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.sub.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 -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.sub.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.sub.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.sub.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 -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.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention specifically relates to a process for the anti-corrosion pretreatment of a plurality of components in series, wherein each component in the series at least partly has zinc and/or iron surfaces and first undergoes a process step (i) for activating zinc and/or iron surfaces and immediately afterwards a process step (ii) for zinc phosphating, [0035] 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 [0036] 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, [0037] and at least one polymeric organic compound (P2), are brought into contact, 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, preferably per square meter of the zinc and/or iron surfaces of each component in 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 [0038] (A) 5-50 g/kg of phosphates dissolved in water, calculated as PO.sub.4, [0039] (B) 0.3-3 g/kg of zinc ions, [0040] (C) free fluoride, and [0041] (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 [0042] least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partly selected from hopeite, phosphophyllite, scholzite and/or hureaulite, [0043] and at least one polymeric organic compound (P2).

[0044] A pretreatment in series occurs when the individual components in the series undergo process steps (i) and (ii) of zinc phosphating one after the other, and thus at separate times, in accordance with the process according to the invention and are therefore brought into contact with the corresponding aqueous compositions stored in system tanks in immediate succession, as intended. The system tank in process step (i) is the container in which the aqueous dispersion is held for the purpose of activating the zinc and/or iron surfaces by wetting, and the system tank in process step (ii) is correspondingly the container containing the acidic aqueous composition for zinc phosphating. The components can be brought into contact with the acidic aqueous composition in process step (ii) inside the system tank, for example by immersion, or outside the system tank, for example by spraying-on the bath acidic aqueous composition stored in the system tank. The zinc and/or iron surfaces of each component in the series are brought into contact with the aqueous dispersion in process step (i) by dispensing a defined volume of the dispersion from the supply onto the surfaces to be activated, preferably in such a way that the volume of aqueous dispersion dispensed once for each component is not returned to the system tank holding the dispersion, for example by wetting the surfaces to be activated outside the system tank from where the stored aqueous dispersion is dispensed for each component.

[0045] The components treated according to the present invention can be three-dimensional structures of any shape and design that originate from a manufacturing process, in particular also including semi-finished products such as strips, sheets, rods, pipes, etc., and composite structures assembled from said semi-finished products, the semi-finished products preferably being interconnected by means of adhesion, welding and/or flanging to form a composite structure.

[0046] The process according to the invention is particularly effective for producing compact, closed and crystalline phosphate coatings on the zinc surfaces such that preferred components in the series are those which at least have zinc surfaces. The process according to the invention is also well-suited for the layer-forming phosphating of aluminum such that even components having a mixed construction, e.g. automobile bodies, composed of the materials zinc, iron and aluminum can be phosphated effectively and in a resource-saving manner in accordance with the present invention. However, aluminum surfaces generally do not require pre-activation in process step (i) and sufficient layer formation occurs when the aluminum surfaces are brought into contact with the acidic aqueous composition in process step (ii). In a particular embodiment of the process according to the invention, the components in the series, which at least partially have zinc and/or iron surfaces, additionally also have surfaces of the metal aluminum, wherein the surfaces of the metal aluminum are preferably not brought into contact with the dispensed aqueous dispersion in process step (i) but are brought into contact with the acidic, aqueous composition in process step (ii).

[0047] In the context of the process according to the invention, a component has at least one surface made of zinc and/or iron if more than 50 at. % of the metal structure on this surface, up to a material penetration depth of at least one micrometer, is composed of zinc and/or iron. This frequently applies to components made of corresponding metal materials, insofar as more than 50 at. % of the metal materials are composed of zinc and/or iron as uniform materials. Components comprising surfaces of zinc are, however, also iron materials provided with metallic coatings, such as, for example, electrolytically galvanized or hot-dip galvanized steel, which can also be alloyed with iron (ZF), aluminum (ZA) and/or magnesium (ZM).

[0048] For the resource-saving operation of the corrosion-protective process pre-treatment based on zinc phosphating in step (ii), the invention provides that process step (ii) immediately follows the activation in step (i). In this way, on the one hand, the degree of activation of the zinc and/or iron surfaces of the components for the zinc phosphating stage is maximally maintained and, on the other hand, the zinc phosphating treatment stage is resharpened with essentialsince they have an activating effectparticulate phosphates, since these are introduced into the phosphating stage via the wet film adhering to the component.

[0049] Accordingly, within the context of the present invention, the direct sequence of activation and zinc phosphating provided according to the invention means that the components undergo after the process step (i) without an intermediate rinsing step or other treatment step which either involves further contact, in particular between the zinc or iron surfaces of the components and an aqueous dispersion containing a water-dispersed, particulate constituent (P) in the manner of process step (i) or preferably contact, in particular between the zinc or iron surfaces of the components and an aqueous dispersion for activation for zinc phosphating or particularly preferably contact with an aqueous composition, wherein in each case preferably no drying step is carried out after process step (i) or before process step (ii). A rinsing step in this context can involve one or more immediately successive process steps which serve to remove as completely as possible soluble residues, particles and/or active components which inevitably remain on the surfaces of the components after they have been discharged from previous wet-chemical process steps, for example by rinsing with city water. A drying step in this context is a process of drying the components, caused by controllable technical provisions, for example by supplying heat or by means of a directed air supply.

[0050] A further advantage of the compact, closed and crystalline coatings accessible on all these metal surfaces using the process according to the invention is their excellent electrocoatability, by means of which high wrap-around behavior can be realized. In this respect, it is preferred if step (ii) is followed by electrocoating, particularly preferably cathodic electrocoating. In principle, the process can be accompanied by any kind of coating with an organic topcoat system that is customary in the prior art, in particular a powder coating, since an excellent undercoat is provided.

Process Step (i)Pre-Activation

[0051] The aqueous dispersion is brought into contact in order to activate at least the zinc and/or iron surfaces by dispensing it from a supply. The dispensing of the aqueous dispersion from a supply for the contacting requires, within the meaning of the present invention, the use of a device for removing a volume of liquid from a supply, for example a container which holds a quantity of the aqueous dispersion sufficient for a plurality of components, and a device for dispensing the volume of liquid removed onto the surfaces of one or more components which are to be brought into contact therewith. Consequently the components are not brought into contact in the stored aqueous dispersion, i.e. not by immersion in the stored aqueous dispersion, but, for example, by direct application using rollers or by spraying/misting with a partial volume of the stored aqueous dispersion taken from the supply. Furthermore, according to the invention, the volume of the aqueous dispersion dispensed from the supply for contact is limited and should be less than 1.00 liter per square meter of the surface of the component or preferably only of the zinc and/or iron surfaces of the component. This ensures that a significantly greater liquid volume of the aqueous dispersion is not dispensed than would be required for complete wetting of the zinc and/or iron surfaces with a liquid film of the aqueous dispersion. It is therefore advantageous in principle if the aqueous dispersion is applied to the surfaces to be treated as effectively as possible and without any excess. In a preferred embodiment of the process according to the invention, contact with the zinc and/or iron surfaces is made by dispensing the aqueous dispersion from a supply such that no more than 0.50 liter, preferably no more than 0.20 liter, of the aqueous dispersion is dispensed per square meter of the surfaces of the component, preferably only the zinc and/or iron surfaces of the component that are to be activated and thus brought into contact therewith.

[0052] In this connection, for the surface-area-related volume of the aqueous dispersion dispensed, the surface area of a component in the series is the surface of the polyhedron that has 12 surfaces, preferably 6 surfaces, and is particularly preferably the cuboid which in each case completely encompasses the component and in so doing has the smallest surface area, each surface of the polyhedron touching the component at at least one point. If the component is an automobile body, its surface area in connection with the surface-area-related dispensing of the aqueous dispersion for conditioning purposes is preferably that of the cuboid that has the smallest surface area that completely encompasses the automobile body, each surface of the cuboid touching the automobile body at at least one point. In the preferred embodiment of the process according to the invention, the upper limit for the surface-area-related aqueous dispersion volume dispensed onto the zinc and/or iron surfaces is standardized. The geometric area of the surfaces of the component made of zinc and/or iron to be activated must then be taken into account. In the treatment of flat products such as strip steel, it can therefore be the entire outer surface of the flat product that already needs to be pre-activated in process step (i), whereas, in the series treatment of automobile bodies in the preferred embodiment, only those outer surfaces of the body that are made from strip steel after forming and joining need to be included, since often only these can be optimally phosphated to form layers and thus pre-activated correspondingly.

