EP4174211A1 - Multistage treatment for activated zinc phosphating of metallic components with zinc surfaces - Google Patents

Abstract

The present invention relates to a method for the anti-corrosion pretreatment of a large number of components in series, in which each component in the series has at least some surfaces of zinc and undergoes successive process steps for the deposition of iron and for zinc phosphating. In the process step for the deposition of iron, a layer of at least 10 milligrams of the element iron per square meter of the zinc surface must be set. The zinc phosphating that follows this iron separation is carried out using an acidic, aqueous composition which, in addition to zinc ions, phosphate ions and free fluoride, also contains a particulate component dispersed in water, which is at least partially composed of hopeite, phosphophyllite, scholzite and/or hureaulite , and is provided by means of an aqueous dispersion of these crystalline solids, which is stabilized with at least one polymeric, organic compound.

Description

The present invention relates to a method for the anti-corrosion pretreatment of a large number of components in series, in which each component in the series has at least some surfaces of zinc and undergoes successive process steps for the deposition of iron and for zinc phosphating. In the process step for the deposition of iron, a layer of at least 10 milligrams of the element iron per square meter of the zinc surface must be set. The zinc phosphating that follows this iron separation is carried out using an acidic, aqueous composition which, in addition to zinc ions, phosphate ions and free fluoride, also contains a particulate component dispersed in water, which is at least partially composed of hopeite, phosphophyllite, scholzite and/or hureaulite , and is provided by means of an aqueous dispersion of these crystalline solids, which is stabilized with at least one polymeric, organic compound.

The layer-forming phosphating is a process that has been practiced and intensively studied for decades for the application of crystalline anti-corrosion coatings on metallic surfaces, in particular on materials made of the metals iron, zinc and aluminium. Zinc phosphating, which is particularly well-established for corrosion protection, takes place in a layer thickness of a few micrometers and is based on corrosive pickling of the metallic material in an acidic, aqueous composition containing zinc ions and phosphates. In the course of pickling, an alkaline diffusion layer forms on the metal surface, which extends into the interior of the solution and within which poorly soluble crystallites form, which precipitate directly at the interface with the metallic material and continue to grow there. Water-soluble compounds, which represent a source of fluoride ions, are often added to support the pickling reaction on materials made of the metal aluminum and to mask the bath poison aluminum, which in dissolved form interferes with the formation of layers on materials made of the metal.

As standard, the zinc phosphating is adjusted in such a way that homogeneous, closed and compact crystalline coatings are achieved on the surfaces of the metals iron, zinc and aluminium. Otherwise, good corrosion protection and Varnish primer cannot be realized. Homogeneous, closed coatings in zinc phosphating are usually reliably achieved from a layer weight of 2 g/m ² . Depending on the metal surface to be phosphated, the pickling described above and the concentration of the active components in the zinc phosphating stage must be adjusted accordingly in order to ensure correspondingly high layer weights on the surfaces of the metals iron or steel, zinc and aluminum.

Another property of zinc phosphating that is important for corrosion protection and paint adhesion, in particular for good electrocoating properties, is that the deposition process is self-limiting, i.e. the dissolution of the phosphate layer, which takes place at the acidic pH value of zinc phosphating, with the application or Continued growth of the phosphate crystallites is in a stationary equilibrium and the layer weight therefore no longer increases, which would be an indication of the growth of a layer coating that is crystalline but porous and therefore not compactly crystalline. In the technical process of zinc phosphating, this means that with a treatment time of usually around 20 seconds to 5 minutes that makes economic sense in the wet-chemical process step of zinc phosphating, the formation of the homogeneous, closed and crystalline zinc phosphate coating must be completed on the one hand and, ideally, the self-limiting thickness of the zinc phosphate coating on the other coating is reached. Technically, this is ensured by the fact that coatings grow with the highest possible number density of phosphate crystallites, so that the layer formation, in turn with the lowest possible layer weights, reaches the range of self-limitation and thus a predetermined boundary layer thickness.

In order to achieve such homogeneous, closed coatings with high compactness or number density of phosphate crystallites, the zinc phosphating in the prior art is always initiated with an activation of the metallic surfaces of the component to be phosphated. Activation is usually a wet-chemical process step that is conventionally brought into contact with colloidal, aqueous solutions of phosphates ("activation stage"), which are immobilized on the metal surface in the subsequent phosphating as a growth nucleus for the formation of the crystalline coating inside serve the alkaline diffusion layer, so that a high number density of growing crystallites is caused and thus in turn a compact crystalline zinc phosphate layer is generated, which provides excellent protection against corrosion and because of its high electrical resistance, it also has excellent electrocoating properties.

Suitable dispersions are colloidal, mostly neutral to alkaline, aqueous compositions based on phosphate crystallites which, in their crystal structure, exhibit only slight crystallographic deviations from the type of zinc phosphate layer to be deposited. That's how she teaches WO 98/39498 A1 in this connection, in particular, bivalent and trivalent phosphates of the metals Zn, Fe, Mn, Ni, Co, Ca and Al, phosphates of the metal zinc preferably being used for activation for subsequent zinc phosphating.

An activation stage based on dispersions of bi- and trivalent phosphates requires a high level of process control in order to keep the activation performance constantly at an optimal level, especially when treating a series of metallic components. For the process to be sufficiently robust, neither foreign ions brought in from previous treatment baths nor aging processes in the colloidal, aqueous solution must lead to a deterioration in the activation performance. A deterioration is initially noticeable in increasing layer weights in the subsequent phosphating and finally leads to the formation of defective or inhomogeneous or less compact phosphate layers. All in all, the layer-forming zinc phosphating with upstream activation is therefore a multi-stage process that is complex to control in terms of process technology, which has also been resource-intensive to date, both in terms of the process chemicals and the energy to be expended.

In the field of automobile production, which is particularly relevant to the present invention, various metallic materials are being used to an increasing extent and joined together in composite structures. In body construction, a wide variety of steels are still mainly used because of their specific material properties, but also increasingly light metals such as aluminum, which are particularly important for a significant weight reduction of the entire body. In particular, there is often the challenge in the automotive industry that the surfaces of zinc must be particularly well activated by the zinc phosphating processes known in the prior art compared to steel surfaces in order to allow the growth of a compact crystalline phosphate layer with usually less than 5.0 g/m ² shift weight in the To ensure zinc phosphating, since above such phosphate layer weights no satisfactory corrosion protection is achieved on the zinc surfaces and the process is then operated neither in a resource-saving nor economical manner due to the high consumption of phosphates.

The WO 2019/238573 A1 addresses a resource-saving process for zinc phosphating and indirectly also a reduction in the complexity of the multi-stage process by presenting a particularly effective activation based on specifically dispersed bi- and trivalent phosphates, which produces a colloidal, aqueous solution based on bi- and provides trivalent phosphates and also enables homogeneous, closed and very compact zinc phosphate coatings with a relatively low particulate content in the activation stage, so that the material requirement due to the layer formation in the zinc phosphating is reduced.

However, there is still a need to optimize the pre-treatment line for zinc phosphating, including the activation and phosphating stage, so that the overall process can be carried out in a less resource-intensive manner and this ideally with simplified process management at the same time. However, a resource-saving overall process must not be at the expense of the properties of the zinc phosphating, which must be provided as a homogeneous, closed and compact crystalline coating with high electrical penetration resistance in order to enable good protection against corrosion and a correspondingly good coverage of the paint in a subsequent electrophoretic coating. In particular, this must always be guaranteed in the most common application, namely the series treatment of components, whereby an economically attractive and resource-saving process must also be provided for components that have zinc surfaces.

Surprisingly, this complex profile of requirements can be met if an amount of a dispersion of particulate zinc phosphates is added to the acidic aqueous composition for zinc phosphating, which evidently results in the composition for zinc phosphating becoming self-activating. The activation performance of the pre-treatment line for zinc phosphating a series of components can then be maintained by metering in an activation aid based on the aforementioned dispersion of particulate zinc phosphates. This makes it possible at least partially or also to dispense entirely with an activation stage upstream of the wet-chemical treatment stage of zinc phosphating and in this way to conduct the overall process of zinc phosphating in a way that is less material and energy-intensive and to reduce procedural complexity in the form of the separate activation stage that has hitherto been absolutely necessary in the prior art. Crucial to the economical, i.e. resource-conserving, operation of a pretreatment line according to the invention, which is used to phosphate components comprising surfaces of zinc satisfactorily in series, is a wet-chemical step upstream of the zinc phosphating for the deposition of an iron layer on the zinc surfaces, which leads to a significant reduction in the phosphate layer weight on them Surfaces leads, so that the object of the present invention, on components comprising surfaces of zinc in series to constantly deliver satisfactory corrosion protection values with low material consumption, is reliably achieved.

• wobei im Verfahrensschritt (i) eine Schichtauflage von mindestens 10 Milligramm des Elements Eisen pro Quadratmeter der Zinkoberflächen des Bauteils herbeigeführt wird, und
• wobei jedes Bauteil im Verfahrensschritt (ii) mit einer sauren, wässrigen Zusammensetzung in Kontakt gebracht wird, die eine Freie Säure in Punkten von größer als Null aufweist, und
  1. (A) 5 - 50 g/kg an in Wasser gelösten Phosphaten berechnet als PO4,
  2. (B) 0,3 - 3 g/kg an Zink-Ionen,
  3. (C) freies Fluorid, und
  4. (D) einen wasserdispergierten, partikulären Bestandteil umfassend Phosphate polyvalenter Metall-Kationen enthält, wobei die Phosphate zumindest teilweise ausgewählt sind aus Hopeit, Phosphophyllit, Scholzit und/oder Hureaulith,
• wobei die saure, wässrige Zusammensetzung erhältlich ist durch Zugabe einer Menge einer wässrigen Dispersion zu einer sauren, wässrigen Zusammensetzung enthaltend die Komponenten (A) - (C), wobei die wässrige Dispersion einen wasserdispergierten, partikulären Bestandteil (P) enthält, der
  • mindestens eine partikuläre anorganische Verbindung (P1), die aus Phosphaten polyvalenter Metall-Kationen zumindest teilweise ausgewählt aus Hopeit, Phosphophyllit, Scholzit und/oder Hureaulith zusammengesetzt ist,
  • sowie mindestens eine polymere organische Verbindung (P2) umfasst.

