Multi-stage treatment for activated zinc phosphating of metallic components

Abstract

Processes for the anti-corrosion pre-treatment of a plurality of components in series, in which each component in the series at least partly has surfaces of zinc and/or iron and at least parts of these surfaces are firstly activated in a targeted manner for subsequent zinc phosphating are provided with targeted activation achieved by means of controlled dispensing of an aqueous dispersion to wet zinc and/or iron surfaces, thus ensuring resource-saving activation; the aqueous dispersion for activation wetting contains a particulate constituent dispersed in water, which is at least partially composed of hopeite, phosphophyllite, scholzite and/or hureaulite and provided as a dispersion of these crystalline solids, stabilized by at least one polymeric organic compound; followed by a zinc phosphating bath comprising a quantity of an aqueous dispersion, in particular the same aqueous dispersion that is used for activation wetting.

Claims: 
     
         1 . A process for the anti-corrosion pretreatment of a plurality of components in series, wherein each component in the series at least partly has surfaces of zinc and/or iron and first undergoes a process step (i) for activating zinc and/or iron surfaces and immediately after a process step (ii) for zinc phosphating, wherein, in process step (i), at least the zinc and/or iron surfaces of each component in the series are brought into contact with an aqueous dispersion containing a water-dispersed particulate component (P), which comprises
 at least one particulate inorganic compound (P1) 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 (P2), wherein this contact is made by dispensing the aqueous dispersion from a supply such that no more than 1.00 liter of the aqueous dispersion is dispensed per square meter of the surface of each component of the series, to be brought into contact with said dispersion, and wherein, in process step (ii), at least the zinc and/or iron surfaces of each component in the series are brought into contact with an acidic aqueous composition having a free acid in points greater than zero, and   (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, wherein the phosphates are at least partly selected from hopeite, phosphophyllite, scholzite and/or hureaulite,   wherein the acidic aqueous composition is obtained by adding an amount of an aqueous dispersion to an acidic aqueous composition containing the components (A)-(C), wherein the aqueous dispersion contains a water-dispersed particulate constituent (P), which comprises   at least one particulate inorganic compound (P1) 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 (P2).   
     
     
         2 . The process according to  claim 1 , wherein the process of bringing at least the zinc and/or iron surfaces of the components into contact with said dispersion in process step (i) is carried out by dispensing the aqueous dispersion from a supply such that no more than 0.50 liter of the aqueous dispersion are dispensed per square meter of the surface of a component in the series. 
     
     
         3 . The process according to  claim 1 , wherein the aqueous dispersion to be brought into contact with said surfaces in process step (i) is dispensed as a spray mist or as a liquid film such that at least the zinc and/or iron surfaces are covered by a liquid film containing the aqueous dispersion, wherein a volume-related coating per square meter of no more than 0.20 liter, results on the zinc and/or iron surfaces. 
     
     
         4 . The process according to  claim 1 , wherein, in process step (i) and/or process step (ii), the aqueous dispersion further comprises at least one thickener selected from urea urethane resins, optionally having an amine value of less than 8 mg KOH/g. 
     
     
         5 . The process according to  claim 1 , wherein, in process step (i) and/or in process step (ii), the polymeric organic compound (P2) in the particulate constituent (P) of the aqueous dispersion is at least partly composed of styrene and/or an α-olefin having no more than 5 carbon atoms, wherein the polymeric organic compound (P2) additionally has units selected from maleic acid, maleic anhydride, maleic imide and combinations thereof; wherein (P2) further comprises polyoxyalkylene units. 
     
     
         6 . The process according to  claim 5 , wherein the polymeric organic compound (P2) in the particulate constituent (P) of the aqueous dispersion comprises maleic acid-styrene copolymer modified with polyoxyalkylene units selected from ethylene oxide units, propylene oxide units and combinations thereof. 
     
     
         7 . The process according to  claim 5 , wherein the proportion of polyoxyalkylene units in all the polymeric organic compounds (P2) does not exceed 70 wt. %. 
     
     
         8 . The process according to  claim 1 , wherein, in process step (i) and/or process step (ii), the proportion of phosphates, calculated as PO 4 , contain in the at least one particulate inorganic compound (P1), in relation to the dispersed inorganic particulate constituent of the aqueous dispersion, is at least 35 wt. %. 
     
     
         9 . The process according to  claim 1 , wherein, in process step (i) and/or process step (ii), the aqueous dispersion contains at least one thickener as a further component. 
     
     
         10 . The process according to  claim 1 , wherein the water-dispersed, particulate constituent (P) of the aqueous dispersion in process step (i) amounts to at least 0.060 g/kg, but no more than 5.0 g/kg, in relation to the aqueous dispersion. 
     
