Resource-saving method for activating a metal surface prior to phosphating

Abstract

A method for phosphating metal surfaces in a layer-forming manner using a colloidal aqueous solution as an activation stage containing a dispersed particulate constituent, the particulate constituent containing dispersed inorganic compounds of phosphates of polyvalent metal cations; plus polymeric organic compounds as dispersing agents, which are composed at least partially of styrene and/or an α-olefin having no more than 5 carbon atoms and are composed at least partially of maleic acid, its anhydride and/or its imide, the polymeric organic compounds additionally comprising polyoxyalkylene units. In the activation stage of the method according to the invention, the addition of condensed phosphates can be dispensed with such that the content of dissolved condensed phosphates in the colloidal aqueous solution is less than 0.25, based on the phosphate content in the particulate constituent thereof, in each case based on the element P.

1 . A method for anti-corrosion pretreatment of a metal material selected from zinc, iron or aluminum or of a component which is composed at least partially of such metal materials, comprising steps of:
 (i) activating the metal material or the component; and then   (ii) phosphating, optionally zinc phosphating, the metal material or component of step (i), in consecutive method steps,   wherein activation in activating step (i) is carried out by contacting the metal material or the component with a colloidal aqueous solution containing, in a dispersed particulate constituent (a) of the colloidal aqueous solution:   (a1) at least one particulate inorganic compound composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, and   (a2) at least one polymeric organic compound composed at least partially of styrene and/or an α-olefin having no more than 5 carbon atoms; at least partially of maleic acid, its anhydride and/or its imide, wherein the at least one polymeric organic compound further comprises polyoxyalkylene units;   wherein, in the colloidal aqueous solution, content of condensed phosphates dissolved in water is less than 0.25, based on phosphate content of the at least one particulate inorganic compound, in each case based on the element P.   
     
     
         2 . The method according to  claim 1 , wherein, in the colloidal aqueous solution, the content of condensed phosphates dissolved in water is less than 0.20, based on the phosphate content of the at least one particulate compound, in each case based on the element P. 
     
     
         3 . The method according to  claim 2 , wherein, in the colloidal aqueous solution, the content of condensed phosphates dissolved in water, calculated as P, is less than 20 mg/kg, based on the colloidal aqueous solution. 
     
     
         4 . The method according to  claim 1 , wherein the colloidal aqueous solution contains an amount of at least 0.5 mmol/L, but no more than 10 mmol/L, of alkaline-earth metal ions dissolved in water. 
     
     
         5 . The method according to  claim 4 , wherein, the colloidal aqueous solution contains at least one complexing agent selected from a-hydroxycarboxylic acids and/or organophosphonic acids. 
     
     
         6 . The method according to  claim 5 , wherein the at least one complexing agent in the colloidal aqueous solution is present in an amount of no more than twice the amount of alkaline-earth metal ions in mmol/L. 
     
     
         7 . The method according to  claim 1 , wherein the colloidal aqueous solution in the activating step (i) has an alkaline pH. 
     
     
         8 . The method according to  claim 1 , wherein content of phosphates, calculated as PO 4 , contained in the at least one particulate inorganic compound (a1), based on the dispersed particulate constituent of the colloidal aqueous solution, is at least 25 wt. %. 
     
     
         9 . The method according to  claim 1 , wherein the at least one polymeric organic compound (a2) of the colloidal aqueous solution contains the polyoxyalkylene units in side chains of the at least one polymeric organic compound, and the polyoxyalkylene units are present in an amount of at least 40 wt. % but not exceeding 70 wt. %, based on total amount of the polymeric organic compounds (a2). 
     
     
         10 . The method according to  claim 9 , wherein the polyoxyalkylene units in the side chains of the polymeric organic compounds (a2) are at least partially end-capped with an N-heterocycle unit. 
     
     
         11 . The method according to  claim 1 , wherein the colloidal aqueous solution contains at least one thickener as a further component b), selected from urea urethane resins. 
     
     
         12 . The method according to  claim 1 , wherein the at least one polymeric organic compounds are present in the colloidal aqueous solution in an amount of at least 3 wt. %, but do not exceed 15 wt. %, based on the dispersed particulate constituent of the colloidal aqueous solution. 
     
     
         13 . The method according to  claim 1 , wherein the colloidal aqueous solution has a D50 value below 1 μm. 
     
     
         14 . The method according to  claim 1 , wherein the particulate constituents of the colloidal aqueous solution are present in an amount of at least 0.05 g/kg, but no more than 10 g/kg, in each case based on the colloidal aqueous solution. 
     
     
         15 . The method according to  claim 1 , wherein the colloidal aqueous solution is obtainable as an aqueous dispersion diluted by a factor of 20 to 100,000, comprising
 based on the aqueous dispersion, at least 5 wt. % of a dispersed particulate constituent (A), which in turn comprises
 (A1) at least one particulate inorganic compound which is composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, 
 (A2) at least one polymeric organic compound which is composed at least partially of styrene and/or an α-olefin having no more than 5 carbon atoms and is composed at least partially of maleic acid, its anhydride and/or its imide, the polymeric organic compound additionally comprising polyoxyalkylene units, and 
   optionally at least one thickener selected from urea urethane resins.   
     
     
         16 . The method according to  claim 1 , wherein the phosphating step (ii) is carried out by contact with an acidic aqueous composition containing 5-50 g/kg of phosphates dissolved in water, calculated as PO 4 , 0.3-3 g/kg of zinc ions and an amount of free fluoride; said acidic aqueous composition containing a total of less than 0.1 g/kg of ions of the elements nickel and cobalt.