Electroplating bath for depositing a black chromium layer, method for depositing, and substrate comprising such a layer

Abstract

The present invention relates to a very specific electroplating bath for depositing a black chromium layer, a respective method thereof, and a respective substrate with said black chromium layer thereon. The substrate comprising said black chromium layer is excellently suited for decorative purposes.

1 . An electroplating bath for depositing a black chromium layer, the electroplating bath comprising:
 (A) trivalent chromium ions;   (B) one or more than one complexing agent for said trivalent chromium ions;   (C) optionally, one or more than one pH buffer compound for said electroplating bath;   (D) thiocyanic acid, salts, esters, and/or isoforms thereof, in a total amount ranging from 100 mmol/L to 250 mmol/L, based on the total volume of the electroplating bath;   (E) one or more than one compound of formula (I), salts, and/or sulfoxides thereof
   R 1 —S—(CH 2 ) n —CH(NH 2 )—R 2   (I),
 
   wherein
 R 1  is a branched or unbranched C1 to C4 alkyl, 
 R 2  is selected from the group consisting of COOH, salts thereof, and (CH 2 ) m —OH, 
 n is an integer ranging from 1 to 4, and 
 m is an integer ranging from 1 to 4. 
   
     
     
         2 . The electroplating bath according to  claim 1  further comprising halogen anions. 
     
     
         3 . The electroplating bath according to  claim 1 , wherein the bath comprises (D) in a total amount ranging from 105 mmol/L to 245 mmol/L, based on the total volume of the electroplating bath. 
     
     
         4 . The electroplating bath according to  claim 1 , wherein said bath comprises (E) in a total amount ranging from 100 mmol/L to 950 mmol/L, based on the total volume of the electroplating bath. 
     
     
         5 . The electroplating bath according to  claim 1 , wherein the molar ratio of (E):(D) is 0.9 or more. 
     
     
         6 . The electroplating bath according to  claim 1 , wherein the molar ratio of (E):(D) is ranging from 0.9 to 2.65. 
     
     
         7 . The electroplating bath according to  claim 1 , wherein R 1  is methyl, ethyl, n-propyl, or iso-propyl. 
     
     
         8 . The electroplating bath according to  claim 1 , wherein R 2  is COOH and/or salts thereof. 
     
     
         9 . The electroplating bath according to  claim 1 , wherein n is 1 or 2. 
     
     
         10 . The electroplating bath according to  claim 1 , wherein in (E) the compound of formula (I) comprises methionine. 
     
     
         11 . A method for electroplating a black chromium layer on a substrate, the method comprising the steps
 (a) providing the substrate,   (b) contacting the substrate with an electroplating bath according to  claim 1 ,   (c) applying an electrical current such that the black chromium layer is electroplated onto the substrate, and   (d) heat-treating the substrate obtained from step (c) at a temperature ranging from 30° C. to 100° C.   
     
     
         12 . The method of  claim 11 , wherein in step (d) the heat-treating is carried out in water. 
     
     
         13 . A substrate comprising a black chromium layer, wherein the black chromium layer has, according to the L*a*b color system, an L* value of 50 or less, and a gloss value ranging from 150 to 230, referenced to a measuring angle of 60°. 
     
     
         14 . The substrate of  claim 13 , wherein the black chromium layer has an a* value ranging from −1.5 to +3,
 or 
 b* value ranging from −2.5 to +6, 
 or both an a* value ranging from −1.5 to +3, and a b* value ranging from −2.5 to +6. 
 
     
     
         15 . The substrate of  claim 13 , wherein the black chromium layer is part of a layer stack, the layer stack comprising, along a direction from the black chromium layer to the substrate:
 (i) the black chromium layer,   (ii) optionally, at least one MPS nickel layer,   (iii) at least one bright-nickel layer and/or at least one satin nickel layer, or both at least one bright nickel layer and at least one satin nickel layer, and   (iv) optionally, at least one semi-bright nickel layer.   
     
     
         16 . The substrate of  claim 13 , wherein the black chromium layer is substantially free of cobalt, or
 comprises cobalt, wherein in the black chromium layer more chromium is present than cobalt.   
     
     
         17 . An electroplating bath for depositing a black chromium layer, the electroplating bath comprising:
 (A) trivalent chromium ions;   (B) one or more than one complexing agent for said trivalent chromium ions;   (C) optionally, one or more than one pH buffer compound for said electroplating bath;   (D) thiocyanic acid, salts, esters, and/or isoforms thereof, in a total amount ranging from 100 mmol/L to 250 mmol/L, based on the total volume of the electroplating bath;   (E) one or more than one compound of formula (I), salts, and/or sulfoxides thereof
   R 1 —S—(CH 2 ) n —CH(NH 2 )—R 2   (I),
 
   wherein
 R 1  is a branched or unbranched C1 to C4 alkyl, 
 R 2  is COOH, and/or salts thereof, 
 n is an integer ranging from 1 to 4, and 
 m is an integer ranging from 1 to 4, and 
   wherein molar ratio of (E):(D) is 0.9 or more.   
     
     
         18 . The electroplating bath according to  claim 1  wherein the trivalent chromium ions are from a inorganic or organic trivalent chromium salt having anions selected from the group consisting of sulfate anions, formate, acetate, malate, and/or oxalate anions 
     
     
         19 . The electroplating bath according to  claim 1  wherein the bath is an electroplating bath, wherein cobalt ions are present in a range from 1 mg/L to 500 mg/L or does not comprise cobalt ions. 
     
     
         20 . The method of  claim 11  wherein in step (d) the heat-treating is a hot water rinse.