JPH0547640B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tin-nickel alloy electroplating bath composition, and more particularly to a plating bath composition that provides a bronze-like plating layer with metallic luster. Various electroplating bath compositions are known that provide tin-nickel alloy plating layers.
Generally, a tin-nickel alloy plating layer has excellent corrosion resistance, is relatively hard, and has high wear resistance. However, the color tone is bright and whitish, which is said to be rose pink or stainless steel color, and they have the disadvantage of lacking decorative value when used as building materials. The present invention provides a plating bath composition that provides a plating layer that is bronze-like and has a metallic luster and is particularly useful for decorative purposes. That is, the gist of the present invention is as follows: (a) a chloride or sulfate of tin and nickel; (b) a monohydroxycarboxylic acid or its salt; (c) a conductive salt; and (d) water, the ratio of tin to nickel being As a metal, the ratio is 1.5:1 to 7:1, and the pH of the bath is 3.5 to 5.5.
The present invention provides a bronze-colored tin-nickel alloy electroplating bath composition characterized in that tin is in a tetravalent state. To explain the present invention in more detail, the bath composition according to the present invention contains tin and nickel as electrodeposited metal components. As these metals, chlorides or sulfates or mixtures thereof are used. Note that tetravalent tin is used because divalent tin is easily oxidized in the bath and therefore the bath is unstable. The concentration of these metals in the bath is usually 5.0 to 40 g of tin,
Nickel is 2.0-10g/. The ratio (weight ratio) of tin to nickel is 1.5:1 to 7:1, preferably 3:1 to 7:1; if the ratio of tin is smaller than this, the plating film formed becomes brittle and corrosion resistant. Sexuality also decreases. On the other hand, if the proportion of tin is higher than this, the color of the film will become whitish.
This defeats the purpose of producing a bronze-colored film. As the monohydroxycarboxylic acid, monocarboxylic acids or polycarboxylic acids such as glycolic acid, lactic acid, citric acid, and malic acid are used. These mohydroxycarboxylic acids may be used as they are, or may be used as salts such as sodium salts, potassium salts, ammonium salts, and the like. The concentration of the monohydroxycarboxylic acid and its salt in the bath is suitably 20 to 200 g/free acid. If the concentration is lower than this, the plating film becomes brittle and corrosion resistance decreases. Moreover, if the concentration is higher than this, the color tone of the film may become white. Preferably a combination of glycolic acid and citric acid, especially glycolic acid 6.5~
It is preferable to use 60g/ of citric acid in combination with 7.5 to 60g/ of citric acid. As the conductive salt, those commonly used in plating baths, such as potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, and ammonium sulfate, are used. Its concentration is 50-300
g/ is suitable; if the concentration is higher than this, streaks are likely to occur in the plating film, and if the concentration is lower than this, the electric resistance of the bath is high and heat generation is large, so both are disadvantageous. The conditions for plating using the plating bath composition according to the present invention are a bath temperature of 30 to 60°C, a cathode current density of
Appropriate values are 0.2 to 2.0 A/dm ² and PH 3.5 to 5.5. If the bath temperature is too low, metal deposition becomes non-uniform, color unevenness tends to occur, and at the same time, the deposition rate becomes slow. On the other hand, at high temperatures exceeding 60°C, the bath evaporates rapidly, which is disadvantageous in terms of bath management. The cathode current density is
If it is less than 0.2 A/dm ² , metal deposition will be slow and productivity will not be good, while if it is larger than 0.2 A/dm ² , there is a risk that the film will be partially scorched or the state of the deposition will be poor. The pH of the bath affects the color tone of the film; if the pH is lower than 3.5, color unevenness is likely to occur, and if the pH is further reduced, the color tone becomes whitish, making it impossible to obtain a bronze-colored film. On the other hand, if the pH is higher than 5.5, the state of metal precipitation may become poor, and tin hydroxide tends to precipitate, making it difficult to obtain bath stability. For the above reasons, the pH of the bath needs to be between 3.5 and 5.5. Generally, an insoluble anode such as graphite or ferrite is used as the anode, but tin or nickel metal itself may be used as the anode or a part thereof so that the metal components consumed by electrodeposition are automatically replenished. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Examples 1 to 8 Using baths with compositions shown in Table 1, Nos. 1 to 8, tin was deposited on brass plates (Nos. 1 to 3) or bright nickel-plated aluminum plates (Nos. 4 to 8). Nickel plating was applied (electrodeposition time: 5 minutes). In all baths, uniform plating films with gloss and bronze color were obtained. When this film was measured by Auger electron spectroscopy, it was found to be a film containing 10 to 40% tin and 60 to 90% nickel in terms of atomic %. The composition of the film (tin/nickel atomic ratio) is shown in the bottom column of Table 1. When this plating film was subjected to a neutral salt spray test specified in JIS H8502 for 24 hours, no change was observed in any of the films. Comparative Example 1 Plating was performed in the same manner as in Example 7, except that hydrochloric acid was added to adjust the pH of the bath to 3.0. The obtained film had a whitish color and did not have a bronze-like luster, and was poor. Comparative Example 2 Plating was performed in the same manner as in Example 8, except that aqueous ammonia was added to adjust the pH of the bath to 6.0. A white precipitate of tin hydroxide was observed in the bath. The resulting film had a brighter color tone, slightly yellowish than bronze tone. 【table】

Claims (1)

[Claims] 1. Consisting of (a) chloride or sulfate of tin and nickel, (b) monohydroxycarboxylic acid or its salt, (c) conductive salt, and (d) water, the ratio of tin and nickel is As a metal, the ratio is 1.5:1 to 7:1, and the pH of the bath is 3.5 to 5.5.
A bronze-colored tin-nickel alloy electroplating bath composition characterized in that the tin is in a tetravalent state. 2 Monohydroxycarboxylic acid or its salt is
The composition according to claim 1, characterized in that it is citric acid and glycolic acid or a salt thereof.