Aqueous, alkaline, cyanide-free bath for the galvanic deposition of zinc alloy coatings

Abstract

An aqueous, alkaline, cyanide-free electrolyte bath for deposition of zinc alloy layers on substrate surfaces is described, which contains cationic pyridinium compounds as brighteners and polyamines as complexing agents. The electrolyte bath is suitable for electroplating bright and even zinc alloy coatings.

1 . Aqueous, alkaline, cyanide-free electrolyte bath for deposition of zinc alloy layers on substrate surfaces, comprising the following components:
 a) a source of zinc ions and a source for further metal ions;   b) hydroxide ions;   c) at least one pyridinium compound of the general formula I or II:   
     
       
         
         
             
             
         
       
       wherein R 1  represents a substituted or unsubstituted, saturated or unsaturated, aliphatic or araliphatic hydrocarbon residue having 1 to 12 carbon atoms, 
       R 1 ′ represents a divalent, substituted or unsubstituted, saturated or unsaturated, aliphatic or araliphatic hydrocarbon residue having 1 to 12 carbon atoms, 
       X 1  represents NR x R y  and X 2  represents NR x R y , wherein R x  and R y  may be the same or different and represent hydrogen or linear and/or branched alkyl groups having 1 to 12 carbon atoms, and 
       Y −  is a counter ion; and 
       d) at least one complexing agent of the general formula III or IV: 
     
     
       
         
         
             
             
         
       
     
     wherein X 1 , X 2  and X 3  may be the same or different and represent an alkoxy group or a primary, secondary or tertiary amino group,
 R1, R2 and R3 may be the same or different and represent hydrogen, a C1-C12 alkyl, C1-C12 alkoxy, allyl, propargyl or benzyl group, and 
 n and m may be the same or different and represent an integer of 0 to 5. 
 
   
   
       2 . Electrolyte bath according to  claim 1 , wherein R 1  represents substituted aryl of the following formulae R 1 a to R 1 I: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein FG represents a residue selected from the group consisting of carboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy, hydroxy, trifluoromethyl, allyl, propargyl-, 4-sulfobutyl, 3-sulfopropyl, 4-carboxybutyl, 3-carboxypropyl residues, hydrogen and halogens, selected from fluorine, chlorine and bromine, and
 R 1 ′ represents but-2-enyl, but-2-ynyl or aryl of the following formulae R1′ a to R1′ r: 
 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       wherein FG represents a residue selected from the group consisting of carboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy, trifluoromethyl residues, hydrogen and halogens, selected from fluorine, chlorine and bromine, wherein all rings or individual fused rings may be substituted. 
     
   
   
       3 . Electrolyte bath according to one of  claim 1 , containing a combination of pyridinium compounds of formulae I or II. 
   
   
       4 . Electrolyte bath according to  claim 1 , containing a combination of complexing agents of formulae III or IV. 
   
   
       5 . Electrolyte bath according to  claim 1 , comprising
 1 to 100 g/l of zinc ions,   0.1 to 50 g/l alloying metal ions,   5 to 100 g/l of at least one compound of general formula III or IV and   0.001 to 20 g/l of at least one compound of general formula I or II or a combination thereof.   
   
   
       6 . Electrolyte bath according to  claim 5 , comprising:
 4 to 30 g/l of zinc ions,   alloying metal ions selected from nickel, iron, cobalt, manganese ions and   0.01 to 10 g/l of at least one compound of general formula I or II or a combination thereof.   
   
   
       7 . Electrolyte bath according to  claim 1 , containing as alloying metal nickel in an amount of 0.1 to 50 g/l, iron in an amount of 10 to 120 mg/l, manganese in an amount of 10 to 100 g/l and/or cobalt in an amount of 10 to 120 mg/l. 
   
   
       8 . Electrolyte bath according to  claim 1 , containing as base an alkali metal hydroxide. 
   
   
       9 . Electrolyte bath according to  claim 8 , wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide and is present in an amount of 50 to 250 g/l. 
   
   
       10 . Electrolyte bath according  claim 1  having a pH of at least 10. 
   
   
       11 . Process for galvanic deposition of bright and even zinc alloy coatings, comprising a step of immersing the substrate to be coated into a bath according to  claim 1 . 
   
   
       12 . Process according to  claim 11 , wherein the bath is operated at a current density of 0.01 to 10 A/dm 2 . 
   
   
       13 . Process according to  claim 11 , wherein the bath is operated at a temperature of 15 to 50° C. 
   
   
       14 . Process according to  claim 11 , wherein the bath is operated at a temperature of about 25° C. 
   
   
       15 . Process according to  claim 11 , wherein the coatings are applied to a conductive substrate by using a drum electroplating process. 
   
   
       16 . Process according to  claim 11 , wherein the coatings are applied to a conductive substrate using a rack electroplating process. 
   
   
       17 . Process according to  claim 1 , wherein a coating of a zinc alloy with one or more metals from the group consisting of cobalt, nickel, manganese and iron is deposited on the substrate.