JP2004018887A - Surface-treated steel sheet showing excellent press-moldability and corrosion resistance and its manufacturing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chromium-free, surface-treated steel sheet showing an excellent press moldability and corrosion resistance. <P>SOLUTION: On the surface of a zinc- or aluminum-plated steel sheet, a surface-treatment coated film is formed by treating the surface of the plated steel sheet with a surface-treatment composition containing a resin compound having a specific chemical structure, a cationic urethane resin having a specific cationic functional group, a silane coupling agent having a specific reactive functional group and, preferably, a Ti compound and a specific acid compound. Above the surface-treatment coated film, a resin coated film wherein adequate amounts of solid lubricant and chromium-free rust-preventive additive are compounded with a base comprising two or more thermosetting solvent resins having different glass transition temperatures, is formed. <P>COPYRIGHT: (C)2004,JPO

Description

一般式（１）中、ベンゼン環に結合しているＹ_１及びＹ_２は、それぞれ互いに独立に水素、又は下記式（２）又は式（３）により表されるＺ基であり、１ベンゼン環当りのＺ基の置換数の平均値は０．２〜１．０である。ｎは２〜５０の整数を表わす。
【化８】

【化９】

式（２）及び式（３）中のＲ_１、Ｒ_２、Ｒ_３、Ｒ_４及びＲ_５は、それぞれ互いに独立に水素原子、炭素数１〜１０のアルキル基又は炭素数１〜１０のヒドロキシアルキル基を表し、Ａ⁻は水素イオン又は酸イオンを表す。
【００１０】
［２］　上記［１］の表面処理鋼板において、表面処理組成物（Ｉ）が、さらにＴｉ化合物（Ｄ）を含有し、該Ｔｉ化合物（Ｄ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｄ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．０５〜０．１０であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
［３］　上記［１］又は［２］の表面処理鋼板において、表面処理組成物（Ｉ）が、さらにリン酸、硝酸、酢酸、およびこれらの塩の中から選ばれる少なくとも１種の酸化合物（Ｅ）を含有し、該酸化合物（Ｅ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｅ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．０５〜０．１５であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
【００１１】
［４］　上記［１］〜［３］のいずれかの表面処理鋼板において、塗料（ＩＩ）中に含まれる非クロム系防錆添加剤が、下記（ｅ１）〜（ｅ５）の中から選ばれる少なくとも１種であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
（ｅ１）酸化ケイ素
（ｅ２）カルシウムおよび／またはカルシウム化合物
（ｅ３）難溶性リン酸化合物
（ｅ４）モリブデン酸化合物
（ｅ５）トリアゾール類、チオール類、チアジアゾール類、チアゾール類、チウラム類の中から選ばれる１種以上の、Ｓ原子を含有する有機化合物
［５］　上記［４］の表面処理鋼板において、非クロム系防錆添加剤として少なくともカルシウムイオン交換シリカを含有することを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
【００１２】
［６］　上記［１］〜［５］のいずれかの表面処理鋼板において、塗料（ＩＩ）中に含まれる、硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂（ａ）が、硬化後のガラス転移温度が５０℃以下である、１種以上の低ガラス転移温度の溶剤系熱硬化型樹脂（ａ_１）と、硬化後のガラス転移温度が５０℃超である、１種以上の高ガラス転移温度の溶剤系熱硬化型樹脂（ａ_２）からなることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
［７］　上記［６］の表面処理鋼板において、低ガラス転移温度の溶剤系熱硬化型樹脂（ａ_１）と、高ガラス転移温度の溶剤系熱硬化型樹脂（ａ_２）との配合比（ａ_１）／（ａ_２）が固形分の質量比で９／１〜１／９であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
【００１３】
［８］　上記［１］〜［７］のいずれかの表面処理鋼板において、塗料（ＩＩ）中に含まれる、硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂（ａ）の各々の主剤樹脂が、水酸基含有ウレタンプレポリマーであることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
［９］　上記［１］〜［８］のいずれかの表面処理鋼板において、塗料（ＩＩ）中に含まれるポリエチレン樹脂からなる固形潤滑剤（ｂ）が、融点９０〜１３０℃、数平均分子量５０００以下であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板。
【００１４】
［１０］　亜鉛系めっき鋼板またはアルミニウム系めっき鋼板の表面に、下記一般式（１）で表わされる樹脂化合物（Ａ）と、第１〜第３アミノ基および第４アンモニウム塩基の中から選ばれる少なくとも１種のカチオン性官能基を有するカチオン性ウレタン樹脂（Ｂ）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の中から選ばれる少なくとも１種の反応性官能基を有するシランカップリング剤（Ｃ）とを含有し、且つ、カチオン性ウレタン樹脂（Ｂ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｂ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．０４〜０．０９であり、シランカップリング剤（Ｃ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｃ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．６〜０．７である表面処理組成物（Ｉ）を塗布し、乾燥することにより皮膜厚が０．０１〜２μｍの表面処理皮膜を形成し、
その上層に、下記成分（ａ）、（ｂ）および（ｃ）を含有する塗料（ＩＩ）を塗布し、加熱硬化させることにより皮膜厚が０．１μｍ以上５μｍ未満の樹脂皮膜を形成し、
（ａ）硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂：１００質量部（固形分割合）
（ｂ）１３０℃以下の融点を有するポリエチレン樹脂からなる固形潤滑剤：１〜３０質量部（固形分割合）
（ｃ）非クロム系防錆添加剤：３〜３０質量部（固形分割合）
前記表面処理皮膜と前記樹脂皮膜の合計膜厚が５μｍ以下となるようにしたことを特徴とする、プレス成形性および耐食性に優れた表面処理鋼板の製造方法。
【化１０】

一般式（１）中、ベンゼン環に結合しているＹ_１及びＹ_２は、それぞれ互いに独立に水素、又は下記式（２）又は式（３）により表されるＺ基であり、１ベンゼン環当りのＺ基の置換数の平均値は０．２〜１．０である。ｎは２〜５０の整数を表わす。
【化１１】

【化１２】

式（２）及び式（３）中のＲ_１、Ｒ_２、Ｒ_３、Ｒ_４及びＲ_５は、それぞれ互いに独立に水素原子、炭素数１〜１０のアルキル基又は炭素数１〜１０のヒドロキシアルキル基を表し、Ａ⁻は水素イオン又は酸イオンを表す。
【００１５】
［１１］　上記［１０］の製造方法において、表面処理組成物（Ｉ）が、さらにＴｉ化合物（Ｄ）を含有し、該Ｔｉ化合物（Ｄ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｄ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．０５〜０．１０であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
［１２］　上記［１０］又は［１１］の製造方法において、表面処理組成物（Ｉ）が、さらにリン酸、硝酸、酢酸、およびこれらの塩の中から選ばれる少なくとも１種の酸化合物（Ｅ）を含有し、該酸化合物（Ｅ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｅ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．０５〜０．１５であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
【００１６】
［１３］　上記［１０］〜［１２］のいずれかの製造方法において、塗料（ＩＩ）中に含まれる非クロム系防錆添加剤が、下記（ｅ１）〜（ｅ５）の中から選ばれる少なくとも１種であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
（ｅ１）酸化ケイ素
（ｅ２）カルシウムおよび／またはカルシウム化合物
（ｅ３）難溶性リン酸化合物
（ｅ４）モリブデン酸化合物
（ｅ５）トリアゾール類、チオール類、チアジアゾール類、チアゾール類、チウラム類の中から選ばれる１種以上の、Ｓ原子を含有する有機化合物
［１４］　上記［１３］の製造方法において、非クロム系防錆添加剤として少なくともカルシウムイオン交換シリカを含有することを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
【００１７】
［１５］　上記［１０］〜［１４］のいずれかの製造方法において、塗料（ＩＩ）中に含まれる、硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂（ａ）が、硬化後のガラス転移温度が５０℃以下である、１種以上の低ガラス転移温度の溶剤系熱硬化型樹脂（ａ_１）と、硬化後のガラス転移温度が５０℃超である、１種以上の高ガラス転移温度の溶剤系熱硬化型樹脂（ａ_２）からなることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
［１６］　上記［１５］の製造方法において、低ガラス転移温度の溶剤系熱硬化型樹脂（ａ_１）と、高ガラス転移温度の溶剤系熱硬化型樹脂（ａ_２）との配合比（ａ_１）／（ａ_２）が固形分の質量比で９／１〜１／９であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
【００１８】
［１７］　上記［１０］〜［１６］のいずれかの製造方法において、塗料（ＩＩ）中に含まれる、硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂（ａ）の各々の主剤樹脂が、水酸基含有ウレタンプレポリマーであることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
［１８］　上記［１０］〜［１７］のいずれかの製造方法において、塗料（ＩＩ）中に含まれるポリエチレン樹脂からなる固形潤滑剤（ｂ）が、融点９０〜１３０℃、数平均分子量５０００以下であることを特徴とするプレス成形性および耐食性に優れた表面処理鋼板の製造方法。
【００１９】
【発明の実施の形態】
以下、本発明の詳細とその限定理由を説明する。
本発明の表面処理鋼板のベースとなる亜鉛系めっき鋼板に特別な制限はなく、例えば、亜鉛めっき鋼板、Ｚｎ−Ｎｉめっき鋼板、Ｚｎ−Ｆｅめっき鋼板（電気めっき、合金化溶融亜鉛めっき）、Ｚｎ−Ｃｒめっき鋼板、Ｚｎ−Ｍｎめっき鋼板、Ｚｎ−Ｃｏめっき鋼板、Ｚｎ−Ｃｏ−Ｃｒ合金めっき鋼板、Ｚｎ−Ｃｒ−Ｎｉめっき鋼板、Ｚｎ−Ｃｒ−Ｆｅめっき鋼板、Ｚｎ−Ａｌめっき鋼板（例えば、Ｚｎ−５％Ａｌ合金めっき鋼板、Ｚｎ−５５％Ａｌ合金めっき鋼板）、さらにはこれらのめっきに金属酸化物、ポリマーなどを分散した亜鉛系複合めっき鋼板（例えば、Ｚｎ−ＳｉＯ_２分散めっき鋼板）などを用いることができる。また、上記のようなめっきのうち、同種または異種のものを２層以上めっきした複層めっき鋼板を用いることができる。また、本発明の表面処理鋼板のベースとなるアルミニウム系めっき鋼板にも特別な制限はなく、例えば、アルミニウムめっき鋼板、Ａｌ−Ｓｉめっき鋼板などを用いることができる。
また、めっき鋼板としては、鋼板面にあらかじめＮｉなどの薄目付けのめっきを施し、その上に上記のような各種めっきを施したものであってもよい。
【００２０】
めっきの方法としては、電解法（水溶液中での電解、非水溶媒中での電解）、溶融法、気相法のうち、実施可能ないずれの方法も採用することができる。さらに、めっきの黒変を防止する目的で、めっき皮膜中にＮｉ，Ｃｏ，Ｆｅの１種以上を１〜２０００ｐｐｍ程度析出させたり、或いはめっき表面にＮｉ，Ｃｏ，Ｆｅの１種以上を含むアルカリまたは酸性水溶液による表面調整処理を施し、それらの元素を析出させるようにしてもよい。
【００２１】
次に、上記亜鉛系めっき鋼板またはアルミニウム系めっき鋼板の表面に形成される表面処理皮膜とこの皮膜形成用の表面処理組成物（Ｉ）について説明する。本発明の表面処理鋼板において、亜鉛系めっき鋼板またはアルミニウム系めっき鋼板の表面に下層として形成される表面処理皮膜は、下記一般式（１）で表わされる樹脂化合物（Ａ）と、第１〜第３アミノ基および第４アンモニウム塩基の中から選ばれる少なくとも１種のカチオン性官能基を有するカチオン性ウレタン樹脂（Ｂ）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の中から選ばれる少なくとも１種の反応性官能基を有するシランカップリング剤（Ｃ）とを含有し、且つ、カチオン性ウレタン樹脂（Ｂ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｂ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．０４〜０．０９であり、シランカップリング剤（Ｃ）と樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量質量比［（Ｃ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］が０．６〜０．７である表面処理組成物（Ｉ）を塗布し、乾燥することにより形成された皮膜厚が０．０１〜２μｍの表面処理皮膜である。
【００２２】
【化１３】

上記一般式（１）中、ベンゼン環に結合しているＹ_１及びＹ_２は、それぞれ互いに独立に水素、又は下記一般式（２）又は（３）により表されるＺ基であり、１ベンゼン環当りのＺ基の置換数の平均値は０．２〜１．０である。ｎは平均重合度を表し、２〜５０の整数である。ここで、Ｚ基の置換数の平均値とは、全Ｚ基導入数を全ベンゼン環数（即ち２ｎ）で除した数値のことである。
上記平均重合度ｎが２未満では耐食性付与効果が不十分であり、一方、５０を超えると水溶性の低下、増粘などにより、処理組成物中での安定性が低下し、保存安定性が不十分となる。
【００２３】
【化１４】

