JP2004002958A - Non-chromium treated, galvanized steel sheet, and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a galvanized steel sheet which has excellent corrosion resistance and abrasion resistance without using chromium. <P>SOLUTION: A primary layer of a treatment liquid (M) and a second layer of a treatment liquid (N) are formed on the surface of the galvanized steel sheet. The treatment liquid (M) consists of an aqueous solution of pH 2.0 to 6.5 comprising a resin in general formula (I) (a), a functional group-containing silane coupling agent (b), and a water soluble titanium compound and/or a zirconium compound (c): in the formula, Y<SB>1</SB>and Y<SB>2</SB>are H or a substituent Z consisting of aminomethyl or ammonium methyl. The treatment liquid (N) consists of an urethane resin having a glass transition temperature of -40 to 0°C (A), a water soluble epoxy resin (B), colloidal silica (C), polyethylene wax dispersed into water by a dispersant compound in general formula (IV) (D), and a water soluble organic solvent (E): in the formula, R<SP>1</SP>is an alkyl or alkenyl group; R<SP>2</SP>is (EO)m-(PO)n (wherein, E is an ethylene group; P is a propyrene group; and m and n are zero or integers); R<SP>3</SP>is H or SO<SB>3</SB>M; and R<SP>4</SP>is H, or an alkyl or alkenyl group. <P>COPYRIGHT: (C)2004,JPO

Description

【００１９】
式中、Ｙ_１およびＹ_２は、それぞれ独立して、水素原子または下記式（ＩＩ）もしくは（ＩＩＩ）で表されるＺ基を意味し、
【００２０】
【化５】

【００２１】
前記式（ＩＩ）および（ＩＩＩ）中のＲ_１、Ｒ_２、Ｒ_３、Ｒ_４およびＲ_５は、それぞれ独立して、水素原子、Ｃ_１〜Ｃ_１０アルキル基またはＣ_１〜Ｃ_１０ヒドロキシアルキル基を表し、
前記重合体分子中のベンゼン環当たりの前記Ｚ基の平均置換数は　０．２〜１．０である。
【００２２】
表面処理液（Ｎ）：　（Ａ）ビスフェノールＡ型骨格を有し、ガラス転移温度が−４０〜０℃の範囲であるウレタン樹脂と、（Ｂ）エポキシ基を１分子中に３個以上有する水溶性エポキシ樹脂と、（Ｃ）コロイダルシリカと、（Ｄ）一般式（ＩＶ）で示される化合物からなる分散剤により平均粒径０．０１〜０．２μｍとなるように水に分散されたポリエチレンワックスと、（Ｅ）水溶性有機溶剤と、水とを含有し、全固形分に対して、（Ａ）＋（Ｂ）の固形分割合が５０〜９５質量％、（Ｃ）の固形分割合が３〜４０質量％、（Ｄ）の固形分割合が２〜２０質量％であり、処理液全量に対する（Ｅ）の割合が１〜１０質量％である水系表面処理液。
【００２３】
【化６】

【００２４】
式中、Ｒ^１は炭素数１〜２０のアルキル基または炭素数２〜２０のアルケニル基を表し、Ｒ^２は　（ＥＯ）ｍ−（ＰＯ）ｎ（式中、Ｅはエチレン基、Ｐはプロピレン基、ｍは５〜２０の整数、ｎは０または１〜１０の整数である）を表し、Ｒ^３は水素原子またはＳＯ_３Ｍ（式中、Ｍは水素原子、アルカリ金属イオンまたはアンモニウムイオンである）を表し、Ｒ^４は水素原子、炭素数１〜４のアルキル基または炭素数２〜４のアルケニル基を表す。
【００２５】
前記第１層に用いる皮膜層の付着量は５０〜５００　ｍｇ／ｍ^２であるのが好ましく、前記第２層に用いる樹脂皮膜層の付着量は　０．１〜３ｇ／ｍ^２であるのが好ましい。
本発明によればまた、亜鉛系めっき鋼板の少なくとも片面に、上記表面処理液（Ｍ）を塗布し、乾燥して第１層皮膜を形成した後、上記表面処理液（Ｎ）を塗布し、乾燥して第２層皮膜を形成することを特徴とする、ノンクロム処理亜鉛系めっき鋼板の製造方法も提供される。
【００２６】
表面処理液（Ｍ）および（Ｎ）の塗布後の乾燥は、いずれも５０〜２００℃の温度で行うことが好ましい。ここで、乾燥温度は、鋼板の到達板温度を意味する。
【００２７】
【発明の実施の形態】
次に、本発明において第１層に用いる下地の表面処理液（Ｍ）および第２層に用いる水系表面処理液（Ｎ）についてより詳しく説明する。
【００２８】
第１層の形成に用いる表面処理液（Ｍ）
第１層の形成に用いる表面処理液（Ｍ）は、一般式（Ｉ）で表される反復単位を有する重合体分子からなる水溶性樹脂（ａ）と、活性水素含有アミノ基、エポキシ基、ビニル基、メルカプト基およびメタクリロキシ基から選ばれた少なくとも１つの官能基を有する１種以上のシランカップリング剤（ｂ）と、チタン化合物およびジルコニウム化合物の少なくとも一方（ｃ）とを含有するｐＨ　２．０〜６．５の水溶液である。
【００２９】
【化７】

