Electroplating bath and method for producing dark chromium layers

1. An electroplating bath for deposition of a dark chromium layer on a workpiece, the electroplating bath comprising:

(A) trivalent chromium ions;

(B) carboxylate ions;

(C) at least one pH buffer substance; and

(D) at least one coloring agent,

wherein the at least one coloring agent comprises a coloring agent selected from:

2-Amino-4-methanesulfinyl-butyric acid,

1,1-Dioxo-1,2-dihydro-1lambda*6*-benzo[d]isothiazol-3-one,

Prop-2-yne-1-sulfonic acid,

Methanesulfinylmethane, and

2-(1,1,3-Trioxo-1,3-dihydro-1lambda*6*-benzo[d]isothiazol-2-yl)-ethanesulfonic acid, and

wherein the at least one coloring agent optionally further comprises at least one coloring agent selected from sulphur containing compounds having the general Formula (II):

wherein

═X represents ═O, or a free electron pair;

R 3 represents —R 5 , —CH═CH 2 , —CH 2 —CH═CH 2 , —CH═CH—CH 3 , —CH 2 —CH 2 —CH═CH 2 , —CH 2 —CH═CH—CH 3 , —CH═CH—CH 2 —CH 3 , —C≡CH, —CH 2 —C≡CH, —C≡C—CH 3 , —CH 2 —CH 2 —C≡CH, —CH 2 —C≡C—CH 3 , —C≡C—CH 2 —CH 3 , —C(—NH 2 )═NH,

R 4 represents —R 5 , —OR 5 , —(CH 2 —)r—CH(—NH 2 )—COOH, —(CH 2 —)r—CH(—NH—CH 3 )—COOH, —(CH 2 —)r—CH(—N(—CH 3 ) 2 )—COOH, —(CH 2 —)r—CH(—NH 2 )—CO—OCH 3 , or —(CH 2 —)r—CH(—NH 2 )—CO—OCH 2 —CH 3;

R 5 represents —H, —CH 3 , —CH 2 —CH 3 —CH 2 —CH 2 —CH 3 or —CH 2 —CH 2 —CH 2 —CH 3 ;

r is an integer from 0 to 4 or;

R 3 and R 4 taken together represent a linear chain structure in order to build one of the following ring structures including the central sulphur atom of Formula (II):

R 10 represents, —CH 3 , or —CH 2 —CH 3 ;

or salts, tautomeric forms, betaine structures thereof; and

(E) ferrous ions.

2. The electroplating bath according to claim 1 , wherein the at least one coloring agent further comprises the coloring agent wherein

R 3 and R 4 taken together represent the linear chain structure in order to build one of the following ring structures including the central sulphur atom of Formula (II):

wherein R 10 represents, —CH 3 , or —CH 2 —CH 3 .

3. The electroplating bath according to claim 1 , further comprising chloride ions.

4. The electroplating bath according to claim 1 , wherein the concentration of the coloring agent according to general Formula (II) ranges from 0.01 g/L to 100 g/L.

5. The electroplating bath according to claim 1 , wherein the concentration of the ferrous ions ranges from 40 mg/L to 280 mg/L.

6. The electroplating bath according to claim 1 , wherein the bath is free of compounds containing phosphorus.

7. The electroplating bath according to claim 1 , wherein the electroplating bath further comprises at least one coloring agent selected from sulphur containing compounds having the general Formula (I):

wherein

n, p, q are independently of each other integers from 0 to 4;

R 1 represents —H, —OH, —COOH, —CO—OCH 3 , —CO—OCH 2 —CH 3 , —(—O—CH 2 —CH 2 —)m—OH, —CH(—NH 2 )—COOH, —CH(—NH—CH 3 )—COOH, —CH(—N(—CH 3 ) 2 )—COOH, —CH(—NH 2 )—CO—OCH 3 , —CH(—NH 2 )—CO—OCH 2 —CH 3 , —CH(—NH 2 )—CH 2 —OH, —CH(—NH—CH 3 )—CH 2 —OH, —CH(—N(—CH 3 ) 2 )—CH 2 —OH, or —SO 3 H;

m represents an integer from 5 to 15;

R 2 represents —H, —OH, —(CH 2 —) p —OH, —(CH 2 —) p —C(—NH 2 )═NH, —CH 2 —CH 2 —(—O—CH 2 —CH 2 —) m —OH, —R 5 , —(CH 2 —) q —COOH, —(CH 2 —) q —CO—OCH 3 , —(CH 2 —) q —CO—OCH 2 —CH 3 , —(CH 2 —)q—S—(CH 2 —) 2 —OH, —CS—CH 3 , —CS—CH 2 —CH 3 , —CS—CH 2 —CH 2 —CH 3 , —CN,

R 1 and R 2 together represent a linear chain structure in order to build one of the following ring structures including the central sulphur atom of Formula (I):

R 5 represents —H, —CH 3 , —CH 2 —CH 3 , —CH 2 —CH 2 —CH 3 , or —CH 2 —CH 2 —CH 2 —CH 3 ;

R 6 , R 7 , R 8 , R 9 represent independently of each other —H, —NH 2 , —SH, —OH, —CH 3 , —CH 2 —CH 3 , —COOH, or —SO 3 H.

8. The electroplating bath according to claim 7 , wherein the coloring agent according to Formula (I) is selected from the group of sulphur containing compounds comprising:

(1) 2-(2-Hydroxy-ethylsulfanyl)-ethanol,

(2) Thiazolidine-2-carboxylic acid,

(3) Thiodiglycol ethoxylate,

(4) 2-Amino-3-ethylsulfanyl-propionic acid,

(5) 3-(3-Hydroxy-propylsulfanyl)-propan-1-ol,

(6) 2-Amino-3-carboxymethylsulfanyl-propionic acid,

(7) 2-Amino-4-methylsulfanyl-butan-1-ol,

(8) 2-Amino-4-methylsulfanyl-butyric acid,

(9) 2-Amino-4-ethylsulfanyl-butyric acid,

(10) 3-Carbamimidoylsulfanyl-propane-1-sulfonic acid,

(11) 3-Carbamimidoylsulfanyl-propionic acid,

(12) Thiomorpholine,

(13) 2-[2-(2-Hydroxy-ethylsulfanyl)-ethylsulfanyl]-ethanol,

(14) 4,5-Dihydro-thiazol-2-ylamine,

(15) Thiocyanic acid.

9. The electroplating bath according to claim 7 , wherein the concentration of the coloring agent according to general Formula (I) ranges from 0.01 g/L to 100 g/L.

10. A method for electrodepositing a dark chromium layer on a workpiece which comprises electroplating said workpiece with the electroplating bath as defined in claim 1 .