JP2016204695A - Manufacturing method of electrogalvanized sheet steel - Google Patents
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本発明は、電気亜鉛めっき鋼板の製造方法に関するものであり、特に、めっき層の表面に酸性水溶液で処理を施すことで、高い白色度を有する電気亜鉛めっき鋼板を得る方法に関するものである。 The present invention relates to a method for producing an electrogalvanized steel sheet, and particularly to a method for obtaining an electrogalvanized steel sheet having high whiteness by treating the surface of a plating layer with an acidic aqueous solution.
化成処理の施された電気亜鉛めっき鋼板は、良好な耐食性を有する点や、コストの点などから、現在、家電製品をはじめ多くの用途に用いられている。かかる電気亜鉛めっき鋼板は、製品の外観がよいという点から、一般的に、高い白色度が要求される。そのため、白色度を向上させるための種々の技術が開発されている。 Electrogalvanized steel sheets that have been subjected to chemical conversion treatment are currently used in many applications including home appliances because of their good corrosion resistance and cost. Such an electrogalvanized steel sheet is generally required to have a high degree of whiteness because the appearance of the product is good. Therefore, various techniques for improving the whiteness have been developed.
ここで、電気亜鉛めっき鋼板の白色度は、めっき後の化成処理によって低下するものの、化成処理前のめっき層の表面状態に大きく依存するため、電気亜鉛めっき条件の適正化を図ることで、白色度の向上を図る技術が数多く開発されている。なお、電気亜鉛めっき鋼板の白色度の指標としては、通常、明度（Ｌ値）が用いられる。 Here, although the degree of whiteness of the electrogalvanized steel sheet is reduced by the chemical conversion treatment after plating, it depends greatly on the surface state of the plating layer before chemical conversion treatment. Many technologies have been developed to improve the degree. In addition, as an index of whiteness of the electrogalvanized steel sheet, brightness (L value) is usually used.
高い白色度を有する電気亜鉛めっき鋼板を製造する方法として、例えば、特許文献１に開示されているように、無機イオン（Tl）を含有させた硫酸塩酸性亜鉛めっき浴中で電気亜鉛めっきを施す製造方法がある。この製造方法を用いれば、Tlの効果によって高い白色度（明度）を得ることができる。 As a method for producing an electrogalvanized steel sheet having high whiteness, for example, as disclosed in Patent Document 1, electrogalvanization is performed in a sulfuric acid chloride galvanizing bath containing inorganic ions (Tl). There is a manufacturing method. If this manufacturing method is used, high whiteness (brightness) can be obtained by the effect of Tl.
また、別の方法としては、所定の有機物を添加した電気亜鉛めっき浴を用いることで、電気亜鉛めっき鋼板の白色度を向上させる方法がある。例えば、特許文献２では、所定濃度のグリシン、アスパラギン酸、カルボン酸基を２つ以上有するカルボン酸又はその塩の群から選択された１種以上を含む硫酸酸性亜鉛めっき浴を用い、特許文献３では、ナフテン酸の金属塩、アニリン誘導体、低級アルカノイル化合物、および有機過酸化物よりなる群から選択される少なくとも１種を、所定量添加した電気亜鉛めっき浴を用いている。 As another method, there is a method of improving the whiteness of the electrogalvanized steel sheet by using an electrogalvanizing bath to which a predetermined organic substance is added. For example, in Patent Document 2, a sulfuric acid acidic zinc plating bath containing at least one selected from the group of glycine, aspartic acid, carboxylic acid having two or more carboxylic acid groups or salts thereof having a predetermined concentration is used. Uses an electrogalvanizing bath in which a predetermined amount of at least one selected from the group consisting of a metal salt of naphthenic acid, an aniline derivative, a lower alkanoyl compound, and an organic peroxide is added.
しかし、特許文献１のように、無機物を含有するめっき浴を用いて製造された電気亜鉛めっき鋼板は、めっき層中に前記無機物が共析するため、めっき層の耐食性が劣化したり、硬度が上昇するといった、亜鉛めっき層の特性が失われるという問題があった。また、特許文献２及び３のように、有機物を添加しためっき浴を用いる製造方法では、電気亜鉛めっき時に電流効率が低下するという問題や、不溶性アノードの寿命が短くなるという問題があった。また、製造された電気亜鉛めっき鋼板は、めっき浴中に添加された有機物がめっき層中で共析するため、めっき層の硬度が上昇する等の亜鉛めっき層の特性が失われるという問題があった。 However, as disclosed in Patent Document 1, the electrogalvanized steel sheet manufactured using a plating bath containing an inorganic substance is co-deposited in the plating layer, so that the corrosion resistance of the plating layer is deteriorated or the hardness is low. There was a problem that the characteristics of the galvanized layer were lost, such as an increase. In addition, as in Patent Documents 2 and 3, the production method using a plating bath to which an organic substance is added has a problem that current efficiency is lowered during electrogalvanization and a problem that the life of the insoluble anode is shortened. In addition, the manufactured electrogalvanized steel sheet has a problem that the characteristics of the galvanized layer are lost, for example, the hardness of the plated layer is increased because the organic matter added to the plating bath is co-deposited in the plated layer. It was.
