JP2004169145A

JP2004169145A - Precoated steel sheet for wiper and wiper

Info

Publication number: JP2004169145A
Application number: JP2002337749A
Authority: JP
Inventors: Katsumi Owa; 尾和　　克美; Hirokazu Yano; 矢野　　宏和; Koji Mori; 浩治森
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2002-11-21
Filing date: 2002-11-21
Publication date: 2004-06-17

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precoated steel sheet which excels in end face corrosion resistance and is adequate as a wiper material. <P>SOLUTION: The steel sheet formed with a Zn-Al-Mg plating layer in which a primary crystal Al phase or the primary crystal Al phase and a Zn single phase coexist in a matrix of a ternary eutectic structure of Al/Zn/Zn<SB>2</SB>Mg is used as a base material. A chrome-free resin coating film dispersed with porous silica particles formed by bonding Ca ions by an ion exchange as a rust inhibitive pigment is formed on the surface of the base material through a chromium-free chemical conversion film in which an oxide or hydroxide and a fluoride of a valve metal whose oxide exhibits high insulation resistance coexist. Further, it is possible that the chemical conversion film contains a polyphosphate. The wiper with which the rust formation at a cut end face is suppressed and which has the excellent end face corrosion resistance even if the precoated steel sheet is cut and is formed to a prescribed shape can be obtained. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】
本発明は、腐食性の湿潤雰囲気下でも切断端面の錆発生を抑えたワイパーに適したプレコート鋼板及びワイパーに関する。
【０００２】
【従来の技術】
塗装鋼板は、家電機器や屋根材，壁材等の外装用途等の広範な分野で使用されている。従来は塗装原板を所定形状に加工した後で塗装するポストコートにより塗膜を鋼板表面に形成していたが、生産性，経済性に劣り環境に与える負荷も大きい。そこで、ポストコートに替え、塗装後に所定形状に加工するプレコート法への転換が進められている。
ポストコートからプレコートへの転換は、塗装鋼板の用途によっては簡単でない。たとえば、常に水に接触する環境で使用されるワイパーは、高い耐食性が要求されることから従来通りのポストコート法で製造されている。プレコート鋼板をワイパー素材に使用すると、ワイパー形状に裁断されたプレコート鋼板の切断端面が塗膜のない剥き出し状態になる。露出した切断端面が湿潤雰囲気に曝されると錆が発生し、外観の劣化は勿論、ワイパーとしての機能も損なわれやすい。
【０００３】
【発明が解決しようとする課題】
切断端面の腐食は、耐食性に優れたステンレス鋼等の高級鋼材を塗装原板に使用することによって防止できる。しかし、高級鋼材の使用は、従来からワイパー素材に使用されているＺｎ系，Ｚｎ−Ａｌ系めっき鋼板等に比較すると材料コストが高くなる。
Ｚｎ系，Ｚｎ−Ａｌ系めっき鋼板等を使用する場合でも、塗装原板をクロメート処理し、クロム酸ストロンチウム等の防錆顔料を塗膜に多量添加することによって切断端面の錆発生をある程度抑制でき、比較的安価なワイパーが得られる。しかし、環境負荷の低減が強く要求されている最近の傾向，ヨーロッパでのＥＬＶ指令の発令等を考慮すると、自動車用ワイパーにクロム化合物を使用しないことが望ましい。クロム化合物の使用に関する法規制は、更に厳しくなることが予想される。
【０００４】
【課題を解決するための手段】
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、基材，化成処理皮膜及び樹脂塗膜の特定された組合せにより、環境負荷を増大させるクロム化合物等を使用することなく端面耐食性に優れたプレコート鋼板製ワイパーを提供することを目的とする。
【０００５】
本発明のワイパー用プレコート鋼板は、その目的を達成するため、Ａｌ：４〜１０質量％，Ｍｇ：１〜４質量％を含み、Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織のマトリックスに初晶Ａｌ相又は初晶Ａｌ相及びＺｎ単相が混在しているＺｎ−Ａｌ−Ｍｇめっき層が形成された鋼板を基材とし、酸化物が高い絶縁抵抗を示すバルブメタルの酸化物又は水酸化物及びフッ化物が共存するクロムフリー化成処理皮膜を介し、Ｃａイオンをイオン交換で結合させた多孔質シリカ粒子を防錆顔料として分散させたクロムフリー樹脂塗膜が基材表面に形成されていることを特徴とする。
