Multi-stage treatment for activated zinc phosphating of metal parts

Abstract

The invention relates to a method for the anti-corrosion pretreatment of a plurality of components in series, wherein each component in series has at least partially a zinc and / or iron surface and at least part of these surfaces are first activated in a targeted manner for subsequent zinc phosphating. Targeted activation is achieved by controlled dispensing of an aqueous dispersion to wet the zinc and / or iron surface, thereby ensuring resource-saving activation. The aqueous dispersion for activating wetting contains particulate components dispersed in water, which are at least partially composed of spurtzite, spurtzite, wurtzite and / or manganwentzite, and which are provided as dispersions of these crystalline solids, which are stabilized by at least one polymerized organic compound, and is characterized in that the particulate components are at least partially composed of spurtzite, spurtzite, wurtzite and / or manganwentzite. The phosphating quality of the acidic aqueous composition of zinc phosphating is ensured and maintained again by adding an amount of aqueous dispersion, in particular the same aqueous dispersion also used to activate wetting.

Description

[0001] The present invention relates to a method for the anticorrosive pretreatment of a plurality of components in series, wherein each component in series has at least partially a surface of zinc and / or iron, and at first at least parts of these surfaces are activated in a targeted manner for the subsequent purpose of zinc phosphation. The targeted activation is achieved by controlled dispensing of an aqueous dispersion for wetting the aforementioned zinc and / or iron surfaces, thereby ensuring a resource-saving activation ("activation wetting"). The aqueous dispersion for activation wetting comprises particulate constituents dispersed in water, which at least partially consist of zinc phosphate, phosphophyllite, whitlockite and / or hureaulite, and are provided as a dispersion of these crystalline solids, which are stabilized by at least one polymeric organic compound. By adding an amount of aqueous dispersion, in particular the same aqueous dispersion also used for activation wetting, it is also ensured and maintained that the phosphating quality of the acidic aqueous composition for zinc phosphation is maintained.

[0002] Phosphating to form layers is a method for applying a crystalline anticorrosive coating to metal surfaces, in particular to metallic iron, zinc and aluminum materials, which has been used for decades and has been intensively researched. In particular the zinc phosphation method established for protection against corrosion is carried out with a layer thickness of a few micrometers and is based on the corrosive pickling of the metal material in an acidic aqueous composition containing zinc ions and phosphates, during which low-solubility microcrystals are formed near the surface, which directly precipitate on the boundary surface with the metal material, where they continue to grow.

[0003] Zinc phosphation is generally set in such a way that a uniform, closed and dense crystalline coating is obtained on the surface of metallic iron, zinc and aluminum. Otherwise, good anticorrosive protection and good coating of the substrate cannot be achieved. A uniform, closed coating is reliably achieved during zinc phosphation with a layer weight of more than 2 g / m 2 .

[0004] In order to achieve such a uniform, closed coating with a high degree of density or high number density of phosphate microcrystals, in the prior art zinc phosphation is generally initiated by activating the metal surfaces of the components to be phosphated. Activation is a wet-chemical method step, which is conventionally carried out by contacting the surfaces with a colloidal aqueous solution of phosphates, which serve as growth nuclei for the formation of a crystalline coating in the subsequent phosphation method, in the case where they are fixed on the metal surfaces, thereby producing a high number density of growing microcrystals and thus again a dense crystalline zinc phosphate layer, which has excellent anticorrosive protection and, due to its high charge transfer resistance, also excellent electrocoating properties.

[0005] Depending on the metal surfaces to be phosphatized, it is necessary in the zinc phosphatizing stage not only to adjust the performance of the above-described activation stage, but also to adjust the pickling process by the concentration of the active components, which often requires an intensified activation in the immersion process and at the same time a sufficient pickling in the presence of fluoride ions in the phosphatizing stage, in particular for metal parts, such as vehicle bodies consisting of a mixture of different materials, in order to achieve a correspondingly high layer weight on all surfaces of the parts, in particular zinc, iron or steel and aluminum.

[0006] However, very recently, a method was described in WO 2022 / 048963, in which even the conventional activation of the surface prior to zinc phosphatizing can be dispensed with, provided that the zinc phosphatizing treatment bath itself has an activating effect and thus contains a sufficient amount of phosphate in dispersed form.

[0007] Although this method for zinc phosphatizing with integrated activation can be used to reliably phosphatize different metals to form layers, the proportion of the dispersed phosphate with an activating effect in the acidic aqueous composition of the phosphatizing bath has to be adapted each time to the parts to be treated. When treating parts made of different metals to protect them from corrosion, the most challenging metal surfaces for activation always determine the total consumption of the active components, i.e. the dispersed phosphate. A less ideal activation in the activation stage or in the phosphatizing stage for a lower consumption of the dispersed phosphate inevitably leads to a higher phosphate layer weight, especially on zinc or iron surfaces, and thus at the expense of a higher consumption of active components during the phosphatizing stage.

[0008] Therefore, there is a need to be able to fully exploit the undisputed method-economic advantages of the integrated method in WO 2022 / 048963 A1, which consist of a reduced pretreatment sequence that can be controlled with less effort, and to reduce the consumption of active components as much as possible without compromising the phosphatizing quality, which corresponds to a resulting uniform, closed and as fine-crystalline as possible phosphate layer with low layer weight, in particular on zinc and / or iron surfaces, very particularly on zinc surfaces of the parts to be treated. Such a resource-saving method with activated zinc phosphatizing must be suitable for fully activating parts consisting of different metal materials to form layers with high phosphatizing quality, despite the material-specific requirements.

[0009] The task profile has been solved in the present case by selectively and controllably dispensing an aqueous dispersion for the activation of wet metal surfaces prior to the actual integrated zinc phosphatizing method. The activation of wet zinc and / or iron surfaces surprisingly makes it possible to significantly reduce the zinc phosphatizing layer weight at the same phosphatizing quality and thus the consumption of active components during zinc phosphatizing likewise significantly.

[0010] The present invention relates in particular to a method for the anticorrosive pretreatment of a plurality of components in series, wherein each component in series has at least partially a zinc and / or iron surface and is first subjected to a method step (i) for the activation of the zinc and / or iron surface and is immediately thereafter subjected to a method step (ii) for zinc phosphating, wherein in method step (i) at least the zinc and / or iron surface of each component in series is contacted with an aqueous dispersion comprising a water-dispersed particulate component (P) which comprises - at least one particulate inorganic compound (P1) which consists of a phosphate of a polyvalent metal cation which is at least partially selected from the group consisting of zincophosphates, phosphatophyllites, calciumzincophosphates and / or red manganophosphates, - and at least one polymeric organic compound (P2), wherein this contacting is carried out by dispensing the aqueous dispersion from a supply such that not more than 1.00 liter of the aqueous dispersion per square meter of the surface of each component in series - preferably not more than 1.00 liter of the aqueous dispersion per square meter of the zinc and / or iron surface of each component in series to be contacted with the dispersion - is dispensed, and wherein in method step (ii) at least the zinc and / or iron surface of each component in series is contacted with an acidic aqueous composition which has a free acid with a point greater than zero, and (A) 5 to 50 g / kg of a phosphate dissolved in water, calculated as PO4, (B) 0.3 to 3 g / kg of zinc ions, (C) free fluorides, and (D) a water-dispersed particulate component of a phosphate of a polyvalent metal cation, wherein the phosphate is at least partially selected from the group consisting of zincophosphates, phosphatophyllites, calciumzincophosphates and / or red manganophosphates, wherein the acidic aqueous composition is obtained by adding an amount of an aqueous dispersion to an acidic aqueous composition comprising components (A) to (C), wherein the aqueous dispersion comprises a water-dispersed particulate component (P) which comprises - at least one particulate inorganic compound (P1) which consists of a phosphate of a polyvalent metal cation which is at least partially selected from the group consisting of zincophosphates, phosphatophyllites, calciumzincophosphates and / or red manganophosphates, - and at least one polymeric organic compound (P2).

[0011] The pretreatment in the series takes place when the individual components in the series one after the other and thus at separate times are subjected to the method steps (i) and (ii) of zinc phosphating according to the application and thus are in immediate succession with the respective aqueous composition stored in the system tank (as intended). The system tank in method step (i) is a container in which the aqueous dispersion is held for the purpose of activating zinc and / or iron surfaces by wetting, and the system tank in method step (ii) is accordingly a container which accommodates the acidic aqueous composition for zinc phosphating. The components can be brought into contact with the acidic aqueous composition in method step (ii) within the system tank, for example by immersion, or outside the system tank, for example by spraying the acidic aqueous composition of the bath stored in the system tank. The zinc and / or iron surfaces of each component in the series are brought into contact with the aqueous dispersion in method step (i) by dispensing a defined volume of the dispersion from the supply onto the surface to be activated, preferably in such a way that the volume of aqueous dispersion dispensed for each component once does not return to the system tank in which the dispersion is held, for example by wetting the surface to be activated outside the system tank from which the stored aqueous dispersion is dispensed for each component.

[0012] The components treated according to the application can be three-dimensional structures of any shape and design which originate from a manufacturing process, in particular also including semi-finished products, such as strips, sheets, rods, tubes and the like, and composite structures assembled from said semi-finished products, which are connected to one another, preferably by bonding, welding and / or crimping, to form the composite structure.

[0013] The method according to the application is particularly effective for producing a dense, closed and crystalline phosphate coating on zinc surfaces, so that the preferred components in the series are those which have at least zinc surfaces. The method according to the application is also very suitable for layer-forming phosphating of aluminium, so that even components having a mixed construction, for example a motor vehicle body composed of the materials zinc, iron and aluminium, can be effectively and in a resource-saving manner phosphated according to the application. However, aluminium surfaces generally do not need to be preactivated in method step (i) and sufficient layer formation occurs when said aluminium surfaces are brought into contact with the acidic aqueous composition in method step (ii). In a particular embodiment of the method according to the application, the components in the series which have at least partly zinc and / or iron surfaces additionally also have surfaces of metallic aluminium, wherein the surfaces of metallic aluminium are preferably not contacted with the aqueous dispersion dispensed in method step (i) but are contacted with the acidic aqueous composition in method step (ii).

