JPH08176882A - Plating bath for producing bright-tin plated material without performing reflow treatment - Google Patents

Abstract

PURPOSE: To provide an acid tin plating bath with which a tin plated steel sheet having beautiful brightness can be produced without performing reflow treatment. CONSTITUTION: This plating bath for performing bright tin plating consists of 0.1 to 1.0mol/l of an organic sulfonic acid, 0.1 to 0.85mol/l of tin (II) and a brightener contg. 5×10<-4> to 0.015mol/l of a surfactant having an oxyethylene chain and 2×10<-3> to 0.02mol/l of an aromatic carbonyl compound having a double bond (s). By using the plating bath, a tin plated steel sheet having beautiful brightness can be produced without performing reflow treatment after the electrolysis and accordingly, the economical effect due to the elimination of this production stage is great.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acidic tin plating bath used for producing tin-plated steel sheets used for materials such as cans. More specifically, it relates to a plating bath that can obtain tin plating having a metallic luster without reflow treatment.

[0002]

2. Description of the Related Art Tin-plated steel sheets represented by tinplate have been used widely since ancient times because they have a beautiful metallic luster and are excellent in corrosion resistance. Regarding the tin plating method, electroplating is now generally used instead of hot dip plating because of the need to reduce the use of tin, which is expensive due to scarce resources.
The most widely used plating bath is a ferrostan bath, which is an acidic plating bath containing phenolsulfonic acid as an acid component. In recent years, a tin plating solution using an alkyl sulfonic acid as an acid component has been developed, as disclosed in JP-A-4-228595.

The tin as electrodeposited by any acidic tin plating bath is white and has a poor metallic luster. This is because the morphology of the electrodeposited tin is microscopic when viewed microscopically and scatters light. Aside from the case where the can wall shows a metallic luster due to ironing as in the case of DI cans, when used for applications where tin on the can wall undergoes almost no processing such as in welded cans, tin is once heated after electroplating. A tin-plated steel sheet having a beautiful metallic luster is manufactured by performing a so-called reflow treatment of melting.

[0004]

It is general to obtain a beautiful metallic luster by the above-mentioned reflow treatment, but the reflow treatment increases the number of steps, consumes energy required for heating, and further increases the operation. It has problems such as the necessity of management. It is an object of the present invention to provide an acidic tin plating bath capable of producing a tin-plated steel sheet having a beautiful metallic luster without performing a reflow treatment after tin plating.

[0005]

The present inventors have accomplished the present invention as a result of various studies on various plating bath compositions including a brightening additive capable of obtaining bright plating. The present invention comprises 0.1 to 1.0 mol / l of organic sulfonic acid,
0.1 to 0.85 mol / l tin (II), and a surfactant having an oxyethylene chain 5 × 10 ^{−4 to} 0.015
The subject is a plating bath capable of obtaining bright tin plating, characterized in that the plating bath contains a brightening additive comprising mol / l and an aromatic carbonyl compound having a double bond of 2 × 10 ^{−3 to} 0.02 mol / l. Is.

[0006]

The present invention will be described in detail below. In the tin plating bath of the present invention, organic sulfonic acid is used as an acid component. The organic sulfonic acid concentration is limited to 0.1 to 1.0 mol / l. The pH of the electrolytic solution is about 1.2 at an organic sulfonic acid concentration of 0.1 mol / l, and tin (II) ions are stable even if the pH rises near the cathode during electrolysis. When the pH increases in the vicinity, the tin (II) ion becomes unstable and hydroxide precipitates. On the other hand, when the concentration of organic sulfonic acid is higher than 1.0 mol / l, the concentration of organic substances in the waste water becomes high, and the treatment cost at the time of discharge increases.

In the present invention, the tin (II) concentration is 0.1 to 0.8.
It is 5 mol / l. Since the present invention is premised on the production of tin-plated steel sheets represented by tinplate, productivity equal to or higher than that of conventional tin plating is required from the economical point of view. Therefore, the current density of tin plating needs to be 10 A / dm ² or more. In the operation in such a current density region, at a tin (II) concentration of less than 0.1 mol / l, the cathode current efficiency is low, and so-called plating burn, in which the deposited tin becomes dendritic, is likely to occur. When tin (II) exceeds 0.85 mol / l, improvement in plating performance due to high concentration is not observed, and sludge (precipitation of tin oxide) increases and strip plating solution carry-out amount increases, which is economical. Is disadvantageous.