[0053] The dispensing of the aqueous dispersion for bringing it into contact with, and thus activating, the zinc and/or iron surfaces at the same time requires and demands that the quantity dispensed from the supply also at least partially reaches these surfaces. In a preferred embodiment, the dispensing of the aqueous dispersion for the contact in process step (i) for sufficient activation is therefore carried out so as to ensure that at least the zinc and/or iron surfaces are covered by a liquid film containing the aqueous dispersion, resulting in a volume-related coating of preferably no more than 1.00 liter, particularly preferably no more than 0.50 liter, very particularly preferably no more than 0.20 liter and particularly preferably no more than 0.10 liter per square meter on the zinc and/or iron surfaces. In contrast to the volume of the aqueous dispersion dispensed for the contact, the volume coating here does not refer to the surface of the component approximated by polyhedra but to the actual geometric surface of the zinc and/or iron surfaces of the components in the series, whereby the volume coating can be determined by differential weighing after blowing off the liquid film, assuming a density of the liquid adhering to the surfaces of 1 g/cm.sup.3 can be determined.

[0054] It should be borne in mind that the components are often already wetted with a liquid film, for example formed by rinsing water from a rinsing step immediately preceding the activation, when they are transferred to the activation stage according to process step (i), before the contact with the zinc and/or iron surfaces then takes place according to the invention by absorption of liquid volumes of the aqueous dispersion in the wet film already adhering to these surfaces. Such a process variant can be particularly advantageous because the active components absorbed by the wet film adhering to the component are better absorbed by the pre-wetted surfaces of the component and then distributed more homogeneously thereon, which in turn promotes uniform activation for the subsequent zinc phosphating step.

[0055] If the device for dispensing and creating contact is alone sufficient to achieve as complete wetting of the zinc and/or iron surfaces to be activated as possible, it may again be advantageous for reasons of efficiency to remove the wet film adhering to the components from previous treatment steps immediately before process step (i) or immediately before the zone in which the aqueous dispersion is dispensed for bringing it into contact with the surfaces, for example by blowing off or wiping, in order to use as efficiently as possible only those aqueous dispersions whose particulate content is relatively low but still just enough to bring about the desired activation.

[0056] Whether or not a liquid film containing the aqueous dispersion is formed on the zinc and/or iron surfaces in process step (i) can be checked by means of fluorescent markers added to the aqueous dispersion supply. The detection can then be carried out by irradiation with UV light and correspondingly recording the fluorescence by means of suitable cameras, which make possible an imaging control of the wetting of the component surfaces with the aqueous dispersion. This is particularly helpful when components with complex surface geometries have to be pre-treated and the type of dispensing of the aqueous dispersion, e.g. the relative orientation and spacing of a spray lance with respect to the component, first has to be adjusted in an iterative process in such a way that the zinc and/or iron surfaces are brought into contact with the aqueous dispersion, in particular in such a way that these surfaces are covered with a liquid film containing the aqueous dispersion. The latter preferred condition does not have to be directly fulfilled by bringing the aqueous dispersion from the supply into contact with the surfaces, i.e. directly by the application device, but it is sufficient if, for example by rotating, pivoting or tilting the components, a liquid film containing the aqueous dispersion that is in contact with the zinc and/or iron surfaces is produced before process step (ii), i.e. before the components are introduced into the zinc phosphating process, preferably at least 5 seconds, particularly preferably at least 10 seconds, very particularly preferably at least 20 seconds, before bringing them into contact with the acidic aqueous composition in process step (ii).

[0057] For the controlled dispensing of the aqueous dispersion required in the process according to the invention for the activation wetting of the zinc and/or iron surfaces, it is advantageous and therefore further preferred if in process step (i) the aqueous dispersion is dispensed as a spray, as a spray mist or as a liquid film, particularly preferably as a spray and/or spray mist, particularly preferably as a spray mist. The aqueous dispersion is brought into contact with the surfaces of the component to be activated as a spray and/or spray mist by means of spraying and misting processes established in the prior art and can be carried out in a locally limited manner by means of a spraying lance, and/or in a manner encompassing the component, at least in part, by means of a spraying ring in which a plurality of atomizer nozzles can be installed. The spraying devices to be used for the dispensing of a spray and/or spray mist are, for example, pressure atomizers, rotary atomizers or two-substance atomizers. A liquid film can be applied to the component by direct application by means of rollers, cloths, brushes, paint brushes or similar tools for applying liquids, depending on the complexity and geometry of the components in the series.

[0058] Preferred controlled and efficient activation wetting with the aqueous dispersion is achieved by setting a spray that is targetedly directed at the zinc and/or iron surfaces to be wetted and/or by providing a spray mist through which the component is transported together with the conveyor frame and which, at a given volume flow, is realized over such a transport path that the surfaces of the component to be wetted are preferably exposed to a closed liquid film containing the aqueous dispersion before the component is brought into contact with the acidic aqueous composition for zinc phosphating in the process step (ii) that immediately follows.

[0059] For example, in order to dispense, for example, as much aqueous dispersion as is necessary for forming a liquid film that covers the surfaces of the component and thus for effective activation wetting, it is preferred according to the invention for the dispersion dispensed as the spray and/or the spray mist in process step (i) to have a mean droplet size of less than 100 m, particularly preferably of less than 60 m, particularly preferably of less than 40 m. In the case of average droplet sizes below 40 m, the aqueous dispersion is atomized so strongly that the boundary region to aerosols is exceeded and a spray mist is formed. If the aqueous dispersion is further atomized and the average droplet size is reduced, the droplets will increasingly be held in suspension and not follow gravity. The spray mist held in suspension is then also moved and possibly swirled due to the air masses displaced while the component is being transported through the spray chamber, and therefore a directed impact on the zinc and/or iron surfaces to be activated is more likely to be thwarted and the component surfaces are less evenly wetted by a liquid film. It is therefore preferred if the dispensed aqueous dispersion in process step (i) has a mean droplet size of not less than 5 m, particularly preferably of not less than 10 m.

[0060] It is also advantageous for the formation of a closed liquid film containing the aqueous dispersion on the surfaces of the components to be contacted if the spray and/or spray mist of the aqueous dispersion is dispensed in such a way that the average speed of the liquid droplets which have the average droplet size is less than 5 m/s, preferably less than 2 m/s, and particularly preferably less than 1 m/s. This applies in particular to sprays and/or spray mists whose average droplet size is less than 100 m, particularly preferably less than 60 m, particularly preferably less than 40 m.

[0061] According to the invention, the average droplet size and average speed of the droplets of a spray or spray mist is determined at the location of the geometric center of gravity of the polyhedron surrounding the component, which is also used for determining the quantity of the agent that is dispensed per surface area of the component, as described above. The determination can be carried out by means of light scattering and the phase Doppler anemometry.

[0062] By means of the preferred embodiments mentioned here regarding how the aqueous dispersion can be dispensed for bringing it into contact with at least the zinc and/or iron surfaces, an extremely efficient process is available in which the amount of aqueous dispersion dispensed from the supply is essentially only applied to the zinc and/or iron surfaces of the components that are to be activated. At the same time, the proportion of the aqueous dispersion introduced by the component into the zinc phosphating treatment stage serves to at least partially compensate for the particulate proportion of the acidic aqueous composition for zinc phosphating that is consumed during the activated zinc phosphating process and removed from the zinc phosphating treatment stage. For the same purpose, in process step (i), the proportion of the aqueous dispersion components which are dispensed but do not remain on the component can also be combined and transferred to the zinc phosphating treatment stage in order to maintain the activation performance. Accordingly, a process is preferred according to the invention in which the proportions of the aqueous dispersion which are dispensed in process step (i) to be brought into contact with at least the zinc and/or iron surfaces of the components, but which do not remain on the component as a wet film until they are brought into contact with the acidic aqueous composition for zinc phosphating in process step (ii), because they sink to the bottom as excess spray, for example, or run off the component and thus remain in the spray chamber in process step (i), are at least partially combined and added to the acidic aqueous composition in process step (ii), and in any case are preferably neither partially nor completely returned to the supply.

[0063] For a sufficient pre-activation of at least the zinc and/or iron surfaces of the components in the series, it is necessary for the aqueous dispersion used to contain a water-dispersed, particulate constituent (P) composed of phosphates of polyvalent metal cations (P1) and a polymeric organic compound (P2) contributing to stabilizing the dispersion.

[0064] It should be emphasized as this point that the preferred proportion of phosphates, calculated as PO.sub.4, contained in the at least one particulate inorganic compound (P1) is, based on the dispersed inorganic particulate constituent (P1) of the aqueous dispersion, at least 25 wt. %, particularly preferably at least 35 wt. %, particularly preferably at least 40 wt. %, very particularly preferably at least 45 wt. %. Further preferred embodiments of the inorganic particulate constituent (P1) can, as already explained, be taken from the corresponding preferred embodiments of the inorganic particulate constituent (P1) of the aqueous dispersion in process step (ii).