上記の課題を解決するべく、本発明者らの一部は、特許文献４に示すように、鋼板に電気亜鉛めっき法によりめっき層を形成した後、硝酸イオン、ヨウ素酸イオン、臭素酸イオン及び塩素酸イオンのうちの少なくとも１種を、合計で0.002〜0.05mol／Lの範囲で含有し、pHが4.5以下である酸性水溶液に、0.5秒以上接触させ、水洗及び乾燥を施した後、前記めっき層の表面に化成皮膜を形成することを特徴とする電気亜鉛めっき鋼板の製造方法を開発した。この製造方法は、めっき層の表面形状の適正化を図る技術であり、この製造方法によれば、得られた電気亜鉛めっき鋼板は白色度が高く、製造時にめっき浴中に無機物や有機物を添加する必要がないため、無機物又は有機物の共析に起因しためっき層の特性劣化及び電気めっき時の電流効率の低下を有効に抑制できる。 In order to solve the above problems, some of the present inventors have formed a plating layer on a steel sheet by electrogalvanization as shown in Patent Document 4, and then nitrate, iodate, bromate and After containing at least one kind of chlorate ions in a range of 0.002 to 0.05 mol / L in total and having a pH of 4.5 or less for 0.5 seconds or more, washing and drying, A method for producing an electrogalvanized steel sheet characterized by forming a chemical conversion film on the surface of the plating layer has been developed. This production method is a technique for optimizing the surface shape of the plating layer. According to this production method, the obtained electrogalvanized steel sheet has high whiteness, and inorganic or organic substances are added to the plating bath during production. Therefore, it is possible to effectively suppress deterioration in the properties of the plating layer and reduction in current efficiency during electroplating due to the eutectoid of inorganic or organic matter.
しかしながら、特許文献４の製造方法により得られる電気亜鉛めっき鋼板は、高い白色度を有するものの、耐黒変性が劣ることを本発明者らは認識した。 However, the present inventors have recognized that the electrogalvanized steel sheet obtained by the production method of Patent Document 4 has high whiteness, but is inferior in blackening resistance.
そこで本発明は、上記課題に鑑み、耐黒変性を低下させることなく、高い白色度を有する電気亜鉛めっき鋼板を製造することが可能な、電気亜鉛めっき鋼板の製造方法を提供することを目的とする。 Therefore, in view of the above problems, the present invention aims to provide a method for producing an electrogalvanized steel sheet capable of producing an electrogalvanized steel sheet having high whiteness without reducing blackening resistance. To do.
本発明者らは、上記の課題を解決するべく検討を重ねた結果、上述した耐黒変性の低下は、酸性水溶液のpH調整剤として使用していた硫酸及び／又は塩酸に起因する硫酸イオン及び／又は塩化物イオンの影響により生じていることを見出した。めっき層を形成した鋼板を前記酸性水溶液に接触させることにより、微細な凹凸を有する前記めっき層の表面が微量溶解して平坦化されることで白色度が上昇するが、このとき、同時に水素イオンが消費されるため、界面（めっき層表面）のpHは上昇する。ここで、前記酸性水溶液中に硫酸イオン及び／又は塩化物イオンが特定濃度以上で存在すると、溶解した亜鉛イオンの一部が硫酸イオン及び／又は塩化物イオンと化合物を形成して表面に残存してしまい、これが耐黒変性を低下させる原因と推定される。そこで、酸性水溶液中の硫酸イオン及び塩化物イオンの合計濃度を所定値未満とすることで、耐黒変性が低下しないことを見出した。 As a result of repeated studies to solve the above-mentioned problems, the present inventors have found that the above-described reduction in blackening resistance is caused by sulfuric acid and / or sulfuric acid ions that have been used as a pH adjuster for acidic aqueous solutions and / or sulfuric acid ions. It was found that it was caused by the influence of chloride ions. By bringing the steel sheet on which the plating layer is formed into contact with the acidic aqueous solution, the surface of the plating layer having fine irregularities is slightly dissolved and flattened to increase the whiteness. Is consumed, the pH of the interface (plating layer surface) rises. Here, when sulfate ions and / or chloride ions are present in the acidic aqueous solution at a specific concentration or more, some dissolved zinc ions form a compound with sulfate ions and / or chloride ions and remain on the surface. This is presumed to be a cause of lowering blackening resistance. Therefore, it has been found that the blackening resistance is not lowered by making the total concentration of sulfate ions and chloride ions in the acidic aqueous solution less than a predetermined value.