[0014] In the context of the method according to the application, a component has at least one surface made of zinc and / or iron, if more than 50 atom-% of the metal structure up to a material penetration depth of at least one micrometer on this surface consists of zinc and / or iron. This often applies to components made of the respective metal material, in the case of more than 50 atom-% of the metal material consisting of zinc and / or iron as a homogeneous material. However, components comprising a zinc surface are also iron materials provided with a metal coating, such as electrogalvanized or hot-dip galvanized steel, which can also be alloyed with iron (ZF), aluminum (ZA) and / or magnesium (ZM).

[0015] For the resource-saving operation of the corrosion protection method based on zinc phosphating in step (ii), the application provides that the method step (ii) is carried out immediately after the activation in step (i). In this way, on the one hand, the degree of activation of the zinc and / or iron surface of the component for the zinc phosphating stage is maximally maintained, and on the other hand, the zinc phosphating treatment stage is resharpened with the necessary (because they have an activating effect) particulate phosphates, since these are introduced into the phosphating stage by adhering them to the component by means of a wet film.

[0016] Thus, in the context of the application, the direct sequence of activation and zinc phosphating provided according to the application means that the component after the method step (i) does not undergo an intermediate rinsing step or other treatment step which involves a further contact, in particular a contact in the manner of the method step (i), or preferably a contact, in particular a contact between the zinc or iron surface of the component and an aqueous dispersion containing a particulate component (P) in an aqueous dispersion, or in particular a contact with an aqueous composition, in each case preferably without a drying step after the method step (i) or before the method step (i). The rinsing step in this case can involve one or more directly consecutive method steps which serve to remove soluble residues, particles and / or active components as completely as possible which remain on the surface of the component after having been discharged from the preceding wet-chemical method step, for example by rinsing with municipal water. The drying step in this case is a process of drying the component caused by controllable technical provisions, for example by heat supply or by directed air supply.

[0017] Another advantage of the dense, closed and crystalline coatings obtainable on all these metal surfaces using the method according to the application is that they have excellent electrocoatability, by which a high wrap-round behaviour can be achieved. In this respect, it is preferred that step (ii) is followed by an electrocoating, particularly preferably cathodic electrocoating. In principle, the method can be implemented by any type of coating - particularly powder coating - with the conventional organic topcoat systems customary in the prior art, since an excellent basecoat is provided.

[0018] Method step (i) - pre-activation: contacting with the aqueous dispersion to activate at least the zinc and / or iron surface by dispensing it from a supply. The contacting with the aqueous dispersion dispensed from a supply requires, within the meaning of the present application, the use of a device for moving a volume of liquid from a supply, such as a container holding an amount of aqueous dispersion sufficient for a plurality of parts, and a device for dispensing said volume of liquid moved on the surface of the part or parts to be contacted therewith. Thus, the parts are not contacted in the stored aqueous dispersion, i.e. not by immersion in the stored aqueous dispersion, but for example by direct application with a roller or by spraying / misting with a partial volume of the stored aqueous dispersion taken from the supply. Furthermore, according to the present application, the volume of aqueous dispersion dispensed from a supply for the contacting is limited, and should be less than 1.00 litre per square metre of the surface of the parts or preferably only the zinc and / or iron surface of the parts. This ensures that significantly larger volumes of liquid of the aqueous dispersion than are required to completely wet the zinc and / or iron surface with a liquid film of the aqueous dispersion are not dispensed. Thus, it is in principle advantageous to apply the aqueous dispersion as efficiently as possible and without any excess to the surface to be treated. In a preferred embodiment of the method according to the application, the contacting with the zinc and / or iron surface is carried out by dispensing the aqueous dispersion from a supply such that not more than 0.50 litre, preferably not more than 0.2 litre of the aqueous dispersion is dispensed per square metre of the surface of the parts, preferably only the zinc and / or iron surface of the parts to be activated, and thus contacted therewith.

[0019] In this connection, the surface area of the components in the series for the surface area-related volume of the dispensed aqueous dispersion is the surface of a polyhedron having 12 surfaces, preferably 6 surfaces, and particularly preferably a cube, which each completely encloses the component and by doing so has the smallest surface area, each surface of the polyhedron contacting the component at at least one point. If the component is a motor vehicle body, the surface area relating to the surface area-related dispensing of the aqueous dispersion for conditioning purposes is preferably that of a cube having the smallest surface area which completely encloses the motor vehicle body, each surface of the cube contacting the motor vehicle body at at least one point. In a preferred embodiment of the method according to the application, the upper limit of the surface area-related aqueous dispersion volume dispensed on the zinc and / or iron surface is standardized. The geometric area of the surface of the component to be activated made of zinc and / or iron must then be taken into account. Thus, in the treatment of flat products, for example steel strips, it can be the entire outer surface of the flat product to be preactivated in method step (i) which is already required; while in the series treatment of motor vehicle bodies in a preferred embodiment, only those outer surfaces of the vehicle body made of steel strip after forming and joining need to be included, since often only these outer surfaces can be optimally phosphatized to form a layer and thus preactivated accordingly.

[0020] The dispensing of the aqueous dispersion for contacting and thus simultaneously activating the zinc and / or iron surface requires and demands that the amount dispensed from the supply also at least partially reaches these surfaces. Thus, in a preferred embodiment, the dispensed aqueous dispersion for contacting in method step (i) for sufficient activation is carried out to ensure that at least the zinc and / or iron surface is covered by a liquid film of the contained aqueous dispersion, resulting in a volume-related coating on the zinc and / or iron surface of preferably not more than 1.00 liter per square meter, particularly preferably not more than 0.50 liter, very particularly preferably not more than 0.20 liter and particularly preferably not more than 0.10 liter. Unlike the volume of the aqueous dispersion dispensed for contacting, the volume coating here does not refer to the surface of the component approximating the polyhedron, but to the actual geometric surface of the zinc and / or iron surface of the component in the series, whereby it is assumed that the density of the liquid adhering to the surface can be determined as 1 g / cm3. 3 The volume coating can then be determined from the differential weighing after blowing off the liquid film.

[0021] It should be remembered that the components are often already wetted with a liquid film, for example formed by rinsing water from a rinsing step carried out immediately prior to activation, when they are transferred to the activation stage according to method step (i), before contact with the zinc and / or iron surfaces, then according to the application by taking up a liquid volume of the aqueous dispersion in the wet film already adhered to these surfaces. This method variant can be particularly advantageous because the active components taken up by the wet film adhered to the components are better taken up by the pre-wetted surfaces of the components and then distributed more uniformly thereon, which in turn promotes uniform activation for the subsequent zinc phosphating step.

[0022] If the equipment used for dispensing and generating contact is individually sufficient to achieve as complete wetting as possible of the zinc and / or iron surfaces to be activated, it can again be advantageous for reasons of efficiency to remove the wet film adhered to the components from a treatment step carried out immediately prior to method step (i) or directly before the region in which the aqueous dispersion is dispensed for bringing it into contact with the surfaces, for example by blowing off or wiping, in order to use only those aqueous dispersions whose particle content is relatively low but still only sufficient to cause the desired activation as efficiently as possible.

[0023] Whether a liquid film comprising the aqueous dispersion is formed on the zinc and / or iron surfaces in method step (i) can be checked by the addition of a fluorescent marker to the aqueous dispersion supply. Detection can then be carried out by irradiation with UV light and corresponding recording of the fluorescence by a suitable camera, which makes imaging control of the wetting of the component surfaces with the aqueous dispersion possible. This is particularly useful when components having a complex surface geometry have to be pretreated and the type of dispensing of the aqueous dispersion (for example the relative orientation and spacing of the spray guns with respect to the components) first has to be adjusted in an iterative process in such a way that the zinc and / or iron surfaces come into contact with the aqueous dispersion, in particular in such a way that these surfaces are covered with a liquid film comprising the aqueous dispersion. The latter preferred condition does not necessarily have to be achieved directly by bringing the aqueous dispersion from the supply into contact with the surfaces (i.e. directly by the application equipment), but it is sufficient, for example, by rotating, pivoting or tilting the components, that a liquid film comprising the aqueous dispersion which comes into contact with the zinc and / or iron surfaces is produced before method step (ii) (i.e. before the components are introduced into the zinc phosphating process, preferably at least 5 seconds, particularly preferably at least 10 seconds, very particularly preferably at least 20 seconds before they are brought into contact with the acidic aqueous composition in method step (ii)).

[0024] For the controlled dispensing of the aqueous dispersion required in the method according to the application for the purpose of the active wetting of zinc and / or iron surfaces, it is advantageous and thus further preferred that the aqueous dispersion is dispensed in method step (i) as a spray, as a spray mist or as a liquid film, particularly preferably as a spray and / or as a spray mist, particularly preferably as a spray mist. The aqueous dispersion is brought into contact with the surface of the component to be activated by means of the spray and / or the spray mist by means of the spray and atomization methods established in the prior art, and the contact can be effected in a locally limited manner by means of a spray gun and / or at least partially in a manner surrounding the component by means of a spraying ring in which a plurality of atomizing nozzles can be installed. The spray devices to be used for the dispensing of the spray and / or the spray mist are, for example, pressure atomizers, rotary atomizers or two-substance atomizers. Depending on the complexity and geometry of the component in the line, the liquid film can be applied to the component by direct application by means of rollers, cloths, brushes, paint brushes or similar tools for the application of liquids.

