Method for electrodepositing a dark chromium layer, substrate comprising same, and electroplating bath thereof

Abstract

The present invention relates to a method for electrodepositing a dark chromium layer on a substrate, a respective electroplating bath for depositing such a dark chromium layer, and a respective substrate comprising said dark chromium layer. The electroplating bath comprises colloidal particles containing the chemical element aluminum. The substrate comprising said dark chromium layer is primarily suited for decorative purposes.

1 . A method for electrodepositing a dark chromium layer on a substrate, the method comprising the steps
 (a) providing the substrate, wherein the substrate comprises a plastic substrate,   (b) providing an aqueous trivalent chromium electroplating bath comprising
 (i) trivalent chromium ions, 
 (ii) one or more than one complexing agent for said trivalent chromium ions, 
 (iii) colloidal particles containing the chemical element aluminum, 
 (iv) a first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below, and 
 (v) optionally a second sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below being different from (iv), 
   (c) contacting the substrate with said electroplating bath and applying an electrical current such that the dark chromium layer is electrolytically deposited on the substrate.   
     
     
         2 . The method of  claim 1 , wherein the aqueous trivalent chromium electroplating bath is a colloidal suspension. 
     
     
         3 . The method of  claim 1 , wherein said colloidal particles comprise nano-particles. 
     
     
         4 . The method of  claim 1 , wherein said colloidal particles have an average particle diameter D 50  of 100 nm or less, based on volume. 
     
     
         5 . The method of  claim 1 , wherein said colloidal particles comprise at least particles with a particle size of 100 nm or less. 
     
     
         6 . The method of  claim 1 , wherein said colloidal particles are present in a total amount ranging from 0.05 g/L to 15 g/L, based on the total volume of the aqueous trivalent chromium electroplating bath. 
     
     
         7 . The method of  claim 1 , wherein said colloidal particles comprise aluminum oxide. 
     
     
         8 . The method of  claim 1 , wherein said colloidal particles comprise Al 2 O 3 . 
     
     
         9 . The method of  claim 1 , wherein the first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below comprises a nitrogen atom. 
     
     
         10 . The method of  claim 1 , wherein the first sulfur-containing compound comprises methionine. 
     
     
         11 . The method of  claim 1 , wherein the second sulfur-containing compound comprises an inorganic sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below. 
     
     
         12 . An aqueous trivalent chromium electroplating bath comprising
 (i) trivalent chromium ions,   (ii) one or more than one complexing agent for said trivalent chromium ions,   (iii) colloidal particles containing the chemical element aluminum,   (iv) a first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below, and   (v) optionally a second sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below being different from (iv).   
     
     
         13 . A substrate comprising a dark chromium layer, wherein the dark chromium layer comprises the chemical element aluminum and has, according to the L*a*b color system, a L* value of 60 or less.
 wherein the substrate comprises a plastic substrate.   
     
     
         14 . The substrate according to  claim 13 , wherein the dark chromium layer has a a* value ranging from −0.5 to +3.0. 
     
     
         15 . The substrate according to  claim 14 , wherein the dark chromium layer has a b* value ranging from +3.1 to +7.