[0065] It should also be emphasized that, for excellent dispersion stability, the polymeric organic compound (P2) in the particulate constituent (P) of the aqueous dispersion is at least partly composed of styrene and/or an -olefin having no more than 5 carbon atoms, wherein the polymeric organic compound (P2) additionally has units of maleic acid, its anhydride and/or its imide, and preferably additionally polyoxyalkylene units, particularly preferably polyoxyalkylene units in its side chains which are in turn preferably at least partially end-capped with aliphatic alkyl groups having no more than four carbon atoms. Furthermore, it is particularly advantageous if the polymeric organic compound (P2) in the particulate component (P) of the aqueous dispersion additionally comprises imidazole units. The proportion of polyoxyalkylene units in the polymeric organic compounds (P2) as a whole is preferably at least 40 wt. %, particularly preferably at least 50 wt. %, but is preferably not above 70 wt. %. Further preferred embodiments of the polymeric organic compound (P2) can, as already explained, be taken from the corresponding preferred embodiments of the polymeric organic compound (P2) of the aqueous dispersion in process step (ii).

[0066] Besides and in addition to the aforementioned embodiments of the particulate component (P) of the aqueous dispersion in process step (i), the presence of a thickener is advantageous for providing a stable dispersion which can be stored in the system tank of process step (i) over a relatively long period of time. In a preferred embodiment of the process according to the invention, the aqueous dispersion in process step (i) therefore contains at least one thickener as a further component, which is preferably selected from urea urethane resins, particularly preferably from urea urethane resins which have an amine value of less than 8 mg KOH/g, preferably of less than 5 mg KOH/g, particularly preferably of less than 2 mg KOH/g, Further preferred embodiments of the thickener are described in connection with the aqueous dispersion added in process step (ii) of zinc phosphating, which are also advantageous and also included here as preferred embodiments with regard to the aqueous dispersions used for pre-activation.

[0067] Further preferred embodiments of the aqueous dispersion containing the water-dispersed, particulate constituent (P) used in step (i) according to the invention can be found in the description of particularly suitable activating aids.

[0068] The extent to which the zinc and/or iron surfaces are pre-activated can be controlled by the particulate proportion of the aqueous dispersion that is dispersed in water. It has been found that the zinc and/or iron surfaces are pre-activated particularly reliably during typical activation times, i.e. a duration of contact in the range of 5 to 120 seconds, when the particulate proportion (P) is at least 0.060 g/kg in relation to the aqueous dispersion. Short activation times can be compensated for by higher proportions of the particulate proportion (P) so that overall it is advantageous if the water-dispersed, particulate constituent (P) of the aqueous dispersion in process step (i) is at least 0.060 g/kg, particularly preferably at least 0.100 g/kg. Significantly higher contents are associated with higher economic outlay, which is not rendered worthwhile by a significant improvement in the compactness of the zinc phosphate coatings that are then achieved, and are also often not required for resharpening the proportion of particulate constituents in the acidic, aqueous composition for zinc phosphating by carryover, thus counteracting the intention of the present invention to establish a particularly resource-efficient zinc phosphating process. Accordingly, it is preferred for the water-dispersed, particulate constituent (P) of the aqueous dispersion in process step (i) to be no more than 5.0 g/kg, particularly preferably no more than 1.0 g/kg in relation to the aqueous dispersion.

[0069] The pH value of the aqueous dispersion for pre-activation is preferably set such that pickling of the metal materials of the components, in particular the components made of zinc, iron or aluminum, is avoided. Accordingly, it is preferred if the aqueous dispersion in process step (i) for activating the zinc surfaces has a pH value above 6.0, particularly preferably above 6.5, but preferably does not exceed a pH value of 9.0, particularly preferably 8.5, very particularly preferably 8.0 and particularly preferably 7.5.

Process Step (ii)Activated Zinc Phosphating

[0070] In process step (ii), according to the invention, the zinc phosphating of at least the zinc and/or iron surfaces of the components in the series that are pre-activated in process step (i) is carried out by means of an acidic, aqueous composition, which in turn activates the growth of a highly compact, closed but crystalline zinc phosphate layer, and for this purpose, also like the aqueous dispersion in pre-activation, contains a dispersed particulate constituent. In addition to this activating particulate component (D) comprising phosphates of polyvalent metal cations which are at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, the acidic, aqueous composition contains the following for the formation of a zinc phosphate layer: [0071] (A) 5-50 g/kg of phosphates dissolved in water, calculated as PO.sub.4, [0072] (B) 0.3-3 g/kg of zinc ions, and [0073] (C) free fluoride, wherein the zinc phosphating composition is adjusted to have a free acid in points greater than zero.

[0074] The acidic, aqueous zinc phosphating is thus provided for activating the growth of a crystalline phosphate coating on the zinc and/or surfaces iron due to its particulate constituent (D) and is obtainable as such by appropriate addition of an amount of an aqueous dispersion to an acidic, aqueous composition containing the aforementioned components (A)-(C).

[0075] This aqueous dispersion intended for addition to an acidic aqueous composition containing components (A)-(C) contains a particulate constituent (P) in water-dispersed form, which [0076] 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, [0077] and at least one polymeric organic compound (P2), wherein the aqueous dispersion for the provision of the acidic, aqueous composition for zinc phosphating in process step (ii) is preferably added in such an amount that the weight proportion of the phosphates of the water-dispersed, particulate constituent (D) of the acidic aqueous composition is at least 0.1 mg/kg, particularly preferably at least 0.5 mg/kg, very particularly preferably at least 1.0 mg/kg and particularly preferably at least 2.0 mg/kg, each calculated as a phosphate (PO.sub.4) and in relation to the acidic aqueous composition.

[0078] In a preferred embodiment, which permits a particularly resource-saving and economical operation of the process according to the invention, the components in the series are brought into contact with an acidic aqueous composition in step (ii) of the process according to the invention, wherein the acidic aqueous composition contains [0079] (A) 5-50 g/kg of phosphates dissolved in water, calculated as PO.sub.4, [0080] (B) 0.3-3 g/kg of zinc ions, and [0081] (C) free fluoride, [0082] and has a free acid in points greater than zero, wherein an amount of the aqueous dispersion containing the particulate constituent (P) is continuously or discontinuously added to the acidic aqueous composition in process step (ii) for zinc phosphating that, under the selected conditions of process step (ii) for zinc phosphating, is sufficient to maintain the property of the acidic aqueous composition of depositing a zinc phosphate layer having a layer weight of less than 4.5 g/m.sup.2, preferably less than 4.0 g/m.sup.2, particularly preferably less than 3.5 g/m.sup.2, very particularly preferably less than 3.0 g/m.sup.2, on a hot-dip galvanized steel surface (Z), wherein the particulate constituent (P) of the aqueous dispersion in the [0083] 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, [0084] and at least one polymeric organic compound (P2).

[0085] In this way, only the required amount of the aqueous dispersion is added to the acidic aqueous composition for zinc phosphating and an overdispensing is systematically avoided.

[0086] In a particularly preferred variant of the process according to the invention, in process step (i) for the pre-activation, for each component such an amount of the activating aid to be brought into contact with the zinc and/or iron surfaces is dispensed that is sufficient, as a wet film remaining on the component and introduced into the subsequent process step (ii) of zinc phosphating, to maintain in the acidic, aqueous composition containing components (A)-(C) a weight proportion of the phosphates of the water-dispersed, particulate component (D) comprising phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite of at least 0.1 mg/kg, particularly preferably at least 0.5 mg/kg, very particularly preferably at least 1.0 mg/kg and particularly preferably at least 2.0 mg/kg, in each case calculated as phosphate (PO.sub.4) and in relation to the acidic aqueous composition.

[0087] Alternatively, in an equally preferred variant, in process step (i) for pre-activation, per component an amount of the activating aid is dispensed for being brought into contact with the zinc and/or iron surfaces that is sufficient as a wet film remaining on the component and introduced into the subsequent process step (ii) of zinc phosphating to set a minimum amount of the water-dispersed, particulate component (D) comprising phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite in the acidic, aqueous composition containing components (A)-(C) that is sufficient to maintain, under the selected conditions of process step (ii) of zinc phosphating, the property of the acidic aqueous composition of depositing a zinc phosphate layer with a layer weight of less than 4.5 g/m.sup.2, preferably less than 4.0 g/m.sup.2, particularly preferably less than 3.5 g/m.sup.2, very particularly preferably less than 3.0 g/m.sup.2, on a hot-dip galvanized steel surface (Z).