The present invention therefore relates to a method for the anti-corrosion pretreatment of a large number of components in series, in which each component in the series has at least some surfaces of zinc and first a wet-chemical process step (i) for the deposition of iron on the zinc surfaces and then a process step (ii ) goes through to zinc phosphating,

• wherein in process step (i) a coating of at least 10 milligrams of the element iron per square meter of the zinc surfaces of the component is brought about, and
• wherein in step (ii) each component is contacted with an acidic aqueous composition having a Free Acid in points greater than zero, and
  1. (A) 5 - 50 g/kg of phosphates dissolved in water calculated as PO4,
  2. (B) 0.3 - 3 g/kg of zinc ions,
  3. (C) free fluoride, and
  4. (D) contains a water-dispersed, particulate component comprising phosphates of polyvalent metal cations, the phosphates being at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite,
• wherein the acidic, aqueous composition is obtainable by adding an amount of an aqueous dispersion to an acidic, aqueous composition containing components (A)-(C), wherein the aqueous dispersion contains a water-dispersed, particulate component (P) which
  • at least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite,
  • and at least one polymeric organic compound (P2).

A pretreatment in series is when the components of the series each go through a process step for zinc phosphating according to the method according to the invention and are brought into contact with at least one bath liquid for zinc phosphating provided in a system tank, the individual components being brought into contact one after the other and is therefore separated in time. The system tank is the container in which the acidic aqueous composition is located for the purpose of zinc phosphating by means of a wet-chemical pre-treatment. The components can be brought into contact with the bath liquid of the system tank inside the system tank, for example by immersion, or outside of the system tank, for example by spraying or spraying on the bath solution stored in the system tank.

The components treated according to the present invention can be any three-dimensional structure of any shape and design that originates from a manufacturing process, in particular semi-finished products such as strips, sheet metal, rods, pipes, etc. and composite structures assembled from the aforementioned semi-finished products, the semi-finished products preferably being assembled by gluing, Welding and / or flanging are connected to the composite structure.

In the context of the method according to the invention, a component has at least one surface of zinc or one of the metals iron or aluminum if the metallic structure on this surface consists of more than 50 at. composed of iron or aluminum. This regularly applies to components made of corresponding metallic materials, insofar as the metallic materials are made up of more than 50 at % of zinc or iron or aluminum as uniform materials. However, components comprising zinc surfaces are also iron materials provided with metallic coatings, such as electrolytically galvanized or hot-dip galvanized strip steel, which can also be alloyed with iron (ZF), aluminum (ZA) and/or magnesium (ZM).

Process step (i) - deposition of iron:

According to the invention, the deposition of a layer covering, based on the element iron, of at least 10 milligrams per square meter of the zinc surfaces of the component is required. Higher layers of iron are advantageous for the reduction of the phosphate layer weight in the subsequent process step (ii), so that in the process according to the invention in the wet-chemical process step (i) on the surfaces of the components that are formed by zinc, a layer, based on the element iron, of at least 20 milligrams, more preferably at least 40 milligrams, most preferably at least 60 milligrams. However, it can often be observed that significantly higher layers of iron on the zinc surface prove to be disadvantageous for the process according to the invention, since poorer adhesion results to organic topcoats are achieved in conjunction with the zinc phosphating. Accordingly, it is preferred if the layer of iron is limited to less than 150 milligrams, particularly preferably less than 120 milligrams per square meter of the zinc surfaces of the component in wet-chemical process step (i).

A wet-chemical treatment step within the meaning of process step (i) occurs when the components of the series are brought into contact with a water-based composition that contains the active components for separating iron dissolved or dispersed in the water-based phase. The composition is water-based if the proportion of water is at least 50% by weight, preferably at least 70% by weight, particularly preferably at least 80% by weight, based in each case on the total composition.

Suitable wet-chemical processes for depositing iron in the desired layer are known to the person skilled in the art. In this case, precipitation typically takes place by bringing at least the surfaces of zinc into contact with aqueous compositions containing iron(II) and/or iron(III) ions, the proportion of iron ions dissolved in water being at least 50 mg/L, preferably at least 100 mg/L.

The iron layer on the zinc surfaces can be determined by means of pickling and photometric analysis. For the quantitative determination, a defined Sample volume of a 5 wt. 0% sodium thiocyanate solution is presented, transferred to determine the absorption at a wavelength of 517 nm and a temperature of 25 ° C. Calibration is carried out using the two-point method by determining the absorption values of two standard solutions of iron(III) nitrate in 5% by weight nitric acid.

In order to avoid the metallic deposition of noble elements, which weaken the positive effect of the iron layer on the zinc surfaces for the formation of the zinc phosphate layer, and also for ecological reasons, it is preferred if the aqueous compositions for the deposition of iron in process step (i) contain less than 10 mg /L of ionic compounds of the metals copper, nickel, cobalt, particularly preferably a total of less than 10 mg/L of ionic compounds of the metals copper, nickel, cobalt, tin, manganese, molybdenum, chromium and/or cerium, particularly preferably less than in each case 1 mg/L of ionic compounds of the metals nickel and cobalt, each based on the metallic element, are contained in the aqueous composition.

Analogously, to avoid layer formation competing with the iron deposition in process step (i), it is preferred if the aqueous compositions for the deposition of iron contain a total of less than 20 mg/L of water-soluble compounds of the elements Zr, Ti, Hf and/or Si, particularly preferred less than 5 mg/l in each case, particularly preferably less than 1 mg/l in each case, of water-soluble compounds of the elements Zr, Ti, Hf or Si.

A deposition of iron on zinc from acidic, aqueous compositions is in WO2008/135478 A1 in the presence of iron(II) ions. Such a method is also suitable in the context of the present invention and is particularly advantageous because of the compatibility in terms of pH value with the subsequent zinc phosphating in method step (ii). In this regard, it is therefore preferred to bring it into contact with an acidic aqueous composition with a pH in the range of 2.0-6.0 containing at least 50 mg/L of iron(II) ions and preferably an α-hydroxycarboxylic acid, preferably in a molar ratio to the iron ions of 5:1 to 1:5, and particularly preferably additionally selected from at least one reducing agent Oxoacids of phosphorus or nitrogen and their salts, where at least one phosphorus or nitrogen atom is in a medium oxidation state, hydrazine, hydroxylamine, nitroguanidine, N-methylmorpholine-N-oxide, glucoheptonate, ascorbic acid and/or reducing sugars.

Alternatively and because of the particular efficiency for reducing the phosphate layer weight on the surfaces of zinc in the subsequent zinc phosphating, the deposition of the iron coating from alkaline, aqueous compositions is particularly advantageous, the pH of the alkaline, aqueous compositions containing iron (II) and /or iron(III) ions preferably not below 8.5, particularly preferably not below 9.5, very particularly preferably not below 10.5, but preferably not above 13.5, particularly preferably not above 12 .5 and most preferably not above 11.5.

1. (a) mindestens 50 mg/L, vorzugsweise mindestens 100 mg/L, besonders bevorzugt mindestens 200 mg/L an Eisen(III)-Ionen, und
2. (b) mindestens 100 mg/L an Komplexbildnern ausgewählt aus organischen Verbindungen (b1), die zumindest eine funktionale Gruppe ausgewählt aus COOX, OPO₃X und/oder PO₃X aufweisen, wobei X entweder ein H Atom oder ein Alkali- und/oder Erdalkalimetall-Atom darstellt, und/oder kondensierten Phosphaten (b2) berechnet als PO4,

enthalten, wobei die Zusammensetzung vorzugsweise eine freie Alkalität von zumindest 1 Punkt, aber vorzugsweise weniger als 6 Punkten aufweist.In a preferred embodiment of such an alkaline, aqueous composition, in step (i) of the method according to the invention

1. (a) at least 50 mg/L, preferably at least 100 mg/L, particularly preferably at least 200 mg/L of iron(III) ions, and
2. (b) at least 100 mg/L of complexing agents selected from organic compounds (b1) which have at least one functional group selected from COOX, OPO ₃ X and/or PO ₃ X, where X is either an H atom or an alkali and/or or represents alkaline earth metal atom, and/or condensed phosphates (b2) calculated as PO4,

preferably wherein the composition has a free alkalinity of at least 1 point, but preferably less than 6 points.

The term "condensed phosphates" according to component (b1) are the room temperature water-soluble metaphosphates (Me _n [P _n O _3n ]), di- tri- and polyphosphates (Me _{n + 2} [P _n O _{3n + 1} ] or Me _n [H ₂ P _n O _3n+1 ]), the isometaphosphates and the crosslinked polyphosphates, where Me are either alkali metal or alkaline earth metal atoms. Of course, instead of the water-soluble salts, the corresponding condensed acids of phosphoric acid can also be used for the formulation of the alkaline, aqueous compositions, provided that the free alkalinity is adjusted as indicated. The mass-related proportion of "condensed phosphates" according to component (b1) is always calculated as a corresponding amount of PO4. Analogously, for the determination of those molar ratios that include a quantity of condensed phosphates, this quantity of condensed phosphates is always related to the equivalent quantity of PO4.

It has been found that an alkaline, aqueous composition in step (i) of the method according to the invention in particular brings about a layer of iron suitable for the subsequent zinc phosphating on the surfaces of zinc, which particularly reliably allows compact, crystalline zinc phosphate layers to grow if the free Alkalinity is less than 5 points. For the application of the alkaline, aqueous composition by spraying, a suitable layer of iron is achieved in particular when the free alkalinity is less than 4 points. Surprisingly, as already mentioned, it has been found that large layers of iron on zinc surfaces of more than 150 mg/m ² tend to be disadvantageous for the process according to the invention, since poorer adhesion results to organic topcoats are achieved in conjunction with the zinc phosphating, so that the alkaline, aqueous compositions in step (i) must not have too high a free alkalinity. However, the free alkalinity should preferably be at least 2 points in order to produce optimum layer coverage on zinc surfaces of at least 20 mg/m ² based on the element iron. Alkaline, aqueous compositions which have a free alkalinity above 6 points result in high layers of iron on the zinc surfaces, but the adhesion to paint layers possibly applied after step (ii) is significantly reduced by high layers based on the element iron , so that the corrosion protection is less effective or insufficient.

The free alkalinity is determined by titrating 2 ml of bath solution, preferably diluted to 50 ml, with a 0.1N acid such as hydrochloric acid or sulfuric acid to a pH of 8.5. The consumption of acid solution in ml gives the free alkalinity score.

Ideally, the alkaline, aqueous composition in step (i) of the process according to the invention has a pH of at least 9.5, particularly preferably at least 10.5. Below a pH value of 10.5, layers are applied Iron of at least 20 mg/m ² is formed on the zinc surfaces upon contacting them with a composition containing ferrous and/or ferric ions only in the presence of a reducing agent. Such compositions for depositing an iron layer are in WO2011/098322 A1 disclosed which contain an amino acid and additionally a reducing agent selected from oxoacids of phosphorus or nitrogen and their salts, wherein at least one phosphorus or nitrogen atom is present in an intermediate oxidation state, and as such are also suitable in the context of the present invention.

