌ：４〜１０質量％，Ｍｇ：１〜４質量％，Ｔｉ：０．００２〜０．１質量％，Ｂ：０．００１〜０．０４５質量％、残部がＺｎ及び不可避的不純物からなるめっき層を有する金属板を使用すると、めっき層中にＡｌ及びＭｇを含有しているので金属板の平坦部の耐食性はもとより、塗装金属板の塗膜傷付き部や切断端面部近傍の塗膜下ではめっき層中のＡｌとＭｇが緻密で難溶性の腐食生成物を形成する作用を示し、さらに、この安定な腐食生成物が外部から侵入してくる腐食性イオンを遮蔽する作用を有しているため、塗膜傷付き部，切断端面やその近傍に塗膜ふくれやさびが発生しにくい。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a coated metal sheet having excellent corrosion resistance. More specifically, a Zn—Al—Mg-based plating layer composed of Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and the balance being Zn and unavoidable impurities, or Al: 4 to 10% by mass, Mg: 1 ４4% by mass, Ti: 0.002 to 0.1% by mass, B: 0.001 to 0.45% by mass, and the balance being Zn and Al-Mg (-Ti-B) based on unavoidable impurities The present invention relates to a coated metal sheet having excellent corrosion resistance and having a plating layer.
[0002]
[Prior art]
2. Description of the Related Art Painted hot-dip galvanized steel sheets and the like have conventionally been used as metal sheets for building materials inside and outside of buildings. In recent years, air pollution has progressed, and the air and rainwater have been acidified by sulfur oxides and nitrogen oxides. The corrosion rate of the galvanized layer increases under a coating film such as a damaged portion, and durability is concerned. For example, the corrosion of the flat part is Cl ⁻ Corrosive ions such as ions permeate the coating film, causing corrosion of the galvanized layer and pushing up the coating film by a Zn-based corrosive substance that has expanded in volume. As a result, the coating film is visually recognized as a blister.
[0003]
Therefore, there is a tendency that the ratio of using a hot-dip Zn—Al-based coated steel sheet having better corrosion resistance as a coating base sheet instead of the conventional hot-dip galvanized steel sheet having a problem in terms of corrosion resistance is increasing. That is, when the content of Al in the Zn—Al-based plating layer is increased, the corrosion resistance of a flat portion, a coating film scratched portion, and the like can be improved. However, by increasing the Al content of the coated hot-dip Zn-Al-plated steel sheet, it is possible to improve the corrosion resistance of the flat portion and the scratched portion of the coating film, but the corrosion resistance of the cut end face portion is not always satisfactory. Absent. For example, at the cut end surface of a painted hot-dip Zn-55% Al-plated steel sheet, the Zn-rich phase of the Zn-Al plating layer is selectively corroded to produce a corrosion product, and the corrosion product raises the coating film. Therefore, there is a problem that the coating film swelling or peeling of the coating film, which is called edge creep, occurs, and the corrosion resistance is reduced.
[0004]
On the other hand, as a method of improving the corrosion resistance of the cut end face of the painted hot-dip Zn-55% Al-plated steel sheet, for example, strontium chromate or calcium chromate is blended in an amount of 30 to 70% by mass with respect to the nonvolatile content of the undercoat paint. A method of improving the end face corrosion resistance by using a coated paint (Japanese Patent Publication No. 2-36384) is known.
[0005]
However, in the coated hot-dip Zn-55% Al-plated steel sheet treated by this method, in the evaluation of the salt spray test, the end face corrosion resistance was improved to some extent as compared with the same coated steel sheet using the undercoat paint conventionally used. It has been found that the improvement effect is not remarkable under the atmospheric environment of the actual use environment. Furthermore, the coated hot-dip Zn-55% Al-plated steel sheet treated by this method does not show sufficient moisture resistance in a high-temperature and high-humidity environment, and may cause blistering of the coating film even in a flat portion.
In addition to steel plates for building interior and exterior building materials, the same applies to metal plates used in home appliances such as refrigerators, washing machines, microwave ovens, vending machines, office equipment, automobiles, and air conditioner outdoor units. Therefore, high corrosion resistance is desired.
[0006]
[Problems to be solved by the invention]
That is, in the coated hot-dip galvanized steel sheet, although the corrosion resistance of the flat portion and the damaged portion of the coating film was improved as compared with the conventional hot-dip galvanized steel sheet, the corrosion resistance of the cut end face was not always satisfactory. I couldn't do it.
