JPH06346273A - Sludge inhibitor for tinning sulfuric acid bath and tinning method - Google Patents

Abstract

PURPOSE:To obtain a sludge inhibitor for a tinning sulfuric acid bath obtain and to provide a thinning method used for producing tin plate and a thin tinned steel sheet used for a can, a can cover, etc. CONSTITUTION:The objective sludge inhibitor for a tinning sulfuric acid bath is an arom. compd. soluble in a soln. and having two or more electron donative substituents including at least one hydroxy group. This sludge inhibitor is added to a sulfuric acid bath having 5-50g/l concn. of sulfuric acid and a steel sheet is electrolytically tinned with the sulfuric acid bath at 30-70 deg.C bath temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sludge inhibitor for a tin-plating sulfuric acid bath and a tin-plating method for use in the production of electroplated tinplate and thin tin-plated steel sheets used for cans, can lids and other applications. is there.

[0002]

2. Description of the Related Art As tin plating baths used for the production of tin-plated steel sheets such as tin plates, halogen baths, ferrostane baths (phenol sulfonic acid baths), alkali baths and the like have been well known. The alkaline bath uses tetravalent tin, sodium stannate, as the tin source. Therefore, in order to obtain the same amount of deposition as when using other baths using divalent tin, about twice the amount of electricity is required. It is necessary, and for economic reasons, there are few electroplating lines currently using it both in Japan and abroad. Halogen baths have the advantage that they can be plated at high current densities, but due to their corrosive nature they have the disadvantage that maintenance of equipment is more cumbersome than other baths and that insoluble anodes cannot be used. , Has not been widely used. At present, most of the tinplate lines in the world use a ferrostane bath mainly containing phenolsulfonic acid as an acid component.

[0003]

Tinplate obtained from a ferrostan bath has excellent appearance such as gloss, corrosion resistance, and workability. For the last several decades, TFS-CT (tin-free steel chrome type) and nickel plating have been used. Despite the invention and practical application of surface-treated steel sheets for other containers such as steel sheets,
The demand continues to this day. But,
The ferrostane bath was not an ideal tin plating bath for tin production. This is due to the following two reasons.

The first is its harmfulness. Since the plating waste liquid contains a large amount of phenolsulfonic acid, a treatment process for decomposing it before disposal is indispensable. Further, plating in a ferrostane bath is usually performed at about 40 to 45 ° C., but at this temperature, phenolsulfonic acid is slightly volatilized,
Even though local exhaust is performed, a small amount is inhaled by the worker.

Second, the cost is high. Phenolsulfonic acid is industrially mass-produced for manufacturing tinplate, and although the price is low, it is still very expensive as compared with inorganic acids such as sulfuric acid. Further, as described above, it is not easy to dispose of the waste liquid, which is one of the causes of cost increase.

A sulfuric acid bath is considered as a plating bath that overcomes the above two points. Sulfuric acid baths have traditionally been used for small batch plating in batches. The sulfuric acid concentration is 100 g /
It is 1 or more. It is difficult to use this plating bath as it is for tin production. This is because when the concentration of sulfuric acid is high, there are problems such as poor plating deposition efficiency and severe deterioration of equipment. Therefore, it is easily conceivable to reduce the concentration of sulfuric acid, but there arises a problem that the amount of sludge containing SnO ₂ as a main component is extremely large.

From the tin plating bath containing divalent tin ions,
The tin (I
I) is oxidized to tin (IV), and sludge containing SnO ₂ as a main component is easily generated. SnO ₂ does not actually function as tin to be electrodeposited, but it is usually recovered and regenerated. Further, when tetravalent tin is used for electrodeposition, it requires twice as much electricity as divalent tin, resulting in a decrease in apparent current efficiency, which is economically disadvantageous. In the conventional ferrostan bath, about 5-8% of the added tin is removed as sludge. Tin (II) is more unstable in a sulfuric acid bath with an acid concentration similar to that of a ferrostane bath, and more sludge is produced, so it is not suitable for tin production as it is, and it is necessary to take measures to suppress sludge. is there. Therefore, an object of the present invention is to provide a method capable of suppressing the generation of sludge and a low-pollution, low-cost tin plating method.

