JPH0711474A - Method for suppressing oxidation of tin ion by iron ion - Google Patents

Abstract

PURPOSE:To suppress the oxidation of tin ion by iron ion and to realize tinning using an insoluble electrode at a high current density in the production of an electrotinned steel sheet by adding a specified amt. of a specified aromatic compd. to a tinning bath of specified composition. CONSTITUTION:A high-current-density tinning sulfuric acid bath contg. 5-50g/l of sulfuric acid and 40-100g/l of tin(II) is used to produce an electrotinned steel sheet or tinned thin steel sheet. The bath contains >=2 electron-donative substituent, kind among the substituents are hydroxyl, and 0.01-2g/l of an aromatic compd. coordinated to the ortho or para-positions of the benzene ring is added. The compd. has a strong reducing power and tends to bond to the positive iron ion. Consequently, Fe(II) ion generated by the dissolution of steel strip and causing the oxidation of tin ion in the sulfuric acid bath is oxidized to Fe(III) ion, and the oxidation of the tin ion is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of electroplated tin plates and thin tin-plated steel sheets, and relates to a method for preventing tin ion oxidation by iron ions in a bath when tin plating is performed at a high current density using an insoluble electrode. It is a thing.

[0002]

2. Description of the Related Art Tin-plated steel sheets such as tin plates are currently manufactured mainly using a ferrostane bath (phenol sulfonic acid bath) as a plating bath at a low current density of about 20 A / dm ² . Further, the electrode in this case has been changed from a soluble tin electrode to an insoluble electrode such as platinum-plated titanium having a large cost advantage.

Therefore, the current tinplate manufacturing technology is industrially unsatisfactory in terms of both productivity and environment. That is, in order to achieve the high productivity of the first point, it is necessary to have a technology capable of high current density and high-speed and low-cost plating. However, in a phenolsulfonic acid bath, if plating is performed at high current density, So-called plating burn occurs and is not practical. In the second environmental aspect, wastewater treatment is difficult because it contains a large amount of phenolsulfonic acid, and the recently developed plating bath containing an acid component of alkylsulfonic acid is easy to treat waste liquid. The use of a large amount of sulfonic acid leads to an increase in COD, and it is unlikely that discharging without treatment will have no environmental impact. As described above, it can be said that it is difficult to manufacture tin plating which can be plated at a high current density capable of speeding up, is environmentally friendly, and is low in cost with the conventional technology.

[0004]

DISCLOSURE OF THE INVENTION The present inventors have focused on a sulfuric acid bath aiming at the completion of a plating technique having a high current density and an environment-friendly property exceeding the above-mentioned conventional techniques. However, the sulfuric acid bath has a sulfuric acid concentration of 100 g /
It is used at a high concentration of 1 or more, but it can not be used at this concentration for plating in the tin plate manufacturing line because it causes corrosion of the equipment. Furthermore, the sulfuric acid concentration is lowered and the insoluble electrode is used. Then, there is a big problem that the generation of sludge becomes extremely large.

This sludge is tin oxide, and as will be described in detail later, it is produced by oxidizing tin (II) ions by iron (III) ions dissolved in the plating solution. When a soluble tin electrode is used as the electrode, iron (III) ions are reduced by tin, so that the generation of sludge is suppressed, but when an insoluble electrode is used, this action does not work. Therefore,
In order to realize tin plating with high current density using an insoluble electrode, it is necessary to study the bath composition and plating conditions in terms of plating properties, and to solve the problem of significantly suppressing the oxidation of tin ions by iron ions. There are issues to be solved. Therefore, an object of the present invention is to provide a method for preventing oxidation of tin ions by iron ions in a sulfuric acid bath when tin plating is performed at a high current density using an insoluble electrode.

[0006]

The inventors of the present invention have found that the cause of oxidation of tin ions in a sulfuric acid bath is iron (II) ions produced by oxidation of iron (II) ions produced by dissolution of steel strip. Focusing on the above, the relationship between the reducing property of the iron (III) ion and the aromatic compound was studied in detail, and the aromatic compound having a reducing effect was successfully selected, and the present invention was achieved.

That is, according to the present invention, in the tin plating production using the insoluble electrode, 5 to 50 g / l of sulfuric acid, 40 to
A high current density tin-plating sulfuric acid bath containing 100 g / l of tin (II) has two or more electron-donating substituents, at least one of which is a hydroxy group, A method for suppressing oxidation of tin ions, which comprises adding 0.01 to 2 g / l of an aromatic compound having an ortho position or a para position.