Therefore, an object of the present invention is to solve such a problem, and to provide a coated metal having both excellent corrosion resistance in a flat portion and a damaged portion of a coating film and excellent corrosion resistance in a cut end surface portion and a damaged portion of a coating film. Is to provide a board.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have a specific Zn-Al-Mg-based plating layer or Zn-Al-Mg (-Ti-B) -based plating layer as a metal plate. Using a metal plate and providing a chemical conversion coating, an undercoat and an overcoat on it, the corrosion resistance at the cut end and the corrosion resistance at the scratched part of the coating are excellent in a well-balanced manner in the prior art. The present inventors have found that a coated metal plate having a good balance of properties can be obtained, and have completed the present invention.
[0008]
That is, the coated metal sheet having excellent corrosion resistance according to the first embodiment of the present invention is composed of Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and the balance consisting of Zn and inevitable impurities, [Al / Zn / Zn ₂ In a metal plate having a plating layer having a metal structure in which [primary Al phase] or [primary Al phase] and [Zn single phase] are mixed in a base material of Mg ternary eutectic structure, A chemical conversion film formed on the surface of the plating layer, an undercoat film formed on the surface of the chemical conversion film, and a topcoat film formed on the undercoat film are provided.
[0009]
Further, the coated metal sheet having excellent corrosion resistance in the second embodiment of the present invention contains 4 to 10% by mass of Al, 1 to 4% by mass of Mg, 0.002 to 0.1% by mass of Ti, and 0% of B. 0.001 to 0.45% by mass and the balance consisting of Zn and inevitable impurities, [Al / Zn / Zn ₂ The base material is a metal plate having a plating layer having a metal structure in which [primary Al phase] or a mixture of [primary Al phase] and [Zn single phase] is contained in a matrix having a ternary eutectic structure of Mg. And a chemical conversion coating formed on the surface of the plating layer, an undercoat coating formed on the surface of the chemical conversion coating and a topcoat coating formed on the undercoat coating. Is what you do.
[0010]
The coated metal plate excellent in corrosion resistance in these first and second aspects according to the present invention, since the plating layer contains Al and Mg, the corrosion resistance of the flat portion of the metal plate as well as the coated metal plate, Al and Mg in the plating layer show the action of forming a dense and hardly soluble corrosion product under the coating near the damaged part and the cut end face, and the stable corrosion product invades from the outside. Since it has an action of shielding the corrosive ions that are generated, coating film swelling and rust are less likely to occur at the damaged portion of the coating film, at the cut end surface, and in the vicinity thereof.
[0011]
In the coated metal sheet having excellent corrosion resistance according to the first and second aspects, the chemical conversion coating may be a conventional chromium-based chemical conversion coating or a non-chromium-based chemical conversion coating.
Chromium compounds are increasingly being included in steel materials in which it is preferable not to include them in consideration of the environment. Therefore, when the chemical conversion treatment film is a non-chromium-based chemical conversion treatment film, it is possible to provide a highly durable steel sheet that is environmentally friendly.
[0012]
Further, in the coated metal sheet having excellent corrosion resistance according to the first and second aspects, a coating film containing 10 to 60% by mass of strontium chromate as a rust inhibitor based on a nonvolatile component is formed on the surface of the chemical conversion coating film. And an overcoat formed on the undercoat.
Strontium chromate is a compound that exhibits a very excellent rust prevention effect. In the coated metal sheet according to the first and second aspects of the present invention, by using strontium chromate as a rust preventive on the surface of the chemical conversion coating, the coating film is particularly suitable for a damaged portion, a cut end face and its vicinity. Exhibits an excellent rust prevention effect.
[0013]
Further, in the coated metal sheet having excellent corrosion resistance in the first and second aspects, a non-chromium-based rust preventive, for example, a silica-calcium-based rust preventive is added to the surface of the chemical conversion treatment film in an amount of 2 to 50 with respect to the nonvolatile component. An undercoating film formed with a coating film in which the coating is blended by mass% and an overcoating film formed on the undercoating film are provided.
