JP3835017B2 - Zn-plated surface-treated steel sheet for fuel containers - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、燃料容器用、特にガソリンを燃料とする自動車の燃料タンク用の素材として使用するのに適した表面処理鋼板に関する。
【０００２】
【従来の技術】
ガソリンを燃料とする一般的な自動車用燃料タンク用途には、ターンめっきと呼ばれるPb−Sn合金めっき鋼板が従来より広く使用されてきたが、環境問題からPbを含有しない材料が求められてきている。また、燃料に対する耐食性についても、有機酸を含む劣化ガソリンに対する耐食性が求められるなど、より高度なレベルが要求されている。
【０００３】
この要請に対し、Alめっき鋼板 (例えば、特開平10−46358 号公報) 、Sn−Zn合金めっき鋼板 (例えば、特開平８−269733号公報) などが代替品として開発されている。このうち、Alめっき鋼板は、溶接やハンダ付け等の接合性に問題があり、加工メーカー等では、容易に接合できるより使い勝手のよい材料を望んでいる。一方、Sn−約８％Zn合金めっき鋼板は性能的なバランスがよいとされているが、この合金めっきの用途がほぼ燃料タンクだけに限定されるため、小ロットでの生産となり、安定供給や価格面に問題がある。この点、一般に広く用いられているZn系めっき（ZnめっきおよびZn合金めっき）を自動車燃料タンク用途に適用することができれば有利である。
【０００４】
Zn系めっき鋼板を自動車用燃料タンク用途に適用した従来技術として、特開平10−137681号公報に、Zn系めっき鋼板のタンク内面側にNiおよびAl金属粉を含有する樹脂を、外面側にはワックスを含有する樹脂を塗布した表面処理鋼板が提案されている。
【０００５】
ところが、この表面処理鋼板は、Zn系めっき鋼板をクロメート処理した上で上記の樹脂を塗布するものであり、クロメート処理が必須である。クロメート処理で形成されたクロメート被膜は、この公報に記載されているように６価クロムを含有する。しかし、最近になって、やはり環境問題から、６価クロムを含有しない材料の要望が強くなってきている。そのため、６価クロムを含まない（つまり、クロメート処理を利用しない）自動車燃料タンク用表面処理鋼板の開発が急務となっている。
【０００６】
しかし、燃料タンクは自動車の重要保安部品であり、燃料に対する高度の耐食性が要求される。Zn系めっき鋼板を母材とした表面処理鋼板の場合、６価クロムを含有するクロメート処理が耐食性の確保に極めて有効であるため、高度の耐食性が要求される用途にはクロメート処理を行うのが普通であった。従って、６価クロムを含有させずに性能バランスが良好な自動車燃料タンク用素材を得ることは容易ではない。
【０００７】
【発明が解決しようとする課題】
自動車燃料タンクに求められる性能は、タンクの内面側と外面側とで異なる。タンク内面側は、ガソリン環境、特にギ酸等の有機酸を含有する劣化ガソリンに対する耐食性が最も重要である。一方、外面側に求められる特性としては、ハンダ付け性、加工メーカーでの後塗装性、塗装後の耐食性、および溶接性等が挙げられる。
【０００８】
本発明は、環境面で問題のある鉛と６価クロムを含有させずに、このようなタンク内面側および外面側の要求特性を満たす、自動車燃料タンク用に適した表面処理鋼板を提供することを課題とする。具体的には、Zn系めっき鋼板を母材として、クロメート処理を利用せずに、上記要求特性を満たす表面処理鋼板を開発することである。
【０００９】
【課題を解決するための手段】
本発明者らは、ZnまたはZn系合金めっき鋼板を母材として用いて、クロメート処理を行わずに、自動車燃料タンク用鋼板に要求される特性を得るべく検討した結果、このZn系めっき鋼板の両面のめっき面上に、珪酸化合物と樹脂とを主成分とする薄い第１層を形成した後、さらに燃料タンクの内面となる片面には、その上にNiとAlを含む金属粉末を含有する比較的厚い樹脂被覆層を設けて内面の耐食性を確保し、外面となる他面は、第１層のままか、またはさらに熱可塑性樹脂層を薄く形成することにより、上記要求特性を満たす、燃料容器用の表面処理鋼板が得られることを見出した。
【００１０】
「ここに、本発明は、 ＺｎまたはＺｎ系合金両面めっき鋼板の両面のめっき面上に、樹脂と珪酸化合物とを主被膜形成成分とする処理液から形成された０．０５〜２μｍ厚の第１層を有し、さらに片面（以下、第１面） に、その上層として、ＮｉとＡｌを含む金属粉を含有する樹脂被膜からなる２〜１０μｍ厚の第２層が形成されており、第２層中の金属粉の割合が金属粉以外の成分の合計１００ 重量部に対して５〜１５０重量部の範囲であり、前記第１面と反対側の面（以下、第２面）に、前記第１層の上層として、熱可塑性樹脂からなる第２層が、第１層との合計厚みが２μｍ以下となる厚みで形成されていることを特徴とする、燃料容器用表面処理鋼板である。」
【００１１】
本発明の表面処理鋼板は、自動車燃料タンク用、特にガソリン用燃料タンクに非常に適しているが、自動車以外の燃料容器 (例、バイク、トラクター等の燃料タンク、携帯用燃料タンク等) にも使用できることはいうまでもない。
【００１２】
【発明の実施の形態】
母材めっき鋼板
めっき素材の鋼板は、通常用いられている一般的な冷延鋼板でよい。ただし燃料タンク用途は、一般に厳しい成形加工を受けるため、例えば極低炭素鋼で、かつTi、Nb、Ｂの１種または２種以上が添加された成分系といった、プレス成形性に優れた鋼板であるほうが好ましい。
【００１３】
鋼板に施すめっきは、耐食性確保の目的で広く利用されているZnもしくはZn合金めっきである。めっき種としては、これらに制限されるものではないが、例えば、Zn、Zn−Al、Zn−Al−Si、Zn−Ni、Zn−Fe、Zn−Cr、Zn−Mg、Zn−Sn、Zn−Coなどが挙げられる。また、めっき方法は、溶融めっき法、電気めっき法、蒸着めっき法などのいずれでもよい。めっき被膜は、少量の有機インヒビター、デキストリン、デキストランなどの有機化合物を含有していてもよい。めっき付着量は、耐食性の観点から、片面あたり10 g/m2 以上が好ましい。付着量が多すぎると、コストおよび加工性の面で問題となる。より好ましい付着量は、片面当たり15〜100 g/m2である。
【００１４】
第１層
この層に求められる性能としては、内面では第２層との密着性および燃料、特に有機酸を含有する劣化した燃料に対する耐食性、外面では加工メーカーで施される外面用塗料との密着性、塗装後の耐食性、接合性 (ハンダ付け性、ロウ付け性、溶接性等) である。
【００１５】
これらの全ての要求を満たすため、本発明では、Zn系メッキ鋼板の表面に形成する第１層は、珪酸化合物と樹脂を主被膜形成成分とする処理液から形成された、珪素質＋樹脂質の被膜とする。それにより、内面と外面のいずれも同じ材料から第１層を形成することができる。第１層の形成は、常法に従って、母材めっき鋼板の両面に処理液を塗布し、塗膜を乾燥 (または焼付け) することにより行えばよい。
【００１６】
第１層が樹脂を含むことで、内面第２層の樹脂や外面第２層または外面用塗料の樹脂との密着性が確保される。樹脂成分だけでは、内外面とも、必要な耐食性を得るために膜厚を相当厚くする必要があり、そうなると、外面の溶接性、ハンダ付け性、ロウ付け性に不利である。そこで、薄膜で耐食性を確保するために、樹脂に珪酸化合物を添加する。樹脂中に珪酸化合物を共存させると被膜の耐食性が向上するのは、膜中に−Si−Ｏ−のシロキサン結合が生成し、樹脂と架橋構造を形成したり、或いは樹脂の重合体分子と絡み合うことで被膜を緻密化することができるためではないかと考えられる。そのため、薄膜でも耐食性が得られるので、溶接性、ロウ付け性、ハンダ付け性も同時に確保することができる。