【００３０】
式中、Ｙ_１およびＹ_２は、それぞれ独立して、水素原子、または下記式（ＩＩ）もしくは（ＩＩＩ）により表されるＺ基を意味し、
【００３１】
【化８】

【００３２】
前記式（ＩＩ）および（ＩＩＩ）中のＲ_１、Ｒ_２、Ｒ_３、Ｒ_４およびＲ_５は、それぞれ独立して、水素原子、Ｃ_１〜Ｃ_１０アルキル基またはＣ_１〜Ｃ_１０ヒドロキシアルキル基を表し、
前記重合体分子中のベンゼン環当たりの前記Ｚ基の平均置換数は　０．２〜１．０である。
【００３３】
本発明で使用する表面処理液（Ｍ）（水溶液）のｐＨは　２．０〜６．５の範囲である。処理液のｐＨが２．０より小さいと、塗布される処理液と基体表面　（亜鉛系めっき）との反応性が過度に高くなり、被覆不良が発生しやすくなるため、得られる金属板材料の耐食性、塗装性、加工性などが不十分になる。ｐＨが６．５を超えると、水溶性樹脂（ａ）が処理液中から沈殿析出し易くなり、処理液の寿命が短くなる。
【００３４】
水溶性樹脂（ａ）は、前記式（Ｉ）で示される反復単位を含むオリゴマーまたはポリマーであり、式（Ｉ）の反復単位の平均重合度（ｎ）は２〜５０である。
式（Ｉ）において、ベンゼン環に結合しているＹ_１およびＹ_２はそれぞれ独立して、水素原子、または式（ＩＩ）もしくは（ＩＩＩ）により表されるＺ基を意味する。式（ＩＩ）および（ＩＩＩ）の中のＲ_１、Ｒ_２、Ｒ_３、Ｒ_４およびＲ_５は、それぞれ独立して、水素原子、Ｃ_１〜Ｃ_１０アルキル基またはＣ_１〜Ｃ_１０ヒドロキシアルキル基を表し、前記重合体分子中のベンゼン環当たりの前記Ｚ基の平均置換数は　０．２〜１．０である。
【００３５】
Ｚ基の平均置換数が０．２未満であると、樹脂の基体表面への密着性が不十分となり、塗装性が悪くなる。また、それが１．０を越えると、樹脂の親水性が大きくなりすぎ、表面処理した鋼板の耐食性が不十分となる。
【００３６】
式（ＩＩ）および（ＩＩＩ）の中のＲ_１、Ｒ_２、Ｒ_３、Ｒ_４およびＲ_５は、それぞれ独立して、水素原子、Ｃ_１〜Ｃ_１０のアルキル基またはＣ_１からＣ_１０のヒドロキシアルキル基を表す。これらの基の炭素数が１１以上になると、形成される表面処理液の成膜性が低下し、耐食性、塗装性、、加工性などが不十分になる。
【００３７】
表面処理液（Ｍ）に用いるシランカップリング剤（ｂ）は、１分子中に反応性の官能基として、活性水素含有アミノ基、エポキシ基、ビニル基、メルカプト基及びメタクリロキシ基から選ばれた少なくとも１つの官能基を含むものであれば、特に構造は限定されない。その具体例を以下に挙げる。
【００３８】
▲１▼アミノ基を有するもの
Ｎ−（２−アミノエチル）−３−アミノプロピルメチルジメトキシシラン、　Ｎ−（アミノエチル）−３−アミノプロピルトリメトキシシラン、３−アミノプロピルトリエトキシシラン；
▲２▼エポキシ基を有するもの
３−グリシドキシプロピルトリメトキシシラン、３−グリシドキシプロピルメチルジメトキシシラン、　２−（３，４−エポキシシクロへキシル）エチルトリメトキシシラン；
▲３▼ビニル基を有するもの
ビニルトリエトキシシラン；
▲４▼メルカプト基を有するもの
３−メルカプトプロピルトリメトキシシラン；
▲５▼メタクリロキシ基を有するもの
３−メタクリロキシプロピルトリメトキシシラン、３−メタクリロキシプロピルメチルジメトキシシラン。
【００３９】
表面処理液（Ｍ）に用いるシランカップリング剤（ｂ）は、１つ以上の活性水素含有基　（例、アミノ基、メルカプト基）を有する１種以上のシランカップリング剤（ア）と、１つ以上のエポキシ基を有する１種以上のシランカップリング（イ）とからなる、シランカップリング剤の混合物であることが好ましい。この場合、活性水素含有基を含有するシランカップリング剤（ア）とエポキシ基含有シランカップリング剤（イ）の配合割合は、シランカップリング剤の混合物中に含まれる活性水素含有基のエポキシ基に対する当量比が、３：１〜１：３の範囲となるようにすることが好ましい。当量比が３：１〜１：３の範囲を超えた場合、成膜性が悪くなり、耐食性、塗装性、加工性が不十分になる。
【００４０】
第１層に用いる表面処理液（Ｍ）において、水溶性樹脂（ａ）とシランカップリング剤（ｂ）の合計量に対するシランカップリング剤（ｂ）の含有量は、質量％で１０〜９０％であることが好ましく、より好ましくは２０〜５０％である。シランカップリング剤（ｂ）の含有量が１０％より少ないと、基体表面との接着力が低下するため、耐食性、塗装性が不十分になる。また、シランカップリング剤（ｂ）の含有量が９０％より多いと、表面処理液（Ｍ）の成膜性が低下するため、耐食性、塗装性が不十分となる。
【００４１】
表面処理液（Ｍ）に用いるチタン化合物およびジルコニウム化合物（ｃ）は、いずれも水溶性の化合物である。チタン化合物については、たとえば硫酸チタン、オキシ硫酸チタン、チタンフッ化水素酸、チタンフツ化アンモニウムなどの水溶性無機チタン化合物や、しゅう酸チタンカリウム、クエン酸チタンなどの有機酸チタン塩やチタンのアルコキシドなどが挙げられる。チタネート系カップリング剤も使用できる。ジルコニウム化合物については、硫酸ジルコニウム、オキシ塩化ジルコニウム、硝酸ジルコニウム、ジルコンフッ化水素酸、ジルコンフッ化アンモニウムなどの水溶性無機ジルコニウム化合物や、プロピオン酸ジルコニウムのほか、酢酸ジルコニウムなどの有機酸ジルコニウム塩や、ジルコニウムのアルコキシド、ジルコネートカップリング剤などが挙げられる。
【００４２】
チタン化合物およびジルコニウム化合物の少なくとも一方（ｃ）の合計量は、処理液１ｋｇあたりに０．００１０モル以上であることが好ましい。チタン化合物およびジルコニウム化合物（ｃ）の含有量が０．００１０モル未満では、その添加効果、即ち、耐食性の改善効果が十分に発現せず、表面処理鋼板の耐食性が不十分となる。
【００４３】
チタン化合物とジルコニウム化合物を比較すると、耐食性に及ぼす影響はほぼ同等であるが、チタン化合物を含有すると、皮膜がわずかながら黄色味を帯びるようになる。無色の外観が要求される場合は、ジルコニウム化合物のみ、もしくはできるだけジルコニウム化合物のチタン化合物に対する割合が大きい方が好ましい。
【００４４】
第２層に用いる水系表面処理液（Ｎ）
本発明の第２層に用いる水系表面処理液（Ｎ）の特徴は、特定の成分（Ａ）ないし（Ｅ）を一定の質量比で含有することである。