さらに、本発明者らは、上記酸性水溶液中の硫酸イオン及び塩化物イオンの合計濃度に関わらず、酸性水溶液中の亜鉛イオン濃度も耐黒変性と相関があることを見出した。めっき層を形成した鋼板を酸性水溶液中に連続的に接触させていく連続操業の過程で、酸性水溶液中にはめっき層の亜鉛が溶解し不可避的に亜鉛イオンが混入する。そして、亜鉛イオン濃度が所定値を超えた酸性水溶液で処理された電気亜鉛めっき鋼板は、耐黒変性が劣っていることを本発明者らは見出した。 Furthermore, the present inventors have found that the zinc ion concentration in the acidic aqueous solution is correlated with the blackening resistance regardless of the total concentration of sulfate ions and chloride ions in the acidic aqueous solution. In the process of continuous operation in which the steel sheet on which the plating layer is formed is continuously brought into contact with the acidic aqueous solution, zinc in the plating layer is dissolved in the acidic aqueous solution, and zinc ions are inevitably mixed. The inventors have found that the electrogalvanized steel sheet treated with an acidic aqueous solution having a zinc ion concentration exceeding a predetermined value is inferior in blackening resistance.
本発明は、上記の知見によって完成されたものであり、その要旨構成は以下のとおりである。
（１）鋼板上に、電気亜鉛めっき法によって、亜鉛含有量が97質量％以上であるめっき層を形成する工程と、
前記めっき層を形成した鋼板を、硝酸イオン、ヨウ素酸イオン及び臭素酸イオンのうちの少なくとも１種を合計で0.002mol／L以上1.0mol／L以下の濃度で含有し、硫酸イオン及び塩化物イオンの合計濃度が0.01mol／L未満であり、亜鉛イオン濃度が1.0mol／L以下であり、pHが3以下である酸性水溶液に、0.5秒以上接触させる工程と、
前記めっき層上に化成皮膜を形成する工程と、
を有することを特徴とする電気亜鉛めっき鋼板の製造方法。
This invention is completed by said knowledge, The summary structure is as follows.
(1) forming a plating layer having a zinc content of 97% by mass or more on a steel sheet by electrogalvanizing;
The steel sheet on which the plating layer is formed contains at least one of nitrate ion, iodate ion and bromate ion at a concentration of 0.002 mol / L to 1.0 mol / L in total, sulfate ion and chloride ion A step of contacting an acidic aqueous solution having a total concentration of less than 0.01 mol / L, a zinc ion concentration of 1.0 mol / L or less, and a pH of 3 or less for 0.5 seconds or more,
Forming a chemical conversion film on the plating layer;
A method for producing an electrogalvanized steel sheet, comprising:
（２）前記化成皮膜の片面当たりの付着量が、0.05g／m2以上1g／m2以下である上記（１）に記載の電気亜鉛めっき鋼板の製造方法。 (2) the adhesion amount per one side of the conversion coating, the method of manufacturing an electro-galvanized steel sheet according to 0.05 g / m 2 or more 1 g / m 2 or less above (1).
本発明の電気亜鉛めっき鋼板の製造方法によれば、耐黒変性を低下させることなく、高い白色度を有する電気亜鉛めっき鋼板を製造することが可能である。 According to the method for producing an electrogalvanized steel sheet of the present invention, it is possible to produce an electrogalvanized steel sheet having high whiteness without reducing blackening resistance.
本発明の一実施形態による電気亜鉛めっき鋼板の製造方法は、鋼板上に、電気亜鉛めっき法によって、亜鉛含有量が97質量％以上であるめっき層を形成する工程と、前記めっき層を形成した鋼板を、硝酸イオン、ヨウ素酸イオン及び臭素酸イオンのうちの少なくとも１種を合計で0.002mol／L以上1.0mol／L以下の濃度で含有し、硫酸イオン及び塩化物イオンの合計濃度が0.01mol／L未満であり、亜鉛イオン濃度が1.0mol／L以下であり、pHが3以下である酸性水溶液に、0.5秒以上接触させる工程と、前記めっき層上に化成皮膜を形成する工程と、を有することを特徴とする。以下、各工程について詳細に説明する。 The method for producing an electrogalvanized steel sheet according to an embodiment of the present invention includes a step of forming a plated layer having a zinc content of 97% by mass or more on the steel sheet by an electrogalvanizing method, and forming the plated layer. The steel sheet contains at least one of nitrate ion, iodate ion and bromate ion at a total concentration of 0.002 mol / L to 1.0 mol / L, and the total concentration of sulfate ion and chloride ion is 0.01 mol. / L, a zinc ion concentration of 1.0 mol / L or less, a step of contacting an acidic aqueous solution having a pH of 3 or less for 0.5 seconds or more, and a step of forming a chemical conversion film on the plating layer. It is characterized by having. Hereinafter, each step will be described in detail.