【００１７】
第１層の膜厚は0.05〜２μｍの範囲とする。0.05μｍより薄いと、内外面ともに耐食性が劣り、２μｍより厚いと、溶接性、ロウ付け性、ハンダ付け性が劣る。好ましい範囲は 0.1〜0.5 μｍである。なお、第１層の膜厚は、内面と外面で同じであっても、異なっていてもよい。例えば、外面に第２層を設けない場合には、外面の第１層を内面より厚くしてもよく、逆に外面に第２層を設ける場合には外面の第１層を内面より薄くしてもよい。また、必要ないが、第１層の被膜組成を、本発明の範囲内で内面と外面とで変化させることも可能である。
【００１８】
第１層の形成に用いる珪酸化合物としては、コロイダルシリカ、乾式シリカ、アルカリ金属珪酸塩、シランカップリング剤、および珪酸アルキルエステルの１種または２種以上を使用することができる。
【００１９】
ここで、シランカップリング剤とは、ケイ素１原子にｎ個 (ｎ＝２〜３) の加水分解性の基 (代表的にはアルコキシ基、特にメトキシ基もしくはエトキシ基であるが、塩素でもよい) と (ｎ−１) 個の非加水分解性の有機基 (例えば、エチル、プロピルなどの低級アルキル基、アミノ、エポキシ等の官能性置換基を含有する低級アルキル基、ビニル基等) とが結合した化合物である。本発明において第１層に用いるシランカップリング剤として好ましいのは、非加水分解性の有機基がアルキル基であるもの、例えば、エチルトリメトキシシラン、プロピルトリメトキシシラン、エチルトリエトキシシラン等である。これらはシランカップリング剤としてあまり使用されてはいないが、本発明ではシランカップリング剤に含める。珪酸アルキルエステルは、ケイ素にアルコキシ基が結合した化合物であり、代表的にはテトラアルコキシシラン (＝アルキルシリケート)(例、エチルシリケート) である。
【００２０】
シランカップリング剤は、処理液中または塗膜中で加水分解と重縮合を受けて、ポリシロキサン型の重合体になる。珪酸アルキルエステルも同様に加水分解と重縮合を受け、最終的にはシリカになる。従って、上記の珪酸化合物は、シリカ質の膜、または一部有機分が残ったポリシロキサン構造の膜を形成できる化合物である。
【００２１】
第１層の樹脂成分としては、第２層との密着性の点から、水酸基、カルボキシル基、アミノ基、グリシジル基、イソシアネート基等の１種または２種以上を有する熱可塑性樹脂が望ましい。樹脂系としては、たとえばウレタン、アクリル、ポリエステル、エポキシ、メラミン樹脂、アルキッド樹脂が挙げられる。処理液は有機溶媒を使用した溶剤系とすることもできるが、作業環境の面からは、水溶性もしくは水分散性の樹脂を用いた水系処理液であることが望ましい。なお、水系処理液の場合には、乾式シリカは水系では分散性があまり良好ではないので、それ以外の珪酸化合物が好ましい。
【００２２】
珪酸化合物と樹脂との重量比は５：95〜80：20とすることが好ましい。樹脂が多すぎると、上述のように耐食性に劣る。一方、珪酸化合物が多すぎると、薄膜でも平板の耐食性はかなり良好だが、加工物質または疵部での耐食性が樹脂のみの場合よりかえって劣る。また、珪酸塩化合物の膜は親水性が強く、塗装後の二次密着性にも不利である。上記重量比のより好ましい範囲は10：90〜75：25である。
【００２３】
第１層中に、リン酸化合物を含有させると、耐食性改善に効果的である。ただし含有量が多すぎると、第２層との密着性に不利になるため、Ｐ／Siの原子数比が２以下の範囲内で含有させる。Ｐ／Siの原子数比は好ましくは 0.1〜1.5 の範囲内である。リン酸化合物としては、リン酸、亜リン酸、次亜リン酸およびこれらのアルカリ金属塩が挙げられ、１種もしくは２種以上を使用できる。
【００２４】
また、耐食性等の性能改善のために、こうした効果があることが知られている３価クロム化合物、モリブデン酸等を第１層に含有させてもよい。さらに、着色顔料、防錆顔料、導電顔料、界面活性剤等も、本発明で目的とする諸性能を大きく阻害しない限り、第１層中に含有させてもよい。また、下地めっき表面との反応性を向上させるために、フッ化ケイ素酸、フッ化チタン酸などのフッ酸系化合物を第１層中に含有させることもできる。ただし環境問題から鉛、６価クロムは、不可避的に混入する以外は含有させない。
【００２５】
第１層中に、溶接性改善の観点から、さらに金属粉もしくは導電顔料 (以下単に金属粉) を含有させてもよい。金属粉の種類としては、Zn、Ni、Al、Sn、およびこれらの金属間の合金、さらにはステンレス鋼、リン化鉄、フェロシリコンなどが挙げられる。第１層中の金属粉含有量は、金属粉以外の成分の合計量100 重量部に対して５〜150 重量部、好ましくは20〜80重量部の範囲内とする。５重量部未満では溶接性改善効果が認められず、150 重量部超では、処理液の流動性が低下して、めっき面上での被膜形成そのものが困難になったり、あるいは被膜形成後の成形加工時にパウダリングを生じるためである。
【００２６】
なお金属粉の大きさおよび形状は、成形加工時のパウダリング性の問題から、粒状の場合は第１層の膜厚の３倍以下の範囲、もしくは径が10μｍ程度以下の鱗片状が好ましい。
【００２７】
第２層 ( 内面 )
燃料容器 (タンク) の内面は、上記の第１層だけでは、特に劣化ガソリンに対する耐食性が十分ではなく、また溶接性も不足する。そのため、本発明の表面処理鋼板の内面となる片面 (請求項では第１面) には、第１層の上にさらに第２層を形成する。この第２層も、処理液の塗布と乾燥または焼付けにより形成すればよい。
【００２８】
この第２層に求められる性能は、内面のガソリン環境での耐食性、第１層との密着性、および溶接性である。これらの性能を満たすため、第２層は、NiとAlを含む金属粉を含有する厚さ２〜10μｍの樹脂被膜とする。この金属粉は、Ni粉、Al粉、およびNi−Al合金粉を適宜組合わせたものでよい。
【００２９】
被膜に存在させうる金属粉のうち、Ni粉は主に溶接性改善を目的として添加する。溶接性は被膜の導電性増大により改善されるが、耐食性と導電性の両立の点ではNiが最適であることが判明した。一方、Al粉は、主に耐食性改善を目的として添加する。特にガソリンが劣化してくると、ギ酸、酢酸等の有機酸が発生し、ガソリン環境の腐食性がより厳しくなるが、このような環境においてAl粉は特に有効である。また、Al粉の添加は溶接性の改善効果もある程度は認められるが、Ni粉との混合添加またはNi−Al合金の添加で、溶接性がより大きく改善されることが判明した。そのため、第２層中には、NiとAlを含む金属粉、例えば、Ni粉とAl粉との混合物、またはNi−Al合金粉を含有させる。
【００３０】
第２層中の金属粉の配合量は、第２層中の金属粉以外の成分の合計100 重量部に対して、金属粉の合計量が５〜150 重量部の範囲内となる割合が好ましい。金属粉の合計量が５重量部より少ないと溶接性に劣り、150 重量部を超えると、処理液の流動性低下による均一塗布が非常に困難になり、また被膜形成後のプレス成形性時に金属粉の脱離を生じる。
【００３１】