【００４５】
ウレタン樹脂 （Ａ）
本発明では、皮膜を形成するベース樹脂として、ビスフェノールＡ型骨格を有し、ガラス転移温度が−４０〜０℃の範囲であるウレタン樹脂（Ａ）を使用するが、それは、この樹脂が耐食性、耐摩耗性、耐薬品性のバランスに優れているからである。
【００４６】
本発明に使用するウレタン樹脂（Ａ）は、ビスフェノールＡ型骨格を有していることが必要である。ビスフェノールＡ型骨格は、素材との密着性、耐薬品性に優れており、この骨格をウレタン樹脂中に導入することにより、優れた耐食性を得ることができる。ウレタン樹脂に対するビスフェノールＡ型骨格の導入量は、樹脂固形分１００％に対して１０〜５０質量％の範囲であることが好ましく、より好ましくは１５〜４０質量％である。ビスフェノールＡ型骨格の導入量が１０質量％未満であると、その導入による耐食性の向上効果が乏しく、一方５０質量％を超えると、ビスフェノールＡ型骨格が剛直な骨格であるため、皮膜が硬くなり過ぎて、密着性が低下する。
【００４７】
本発明で用いるウレタン樹脂（Ａ）のガラス転移温度は−４０〜０℃であり、好ましくは−３５〜−５℃、より好ましくは−３５〜−１０℃の範囲である。ガラス転移温度が−４０℃未満であると、形成される皮膜の耐ブロッキング性が劣る。また、樹脂の皮膜物性はガラス転移温度を境に大きく変化する傾向にある。通常、成形加工後の製品が取り扱われる温度は、１０〜５０℃の範囲であるが、この温度範囲内にガラス転移温度がある場合は、気温により樹脂の皮膜物性の変化が起こり、皮膜の耐擦り傷性が劣る可能性が高い。さらに、ガラス転移温度が５０℃を超える場合は、皮膜の造膜性が低下するため、塗布後の乾燥温度を高くする必要があり、経済的に無駄となる。従って、樹脂のガラス転移温度は−４０〜０℃の範囲にするのが好ましい。
【００４８】
樹脂のガラス転移温度は、市販の動的粘弾性測定装置（例えば、東洋精機製作所製レオログラフソリッドＳ−１）で測定できる。試験片は、１００℃で３０分間乾燥させた膜厚１００μｍ、幅８ｍｍ、長さ３０　ｍｍのものを用い、周波数１００　Ｈｚにて測定を行い、弾性損失率の変曲点からガラス転移温度を求めた。
【００４９】
ウレタン樹脂（Ａ）は、乳化剤と呼ばれる界面活性剤を使用していないものが好ましい。界面活性剤を使用して水に分散しているウレタン樹脂は、界面活性剤の影響で得られる皮膜の耐水性が低下することがある。従って、本発明に好適なウレタン樹脂（Ａ）としては、カルボキシル基を樹脂中に導入し、このカルボキシル基をアンモニア、アミンなどで中和することにより、水分散性あるいは水溶性にしたものである。
【００５０】
エポキシ樹脂 （Ｂ）
ウレタン樹脂（Ａ）単独でもある程度の耐食性を得ることはできるが、耐食性をさらに高めるため、エポキシ基を１分子中に３個以上含有する水溶性エポキシ樹脂（Ｂ）を処理液中に配合する。
【００５１】
このような水溶性エポキシ樹脂（Ｂ）の例としては、ソルビトールポリグリシジルエーテル、グリセロールポリグリシジルエーテル、ポリグリセロールポリグリシジルエーテル、ペンタエリスリトールポリグリシジルエーテル、ジグリセロールポリグリシジルエーテル、トリメチロールプロパンポリグリシジルエーテル、などが挙げられる。
【００５２】
水系表面処理液（Ｎ）中の成分　（Ａ）〜（Ｄ）の全固形分に対する（Ａ）＋（Ｂ）の固形分の割合は５０〜９５質量％であり、６０〜８５質量％であることが好ましく、より好ましくは６５〜８０質量％である。この割合が５０質量％未満であると、皮膜自体の耐水性が低下する。一方、この割合が　９５質量％を超えると、擦り傷部の耐食性が低下する。
【００５３】
コロイダルシリカ （Ｃ）
コロイダルシリカ（Ｃ）は、粒径、形状、種類については特に限定するものではないが、粒径に関しては３〜３０　ｎｍの範囲であることが好ましい。水系表面処理液（Ｎ）中の成分　（Ａ）〜（Ｄ）の全固形分に対するコロイダルシリカの固形分の割合は３〜４０質量％であり、１０〜３０質量％が好ましい。この割合が３質量％未満であると、耐食性の向上効果が乏しく、４０質量％の超えると、樹脂（Ａ）のバインダー効果が小さくなり、耐食性が低下する。
【００５４】
ポリエチレンワックス （Ｄ）
ポリエチレンワックス（Ｄ）は、耐擦り傷性のレベルを向上させるために配合する。その平均粒径は０．０１〜０．２μｍであり、０．０５〜０．１８μｍであることが好ましい。
【００５５】
一般に、潤滑性の指標として用いられる摩擦係数は、ワックス粒径が大きくなると低くなる傾向にある。しかし、この摩擦係数と耐擦り傷性は必ずしも一致せず、摺動回数　（あるいは摺動距離）と摩擦係数との関係（耐かじり性）の方が重要である。本発明者らは、ワックスの平均粒径と摺動回数との関係を鋭意検討した結果、ワックスの平均粒径を０．０１〜０．２μｍとすることにより、優れた耐擦り傷性が得られることを見出した。ワックスの平均粒径が０．０１μｍ未満であると、ワックスの製造により高性能の機械を使用する必要があるため、経済的でない。一方、ワックスの平均粒径が０．２μｍを超えると、皮膜表面から突出したワックスが摺動時に取れやすくなり、結果として連続摺動性が低下する。
【００５６】
ポリエチレンワックスの分子量、融点については特に限定はないが、酸価は５〜５０　（ＮａＯＨ　ｍｇ／ｇ）の範囲が好ましく、１０〜３０　（ＮａＯＨ　ｍｇ／ｇ）の範囲がより好ましい。酸価が５ＮａＯＨ　ｍｇ／ｇ未満の場合は、ワックスと樹脂とがほとんど相溶しないため、皮膜形成時にワックスが皮膜表面に完全に配向し、耐擦り傷性および塗装密着性の低下を引き起こすので好ましくない。一方、酸価が５０　ＮａＯＨ　ｍｇ／ｇを超える場合は、ワックスの親水性が強くなるため、ワックス自体が持つ滑性が低下し、耐擦り傷性が低下するので好ましくない。
【００５７】
通常、樹脂や顔料等の分散には、分散剤と呼ばれる界面活性剤が使用される。界面活性剤は、樹脂や顔料に対する配合量が少ない場合は分散不良（樹脂や顔料が凝集して分離沈降あるいは浮上する）を生じ、一方、配合量が多い場合は得られる皮膜の耐水性を低下させる。
【００５８】
本発明者らは、ポリエチレンワックスの分散剤について鋭意検討した結果、下記式（ＩＶ）で示される化合物を用いてポリエチレンワックスを水に分散させることにより、優れた均一分散安定性と耐水性を得ることができた。
【００５９】
【化９】

