JP3546271B2 - Manufacturing method of anticorrosion coated steel - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、厳しい腐食環境下で使用されるラインパイプ、海洋構造物等に好適な防食被覆を有する防食被覆鋼材に係り、とくに防食被覆の接着耐久性の向上に関する。本発明でいう鋼材は、鋼管、鋼板、形鋼、棒鋼、線材を含むものとする。
【０００２】
【従来の技術】
ガス、水道、電気配線等の配管、光ケーブル保護管、ラインパイプなどの地中埋設管や、港湾、河川などの土木工事において使用される鋼管杭、鋼管矢板、鋼矢板の土木建材や、建築屋根材、壁材などには、鋼材の防食用に有機樹脂の塗装等による防食被覆処理が施される。防食被覆処理としては、耐久性などの要求仕様に応じて様々な種類や膜厚の塗装が施されている。
【０００３】
最近では、ライフサイクルコストの観点から、防食被覆処理が施された鋼材には、ますます長い防食寿命を有することが期待されるようになってきた。とくに、地中埋設管や土木建材などは社会的インフラということもあり、数十年以上の防食寿命が望まれている。
従来から、鋼材への防食被覆処理を施すに際しては、予め、酸洗、ブラスト処理などの鋼板表面の酸化被膜除去処理を行ったのちに、防食被覆処理のための下地処理が施されている。
【０００４】
鋼材表面に施される防食被覆の寿命は、▲１▼被膜（塗膜）と下地との密着性、▲２▼被覆（塗装）材料自体の劣化、の２点から決定されるといわれている。被膜（塗膜）と下地との密着性が良好であっても、被覆（塗装）材料自体が、例えば、屋外であれば太陽光に起因する紫外線による耐候劣化や、地中埋設管などであれば耐熱劣化などにより、劣化し、被覆の防食性が低下する場合がある。また、被覆（塗装）材料自体の劣化がなく健全であっても、被膜（塗膜）と下地との密着性が低下して鋼材への保護性を失う（防食性の低下）という場合もある。
【０００５】
しかしながら、近年、被覆（塗装）材料自体の改良が著しくすすみ、防食被覆の寿命は、被膜（塗膜）と下地との密着性により決定されることが多くなっている。
有機樹脂の塗装による防食被覆では、塗膜と下地との密着性不良により、例えば、端面からの塗膜の剥離、あるいは、全体的な接着強度の低下、ふくれなどの不具合が生じる。このような不具合が発生すると、塗装の補修あるいは塗り直しといった作業が必要になる。これらの作業には莫大な費用を要し、特に社会的インフラの場合には社会的コスト負担も大きくなる。したがって、塗膜と下地との密着性、塗膜と下地との接着耐久性を向上し、防食被覆の寿命を長寿命化して、補修や塗り替えを極力回避することが必要である。
【０００６】
鋼材の防食被覆処理のための下地処理としては、従来から例えば、リン酸塩処理、クロメート処理、各種カップリング剤処理、陽極酸化処理、などが知られている。クロメート処理以外の下地処理では、被膜（塗膜）が剥離しやすく防食性が不十分であった。一方、クロメート処理は、十分な防食性を保持するためには塗布量を多くしなければならず、また比較的高い加熱温度を必要とし、生産性が低下するなどの問題があった。
【０００７】
このような問題に対し、例えば、特開平9-268374号公報には、ブラスト処理した鋼管の外面に、２〜８重量％のモリブデン酸アンモニウム、0.5 〜２重量％のリン酸、0.1 〜0.5 重量％のエチレンジアミン四酢酸と0.5 〜５重量％のポリビニルアルコールを含む混合水溶液を、被膜乾燥重量が30〜100mg/m2になるように塗布したのち、120 〜180 ℃で加熱焼き付けし、ついで有機樹脂の防食被覆を施す塗覆装鋼管の製造方法が提案されている。特開平9-268374号公報に記載された技術によれば、耐陰極剥離性と経済性を兼ね備えた防食被覆鋼管が得られるとしている。
【０００８】
しかしながら、これらの下地処理では、処理に長時間を要するうえ、厳しい腐食環境下では、依然として被膜（塗膜）と下地との密着性が不足し、防食被覆の防食性が不十分であるという問題があった。
【０００９】
【発明が解決しようとする課題】
