JP3643473B2

JP3643473B2 - Surface-treated steel sheet with excellent high-speed seam weldability, adhesion, and corrosion resistance, and its manufacturing method

Info

Publication number: JP3643473B2
Application number: JP01300598A
Authority: JP
Inventors: 伸一山口; 茂平野; 和成長谷川
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1998-01-26
Filing date: 1998-01-26
Publication date: 2005-04-27
Anticipated expiration: 2018-01-26
Also published as: JPH11209894A

Description

【０００１】
【発明の属する技術分野】
本発明は、錫系めっき鋼板に塗料密着性及び耐食性及び溶接性に優れた化学処理被膜を形成させる方法に関するものである。
【０００２】
【従来の技術】
錫めっき鋼板は、缶詰、乾電池など種々の金属容器用の材料として広く使用されているが、近年錫の付着量を低減し、缶内外に塗装を施して耐食性を確保するという使われ方が増加している。この場合塗膜密着性の良否が耐食性を左右する重要な因子となる。錫めっき鋼板の塗膜密着性を高める方法として硫酸、フッ素化合物などを助剤として含有する無水クロム酸系処理浴中で陰極電解することにより、金属クロム（以後Ｍｅ−Ｃｒという）と水和酸化クロム（以後Ｏｘ−Ｃｒという）からなる被膜を形成させる方法が知られているが、単に無水クロム酸系浴中で陰極電解処理を行っただけでは下記のような問題点がある。
【０００３】
すなわち、塗料密着性向上を得るのに必要なＭｅ−Ｃｒ量を生成させた場合、同時に生成するＯｘ−Ｃｒ量が多くなり過ぎる傾向にあり、シーム溶接性を損なうとともに、Ｏｘ−Ｃｒ生成量の不均一による外観ムラが生じやすい。
この問題を解決するために、Ｏｘ−Ｃｒ量の低減及びこれに伴う半田性、溶接性、外観均一性、塗料密着性の向上効果をもたらす技術として特開昭６１−１２８９６号公報では通常より硫酸根含有率の低い低濃度無水クロム酸水溶液中での陰極電解処理に引き続いて、比較的高濃度の無水クロム酸水溶液への浸漬処理を行う処理法を発明している。確かにこのような発明による製造方法は、半田性、溶接性、外観均一性、塗料密着性の向上効果をもたらす。
【０００４】
【発明が解決しようとする課題】
しかしながら、この製造方法の無水クロム酸系浴中において電解で生成したＯｘ−Ｃｒは溶解速度が遅く、かつ浴組成の全く異なる２種類の浴を必要とするため、連続製造ラインでのラインスピード低下、厳格浴濃度管理等の操業上の制約が伴うので連続製造ラインでの操業は困難である。
そこで、発明者らは鋭意検討した結果、請求項記載の無水クロム酸系浴での高電流密度電解によって生成するＭｅ−Ｃｒ、Ｏｘ−Ｃｒの被覆性は共に良好で、さらに電解浴温度を低下するほどＯｘ−Ｃｒ量は増加するものの、このとき生成したＯｘ−Ｃｒ被膜中上層のオール型Ｏｘ−Ｃｒは硫酸イオンの共析量が多いため溶解性の高く、電解した後高温のクロム酸浴に浸漬することで容易に溶解することができ、また、このとき残留したＯｘ−Ｃｒはオキソ化度〔ＯＣｒＯ／（ＯＣｒＯ＋ＨＯＣｒＯＨ）〕の高い密着性に優れた被膜であることを明らかにした。
【０００５】
すなわち、本発明は所定の浴組成、低温浴での高電流密度による電解によるＭｅ−Ｃｒの被覆性向上及び高温浴での浸漬処理により効率的なＯｘ−Ｃｒの低減により、半田性、溶接性、外観均一性の向上、連続製造ラインでの生産性向上を図り、さらに塗料密着性に対しても著しい効果をもたらす錫系めっき鋼板の化学処理方法を提供することを目的としている。