In order to minimize the pickling attack on the zinc surfaces of the component, it is also preferred that the pH in the alkaline, aqueous composition in step (i) of the method according to the invention is not above 13.5, particularly preferably not above 12.5 lies. In the event that the component also has aluminum surfaces in addition to the zinc surfaces, it is advantageous if the pH value in the composition in step (i) of the method according to the invention does not assume values above 11.5, since otherwise the increased pickling attack causes an intensive black discoloration of the aluminum surfaces, the so-called "stain blackness", which has an adverse effect on the effectiveness of a subsequent conversion treatment, e.g. ii) to an acidic subsequent passivation based on water-soluble inorganic compounds of the elements zirconium and/or titanium, which follows the process according to the invention.

The iron ions are present primarily as iron(III) ions at the preferred pH value and in the alkaline, aqueous composition when saturated with atmospheric oxygen. In step (i) of the method according to the invention, their proportion is preferably not more than 2000 mg/L. Higher proportions of iron(III) ions are unfavorable for the process, since the solubility of the iron(III) ions in the alkaline medium must be maintained by correspondingly high proportions of complexing agent, without achieving more favorable properties with regard to the iron layer on the zinc surfaces become. However, preference is given to alkaline, aqueous compositions in step (i) of the process according to the invention in which the proportion of iron(III) ions is at least 100 mg/L, particularly preferably at least 200 mg/L, in order on the one hand to be on the zinc surfaces in step (i) of the process according to the invention to ensure a sufficient layer of iron within process-typical treatment times of less than two minutes and, on the other hand, in step (ii) of the process according to the invention Process to obtain phosphate layers in excellent layer quality on the surfaces of zinc.

The complexing agents according to component (b) of the alkaline, aqueous composition in step (i) of the process according to the invention are preferably present in an amount such that the molar ratio of all components (b) to iron(III) ions is greater than 1:1 and more preferably at least 2:1, most preferably at least 5. It has been shown that the use of the amount of complexing agents in a stoichiometric excess is advantageous for the conduct of the process, since in this way the proportion of iron(III) ions is permanently kept in solution. The precipitation of insoluble iron hydroxides is completely suppressed in this way, so that the alkaline, aqueous composition remains permanently stable and is not depleted of iron(III) ions. At the same time, an inorganic layer containing iron ions is sufficiently deposited on the zinc surfaces. For reasons of economy and for resource-saving use of the complexing agent, it is nevertheless preferred that the molar ratio of components (b) to iron(III) ions in composition (A) does not exceed 10.

In a preferred embodiment, the alkaline, aqueous composition can additionally contain at least 100 mg/L of phosphate ions in step (i) of the method according to the invention. This proportion of phosphate ions means that, in addition to the iron ions, phosphate ions also represent an essential component of the layer containing iron produced in step (i) on the zinc surfaces. It has been found that layers of this type are advantageous for the subsequent zinc phosphating and, in conjunction with the zinc phosphating, provide good adhesion to subsequently applied paint layers. Accordingly, it is further preferred in step (i) of the method according to the invention that the alkaline, aqueous composition contains at least 200 mg/L, particularly preferably at least 500 mg/L, of phosphate ions. The properties of the passive layer, which forms when the zinc surface of the component is brought into contact with compositions (A) in step (i) of the method according to the invention, are no longer positively influenced above a proportion of phosphate ions of 4 g/L, so that, for reasons of economy, the proportion of phosphate ions in the alkaline, aqueous composition in step (i) of the method according to the invention should preferably be below 10 g/l.

The ratio of iron(III) ions to phosphate ions can be varied within a wide range. The mass-related ratio of iron(III) ions to phosphate ions in the alkaline, aqueous composition in step (i) of the method according to the invention is preferably in a range from 1:20 to 1:2, particularly preferably in a range from 1: 10 to 1:3. Alkaline, aqueous compositions which have such a mass ratio of iron(III) ions to phosphate ions produce homogeneous black-grey layers containing phosphate ions with readily adjustable layer thicknesses after contact with a zinc surface in the range of 20-150 mg/m ² based on the element iron.

Condensed phosphates (b2) are able to keep iron(III) ions in solution in an alkaline medium by complexing. Although there are no particular restrictions on the type of condensed phosphates with regard to their usability for alkaline, aqueous compositions in step (i) of the process according to the invention, preference is given to those condensed phosphates which are selected from pyrophosphates, tripolyphosphates and/or polyphosphates, particularly preferably from pyrophosphates , as these are particularly easily soluble in water and very easily accessible.

As organic compounds (b1), which are also or alternatively to the condensed phosphates (b2) as complexing agents in the alkaline, aqueous composition, such compounds are preferred in step (i) of the process according to the invention, which in their acid form (X = H -atom), have an acid number of at least 250. Lower acid numbers give the organic compounds surface-active properties, so that organic compounds (b1) with acid numbers below 250 can have a strong emulsifying effect as anionic surfactants. In this context, it is further preferred that the organic compounds are not high molecular weight and do not exceed a number average molecular weight of 5,000 µ, particularly preferably 1,000 µ. If the preferred acid number and possibly the preferred molecular weight are exceeded, the emulsifying effect of the organic compounds (b1) can be so pronounced that contaminants in the form of oils and drawing fats brought in from the cleaning stage via the component can only be removed via complex separation processes from the treatment stage to separate the Iron layer can be removed, e.g. by adding cationic surfactants, so that other process parameters can be controlled. It is therefore more advantageous to set the alkaline, aqueous composition to be only slightly emulsifying in step (i) of the process according to the invention, in order to enable conventional removal of the floating oils and fats.

In addition, anionic surfactants tend to form pronounced foam, which is particularly disadvantageous, for example, when the alkaline, aqueous composition is applied by spraying. In step (i) of the process according to the invention, preference is therefore given to using organic complexing agents (b1) with acid numbers of at least 250 in the composition. The acid number indicates the amount of potassium hydroxide in milligrams that is required to neutralize 1 g of the organic compound (b1) in 100 g of water in accordance with DIN EN ISO 2114.

Preferred organic complexing agents (b1) in the alkaline, aqueous composition in step (i) of the process according to the invention are selected from α-, β- and/or γ-hydroxycarboxylic acids, hydroxyethane-1,1-diphosphonic acid, [(2-hydroxyethyl)( phosphonomethyl)amino]methylphosphonic acid, diethylenetriaminepentakis(methylenephosphonic acid) and/or amino-tris(methylenephosphonic acid) and salts thereof, particularly preferably hydroxyethane-1,1-diphosphonic acid, [(2-hydroxyethyl)(phosphonomethyl)amino]methylphosphonic acid, diethylenetriaminepentakis( methylenephosphonic acid) and/or amino-tris-(methylenephosphonic acid) and salts thereof.

According to the invention, those alkaline, aqueous compositions are thus explicitly included in step (i) of the method according to the invention which contain exclusively condensed phosphates (b2), exclusively organic complexing agents (b1) or a mixture of both. However, the proportion of organic complexing agent (b1) in the alkaline, aqueous composition can be reduced to the extent that complexing agent (b2) selected from condensed phosphates is present. In a particular embodiment of the method according to the invention, the alkaline, aqueous composition in step (i) contains both complexing agents (b2) selected from condensed phosphates and organic complexing agents (b1), the molar ratio of all components (b) to iron(III ) ions is greater than 1:1, but the molar ratio of components (b1) to iron(III) ions is less than 1:1, particularly preferably less than 3:4, but is preferably at least 1:5. A mixture of the two complexing agents (b1) and (b2) is advantageous insofar as the condensed phosphates in the alkaline medium are in equilibrium at elevated temperature with the phosphate ions of the alkaline, aqueous composition, so that phosphate ions consumed by layer formation on the zinc surfaces Ions are slowly reproduced from the condensed phosphates. Conversely, however, the presence of condensed phosphates alone is not sufficient to create a coating based on iron and To bring about phosphate on the zinc surfaces, so that a proportion of phosphate ions in the alkaline, aqueous composition in step (i) of the method according to the invention is always preferred. In the presence of the condensed phosphates, however, the precipitation of sparingly soluble phosphates, e.g Complexing agents present in step (i) of the process according to the invention are preferred, care preferably being taken to ensure that the molar ratio of components (b1) to iron(III) ions is at least 1:5.

In order to increase the cleaning power for the series components to be treated in the process according to the invention, the alkaline, aqueous composition in step (i) can additionally contain nonionic surfactants. The nonionic surfactants are preferably selected from one or more ethoxylated and / or propoxylated C10-C18 fatty alcohols with a total of at least two but not more than 12 alkoxy groups, particularly preferably ethoxy and / or propoxy groups, some with an alkyl radical, particularly preferably with one Methyl, ethyl, propyl, butyl radical may be end-capped.