【００６０】
式中、Ｒ^１は炭素数１〜２０のアルキル基または炭素数２〜２０のアルケニル基を表し、Ｒ^２は　（ＥＯ）ｍ−（ＰＯ）ｎ（式中、Ｅはエチレン基、Ｐはプロピレン基、ｍは５〜２０の整数、ｎは０または１〜１０の整数である）を表し、Ｒ^３は水素原子またはＳＯ_３Ｍ（式中、Ｍは水素原子、アルカリ金属イオンまたはアンモニウムイオンである）を表し、Ｒ^４は水素原子、炭素数１〜４のアルキル基または炭素数２〜４のアルケニル基を表す。
【００６１】
ポリエチレンワックスの分散剤として使用する、式（ＩＶ）で示される化合物において、Ｒ^１は炭素数５〜２０のアルキル基または炭素数２〜５のアルケニル基であることが好ましい。Ｒ^３としては水素原子またはＳＯ_３ＮＨ_４であることが好ましく、Ｒ^４としては水素原子または炭素数２〜４のアルケニル基であることが好ましい。
【００６２】
ポリエチレンワックスを水に分散させる方法については特に限定はなく、工業的に用いる方法によれば良い。前述したポリエチレンワックスの平均粒径は、こうして得られる水分散体中での値である。
【００６３】
得られた水分散体の全固形分　（ワックス＋分散剤）に対する化合物（ＩＶ）の固形分の割合は５〜４０質量％であることが好ましく、５〜３０質量％であることがより好ましい。上記割合が５質量％未満では、ポリエチレンワックスの分散が不十分となるので好ましくない。また、上記割合が４０質量％を超える場合は、得られる皮膜の耐水性が低下するので好ましくない。
【００６４】
本発明の水系表面処理液中の成分　（Ａ）〜（Ｄ）の全固形分に対する上記水分散体の割合は、（Ｄ）の固形分の割合として２〜２０質量％であり、３〜２０質量％であることが好ましく、３〜１８質量％であることがさらに好ましい。この割合が２質量％未満では、耐擦り傷性の改善効果が乏しく、一方、２０質量％を超える場合は、上塗り塗装性が低下するため好ましくない。
【００６５】
水溶性有機溶剤 （Ｅ）
水系表面処理液は、造膜性を向上させる目的で、水溶性有機溶剤（Ｅ）を表面処理液中に１〜１０質量％配合する。水溶性有機溶剤は水と共沸可能なものが好ましい。このような有機溶剤としては、例えば、アセトン、メチルエチルケトン、Ｎ−メチル−２−ピロリドン、ジオキサン、イソプロピルアルコールなどが挙げられ、この中ではＮ−メチル−２−ピロリドンが好ましい。
【００６６】
表面処理液中の有機溶剤（Ｅ）の配合量は、処理液全体の１〜１０質量％の範囲であることが好ましく、２〜８質量％であることがより好ましい。上記割合が１質量％未満の場合は、造膜性向上の効果が乏しく、一方、１０質量％を超える場合は造膜性向上効果が飽和するため経済的でない。
【００６７】
本発明の表面処理液には、任意成分として、被塗面に均一な皮膜を形成させるための濡れ性向上剤と称せられる界面活性剤や、溶接性向上のための導電性物質、意匠性向上のための着色顔料などを含有させても良い。
【００６８】
上記成分（Ａ），　（Ｂ），　（Ｃ），　（Ｄ）および（Ｅ）を適宜量の水と混合して、溶解ないし分散させることにより、本発明の表面処理液（Ｎ）を得ることができる。成分の添加順序は特に限定はないが、混合は、例えばプロペラ式攪拌機などを用いて攪拌することにより行うのが適当である。
【００６９】
得られる本発明の表面処理液（Ｎ）は、固形分濃度が５〜５０質量％の範囲内であることが好ましく、５〜４０質量％の範囲内であることがより好ましい。固形分濃度が５質量％未満の場合は、乾燥時間が長くなるので好ましくない。一方、固形分濃度が５０質量％を超える場合は、表面処理液自体の粘度が高く、取り扱い上支障を来す恐れがある。
【００７０】
本発明の第１層および第２層の表面処理液を塗布する亜鉛系めっき鋼板は、亜鉛または亜鉛合金を電気めっきまたは溶融めっきした任意の鋼板でよい。好ましい亜鉛系めっき鋼板の例としては、電気亜鉛めっき鋼板、溶融亜鉛めっき鋼板、５％アルミニウム含有亜鉛めっき鋼板、合金化溶融亜鉛めっき鋼板、電気亜鉛−ニッケル合金めっき鋼板が挙げられる。
【００７１】
これらの表面処理液（Ｍ）および（Ｎ）を塗布する方法は、特に限定されないが、ロールコータ法、浸漬法、静電塗布法などを用いることができる。
好ましい処理方法において、表面処理液（Ｍ）を１０〜５０℃で塗布し、到達板温度で５０〜２００℃、より好ましくは６０〜１８０℃の温度で乾燥させて第１層の皮膜を形成し、次に表面処理液（Ｎ）を同様に１０〜５０℃で塗布し、到達板温度５０〜２００℃、より好ましくは６０℃〜１８０℃の温度で乾燥させて第２層の皮膜を形成することにより、クロムを含まずに、優れた耐食性、耐擦り傷性を有する皮膜を亜鉛系めっき鋼板の表面に形成することができる。
【００７２】
第１層および第２層の乾燥温度が５０℃より低いと、満足できる耐食性を得ることができず、この乾燥温度が２００℃を超えると、乾燥にかかるコストが高くなるため経済的ではない。
【００７３】
第１層の皮膜の付着量は０．０５〜１ｇ／ｍ^２　（＝５０〜１０００　ｍｇ／ｍ^２）、好ましくは　０．１〜０．５　ｇ／ｍ^２である。第１層の付着量が０．０５　ｇ／ｍ^２未満であると、満足できる耐食性を得ることができず、一方、１ｇ／ｍ^２を超えると、耐食性の効果が飽和するため経済的でない。
【００７４】
第２層の皮膜の付着量は　０．１〜３ｇ／ｍ^２であり、好ましくは　０．２〜２ｇ／ｍ^２であり、より好ましくは　０．３〜２ｇ／ｍ^２である。第２層の付着量が０．１　ｇ／ｍ^２未満であると満足できる耐食性を得ることができず、３ｇ／ｍ^２を超えると耐食性の効果が飽和するため経済的でない。
【００７５】
本発明の表面処理液は、酸洗、りん酸塩化成処理などのクロムを含まない処理方法にて処理した亜鉛系めっき鋼板に塗布しても構わない。
本発明によって得られる耐擦り傷性に優れた亜鉛系めっき鋼板は、平面部耐食性、擦り傷部耐食性および塗装密着性に優れている。
【００７６】
本発明にかかるクロムを含まない皮膜を有する亜鉛系めっき鋼板は、そのままで使用してもよいが、通常は、塗装して使用される。そのときの耐擦り傷性に優れた亜鉛系めっき鋼板に塗布する上塗り塗料としては特に限定はないが、例えば、常乾型メラミンアルキッド系塗料、焼き付け型メラミンアルキッド系塗料、アクリル樹脂系塗料、紫外線硬化型樹脂系塗料などが挙げられる。
【００７７】
【実施例】
以下の実施例および比較例により、本発明の作用効果を具体的に例示する。実施例は本発明の例示にすぎず、本発明を何ら限定するものではない。実施例中、％は特に指定しない限り、質量％である。
【００７８】
［試験板の作製］
（１）　供試材
下記の示した市販の両面亜鉛系めっき鋼板を供試材として使用した。なお、供試材のサイズは２００　ｍｍ×３００　ｍｍである。
【００７９】
・電気亜鉛めっき鋼板　（ＥＧ）
板厚０．８　ｍｍ、目付量＝　２０／２０　（ｇ／ｍ^２）
・溶融亜鉛めっき鋼板　（ＧＩ）
板厚０．８　ｍｍ、目付量＝　６０／６０　（ｇ／ｍ^２）
・５％アルミニウム含有亜鉛めっき鋼板　（ＧＦ）
板厚０．８　ｍｍ、目付量＝　９０／９０　（ｇ／ｍ^２）
（２）脱脂処理
上記の各供試材をシリケート系アルカリ脱脂剤のファインクリーナー４３３６（登録商標：日本パーカライジング製）で脱脂処理した。濃度２０　ｇ／Ｌの脱脂剤を用いて、温度６０℃で２分間スプレー処理した後、水道水で洗浄した。
【００８０】
（３）　第１層皮膜の形成
脱脂処理した供試材の片面に、表１に記載の表面処理液　（Ｍ１〜Ｍ４）を室温にてバーコートにより塗布し、到達板温度１００℃で乾燥して、第１層の皮膜を形成した。表１の記号Ｍ４の表面処理液は、水溶性樹脂を含有せず、記号Ｍ２の処理液に使用したのと同じ種類および量のシランカップリング剤およびチタン化合物だけを含有していた。付着量の調整は、表面処理液の固形分濃度およびバーコータの種類を適宜変更することで行った。比較として反応型クロメート処理液であるジンクロム３５７（登録商標：日本パーカライジング製）を用い、液温度５０℃で５秒間スプレー処理を行って、水道水で洗浄後に風乾した。
【００８１】
（４）　第２層皮膜の形成
（４−１）水系表面処理液の調製
室温にて、表２記載のウレタン樹脂（Ａ）、表３記載のエポキシ樹脂（Ｂ）、表４記載のコロイダルシリカ（Ｃ）、表５記載のワックス水分散体（Ｄ）、および表６記載の有機溶剤（Ｅ）を、この順にプロペラ攪拌機を用いて攪拌しながら混合し、蒸留水を加えて固形分濃度を調整し、表７に示す組成の第２層形成用の水系表面処理液（１〜１２）を調製した。ワックス水分散体（Ｄ）は、表５に示すワックスと分散剤化合物（ＩＶ）および水を、全量オートクレーブに入れて、温度１３０℃に加熱して攪拌することにより調製した。
【００８２】
（４−２）塗布と乾燥
調製した各表面処理液を、室温にてバーコータにより、上記試験板の第１層皮膜の上に塗布し、２４０℃の雰囲気温度で１０秒間乾燥した。この際の到達板温度は１２０℃であった。付着量の調整は、表面処理液の固形分濃度およびバーコータの種類を適宜変更することで行った。
【００８３】
（５）　性能試験
（５−１）平面部耐食性
ＪＩＳ−Ｚ−２３７１による塩水噴霧試験を、ＥＧ材の場合は２４０時間、ＧＦ材の場合は４８０時間行い、白錆発生状況を観察し、下記基準により評価した。
【００８４】
＜評価基準＞
◎：白錆発生面積が全面積の３％未満、
○：白錆発生面積が全面積の３％以上１０％未満、
△：白錆発生面積が全面積の１０％以上３０％未満、
×：白錆発生面積が全面積の３０％以上。
【００８５】
（５−２）擦り傷部耐食性
試験片を３０　ｍｍ×３００　ｍｍのサイズに切断し、ドロービード試験（ビード先端１ｍｍＲ、ビード高さ４ｍｍ、ダイス肩１ｍｍＲ、圧着荷重５００　ｋｇ、温度３０℃）を行った。この試験片の摺動部分についてＪＩＳ−Ｚ−２３７１による塩水噴霧試験を、ＥＧ材の場合は１２０時間、ＧＦ材の場合は２４０時間行い、白錆発生状況を観察し、下記基準により評価した。
【００８６】
＜評価基準＞
◎：白錆発生面積が全面積の　３％未満、
○：白錆発生面積が全面積の　３％以上１０％未満、
△：白錆発生面積が全面積の１０％以上３０％未満、
×：白錆発生面積が全面積の３０％以上。
【００８７】
（５−３）塗装密着性
メラミンアルキッド系塗料（登録商標アミラックＮｏ．１０００、関西ペイント製）を焼付け乾燥後の膜厚が２５μｍになるように塗布して、１２５℃で２０分間焼き付けた。焼付け後２４時間経過した試験片を用い、ＪＩＳ−Ｚ−５４００により１ｍｍ碁盤目を１００個描画してから、セロテープ（登録商標）により塗膜を剥離し、下記基準により評価した。
【００８８】
＜評価基準＞
◎：塗膜剥離なし、塗膜残個数１００個、
○：極僅かに塗膜剥離あり、塗膜残個数１００個、
△：塗膜残個数９５〜９９個、
×：塗膜残個数９４個以下。
【００８９】
（５−４）表面色調
一部の試験片について、試験片の表面色調　（黄色味の指標であるＪＩＳ　Ｚ８７２９のｂ＊値）を測定した。
【００９０】
試験結果を表８および表９に示す。
【００９１】
【表１】