【化１５】

上記一般式（２）及び（３）中、Ｒ_１、Ｒ_２、Ｒ_３、Ｒ_４及びＲ_５は、それぞれ互いに独立に水素原子、炭素数１〜１０のアルキル基又は炭素数１〜１０のヒドロキシアルキル基を表す。アルキル基又はヒドロキシアルキル基の炭素数が１０を超えると樹脂化合物（Ａ）を十分に水溶化することができず、処理組成物中での安定性を欠くため適用できない。Ｒ_１、Ｒ_２、Ｒ_３、Ｒ_４及びＲ_５としては、例えば、メチル、エチル、プロピル、ブチル、ヒドロキシエチル、２−ヒドロキシプロピル、ヒドロキシイソブチルなどを挙げることができる。また、Ａ⁻は水酸イオン又は酸イオンを表す。酸イオンの具体例としては、硫酸イオン、硝酸イオン、酢酸イオンなどを挙げることができる。
一般式（１）で表される樹脂化合物（Ａ）はビスフェノール−ホルマリン縮合物であり、その合成方法は特定しないが、例えば、アルカリ触媒存在下で、ビスフェノールＡにホルマリンとアミンを作用させることで得ることができる。
【００２４】
前記カチオン性ウレタン樹脂（Ｂ）は、第１〜第３アミノ基および第４アンモニウム塩基の中から選ばれる少なくとも１種のカチオン性官能基を有するものであれば、構成されるモノマー成分であるポリオール、イソシアネート成分および重合方法は特に限定されるものではない。カチオン性官能基としては、例えば、アミノ基、メチルアミノ基、エチルアミノ基、ジメチルアミノ基、ジエチルアミノ基、トリメチルアミノ基、トリエチルアミノ基などが挙げられる。カチオン性ウレタン樹脂は２種以上を混合して用いてもよい。
【００２５】
カチオン性ウレタン樹脂（Ｂ）の配合量は、樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｂ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］で０．０４〜０．０９とする。カチオン性ウレタン樹脂（Ｂ）をこのような配合量で含有させることにより、腐食初期に発生しやすい極く薄い白錆を効果的に防ぐことができる。この理由は必ずしも明らかではないが、カチオン性ウレタン樹脂を適量配合することにより造膜性が向上するためであると考えられる。しかしながら、上記質量比が０．０４未満では初期の薄錆発生の抑制効果が不十分であり、一方、０．０９を超えると長期の耐食性が不十分となる。
【００２６】
前記シランカップリング剤（Ｃ）は、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の中から選ばれる少なくとも１種の反応性官能基を有するシランカップリング剤であれば特に限定されるものではなく、例えば、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、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エポキシシクロヘキシル）エチルトエリメトキシシラン、ビニルトリエトキシシラン、３−メルカプトプロピルトリメトキシシランなどの１種以上が使用できる。シランカップリング剤（Ｃ）の配合量は、樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｃ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］で０．６〜０．７とする。この質量比が０．６未満では耐食性および塗装性が不十分であり、一方、０．７を超えると成形後の外観性と耐食性が劣る。
【００２７】
表面処理組成物（Ｉ）には、さらに耐食性および耐黒変性の改善を目的としてＴｉ化合物（Ｄ）を添加することが好ましい。Ｔｉ化合物（Ｄ）は、Ｔｉの供給源となるのもであれば，特に対となるアニオンを限定するものではなく、例えば、酢酸チタン、硝酸チタン、硫酸チタン、リン酸チタン、炭酸チタン、チタンフッ化水素酸などの１種以上が使用できる。
Ｔｉ化合物（Ｄ）の配合量は、樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｄ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］で０．０５〜０．１０とすることが好ましい。この質量比が０．０５未満では耐食性および耐黒変性の改善効果が不十分であり、一方、０．１０を超えると表面処理組成物の可使用時間が短くなり、実質的な使用が困難になる。
【００２８】
表面処理組成物（Ｉ）には、さらに耐食性の改善を目的として酸化合物（Ｅ）を添加することができる。この酸化合物（Ｅ）は、リン酸、硝酸、酢酸、およびこれらの塩の中から選ばれる少なくとも１種の酸化合物であれば特に限定するものではなく、例えば、オルソリン酸、ピロリン酸、トリメタリン酸、テトラメタリン酸、ヘキサメタリン酸、リン酸二水素アンモニウム、リン酸水素二アンモニウム、リン酸三アンモニウム、リン酸二水素ナトリウム、リン酸水素二ナトリウム、リン酸三ナトリウム、硝酸、硝酸アンモニウム、硝酸ナトリウム、酢酸、酢酸アンモニウム、酢酸ナトリウムなどの１種以上が使用できる。
酸化合物（Ｅ）の配合量は、樹脂化合物（Ａ）、カチオン性ウレタン樹脂（Ｂ）およびシランカップリング剤（Ｃ）の合計量との固形分の質量比［（Ｅ）／｛（Ａ）＋（Ｂ）＋（Ｃ）｝］で０．０５〜０．１５とすることが好ましい。この質量比が０．０５未満では耐食性の改善効果が不十分であり、一方、０．１５を超えると上層の樹脂皮膜との密着性が低下し、その結果、成形後の外観性及び耐食性が劣ったものとなる。
【００２９】
表面処理組成物（Ｉ）には、さらに必要に応じて固形潤滑剤を配合することができる。この固形潤滑剤としては、ポリエチレンワックスなどの炭化水素系潤滑剤、ポリ４フッ化エチレン樹脂などのフッ素樹脂系潤滑剤、ステアリン酸アミドなどの脂肪酸アミド系潤滑剤などをはじめとする任意のものが使用できる。
表面処理組成物（Ｉ）（処理液）はｐＨ０．５〜６、好ましくは１〜４に調整することが適当である。表面処理組成物（Ｉ）のｐＨが０．５未満では処理液の反応性が強すぎるため外観ムラが生じやすく、一方、ｐＨが６を超えると処理液の反応性が低くなり、めっき金属と表面処理皮膜との結合が不十分となりやすく、耐食性が低下する傾向がある。
【００３０】
次に、上記表面処理皮膜の上層に形成される樹脂皮膜とこの皮膜形成用の塗料（ＩＩ）について説明する。
上記表面処理皮膜の上層に形成される樹脂皮膜は、下記成分（ａ）、（ｂ）および（ｃ）を含有する塗料（ＩＩ）を塗布し、加熱硬化させることにより形成された皮膜厚が０．１μｍ以上５μｍ未満の樹脂皮膜である。
（ａ）硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂：１００質量部（固形分割合）
（ｂ）１３０℃以下の融点を有するポリエチレン樹脂からなる固形潤滑剤：１〜３０質量部（固形分割合）
（ｃ）非クロム系防錆添加剤：３〜３０質量部（固形分割合）
【００３１】
ベース樹脂として溶剤系熱硬化型樹脂（ａ）を用いる理由は、以下のとおりである。
▲１▼溶剤系樹脂は、水系樹脂に比較して、樹脂中に添加される潤滑剤および防錆添加剤などとの相溶性、および塗料としての長期安定性に優れている。
▲２▼可塑性樹脂と異なり、熱硬化性樹脂には融点が存在しないので、高温時の機械的強度が高い。したがって、このような樹脂からなる塗料によって皮膜を形成すれば、プレス成形時の摩擦熱により鋼板の表面温度が上昇しても、樹脂皮膜の剥離や変形が生じにくい。
【００３２】
また、樹脂皮膜のベース樹脂として、硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂（ａ）を使用する理由は次のとおりである。
すなわち、ガラス転移温度の低い溶剤系熱硬化型樹脂は低温時における柔軟性に優れている。したがって、このような樹脂をベース樹脂とした樹脂皮膜が形成されためっき鋼板をプレス成形する場合、プレス成形条件が緩やかな場合または緩やかな部分では、プレス成形性及びプレス成形後の外観が良好である。しかしながら、プレス成形条件が、表面が高温になるような厳しい場合または厳しい部分では、樹脂皮膜が軟化してめっき鋼板から剥離し、剥離した樹脂皮膜が成形用金型に付着する結果、プレス成形性およびプレス成形後の外観の劣化を招く。
【００３３】
一方、ガラス転移温度の高い溶剤系熱硬化型樹脂は高温強度に優れている。したがって、このような樹脂をベース樹脂とした樹脂皮膜が形成されためっき鋼板をプレス成形する場合、プレス成形条件が厳しい場合または厳しい部分でも、樹脂皮膜が軟化してめっき鋼板から剥離するようなことはない。しかしながら、ガラス転移温度の高い溶剤系熱硬化型樹脂は低温時における柔軟性が悪いために、プレス成形条件が緩やかな場合または緩やかな部分では、樹脂皮膜が粉化してめっき鋼板から剥離し、剥離した樹脂皮膜が成形用金型に付着する結果、プレス成形性及びプレス成形後の外観の劣化を招く。
【００３４】
そこで、本発明においては、樹脂皮膜にプレス成形する際の低温時における柔軟性および高温時における強度をともに付与するため、樹脂皮膜のベース樹脂を硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂によって構成した。好ましい溶剤系熱硬化型樹脂は、硬化後のガラス転移温度が５０℃以下である１種以上の低ガラス転移温度の溶剤系熱硬化型樹脂と、硬化後のガラス転移温度が５０℃超である１種以上の高ガラス転移温度の溶剤系熱硬化型樹脂とによって構成された樹脂である。上記低ガラス転移温度の溶剤系熱硬化型樹脂の特に好ましいガラス転移温度は１０〜５０℃の範囲である。また、上記高ガラス転移温度の溶剤系熱硬化型樹脂の特に好ましいガラス転移温度は５０℃超〜１００℃の範囲である。
【００３５】
低ガラス転移温度の溶剤系熱硬化型樹脂（ａ_１）と高ガラス転移温度の溶剤系熱硬化型樹脂（ａ_２）の配合比（ａ_１）／（ａ_２）は、固形分の質量比で９／１〜１／９の範囲とすることが好ましい。この配合比（ａ_１）／（ａ_２）が９／１を超えると、樹脂皮膜が形成されためっき鋼板のプレス成形時に、その成形条件が鋼板表面が高温になるような厳しい場合に、樹脂皮膜が軟化してめっき鋼板から剥離する問題が生じやすい。一方、上記配合比（ａ_１）／（ａ_２）が１／９未満では、上記成形条件が鋼板表面がそれほど高温にならないような緩やかな場合に、樹脂皮膜が粉化してめっき鋼板から剥離する問題が生じやすい。低ガラス転移温度の溶剤系熱硬化型樹脂（ａ_１）と高ガラス転移温度の溶剤系熱硬化型樹脂（ａ_２）のより好ましい配合比（ａ_１）／（ａ_２）は９／１〜５／５の範囲である。
【００３６】
上述した硬化後のガラス転移温度が異なる２種以上の溶剤系熱硬化型樹脂の主剤樹脂成分は、硬化後のガラス転移温度が異なる２種以上の水酸基含有ウレタンプレポリマーであることが好ましい。また、これら各水酸基含有ウレタンプレポリマーは、ポリエーテルポリオール、ポリエステルポリオールおよびポリエーテルポリエステルポリオールの中から選ばれる少なくとも１種のポリオール（ｄ）と、イソシアネート化合物（ｅ）と、２価アルコール（ｆ）とから得られるものが好ましい。
また、上記各水酸基含有ウレタンプレポリマーの硬化剤成分（架橋剤）としては、ブロックポリイソシアネート化合物およびアミノ樹脂の中から選ばれる少なくとも１種を用いることが好ましい。硬化剤としては、ガラス転移温度が異なる２種以上の水酸基含有ウレタンプレポリマーに対して１種又は２種以上の硬化剤を用いることができる。なお、硬化後のガラス転移温度はウレタンプレポリマーと硬化剤（架橋剤）との反応によって得られるものであるが、硬化後のガラス転移温度が異なる２種以上のウレタンプレポリマーを使用することにより、１種類の硬化剤を用いて硬化後のガラス転移温度を変えることができる。
【００３７】
以下、上記水酸基含有ウレタンプレポリマーの構成成分と硬化剤成分について説明する。
前記ポリエーテルポリオールとしては、例えば、ポリエチレングリコール、ポリプロピレングリコール、グリセリンのエチレンオキサイドまたはプロピレンオキサイド付加物のような直鎖状ポリアルキレンポリオールなどが挙げられる。
前記ポリエステルポリオールとしては、例えば、二塩基酸と低分子ポリオールとを反応させて得られる分子鎖中にＯＨ基を有する線状ポリエステルなどを使用できる。前記塩基酸としては、例えば、アジピン酸、アゼライン酸、ドデカン二酸、ダイマー酸、イソフタル酸、ヘキサヒドロ無水フタル酸、テレフタル酸、ジメチルテレフタレート、イタコン酸、フマル酸、無水マレイン酸などのような二塩基酸またはそのエステル類などが挙げられる。
【００３８】
前記ポリエーテルポリエステルポリオールとしては、前記塩基酸と前記ポリエーテルポリオール、またはこれと前記低分子ポリオールとの混合物をエステル化反応させて得られる分子鎖中にＯＨ基を有する線状ポリエステル、並びに、末端にカルボキシル基および／または水酸基を有するポリエステルに、アルキレンオキサイド（例えば、エチレンオキサイド、プロピレンオキサイドなど）を付加反応させて得たポリエーテルなどが挙げられる。
【００３９】
前記イソシアネート化合物としては、例えば、ヘキサメチレンジイソシアネート、ｏ−、ｍ−、またはｐ−フェニレンジイソシアネート、２，４−または２，６−トリレンジイソシアネート、芳香環が水素添加された２，４−または２，６−トリレンジイソシアネート、ジフェニルメタン−４，４′−ジイソシアネート、３，３′−ジメチル−４，４′−ビフェニレンジイソシアネート、ジシクロヘキシルメタン−４，４′−ジイソシアネート、ω，ω′−ジイソシアネート−１，４−ジメチルベンゼン、ω，ω′−ジイソシアネート−１，３−ジメチルベンゼンなどの、芳香族環を有するイソシアネート化合物、または、イソホロンジイソシアネートなどの脂環族イソシアネート化合物などが挙げられる。
前記２価アルコールとしては、例えば、エチレングリコール、ブチレングリコール、ジエチレングリコール、水添ビスフェノールＡのようなオール類が使用できる。
【００４０】
硬化剤であるブロックポリイソシアネート化合物の代表的なものは、いわゆるポリイソシアネートを公知のブロック剤を使用してブロック化させたブロックポリイソシアネートプレポリマーであって、例えば、商品名「バーノックＤ−５５０」、「バーノックＤ−５００」、「バーノックＢ７−８８７」（以上、大日本インキ化学工業（株）製）、商品名「タケネート　Ｎ−８１５−Ｎ」（武田薬品工業（株）製）、商品名「アヂイトール（ＡＤＤＩＴＯＬ）　ＶＸＬ−８０」（ヘキスト合成（株）製）など挙げられる。
硬化剤であるアミノ樹脂としては、メラミン尿素アセトグアナミン、ベンゾグアナミン、ステログアナミンまたはスピログアナミンなどのアミノ成分と、ホルムアルデヒド、パラホルム、アセトアルデヒド、グリオキサールなどのアルデヒド成分と、メタノール、エタノール、イソプロパノール、ｎ−ブタノール、ｉｓｏ−ブタノール、ｓｅｃ−ブタノールなどのアルコール成分とを反応させて得られる樹脂が使用できる。
【００４１】
塗料（ＩＩ）中に添加する固形潤滑剤（ｂ）としては、ポリエチレン樹脂（微粒子）を使用する。ポリエチレン樹脂からなる固形潤滑剤は、連続プレス成形などにおいて、鋼板に対して摺動、変形および摩耗に対する抵抗性を付与し、“かじり”や板破断などの鋼板の損傷や金型の損傷を防止する作用を有している。
ポリエチレン樹脂は、一般に数平均分子量が数百から数百万である結晶性熱可塑性樹脂であり、そのガラス転移点は約−１００℃であって常温よりも低く、その融点は９０〜１４０℃であって常温では柔軟な性質を有している。さらに、その臨界表面張力は約３０ｄｙｎｅ／ｃｍであり、表面エネルギーが低いので濡れ性および付着性が低く、このため優れた潤滑作用を有している。本発明のようにポリエチレン樹脂粒子を表面処理鋼版の樹脂皮膜形成用の塗料中に潤滑剤として含有させる場合には、塗料中での分散性および薄膜形成の観点から、ポリエチレン樹脂粒子の粒径は２０μｍ以下、より好ましくは１０μｍ以下、さらに好ましくは約５μｍとすることが望ましい。このような微粉末ではないポリエチレン樹脂では、所望の潤滑効果を得ることが困難となる。
【００４２】
ポリエチレン樹脂の融点は潤滑性に影響を与える。すなわち、その融点が高いほど常温近傍における力学的強度（変形抵抗）が高く、ポリエチレン樹脂を含有する樹脂皮膜の潤滑性（摺動性）が低下する。したがって、本発明において潤滑剤として使用するポリエチレン樹脂の融点は、１３０℃以下、好ましくは９０〜１２０℃の範囲内であることが必要である。また、製膜性の観点から、ポリエチレン樹脂の数平均分子量は５０００以下であることが好ましい。なお、上述した範囲内の融点、数平均分子量及び粒径を有する２種以上のポリエチレン微粉末を使用してもよい。
【００４３】
ポリエチレン樹脂からなる固形潤滑剤（ｂ）の含有量は、溶剤系熱硬化性樹脂（ａ）の固形分１００質量部に対して、固形分の割合で１〜３０質量部とする。固形潤滑剤（ｂ）の含有量が、溶剤系熱硬化性樹脂の固形分１００質量部に対して１質量部未満では、潤滑性の向上効果が十分に得られず、一方、３０質量部を超えると、樹脂皮膜自体の凝集力および強度が低下する結果、プレス成形時に樹脂皮膜の剥離が増加する問題が生ずる。ポリエチレン樹脂のより好ましい含有量は、溶剤系熱硬化性樹脂の固形分１００質量部に対して５〜２０質量部である。
【００４４】