（めっき層形成工程）
まず、電気亜鉛めっき法によって、鋼板上にめっき層を形成する。電気亜鉛めっき法に用いられる浴種については特に限定はされず、例えば、硫酸浴、塩化物浴、ジンケート浴又はシアン浴等を用いることができるが、ジンケート浴やシアン浴等のアルカリ浴を用いた場合、不純物としてのアニオンや添加剤の影響が避けられないため、硫酸浴又は塩化物浴を用いることが好ましい。また、前記めっき層は、意図的に含有させた成分や不可避的に含有する不純物（原板から溶出する鋼成分や、混入する恐れがあるNi、Co等）を少量含んでいても問題はなく、本実施形態では、めっき層中の亜鉛の含有量は97質量％以上とする。97質量％未満では、亜鉛以外の成分の影響が大きくなり、安定した性能を発揮できない恐れがあり、また、電気亜鉛めっき鋼板が本来有する白色度が低下するためである。なお、前記めっき層中の亜鉛の含有量は、希塩酸等の酸液との接触によりめっき層を溶解させ、溶解成分を湿式分析することで求めることができる。
(Plating layer forming process)
First, a plating layer is formed on a steel plate by electrogalvanizing. There are no particular limitations on the type of bath used in the electrogalvanizing method. For example, a sulfuric acid bath, a chloride bath, a zincate bath, or a cyan bath can be used, but an alkaline bath such as a zincate bath or a cyan bath is used. In this case, it is preferable to use a sulfuric acid bath or a chloride bath because the influence of anions and additives as impurities cannot be avoided. In addition, the plating layer may contain a small amount of intentionally contained components and inevitably contained impurities (steel components eluted from the original plate, Ni, Co, etc. that may be mixed), In the present embodiment, the zinc content in the plating layer is 97% by mass or more. If it is less than 97% by mass, the influence of components other than zinc is increased, and there is a possibility that stable performance cannot be exhibited, and the whiteness inherent to the electrogalvanized steel sheet is reduced. The zinc content in the plating layer can be determined by dissolving the plating layer by contact with an acid solution such as dilute hydrochloric acid and performing wet analysis on the dissolved components.
前記めっき層の片面当たりの付着量は、電気亜鉛めっき層の特性と白色度を確保する点から、5〜30g／m2であることが好ましい。なお、前記めっき層の付着量は、めっき層の付着面積を把握した上で、希塩酸等の酸液との接触によりめっき層を溶解させた前後の鋼板の質量変化、又は、溶解しためっき成分の定量化により求めることができる。 The adhesion amount per one side of the plating layer is preferably 5 to 30 g / m 2 from the viewpoint of ensuring the characteristics and whiteness of the electrogalvanized layer. In addition, after the amount of adhesion of the plating layer grasps the adhesion area of the plating layer, the mass change of the steel sheet before and after dissolving the plating layer by contact with an acid solution such as dilute hydrochloric acid, or the dissolved plating component It can be determined by quantification.
（酸性水溶液による処理工程）
次に、前記めっき層を形成した鋼板を、硝酸イオン、ヨウ素酸イオン及び臭素酸イオンのうちの少なくとも１種を合計で0.002mol／L以上1.0mol／L以下の濃度で含有し、硫酸イオン及び塩化物イオンの合計濃度が0.01mol／L未満であり、亜鉛イオン濃度が1.0mol／L以下であり、pHが3以下である酸性水溶液に、0.5秒以上接触させる。酸性水溶液中に硝酸イオン、ヨウ素酸イオン及び臭素酸イオンは、前記めっき層の表層を一定量除去することで、めっき結晶の微細な凹凸を平坦化できる。その結果、有効に入射光を反射でき、白色度を高めることができる。これら以外のイオンを用いた場合では、同様の効果を奏することができない。
(Processing with acidic aqueous solution)
Next, the steel sheet on which the plating layer is formed contains at least one of nitrate ion, iodate ion and bromate ion at a total concentration of 0.002 mol / L to 1.0 mol / L, Contact with an acidic aqueous solution having a total chloride ion concentration of less than 0.01 mol / L, a zinc ion concentration of 1.0 mol / L or less, and a pH of 3 or less for 0.5 seconds or more. Nitrate ions, iodate ions, and bromate ions in the acidic aqueous solution can flatten fine irregularities of the plating crystal by removing a certain amount of the surface layer of the plating layer. As a result, incident light can be effectively reflected and whiteness can be increased. When ions other than these are used, the same effect cannot be obtained.
酸性水溶液中のこれらイオンの合計濃度は0.002mol／L以上1.0mol／L以下とする。合計濃度が0.002mol／L未満では、イオンの量が少なすぎるため、前記めっき層の表面の平坦化が十分に行えず、所望の白色度を得ることができない。一方、合計濃度が1.0mol／Lを超えると、界面のpH上昇効果が大きくなり、亜鉛溶解が抑制されるため、前記めっき層の表面の平坦化が十分に行えず、所望の白色度を得ることができない。より高い白色度を得る観点からは、合計濃度は0.1mol／L以上とすることが好ましい。 The total concentration of these ions in the acidic aqueous solution is 0.002 mol / L or more and 1.0 mol / L or less. When the total concentration is less than 0.002 mol / L, since the amount of ions is too small, the surface of the plating layer cannot be sufficiently flattened and desired whiteness cannot be obtained. On the other hand, when the total concentration exceeds 1.0 mol / L, the effect of increasing the pH at the interface is increased, and zinc dissolution is suppressed, so that the surface of the plating layer cannot be sufficiently flattened and desired whiteness is obtained. I can't. From the viewpoint of obtaining higher whiteness, the total concentration is preferably 0.1 mol / L or more.