[0025] The preferred controlled and effective activation wetting with the aqueous dispersion is achieved by means of a targeted spray directed at the zinc and / or iron surface to be wetted and / or by means of a spray mist through which the component is conveyed together with the conveyor frame, and which is effected with a given volume flow on the conveying path, which is such that the surface of the component to be wetted is exposed to an enclosed liquid film comprising the aqueous dispersion, preferably before the component is brought into contact with the acidic aqueous composition for phosphatizing of the zinc in the immediately subsequent method step (ii).

[0026] For example, in order to dispense the amount of aqueous dispersion required for the formation of a liquid film which covers the surface of the component and thus serves for the effective active wetting, it is preferred according to the application that the dispersion dispensed in method step (i) as a spray and / or as a spray mist has an average droplet size of less than 100 μιη, particularly preferably less than 60 μιη, particularly preferably less than 40 μιη. In the case of an average droplet size below 40 μιη, the aqueous dispersion is strongly atomized, so that the boundary region of the aerosol is exceeded and a spray mist is formed. If the aqueous dispersion is further atomized and the average droplet size is reduced, the droplets will increasingly remain suspended and do not follow the force of gravity. The spray mist which remains suspended then also moves and can whirl due to the moving air masses when the component is conveyed through the spray chamber, and the directed impact on the zinc and / or iron surface to be activated is thus more likely to be impeded and the component surface is wetted less uniformly by the liquid film. It is therefore preferred that the aqueous dispersion dispensed in method step (i) has an average droplet size of not less than 5 μιη, particularly preferably not less than 10 μιη.

[0027] It is also advantageous for the formation of an enclosed liquid film comprising the aqueous dispersion on the surface of the components to be contacted that the spraying and / or atomizing of the aqueous dispersion is dispensed in such a way that the average velocity of the 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 spraying and / or atomizing with an average droplet size of less than 100 μm, particularly preferably less than 60 μm, particularly preferably less than 40 μm.

[0028] According to the application, the average droplet size and the average velocity of the sprayed or atomized droplets are determined at a position which surrounds the geometrical center of gravity of the polyhedron of the component, which position is also used to determine the amount of the dispensed reagent per surface area of the component, as described above. The determination can be carried out by means of light scattering and phase Doppler anemometry.

[0029] By the preferred embodiments mentioned here with respect to how the aqueous dispersion can be dispensed for contacting it with at least zinc and / or iron surfaces, an extremely efficient process can be achieved in which the amount of the aqueous dispersion dispensed from the supply is applied essentially only to the zinc and / or iron surfaces of the components to be activated. At the same time, the proportion of the aqueous dispersion introduced by the components into the zinc phosphatizing stage serves to at least partially compensate for the particulate fraction of the acidic aqueous composition for zinc phosphatizing which is consumed during the activation zinc phosphatizing process and removed from the zinc phosphatizing stage. For the same purpose, the fraction of the aqueous dispersion component dispensed in process step (i) but not remaining on the components can also be combined and transferred to the zinc phosphatizing stage in order to maintain the activation performance. It is therefore preferred according to the application that a process in which the fraction of the aqueous dispersion dispensed in process step (i) to contact at least the zinc and / or iron surfaces of the components but not remaining as a wet film on the components until they are contacted with the acidic aqueous composition for zinc phosphatizing in process step (ii) because they, for example, sink to the bottom as excess spray liquid or flow out of the components and thus remain in the spray chamber in process step (i) is at least partially combined and added to the acidic aqueous composition in process step (ii) and in any case preferably neither partially nor completely returned to the supply.

[0030] In order to achieve sufficient pre-activation of at least the zinc and / or iron surfaces of the components in the series, it is necessary that the aqueous dispersion used comprises a water-dispersible particulate component (P) which consists of a phosphate of polyvalent metal cations (P1) and a polymeric organic compound which contributes to the stabilization of the dispersion (P2).

[0031] As a point to be emphasized, the proportion of the phosphate contained in the at least one particulate inorganic compound (P1 ) in the dispersed inorganic particulate component (P1 ) of the aqueous dispersion is preferably at least 25% by weight, particularly preferably at least 35% by weight, particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight, calculated as PO4. As already explained, further preferred embodiments of the inorganic particulate component (P1 ) can be taken from the respective preferred embodiments of the inorganic particulate component (P1 ) of the aqueous dispersion in process step (ii).

[0032] It should also be emphasized that, for excellent dispersion stability, the polymeric organic compound (P2) in the particulate component (P) of the aqueous dispersion is at least partially composed of styrene and / or alpha-olefins having no more than 5 carbon atoms, wherein the polymeric organic compound (P2) additionally has units of maleic acid, its anhydride and / or its imide, and preferably additionally has polyalkylene oxide units, particularly preferably in side chains, which in turn are preferably at least partially capped by aliphatic alkyl groups having no more than 4 carbon atoms. Furthermore, it is particularly advantageous if the polymeric organic compound (P2) in the particulate component (P) of the aqueous dispersion additionally comprises imidazole units. The proportion of polyalkylene oxide units in the polymeric organic compound (P2) is preferably at least 40% by weight, particularly preferably at least 50% by weight, but preferably no more than 70% by weight, as a whole. As already explained, further preferred embodiments of the polymeric organic compound (P2) can be taken from the respective preferred embodiments of the polymeric organic compound (P2) of the aqueous dispersion in process step (ii).

[0033] In addition to the above-described embodiments of the particulate component (P) of the aqueous dispersion in process step (i), the presence of a thickener is advantageous for providing a stable dispersion which can be stored in the system tank of process step (i) over a relatively long period of time. Thus, in a preferred embodiment of the process according to the application, the aqueous dispersion in process step (i) comprises at least one thickener as further component, which is preferably selected from urea carbamate resins, particularly preferably from urea carbamate resins having an amine value 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 phosphatizing, which are also advantageous and are included here as preferred embodiments with respect to the aqueous dispersion for pre-activation.

[0034] Further preferred embodiments of the aqueous dispersion comprising the water-dispersed particulate component (P) used in step (i) according to the application can be found in the description of particularly suitable activation aids.

[0035] The degree of pre-activation of the zinc and / or iron surfaces can be controlled by the particulate fraction of the aqueous dispersion dispersed in water. It has been found that a particularly reliable pre-activation of the zinc and / or iron surfaces during the typical activation time, i.e. a contact duration in the range from 5 to 120 seconds, is achieved when the particulate fraction (P) relative to the aqueous dispersion is at least 0.060 g / kg. A short activation time can be compensated by a higher proportion of the particulate fraction (P), so that it is overall advantageous for the water-dispersed particulate component (P) of the aqueous dispersion in process step (i) to be at least 0.060 g / kg, particularly preferably at least 0.100 g / kg. Significantly higher contents are associated with a higher economic outlay, which is not justified by the significant improvement in the density of the zinc phosphate coating achieved as a result, and also often not required by the recrystallisation of the proportion of the particulate component in the acidic aqueous composition for zinc phosphating by entrainment, thus counteracting the intention of the present application to establish a particularly resource-efficient method for zinc phosphating. It is therefore preferred for the water-dispersed particulate component (P) of the aqueous dispersion in process step (i) to be no more than 5.0 g / kg, particularly preferably no more than 1.0 g / kg, relative to the aqueous dispersion.

[0036] The pH value of the aqueous dispersion used for pre-activation is preferably set such that pickling of the metal material of the component, in particular of components made of zinc, iron or aluminium, is avoided. Accordingly, it is preferred for the pH value of the aqueous dispersion in process step (i) for activation of the zinc surfaces to be higher than 6.0, particularly preferably higher than 6.5, but preferably no more than 9.0, particularly preferably no more than 8.5, very particularly preferably no more than 8.0 and particularly preferably no more than 7.5.

[0037] Method step (ii) - activated zinc phosphatization: In process step (ii), the zinc phosphating of at least the zinc and / or iron surfaces of the component pre-activated in series in process step (i) according to the application is carried out by means of an acidic aqueous composition which in turn activates the growth of a highly dense, closed but crystalline zinc phosphate layer and, for this purpose, like the aqueous dispersion in pre-activation, comprises a dispersed particulate component. In addition to this activating particulate component (D) which comprises phosphates of polyvalent metal cations, at least partially selected from the group consisting of hopeite, libethenite, hopeite and / or redplumite, the acidic aqueous composition also comprises the following for the formation of the zinc phosphate layer: (A) 5 to 50 g / kg of phosphate dissolved in water, calculated as PO4, (B) 0.3 to 3 g / kg of zinc ions, and (C) free fluoride, wherein the zinc phosphating composition is adjusted to have a point greater than zero of free acid.

[0038] The acidic aqueous zinc phosphatizing is thus provided for activating the growth of crystalline phosphate coatings on zinc and / or iron surfaces due to its particulate component (D) and it can likewise be obtained by suitably adding an amount of an aqueous dispersion to the acidic aqueous composition comprising the aforementioned components (A) to (C).

[0039] This aqueous dispersion intended for addition to the acidic aqueous composition comprising components (A) to (C) comprises a particulate component (P) in water-dispersed form, which comprises - at least one particulate inorganic compound (P1) consisting of a phosphate of polyvalent metal cations at least partially selected from the group consisting of zinc phosphate, iron phosphate, calcium zinc phosphate and / or red manganese phosphate, - and at least one polymeric organic compound (P2), wherein the aqueous dispersion for providing the acidic aqueous composition for zinc phosphatizing in method step (ii) is preferably added in such an amount that the proportion by weight of the phosphate of the water-dispersed particulate component (D) of the acidic aqueous composition is at least 0.1 mg / kg, particularly preferably at least 0.5 mg / kg, very particularly preferably at least 1.0 mg / kg and particularly preferably at least 2.0 mg / kg, wherein the proportion by weight is each calculated as phosphate (PO4) and in relation to the acidic aqueous composition.