塗料（ＩＩ）には、耐食性向上を目的として、非クロム系防錆添加剤（ｃ）を配合する。塗料（ＩＩ）中にこのような非クロム系防錆添加剤を配合することにより、特に優れた耐食性能（自己補修性）を得ることができる。この非クロム系防錆添加剤としては、特に下記（ｅ１）〜（ｅ５）の中から選ばれる１種又は２種以上を用いることが好ましい。
（ｅ１）酸化ケイ素
（ｅ２）カルシウムおよび／またはカルシウム化合物
（ｅ３）難溶性リン酸化合物
（ｅ４）モリブデン酸化合物
（ｅ５）トリアゾール類、チオール類、チアジアゾール類、チアゾール類、チウラム類の中から選ばれる１種又は２種以上のＳ原子を含有する有機化合物
【００４５】
これら（ｅ１）〜（ｅ５）の非クロム系防錆添加剤の詳細および防食機構は以下の通りである。
まず、上記（ｅ１）の成分としては、微粒子シリカであるコロイダルシリカや乾式シリカを使用することができるが、耐食性の観点からは、特にカルシウムをその表面に結合させたカルシウムイオン交換シリカを使用するのが好ましい。コロイダルシリカは、例えば、日産化学（株）製のスノーテックス０、スノーテックス２０、スノーテックス３０、スノーテックス４０、スノーテックスＣ、スノーテックスＳ（いずれも商品名）を用いることができ、ヒュームドシリカとしては、日本アエロジル（株）製のＡＥＲＯＳＩＬ　Ｒ９７１、ＡＥＲＯＳＩＬ　Ｒ８１２、ＡＥＲＯＳＩＬ　ＡＥＲＯＳＩＬ　Ｒ８１１、ＡＥＲＯＳＩＬ　Ｒ９７４、ＡＥＲＯＳＩＬ　Ｒ２０２、ＡＥＲＯＳＩＬ　Ｒ８０５、ＡＥＲＯＳＩＬ　１３０、ＡＥＲＯＳＩＬ　２００、ＡＥＲＯＳＩＬ　３００、ＡＥＲＯＳＩＬ　３００ＣＦ　（いずれも商品名）を用いることができる。
また、カルシウムイオン交換シリカとしては、Ｗ．Ｒ．Ｇｒａｃｅ＆Ｃｏ．製のＳＨＩＥＬＤＥＸ　Ｃ３０３、ＳＨＩＥＬＤＥＸ　ＡＣ３、ＳＨＩＥＬＤＥＸ　ＡＣ５（いずれも商品名）、富士シリシア化学（株）製のＳＨＩＥＬＤＥＸ、ＳＨＩＥＬＤＥＸ　ＳＹ７１０（いずれも商品名）などを挙げることができる。これらシリカは、腐食環境下において緻密で安定な亜鉛の腐食生成物の生成に寄与し、この腐食生成物がめっき表面に緻密に形成されることによって、腐食の促進を抑制する。
【００４６】
また、上記（ｅ２）、（ｅ３）は沈殿作用によって特に優れた防食性能（自己補修性）を発現する。上記（ｅ２）の成分であるカルシウム化合物は、カルシウム酸化物、カルシウム水酸化物、カルシウム塩のいずれでもよく、これらの１種または２種以上を使用できる。また、カルシウム塩の種類にも特に制限はなく、ケイ酸カルシウム、炭酸カルシウム、リン酸カルシウムなどのようなカチオンとしてのカルシウムのみを含む単塩のほか、リン酸カルシウム、亜鉛、リン酸カルシウム、マグネシウムなどのようなカルシウム以外のカチオンを含む複塩を使用してもよい。この（ｅ２）成分は腐食環境下においてめっき金属である亜鉛やアルミニウムよりも卑なカルシウムが優先溶解し、これがカソード反応により生成したＯＨ⁻と緻密で難溶性の生成物として欠陥部を封鎖、腐食反応を抑制する。また、上記のようなシリカとともに配合された場合には表面にカルシウムイオンが吸着し、表面電荷を電気的に中和して凝集する。その結果、緻密かつ難溶性の保護皮膜が生成して腐食起点を封鎖し、腐食反応を抑制する。
【００４７】
また、上記（ｅ３）である難溶性リン酸化合物としては、難溶性リン酸塩を用いることができる。この難溶性リン酸塩は単塩、複塩などのすべての種類の塩を含む。また、それを構成する金属カチオンに限定はなく、難溶性のリン酸亜鉛、リン酸マグネシウム、リン酸カルシウム、リン酸アルミニウムなどのいずれの金属カチオンでもよい。また、リン酸イオンの骨格や縮合度などにも限定はなく、正塩、二水素塩、一水素塩または亜リン酸塩のいずれでもよく、さらに、正塩はオルトリン酸塩の他、ポリリン酸塩などの全ての縮合リン酸を含む。この難溶性リン化合物は腐食によって溶出しためっき金属の亜鉛やアルミニウムが、加水分解により解離したリン酸イオンと錯形成反応により緻密かつ難溶性の保護皮膜を生成して腐食起点を封鎖し、腐食反応を抑制する。
【００４８】
また、上記（ｅ４）のモリブデン酸化合物としては、例えば、モリブデン酸塩を用いることができる。このモリブデン酸塩は、その骨格、縮合度に限定はなく、例えばオルトモリブデン酸塩、パラモリブデン酸塩、メタモリブデン酸塩などが挙げられる。また、正塩、複塩などのすべての塩を含み、複塩としてはリンモリブデン酸塩などが挙げられる。モリブデン酸化合物は不動態化効果によって自己補修性を発現する。すなわち、腐食環境下で溶存酸素と共にめっき皮膜表面に緻密な酸化物を形成することで腐食起点を封鎖し、腐食反応を抑制する。
【００４９】
また、上記（ｅ５）のＳ原子を含有する有機化合物としては、例えば、以下のようなものが挙げることができる。すなわち、トリアゾール類としては１，２，４−トリアゾール、３−アミノ−１，２，４−トリアゾール、３−メルカプト−１，２，４−トリアゾール、５−アミノ−３−メルカプト−１，２，４−トリアゾール、１Ｈ−ベンゾトリアゾールなどが、またチオール類としては、１，３，５−トリアジン−２，４，６−トリチオール、２−メルカプトベンツイミダゾールなどが、またチアジアゾール類としては５−アミノ−２−メルカプト−１，３，４−チアジアゾール、２，５−ジメルカプト−１，３，４−チアジアゾールなどが、またチアゾール類としては２−Ｎ，Ｎ−ジエチルチオベンゾチアゾール、２−メルカプトベンゾチアゾール類などが、またチウラム類としては、テトラエチルチウラムジスルフィドなどが、それぞれ挙げられる。これらの有機化合物は吸着効果によって自己補修性を発現する。すなわち、腐食によって溶出した亜鉛やアルミニウムが、これらの有機化合物が有する硫黄を含む極性基に吸着して不活性皮膜を形成して腐食起点を封鎖し、腐食反応を抑制する。
【００５０】
なお、これらの中でも、耐食性の観点からは特に、カルシウムをその表面に結合させたカルシウムイオン交換シリカを使用するのが好ましい。また、上記（ｅ１）〜（ｅ５）の防錆添加剤を２種以上複合添加してもよく、この場合にはそれぞれ固有の防食作用が複合化されるため、より高度の耐食性が得られる。特に上記（ｅ１）の成分としてカルシウム交換シリカを用い、且つこれに（ｅ３）、（ｅ４）、（ｅ５）の成分の１種以上、特に好ましくは（ｅ３）〜（ｅ５）の成分の全部を複合添加した場合に特に優れた耐食性が得られる。
【００５１】
非クロム系防錆添加剤（ｃ）の含有量は、溶剤系熱硬化性樹脂（ａ）の固形分１００質量部に対して、固形分の割合で３〜３０質量部とする。非クロム系防錆添加剤の含有量が、溶剤系熱硬化性樹脂の固形分１００質量部に対して３質量部未満では、耐食性の向上効果が得られず、一方、３０質量部を超えて配合しても、それに見合う耐食性向上効果が得られないだけでなく、樹脂皮膜の凝集力が低下するため、プレス成形時に樹脂皮膜の剥離を増長させる問題が生ずる。非クロム系防錆添加剤のより好ましい含有量は、溶剤系熱硬化性樹脂の固形分１００質量部に対して５〜２０質量部である。
【００５２】
塗料（ＩＩ）中には、上述した溶剤系熱硬化型樹脂、固形潤滑剤および防錆添加剤のほかに、必要に応じて、他の成分、例えば、顔料、染料などの着色剤、溶剤、界面活性剤、安定剤等を含有させてもよい。
表面処理組成物（Ｉ）により形成される表面処理皮膜（下層）は乾燥膜厚が０．０１〜２μｍ、好ましくは０．３〜０．８μｍとする。乾燥膜厚が０．０１μｍ未満では耐食性が不十分であり、一方、２μｍを超えると成形後の外観が悪くなる。また、その上層に塗料（ＩＩ）により形成される樹脂皮膜は乾燥膜厚を０．１μｍ以上５μｍ未満にするとともに、両皮膜（表面処理皮膜および樹脂皮膜）の合計を５μｍ以下とする。合計皮膜厚が５μｍを超えると、溶接による接合が困難になる。一方、樹脂皮膜の膜厚が０．１μｍ未満では充分な潤滑性が得られない。
【００５３】
次に、本発明の表面処理鋼板の製造方法について説明する。
亜鉛系めっき鋼板またはアルミニウム系めっき鋼板の表面に上記表面処理皮膜および樹脂皮膜を形成するには、上述した組成を有する表面処理組成物（Ｉ）（処理液）を乾燥皮膜厚が上記範囲となるように塗布し、水洗することなく加熱乾燥させた後、塗料（ＩＩ）をさらに塗布し、水洗することなく乾燥させる。
表面処理組成物（Ｉ）や塗料（ＩＩ）を塗布する方法は、塗布法、浸漬法、スプレー法のいずれでもよい。塗布処理方法としては、ロールコーター（３ロール方式、２ロール方式など）、スクイズコーター、ダイコーターなどいずれの方法でもよい。また、スクイズコーターなどによる塗布処理、或いは浸漬処理、スプレー処理の後に、エアナイフ法やロール絞り法により塗布量の調整、外観の均一化、膜厚の均一化を行うことも可能である。
【００５４】
表面処理組成物（Ｉ）や塗料（ＩＩ）をコーティングした後は、水洗することなく加熱乾燥を行う。加熱乾燥手段としては、ドライヤー、熱風炉、高周波誘導加熱炉、赤外線炉などを用いることができる。加熱処理は、表面処理組成物（Ｉ）では到達板温で３０〜３００℃、好ましくは６０〜２５０℃の範囲で行うことが適当である。この加熱温度が３０℃未満では皮膜中の水分が多量に残り、耐食性が不十分となる。また、３００℃を越えると非経済的であるばかりでなく、皮膜に欠陥が生じ耐食性が低下する。また、塗料（ＩＩ）では１５０〜２７０℃の範囲で行うことが適当である。加熱温度が１５０℃未満では硬化が不十分で耐食性、潤滑性、成形後外観が低下し、２７０℃を超えると、１５０℃未満の場合と同様に耐食性、潤滑性、成形後外観が低下する。
なお、上述した表面処理皮膜および樹脂皮膜はめっき鋼板の片面、両面のいずれに形成してもよい。
【００５５】
【実施例】
下層である表面処理皮膜形成用の表面処理組成物（Ｉ）を以下のようにして調整した。
［表面処理組成物（Ｉ）の製造］
表面処理組成物用の樹脂化合物（Ａ）として表２に示す化学構造を有する水分散性樹脂を用い、これに表３に示すカチオン性ウレタン樹脂（Ｂ）、表４に示すシランカップリング剤（Ｃ）、表５に示すＴｉ化合物（Ｄ）、表６に示す酸化合物（Ｅ）、さらに表７に示す固形潤滑剤を適宜配合し、攪拌機を用いて所要時間攪拌し、表面処理組成物（Ｉ）を調製した。
【００５６】
上層である樹脂皮膜形成用の塗料（ＩＩ）を以下のようにして調整した。
塗料（ＩＩ）を調整するために、溶剤系熱硬化型樹脂中の水酸基含有ウレタンプレポリマーとして、表８に示すものを製造した。
以下に、表８のＮｏ．１の水酸基含有ウレタンプレポリマーの製造例について述べる。加熱装置、攪拌機、水分離器および温度計を備えた反応装置に、ポリエステルポリオールとして芳香族ポリエステルポリオール（ＡＲ）：９１５質量部および脂肪族ポリエステルポリオール（ＡＬ）：９１５質量部を、不活性ガス存在下において仕込み、加熱した。上記原料が融解した後、加熱しながら撹拌を開始した。融解した原料が１００℃まで昇温した後、その温度で３０〜６０分間保温し、次いで脱水した。
【００５７】
次いで、融解した原料の温度を７０℃まで下げ、その温度下において、２価アルコールとして１，４−ブタンジオール：２８質量部、イソシアネート化合物としてジフェニルメタン−４，４−ジイソシアネート：３１３質量部、反応触媒としてジブチルチンラウリレート：０．５５質量部および溶剤としてシクロヘキサノン：９４０質量部を仕込み、７０℃の温度で５〜１０時間反応を継続し、所定の粘度に達したところで、２価アルコールとして１，３−ブタンジオール：１０質量部を加えて反応を終了させた。さらに、溶剤としてシクロヘキサノン：４１５０質量部を加え、これにより不揮発分：３０％、粘度１：４００ｃｐｓの水酸基含有ウレタンプレポリマーＮｏ．１を調製した。
【００５８】
表８のＮｏ．２〜Ｎｏ．８についても、同表に示す各成分を配合して上記方法に準じて水酸基含有ウレタンプレポリマーＮｏ．２〜Ｎｏ．８を調製した。このようにして得られた水酸基含有ウレタンプレポリマーを硬化剤であるヘキサメチレンジイソシアネート３量体とＮＣＯ／ＯＨ＝１／１の当量比で架橋硬化させた熱硬化型樹脂のガラス転移温度を表８に併せて示す。
表８の水酸基含有ウレタンプレポリマーを表９に示すように組み合わせて、本発明例で使用する９種類の溶剤系熱硬化型樹脂Ａ〜Ｉを調製した。また、表９に比較例で使用される樹脂Ｊ〜Ｍを併せて示す。なお、溶剤系熱硬化型樹脂Ａ〜Ｉ、Ｌ、Ｍの硬化剤としては、ヘキサメチレンジイソシアネート３量体をＮＣＯ／ＯＨの当量比が１／１となるような配合比で用いた。
【００５９】
冷延鋼板（板厚０．８ｍｍ）をベースとした家電、建材、自動車部品用のめっき鋼板である、表１に示すめっき鋼板を処理原板として用いた。このめっき鋼板の表面をアルカリ脱脂処理、水洗、乾燥した後、上記表面処理組成物（Ｉ）をロールコーターにより塗布し、水洗することなく誘導加熱装置により所定の焼付温度（到達板温）で加熱乾燥し、表面処理皮膜を形成した。皮膜の膜厚は、表面処理組成物の固形分（加熱残分）または塗布条件（ロールの圧下力、回転速度など）により調整した。
【００６０】
さらにその上層に、表９に示す溶剤系熱硬化型樹脂に表１０に示す固形潤滑剤および防錆添加剤であるシリカを添加して塗料（ＩＩ）を調整し、この塗料（ＩＩ）をロールコーターにより上記表面処理皮膜の上に塗布し、次いで水洗することなく誘導加熱装置により２３０℃の焼付温度（到達板温）で加熱乾燥した。また、比較例として表面処理組成物（Ｉ）を塗布乾燥することで得られた表面処理鋼板にプレス油を２ｇ／ｍ^２塗布したものも作製した。
このようにして作製した表面処理鋼板の皮膜組成、および品質性能（潤滑性、成形後の外観性、成形後の耐食性）の各試験を行った結果を表１１〜表２６に示す。なお、品質性能の評価は以下のようにして行った。
【００６１】
（１）潤滑性
図１に概略正面図で示す試験機を使用した。この試験機は、箱状の枠２の一側２ａに固定されたフラット面を有する雌ダイス１と、この雌ダイス１と向き合った、所定高さの実質的に水平な突条３を有する雄ダイス４と、この雄ダイス４を支持し、雄ダイス４を雌ダイス１に向けて水平移動させるための、枠２の他側２ｂに固定された油圧シリンダ５とからなっている。前記雄ダイス４は、油圧シリンダ５のロッド５ａにロードセル６を介して固定されている。なお、雄ダイス４の突条３の幅は１０ｍｍであり、その先端の長さは１ｍｍである。
各実施例の表面処理鋼板から切り出された試験片７を、雌ダイス１と雄ダイス４との間隙に垂直に挿入し、油圧シリンダ５を作動させて、雌ダイス１と雄ダイス４とにより試験片７を５０ｋｇｆ（５００ｋｇｆ／ｃｍ^２）の圧力で押しつけた。次いで、試験片７を矢印に示すように、１００ｍｍ／分の速度で上方に引き抜き、そのときの動摩擦係数を調べ、これによって潤滑性を評価した。なお、試験は常温（２０℃）の試験片のほか、実際のプレス作業時の板温上昇を考慮して１５０℃の高温試験片についても行った。評価の基準は次のとおりである。
○：動摩擦係数０．１未満
△：動摩擦係数０．１以上、０．２未満
×：動摩擦係数０．２以上
【００６２】
（２）プレス成形性
各実施例の表面処理鋼板から切り出した円板状の試験片を、ポンチ径：５０ｍｍ、ダイス径：５１．９１ｍｍ、しわ押さえ力：１トンの条件でカップ状に成形したときの限界絞り比を調べ、これによってプレス成形性を評価した。評価基準は次のとおりである。
○：限界絞り比２．３０以上
△：限界絞り比２．２０以上、２．３０未満
×：限界絞り比２．２０未満
【００６３】
（３）成形後の外観性
図２に概略正面図で示す試験機を使用した。この試験機は、箱状の枠２の一側２ａに固定された、所定高さの実質的に水平な突条８を有する雄ダイス９と、この雄ダイス９の突条８と向き合った所定深さの溝１０を有する雌ダイス１１と、この雌ダイス１１を支持し、雌ダイス１１を雄ダイス９の突条８に向けて水平に移動させるための、枠２の他側２ｂに固定された油圧シリンダ５とからなっている。前記雌ダイス１１は、油圧シリンダ５のロッド５ａにロードセル６を介して固定されている。なお、雄ダイス９の突条８の幅は３０ｍｍであり、突条８の先端の半径は０．２５ｍｍである。
各実施例の表面処理鋼板から切り出した試験片を、雄ダイス９と雌ダイス１１との間隙に垂直に挿入し、油圧シリンダ５を作動させて、雄ダイス９と雌ダイス１１とにより試験片７を５０ｋｇｆ（５００ｋｇｆ／ｃｍ^２）の圧力で押しつけた。次いで、試験片７を矢印に示すように、１００ｍｍ／分の速度で上方に引き抜き、そのときの試験片の外観を目視によって調べ、傷つき程度および黒化程度を評価した。評価基準は次のとおりである。
◎：全面にわたって殆ど変化なく、外観が均一
○：傷つきおよび黒化が少し発生し、外観が多少不均一
△：局部的に傷つきおよび黒化が発生し、外観が明らかに不均一
×：コーナー部を中心に傷つきおよび黒化が激しく発生
【００６４】
（４）成形後の耐食性
図２に概略正面図で示した試験機を使用し、各実施例の表面処理鋼板から切り出された試験片を、前述したと同様の方法によって雄ダイス９と雌ダイス１１とにより押しつけた状態で上方に引き抜いた。このようにして引き抜かれた試験片の端縁部を、タールエポキシ塗料によってシールした後、ＪＩＳ　Ｚ　２３７１に基づく塩水噴霧試験を２４０時間施して白錆の発生率を調べ、これによって成形後の耐食性を評価した。評価基準は次のとおりである。
◎　：白錆面積率５％未満
○　：白錆面積率５％以上、１０％未満
○−：白錆面積率１０％以上、２５％未満
△　：白錆面積率２５％以上、５０％未満
×　：白錆面積率５０％以上、１００％以下
【００６５】
【表１】

