JPH073493A - High current density tin plating method using circular-arcuately shaped plating cell - Google Patents

Abstract

PURPOSE:To perform the high current density tin plating at a high speed while controlling the amount of the sludge to be formed by using a circular-arcuately shaped plating cell contg. an electrolyte which has specified respective concn. of sulfuric acid, divalent tin ion and a specific aromatic compound mixture and specifying the plating bath temp. and the current density. CONSTITUTION:At the time of performing the tin plating on a steel strip by using a circular-arcuately shaped plating cell, the concn. in the plating solution of sulfuric acid, divalent tin ion and an aromatic compound mixture are adjusted to 5 to 50g/l, 40 to 100g/l and 0.01 to 2g/l respectively. The above aromatic compound mixture consists of an aromatic compound having at least two hydroxyl groups such as catechol, pyrogallol and another aromatic compound having one hydroxyl group and an electron donative substituent than coordinates through a nitrogen or oxygen coordinating atom such as aminophenol in the ratio of 4:1. The tin plating on a steel strip is performed by electrocrystallizing tin on the steel strip in the above plating solution (electrolyte) at 30 to 70 deg.C bath temp. with a >=50A/dm<2> current density. Thus the high speed tin plating using the sulfuric acid bath which has good environmental properties and can be produced at a low cost is performed without forming the sludge in the bath even at the time of performing the tin plating with a high current density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc-shaped plating cell high current density tin plating method used for the production of tin-plated, thin tin-plated steel sheets and other electric tin-plated steel sheets.

[0002]

2. Description of the Related Art The production of tin electroplated steel sheets such as tinplate and thin tin plated steel sheets is usually carried out using a vertical plating cell, a halogen bath, a ferrostane bath, an alkaline bath, etc., and a current density of 20 A / It is performed at a relatively low current density of about dm ² . Therefore, there is a point that is not always satisfactory from the viewpoint of productivity, and there has been a strong demand for development of a technique capable of plating at high current density and at high speed and at low cost in order to achieve high productivity. In order to enable such high-speed tin plating technology, both so-called hardware technology that devises the shape of the plating cell and so-called soft technology that devises the plating conditions such as plating bath and temperature. Technology is required.

Regarding the plating cell shape as a technique for the hard surface, the immersion vertical cell is usually used for tin plating, but in this case, it is difficult to increase the flow velocity of the liquid required for high current density. And Japanese Patent Publications 58-32239, 61-21
In the plating cell disclosed in Japanese Patent No. 319, it is possible to increase the flow rate of the plating solution, but it is necessary to correct the position and shape of the strip by causing a static pressure difference in the amount of the plating solution between the electrode and the strip. Therefore, a certain amount of plating solution is required, and 10 mm while maintaining the position and shape of the steel strip.
There are difficulties in achieving the following electrode-steel strip distances. On the other hand, the present inventors have previously proposed an arc-shaped plating cell capable of almost completely correcting the center displacement and defective shape of the steel strip, and reducing the electrode-steel strip distance (Japanese Patent Application No. 5-042674). ).

On the other hand, the plating bath as a soft technique is the ferrostane bath which is most widely used among the above-mentioned plating baths. However, even if this bath is used, it will cause severe plating burn at 50 A / dm ² or more. Therefore, it is difficult to increase the current density. For this, Japanese Patent Laid-Open No. 4-2285
There is a plating bath containing an alkyl sulfonic acid as an acid component as disclosed in Japanese Patent Laid-Open No. 95. However, as another condition of the plating bath, it is a very important requirement that there is no environmental problem in the waste liquid represented by the COD value. However, there is a problem with this environment. As described above, it can be said that the conventional technique is difficult to perform plating at a high current density capable of speeding up, good environmental friendliness, and low cost.