Chromium compounds are increasingly being included in steel materials in which it is preferable not to include them in consideration of the environment. Therefore, when the chemical conversion treatment film is a non-chromium-based chemical conversion treatment film, it is possible to provide a highly durable steel sheet that is environmentally friendly.
Further, in the coated metal sheet having excellent corrosion resistance according to the first and second aspects, an undercoat film containing no rust preventive agent is provided on the surface of the chemical conversion coating film.
In the present invention, a metal plate having high durability can be obtained even if the undercoating film does not contain a rust-preventive pigment.
[0014]
Further, in the coated metal sheet having excellent corrosion resistance in the first and second aspects, the coated metal sheet may be a steel sheet for building interior / exterior building materials, a home appliance, a vending machine, an office machine, an automobile or an air conditioner outdoor. It is a metal plate for a machine.
2. Description of the Related Art Steel plates for building interior and exterior building materials, home appliances, vending machines, office equipment, metal plates for automobiles or air conditioner outdoor units, particularly steel plates, are required to have high durability. By using the coated metal plate of the present invention, it is possible to manufacture a product in which coating film swelling and rust hardly occur at a portion where the coating film is damaged, at the cut end face, or in the vicinity thereof.
[0015]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present invention will be described in detail.
The metal plate used in the present invention is a Zn-Al-Mg-based plated steel plate, and is a hot-dip Zn-Al-Mg-based plated metal plate disclosed in Japanese Patent Application Laid-Open No. 10-226865 of the present applicant (the first plate). Embodiment) or a hot-dip Zn-Al-Mg-based plated metal plate (second embodiment) disclosed in Japanese Patent Application Laid-Open No. 10-306357 of the present applicant. The molten Zn—Al—Mg-based plated metal sheet according to the first aspect of the present invention is a molten Zn—Al—Mg based metal sheet containing Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and the balance being Zn and unavoidable impurities. It is a hot-dip galvanized metal plate having excellent corrosion resistance in which a Mg plating layer is formed on the surface of the metal plate, and the plating layer is [Al / Zn / Zn ₂ It has a [primary crystal Al phase] or a metal structure in which [primary crystal Al phase] and [Zn single phase] are mixed in a matrix having a ternary eutectic structure of Mg.
[0016]
Further, the hot-dip Zn—Al—Mg (—Ti—B —)-based plated metal plate in the second embodiment of the present invention has Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and Ti: 0.002. 0.1% by mass, B: 0.001% to 0.045% by mass, with the balance being a hot-dip galvanized metal having excellent corrosion resistance in which a hot-dip Zn-Al-Mg plating layer composed of Zn and unavoidable impurities is formed on the surface of the metal plate. Plate, and the plating layer is [Al / Zn / Zn ₂ It has a [primary crystal Al phase] or a metal structure in which [primary crystal Al phase] and [Zn single phase] are mixed in a matrix having a ternary eutectic structure of Mg.
[0017]
The difference between the metal plates in the first embodiment and the second embodiment lies in whether or not a predetermined amount of Ti and B is contained in the plating layer, and each shows the same effect.
Al in the plating layer of the metal plate in the first and second embodiments has an effect of improving the corrosion resistance of the plating layer and suppressing dross generation in a plating bath during the production of the metal plate. . The Al content was specified in the range of 4 to 10% by mass for the following reason.
That is, if the Al content is less than 4% by mass, the effect of improving the corrosion resistance is not sufficient, and the effect of suppressing the generation of top oxide dross of Mg oxide is low, and the surface smoothness after plating is poor, and the appearance of the coating is impaired. It becomes. Conversely, when the Al content exceeds 10% by mass, the growth of the Fe-Al-based alloy layer becomes remarkable at the interface between the plating layer and the base steel sheet, and the workability of the plating layer and the adhesion of the plating layer decrease. In addition, when a painted steel plate is processed, it causes large cracks in the coating film and peeling of the coating film. The most preferred Al content is 5.0 to 7.0% by mass.
[0018]
Mg in the plating layer of the metal plate has a function of generating a uniform, dense, and stable corrosion product on the plating layer surface, thereby significantly increasing the corrosion resistance of the plating layer. The reason for specifying the Mg content in the range of 1 to 4% by mass is as follows.