【００６６】
【表２】

【００６７】
【表３】

【００６８】
【表４】

【００６９】
【表５】

【００７０】
【表６】

【００７１】
【表７】

【００７２】
【表８】

【００７３】
【表９】

【００７４】
【表１０】

【００７５】
【表１１】

【００７６】
【表１２】

【００７７】
【表１３】

【００７８】
【表１４】

【００７９】
【表１５】

【００８０】
【表１６】

【００８１】
【表１７】

【００８２】
【表１８】

【００８３】
【表１９】

【００８４】
【表２０】

【００８５】
【表２１】

【００８６】
【表２２】

【００８７】
【表２３】

【００８８】
【表２４】

【００８９】
【表２５】

【００９０】
【表２６】

【００９１】
【発明の効果】
以上述べたように本発明によれば、皮膜にクロムを含有することなく、プレス成形性と耐食性に優れた表面処理鋼板が得られる。
【図面の簡単な説明】
【図１】試験片の潤滑性を評価するための試験機の概略正面図
【図２】試験片の成形後の外観性および成形後の耐食性を評価するための試験機の概略正面図
【符号の説明】
１：雌ダイス、２：枠、３：突条、４：雄ダイス、５：油圧シリンダ、６：ロードセル、７：試験片、８：突条、９：雄ダイス、１０：溝、１１：雌ダイス[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is an automobile, a household appliance, a surface-treated steel sheet most suitable for building materials, particularly contains no heavy metals such as chromium at the time of production and in the product, and even without applying a lubricating oil or the like on the surface thereof The present invention relates to an environment-adaptive surface-treated steel sheet having excellent press formability and good corrosion resistance, and a method for producing the same.
[0002]
[Prior art]
For the purpose of improving corrosion resistance (white rust resistance and red rust resistance), chromic acid has been used on steel sheets for household appliances, building materials, and automobiles. BACKGROUND ART Steel sheets that have been subjected to chromate treatment with a treatment liquid containing dichromic acid or a salt thereof as a main component are widely used. This chromate treatment is an economical treatment method that has excellent corrosion resistance and can be performed relatively easily.
[0003]
Chromate treatment uses hexavalent chromium, which is a pollution control substance, and this hexavalent chromium is treated in a closed system in the treatment process, is not completely reduced and recovered, and is not released to nature. Since the elution of chromium from the chromate film can be almost eliminated by the sealing action of the organic film, the environment and the human body are not substantially contaminated by hexavalent chromium. However, due to recent global environmental problems, there is a growing movement to voluntarily reduce the use of heavy metals including hexavalent chromium. Further, in order to prevent the environment from being polluted when dumping shredder dust of waste products, there has been a movement to reduce or eliminate heavy metals in products as much as possible.
[0004]
For this reason, many processing techniques that do not rely on chromate treatment, that is, so-called chromium-free techniques, have been proposed in order to prevent the generation of white rust on galvanized steel sheets. For example, there is a method in which a thin film is formed by a method such as immersion, coating, or electrolytic treatment using an inorganic compound, an organic compound, an organic polymer material, or a combination thereof. Specifically, Japanese Patent Application Laid-Open No. Sho 53-121034 discloses a method in which an aqueous solution containing water-dispersible silica, an alkyd resin and a trialkoxysilane compound is applied to a metal surface and dried to form a coating film. Have been. Further, using a water-soluble resin composed of a hydroxypyrone compound derivative, a surface treatment method aimed at imparting corrosion resistance to the metal material, and a metal material using an aqueous solution or a water-dispersible polymer of a hydroxystyrene compound. Methods for imparting corrosion resistance are disclosed in, for example, JP-A-57-47451 and JP-A-1-177380.
[0005]
[Problems to be solved by the invention]
However, none of the above methods can form a film that imparts high corrosion resistance that can be substituted for a chromate film. Therefore, there is a strong demand for the development of a non-chromium-based surface treatment agent and a treatment method for metal materials having excellent corrosion resistance.
On the other hand, when surface-treated steel sheets such as galvanized steel sheets are used as parts for automobiles, home appliances, OA equipment, etc., various press moldings are performed, and when they are used as materials for motor covers, cartridge tanks, etc. Is subjected to drawing. In order to improve the press formability of a galvanized steel sheet, a lubricating oil or a rust-preventive oil is generally applied on the surface thereof. However, the application of a lubricating oil or the like complicates the manufacturing process and worsens the working environment. Not only that, even when lubricating oil is applied and press-formed, if the forming conditions are severe, the galvanized steel sheet to be formed may seize and not only deteriorate the appearance, but also deteriorate the corrosion resistance. is there. In addition, chromate-coated galvanized steel sheets with a chromate film or a chromate film and a resin film formed on the surface of a galvanized steel sheet are subjected to press forming with or without the application of lubricating oil. There is a problem that a blackening phenomenon of discoloring black occurs, which significantly impairs the appearance of a molded part and deteriorates corrosion resistance. In the case of a chromium-free chemical conversion treated steel sheet, the corrosion resistance is even lower.
[0006]
As a surface-treated steel sheet which solves the above-mentioned problems and can obtain excellent press formability without applying a lubricating oil or the like on the surface, and also has a good corrosion resistance, for example, it is disclosed in Japanese Patent No. 2943472. A film composed of a solvent-based thermosetting resin using two types of urethane prepolymers having different glass transition points, a specific polyethylene resin, and a rust-preventive pigment is applied to the surface of a zinc-based plated steel sheet on which a chromate film is formed. What was formed is mentioned.
[0007]
However, this surface-treated steel sheet requires a chromate film to ensure a predetermined corrosion resistance.If the chromate film is omitted, good press-formability is obtained, but the corrosion resistance is extremely poor. It will be. Even when combined with the chromate film alternative technology described above, corrosion resistance comparable to that of a surface-treated steel sheet with a chromate film formed cannot be obtained. Remarkable.
Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a non-chromium-based surface-treated steel sheet excellent in both press formability and corrosion resistance, and a method for producing the same.
[0008]
[Means for Solving the Problems]
The present inventors have studied the coating composition of the surface-treated steel sheet in order to solve the above-described problems. As a result, first, as for the lower coating, a specific resin compound and a cationic urethane having a specific cationic functional group are used. A surface treatment film is formed by treating the surface of a plated steel sheet with a resin, a silane coupling agent having a specific reactive functional group, and more preferably a surface treatment composition containing a Ti compound and a specific acid compound. By forming a resin film based on two or more types of solvent-based thermosetting resins having different glass transition temperatures and blending an appropriate amount of a specific solid lubricant and a non-chromium-based rust preventive additive in the upper layer. It has been found that a surface-treated steel sheet having excellent press formability and corrosion resistance comparable to a chromate film can be obtained.
[0009]
The present invention has been made based on such findings, and the features are as follows.
[1] On a surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, at least a resin compound (A) represented by the following general formula (1) and at least one selected from primary to tertiary amino groups and quaternary ammonium bases A cationic urethane resin (B) having one type of cationic functional group and at least one type of reactive functional group selected from active hydrogen-containing amino, epoxy, vinyl, mercapto and methacryloxy groups The solid content of the silane coupling agent (C) and the total amount of the cationic urethane resin (B) and the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) Has a mass ratio [(B) / {(A) + (B) + (C)}] of 0.04 to 0.09, and the silane coupling agent (C) and the resin compound (A) The mass ratio [(C) / {(A) + (B) + (C)}] of the solid content to the total amount of the on-urethane resin (B) and the silane coupling agent (C) is 0.6 to 0. A surface treatment film having a thickness of 0.01 to 2 μm formed by applying and drying the surface treatment composition (I) which is 0.7.
On the upper layer, a coating (II) containing the following components (a), (b) and (c) is applied and cured by heating to form a resin coating having a thickness of 0.1 μm or more and less than 5 μm. And
(A) Two or more solvent-based thermosetting resins having different glass transition temperatures after curing: 100 parts by mass (solid content ratio)
(B) Solid lubricant composed of polyethylene resin having a melting point of 130 ° C. or less: 1 to 30 parts by mass (solid content ratio)
(C) Non-chromium rust preventive additive: 3 to 30 parts by mass (solid content ratio)
A surface-treated steel sheet having excellent press formability and corrosion resistance, wherein the total thickness of the surface-treated film and the resin film is 5 μm or less.
Embedded image