Ｚｎ−Ａｌ−Ｍｇめっき層は更にＴｉ：０．００２〜０．１質量％，Ｂ：０．００１〜０．４５質量％の１種又は２種を、クロムフリー樹脂塗膜は更にポリリン酸塩を含むことができる。当該プレコート鋼板を裁断して所定形状に成形加工しても、切断端面の錆発生が抑制され、端面耐食性に優れたワイパーが得られる。
【０００６】
【実施の形態】
〔塗装原板〕
本発明のワイパー用プレコート鋼板は、Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織のマトリックスに初晶Ａｌ相，或いは更にＺｎ単相が分散しているＺｎ−Ａｌ−Ｍｇめっき鋼板を塗装原板に使用している。かかる組織のめっき層を形成するため、Ａｌ，Ｍｇ含有量をそれぞれ４〜１０質量％，１〜４質量％に調整している。Ｚｎ−Ａｌ−Ｍｇめっき鋼板は、本出願人が特開平１０−２２６８６５号公報で紹介した高耐食めっき鋼板であり、めっき層に含まれるＡｌ，Ｍｇが緻密で難溶性の腐食生成物となってめっき層表面を覆う。任意成分として添加されるＴｉ，Ｂは、塗装後の表面外観や耐食性に悪影響を及ぼすＺｎ_１１Ｍｇ_２相の晶出を抑制する作用を呈する。
【０００７】
腐食生成物から形成される防錆皮膜は、外部から侵入してくる腐食性イオンが下地鋼に達することを防止し、下地金属が露出する切断端面等の部位においても優れた耐食性を発現し、塗膜フクレや錆発生を抑制する。Ｍｇを含む防錆皮膜は、赤錆を発生した後で徐々に黒色に近い褐色を呈する。この点、冷延鋼板や亜鉛系めっき鋼板の表面に発生する赤錆や白錆（後に赤錆となる）と異なり、長期間に渡って屋外に曝露しても白錆が目立たない。したがって、自動車のフロントウインドウに取り付けたワイパーを運転席から見た場合に切断端面が極めて目立ちがたく、運転の支障にならない。
【０００８】
〔クロムフリー化成処理皮膜〕
Ｚｎ−Ａｌ−Ｍｇめっき鋼板の上に、酸化物が高い絶縁抵抗を示すバルブメタルの酸化物又は水酸化物及びフッ化物が共存するクロムフリー化成処理皮膜が形成される。当該クロムフリー化成処理皮膜は、本出願人がクロメート皮膜に替わる自己修復作用のある化成処理皮膜について種々調査・検討した結果から見出された皮膜（特願２００２−１０５４７７号）であり、バルブメタルの酸化物又は水酸化物で環境遮断能を発現させ、可溶性のフッ化物で自己修復作用を付与している。バルブメタルには、Ｔｉ，Ｚｒ，Ｈｆ，Ｖ，Ｎｂ，Ｔａ，Ｍｏ，Ｗから選ばれた１種又は２種以上が使用され、好ましくは原子比率の濃度比Ｆ／Ｏで１／１００以上のＦ及びＯを含んでいる。金属イオンを安定して化成処理皮膜中に維持させるため、キレート作用のある有機酸を化成処理皮膜に含ませても良い。
【０００９】
クロムフリー化成処理皮膜は、所定組成に調整された化成処理液を塗装原板に塗布することによってめっき層表面に形成される。化成処理液の塗布に先立ち酸洗，Ｎｉ析出，Ｃｏ析出等の表面処理を塗装原板に施すと、下地鋼に対するクロムフリー化成処理皮膜の密着性が向上する。
化成処理液はロールコート法，スピンコート法，スプレー法等で塗布され、十分な耐食性を確保するため好ましくはバルブメタルの付着量が１ｍｇ／ｍ^２以上となるように塗布量が調整される。化成処理液を塗布した塗装原板を水洗せずに乾燥することにより、目標とするクロムフリー化成処理皮膜がめっき層表面に形成される。乾燥は常温でも可能であるが、連続操業を考慮すると５０℃以上に保持して乾燥時間を短縮することが好ましい。
【００１０】
〔クロムフリー樹脂塗膜〕
クロムフリー化成処理皮膜上に、クロムフリー樹脂塗膜が形成される。クロムフリー樹脂塗膜の形成には、ウレタン樹脂，エポキシ樹脂，ポリエチレン，ポリプロピレン，エチレン−アクリル酸共重合体等のオレフィン系樹脂、ポリスチレン等のスチレン系樹脂、ポリエステル樹脂、或いはこれらの共重合体又は変生物、アクリル系樹脂をベースとし、変性シリカ及び必要に応じてポリリン酸塩を添加した塗料組成物が使用される。
【００１１】
変性シリカは、Ｃａイオンをイオン交換で結合させた多孔質シリカ粒子であり、Ｈイオン等の腐食性イオンをＣａイオンで捕捉することにより、下地のクロムフリー化成処理皮膜と相俟って従来のクロム系防錆顔料を凌駕する腐食防止機能を呈する。樹脂塗膜の耐食性は、ピロリン酸アルミニウム，メタ燐酸アルミニウム，トリポリ燐酸アルミニウム等のポリリン酸塩を含ませることにより更に向上する。変性シリカ，ポリリン酸塩を共存させると、樹脂塗膜からのＣａイオン溶出が抑制され、変性シリカの腐食抑制能が長期間にわたって維持される。変性シリカは、防錆顔料の作用を実効的にするために塗膜の樹脂分１００質量部に対して２〜５０質量部含ませることが好ましい。更にポリリン酸塩を加える場合、変性シリカ／ポリリン酸塩の質量比を６０／４０〜５／９５の範囲に調整することが好ましい。
【００１２】
塗料組成物は、好ましくは膜厚０．１〜２０μｍのクロムフリー樹脂塗膜が形成される割合で化成処理後のＺｎ−Ａｌ−Ｍｇめっき鋼板に塗布される。塗布・焼付けには、常法に従ってロールコータ，熱風乾燥機能等を備えた連続塗装設備を使用できる。クロムフリー樹脂塗膜は、膜厚が０．１μｍ以上になるとピンホール，未塗装部等の欠陥がない連続塗膜になるが、２０μｍを超える厚膜では加工性が低下する。
【００１３】
クロムフリー樹脂塗膜を形成した塗装鋼板をそのまま１コートのプレコート鋼板として出荷することも可能であるが、クロムフリー樹脂塗膜の上に更に一層又は二層の塗膜を設けることも可能である。上塗り塗膜，中塗り塗膜用には、ウレタン樹脂，エポキシ樹脂，ポリエチレン，ポリプロピレン，エチレン−アクリル酸共重合体等のオレフィン系樹脂、ポリスチレン等のスチレン系樹脂、ポリエステル樹脂、或いはこれらの共重合体又は変性物、アクリル系樹脂等をベースとした塗料組成物が使用される。この塗料組成物にも、必要に応じて変性シリカを添加しても良い。
上塗り，中塗り用の塗料組成物は、個々のワイパーの形状に応じて適宜選択されるが、具体的には高分子ポリエステル塗料を２３０℃×４０秒で焼き付けた膜厚１５〜２０μｍの上塗り塗膜がある。塗布・焼付けには、常法に従ってロールコータ，熱風乾燥機能等を備えた連続塗装設備を使用できる。
【００１４】
【実施例】
表１に示した各種Ｚｎめっき層を片面当り付着量３０ｇ／ｍ^２で形成した板厚０．５ｍｍのめっき鋼板を塗装原板に使用した。
【００１５】