That is, if the Mg content is less than 1% by mass, the effect of uniformly generating corrosion products is not sufficient, and if it exceeds 4% by mass, the effect of improving the corrosion resistance by Mg is saturated, and conversely, the top of the Mg oxide system Dross is likely to occur, causing a deterioration in the appearance after painting. On the other hand, when the Mg content exceeds 4% by mass, the workability of the plating layer is reduced, and when a coated steel sheet is processed, it causes large coating film cracks. The most preferred Mg content is 2.5-3.5% by mass.
[0019]
In such a ternary composition of Zn-Al-Mg containing Al and Mg in Zn in such an amount, Zn is contained in the molten Zn-Al-Mg plating layer. ₁₁ Mg ₂ When the system phase is crystallized, Zn ₁₁ Mg ₂ Since the phase has a high gloss, the phase becomes a conspicuous pattern, deteriorating the surface appearance and deteriorating the corrosion resistance (see JP-A-10-226865 and JP-A-10-306357). This Zn ₁₁ Mg ₂ The phase becomes a conspicuous pattern even after painting, deteriorating the surface appearance and deteriorating corrosion resistance.
Therefore, as a result of the inventor's intensive studies, Zn ₁₁ Mg ₂ It was found that the size of the phase was dependent on the temperature of the hot-dip bath and the speed of the hot-dip layer (see JP-A-10-226865).
Therefore, in the production of a hot-dip Zn-Al-Mg-plated metal sheet used in the first embodiment of the present invention, for example, a hot-dip Zn-Al-Mg-plated steel sheet, for example, the bath temperature of a hot-dip bath is set to a melting point or higher and 450 ° C or lower, When the cooling rate after plating is controlled to 10 ° C./sec or more, the above Zn ₁₁ Mg ₂ No phase appears and a metal structure free of surface defects is obtained.
[0020]
Further, in the second aspect of the present invention, Ti and B in the plating layer of the metal plate are Zn and Zn in the molten Zn-Al-Mg plating layer. ₁₁ Mg ₂ It has the effect of suppressing the generation and growth of phases (see Japanese Patent Application Laid-Open No. 10-306357). Zn ₁₁ Mg ₂ Since the phase has high gloss, the pattern has a conspicuous pattern, deteriorates the appearance after coating, and deteriorates corrosion resistance.
In this case, if the Ti content is less than 0.002% by mass, Zn ₁₁ Mg ₂ If the effect of suppressing the generation and growth of the phase is not sufficient, and if the content exceeds 0.1% by mass, a Ti-Al-based precipitate grows in the plating layer, causing irregularities on the plating layer surface and impairing the appearance after coating. Therefore, the Ti content needs to be in the range of 0.002 to 0.1% by mass. If the B content is less than 0.001% by mass, Zn ₁₁ Mg ₂ When the effect of suppressing the generation and growth of the phase is not sufficient, and when the content exceeds 0.045% by mass, a Ti-B or Al-B-based precipitate grows in the plating layer, and irregularities are generated on the plating layer surface. The B content needs to be in the range of 0.001 to 0.045% by mass because it causes the appearance to be impaired.
[0021]
When the metal plate having the molten Zn—Al—Mg plating layer according to the first and second aspects of the present invention as described above is used, since the plating contains 4% by mass or more of Al, Corrosion rate and suppressed, furthermore by containing Mg, the corrosion rate of the plating layer is further suppressed, so not only the corrosion resistance of the flat part, but also the vicinity of the coating metal sheet scratched part and the cut end face Under the coating film, Al and Mg in the plating layer have a function of forming a dense and hardly soluble corrosion product, and furthermore, this stable corrosion product has a function of shielding corrosive ions entering from the outside. Therefore, it has a remarkable feature that coating film swelling and rust hardly occur at a portion where the coating film is damaged, at the cut end surface and in the vicinity thereof.
[0022]
The coated metal sheet of the present invention is manufactured using a continuous coating line in the same manner as a conventional coated metal sheet. First, a chemical conversion treatment is performed on the surface of the metal having the specific plating layer. The chemical conversion coating at this time is not particularly limited, and may be a chromate coating or a non-chromate coating. For example, in the case of a chromate-based film, in order to ensure corrosion resistance and film adhesion, the total amount of Cr is set to 5 to 100 mg / m2 with respect to the amount of chromium deposited. ² It is preferred that Furthermore, in the case of a non-chromate coating, the coating amount is 10 to 100 mg / m2 in order to secure corrosion resistance and coating adhesion. ² Is preferable.