[0088] The property preferred according to the invention of the acidic aqueous composition for zinc phosphating of bringing about, in process step (ii), the growth of a zinc phosphate layer on hot-dip galvanized steel surfaces (Z) that has a layer weight below 4.5 g/m.sup.2, preferably below 4.0 g/m.sup.2, particularly preferably below 3.5 g/m.sup.2 and very particularly preferably below 3.0 g/m.sup.2, (hereinafter referred to as the phosphating quality) is to be checked on (Z) substrates that have been cleaned and degreased and are not subjected to any further wet-chemical pre-treatment steps or any rinsing steps before being brought into contact with the acidic aqueous composition of the process according to the invention in step (ii) and after the pre-activation of the zinc surfaces in step (i). Cleaning and degreasing of the (Z) substrates occurs when the (Z) surface has a carbon coating of less than 0.10 g carbon per square meter of the (Z) surface after cleaning and degreasing. The layer thickness of carbon can be determined by pyrolytic decomposition. For this purpose, the (Z) substrate is brought to a substrate temperature (PMT) of 550 C. in an oxygen atmosphere, and the quantity of carbon dioxide released is determined quantitatively by means of infrared sensors as an amount of carbon, for example by means of the analysis device LECO RC-412 Multiphase Carbon Determinator (Leco Corp.).

[0089] In order to check the phosphating quality of the acidic aqueous composition, hot-dip galvanized steel (Z) is thus first cleaned using an alkaline cleaning agent formulated as 2 wt. % Bonderite C-AK 1565 A and 0.2 wt. % Bonderite C-AD 1270 in deionized water (K<1 Scm.sup.1) at a pH of 11.0 and 55 C. for 5 minutes by immersion. The substrates cleaned and degreased (Z) in this way are rinsed with deionized water (K<1 Scm.sup.1) at room temperature and are then supplied to the treatment stages according to process steps (i) and (ii) according to the selected process conditions. According to the selected process conditions means, when the temperature, application duration and bath circulation are the same and the wet-chemical treatment stages intended for the phosphating quality specified as being preferred according to the invention are used, i.e. the resulting target layer weights on hot-dip galvanized steel (Z), are to be below 4.5 g/m.sup.2, preferably below 4.0 g/m.sup.2, particularly preferably below 3.5 g/m.sup.2 and very particularly preferably below 3.0 g/m.sup.2. The phosphating quality can therefore be determined in the current process according to the invention by cleaned and degreased sheets of hot-dip galvanized steel (Z) also being introduced, together with the components in the series, for process steps (i) and (ii), and the layer weight of zinc phosphate on the sheets, and thus the phosphating quality of the acidic aqueous composition for zinc phosphating, then being determined in process step (ii). It should be noted that the outer surfaces of such test sheet metals to be phosphated in process step (i) have formed a complete liquid film containing the aqueous dispersion before contact with the acidic aqueous composition in process step (ii).

[0090] The cleaned and degreased sheets of hot-dip galvanized steel (Z), in their function as test sheets for determining phosphating quality, are preferably rigidly connected to the component or the conveying frame in order to ensure that the flow conditions during transport of the component together with the conveying frame through the phosphating bath are reproduced as similarly as possible for the test sheet. For this purpose, the test sheets should ideally be connected to the component or the conveying frame in such a way that the transport of a test sheet together with the component and the conveying frame, compared to the transport of the component and the conveying frame without such a test sheet, has no influence on the flow conditions that is to be considered, and that the flow conditions are substantially identical in both cases and thus substantially correspond to the flow conditions of at least a portion of the components of the series. This can be achieved, for example, by adapting the size and/or the shape of the test sheet to the size and shape of the component and/or of the conveying frame which is arranged adjacent to the test sheet in each case. It is conceivable in this case, in particular when a test sheet is arranged on an outer surface portion of the component or the conveying frame, for the dimensions of the test component to correspondingly be smaller than those of said surface portion, for example in order to prevent the test component from protruding beyond the surface portion. Alternatively or additionally, the test component may follow a curvature or other planar deviation of the surface portion or the conveying frame. It has proven to be particularly expedient to select a sheet portion that is sufficiently small compared to the size of a suitable outer surface of the component, with an outer surface being particularly suitable if it is located at a location that has a particularly low curvature or at the location that has the lowest curvature of the component, and the test sheet metal then being mounted substantially in parallel so as to be spaced apart along the surface normal of such an outer surface. It is particularly useful and preferred if the test sheet metal is spaced apart along a surface normal with respect to a zinc and/or iron surface of the component in order to ensure in the simplest way possible that in process step (i) a liquid film containing the aqueous dispersion dispensed in said step for being brought into contact with said surfaces is applied without the device for dispensing the aqueous dispersion in process step (i) having to be complexly adapted.

[0091] The phosphating quality is obtained directly during the series treatment of such components, which also have a surface of hot-dip galvanized steel (Z) as the surfaces of zinc. Such components are also preferred in a preferred embodiment of the process according to the invention.

[0092] It is additionally preferred for the phosphating quality that, if the contact is extended by one minute, the layer weight on hot-dip galvanized steel (Z) increases by no more than 0.2 g/m.sup.2, and thus the layer formation under the selected conditions is already in the self-limitation range so that the property of the acidic aqueous composition for zinc phosphating of producing compact crystalline zinc phosphate layers in step (ii) of the process according to the invention is ensured. Accordingly, it is preferred that in the zinc phosphating process step, an amount of the aqueous dispersion containing the particulate constituent (P) is added that, under the selected conditions of the zinc phosphating process step in the process according to the invention, is sufficient to maintain the property of the acidic aqueous composition of depositing a zinc phosphate layer having a layer weight of less than 4.5 g/m.sup.2, preferably less than 4.0 g/m.sup.2, particularly preferably less than 3.5 g/m.sup.2 and very particularly preferably less than 3.0 g/m.sup.2 on a hot-dip galvanized steel surface (Z), wherein the layer weight achieved under the conditions selected for the process step (ii) of zinc phosphating in the process according to the invention increases by no more than 0.2 g/m.sup.2 when the contact time with the acidic aqueous composition is extended by 60 seconds.

[0093] Usually, the phosphating quality is determined and monitored in the process that is preferred according to the invention by hot-dip galvanized steel (Z), which has been cleaned and degreased as described above, also undergoing the zinc phosphating process step at regular intervals during series treatment and then being subjected to layer weight determination. As already mentioned, the phosphating quality is obtained directly during the series treatment of such components, which also have at least one surface of hot-dip galvanized steel (Z) as the surfaces of zinc. Insofar as the phosphating quality of the acidic aqueous composition is ensured by the metered addition of the aqueous dispersion, homogeneous, closed and compact crystalline zinc phosphate coatings are deposited on the components in the series, which have surfaces consisting of the metals zinc and/or iron, at the usual treatment times of 20 seconds to 5 minutes.

[0094] The layer weight of zinc phosphate is determined within the scope of the present invention by removing the zinc phosphate layer using aqueous 5 wt. % CrO.sub.3 as a pickling solution that is brought into contact with a defined area of the phosphated material or component at 25 C. for 5 min immediately following the zinc phosphating and rinsing with deionized water (K<1 Scm.sup.1), and subsequently determining the phosphorus content in the same pickling solution by means of ICP-OES. The layer weight of zinc phosphate can be found by multiplying the surface area-related amount of phosphorus in grams per square meter by a factor of 6.23.

[0095] The addition of the aqueous dispersion containing the particulate component (P) to the acidic aqueous composition for the zinc phosphating process is carried out in the process according to the invention for the purpose of maintaining the phosphating quality in process step (ii). In order to maintain the phosphating quality in the series treatment process, the addition can be made by means of continuous or discontinuous metered addition to the zinc phosphating system tank. Continuous metered addition is preferred if the components are pretreated in series directly one after the other and the decrease in the phosphating quality per time interval can be determined with sufficient accuracy so that a quantity of the activating agent can in turn be continuously added by metering to compensate for the loss in performance. This process has the advantage that, after starting up the pretreatment line and the determination of the material flows for the metered addition of the aqueous dispersion and other active components, the phosphating quality does not have to be checked further as long as the series treatment remains unchanged in terms of timings and quality of the components to be treated and the treatment parameters in the process step (ii) for zinc phosphating. However, if the system does not ensure or require a constant mode of operation during series treatment, discontinuous metered addition of the aqueous dispersion containing the particulate constituent (P) will be advantageous and may even be advisable. In this case, the phosphating quality of the acidic aqueous composition in step (ii) is preferably monitored continuously or at defined time intervals, and a specified amount of the activating aid is then metered-in if the layer weight on hot-dip galvanized steel (Z) no longer reaches a certain value below 4.5 g/m.sup.2, preferably below 4.0 g/m.sup.2, particularly preferably below 3.5 g/m.sup.2 and very particularly preferably below 3.0 g/m.sup.2. The continuous or quasi-continuous determination of the phosphating quality, which takes place at defined time intervals, can also be carried out using proxy data that correlate with the actual zinc phosphate layer weight. The non-destructive determination of the layer thickness, for example using the eddy current process or even contact-free optical determination methods such as ellipsometry or spectral reflectivity measurement, provides suitable proxy data for the layer weight of zinc phosphate, which data can be reliably measured on the surfaces of zinc of the components in a pretreatment line and can be correlated with the actual layer weight on hot-dip galvanized parts steel (Z). The crystallite size and thus the determination of the roughness by means of optical profilometry can also provide proxy data for the layer weight, since a higher layer weight on hot-dip galvanized steel (Z) is associated with a low number density of crystallites, which, however, are relatively larger, so that the roughness increases with the layer weight.

