JP3905786B2

JP3905786B2 - Surface-treated galvanized steel sheet

Info

Publication number: JP3905786B2
Application number: JP2002103014A
Authority: JP
Inventors: 敦史木原; 富男梶田; 雅司今堀; 秀和井戸
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2002-04-04
Filing date: 2002-04-04
Publication date: 2007-04-18
Anticipated expiration: 2022-04-04
Also published as: JP2003293151A

Description

【０００１】
【発明の属する技術分野】
本発明は表面処理亜鉛系メッキ鋼板に関し、特に、亜鉛系メッキ層の上に、有害な６価クロムを一切含まず、しかも従来の６価クロムを含むクロメート処理鋼板に匹敵する耐食性と塗膜密着性を有する表面処理亜鉛系メッキ鋼板に関するものである。
【０００２】
【従来の技術】
自動車用、家電用、建築材料用などに適用される鋼板としては、耐食性の観点から亜鉛系メッキ鋼板が汎用されてきた。しかし、亜鉛系メッキのみでは耐食性（耐白錆性）が不十分である他、塗装下地として使用する場合に塗料との密着性も確保し難いことから、改善策としてクロメート処理やリン酸塩処理が行われている。
【０００３】
ところがクロメート処理の場合、白錆抑制効果には優れている反面、塗膜との密着性が十分とは言えず、加えて有害な６価クロムを多量含むという問題がある。特に近年、環境問題への意識が高まってくるにつれてクロメート処理は回避される傾向にあり、殆どの用途ではノンクロメート処理に移行しつつある。
【０００４】
一方、リン酸塩処理の場合、塗膜との密着性は比較的良好であるが、リン酸塩処理ままの裸で使用したときの白錆抑制効果が乏しいため汎用性を欠く。また表面処理亜鉛系メッキ鋼板では、塗膜密着性などの向上を期して、表面に付着している油等の汚れを除去して清浄化するため脱脂処理されるので、ノンクロメート処理鋼板に対しても、アルカリ脱脂後の耐食性や塗膜密着性が求められる。
【０００５】
こうした状況の下で、クロメートを用いない表面処理法についても多くの改良研究が進められている。例えば特開２０００−１４４４４４号公報には、シリカやシリカゾルとリン酸化合物、および特定の金属の酸化物や水酸化物を好適比率で含む酸性処理液で亜鉛系メッキ鋼板を処理した後、加熱乾燥することによって、所定厚みの化成処理皮膜を形成する方法が開示されている。また特開２０００−１２９４６０号公報には、第１層として亜鉛メッキ、第２層として多価金属の第一リン酸塩と金属酸化物ゾルの混合水溶液を塗布乾燥してなる非晶質皮膜、第３層として有機皮膜を形成し多層構造とする方法が開示されている。
【０００６】
更には、亜鉛系メッキをクロム未含有の有機皮膜で直接被覆する方法についても、例えば特開平６−３１６６８５号、同８−６７８３４号、同８−２３９７７６号、同８−２６７００４号、同９-２２１５９５号等に見られる如く多くの提案がなされている。
【０００７】
【発明が解決しようとする課題】
ところが、上述した様なノンクロメート処理法には次の様な課題が残されている。即ち
▲１▼クロメート処理を廃して直接有機皮膜で被覆する方法では、亜鉛系メッキ層に対する有機皮膜の密着性が十分でなく、塗装下地処理として採用した時に、塗膜密着性試験で有機皮膜と亜鉛系メッキの界面でしばしば剥離を起こす。
【０００８】
▲２▼シリカゾルやリン酸塩、金属水酸化物の如き無機系処理剤を塗布乾燥したままの皮膜にはピンホールが形成され易く、該ピンホールから水や腐食性酸などが浸入するため耐食性に劣る。
【０００９】
▲３▼上記特開２０００−１４４４４４号や同２０００−１２９４６０号公報等に記載されているリン酸化合物、或いは水溶性金属イオンやその酸化物・水酸化物、多価金属の第一リン酸塩等を塗布・乾燥した皮膜には、水可溶性成分が残存し易いため、アルカリ脱脂後の耐食性に劣る他、塗膜密着性の促進試験である耐水二次密着性も十分とは言えない。
【００１０】