【０００６】
【課題を解決するための手段】
本発明の要旨は次の通りである。
（１）錫系めっき鋼板に３５〜２００ｇ／ｌのＣｒＯ ₃ 及びＣｒＯ ₃ との重量比で１／５０〜１／２００のＨ ₂ ＳＯ ₄ を含有し残部水及び不可避的不純物からなる浴温４５℃未満の陰極電解処理浴中で陰極電解を行い、引き続いて３５〜２００ｇ／ｌのＣｒＯ ₃ を含有し残部水及び不可避的不純物からなる浴温４５℃以上の浸漬処理浴中で浸漬処理を行い、錫系めっき鋼板表面に０．５〜２０ｍｇ／ｍ ² の金属クロム層を形成し、その表面にさらに金属クロム換算で０．５〜１５ｍｇ／ｍ ² でかつオキソ化合物の割合が０．６以上であるオキサイドクロム層を形成することを特徴とする高速シーム溶接性、耐食性、密着性に優れた表面処理鋼板の製造方法。
【０００７】
（２）浸漬処理浴中にＣｒＯ ₃ との重量比で１／５０〜１／２００のＨ ₂ ＳＯ ₄ 及び不可避的不純物を含むことを特徴とする前記（１）に記載の高速シーム溶接性、耐食性、密着性に優れた表面処理鋼板の製造方法。
【０００８】
（３）陰極電解処理浴中において２０Ａ／ｄｍ²以上の電流密度で陰極電解を行うことを特徴とする前記（１）〜（２）に記載の高速シーム溶接性、耐食性、密着性に優れた表面処理鋼板の製造方法。
（４）錫系めっき鋼板に、予め酸性浴中で陰極電解処理もしくは浸漬処理を行うことを特徴とする前記（１）〜（３）に記載の高速シーム溶接性、耐食性、密着性に優れた表面処理鋼板の製造方法。
【０００９】
（５）錫系めっき鋼板が、錫めっきの下地としてＦｅ−Ｎｉ合金めっき層を形成していることを特徴とする前記（１）〜（４）に記載の高速シーム溶接性、耐食性、密着性に優れた表面処理鋼板の製造方法。
（６）錫系めっき鋼板が、錫めっきの下地としてＮｉめっき層を形成していることを特徴とする前記（１）〜（４）に記載の高速シーム溶接性、耐食性、密着性に優れた表面処理鋼板の製造方法。
（７）錫めっき層を形成した後溶錫処理を行うことを特徴とする前記（５）〜（６）に記載の高速シーム溶接性、耐食性、密着性に優れた表面処理鋼板の製造方法にある。
【００１０】
以下、本発明をさらに詳細に説明する。
本発明において、錫系めっき鋼板とは一般に“ぶりき”と呼ばれる通常の錫めっき鋼板だけでなく、いわゆる溶接缶などの用途に用いられる錫付着量低減による耐食性低下を何らかの方法で補った種々の材料（すなわちＮｉなど錫以外の金属を含有させた錫系合金めっき鋼板、Ｎｉ、Ｆｅ−Ｎｉなどの下地めっき処理あるいは、Ｎｉめっきを施しさらに熱拡散処理を施した下地層上に薄目付錫めっきを施した錫系積層めっき鋼板など）が対象となり、これらのいずれに対しても本発明方法の適用が可能である。
【００１１】
錫系めっきを施した後、めっき表面の酸化物等を除去するために酸溶液中での陰極電解あるいは浸漬処理など表面活性処理を行うことが好ましい。ただし、ノーリフロー仕上げのめっきなど表面の活性なものに対してはこのような表面活性処理は行わなくてもかまわない。処理条件としては通常のぶりきで実施される条件と同一で良く、具体的には浴濃度２〜１０％硫酸、浴温３０〜８０℃の酸性浴に浸漬するか、あるいは前記酸性浴中で陰極電気量密度５ｃ／ｄｍ²程度以下の陰極電解処理を行えばよい。
【００１２】
上記の表面活性化処理及び水洗の後に、請求項記載の低温無水クロム酸系浴中で陰極電解処理及び同組成高温浴への浸漬処理によりＭｅ−ＣｒとＯｘ−Ｃｒからなる被膜を形成させるがその付着量はそれぞれ０．５〜２０ｍｇ／ｍ² 及び０．５〜１５ｍｇ／ｍ² （いづれも片面当たり）が望ましい。Ｍｅ−Ｃｒ０．５ｍｇ／ｍ² 未満あるいはＯｘ−Ｃｒ０．５ｍｇ／ｍ² 未満では十分な塗料密着性向上効果が得られず、Ｍｅ−Ｃｒの増大に伴って塗膜密着性は向上するが、Ｍｅ−Ｃｒ２０ｍｇ／ｍ² 超、もしくはＯｘ−Ｃｒ１５ｍｇ／ｍ² 超では効果が飽和すると共に、半田性、シーム溶接性に悪影響を与えるためである。
