Multi-stage treatment for activated zinc phosphating of metallic components

Abstract

The present invention relates to a method 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. Targeted activation is achieved by means of controlled dispensing of an aqueous dispersion to wet said zinc and / or iron surfaces, thus ensuring resource-saving activation. The aqueous dispersion for activation wetting contains a particulate component dispersed in water, which is at least partially composed of hopeite, phosphophyllite, scholzite and / or hureaulite, provided as a dispersion of these crystalline solids, which is stabilised with at least one polymeric organic compound. The phosphating quality of the acidic, aqueous composition of the zinc phosphating is again ensured and maintained by adding a quantity of an aqueous dispersion, in particular the same aqueous dispersion that is also used for activation wetting.

Description

[0001] Multi-stage treatment for activated zinc phosphating of metallic components'

[0002] The present invention relates to a method for the corrosion-protective pretreatment of a large number of components in series, in which each component of the series at least partially has surfaces made of zinc and / or iron, and at least parts of these surfaces are first specifically activated for subsequent zinc phosphating. The targeted activation is achieved by means of controlled dispensing of an aqueous dispersion for wetting the said surfaces of zinc and / or iron, thus ensuring resource-saving activation ("activation wetting"). The aqueous dispersion for activation wetting contains a particulate component dispersed in water, which is at least partially composed of hopeite, phosphophyllite, scholzite, and / or hureaulite, provided as a dispersion of these crystalline solids stabilized with at least one polymeric, organic compound.The phosphating quality of the acidic, aqueous composition of the zinc phosphating is in turn ensured and maintained by adding an amount of an aqueous dispersion, in particular the same aqueous dispersion that is also used for activation wetting.

[0003] Film-forming phosphating is a process that has been practiced and intensively researched for decades for applying crystalline corrosion-protective coatings to metallic surfaces, particularly on iron, zinc, and aluminum. Zinc phosphating, which is particularly well-established for corrosion protection, is applied in a layer thickness of a few micrometers and is based on a corrosive pickling of the metallic material in an acidic aqueous solution containing zinc ions and phosphates. During this process, poorly soluble crystallites form near the surface, precipitate directly at the interface with the metallic material, and continue to grow there.

[0004] Typically, zinc phosphating is adjusted to achieve homogeneous, closed, and compact crystalline coatings on the surfaces of iron, zinc, and aluminum. Otherwise, good corrosion protection and paint adhesion cannot be achieved. Homogeneous, closed coatings in zinc phosphating are typically achieved with a layer weight of 2 g / m2 or more. 2 reliably achieved.

[0005] To achieve such homogeneous, continuous coatings with a high compactness or number density of phosphate crystallites, zinc phosphating is usually initiated by activating the metallic surfaces of the component to be phosphated. Activation is a wet-chemical process step that conventionally involves bringing the component into contact with colloidal, aqueous solutions of phosphates ("activation step"). These, immobilized on the metal surface, serve as growth nuclei for the formation of the crystalline coating during the subsequent phosphating process, resulting in a high number density of growing crystallites, thus generating a compact, crystalline zinc phosphate layer that provides excellent corrosion protection and, due to its high electrical resistance, also offers excellent electrocoatability.

[0006] Depending on the metal surface to be phosphated, it is necessary to adapt the performance of the previously described activation stage and also the pickling via the concentration of the active components in the zinc phosphating stage, which often requires intensive activation in the immersion process and, at the same time, a sufficient pickling in the presence of fluoride ions in the phosphating stage, particularly for metallic components such as automobile bodies that consist of a mix of different materials, in order to achieve correspondingly high layer weights on all surfaces of the component, in particular zinc, iron or steel and aluminum.

[0007] Recently, however, a process has been described in WO 2022 / 048963 A1 in which conventional activation of the surfaces prior to zinc phosphating can be dispensed with, provided that the zinc phosphating treatment bath itself is set to be activating and contains a sufficient amount of phosphates in dispersed form.

[0008] Even though this zinc phosphating process with integrated activation can reliably phosphate a variety of metals to form a layer, the proportion of dispersed phosphates, which have an activating effect in the acidic, aqueous composition of the phosphating bath, must be adjusted to the components to be treated. In the corrosion-protective treatment of components composed of different metals, the metal surface requiring the most activation always determines the total consumption of active components, i.e., dispersed phosphates. Accepting less optimal activation for lower consumption of dispersed phosphates in the activation or phosphating stage inevitably leads to higher phosphate layer weights, especially on zinc or iron surfaces, and thus comes at the expense of higher consumption of active components in the phosphating stage.

[0009] There is therefore a need to fully utilize the undeniable process-economic advantages of the integrated process of WO 2022 / 048963 A1, which consist of a reduced pretreatment sequence that is easier to control, while reducing the consumption of active components as much as possible, but not at the expense of phosphating quality, which is equivalent to the resulting homogeneous, closed, and, if possible, fine-crystalline phosphate layers with a low layer weight, particularly on the surfaces of zinc and / or iron, and especially on the zinc surfaces of the components to be treated. Such a resource-saving process with an activating zinc phosphating effect must be suitable for activating components composed of various metallic materials sufficiently to form layers with a high phosphating quality despite different material-specific requirements.The task was solved in this case by the selective and controlled dispensing of an aqueous dispersion for the activating wetting of metal surfaces prior to the actual integrated zinc phosphating process. Surprisingly, the activating wetting of the zinc and / or iron surfaces enables a significant reduction in the coating weight of the zinc phosphating while maintaining the same phosphating quality, and thus a similarly significantly reduced consumption of active components in the zinc phosphating process.

[0010] The present invention specifically relates to a method for the corrosion-protective pretreatment of a large number of components in series, in which each component of the series has at least partially surfaces of zinc and / or iron and first undergoes a process step (i) for activating the surfaces of zinc and / or iron and immediately subsequently a process step (ii) for zinc phosphating, wherein in process step (i) at least the surfaces of zinc and / or iron of each component of the series are brought into contact with an aqueous dispersion containing a water-dispersed, particulate component (P) comprising 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),wherein the contacting is carried out by dispensing the aqueous dispersion from a supply in such a way that no more than 1.00 litre of the aqueous dispersion is dispensed per square metre of the surface of each component of the series, preferably per square metre of the surfaces of zinc and / or iron of each component of the series to be brought into contact, and wherein in process step (ii) at least the surfaces of zinc and / or iron of each component of the series are brought into contact with an acidic, aqueous composition having a free acidity in points greater than zero, and,

[0011] (A) 5 - 50 g / kg of phosphates dissolved in water calculated as PO4,

[0012] (B) 0.3 - 3 g / kg of zinc ions,

[0013] (C) free fluoride, and

[0014] (D) a water-dispersed, particulate component comprising phosphates of polyvalent metal cations, wherein the phosphates are at least partially selected from hopeite, phosphophyllite, scholzite and / or hureaulite, wherein the acidic, aqueous composition is obtainable by adding an amount of an aqueous dispersion to an acidic, aqueous composition comprising components (A) - (C), wherein the aqueous dispersion contains a water-dispersed, particulate component (P) 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).

[0015] Pretreatment in series occurs when the individual components of the series are successively and thus separated in time from one another, each undergoing process steps (i) and (ii) for zinc phosphating according to the process according to the invention and are brought into contact with the corresponding aqueous compositions stored in system tanks in the intended immediate sequence. The system tank of process step (i) is the container in which the aqueous dispersion is kept for the purpose of activating the wetting of the surfaces of zinc and / or iron, and the system tank of process step (ii) is accordingly the container containing the acidic aqueous composition for the purpose of zinc phosphating. The bringing into contact of the components in process step (ii) with the acidic, aqueous composition can take place inside the system tank, e.g. by immersion, or outside the system tank, e.g.by spraying or injecting the acidic aqueous composition stored in the system tank. The contacting of the zinc and / or iron surfaces of each component in the series with the aqueous dispersion in process step (i) is carried out by dispensing a defined volume of the dispersion from the reservoir onto the surfaces to be activated, preferably in such a way that the volume of aqueous dispersion dispensed once per component is not returned to the system tank storing the dispersion, for example by wetting the surfaces to be activated outside the system tank from which the stored aqueous dispersion is dispensed for each component.

[0016] The components treated according to the present invention can be any spatial structures of any shape and design that originate from a manufacturing process, in particular also semi-finished products such as strips, sheets, rods, pipes, etc. and composite structures assembled from the aforementioned semi-finished products, wherein the semi-finished products are preferably connected to one another by gluing, welding and / or flanging to form the composite structure.

