Gold electroplating solution and its use for electrodepositing gold with an aged appearance

Abstract

The invention relates to a gold electroplating solution comprising gold in the form of a complex with a compound of formula (I) or a salt thereof: R 1 S—Ar—CO 2 H  (I) Wherein: R 1 is H, a C 1 -C 6 alkyl group or —S—Ar—CO 2 H, Ar is, at each occurrence, independently, selected from a C 6 -C 10 arylene or a 5 to 10 membered heteroarylene group, notably a phenylene, a pyridinylene, a furanylene, a pyrrolylene, or a thienylene group.

1 . A gold electroplating solution comprising gold in the form of a complex with a compound of formula (I) or a salt thereof:
   R 1 S—Ar—CO 2 H  (I)
   wherein:   R 1  is H, a C 1 -C 6  alkyl group or —S—Ar—CO 2 H, Ar is, at each occurrence, independently, selected from a C 6 -C 10  arylene or a 5 to 10 membered heteroarylene group, notably a phenylene, a pyridinylene, a furanylene, a pyrrolylene, or a thienylene group, and wherein the concentration of the compound of formula (I) is from 1 to 10 g/L.   
     
     
         2 . The gold electroplating solution of  claim 1 , further comprising at least one of a base and a conductive salt. 
     
     
         3 . The gold electroplating solution according to  claim 1 , characterised in that it does not comprise any cyanide compound. 
     
     
         4 . The gold electroplating solution according to according to  claim 1 , wherein the compound of formula (I) is selected from nicotinic compounds of formula (Ia), 
       
         
           
           
               
               
           
         
       
       or selected from thiobenzoic acid compounds of formula (Ib) 
       
         
           
           
               
               
           
         
       
     
     
         5 . The gold electroplating solution according to  claim 1 , wherein the compound of formula (I) is selected from 2,2′-dithiobenzoic acid, 2-mercaptobenzoic acid, 2-mercaptonicotinic acid, 2-(methylthio) nicotinic acid 4-mercaptobenzoic acid, 6,6′-dithionicotinic acid, 6-mercaptonicotinic acid, 2-(methylthio)benzoic acid, or 3-mercaptobenzoic acid, and mixtures thereof. 
     
     
         6 . The gold electroplating solution according to  claim 1 , wherein the compound of formula (I) is selected from nicotinic compounds of formula (Ia) 
       
         
           
           
               
               
           
         
       
       wherein the compound of formula (Ia) is selected from 2-mercaptonicotinic acid, 2-(methylthio) nicotinic acid, 6,6′-dithionicotinic acid, 6-mercaptonicotinic acid, and mixtures thereof. 
     
     
         7 . The gold electroplating solution according to  claim 1 , further comprising an additional complexing agent selected from hydantoin, hypoxanthine and derivatives thereof. 
     
     
         8 . The gold electroplating solution according to  claim 1 , further comprising a soluble species of an alloyable metal for the purpose of producing an alloyed gold electrodeposit. 
     
     
         9 . The gold electroplating solution according to  claim 1 , further comprising one or more additives selected from a levelling agent, a brightening agent, a surfactant and a mixture thereof. 
     
     
         10 . A method of producing an electrodeposit of gold or gold alloy on a substrate, the method comprising using gold electroplating solution as defined in  claim 1  as an electrodeposition bath. 
     
     
         11 . The method according to  claim 10 , wherein the substrate comprises at least an electrically conductive portion. 
     
     
         12 . The method according to  claim 11 , wherein the substrate is selected from a metal or a metal alloy. 
     
     
         13 . A method of electroplating gold or gold alloy on a substrate, comprising the steps of:
 a) immersing the substrate in an electroplating solution according to  claim 1 , a surface of said substrate having an electrically conductive portion in contact with said solution;   b) passing an electric current through said conductive portion and said solution to cause electrodeposition of gold on said electrically conductive portion of said substrate; and   c) recovering the obtained gold or gold alloy electroplated substrate.   
     
     
         14 . The method according to  claim 13 , further comprising a surface treatment step d) of the gold alloy electrodeposit and a step e) of applying a transparent protective layer to the gold or gold alloy electrodeposit after step c) or d). 
     
     
         15 . A method of electroplating gold or gold alloy onto a substrate, the method comprising using a compound of formula (I) as defined in  claim 1 , as a complexing agent. 
     
     
         16 . A gold or gold alloy electroplated substrate obtainable by the method of  claim 13 .