JP3481378B2 - Method for suppressing formation of tin sludge by iron (III) ions in plating bath - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to iron (III) in an acidic tin plating bath in the production of tin electroplated steel sheets such as tinplate.
The present invention relates to a method for suppressing the generation of tin sludge increased by ions.

[0002]

2. Description of the Related Art Tin-plated steel sheets such as tin plates are currently manufactured mainly by using a ferrostane bath (phenol sulfonic acid bath) as a plating bath and performing tin plating at a current density of about 20 A / dm ² . Metal tin was once used for the anode of electrotin plating, but it is difficult to maintain a constant distance from the strip of the cathode because it dissolves by electrolysis, and replacement is complicated. In many cases, an insoluble electrode whose titanium surface is coated with a noble metal is used.

When an insoluble anode is used, as a means for replenishing tin ions in the plating bath lost in electroplating,
A method of promoting the oxidation of metal tin to tin (II) ions by flowing metal tin particles in a plating solution and blowing oxygen as an oxidant into a plating bath has been adopted. At this time, tin (I
I) is further oxidized to precipitate tin (IV) oxide, that is, sludge. Also, highly reactive oxygen was generated from the surface of the insoluble anode, tin (II) ions in the plating bath were converted to tin (IV), and iron (I
I) Ions are oxidized to iron (III) ions. Iron (III) ions have a strong oxidizing power and oxidize tin (II) ions to tin (IV). The tin (IV) solution solubility is low, producing oxide precipitates or sludges.

Regarding such sludge formation, Japanese Patent Application Laid-Open No. 4-333590 suppresses the formation of tin sludge by iron (III) ions generated by oxidizing iron (II) ions by dissolved oxygen in the plating bath. As a method to do so, there is a method of suppressing the oxidation of tin (II) by adding α-oxycarboxylic acid to the plating bath and combining the —COOH group or —OH group contained therein with iron (III) ions. It is provided. That is, the reaction of Sn ²⁺ + 2Fe ³⁺ → Sn ⁴⁺ + 2Fe ²⁺ is suppressed by masking iron (III) ions.

[0005]

However, when the present inventors reproduced the method described in Japanese Patent Laid-Open No. 4-333590 in the laboratory, iron (III) was added until the second day of the test. Although the generation of tin sludge due to ions could be well suppressed, a large amount of white precipitate, which was different from ordinary sludge, was generated on the third day. This is tin (II) in the plating bath
The precipitation was mainly due to the oxidation of the ions to form tin (IV) ions, which was bound to α-oxycarboxylic acid. Thus, it is judged that adding α-oxycarboxylic acid to the ferrostane bath as an iron (III) ion masking agent has little merit.

However, the production of a large amount of tin sludge by iron (III) ions causes a large cost problem,
This solution was desired. Therefore, an object of the present invention is to provide a method for suppressing the amount of sludge formed of tin oxide or tin hydroxide in an acidic bath used for electrotin plating and preventing the precipitation of other tin salts. is there.

[0007]

The present invention provides an acidic tin plating bath containing at least salicylic acid or 5-sulfosalicylic acid.
Is a method of suppressing the generation of tin sludge due to iron (III) ions, which is characterized by adding 0.1 to 0.5 mol / l of one kind . The acid concentration is 5 to 100 g / l in terms of sulfuric acid,
It is preferable that the tin (II) concentration is 10 to 100 g / l.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. When the work of continuously tin-plating the steel strip in the acid tin plating line is continued, iron (II) ions are dissolved from the steel strip into the plating bath. Iron (II) ions are oxidized by the anode during plating and by oxygen during dissolution of metallic tin to be converted into iron (III) ions. Iron (III) ions are strong oxidants and oxidize tin (II) ions in the plating bath to produce a large amount of sludge. Therefore, iron (II
I) Ions must be masked so that they do not act as oxidants.

The present inventors have conducted various studies on substances that effectively mask iron (III) ions and do not cause precipitation of tin salts, and as a result, salicylic acid or 5-sulfosalicylic acid.
It has been found that at least one of the acids is an effective masking agent.

These actions and effects are due to the carboxyl group (-
COOH group) or hydroxyl group (-OH group) dissociates with acid to electrostatically bond with iron (III) ion, and the non-shared electron pair of oxygen atom of hydroxyl group (-OH group) is vacant of iron (III) ion. By forming a stable 5-membered ring or 6-membered ring chelate by coordinating to the electron orbit of It is unclear why the introduction of a sulfo group into the aromatic ring increases the selectivity for iron (III) ions, but it is believed that the charge density of the carboxyl and hydroxyl groups is optimal for iron (III) chelate formation. Be done.

A small amount of salicylic acid or 5-sulfosalicylic acid
At least one kind of additive amount is specified to be 0.1 to 0.5 mol / l. If it is less than 0.1 mol / l, the effect is small especially when the iron (III) ion concentration is high. Even if the amount exceeds 0.5 mol / l, no adverse effect on the plating is recognized, but at a normal iron (III) ion concentration, the addition is not necessary because the effect is saturated. Iron (III) concentration in the plating bath is usually 2 to
20 g / l, that is, in the range of 0.036 to 0.36 mol / l, the salicylic acid or 5-sulfosalicylic acid content is low.
Since at least 1 : 1 complex is formed with salicyl
Most preferably, the concentration of at least one acid or 5-sulfosalicylic acid is higher than this.