[0017] The process according to the invention is particularly effective for producing compact, closed, and crystalline phosphate coatings on zinc surfaces, so that series components that have at least zinc surfaces are preferred. The process according to the invention is also well suited for the layer-forming phosphating of aluminum, so that even components of mixed construction, e.g., automobile bodies, assembled from the materials zinc, iron, and aluminum can be phosphated effectively and in a resource-saving manner within the meaning of the present invention. However, aluminum surfaces generally do not require pre-activation in process step (i), and sufficient layer formation occurs upon contacting the aluminum surfaces with the acidic aqueous composition in process step (ii).In a particular embodiment of the method according to the invention, the components of the series which at least partially have surfaces of zinc and / or iron 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).

[0018] Within the scope of the method according to the invention, a component has at least one surface made of zinc and / or iron if the metallic structure on this surface is composed of more than 50 at.% zinc or iron up to a material penetration depth of at least one micrometer. This generally applies to components made of corresponding metallic materials, insofar as the metallic materials, as uniform materials, are composed of more than 50 at.% zinc or iron. Components comprising surfaces made of zinc also include ferrous materials provided with metallic coatings, such as electrolytically galvanized or hot-dip galvanized strip steel, which can also be alloyed with iron (ZF), aluminum (ZA) and / or magnesium (ZM).

[0019] For resource-efficient operation of the corrosion-protective pretreatment 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 is maintained to a maximum for the zinc phosphating step, and on the other hand, the zinc phosphating treatment step is enhanced with essential, activating particulate phosphates, which are introduced into the phosphating step via the wet film adhering to the component.

[0020] Accordingly, the direct sequence of activation and zinc phosphating provided for according to the invention in the context of the present invention means that the components undergo the process step (i) without an intermediate rinsing step or other treatment step which either comprises a further contacting, in particular of the zinc or iron surfaces of the components, with an aqueous dispersion containing a water-dispersed, particulate constituent (P) in the manner of process step (i) or preferably a contacting, in particular of the zinc or iron surfaces of the components, with an aqueous dispersion for activation for zinc phosphating or particularly preferably a contacting with an aqueous composition, wherein in each case also preferably no drying step is carried out after process step (i) and before process step (ii).A rinsing step in this context can comprise one or more consecutive process steps designed to remove, as completely as possible, any soluble residues, particles, and / or active components that inevitably remain on the surfaces of the components after they have been removed from the components in previous wet-chemical process steps, e.g., by rinsing with tap water. A drying step in the same context is the drying of the components achieved by controllable technical measures, e.g., by applying heat or by applying directed air.

[0021] A further advantage of the compact, closed, and crystalline coatings obtainable on all these metal surfaces using the process according to the invention is their excellent electrocoatability, which allows for high coverage. Therefore, it is preferred if step (ii) is followed by electrocoating, particularly preferably cathodic electrocoating. In principle, any coating conventionally used in the prior art with an organic topcoat system, in particular a powder coating, can follow the process, since an excellent paint adhesion base is provided.

[0022] Process step (T) - Pre-activation:

[0023] The aqueous dispersion is brought into contact to activate at least the surfaces of zinc and / or iron by dispensing it from a reservoir. Dispensing the aqueous dispersion from a reservoir for contacting requires, within the meaning of the present invention, the use of a device for withdrawing a volume of liquid from a reservoir, e.g., a container that stores a sufficient amount of the aqueous dispersion for a large number of components, and a device for dispensing the withdrawn volume of liquid onto the surfaces of one or more components to be brought into contact. Accordingly, 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 / fogging with a partial volume of the stored aqueous dispersion taken from the reservoir.Furthermore, according to the invention, the volume of the aqueous dispersion dispensed from the reservoir for contacting is limited and should be less than 1.00 liters per square meter of the surface of the component, or preferably only the zinc and / or iron surfaces of the component. This ensures that not significantly more liquid volume of the aqueous dispersion is 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 fundamentally advantageous if the aqueous dispersion is applied to the surfaces to be treated as effectively as possible and without excess quantity.In a preferred embodiment of the method according to the invention, the contacting of the zinc and / or iron surfaces is carried out by dispensing the aqueous dispersion from a reservoir to such an extent that no more than 0.50 liters, preferably no more than 0.20 liters, of the aqueous dispersion is dispensed per square meter of the component's surfaces, preferably only those surfaces of zinc and / or iron of the component that are to be activated and thus brought into contact. In this context, the area-related volume dispensing of the aqueous dispersion is such that the area of ​​a component in the series represents the surface of the polyhedron with 12 faces, preferably with 6 faces, and is particularly preferably the cuboid that completely surrounds the component and has the smallest surface area, whereby each face of the polyhedron touches the component at at least one point.If the component is an automobile body, its area in relation to the area-related output of the aqueous dispersion for conditioning is preferably that of the cuboid with the smallest surface area that completely encompasses the automobile body, with each surface of the cuboid touching the automobile body at least one point. In the preferred embodiment of the method according to the invention, the respective upper limit of the area-related volume output of the aqueous dispersion is standardized to the surfaces of zinc and / or iron. In this case, the geometric area of ​​the surfaces of the component made of zinc and / or iron to be activated is taken into account.When treating flat products such as strip steel, it may therefore be the entire outer surface of the flat product that 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 of strip steel after forming and joining need to be included, since often only these can be optimally phosphated to form a layer and thus pre-activated accordingly.

[0024] The dispensing of the aqueous dispersion for bringing into contact and thus activating the surfaces of zinc and / or iron requires and requires that the amount dispensed from the reservoir also reaches these surfaces at least partially. In a preferred embodiment, the dispensing of the aqueous dispersion for bringing into contact in process step (i) for sufficient activation therefore takes place in such a way that it is ensured that at least the surfaces of zinc and / or iron are covered by a liquid film containing the aqueous dispersion, whereby a volume-related coating per square meter of preferably no more than 1.00 liter, more preferably no more than 0.50 liter, most preferably no more than 0.20 liter and especially preferably no more than 0.10 liter results on the surfaces of zinc and / or iron.In contrast to the volume output of the aqueous dispersion for contacting, the volume application here does not refer to the surface of the component approximated by polyhedra, but to the respective actual geometric surface of the surfaces of zinc and / or iron of the components of the series, whereby the volume application is determined by differential weighing after blowing off the liquid film, assuming a density of the liquid adhering to the surfaces of 1 g / cm. 3 can be determined.

[0025] It should be noted that the components are often already wetted with a liquid film, e.g., formed by rinse water from a rinsing step immediately preceding the activation, when they are transferred to the activation stage according to process step (i), before the inventive contacting of the zinc and / or iron surfaces takes place by absorbing liquid volumes of the aqueous dispersion into 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 over them, which in turn promotes uniform activation for the subsequent zinc phosphating.

[0026] If a largely complete wetting of the surfaces of zinc and / or iron to be activated is achieved solely by means of the device for dispensing and bringing into contact, it may in turn 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 into contact, 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 sufficient to bring about the desired activation.

[0027] Whether a liquid film containing the aqueous dispersion has formed on the surfaces of zinc and / or iron in process step (i) can be verified using fluorescent markers added to the aqueous dispersion supply. Detection can then be carried out by irradiating with UV light and recording the fluorescence using suitable cameras that enable imaging control of the wetting of the component surfaces with the aqueous dispersion. This is particularly helpful when components with complex surface geometries must be pretreated and the method of dispensing the aqueous dispersion, e.g., is important.The relative orientation and spacing of a spray lance to the component must first be adjusted in an iterative process so that the surfaces of zinc and / or iron are brought into contact with the aqueous dispersion, in particular such that these surfaces are covered with a liquid film containing the aqueous dispersion. This latter preferred condition does not have to be met directly by bringing the aqueous dispersion from the reservoir into contact, 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 in contact with the surfaces of zinc and / or iron is produced before process step (ii), i.e. before the components are introduced into the zinc phosphating, preferably at least 5 seconds, particularly preferably at least 10 seconds, most particularly preferably at least 20 seconds, before bringing them into contact with the acidic aqueous composition in process step (ii).

[0028] For the controlled dispensing of the aqueous dispersion required in the process according to the invention for activating the wetting of the surfaces of zinc and / or iron, it is advantageous and therefore further preferred if, in process step (i), the aqueous dispersion is dispensed as a spray, a mist, or a liquid film, particularly preferably as a spray and / or a mist, especially preferably as a spray. The aqueous dispersion is brought into contact with the surfaces of the component to be activated as a spray and / or a mist using methods for spraying and misting established in the prior art and can be carried out locally using a spray lance and / or at least partially enclosing the component using a spray ring in which a plurality of atomizing nozzles can be installed.Spray devices used to deliver a spray and / or mist include pressure atomizers, rotary atomizers, or dual-component atomizers. Depending on the complexity and geometry of the components in the series, a liquid film can be applied to the component using a direct application method, such as rollers, cloths, brushes, or similar liquid application tools.

