Method for forming a black-passivation layer on a zinc-iron alloy and black- passivation composition

Abstract

The present invention relates to a method for forming a black-passivation layer on a zinc-iron alloy of a substrate, a black-passivation composition for depositing a black-passivation layer on such, in which the black-passivation composition includes one or more than one blackening agent selected from the group consisting of formula (I) and formula (II) as described hereinafter, and a respective use of said blackening agents for blackening a zinc-iron alloy.

1 . A method for forming a black-passivation layer on a zinc-iron alloy, the method comprising the steps:
 (a) providing a substrate comprising the zinc-iron alloy,   (b) providing a black-passivation composition for depositing the black-passivation layer on the zinc-iron alloy, the composition comprising
 (i) one or more than one blackening agent selected from the group consisting of formula (I), 
   
       
         
           
           
               
               
           
         
         
           
             wherein
 R 1  and R 2  are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, 
 R 3  is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and 
 n is 1, 2, 3, 4, or 5, 
 
           
           and formula (II), 
         
       
       
         
           
           
               
               
           
         
         
           
             wherein
 R 4  is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and 
 m is 1, 2, 3, 4, or 5, and 
 
           
           (ii) one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, and 
         
         (c) contacting the substrate with said black-passivation composition such that the black-passivation layer is formed on the zinc-iron alloy. 
       
     
     
         2 . The method of  claim 1 , wherein in the zinc-iron alloy the amount of iron ranges from 0.1 wt.-% to 30 wt.-%, based on the total weight of the zinc-iron alloy. 
     
     
         3 . The method of  claim 1 , wherein the black-passivation composition is acidic. 
     
     
         4 . The method of  claim 1 , wherein in the black-passivation composition the one or more than one blackening agent has a total concentration ranging from 0.2 mmol/L to 100 mmol/L, based on the total volume of the black-passivation composition. 
     
     
         5 . The method of  claim 1 , wherein the black-passivation composition comprises one or more than one blackening agent of formula (I) in a total concentration ranging from 0.4 mmol/L to 25.0 mmol/L, based on the total volume of the black-passivation composition. 
     
     
         6 . The method of  claim 1 , wherein R 1  and R 2  are independently selected from the group consisting of hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl. 
     
     
         7 . The method of  claim 1 , wherein R 3  comprises at least sulfonic acid, salts and/or esters thereof. 
     
     
         8 . The method of  claim 1 , wherein R 4  comprises at least sulfonic acid, salts and/or esters thereof. 
     
     
         9 . The method of  claim 1 , wherein said one or more than one species of metal ions has a total concentration ranging from 0.1 g/L to 30 g/L, based on the total volume of the black-passivation composition and based on the mass of the free ions. 
     
     
         10 . The method of  claim 1 , wherein the black-passivation composition is substantially free of, preferably does not comprise, tungsten. 
     
     
         11 . The method of  claim 1 , wherein the black-passivation composition is further comprising
 (iii) one or more than one species of halogen ions, or   (iv) one or more than one carboxylic acid and/or salts thereof,   or both (iii) and (iv).   
     
     
         12 . The method of  claim 1 , wherein in step (c) the black-passivation composition has a temperature in a range from 10° C. 
     
     
         13 . The method of  claim 1 , wherein in step (c) the contacting is performed for a time period from 10 seconds to 200 seconds. 
     
     
         14 . A black-passivation composition for depositing a black-passivation layer on a zinc-iron alloy, the composition comprising
 (i) one or more than one blackening agent selected from the group consisting of   formula (I),   
       
         
           
           
               
               
           
         
         
           wherein 
           R 1  and R 2  are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, 
           R 3  is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and 
           n is 1, 2, 3, 4, or 5, 
         
         and formula (II), 
       
       
         
           
           
               
               
           
         
         
           wherein 
           R 4  is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and 
           m is 1, 2, 3, 4, or 5, and 
         
         (ii) one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, 
         with the proviso that
 the black-passivation composition is substantially free of nickel ions, cobalt ions, and tungsten ions. 
 
       
     
     
         15 . (canceled) 
     
     
         16 . The method of  claim 1 , wherein in the zinc-iron alloy the amount of iron ranges from 6.1 wt.-% to 15 wt.-%, based on the total weight of the zinc-iron alloy. 
     
     
         17 . The method of  claim 1 , wherein formula (I) comprises the compound 3-(N,N-Dimethylthiocarbamoyl)-thiopropanesulfonic acid, salts and/or esters thereof. 
     
     
         18 . The method of  claim 1 , wherein formula (II) comprises the compound 3-(2-Benzthiazolylthio)-1-propanesulfonic acid, salts and/or esters thereof. 
     
     
         19 . The method of  claim 1 , wherein
 in the zinc-iron alloy the amount of iron ranges from 2.1 wt.-% to 25 wt.-%, based on the total weight of the zinc-iron alloy,   the black-passivation composition has a pH from 1.0 to 4.5,   in the black-passivation composition the one or more than one blackening agent has a total concentration ranging from 0.2 mmol/L to 100 mmol/L, based on the total volume of the black-passivation composition, and   said one or more than one species of metal ions has a total concentration ranging from 0.1 g/L to 30 g/L, based on the total volume of the black-passivation composition and based on the mass of the free ions.