JP3018607B2 - Electrotin plating method with less sludge generation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an acid tin plating solution, an insoluble anode, and a method for replenishing the acid tin plating solution with tin oxide as tin ions. And a method for forming a tin-plated layer on the surface of the steel sheet.

[0002]

2. Description of the Related Art For canning of foods and beverages,
Until now, tin-plated steel sheets have been used. Conventionally, as a method for producing an electro-tin plated steel sheet, a self-soluble anode method in which tin ions are automatically replenished when a tin anode is melted out has been generally used. Further, as a plating bath of such a method, an electrotin plating method using an acidic plating solution such as phenolsulfonic acid, sulfuric acid, and hydrochloric acid has been generally used.

In recent years, an electrotin plating method using an insoluble anode has been developed, and has been put to practical use in several lines. The reason for this is that in the case of a self-soluble anode, it is difficult to replace an anode that has been thinned by melting. Therefore, insoluble anodization is performed for the purpose of rationalizing this exchange work. In the insoluble anode method, since tin ions are not automatically replenished, it is necessary to replenish tin ions from outside. For example, tin particles (pure tin)
And a method of chemically dissolving tin particles in an acidic plating solution using oxygen has been devised, registered and put into practical use (JP-B-53-17979, JP-B-56-5).
No. 4079) (hereinafter referred to as "prior art 1") However, in the method of prior art 1, since oxygen is forcibly blown, tin ions dissolved into the plating solution are oxidized by the oxygen. As shown in the following equation (1), there is a problem that sludge is formed. Since the amount of sludge generated by this sludge formation is very large, a method of reducing the generated sludge to metallic tin in a hydrogen atmosphere after roasting has already been registered.
(Japanese Patent Publication No. 57-53880) (hereinafter referred to as “prior art 2”).

[0004] However, in the prior art 2, although sludge can be collected, facilities and sites for sludge collection are required, and expenses for sludge collection are naturally required. If the amount of oxygen blown is suppressed, the amount of sludge generated can be reduced, but since the dissolution rate of metallic tin depends on the amount of oxygen blown, reducing the amount of oxygen blown is actually limited. In view of these problems, a technique for replenishing tin ions in an acidic plating solution using tin oxide (SnO) has already been devised and disclosed (JP-A-61-41799, JP-A-2-194,192) (hereinafter referred to as "prior art 3").

Since tin oxide (SnO) dissolves very easily and quickly when added to an acidic plating solution, there is no need to blow oxygen at all as in the case of dissolving tin particles in a plating solution. Therefore, the method of dissolving tin oxide in the plating solution according to the prior art 3 is based on the conventional techniques 1 and 2 using tin particles.
This has the advantage that the amount of generated sludge is extremely small, and the sludge recovery device can be extremely small. However, although not so much as in the method of dissolving tin particles in the plating solution, prior art 3 also has a problem that tin oxide is slightly insolubilized (sludged) by oxygen and moisture during storage of tin oxide. When the tin oxide during storage becomes sludge in this way, the amount of sludge generated is small, but when scraping the tin oxide from a storage device such as a hopper, the tin oxide is partially solidified, and dispensing from the hopper is impossible or difficult. There was a problem that becomes.

In order to control the content of tin ions in the plating solution during plating using tin oxide, tin oxide must be supplied quantitatively and continuously (or a fixed amount at predetermined intervals) from a hopper. Must. Therefore, as described above, the problem that the dispensing of tin oxide from the hopper becomes impossible or difficult becomes a major obstacle in controlling the content of tin ions in the plating solution. further,
When the tin oxide is sludged, the dissolution rate in the plating solution is significantly lower than that of the unsludged tin oxide, and there is a problem that the tin ion content of the plating solution cannot be quickly controlled.

[0007] As a method for preventing the tin oxide from being sludged in the hopper, the hopper is made to have a closed structure so as to prevent the intrusion of moisture and oxygen, the nitrogen in the hopper is replaced with nitrogen, or the air in the hopper is replaced with nitrogen. Although measures such as vacuum drying are conceivable, these methods are not practical due to problems such as an increase in equipment size and an increase in cost.