金属粉中のNiとAlの重量比率は、Ni：Al＝10：90〜95：５の範囲が好ましく、耐食性と溶接性のバランスからは、Ni：Al＝30：70〜90：10の範囲がより好ましい。Al単独添加では、Alと有機酸との反応によると思われる耐食性改善効果を発現するが、溶接性の改善効果が小さい。また、後述するようにリン化鉄やフェロシリコンを添加する場合、Niを含有しないと、耐食性が劣化する。一方、Niの単独添加では、溶接性の改善効果があるが、ガソリン環境での耐食性の改善効果が小さい。
【００３２】
第２層中の樹脂は、金属粉のバインダーとして役割に加えて、バリアとしての効果も発揮することが望ましく、従って樹脂自体がガソリン成分に対して溶解、膨潤もしくは透過を起こしにくいものがよい。
【００３３】
この目的には、熱可塑性樹脂よりも熱硬化性樹脂が適している。適当な熱硬化性樹脂の具体例としては、エポキシ系、アクリル系、ウレタン系、ポリエステル系、フェノール系樹脂等が挙げられ、特にウレタン変性エポキシ樹脂が好ましい。ウレタン変性エポキシ樹脂は、エポキシ系樹脂に脂肪族二塩基酸を反応させてカルボン酸基を導入し、さらにジイソシアネートを反応させてウレタン基を導入したものである。この樹脂の成膜前の分子量は5000〜50,000の範囲が好ましい。これより低分子量ではガソリンに対して膨潤し易くなり、高分子量では、工業的に得られにくいことのほかに、処理液の粘度が高くなりすぎ、生産性が低下する。このウレタン変性エポキシ樹脂とNi粉および／またはAl粉との組み合わせが、ガソリン環境での耐食性が最も良好であった。成膜に使用する樹脂液は水系でも溶剤系でもよいが、通常は溶剤系である。
【００３４】
上記の金属粉含有樹脂被膜からなる第２層の膜厚は２〜10μｍ、好ましくは３〜５μｍの範囲とする。膜厚が２μｍより薄いと、ガソリン環境での耐食性が劣化し、10μｍより厚いと、効果が飽和しコストが上昇する上、溶接性、成形加工時のパウダリング性でも不利になる。
【００３５】
第２層の金属粉の大きさは、Ni粉またはNi−Al合金粉では、0.5 〜10μｍの範囲が好ましく、第２層の膜厚が５μｍ以上の場合には膜厚の５〜100 ％の範囲であることがより好ましい。金属粉が小さすぎると第２層の導電性が低下し、大きすぎると溶接時の重ね合わせ部で金属粉同士の距離が遠くなり、いずれも溶接性が低下する。Al粉の大きさは、化学作用による耐食性改善の意味からは特に制限されない。ただし、特開平10−137681号公報に記載されているように、長径が10〜20μｍ程度の鱗片状の形状であると、ガソリン透過に対する物理的な遮蔽効果が期待できるのでより好ましいと考えられる。
【００３６】
第２層は、樹脂と上記金属粉以外に他の成分を含有していてもよい。このような他の成分としては、着色顔料、防錆顔料、導電顔料、シリカ、シランカップリング剤等が挙げられ、第２層の要求性能を阻害しない範囲で第２層に含有させることができる。特に溶接性が重視される場合には、導電顔料としてリン化鉄やフェロシリコンを含有していると溶接性が格段に向上する。ただし、その含有量が多過ぎると耐食性が劣化するため、含有量は全体の10重量％以下とすることが望ましい。環境問題から、鉛と６価クロムは、不可避的に混入する以外は含有させない。
【００３７】
第２層 ( 外面 )
本発明に係る表面処理鋼板では、外面（請求項では第２面）については、第１層のみで所定の性能が得られるため、外面の第２層は特に必要としない。しかし、自動車用燃料タンク用途では、通常は厳しい成形加工がなされるため、第１層の損傷防止の目的で、タンク外面側の表面に潤滑被膜もしくは保護被膜がある方が望ましい。この被膜は、溶剤やアルカリ等による脱脂工程で除去される脱膜性の被膜であるか、または非脱膜性の被膜の場合には、下記条件を満たす被膜であることが望ましい。
【００３８】
すなわち、非脱膜性の被膜の場合、下層である第１層の保護やその耐食性の改善には有利に働くものの、溶接性やハンダ付け性、ロウ付け性に対して不利に働く。そこで、樹脂系は溶接やハンダ付け、ロウ付け時に変形しやすい熱可塑性樹脂が望ましく、膜厚は第１層と合わせて２μｍ以下であることが望ましい。外面に第２層を設ける場合、第２層のより望ましい膜厚は 0.3〜２μｍの範囲で、但し第１層と合わせて２μｍ以下である。
【００３９】
この外面の第２層の樹脂被膜中にも、第１層と同様に、Zn、Ni、Al、Sn、およびこれらの金属間の合金、さらにはステンレス鋼、リン化鉄、フェロシリコンなどを含む１種または２種以上の金属粉を、金属粉以外の成分の合計量100 重量部に対して５〜150 重量部、好ましくは20〜80重量部の範囲の割合で含有させて、溶接性やハンダ付け性を改善させることもできる。さらに、第２層の樹脂被膜は、外面の塗料密着性が確保される限り、潤滑成分としてフッ素樹脂粒子やポリオレフィンワックスを含んでいてもよく、成形加工性の向上にはむしろ望ましい。また、耐食性改善のためシリカやシランカップリング剤を含んでいてもよい。
【００４０】
また、本発明に係る表面処理鋼板の内外の表面に防錆油を塗布したり、成形加工時に潤滑油を塗布することは、必ずしも必要ではないが、保管時の防錆や成形時の潤滑性の点からは望ましい。
【００４１】
【実施例】
（実施例１）
本実施例は、第１層の組成を変動させた場合の表面処理鋼板の性能の変化を示す。
【００４２】
供試材
10.8 mm 厚の電気Zn−13％Ni合金めっき鋼板 (両面めっき、めっき付着量：片面当たり30 g/m2)を、250 mm×310 mmに切断したのち、表１に示す第１層用の材料 (樹脂、珪酸化合物と、場合によりさらにリン酸化合物および金属粉) を適宜組合わせて混合する (金属粉を添加する場合には最後に添加しして十分に懸濁させる) ことにより調製した水系処理液を用いて両面に第１層を形成した。第１層の形成は、処理液を片面づつバーコート法で塗布し、100 ℃で乾燥させることにより行った。処理液の組成と第１層の膜厚は表２に示した通りである。
【００４３】
【表１】
その後、内面を想定した片面 (第１面) に、第２層を上記と同様にバーコート法により形成した。第２層形成用の処理液は、熱硬化性のウレタン変性エポキシ樹脂 (溶剤系樹脂液、平均分子量20,000 )に、樹脂液中の樹脂固形分100 重量部当たり平均粒径１μｍのNi粉23重量部と平均粒径14μｍのフレーク状Al粉31重量部とを懸濁させて調製した。塗布は乾燥膜厚が５μｍとなるように行い、塗布後に220 ℃で焼付けた。
【００４５】
得られた片面 (内面側) が第１層と第２層の２層樹脂被覆 (表面は第２層) 、他面 (外面側) が第１層のみの樹脂被覆である表面処理鋼板について、下記の方法で内外両面の性能を評価した。試験結果を表２に併せて示す。
【００４６】
評価方法
(1) 内面耐食性
後述する絞り条件で、第２層表面が内面となるようにカップ絞り成形を行い、得られたカップに3000 ppm濃度のギ酸水溶液10 cc とガソリン20 cc とを入れて密閉し、50℃に保持した。評価は、20日後の腐食生成物 (液のにごり) 状況で以下の通り判断した( ○までが合格) 。
【００４７】
◎：ほとんど変化なし、
○：上から見て10〜40％程度のにごり発生、
△：上から見て40〜70％程度のにごり発生 (底面の観察がかなり困難) 、
×：ほぼ液全体に赤錆が浮遊している (底面、側面の観察がかなり困難) またはカット部、その他から内面樹脂の剥離、ふくれが認められる。
【００４８】
(絞り条件) ブランク 100 mm径
パンチ 50 mm 径−５Ｒ
ダイス 52.5 mm 径−５Ｒ
絞り高さ 25 mm
潤滑油使用、絞り成形後アルカリ脱脂。
【００４９】
(2) 後塗装性
(温水密着性)