[0008] Tin in the bath is added as a soluble divalent tin salt, metallic tin or tin (II) oxide SnO. Due to the low dissolution rate of metallic tin and SnO, the use of tin salts is preferred for rapid bath construction. Although it is optimal to add tin (II) organic sulfonate corresponding to the acid component of the plating bath, tin (II) sulfate, which is relatively inexpensive, may be used for economic reasons. Organic sulfonic acid is added in advance to adjust the pH to less than 2, preferably 1.2 or less, and the solution is gradually added while being dissolved. Addition of a large amount at one time tends to cause precipitation of hydroxide.

When electrolytic tin plating is carried out in an acidic organic sulfonic acid bath, if a gloss additive is not added, the deposited tin will have a rough columnar shape, and the deposition effect, gloss, plating adhesion and corrosion resistance will be markedly deteriorated. Such a tin-plated steel sheet cannot be used as a material for cans. When a surfactant having an oxyethylene chain (CH ₂ CH ₂ O) _n is used alone as a gloss additive, the oxyethylene chain of this surfactant is preferentially applied to the tin crystal growth point on the surface of the steel plate where the cathode is the cathode. Since it is adsorbed and inhibits crystal growth, the throwing power is improved and relatively fine crystals are produced. Electrodeposited tin is 1 μm
Since the particles have a certain degree of granularity and the surface has irregularities, the surface appearance is white and so-called metallic luster does not occur. The surface roughness Ra of the plating original plate is 0.19 μ in the rolling direction of the steel plate.
m, when using a steel plate of 0.27 μm in the width direction, JIS
60 measured in the rolling direction of the steel sheet according to Z 8741
The specular glossiness (Gs60 °) was 430 for the tin-plated steel sheet having the highest gloss. Sufficient luster can be obtained by subjecting this to reflow treatment, but the purpose of the present invention of obtaining a tin-plated steel sheet with excellent luster by only electrolytic treatment is not achieved.

Therefore, the inventors of the present invention have made extensive studies as to a gloss additive for obtaining a tin-plated steel sheet having a beautiful metallic luster only by electrolytic treatment, and as a result, as a gloss additive, oxyethylene chain (CH ₂ CH _{2 2} O) _n not only a surfactant but also an aromatic carbonyl compound having a double bond φ-CH = CH-CO- (φ is an aromatic ring) is used together to provide tin having a metallic luster similar to that of reflow tin. We have found that plating can be realized. That is, in addition to the effect of the surfactant to refine the crystal of tin and improve the uniform electrodeposition property, it is strongly adsorbed to the physical convex portion of the steel sheet and inhibits the electrodeposition of that portion, so that the deposited tin is The synergistic effect of the simultaneous effect of the smoothing aromatic carbonyl compound makes it possible to obtain a metallic luster comparable to that of the reflow treated material, that is, 550 or more at Gs 60 °.

As the surfactant having an oxyethylene chain, POOA (polyoxyethylene octadecylamine), ENSA (ethoxylated α-naphtholsulfonic acid), PEG (polyethylene glycol) may be used. A suitable concentration is 5 × 10 ^{−4 to} 0.015 mol / l. When the concentration is lower than 5 × 10 ⁻⁴ mol / l, the amount adsorbed on the cathode is small, and tin is electrodeposited uniformly, which is not effective as a gloss additive. On the other hand, 0.015 mol
When the concentration is higher than 1 / l, the amount of adsorption to the cathode is too large, resulting in poor plating adhesion.

As the aromatic carbonyl compound having a double bond, benzalacetone or cinnamaldehyde may be used. The concentration of aromatic carbonyl compound is 2 × 10
^{-3 to} 0.02 mol / l is preferable. When the concentration is higher than 0.02 mol / l, the amount of adsorption on the cathode becomes excessive and the plating adhesion,
Cathode current efficiency decreases. On the other hand, 2 × 10 ^-3 mol / l
At a lower concentration, there is no difference from when plating is performed by using a surfactant alone, and bright plating cannot be obtained.

If it is necessary to suppress the amount of sludge generated by the iron ions in the plating bath to a lower level, an iron ion masking agent such as α-oxycarboxylic chain may be added to the plating bath. The appearance of bright plating differs depending on the amount of adhesion, but this tendency is the same as with ordinary tin-plated steel sheets. This is because the hiding ratio of the steel sheet surface is lower as the coating amount is smaller. With bright tin plating, tin is electrodeposited uniformly, so the amount of coating is lower and the hiding ratio of the original plate is higher than with conventional tin-plated steel plates. The effect of bright plating is 0.4g /
This is the case when the adhesion amount is m ² or more. Among the commonly used tin-plated steel sheets, the phenomenon showing an excessive coating weight did not appear up to 22.4 g / m ^2, which had the highest coating weight. It was not confirmed that the amount of adhesion was higher than that of commercial value because it had low commercial value.

