Method for etching at least one surface of a plastic substrate

Abstract

The present invention relates to a method for etching at least one surface of a plastic substrate, the method comprising steps (A) to (C), wherein step (B) comprises a contacting with a pre-treatment composition comprising one or more than one fluorine-free surface active compound, and step (C) comprises a contacting with an etching composition comprising chromic acid, wherein after step (B) and prior to step (C) no rinsing is applied, and the etching composition is substantially free of fluorine-containing surface active compounds.

1 . A method for etching at least one surface of a plastic substrate, the method comprising the steps
 (A) providing the substrate,   (B) contacting the substrate with an aqueous pre-treatment composition such that a pre-treated substrate is obtained, the pre-treatment composition comprising
 (B-a) one or more than one fluorine-free surface active compound, and 
   (C) contacting the pre-treated substrate with an etching composition in an etching compartment such that an etched substrate is obtained, the etching composition comprising
 (C-a) chromic acid, and 
 (C-b) trivalent chromium ions, 
   characterized in that
 the pre-treated substrate is not rinsed after step (B) and prior to step (C), and 
 the etching composition is substantially free of fluorine-containing surface active compounds. 
   
     
     
         2 . The method of  claim 1 , wherein in step (A) the substrate comprises acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene styrene—polycarbonate (ABS-PC), polypropylene (PP), polyamide (PA), polyetherimide (PEI), a polyetherketone (PEK), or mixtures thereof. 
     
     
         3 . The method of  claim 1 , wherein in (B-a) the one or more than one fluorine-free surface active compound comprises a non-ionic surfactant. 
     
     
         4 . The method of  claim 3 , wherein the non-ionic surfactant is a non-ionic alcohol alkoxylate, wherein in the non-ionic alcohol alkoxylate the alcohol comprises 6 to 20 carbon atoms. 
     
     
         5 . The method of  claim 1 , wherein in the pre-treatment composition (B-a) has a total concentration ranging from 0.1 wt.-% to 40 wt.-%, based on the total weight of the pre-treatment composition. 
     
     
         6 . The method of  claim 1 , wherein in the pre-treatment composition water and (B-a) together form 98 wt.-% or more of the total weight of the pre-treatment composition. 
     
     
         7 . The method of  claim 1 , wherein in the etching composition (C-a) has a total concentration ranging from 100 g/L to 450 g/L, based on the total volume of the etching composition and referenced to CrO 3 . 
     
     
         8 . The method of  claim 1 , wherein the one or more than one fluorine-free surface active compound in the pre-treatment composition is at least partly dragged out from the pre-treatment composition and dragged in into the etching composition. 
     
     
         9 . The method of  claim 1 , wherein any total amount of fluorine-free surface active compounds in the etching composition originates from the pre-treatment composition. 
     
     
         10 . The method of  claim 1 , wherein in the etching composition (C-b) has a total concentration of 35 g/L or below. 
     
     
         11 . The method of  claim 1 , wherein at least a portion of the trivalent chromium ions in the etching composition is oxidized through an electrical current such that chromium with the oxidation number (VI) is obtained. 
     
     
         12 . The method of  claim 1 , wherein in step (C) the contacting is carried out for a time ranging from 1 minute to 120 minutes. 
     
     
         13 . The method of  claim 1 , wherein in step (C) the contacting is carried at a temperature ranging from 50° C. to 80° C. 
     
     
         14 . The method of  claim 1  wherein the pre-treatment composition and the etching composition are substantially free of fluorinated surface active compounds. 
     
     
         15 . The method of  claim 1 , wherein the pre-treatment composition and the etching composition comprise identical fluorine-free surface active compounds.