第１層表面を軽くアルカリ脱脂した後、外面塗料として日本ペイント製オーデラック9200TSブラックを約20μｍ厚に塗布した。その後、40℃の温水中に10日浸漬してから、直ちにクロスカットをいれ、さらにエリクセンで７mm張り出し、張り出し部のテープ剥離状況を調査した。
【００５０】
○：剥離なし
△：微小ブリスター部で剥離
×：大きく剥離
(塗装後耐食性)
上記と同様に外面塗料を塗布した後、クロスカットをいれ、さらにエリクセンで７mm張り出し、JIS Z2371 の塩水噴霧試験に供した。評価は480 時間後の錆発生状況で調査した。
【００５１】
◎：赤錆発生なし
○：カット部の赤錆５％以下
△： 〃 20％以下
×： 〃 20％超
(3) ハンダ付け／ロウ付け性
ハンダとロウとしてタルチン製Sn−Ag系合金と黄銅の２種類について調査した。フラックスはそれぞれタルチン製L305 (塩素系) とホウ酸を用いた。評価は、供試材外面にハンダ0.5gとフラックス0.5 ccを乗せ、Sn−Ag合金ハンダ系は350 ℃、黄銅ロウ系は800 ℃に加熱して、２分後の濡れ広がり面積で評価した。
【００５２】
○：濡れ面積が100 mm2 以上
×：濡れ面積が100 mm2 未満か、濡れない
(4) 抵抗溶接性
２枚の供試材を、内面第２層表面を内側にして重ねた後、加圧300 kgf 、通電12サイクル、電流８kAの条件でスポット溶接を行い、１サイクル目の電極間抵抗を測定して、次のように評価した (○までが合格) 。
【００５３】
◎：電極間抵抗が300 μΩ以下
○：電極間抵抗が300 μΩ以上、
もしくは軽度のチリ発生
△：かなり大きなチリ発生
×：通電しない (溶接不能)
(5) 成形性
内面耐食性の評価法について説明したのと同様にカップ絞り成形した供試材について、絞り内面側壁の粘着テープによる剥離状況を目視で評価した (○までが合格) 。
【００５４】
◎：剥離なし
○：テープでややキラキラ感あり
△：テープで明らかに剥離が認められる
×：ほぼ全面にわたって剥離が認められる
【００５５】
【表２−１】
【表２−２】
【表２−３】
表２の結果よりわかるように、第１層として熱可塑性樹脂と珪酸化合物を主成分とする被膜を用いることで、諸性能に優れた燃料容器用表面処理鋼板が得られる。この被膜中に金属粉を含有させると溶接性、ハンダ付け性が向上する。
【００５９】
（実施例２）
本実施例は、内面側に施す第２層の組成を変動させた場合の表面処理鋼板の内面性能の変化を示す。
【００６０】
供試材
実施例１と同様にして、Zn電気めっき鋼板の両面のめっき面上に第１層の樹脂被膜を形成した。使用した処理液は、ウレタン系熱可塑性水系樹脂液に樹脂固形分との合計量に対して15重量％のコロイダルシリカ (実施例１で使用したものと同じ) を混合したものであり (金属粉とリン酸化合物は含有せず) 、膜厚は0.2 μｍであった。
【００６１】
その後、内面を想定した片面 (第１面) に、第２層をバーコート法により形成した。第２層形成用の処理液は、表３に示す内面第２層用の材料 (熱硬化性または熱可塑性樹脂と金属粉と場合によりリン化鉄) を適宜組合わせたものであり、いずれも溶剤系の樹脂液に金属粉と場合によりリン化鉄を添加しして十分に懸濁させることにより調製した。塗布後は200 ℃で焼付けを行った。処理液の組成と内面第２層の膜厚は表４に示した通りである。
【００６２】
【表３】
評価方法
各供試材について、内面側の性能、即ち、内面耐食性、溶接性、成形性を実施例１と同様の方法で評価した。試験結果を表４に一緒に示す。
【００６４】
【表４−１】
【表４−２】
表４の結果から、内面の表面にNi粉およびAl粉を含有した樹脂被膜を設けることにより、燃料容器用鋼板として優れた内面耐食性を有し、他の性能面も良好な表面処理鋼板を得られることがわかる。但し、表２の試験No.1からわかるように、第２層単独では内面耐食性は悪く、本発明の第１層の上にこの第２層を形成することで初めて良好な内面耐食性が得られる。内面耐食性は、第２層被覆の樹脂が熱可塑性樹脂 (Ｅ')になるとやや低下した。
【００６７】
（実施例３）
本実施例は、外面側に第２層を施した場合の該第２層の組成変動による表面処理鋼板の性能の変化を示す。
【００６８】
供試材
実施例１と同様にして、Zn電気めっき鋼板の両面のめっき面上に第１層の樹脂被膜を形成した。使用した処理液は、実施例２と同じもの、即ち、ウレタン系熱可塑性水系樹脂液に樹脂固形分との合計量に対して15重量％のコロイダルシリカ (実施例１と同じ) を混合したものであり (金属粉とリン酸化合物は含有せず) 、膜厚は0.2 μｍであった。
【００６９】
その後、内面への第２層の形成は省略し、外面を想定した片面 (第２面) に、第２層をバーコート法により形成した。第２層形成用の処理液は、表５に示す外面第２層用の材料 (非脱膜性の熱可塑性もしくは熱硬化性樹脂と金属粉) を適宜組合わせたものからなり、いずれも水系の樹脂液に金属粉を添加しして十分に懸濁させることにより調製した。塗布後の焼付けは、樹脂が熱可塑性の場合は100 ℃、樹脂が熱硬化性の場合は220 ℃で行った。処理液の組成と内面第２層の膜厚は表６に示した通りである。
【００７０】
【表５】
評価方法
各供試材について、外面側の性能、即ち、後塗装性、溶接性、ハンダ付け／ロウ付け性、成形性を実施例１と同様の方法で評価した。但し、成形性は、外面第２層の形成により向上しているため、特に絞り側壁部の型カジリが小さいものを「◎＋」と評価した。試験結果を表６に一緒に示す。
【００７２】
【表６】
表６に示した結果より、外面に熱可塑性樹脂被膜を設けることにより、成形性が非常に優れた燃料容器用鋼板として優れた表面処理鋼板を得られることがわかる。
【００７４】
【発明の効果】
本発明により、入手の容易なZn系めっき鋼板を母材として、自動車のガソリン燃料用燃料タンクとして内外両面の諸性能 (例えば、劣化ガソリンに対しても良好な内面耐食性、外面用塗料との密着性、塗装後の耐食性、ハンダ付け性、ロウ付け性、溶接性、成形加工性) にすぐれた表面処理鋼板を提供することが可能になる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface-treated steel sheet suitable for use as a material for a fuel container, in particular, a fuel tank of an automobile using gasoline as fuel.
[0002]
[Prior art]
Pb-Sn alloy-plated steel plates called turn plating have been widely used for general automotive fuel tank applications that use gasoline as fuel, but materials that do not contain Pb have been demanded from environmental issues. . Further, with respect to the corrosion resistance to fuel, a higher level is required, for example, corrosion resistance to deteriorated gasoline containing an organic acid is required.
