JP3810677B2 - Coating plate, surface preparation method of coating plate and method of manufacturing coated steel plate with excellent corrosion resistance - Google Patents
Coating plate, surface preparation method of coating plate and method of manufacturing coated steel plate with excellent corrosion resistance Download PDFInfo
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- JP3810677B2 JP3810677B2 JP2001375868A JP2001375868A JP3810677B2 JP 3810677 B2 JP3810677 B2 JP 3810677B2 JP 2001375868 A JP2001375868 A JP 2001375868A JP 2001375868 A JP2001375868 A JP 2001375868A JP 3810677 B2 JP3810677 B2 JP 3810677B2
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
- C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
- C23C28/3225—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only with at least one zinc-based layer
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
- C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
Description
【０００１】
【産業上の利用分野】
本発明は、溶融亜鉛めっき鋼板，溶融Ｚｎ−Ａｌ系めっき鋼板あるいは溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板を塗装原板として、これに塗布型クロメート処理液を塗布するクロメート処理を施した後、樹脂塗装を施して塗装鋼板を製造する際の塗装原板の表面調整技術に関する。
【０００２】
【従来の技術】
溶融亜鉛めっき鋼板，溶融Ｚｎ−Ａｌ系めっき鋼板あるいは溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板に樹脂塗装する前の塗装前処理として、通常、塗布型クロメート処理が行われている。この処理は、めっき鋼板に直接あるいは脱脂処理しただけで塗布したのでは、めっき鋼板表面の濡れ性が悪く、クロメート液を塗布しても、均一なクロメート皮膜の形成が困難で、クロメート処理皮膜の密着性も劣り、塗装後の塗膜剥離が生じる原因となる。このため、クロメート液を塗布する前に塗装原板を表面調整することが必要不可欠になっている。この表面調整方法として、従来から、Ｎｉイオンを含む酸性水溶液で塗装原板を処理して、金属Ｎｉをめっき層の表面に置換析出させている。
【０００３】
【発明が解決しようとする課題】
しかしながら、この表面調整液はｐＨ：２．５〜３．５の酸性であり、例えば、溶融亜鉛めっき鋼板や溶融Ｚｎ−Ａｌ系めっき鋼板の場合、表面調整処理でめっき極表層部に濃化した耐食性に優れたＡｌ系酸化物がエッチングされ、また、溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板では、表面調整処理でめっき極表層部に濃化した耐食性に優れたＭｇ系酸化物およびＡｌ系酸化物がエッチングされることになる。その結果、塗装原板のめっき層表面部と下塗り塗膜との界面腐食を低下させるものであった。特に、塗装鋼板を折り曲げ加工して、めっき層と塗膜に割れが無数に生じた部位では、他の平坦部や塗膜傷付き部等の耐食性に比べて満足できるものではなかった。
【０００４】
近年、大気汚染の進行に伴ってイオウ酸化物，窒素酸化物等による大気や雨水の酸性化が著しく、塗装鋼板の折り曲げ加工部，切断端面部，塗膜傷付き部等の塗膜下でめっき層の腐食が促進されることから、外装建材等として用いられる塗装鋼板の耐久性が懸念される状況になっている。塗装鋼板は成形加工されて使用されるため、平坦部を除けば折り曲げ加工部が製品に占める割合が最も高い。そこで、特に折り曲げ加工部の耐食性向上が望まれている。
【０００５】
