PLATING SOLUTION FOR COLORING, AND COLORING METHOD

TECHNICAL FIELD

The present invention relates to a plating solution for coloring capable of coloring a member to be plated in a desired color, a coloring method using this solution, and the like.

BACKGROUND ART

It is known that coloring is performed for enhancing the decorativeness of a member having a metal surface. As a coloring method, a method for coloring the member by immersing it in a coloring agent, a method for coloring the member by thinly depositing another metal thereon, and other methods are known.

As a technique for coloring the member by thinly depositing another metal thereon, for example, a method in which electrolysis is performed using the member as a cathode in an aqueous solution containing a compound such as chromic acid, an inorganic cyanide, or a phosphate, and a molybdate, thereby forming a colored film on the surface of the member is known (PTL 1).

CITATION LIST
Patent Literature

PTL 1: JP-A-58-27998

SUMMARY OF INVENTION
Technical Problem

The above-mentioned method has, however, a problem with waste water, poor stability of color development or deposition, or the like caused by the use of a compound with a high environmental load such as chromic acid, an inorganic cyanide, or a phosphate.

Solution to Problem

In view of this, an object of the present invention is to provide a technique for coloring free from any problem with waste water or stability of color development or deposition.

The present inventors made intensive studies for achieving the above object, and as a result, they found that a plating solution, which uses a molybdate and a specific carboxylic acid or a salt thereof as a complexing agent for molybdenum, and is set to a specific pH, can achieve the object, and thus completed the present invention.

Specifically, the present invention is directed to a plating solution for coloring, characterized by containing a molybdate and a carboxylic acid having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms or a salt thereof, and having a pH of 4.5 to 7.5.

Further, the present invention is directed to a coloring method, characterized by electrolyzing a member to be plated as a cathode in the above-mentioned plating solution for coloring.

In addition, the present invention is directed to a colored product obtained by electrolyzing a member to be plated as a cathode in the above-mentioned plating solution for coloring.

Advantageous Effects of Invention

The plating solution for coloring of the present invention does not use a compound with a high environmental load such as chromic acid, an inorganic cyanide, or a phosphate, and therefore has no problem with waste water.

Further, the colored product of the present invention can maintain the metallic appearance of a substrate, and moreover also has high stability of color development or deposition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing appearance after plating (Example Products 1 to 5 sequentially from the left).

FIG. 2 is a view showing appearance after plating (Comparative Products 1 to 5 sequentially from the left).

FIG. 3 is a view showing appearance after plating (Example Products 7 to 14 sequentially from the left).

FIG. 4 is a view showing appearance after plating (Example Products 15 to 16 sequentially from the left).

DESCRIPTION OF EMBODIMENTS

The molybdate used in the plating solution for coloring of the present invention is not particularly limited, but examples thereof include alkali metal salts of molybdic acid such as sodium molybdate and potassium molybdate and ammonium salts of molybdic acid. Among these, sodium molybdate is preferred. Among these molybdates, one type or two or more types can be used. The content of the molybdate in the plating solution for coloring of the present invention is not particularly limited, but is from 0.1 to 50 g/L, preferably from 1 to 20 g/L.

The carboxylic acid having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms or a salt thereof used in the plating solution for coloring of the present invention is not particularly limited, but preferred examples thereof include carboxylic acids having 1 to 5 carboxyl groups and 1 to 8 hydroxy groups and having 2 to 10 carbon atoms, and more preferred examples thereof include carboxylic acids having 1 to 3 carboxyl groups and 1 to 6 hydroxy groups and having 2 to 8 carbon atoms, alkali metal salts such as sodium salts and potassium salts of the above-mentioned carboxylic acids, and ammonium salts of the above-mentioned carboxylic acids. Further, the carbon chain of the carboxylic acid may be branched or cyclic. Incidentally, in this description, a hydroxy group in the carboxyl group is not counted as a hydroxy group. Therefore, those containing only a carboxyl group such as acetic acid, oxalic acid, and EDTA are not included in the carboxylic acid having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms used in the plating solution for coloring of the present invention.

Specific examples of the carboxylic acid having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms or a salt thereof include citric acid, lactic acid, malic acid, tartaric acid, gluconic acid, and alkali metal salts such as sodium salts and potassium salts, and ammonium salts of these carboxylic acids. Among these, sodium gluconate is preferred.

In the plating solution for coloring of the present invention, one type or two or more types of the above-mentioned carboxylic acids having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms or salts thereof can be used. Further, the content of the carboxylic acid having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms or a salt thereof in the plating solution for coloring of the present invention is not particularly limited, but is from 10 to 100 g/L, preferably from 20 to 80 g/L.

