JPH0224918B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to additives for acidic tinning baths. More specifically, using an insoluble anode as an anode in an acidic tin plating bath using phenolsulfonic acid,
This invention relates to an additive for acidic tin plating baths for electroplating tin on ferrous materials. Industrially, electrolytic tin plating of metal objects is carried out using acidic baths such as stannous sulfate bath, tin phenolsulfonate bath, boric acid fluoride bath, and sodium stannate bath, potassium stannate bath, etc. An alkaline bath is used. The use of a soluble tin anode has the advantage that cations lost from the bath as the plating operation progresses are automatically replenished. In both cases of acids and alkalis, a metal tin anode is used as the anode, and a direct current is passed through the metal object as the cathode to reduce the tin ions in the bath to metal tin and precipitate it on the cathode. The tin ions lost from the bath are replenished by anodic dissolution of the metallic tin anode. That is, a soluble anode is used. On the other hand, it has already been proposed in JP-A-49-76735 that when a soluble anode is used, various disadvantages arise. Compared to soluble anodes, insoluble anodes have advantages such as reduced tin loss, easier plating bath management, easier electrode gap management,
Insoluble anodes have many advantages in terms of work efficiency, gloss, etc. In acid tin plating carried out industrially,
U.S. Patent No. 2457152 was developed for the purpose of obtaining a tin plating layer that is smooth, glossy, and has good adhesiveness, and is composed of an acid component such as sulfuric acid or phenolsulfonic acid, a soluble tin salt component, and an additive component. Ethoxylated naphthol (number of moles of ethylene oxide added; 3 to 15) proposed in No. 1, and ethoxylated naphtholsulfonic acid (number of moles of ethylene oxide added; 6 to 7) described in JP-A-50-130648. has been proposed as effective for acid tin plating using a soluble anode. When an insoluble anode is used instead of a soluble anode in acid tin plating, especially in a plating bath using phenolsulfonic acid as an electrolyte, the denaturation due to the anodic oxidation phenomenon of phenolsulfonic acid is significant, and ethoxylated naphtholsulfonic acid (ethylene oxide addition) When the number of moles is 6 to 7), it is impossible to reduce the amount of modified substances produced. Furthermore, in the case of adducts of 3 to 15 moles of ethylene oxide to ethoxylated naphthol, at a level of 3 to 6 moles, it has a cloud point below the normal plating temperature (40 to 60°C), which reduces the amount of modified substances produced. Not only is it impossible, but ethoxylation (3
~6 Molar Adduct) It has been observed that the naphthol itself deposits on the anode, increasing the anodic deposit product. Further, at the level of the 13 mole ethylene oxide adduct of ethoxylated naphthol, the foaming property is so high that it cannot be put to practical use. The present inventors have arrived at the present invention as a result of intensive research in order to solve the problems of the prior art. That is, an insoluble anode is used as an anode in an acidic tin plating bath using phenolsulfonic acid at a temperature of 30 to 60°C.
The present invention provides an additive for acidic tin plating baths comprising a compound represented by the following general formula for electroplating tin on iron-based materials by passing a current at a current density of at least 5 A/dm ² . general formula, (However, in the general formula, n is 7 to 12.) In the ethoxylated naphthol represented by the above general formula, which is an additive for acidic tinning baths of the present invention,
When the number of moles of ethylene oxide added is less than 7, it is not possible to reduce the amount of anodic oxidation-modified substances in the produced phenolsulfonic acid. Furthermore, if the number of moles of ethylene oxide added is greater than 12, the foaming property is poor and it cannot be put to practical use. When electroplating tin on iron-based materials using an insoluble anode in an acidic tin plating bath using phenolsulfonic acid, the additive for acidic tin plating baths of the present invention can be used to reduce tin loss and manage the plating bath. The cleaning of the plating bath, which was the biggest problem when using an insoluble anode as an anode, was achieved. By reducing or almost eliminating modified substances generated by anodization caused by phenolsulfonic acid, the quality and yield of the plated product can be improved. The amount of the acidic tin plating bath additive of the present invention to be used is usually 5 to 30 g per plating bath. Next, the present invention will be specifically explained using examples. Examples The acidic tin plating bath additives shown in Table 1 were tested according to the following test method, and the results are shown in Table 2 based on the following comprehensive evaluation criteria. Test method (a) Clouding point measurement Clouding point measurement is performed using 10 g/aqueous solution of Samples No. 1 to 9. (b) Simple foaming test Phenolsulfonic acid (sulfuric acid equivalent) 20g/
Adjust each sample material to a predetermined concentration aqueous solution using a
℃, and the foam (ml) generated after shaking 50 times/30 seconds was expressed as foamability. (c) Modified product formation test Using 20 g of phenolsulfonic acid (sulfuric acid equivalent) as the model bath composition, test Nos.
11 was prepared, and the model bath composition was electrolyzed using a platinum-based soluble anode at an electrolysis temperature of 50℃, an electrolysis time of 100 minutes, and a current density of 5A/ ^dm2 , and the amount of phenolsulfonic acid modified substance produced on the anode ( ml) was measured. Comprehensive evaluation criteria ◎: Excellent effect in reducing the amount of foamable modified substances, and can be used for practical purposes. ○: The effect of reducing the amount of foamable calming substance is good, and it can be used for practical use. Δ: The effect of reducing the amount of foamable modified substance is poor, causing a practical problem. ×: The effect of reducing the amount of foamable modified substance is extremely poor and cannot be put to practical use.

【table】

【table】

[Table] As is clear from Table 2, ethoxylated α-naphthol adducts with 4 to 6 moles of ethylene oxide, Test Nos. 4 and 5, had good foaming properties at a low level, but the amount of modified substances was low. The mitigation effect is poor and cannot be put to practical use. Especially test No.
In No. 4, a significant cloud point product coexisted. Although Sample No. 6, an adduct of ethoxylated α-naphthol with 15 moles of ethylene oxide, has the effect of reducing the amount of modified substances, it has a high foaming property and is not practical. Sample Nos. 7, 8, and 9, which are ethoxylated α-naphtholsulfonic acids, were found to be effective in reducing the amount of modified substances, but their foaming properties were significant. Even in the case of the 8 mole ethylene oxide adduct of ethoxylated α-naphthol (product of the present invention), when the addition amount was 40 g/l, the effect of reducing the amount of modified substances was sufficient, but a problem occurred in foamability. In the case of the 12 mole ethylene oxide adduct of ethoxylated α-naphthol (product of the present invention), foaming properties were good at an addition amount of 4 g/l, but the effect of reducing the amount of modified substances was significantly poor. Therefore, in acid tin plating using phenolsulfonic acid, when an insoluble anode is used, adding 5 to 30 g of an adduct of 7 to 12 moles of ethylene oxide of ethoxylated α-naphthol improves the quality of the plated product. , are desirable processing conditions to achieve yield improvement.

Claims (1)

[Claims] 1. An insoluble anode is used as an anode in an acidic tin plating bath using phenolsulfonic acid, and the temperature is 30 to 60.
An additive for acidic tin plating baths comprising a compound represented by the following general formula for electroplating tin on ferrous materials by passing a current at a current density of at least 5 A/dm ² at a temperature of at least 5 A/dm 2 . general formula, (However, in the general formula, n is 7 to 12.)