[0029] A preferred controlled and efficient activation wetting with the aqueous dispersion is achieved by setting a spray rain that is specifically directed onto the surfaces of zinc and / or iron to be wetted, and / or by providing a spray mist through which the component together with the conveyor frame is transported and which, at a given volume flow, is realized over a transport distance such 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 immediately following process step (ii).

[0030] In order to dispense approximately as much aqueous dispersion as is required to form a liquid film covering the surfaces of the component and thus for good activation wetting, it is preferred according to the invention if the dispersion dispensed as spray and / or as a spray mist in process step (i) has an average droplet size of less than 100 pm, particularly preferably less than 60 pm, especially preferably less than 40 pm. With average droplet sizes below 40 pm, the aqueous dispersion is so highly atomized that the boundary area 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 increasingly remain in suspension and do not follow gravity.The suspended spray mist is then also moved and possibly swirled due to the air masses displaced during the transport of the component through the spray chamber, so that 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. Therefore, it is preferred if the dispensed aqueous dispersion in process step (i) has an average droplet size of no less than 5 μm, particularly preferably no less than 10 μm.

[0031] Likewise advantageous for the formation of a continuous liquid film containing the aqueous dispersion on the surfaces of the components to be brought into contact is when the spray and / or mist of the aqueous dispersion is dispensed such that the average velocity of the liquid droplets having 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 mist whose average droplet size is less than 100 pm, particularly preferably less than 60 pm, and especially preferably less than 40 pm.

[0032] According to the invention, the average droplet size and average velocity of the droplets of a spray or mist are determined at the location of the geometric center of gravity of the polyhedron enclosing the component, which is also used to determine the amount of agent dispensed per area of ​​the component, as described above. The determination can be carried out using light scattering and phase Doppler anemometry. The preferred embodiments mentioned here regarding how the aqueous dispersion can be dispensed for contact with at least the surfaces of zinc and / or iron allow for an extremely efficient process in which the amount of aqueous dispersion dispensed from the reservoir is applied essentially only to the zinc and / or iron surfaces of the components to be activated.At the same time, the portion of the aqueous dispersion entrained with the component into the zinc phosphating treatment stage serves to at least partially compensate for the particulate portion of the acidic aqueous composition for zinc phosphating consumed during the activated zinc phosphating and entrained from the zinc phosphating treatment stage. For the same purpose, in process step (i), the portion of the components of the aqueous dispersion that are released but not remaining on the component can also be combined and transferred to the zinc phosphating treatment stage to maintain the activation performance.Accordingly, a process is preferred according to the invention in which the portions of the aqueous dispersion which are dispensed in process step (i) for bringing into contact with at least the surfaces of zinc and / or iron 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 or run off the component and thus remain in the spray chamber of process step (i), are at least partially combined and added to the acidic aqueous composition of process step (ii), and in any case preferably are neither partially nor completely returned to the supply.

[0033] For sufficient pre-activation of at least the zinc and / or iron surfaces of the series components, the aqueous dispersion used must contain a water-dispersed, particulate component (P) composed of phosphates of polyvalent metal cations (P1) and a polymeric organic compound (P2) that contributes to the stabilization of the dispersion. It should be emphasized at this point that the preferred proportion of phosphates, calculated as PO4, contained in the at least one particulate inorganic compound (P1), based on the dispersed, inorganic particulate component (P1) of the aqueous dispersion is at least 25 wt. %, particularly preferably at least 35 wt. %, especially preferably at least 40 wt. %, most particularly preferably at least 45 wt.Further preferred embodiments of the inorganic particulate component (P1) can, as already explained, be taken from the corresponding preferred embodiments of the inorganic particulate component (P1) of the aqueous dispersion of process step (ii).

[0034] 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 partially composed of styrene and / or an α-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, which in turn are 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 constituent (P) of the aqueous dispersion additionally comprises imidazole units.The proportion of polyoxyalkylene units in the total of the polymeric organic compounds (P2) is preferably at least 40 wt.%, particularly preferably at least 50 wt.%, but preferably not more than 70 wt.%. Further preferred embodiments of the polymeric organic compound (P2) can, as already explained, correspond to the corresponding preferred ones.

[0035] Embodiments of the polymeric organic compound (P2) of the aqueous dispersion of process step (ii).

[0036] In addition to and in addition to the aforementioned embodiments of the particulate constituent (P) of the aqueous dispersion of process step (i), the presence of a thickener is advantageous for providing a stable dispersion that can be stored in the system tank of process step (i) over a longer period. 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 having an amine number of less than 8 mg KOH / g, preferably less than 5 mg KOH / g, particularly preferably 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 the zinc phosphating, which are also advantageous with respect to the aqueous dispersions used in the preactivation and are also included here as preferred. Further preferred embodiments of the aqueous dispersion used in step (i) according to the invention, containing the water-dispersed, particulate constituent (P), can be found in the description of particularly suitable activation aids.

[0037] The extent of preactivation of the zinc and / or iron surfaces can be controlled via the water-dispersed particulate portion of the aqueous dispersion. It has been found that, at typical activation times, i.e., a contact time in the range of 5 to 120 seconds, the zinc and / or iron surfaces are preactivated particularly reliably when the particulate portion (P) is at least 0.060 g / kg, based on the aqueous dispersion. Short activation times can be compensated with higher portions of the particulate portion (P), so that overall it is advantageous if the water-dispersed particulate component (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 costs, which are not compensated for by a significant improvement in the compactness of the resulting zinc phosphate coatings. Furthermore, they are often not required for adjusting the proportion of particulate constituents in the acidic, aqueous composition of the zinc phosphating by carryover, thus counteracting the intention of the present invention to establish a particularly resource-saving process for zinc phosphating. Accordingly, it is preferred that the water-dispersed, particulate constituent (P) of the aqueous dispersion in process step (i) does not exceed 5.0 g / kg, particularly preferably not exceed 1.0 g / kg, based on the aqueous dispersion.

[0038] The pH of the aqueous dispersion for pre-activation is preferably adjusted so that pickling of the metallic materials of the components, in particular those 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 above 6.0, particularly preferably above 6.5, but preferably does not exceed a pH of 9.0, particularly preferably 8.5, very particularly preferably 8.0, and especially preferably 7.5.

[0039] Process step (ii) - activated zinc phosphating:

[0040] In process step (ii), according to the invention, the zinc phosphating of at least the zinc and / or iron surfaces of the series components pre-activated in process step (i) is carried out using an acidic, aqueous composition, which in turn is formulated to activate the growth of a highly compact, closed, but crystalline zinc phosphate layer and, like the aqueous dispersion in the pre-activation, contains a dispersed particulate component for this purpose. 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 for the formation of a zinc phosphate layer contains:

[0041] (A) 5 - 50 g / kg of phosphates dissolved in water calculated as PO4,

[0042] (B) 0.3 - 3 g / kg of zinc ions, and

[0043] (C) free fluoride, wherein the zinc phosphating composition is adjusted to have a free acidity greater than zero.

[0044] The acidic, aqueous zinc phosphating is thus provided in an activating manner due to its particulate component (D) for the growth of a crystalline phosphate coating on the surfaces of zinc and / or iron and is obtainable as such by appropriately adding an amount of an aqueous dispersion to an acidic, aqueous composition containing the aforementioned components (A) - (C).

[0045] This aqueous dispersion intended for addition to an acidic aqueous composition containing components (A) - (C) contains a particulate constituent (P) dispersed in water, 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), wherein the addition of the aqueous dispersion for providing the acidic, aqueous composition for zinc phosphating in process step (ii) is preferably carried out in an amount such that the weight fraction 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 especially preferably at least 2.0 mg / kg each calculated as phosphate (PO4) and based on the acidic aqueous composition.

[0046] In a preferred embodiment, which allows a particularly resource-saving and economical operation of the process according to the invention, the components of the series are brought into contact in step (ii) of the process according to the invention with an acidic aqueous composition, wherein the acidic aqueous composition

[0047] (A) 5 - 50 g / kg of phosphates dissolved in water calculated as PO4,

[0048] (B) 0.3 - 3 g / kg of zinc ions, and

[0049] (C) contains free fluoride, and has a free acidity greater than zero, wherein in process step (ii) for zinc phosphating, an amount of the aqueous dispersion containing the particulate component (P) is added continuously or discontinuously to the acidic aqueous composition which is sufficient under the selected conditions of process step (ii) for zinc phosphating, the property of the acidic aqueous composition to form a zinc phosphate layer with a layer weight of less than 4.5 g / m 2 , preferably less than 4.0 g / m 2 , particularly preferably less than 3.5 g / m 2 , most preferably less than 3.0 g / m 2to deposit, to maintain, wherein the particulate constituent (P) of the aqueous dispersion comprises at least one particulate inorganic compound (P1) which is 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).

