JPH05156488A - Acidic sn plating bath reduced in deposition of sn sludge - Google Patents

Abstract

PURPOSE:To prepare an acidic Sn plating bath appropriate for incoluble-anode plating and reduced in deposition of Sn sludge by using a surfactant having specified contents of a beta-alkanolsulfonic acid and Sn<2+> under specified conditions. CONSTITUTION:An acidic Sn plating bath contg. a beta-alkanolsulfonic acid (e.g. 2-hydsroxypropane-1-sulfonic acid) having a hydroxyl group at the beta-position and 15-60g/l of Sn<2+>, wherein the molarity ratio of the acid to Sn<2+> is controlled to 1.4 to 2.3 and mixed as a brightener with 0.5 to 10g/l of one of >=2 kinds of surfactants (etholynaphtholsulfonic acid, ethoxynaphthol polyethylene glycol, etc.,) shown by formula I (n is an integer of 3 to 20), formula II (n is an integer of 3 to 10) and formula III (n is an integer of 20 to 100) is prepared. The deposition of Sn sludge is suppressed by using this bath, and high-current-density plating is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Sn plating bath suitable for an electric Sn plating method using an insoluble anode, in place of the Sn plating bath used in the production of an electric tin plate for performing Sn plating on a steel sheet at high speed. Is.

[0002]

2. Description of the Related Art Ferrostan plating baths using phenolsulfonic acid, borofluoride baths, halogen baths and the like are well known as Sn plating baths used for high-speed Sn plating of steel sheets. In particular, a ferrostane plating bath using phenolsulfonic acid is widely used.

Further, in recent years, since a phenol sulfonic acid bath, a fluorinated bath, etc. have a problem of waste liquid treatment, an Sn plating bath using alkane sulfonic acid and alkanol sulfonic acid has been proposed (Japanese Patent Laid-Open No. 62-196391).
JP-A-59-182986, JP-A-63-161
183). However, these are all related to the Sn plating method with a soluble anode using metallic tin as the anode, and the insoluble anode plating method is said to be difficult.

[0004]

A conventional soluble anode (metal tin is used as an anode, Sn ²⁺ ions are electrochemically
It is replenished by melting the anode tin. ) The Sn plating using, but no problem in any of the plating bath described above, the insoluble anode (generally, electrodes of platinum plated titanium is used as the anode, Sn ²⁺ ions, Sn ² provided separately ⁺ Is replenished by chemical dissolution of metal tin with an ion replenishing device), only phenol sulfonic acid bath can be used, and Sn sludge is often generated in alkane sulfonic acid bath, alkanol sulfonic acid bath, etc. It was unsuitable for Sn plating using a totally insoluble anode. Further, in a halogen bath, a fluorinated bath, etc., Sn plating with an all-insoluble anode has been difficult due to problems such as corrosion of the insoluble anode.

The present invention has found an optimum bath composition for carrying out electro Sn plating in an alkane sulfonic acid or alkanol sulfonic acid bath, which is easy for wastewater treatment to a phenol sulfonic acid bath, with a totally insoluble anode. is there.

The alkane sulfonic acid bath and the alkanol sulfonic acid bath are the plating bath systems to be used by all means in the totally insoluble anode Sn plating method, because the waste liquid treatment is easy as described in the above-mentioned reference. Anode Sn
It has been desired to develop an alkanesulfonic acid bath or an alkanolsulfonic acid bath to which the plating method can be applied.

[0007]

Means for Solving the Problems As a result of intensive studies on the mechanism of tin sludge generation, the present inventors have found that Sn sludge can be obtained by using a particularly limited alkanol sulfonic acid in a very limited concentration range. It has been found that the occurrence of the phenomenon can be suppressed, and the all-insoluble anode Sn plating can be performed.

There are mainly two reasons why tin sludge is generated in the electro Sn plating using the insoluble anode. First, Sn ²⁺ is oxidized to Sn ⁴⁺ by the following formula (4) by oxygen used for chemically dissolving tin, and precipitates as a hydroxide. Also, it is considered that Sn ²⁺ ions are oxidized by the same formula (4) also by oxygen generated at the anode and precipitate as hydroxide to form tin sludge. Sn ²⁺ + O ₂ + 2H ₂ O → Sn (OH) ₄ [precipitation] (4) As apparent from the formula (4), Sn ²⁺ is prevented from being oxidized by Sn plating bath. It is necessary to reduce the dissolved oxygen concentration in the inside as much as possible, but conversely, when the dissolved oxygen concentration is low, the dissolution rate of metallic tin decreases and the supply amount of Sn ²⁺ becomes insufficient. Because the dissolution of metallic tin (reaction (5) below)
This is because oxygen is required, and when the dissolved oxygen concentration is low, the amount of oxygen required for dissolving the metal tin is insufficient.