[0008]

The present inventors have found that low pollution,
The present invention has been achieved as a result of various studies focusing on sulfuric acid as an acid component from the viewpoint of low cost, and various methods for increasing the current density of a favorable platable current and reducing sludge formation. The present invention provides a sludge inhibitor for a tin-plating sulfuric acid bath, which is a solution-soluble aromatic compound having two or more electron-donating substituents, at least one of which is a hydroxy group, and the sludge inhibitor. Bath temperature 3 using the sulfuric acid bath with added sulfuric acid concentration of 5 g / l or more and 50 g / l or less
A method of electroplating a steel sheet at 0 to 70 ° C., preferably, the sludge inhibitor is the o-position or p of the hydroxy group.
An aromatic compound having a substituent in which oxygen is bonded to the carbon of the benzene ring at the -position is used in a concentration range of 0.01 to 2 g / l, and the substituent in which oxygen is bonded to the carbon of the benzene ring is a hydroxy group. This is a tin plating method in which the aromatic compound in the m-position and the aromatic compound in which the carbon atom of the benzene ring is nitrogen are used in a concentration range of 0.1 to 2 g / l.

[0009]

The present invention will be described in detail below. The amount of sludge produced decreases as the concentration of sulfuric acid in the bath increases. When the concentration of sulfuric acid is increased to about 100 g / l, the amount of sludge generated is about the same as that of the ferrostan bath, but the high concentration of sulfuric acid causes a harmful effect. That is, as the amount of hydrogen generated increases with the precipitation of tin during electrolysis, the deposited tin is dissolved and the apparent deposition efficiency of the plating decreases. In addition, the corrosion of the surrounding devices increases. Therefore, it is preferable to utilize the action of other chemicals instead of increasing the concentration of sulfuric acid to suppress the generation of sludge. When various chemical agents having such an action were examined, it was found that two or more hydrogen atoms of benzene were replaced by a substituent, and at least the position of the substituent was a hydroxy group (hydroxyl group) had the above action. It was

As the substituent effective as the second substituent, a substituent having an electron-donating E effect such as a hydroxy group, an amino group and a methoxy group was effective. Specifically, monohydroxyphenyl compounds (o-hydroxyanisole, m-hydroxyanisole, p-hydroxyanisole, o-aminophenol, m-aminophenol, p-aminophenol, etc.), dihydroxyphenyl compounds (catechol, resorcinol, Hydroquinone, 2,3-hydroxybenzoic acid, 3,4-dihydroxybenzaldehyde, 3,5-dihydroxytoluene, etc., trihydroxyphenyl compound (pyrogallol,
Phloroglucin, gallic acid, n-propyl gallate,
3,4,5-trihydroxybenzoic acid).

Further, it has been found that the positions of a plurality of substituents are ortho (o-) or para (p-) with respect to each other, and the effect is great even at low concentrations. That is, o- and p-hydroxyanisole were produced from m-hydroxyanisole, pyrogallol and gallic acid were produced from phloroglucin, and o-aminophenol and p-aminophenol were produced sludge from m-aminophenol. The effect of suppressing As the kind of the substituent, a methoxy group or a hydroxy group has a larger sludge suppressing effect than an amino group. Other than that, thiphenols such as 2-mercaptophenol also have a sludge suppressing effect, but they are not practical because of their bad odor.

The concentration of the sludge inhibitor required depends on its type for the above reasons. o-hydroxyanisole, p-hydroxyanisole, catechol,
Hydroquinone, pyrogallol, gallic acid, gallic acid n-
Propyl, 2,3-dihydroxybenzoic acid, 3,4,5
-Trihydroxybenzoic acid, 3,4-dihydroxybenzaldehyde and the like, a sludge inhibitor having a substituent in which oxygen bonds to carbon of a benzene ring at the o-position or p-position of a hydroxy group has a large sludge-inhibiting effect. .01
Sludge formation can be suppressed at g / l.

