Electroplating composition and method for depositing a chromium coating on a substrate

Abstract

The present invention refers to an electroplating composition for depositing a chromium coating on a substrate, the composition including:(i) trivalent chromium ions,(ii) at least one complexing agent for the trivalent chromium ions, and(iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof.

1 . An electroplating composition for depositing a chromium coating on a substrate, the composition comprising:
 (i) trivalent chromium ions,   (ii) at least one complexing agent for the trivalent chromium ions, and   (iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof.   
     
     
         2 . The electroplating composition according to  claim 1 , wherein the electroplating composition comprises at least one or more than one betaine independently comprising at least 10 carbon atoms. 
     
     
         3 . The electroplating composition according to  claim 1 , wherein the betaines independently comprise:
 a positively charged quaternary nitrogen atom, and   a negatively charged sulfonate group or negatively charged carboxylate group,   
       with the proviso that the positive charge cannot be removed by deprotonation. 
     
     
         4 . The electroplating composition according to  claim 1 , wherein the betaines are selected from the group consisting of N-substituted-N,N-Dialkyl-ammonium sulfobetaines. 
     
     
         5 . The electroplating composition according to  claim 1 , wherein the betaines comprise one or more of N,N-Dimethyl-N-(3-cocoamidopropyl)-N-(2-hydroxy-3-sulfopropyl) ammonium betaine, N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-Octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-Decyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-Tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-Hexadecyl-N,N -dimethyl-3-ammonio-1-propanesulfonate, N-Octadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, and N,N-Dimethyl-N-dodecylglycine betaine. 
     
     
         6 . The electroplating composition according to  claim 1 , wherein the electroplating composition comprises at least one betaine and in addition one or more than one monomeric diol. 
     
     
         7 . The electroplating composition according to  claim 1 , wherein the electroplating composition comprises the betaines in a total concentration in a range from 0.0005 g/L to 1 g/L, based on the total volume of the electroplating composition. 
     
     
         8 . The electroplating composition according to  claim 1 , wherein the electroplating composition has a pH in a range from 4.1 to 7.0. 
     
     
         9 . The electroplating composition according to  claim 1 , wherein
 the electroplating composition comprises one or more than one betaine and one or more than one monomeric diol,   with the proviso that the one or more than one monomeric diol comprises one or more than one C 11 -C 25  diol comprising one, two or more than two iso-propyl moieties.   
     
     
         10 . A method for depositing a chromium coating on a substrate, the method comprising the following steps:
 (a) providing the substrate,   (b) providing an electroplating composition for depositing a chromium coating on the substrate, the composition comprising:
 (i) trivalent chromium ions, 
 (ii) at least one complexing agent for the trivalent chromium ions, and 
 (iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof, 
   (c) contacting the substrate with said electroplating composition and applying an electrical current such that the chromium coating is deposited on at least one surface of said substrate.   
     
     
         11 . The method of  claim 10 , wherein in step (c) the cathodic current efficiency (CCE) is 11% or more. 
     
     
         12 . The method of  claim 10 , wherein in step (c) the chromium coating has a thickness in a range from 1.1 μm to 500 μm. 
     
     
         13 . The method of  claim 10 , wherein in step (c) the concentration of the at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof, is continually or semi-continually monitored, wherein
 the monitored concentration is compared to a target concentration of said at least one additive, and   if the monitored concentration is below the target concentration than the at least one additive is added to the electroplating composition.   
     
     
         14 . A substrate with a surface, wherein the surface of the substrate comprises a chromium coating obtained by a method for depositing according to  claim 10 . 
     
     
         15 . (canceled) 
     
     
         16 . The electroplating composition according to  claim 1 , wherein the electroplating composition comprises the betaines in a total concentration in a range from 0.01 g/L to 0.2 g/L, based on the total volume of the electroplating composition. 
     
     
         17 . The method of  claim 10 , wherein in step (c) the chromium coating has a thickness in a range from 10 μm to 250 μm.