JPS58758B2 - black electroplating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a black plating method, and more specifically, a plating solution containing an alkali metal salt of stannous salt, nickel salt, gluconic acid or glucoheptonic acid is mixed with aqueous ammonia to pH 7.0 to 10. This invention relates to a black plating method using tin-nickel alloy plating adjusted to .0.

Conventionally, black chrome plating and black nickel plating are known as methods for obtaining black plating.

However, the plating film obtained from a black chromium plating bath has difficulty in obtaining a uniform black appearance, has a poor metallic appearance, and requires low temperature and high current density during plating, which poses operational difficulties.

Furthermore, since hexavalent chromium is used, the working environment is poor and there are concerns about the effects on the human body, and drainage is also a major danger.

Black plating from a black nickel plating bath has a narrow current density range for achieving black color, the plating bath is unstable and bath management is difficult, and the deposited film has poor mechanical strength, corrosion resistance, and discoloration resistance. There are drawbacks.

The present invention was made for the purpose of improving the drawbacks of the black plating bath and providing a plating bath for obtaining excellent black plating. Adjust the pH of the plating solution mainly composed of alkali metal salts to 7.0 to 10 with ammonia water.
．． This is a black plating method using tin-nickel alloy plating, which is characterized in that the tin-nickel alloy plating is adjusted to zero.

The plating film obtained by the tin-nickel alloy plating according to the present invention exhibits a uniform black appearance with good coverage, is excellent in corrosion resistance and discoloration resistance, and does not contain harmful substances and is easy to treat as wastewater.

In the present invention, the pH of the plating bath is 7.0 to 10.0, preferably 7.5 to 9.0.

If the pH is less than 7.0, no black plating will be obtained, but a white matte plating will be obtained, and if the pH exceeds 10.0, a gray-black matte plating will be obtained.

In addition, as a pH adjuster, alkaline agents other than ammonia water,
For example, use sodium hydroxide, potassium hydroxide, sodium carbonate, or amines to adjust the pH to 7.0-1.
Even if adjusted to 0.0, black plating is not obtained, but white matte plating or stainless steel plating is obtained.

The following compounds and concentrations can be used for each component and concentration of the plating bath in the present invention.

As stannous salts, stannous chloride, stannous sulfate, stannous acetate, stannous gluconate, etc. are used;
5 g/l, preferably 4-10 g/l.

If it is less than 1 g/l, the plating will be nickel-colored, and if it exceeds 25 g/l, the plating will be white.

Examples of nickel salts include nickel chloride, nickel sulfate, nickel acetate, nickel gluconate, etc., and the amount of metal nickel is 4 to 25 g/l, preferably 7 to 16 g/l.
used in

If there is no drop of 4 g/l, the plating will be whiteish, and 25
If it exceeds g/l, it becomes nickel colored.

Suitable alkali metal salts of gluconic acid or glucoheptonate include sodium gluconate and sodium glucoheptonate, and the concentration used is 30 to 350 g/l.
is preferred.

If the content is less than the lower limit, tin and nickel will be difficult to dissolve, and if the content exceeds the upper limit, it will be economically disadvantageous, so the above range is appropriate.

The temperature of the plating bath of the present invention is 20 to 60°C, preferably 30 to 50°C.

The current density is 0.1 to 3 A/dm2, preferably 0
．． Plating is performed at 3 to 1 A/dm2.

Mechanical stirring and a cathode rocker are required, but good results can be obtained even under static conditions if plating is carried out at a low current density.

Note that air agitation is unsuitable because it oxidizes the stannous salt to stannic salt.

The anode is preferably an insoluble anode, such as carbon, stainless steel,
A platinum-plated anode on titanium is preferred.

Next, the present invention will be explained in detail based on Examples and Comparative Examples.

Example 1 A basic plating solution containing 15 g/l of stannous chloride/trihydrate, 50 g/l of nickel chloride/hydrochloride, and 100 g/l of sodium gluconate was adjusted to pH 8.0 with aqueous ammonia.

Using a steel plate plated with carbon as an anode and bright nickel as a cathode, plating was carried out at 40° C. for 3 minutes at a cathode current density of 1 A/dm 2 with mechanical stirring.

A glossy black tin-nickel alloy plating was obtained.

Table 1 shows the liquid composition, appearance, etc. mentioned above.

Example 2 A basic plating solution containing 10 g/l of stannous chloride/trihydrate, 60 g/l of nickel chloride/hydrochloride, and 150 g/l of sodium gluconate was adjusted to pH 90 with aqueous ammonia.

The same operations as in Example 1 were carried out, and the results shown in Table 1 were obtained.

Comparative Example 1 The pH of the basic plating solution in Example 1 was adjusted to pH 6.0 with aqueous ammonia, and plating was performed in the same manner as in Example 1, but black gloss was not obtained and white matte plating was obtained. there were.

Example 3 Stannous sulfate 18g/l, nickel sulfate large hydrate salt 70g/l
A basic plating solution containing 150 g/l of sodium glucoheptonate was adjusted to pH 8.5 with aqueous ammonia.

Plating was carried out under the conditions shown in Table 2, and a glossy black tin-nickel alloy plating was obtained.

Example 4 Stannous sulfate 12g/l, nickel sulfate large hydrate salt 50g/l
A basic plating solution containing 100 g/l of sodium glucoheptonate was adjusted to pH 7.5 with aqueous ammonia.

The same operations as in Example 3 were carried out, and the results shown in Table 2 were obtained.

Comparative Example 2 In Example 3, the pH of the basic plating solution was adjusted to pH 8.5 with sodium hydroxide and plating was performed in the same manner as in Example 3, but black gloss was not obtained and white matte plating was obtained. there were.

As explained above, a plating solution containing a stannous salt, a nickel salt, an alkali metal salt of gluconic acid or glucoheptonic acid as a main component was mixed with ammonia water to a pH of 7.0 to 10.
The black plating method of the present invention adjusted to 0 provides a tin-nickel alloy plating with a uniform black gloss over a wide range of current densities.

Furthermore, the resulting plating film has excellent corrosion resistance and discoloration resistance, and therefore has a wide range of decorative uses.

Claims (1)

[Claims] 1 Contains as a main component a stannous salt, a nickel salt, an alkali metal salt of gluconic acid or glucoheptonic acid,
and the tin salt and the nickel salt are converted into metal,
Aqueous ammonia is added to a basic plating solution containing 1 to 25 g/l of tin and 4 to 25 g/l of nickel, and 30 to 350 g/l of an alkali metal salt of gluconic acid or glucoheptonic acid. pH 7.0~
Using a tin-nickel plating solution adjusted to 10.0, the bath temperature is 20 to 60°C and the current density is 0.1 to 3 A/dm.
A black electroplating method characterized by plating with step 2.