なお、特許文献４では、これらの合計濃度の上限を0.05mol／Lとしたが、本実施形態では、後述のとおり、硫酸イオン及び塩化物イオンの合計濃度を0.01mol／L未満とし、この場合、硝酸イオン、ヨウ素酸イオン及び臭素酸イオンのうちの少なくとも１種の合計濃度が0.05mol／Lを超えても、白色度は低下しない。 In Patent Document 4, the upper limit of the total concentration is 0.05 mol / L. However, in this embodiment, as described later, the total concentration of sulfate ions and chloride ions is less than 0.01 mol / L. Even when the total concentration of at least one of nitrate ion, iodate ion and bromate ion exceeds 0.05 mol / L, the whiteness does not decrease.
硝酸イオン、ヨウ素酸イオン及び臭素酸イオンのイオン源は、特に限定されない。例えば、それぞれの酸性水溶液や、金属塩、又はこれらの混合物など、イオンの含有量等を考慮して適宜選択することができる。 The ion source of nitrate ion, iodate ion and bromate ion is not particularly limited. For example, each acidic aqueous solution, metal salt, or a mixture thereof can be appropriately selected in consideration of the ion content and the like.
本実施形態では、酸性水溶液中の硫酸イオン及び塩化物イオンの合計濃度を0.01mol／L未満とする必要がある。この合計濃度が0.01mol／L以上では、上述した様に、十分な耐黒変性が得られないからである。本実施形態は、この合計濃度が0mol／Lの場合も包含する。 In the present embodiment, the total concentration of sulfate ions and chloride ions in the acidic aqueous solution needs to be less than 0.01 mol / L. This is because when the total concentration is 0.01 mol / L or more, sufficient blackening resistance cannot be obtained as described above. This embodiment includes the case where this total concentration is 0 mol / L.
本実施形態では、酸性水溶液中の亜鉛イオン濃度は1.0mol／L以下とする必要がある。亜鉛イオン濃度が1.0mol／Lを超えると、上述したように、十分な耐黒変性が得られないからである。なお、めっき層を形成した鋼板を酸性水溶液中に連続的に接触させていく連続操業では、酸性水溶液は循環して用いられるため、時間の経過に伴い、酸性水溶液中の亜鉛濃度は不可避的に増加する。そのため、酸性水溶液中の亜鉛イオン濃度が1.0mol／Lを超えない段階で、酸性水溶液を一部廃却し、亜鉛イオン濃度の低い新たな酸性水溶液を追加添加するなどして、酸性水溶液中の亜鉛イオン濃度を常時1.0mol／L以下とする。なお、本実施形態は亜鉛イオン濃度が0mol／Lの場合も包含するが、連続的な操業を想定すると、亜鉛イオン濃度は通常0.01mol／L以上となる。 In this embodiment, the zinc ion concentration in the acidic aqueous solution needs to be 1.0 mol / L or less. This is because when the zinc ion concentration exceeds 1.0 mol / L, sufficient blackening resistance cannot be obtained as described above. In continuous operation in which the steel sheet on which the plating layer is formed is continuously brought into contact with the acidic aqueous solution, the acidic aqueous solution is circulated and used. Therefore, the zinc concentration in the acidic aqueous solution is unavoidable over time. To increase. Therefore, when the zinc ion concentration in the acidic aqueous solution does not exceed 1.0 mol / L, some of the acidic aqueous solution is discarded, and a new acidic aqueous solution with a low zinc ion concentration is added. The zinc ion concentration is always 1.0 mol / L or less. In addition, although this embodiment includes the case where a zinc ion concentration is 0 mol / L, when a continuous operation is assumed, a zinc ion concentration will be 0.01 mol / L or more normally.