これら塗膜と下地との密着性不良現象には、塗膜の環境遮断性も関係するが、とくに塗膜と下地との接着界面における接着特性および電気化学的な特性が大きく関係している。このようなことから、塗膜と下地との密着性を向上し、防食被覆の寿命（耐久性）を向上させるためには、適切な下地処理を施すことが肝要となる。
【００１０】
本発明は、上記した従来技術の問題を解決し、被膜と下地との密着性、接着耐久性を向上し、耐久性に優れた防食被覆を有する、防食被覆鋼材の製造方法を提供することを目的とする。
【００１１】
【課題を解決するための手段】
本発明者らは、上記した課題を達成するために、防食被覆処理の下地処理方法について鋭意検討した。その結果、鋼材表面にモリブデン酸ナトリウム（Na2MoO4 ・2H2O）とモリブデン酸アンモニウム((NH4)6Mo7O24 ・4H2O）の混合水溶液を接触させることにより、下地処理時間を短縮できるとともに、被膜と下地との密着性、接着耐久性が向上し、防食被覆の耐久性が格段に向上することを知見した。
【００１２】
本発明は、上記した知見に基づいて、さらに検討を加え完成されたものである。
すなわち、本発明は、鋼材表面に下地処理を施したのち、好ましくは乾燥処理を施し、ついで防食被覆処理を施す防食被覆鋼材の製造方法において、前記下地処理が、前記鋼材表面に、0.001M〜1.0Mのモリブデン酸ナトリウムと0.001M〜1.0Mのモリブデン酸アンモニウムとを含む混合水溶液を接触させる処理であることを特徴とする防食被覆鋼材の製造方法であり、また、本発明では、前記混合水溶液が、さらに0.001M〜1.0Mのリン酸を含むことが好ましく、また、本発明では、前記混合水溶液を接触させる処理が、鋼材表面に厚さ：２〜100nm のモリブデンを含む反応層を形成する処理であることが好ましい。
【００１３】
【発明の実施の形態】
本発明は、鋼材表面に防食被覆を施し、鋼材の防食性を向上させた防食被覆鋼材の製造方法である。本発明では、防食被覆処理を施す前に、鋼材表面に下地処理を施す。なお、本発明では、鋼材表面にめっき層が存在しても何ら問題ない。本発明における下地処理は、鋼材表面に、0.001M〜1.0Mのモリブデン酸ナトリウム（Na2MoO4 ・2H2O）と0.001M〜1.0Mのモリブデン酸アンモニウム((NH4)6Mo7O24 ・4H2O）とを含む混合水溶液を接触させる処理である。本発明では、モリブデン酸ナトリウムとモリブデン酸アンモニウムとを混合した水溶液を用いて下地処理を行うことに特徴がある。モリブデン酸ナトリウム単独、あるいはモリブデン酸アンモニウム単独では、被膜と下地との接着耐久性が低く、また、所定の接着強度あるいは接着耐久性を得るためには反応時間が長すぎて生産性が低下する。
【００１４】
モリブデン酸ナトリウムは、暖房用温水配管のインヒビターとして知られており、鋼材表面を不動態化する。これは、モリブデン酸の鋼材表面への吸着により達成されると考えられているが、メカニズムは現在のところ不明である。
混合水溶液中のモリブデン酸ナトリウム、モリブデン酸アンモニウムの濃度はいずれも0.001M〜1.0Mの範囲に限定した。モリブデン酸ナトリウム、モリブデン酸アンモニウムの濃度がそれぞれ0.001M未満では、鋼板板面全体に十分な被膜の生成がなく、被膜と下地との接着耐久性向上効果が少なく、一方、モリブデン酸ナトリウム、モリブデン酸アンモニウムの濃度が1.0Mを超えると、▲１▼反応層が厚くなりすぎ脆くなる、▲２▼被膜と下地との接着耐久性向上効果が飽和し、含有量に見合う効果が期待でなくなり、経済的に不利となる。このため、混合水溶液中のモリブデン酸ナトリウムの濃度は0.001M〜1.0M、モリブデン酸アンモニウムの濃度は0.001M〜1.0Mに限定した。なお、モリブデン酸ナトリウムの濃度はより好ましくは0.01M 〜0.2Mであり、モリブデン酸アンモニウムの濃度はより好ましくは0.01M 〜0.2Mである。
【００１５】