[0003]
In response to this demand, Al-plated steel plates (for example, Japanese Patent Laid-Open No. 10-46358), Sn-Zn alloy-plated steel plates (for example, Japanese Patent Laid-Open No. 8-269733) have been developed as alternatives. Among these, the Al-plated steel sheet has a problem in joining properties such as welding and soldering, and a processing manufacturer or the like desires a material that is easier to use than can be easily joined. On the other hand, Sn—approx. 8% Zn alloy-plated steel sheet is said to have a good balance of performance, but the use of this alloy plating is almost limited to fuel tanks, so production in small lots, stable supply and There is a price problem. In this respect, it is advantageous if Zn-based plating (Zn plating and Zn alloy plating) which is widely used can be applied to automobile fuel tank applications.
[0004]
As a conventional technique in which a Zn-based plated steel sheet is applied to an automotive fuel tank, JP-A-10-137681 discloses a resin containing Ni and Al metal powder on the inner surface side of a Zn-based plated steel sheet on the outer surface side. A surface-treated steel sheet coated with a resin containing wax has been proposed.
[0005]
However, this surface-treated steel sheet is obtained by applying the above resin after chromate treatment of a Zn-based plated steel sheet, and chromate treatment is essential. The chromate film formed by the chromate treatment contains hexavalent chromium as described in this publication. However, recently, due to environmental problems, there is an increasing demand for materials that do not contain hexavalent chromium. Therefore, there is an urgent need to develop a surface-treated steel sheet for automobile fuel tanks that does not contain hexavalent chromium (that is, does not use chromate treatment).
[0006]
However, the fuel tank is an important safety part of an automobile and requires high corrosion resistance against fuel. In the case of surface-treated steel sheets based on Zn-plated steel sheets, chromate treatment containing hexavalent chromium is extremely effective in ensuring corrosion resistance. Therefore, chromate treatment is required for applications that require high corrosion resistance. It was normal. Therefore, it is not easy to obtain a material for an automobile fuel tank having a good performance balance without containing hexavalent chromium.
[0007]
[Problems to be solved by the invention]
The performance required for the automobile fuel tank differs between the inner surface side and the outer surface side of the tank. On the inner surface side of the tank, the corrosion resistance to the gasoline environment, particularly deteriorated gasoline containing an organic acid such as formic acid is most important. On the other hand, characteristics required for the outer surface include solderability, post-coating property at a processing manufacturer, corrosion resistance after painting, weldability, and the like.
[0008]
The present invention provides a surface-treated steel sheet suitable for an automobile fuel tank that satisfies the required characteristics on the inner surface side and outer surface side of such a tank without containing lead and hexavalent chromium which are problematic in terms of environment. Is an issue. Specifically, it is to develop a surface-treated steel sheet that satisfies the above-mentioned required characteristics without using a chromate treatment using a Zn-based plated steel sheet as a base material.
[0009]
[Means for Solving the Problems]
As a result of studying to obtain characteristics required for a steel plate for an automobile fuel tank without performing chromate treatment using the Zn or Zn-based alloy plated steel plate as a base material, the present inventors have found that this Zn-based plated steel plate After forming a thin first layer mainly composed of a silicate compound and a resin on both plating surfaces, one side which is the inner surface of the fuel tank further contains a metal powder containing Ni and Al thereon. A fuel that satisfies the above-mentioned required characteristics by providing a relatively thick resin coating layer to ensure the corrosion resistance of the inner surface, while the other surface that is the outer surface remains the first layer, or by further forming a thin thermoplastic resin layer It discovered that the surface-treated steel plate for containers was obtained.
[0010]
“Here, the present invention relates to a 0.05 to 2 μm-thick first layer formed from a treatment liquid containing a resin and a silicate compound as main film forming components on both surfaces of a Zn or Zn-based alloy double-side plated steel sheet. A second layer having a thickness of 2 to 10 μm formed of a resin coating containing metal powder containing Ni and Al is formed on one side (hereinafter referred to as the first side). The proportion of the metal powder in the two layers is in the range of 5 to 150 parts by weight with respect to 100 parts by weight of the total components other than the metal powder.There is a second layer made of a thermoplastic resin as the upper layer of the first layer on the surface opposite to the first surface (hereinafter referred to as the second surface), and the total thickness with the first layer is 2 μm or less. It is formed with thicknessThis is a surface-treated steel sheet for fuel containers. "
[0011]
The surface-treated steel sheet of the present invention is very suitable for fuel tanks for automobiles, especially gasoline fuel tanks, but also for fuel containers other than automobiles (e.g., fuel tanks for motorcycles, tractors, etc., portable fuel tanks, etc.). Needless to say, it can be used.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Base metal plated steel plate
The plated steel sheet may be a general cold-rolled steel sheet that is usually used. However, fuel tank applications are generally subjected to severe forming processes, so for example, steel sheets with excellent press formability such as ultra-low carbon steel and component systems to which one or more of Ti, Nb and B are added. Some are preferred.
[0013]
The plating applied to the steel sheet is Zn or Zn alloy plating widely used for the purpose of ensuring corrosion resistance. The plating type is not limited to these, for example, Zn, Zn-Al, Zn-Al-Si, Zn-Ni, Zn-Fe, Zn-Cr, Zn-Mg, Zn-Sn, Zn -Co and the like. The plating method may be any one of a hot dipping method, an electroplating method, a vapor deposition plating method, and the like. The plating film may contain a small amount of an organic compound such as an organic inhibitor, dextrin, or dextran. The coating weight is 10 g / m per side from the viewpoint of corrosion resistance.2The above is preferable. If the adhesion amount is too large, there will be a problem in terms of cost and workability. More preferable adhesion amount is 15-100 g / m per side2It is.
[0014]
1st layer
The performance required for this layer includes adhesion to the second layer on the inner surface and corrosion resistance to fuel, particularly deteriorated fuel containing organic acids, adhesion to the outer surface coating applied by the processing manufacturer on the outer surface, painting Later corrosion resistance and bondability (solderability, brazeability, weldability, etc.).
[0015]
In order to satisfy all these requirements, in the present invention, the first layer formed on the surface of the Zn-plated steel sheet is formed from a treatment liquid containing a silicate compound and a resin as a main film-forming component. It is set as this film. Thus, the first layer can be formed from the same material on both the inner surface and the outer surface. The formation of the first layer may be performed by applying a treatment liquid to both surfaces of the base material plated steel sheet and drying (or baking) the coating film according to a conventional method.
[0016]
By including the resin in the first layer, adhesion with the resin of the inner surface second layer, the outer surface second layer, or the resin of the outer surface coating is ensured. With the resin component alone, the inner and outer surfaces need to be considerably thicker in order to obtain the necessary corrosion resistance, which is disadvantageous for the weldability, solderability, and brazing properties of the outer surface. Therefore, in order to ensure corrosion resistance with the thin film, a silicate compound is added to the resin. Coexistence of a silicate compound in the resin improves the corrosion resistance of the film because a -Si-O- siloxane bond is formed in the film, forming a crosslinked structure with the resin, or entangled with the polymer molecules of the resin. This is probably because the film can be densified. Therefore, since corrosion resistance is obtained even with a thin film, weldability, brazeability, and solderability can be simultaneously ensured.
[0017]
The film thickness of the first layer is in the range of 0.05 to 2 μm. If it is thinner than 0.05 μm, the inner and outer surfaces are inferior in corrosion resistance, and if it is thicker than 2 μm, the weldability, brazing property and solderability are inferior. A preferred range is 0.1 to 0.5 μm. The film thickness of the first layer may be the same on the inner surface and the outer surface or may be different. For example, when the second layer is not provided on the outer surface, the first layer on the outer surface may be thicker than the inner surface, and conversely, when the second layer is provided on the outer surface, the first layer on the outer surface is made thinner than the inner surface. May be. Although not necessary, the film composition of the first layer can be changed between the inner surface and the outer surface within the scope of the present invention.