溶融Ｚｎ−Ａｌ系めっき鋼板では、めっき層のＡｌ含有量を増加させると、折り曲げ加工部，平坦部および塗膜傷付き部の耐蝕性が増加する。しかし、Ａｌ含有量を増加しても、切断端面部の耐食性は必ずしも満足されない。例えば、塗装溶融Ｚｎ−５５％Ａｌめっき鋼板の切断端面では、めっき層のＺｎリッチ相が選択的に腐食される。腐食生成物によって塗膜が持ち上げられると、エッジクリープと称される塗膜膨れや塗膜の剥離が生じ、塗膜との組み合わせによっては、耐食性が低下する場合がある。このように、塗装原板のめっき層のＡｌ含有量を増加しても、必ずしも、平坦部，折り曲げ加工部，塗膜傷付き部および切断端面部の全ての耐食性が向上するものではなく、バランスがとれた塗装鋼板を得ることはできなかった。
【０００６】
本発明は、このような問題を解消すべく案出されたものであり、溶融亜鉛めっき鋼板，溶融Ｚｎ−Ａｌ系めっき鋼板または溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板からなる塗装原板を、Ｎｉイオンの他にＭｇイオンを含む表面調整液で処理して、塗布型クロメート処理液を塗布する直前のめっき層表面にＭｇを置換析出させることによって、塗装後、塗膜密着性は勿論、折り曲げ加工部において優れた耐食性を有するクロム系塗装鋼板を得ることを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、その目的を達成するため、溶融亜鉛めっき鋼板，溶融Ｚｎ−Ａｌ系めっき鋼板または溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板からなる塗装原板を、Ｎｉイオンの他に１０〜１００００ｐｐｍのＭｇイオンを含有する酸性水溶液（ただし、りん酸塩処理液を除く）で処理して表面調整し、めっき層表面にＭｇ換算付着量で０．１〜１００ｍｇ／ｍ2のＭｇ化合物を置換析出させることを特徴とする。
その後、塗布型クロメート処理液を塗布するクロメート処理を施した後、樹脂塗装する。
【０００８】
【作用】
表面調整液は酸性であるために、表面調整で溶融亜鉛めっき鋼板や溶融Ｚｎ−Ａｌ系めっき鋼板のめっき極表層部に濃化した耐食性に優れたＡｌ系酸化物がエッチングされ、また、溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板ではめっき極表層部に濃化した耐食性に優れるＭｇ系酸化物およびＡｌ系酸化物がエッチングされる。しかし、表面調整液中にあらかじめＭｇイオンを含有させておくと、表面調整した後のめっき層表面に水溶液中のＭｇが、金属Ｍｇの他に、例えばＭｇ（ＯＨ）2，ＭｇＡｌ2Ｏ4，ＭｇＦ2等として置換析出する。本発明では、これらの析出物をＭｇ化合物と総称する。この化合物中のＭｇの作用により、めっき層と塗膜に微細割れが生じた塗装鋼板の折り曲げ加工部のめっき層の腐食が抑制される。また、めっき層と下塗り塗膜の界面近傍の腐食も抑制され、めっき層と下塗り塗膜近傍での塗膜膨れや、それに続くめっき層自体の塗膜下腐食が抑制される。
【０００９】
塗装原板のめっき層表面にＭｇ化合物が置換析出した上に塗布型クロメート処理液を塗布すると、表面調整処理でめっき層の表層部に置換析出した化合物中のＭｇが塗布型クロメート処理液の酸成分によってイオン化して溶出する。その結果、めっき層表面から溶出してきたＭｇイオンとクロメート処理液中の有機樹脂（アクリル樹脂）が複合されたクロメート皮膜がめっき層表面に形成される。
【００１０】
めっき層の表層部に置換析出した化合物中のＭｇによる塗装鋼板の折り曲げ加工部の耐食性向上の理由は明らかではないが、めっき層の表層に置換析出したＭｇがクロメート皮膜に取り込まれるため、クロメート皮膜は、優れた付着性でめっき層に付着し、耐湿性も向上する。また、めっき層の表層からクロメート皮膜中に取り込まれたＭｇは腐食環境下において溶出し、めっき層と下塗り塗膜との界面腐食が抑制され、さらに、微細なめっき層と塗膜割れ部に緻密で難溶性のＺｎの腐食生成物を形成・蓄積させる。生成したＭｇを含有する腐食生成物は、外部から侵入してくる腐食性イオンに対するバリアとしても作用する。その結果、塗膜下におけるめっき層の腐食が抑制されると推察される。
【００１１】
【発明の実施の態様】
本発明に使用される塗装原板としては、通常、連続溶融めっきラインでＺｎめっき層，Ｚｎ−Ａｌ系めっき層あるいはＺｎ−Ａｌ−Ｍｇ系めっき層が形成された、溶融亜鉛メッキ鋼板，溶融Ｚｎ−５％Ａｌ系めっき鋼板，溶融Ｚｎ−４〜２２％Ａｌ−１〜４Ｍｇ（−Ｔｉ−Ｂ−Ｓｉ）系めっき鋼板が挙げられる。連続塗装ラインでは、前記塗装原板表面に塗装前処理としてのクロメート処理に先立ち、塗装原板の溶融めっき層の濡れ性を良くして、均一なクロメート皮膜を形成させるための表面調整処理が施される。
【００１２】