[0096] It has been found that the phosphating quality will have already been sufficiently adjusted in most cases if the aqueous dispersion containing the particulate constituent (P) for activating the zinc phosphating composition is continuously or discontinuously added in an amount that is suitable for producing a steady amount of preferably at least 0.1 mg/kg, particularly preferably at least 0.5 mg/kg, particularly preferably at least 1.0 mg/kg of phosphates contained in the water-dispersed, particulate component (D), in the acidic aqueous composition, in each case calculated as the amount of phosphate (PO.sub.4) and in relation to the acidic aqueous composition during pre-treatment of the components in series. This applies in particular to the contact of the components by immersing them in the zinc phosphating system tank containing the acidic aqueous composition.

[0097] In conjunction with process step (i), which causes pre-activation of the zinc and/or iron surfaces, the activated zinc phosphating in step (ii) can be carried out in a particularly resource-efficient manner and the consumption of active components can be significantly reduced without any loss of phosphating quality. This applies to the added proportion of the aqueous dispersion containing the particulate constituent (P) and, due to the excellent phosphating quality achieved on the zinc and/or iron surfaces, also to the consumption of active components (A)-(C) of the acidic aqueous zinc phosphating composition.

[0098] With regard to the acidic aqueous composition for zinc phosphating, it is imperative for the formation of homogeneous, closed zinc phosphate layers that, in step (ii) of the process according to the invention, said composition contains at least [0099] A) 5-50 g/kg of phosphates dissolved in water, calculated as PO.sub.4, [0100] (B) 0.3-3 g/kg of zinc ions, and [0101] (C) free fluoride, [0102] and a free acid in points greater than zero.

[0103] In this context, the amount of phosphate ions includes orthophosphoric acid and the anions, dissolved in water, of the salts of orthophosphoric acid, calculated as PO.sub.4.

[0104] The proportion of the free acid in points in the acidic aqueous composition for zinc phosphating in step (ii) of the process according to the invention is preferably greater than 0.5, particularly preferably greater than 0.8, very particularly preferably greater than 1.0, but preferably no more than 3.0, particularly preferably no more than 2.0. The proportion of the free acid in points is determined by diluting 10 ml sample volume of the acidic aqueous composition to 60 ml and titrating with 0.1 N sodium hydroxide solution to a pH value of 3.6. The consumption of ml of sodium hydroxide solution indicates the point number of free acid.

[0105] The pH of the acidic aqueous composition is preferably usually below 3.6, particularly preferably below 3.4, very particularly preferably below 3.2, but preferably above 2.5, particularly preferably above 2.7. The pH value, as used in the context of the present invention, corresponds to the negative decadic logarithm of the hydronium ion activity at 20 C. and can be determined by means of pH-sensitive glass electrodes.

[0106] A quantity of free fluoride or a source of free fluoride ions is essential for the layer-forming zinc phosphating process. Insofar as components comprising iron or aluminum surfaces in addition to zinc surfaces are to be zinc-phosphated so as to form layers, as is necessary, for example, in the zinc phosphating of automobile bodies that are at least partially also made of aluminum, it is advantageous if the amount of free fluoride in the acidic aqueous composition in step (ii) is at least 10 mg/kg, particularly preferably at least 40 mg/kg. The concentration of free fluoride should not exceed values above which the phosphate coatings exhibit loose adhesions that can be easily wiped off. For this reason, it is advantageous and thus preferred if, in step (ii) of the process according to the invention, the concentration of free fluoride in the acidic aqueous composition for zinc phosphating is below 300 mg/kg, particularly preferably below 250 mg/kg and particularly preferably below 200 mg/kg.

[0107] The amount of free fluoride is to be determined potentiometrically by means of a fluoride-sensitive measuring electrode at 20 C. in the relevant acidic aqueous composition after calibration with fluoride-containing buffer solutions without pH buffering. Suitable sources of free fluoride ions are hydrofluoric acid and the water-soluble salts thereof, such as ammonium bifluoride and sodium fluoride, as well as complex fluorides of the elements Zr, Ti and/or Si, in particular complex fluorides of the element Si. In a phosphating process according to the present invention, the source of free fluoride is therefore preferably selected from hydrofluoric acid and the water-soluble salts thereof and/or complex fluorides of the elements Zr, Ti and/or Si. Salts of hydrofluoric acid are water-soluble within the meaning of the present invention if their solubility in deionized water (K<1 Scm.sup.1) at 60 C. is at least 1 g/L, calculated as F.

[0108] In order to suppress what is known as pin-holing on the surfaces of the metal materials that are made of zinc, it is preferred, in such processes according to the invention, for the source of free fluoride in step (ii) to be at least partly selected from complex fluorides of the element Si, in particular from hexafluorosilicic acid and the salts thereof. The term pin-holing is understood by a person skilled in the art of phosphating to mean the phenomenon of local deposition of amorphous, white zinc phosphate in an otherwise crystalline phosphate layer on the treated zinc surfaces or on the treated galvanized or alloy-galvanized steel surfaces.

[0109] In the process according to the invention, the accelerators known in the prior art can be added to the acidic aqueous composition for increasing the rate of layer formation. These accelerators are preferably selected from 2-hydroxymethyl-2-nitro-1,3-propanediol, nitroguanidine, N-methylmorpholine-N-oxide, nitrite, hydroxylamine and/or hydrogen peroxide. It can be seen that when nitroguanidine or hydroxylamine is used as the accelerator, a comparatively lower metered addition of aqueous dispersion containing the water-dispersed particulate constituent (P) is necessary for providing the acidic aqueous composition or a lower steady amount of the water-dispersed particulate constituent (P) must be maintained in the acidic aqueous composition for the zinc phosphating process in step (ii) so that nitroguanidine or hydroxylamine, in particular nitroguanidine, is particularly preferred as the accelerator in the acidic aqueous composition in step (ii) of the process according to the invention in terms of a particularly low material use for maintaining the phosphating quality.

[0110] An embodiment in which a total of less than 10 ppm of nickel and/or cobalt ions are contained in the acidic aqueous composition for zinc phosphating in step (ii) of the process according to the invention is particularly preferred from an ecological point of view.

[0111] Furthermore, in the process according to the invention, can also make use of additives well-known in the art in zinc phosphating processes.

[0112] Preferred embodiments of the aqueous dispersion used in step (ii) according to the invention and containing the water-dispersed particulate constituent (P) can be found in the description of particularly suitable activating aids.

Suitable Activating Aids

[0113] The definitions and preferred specifications given below apply to the dispersed particulate constituent (P) of the aqueous dispersion and the at least one particulate inorganic compound (P1) or polymeric organic compound (P2), regardless of whether the dispersed particulate constituent (P) is a constituent of the aqueous pre-activation dispersion in process step (i) or a constituent of the aqueous dispersion for providing the self-activating acidic aqueous composition for zinc phosphating in process step (ii). For the sake of simplicity, reference is made below only to the activating aid instead of the respective aqueous dispersions containing a dispersed constituent (P). The preferred activating aids are characterized in that they have high stability with respect to agglomeration, thus being particularly suitable for the formation of crystalline phosphate coatings and, in particular when used as per the invention, they release a high proportion of activating phosphate particles or provide them for the activation of the zinc and/or iron surfaces so that compact, closed, crystalline coatings with a relatively low layer weight can be achieved particularly reliably in the process according to the invention.

[0114] Activating aids that are used according to the invention, i.e. for the pre-activation in step (i) and for maintaining the phosphating quality or providing the acidic aqueous composition for zinc phosphating in step (ii), are therefore aqueous dispersions containing a particulate constituent (P) in water-dispersed form which comprises at least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, and at least one polymeric organic compound (P2).

[0115] The use of polyvalent metal cations in the form of phosphates is responsible for the good (pre)activation performance, which should therefore be contained in the activating aid with a sufficiently high proportion thereof in the dispersed particulate constituent (P). Accordingly, the proportion of phosphates contain in the particulate inorganic compounds (P1), in relation to the dispersed inorganic constituent of the activating aid, is preferably at least 25 wt. %, particularly preferably at least 35 wt. %, particularly preferably at least 40 wt. %, very particularly preferably at least 45 wt. %.

