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

Abstract

The invention relates to an aqueous, alkaline cyanide-free electrolyte bath for de-positing zinc and zinc alloy coatings on substrate surfaces comprising (a) a source for zinc ions and optionally a source for further metal ions, (b) hydroxide ions, (c) a polymer of general formula I which is soluble in the bath and (d) at least one pyridinium compound of general formula II or III. The electrolyte bath is suitable for the galvanic deposition of bright and even zinc and zinc alloy coatings.

1 . Aqueous, alkaline, cyanide-free electrolyte bath for the deposition of zinc and zinc alloy coatings on substrate surfaces, which bath comprises the following components:
 a) a source of zinc ions and, optionally, a source of further metal ions,   b) hydroxide ions,   c) a polymer which is soluble in the bath of the general formula I   
       
         
           
           
               
               
           
         
         wherein 
         m represents an integer of 1 to 5, 
         n represents an integer greater than 1, 
         R1, R2, R3, R4 may be the same or different and each represents a substituted or unsubstituted hydrocarbon residue having 1 to 6 carbon atoms or —CH 2 CH 2 (OCH 2 CH 2 ) y —OH, wherein y lies between 0 and 6, 
         R5 represents (CH 2 ) p , wherein p represents an integer of 2 to 12 or a —(CH 2 ) 2 —O—(CH 2 ) 2 — or —(CH 2 ) 2 —O—(CH 2 ) 2 —O—(CH 2 ) 2 — group and 
         X −  represents a counter ion, and 
         d) at least one pyridinium compound of general formula II or III 
       
       
         
           
           
               
               
           
         
         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  and X 2  represent NR x R y , wherein R x  and R y  may be the same or different and represent hydrogen or linear or branched alkyl groups having 1 to 12 carbon atoms, and 
         Y −  is a counter ion. 
       
     
     
         2 . Electrolyte bath according to  claim 1 , wherein R 1  in formula II represents a substituted aryl residue of the following formulae R1a to R1I: 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         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 wherein all rings or individual fused rings may be substituted. 
       
     
     
         3 . Electrolyte bath according to  claim 1 , wherein R 1 ′ in formula III represents but-2-enyl, but-2-ynyl or an aryl residue of the following formulae R 1 ′ a to R 1 ′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. 
       
     
     
         4 . Electrolyte bath according to  claim 1 , wherein R 1  in Formula II and/or R 1 ′ in Formula III is/are bound to the pyridinium residue via a methylene group. 
     
     
         5 . Electrolyte bath according to  claim 1 , wherein Y −  in Formula II or III is a halide or pseudo-halide. 
     
     
         6 . Electrolyte bath according to  claim 1 , wherein the polymer of general formula I which is soluble in the bath is present in an amount of 0.1 to 50 g/l. 
     
     
         7 . Electrolyte bath according to  claim 6 , wherein the polymer of general formula I which is soluble in the bath is present in an amount of 0.25 to 10 g/l. 
     
     
         8 . Electrolyte bath according to  claim 1 , wherein the at least one pyridinium compound of formula II or III is present in an amount of 0.001 to 20 g/l. 
     
     
         9 . Electrolyte bath according to  claim 8 , wherein the at least one pyridinium compound of formula II or III is present in an amount of 0.001 to 10 g/l. 
     
     
         10 . Electrolyte bath according to  claim 1 , containing a combination of pyridinium compounds of formulae II and III. 
     
     
         11 . Electrolyte bath according to  claim 1 , containing a combination of different soluble polymers of general formula I. 
     
     
         12 . Electrolyte bath according to  claim 1 , wherein the source of zinc ions is zinc oxide or zinc hydroxide. 
     
     
         13 . Electrolyte bath according to  claim 1 , wherein the concentration of zinc ions is from 0.1 to 100 g/l. 
     
     
         14 . Electrolyte bath according to  claim 13 , wherein the concentration of zinc ions is from 0.1 to 30 g/l. 
     
     
         15 . Electrolyte bath according to  claim 1 , wherein the further metal ions are cobalt, nickel, manganese and/or iron ions. 
     
     
         16 . Electrolyte bath according to  claim 15 , wherein the zinc is present in an amount of 0.1 to 30 g/l and the cobalt is present in an amount of 10 to 120 mg/l, the nickel is present in an amount of 0.3 to 3 g/l, the manganese is present in an amount of 10 to 100 g/l and/or the iron is present in an amount of 10 to 120 mg/l. 
     
     
         17 . Electrolyte bath according to  claim 1 , containing alkali metal hydroxide as base. 
     
     
         18 . Electrolyte bath according to  claim 17 , wherein the alkali metal hydroxide is lithium hydroxide, sodium hydroxide and/or potassium hydroxide and is present in an amount of 50 to 250 g/l. 
     
     
         19 . Electrolyte bath according to  claim 1 , wherein the pH of the bath is at least 10. 
     
     
         20 . Electrolyte bath according to  claim 1 , wherein the bath does not contain additional brightening agents. 
     
     
         21 . Electrolyte bath according to  claim 1 , containing a complexing agent or a water-softening agent. 
     
     
         22 . Electrolyte bath according to  claim 21 , wherein the complexing agent is a chelate-forming agent. 
     
     
         23 . Electrolyte bath according to  claim 21 , wherein the complexing agent is present in an amount of 2 to 200 g/l. 
     
     
         24 . Electrolyte bath according to  claim 1 , wherein the bath contains a sulfur compound as leveling agent. 
     
     
         25 . Electrolyte bath according to  claim 24 , wherein the leveling agent contains 3-mercapto-1,2,4-triazole and/or thiourea. 
     
     
         26 . Electrolyte bath according to  claim 24 , wherein the sulfur compound is present in an amount of 0.01 to 0.50 g/l. 
     
     
         27 . Process for the galvanic deposition of bright and even zinc and zinc alloy coatings, comprising the step of immersing the substrate to be coated into a bath according to  claim 1 . 
     
     
         28 . Process according to  claim 27 , wherein the bath is operated at a current density of 0.01 to 10 A/dm 2 . 
     
     
         29 . Process according to  claim 27 , wherein the bath is operated at a temperature of 15 to 50° C. 
     
     
         30 . Process according to  claim 29 , wherein the bath is operated at a temperature of 25 to 35° C. 
     
     
         31 . Process according to  claim 27 , wherein the coatings are deposited on a conductive substrate by using a drum electroplating process. 
     
     
         32 . Process according to  claim 27 , wherein the coatings are deposited on a conductive substrate by using a rack electroplating process. 
     
     
         33 . Process according to  claim 27 , wherein a zinc coating is deposited on the substrate. 
     
     
         34 . Process according to  claim 27 , wherein a zinc alloy coating is deposited on the substrate. 
     
     
         35 . Process according to  claim 34 , wherein a coating of a zinc alloy with one or more metals from the group consisting of cobalt, nickel, manganese and/or iron is deposited on the substrate.