Therefore, in the totally insoluble anode Sn plating method, with the amount of oxygen required for dissolving the metal tin being secured,
In addition, it is necessary to operate by reducing the dissolved oxygen concentration as much as possible so that the oxidation of Sn ^{2+ in} the formula (4) can be suppressed. _{Sn + 1 / 2O 2 + H} 2 O → Sn 2+ + 2OH - ............... (5) In fact, in all the insoluble anode Sn plating using phenolsulfonic acid bath that is currently operating, extremely severe dissolved oxygen concentration Is being managed. The present inventors, as with the phenolsulfonic acid bath, also in the alkanesulfonic acid and alkanolsulfonic acid-based baths, by controlling the dissolved oxygen concentration, the results of diligent study on the production of electrotin plating by the all-insoluble anode method If you use extremely limited alkanol sulfonic acid under limited conditions,
It was found that the generation of tin sludge can be suppressed.

The contents of the present invention will be described in detail below. First, regarding the alkanol sulfonic acid used in the present invention, only the alkanol sulfonic acid having a hydroxyl group at the β position has an inhibitory effect on the generation of Sn sludge, and when the hydroxyl group is present at other positions, Sn sludge is present. It was found that it had no suppressive effect on the occurrence of. Therefore, the present invention is limited to the Sn plating bath using the β alkanol sulfonic acid having a hydroxyl group at the β position. General formula of β alkanol sulfonic acid having a hydroxyl group at β position (R is an alkyl group)

[Chemical 2] β alkanol sulfonic acid having a hydroxyl group at the β position,
As a result of diligent studies on the reason why it is effective in suppressing the generation of Sn sludge, the present inventors have found that the complex-forming ability of alkanol sulfonic acid with Sn ²⁺ has a great influence.
Only alkanol sulfonic acid with a hydroxyl group at the position
It was concluded that the complex formation ability with Sn ²⁺ is large and stabilizes Sn ²⁺ in the plating bath.

[Chemical 3] That is, as shown in formula (7), when a hydroxyl group is present at the β position, a complex compound of alkanolsulfonic acid and Sn ²⁺ is formed between the hydroxyl group at the β position and the sulfone group to form Sn.
It is thought that ²⁺ is stabilized. In the β-alkanol sulfonic acid having a hydroxyl group at the β-position, the complex compound forms a six-membered ring, so that the complex compound is very stable,
As a result, it is considered that Sn ²⁺ becomes stable, the oxidation of Sn ^{2+ in} the equation (4) is suppressed, and the generation of Sn sludge is reduced.

On the other hand, when there is a hydroxyl group other than the β position, for example, an alkanol sulfonic acid having a hydroxyl group at the α position also forms a complex compound with Sn ²⁺ between the hydroxyl group at the α position and the sulfone group. Since the complex compound formed is a five-membered ring, the complex compound becomes unstable as compared with β-alkanolsulfonic acid having a hydroxyl group at the β-position, which is a six-membered ring, and Sn
^It is considered that ²⁺ is easily oxidized. Similarly, in the case of the γ position and the δ position, the complex compound formed becomes a 7-membered ring and an 8-membered ring, respectively, which is more unstable than that of the 6-membered complex compound and it is considered that Sn ²⁺ oxidation cannot be suppressed. ..

The β-alkanol sulfonic acid suitable for the purpose of the present invention includes 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-
1-sulfonic acid and the like, and these β-alkanol sulfonic acids can be used alone or in a mixture of two or more kinds. At that time, the molar concentration needs to be within the following concentration range (when two or more kinds are used, the sum of the respective molar concentrations).

The present invention provides an alkanesulfonic acid-based and alkanolsulfonic acid-based tin plating bath capable of electro Sn plating with an all-insoluble anode. For the above reasons, alkanesulfonic acid is unsuitable. It is a tin plating bath using an alkanol sulfonic acid that can perform electro Sn plating with an all-insoluble anode, and it is an essential condition that the alkanol sulfonic acid used is a β alkanol sulfonic acid having a hydroxyl group at the β position.

