JP5831123B2 - Method for producing tin-plated steel strip - Google Patents

Description

  The present invention relates to a method for producing a tin-plated steel strip by electroplating using a tin plating bath containing methanesulfonic acid.

  When electrotin plating is applied to a steel strip, a plating bath containing tin ions as a main component and containing a conductive assistant and a brightener or further an antioxidant is used. Plating baths are classified according to the type of conductive aid used. Halogen baths using halogens such as chlorine and fluorine, alkyl sulfonic acid baths using alkyl sulfonic acids such as methane sulfonic acid, and ferrostane baths using phenol sulfonic acid An alkanol sulfonic acid bath using alkanol sulfonic acid is used.

  In recent years, as environmental problems have been closed up, it has become difficult to treat sludge containing halogen ions, and switching from a halogen bath to a methanesulfonic acid bath has been performed. Also, since ferrostannic baths use aromatic phenol sulfonic acid, they are also being switched to methane sulfonic acid baths.

  However, in the methanesulfonic acid bath, since the pH of the plating bath is low, the elution rate of iron from the steel strip is faster than in the halogen bath and ferrostan bath, and the iron ion concentration in the plating bath is high, and under high current density conditions. It is known that when electrotin plating is performed, the plating uniformity is deteriorated due to the non-uniformity of the amount of tin adhesion (see, for example, Non-Patent Document 1).

Therefore, Patent Document 1 discloses that in a method for producing a tin-plated steel strip in which electroplated steel strip is applied to a steel strip to be conveyed, 10 to 80 g / l (liter) of tin ions, 15 to 70 g / l of free methane. Uses plating bath containing sulfonic acid, 0.1-10 g / l brightener and 0.1-5 g / l antioxidant, and current density during electrotin plating is CA / dm ² , conveying steel strip When the speed is R m / min and the iron ion concentration in the plating bath is [Fe] g / l, the tin ion concentration [Sn] g / l in the plating bath satisfies the following formula (2) A method has been proposed that can be adjusted to produce a tin-plated steel strip with excellent plating uniformity under high current density conditions.

  [Sn] ≧ (7.2 + 0.3 × C−0.05 × R + 0.65 × [Fe]) (2)

George A. Federman et al: “5th International Tinplate Conference” (Industrial Tin Research Institute), 1992, P.88-98

JP 2006-328446 A

However, in the method for producing a tin-plated steel strip in a methanesulfonic acid bath as described in Patent Document 1, tin adheres under a low current density condition of 50 A / dm ² or less, generally about 20 to 40 A / dm ^2. When producing tin-plated steel strips with a weight of 1.2 g / m ² or less, if the iron ion concentration is high, uneven plating occurs due to unevenness in the amount of tin, resulting in plating uniformity. There was a problem that it might lead to deterioration.

  An object of the present invention is to provide a method for producing a tin-plated steel strip that can obtain excellent plating uniformity under a low current density condition using a plating bath containing methanesulfonic acid similar to Patent Document 1. .

  The present inventors diligently studied to achieve the above-mentioned object. As long as the current density is higher than a predetermined current density depending on the iron ion concentration of the plating bath, a tin-plated steel strip is manufactured under a low current density condition. It has been found that excellent plating uniformity can be obtained even in the case of performing.

The present invention has been made on the basis of such knowledge, and in a method for producing a tin-plated steel strip in which electrotin plating is performed on a steel strip to be conveyed, 10 to 80 g / l of tin ions, 15 to 70 g / current density CA / using a plating bath containing 1 free methanesulfonic acid, 0.1-10 g / l brightener and 0.1-5 g / l antioxidant and satisfying the following formula (1) Provided is a method for producing a tin-plated steel strip, characterized by performing electrotin plating at dm ² .

50 ≧ C ≧ 2.9 × [Fe] -14.3 ... (1)
However, [Fe] represents the Fe ion concentration (g / l) in the plating bath.