【００１３】
また、Ｏｘ−Ｃｒをさらに細かく分類するとオキソ化合物とオール化合物の２種類に分けられる。Ｏｘ−Ｃｒ最表層においてこのオール化合物の割合が増加すると塗料焼き付け時の脱水反応によるＯｘ−Ｃｒの体積収縮が起き、密着力を低下させる。そのため、Ｏｘ−Ｃｒ最表層では、ある一定割合以上オキソ化合物が必要となる。錫めっき上における上記のＣｒ付着量範囲ではＯｘ−Ｃｒ最表層のオキソ化度が０．６以上で優れた塗料密着性を示すことを見いだした。
【００１４】
上述のような低付着量のＭｅ−Ｃｒ被膜を生成させる場合、高電流密度での短時間処理が被膜の均一性に有効であり、２０Ａ／ｄｍ² 以上望ましくは３０Ａ／ｄｍ² 以上の高電流密度処理することが必要である。電流密度の上限は特に設けないが高くなりすぎると水素発生増大による電析効率の低下が見られるので１５０Ａ／ｄｍ² 以下で電解するのが望ましい。
このような、高電流密度で低付着量の均一なＭｅ−Ｃｒ被膜を形成させるためには、電解処理浴中に含まれるＣｒＯ₃濃度を３５ｇ／ｌ以上にする必要があり、あまり高すぎると電流効率の低下が生じるため２００ｇ／ｌを上限とする。より望ましくは７０〜１３０ｇ／ｌである。
【００１５】
処理浴への硫酸添加はＭｅ−Ｃｒの生成には不可欠であり、無水クロム酸に対する重量比（以下硫酸濃度比という）１／５０〜１／２００とする必要がある。硫酸濃度比は、高すぎても低すぎてもＭｅ−Ｃｒ電析効率が著しく低下するので、硫酸濃度比の下限は１／２００、上限は１／５０とする。
なお、上記処理浴はＯｘ−Ｃｒ析出助剤として、硫酸以外にケイフッ化ナトリウム、ホウフッ化ナトリウム、フッ化アンモニウムなどのフッ素化合物を含有してもかまわない。また、処理浴中への三価のクロムイオンの混入量が０．１〜５ｇ／ｌではクロメート被膜の均一化に効果があるので混入してもかまわない。
【００１６】
この発明の特に重要なポイントは電解させる浴を低温化させることである。Ｏｘ−Ｃｒは上層にオール型化合物、下層にオキソ型化合物の２層構造を呈しており、電解処理浴の低温下によりオール型及びオキソ型Ｏｘ−Ｃｒの析出量は増加するが、この際、上層のオール型Ｏｘ−Ｃｒ中への硫酸イオンの共析量が増加し、次工程でのオール型Ｏｘ−Ｃｒの溶解性が増す。そのため電解処理浴の浴温は４５℃未満が必要であり、望ましくは３５℃以下である。電解処理浴温の下限については特に設けないがあまり低すぎると強力な冷却器の設置が必要となり不経済であるため、１０℃を下限とするのが好ましい。
【００１７】
上記処理浴中での陰極電解処理に引き続いて、この陰極電解処理で過剰に生成したオキソ型Ｏｘ−Ｃｒ量の低減及び高オキソ化度のＯｘ−Ｃｒの形成による塗膜密着性の向上を目的とした無水クロム酸水溶液浸漬処理が行われる。オール型Ｏｘ−Ｃｒの溶解能力は浴中のクロム酸濃度、浴温および処理時間に影響される。無水クロム酸濃度３５ｇ／ｌ未満では余分なＯｘ−Ｃｒを溶解する能力が著しく低下するため、これ以上の濃度が必要であり、好ましくは７０ｇ／ｌ以上である。また、２００ｇ／ｌ超の高濃度とすると、エッチング作用が強すぎてオキソ型Ｏｘ−Ｃｒも溶解されるため塗料密着性、耐食性の低下につながることがある。そこで無水クロム酸濃度の上限を２００ｇ／ｌとする。
【００１８】
また、この浴中に硫酸イオンを添加することによりＯｘ−Ｃｒの溶解能力を向上させることができるので添加することが望ましい。硫酸濃度比が１／２００以上の添加からその効果が認められ、添加量の増加と共に溶解能力は向上する。しかし１／５０以上になるとその効果は一定になるので上限を１／５０、下限を１／２００とする。さらに、三価のクロムイオンやその他不可避的不純物が混入してもかまわないし、浸漬処理液は電解処理浴と同一組成でもかまわない。