1. a) 0,05 bis 2 g/L an Eisen(III)-Ionen,
2. b) zumindest 0,1 g/L an Komplexbildnern ausgewählt aus organischen Verbindungen (b1), die zumindest eine funktionale Gruppe ausgewählt aus COOX, OPO₃X und/oder PO₃X aufweisen, wobei X entweder ein H-Atom oder ein Alkali- und/oder Erdalkalimetall-Atom darstellt, und/oder kondensierten Phosphaten (b2) berechnet als PO4,
3. c) 0,1 bis 4 g/L an Phosphat-Ionen,
4. d) insgesamt 0,01 bis 10 g/L an nichtionischen Tensiden, die vorzugsweise ausgewählt aus einem oder mehreren ethoxylierten und/oder propoxylierten C10-C18 Fettalkoholen mit insgesamt zumindest zwei aber nicht mehr als 12 Alkoxygruppen, besonders bevorzugt Ethoxy- und/oder Propoxygruppen, die teilweise mit einem Alkylrest, besonders bevorzugt mit einem Methyl-, Ethyl-, Propyl-, Butyl-Rest endgrupppenverschlossen vorliegen,
5. e) insgesamt weniger als 10 mg/L an ionischen Verbindungen der Metalle Kupfer, Nickel, Cobalt, Zinn, Mangan, Molybdän, Chrom und/oder Cer, insbesondere jeweils weniger als 1 mg/L an ionischen Verbindungen der Metalle Nickel und Cobalt jeweils bezogen auf das metallische Element,

wobei nicht mehr als 10 g/L an kondensierten Phosphaten (b2) berechnet als PO4 enthalten sind und das molare Verhältnis der Summe der Komponenten (b1) und (b2) zu Eisen(III)-Ionen größer als 1 : 1 ist und wobei die freie Alkalität zumindest 1 Punkt, aber weniger als 6 Punkte beträgt, und der pH-Wert zumindest 10,5 ist.In a particular embodiment of the method according to the invention, the alkaline, aqueous composition in step (i)

1. a) 0.05 to 2 g/L of iron(III) ions,
2. b) at least 0.1 g/L of complexing agents selected from organic compounds (b1) which have at least one functional group selected from COOX, OPO ₃ X and/or PO ₃ X, where X is either an H atom or an alkali and/or alkaline earth metal atom, and/or condensed phosphates (b2) calculated as PO4,
3. c) 0.1 to 4 g/L of phosphate ions,
4. d) a total of 0.01 to 10 g/L of nonionic surfactants, preferably selected from one or more ethoxylated and/or propoxylated C10-C18 fatty alcohols with a total of at least two but not more than 12 alkoxy groups, particularly preferably ethoxy and/or propoxy groups some of which are end-capped with an alkyl radical, particularly preferably with a methyl, ethyl, propyl or butyl radical,
5. e) a total of less than 10 mg/L of ionic compounds of the metals copper, nickel, cobalt, tin, manganese, molybdenum, chromium and/or cerium, in particular less than 1 mg/L of ionic compounds of the metals nickel and cobalt based on each other on the metallic element,

where not more than 10 g/L of condensed phosphates (b2) calculated as PO4 are included and the molar ratio of the sum of components (b1) and (b2) to iron(III) ions is greater than 1:1 and where the free alkalinity is at least 1 point but less than 6 points and the pH is at least 10.5.

In a preferred embodiment of the method according to the invention, the component is treated in series in step (i) for at least 30 seconds but not more than 4 minutes at a temperature of at least 30 ° C, particularly preferably at least 40 ° C, but no more than 70°C, particularly preferably not more than 60°C, with an aqueous composition for removing iron, in particular an alkaline, aqueous composition containing iron(II) and/or iron(III) ions. The preferred treatment or contact times should be selected in step (i) of the process according to the invention so that the layer coverage of iron is at least 10 mg/m ² , preferably at least 20 mg/m ² . The treatment and contact times for the realization of such a minimum layer application vary depending on the type of application and depend in particular on the flow of the aqueous fluids acting on the metal surface to be treated. Thus, the formation of the minimum layer of iron in processes in which the composition is applied by spraying occurs more quickly than in dip applications.

Process step (ii) - activated zinc phosphating:

The zinc phosphating of the components of the series that takes place in process step (ii) is carried out using acidic, aqueous compositions for zinc phosphating containing dispersed phosphates of polyvalent metal cations as a particulate component, the phosphates being at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite . The acidic, aqueous zinc phosphating is therefore self-activating—does not require any previous separate activation—and as such can be obtained by appropriately adding an amount of an aqueous dispersion to an acidic, aqueous composition containing the components (A)-(C) according to claim 1 of the present invention .

• mindestens eine partikuläre anorganische Verbindung (P1), die aus Phosphaten polyvalenter Metall-Kationen zumindest teilweise ausgewählt aus Hopeit, Phosphophyllit, Scholzit und/oder Hureaulith zusammengesetzt ist,
• sowie mindestens eine polymere organische Verbindung (P2) umfasst,

wobei die Zugabe der wässrigen Dispersion für die Bereitstellung der sauren, wässrigen Zusammensetzung zur Zinkphosphatierung des Verfahrensschrittes (ii) vorzugsweise in einer solchen Menge erfolgt, dass der Gewichtsanteil von Phosphaten aus dem partikulären Bestandteil der wässrigen Dispersion bezogen auf die saure wässrige Zusammensetzung enthaltend die Komponenten (A) - (C) mindestens 0,004 g/kg, vorzugsweise mindestens 0,01 g/kg, besonders bevorzugt mindestens 0,05 g/kg und ganz besonders bevorzugt mindestens 0,08 g/kg beträgt.The aqueous dispersion contains a particulate component (P) dispersed in water, the

• at least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite,
• and at least one polymeric organic compound (P2),

wherein the aqueous dispersion for providing the acidic, aqueous composition for zinc phosphating in process step (ii) is preferably added in an amount such that the proportion by weight of phosphates from the particulate component of the aqueous dispersion, based on the acidic, aqueous composition containing the components ( A) - (C) is at least 0.004 g/kg, preferably at least 0.01 g/kg, more preferably at least 0.05 g/kg and most preferably at least 0.08 g/kg.

1. (A) 5 - 50 g/kg an in Wasser gelösten Phosphaten berechnet als PO4,
2. (B) 0,3 - 3 g/kg an Zink-Ionen, und
3. (C) freies Fluorid enthält,

• sowie eine Freie Säure in Punkten von größer als Null aufweist,
• wobei der sauren wässrigen Zusammensetzung im Verfahrensschritt (ii) zur Zinkphosphatierung kontinuierlich oder diskontinuierlich eine solche Menge eines Aktivierhilfsmittels hinzugegeben wird, die unter den gewählten Bedingungen des Verfahrensschritts (ii) der Zinkphosphatierung ausreicht, die Eigenschaft der sauren wässrigen Zusammensetzung, auf einer schmelztauchverzinkten Stahloberfläche (Z) eine Zinkphosphatschicht mit einem Schichtgewicht von weniger als 5,0 g/m², vorzugsweise weniger als 4,5 g/m², besonders bevorzugt weniger als 4,0 g/m², ganz besonders bevorzugt weniger als 3,5 g/m² abzuscheiden, aufrecht zu erhalten,
• wobei das Aktivierhilfsmittel einen partikulären Bestandteil (P) in Wasser dispergierter Form enthält, der
  • mindestens eine partikuläre anorganische Verbindung (P1), die aus Phosphaten polyvalenter Metall-Kationen zumindest teilweise ausgewählt aus Hopeit, Phosphophyllit, Scholzit und/oder Hureaulith zusammengesetzt ist,
  • sowie mindestens eine polymere organische Verbindung (P2) umfasst.

In an alternative or preferred embodiment, the components of the series are brought into contact with an acidic aqueous composition in step (ii) of the method according to the invention, the acidic aqueous composition

1. (A) 5 - 50 g/kg of phosphates dissolved in water calculated as PO4,
2. (B) 0.3 - 3 g/kg of zinc ions, and
3. (C) contains free fluoride,

• and has a free acid in points greater than zero,
• wherein the acidic aqueous composition in process step (ii) for zinc phosphating is added continuously or discontinuously such an amount of an activating agent that is sufficient under the selected conditions of process step (ii) the zinc phosphating, the property of the acidic aqueous composition, on a hot-dip galvanized steel surface (Z ) a zinc phosphate layer with a layer weight of less than 5.0 g/m ² , preferably less than 4.5 g/m ² , particularly preferably less than 4.0 g/m ² , very particularly preferably less than 3.5 g/m m ² to separate, to maintain,
• wherein the activating aid contains a particulate component (P) in water-dispersed form which
  • at least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite,
  • and at least one polymeric organic compound (P2).

The inventive property of the acidic aqueous composition for zinc phosphating in process step (ii) on hot-dip galvanized steel surfaces (Z) is the growth of a zinc phosphate layer with a layer weight below 5.0 g/m ² , preferably below 4.5 g/m ² , particularly preferred below 4.0 g/m ² and very particularly preferably below 3.5 g/m ² (referred to below as "phosphating quality") is to be checked on cleaned and degreased (Z) substrates that are before in-contact -Bringing with the acidic aqueous composition of the method according to the invention in step (ii) and after the deposition of iron on the zinc surfaces in step (i) are not subjected to any further wet chemical pretreatment step. To check the phosphating quality of the acidic aqueous composition, hot-dip galvanized steel (Z) is first prepared with an alkaline cleaner as 2% by weight Bonderite ^® C-AK 1565 A and 0.2% by weight Bonderite ^® C-AD 1270 in deionized water (κ<1µScm ^-1 ) at pH 11.0 and 55 °C for 5 minutes in immersion. The thus cleaned and degreased (Z) substrates are rinsed at room temperature with deionized water (κ<1 μScm ^-1 ) and then fed to the treatment stages according to process steps (i) and (ii) according to the process conditions selected in each case. Corresponding to the selected process conditions means with identical temperature, application time and bath circulation and using those wet-chemical treatment stages for which the phosphating quality specified according to the invention should apply, ie the resulting target layer weights on hot-dip galvanized steel (Z) below 5.0 g/m ² , preferably below 4.5 g/m ² , particularly preferably below 4.0 g/m ² and very particularly preferably below 3.5 g/m ² . The phosphating quality can therefore be determined in the ongoing process according to the invention by also introducing cleaned and degreased sheets of hot-dip galvanized steel (Z) for process steps (i) and (ii) with the components of the series, and then the layer weight of zinc phosphate the metal sheets and thus the phosphating quality of the acidic aqueous composition for zinc phosphating in process step (ii) is determined. Preferably, the cleaned and degreased sheets of hot-dip galvanized steel (Z) are rigidly connected to the component or the conveyor frame in their function as sample sheets for determining the phosphating quality in order to control the flow conditions Transport of the component together with the conveyor frame through the phosphating bath should be reproduced for the test panel as far as possible. For this purpose, the sample sheets should ideally be connected to the component or the conveyor frame in such a way that the transport of a sample sheet together with the component and the conveyor frame does not have any influence on the flow conditions to be considered compared to the transport of the component and the conveyor frame without such a sample sheet and that the flow conditions are essentially identical in both cases and thus essentially correspond to the flow conditions of at least a partial area of the components of the series. This can be achieved, for example, by adapting the size and/or the shape of the sample sheet to the size and shape of the component and/or the conveyor frame which is arranged adjacent to the sample sheet in each case. It is conceivable here, particularly when a test sheet metal is arranged on an outer surface section of the component or the conveyor frame, to dimension the test component correspondingly smaller than said surface section, for example to prevent the test component from protruding beyond the surface section. Alternatively or additionally, the sample component can follow a curvature or other planar deviation of the surface section or the conveyor frame. It has proven to be particularly useful to select a sheet metal section that is sufficiently small compared to the size of a suitable outer surface of the component, with an outer surface being particularly suitable if it is located at a location of the component that is particularly small or at the location of the smallest curvature and the test sheet metal is then mounted spaced apart substantially parallel along the surface normal of such an outer surface. The quality of the phosphating results directly from the series treatment of components that also have a surface of hot-dip galvanized steel (Z) as a surface of zinc. Such components are preferred in a preferred embodiment of the method.