     
         11 . The process according to  claim 1 , wherein the aqueous dispersion in method step (i) for activating the zinc surfaces has a pH value above 6.0 and does not exceed a pH value of 9.0. 
     
     
         12 . The process according to  claim 1 , wherein, in process step (ii), such an amount of the aqueous dispersion is added that the weight proportion of the phosphates of the water-dispersed particulate constituent (D) is, based on the acidic aqueous composition, at least 0.1 mg/kg. 
     
     
         13 . The process according to  claim 1 , wherein the acidic aqueous composition for zinc phosphating in process step (ii) has a pH value below 3.6, wherein the free acid is greater than 0.5 points. 
     
     
         14 . The process according to  claim 1 , wherein the components in the series at least partly have zinc surfaces, iron surfaces, aluminum surfaces or a combination of two or more of said surfaces. 
     
     
         15 . A process for the anti-corrosion pretreatment of a plurality of components in series, wherein each component in the series at least partly has surfaces of zinc and/or iron and first undergoes a process step (i) for activating zinc and/or iron surfaces and immediately after a process step (ii) for zinc phosphating, wherein, in process step (i), at least the zinc and/or iron surfaces of each component in the series are brought into contact with an aqueous dispersion containing a water-dispersed particulate component (P), which comprises
 at least one particulate inorganic compound (P1) 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 (P2),   wherein this contact is made by dispensing the aqueous dispersion from a supply such that no more than 1.00 liter of the aqueous dispersion is dispensed per square meter of the zinc and/or iron surfaces of each component of the series, to be brought into contact with said dispersion, and wherein, in process step (ii), at least the zinc and/or iron surfaces of each component in the series are brought into contact with an acidic aqueous composition having a free acid in points greater than zero, and   (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, wherein the phosphates are at least partly selected from hopeite, phosphophyllite, scholzite and/or hureaulite,   wherein the acidic aqueous composition is obtained by adding an amount of an aqueous dispersion to an acidic aqueous composition containing the components (A)-(C), wherein the aqueous dispersion contains a water-dispersed particulate constituent (P), which comprises   at least one particulate inorganic compound (P1) 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 (P2);   wherein, in process step (i) and/or process step (ii), the proportion of phosphates, calculated as PO 4 , contain in the at least one particulate inorganic compound (P1), in relation to the dispersed inorganic particulate constituent of the aqueous dispersion, is at least 25 wt. %.   
     
     
         16 . The process according to  claim 15 , wherein the process of bringing at least the zinc and/or iron surfaces of the components into contact with said dispersion in process step (i) is carried out by dispensing the aqueous dispersion from a supply such that no more than 0.20 liter, of the aqueous dispersion are dispensed per square meter of the zinc and/or iron surfaces of the components in the series to be activated, which surfaces are to be brought into contact with said dispersion and the aqueous dispersion is dispensed in process step (i) as a spray mist. 
     
     
         17 . The process according to  claim 15 , wherein the aqueous dispersion to be brought into contact with said surfaces in process step (i) is dispensed such that at least the zinc and/or iron surfaces are covered by a liquid film containing the aqueous dispersion, wherein a volume-related coating per square meter of no more than 0.50 liter, results on the zinc and/or iron surfaces. 
     
     
         18 . The process according to  claim 15 , wherein, in process step (i) and/or in process step (ii), the polymeric organic compound (P2) in the particulate constituent (P) of the aqueous dispersion is at least partly composed of styrene and/or an α-olefin having no more than 5 carbon atoms, wherein the polymeric organic compound (P2) additionally has units selected from polyoxyalkylene units, maleic acid units, maleic acid anhydride units, maleic acid imide units and mixtures thereof, optionally further comprising imidazole units. 
     
     
         19 . The process according to  claim 18 , wherein, the proportion of polyoxyalkylene units in all the polymeric organic compounds (P2) is at least 40 wt. %; and at least some of the polyoxyalkylene units are present in side chains, which are at least partially end-capped with aliphatic alkyl groups having no more than four carbon atoms. 
     
     
         20 . The process according to  claim 15 , wherein, in process step (i) and/or process step (ii), the aqueous dispersion contains at least one thickener as a further component. 
     
     
         21 . The process according to  claim 20 , wherein the water-dispersed, particulate constituent (P) of the aqueous dispersion in process step (i) amounts to at least at least 0.100 g/kg, but no more than 5.0 g/kg, in relation to the aqueous dispersion. 
     
     
         22 . The process according to  claim 20  wherein, in process step (ii), such an amount of the aqueous dispersion is added that the weight proportion of the phosphates of the water-dispersed particulate constituent (D) is, based on the acidic aqueous composition, at least 0.5 mg/kg.