本実施形態では、酸性水溶液のpHを3以下とする必要がある。酸性水溶液のpHが3を超えると、酸性水溶液の反応性が不十分となり、前記めっき層の表面の平坦化が十分に行えず、所望の白色度を得ることができない。さらに、酸性水溶液のpHは1.0以上とすることが好ましい。酸性水溶液のpHが1.0未満の場合、白色度の向上効果は得られるものの、酸性水溶液への接触時にめっき層の溶解量が多くなるため、めっき層を予め多く形成する必要性が生じ、めっき層形成のためのコストアップを招くためである。所望の白色度向上効果が得られ、めっき層の溶解量も少なくできるという点から、酸性水溶液のpHは2.0以上3.0以下とすることが好ましい。なお、pHの調整については、硫酸イオン及び塩化物イオンの合計濃度を0.01mol／L未満とするため、硫酸及び塩酸は使用せず、硝酸を使用するのが望ましい。 In this embodiment, the pH of the acidic aqueous solution needs to be 3 or less. If the pH of the acidic aqueous solution exceeds 3, the reactivity of the acidic aqueous solution becomes insufficient, the surface of the plating layer cannot be sufficiently flattened, and the desired whiteness cannot be obtained. Furthermore, the pH of the acidic aqueous solution is preferably 1.0 or more. If the pH of the acidic aqueous solution is less than 1.0, the effect of improving the whiteness can be obtained, but the amount of dissolution of the plating layer increases upon contact with the acidic aqueous solution, so that it is necessary to form a large number of plating layers in advance. This is to increase the cost for forming. The pH of the acidic aqueous solution is preferably 2.0 or more and 3.0 or less from the viewpoint that a desired whiteness improvement effect can be obtained and the amount of dissolution of the plating layer can be reduced. Regarding pH adjustment, it is desirable not to use sulfuric acid and hydrochloric acid but to use nitric acid so that the total concentration of sulfate ions and chloride ions is less than 0.01 mol / L.
本実施形態では、めっき層の酸性水溶液との接触時間を0.5秒以上とする必要がある。接触時間が0.5秒未満の場合、接触時間が短すぎるため、前記めっき層の表面の平坦化が十分に行えず、所望の白色度を得ることができないからである。なお、接触時間の上限については、高い白色度を得る観点からは特に限定されないが、生産性の点からは、5秒以下とすることが好ましい。また、接触方法は特に限定されず、例えば、鋼板を酸性水溶液に浸漬させる方法、鋼板に酸性水溶液を塗布する方法、鋼板に酸性水溶液をスプレーする方法等を用いることができる。 In the present embodiment, the contact time of the plating layer with the acidic aqueous solution needs to be 0.5 seconds or longer. This is because when the contact time is less than 0.5 seconds, the contact time is too short, so that the surface of the plating layer cannot be sufficiently flattened, and desired whiteness cannot be obtained. The upper limit of the contact time is not particularly limited from the viewpoint of obtaining high whiteness, but is preferably 5 seconds or less from the viewpoint of productivity. Moreover, a contact method is not specifically limited, For example, the method of immersing a steel plate in acidic aqueous solution, the method of apply | coating acidic aqueous solution to a steel plate, the method of spraying acidic aqueous solution on a steel plate, etc. can be used.
酸性水溶液の温度についても、特に限定されないが、定温保持性や昇温コストの点から、30〜60℃の範囲とすることが好ましい。また、酸性水溶液中には、pH緩衝剤を含有する場合もあり、不可避的不純物が含有されることも考えられる。加えて、めっき層からの溶出成分（Fe、Ni等）や、めっき浴の汚染成分を少量含有していても構わない。 The temperature of the acidic aqueous solution is not particularly limited, but is preferably in the range of 30 to 60 ° C. from the viewpoint of constant temperature retention and temperature increase cost. Further, the acidic aqueous solution may contain a pH buffer, and it is considered that unavoidable impurities are contained. In addition, it may contain a small amount of components eluted from the plating layer (Fe, Ni, etc.) and contamination components of the plating bath.
本実施形態による酸性水溶液による処理工程によれば、めっき浴中に共析物となる無機物や有機物を添加する必要がないため、めっき層の特性（硬度、耐食性、耐黒変性や被加工時の耐剥離性など）及び電気亜鉛めっき時の電流効率も、十分に確保できる。なお、酸性水溶液による処理工程後は、その後の工程への悪影響（化成皮膜へのコンタミネーション等）をなくすため、前記鋼板の水洗及び乾燥を行うことが好ましい。 According to the treatment process with an acidic aqueous solution according to the present embodiment, it is not necessary to add inorganic substances and organic substances that become eutectoids in the plating bath, so the characteristics of the plating layer (hardness, corrosion resistance, blackening resistance and processing at the time of processing) (Peeling resistance, etc.) and current efficiency during electrogalvanization can be sufficiently secured. In addition, after the process process by acidic aqueous solution, in order to eliminate the bad influence (contamination etc. to a chemical conversion film) to a subsequent process, it is preferable to wash and dry the said steel plate.