【００１６】
塗装原板にＮｉ析出型の表面調整処理を施し、湯洗，水洗を経て乾燥させた。次いで、Ｔｉをバルブメタルとする化成処理液を塗装原板の乾燥表面に塗布し、水洗することなくオーブンに装入し、板温１００℃で加熱・乾燥した。化成処理には、バルブメタルとしてＴｉを選択し、Ｔｉ濃度で２０ｇ／ｌ，Ｆ濃度で４７．５ｇ／ｌの（ＮＨ_４）_２ＴｉＦ_６，Ｐ濃度で４０ｇ／ｌのＨ_３ＰＯ_４，４ｇ／ｌのタンニン酸を含む処理液を使用した。
乾燥後のめっき層表面を観察したところ、Ｔｉ換算付着量１５ｍｇ／ｍ^２のクロムフリー化成処理皮膜が形成されていた。化成処理皮膜を蛍光Ｘ線分析した結果、元素濃度比がＴｉ：４％，Ｏ：７１％，Ｆ：１３％，Ｐ：１２％であった。
【００１７】
次いで、樹脂固形分に対しそれぞれ１５質量％，３０質量％の割合で変性シリカ，ポリリン酸塩を分散させたエポキシ変性高分子ポリエステル系樹脂塗料を乾燥後のクロムフリー化成処理皮膜上に塗布し、最高到達板温２１５℃で４０秒間焼き付けることにより膜厚５μｍのクロムフリー樹脂塗膜を形成した。
クロムフリー樹脂塗膜を下塗り塗膜とし，更に同様な高分子ポリエステル系樹脂塗料の塗布・焼付けによって膜厚１５μｍの上塗り塗膜を形成した。
【００１８】
製造された各塗装鋼板から試験片を切り出し、促進腐食試験に供した。促進腐食試験では，切断端面を露出させた試験片にＪＩＳＫ５６００に準拠し塩水を２４０時間噴霧した。また、４９℃，９８％ＲＨの湿潤雰囲気に２４０時間放置した。
塩水噴霧試験，湿潤試験後に試験片を観察し、切断端面から発生した塗膜のフクレ（エッジクリープ）幅，切り口の赤錆発生率を測定した。測定結果から、塗膜フクレ幅が１．０ｍｍ以下を◎，１．０〜２．０ｍｍを○，２．０〜３．０ｍｍを△，３．０ｍｍ以上を×とし、端面赤錆発生率が０〜５％を◎，５〜１０％を○，１０〜３０％を△，３０％以上を×として端面耐食性を評価した。
【００１９】
表２の調査結果にみられるように、Ｚｎ−Ａｌ−Ｍｇめっき鋼板を塗装原板とし、クロムフリー化成処理皮膜，クロムフリー樹脂塗膜を設けた本発明例では、塩水噴霧試験，湿潤試験共に優れた端面耐食性を呈し、ワイパー機能を低下させる錆発生が検出されなかった。他方、Ｚｎ−Ａｌめっき鋼板を塗装原板とした比較例では、塩水噴霧試験，湿潤試験の何れにおいても端面耐食性に劣り、ワイパーの外観を劣化させる錆発生も散見された。この対比結果は、めっき層に含まれているＭｇが腐食抑制に効果を発揮していることを示している。
【００２０】