[0023]
In the first and second aspects of the present invention, an undercoat film is further applied to the surface of the metal plate having the Zn-Al-Mg- (Ti-B) -based plating layer on which the chemical conversion treatment film is formed as described above. The undercoating film at this time can be formed by the same method using the same coating thickness and coating resin as the conventional hot-dip galvanized steel sheet and hot-dip Zn-Al coated steel sheet.
The coating thickness is in the range of 3 to 7 μm, which is the same as that of a conventional hot-dip galvanized steel sheet or hot-dip Zn-Al coated steel sheet. Similarly, an epoxy resin, an epoxy / urethane resin, an acrylic resin, a polyester resin, a phenoxy resin, or the like can be used as the coating resin. Further, as a rust-preventive pigment in the undercoat paint, chromic acid-based rust-preventive pigments such as strontium chromate, calcium chromate, barium chromate, zinc chromate, aluminum phosphate, zinc phosphate, calcium phosphate, calcium carbonate, silica -An undercoating film can be formed by adding a non-chromate type rust preventive pigment such as a calcium type alone or by adding two or more kinds to a coating resin.
[0024]
For example, in the case of strontium chromate which is typically used as a chromic acid-based rust preventive pigment, the content of strontium chromate is preferably in the range of 10 to 60% by mass, more preferably 25 to 30% by mass, based on the nonvolatile content. . In general, when the content of strontium chromate is less than 10% by mass, the steel sheet has better corrosion resistance than conventional hot-dip galvanized steel sheet and hot-dip Zn-Al coated steel sheet, but does not have sufficient corrosion resistance for heavy corrosion protection. %, The effect of improving the corrosion resistance is saturated, the workability of the coating film and the adhesion of the coating film are reduced, and when a coated metal plate is processed, large coating film cracking or coating film peeling is caused.
[0025]
Further, as a non-chromate rust preventive pigment, for example, in the case of an anticorrosion inhibitor in which calcium ions are bonded to porous silica particles by ion exchange (hereinafter, referred to as silica-calcium), a silica-calcium rust preventive pigment is used. It is preferably added in the range of 2 to 50% by mass, more preferably 5 to 25% by mass, based on the nonvolatile content.
In another embodiment of the present invention, it may not be necessary to add a rust inhibitor. In the structure of the present invention, sufficient durability may be obtained without adding a rust preventive agent. In particular, when a non-chromate chemical conversion film is used, a chromium-free coated metal plate is obtained.
[0026]
In the present invention, an overcoat film is further formed on the undercoat film, and the overcoat film at this time also has the same coating thickness and coating as the conventional hot-dip galvanized steel sheet or hot-dip Zn-Al coated steel sheet. It can be formed by a similar method using a resin.
That is, the resin of the overcoat film is not particularly limited, and for example, a heat-sensitive resin such as a polyester resin, a urethane resin, an acrylic resin, a silicone-modified polyester resin, a silicone acrylic resin, a polyvinyl chloride resin, and a vinylidene fluoride fluororesin. Either a curing type or a thermoplastic type coating resin may be used. Also, it may be a color coating coated with pigments or a transparent clear coating, and if necessary, an inorganic or organic resin-based aggregate or powder may be added to these resins. can do. Further, these coating films can be formed by applying a paint with a roll coater or the like or by laminating resin films.
[0027]
Thus, a metal plate having a specific Zn-Al-Mg-based plating layer (first embodiment) or a Zn-Al-Mg (-Ti-B) -based plating layer according to the present invention is used as the metal plate, If a chemical conversion treatment film, an undercoat film, and an overcoat film are provided thereon, since the plating layer contains Al and Mg, not only the excellent corrosion resistance of the flat portion of the metal plate but also impossible with the conventional technology. In addition, a coated metal plate having excellent corrosion resistance at the edge of the plated metal plate and excellent corrosion resistance at the portion with a coating film flaw can be obtained, and the coated metal plate thus obtained is used for interior and exterior building materials for construction. It can be suitably used as a metal plate, refrigerator, washing machine, household electric appliance such as a microwave oven, a vending machine, an office machine, a car, an outdoor unit of an air conditioner, or the like, which is required to have corrosion resistance.
[0028]
【Example】
Hereinafter, the present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to these examples.