【００１９】
浸漬処理液への浸漬時間は、必要Ｏｘ−Ｃｒ量で異なるため、特に設定しないが長時間浸漬するとエッチング作用が強すぎてオキソ型Ｏｘ−Ｃｒも溶解されるため塗料密着性、耐食性の低下につながることがある。
また、Ｏｘ−Ｃｒの溶解能力は浴温の上昇と共に増加し、効率的に溶解させるためには４５℃以上の浴温が必要であり、５５℃以上が望ましい。浴温の上限は特に規定しないが、あまり高温にすると浴のヒューム回収が大がかりとなり不経済であるため、７０℃を上限とするのが望ましい。
【００２０】
以下、本発明の実施例について説明する。
【実施例】
冷間圧延、焼鈍及び調質圧延を施した鋼板に、脱脂・酸洗したのちフェロスタン浴により片面当たり２．８ｇ／ｍ² の錫めっき及び加熱溶融処理を施した素材Ａ、および脱脂・酸洗したのちＦｅ−Ｎｉめっきを行った後フェロスタン浴により片面当たり１．２ｇ／ｍ² の錫めっき及び加熱溶融処理を施した素材Ｂさらに脱脂・酸洗したのちＮｉめっきを行った後フェロスタン浴により片面当たり１．２ｇ／ｍ² の錫めっき及び加熱溶融処理を施した素材Ｃに種々の条件で化学処理を施し、外観均一性、シーム溶接性、塗膜密着性、耐食性への影響を調べた。
【００２１】
なお、ノーリフロー仕上げのめっき鋼板以外のものは、各化学処理に先立って、５％硫酸溶液（常温）中４ｃ／ｄｍ² の陰極電解処理による表面活性化を実施した。
各処理材について、以下に示す（Ａ）〜（Ｅ）の各項目について実施し、その性能を評価した。
（Ａ）オキソ化度
測定方法：ＥＳＣＡの波形分離法によりＯｘ−Ｃｒのオキソ化合物とオール化合物のピーク面積を求め、
下記式によりオキソ化度を測定
オキソ化度＝（オキソ化合物のピーク面積）／（オキソ化合物のピーク面積＋オール化合物のピーク面積）
【００２２】
（Ｂ）外観均一性
目視により下記の通り評価した。
〇：色調ムラ無し
×：色調ムラ有り
（Ｃ）シーム溶接性
ラップ代０．５ｍｍ、加圧力４５ｋｇｆ、溶接ワイヤスピード１００ｍ／ｍｉｎの条件で、電流を変更して溶接を実施し十分な溶接強度が得られる最小電流値とチリなどの溶接欠陥が目立ち始める最大電流値からなる適正電流範囲の広さから総合的に判断し、３段階（◎：非常に広い、〇：実用上問題なし、×：狭い）で評価した。
【００２３】
（Ｄ）塗料密着性
試験片の缶内面側に相当する面にエポキシフェノール系の塗料を５５ｍｇ／ｄｍ² 塗布し、さらに缶外面に相当する面にクリヤーラッカーを４０ｍｇ／ｄｍ² 塗布し、２９０℃まで１５ｓｅｃの焼き付け条件で乾燥硬化した。引き続き、各々の面に１ｍｍ間隔でスクラッチを入れ、１００個の碁盤目を作製し、速やかにテープ剥離し、その剥離状況を観察し、３段階（◎：剥離無し、〇：１〜４個剥離、×：５個以上剥離）で塗料密着性を評価した。
【００２４】
（Ｅ）ＵＣＣ（アンダーカッティングコロージョン）評価テスト
試験片の缶内面に相当する面の耐食性を評価するため、缶内面側に相当する面に厚さ１５μｍのＰＥＴ（ポリエチレンテレフタレート）系フィルムをラミネートした。その後地鉄に達するまでクロスカットを入れ、１．５％クエン酸−１．５％食塩混合液からなる試験液中に大気開放下５５℃×４日間浸漬した。試験終了後、速やかにスクラッチ部および平面部をテープで剥離して、スクラッチ部近傍の腐食状況、スクラッチ部のピッティング状況および平面部のフィルム剥離状況を３段階（◎：剥離が無く腐食も認められない、〇：僅かな剥離があるが腐食は認められない、×：大部分で剥離し激しい腐食が認められる）で総合的に評価した。
表１に示すように、本発明により化学処理された錫系めっき鋼板は、優れたシーム溶接性、密着性および耐食性を有することが明らかになった。
【００２５】
【表１】