The acid concentration of the plating bath is 5 to 100 in terms of sulfuric acid.
It is preferably used in the range of g / l. If it is less than 5 g / l, the plating gloss is not excellent, the pH of the bath is high, and the pH is further increased near the cathode during electrolysis, and tin is likely to precipitate in the form of hydroxide or oxide. If it exceeds 100 g / l, the amount of hydrogen generated during electrolysis increases, and tin that has been once deposited is likely to dissolve, resulting in a decrease in apparent plating efficiency.

As a tin at the time of building a bath, a divalent tin salt such as tin (II) sulfate is added. Tin (II) concentration is 10-100
g / l is preferred. If it is less than 10 g / l, so-called plating burn occurs when plating is performed at a high current density, and it is difficult to obtain a high-quality tin plate. If it exceeds 100 g / l, the amount of tin (II) ions carried out by the strip increases, which is economically disadvantageous. The method of adding tin (II) to the plating bath, which decreases by electrolysis, may be either a method of using metallic tin for the anode or a method of oxidizing metallic tin with oxygen in a plating solution.

There is no particular limitation on the gloss additive for tin plating.
Organic compounds having an ethylene oxide chain, such as polyethylene glycol, are particularly excellent as gloss additives. When using acid such as sulfuric acid which does not suppress tin (II) ion oxidation, it is desirable to add a sludge suppressor. The sludge inhibitor has two or more electron-donating substituents, at least one of which is a hydroxy group, and another electron-donating substituent is an aromatic compound in the ortho or para position of the hydroxy group. Preferably, specific examples thereof include hydroquinone, o-hydroxyanisole, p-hydroxyanisole, pyrogallol, o-aminophenol, p-aminophenol and the like. The cathode current efficiency of electrodeposition using the plating bath of the present invention is good, the plating appearance and corrosion resistance are also good, and the salicylic acid or 5-sulfosalicylic acid content is low.
Even if there is no adverse effect on one kind of plating.

[0015]

EXAMPLE Sludge formation was tested by the method described below. For all plating baths, the brightening additive, iron (III), had the following concentrations. Gloss additive 4.0 g / l Iron (III) 5.0 g / l Other plating bath components are shown in Table 1. The plating bath temperatures were all unified at 45 ° C. 5 kg of tin particles with a particle size of 2.8 mm are placed in a tin dissolution tank with an inner diameter of 105 mm and a height of 800 mm.
After filling, 80 liters of plating solution was circulated at 60 liters / minute, and 1.5 liters / minute of oxygen was blown therein. The pressure in the dissolution tank was 2 kgf / cm ² . Blow oxygen 2
After 2 hours, 48 liters of the plating solution was filtered, and the weight of the sludge produced was measured. 2 in 48 hours
It was determined that g / l or less had a sufficient sludge suppressing effect.
After electrolytically degreasing the steel sheet and washing with sulfuric acid, tin plating was performed under the following conditions using the plating baths of the present invention and comparative examples. The plating property was judged by visually observing the plating appearance. Plating conditions Bath temperature 45 ° C Current density 50A / dm ² Electrolysis time 1.0 seconds

[0016]

[Table 1]

Inventive Example No. In Nos. 1 to 7 , the type and concentration of the iron (III) masking agent were appropriate, and a sufficient sludge suppressing effect was recognized. In addition, in all cases, the obtained plating appearance was good. Comparative Example No. In No. 1, the iron (III) masking agent concentration was low, the effect of iron (III) ions remained, and a large amount of sludge was generated. Comparative Example No. No. 2 was tartaric acid whose iron (III) masking agent was a type of α-oxycarboxylic acid, and a large amount of white precipitate was produced in the test for 48 hours. Comparative Example No. In No. 3, the concentration of the iron (III) masking agent was low, the influence of iron (III) ions remained, and a large amount of sludge was generated. Comparative Example No. No. 4 had a low acid concentration, and the gloss of the plating was poor. Comparative Example No. In No. 5, since the tin (II) concentration in the plating bath was low, plating burn occurred.

[0018]

According to the method of the present invention, it is possible to effectively suppress the formation of tin sludge caused by iron ions inevitably mixed in the plating bath.

Continuation of front page (56) Reference JP-A-7-11474 (JP, A) JP-A-6-346273 (JP, A) JP-A-6-128790 (JP, A) JP-A-5-195283 (JP , A) JP 5-171489 (JP, A) JP 5-125582 (JP, A) JP 2-301589 (JP, A) JP-B 2-41589 (JP, B2) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C25D 3/32 C25D 5/26

Claims (2)

(57) [Claims] 1. Salicylic acid or 5-
0.1 to 0.5 m of at least one sulfosalicylic acid
A method for suppressing the generation of tin sludge due to iron (III) ions, characterized by adding ol / l. 2. The acid concentration is 5 to 100 g / l in terms of sulfuric acid,
The method for suppressing the generation of tin sludge by iron (III) ions according to claim 1, wherein the tin (II) concentration is 10 to 100 g / l.