[0040] In a preferred embodiment allowing a particularly resource-saving and economic operation of the method according to the application, the components in series are contacted with the acidic aqueous composition in step (ii) of the method according to the application, wherein the acidic aqueous composition comprises (A) 5 to 50 g / kg of phosphate dissolved in water, calculated as PO4, (B) 0.3 to 3 g / kg of zinc ions, and (C) free fluoride, and has a free acid having a point greater than zero, wherein an amount of an aqueous dispersion comprising a particulate component (P) is continuously or discontinuously added to the acidic aqueous composition in method step (ii) for zinc phosphatizing, which is sufficient under the selection conditions of method step (ii) for zinc phosphatizing to maintain the characteristic of the zinc phosphate layer deposited on the hot-dip galvanized steel surface (Z) 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 , very particularly preferably less than 3.0 g / m 2 , wherein the particulate component (P) of the aqueous dispersion comprises - at least one particulate inorganic compound (P1) consisting of a phosphate of polyvalent metal cations at least partially selected from the group consisting of zinc phosphate, iron phosphate, calcium zinc phosphate and / or red manganese phosphate, - and at least one polymeric organic compound (P2).

[0041] In this way, only the required amount of aqueous dispersion is added to the acidic aqueous composition for zinc phosphating, and over-dosing is systematically avoided.

[0042] In a particularly preferred variant of the method according to the application, in the method step (i) for pre-activation, for each part, an amount of activation aid to be brought into contact with the zinc and / or iron surface is dosed, which is sufficient for the wet film remaining on the part and being introduced into the subsequent method step (ii) of zinc phosphating to maintain a certain weight proportion of the water-dispersed particulate component (D) of the acidic aqueous composition comprising components (A) to (C), wherein the component (D) comprises a phosphate of polyvalent metal cations at least partially selected from the group consisting of zinc phosphate, iron phosphate, calcium zinc phosphate and / or red manganese phosphate, in an amount of at least 0.1 mg / kg, particularly preferably at least 0.5 mg / kg, very particularly preferably at least 1.0 mg / kg and particularly preferably at least 2.0 mg / kg, the above-mentioned amounts each being calculated as phosphate (P04) and in relation to the acidic aqueous composition.

[0043] Alternatively, in an equally preferred variant, in the method step (i) for pre-activation, each part is dosed with an amount of activation aid for contact with the zinc and / or iron surface, which is sufficient for the wet film remaining on the part and being introduced into the subsequent method step (ii) of zinc phosphating to set a minimum amount of the water-dispersed particulate component (D) comprising a phosphate of polyvalent metal cations in the acidic aqueous composition comprising components (A) to (C), wherein the phosphate is at least partially selected from the group consisting of zinc phosphate, iron phosphate, calcium zinc phosphate and / or red manganese phosphate, which is sufficient to maintain the property of the zinc phosphate layer deposited on the hot-dip galvanized steel surface (Z) of the acidic aqueous composition 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 , very particularly preferably less than 3.0 g / m 2 under the selection conditions of the method step (ii) of zinc phosphating.

[0044] In the method step (ii), the growth of a layer on the hot-dip galvanized steel surface (Z) is induced which has 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 2Furthermore, it is extremely preferred that the concentration be less than 3.0 g / m³. 2 The preferred properties of the acidic aqueous composition for zinc phosphating according to the invention (hereinafter referred to as "phosphating quality") of the zinc phosphate layer are to be examined on a (Z) substrate, wherein the (Z) substrate has been cleaned and degreased and has not undergone any further wet chemical pretreatment or rinsing steps before contact with the acidic aqueous composition according to the method of the invention in step (ii) and after the pre-activation of the zinc surface in step (i). The cleaning and degreasing of the (Z) substrate occurs when the (Z) surface has a carbon coating of less than 0.10 g of carbon per square meter of (Z) surface after cleaning and degreasing. The carbon layer thickness can be determined by high-temperature decomposition. For this purpose, the (Z) substrate is subjected to a substrate temperature (PMT) of 550°C in an oxygen atmosphere, and the amount of carbon dioxide released is quantitatively determined as the amount of carbon by an infrared sensor—for example, by an analytical device LECO® RC-412 multiphase carbon analyzer (Leco Corp.).

[0045] Therefore, in order to check the phosphating quality of the acidic aqueous composition, hot-dip galvanized steel (Z) was first used as a phosphate bath in deionized water (k < 1 µS / cm). -1 An alkaline cleaner formulated with 2% by weight Bonderite® C-AK 1565 A and 0.2% by weight Bonderite® C-AD1270 was used for immersion cleaning at pH 11.0 and 55°C for 5 minutes. The substrate (Z) cleaned and degreased in this manner was then rinsed at room temperature with deionized water (k < 1 µS / cm). -1 The material is rinsed and then supplied to the treatment stages according to method steps (i) and (ii) according to the selected method conditions. "According to the selected method conditions" means that the temperature, application duration, and bath circulation are the same and the desired phosphating quality (i.e., the target layer weight on hot-dip galvanized steel (Z)) is less than 4.5 g / m² according to the preferred specific specifications of the invention. 2 Especially preferred is below 4.0 g / m 2 Especially preferred is below 3.5 g / m 2 And it is extremely preferred that the concentration is below 3.0 g / m³. 2The phosphating quality can be determined in the current method according to the application by the following means: A cleaned and degreased sheet of hot-dip galvanized steel (Z) is also introduced into the assembly in series for method steps (i) and (ii) and then the layer weight of zinc phosphate on the sheet and thus the phosphating quality of the acidic aqueous composition for zinc phosphating is determined in method step (ii). It should be noted that the outer surface of this test metal sheet to be phosphated in method step (i) has already formed a complete liquid film comprising the aqueous dispersion before the outer surface was contacted with the acidic aqueous composition in method step (ii).

[0046] The cleaned and degreased sheet of hot-dip galvanized steel (Z) as test sheet for determining the phosphating quality is preferably rigidly connected with the component or the transport frame to ensure that the flow conditions during the transport of the component with the transport frame through the phosphating bath are as similar as possible to the test sheet. For this purpose, the test sheet should be ideally connected to the component or the transport frame in such a way that the test sheet is transported with the component and the transport frame without such a test sheet having an influence on the flow conditions to be considered compared to the test sheet being transported with the component and the transport frame; and the flow conditions are essentially the same in both cases and thus essentially correspond to the flow conditions of at least a portion of the component in the series. This can be achieved, for example, by adapting the size and / or shape of the test sheet to the size and shape of the component and / or the transport frame which is respectively arranged in the vicinity of the test sheet. It is conceivable in this case, in particular when the test sheet is arranged on an outer surface portion of the component or the transport frame, that the size of the test component correspondsingly is smaller than those of the surface portion, for example to avoid the test component protruding beyond the surface portion. Alternatively or additionally, the test component can follow the curvature or other planar deviations of the surface portion or the transport frame. It has proven particularly advantageous to select a sheet portion which is sufficiently small compared to the size of a suitable outer surface of the component, wherein the outer surface is particularly suitable if it is located at a location having a particularly low curvature or at a location having the lowest curvature of the component and the test metal sheet is then mounted essentially in parallel in order to be spaced apart along the surface normal of such an outer surface. It is particularly useful and preferred that the test metal sheet is spaced apart along the surface normal with respect to a zinc and / or iron surface of the component in order to ensure in the most simple manner possible that in method step (i) a liquid film comprising the aqueous dispersion which is dispensed in said step for contact with said surface is applied without having to complexly adapt the equipment for dispensing the aqueous dispersion in method step (i).

[0047] The phosphating quality is directly obtained during the series treatment of these components which also have a surface of hot-dip galvanized steel (Z) as a zinc surface. Such components are also preferred in the preferred embodiment of the method according to the application.

[0048] For the phosphating quality, it is furthermore preferred that the layer weight on hot-dip galvanized steel (Z) increases by no more than 0.2 g / m 2 and that the layer formation under the selected conditions has already been within self-limiting ranges, thus ensuring the properties of the acidic aqueous composition for the production of a dense crystalline zinc phosphate layer in step (ii) of the method according to the application. It is therefore preferred that in the zinc phosphating method step, an amount of the aqueous dispersion comprising the particulate component (P) is added, so that under the selected conditions of the zinc phosphating method step in the method according to the application, the properties of the acidic aqueous composition are sufficient to maintain a zinc phosphate layer on the surface of the hot-dip galvanized steel (Z) 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 very particularly preferably less than 3.0 g / m 2 , wherein the layer weight increase achieved under the selected conditions of the method step (ii) of the zinc phosphating in the method according to the application is no more than 0.2 g / m 2 when the contact time with the acidic aqueous composition is extended by 60 seconds.

[0049] In general, in the preferred method according to the application, the phosphating quality is determined and monitored by hot-dip galvanized steel (Z) which has been cleaned and degreased as described above, also being subjected to the zinc phosphating method step at regular intervals during the inline processing and then the layer weight determination. As described above, the phosphating quality is obtained directly during the inline processing of such components which also have at least one hot-dip galvanized steel (Z) surface as zinc surface. In the case of the phosphating quality of the acidic aqueous composition being ensured by the metered addition of the aqueous dispersion, a uniform, closed and dense crystalline zinc phosphate coating is deposited on the components in the inline having a surface consisting of metallic zinc and / or iron within a usual processing time of 20 seconds to 5 minutes.