[0050] In this way, only a required amount of the aqueous dispersion of the acidic aqueous composition for zinc phosphating is added and overdosing is systematically avoided.

[0051] In a particularly preferred variant of the process according to the invention, in process step (i) for pre-activation, such an amount of the activating aid is dispensed per component for bringing into contact with the surfaces of zinc and / or iron that is sufficient to maintain, as a wet film remaining on the component and introduced into the subsequent process step (ii) of zinc phosphating, in the acidic, aqueous composition containing components (A) - (C), a weight fraction of the phosphates of the water-dispersed, particulate constituent (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 especially preferably at least 2.0 mg / kg, in each case calculated as phosphate (PC ) and based on the acidic aqueous composition.

[0052] Alternatively, in an equally preferred variant, in process step (i) for pre-activation, such an amount of the activating aid is dispensed per component for bringing into contact with the surfaces of zinc and / or iron that is sufficient as a wet film remaining on the component and introduced into the subsequent process step (ii) of zinc phosphating to adjust in the acidic, aqueous composition containing components (A) - (C) such 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 that is sufficient to ensure, under the selected conditions of process step (ii) of zinc phosphating, the property of the acidic aqueous composition to form a zinc phosphate layer with a layer weight of less than 4.5 g / m 2, preferably less than 4.0 g / m 2 , particularly preferably less than 3.5 g / m 2 , most preferably less than 3.0 g / m 2 to separate, to maintain.

[0053] The preferred property of the acidic aqueous composition for zinc phosphating according to the invention, in process step (ii) on hot-dip galvanized steel surfaces (Z), is the growth of a zinc phosphate layer with a layer weight below 4.5 g / m 2 , preferably below 4.0 g / m 2 , particularly preferably below 3.5 g / m 2 and most preferably below 3.0 g / m 2(hereinafter referred to as "phosphating quality"), is to be tested on cleaned and degreased (Z) substrates which are not subjected to any further wet-chemical pretreatment step or rinsing step 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 is present if the (Z) surface, after cleaning and degreasing, has a carbon coating of less than 0.10 g of carbon per square meter of the (Z) surface. The carbon coating can be determined by means of pyrolytic decomposition.For this purpose, the (Z) substrate is brought to 550°C substrate temperature (PMT) in an oxygen atmosphere and the amount of released carbon dioxide is quantitatively measured as the amount of carbon using an infrared sensor, for example using the LECO® RC-412 Multiphase Carbon Determinator (Leco Corp.) analyzer.

[0054] To check the phosphating quality of the acidic aqueous composition, hot-dip galvanized steel (Z) is first treated with an alkaline cleaner as 2 wt.% Bonderite® C-AK 1565 A and 0.2 wt.% Bonderite® C-AD 1270 in deionized water (K<1 pScrn -1 ) at pH 11.0 and 55 °C for 5 minutes by immersion. The thus cleaned and degreased (Z) substrates are rinsed at room temperature with deionized water (K<1 pScm -1) and then fed to the treatment stages according to process steps (i) and (ii) in accordance with the respectively selected process conditions. According to the selected process conditions means, at identical temperature, application time and bath circulation, and using those wet-chemical treatment stages that are to apply to the phosphating quality preferably specified according to the invention, ie the resulting target layer weights on hot-dip galvanized steel (Z) below 4.5 g / m 2 , preferably below 4.0 g / m 2 , particularly preferably below 3.5 g / m 2 and most preferably below 3.0 g / m 2The phosphating quality can therefore be determined in the ongoing process according to the invention by introducing cleaned and degreased sheets of hot-dip galvanized steel (Z) for process steps (i) and (ii) along with the components of the series, and then determining the layer weight of zinc phosphate on the sheets and thus the phosphating quality of the acidic aqueous

[0055] Composition for zinc phosphating is determined in process step (ii). It should be noted that the outer surfaces of such sample sheets to be phosphated have formed a complete liquid film containing the aqueous dispersion in process step (i) before contact with the acidic aqueous composition occurs in process step (ii).

[0056] Preferably, the cleaned and degreased sheets of hot-dip galvanized steel (Z) are rigidly connected to the component or the conveyor frame in their function as test sheets for determining the phosphating quality in order to reproduce the flow conditions during transport of the component together with the conveyor frame through the phosphating bath as closely as possible for the test sheet. For this purpose, the test sheets should ideally be connected to the component or the conveyor frame in such a way that the transport of a test sheet together with the component and the conveyor frame has no significant influence on the flow conditions compared to the transport of the component and the conveyor frame without such a test sheet, and that the flow conditions in both cases are essentially identical and thus essentially correspond to the flow conditions of at least a portion of the components in the series.This can be achieved, for example, by adapting the size and / or shape of the sample sheet to the size and shape of the component and / or the conveyor frame, which is arranged adjacent to the sample sheet. Particularly when a sample sheet is arranged on an outer surface section of the component or the conveyor frame, it is conceivable to dimension the sample component correspondingly smaller than said surface section, for example, to prevent the sample component from projecting beyond the surface section. Alternatively or additionally, the sample component can follow a curvature or other plane deviation of the surface section or the conveyor frame.It has proven particularly expedient to select a sheet metal section that is sufficiently small compared to the size of a suitable outer surface of the component. An outer surface is particularly suitable if it is located at a location of particularly low or lowest curvature of the component, and the sample sheet is then attached at a distance substantially parallel to the surface normal of such an outer surface. It is particularly expedient and preferred if the spacing of the sample sheet occurs along a surface normal to a surface of zinc and / or iron of the component in order to ensure in the simplest possible way that, in process step (i), a liquid film containing the aqueous dispersion dispensed there for contacting is applied, without the device for dispensing the aqueous dispersion in process step (i) having to be laboriously adapted.

[0057] The phosphating quality is directly achieved during the serial treatment of components that have a surface of hot-dip galvanized steel (Z) as a zinc surface. Such components are also preferred in a preferred embodiment of the process according to the invention.

[0058] For the phosphating grade, it is also preferred that if the contact time is extended by one minute, the coating weight on hot-dip galvanized steel (Z) should not increase by more than 0.2 g / m 2increases and thus the layer formation under the selected conditions is already in the range of self-limiting, so that the property of the acidic aqueous composition for zinc phosphating to produce 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 step, such an amount of the aqueous dispersion containing the particulate constituent (P) is added that is sufficient under the selected conditions of the zinc phosphating step in the process according to the invention to ensure the property of the acidic aqueous composition to produce a zinc phosphate layer with a layer weight of less than 4.5 g / m 2 , preferably less than 4.0 g / m 2 , particularly preferably less than 3.5 g / m 2 and most preferably less than 3.0 g / m 2to deposit, to maintain, wherein the layer weight achieved under the selected conditions of process step (ii) of the zinc phosphating in the process according to the invention does not decrease by more than 0.2 g / m 2 increases.

[0059] Typically, in the process preferred according to the invention, the phosphating quality is determined and monitored by subjecting hot-dip galvanized steel (Z), which has been cleaned and degreased as described above, to the zinc phosphating process step at regular intervals during the series treatment and then subjecting it to a layer weight determination. As already mentioned, the phosphating quality is determined directly during the series treatment of components that have at least one surface of hot-dip galvanized steel (Z) as a zinc surface. To the extent that the phosphating quality of the acidic aqueous composition is ensured by the addition of the aqueous dispersion, homogeneous, closed, and compactly crystalline zinc phosphate coatings are deposited on the components in the series that have surfaces of the metals zinc and / or iron in typical treatment times of 20 seconds to 5 minutes.

[0060] The layer weight of zinc phosphate is determined in the context of the present invention by removing the zinc phosphate layer with aqueous 5 wt.% CrOa as a pickling solution, which is applied immediately after zinc phosphating and rinsing with deionized water (K<1 pScm -1 ) is brought into contact with a defined area of ​​the phosphated material or component at 25 °C for 5 minutes, followed by determining the phosphorus content in the same pickling solution using ICP-OES. The coating weight of zinc phosphate is determined by multiplying the area-related amount of phosphorus in grams per square meter by a factor of 6.23.