本発明は上記の様な従来技術の問題点に鑑みてなされたものであり、その目的は、従来技術に指摘される前述した様な問題を解消し、クロメート処理に勝るとも劣らない耐食性を有すると共に塗装下地として有機皮膜に対しても優れた塗膜密着性を有するノンクロメート系の表面処理亜鉛系メッキ鋼板を提供することにある。
【００１１】
【課題を解決するための手段】
上記課題を解決することのできた本発明にかかる表面処理亜鉛系メッキ鋼板とは、亜鉛系メッキ鋼板における亜鉛系メッキ層の上に、Ａｌ，Ｓｉ，Ｐを含む表面改質層が形成され、該表面改質層中に含まれるＡｌとＳｉおよびＰとＡｌの質量比率が、下記式(1),(2)の関係を満たすところに要旨を有している。
【００１２】
０．１０＜［Ａｌ％］／［Ｓｉ％］＜３．０……(1)
０．９０＜［Ｐ％］／［Ａｌ％］＜２．０……(2)
【００１３】
【発明の実施形態】
上記の様に本発明の表面処理亜鉛系メッキ鋼板は、亜鉛系メッキ鋼板における亜鉛系メッキ層の上に、Ａｌ，Ｓｉ，Ｐを含む表面改質層が形成され、該表面改質層中に含まれるＡｌとＳｉおよびＰとＡｌの質量比率が前記式(1),(2)の関係満たすように定めたところに特徴を有しており、かかる要件を特定することによって、亜鉛系メッキ層との間で優れた密着性を有し、ピンホール欠陥などのない緻密な処理層を形成して優れた耐食性を発揮すると共に、塗装下地として利用する場合は上塗り塗膜との間で優れた塗膜密着性を示し、しかも、乾燥皮膜中の水可溶性成分が少ないため、アルカリ脱脂後の耐食性や塗膜密着性においても優れた性能を発揮する。
【００１４】
こうした特徴を有効に発揮させるには、前掲の如く、改質層中におけるＡｌ，Ｓｉ，Ｐの各含有量（付着量：質量比）［Ａｌ％］，［Ｓｉ％］，［Ｐ％］が、前記式(1)、(2)の関係を満たすものでなければならない。
【００１５】
上記において、［Ａｌ％］／［Ｓｉ％］の比を上記の様に定めたのは、Ａｌの酸化物や水酸化物に由来する皮膜形成による水分などのバリアー効果と、特にシリカに由来する亜鉛メッキの腐食抑制効果を有効に発揮させると共に、前者の欠点である成分比による水への可溶化と、後者の欠点である皮膜の形成し難さ（造膜性不良）を最小限に抑え、トータルとして緻密で水可溶性成分が少なく、アルカリ脱脂後においても高レベルの耐食性と二次密着性を発揮させるためである。
【００１６】
ちなみに、［Ａｌ％］／［Ｓｉ％］比が０．１０未満では、処理層が十分に緻密なものにならないため満足のいく耐食性が得られず、一方この比が逆に高過ぎて３．０を超えると、処理層中の水可溶性成分量が多くなり、アルカリ脱脂後の耐食性と二次密着性が劣悪になる。緻密で且つ可溶性成分量を極力少なく抑えてより優れた耐食性と二次密着性を与えるには、［Ａｌ％］／［Ｓｉ％］比を、０．２０以上、０．９０以下にすることが望ましい。
【００１７】
次に、［Ｐ％］／［Ａｌ％］の比を上記の様に定めたのは、リン酸またはリン酸化合物と上記Ａｌに由来するバリアー効果を有効に発揮させると共に、欠点である成分比により水に可溶化する障害を最小限に抑え、トータルとしてピンホール欠陥のない緻密且つ強固で水可溶性成分が少なく、アルカリ脱脂後においても高レベルの耐食性と二次密着性を発揮させるためである。
【００１８】
ちなみに、［Ｐ％］／［Ａｌ％］比が０．９０未満では、リン酸又はリン酸化合物による亜鉛系メッキ層との反応が十分に進み難くなって耐食性不足となり、逆にこの比が高くなり過ぎて２．０を超えると、処理層にピンホール欠陥が生じ易くなるばかりでなく水可溶性成分量も多くなって耐食性不足となり、アルカリ脱脂後の耐食性と二次密着性も劣悪になる。亜鉛系メッキ層との反応を速やかに進めると共に可溶性成分の残存量を極力少なく抑え、より優れた耐食性と二次密着性を確保するうえで特に好ましい［Ｐ％］／［Ａｌ％］比は、１．０以上、１．３以下である。
【００１９】
該反応層中の［Ａｌ％］，［Ｓｉ％］，［Ｐ％］を上記範囲に調整する方法は特に制限されないが、［Ａｌ％］は処理液中のＡｌの酸化物や水酸化物などの含有量により、［Ｓｉ％］は同処理液中のシリカや珪酸塩などの含有量により、また［Ｐ％］は同処理液中のリン酸やリン酸塩等の含有量に依存するので、処理液中のこれら成分の含有量を適正に制御することによって行えばよい。
【００２０】