[0008]

The present invention will be described in detail below. The chemical reaction relationship with tin ions, iron ions, metallic tin as an electrode metal, and metallic iron as a plated steel sheet in a sulfuric acid bath is considered to follow the following formula. Dissolution of tin electrode: Sn → Sn ²⁺ ＋ 2e (1) Dissolution of steel strip: Fe → Fe ²⁺ ＋ 2e (2) Air oxidation of iron (II) ions: Fe ²⁺ ＋ O ₂ → Fe ³⁺ (3) Iron Oxidation of tin ion by (III) ion: 2Fe ³⁺ + Sn ²⁺ → 2Fe ²⁺ + Sn (IV) (4) Sludge formation: Sn (IV) + O ₂ → SnO ₂ (5) Iron (III) ion Reduction with tin electrode: 2Fe ³⁺ ＋ Sn → 2Fe ²⁺ ＋ Sn ²⁺ (6) Reduction of tin (IV) ion with tin electrode: Sn (IV) ＋ Sn → 2Sn ²⁺ (7)

The tin (II) ion represented by the formula (4) is mainly added as a plating bath, and this ion is oxidized by the iron (III) ion according to (4) to produce tin (II) ion. IV) Ions and tin oxide form sludge. In this case, the reason why sludge is less generated when the soluble tin electrode is used is that iron (III) ions and tin (IV) ions are reduced according to (6) and (7), respectively. In the case of an insoluble electrode, since this reaction does not occur, the number of generations increases. In order to suppress sludge formation when using an insoluble electrode, the air oxidation of iron (II) ions in (3) should be suppressed, or the iron ( III) Ions may be reduced to reduce the amount of iron (III) ions.

The present inventors consider the molecular structure from the viewpoint of reduction, consider that a compound having a hydroxy group having a strong reducing power is preferable, and make it easy for the compound to have a positive ion of iron ion, so that electron excess easily occurs. We thought that compounds with a molecular structure were suitable. That is, it is an aromatic compound having two or more electron-donating substituents, at least one of which is a hydroxy group, and the arrangement on the benzene ring is at the ortho position or the para position.

Since the benzene ring of the aromatic compound having two or more electron-donating substituents is electron-excessive due to the electron donation from the substituents, it is easy to bond with the iron (III) ion. Further, the reason why the coordinate position of the substituent is limited to the ortho position and the para position is that electron donation to the benzene ring is likely to occur at this position. The reason why at least one of the electron-donating substituents is a hydroxy group is for imparting a reducing property, and preferably two or more.

As a result of examining various compounds based on such a basic idea, it was found that specifically o-hydroxyanisole, o-aminophenol, 2,3-dihydroxybenzoic acid, pyrogallol and the like are suitable. . The amount of the above-mentioned aromatic compound added is 0.01 to 2 g / l. That is, if it is less than 0.01 g / l, the antioxidant effect is not sufficient, and if it exceeds 2 g / l, the effect is saturated, and it is contrary to the gist of the present invention aiming to improve the environment by reducing organic substances in the bath. Because.

The tin plating bath of the present invention is a sulfuric acid bath, and the amount of sulfuric acid and the amount of tin (II) were determined from the viewpoints of plating property and suppression of tin ion oxidation. First, although sulfuric acid produces a slight amount of mist, it is essentially non-volatile and has little pollution in the working environment and air, and it has less problems in waste liquid treatment compared to conventional baths using organic sulfonic acid, and it has a low level. The price is industrially advantageous, but the sulfuric acid concentration is 5 to 50 g / l. At a sulfuric acid concentration of 5 g / l, the pH of the electrolyte is about 1.2, and tin (II) ions are stable. However, at lower concentrations, tin (II) ions are generated because the pH increases near the cathode during electrolysis. It becomes unstable and precipitates easily. Moreover, the gloss of the electrodeposited tin is not excellent. On the other hand, if the concentration is higher than 50 g / l, various problems such as accelerated deterioration of the bath due to an increase in iron concentration in the bath due to dissolution of the steel strip and accelerated corrosion of the equipment will occur.