[0061] The addition of the aqueous dispersion containing the particulate constituent (P) to the acidic aqueous composition for zinc phosphating is carried out in the process according to the invention for the purpose of maintaining the phosphating quality in process step (ii). To maintain the phosphating quality during the serial treatment process, the addition can be carried out by continuous or discontinuous dosing into the zinc phosphating system tank. Continuous dosing is preferred when the pretreatment of the components follows one another in series and the decrease in phosphating quality per time interval can be determined with sufficient accuracy, so that a continuous dosing of an amount of the activating agent can be carried out to compensate for the loss in performance.This process has the advantage that the phosphating quality does not need to be further monitored after the pretreatment line has been started up and the material flows for dosing the aqueous dispersion and other active components have been determined, as long as the serial treatment remains unchanged with regard to the timing and nature of the components to be treated, as well as the treatment parameters in process step (ii) of zinc phosphating. However, if a constant procedure in the serial treatment is not guaranteed or desired due to plant conditions, a discontinuous dosing of the aqueous dispersion containing the particulate component (P) is advantageous and may even be indicated.In this case, the phosphating quality of the acidic aqueous composition in step (ii) is preferably monitored continuously or at defined time intervals and then a predetermined amount of the activating aid is added when the coating weight on hot-dip galvanized steel (Z) reaches a certain value below 4.5 g / m. 2 , preferably below 4.0 g / m 2 , particularly preferably below 3.5 g / m 2 and most preferably below 3.0 g / m 2no longer achieved. The continuous or quasi-continuous determination of the phosphating quality, carried out at defined intervals, can also be carried out using proxy data that correlate with the actual zinc phosphate coating weight. For example, non-destructive determination of the coating thickness, for example, using the eddy current method, or even non-contact optical determination methods such as ellipsometry or spectral reflectivity measurement, provides suitable proxy data for the zinc phosphate coating weight, which can be reliably measured on the zinc surfaces of the components in a pretreatment line and correlated with the actual coating weight on hot-dip galvanized steel (Z).Likewise, the crystallite size and thus the determination of the roughness by means of optical profilometry can provide proxy data for the coating weight, since a higher coating weight on hot-dip galvanized steel (Z) is associated with a low number density of crystallites, which are, however, relatively larger, so that the roughness increases with the coating weight.

[0062] It has been found that the phosphating quality is already sufficiently adjusted in most cases if the aqueous dispersion containing the particulate component (P) for activating the zinc phosphating composition is metered in continuously or discontinuously in an amount suitable for maintaining a stationary amount of preferably at least 0.1 mg / kg, more preferably at least 0.5 mg / kg, especially 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 (PC) and based on the acidic aqueous composition during the pretreatment of the components in series. This applies in particular to bringing the components into contact by immersing them in the zinc phosphating system tank containing the acidic aqueous composition.

[0063] In conjunction with process step (i), which pre-activates the surfaces of zinc and / or iron, the activated zinc phosphating in step (ii) can be carried out in a particularly resource-efficient manner, significantly reducing the consumption of active components without any loss of phosphating quality. This applies to the added portion of the aqueous dispersion containing the particulate component (P) and, due to the excellent phosphating quality achieved on the surfaces of zinc and / or iron, also to the consumption of active components (A) - (C) of the acidic aqueous composition for zinc phosphating.

[0064] With regard to the acidic aqueous composition for zinc phosphating, it is essential for the formation of homogeneous, closed zinc phosphate layers that in step (ii) of the process according to the invention, these at least

[0065] (A) 5 - 50 g / kg of phosphates dissolved in water calculated as PO4,

[0066] (B) 0.3 - 3 g / kg of zinc ions, and

[0067] (C) contains free fluoride and has a free acidity greater than zero.

[0068] In this context, the amount of phosphate ions includes the orthophosphoric acid as well as the anions of the salts of orthophosphoric acid dissolved in water, calculated as PO4.

[0069] The proportion of free acid in points in the acidic aqueous composition of the zinc phosphating in step (ii) of the process according to the invention is preferably greater than 0.5, more preferably greater than 0.8, most preferably greater than 1.0, but preferably not more than 3.0, more preferably not more than 2.0. The proportion of free acid in points is determined by diluting 10 ml of sample volume of the acidic, aqueous composition to 60 ml and titrating with 0.1 N sodium hydroxide solution to a pH of 3.6. The consumption in ml of sodium hydroxide solution indicates the point value of free acid.

[0070] The preferred pH of the acidic, aqueous composition is typically below 3.6, more preferably below 3.4, most preferably below 3.2, but preferably above 2.5, most preferably above 2.7. The "pH" as used in the present invention corresponds to the negative decimal logarithm of the hydronium ion activity at 20 °C and can be determined using pH-sensitive glass electrodes.

[0071] A quantity of free fluoride or a source of free fluoride ions is essential for the layer-forming zinc phosphating process. If components comprising not only zinc surfaces but also iron or aluminum surfaces are to be zinc phosphated to form a layer, as is required, for example, in the zinc phosphating of automobile bodies that are at least partially made of aluminum, it is advantageous if the quantity 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 are easily wiped off.It is therefore advantageous and therefore preferred if, in step (ii) of the process according to the invention, the concentration of free fluoride in the acidic aqueous composition of the zinc phosphating is below 300 mg / kg, particularly preferably below 250 mg / kg and especially preferably below 200 mg / kg.

[0072] The amount of free fluoride is to be determined potentiometrically at 20 °C in the respective acidic, aqueous composition after calibration with fluoride-containing buffer solutions without pH buffering using a fluoride-sensitive measuring electrode. Suitable sources of free fluoride ions are hydrofluoric acid and its water-soluble salts, 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. Preferably, the source of free fluoride in a phosphating according to the present invention is therefore selected from hydrofluoric acid and its water-soluble salts 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 ​​< I pScnr 1 ) at 60°C is at least 1 g / L calculated as F.

[0073] To suppress so-called speck formation on the surfaces of metallic materials made of zinc, it is preferred if, in such processes according to the invention, the source of free fluoride in step (ii) is at least partially selected from complex fluorides of the element Si, in particular from hexafluorosilicic acid and its salts. In phosphating, those skilled in the art understand speck formation to be the phenomenon of the 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.

[0074] In the process according to the invention, the accelerators known in the prior art can be added to the acidic, aqueous composition to increase the layer formation rate. These are preferably selected from 2-hydroxymethyl-2-nitro-1,3-propanediol, nitroguanidine, N-methylmorpholine N-oxide, nitrite, hydroxylamine, and / or hydrogen peroxide. It has been shown that a comparatively smaller addition of aqueous dispersion containing the water-dispersed, particulate component (P) is necessary to provide the acidic, aqueous composition.a smaller stationary amount of the water-dispersed, particulate component (P) has to be maintained in the acidic, aqueous composition for zinc phosphating in step (ii) when nitroguanidine or hydroxylamine is used as accelerator, so that nitroguanidine or hydroxylamine, in particular nitroguanidine, are particularly preferred as accelerators in the acidic aqueous composition in step (ii) of the process according to the invention with regard to a particularly low use of material to maintain the phosphating quality.

[0075] From an ecological point of view, 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.

[0076] Furthermore, the process according to the invention can also make use of the additives known in zinc phosphating processes.

[0077] Preferred embodiments of the aqueous dispersion containing the water-dispersed, particulate component (P) used in step (ii) according to the invention can be found in the description of particularly suitable activating aids.

[0078] Suitable activating agents

[0079] 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 dispersion for preactivation 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 "activation aid" instead of the respective "aqueous dispersions containing a dispersed constituent (P)".The preferred activating aids are characterized in that they have a high stability towards agglomeration, thus being particularly suitable for the formation of crystalline phosphate coatings and, in particular when used according to the invention, releasing a high proportion of activating phosphate particles or providing them for the activation of the surfaces of zinc and / or iron, so that compact, closed, crystalline coatings with a relatively low layer weight can be achieved particularly reliably in the process according to the invention.

[0080] Activation aids which are used according to the invention, i.e. both for pre-activation in step (i) and for maintaining the phosphating quality or for providing the acidic, aqueous composition for zinc phosphating in step (ii), are therefore aqueous dispersions containing a particulate constituent (P) dispersed in water, which comprises at least one particulate inorganic compound (P1) which is 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).

[0081] The use of polyvalent metal cations in the form of phosphates is responsible for the good (pre)activation performance, which should therefore be present in the activating aid at a sufficiently high proportion in the dispersed particulate component (P). Accordingly, the proportion of phosphates contained in the particulate inorganic compounds (P1), based on the dispersed inorganic component of the activating aid, is preferably at least 25 wt.%, particularly preferably at least 35 wt.%, especially preferably at least 40 wt.%, and most preferably at least 45 wt.%.

[0082] The dispersed particulate component (P) of the activating agent – ​​or the water-dispersed particulate component (D) of the acidic aqueous composition in step (ii) – is the solid fraction remaining after drying the retentate of an ultrafiltration of a defined sub-volume of the activating agent – ​​or of the acidic aqueous composition – with a nominal molecular weight cut-off of 10 kD (NMWC). The ultrafiltration is carried out with the addition of deionized water (K ​​< 1 pScm -1 ) until the conductivity in the filtrate is below 10 pScrn -1is measured. The inorganic particulate component of the activating aid - or the inorganic, water-dispersed, particulate component of the acidic aqueous composition in step (ii) - is in turn the component that remains when the particulate component (P) or (D) obtained from the drying of the ultrafiltration retentate is pyrolyzed in a reaction furnace with the addition of a CO2-free oxygen stream at 900 °C without the addition of catalysts or other additives until an infrared sensor in the outlet of the reaction furnace delivers a signal identical to that of the CO2-free carrier gas (blank value). The phosphates contained in the respective inorganic particulate component, calculated as PO4, are determined after acid digestion of the same with aqueous 10 wt.% HNO3 solution at 25 °C for 15 min by means of atomic emission spectrometry (ICP-OES) directly from the acid digestion as phosphorus content multiplied by the factor 3.07.