酸性表面調整処理液は、従来から一般に使用されているＮｉイオンを含有する市販の水溶液にＭｇイオンを１０〜１００００ｐｐｍ添加して調整される。酸性表面調整処理液中にＭｇイオンを含有させる手法は特に限定されないが、Ｎｉイオンを含む水溶液として主に硫酸塩系のものが用いられる場合が多いため、硫酸マグネシウム（七水和物）を添加することが好ましい。この表面調整処理液に漬すかスプレーして、数秒間処理した後、水洗・乾燥すると、処理後の塗装原板のめっき層表面には、Ｍｇ化合物がＭｇ換算付着量で０．１〜１００ｍｇ／ｍ2で置換析出している。その後クロメート処理と塗装を施した塗装鋼板の加工部の耐食性は、酸性表面調整処理液中のＭｇイオン濃度が１０ｐｐｍ未満、めっき層表面に置換析出したＭｇ量が０．１ｍｇ／ｍ2未満では、塗装鋼板の折り曲げ加工部の耐食性向上が十分発現されない。逆に、酸性表面調整処理液中のＭｇイオン濃度が１００００ｐｐｍを超え、めっき層表面のＭｇ析出量が１００ｍｇ／ｍ2を超えても、塗装鋼板の折り曲げ加工部の耐食性がさらに向上することはない。過多のＭｇ含有は、表面調整液をコスト高にすることからもメリットはない。
【００１３】
表面調整された塗装原板には、従来と同様なクロメート皮膜を塗装原板の表面に形成することにより、塗膜密着性を向上させる。クロメート皮膜は、耐食性および塗膜密着性を確保するためにＣｒ換算付着量５〜１００ｍｇ／ｍ2の割合で形成することが好ましい。このクロム付着量は、クロメート皮膜が水溶性もしくは水分散性の樹脂やシリカを含有する場合でも、クロメート皮膜がリン酸−クロム酸系処理液により形成されたものであっても同様とする。
【００１４】
クロメート皮膜が形成された塗装原板の表面には、従来と同様の樹脂塗膜を従来と同様の方法で形成する。
この際の下塗り塗膜樹脂には、エポキシ系，エポキシ・ウレタン系，ポリエステル系，アクリル系，エポキシ変性ポリエステル系，フェノキシ系等の樹脂が使用される。下塗り塗膜の膜厚は、従来と同様の３〜１０μｍの範囲とする。また、下塗り塗膜樹脂には、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，クロム酸亜鉛等のクロム酸系防錆顔料を、単独であるいは２種以上組み合わせて添加して下塗り塗膜を形成することもできる。さらに、下塗り塗膜樹脂には、防錆顔料の他に酸化チタン等の着色顔料、炭酸カルシウム，硫酸バリウム等の体質顔料や各種の有機樹脂ビーズ，有機樹脂粉末，無機骨材等の添加剤を含有してもよい。下塗り塗膜樹脂の分子量，ガラス転移温度あるいは顔料，骨材等の添加量は、塗装鋼板の用途に応じて適宜調整される。
【００１５】
下塗り塗膜の上にはさらに上塗り塗膜が形成される。
この際の上塗り塗膜樹脂には、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，ポリフッ化ビニリデン−アクリル系等、熱硬化性樹脂または熱可塑性樹脂が使用される。また、必要に応じ有機系骨材，無機系骨材，メタリック粉末，潤滑剤，汚れ防止剤，防かび剤，紫外線吸収剤，光安定剤（酸化防止剤），光触媒粒子，つや消し剤や各種の粉末等が添加される。
【００１６】
このように、溶融亜鉛めっき鋼板，溶融Ｚｎ−Ａｌ系めっき鋼板あるいは溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板からなる塗装原板を、Ｍｇイオンを１０〜１００００ｐｐｍ添加した酸性の表面調整液で処理すると、塗装原板のめっき層表面にＭｇが０．１〜１００ｍｇ／ｍ2の範囲で置換析出する。その上に塗布型クロメート液を塗布すると、めっき層の表層部に置換析出したＭｇが塗布型クロメート処理液中に溶出する。この処理液皮膜を乾燥すると、めっき層表面から溶出したＭｇイオンとクロメート処理液中の有機樹脂が複合された、優れた付着性，耐湿性，耐食性を有するクロメート皮膜がめっき層表面に形成される。めっき層の表層からクロメート皮膜中に取り込まれたＭｇは腐食環境下において溶出し、めっき層と下塗り塗膜との界面近傍が選択的に腐食される界面腐食が抑制される。さらに、Ｍｇは、微細なめっき層と塗膜割れ部に緻密で難溶性のＺｎの腐食生成物を形成・蓄積させる。生成した均一かつ緻密で安定なＭｇを含有する腐食生成物は、外部から侵入してくる腐食性イオンに対するバリアとしても作用する。その結果、加工部の耐食性に優れた塗装鋼板が得られる。
【００１７】
【実施例】
表１に示す、溶融亜鉛めっき鋼板（板厚：０．６ｍｍ，片面メッキ付着量：１４０ｇ／ｍ2）、溶融Ｚｎ−４％Ａｌ−０．１％Ｍｇめっき鋼板（板厚：０．６ｍｍ，片面メッキ付着量：１３５ｇ／ｍ2）、および溶融Ｚｎ−６％Ａｌ−３％Ｍｇ（−Ｔｉ−Ｂ）めっき鋼板（板厚：０．６ｍｍ，片面メッキ付着量：１２０ｇ／ｍ2）をゼンジミア方式の連続溶融めっきラインで製造した。
【００１８】
これらのめっき鋼板を、Ｎｉイオンを含有する酸性表面調整液（日本ペイント株式会社製、商品名：ＮＰコンディショナー７１０）に硫酸マグネシウム七水和物を添加してＭｇイオン濃度を２０００ｐｐｍに調整した。さらに、液温６５℃でｐＨ２．５〜３．５に調整した後に水溶液をスプレーし、その後、水洗により洗浄して乾燥した。