In the general formula (1), Y bonded to a benzene ring ₁ And Y ₂ Are each independently hydrogen or a Z group represented by the following formula (2) or (3), and the average number of substitutions of the Z group per benzene ring is from 0.2 to 1.0. is there. n represents an integer of 2 to 50.
Embedded image

Embedded image

R in the formulas (2) and (3) ₁ , R ₂ , R ₃ , R ₄ And R ₅ Each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, ⁻ Represents a hydrogen ion or an acid ion.
[0010]
[2] In the surface-treated steel sheet according to the above [1], the surface treatment composition (I) further contains a Ti compound (D), and the Ti compound (D), the resin compound (A), and the cationic urethane resin ( The mass ratio [(D) / {(A) + (B) + (C)}] of the solid content to the total amount of B) and the silane coupling agent (C) is 0.05 to 0.10. Surface treated steel sheet with excellent press formability and corrosion resistance.
[3] In the surface-treated steel sheet according to the above [1] or [2], the surface treatment composition (I) further comprises at least one acid compound selected from phosphoric acid, nitric acid, acetic acid, and salts thereof ( E), and the mass ratio of the solid content of the acid compound (E) and the total amount of the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) [(E) / ｛ (A) + (B) + (C)}] is 0.05 to 0.15, wherein the surface-treated steel sheet is excellent in press formability and corrosion resistance.
[0011]
[4] In the surface-treated steel sheet according to any one of the above [1] to [3], the non-chromium-based rust-preventive additive contained in the paint (II) is selected from the following (e1) to (e5). A surface-treated steel sheet excellent in press formability and corrosion resistance, which is at least one kind.
(E1) Silicon oxide
(E2) Calcium and / or calcium compound
(E3) Poorly soluble phosphate compound
(E4) Molybdate compound
(E5) One or more organic compounds containing an S atom selected from triazoles, thiols, thiadiazoles, thiazoles, and thiurams
[5] The surface-treated steel sheet having excellent press formability and corrosion resistance, characterized in that the surface-treated steel sheet according to the above [4], which contains at least calcium ion exchange silica as a chromium-free rust preventive additive.
[0012]
[6] In the surface-treated steel sheet according to any one of the above [1] to [5], two or more solvent-based thermosetting resins (a) contained in the paint (II) and having different glass transition temperatures after curing. Is one or more solvent-based thermosetting resins having a low glass transition temperature having a glass transition temperature of 50 ° C. or lower after curing (a ₁ ) And one or more solvent-based thermosetting resins having a high glass transition temperature (a) ₂ ), A surface-treated steel sheet having excellent press formability and corrosion resistance.
[7] In the surface-treated steel sheet according to the above [6], the solvent-based thermosetting resin (a ₁ ) And a solvent-based thermosetting resin having a high glass transition temperature (a ₂ ) And (a) ₁ ) / (A ₂ ) Is a solid content mass ratio of 9/1 to 1/9, wherein the surface-treated steel sheet is excellent in press formability and corrosion resistance.
[0013]
[8] In the surface-treated steel sheet according to any one of the above [1] to [7], two or more solvent-based thermosetting resins (a) contained in the paint (II) and having different glass transition temperatures after curing. A surface-treated steel sheet having excellent press formability and corrosion resistance, wherein each of the base resins is a hydroxyl group-containing urethane prepolymer.
[9] In the surface-treated steel sheet according to any one of the above [1] to [8], the solid lubricant (b) composed of a polyethylene resin contained in the paint (II) has a melting point of 90 to 130 ° C and a number average molecular weight of 5000. A surface-treated steel sheet excellent in press formability and corrosion resistance characterized by the following.
[0014]
[10] A resin compound (A) represented by the following general formula (1) and at least one selected from primary to tertiary amino groups and quaternary ammonium bases on the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet. A cationic urethane resin (B) having one type of cationic functional group and at least one type of reactive functional group selected from active hydrogen-containing amino, epoxy, vinyl, mercapto and methacryloxy groups The solid content of the silane coupling agent (C) and the total amount of the cationic urethane resin (B) and the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) Has a mass ratio [(B) / {(A) + (B) + (C)}] of 0.04 to 0.09, and the silane coupling agent (C) and the resin compound (A) The mass ratio [(C) / {(A) + (B) + (C)}] of the solid content to the total amount of the thionic urethane resin (B) and the silane coupling agent (C) is 0.6 to 0. And applying a surface-treating composition (I) of 0.7 and drying to form a surface-treated film having a thickness of 0.01 to 2 μm.
On the upper layer, a coating (II) containing the following components (a), (b) and (c) is applied and cured by heating to form a resin film having a film thickness of 0.1 μm or more and less than 5 μm,
(A) Two or more solvent-based thermosetting resins having different glass transition temperatures after curing: 100 parts by mass (solid content ratio)
(B) Solid lubricant composed of polyethylene resin having a melting point of 130 ° C. or less: 1 to 30 parts by mass (solid content ratio)
(C) Non-chromium rust preventive additive: 3 to 30 parts by mass (solid content ratio)
A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance, wherein the total film thickness of the surface-treated film and the resin film is 5 μm or less.
Embedded image

In the general formula (1), Y bonded to a benzene ring ₁ And Y ₂ Are each independently hydrogen or a Z group represented by the following formula (2) or (3), and the average number of substitutions of the Z group per benzene ring is from 0.2 to 1.0. is there. n represents an integer of 2 to 50.
Embedded image

