JPH0320478B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a bright copper-zinc alloy electroplating bath (hereinafter referred to simply as "electroplating bath") that does not contain cyanide compounds. Conventional technology and its problems Copper-zinc alloy plating, also called brass plating or brass plating, is used for decoration to give brass-colored metallic luster and color tone to metal products, plastic products, ceramic products, etc. Widely used as plating. Copper-zinc alloy plating is also used to improve the adhesion between the reel cord and rubber for radial tires. However, all copper-zinc alloy plating baths that are currently widely used industrially contain large amounts of cyanide, and their toxicity is a major problem. Although many reports have been made regarding copper-zinc plating baths that do not contain cyanide compounds, none of them have been put to practical use. For example, a soaking bath using potassium pyrophosphate, oxycarboxylic acid, etc. as a complexing agent has been proposed. The study by T.L. Ramatyah [Electroplating and Metal Finishing, 12 , 326 (1959)] on a plating bath using potassium pyrophosphate as a complexing agent is famous; However, the copper-zinc alloy plating has disadvantages such as a narrow range of golden luster and a tendency for the anode to become passivated. Koshiura et al. attempted to solve the above drawback by adding a polymer of alkanol polyamine and epihalohydrin to a potassium pyrophosphate bath (Japanese Patent Laid-Open No. 59-215492).
issue). However, in this method, the metal ratio of the deposited alloy is Cu:Zn = 7-8:3-2, whereas the metal concentration ratio in the plating bath is Cu:Zn = approximately 1:9. However, it has the disadvantage that it is difficult to select an anode for stable and continuous operation. In addition, examples of baths using oxycarboxylic acid or its salt as a complexing agent include the tartaric acid bath of Aoya et al. No.) etc. are known. However, the tartaric acid bath described above is not a completely cyanide-free bath because it contains 0.8 to 8 g/metal cyanide salt as a brightening agent. On the other hand, when plating is performed in a glucoheptonic acid bath, ball polishing must be performed after plating to obtain gloss. Means for Solving the Problems As a result of intensive research in view of the problems of the above-mentioned prior art, the inventors have found that, together with copper salts and zinc salts,
By using a non-toxic bath containing an alkali metal salt of pyrophosphoric acid or an alkali metal salt of polyphosphoric acid and an oxycarboxylic acid or a salt thereof as a complexing agent, and an amino acid or a salt thereof and not containing a cyanide. They have now discovered that a gold-colored copper-zinc alloy plating film with extremely excellent gloss and high decorative value can be obtained over a wide current density range, and have completed the present invention. That is, the present invention provides at least one selected from (a) copper salts and zinc salts, (b) alkali metal salts of pyrophosphoric acid and alkali metal salts of polyphosphoric acid, and (c) oxycarboxylic acids and their salts. at least one type of
(d) A cyanide-free bright copper-zinc alloy electroplating bath characterized by containing at least one selected from amino acids and salts thereof. In the present invention, in addition to copper salts and zinc salts, metal salts of pyrophosphoric acid or alkali metal salts of polyphosphoric acid and oxycarboxylic acids or salts thereof as complexing agents,
The desired effects of the present invention can only be achieved when three types of compounds, including amino acids and amino acids or salts thereof, are used in combination. When using a bath consisting only of copper salts, zinc salts and alkali metal salts of pyrophosphoric acid or polyphosphoric acid,
At low current densities, copper preferentially precipitates in the resulting plating film, giving it a coppery color, while at high current densities, it becomes discolored. In a very narrow range of current density between that range, i.e., the optimum current density of ±0.1 A/dm ² determined by the bath composition, a gold-colored (brass-colored) plating film can be obtained, but gas traces are severe and The gloss is insufficient. In a bath consisting of a copper salt, a zinc salt, and an oxycarboxylic acid or its salt, the plating film becomes dark green, and a golden plating film cannot be obtained. The use of two types, an alkali metal salt of pyrophosphoric acid or polyphosphoric acid and an oxycarboxylic acid or its salt, eliminates the preferential precipitation of copper at low current densities, resulting in a shiny copper-zinc alloy over a fairly wide current density range. A plated film is obtained. However, as the current density increases, the color tone changes from yellow-green to golden yellow to brass-colored, resulting in color unevenness, which is insufficient for practical use as decorative plating. However, when an amino acid or a salt thereof is added together with the two compounds as complexing agents, a bright copper-zinc alloy plated film having a completely homogeneous golden color can be obtained over a very wide range of current densities. . In the present invention, by appropriately changing the bath composition, it is possible to obtain a golden copper-zinc alloy plating film with extremely excellent gloss in a significantly wide current density range of approximately 0.05 to 5 A/ ^dm2 . Can be done. Any known copper salt can be used,
For example, copper pyrophosphate, copper sulfate, cupric chloride, copper sulfamate, copper bromate, cupric acetate, basic copper carbonate, cupric bromide, copper formate, copper hydroxide, cupric oxide.
Copper, copper phosphate, copper silicate, copper stearate,
Examples include cupric citrate. Any known zinc salt can be used, such as zinc pyrophosphate, zinc sulfate, zinc chloride, zinc sulfamate, zinc oxide, zinc acetate,