M-Hydroxyanisole, resorcinol, phloroglucin, 3,5-dihydroxytoluene, etc., in which the substituent in which oxygen is bonded to the carbon of the benzene ring is at the m-position of the hydroxy group and o-aminophenol, m-amino Phenol, p-aminophenol, etc.
When the atom bonded to the carbon of the benzene ring is nitrogen, the addition amount of 0.1 g / l or more is desirable. The upper limit of the concentration of these sludge inhibitors is 2 g / l. The addition of more than this will saturate the effect, so it should be avoided because it is against the economic reason and the purpose of the present invention aimed at reducing pollution by reducing the use of phenols.

Next, the plating method of the present invention will be described. The steel sheet to be tin-plated in a sulfuric acid bath containing the sludge inhibitor of the present invention is not particularly limited, and a suitable steel sheet may be used depending on the application. As a pretreatment, the surface is cleaned and activated by electrolytic alkaline degreasing and sulfuric acid pickling. Further, depending on the application, it is also possible to use a steel plate plated with a base such as nickel-plated Ni-Fe alloy plating.

The bath temperature for tin plating is 30 to 70 ° C. Three
In order to obtain a bath temperature of less than 0 ° C., the cost for cooling is high, which is not economical, and plating having excellent appearance and corrosion resistance cannot be obtained. Operation at bath temperatures above 70 ° C
It should be avoided because it accelerates the deterioration of the bath due to the corrosion of equipment and the accelerated elution of iron from the steel sheet, and the generation of steam increases, which worsens the working environment.

The cathode current efficiency of electrodeposition using the plating bath of the present invention is good, the appearance of the plating is also good, and no adverse effect of the sludge inhibitor on the plating is observed. The anode may be either soluble or insoluble. The insoluble anode may be a conventional one in which titanium is a base material and platinum is plated. Depending on the application, reflow treatment is applied to the steel plate after tin plating. In the conventional ferrostan bath and the like, the diluted solution of the plating solution can be directly used as the flux. Therefore, the purpose of flux application is usually achieved only 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,
If you need a very smooth and glossy tinplate,
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.

In the present invention, sulfuric acid is used as the acid component of the plating bath. Sulfuric acid produces a little mist, but is inherently non-volatile, has little pollution in the working environment and air, and has less problems in waste liquid treatment compared to conventional baths using organic sulfonic acid, and at a low price. Certain points are also industrially advantageous. The sulfuric acid concentration is 5 to 50 g / l. If it is less than 5 g / l, the plating gloss is not excellent, the pH of the bath is high, and the pH is further increased near the cathode during electrolysis, and tin precipitates in the form of hydroxide or oxide. When the amount is 50 g / l or more, the plating property is saturated, and the amount of hydrogen generated during electrolysis increases, and the tin that has been once deposited is slightly dissolved, so that the apparent deposition efficiency decreases, which is not economically preferable. In addition, the amount of iron eluted into the bath increases, making it impossible to use the bath stably for a long period of time. Furthermore, it becomes highly corrosive, which adversely affects the equipment.

A divalent tin salt is added as tin during bathing.
It is particularly desirable to add it as tin (II) sulfate. During operation, a tin anode may be used to replenish the tin (II) ions lost by electrolysis due to the dissolution of the anode, or an insoluble anode such as a platinum electrode plated with platinum may be used to remove the tin (II ) Ion replenishment may be performed by another method, for example, by immersing metal tin particles in a plating solution and blowing oxygen or air into the plating solution to use an oxidation reaction by oxygen. The tin plating additive is not particularly limited. Additives used in organic sulfonic acid baths can be used as well. As an example, ENSA (ethoxylated α-naphthol sulfonic acid) used in ferrostane baths can be used without problems.