乾燥後のめっき層の表面には、Ｍｇ換算付着量で２０ｍｇ／ｍ2の割合でＭｇ化合物が析出していた。比較のため、同様にＭｇイオンを添加しない酸性表面調整液をスプレーした後、水洗により洗浄して乾燥した。表面調整処理後のめっき層表面のＭｇ析出量を表２に示す。
【００２０】
その後、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換算付着量が４０ｍｇ／ｍ2のクロメート皮膜を形成した。
次いで、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、その他に着色顔料として酸化チタン，体質顔料として硫酸バリウムおよ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になるように塗装し、２１５℃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、ポリエステル系樹脂の上塗り塗料を乾燥膜厚で１５μｍ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た。
【００２２】
このようにして作製された各塗装鋼板から試験片を切り出し、次の塗膜密着性試験、促進耐食性試験に供した。
塗膜密着性試験では、２０℃に調整された室内で評価する塗膜面が外側になるように２ｔの１８０度の折り曲げ加工を施し、その折り曲げ部に粘着テープを貼り付け引き剥がし、塗膜の剥離状況を観察した。観察結果から、塗膜剥離が発生しなかったものを◎，剥離が発生したものを×として塗膜密着性を評価した。
【００２３】
促進耐食性試験では、塗装鋼板の上部の塗膜面が外側になるように４ｔ折り曲げ加工を施した後に、左部，右部，下部の切断端面および裏面を塗料で補修した試験片を用意した。６００サイクルの酸性雨複合腐食試験［１サイクル：０．１％ＮａＣｌ腐食液噴霧（３５℃×１時間，硫酸でｐＨ４に調整）→乾燥（５０℃×４時間）→湿潤（５０℃×３時間，相対湿度９８％）後に、４ｔ折り曲げ加工部から発生した白錆び発生率を測定した。
【００２４】
白錆び発生率は、酸性雨複合腐食試験で４ｔ折り曲げ加工部に発生した白錆びを観察し、試験対象部の面積１００に対する白錆びの発生率（％）を求めた。
４ｔ折り曲げ加工部に白錆びが検出されなかったものを◎，５％以下を○，５〜２０％を△，２０％以上を×として耐白錆び性を評価した。
各評価試験結果を表３に示す。
【００２５】
表３の結果からわかるように、Ｍｇイオンを２０００ｐｐｍ添加した表面調整液で処理しためっき鋼板を塗装原板とした試験番号１〜３では、屋外での腐食挙動を再現する酸性雨促進耐食性試験において、折り曲げ加工部の白錆びの発生率が低く、優れた加工部耐食性を示していた。
これに対して、従来のＭｇイオン無添加の表面調整液で処理しためっき鋼板を塗装原板とする試験番号４〜６では、折り曲げ加工部の白錆び発生率は高く、加工部耐食性は十分ではなかった。
【００２７】
【発明の効果】
以上に説明したように、溶融亜鉛めっき鋼板，溶融Ｚｎ−Ａｌ系めっき鋼板または溶融Ｚｎ−Ａｌ−Ｍｇ系めっき鋼板からなる塗装原板に、クロメート処理を施した後塗装して塗装鋼板を製造する際、クロメート処理に先立って、Ｎｉイオンの他に１０〜１００００ｐｐｍのＭｇイオンを含有する酸性水溶液で表面調整処理して、めっき層表面にＭｇ換算付着量で０．１〜１００ｍｇ／ｍ2のＭｇ化合物を置換析出させておくことにより、めっき層表面に析出したＭｇを取り込んだクロメート皮膜の優れた防食作用で、めっき層と塗膜に微細な割れが生じた塗装鋼板の折り曲げ加工部の塗膜下腐食が抑制されるため、加工部耐食性に優れた塗装鋼板が得られる。
このようにして得られた塗装鋼板は、外装建材，内装建材，家電製品，自動販売機，事務機器，自動車用鋼板，エアコン室外機等、広範な分野で使用される。[0001]
[Industrial application fields]
The present invention uses a hot-dip galvanized steel sheet, a hot-dip Zn-Al-based steel sheet or a hot-dip Zn-Al-Mg-plated steel sheet as a coating base plate, and after applying chromate treatment to apply a coating-type chromate treatment liquid thereto, resin coating The present invention relates to a technology for adjusting the surface of a coated original plate when producing a coated steel sheet.