[0018]
As the silicic acid compound used for forming the first layer, one or more of colloidal silica, dry silica, alkali metal silicate, silane coupling agent, and silicic acid alkyl ester can be used.
[0019]
Here, the silane coupling agent is n (n = 2 to 3) hydrolyzable groups per silicon atom (typically an alkoxy group, particularly a methoxy group or an ethoxy group, but may be chlorine. ) And (n-1) non-hydrolyzable organic groups (for example, lower alkyl groups such as ethyl and propyl, lower alkyl groups containing functional substituents such as amino and epoxy, vinyl groups, etc.) It is a bound compound. Preferred as the silane coupling agent used in the first layer in the present invention is one in which the non-hydrolyzable organic group is an alkyl group, such as ethyltrimethoxysilane, propyltrimethoxysilane, and ethyltriethoxysilane. . These are not often used as silane coupling agents, but are included in the silane coupling agents in the present invention. Silicic acid alkyl ester is a compound in which an alkoxy group is bonded to silicon, and is typically tetraalkoxysilane (= alkyl silicate) (eg, ethyl silicate).
[0020]
The silane coupling agent undergoes hydrolysis and polycondensation in the treatment liquid or coating film to become a polysiloxane type polymer. Silicic acid alkyl esters are similarly subjected to hydrolysis and polycondensation, and finally become silica. Therefore, the above-mentioned silicic acid compound is a compound that can form a siliceous film or a film having a polysiloxane structure in which a part of organic components remain.
[0021]
The resin component of the first layer is preferably a thermoplastic resin having one or more of hydroxyl group, carboxyl group, amino group, glycidyl group, isocyanate group and the like from the viewpoint of adhesion with the second layer. Examples of the resin system include urethane, acrylic, polyester, epoxy, melamine resin, and alkyd resin. The treatment liquid may be a solvent system using an organic solvent, but from the viewpoint of the working environment, an aqueous treatment liquid using a water-soluble or water-dispersible resin is desirable. In the case of an aqueous processing solution, dry silica is not very good in dispersibility in an aqueous system, and other silicic acid compounds are preferable.
[0022]
The weight ratio between the silicic acid compound and the resin is preferably 5:95 to 80:20. When there is too much resin, it is inferior to corrosion resistance as mentioned above. On the other hand, if the silicate compound is too much, the corrosion resistance of the flat plate is considerably good even in the thin film, but the corrosion resistance of the processed material or the collar portion is inferior to that of the resin alone. Moreover, the film | membrane of a silicate compound has strong hydrophilicity, and is disadvantageous also for the secondary adhesiveness after coating. A more preferable range of the weight ratio is 10:90 to 75:25.
[0023]
When a phosphoric acid compound is contained in the first layer, it is effective for improving the corrosion resistance. However, if the content is too large, the adhesiveness to the second layer is disadvantageous, so the P / Si atomic ratio is contained within a range of 2 or less. The atomic ratio of P / Si is preferably in the range of 0.1 to 1.5. Examples of the phosphoric acid compound include phosphoric acid, phosphorous acid, hypophosphorous acid, and alkali metal salts thereof, and one or more of them can be used.
[0024]
Further, in order to improve performance such as corrosion resistance, a trivalent chromium compound, molybdic acid or the like that is known to have such effects may be contained in the first layer. Further, coloring pigments, rust preventive pigments, conductive pigments, surfactants, and the like may be contained in the first layer as long as the various performances targeted by the present invention are not significantly impaired. Moreover, in order to improve the reactivity with the surface of the base plating, a hydrofluoric acid compound such as fluorinated silicon acid or fluorinated titanic acid can be contained in the first layer. However, lead and hexavalent chromium are not included except for unavoidable mixing because of environmental problems.
[0025]
From the viewpoint of improving weldability, the first layer may further contain a metal powder or a conductive pigment (hereinafter simply referred to as a metal powder). Examples of the metal powder include Zn, Ni, Al, Sn, alloys of these metals, stainless steel, iron phosphide, ferrosilicon, and the like. The metal powder content in the first layer is in the range of 5 to 150 parts by weight, preferably 20 to 80 parts by weight with respect to 100 parts by weight of the total amount of components other than the metal powder. If the amount is less than 5 parts by weight, the weldability improvement effect is not recognized. If the amount exceeds 150 parts by weight, the fluidity of the treatment liquid decreases, and it becomes difficult to form a film on the plated surface, or molding after the film is formed. This is because powdering occurs during processing.
[0026]
The size and shape of the metal powder is preferably a scaly shape having a particle size of not more than 3 times the film thickness of the first layer or a diameter of about 10 μm or less because of powdering problems during molding.
[0027]
2nd layer ( Inside )
If the inner surface of the fuel container (tank) is only the first layer, the corrosion resistance to the deteriorated gasoline is not sufficient, and the weldability is also insufficient. Therefore, a second layer is further formed on the first layer on one side (the first side in the claims) which is the inner surface of the surface-treated steel sheet of the present invention. This second layer may also be formed by applying a treatment liquid and drying or baking.
[0028]
The performance required for the second layer is corrosion resistance in the gasoline environment on the inner surface, adhesion with the first layer, and weldability. In order to satisfy these performances, the second layer is a resin film having a thickness of 2 to 10 μm containing metal powder containing Ni and Al. This metal powder may be a combination of Ni powder, Al powder, and Ni-Al alloy powder as appropriate.
[0029]
Of the metal powders that can be present in the coating, Ni powder is added mainly for the purpose of improving weldability. Weldability is improved by increasing the conductivity of the coating, but Ni has been found to be optimal in terms of both corrosion resistance and conductivity. On the other hand, Al powder is added mainly for the purpose of improving corrosion resistance. Particularly when gasoline deteriorates, organic acids such as formic acid and acetic acid are generated, and the corrosiveness of the gasoline environment becomes more severe. In such an environment, Al powder is particularly effective. In addition, the addition of Al powder also has an effect of improving weldability to some extent, but it has been found that the weldability is greatly improved by the addition of Ni powder or the addition of Ni-Al alloy. Therefore, the second layer contains metal powder containing Ni and Al, for example, a mixture of Ni powder and Al powder, or Ni—Al alloy powder.
[0030]
The blending amount of the metal powder in the second layer is preferably such that the total amount of the metal powder is within the range of 5 to 150 parts by weight with respect to the total of 100 parts by weight of the components other than the metal powder in the second layer. . If the total amount of the metal powder is less than 5 parts by weight, the weldability is inferior, and if it exceeds 150 parts by weight, uniform application due to a decrease in the fluidity of the treatment liquid becomes very difficult, and the metal during press formability after coating is formed. This causes detachment of the powder.
[0031]
The weight ratio of Ni and Al in the metal powder is preferably in the range of Ni: Al = 10: 90 to 95: 5. From the balance of corrosion resistance and weldability, the range of Ni: Al = 30: 70 to 90:10 Is more preferable. When Al is added alone, the effect of improving corrosion resistance, which seems to be due to the reaction between Al and organic acid, is exhibited, but the effect of improving weldability is small. Further, when adding iron phosphide or ferrosilicon as will be described later, corrosion resistance deteriorates if Ni is not contained. On the other hand, the addition of Ni alone has an effect of improving weldability, but has a small effect of improving corrosion resistance in a gasoline environment.
[0032]
The resin in the second layer desirably exhibits a barrier effect in addition to serving as a binder for the metal powder, and therefore the resin itself is less likely to dissolve, swell or permeate the gasoline component.
