JPH08269772A - Tin plating sulfuric acid bath for high plating current density plating having excellent tin solubility and sludge depressing effect and tin plating method - Google Patents

Abstract

PURPOSE: To provide a sulfuric acid bath for tin plating and a tin plating method capable of continuously operating stable tin plating with high current density. CONSTITUTION: Tin is electrodeposited on a steel strip at the bath temp. of 30-70 deg.C with the current density of 50A/dm<2> with the tin plating sulfuric acid bath for high current density plating, which is excellent in tin solubility and sludge depressing effect and contains 5-50g/l sulfuric acid, 40-100g/l tin (11), a brightener and 2-10g/l sludge depressant as essentail components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tin plating sulfuric acid bath with a high current density and a tin plating method used in the production of electroplated tinplate and thin tin-plated steel sheets used for container materials and other applications.

[0002]

2. Description of the Related Art As a tin plating bath used for the production of tin-plated steel sheets such as tinplate, a halogen bath, a ferrostane bath (phenol sulfonic acid bath), an alkaline bath and the like have been well known. Since the alkaline bath uses tetravalent tin, sodium stannate, as the tin source, approximately twice the amount of electricity is required to obtain the same tin deposition amount as other baths using divalent tin. However, for economic reasons, there are few electroplating lines that currently use it both in Japan and overseas. Halogen baths have the advantage that they can be plated at high current densities, but due to their corrosive nature, maintenance of the equipment is more cumbersome than other baths, and insoluble anodes cannot be used. It has not been widely used. For this reason, at present, most of the tin lines in the world mainly use the phenolsulfonic acid bath. Tinplate produced from a phenol sulfonic acid bath has excellent characteristics such as appearance and corrosion resistance, but there is a drawback that so-called plating burn occurs in plating at a high current density. In addition, since it contains a large amount of phenolsulfonic acid, it is difficult to treat wastewater, which is one of the causes of cost increase.

On the other hand, in recent years, a plating bath containing an alkyl sulfonic acid as an acid component has begun to be used. One of the characteristics of this bath is that the waste liquid treatment is simple. According to JP-A-4-228595, the water for rinsing is
After the tin ion is recovered by neutralization, it can be discharged by a usual method because it does not contain a component harmful to the environment. However, the use of a large amount of organic sulfonic acid leads to an increase in COD, and it is unlikely that discharging without treatment has no environmental impact.

Under these circumstances, the inventors of the present invention have disclosed in Japanese Patent Application No. Hei 5-141616 that electroplating of tin at high current density does not cause plating burns and lowers the cathode current efficiency. The present invention provides a low-pollution, low-cost sulfuric acid bath capable of obtaining a tin plate excellent in plating appearance and corrosion resistance, and a plating method using the plating bath. However, the following problems newly became apparent when tinplate was produced using this sulfuric acid bath for tin plating.

When tin plating is performed at a high current density using this sulfuric acid bath, a large amount of divalent tin ions (hereinafter referred to as tin (II)) in the bath are consumed in a short time, and the bath balance is improved. It becomes difficult to operate at high current density. It is industrially suitable to supply tin (II) to the tin plating bath by using a fluidized tank to dissolve the metal tin particles in the plating bath. At this time, it is common to blow oxygen in order to promote further dissolution of tin. In particular, when performing tin plating at a high current density, it is necessary to blow oxygen in a larger amount than usual and supply tin (II) consumed in plating to the plating bath at a sufficient rate.

However, when a large amount of oxygen is blown, tin sludge is thinly formed on the surface of the tin particles, and the dissolution rate of tin decreases,
There was a problem that the supply rate of tin (II) to the plating bath also decreased. This is because, at the moment when metallic tin is dissolved in tin (II) by the acid and oxygen of the plating solution, the oxidation proceeds due to the excess oxygen and becomes tin oxide, that is, sludge. Since tin sludge is insoluble, when sludge is generated on the surface of tin particles, the dissolution rate from metallic tin is significantly hindered. This problem is a serious problem from the viewpoint of stable operation in order to manufacture tinplate by plating with a high current density using a sulfuric acid bath.

[0007]

Therefore, the present invention provides a tin-plating sulfuric acid bath and a tin-plating method which solve the above problems and enable stable continuous tin plating operation at high current density. is there.

[0008]

The present inventors have found that low pollution,
As a result of various studies on a plating bath and a plating method capable of obtaining good operability at high current density, paying attention to sulfuric acid which is an inorganic acid as an acid component from the viewpoint of low cost, the present invention has been achieved. The gist of the present invention is 5 to 5 as a main component.
High current with good tin solubility and sludge inhibiting effect, characterized in that it contains 0 g / l sulfuric acid, 40-100 g / l tin (II), gloss additive and 2-10 g / l sludge inhibitor Tin plating sulfuric acid bath for density plating, and using this sulfuric acid plating bath, bath temperature 30 to 70 ° C, current density 50A
/ Dm ² or more, there is a tin plating method using a high current density for depositing tin on a steel strip.