In the electrotin plating using an insoluble anode (including both a method of replenishing tin particles in a plating solution and a method of replenishing tin oxide), an oxygen generation reaction occurs as a reaction on the insoluble anode. This causes a reaction in which tin ions (Sn ²⁺ ) in the plating solution are oxidized by oxygen generated on the insoluble anode, and the tin ions are turned into sludge. However,
In the method of replenishing tin ions by dissolving tin oxide, the dissolved oxygen content in the plating solution is lower than in the method of dissolving tin particles by oxygen blowing, since oxygen is not blown into the plating solution, and the sludge Is less likely to occur. However, the smaller the amount of sludge generated, the better. This is because not only is the economical aspect that the amount of tin, which is a loss, is reduced, but also the operational advantage that the occurrence of plating defects due to the inclusion of sludge is reduced.

Therefore, in the method of replenishing tin particles and the method of replenishing tin oxide in the plating solution, a method of adding tartaric acid and dextrin to the plating solution has already been proposed as a method of suppressing sludge formation in the plating solution. (Plating, 1960, July P805-810) (hereinafter referred to as "prior art 4"). However, in prior art 4, there is a problem that the addition amounts of tartaric acid and dextrin are as large as 10 g / l or more, and tin plating property and corrosion resistance are not considered.

[0010]

As described above, in an electrotin plating method using an acidic tin plating solution and an insoluble anode, tin ions are supplied by dissolving tin oxide in the plating solution. This method is clearly advantageous in reducing the amount of sludge generated. However, the above method has the following problems. (1) Tin oxide forms sludge during storage, causing supply problems (poor delivery). Also, tin oxide partially sludge has poor solubility in the plating solution, and it is difficult to quickly control the tin content in the plating solution. (2) In electrotin plating using an insoluble anode, oxygen generated on the surface of the insoluble anode during plating causes a reaction of oxidizing sludge of tin ions.

Accordingly, an object of the present invention is to provide an electrotin plating method in which an insoluble anode is used, tin oxide is dissolved in an acid tin plating solution, and tin ions are supplied to the acid tin plating solution. It is an object of the present invention to provide an electrotin plating method that can suppress the formation of sludge of tin and suppress the formation of sludge of tin ions due to oxygen in a tin plating solution and that generates a small amount of sludge.

[0012]

The present invention uses an acidic tin plating solution, uses an insoluble anode, and replenishes the acidic tin plating solution with tin oxide as tin ions.
In the electric tin plating method of passing a direct current between the insoluble anode and the steel sheet, thus forming a tin plating layer on the surface of the steel sheet, replenishment of tin oxide as tin ions into the acidic tin plating solution is performed. Ascorbic acid on its surface,
Gluconic acid, citric acid, tartaric acid, erythorbic acid, salicylic acid, mannonic acid, L-glutamic acid, saccharin,
In addition, the method is characterized by using tin oxide coated with at least one compound of these salts. Further, the content of the compound in the tin oxide is in the range of 50 ppm to 3000 ppm.

Next, the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a tin oxide coated and stored with a compound according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a conventional tin oxide stored. As shown in FIG. 2, in the case of the conventional tin oxide, the surface thereof becomes sludge by oxidation during storage (portion 3 shown in FIG. 2).
Oxidation proceeds from the surface toward the inside, and the inside tin oxide (portion 2 in FIG. 2) becomes sludge.

On the other hand, as shown in FIG. 1, ascorbic acid, gluconic acid, citric acid, tartaric acid,
Coating at least one compound of erythorbic acid, salicylic acid, mannonic acid, L-glutamic acid, saccharin, and a salt thereof, and coating the compound on the surface of tin oxide (part 1 shown in FIG. 1) Once coated, the entry of oxygen into the tin oxide inside is prevented, and not only the outermost surface layer of the tin oxide, but also the tin oxide inside (part 2 shown in FIG. 1) becomes sludge. Can also be suppressed.