[0005]

The present inventors have paid attention to a sulfuric acid bath as a plating bath which is a soft technique for high-speed tin plating, from the viewpoint of low cost and good environment. However, the most weak point of the sulfuric acid bath is that sludge is extremely generated especially in the high current density region. If a large amount of this sludge is generated, there is a problem that not only the effective tin ions are wasted but the manufacturing cost is raised, but also the plating quality adheres to the plating film during plating and the plating quality is impaired. Therefore, when performing tin plating with a high current density using a sulfuric acid bath, in terms of soft technology, the generation of sludge is suppressed, and in order to facilitate flow, a plating bath that reduces its shape and sludge from a hard technology side are used. There is a need for a plating cell capable of flushing away and capable of high flow rates. Therefore, an object of the present invention is to provide an arc-shaped plating cell high current density tin plating method in which a plating bath with less sludge generation and a smaller shape and a plating cell capable of high flow rate are combined.

[0006]

As conventionally known, tin ions in a tin plating solution exist as Sn ²⁺ , but they are oxidized by oxygen in the solution and tin is converted according to the following formula (1). It becomes an oxide. This tin oxide is sludge. Sn ²⁺ + O ₂ → SnO ₂ (1) With respect to the above-mentioned problems, the present inventors have studied in detail the oxidation of the relationship between Sn ²⁺ ions and an organic compound and the miniaturization of sludge generated. In addition, as a result of various studies on various combinations with plating cells capable of high flow rate,
The present invention has been achieved.

That is, according to the present invention, the steel strip running line is bent into an arc shape at the electrolytic plating position, the electrodes are arranged along the inside and outside of the arc-shaped portion, and the electrolysis is performed between the electrode and the steel strip. Using an arc-shaped plating cell in which the solution is placed, sulfuric acid 5 to 50 g / l, divalent tin ion 40 to 100
An aromatic compound having g / l and two or more hydroxy groups, and an aromatic compound having one hydroxy group and an electron-donating substituent coordinated with nitrogen or oxygen are used.
Aromatic compound mixed in a ratio of 1 to 0.01 to 2 g / l
Is an arc-shaped plating cell high current density tin plating method in which tin is electrodeposited on a steel strip at a bath temperature of 30 to 70 ° C. and a current density of 50 A / dm ² or more using an electrolytic solution containing as a main component. Incidentally, the arc shape represented in the present invention, in addition to a circle and an ellipse,
It means a state where there is no bending point and it is smoothly bent along one direction.

[0008]

The present invention will be described in detail below. First, the plating bath as a soft technique will be described. First, the sulfuric acid concentration of the plating solution is set to 5 to 50 g / l. At 5 g / l, the pH of the electrolytic solution is about 1.2, and the divalent tin ion is stable. However, at a concentration lower than this, the pH becomes high in the vicinity of the cathode during electrolysis, so the divalent tin ion is not stable. It becomes stable and easily precipitates, and the gloss of 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 apparatus will occur.

The divalent tin ion concentration is 40 to 100 g / l.
And 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 high-quality tinplate. When it exceeds 100 g / l, in addition to the large amount of divalent tin ions carried out by the steel strip, a large amount of sludge is generated, which is economically disadvantageous.

An aromatic compound having an effect of suppressing oxidation is further added to the plating solution. As a compound that suppresses oxidation, the effect of forming a complex with a divalent tin ion to make it difficult to oxidize, and the effect of reducing the oxidized tetravalent tin ion back to divalent It is desirable to share. An aromatic compound having two or more hydroxy groups has two such effects. That is, by having a hydroxy group, it has a reducing property, and when it has two or more, it has an electron donating property, so that the electron density of the benzene ring becomes high, and it becomes easy to form a complex with a divalent tin ion.

Since the substituents other than the hydroxy group may be a hydroxy group, an amino group, a methoxy group, etc., specific examples of the compound include dihydroxyphenyl compounds (catechol, hydroquinone, 2,3-dihydroxybenzoic acid,
3,4-dihydroxybenzaldehyde, 3,5-dihydroxytoluene, etc.) and trihydroxyphenyl compounds (pyrogallol, phloroglucin, gallic acid, n-propyl gallate, 3,4,5-trihydroxybenzoic acid, etc.).