【００９２】
【表２】

【００９３】
【表３】

【００９４】
【表４】

【００９５】
【表５】

【００９６】
【表６】

【００９７】
【表７】

【００９８】
【表８】

【００９９】
【表９】

【０１００】
表８からわかるように、本発明の表面処理液を用いた実施例１〜２４では、平面部耐食性、擦り傷部耐食性および塗装密着性の何れも良好であり、比較例１９の従来のクロメート処理を行った場合と同等であった。これに対し、本発明の範囲外である表面処理液を用いた比較例１〜１８では、平面部耐食性、擦り傷部耐食性および塗装密着性のすべての性能を満足するものは得られなかった。
【０１０１】
第１層皮膜がチタン化合物を含有する実施例４と、ジルコニウム化合物を含有する実施例１５について、表面外観　（黄色味）を光学検査装置で比較したところ、表９に示すように、チタン化合物を含有する実施例４の方が黄色みが強かった。ただし、実施例４の皮膜でもそれほど黄色みは強くない。目視で観察した場合の実施例４と実施例１５の試験片の表面色調の差は、それぞれ単独では判断しづらく、並べて観察した時に実施例４の皮膜がわずかに黄色味を帯びていることを認識できる程度である。
【０１０２】
【発明の効果】
以上説明したように、亜鉛系めっき鋼板表面の第１層、第２層にそれぞれ、本発明の表面処理液を塗布し、乾燥することにより、クロムを使用せず平面部耐食性、擦り傷部耐食性および塗装密着性に優れた耐擦り傷性に優れた亜鉛系めっき鋼板を得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a non-chromium (not including chromium) treated galvanized steel sheet having a resin film formed on a surface of a galvanized steel sheet having excellent flat surface corrosion resistance, scratch resistance, and coating adhesion, and a method for producing the same. .
[0002]
[Prior art]
Household appliances and building materials include galvanized steel sheets, hot-dip galvanized steel sheets, 5% aluminum-containing galvanized steel sheets, and other zinc or zinc alloy coated steel sheets. (In the present invention, these are collectively referred to as galvanized steel sheets. ) Is widely used. Zinc-plated steel sheets are insufficient in corrosion resistance and paint adhesion (top coat paintability) as they are, so they are subjected to chromate chemical conversion treatment and phosphate chemical conversion treatment, followed by forming such as pressing and bending. It is often painted. However, depending on the application, there are many cases where the composition is used as it is without painting.
[0003]
When used without painting, chromate conversion-treated steel sheets with good corrosion resistance are often used, but they have problems such as adhesion of fingerprints during molding and assembly, and variations in color tone due to differences in the amount of chromate film. I have. In order to solve these problems, fingerprint-resistant steel sheets having an organic film formed on a chromate film have come to be used. This fingerprint-resistant steel sheet has an organic resin layer having a thickness of about 1 μm on the surface of a zinc-plated steel sheet subjected to chromate treatment for the purpose of preventing adhesion of fingerprints. This fingerprint-resistant steel sheet is required to have various film properties such as corrosion resistance, solvent resistance, paint adhesion, and scratch resistance in addition to fingerprint resistance.
[0004]
Among these performances, in recent years, there has been a strong demand for abrasion resistance. The reason why abrasion resistance is required is that vibrations generated when the product is transported after the molding process causes the molded products to rub against each other or the container (such as a cardboard box) containing the molded products, This is because the surface is scratched. Since the abraded portion is inferior in corrosion resistance to a normal organic coating portion, the quality is inevitably reduced.
[0005]
For this reason, some techniques relating to surface-treated steel sheets have been proposed in consideration of scratch resistance in addition to corrosion resistance and paint adhesion. Such a technique is described in Patent Documents 1 to 3, for example.
[0006]
Patent Document 4 discloses a resin film in which a fluorine-based resin particle and a silica particle are mixed with a urethane-modified polyolefin resin. The feature is that the scratches are protected by using the fluorine-based resin particles, and the use of a surfactant is indispensable to uniformly disperse the fluorine-based particles in an aqueous solution. However, satisfactory corrosion resistance could not be obtained because the level of corrosion resistance was reduced overall by the use of surfactants.
[0007]
Patent Document 2 discloses a coating containing a polyester resin, a crosslinking agent, and a polyethylene wax having an average molecular weight of 2,000 to 8,000. Since this film uses a polyester resin as a base resin, the film itself has insufficient hydrolysis resistance, so that satisfactory corrosion resistance cannot be obtained.
[0008]
With regard to chromate treatment, hexavalent chromium in a chromate treatment solution, which has a drawback that directly affects the human body, tends to be avoided due to an increase in awareness of environmental protection in recent years. Further, the wastewater containing hexavalent chromium needs to be subjected to a special treatment specified in the Water Pollution Control Law, which causes a considerable increase in cost as a whole. Further, the steel sheet subjected to the chromate treatment has a major drawback that it cannot be recycled when it becomes chromium-containing industrial waste, which is a social problem.
[0009]
As a surface treatment method other than the chromate treatment, a treatment with a surface treatment solution containing tannic acid containing a polyhydric phenol carboxylic acid is well known. When a metal material is treated with an aqueous solution of tannic acid, a protective film formed by a reaction between the tannic acid and the surface of the metal material serves as a barrier against the intrusion of corrosive substances, and is considered to improve the corrosion resistance of the metal material. I have. However, in recent years, with the improvement in quality of metal products, high corrosion resistance of the film itself has been required, and therefore, a film obtained by using tannic acid alone or in combination with an inorganic component has insufficient corrosion resistance. However, practical application at present is impossible.
[0010]
As a treatment method for improving the corrosion resistance of a metal material, Patent Literature 5 discloses a steel sheet with a film formed by applying an aqueous solution containing water-dispersible silica, an alkyd resin, and a trialkoxysilane compound to a metal surface and drying the coating. Coating is disclosed. Patent Document 6 and the like disclose a method for imparting corrosion resistance to a metal material using a water-soluble or water-dispersible polymer of a hydroxystyrene compound.
[0011]
However, none of the above-mentioned methods can form a film capable of imparting high corrosion resistance that can be substituted for a chromate film, and the above problem has not been solved as a practical problem.
[0012]
As described above, at present, a surface-treated steel sheet which does not use chromium, has excellent corrosion resistance and paint adhesion, and has good corrosion resistance at a scratch portion has not been obtained.
It contains a urethane resin and / or an epoxy resin, silica or silica particles, and a polyethylene wax used for forming a resin film on a cold-rolled steel sheet, a galvanized steel sheet, or an aluminum-based metal sheet (aqueous). As lubricating paints, those described in Patent Literatures 7 to 9 are known, but these inventions are different from the present invention described below in constitutional requirements and effects of the invention.
[0013]
[Patent Document 1] JP-A-3-2562055
[Patent Document 2] Japanese Patent Publication No. 6-104799
[Patent Document 3] JP-A-6-262927
[Patent Document 4] JP-A-3-17189
[Patent Document 5] JP-A-53-121034
[Patent Document 6] JP-A-1-177380
[Patent Document 7] JP-A-5-117550
[Patent Document 8] Japanese Patent No. 2719571
[Patent Document 9] Japanese Patent No. 261838
[0014]
[Problems to be solved by the invention]
The present invention is to solve the problems of the prior art, corrosion resistance, not to mention coating adhesion, provided an organic resin film excellent in corrosion resistance of the abrasion portion without using chromium, An object of the present invention is to provide a non-chromium-treated zinc-based plated steel sheet and a method for producing the same.
[0015]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on means for solving the problems of the prior art, and as a result, the first layer has a specific water-soluble resin (a), a silane coupling agent (b), A film formed by applying and drying a surface treatment solution containing at least one of a titanium compound and a zirconium compound (c) is provided, and a urethane resin (A), an epoxy resin (B), and a colloidal silica (C) are formed on the second layer. A water-soluble organic solvent (E) having a specific particle size dispersed in water, and a water-soluble organic solvent (E), and a water-based surface treatment solution containing water to form a film formed by application and drying. They have found that the problem can be solved, and have completed the present invention.
[0016]
According to the present invention, at least one surface of a galvanized steel sheet has a dried film of the following surface treatment liquid (M) as a first layer, and a dried film of the following surface treatment liquid (N) as a second layer thereon. A non-chromium-treated galvanized steel sheet having excellent scratch resistance is provided.
[0017]
Surface treatment liquid (M): a water-soluble resin (a) comprising a polymer molecule having a repeating unit represented by the general formula (I), an active hydrogen-containing amino group, an epoxy group, a vinyl group, a mercapto group and a methacryloxy group Aqueous solution containing at least one silane coupling agent (b) having at least one functional group selected from the group consisting of: and a titanium compound and / or a zirconium compound (c) at a pH of about 2.0 to 6.5. .
[0018]
Embedded image

[0019]
Where Y₁And Y₂Each independently represents a hydrogen atom or a Z group represented by the following formula (II) or (III);
[0020]
Embedded image

[0021]
R in the above formulas (II) and (III)₁, R₂, R₃, R₄And R₅Is independently a hydrogen atom, C₁~ C₁₀Alkyl group or C₁~ C₁₀Represents a hydroxyalkyl group,
The average number of substitutions of the Z group per benzene ring in the polymer molecule is about 0.2 to 1.0.
[0022]
Surface treatment liquid (N): {(A) a urethane resin having a bisphenol A type skeleton and a glass transition temperature in the range of -40 to 0 ° C., and (B) a water solution having three or more epoxy groups in one molecule. Polyethylene wax dispersed in water with a dispersant comprising a hydrophilic epoxy resin, (C) colloidal silica, and (D) a compound represented by the general formula (IV) so as to have an average particle size of 0.01 to 0.2 μm. And (E) a water-soluble organic solvent and water, wherein the solid content ratio of (A) + (B) is 50 to 95% by mass and the solid content ratio of (C) is based on the total solid content. A water-based surface treatment liquid having a solid content ratio of 3 to 40% by mass, (D) of 2 to 20% by mass, and a ratio of (E) of 1 to 10% by mass with respect to the total amount of the treatment solution.
[0023]
Embedded image

[0024]
Where R¹Represents an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms;²Represents (EO) m- (PO) n (wherein E is an ethylene group, P is a propylene group, m is an integer of 5 to 20, and n is 0 or an integer of 1 to 10);³Is a hydrogen atom or SO₃M (wherein M is a hydrogen atom, an alkali metal ion or an ammonium ion);⁴Represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms.
[0025]
The coating amount of the coating layer used for the first layer is 50 to 500 mg / m.²It is preferable that the adhesion amount of the resin film layer used for the second layer is 0.1 to 3 g / m2.²It is preferred that
According to the present invention, the surface treatment liquid (M) is applied to at least one surface of a zinc-based plated steel sheet, dried to form a first layer film, and then the surface treatment liquid (N) is applied. A method for producing a non-chromium-treated galvanized steel sheet, characterized by drying to form a second layer film, is also provided.
[0026]
The drying after the application of the surface treatment liquids (M) and (N) is preferably performed at a temperature of 50 to 200 ° C. Here, the drying temperature means the ultimate plate temperature of the steel sheet.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the underlayer surface treatment liquid (M) used for the first layer and the aqueous surface treatment liquid (N) used for the second layer in the present invention will be described in more detail.
[0028]
Surface treatment liquid (M) used for forming the first layer
The surface treatment liquid (M) used for forming the first layer includes a water-soluble resin (a) composed of a polymer molecule having a repeating unit represented by the general formula (I), an active hydrogen-containing amino group, an epoxy group, PH containing at least one silane coupling agent (b) having at least one functional group selected from a vinyl group, a mercapto group and a methacryloxy group, and at least one of a titanium compound and a zirconium compound (c). It is an aqueous solution of 0 to 6.5.
[0029]
Embedded image

[0030]
Where Y₁And Y₂Each independently represents a hydrogen atom or a Z group represented by the following formula (II) or (III);
[0031]
Embedded image