Ascorbic acid, gluconic acid, citric acid,
Tartaric acid, erythorbic acid, salicylic acid, mannic acid, L
-The reason why at least one compound of glutamic acid, saccharin and salts thereof suppresses sludge formation by oxidation of tin in tin oxide during storage is not clearly understood, The carboxylic acid group (-COOH) and hydroxyl group (-OH) present on the surface of the tin oxide cover the tin oxide (Sn ²⁺ ), thus inhibiting the bond between oxygen and tin. Conceivable.

In the above, the antioxidant effect of tin oxide during storage (the effect of preventing the formation of sludge of tin oxide) has been described. During the plating, the compound is dissolved in the plating solution simultaneously with the dissolution of the tin oxide. Add and dissolve. The reason why the compound added and dissolved in the plating solution suppresses the formation of sludge of tin ions in the plating solution is considered as follows. That is, the carboxylic acid group present in the compound molecule
The affinity between (-COOH) and the hydroxyl group (-OH) and the tin ion (Sn ²⁺ ) is considered to maintain its effect even in the plating solution. Therefore, the carboxylic acid group (-COOH) and the hydroxyl group
It is considered that the bond between (-OH) and tin ions (Sn ²⁺ ) suppresses the bond between oxygen and tin ions in the plating solution, thus suppressing the sludge formation of tin ions during plating.

Ascorbic acid, gluconic acid, citric acid,
Tartaric acid, erythorbic acid, salicylic acid, mannic acid, L
The content in tin oxide of said glutamic acid, saccharin and at least one of the salts thereof (compound / tin oxide) should be limited to the range from 50 ppm to 3000 ppm; If the content of the compound is less than 50 ppm, the desired effect on the sludge formation of tin oxide during storage and the sludge formation of tin ions in the plating solution during plating cannot be obtained. On the other hand, even if the compound is added in excess of 3000 ppm, the effect is saturated, which is economically disadvantageous. Thus, ascorbic acid, gluconic acid, citric acid, tartaric acid,
The content of erythorbic acid, salicylic acid, mannonic acid, L-glutamic acid, saccharin, and at least one of these salts in tin oxide is from 50 ppm.
It should be limited to 3000 ppm.

As a method for coating the surface of tin oxide with the compound, a method of applying an aqueous solution of the compound on the surface of solid tin oxide and then drying, or a method in which tin oxide is dispersed. A method in which the compound is added to the solution and then dried.

[0019]

Next, the present invention will be described with reference to embodiments.
By mixing tin chloride solution and caustic soda solution,
Tin oxide was formed in the liquid. Before the tin oxide is formed and the dispersed liquid is dried, the compounds shown in Table 1 are added to the liquid (tin oxide) and then dried, and thus the surface is uniformly coated with the compound. Tin oxide (solid) was prepared. At this time, test samples Nos. 1 to 16 of the present invention were prepared such that the content of the above compounds in the tin oxide after drying was within the range of the present invention. For comparison, comparative specimens Nos. 2 to 5 were prepared such that the content of the compound after drying was out of the range of the present invention. Further, a comparative sample No. 1 was prepared without coating the compound on the tin oxide. Then, the following (1) to (3) were evaluated using the prepared specimens Nos. 1 to 16 of the present invention and comparative specimens Nos. 1 to 5.

(1) The amount of sludge of tin oxide during storage was evaluated by the following method. That is, each specimen was left under an atmosphere of 50 ° C. and 80% humidity for 2 weeks. Then
10 g of each test sample was added to 1 liter of tin phenolsulfonate plating solution.
And stirred for 3 minutes, and the stirred plating solution was filtered. Then, the amount of undissolved tin oxide was measured, and the amount was measured as a ratio to the total amount of tin oxide (the amount of undissolved tin oxide /
(The total amount of tin oxide), whereby the amount of sludge-formed tin oxide was evaluated. Table 1 shows the results.