[0033]
For this purpose, a thermosetting resin is more suitable than a thermoplastic resin. Specific examples of suitable thermosetting resins include epoxy-based, acrylic-based, urethane-based, polyester-based and phenol-based resins, and urethane-modified epoxy resins are particularly preferable. The urethane-modified epoxy resin is obtained by reacting an epoxy resin with an aliphatic dibasic acid to introduce a carboxylic acid group, and further reacting diisocyanate to introduce a urethane group. The molecular weight of this resin before film formation is preferably in the range of 5000 to 50,000. If the molecular weight is lower than this, it easily swells with respect to gasoline, and if it has a high molecular weight, besides being difficult to obtain industrially, the viscosity of the treatment liquid becomes too high and the productivity is lowered. The combination of this urethane-modified epoxy resin and Ni powder and / or Al powder had the best corrosion resistance in a gasoline environment. The resin liquid used for film formation may be aqueous or solvent-based, but is usually solvent-based.
[0034]
The film thickness of the second layer made of the metal powder-containing resin coating is 2 to 10 μm, preferably 3 to 5 μm. If the film thickness is thinner than 2 μm, the corrosion resistance in a gasoline environment is deteriorated. If it is thicker than 10 μm, the effect is saturated and the cost is increased, and weldability and powdering properties at the time of forming are disadvantageous.
[0035]
The size of the metal powder of the second layer is preferably in the range of 0.5 to 10 μm in the case of Ni powder or Ni-Al alloy powder, and is 5 to 100% of the film thickness when the film thickness of the second layer is 5 μm or more. A range is more preferable. If the metal powder is too small, the conductivity of the second layer is lowered, and if it is too large, the distance between the metal powders is increased at the overlapping portion during welding, and the weldability is lowered in both cases. The size of the Al powder is not particularly limited from the viewpoint of improving the corrosion resistance by chemical action. However, as described in JP-A-10-137681, a scaly shape having a major axis of about 10 to 20 μm is considered preferable because a physical shielding effect against gasoline permeation can be expected.
[0036]
The second layer may contain other components in addition to the resin and the metal powder. Examples of such other components include color pigments, rust preventive pigments, conductive pigments, silica, silane coupling agents, and the like, and can be contained in the second layer within a range that does not impair the required performance of the second layer. . In particular, when the weldability is important, the weldability is remarkably improved if iron phosphide or ferrosilicon is contained as the conductive pigment. However, if the content is too large, the corrosion resistance deteriorates, so the content is preferably 10% by weight or less. Due to environmental problems, lead and hexavalent chromium are not included except for unavoidable mixing.
[0037]
2nd layer ( Exterior )
In the surface-treated steel sheet according to the present invention, for the outer surface (second surface in the claims), a predetermined performance can be obtained only by the first layer, and therefore the second layer on the outer surface is not particularly required. However, in automobile fuel tank applications, since usually severe molding is performed, it is desirable to have a lubricating coating or a protective coating on the outer surface of the tank for the purpose of preventing damage to the first layer. This film is preferably a film that can be removed by a degreasing process using a solvent, alkali, or the like, or, in the case of a non-film-removable film, a film that satisfies the following conditions.
[0038]
That is, in the case of a non-delaminating film, although it works advantageously for protecting the first layer, which is the lower layer, and improving its corrosion resistance, it works against weldability, solderability and brazing. Therefore, the resin system is desirably a thermoplastic resin that is easily deformed during welding, soldering, or brazing, and the film thickness is desirably 2 μm or less, including the first layer. When the second layer is provided on the outer surface, the more desirable film thickness of the second layer is in the range of 0.3 to 2 μm, but it is 2 μm or less together with the first layer.
[0039]
The resin film of the second layer on the outer surface also contains Zn, Ni, Al, Sn, and an alloy between these metals, as well as stainless steel, iron phosphide, ferrosilicon, etc., as in the first layer. One type or two or more types of metal powder are contained in a ratio of 5 to 150 parts by weight, preferably 20 to 80 parts by weight, with respect to 100 parts by weight of the total amount of components other than the metal powder. Solderability can also be improved. Further, the resin coating of the second layer may contain fluororesin particles or polyolefin wax as a lubricating component as long as the paint adhesion of the outer surface is ensured, and is rather desirable for improving the molding processability. Further, silica or a silane coupling agent may be included for improving the corrosion resistance.
[0040]
In addition, it is not always necessary to apply rust-preventing oil to the inner and outer surfaces of the surface-treated steel sheet according to the present invention, or to apply lubricating oil during forming processing, but rust prevention during storage and lubricity during forming This is desirable.
[0041]
【Example】
(Example 1)
This example shows changes in the performance of the surface-treated steel sheet when the composition of the first layer is varied.
[0042]
Specimen
10.8 mm thick electric Zn-13% Ni alloy plated steel sheet (double-sided plating, plating coverage: 30 g / m per side)2) Is cut into 250 mm × 310 mm, and the materials for the first layer shown in Table 1 (resin, silicic acid compound, and in some cases, phosphoric acid compound and metal powder) are appropriately combined and mixed (metal powder) The first layer was formed on both sides using an aqueous processing solution prepared by adding the final solution to make it fully suspended. The first layer was formed by applying the treatment liquid one side at a time by a bar coating method and drying at 100 ° C. The composition of the treatment liquid and the film thickness of the first layer are as shown in Table 2.
[0043]
[Table 1]
Thereafter, the second layer was formed on one surface (first surface) assuming the inner surface by the bar coating method in the same manner as described above. The treatment liquid for forming the second layer is a thermosetting urethane-modified epoxy resin (solvent-based resin liquid, average molecular weight 20,000), and 23 weight parts of Ni powder having an average particle diameter of 1 μm per 100 parts by weight of resin solid content in the resin liquid. And 31 parts by weight of flaky Al powder having an average particle size of 14 μm were suspended. The coating was performed so that the dry film thickness was 5 μm, and baked at 220 ° C. after coating.
[0045]
Regarding the surface-treated steel sheet in which the obtained one side (inner side) is a two-layer resin coating of the first layer and the second layer (the surface is the second layer) and the other side (outer side) is a resin coating of only the first layer. The performance of both the inside and outside was evaluated by the following method. The test results are also shown in Table 2.
[0046]
Evaluation methods
(1) Internal corrosion resistance
Cup drawing is performed under the drawing conditions described below so that the surface of the second layer is the inner surface. The resulting cup is sealed with 10 cc of 3000 ppm formic acid aqueous solution and 20 cc of gasoline and kept at 50 ° C. did. The evaluation was made as follows according to the state of corrosion products (liquid mist) after 20 days (accepted up to ○).
[0047]
◎: Almost no change
○: 10-40% dust generated from above,
△: 40% to 70% fog generated when viewed from above (observation of bottom surface is quite difficult),
X: Red rust floats almost throughout the liquid (observation of the bottom and sides is quite difficult), or peeling or swelling of the inner surface resin is observed from the cut part and others.
[0048]
(Aperture condition) Blank 100 mm diameter
Punch 50 mm diameter-5R
Dice 52.5 mm Diameter-5R
Aperture height 25 mm
Use lubricating oil, alkali degreasing after drawing.
[0049]
(2) Post-paintability
(Hot water adhesion)
After the surface of the first layer was lightly alkaline degreased, Oderak 9200TS Black made by Nippon Paint was applied to the thickness of about 20 μm as an external coating. Then, after dipping in warm water of 40 ° C. for 10 days, a cross cut was immediately made, and further, 7 mm overhang was conducted with Erichsen, and the tape peeling state of the overhang portion was investigated.
[0050]
○: No peeling
Δ: Peeling at minute blister
X: Large peeling
(Corrosion resistance after painting)
After applying the outer surface paint in the same manner as described above, a cross cut was made, and further, 7 mm was overhanged with Erichsen, and subjected to a JIS Z2371 salt spray test. The evaluation was conducted based on rust generation after 480 hours.