[0032]
R in the above formulas (II) and (III)₁, R₂, R₃, R₄And R₅Is independently a hydrogen atom, C₁~ C₁₀Alkyl group or C₁~ C₁₀Represents a hydroxyalkyl group,
The average number of substitutions of the Z group per benzene ring in the polymer molecule is about 0.2 to 1.0.
[0033]
The pH of the surface treatment solution (M) (aqueous solution) used in the present invention is in the range of $ 2.0 to 6.5. If the pH of the treatment liquid is less than 2.0, the reactivity between the treatment liquid to be applied and the substrate surface 基 体 (zinc-based plating) becomes excessively high, and coating defects easily occur. Corrosion resistance, paintability, workability, etc. become insufficient. If the pH exceeds 6.5, the water-soluble resin (a) tends to precipitate out of the processing liquid, and the life of the processing liquid is shortened.
[0034]
The water-soluble resin (a) is an oligomer or a polymer containing the repeating unit represented by the formula (I), and the repeating unit of the formula (I) has an average degree of polymerization (n) of 2 to 50.
In the formula (I), Y bonded to a benzene ring₁And Y₂Each independently represents a hydrogen atom or a Z group represented by the formula (II) or (III). R in formulas (II) and (III)₁, R₂, R₃, R₄And R₅Is independently a hydrogen atom, C₁~ C₁₀Alkyl group or C₁~ C₁₀Represents a hydroxyalkyl group, and the average number of substitutions of the Z group per benzene ring in the polymer molecule is about 0.2 to 1.0.
[0035]
When the average number of substitution of the Z group is less than 0.2, the adhesion of the resin to the substrate surface becomes insufficient, and the coating property is deteriorated. On the other hand, if it exceeds 1.0, the hydrophilicity of the resin becomes too large, and the corrosion resistance of the surface-treated steel sheet becomes insufficient.
[0036]
R in formulas (II) and (III)₁, R₂, R₃, R₄And R₅Is independently a hydrogen atom, C₁~ C₁₀Alkyl group or C₁To C₁₀Represents a hydroxyalkyl group. When the carbon number of these groups is 11 or more, the film forming property of the formed surface treatment liquid is reduced, and the corrosion resistance, coating property, workability and the like become insufficient.
[0037]
The silane coupling agent (b) used in the surface treatment liquid (M) has at least one reactive hydrogen-containing functional group selected from active hydrogen-containing amino group, epoxy group, vinyl group, mercapto group and methacryloxy group in one molecule. The structure is not particularly limited as long as it contains one functional group. Specific examples are given below.
[0038]
(1) having an amino group
N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, {N- (aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane;
(2) Those having an epoxy group
3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, {2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane;
(3) Having a vinyl group
Vinyltriethoxysilane;
(4) having a mercapto group
3-mercaptopropyltrimethoxysilane;
(5) Having a methacryloxy group
3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane.
[0039]
The silane coupling agent (b) used in the surface treatment liquid (M) includes one or more silane coupling agents (a) having one or more active hydrogen-containing groups (eg, amino groups and mercapto groups), and 1 It is preferable that the mixture is a mixture of a silane coupling agent and one or more silane couplings (a) having two or more epoxy groups. In this case, the mixing ratio of the silane coupling agent containing an active hydrogen-containing group (a) and the silane coupling agent containing an epoxy group (a) depends on the epoxy group of the active hydrogen-containing group contained in the mixture of the silane coupling agent. It is preferable that the equivalent ratio to is within the range of 3: 1 to 1: 3. When the equivalent ratio exceeds the range of 3: 1 to 1: 3, the film-forming property is deteriorated, and the corrosion resistance, the coating property, and the workability are insufficient.
[0040]
In the surface treatment liquid (M) used for the first layer, the content of the silane coupling agent (b) with respect to the total amount of the water-soluble resin (a) and the silane coupling agent (b) is 10 to 90% by mass%. And more preferably 20 to 50%. When the content of the silane coupling agent (b) is less than 10%, the adhesion to the substrate surface is reduced, so that the corrosion resistance and the coating property become insufficient. On the other hand, when the content of the silane coupling agent (b) is more than 90%, the film forming property of the surface treatment liquid (M) is reduced, so that the corrosion resistance and the coating property become insufficient.
[0041]
The titanium compound and the zirconium compound (c) used in the surface treatment liquid (M) are both water-soluble compounds. Examples of the titanium compound include water-soluble inorganic titanium compounds such as titanium sulfate, titanium oxysulfate, titanium hydrofluoric acid, and titanium ammonium fluoride; organic acid titanium salts such as titanium potassium oxalate and titanium citrate; and alkoxides of titanium. No. Titanate-based coupling agents can also be used. As for the zirconium compound, zirconium sulfate, zirconium oxychloride, zirconium nitrate, zircon hydrofluoric acid, water-soluble inorganic zirconium compounds such as ammonium zircon fluoride, and zirconium propionate, zirconium acetate and other organic acid zirconium salts, zirconium acetate, etc. Alkoxides, zirconate coupling agents and the like can be mentioned.
[0042]
The total amount of at least one of the titanium compound and the zirconium compound (c) is preferably 0.0010 mol or more per 1 kg of the treatment liquid. If the content of the titanium compound and the zirconium compound (c) is less than 0.0010 mol, the effect of the addition, that is, the effect of improving the corrosion resistance is not sufficiently exhibited, and the corrosion resistance of the surface-treated steel sheet becomes insufficient.
[0043]
When a titanium compound and a zirconium compound are compared, the effect on corrosion resistance is almost the same, but when the titanium compound is contained, the film becomes slightly yellowish. When a colorless appearance is required, it is preferable that only the zirconium compound or the ratio of the zirconium compound to the titanium compound be as large as possible.
[0044]
Aqueous surface treatment liquid (N) used for the second layer
The feature of the aqueous surface treatment liquid (N) used in the second layer of the present invention is that it contains specific components (A) to (E) at a constant mass ratio.
[0045]
Urethane resin (A)
In the present invention, a urethane resin (A) having a bisphenol A type skeleton and a glass transition temperature in the range of -40 to 0 ° C. is used as a base resin for forming a film. This is because they have an excellent balance between wear resistance and chemical resistance.
[0046]
The urethane resin (A) used in the present invention needs to have a bisphenol A type skeleton. The bisphenol A type skeleton is excellent in adhesion to materials and chemical resistance, and by introducing this skeleton into the urethane resin, excellent corrosion resistance can be obtained. The amount of the bisphenol A-type skeleton introduced into the urethane resin is preferably in the range of 10 to 50% by mass, more preferably 15 to 40% by mass, based on 100% of the resin solid content. When the introduction amount of the bisphenol A type skeleton is less than 10% by mass, the effect of improving the corrosion resistance by the introduction is poor. On the other hand, when it exceeds 50% by mass, the film becomes hard because the bisphenol A type skeleton is a rigid skeleton. Too much and the adhesion is reduced.
[0047]
The glass transition temperature of the urethane resin (A) used in the present invention is −40 to 0 ° C., preferably −35 to −5 ° C., and more preferably −35 to −10 ° C. When the glass transition temperature is lower than −40 ° C., the formed film has poor blocking resistance. In addition, the film properties of the resin tend to greatly change around the glass transition temperature. Usually, the temperature at which the molded product is handled is in the range of 10 to 50 ° C., but if the glass transition temperature is within this temperature range, the film properties of the resin change with the temperature, and the resistance of the film to the resistance is increased. The abrasion resistance is likely to be poor. Further, when the glass transition temperature exceeds 50 ° C., the film-forming property of the film is reduced, so that it is necessary to increase the drying temperature after application, which is economically wasteful. Therefore, the glass transition temperature of the resin is preferably in the range of -40 to 0C.
[0048]
The glass transition temperature of the resin can be measured with a commercially available dynamic viscoelasticity measuring device (for example, Rheolograph Solid S-1 manufactured by Toyo Seiki Seisaku-sho, Ltd.). The test piece was measured at a frequency of 100 Hz using a film having a thickness of 100 µm, a width of 8 mm, and a length of 30 mm dried at 100 ° C for 30 minutes, and the glass transition temperature was determined from the inflection point of the elastic loss rate. Was.
[0049]
The urethane resin (A) preferably does not use a surfactant called an emulsifier. The urethane resin dispersed in water by using a surfactant may lower the water resistance of a film obtained by the effect of the surfactant. Therefore, the urethane resin (A) suitable for the present invention is a resin which is made water-dispersible or water-soluble by introducing a carboxyl group into the resin and neutralizing the carboxyl group with ammonia, an amine or the like. .
[0050]
Epoxy resin (B)
Although the urethane resin (A) alone can provide a certain level of corrosion resistance, a water-soluble epoxy resin (B) containing three or more epoxy groups in one molecule is blended in the treatment liquid in order to further increase the corrosion resistance.
[0051]
Examples of such a water-soluble epoxy resin (B) include sorbitol polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, And the like.
[0052]
The ratio of the solid content of (A) + (B) to the total solid content of the components (A) to (D) in the aqueous surface treatment liquid (N) is 50 to 95% by mass, and is 60 to 85% by mass. Preferably, it is more preferably 65 to 80% by mass. If this proportion is less than 50% by mass, the water resistance of the film itself will decrease. On the other hand, if this proportion exceeds 95% by mass, the corrosion resistance of the abrasion portion decreases.
[0053]
Colloidal silica (C)
The colloidal silica (C) is not particularly limited in particle size, shape and type, but preferably has a particle size in the range of 3 to 30 nm. The ratio of the solid content of the colloidal silica to the total solid content of the components (A) to (D) in the aqueous surface treatment liquid (N) is 3 to 40% by mass, preferably 10 to 30% by mass. If the proportion is less than 3% by mass, the effect of improving the corrosion resistance is poor, and if it exceeds 40% by mass, the binder effect of the resin (A) is reduced and the corrosion resistance is reduced.
[0054]
Polyethylene wax (D)
Polyethylene wax (D) is blended to improve the level of scratch resistance. The average particle size is from 0.01 to 0.2 μm, preferably from 0.05 to 0.18 μm.
[0055]
Generally, the coefficient of friction used as an index of lubricity tends to decrease as the wax particle size increases. However, the friction coefficient does not always match the abrasion resistance, and the relationship between the number of sliding times (or the sliding distance) and the friction coefficient (galling resistance) is more important. The present inventors have intensively studied the relationship between the average particle size of the wax and the number of times of sliding. As a result, by setting the average particle size of the wax to 0.01 to 0.2 μm, excellent scratch resistance can be obtained. I found that. If the average particle size of the wax is less than 0.01 μm, it is not economical because it is necessary to use a high-performance machine for producing the wax. On the other hand, if the average particle diameter of the wax exceeds 0.2 μm, the wax protruding from the film surface is easily removed during sliding, and as a result, continuous slidability is reduced.
[0056]
The molecular weight and melting point of the polyethylene wax are not particularly limited, but the acid value is preferably in the range of 5 to 50 ° (NaOH mg / g), and more preferably in the range of 10 to 30 (NaOH mg / g). If the acid value is less than 5 NaOH mg / g, the wax and the resin are hardly compatible with each other, so that the wax is completely oriented on the surface of the film when the film is formed, causing a decrease in scratch resistance and coating adhesion, which is not preferable. . On the other hand, if the acid value exceeds 50% NaOH mg / g, the hydrophilicity of the wax becomes strong, so that the slipperiness of the wax itself decreases and the scratch resistance decreases, which is not preferable.
[0057]
Usually, a surfactant called a dispersant is used for dispersing a resin, a pigment, and the like. When the amount of the surfactant is small with respect to the resin or the pigment, poor dispersion (the resin or the pigment is aggregated to separate and settle or float) is caused. On the other hand, when the amount of the surfactant is large, the water resistance of the obtained film is reduced. Let it.
[0058]
The present inventors have conducted intensive studies on a dispersant for polyethylene wax, and as a result, obtained excellent uniform dispersion stability and water resistance by dispersing polyethylene wax in water using a compound represented by the following formula (IV). I was able to.
[0059]
Embedded image