(Examples 1 to 18 and Comparative Examples 1 to 8)
Hot-dip Zn-Al-Mg-based plated steel sheet and Zn-Al-Mg- (Ti-B) -based plated steel sheet having a Zn, Al, Mg, Ti and B content shown in Table 1 (sheet thickness: 0.4 mm) , Single-side plating adhesion amount: 120 g / m ² ) Was manufactured on a continuous hot-dip galvanizing line (commercial production machine) of Sendzimir method. These plated steel sheets were subjected to a surface conditioning treatment, washed with hot water and water, and dried. Thereafter, a coating type chromate treatment solution [Nippon Paint Co., Ltd., trade name; Surfcoat NRC300NS] is applied by a roll coater and dried at 100 ° C. without washing with water, and the total amount of Cr is 40 mg / m 2. ² Was formed.
[0029]
Next, on the chromate film formed in this manner, strontium chromate was blended at 25% by mass with respect to the non-volatile content, and an undercoat paint of an epoxy resin blended with titanium oxide and silica powder as an extender was dried. It was applied to a thickness of 5 μm and dried at 200 ° C. to form an undercoat film. On the undercoat film thus formed, a topcoat of vinylidene fluoride-based fluororesin is applied to a dry film thickness of 22 μm, and dried at 250 ° C. in the same manner to form an overcoat film. Then, coated metal plates 1 to 9 of the present invention having a fluororesin-based coating film as a top coating film were prepared (Examples 1 to 9).
On the chromate film, an undercoat paint of epoxy resin containing strontium chromate in an amount of 25% by mass based on the non-volatile content and titanium oxide powder and silica as an extender is 5 μm in dry film thickness. After drying at 215 ° C to form an undercoat film, a polyester resin topcoat is applied to a dry film thickness of 13 µm and dried at 215 ° C in the same manner. Films were formed, and coated metal plates 10 to 18 of the present invention having a polyester-based resin coating film as an overcoat coating film were prepared (Examples 10 to 18).
[0030]
For comparison, a similar coating was performed using a hot-dip zinc (0.2% Al) -plated steel sheet, a hot-dip Zn-5% Al-plated steel sheet, and a hot-dip Zn-55% Al-plated steel sheet to form a fluororesin-based resin. Comparative coated steel plates 1 to 3 having a coating film (Comparative Examples 1 to 3) and comparative coated metal plates 5 to 7 having a polyester resin were prepared (Comparative Examples 5 to 7).
Further, using a hot-dip Zn-55% Al-plated steel sheet, an undercoat paint containing 50% by mass of strontium chromate with respect to the non-volatile content is applied, and a fluororesin top coat and a polyester top coat are respectively formed. Comparative coated steel sheets 4 and 8 were prepared (Comparative Examples 4 and 8).
[0031]
The coated steel sheet according to the present invention and the comparative coated steel sheet thus prepared were subjected to the following corrosion resistance test.
(1) Accelerated corrosion resistance test
The coated upper and lower cut end surfaces and the back surface were repaired with paint, and the coating film on the flat part was scratched with a cutter knife. A 600-cycle acid rain combined corrosion test [1 cycle: ▲ 1] ▼ Spraying 0.1% NaCl etchant (temperature: 35 ° C x 1 hour, pH: 4, adjusted with sulfuric acid) → 2) Drying (temperature: 50 ° C x 4 hours) → 3) Wet (temperature: 50 ° C) × 3 hours, relative humidity: 98%)], and the coating bulge (edge creep) generated from the unrepaired cut end face and the occurrence rate of red rust at the cut end of the cut end face were measured. Further, the rust generation rate from the scratched portion of the coating film was measured.
The symbol ◎ indicates that the coating blister width from the cut end face not repaired was 0.5 mm or less, the symbol ○ indicates that the coating blister width was 0.6 to 1.0 mm, and the coating blister width was 1.1 to 1.1. Those having a thickness of 2.0 mm were evaluated with a symbol △, and those having a coating blister width of more than 2.0 mm were evaluated with a symbol x.
Next, the rate of occurrence of red rust was determined as the rate of occurrence of red rust generated in this portion in a corrosion resistance test with respect to the area 100 of the test target portion of the cut surface cut face, and no occurrence of red rust was observed at the cut face of the cut end face. Those were evaluated with the symbol ◎, those with 5% or less were evaluated with the symbol ○, those with 6 to 20% were evaluated with the symbol △, and those with more than 20% were evaluated with the symbol ×.