[0083] As already mentioned, the active components of the activating agent 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 most preferably at least partially selected from hopeite. Achieving the desired phosphating quality on the surfaces of zinc and / or iron in the process according to the invention is essentially based on the phosphates in particulate form contained in the activating agent. Hopeites, without taking crystal water into account, stoichiometrically comprise Zns(PO4)2 as well as the nickel and manganese-containing variants Zn2Mn(PO4)3, Zn2Ni(PO4)3, whereas phosphophyllite consists of Zn2Fe(PC>4)3, scholzite of Zn2Ca(PC>4)3 and hureaulite of Mn3(PC>4)2.The existence of the crystalline phases hopeite, phosphophyllite, scholzite and / or hureaulite in the activating aid can be demonstrated by X-ray diffraction (XRD) methods after separation of the particulate component (P) by ultrafiltration with a nominal exclusion limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off) as described above and drying of the retentate to constant mass at 105°C.

[0084] Due to the preference for the presence of phosphates which comprise zinc ions and have a certain crystallinity, it is preferred for the formation of firmly adhering crystalline zinc phosphate coatings if, in the process according to the invention, the activating aid contains at least 20% by weight, particularly preferably at least 30% by weight, especially preferably at least 40% by weight of zinc in the inorganic particulate component based on the phosphate content of the inorganic particulate component, calculated as PO4.

[0085] However, the activating aid should preferably not additionally contain any titanium phosphates, since these can also have an activating effect as such, but in the context of the present invention do not further positively influence the phosphating quality. In a preferred embodiment of the process according to the invention, the proportion of titanium in the inorganic particulate component of the activating aid is therefore less than 0.01 wt. %, particularly preferably less than 0.001 wt. %, based on 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.

[0086] The polymeric organic compound (P2) that stabilizes the particulate component (P) of the respective dispersion exerts a significant influence on the effectiveness of the activating agent. It turns out that the selection of the polymeric organic compound is crucial for the extent of pre-activation of the zinc and / or iron surfaces in process step (i) and the phosphating quality ultimately achieved through integrated activation in step (ii).

[0087] For the purposes 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 respective reference quantity, determined experimentally using size-exclusion chromatography with a concentration-dependent refractive index detector at 30 °C and calibrated against polyethylene glycol standards. The molar mass averages are evaluated computer-assisted using the strip method with a third-order calibration curve. Hydroxylated polymethacrylate is suitable as the 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 used as the eluent.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 α-olefin having not 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.

[0088] The α-olefin is preferably selected from ethene, 1-propene, 1-butene, isobutylene, 1-pentene, 2-methylbut-1-ene, and / or 3-methylbut-1-ene, and particularly preferably selected from isobutylene. It is clear to the 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.

[0089] Preferred activating aids include those polymeric organic compounds (P2) which are at least partly composed of styrene.

[0090] The polymeric organic compounds (P2) used for the colloidal stabilization of the particulate constituent (P) of the activating aid preferably have polyoxyalkylene units, which in turn are preferably composed of 1,2-ethanediol and / or 1,2-propanediol, particularly preferably both from 1,2-ethanediol and from 1,2-propanediol, wherein the proportion of 1,2-propanediols in the totality of the polyoxyalkylene units is preferably at least 15 wt. %, but particularly preferably not exceeding 40 wt. %, based on the totality of the polyoxyalkylene units. Furthermore, the polyoxyalkylene units are preferably present in the side chains of the polymeric organic compounds (P2). A proportion of the polyoxyalkylene units in the totality of the polymeric organic compounds (P2) of preferably at least 40 wt. %, particularly preferably at least 50 wt. %, but preferably not more than 70 wt.-% is beneficial for their dispersibility.

[0091] For the anchoring of the polymeric organic compound (P2) with the inorganic particulate component (P1) of the activating aid, which is at least partially formed by polyvalent metal cations in the form of phosphates selected from hopeite, phosphophyllite, scholzite and / or hurealite, and an increased stability and ability of the particulate component (P) to activate the surfaces of zinc and / or iron, the organic polymeric compounds (P2) additionally also have imidazole units, particularly preferably in the side chains of the polymeric compounds (P2).

[0092] In a preferred embodiment, the amine number of the organic polymeric compounds (P2) is at least 25 mg KOH / g, more preferably at least 40 mg KOH / g, but preferably less than 125 mg KOH / g, particularly preferably less than 80 mg KOH / g, so that in a preferred embodiment, the totality of the polymeric organic compounds in the particulate constituent (P) of the activating aid also has these preferred amine numbers. The amine number is determined in each case based on a weight of approximately 1 g of the respective reference quantity—organic polymeric compounds (P2) or totality of the polymeric organic compounds in the particulate constituent (P)—in 100 ml of ethanol, titrating with 0.1 N HCl standard solution against the indicator bromophenol blue until the color changes to yellow at an ethanolic solution temperature of 20 °C.The amount of standard HCl solution used in milliliters multiplied by the factor 5.61 divided by the exact mass of the sample in grams corresponds to the amine number in milligrams of KOH per gram of the respective reference quantity.

[0093] It has also proven advantageous if the polymeric organic compounds (P2), preferably also the entirety of the polymeric organic compounds in the particulate constituent (P), have an acid number according to DGF CV 2 (06) (as of April 2018) of at least 25 mg KOH / g, but preferably less than 100 mg KOH / g, particularly preferably less than 70 mg KOH / g, in order to ensure a sufficient number of polyoxyalkylene units. Furthermore, it is preferred if the polymeric organic compounds (P2), preferably also the entirety of the polymeric organic compounds in the particulate constituent (P), have a hydroxyl number of less than 15 mg KOH / g, particularly preferably less than 12 mg KOH / g, especially preferably less than 10 mg KOH / g, in each case determined according to Method A of 01 / 2008:20503 from European Pharmacopoeia 9.0.

[0094] 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 (Münzing Chemie GmbH), a maleic acid-styrene copolymer modified with EO / PO and imidazole units.

[0095] For a stable dispersion of the inorganic particulate constituents in the activating aid, it is sufficient if the proportion of the polymeric organic compounds (P2), preferably the totality of the polymeric organic compounds in the particulate constituent (P), based on the particulate constituent (P), is at least 3 wt.%, particularly preferably at least 6 wt.%, but preferably does not exceed 15 wt.%.

[0096] The activating aid preferably contains no more than 40% by weight of particulate constituent (P), based on the agent, since otherwise the stability of the dispersion and the process-technical manageability in process steps (i) for pre-activation by wetting using spray devices and in process step (ii) for metering the agent into the acidic, aqueous composition for zinc phosphating using metering pumps are no longer guaranteed or at least complex. According to the invention, it has been shown that for the metering 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% by weight, but particularly preferably no more than 30% by weight, of particulate constituent (P), based on the agent.The activating aid of process step (i), which is used as an aqueous dispersion for wetting the surfaces of zinc and / or iron, is, however, preferably to be concentrated less for wetting by misting and preferably contains not more than 5% by weight of particulate component (P) based on the agent, but for good activation preferably at least 0.005% by weight of the particulate component (P) based on the agent.

[0097] In concentrated aqueous dispersions, i.e. those activating auxiliaries with a proportion of at least 5% by weight of particulate constituent (P), based on the agent, the agent can additionally be characterized by its D50 value of more than 10 pm, which is correspondingly preferred. For good applicability, in particular in process step (i), however, it is preferred if the aqueous dispersion of the particulate constituents (P) has a D90 value of less than 150 pm, preferably less than 100 pm, in particular less than 80 pm. The D50 value or the D90 value, respectively, in the context of the present invention, denotes the particle diameter which 50% by volume or 90% by volume, respectively, of the particulate constituents present in the aqueous dispersion do not exceed. The D50 value orAccording to ISO 13320:2009, the D90 value can be determined by light scattering analysis according to the Mie theory from volume-weighted cumulative particle size distributions immediately after dilution of the activating agent to a dispersed particulate component of 0.05 wt.% with an appropriate amount of deionized water (K ​​< 1 pScm. -1) at 20 °C, assuming spherical particles and a refractive index of the scattering particles of nD = 1.52 - i 0.1. Dilution is carried out by adding an appropriate amount of the activating agent to a volume of 200 ml of deionized water in the sample vessel of the LA-950 V2 particle size analyzer from Horiba Ltd., and then mechanically circulating the water into the measuring chamber (circulation pump setting on the LA-950 V2: stage 5 = 1167 rpm for a flow rate of 3.3 liters / minute). The particle size distribution is measured within 120 seconds after the activating agent is added to the dilution volume.