It is also preferred for the phosphating quality that if the contact is extended by one minute, the layer weight on hot-dip galvanized steel (Z) increases by no more than 0.2 g/m ² and thus the layer formation under the selected conditions is already in the range of self-limitation, so that the property of the acidic, aqueous composition for zinc phosphating is ensured, in step (ii) of the method according to the invention to produce compact, crystalline zinc phosphate layers. Accordingly, it is preferred that in the process step for zinc phosphating such an amount of an activating agent is added that under the chosen conditions of the process step of zinc phosphating in the invention Method sufficient, the property of the acidic aqueous composition, on a hot-dip galvanized steel surface (Z) a zinc phosphate layer with a layer weight of less than 5.0 g / m ² , preferably less than 4.5 g / m ² , particularly preferably less than 4, 0 g/m ² and very particularly preferably less than 3.5 g/m ² to be deposited, the layer weight achieved under the selected conditions of process step (ii) of zinc phosphating in the process according to the invention when the contact time with the acidic , aqueous composition does not increase by more than 0.2 g/m ² for 60 seconds.

Usually, the phosphating quality is determined and monitored in the method according to the invention, in that hot-dip galvanized steel (Z), which has been cleaned and degreased as described above, also undergoes the zinc phosphating process step at regular intervals during the series treatment and is then subjected to a coating weight determination. As already mentioned, the phosphating quality results directly from the series treatment of components that also have at least one surface of hot-dip galvanized steel (Z) as the surface of zinc. Insofar as the phosphating quality of the acidic, aqueous composition is ensured by metering in the activating aid, homogeneous, closed and compact crystalline zinc phosphate coatings are deposited on the components that have the surfaces of the metals zinc, iron and aluminum in the usual treatment times of 20 seconds to 5 minutes.

The ^layer weight of zinc phosphate is determined within the scope of the present _invention by detaching the zinc phosphate layer with aqueous 5 wt 5 min is brought into contact with a defined area of the phosphated material or component and subsequent determination of the phosphorus content in the same pickling solution with ICP-OES. The layer weight of zinc phosphate results from multiplying the surface-related amount of phosphorus by a factor of 6.23.

In the process according to the invention, the activating aid is added to the acidic aqueous composition for zinc phosphating for the purpose of maintaining the phosphating quality in process step (ii) for zinc phosphating. The addition can be used to maintain the phosphating quality in the process Series treatment can be carried out by continuous or discontinuous dosing into the system tank. Continuous dosing is preferred when the pretreatment of the components in series follows immediately after one another and the decrease in the phosphating quality can be determined over time, so that a quantity of the activating agent can be continuously added over time. This process has the advantage that the phosphating quality does not have to be checked further after the pre-treatment line has been started up and the material flows for dosing the activating agent and other active components have been determined, as long as the series treatment in terms of timing and condition of the components to be treated and the treatment parameters in process step ( ii) the zinc phosphating remains unchanged. However, if a constant mode of operation in series treatment cannot be guaranteed or is not desired due to the system, discontinuous dosing of the activation aid is advantageous and may even be indicated. In this case, the phosphating quality of the acidic, aqueous composition is monitored in step (ii), preferably continuously or at defined time intervals, and then a specified amount of the activation aid is metered in when the layer weight on hot-dip galvanized steel (Z) has a certain value below 5.0 g/ m ² , preferably below 4.5 g/m ² , more preferably below 4.0 g/m ² and most preferably below 3.5 g/m ² . The continuous or quasi-continuous determination of the phosphating quality, which takes place at defined time intervals, can also be carried out using proxy data that correlate with the actual zinc phosphate layer weight. The non-destructive determination of the layer thickness, for example using the eddy current method or even contact-free optical determination methods such as ellipsometry or spectral reflectivity measurement, provides suitable proxy data for the layer weight of zinc phosphate, which is reliably measured in a pre-treatment line on the zinc surfaces of the components and with the actual coating weight on hot-dip galvanized steel (Z) can be correlated. The crystallite size and thus the determination of the roughness by means of optical profilometry can also provide proxy data for the layer weight, since a higher layer weight on hot-dip galvanized steel (Z) is associated with a low number density of crystallites, which, however, are relatively larger, so that the roughness with the layer weight increases.

It has been found that the phosphating quality is in most cases already set adequately if the activating aid is metered in continuously or discontinuously in such an amount that is suitable for a stationary amount of preferably at least 0.001 g/kg, particularly preferably at least 0.005 g/kg, particularly preferably at least 0.01 g/kg of particulate component (P) in the acidic aqueous composition during the pretreatment of the components in series. This applies in particular to the contacting of the acidic aqueous composition by spraying, whereas in the case of dip application a stationary amount of preferably at least 0.002 g/kg, particularly preferably 0.01 g/kg and particularly preferably 0.02 g/kg kg of particulate component (P) should be contained in the acidic aqueous composition for zinc phosphating.

The present invention thus shows in a surprising way that the addition of an activating agent, as is known in the art and for example in WO 98/39498 A1 is described, the metal surfaces can be activated immediately with the acidic, aqueous treatment solution for zinc phosphating in step (ii), so that homogeneous, closed and compact crystalline zinc phosphate coatings with high electrical penetration resistance grow on the metal surfaces, due to the process step (i) brought about Deposition of iron on the surfaces of zinc such high-quality phosphate coatings for corrosion protection and paint adhesion can be achieved. The present invention makes use of this effect in that, in the series treatment of components, zinc phosphating is carried out using an acidic, aqueous composition which, in addition to zinc ions, phosphate ions and free fluoride, also contains a particulate component (P) dispersed in water and/or or to maintain the phosphating quality by metering in the activating aid to the acidic, aqueous composition for zinc phosphating. For the desired phosphating quality, it is possible to simply switch to adding the aqueous dispersion or metering in the activation aid containing the particulate component (P), without the components in the series undergoing a wet-chemical activation stage prior to the zinc phosphating process step, e.g. based on the aqueous dispersion or the activating aid. This means that a complete process step, including the necessary bath care, circulation, temperature management and chemical additives, e.g. with water-soluble condensed phosphates, can be saved, so that an extremely resource-saving and economical operation of a pre-treatment line for zinc phosphating is possible for the first time.

For the dispersed particulate component (P) and the at least one particulate inorganic compound (P1) or polymeric organic compound (P2), the im The following definitions and preferred specifications made, regardless of whether the dispersed particulate component (P) is part of the aqueous dispersion for providing the self-activating acidic, aqueous composition for zinc phosphating or the activating aid for maintaining the activating performance of the acidic, aqueous composition in process step (ii) of method according to the invention. For the sake of simplicity, reference is made below only to the activation aid. The statements regarding the activating aid accordingly also apply to the aqueous dispersion for providing the self-activating acidic, aqueous composition for zinc phosphating.

Activating aids which can be used according to the invention, i.e. which maintain the phosphating quality when added to the acidic, aqueous composition for zinc phosphating - or which provide the acidic, aqueous composition for zinc phosphating in step (ii) for the first time - are aqueous dispersions and thus contain a particulate component ( P) in water-dispersed form, which comprises at least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, and at least one polymeric organic compound (P2). .

The use of polyvalent metal cations in the form of phosphates is responsible for the good activation performance or suitability of the activating aid to maintain the phosphating quality of the acidic, aqueous composition for zinc phosphating, which is therefore contained in the activating aid with a sufficiently high proportion in the dispersed particulate component (P ) should be included. Accordingly, the proportion of phosphates contained in the at least one particulate inorganic compound (P1) based on the dispersed particulate component (P) in the activation aid is preferably at least 25% by weight, particularly preferably at least 35% by weight, particularly preferably at least 40% by weight %, most preferably at least 45% by weight. The dispersed particulate component (P) of the activating aid is that solids content which remains after drying the retentate of an ultrafiltration of a defined partial volume of the activating aid with a nominal exclusion limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off). The ultrafiltration is carried out with the supply of deionized water (κ<1 μScm ^-1 ) until a conductivity below 10 μScm ^-1 is measured in the filtrate. The inorganic particulate component in the activation aid is in turn that which remains when the residue obtained from drying the ultrafiltration retentate particulate component (P) is pyrolyzed in a reaction furnace with the supply of a CO ₂ -free oxygen stream at 900 °C without the addition of catalysts or other additives until an infrared sensor in the outlet of the reaction furnace is filled with the CO ₂ -free carrier gas (blank value ) delivers identical signal. The phosphates contained in the inorganic particulate component are determined directly from the acid digestion as the phosphorus content by means of atomic emission spectrometry (ICP-OES) after acid digestion of the same with aqueous 10% by weight HNO ₃ solution at 25° C. for 15 minutes.

The active components of the activation aid, which - as soon as they are added in sufficient quantities to the acidic aqueous composition for zinc phosphating - promote the formation of a homogeneous, closed and compact crystalline phosphate coating on the metal surfaces and in particular the surfaces of zinc and in this sense activate the metal surfaces as already mentioned, composed primarily of phosphates, which in turn are at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, preferably at least partially selected from hopeite, phosphophyllite and/or scholzite, particularly preferably at least partially selected from hopeite and/or phosphophyllite and entirely particularly preferably at least partially selected from hopeite. The maintenance of the phosphating quality in the acidic, aqueous composition is therefore essentially based on the metered-in phosphates in particulate form contained in the activation aid. Without taking crystal water into account, hopeites stoichiometrically comprise Zn ₃ (PO ₄ ) ₂ and the variants Zn ₂ Mn(PO ₄ ) ₃ , Zn 2 Ni(PO 4 ) 3 , Zn ₂ Ni(PO ₄ ) ₃ containing nickel and manganese, whereas phosphophyllite consists of Zn ₂ Fe(PO ₄ ) ₃ , scholzite consists of Zn ₂ Ca(PO ₄ ) ₃ and hureaulite consists of Mn ₃ (PO ₄ ) ₂ . The existence of the crystalline phases hopeite, phosphophyllite, scholzite and/or hureaulite in the activation aid can be determined after the particulate component (P) has been separated off by means of ultrafiltration with a nominal exclusion limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off) as described above and drying of the retentate can be detected up to constant mass at 105°C using X-ray diffractometric methods (XRD).