Next, the Sn ²⁺ ion concentration in the tin plating bath,
The reasons for limiting the concentration of β-alkanol sulfonic acid will be described. As described above, the object of the present invention (suppressing sludge generation in electrotin plating with an all-insoluble anode)
To achieve, use β-alkanol sulfonic acid,
Moreover, the concentration of β-alkanol sulfonic acid needs to be 1.4 to 2.3 in terms of molar concentration ratio with Sn ²⁺ ion concentration. Further, the Sn ²⁺ ion concentration is set to 15 to 60 g / l in the present invention, which enables high-speed electrical Sn plating on a steel sheet.

The Sn ²⁺ ion concentration is 15 to 60 g /
1 (0.12 to 0.50 mol / l), the β-alkanolsulfonic acid concentration is 0.16 to 1.15 mol / l.
And need to. The reason for the concentration of Sn ²⁺ is limited with 15 to 60 g / l, the conventional Ferrostan bath, and alkanol sulfonic acid, Sn ²⁺ in the alkanesulfonic acid-based bath
This is almost the same as the reason for limiting the concentration.

That is, the Sn ²⁺ ion concentration is set to 15 g / l or more because it is difficult to perform the electric Sn plating at a high current density of 20 A / dm ² or more below this concentration.
Further, the upper limit of 60 g / l is the upper limit of the practically high current density, when the concentration exceeds this concentration, the effect of high current density operation is saturated, and further increase of Sn ²⁺ ion concentration is This is because the use of the plating solution by the steel plate deteriorates the utilization efficiency of Sn ²⁺ ions, which is economically disadvantageous.

When the molar concentration ratio of β alkanol sulfonic acid concentration to Sn ²⁺ ion is less than 1.4, 1.
When it is less than 4, complex formation of β-alkanol sulfonic acid is insufficient and Sn sludge is often generated. FIG. 1 shows the relationship between the molar concentration ratio of β-alkanol sulfonic acid and Sn ²⁺ ion and the amount of Sn sludge generation. Although the generation of Sn sludge decreases rapidly from about 1.2, in the present invention, The concentration ratio was set to 1.4 or more, which sufficiently suppresses the generation of Sn sludge.

In FIG. 1, 2-hydroxypropane-1-sulfonic acid is used as the β-alkanolsulfonic acid, but 2-hydroxyethane-1-sulfonic acid,
Also in the case of 2-hydroxybutane-1-sulfonic acid and 2-hydroxypentane-1-sulfonic acid, almost the same Sn sludge generation state was shown.

The amount of Sn sludge generated in FIG. 1 was measured by adding air (2) to a 1 l Sn plating bath at 50 ° C. in a 1 l beaker.
The amount of Sn sludge was measured by bubbling (00 ml / min, 1.2 atm), and after 2 hours in an air-saturated state, the generated Sn sludge was filtered and dried at 100 ° C. for 24 hours.

Next, β alkanol sulfonic acid and Sn ²⁺
The reason why the upper limit of the molar concentration ratio with ions is set to 2.3 will be described. β alkanol sulfonic acid concentration is Sn
^When it is higher than the ²⁺ ion concentration, the hydrogen ion concentration of the bath increases, and the current efficiency of Sn plating decreases. This tendency becomes remarkable when the above concentration ratio exceeds 2.3, and in the present invention, Sn, which is considered to be the upper limit of practicality, is used.
Plating efficiency ・ Molar concentration ratio that ensures 85% or more 2.3
Below.

Next, regarding the brightener, the above β
The alkanol sulfonic acid alone is not preferable because the crystals deposited in the electro Sn plating are coarse. Therefore, also in the present plating bath, it is generally necessary to use a brightening agent as in the electro Sn plating.

Although various kinds of surfactants can be considered as the brightener, in the present invention, one of ethoxy naphthol sulfonic acid, ethoxy naphthol and polyethylene glycol represented by the formulas (1), (2) and (3) is used. One kind or two or more kinds can be used, and the concentration of the brightener may be 0.5 to 10 g / l, which is the concentration range used in a usual ferrostane bath.