In the plating solution for coloring of the present invention, further, a metal acid salt other than the molybdate may be incorporated. According to this, a plating time can be reduced. The metal acid salt other than the molybdate is not particularly limited, but examples thereof include alkali metal salts of metal acids such as tungstic acid, aluminic acid, titanic acid, and vanadic acid. Among these, tungstic acid, aluminic acid, and titanic acid are preferred. Among these metal acid salts other than the molybdate, one type or two or more types can be used. The content of the metal acid salt other than the molybdate in the plating solution for coloring of the present invention is not particularly limited, but is from 0.01 to 10 g/L, preferably from 0.05 to 5 g/L.

In addition, in the plating solution for coloring of the present invention, a surfactant or the like may be incorporated as long as the effect of the present invention is not impaired.

The pH of the plating solution for coloring of the present invention is from 4.5 to 7.5, preferably from 5.5 to 6.5. In the adjustment of the pH thereof, an acidic substance such as boric acid or sulfuric acid or an alkaline substance such as sodium hydroxide may be used.

Incidentally, the plating solution for coloring of the present invention only need to contain the above-mentioned components, and it is not necessary to incorporate chromic acid or a salt thereof, an inorganic cyanide, or a phosphate or a salt thereof having a high environmental load.

The plating solution for coloring of the present invention described above can be prepared by adding and mixing the above-mentioned components in water, followed by adjusting the pH of the resulting mixture.

Further, by electrolyzing a member to be plated as a cathode in the plating solution for coloring of the present invention, the member to be plated can be colored.

The member to be plated that is colored with the plating solution for coloring of the present invention is not particularly limited as long as it has a metal surface, and examples thereof include metal products made of stainless steel, chromium, brass, nickel, or the like, and resins such as ABS and PC/ABS previously plated such as copper-plated, nickel-plated, or chromium-plated.

The conditions of electrolyzing the member to be plated as a cathode in the plating solution for coloring of the present invention are not particularly limited, but, for example, electrolysis may be performed in the plating solution for coloring at 20 to 40° C. with a current density of 0.01 to 0.5 A/dm²using the member to be plated as a cathode and using carbon, iridium oxide, or the like as an anode for a time of about 1 to 180 minutes to obtain a desired color. After electrolysis, washing with water or the like may be performed.

By electrolyzing the member to be plated in the plating solution for coloring of the present invention, a product colored in brown, purple, bluish purple, blue, yellow, green, red, or the like can be obtained.

This colored product has a very thin plating thickness, and it is difficult in reality to perform an analysis other than an analysis of appearance color, and it is completely not practical to make a determination by other than the production method.

The colored product can be mainly used for ornaments, faucet metal fittings, automobile components, building materials, or the like.

EXAMPLES

Hereinafter, the present invention will be described in detail with reference to Examples; however, the invention is by no means limited to these Examples.

Example 1

Coloring Plating:

Plating solutions for coloring having a formulation shown in Table 1 were prepared by mixing respective components with water. In each of these plating solutions for coloring, coloring plating was performed using a member obtained by glossy nickel-plating a bent cathode made of brass as a cathode and using carbon as an anode under conditions shown in Table 1. The appearance color after plating was evaluated by visual observation, and also color uniformity and polarizability were evaluated by visual observation based on the following evaluation criteria. The results are shown in Table 2.

TABLE 1

Example
Example
Example
Example
Example
Example

Product 1
Product 2
Product 3
Product 4
Product 5
Product 6

Sodium molybdate (g/L)
10
10
10
10
10
10

Sodium gluconate (g/L)
60
60
60
60
60
0

Triammonium citrate (g/L)
0
0
0
0
0
50

Boric acid (g/L)
30
30
30
30
30
30

pH
6.0
6.0
6.0
6.0
6.0
6.0

Bath temperature (° C.)
25
25
25
25
25
25

Current density (A/dm²)
0.05
0.05
0.05
0.05
0.05
0.05

Plating time (min)
8.5
10
12.5
15
20
8.5

(Contents): (Evaluation)

A case where the entire surface has the same color: A

A case where the entire surface does not have the same color: B

(Contents): (Evaluation)

A case where there is no interference when the plated product is inclined at 45°: A

A case where there is interference when the plated product is inclined at 45°: B

TABLE 2

Appearance color
Color uniformity
Polarizability

Example Product 1
brown
A
A

Example Product 2
purple
A
A

Example Product 3
bluish purple
A
A

Example Product 4
blue
A
A

Example Product 5
yellow
A
A

Example Product 6
brown
A
A

From the above results, it was found that by using the plating solution for coloring of the present invention, the appearance color can be changed, and there are no problems with color uniformity and polarizability.

Comparative Example 1

Coloring Plating:

Coloring plating was performed in the same manner as in Example 1 except that plating solutions for coloring shown in Table 3 were used. Further, the appearance color after plating, color uniformity, and polarizability were evaluated in the same manner as in Example 1. The results are shown in Table 4.