Due to the preference for the presence of phosphates, which include zinc ions and have a certain crystallinity, it is preferred for the formation of firmly adhering crystalline zinc phosphate coatings if at least 20% by weight, particularly preferably at least 30% by weight, -%, particularly preferably at least 40% by weight of zinc in the inorganic particulate Component based on the phosphate content of the inorganic particulate component, calculated as PO ₄ , are included.

However, the activation aid should preferably not additionally contain any titanium phosphates, since these do not have a positive effect on the phosphating quality when metered in. In a preferred embodiment of the process according to the invention, the proportion of titanium in the inorganic particulate component of the activating aid is less than 0.01% by weight, particularly preferably less than 0.001% by weight, based on the activating aid. In a particularly preferred embodiment, the activation aid contains a total of less than 10 mg/kg, particularly preferably less than 1 mg/kg, of titanium.

The polymeric organic compound (P2) which stabilizes the particulate component exerts a major influence on the effectiveness of the particulate component (P) added via the activation aid. It is found that the selection of the polymeric organic compound is critical to the degree of metal surface activation in the acidic aqueous zinc phosphating composition in step (ii) which is known to be brought about by the dispersed polyvalent phosphates and which, like the present invention shows that, surprisingly, it can also take place at the same time as the layer formation.

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

It has been shown that the maintenance of the phosphating quality and thus activation of the metal surfaces in the zinc phosphating process step when brought into contact with the acidic, aqueous composition is then particularly good, ie with use relatively small amounts of active components of the activation aid, if the polymeric organic compound (P2) used to disperse the particulate inorganic compound (P1) is at least partly composed of styrene and/or an α-olefin having no more than 5 carbon atoms, where the polymeric organic compound (P2) additionally has units of maleic acid, its anhydride and/or its imide and preferably additionally polyoxyalkylene units, particularly preferably polyoxyalkylene units, in its side chains. Such polymeric organic compounds (P2) are therefore preferred according to the invention in the particulate component (P) of the activation aid.

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

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

In the context of the present invention, preference is given to those polymeric organic compounds (P2) which are composed at least partly of styrene.

The polymeric organic compounds (P2) used for the colloidal stabilization of the particulate component (P) of the activation aid preferably have polyoxyalkylene units which in turn are preferably made up of 1,2-ethanediol and/or 1,2-propanediol, particularly preferably both 1,2-ethanediol and 1,2-propanediol, the proportion of 1,2-propanediols in all of the polyoxyalkylene units preferably being at least 15% by weight, but particularly preferably 40% by weight, based on the total of the polyoxyalkylene units does not exceed. Furthermore, the polyoxyalkylene units are preferably in the side chains of the polymeric organics Compounds (P2) included. A proportion of the polyoxyalkylene units in the total of the polymeric organic compounds (P2) of preferably at least 40% by weight, particularly preferably at least 50% by weight, but preferably not more than 70% by weight, is advantageous for them dispersibility.

For the anchoring of the polymeric organic compound (P2) with the inorganic particulate component (P1) of the activation aid, which is at least partially formed by polyvalent metal cations in the form of phosphates selected from hopeite, phosphophyllite, scholzite and/or hurealite, and an increased Stability and ability of the particulate component (P) to activate in the acidic, aqueous composition of the zinc phosphating, the organic polymeric compounds (P2) also have imidazole units, preferably in the side chains, particularly preferably as part of the polyoxyalkylene units of the polymeric organic compounds (P2).

In a preferred embodiment, the amine number of the organic polymeric compounds (P2) is at least 25 mg KOH/g, particularly preferably at least 40 mg KOH/g, but preferably less than 125 mg KOH/g, particularly preferably less than 80 mg KOH / g, so that in a preferred embodiment all of the polymeric organic compounds in the particulate component (P) of the activating aid have these preferred amine numbers. The amine number is determined in each case by weighing approximately 1 g of the respective reference quantity - organic polymeric compounds (P2) or all of the polymeric organic compounds in the particulate component (P) - in 100 ml of ethanol, with 0.1N HCl standard solution titrated against the indicator bromphenol blue until the color changes to yellow at a temperature of the ethanolic solution of 20 °C. The amount of standard HCl solution consumed in milliliters multiplied by the factor 5.61 divided by the exact mass of the sample in grams corresponds to the amine number in milligrams of KOH per gram of the respective reference value.

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

For a stable dispersion of the inorganic particulate components in the activation aid, it is sufficient if the proportion of the polymeric, organic compounds (P2), preferably all of the polymeric, organic compounds in the particulate component (P), based on the particulate component (P) at least 3% by weight, more preferably at least 6% by weight, but preferably not exceeding 15% by weight. The dispersed particulate component (P) of the activating aid is that solids content which remains after drying the retentate of an ultrafiltration of a defined partial volume of the activating aid with a nominal exclusion limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off). The ultrafiltration is carried out with the supply of deionized water (κ<1 μScm ^-1 ) until a conductivity below 10 μScm ^-1 is measured in the filtrate.

The activating aid preferably no longer contains 40% by weight of particulate component (P) based on the agent, otherwise the stability of the dispersion and the technical manageability for continuous or discontinuous dosing of the agent to the acidic, aqueous composition of the zinc phosphating by means of metering pumps are not possible more guaranteed or at least expensive. This applies in particular with regard to the overall low amounts of particulate constituents (P) required to maintain the phosphating quality of a reference amount of the acidic, aqueous composition for zinc phosphating. On the other hand, it is advantageous if the activation aid is provided as a dispersion which is as stable as possible and at the same time as highly concentrated as possible. This can be achieved in particular when using the preferred polymeric organic compounds (P2) for dispersing the particulate inorganic compound (P1), so that activation aids are preferably used which contain at least 5% by weight, but preferably not more than 30% by weight. contain particulate component (P) based on the agent.

In such concentrated aqueous dispersions of the activation aid, i.e. those with a proportion of 5% by weight of particulate component (P) based on the agent, this can In the process according to the invention, activation aids can also be characterized by their D50 value of more than 10 μm, which is correspondingly preferred. The agglomerates of the dispersed particles contained in the dispersion cause the thixotropic flow properties, which are favorable for the activating aid to be able to be handled. The tendency of the agglomerates to be highly viscous at low shear favors their long shelf life, while the loss of viscosity at shear conditions their pumpability. Favorable flow properties are also obtained if the dispersion does not significantly exceed a D90 value of 150 μm, so that according to the invention a D90 value of the aqueous dispersion of less than 150 μm, preferably less than 100 μm, in particular less than 80 μm, is preferred is. In the context of the present invention, the D50 value or the D90 value denotes the particle diameter which 50% by volume or 90% by volume, respectively, of the particulate components present in the aqueous dispersion do not exceed. The D50 value or D90 value can be determined according to ISO 13320:2009 by means of scattered light analysis according to the Mie theory from volume-weighted cumulative particle size distributions immediately after dilution of the activation aid in the form of the concentrated aqueous dispersion to a dispersed particulate component of 0.05% by weight. with an appropriate amount of deionized water (κ < 1µScm ^-1 ) at 20 °C, based on spherical particles and a refractive index of the scattering particles of nD = 1.52 - i·0.1. The dilution is carried out in such a way that an amount of the concentrated dispersion corresponding to a volume of 200 ml deionized water is poured into the sample vessel of the LA-950 V2 particle size analyzer from Horiba Ltd. is added and circulated mechanically into the measuring chamber (setting of the circulating pump on the LA-950 V2: level 5 = 1167 rpm for a volume flow of 3.3 liters/minute). The particle size distribution is measured within 120 seconds of adding the dispersion to the dilution volume.

The presence of a thickener can be advantageous for preventing the irreversible agglomeration of primary particles of the particulate constituent (P), particularly when the activation aid is present as a concentrated dispersion as described above. In a preferred embodiment of the process according to the invention, the activating aid accordingly contains a thickener, preferably in an amount which gives the activating aid in the shear rate range from 0.001 to 0.25 reciprocal seconds a maximum dynamic viscosity at a temperature of 25° C. of at least 1000 Pa s. but preferably below 5000 Pa·s, and preferably results in shear-thinning behavior at shear rates above those that exist at the maximum dynamic viscosity at 25° C., ie a decrease in viscosity with increasing Shear rate results, so that the activation aid has an overall thixotropic flow behavior. The viscosity over the specified shear rate range can be determined using a plate/cone viscometer with a cone diameter of 35 mm and a gap width of 0.047 mm.

A thickener within the meaning of the present invention is a polymeric chemical compound or a defined mixture of chemical compounds which, as a 0.5% by weight component in deionized water (κ <1 μScm ^-1 ) at a temperature of 25° C., has a Brookfield Viscosity of at least 100 mPas at a shear of 60 rpm (= rounds per minute) using a size 2 spindle. To determine this thickening property, prepare the mixture with water in such a way that the appropriate amount of the polymeric chemical compound is added to the water phase while stirring at 25 °C and the homogenized mixture is then freed of air bubbles in an ultrasonic bath and left to stand for 24 hours. The viscosity reading is then read immediately within 5 seconds after application of 60 rpm shear by spindle number 2.

The activation aid preferably contains a total of at least 0.5% by weight, but preferably no more than 4% by weight, particularly preferably no more than 3% by weight, of one or more thickeners, with the total proportion of polymeric organic compounds in the non-particulate component of the aqueous dispersion does not exceed 4% by weight (based on the dispersion). The non-particulate component is the solids content of the aqueous dispersion in the permeate of the ultrafiltration already described after it has been dried to constant mass at 105° C.—ie the solids content after the particulate component has been separated off by means of ultrafiltration.

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

Urea urethane resins which are particularly suitable and therefore preferred according to the invention can be obtained by first reacting a diisocyanate, for example toluene-2,4-diisocyanate, with a polyol, for example a polyethylene glycol, to form NCO-terminated urethane prepolymers, then with a primary monoamine and/or with a primary diamine , For example, m-xylylenediamine, is further implemented. Particular preference is given to urea-urethane resins which have neither free nor blocked isocyanate groups. Such urea-urethane resins, as a component of the activating agent, promote the formation of loose agglomerates of primary particles, which are protected against further agglomeration and, when added to the acidic, aqueous composition for zinc phosphating, dissociate into primary particles. In order to further promote this profile of properties, urea urethane resins which have neither free or blocked isocyanate groups nor terminal amine groups are preferably used as thickeners. In a preferred embodiment, the thickener, which is a urea urethane resin, therefore has an amine number of less than 8 mg KOH/g, particularly preferably less than 5 mg KOH/g, particularly preferably less than 2 mg KOH/g, determined in each case according to the method as previously described for the organic polymeric compound (P2). Since the thickener is essentially dissolved in the aqueous phase of the activation aid and can therefore be assigned to the non-particulate component, while component (P2) is essentially bound in the particulate component (P), an activation aid is accordingly preferred in which the The totality of the polymeric organic compounds in the non-particulate component preferably has an amine number of less than 16 mg KOH/g, particularly preferably less than 10 mg KOH/g, particularly preferably less than 4 mg KOH/g. Furthermore, it is preferred that the urea urethane resin is a Hydroxyl number in the range from 10 to 100 mg KOH/g, particularly preferably in the range from 20 to 60 mg KOH/g, determined by method A of 01/2008:20503 from European Pharmacopoeia 9.0. With regard to the molecular weight, a weight-average molar mass of the urea-urethane resin in the range from 1000 to 10000 g/mol, preferably in the range from 2000 to 6000 g/mol, is advantageous according to the invention and therefore preferred, in each case determined experimentally as before in connection with the inventive definition of a polymeric organic connection described.