The tin (II) concentration is 40 to 100 g / l. If it is less than 40 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. 1
If the amount exceeds 00 g / l, the amount of tin (II) ions carried out by the strip will increase, and in addition to the above-mentioned aromatic compound addition, the oxidation limit of tin ions will be exceeded, and a large amount of sludge will be generated, which is economical. Is disadvantageous to

Next, the plating conditions in the case of using the plating bath of the present invention may be those required for plating at high current density, and basically there is no special consideration other than that. . That is, the flow rate of the plating solution is 100 m / min
The above-mentioned high speed is desirable, and the pretreatment may be usual electrolytic alkaline degreasing, sulfuric acid pickling, or further underlying plating such as nickel flash plating. The bath temperature may be 30 to 70 ° C. The cathode current density is preferably as high as possible as long as the cathode current efficiency is high and good plating can be obtained. The reason is not only the economic advantage due to improved productivity, but also a large number of fine plating nuclei generated during electrodeposition, resulting in dense plating and improved corrosion resistance. In the present invention, plating is performed at a high current density of 50 A / dm ² or more, which has been difficult to achieve with the ferrostane bath which has been used most often.

The steel plate after tin plating is subjected to a reflow treatment depending on the application. In conventional ferrostan baths, etc., the diluted solution of the plating solution could be directly used as flux, so the purpose of flux application could be achieved simply by passing the strip through the dragout bath. However, since the plating bath of the present invention does not act as a flux even when diluted, when an extremely smooth and glossy tin plate is required, it is desirable to include a step of applying flux after plating and washing with water. However, even if the reflow is performed without applying the flux, a tin plate having practically sufficient gloss can be obtained. The chemical conversion treatment may be performed by an ordinary method depending on the application.

[0017]

EXAMPLES The present invention will be specifically described below based on examples. Iron (III) ions were added as iron sulfate to a plating solution having the composition shown below, and the effects of the aromatic compounds shown in Table 1 were tested. Plating solution: tin (II) sulfate 108.6 g / l (60 g / l as tin) sulfuric acid 16.7 g / l ENSA 4.0 g / l iron (III) ion 10.0 g / l

The test is carried out with an inner diameter of 105 mm and a height of 800 mm.
The tin dissolving tank of 5 is filled with 5 kg of tin particles of 2.8 mm in diameter,
Circulating liter of plating solution at 60 liters / minute,
Bubbling oxygen at 1.5 liter / min. The pressure in the dissolution tank was 2 kgf / cm ² . 2 liters of the plating solution after 2 hours of blowing oxygen was filtered and the weight of the sludge was measured.
As shown in the test results in Table 1, in the case of containing an aromatic compound, the oxidation of tin ions by iron ions was significantly suppressed,
Sludge generation is extremely low.

[0019]

[Table 1]

Next, in order to suppress sludge formation during electrolysis and to confirm the plating property, the following two test solutions were circulated using a horizontal circulation cell with a solution flow rate of 200 m / min to obtain a current density of 150 A.
/ Dm ^2, 50 were tin plating of Coulomb / dm ^2.
The electrode used was an insoluble electrode formed by plating platinum on titanium.
Plating properties include cathode current efficiency, plating gloss, corrosion resistance (AT
C test) and the sludge formation suppressing effect was judged from the amount in the liquid after plating.

Test liquid 1 108.6 g of tin (II) sulfate
/ L (60 g / l as tin) Sulfuric acid 16.7 g / l ENSA 4.0 g / l Iron (III) ion 10.0 g / l 2,3-Dihydroxyanisole 1.2 g / l Test liquid 2 Tin (II) sulfate 108.6 g / l (60 g / l as tin) Sulfuric acid 16.7 g / l ENSA 4.0 g / l Iron (III) ion 20.0 g / l Pyrogallol 0.5 g / l The results are shown in Table 2, but the present invention All of the examples relating to (1) showed good plating properties and sludge formation suppressing effect.

[0022]

[Table 2]

[0023]

As is apparent from the above examples, according to the present invention, even when an insoluble electrode is used, the oxidation of tin ions due to iron ions can be suppressed, so that tin plating at high current density is possible. In addition, in order to maintain a good environment,
The industrial value in terms of manufacturing such as tinplate is extremely high.

Claims (1)

[Claims] 1. In the tin plating production using an insoluble electrode, two or more electron donors are added to a high current density tin plating sulfuric acid bath containing 5 to 50 g / l sulfuric acid and 40 to 100 g / l tin (II). Aromatic compound having a polar substituent, at least one of which is a hydroxy group, and the coordination to the benzene ring is ortho or para is 0.01 to 2
A method for suppressing the oxidation of tin ions by iron ions, which comprises adding g / l.