また、本発明では、混合水溶液に、0.001M〜1.0Mのモリブデン酸ナトリウムと0.001M〜1.0Mのモリブデン酸アンモニウムに加えて、0.001M〜1.0Mのリン酸（H3PO4 ）を含むことが好ましい。混合水溶液中に、モリブデン酸ナトリウム、モリブデン酸アンモニウムに加えて、リン酸を含むことにより、鋼材との反応性、塗膜と下地との接着耐久性が顕著に向上し、防食被覆鋼材の防食性が向上する。リン酸の濃度が0.001M未満では、上記した効果が少なく、一方、1.0Mを超えると、リン酸によるエッチング効果が強くなり反応層が形成しないため、塗膜と下地との接着耐久性が低下する。なお、リン酸の濃度はより好ましくは0.01M 〜0.1Mである。
【００１６】
上記した混合水溶液を鋼材表面に接触させる方法としては、とくに限定されないが、鋼材表面に混合水溶液を塗布するか、あるいは鋼材を混合水溶液中に浸漬するのが好ましい。混合水溶液と鋼材表面との反応により、鋼材表面にモリブデン（Mo）を含む反応層が形成される。反応層の厚さは、２〜100nm とするのが好ましい。この厚さの反応層を形成するためには、数十秒〜数十分程度の処理時間を必要とする。
【００１７】
この反応層の厚さは、オージェ電子分光装置の深さ方向分析によって測定されるMo付着量で評価することができる。
本発明では、下地処理に使用する上記した濃度の混合水溶液の温度はとくに限定されないが、反応を促進する意味から、溶液あるいは鋼材の温度を室温以上、好ましくは20〜40℃に調整して使用してもよい。溶液または鋼材の温度が高すぎると、反応が進行しすぎて反応層が脆弱となる。
【００１８】
なお、下地処理を施す前に、表面の汚れ、汚染物質、スケールなどをできる限り除去しておくことが好ましく、ブラスト処理や酸洗などを行うのが好ましい。また、上記した下地処理を施したのちに、カップリング剤処理などの他の下地処理を施しても何ら問題はない。
下地処理を施された鋼材は、ついで水洗してもよい。また、適度な反応時間の後、水分を飛ばす意味で、乾燥処理を行うのが好ましい。乾燥処理の方法は、下地処理後の鋼材を、室温で放置してもよく、また、処理時間を短縮するために、ブローア等により、常温空気吹付け、あるいは温風吹付け、あるいは鋼材を80〜120 ℃に加熱する処理としてもよく、とくに限定されない。
【００１９】
下地処理を施され、好ましくは乾燥処理を施された鋼材は、ついで表面に防食被覆処理を施される。防食被覆処理としては、通常の有機樹脂の防食被覆とするのが好ましい。有機樹脂の防食被覆は、例えば、ポリオレフィン樹脂、エポキシ樹脂、アクリル樹脂またはポリエステル樹脂、ウレタン樹脂を含む塗料を、鋼材表面にスプレー塗装、刷毛塗り、ロールコーター等により所定の膜厚を被覆するのが好ましい。
【００２０】
また、防食被覆は、有機樹脂のライニングとしてもよい。有機樹脂のライニングは、接着剤を被覆し、その上層としてポリエチレン樹脂、ポリプロピレン樹脂、ポリブテン樹脂等をホットプレス、加熱圧着ロール等により圧着して、所定の厚さに調整して被覆するのが好ましい。
【００２１】
【実施例】
以下、本発明を実施例にて詳細に説明する。
鋼材として、軟鋼板を用意した。まず、軟鋼板に、表面汚染物質ならびに酸化層を除去するため、ブラスト処理を施した。その後、表１に示す条件で下地処理を施した。下地処理に用いた混合水溶液は、純水に、工業用試薬である、モリブデン酸ナトリウム(Na2MoO4・2H2O) とモリブデン酸アンモニウム((NH4)6Mo7O24 ・4H2O) あるいはさらにおよびリン酸(H3PO3) を表１に示す濃度になるように、それぞれ所定量溶解し、調整した溶液を用いた。なお、溶液の温度は、表１に示す温度とし、ヒータで加熱保持した。
【００２２】
また、下地処理は、上記した混合水溶液を鋼材表面に接触させることにより行い、接触方法としては、▲１▼混合水溶液をナイロン製刷毛で軟鋼板に塗布する方法（刷毛）、▲２▼軟鋼板を混合水溶液中に浸漬する方法（浸漬）を用いた。なお、▲１▼の方法では、混合水溶液を塗布し３min 後純水で純水で軟鋼板表面を洗い流した。また、▲２▼の方法では、浸漬時間を２min とした。なお、いずれの場合でも、軟鋼板は40℃に予熱した。
【００２３】
下地処理後、軟鋼板を純水で水洗した。水洗後、200 ℃雰囲気（炉内）中で、約３min保持する乾燥処理を実施した。