【００２１】
【実施例２】
片面当り付着量３０ｇ／ｍ^２，板厚０．５ｍｍのＺｎ−Ａｌ−Ｍｇめっき鋼板を塗装原板に使用し、表３の組成をもつ化成処理液を用いて実施例１と同様に化成処理した。めっき層表面に形成された化成処理皮膜を分析したところ、表４に示す濃度で各成分が含まれていた。
【００２２】

【００２３】

【００２４】
化成処理皮膜の上に実施例１と同様に塗膜を形成した後、製造された各塗装鋼板から試験片を切り出し、２ｔ曲げ試験に供した。曲げ加工した試験片に塩水を２４０時間噴霧した後、試験片表面を観察した。切断端面については、実施例１と同様に耐食性を評価した。加工部に発生しがちな塗膜フクレに関し、塗膜にフクレが全く生じていない試験片を◎，ごく僅かなフクレが検出された試験片を○，５０％未満を△，５０％を超えるフクレが発生した試験片を×として耐塗膜フクレ性を評価した。
表５の調査結果にみられるように、本発明に従って製造された試験番号１〜７の塗装鋼板では、切断端面，加工部共に優れた耐食性を呈した。これに対し、可溶性のチタンフッ化物を含まない化成処理液を用いた試験番号８やチタン化合物を全く含まない化成処理液を用いた試験番号９では、切断端面，加工部共に耐食性が低下していた。
【００２５】

【００２６】
【実施例３】
実施例２で耐食性に優れた試験番号１の化成処理皮膜をＺｎ−Ａｌ−Ｍｇめっき鋼板に形成した後、クロムフリー樹脂塗装を施した。クロムフリー樹脂塗料には、変性シリカ，ポリリン酸塩を種々の割合で配合したエポキシ変性ポリエステル系樹脂塗料（表６）を使用した。
塗装原板に塗布したクロムフリー樹脂塗料を最高到達板温２３０℃×４０秒で焼き付け，膜厚５μｍのクロムフリー樹脂塗膜を形成した。更に、クロムフリー樹脂塗膜を下塗り塗膜として、上塗り塗料に高分子ポリエステル塗料を使用し、下塗り塗装と同様に塗布・焼付けすることにより膜厚１５μｍの上塗り塗膜を形成した。
【００２７】
得られた各塗装鋼板から試験片を切り出し、実施例２と同様に２ｔ曲げ試験に供した後、２４０時間の塩水噴霧試験で耐食性を評価した。
何れのクロムフリー樹脂塗膜を形成した場合でも、切断端面のフクレ幅が１ｍｍ以下とごく僅かであり、切断端面に発生する赤錆も５％未満であった。加工部にも塗膜フクレが生じなかった。比較のため、変性シリカ無添加のエポキシ変性高分子ポリエステル系樹脂塗料を用いて樹脂塗膜を形成した塗装鋼板を同様に試験したところ、切断端面に最大フクレ幅が５ｍｍを超える塗膜フクレが発生し、加工部では全面に塗膜フクレが発生していた。
【００２８】