[0002]
[Prior art]
As a pre-coating treatment prior to resin coating on a hot-dip galvanized steel sheet, hot-dip Zn-Al-based steel sheet or hot-dip Zn-Al-Mg-plated steel sheet, a coating type chromate treatment is usually performed. If this treatment is applied directly to the plated steel sheet or simply by degreasing, the wettability of the plated steel sheet surface is poor, and even if a chromate solution is applied, it is difficult to form a uniform chromate film. Adhesiveness is also inferior, which causes peeling of the coating film after painting. For this reason, it is indispensable to adjust the surface of the coating original plate before applying the chromate solution. As a surface adjustment method, conventionally, a coating original plate is treated with an acidic aqueous solution containing Ni ions to displace and deposit metal Ni on the surface of the plating layer.
[0003]
[Problems to be solved by the invention]
However, this surface conditioning solution is acidic with a pH of 2.5 to 3.5. For example, in the case of a hot-dip galvanized steel sheet or a hot-dip Zn-Al-based steel sheet, it is concentrated on the surface layer of the plating electrode by the surface conditioning treatment. Al-based oxides with excellent corrosion resistance are etched, and in hot-dip Zn-Al-Mg-based plated steel sheets, Mg-based oxides and Al-based oxides with excellent corrosion resistance concentrated on the surface layer of the plated electrode by surface conditioning treatment Will be etched. As a result, interfacial corrosion between the coating layer surface portion of the coating original plate and the undercoat coating film was reduced. In particular, in a portion where the coated steel sheet was bent and numerous cracks were generated in the plating layer and the coating film, it was not satisfactory compared to the corrosion resistance of other flat portions, coating film scratched portions, and the like.
[0004]
In recent years, with the progress of air pollution, the acidification of air and rainwater due to sulfur oxides, nitrogen oxides, etc. has been remarkable, and plating has been performed under paint films such as bent parts of coated steel sheets, cut end faces, and scratched parts of paint films. Since corrosion of the layer is promoted, there is a concern about the durability of the coated steel sheet used as an exterior building material or the like. Since the coated steel sheet is used after being formed, the ratio of the bent portion to the product is the highest except for the flat portion. Therefore, improvement of the corrosion resistance of the bent portion is particularly desired.
[0005]
In the hot-dip Zn-Al-based plated steel sheet, when the Al content of the plating layer is increased, the corrosion resistance of the bent portion, the flat portion, and the scratched portion of the coating film is increased. However, even if the Al content is increased, the corrosion resistance of the cut end face portion is not always satisfied. For example, the Zn-rich phase of the plating layer is selectively corroded at the cut end surface of the coated hot-melt Zn-55% Al-plated steel sheet. When the coating film is lifted by the corrosion product, coating film swelling called edge creep or peeling of the coating film occurs, and depending on the combination with the coating film, the corrosion resistance may be lowered. Thus, even if the Al content of the plating layer of the coating original plate is increased, not all the corrosion resistance of the flat portion, the bent portion, the scratched portion of the coating film, and the cut end surface portion is improved, and the balance is not improved. It was not possible to obtain a coated steel sheet.
[0006]
The present invention has been devised to solve such a problem, and a coating original plate made of a hot dip galvanized steel plate, a hot dip Zn-Al based plated steel plate or a hot dip Zn-Al-Mg based steel plate is used as a Ni ion. In addition to coating, the coating layer adhesion and, of course, the bent processed part by coating with Mg on the surface of the plating layer just before applying the coating chromate treatment liquid. An object of the present invention is to obtain a chromium-based coated steel sheet having excellent corrosion resistance.
[0007]
[Means for Solving the Problems]
In order to achieve the object of the present invention, a coated base plate made of a hot dip galvanized steel plate, a hot dip Zn-Al-based steel plate or a hot-dip Zn-Al-Mg-based steel plate is used in addition to Ni ions, and 10 to 10,000 ppm of Mg ions. Surface adjustment by treatment with an acidic aqueous solution (excluding phosphate treatment solution) containing 0.1 to 100 mg / m 2 of Mg compound in terms of Mg equivalent deposition amount on the plating layer surface. Features.
Thereafter, a chromate treatment for applying a coating type chromate treatment solution is performed, and then resin coating is performed.