[0116] The dispersed particulate constituent (P) of the activating aidor also the water-dispersed particulate constituent (D) of the acidic aqueous composition in step (ii) is the solids content that remains after drying the retentate from the ultrafiltration of a defined partial volume of the activating aidor of the acidic aqueous compositionwith a nominal cut-off of 10 kD (NMWC, nominal molecular weight cut-off). Ultrafiltration is carried out by supplying deionized water (K<1 Scm.sup.1) until a degree of conductivity of below 10 Scm.sup.1is measured in the filtrate. The inorganic particulate constituent of the activating aidor the inorganic water-dispersed particulate constituent of the acidic aqueous composition in step (ii)is, in turn, the one that remains when the particulate constituent (P) or (D) obtained from drying the ultrafiltration retentate is pyrolyzed in a reaction furnace by supplying a CO.sub.2-free oxygen flow at 900 C. without adding catalysts or other additives until an infrared sensor provides a signal identical to the CO.sub.2-free carrier gas (blank value) at the outlet of the reaction furnace. The phosphates contained in the corresponding inorganic particulate constituent, calculated as PO.sub.4, are determined by means of atomic emission spectrometry (ICP-OES) after acid digestion thereof with aqueous 10 wt. % HNO.sub.3 solution at 25 C. for 15 min directly from the acid digestion process as phosphorus content multiplied by the factor 3.07.

[0117] As already mentioned, the active components of the activating aid are primarily composed of phosphates, which in turn are at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, preferably at least partially selected from hopeite, phosphophyllite and/or scholzite, particularly preferably at least partially selected from hopeite and/or phosphophyllite and very particularly preferably at least partially selected from hopeite. The achievement of the desired phosphating quality on the zinc and/or iron surfaces in the process according to the invention is substantially based on the phosphates contained in particulate form in the activating aid. Without taking into account water of crystallization, hopeites stoichiometrically comprise Zn.sub.3(PO.sub.4).sub.2 and the nickel-containing and manganese-containing variants Zn.sub.2Mn(PO.sub.4).sub.3, Zn.sub.2Ni(PO.sub.4).sub.3, whereas phosphophyllite consists of Zn.sub.2Fe(PO.sub.4).sub.3, scholzite consists of Zn.sub.2Ca(PO.sub.4).sub.3 and hureaulite consists of Mn3(PO.sub.4).sub.2. The existence of the crystalline phases hopeite, phosphophyllite, scholzite and/or hureaulite in the activating aid can be demonstrated by means of X-ray diffractometric methods (XRD) after separation of the particulate constituent (P) by means of ultrafiltration with a nominal cutoff limit of 10 kD (NMWC: nominal molecular weight cutoff), as described above, and drying of the retentate to constant mass at 105 C.

[0118] Due to the preference for the presence of phosphates comprising zinc ions and having a certain crystallinity, it is preferred for the formation of firmly adhering crystalline zinc phosphate coatings for, in the process according to the invention, the activating aid to contain at least 20 wt. %, particularly preferably at least 30 wt. %, particularly preferably at least 40 wt. %, of zinc in the inorganic particulate constituent, based on the phosphate content of the inorganic particulate constituent, calculated as PO.sub.4.

[0119] However, the activating aid is preferably not intended to additionally contain any titanium phosphates, since these can also have an activating effect as such, but do not have any further positive effect on the phosphating quality within the context of the present invention. In a preferred embodiment of the process according to the invention, the proportion of titanium in the inorganic particulate constituent of the activating aid is therefore less than 0.01 wt. %, particularly preferably less than 0.001 wt. %, in relation to the activating aid. In a particularly preferred embodiment, the activating aid contains a total of less than 10 mg/kg, particularly preferably less than 1 mg/kg, of titanium.

[0120] The polymeric organic compound (P2) that stabilizes the particulate constituent (P) of each dispersion has a major influence on the effectiveness of the activating aid. It appears that the choice of polymeric organic compound is crucial for the degree of the pre-activation of the zinc and/or iron surfaces in process step (i) and the phosphating quality ultimately achieved via the integrated activation in step (ii).

[0121] In the context of the present invention, an organic compound is polymeric if its weight-average molar mass is greater than 500 g/mol. The molar mass is determined using the molar mass distribution curve of a sample of the relevant reference size, which curve is established experimentally at 30 C. by means of size-exclusion chromatography using a concentration-dependent refractive index detector and is calibrated against polyethylene glycol standards. The average molar masses are evaluated with the aid of a computer according to the strip method using a third-order calibration curve. Hydroxylated polymethacrylate is suitable as a column material, and an aqueous solution of 0.2 mol/L sodium chloride, 0.02 mol/L sodium hydroxide, and 6.5 mmol/L ammonium hydroxide is suitable as an eluent.

[0122] A particularly efficient activating aid, which is preferably used in processes according to the invention, is present when the polymeric organic compound (P2) used to disperse the particulate inorganic compound (P1) is at least partly composed of styrene and/or an -olefin having no more than 5 carbon atoms, wherein the polymeric organic compound (P2) additionally comprises units of maleic acid, its anhydride and/or its imide, and preferably additionally polyoxyalkylene units, particularly preferably polyoxyalkylene units in its side chains.

[0123] The -olefin in this case is preferably selected from ethene, 1-propene, 1-butene, isobutylene, 1-pentene, 2-methyl-but-1-ene and/or 3-methyl-but-1-ene and particularly preferably selected from isobutylene. It is clear to a person skilled in the art that the polymeric organic compounds (P2) contain these monomers as structural units in unsaturated form covalently linked to one another or to other structural units.

[0124] Preferred activating aids comprise polymeric organic compounds (P2) that are at least partly composed of styrene.

[0125] The polymeric organic compounds (P2) used for colloidal stabilization of the particulate constituent (P) of the activating aid preferably have polyoxyalkylene units that in turn are preferably composed of 1,2-ethanediol and/or 1,2-propanediol, particularly preferably of both 1,2-ethanediol and 1,2-propanediol, the proportion of 1,2-propanediols in the entirety of the polyoxyalkylene units being preferably at least 15 wt. %, but particularly preferably not exceeding 40 wt. %, based on the entirety of the polyoxyalkylene units. Furthermore, the polyoxyalkylene units are preferably contained in the side chains of the polymeric organic compounds (P2). A proportion of the polyoxyalkylene units in the entirety of the polymeric organic compounds (P2) of preferably at least 40 wt. %, particularly preferably at least 50 wt. %, but preferably no more than 70 wt. %, is advantageous for the dispersibility of said compounds.

[0126] For anchoring the polymeric organic compound (P2) to the inorganic particulate constituent (P1) of the activating aid, which is at least partly formed of polyvalent metal cations in the form of phosphates selected from hopeite, phosphophyllite, scholzite and/or hureaulite, and increased stability and ability of the particulate constituent (P) in order to activate the zinc and/or iron surfaces, the organic polymeric compounds (P2) also have imidazole units, particularly preferably in the side chains of the polymeric compounds (P2).

[0127] In a preferred embodiment, the amine value of the organic polymeric compounds (P2) is at least 25 mg KOH/g, particularly preferably at least 40 mg KOH/g, but preferably less than 125 mg KOH/g, particularly preferably less than 80 mg KOH/g, and therefore, in a preferred embodiment, the entirety of the polymeric organic compounds in the particulate constituent (P) of the activating aid also have these preferred amine values. The amine value is determined in each case by weighing out approximately 1 g of the relevant reference sizeorganic polymeric compounds (P2) or all the polymeric organic compounds in the particulate constituent (P)in 100 ml of ethanol, titration being carried out using 0.1 N HCl titrant solution against the indicator bromophenol blue until the color changes to yellow at an ethanolic solution temperature of 20 C. The amount of HCl titrant solution used in milliliters multiplied by the factor 5.61 divided by the exact mass of the weight in grams corresponds to the amine value in milligrams KOH per gram of the relevant reference value.

[0128] It has also been proven to be advantageous for the polymeric organic compounds (P2), preferably also the entirety of the polymeric organic compounds in the particulate constituent (P), to have an acid number according to DGF C-V 2 (06) (as of April 2018) of at least 25 mg KOH/g, but preferably of less than 100 mg KOH/g, particularly preferably of less than 70 mg KOH/g, to ensure a sufficient number of polyoxyalkylene units. It is also preferred for the polymeric organic compounds (P2), preferably also the entirety of the polymeric organic compounds in the particulate constituent (P), to have a hydroxyl number of less than 15 mg KOH/g, particularly preferably of less than 12 mg KOH/g, more particularly preferably of less than 10 mg KOH/g, determined according to method A of 01/2008:20503 from European Pharmacopoeia 9.0 in each case.