【００２９】
【発明の効果】
以上に説明したように、Ｚｎ−Ａｌ−Ｍｇめっき鋼板を塗装原板に使用し、バルブメタルの酸化物又は水酸化物及びフッ化物が共存するクロムフリー化成処理皮膜を介し、変性シリカ，ポリリン酸塩を防錆顔料として分散させたクロムフリー樹脂塗膜を形成することにより、クロム化合物等の環境負荷物質を使用する必要なく、端面耐食性に優れたワイパー用プレコート鋼板が得られる。仮に切断端面に錆が発生した場合でも黒色に近い褐色の色調を呈するので、ワイパーの外観劣化が少ない。[0001]
[Industrial applications]
The present invention relates to a precoated steel sheet and a wiper suitable for a wiper that suppresses rust generation on a cut end surface even in a corrosive moist atmosphere.
[0002]
[Prior art]
BACKGROUND ART Painted steel sheets are used in a wide range of fields such as home appliances, roofing materials, exterior materials such as wall materials, and the like. Conventionally, a coating film is formed on the surface of a steel sheet by post-coating, which is performed after a coating original plate is processed into a predetermined shape, but the productivity and economy are poor and the load on the environment is large. Therefore, conversion to a pre-coat method, in which a post-coating is processed into a predetermined shape, has been promoted instead of the post-coat.
Converting from post-coat to pre-coat is not easy depending on the application of the coated steel sheet. For example, a wiper used in an environment that is always in contact with water is manufactured by a conventional post-coating method because high corrosion resistance is required. When a precoated steel sheet is used as a wiper material, the cut end surface of the precoated steel sheet cut into a wiper shape is exposed without a coating film. When the exposed cut end face is exposed to a humid atmosphere, rust is generated, and not only the appearance is deteriorated, but also the function as a wiper is easily damaged.
[0003]
[Problems to be solved by the invention]
Corrosion of the cut end surface can be prevented by using a high-grade steel material such as stainless steel having excellent corrosion resistance for the original plate for painting. However, the use of a high-grade steel material increases the material cost as compared with a Zn-based, Zn-Al-based plated steel sheet or the like conventionally used for a wiper material.
Even when using a Zn-based or Zn-Al-based plated steel plate, the coated base plate is subjected to chromate treatment and a large amount of a rust-preventive pigment such as strontium chromate is added to the coating film to suppress the generation of rust on the cut end surface to a certain extent. A relatively inexpensive wiper is obtained. However, in view of the recent tendency to strongly reduce the environmental load, the issuance of the ELV directive in Europe, and the like, it is desirable not to use a chromium compound for a wiper for an automobile. Legislation on the use of chromium compounds is expected to become more stringent.
[0004]
[Means for Solving the Problems]
The present invention has been devised to solve such a problem, and the use of a specified combination of a base material, a chemical conversion coating, and a resin coating allows the use of a chromium compound or the like that increases environmental load without using a chromium compound. An object of the present invention is to provide a wiper made of precoated steel sheet having excellent end face corrosion resistance.
[0005]
In order to achieve the object, the precoated steel sheet for a wiper of the present invention contains Al: 4 to 10% by mass and Mg: 1 to 4% by mass, and has a ternary eutectic structure matrix of Al / Zn / Zn ₂ Mg. The base material is a steel sheet on which a Zn-Al-Mg plating layer in which a primary Al phase or a primary Al phase and a Zn single phase are mixed is used as a base material, and the oxide or water of a valve metal exhibiting high insulation resistance is used as an oxide. Through a chromium-free chemical conversion coating in which oxides and fluorides coexist, a chromium-free resin coating in which porous silica particles in which Ca ions are bonded by ion exchange are dispersed as a rust-preventive pigment is formed on the substrate surface. It is characterized by having.
The Zn—Al—Mg plating layer further contains one or two types of Ti: 0.002 to 0.1% by mass and B: 0.001 to 0.45% by mass, and the chromium-free resin coating further comprises a polyphosphate. Can be included. Even if the precoated steel sheet is cut and formed into a predetermined shape, rust generation on the cut end surface is suppressed, and a wiper excellent in end surface corrosion resistance can be obtained.
[0006]
Embodiment
(Coating original plate)
The precoated steel sheet for a wiper according to the present invention is obtained by coating a Zn—Al—Mg plated steel sheet in which a primary Al phase or a Zn single phase is dispersed in a matrix having a ternary eutectic structure of Al / Zn / Zn ₂ Mg. Used for In order to form a plating layer having such a structure, the contents of Al and Mg are adjusted to 4 to 10% by mass and 1 to 4% by mass, respectively. The Zn-Al-Mg plated steel sheet is a highly corrosion-resistant plated steel sheet introduced by the present applicant in Japanese Patent Application Laid-Open No. Hei 10-226865, in which Al and Mg contained in the plating layer are dense and hardly soluble corrosion products. Cover the plating layer surface. Ti and B added as optional components exhibit an effect of suppressing crystallization of the Zn ₁₁ Mg ₂ phase, which adversely affects the surface appearance and corrosion resistance after coating.
[0007]
The anti-corrosion film formed from the corrosion products prevents corrosive ions entering from the outside from reaching the base steel, and exhibits excellent corrosion resistance even at the cut end face where the base metal is exposed, Suppresses blistering and rust on the coating. The rust-preventive film containing Mg gradually shows a brown color close to black after generating red rust. In this respect, unlike red rust and white rust (which will later become red rust) generated on the surface of a cold-rolled steel sheet or galvanized steel sheet, white rust is not conspicuous even when exposed outdoors for a long period of time. Therefore, when the wiper attached to the front window of the automobile is viewed from the driver's seat, the cut end face is extremely inconspicuous, and does not hinder driving.