The activating aid is an aqueous dispersion which preferably has a pH in the range of 6.5-8.0 and particularly preferably no pH-regulating, water-soluble compounds with a _pK a value of less than 6 or a pK _b value of less than 5 contains.

The activating aid can also contain other auxiliaries, for example selected from preservatives, wetting agents and defoamers, which are present in the amount required for the particular function. The proportion of auxiliaries, particularly preferably other compounds in the non-particulate component that are not thickeners, is preferably less than 1% by weight.

1. i) Bereitstellen einer Pigmentpaste durch Verreiben von 10 Massenteilen einer anorganischen partikulären Verbindung (P1) mit 0,5 bis 2 Massenteilen der polymeren organischen Verbindung (P2) in Gegenwart von 4 bis 7 Massenteilen Wasser und Vermahlen bis zum Erreichen eines D50-Wert von weniger als 1 µm bestimmt mittels dynamischer Lichtstreuung nach Verdünnung mit Wasser um den Faktor 1000, bspw. mittels Zetasizer^® Nano ZS, Fa. Malvern Panalytical GmbH;
2. ii) Verdünnen der Pigmentpaste mit einer solchen Menge an Wasser, vorzugsweise entionisiertem Wasser (κ<1µScm^-1) oder Brauchwasser, und eines Verdickers, dass ein dispergierter partikulärer Bestandteil (P) von mindestens 5 Gew.-% und eine maximale dynamische Viskosität von mindestens 1000 Pa s bei einer Temperatur von 25 °C im Scherratenbereich von 0,001 bis 0,25 reziproken Sekunden eingestellt ist,

wobei bevorzugte Ausführungsformen des Aktivierhilfsmittels durch Auswahl entsprechender Komponenten (P1), (P2) und des Verdickers in der jeweils ggf. vorgesehenen bzw. erforderlichen Menge auf analoge Weise erhalten werden. Eine solche konzentrierte wässrige Dispersion weist eine hervorragende Stabilität und aufgrund ihres thixotropen Fließverhaltens auch eine gute Pumpbarkeit auf, so dass eine kontrollierte Zudosierung der konzentrierten Dispersion unmittelbar in den Systemtank der Zinkphosphatierung gut erfolgen kann.The activating aid is preferably obtainable as a concentrated aqueous dispersion

1. i) providing a pigment paste by triturating 10 parts by mass of an inorganic particulate compound (P1) with 0.5 to 2 parts by mass of the polymeric organic compound (P2) in the presence of 4 to 7 parts by mass of water and grinding until a D50 value of less is reached determined as 1 μm by means of dynamic light scattering after dilution with water by a factor of 1000, for example by means of ^Zetasizer® Nano ZS, from Malvern Panalytical GmbH;
2. ii) Diluting the pigment paste with such an amount of water, preferably deionized water (κ<1μScm ^-1 ) or process water, and a thickener that a dispersed particulate component (P) of at least 5% by weight and a maximum dynamic viscosity of at least 1000 Pa s at a temperature of 25 °C in the shear rate range of 0.001 to 0.25 reciprocal seconds,

preferred embodiments of the activation aid being selected by selecting appropriate components (P1), (P2) and the thickener in the respectively provided or required amount can be obtained in an analogous manner. Such a concentrated aqueous dispersion has excellent stability and, due to its thixotropic flow behavior, also good pumpability, so that the concentrated dispersion can be metered directly into the zinc phosphating system tank in a controlled manner.

1. (A) 5 - 50 g/kg an in Wasser gelösten Phosphaten berechnet als PO₄,
2. (B) 0,3 - 3 g/kg an Zink-Ionen, und
3. (C) freies Fluorid enthält,

sowie eine Freie Säure in Punkten von größer als Null aufweist.With regard to the acidic, aqueous composition for zinc phosphating, it is imperative for the formation of homogeneous, closed zinc phosphate layers that these in step (ii) of the method according to the invention at least

1. (A) 5 - 50 g/kg of phosphates dissolved in water calculated as PO ₄ ,
2. (B) 0.3 - 3 g/kg of zinc ions, and
3. (C) contains free fluoride,

and a free acid in points greater than zero.

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

The proportion of the free acid in points in the acidic, aqueous composition of the zinc phosphating in step (ii) of the process according to the invention is preferably at least 0.4, but preferably not more than 3.0, particularly preferably not more than 2.0. The percentage of free acid in points is determined by diluting a 10 ml sample volume of the acidic aqueous composition to 60 ml and titrating with 0.1 N sodium hydroxide solution to a pH of 3.6. The consumption of ml of sodium hydroxide indicates the number of free acid points.

The preferred pH of the acidic, aqueous composition is usually above 2.5, particularly preferably above 2.7, but preferably below 3.5, particularly preferably below 3.3. The "pH value" as used in the context of the present invention corresponds to the negative decadic logarithm of the hydronium ion activity at 20° C. and can be determined using pH-sensitive glass electrodes.

A quantity of free fluoride or a source of free fluoride ions is essential for the zinc phosphating layer-forming process. Insofar as components including surfaces of zinc and surfaces of iron or aluminum are to be zinc-phosphated in a layer-forming manner, as is necessary, for example, in the zinc phosphating of automobile bodies that are at least partially made of aluminum, it is advantageous if the amount of free fluoride in of the acidic aqueous composition in step (ii) is at least 0.5 mmol/kg, particularly preferably at least 2 mmol/kg. The concentration of free fluoride should not exceed values above which the phosphate coatings show loose adhesions that can be easily wiped off, since this defect can also be caused by an increased dosage of activation aid or by an increased stationary amount of particulate components (P) in the acidic, aqueous composition for zinc phosphating often cannot be compensated. It is therefore advantageous and therefore preferred if, in step (ii) of the method according to the invention, the concentration of free fluoride in the acidic aqueous composition of the zinc phosphating is below 15 mmol/kg, particularly preferably below 10 mmol/kg and particularly preferably below 8 mmol /kg lies.

After calibration with fluoride-containing buffer solutions without pH buffering, the amount of free fluoride is to be determined potentiometrically at 20 °C in the respective acidic, aqueous composition using a fluoride-sensitive measuring electrode. Suitable sources for free fluoride ions are hydrofluoric acid and its water-soluble salts, such as ammonium bifluoride and sodium fluoride, and complex fluorides of the elements Zr, Ti and/or Si, in particular complex fluorides of the element Si. The source of free fluoride in a phosphating according to the present invention is therefore preferably selected from hydrofluoric acid and its water-soluble salts and/or complex fluorides of the elements Zr, Ti and/or Si. Salts of hydrofluoric acid are water-soluble in the context of the present invention if their solubility in deionized water (κ<1 μScm ⁻¹ ) at 60° C. is at least 1 g/L calculated as F.

In order to suppress the so-called speckle formation on the surfaces of the metallic materials made of zinc, it is preferred if the source of free fluoride in step (ii) in such a method according to the invention is at least partially selected from complex fluorides of the element Si, in particular from Hexafluorosilicic acid and its salts. Those skilled in the art of phosphating understand the formation of specks as the phenomenon of local deposition of amorphous, white zinc phosphate in an otherwise crystalline phosphate layer on the treated zinc surfaces or on the treated galvanized or alloy galvanized steel surfaces.

The accelerators known in the prior art can be added to the acidic, aqueous composition in the process according to the invention for more rapid layer formation. These are preferably selected from 2-hydroxymethyl-2-nitro-1,3-propanediol, nitroguanidine, N-methylmorpholine-N-oxide, nitrite, hydroxylamine and/or hydrogen peroxide. It has been found that a comparatively smaller dosage of activation aid is necessary or a smaller stationary amount of particulate components (P) in the acidic, aqueous composition for zinc phosphating in step (ii) has to be maintained if nitroguanidine or hydroxylamine is used as an accelerator is, so that nitroguanidine or hydroxylamine, in particular nitroguanidine, are particularly preferred as an accelerator in the acidic aqueous composition in step (ii) of the process according to the invention with regard to a particularly low substance consumption of the activating aid for maintaining the phosphating quality.

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

Furthermore, in the process according to the invention, the additives known in the art in processes of zinc phosphating can also be used.

Optional process steps:

In a preferred embodiment of the method according to the invention, the components of the series are therefore not treated with a colloidal, aqueous solution for activation containing hopeite, phosphophyllite, Scholzite and / or hureaulite, preferably phosphates of polyvalent metal cations, or sparingly soluble salts of the element Ti brought into contact. Particularly preferred are the assemblies of the series prior to contacting with the acidic aqueous composition in process step (ii) of zinc phosphating, they are not brought into contact with any colloidal, aqueous solution to activate the surfaces of the components for zinc phosphating and very particularly preferably the components of the series do not go through an activation stage for activation before being brought into contact in process step (ii). the surfaces of the components for zinc phosphating.

However, as a process step preceding the zinc phosphating in step (ii) and the separation of iron in step (i), a cleaning and degreasing stage cannot generally be dispensed with. In order to achieve reproducible layer coatings that are as equivalent as possible, in a preferred embodiment of the method according to the invention at least the metallic surfaces of the components are cleaned and optionally degreased before method step (i) in a separate cleaning stage or together with method step (i). The cleaning is preferably carried out by bringing it into contact with an aqueous, preferably neutral or alkaline cleaning agent, with process step (i) immediately following the cleaning stage with or without an intermediate rinsing step, preferably without an intermediate rinsing step.

In connection with the cleaning and, if necessary, degreasing of the components, alkaline cleaning is characterized by the fact that the metal surfaces, in particular the surfaces that contain metallic aluminum, whether as a material or as an alloy component of hot-dip galvanized steel, are pickled, which leads to a additional uniformity of the metal surfaces and is therefore advantageous for the growth of homogeneous zinc phosphate coatings.