[0098] The presence of a thickener can be advantageous for preventing the irreversible agglomeration of primary particles of the particulate constituent (P), particularly when the activating agent, as described above, contains at least 5% by weight of particulate constituent (P), based on the agent. Accordingly, the activating agent preferably contains a thickener, again preferably in an amount that imparts to the activating agent, in the shear rate range from 0.001 to 0.25 reciprocal seconds, a maximum dynamic viscosity at a temperature of 25°C of at least 1000 Pa s, but preferably below 5000 Pa s, and preferably results in shear-thinning behavior, i.e., a decrease in viscosity with increasing shear rate, at shear rates above that present at the maximum dynamic viscosity at 25°C, so that the activating agent exhibits thixotropic flow behavior overall.The viscosity over the specified shear rate range can be determined using a plate / cone viscometer with a cone diameter of 35 mm and a gap width of 0.047 mm.

[0099] A thickener in the sense of the present invention is a polymeric chemical compound or a defined mixture of chemical compounds which is used as a 0.5 wt.% component in deionized water (K ​​< 1 pScm -1) at a temperature of 25 °C has a Brookfield viscosity of at least 100 mPa s at a shear rate of 60 rpm (= rounds per minute) using a size 2 spindle. When determining this thickening property, the mixture with water must be prepared in such a way that the appropriate amount of the polymeric chemical compound is added to the water phase while stirring at 25 °C. The homogenized mixture is then freed of air bubbles in an ultrasonic bath and left to stand for 24 hours. The measured viscosity value is then read immediately within 5 seconds after a shear rate of 60 rpm is applied using spindle number 2.

[0100] The activating agent 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, wherein the total proportion of polymeric organic compounds in the non-particulate component of the activating agent preferably does not exceed 4 wt. % (based on the agent). The non-particulate component is the solids content of the respective aqueous dispersion or of the activating agent in the permeate of the previously described ultrafiltration after drying to constant mass at 105°C – i.e., the solids content after separation of the particulate component by ultrafiltration.

[0101] Certain classes of polymeric compounds are particularly suitable thickeners and are also readily available commercially. 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, especially those urea urethane resins that are a mixture of polymeric compounds resulting from the reaction of a polyfunctional isocyanate with a polyol and a mono- and / or diamine.In a preferred embodiment, the urea urethane resin is derived from a polyfunctional 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 is derived 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, particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23 oxyalkylene units.

[0102] Particularly suitable and therefore preferred urea urethane resins according to the invention are obtainable by a first reaction of 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 contain neither free nor blocked isocyanate groups are particularly preferred. As a component of the activating aid, such urea urethane resins promote the formation of loose agglomerates of primary particles that are protected against further agglomeration and dissociate into primary particles upon dilution, for example during contacting in step (i), or when added to the acidic, aqueous composition in step (ii).To further enhance this property profile, urea urethane resins that contain neither free or blocked isocyanate groups nor terminal amine groups are preferably used as thickeners. In a preferred embodiment, the thickener, which is a urea urethane resin, therefore has an amine number of less than 8 mg KOH / g, more preferably less than 5 mg KOH / g, and most preferably less than 2 mg KOH / g, determined in each case by the method described above for the organic polymeric compound (P2).Since the thickener is essentially dissolved in the aqueous phase of the activating aid and can thus be assigned to the non-particulate constituent, while component (P2) is essentially bound in the particulate constituent (P), an activating aid is accordingly preferred in which the totality of the polymeric organic compounds in the non-particulate constituent preferably has an amine number of less than 16 mg KOH / g, more preferably less than 10 mg KOH / g, especially preferably less than 4 mg KOH / g. Furthermore, it is preferred that the urea urethane resin has a hydroxyl number in the range from 10 to 100 mg KOH / g, more preferably in the range from 20 to 60 mg KOH / g, determined according to Method A of 01 / 2008:20503 from European Pharmacopoeia 9.0.With regard to molecular weight, a weight-average molar mass of the urea urethane resin in the range of 1000 to 10,000 g / mol, preferably in the range of 2000 to 6000 g / mol, is advantageous according to the invention and therefore preferred, determined experimentally as described above in connection with the inventive definition of a polymeric organic compound. The activating aid is an aqueous dispersion that preferably has a pH in the range of 6.0-9.0 and particularly preferably contains no pH-regulating, water-soluble compounds with a pKa value of less than 6 or a pKa value of less than 5.

[0103] The activating agent may also contain other excipients, for example selected from preservatives, wetting agents, and defoamers, in the amount required for their respective function. The proportion of excipients, particularly preferably other compounds in the non-particulate component that are not thickeners, is preferably less than 1% by weight.

[0104] The activating aid is preferably obtainable by a) providing a pigment paste by grinding 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 pm is reached, determined by means of dynamic light scattering after dilution with water by a factor of 1000, e.g. using Zetasizer® Nano ZS, Malvern Panalytical GmbH; b) diluting the pigment paste with such an amount of water, preferably deionized water (K<1 pScrrr 1) or process water, and a thickener, that a dispersed particulate component (P) of at least 5 wt.% and a maximum dynamic viscosity of at least 1000 Pa s at a temperature of 25 °C in the shear rate range of 0.001 to 0.25 reciprocal seconds is set, wherein preferred embodiments of the activating aid are obtained by selecting corresponding components (P1), (P2) and the thickener in the amount possibly provided or required in each case in an analogous manner.

[0105] Within the scope of the present invention, it is preferred, particularly for reasons of process economy, if the activating aids in process steps (i) and (ii) are each based on identical water-dispersed, particulate components (P). The water-dispersed, particulate components (P) are considered identical if components (P1) and (P2) do not differ from one another in their chemical constitution, i.e., if the water-dispersed, particulate components (P) of the respective aqueous dispersions contain the stoichiometrically identical phosphate of the same polyvalent cation and, with respect to the polymeric organic compounds, the same constitutional repeating units. Embodiments:

[0106] In the following, it will be shown that wetting of metallic substrates with an activating agent prior to an activating zinc phosphating bath can reduce the layer weight and at the same time save the activating agent required to set an activating zinc phosphating bath.

[0107] For this purpose, test panels (105x190 mm, Gardobond®, Chemetall) made of cold-rolled steel (CRS), hot-dip galvanized steel (HDG) and aluminum (alloy AA6014) were first wetted with an activating agent and immediately subsequently zinc phosphated.

[0108] For the procedure sequences listed and completed in Table 1, the following treatment stages (1)-(6) were provided:

[0109] (1) Spray degreasing at 1 .0 bar for 60 seconds at a temperature of the spray medium of 54°C, whereby the spray medium with a pH value of 11 .2 was composed of

[0110] 30 g / kg Bonderite® C-AK 1574 A

[0111] 3 g / kg Bonderite® C-AD 1270

[0112] 1 g / kg Bonderite® M-AD 100 each product of Henkel AG & Co. KGaA a quantity of NaHCOs for pH adjustment

[0113] Rest: deionized water (K ​​< I pScnr 1 )

[0114] (2) Immersion degreasing for 180 seconds at a temperature of the immersion medium of 55 °C, whereby the immersion medium with a pH value of 11.2 was identical to the medium of the spray degreasing (1)

[0115] (3) Rinse with deionized water (K ​​< 1 pScm -1 ) at a temperature of the rinsing medium of about 20 °C for about 60 seconds

[0116] (4) Wetting activation by misting the test panels at about 20°C with an activating agent with a pH value of 10.0 and composed of

[0117] 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) a quantity of 10 wt.% NaOH solution for pH adjustment Rest: deionized water (K ​​< I pScnr 1 )

[0118] Inorganic particulate component (P1): Hopeite (Zns(PO4)2)

[0119] Polymeric organic compound (P2): Maleic acid-styrene copolymer modified with EO / PO units Amount of the particulate component (P) in the activating agent: 60 mg / kg (a), 100 mg / kg (b) or 600 mg / kg (c)

[0120] The spraying was carried out using a spray bottle (Würth; Art. No. 0891 502 002; 500 ml), whereby three sprays per side of the sheet were sufficient to completely wet the surface. The thus wetted sheets were immersed in the zinc phosphating bath of step (5) after a contact time of approximately 5 seconds.