[0129] Suitable commercially available representatives of polymeric organic compounds (P2) are, for example, Dispex CX 4320 (BASF SE), a maleic acid-isobutylene copolymer modified with polypropylene glycol, Tego Dispers 752 W (Evonik Industries AG), a maleic acid-styrene copolymer modified with polyethylene glycol, or Edaplan 490 (Mnzing Chemie GmbH), a maleic acid-styrene copolymer modified with EO/PO and imidazole units.

[0130] For a stable dispersion of the inorganic particulate constituents in the activating aid, it is sufficient for the proportion of the polymeric organic compounds (P2), preferably the entirety of the polymeric organic compounds in the particulate constituent (P), in relation to the particulate constituent (P), to be at least 3 wt. %, particularly preferably at least 6 wt. %, but preferably not exceeding 15 wt. %.

[0131] The activating aid preferably contains no more than 40 wt. % of particulate constituent (P), based on the agent, since otherwise the stability of the dispersion and the operability of the process in process step (i) for pre-activation by wetting using spray devices and process step (ii) for metered addition of the agent to the acidic aqueous composition for zinc phosphating by means of metering pumps are no longer ensured or are at least complex. According to the invention, it has been shown that for the purposes of metered addition to the acidic aqueous composition in process step (ii), both good storage and applicability are achieved when activating aids are used which preferably contain at least 5 wt. %, but particularly preferably no more than 30 wt. %, of particulate constituent (P), in relation to the agent. The activating aid in process step (i), which is used as an aqueous dispersion for wetting the zinc and/or iron surfaces, should, however, preferably be less concentrated for wetting by misting and preferably contains no more than 5 wt. % of particulate constituent (P), the agent, but preferably contains at least 0.005 wt. % of particulate constituent (P), in relation to the agent, for good activation.

[0132] In concentrated aqueous dispersions, i.e. activating aids having a proportion of at least 5 wt. % of particulate constituent (P) in relation to the agent, the agent can additionally be characterized by its D50 value of more than 10 m, which is correspondingly preferred. However, for good applicability, in particular in process step (i), it is preferred if the aqueous dispersion of the particulate constituents (P) has a D90 value of less than 150 m, preferably less than 100 m, in particular less than 80 m. In the context of the present invention, the D50 value or the D90 value denotes the particle diameter that is not exceeded by 50 vol. % or 90 vol. %, respectively, of the particulate constituents contained in the aqueous dispersion. According to ISO 13320:2009, the D50 value or D90 value can be determined from volume-weighted cumulative particle size distributions by means of scattered light analysis according to the Mie theory immediately after dilution of the activating aid to a dispersed particulate constituent of 0.05 wt. % with a corresponding amount of deionized water (K<1 Scm.sup.1) at 20 C., using spherical particles and a refractive index of the scattering particles of nD=1.52i.0.1. The dilution is carried out in such a way that an amount of activating aid corresponding to a volume of 200 ml of deionized water is added to the sample vessel of the LA-950 V2 particle size analyzer from Horiba Ltd., where it is mechanically circulated into the measuring chamber (setting the circulating pump on the LA-950 V2: level 5=1167 rpm for a volume flow of 3.3 liters/minute). The particle size distribution is measured within 120 seconds after the activating aid has been added to the dilution volume.

[0133] The presence of a thickener can be advantageous for preventing the irreversible agglomeration of primary particles of the particulate constituent (P), in particular if the activating aid contains, as described above, at least 5 wt. % of particulate constituent (P), in relation to the agent. Preferably, the activating aid therefore contains a thickener, in turn preferably in an amount which, in the shear rate range of from 0.001 to 0.25 reciprocal seconds, gives the activating aid a maximum dynamic viscosity of at least 1000 Pa.Math.s, but preferably below 5000 Pa.Math.s, at a temperature of 25 C., and preferably leads to shear-thinning behavior, i.e. a decrease in viscosity with increasing shear rate, at 25 C. and at shear rates above those present at the maximum dynamic viscosity, so that the activating aid on the whole has thixotropic flow behavior. The viscosity over the specified shear rate range can in this case be determined by means of a cone and plate viscometer having a cone diameter of 35 mm and a gap width of 0.047 mm.

[0134] Within the meaning of the present invention, a thickener is a polymeric chemical compound or a defined mixture of chemical compounds which, as a 0.5 wt. % constituent in deionized water (K<1 Scm.sup.1) at a temperature of 25 C., has a Brookfield viscosity of at least 100 mPa.Math.s at a shear rate of 60 rpm (=rounds per minute) using a size 2 spindle. When determining this thickener property, the mixture with water should be prepared in such a way that the corresponding amount of the polymeric chemical compound is added to the water phase at 25 C. while stirring and the homogenized mixture is then freed of air bubbles in an ultrasonic bath and left to stand for 24 hours. The measurement value of the viscosity is then read within 5 seconds immediately after application of a shear rate of 60 rpm by the number 2 spindle.

[0135] The activating aid preferably contains a total of at least 0.5 wt. %, but preferably no more than 4 wt. %, particularly preferably no more than 3 wt. %, of one or more thickeners, the total proportion of polymeric organic compounds in the non-particulate constituent of the activating aid further preferably not exceeding 4 wt. % (in relation to the agent). The non-particulate constituent is the solids content of the relevant aqueous dispersion or the activating aid in the permeate of the aforementioned ultrafiltration after it has been dried until it has a constant mass at 105 C., i.e. the solids content after the particulate constituent has been separated by means of ultrafiltration.

[0136] Certain classes of polymeric compounds are particularly suitable thickeners and are also readily commercially available. Thus, the thickener is preferably selected from polymeric organic compounds, which, in turn, are preferably selected from polysaccharides, cellulose derivatives, aminoplasts, polyvinyl alcohols, polyvinylpyrrolidones, polyurethanes and/or urea urethane resins, and particularly preferably from urea urethane resins, in particular urea urethane resins that are a mixture of polymeric compounds resulting from the reaction of a polyvalent isocyanate with a polyol and a mono- and/or diamine. In a preferred embodiment, the urea urethane resin results from a polyvalent isocyanate, preferably selected from 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2(4),4-trimethyl-1,6-hexamethylene diisocyanate, 1,10-decamethylene diisocyanate, 1,4,-cyclohexylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 2,6-toluene diisocyanate, 2,4-toluene diisocyanate and mixtures thereof, p-and m-xylylene diisocyanate, and 4-4-diisocyanatodicyclohexylmethane, particularly preferably selected from 2,4-toluene diisocyanate and/or m-xylylene diisocyanate. In a particularly preferred embodiment, the urea urethane resin results from a polyol selected from polyoxyalkylene diols, particularly preferably from polyoxyethylene glycols, which in turn are preferably composed of at least 6, particularly preferably at least 8, more particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23, oxyalkylene units.

[0137] Urea urethane resins that are particularly suitable and therefore preferred according to the invention can be obtained by first reacting a diisocyanate, for example toluene-2,4-diisocyanate, with a polyol, for example a polyethylene glycol, to form NCO-terminated urethane prepolymers, followed by further reaction with a primary monoamine and/or with a primary diamine, for example m-xylylenediamine. Urea urethane resins that have neither free nor blocked isocyanate groups are particularly preferred. Such urea urethane resins, as a constituent of the activating aid, promote the formation of loose agglomerates of primary particles which are protected against further agglomeration and dissociate into primary particles when diluted, e.g. during the contact in step (i), or when added to the acidic, aqueous composition in step (ii). To further promote this property profile, urea urethane resins that have neither free or blocked isocyanate groups nor terminal amine groups are preferably used as the thickener. In a preferred embodiment, the thickener, which is a urea urethane resin, therefore has an amine value of less than 8 mg KOH/g, particularly preferably of less than 5 mg KOH/g, more particularly preferably of less than 2 mg KOH/g, determined in each case according to the method as previously described for the organic polymeric compound (P2). Since the thickener is substantially dissolved in the aqueous phase of the activating aid and can thus be assigned to the non-particulate constituent, while component (P2) is substantially bound in the particulate constituent (P), an activating aid in which the entirety of the polymeric organic compounds in the non-particulate constituent preferably has an amine value of less than 16 mg KOH/g, particularly preferably of less than 10 mg KOH/g, more particularly preferably of less than 4 mg KOH/g, is preferred. It is further preferred for the urea urethane resin to have a hydroxyl number in the range of from 10 to 100 mg KOH/g, particularly preferably in the range of from 20 to 60 mg KOH/g, determined according to method A of 01/2008:20503 from European Pharmacopoeia 9.0. With regard to the molecular weight, a weight-average molar mass of the urea urethane resin in the range of from 1000 to 10000 g/mol, preferably in the range of from 2000 to 6000 g/mol, in each case determined experimentally as previously described in connection with the definition according to the invention of a polymeric organic compound, is advantageous according to the invention and is therefore preferred.