【００２６】
【発明の効果】
以上述べたように、本発明による所定の浴組成、低温浴での高電流密度による電解によるＭｅ−Ｃｒの被覆性向上及び高温浴での浸漬処理による効率的なＯｘ−Ｃｒの低減により、半田性、溶接性、外観均一性の向上、連続製造ラインでの生産性向上を図り、さらに塗料密着性に対しても著しい効果を奏するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a chemically treated coating excellent in paint adhesion, corrosion resistance, and weldability on a tin-based plated steel sheet.
[0002]
[Prior art]
Tin-plated steel sheet is widely used as a material for various metal containers such as cans and dry batteries, but in recent years it has been increasingly used to reduce the amount of tin deposited and to ensure corrosion resistance by coating the inside and outside of the can. doing. In this case, the quality of the coating film adhesion is an important factor affecting the corrosion resistance. Hydrated oxidation with metallic chromium (hereinafter referred to as Me-Cr) by cathodic electrolysis in a chromic anhydride-based treatment bath containing sulfuric acid, fluorine compounds and the like as a method for enhancing the adhesion of the tin-plated steel sheet. Although a method of forming a film made of chromium (hereinafter referred to as Ox-Cr) is known, there is a problem as described below simply by performing cathodic electrolysis in a chromic anhydride bath.
[0003]
That is, when the amount of Me-Cr necessary for improving paint adhesion is generated, the amount of Ox-Cr generated at the same time tends to be excessively increased, the seam weldability is impaired, and the amount of Ox-Cr generated is reduced. Appearance unevenness easily occurs due to non-uniformity.
In order to solve this problem, Japanese Patent Application Laid-Open No. 61-12896 discloses a technique for reducing the amount of Ox—Cr and improving the solderability, weldability, appearance uniformity, and paint adhesion accompanying this. The present inventors have invented a treatment method in which immersion treatment in a relatively high concentration chromic anhydride aqueous solution is carried out following the cathodic electrolysis treatment in a low concentration chromic anhydride aqueous solution having a low root content. Certainly, the manufacturing method according to the invention brings about an effect of improving solderability, weldability, appearance uniformity, and paint adhesion.
[0004]
[Problems to be solved by the invention]
However, since Ox-Cr produced by electrolysis in the chromic anhydride bath of this production method has a slow dissolution rate and requires two types of baths with completely different bath compositions, the line speed in the continuous production line is reduced. In addition, operation on a continuous production line is difficult due to operational restrictions such as strict bath concentration management.
Therefore, the inventors have intensively studied, and as a result, the coverage of Me-Cr and Ox-Cr produced by high current density electrolysis in the chromic anhydride bath described in the claims is good, and the electrolytic bath temperature is further lowered. Although the amount of Ox-Cr increases as the amount of Ox-Cr increases, the all-type Ox-Cr in the upper layer of the Ox-Cr film formed at this time has a high solubility due to a large amount of eutectoid of sulfate ions. It was clarified that the Ox-Cr remaining at this time was a film excellent in adhesion with a high degree of oxonation [OCrO / (OCrO + HOCrOH)].
[0005]
That is, the present invention improves solderability and weldability by improving coverage of Me-Cr by electrolysis due to high current density in a predetermined bath composition, low temperature bath, and reducing Ox-Cr efficiently by immersion treatment in a high temperature bath. An object of the present invention is to provide a chemical treatment method for a tin-based plated steel sheet that improves the uniformity of appearance, improves the productivity in a continuous production line, and also has a significant effect on paint adhesion.
[0006]
[Means for Solving the Problems]
The gist of the present invention is as follows.
(1) A bath temperature of 45 to 200 g / l of CrO ₃ and CrO ₃ in a weight ratio of 1/50 to 1/200 of H ₂ SO ₄ in the tin-based plated steel sheet, the balance being water and inevitable impurities. Cathodic electrolysis is carried out in a cathode electrolysis bath of less than 0 ° C., followed by immersion treatment in an immersion bath at a bath temperature of 45 ° C. or more containing 35 to 200 g / l of CrO ₃ and the balance water and unavoidable impurities. Further, a metal chromium layer of 0.5 to 20 mg / m ² is formed on the surface of the tin-based plated steel sheet , and the surface is further 0.5 to 15 mg / m ² in terms of metal chromium , and the ratio of the oxo compound is 0.6 or more. A method for producing a surface-treated steel sheet excellent in high-speed seam weldability, corrosion resistance, and adhesion, characterized by forming an oxide chromium layer.
[0007]
(2) The high-speed seam weldability according to (1) above, wherein the immersion treatment bath contains H ₂ SO ₄ of 1/50 to 1/200 in weight ratio to CrO ₃ and unavoidable impurities, A method for producing a surface-treated steel sheet having excellent corrosion resistance and adhesion.
[0008]
( 3 ) Cathodic electrolysis is carried out at a current density of 20 A / dm ² or more in a cathodic electrolysis treatment bath, which is excellent in high-speed seam weldability, corrosion resistance, and adhesion as described in (1) to ( 2 ) above Manufacturing method of surface-treated steel sheet.
( 4 ) Cathodic electrolytic treatment or immersion treatment in an acid bath is performed on the tin-based plated steel sheet in advance, which is excellent in high-speed seam weldability, corrosion resistance, and adhesion as described in the above (1) to ( 3 ) Manufacturing method of surface-treated steel sheet.
[0009]
( 5 ) The high-speed seam weldability, corrosion resistance, and adhesion according to (1) to ( 4 ) above, wherein the tin-based plated steel sheet forms an Fe—Ni alloy plating layer as a base for tin plating. production how of excellent surface-treated steel sheet to.