[0050] The layer weight of the zinc phosphate is determined within the scope of the application by removing the zinc phosphate layer using a 5% by weight CrC03aqueous solution as pickling solution, which is contacted with the defined area of the phosphated material or component immediately after the zinc phosphating at 25°C for 5 minutes and rinsed with deionized water (k<1 µS cm -1 ) and the phosphorus content in the same pickling solution is then determined by ICP-OES. The layer weight of the zinc phosphate can be obtained by multiplying the surface-area-related amount of phosphorus (in g / m

[0051] The addition of the aqueous dispersion comprising the particulate component (P) to the acidic aqueous composition used for the zinc phosphating process is carried out in the method according to the application for the purpose of maintaining the phosphating quality in process step (ii). For maintaining the phosphating quality in a series process, the addition can be carried out by continuous or discontinuous metering into the zinc phosphating system tank. Continuous metering is preferred if the components are pretreated one after the other directly in series and the decrease in phosphating quality per time interval can be determined with sufficient accuracy so that a certain amount of activator can again be added by metering to compensate for the loss in performance. This method has the advantage that after starting the pretreatment line and determining the material flow for metering the aqueous dispersion and further active components, no further examination of the phosphating quality is necessary as long as the series process remains unchanged in terms of the time schedule of the components to be treated and the quality and the treatment parameters in process step (ii) for zinc phosphating. However, if the system does not ensure or does not require a constant mode of operation during the series process, then discontinuous metering of the aqueous dispersion comprising the particulate component (P) would be advantageous and even possible. In this case, it is preferred to monitor the phosphating quality of the acidic aqueous composition in step (ii) continuously or at defined time intervals; and then, if the layer weight on the hot-dip galvanized steel (Z) no longer reaches a certain value 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 very particularly preferably less than 3.0 g / m 2 , a defined amount of activator is metered in. The continuous or quasi-continuous determination of the phosphating quality occurring at defined time intervals can also be carried out using proxy data related to the actual zinc phosphate layer weight. Non-destructive determination of the layer thickness, for example using the eddy current method or even non-contact optical measurement methods such as ellipsometry or spectroscopic reflectometry, provides suitable proxy data for the layer weight of zinc phosphate, which can be reliably measured on the zinc surface of the components in the pretreatment line and can be correlated with the actual layer weight on the hot-dip galvanized steel (Z) component. The crystallite size and thus the roughness determination by optical profilometry can also provide proxy data for the layer weight, since a higher layer weight on the hot-dip galvanized steel (Z) is associated with a low number density of crystallites, which, however, are relatively large, so that the roughness increases with increasing layer weight.

[0052] It has been found that if the aqueous dispersion comprising particulate component (P) for activating the zinc phosphating composition is added continuously or discontinuously during pretreatment of the series of components in an amount suitable for producing a stable amount of phosphate contained in the water-dispersed particulate component (D) in the acidic aqueous composition, preferably at least 0.1 mg / kg, particularly preferably at least 0.5 mg / kg, particularly preferably at least 1.0 mg / kg, in each case calculated as the amount of phosphate (PO4) and in relation to the acidic aqueous composition, in most cases the phosphating quality has been sufficiently adjusted. This applies in particular to the contacting of the components by immersing them in a zinc phosphating system tank comprising the acidic aqueous composition.

[0053] In connection with the method step (i) which brings about the preactivation of the zinc and / or iron surfaces, the activation of the zinc phosphating in step (ii) can be carried out in a particularly resource-efficient manner and the consumption of active components can be significantly reduced without any loss of phosphating quality. This applies to the proportion of the addition of the aqueous dispersion comprising particulate component (P) and, due to the excellent phosphating quality achieved on the zinc and / or iron surfaces, also to the consumption of the active components (A) to (C) of the acidic aqueous zinc phosphating composition.

[0054] With regard to the acidic aqueous composition for zinc phosphating, it is essential for the formation of a uniform, closed zinc phosphate layer that, in step (ii) of the method according to the application, the composition comprises at least (A) 5 to 50 g / kg of phosphate dissolved in water, calculated as PO4, (B) 0.3 to 3 g / kg of zinc ions, and (C) free fluoride, and a point greater than zero of free acid.

[0055] In this case, the amount of phosphate ions includes orthophosphoric acid and the anions of salts of orthophosphoric acid dissolved in water, calculated as PO4.

[0056] The proportion of free acid in point in the acidic aqueous composition for zinc phosphating in step (ii) of the method according to the application is preferably greater than 0.5, particularly preferably greater than 0.8, very particularly preferably greater than 1.0, but preferably not more than 3.0, particularly preferably not more than 2.0. The proportion of free acid in point is determined by diluting a sample volume of 10 ml of the acidic aqueous composition to 60 ml and titrating to a pH value of 3.6 with a 0.1 N sodium hydroxide solution. The consumption of the sodium hydroxide solution in ml represents the number of points of free acid.

[0057] The pH of the acidic aqueous composition is preferably generally below 3.6, particularly preferably below 3.4, very particularly preferably below 3.2, but preferably above 2.5, particularly preferably above 2.7. As used in the context of the present application, the "pH value" corresponds to the negative base-10 logarithm of the activity of the hydrated hydrogen ion at 20°C and can be determined by means of a pH-sensitive glass electrode.

[0058] An amount of free fluoride ions or a source of free fluoride ions is necessary for the layer-forming zinc phosphating process. In the case of zinc phosphating of parts which, in addition to zinc surfaces, also comprise iron or aluminum surfaces in order to form layers, it is advantageous, if desired, for example in the zinc phosphating of automobile bodies which are at least partially also made of aluminum, if the amount of free fluoride in the acidic aqueous composition in step (ii) is at least 10 mg / kg, particularly preferably at least 40 mg / kg. The concentration of free fluoride should not exceed a value above which the phosphate coating exhibits a loose adhesion which can be easily removed. For this reason, it is advantageous and therefore preferred if, in step (ii) of the process according to the application, the concentration of free fluoride in the acidic aqueous composition for zinc phosphating is below 300 mg / kg, particularly preferably below 250 mg / kg, and particularly preferably below 200 mg / kg.

[0059] The amount of free fluoride is to be determined potentiometrically in the relevant acidic aqueous composition at 20°C after calibration with a fluoride-containing buffer solution which has no pH buffer, by means of a fluoride-sensitive measuring electrode. Suitable sources of free fluoride ions are hydrofluoric acid and its water-soluble salts, such as ammonium fluoride and sodium fluoride, and complex fluorides of the elements Zr, Ti and / or Si, in particular complex fluorides of the element Si. Thus, in the phosphating process according to the application, the source of free fluoride is preferably selected from hydrofluoric acid and its water-soluble salts and / or complex fluorides of the elements Zr, Ti and / or Si. A salt of hydrofluoric acid is water-soluble within the meaning of the present application if its solubility in deionized water (k < 1 μS cm -1 ) at 60°C is at least 1 g / L (calculated as F).

[0060] In order to suppress so-called "pinholes" on the surface of metallic materials made of zinc, it is preferred that, in such a process according to the application, the source of free fluoride in step (ii) is at least partially selected from complex fluorides of the element Si, in particular hexafluorosilicic acid and its salts. The term pinholes is understood by the person skilled in the art of phosphating to mean the phenomenon of local deposition of amorphous white zinc phosphate in an otherwise crystalline phosphate layer on the treated zinc surface or on the treated zinc-plated or zinc-alloy-plated steel surface.

[0061] In the process according to the application, accelerators known from the prior art can be added to the acidic aqueous composition in order to increase the rate of layer formation. These accelerators are preferably selected from the group consisting of 2-hydroxymethyl-2-nitro-1,3-propanediol, nitroguanidine, N-methylmorpholine-N-oxide, nitrite, hydroxylamine and / or hydrogen peroxide. It can be seen that when nitroguanidine or hydroxylamine is used as an accelerator, a comparatively low metering of the aqueous dispersion comprising the water-dispersed particulate ingredient (P) is necessary in order to provide the acidic aqueous composition, or a comparatively low stable amount of the water-dispersed particulate ingredient (P) must be maintained in the acidic aqueous composition for the zinc phosphatizing in step (ii), so that nitroguanidine or hydroxylamine, in particular nitroguanidine, is particularly preferred as an accelerator in the acidic aqueous composition in step (ii) of the process according to the application in particular in terms of particularly low material use for maintaining the phosphatizing quality.

[0062] Embodiments in which a total of less than 10 ppm of nickel and / or cobalt ions are contained in the acidic aqueous composition for the zinc phosphatizing in step (ii) of the process according to the application are particularly preferred from an ecological point of view.

[0063] Furthermore, in the process according to the application, the additivation with additives known in the art can also be used in the zinc phosphatizing process.

[0064] Preferred embodiments of the aqueous dispersion used in step (ii) according to the application and comprising the water-dispersed particulate ingredient (P) can be found in the description of particularly suitable activation aids.

[0065] Suitable activation aids The definitions and preferred details given below apply to the dispersed particulate ingredient (P) and the at least one particulate inorganic compound (P1 ) or polymeric organic compound (P2) of the aqueous dispersion, irrespective of whether the dispersed particulate ingredient (P) is an ingredient of the aqueous pre-activation dispersion in process step (i) or of the aqueous dispersion for providing the self-activating acidic aqueous composition for the zinc phosphatizing in process step (ii). For the sake of simplicity, only reference is made below to "activation aids" instead of the corresponding "aqueous dispersion comprising the dispersed ingredient (P)". Preferred activation aids are characterized in that they have a high stability with respect to agglomeration, are therefore particularly suitable for forming a crystalline phosphate coating, and in particular when used according to the application, they release or provide a high proportion of activated phosphate particles for the activation of zinc and / or iron surfaces, so that a dense, closed crystalline coating with a relatively low layer weight can be achieved particularly reliably in the process according to the application.

[0066] Therefore, the activation aid used according to the application (i.e. for the pre-activation in step (i) and for maintaining the phosphating quality or for providing the acidic aqueous composition for the zinc phosphating in step (ii)) is an aqueous dispersion comprising a particulate ingredient (P) in water-dispersed form, which particulate ingredient (P) comprises at least one particulate inorganic compound (P1 ) and at least one polymeric organic compound (P2), the particulate inorganic compound (P1 ) consisting of a phosphate of polyvalent metal cations at least partially selected from the group consisting of phosphorite, libethenite, hopeite and / or redplumite.

[0067] The use of polyvalent metal cations in the form of phosphates is the reason for the good (pre-)activation performance, which should therefore be contained in the activation aid in a sufficiently high proportion in the dispersed particulate ingredient (P). Therefore, the proportion of the phosphate contained in the particulate inorganic compound (P1 ) relative to the dispersed inorganic ingredient of the activation aid is preferably at least 25% by weight, particularly preferably at least 35% by weight, particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight.