[0138] The activating aid is an aqueous dispersion that preferably has a pH value in the range of 6.0-9.0 and particularly preferably does not contain any pH-regulating, water-soluble compounds with a pK.sub.S value of less than 6 or a pK.sub.B value of less than 5.

[0139] The activating aid can also contain auxiliaries, for example selected from preservatives, wetting agents and defoamers, which are contained in the amount necessary for the relevant function. The proportion of auxiliaries, particularly preferably of other compounds in the non-particulate constituent which are not thickeners, is preferably less than 1 wt. %.

[0140] The activating aid is preferably obtainable by [0141] a) providing a pigment paste by triturating 10 parts by mass of an inorganic particulate compound (P1) with 0.5 to 2 parts by mass of the polymeric organic compound (P2) in the presence of 4 to 7 parts by mass of water and grinding until a D50 value of less than 1 m has been reached, as determined by means of dynamic light scattering after dilution with water by a factor of 1000, for example by means of Zetasizer Nano ZS from Malvern Panalytical GmbH; [0142] b) diluting the pigment paste with an amount of water, preferably deionized water (K<1 Scm.sup.1) or service water and a thickener such that a dispersed particulate constituent (P) of at least 5 wt. % and a maximum dynamic viscosity of at least 1000 Pa.Math.s at a temperature of 25 C. in the shear rate range of from 0.001 to 0.25 reciprocal seconds is provided, [0143] wherein preferred embodiments of the activating aid are obtained in an analogous manner by selecting corresponding components (P1), (P2) and the thickener in the amount that may be provided or required in each case.

[0144] In the context of the present invention, it is preferred, in particular for reasons of process economy, for the activating aids in process steps (i) and (ii) to each be based on identical water-dispersed particulate constituents (P). The water-dispersed particulate constituents (P) are already considered to be identical if the constituents (P1) and (P2) do not differ from one another in terms of their chemical constitution, i.e. the water-dispersed particulate constituents (P) of the respective aqueous dispersions contain the stoichiometrically identical phosphate of the same polyvalent cation and, with regard to the polymeric organic compounds, the same constitutional repeating units.

Exemplary Embodiments

[0145] The following intends to demonstrate that wetting metal substrates with an activating aid prior to an activating zinc phosphating process makes it possible to reduce the layer weights and at the same time save the amount of activating aid required to set an activating zinc phosphating bath.

[0146] For this purpose, test sheet metals (105190 mm, Gardobond by Chemetall) made of cold-rolled steel (CRS), hot-dip galvanized (HDG) steel and aluminum (alloy AA6014) were each first wetted with an activating aid and zinc phosphated immediately afterwards.

[0147] For the process sequences listed in Table 1 and carried out, the following treatment steps (1)-(6) were provided: [0148] (1) Spray degreasing at 1.0 bar for 60 seconds at a spray medium temperature of 54 C., wherein the spray medium having a pH value of 11.2 was composed of [0149] 30 g/kg Bonderite C-AK 1574 A [0150] 3 g/kg Bonderite C-AD 1270 [0151] 1 g/kg Bonderite M-AD 100 [0152] all products from Henkel AG & Co.KGaA [0153] an amount of NaHCO.sub.3 for setting the pH [0154] Remainder: deionized water (K<1 Scm.sup.1). [0155] (2) Immersion degreasing for 180 seconds at an immersion medium temperature of 55 C., wherein the immersion medium having a pH value of 11.2 had an identical composition to the medium for spray degreasing (1). [0156] (3) Rinsing with deionized water (K<1 Scm.sup.31 1) at a rinsing medium temperature of about 20 C. for about 60 seconds. [0157] (4) Wetting activation by fogging the test sheet metals at about 20 C. with an activating aid having a pH value of 10.0 and composed of [0158] 0.3 g/kg (a), 0.5 g/kg (b) or 3.0 g/kg (c) Bonderite M-AC AC 3000 (Henkel AG & Co KGaA) [0159] an amount of 10 wt. % NaOH solution for setting the pH [0160] Remainder: deionized water (K<1 Scm.sup.1) [0161] Inorganic particulate constituent (P1): hopeite (Zn.sub.3(PO.sub.4).sub.2) [0162] Polymeric organic compound (P2): maleic acid-styrene copolymer modified with EO/PO units [0163] Amount of particulate constituent (P) in the activating aid: 60 mg/kg (a), 100 mg/kg (b) or 600 mg/kg (c); [0164] Misting was carried out using a spray bottle (from Wrth; item no. 0891 502 002; 500 ml), wherein three bursts of spray on each side of the sheet were sufficient to completely wet the surface. The sheets wetted in this way were immersed in the zinc phosphating bath from step (5) after leaving the sprays to activate for approximately 5 seconds. [0165] (5) Activated trication zinc phosphating by immersion in the phosphating bath at 51 C. for 180 seconds, wherein the phosphating bath had a free acid of 1.1 points, a total acid of 26.5 points and 170 mg/kg free fluoride and had the following composition: [0166] 1.3 g/kg zinc ions [0167] 0.8 g/kg manganese ions [0168] 0.9 g/kg nickel ions [0169] 14.7 g/kg phosphate anions [0170] 1.0 g/kg SiF.sub.6 anions [0171] 1.3 g/kg NaNO.sub.3 [0172] 1.0 g/kg hydroxylamine [0173] Amount of activating aid added: 1.0 g/kg (a) or 0.2 g/kg (b) Bonderite M-AC 3000 (by Henkel AG & Co KGaA) in deionized water (K<1 Scm.sup.1) [0174] Amount of water-dispersed particulate constituent (D): 200 mg/kg (a) or 40 mg/kg (b). [0175] (6) Rinsing with deionized water (K<1 Scm.sup.1) at a rinsing medium temperature of about 20 C. for about 60 seconds. [0176] (7) Drying the sheet by blowing it with compressed air.

[0177] Table 1 lists each of the layer weights achieved according to the process sequences listed in said table. It can be seen that pre-activation of the zinc surfaces leads to a significant layer weight reduction in the activating zinc phosphating process (V1 vs. E1), which already occurs during misting with the low-concentration aqueous dispersion for activation wetting. At a concentration increased by a factor of 10, a further layer weight reduction of about 2 g/m.sup.2 occurs on the zinc surfaces while still achieving a closed, homogeneous phosphate layer (E1 vs. E2). Even on the steel surfaces, pre-activation by misting then again considerably reduces the layer weight, which is already well below 3 g/m.sup.2 (CRS: V1) even without pre-activation, and even reduced to values below 2 g/m.sup.2 (CRS: E1 vs. E2) without losing phosphating quality during layer formation. The layer formation process on the aluminum surfaces is only slightly dependent on the corresponding process sequence and is in the region of 2 g/m.sup.2 with or without pre-activation. Overall, the process according to the invention makes it possible to level out the layer weight coatings, which still differ on the different substrates during activated zinc phosphating. For components made of zinc, iron and aluminum, it is sufficient to simply wet the zinc or zinc and iron surfaces with an activating aid in order to obtain closed, homogeneous and crystalline zinc phosphate coatings with a layer weight in the region of 2 g/m.sup.2 after activated zinc phosphating on all substrates. The two-stage process is also very effective with regard to the use of activating aids and, similarly to what the process sequence according to type E3 shows, can also be optimized in such a way that less activating aid has to be used overall compared to simple activated zinc phosphating. In the process sequence according to type E3, the amount of activating aid in the zinc phosphate bath can thus be reduced to a fifth of the amount according to the process sequence V1, and yet significantly lower layer weights are still achieved on HDG. Only the pre-activation of the zinc surfaces is required and thus only a fraction of the activation aid needs to be used, which would otherwise have to be added to the zinc phosphate bath in a process sequence according to type V1 in order to maintain the phosphating quality. It should also be borne in mind that some of the activation aid that remains on the pre-activated zinc surfaces directly enters the zinc phosphate bath with the components where it contributes to maintaining the phosphating quality, and therefore on the whole the process according to the invention makes a very resource-efficient zinc phosphating process available.

TABLE-US-00001 TABLE 1 Method Layer weight .sup.1/gm.sup.2 Type sequence HDG CRS Al V1 1-2-3-5a-6-7 3.5 2.4 1.9 E1 (low*) 1-2-3-4a-5a-6-7 2.7 2.3 1.9 E2 (high) 1-2-3-4c-5a-6-7 2.1 1.8 1.7 E3 (medium) 1-2-3-4b-5b-6-7 2.8 2.2 2.2 *low/medium/high: based on the concentration of the activating aid during pre-activation .sup.1 differential gravimetric analysis after removal of the phosphate layer in 0.5 wt. % chromic acid solution (HDG, CRS) or 50 wt. % nitric acid (Al)