( 6 ) The tin-based plated steel sheet is excellent in high-speed seam weldability, corrosion resistance, and adhesion as described in (1) to ( 4 ) above, wherein a Ni plating layer is formed as a base for tin plating. production how of surface-treated steel sheet.
( 7 ) The method for producing a surface-treated steel sheet excellent in high-speed seam weldability, corrosion resistance, and adhesion according to the above ( 5 ) to ( 6 ), wherein a tin-plating process is performed after forming a tin plating layer. is there.
[0010]
Hereinafter, the present invention will be described in more detail.
In the present invention, the tin-based plated steel sheet is not only a normal tin-plated steel sheet generally called “blink”, but also a variety of methods that compensate for a decrease in corrosion resistance due to a reduction in the amount of tin adhesion used in applications such as so-called welding cans. Material (namely, tin-based alloy-plated steel sheet containing metal other than tin such as Ni, Ni, Fe-Ni, etc., underplating, or Ni plating and thermal diffusion treatment) The tin-based laminated plated steel sheet and the like subjected to the above are the objects, and the method of the present invention can be applied to any of these.
[0011]
After the tin-based plating, it is preferable to perform a surface activation treatment such as cathodic electrolysis or immersion treatment in an acid solution in order to remove oxides and the like on the plating surface. However, such surface activation treatment does not need to be performed for active surfaces such as plating with no reflow finish. The treatment conditions may be the same as those performed in normal tinting. Specifically, the treatment conditions are immersed in an acid bath having a bath concentration of 2 to 10% sulfuric acid and a bath temperature of 30 to 80 ° C., or in the acid bath. What is necessary is just to perform the cathodic electrolysis process of cathode electric quantity density of about 5 c / dm < ² > or less.
[0012]
After the surface activation treatment and washing with water, a film made of Me-Cr and Ox-Cr is formed by cathodic electrolysis treatment and immersion treatment in the same composition high-temperature bath in the low-temperature chromic anhydride-based bath according to claim. The adhesion amounts are preferably 0.5 to 20 mg / m ² and 0.5 to 15 mg / m ² (both per side). When Me-Cr is less than 0.5 mg / m ² or less than Ox-Cr 0.5 mg / m ² , a sufficient paint adhesion improving effect cannot be obtained, and the coating film adhesion improves with an increase in Me-Cr. When Cr exceeds 20 mg / m ² or when Ox—Cr exceeds 15 mg / m ² , the effect is saturated and the solderability and seam weldability are adversely affected.
[0013]
Ox-Cr can be further classified into two types: oxo compounds and all compounds. When the ratio of this all compound increases in the Ox-Cr outermost layer, volume shrinkage of Ox-Cr occurs due to a dehydration reaction at the time of baking the paint, thereby reducing the adhesion. Therefore, the Ox—Cr outermost layer requires an oxo compound at a certain ratio or more. It was found that in the above-mentioned Cr adhesion amount range on the tin plating, the Ox-Cr outermost layer has an oxo degree of oxidation of 0.6 or more and excellent paint adhesion.
[0014]
When producing a Me—Cr film with a low adhesion amount as described above, short-time treatment at a high current density is effective for film uniformity, and a high current of 20 A / dm ² or more, preferably 30 A / dm ² or more. It is necessary to process the density. Since lowering of the upper limit especially when not provided too high due to electrostatic析効rate of hydrogen generation increase in current density is observed to electrolysis at 150A / dm ² or less.
In order to form such a uniform Me—Cr film having a high current density and a low adhesion amount, the concentration of CrO ₃ contained in the electrolytic treatment bath needs to be 35 g / l or more. Since current efficiency is reduced, the upper limit is set to 200 g / l. More desirably, it is 70 to 130 g / l.
[0015]
The addition of sulfuric acid to the treatment bath is indispensable for the production of Me—Cr, and it is necessary to make the weight ratio to chromic anhydride (hereinafter referred to as sulfuric acid concentration ratio) 1/50 to 1/200. If the sulfuric acid concentration ratio is too high or too low, the Me—Cr electrodeposition efficiency is remarkably reduced, so the lower limit of the sulfuric acid concentration ratio is 1/200 and the upper limit is 1/50.
In addition, the said treatment bath may contain fluorine compounds, such as sodium silicofluoride, sodium borofluoride, and ammonium fluoride other than a sulfuric acid, as an Ox-Cr precipitation adjuvant. Further, if the mixing amount of trivalent chromium ions in the treatment bath is 0.1 to 5 g / l, it is effective for uniforming the chromate film.
[0016]
A particularly important point of the present invention is to lower the temperature of the electrolyzed bath. Ox-Cr has a two-layer structure of an all-type compound in the upper layer and an oxo-type compound in the lower layer, and the precipitation amount of all-type and oxo-type Ox-Cr increases with the low temperature of the electrolytic treatment bath. The eutectoid amount of sulfate ions in the upper layer of all-type Ox-Cr increases, and the solubility of all-type Ox-Cr in the next step increases. Therefore, the bath temperature of the electrolytic treatment bath needs to be lower than 45 ° C., desirably 35 ° C. or lower. The lower limit of the electrolytic treatment bath temperature is not particularly provided, but if it is too low, a powerful cooler needs to be installed, which is uneconomical.
[0017]