Examples include zinc bromide, basic zinc carbonate, zinc oxalate, zinc phosphate, zinc silica, zinc stearate, and zinc lactate. Two or more types of copper salts and zinc salts may be used in combination. Any known alkali metal salts of pyrophosphoric acid and alkali metal salts of polyphosphoric acid can be used, and examples thereof include sodium salts and potassium salts thereof. Any known oxycarboxylic acid can be used, and examples thereof include glycolic acid, lactic acid, malic acid, citric acid, tartaric acid, gluconic acid, and glucoheptonic acid. Examples of the salts include lithium salts, sodium salts, potassium salts, calcium salts, and the like. Furthermore, as the tartrate, in addition to the above-mentioned salts, tartarite (antimonyl potassium tartrate), Rothsiel's salt (sodium potassium tartrate), etc. can also be used. As the amino acid, any known amino acid can be used, such as α-amic acid such as glycine, alanine, glutamic acid, aspartic acid, threonine, serine, proline, tryptophan, histidine, or its hydrochloride, sodium salt, etc. be able to. In the present invention, two or more of the alkali metal salts of pyrophosphoric acid, alkali metal salts of polyphosphoric acid, oxycarboxylic acids, and amino acids and salts thereof may be used in combination. The blending amount of each of the above components in the bath of the present invention is not particularly limited and may be selected as appropriate. However, considering the ease of industrial handling, the copper salt should be
~40g/about, zinc salt 0.5~30 in terms of zinc content
g/degree, alkali metal salt of pyrophosphoric acid and/or
Or 150-400g/alkali metal salt of polyphosphoric acid
degree, oxycarboxylic acid and/or its salts to 50%
~400g/approximately and amino acids and/or their salts may be blended in an amount of approximately 0.5~50g/approximately. The concentration ratio of Cu and Zn (Cu:Zn) in the plating bath is not particularly limited and can be selected as appropriate, but it is usually about 9 to 1:1, and this will result in a golden (brass) color. A coating film can be obtained. However, taking into consideration stable and continuous work, the copper salt should be used at a rate of 5 to 15 g in terms of copper content, and the zinc salt should be used in an amount of 1 to 15 g in terms of zinc content.
It is preferable to add about 10 g/concentration ratio of about 5 to 1.5:1. Further, when using a pyrophosphate such as a copper salt or a zinc salt, the total pyrophosphate concentration including this pyrophosphate may be within the above range. When applying bright copper-zinc alloy plating using the bath of the present invention, any ordinary electroplating method can be used.
degree, bath pH 10.0~14.0, cathode current density 0.1~
Electroplating may be carried out under plating conditions of about 5 A/dm ² without stirring, mechanical stirring, or air stirring. In this case, as the anode, any one used for ordinary electroplating of copper-zinc alloys can be used. The body to be plated may be subjected to conventional pretreatments such as buffing, degreasing, and dipping in dilute acid according to conventional methods before electroplating, or may be subjected to undercoat plating such as glossy nickel plating. may be applied. After plating, usual operations such as washing with water, hot water, and drying may be performed, and further, if necessary, immersion in a dilute dichromic acid solution, clear coating, etc. may be performed. In the present invention, the body to be plated is not particularly limited, and any body that is normally coated with a copper-zinc alloy plating film can be used, such as metal products, plastic products, ceramic products, etc. Before plating with the bath of the present invention, it is preferable to apply base plating to these according to a conventional method. Effects of the Invention According to the bath of the present invention, it has extremely excellent gloss;
A golden copper-zinc alloy plating film with high decorative value can be obtained over a wide current density range. Also,
Since the bath of the present invention does not contain cyanide compounds, it does not generate toxic gases or the like, and is harmless and stable without the formation of precipitates. Copper positive
When using zinc alloys, the dissolution is uniform;
The plating bath composition remains stable. Furthermore, a golden plating film can be obtained even when the Cu:Zn concentration ratio in the plating bath is in the range of 2 to 1.5:1, which is close to the composition of the plating film. Even when using a copper salt and a zinc salt, stable continuous operation is possible just by replenishing a mixture of a fixed composition of copper salts and zinc salts. Examples Examples and comparative examples are given below to further clarify the characteristics of the present invention. Examples 1 to 5 and Comparative Examples 1 to 3 Table 1 (Examples 1 to 5) and Table 2 (Comparative Example 1
Electroplating was performed using the plating bath composition (the amount of each component added is all g/) and the plating conditions described in 3) to 3), and the appearance and color tone of the resulting matted film were observed. The results are shown in Table 3. In addition, in Tables 1 and 2, the values shown in parentheses in the copper salt and zinc salt terms are the respective metal equivalent roots (g/).

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【table】

【table】

[Table] From Table 3, in the bright copper-zinc alloy plating bath of the present invention, (1) an alkali metal salt of pyrophosphoric acid and/or an alkali metal salt of polyphosphoric acid, (2) an oxycarboxylic acid and/or its Through the synergistic action of the salt and (3) the amino acid and/or its salt, a copper-zinc alloy plating film with high decorative value and extremely high gloss can be obtained over a wide current density range. I understand that.

Claims (1)

[Claims] 1 (a) At least one selected from copper salts and zinc salts, (b) alkali metal salts of pyrophosphoric acid and alkali metal salts of polyphosphoric acid, (c) at least one selected from oxycarboxylic acids and their salts. A cyanide-free bright copper-zinc alloy electroplating bath characterized by containing at least one selected from amino acids and (d) amino acids and their salts.