Method for electrodepositing a dark chromium layer on a substrate and substrate having at least one side fully covered with a dark chromium layer

Abstract

The present invention relates to a method for electrodepositing a dark chromium layer on a substrate and a substrate having at least one side fully covered with a dark chromium layer. The method includes utilizing an aqueous trivalent chromium electroplating bath comprising colloidal particles and a step of treating the substrate with a rinse liquid having a temperature of 50° C. or more.

1 . A method for electrodepositing a dark chromium layer on a substrate, the method comprising the steps
 (a) providing a 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, and 
 (iv) one or more than one sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below, 
   (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 and is fully covering at least one side of the substrate,   (d) treating the substrate comprising the electrolytically deposited dark chromium layer with a rinse liquid, wherein the rinse liquid has a temperature of 50° C. or more and wherein during step (d) no electrical current is applied.   
     
     
         2 . The method of  claim 1 , wherein the colloidal particles comprise one or more than one chemical element selected from the group consisting of silicon, aluminum, and carbon. 
     
     
         3 . The method of  claim 1 , wherein said colloidal particles comprise nano-particles. 
     
     
         4 . The method of  claim 1 , wherein said colloidal particles comprise at least particles with a particle size of 100 nm or less. 
     
     
         5 . The method of  claim 2 , wherein the colloidal particles comprising the chemical element silicon, comprise silica. 
     
     
         6 . The method of  claim 2 , wherein the colloidal particles comprising the chemical element aluminum, comprise aluminum oxide. 
     
     
         7 . The method of  claim 2 , wherein the colloidal particles comprising the chemical element carbon, comprise nanodiamonds. 
     
     
         8 . The method of  claim 1 , wherein in step (b) said colloidal particles are present in a total amount ranging from 0.05 g/L to 100 g/L, based on the total volume of the aqueous trivalent chromium electroplating bath. 
     
     
         9 . The method of  claim 1 , wherein (iv) comprises thiocyanate anions. 
     
     
         10 . The method of  claim 1 , wherein (iv) comprises
 at least an organic sulfur-containing compound having a sulfur atom with an oxidation number of +5 or below and additionally having a nitrogen atom.   
     
     
         11 . The method of  claim 1 , wherein the dark chromium layer fully covering said at least one side has a highest L* value L2*, according to the L*a*b color system, of 55 or less. 
     
     
         12 . The method of  claim 1 , wherein the dark chromium layer fully covering said at least one side has a highest b* value b2*, according to the L*a*b color system, of +6 or below. 
     
     
         13 . A substrate having at least one side fully covered with a dark chromium layer, wherein said dark chromium layer fully covering said at least one side has
 a lowest L* value L1* and a highest L* value L2*,   a lowest a* value a1* and a highest a* value a2*, and   a lowest b* value b1* and a highest b* value b2*,
 wherein according to 
 ΔE=√{square root over ((L2*−L1*) 2 +(a2*−a1*) 2 +(b2*−b1*) 2 )}, ΔE is ranging from 0.0001 to 3.5, based on said dark chromium layer fully covering said at least one side, and 
   L2* is 50 or less.   
     
     
         14 . The substrate of  claim 13 , wherein b2* is +7 or less. 
     
     
         15 . The substrate of  claim 13 , wherein the dark chromium layer comprises aluminum and/or silicon. 
     
     
         16 . The method of  claim 1 , wherein in step (d) the rinse liquid consists of water. 
     
     
         17 . The method of  claim 1 , wherein, in step (c) the contacting is carried out at a temperature ranging from 20° C. to 60° C., and in step (d) the rinse liquid has a temperature greater than the temperature in step (c).