下地処理（乾燥処理）後、軟鋼板に防食被覆処理を行い、防食被覆鋼材とした。防食被覆処理は、有機樹脂の塗装、または有機樹脂のライニングとした。有機樹脂の塗装は、塗料としてエポキシ系樹脂塗料とし、スプレー塗装により所定の膜厚（100 μm ）の塗装を行った。また、有機樹脂のライニングは、エポキシ系接着剤を塗装したのち、ポリエチレン樹脂をホットプレスにて圧着し、接着層を介し1.5mm の低密度ポリエチレン層を形成した。
【００２４】
得られた防食被覆鋼材から、試験片（大きさ：100 ×100mm ）を採取し、塩水噴霧試験、温塩水浸漬試験を実施した。なお、防食被覆として有機樹脂のライニングを施した防食被覆鋼材についてはさらに、陰極剥離試験を実施した。試験方法はつぎの通りとした。
（１）塩水噴霧試験
各試験片の中央部に、50×50mmの大きさのクロスカット（幅 1mm）を導入し、JIS Z 2371の規定に準拠して塩水噴霧試験を90日間実施した。試験後、クロスカットからの防食被覆の剥離幅を測定した。
（２）温塩水浸漬試験
各試験片の端部を2mm 程度研削し端部を揃えたのち、濃度：３質量％NaClの温塩水（液温度：60℃）に、1000時間浸漬した。浸漬後、端部からの防食被覆の剥離距離を測定した。また、ポリエチレン樹脂ライニング材については被覆を、10mm幅で鋼材表面に対し直角方向に約60mm引張り、防食被覆が剥離するときの単位長さ当たりの平均剥離荷重を求め、接着強度（Ｎ／mm）と定義し、試験前の接着強度に対する比を求め、接着強度保持率（％）としてを評価した。エポキシ系樹脂塗装材については、断面積が100 mm2 の断面形状が円形の鋼製治具を、接着剤を介して塗装表面に接着し、その後、治具まわりの塗装を強制的に剥離し、治具をつかんで引張試験を実施し、接着部分が破断する最大荷重を求め、接着強度(MPa) と定義し、試験前の接着強度に対する比を求め、接着強度保持率（％）として評価した。
（３）陰極剥離試験
陰極剥離試験は、ASTM G8 の規定に準拠して実施した。各試験片の中央部に、５mmφの人工欠陥を設け、70mmφの円筒を立て中に３質量％NaCl溶液を満たした。また、対極を白金電極として、鋼材面を参照電極(SCE) に対して−1.5Vに保持した。これを60℃の電気炉中に30日間暴露した。試験後、欠陥部から広がった剥離距離を測定した。
【００２５】
これらの結果を表１に示す。
【００２６】
【表１】
本発明例は、いずれも剥離距離は少なく、接着強度保持率も高く、耐塩水噴霧性、耐温塩水浸漬性に優れ、また、有機樹脂のライニングの防食被覆では耐陰極剥離性に優れている。これに対し、本発明の範囲を外れる比較例では、耐塩水噴霧性、耐温塩水浸漬性、耐陰極剥離性が低下していた。
【００２８】
【発明の効果】
以上、説明したように、本発明によれば、被膜と下地との接着耐久性が向上し、防食被覆鋼材の防食寿命を長寿命化することができる。また、本発明によれば、長期間にわたり、防食被覆の補修、再被覆等を行う必要がなくなり、経費の節減ができ、産業上格段の効果を奏する。また、厳しい腐食環境においても、長期間の防食が可能になり、腐食および塗装劣化による社会的損失を回避することができるという効果もある。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an anticorrosion-coated steel material having an anticorrosion coating suitable for line pipes, marine structures, and the like used under severe corrosive environments, and particularly to an improvement in the adhesion durability of the anticorrosion coating. The steel material referred to in the present invention includes a steel pipe, a steel plate, a shaped steel, a steel bar, and a wire.