TABLE 3

Comparative
Comparative
Comparative
Comparative
Comparative

Product 1
Product 2
Product 3
Product 4
Product 5

Sodium molybdate
10
10
10
10
10

(g/L)

Sodium tungstate
2.7
2.7
2.7
2.7
2.7

(g/L)

Ammonium acetate
0
25
50
0
0

(g/L)

EDTA-4 Na
0
0
0
38
76

(g/L)

Boric acid
30
30
30
30
30

(g/L)

pH
6.0
6.0
6.0
6.0
6.0

Bath temperature
25
25
25
25
25

(° C.)

Current density
0.05
0.05
0.05
0.05
0.05

(A/dm²)

Plating time
3
3
3
5
5

(min)

TABLE 4

Color

Appearance color
uniformity
Polarizability
Others

Comparative
interference color
B
B

Product 1

Comparative
interference color
B
B
Film peeling

Product 2

Comparative
interference color
B
B
Film peeling

Product 3

Comparative
non-evaluable
No

Product 4

deposition

Comparative
non-evaluable
No

Product 5

deposition

From the above results, it was found that even if a salt of a carboxylic acid is contained, when it is not a salt of a carboxylic acid having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms such as ammonium acetate or EDTA-4 Na, colored plating is not deposited or coloration cannot be uniformly made.

Example 2

Coloring Plating:

Coloring plating was performed in the same manner as in Example 1 except that plating solutions for coloring shown in Table 5 were used. Further, the appearance color after plating, color uniformity, and polarizability were evaluated in the same manner as in Example 1. The results are shown in Table 6.

TABLE 5

Example
Example
Example
Example
Example
Example
Example
Example

Product 7
Product 8
Product 9
Product 10
Product 11
Product 12
Product 13
Product 14

Sodium molybdate (g/L)
10
10
10
10
10
10
10
10

Sodium tungstate (g/L)
2.7
2.7
2.7
2.7
2.7
2.7
0
0

Sodium aluminate
0
0
16
16
16
16
0
0

solution (ml/L)

Sodium titanate (g/L)
0
0
0
0
0
0
1
1

Sodium gluconate (g/L)
60
60
60
60
60
60
60
60

Tri ammonium citrate (g/L)
0
0
0
0
0
0
0
0

Boric acid (g/L)
30
30
30
30
30
30
30
30

pH
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0

Bath temperature (° C.)
25
25
25
25
25
25
25
25

Current density (A/dm²)
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05

Plating time (min)
8.5
12.5
1.5
2
3
5
5
8.5

TABLE 6

Appearance color
Color uniformity
Polarizability

Example Product 7
purple
A
A

Example Product 8
blue
A
A

Example Product 9
brown
A
A

Example Product 10
purple
A
A

Example Product 11
blue
A
A

Example Product 12
yellow
A
A

Example Product 13
brown
A
A

Example Product 14
blue
A
A

From the above results, it was found that by combining a molybdate with a metal salt other than the molybdate in the plating solution for coloring of the present invention, the appearance color can be changed in a shorter time than in the case of using only the molybdate, and there are no problems with color uniformity and polarizability.

Comparative Example 2

Coloring Plating:

Coloring plating was attempted in the same manner except that 76 g/L of EDTA-4 Na was replaced with 35 g/L of sodium oxalate in the plating solution for coloring of Comparative Product 5 in Comparative Example 1; however, colored plating was not even deposited.

Example 3

Coloring Plating:

Plating solutions for coloring having a formulation shown in Table 7 were prepared by mixing respective components with water. In each of these plating solutions for coloring, coloring plating was performed using a member obtained by glossy nickel-plating a bent cathode made of brass as a cathode and using carbon as an anode under conditions shown in Table 7. The appearance color after plating, color uniformity, and polarizability were evaluated in the same manner as in Example 1. The results are shown in Table 8.

TABLE 7

Example Product 15
Example Product 16

Sodium molybdate (g/L)
10
10

Sodium gluconate (g/L)
60
60

Boric acid (g/L)
30
30

pH
6.0
6.0

Bath temperature (° C.)
25
25

Current density (A/dm²)
0.05
0.05

Plating time (min)
60
170

TABLE 8

Appearance color
Color uniformity
Polarizability

Example Product 15
green
A
A

Example Product 16
red
A
A

By combining the results of Example 1 and Example 2, it was found that according to the present invention, colored products colored in brown, purple, bluish purple, blue, yellow, green, and red can be obtained.

INDUSTRIAL APPLICABILITY

The present invention can be utilized for producing a colored product having high decorativeness.

PLATING SOLUTION FOR COLORING, AND COLORING METHOD

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