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

Abstract

The present invention relates to 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, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, 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. The cleaning and rinsing stages preceding the activation stage as well as the activation stage itself can be carried out using service water in a resource-saving manner without any loss of activation performance, the colloidal aqueous solution containing at least 0.5 mmol/L of alkaline-earth metal ions dissolved in water.

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, wherein the metal material or the component undergoes firstly activation (i) and then phosphating (ii), in particular zinc phosphating, in consecutive method steps, wherein the activation in method step (i) is carried out by bringing the metal material or the component into contact with a colloidal aqueous solution containing a dispersed particulate constituent (a) comprising:
 (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; and   (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 partially of maleic acid, its anhydride and/or its imide, wherein the at least one polymeric organic compound additionally comprises polyoxyalkylene units;   
       wherein the colloidal aqueous solution contains an amount of at least 0.5 mmol/L of alkaline-earth metal ions dissolved in water. 
     
     
         2 . The method according to  claim 1 , wherein the colloidal aqueous solution contains at least 1.0 mmol/L and no more than 10 mmol/L of the alkaline-earth metal ions dissolved in water. 
     
     
         3 . The method according to  claim 2 , wherein, in the colloidal aqueous solution, amount 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. 
     
     
         4 . The method according to  claim 2 , wherein the colloidal aqueous solution contains at least 1.5 mmol/L, but no more than 10 mmol/L, of the alkaline-earth metal ions dissolved in water. 
     
     
         5 . The method according to  claim 1 , wherein the colloidal aqueous solution has an alkaline pH and contains at least one complexing agent selected from α-hydroxycarboxylic acids, organophosphonic acids and combinations thereof. 
     
     
         6 . The method according to  claim 5 , wherein the complexing agents in the colloidal aqueous solution are present in an amount that is no more than twice the molar amount of the alkaline-earth metal ions dissolved in water. 
     
     
         7 . The method according to  claim 1 , wherein the colloidal aqueous solution in the activation (i), has a pH above 8.0, but below 11.0. 
     
     
         8 . The method according to  claim 1 , wherein phosphate content, calculated as PO 4 , 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 contain the polyoxyalkylene units in their side chains, the polyoxyalkylene units being present in an amount of at least 40 wt. % but not exceeding 70 wt. %, based on total amount of the at least one polymeric organic compounds (a2). 
     
     
         10 . The method according to  claim 9 , wherein the at least one polymeric organic compounds (a2) of the colloidal aqueous solution further comprise N-heterocycle units comprising one or more of pyridine, imidazole, imidazoline, morpholine, pyrrole and pyrrolidone units; the N-heterocycle units being part of the side chains of the at least one polymeric organic compound (a2). 
     
     
         11 . The method according to  claim 9 , wherein the polyoxyalkylene units of the at least one polymeric organic compound (a2) are at least partially end-capped with an N-heterocycle unit. 
     
     
         12 . The method according to  claim 1 , wherein the colloidal aqueous solution contains at least one thickener as a further component b). 
     
     
         13 . The method according to  claim 1 , wherein total amount of the at least one polymeric organic compounds in the dispersed particulate constituent of the colloidal aqueous solution is at least 3 wt. %, but preferably does not exceed 15 wt. %, based on the dispersed particulate constituent. 
     
     
         14 . The method according to  claim 1 , wherein the colloidal aqueous solution has a D50 value below 1 μm, preferably below 0.4 μm. 
     
     
         15 . The method according to  claim 1 , wherein, in the colloidal aqueous solution, amount 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. 
     
     
         16 . The method according to  claim 15 , wherein the colloidal aqueous solution contains the dispersed particulate constituents present in an amount of at least 0.05 g/kg, but no more than 10 g/kg, based on the colloidal aqueous solution; the alkaline-earth metal ions dissolved in water present in an amount of at least 1.5 mmol/L, but no more than 10 mmol/L, based on the colloidal aqueous solution; at least one complexing agent present in no more than an equimolar amount of the alkaline-earth metal ions; and
 wherein total amount of the at least one polymeric organic compounds (a2) in the dispersed particulate constituent of the colloidal aqueous solution is at least 6 wt. %, but does not exceed 15 wt. %, based on the dispersed particulate constituent; and wherein the at least one polymeric organic compounds (a2) of the colloidal aqueous solution contain the polyoxyalkylene units in their side chains, the polyoxyalkylene units being present in an amount of at least at least 50 wt. %, based on total amount of the at least one polymeric organic compound (a2) and the polyoxyalkylene units of the at least one polymeric organic compound (a2) are at least partially end-capped with imidazole and/or imidazoline units.   
     
     
         17 . The method according to  claim 1 , wherein the colloidal aqueous solution is obtained 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 at least one polymeric organic compound additionally comprising polyoxyalkylene units, and   optionally at least one thickener (B) selected from urea urethane resins, the dilution being carried out with water containing at least 0.5 mmol/L of alkaline-earth metal ions dissolved in water.   
     
     
         18 . The method according to  claim 15 , wherein the alkaline-earth metal ions are present in an amount of at least 1.5 mmol/L. 
     
     
         19 . The method according to  claim 1 , wherein the phosphating in method 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; which contains a total of less than 0.1 g/kg of ions of the elements nickel and cobalt.