Further, in order to reduce the shape of the sludge formed, the aromatic compound having two or more hydroxy groups and one hydroxy group and an electron donating substituent coordinated with nitrogen or oxygen are used. It has been found that an aromatic compound obtained by mixing the aromatic compound with the aromatic compound in a ratio of 4: 1 has an extremely large effect. As a concrete example of the latter,
There are aminophenol and hydroxyanisole.

The formation of sludge is such that when it becomes tin oxide in the liquid, it crystallizes due to its low solubility and precipitates when it reaches a certain size, but it is generally well known. As described above, the more production sites, the smaller the shape during crystallization. When these two kinds of aromatic compounds are added, the detailed mechanism is unknown, but those that directly oxidize without forming a complex from the beginning, once form a complex with an aromatic compound having one hydroxy group, and then It does not oxidize under uniform conditions, such as those that oxidize at a distance for some reason, or that once complex with an aromatic compound having two hydroxy groups and then oxidize at a distance for some reason, do not oxidize under uniform conditions. It is thought that it will be a small shape. The addition concentration of these compounds was 0.
The optimum value is 01 to 2 g / l. This is because if it is less than 0.01 g / l, there is no effect, and if it exceeds 2 g / l, there is an effect, but it is saturated, so it is not economical and there is a downside to maintaining good environment.

Furthermore, when the above compounds are examined in detail, the effect changes depending on the coordination site of the substituent,
In particular, since the effect is maximized at the ortho position (o-) and the para position (p-), it is preferable that the aromatic compound coordinated to the ortho position (o-) and the para position (p-) is used. Good. That is, pyrogallol is more effective than phloroglucin, and o- and p-aminophenol is more effective than m-aminophenol. It is considered that this is related to the fact that electrons are easily collected in the benzene ring due to its molecular structure and the complex formation is facilitated, though the details are unknown, and the addition amount of these ortho-positions and para-positions is 0. 0.01-0.1 g / l
And a small amount is effective.

Among the plating conditions, the bath temperature is 30 to 7
Set to 0 ° C. Due to heat generation due to electrolysis, stirring, etc., it takes a cost for cooling to obtain a bath temperature of less than 30 ° C., which is not economical and plating excellent in appearance and corrosion resistance cannot be obtained. Operation at a bath temperature of over 70 ° C should be avoided because the corrosion of the equipment and the deterioration of the bath due to the accelerated elution of iron from the steel sheet are accelerated, and the generation of steam increases and the working environment deteriorates. .

The current density is 50 A / dm ² or more, which is difficult in the ferrostan bath, and plating is performed at a high current density.
This is because if it is less than 50 A / dm ² , it is impossible to achieve the high speed as the object of the present invention. Other plating conditions,
That is, for the brightener added to the plating solution, the pretreatment of the steel strip, the electrode type, the reflow treatment after plating, and the like, the method usually performed using a ferrostane bath may be used.

Secondly, regarding the plating cell which is a hard technique, in the present invention, the steel strip running line is bent in an arc shape at the electrolytic plating position, and the electrodes are arranged along the inside and outside of this arc-shaped portion. , An arc-shaped plating cell in which an electrolytic solution is inserted between the electrode and the steel strip. FIG. 1 shows its typical shape. As described above, since the first electrode pad is of the vent floater type, static pressure is generated between the strip and the pad, and the strip can be held along the required line. Since the arc portion is formed by bending the line, the rigidity is increased in the strip width direction and the defective shape is corrected. Therefore, high current density and 10m / s of liquid
The above high flow rate is possible. Since the stirring of the liquid is also very effective in reducing the size of the sludge, it is possible to further reduce the size of the sludge and render it harmless by combining the above-mentioned plating bath and the arc-shaped plating cell.