Further, similarly, ◎ indicates no occurrence of rust from the scratched portion of the coating film, 、 indicates 25% or less, △ indicates 26-50%, and × indicates more than 50%. did.
[0032]
(2) Outdoor exposure corrosion resistance test
The test specimens whose upper and lower cut ends and the back side of the coated steel plate were repaired with paint were not repaired after performing an outdoor exposure test for 3 years and 3 months at an exposure test site 800 m inland from Tokyo Bay shore in Ichikawa City, Chiba Prefecture. The width of the coating blister generated from the cut end face and the rate of occurrence of red rust at the cut end of the cut end face were measured.
The symbol ◎ indicates that the coating blister width from the unrepaired cut end face is 0.5 mm or less, the symbol ０．６ indicates 0.6 to 1.0 mm, and the symbol △ indicates 1.1 to 2.0 mm. Those having a diameter of more than 0.0 mm were evaluated with the symbol x.
In addition, the symbol ◎ indicates that no red rust was observed at the cut edge of the cut end face, and the symbol 、５ indicates the symbol of 5% or less and the symbol ０．６ indicates the symbol of 0.6 to 20% or less, and the symbol × indicates that the symbol exceeded 20%. .
Tables 1 and 2 show these results.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
From the above results, the coated steel sheet of the present invention is excellent in both accelerated corrosion resistance and exposure corrosion resistance. In particular, it should be noted that the coated steel sheet of the present invention is excellent in both the cut end face and the corrosion resistance of the coating scratched part in a well-balanced manner.
Further, Examples (Examples 1 to 3 and Examples 7 to 9) using a hot-dip Zn-Al-Mg-based plated steel sheet as a base material and Zn-Al-Mg- (Ti-B) -based plated steel sheets were used. It was found that excellent effects were obtained as in the examples (Examples 4 to 6 and Examples 10 to 12) used as the base material.
[0036]
(Examples 19 and 20, Reference Examples and Comparative Examples 1 to 11)
Hot-dip Zn-Al-Mg (Ti-B) -based plated steel sheet containing Zn, Al, Mg, Ti and B shown in Table 3, and hot-dip Zn-Al-Mg-based plated steel sheet containing Zn, Al and Mg ( Plate thickness: 0.4 mm, single-side plating adhesion amount: 120 g / m ² ) Was manufactured on a continuous hot-dip galvanizing line (commercial production machine) of Sendzimir method. These plated steel sheets were subjected to a surface conditioning treatment, washed with hot water and water, and dried. Thereafter, one of the hot-dip Zn—Al—Mg-based plated steel sheets produced in this manner is subjected to (a) a coating-type titanium-based non-chromium treatment on both sides, and at a final sheet temperature of 100 ° C. without washing with water. Dry, total film weight 75mg / cm ² A titanium-based coating type pretreatment film was formed. The other of the hot-dip Zn—Al—Mg-based coated steel sheets produced in this manner is subjected to the coating-type chromate treatment on both sides in the same manner as in (b), and the total Cr content is 40 mg / m 2. ² Was formed.
[0037]
Then, an undercoat paint of epoxy resin containing titanium oxide and silica powder as an extender pigment and having no rust preventive pigment was applied on the thus-prepared pre-coating film so as to have a dry film thickness of 5 μm. Then, it was dried and baked at an ultimate plate temperature of 215 ° C. to form an undercoat film. On the undercoat film thus formed, a top coat of polyester resin is applied so as to have a dry film thickness of 13 μm, and dried and baked at an ultimate plate temperature of 215 ° C. to form an overcoat film. Metal plates were produced (Examples 19 to 22).
[0038]
On the other hand, for comparison, a hot-dip galvanized steel sheet (0.2% Al) and a hot-dip Zn-5% Al-plated steel sheet were used as the base material, and the same treatment and coating as in the example were performed to produce a coated steel sheet ( Comparative Examples 9, 11, 12, 14, and 15). A non-chromic rust-preventive pigment (silica-calcium-based) was added to the undercoat paint in an amount of 25% by mass based on the nonvolatile component, and the coated steel sheet was prepared in the same manner as described above under other conditions (Comparative Example 10). , 13 and 16). Further, each substrate was coated with 25% by mass of strontium chromate as an undercoating film based on the non-volatile component, and coated, and the other conditions were the same as those described above to produce a coated steel sheet (Reference Example and Comparative Example). 17-19).