[0008]
[Chromium-free chemical conversion coating]
A chromium-free chemical conversion treatment film is formed on a Zn-Al-Mg plated steel sheet, in which an oxide or hydroxide of a valve metal having a high insulation resistance and a fluoride coexist. The chromium-free chemical conversion coating is a coating (Japanese Patent Application No. 2002-105477) found from the results of various investigations and studies by the present applicant on a self-healing chemical conversion coating instead of a chromate coating. The oxides or hydroxides of the above exhibit environmental barrier properties, and the soluble fluorides impart a self-healing effect. As the valve metal, one or more selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W is used. Preferably, the concentration ratio of atomic ratio F / O is 1/100 or more. Contains F and O. In order to stably maintain the metal ions in the chemical conversion coating, an organic acid having a chelating action may be included in the chemical conversion coating.
[0009]
The chromium-free chemical conversion treatment film is formed on the plating layer surface by applying a chemical conversion treatment solution adjusted to a predetermined composition to a coating original plate. If surface treatments such as pickling, Ni precipitation, and Co precipitation are applied to the original coating plate prior to the application of the chemical conversion solution, the adhesion of the chromium-free chemical conversion coating to the base steel is improved.
The chemical conversion treatment liquid is applied by a roll coating method, a spin coating method, a spraying method, or the like, and the application amount is preferably adjusted so that the adhesion amount of the valve metal is 1 mg / m ² or more in order to secure sufficient corrosion resistance. The target chromium-free chemical conversion treatment film is formed on the surface of the plating layer by drying the coating base plate coated with the chemical conversion treatment solution without washing with water. Drying is possible at room temperature, but considering continuous operation, it is preferable to keep the temperature at 50 ° C. or higher to shorten the drying time.
[0010]
[Chrome-free resin coating]
A chromium-free resin coating is formed on the chromium-free chemical conversion coating. For forming a chromium-free resin coating film, urethane resin, epoxy resin, olefin resin such as polyethylene, polypropylene, ethylene-acrylic acid copolymer, styrene resin such as polystyrene, polyester resin, or a copolymer of these resins or A coating composition based on a modified organism or an acrylic resin to which modified silica and optionally a polyphosphate are added is used.
[0011]
Modified silica is porous silica particles in which Ca ions are bonded by ion exchange. By capturing corrosive ions such as H ions with Ca ions, the modified silica is combined with the underlying chromium-free chemical conversion coating film to form a conventional silica. It has a corrosion prevention function that surpasses that of chrome-based rust preventive pigments. The corrosion resistance of the resin coating is further improved by including a polyphosphate such as aluminum pyrophosphate, aluminum metaphosphate, aluminum tripolyphosphate and the like. When modified silica and polyphosphate coexist, elution of Ca ions from the resin coating is suppressed, and the ability of the modified silica to inhibit corrosion is maintained for a long period of time. The modified silica is preferably contained in an amount of 2 to 50 parts by mass based on 100 parts by mass of the resin component of the coating film in order to make the effect of the rust preventive pigment effective. When a polyphosphate is further added, the mass ratio of the modified silica / polyphosphate is preferably adjusted in the range of 60/40 to 5/95.
[0012]
The coating composition is preferably applied to the Zn-Al-Mg plated steel sheet after the chemical conversion treatment in such a ratio that a chromium-free resin coating film having a thickness of 0.1 to 20 µm is formed. For coating and baking, a continuous coating equipment having a roll coater, a hot air drying function and the like can be used according to a conventional method. When the chromium-free resin coating film has a thickness of 0.1 μm or more, it becomes a continuous coating film having no defects such as pinholes and unpainted portions. However, when the thickness exceeds 20 μm, the workability is reduced.
[0013]
It is possible to ship the coated steel sheet with the chromium-free resin coating as it is as a one-coat pre-coated steel sheet, but it is also possible to provide one or more coatings on the chromium-free resin coating. . For the top coat and intermediate coat, urethane resin, epoxy resin, olefin resin such as polyethylene, polypropylene, ethylene-acrylic acid copolymer, styrene resin such as polystyrene, polyester resin, or copolymer of these Coating compositions based on coalesced or modified products, acrylic resins and the like are used. Modified silica may be added to this coating composition as needed.
The coating composition for the top coat and the middle coat is appropriately selected depending on the shape of each wiper. Specifically, the top coat having a film thickness of 15 to 20 μm obtained by baking a high-molecular polyester paint at 230 ° C. for 40 seconds. There is a membrane. For coating and baking, a continuous coating equipment having a roll coater, a hot air drying function and the like can be used according to a conventional method.
[0014]
【Example】
A 0.5 mm-thick plated steel sheet in which various Zn plating layers shown in Table 1 were formed at an adhesion amount of 30 g / m ² on one side was used as a coating original sheet.
[0015]