The plating bath temperature is preferably 30 to 70 ° C. Three
If the temperature is lower than 0 ° C, bright plating cannot be obtained and plating burns easily. On the other hand, when the temperature is higher than 70 ° C., steam containing acid is often generated and the operability is deteriorated. Current density is 10
˜200 A / dm ² is preferable. At a current density lower than 10 A / dm ² , sufficient gloss cannot be obtained. On the other hand, 200A /
At a current density higher than dm ² , plating burn is likely to occur. However, this is the case of plating using a conventional ferrostan line, and if a line where the strip and the plating solution have a higher relative speed is used, it is possible to manufacture at a higher current density. Ah

Bright plating is difficult to obtain by electrolysis with both the plating solution and the strip being stationary, but the strip running speed in a normal tin line, that is, 100 m
If it is not less than / minute, the relative speed between the strip and the plating solution is sufficient, and the production can be performed without particularly considering the flow of the plating solution.

[0016]

Embodiments of the present invention will be described below. The surface roughness Ra is 0.19 μm in the rolling direction of the steel sheet and 0.2 in the width direction.
After degreasing, pickling, and washing a 7-μm cold-rolled steel sheet, as shown in Table 1, organic sulfonic acid, tin (II), a surfactant having an oxyethylene chain, and an aromatic carbonyl compound having a double bond are contained. It electroplated using the plating solution.

Electroplating is carried out at a bath temperature of 45 ° C. and a current density of 10
Was performed energized so that the tin coating weight 2.8 g / m ² at 0A / dm ^2. The anode used was an insoluble anode made by plating platinum on titanium. The following evaluation was performed on the obtained tin-plated steel sheet. a) Cathode current efficiency The amount of tin deposited on the plated steel sheet was measured by electrolytic stripping in dilute hydrochloric acid, and the percentage of the theoretical amount deposited was defined as the cathode current efficiency. The cathode current efficiency is required to be 95% or more.

B) Plating Luster The gloss Gs 60 ° of the tin-plated steel sheet was measured by the method of JIS Z 8741. The incident and reflected directions of light are
The rolling direction of the original plating plate was used. In the case of the steel plate surface roughness used in this example, a glossiness of 550 or more is desired in terms of appearance. c) Plating adhesion Scratch that reaches the base metal with a cutter on a tin-plated steel sheet 1
It was put in a grid shape of mm and bonded to Tin-free steel with a two-liquefied epoxy phenol adhesive (comprising a main agent and a curing agent). The tin-plated steel plate and the tin-free steel were peeled off by a tensile tester, and 5% or more of the grid was peeled off at the interface between the base metal and the tin plating, and the adhesion was poor.

Table 1 shows the various evaluation methods described above. Table 1
As is clear from the above, when a plating solution consisting of the organic sulfonic acid concentration, the tin (II) concentration, the surfactant concentration, and the aromatic carbonyl compound concentration specified in the present invention is used, tin plating with extremely high gloss can be obtained with high current efficiency. Was obtained. The plating adhesion was also good.

In Comparative Example 1, since the organic sulfonic acid concentration was low, the pH in the vicinity of the cathode was increased to the tin (II) ion unstable region by electrolysis, and tin hydroxide precipitates. Comparative Example 2 has a high organic sulfonic acid concentration and can obtain a good tin-plated steel sheet, but it has an economical problem of wastewater treatment. In Comparative Example 3, the tin (II) concentration was low, plating burns occurred, and the current efficiency was low.

In Comparative Example 4, excellent tin plating was obtained,
There is no difference from the tin plating from a bath with a lower tin concentration, so the tin concentration range is a method that is economically avoided. In Comparative Example 5, the surfactant concentration was low, the distribution of the precipitated tin was non-uniform, and a glossy appearance was not obtained. In Comparative Example 6, since the surfactant concentration was too high, the plating adhesion was poor.

In Comparative Example 7, the concentration of the aromatic carbonyl compound was low, and sufficient luster was obtained as an ordinary tin-plated steel sheet, but not sufficient luster plating for use in place of the reflow treatment tin plate. In Comparative Example 8, the aromatic carbonyl compound concentration was high and the plating adhesion was poor.

[0023]

[Table 1]

[0024]

According to the present invention, a tin-plated steel sheet having a beautiful luster can be obtained without performing a reflow treatment after electrolysis. Therefore, the economical effect is large by omitting the steps.

Claims (1)

[Claims] 1. A surfactant having an organic sulfonic acid of 0.1 to 1.0 mol / l, tin (II) of 0.1 to 0.85 mol / l, and an oxyethylene chain of 5 × 10 ^{−4 to} 0. ．
A plating bath capable of obtaining bright tin plating, characterized by containing a brightening additive composed of 015 mol / l and an aromatic carbonyl compound having a double bond of 2 × 10 ^{−3 to} 0.02 mol / l.