Following the cathodic electrolysis in the treatment bath, the purpose is to reduce the amount of oxo-type Ox-Cr produced excessively by the cathodic electrolysis and to improve the adhesion of the coating film by forming Ox-Cr having a high degree of oxoation. The chromic anhydride aqueous solution immersion treatment was performed. The dissolution ability of all-type Ox-Cr is affected by the chromic acid concentration in the bath, the bath temperature and the treatment time. If the chromic anhydride concentration is less than 35 g / l, the ability to dissolve excess Ox-Cr is remarkably reduced, so a concentration higher than this is necessary, and preferably 70 g / l or more. On the other hand, if the concentration is higher than 200 g / l, the etching action is too strong and the oxo-type Ox—Cr is dissolved, which may lead to a decrease in paint adhesion and corrosion resistance. Therefore, the upper limit of the chromic anhydride concentration is set to 200 g / l.
[0018]
In addition, it is desirable to add the sulfate ion to the bath because the dissolving ability of Ox-Cr can be improved. The effect is recognized from the addition of sulfuric acid concentration ratio of 1/200 or more, and the dissolving ability is improved as the addition amount is increased. However, since the effect becomes constant when it becomes 1/50 or more, the upper limit is set to 1/50 and the lower limit is set to 1/200. Further, trivalent chromium ions and other inevitable impurities may be mixed, and the immersion treatment liquid may have the same composition as the electrolytic treatment bath.
[0019]
Since the immersion time in the immersion treatment liquid varies depending on the amount of Ox-Cr required, it is not particularly set, but if immersed for a long time, the etching action is too strong and the oxo-type Ox-Cr is also dissolved, resulting in a decrease in paint adhesion and corrosion resistance. May be connected.
In addition, the dissolving ability of Ox—Cr increases with an increase in bath temperature, and a bath temperature of 45 ° C. or higher is necessary for efficient dissolution, and 55 ° C. or higher is desirable. The upper limit of the bath temperature is not particularly specified, but if the temperature is too high, the recovery of bath fume becomes large and uneconomical, so it is desirable to set the upper limit at 70 ° C.
[0020]
Examples of the present invention will be described below.
【Example】
A steel sheet that has been cold-rolled, annealed and temper-rolled, degreased and pickled, and then subjected to 2.8 g / m ² tin plating and heat-melting treatment on one side using a ferrostan bath, and degreased and pickled After that, after performing Fe-Ni plating, material B subjected to tin plating of 1.2 g / m ² per side with a ferrostan bath and heat-melting treatment, further degreasing and pickling, and after Ni plating after one side with a ferrostan bath Chemical treatment was performed under various conditions on the raw material C subjected to tin plating of 1.2 g / m ² and heat melting treatment, and the influence on appearance uniformity, seam weldability, coating film adhesion, and corrosion resistance was examined.
[0021]
In addition, except for the no-reflow-plated steel sheet, prior to each chemical treatment, surface activation was performed by cathodic electrolysis of 4 c / dm ^{2 in} a 5% sulfuric acid solution (normal temperature).
About each processing material, it implemented about each item of (A)-(E) shown below, and evaluated the performance.
(A) Oxidation degree measurement method: The peak area of the Ox-Cr oxo compound and all compound was determined by the waveform separation method of ESCA,
The degree of oxonation is measured by the following formula: degree of oxolation = (peak area of oxo compound) / (peak area of oxo compound + peak area of all compound)
[0022]
(B) Appearance uniformity The visual evaluation was as follows.
○: No color tone unevenness ×: Color tone unevenness (C) Seam weldability Wrap allowance is 0.5mm, pressure is 45kgf, welding wire speed is 100m / min. Judging comprehensively from the width of the appropriate current range consisting of the minimum current value obtained and the maximum current value at which welding defects such as dust start to stand out, three levels (◎: very wide, ○: practically no problem, ×: Narrow).
[0023]
(D) 55 mg / dm ² of epoxyphenol-based paint was applied to the surface corresponding to the inner surface of the can of the paint adhesion test piece, and 40 mg / dm ² of clear lacquer was applied to the surface corresponding to the outer surface of the can. Until it was dried and cured under a baking condition of 15 sec. Subsequently, scratches are made on each surface at intervals of 1 mm, 100 grids are produced, the tape is peeled off quickly, and the peeled state is observed. Three stages (◎: no peeling, ○: 1 to 4 pieces are peeled off) , X: peeling 5 or more), and paint adhesion was evaluated.
[0024]
(E) UCC (Under Cutting Corrosion) Evaluation In order to evaluate the corrosion resistance of the surface corresponding to the inner surface of the can of the test specimen, a PET (polyethylene terephthalate) film having a thickness of 15 μm was laminated on the surface corresponding to the inner surface of the can. After that, a cross cut was put in until it reached the ground iron, and it was immersed in a test solution composed of a 1.5% citric acid-1.5% sodium chloride mixture at 55 ° C. for 4 days under open air. Immediately after the test, the scratch part and the flat part are peeled off with tape, and the corrosion situation near the scratch part, the pitting situation of the scratch part, and the film peel situation of the flat part are classified into three stages (◎: no peeling and corrosion is recognized) No, ○: There is slight peeling, but no corrosion is observed, and X: Most peeling and severe corrosion are recognized).
As shown in Table 1, it was revealed that the tin-plated steel sheet chemically treated according to the present invention has excellent seam weldability, adhesion, and corrosion resistance.
[0025]
[Table 1]