If it is less than 0.5 g / l, the effect as a brightening agent cannot be obtained, and the plated Sn particles are coarse.
This is because a beautiful specular gloss of electric tint cannot be obtained even by the melting treatment, and even if it exceeds 10 g / l, the effect is saturated.

As described above, when the essence of the present invention is re-arranged, in recent years, since wastewater treatment is difficult, instead of the ferrostan bath using a high concentration of phenolsulfonic acid, alkanolsulfonic acid or alkanesulfonic acid, which is easy to treat wastewater, is used. Electric Sn plating in a bath is becoming popular. However, all of these Sn platings are soluble anode electroplating methods using metal tin for the anode, and various alkanesulfonic acid and alkanolsulfonic acid baths have been developed and put into practical use.

However, up to now, the total insoluble Sn plating in the alkanol sulfonic acid or alkane sulfonic acid type bath produces a large amount of Sn sludge as compared with the conventional ferrostane bath. Therefore, the all insoluble anodic electro Sn plating is possible. Sulfonic acid, alkanol sulfonic acid S
The n-plating bath was said to be difficult.

As a result of earnest studies, the inventors of the present invention used β-alkanol sulfonic acid and set the β-alkanol sulfonic acid concentration to 1.4 to 2.3 with respect to the Sn ²⁺ ion concentration, thereby making it completely insoluble. It has been found that it becomes possible to suppress the generation of Sn sludge, which is a problem at the anode, and it is possible to carry out all-insoluble anode Sn plating in an alkanol sulfonic acid bath.

The contents of the present invention will be described in detail below based on examples, but the present invention is not limited to these examples, and the composition of the plating bath and the plating conditions are based on the above-mentioned purpose and the reason for the limitation. Can be changed as appropriate.

[0028]

[Example] Normal low carbon cold rolled steel sheet, normal degreasing (NaO
The present invention shown in Table 1 and Table 2 after electrolytic treatment at 10 A / dm ² for 1 second in H 20 g / l) and pickling treatment (soaking for 1 second in 50 g / l H ₂ SO ₄ ) Sn plating is performed under the Sn plating bath composition and plating conditions of the examples and the comparative examples. The Sn plating amount was 5.0 g / m ² . Sn
All plating was performed by a circulation cell plating device with a flow rate of 2 m / sec.

Table 3 shows the results of investigations on the quality of plated products and the amount of Sn sludge generated. The plating appearance gloss is 2
It was judged by the gloss after the melt processing at 50 ° C. for 2 seconds. The criteria for evaluation were that the gloss equivalent to or higher than that of the electric tinplate produced in the current ferrostan bath was ◯, and the others were x.

The evaluation of the generation of Sn sludge was carried out in a 1 L beaker in a Sn plating bath at 50 ° C. with air (200 L / l).
(1.2 min., 1.2 atm), and after 2 hours under the condition of air saturation, the generated Sn sludge was filtered and
The amount of Sn sludge was measured by drying at 0 ° C. for 24 hours. S
As the evaluation of n sludge amount, when the same test was performed,
The amount of Sn sludge generated from the current ferrostan bath is 1
Since it was 20 to 150 mg / l, if it was less than this, it was judged to be suitable as a Sn plating bath for all insoluble anodes.

[0031]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[0032]

According to the present invention, Sn with less generation of Sn sludge is produced.
By using a plating bath, S due to the generation of Sn sludge
In addition to reducing the n loss, it is possible to use a high flow rate cell with vigorous bath agitation, which enables high current density plating.

[Brief description of drawings]

FIG. 1 is a chart showing the relationship between the amount of generated Sn sludge and the concentration ratio of β-alkanol sulfonic acid (2-hydroxypropanol-1-sulfonic acid) and Sn ²⁺ .

Claims (1)

[Claims] 1. A beta beta alkanol sulfonic acid having a hydroxyl group at position, and includes a Sn ^2+, the concentration of Sn ²⁺ 15
~ 60g / l, and β alkanol sulfonic acid and Sn ²⁺
And a molar concentration ratio of 1.4 to 2.3, and 0.5 or more of one or more surfactants represented by the following formulas (1), (2) and (3) as a brightening agent. An acidic Sn plating bath with little generation of Sn sludge suitable for an insoluble anodic plating method, which is characterized by adding 10 to 10 g / l. [Chemical 1]