（化成皮膜形成工程）
次に、前記酸性水溶液に接触させ、水洗及び乾燥を施した電気亜鉛めっき鋼板の表面に、化成皮膜を形成する。この化成皮膜は、前記鋼板表面に、耐食性や、密着性、耐疵付き性などを備えることができるように設けられる層であり、白色度の低下を防ぐ点から、その付着量が片面当たり0.05g／m2以上1g／m2以下の範囲であることが好ましい。
(Chemical conversion film formation process)
Next, a chemical conversion film is formed on the surface of the electrogalvanized steel sheet that has been brought into contact with the acidic aqueous solution and washed and dried. This chemical conversion film is a layer provided on the surface of the steel sheet so as to be provided with corrosion resistance, adhesion, scratch resistance, etc., and from the viewpoint of preventing a decrease in whiteness, its adhesion amount is 0.05 per side. it is preferably g / m 2 or more 1 g / m 2 or less.
また、前記化成皮膜は、特に限定されず、任意の化成皮膜を使用することができ、例えば、無機皮膜、有機皮膜、有機無機複合皮膜、又はこれらの複層皮膜を用いることができる。要求される特性、つまり、上述の耐食性、耐黒変性、密着性、耐疵付き性に応じて、その種類、成分、付着量を適宜選択すればよい。 Moreover, the said chemical film is not specifically limited, Arbitrary chemical films can be used, For example, an inorganic film, an organic film, an organic inorganic composite film, or these multilayer films can be used. The type, component, and adhesion amount may be appropriately selected according to the required characteristics, that is, the above-described corrosion resistance, blackening resistance, adhesion, and wrinkle resistance.
以下、実施例を挙げて本発明をより詳細に説明するが、本発明はこれらに限定されるものではない。 EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.
以下の工程（ｉ）〜（ｉｉｉ）を行い、サンプルNo.1-25の25種類の電気亜鉛めっき鋼板を作製した。 The following steps (i) to (iii) were performed to prepare 25 types of electrogalvanized steel sheets of Sample No. 1-25.
（ｉ）冷延鋼板に対して、脱脂・酸洗処理を施した後、電気亜鉛めっき法（条件は、めっき浴：Zn2+イオン1.5mol／L含有する硫酸酸性浴（pH2.0、温度50℃）、相対流速：1.5m／秒、電流密度：50A／dm2）によって、表１に示す片面当たりの付着量で、亜鉛含有量が97質量％以上の亜鉛めっき層を形成し、その後、水洗・乾燥を行った。 (I) After degreasing and pickling treatment on cold-rolled steel sheet, electrogalvanization method (conditions are plating bath: sulfuric acid acidic bath containing 1.5 mol / L of Zn 2+ ions (pH 2.0, temperature 50 ° C.), relative flow rate: 1.5 m / second, current density: 50 A / dm 2 ), a zinc plating layer having a zinc content of 97% by mass or more with the amount of adhesion per one side shown in Table 1 was formed. , Washed with water and dried.
（ｉｉ）作製した前記電気亜鉛めっき鋼板を、表１に示すイオンを含有する酸性水溶液に接触させた。酸性水溶液の条件、及び、酸性水溶液を用いた処理条件は、表１に示す。なお、サンプルNo.25については、酸性水溶液による処理を実施しなかった（表１を参照）。また、連続操業中の種々のタイミングで実験を行うことで、各サンプルにおいて、酸性水溶液中の亜鉛イオン濃度を表１に示す値に設定した。 (Ii) The produced electrogalvanized steel sheet was brought into contact with an acidic aqueous solution containing ions shown in Table 1. The conditions of the acidic aqueous solution and the treatment conditions using the acidic aqueous solution are shown in Table 1. In addition, about sample No. 25, the process by acidic aqueous solution was not implemented (refer Table 1). In addition, by conducting experiments at various timings during continuous operation, the zinc ion concentration in the acidic aqueous solution was set to the value shown in Table 1 for each sample.
（ｉｉｉ）次に、上述の酸性水溶液処理を施した鋼板を、水洗、乾燥させた後、前記鋼板の表面上に、第一リン酸マンガン100質量部に対し、シリカ（平均粒径：7nm）70質量部を含有する化成処理液をロールコーターで塗布し、140℃の熱風炉で焼付け、乾燥させることで、片面当たりの付着量が0.4g／m2である無機皮膜からなる化成皮膜を形成した。 (Iii) Next, after washing and drying the steel sheet subjected to the acidic aqueous solution treatment, silica (average particle diameter: 7 nm) is formed on the surface of the steel sheet with respect to 100 parts by mass of the first manganese phosphate. A chemical conversion film containing 70 parts by mass is applied with a roll coater, baked in a hot air oven at 140 ° C, and dried to form a chemical conversion film consisting of an inorganic film with an adhesion amount of 0.4 g / m 2 per side. did.
以上のようにして得られた各電気亜鉛めっき鋼板のサンプルNo.1〜25について以下の評価を行った。 The following evaluation was performed about sample No. 1-25 of each electrogalvanized steel plate obtained by making it above.
