Resource-saving method for zinc phosphating of a metal surface

Abstract

The present invention relates to a method for zinc phosphating of metal surfaces using a colloidal aqueous solution as activation stage, a zinc phosphate layer having a layer weight of less than 2.0 g/m2 being deposited on surfaces of zinc in the method step following activation. The activation stage is based on a colloidal aqueous solution containing a dispersed particulate constituent, the particulate constituent containing, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, a polymeric organic compound as a dispersing agent that is composed at least partially of styrene and/or an α-olefin having no more than 5 carbon atoms, the polymeric organic compound additionally comprising units of maleic acid, their anhydride and/or their imide and the polymeric organic compound additionally comprising polyoxyalkylene units.

1 . A method for anti-corrosion pretreatment of a metal material that at least partially has surfaces of zinc or of a component that is composed at least partially of such a metal material, in which method the metal material or the component undergoes firstly (i) an activation step and then (ii) a zinc phosphation step, in consecutive method steps,
 wherein the activation step (i) is carried out by contacting the metal material or the component with a colloidal aqueous solution containing (a) a dispersed particulate constituent of the solution comprising:   (a1) at least one particulate inorganic compound that 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 that is composed at least partially of styrene and/or an α-olefin having no more than 5 carbon atoms, the at least one polymeric organic compound additionally comprising units of maleic acid, maleic anhydride and/or the imide thereof and the polymeric organic compound additionally comprising polyoxyalkylene units,   the content of the dispersed particulate constituents of the colloidal aqueous solution being at least 4 g/kg based on the colloidal aqueous solution; and   a zinc phosphate layer having a layer weight of less than 2.0 g/m 2  being deposited on the surfaces of zinc in method step (ii).   
     
     
         2 . The method according to  claim 1 , wherein the colloidal aqueous solution contains condensed phosphates dissolved in water, calculated as the element P, in an amount less than 100 mg/kg. 
     
     
         3 . The method according to  claim 1  wherein the colloidal aqueous solution in the activation step (i) has an alkaline pH. 
     
     
         4 . The method according to  claim 1 , wherein phosphates, calculated as PO 4 , contained in the at least one particulate inorganic compound (a1), based on the dispersed inorganic particulate constituent of the colloidal aqueous solution, are present in an amount of at least 25 wt. %. 
     
     
         5 . The method according to  claim 1 , wherein the polymeric organic compounds (a2) of the colloidal aqueous solution contain the polyoxyalkylene units in their side chains, wherein content of polyoxyalkylene units in in total of the polymeric organic compounds (a2) is at least 40 wt. %. 
     
     
         6 . The method according to  claim 1 , wherein the organic polymeric compounds (a2) of the colloidal aqueous solution also have imidazole units, optionally at least some of the polyoxyalkylene units of the polymeric organic compounds (a2) are end-capped with an imidazole group. 
     
     
         7 . The method according to  claim 1 , wherein the colloidal aqueous solution contains at least one thickener as a further component b), which is selected from urea urethane resins, having an amine value of less than 8 mg KOH/g. 
     
     
         8 . The method according to  claim 1 , wherein a total of polymeric organic compounds in and based on the particulate constituent of the colloidal aqueous solution is at least 3 wt. % and does not exceed 15 wt. %. 
     
     
         9 . The method according to  claim 1 , wherein the colloidal aqueous solution has a D50 value<1 μm. 
     
     
         10 . The method according to  claim 1 , wherein the content of the particulate constituents of the colloidal aqueous solution is at least 6 g/kg but no more than 20 g/kg, in each case based on the colloidal aqueous solution. 
     
     
         11 . 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 contains   (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 that is composed at least partially of styrene and/or an α-olefin having no more than 5 carbon atoms, wherein the polymeric organic compound additionally has units of maleic acid, its anhydride and/or its imide and the polymeric organic compound additionally comprises polyoxyalkylene units, and
 optionally at least one thickener selected from urea urethane resins having an amine value of less than 5 mg KOH/g. 
   
     
     
         12 . The method according to  claim 1  wherein a zinc phosphate layer having a layer weight of less than 1.8 g/m 2  is deposited on the surfaces of zinc in method step (ii). 
     
     
         13 . The method according to  claim 1 , wherein the zinc phosphation in method step (ii) is carried out by contact with an acidic aqueous composition containing free fluoride, 5-50 g/kg of phosphates dissolved in water, calculated as PO 4 , 0.3-3 g/kg of zinc ions and contains a total of less than 0.1 g/kg of ions of the elements nickel and cobalt. 
     
     
         14 . The method according to  claim 1 , wherein components that are treated, comprise surfaces of iron and/or aluminum, in addition to the surfaces of zinc; and a zinc phosphate layer having a layer weight of less than 2.0 g/m 2  is deposited on all surfaces of zinc, iron and aluminum in method step (ii).