Embedded image

R in the formulas (2) and (3) ₁ , R ₂ , R ₃ , R ₄ And R ₅ Each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms; ⁻ Represents a hydrogen ion or an acid ion.
[0015]
[11] In the production method according to the above [10], the surface treatment composition (I) further contains a Ti compound (D), and the Ti compound (D), the resin compound (A), and the cationic urethane resin (B). ) And the total mass of the silane coupling agent (C) with respect to the solid content [(D) / {(A) + (B) + (C)}] is 0.05 to 0.10. A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance.
[12] In the production method according to the above [10] or [11], the surface treatment composition (I) further comprises at least one acid compound (E) selected from phosphoric acid, nitric acid, acetic acid, and salts thereof. ), And the mass ratio of the solid content of the acid compound (E) and the total amount of the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) [(E) / ｛( A) + (B) + (C)}] is from 0.05 to 0.15, the method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance.
[0016]
[13] In the production method according to any one of the above [10] to [12], the non-chromium-based rust-preventive additive contained in the paint (II) is at least one selected from the following (e1) to (e5). A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance, characterized by being one type.
(E1) Silicon oxide
(E2) Calcium and / or calcium compound
(E3) Poorly soluble phosphate compound
(E4) Molybdate compound
(E5) One or more organic compounds containing an S atom selected from triazoles, thiols, thiadiazoles, thiazoles, and thiurams
[14] A method for producing a surface-treated steel sheet excellent in press formability and corrosion resistance, which comprises at least calcium ion exchange silica as a chromium-free rust preventive additive in the production method of the above [13].
[0017]
[15] In the production method according to any one of the above [10] to [14], two or more types of solvent-based thermosetting resins (a) contained in the paint (II) and having different glass transition temperatures after curing are used. One or more solvent-based thermosetting resins having a low glass transition temperature having a glass transition temperature of 50 ° C. or lower after curing (a ₁ ) And one or more solvent-based thermosetting resins having a high glass transition temperature (a) ₂ A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance, characterized by comprising:
[16] The method according to [15], wherein the solvent-based thermosetting resin (a) has a low glass transition temperature. ₁ ) And a solvent-based thermosetting resin having a high glass transition temperature (a ₂ ) And (a) ₁ ) / (A ₂ ) Is from 9/1 to 1/9 in terms of mass ratio of solid content, and a method for producing a surface-treated steel sheet excellent in press formability and corrosion resistance.
[0018]
[17] In the production method according to any one of the above [10] to [16], two or more solvent-based thermosetting resins (a) contained in the paint (II) and having different glass transition temperatures after curing. A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance, wherein each base resin is a hydroxyl group-containing urethane prepolymer.
[18] In the production method according to any one of the above [10] to [17], the solid lubricant (b) composed of a polyethylene resin contained in the paint (II) has a melting point of 90 to 130 ° C and a number average molecular weight of 5,000 or less. A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance, characterized in that:
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the details of the present invention and the reasons for the limitation will be described.
There is no particular limitation on the zinc-based galvanized steel sheet serving as the base of the surface-treated steel sheet of the present invention, and examples thereof include a galvanized steel sheet, a Zn—Ni plated steel sheet, a Zn—Fe plated steel sheet (electroplating, galvannealed zinc), and Zn. -Cr plated steel sheet, Zn-Mn plated steel sheet, Zn-Co plated steel sheet, Zn-Co-Cr alloy plated steel sheet, Zn-Cr-Ni plated steel sheet, Zn-Cr-Fe plated steel sheet, Zn-Al plated steel sheet (for example, Zn-5% Al alloy-plated steel sheet, Zn-55% Al alloy-plated steel sheet), and a zinc-based composite plated steel sheet (for example, Zn-SiO ₂ Dispersion-plated steel sheet) can be used. Further, among the above platings, a multi-layer plated steel sheet obtained by plating two or more layers of the same type or different types can be used. Further, there is no particular limitation on the aluminum-plated steel sheet serving as the base of the surface-treated steel sheet of the present invention. For example, an aluminum-plated steel sheet, an Al—Si-plated steel sheet, or the like can be used.
Further, the plated steel sheet may be one in which the surface of the steel sheet is preliminarily plated with a thin coating of Ni or the like, and then various platings as described above are provided thereon.
[0020]
As a plating method, any practicable method can be adopted among an electrolysis method (electrolysis in an aqueous solution, electrolysis in a non-aqueous solvent), a melting method, and a gas phase method. Further, in order to prevent blackening of the plating, one or more of Ni, Co, and Fe are precipitated in the plating film at about 1 to 2000 ppm, or an alkali containing one or more of Ni, Co, and Fe is deposited on the plating surface. Alternatively, a surface conditioning treatment using an acidic aqueous solution may be performed to precipitate those elements.
[0021]
Next, the surface treatment film formed on the surface of the zinc-based plated steel sheet or the aluminum-based plated steel sheet and the surface treatment composition (I) for forming the film will be described. In the surface-treated steel sheet of the present invention, the surface-treated film formed as a lower layer on the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet includes a resin compound (A) represented by the following general formula (1), A cationic urethane resin (B) having at least one cationic functional group selected from a triamino group and a quaternary ammonium base, and an active hydrogen-containing amino group, an epoxy group, a vinyl group, a mercapto group and a methacryloxy group; A silane coupling agent (C) having at least one reactive functional group selected from among them, and a cationic urethane resin (B) and a resin compound (A); a cationic urethane resin (B); The mass ratio [(B) / {(A) + (B) + (C)}] of the solid content to the total amount of the silane coupling agent (C) is 0.04 to 0.09. Yes, the total mass ratio of the silane coupling agent (C) and the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) [(C) / ｛(A) + (B) + (C)｝] is a surface-treated film having a thickness of 0.01 to 2 μm formed by applying and drying the surface-treating composition (I) having 0.6 to 0.7.
[0022]
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In the general formula (1), Y bonded to a benzene ring ₁ And Y ₂ Are each independently hydrogen or a Z group represented by the following general formula (2) or (3), and the average number of substitutions of the Z group per benzene ring is 0.2 to 1.0. is there. n represents an average degree of polymerization and is an integer of 2 to 50. Here, the average value of the number of substitution of the Z group is a value obtained by dividing the total number of introduced Z groups by the total number of benzene rings (that is, 2n).
When the average degree of polymerization n is less than 2, the effect of imparting corrosion resistance is insufficient. On the other hand, when the average polymerization degree n exceeds 50, the stability in the treatment composition is reduced due to a decrease in water solubility, a viscosity increase, and the storage stability. Will be insufficient.
[0023]
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In the above general formulas (2) and (3), R ₁ , R ₂ , R ₃ , R ₄ And R ₅ Each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms. If the alkyl group or hydroxyalkyl group has more than 10 carbon atoms, the resin compound (A) cannot be sufficiently water-soluble and cannot be applied because of lack of stability in the treatment composition. R ₁ , R ₂ , R ₃ , R ₄ And R ₅ Examples thereof include methyl, ethyl, propyl, butyl, hydroxyethyl, 2-hydroxypropyl, hydroxyisobutyl and the like. Also, A ⁻ Represents a hydroxyl ion or an acid ion. Specific examples of the acid ion include a sulfate ion, a nitrate ion, and an acetate ion.
The resin compound (A) represented by the general formula (1) is a bisphenol-formalin condensate, and its synthesis method is not specified. For example, by reacting bisphenol A with formalin and an amine in the presence of an alkali catalyst. Obtainable.
[0024]
As long as the cationic urethane resin (B) has at least one kind of cationic functional group selected from primary to tertiary amino groups and quaternary ammonium bases, a polyol which is a monomer component is constituted. The isocyanate component and the polymerization method are not particularly limited. Examples of the cationic functional group include an amino group, a methylamino group, an ethylamino group, a dimethylamino group, a diethylamino group, a trimethylamino group, a triethylamino group, and the like. Two or more cationic urethane resins may be used as a mixture.
[0025]
The compounding amount of the cationic urethane resin (B) is determined by the mass ratio of the solid content to the total amount of the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) [(B) / ｛( A) + (B) + (C)}] to 0.04 to 0.09. By including the cationic urethane resin (B) in such an amount, it is possible to effectively prevent extremely thin white rust which is likely to occur in the early stage of corrosion. Although the reason for this is not necessarily clear, it is considered that the film forming property is improved by blending an appropriate amount of the cationic urethane resin. However, if the mass ratio is less than 0.04, the effect of suppressing the initial generation of thin rust is insufficient, while if it exceeds 0.09, the long-term corrosion resistance becomes insufficient.
[0026]
The silane coupling agent (C) is particularly a silane coupling agent having at least one reactive functional group selected from active hydrogen-containing amino group, epoxy group, vinyl group, mercapto group and methacryloxy group. Without being limited, for example, N- (aminoethyl) 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane , 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltrimethoxysilane and the like can be used. The blending amount of the silane coupling agent (C) is determined by the mass ratio of the solid content to the total amount of the resin compound (A), the cationic urethane resin (B), and the silane coupling agent (C) [(C) / ｛( A) + (B) + (C)}] to 0.6 to 0.7. If the mass ratio is less than 0.6, the corrosion resistance and coating properties are insufficient, while if it exceeds 0.7, the appearance and corrosion resistance after molding are inferior.
[0027]
It is preferable to further add a Ti compound (D) to the surface treatment composition (I) for the purpose of improving corrosion resistance and blackening resistance. The Ti compound (D) is not particularly limited as a pair of anions as long as it serves as a source of Ti, and examples thereof include titanium acetate, titanium nitrate, titanium sulfate, titanium phosphate, titanium carbonate, and titanium fluoride. One or more types such as hydrofluoric acid can be used.
The compounding amount of the Ti compound (D) is the mass ratio of the solid content to the total amount of the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) [(D) / ｛(A) + (B) + (C)}] to 0.05 to 0.10. When the mass ratio is less than 0.05, the effect of improving corrosion resistance and blackening resistance is insufficient. On the other hand, when the mass ratio exceeds 0.10, the usable time of the surface treatment composition becomes short, and practical use becomes difficult. Become.
[0028]
An acid compound (E) can be added to the surface treatment composition (I) for the purpose of further improving corrosion resistance. The acid compound (E) is not particularly limited as long as it is at least one acid compound selected from phosphoric acid, nitric acid, acetic acid, and salts thereof. For example, orthophosphoric acid, pyrophosphoric acid, trimetaphosphoric acid , Tetrametaphosphate, hexametaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, nitric acid, ammonium nitrate, sodium nitrate, acetic acid , Ammonium acetate, sodium acetate and the like.
The compounding amount of the acid compound (E) is the mass ratio of the solid content to the total amount of the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C) [(E) / ｛(A) + (B) + (C)}] to 0.05 to 0.15. If the mass ratio is less than 0.05, the effect of improving the corrosion resistance is insufficient, while if it exceeds 0.15, the adhesion to the upper resin film is reduced, and as a result, the appearance and corrosion resistance after molding are reduced. It will be inferior.
[0029]
The surface treatment composition (I) may further contain a solid lubricant as required. Examples of the solid lubricant include hydrocarbon lubricants such as polyethylene wax, fluororesin lubricants such as polytetrafluoroethylene resin, and fatty acid amide lubricants such as stearamide. Can be used.
The pH of the surface treatment composition (I) (treatment liquid) is suitably adjusted to 0.5 to 6, preferably 1 to 4. When the pH of the surface treatment composition (I) is less than 0.5, the reactivity of the treatment solution is too strong, and thus the appearance unevenness tends to occur. On the other hand, when the pH exceeds 6, the reactivity of the treatment solution becomes low, and the plating metal and Bonding to the surface treatment film tends to be insufficient, and the corrosion resistance tends to decrease.
[0030]
Next, the resin film formed on the surface treatment film and the paint (II) for forming the film will be described.
The thickness of the resin film formed by applying a paint (II) containing the following components (a), (b) and (c) and heat-curing the resin film formed on the surface-treated film is 0. .1 μm or more and less than 5 μm.
(A) Two or more solvent-based thermosetting resins having different glass transition temperatures after curing: 100 parts by mass (solid content ratio)
(B) Solid lubricant composed of polyethylene resin having a melting point of 130 ° C. or less: 1 to 30 parts by mass (solid content ratio)
(C) Non-chromium rust preventive additive: 3 to 30 parts by mass (solid content ratio)
[0031]
The reason for using the solvent-based thermosetting resin (a) as the base resin is as follows.
{Circle around (1)} The solvent-based resin is superior to the water-based resin in the compatibility with the lubricant and the rust-preventive additive added to the resin and the long-term stability as a paint.
{Circle around (2)} Unlike a thermoplastic resin, a thermosetting resin has no melting point, and thus has high mechanical strength at high temperatures. Therefore, if a film is formed with such a resin coating, even if the surface temperature of the steel sheet rises due to frictional heat during press forming, the resin film hardly peels or deforms.
[0032]
The reason why two or more types of solvent-based thermosetting resins (a) having different glass transition temperatures after curing are used as the base resin of the resin film is as follows.
That is, a solvent-based thermosetting resin having a low glass transition temperature has excellent flexibility at low temperatures. Therefore, when press-forming a plated steel sheet on which a resin film having such a resin as a base resin is formed, if the press-forming conditions are moderate or gentle, the press-formability and appearance after press-forming are good. is there. However, when the press molding conditions are severe or where the surface becomes high temperature, the resin film softens and peels from the plated steel sheet, and the peeled resin film adheres to the molding die. In addition, the appearance after press molding is deteriorated.
[0033]
On the other hand, a solvent-based thermosetting resin having a high glass transition temperature has excellent high-temperature strength. Therefore, when press-forming a plated steel sheet with a resin film formed using such a resin as a base resin, the resin film may soften and peel off from the plated steel sheet even under severe or severe press-forming conditions. There is no. However, solvent-based thermosetting resins with a high glass transition temperature have poor flexibility at low temperatures, so when the press molding conditions are mild or in gentle areas, the resin film powders and peels off from the plated steel sheet, and peels off. As a result of the adhered resin film adhering to the molding die, the press formability and the appearance after press molding are deteriorated.
[0034]
Therefore, in the present invention, in order to impart both flexibility at low temperature and strength at high temperature when press-molding a resin film, two or more solvents having different glass transition temperatures after curing the base resin of the resin film. It was composed of a system thermosetting resin. Preferred solvent-based thermosetting resins are one or more solvent-based thermosetting resins having a low glass transition temperature of 50 ° C. or less after curing, and a glass transition temperature of more than 50 ° C. after curing. It is a resin composed of one or more solvent-based thermosetting resins having a high glass transition temperature. A particularly preferred glass transition temperature of the solvent-based thermosetting resin having a low glass transition temperature is in the range of 10 to 50 ° C. The particularly preferable glass transition temperature of the above-mentioned solvent-based thermosetting resin having a high glass transition temperature is in the range of more than 50 ° C to 100 ° C.
[0035]
Low glass transition temperature solvent-based thermosetting resin (a ₁ ) And a solvent-based thermosetting resin having a high glass transition temperature (a ₂ ) Compounding ratio (a ₁ ) / (A ₂ ) Is preferably in the range of 9/1 to 1/9 by mass ratio of solids. This compounding ratio (a ₁ ) / (A ₂ ) Is more than 9/1, the resin film is softened and peeled off from the plated steel sheet when the forming conditions are severe such that the surface of the steel sheet becomes high temperature during press forming of the plated steel sheet on which the resin film is formed. Tends to occur. On the other hand, the mixing ratio (a ₁ ) / (A ₂ ) Is less than 1/9, when the above-mentioned forming conditions are mild so that the surface of the steel sheet does not become so high, a problem that the resin film is powdered and peels off from the plated steel sheet easily occurs. Low glass transition temperature solvent-based thermosetting resin (a ₁ ) And a solvent-based thermosetting resin having a high glass transition temperature (a ₂ )) (A) ₁ ) / (A ₂ ) Is in the range of 9/1 to 5/5.
[0036]
The main resin component of the two or more solvent-based thermosetting resins having different glass transition temperatures after curing is preferably two or more hydroxyl group-containing urethane prepolymers having different glass transition temperatures after curing. Further, each of these hydroxyl group-containing urethane prepolymers comprises at least one polyol (d) selected from a polyether polyol, a polyester polyol and a polyether polyester polyol, an isocyanate compound (e), and a dihydric alcohol (f). Are preferred.
Further, as the curing agent component (crosslinking agent) of each of the hydroxyl group-containing urethane prepolymers, it is preferable to use at least one selected from a blocked polyisocyanate compound and an amino resin. As the curing agent, one or more curing agents can be used for two or more hydroxyl group-containing urethane prepolymers having different glass transition temperatures. The glass transition temperature after curing is obtained by a reaction between a urethane prepolymer and a curing agent (crosslinking agent). However, by using two or more urethane prepolymers having different glass transition temperatures after curing. The glass transition temperature after curing can be changed by using one kind of curing agent.
[0037]
Hereinafter, the constituent components and the curing agent component of the hydroxyl group-containing urethane prepolymer will be described.
Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, and linear polyalkylene polyols such as glycerin ethylene oxide or propylene oxide adducts.
As the polyester polyol, for example, a linear polyester having an OH group in a molecular chain obtained by reacting a dibasic acid and a low molecular polyol can be used. Examples of the basic acid include dibasic acids such as adipic acid, azelaic acid, dodecane diacid, dimer acid, isophthalic acid, hexahydrophthalic anhydride, terephthalic acid, dimethyl terephthalate, itaconic acid, fumaric acid, and maleic anhydride. Examples thereof include acids and esters thereof.
[0038]
As the polyether polyester polyol, a linear polyester having an OH group in a molecular chain obtained by subjecting a mixture of the basic acid and the polyether polyol or a mixture thereof to the low-molecular polyol to an esterification reaction, and a terminal And polyethers obtained by adding an alkylene oxide (eg, ethylene oxide, propylene oxide, etc.) to a polyester having a carboxyl group and / or a hydroxyl group.
[0039]
Examples of the isocyanate compound include hexamethylene diisocyanate, o-, m-, or p-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, and 2,4- or 2 having an aromatic ring hydrogenated. , 6-Tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, ω, ω'-diisocyanate-1, Examples include isocyanate compounds having an aromatic ring such as 4-dimethylbenzene and ω, ω'-diisocyanate-1,3-dimethylbenzene, and alicyclic isocyanate compounds such as isophorone diisocyanate.
As the dihydric alcohol, for example, all such as ethylene glycol, butylene glycol, diethylene glycol, and hydrogenated bisphenol A can be used.
[0040]
A typical example of the blocked polyisocyanate compound as a curing agent is a blocked polyisocyanate prepolymer obtained by blocking a so-called polyisocyanate using a known blocking agent, and is, for example, a trade name “Bernock D-550”. "Barnock D-500", "Barnock B7-887" (all manufactured by Dainippon Ink and Chemicals, Inc.), trade name "Takenate N-815-N" (manufactured by Takeda Pharmaceutical Co., Ltd.), trade name "ADDITOL VXL-80" (manufactured by Hoechst Gosei Co., Ltd.).
Examples of the amino resin as a curing agent include an amino component such as melamine urea acetoguanamine, benzoguanamine, sterogamine or spirologamine, and an aldehyde component such as formaldehyde, paraform, acetaldehyde, and glyoxal, and methanol, ethanol, isopropanol, n-butanol, and the like. Resins obtained by reacting with alcohol components such as iso-butanol and sec-butanol can be used.
[0041]