[0068] The dispersed particulate ingredient (P) of the activation aid - or also the water-dispersed particulate ingredient (D) of the acidic aqueous composition in step (ii) - is the solid content remaining after the retentate material of an ultrafiltration with a nominal cut-off of 10 kD (NMWC, nominal molecular weight cut-off) from a defined partial volume of the activation aid - or of the acidic aqueous composition - is dried. The ultrafiltration is carried out by supplying deionized water (k < 1 μS cm -1 ) until a conductivity degree of less than 10 μS cm -1 is measured in the filtrate. The inorganic particulate ingredient of the activation aid - or the inorganic water-dispersed particulate ingredient of the acidic aqueous composition in step (ii) - is again the particulate ingredient (P) or (D) obtained from the dried ultrafiltration retentate material when this is pyrolyzed in a reaction oven by supplying a CO2-free oxygen stream at 900°C without the addition of catalysts or other additives until an infrared sensor at the outlet of the reaction oven provides the same signal as the CO2-free carrier gas (blank value). The phosphate (calculated as PO4) contained in the respective inorganic particulate ingredient is determined by atomic emission spectroscopy (ICP-OES) after acid digestion thereof with 10% by weight of an aqueous HNO3 solution at 25°C for 15 minutes, the phosphorus content directly from the acid digestion process being multiplied by the factor 3.07.

[0069] As already mentioned, the active components of the activation aid are mainly composed of phosphates which are at least partially selected from the group consisting of phosphor-zwieselite, phosphor-fermite, phosphor-willemite and / or phosphor-ferroplatinum, preferably at least partially selected from the group consisting of phosphor-zwieselite, phosphor-fermite and / or phosphor-willemite, particularly preferably at least partially selected from the group consisting of phosphor-zwieselite and / or phosphor-fermite and very particularly preferably at least partially selected from phosphor-zwieselite. The achievement of the desired phosphating quality on the zinc and / or iron surfaces in the process according to the application is essentially based on the phosphates which are contained in the activation aid in particulate form. Without taking into account the crystal water, phosphor-zwieselite comprises stoichiometrically Zn3(P04)2as well as the nickel-containing and manganese-containing modifications Zn2Mn(P04)3, Zn2Ni(P04)3, while phosphor-fermite consists of Zn2Fe(P04)3, phosphor-willemite of Zn2Ca(P04)3and phosphor-ferroplatinum of Mn3(P04)2. The presence of the crystalline phases phosphor-zwieselite, phosphor-fermite, phosphor-willemite and / or phosphor-ferroplatinum in the activation aid can be proven after the separation of the particulate component (P) by ultrafiltration with a nominal cut-off limit of 10 kD (NMWC: nominal molecular weight cut-off) as described above and drying of the retentate material to constant mass at 105°C by the X-ray diffraction method (XRD).

[0070] Since phosphates containing zinc ions and having a certain degree of crystallinity are preferably present, it is preferred for the formation of a firmly adhering crystalline zinc phosphate coating that the activation aid comprises at least 20% by weight, particularly preferably at least 30% by weight, particularly preferably at least 40% by weight of zinc, based on the phosphate content (calculated as P04) of the inorganic particulate component in the process according to the application.

[0071] However, the activation aid is preferably not intended to additionally comprise any titanium phosphates, since these substances can also have the same activation effect, but have no further positive effect on the phosphating quality in the context of the present application. In a preferred embodiment of the process according to the application, the proportion of titanium in the inorganic particulate component of the activation aid is thus less than 0.01% by weight, particularly preferably less than 0.001% by weight, relative to the activation aid. In a particularly preferred embodiment, the activation aid comprises less than 10 mg / kg, particularly preferably less than 1 mg / kg, of titanium in total.

[0072] The effectiveness of the polymeric organic compound (P2) which stabilizes the particles of each dispersion (P) has a major influence on the activation aid. It appears that the choice of the polymeric organic compound is crucial for the degree of pre-activation of the zinc and / or iron surfaces in process step (i) and the phosphating quality ultimately achieved by the integrated activation in step (ii).

[0073] In the context of the present application, an organic compound is polymeric if its weight average molar mass is greater than 500 g / mol. The molar mass is determined using the molar mass distribution curve of a sample of the relevant reference dimension, which is experimentally established at 30°C using size exclusion chromatography with a concentration-dependent refractive index detector and calibrated against polyethylene glycol standards. The average molar mass is evaluated by means of a computer according to the strip method using a third order calibration curve. Hydroxylated polymethacrylates are suitable as column material and an aqueous solution containing 0.2 mol / L sodium chloride, 0.02 mol / L sodium hydroxide and 6.5 mmol / L ammonium hydroxide is suitable as eluent.

[0074] When the polymeric organic compound (P2) used to disperse the particulate inorganic compound (P1 ) consists at least partially of styrene and / or an alpha-olefin having not more than 5 carbon atoms, there is a particularly effective activation aid, which is preferably used in the process according to the application, wherein the polymeric organic compound (P2) additionally comprises units of maleic acid, its anhydride and / or its imide, and preferably additionally comprises polyalkylene oxide units, particularly preferably in side chains thereof.

[0075] The alpha-olefin in this case is preferably selected from the group consisting of ethylene, 1 -propene, 1 -butene, isobutene, 1 -pentene, 2-methyl-but-1 -ene and / or 3-methyl-but-1 -ene, and is particularly preferably selected from isobutene. It is clear to the person skilled in the art that the polymeric organic compound (P2) comprises these monomers as structural units in unsaturated form, which are covalently linked to one another or to further structural units.

[0076] Preferred activation aids comprise a polymeric organic compound (P2) which consists at least partially of styrene.

[0077] The polymeric organic compound (P2) for the colloidal stabilization of the particulate component (P) of the activation aid preferably has polyalkylene oxide units, which in turn are preferably composed of 1,2-ethanediol and / or 1,2-propanediol, particularly preferably of both 1,2-ethanediol and 1,2-propanediol, wherein the proportion of 1,2-propanediol in the total polyalkylene oxide units is preferably at least 15% by weight, but particularly preferably not more than 40% by weight, based on the total polyalkylene oxide units. Furthermore, the polyalkylene oxide units are preferably contained in side chains of the polymeric organic compound (P2). It is advantageous for the dispersibility of the polymeric organic compound (P2) that the proportion of polyalkylene oxide units in the total of said compound is preferably at least 40% by weight, particularly preferably at least 50% by weight, but preferably not more than 70% by weight.

[0078] In order to anchor the polymeric organic compound (P2) to the inorganic particulate component (P1 ) of the activation aid, which is formed at least partially from polyvalent metal cations in the form of phosphates selected from the group consisting of phosphorous zeolites, phosphorous phyllites, phosphorous calciozincite and / or phosphorous red manganite, and in order to increase the stability and the ability of the particulate component (P) to activate zinc and / or iron surfaces, the organic polymeric compound (P2) also has imidazole units, particularly preferably in the side chains of the polymeric compound (P2).

[0079] In a preferred embodiment, the amine number of the organic polymeric compound (P2) is at least 25 mg KOH / g, particularly preferably at least 40 mg KOH / g, but preferably less than 125 mg KOH / g, particularly preferably less than 80 mg KOH / g; and accordingly, in a preferred embodiment, also all polymeric organic compounds in the particulate component (P) of the activation aid have these preferred amine numbers. The amine number is determined in each case by weighing out about 1 g of the relevant reference size (organic polymeric compound (P2) or all polymeric organic compounds in the particulate component (P)) in 100 mL of ethanol, titrating against the indicator bromophenol blue using a 0.1 N HCI titrant solution until the colour changes to yellow at an ethanol solution temperature of 20°C. The amount of HCI titrant solution used in millilitres is multiplied by the factor 5.61, divided by the exact mass of the weight in grams, the result corresponding to the amine number of the relevant reference value in milligrams KOH / gram.

[0080] It has also proven advantageous for the polymeric organic compound (P2), preferably also all polymeric organic compounds in the particulate component (P), to have an acid number of at least 25 mg KOH / g, but preferably less than 100 mg KOH / g, particularly preferably less than 70 mg KOH / g, according to DGF C-V 2(06) (from April 2018), in order to ensure a sufficient number of polyalkylene oxide units. It is also preferred for the polymeric organic compound (P2), preferably also all polymeric organic compounds in the particulate component (P), to have a hydroxyl number of less than 15 mg KOH / g, particularly preferably less than 12 mg KOH / g, more particularly preferably less than 10 mg KOH / g, the hydroxyl number being determined in each case according to method A from European Pharmacopoeia 9.0 01 / 2008:20503.

[0081] Suitable commercially available representatives of polymeric organic compounds (P2) are, for example: Dispex® CX 4320 (BASF SE), maleic acid-isobutene copolymer modified with polypropylene glycol; Tego® Dispers 752 W (Evonik Industries AG), maleic acid-styrene copolymer modified with polyethylene glycol; or Edaplan® 490 (Münzing Chemie GmbH), maleic acid-styrene copolymer modified with EO / PO and imidazole units.

[0082] For a stable dispersion of the inorganic particulate ingredient in the activation aid, it is sufficient that the proportion of polymeric organic compounds (P2), preferably all polymeric organic compounds in the particulate ingredient (P), relative to the particulate ingredient (P) is at least 3% by weight, particularly preferably at least 6% by weight, but preferably not more than 15% by weight.