[0060]
Where R¹Represents an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms;²Represents (EO) m- (PO) n (wherein E is an ethylene group, P is a propylene group, m is an integer of 5 to 20, and n is 0 or an integer of 1 to 10);³Is a hydrogen atom or SO₃M (wherein M is a hydrogen atom, an alkali metal ion or an ammonium ion);⁴Represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms.
[0061]
In the compound represented by the formula (IV) used as a dispersant for polyethylene wax,¹Is preferably an alkyl group having 5 to 20 carbon atoms or an alkenyl group having 2 to 5 carbon atoms. R³Is a hydrogen atom or SO₃NH₄It is preferable that R⁴Is preferably a hydrogen atom or an alkenyl group having 2 to 4 carbon atoms.
[0062]
The method for dispersing the polyethylene wax in water is not particularly limited, and may be a method used industrially. The above-mentioned average particle size of the polyethylene wax is a value in the aqueous dispersion thus obtained.
[0063]
The ratio of the solid content of the compound (IV) to the total solid content of the obtained aqueous dispersion (wax + dispersant) is preferably 5 to 40% by mass, more preferably 5 to 30% by mass. If the ratio is less than 5% by mass, the dispersion of the polyethylene wax becomes insufficient, which is not preferable. On the other hand, when the above ratio exceeds 40% by mass, the water resistance of the resulting film is undesirably reduced.
[0064]
The ratio of the aqueous dispersion with respect to the total solids of the components (A) to (D) in the aqueous surface treatment liquid of the present invention is 2 to 20% by mass as the solids of (D), and 3 to 20% by mass. %, More preferably 3 to 18% by mass. If this proportion is less than 2% by mass, the effect of improving the scratch resistance is poor, while if it exceeds 20% by mass, the overcoating property is undesirably reduced.
[0065]
Water-soluble organic solvent (E)
The aqueous surface treatment liquid contains 1 to 10% by mass of a water-soluble organic solvent (E) in the surface treatment liquid for the purpose of improving the film forming property. It is preferable that the water-soluble organic solvent can be azeotropic with water. Examples of such an organic solvent include acetone, methyl ethyl ketone, N-methyl-2-pyrrolidone, dioxane, and isopropyl alcohol, and among them, N-methyl-2-pyrrolidone is preferable.
[0066]
The compounding amount of the organic solvent (E) in the surface treatment liquid is preferably in the range of 1 to 10% by mass, more preferably 2 to 8% by mass of the whole treatment solution. When the proportion is less than 1% by mass, the effect of improving the film-forming property is poor, while when it exceeds 10% by mass, the effect of improving the film-forming property is saturated, so that it is not economical.
[0067]
The surface treatment liquid of the present invention includes, as an optional component, a surfactant called a wettability improver for forming a uniform film on the surface to be coated, a conductive substance for improving weldability, and improving design. For example, may be added.
[0068]
The surface treatment liquid (N) of the present invention is obtained by mixing the above components (A), お よ び (B), (C), (D) and (E) with an appropriate amount of water and dissolving or dispersing the same. Can be. The order of addition of the components is not particularly limited, but mixing is suitably performed, for example, by stirring using a propeller-type stirrer.
[0069]
The obtained surface treatment liquid (N) of the present invention preferably has a solid content concentration of 5 to 50% by mass, and more preferably 5 to 40% by mass. If the solid concentration is less than 5% by mass, the drying time is undesirably long. On the other hand, when the solid content concentration exceeds 50% by mass, the viscosity of the surface treatment liquid itself is high, which may cause trouble in handling.
[0070]
The zinc-based plated steel sheet to which the surface treatment solution of the first and second layers of the present invention is applied may be any steel sheet obtained by electroplating or hot-dip zinc or a zinc alloy. Examples of preferred galvanized steel sheets include electro-galvanized steel sheets, hot-dip galvanized steel sheets, galvanized steel sheets containing 5% aluminum, galvannealed steel sheets, and electro-zinc-nickel alloy-coated steel sheets.
[0071]
The method of applying these surface treatment liquids (M) and (N) is not particularly limited, but a roll coater method, a dipping method, an electrostatic coating method, or the like can be used.
In a preferred treatment method, the surface treatment liquid (M) is applied at 10 to 50 ° C., and dried at a temperature of 50 to 200 ° C., more preferably 60 to 180 ° C. at the ultimate plate temperature to form a first layer film. Then, the surface treatment liquid (N) is similarly applied at 10 to 50 ° C., and dried at a reaching plate temperature of 50 to 200 ° C., more preferably at a temperature of 60 to 180 ° C. to form a second layer film. This makes it possible to form a film having excellent corrosion resistance and abrasion resistance on the surface of the galvanized steel sheet without containing chromium.
[0072]
If the drying temperature of the first layer and the second layer is lower than 50 ° C., satisfactory corrosion resistance cannot be obtained, and if the drying temperature exceeds 200 ° C., the cost for drying increases, which is not economical.
[0073]
The adhesion amount of the first layer film is 0.05 to 1 g / m.²(= 50-1000 mg / m²), Preferably {0.1-0.5} g / m²It is. The adhesion amount of the first layer is 0.05 g / m²If it is less than 1, satisfactory corrosion resistance cannot be obtained, while 1 g / m²When it exceeds, the effect of corrosion resistance is saturated, so that it is not economical.
[0074]
The coating amount of the second layer is 0.1 to 3 g / m.²And preferably $ 0.2-2 g / m²And more preferably $ 0.3-2 g / m²It is. 0.1 g / m of the adhesion amount of the second layer²If it is less than 3, satisfactory corrosion resistance cannot be obtained, and 3 g / m²If it exceeds, the effect of corrosion resistance is saturated, so that it is not economical.
[0075]
The surface treatment solution of the present invention may be applied to a galvanized steel sheet treated by a chromium-free treatment method such as pickling and phosphate conversion treatment.
The galvanized steel sheet having excellent scratch resistance obtained by the present invention is excellent in flat part corrosion resistance, scratch part corrosion resistance, and paint adhesion.
[0076]
The galvanized steel sheet having a coating not containing chromium according to the present invention may be used as it is, but is usually used after being painted. There is no particular limitation on the top coating applied to the galvanized steel sheet having excellent scratch resistance at that time. Mold resin-based paints and the like.
[0077]
【Example】
The operation and effect of the present invention will be specifically illustrated by the following Examples and Comparative Examples. The examples are only illustrative of the present invention and do not limit the present invention in any way. In Examples,% is% by mass unless otherwise specified.
[0078]
[Preparation of test plate]
(1) Test material
The following commercially available double-sided zinc-based plated steel sheets were used as test materials. The size of the test material is 200 mm x 300 mm.
[0079]
・ Electro-galvanized steel sheet (EG)
Sheet thickness 0.8 mm, basis weight = {20/20} (g / m²)
・ Hot-dip galvanized steel sheet (GI)
Sheet thickness 0.8 mm, basis weight = {60/60} (g / m²)
・ Galvanized steel sheet containing 5% aluminum (GF)
Sheet thickness 0.8 mm, basis weight = {90/90} (g / m²)
(2) Degreasing treatment
Each of the test materials was degreased with a silicate-based alkaline degreasing agent Fine Cleaner 4336 (registered trademark: manufactured by Nippon Parkerizing). After spraying at a temperature of 60 ° C. for 2 minutes using a degreasing agent having a concentration of 20 μg / L, the resultant was washed with tap water.
[0080]
(3) Formation of first layer coating
One surface of the degreased test material is coated with a surface treatment solution (M1 to M4) described in Table 1 at room temperature by a bar coater, and dried at an ultimate plate temperature of 100 ° C. to form a first layer film. did. The surface treatment liquid indicated by the symbol M4 in Table 1 did not contain a water-soluble resin, and contained only the same type and amount of the silane coupling agent and the titanium compound used in the treatment liquid indicated by the symbol M2. The adhesion amount was adjusted by appropriately changing the solid concentration of the surface treatment liquid and the type of the bar coater. For comparison, a spray treatment was carried out at a liquid temperature of 50 ° C. for 5 seconds using Zinchrome 357 (registered trademark: manufactured by Nippon Parkerizing Co., Ltd.) which is a reaction type chromate treatment liquid, followed by washing with tap water and air drying.
[0081]
(4) Formation of second layer coating
(4-1) Preparation of aqueous surface treatment liquid
At room temperature, urethane resin (A) shown in Table 2, epoxy resin (B) shown in Table 3, colloidal silica (C) shown in Table 4, wax aqueous dispersion (D) shown in Table 5, and Table 6 shown in Table 6 The organic solvent (E) was mixed in this order with stirring using a propeller stirrer, and distilled water was added to adjust the solid content concentration. The aqueous surface treatment liquid for forming the second layer having the composition shown in Table 7 (Table 7) 1-12) were prepared. The aqueous wax dispersion (D) was prepared by putting all of the wax, dispersant compound (IV) and water shown in Table 5 into an autoclave, heating the mixture to a temperature of 130 ° C, and stirring.
[0082]
(4-2) Coating and drying
Each of the prepared surface treatment liquids was applied on the first layer film of the test plate at room temperature by a bar coater, and dried at an atmosphere temperature of 240 ° C. for 10 seconds. At this time, the reached plate temperature was 120 ° C. The adhesion amount was adjusted by appropriately changing the solid concentration of the surface treatment liquid and the type of the bar coater.
[0083]
(5) Performance test
(5-1) Plane corrosion resistance
The salt spray test according to JIS-Z-2371 was performed for 240 hours for the EG material and 480 hours for the GF material, and the white rust occurrence was observed and evaluated according to the following criteria.
[0084]
<Evaluation criteria>
◎: White rust generation area is less than 3% of total area,
：: White rust generation area is 3% or more and less than 10% of the entire area,
Δ: White rust generation area is 10% or more and less than 30% of the entire area,
X: White rust generation area is 30% or more of the entire area.
[0085]
(5-2) Corrosion resistance of scratches
The test piece was cut into a size of 30 mm x 300 mm, and a draw bead test (bead tip 1 mmR, bead height 4 mm, die shoulder 1 mmR, crimp load 500 kg, temperature 30 ° C) was performed. The sliding portion of this test piece was subjected to a salt spray test according to JIS-Z-2371 for 120 hours for the EG material and 240 hours for the GF material. The white rust occurrence was observed and evaluated according to the following criteria.
[0086]
<Evaluation criteria>
◎: White rust generation area is less than 3% of total area,
：: White rust generation area is not less than 3% to less than 10% of the whole area,
Δ: White rust generation area is 10% or more and less than 30% of the entire area,
X: White rust generation area is 30% or more of the entire area.
[0087]
(5-3) Paint adhesion
A melamine alkyd paint (Amirac No. 1000, manufactured by Kansai Paint) was applied so that the film thickness after baking and drying was 25 μm, and baked at 125 ° C. for 20 minutes. Using test pieces 24 hours after baking, 100 1-mm squares were drawn according to JIS-Z-5400, and then the coating film was peeled off using Cellotape (registered trademark), and evaluated according to the following criteria.
[0088]
<Evaluation criteria>
◎: No peeling of coating film, 100 remaining coating films,
：: Very little peeling of the coating film, 100 remaining coating films,
Δ: 95 to 99 remaining coating films,
X: The remaining number of coating films is 94 or less.
[0089]
(5-4) Surface color
For some of the test pieces, the surface color tone (b * value of JIS Z8729, which is an index of yellowishness) of the test piece was measured.
[0090]
The test results are shown in Tables 8 and 9.
[0091]
[Table 1]