中でも特に好ましいのは、処理液としてリン酸や重リン酸、亜リン酸、重亜リン酸などのアルミニウム塩とコロイダルシリカを含む酸性水溶液を用いる方法であり、この方法を採用すれば、酸性水溶液下で亜鉛系メッキ層がエッチングされながら、亜鉛系メッキ層表面に不溶性のリン酸アルミニウム主体の反応層が形成されると共に、該反応層にシリカが取り込まれることで、エッチングにより溶出した亜鉛との間で緻密な反応層が形成され、優れた耐食性と二次密着性を示す処理層を容易に形成できる。
【００２１】
より具体的には、処理液としてリン酸(または重リン酸、亜リン酸、重亜リン酸)Ａｌ塩；４０〜６０質量％とコロイダルシリカ；４０〜６０質量％を含み、ｐＨが２〜３の範囲の酸性水溶液を使用することが推奨される。
【００２２】
これらの処理液を塗布した後は、適度に水洗することによって可溶性成分を除去し、３０〜８０℃程度に加熱して水分を乾燥除去すれば、耐食性や二次密着性の一層優れた処理層を得ることができるので好ましい。
【００２３】
反応層の付着量は特に制限されないが、好ましい範囲としては３０〜９０ｍｇ／ｍ²の範囲が推奨される。少なすぎると亜鉛メッキ表面を覆うことができないため耐食性が劣り、多過ぎると、硬い無機皮膜が加工に追従できなくなるため、加工後の塗膜密着性が劣化する。
【００２４】
上記処理液を亜鉛系メッキ鋼板にコーティングする方法としては、スプレー、浸漬またはロールコーティングなど何れの手段を用いても構わない。中でもスプレーによるコーティング法は、亜鉛メッキとの反応を促進させるうえでより好ましい方法であり、その際の好ましいスプレー圧力は２５〜１００ｋＰａ（約０．２５〜１．０ｋｇｆ／ｃｍ²）、スプレー時間は２〜１０秒の範囲である。
【００２５】
尚、処理層中の［Ａｌ％］，［Ｓｉ％］，［Ｐ％］の量は、例えば蛍光Ｘ線法などによって確認すればよい。
【００２６】
また本発明が適用される亜鉛系メッキ鋼板としては、亜鉛単独メッキ鋼板の他、亜鉛−Ｎｉ、亜鉛−Ｆｅ、亜鉛−Ａｌ等の亜鉛合金メッキ鋼板が全て適用でき、またメッキ法も溶融メッキ法、電気メッキ法、置換メッキ法などの如何を問わない。
【００２７】
本発明によって得られる表面処理亜鉛系メッキ鋼板は、上記の様に亜鉛系メッキ層の表面にＡｌ，Ｓｉ，Ｐを含む処理層が形成されたもので、この処理鋼板はそのままでも緻密な皮膜によって亜鉛系メッキ表面の白錆を抑えて優れた耐食性を発揮し、また塗装下地として例えば有機塗膜を形成する際にも優れた塗膜密着性を発揮する。しかし、耐食性や塗膜密着性、加工性などの一層の向上を期して、更にその上に各種有機系もしくは無機系の皮膜を形成することも勿論有効である。
【００２８】
【実施例】
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも可能であり、それらは何れも本発明の技術的範囲に含まれる。
【００２９】
実施例
厚さ０．８ｍｍの鋼板（品番；ＳＥＣＣ）の表面に電気メッキ法により厚さ亜鉛付着量２０ｇ／ｍ²亜鉛メッキを施した亜鉛メッキ鋼板をアルカリ脱脂してから水洗、乾燥したものを原板として使用した。
【００３０】
処理液として、５０質量％重リン酸アルミニウム（日本化学工業社製）４０〜６０質量部と、コロイダルシリカ「ＳＴ−Ｏ」(日産化学工業社製)４０〜６０質量部との混合液（ｐＨ２〜３）を使用し、これらを脱脂後の亜鉛メッキ鋼板表面に、スプレー圧２５ｋＰａ（約０．２５ｋｇ／ｃｍ²）でスプレー塗布してから水洗し、４０℃で乾燥することにより、亜鉛メッキ層上に反応層を形成した。反応層は、平均付着量が約５０ｍｇ／ｍ²となる様に塗布量を調整した。これを、反応ままの供試材とした。
【００３１】
反応層中に含まれるＡｌとＳｉの比（［Ａｌ％］／［Ｓｉ％］）およびＰとＡｌの比（[Ｐ％]／［Ａｌ％］）は、島津製作所製の蛍光Ｘ線装置「ＭＩＦ−２１００」を用いて測定した。
【００３２】
また上記反応層の上に、ポリエチレン系樹脂エマルションを固形分換算で２０質量％配合した混合液を塗布し、８０℃で乾燥することにより、固形分付着量が約１ｇ／ｍ²の皮膜を形成した。これを、上塗り樹脂被覆後の供試材とした。
【００３３】
なお、反応層中の上記［Ａｌ％］／［Ｓｉ％］比および[Ｐ％]／［Ａｌ％］比は、上記処理液を調製する際の重リン酸アルミニウムとコロイダルシリカの各濃度と配合比率およびスプレー処理時間を変えることによって調整した。
【００３４】
得られた各供試材について、下記の方法で耐食性および塗膜密着性の評価試験を行い、結果を表１，２に示した。