[0039]
A corrosion resistance test was performed on the coated steel sheet thus produced in the same manner as in Examples 1 to 18 and Comparative Examples 1 to 8 described above. Table 3 shows the results.
[0040]
[Table 3]

[0041]
From the results shown in Table 3, it can be seen that the coated steel sheet of the present invention is excellent in corrosion resistance even if the undercoat paint does not contain a rust-preventive pigment, and particularly excellent in the cut end face and the coating film damaged portion. In particular, it is remarkable that the same effects are obtained in Examples 19 and 20 in which the chromate film was not applied.
[0042]
【The invention's effect】
As described above, in the coated metal plate on which the undercoating film is formed on the surface of the metal plate on which the chemical conversion coating film is formed, and on which the overcoating film is formed, as the metal plate, Al: 4 to 10% by mass , Mg: 1 to 4% by mass and the balance being Zn and unavoidable impurities or a plating layer or Al: 4 to 10% by mass, Mg: 1 to 4% by mass, Ti: 0.002 to 0.1% by mass, B : When a metal plate having a plating layer composed of 0.001 to 0.045% by mass, the balance being Zn and unavoidable impurities is used, since the plating layer contains Al and Mg, the corrosion resistance of the flat portion of the metal plate Of course, under the coating near the coating scratched portion or cut end surface of the coated metal plate, Al and Mg in the plating layer show a dense and hardly soluble corrosion product, and furthermore, this stable Corrosive ions from which corrosion products enter from outside Because it has the effect of shielding, coating scratch portion, coating Fukureya rust hardly occurs to the cut end surface and the vicinity thereof.

Claims

Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and the balance consisting of Zn and unavoidable impurities, and in the [Al / Zn / Zn ₂ Mg ternary eutectic structure] base material, ] Or [Primary Al phase] and [Zn single phase] a metal plate having a plating layer having a mixed metal structure, a chemical conversion coating formed on the surface of the plating layer, the conversion coating A coated metal sheet having excellent corrosion resistance, comprising an undercoat film formed on the surface and an overcoat film formed on the undercoat film.

Al is 4 to 10% by mass, Mg is 1 to 4% by mass, Ti is 0.002 to 0.1% by mass, B is 0.001 to 0.45% by mass, and the balance is Zn and unavoidable impurities. A plating layer having a metal structure in which [primary Al phase] or [primary Al phase] and [Zn single phase] are mixed in a [Al / Zn / Zn ₂ Mg ternary eutectic] base material With a metal plate having a base material, a chemical conversion coating formed on the surface of the plating layer, an undercoat formed on the surface of the chemical conversion coating, and a topcoat formed on the undercoat. Painted metal plate with excellent corrosion resistance.

The coated metal sheet having excellent corrosion resistance according to claim 1 or 2, wherein the chemical conversion treatment film is a non-chromium-based chemical conversion treatment film.

An undercoating film formed on the surface of the chemical conversion coating film by adding 10 to 60% by mass of strontium chromate as a rust inhibitor to a nonvolatile component, and an overcoating film formed on the undercoating film. The coated metal sheet excellent in corrosion resistance according to any one of claims 1 to 3, wherein the coated metal sheet is provided.

On the surface of the chemical conversion coating film, an undercoat film formed by coating a non-chromium-based rust inhibitor in an amount of 2 to 50% by mass with respect to the nonvolatile component is formed, and an overcoat film formed on the undercoat film is provided. The coated metal sheet excellent in corrosion resistance according to any one of claims 1 to 3, characterized in that the metal sheet is coated.

The coated metal excellent in corrosion resistance according to any one of claims 1 to 3, wherein the undercoat formed on the surface of the chemical conversion coating contains no rust preventive other than the extender pigment. Board.

7. The coated metal plate according to claim 1, wherein the metal plate is a steel plate for building interior and exterior building materials, a home appliance, a vending machine, an office machine, a car or an outdoor unit of an air conditioner. A coated metal steel sheet having excellent corrosion resistance according to any one of the preceding claims.