[0002]
[Prior art]
Piping for gas, water, electric wiring, etc., underground pipes such as optical cable protection pipes and line pipes, steel pipe piles, steel pipe sheet piles used in civil engineering works such as ports and rivers, civil engineering construction materials such as steel sheet piles, and building roofs Materials, wall materials, and the like are subjected to anticorrosion coating treatment such as painting of an organic resin for corrosion prevention of steel materials. As the anticorrosion coating treatment, various types and thicknesses of coating are applied according to required specifications such as durability.
[0003]
Recently, from the viewpoint of life cycle cost, it has been expected that a steel material subjected to anticorrosion coating treatment has an even longer anticorrosion life. In particular, underground pipes and civil engineering materials are social infrastructures, and anticorrosion life of more than several decades is desired.
2. Description of the Related Art Conventionally, when a steel material is subjected to an anticorrosion coating treatment, an oxide film removal treatment such as pickling and blasting is performed on a steel sheet surface, and then a base treatment for the anticorrosion coating treatment is performed.
[0004]
It is said that the life of the anticorrosion coating applied to the steel surface is determined from two points: (1) adhesion between the coating (coating) and the base, and (2) deterioration of the coating (painting) material itself. . Even if the adhesion between the coating (coating) and the substrate is good, if the coating (coating) material itself is, for example, outdoors, it may be weather-resistant deterioration due to ultraviolet rays caused by sunlight, or an underground pipe. For example, the coating may be deteriorated due to heat resistance deterioration or the like, and the corrosion prevention of the coating may be reduced. In addition, even if the coating (coating) material itself is healthy without deterioration, the adhesion between the coating film (coating film) and the base may be reduced and the protection to the steel material may be lost (decreased corrosion protection). .
[0005]
However, in recent years, the coating (coating) material itself has been significantly improved, and the life of the anticorrosive coating is often determined by the adhesion between the coating (coating) and the base.
In the anticorrosion coating by coating with an organic resin, poor adhesion between the coating film and the base causes problems such as peeling of the coating film from the end face, reduction in overall adhesive strength, and blistering. When such a problem occurs, work such as repairing or repainting the paint is required. These operations are enormous and costly, especially in the case of social infrastructure. Therefore, it is necessary to improve the adhesion between the coating film and the base and the adhesion durability between the coating film and the base, prolong the life of the anticorrosion coating, and avoid repair and repainting as much as possible.
[0006]
As a base treatment for the anticorrosion coating treatment of a steel material, for example, phosphate treatment, chromate treatment, various coupling agent treatments, anodization treatment, and the like are conventionally known. In the base treatment other than the chromate treatment, the coating (coating) was easily peeled, and the corrosion resistance was insufficient. On the other hand, the chromate treatment has problems that the coating amount must be increased in order to maintain sufficient anticorrosion properties, a relatively high heating temperature is required, and productivity is reduced.
[0007]
To cope with such a problem, for example, Japanese Patent Application Laid-Open No. 9-268374 discloses that the outer surface of a blasted steel pipe is coated with 2 to 8% by weight of ammonium molybdate, 0.5 to 2% by weight of phosphoric acid, 0.1 to 0.5% by weight. % Of ethylenediaminetetraacetic acid and 0.5 to 5% by weight of polyvinyl alcohol, and then applied at a dry weight of 30 to 100 mg / m 2 and baked at 120 to 180 ° C. A method for manufacturing a coated steel pipe to be provided with the anticorrosion coating has been proposed. According to the technique described in Japanese Patent Application Laid-Open No. 9-268374, it is said that a corrosion-resistant coated steel pipe having both cathodic peeling resistance and economy can be obtained.
[0008]
However, these substrate treatments require a long time for the treatment, and in a severe corrosive environment, the adhesion between the film (coating film) and the substrate is still insufficient, and the corrosion resistance of the anticorrosive coating is insufficient. was there.
[0009]
[Problems to be solved by the invention]
The phenomenon of poor adhesion between the coating film and the base material is related to the environmental barrier properties of the coating film, but the adhesion characteristics and the electrochemical characteristics at the bonding interface between the coating film and the base material are significantly related. For this reason, in order to improve the adhesion between the coating film and the base and to improve the life (durability) of the anticorrosion coating, it is important to perform an appropriate base treatment.