【００３５】
「評価試験法」
▲１▼供試材ままの耐食性
反応まま及び上塗り樹脂被覆後の供試材の端面にエッジシールを施し、ＪＩＳ−Ｚ−２３７１に規定されている塩水噴霧試験を行い、各経過時間で平面部に発生した白錆の面積率を測定する。
【００３６】
評価基準１：反応ままの場合、塩水噴霧１２時間後の白錆発生面積率で評価する、
◎；５％未満
○；５〜２０％未満
△；２０〜５０％未満
×；５０％超
【００３７】
評価基準２：上塗り樹脂被覆後の場合、塩水噴霧２４０時間後の白錆発生面積率で評価する、
◎；５％未満
○；５〜２０％未満
△；２０〜５０％未満
×；５０％超
【００３８】
▲２▼アルカリ脱脂後の耐食性
反応まま及び上塗り樹脂被覆後の供試材に、アルカリ脱脂剤「ＦＣ−４３８６」（日本パーカライジング社製）を２０ｇ／リットルに調整した液を６０℃で５秒間スプレー処理した後、水洗、乾燥する。その後供試材の端面をエッジシールしてから、ＪＩＳ−Ｚ−２３７１に定める塩水噴霧試験を行い、各経過時間における平面部に発生した白錆の面積率を測定する。
【００３９】
評価基準３：反応ままの場合、塩水噴霧１２時間後の白錆発生面積率で評価する、
◎；５％未満
○；５〜２０％未満
△；２０〜５０％未満
×；５０％超
【００４０】
評価基準４：上塗り樹脂被覆後の場合、塩水噴霧２４０時間後の白錆発生面積率で評価する、
◎；５％未満
○；５〜２０％未満
△；２０〜５０％未満
×；５０％超
【００４１】
▲３▼塗膜密着性
反応まま及び上塗り樹脂被覆後の供試材に、関西ペイント社製の「マジクロン＃１０００」を塗布した後、１６０℃で焼付処理を行う（膜厚は、１６０℃焼付後の塗膜厚さで約２０μｍに調整）
【００４２】
一次密着性は、塗膜に１ｍｍ角の碁盤目を１００マス入れ、テープ剥離した後の塗膜残存率によって求める。また二次密着性は、塗装後の供試材を沸騰水中に１時間浸漬してから水を拭き取った後、塗膜に１ｍｍ角の碁盤目を１００マス入れ、同様にして塗膜残存率を求める、
◎；９０％以上
○；７０％以上、９０％未満
△；５０％超７０％未満
×；５０％未満
【００４３】
【表１】

【００４４】
【表２】

【００４５】
上記表１，２において、符号１〜１０および１５〜２５は何れも本発明の規定要件を満たす実施例であり、反応まま及び上塗り樹脂被覆後の状態の何れにおいても、供試材まま、アルカリ脱脂後の如何を問わず優れた耐食性を示すと共に、一次密着性や二次密着性においても優れた性能を示している。
【００４６】
これらに対し、符号１１〜１４および２５〜２８は、本発明で定める一部の規定要件を欠くものであり、反応まま及び上塗り樹脂被覆後の何れの状態でも、また供試材まま及びアルカリ脱脂後の何れかで耐食性が悪く、一次密着性や二次密着性においても明らかに劣っていることが分る。
【００４７】
【発明の効果】
本発明は以上の様に構成されており、特に亜鉛系メッキ鋼板における亜鉛系メッキ層の上に、耐食性と塗膜密着性向上を期して形成される表面改質層中の［Ａｌ％］／［Ｓｉ％］と［Ｐ％］／［Ａｌ％］を適正範囲に調整することにより、公害面から忌避されているクロムを含まない系でありながら、クロメート処理に匹敵し或いはこれを上回る耐食性と塗膜密着性を備えた表面処理亜鉛系メッキ鋼板を提供し得ることになった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface-treated zinc-based plated steel sheet, and in particular, corrosion resistance and coating film adhesion comparable to those of a conventional chromate-treated steel sheet that does not contain any harmful hexavalent chromium on the zinc-based plated layer and also contains hexavalent chromium. The present invention relates to a surface-treated zinc-based plated steel sheet having properties.