（１）白色度（Ｌ値）
各サンプルについて、色差計（日本電色工業（株）製のＳＥ２０００）を用いてＳＣＥ（正反射光除去）による明度（Ｌ値）の測定を行った。評価は、以下の基準に従って行い、測定値及び評価結果を表２に示す。
◎：Ｌ値が66以上
○：Ｌ値が64以上66未満
×：Ｌ値が64未満
(1) Whiteness (L value)
About each sample, the brightness (L value) by SCE (regular reflection light removal) was measured using the color difference meter (SE2000 by Nippon Denshoku Industries Co., Ltd.). Evaluation is performed according to the following criteria, and the measured values and evaluation results are shown in Table 2.
◎: L value is 66 or more ○: L value is 64 or more and less than 66 ×: L value is less than 64
（２）耐黒変性
各サンプルを７０ｍｍ×１５０ｍｍのサイズに２枚切り出し、対象面を重ね合わせてトルク強度２０ｋｇｆで締め付けたものを、５０℃、９８％ＲＨの恒温槽に４週間保持し、保持前後の試験片の明度（Ｌ値）変化（ΔＬ）を測定した。評価は、以下の基準に従って行い、測定値及び評価結果を表２に示す。
◎：−３≦ΔＬ
○：−５≦ΔＬ＜−３
×：ΔＬ＜−５
(2) Blackening resistance Two samples each cut to a size of 70 mm x 150 mm, the target surfaces overlapped and tightened with a torque strength of 20 kgf are held in a constant temperature bath at 50 ° C and 98% RH for 4 weeks and held The lightness (L value) change (ΔL) of the test pieces before and after was measured. Evaluation is performed according to the following criteria, and the measured values and evaluation results are shown in Table 2.
A: −3 ≦ ΔL
○: −5 ≦ ΔL <−3
×: ΔL <−5
（３）酸性水溶液処理工程におけるめっき層の溶解量
各サンプルについて、酸性水溶液処理前後における、前記酸性水溶液中のめっき層成分（Zn）濃度を、ＩＣＰ分析装置を用いて分析し、Zn濃度の増加分からめっきの溶解量（単位面積当たりの溶解量（g／m2））を算出し、評価を行った。算出結果を表２に示す。
(3) Amount of dissolution of the plating layer in the acidic aqueous solution treatment step For each sample, the plating layer component (Zn) concentration in the acidic aqueous solution before and after the acidic aqueous solution treatment was analyzed using an ICP analyzer, and the Zn concentration increased. The dissolution amount of plating (dissolution amount per unit area (g / m 2 )) was calculated from the minute and evaluated. Table 2 shows the calculation results.
表２の結果から、各本発明例では、比較例（サンプルNo.1,2,13,20,24,25）に比べて、いずれも高い白色度が得られたことがわかる。これは、酸性水溶液接触工程の違いによると考えられる。さらに、各本発明例では、比較例（サンプルNo.7,8,9,14）に比べて、耐黒変性に優れることがわかる。これは、酸性水溶液中の硫酸イオン及び塩化物イオン濃度の濃度、並びに亜鉛イオン濃度の違いによると考えられる。 From the results shown in Table 2, it can be seen that in each of the inventive examples, a higher whiteness was obtained than in the comparative examples (sample Nos. 1, 2, 13, 20, 24, 25). This is considered due to the difference in the acidic aqueous solution contact process. Furthermore, it can be seen that each example of the present invention is superior in resistance to blackening compared to the comparative examples (sample Nos. 7, 8, 9, 14). This is considered to be due to the difference in the concentration of sulfate ion and chloride ion in the acidic aqueous solution and the concentration of zinc ion.
本発明の電気亜鉛めっき鋼板の製造方法によれば、耐黒変性を低下させることなく、高い白色度を有する電気亜鉛めっき鋼板を製造することが可能である。 According to the method for producing an electrogalvanized steel sheet of the present invention, it is possible to produce an electrogalvanized steel sheet having high whiteness without reducing blackening resistance.
Claims (2)
前記めっき層を形成した鋼板を、硝酸イオン、ヨウ素酸イオン及び臭素酸イオンのうちの少なくとも１種を合計で0.002mol／L以上1.0mol／L以下の濃度で含有し、硫酸イオン及び塩化物イオンの合計濃度が0.01mol／L未満であり、亜鉛イオン濃度が1.0mol／L以下であり、pHが3以下である酸性水溶液に、0.5秒以上接触させる工程と、
前記めっき層上に化成皮膜を形成する工程と、
を有することを特徴とする電気亜鉛めっき鋼板の製造方法。 Forming a plating layer having a zinc content of 97% by mass or more on a steel sheet by electrogalvanizing;
The steel sheet on which the plating layer is formed contains at least one of nitrate ion, iodate ion and bromate ion at a concentration of 0.002 mol / L to 1.0 mol / L in total, sulfate ion and chloride ion A step of contacting an acidic aqueous solution having a total concentration of less than 0.01 mol / L, a zinc ion concentration of 1.0 mol / L or less, and a pH of 3 or less for 0.5 seconds or more,
Forming a chemical conversion film on the plating layer;
A method for producing an electrogalvanized steel sheet, comprising:
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