(2) Next, the solubility of each specimen was evaluated by the following method. During the stirring in the above (1), it was measured how long it took from the start of stirring to dissolve 90% of the tin oxide in the plating solution, and the solubility was evaluated based on the time. At this time, stirring was not stopped until the tin oxide was dissolved by 90%. The method for measuring the solubility of tin oxide was as follows. That is, a minute amount of the plating solution being stirred is withdrawn with a microsyringe every minute, the extracted plating solution is attached to filter paper, and the tin content in the attached plating solution is measured by X-ray fluorescence, and the increase is measured. The content was determined from the amount. The solubility of tin oxide is evaluated by calculating the amount of dissolved Sn from the Sn content and measuring the time required to reach a predetermined concentration (tin content) of 90 wt.% Calculated from the added amount. did. Table 1 shows the results.

(3) Further, using each specimen, the amount of sludge of tin ions in the plating solution which was sludged by oxidation during plating was measured and evaluated by the following method. That is, using each specimen, tin (Sn): 30 g / l,
Prepare a plating solution consisting of free acid (free phenolsulfonic acid): 15 g / l and brightener (ethoxy α-naphthol): 5 g / l, and apply a current density of 30 A on the surface of the steel sheet at a treatment time of 3 hours. After the electro-tin plating, the amount of sludge increased in the plating solution was measured and evaluated. In the sludge measurement method, 0.1 l of the plating solution was sampled, filtered and dried in the same manner as in the evaluation test method shown in (1) above, and the amount (weight) of sludge adhering to the filter paper was measured with a balance. Table 1 shows the results.

[0023]

[Table 1]

As is clear from Table 1, the specimen No.
In Nos. 1 to 16, both the amount of generated sludge of tin oxide during storage and the amount of generated sludge of tin ions in the plating solution during plating were small, and the dissolution time of tin oxide in the plating solution was also 1%.
It can be seen that the dissolution rate is very short, that is, within minutes. On the other hand, it can be seen that Comparative Sample Nos. 1 to 5 have extremely large amounts of generated sludge of tin oxide during storage as compared with Samples Nos. 1 to 16 of the present invention. Also, the dissolution time of tin oxide in the plating solution is longer than that of the test sample of the present invention. As a result, it can be seen that the longer the amount of generated sludge of tin oxide, the longer the dissolution time in the plating solution. Further, the comparative specimen had a larger amount of sludge generation of tin ions in the plating solution during plating than the specimen of the present invention, and did not completely dissolve and remained as sludge in the plating solution. .

[0025]

As described above, according to the present invention, the formation of sludge of tin oxide during storage and the formation of sludge of tin ions due to oxygen in a tin plating solution during plating are suppressed. In addition, the tin oxide can be dissolved in the plating solution in a short time, and an electrotin plating method with a small amount of sludge generation during storage and plating can be provided, thus providing an industrially useful effect. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of tin oxide coated and stored with a compound according to one embodiment of the method of the present invention.

FIG. 2 is a cross-sectional view of a stored conventional tin oxide.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Coated compound 2 Tin oxide (SnO) 3 Sludge-ized tin oxide (SnO ₂ )

Claims (2)

(57) [Claims] 1. An acidic tin plating solution is used, an insoluble anode is used, and a direct current is applied between the insoluble anode and the steel sheet while replenishing tin oxide as tin ions in the acidic tin plating solution. In the electro-tin plating method of flowing and thus forming a tin plating layer on the surface of the steel sheet, replenishment of tin oxide as tin ions into the acidic tin plating solution includes ascorbic acid, gluconic acid, citric acid on the surface. Acid, tartaric acid, erythorbic acid, salicylic acid, mannonic acid, L-glutamic acid, saccharin, and the amount of sludge produced by using tin oxide coated with at least one compound of these salts. Electrotin plating method with less noise. 2. The content of the compound in the tin oxide is as follows:
2. The method according to claim 1, wherein the amount of sludge is in the range of 50 ppm to 3000 ppm.