[0002]
[Prior art]
Zinc-based plated steel sheets have been widely used as steel sheets applied to automobiles, home appliances, building materials, and the like from the viewpoint of corrosion resistance. However, corrosion resistance (white rust resistance) is not sufficient with zinc-based plating alone, and it is difficult to ensure adhesion to paint when used as a coating base. Has been done.
[0003]
However, in the case of the chromate treatment, the white rust suppressing effect is excellent, but the adhesion to the coating film is not sufficient, and in addition, there is a problem that a large amount of harmful hexavalent chromium is contained. In particular, in recent years, as the awareness of environmental problems has increased, chromate treatment tends to be avoided, and in most applications, it is shifting to non-chromate treatment.
[0004]
On the other hand, in the case of phosphating, the adhesion to the coating film is relatively good, but lacks versatility because of its poor white rust inhibiting effect when used as-treated naked. In addition, surface-treated zinc-based plated steel sheets are degreased in order to improve the adhesion of the coating film, etc., to remove and clean dirt such as oil adhering to the surface. However, the corrosion resistance and coating film adhesion after alkali degreasing are required.
[0005]
Under these circumstances, many researches on the surface treatment method that does not use chromate are underway. For example, in Japanese Patent Application Laid-Open No. 2000-144444, a zinc-based plated steel sheet is treated with an acidic treatment liquid containing silica or silica sol and a phosphoric acid compound, and a specific metal oxide or hydroxide in a suitable ratio, and then dried by heating. A method for forming a chemical conversion film having a predetermined thickness is disclosed. JP-A-2000-129460 discloses an amorphous film formed by applying and drying a mixed solution of a polyvalent metal primary phosphate and a metal oxide sol as a first layer, as a first layer, A method for forming a multilayer structure by forming an organic film as the third layer is disclosed.
[0006]
Furthermore, with regard to a method of directly coating zinc-based plating with a chromium-free organic film, for example, JP-A-6-316685, JP-A-8-67834, JP-A-8-239976, JP-A-8-267004, JP-A-9- Many proposals have been made as seen in No. 221595.
[0007]
[Problems to be solved by the invention]
However, the following problems remain in the non-chromate treatment method as described above. In other words, (1) The method of eliminating the chromate treatment and coating directly with an organic film does not provide sufficient adhesion of the organic film to the zinc-based plating layer. Delamination often occurs at the zinc-based plating interface.
[0008]
(2) Corrosion resistance due to easy formation of pinholes in the film as it is dried by applying an inorganic treatment agent such as silica sol, phosphate, or metal hydroxide, and water and corrosive acids enter through the pinholes. Inferior to
[0009]
(3) Phosphate compounds described in JP 2000-144444 and 2000-129460, or water-soluble metal ions, oxides / hydroxides thereof, and polyvalent metal primary phosphates Since the water-soluble component tends to remain in the film coated and dried, etc., it is inferior in corrosion resistance after alkaline degreasing, and it cannot be said that the water-resistant secondary adhesion, which is a coating adhesion promotion test, is sufficient.
[0010]
The present invention has been made in view of the problems of the prior art as described above, and the object thereof is to solve the above-described problems pointed out in the prior art and to have corrosion resistance not inferior to chromate treatment. Another object of the present invention is to provide a non-chromate surface-treated galvanized steel sheet having excellent coating film adhesion to an organic film as a coating base.
[0011]
[Means for Solving the Problems]
The surface-treated zinc-based plated steel sheet according to the present invention that has been able to solve the above-mentioned problems is that a surface modification layer containing Al, Si, P is formed on the zinc-based plated layer in the zinc-based plated steel sheet, The main point is that the mass ratios of Al and Si and P and Al contained in the surface modified layer satisfy the relationship of the following formulas (1) and (2).