[0008]
[Action]
Since the surface conditioning liquid is acidic, the Al-based oxide with excellent corrosion resistance concentrated on the surface layer of the hot-dip galvanized steel sheet and hot-dip Zn-Al-based steel sheet is etched, and the molten Zn -In the Al-Mg-based plated steel sheet, Mg-based oxide and Al-based oxide having excellent corrosion resistance concentrated on the surface layer of the plated electrode are etched. However, if Mg ions are included in the surface conditioning solution in advance, the Mg in the aqueous solution is added to the surface of the plating layer after the surface conditioning, for example, Mg (OH) 2 , MgAl 2 O 4 , Substitutional precipitation as MgF 2 or the like. In the present invention, these precipitates are collectively referred to as Mg compounds. Due to the action of Mg in this compound, corrosion of the plating layer in the bent portion of the coated steel sheet in which fine cracks have occurred in the plating layer and the coating film is suppressed. Moreover, corrosion near the interface between the plating layer and the undercoat coating film is also suppressed, and swelling of the coating film in the vicinity of the plating layer and the undercoat coating film and subsequent corrosion under the coating film of the plating layer itself are suppressed.
[0009]
When the coating type chromate treatment liquid is applied on the surface of the plating layer of the coating original plate and the coating type chromate treatment liquid is applied, the Mg in the compound deposited and substituted on the surface layer portion of the plating layer by the surface conditioning treatment is the acid component of the coating type chromate treatment liquid. To ionize and elute. As a result, a chromate film in which Mg ions eluted from the surface of the plating layer and an organic resin (acrylic resin) in the chromate treatment liquid is combined is formed on the surface of the plating layer.
[0010]
The reason for improving the corrosion resistance of the bent portion of the coated steel sheet due to Mg in the compound deposited by substitution on the surface layer of the plating layer is not clear, but since the Mg deposited by substitution on the surface layer of the plating layer is incorporated into the chromate film, the chromate film Adheres to the plating layer with excellent adhesion and improves moisture resistance. In addition, Mg taken into the chromate film from the surface layer of the plating layer is eluted in a corrosive environment, interfacial corrosion between the plating layer and the undercoat film is suppressed, and the fine plating layer and the cracked part of the coating film are dense. Form and accumulate hardly soluble Zn corrosion products. The produced corrosion product containing Mg also acts as a barrier against corrosive ions entering from the outside. As a result, it is assumed that corrosion of the plating layer under the coating film is suppressed.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
As a coating original plate used in the present invention, a hot dip galvanized steel sheet, hot dip galvanized steel sheet in which a Zn plating layer, a Zn—Al plating layer or a Zn—Al—Mg plating layer is usually formed in a continuous hot dip plating line. Examples thereof include 5% Al-based plated steel sheets and hot-dip Zn-4 to 22% Al-1 to 4Mg (-Ti-B-Si) -based plated steel sheets. In the continuous coating line, prior to the chromate treatment as a pretreatment for coating, the surface of the coating original plate is subjected to a surface conditioning treatment to improve the wettability of the hot-dip coating layer of the coating original plate and form a uniform chromate film. .
[0012]
The acidic surface conditioning solution is prepared by adding 10 to 10,000 ppm of Mg ions to a commercially available aqueous solution containing Ni ions that have been generally used. The method of adding Mg ions to the acidic surface conditioning solution is not particularly limited, but since sulfate-based solutions are often used mainly as aqueous solutions containing Ni ions, magnesium sulfate (septahydrate) is added. It is preferable to do. When immersed in this surface conditioning solution or sprayed, treated for several seconds, washed with water and dried, Mg compound is deposited on the surface of the plated layer of the treated coating original plate in an amount of 0.1 to 100 mg / m in terms of Mg. Substitutive precipitation at 2 . Thereafter, the corrosion resistance of the processed portion of the coated steel sheet subjected to the chromate treatment and coating is such that the Mg ion concentration in the acidic surface adjustment treatment liquid is less than 10 ppm, and the amount of Mg deposited by substitution on the plating layer surface is less than 0.1 mg / m 2 , The improvement in corrosion resistance of the bent portion of the coated steel sheet is not sufficiently exhibited. Conversely, even if the Mg ion concentration in the acidic surface conditioning solution exceeds 10,000 ppm and the Mg precipitation amount on the surface of the plating layer exceeds 100 mg / m 2 , the corrosion resistance of the bent portion of the coated steel sheet is not further improved. . Excessive Mg content also has no merit from increasing the cost of the surface conditioning solution.
[0013]
The surface of the coated original plate is coated with a chromate film similar to the conventional one on the surface of the coated original plate, thereby improving coating film adhesion. The chromate film is preferably formed at a rate of 5 to 100 mg / m 2 in terms of Cr equivalent in order to ensure corrosion resistance and coating film adhesion. This chromium adhesion amount is the same even when the chromate film contains a water-soluble or water-dispersible resin or silica, or even when the chromate film is formed with a phosphoric acid-chromic acid treatment solution.
