Solutions of Organic Salts as Pretreatments for Plastic Prior to Etching

Abstract

A method of preparing a plastic substrate to accept metal plating thereon is described. The method includes the steps of pretreating the plastic substrate by contacting the plastic substrate with an aqueous electrolyte comprising an organic salt to raise the surface energy of the plastic substrate. Thereafter, the plastic substrate can be etched and metal plated.

1 . A method of treating a plastic substrate to accept metal plating thereon, the method comprising the steps of:
 a) pretreating the plastic substrate by contacting the plastic substrate with an aqueous electrolyte comprising an organic salt; and thereafter   b) etching the treated plastic substrate with an etchant.   
     
     
         2 . The method according to  claim 1 , wherein the etchant is a chrome based etchant. 
     
     
         3 . The method according to  claim 1 , wherein the etchant is chrome-free. 
     
     
         4 . The method according to  claim 1 , wherein the organic salt comprises an ionic liquid and combinations thereof. 
     
     
         5 . The method according to  claim 4 , wherein the ionic liquid comprises an imidazolium compound having the formula: 
       
         
           
           
               
               
           
         
         wherein R1 and R3 are each, independently of one another, an organic radical having from 1 to 20 carbon atoms, R2, R4 and R5 are each, independently of one another, an H atom or an organic radical having from 1 to 20 carbon atoms, X is an anion and n is 1, 2 or 3. 
       
     
     
         6 . The method according to  claim 5 , wherein the imidazolium compound is selected from the group consisting of 1,3-dimethylimidazolium methylsulfate, 1,3-dimethylimidazolium hydrogensulfate, 1,3-dimethylimidazolium dimethylphosphate, 1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium hydrogensulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium methanesulfonate, 1-ethyl-3-methylimidazolium diethylphosphate, 1-(1-butyl)-3-methylimidazolium methylsulfate, 1-(1-butyl)-3-methylimidazolium hydrogensulfate, 1-(1-butyl)-3-methylimidazolium thiocyanate, 1-(1-butyl)-3-methylimidazolium acetate, 1-(1-butyl)-3-methylimidazolium methanesulfonate, 1-(1-do decyl)-3-methylimidazolium methylsulfate, 1-(1-dodecyl)-3-methylimidazolium hydrogensulfate, 1-(1-tetradecyl)-3-methylimidazolium methylsulfate, 1-(1-tetradecyl)-3-methylimidazolium hydrogensulfate, 1-(1-hexadecyl)-3-methylimidazolium methylsulfate or 1-(1-hexadecyl)-3-methylimidazolium hydrogensulfate, and combinations of one or more of the foregoing. 
     
     
         7 . The method according to  claim 4 , wherein the ionic liquid comprises 2-hydroxyethylammonium formate or methyltributylammonium methylsulfate. 
     
     
         8 . The method according to  claim 6  or  7 , wherein the ionic liquid comprises at least one of 1-ethyl-2-methylimidazolium acetate and methyltributylammonium methylsulfate. 
     
     
         9 . The method according to  claim 1 , wherein the aqueous electrolyte comprises less than 50% by weight of the organic salt. 
     
     
         10 . The method according to  claim 9 , wherein the aqueous electrolyte comprises less than 30% by weight of the organic salt. 
     
     
         11 . The method according to  claim 10 , wherein the aqueous electrolyte comprises less than about 20% by weight of the organic salt. 
     
     
         12 . The method according to  claim 1 , further comprising the step of degreasing and cleaning the plastic substrate prior to step a). 
     
     
         13 . The method according to  claim 1 , wherein the plastic substrate comprises an acrylonitrile-butadiene-styrene copolymer of acrylonitrile-butadiene-styrene-polycarbonate. 
     
     
         14 . The method according to  claim 1 , wherein the plastic substrate is contacted with the aqueous electrolyte by spraying or by immersion. 
     
     
         15 . The method according to  claim 1 , wherein the aqueous electrolyte is maintained at a temperature of between 0° C. and about 120° C. 
     
     
         16 . The method according to  claim 1 , wherein the plastic substrate is contacted with the aqueous electrolyte for a period of time sufficient to raise the surface energy of the plastic substrate. 
     
     
         17 . The method according to  claim 16 , wherein the plastic substrate is contacted with the aqueous electrolyte for between about 30 seconds and about 10 minutes. 
     
     
         18 . The method according to  claim 1 , wherein more than 4 molecules of water per ion of organic salt are available for solvation. 
     
     
         19 . The method according to  claim 18 , wherein more than 9 molecules of water per ion of organic salt are available for solvation. 
     
     
         20 . The method according to  claim 19 , wherein more than 10 molecules of water per ion of organic salt are available for solvation. 
     
     
         21 . The method according to  claim 1 , further comprising the step of rinsing the substrate after step a) and before step b). 
     
     
         22 . The method according to  claim 21 , wherein the rinsing step is carried out for between about 30 seconds and about 5 minutes. 
     
     
         23 . The method according to  claim 22 , wherein the rinsing step is carried out for about 1 minute to about 3 minutes.