[0018]

EXAMPLES The present invention will be specifically described below based on examples. First, examples of the amount and shape of sludge produced will be shown, and then examples of plating production will be shown. (1) Sludge Generation Amount and Shape Test The aromatic compounds shown in Table 1 were added to a plating solution having the composition shown below and oxygen-oxidized. Plating solution: tin sulfate (II) 108.6 g / l (60 g / l as tin) sulfuric acid 16.7 g / l ENSA 4.0 g / l

The test is 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 . Two hours after the oxygen was blown, 2 liters of the plating solution was filtered, and the weight of the sludge was measured. Since it is difficult to quantitatively evaluate the shape of sludge, the size of sludge was judged by visual observation during oxidation. As shown in Table 1, the test results show that the sludge formation was significantly suppressed by the addition of the aromatic compound, and the shape was reduced by the addition of the two kinds of aromatic compounds in mixture.

[0020]

[Table 1]

(2) Plating test Using the arc-shaped plating cell shown in FIG. 1 (main specifications are as follows),
The plating was performed under the following plating conditions. Cell main specifications Electrode pad diameter: R = 500 mm First and second electrode pad spacing: H = 20 mm Slit nozzle spacing: t = 5 mm Pad width: W = 1200 mm Pad arc angle: 180 degrees Electrode material: Pt on Ti base material Plating

Plating conditions Plating bath-1 Tin (II) sulfate 108.6 g / l (60 g / l as tin) Sulfuric acid 16.7 g / l ENSA 4.0 g / l Pyrogallol 0.08 g / l o-Aminophenol 0.02 g / l Plating bath-2 Tin (II) sulfate 108.6 g / l (60 g / l as tin) Sulfuric acid 16.7 g / l ENSA 4.0 g / l Pyrogallol 0 .12 g / l p-hydroxyanisole 0.03 g / l bath temperature 45 ° C. current density 150 A / dm ² basis weight 2 g / m ²

Operating conditions: strip running speed 400 to 1,0
00 mpm Steel strip dimensions Width 1,000 x thickness 0.2 mm Tension 1 kgf / mm ² Nozzle flow velocity of plating solution ul-3m / s, u2-1m / s, u3-2m / s Plating-1 and Plating-2 In the case of, there is no problem in the plating operation, and the obtained tin-plated steel sheet has a plating gloss (measured by the method of JIS Z 8741) and a corrosion resistance (AT
C test) was good. Moreover, sludge generation was small.

[0024]

As is apparent from the above embodiments, according to the present invention, even in tin plating with high current density, the cost is low, and the amount of sludge generated is suppressed in a sulfuric acid bath of good environment to achieve high-speed plating. Therefore, the industrial value in terms of quality, cost and environment in manufacturing tinplate and the like is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structural example of a plating cell according to the present invention.

[Explanation of symbols]

 1 1st electrode pad 2 2nd electrode pad 3 Metal strip 4 Jet nozzle of 1st electrode pad 5 Jet nozzle of 2nd electrode pad 6 Conductor roll 7 Plating solution tank 8 Plating solution discharge hole 9 Liquid cutting roll u1 Nozzle 1 Flow rate u2 Nozzle 2 flow rate u3 Nozzle 3 flow rate t Slit nozzle spacing H First and second electrode pad spacing R Pad diameter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Akita 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. A circle in which a steel strip running line is bent into an arc at an electrolytic plating position, electrodes are arranged along the inside and outside of the arc, and an electrolytic solution is placed between the electrode and the steel strip. Using an arc-shaped plating cell, sulfuric acid 5-50
g / l, divalent tin ion 40 to 100 g / l and an aromatic compound having two or more hydroxy groups, and an aromatic compound having one hydroxy group and an electron-donating substituent coordinated with nitrogen or oxygen. And an electrolytic solution containing 0.01 to 2 g / l of an aromatic compound as a main component, which are mixed at a ratio of 4 to 1, using a bath temperature of 30 to 70 ° C. and a current density of 50 A / dm ^2.
The arc-shaped plating cell high current density tin plating method of depositing tin on a steel strip as described above.