[0016]
The coated original plate was subjected to a Ni-precipitation type surface conditioning treatment, washed with hot water, washed with water, and dried. Next, a chemical conversion treatment liquid using Ti as a valve metal was applied to the dried surface of the original coating plate, placed in an oven without washing with water, and heated and dried at a plate temperature of 100 ° C. For the chemical conversion treatment, Ti was selected as a valve metal, (NH ₄ ) ₂ TiF ₆ having a Ti concentration of 20 g / l, an F concentration of 47.5 g / l, and a P concentration of 40 g / l H ₃ PO ₄ , 4 g. A treatment solution containing / l of tannic acid was used.
Observation of the surface of the plating layer after drying revealed that a chromium-free chemical conversion treatment film having a Ti equivalent adhesion amount of 15 mg / m ² was formed. As a result of X-ray fluorescence analysis of the chemical conversion treatment film, the element concentration ratio was Ti: 4%, O: 71%, F: 13%, P: 12%.
[0017]
Next, an epoxy-modified high-molecular polyester resin coating in which modified silica and polyphosphate are dispersed at a ratio of 15% by mass and 30% by mass with respect to the resin solid content, respectively, is applied on the dried chromium-free chemical conversion coating film, By baking at a maximum temperature of 215 ° C. for 40 seconds, a chromium-free resin coating film having a thickness of 5 μm was formed.
The chromium-free resin film was used as an undercoat film, and a similar high-molecular polyester resin paint was applied and baked to form an overcoat film having a thickness of 15 μm.
[0018]
A test piece was cut out from each of the manufactured coated steel sheets and subjected to an accelerated corrosion test. In the accelerated corrosion test, salt water was sprayed on the test piece with the cut end surface exposed for 240 hours in accordance with JIS K5600. It was left in a humid atmosphere of 49 ° C. and 98% RH for 240 hours.
The test pieces were observed after the salt spray test and the wet test, and the blister (edge creep) width of the coating film generated from the cut end face and the rate of occurrence of red rust at the cut end were measured. From the measurement results, the swelling width of the coating film was 1.0 mm or less, ◎; 1.0 to 2.0 mm, ，; 2.0 to 3.0 mm, Δ; The edge corrosion resistance was evaluated by setting ◎ to 5%, を to 5 to 10%, Δ to 10 to 30%, and × to 30% or more.
[0019]
As can be seen from the investigation results in Table 2, in the present invention example in which a Zn-Al-Mg plated steel sheet was used as a coating base plate and a chromium-free chemical conversion coating film and a chromium-free resin coating film were provided, both the salt spray test and the wet test were excellent. No corrosion was observed, and no rusting that reduced the wiper function was detected. On the other hand, in the comparative example in which the Zn-Al plated steel sheet was used as the original plate for coating, in both the salt spray test and the wet test, the end face corrosion resistance was inferior, and rust generation that deteriorated the appearance of the wiper was observed. This comparison result indicates that Mg contained in the plating layer is effective in suppressing corrosion.
[0020]