[0012]
0.10 <[Al%] / [Si%] <3.0 (1)
0.90 <[P%] / [Al%] <2.0 (2)
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the surface-treated zinc-based plated steel sheet of the present invention has a surface-modified layer containing Al, Si, P formed on the zinc-based plated layer in the zinc-based plated steel sheet. It is characterized in that the mass ratio of Al and Si and P and Al contained is determined so as to satisfy the relationship of the above formulas (1) and (2). By specifying such requirements, the zinc-based plating layer In addition to exhibiting excellent corrosion resistance by forming a dense treatment layer free of pinhole defects etc., when used as a coating base, it is excellent with the top coat film It exhibits coating film adhesion, and also exhibits excellent performance in corrosion resistance and coating film adhesion after alkaline degreasing because there are few water-soluble components in the dried film.
[0014]
In order to effectively exhibit these characteristics, as described above, the contents of Al, Si, and P in the modified layer (attachment amount: mass ratio) [Al%], [Si%], and [P%] In addition, the relationship of the above formulas (1) and (2) must be satisfied.
[0015]
In the above, the ratio of [Al%] / [Si%] is determined as described above because of the barrier effect such as moisture due to the formation of a film derived from the oxide or hydroxide of Al, and particularly from silica. Effectively exhibits the corrosion-inhibiting effect of galvanization, while minimizing solubilization in water due to the component ratio, which is the former defect, and the difficulty of forming a film (poor film formation), which is the latter defect This is because, as a whole, it is dense and has few water-soluble components, and exhibits a high level of corrosion resistance and secondary adhesion even after alkaline degreasing.
[0016]
Incidentally, when the [Al%] / [Si%] ratio is less than 0.10, the treatment layer does not become sufficiently dense and satisfactory corrosion resistance cannot be obtained, while this ratio is too high. When it exceeds 0, the amount of water-soluble components in the treatment layer increases, and the corrosion resistance and secondary adhesion after alkali degreasing become poor. In order to provide fine corrosion resistance and secondary adhesion by minimizing the amount of the soluble component, the [Al%] / [Si%] ratio should be 0.20 or more and 0.90 or less. desirable.
[0017]
Next, the ratio of [P%] / [Al%] is determined as described above, because the barrier effect derived from phosphoric acid or a phosphoric acid compound and the above Al is effectively exhibited, and the component ratio which is a defect This is to minimize the obstacle to solubilization in water, and as a whole it is dense and strong without pinhole defects and has few water-soluble components, and exhibits high level of corrosion resistance and secondary adhesion even after alkaline degreasing. .
[0018]
Incidentally, when the [P%] / [Al%] ratio is less than 0.90, the reaction with the zinc-based plating layer by phosphoric acid or phosphoric acid compound is difficult to proceed sufficiently, resulting in insufficient corrosion resistance. Conversely, this ratio is high. If it becomes too much and exceeds 2.0, not only will pinhole defects easily occur in the treated layer, but the amount of water-soluble components will increase, resulting in insufficient corrosion resistance, and poor corrosion resistance and secondary adhesion after alkaline degreasing. [P%] / [Al%] ratio that is particularly preferable for promptly proceeding with the reaction with the zinc-based plating layer and suppressing the residual amount of the soluble component as much as possible to ensure better corrosion resistance and secondary adhesion, 1.0 or more and 1.3 or less.
[0019]
A method for adjusting [Al%], [Si%], and [P%] in the reaction layer to the above ranges is not particularly limited, but [Al%] is an oxide or hydroxide of Al in the treatment liquid. [Si%] depends on the content of silica, silicate, etc. in the treatment liquid, and [P%] depends on the contents of phosphoric acid, phosphate, etc. in the treatment liquid. The content of these components in the treatment liquid may be controlled appropriately.
[0020]
Particularly preferred among these is a method using an acidic aqueous solution containing aluminum salt such as phosphoric acid, heavy phosphoric acid, phosphorous acid, biphosphorous acid and colloidal silica as the treatment liquid. While the zinc-based plating layer is etched below, an insoluble aluminum phosphate-based reaction layer is formed on the surface of the zinc-based plating layer, and silica is incorporated into the reaction layer, so that the zinc eluted from the etching A dense reaction layer is formed between them, and a treatment layer exhibiting excellent corrosion resistance and secondary adhesion can be easily formed.
[0021]
More specifically, the treatment liquid contains phosphoric acid (or heavy phosphoric acid, phosphorous acid, biphosphorous acid) Al salt; 40 to 60% by mass and colloidal silica; 40 to 60% by mass, and has a pH of 2 to 2. It is recommended to use an acidic aqueous solution in the range of 3.