[0014]
On the surface of the coating original plate on which the chromate film is formed, a resin coating film similar to the conventional one is formed by the same method as the conventional one.
In this case, epoxy, epoxy / urethane, polyester, acrylic, epoxy-modified polyester, phenoxy, or the like is used as the undercoat resin. The film thickness of the undercoat film is in the range of 3 to 10 μm as in the conventional case. In addition, undercoat resin is formed by adding chromic acid-based rust preventive pigments such as strontium chromate, calcium chromate, barium chromate, zinc chromate alone or in combination of two or more kinds. You can also In addition to rust-preventive pigments, additives such as titanium oxide and other pigments, extender pigments such as calcium carbonate and barium sulfate, various organic resin beads, organic resin powders, and inorganic aggregates are added to the undercoat paint resin. You may contain. The molecular weight of the undercoat coating resin, the glass transition temperature, or the added amount of pigment, aggregate, etc. is appropriately adjusted according to the application of the coated steel sheet.
[0015]
A top coat film is further formed on the undercoat film.
The top coat resin at this time may be a thermosetting resin or a thermoplastic resin such as polyester, urethane, acrylic, silicone-modified polyester, silicone acrylic, polyvinyl chloride, polyvinylidene fluoride-acrylic. used. In addition, organic aggregates, inorganic aggregates, metallic powders, lubricants, antifouling agents, fungicides, UV absorbers, light stabilizers (antioxidants), photocatalyst particles, matting agents and various types Powder etc. are added.
[0016]
In this way, when a coating original plate made of a hot-dip galvanized steel sheet, a hot-dip Zn-Al-based plated steel sheet or a hot-dip Zn-Al-Mg-plated steel sheet is treated with an acidic surface conditioning solution to which 10 to 10,000 ppm of Mg ions are added, Mg is substituted and deposited on the plating layer surface of the original plate in the range of 0.1 to 100 mg / m 2 . When a coating type chromate solution is applied thereon, Mg deposited by substitution on the surface layer portion of the plating layer is eluted into the coating type chromate treatment solution. When this treatment liquid film is dried, a chromate film having excellent adhesion, moisture resistance, and corrosion resistance is formed on the surface of the plating layer, which is a composite of Mg ions eluted from the plating layer surface and the organic resin in the chromate treatment liquid. . Mg taken into the chromate film from the surface layer of the plating layer is eluted in a corrosive environment, and interfacial corrosion in which the vicinity of the interface between the plating layer and the undercoat film is selectively corroded is suppressed. Further, Mg forms and accumulates a dense and hardly soluble corrosion product of Zn in the fine plating layer and the cracked portion of the coating film. The formed uniform, dense and stable corrosion product containing Mg also acts as a barrier against corrosive ions entering from the outside. As a result, a coated steel sheet having excellent corrosion resistance of the processed part is obtained.
[0017]
【Example】
As shown in Table 1, hot-dip galvanized steel sheet (plate thickness: 0.6 mm, single-sided plating adhesion amount: 140 g / m 2 ), hot-dip Zn-4% Al-0.1% Mg-plated steel sheet (plate thickness: 0.6 mm, Sendzimir is a single-sided plating adhesion amount: 135 g / m 2 ) and a molten Zn-6% Al-3% Mg (-Ti-B) -plated steel sheet (plate thickness: 0.6 mm, single-sided plating adhesion amount: 120 g / m 2 ). Manufactured on a continuous hot dip plating line.
[0018]
These plated steel sheets were adjusted to an Mg ion concentration of 2000 ppm by adding magnesium sulfate heptahydrate to an acidic surface conditioner (Nihon Paint Co., Ltd., trade name: NP Conditioner 710) containing Ni ions. Furthermore, after adjusting the pH to 2.5 to 3.5 at a liquid temperature of 65 ° C., the aqueous solution was sprayed, then washed with water and dried.
On the surface of the plated layer after drying, an Mg compound was deposited at a rate of 20 mg / m 2 in terms of Mg equivalent adhesion amount. For comparison, after spraying an acidic surface conditioning solution to which no Mg ions were added, the plate was washed with water and dried. Table 2 shows the amount of Mg deposited on the surface of the plating layer after the surface conditioning treatment.
[0020]
Thereafter, a coating type chromate treatment liquid (manufactured by Nippon Paint Co., Ltd., trade name: Surfcoat NRC300NS) is applied with a roll coater and dried at 100 ° C. without being washed with water, and the total Cr equivalent adhesion amount is 40 mg / m 2. A chromate film was formed.