[0021]
Embodiment 2
A Zn—Al—Mg plated steel sheet having an adhesion amount of 30 g / m ² per side and a sheet thickness of 0.5 mm was used as a base plate for coating, and subjected to a chemical conversion treatment in the same manner as in Example 1 using a chemical conversion treatment solution having the composition shown in Table 3. . When the chemical conversion treatment film formed on the plating layer surface was analyzed, each component was contained at the concentration shown in Table 4.
[0022]

[0023]

[0024]
After forming a coating film on the chemical conversion coating film in the same manner as in Example 1, a test piece was cut out from each of the manufactured coated steel sheets and subjected to a 2t bending test. After spraying salt water on the bent test piece for 240 hours, the test piece surface was observed. The corrosion resistance of the cut end face was evaluated in the same manner as in Example 1. Regarding paint blisters that tend to occur in the processed part, the test pieces with no blisters on the paint film are marked with ◎, the test pieces with very slight blisters detected are marked with ○, less than 50% are marked with Δ, and more than 50% are blistered. The test piece in which occurred was evaluated as ×, and the coating blister resistance was evaluated.
As can be seen from the investigation results in Table 5, the coated steel sheets of Test Nos. 1 to 7 manufactured according to the present invention exhibited excellent corrosion resistance at both the cut end face and the processed portion. In contrast, in Test No. 8 using a chemical conversion treatment solution containing no soluble titanium fluoride and in Test No. 9 using a chemical conversion treatment solution containing no titanium compound, the corrosion resistance of both the cut end face and the processed portion was reduced. .
[0025]

[0026]
Embodiment 3
In Example 2, after forming a chemical conversion treatment film of Test No. 1 having excellent corrosion resistance on a Zn-Al-Mg plated steel sheet, a chromium-free resin coating was applied. As the chromium-free resin coating, an epoxy-modified polyester resin coating (Table 6) containing modified silica and polyphosphate in various ratios was used.
The chromium-free resin coating applied to the original coating plate was baked at a maximum temperature of 230 ° C. for 40 seconds to form a chromium-free resin coating having a thickness of 5 μm. Further, a chromium-free resin coating film was used as an undercoating film, and a high-molecular polyester paint was used as the overcoating material, and the coating and baking were performed in the same manner as the undercoating to form a 15 μm-thick overcoating film.
[0027]
A test specimen was cut out from each of the obtained coated steel sheets, subjected to a 2t bending test in the same manner as in Example 2, and evaluated for corrosion resistance by a 240-hour salt spray test.
Regardless of which chromium-free resin coating film was formed, the blister width of the cut end face was very small, 1 mm or less, and red rust generated on the cut end face was less than 5%. No coating blisters occurred in the processed part. For comparison, when a coated steel sheet having a resin coating formed using an epoxy-modified high-molecular polyester resin coating containing no modified silica was similarly tested, coating blisters with a maximum blister width exceeding 5 mm occurred on the cut end surface. However, in the processed part, the coating film blister was generated on the entire surface.
[0028]

[0029]
【The invention's effect】
As described above, a Zn-Al-Mg-plated steel sheet is used as a base plate for coating, and a modified silica, polyphosphate is passed through a chromium-free chemical conversion coating in which an oxide or hydroxide and a fluoride of a valve metal coexist. By forming a chromium-free resin coating in which is dispersed as a rust-preventive pigment, a precoated steel sheet for wipers having excellent end face corrosion resistance can be obtained without using an environmental load substance such as a chromium compound. Even if rust is generated on the cut end surface, it exhibits a brown color close to black, so that the appearance of the wiper is hardly deteriorated.

Claims

Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and a primary ternary eutectic structure matrix of Al / Zn / Zn ₂ Mg in which a primary Al phase or a primary Al phase and a Zn single phase are mixed. The base material is a steel plate on which a Zn-Al-Mg plating layer is formed, and the oxide has a high insulation resistance through a chromium-free chemical conversion treatment film in which an oxide or hydroxide and a fluoride of a valve metal coexist. A precoated steel sheet for a wiper, wherein a chromium-free resin coating film in which porous silica particles having Ca ions bonded thereto by ion exchange are dispersed as a rust-preventive pigment is formed on the surface of a substrate.

The precoated steel sheet for a wiper according to claim 1, wherein the Zn-Al-Mg plating layer further contains one or two kinds of Ti: 0.002 to 0.1% by mass and B: 0.001 to 0.45% by mass.

The precoated steel sheet for a wiper according to claim 1, wherein the chromium-free resin coating further contains a polyphosphate.

A wiper produced by forming the precoated steel sheet according to claim 1.