[0083] Based on the agent, the activation aid preferably contains not more than 40% by weight of particulate ingredient (P), because otherwise the stability of the dispersion and the operability of the process for pre-activation in process step (i) by wetting using a spray device and in process step (ii) by metering the agent into the acidic aqueous composition for zinc phosphatizing by means of a metering pump are no longer ensured, or said stability and said operability are at least complicated. According to the application, it has been shown that, for the purpose of metering into the acidic aqueous composition in process step (ii), good storage and applicability are achieved at the same time when using an activation aid; wherein the activation aid, relative to the agent, preferably contains at least 5% by weight, but particularly preferably not more than 30% by weight, of particulate ingredient (P). However, the activation aid used in process step (i) as aqueous dispersion for wetting the zinc and / or iron surface should preferably be less concentrated for wetting by atomization, and relative to the agent, preferably contains not more than 5% by weight of particulate ingredient (P), but relative to the agent, preferably contains at least 0.005% by weight of particulate ingredient (P) for good activation.

[0084] In concentrated aqueous dispersions, i.e. with a proportion of at least 5% by weight of particulate constituents (P) relative to the agent, the agent can additionally be characterized by its D50 value of greater than 10 pm, which is correspondingly preferred. However, for good applicability, in particular in process step (i), it is preferred that the D90 value of the aqueous dispersion of particulate constituents (P) is less than 150 pm, preferably less than 100 pm, in particular less than 80 pm. In the context of the present application, the D50 value or the D90 value indicates the particle diameter at which 50% by volume or 90% by volume, respectively, of the particulate constituents contained in the aqueous dispersion do not exceed. According to ISO 13320:2009, the D50 value or the D90 value can be determined from the volume-weighted cumulative particle size distribution immediately after the following operation by means of scattered light analysis according to the Mie theory: dilution of the activation aid to 0.05% by weight of the dispersed particulate constituents at 20°C with a corresponding amount of deionized water (k < 1 pm cm -1 ) using a refractive index nD= 1.52 for spherical particles and scattering particles. The dilution is carried out in such a way that an amount of activation aid corresponding to a volume of 200 ml of deionized water is added to the sample container of a LA-950 V2 particle size analyzer from Horiba Ltd., where it is mechanically circulated into the measurement chamber (circulation pump set on the LA-950 V2: 5 gears = 1167 rpm, corresponding to a volume flow of 3.3 liters / minute). The particle size distribution is measured within 120 seconds after the addition of the activation aid to the dilution volume.

[0085] The presence of a thickening agent can be advantageous for preventing irreversible agglomeration of the primary particles of the particulate constituents (P), in particular if the activation aid comprises at least 5% by weight of particulate constituents (P) relative to the agent, as described above. Preferably, the activation aid thus comprises a thickening agent, the amount of which in turn preferably imparts a maximum dynamic viscosity of at least 1000 Pa s, but preferably below 5000 Pa s, at a temperature of 25°C in the shear rate range of 0.001 to 0.25 s -1 In this case, the viscosity in the specified shear rate range can be determined by means of a cone-plate viscometer with a cone diameter of 35 mm and a gap width of 0.047 mm.

[0086] Within the meaning of the present application, a thickening agent is a polymeric compound or a defined mixture of compounds, which, as deionized water (k < 1 pm cm -1The 0.5 wt.-% ingredient in the mixture with water has a Brookfield viscosity of at least 100 mPa-s at a shear rate of 60 rpm (= revolutions per minute) using a size 2 spindle. When determining this thickener property, the mixture with water should be prepared in such a way that the respective amount of the polymeric compound is added to the water phase at 25 °C while stirring, then the homogenized mixture is freed of air bubbles in an ultrasonic bath and left to stand for 24 hours. Then, the measurement of the viscosity is read within 5 seconds immediately after applying a shear rate of 60 rpm by the size 2 spindle.

[0087] The activation aid preferably comprises at least 0.5 wt.-%, but preferably not more than 4 wt.-%, particularly preferably not more than 3 wt.-%, of one or more thickening agents, wherein the total proportion of polymeric organic compounds in the non-particulate ingredients of the activation aid is further preferably not more than 4 wt.-% (relative to the reagent). The non-particulate ingredients are the solid contents of the relevant aqueous dispersion or of the activation aid after it has been dried at 105 °C until it has a constant mass, i.e. after the particulate ingredients have been separated by ultrafiltration.

[0088] Certain classes of polymeric compounds are particularly suitable thickening agents and are also readily commercially available. Thus, the thickening agent is preferably selected from polymeric organic compounds, which in turn are preferably selected from polysaccharides, cellulose derivatives, aminoplasts, polyvinyl alcohol, polyvinylpyrrolidone, polyurethanes and / or urea urethanes resins, and particularly preferably from urea urethanes resins, in particular urea urethanes resins which are mixtures of polymeric compounds resulting from the reaction of polyvalent isocyanates with polyols and mono- and / or di- amines. In a preferred embodiment, the urea urethanes resins result from polyvalent isocyanates which are 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-xylylene diisocyanate and m-xylylene diisocyanate, and 4-4'-diisocyanatodicyclohexylmethane, particularly preferably from 2,4-toluene diisocyanate and / or m-xylylene diisocyanate. In a particularly preferred embodiment, the urea urethanes resins result from polyols selected from polyoxyalkylene glycols, particularly preferably polyoxyethylene glycols, which in turn preferably consist of at least 6, particularly preferably at least 8, more particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23, alkylene oxide units.

[0089] Urethane resins which are particularly suitable and thus preferred according to the application can be obtained by first reacting a diisocyanate (e.g. toluene-2,4-diisocyanate) with a polyol (e.g. polyethylene glycol) to form an NCO-terminated urethane prepolymer, and then further reacting with a primary monoamine and / or with a primary diamine (e.g. m-xylylenediamine). Urethane resins which have neither free isocyanate groups nor blocked isocyanate groups are particularly preferred. Such urethane resins as components of the activation aid facilitate the formation of loose agglomerates of primary particles, wherein said loose agglomerates are protected from further agglomeration and disintegrate into primary particles when being diluted (e.g. during the contacting in step (i), or when being added to the acidic aqueous composition in step (ii)). In order to further facilitate this profile of properties, it is preferred to use urethane resins which have neither free or blocked isocyanate groups nor terminal amine groups as thickening agents. In a preferred embodiment, the thickening agent which is a urethane resin thus has an amine value of less than 8 mg KOH / g, particularly preferably less than 5 mg KOH / g, more particularly preferably less than 2 mg KOH / g, the amine value in each case being determined according to the method as previously described for the organic, polymeric compounds (P2). Since the thickening agent is essentially dissolved in the aqueous phase of the activation aid and thus can be assigned to the non-particulate components, and since the components (P2) are essentially bound in the particulate components (P), it is preferred that the activation aid, wherein the amine value of all polymeric organic compounds in the non-particulate components is preferably less than 16 mg KOH / g, particularly preferably less than 10 mg KOH / g, more particularly preferably less than 4 mg KOH / g. It is further preferred that the urethane resin has a hydroxyl value in the range from 10 to 100 mg KOH / g, particularly preferably in the range from 20 to 60 mg KOH / g, the hydroxyl value being determined according to the method A from European Pharmacopoeia 9.0 of 01 / 2008: 20503. With regard to the molecular weight, it is advantageous and thus preferred according to the application that the weight average molar mass of the urethane resin is in the range from 1000 to 10 000 g / mol, preferably in the range from 2000 to 6000 g / mol, the weight average molar mass in each case being determined experimentally as previously described in connection with the definition of the polymeric organic compounds according to the application.

[0090] The activation aid is an aqueous dispersion which preferably has a pH value in the range from 6.0 to 9.0, and particularly preferably does not comprise any pH-adjusting water-soluble compounds having a pK S value of less than 6 or a pK B value of less than 5.

[0091] The activation aid can also comprise auxiliaries, for example selected from the group consisting of preservatives, wetting agents and antifoams, which are contained in the amounts required for the relevant function. The proportion of auxiliaries, in particular preferred other compounds in the non-particulate constituents which are not thickening agents, is preferably less than 1 % by weight.

[0092] The activation 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 a 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 achieved, as determined by dynamic light scattering after dilution 1000-fold with water, for example by Zetasizer® Nano ZS from Malvern Panalytical GmbH; b) diluting the pigment paste with an amount of water, preferably deionized water (k < 1 pm cm -1 ) or service water, and a thickening agent, thereby providing at least 5% by weight of dispersed particulate constituents (P) and a maximum dynamic viscosity of at least 1000 Pa s in a shear rate range of 0.001 to 0.25 s -1 at a temperature of 25°C, wherein the preferred embodiments of the activation aid are obtained in an analogous manner by selecting the respective components (P1), (P2) and thickening agent in the amounts which can be provided or required in each case.

[0093] In the context of the present application, it is preferred, in particular for reasons of method economy, that the activation aids in method steps (i) and (ii) are each based on the same water-dispersed particulate constituents (P). If the components (P1) and (P2) do not differ from one another in their chemical composition (i.e. the water-dispersed particulate constituents (P) of the respective aqueous dispersions comprise stoichiometrically identical phosphates of the same polyvalent cation, and with regard to the polymeric organic compounds, comprise the same structural repeat unit), the water-dispersed particulate constituents (P) are already considered to be identical.

[0094] Exemplary embodiments: The following is intended to demonstrate that wetting the metal substrate with an activation aid prior to the activation zinc phosphatizing process makes it possible to reduce the layer weight and at the same time to save the amount of activation aid required for setting up the activation zinc phosphatizing bath.

[0095] For this purpose, test metal sheets (105 x 190 mm, Gardobond® provided by Chemetall) made of cold-rolled steel (CRS), hot-dip galvanized (HDG) steel and aluminum (alloy AA6014) were each wetted with an activation aid and then immediately subjected to zinc phosphatizing.

