One-stage process for zinc phosphating

Abstract

The present invention relates to a process for anticorrosion pretreatment of multiple components in series, each component in the series at least partly comprises metal surfaces of zinc, iron and/or aluminum and undergoes a zinc phosphating step in which the component is contacted with an acidic aqueous composition containing an amount of an activating aid sufficient to ensure a layer weight below 5.5 g/m2 on a cleaned, untreated hot-dip galvanized steel surface (Z), wherein the activating aid is based on a water-dispersed particulate constituent at least partly selected from hopeite, phosphophyllite, scholzite and/or hureaulite, and at least one polymeric organic compound; and further relates to acidic aqueous zinc phosphating compositions obtainable by adding a particular amount of a colloidal aqueous solution containing the dispersed particulate constituent to an acidic aqueous composition containing zinc ions, phosphate ions and free fluoride.

1 . A process for anticorrosion pretreatment of a multitude of components in series, in which each component of the series at least partly has surfaces of the metals zinc, iron and/or aluminum and undergoes a zinc phosphating process step comprising contacting the surfaces of the metals with an acidic aqueous composition containing:
 (A) 5-50 g/kg of phosphates dissolved in water, calculated as PO 4 ,   (B) 0.3-3 g/kg of zinc ions, and   (C) free fluoride,   and having a free acid in points greater than zero,   
       wherein, in the zinc phosphating process step, an activating aid (D) is added continuously or discontinuously to the acidic aqueous composition in an amount that is sufficient, under selected conditions of the zinc phosphating process step, to maintain deposition by the acidic aqueous composition of a zinc phosphate layer having a layer weight of less than 5.5 g/m 2  on a hot-dip galvanized steel surface (Z), 
       the activating aid (D) containing a particulate constituent (a) in water-dispersed form, which constituent comprises:
 at least one particulate inorganic compound (a1) composed of phosphates of polyvalent metal cations at least partly selected from hopeite, phosphophyllite, scholzite and/or hureaulite, 
 and at least one polymeric organic compound (a2). 
 
     
     
         2 . The process according to  claim 1 , wherein the polymeric organic compound (a2) is at least partly composed of styrene and/or an α-olefin having no more than 5 carbon atoms, the polymeric organic compound (a2) additionally having units of maleic acid, its anhydride and/or its imide, and optionally additionally having polyoxyalkylene units in side chains of the polymeric organic compound (a2). 
     
     
         3 . The process according to  claim 2 , wherein the polymeric organic compound (a2) in the particulate constituent (a) of the activating agent (D) additionally has imidazole units. 
     
     
         4 . The process according to  claim 2 , wherein a portion of the polyoxyalkylene units present in the polymeric organic compounds (a2) are at least partly end-capped with an imidazole group. 
     
     
         5 . The process according to  claim 1 , wherein the proportion of polyoxyalkylene units in the polymeric organic compounds (a2) is at least 40 wt. % and does not exceed 70 wt. %. 
     
     
         6 . The process according to  claim 1 , wherein proportion of phosphates, calculated as PO 4 , contained in the at least one particulate inorganic compound (a1), based on the dispersed inorganic particulate constituent (a1) of the activating agent (D), is at least 25 wt. %. 
     
     
         7 . The process according to  claim 1 , wherein the activating agent (D) further comprises at least one thickener (b) selected from urea urethane resins. 
     
     
         8 . The process according to  claim 7 , wherein the urea urethane resins of (b) have an amine value of less than 8 mg KOH/g. 
     
     
         9 . The process according to  claim 1 , wherein a total amount of the polymeric organic compounds (a2) in and based on the particulate constituent (a) of the activating agent (D) is at least 3 wt. %, but does not exceed 15 wt. %. 
     
     
         10 . The process according to  claim 1 , wherein the acidic aqueous composition for zinc phosphating has a pH below 3.6, and a free acid greater than 0.5 points. 
     
     
         11 . The process according to  claim 1 , wherein the acidic aqueous composition for zinc phosphating contains a source of free fluoride and at least 10 mg/kg, but no more than 200 mg/kg of free fluoride. 
     
     
         12 . The process according to  claim 1 , wherein the acidic aqueous composition contains an accelerator selected from 2-hydroxymethyl-2-nitro-1,3-propanediol, nitroguanidine, N-methylmorpholine-N-oxide, nitrite, hydroxylamine and hydrogen peroxide. 
     
     
         13 . The process according to  claim 12 , wherein the accelerator is nitroguanidine or hydroxylamine. 
     
     
         14 . The process according to  claim 1 , wherein, before contacting with the acidic aqueous composition in the zinc phosphating process step, the components of the series:
 (A) are not contacted with a colloidal, aqueous solution containing, in the particulate constituent, hopeite, phosphophyllite, scholzite and/or hureaulite; phosphates of polyvalent metal cations, or sparingly soluble salts of the element Ti; and/or   (B) are not contacted with a colloidal aqueous solution for activating the surfaces of the particulate constituents for zinc phosphating; and/or   (C) do not go through an activation stage for activating the surfaces of the components for zinc phosphating.   
     
     
         15 . The process according to  claim 1 , wherein, before contact with the acidic aqueous composition in the zinc phosphating process step, the components of the series are cleaned and optionally degreased in a cleaning stage. 
     
     
         16 . The process according to  claim 15 , wherein, the components are cleaned by contact in with an aqueous, alkaline cleaning agent, followed by the zinc phosphating process step, with or without an intermediate rinsing step, and the cleaning stage optionally does not include contact with an aqueous, alkaline cleaning agent containing a particulate constituent comprising hopeite, phosphophyllite, scholzite and/or hureaulite or sparingly soluble salts of the element Ti. 
     
     
         17 . The process according to  claim 1 , wherein the components of the series at least partly have hot-dip galvanized steel surfaces, and additionally have surfaces of the metals aluminum and iron. 
     
     
         18 . The process according to  claim 13 , wherein a zinc phosphate layer having a layer weight of at least 1.0 g/m 2 , is deposited on the zinc surfaces. 
     
     
         19 . An acidic aqueous composition for zinc phosphating, which has a free acid in points greater than zero and contains
 (A) 5-50 g/kg of phosphates dissolved in water, calculated as PO 4 ,   (B) 0.3-3 g/kg of zinc ions,   (C) free fluoride, and   (D) a water-dispersed particulate constituent comprising phosphates of polyvalent metal cations, the phosphates at least partly being selected from hopeite, phosphophyllite, scholzite and/or hureaulite,   obtained by adding an amount of an aqueous dispersion to an acidic aqueous composition containing the components (A)-(C),   the aqueous dispersion containing a particulate constituent (a) in water-dispersed form, comprising
 at least one particulate inorganic compound (a1) composed of phosphates of polyvalent metal cations at least partly selected from hopeite, phosphophyllite, scholzite and/or hureaulite, 
 and at least one polymeric organic compound (a2), 
   the aqueous dispersion being added in an amount such that proportion by weight of phosphates from the particulate constituent of the aqueous dispersion, based on the acidic aqueous composition containing components (A)-(C), is at least 0.0005 g/kg.