[0022]
After applying these treatment liquids, the soluble components are removed by washing with water moderately, and if the moisture is dried and removed by heating to about 30 to 80 ° C., a treatment layer with further excellent corrosion resistance and secondary adhesion. Is preferable.
[0023]
The amount of the reaction layer deposited is not particularly limited, but a preferable range is 30 to 90 mg / m ² . If the amount is too small, the galvanized surface cannot be covered and the corrosion resistance is inferior. If the amount is too large, the hard inorganic film cannot follow the processing, and the coating adhesion after processing deteriorates.
[0024]
Any method such as spraying, dipping, or roll coating may be used as a method for coating the galvanized steel sheet with the treatment liquid. Among these, the spray coating method is a more preferable method for accelerating the reaction with galvanization, and the preferable spray pressure at that time is 25 to 100 kPa (about 0.25 to 1.0 kgf / cm ² ), and the spray time is The range is 2 to 10 seconds.
[0025]
In addition, what is necessary is just to confirm the quantity of [Al%], [Si%], [P%] in a process layer, for example by the fluorescent X ray method.
[0026]
Further, as the zinc-based plated steel sheet to which the present invention is applied, all zinc alloy-plated steel sheets such as zinc-Ni, zinc-Fe, zinc-Al, etc. can be applied in addition to the zinc-only plated steel sheet. Any method such as electroplating or displacement plating may be used.
[0027]
The surface-treated galvanized steel sheet obtained by the present invention has a treated layer containing Al, Si, P formed on the surface of the zinc-based plated layer as described above. It exhibits excellent corrosion resistance by suppressing white rust on the surface of the zinc-based plating, and also exhibits excellent coating adhesion when, for example, an organic coating is formed as a coating base. However, it is of course also effective to further improve the corrosion resistance, coating film adhesion, processability, etc., and to form various organic or inorganic films thereon.
[0028]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.
[0029]
Example A galvanized steel sheet having a zinc coating thickness of 20 g / m ² galvanized by electroplating on the surface of a 0.8 mm thick steel sheet (product number: SECC) was washed with water, dried, and dried. Used as an original plate.
[0030]
As a treatment liquid, a mixed liquid (pH 2) of 40 to 60 parts by mass of 50% by mass aluminum phosphate (manufactured by Nippon Chemical Industry Co., Ltd.) and 40 to 60 parts by mass of colloidal silica “ST-O” (manufactured by Nissan Chemical Industries, Ltd.) ~ 3), and after applying these to the surface of the galvanized steel sheet after degreasing with a spray pressure of 25 kPa (about 0.25 kg / cm ² ), washing with water and drying at 40 ° C., a galvanized layer A reaction layer was formed on top. The coating amount of the reaction layer was adjusted so that the average adhesion amount was about 50 mg / m ² . This was used as a reaction specimen.
[0031]
The ratio of Al to Si contained in the reaction layer ([Al%] / [Si%]) and the ratio of P to Al ([P%] / [Al%]) are determined by the fluorescent X-ray apparatus “Shimadzu Corporation”. It measured using "MIF-2100".
[0032]
On the reaction layer, a mixed liquid containing 20% by mass of a polyethylene resin emulsion in terms of solid content is applied and dried at 80 ° C. to form a film having a solid content of about 1 g / m ^2. did. This was used as a test material after the top coat resin coating.
[0033]
In addition, the above [Al%] / [Si%] ratio and [P%] / [Al%] ratio in the reaction layer are determined based on the respective concentrations and blends of aluminum biphosphate and colloidal silica when the treatment liquid is prepared. Adjusted by changing the ratio and spray treatment time.
[0034]
About each obtained test material, the corrosion resistance and the coating-film adhesiveness evaluation test were done with the following method, and the result was shown to Table 1,2.
[0035]
"Evaluation test method"
(1) Edge seal is applied to the end surface of the test material after the corrosion resistance reaction as it is, and after coating with the top coat resin, and the salt spray test specified in JIS-Z-2371 is performed. Measure the area ratio of the white rust generated.
[0036]
Evaluation Criteria 1: When the reaction remains as it is, the white rust generation area ratio after 12 hours of salt spray is evaluated.
◎; Less than 5% ○; Less than 5 to 20% △; Less than 20 to 50% ×; More than 50%
Evaluation criteria 2: In the case of coating with a top coat resin, the white rust generation area ratio after 240 hours of salt spray is evaluated.