The cleaning stage - or combined cleaning and icing stage - is preferably not carried out by bringing it into contact with an aqueous, preferably neutral or alkaline cleaner containing a particulate component comprising hopeite, phosphophyllite, scholzite and/or hureaulite or sparingly soluble salts of the element Ti, since as explained above, any activation of the metal surfaces before the zinc phosphating in step (ii) can be dispensed with according to the invention. As already mentioned, a rinsing step after cleaning is optional and, in the context of the present invention, is used exclusively for the complete or partial removal of soluble residues, particles and active components that are carried over from a previous wet-chemical treatment step - here the cleaning and degreasing step - adhering to the component , from the component to be treated, without being in the rinsing liquid itself Active components based on metallic or semi-metallic elements are contained, which are consumed simply by bringing the metallic surfaces of the component into contact with the rinsing liquid. Thus, the rinsing liquid can only be city water or deionized water or, if necessary, it can also be a rinsing liquid which contains surface-active compounds to improve the wettability with the rinsing liquid.

Components:

Since the phosphating quality in the method according to the invention on hot-dip galvanized steel is technically optimized, methods are naturally also preferred according to the invention in which the components of the series which at least partially have zinc surfaces also include surfaces of hot-dip galvanized steel. In principle, the phosphating quality of the acidic, aqueous composition, which is maintained in step (ii) by adding the activating aid, is such that components that are made of multi-metal construction, such as automobile bodies, can also be zinc-phosphated with very good properties and also on the Very homogeneous, closed and compact zinc phosphate coatings are accessible on iron and aluminum surfaces. In the method according to the invention, it is therefore preferred if the components in the series also have surfaces made of the metal iron or, specifically for lightweight construction in bodywork production, additional aluminum. In a particularly preferred embodiment, specifically in bodywork production, the components have surfaces of the metals zinc, iron and aluminum next to one another.

In the method according to the invention, it is preferred that the components of the series are brought into contact with the acidic, aqueous composition in step (ii) for at least a period of time which is sufficient for a layer weight of at least 1 0 g/m ² deposited, since it is then ensured that a sufficiently homogeneous, closed zinc phosphate coating is selected from zinc, iron and aluminum on all metal surfaces of the components. Accordingly, preference is given to a method according to the invention in which a zinc phosphate layer with a layer weight of at least 1.0 g/m ² , preferably at least 1.5 g/m ^{2 ,} is deposited on the surfaces of zinc. Since the phosphating quality of the acidic, aqueous composition for zinc phosphating in step (ii) is preferably maintained as a controlled variable in the process according to the invention or the acidic, aqueous composition has a sufficient activation capacity, this is also always the case ensures that the zinc surfaces of the component have a homogeneous, closed and compact crystalline zinc phosphate layer, the layer thickness of which is in the self-limiting range, so that, according to the invention, the layer weight of the zinc phosphate layer on the zinc surfaces of the component, as required by the range of tasks, is preferably below 5.0 g/ m ² , preferably below 4.5 g/m ² , more preferably below 4.0 g/m ² and most preferably below 3.5 g/m ² .

In the process according to the invention, a good primer for paint adhesion is achieved for a subsequent dip coating or powder coating, in the course of which an essentially organic top coat is applied. Accordingly, in a preferred embodiment of the method according to the invention, the zinc phosphating in step (ii) follows with or without an intermediate rinsing and/or drying step, but preferably with a rinsing step but without a drying step, followed by a dip coating or powder coating, particularly preferably an electro-dip coating, particularly preferably a cathodic one Electrocoating preferably containing water-soluble or water-dispersible salts of yttrium and/or bismuth in addition to the dispersed resin, which preferably comprises an amine-modified polyepoxide.

Claims (15)

Process for the anti-corrosive pretreatment of a large number of components in series, in which each component in the series has at least some surfaces of zinc and first undergoes a wet-chemical process step (i) for the deposition of iron on the zinc surfaces and then a process step (ii) for zinc phosphating, wherein in process step (i) a coating of at least 10 milligrams of the element iron per square meter of the zinc surfaces of the component is brought about, and wherein in step (ii) each component is contacted with an acidic aqueous composition having a Free Acid in points greater than zero, and (A) 5 - 50 g/kg of phosphates dissolved in water calculated as PO ₄ , (B) 0.3 - 3 g/kg of zinc ions, (C) free fluoride, and (D) contains a water-dispersed, particulate component comprising phosphates of polyvalent metal cations, the phosphates being at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, wherein the acidic, aqueous composition is obtainable by adding a quantity of an aqueous dispersion to an acidic, aqueous composition containing the components (A) - (C), wherein the aqueous dispersion contains a water-dispersed, particulate component (P) which - at least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, - and at least one polymeric organic compound (P2). Process according to Claim 1, characterized in that the aqueous dispersion is added to provide the acidic, aqueous composition for process step (ii) in such an amount that the proportion by weight of phosphates is based on the particulate component (P) of the aqueous dispersion on the acidic, aqueous composition is at least 0.004 g/kg, preferably at least 0.01 g/kg, more preferably at least 0.05 g/kg and most preferably at least 0.08 g/kg. The method according to one or both of the preceding claims, characterized in that the acidic, aqueous composition in process step (ii) of zinc phosphating continuously or discontinuously such an amount of an activating agent containing a particulate component (P) in water-dispersed form, the - at least one particulate inorganic compound (P1) composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, - and at least one polymeric organic compound (P2) is added, which is sufficient under the selected conditions of process step (ii), the property of the acidic, aqueous composition, on a hot-dip galvanized steel surface (Z) a zinc phosphate layer with a layer weight of less than 5.0 g/m ² , preferably less than 4.5 g/m ² , more preferably less than 4.0 g/m ² , most preferably less than 3.5 g/m ² . Process according to one or more of the preceding claims, characterized in that in process step (ii) the polymeric organic compound (P2) in the particulate component (P) of the aqueous dispersion or of the activating aid is composed at least in part of styrene and/or an a -Olefin having not more than 5 carbon atoms, the polymeric organic compound (P2) additionally having units of maleic acid, its anhydride and/or its imide and preferably additional polyoxyalkylene units, particularly preferably polyoxyalkylene units in its side chains, the polymeric organic compound (P2) additionally also has imidazole units, preferably in the side chains. Process according to one or more of the preceding claims, characterized in that the acidic, aqueous composition for zinc phosphating in process step (ii) has a pH below 3.6, preferably below 3.4, particularly preferably below 3.2, the free acid preferably being greater than 0.5 point, particularly preferably greater than 0.8 point and particularly preferably greater than 1.0 point. Process according to one or more of the preceding claims, characterized in that the acidic aqueous zinc phosphating composition in process step (ii) contains a source of free fluoride and preferably at least 10 mg/kg, more preferably at least 40 mg/kg, but preferably not contain more than 200 mg/kg of free fluoride. Method according to one or more of the preceding claims, characterized in that in the wet-chemical process step (i) on the surfaces of the components formed by zinc, a coating layer based on the element iron of at least 20 milligrams, preferably at least 40 milligrams, very particularly preferably at least 60 milligrams, but preferably less than 150 milligrams, particularly preferably less than 120 milligrams in each case per square meter of the zinc surfaces of the component. Method according to one or more of the preceding claims, characterized in that the wet chemical process step (i) preferably by contacting at least the surfaces of zinc of the components of the series with an aqueous composition containing iron (II) and / or iron (III) ions, the proportion of iron ions dissolved in water being at least 50 mg/L, preferably at least 100 mg/L, but preferably less than 10 mg/L in total of ionic compounds of the metals copper, nickel, cobalt , tin, manganese, molybdenum, chromium and/or cerium, in particular less than 1 mg/L each of ionic compounds of the metals nickel and cobalt, based on the metallic element, are contained in the aqueous composition. Process according to Claim 8, characterized in that the wet-chemical process step (i) is brought into contact with an alkaline, aqueous composition, the pH of which is preferably not below 8.5, particularly preferably not below 9.5, very particularly preferably not below 10.5, but preferably not above 13.5, particularly preferred is not above 12.5 and most preferably not above 11.5, and the (a) at least 50 mg/L, preferably at least 100 mg/L, particularly preferably at least 200 mg/L of iron(III) ions, and (b) at least 100 mg/L of complexing agents selected from organic compounds (b1) which have at least one functional group selected from COOX, OPO ₃ X and/or PO ₃ X, where X is either an H atom or an alkali and/or or represents an alkaline earth metal atom, and/or contains condensed phosphates (b2) calculated as PO ₄ , preferably wherein the composition has a free alkalinity of at least 1 point, but preferably less than 6 points. Method according to Claim 9, characterized in that the alkaline, aqueous composition additionally contains at least 100 mg/L, preferably at least 200 mg/L, particularly preferably at least 500 mg/L, but not more than 10 g/L of phosphate ions, wherein the mass ratio of ferric ions to phosphate ions in the alkaline aqueous composition is in a range of 1:20 to 1:2. Method according to one or both of the preceding claims 9 - 10, characterized in that the molar ratio of all components (b) to iron (III) ions in the alkaline, aqueous composition is greater than 1: 1 and preferably at least 2: 1, more preferably at least 5. Method according to one or more of the preceding claims, characterized in that the components of the series before being brought into contact with the acidic, aqueous composition in method step (ii) of zinc phosphating are not treated with a colloidal, aqueous solution containing hopeite in the particulate component, Phosphophyllite, scholzite and/or hureaulite, preferably phosphates of polyvalent metal cations, or sparingly soluble salts of the element Ti, and preferably with no colloidal prior to contacting with the acidic aqueous composition in process step (ii) of zinc phosphating , Aqueous solution to activate the surfaces of the components for zinc phosphating are brought into contact and particularly preferably none Go through activation stage to activate the surfaces of the components for zinc phosphating. Method according to one or more of the preceding claims, characterized in that the components of the series are cleaned and optionally degreased before or together with method step (i) in a cleaning stage, in particular by bringing them into contact with an aqueous, preferably alkaline cleaner wherein process step (i) immediately follows the cleaning step with or without an intermediate rinsing step, preferably without an intermediate rinsing step. Method according to one or more of the preceding claims, characterized in that the components of the series additionally have surfaces of the metal aluminum, particularly preferably additionally surfaces of the metals aluminum and iron. Method according to one or more of the preceding claims, characterized in that a zinc phosphate layer with a layer weight of at least 1.0 g/m ² , preferably at least 1.5 g/m ^{2 ,} is deposited on the surfaces of zinc.