[0009]

The present invention will be described in detail below. In the tin plating bath of the present invention, sulfuric acid is used as an acid component. Sulfuric acid produces a little mist, but is inherently non-volatile, so there is little pollution of the work environment and air, and there are problems with waste liquid treatment.
Compared with conventional baths using organic sulfonic acids, the number of baths is low and the cost is low, which is industrially advantageous. Sulfuric acid concentration is 5-5
Should be 0 g / l. At a sulfuric acid concentration of 5 g / l, the pH of the electrolytic solution is about 1.2, and tin (II) ions are stable. However, at a lower concentration, 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, 50g
If it is higher than / l, its effect will be saturated and economically disadvantageous.

[0010] Tin in the bath is added as a soluble divalent tin salt. Since unnecessary components are not put in the bath, tin sulfate (I
Most preferably I) is used. Add it while gradually dissolving it in the solution to which sulfuric acid had been added. Precipitation occurs when a large amount is added at one time. Tin (II) sulphate should not be kept unnecessarily large, as it will undergo air oxidation to form insoluble tin (IV) after long-term storage. It is desirable to store in a cool, dark place, and if possible, in a nitrogen atmosphere. It is possible to use tin (II) oxide or metallic tin in the building bath, but it takes a long time to dissolve.

The tin (II) concentration is 40 to 100 g / l. If it is less than 40 g / l, so-called plating burn will occur when plating is performed at a high current density, and it is difficult to obtain a high-quality tin plate. 1
If it exceeds 00 g / l, the amount of tin (II) ions carried out by the strip increases, which is economically disadvantageous. The brightening agent for tin plating does not have to be particularly limited. As an example, ENSA (ethoxylated α-naphthol sulfonic acid) used in ferrostane baths can be used without problems. Its concentration is 2
Good plating is possible at ~ 6 g / l.

Since the sulfuric acid bath produces a large amount of sludge, it is necessary to use a sludge inhibitor. Suitable sludge inhibitors are electrolyte soluble aromatics having two or more electron donating substituents, at least one of which is a hydroxy group. Among these, an aromatic compound having a substituent in which oxygen is bonded to carbon of an aromatic ring at the o-position or p-position of a hydroxy group, or a substituent in which oxygen is bonded to carbon of an aromatic ring is the m-position of a hydroxy group. And an aromatic compound in which the atom bonded to the carbon of the aromatic ring is nitrogen, and the addition amount thereof is 2 g / l to 10 g / l.
It is desirable to use. When the concentration is less than 2 g / l, a thin sludge layer is formed on the surface of the tin particles by the oxygen-blended tin particle dissolution method, and the dissolution of metallic tin is hindered, so the tin (II) concentration in the bath is balanced. It becomes difficult to continue good tin plating with high current density for a long time.

Further, sludge is often generated at the time of blowing oxygen, and the sludge suppressing effect is not sufficient. Sludge is also produced by air oxidation or an oxidation reaction on the electrode surface when an insoluble electrode is used, but it is smaller than sludge generation when tin is dissolved. Further, when it exceeds 10 g / l, the effect is saturated, an economical demerit is generated, and it is contrary to the purpose of the present invention aiming at low pollution by reducing organic substances in the bath.

Next, the plating method of the present invention will be described. In the tin plating for high current density in the present invention, the relative speed between the electrolytic solution and the steel strip is 100 m / min.
It is desirable to flow at the above high speed. The steel plate to be tin-plated with the plating bath of the present invention is not particularly limited, and a suitable steel plate may be used depending on the application. As a pretreatment, the surface is cleaned and activated by electrolytic alkaline degreasing and electrolytic pickling. Furthermore, the provision of nickel-based flash plating or other undercoating is not specified.

The tin plating is performed at a bath temperature of 30 to 70 ° 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. 70
Operation at a bath temperature in excess of ℃ 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, which deteriorates the working environment. The amount of tin plating is not particularly specified, and an appropriate amount of tin plating may be applied depending on the intended use.

The higher the cathode current density is, the more preferable as long as the cathode current efficiency is high and good plating can be obtained.
In addition to the economic advantage due to improved productivity, a large number of fine plating precipitation nuclei are generated during electrodeposition, resulting in a dense plating, which improves corrosion resistance. Also in the case of the reflow treatment, the denser the electrodeposited tin before the reflow is, the denser the tin-iron alloy is formed, the iron surface is not exposed, and the corrosion resistance is good. 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. This can also improve the corrosion resistance as described above.