◎; Less than 5% ○; Less than 5 to 20% △; Less than 20 to 50% ×; More than 50%
(2) Spray a solution prepared by adjusting the alkali degreasing agent “FC-4386” (manufactured by Nihon Parkerizing Co., Ltd.) to 20 g / liter for 5 seconds at 60 ° C. while keeping the corrosion resistance reaction after alkali degreasing and after coating with the top coat resin. After the treatment, it is washed with water and dried. Then, after end-sealing the end face of the test material, a salt spray test as defined in JIS-Z-2371 is performed, and the area ratio of white rust generated on the flat portion at each elapsed time is measured.
[0039]
Evaluation Criteria 3: When the reaction is continued, the white rust generation area ratio after 12 hours of salt spray is evaluated.
◎; Less than 5% ○; Less than 5 to 20% △; Less than 20 to 50% ×; More than 50%
Evaluation criteria 4: In the case of coating with a top coat resin, the white rust generation area ratio after 240 hours of salt spray is evaluated.
◎; Less than 5% ○; Less than 5 to 20% △; Less than 20 to 50% ×; More than 50%
(3) After coating “Magiclon # 1000” manufactured by Kansai Paint Co., Ltd. on the test material after coating film adhesion reaction and coating with top coat resin, baking treatment is performed at 160 ° C. (film thickness is baking at 160 ° C. (Adjusted to about 20μm by the thickness of the later coating)
[0042]
The primary adhesion is determined by the coating film remaining rate after 100 squares of 1 mm square grids are put in the coating film and the tape is peeled off. The secondary adhesion was determined by immersing the test material after painting in boiling water for 1 hour and wiping off the water, and then putting 100 squares of 1 mm square grids on the coating film. Ask,
◎; 90% or more ○; 70% or more, less than 90% Δ; more than 50%, less than 70% ×; less than 50%
[Table 1]

[0044]
[Table 2]

[0045]
In Tables 1 and 2 above, reference numerals 1 to 10 and 15 to 25 are examples that satisfy the prescribed requirements of the present invention. In both the reaction state and the state after coating with the top coat resin, the sample material remains alkaline. In addition to exhibiting excellent corrosion resistance regardless of whether it has been degreased, it also exhibits excellent performance in terms of primary adhesion and secondary adhesion.
[0046]
On the other hand, reference numerals 11 to 14 and 25 to 28 lack some of the defined requirements defined in the present invention, and remain in the reaction state and after coating with the top coat resin, as the test material, and alkaline degreasing. It can be seen that the corrosion resistance is poor at any later point, and the primary adhesion and secondary adhesion are clearly inferior.
[0047]
【The invention's effect】
The present invention is configured as described above. In particular, [Al%] / [Al%] / in the surface-modified layer formed on the zinc-based plated layer in the zinc-based plated steel sheet for the purpose of improving corrosion resistance and coating film adhesion. By adjusting [Si%] and [P%] / [Al%] to an appropriate range, the corrosion resistance is comparable to or exceeding that of chromate treatment, though it is a system that does not contain chromium, which has been avoided from pollution. It has become possible to provide a surface-treated zinc-based plated steel sheet having coating film adhesion.

Claims

A surface modified layer containing Al, Si, P obtained from an acidic aqueous solution containing aluminum biphosphate and colloidal silica is formed on the zinc-based plated layer in the galvanized steel sheet. A surface-treated galvanized steel sheet excellent in corrosion resistance, characterized in that the mass ratios of Al and Si and P and Al contained in the above satisfy the relationship of the following formulas (1) and (2).
0.10 <[Al%] / [Si%] <3.0 (1)
0.90 <[P%] / [Al%] <2.0 (2)

The surface-treated zinc-based plated steel sheet according to claim 1, wherein the surface-modified layer is made of aluminum phosphate into which silica is incorporated.

The surface-treated galvanized steel sheet according to claim 1 or 2, wherein the surface-modified layer does not contain a water-soluble component.

A method for producing a surface-treated zinc-based plated steel sheet in which a surface modification layer containing Al, Si, P is formed on a zinc-based plated layer in a zinc-based plated steel sheet,
A step of preparing an acidic aqueous solution containing 40 to 60% by mass of aluminum biphosphate and 40 to 60% by mass of colloidal silica and having a pH of 2 to 3,
The acidic aqueous solution is applied onto the galvanized steel sheet, and is heat-dried so that the mass ratio of Al and Si and P and Al satisfies the relationship of the following formulas (1) and (2). Forming a layer;
A method for producing a surface-treated galvanized steel sheet having excellent corrosion resistance.
0.10 <[Al%] / [Si%] <3.0 (1)
0.90 <[P%] / [Al%] <2.0 (2)