  In the method for producing a tin-plated steel strip of the present invention, [Fe] in the plating bath is preferably adjusted to 20 g / l or less.

  According to the present invention, a tin-plated steel strip having excellent plating uniformity can be stably produced when a thin-plated tin-plated steel strip is produced under a low current density condition using a plating bath containing methanesulfonic acid. It became so.

[Fe] is a diagram showing the relationship between the current density and the presence or absence of mottled defective gloss. It is a figure which shows the relationship between [Fe] and a tin oxidation rate.

1) About the plating bath As described above, the plating bath used in the present invention includes 10 to 80 g / l tin ion, 15 to 70 g / l free methanesulfonic acid, 0.1 to 10 g / l. Contains brightener and 0.1-5 g / l antioxidant. The reasons for limiting the content of each component will be described below.

  Tin ion concentration: When tin plating is performed on the steel strip to be conveyed, if the tin ion concentration is low, a tin-plated steel strip excellent in plating uniformity cannot be obtained. Since a large amount of iron ions are eluted in the plating bath of methanesulfonic acid, tin is oxidized and the tin ion concentration is likely to decrease. Therefore, the lower limit value of the tin ion concentration is 10 g / l. On the other hand, if the tin ion concentration exceeds 80 g / l, the amount of tin ions taken out from the plating bath to the rinsing tank as a plating solution film adhering to the steel strip surface increases, and the cost increases. In this case, tin tends to adhere to the surface of the steel and cause contamination of the steel strip surface, so the upper limit of the tin ion concentration is 80 g / l. More preferably, it is 20-40 g / l.

  Free methanesulfonic acid: In the present invention, it is important to adjust the concentration of free methanesulfonic acid as the concentration of methanesulfonic acid. When the concentration of free methanesulfonic acid is low, the resistance of the plating bath increases, and the power consumption due to the voltage increase increases. In addition, the concentration of free methanesulfonic acid is 15 g / l or more because it affects the plating uniformity and plating appearance as described above. On the other hand, when the concentration of free methane sulfonic acid is high, the amount of free methane sulfonic acid taken out from the plating bath to the rinsing tank as a liquid film adhering to the steel strip surface increases, resulting in high costs and low pH. Since the elution amount of iron ions from the band increases, the upper limit of the concentration of free methanesulfonic acid is 70 g / l. More preferably, it is 20-40 g / l. As described above, the concentration of free methanesulfonic acid must be 15 to 70 g / l. However, as described above, the amount of free methanesulfonic acid decreases as the amount of iron ions eluted from the steel strip increases. To do. Therefore, it is necessary to replenish it during actual operation, and methanesulfonic acid may be used for that purpose.

  Brightener: The brightener is a component necessary for producing a tin-plated steel strip excellent in plating uniformity. Nonionic surfactants such as polyethylene glycol and polypropylene glycol, aliphatic or aromatic alkylene oxide condensates, petines, alkylene oxide condensates, imidazolinium compounds, quaternary ammonium compounds, amine ethylene oxides as brighteners for plating baths Derivatives are preferably used. The alkylene oxide condensate may be a condensate composed of a single alkylene oxide or may be a condensate composed of two or more alkylene oxides. Further, one or more of these condensates can be used. Further, it is necessary to use a brightening agent having a low foaming property or a high antifoaming property. This is because bubbles are likely to be generated when the plating bath is used under vigorous stirring conditions such as a tin production line. The concentration of the brightener in the plating bath varies depending on the brightener used, but may be 0.1 to 10 g / l. If the concentration is less than 0.1 g / l, sufficient plating uniformity cannot be obtained, so the lower limit of the concentration of the brightener is 0.1 g / l. On the other hand, even if the concentration exceeds 10 g / l, the effect is saturated, and the amount of brightener taken out from the plating bath to the rinsing tank as a liquid film adhering to the steel strip surface increases, resulting in high costs and foaming. The upper limit of the concentration of the brightening agent is set to 10 g / l because the properties increase and the appearance of the plating is impaired. More preferably, it is 0.5-5 g / l.