[0092]
[Table 2]

[0093]
[Table 3]

[0094]
[Table 4]

[0095]
[Table 5]

[0096]
[Table 6]

[0097]
[Table 7]

[0098]
[Table 8]

[0099]
[Table 9]

[0100]
As can be seen from Table 8, in Examples 1 to 24 using the surface treatment liquid of the present invention, both the flat part corrosion resistance, the abrasion part corrosion resistance and the paint adhesion were good, and the conventional chromate treatment of Comparative Example 19 was performed. It was equivalent to the case where it went. On the other hand, in Comparative Examples 1 to 18 using the surface treatment liquids outside the scope of the present invention, none of those satisfying all the performances of the flat part corrosion resistance, the abrasion part corrosion resistance and the paint adhesion were obtained.
[0101]
1st layerThe surface appearance (yellow tint) of the coating containing Example 4 containing a titanium compound and that of Example 15 containing a zirconium compound were compared with an optical inspection device. Example 4 was more yellowish. However, the yellowness of the film of Example 4 was not so strong. The difference in the surface tone between the test pieces of Example 4 and Example 15 when visually observed was difficult to judge independently, and it was found that the film of Example 4 had a slight yellow tint when observed side by side. Recognizable.
[0102]
【The invention's effect】
As described above, the surface treatment liquid of the present invention is applied to the first layer and the second layer on the surface of the galvanized steel sheet, respectively, and dried, so that chromium is not used, and the flat part corrosion resistance, the abrasion part corrosion resistance and A zinc-coated steel sheet having excellent paint adhesion and excellent scratch resistance can be obtained.

Claims (5)

A galvanized steel sheet has on at least one surface thereof a dried film of the following surface treatment solution (M) as a first layer, and a dried film of the following surface treatment solution (N) as a second layer thereon. Chromium-free galvanized steel sheet.
Surface treatment liquid (M): a water-soluble resin (a) comprising a polymer molecule having a repeating unit represented by the general formula (I), an active hydrogen-containing amino group, an epoxy group, a vinyl group, a mercapto group and a methacryloxy group Aqueous solution containing at least one silane coupling agent (b) having at least one functional group selected from the group consisting of: and a titanium compound and a zirconium compound (c) at a pH of 2.0 to 6.5. .

In the formula, Y ₁ and Y ₂ each independently represent a hydrogen atom or a Z group represented by the following formula (II) or (III);

R ₁ , R ₂ , R ₃ , R ₄ and R ₅ in the formulas (II) and (III) are each independently a hydrogen atom, a C ₁ -C ₁₀ alkyl group or a C ₁ -C ₁₀ hydroxyalkyl Represents a group,
The average substitution number of the Z group per benzene ring in the polymer molecule is 0.2 to 1.0.
Surface treatment liquid (N): (A) a urethane resin having a bisphenol A type skeleton and a glass transition temperature in the range of -40 to 0 ° C., and (B) a water solution having three or more epoxy groups in one molecule. Polyethylene wax dispersed in water with a dispersant comprising a hydrophilic epoxy resin, (C) colloidal silica, and (D) a compound represented by the general formula (IV) so as to have an average particle size of 0.01 to 0.2 μm. And (E) a water-soluble organic solvent and water, wherein the solid content ratio of (A) + (B) is 50 to 95% by mass and the solid content ratio of (C) is based on the total solid content. A water-based surface treatment liquid having a solid content ratio of 3 to 40% by mass, (D) of 2 to 20% by mass, and a ratio of (E) of 1 to 10% by mass with respect to the total amount of the treatment solution.

In the formula, R ¹ represents an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, and R ² represents (EO) m- (PO) n (where E is an ethylene group, and P is propylene A group, m is an integer of 5 to 20, n is 0 or an integer of 1 to 10, and R ³ is a hydrogen atom or SO ₃ M (where M is a hydrogen atom, an alkali metal ion or an ammonium ion) R ⁴ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms. Galvanized steel sheet according to claim 1 film deposition amount of the first layer is 50~1000 mg / ^{m 2.} The galvanized steel sheet according to claim 1, wherein the coating amount of the second layer is 0.1 to 3 g / m ² . The surface treatment liquid (M) according to claim 1 is applied to at least one surface of a galvanized steel sheet, and dried to form a first layer film, and then the surface treatment liquid (N) according to claim 1 is applied. A method for producing a non-chromium-treated galvanized steel sheet, wherein the second layer film is formed by drying. The method for producing a non-chromium-treated galvanized steel sheet according to claim 4, wherein the drying after the application of the surface treatment liquids (M) and (N) is performed at a temperature of 50 to 200 ° C.