[0010]
The present invention solves the above-mentioned problems of the prior art, improves the adhesion between the coating film and the base, improves the adhesion durability, and has a corrosion-resistant coating with excellent durability, and provides a method for producing a corrosion-resistant coated steel material. Aim.
[0011]
[Means for Solving the Problems]
Means for Solving the Problems In order to achieve the above object, the present inventors have intensively studied a base treatment method for anticorrosion coating treatment. As a result, by bringing a mixed aqueous solution of sodium molybdate (Na 2 MoO 4 .2H 2 O) and ammonium molybdate ((NH 4 ) 6 Mo 7 O 24 .4H 2 O) into contact with the steel surface, It has been found that the resistance to corrosion can be shortened, the adhesion between the coating and the base, the adhesion durability can be improved, and the durability of the anticorrosion coating can be significantly improved.
[0012]
The present invention has been completed based on the above findings and further studies.
That is, the present invention provides a method for producing a corrosion-resistant coated steel material that is preferably subjected to a drying treatment after a steel material surface is subjected to a base treatment, and then subjected to a corrosion protection coating treatment, wherein the base treatment is performed on the steel material surface at 0.001M or more. A method for producing an anticorrosion-coated steel material, which is a treatment in which a mixed aqueous solution containing 1.0 M sodium molybdate and 0.001 M to 1.0 M ammonium molybdate is brought into contact, and in the present invention, the mixed aqueous solution However, it is preferred that the mixed solution further contains 0.001M to 1.0M phosphoric acid. In the present invention, the treatment of contacting the mixed aqueous solution forms a reaction layer containing molybdenum having a thickness of 2 to 100 nm on the surface of the steel material. Preferably, it is a treatment.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is a method for producing an anticorrosion-coated steel material in which an anticorrosion coating is applied to the surface of the steel material to improve the corrosion resistance of the steel material. In the present invention, before the anticorrosion coating treatment is applied, the steel material surface is subjected to a base treatment. In the present invention, there is no problem even if a plating layer exists on the surface of the steel material. In the undercoating treatment in the present invention, 0.001 M to 1.0 M sodium molybdate (Na 2 MoO 4 .2H 2 O) and 0.001 M to 1.0 M ammonium molybdate ((NH 4 ) 6 Mo 7 O 24・ This is a treatment in which a mixed aqueous solution containing 4H 2 O) is brought into contact. The present invention is characterized in that the base treatment is performed using an aqueous solution in which sodium molybdate and ammonium molybdate are mixed. When sodium molybdate alone or ammonium molybdate alone is used, the adhesion durability between the film and the base is low, and the reaction time is too long to obtain a predetermined adhesion strength or adhesion durability, and the productivity is reduced.
[0014]
Sodium molybdate is known as an inhibitor in hot water piping for heating and passivates the surface of steel. It is believed that this is achieved by the adsorption of molybdic acid on the steel surface, but the mechanism is currently unknown.
The concentrations of sodium molybdate and ammonium molybdate in the mixed aqueous solution were both limited to the range of 0.001M to 1.0M. If the concentrations of sodium molybdate and ammonium molybdate are each less than 0.001M, a sufficient film is not formed on the entire surface of the steel sheet, and the effect of improving the adhesion durability between the film and the substrate is small. If the concentration of ammonium exceeds 1.0M, (1) the reaction layer becomes too thick and becomes brittle, (2) the effect of improving the adhesion durability between the coating and the base is saturated, and the effect corresponding to the content is not expected, and the economy is low. Disadvantageous. For this reason, the concentration of sodium molybdate in the mixed aqueous solution was limited to 0.001M to 1.0M, and the concentration of ammonium molybdate was limited to 0.001M to 1.0M. The concentration of sodium molybdate is more preferably 0.01M to 0.2M, and the concentration of ammonium molybdate is more preferably 0.01M to 0.2M.
[0015]
In the present invention, the mixed aqueous solution contains 0.001 M to 1.0 M phosphoric acid (H 3 PO 4 ) in addition to 0.001 M to 1.0 M sodium molybdate and 0.001 M to 1.0 M ammonium molybdate. Is preferred. By containing phosphoric acid in addition to sodium molybdate and ammonium molybdate in the mixed aqueous solution, the reactivity with the steel material and the durability of the adhesion between the coating film and the base material are remarkably improved. Is improved. If the concentration of phosphoric acid is less than 0.001M, the above effects are small, while if it exceeds 1.0M, the etching effect due to phosphoric acid becomes stronger and a reaction layer is not formed, so that the adhesion durability between the coating film and the base decreases. I do. The concentration of phosphoric acid is more preferably 0.01M to 0.1M.