Next, 25 wt% of strontium chromate is mixed on the chromate film with a non-volatile content of 25% by mass. In addition, an epoxy resin primer is dried which contains titanium oxide as a color pigment and barium sulfate and silica powder as an extender pigment. The film was coated to a thickness of 5 μm and dried at 215 ° C. to form an undercoat film. On the thus formed undercoat film, a polyester resin topcoat paint was applied so as to have a dry film thickness of 15 μm, and similarly dried at 215 ° C. to form a topcoat film.
[0022]
A test piece was cut out from each coated steel plate thus prepared and subjected to the following coating film adhesion test and accelerated corrosion resistance test.
In the coating film adhesion test, a 2t 180 degree bending process was applied so that the coating film surface to be evaluated inside was adjusted to 20 ° C., and an adhesive tape was attached to the bent portion and peeled off. The peeling state of was observed. From the observation results, the adhesion of the coating film was evaluated with ◎ indicating that the coating film did not peel off and × indicating that the peeling film was generated.
[0023]
In the accelerated corrosion resistance test, a test piece was prepared in which the left, right, and lower cut end surfaces and the back surface were repaired with paint after 4t bending was performed so that the upper coated surface of the coated steel sheet was on the outside. 600 cycles acid rain combined corrosion test [1 cycle: spraying with 0.1% NaCl corrosion solution (35 ° C. × 1 hour, pH 4 adjusted with sulfuric acid) → drying (50 ° C. × 4 hours) → wet (50 ° C. × 3 hours) , Relative humidity 98%), the occurrence rate of white rust generated from the 4t bent portion was measured.
[0024]
The white rust occurrence rate was determined by observing the white rust generated in the 4t-bending portion in the acid rain combined corrosion test, and obtaining the white rust occurrence rate (%) with respect to the area 100 of the test target portion.
The white rust resistance was evaluated by evaluating the case where no white rust was detected in the 4t-folded part as ◎, 5% or less as ◯, 5 to 20% as △, and 20% or more as ×.
Table 3 shows the results of the evaluation tests.
[0025]
As can be seen from the results in Table 3, in test numbers 1 to 3 in which the coated steel sheet treated with the surface conditioning solution to which 2000 ppm of Mg ion was added was used as the coating original sheet, in the acid rain accelerated corrosion resistance test reproducing the outdoor corrosion behavior, The incidence of white rust in the bent part was low, and excellent processed part corrosion resistance was shown.
On the other hand, in Test Nos. 4 to 6 in which the coated steel sheet treated with the conventional surface conditioning solution containing no Mg ions was used as the coating original sheet, the white rust occurrence rate of the bent part was high, and the corrosion resistance of the processed part was not sufficient. It was.
[0027]
【The invention's effect】
As described above, when a coated steel sheet made of a hot-dip galvanized steel sheet, a hot-dip Zn-Al-based steel sheet or a hot-dip Zn-Al-Mg-based steel sheet is subjected to chromate treatment and then coated to produce a coated steel sheet Prior to the chromate treatment, the surface is adjusted with an acidic aqueous solution containing 10 to 10000 ppm of Mg ions in addition to the Ni ions, and the Mg compound has an Mg equivalent adhesion amount of 0.1 to 100 mg / m 2 on the plating layer surface. By substituting and precipitating, the excellent anticorrosive action of the chromate film incorporating Mg deposited on the surface of the plating layer, and the coating layer under the bent portion of the coated steel sheet where fine cracks occurred in the plating layer and the coating film. Since corrosion is suppressed, a coated steel sheet having excellent processed portion corrosion resistance can be obtained.
The coated steel sheet thus obtained is used in a wide range of fields such as exterior building materials, interior construction materials, home appliances, vending machines, office equipment, automotive steel sheets, and air conditioner outdoor units.
Claims (3)
Priority Applications (1)
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| JP2001375868A JP3810677B2 (en) | 2001-12-10 | 2001-12-10 | Coating plate, surface preparation method of coating plate and method of manufacturing coated steel plate with excellent corrosion resistance |
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| JP2001375868A JP3810677B2 (en) | 2001-12-10 | 2001-12-10 | Coating plate, surface preparation method of coating plate and method of manufacturing coated steel plate with excellent corrosion resistance |
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| KR101068708B1 (en) | 2006-02-20 | 2011-09-28 | 수미도모 메탈 인더스트리즈, 리미티드 | Method for manufacturing hot-dip galvanized steel sheet having zinc phosphate coating |
| JP2010112667A (en) | 2008-11-10 | 2010-05-20 | Mitsubishi Electric Corp | Air conditioner |
| JP2017001312A (en) | 2015-06-11 | 2017-01-05 | 吉田 英夫 | Film-forming structure for workpiece and film-forming method for workpiece |
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