[0121] (5) Activated trication zinc phosphating by immersion in the phosphating bath at 51 °C for 180 seconds, the phosphating bath having a free acidity of 1.1 points, a total acidity of 26.5 points and 170 mg / kg free fluoride and being composed as follows:

[0122] 1.3 g / kg zinc ions

[0123] 0.8 g / kg manganese ions

[0124] 0.9 g / kg nickel ions

[0125] 14.7 g / kg phosphate anions 1.0 g / kg SiFe anions 1.3 g / kg NaNO3 1.0 g / kg hydroxylamine

[0126] Amount of added activating agent: 1.0 g / kg (a) or 0.2 g / kg (b) Bonderite® M-AC 3000 (Henkel AG & Co KGaA) in deionized water (K ​​< 1 pScnT 1 )

[0127] Amount of water-dispersed particulate matter (D): 200 mg / kg (a) or 40 mg / kg (b)

[0128] (6) Rinse with deionized water (K ​​< 1 pScm -1 ) at a temperature of the rinsing medium of about 20 °C for about 60 seconds

[0129] (7) Drying the sheet by blowing with compressed air

[0130] Table 1 lists the coating weights achieved according to the process sequences listed therein. It shows that pre-activation of the zinc surfaces leads to a significant reduction in coating weight in the activating zinc phosphating (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 reduction in coating weight of approximately 2 g / m² occurs on the zinc surfaces. 2 while still achieving a closed, homogeneous phosphate layer (E1 vs. E2). Pre-activation by fogging also reduces the coating weight on steel surfaces, which is already well below 3 g / m 2 (CRS: V1), significantly reduced and even to values ​​below 2 g / m 2(CRS: E1 vs. E2) without any loss of phosphating quality in the layer formation. The layer formation process on the surfaces of aluminum is only slightly dependent on the respective process sequence and is in the range of 2 g / m with or without pre-activation. 2 Overall, the process according to the invention makes it possible to level the coating weights, which still vary on different substrates during activated zinc phosphating. For example, for components made of zinc, iron, and aluminum, it is sufficient to simply wet the surfaces of the zinc or zinc and iron with an activating agent to achieve closed, homogeneous, and crystalline zinc phosphate coatings with a coating weight in the range of 2 g / m² on all substrates after activated zinc phosphating. 2The two-stage process is also very effective with regard to the use of activating aids and, as the type E3 process sequence shows, can be optimized so that less activating aid is needed overall compared to a purely activated zinc phosphating process. Thus, with the type E3 process sequence, the amount of activating aid in the zinc phosphate bath can be reduced to a fifth of the amount used in process sequence V1, and yet significantly lower coating weights are still achieved on HDG. Only pre-activation of the zinc surfaces is required, meaning that only a fraction of the activating aid needs to be used; this would otherwise have to be added to the zinc phosphate bath in a type V1 process sequence to maintain the phosphating quality.It should also be considered that part of the activation aid remaining on the pre-activated surfaces of zinc enters the zinc phosphate bath directly with the components and contributes to maintaining the phosphating quality, so that overall, the process according to the invention makes a very resource-saving process control in zinc phosphating accessible.

[0131] Table 1

[0132] * low / medium / high: related to the concentration of the activating agent in the pre-activation

[0133] 1 differential gravimetric determination after removal of the phosphate layer in 0.5 wt.% chromic acid solution (HDG, CRS) or 50 wt.% nitric acid (AI)

Claims

Claims:

1. A method for the corrosion-protective pretreatment of a large number of components in series, in which each component of the series has at least partially surfaces of zinc and / or iron and first undergoes a process step (i) for activating the surfaces of zinc and / or iron and immediately thereafter a process step (ii) for zinc phosphating, wherein in process step (i) at least the surfaces of zinc and / or iron of each component of the series are brought into contact with an aqueous dispersion containing a water-dispersed, particulate component (P) comprising 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),wherein the contacting is carried out by dispensing the aqueous dispersion from a supply in such a way that per square meter of the surface of each component of the series, preferably per square meter of the surfaces of zinc and / or iron of each component of the series to be brought into contact, not more than, 1.00 litres of the aqueous dispersion is dispensed, and wherein in process step (ii) at least the surfaces of zinc and / or iron of each component of the series are brought into contact with an acidic, aqueous composition having a free acidity in points greater than zero, and (A) 5 - 50 g / kg of phosphates dissolved in water calculated as PO4, (B) 0.3 - 3 g / kg of zinc ions, (C) free fluoride, and (D) a water-dispersed, particulate component comprising phosphates of polyvalent metal cations, wherein the phosphates are at least partially selected from hopeite, phosphophyllite, scholzite and / or hureaulite, wherein the acidic, aqueous composition is obtainable by adding an amount of an aqueous dispersion to an acidic, aqueous composition comprising components (A) - (C), wherein the aqueous dispersion contains a water-dispersed, particulate component (P) 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).

2. Method according to one or both of the preceding claims, characterized in that the bringing into contact of at least the surfaces of zinc and / or iron of the components in method step (i) is carried out by dispensing the aqueous dispersion from a supply in such a way that per square meter of the surfaces of zinc and / or iron of the components of the series to be activated that are to be brought into contact, preferably per square meter of the surface of a component of the series, not more than 0.50 litres, preferably not more than 0.20 litres of the aqueous dispersion is dispensed.

3. Method according to one or more of the preceding claims, characterized in that the dispensing of the aqueous agent for bringing into contact in method step (i) takes place in such a way that at least the surfaces of zinc and / or iron are covered by a liquid film containing the aqueous dispersion, whereby on the surfaces of zinc and / or iron a volume-related coating per square meter of preferably not more than 1.00 litres, particularly preferably not more than 0.50 litres, very particularly preferably not more than 0.20 litres and especially preferably not more than 0.10 litres results.

5. Method according to one or more of the preceding claims, characterized in that the aqueous agent is dispensed in method step (i) as a spray, as a mist or as a liquid film, preferably as a spray and / or a mist, particularly preferably as a spray.

6. The process according to one or more of the preceding claims, characterized in that in process step (i) and / or in process step (ii) the polymeric organic compound (P2) in the particulate constituent (P) of the aqueous dispersion is at least partly composed of styrene and / or an α-olefin having not 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, which in turn are preferably at least partly end-capped with aliphatic alkyl groups having not more than four carbon atoms.

7. The method according to claim 6, characterized in that the polymeric organic compound (P2) in the particulate component (P) of the aqueous dispersion additionally also contains imidazole units.

8. Process according to one or both of the preceding claims 6 and 7, characterized in that the proportion of polyoxyalkylene units in the total of the polymeric organic compounds (P2) is at least 40 wt.%, preferably at least 50 wt.%, but preferably does not exceed 70 wt.%.

9. Process according to one or more of the preceding claims, characterized in that in process step (i) and / or process step (ii) the proportion of phosphates calculated as PO4 contained in the at least one particulate inorganic compound (P1) based on the dispersed, inorganic particulate constituent of the aqueous dispersion is at least 25 wt.%, preferably at least 35 wt.%, particularly preferably at least 40 wt.%, very particularly preferably at least 45 wt.%.

10. The process according to one or more of the preceding claims, characterized in that in process step (i) and / or process step (ii) the aqueous dispersion contains at least one thickener as a further component, which is preferably selected from urea urethane resins, preferably from urea urethane resins which have an amine number of less than 8 mg KOH / g, particularly preferably less than 5 mg KOH / g, very particularly preferably less than 2 mg KOH / g.

11. Process according to one or more of the preceding claims, characterized in that the water-dispersed, particulate component (P) of the aqueous dispersion in process step (i) is at least 0.060 g / kg, preferably at least 0.100 g / kg, but preferably not more than 5.0 g / kg, particularly preferably not more than 1.0 g / kg, based on the aqueous dispersion.

12. Process according to one or more of the preceding claims, characterized in that the aqueous dispersion in process step (i) for activating the zinc surfaces has a pH above 6.0, preferably above 6.5, but preferably does not exceed a pH of 9.0, particularly preferably of 8.5, most particularly preferably of 8.0 and especially preferably of 7.

5.

13. Process according to one or more of the preceding claims, characterized in that in process step (ii) the aqueous dispersion is added in such an amount that the weight fraction of the phosphates of the water-dispersed, particulate component (D) based on the acidic aqueous composition is at least 0.1 mg / kg, preferably at least 0.5 mg / kg, particularly preferably at least 1.0 mg / kg and most preferably at least 2.0 mg / kg.

14. Process according to one or more of the preceding claims, characterized in that the acidic aqueous composition for zinc phosphating in process step (ii) has a pH value below 3.6, preferably below 3.4, particularly preferably below 3.2, wherein the free acid is preferably greater than 0.5 points, more preferably greater than 0.8 points and especially preferably greater than 1.0 points.

15. Method according to one or more of the preceding claims, characterized in that the components of the series at least partially have surfaces of zinc and preferably also surfaces of iron and very particularly preferably additionally surfaces of aluminum.

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