[0019]

EXAMPLES Examples of the present invention will be described below. The composition common to the plating baths of the examples is as follows. Tin (II) sulphate 36.2 g / l (20 g / l as tin) Sulfuric acid 16.7 g / l ENSA 4.0 g / l Table 1 and Table 2 show the conditions of the plating baths of the examples not described here. Described. All the bath temperatures were unified to 45 ° C. According to the method described below, (1) sludge generation,
(2) Tin dissolution, (3) Platability and plated steel sheet characteristics were tested.

(1) Sludge Generation Test a) Generation of Sludge by Oxygen A tin dissolution tank having an inner diameter of 105 mm and a height of 800 mm has a particle size of 2.
5 kg of 8 mm tin particles were filled, 80 liters of plating solution was circulated at 60 liters / minute, and oxygen was blown at 1.5 liters / minute. 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.

B) Generation of sludge by electrolysis: The plated steel sheet is kept stationary, 2 liters of the plating solution at 45 ° C. is circulated in a plating cell in which the plating solution is circulated, and platinum-plated titanium is used as the anode, and the anode current density is 25 A. The amount of sludge produced was measured by electrolysis of 30,000 coulombs at / dm ² .

(2) Tin Dissolution Test In a tin dissolution tank having an inner 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 liters of plating solution was circulated at 60 liters / minute, and oxygen was blown at 1.5 liters / minute. The pressure in the dissolution tank was 2 kgf / cm ² . Sn ²⁺ in the liquid after 2 hours was determined by iodometric titration.

(3) Platability and characteristics of plated steel sheet A test solution (bath temperature 45 ° C.) was circulated using a horizontal circulation cell and a platinum-plated titanium electrode was used as an insoluble anode, and 50 Coulomb / dm ² at 25 A / dm ^{2. 2} tin plating was performed. 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 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. b) Corrosion resistance ATC test A steel plate was tin-plated, then reflowed at 260 ° C, degreased, and electrolytically stripped of metallic tin to prepare a test piece.
Sealed leaving a 2.25 cm ² current-carrying part, 26.7 ° C
Was immersed in the tomato juice and the couple current flowing between the test piece and the tin electrode after 20 hours was measured.

[0025]

[Table 1]

[0026]

[Table 2]

The above test results are shown in Table 1 of the present invention and Table 2.
Comparative examples are shown in each. As is clear from these results, according to the method of the present invention, it is possible to suppress the generation of sludge and perform good tin plating.

[0028]

EFFECTS OF THE INVENTION According to the method of the present invention, while having the advantages of low cost and low pollution, sludge generation is suppressed even in a sulfuric acid bath which is considered not practical for tin production. Since tin plating can be carried out, the harmfulness of the plating waste liquid can be reduced, the waste liquid can be easily treated, and expensive acids can be dispensed with in the bath, so the manufacturing cost can be reduced.

Claims (4)

[Claims] 1. A sludge inhibitor for a tin-plating sulfuric acid bath, which is an electrolyte-soluble aromatic compound having two or more electron-donating substituents, at least one of which is a hydroxy group. 2. A steel sheet is electrotin-plated at a bath temperature of 30 to 70 ° C. using a sulfuric acid bath containing the sludge inhibitor according to claim 1 and having a sulfuric acid concentration of 5 g / l or more and 50 g / l or less. And tin plating method. 3. The sludge inhibitor is a hydroxy group o-.
Is an aromatic compound having a substituent in which oxygen bonds to the carbon of the benzene ring at the p-position or p-position, and the concentration range is 0.01
The tin plating method according to claim 2, wherein the tin plating method is used at 2 g / l. 4. The sludge inhibitor is an aromatic compound in which a substituent in which oxygen is bonded to a carbon of a benzene ring is in the m-position of a hydroxy group, and an aromatic compound in which an atom bonded to a carbon of the benzene ring is nitrogen. Yes, concentration range 0.1-2g /
The tin-plating method according to claim 2, wherein the tin-plating method is used in 1 l.