[0051]
A: No occurrence of red rust
○: 5% or less of red rust in the cut part
△: 〃 20% or less
×: 〃 More than 20%
(3) Soldering / brazing property
Two types of solder, solder and tartin Sn-Ag alloy and brass were investigated. The fluxes used were Tartin L305 (chlorine) and boric acid, respectively. Evaluation was carried out by placing solder 0.5 g and flux 0.5 cc on the outer surface of the test material, heating the Sn-Ag alloy solder system to 350 ° C. and the brass solder system to 800 ° C., and measuring the wet spread area after 2 minutes.
[0052]
○: Wet area is 100 mm2 more than
×: Wetting area is 100 mm2 Less than or not wet
(4) Resistance weldability
After stacking the two test materials with the inner surface of the second layer facing inside, spot welding was performed under the conditions of 300 kgf of pressure, 12 cycles of energization, and 8 kA of current, and the resistance between the electrodes in the first cycle was measured. And evaluated as follows (up to ○ passed).
[0053]
A: Resistance between electrodes is 300 μΩ or less
○: Interelectrode resistance is 300 μΩ or more,
Or mild dust generation
Δ: Much dust generation
×: Not energized (not weldable)
(5) Formability
About the test material which carried out cup draw molding similarly to having demonstrated the evaluation method of inner surface corrosion resistance, the peeling condition by the adhesive tape of the inner surface of a drawing inner surface was evaluated visually (up to (circle) passed).
[0054]
A: No peeling
○: The tape is slightly glittering
Δ: Clearly peeled on the tape
X: Peeling over almost the entire surface
[0055]
[Table 2-1]
[Table 2-2]
[Table 2-3]
As can be seen from the results in Table 2, a surface-treated steel sheet for a fuel container excellent in various performances can be obtained by using a coating mainly composed of a thermoplastic resin and a silicate compound as the first layer. When metal powder is contained in the coating, weldability and solderability are improved.
[0059]
(Example 2)
This example shows the change in the inner surface performance of the surface-treated steel sheet when the composition of the second layer applied to the inner surface side is varied.
[0060]
Specimen
In the same manner as in Example 1, a first-layer resin film was formed on both surfaces of the Zn electroplated steel sheet. The treatment liquid used was a mixture of urethane-based thermoplastic water-based resin liquid with 15% by weight of colloidal silica (the same as that used in Example 1) based on the total amount of resin solids (metal powder). And no phosphoric acid compound), and the film thickness was 0.2 μm.
[0061]
Thereafter, the second layer was formed on one side (first side) assuming the inner surface by a bar coating method. The treatment liquid for forming the second layer is an appropriate combination of the materials for the inner surface second layer shown in Table 3 (thermosetting or thermoplastic resin and metal powder and optionally iron phosphide). It was prepared by adding metal powder and optionally iron phosphide to a solvent-based resin solution and sufficiently suspending it. After application, baking was performed at 200 ° C. The composition of the treatment liquid and the film thickness of the inner surface second layer are as shown in Table 4.
[0062]
[Table 3]
Evaluation methods
For each specimen, the performance on the inner surface side, that is, the inner surface corrosion resistance, weldability, and formability were evaluated in the same manner as in Example 1. The test results are shown together in Table 4.
[0064]
[Table 4-1]
[Table 4-2]
From the results of Table 4, by providing a resin coating containing Ni powder and Al powder on the inner surface, a surface-treated steel sheet having excellent inner surface corrosion resistance as a steel plate for a fuel container and having other excellent performance surfaces is obtained. I understand that However, as can be seen from Test No. 1 in Table 2, the internal corrosion resistance of the second layer alone is poor, and good internal corrosion resistance can be obtained only by forming the second layer on the first layer of the present invention. . The inner surface corrosion resistance was slightly lowered when the resin of the second layer coating became a thermoplastic resin (E ′).
[0067]
(Example 3)
This example shows the change in the performance of the surface-treated steel sheet due to the composition variation of the second layer when the second layer is applied to the outer surface side.
[0068]
Specimen
In the same manner as in Example 1, a first-layer resin film was formed on both surfaces of the Zn electroplated steel sheet. The treatment liquid used was the same as in Example 2, ie, a mixture of urethane-based thermoplastic aqueous resin liquid and 15% by weight of colloidal silica (same as in Example 1) with respect to the total amount of resin solids. (The metal powder and phosphate compound were not contained), and the film thickness was 0.2 μm.
[0069]
Thereafter, the formation of the second layer on the inner surface was omitted, and the second layer was formed on one side (second surface) assuming the outer surface by a bar coating method. The treatment liquid for forming the second layer consists of an appropriate combination of the materials for the second layer of the outer surface shown in Table 5 (non-delaminating thermoplastic or thermosetting resin and metal powder), both of which are water-based It was prepared by adding metal powder to the resin solution and sufficiently suspending. Baking after application was performed at 100 ° C. when the resin was thermoplastic and at 220 ° C. when the resin was thermosetting. The composition of the treatment liquid and the film thickness of the inner surface second layer are as shown in Table 6.
[0070]
[Table 5]
Evaluation methods
About each test material, the performance on the outer surface side, that is, post-coating property, weldability, soldering / brazing property, and formability were evaluated in the same manner as in Example 1. However, since the moldability was improved by the formation of the second outer surface layer, the case where the mold side of the drawn side wall portion was small was evaluated as “◎ +”. The test results are shown together in Table 6.
[0072]
[Table 6]
From the results shown in Table 6, it can be seen that by providing a thermoplastic resin coating on the outer surface, it is possible to obtain a surface-treated steel sheet that is excellent as a steel sheet for a fuel container with very excellent formability.
[0074]
【The invention's effect】
According to the present invention, an easily available Zn-based plated steel sheet is used as a base material, and various performances on both the inside and outside of a fuel tank for gasoline fuel for automobiles (for example, good inner surface corrosion resistance against deteriorated gasoline, adhesion to outer surface paints) It is possible to provide a surface-treated steel sheet having excellent properties, corrosion resistance after painting, solderability, brazing, weldability, and formability.
Claims (5)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30269498A JP3835017B2 (en) | 1998-10-23 | 1998-10-23 | Zn-plated surface-treated steel sheet for fuel containers |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30269498A JP3835017B2 (en) | 1998-10-23 | 1998-10-23 | Zn-plated surface-treated steel sheet for fuel containers |
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| Publication Number | Publication Date |
|---|---|
| JP2000129461A JP2000129461A (en) | 2000-05-09 |
| JP3835017B2 true JP3835017B2 (en) | 2006-10-18 |
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| JP30269498A Expired - Fee Related JP3835017B2 (en) | 1998-10-23 | 1998-10-23 | Zn-plated surface-treated steel sheet for fuel containers |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2002254555A (en) * | 2001-03-01 | 2002-09-11 | Nippon Steel Corp | Metallic material with treated surface showing superb corrosion resistance |
| KR100447599B1 (en) * | 2001-12-21 | 2004-09-07 | 주식회사 포스코 | Chromium-Free Surface Treatment Composition for Galvanized Steel |
| KR101091276B1 (en) * | 2004-12-28 | 2011-12-07 | 주식회사 포스코 | Chromium Free Solution for Treating Steel Sheet of Automobile Fuel Tank with Excellent Corrosion Resistance and Anti-Fuel Property and Steel Sheet Treated Therewith |
| KR100931241B1 (en) | 2007-12-17 | 2009-12-10 | 주식회사 포스코 | Chrome-free treatment liquid of baffle fuel tank steel plate with excellent boiling resistance and corrosion resistance, manufacturing method of baffle fuel tank steel plate using the same and baffle fuel tank steel plate |
| KR101132668B1 (en) | 2009-12-30 | 2012-04-03 | 주식회사 포스코 | Steel sheet having superior heat-resistance, chemical resistance, thermo-conductivity, heat emissivity and adhesiveness |
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1998
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