[0016]
The method of bringing the mixed aqueous solution into contact with the surface of the steel material is not particularly limited, but it is preferable to apply the mixed aqueous solution to the surface of the steel material or to immerse the steel material in the mixed aqueous solution. The reaction between the mixed aqueous solution and the steel material surface forms a reaction layer containing molybdenum (Mo) on the steel material surface. The thickness of the reaction layer is preferably 2 to 100 nm. In order to form a reaction layer having this thickness, a processing time of about several tens of seconds to several tens of minutes is required.
[0017]
The thickness of this reaction layer can be evaluated by the amount of Mo adhesion measured by the depth direction analysis of the Auger electron spectrometer.
In the present invention, the temperature of the mixed aqueous solution having the above-described concentration used for the base treatment is not particularly limited, but from the viewpoint of accelerating the reaction, the temperature of the solution or the steel material is adjusted to room temperature or higher, preferably 20 to 40 ° C. May be. If the temperature of the solution or the steel material is too high, the reaction proceeds too much and the reaction layer becomes brittle.
[0018]
It is preferable to remove surface dirt, contaminants, scale, and the like as much as possible before performing the base treatment, and it is preferable to perform blast treatment, pickling, or the like. In addition, there is no problem even if another base treatment such as a coupling agent treatment is performed after the above-described base treatment is performed.
The steel material subjected to the base treatment may then be washed with water. After an appropriate reaction time, it is preferable to perform a drying treatment in order to remove moisture. The method of the drying treatment may be as follows: the steel material after the base treatment may be left at room temperature, and in order to shorten the treatment time, blow the room temperature air with a blower or the like, or blow the steel material with 80 to 80 ° C. The treatment may be performed by heating to 120 ° C., but is not particularly limited.
[0019]
The steel material which has been subjected to the base treatment and preferably subjected to the drying treatment is then subjected to a corrosion protection coating treatment on the surface. The anticorrosion coating treatment is preferably a normal organic resin anticorrosion coating. The anticorrosion coating of the organic resin is, for example, coating a coating containing a polyolefin resin, an epoxy resin, an acrylic resin or a polyester resin, or a urethane resin on a steel material surface with a predetermined thickness by spray coating, brush coating, a roll coater, or the like. preferable.
[0020]
Further, the anticorrosion coating may be an organic resin lining. It is preferable that the lining of the organic resin is coated with an adhesive, and as an upper layer thereof, polyethylene resin, polypropylene resin, polybutene resin, or the like is pressed by a hot press, a heat pressing roll, or the like, and is adjusted to a predetermined thickness and coated. .
[0021]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
A mild steel plate was prepared as a steel material. First, a mild steel plate was subjected to a blast treatment in order to remove surface contaminants and an oxide layer. Thereafter, a base treatment was performed under the conditions shown in Table 1. The mixed aqueous solution used for the base treatment is pure water, industrial reagents, sodium molybdate (Na 2 MoO 4・ 2H 2 O) and ammonium molybdate ((NH 4 ) 6 Mo 7 O 24・ 4H 2 O) Alternatively, a solution prepared by dissolving predetermined amounts of phosphoric acid (H 3 PO 3 ) and the phosphoric acid (H 3 PO 3 ) in the respective concentrations shown in Table 1 was used. The temperature of the solution was as shown in Table 1, and the solution was heated and held by a heater.
[0022]
The base treatment is carried out by bringing the above mixed aqueous solution into contact with the surface of the steel material. The contact method includes (1) a method of applying the mixed aqueous solution to a mild steel plate with a nylon brush (brush), and (2) a mild steel plate. Was immersed in a mixed aqueous solution (immersion). In the method (1), the mixed aqueous solution was applied, and after 3 minutes, the surface of the mild steel plate was washed away with pure water with pure water. In the method (2), the immersion time was 2 minutes. In each case, the mild steel sheet was preheated to 40 ° C.
[0023]
After the base treatment, the mild steel sheet was washed with pure water. After washing with water, a drying treatment was performed in a 200 ° C. atmosphere (in a furnace) for about 3 minutes.