As the solid lubricant (b) to be added to the paint (II), a polyethylene resin (fine particles) is used. Solid lubricant made of polyethylene resin imparts resistance to sliding, deformation and abrasion to the steel sheet in continuous press forming, etc., and prevents damage to the steel sheet such as galling and breakage of the sheet and damage to the mold It has the effect of doing.
Polyethylene resin is a crystalline thermoplastic resin having a number average molecular weight of several hundreds to several millions in general, its glass transition point is about −100 ° C., lower than room temperature, and its melting point is 90 to 140 ° C. At room temperature, it has a flexible property. Further, its critical surface tension is about 30 dyne / cm, and its surface energy is low, so that it has low wettability and adhesion, and therefore has an excellent lubricating action. When the polyethylene resin particles are contained as a lubricant in a coating for forming a resin film of a surface-treated steel plate as in the present invention, from the viewpoint of dispersibility and thin film formation in the coating, the particle size of the polyethylene resin particles is reduced. Is preferably 20 μm or less, more preferably 10 μm or less, and still more preferably about 5 μm. It is difficult to obtain a desired lubricating effect with a polyethylene resin that is not such a fine powder.
[0042]
The melting point of polyethylene resin affects lubricity. That is, the higher the melting point, the higher the mechanical strength (deformation resistance) near normal temperature, and the lower the lubricity (slidability) of the resin film containing the polyethylene resin. Therefore, it is necessary that the melting point of the polyethylene resin used as the lubricant in the present invention is 130 ° C. or less, preferably in the range of 90 to 120 ° C. Further, from the viewpoint of film forming property, the number average molecular weight of the polyethylene resin is preferably 5,000 or less. In addition, two or more types of polyethylene fine powder having a melting point, a number average molecular weight, and a particle size within the above-described ranges may be used.
[0043]
The content of the solid lubricant (b) made of a polyethylene resin is 1 to 30 parts by mass in terms of the solid content with respect to 100 parts by mass of the solid content of the solvent-based thermosetting resin (a). When the content of the solid lubricant (b) is less than 1 part by mass with respect to 100 parts by mass of the solid content of the solvent-based thermosetting resin, the lubricating property improving effect cannot be sufficiently obtained. If it exceeds, the cohesive force and strength of the resin film itself decrease, and as a result, there is a problem that the peeling of the resin film increases during press molding. A more preferable content of the polyethylene resin is 5 to 20 parts by mass based on 100 parts by mass of the solid content of the solvent-based thermosetting resin.
[0044]
The paint (II) is blended with a chromium-free rust preventive additive (c) for the purpose of improving corrosion resistance. By blending such a non-chromium-based rust-preventive additive in the paint (II), particularly excellent corrosion resistance (self-repairing property) can be obtained. As the chromium-free rust preventive additive, it is particularly preferable to use one or more selected from the following (e1) to (e5).
(E1) Silicon oxide
(E2) Calcium and / or calcium compound
(E3) Poorly soluble phosphate compound
(E4) Molybdate compound
(E5) An organic compound containing one or more S atoms selected from triazoles, thiols, thiadiazoles, thiazoles, and thiurams
[0045]
Details of these (e1) to (e5) non-chromium rust preventive additives and the anticorrosion mechanism are as follows.
First, as the component (e1), colloidal silica or dry silica as fine particle silica can be used. From the viewpoint of corrosion resistance, calcium ion exchange silica having calcium bonded to its surface is particularly used. Is preferred. As the colloidal silica, for example, Snowtex 0, Snowtex 20, Snowtex 30, Snowtex 40, Snowtex C and Snowtex S (all trade names) manufactured by Nissan Chemical Industries, Ltd. can be used. As silica, AEROSIL R971, AEROSIL R812, AEROSIL AEROSIL R811, AEROSIL R974, AEROSIL R202, AEROSIL R805, AEROSIL 130, AEROSIL 200, AEROSIL 300, and AEROSIL 300CF manufactured by Nippon Aerosil Co., Ltd. Can be.
Examples of calcium ion exchange silica include W.I. R. Grace & Co. SHIELDEX C303, SHIELDEX AC3, and SHIELDEX AC5 (all are trade names) manufactured by Fuji Silysia Chemical Ltd., and SHIELDEX and SHIELDEX SY710 (all are trade names). These silicas contribute to the generation of dense and stable zinc corrosion products in a corrosive environment, and the corrosion products are formed densely on the plating surface, thereby suppressing the promotion of corrosion.
[0046]
Further, (e2) and (e3) exhibit particularly excellent anticorrosion performance (self-repairing property) due to the precipitation action. The calcium compound as the component (e2) may be any of calcium oxide, calcium hydroxide, and calcium salt, and one or more of these can be used. There is no particular limitation on the type of calcium salt, and other than a single salt containing only calcium as a cation, such as calcium silicate, calcium carbonate, calcium phosphate, etc., other than calcium such as calcium phosphate, zinc, calcium phosphate, magnesium, etc. May be used. In the (e2) component, calcium, which is more noble than zinc or aluminum, which is a plating metal, is preferentially dissolved in a corrosive environment, and this dissolves in the OH generated by the cathode reaction. ⁻ As a dense and hardly soluble product, it seals the defective part and suppresses the corrosion reaction. In addition, when mixed with the above-mentioned silica, calcium ions are adsorbed on the surface and electrically neutralize the surface charge to aggregate. As a result, a dense and hardly soluble protective film is formed to block the corrosion starting point and suppress the corrosion reaction.
[0047]
Further, as the sparingly soluble phosphate compound (e3), a sparingly soluble phosphate can be used. The poorly soluble phosphate includes all kinds of salts such as simple salts and double salts. Further, the metal cation constituting the metal cation is not limited, and may be any metal cation such as hardly soluble zinc phosphate, magnesium phosphate, calcium phosphate, and aluminum phosphate. The skeleton of the phosphate ion and the degree of condensation are not limited, and may be any of a normal salt, a dihydrogen salt, a monohydrogen salt, or a phosphite. Includes all condensed phosphoric acids such as salts. This hardly soluble phosphorus compound forms a dense and hardly soluble protective film by the complexing reaction between the zinc and aluminum of the plating metal eluted by the corrosion and the phosphate ion dissociated by the hydrolysis, thereby blocking the corrosion starting point and causing the corrosion reaction. Suppress.
[0048]
Further, as the molybdate compound (e4), for example, molybdate can be used. The molybdate is not limited in its skeleton and degree of condensation, and includes, for example, orthomolybdate, paramolybdate, metamolybdate and the like. Further, it includes all salts such as normal salt and double salt, and examples of the double salt include phosphomolybdate. Molybdate compounds exhibit self-healing properties through a passivating effect. In other words, a dense oxide is formed on the surface of the plating film together with dissolved oxygen in a corrosive environment to block a corrosion starting point and suppress a corrosion reaction.
[0049]
Examples of the organic compound containing an S atom of the above (e5) include the following. That is, as triazoles, 1,2,4-triazole, 3-amino-1,2,4-triazole, 3-mercapto-1,2,4-triazole, 5-amino-3-mercapto-1,2,2,3-triazole. 4-triazole, 1H-benzotriazole and the like, thiols as 1,3,5-triazine-2,4,6-trithiol, 2-mercaptobenzimidazole and the like, and thiadiazoles as 5-amino- 2-mercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole and the like, and thiazoles such as 2-N, N-diethylthiobenzothiazole and 2-mercaptobenzothiazole And the thiurams include tetraethylthiuram disulfide and the like, respectively. These organic compounds exhibit self-healing properties due to the adsorption effect. That is, zinc and aluminum eluted by the corrosion are adsorbed on the sulfur-containing polar groups of these organic compounds to form an inert film, block the corrosion starting point, and suppress the corrosion reaction.
[0050]
Among these, from the viewpoint of corrosion resistance, it is particularly preferable to use calcium ion-exchanged silica in which calcium is bonded to the surface. In addition, two or more of the above-mentioned rust preventive additives (e1) to (e5) may be added in combination, and in this case, a unique anticorrosion action is compounded, so that higher corrosion resistance is obtained. In particular, calcium-exchanged silica is used as the component (e1), and one or more of the components (e3), (e4) and (e5), particularly preferably all of the components (e3) to (e5) are added thereto. Particularly excellent corrosion resistance is obtained when a composite is added.
[0051]
The content of the non-chromium-based rust-preventive additive (c) is 3 to 30 parts by mass in terms of the solid content with respect to 100 parts by mass of the solid content of the solvent-based thermosetting resin (a). When the content of the non-chromium-based rust-preventive additive is less than 3 parts by mass with respect to 100 parts by mass of the solid content of the solvent-based thermosetting resin, the effect of improving corrosion resistance cannot be obtained. Even if it is blended, not only is it not possible to obtain a corresponding effect of improving corrosion resistance, but also the cohesive force of the resin film is reduced, which causes a problem of increasing the peeling of the resin film during press molding. The more preferable content of the non-chromium rust preventive additive is 5 to 20 parts by mass based on 100 parts by mass of the solid content of the solvent-based thermosetting resin.
[0052]
In the paint (II), in addition to the solvent-based thermosetting resin, the solid lubricant and the rust-preventive additive described above, if necessary, other components such as a coloring agent such as a pigment and a dye, a solvent, A surfactant, a stabilizer and the like may be contained.
The surface treatment film (lower layer) formed by the surface treatment composition (I) has a dry film thickness of 0.01 to 2 μm, preferably 0.3 to 0.8 μm. If the dry film thickness is less than 0.01 μm, the corrosion resistance is insufficient, while if it exceeds 2 μm, the appearance after molding deteriorates. In addition, the resin film formed by the coating material (II) on the upper layer has a dry film thickness of 0.1 μm or more and less than 5 μm, and the total of both films (surface treatment film and resin film) is 5 μm or less. When the total film thickness exceeds 5 μm, joining by welding becomes difficult. On the other hand, if the thickness of the resin film is less than 0.1 μm, sufficient lubricity cannot be obtained.
[0053]
Next, a method for producing the surface-treated steel sheet of the present invention will be described.
In order to form the surface treatment film and the resin film on the surface of the galvanized steel sheet or the aluminum-based steel sheet, the dried film thickness of the surface treatment composition (I) (treatment liquid) having the above-described composition falls within the above range. After coating and drying by heating without washing with water, the coating material (II) is further applied and dried without washing with water.
The method of applying the surface treatment composition (I) or the paint (II) may be any of an application method, a dipping method, and a spray method. As a coating treatment method, any method such as a roll coater (three-roll method, two-roll method, etc.), a squeeze coater, a die coater and the like may be used. In addition, after the application treatment using a squeeze coater or the like, or the dipping treatment or the spray treatment, the application amount can be adjusted, the appearance can be made uniform, and the film thickness can be made uniform by an air knife method or a roll drawing method.
[0054]
After coating with the surface treatment composition (I) and the paint (II), heating and drying are performed without washing with water. As the heating and drying means, a dryer, a hot air oven, a high-frequency induction heating oven, an infrared oven, or the like can be used. The heat treatment of the surface treatment composition (I) is suitably performed at a temperature of 30 to 300 ° C., preferably 60 to 250 ° C. at the ultimate plate temperature. If the heating temperature is lower than 30 ° C., a large amount of water in the film remains, and the corrosion resistance becomes insufficient. On the other hand, when the temperature exceeds 300 ° C., it is not only uneconomical, but also a defect occurs in the film and the corrosion resistance is lowered. In the case of the paint (II), it is appropriate to carry out the coating in the range of 150 to 270 ° C. If the heating temperature is lower than 150 ° C., the curing is insufficient and the corrosion resistance, lubricity, and appearance after molding are reduced. If the heating temperature is higher than 270 ° C., the corrosion resistance, lubricity, and appearance after molding are reduced as in the case of less than 150 ° C.
The above-mentioned surface treatment film and resin film may be formed on either one side or both sides of the plated steel sheet.
[0055]
【Example】
The surface treatment composition (I) for forming the surface treatment film as the lower layer was prepared as follows.
[Production of surface treatment composition (I)]
As the resin compound (A) for the surface treatment composition, a water-dispersible resin having a chemical structure shown in Table 2 was used, and a cationic urethane resin (B) shown in Table 3 and a silane coupling agent shown in Table 4 ( C), a Ti compound (D) shown in Table 5, an acid compound (E) shown in Table 6, and a solid lubricant shown in Table 7 are appropriately blended, and the mixture is stirred for a required time using a stirrer to obtain a surface treatment composition ( I) was prepared.
[0056]
The upper layer coating material (II) for forming a resin film was prepared as follows.
In order to prepare the paint (II), those shown in Table 8 were produced as the hydroxyl group-containing urethane prepolymer in the solvent-based thermosetting resin.
In the following, No. 8 in Table 8 is used. A production example of No. 1 hydroxyl group-containing urethane prepolymer will be described. In a reaction apparatus equipped with a heating device, a stirrer, a water separator, and a thermometer, 915 parts by mass of an aromatic polyester polyol (AR) and 915 parts by mass of an aliphatic polyester polyol (AL) are present as a polyester polyol in the presence of an inert gas. It was charged and heated below. After the raw materials were melted, stirring was started while heating. After the temperature of the melted raw material was raised to 100 ° C., it was kept at that temperature for 30 to 60 minutes, and then dehydrated.
[0057]
Next, the temperature of the melted raw material was lowered to 70 ° C., and at that temperature, 28 parts by mass of 1,4-butanediol as a dihydric alcohol, 313 parts by mass of diphenylmethane-4,4-diisocyanate as an isocyanate compound, and a reaction catalyst Of dibutyltin laurate: 0.55 parts by mass as a solvent and 940 parts by mass of cyclohexanone as a solvent, and the reaction was continued at a temperature of 70 ° C. for 5 to 10 hours. The reaction was terminated by adding 10 parts by mass of 3-butanediol. Further, 4150 parts by mass of cyclohexanone was added as a solvent, whereby a non-volatile content of 30% and a viscosity of 1: 400 cps were used. 1 was prepared.
[0058]
No. of Table 8 2-No. Also, with respect to No. 8, the components shown in the same table were blended, and the hydroxyl group-containing urethane prepolymer No. 8 was prepared according to the above method. 2-No. 8 was prepared. Table 8 shows the glass transition temperature of the thermosetting resin obtained by crosslinking and curing the thus obtained hydroxyl group-containing urethane prepolymer with hexamethylene diisocyanate trimer as a curing agent at an equivalent ratio of NCO / OH = 1/1. Are also shown.
The hydroxyl group-containing urethane prepolymers in Table 8 were combined as shown in Table 9 to prepare nine types of solvent-based thermosetting resins A to I used in the examples of the present invention. Table 9 also shows the resins J to M used in Comparative Examples. As the curing agent for the solvent-based thermosetting resins A to I, L, and M, hexamethylene diisocyanate trimer was used in a mixing ratio such that the equivalent ratio of NCO / OH was 1/1.
[0059]
A plated steel sheet shown in Table 1, which is a plated steel sheet for home appliances, building materials, and automobile parts based on a cold-rolled steel sheet (sheet thickness 0.8 mm), was used as a processing base sheet. After the surface of the plated steel sheet is subjected to alkali degreasing treatment, water washing and drying, the surface treatment composition (I) is applied by a roll coater and heated at a predetermined baking temperature (attained sheet temperature) by an induction heating device without washing with water. It dried and the surface treatment film was formed. The film thickness of the film was adjusted according to the solid content of the surface treatment composition (residual residue after heating) or the application conditions (roll rolling force, rotation speed, etc.).
[0060]
Further, a coating (II) was prepared by adding a solid lubricant and silica as a rust preventive additive shown in Table 10 to a solvent-based thermosetting resin shown in Table 9 on the upper layer to prepare a coating (II). The composition was applied on the above-mentioned surface treatment film by a coater, and then heated and dried at 230 ° C. baking temperature (attained plate temperature) by an induction heating device without washing with water. As a comparative example, press oil was applied to a surface-treated steel sheet obtained by applying and drying the surface-treatment composition (I) at 2 g / m 2. ² Coated ones were also made.
Tables 11 to 26 show the results of each test of the coating composition and the quality performance (lubricity, appearance after forming, corrosion resistance after forming) of the surface-treated steel sheet thus manufactured. The quality performance was evaluated as follows.
[0061]
(1) Lubricity
The tester shown in the schematic front view in FIG. 1 was used. The tester includes a female die 1 having a flat surface fixed to one side 2a of a box-shaped frame 2 and a male having a substantially horizontal ridge 3 of a predetermined height facing the female die 1. It comprises a dice 4 and a hydraulic cylinder 5 fixed to the other side 2b of the frame 2 for supporting the male dice 4 and horizontally moving the male dice 4 toward the female dice 1. The male die 4 is fixed to a rod 5 a of a hydraulic cylinder 5 via a load cell 6. In addition, the width | variety of the protrusion 3 of the male die 4 is 10 mm, and the length of the front-end | tip is 1 mm.
The test piece 7 cut out from the surface-treated steel sheet of each embodiment is inserted vertically into the gap between the female die 1 and the male die 4, and the hydraulic cylinder 5 is operated to test with the female die 1 and the male die 4. The piece 7 is weighed 50 kgf (500 kgf / cm ² ). Next, the test piece 7 was pulled upward at a speed of 100 mm / min, as indicated by an arrow, and the dynamic friction coefficient at that time was examined, thereby evaluating the lubricity. In addition, the test was performed not only on a test piece at normal temperature (20 ° C.) but also on a high-temperature test piece at 150 ° C. in consideration of an increase in the sheet temperature during actual press work. The evaluation criteria are as follows.
○: Dynamic friction coefficient less than 0.1
Δ: Dynamic friction coefficient 0.1 or more, less than 0.2
×: Dynamic friction coefficient 0.2 or more
[0062]
(2) Press formability
The limit drawing ratio when a disk-shaped test piece cut out from the surface-treated steel sheet of each example was formed into a cup under the conditions of a punch diameter: 50 mm, a die diameter: 51.91 mm, and a wrinkle holding force: 1 ton was determined. The press formability was evaluated by this. The evaluation criteria are as follows.
：: Limit drawing ratio 2.30 or more
Δ: Limit drawing ratio of 2.20 or more and less than 2.30
×: Limit drawing ratio less than 2.20
[0063]
(3) Appearance after molding
The tester shown in the schematic front view in FIG. 2 was used. The tester includes a male die 9 fixed to one side 2a of a box-shaped frame 2 and having a substantially horizontal ridge 8 having a predetermined height, and a predetermined die facing the ridge 8 of the male die 9. A female die 11 having a groove 10 of a depth, and fixed to the other side 2b of the frame 2 for supporting the female die 11 and moving the female die 11 horizontally toward the ridge 8 of the male die 9. And a hydraulic cylinder 5. The female die 11 is fixed to a rod 5 a of a hydraulic cylinder 5 via a load cell 6. The width of the ridge 8 of the male die 9 is 30 mm, and the radius of the tip of the ridge 8 is 0.25 mm.
A test piece cut from the surface-treated steel sheet of each embodiment is inserted vertically into the gap between the male die 9 and the female die 11, and the hydraulic cylinder 5 is actuated. 50 kgf (500 kgf / cm ² ). Next, the test piece 7 was pulled upward at a speed of 100 mm / min, as indicated by an arrow, and the appearance of the test piece at that time was visually inspected to evaluate the degree of damage and the degree of blackening. The evaluation criteria are as follows.
：: The appearance is uniform with almost no change over the entire surface
：: Some scratching and blackening occurred, and the appearance was somewhat uneven
Δ: Scratch and blackening occurred locally, and appearance was clearly uneven
×: Severe damage and blackening occurred at the corners
[0064]
(4) Corrosion resistance after molding
Using a test machine shown in a schematic front view in FIG. 2, a test piece cut out from the surface-treated steel sheet of each example was pressed by a male die 9 and a female die 11 in the same manner as described above. Pulled up. The edge of the test piece pulled out in this way was sealed with a tar epoxy paint, and then subjected to a salt spray test based on JIS Z 2371 for 240 hours to examine the occurrence rate of white rust. Was evaluated. The evaluation criteria are as follows.
◎: White rust area ratio less than 5%
：: White rust area ratio 5% or more and less than 10%
○-: White rust area ratio 10% or more and less than 25%
Δ: White rust area ratio 25% or more and less than 50%
×: White rust area ratio 50% or more, 100% or less
[0065]
[Table 1]

