JPH08988B2 - Gold plating remover - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gold plating stripping solution for gold plating using a metal containing nickel as a base.

(Conventional Technology and Problems Thereof) Generally, when the exterior plating or the like is defective, the defective plating is peeled off and the product is re-plated. In this case, a stripping solution is required to have a small attack on the base material and the base plating so as not to damage the base material and the base plating.

By the way, conventionally, nickel or iron-nickel alloy, iron-
There has been no suitable stripping solution for stripping gold plating applied on a base metal containing nickel such as nickel-cobalt alloy at high speed without damaging the base.

For example, nitro-substituted benzoic acid and alkali cyanide,
Although a lead acetate-based stripping solution is known, this stripping solution has a relatively high stripping rate, but has a large attack on nickel and has a problem of damaging a base metal containing nickel.

As a result of intensive studies to solve the above problems, the inventor has realized that a desired stripping solution can be obtained by adding a thallium compound and a sulfur compound in place of lead acetate.

That is, an object of the present invention is to provide a gold plating stripping solution capable of stripping gold plating at high speed without damaging a base metal containing nickel.

(Summary of the Invention) The gold plating stripper according to the present invention for the above object has the following constitution.

That is, nitro-substituted benzoic acids such as P-nitrobenzoic acid and 2-chloro-4-nitrobenzoic acid, alkali cyanide, pH adjusting agents such as alkali hydroxide, and thallium compounds such as thallium nitrate and thallium acetate. , = S group or -SH group, and a sulfur compound such as thiazolidine-4-carboxylic acid or L-cystine.

As the nitro-substituted benzoic acid, P-nitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, 2-chloro-5-nitrobenzoic acid, 3-chloro-2-nitrobenzoic acid, m-nitrobenzoic acid or the like is used. The amount is preferably 1 to 100 g / l. These nitro-substituted benzoic acids act as oxidizing agents.

As the alkali cyanide, potassium cyanide, sodium cyanide and the like can be used, and the amount is preferably 1 to 100 g / l. Alkali cyanide holds dissolved gold in the liquid as a complex. The above-mentioned nitro-substituted benzoic acid acts as an oxidizing agent in that case.

As the pH adjuster, alkali hydroxide, phosphate or the like can be used.

As the thallium compound, thallium nitrate, thallium acetate, thallium sulfate, thallium malonate, or the like can be used, and the amount is preferably 0.005 to 10 g / l.

As the sulfur compound, thiazolidine-4-carboxylic acid, L-cystine, mercaptobenzothiazole, sodium mercaptobenzothiazole, β-mercaptopropionic acid or the like having an = S group or a -SH group is used, and in terms of quantity, 0.005-10 g / l is preferred.

Thallium compounds and sulfur compounds act synergistically,
It accelerates the dissolution of gold and, after stripping of the gold plating, selectively adsorbs on the underlying metal of the exposed nickel to form a kind of protective film, suppressing the elution of nickel into the stripping solution. it is conceivable that.

In addition to thallium compounds and sulfur compounds, EDTA
Or sodium EDTA, potassium EDTA, EDTA.4H, methyl
Addition of compounds derived from EDTA such as EDTA could further suppress the elution of nickel.

(Example) The following gold plating stripping solutions of Comparative Examples 1 and 2 and Examples 1, 2 and 3 were prepared.

Comparative Example 1 P-nitrobenzoic acid 12g / l KCN 50g / l KOH 20g / l Lead acetate 0.6g / l Comparative Example 2 P-nitrobenzoic acid 12g / l KCN 50g / l KOH 20g / l Lead acetate 0.6g / l L-Cysteine 0.02 g / l EDTA.3K 0.1 g / l Example 1 P-nitrobenzoic acid 12 g / l KCN 50 g / l KOH 20 g / l First thallium nitrate 0.6 g / l L-cysteine 0.02 g / l Example 2 P-nitrobenzoic acid 12 g / l KCN 50 g / l KOH 20 g / l first thallium nitrate 0.6 g / l L-cysteine 0.02 g / l EDTA.3K 0.1 g / l Example 3 2-chloro-4-nitrobenzoic acid Acid 12g / l KCN 50g / l KOH 20g / l Thallium acetate 0.6g / l Thiazolidine-4-carboxylic acid 0.1g / l Methyl EDTA 0.1g / l As sample, the eyelet (external metal ring) is iron-nickel- An airtight glass terminal made of a cobalt alloy was plated with nickel undercoat, and 1.3 μm of gold was plated on it.

In 150 ml (40 ° C.) of the stripping solution of each of the above examples, 30 samples were stripped 10 times in total. Average peeling speed at that time,
Table 1 shows the final gold concentration and the final eluted nickel concentration.

As is clear from Table 1, Comparative Example 1 has a large amount of eluted nickel and a large attack on the underlying nickel. On the other hand, in Example 1, the amount of eluted nickel is as small as 1/10 or less, and the attack on the nickel underlayer is gentle. Further, the peeling speed is about 1.5 times faster than that of Comparative Example 1, and there is no problem in practical use. Example 2 has the same composition as in Example 1 with EDTA / 3K.
Is added, the attack on the underlying nickel is more gradual, and the peeling speed is almost the same. In Comparative Example 2, the first thallium nitrate of Example 2 was replaced with lead acetate. As is clear from the comparison between Comparative Example 2 and Example 2, when a thallium compound is used,
It can be seen that the attack on the underlying nickel is much lower than when a lead compound is used. In Example 3, 2-chloro-4-nitrobenzoic acid was used as an oxidizing agent, thallium acetate was used instead of the first thallium nitrate, thiazoline-4-carboxylic acid was used instead of L-cystine, and EDTA · 3K was used instead. With the composition using methyl EDTA and the peeling speed was slightly slow, the same effect as in Example 2 was obtained.

In the case of an iron-nickel alloy or an iron-nickel-cobalt alloy that is gold-plated as a base material,
Not only the elution amount of nickel but also the elution amount of iron could be suppressed, and the attack on the base metal was small.

Although the present invention has been variously described with reference to the preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. Is.

(Effects of the Invention) As described above, according to the gold plating stripper of the present invention,
The gold plating can be removed at high speed without damaging the underlying metal containing nickel.

Claims (4)

[Claims] 1. A nitro-substituted benzoic acid such as P-nitrobenzoic acid or 2-chloro-4-nitrobenzoic acid, an alkali cyanide, a pH adjusting agent such as an alkali hydroxide, thallium nitrate, thallium acetate or the like. A gold-plating stripper for gold-plating a metal containing nickel, which contains a thallium compound and a sulfur compound such as thiazolidine-4-carboxylic acid or L-cystine having a = S group or a -SH group. 2. The gold plating stripper according to claim 1, wherein the content of the thallium compound is 0.005 to 10 g / l. 3. The gold plating stripper according to claim 1, wherein the sulfur compound content is 0.005 to 10 g / l. 4. The gold plating stripping solution according to claim 1, 2 or 3, which is obtained by adding EDTA or a derivative compound thereof.