After the base treatment (drying treatment), the mild steel plate was subjected to an anticorrosion coating treatment to obtain an anticorrosion coated steel material. The anticorrosion coating treatment was an organic resin coating or an organic resin lining. The coating of the organic resin was made of an epoxy resin paint, and a predetermined thickness (100 μm) was applied by spray coating. The lining of the organic resin was coated with an epoxy adhesive, and then the polyethylene resin was pressed with a hot press to form a 1.5-mm low-density polyethylene layer via the adhesive layer.
[0024]
A test piece (size: 100 × 100 mm) was sampled from the obtained anticorrosion-coated steel material and subjected to a salt spray test and a hot salt water immersion test. Note that a cathodic peel test was further performed on the anticorrosion-coated steel material provided with an organic resin lining as the anticorrosion coating. The test method was as follows.
(1) Salt Spray Test A 50 × 50 mm cross cut (1 mm width) was introduced at the center of each test piece, and a salt spray test was conducted for 90 days in accordance with the provisions of JIS Z 2371. After the test, the peel width of the anticorrosion coating from the cross cut was measured.
(2) Warm salt water immersion test The end of each test piece was ground by about 2 mm and the ends were aligned. Then, the test piece was immersed in warm salt water (concentration: 3% by mass NaCl, liquid temperature: 60 ° C.) for 1000 hours. After immersion, the peel distance of the anticorrosion coating from the end was measured. For the polyethylene resin lining material, the coating was pulled about 10 mm in width at right angles to the steel surface by about 60 mm, and the average peeling load per unit length when the anticorrosion coating was peeled was determined. The adhesive strength (N / mm) The ratio to the adhesive strength before the test was determined, and the adhesive strength retention (%) was evaluated. The epoxy resin coating material, the cross-sectional area is the cross-sectional shape of 100 mm 2 circular steel jig via the adhesive adhered to the painted surface, then forcibly peeled off the paint around the jig , Grasp the jig and conduct a tensile test, find the maximum load at which the bonded part breaks, define it as the bond strength (MPa), find the ratio to the bond strength before the test, and evaluate it as the bond strength retention (%) did.
(3) Cathode peel test The cathode peel test was performed in accordance with the provisions of ASTM G8. An artificial defect of 5 mmφ was provided in the center of each test piece, and a 70 mmφ cylinder was filled with a 3% by mass NaCl solution while standing. The counter electrode was a platinum electrode, and the steel surface was kept at -1.5 V with respect to the reference electrode (SCE). This was exposed to an electric furnace at 60 ° C. for 30 days. After the test, the peel distance extending from the defect was measured.
[0025]
Table 1 shows the results.
[0026]
[Table 1]
The examples of the present invention all have a small peeling distance, a high adhesive strength retention rate, excellent salt water spray resistance, excellent resistance to hot salt water immersion, and excellent cathodic peel resistance in an anticorrosive coating of an organic resin lining. . On the other hand, in the comparative examples outside the range of the present invention, the salt spray resistance, the warm salt water immersion resistance, and the cathode peeling resistance were reduced.
[0028]
【The invention's effect】
As described above, according to the present invention, the adhesion durability between the coating and the base is improved, and the anticorrosion life of the anticorrosion-coated steel material can be extended. Further, according to the present invention, there is no need to repair or recoat the anticorrosion coating for a long period of time, thereby reducing costs and providing a remarkable industrial effect. Further, even in a severely corrosive environment, there is an effect that long-term anticorrosion becomes possible and social loss due to corrosion and paint deterioration can be avoided.
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| JP5217507B2 (en) * | 2008-03-03 | 2013-06-19 | Ｊｆｅスチール株式会社 | Method for producing resin-coated steel |
| JP5217508B2 (en) * | 2008-03-03 | 2013-06-19 | Ｊｆｅスチール株式会社 | Method for producing resin-coated steel |
| JP5651912B2 (en) * | 2008-03-03 | 2015-01-14 | Ｊｆｅスチール株式会社 | Method for producing resin-coated steel |
| CN105369236A (en) * | 2015-12-17 | 2016-03-02 | 山东建筑大学 | Non-chrome passivating agent for brown zinc coating |
| CN105369237A (en) * | 2015-12-17 | 2016-03-02 | 山东建筑大学 | Brown passivant |
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