[0066]
[Table 2]

[0067]
[Table 3]

[0068]
[Table 4]

[0069]
[Table 5]

[0070]
[Table 6]

[0071]
[Table 7]

[0072]
[Table 8]

[0073]
[Table 9]

[0074]
[Table 10]

[0075]
[Table 11]

[0076]
[Table 12]

[0077]
[Table 13]

[0078]
[Table 14]

[0079]
[Table 15]

[0080]
[Table 16]

[0081]
[Table 17]

[0082]
[Table 18]

[0083]
[Table 19]

[0084]
[Table 20]

[0085]
[Table 21]

[0086]
[Table 22]

[0087]
[Table 23]

[0088]
[Table 24]

[0089]
[Table 25]

[0090]
[Table 26]

[0091]
【The invention's effect】
As described above, according to the present invention, a surface-treated steel sheet excellent in press formability and corrosion resistance can be obtained without containing chromium in the film.
[Brief description of the drawings]
FIG. 1 is a schematic front view of a testing machine for evaluating the lubricity of a test piece.
FIG. 2 is a schematic front view of a testing machine for evaluating the appearance of a test piece after molding and the corrosion resistance after molding.
[Explanation of symbols]
1: female die, 2: frame, 3: protrusion, 4: male die, 5: hydraulic cylinder, 6: load cell, 7: test piece, 8: protrusion, 9: male die, 10: groove, 11: female dice

Claims (18)

On a surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, a resin compound (A) represented by the following general formula (1) and at least one selected from primary to tertiary amino groups and quaternary ammonium bases Cationic urethane resin (B) having a cationic functional group, and silane coupling having at least one reactive functional group selected from active hydrogen-containing amino group, epoxy group, vinyl group, mercapto group and methacryloxy group Mass ratio of the solid content of the cationic urethane resin (B) and the total amount of the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C), containing the agent (C). [(B) / {(A) + (B) + (C)}] is 0.04 to 0.09, and the silane coupling agent (C) and the resin compound (A) are cationic. The mass ratio [(C) / {(A) + (B) + (C)}] of the solid content to the total amount of the urethane resin (B) and the silane coupling agent (C) is 0.6 to 0.7. A surface treatment composition having a thickness of 0.01 to 2 μm formed by applying and drying the surface treatment composition (I),
On the upper layer, a coating (II) containing the following components (a), (b) and (c) is applied and cured by heating to form a resin coating having a thickness of 0.1 μm or more and less than 5 μm. And
(A) Two or more solvent-based thermosetting resins having different glass transition temperatures after curing: 100 parts by mass (solid content ratio)
(B) Solid lubricant composed of polyethylene resin having a melting point of 130 ° C. or less: 1 to 30 parts by mass (solid content ratio)
(C) Non-chromium rust preventive additive: 3 to 30 parts by mass (solid content ratio)
A surface-treated steel sheet having excellent press formability and corrosion resistance, wherein the total thickness of the surface-treated film and the resin film is 5 μm or less.

In the general formula (1), Y ₁ and Y ₂ bonded to the benzene ring are each independently hydrogen or a Z group represented by the following formula (2) or (3), The average value of the number of substitutions per Z group is 0.2 to 1.0. n represents an integer of 2 to 50.

R ₁ , R ₂ , R ₃ , R ₄ and R ₅ in the formulas (2) and (3) each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxy group having 1 to 10 carbon atoms. It represents an alkyl group, a ^- represents a hydrogen ion or an ion. The surface treatment composition (I) further contains a Ti compound (D), and the total amount of the Ti compound (D), the resin compound (A), the cationic urethane resin (B), and the silane coupling agent (C) The press-formability according to claim 1, wherein the mass ratio [(D) / {(A) + (B) + (C)}] of the solid content is 0.05 to 0.10. And surface treated steel sheet with excellent corrosion resistance. The surface treatment composition (I) further contains at least one acid compound (E) selected from phosphoric acid, nitric acid, acetic acid, and salts thereof, and the acid compound (E) and the resin compound (A) ), The mass ratio of the solid content [(E) / {(A) + (B) + (C)}] to the total amount of the cationic urethane resin (B) and the silane coupling agent (C) is 0.05. The surface-treated steel sheet having excellent press formability and corrosion resistance according to claim 1 or 2, wherein the thickness is from 0.15 to 0.15. The chromium-free rust preventive additive contained in the paint (II) is at least one selected from the following (e1) to (e5). Surface treated steel sheet with excellent press formability and corrosion resistance.
(E1) silicon oxide (e2) calcium and / or calcium compound (e3) sparingly soluble phosphate compound (e4) molybdate compound (e5) selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams One or more organic compounds containing S atoms The surface-treated steel sheet having excellent press formability and corrosion resistance according to claim 4, characterized in that it contains at least calcium ion exchange silica as a chromium-free rust preventive additive. Two or more types of solvent-based thermosetting resins (a) having different glass transition temperatures after curing contained in the coating material (II) have one or more low-temperature resins having a glass transition temperature of 50 ° C. or lower after curing. It is composed of a solvent-based thermosetting resin (a ₁ ) having a glass transition temperature and one or more solvent-based thermosetting resins (a ₂ ) having a glass transition temperature of more than 50 ° C. after curing and having a high glass transition temperature. The surface-treated steel sheet excellent in press formability and corrosion resistance according to claim 1, 2, 3, 4, or 5. A low glass transition temperature of the solvent-based thermosetting resin (a _1), a high glass transition temperature of the solvent-based thermosetting resin (a ₂₎ and the mixing ratio of _{(a 1) / (a 2} ) is the mass of solids The surface-treated steel sheet having excellent press formability and corrosion resistance according to claim 6, wherein the ratio is 9/1 to 1/9. The main resin of each of the two or more solvent-based thermosetting resins (a) having different glass transition temperatures after curing contained in the paint (II) is a hydroxyl group-containing urethane prepolymer. Item 1. A surface-treated steel sheet excellent in press formability and corrosion resistance according to item 1, 2, 3, 4, 5, 6, or 7. The solid lubricant (b) composed of a polyethylene resin contained in the coating material (II) has a melting point of 90 to 130 ° C and a number average molecular weight of 5,000 or less. A surface-treated steel sheet excellent in press formability and corrosion resistance according to 6, 7, or 8. On a surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, a resin compound (A) represented by the following general formula (1) and at least one selected from primary to tertiary amino groups and quaternary ammonium bases Cationic urethane resin (B) having a cationic functional group, and silane coupling having at least one reactive functional group selected from active hydrogen-containing amino group, epoxy group, vinyl group, mercapto group and methacryloxy group Mass ratio of the solid content of the cationic urethane resin (B) and the total amount of the resin compound (A), the cationic urethane resin (B) and the silane coupling agent (C), containing the agent (C). [(B) / {(A) + (B) + (C)}] is 0.04 to 0.09, and the silane coupling agent (C) and the resin compound (A) are cationic. The mass ratio [(C) / {(A) + (B) + (C)}] of the solid content to the total amount of the urethane resin (B) and the silane coupling agent (C) is 0.6 to 0.7. Is applied and dried to form a surface-treated film having a film thickness of 0.01 to 2 μm,
On the upper layer, a coating (II) containing the following components (a), (b) and (c) is applied and cured by heating to form a resin film having a film thickness of 0.1 μm or more and less than 5 μm,
(A) Two or more solvent-based thermosetting resins having different glass transition temperatures after curing: 100 parts by mass (solid content ratio)
(B) Solid lubricant composed of polyethylene resin having a melting point of 130 ° C. or less: 1 to 30 parts by mass (solid content ratio)
(C) Non-chromium rust preventive additive: 3 to 30 parts by mass (solid content ratio)
A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance, wherein the total film thickness of the surface-treated film and the resin film is 5 μm or less.

In the general formula (1), Y ₁ and Y ₂ bonded to the benzene ring are each independently hydrogen or a Z group represented by the following formula (2) or (3), The average value of the number of substitutions per Z group is 0.2 to 1.0. n represents an integer of 2 to 50.

R ₁ , R ₂ , R ₃ , R ₄ and R ₅ in the formulas (2) and (3) each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxy group having 1 to 10 carbon atoms. It represents an alkyl group, a ^- represents a hydrogen ion or an ion. The surface treatment composition (I) further contains a Ti compound (D), and the total amount of the Ti compound (D), the resin compound (A), the cationic urethane resin (B), and the silane coupling agent (C) The press formability according to claim 10, wherein the mass ratio [(D) / {(A) + (B) + (C)}] of the solid content is 0.05 to 0.10. And a method for producing a surface-treated steel sheet having excellent corrosion resistance. The surface treatment composition (I) further contains at least one acid compound (E) selected from phosphoric acid, nitric acid, acetic acid, and salts thereof, and the acid compound (E) and the resin compound (A) ), The mass ratio of the solid content [(E) / {(A) + (B) + (C)}] to the total amount of the cationic urethane resin (B) and the silane coupling agent (C) is 0.05. The method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance according to claim 10 or 11, wherein the thickness is from 0.15 to 0.15. The chromium-free rust preventive additive contained in the paint (II) is at least one selected from the following (e1) to (e5). A method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance.
(E1) silicon oxide (e2) calcium and / or calcium compound (e3) sparingly soluble phosphate compound (e4) molybdate compound (e5) selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams One or more organic compounds containing S atoms 14. The method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance according to claim 13, comprising at least calcium ion exchange silica as a non-chromium-based rust-preventive additive. Two or more types of solvent-based thermosetting resins (a) having different glass transition temperatures after curing contained in the coating material (II) have one or more low-temperature resins having a glass transition temperature of 50 ° C. or lower after curing. It is composed of a solvent-based thermosetting resin (a ₁ ) having a glass transition temperature and one or more solvent-based thermosetting resins (a ₂ ) having a glass transition temperature of more than 50 ° C. after curing and having a high glass transition temperature. The method for producing a surface-treated steel sheet excellent in press formability and corrosion resistance according to claim 10, 11, 12, 13, or 14. A low glass transition temperature of the solvent-based thermosetting resin (a _1), a high glass transition temperature of the solvent-based thermosetting resin (a ₂₎ and the mixing ratio of _{(a 1) / (a 2} ) is the mass of solids The method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance according to claim 15, wherein the ratio is 9/1 to 1/9. The main resin of each of the two or more solvent-based thermosetting resins (a) having different glass transition temperatures after curing contained in the paint (II) is a hydroxyl group-containing urethane prepolymer. Item 10. The method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance according to item 10, 11, 12, 13, 14, 15, or 16. The solid lubricant (b) composed of a polyethylene resin contained in the paint (II) has a melting point of 90 to 130 ° C and a number average molecular weight of 5,000 or less, wherein the solid lubricant (b) has a number average molecular weight of 5,000 or less. 15. The method for producing a surface-treated steel sheet having excellent press formability and corrosion resistance according to 15, 16, or 17.

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