[0026]
【The invention's effect】
As described above, the predetermined bath composition according to the present invention, improved coverage of Me—Cr by electrolysis due to high current density in a low temperature bath, and efficient reduction of Ox—Cr by immersion treatment in a high temperature bath, This improves the productivity, weldability, appearance uniformity, and productivity in a continuous production line, and also has a remarkable effect on paint adhesion.

Claims

35-200 g / l CrO on tin-plated steel sheet _{3 Three} And CrO _{3 Three} H of 1/50 to 1/200 in weight ratio _{2 2} SO _{4 Four} The cathode is electrolyzed in a cathodic electrolysis bath having a bath temperature of less than 45 ° C. containing the remaining water and inevitable impurities, followed by 35 to 200 g / l CrO. _{3 Three} In the immersion treatment bath with a bath temperature of 45 ° C. or more comprising the remaining water and inevitable impurities, the surface of the tin-based plated steel sheet is 0.5 to 20 mg / m ²² A metal chromium layer of 0.5 to 15 mg / m in terms of metal chromium is further formed on the surface. ²² And a method for producing a surface-treated steel sheet excellent in high-speed seam weldability, corrosion resistance, and adhesion, characterized in that an oxide chromium layer having an oxo compound ratio of 0.6 or more is formed.

The high-speed seam weldability, corrosion resistance, and adhesion according to claim 1, wherein the immersion treatment bath contains H ₂ SO ₄ and inevitable impurities in a weight ratio of 1/50 to 1/200 with CrO ₃ . A method for producing a surface-treated steel sheet with excellent resistance.

^{3. The} method for producing a surface-treated steel sheet excellent in high-speed seam weldability, corrosion resistance, and adhesion according to claim 1 or 2 , wherein cathodic electrolysis is performed at a current density of 20 A / dm ² or more in a cathodic electrolysis bath. .

The method for producing a surface-treated steel sheet excellent in high-speed seam weldability, corrosion resistance, and adhesion according to claims 1 to 3, wherein the tin-plated steel sheet is previously subjected to cathodic electrolysis treatment or immersion treatment in an acid bath. .

The surface-treated steel sheet excellent in high-speed seam weldability, corrosion resistance, and adhesion according to claim 1, wherein the tin-based plated steel sheet forms a Fe—Ni alloy plating layer as a base for tin plating. Manufacturing method.

Tin-plated steel sheet, high-speed seam weldability according to claim 1-4, characterized in that forming the Ni plating layer as an underlayer for tin plating, corrosion resistance, manufacture lateral superior surface treated steel sheet adhesion Law.

The method for producing a surface-treated steel sheet excellent in high-speed seam weldability, corrosion resistance, and adhesion according to claim 5 , wherein a tin-plating process is performed after the tin plating layer is formed .