Method for depositing a chromium-comprising passivation layer on a zinc-comprising coating

Abstract

The present invention refers to a method for depositing a chromium-comprising passivation layer on a zinc-comprising coating, wherein the zinc-comprising coating additionally comprises Fe, Sn, Mn, or mixtures thereof. The method utilizes a passivation composition comprising 0.001 mg/L to 200 mg/L, based on the total volume of the passivation composition, of at least one corrosion-inhibiting agent selected from the group consisting of unsubstituted azole compounds, substituted azole compounds, unsubstituted aliphatic organic acids with at least one mercapto-group, substituted aliphatic organic acids with at least one mercapto-group, salts, and mixtures thereof.

1 . A method for depositing a chromium-comprising passivation layer on a zinc-comprising coating, the method comprising the following steps:
 (a) providing a substrate comprising the zinc-comprising coating,   (b) providing a passivation composition for depositing the chromium-comprising passivation layer, the composition comprising
 (i) trivalent chromium ions; 
 (ii) at least one complexing agent for the trivalent chromium ions, being different from the at least one corrosion-inhibiting agent; and 
 (iii) 0.001 mg/L to 200 mg/L, based on the total volume of the passivation composition, of at least one corrosion-inhibiting agent selected from the group consisting of unsubstituted azole compounds, substituted azole compounds, unsubstituted aliphatic organic acids with at least one mercapto-group, substituted aliphatic organic acids with at least one mercapto-group, salts, and mixtures thereof; and 
   (c) contacting said substrate with said passivation composition such that the chromium-comprising passivation layer is deposited on the zinc-comprising coating,   wherein the zinc-comprising coating additionally comprises Fe, Sn, Mn, or mixtures thereof.   
     
     
         2 . The method of  claim 1 , wherein the zinc-comprising coating is substantially free of nickel. 
     
     
         3 . The method of  claim 1 , wherein the zinc-comprising coating comprises Fe, Sn, or mixtures thereof. 
     
     
         4 . The method of  claim 1 , wherein in the passivation composition (iii) has a total concentration ranging from 0.005 mg/L to 180 mg/L, based on the total volume of the passivation composition. 
     
     
         5 . The method of  claim 1 , wherein in the passivation composition (iii) has a total concentration ranging from 0.01 mg/L to 150 mg/L, based on the total volume of the passivation composition. 
     
     
         6 . The method of  claim 1 , wherein in the passivation composition (iii) has a total concentration ranging from 0.001 mg/L to 9.9999 mg/L, based on the total volume of the passivation composition. 
     
     
         7 . The method of  claim 1 , wherein in the passivation composition the substituted azole compounds, salts, and mixtures thereof independently comprise one or more than one substituent selected from the group consisting of amino, nitro, carboxy, hydroxy, sulfonate, and thiol. 
     
     
         8 . The method of  claim 1 , wherein in the passivation composition the unsubstituted, and substituted azole compounds, salts, and mixtures thereof are independently selected from the group consisting of monoazoles, diazoles, triazoles, and tetrazoles. 
     
     
         9 . The method of  claim 1 , wherein in the passivation composition the unsubstituted and substituted azole compounds, salts, and mixtures thereof are independently selected from the group consisting of 1,2,4-triazoles. 
     
     
         10 . The method of  claim 1 , wherein in the passivation composition the substituted azole compounds, salts, and mixtures thereof independently comprise at least a mercaptotriazole. 
     
     
         11 . The method of  claim 1 , wherein in the passivation composition the unsubstituted aliphatic organic acids with at least one mercapto-group, salts, and mixtures thereof comprise at least 3-mercaptopropionic acid and/or salts thereof. 
     
     
         12 . The method of  claim 1 , wherein in the passivation composition the at least one complexing agent for the trivalent chromium ions is selected from the group consisting of monocarboxylic acids, dicarboxylic acids, salts thereof, halogen ions, and mixtures thereof. 
     
     
         13 . The method of  claim 1 , wherein in the passivation composition the at least one complexing agent for the trivalent chromium ions is selected from the group consisting of unsubstituted monocarboxylic acids, hydroxyl-substituted monocarboxylic acids, amino-substituted monocarboxylic acids, unsubstituted dicarboxylic acids, hydroxyl-substituted dicarboxylic acids, amino-substituted dicarboxylic acids, salts thereof, halogen ions, and mixtures thereof. 
     
     
         14 . The method of  claim 1 , wherein in the passivation composition the at least one complexing agent for the trivalent chromium ions has a total concentration in a range from 0.05 wt.-% to 15 wt.-%, based on the total weight of the passivation composition. 
     
     
         15 . The method of  claim 1 , wherein the passivation composition further comprises
 (v) iron ions in a total concentration ranging from 0 mg/L to 2000 mg/L, based on the total volume of the passivation composition.