  Antioxidant: Antioxidant is a component necessary for suppressing the generation of sludge. In particular, it is necessary to use an antioxidant because tin is easily oxidized in a plating bath containing iron ions. Further, as described above, the antioxidant is an effective component because it has a positive influence on the plating uniformity together with the brightener. As the antioxidant, any water-soluble and reducing action may be used, and hydroquinone having an OH group on the benzene ring, catechol, resorcinol, catechol sulfonic acid, naphthol disulfonic acid and the like are preferably used. If the concentration is less than 0.1 g / l, a sufficient antioxidant effect cannot be obtained, the amount of sludge generated increases, the consumption of tin ions increases, the cost increases, and the plating uniformity is improved. Therefore, the lower limit of the antioxidant concentration is 0.1 g / l. On the other hand, even if the concentration exceeds 5 g / l, the effect is saturated, and the amount of antioxidant taken out from the plating bath to the rinsing tank as a liquid film adhering to the steel strip surface increases, resulting in high costs. The upper limit of the antioxidant concentration is 5 g / l. More preferably, it is 0.5-3 g / l.

2) Current density during electrotin plating Plating bath according to the present invention described above (tin ion: 20-40 g / l, free methanesulfonic acid: 20-40 g / l, brightener: 0.5-5 g / l , Antioxidant: 0.5 to 3 g / l), changing the iron concentration in the plating solution, the steel plate width, the line speed, and the number of plating cells used, and the tin adhesion amount is 1.2 g / m ² at low current density conditions. The following thin tin-plated steel strips were manufactured, and the relationship between [Fe] g / l, current density CA / dm ² and the occurrence of mottled luster defects due to uneven tin adhesion was investigated. . Here, the iron concentration in the plating solution was changed by introducing an iron removing device or a new plating solution.

  The presence or absence (x) or absence (O) of the mottled glossy defective portion was evaluated by visual observation of the plated surface.

  FIG. 1 shows the relationship between [Fe], current density, and the presence or absence of mottled defective gloss.

In this way, if electrotin plating is performed at a current density that satisfies the above formula (1), under the current density condition of 50 A / dm ² or less, there is no mottled defective gloss and excellent plating uniformity. It turns out that it is obtained. Incidentally, if the electric tin plating in this condition, 40 A / dm ² or less, or even better plating uniformity in the production of plated steel strip thin with at 40 A / dm ² under a low current density conditions give It is done.

  FIG. 2 shows the relationship between [Fe] and the tin oxidation rate. When [Fe] exceeds 20 g / l, the tin oxidation rate increases rapidly, and the amount of sludge generated increases. [Fe] is preferably 20 g / l or less.

Furthermore, from the viewpoint of productivity, the current density is preferably 10 A / dm ² or more.

  Actually, when a tin-plated steel strip with a light weight was manufactured by the method of the present invention, there was no occurrence of mottled glossy defects of about 0.1% which were recognized when manufactured by the conventional method.

Claims (2)

In the method for producing a tin-plated steel strip, in which the steel strip to be conveyed is electrotin plated, 10 to 80 g / l (liter) of tin ions, 20 to 40 g / l of free methanesulfonic acid, 0.1 to 10 g / liter Using electroplating at a current density CA / dm ² satisfying the following formula (1) using a plating bath containing l brightener and 0.1-5 g / l antioxidant And a method for producing a tin-plated steel strip having a tin plating adhesion amount of 1.2 g / m ² or less ;
50 ≧ C ≧ 2.9 × [Fe] -14.3 ... (1)
However, [Fe] represents the Fe ion concentration (g / l) in the plating bath. The [Fe] in the plating bath and adjusting below 20 g / l, of claim 1, the method for manufacturing a tin-plated steel strip is tin coating weight is 1.2 g / m ² or less.

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