[0096] For the method sequence listed and carried out in Table 1 the following treatment steps (1) to (6) are provided: (1) Spray degreasing at 54°C spray medium temperature for 60 seconds at 1.0 bar, wherein the spray medium with a pH value of 11.2 consists of: 30 g / kg Bonderite® C-AK 1574 A 3 g / kg Bonderite® C-AD 1270 1 g / kg Bonderite® M-AD 100 All products from Henkel AG & Co KGaA NaHC03 in an amount for setting the pH remainder: deionized water (k < 1 μS cm -1 ) (2) Immersion degreasing at 55°C immersion medium temperature for 180 seconds, wherein the immersion medium with a pH value of 11.2 has the same composition as the medium used for spray degreasing (1) (3) Rinsing at about 20°C medium temperature with deionized water (k < 1 μS cm -1 ) for about 60 seconds (4) Wet activation by atomizing the test metal sheet at about 20°C with an activation aid with a pH value of 10.0, which consists of: 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) 10% by weight NaOH solution in an amount for setting the pH remainder: deionized water (k < 1 μS cm -1 ) Inorganic particulate component (P1): Phosphorite (Zn3(P04)2) Polymeric organic compound (P2): Maleic acid-styrene copolymer modified with EO / PO units Amount of particulate component (P) in the activation aid: 60 mg / kg (a), 100 mg / kg (b) or 600 mg / kg (c) Atomization is carried out using a spray bottle (from Würth; item no. 0891 502 002; 500 ml), wherein the sheet is sprayed three times on each side with sufficient wetting of the surface. After allowing the spray to activate for about 5 seconds, the sheet wetted in this way is immersed in the zinc phosphatizing bath from step (5).

[0097] (5) trivalent zinc phosphatizing by activation in a phosphatizing bath at 51 °C for 180 seconds, wherein the phosphatizing bath has a free acid of 1.1 points, a total acid of 26.5 points and 170 mg / kg free fluoride and has the following composition: 1.3 g / kg zinc ions 0.8 g / kg manganese ions 0.9 g / kg nickel ions 14.7 g / kg phosphate anions 1.0 g / kg SiF6anions 1.3 g / kg NaNO3 1.0 g / kg hydroxylamine amount of added activation adjuvants: 1.0 g / kg (a) or 0.2 g / kg (b) Bonderite® M-AC 3000 (provided by Henkel AG & Co KGaA) in deionized water (k < 1 μS cm -1 ) amount of water-dispersed particulate component (D): 200 mg / kg (a) or 40 mg / kg (b) (6) rinsing for about 60 seconds at a rinsing medium temperature of about 20 °C with deionized water (k < 1 μS cm -1 ) (7) drying the sheet by blowing the sheet with compressed air Table 1 lists the layer weights achieved according to the method sequences listed in the table. It can be seen that the pre-activation of the zinc surface leads to a significant reduction in the layer weight during the activation zinc phosphatizing (V1 vs. E1), which already occurs during the activation wetting with the low-concentration aqueous dispersion atomized. At a 10-fold increase in concentration, a further layer weight reduction of about 2 g / m 2 occurs on the zinc surface, while still achieving a closed, uniform phosphate layer (E1 vs. E2). Even on the steel surface, the pre-activation by atomization then reduces the layer weight significantly, which is already far below or even without pre-activation of 3 g / m 2 (CRS: V1), and even down to values below 2 g / m 2 (CRS: E1 vs. E2), without loss of phosphatizing quality during layer formation. The layer formation process on the aluminum surface only slightly depends on the respective method sequence and is both with and without pre-activation at 2 g / m 2left and right. Overall, the method according to the application makes it possible to level the layer build-up, wherein the coating is still different on the different substrates during the activated zinc phosphatization. For parts made of zinc, iron and aluminum, the zinc or zinc and iron surfaces are simply wetted with the activation aid in order to obtain a layer build-up of 2 g / m 2 left and right. Overall, the method according to the application makes it possible to level the layer build-up, wherein the coating is still different on the different substrates during the activated zinc phosphatization. For parts made of zinc, iron and aluminum, the zinc or zinc and iron surfaces are simply wetted with the activation aid in order to obtain a layer build-up of 2 g / m

Claims

1. A method for pretreating a plurality of components in series for corrosion protection, wherein each component in series has at least partially a zinc and / or iron surface, and first undergoes a method step (i) for activating the zinc and / or iron surface, and then immediately undergoes a method step (ii) for zinc phosphating. in, In method step (i), at least the zinc and / or iron surface of each component in the series is brought into contact with an aqueous dispersion comprising a water-dispersed granular portion (P), said granular portion (P) containing... - At least one particulate inorganic compound (P1) consisting of a phosphate of a polyvalent metal cation selected at least partially from zinc phosphate rock, phosphogypsum, zinc phosphate rock, and / or manganese phosphate rock. - and at least one polymerized organic compound (P2). This contact is achieved by dispensing the aqueous dispersion from the supply such that no more than 1.00 liters of the aqueous dispersion are dispensed per square meter of the surface of each component in series—preferably per square meter of the zinc and / or iron surface of each component in series to be in contact with the dispersion. Furthermore, in method step (ii), at least the zinc and / or iron surface of each component in the series is brought into contact with an acidic aqueous composition having a free acid concentration greater than zero. (A) 5 to 50 g / kg of phosphate dissolved in water, calculated as PO4, (B) 0.3 to 3 g / kg of zinc ions, (C) Free fluoride, and (D) An aqueously dispersed particulate component comprising a polyvalent metal cation, wherein the phosphate is at least partially selected from zinc phosphate rock, phosphogypsum, zinc phosphate rock, and / or manganese phosphate rock. The acidic aqueous composition is obtained by adding a certain amount of an aqueous dispersion to an acidic aqueous composition containing components (A) to (C), wherein the aqueous dispersion contains a water-dispersed particulate component (P) containing - At least one particulate inorganic compound (P1) consisting of a phosphate of a polyvalent metal cation selected at least partially from zinc phosphate rock, phosphogypsum, zinc phosphate rock, and / or manganese phosphate rock. - and at least one polymerized organic compound (P2).

2. The method according to any one of the preceding claims, characterized in that... The method step (i) of contacting at least the zinc and / or iron surfaces of the components with the dispersion is carried out by dispensing an aqueous dispersion from a supply such that no more than 0.50 liters, preferably no more than 0.20 liters, of the aqueous dispersion are dispensed per square meter of the zinc and / or iron surfaces of each component in the series to be activated—preferably per square meter of the surfaces of the components in the series, wherein the surfaces are to be contacted with the dispersion.

3. The method according to any one of the preceding claims, characterized in that... In step (i), the aqueous reagent to be in contact with the surface is dispensed such that at least the zinc and / or iron surfaces are covered with a liquid film containing the aqueous dispersion, wherein a volume-dependent coating is formed on the zinc and / or iron surfaces, preferably not exceeding 1.00 liters, particularly preferably not exceeding 0.50 liters, extremely particularly preferably not exceeding 0.20 liters, and particularly preferably not exceeding 0.10 liters per square meter.

4. The method according to any one of the preceding claims, characterized in that... The aqueous reagent is dispensed in method step (i) as a spray, as a mist, or as a liquid film – preferably as a spray and / or mist, particularly preferably as a mist.

5. The method according to any one of the preceding claims, characterized in that, In method step (i) and / or method step (ii), the polymerized organic compound (P2) in the particulate component (P) containing the aqueous dispersion is at least partially composed of styrene and / or an α-olefin having no more than 5 carbon atoms, wherein the polymerized organic compound (P2) further comprises units of maleic acid, its anhydride and / or imide, and preferably additionally comprises polyoxyethylene units, particularly preferably polyoxyethylene units in its side chains, which are preferably at least partially capped by aliphatic alkyl groups having no more than 4 carbon atoms.

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

7. The method according to any one of claims 6 and 7, characterized in that... The proportion of polyoxyethylene units in all polymerized organic compounds (P2) is at least 40% by weight, preferably at least 50% by weight, but preferably not more than 70% by weight.

8. The method according to any one of the preceding claims, characterized in that, In method step (i) and / or method step (ii), the proportion of phosphate contained in the at least one particulate inorganic compound (P1) relative to the dispersed inorganic particulate component of the aqueous dispersion—calculated as PO4—is at least 25% by weight, preferably at least 35% by weight, particularly preferably at least 40% by weight, and extremely particularly preferably at least 45% by weight.

9. The method according to any one of the preceding claims, characterized in that, In method step (i) and / or method step (ii), the aqueous dispersion contains at least one thickener as an additional component, preferably selected from urea carbamate resins, preferably urea carbamate resins with an amine value of less than 8 mg KOH / g, particularly preferably less than 5 mg KOH / g, and extremely particularly preferably less than 2 mg KOH / g.

10. The method according to any one of the preceding claims, characterized in that, Relative to the aqueous dispersion, in method step (i) the amount of the water-dispersed particulate component (P) of the aqueous dispersion is equal to at least 0.060 g / kg, preferably at least 0.100 g / kg, but preferably not more than 5.0 g / kg, and particularly preferably not more than 1.0 g / kg.

11. The method according to any one of the preceding claims, characterized in that, The pH of the aqueous dispersion in step (i) of the method for activating the zinc surface is higher than 6.0, preferably higher than 6.5, but preferably not more than 9.0, particularly preferably not more than 8.5, extremely particularly preferably not more than 8.0 and particularly preferably not more than 7.

5.

12. The method according to any one of the preceding claims, characterized in that, In step (ii) of the method, a certain amount of aqueous dispersion is added so that the phosphate of the water-dispersed particulate component (D) is at least 0.1 mg / kg, preferably at least 0.5 mg / kg, particularly preferably at least 1.0 mg / kg and extremely particularly preferably at least 2.0 mg / kg based on the weight ratio of the acidic aqueous composition.

13. The method according to any one of the preceding claims, characterized in that, The pH of the acidic aqueous composition used for zinc phosphating in step (ii) is less than 3.6, preferably less than 3.4, particularly preferably less than 3.2, wherein the free acid is preferably greater than 0.5, particularly preferably greater than 0.8, and particularly preferably greater than 1.

0.

14. The method according to any one of the preceding claims, characterized in that, The components in the series connection have at least a zinc surface, and preferably also an iron surface, and extremely preferably also an aluminum surface.

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