The anode may be either soluble or insoluble, but when plating is performed at a high current density, it is preferable to use an insoluble anode because the amount of tin anode is reduced and the replacement frequency increases. The insoluble anode is preferably a platinum group metal or its oxide, but it is expensive, and therefore titanium may be used as a base material and plated with platinum or the like. When an insoluble anode is used, tin ions can be replenished to the plating solution by blowing oxygen or air into the electrolytic solution in which the metal tin particles are immersed as described above to dissolve the tin.
When tin plating is performed at a high current density as in the present invention, it is preferable to use an oxygen blowing method with a high tin dissolution rate in order to keep the tin (II) concentration in the bath constant.

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. In the invention, even if the reflow is performed without applying the flux, a tin plate having practically sufficient gloss can be obtained. As the chemical conversion treatment, an appropriate chemical conversion treatment may be performed depending on the application. For example, the chemical conversion treatment conditions may be appropriately selected according to various required characteristics and applications, such as immersion treatment in a sodium dichromate aqueous solution or a chromate-anion aqueous solution or electrolytic treatment.

[0019]

Embodiments of the present invention will be described below. Sheet thickness 0.
After degreasing a 2 mm original plating plate and electrolytic pickling, tin-plated steel sheets were manufactured under various plating bath compositions, conditions and plating conditions as shown in Table 1. These tin-plated steel sheets were tested for (1) platability and plated steel sheet characteristics, (2) tin solubility, (3) tin solubility, and (4) sludge formation by the methods described below.

(1) Platability and characteristics of plated steel sheet Liquid flow rate 230 m / min. The test solution was circulated using the horizontal circulation cell of No. 1 to perform tin plating at various current densities. The number of Coulombs supplied at that time was appropriately adjusted so as to obtain a desired tin plating amount. The anode used was an insoluble anode made by plating platinum on titanium. The platability and the characteristics of the plated steel sheet were evaluated by the following methods.

(A) Cathode current efficiency The amount of tin deposited on the galvanized 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 higher the current efficiency, the more preferable it is, but practically 90% or more causes no problem. (B) Plating Gloss The gloss Gs 60 ° of the as-plated and reflowed plated steel sheet was measured by the method of JIS Z 8741. The direction of incidence and reflection of light was the rolling direction of the original plating plate. Plating gloss Gs 60 ° as tin plate is 250
The above is desired. (C) Corrosion resistance (ATC test) After the steel plate is tin-plated, reflow treatment is performed at 260 ° C.
A test piece was prepared by degreasing and electrolytically stripping metallic tin. 2.
A 25 cm ² current-carrying portion was left sealed and immersed in tomato juice at 26.7 ° C., and after 20 hours, a couple current flowing between the test piece and the tin electrode was measured. As the ATC value,
0.3 μA / cm ² or less is desired.

(2) Tin dissolution test In a tin dissolution tank having an internal diameter of 105 mm and a height of 800 mm, a particle size of 2.
5 kg of 8 mm tin particles were filled, 80 liter of plating solution was circulated at a rate of 60 liter / min, and 2.0 liter / min of oxygen was blown therein. The pressure in the dissolution tank was 2.3 kgf / cm ² . Before the experiment, the tin (II) concentration in the bath was measured in advance by iodine titration, and the tin (II) concentration in the bath after 3 hours of the test was measured to determine the difference in the tin (II) concentration before and after the test. The amount of dissolution was defined as tin dissolution rate.
The tin dissolution rate is preferably 1.5 g / min or more.

(3) Sludge Generation Test After the above tin dissolution test, 2 liters of the plating solution was sampled and the weight of the sludge generated after filtration was measured. Although it is preferable that the amount of sludge generated is small, 50 g or less was judged to have a suppressing effect. Table 1 shows the above test evaluation results. Examples 1 to 1 of the present invention
No. 7 shows a good result as a comprehensive evaluation. In particular,
Examples 2 to 5 shown by ⊚ are particularly excellent in performance.

[0024]

[Table 1]

[0025]

EFFECTS OF THE INVENTION According to the present invention, it is possible to perform a good continuous plating operation with a high current density using a low-pollution, low-cost sulfuric acid bath, (1) reduction of total cost, (2) reduction of environmental pollution, ( 3) Advantages such as improved corrosion resistance of tin-plated steel sheets can be obtained.

Claims (3)

[Claims] 1. Sulfuric acid of 5 to 50 g / l as a main component, 4
0-100 g / l tin (II), gloss additive and 2-1
A tin-plating sulfuric acid bath for high current density plating, which has a good tin solubility and a sludge-suppressing effect, containing 0 g / l of a sludge-suppressing agent. 2. The plating bath according to claim 1, wherein the bath temperature is 3
A high current density tin plating method in which tin is electrodeposited on a steel strip at 0 to 70 ° C. and a current density of 50 A / dm ² or more. 3. The tin plating method according to claim 2, wherein a high concentration of oxygen is blown in at the time of supplying tin (II) to the plating bath.